final presentation for (municipal, domestic and industrial) thesis

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timer Asked: Jun 13th, 2018
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Question description

Hello lesser genius

Since you’re the one that worked with our thesis you would know how to deal with this

Presentation and finish it fast.

This is really not much to do, whats below is just instructions of what you need to follow

Now the 3 of us (domestic, municipal and industrial) have a common presentation, we want this presentation to be creative and professional.

We will attach you a presentation so you see how the format is and follow it.

Follow the same outline in the presentation will send,

So write the same headings in the outline but regarding our titles would be:

  • ASSESMENT AND REVIEW OF CONSTRUCTED WETLAND FOR MUNICIPAL WASTEWATER: SELECTED CASE STUDIES
  • ASSESMENT AND REVIEW OF CONSTRUCTED WETLAND FOR DOMESTIC WASTEWATER: SELECTED CASE STUDIES
  • ASSESMENT AND REVIEW OF CONSTRUCTED WETLAND FOR INDUSTRIAL WASTEWATER: SELECTED CASE STUDIES

But whatever is written under the title make it the same as the outline for example: methodology, results, conclusion and recommendation. In the end add a slide regarding the references for the whole thing, make sure you follow the template attached so you know what to add.

In the general part ex: introduction, problem statement, aim and objectives (of each one), project limitation, literature review - (for this part follow the domestic report and write whatever’s under the heading from the domestic report to make it easier since its common)

For each of our methodologies write in general what we have done for example you can use what’s written in our overview briefly.

And regarding the results first write in general (you can use from overview) then for each of us you will have to include the summary and comparison in one slide,

You can write the type of design on top to show you are comparing

And then under each design add points regarding their similarities and differences (make sure it’s in bullets and not paragraphs)

And then add another slide and write about the case mentioned in the conclusion which is one of the best systems for each of us

-And add a slide regarding “Municipal wastewater treatment using vertical flow constructed wetlands planted with Canna, Phragmites and Cyprus” for municipal

-And a slide with the tile “CW of Lepironia arciculata for household greywater treatment” for domestic

Add For the industrial you chose about a study case to write about

for those results focus on the parameters, treatment efficiency and mention why the paraments are high or low in points.

then add another common slide between municipal and domestic which is Haya water (and mention how it complies with the standards)

we will attach our thesis again so you can take points from the conclusion and recommendation

make sure the slides are in order first municipal then domestic and then industrial.

thankyou

ENG 4 133 Bachelor Thesis German University of Technology in Oman (GUtech) Department of Engineering ASSESMENT AND REVIEW OF CONSTRUCTED WETLAND FOR DOMESTIC WASTEWATER: SELECTED CASE STUDIES Course Coordinator: Dr.-Ing. Najah Al Mhanna Project Supervisor: Main supervisor: Dr.Hind Bargash Student Name: Nujoom Hamdan Al Amri Spring 2018 Approval of the Dean of the Faculty of Engineering and Computer Science Dr.-Ing. Najah Al Mhanna I certify that this Thesis satisfies the requirements of a Bachelors Thesis for the Degree of Bachelor of Engineering in Environmental Engineering. Dr.-Ing. Najah Al Mhanna Head, Department of Engineering I certify that I have read this Thesis and that it is my opinion that the Thesis is fully adequate in scope and quality as a Bachelors Thesis for the Degree of Bachelor of Environmental Engineering. Name Supervisor Examining Committee 1. Name 2. Name i Declaration: In accordance with the requirements of the degree of Bachelor of Engineering at German University of Technology in Oman, I present the following thesis titled “Assessment and review of constructed wetland for domestic wastewater: selected case studies”. This work was performed under the supervision of Dr. Hind Barghash. I hereby declare that the work submitted in this thesis is my own and based on the results found solely by myself. Materials of work found by other researchers are clearly cited and listed in reference list. This thesis, neither in whole nor in part, has been previously submitted for any degree. The author confirms that the library may lend or copy this thesis upon request, for academic purposes. Name: Nujoom Hamdan Alamri Signature: ii ABSTRACT Domestic wastewater from single-family households of up to 30 PEs can be managed by the installation of a sizeable wastewater system, based on CWs, which are highly flexible. Different design strategies of CWs can be applied, including VF, HF and hybrid designs with flow variations. This report explains the methodologies used in various case studies of domestic CWs, and summarises the data found that will allow for sensible discussions and conclusions to be made concerning the effectiveness of single-household CW systems, in terms of design strategy and removal efficiency rate. The most common physiological and chemical components required to be removed from domestic wastewater are FCs, TCs, TSSs, TN, TP, TKN, COD, BOD5, bacteria and ammonia. The highest removal efficiencies among all studies were observed as follows ; 99.4% BOD, 98.9% COD, 99.8% TSS, 99.99%coliforms, 98%Ammonium-nitrogen (NH4+-N), 99.6% Ammonia-nitrogen (NH3—N), 90.4% TN, 99.1% TP, 97.9% turbidity, 99.86% detergent, 99.2% MRP , 98.1% Oil and Grease (O&G), and 98% viable helminth ova (VHO) .Domestic CWs are important, not only because they improve water quality, but also because they improve the chances of treated effluent being reused, especially when there is no way of releasing it back into the environment. Such treated effluent can be used to irrigate nursery beds, flower beds, or even gardens around the household. Single-household CWs allow people to individually contribute to cleaning and conserving their own environment by providing a lowcost, low-maintenance, easy-to-operate, highly-effective sewage treatment system. Individual conservation efforts, if embraced, can greatly contribute to solving one of the world’s greatest problems, which is pollution. i Keywords: constructed wetlands (CWs), domestic wastewater, single-household system, subsurface flow, macrophytes ii ‫انخالصت‬ ‫‪ًٚ‬كٍ إداسة ي‪ٛ‬بِ انًجبس٘ يٍ االسخخذايبث انًُضن‪ٛ‬ت يٍ يُبصل األسش انخ‪ ٙ‬حصم إنٗ ‪ 03‬يعبدل سكبَ‪ ٙ‬يٍ خالل حشك‪ٛ‬ب َظبو‬ ‫صشف ي‪ٛ‬بِ ضخى ٔانخ‪ ٙ‬حزبج يشَٔت األساض‪ ٙ‬انشطبت (األْٕاس) انخ‪ٚ ٙ‬خى اَشبؤْب يًب ‪ًٚ‬كُٓب يٍ خذيت أ٘ عذد يٍ انسكبٌ‪.‬‬ ‫‪ًٚ‬كٍ حطب‪ٛ‬ق حصبي‪ٛ‬ى يخخهفت نألساض‪ ٙ‬انشطبت انًُشأة ٔانخ‪ ٙ‬حخضًٍ انخذفق انشأس‪ٔ ٙ‬انخذفق األفق‪ٔ ٙ‬انخصبي‪ٛ‬ى انٓج‪ُٛ‬ت يع‬ ‫يخغ‪ٛ‬شاث انخذفق‪ٚ .‬ششح انخقش‪ٚ‬ش انًُٓج‪ٛ‬بث انًسخخذيت ف‪ ٙ‬كز‪ٛ‬ش يٍ دساسبث انذبنت نًُشئبث األساض‪ ٙ‬انشطبت انًُضن‪ٛ‬ت ٔ‪ٚ‬عشض‬ ‫ببسخفبضت انب‪ٛ‬بَبث نخأس‪ٛ‬س يُبقشبث راث جذٖٔ عه‪ٓٛ‬ب ٔانخٕصم السخُخبجبث دٕل فعبن‪ٛ‬ت ٔكفبءة َظبو يُشأة األساض‪ ٙ‬انشطبت‬ ‫انفشد‪ٚ‬ت ف‪ًٛ‬ب ‪ٚ‬خعهق بخصً‪ٛ‬ى االسخشاح‪ٛ‬ج‪ٛ‬ت ٔيعذل اإلصانت‪ .‬حخضًٍ انعُبصش انكً‪ٛ‬بئ‪ٛ‬ت ٔانذ‪ٕٚٛ‬ت انخ‪ٚ ٙ‬خع‪ ٍٛ‬إصانخٓب يٍ ي‪ٛ‬بِ‬ ‫ا نًجبس٘ كم يٍ انقٕنَٕ‪ٛ‬بث انبشاص‪ٚ‬ت ٔانقٕنَٕ‪ٛ‬بث انكه‪ٛ‬ت ٔانًٕاد انصهبت انعبنقت انكه‪ٛ‬ت ٔانُ‪ٛ‬خشٔج‪ ٍٛ‬انكه‪ٔ ٔ ٙ‬انفسفٕسٔص انكه‪ٔ ٙ‬‬ ‫َخشٔج‪ ٍٛ‬ك‪ٛ‬هذال انكه‪ ٔ ٙ‬انطهب انب‪ٕٛ‬نٕج‪ ٙ‬انك‪ًٛٛ‬بئ‪ ٙ‬عهٗ األكسج‪ ٔ ٍٛ‬انطهب انب‪ٕٛ‬نٕج‪ ٙ‬انك‪ًٛٛ‬بئ‪ ٙ‬عهٗ األكسج‪ٔ ٍٛ‬انبكخش‪ٚ‬ب‬ ‫ٔاأليَٕ‪ٛ‬ب‪ .‬كبَج أعهٗ يعذالث اإلصانت انًسجهت عبش كبفت انذساسبث عهٗ انُذٕ انخبن‪ %...9:ٙ‬يٍ انطهب انب‪ٕٛ‬نٕج‪ ٙ‬انك‪ًٛٛ‬بئ‪ٙ‬‬ ‫عهٗ األكسج‪ %....ٔ ٍٛ‬يٍ انطهب انك‪ًٛٛ‬بئ‪ ٙ‬عهٗ األكسج‪ %.... ٔ ٍٛ‬يٍ انًٕاد انصهبت انعبنقت انكه‪ٛ‬ت ٔ‪ %.....‬يٍ‬ ‫انقٕنَٕ‪ٛ‬بث ٔ‪ %..‬يٍ َ‪ٛ‬خشٔج‪ ٍٛ‬األيَٕ‪ٕٛ‬و ٔ‪ %...9‬يٍ َ‪ٛ‬خشٔج‪ ٍٛ‬األيَٕ‪ٛ‬ب ٔ‪ %.3.9‬يٍ انُخشٔج‪ ٍٛ‬انكه‪ %...9ٔ ٙ‬يٍ‬ ‫انفسفٕسٔص انكه‪ %....ٔ ٙ‬يٍ انًٕاد انًعكشة ٔ‪ %....9‬يٍ يٕاد انخُظ‪ٛ‬ف ٔ‪ %...9‬يٕنب‪ٛ‬ذ انفٕسفٕس انخفبعه‪%...9ٔ ٙ‬‬ ‫يٍ انُفظ ٔانشذٕو ٔ ‪ %..‬يٍ انذ‪ٚ‬ذاٌ انطف‪ٛ‬ه‪ٛ‬ت‪.‬د‪ٛ‬ذ ال حقخصش أًْ‪ٛ‬ت األساض‪ ٙ‬انشطبت انًُشأة انًُضن‪ٛ‬ت عهٗ حذس‪ ٍٛ‬جٕدة‬ ‫ضب يٍ فشص يعبنجت ي‪ٛ‬بِ انًجبس٘ ٔيٍ رى إعبدة اسخخذايٓب ف‪ ٙ‬دبنت حعزس انٕس‪ٛ‬هت إلعبدة اطالقٓب ف‪ٙ‬‬ ‫انً‪ٛ‬بِ ٔنكُٓب حذسٍ أ‪ً ٚ‬‬ ‫انب‪ٛ‬ئت‪ًٚ .‬كٍ اسخخذاو انًخهفبث انسبئهت انًعبنجت نش٘ انًشبحم أٔ أدٕاض انضْٕس أٔ انذذائق انًُضن‪ٛ‬ت‪ًٚ .‬كٍ أٌ حخ‪ٛ‬خ يُشأة‬ ‫أساض‪ ٙ‬سطبت ٔادذة ن ألفشاد انًسبًْت عهٗ يسخٕٖ كم فشد يُٓى ف‪ ٙ‬حُظ‪ٛ‬ف انب‪ٛ‬ئت ٔدًب‪ٚ‬خٓب يٍ خالل حٕف‪ٛ‬ش َظبو نًعبنجت ي‪ٛ‬بِ‬ ‫انًجبس٘ ٔانز٘ ‪ٚ‬عًم بطش‪ٚ‬قت سٓهت ٔيُخفضت انخكبن‪ٛ‬ف ٔال حذخبس نعًه‪ٛ‬بث ص‪ٛ‬بَت يعقذة ٔحخًخع ف‪ ٙ‬انٕقج راحّ بًسخٕٖ عبل‬ ‫يٍ انكفبءة ٔانفعبن‪ٛ‬ت‪ .‬دش٘ ببنزكش أَّ ف‪ ٙ‬دبنت حبُ‪ ٙ‬ا نجٕٓد انفشد‪ٚ‬ت نهذفبظ عهٗ انب‪ٛ‬ئت فإٌ رنك يٍ شأَّ انًسبًْت انفبعهت ف‪ٙ‬‬ ‫دم ٔادذة يٍ أكبش انًشكالث ٔانخذذ‪ٚ‬بث انخ‪ ٙ‬حٕاجّ انعبنى أال ْٔ‪ ٙ‬يشكهت انخهٕد‪.‬‬ ‫الكلمات الداللية‪:‬يُشئبث األساض‪ ٙ‬انشطبت (األْٕاس) ‪،‬ي‪ٛ‬بِ انًجبس٘ ‪،‬يُضل ٔادذ ‪,‬انخذفق حذج انسطذ‪، ٙ‬يُضن‪َ ،ٙ‬ببحبث ذات‬ ‫أوراق كبيرة‪.‬‬ ‫‪iii‬‬ ACKNOWLEDGMENT I would like to express my sincere gratitude to my beloved supervisor Dr. Hind Bargash for her support guidance, motivation and patience. I could not have imagined having a better advisor and mentor for my Bachelor Thesis. Special Thanks to my parents Hamdan Al Amri, Nadia Al Amri, and my siblings whose prayers and support have encouraged me to work hard. May God give me the ability to make my family and Supervisor proud. Further, I acknowledge my sister Buraq and my group members of this project Hawra Al ajmi and Thuraiya Al busaidi for their care, support and advise throughout accomplishing this project. I would like to express my gratitude to almighty god for providing me knowledge and strength. iv TABLE OF CONTENTS ABSTRACT ..................................................................................................................................... i ACKNOWLEDGMENT................................................................................................................ iv LIST OF FIGURES ..................................................................................................................... viii LIST OF TABLES .......................................................................................................................... x LIST OF GRAPHS ....................................................................................................................... xii LIST OF ABBREVIATIONS ...................................................................................................... xiii INTRODUCTION .......................................................................................................................... 1 1.1. Background ........................................................................................................................................ 1 1.2. Limitations of CWs ............................................................................................................................ 3 1.3. Problem Statement ............................................................................................................................. 4 1.4. Aim and Objectives............................................................................................................................ 4 LITERATURE REVIEW ............................................................................................................... 5 2.1. Domestic, Municipal and Industrial Wastewater ............................................................................... 5 2.2. Conventional Wastewater Treatment ................................................................................................. 6 2.2.1. Primary Treatment ...................................................................................................................... 7 2.2.2. Secondary Treatment .................................................................................................................. 7 2.2.3. Tertiary Treatment ...................................................................................................................... 8 2.3. Constructed Wetlands (CWs)............................................................................................................. 9 v 2.4. Main Benefits and Outcomes of CWs................................................................................................ 9 2.5. Types of CWs .................................................................................................................................. 10 2.6. Components of CWs ........................................................................................................................ 10 2.6.1. Water ......................................................................................................................................... 10 2.6.2. Substrates, Sediments and Litter ............................................................................................... 11 2.6.3. Vegetation ................................................................................................................................. 12 2.6.4. Microorganisms ........................................................................................................................ 13 2.6.5. Animals ..................................................................................................................................... 13 2.7. Literature Summary ......................................................................................................................... 14 METHODOLOGY ....................................................................................................................... 15 3.1. Overview .......................................................................................................................................... 15 3.2. Methodologies.................................................................................................................................. 15 3.2.1. HSSF CWs for On-Site Wastewater Treatment ........................................................................ 15 3.2.2. Use of VF CWs for On-Site Treatment of Domestic Wastewater: New Danish Guidelines .... 18 3.2.3. The Attenuation Capacity of CWs to Treat Domestic Wastewater in Ireland .......................... 21 3.2.4. A Recirculating VF CW for the Treatment of Domestic Wastewater ...................................... 23 3.2.5. A Hybrid CW System for Decentralised Wastewater Treatment ............................................. 25 3.2.6. CW of Lepironia articulata for Household Greywater Treatment ........................................... 27 3.2.7. CW System for Wastewater Treatment..................................................................................... 29 3.2.8. Use of Macrophyte Plants, Sand and Gravel Materials in CWs for Greywater Treatment ...... 31 3.2.9. Integrated CWs for Treating Domestic Wastewater ................................................................. 31 3.2.10. Efficiency of Small CWs for Subsurface Treatment of Single-Family Domestic Effluent..... 35 3.2.11. Reed bed CW system .............................................................................................................. 36 RESULTS AND DISCUSSION ................................................................................................... 41 vi 4.1 Overview ........................................................................................................................................... 41 4.2. Results and Discussion .................................................................................................................... 41 4.2.1. HSSF CWs for On-Site Wastewater Treatment ........................................................................ 41 4.2.2. Use of VF CWs for On-Site Treatment of Domestic Wastewater: New Danish Guidelines .... 43 4.2.3. The Attenuation Capacity of CWs to Treat Domestic Wastewater in Ireland .......................... 45 4.2.4. A Recirculating VF CW for the Treatment of Domestic Wastewater ...................................... 48 4.2.5. A Hybrid CW System for Decentralised Wastewater Treatment ............................................. 52 4.2.6. CW of Lepironia articulata for Household Greywater Treatment ........................................... 55 4.2.7. CW System for Wastewater Treatment..................................................................................... 58 4.2.8. Use of Macrophyte Plants, Sand and Gravel Materials in CW for Greywater Treatment ........ 59 4.2.9. Integrated CWs for Treating Domestic Wastewater ................................................................. 61 4.2.10. Efficiency of Small CWs for Subsurface Treatment of Single-Family Domestic Effluent..... 62 4.2.11. Reed bed CW system .............................................................................................................. 67 4.3. Summary and Comparison ............................................................................................................... 70 CONCLUSION ............................................................................................................................. 72 RECOMMENDATIONS .............................................................................................................. 75 REFERENCES ............................................................................................................................. 76 vii LIST OF FIGURES Figure 3.1: Layout of a VF CW system for a single household. Raw sewage is pre-treated in a 2 m3 sedimentation tank. Firm sewage is pulse-loaded onto the shallow end of the bed by a level-controlled pump. Treated effluent is collected in a system of drainage pipes, and about half the effluent is recirculated back to the pumping well, or to the sedimentation tank (Brix & Arias, 2005) .................................................................. 21 Figure 3.2: Schematic representation of a pilot recirculating VF CW for the treatment of domestic wastewater. The upper container is a VF CW bed. Wastewater is applied to the root zone, trickles through the bed, and drips into the lower container, from where it is recirculated back to the root zone, until the required water quality is achieved (Sklarz, Gross, Yakirevich, & Soares, 2009) ............................................. 24 Figure 3.3: Hybrid CW schematics (Kinsley, Crolla, Rode, & Zytner, 2014) ............................. 27 Figure 3.4:Schematic diagram of a mini-CW system (Wurochekke, Harun, Mohamed, & Kassima, 2014) .......................................................................................................... 28 Figure 3.5: General layout of a single-household VF CW system (Farooqi, Basheer, & Chaudhari, 2008) ....................................................................................................... 30 Figure 3.6: Sketch showing groundwater and surface water monitoring, and inlet and outlet points, for the integrated CW in Glaslough, near Monaghan, Ireland (Scholz, 2011) ................................................................................................................................... 33 Figure 3.7: Sketch showing groundwater and surface water monitoring, and inlet and outlet points for the integrated CW system at Dunhill, near Waterford, Ireland (Scholz, 2011) .......................................................................................................................... 34 viii Figure 3.8: Typical three-cell design of a single-family domestic CW system (Steer, Fraser, & Boddy, 2002) ............................................................................................................. 36 Figure 3.9: Description of the process for treated effluent (Haya Water, 2017) .......................... 38 Figure 3.10: Stage A (Haya Water, 2017) .................................................................................... 39 Figure 3.11: Stage B (Haya Water, 2017)..................................................................................... 39 Figure 3.12: Photographs after both stages (Haya Water, 2017) .................................................. 40 Figure 4.1: Values of TSSs (a), COD (b) and BOD5 (c) in raw and treated domestic wastewater from planted and unplanted recirculating VF CWs using several RFRs (Sklarz, Gross, Yakirevich, & Soares, 2009) .......................................................................... 49 Figure 4.2: Changes in BOD5 with season and HLR (Q = 2.8 m3/d) (Kinsley, Crolla, Rode, & Zytner, 2014) ............................................................................................................. 53 Figure 4.3: TSSs with season and HLR (Q = 2.8 m3/d) (Kinsley, Crolla, Rode, & Zytner, 2014) ................................................................................................................................... 54 Figure 4.4: Percentage removal of greywater produced by household activities (Wurochekke, Harun, Mohamed, & Kassima, 2014)........................................................................ 56 ix LIST OF TABLES Table 3.1: RB1 and RB2 design characteristics (O'Luanaigh & Gill,nd) ..................................... 22 Table 3.2: RB1 and RB2 mean hydraulic parameters (O'Luanaigh & Gill, nd) ........................... 22 Table 3.3: Design criteria for a double-stage VF reed bed after pre-treatment (septic tank) (Haya Water, 2017) ............................................................................................................... 37 Table 4.1: Surface discharge limits (maximum concentrations) (OEPA, 2001; Hoddinott, 2006) ..................................................................................................................................... 41 Table 4.2: Performance data (mean±1 SD) for some single-household VF CWs (Brix & Arias, 2005) ........................................................................................................................... 44 Table 4.3: Average influent and effluent nitrogen loads from RB1 and RB2 ( O'Luanaigh & Gill, nd) ............................................................................................................................... 46 Table 4.4: Average influent and effluent E. coli concentrations from RB1 and RB2 (O'Luanaigh & Gill, nd) ................................................................................................................... 47 Table 4.5: Household water consumption in the case study (Wurochekke, Harun, Mohamed, & Kassima, 2014) ........................................................................................................... 55 Table 4.6: Analytical results of greywater loading before treatment (Wurochekke, Harun, Mohamed, & Kassima, 2014) ..................................................................................... 56 Table 4.7: Preliminary results of raw greywater in the morning and evening (Wurochekke, Harun, Mohamed, & Kassima, 2014) ......................................................................... 56 Table 4.8: Effectivenes of pollutant removal in CWs with natural substrates and local macrophytes (Qomariyah, Ramelan, Sobriyah, & Setyono, 2017)............................. 59 Table 4.9: System performance (Steer, Fraser, & Boddy, 2002) .................................................. 63 x Table 4.10: Wetland data base summary (Steer, Fraser, & Boddy, 2002) ................................... 67 Table 4.11: Data for the treatment of effluent by the reed bed system (Haya Water, 2017; Oman Government, 2018) ..................................................................................................... 68 xi LIST OF GRAPHS Graph 4.1: Relationship between treated effluent, the MECA standard and removal efficiency (Haya Water, 2017; Oman Government, 2018) .......................................................... 69 xii LIST OF ABBREVIATIONS BOD Biological oxygen demand COD Chemical oxygen demand CW Constructed wetland EPA Environmental protection agency FC Fecal coliform FWS Free water surface HF Horizontal flow HLR Hydraulic loading rate HRT Hydraulic retention time HSSF MECA Horizontal subsurface flow Ministry of the Environment and Climate Affairs MRP molybdate-reactive phosphorus PE Population equivalent RBC Rotating biological conductor RFR Recirculation flow rate xiii SSF Subsurface flow SF Surface flow TC Total coliform TE Treated effluent TKN Total Kjeldahl nitrogen TN Total nitrogen TP Total phosphorous TSS Total suspended solid VF Vertical flow xiv Chapter 1 INTRODUCTION 1.1. Background The most vital element that contributes to the creation and sustenance of a satisfactory and healthy life for living organisms is water. Water is a crucial element on planet Earth because it supports life. For this reason, it is wise for mankind to protect all water resources. Water pollution is a major environmental hazard, which poses a continuous threat to the environment in general, as well as to individual water bodies. To a large extent, exhaust fumes and industrial waste contribute to the pollution of water. The discharge of untreated industrial, domestic and municipal waste into water resources and onto land facilitates degradation of the environment, and places members of the public under threat of contracting health-related issues from polluted water (Postel, 2000). Public information on the need to preserve water resources should be enhanced, in order to try and curb the water pollution that results from municipal, industrial and domestic wastewater. If people are educated on the importance of protecting their own water resources, the majority of water pollution and environmental degradation can be avoided or minimised. Wastewater recycling via CW treatment systems is financially effective in populations that struggle with water scarcity. This strategy of conserving water benefits both society and the environment. 1 Sustainability is a concept that can be integrated into human activities, and human society in general (Praewa, 2017). When human activities become unsustainable, there are adverse effects on the ecosystem, which is crucial to the sustenance and support of human life. Modern approaches have been designed to integrate sustainability, environmental ethics and public effort to develop society-based projects. In most cases, both known and unknown substances are added to public water from its commercial, domestic and industrial use, and as a result of these additives, the public water ends up as municipal, domestic and industrial wastewater. Sustainable wetlands can be constructed for the treatment of wastewater from municipal, domestic and industrial sources. These allow for water reclamation and reuse in most of the sustainable water resource management programs across the globe (Praewa, 2017). CWs are engineered and managed wetland systems for wastewater treatment and reclamation that are receiving increasing global attention. Such systems involve a naturally-occurring pollutant-removal process, mediated by complex interactions between water, soil/gravel, vegetation and its associated microbial assemblages, and the environment to improve water quality in a sustainable way. CWs are designed to exploit the physical, chemical and biological treatment processes that naturally occur in wetlands, providing for reductions in organic matter, TSSs, nutrients, BOD, metals and pathogenic organisms. CWs are cost-effective and easily operated and maintained, and they have proven to be applicable for household, municipal and industrial wastewater treatment. 2 1.2. Limitations of CWs CW systems have limitations that can undermine their utilisation. They make use of larger pieces of land than other, conventional wastewater systems. In some cases, the economic implications of having to obtain a large enough tract of land for the installation of a CW can limit its availability to people who do not have money to buy more land; and so, in some case, the CW system is too expensive (Jhansi & Mishra , 2013). Since biological components in wastewater are generally sensitive to chemicals, then any water surges would undermine the effectiveness of CW water treatment. Whilst CWs are designed in such a way as to be able to be maintained using minimal amounts of water, they cannot survive in completely dry regions, or rather they are not engineered to survive under extreme environmental circumstances. Very cold weather conditions, and high temperatures that may result from dry spells and drought, can undermine, and limit the effectiveness, of CW systems. Conversely, heavy rains can also have a deleterious affect on CW systems, especially during the spring season. The system is also generally susceptible to changeable weather patterns, and again its effectiveness can be undermined (Crawford & Sandino, 2010). The use of CW systems for municipal, industrial and domestic wastewater treatment is a relatively new concept (Crawford & Sandino, 2010), and, for this reason, technologies that could be used to enhance their effectiveness have, as yet, been underdeveloped. Some ecological and environmental critiques have argued that more should be done to attain better effectiveness of such systems. 3 1.3. Problem Statement Many developing countries are faced with the challenge of industrial, municipal and domestic wastewater management, but have problems in finding effective and low-cost technologies. Wastewater management has the primary purpose of preventing the spread of disease and infection. Nutrients recovery, water reclamation, and reuse as well as conserving water resources are other wastewater management goals that most world organizations are trying to achieve. A shift from conventional wastewater management to a more sustainable system should, therefore, be globally embraced, so that water and environmental resources can be conserved (Praewa, 2017). Whilst effluent and other discharges that result in water pollution should be handled so as to avoid the spread of disease and infection to members of the public, there is also a risk of people contracting malaria from mosquitoes breeding in stagnant, polluted water bodies that must also be addressed (Praewa, 2017). 1.4. Aim and Objectives The aim of this study is to provide an assessment of the various types of CW wastewater treatment systems, through a review of their design for use in single households, and a discussion of their performance, in terms of onsite wastewater treatment, influent/effluent quality and the percentage removal of pollutants, and water reuse criteria. Several case studies are used as examples. 4 Chapter 2 LITERATURE REVIEW 2.1. Domestic, Municipal and Industrial Wastewater In this day and age, the issue of municipal, industrial and domestic wastewater is of great concern because it can cause severe environmental problems, and can also impact people in terms of their health. Studies have estimated that wastewater comprises 99% water, with the remaining 1% being a mixture of suspended and dissolved organic solids, detergents and chemicals (Secretariat, 2014). Sewage is wastewater that comprises household waste from toilets, sinks and showers/baths that is disposed of via sewers. Municipal wastewater includes input that ranges from, for example, shops, to restaurants and bars, and car washes (Secretariat, 2014). Frequently, pretreated industrial wastewater is included in with the municipal wastewater. A wide variety of processes result in the formation of industrial wastewater, including plastic manufacturing, wood pulping, petroleum refinement and food processing. According to Secretariat (2014), these different types of wastewater have varying compositions, containing, for instance, different pathogens, bacteria and nutrients. Untreated wastewater 5 components can be organised into three categories – physical, biological and chemical. Solid and inorganic constituents in wastewater comprise the physical components. The biological components are bacteria, viruses, protozoa and other pathogens. Lastly, the chemical components include dissolved materials and organic matter, as well as nutrients and metals, which, in most cases, are heavy metals. In rare cases, wastewater might contain reusable resources – for example, water, carbon and other nutrients – that could be recovered. For effective effluent regulatory standards to be met, wastewater needs to undergo appropriate treatment in order to get rid of the pollutants and, according to Crawford & Sandino (2010), this process should be focused on the recovery of resources, so as to be self-sustaining. Advances in scientific knowledge, and a greater consciousness about the environment and water as a resource, have given rise to new and improved technologies and treatment systems that are effective in dealing with wastewater pollution and also in reducing the energy used in recycling wastewater; however, selection of the appropriate technology to solve a specific wastewater problem should be undertaken with great care. Generally, there are two types of wastewater treatment systems – conventional and sustainable CW. 2.2. Conventional Wastewater Treatment Conventional wastewater treatment comprises physical, chemical and biological processes, involving three stages, referred to as primary, secondary and tertiary treatments. 6 2.2.1. Primary Treatment This treatment is used in the removal and separation of particulate inorganic materials and solids, which would otherwise clog and destroy water pipes of the network. This type of treatment entails screening, grit removal and sedimentation. Screens are used to get rid of large debris, including plastics and cans. The grit chamber system is used to remove, settle, gravel- and sandsized particles. According to Nelson et al. (2007), the wastewater is then moved into a quiescent basin, where it is temporarily retained so that the remaining heavier solids can settle to the bottom of the basin, while the lighter solids, including grease and oil, can accumulate on the surface. Finally, skimming and sedimentation processes are used to remove both the floating and settled pollutants. The liquid that remains is transferred to the secondary treatment. In this primary stage, 50% of the TSSs and 30–40% of the BOD are removed (Nelson, Bishay, Van Roodselaar, Ikonomou, & Law, 2007). 2.2.2. Secondary Treatment Dissolved and biological matter is removed in the secondary treatment. According to Nelson et al. (2007), 90% of the organic matter in the wastewater is removed at this stage. The attached and suspended growth processes are the two most suitable conventional methods used in secondary treatment. In the attached growth process, algae, bacteria and other microorganisms are grown on the surface of the wastewater, resulting in the formation of biomass, which breaks down the organic 7 waste. Trickling filters, bio-towers and rotating biological contactors are included in the attached growth process unit. In the suspended growth process, the microbial growth is suspended in an aerated water mixture; however, activated sludge, in which a biomass of aerobic bacteria and other microorganisms is grown, is the most common type of suspended growth process. 2.2.3. Tertiary Treatment The tertiary treatment is more advanced, aimed at producing a better-quality, more purified effluent for discharge into estuaries and low-flow river ecosystems. Coagulation sedimentation, filtration, reverse osmosis and extended secondary biological treatments are some of the methods that are used in this stage. These methods remove nutrients and stabilise oxygen in oxygendemanding substances. The treated effluent can then be safely reused, recycled or discharged (Praewa, 2017). In most circumstances, a final disinfection process is needed before tertiary-treated wastewater can be discharged. Disinfectants can be added to kill off pathogens and microorganisms, and. chlorine and ultraviolet light are also commonly used. The treated water can then either be discharged into different water bodies, including recharging underground reserves, or used in agricultural irrigation (Praewa, 2017), as long as it meets the required standards. 8 2.3. Constructed Wetlands (CWs) CW systems for single-household, municipal, and industrial wastewater are designed in ways that imitate the natural processes at work in wetlands, but include features that provide advantages over natural wetland processes. Such CWs incorporate chemical, biological and physical processes that are used to remove the pollutants and enhance and improve the quality of the wastewater (Vymazal & Kropfelova, 2008). These design systems use aquatic macrophyte and microbial communities, and plant roots and their host minerals to effectively remove pollutants, which include nitrogen, metals and pathogenic organisms, among many others. In 1904, the first CW was built in Australia (Vymazal & Kropfelova, 2008). Despite this, technological advancement in the field has been slow (Vymazal & Kropfelova, 2008). As the number of CWs increases around the world, and the benefits and effectiveness of the system over conventional treatment systems become better understood, CWs are finding wider favour among ecologists, scientists and water and environmental engineers, and this is leading to their popularisation even among developing countries. 2.4. Main Benefits and Outcomes of CWs The CW is a beneficial wastewater system because, upon treatment, the water that is discharged can either be used for domestic activities, or can be directly discharged into the environment. It is also beneficial to the end-users, as construction costs are minimal, and the costs of operation and maintenance are affordable. The operation and maintenance of CWs are periodic, unlike 9 conventional water treatment systems, which in most cases require continuous, on-site labour (Crawford & Sandino, 2010). The CW system facilitates the recycling and reuse of water, thereby defraying the costs of installation, operation and maintenance. The CW system not only provides a habitat for wetland organisms, but is also engineered in a way that finds favour with the public because of its many benefits. 2.5. Types of CWs There are various types of CWs that depend on the available landscape, including SF and SSF systems. SF CWs have shallow flow and lower velocity over the substrates, whilst SSF CWs have either VF or HF over the substrates. Hybrid CWs combine both VF and HF (Vymazal & Kropfelova, 2008). Each type of CW system has its benefits and drawbacks, and each differ in the treatment process used. SF CWs make use of plant stems, leaves and rhizomes to effectively treat wastewater. In dense vegetation, however, the process can be limited because there is not enough circulation of oxygen, which is vital for the organisms. In SSF CWs, roots are used in the treatment of effluents as water passes through a series of gravel beds. This process is considered to be superior to, and more effective than, that used in SF CWs. 2.6. Components of CWs 2.6.1. Water 10 Locations in which landforms predominantly direct surface water straight into shallow basins, or where impermeable subsurface layers hinder the ground from absorbing surface water, are the most likely places for wetlands to form naturally. Such conditions in a location can be engineered to create wetlands (Jhansi, & Mishra, 2013). Land can be structured in such a way that surface water is collected, and such basins can be sealed in order to retain the collected surface water. Once a landscape has been modified in this way, a wetland can be constructed. In the construction of a wastewater wetland system, hydrology is among the most important factors to be considered. This is because it not only links all of the functions of the wetland, but it is also a key factor in the CWs failure or success in a given landscape. The hydrology of the CW is important in relation to the hydrology of other surface water in the area. Small, natural hydrological changes can promote significant effects in the CW, impacting on its utility. Through rainfall and evapotranspiration, there is substantial interaction between the wetland system and the atmosphere because of the wetland water is shallow and covers a large surface area. The hydrology, in most cases, is also affected by vegetation density in the wetland, which can obstruct the flow of water. 2.6.2. Substrates, Sediments and Litter Soil, sand, gravel and rock, as well as organic materials, such as compost, are used to make the substrates for the wastewater to flow over. Due to the high biological productivity and low water velocities in wetlands, it is possible to easily accumulate sediments and litter (i.e., organic 11 matter). These substrates, sediments and litter are vitally importance because they support all of the living organisms that dwell in wetlands (Secretariat, 2014). For many contaminants in a wetland, the substrate acts as a sink. The substrate is also important because its permeability affects the movement of water passing through the CW. 2.6.3. Vegetation In any CW, the presence of both vascular and non-vascular plants is of vital importance (Praewa, 2017), vascular plants being the higher plants, whereas non-vascular plants are the algae. When algae undergo photosynthesis, they increase the dissolved oxygen content in the water, which significantly affects the metals and nutrients present in the water. The presence of plants in a CW system, therefore, is very important, since they also penetrate the substrate structure, transferring oxygen into the substrate, a process that is not possible or achievable, even using diffusion. The presence of submerged leaves, stalks and litter is important in FWS wetlands in terms of attached microbial growth, wherein the leaves, stalks and litter themselves serve as substrates. Wastewater wetlands are mostly characterised by the absence of emergent plants, although natural wetland systems commonly include reeds, rushes and cattails. Cattails have the ability to survive and thrive under diverse environmental conditions, and they can produce massive annual biomass. Rushes –particularly bulrushes – are perennial, grass-like plants that are capable of growing and thriving in clumps. They tend to grow better in water that ranges from 5 cm to 3 m deep (Wetzel, 12 1993). Most bulrushes grow well in water that has a pH of 4–9. Reeds are tall, annual grasses with a perennial rhizome. Reeds are among the most widespread emergent aquatic plants. CWs that use reeds are at an advantage because the reeds have the ability to transfer oxygen into the substrate, thus improving the effectiveness of the system. 2.6.4. Microorganisms The functions of CWs are, in some way, controlled and regulated by the presence of microorganisms and their metabolic processes. Algae, protozoa, fungi and yeasts are examples of microorganisms that are found in wetlands. Microbial activity in the system is important because this is how nutrients are recycled. Microbial activity also affects the processing capacity of the wetland because it can cause reduced conditions in the substrate. In CWs, microbial communities are affected by toxic chemicals, such as those found in pesticides (Wetzel, 1993). 2.6.5. Animals Certain vertebrates and invertebrates take up residence in CW systems. Insects and worms are (invertebrates) are significant contributors to the treatment process (Wetzel, 1993), making it safe and more effective. 13 2.7. Literature Summary CWs for municipal, industrial and domestic wastewater treatment can be designed in appropriate and specific ways to meet most intended purposes. Wetland systems can be engineered to take advantage of the various features of a site. CWs are an effective approach that can be employed in improving wastewater quality and allowing for its reclamation and reuse. Moreover, CW systems are of economic and thus they are globally applicable. 14 Chapter 3 METHODOLOGY 3.1. Overview In this chapter, case studies are used to describe the various methods for treating specifically domestic wastewater of certain PE, and includes information on the parameters used in CWs, such as measurements of areas, slopes and aspect ratios, whilst the methods and equations used to analyse data related to various comparative physiological and chemical components in the (treated) wastewater are highlighted. Background information on the site locations is also provided. 3.2. Methodologies 3.2.1. HSSF CWs for On-Site Wastewater Treatment The methodologies commonly used in Czech CWs are summarised, with the intention of determining whether indeed SSF CWs are more efficient than conventional treatment systems. Moreover, the study aims to assess whether SFF systems can meet the standards set for Ohio (USA) home systems through scientific analyses, including assessing treatment efficiencies in relation to TSS, BOD, TN, TP and FCs.This study’s methodologies are discussed using the following design parameters: Pre-treatment: HSSF CWs are for the secondary treatment of wastewater, and mainly employ a septic tank to remove TSSs, which settle to the bottom of the tank where they are anaerobically 15 degraded. Regular pumping of the tank after initial installation is necessary. Such septic tanks are common in single-family households. Surface area and configuration of the beds: The general rule-of-thumb formula for determining the surface area for wetland cells is given below, for cells with a total area of 5 m2 per PE. Most of the Czech designs use two cells, the first lined, to avoid leaching, and the second unlined, to reduce discharge, especially in cases where the water table is high (Hoddinott, 2006). ( ) ( ) , where Ah is the surface area of the bed in m2 , Qd is the average flow in m3 per day, Co is the influent BOD5 in mg l-1 , C is the effluent BOD5 in mg l-1, and KBOD is the rate constant in m day-1 (Hoddinott, 2006). Aspect ratio: Darcy’s law is used to calculate the length to width ratio of the cell bed. The correct ratio is necessary for maintaining adequate flow. CWs in the Czech Republic are designed with an aspect ratio of <2 because a wider inflow ensures optimal flow and reduces clogging at the inlet. Inlet clogging can also be reduced by using earthworms or larger-sized gravel at the inlet, to promote for greater flow. [ ( ( )] ) , where Ac is the cross-sectional area of the bed in m2, Qs is the average flow in m s-1, Kf is the hydraulic conductivity of the medium in m s-1, and dH/ds is the slope in m m-1 (Hoddinott, 2006). 16 Bottom slope and depth: The maximum macrophage depth of Phragmites australis (the common reed) is used in Czech designs to determine the depth of a CW cell, being 0.6–0.8 m. Coarse substrates call for a slope of 2.5% or less, while fine substrates need a slope of 1% or less (Hoddinott, 2006). Other studies have shown that a water depth of 0.27 m is the most efficient when it comes to removal rates (Hoddinott, 2006). Filtration media: Such media should facilitate macrophage growth, provide high filtration and maintain high hydraulic conductivity. Gravel of 10 mm dimensions fulfills these requirements. In addition, coarser particles of gravel at the inlet and outlet reduce clogging. Bed sealing: According to Czech regulations (Hoddinott, 2006), plastic liners should be used to seal beds. The liners should be between 0.8 and 2.0 mm thick. Sand or geotextiles should be used to protect the liners on both sides, to prevent damage by root penetration or sharp edges. Home systems can use ready-made plastic tubs that are inexpensive. Vegetation: Macrophages should be able to control erosion, ensure filtration and provide surface substrates for microorganism growth. Nitrogen removal is best facilitated by oxygen flux, which is ideal when root rhizome separation is 35–70 mm, a condition that is met by Phragmites australis. This species has also proved to be the best at facilitating greater bacterial growth. The consensus from various studies (Hoddinott, 2006), is that planted wetlands are more efficient than unplanted ones, especially with the integration of a pretreatment phase. 17 Insulation: Four to eight seedlings per m2 provides good insulation when the plants grow and begin to litter. Keeping the flowing influent warm is necessary to ensure optimal functioning of the microorganisms. Other studies have shown that insulation that consists of reed–sedge peat or yard waste compost is effective, even at -20°C (Hoddinott, 2006). 3.2.2. Use of VF CWs for On-Site Treatment of Domestic Wastewater: New Danish Guidelines New guidelines have been established by the Danish Ministry of the Environment regarding treatment requirements for single households in rural areas (Brix & Arias, 2005). Methodologies for analysing the BOD, COD, TSSs, TP and TN in wastewater are discussed below. The standard VF system for a five-PE household should have a total surface area of 16 m2 (Brix & Arias, 2005). The filter depth should be 1.4 m, with a 0.2 m drainage layer, 1.0 m sand filter layer and 0.2 m insulation layer (Brix & Arias, 2005). To prevent the sewage from entering the surrounding environment, a 0.2 m embankment should be raised around the bed. A tight membrane, with a minimum thickness of 0.5 mm, protected by a geotextile layer on both sides, should be used to enclose the bed. In addition, the drainage layer should be made up of coarse gravel that is 8–16 mm in size, in which 70 mm diameter drainage pipes should be placed. All of the pipes should be connected on one side to a collection pipe for discharge of the effluent. Passive aeration should be carried out in the drainage system, using vertical pipes extending 0.3 m over the filter bed surface (Brix & Arias, 2005). The new Danish guidelines for systems serving up to 30 PEs are outlined below. 18 Pre-treatment: Septic tanks, or chamber sedimentation tanks, with two or three chambers must be used for pre-treatment before discharging wastewater into a VF wetland. Single-household systems with up to 5 PEs should use a tank measuring 2 m3. The higher the PE, the larger the volume of the tank should be. In two-chamber tanks, the first chamber should constitute 70–90% of the total tank volume, while for a three-chamber tank, the first chamber should constitute 50– 70% of the total tank volume. The remaining volume should be evenly distributed between the other two chambers. Sludge removal should be carried out once a year. System operation and layout: VF CWs are required to have a planted filter bed at the point where wastewater is loaded onto the surface. The surface area of the bed should be 3.2 m 2 PE-1. The filter should not be too saturated with water. Treated wastewater is collected in a passivelyaerated system of drainage pipes positioned in the bottom of the filter. Filter medium: The standard filter medium is sand. Clay and silt, or any particles <0.125 mm in size, should be less than 0.5% (Brix & Arias, 2005). The filter depth is recommended to be 1.0 m, and the filter surface should be leveled out. The bed should be lined with an open geotextile material, or a layer of graded gravel, to prevent sand from entering the drainage layer. Distribution system: Pressurised distribution pipes are used to distribute the sewage evenly over the bed surface. The pipes should have a diameter of 32–45 mm, with 5–7 mm diameter holes drilled through the bottom of the pipes, every 0.4–0.7 m (Brix & Arias, 2005). The pump volume 19 should be at least thrice the distribution pipe system volume. Insulation against freezing should be provided, using a 0.2 m layer of coarse wood chips or sea shells positioned on the filter surface. Effluent recirculation: A split well, with two V-notch weirs, should be placed at the system outlet (Brix & Arias, 2005). The surfeit from one weir is recirculated to the first compartment of the sedimentation tank by gravity. Half of the effluent is recirculated. An alternative is to recirculate the effluent to the pumping well. Planting: Phragmites australis is used for wetland vegetation at a density of four plants per m2. Potted seedlings or rhizome pieces can be used for planting. 20 Figure 3.1: Layout of a VF CW system for a single household. Raw sewage is pre-treated in a 2 m3 sedimentation tank. Firm sewage is pulse-loaded onto the shallow end of the bed by a levelcontrolled pump. Treated effluent is collected in a system of drainage pipes, and about half the effluent is recirculated back to the pumping well, or to the sedimentation tank (Brix & Arias, 2005) 3.2.3. The Attenuation Capacity of CWs to Treat Domestic Wastewater in Ireland An Irish Environmental Protection Agency-funded project was established to investigate the removal efficiency of CWs in treating chemical and microbial wastewater contaminants found in domestic wastewater effluent in Ireland (O'Luanaigh & Gill, nd). Two HSSF beds, Reed Bed 1(RB1) and Reed Bed 2 (RB2), were constructed on-site for surveillance during their first 26 months of operation. Pre-treatment took place in a RBC, and acted as the primary treatment. The secondary treatment was administered to RB1, while RB2 received tertiary treatment. RB1 can 21 serve three PEs, while RB2 can serve two. Table 3.1 shows the design parameters for the two beds. Table 3.1: RB1 and RB2 design characteristics (O'Luanaigh & Gill,nd) Reed Bed ID Influent Type Plant Species RB1 STE RB2 TE Phragmites australis Iris and Typha Dimensions l*b*h (m) 5.8×2.6×0.6 Area m2 4.0×1.0×0.6 4 15 The beds were sealed using one sheet of butyl rubber liner filled with limestone gravel, 5–15 mm in diameter. Gravel (15–30 mm in diameter) was used at the inlet and outlet. The vegetation was planted in blocks of 4 m2. The hydraulic parameters for the beds are shown in Table 3.2. Table 3.2: RB1 and RB2 mean hydraulic parameters (O'Luanaigh & Gill, nd) Reed Bed ID Influent Type Inflow (L d-1) HLR (mm d-1) RB1 RB2 STE SE 327.3 136.9 21.8 34.2 Design (mm d-1) 36 90 HLR RB2 received almost twice the daily flow per unit surface area than RB1, although the secondary and tertiary treatment reed beds were overdesigned when equating the respective HLR values, as a consequence of lower-than-expected on-site hydraulic loads. Nevertheless, there was a disparity between the respective HLRs (O'Luanaigh & Gill, nd). 22 3.2.4. A Recirculating VF CW for the Treatment of Domestic Wastewater One objective of this research was to apply a recirculating VF CW – a decentralised, small-scale system – to the treatment of domestic wastewater, adjusting it where necessary to produce effluents that would conform to Israeli regulations for urban landscape irrigation (Sklarz, Gross, Yakirevich, & Soares, 2009) and, in addition, to determine the effluent water quality every 2–3 weeks over the course of a year by analysing BOD5, COD, TSSs and TN. The process is described in Figure 3.2. Two pilot recirculating VF CWs, designated R and L, were constructed at Midreshet Ben Gurion, in the Negev Desert, Israel (Sklarz, Gross, Yakirevich, & Soares, 2009), to treat primarily settled domestic wastewater from a residential neighborhood. Each recirculating VF CW was composed of two 0.9 m wide x 1.1 m long x 0.6 m high plastic containers placed one on top of the other (Sklarz, Gross, Yakirevich, & Soares, 2009). The container on the top acted as the VF CW, and was perforated with holes of 8 mm diameter. Each container was then filled with a 5 cm-thick pebble layer, followed by a 40 cm-thick layer of highly-porous plastic beads with a high surface area of 860 m2 m-3. The domestic wastewater fed into the upper tank trickled into the lower container. Initially, the R and L systems were operated without an upper soil–plant component, and the wastewater was applied daily, in three 100 L batches, at 9 am, 1 pm and 8 pm. The wastewater was recirculated through the bed at a RFR of 4.5 m3 h-1, and was sampled 12 h after the addition of the last batch (Sklarz, Gross, Yakirevich, & Soares, 2009). An 8 cm-thick layer of peat, planted with Juncus alpigenus (rush) and Cyperus haspen (sedge), was added to system R, and the RFR was reduced to 2.5 m3 h-1 in both systems; however, the RFR in the unplanted system had to be increased back up to 4.5 m3 h-1 and then gradually decreased to 2.5 m3 h-1.Manipulation of the flow rate in the planted system was restricted, and 23 found not to be practical because of the limited hydraulic conductivity of the peat layer (Sklarz, Gross, Yakirevich, & Soares, 2009). Figure 3.2: Schematic representation of a pilot recirculating VF CW for the treatment of domestic wastewater. The upper container is a VF CW bed. Wastewater is applied to the root zone, trickles through the bed, and drips into the lower container, from where it is recirculated back to the root zone, until the required water quality is achieved (Sklarz, Gross, Yakirevich, & Soares, 2009) 24 3.2.5. A Hybrid CW System for Decentralised Wastewater Treatment A hybrid CW, incorporating a reactive phosphorus barrier in the HF bed, which is followed by a VF bed, was studied. The HF removes organic matter and solids, while mitigating clogging risks, and the VF converts ammonia to nitrate, a process called nitrification. The reactive phosphorus barrier is used to remove phosphorus. Denitrification is the process wherein nitrate is converted to N2 gas. The conditions necessary for denitrification are an anoxic environment and a carbon source. The carbon is acquired from the incoming wastewater. Denitrification of the wastewater is achieved by recycling the nitrified effluent back to the HF inlet; this process reduces TN by up to 70%. A hybrid system, located at the Ontario Rural Wastewater Centre’s On-site Wastewater Testing Facility in eastern Ontario, Canada, has a flow rate of 2.8 m3 d-1, which can serve two singlefamily households. Two parallel systems were constructed to study the effects of flow rate and recycle rate on the performance of the system. Pilot wetlands were fed with raw wastewater from the Alfred municipal sewer line. A septic tank, with a volume of 5.6 m3, provided the primary treatment. The HF wetland measures 5.0 x 9.0 x 0.7 m, and has an operating depth of 0.55 m. The bed was lined with a 30 mil polyvinyl chloride (PVC) liner. The filter medium used in the first 1.0 m was washed coarse gravel, 25–50 mm in diameter. The remainder of the cell was filled with 13–20 mm washed gravel. The HRT of the cell is 4.5 days, with a design flow of 2.8 m3 d-1. The header pipe is a 10 cm in diameter perforated PVC pipe that was laid across the width of the wetland (Kinsley, Crolla, Rode, & Zytner, 2014). The HF cells were planted with Phragmites australis (reed) at a density of 9 seedlings/m2. The last 2.0 m were planted with hybrid sandbar willow at a density of 1 cutting/m2. The medium selected for the phosphorous filter was blast-furnace slag. The slag filters measured 5.0 x 2.5 x 0.7 m, with an active depth of 25 0.55m and a HRT of 1 day. The slag measured 25–50 mm in diameter. A PVC footer, measuring 2.5 cm in diameter, with a 0.55 m standpipe, was positioned at the outlet of the slag filter. The outlet pipe flows into a pump chamber that feeds the VF beds (Kinsley, Crolla, Rode, & Zytner, 2014). The VF bed has a layer of peat to neutralise the high pH of the effluent flowing from the slag filter. The VF bed measures 2.5 x 2.5 x 0.8 m in size. The filter comprises, from top to bottom, a 0.2 m-thick layer of Sphagnum peat moss, a 0.4 m-thick layer of 1–5 mm in diameter washed sand, a 0.2 m-thick drainage layer of 13–20 mm washed gravel, and a 30 mil PVC liner. The dosing array is made up of six lines (38 mm in diameter PVC dosing pipe), inserted every 50 cm, with a 7.5 mm opening spaced every 50 cm (Kinsley, Crolla, Rode, & Zytner, 2014). A 28 L dose of the effluent is delivered to the filter, in which P. australis was planted at a density of 9 seedlings/m2. The dosage is controlled using a float-controlled pump (Kinsley, Crolla, Rode, & Zytner, 2014). Effluent drains through 3 x 10 cm perforated PVC pipes connected to a footer line, and flows to a pump chamber. A pump in the effluent pump chamber recycles part of the treated effluent back to the HF inlet (Kinsley, Crolla, Rode, & Zytner, 2014). The system is summarised in Figure 3.3. 26 Figure 3.3: Hybrid CW schematics (Kinsley, Crolla, Rode, & Zytner, 2014) 3.2.6. CW of Lepironia articulata for Household Greywater Treatment This study was established in a village to observe, and determine the characteristics of, greywater loading, and to provide a suitable on-site mini-wetland for determining the system’s effectiveness (Wurochekke, Harun, Mohamed, & Kassima, 2014). In addition, the study aimed to determine the efficiency of Lepironia articulata (sedge) in pollutant removal, and to see whether treated wastewater could be safely reused for purposes such as irrigation. There were six people in the study, all female, 20 to 30 years old. The house comprised three bedrooms, two bathrooms, a living room and a kitchen where everyone regularly cooked in the 27 morning and at night (Wurochekke, Harun, Mohamed, & Kassima, 2014). The bathroom was used twice daily by each occupant, and the washing machine was used twice a week (Wurochekke, Harun, Mohamed, & Kassima, 2014). Figure 3.4: Schematic diagram of a mini-CW system (Wurochekke, Harun, Mohamed, & Kassima, 2014) The system (Figure 3.4) was made using three HDPE plastic containers and PVC pipes. Water flow was gravity-driven. Pre-treatment took place in a 20 L cylindrical container, with a gravel (<25 mm diameter) filter medium, then charcoal, fine sand (diameter 0.2 mm) and another layer of gravel (diameter <15 mm). Wastewater from the pre-treatment container flowed into the 28 second and third HDPE containers. Each of the containers measured 34 x 18 x 14 cm and acted as a mini-CW. The second container had a filter medium of fine sand (diameter <0.2 mm) and gravel (diameter <15 mm). The L. articulata was planted at the top soil of tube sedge as a biological treatment. The filtered water exited the second container through holes in the bottom of the container. The effluent was collected in an insulated black container and taken for the analysis of BOD, COD, TSSs, Ammonia nitrogen (AN) and turbidity. The third container acted as the control, having the same dimensions as the second container. Samples were collected at 10 am and 9 pm every day for four days (between 5 March 2013 and 17 March 2013). These samples were analysed using standard methods for water and wastewater (Wurochekke, Harun, Mohamed, & Kassima, 2014). 3.2.7. CW System for Wastewater Treatment The aim of this study was to establish a full-scale system to treat sewage from a single household, based on experimental systems (Farooqi, Basheer, & Chaudhari, 2008). Pollutant removal was done through a combination of chemical, physical and biological processes associated with sedimentation, vegetation and microbial activity. The following equation (Eq. 3), designed by Kikuth (1977), can be used for SSF CWs treating domestic wastewater to determine size: ( ) 29 , where Ah is the surface flow of the bed in m2, Qd is the average flow rate in m3 d-1, Cin is the influent BOD5 in mg l-1, Cout is the effluent BOD5, and KBOD is the rate constant d-1 (Farooqi, Basheer, & Chaudhari, 2008). An experimental VF CW (Figure 3.5) was established in a traditional municipal wastewater plant in order to manipulate the HLRs as desired. Based on the outcomes of the experiment, a fullscale system was constructed for a single household of four PEs. The system was constructed as a 2 m3, three-chambered sedimentation tank, with a level-controlled pump and a 15 m2 VF CW (Farooqi, Basheer, & Chaudhari, 2008). Effluent recirculation was applied in the system through the sedimentation tank, in order to improve TN removal through denitrification. Phosphorous removal was performed using chemical precipitation in the sedimentation tank. Figure 3.5: General layout of a single-household VF CW system (Farooqi, Basheer, & Chaudhari, 2008) 30 3.2.8. Use of Macrophyte Plants, Sand and Gravel Materials in CWs for Greywater Treatment This study aims to present the results concerning the removal of BOD, COD, TSSs, pathogens and detergents that are outlined in chapter 4, based on recent studies of CW used in Central Java Indonesia, and some similar studies in West Java Indonesia, Thailand and Costa Rica. This also illustrates the successful performance of local macrophytes and natural substrates (Qomariyah, Ramelan, Sobriyah, & Setyono, 2017). The Methodology of the recent study Central Java Indonesia are discussed in this chapter. An experimental single HSSF was constructed with dimensions of 1.7 x 0.7 x 0.7m (l x w x h). The experiment was conducted in Sukarta, Indonesia, and the effluent was collected from a single house in 2015. River sand and gravel were used as the substrates. The CW was filled to a depth of 50 cm, with a 20 cm length of gravel at the inlet and outlets, and 130 cm Length of river sand. Cyperus papyrus (paper reed) was planted at 25 cm intervals. The wastewater was pretreated in a sedimentation tank, and then loaded gradually, increasing from 25 to 100% over four weeks, so as to acclimatise the plants. The HRT was one day. The experiment was monitored for three months, and samples were collected twice a month. 3.2.9. Integrated CWs for Treating Domestic Wastewater This study focused on the treatment of domestic wastewater on small and industrial scales (after a year of experimental operation), using integrated CWs. The main features of integrated CWs are a shallow water depth, emergent vegetation and the use of in-situ soils that imitate those found in natural ecosystems (Scholz, 2011). Artificial liners are not used in integrated CWs. The 31 nutrient removal performance, and the impact of seasonal and annual changes on the parameters, are compared between both systems in Chapter 4. The CW for treating domestic water in Ireland was constructed in Glaslough, Monaghan County. Inflow rates ranged from 85–105 m2 d-1 and outflow rates from 1–50 m3 d-1, which was very low due to evapotranspiration and the infiltration of treated wastewater (Scholz, 2011). The wastewater dilution was 35–65%. The system served about 1750 PEs and had an area of 6.74 ha, with a water surface area of 3.25 ha. The system consisted of a small pumping station, two sludge cells and five shallow, vegetated cells, as shown in Figure 3.6. Domestic sewage from the village was pumped to an on-site pump and into one of the sludge cells. From the sludge cells, wastewater flowed by gravity through the five vegetated cells, and the effluent discharged into Mountain Water River. The wetlands were planted with Carex riparia, Curtis, P. australis, Typha latifolia, Iris pseudacorus, Glyceria maxima, G. fluitans, Juncus effusus, Sparganium erectum, Elisma natans and Scirpus pendulus (Scholz, 2011). Hi-tech automatic sampling and monitoring was performed weekly. In addition, the Glaslough stream was monitored regularly (Scholz, 2011). Groundwater was monitored using six piezometric ground-water monitoring cells placed within the system and along the suspected flow of contaminants (Scholz, 2011). 32 Figure 3.6: Sketch showing groundwater and surface water monitoring, and inlet and outlet points, for the integrated CW in Glaslough, near Monaghan, Ireland (Scholz, 2011) Another system, at Dunhill, Waterford County, southern Ireland, was Constructed. Here, the water inflow was about 40 m3 d-1 and the outflow about 24 m3 d-1. The wastewater dilution was 33 about 5–20%. The total area of the system was 0.3 ha. The primary vegetation used was an emergent species of helophyte (bog plant). The system was gravity fed, and therefore no energy was required. The wastewater was collected from the households using the sewage system, and then transported to the wetland system. Grab samples from the inlet and outlet were analysed, and Mountain Water River was regularly monitored. Two piezometric groundwater-monitoring cells were sampled at a depth of 5 m to monitor contamination of the groundwater. Figure 3.7: Sketch showing groundwater and surface water monitoring, and inlet and outlet points for the integrated CW system at Dunhill, near Waterford, Ireland (Scholz, 2011) Water samples were analysed for parameters including BOD, COD, ammonia–nitrogen, nitrate– nitrogen and molybdate-reactive phosphorus (MRP). 34 3.2.10. Efficiency of Small CWs for Subsurface Treatment of Single-Family Domestic Effluent The main aim of this study was to evaluate the effectiveness of single family CWs in Ohio, USA in improving water quality, and determining whether they met US Environmental Protection Agency guidelines. Samples from the CWs were collected quarterly, from 1994–2001. Twentyone domestic CWs, serving 21 single-family homes, each with one to seven family members, were assessed, all sharing a common three-stage design. Each system had a septic tank that provided primary treatment, followed by two wetland treatment cells. Water from the septic tank entered the primary cell using a manually-controlled water-level control box. The cells measured 4.5 x 5.5 x 0.46 m (l x w x d). Riverbed gravel (3 cm diameter) was predominantly used, with larger gravel (6 cm diameter) at the inlets and outlets. The first cell was a minimum of 10 cm higher than the second to facilitate gravity flow. Two of the systems were aerated, while one was designed with longer, narrower cells. Earthen berms were used to prevent runoff into the environment. The first cell was lined with impermeable clay or rubber, while the second was left unlined. Arrowheads or bulrushes were planted in Cell 1, while Cell 2 was generally planted with ornamental wetland plants. Phragmites invaded some of the systems. Trained technicians collected samples, quarterly, at the septic tank, the inlet box between Cells 2 and 3, and the outlet box in Cell 3; TSSs, BOD5, ammonia, FCs and TP were tested for. ANOVA t-tests were used to analyse the relationships among input, output and treatment efficiency of the systems that met EPA effluent guidelines, compared to those that did not (Steer, Fraser, & Boddy, 2002). 35 Figure 3.8: Typical three-cell design of a single-family domestic CW system (Steer, Fraser, & Boddy, 2002) 3.2.11. Reed bed CW system A study performed at Haya Water Company in Quriyat, Oman involved designing, building and operating a CW, and studiying the performance of the system for a year (12 June 2016–12 July 2017). The aim of the study was to evaluate the efficiency of a reed bed treatment system for domestic and partially non-domestic wastewater. Haya water used a double stage VF reed bed, with an anoxic tank (Haya Water, 2017). The parameters analysed included TSSs, (O&G), (VHO), COD, BOD, TP, TN and NH3–N; the results were compared to Oman's Ministerial Decision 145/1993 Standards (A) to determine whether the effluent quality was acceptable for irrigation purposes (Haya Water, 2017; Oman Government, 2018). The capacity of the reed bed was 50 m3, while the area was 1300 m2. The reed bed received water from a balancing tank. Phragmites australis (common reed) was used for vegetation. The reed bed was divided into two stages. The filter used in the first stage was >1 in size, with fine gravel filter material (thickness of 2–2.8 mm) to a depth of >30 cm. The filter used in the second 36 stage was also >1 in size, while the filter material had a thickness of 0.25–0.4 mm and a depth of >30 cm (Haya Water, 2017). Table 3.3 illustrates the design criteria for the double-stage VF reed bed. Table 3.3: Design criteria for a double-stage VF reed bed after pre-treatment (septic tank) (Haya Water, 2017) There were two major stages in the system: Stage A had three basins – A1, A2 and A3 – and Stage B hasd two basins – B1 and B2. The system had a buffer tank, an anoxic tank, a TE storage tank, along with three pumps. The process started at the buffer tank, which acted as the measuring can. From the buffer tank, raw sewage discharged into the anoxic tank, where the wastewater underwent partial denitrification (Haya Water, 2017). 37 Stage A was the settlement stage, in which untreated effluent took two hours to be loaded into each compartment. This was where 50% of TSSs and 20% of BOD were removed, and partial denitrification took place. From Stage A, the treated effluent was loaded into Stage B, where a biological treatment took place. This stage was known as the aeration stage due to the nature of processes that took place in there, including nitrification (ammonia to nitrate) and biological reactions. Further denitrification was achieved through partial effluent recirculation into the anoxic tank, where nitrates were converted to nitrogen gas (Haya Water, 2017). The remaining effluent flowed to the Treated Sewage Effluent storage for further disinfection. Figure 3.9 demonstrates this process of wastewater effluent treatment. Figure 3.9: Description of the process for treated effluent (Haya Water, 2017) Figures 3.10 and 3.11 illustrate Stages A (initiation) and B, and Figure 3.12 shows the P. australis after both stages (Haya Water, 2017). 38 Figure 3.10: Stage A (Haya Water, 2017) Figure 3.11: Stage B (Haya Water, 2017) 39 Figure 3.12: Photographs after both stages (Haya Water, 2017) 40 Chapter 4 RESULTS AND DISCUSSION 4.1 Overview In this chapter, a detailed discussion of the results from the case studies introduced in Chapter 3 is presented. This chapter provides the efficiency removal rates for various parameters, such as COD, BOD5, TSSs, TKN, TN, TP, FCs, TCs, bacteria and ammonia, as related to each case study. The effectiveness of the design strategies are also discussed. To determine which design is the best, a comparison is made between two related case studies that used different CW designs. The comparison is based on methodologies used and removal efficiencies observed. 4.2. Results and Discussion 4.2.1. HSSF CWs for On-Site Wastewater Treatment In line with the objectives of the original study, the results for TSSs, BOD, FCs, nitrogen and ammonia are discussed extensively below. The Ohio Environmental Protection Agency (OEPA) guidelines for discharge standards are shown in Table 4.1. Table 4.1: Surface discharge limits (maximum concentrations) (OEPA, 2001; Hoddinott, 2006) Pathogen FCs BOD5 TSSs Ammonia Phosphorous Concentration 2000 15 18 1.5 1 Unit Counts/100 ml mg l-1 mg l-1 mg l-1 mg l-1 41 The average BOD5 removal in the Czech case study CWs was 88%, and the average outflow concentration was 10.5 mg l-1, which are below the OEPA standards (Hoddinott, 2006). Moreover, the average COD removal was 75%, with an average outflow concentration of 53 mg l-1. COD removal was less than BOD removal because of the presence of non-biodegradable pollutants (Hoddinott, 2006); however, it was observed that BOD and COD removal was not affected by the seasons. TSS removal was recorded at an average of 84.3%, and effluent concentrations averaged 10.2 mg l-1, within the OEPA limit of 18 mg l-1. TP concentrations in the discharge in all the CWs were above 3mg l-1. The required concentration is <1mg l-1, a figure deemed to be unobtainable for home systems. From the observations, Phragmites increased TP removal to 97 from 50%. Mechanical technologies to remove phosphorus were not recommended because the study aimed to maintain simplicity and low costs for the CW project. Ammonia removal rates in the Czech CWs averaged 43%. Individual rates ranged from 9–73% in the CWs.There was no significant seasonal variation observed in the removal of ammonia (Hoddinott, 2006). Planted CWs were more effective at nitrogen removal than unplanted CWs, but the effluent concentrations were below the OEPA guidelines of 1.5mg l-1 in both cases. SSF CWs produced almost 100% removal of coliforms and other bacteria, which fulfills one of this study’s objectives. Seeding experiments using Salmonella showed removal rates of 95– 99.8% in winter and summer, which meet the OEPA standards. Planted CWs recorded a 90% removal of bacteria, Giardia, Cryptosporidium and enteric viruses (Hoddinott, 2006). In addition, the CWs proved efficient in the removal of Cryptosporidium oocysts through protozoan 42 predation, which has been unresponsive to ordinary chlorination treatment efforts (Hoddinott, 2006). In summary, the study showed that iron added to the substrate improved the degradation of nitrogen and phosphorus to almost 100%, and that Phragmites was the best species for vegetation, which goes to prove that the plants and substrate medium are essential to the CW pollutant removal process. 4.2.2. Use of VF CWs for On-Site Treatment of Domestic Wastewater: New Danish Guidelines The results from the review of a VF system that should achieve 95% BOD removal, 90% nitrification and 90% phosphorus removal, according to a new set of guidelines set by the Danish government (Brix & Arias, 2005), are discussed. It was discovered that filter sand that is too coarse results in water passing through too fast and, hence, lower nitrification rates. In addition, the bed depth should be less than 1 m, in accordance with the guidelines, since most of the removal actually takes place in the upper few centimeters (Brix & Arias, 2005). According to the study, if the hydraulics of a system are not up to standard, there is a risk that the wastewater will bypass the thin filters too quickly (Brix & Arias, 2005). Since the VF2 and VF3 systems were loaded by gravity, water was not effectively distributed over the surface beds, as is the case in a pump-loaded system. The two systems received greywater only, while VF1 received recirculated influent. Effluent recirculation resulted in lower effluent concentrations and, therefore, better performance. Due to the recirculation, the influent concentration decreased, albeit artificially, because of dilution by the recirculated effluent. Ammonium–nitrogen concentrations in sewage can be higher than 100 mg l-1, which is why recirculation is important for lowering concentrations. The new Danish guidelines require effluent concentrations of <40 mg l -1 for 43 BOD, <150 mg l-1 for COD and >2.5 m2 PE-1 for surface area. The need for a smaller area in the VF ensures efficient BOD removal and nitrification; however, systems with <2 m2 are efficient in BOD and TSS removal, especially in domestic wastewater. Table 4.2 shows the removal efficiencies for various parameters in the VF beds. Table 4.2: Performance data (mean±1 SD) for some single-household VF CWs (Brix & Arias, 2005) System Parameter VF1 (without TSS recirculation) BOD5 NH4–N NO2+ NO3–N TN TP VF1 (with 100% TSS recirculation) BOD5 NH4–N NO2+ NO3–N TN TP VF2 TSS BOD5 NH4–N NO2+ NO3–N TN TP VF3 TSS BOD5 NH4–N NO2+ NO3–N TN TP Inlet (mg l-1) 85±28 254±123 105±45 <0.1 125±51 17.2±7.0 68±22 100±35 45±13 0.13± 0.09 57 ±13 5.2± 1.7 88 ±8 507± 395 242 ±75 0.1± 0.1 350 ±5 20.6± 7.5 124± 135 320 ±139 18 ±22 0.5± 0.5 30± 23 4.6 ±3.6 Outflow (mg l-1) 8± 3 19± 4 23 ±17 40 ±13 72 ±28 13.0 ±6.6 3± 1 11 ±3 7± 1 36 ±4 44± 5 5.7 ±1.2 7± 5 7 ±2 59± 11 141 ±40 190 ±37 7.5± 4.8 4± 3 2 ±1 0.4 ±0.2 8.0± 2.6 9 ±3 4.5 ±2.6 Efficiency % 91 92 78 43 25 96 89 85 23 0 92 98 76 46 64 97 99 98 63 2 To summarise, system clogging was observed as a risk in such beds, but can be minimised by allowing wastewater to fully pass through the bed before loading the next dose of wastewater. Planted reeds also prevent clogging, but substrate texture also plays a big role. The rate of 44 oxygen transfer from the atmosphere and the aerated drainage layer to the bed medium should be high. The case study proved that all of the Danish guidelines could be met, yielding a good performance. 4.2.3. The Attenuation Capacity of CWs to Treat Domestic Wastewater in Ireland Based on the parameters measured in Chapter 3, the following measurements and analytical parameters from the case study, along with seasonal variations, can be discussed. Water balance: RB1’s mean inflow was 327.3 L d-1 and mean outflow 349.9 L d-1, while RB2’s mean inflow was 136.9 L d-1 and mean outflow 149.2 L d-1. Neither bed had any significant effect on incoming HLRs, acting to increase RB1 and RB2 winter flows by 6.4 and 7.2%, and summer flows by 0.5 and 1.7%, respectively (O'Luanaigh & Gill, nd). HRT: Results from two tracer studies performed at the end of the first sampling year and during the final sampling phase, show that RB1 had a HRT of 6.5 days, while RB2 had a HRT of 5 days. The results were similar to calculated nominal retention times, meaning that dead zones were largely absent. Organic matter removal: COD concentrations at the inlet and outlet showed similar removal rates of RB1 67% and RB2 55%. According to a temporal variation analysis, COD removal in both beds showed a steady performance increase with time. There was minimal seasonal influence on performance, meaning that temperatures did not necessarily affect reed bed function. 45 Nitrogen removal: TN removal in both beds was limited by slow rates of mineralisation and little nitrification because of the anoxic environment. Only about half of the organic nitrogen fraction was converted to ammonium–nitrogen. There was a slight declining trend over the first three years of operation. Ammonium–nitrogen constituted the highest fraction of TN concentrations at both the inlet and outlet of RB1 (O'Luanaigh & Gill, nd). Nitrogen removal was highest during the first year of operation; however, there was a decreasing trend through the three years. Seasonal influence was minimal. RB2 had 41% TN removal, despite effluent from the RBC being partially nitrified, and nutrient removal, and denitrification in particular, often being a key focus for tertiary treatment (O'Luanaigh & Gill, nd). Denitrification in the reed bed was compromised, however, by the inability of the RBC to mineralise all of the organic–nitrogen to ammonium–nitrogen, and then fully nitrify the effluent. Table 4.3: Average influent and effluent nitrogen loads from RB1 and RB2 ( O'Luanaigh & Gill, nd) COD mg/l g/d RB1 514 182 in RB2 195 61 out TN Org–N NH4–N TKN NO3–N mg/l g/d mg/l g/d mg/l g/d mg/l g/d mg/l g/d 105.5 38.6 26.5 10.1 74.9 27.5 101.4 37.6 3.9 1.0 NO2–N mg/l g/d 0.2 0 76.9 27.3 13.1 4.7 61.0 21.1 74.1 25.8 2.8 0.05 0 RB1 193 in RB2 107 out 32 92.8 15.6 25.0 4.1 22.1 4.0 47.1 8.1 37.9 5.1 7.8 2.4 15 63.9 9.2 20.7 2.6 32.5 4.4 26.7 3.9 4.7 0.9 11.8 1.8 1.5 Phosphorous removal: The removal of TP averaged out at 45%. Efficiency slightly decreased after the first year, and stabilised over the next 18 months. Summer removal rates were higher 46 than those of winter, which could be attributed to plant growth (plants accumulating biomass better in summer than winter). According to O'Luanaigh and Gill (nd), the temporal variations of phosphate–phosphorus effluent concentrations showed the same pattern as the influent values, and it appears that adhesion sites were still readily available after the 26 months of monitoring. Bacterial removal: The mean removal of TCs and Escherichia coli in RB1 was 98.5% (1.8 log units) and 96% (1.4 log units), respectively, while the mean removal rates for TCS and E. coli in RB2 were 1.3 log units and 1.7 log units, respectively. There was little seasonal or annual variation in either indicator organisms in RB1 and RB2. In addition, an analysis of samples from intermediate sampling points in the middle section of the reed bed showed an exponential decrease in the concentrations of both coliform species, with longitudinal distances of r2 = 0.947 (TCs) and r2 = 0.977 (E. coli).Table 4.4 shows the E. coli concentrations from the two Beds Table 4.4: Average influent and effluent E. coli concentrations from RB1 and RB2 (O'Luanaigh & Gill, nd) RB1 in RB1out RB2 in RB2 out E. coli concentration (MPN/100 ml) 7.44 x 105 2.80 x 104 1.10 x 104 2.39 x 102 Removal (log-unit) 1.4 1.7 Under HSSF CWs, in on-site wastewater treatment, the results showed that the system could achieve good hydraulic distribution using an aspect ratio of 3:1. According to the research, a common misconception is that such systems do not significantly reduce effluent HLR because of evapotranspiration. Tertiary treatment beds can be used to remove nitrogen, since they provide good environments for denitrification, especially if they are receiving nitrified effluent. There 47 was no significant TN removal in secondary beds receiving effluent from a septic tank. Both secondary and tertiary beds provided low TP removal during the first years of operation, a situation that was expected to deteriorate with time, if the sites for adsorption and precipitation became saturated. Plant uptake and harvesting did not have significant results on TP removal. 4.2.4. A Recirculating VF CW for the Treatment of Domestic Wastewater The general performance of the recirculating VF CW was assessed by comparing the quality of raw versus treated domestic wastewater, and by the conformity of the effluents to Israeli regulations for irrigation of the urban landscape (Sklarz, Gross, Yakirevich, & Soares, 2009). Figure 4.1 shows the results for the various parameters analysed. 48 Figure 4.1: Values of TSSs (a), COD (b) and BOD5 (c) in raw and treated domestic wastewater from planted and unplanted recirculating VF CWs using several RFRs (Sklarz, Gross, Yakirevich, & Soares, 2009) 49 With reference to the results presented in Figure 4.1, the unplanted systems were found, on average, to reduce TSSs by approximately 90%, from 90 to 10 mg l-1, BOD5 by 95%, from 120 to 5 mg l-1 and COD by 84%, from 270 to 40 mg l-1, using an RFR of 4.5 m3 h-1 and 12 hours of treatment. The ratio of COD to BOD5 increased from 2.25 to 8, apparently due to the favoured removal of biodegradable organic matter over less biodegradable organic matter (Sklarz, Gross, Yakirevich, & Soares, 2009). TSSs and BOD5 levels conform to Israeli regulations, at 10 mg l-1 each for urban landscape irrigation. It was observed that nitrification was efficient because the ammonia levels dropped from an average of 37 mg N l-1 in the raw domestic wastewater to 3 mg N l-1 in the effluent, followed by an increase in nitrate, from negligible levels to 25 mg N l-1 in the effluent; the transitory accumulation of nitrite was consistently low, at levels of 3 mg N l-1 (Sklarz, Gross, Yakirevich, & Soares, 2009). It is important to note that the maximum concentration of nitrogen for unrestricted irrigation, according to the Israeli recommendations, is 25 mgl-1 , but concentrations of over 50 mg l-1 are commonly used for fertilisation purposes in landscape irrigation and agricultural practices (Sklarz, Gross, Yakirevich, & Soares, 2009). Therefore, the results for TN removal conformed to the Israeli standards. When a peat layer was added, the observation was that the planted system continued to perform the same as before it was planted, but that the unplanted system deteriorated in terms of TSSs, COD and BOD removal. Moreover, ammonia was reduced to less than 5 mg N l-1. There were no changes in the transformation of nitrogen; however, small amounts of nitrite did accumulate, and nitrate accumulated up to about 25 mg N l-1. The decreasing performance in the unplanted system was likely due to the reduction in the RFR. When the RFR was increased, in order to test this theory, the effluent quality in the unplanted bed went back to the original, and remained high 50 even when the RFR was again decreased. This means that the sudden RFR reduction could have caused changes in the recirculating VF CW biofilm, which had acclimatised to working under high RFR conditions. These changes consisted of sloughing of the old biofilm, which may have increased solids and organic matter levels. After the second RFR reduction, the process did not repeat itself. According to the study (Sklarz, Gross, Yakirevich, & Soares, 2009), plants are thought to improve efficiency by taking up different components from the wastewater, enhancing oxygen transport, releasing enzymes and other agents that enhance degradation, and by providing a favourable environment for microbial population development; however, other studies have demonstrated that equal treatment efficiencies of wetlands can be achieved with and without plants (Sklarz, Gross, Yakirevich, & Soares, 2009). Additionally, due to the continuous recirculation in the recirculating VF CW, the planted area was small in relation to the amount of wastewater that was being treated and, hence, the role of plants in this case was limited (Sklarz, Gross, Yakirevich, & Soares, 2009). To summarise, recirculating VF CW effluents were overall of high quality – even when operated without the soil–plant component – and conformed to the Israeli regulations. The potential organic load capacity in this case was higher than that in previous studies. The contribution of the plant–soil component requires further study. Nitrogen was converted to nitrate with relatively small losses, and the nitrate in the effluents partially fulfilled the plant nutrient requirements, reducing the need for fertiliser, thereby providing environmental and economic benefits (Sklarz, Gross, Yakirevich, & Soares, 2009). 51 4.2.5. A Hybrid CW System for Decentralised Wastewater Treatment Analysis of the chemical and physiological parameters discussed in the methodology of the case study (Kinsley, Crolla, Rode, & Zytner, 2014) are here discussed in terms of absolute values and their reactions to seasonal variation. According to the study results, during the summer, the combined HF–VF system reduced BOD5 concentrations to virtually undetectable levels (<2 mg/l) at all HLRs (Figure 4.2); however, during the winter, the VF effluent concentrations increased from 3 to 9 mg/l with an increasing HLR. Average TSSs varied between 8 and 12 mg/l during the summer (Figure 4.3), and between 11 and 18 mg/l during the winter, with no significant differences between the HF and VF values (Kinsley, Crolla, Rode, & Zytner, 2014). The TSS values were not affected by increasing HLRs. 52 Figure 4.2: Changes in BOD5 with season and HLR (Q = 2.8 m3/d) (Kinsley, Crolla, Rode, & Zytner, 2014) 53 Figure 4.3: TSSs with season and HLR (Q = 2.8 m3/d) (Kinsley, Crolla, Rode, & Zytner, 2014) Without recycling, TN was reduced by only 19 and 24% during summer and winter, respectively; with recycling, the outlet TN ranged between 9.6 and 11.8 mg/l, with no significant differences observed, either between seasons or with an increased recycling ratio (Kinsley, Crolla, Rode, & Zytner, 2014). The more the recycle ratio was increased, the more TKN increased and nitrate decreased between summer and winter. This observation means that the more the flow was increased, the more the VF became saturated, leading to the reduced transfer of oxygen and decreased nitrification. In light of the study, it was observed that phosphorus was reduced to below 1.0 mg/l for the first 18 months of the study, after which TP concentrations increased; during this time, pH at the HF outlet remained above pH10 (Kinsley, Crolla, Rode, & Zytner, 2014). This indicates that the best removal mechanism for phosphorus was precipitation in a high-pH environment. Furthermore, the peat layer in the VF filter was effective at maintaining that high-pH environment at between pH7 and 8. The phosphorus attenuation of the material declined very quickly when highly- 54 soluble calcium was released from the surface of the blast-furnace slag (Kinsley, Crolla, Rode, & Zytner, 2014). For E. coli, during the summer, a total of 3.4 logs were removed, while during the winter, a total of 2.3 logs were removed (Kinsley, Crolla, Rode, & Zytner, 2014). Removal was not satisfactory, and the study suggests further treatment using ultraviolet light or chlorination, especially if the effluent is to be reused. The concentration standards required for E. coli in effluent that is to be reused for irrigation is <103 CFU/100 ml. This study demonstrated high removal rates for all physiological and chemical parameters; however, the system was affected by seasonal variation. Removals during winter were not as high as in the summer. 4.2.6. CW of Lepironia articulata for Household Greywater Treatment This study discussed the removal of BOD, COD, AN, TSSs and turbidity. Table 4.5 and figure 4.4 document water consumption in the household, showing that the washing machine produced the highest quantity of greywater, while the kitchen had the lowest. Table 4.5: Household water consumption in the case study (Wurochekke, Harun, Mohamed, & Kassima, 2014) Household activity Kitchen Bathroom Washing machine Quantity of greywater (m3/day) 5000 37000 136500 55 Removal Percentage 3% Washing machine 21% Bathroom Kitchen 76% Figure 4.4: Percentage removal of greywater produced by household activities (Wurochekke, Harun, Mohamed, & Kassima, 2014) The model produced the results shown in Table 4.6 for greywater loading discharged from the house. Table 4.6: Analytical results of greywater loading before treatment (Wurochekke, Harun, Mohamed, & Kassima, 2014) No. 1 2 3 Water volume (m3) 0.021 0.014 0.010 Time (s) 419 279 627 Flow rate x 10-5 (m3/s) 5.012 5.018 1.595 A preliminary analysis was conducted before treatment to determine the concentrations of the pollutants in the greywater. Table 4.7 records the results found during the morning and evening sampling times. Table 4.7: Preliminary results of raw greywater in the morning and evening (Wurochekke, Harun, Mohamed, & Kassima, 2014) 56 Sampling date Time/parameters BOD (mg/l) 05/03/2013 10.00 am 9.00 pm 17/03/2013 10.00 am 9.00 pm 271 60 309 167 COD (mg/l) TSSs (mg/l) AN (mg/l NH3–N) Turbidity (NTU) 807 705 1103 469 153 78 54 83 3.83 1.72 2.6 1.24 132 67.9 35.1 52.2 According to the study (Wurochekke, Harun, Mohamed, & Kassima, 2014), the mini-CW model provided a high removal performance of 81.42% BOD, 84.57% COD, 39.83% AN, 54.70% TSSs and 45.01% turbidity. The highest reductions in pollutants after treatment were BOD (81.42%) and COD (84.57%), signifying that the treatment system was capable of reducing the solid fraction of BOD and, thus, the remaining part after treatment was probably soluble (Wurochekke, Harun, Mohamed, & Kassima, 2014). The reduction in organic matter is significant, although COD was the most affected. The organic constituents decomposed and facilitated the growth of plants, with minerals being converted to protein, since they are able to remove organic compounds by the uptake of those organic compounds as carbohydrates and amino acids. In accordance with the study findings (Wurochekke, Harun, Mohamed, & Kassima, 2014), TSS reduction, on average, was 54.7%, which indicates some inefficiency because only physical sedimentation was used to remove the TSSs. AN reduction was low as well, being at 39.83%, on average, which could be attributed to the short treatment time. The ideal treatment time for AN reduction would have been eight days or longer, according to previous studies. Colour removal was low, and the study suggested further degradation. Turbidity removal showed the system to be inefficient, since the rate was low, at 45.01%. 57 The organic matter in the wastewater had high removal rates, although the system was generally inefficient at removing colour, turbidity, TSSs and AN due to various factors. The study would have been more efficient with adjustments to resolve these limiting factors. 4.2.7. CW System for Wastewater Treatment The study showed that VF CWs are most suitable when it comes to meeting high removal standards, such as 95% for BOD, 90% for TP and 90% nitrification. The VF bed for BOD removal and nitrification was very effective at high HLRs, even during winter. TSSs removal in the system was also very high. As reported by the authors (Farooqi, Basheer, & Chaudhari, 2008), a recycling rate of 1:1 (100% recycling) resulted in about 50% denitrification, which improved and stabilised the overall treatment performance of the system (Farooqi, Basheer, & Chaudhari, 2008). In addition, the removal of indicator bacteria in the system was about 2 logunits, although TP removal in the VF CWs was very limited, since it was not possible to acquire a sand bed medium with enough capacity to bind the phosphorus (Farooqi, Basheer, & Chaudhari, 2008). To combat this challenge, however, phosphorus removal can be obtained by simple precipitation with an aluminum compound in the sedimentation tank, prior to the CW (Farooqi, Basheer, & Chaudhari, 2008). The single-household system performance was monitored with and without recirculation, and the results proved that recirculation is essential in efficient pollutant removal. 58 4.2.8. Use of Macrophyte Plants, Sand and Gravel Materials in CW for Greywater Treatment To demonstrate that local macrophyte plants and natural substrates could successfully treat domestic wastewater, the results of studies based in West Java, Indonesia and Thailand and Costa Rica (Qomariyah, Ramelan, Sobriyah, & Setyono, 2017) are included in the Table 4.8. Table 4.8: Effectivenes of pollutant removal in CWs with natural substrates and local macrophytes (Qomariyah, Ramelan, Sobriyah, & Setyono, 2017) In agreement with the research findings, the treatment efficiency of BOD and COD varied between 76.03-99.4% and 78.89-98.46%, respectively, except for COD removal in the Thailand study, which varied between 42 and 83% (Qomariyah, Ramelan, Sobriyah, & Setyono, 2017) .The system in Thailand was still efficient because the influent concentrations of COD were low due to high degradation rates that occurred in the settling tank and the collection systems. The most recent study (Qomariyah, Ramelan, Sobriyah, & Setyono, 2017) showed inlet BOD concentrations of 496–850 mg/l, which were reduced to 2.19–17.2 mg/l, a value that was lower than the EPA guidelines of 30mg/l. According to (Qomariyah, Ramelan, Sobriyah, & Setyono, 59 2017), detergent in the wastewater was removed at an efficiency rate of 99.86%. Similarly, TSS removal through sedimentation and interception yielded results ranging from 95.47 to 99.56%, with an average of 98.06%. Outlet concentrations of TSSs were at 2–10 mg/l, which is below the EPA guideline and the Indonesian wastewater reuse standard. The Thailand study used both Canna and Heliconia (flowering plants) and gravel as the substrate, which resulted in TSS removals of 88–96% for both plants. The average removal of TCs in Indonesia and FCs in Costa Rica was 99.45 and 99.99%, respectively, which is a very high efficiency. As observed in the study, the Thai case produced a low removal of TP (6–35%) and TN (4–37%), unlike the other studies. Substrates that contain high calcium, aluminium and iron have high phosphorus, so that the high removal of phosphorus in the study might due to the high amount of iron-rich sand in the substrate used. Nutrient removal is not a wastewater reuse criterion; hence, if the treated effluent is to be used for irrigation, then nutrient removal is likely to become unnecessary (Qomariyah, Ramelan, Sobriyah, & Setyono, 2017). In the Costa Rica case, on the other hand, a longer HRT of 7.9 days was used, resulting in a level of treatment that exceeded the requirement of the local standards for wastewater reuse, in terms of BOD (average <10 mg/l) and FCs (average 122 cfu/100 ml), and with effective removal of E. coli (99.99%) (Qomariyah, Ramelan, Sobriyah, & Setyono, 2017). Sand, gravel, plant species and crushed rock are all materials that can be found locally, all yielding high performance in greywater treatment. Organic pollutants and pathogens have high removal rates in such systems and, therefore, the treated effluent can be reused for irrigation, for example. No energy is required to operate these CWs, therefore the systems are affordable. They are also a better alternative than conventional methods, as they can be employed as decentralised systems in developing countries. 60 4.2.9. Integrated CWs for Treating Domestic Wastewater The new integrated CW system in Glaslough is here compared to the mature integrated CW system in Dunhill, in relation to their nutrient removal perfomances and the impact of seasonal and annual changes. The two systems show impressive removal efficiencies of BOD and COD. Regarding the water quality data, ammonia–nitrogen, nitrate–nitrogen and MRP removal for the Glaslough system were high, at 99.0, 93.5 and 99.2%, respectively, whereas the Dunhill CW had removal efficiencies of 58, 80.8 and 34.0%, respectively (Scholz, 2011). In agreement with the study (Scholz, 2011), MRP and nitrate–nitrogen concentrations in the effluent increased gradually. In the Dunhill system, the decrease was attributed to an overload of the system. In the fourth year, the concentrations of the two parameters, as well as ammonia– nitrogen, were three times more than in the first three years. In the effluent, nitrate–nitrogen concentrations were higher than in the influent, suggesting that the nitrification process contributed to the transfer of some ammonia–nitrogen into nitrate–nitrogen. Both ammonia– nitrogen and nitrate–nitrogen, however, were released by the system. In both systems, according to the study (Scholz, 2011), effluent concentrations of COD and BOD were higher in summer and autumn than in spring and winter, but the removal efficiencies for these did not vary greatly in either system because of an increased Organic loading rate caused by increased evaporation and decreased precipitation (Scholz, 2011). Effluent concentrations of ammonia–nitrate, nitrate–nitrogen and MRP in the Glaslough system did not change significantly, but increased in the Dunhill system because of the higher HRTs provided by the sytem in Glaslough, which removed 99.2% more MRP than at Dunhill (Scholz, 2011). 61 The difference in the reduction of MRP between the systems could be because the subsoil and sediments in Glaslough did not reach saturation. Therefore, the results indicate that the integrated CW in Glaslough had a higher pollutant reduction capacity than did Dunhill. This is most likely due to overloading of the CW system at Dunhill. 4.2.10. Efficiency of Small CWs for Subsurface Treatment of Single-Family Domestic Effluent The 21 wetlands studied (Steer, Fraser, & Boddy, 2002) are numbered from one to 21 in Table 4.9, which shows their individual removal values for the relevant parameters from the study. 62 Table 4.9: System performance (Steer, Fraser, & Boddy, 2002) 63 According to Table 4.9a (which appears as 2a on the table) from the case study, the CWs individually reduced FCs from 82.7 to 99.9%, with the exception of CW 18, at 27.9%; however, overall FCs were reduced to 87.9±27.1% between the input and the output in these systems (Steer, Fraser, & Boddy, 2002). According to the study, the failure of that one system was attributed to a delay in planting the vegetation in the second cell, and a disrupted flow through the cell as a result of breaches in the clay liners, full blockage of the transfer pipes, or partial/full obstruction of the substrate (Steer, Fraser, & Boddy, 2002). The disruption of flow might have changed the retention time, hence reducing time available for protozoa to consume the FCs. In agreement with the study (Steer, Fraser, & Boddy, 2002), effluent was discharged from the polishing cell of these wetlands at levels below the EPA’s recommended 1000 counts/100 ml for 74% of the samples collected (Steer, Fraser, & Boddy, 2002). Two wetlands – CW18 and 19 – 64 failed to meet all the requirements on every occasion, while nine (CWs 1, 3, 7, 8, 9, 10, 11, 17, 21) met all the requirements for pollutant removal on every occasion. The systems that did not meet the guidelines were 15% less efficient at reducing loads than those that met the guidelines (Steer, Fraser, & Boddy, 2002). The data was unsuitable for determining seasonal effects. Furthermore, according to Table 4.9a (2a on the table), these CWs individually reduced TSSs, with efficiencies ranging from 25.0 to 89.1%, with the exception of CW 17 at -250%. In general, TSSs were reduced by 55.8±52.8% using the subsurface treatment CW process (Steer, Fraser, & Boddy, 2002); however, the negative efficiency at CW 17 resulted from remobilisation of the solids, failing because the overall effectiveness and longevity of the system was affected. Nevertheless, no observations could explain why the solids were remobilised (Steer, Fraser, & Boddy, 2002). Two systems (CW 4 and 12) failed to meet all the standards, but five systems (CW 5, 7, 11, 13, 15) did meet all the required standards. At total of 79% of the samples released TSSs below the recommended EPA level of 30 mg/l.The data was unsuitable for determining seasonal effects. According to Table 4.9b (2b on the table), BOD5 was reduced individually in the wetlands, from 70.9 to 95.9%, with the exception of CW 1 at 27.2%; overall these treatment wetlands reduced BOD5 by an average of 70.3±48.5% (Steer, Fraser, & Boddy, 2002). At total of 89% of the samples met EPA guidelines for BOD output at lower than 30 mg/l. CWs 16 and 18 failed to meet the EPA guidelines in all the samples. In addition, the samples that did not meet the standards had double the input loads of samples that did (Steer, Fraser, & Boddy, 2002). BOD reduction was 10% less in the winter, compared to summer, autumn and spring. 65 According to Table 4.9b (2b on the table), ammonia was the least efficiently reduced, by only 19.8–98.4% in that individual wetlands, and 56.5±31.3% in general, from input to output. Only 16% of the samples met the effluent guidelines, and all of the wetland samples failed to meet the EPA standard of 1.5 mg/l. CW 1 had the least ammonia reduction and the lowest input load due to aeration being performed prior to Cell 1. All the system samples failed to meet the guidelines on one or more occasion (Steer, Fraser, & Boddy, 2002). Treatment efficiency in the few systems that passed was 97%, with those that failed at only 53%. Ammonia reduction was 20% more efficient in autumn than winter, spring or summer, being most efficient in September and October. In agreement with the study’s findings (Steer, Fraser, & Boddy, 2002) , the CWs were individually capable of reducing 37.5–99.1% TP and 80.5±19.8% in general (Steer, Fraser, & Boddy, 2002). Three of the systems – CW 16, 17 and 18 – removed <50% TP. CW 16 failed to meet the standards on all occasions, while CW 7 and 8 met all the standards on every occasion. The EPA guidelines were exceeded by 50% of the systems. Reduction efficiency was high, at 94%, compared to 65% efficiency when it was not met (Steer, Fraser, & Boddy, 2002). The variable TP removal could not be attributed to substrate type, since all of the systems had the same substrate, nor to input loads or maintenance. Annual harvesting was not performed and, therefore, the decaying biomass could have provided another source of phosphorus. Phosphorous reduction in winter was 10% less than in summer and spring, and 20% less than in autumn. Table 4.10 shows the results for the various parameters analysed in the CWs related to initial concentrations, final concentrations and average reductions. 66 Table 4.10: Wetland data base summary (Steer, Fraser, & Boddy, 2002) Pathogen Samples (n) Fecal TSS BOD5 NH3 P 132 131 131 125 125 Average input cnts or mg/l 36410 55.4 104.7 47.7 8.36 SD input cnts or mg/l 63300 62.1 77 32.3 3.75 Average output cnts or mg/l 2150 18.8 13.7 18.4 1.71 SD output cnts or mg/l 5670 17.3 18.4 16.7 2.41 Average SD % % reduction reduction 87.9 55.8 70.3 56.5 80.5 27.1 52.8 48.5 31.3 19.8 In summary, the study showed that phosphorous, ammonia, and BOD removal were influenced by seasonal effects. Winter had the lowest BOD removal which was 10% less when compared to the other seasons spring, summer, and fall. Nevertheless, the system successfully reduced pollutants and improved water quality. 4.2.11. Reed bed CW system The results from the analysis of various parameters from this study are discussed, and compared to the Oman MECA Standard (A) in order to determine the effectiveness and efficiency of the system. Table 4.11 shows the removal efficiency for various components of a double-stage VF reed bed. 67 Table 4.11: Data for the treatment of effluent by the reed bed system (Haya Water, 2017; Oman Government, 2018) Parameter Raw Sewage (mg/ l ) Treated Effluent MECA Standard Removal (mg/ l) (A) Efficiency COD 1206 12.7 150 98.9 BOD 372.3 3.9 15 98.9 NH3–N 58.2 0.2 5 99.6 NO3–N - 32.9 50 (NO3) - TN 90.7 8.7 15 90.4 TP 11.3 0.1 30 99.1 TSSs 633.3 1.2 15 99.8 O&G 36 0.3 0.5 98.1 FCs - 117 200 per 100ml - VHO 22 <1 <1 per l 98 68 Excellent efficiency levels were obtained for the various parameters analysed, as follows: COD (98.9%), BOD (98.9%), ammonia–nitrogen (99.6%), TN (90.4%), TP (99.1%), TSSs (99.8%), O&G (98.1%) and VHO (98%). When compared to MECA Standard (A), due to the high efficiencies, the parameters are in compliance (Haya Water, 2017). Graph 4.1 shows a representation of treated effluent (mg/l) and the MECA Standard (A), as well as its removal efficiencies for all the above-mentioned parameters. Graph 4.1: Relationship between treated effluent, the MECA standard and removal efficiency (Haya Water, 2017; Oman Government, 2018) Relationship Between the Treated Effluent, its MECA Standard (A) and their Removal Efficiency 150 117 98.9 98.9 12.7 15 3.9 99.6 90.4 32.9 COD BOD 5 0.2 NH3-N 0 NO3-N Treated Effluent (mg/L) 99.1 99.8 98.1 15 1.2 TSS 0.5 0.3 O&G 98 30 15 8.7 TN 0.1 TP MECA Standard A 0 FC 0 VHO Removal Efficiency From Graph 4.1, it can be seen that the high levels of removal efficiencies for the solids (COD and BOD) mean that they can be easily removed from the treated effluent. Moreover, there are high levels of removal efficiencies recorded for ammonia–nitrogen, TN, TP, TSSs, O&G, FCs and VHO, which means that they comply entirely with the MECA standards (Haya Water, 2017). High levels of ammonia, nitrogen and phosphorus show that the soils through which the 69 effluent passed are highly nutritious. Moreover, the lack of nitrates in the TE sped up aeration and eutrophication. The lack of FCs in the TE means that the water quality, in terms of cleanliness, was very high. The design made the system highly efficient and effective. The system regulated the flow to maintain an optimal retention time for pollutant removal, while still reducing cost and size. The retention time depended on the type of wastewater being treated and, hence, it was observed that non-domestic wastewater took a longer time to be treated because it contained a heavier concentration of pollutants than domestic wastewater. Phragmites australis showed a relatively constant growth and high substrate levels, which contributed to the high efficiency of the system because the plant had high pollutant- and nutrient-absorption capacities. In summary, analysis of the chemical, physical and biological parameters in the Haya study showed that the system was highly efficient and effective, meaning that the system should be adopted, since it is advantageous in terms of size, cost and time. 4.3. Summary and Comparison A comparison is made between two related case studies that used different CW designs (HSSF) and (VF). Case study 1 “HSSF CW for On-Site Wastewater Treatment” (Hoddinott, 2006) and case study 2 “The use of VF CW for on-site treatment of domestic water: New Danish guidelines” (Brix & Arias, 2005) are compared, in terms of methodology and results. 70 Pretreatment for Case 1 required the use of a septic tank, which provided primary treatment by removing TSSs anaerobically, while maintaining regular pumping of the septic tank. Case 2 pretreatment also required the use of septic tanks, or chamber sedimentation tanks. Case 1, however, did not provide specific measurement requirements, as opposed to Case 2. The vegetation in Case 1 was recommend to be P. australis, the same as for Case 2, because it facilitates better bacterial growth and is quite tolerant of toxicity. In both cases, effluent recirculation was suggested at a rate of 50% for the purpose of enhancing denitrification. Case 1 recommended the use of gravel as the filtration medium, while Case 2 suggested the use of sand. Both cases, however, agreed that the bed should be lined using geotextile or gravel to prevent the filtration medium from entering the drainage layer. Both cases provided information on bed size and dimensions, but Case 1 was more detailed, even providing equations for calculating surface area and aspect ratio. Case 2, on the other hand, provided information regarding the distribution system, while Case 1 did not. From Table 4.2 in Case 2, the average removal efficiency for TSSs was 94%, while Case 1 recorded an average of 84.3% in the discussion of the results, which was well within the EPA standards, according to Table 4.1. BOD5 removal in Case 1 was 88%, while in Case 2, it was 94.5%. With reference to Table 4.1, COD, BOD, ammonia, coliforms and TSS removals were all within the stated OEPA standards for effluent concentrations (Hoddinott, 2006). TN removal in Case 1 averaged at 43%, while for Case 2 it was 43.75%. TP removal in Case 1 was 97%, using Phragmites, but in Case 2, the removal efficiency for the same averaged 22.75%. From this comparison, it can be concluded that the VF system is better at removing TSSs and BOD5. On the other hand, the HSSF system is better at TP removal. Both systems, however, had no significant difference in TN removal. 71 Chapter 5 CONCLUSION Single-household wastewater management is a challenge in most developing countries. It is difficult to find a system that is, at the same time, efficient, easy to operate and maintain, and low in cost. Nevertheless, water being a key element for the world’s survival, a sustainable solution is required for the problem. Effluent mismanagement is one of the factors that contributes to massive water pollution of water bodies and water courses, since the effluent is often discharged directly, without treatment. Water is essential to life and so it must be conserved and its quality maintained. CWs come in handy for single-family homes to manage and treat their own wastewater. The systems are convenient, since they do not necessarily require large pieces of land to be operated on. In the absence of adequate land, consumers might have to purchase manufactured systems that could be more costly, but such costs should be weighed against the effects pollution inflicts on the environment and public health. In addition, these systems are very easy to maintain and, therefore, are perfect for domestic use, wherein the consumers do not necessarily need extensive knowledge about the technicalities of the system. It is important for public awareness programs to be initiated to teach people about CWs, so that they can fully understand the benefits of such systems, and so will be more likely to adopt these systems in their homes. The methodologies discussed included information about flow type, design type, effluent recirculation, bed dimensions, aspect ratios, distribution, sealing, insulation, substrate media, 72 construction materials, vegetation, water balance, reuse criteria, influent/effluent quality, location, PEs, surface area needs, sampling and energy requirements. From assessment of all of this information, it was determined that the basic design for a single-household system should consist of pre-treatment (usually in a septic tank), which acts as the primary treatment, followed by secondary and tertiary treatments. This basic design was replicated throughout the case studies outlined in this report. Some systems had modifications or additions to the basic design, such as aeration and the use of technologically-advanced machines, such as the RBC. Results from the analysed samples showed removal efficiencies for both chemical and physiological parameters, such as COD, BOD5, TCs, TN, TKN, TP, FCs and TSSs. The efficiencies of the systems were also evaluated, in relation to how seasonal variations affected performance. Colder temperatures in winter seemed to slow down system functions in general, compared to times of warmer temperatures, in spring, autumn and summer. This phenomenon has been attributed to the death of plants during winter, slowing down the microbial function that is essential to pollutant removal through, for example, protozoan predation. System performance was also discussed, in relation to the role and capacity of vegetation to take up pollutants, the suitability of substrate media and the effects of HLRs and HRTs on the beds. Based on the research findings, the study “A Recirculating VF CW for the Treatment of Domestic Wastewater” was the best system assessed. The study’s efficiency was measured both by percentage removal of pollutants, and also by their conformity to the Israeli regulations, which makes the study very reliable. TSSs, BOD5 and COD removals were 90, 95 and 84%, respectively. These three parameters conformed to the Israeli standards. There was efficient nitrification as well, and there were very low nitrate and nitrite concentrations, also conforming 73 to the Israeli regulations. The soil-component ensured that ammonia removal was <5 mg N l-1, a value that is often difficult to achieve. In conclusion, single-household CWs are a good solution for wastewater management in singlefamily homes, as they are low cost, easy to operate and maintain, and highly effective. They should be adopted as a matter of public policy as part of the global effort to conserve, and maintain the quality of, water. 74 Chapter 6 RECOMMENDATIONS Based on the discussions reported here, a number of recommendations can be made:  CWs should be installed where large areas of land are available and the price is cheap  In the case of water surges, good-quality construction materials should be used in the building of CW systems. The following recommendations can be made for future work in Oman study:  A VF–HF hybrid design should be implemented in Oman to produce the most efficient and effective system for treating wastewater and ensuring easy and adequate cleaning of the sewage within the shortest amount of time.  To increase the number of CWs in Oman, companies similar to Haya Water should be encouraged to invest in CW projects. As a start, the Oman government could discount the cost of the pipes and chemicals used in such treatments.  It is recommended to implement Reed Bed Treatment Technology as a sustainable solution in Regional Governorates since there are huge empty areas.  Future studies should further address the details of water balance, energy balance and CW design parameters. 75 REFERENCES Brix , H., & Arias, C. A. (2005). 2. The use of vertical flow constructed wetlands for on-site treatment of domestic wastewater: New Danish guidelines. Ecological Engineering, 25(5), 491-500. Crawford, G., & Sandino, J. (2010). Energy efficiency in wastewater treatment in North America: A compendium of best practices and case studies of novel approaches. Retrieved from Water Environment Research Foundation.: https://www.nyserda.ny.gov//...Water-Wastewater.../north-american-drinking-water-u... Farooqi, I. H., Basheer, F., & Chaudhari , R. J. (2008). Constructed Wetland System (CWS) for Wastewater Treatment. Proceedings of Taal2007: The 12th World Lake Conference, 1004-1008. Haya Water (2017). Haya Water. Retrieved from: https://haya.om/en/Pages/Home.aspx [Accessed 17th of May 2018] Hoddinott, B. C. (2006). Horizontal Subsurface Flow Constructed Wetlands for On-Site Wastewater Treatment. Dayton, Ohio: Wright State University. Jhansi, S. C., & Mishra , S. K. (2013). Wastewater treatment and reuse: Sustainability options. Consilience: The Journal of Sustainable Development, 10(1), 1-15. Kinsley, C., Crolla, A., Rode, J., & Zytner, R. (2014). 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ENG 4 133 Bachelor Thesis German University of Technology in Oman (GUtech) Department of Engineering Title of the Thesis ASSESMENT AND REVIEW OF CONSTRUCTED WETLAND FOR MUNICIPAL WASTEWATER: SELECTED CASE STUDIES Course Coordinator: Dr.-Ing. Najah Al Mhanna Project Supervisor: Main supervisor: Dr.Hind Bargash Student Name: Al Hawra Al Ajmi Spring 2018 Approval of the Dean of the Faculty of Engineering and Computer Science Dr.-Ing. Najah Al Mhanna I certify that this Thesis satisfies the requirements of a Bachelors Thesis for the Degree of Bachelor of Engineering in Environmental Engineering. Dr.-Ing. Najah Al Mhanna Head, Department of Engineering I certify that I have read this Thesis and that it is my opinion that the Thesis is fully adequate in scope and quality as a Bachelors Thesis for the Degree of Bachelor of Environmental Engineering. Name Supervisor Examining Committee 1. Name 2. Name i Declaration: In accordance with the requirements of the degree of Bachelor of Engineering at German University of Technology in Oman, I present the following thesis titled “Assessment and review of constructed wetland for Municipal wastewater: selected case studies”. This work was performed under the supervision of Dr. Hind Bargash. I hereby declare that the work submitted in this thesis is my own and based on the results found solely by myself. Materials of work found by other researchers are clearly cited and listed in reference list. This thesis, neither in whole nor in part, has been previously submitted for any degree. The author confirms that the library may lend or copy this thesis upon request, for academic purposes. Name: Hawra Mohsin Al Ajmi Signature: ii ABSTRACT Municipals can be classified as small towns whose major wastewater effluents are composed of rainwater, domestic water and extremely small percentages of industrial water which are negligible because they do not really affect the constituents found in the wastewater. As a result, few municipal wastewater effluents contain heavy metals. The most common constituents required to be removed from the wastewater are BOD, COD, TSS, TKN, TP, FC, TC, N and Ammonia. This report aims to identify the various methodologies, designs, and innovations that can be used to treat municipal wastewater through constructed wetlands. The results of the various studies are as well presented to show the efficiency removal rates, designs, strategies, and cost parameters that can be adopted by municipalities to effectively treat wastewater in a way that barely intrudes on the ecosystem and the environment. The highest removal rates recorded among all studies were; 99.1% TP, 77% TKN, 98.9% COD, 98.9% BOD. 99.8% TSS, 90.4% TN, 99% TC, 99% FC, 95% nitrogen organic (NORG), 84% Ammonium-nitrogen (NH4 +-N), 79% nitrate-nitrogen (NO3—N), 99.6% Ammonia-nitrogen (NH3-N), 98% Viable helminths ova(VHO), 98.1% Oil &Grease (O&G) and 98% Escherichia coli (E. coli). The successful removal of such pollutants leads to wholesome integration of treated wastewater back to the environment via discharge into streams or rivers. Treated effluent can be collected and reused for purposes such as irrigation. Keywords: Municipal wastewater, effluent, removal rates, cost, efficiency, plants species i ‫الخالصة‬ ‫يمكن تصنيف البلديات على أنها بلدات صغيرة حيث تتكون مياه المجاري فيها من مياه األمطار والمخلفات المائية من االستخدامات‬ ‫المنزلية ونسبة مئوية متناهية في الصغر من المخلفات السائلة من االستخدامات الصناعية وهي النسبة التي ال تذكر إلنعدام تأثيرها‬ ‫الفعلي على المكونات الموجودة في مياه الصرف الصحي‪ .‬ونتيجة لذلك‪ ،‬فنسبة صغيرة للغاية من المخلفات السائلة للبلديات تحتوي‬ ‫على معادن ثقيلة‪ .‬وعلى خالف ندرة المعادن الثقيلة في هذه المخلفات فإن العناصر المطلوب إزالتها من مياه المجاري تتضمن‬ ‫الطلب البيولوجي الكيميائي على األكسجين و الطلب البيولوجي الكيميائي على األكسجين والمواد الصلبة العالقة الكلية و نتروجين‬ ‫كيلدال الكلي والفسفوروز الكلي والقولونيات البرازية والقولونيات الكلية والنيتروجين واألمونيا۔ يهدف هذا التقرير إلى تحديد‬ ‫مختلف المنهجيات والتصاميم والمبتكرات التي يمكن استخدامها في معالجة مياه المجاري البلدية من خالل األراضي الرطبة‬ ‫(األهوار) التي يتم إنشاؤها‪ .‬كما يستعرض التقرير الحالي نتائج الدراسات المختلفة إلظهار معدالت كفاءة إزالة الملوثات‬ ‫والتصاميم واالستراتيجيات ومعايير التكلفة التي يمكن للبلديات تبنيها والعمل بها لمعالجة مياه المجاري على نحو فعال بطريقة ال‬ ‫تكاد تتطفل على النظام البيئي والبيئة‪ .‬كانت أعلى معدالت اإلزالة المسجلة عبر كافة الدراسات على النحو التالي ‪ 99.1%.:‬من‬ ‫الفسفوروز الكلي و‪ %77‬من نتروجين كيلدال الكلي و‪ %98.9‬من الطلب الكيميائي على األكسجين و‪ %98.9‬من الطلب‬ ‫البيولوجي الكيميائي على األكسجين و‪ %99.8‬من المواد الصلبة العالقة الكلية و‪ %90.4‬من النيتروجين الكلي و‪ %99‬من‬ ‫القولونيات الكلية و‪ %99‬من القولونيات البرازية و‪ %95‬من النيتروجين العضوي و‪ %84‬من األمونيوم و‪ %79‬من نيترات‬ ‫النيتروجين و ‪ %99.6‬من نيتروجين األمونيا و‪ %98‬من الديدان الطفيلية و‪ %98.1‬من النفط والشحوم و‪ %98‬من اإلشريكية‬ ‫القولونية۔ ومع إزالة مثل هذه الملوثات بنجاح‪ ،‬يسهل دمج المياه المعالجة في البيئة من خالل إعادة تصريفها في الجداول واألنهار‬ ‫‪ .‬يُمكن تجميع مياه المجاري ال ُمعالجة وإعادة استخدامها ألغراض متنوعة مثل عمليات الري‪.‬‬ ‫الكلمات الداللية‪ :‬مياه املجاري البلدية فضالت‪,‬معدالت اإلزالة‪ ,‬التكلفة ‪,‬الكفاءة‬ ‫‪ii‬‬ ACKNOWLEDGMENT The completion of this study could not have been possible without the help, support and guidance of my beloved supervisor, the expertise Dr Hind Bargash, I would like to thank her for her constant contribution and patience throughout. It was truly a pleasure having her as my mentor. I would like to express my special gratitude towards my supportive family. My parents; Fatma AlAjmi and Mohsin Al-Ajmi, my siblings; Alaa, Alya and Mohammed and my uncle; Yassir AlAjmi for being by my side and believing in me, their constant motivation and encouragement was a reason for my accomplishment. Special thanks to my group members and partners Nujoom Al-Amri and Thuraya Al-Busaidi for assisting, advising and collaborating with me through this whole journey. Last but not least I would like to thank my friends who directly and indirectly supported me and helped me survive through the stress of accomplishing this study. iii TABLE OF CONTENTS ABSTRACT ..................................................................................................................................... i ‫ الخالصة‬............................................................................................................................................... ii ACKNOWLEDGMENT................................................................................................................ iii LIST OF FIGURES ..................................................................................................................... viii LIST OF TABLES ......................................................................................................................... ix LIST OF GRAPHS ........................................................................................................................ xi LIST OF ABBREVIATIONS ....................................................................................................... xii INTRODUCTION .......................................................................................................................... 1 1.1 Background ......................................................................................................................................... 1 1.2 Limitations of Constructed Wetlands ................................................................................................. 2 1.3 Problem Statement .............................................................................................................................. 3 1.4 Aim and Objectives............................................................................................................................. 4 LITERATURE REVIEW ............................................................................................................... 5 2.1. Domestic, Municipal and Industrial Wastewater ............................................................................... 5 2.2. Conventional Wastewater Treatment ............................................................................................... 6 2.2.1. Primary Treatment ...................................................................................................................... 7 2.2.2. Secondary Treatment .................................................................................................................. 7 2.2.3. Tertiary Treatment ...................................................................................................................... 8 2.3. Constructed Wetlands (CWs) ............................................................................................................. 8 iv 2.4. Main Benefits and Outcomes of CWs ................................................................................................ 9 2.5. Types of CWs .................................................................................................................................... 10 2.6. Components of CWs ........................................................................................................................ 10 2.6.1. Water ........................................................................................................................................ 10 2.6.2. Substrates, Sediments and Litter .............................................................................................. 11 2.6.3. Vegetation ................................................................................................................................. 11 2.6.4. Microorganisms ........................................................................................................................ 12 2.6.5. Animals...................................................................................................................................... 13 2.7. Literature Summary ......................................................................................................................... 13 METHODOLOGY ....................................................................................................................... 14 3.1 Overview ........................................................................................................................................... 14 3.2 Methodologies................................................................................................................................... 14 3.2.1 Performance and Cost Comparison of a FWS and a VSF Constructed Wetland System .......... 14 3.2.2 Horizontal Sub-Surface Flow and Hybrid Constructed Wetlands Systems for Wastewater Treatment ............................................................................................................................................ 16 3.2.3 Municipal Wastewater Treatment using Constructed Wetlands ................................................ 19 3.2.4 Efficiency of a Horizontal Sub-Surface Flow Constructed Wetland Treatment System in an Arid Area ............................................................................................................................................ 21 3.2.5 Feasibility of Using Constructed Treatment Wetlands for Municipal Wastewater Treatment in the Bogotá Savannah, Colombia ......................................................................................................... 23 3.2.6 Performance of Four Full-Scale Artificially Aerated Horizontal Flow Constructed Wetlands for Domestic Wastewater Treatment ........................................................................................................ 25 3.2.7 A review on the sustainability of constructed wetlands for wastewater treatment: Design and operation ............................................................................................................................................. 27 v 3.2.8 Constructed Wetlands as a Sustainable Solution for Wastewater Treatment in Small Villages 28 3.2.9 Municipal Wastewater Treatment using Vertical Flow Constructed Wetlands Planted with Canna, Phragmites and Cyprus ........................................................................................................... 29 3.2.10 Development of Constructed Wetlands in Performance Intensifications for Wastewater Treatment: A Nitrogen and Organic Matter Targeted Review ........................................................... 30 3.2.11. Reed bed CW system .............................................................................................................. 31 RESULTS AND DISCUSSION ................................................................................................... 36 4.1 Overview ........................................................................................................................................... 36 4.2 Results and discussions ..................................................................................................................... 36 4.2.1 Performance and Cost Comparison of a FWS and a VSF Constructed Wetland System .......... 36 4.2.2 Horizontal Sub-Surface Flow and Hybrid Constructed Wetlands Systems for Wastewater Treatment ............................................................................................................................................ 38 4.2.3 Municipal wastewater treatment using constructed wetlands .................................................... 43 4.2.4 Efficiency of a Horizontal Sub-Surface Flow Constructed Wetland Treatment System in an Arid Area ............................................................................................................................................ 44 4.2.5 Feasibility of using constructed treatment wetlands for municipal wastewater treatment in the Bogotá Savannah, Colombia ............................................................................................................... 47 4.2.6 Performance of Four Full-Scale Artificially Aerated Horizontal Flow Constructed Wetlands for Domestic Wastewater Treatment ........................................................................................................ 49 4.2.7 A review on the sustainability of constructed wetlands for wastewater treatment: Design and operation ............................................................................................................................................. 51 4.2.8 Constructed Wetlands as a Sustainable Solution for Wastewater Treatment in Small Villages 52 4.2.9 Municipal wastewater treatment using vertical flow constructed wetlands planted with Canna, Phragmites and Cyprus ....................................................................................................................... 56 vi 4.2.10 Development of constructed wetlands in performance intensifications for wastewater treatment: A nitrogen and organic matter targeted review .................................................................. 58 4.2.11. Reed bed CW system .............................................................................................................. 60 4.3 Summary and Comparison ...................................................................................................... 63 CONCLUSION ............................................................................................................................. 65 RECOMMENDATIONS .............................................................................................................. 67 REFERENCES ............................................................................................................................. 68 vii LIST OF FIGURES Figure 3.1: Flow diagram of Korestia facility (Gikas & Tsihrintzis, 2014). ................................ 21 Figure 3.2: The horizontal sub-surface flow constructed wetland treatment (HSF-CW) system layout (Albalawneh, Chang, Chou, & Naoum, 2016)................................................. 22 Figure 3.3: Site process flowsheets of aerated HSSF CW sites( Butterworth, et al., 2016). ........ 26 Figure 3.4 Design of VFCW (Abou-Elela & Hellal, 2012). ......................................................... 30 Figure 3.5: Description of the process for treated effluent (Haya Water, 2017). ......................... 33 Figure 3.6: Stage A (Haya Water, 2017) ...................................................................................... 34 Figure 3.7: Stage B (Haya Water, 2017)....................................................................................... 34 Figure 3.8: Photographs after both stages (Haya Water, 2017) .................................................... 35 Figure 4.1: Concentrations of COD, BOD and TSS in treated effluent (Abou-Elela & Hellal, 2012) ........................................................................................................................... 56 viii LIST OF TABLES Table 3.1: Design criteria for a double-stage VF reed bed after pre-treatment (septic tank) (Haya Water, 2017). .............................................................................................................. 32 Table 4.1: Capital and operating costs (€) for the two facilities( Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007)................................................................................ 37 Table 4.2: Treatment efficiency of vegetated beds of HSSF CWs—world wide experience(data from Australia, Austria, Brazil, Canada, Czech Republic, Denmark, Germany, India, Mexico, New Zealand, Poland, Slovenia, Sweden, USA and UK)( Vyzamal, 2005). 38 Table 4.3: Performance of on-site HF CW at Zitenice, Czech Republic during the period January 2003–September 2004( Vyzamal, 2005) .................................................................... 39 Table 4.5: Performance data from Oaklands Park VF-HF CW (August 1989–September 1991, numbers in mgl-1)( Vyzamal, 2005) ............................................................................ 41 Table 4.7: Treatment performance of a hybrid HF-VF constructed wetland at Darzlubie, Poland; concentrations in mgl-1 (Vyzamal, 2005)..................................................................... 42 Table 4.8: Construction cost of Korestia facility (Gikas & Tsihrintzis, 2014). ............................ 43 Table 4.9: BOD5, COD, TSS, FC, and P removal (Albalawneh, Chang, Chou, & Naoum, 2016) ..................................................................................................................................... 45 Table 4.10: Estimated percent removal of pollutants for the three treatment systems evaluated (Arias & Brown, 2009). .............................................................................................. 48 Table 4.11: Summer and winter ammonium inlet loadings and effluent concentrations (Butterworth, et al., 2016) ........................................................................................... 49 ix Table 4.13: Percentages of removal of biochemical oxygen demand(BOD), chemical oxygen demand(COD) and total suspended solids(TSS), during the second year of wetland operation (Solano, Soriano, & Ciria, 2004) ................................................................ 53 Table 4.15: Pathogen removal during the second year of wetland operation (Solano, Soriano, & Ciria, 2004) ................................................................................................................. 55 x LIST OF GRAPHS Graph 4.1: Relationship between treated effluent, the MECA standard and removal efficiency (Haya Water, 2017) (Oman Government, 2018) ....................................................... 61 xi LIST OF ABBREVIATIONS CW constructed wetlands HF horizontal flow VF vertical flow SSF sub-surface flow HSSF horizontal sub-surface flow VSSF vertical sub-surface flow FWS free water surface HRT hydraulic retention time HLR hydraulic loading rate P.e population equivalent BOD Biological oxygen demand COD chemical oxygen demand EC electrical conductivity TSS total suspended solids FC fecal coliforms TC total coliforms xii TKN total kjeldahl nitrogen TP total phosphorous TN total nitrogen TE treated effluent SF surface Flow RBC rotating biological conductor MECA Ministry of Environment and Climate Affairs xiii CHAPTER 1 INTRODUCTION 1.1 Background Water is one of the essentials that contribute primarily to the sustenance of life for living things. Water is “life”, meaning the existence of all inhabitants on Earth is dependent on this resource. Therefore, mankind must care to protect all water resources. Despite water being essential for life, sustenance water pollution has become a significant threat to water sources. Industrial wastes and exhaust fumes are the major contributors of water pollution across the globe, and the growth in industrial development across the world has caused more wastes to be released in the water bodies. The untreated waste discharged from single household, municipal and industrial activities into the water sources and land have endangered marine life, degraded the environment, and increased the risk of humans contracting water-borne diseases. (Postel, 2000). Water pollution control mechanisms must include public awareness, and the public need to be educated on the importance of preserving water resources by properly disposing wastes to prevent municipal, industrial and domestic wastewater. If the public understand the need to keep water safe, then the pollution of water and environmental degradation can be eluded. CW treatment systems for wastewater recycling is cost effective and can help those people struggling with the scarcity. The strategy of conserving water benefits the society and helps the environment and water utilities. 1 The concept of sustainability can be integrated into both human activities and the general human society (Praewa, 2017). If the human activities are less sustaining, there are adverse effects on the ecosystem which is essential for sustenance and support of human life. Present-day approaches have been designed to incorporate sustainability, environmental ethics and the participation of public efforts in creating developmental projects in the communities. Known and unknown water substances being added to the public water used in industries, households and for commercial purposes transforms the water into household, municipal and industrial wastewaters. CWs is a sustainable approach for municipal, single household and industrial wastewater treatment. These enhance the basis for water reclamation and reuse of most essential water resources management programs across the globe (Praewa, 2017). CWs are managed and engineered wetland systems that are gaining worldwide popularity in wastewater reclamation and treatment. Moreover, they naturally perform pollutant removing processes mediated by complex interactions between soil/gravel media, water, vegetation and their associated microbial assemblages and the environment to improve water quality viably. CWs are designed to exploit the physical, chemical, and biological treatment processes that are found in wetlands and provide a provision for organic material reduction, nutrients, metals, total suspended solids, pathogenic organisms and biological oxygen demand. CWs cost less and have easier operation and maintenance, and they proved to have a great potential for application in households, industries, and municipals wastewater treatment. 1.2 Limitations of Constructed Wetlands 2 CW systems have limitations that sabotage their effectiveness. In contrast with other conventional wastewater systems that accomplish the same purpose, they tend to occupy large pieces of land. CW system has an economic deficit, making it impossible for people who do not have money to buy more land, the ability to install a CW. Therefore, in some cases, constructing a wetland system is expensive (Jhansi & Mishra, 2013). Water treatment effectiveness is hindered because biological components in wastewater are in most cases sensitive to chemicals such that any water surges would affect the process of CW. Although the wetlands are designed to survive in very little amounts of water, they cannot survive completely in areas that are dry. Cold weather conditions weaken the effectiveness of the wetland system, and high temperatures that may be a result of dry periods and drought, also affects the performance of the system. Heavy rains also have an impact on the effectiveness of the constructed wetland systems, most especially during the spring season. The system effectiveness is dependent on many changing weather patterns; therefore, their effectiveness in the treatment process are gradually compromised (Crawford & Sandino , 2010). Applying constructed wetland systems for municipal, industrial and single household wastewaters is a new concept (Crawford & Sandino, 2010), and consequently, the technology to reinforce its effectiveness is not fully developed. Some ecological and environmental critiques believe that more should be done to realize full efficiency of the constructed design system. 1.3 Problem Statement Most developing countries have challenges regarding industrial, municipal and single household wastewater management because they have limitations in obtaining wastewater management technologies that are economical, usable and effective. The sole purpose of 3 wastewater management is to prevent the spread of diseases and infections that are caused by water contamination. Nutrients recovery, water reuse, and reclamation, including conserving water resources are other wastewater management objectives that most world organizations are working to attain. Changing from conventional wastewater management to more efficient and effective wastewater management should be embraced globally (Praewa, 2017). The discharges and effluents that emerge because of water pollution should be disposed of in a way to not spread diseases and infections to the members of the society. Stagnant, polluted water bodies give mosquitoes a good breeding site, placing people at very high risk of contracting malaria (Praewa, 2017). 1.4 Aim and Objectives The aim of this study is to provide an assessment of the various types of CW wastewater treatment systems, through a review of their design for use in municipals, and a discussion of their performance, in terms of onsite wastewater treatment, percentage removal of pollutants, water reuse criteria and influent/effluent quality. Using several study cases as examples. 4 CHAPTER 2 LITERATURE REVIEW 2.1. Domestic, Municipal and Industrial Wastewater In this day and age, the issue of municipal, industrial and domestic wastewater is of great concern because it can cause severe environmental problems and can also impact people in terms of their health. Studies have estimated that wastewater comprises 99% water, with the remaining 1% being a mixture of suspended and dissolved organic solids, detergents and chemicals (Secretariat, 2014). Sewage is wastewater that comprises household waste from toilets, sinks and showers/baths that is disposed of via sewers. Municipal wastewater includes input that ranges from, for example, shops, to restaurants and bars, and car washes (Secretariat, 2014). Frequently, pretreated industrial wastewater is included in with the municipal wastewater. A wide variety of processes result in the formation of industrial wastewater, including plastic manufacturing, wood pulping, petroleum refinement and food processing. According to Secretariat (2014), these different types of wastewater have varying compositions, containing for instance, different pathogens, bacteria and nutrients. Untreated wastewater components can be organised into three categories – physical, biological and chemical. Solid and inorganic constituents in wastewater comprise the physical components. The biological 5 components are bacteria, viruses, protozoa and other pathogens. Lastly, the chemical components include dissolved materials and organic matter, as well as nutrients and metals, which, in most cases, are heavy metals. In rare cases, wastewater might contain reusable resources for example, water, carbon and other nutrients that could be recovered. For effective effluent regulatory standards to be met, wastewater needs to undergo appropriate treatment in order to get rid of the pollutants and, according to Crawford & Sandino (2010), this process should be focused on the recovery of resources, so as to be self-sustaining. Advances in scientific knowledge, and a greater consciousness about the environment and water as a resource, have given rise to new and improved technologies and treatment systems that are effective in dealing with wastewater pollution and also in reducing the energy used in recycling wastewater; however, selection of the appropriate technology to solve a specific wastewater problem should be undertaken with great care. Generally, there are two types of wastewater treatment systems – conventional and sustainable CW. 2.2. Conventional Wastewater Treatment Conventional wastewater treatment comprises physical, chemical and biological processes, involving three stages, referred to as primary, secondary and tertiary treatments. 6 2.2.1. Primary Treatment This treatment is used in the removal and separation of particulate inorganic materials and solids, which would otherwise clog and destroy water pipes of the network. This type of treatment entails screening, grit removal and sedimentation. Screens are used to get rid of large debris, including plastics and cans. The grit chamber system is used to remove, settle, gravel- and sand-sized particles. According to Nelson et al. (2007), the wastewater is then moved into a quiescent basin, where it is temporarily retained so that the remaining heavier solids can settle to the bottom of the basin, while the lighter solids, including grease and oil, can accumulate on the surface. Finally, skimming and sedimentation processes are used to remove both the floating and settled pollutants. The liquid that remains is transferred to the secondary treatment. In this primary stage, 50% of the TSS and 30–40% of the BOD are removed (Nelson, Bishay, Van Roodselaar, Ikonomou, & Law, 2007). 2.2.2. Secondary Treatment Dissolved and biological matter is removed in the secondary treatment. According to Nelson et al. (2007), 90% of the organic matter in the wastewater is removed at this stage. The attached and suspended growth processes are the two most suitable conventional methods used in secondary treatment. In the attached growth process, algae, bacteria and other microorganisms are grown on the surface of the wastewater, resulting in the formation of biomass, which breaks down the organic waste. Trickling filters, bio-towers and rotating biological contactors are included in the attached growth 7 process unit. In the suspended growth process, the microbial growth is suspended in an aerated water mixture; however, activated sludge, in which a biomass of aerobic bacteria and other microorganisms is grown, is the most common type of suspended growth process. 2.2.3. Tertiary Treatment The tertiary treatment is more advanced, aimed at producing a better-quality, more purified effluent for discharge into estuaries and low-flow river ecosystems. Coagulation sedimentation, filtration, reverse osmosis and extended secondary biological treatments are some of the methods that are used in this stage. These methods remove nutrients and stabilise oxygen in oxygendemanding substances. The treated effluent can then be safely reused, recycled or discharged (Praewa, 2017). In most circumstances, a final disinfection process is needed before tertiary-treated wastewater can be discharged. Disinfectants can be added to kill off pathogens and microorganisms, and. chlorine and ultraviolet light are also commonly used. The treated water can then either be discharged into different water bodies, including recharging underground reserves, or used in agricultural irrigation (Praewa, 2017), as long as it meets the required standards. 2.3. Constructed Wetlands (CWs) CW systems for single-household, municipal, and industrial wastewater are designed in ways that imitate the natural processes at work in wetlands but include features that provide advantages over natural wetland processes. Such CWs incorporate chemical, biological and physical processes that 8 are used to remove the pollutants and enhance and improve the quality of the wastewater (Vymazal & Kropfelova, 2008). These design systems use aquatic macrophyte and microbial communities, and plant roots and their host minerals to effectively remove pollutants, which include nitrogen, metals and pathogenic organisms, among many others. In 1904, the first CW was built in Australia (Vymazal & Kropfelova, 2008). Despite this, technological advancement in the field has been slow (Vymazal & Kropfelova, 2008). As the number of CWs increases around the world, and the benefits and effectiveness of the system over conventional treatment systems become better understood, CWs are finding wider favor among ecologists, scientists and water and environmental engineers, and this is leading to their popularisation even among developing countries. 2.4. Main Benefits and Outcomes of CWs The CW is a beneficial wastewater system because, upon treatment, the water that is discharged can either be used for domestic activities or can be directly discharged into the environment. It is also beneficial to the end-users, as construction costs are minimal, and the costs of operation and maintenance are affordable. The operation and maintenance of CWs are periodic, unlike conventional water treatment systems, which in most cases require continuous, on-site labour (Crawford & Sandino, 2010). The CW system facilitates the recycling and reuse of water, thereby defraying the costs of installation, operation and maintenance. The CW system not only provides a habitat for wetland organisms but is also engineered in a way that finds favor with the public because of its many benefits. 9 2.5. Types of CWs There are various types of CWs that depend on the available landscape, including SF and SSF systems. SF CWs have shallow flow and lower velocity over the substrates, whilst SSF CWs have either VF or HF over the substrates. Hybrid CWs combine both VF and HF (Vymazal & Kropfelova, 2008). Each type of CW system has its benefits and drawbacks, and each differ in the treatment process used. SF CWs make use of plant stems, leaves and rhizomes to effectively treat wastewater. In dense vegetation, however, the process can be limited because there is not enough circulation of oxygen, which is vital for the organisms. In SSF CWs, roots are used in the treatment of effluents as water passes through a series of gravel beds. This process is considered to be superior to, and more effective than that used in SF CWs. 2.6. Components of CWs 2.6.1. Water Locations in which landforms predominantly direct surface water straight into shallow basins, or where impermeable subsurface layers hinder the ground from absorbing surface water, are the most likely places for wetlands to form naturally. Such conditions in a location can be engineered to create wetlands (Jhansi, & Mishra, 2013). Land can be structured in such a way that surface water is collected, and such basins can be sealed in order to retain the collected surface water. Once a landscape has been modified in this way, a wetland can be constructed. 10 In the construction of a wastewater wetland system, hydrology is among the most important factors to be considered. This is because it not only links all of the functions of the wetland, but it is also a key factor in the CWs failure or success in a given landscape. The hydrology of the CW is important in relation to the hydrology of other surface water in the area. Small, natural hydrological changes can promote significant effects in the CW, impacting on its utility. Through rainfall and evapotranspiration, there is substantial interaction between the wetland system and the atmosphere because of the wetland water is shallow and covers a large surface area. The hydrology, in most cases, is also affected by vegetation density in the wetland, which can obstruct the flow of water. 2.6.2. Substrates, Sediments and Litter Soil, sand, gravel and rock, as well as organic materials, such as compost, are used to make the substrates for the wastewater to flow over. Due to the high biological productivity and low water velocities in wetlands, it is possible to easily accumulate sediments and litter (i.e., organic matter). These substrates, sediments and litter are vitally importance because they support all of the living organisms that dwell in wetlands (Secretariat, 2014). For many contaminants in a wetland, the substrate acts as a sink. The substrate is also important because its permeability affects the movement of water passing through the CW. 2.6.3. Vegetation In any CW, the presence of both vascular and non-vascular plants is of vital importance (Praewa, 2017), vascular plants being the higher plants, whereas non-vascular plants are the algae. When algae undergo photosynthesis, they increase the dissolved oxygen content in the water, which 11 significantly affects the metals and nutrients present in the water. The presence of plants in a CW system, therefore, is very important, since they also penetrate the substrate structure, transferring oxygen into the substrate, a process that is not possible or achievable, even using diffusion. The presence of submerged leaves, stalks and litter is important in FWS wetlands in terms of attached microbial growth, wherein the leaves, stalks and litter themselves serve as substrates. Wastewater wetlands are mostly characterised by the absence of emergent plants, although natural wetland systems commonly include reeds, rushes and cattails. Cattails have the ability to survive and thrive under diverse environmental conditions, and they can produce massive annual biomass. Rushes –particularly bulrushes – are perennial, grass-like plants that are capable of growing and thriving in clumps. They tend to grow better in water that ranges from 5 cm to 3 m deep (Wetzel, 1993). Most bulrushes grow well in water that has a PH of 4–9. Reeds are tall, annual grasses with a perennial rhizome. Reeds are among the most widespread emergent aquatic plants. CWs that use reeds are at an advantage because the reeds have the ability to transfer oxygen into the substrate, thus improving the effectiveness of the system. 2.6.4. Microorganisms The functions of CWs are, in some way, controlled and regulated by the presence of microorganisms and their metabolic processes. Algae, protozoa, fungi and yeasts are examples of microorganisms that are found in wetlands. Microbial activity in the system is important because this is how nutrients are recycled. Microbial activity also affects the processing capacity of the 12 wetland because it can cause reduced conditions in the substrate. In CWs, microbial communities are affected by toxic chemicals, such as those found in pesticides (Wetzel, 1993). 2.6.5. Animals Certain vertebrates and invertebrates take up residence in CW systems. Insects and worms are (invertebrates) are significant contributors to the treatment process (Wetzel, 1993), making it safe and more effective. 2.7. Literature Summary CWs for municipal, industrial and domestic wastewater treatment can be designed in appropriate and specific ways to meet most intended purposes. Wetland systems can be engineered to take advantage of the various features of a site. CWs are an effective approach that can be employed in improving wastewater quality and allowing for its reclamation and reuse. Moreover, CW systems are of economic and thus they are globally applicable. CHAPTER 3 13 METHODOLOGY 3.1 Overview This section elaborates in detail the methodology employed in various CW projects as presented in a number of case studies. The CWs, although employ different designs, all serve municipal needs for wastewater treatment. This chapter explains the designs used, population equivalent served, the construction costs, operation and maintenance costs, size of the CW, and the overall methods used to treat municipal wastewater. 3.2 Methodologies 3.2.1 Performance and Cost Comparison of a FWS and a VSF Constructed Wetland System The study compares two CWs designs to define which is more appropriate for a municipal in terms of design considerations, construction cost, constituent removal performance, and operation and maintenance(O&M) costs(Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). Both CWs treat domestic wastewater from municipals. The first CW is an FWS CW found in Pompia, Crete, in South Greece, while the second is a VSF CW located in Gomati, Chalkidiki, in North Greece. The FWS CW is designed for a population of 1200 p.e., and its total construction cost is €305,000. The capital and O&M cost is €22.07 p.e.-1 yr-1 or €0.50 m-3 of influent. The design of the FWS system comprises a septic tank with three screen vault filters (up-flow reactor simulation), a FWS CW comprising a series of two basins with surface areas of 4300m2 and 1200m2, a chamber in each basin to regulate water level, small pumps and a pipeline system for recirculating effluent back into the inlet of the first basin, and a compost filter to control odor in the septic tank(Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). In the basins, the inflow is 14 distributed uniformly at the inlet of each of the two basins using manifolds. The plant species planted in the wetland areas are Phragmites australis and Arundo donax. The reeds were planted in the winter of 1999 and experienced speedy growth due to advantageous climatic conditions (Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). By the end of the year, the vegetation was dense and the plants had grown more than two meters in height. The basic parameters used in the FWS CW are the following: mean daily flow rate 144 m3 d-1, maximum daily flow rate, 216 m3 d-1; maximum hourly flow rate, 27.7 m3 h-1; retention time, 5-14 d(depending on the season of the year); sewage average temperature of 10°C in the winter and of 22°C in the summer(Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). The VSF CW is designed for a capacity of 1000 p.e., and its total construction cost is €410,850. The capital and O&M costs are €36.81 p.e.-1 yr-1 or €0.56 m-3 of influent. The VSF system comprises an inflow structure, a rotating disk screen with openings of 1 mm, a closed twin settling tank(48 m3 each chamber; dimensions 4 m x 6 m x 2.5 m), closed twin sludge digestionstabilization tank(48 m3 each chamber; dimensions 4 m x 6 m x 2.5 m), an open siphon tank(3.2 m3; dimensions 1.0 m x 4.2 m x 0.8 m) for intermittent wastewater feeding, a stage I VSF circular basin(4 cells, 640 m2, sand and gravel fill, 1 m deep), a stage II VSF circular basin(4 cells, 360 m2, sand and gravel fill, 1 m deep), a stage III rectangular HSF cell(800 m2, sand and gravel fill, 0.5 m deep) and a VSF circular basin(4 cells, 240 m2) which receives digested-stabilized sludge for drying and storage(Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). All the basins are planted with Phragmites australis. The HSF cell was not planted at the time of the study and was out of the wastewater stream. The VSF was planted and put into operation in May 2003. The wastewater flows from the inflow structure to the rotating disk screen and then to the settling tanks. From there, sludge is collected from the settling tank and pumped into the sludge digestion15 stabilization tank and then into the VSF sludge basins. From the VSF sludge basins, the leachate is pumped back to the siphon with wastewater from the settling tanks to feed the stage I VSF basin and then the stage II VSF basin. The effluent is then discharged into a stream. The basic parameters for the design are the following: mean daily flow of the system, 180 m3 d-1; maximum hourly flow, 28.5 m3 h-1, hydraulic loading rate, 36 m yr-1; organic loading rate, 196 kg ha-1 d-1(Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). Samples for the FWS system were frequently composed of the inflow, settling tank outflow and system outflow; while samples for the VSF system were often assembled from the inlet, settling tank outflow, siphon, stage I VSF outflow and stage II VSF outflow(Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). The monitoring period totaled 3 years from August 1999 to August 2003 for the FWS, while the monitoring period for the VSF was July 2003 to August 2004. The samples were analyzed for TKN, TP, TC, FC, TSS, COD, and BOD5. 3.2.2 Horizontal Sub-Surface Flow and Hybrid Constructed Wetlands Systems for Wastewater Treatment The purpose of the study is to discuss the methodologies and results of several case studies for HSSF and Hybrid CWs that are sampled regionally and are as follows: The HSSF System: The most widely used HSSF concept was developed in Germany by Kathe Seidel. The design comprises a four-sided cot imbedded with Phragmites australis and lined with an impermeable membrane. Wastewater is treated with mechanical methods before it is fed into the CW inlet. From the inlet, the wastewater is passed slowly through the filtration medium and is finally collected at the outlet. Another system was designed by Reinhard Kickuth to improve on the first by using 16 cohesive soils with a high content of clay. The full- scale municipal sewage treatment operation measured an area of 22ha and was located in Liebenburg-Othfresen. The system uses soil as its medium with a size of 2m2 p.e-1 for the vegetated beds. In Denmark, beds were built with an area of 3 and 5 m2 p.e-1. The systems are structured with minimum proportion and a subdivided inlet trench that was divided into two or more units. In contrast, in the United Kingdom, reed bed treatment systems designed with an area of 5 m2 p.e-1 were used. The substrate is composed of very course material to ensure sub-surface flow. The general equation used to determine the sizing of HSSF CWs is as follows: 𝐴ℎ = 𝑄𝑑 (𝑙𝑛𝐶𝑜 − 𝑙𝑛𝐶) … … … … … … … … … … … … … … … … … … … … … … . … . . … … (3.1) 𝐾𝐵𝑂𝐷 Where Ah is the surface flow of bed (m2), Qd is the average flow (m3 day-1), Cin is the influent BOD5 (mgl-1), Cout is the effluent BOD5 (mgl-1) and KBOD is the rate constant (mday-1). Typically, the HF CW has a filtration bed of a depth of about 0.6–0.8m and is planted with Phragmites to allow the roots of the plant species to penetrate the whole bed. The oxygen released from the roots and their rhizomes should be enough to satisfy the demand for physiological needs. In the soil zone below the Fe3+ reduction zone is where anaerobic respiration occurs through facultative or obligate anaerobes. In the flooded soils and sediments, acetic acid is the primary acid that is formed; however, over-production of the acid can result in very low pH levels. SS that are not removed during pre-treatment are removed through filtration and settlement, but removal of SS in the pre-treatment stage is ideal to prevent clogging of the substrate. Nitrogen removal is done through nitrification or denitrification while phosphorous is removed mainly by ligand exchange reactions(Vyzamal, 2005). 17 A case of an HF CW found in Zitenice, Czech Republic, was built in 1993 for a population of 4 p.e. The system was composed of a pre-treatment section made up of an advanced septic tank and built-in baffles. The retention time of the tank is 12 hours. The area of the bed is 18 m2, and the bed is filled with 1–4 mm of coarse sand as the filtration material. The facility was first planted with Phragmites australis and Typha latifolia, and then these were replaced by Iris pseudacorus and Iris sibirica in 2002. Another case study located in Spalene Porici, Czech Republic is presented. The facility was designed for a population of 700 p.e. and was built in 1992. The pre-treatment section comprised an Imhoff tank and local septic tanks. The sewerage system is combined with an average flow of 200 m3 day-1. The vegetated bed is then divided into four sections and has an area of 2500 m2. The four beds are equal in size and two of them are parallel to each other. The beds are filled with 0-16mm of gravel and the beds are planted with Phragmites australis and Phalaris arundinacea. In later years, P. australis takes over the other plant species and becomes dominant. Another case study located in Spalene Porici, Czech Republic is presented. The facility was designed for a population of 700 p.e. and was built in 1992. The pre-treatment section comprised an Imhoff tank and local septic tanks. The sewerage system is combined with an average flow of 200 m3 day-1. The vegetated bed is then divided into four sections and has an area of 2500 m2. The four beds are equal in size and two of them are parallel to each other. The beds are filled with 0-16mm of gravel and the beds are planted with Phragmites australis and Phalaris arundinacea. In later years, P. australis takes over the other plant species and becomes dominant. The Hybrid System(VF-HF): 18 In Oaklands Park, UK, a VF-HF system was built in 1987. The first stage is made up of six vertical beds with an area of 8m2 and planted with P. australis. The second stage is made up of three vertical beds with an area of 5m2 each and planted with P. australis, yellow flag and bulrushes. The third stage is a HF bed measuring an area of 8m2 and planted with yellow flag while the fourth is a 20m2 bed planted with bulrush, bur reed, and sweet flag. Another system known as the Colecott system designed for 60 p.e based on the original Seidel’s concept is presented. The system is made up of four VF beds in the first stage measuring a total area of 64m2, two VF beds in the second stage measuring 60m2, and one HF bed with an area of 60m2 as well in the third stage(Vyzamal, 2005). The Hybrid System(HF-VF): A case study in Poland shows that HF and VF constructed wetlands could also be combined in more than two stages(Vyzamal, 2005). The system in Darzlubie in Poland consists of a combination of HF bed measuring 1200m2, cascade of five alternate HF and VF beds (total are of 270m2), and HF(II) bed (500m2)(Vyzamal, 2005). After this point 50% of the flow is directed to two VF(II) beds(total area 500m2) and the final stage of the treatment system is a 1000m2 HF bed where the outflow from VF(II) and HF(II) are combined(Vyzamal, 2005). 3.2.3 Municipal Wastewater Treatment using Constructed Wetlands The case study describes and discusses the Korestia wastewater treatment plant located in the northern part of Kastoria, Northwest Greece, which focuses on expanding constructed wetland use as the preferred wastewater treatment system in small municipalities and settlements. The municipality of Korestia has an area of 12,228 ha. The population of Korestia at the time of the 19 CW was about 500 residents and practices mainly agriculture and livestock keeping. The entire project is designed to serve a population of 600 p.e. The system is a hybrid series consisting of three stages. The first stage is composed of three identical VF beds measuring a total area of 891 m2 or 1.5 m2/ p.e. The second stage is composed of two identical VF beds with a total surface area of 594 m2 or 1.0 m2/p.e. The third stage is composed of one HSF bed (added for denitrification) measuring a total surface area of 903 m2 or 1.5 m2/p.e. The total construction cost was 286,282 € or 477 €/p.e., while the operation cost came to 7,121 €/year, or 11.87 €/p.e./year. The wastewater discharge per p.e. was calculated as 150 L/d, and the total flow of wastewater was 90 m3/d(Gikas & Tsihrintzis, 2014). High-density polyethylene geomembrane (1 mm) was used to completely waterproof the beds to avoid leaching of the sewage water to groundwater. The geomembrane is protected on all sides using a special geotextile that prevents damage from a substrate material that may cause tearing and holes. The substrate used for the beds is porous inert material from a quarry or torrent deposits, and the porous media of the beds are as follows: 1st stage CWs have a depth of 0.90 m and consist of 3 layers from the bottom to the top: cobbles 0.2 m(diameter 20–40 mm), coarse gravel 0.2 m(diameter 5– 20 mm) and fine gravel 0.5 m(diameter 2–8 mm) 2nd stage CWs have a depth of 0.90 m and consists of 3 layers from bottom to top: cobbles 0.2 m(diameter 20–40 mm), fine gravel 0.3 m(diameter 3–8 mm) and river sand 0.4 m(diameter 0.2–4.0 mm); the 3rd stage CW is filled with 50 cm of gravel(diameter 18–30 mm)(Gikas & Tsihrintzis, 2014). Phragmites australis is the plant species used for all the beds. Two polyvinyl chloride pipes (PVC) route wastewater from Korestia village into the treatment facility and into a pump vault. The pump vault has two submerged pumps that operate alternately, first pumping the wastewater to the first stage VF beds by using electricity. The rest of the facility, 20 however, uses gravity. Each bed in the first CW stage receives an entire load of about 14 m3 during a two-day feeding phase and then rests for four days during which another basin is fed. The design parameter concentrations to be analyzed were BOD, TSS, TKN and TP(Gikas & Tsihrintzis, 2014). Figure 3.1 shows the flow diagram of Korestia facility. Figure 3.1: Flow diagram of Korestia facility (Gikas & Tsihrintzis, 2014). 3.2.4 Efficiency of a Horizontal Sub-Surface Flow Constructed Wetland Treatment System in an Arid Area The study was performed in Al-Samra Agricultural Research Station located in Central Jordan. The station is found 36 km downtown of Amman and has an elevation of 550 m above sea level. A benchmark project site was developed in 2008 for an HSF CW. Partially treated municipal wastewater was held in a 300 m3 pond and then directed into the HSF CW to be retreated. The treated effluent was then collected in another 150 m3 holding pond and used for the irrigation of forest trees. For this project, the system was made up of 17 HSSF CWs, and the mean hydraulic residence time was 2 days. The system was divided into two main categories. In the first category, there are a total of 9 beds with each measuring 9.5 m x 1.7 m x 0.8 m in terms of length, width, and height. The wetland media used is coarse volcanic tuff measuring 10–20 mm in diameter. Three of the beds had Phragmites australis, another three had the kenaf plant, and the last three had no vegetation and 21 were used as controls. The second category had 8 beds measuring 6.5 m x 2.5 m x 0.8 m in length, width and height. The wetland media used for four of the beds was coarse volcanic tuff 10–20 mm in diameter, while the other four beds were filled with fine volcanic tuff 4–8 mm in diameter. Two of the beds filled with fine media and two filled with coarse media were planted with reeds, while the rest had no vegetation and were used as controls. Each bed was outfitted with a tube in the middle to measure water temperature daily. All the beds had the same volume of 13 m3. The total HSF CW volume was 221m3, while the total surface area was 275m2. Figure 3.2 shows the HSFCW layout. Figure 3.2: The horizontal sub-surface flow constructed wetland treatment (HSF-CW) system layout (Albalawneh, Chang, Chou, & Naoum, 2016). The following abbreviations are used: Long bed(L), short bed(S), coarse media(C), and fine media(F), reeds(R), kenaf(K), and no vegetation(N)(Albalawneh, Chang, Chou, & Naoum, 2016). The influent and effluent were sampled and analyzed on a bimonthly basis for 18 months from November 2008 to August 2011. The chemical and biological characteristics of wastewater 22 focused on in this study are: BOD5, COD, TSS, FC and P. (Albalawneh, Chang, Chou, & Naoum, 2016). Removal efficiency(%) for each parameter of water quality was calculated based on mass flow difference between the effluent and influent relative to the influent(Albalawneh, Chang, Chou, & Naoum, 2016). 3.2.5 Feasibility of Using Constructed Treatment Wetlands for Municipal Wastewater Treatment in the Bogotá Savannah, Colombia A treatment wetland model for pollutant removal is developed using data from literature whose performance is then compared to a waste stabilization ponds and sequencing batch reactor to quantify its performance and sustainability(Arias & Brown, 2009). The three systems are compared in terms of cost and emergy. Two sites are used for the study. The first site is Tabio, and it is located 50 km northwest of Bogota and has a population of 14,000 with an average temperature of 14°C. The municipality was designed to treat 20 L/s of wastewater. In addition, the plant has an area of 3.4 ha and was constructed in 1992. The system consists of a screen, sedimentation tank, anaerobic basin, and two series of facultative lagoons each with two basins(Arias & Brown, 2009). The second site is at LaCalera, and it is located 30 km east of Bogota and hosts a sequencing batch reactor (SBR) that was constructed in 2002. It is designed with a flow of 36.5 L/s and for a population of 16,000. The system comprises a manual screen and sedimentation tank for primary treatment, two reactor tanks for secondary treatment, sludge digester, and sludge drying beds(Arias & Brown, 2009). A hypothetical CW treatment system is developed from the previously mentioned two actual designs, and its location is assumed to be Tabio. The system consists of screens, sedimentation tanks, an anaerobic basin, and a combination of modeled SSF and SF wetland units(Arias & 23 Brown, 2009). Data for wastewater was derived from raw wastewater quality data from Tabio and used to size the hypothetical system. The area of the plant was determined from the 3.4 ha of the plant, minus 2900 m2 taken up by the anaerobic basin, minus 30% of the extra area set aside for pre-treatment structures and open areas(Arias & Brown, 2009). The model was subject to a sensitivity analysis to determine the effect of the system configuration on the overall feasibility study, and this analysis was performed by estimating the pollutant removal and the cost for different area distributions between SSF and SF wetlands; the configuration used in this study was found at the point where maximum pollutant removal and minimum cost intersected(Arias & Brown, 2009). Effluent concentration in each unit was calculated using the following model: 𝐶𝑒 = 𝐶 ∗ + (𝐶𝑖 − 𝐶 ∗ ) exp ( −𝑘𝐴 ) … … … … … … … … … … … … … … … … … … … . … … … … . .3.2 0.0365𝑄 Where Ce is outlet concentration(mg/L),Ci is inlet concentration(mg/L),C* is background concentration(mg/L),A is wetland area(ha), Q is water flow rate(m3/day), and k is first-order areal rate constant(m/yr)(Arias & Brown, 2009). The net annual cost of treatment was estimated as the following: 𝑁𝑒𝑡 𝐴𝑛𝑛𝑢𝑎𝑙 𝐶𝑜𝑠𝑡 = 𝑂&𝑀 + 𝐶𝑜𝑛𝑠𝑡𝑟𝑢𝑐𝑡𝑖𝑜𝑛 𝐿𝑖𝑓𝑒𝑡𝑖𝑚𝑒 …………………………………………………(3.3) Where net annual cost, construction, and annual O&M were calculated in 2003 dollars, and lifetime refers to the facility design lifetime, which is assumed to be 25 years for the three systems(Arias & Brown, 2009). 24 3.2.6 Performance of Four Full-Scale Artificially Aerated Horizontal Flow Constructed Wetlands for Domestic Wastewater Treatment An evaluation of the recital of four full-scale aerated horizontal flow constructed wetlands was conducted to regulate the efficacy of the technology on sites receiving high and variable ammonia loading rates not yet described in the data(Butterworth et al., 2016). The typical HSSF system serves about 2000 PE. All aeration systems consist of 1.6 kW air blower, dispersal header and loops of perforated LDPE 12 mm piping with 2 mm holes (Butterworth, Richards, Jones, Jefferson, & et, 2016) drilled into it at 300 mm intervals placed on top of the impermeable liner covering the surface area of the bed floor(Butterworth et al., 2016). Sites A, B, and D are planted with P.Australis, while Site C is planted with T.latifolia. “Site A consists of a primary settling tank, a submerged aerated filter, and tertiary treatment is via two HSSF CWs with a separately combined sewer overflow(CSO) HSSF CW that receives the wastewater exceeding six times the dry weather flow”(Butterworth et al., 2016). Site A, in addition, obliges as a control site with side by side wetlands of equal size where the aeration of the test bed began 3 March 2011 and was left dormant in the control bed. The standard pass to respective bed was 46 m3/d, the resultant to standard hydraulic loadings was 0.46 m3/m2/d and the average inlet loadings to the bed through the trial were 12 gBOD/m2/d, 25 gTSS/m2/d and 9.1 g ammonium nitrogen(NH4+-N/m2/d)(Butterworth et al., 2016). Site B treatment is via an integral RBC which is followed by a combined wetland. The bed was retrofitted and has been operated with intermittent aeration. The mean flow of the bed is 45 m3/d, the mean hydraulic loading is 0.1 m3/m2/d and the average loadings to the bed during the trial are 11 gBOD/m2/d, 1 gTSS/m2/d and 1.6 gNH4 +-N/m2/d(Butterworth et al., 2016). 25 Site C comprises two fundamental RBCs and a collective tertiary reed bed and the driver for aeration at this site was the addition of an ammonia effluent consent at a site that was not originally designed to nitrify(Butterworth et al., 2016).“The average trickle to the bed is 248 m3/d, followingon in average hydraulic loadings of 0.4 m3/m2/d and average loadings to the bed during the trial were 8 g BOD/m2/d, 17 gTSS/m2/d, and 8.9 gNH4+-N/m2/d”(Butterworth et al., 2016). Site D is the only secondary bed consisting of a septic tank and a combined reed bed. The bed was refurbished in March 2010 and fitted with aeration on 30 March 2011, and because the consented flow is below 50 m3/d, this site had no flow measurement during the trial(Butterworth et al., 2016). Figure 3.3 shows all the site designs for sites A through D: Figure 3.3: Site process flowsheets of aerated HSSF CW sites( Butterworth, et al., 2016). Composite samples were unruffled fortnightly (every 15 min over 24 h) during the first year and monthly. “In this context, robustness is described as the ability of a treatment unit to produce consistent effluent quality under varying influent characteristics and differentiates from resilience, which is defined as the ability to return to normal after a dynamic event.”(Butterworth, et al., 2016). 26 Robustness index indicates the robustness of a process and is calculated by the following: 𝐺% 𝑇 𝑇50 𝑅𝐼 = [(1 − 100) × 𝑇90 ] + [𝑇 50 𝑔𝑜𝑎𝑙 𝐺% × 100]………………………………………………………..(3.4) Where RI is the robustness index, G% is the percentage time spent under Tgoal, T90 is the 90th percentile value(mgNH4+-N/L), T50 is the 50th percentile value(mgNH4+-N/L) and Tgoal is the treatment goal(mgNH4+-N/L)(Butterworth et al., 2016). 3.2.7 A review on the sustainability of constructed wetlands for wastewater treatment: Design and operation The study discusses various CW designs and parameters including plant species, substrate types, water depth, HRT, HLR and feeding mode to determine the most sustainable factors that ensure a CW is suitable, stable and sustainable. In agreement with the study(Wu et al., 2015), regarding plant selection, factors such as the tolerance of waterlogged anoxic, hyper-eutrophic conditions, and the capacity of pollutant absorption should be used to choose the most suitable plant. In addition, there are three types of plants used for vegetation that should be considered during plant selection: emergent plants, submerged plants, and floating plants. Plant tolerance to wastewater toxicity and environmental stress should be monitored to ensure proper and rapid growth. Plants can accumulate toxic components in the water; therefore, the capacity for a species to remove pollutants is another important factor. The substrate chosen for the CW is another critical factor since it provides a growing medium for the plants and facilitates movement of wastewater. Therefore, substrate selection should be considered in terms of capacity for pollutant sorption (through exchange, complexation, precipitation and adsorption) and hydraulic permeability(Wu et al., 2015). 27 HLR and HRT rates are essential for controlling wetlands, and their rates should be carefully regulated for performance efficiency. In addition, the design of the feeding mode of the influent (continuous, batch, intermittent) may be instrumental in influencing oxidation-reduction conditions and oxygen transfer and diffusion hence influencing removal rates(Wu et al., 2015). 3.2.8 Constructed Wetlands as a Sustainable Solution for Wastewater Treatment in Small Villages A pilot-scale SSF CW is constructed with the aim of removing pollutants from wastewater from small villages. The CW is located near Soria sewage treatment plant, North Spain, in a Mediterranean semi-arid area with minimum and maximum temperatures of 22 and 50°C. The system comprises two series with different HAR values of 150 and 75 mm day-1 and HRTs of 1.5 and 3 days, respectively. Each bed has an area of 40 m2, length to width ratio of 10:1, depth of 1 m, diameter gravel of 0.5–1 cm and gravel depth of 0.40 m. In addition, each bed is lined with impermeable plastic to prevent groundwater contamination. The inlet and outlet zones measure 1 m each and have large stones of diameter 5–10 cm, and each inlet has a PVC pipe at the top. The influent feeding the beds is collected from urban runoffs, domestic water, and a small manually controlled percentage between 1.5 and 3 from the industrial food processing industry. Each bed is fitted with two sampling tubes at the head and at the end. Typha sp. and Phragmites sp. are planted in the beds. Sampling began two months after establishment (June of the first year) and was performed every month during an 18-month period (up to November of the second year). Samples were tested for 28 BOD, COD, TSS, TC and FC bacteria and fecal streptococci bacteria and were analysed. (Solano, Soriano, & Ciria, 2004). Treatment efficiency was calculated by the following equation: 𝑅 = (1 − 𝐶𝑒 ⁄𝐶𝑖 )100……………………………………………………………...(3.5) Where Ci and Ce are the influent and effluent concentrations in mg l-1. 3.2.9 Municipal Wastewater Treatment using Vertical Flow Constructed Wetlands Planted with Canna, Phragmites and Cyprus A pilot-scale VF plant was developed to treat wastewater near a wastewater treatment plant in North Cairo, Egypt. The plant has a total surface area of 457.56 m2. The system series comprises a coarse screen, oil removal, primary settling tank, and a wetland basin. The influent flow rate is at 20 m3/day and the surface loading rate is between 26.2 kg BOD ha-1day-1 and 76.5 kg BOD ha1 day-1 with a detention time of 7.7 days(Abou-Elela & Hellal, 2012). The CW is fed influent using a submersible pump and a network of PVC pipes. The flow rate and pump runoff are controlled by use of SCADA software, and water flow is measured by electromagnetic flow(Abou-Elela & Hellal, 2012). All climatic parameters that can affect the hydro-balance are monitored. The beds are planted with Canna, P.australis and Cyprus papyrus and are used to estimate biomass, water content, and nutrient content when harvested. Figure 3.4 shows the design of the VFCW. 29 Figure 3.4 Design of VFCW (Abou-Elela & Hellal, 2012). Samples of wastewater were collected every week from the inlet and the outlet for about two years. The physio-chemical and biological analyses is performed for raw wastewater, treated wastewater, and harvested biomass to determine TC, Escherichia coli, and FC. All the analysis were carried out according to Standard Methods for the Examination of Water and Wastewater(APHA,2005) (Abou-Elela & Hellal, 2012). 3.2.10 Development of Constructed Wetlands in Performance Intensifications for Wastewater Treatment: A Nitrogen and Organic Matter Targeted Review The study proposes a number of operational strategies to improve the efficiency removal rates of CWs. The following operational strategies are proposed: 1. Effluent recirculation: A part of the effluent is extracted and then transferred back to the inflow of the system. 2. Artificial aeration: Involves aeration of CWs with compressed air. 3. Tidal operation: It is categorized by numerous serial overflow and channel sequences per day creating a repeat pattern of flooding and draining. 4. Drop aeration: Involves a multilevel (six) two layer drop aeration system which has been tested in two pilot scale VF CWs measuring an area of 0.75m2 each(Wu, Kuschk, Brix, Vymazal, & Dong, 2014). 5. Flow direction reciprocation: Involves altering the path of the current occasionally. 30 6. Earthworms: are introduced into SSF CWs to clean clogged substrates. 7. Bio-augmentation: involves the supplementation of microbes that possess favorable metabolic traits into wetland The following design strategies are proposed: 1. Circular-flow corridor CW: The system involves partial recirculation of wastewaters within the beds. 2. Towery hybrid system: comprises three stages. The first and the third stages are rectangular HSSF CWs while the second is a circular three-layer FWS CW. 3. Baffled SSF CW: incorporates sequential up and down flows by inserting vertical baffles along the wetland width which makes water flow up and down instead of horizontally. 4. Microbial fuel cell CWs: are made up of two chambers (one aerobic and the other anaerobic), where oxidation and reduction occur. A cathode electrode is placed on the aerobic side (near the plant roots) while an anode is placed on the anaerobic side (near the bottom of the microcosm) where electricity production is monitored. 3.2.11. Reed bed CW system Haya water company conducted a study to design, build, and operate a CW in Quriyat. The aim of the study was to evaluate the efficiency of a reed bed system as an alternative and sustainable treatment of domestic and partially non-domestic wastewater solution (Haya Water, 2017). The system used a double stage VF CW with an anoxic tank. The full study occurred for a year from 12 June 2016 to 12 July 2017. BOD, TSS, COD, O&G, VHO, TP, TN, and NH3-N were analyzed to determine the quality of treated effluent and whether it could be used for irrigation purposes, 31 their results were then compared with the regulations set by ministerial decision 145/1993 Standard(A) (Oman Government, 2018). The area of the reed bed was 1300 m2 designed to hold a capacity of 50 m3 of wastewater daily. The reed bed received influent from a balancing tank and the vegetation used was P.Australis. The reed bed was divided into two stages as illustrated in table 3.1. The filter used in stage 1 was >1 in size, and the filter material was a fine gravel of a thickness between 2-2.8mm and a depth of >30cm. The filter used in stage 2 was >1 in size, and the filter material thickness was between 0.25 and 0.4 mm and had a depth of greater than 30 cm. Table 3.1 demonstrates the design criteria of the reed bed: Table 3.1: Design criteria for a double-stage VF reed bed after pre-treatment (septic tank) (Haya Water, 2017). The two stages in the system were presented as stage A and stage B. Stage A had three basins, A1, A2, and A3; and stage B had two basins, B1 and B2. There were three tanks used; anoxic tank, buffer tank, and TE storage tank all alongside three pumps. The buffer tank acted as the measuring 32 can and was where the process began. The raw sewage was discharged into the anoxic tank from the buffer tank, and that’s where partial denitrification occurred. Stage A was the settlement stage where 50% TSS and 20% BOD were removed and it took 2 hours for wastewater to be pumped into each compartment. Partial denitrification also occurred in stage A. Wastewater was then pumped into stage B for biological treatment. Stage B was the aeration stage, because that’s where nitrification (ammonia converted to nitrate) and biological processes occurred. Also, 50% effluent recirculation to the anoxic tank was applied to allow for further denitrification (nitrate converted to nitrogen gas) (Haya Water, 2017). The rest of the effluent was discharged to the treated sewage effluent storage tank for disinfection. Figure 3.5 demonstrates the process of the wastewater effluent treatment. Figure 3.5: Description of the process for treated effluent (Haya Water, 2017). The figures below show the stages from its initiation at “stage A” and “stage B” and the two final figures represents the final product of Phragmites Australis plants after both stages (Haya Water, 2017). 33 Figure 3.6: Stage A (Haya Water, 2017) Figure 3.7: Stage B (Haya Water, 2017) 34 Figure 3.8: Photographs after both stages (Haya Water, 2017) 35 CHAPTER 4 RESULTS AND DISCUSSION 4.1 Overview This chapter provides a broadened interpretation of the results and gives feasible solutions based on the research regarding the presented methodologies discussed in Chapter 3. This section, in addition, provides a discussion of the results found in terms of their effects on the efficiencies and effectiveness of the CWs. At the end of the chapter, a comparison is made between two related case studies to sample the differences and similarities. 4.2 Results and discussions 4.2.1 Performance and Cost Comparison of a FWS and a VSF Constructed Wetland System As mentioned in the methodology’s objective, a comparative analysis in terms of removal efficiency and cost during the monitoring period of both systems are discussed in this section. In reference to the study’s results (Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007), the overall removal efficiencies showed that BOD, COD and TSS had an average removal of 94.4%, 96.1% and 95.5% in the FWS which were similar to the BOD and TSS removals of the VSF system recorded at 92% and 95%, while the COD was 89%. The FWS reduction for TKN and TP were 53% on average while for TC and FC they were 98.7% and 97.1% respectively. On the other hand, the VSF system recorded average TKN removal at 77% and average phosphorous removal at 62%(Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). The lower removal rates for COD in the VSF could be attributed to the newness of the design and the under developed 36 macrophytes. Moreover, another reason could be because the HSF basin was not operated during the study of the system(Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). The capital and operating costs for the two facilities are shown in table 4.1 as follows: Table 4.1: Capital and operating costs (€) for the two facilities( Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). Cost (€) Cost category FWS system Capital, including (construction cost) VAT 344,615 VSF system 410850 Construction cost per p.e 287.18 410.85 Net-present-value cost 25036 29848 Annual average O&M cost 1445 6960 O&M cost per p.e. per year 1.20 6.96 O&M cost per m3 per year 0.03 0.11 Total annual cost (capital and 26481 O&M) 36808 Total annual cost per p.e 36.81 22.07 Total annual cost per m3 of 0.50 influent 0.56 In summary of what has been observed, both systems proved to be effective in producing high effluent quality. The VSF somehow provided a better treatment at a lower area than the FWS at a higher design flow rate and lower temperatures of operation. However, the VSF, being more complex, is more susceptible to design, construction and operation and maintenance problems. When it comes to comparing the costs of both systems, the VSF system is slightly more expensive because of the higher use of concrete and pumps. The FWS system, in contrast, is simpler and less 37 expensive in capital and operational costs. Nonetheless, both systems are less expensive when compared to conventional treatment systems in the same area. If land availability is not an issue, the FWS would be preferable, but if the amount of land is an issue, the VSF should be used but with careful monitoring to avoid operation related problems. 4.2.2 Horizontal Sub-Surface Flow and Hybrid Constructed Wetlands Systems for Wastewater Treatment The results of the various case studies that have been discussed in Chapter 3 and are as follows: Table 4.2: Treatment efficiency of vegetated beds of HSSF CWs—world wide experience(data from Australia, Austria, Brazil, Canada, Czech Republic, Denmark, Germany, India, Mexico, New Zealand, Poland, Slovenia, Sweden, USA and UK)( Vyzamal, 2005). Parameter Inflow (mg l-1) Outflow (mg l-1) Efficiency (%) N BOD5 108 16.0 85 164 COD 284 72 75 131 TSS 107 18.1 83 158 TP 8.74 5.15 41 149 TN 46.6 26.9 42 137 NH4+-N 38.9 20.1 48 151 NO3—N 4.38 2.87 35 79 FC (CFU/100ml) 1.27 × 107 9.96 × 105 92 51 38 Table 4.3: Performance of on-site HF CW at Zitenice, Czech Republic during the period January 2003–September 2004( Vyzamal, 2005) Parameter Inflow (mg l-1) After pre- Outflow (mg l-1) Efficiency (%) treatment (mg l1 ) BOD5 373 73 9.7 97 COD 1118 182 37 97 TSS 639 44 9.1 99 TP 17.1 10.6 10.6 38 NH4+-N 59 62 51 14 NO3—N 0 0 2.9 - NORG 24.2 9.1 1.1 95 TN 85 72 55 35 Table 4.3 shows very high removal rates for organics (BOD5 and COD) both being at 97% and yielding very low removal rates for nutrients (TP, TN, NH4+-N, and NO3—N), all being below 38% and below. The highest removal rate exhibited is for TSS, which is almost at 100% efficiency, meaning that the system successfully eliminates the deferred objects. 39 Table 4.4: Treatment efficiency of HF CW at Spalene Porıcı, Czech Republic during the period November 1992–December 2002; Values in mgl−1, bacteria in log10 CFU/100ml, efficiency in % for chemical parameters, in log units for bacteria. Standard deviations in parentheses( Vyzamal, 2005) Parameter Inflow Outflow Efficiency BOD5 23.3 (43) 4.6(3.4) 80 COD 85 (147) 26.1(11.5) 69 TSS 91 (228) 9.5(8.0) 90 NH4+-N 11.6 (5.9) 9.4(5.0) 19 NO3—N 3.0 (2.9) 1.79(2.2) 40 TP 2.25 (1.25) 2.09(1.52) 7 TC 6.14 (6.47) 5.01(5.42) 1.1 FS 4.47 (4.64) 3.62 (4.03) 0.9 In table 4.4, fluctuations in inflow are high while fluctuations in outflow are steady. The inflow concentration of the organics is too low to be treated using conventional systems such as activated sludge because such systems would most likely fail(Vyzamal, 2005) According to table 4.5; the highest removals were of BOD5 and TSS. In comparison to the HF systems, the results of the Hybrid system show higher removals of nitrogen because of the presence of nitrification in the VF bed. The HF bed, in addition, successfully reduces nitrates produced in the VF bed. TP removals are however very low. 40 Table 4.5: Performance data from Oaklands Park VF-HF CW (August 1989–September 1991, numbers in mgl-1)( Vyzamal, 2005) Parameter Influent Effluent Stage 1 VF Stage 2 VF Stage 3 HF Stage 4 HF BOD5 285 57 14 15 7 TSS 169 53 17 11 9 NH4+ -N 50.5 29.2 14 15.4 11.1 NO2,3—N 1.7 10.2 22.5 10.0 7.2 Ortho P 22.7 18.3 16.9 14.5 11.9 Table 4.6: Performance of the VF–HF Colecott hybrid system; concentrations in mgl-1, efficiency in % (Vyzamal, 2005). Parameter Inflow VF1out VF2out Hfout Efficiency COD 462 210 66 47 89 BOD5 269 171 43 23 91 TSS 53 28 3 1 98 NH4+-N 45 28 16 7 84 NO3- -N 0.1 4.7 3.8 2.7 - NO2—N 0.1 0.2 0.1 0.1 - PO4 18 16 15 11 39 Similar to table 4.5, table 4.6 shows very high organics and TSS removals, while TP removal records the lowest value. TN removal is again higher in this system due to nitrification in the VF. 41 Table 4.7: Treatment performance of a hybrid HF-VF constructed wetland at Darzlubie, Poland; concentrations in mgl-1 (Vyzamal, 2005). Inflow Outflow Removal % BOD5 265 29.2 89 COD 574 68.9 88 TSS 308 55.5 82 TN 101 14.1 86 NH4+ -N 28.5 5.7 80 TP 5.0 1.0 80 Table 4.7 shows high removal rates for all components. The most efficient removals are for BOD5 and COD followed by TN. However, the system seems to be more effective in nutrient and TP removal than its counterpart, the VF-HF bed. In summary, HSSFs are the systems to use when the target is mainly to remove organics and suspended solids. Nitrogen and phosphorous usually have low removal rates in HSSFs (below 50%) for municipal wastewater, especially when systems are designed with an area of 5 m2 per PE. The removal of phosphorous is hindered by the low capacity of sorption of filtration materials, and the removal of nitrogen is hindered by the lack of oxygen in the filtration and hence low nitrification rates. In contrast, VF systems provide a good condition for nitrification, but no denitrification occurs in these systems. Therefore, a hybrid system is preferred, since it combines both the VF and HF systems to complement each other and to achieve higher removal rates, especially for nitrogen removal. 42 4.2.3 Municipal wastewater treatment using constructed wetlands According to Gikas & Tsihrintzis (2014) the initial design parameters concentration of the Korestia facility were 333 mg/L BOD, 350 mg/L TSS, 67 mg/L TKN and 8 mg/L TP. However, the expected concentrations of the effluent after treatment are: BOD <20 mg/L, SS <15 mg/L, TKN <6 mg/L and TP <4 mg/L(Gikas & Tsihrintzis, 2014). In addition, the constructions costs of the facility are presented in Table 4.8. Table 4.8: Construction cost of Korestia facility (Gikas & Tsihrintzis, 2014). COST (€) Inlet works, screening 29,623 First stage VF CWs 38,671 Second stage VF CWs 33,296 Third stage HSF CWs 33,162 Ancillary works (pipe network, siphon) 15,743 Electrical 19,586 Infrastructure and landscape restoration 27,164 Construction cost 197,245 Total construction cost (including professional 286,282 engineers’ and contractors’ fees Total construction cost / p.e. (€/p.e.) 477.13 Hybrid systems in European countries and in Greece similar to the one discussed operate at high efficiency in removing pollutants. From the results presented, it is proposed that the use of CWs for wastewater treatment should be adopted in small municipalities and settlements since the Korestia facility proves that it can be a preferable alternative to conventional systems because it 43 can be low in cost, effective in the use of CW technology, instrumental in the disposal and management of sludge, and can operate smoothly with minimal problems. 4.2.4 Efficiency of a Horizontal Sub-Surface Flow Constructed Wetland Treatment System in an Arid Area According to the study, the influent water was fed continuously to the beds while the HSF-CW had an overall mean influent flow of 28 m3 day-1. However, after the effluent passed through the beds, it effluent was reduced to 23 m3 day-1 with an overall loss of 17%(Albalawneh, Chang, Chou, & Naoum, 2016). Table 4.9 shows the performance of the HSF CW in the mass flow removals of BOD, COD, TSS and P and the FC count. 44 Table 4.9: BOD5, COD, TSS, FC, and P removal (Albalawneh, Chang, Chou, & Naoum, 2016) Parameter Long Beds Coarse media No plant Kenaf Short Beds Coarse media Reed No plant Group 1 Reed Short Beds Coarse Fine media media Fine media No plant Group 2 Reed Group 3 Group 4 BOD5 Mass 51 flow removal * efficiency (%) Number of 41 samples 56 66G1 37 62G2 50 67G3 50 59G4 42 41 22 22 22 22 40 40 COD Mass 42 flow removal * efficiency (%) Number of 38 samples 49 58 38 56 47 64 47 55 38 38 24 24 24 23 48 47 TSS Mass 56 flow removal* efficiency (%) Number of 53 samples 64 73 67 79 65 64 73 63 54 53 34 34 34 34 68 68 P Mass flow 38 removal * efficiency (%) Number of samples 53 46 64G1 35 61G2 58 75G3 49 67G4 54 53 34 34 34 34 68 68 FC Log 0.4 reduction * Number of samples 47 0.5 0.5 0.6 0.9 1.2 1.2 0.8 1.1G4 48 48 26 26 26 26 52 52 (1)*All the effluents were significantly(p<0.05)lower than the influent, for the same parameter; G1: significant differences (p<0.05)compared to others in group1, for the same parameter;G2: significant differences(p<0.05)compared to others in group 2,for the same parameter;G3: significant differences(p < 0.05)compared to others in group 3,for the same parameter;G4: significant differences(p < 0.05)compared to others in group 4,for the same parameter;(2) 1: Short coarse media =mean of(short bed, coarse media, no plant- beds) and(short bed, coarse media, reed-beds);2: Short fine media=mean of(short bed, fine media, no plant- beds) and(short bed, fine media, reed-beds)(Albalawneh, Chang, Chou, & Naoum, 2016). 45 Based on the studies observation, BOD5, COD, TSS and phosphorous demonstrated average efficiency removals of 55%, 51%, 67% and 55%, respectively. However, Albalawneh, Chang, Chou, & Naoum, (2016) also stated that HSF CW systems had different removal rates for BOD ranging from 37% under SCN conditions to 67% under SFR conditions; the removal efficiency for COD ranged from 38% under SCN conditions to 64% under SFR conditions(Albalawneh, Chang, Chou, & Naoum, 2016). Reed plants were more efficient in BOD removal than kenaf and unplanted beds, while COD removals among the three beds showed no significant difference. Bed dimensions did not affect BOD and COD removal. The fine media was more efficient than coarse media in BOD and COD removal, but the differences between their effluents were not significant. Pursuant to the study objectives, TSS removal efficiency ranged from 56% under LCN to 79% under SCR while the mean log reduction of FC ranged from 0.4 under LCN to 1.2 under SFN and SFR with a mean of 0.8(Albalawneh, Chang, Chou, & Naoum, 2016). Bed dimensions did not affect TSS and FC removal, and fine media showed lower FC concentration in the effluent than coarse media. There were no significant differences in FC removal regarding the vegetation type. Overall phosphorous removal was 55% and ranged from 35% in SCN conditions to 75% in SFR conditions. Fine media was more efficient in phosphorous removal than coarse media, and the mass flow of phosphorous in the reed bed was significantly lower than the flow in the kenaf and unplanted beds. The bed dimensions showed no significant differences in phosphorous removal. In conclusion, the system removed BOD, COD, P and TSS efficiently. The aspect ratios of the bed did not affect the removal significantly, but the plants, although efficient, consumed too much water and concentrated the effluent. The removal efficiencies were based on mass flow and not concentration due to the evaporation that concentrated the effluent because of the water losses. 46 Fine and coarse media without vegetation reduced water loss by 4% while improving pollutant removal. 4.2.5 Feasibility of using constructed treatment wetlands for municipal wastewater treatment in the Bogotá Savannah, Colombia According to the study(Arias & Brown, 2009), the economic analysis suggested that the net annual cost of the treatment wetland was US$ 14,672, compared to US$ 14,201 for the stabilization ponds and US$ 54,887 for the batch reactor. The key differences among these cost evaluations were the cost for the gravel media used in the CWTS (US$ 50,477 for the 0.4ha), along with the greater amount of excavation necessary for the WSP, resulting in an added US$ 48,706 of manual labor costs. Gravel being the costliest item for this CWTS implies that the potential of using this material in a large-scale SSF in this region is limited thus minimizing its use can result in great cost reduction, as illustrated with the sensitivity analysis. The main components in the SBR construction that lead to this increased cost were concrete and steel, in addition to a number of other necessary materials only needed for the construction of this system and not the other two(Arias & Brown, 2009). In contrast, the emergy evaluations show that the ponds have the lowest annual emergy flow(6.65+16sej/yr), followed by the constructed wetland(2.88E+17sej/yr) and the batch reactor(8.86E+17sej/yr). A sensitivity analysis showed that a ratio of SSF to SF wetland area of 1–4 yielded appropriate removal while maintaining construction costs as low as possible(Arias & Brown, 2009). The proposed hypothetical system has the potential of getting high removal efficiencies, especially of BOD and TSS as compared to the other two systems according to Table 4.10. The WSPs, however, recorded higher removal of E. coli than the CWTS, which can be attributed to higher storage volumes in the WSPs and hence higher detention times. The results for the CWTS 47 are based on results of an empirical model which is accurate, but parameters such as design and cost are crucial to consider when gauging the performance of a system. Table 4.10 demonstrates the comparison of the removal efficiencies for the three systems. Table 4.10: Estimated percent removal of pollutants for the three treatment systems evaluated (Arias & Brown, 2009). Constituent CWTS WSPs SBR SS 97 79 73 BOD 92 86 79 E. coli 98 99.5 84 TN 62 - - NH4 62 -8 - TP 47 -35 30 The study proves that a CW system should be adopted in Bogota. Due to the observations of the study, the CWTS had the highest performance for treatment, the most value for investment, and achieved the highest pollutant removal rates. Therefore, the system is preferred and can be used instead of conventional systems, especially when land is available. 48 4.2.6 Performance of Four Full-Scale Artificially Aerated Horizontal Flow Constructed Wetlands for Domestic Wastewater Treatment In agreement with the Butterworth et al findings, the competence of systems to yield ammonium effluent concentrations <3 mgNH4+-N/L was observed across all sites in systems receiving variable loadings between 0.1 and 13.0gNH4+-N/m2/d while potential pliability issues were detected in relation to spike loadings posited to be due to an insufficient nitrifying population within the beds(Butterworth et al., 2016). Nitrification was adequately efficient and constant across all loading rates. In addition, nitrification rates in aerated units increased linearly with increased loadings, while the non-aerated wetlands showed non-linear rates. There was no significant difference between effluent concentrations in tertiary beds A and B, except for the variations recorded upstream. According to Butterworth et al, achieving low effluent concentrations and the increased spread in the data at Site C compared to consistently low concentrations in Sites A and B means that the effluent data could not be categorized as statistically the same(Butterworth et al., 2016). Sites C and D, however, had statistically effluent concentrations. The nitrification rate is not the controlling factor when it comes to design. TSS reduction was significant in sites B through D, but site A showed no significant TSS reduction in both aerated and non-aerated beds. BOD concentrations in both influent and effluent were low in all sites. No significant difference in the median of effluent concentration was observed between the aerated bed and control bed in site A. BOD loading did not affect effluent concentration, and aeration did not enhance BOD removal. Table 4.11 shows the seasonal effects on the different sites Table 4.11: Summer and winter ammonium inlet loadings and effluent concentrations (Butterworth, et al., 2016) 49 Season Site Loading (gNH4+-N/m2/d) Median mean max Outlet Concentration (mgNH4+N/L) Median mean max n Summer Site A 2.0 (aerated) 0.3 11.5 0.1 0.02 1.4 19 Site A 2.0 (controlled) 0.3 11.5 6.5 0.03 20.6 19 Site B 0.08 0.02 1.9 0.1 0.01 1.5 20 Site C 0.04 0.01 0.07 0.2 0.04 0.3 5 Site D n/a n/a n/a 0.5 0.1 2.6 11 Site A 2.8 (aerated) 0.07 12.5 0.1 0.02 0.6 23 Site A 2.8 (controlled) 0.07 12.5 8.4 0.1 22.1 23 Site B 0.2 0.02 10.9 0.2 0.02 15.0 22 Site C 4.3 0.4 11.9 0.9 0.2 5.3 29 Site D n/a n/a n/a 1.2 0.1 13.3 20 Winter For the aerated wetlands, seasonal impacts show a small decrease of ammonium in the effluent, and this effect is concurrent with the increased HLR that can be attributed to heavy rainfall and hence less residence time in the bed. As observed from table 4.11, sites C and D had an increase in median outlet concentrations during winter in the aerated beds as opposed to summer. In site A (aerated bed), the mean effluent ammonium remained the same during both summer and winter. In contrast, in site A(non-aerated), there were higher mean outlet concentrations in winter when the temperature decreased. Conclusively, the study shows that the system was able to produce nitrified products that were down to 3mgNH4+-N/l in both the secondary and tertiary stages of the system. There was, however, 50 limited resilience to spike loads in all the systems. The system was proved to be highly efficient in ammonia removal for sites that were small in size and could receive high but variable rates of flow. 4.2.7 A review on the sustainability of constructed wetlands for wastewater treatment: Design and operation FWS and SSF CWs mainly use emergent plants. FWS CWs use P. australis, T.latofllia, Cyprus papyrus, Scirpus validus and T.domingensis as the most common emergent plant species. On the other hand, SSF CWs commonly use P. australis and Typha spp. In terms of plant tolerance to toxicity in wastewater, T.latifolia was stressed by ammonia concentrations of about 160–170 mg/L, while S.validus was the most tolerant. In a range of 20.5–82.4 mg/L concentration, Scirpus actus is the least tolerant to ammonia(Wu et al., 2015). Concentrations of up to 400 mg/L showed that Zornia latifolia had the highest tolerance to ammonia. High COD levels can disrupt the metabolism of P. australis. Arundo donax and Sarcoconia fruticose have the highest tolerance to salinity. Typha angustata had the highest tolerance for Cr, while P. australis has the highest tolerance for antibiotics. Wetland plants had a major role in the removal of carbamazepine, sulfonamides and trimethoprim when cast-off in CW sewage handlings; however, E. acicularis had an excellent ability to accumulate metals from water such as In, Ag, Pb, Cu, Cd, and Zn(Wu et al., 2015). According to Wu et al., (2015), phosphorous removal can be enhanced using gravel, sand, clay, calcite, marble, vermiculite, slag, fly ash, bentonite, dolomite, limestone, shell, zeolite, wollastonite, activated carbon, and lightweight aggregates; however, sand, gravel and rock are poor candidates for longterm phosphorus storage(Wu et al., 2015). 51 A higher HLR facilitates faster flow of wastewater through the bed, reducing the optimal time for contact. Increased HRT, on the other hand, allows for better microbial growth and hence better removals for TN and ammonium (Wu et al., 2015). Results of studies conducted show that the batch feeding mode obtained better performance than continuous in terms of providing oxidising conditions. Also, CW with the batch feeding mode showed higher ammonium removal efficiency (95.2%) than continuous systems (80.4%) (Wu et al., 2015). On the other hand, the intermitted feeding mode had higher nitrogen removal in CW than in continuous feeding mode. However, continuously fed systems showed a better sulphate removal than intermitted systems (Wu et al., 2015). Summarily, the study has been observed to majorly focus on CW design factors which have proved to be very essential to the success and sustainability of a CW project. 4.2.8 Constructed Wetlands as a Sustainable Solution for Wastewater Treatment in Small Villages The section discusses the removal rates for BOD, COD, TSS, TC, FC, and FS in relation to their HAR rates during the first and second year of wetland operation as observed in the tables 4.124.15 below. 52 Table 4.12: Biochemical oxygen demand(BOD), chemical oxygen demand(COD) and total suspended solids(TSS) removals during the first year of wetland operation (Solano, Soriano, & Ciria, 2004). Species HAR, mmday-1 BOD removal % Summer autumn COD removal % Summer autumn TSS removal % Summer autumn Cattail 150 75 86 81 71 76 78 76 64 69 87 90 88 90 Reed 150 75 77 85 NS 68 77 NS 68 77 NS 50 73 NS 87 91 NS 70 93 NS N S, values in these columns were not significantly different (probability α=0.05). HAR-hydraulic application rate (Solano, Soriano, & Ciria, 2004). Table 4.13: Percentages of removal of biochemical oxygen demand(BOD), chemical oxygen demand(COD) and total suspended solids(TSS), during the second year of wetland operation (Solano, Soriano, & Ciria, 2004) Species HAR, BOD removal % mmday-1 S S A W COD removal % S S A W TSS removal % S S A W Cattail 150 75 70b 70b 83b 75b 63 92a 83b 64 68c 77b 77b 88a 50b 51b 76a 67a 58b 85a 94a 93a 69b 81 69b 88 Reed 150 75 74b 84a 83b 63c 63 48d 93a 90a 90 87a NS 68b 85a 52b 54b 77a 69a 64b 90a 75b 91b 67b 83 83a 82 NS Values in columns with different letters indicate significant differences (probability α=0.05). N S, values in these columns were not significantly different (probability α=0.05). HAR, hydraulic application rate. During the first year, there was no significant relationship between the parameters that were measured and the HAR. During the second year, the reed beds with the lowest HAR had 53 significantly higher removal rates. The behavior of the beds with cattails was unclear since some of the plants died in autumn and summer in the bed that had the highest HAR. In the first year, there were no seasonal differences found in removal performance of BOD, COD, and TSS because the sampling period for the year ranged from June to November and the planting had been done two months earlier in April. In the second year, lower BOD removals were observed during winter which is generally attributed to microbial functions being limited by low oxygen levels. Therefore, the low BOD removals might have been a result of the lack of above ground biomass since the plants were harvested in autumn and hence led to lower the oxygen levels in the root zone. However, regarding the COD and TSS, there were no significant differences for percentage removals for that sampling season and the rest of the year. In reference to the study’s results, the performance shown by both plants at removing BOD, COD and TSS was similar and even higher; between 63 and 93% for BOD, 50 and 88% for COD and 58 and 93% for TSS when compared to performance of other authors between 65 and 91% for BOD, 48 and 75% for COD and 58 and 88% for TSS (Solano, Soriano, & Ciria, 2004). Table 4.14: Pathogen removal during the first year of wetland operation (Solano, Soriano, & Ciria, 2004) Species HAR, mmday-1 Total coliforms Faecal coliforms Faecal streptococci removal % removal % removal % Summer autumn Summer autumn Summer autumn Cattail 150 75 85 85 89 91 93 98 98 99 85 93 92 86 Reed 150 75 99 99 NS 93 98 NS 87 91 NS 97 99 NS 85 93 NS 90 93 NS N S, values in these columns were not significantly different (probability α= 0.05). HAR-hydraulic application rate (Solano, Soriano, & Ciria, 2004). 54 Table 4.15: Pathogen removal during the second year of wetland operation (Solano, Soriano, & Ciria, 2004) Species HAR, Total coliforms Fecal mmday-1 removal % removal % S S A W S S coliforms Fecal streptococci removal % A W S S A W Cattail 150 75 62b 80a 80b 81b 65b 75b 91a 98a 78a 85a 69b 93a 71b 50b 93a 85a 33b 43a 62b7 71b 41b 6a 84a 50a Reed 150 75 40b 82a 75b 82b 40c 59b 97a 91a 81a 85a 77b 93a 86b 43b 92a 76a 51a 58a 62b 85a 74b 49b 80a 66a Values in columns with different letters indicate significant differences (probability α=0.05). HAR, hydraulic application rate. TC, FC, and FS removals varied widely according to the tables presented. HAR did not significantly affect the removal of these parameters in the first year; however, in the second year, the bed that had the lowest HAR of 75 mmday-1 and the longest retention time of 3 days (both for cattail and reed beds) had the best removal rates. There was little effect of seasonal variation in the first year on removals, but in the second-year, summer and autumn had the best removals. In addition, there was maximum plant growth in the second year. However, when the two vegetative cycles are compared, the first year had higher removals than the second year, and this could be attributed to a deficiency of oxygen in the root zones during the second year. Summarily, both reed beds had high removals of chemical and physiological parameters. However, only winter showed a slight lower removal rates which was because of the lower oxygen levels in the root zone. The beds with the lowest HAR rates were the most suitable for efficient removals. In conclusion, the results obtained being satisfying proved that the system can be a suitable 55 treatment for small villages, however, it would be required to have a previous pretreatment for the removal of heavy metals, grit and floatable materials(Solano, Soriano, & Ciria, 2004). 4.2.9 Municipal wastewater treatment using vertical flow constructed wetlands planted with Canna, Phragmites and Cyprus During the study period, the organic loading rate of VFCW’s influent samples varied between 185 and 335(mg/L) for COD and between 59 and 175(mg/L) for BOD, while the average concentrations of TSS, NH4+-N, TKN and TP were 94, 16.7, 30.7 and 3.15(mg/L) respectively. The average bacterial indicators counts were 2.8×107 MPN/100 ml for TC, 2.3×106 MPN/100 ml for FC and 2.4×106 MPN/100 ml for E. coli (Abou-Elela & Hellal, 2012). As reported by Abou-Elela & Hellal, (2012), the average removal efficiencies for COD, BOD, and TSS in the final effluent were 88%, 90%, and 92% respectively, which could be attributed to the presence of diverse plant species, quick removal of settleable organics and fast degradation of organic compounds. Their corresponding residual values were 30.60, 13.20, and 8.50(mg/L). Figure 4.1 represents the COD, BOD, and TSS concentrations in the treated effluent. Figure 4.1: Concentrations of COD, BOD and TSS in treated effluent (Abou-Elela & Hellal, 2012) 56 Both nitrification and denitrification occurred during the two-year operation. Ammonia concentration decreased from 18.3 to 7.9(mg/L), while nitrate absorption in the waste increased from 0.12 to 0.52(mg/L). TKN removal was observed along the monitoring period. According to the study, the TKN removal efficiencies varied between 31% and 70% with an average percentage removal of 53%. The average TKN removal efficiencies throughout this study were within the removal range reported in other studies of constructed wetlands (Abou-Elela & Hellal, 2012). Phosphorous removal averaged at 62% with a concentration of between 0.4 and 2 mg/l in the treated wastewater (Abou-Elela & Hellal, 2012). The high removal rate is attributed to a long contact time that is 7.7 days and the use of three different species of plants on the same basis, leading to an increase in phosphorous removal. According to Abou-Elela & Hellal, (2012), the concentrations of the bacterial indicators in the TE were 2.6×103 MPN/100 ml for TC, 1.25×103 MPN/100 ml for FC and 1.1×103 MPN/100 ml for E. coli with an average removal efficiency ranging from 94% to 99.99%. These efficiencies can be clarified by the large concentration of oxygen in the VFCW. The high temperatures of 25–30°C in the VF CW caused an aerobic environment which led to higher removal rates. Biomass harvesting for P. australis and Canna was conducted after 12 months of project operation, but Cyprus was not harvested because it was too short. The yield for dry biomass of P. australis was 3.26 kg/m2, while the same for Canna was 4.83 kg/m2. Canna uptake for nitrogen and phosphorous was 68.1 g/m2 and 32.55 g/m2, respectively. For Phragmites, the uptake was 48.6 gN/m2 for nitrogen and 28.91 gP/m2 for phosphorous (Abou-Elela & Hellal, 2012). The results show that Canna had better uptake rates than Phragmites, and this effect can be attributed to the roots of Canna being more widely distributed in the reed bed. In contrast, in reference to the study, 57 Cyprus proved much more efficient at nitrogen removal, phosphorous removal, and the removal of heavy metals than the other two species. In terms of bacterial analysis, it was indicated that canna was more effective in the removal of microorganisms. However, according to Abou-Elela & Hellal(2012) in the TE, the residual bacterial counts showed a slight exceed (103 MPN/100ml) to the permissible limits stated in national regulatory standards of wastewater reuse in restricted irrigation(ECP501,2005). Conclusively, the presence of a diverse species of plants ensured that there were higher removal rates of BOD, COD, TSS, N, and TP because they provide more effective and efficient distribution of the root system, and hence, a more diverse habitat for microbes. In addition, the physio-chemical characteristics of treated wastewater were in compliance to the national regulatory for treated wastewater reuse in restricted irrigation. However, the TE would require a slight disinfection to eliminate the residual pathogens. In conclusion, the quality of treated effluent proved that the use of VFCW is an effective technology for wastewater treatment and could be used for irrigation purposes in rural areas and small communities. 4.2.10 Development of constructed wetlands in performance intensifications for wastewater treatment: A nitrogen and organic matter targeted review The following results are observed for the proposed operational strategies: 1. Effluent recirculation improves the effluent quality by enhancing aerobic microbial activity without significantly modifying the whole system operation. 58 2. Artificial aeration improves the poor oxygen transfer rates observed in traditional HSSFs and improves the removal of organic matter, E.coli, and ammonium. Artificial aeration, however, does not have a significant influence on phosphorous removal. 3. According to the research, the tidal operation also solves oxygen transfer limitations in tidal CWs and improves nitrogen removal by enhancing alternate aerobic and anaerobic environments(Wu, Kuschk, Brix, Vymazal, & Dong, 2014). 4. Drop aeration shows the increase of BOD5 removal load from 8.1 to 14.2 g/m2 within five days. The system has low capital costs, high HLR, high pollutant removal efficiencies, easy maintenance, low operation costs, and minimal clogging. 5. Flow direction reciprocation shows better pollutant removal efficiencies, higher microorganisms populations and hence lower organic compound accumulation and minimal clogging. 6. The study results explain that earthworm integration in SSF CWs reduces clogging, enhances break down large quantities of organic matter, enhances density and biomass of wetland plants and hence improving nitrogen and phosphorus uptake, and reduces sludge production in VFCWs, hence reducing sludge maintenance costs(Wu, Kuschk, Brix, Vymazal, & Dong, 2014). 7. Bio-augmentation accelerates degradation of pollutants such as pesticides and heavy metals by shortening adaptation period and hence accelerating the suitable habitat conditions for microbial growth. The following are results observed for the innovative strategies proposed in the study: 59 1. Circular flow corridor CW enhances TN removal, dilutes inflow water to reduce the toxicity effect on plants and delays clogging of media while improving P removal. The system is cost effective. 2. Towery hybrid CW enhances N removal by improving nitrification and denitrification rates. Average percentage removal efficiencies for TSS, COD, NH4 –N, TN, and TP are 89, 85, 83, 83, and 64%, respectively. 3. Baffled SSF CW enhances pollutant removal. The unit, recorded percentage removal rates of 74, 84, and 99% were higher than the conventional CW; which yielded results of 55, 70, and 96% using HRTs of 2, 3, and 5 days, respectively. 4. Microbial fuel cell yields the results that CWs enhanced pollutant removal and simultaneously generated power. 4.2.11. Reed bed CW system The results of the study were compared with the MECA standard (A) to determine effectiveness and efficiency (Oman Government, 2018). Table 4.16 shows the removal efficiency for various components of a double stage vertical flow reed bed. 60 Table 4.16: Data for the treatment of effluent by the reed bed system (Haya Water, 2017; Oman Government, 2018) Parameter Raw Sewage Treated MECA Standard Removal (mg/L) Effluent(mg/L) (A) Efficiency COD 1206 12.7 150 98.9 BOD 372.3 3.9 15 98.9 NH3-N 58.2 0.2 5 99.6 NO3-N - 32.9 50 (NO3) - TN 90.7 8.7 15 90.4 TP 11.3 0.1 30 99.1 TSS 633.3 1.2 15 99.8 O&G 36 0.3 0.5 98.1 FC - 117 200 per 100ml - VHO 22 <1 <1 per L 98 The Haya water CW showed removals of COD (98.9%), BOD (98.9%), NH3-N (99.6%), TN (90.4%), TP (99.1%), TSS (99.8%), O&G (98.1%) and VHO(98%). The results for all the parameters being excellent in treatment efficiency, showed compliance to the MECA standard (A) (Oman Government, 2018). Graph 4.1 shows a representation of Treated Effluent(mg/L) and the MECA Standard(A) as well as the removal efficiencies for all the above-mentioned parameters. Graph 4.1: Relationship between treated effluent, the MECA standard and removal efficiency (Haya Water, 2017) (Oman Government, 2018) 61 Relationship Between the Treated Effluent, its MECA Standard (A) and their Removal Efficiency 150 117 98.9 98.9 12.7 15 3.9 BOD 99.6 99.1 90.4 32.9 COD 5 0.2 NH3-N 0 NO3-N Treated Effluent (mg/L) 99.8 98.1 15 1.2 TSS 0.5 0.3 O&G 98 30 15 8.7 0.1 TP TN MECA Standard A 0 FC 0 VHO Removal Efficiency The graph shows the high removal of COD and BOD, meaning that the solids can easily be removed from the wastewater. In addition, the high removals for TN, TP, VHO, FC, TSS, O&G, and NH3-N mean that the effluent concentrations were in compliance with MECA standards (Haya Water, 2017). On the other hand, the high percentages of ammonia, phosphorous, and nitrogen show that the soils in which the effluent was passing through were highly nutritious. The absence of nitrate in the treated effluent catalyzed the process of eutrophication and aeration. Also, the absence of FC showed that the treated effluent was very clean. The design chosen was used to ensure the effectiveness and efficiency of the system. Moreover, it reduced the cost and size at the same time while regulating the flow to optimize retention time for efficient pollutant removal. However, the retention time was determined based on the type of effluent being treated. Domestic wastewater took less time to treat since it had less pollutant concentration than the non-domestic wastewater. 62 The plants used (Phragmites Austrails) in the system showed high treatment efficiency since the species chosen had relatively constant growth and high substrate levels. Conclusively, the system after an analysis of physical, biological, and chemical parameters, yielded high removal efficiencies that complied with MECA Standards (A), proving that it was an effective and viable solution to treatment. 4.3 Summary and Comparison For the comparison, two HSSF case studies, referred to as case 1” Horizontal Sub-Surface Flow and Hybrid Constructed Wetlands Systems for Wastewater Treatment” (Vyzamal, 2005) and case 2 “Efficiency of a Horizontal Sub-Surface Flow Constructed Wetland Treatment System in an Arid Area” (Albalawneh, Chang, Chou, & Naoum, 2016). are compared in terms of methodology and results. In case 1, the HSSF CW methodology is analyzed against case 2 HSSF CW methodology. Case 1 used P. australis as its principle wetland vegetation while case 2 used P. australis, kenaf plant and no vegetation in the control beds. Case 1 summarized the typical or general HSSF CWs designs and parameters used all over the world in regions that are not arid while case 2 focused on a project located in Al Samra Agricultural Research Station in Central Jordan which is majorly an arid area. The substrate media used in case 1 is soil and coarse substrate while case 2 uses coarse volcanic tuff and fine volcanic tuff. The biggest area used for reed beds is 5m2 in case 1 while case 2 uses an average area of 16.25m2. In case study 1 the removal efficiencies were based on the concentration, however in case number 2 the removal efficiencies were based on mass flow. The results of the two cases can be compared in terms of performance efficiency rates presented in percentage. With reference to table 4.2, the 63 removal of BOD in case 1 is at 85%, while that for case 2 is 55%. COD removal in case 1 is higher than in case 2 since it is at 75% for case 1 and 51% in case 2. Similarly, TSS in case 2 being at 67% is lower than TSS removal in case 1 being at 83%. Perhaps, the lower removal rates of case 2 could be attributed to harsh climatic conditions since the area is arid, which is unlike the areas discussed in case 1. Another reason could be that case 2 was based on mass flow and not concentration (because evaporation caused water losses and concentrated the effluents). In addition, the use of kenaf plants could have yielded lower removal rates in case 2. 64 CHAPTER 5 CONCLUSION Water is one of the most important elements and it is essential to the survival of not only the human race but whole world with all its living inhabitants. Unfortunately, the human race has made water pollution a global crisis, a state of affairs which threatens the possibility of survival. Often, effluents from our towns in sewage collection systems are discharged directly into water bodies and water courses without any treatment effort. In some cases, efforts for treatment are made using conventional treatment methods that are almost always expensive to construct, operate, and maintain and at the same time may not be as effective or efficient in wastewater treatment. Hence, the introduction of CWs as a cost effective and more efficient alternative for wastewater treatment in comparison to conventional treatment methods has been proposed. CWs are cheaper to construct, easier to operate and maintain, and according to this report it has been proved that they are much more efficient than other systems. Apart from water conservation efforts, constructed wetlands assist in animal conservation efforts especially for the species that live in water bodies. By controlling direct discharge of harmful effluents into large water bodies and improving water quality, water species have a greater chance of survival. However, CWs can be a disadvantage in some cases in terms of land since some require large land areas. Moreover, they can also allow for mosquito breeding which is a threat to human health. The review of CWs for municipal wastewater using case studies has been the main objective of this report. The main aspects discussed throughout the whole report have been water quality, design type, and reuse criteria. More specifically, the methodology section explores all possible methods used in construction and design of CWs for municipal wastewater management. 65 Parameters such as location, PE, pre-treatment, secondary treatment, tertiary treatment, flow design, surface area, aspect ratio, bed dimensions, energy requirements, loading rates, loading designs, aeration, retention times, construction materials, substrate media, distribution layer design, vegetation, and sampling methods are discussed and specified according to treatment demand. From the samples, an array of chemical and physiological parameters is analyzed whose results are then discussed in relation to efficiency of removal, conformation to set standards and reuse criteria. The parameters include COD, BOD5, TSS, FC, TC, TN, TP, bacteria (E.coli) and in few cases some heavy metals. The results are as well discussed in regard to seasonal variations and their effects on the removal efficiencies for the pathogens. Moreover, the role of plant species used in vegetation is discussed in terms their contribution to pollutant removal. It has been established in almost all cases that planted CWs are more efficient than unplanted CWs and that the most common and effective plant species are Typha spp. and Phragmites. Based on the research findings the study “Feasibility of using constructed treatment wetlands for municipal wastewater treatment in the Bogotá Savannah, Colombia” is the best case study. Although the model discussed is hypothetical, comparing it to real and existing models makes it relevant and reliable. The CWTS model shows among the highest COD, SS, and E.coli removals ranging from 92%–98%. TN, NH4, and TP removals are also higher than the other two systems used for comparison. The study shows that it is cost-effective and highly efficient. Summarily, CWs have proved to be an efficient and cost effective alternative to conventional wastewater treatment, even in developing countries. 66 CHAPTER 6 RECOMMENDATIONS In light of the details discussed in the report, the following general recommendations can be made for future works: • A proper recommendation would entail considering the building mechanisms of constructed wetlands that would not have to incur large operation and maintenance costs. • The rate of water surges in the wetlands bed need to be controlled to avoid the efficiency of the system in the pollutant removal rates. For the Oman study, the following recommendations can be made for future work: • A VF-HF design should be implemented in Oman because it is easier to clean and can be maintained within a very short time while being very effective and efficient. • Other companies such as Haya should be encouraged by the government to invest in similar projects to increase the number of CWs for wastewater treatment. Therefore, the government can introduce discounts on the materials used for construction. • It is recommended to implement reed bed treatment technology as a sustainable solution in regional governorates since there are large empty areas. • Water balance, energy balance and design parameters should be considered more in the studies. 67 REFERENCES Abou-Elela, S. I., & Hellal, M. S. (2012). Municipal Wastewater Treatment using Vertical Flow Constructed Wetlands Planted with Canna, Phragmites and Cyprus. Ecological Engineering 47, 209-213. Albalawneh, A., Chang, T. K., Chou, C. S., & Naoum, S. 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ENG 4 133 Bachelor Thesis German University of Technology in Oman (GUtech) Department of Engineering ASSESSMENT AND REVIEW OF CONSTRUCTED WETLANDS FOR INDUSTRIAL WASTEWATER: SELECTED CASE STUDIES Course Coordinator: Dr.-Ing. Najah Al Mhanna Project Supervisor: Main supervisor: Dr. Hind Barghash Co-supervisor: Dr.Alexandros Stefanakis Student Name: Al Thuraiya Hilal Al Busaidi Spring 2018 1 Approval of the Dean of the Faculty of Engineering and Computer Science Dr.-Ing. Najah Al Mhanna I certify that this Thesis satisfies the requirements of a Bachelors Thesis for the Degree of Bachelor of Engineering in Environmental Engineering. Dr.-Ing. Najah Al Mhanna Head, Department of Engineering I certify that I have read this Thesis and that it is my opinion that the Thesis is fully adequate in scope and quality as a Bachelors Thesis for the Degree of Bachelor of Environmental Engineering Name Supervisor Examining Committee 1. Name ________________________________ 2. Name ________________________________ i Declaration In accordance with the requirements of the degree of Bachelor of Engineering at German University of Technology in Oman, I present the following thesis titled “Assessment and Review of Constructed Wetlands For Industrial Wastewater: Selected Case Studies”. This work was performed under the supervision of Dr. Hind Barghash I hereby declare that the work submitted in this thesis is my own and based on the results found solely by myself. Materials of work found by other researchers are clearly cited and listed in reference list. This thesis, neither in whole nor in part, has been previously submitted for any degree. The author confirms that the library may lend or copy this thesis upon request, for academic purposes. Name: Al Thuraiya Hilal Al Busaidi Signature: ALTHURAIYA ii ABSTRACT Water is the life source of all living and non-living organisms and as such one would think it is one of the most conserved resources in the world. However, this is not the case. Water pollution is a major crisis threatening the world’s survival. One of the main sources of water pollution is toxic effluent from industries that is released directly into watercourses and water bodies. Conventional wastewater treatment efforts, although successful in some cases, still are not efficient enough when it comes to improving the water quality of such effluents. Due to this challenge, scientists have come up with an efficient wastewater treatment system. Constructed wetlands have been tried, tested, and proved to be efficient in removal of both chemical and physiological components of industrial effluent. Such components include heavy metals (arsenic, copper, lead, cadmium, lithium, manganese among others), BOD, COD, TSS, FC, TC, ammonia, and phosphorous. The highest recorded constituent removals among all study cases are as follows: 93%COD,98%BOD, 87%TSS, 99%phenols, 75%manganese, 97%arsenic, 98%iron, 90%cobalt 94%copper,97%uranium, and 96%zinc. Studies have been conducted using experimental and established CWs treating industrial wastewater determine their efficiencies in pollutant removal. The report gives an introduction and background to the concept of constructed wetlands, explains the various methodologies used in CWs (in terms of CW type, measurements, dimensions, vegetation, effluent type, and substrate type), and explains the results gained from such studies in terms of efficiencies and wetland performance. Finally, the report gives a comparison of the wetlands, recommendations, and a summary to conclude it all. Keywords: Wastewater treatment; Organic matter; Constructed wetlands; Industrial effluent; Efficiencie i ‫الخالصة‬ ‫الماء هو مصدر الحياة لجميع الكائنات الحية وغير الحية ‪ ،‬وعلى هذا األساس يعتقد أنه من أكثر الموارد المحفوظة في العالم و‬ ‫أحد المصادر الرئيسية لتلوث المياه هو مخلفات المصانع ‪.‬التلوث المائي هو أزمة كبيرة تهدد بقاء العالم ‪.‬لكن هذه ليست القضية‬ ‫ومع ذلك ‪ ،‬ال تزال جهود معالجة مياه الصرف ‪.‬السامة التي يتم تفريغها بشكل مباشر في المجاري المائية واألجسام المائية‬ ‫نتيجة ‪.‬من هذه النفايات السائلة التقليدية ‪ ،‬على الرغم من نجاحها في بعض الحاالت ‪ ،‬ما زالت غير كافية لتحسين جودة الماء‬ ‫تمت تجربة األراضي الرطبة المبنية واختبارها ‪.‬أكشتف العلماء طريقة جديدة و فعالة لمعالجة مياة الصرف الصحي لهذا التحدي ‪،‬‬ ‫تحتوي هذه المكونات علی المعادن ‪.‬وأثبتت فعاليتها في إزالة المكونات الكيميائية والفسيولوجية في النفايات الصناعية السائلة‬ ‫‪ ،‬الطلب على األكسجين البيولوجي‪ ، ،‬الطلب )الزرنيخ ‪ ،‬النحاس ‪ ،‬الرصاص ‪ ،‬الكادميوم ‪ ،‬الليثيوم ‪ ،‬المنغنيز وغيرها(الثقيلة‬ ‫أعلى ‪.‬الكيميائي ‪ ،‬مجموع المواد الصلبة العالقة ‪ ،‬البراز القولوني ‪ ،‬مجموع القولون ‪ ،‬األمونيا ‪ ،‬والفوسفور على االكسجين‬ ‫كالتالي‪ ٪٨٩:‬من الطلب على االكسجين الكيميائي‪ ٪٨٩ ،‬من الطلب على معدالت اإلزالة المسجلة بين جميع حاالت الدراسة هي‬ ‫الزرنيخ‪ ٪٨٩ ،‬من المنغنيز‪ ٪٨٨ ،‬من من الفينول‪ ٪٨٧ ،‬من مجموع المواد الصلبة العالقة‪ ٪٨٨ ،‬األكسجين البيولوجي‪٪٩٨ ،‬‬ ‫تم إجراء الدراسات باستخدام أنظمة من الكوبالت‪ ٪٨٩ ،‬من النحاس‪ ٪٨٨ ،‬من اليورانيوم‪ ٪٨٩ ،‬من الزنك‪ .‬من الحديد‪٪٨٩ ،‬‬ ‫معالجة مجهزة إلثبات فعاليتها في معالجة المياه العادمة الصناعية لتحديد كفاءاتها في إزالة الملوثات‪ .‬يقدم التقرير مقدمة وخلفية‬ ‫من حيث نوع األراضي الرطبة (األراضي الرطبة لمفهوم األراضي الرطبة المبنية‪ ،‬ويشرح المنهجيات المختلفة المستخدمة في‬ ‫واألبعاد ‪ ،‬والغطاء النباتي ‪ ،‬ونوع النفايات السائلة ‪ ،‬ونوع الركازة)‪ ،‬ويشرح النتائج المكتسبة من مثل هذه الدراسات ‪ ،‬والقياسات‬ ‫صا ‪.‬من حيث الكفاءة واألداء في األراضي الرطبة‬ ‫وفي الختام ‪ ،‬يقدم التقرير مقارنة بين األراضي الرطبة والتوصيات وملخ ً‬ ‫إلتمامها‪.‬‬ ‫الكلمات المفتاحية‪ :‬مياه الصرف الصحي‪ ،‬االراضي الرطبة‪ ،‬مخلفات المصانع‪.‬‬ ‫‪ii‬‬ ACKNOWLEDGMENTS Foremost, I would like to express my sincere gratitude to my supervisor Dr. Hind Barghash for the continuous support , her patience, motivation, enthusiasm, and immense knowledge. Her guidance helped me in all the time of research and writing of this thesis. I would like to thank my friends for motivating and supporting me during the whole duration of the research I am also grateful to my team member of this project Al Hawra Al Ajmi and Nujoom Al Amri who supported me through this venture. Finally and most importantly, huge thank goes to my parents and my family for the unceasing encouragement, support and attention. iii TABLE OF CONTENTS Contents ABSTRACT........................................................................................................................... I ‫ الخالصة‬............................................................................................................................. II ACKNOWLEDGMENTS ................................................................................................ III LIST OF TABLES ........................................................................................................ VIII LIST OF ABBREVIATIONS .......................................................................................... IX CHAPTER 1 .................................................................................................................... 1 INTRODUCTION ............................................................................................................. 1 1.1. Background .......................................................................................................................................... 1 1.2. Limitations of Constructed Wetlands ................................................................................................ 4 1.3. Problem Statement .............................................................................................................................. 4 1.4. Objectives ............................................................................................................................................. 5 CHAPTER 2 .................................................................................................................... 6 LITERATURE REVIEW .................................................................................................. 6 2.1. Domestic, Municipal and Industrial Wastewater .............................................................................. 6 2.2. Conventional Wastewater Treatment ................................................................................................. 7 2.2.1. Primary Treatment.............................................................................................................................. 7 2.2.2. Secondary Treatment .......................................................................................................................... 8 2.2.3. Tertiary Treatment.............................................................................................................................. 9 2.3. Constructed Wetlands (CWs) ............................................................................................................. 9 2.4. Main Benefits and Outcomes of CWs .............................................................................................. 10 2.5. Types of CWs ..................................................................................................................................... 11 2.6. Components of CWs .......................................................................................................................... 11 iv 2.6.1. Water .............................................................................................................................................. 11 2.6.2. Substrates, Sediments and Litter ........................................................................................................ 12 2.6.3. Vegetation ....................................................................................................................................... 13 2.6.4. Microorganisms ............................................................................................................................... 14 2.6.5. Animals ........................................................................................................................................... 14 2.7. Literature Summary ........................................................................................................................... 14 CHAPTER 3 .................................................................................................................. 15 METHODOLOGY .......................................................................................................... 15 3.1. Overview ............................................................................................................................................. 15 3.2. Treatment Of Effluents With Significant Amounts Toxic Heavy Metals ....................................... 15 3.2.1. Industrial Wastewater Treatment using Reed bed Constructed Wetland ................................................ 15 3.2.2. Wetlands for Industrial Wastewater Treatment at the Savannah River Site ............................................ 17 3.2.3. The Use of Constructed Wetlands for the Treatment Of Industrial Wastewater ...................................... 18 3.2.4. Phytoremediation of Heavy Metals from Industrial Effluent Using Constructed Wetland Technology ..... 20 3.2.5. Case Studies Of Wetland Filtration Of Mine Waste Water In Constructed And Naturally Occurring Systems In Northern Australia .................................................................................................................... 21 3.3. Treatment Of Wastewater With Insignificant Or No Amounts Of Toxic Heavy Metals ............... 21 3.3.1. Constructed Wetlands in the Treatment of Agro-Industrial Wastewater: A Review ................................ 21 3.3.2. Design of Horizontal and Vertical Subsurface Flow Constructed Wetlands Treating Industrial Wastewater ................................................................................................................................................................ 23 3.3.3. Treatment of Industrial Wastewater with Two-Stage Constructed Wetlands Planted with Typha latifolia and Phragmites australis ............................................................................................................................. 24 3.3.4. Constructed Wetlands for Industrial Wastewater Treatment and Removal of Nutrients ........................... 25 3.3.5. Surface-flow wetland for water reclamation at Batamindo Industrial Park ............................................. 26 CHAPTER 4 .................................................................................................................. 27 RESULTS AND DISCUSSION ..................................................................................... 27 4.1Overview ............................................................................................................................................... 27 4.2. Treatment of Effluents With Significant Amounts Of Heavy Toxic Metals .................................. 27 4.2.1. Industrial Wastewater Treatment using Reed bed Constructed Wetland ................................................ 27 4.2.2. Wetlands for Industrial Wastewater Treatment at the Savannah River Site ............................................ 29 4.2.3. The Use of Constructed Wetlands for The Treatment Of Industrial Wastewater ..................................... 30 4.2.4. Phytoremediation of Heavy Metals from Industrial Effluent Using Constructed Wetland Technology ..... 33 4.2.5. Case Studies Of Wetland Filtration Of Mine Waste Water In Constructed And Naturally Occurring Systems In Northern Australia .................................................................................................................... 37 4.3. Treatment of Effluents with Insignificant Or No Amounts Of Heavy Toxic Metals ..................... 39 4.3.1. Constructed Wetlands in the Treatment of Agro-Industrial Wastewater: A Review ................................ 39 4.3.2. Design of Horizontal and Vertical Subsurface Flow Constructed Wetlands Treating Industrial Wastewater ................................................................................................................................................................ 41 4.3.3. Treatment of Industrial Wastewater with Two-Stage Constructed Wetlands Planted with Typha latifolia and Phragmites australis ............................................................................................................................. 42 4.3.4. Constructed Wetlands for Industrial Wastewater Treatment and Removal of Nutrients ........................... 44 v 4.3.5. Surface-flow wetland for water reclamation at Batamindo Industrial Park ............................................. 46 4.4. Comparison and Summary ............................................................................................................... 47 CHAPTER 5 .................................................................................................................. 51 CONCLUSION .............................................................................................................. 51 CHAPTER 6 .................................................................................................................. 53 RECOMMENDATIONS AND FUTURE WORK ............................................................ 53 REFERENCES .............................................................................................................. 55 vi LIST OF FIGURES Figure 3-1 Set up of Reed bed and Control bed. (Sangola, Aribisala, & Awopetu, 2015)........... 16 Figure 4-1 concentration of metals in untreated wastewater, Reed bed with and without plants. (Sangola, Aribisala, & Awopetu, 2015)........................................................................................ 29 vii LIST OF TABLES Table 4-1 Concentration of heavy metals in untreated industrial wastewater, control bed wastewater and reed bed wastewater (Sangola, Aribisala, & Awopetu, 2015) ............................ 28 Table 4-2 Treatment efficiency of a HF-VF hybrid constructed wetland for treatment of winery wastewater in Spain (Skrzypiec & Gajewska, 2017) .................................................................... 31 Table 4-3 Removal efficiency rates for HSSF CW (Skrzypiec & Gajewska, 2017) .................... 32 Table 4-4 Removal efficiency rates for HSSF CW (Skrzypiec & Gajewska, 2017) .................... 32 Table 4-5 Uptake of lead from TTP effluent (Sukumaran, 2013) ................................................ 34 Table 4-6 Uptake of arsenic from TTP effluent (Sukumaran, 2013) ............................................ 35 Table 4-7 Uptake of copper from TTP effluent (Sukumaran, 2013) ............................................ 36 Table 4-8 Uptake of cadmium from TTP effluent (Sukumaran, 2013) ........................................ 37 Table 4-9 Concentrations of selected trace elements in waters at and nearby Tom's Gully gold mine N.T (Noller, Woods, & Ross, 1994) .................................................................................... 38 Table 4-10 Maximum flow rates (m3 d-1) to obtain an effluent suitable for the discharge for each wastewater attending to different pollutant discharge (Mena, Rodriguez , Nunez, Fernandez, & Villasenor, 2008)........................................................................................................................... 41 Table 4-11 Pollutant concentrations at the different sampling points during campaign 3 (mg/L). Concentrations are presented in average. BDL: Below detection limit (Varga , et al., 2017)...... 46 viii LIST OF ABBREVIATIONS CW Constructed wetlands BOD Biochemical oxygen demand COD Chemical oxygen demand TDS Total dissolved solids pH Potential of hydrogen DO Dissolved oxygen TC Total coliform FC Fecal coliform TSS Total suspended solids SS Suspended solids MRP Molybdate Reactive Phosphate HSF Horizontal surface flow HSSF Horizontal subsurface flow FWS Free water surface EP Emergent plants SP Sub-emergent plants FFP Free floating plants FLP Floating leaved plants SSF Subsurface flow VF Vertical flow VSF Vertical surface flow VSSF Vertical subsurface flow HF Horizontal flow HCW Hybrid constructed wetland ix FMR Filtralite MR 3–8 HUSB Hydrolytic up-flow sludge bed BCF Bio-concentration factor STP Sewage Treatment Plant x Chapter 1 INTRODUCTION 1.1. Background Water is one of the key elements we all need for survival. Healthy life not only receives facilitation from other things but also this thing we call water. It is helps living and non- living organism achieve good and proper healthy life. Water is part of all elements that help in supporting life. It is beneficial to both living organisms and non-living organism in its sustenance. Water is something no human being can do without; this is one of the core reasons we humankind have a huge mandate of protecting all water resources. Despite these efforts of securing our sources, water pollution is one of the big problems threatening the survival of water bodies. In as much as it seems impossible in protection of these water bodies, it is still a mandate we humans have to fulfill in order for us to live. Pollution of water is being affected majorly by untreated industrial discharge inclusive of municipal wastes. In summary, the environment is highly affected by these wastes (Postel, 2000) and our household’s wastes that are set out to draw into our water sources. This menace can only be curbed by educating the public on sensitization and the importance of looking after these resources generally. If the society continues with this bad habit of neglecting water resources and not bothering to protect them, we will end up having future predicaments that nothing can be done 1 to protect it. Discharging of industrial wastewaters in our water bodies remains to be the biggest problem we suffer from and we will suffer from all through. A prediction has already been done, that this pollution of water bodies will really affect us dearly in the near future, this demands us to start solving this future nightmare before worse comes to worse. It is no longer something that we do not know but fully aware, this amounts to negligence. What can be done is to educate the public at large on the importance of protecting water bodies and be made enforceable (Postlel,2000) in that it not only remains us a talk but something that is actualized. These public education tutorials should entail things such as the importance of recycling, managing what one can have, in that people should not only rely on having so much so as to survive but learn to manage. In as much as we can say that this might fail just as other means have, it remains as our last hope. It is obvious and very right to conclude that indeed the discharge of industrial waste interferes with not only our water bodies but also the environment in general. It is an establishment that, water recycling from the wetland treatment system actually does saves as a huge chunk of money in areas with scarce water. Wastewater wetlands is something tht has really helped people in the society in saving water. To solve this water nightmare in such areas, farming ought to be practiced and development of proper and better sewerage system to avoid the problem of water scarcity. In as much as it might not really cut this problem, at least it will help in prevention of further problems developing in regards to water scarcity. Public sensitization ought to be adopted for purposes of helping in curbing and preventing this problem affecting us. Besides having to conduct public awareness, this is also one of the ways to help in setting out the message to the public the need of preserving our water bodies inclusive of the water reservoirs. 2 It is evident various organizations are standing out trying to end the problem at hand. However, I still advocate for the creation of public awareness in order to reach a bigger number. This will help in better conservation of water simply because the initiative of reaching everyone will be achieved. We humans ought to prioritize what we put our money into, one of this thing remain to be conserving water. Integrating our money into these areas will highly help in saving human lives. By saving water sources, it not only is beneficial to us humans but also the environment at large. Failure of preserving our water bodies will sure amount to degradation of the environment that is a habitat to many in the society. Water is a daily need that we all need to survive this life. Not minding ones standard, race, tribe or even background we all need water in our lives. It is the core reason we are advocating for saving water bodies is something many organizations are fighting for. It is out of negligence that people decide to spoil the few water resources we have and not making any effort on preserving them. “Sustainability is a concept that can be integrated into human activities as well as the entire human society” (Calheiros, Rangel, & Castro, 2007). Sustaining is crucial area that major focus has been put on. As it is clear, a wider group is slowly exhausting the amount of water they have, this leaves them with no option, but recycling and conserving water already exists in their society. This is the only way that will help them deal with this menace slowly creeping into their lives. Lack of water simply means loss of lives. Interference of public water by addition of known and unknown water constituents is something that is highly practiced. CW is set to exploit the physical among other treatments that occurs in wetlands and provide for the reduction in organic material among other organisms. This system is cost effective and very easy to maintain, in addition to the aforementioned the system is easy to operate. It is highly applicable in households and industries due to its nature of easy operation and maintenance. 3 1.2. Limitations of Constructed Wetlands Constructed Wetlands core goal remains to be a system for municipal, industrial, and single household wastewaters approach. However, they have limitations that undermine the system effectiveness in the landscape. Constructed wetlands water waste system is set in a way that use larger pieces of land as opposed to other wastewater systems in as much as they are used for the same purpose. This nature makes it very convenient for areas with available land space at affordable rates (Díaz, Anthony, & Dahlgre, 2012). This system becomes very costly for persons who have no lands and are left with no option but purchasing. One of the reasons why some areas have not adapted this wastewater system as it is rendered expensive.(Jhansi,& Mishra 2013) This system of wetlands is not advisable in dry areas as they are less effective in such conditions. Building and installing the system becomes so much a task. This system is also highly affected by heavy rains upon occurrence more so during spring seasons. In conclusion, we can say that in as much as it serves its purpose of protecting the water resources, it is highly affected by weather changes easily (Imfeld, Braeckevelt, Kuschk, & Richnow, 2009). This gradually undermines its effectiveness to fulfill the main purpose. The only technology that can improve the preceding statement is still underdeveloped. For attainment and sustainment of the effectiveness of this system, more should be done in relation to improving the system and other surrounding bodies. 1.3. Problem Statement 4 Industrial, municipal, and single household wastewater management is problem in so many developing countries worldwide. This is due to the hardship in finding a low cost wastewater management technology for application of producing effective effluents to meet all this needed function. By having this wastewater, management helps in prevention of disease spread and infections. Wastewater management is something that has to be at the forefront of every person thoughts globally (Vymazal, 2010). The main goal for developing the wastewater treatment systems is to help in water conservation inclusive of other environmental resources. All the harmful that come because of this discharges ought to be handled well to avoid any harm. This is to enable us handle and prevent the spread of diseases and any infections to the members of the public at large. Pollution of water is a dangerous thing as it brings up so many risks not only to the human but also to the environment. We all are aware mosquitoes best environment is water, more so stagnant polluted water. Existence of mosquitoes clearly tells us a larger number of people contacting malaria (Healy, Rodgers, & Mulqueen, 2007). Construction of wetlands has highly helped in conservation of huge pieces of land that is costly at certain given times. 1.4. Objectives Design of Constructed Wetland for municipal and industrial applications: This study discusses the design, performance, percentage removal and water balance of assorted designs of the constructed wetlands treatment system for the use of treating wastewater. 1. Review of Constructed Wetland designs for the industrial wastewater – influent/effluent quality, designs, reuse criteria, examples - case studies. 5 Chapter 2 LITERATURE REVIEW 2.1. Domestic, Municipal and Industrial Wastewater In this day and age, the issue of municipal, industrial and domestic wastewater is of great concern because it can cause severe environmental problems, and can also impact people in terms of their health. Studies have estimated that wastewater comprises 99% water, with the remaining 1% being a mixture of suspended and dissolved organic solids, detergents and chemicals (Secretariat, 2014). Sewage is wastewater that comprises household waste from toilets, sinks and showers/baths that is disposed of via sewers. Municipal wastewater includes input that ranges from, for example, shops, to restaurants and bars, and car washes (Secretariat, 2014). Frequently, pretreated industrial wastewater is included in with the municipal wastewater. A wide variety of processes result in the formation of industrial wastewater, including plastic manufacturing, wood pulping, petroleum refinement and food processing. According to Secretariat (2014), these different types of wastewater have varying compositions, containing, for instance, different pathogens, bacteria and nutrients. Untreated wastewater components can be organised into three categories – physical, biological and chemical. Solid and inorganic constituents in wastewater comprise the physical components. The biological 6 components are bacteria, viruses, protozoa and other pathogens. Lastly, the chemical components include dissolved materials and organic matter, as well as nutrients and metals, which, in most cases, are heavy metals. In rare cases, wastewater might contain reusable resources – for example, water, carbon and other nutrients – that could be recovered. For effective effluent regulatory standards to be met, wastewater needs to undergo appropriate treatment in order to get rid of the pollutants and, according to Crawford & Sandino (2010), this process should be focused on the recovery of resources, so as to be self-sustaining. Advances in scientific knowledge, and a greater consciousness about the environment and water as a resource, have given rise to new and improved technologies and treatment systems that are effective in dealing with wastewater pollution and also in reducing the energy used in recycling wastewater; however, selection of the appropriate technology to solve a specific wastewater problem should be undertaken with great care. Generally, there are two types of wastewater treatment systems – conventional and sustainable CW. 2.2. Conventional Wastewater Treatment Conventional wastewater treatment comprises physical, chemical and biological processes, involving three stages, referred to as primary, secondary and tertiary treatments. 2.2.1. Primary Treatment 7 This treatment is used in the removal and separation of particulate inorganic materials and solids, which would otherwise clog and destroy water pipes of the network. This type of treatment entails screening, grit removal and sedimentation. Screens are used to get rid of large debris, including plastics and cans. The grit chamber system is used to remove, settle, gravel- and sand-sized particles. According to Nelson et al. (2007), the wastewater is then moved into a quiescent basin, where it is temporarily retained so that the remaining heavier solids can settle to the bottom of the basin, while the lighter solids, including grease and oil, can accumulate on the surface. Finally, skimming and sedimentation processes are used to remove both the floating and settled pollutants. The liquid that remains is transferred to the secondary treatment. In this primary stage, 50% of the TSSs and 30–40% of the BOD are removed (Nelson, Bishay, Van Roodselaar, Ikonomou, & Law, 2007). 2.2.2. Secondary Treatment Dissolved and biological matter is removed in the secondary treatment. According to Nelson et al. (2007), 90% of the organic matter in the wastewater is removed at this stage. The attached and suspended growth processes are the two most suitable conventional methods used in secondary treatment. In the attached growth process, algae, bacteria and other microorganisms are grown on the surface of the wastewater, resulting in the formation of biomass, which breaks down the organic waste. Trickling filters, bio-towers and rotating biological contactors are included in the attached growth process unit. In the suspended growth process, the microbial growth is suspended in an aerated 8 water mixture; however, activated sludge, in which a biomass of aerobic bacteria and other microorganisms is grown, is the most common type of suspended growth process. 2.2.3. Tertiary Treatment The tertiary treatment is more advanced, aimed at producing a better-quality, more purified effluent for discharge into estuaries and low-flow river ecosystems. Coagulation sedimentation, filtration, reverse osmosis and extended secondary biological treatments are some of the methods that are used in this stage. These methods remove nutrients and stabilise oxygen in oxygendemanding substances. The treated effluent can then be safely reused, recycled or discharged (Praewa, 2017). In most circumstances, a final disinfection process is needed before tertiary-treated wastewater can be discharged. Disinfectants can be added to kill off pathogens and microorganisms, and. chlorine and ultraviolet light are also commonly used. The treated water can then either be discharged into different water bodies, including recharging underground reserves, or used in agricultural irrigation (Praewa, 2017), as long as it meets the required standards. 2.3. Constructed Wetlands (CWs) CW systems for single-household, municipal, and industrial wastewater are designed in ways that imitate the natural processes at work in wetlands, but include features that provide advantages over natural wetland processes. Such CWs incorporate chemical, biological and physical processes that 9 are used to remove the pollutants and enhance and improve the quality of the wastewater (Vymazal & Kropfelova, 2008). These design systems use aquatic macrophyte and microbial communities, and plant roots and their host minerals to effectively remove pollutants, which include nitrogen, metals and pathogenic organisms, among many others. In 1904, the first CW was built in Australia (Vymazal & Kropfelova, 2008). Despite this, technological advancement in the field has been slow (Vymazal & Kropfelova, 2008). As the number of CWs increases around the world, and the benefits and effectiveness of the system over conventional treatment systems become better understood, CWs are finding wider favour among ecologists, scientists and water and environmental engineers, and this is leading to their popularisation even among developing countries. 2.4. Main Benefits and Outcomes of CWs The CW is a beneficial wastewater system because, upon treatment, the water that is discharged can either be used for domestic activities, or can be directly discharged into the environment. It is also beneficial to the end-users, as construction costs are minimal, and the costs of operation and maintenance are affordable. The operation and maintenance of CWs are periodic, unlike conventional water treatment systems, which in most cases require continuous, on-site labour (Crawford & Sandino, 2010). The CW system facilitates the recycling and reuse of water, thereby defraying the costs of installation, operation and maintenance. The CW system not only provides a habitat for wetland organisms, but is also engineered in a way that finds favour with the public because of its many benefits. 10 2.5. Types of CWs There are various types of CWs that depend on the available landscape, including SF and SSF systems. SF CWs have shallow flow and lower velocity over the substrates, whilst SSF CWs have either VF or HF over the substrates. Hybrid CWs combine both VF and HF (Vymazal & Kropfelova, 2008). Each type of CW system has its benefits and drawbacks, and each differ in the treatment process used. SF CWs make use of plant stems, leaves and rhizomes to effectively treat wastewater. In dense vegetation, however, the process can be limited because there is not enough circulation of oxygen, which is vital for the organisms. In SSF CWs, roots are used in the treatment of effluents as water passes through a series of gravel beds. This process is considered to be superior to, and more effective than, that used in SF CWs. 2.6. Components of CWs 2.6.1. Water Locations in which landforms predominantly direct surface water straight into shallow basins, or where impermeable subsurface layers hinder the ground from absorbing surface water, are the most likely places for wetlands to form naturally. Such conditions in a location can be engineered to create wetlands (Jhansi, & Mishra, 2013). Land can be structured in such a way that surface water is collected, and such basins can be sealed in order to retain the collected surface water. Once a landscape has been modified in this way, a wetland can be constructed. 11 In the construction of a wastewater wetland system, hydrology is among the most important factors to be considered. This is because it not only links all of the functions of the wetland, but it is also a key factor in the CWs failure or success in a given landscape. The hydrology of the CW is important in relation to the hydrology of other surface water in the area. Small, natural hydrological changes can promote significant effects in the CW, impacting on its utility. Through rainfall and evapotranspiration, there is substantial interaction between the wetland system and the atmosphere because of the wetland water is shallow and covers a large surface area. The hydrology, in most cases, is also affected by vegetation density in the wetland, which can obstruct the flow of water. 2.6.2. Substrates, Sediments and Litter Soil, sand, gravel and rock, as well as organic materials, such as compost, are used to make the substrates for the wastewater to flow over. Due to the high biological productivity and low water velocities in wetlands, it is possible to easily accumulate sediments and litter (i.e., organic matter). These substrates, sediments and litter are vitally importance because they support all of the living organisms that dwell in wetlands (Secretariat, 2014). For many contaminants in a wetland, the substrate acts as a sink. The substrate is also important because its permeability affects the movement of water passing through the CW. 12 2.6.3. Vegetation In any CW, the presence of both vascular and non-vascular plants is of vital importance (Praewa, 2017), vascular plants being the higher plants, whereas non-vascular plants are the algae. When algae undergo photosynthesis, they increase the dissolved oxygen content in the water, which significantly affects the metals and nutrients present in the water. The presence of plants in a CW system, therefore, is very important, since they also penetrate the substrate structure, transferring oxygen into the substrate, a process that is not possible or achievable, even using diffusion. The presence of submerged leaves, stalks and litter is important in FWS wetlands in terms of attached microbial growth, wherein the leaves, stalks and litter themselves serve as substrates. Wastewater wetlands are mostly characterised by the absence of emergent plants, although natural wetland systems commonly include reeds, rushes and cattails. Cattails have the ability to survive and thrive under diverse environmental conditions, and they can produce massive annual biomass. Rushes –particularly bulrushes – are perennial, grass-like plants that are capable of growing and thriving in clumps. They tend to grow better in water that ranges from 5 cm to 3 m deep (Wetzel, 1993). Most bulrushes grow well in water that has a pH of 4–9. Reeds are tall, annual grasses with a perennial rhizome. Reeds are among the most widespread emergent aquatic plants. CWs that use reeds are at an advantage because the reeds have the ability to transfer oxygen into the substrate, thus improving the effectiveness of the system. 13 2.6.4. Microorganisms The functions of CWs are, in some way, controlled and regulated by the presence of microorganisms and their metabolic processes. Algae, protozoa, fungi and yeasts are examples of microorganisms that are found in wetlands. Microbial activity in the system is important because this is how nutrients are recycled. Microbial activity also affects the processing capacity of the wetland because it can cause reduced conditions in the substrate. In CWs, microbial communities are affected by toxic chemicals, such as those found in pesticides (Wetzel, 1993). 2.6.5. Animals Certain vertebrates and invertebrates take up residence in CW systems. Insects and worms are (invertebrates) are significant contributors to the treatment process (Wetzel, 1993), making it safe and more effective. 2.7. Literature Summary CWs for municipal, industrial and domestic wastewater treatment can be designed in appropriate and specific ways to meet most intended purposes. Wetland systems can be engineered to take advantage of the various features of a site. CWs are an effective approach that can be employed in improving wastewater quality and allowing for its reclamation and reuse. Moreover, CW systems are of economic and thus they are globally applicable. 14 Chapter 3 METHODOLOGY 3.1. Overview The methodology section of this paper offers an insight into the various methods used to design appropriate and suitable CWs for optimal performance. Various parameters such as size, area, flow design, capacity, vegetation type, wastewater type, cell structure and components are crucial to the success of a CW and hence these case studies provide accurate information about the above mentioned parameters. The section also shows different methodologies for CWs for different types of wastewater including industrial wastewater, agro-industrial wastewater, and mine wastewater. The structures for each type of wastewater are different in size and design based on the components contained. As such, the methodologies are unique for each case study. 3.2. Treatment Of Effluents With Significant Amounts Toxic Heavy Metals 3.2.1. Industrial Wastewater Treatment using Reed bed Constructed Wetland The first step carried out in this study involves the testing of wastewater samples from a battery industry for toxic metals. Two pilot VSF experimental wetlands measuring 1200mm by 600mm are then constructed, the first to measure retention period of the reed plants Phragmites karka and 15 the second to observe the removal efficiency rate. The first bed is planted with wetland vegetation and substrates while the second bed, a control bed, is only filled with wastewater and substrates only without a reed plant. The reed cuttings are planted 150mm apart and then irrigated in 40 liters potable water for ten days so as to make sure they grow quickly and properly before introducing the wastewater. The supply of wastewater adopts vertical subsurface flow. The retention periods of the two beds are then recorded between 3-19 days. Effluents are then analyzed for toxic metals in comparison to the analysis results of untreated wastewater. After the pilot experiment, two reed beds are constructed in 1000 liter plastic tanks measuring 1200mm by 1000mm by 600mm. 450mm of granite makes the bottom layer while 150mm of washed sand makes the top layer. Similar to the pilot experiment, the first bed is planted with reeds while the second is not planted with any vegetation. Industrial wastewater is harvested from Elewi-Odo stream and the influent is drained in 3, 7, 11, 15, and 19 days for both beds (Sangola, Aribisala, & Awopetu, 2015). Figure 3-1 Set up of Reed bed and Control bed. (Sangola, Aribisala, & Awopetu, 2015). 16 3.2.2. Wetlands for Industrial Wastewater Treatment at the Savannah River Site The CW under study is located in South Carolina and its objective is to treat copper, lead, mercury, zinc, BOD, pH, trichloroethylyne, tetrachloroethylyne, oil, grease, total residual chlorine, total suspended solids and chronic toxicity. The system consists of two 90 foot by 484 foot cells divided into four separate treatment trains and a solar powered flow monitoring station. The wastewater which includes storm water moves through the cells by gravity. The materials used to construct the cells are inert in order to avoid leaching of metals and any other contaminants into the influent and effluent. Prior to the building of the actual CW, bench-scale and on site pilot scale models are constructed to test the efficacy of the method of wastewater treatment and the suitability of the design of the CW. The vegetation chosen for the CW is bulrushes, which are required to transplanted into the CW early enough to mitigate the effects of climate stress and transplant shock for successful growth in the CW (Lehman, et al.). The design’s performance is highly dependent on constant monitoring of the flow management basin to manage optimal performance capacity during both high flows and low flows. The flow management basin should be maintained at near empty during high flows when rainfall is heavy. During low flows, a minimum base flow of approximately 0.3 million gallons of wastewater per day should be run through from the process stream. Water depth in the CW cells is monitored to determine redox potential. In addition, hydrosoil samples are collected and analyzed regularly to determine their suitability for bulrush growth. 17 3.2.3. The Use of Constructed Wetlands for the Treatment Of Industrial Wastewater The case study explores the various types of CW based on the flow type. There are two main types of CWs that are then further broken down into more specific types. FWS CWs are constructed in such a way that the wastewater flows above a substrate medium which forms a free water surface and a water column depth of about a few centimeters (Skrzypiec & Gajewska, 2017). FWS CWs are either vegetated with EP, SP, FFP, or FLP. The second type of CW is SSF CWs which entails wastewater flowing through a porous substrate. SSF CWs are then classified depending on whether the flow is vertical or horizontal. Finally, the different CW designs can be combined to form a hybrid system (HCW). PETROCHEMICAL INDUSTRY: The petrochemical industry produces wastewater that consists of ammonia, oil and grease, SS, phenolics, hydrocarbons, heavy metals, organics and H2S. An example of a CW that treats petrochemical wastewater for hydrocarbon contamination is one in Amoco’s Mandan, North Dakota (Skrzypiec & Gajewska, 2017). The wastewater flows from an oil separator and a lagoon measuring 6ha in area into the CW. The CW itself is made of 11 ponds totaling an area of 16.6ha. PULP AND PAPER INDUSTRY: The pulp and paper industry wastewater contains organic matter, and SS although the components vary with type of process, technology, amount of water used in the process, type of wood material, and internal recirculation of the effluent for the purposes of recovery (Skrzypiec & Gajewska, 2017). Western Kenya hosts a pilot scale CW used to remove phenols from wastewater. The HSSF CW was operated for 15 months under various HRTs with batch loading. 18 METALLURGICAL INDUSTRY: A lab scale CW was used to treat steel wastewater from a metallurgical industry. Two VSSF beds were constructed, one filled with manganese ore and the other filled with gravel. The monitored parameters were iron, manganese, turbidity, TP, and COD (Skrzypiec & Gajewska, 2017). In Taiwan, In Taiwan, a HSSF mesocosm for treatment of steel mill wastewaters was filled with gravel, planted with common reed and bulrush and operated at a HLR of 2.6 cm∙d–1 and HRT of 7 days (Skrzypiec & Gajewska, 2017). ALCOHOL FERMENTATION INDUSTRY : Cases of an alcohol fermentation industry (winery) use the HSSF CWs and hybrid (HF-VF) CWs. Direct feeding of winery wastewater with high concentration organic compounds into CWs often shows limits in the tolerance of wetlands and have a serious negative effect, such as clogging which reduces oxygen infiltration into the growth media and typically causes rapid failure of the wetland system (Skrzypiec & Gajewska, 2017). Therefore, HSSF and hybrid CWs are used because of their passive nature. Sometimes the wastewater is treated first before being pumped into the CW. FOOD PROCESSING INDUSTRY: A slaughter house wastewater HSSF CW (food processing industry) in New Mexico treats anaerobically digested abattoir effluent (Skrzypiec & Gajewska, 2017). The CW has an area 1144 m2 and is filled with gravel at the base. The wetland is planted with alternating strips of common reed and bulrushes. MILK AND CHEESE INDUSTRY – DAIRY WASTEWATER: Dairy wastewater is majorly treated using HSSF systems. Prior treatment is essential to remove SS to avoid clogging of porous media in the CW. Settling basins are used to pretreat the wastewater (Skrzypiec & Gajewska, 2017). Plant species used include pumpkin, woodland ragwort, common reed, common nettle, and flowering rush. Use of VSSF CWs for this industry is rare but some systems combine HSSF and VSSF. 19 FISH AND SEAFOOD PROCESSING: HSSF systems are used for wastewater from sea food processing. From the study (Skrzypiec & Gajewska, 2017), two wetlands measuring 1m by 4m are filled with 0.3m of crushed limestone as a base. One of the wetlands is planted with common reed and the other with smooth cordgrass. LAUNDRY: A pilot scale HSSF CW in Barcelona that treats laundry wastewater for linear alkylbenzene sulfonates (LAS) is analyzed. The plant species used for vegetation are bulrush and marsh club-rush mixed together. The HRT is 6.1days. 3.2.4. Phytoremediation of Heavy Metals from Industrial Effluent Using Constructed Wetland Technology In Travancore Titanium Products (TTP), Kerala, India, the experimental CW is made in plastic tubs measuring 100 x 45 x 45 (cm) filled with 3cm of gravel and above that 5cm of wetland soil. The plants used for planting in the CW cells are collected from nearby wetland, cleaned and acclimatized in fresh water tanks for one month. The wetland plants used are Typha latifolia, Eichhornia crassipes, Salvinia molesta and Pistia stratiotes (Sukumaran, 2013). The effluents used are from titanium sponge production factory. The effluents are analyzed for heavy metal content before and after treatment for comparison. Additionally, each wetland plant species is analyzed after treatment to determine the level of absorption of heavy metals from the effluent. The analysis is done using the bio-concentration factor which involves dividing the trace element concentration in plant tissues (ppm) at harvest by initial concentration of the element in the external nutrient solution (ppm) (Sukumaran, 2013).The whole treatment process takes fifteen days. 20 3.2.5. Case Studies Of Wetland Filtration Of Mine Waste Water In Constructed And Naturally Occurring Systems In Northern Australia The study focuses majorly on treatment of mine wastewater containing high levels of toxic heavy metals using wetlands, some constructed and some naturally occurring. Quite a number of mines the tropical north of the Northern Territory accumulate a lot of excess water due to rainfall and inflow from groundwater (Noller, Woods, & Ross, 1994). Disposal methods for the water prove to be challenging. If the water is suitable in quality, it is released back into the environment or stored for later use in dams through open drains. The drains and drums are colonized by wetland vegetation and the effect on water quality is being investigated. 230km east of Darwin lies the Ranger uranium mine in the Alligator River area. There exists a small wetland with area of 0.3ha in a creek bed that is supplied with run-off water containing nontoxic amounts of manganese, uranium, calcium, and sulfate magnesium. The amounts of the elements are measurement and analyzed. Similarly, three other mine cases (Tom’s Gully mine, Woodcutters mine, and Woolwonga mine) with different wetlands areas including a billabong system, artificial CWs, and natural swamplands respectively are presented with the most common type of vegetation being Typha spp. 3.3. Treatment Of Wastewater With Insignificant Or No Amounts Of Toxic Heavy Metals 3.3.1. Constructed Wetlands in the Treatment of Agro-Industrial Wastewater: A Review 21 CWs for agro-industrial wastewater are diverse since the wastewater comes from a variety of agroindustrial process, hence different chemicals are found in the wastewater. Due to this fact, agroindustrial wastewater has to go through prior treatment processes using diluters, stabilization lagoons, septic tanks, sludge digesters, settling tanks, biological treatments, biological filters, solid separation or coagulation according to the type of wastewater based on the agricultural process and before being pumped into CWs. The type of plant vegetation that should be used is observed. The two most common wetland plant species are Phragmites spp. and Typha spp. Both species efficiencies are measured using biomass, ability to grow in saline and fresh waters, tolerance to organic matter and toxic effects to COD, TKN and TP in wastewater. Moreover, the efficiency of various CW designs such as FWS, HSF, VF and Hybrid in relation to various agro-industrial wastewater types is evaluated in terms of ability to purify varying loads and amounts of pollutants in the wastewater (Sultana, Akratos, Vayenas, & Pavlou, 2015). FWS CWs have been widely applied for the treatment of a variety of agro-industrial wastewaters such as animal farm, dairy, and OMW. The applications range from pilot-scale experiments to fullscale wetland plants as their areas vary from 120.6 to 4000 m2 (Sultana, Akratos, Vayenas, & Pavlou, 2015). Additionally, according to (Sultana , Akratos, Vayenas, & Pavlou, 2015), FWS CWs have been operated with various pollutant surface loads ranging from 1.9 to 259.4 g/m2 per day for organic matter, from 0.4 to 77 g/m2 per day for TKN, from 0.05 to 12.7 g/m2 per day for phosphorus, and from 2.55 to 949 g/m2 per day for TSS. The HRTs applied on FWS CWs are from 4 to 120 days. HSF CWs can treat a wider range of agro-industrial wastewater for example, dairy, winery, sugarcane, and trout farm. They have been used at several scales from laboratory experiments to full-scale applications with surfaces areas ranging from 0.25 to 7600 m2. HSF CWs operated under 22 similar pollutant surface loads with FWS CWs varying from 0.17 to 376 g/m2 per day for organic matter, 0.007 to 2.7 g/m2 per day for TKN, 0.004 to 4.7 g/m2 per day for phosphorus, and from 0.2 to 62.4 g/m2 per day for TSS (Sultana , Akratos, Vayenas, & Pavlou, 2015). VF CWs can handle pollutant surface loads ranging from 10 to 6589 gr/m2 day for organic matter, 0.6 to 575 g/m2 per day for TKN, 0.08 to 20 g/m2 per day for phosphorus, and 35 to 1836 g/m2 per day for TSS (Sultana , Akratos, Vayenas, & Pavlou, 2015). Hybrid CWs operate on high pollutants surface loads of 1.28 to 1500 g/m2 per day for organic matter, 0.3 to 1500 g/m2 per day for TKN, 0.06 to 40 g/m2 per day for phosphorus and 1.96 to 400 g/m2 per day for TSS (Sultana , Akratos, Vayenas, & Pavlou, 2015). 3.3.2. Design of Horizontal and Vertical Subsurface Flow Constructed Wetlands Treating Industrial Wastewater The CW design is critical to the success of the whole wastewater treatment project. There are majorly two types of tools used to determine the most appropriate CW system for a project. Mechanistic tools involve creating mathematical models of all the main processes happening in the CW. On the other hand, non-mechanistic models overlook the interactions between the atmospheres, soil, plants, water, and micro-organisms (Mena, Rodriguez, Nunez, Fernandez, & Villasenor, 2008). The CW is treated as a black box. Rules of thumb, model of first-order reaction in an ideal plug flow reactor, and regression equations are employed instead. The study proceeds to give an example of a CW located in Daimiel, Spain that consists of two sets of double VSSF cells measuring 15m x 7.5m x 0.8m with a slope of 1% at the bottom to aid gravity. The VSSF cells are based with gravel. The next part of the CW is a HSSF measuring 57.5m x 15m x 0.6m and similarly filled with gravel except for the first two meters. The wastewater fed into the system 23 originates from an activated sludge treatment and alternatively raw wastewater from a filtration system (Mena, Rodriguez, Nunez, Fernandez, & Villasenor, 2008). The CW is tested for components such as COD, TN, TP, and Norg using mathematical equations. The mass balances of the components were calculated using the following equation: C = (Ci - C*) . exp ( - K . A/Q) + C* 3.3.3. Treatment of Industrial Wastewater with Two-Stage Constructed Wetlands Planted with Typha latifolia and Phragmites australis The wastewater used for this particular case is tannery wastewater from a leather plant in Portugal. The HSSF CWs are of two series each having two beds; one is vegetated with Typha latifolia named UT and the other with Phragmites australis named UP (Calheiros, Rangel, & Castro, 2009). The substrate used for the beds is FMR with particle size ranging from 3-8mm. Each of the beds has an area of 1.2m2. The first unit of the series had been in operation for 17 months by the time the second series began. The vegetation in the second series was transplanted from an industrial polluted site in Estarreja, Portugal. In total, the series are operated for 31 months under different conditions arising from hydraulic conditions and interruptions. Interruptions include maintenance days and days when the plant producing the wastewater was shut down. Both series are filled with water three weeks before the introduction of wastewater from the tannery. The inlet and outlet flows are measured at the scheduled sampling time. The vegetation is also frequently measured and tested for signs of toxicity, chlorophyll content and peroxidase activity determination (POD). Wastewater samples are analyzed for COD, BOD, TSS, TKN, nitrate nitrogen, TP, TC, temperature, ammonia nitrogen, sulphates, and hexavalent chromium (Calheiros, Rangel, & Castro, 2009). 24 3.3.4. Constructed Wetlands for Industrial Wastewater Treatment and Removal of Nutrients The first case study CW is a full scale hybrid plant located in Spain in 2008. The plant was constructed to treat the wastewater coming from a winery with a production capacity of 315000 L of white wine. The constructed-wetland system consists of a HUSB anaerobic digester 6 m3 in volume, a VF CW 50 m2 in area and three HSSF CWs with an area of 100 m2 each (Varga , et al., 2017). The water depth for the first HSSF was 0.3 m, while the depth for second and third HSSFs was 0.6 m, respectively. CWs were planted with three to four units/m2 of Phragmites australis (VF) and Juncus effusus (HF). The second case study CW is called “Performance and validation of HIGH-rate constructed WETlands” (HIGHWET) (Varga, et al., 2017). The pilot version of the CW was situated in Spain to treat domestic wastewater while the real plant is located in Denmark to treat wastewater from a dairy factory, a house inhabited by factory workers, and a food production company (Varga, et al., 2017). The design consists of aerated CWs, conventional CWs and an aerobic HUSB reactor. The chain of slow begins from a pumping well into the HUSB reactor. After that, there are two treatment trains. The first one consists of an aerated VF, aerated HSSF, and a tobermorite filled well for phosphorous removal. The second one is composed of a conventional VF, aerated HSSF, and a polonite filled well for phosphorous removal. The VF beds have an area of 16m2 while the HSSF cells have an area of 9m2. 25 3.3.5. Surface-flow wetland for water reclamation at Batamindo Industrial Park Wastewater influent is conducted into an STP using sequential batch reactor (SBR) then directed into an intermediate collection tank before entering the CW in order to regulate flow (Salim, Rachmania, & Dewi, 2017). Effluent from the CW is collected for sampling and most of it disposed. The plant vegetation used for the CW is water hyacinth well known for its resilience. The wetland cells measure 5 m x 10 m x 1 m with a soil layer of height 0.4m (Salim, Rachmania, & Dewi, 2017). The flow rate from the STP is adjusted at a HRT of 0.5, 1, or 2 days. Both influents and effluents are sampled every day. Plant growth is visually monitored. The water samples are analyzed for COD, TSS, DO, and turbidity. 26 Chapter 4 RESULTS AND DISCUSSION 4.1Overview The chapter provides detailed information regarding the results of the presented methodologies discussed in chapter 3. The section, in addition, provides a discussion of the results found in terms of their effects on the efficiencies and effectiveness of the CWs. Results of physiological and chemical components of wastewater are provided, both for treated and untreated wastewater in most cases. Components such as TSS, COD, BOD, TN, TK, and heavy metals are some of the parameters discussed in this chapter. At the end of the chapter, a comparison is made between a number of related case studies to sample the differences and similarities. 4.2. Treatment of Effluents With Significant Amounts Of Heavy Toxic Metals 4.2.1. Industrial Wastewater Treatment using Reed bed Constructed Wetland The analysis of the untreated and treated wastewater for the presence of toxic metals produces a number of results. The toxic chemicals that were found in the untreated wastewater include mercury, lead, cadmium, lithium, zinc, manganese, silver, and nickel (Sangola, Aribisala, & Awopetu, 2015). As the hydraulic retention times (HRT) increased, the performance efficiency of both beds (with and without reeds) increased as well. The reed bed recorded a percentage of 36.8 27 to 61.5 while the control bed recorded 28.7 to 58.3 in terms of removal of toxic metals from the wastewater (Sangola, Aribisala, & Awopetu, 2015). The table 4-1 shows the amounts of toxic metals in untreated wastewater, vegetated reed bed, and unplanted reed bed (control bed) recorded from the study (Sangola, Aribisala, & Awopetu, 2015). Table 4-1 Concentration of heavy metals in untreated industrial wastewater, control bed wastewater and reed bed wastewater (Sangola, Aribisala, & Awopetu, 2015) Chemicals Initial Reed concentration with of metals (mg/l) (mg/l) bed Control bed Percentage Percentage plant without plant reduction for reduction for (mg/l) reed bed control bed Lithium 11.13 7.03 7.87 36.8 29.3 Cadmium 31.59 19.54 21.01 37.2 33.5 Mercury 138.76 56.48 57.86 59.3 53.4 Zinc 116.27 52.21 52.21 55.1 55.1 Nickel 12.95 7.98 7.98 38.4 28.7 Manganese 12.47 7.54 7.54 38.1 35.2 Lead 149.87 57.69 57.69 61.5 58.3 Silver 84.18 49.75 49.75 41.3 40.2 The equation used to calculate percentage reduction of chemicals, which is equivalent to removal efficiency, is given above. It is derived from deducting the reed bed concentration from the initial concentration without treatment and dividing the solution by the figure for the initial concentration 28 without treatment. The solution is then multiplied by 100 to make a percentage. The equation applies to all chemical components uniformly. Figure 4-1 concentration of metals in untreated wastewater, Reed bed with and without plants. (Sangola, Aribisala, & Awopetu, 2015) It is evident from the comparison of the results in figure 4-1 that the wetland plants (Phragmites karka) are essential to the treating of wastewater. The reed bed records a higher percentage of toxic metal removal as compared to the control bed. 4.2.2. Wetlands for Industrial Wastewater Treatment at the Savannah River Site An analysis of the system performance in 2001 shows the toxicity of the influent based on its effects on Ceriodaphnia dubia was recorded at 100% mortality. The effluent on the other hand had 0% mortality on Ceriodaphnia dubia meaning that the toxicity levels of the wastewater had been 29 efficiently treated by the removal of toxic metals such as copper, lead, mercury, and zinc. The mortalities were measured based on a 7-day exposure. According to (Lehman , et al.), the levels of copper in the wastewater influent ranged from 5-40 µg/l in the total recoverable influent, the acid soluble influent, and the soluble influent. After treatment, the levels of copper ranged from 05 µg/l in the total recoverable effluent, the acid soluble effluent, and the soluble effluent. The CW, therefore, proved to be suitable for toxicity removal based on the results. 4.2.3. The Use of Constructed Wetlands for The Treatment Of Industrial Wastewater PETROCHEMICAL INDUSTRY : For the petrochemical industry, the CW has a very good efficiency level of BOD (98%), COD (93%), ammonia (84%), sulphides (100%), phenols (99%), oils and grease (99%) at the hydraulic loading rate (HLR) of 1.2 cm∙d-1 (Skrzypiec & Gajewska, 2017). PULP AND PAPER INDUSTRY: Removal of phenols from wastewater from the paper and pulp industry is recorded at 60% at 5-day HRT and 77% at 3-day HRT on average (Skrzypiec & Gajewska, 2017). Evidently, the longer HRT of 5 days achieves a less percentage of removal than the HRT of 3 days. This could be because the longer HRT might have led to the deficiency of oxygen and nutrients. METALLURGICAL INDUSTRY :The reclamation of steel water using a VSSF CW records effluent concentrations of both elements (iron and manganese) below 0.05 mg∙dm-3. The HSSF CW records removal efficiency for COD and TP of 50% and 6%, respectively, and most heavy metals were not below the detection limit in the discharged water (Skrzypiec & Gajewska, 2017). 30 ALCOHOL FERMENTATION INDUSTRY: Winery wastewater treatment using a hybrid HF-VF system proves highly efficient even though most CWs treating winery wastewater are HSSF. The efficiency of removal of TSS is at 87%, COD is 71%, BOD5 is 70%, TKN is 52%, N-NH3 is 55%, and PO43- is at 17% as shown in table 4-2. Table 4-2 Treatment efficiency of a HF-VF hybrid constructed wetland for treatment of winery wastewater in Spain (Skrzypiec & Gajewska, 2017) Parameter TSS COD BOD5 TKN N-NH3 PO43- Inflow, mg∙dm–3 129 1.558 942 52.9 28 2.3 VSSFout, 65 711 418 26.0 19.4 2.4 17 448 279 25.2 12.5 1.9 87 71 70 52 55 17 mg∙dm–3 HSSFout, mg∙dm–3 Efficiency, % The table 4-3 shows removal efficiency for various components of a HSSF CW treating abattoir wastewater in the food processing industry according to (Skrzypiec & Gajewska, 2017). The reduction of fecal coliforms and total coliforms added up to 5.5 and 5.0 log units respectively according to the study. The average organic loads for COD, and BOD5 were 82 g∙m-2∙d-1 and 33 g∙m-2∙d-1 respectively, which are very high values. 31 Table 4-3 Removal efficiency rates for HSSF CW (Skrzypiec & Gajewska, 2017) Parameter Inflow Inflow CW Outflow CW Removal 1) COD 3633 1440 375 90 (74) BOD5 1593 585 137 91 (77) TSS 1531 421 236 75 (44) Norg 26.6 10.1 5.3 80 (48) Table 3 Key: 1) removal efficiency in % in parentheses (Skrzypiec & Gajewska, 2017) FOOD PROCESSING INDUSTRY: The table 4-4 shows removal efficiency for various components of a HSSF CW treating abattoir wastewater in the food processing industry according to (Skrzypiec & Gajewska, 2017). The reduction of fecal coliforms and total coliforms added up to 5.5 and 5.0 log units respectively according to the study. The average organic loads for COD, and BOD5 were 82 g∙m-2∙d-1 and 33 g∙m-2∙d-1 respectively, which are very high values. Table 4-4 Removal efficiency rates for HSSF CW (Skrzypiec & Gajewska, 2017) Parameter Inflow Inflow CW Outflow CW Removal 1) COD 3633 1440 375 90 (74) BOD5 1593 585 137 91 (77) TSS 1531 421 236 75 (44) Norg 26.6 10.1 5.3 80 (48) Table 4-4 Key: 1) removal efficiency in % in parentheses (Skrzypiec & Gajewska, 2017) 32 MILK AND CHEESE INDUSTRY – DAIRY WASTEWATER: For the dairy wastewater, At HLR varying from 1.28 to 4.27 cm∙d-1, the inflow concentrations of BOD5 and ammonia of 125 mg∙dm3 and 95 mg∙dm-3 were reduced to respective outflow concentrations of 7–11 mg∙dm-3 and 5– 54 mg∙dm-3 (Skrzypiec & Gajewska, 2017). The difference in decrease between BOD5 and ammonia levels proves that HLR levels prove influence ammonia removal more than BOD5 removal. FISH AND SEAFOOD PROCESSING: For the seafood industry case study, at HLR varying from 1.28 to 4.27 cm∙d-1, the inflow concentrations of BOD5 and ammonia of 125 mg∙dm-3 and 95 mg∙dm-3 were reduced to respective outflow concentrations of 7–11 mg∙dm-3 and 5– 54 mg∙dm-3 (Skrzypiec & Gajewska, 2017). The HLR had much greater influence on removal of ammonia than BOD5 (Skrzypiec & Gajewska, 2017). LAUNDRY: For the laundry industry At the HRT of 6.1 days the removal of BOD5, TSS, TN and TP amounted to 61%, 83%, 62% and 32%, respectively (Skrzypiec & Gajewska, 2017). Furthermore, it was observed that LAS removal was highly dependent on temperature and HLR. High levels of LAS oxidation were observed in shallow beds where the environment was more oxidized. 4.2.4. Phytoremediation of Heavy Metals from Industrial Effluent Using Constructed Wetland Technology The initial concentration of lead in the effluent was 2.984 ppm. In all the different plant based CWs there was no significant lead decrease. However, Eichhornia sp. recorded the highest lead uptake from the effluent while Pistia sp. recorded the lowest lead uptake and was therefore the least efficient (Sukumaran, 2013). Typha sp. had the highest BCF of 174.60 as shown in table 44. 33 Table 4-5 Uptake of lead from TTP effluent (Sukumaran, 2013) Conc. of lead in TTP effluent* Conc. of lead in plants (mg/g) BCF (ppm) Plants Initial Final Initial Final Typha sp Leaf 2.984±0.021 1.324±0.12* 0.006±0.002 0.521±0.023 174.60 Root 2.984±0.021 1.324±0.14* 0.021±0.006 0.624±0.031 209.12 Pistia sp Leaf 2.984±0.021 2.043±0.18 0.046±0.004 0.197±0.012 66.02 Root 2.984±0.021 2.043±0.13 0.012±0.002 0.276±0.014 92.49 Salvinia sp Leaf 2.984±0.021 1.964±0.19 0.013±0.001 0.186±0.011 62.33 Root 2.984±0.021 1.964±0.09 0.027±0.004 0.290±0.021 97.18 Eichhornia Sp Leaf 2.984±0.021 1.012±0.14 0.006±0.001 0.191±0.018 64.01 Root 2.984±0.021 1.012±0.11 0.008±0.002 0.211±0.016 70.71 * Values are mean of triplicates • Statistically significant at 0.05% level (Sukumaran, 2013) For arsenic, the initial amount in the effluent was 0.016 ppm. There was a considerable reduction of the metal after treatment. Salvinia sp. was the least efficient in removing arsenic (Sukumaran, 2013). The initial concentration of the plant leaf was 0.005mg/g which only increased to 0.010 mg/g. In the case of Salvinia sp. root, the initial concentration was 0.001mg/g, which then increased to 0.008 mg/g. Pistia sp. had the highest BCF factor of 1125. 34 Table 4-6 Uptake of arsenic from TTP effluent (Sukumaran, 2013) Plants Conc. of arsenic in TTP effluent* Conc. of arsenic in plants (mg/g) (ppm) Initial Final Initial Final BCF Typha sp Leaf 0.016±0.004 0.002±0.0003 0.002±0.001 0.021±0.007 1312.5 Root 0.016±0.004 0.002±0.0002 0.003±0.001 0.024±0.012 1500 Pistia sp Leaf 0.016±0.004 0.004±0.0002 0.006±0.002 0.014±0.021 875 Root 0.016±0.004 0.004±0.0003 0.001±0.001 0.018±0.020 1125 Salvinia sp Leaf 0.016±0.004 0.011±0.0004 0.005±0.002 0.010±0.019 625 Root 0.016±0.004 0.011±0.0003 0.001±0.002 0.008±0.018 500 Eichhornia Sp Leaf 0.016±0.004 0.005±0.0005 0.001±0.001 0.012±0.013 750 Root 0.016±0.004 0.005±0.0006 0.004±0.002 0.017±0.017 1062.5 * Values are mean of triplicates • Statistically significant at 0.05% level (Sukumaran, 2013) The amount of copper in TTP effluent was 0.096 ppm. Salvinia sp. concentrated significant amount of copper from TTP effluent of which the most efficient was Typha sp. based CWs. After 15 days of treatment, concentration of copper in Typha sp. leaf increased from 0.005 mg/g to 0.086 mg/g. The bio-concentration factor was 895.83. In case of Typha sp. root, the initial concentration was 0.031 mg/g, which increased to 0.101 mg/g and a BCF of 1052.08 which was the highest. 35 Table 4-7 Uptake of copper from TTP effluent (Sukumaran, 2013) Plants Conc. of 0.096±0.012copper in Conc. of copper in plants (mg/g) TTP effluent* (ppm) BCF Initial Final Initial Final Leaf 0.096±0.012 0.024±0.002* 0.005±0.001 0.086±0.009 895.83 Root 0.096±0.012 0.024±0.009* 0.031±0.008 0.101±0.011 1052.08 Pistia sp Leaf 0.096±0.012 0.028±0.012 0.002±0.001 0.064±0.016 666.67 Root 0.096±0.012 0.028±0.011 0.057±0.009 0.071±0.016 739.58 Salvinia sp Leaf 0.096±0.012 0.025±0.003* 0.068±0.008 0.083±0.009 864.58 Root 0.096±0.012 0.025±0.005* 0.123±0.023 0.072±0.014 750.00 Eichhornia Sp Leaf 0.096±0.012 0.062±0.004* 0.005±0.001 0.069±0.008 718.75 Root 0.096±0.012 0.062±0.005* 0.014±0.005 0.046±0.007 479.17 Typha sp * Values are mean of triplicates • Statistically significant at 0.05% level (Sukumaran, 2013) Cadmium concentration in TTP effluent was 0.253 ppm. CWs using Eichhornia sp., Typha sp. was very effective in removing the cadmium from the effluent, which was statistically significant (Sukumaran, 2013). Among these, Typha sp. based system was more effective and had the highest BCF of 185.77 for the root case. The initial leaf concentration was 0.001mg/g which increased to 0.027mg/g. The root had an initial concentration of 0.001mg/g which then increased to 0.047mg/g. The least efficient was Salvinia sp. based CWs. 36 Table 4-8 Uptake of cadmium from TTP effluent (Sukumaran, 2013) Plants Conc. of cadmium in TTP effluent* Conc. of cadmium in plants (mg/g) BCF (ppm) Initial Final Initial Final Typha Sp Leaf 0.253±0.019 0.102±0.015* 0.001±0.0002 0.027±0.005 106.72 Root 0.253±0.019 0.102±0.016* 0.001±0.0003 0.047±0.006 185.77 Pistia Sp Leaf 0.253±0.019 0.184±0.009 0.003±0.001 0.032±0.004 126.48 Root 0.253±0.019 0.184±0.007 0.004±0.002 0.02±0.005 79.05 Salvinia Sp Leaf 0.253±0.019 0.206±0.012 0.002±0.001 0.017±0.004 67.19 Root 0.253±0.019 0.206±0.014 0.003±0.001 0.021±0.007 83.00 Eichhornia Sp Leaf 0.253±0.019 0.132±0.009* 0.003±0.001 0.015±0.001 59.29 Root 0.253±0.019 0.132±0.008* 0.003±0.001 0.024±0.002 94.86 * Values are mean of triplicates • Statistically significant at 0.05% level (Sukumaran, 2013) Plants having BCF values over 1000 are generally considered a positive plant for phytoremediation and lead from TTP effluent was removed maximum by Eichhornia crassipes but all the other heavy metals/metalloid viz. copper, cadmium and arsenic was removed prominently by Typha latifolia (Sukumaran, 2013). Therefore, Typha latifolia can be considered as the best plant for the phytoremediation of the effluent. 4.2.5. Case Studies Of Wetland Filtration Of Mine Waste Water In Constructed And Naturally Occurring Systems In Northern Australia For the Ranger uranium mine, unpublished mining company data for these tests was interpreted as indicating attenuation of magnesium, sulfate and uranium; manganese was not reduced but appeared to have been mobilized from the soils. Attenuation was considerably greater for the first 37 test with the much greater retention time. Department of Mines and Energy data confirmed some attenuation of sulfate and magnesium but another source suggested that there was no attenuation of calcium and magnesium, but found that uranium and radium were adsorbed (Noller, Woods, & Ross, 1994). In Tom Gully’s mine, arsenic and all metals listed except manganese were reduced by over 90%. Manganese was reduced by 75%. The, concentrations of arsenic, iron, cobalt, nickel, copper, lead and uranium at the downstream site in the creek fell to levels equivalent or less than upstream values, although manganese and zinc were apparently higher, despite the efficient removal of zinc (Noller, Woods, & Ross, 1994). Table 4-9 Concentrations of selected trace elements in waters at and nearby Tom's Gully gold mine N.T (Noller, Woods, & Ross, 1994) Mn Fe Co Ni Cu Zn Pb U Mt. Bundey Ck 3 upstream (2km) 46 210 0.5 <5 4 6 0.8 0.1 Dewatering 39 bore discharge to billabong 1500 4100 6 23 2 240 2 0.2 Adit discharge 96 to billabong 1100 2000 21 81 23 1800 15 3 Average discharge 1300 3050 14 52 13 1000 9 1.6 Mt. Bundey Ck <1 downstream (2km) 330 <50 0.8 <5 0.5 23 0.5 <0.05 Percent reduction 75 >98 94 >90 96 98 94 >97 Sites/Trace As elements (µg/l) 68 >99 38 In the Woodcutter’s mine, arsenic shows an absolute decrease but is effectively conservative. Copper fell in absolute terms but increased relative to sulfate; however, all values are low. Iron on the other hand shows both absolute and relative increases, while aluminum and silica were relatively constant in absolute terms (Noller, Woods, & Ross, 1994). These constituents have abundant sources in local soils. Chromium was at the detection limit in all samples. The initial dewatering bores produced 36 ml/d of water which was a good quality and was discharged directly into Woodcutter’s Creek. However, the increased mining activities have reduced dewatering to 10ml/d which is excess of requirements. Woolwonga mine is yet to be investigated concerning the effects of the natural occurring wetlands on improvement of water quality. 4.3. Treatment of Effluents with Insignificant Or No Amounts Of Heavy Toxic Metals 4.3.1. Constructed Wetlands in the Treatment of Agro-Industrial Wastewater: A Review The efficiency of removal in FWS CWs show a wide range of variations, ranging from 3 to 98% for organic matter, from 26 to 96% for TKN, from 8 to 92% for TP, and from 26 to 99% for TSS, depending on the HRT applied and the metrological conditions (Sultana , Akratos, Vayenas, & Pavlou, 2015). In most of the projects, higher performance in removal efficiency was observed the pollutant load was low. The FWS CWs were not highly effective when pollutant loads exceeded 20000 mg/l because anoxic or anaerobic conditions are formed in the water column. The 39 phenomenon in turn greatly reduces the amount of oxygen available for microbial organic matter oxidization (Sultana, Akratos, Vayenas, & Pavlou, 2015). Additionally, when low HRTs of 4-15 days are used, the wetlands record very low removal efficiencies of between 40-60%. On the other hand, when HRTs of above 60 days are used, higher removal rates are recorded. The percentage performance of removal for HSF CWs is similar in range with FWS CWs. The study recorded from 28 to 99% for organic matter, 10 to 99% for TKN, 2 to 99% for TP, and from 76 to 99% for TSS all depending on the metrological conditions and the HRTs applied (Sultana, Akratos, Vayenas, & Pavlou, 2015). Similar to FWS CWs, the load of pollutants is best treated when low. However, HRTs are more efficient with HRTs of below 60 days as opposed to FWS CWs which need a higher number of HRT days to be more efficient. VF CWs record a high efficient rate of removal ranging from 24 to 95% for organic matter, 10 to 99% for TKN, 47 to 95% for TP, and from 21 to 99% for TSS (Sultana, Akratos, Vayenas, & Pavlou, 2015). TSS however has the ability to clog porous media hence damaging the system and so it should be paid attention to. Moreover, extremely high pollutant loads are not the best for VF systems because they can lead to anoxic or anaerobic conditions in the water. The highest removal rate recorded among the four CW designs tested is the hybrid CW with removal rates of 83 to 96% for organic matter, 55 to 92% for TKN, 52 to 96% for TP, and 83 to 99% for TSS (Sultana , Akratos, Vayenas, & Pavlou, 2015) making it the most efficient for agroindustrial treatment of wastewater. 40 4.3.2. Design of Horizontal and Vertical Subsurface Flow Constructed Wetlands Treating Industrial Wastewater The winery wastewater requires lower flow rate to reach the discharge limits because of its higher loading. Moreover, TP is the parameter that limits stricter the flow rate. Because of this fact, the main part of the wetlands was designed only for nitrogen and COD removal. For the TP removal, an interchangeable module of a material with high potential of phosphate precipitation can be used. Regarding the maximum value of the organic loading in the VSSF CW, the maximum flow rates were 12.9 and 1 m3 d-1 for urban and winery wastewater treatment, respectively (Mena, Rodriguez, Nunez, Fernandez, & Villasenor, 2008). Despite this recommendation, many experiments successfully treated wastewater with higher organic loading (up to 75 g BOD5 m-2 d-1). Table 4-10 Maximum flow rates (m3 d-1) to obtain an effluent suitable for the discharge for each wastewater attending to different pollutant discharge (Mena, Rodriguez , Nunez, Fernandez, & Villasenor, 2008). Urban Winery COD 134.6 62.0 TN 24.6 19.7 TP 8.5 6.6 HSSF CW had a faster removal of COD than the VSSF one. However, the value of VSSF removal rate was higher than that of the HSSF one. This is because the HSSF has higher area and hydraulic 41 residence time. In the VSSF CWs, the main part of the Norg was hydrolyzed forming N-NH4 + (Mena, Rodriguez, Nunez, Fernandez, & Villasenor, 2008). As a consequence, a slight increase of its concentration was observed in the VSSF CW 1. At the same time, the N-NH4 + was being nitrified, increasing the N-NO3 - concentration considerably. The entire formed N-NO3 - was removed in the HSSF CW by denitrification, which was the only mechanism that eliminated TN from the CW. For the TP removal, a similar behavior was observed. A faster removal in the HSSF CW was obtained because of its higher hydraulic residence time (Mena, Rodriguez, Nunez, Fernandez, & Villasenor, 2008). 4.3.3. Treatment of Industrial Wastewater with Two-Stage Constructed Wetlands Planted with Typha latifolia and Phragmites australis Using a HLR of 18cm d-1 the numbers of shoots for UT1 was 23, UT2 and UP2 was 13. For UP1, the shoots were already well established at a number of 400 at the beginning of the operation and remained proliferated at the end of the experiment. By day 92, the second feeding period, UT1 had 27 shoots, UT2 had 15 shoots, and UP2 had 21. By day 765 which was the third feeding period, UT1 had 52 shoots, UT2 had 62 shoots, and UP2 had 201. Finally, on day 928 at the end of the experiment, UT1 had 56, UT2 had 65, and UP2 had 305. Shoot counting in each zone (A, B, C, D) within every cell bed revealed that shoot numbers were lower at the entrance point as compared to the outlet point. The animal species found in UT1 and UT2 include snails, aphids, and other plant insects. UP1 and UP2 were observed to have millipedes. In addition, garden spiders and leaf hoppers were observed in both series. 42 There were no big differences in the removal of TKN, COD, BOD, NH3 and SO4 3-. The average pH for inlet of the CW ranged between 6.36 and7.82. The average pH for the outlet ranged between 7.82 and 8.27. According to (Calheiros, Rangel, & Castro, 2009) series UT and UP presented an overall COD and BOD5 removal efficiency of 79 ± 2% (for an inlet varying between 808 and 2449mg L-1) and 71 ±2% (for an inlet varying between 420 and 1000 mgL-1), respectively, reaching in some stages removal levels of up to 92% for COD and 88% for BOD5. Each series presented a TSS removal efficiency of 89 ± 1% (for an inlet varying between 32 and 324mg L-1), reaching levels of up to 97% in some occasions, with no clogging tendency occurring (Calheiros, Rangel, & Castro, 2009). It was observed that TKN removal efficiencies were lower, 55 ±1% for UT and 57 ± 1% for UP, considering an inlet varying between 87 and 160 mgL-1, reaching in some stages removal levels of up to 67% and the same was observed for NH3, for which average removals of 50 ± 1% for UT and 55 ±1% for UP were achieved considering an inlet varying be- tween 60 and 98 mg L-1, reaching in some stages higher removal levels, up to 69% (Calheiros, Rangel, & Castro, 2009). At the same time, (Calheiros, Rangel, & Castro, 2009) states that “The efficiency for color removal varying between 132 and 610 Pt/Co were 58 ± 4% for UT and 59 ± 4% for UP, reaching in some stages high removal levels – up to 90%. Each series presented a SO4 2- removal efficiency of 52 ± 2% (for an inlet varying between 78 and 2206 mgL1), reaching removal levels of up to 81%.” Additionally, the phosphorus and chromium (total and hexavalent) at the outlet and inlet points of the CWs were detected at low concentrations. The UP series was most successful in removal proving that Phragmites australis was the better choice of plant species. However, the T.latifolia species showed great resistance in terms of HLRs loaded in the system. The number of shoots at the inlet being lower than the other zones is because the organic load for the inlet was higher than the other areas, hence causing a higher level of 43 toxicity. Nevertheless, P.australis grows better and faster than the other plant species. The level of extraction and accumulation of chromium in P.australis in the leaves and roots is greater than that of T.latifolia. Phytotoxicity was not evident in the two plant species but their height as lower than that of the origin plants due to the toxicological load of the wastewater from the tannery. P.australis had higher chlorophyll content than T.latifolia which would explain the better performance of the former as compared to the latter. 4.3.4. Constructed Wetlands for Industrial Wastewater Treatment and Removal of Nutrients For the treatment of winery effluent, the influent temperature was on average 20.2 0C while the average influent temperature was 17.2 0C. The average influent pH was 6.41 while the average pH was 6.7 and while passing through the HSSF wetlands, the wastewater increased in pH by 0.5 units. VF unit reached high surface removal rates of up to 153 g COD/m2d and 107 g BOD5/m2/d while influent TSS levels to HSSF were generally low as they had been efficiently removed in the prior steps of the plant (HUSB reactor), therefore, SLR of suspended solids remained low (ranging from 0.5 to 5 g TSS/m2·d) and solids have been efficiently removed in HSSF units, which reached TSS effluent concentrations below 44 mg/L (17 mg/L on average) and TSS removal efficiencies of about 74% (Varga, et al., 2017). Influent COD and BOD5 were highly variable, ranging from 50 to 4000 mg COD/L and from 12 to 2400 mg BOD5/L. Variable concentrations of nitrogen and phosphorus compounds were present in the influent, because of touristic and restaurant component of the wastewater (Varga, et al., 2017). Influent TKN of VF CW was between 19 and 109 mg N/L (average of 52.9 mg N/L) and the VF effluent ranged from 11 to 63 mg N/L (average of 26 mg 44 N/L) while ammonium concentration ranged from 1 to 101 mg NH3/L in the VF influent (average of 28 mg NH3/L) and from 0.6 to 76 mg N/L (average of 19 mg NH3/L) in the VF effluent with an average removal of 32% (Varga , et al., 2017). This relatively low nitrification might be due to high organic load in the VF CW which primary consumed the oxygen present and subsequently reducing nitrification (Varga, et al., 2017). Phosphate in the VF influent ranged from 0.28 to 5 mg P/L (average of 2.3 mg P/L) and from 0.9 to 6.3 mg P/L (average of 2.4 mg P/L) in the VF effluent while HSSF effluent concentrations of TKN, ammonia and phosphate ranged from 12 to 52 mg N/L, from 2 to 52 mg and from 0.3 to 6 (average of 1.9 m/L), respectively (Varga, et al., 2017). Removal of nitrogen compounds and phosphate in HSSF units was reduced, ranging from 6 to 29% on average (Varga, et al., 2017). Limited data indicates that polyphenols removal averaged 39% in HSSF units. The full-scale hybrid CW system successfully treated winery wastewater (Varga, et al., 2017). Surface removal rates up 41 g COD/m2·d, 25 gBOD5/m2·d and 4.4 g TSS/m2·d were reached by the overall (VF + HF) system (Varga , et al., 2017). Overall percentage removals ranged from 54% to 93% of COD, 45% to 95% of BOD5 and 75% to 94% of TSS and the overall system also removed up to 1.4 gTKN/m2·d (52%), 0.7 gNH3/m2·d and 0.04 g PO43-/ m2·d (17%) (Varga , et al., 2017). 45 Table 4-11 Pollutant concentrations at the different sampling points during campaign 3 (mg/L). Concentrations are presented in average. BDL: Below detection limit (Varga , et al., 2017) TSS COD BOD5 NH4+ TN TP Inlet 117 5268 4167 250 382 25.1 After HUSB 25.2 2055 1383 197 201 18.2 aerated 22.6 211 44 5.2 11 5.2 After aerated 33.6 HSSF 156 6 0.12 9 4.0 After tobermorite 156 6 0.14 11 2.2 Sampling Point Aerated Train After VF 33.8 Conventional Train After VF 86.5 1774 3 0.10 42 2.9 After HSSF 101.7 82 2 BDL 40 1.2 After polonite 102.7 61 2 0.7 45 0.5 4.3.5. Surface-flow wetland for water reclamation at Batamindo Industrial Park The initial number of water hyacinth units in the CW was 30 which increased to 680 in 36 days. The plant growth can be attributed to the nutrients found in the STP effluent without any external nutritional sources. Plant growth did not increase much after 29 days due to saturation of the bed. The plants were however visually observed to be submerged and withered. 46 The pH of the water generally remained neutral but showed a spike to 10 during plant growth which stabilized after the plants had reached saturation. TSS and turbidity were lowered and maintained at a minimum level (Salim, Rachmania, & Dewi, 2017). For the DO level, the wetland can improve and stabilize the DO concentration from one as low as 2 mg/L up to around 5-6 mg/L however there was a spike in concentration during plant growth before saturation (Salim, Rachmania, & Dewi, 2017). The decrease of HRT or the increase of influent flow rate did not reduce the water quality in terms of pH, DO, TSS and turbidity. With a lower HRT or a higher flow rate, the treatment capacity of the wetland is increased, meaning that smaller wetland area is necessary to treat certain amount of wastewater, or in other words, larger amount of wastewater can be treated using a certain area of wetland (Salim, Rachmania, & Dewi, 2017). Water quality of wetland effluent was improved considerably where BOD were lowered significantly from 48 mg/L to a range of 5-10 mg/L while COD were lowered from 112 mg/L to a range of 11-34 mg/L and the wetland could also suppress the number of pathogenic microorganisms as shown by the minimization of the number of Escherichia coli and Total Coliform (Salim, Rachmania, & Dewi, 2017). 4.4. Comparison and Summary Two case studies with similar research parameters are “Industrial Wastewater Treatment using Reed bed Constructed Wetland” (study 1) and “Phytoremediation of Heavy Metals from Industrial Effluent Using Constructed Wetland Technology” (study 2). Both cases are concerned with 47 studying the removal of heavy metals from industrial wastewater using plant species as the main component for removal. The studies analyze the ability of plant species to absorb heavy metals in their leaves and roots hence improving the effluent’s water quality. Study 1 uses the plant species Phragmites karka while study 2 uses a range of species, the most effective being Typha sp. for the treatment and removal of cadmium, copper, and arsenic. According to table 1, the removal efficiency rate for cadmium is 37.2% while that for study 2 is 4.6%. It is important to know that the study 1 sample was taken from water while the study 2 sample was taken from soil or substrate therefore there will be a difference. However, with that being said, assuming all variables are constant, Phragmites karka is the more suitable plant species for removal of heavy metals through absorption by the plant species because its removal rates are higher than those of Typha sp. Another similar case study that can be compared with “Industrial Wastewater Treatment using Reed bed Constructed Wetland (study 1)” and “Phytoremediation of Heavy Metals from Industrial Effluent Using Constructed Wetland Technology (study 2)” is “Treatment of Industrial Wastewater with Two-Stage Constructed Wetlands Planted with Typha latifolia and Phragmites australis (study 3).” Study 3 falls under the category of CWs that have insignificant or no heavy metals. However, the study is worthy of comparison because it employs similar treatment methodology to study 1 and study 2. The plant species used in study 3 are Phragmites australis and Typha latifolia. Study 1 uses Phragmite karka which is in the same genus as Phragmites australis in study 3. In addition, study 3 uses Typha latifolia which is also in the same species as Typha sp. in study 2 which shares the same genus. From the results observed in study 3 the removal efficiency rates of Phragmites australis are higher than those of Typha latifolia meaning that the former is more effective. P.asutralis was considered the better choice because it had higher removal efficiency rates than T.latifolia. It also recorded better and faster growth in the reed bed. 48 P. australis had a higher level of chromium absorption in its leaves as compared to T.latifolia. Moreover, P.australis had a higher chlorophyll content which explains the better performance of the species. Overall, wetland plants within the genus Phragmites are more suitable for reed bed vegetation due to their outstanding performance as compared to the genus Typha. A comparison between table 4-1 under “Industrial Wastewater Treatment using Reed bed Constructed Wetland” and table 4-8 under “Case Studies of Wetland Filtration of Mine Waste Water in Constructed and Naturally Occurring Systems in Northern Australia” can be done regarding the removal efficiencies of the CWs for various heavy metals. Table 4-1 shows removal efficiencies for both a planted and unplanted reed bed but for the purpose of uniformity in comparison, only the results of the planted reed bed are used. In addition, only the results for common metals in both tables are compared. For table 4-1, the removal efficiency of zinc is 55.1 % while for table 8 it is 98%. For nickel, table 1 shows a removal efficiency of 38.4% while table 8 shows >90%. Manganese in table 4-1 is removed by 38.1% while in table 8 it is removed by 75%. Lead is removed by 61.5% in table 1 and by 94% in table 4-8. In general, table 4-8 shows higher removal rates for all the heavy metals compares than table 4-1. The plant species used for table 4-1 is Phragmites karka while the plant species used for table 4-8 is Typha spp as the dominant species. Unlike previous comparisons, it is evident in this case that Typha produces better results than Phragmites due to the higher removal rates shown in table 4-8. It is however important to consider that the case study represented in table 4-8 is a semi-constructed wetland meaning that part of it is natural while that represented by table 4-1 is fully constructed. The higher removal rates in table 4-8 can therefore be attributed to the dissimilarity of features of 49 the CWs being compared. It could be that the fully constructed wetland may lack some important features found in the semi-constructed wetland that can only be naturally found and are crucial to the removal of heavy metals. Table 4-2 and table 4-3, both under “The Use of Constructed Wetlands for the Treatment of Industrial Wastewater” can also be compared since their respective studies are similar in the essence that they aim to remove chemical and physiological components such as COD, BOD5, TSS and nitrogen. The tables are shown below: The systems are however different in design seeing as that table 4-2 represents a HF-VF system while table 4-3 represents a HSSF system. TSS removal in table 4-2 is at 87% efficiency while table 4-3 is at 44% efficiency. COD removal efficiency for table 4-2 is 71% while for table 4-3 is 74%. BOD5 removal in table 4-2 is 70% while table 4-3 is 77%. According to these result comparisons, it can be concluded that the hybrid system is far more efficient and the removal of TSS than the HSSF system. For COD, the difference between the two systems is not too significant but the HSSF system proves to be more efficient. Similarly, the HSSF system proves more efficient in the removal of BOD5 by recording a difference of 7%. The HSSF system is therefore more efficient in the removal of organics and can be applied when the target is the same. The hybrid system is more efficient at removal of suspended solids and can be applied when the major target is the same. 50 Chapter 5 CONCLUSION From the case studies reported on above, there are a number of factors to be considered when choosing the design and type of CW suitable and appropriate for a given area. Parameters such as plant type and flow type along with type of effluent (wastewater components) are the main factors to be considered when designing a CW. When choosing the plant species for the CW, it is required that considerations are made as to the availability of the plant in the given area and the effectiveness of the plant for treatment performance. Plant availability in the area ensures that the plant will have successful growth rates after transplanting. Sometimes, acclimatization is required before transplanting the wetland vegetation into the CW. The efficiency removal rates of the plant should also be considered especially in light of the components found in the wastewater. Some species are very successful at removing toxic metals from wastewater while others may just succumb to toxicity from the wastewater or have poor growth rates as compared to others due to the toxicity. The type of CW design is also very crucial for determining the success rates for the whole CW project. Some effluents respond well to horizontal flows while others to vertical flows and others to hybrid flow designs. In addition, it is essential to determine whether the wastewater require prior treatment before being directed into the CW. Some effluents may contain high amounts of suspended solids that clog the substrate in the CW hence causing poor removal efficiencies. Apart from the flow type and plant species, the components in the wastewater should be determined to know which design to use. Some effluents may contain very high amounts of 51 toxic metals while others may not and therefore it is important to test effluents before treatment so as not to waste resources employing complex CW designs when the effluent is very easy to treat. According to the research findings, the best case study in the report is “Phytoremediation of Heavy Metals from Industrial Effluent Using Constructed Wetland Technology” because it answers an often answered question regarding which plant species should be chosen when constructing a wetland. Plant species, as discussed, is an important factor to consider when designing a wetland since plants play a major role in pollutant removal. The study measures the capacity for different plant species to remove heavy metals from industrial effluent by measuring the mass flows and concentrations of the heavy metals in the influent and the effluent. According to the researchers, Eichhornia sp. was the best in lead removal; Salvinia sp was the most efficient for arsenic removal; Typha sp. had the highest copper and cadmium removals. Overall, Typha sp. was proved to be the most efficient. It had the highest BCF of 174.60 lead , 1312.5 arsenic ,1052.08 copper and 185.77 cadmium Summarily, the case studies above have proven the efficiency of constructed wetlands in treating wastewater and improving its quality for rehabilitation back to the natural environment. However, care should be taken to determine all necessary parameters to avoid wasting resources to an ineffective system. With the increased industrialization taking place, developed and developing countries should adopt this type of treatment since it is the least intrusive to the ecosystem and promoted biodiversity. When all parameters are determined correctly, CWs will be the leading technology for wastewater rehabilitation. 52 Chapter 6 Recommendations and future work Prior to the construction of any CW, it is important to first determine the most suitable plant species to use since the report has established that plant species is one of the most essential factors when it comes to wastewater treatment. In addition, it is also essential to find a suitable CW design for the area and its population. Hybrid systems containing both VF and HF structure are proving to be more effective than independent VF or HF CWs. Pre-treatment of the wastewater should depend on the type of industry it comes from and serves the purpose of removing too many suspended solids that may cause the clogging of porous media. It is recommended that before the implementation of full-scale projects, project officials should invest in pilot-scale and bench-scale experiments. This allows them to determine the suitability of chosen parameters while at the same time gauging the efficiency rates of the system. Even though previous studies such as this, have established some ground rules for CW construction, each environment is unique and so what works in one place might not work for the other. Hence, the purpose of implementing an experimental scale project first. The following recommendations can be made for future works:  It is recommended that studies include information about whether the CW beds should be sealed using liners such as geotextiles, impermeable clay, or rubber in order to prevent the layer from being damaged by penetration of the roots of plant species or substrate media. 53  Another recommendation is that studies discuss the distribution system design in terms of which type of pipes to use (PVC or other materials) and what dimensions of size and distance should be used to place them in the filter layer.  Insulation of CW beds can be discussed as a recommendation. The material to be used to insulate, whether natural or artificial the CW beds is important because insulation keeps the wastewater being treated warm hence maintaining the optimal temperature for maximum functioning of microorganisms. Apart from using the plants to for insulation, other types of insulation such as yard waste compost and reed-sedge peat are viable options.  Details about effluent recirculation to be provided in terms of its purpose and its application if applicable to the study.  It is recommended that studies provide more detail about aspect ratio of the bed’s length and width and as well more details about bottom slope. 54 References Calheiros, C., Rangel, A., & Castro, P. (2007). Constructed wetland systems vegetated with different plants applied to the treatment of tannery wastewater. Water research, 41(8), 1790-1798. Díaz, F., Anthony, T., & Dahlgre, R. (2012). Agricultural pollutant removal by constructed wetlands: Implications for water management and design. Agricultural Water Management, 104, 171-183. Healy, M., Rodgers, M., & Mulqueen, J. (2007). Treatment of dairy wastewater using constructed wetlands and intermittent sand filters. Bioresource technology, 98(12), 22682281. Imfeld, G., Braeckevelt, M., Kuschk, P., & Richnow, H. (2009). Monitoring and assessing processes of organic chemicals removal in constructed wetlands. Chemosphere, 74(3), 349-362. Vymazal, J. (2010). Constructed wetlands for wastewater treatment: five decades of experience. Environmental science & technology, 45(1), 61-69. Crawford, G., & Sandino, J. (2010). Energy efficiency in wastewater treatment in North America: a compendium of best practices and case studies of novel approaches. Water Environment Research Foundation. Jhansi, S. C., & Mishra, S. K. (2013). Wastewater treatment and reuse: Sustainability options. Consilience: The Journal of Sustainable Development, 10(1), 1-15. 55 Nelson, J., Bishay, F., Van Roodselaar, A., Ikonomou, M., & Law, F. C. (2007). The use of in vitro bioassays to quantify endocrine disrupting chemicals in municipal wastewater treatment plant effluents. The science of the Total Environment, 374(1), 80-90. Postel, S. L. (2000). Entering an era of water scarcity: the challenges ahead. Ecological Applications, 10(4), 941-948. Praewa Wongburi (2017). Sustainable Wastewater Treatment for Thailand. Retrieved March 17, 2018, from https://minds.wisconsin.edu/bitstream/handle/.../MS_Thesis_Wongburi_Praewa.pdf?... Secretariat, R. (2014). Renewables 2014 global status report. REN21, Paris, Tech. Rep. Vymazal, J., & Kröpfelová, L. (2008). Types of constructed wetlands for wastewater treatment. Wastewater Treatment in Constructed Wetlands with Horizontal Sub-Surface Flow, 121-202. Wetzel, R. G. (1993). Micro-communities and micro-gradients: linking nutrient regeneration, microbial mutualism, and high sustained aquatic primary production. Netherland Journal of Aquatic Ecology, 27(1), 3-9. Calheiros, C. S., Rangel, A. O., & Castro, P. M. (2009). Treatment of industrial wastewater with two-stage constructed wetlands planted with Typha latifolia and Phragmites australis. Bioresource Technology, 3205-3213. Chukwunonye, E., Reyes, C. A., & Gutiérrez, J. F. (2015). Constructed Wetland Systems as a Methodology for the Treatment of Wastewater in Bucaramanga Industrial Park. Journal of Geoscience and Environment Protection, 1-14. Guittonny-Philippe, A., Masotti, V., Hohener, P., Boudenne, J.-L., Viglione, J., & LaffontSchwob, I. (2014). Constructed Wetlands to Reduce Metal Pollution from Industrial 56 Catchments in Aquatic Mediterranean Ecosystems: A Review to Overcome Obstacles and Suggest Potential Solutions. Environment International, 1-14. Lehman, R. W., Rodgers, J. H., Murray-Gulde, C., Gladden, J. B., Mooney, F. D., & Bell, J. F. (n.d.). Wetlands For Industrial Wastewater Treatment At The Savannah River Site. Springfield: US Department of Commerce. Mena, J., Rodriguez, L., Nunez, J., Fernandez, F. J., & Villasenor, J. (2008). Design of horizontal and vertical subsurface flow constructed wetlands treating industrial wastewater. WIT Transactions on Ecology and the Environment, 555-563. Noller, B. N., Woods, P. H., & Ross, B. J. (1994). Case Studies of Wetland Filtration of Mine Wastewater in Constructed and Naturally Occurring Systems in Northern Australia. Wal. Sci. Tech, 257-265. Salim, C., Rachmania, A., & Dewi, R. (2017). Surface-flow wetland for water reclamation at Batamindo Industrial Park. MATEC Web of Conferences, 1-5. Sangola, T. M., Aribisala, J. O., & Awopetu, M. S. (2015). Industrial Wastewater Treatment using Reed bed Constructed Wetland. International Journal of Engineering Research and Technology (IJERT), 208-212. Skrzypiec, K., & Gajewska, M. H. (2017). The use of constructed wetlands for the treatment of industrial wastewater. Journal of Water and Land Development, 233-240. Sukumaran, D. (2013). Phytoremediation of Heavy Metals from Industrial Effluent Using Constructed Wetland Technology. Applied Ecology and Environmental Sciences,, 92-97. 57 Sultana, M.-Y., Akratos, C. S., Vayenas, D. V., & Pavlou, S. (2015). Constructed wetlands in the treatment of agro-industrial wastewater: A review. Hem. Ind, 127-142. Varga, D. d., Soto, M., Arias, C. A., Oirschot, D. v., Kilian, R., Pascual, A., & Alvarez, J. A. (2017). Constructed Wetlands for Industrial Wastewater Treatment and Removal of Nutrients. IGI Global book series: Advances in Environmental Engineering and Green Technologies, 202-226. 58
ENG 4 133 Bachelor Thesis German University of Technology in Oman (GUtech) Department of Engineering ASSESMENT AND REVIEW OF CONSTRUCTED WETLAND FOR DOMESTIC WASTEWATER: SELECTED CASE STUDIES Course Coordinator: Dr.-Ing. Najah Al Mhanna Project Supervisor: Main supervisor: Dr.Hind Bargash Student Name: Nujoom Hamdan Al Amri Spring 2018 Approval of the Dean of the Faculty of Engineering and Computer Science Dr.-Ing. Najah Al Mhanna I certify that this Thesis satisfies the requirements of a Bachelors Thesis for the Degree of Bachelor of Engineering in Environmental Engineering. Dr.-Ing. Najah Al Mhanna Head, Department of Engineering I certify that I have read this Thesis and that it is my opinion that the Thesis is fully adequate in scope and quality as a Bachelors Thesis for the Degree of Bachelor of Environmental Engineering. Name Supervisor Examining Committee 1. Name 2. Name i Declaration: In accordance with the requirements of the degree of Bachelor of Engineering at German University of Technology in Oman, I present the following thesis titled “Assessment and review of constructed wetland for domestic wastewater: selected case studies”. This work was performed under the supervision of Dr. Hind Barghash. I hereby declare that the work submitted in this thesis is my own and based on the results found solely by myself. Materials of work found by other researchers are clearly cited and listed in reference list. This thesis, neither in whole nor in part, has been previously submitted for any degree. The author confirms that the library may lend or copy this thesis upon request, for academic purposes. Name: Nujoom Hamdan Alamri Signature: ii ABSTRACT Domestic wastewater from single-family households of up to 30 PEs can be managed by the installation of a sizeable wastewater system, based on CWs, which are highly flexible. Different design strategies of CWs can be applied, including VF, HF and hybrid designs with flow variations. This report explains the methodologies used in various case studies of domestic CWs, and summarises the data found that will allow for sensible discussions and conclusions to be made concerning the effectiveness of single-household CW systems, in terms of design strategy and removal efficiency rate. The most common physiological and chemical components required to be removed from domestic wastewater are FCs, TCs, TSSs, TN, TP, TKN, COD, BOD5, bacteria and ammonia. The highest removal efficiencies among all studies were observed as follows ; 99.4% BOD, 98.9% COD, 99.8% TSS, 99.99%coliforms, 98%Ammonium-nitrogen (NH4+-N), 99.6% Ammonia-nitrogen (NH3—N), 90.4% TN, 99.1% TP, 97.9% turbidity, 99.86% detergent, 99.2% MRP , 98.1% Oil and Grease (O&G), and 98% viable helminth ova (VHO) .Domestic CWs are important, not only because they improve water quality, but also because they improve the chances of treated effluent being reused, especially when there is no way of releasing it back into the environment. Such treated effluent can be used to irrigate nursery beds, flower beds, or even gardens around the household. Single-household CWs allow people to individually contribute to cleaning and conserving their own environment by providing a lowcost, low-maintenance, easy-to-operate, highly-effective sewage treatment system. Individual conservation efforts, if embraced, can greatly contribute to solving one of the world’s greatest problems, which is pollution. i Keywords: constructed wetlands (CWs), domestic wastewater, single-household system, subsurface flow, macrophytes ii ‫انخالصت‬ ‫‪ًٚ‬كٍ إداسة ي‪ٛ‬بِ انًجبس٘ يٍ االسخخذايبث انًُضن‪ٛ‬ت يٍ يُبصل األسش انخ‪ ٙ‬حصم إنٗ ‪ 03‬يعبدل سكبَ‪ ٙ‬يٍ خالل حشك‪ٛ‬ب َظبو‬ ‫صشف ي‪ٛ‬بِ ضخى ٔانخ‪ ٙ‬حزبج يشَٔت األساض‪ ٙ‬انشطبت (األْٕاس) انخ‪ٚ ٙ‬خى اَشبؤْب يًب ‪ًٚ‬كُٓب يٍ خذيت أ٘ عذد يٍ انسكبٌ‪.‬‬ ‫‪ًٚ‬كٍ حطب‪ٛ‬ق حصبي‪ٛ‬ى يخخهفت نألساض‪ ٙ‬انشطبت انًُشأة ٔانخ‪ ٙ‬حخضًٍ انخذفق انشأس‪ٔ ٙ‬انخذفق األفق‪ٔ ٙ‬انخصبي‪ٛ‬ى انٓج‪ُٛ‬ت يع‬ ‫يخغ‪ٛ‬شاث انخذفق‪ٚ .‬ششح انخقش‪ٚ‬ش انًُٓج‪ٛ‬بث انًسخخذيت ف‪ ٙ‬كز‪ٛ‬ش يٍ دساسبث انذبنت نًُشئبث األساض‪ ٙ‬انشطبت انًُضن‪ٛ‬ت ٔ‪ٚ‬عشض‬ ‫ببسخفبضت انب‪ٛ‬بَبث نخأس‪ٛ‬س يُبقشبث راث جذٖٔ عه‪ٓٛ‬ب ٔانخٕصم السخُخبجبث دٕل فعبن‪ٛ‬ت ٔكفبءة َظبو يُشأة األساض‪ ٙ‬انشطبت‬ ‫انفشد‪ٚ‬ت ف‪ًٛ‬ب ‪ٚ‬خعهق بخصً‪ٛ‬ى االسخشاح‪ٛ‬ج‪ٛ‬ت ٔيعذل اإلصانت‪ .‬حخضًٍ انعُبصش انكً‪ٛ‬بئ‪ٛ‬ت ٔانذ‪ٕٚٛ‬ت انخ‪ٚ ٙ‬خع‪ ٍٛ‬إصانخٓب يٍ ي‪ٛ‬بِ‬ ‫ا نًجبس٘ كم يٍ انقٕنَٕ‪ٛ‬بث انبشاص‪ٚ‬ت ٔانقٕنَٕ‪ٛ‬بث انكه‪ٛ‬ت ٔانًٕاد انصهبت انعبنقت انكه‪ٛ‬ت ٔانُ‪ٛ‬خشٔج‪ ٍٛ‬انكه‪ٔ ٔ ٙ‬انفسفٕسٔص انكه‪ٔ ٙ‬‬ ‫َخشٔج‪ ٍٛ‬ك‪ٛ‬هذال انكه‪ ٔ ٙ‬انطهب انب‪ٕٛ‬نٕج‪ ٙ‬انك‪ًٛٛ‬بئ‪ ٙ‬عهٗ األكسج‪ ٔ ٍٛ‬انطهب انب‪ٕٛ‬نٕج‪ ٙ‬انك‪ًٛٛ‬بئ‪ ٙ‬عهٗ األكسج‪ٔ ٍٛ‬انبكخش‪ٚ‬ب‬ ‫ٔاأليَٕ‪ٛ‬ب‪ .‬كبَج أعهٗ يعذالث اإلصانت انًسجهت عبش كبفت انذساسبث عهٗ انُذٕ انخبن‪ %...9:ٙ‬يٍ انطهب انب‪ٕٛ‬نٕج‪ ٙ‬انك‪ًٛٛ‬بئ‪ٙ‬‬ ‫عهٗ األكسج‪ %....ٔ ٍٛ‬يٍ انطهب انك‪ًٛٛ‬بئ‪ ٙ‬عهٗ األكسج‪ %.... ٔ ٍٛ‬يٍ انًٕاد انصهبت انعبنقت انكه‪ٛ‬ت ٔ‪ %.....‬يٍ‬ ‫انقٕنَٕ‪ٛ‬بث ٔ‪ %..‬يٍ َ‪ٛ‬خشٔج‪ ٍٛ‬األيَٕ‪ٕٛ‬و ٔ‪ %...9‬يٍ َ‪ٛ‬خشٔج‪ ٍٛ‬األيَٕ‪ٛ‬ب ٔ‪ %.3.9‬يٍ انُخشٔج‪ ٍٛ‬انكه‪ %...9ٔ ٙ‬يٍ‬ ‫انفسفٕسٔص انكه‪ %....ٔ ٙ‬يٍ انًٕاد انًعكشة ٔ‪ %....9‬يٍ يٕاد انخُظ‪ٛ‬ف ٔ‪ %...9‬يٕنب‪ٛ‬ذ انفٕسفٕس انخفبعه‪%...9ٔ ٙ‬‬ ‫يٍ انُفظ ٔانشذٕو ٔ ‪ %..‬يٍ انذ‪ٚ‬ذاٌ انطف‪ٛ‬ه‪ٛ‬ت‪.‬د‪ٛ‬ذ ال حقخصش أًْ‪ٛ‬ت األساض‪ ٙ‬انشطبت انًُشأة انًُضن‪ٛ‬ت عهٗ حذس‪ ٍٛ‬جٕدة‬ ‫ضب يٍ فشص يعبنجت ي‪ٛ‬بِ انًجبس٘ ٔيٍ رى إعبدة اسخخذايٓب ف‪ ٙ‬دبنت حعزس انٕس‪ٛ‬هت إلعبدة اطالقٓب ف‪ٙ‬‬ ‫انً‪ٛ‬بِ ٔنكُٓب حذسٍ أ‪ً ٚ‬‬ ‫انب‪ٛ‬ئت‪ًٚ .‬كٍ اسخخذاو انًخهفبث انسبئهت انًعبنجت نش٘ انًشبحم أٔ أدٕاض انضْٕس أٔ انذذائق انًُضن‪ٛ‬ت‪ًٚ .‬كٍ أٌ حخ‪ٛ‬خ يُشأة‬ ‫أساض‪ ٙ‬سطبت ٔادذة ن ألفشاد انًسبًْت عهٗ يسخٕٖ كم فشد يُٓى ف‪ ٙ‬حُظ‪ٛ‬ف انب‪ٛ‬ئت ٔدًب‪ٚ‬خٓب يٍ خالل حٕف‪ٛ‬ش َظبو نًعبنجت ي‪ٛ‬بِ‬ ‫انًجبس٘ ٔانز٘ ‪ٚ‬عًم بطش‪ٚ‬قت سٓهت ٔيُخفضت انخكبن‪ٛ‬ف ٔال حذخبس نعًه‪ٛ‬بث ص‪ٛ‬بَت يعقذة ٔحخًخع ف‪ ٙ‬انٕقج راحّ بًسخٕٖ عبل‬ ‫يٍ انكفبءة ٔانفعبن‪ٛ‬ت‪ .‬دش٘ ببنزكش أَّ ف‪ ٙ‬دبنت حبُ‪ ٙ‬ا نجٕٓد انفشد‪ٚ‬ت نهذفبظ عهٗ انب‪ٛ‬ئت فإٌ رنك يٍ شأَّ انًسبًْت انفبعهت ف‪ٙ‬‬ ‫دم ٔادذة يٍ أكبش انًشكالث ٔانخذذ‪ٚ‬بث انخ‪ ٙ‬حٕاجّ انعبنى أال ْٔ‪ ٙ‬يشكهت انخهٕد‪.‬‬ ‫الكلمات الداللية‪:‬يُشئبث األساض‪ ٙ‬انشطبت (األْٕاس) ‪،‬ي‪ٛ‬بِ انًجبس٘ ‪،‬يُضل ٔادذ ‪,‬انخذفق حذج انسطذ‪، ٙ‬يُضن‪َ ،ٙ‬ببحبث ذات‬ ‫أوراق كبيرة‪.‬‬ ‫‪iii‬‬ ACKNOWLEDGMENT I would like to express my sincere gratitude to my beloved supervisor Dr. Hind Bargash for her support guidance, motivation and patience. I could not have imagined having a better advisor and mentor for my Bachelor Thesis. Special Thanks to my parents Hamdan Al Amri, Nadia Al Amri, and my siblings whose prayers and support have encouraged me to work hard. May God give me the ability to make my family and Supervisor proud. Further, I acknowledge my sister Buraq and my group members of this project Hawra Al ajmi and Thuraiya Al busaidi for their care, support and advise throughout accomplishing this project. I would like to express my gratitude to almighty god for providing me knowledge and strength. iv TABLE OF CONTENTS ABSTRACT ..................................................................................................................................... i ACKNOWLEDGMENT................................................................................................................ iv LIST OF FIGURES ..................................................................................................................... viii LIST OF TABLES .......................................................................................................................... x LIST OF GRAPHS ....................................................................................................................... xii LIST OF ABBREVIATIONS ...................................................................................................... xiii INTRODUCTION .......................................................................................................................... 1 1.1. Background ........................................................................................................................................ 1 1.2. Limitations of CWs ............................................................................................................................ 3 1.3. Problem Statement ............................................................................................................................. 4 1.4. Aim and Objectives............................................................................................................................ 4 LITERATURE REVIEW ............................................................................................................... 5 2.1. Domestic, Municipal and Industrial Wastewater ............................................................................... 5 2.2. Conventional Wastewater Treatment ................................................................................................. 6 2.2.1. Primary Treatment ...................................................................................................................... 7 2.2.2. Secondary Treatment .................................................................................................................. 7 2.2.3. Tertiary Treatment ...................................................................................................................... 8 2.3. Constructed Wetlands (CWs)............................................................................................................. 9 v 2.4. Main Benefits and Outcomes of CWs................................................................................................ 9 2.5. Types of CWs .................................................................................................................................. 10 2.6. Components of CWs ........................................................................................................................ 10 2.6.1. Water ......................................................................................................................................... 10 2.6.2. Substrates, Sediments and Litter ............................................................................................... 11 2.6.3. Vegetation ................................................................................................................................. 12 2.6.4. Microorganisms ........................................................................................................................ 13 2.6.5. Animals ..................................................................................................................................... 13 2.7. Literature Summary ......................................................................................................................... 14 METHODOLOGY ....................................................................................................................... 15 3.1. Overview .......................................................................................................................................... 15 3.2. Methodologies.................................................................................................................................. 15 3.2.1. HSSF CWs for On-Site Wastewater Treatment ........................................................................ 15 3.2.2. Use of VF CWs for On-Site Treatment of Domestic Wastewater: New Danish Guidelines .... 18 3.2.3. The Attenuation Capacity of CWs to Treat Domestic Wastewater in Ireland .......................... 21 3.2.4. A Recirculating VF CW for the Treatment of Domestic Wastewater ...................................... 23 3.2.5. A Hybrid CW System for Decentralised Wastewater Treatment ............................................. 25 3.2.6. CW of Lepironia articulata for Household Greywater Treatment ........................................... 27 3.2.7. CW System for Wastewater Treatment..................................................................................... 29 3.2.8. Use of Macrophyte Plants, Sand and Gravel Materials in CWs for Greywater Treatment ...... 31 3.2.9. Integrated CWs for Treating Domestic Wastewater ................................................................. 31 3.2.10. Efficiency of Small CWs for Subsurface Treatment of Single-Family Domestic Effluent..... 35 3.2.11. Reed bed CW system .............................................................................................................. 36 RESULTS AND DISCUSSION ................................................................................................... 41 vi 4.1 Overview ........................................................................................................................................... 41 4.2. Results and Discussion .................................................................................................................... 41 4.2.1. HSSF CWs for On-Site Wastewater Treatment ........................................................................ 41 4.2.2. Use of VF CWs for On-Site Treatment of Domestic Wastewater: New Danish Guidelines .... 43 4.2.3. The Attenuation Capacity of CWs to Treat Domestic Wastewater in Ireland .......................... 45 4.2.4. A Recirculating VF CW for the Treatment of Domestic Wastewater ...................................... 48 4.2.5. A Hybrid CW System for Decentralised Wastewater Treatment ............................................. 52 4.2.6. CW of Lepironia articulata for Household Greywater Treatment ........................................... 55 4.2.7. CW System for Wastewater Treatment..................................................................................... 58 4.2.8. Use of Macrophyte Plants, Sand and Gravel Materials in CW for Greywater Treatment ........ 59 4.2.9. Integrated CWs for Treating Domestic Wastewater ................................................................. 61 4.2.10. Efficiency of Small CWs for Subsurface Treatment of Single-Family Domestic Effluent..... 62 4.2.11. Reed bed CW system .............................................................................................................. 67 4.3. Summary and Comparison ............................................................................................................... 70 CONCLUSION ............................................................................................................................. 72 RECOMMENDATIONS .............................................................................................................. 75 REFERENCES ............................................................................................................................. 76 vii LIST OF FIGURES Figure 3.1: Layout of a VF CW system for a single household. Raw sewage is pre-treated in a 2 m3 sedimentation tank. Firm sewage is pulse-loaded onto the shallow end of the bed by a level-controlled pump. Treated effluent is collected in a system of drainage pipes, and about half the effluent is recirculated back to the pumping well, or to the sedimentation tank (Brix & Arias, 2005) .................................................................. 21 Figure 3.2: Schematic representation of a pilot recirculating VF CW for the treatment of domestic wastewater. The upper container is a VF CW bed. Wastewater is applied to the root zone, trickles through the bed, and drips into the lower container, from where it is recirculated back to the root zone, until the required water quality is achieved (Sklarz, Gross, Yakirevich, & Soares, 2009) ............................................. 24 Figure 3.3: Hybrid CW schematics (Kinsley, Crolla, Rode, & Zytner, 2014) ............................. 27 Figure 3.4:Schematic diagram of a mini-CW system (Wurochekke, Harun, Mohamed, & Kassima, 2014) .......................................................................................................... 28 Figure 3.5: General layout of a single-household VF CW system (Farooqi, Basheer, & Chaudhari, 2008) ....................................................................................................... 30 Figure 3.6: Sketch showing groundwater and surface water monitoring, and inlet and outlet points, for the integrated CW in Glaslough, near Monaghan, Ireland (Scholz, 2011) ................................................................................................................................... 33 Figure 3.7: Sketch showing groundwater and surface water monitoring, and inlet and outlet points for the integrated CW system at Dunhill, near Waterford, Ireland (Scholz, 2011) .......................................................................................................................... 34 viii Figure 3.8: Typical three-cell design of a single-family domestic CW system (Steer, Fraser, & Boddy, 2002) ............................................................................................................. 36 Figure 3.9: Description of the process for treated effluent (Haya Water, 2017) .......................... 38 Figure 3.10: Stage A (Haya Water, 2017) .................................................................................... 39 Figure 3.11: Stage B (Haya Water, 2017)..................................................................................... 39 Figure 3.12: Photographs after both stages (Haya Water, 2017) .................................................. 40 Figure 4.1: Values of TSSs (a), COD (b) and BOD5 (c) in raw and treated domestic wastewater from planted and unplanted recirculating VF CWs using several RFRs (Sklarz, Gross, Yakirevich, & Soares, 2009) .......................................................................... 49 Figure 4.2: Changes in BOD5 with season and HLR (Q = 2.8 m3/d) (Kinsley, Crolla, Rode, & Zytner, 2014) ............................................................................................................. 53 Figure 4.3: TSSs with season and HLR (Q = 2.8 m3/d) (Kinsley, Crolla, Rode, & Zytner, 2014) ................................................................................................................................... 54 Figure 4.4: Percentage removal of greywater produced by household activities (Wurochekke, Harun, Mohamed, & Kassima, 2014)........................................................................ 56 ix LIST OF TABLES Table 3.1: RB1 and RB2 design characteristics (O'Luanaigh & Gill,nd) ..................................... 22 Table 3.2: RB1 and RB2 mean hydraulic parameters (O'Luanaigh & Gill, nd) ........................... 22 Table 3.3: Design criteria for a double-stage VF reed bed after pre-treatment (septic tank) (Haya Water, 2017) ............................................................................................................... 37 Table 4.1: Surface discharge limits (maximum concentrations) (OEPA, 2001; Hoddinott, 2006) ..................................................................................................................................... 41 Table 4.2: Performance data (mean±1 SD) for some single-household VF CWs (Brix & Arias, 2005) ........................................................................................................................... 44 Table 4.3: Average influent and effluent nitrogen loads from RB1 and RB2 ( O'Luanaigh & Gill, nd) ............................................................................................................................... 46 Table 4.4: Average influent and effluent E. coli concentrations from RB1 and RB2 (O'Luanaigh & Gill, nd) ................................................................................................................... 47 Table 4.5: Household water consumption in the case study (Wurochekke, Harun, Mohamed, & Kassima, 2014) ........................................................................................................... 55 Table 4.6: Analytical results of greywater loading before treatment (Wurochekke, Harun, Mohamed, & Kassima, 2014) ..................................................................................... 56 Table 4.7: Preliminary results of raw greywater in the morning and evening (Wurochekke, Harun, Mohamed, & Kassima, 2014) ......................................................................... 56 Table 4.8: Effectivenes of pollutant removal in CWs with natural substrates and local macrophytes (Qomariyah, Ramelan, Sobriyah, & Setyono, 2017)............................. 59 Table 4.9: System performance (Steer, Fraser, & Boddy, 2002) .................................................. 63 x Table 4.10: Wetland data base summary (Steer, Fraser, & Boddy, 2002) ................................... 67 Table 4.11: Data for the treatment of effluent by the reed bed system (Haya Water, 2017; Oman Government, 2018) ..................................................................................................... 68 xi LIST OF GRAPHS Graph 4.1: Relationship between treated effluent, the MECA standard and removal efficiency (Haya Water, 2017; Oman Government, 2018) .......................................................... 69 xii LIST OF ABBREVIATIONS BOD Biological oxygen demand COD Chemical oxygen demand CW Constructed wetland EPA Environmental protection agency FC Fecal coliform FWS Free water surface HF Horizontal flow HLR Hydraulic loading rate HRT Hydraulic retention time HSSF MECA Horizontal subsurface flow Ministry of the Environment and Climate Affairs MRP molybdate-reactive phosphorus PE Population equivalent RBC Rotating biological conductor RFR Recirculation flow rate xiii SSF Subsurface flow SF Surface flow TC Total coliform TE Treated effluent TKN Total Kjeldahl nitrogen TN Total nitrogen TP Total phosphorous TSS Total suspended solid VF Vertical flow xiv Chapter 1 INTRODUCTION 1.1. Background The most vital element that contributes to the creation and sustenance of a satisfactory and healthy life for living organisms is water. Water is a crucial element on planet Earth because it supports life. For this reason, it is wise for mankind to protect all water resources. Water pollution is a major environmental hazard, which poses a continuous threat to the environment in general, as well as to individual water bodies. To a large extent, exhaust fumes and industrial waste contribute to the pollution of water. The discharge of untreated industrial, domestic and municipal waste into water resources and onto land facilitates degradation of the environment, and places members of the public under threat of contracting health-related issues from polluted water (Postel, 2000). Public information on the need to preserve water resources should be enhanced, in order to try and curb the water pollution that results from municipal, industrial and domestic wastewater. If people are educated on the importance of protecting their own water resources, the majority of water pollution and environmental degradation can be avoided or minimised. Wastewater recycling via CW treatment systems is financially effective in populations that struggle with water scarcity. This strategy of conserving water benefits both society and the environment. 1 Sustainability is a concept that can be integrated into human activities, and human society in general (Praewa, 2017). When human activities become unsustainable, there are adverse effects on the ecosystem, which is crucial to the sustenance and support of human life. Modern approaches have been designed to integrate sustainability, environmental ethics and public effort to develop society-based projects. In most cases, both known and unknown substances are added to public water from its commercial, domestic and industrial use, and as a result of these additives, the public water ends up as municipal, domestic and industrial wastewater. Sustainable wetlands can be constructed for the treatment of wastewater from municipal, domestic and industrial sources. These allow for water reclamation and reuse in most of the sustainable water resource management programs across the globe (Praewa, 2017). CWs are engineered and managed wetland systems for wastewater treatment and reclamation that are receiving increasing global attention. Such systems involve a naturally-occurring pollutant-removal process, mediated by complex interactions between water, soil/gravel, vegetation and its associated microbial assemblages, and the environment to improve water quality in a sustainable way. CWs are designed to exploit the physical, chemical and biological treatment processes that naturally occur in wetlands, providing for reductions in organic matter, TSSs, nutrients, BOD, metals and pathogenic organisms. CWs are cost-effective and easily operated and maintained, and they have proven to be applicable for household, municipal and industrial wastewater treatment. 2 1.2. Limitations of CWs CW systems have limitations that can undermine their utilisation. They make use of larger pieces of land than other, conventional wastewater systems. In some cases, the economic implications of having to obtain a large enough tract of land for the installation of a CW can limit its availability to people who do not have money to buy more land; and so, in some case, the CW system is too expensive (Jhansi & Mishra , 2013). Since biological components in wastewater are generally sensitive to chemicals, then any water surges would undermine the effectiveness of CW water treatment. Whilst CWs are designed in such a way as to be able to be maintained using minimal amounts of water, they cannot survive in completely dry regions, or rather they are not engineered to survive under extreme environmental circumstances. Very cold weather conditions, and high temperatures that may result from dry spells and drought, can undermine, and limit the effectiveness, of CW systems. Conversely, heavy rains can also have a deleterious affect on CW systems, especially during the spring season. The system is also generally susceptible to changeable weather patterns, and again its effectiveness can be undermined (Crawford & Sandino, 2010). The use of CW systems for municipal, industrial and domestic wastewater treatment is a relatively new concept (Crawford & Sandino, 2010), and, for this reason, technologies that could be used to enhance their effectiveness have, as yet, been underdeveloped. Some ecological and environmental critiques have argued that more should be done to attain better effectiveness of such systems. 3 1.3. Problem Statement Many developing countries are faced with the challenge of industrial, municipal and domestic wastewater management, but have problems in finding effective and low-cost technologies. Wastewater management has the primary purpose of preventing the spread of disease and infection. Nutrients recovery, water reclamation, and reuse as well as conserving water resources are other wastewater management goals that most world organizations are trying to achieve. A shift from conventional wastewater management to a more sustainable system should, therefore, be globally embraced, so that water and environmental resources can be conserved (Praewa, 2017). Whilst effluent and other discharges that result in water pollution should be handled so as to avoid the spread of disease and infection to members of the public, there is also a risk of people contracting malaria from mosquitoes breeding in stagnant, polluted water bodies that must also be addressed (Praewa, 2017). 1.4. Aim and Objectives The aim of this study is to provide an assessment of the various types of CW wastewater treatment systems, through a review of their design for use in single households, and a discussion of their performance, in terms of onsite wastewater treatment, influent/effluent quality and the percentage removal of pollutants, and water reuse criteria. Several case studies are used as examples. 4 Chapter 2 LITERATURE REVIEW 2.1. Domestic, Municipal and Industrial Wastewater In this day and age, the issue of municipal, industrial and domestic wastewater is of great concern because it can cause severe environmental problems, and can also impact people in terms of their health. Studies have estimated that wastewater comprises 99% water, with the remaining 1% being a mixture of suspended and dissolved organic solids, detergents and chemicals (Secretariat, 2014). Sewage is wastewater that comprises household waste from toilets, sinks and showers/baths that is disposed of via sewers. Municipal wastewater includes input that ranges from, for example, shops, to restaurants and bars, and car washes (Secretariat, 2014). Frequently, pretreated industrial wastewater is included in with the municipal wastewater. A wide variety of processes result in the formation of industrial wastewater, including plastic manufacturing, wood pulping, petroleum refinement and food processing. According to Secretariat (2014), these different types of wastewater have varying compositions, containing, for instance, different pathogens, bacteria and nutrients. Untreated wastewater 5 components can be organised into three categories – physical, biological and chemical. Solid and inorganic constituents in wastewater comprise the physical components. The biological components are bacteria, viruses, protozoa and other pathogens. Lastly, the chemical components include dissolved materials and organic matter, as well as nutrients and metals, which, in most cases, are heavy metals. In rare cases, wastewater might contain reusable resources – for example, water, carbon and other nutrients – that could be recovered. For effective effluent regulatory standards to be met, wastewater needs to undergo appropriate treatment in order to get rid of the pollutants and, according to Crawford & Sandino (2010), this process should be focused on the recovery of resources, so as to be self-sustaining. Advances in scientific knowledge, and a greater consciousness about the environment and water as a resource, have given rise to new and improved technologies and treatment systems that are effective in dealing with wastewater pollution and also in reducing the energy used in recycling wastewater; however, selection of the appropriate technology to solve a specific wastewater problem should be undertaken with great care. Generally, there are two types of wastewater treatment systems – conventional and sustainable CW. 2.2. Conventional Wastewater Treatment Conventional wastewater treatment comprises physical, chemical and biological processes, involving three stages, referred to as primary, secondary and tertiary treatments. 6 2.2.1. Primary Treatment This treatment is used in the removal and separation of particulate inorganic materials and solids, which would otherwise clog and destroy water pipes of the network. This type of treatment entails screening, grit removal and sedimentation. Screens are used to get rid of large debris, including plastics and cans. The grit chamber system is used to remove, settle, gravel- and sandsized particles. According to Nelson et al. (2007), the wastewater is then moved into a quiescent basin, where it is temporarily retained so that the remaining heavier solids can settle to the bottom of the basin, while the lighter solids, including grease and oil, can accumulate on the surface. Finally, skimming and sedimentation processes are used to remove both the floating and settled pollutants. The liquid that remains is transferred to the secondary treatment. In this primary stage, 50% of the TSSs and 30–40% of the BOD are removed (Nelson, Bishay, Van Roodselaar, Ikonomou, & Law, 2007). 2.2.2. Secondary Treatment Dissolved and biological matter is removed in the secondary treatment. According to Nelson et al. (2007), 90% of the organic matter in the wastewater is removed at this stage. The attached and suspended growth processes are the two most suitable conventional methods used in secondary treatment. In the attached growth process, algae, bacteria and other microorganisms are grown on the surface of the wastewater, resulting in the formation of biomass, which breaks down the organic 7 waste. Trickling filters, bio-towers and rotating biological contactors are included in the attached growth process unit. In the suspended growth process, the microbial growth is suspended in an aerated water mixture; however, activated sludge, in which a biomass of aerobic bacteria and other microorganisms is grown, is the most common type of suspended growth process. 2.2.3. Tertiary Treatment The tertiary treatment is more advanced, aimed at producing a better-quality, more purified effluent for discharge into estuaries and low-flow river ecosystems. Coagulation sedimentation, filtration, reverse osmosis and extended secondary biological treatments are some of the methods that are used in this stage. These methods remove nutrients and stabilise oxygen in oxygendemanding substances. The treated effluent can then be safely reused, recycled or discharged (Praewa, 2017). In most circumstances, a final disinfection process is needed before tertiary-treated wastewater can be discharged. Disinfectants can be added to kill off pathogens and microorganisms, and. chlorine and ultraviolet light are also commonly used. The treated water can then either be discharged into different water bodies, including recharging underground reserves, or used in agricultural irrigation (Praewa, 2017), as long as it meets the required standards. 8 2.3. Constructed Wetlands (CWs) CW systems for single-household, municipal, and industrial wastewater are designed in ways that imitate the natural processes at work in wetlands, but include features that provide advantages over natural wetland processes. Such CWs incorporate chemical, biological and physical processes that are used to remove the pollutants and enhance and improve the quality of the wastewater (Vymazal & Kropfelova, 2008). These design systems use aquatic macrophyte and microbial communities, and plant roots and their host minerals to effectively remove pollutants, which include nitrogen, metals and pathogenic organisms, among many others. In 1904, the first CW was built in Australia (Vymazal & Kropfelova, 2008). Despite this, technological advancement in the field has been slow (Vymazal & Kropfelova, 2008). As the number of CWs increases around the world, and the benefits and effectiveness of the system over conventional treatment systems become better understood, CWs are finding wider favour among ecologists, scientists and water and environmental engineers, and this is leading to their popularisation even among developing countries. 2.4. Main Benefits and Outcomes of CWs The CW is a beneficial wastewater system because, upon treatment, the water that is discharged can either be used for domestic activities, or can be directly discharged into the environment. It is also beneficial to the end-users, as construction costs are minimal, and the costs of operation and maintenance are affordable. The operation and maintenance of CWs are periodic, unlike 9 conventional water treatment systems, which in most cases require continuous, on-site labour (Crawford & Sandino, 2010). The CW system facilitates the recycling and reuse of water, thereby defraying the costs of installation, operation and maintenance. The CW system not only provides a habitat for wetland organisms, but is also engineered in a way that finds favour with the public because of its many benefits. 2.5. Types of CWs There are various types of CWs that depend on the available landscape, including SF and SSF systems. SF CWs have shallow flow and lower velocity over the substrates, whilst SSF CWs have either VF or HF over the substrates. Hybrid CWs combine both VF and HF (Vymazal & Kropfelova, 2008). Each type of CW system has its benefits and drawbacks, and each differ in the treatment process used. SF CWs make use of plant stems, leaves and rhizomes to effectively treat wastewater. In dense vegetation, however, the process can be limited because there is not enough circulation of oxygen, which is vital for the organisms. In SSF CWs, roots are used in the treatment of effluents as water passes through a series of gravel beds. This process is considered to be superior to, and more effective than, that used in SF CWs. 2.6. Components of CWs 2.6.1. Water 10 Locations in which landforms predominantly direct surface water straight into shallow basins, or where impermeable subsurface layers hinder the ground from absorbing surface water, are the most likely places for wetlands to form naturally. Such conditions in a location can be engineered to create wetlands (Jhansi, & Mishra, 2013). Land can be structured in such a way that surface water is collected, and such basins can be sealed in order to retain the collected surface water. Once a landscape has been modified in this way, a wetland can be constructed. In the construction of a wastewater wetland system, hydrology is among the most important factors to be considered. This is because it not only links all of the functions of the wetland, but it is also a key factor in the CWs failure or success in a given landscape. The hydrology of the CW is important in relation to the hydrology of other surface water in the area. Small, natural hydrological changes can promote significant effects in the CW, impacting on its utility. Through rainfall and evapotranspiration, there is substantial interaction between the wetland system and the atmosphere because of the wetland water is shallow and covers a large surface area. The hydrology, in most cases, is also affected by vegetation density in the wetland, which can obstruct the flow of water. 2.6.2. Substrates, Sediments and Litter Soil, sand, gravel and rock, as well as organic materials, such as compost, are used to make the substrates for the wastewater to flow over. Due to the high biological productivity and low water velocities in wetlands, it is possible to easily accumulate sediments and litter (i.e., organic 11 matter). These substrates, sediments and litter are vitally importance because they support all of the living organisms that dwell in wetlands (Secretariat, 2014). For many contaminants in a wetland, the substrate acts as a sink. The substrate is also important because its permeability affects the movement of water passing through the CW. 2.6.3. Vegetation In any CW, the presence of both vascular and non-vascular plants is of vital importance (Praewa, 2017), vascular plants being the higher plants, whereas non-vascular plants are the algae. When algae undergo photosynthesis, they increase the dissolved oxygen content in the water, which significantly affects the metals and nutrients present in the water. The presence of plants in a CW system, therefore, is very important, since they also penetrate the substrate structure, transferring oxygen into the substrate, a process that is not possible or achievable, even using diffusion. The presence of submerged leaves, stalks and litter is important in FWS wetlands in terms of attached microbial growth, wherein the leaves, stalks and litter themselves serve as substrates. Wastewater wetlands are mostly characterised by the absence of emergent plants, although natural wetland systems commonly include reeds, rushes and cattails. Cattails have the ability to survive and thrive under diverse environmental conditions, and they can produce massive annual biomass. Rushes –particularly bulrushes – are perennial, grass-like plants that are capable of growing and thriving in clumps. They tend to grow better in water that ranges from 5 cm to 3 m deep (Wetzel, 12 1993). Most bulrushes grow well in water that has a pH of 4–9. Reeds are tall, annual grasses with a perennial rhizome. Reeds are among the most widespread emergent aquatic plants. CWs that use reeds are at an advantage because the reeds have the ability to transfer oxygen into the substrate, thus improving the effectiveness of the system. 2.6.4. Microorganisms The functions of CWs are, in some way, controlled and regulated by the presence of microorganisms and their metabolic processes. Algae, protozoa, fungi and yeasts are examples of microorganisms that are found in wetlands. Microbial activity in the system is important because this is how nutrients are recycled. Microbial activity also affects the processing capacity of the wetland because it can cause reduced conditions in the substrate. In CWs, microbial communities are affected by toxic chemicals, such as those found in pesticides (Wetzel, 1993). 2.6.5. Animals Certain vertebrates and invertebrates take up residence in CW systems. Insects and worms are (invertebrates) are significant contributors to the treatment process (Wetzel, 1993), making it safe and more effective. 13 2.7. Literature Summary CWs for municipal, industrial and domestic wastewater treatment can be designed in appropriate and specific ways to meet most intended purposes. Wetland systems can be engineered to take advantage of the various features of a site. CWs are an effective approach that can be employed in improving wastewater quality and allowing for its reclamation and reuse. Moreover, CW systems are of economic and thus they are globally applicable. 14 Chapter 3 METHODOLOGY 3.1. Overview In this chapter, case studies are used to describe the various methods for treating specifically domestic wastewater of certain PE, and includes information on the parameters used in CWs, such as measurements of areas, slopes and aspect ratios, whilst the methods and equations used to analyse data related to various comparative physiological and chemical components in the (treated) wastewater are highlighted. Background information on the site locations is also provided. 3.2. Methodologies 3.2.1. HSSF CWs for On-Site Wastewater Treatment The methodologies commonly used in Czech CWs are summarised, with the intention of determining whether indeed SSF CWs are more efficient than conventional treatment systems. Moreover, the study aims to assess whether SFF systems can meet the standards set for Ohio (USA) home systems through scientific analyses, including assessing treatment efficiencies in relation to TSS, BOD, TN, TP and FCs.This study’s methodologies are discussed using the following design parameters: Pre-treatment: HSSF CWs are for the secondary treatment of wastewater, and mainly employ a septic tank to remove TSSs, which settle to the bottom of the tank where they are anaerobically 15 degraded. Regular pumping of the tank after initial installation is necessary. Such septic tanks are common in single-family households. Surface area and configuration of the beds: The general rule-of-thumb formula for determining the surface area for wetland cells is given below, for cells with a total area of 5 m2 per PE. Most of the Czech designs use two cells, the first lined, to avoid leaching, and the second unlined, to reduce discharge, especially in cases where the water table is high (Hoddinott, 2006). ( ) ( ) , where Ah is the surface area of the bed in m2 , Qd is the average flow in m3 per day, Co is the influent BOD5 in mg l-1 , C is the effluent BOD5 in mg l-1, and KBOD is the rate constant in m day-1 (Hoddinott, 2006). Aspect ratio: Darcy’s law is used to calculate the length to width ratio of the cell bed. The correct ratio is necessary for maintaining adequate flow. CWs in the Czech Republic are designed with an aspect ratio of <2 because a wider inflow ensures optimal flow and reduces clogging at the inlet. Inlet clogging can also be reduced by using earthworms or larger-sized gravel at the inlet, to promote for greater flow. [ ( ( )] ) , where Ac is the cross-sectional area of the bed in m2, Qs is the average flow in m s-1, Kf is the hydraulic conductivity of the medium in m s-1, and dH/ds is the slope in m m-1 (Hoddinott, 2006). 16 Bottom slope and depth: The maximum macrophage depth of Phragmites australis (the common reed) is used in Czech designs to determine the depth of a CW cell, being 0.6–0.8 m. Coarse substrates call for a slope of 2.5% or less, while fine substrates need a slope of 1% or less (Hoddinott, 2006). Other studies have shown that a water depth of 0.27 m is the most efficient when it comes to removal rates (Hoddinott, 2006). Filtration media: Such media should facilitate macrophage growth, provide high filtration and maintain high hydraulic conductivity. Gravel of 10 mm dimensions fulfills these requirements. In addition, coarser particles of gravel at the inlet and outlet reduce clogging. Bed sealing: According to Czech regulations (Hoddinott, 2006), plastic liners should be used to seal beds. The liners should be between 0.8 and 2.0 mm thick. Sand or geotextiles should be used to protect the liners on both sides, to prevent damage by root penetration or sharp edges. Home systems can use ready-made plastic tubs that are inexpensive. Vegetation: Macrophages should be able to control erosion, ensure filtration and provide surface substrates for microorganism growth. Nitrogen removal is best facilitated by oxygen flux, which is ideal when root rhizome separation is 35–70 mm, a condition that is met by Phragmites australis. This species has also proved to be the best at facilitating greater bacterial growth. The consensus from various studies (Hoddinott, 2006), is that planted wetlands are more efficient than unplanted ones, especially with the integration of a pretreatment phase. 17 Insulation: Four to eight seedlings per m2 provides good insulation when the plants grow and begin to litter. Keeping the flowing influent warm is necessary to ensure optimal functioning of the microorganisms. Other studies have shown that insulation that consists of reed–sedge peat or yard waste compost is effective, even at -20°C (Hoddinott, 2006). 3.2.2. Use of VF CWs for On-Site Treatment of Domestic Wastewater: New Danish Guidelines New guidelines have been established by the Danish Ministry of the Environment regarding treatment requirements for single households in rural areas (Brix & Arias, 2005). Methodologies for analysing the BOD, COD, TSSs, TP and TN in wastewater are discussed below. The standard VF system for a five-PE household should have a total surface area of 16 m2 (Brix & Arias, 2005). The filter depth should be 1.4 m, with a 0.2 m drainage layer, 1.0 m sand filter layer and 0.2 m insulation layer (Brix & Arias, 2005). To prevent the sewage from entering the surrounding environment, a 0.2 m embankment should be raised around the bed. A tight membrane, with a minimum thickness of 0.5 mm, protected by a geotextile layer on both sides, should be used to enclose the bed. In addition, the drainage layer should be made up of coarse gravel that is 8–16 mm in size, in which 70 mm diameter drainage pipes should be placed. All of the pipes should be connected on one side to a collection pipe for discharge of the effluent. Passive aeration should be carried out in the drainage system, using vertical pipes extending 0.3 m over the filter bed surface (Brix & Arias, 2005). The new Danish guidelines for systems serving up to 30 PEs are outlined below. 18 Pre-treatment: Septic tanks, or chamber sedimentation tanks, with two or three chambers must be used for pre-treatment before discharging wastewater into a VF wetland. Single-household systems with up to 5 PEs should use a tank measuring 2 m3. The higher the PE, the larger the volume of the tank should be. In two-chamber tanks, the first chamber should constitute 70–90% of the total tank volume, while for a three-chamber tank, the first chamber should constitute 50– 70% of the total tank volume. The remaining volume should be evenly distributed between the other two chambers. Sludge removal should be carried out once a year. System operation and layout: VF CWs are required to have a planted filter bed at the point where wastewater is loaded onto the surface. The surface area of the bed should be 3.2 m 2 PE-1. The filter should not be too saturated with water. Treated wastewater is collected in a passivelyaerated system of drainage pipes positioned in the bottom of the filter. Filter medium: The standard filter medium is sand. Clay and silt, or any particles <0.125 mm in size, should be less than 0.5% (Brix & Arias, 2005). The filter depth is recommended to be 1.0 m, and the filter surface should be leveled out. The bed should be lined with an open geotextile material, or a layer of graded gravel, to prevent sand from entering the drainage layer. Distribution system: Pressurised distribution pipes are used to distribute the sewage evenly over the bed surface. The pipes should have a diameter of 32–45 mm, with 5–7 mm diameter holes drilled through the bottom of the pipes, every 0.4–0.7 m (Brix & Arias, 2005). The pump volume 19 should be at least thrice the distribution pipe system volume. Insulation against freezing should be provided, using a 0.2 m layer of coarse wood chips or sea shells positioned on the filter surface. Effluent recirculation: A split well, with two V-notch weirs, should be placed at the system outlet (Brix & Arias, 2005). The surfeit from one weir is recirculated to the first compartment of the sedimentation tank by gravity. Half of the effluent is recirculated. An alternative is to recirculate the effluent to the pumping well. Planting: Phragmites australis is used for wetland vegetation at a density of four plants per m2. Potted seedlings or rhizome pieces can be used for planting. 20 Figure 3.1: Layout of a VF CW system for a single household. Raw sewage is pre-treated in a 2 m3 sedimentation tank. Firm sewage is pulse-loaded onto the shallow end of the bed by a levelcontrolled pump. Treated effluent is collected in a system of drainage pipes, and about half the effluent is recirculated back to the pumping well, or to the sedimentation tank (Brix & Arias, 2005) 3.2.3. The Attenuation Capacity of CWs to Treat Domestic Wastewater in Ireland An Irish Environmental Protection Agency-funded project was established to investigate the removal efficiency of CWs in treating chemical and microbial wastewater contaminants found in domestic wastewater effluent in Ireland (O'Luanaigh & Gill, nd). Two HSSF beds, Reed Bed 1(RB1) and Reed Bed 2 (RB2), were constructed on-site for surveillance during their first 26 months of operation. Pre-treatment took place in a RBC, and acted as the primary treatment. The secondary treatment was administered to RB1, while RB2 received tertiary treatment. RB1 can 21 serve three PEs, while RB2 can serve two. Table 3.1 shows the design parameters for the two beds. Table 3.1: RB1 and RB2 design characteristics (O'Luanaigh & Gill,nd) Reed Bed ID Influent Type Plant Species RB1 STE RB2 TE Phragmites australis Iris and Typha Dimensions l*b*h (m) 5.8×2.6×0.6 Area m2 4.0×1.0×0.6 4 15 The beds were sealed using one sheet of butyl rubber liner filled with limestone gravel, 5–15 mm in diameter. Gravel (15–30 mm in diameter) was used at the inlet and outlet. The vegetation was planted in blocks of 4 m2. The hydraulic parameters for the beds are shown in Table 3.2. Table 3.2: RB1 and RB2 mean hydraulic parameters (O'Luanaigh & Gill, nd) Reed Bed ID Influent Type Inflow (L d-1) HLR (mm d-1) RB1 RB2 STE SE 327.3 136.9 21.8 34.2 Design (mm d-1) 36 90 HLR RB2 received almost twice the daily flow per unit surface area than RB1, although the secondary and tertiary treatment reed beds were overdesigned when equating the respective HLR values, as a consequence of lower-than-expected on-site hydraulic loads. Nevertheless, there was a disparity between the respective HLRs (O'Luanaigh & Gill, nd). 22 3.2.4. A Recirculating VF CW for the Treatment of Domestic Wastewater One objective of this research was to apply a recirculating VF CW – a decentralised, small-scale system – to the treatment of domestic wastewater, adjusting it where necessary to produce effluents that would conform to Israeli regulations for urban landscape irrigation (Sklarz, Gross, Yakirevich, & Soares, 2009) and, in addition, to determine the effluent water quality every 2–3 weeks over the course of a year by analysing BOD5, COD, TSSs and TN. The process is described in Figure 3.2. Two pilot recirculating VF CWs, designated R and L, were constructed at Midreshet Ben Gurion, in the Negev Desert, Israel (Sklarz, Gross, Yakirevich, & Soares, 2009), to treat primarily settled domestic wastewater from a residential neighborhood. Each recirculating VF CW was composed of two 0.9 m wide x 1.1 m long x 0.6 m high plastic containers placed one on top of the other (Sklarz, Gross, Yakirevich, & Soares, 2009). The container on the top acted as the VF CW, and was perforated with holes of 8 mm diameter. Each container was then filled with a 5 cm-thick pebble layer, followed by a 40 cm-thick layer of highly-porous plastic beads with a high surface area of 860 m2 m-3. The domestic wastewater fed into the upper tank trickled into the lower container. Initially, the R and L systems were operated without an upper soil–plant component, and the wastewater was applied daily, in three 100 L batches, at 9 am, 1 pm and 8 pm. The wastewater was recirculated through the bed at a RFR of 4.5 m3 h-1, and was sampled 12 h after the addition of the last batch (Sklarz, Gross, Yakirevich, & Soares, 2009). An 8 cm-thick layer of peat, planted with Juncus alpigenus (rush) and Cyperus haspen (sedge), was added to system R, and the RFR was reduced to 2.5 m3 h-1 in both systems; however, the RFR in the unplanted system had to be increased back up to 4.5 m3 h-1 and then gradually decreased to 2.5 m3 h-1.Manipulation of the flow rate in the planted system was restricted, and 23 found not to be practical because of the limited hydraulic conductivity of the peat layer (Sklarz, Gross, Yakirevich, & Soares, 2009). Figure 3.2: Schematic representation of a pilot recirculating VF CW for the treatment of domestic wastewater. The upper container is a VF CW bed. Wastewater is applied to the root zone, trickles through the bed, and drips into the lower container, from where it is recirculated back to the root zone, until the required water quality is achieved (Sklarz, Gross, Yakirevich, & Soares, 2009) 24 3.2.5. A Hybrid CW System for Decentralised Wastewater Treatment A hybrid CW, incorporating a reactive phosphorus barrier in the HF bed, which is followed by a VF bed, was studied. The HF removes organic matter and solids, while mitigating clogging risks, and the VF converts ammonia to nitrate, a process called nitrification. The reactive phosphorus barrier is used to remove phosphorus. Denitrification is the process wherein nitrate is converted to N2 gas. The conditions necessary for denitrification are an anoxic environment and a carbon source. The carbon is acquired from the incoming wastewater. Denitrification of the wastewater is achieved by recycling the nitrified effluent back to the HF inlet; this process reduces TN by up to 70%. A hybrid system, located at the Ontario Rural Wastewater Centre’s On-site Wastewater Testing Facility in eastern Ontario, Canada, has a flow rate of 2.8 m3 d-1, which can serve two singlefamily households. Two parallel systems were constructed to study the effects of flow rate and recycle rate on the performance of the system. Pilot wetlands were fed with raw wastewater from the Alfred municipal sewer line. A septic tank, with a volume of 5.6 m3, provided the primary treatment. The HF wetland measures 5.0 x 9.0 x 0.7 m, and has an operating depth of 0.55 m. The bed was lined with a 30 mil polyvinyl chloride (PVC) liner. The filter medium used in the first 1.0 m was washed coarse gravel, 25–50 mm in diameter. The remainder of the cell was filled with 13–20 mm washed gravel. The HRT of the cell is 4.5 days, with a design flow of 2.8 m3 d-1. The header pipe is a 10 cm in diameter perforated PVC pipe that was laid across the width of the wetland (Kinsley, Crolla, Rode, & Zytner, 2014). The HF cells were planted with Phragmites australis (reed) at a density of 9 seedlings/m2. The last 2.0 m were planted with hybrid sandbar willow at a density of 1 cutting/m2. The medium selected for the phosphorous filter was blast-furnace slag. The slag filters measured 5.0 x 2.5 x 0.7 m, with an active depth of 25 0.55m and a HRT of 1 day. The slag measured 25–50 mm in diameter. A PVC footer, measuring 2.5 cm in diameter, with a 0.55 m standpipe, was positioned at the outlet of the slag filter. The outlet pipe flows into a pump chamber that feeds the VF beds (Kinsley, Crolla, Rode, & Zytner, 2014). The VF bed has a layer of peat to neutralise the high pH of the effluent flowing from the slag filter. The VF bed measures 2.5 x 2.5 x 0.8 m in size. The filter comprises, from top to bottom, a 0.2 m-thick layer of Sphagnum peat moss, a 0.4 m-thick layer of 1–5 mm in diameter washed sand, a 0.2 m-thick drainage layer of 13–20 mm washed gravel, and a 30 mil PVC liner. The dosing array is made up of six lines (38 mm in diameter PVC dosing pipe), inserted every 50 cm, with a 7.5 mm opening spaced every 50 cm (Kinsley, Crolla, Rode, & Zytner, 2014). A 28 L dose of the effluent is delivered to the filter, in which P. australis was planted at a density of 9 seedlings/m2. The dosage is controlled using a float-controlled pump (Kinsley, Crolla, Rode, & Zytner, 2014). Effluent drains through 3 x 10 cm perforated PVC pipes connected to a footer line, and flows to a pump chamber. A pump in the effluent pump chamber recycles part of the treated effluent back to the HF inlet (Kinsley, Crolla, Rode, & Zytner, 2014). The system is summarised in Figure 3.3. 26 Figure 3.3: Hybrid CW schematics (Kinsley, Crolla, Rode, & Zytner, 2014) 3.2.6. CW of Lepironia articulata for Household Greywater Treatment This study was established in a village to observe, and determine the characteristics of, greywater loading, and to provide a suitable on-site mini-wetland for determining the system’s effectiveness (Wurochekke, Harun, Mohamed, & Kassima, 2014). In addition, the study aimed to determine the efficiency of Lepironia articulata (sedge) in pollutant removal, and to see whether treated wastewater could be safely reused for purposes such as irrigation. There were six people in the study, all female, 20 to 30 years old. The house comprised three bedrooms, two bathrooms, a living room and a kitchen where everyone regularly cooked in the 27 morning and at night (Wurochekke, Harun, Mohamed, & Kassima, 2014). The bathroom was used twice daily by each occupant, and the washing machine was used twice a week (Wurochekke, Harun, Mohamed, & Kassima, 2014). Figure 3.4: Schematic diagram of a mini-CW system (Wurochekke, Harun, Mohamed, & Kassima, 2014) The system (Figure 3.4) was made using three HDPE plastic containers and PVC pipes. Water flow was gravity-driven. Pre-treatment took place in a 20 L cylindrical container, with a gravel (<25 mm diameter) filter medium, then charcoal, fine sand (diameter 0.2 mm) and another layer of gravel (diameter <15 mm). Wastewater from the pre-treatment container flowed into the 28 second and third HDPE containers. Each of the containers measured 34 x 18 x 14 cm and acted as a mini-CW. The second container had a filter medium of fine sand (diameter <0.2 mm) and gravel (diameter <15 mm). The L. articulata was planted at the top soil of tube sedge as a biological treatment. The filtered water exited the second container through holes in the bottom of the container. The effluent was collected in an insulated black container and taken for the analysis of BOD, COD, TSSs, Ammonia nitrogen (AN) and turbidity. The third container acted as the control, having the same dimensions as the second container. Samples were collected at 10 am and 9 pm every day for four days (between 5 March 2013 and 17 March 2013). These samples were analysed using standard methods for water and wastewater (Wurochekke, Harun, Mohamed, & Kassima, 2014). 3.2.7. CW System for Wastewater Treatment The aim of this study was to establish a full-scale system to treat sewage from a single household, based on experimental systems (Farooqi, Basheer, & Chaudhari, 2008). Pollutant removal was done through a combination of chemical, physical and biological processes associated with sedimentation, vegetation and microbial activity. The following equation (Eq. 3), designed by Kikuth (1977), can be used for SSF CWs treating domestic wastewater to determine size: ( ) 29 , where Ah is the surface flow of the bed in m2, Qd is the average flow rate in m3 d-1, Cin is the influent BOD5 in mg l-1, Cout is the effluent BOD5, and KBOD is the rate constant d-1 (Farooqi, Basheer, & Chaudhari, 2008). An experimental VF CW (Figure 3.5) was established in a traditional municipal wastewater plant in order to manipulate the HLRs as desired. Based on the outcomes of the experiment, a fullscale system was constructed for a single household of four PEs. The system was constructed as a 2 m3, three-chambered sedimentation tank, with a level-controlled pump and a 15 m2 VF CW (Farooqi, Basheer, & Chaudhari, 2008). Effluent recirculation was applied in the system through the sedimentation tank, in order to improve TN removal through denitrification. Phosphorous removal was performed using chemical precipitation in the sedimentation tank. Figure 3.5: General layout of a single-household VF CW system (Farooqi, Basheer, & Chaudhari, 2008) 30 3.2.8. Use of Macrophyte Plants, Sand and Gravel Materials in CWs for Greywater Treatment This study aims to present the results concerning the removal of BOD, COD, TSSs, pathogens and detergents that are outlined in chapter 4, based on recent studies of CW used in Central Java Indonesia, and some similar studies in West Java Indonesia, Thailand and Costa Rica. This also illustrates the successful performance of local macrophytes and natural substrates (Qomariyah, Ramelan, Sobriyah, & Setyono, 2017). The Methodology of the recent study Central Java Indonesia are discussed in this chapter. An experimental single HSSF was constructed with dimensions of 1.7 x 0.7 x 0.7m (l x w x h). The experiment was conducted in Sukarta, Indonesia, and the effluent was collected from a single house in 2015. River sand and gravel were used as the substrates. The CW was filled to a depth of 50 cm, with a 20 cm length of gravel at the inlet and outlets, and 130 cm Length of river sand. Cyperus papyrus (paper reed) was planted at 25 cm intervals. The wastewater was pretreated in a sedimentation tank, and then loaded gradually, increasing from 25 to 100% over four weeks, so as to acclimatise the plants. The HRT was one day. The experiment was monitored for three months, and samples were collected twice a month. 3.2.9. Integrated CWs for Treating Domestic Wastewater This study focused on the treatment of domestic wastewater on small and industrial scales (after a year of experimental operation), using integrated CWs. The main features of integrated CWs are a shallow water depth, emergent vegetation and the use of in-situ soils that imitate those found in natural ecosystems (Scholz, 2011). Artificial liners are not used in integrated CWs. The 31 nutrient removal performance, and the impact of seasonal and annual changes on the parameters, are compared between both systems in Chapter 4. The CW for treating domestic water in Ireland was constructed in Glaslough, Monaghan County. Inflow rates ranged from 85–105 m2 d-1 and outflow rates from 1–50 m3 d-1, which was very low due to evapotranspiration and the infiltration of treated wastewater (Scholz, 2011). The wastewater dilution was 35–65%. The system served about 1750 PEs and had an area of 6.74 ha, with a water surface area of 3.25 ha. The system consisted of a small pumping station, two sludge cells and five shallow, vegetated cells, as shown in Figure 3.6. Domestic sewage from the village was pumped to an on-site pump and into one of the sludge cells. From the sludge cells, wastewater flowed by gravity through the five vegetated cells, and the effluent discharged into Mountain Water River. The wetlands were planted with Carex riparia, Curtis, P. australis, Typha latifolia, Iris pseudacorus, Glyceria maxima, G. fluitans, Juncus effusus, Sparganium erectum, Elisma natans and Scirpus pendulus (Scholz, 2011). Hi-tech automatic sampling and monitoring was performed weekly. In addition, the Glaslough stream was monitored regularly (Scholz, 2011). Groundwater was monitored using six piezometric ground-water monitoring cells placed within the system and along the suspected flow of contaminants (Scholz, 2011). 32 Figure 3.6: Sketch showing groundwater and surface water monitoring, and inlet and outlet points, for the integrated CW in Glaslough, near Monaghan, Ireland (Scholz, 2011) Another system, at Dunhill, Waterford County, southern Ireland, was Constructed. Here, the water inflow was about 40 m3 d-1 and the outflow about 24 m3 d-1. The wastewater dilution was 33 about 5–20%. The total area of the system was 0.3 ha. The primary vegetation used was an emergent species of helophyte (bog plant). The system was gravity fed, and therefore no energy was required. The wastewater was collected from the households using the sewage system, and then transported to the wetland system. Grab samples from the inlet and outlet were analysed, and Mountain Water River was regularly monitored. Two piezometric groundwater-monitoring cells were sampled at a depth of 5 m to monitor contamination of the groundwater. Figure 3.7: Sketch showing groundwater and surface water monitoring, and inlet and outlet points for the integrated CW system at Dunhill, near Waterford, Ireland (Scholz, 2011) Water samples were analysed for parameters including BOD, COD, ammonia–nitrogen, nitrate– nitrogen and molybdate-reactive phosphorus (MRP). 34 3.2.10. Efficiency of Small CWs for Subsurface Treatment of Single-Family Domestic Effluent The main aim of this study was to evaluate the effectiveness of single family CWs in Ohio, USA in improving water quality, and determining whether they met US Environmental Protection Agency guidelines. Samples from the CWs were collected quarterly, from 1994–2001. Twentyone domestic CWs, serving 21 single-family homes, each with one to seven family members, were assessed, all sharing a common three-stage design. Each system had a septic tank that provided primary treatment, followed by two wetland treatment cells. Water from the septic tank entered the primary cell using a manually-controlled water-level control box. The cells measured 4.5 x 5.5 x 0.46 m (l x w x d). Riverbed gravel (3 cm diameter) was predominantly used, with larger gravel (6 cm diameter) at the inlets and outlets. The first cell was a minimum of 10 cm higher than the second to facilitate gravity flow. Two of the systems were aerated, while one was designed with longer, narrower cells. Earthen berms were used to prevent runoff into the environment. The first cell was lined with impermeable clay or rubber, while the second was left unlined. Arrowheads or bulrushes were planted in Cell 1, while Cell 2 was generally planted with ornamental wetland plants. Phragmites invaded some of the systems. Trained technicians collected samples, quarterly, at the septic tank, the inlet box between Cells 2 and 3, and the outlet box in Cell 3; TSSs, BOD5, ammonia, FCs and TP were tested for. ANOVA t-tests were used to analyse the relationships among input, output and treatment efficiency of the systems that met EPA effluent guidelines, compared to those that did not (Steer, Fraser, & Boddy, 2002). 35 Figure 3.8: Typical three-cell design of a single-family domestic CW system (Steer, Fraser, & Boddy, 2002) 3.2.11. Reed bed CW system A study performed at Haya Water Company in Quriyat, Oman involved designing, building and operating a CW, and studiying the performance of the system for a year (12 June 2016–12 July 2017). The aim of the study was to evaluate the efficiency of a reed bed treatment system for domestic and partially non-domestic wastewater. Haya water used a double stage VF reed bed, with an anoxic tank (Haya Water, 2017). The parameters analysed included TSSs, (O&G), (VHO), COD, BOD, TP, TN and NH3–N; the results were compared to Oman's Ministerial Decision 145/1993 Standards (A) to determine whether the effluent quality was acceptable for irrigation purposes (Haya Water, 2017; Oman Government, 2018). The capacity of the reed bed was 50 m3, while the area was 1300 m2. The reed bed received water from a balancing tank. Phragmites australis (common reed) was used for vegetation. The reed bed was divided into two stages. The filter used in the first stage was >1 in size, with fine gravel filter material (thickness of 2–2.8 mm) to a depth of >30 cm. The filter used in the second 36 stage was also >1 in size, while the filter material had a thickness of 0.25–0.4 mm and a depth of >30 cm (Haya Water, 2017). Table 3.3 illustrates the design criteria for the double-stage VF reed bed. Table 3.3: Design criteria for a double-stage VF reed bed after pre-treatment (septic tank) (Haya Water, 2017) There were two major stages in the system: Stage A had three basins – A1, A2 and A3 – and Stage B hasd two basins – B1 and B2. The system had a buffer tank, an anoxic tank, a TE storage tank, along with three pumps. The process started at the buffer tank, which acted as the measuring can. From the buffer tank, raw sewage discharged into the anoxic tank, where the wastewater underwent partial denitrification (Haya Water, 2017). 37 Stage A was the settlement stage, in which untreated effluent took two hours to be loaded into each compartment. This was where 50% of TSSs and 20% of BOD were removed, and partial denitrification took place. From Stage A, the treated effluent was loaded into Stage B, where a biological treatment took place. This stage was known as the aeration stage due to the nature of processes that took place in there, including nitrification (ammonia to nitrate) and biological reactions. Further denitrification was achieved through partial effluent recirculation into the anoxic tank, where nitrates were converted to nitrogen gas (Haya Water, 2017). The remaining effluent flowed to the Treated Sewage Effluent storage for further disinfection. Figure 3.9 demonstrates this process of wastewater effluent treatment. Figure 3.9: Description of the process for treated effluent (Haya Water, 2017) Figures 3.10 and 3.11 illustrate Stages A (initiation) and B, and Figure 3.12 shows the P. australis after both stages (Haya Water, 2017). 38 Figure 3.10: Stage A (Haya Water, 2017) Figure 3.11: Stage B (Haya Water, 2017) 39 Figure 3.12: Photographs after both stages (Haya Water, 2017) 40 Chapter 4 RESULTS AND DISCUSSION 4.1 Overview In this chapter, a detailed discussion of the results from the case studies introduced in Chapter 3 is presented. This chapter provides the efficiency removal rates for various parameters, such as COD, BOD5, TSSs, TKN, TN, TP, FCs, TCs, bacteria and ammonia, as related to each case study. The effectiveness of the design strategies are also discussed. To determine which design is the best, a comparison is made between two related case studies that used different CW designs. The comparison is based on methodologies used and removal efficiencies observed. 4.2. Results and Discussion 4.2.1. HSSF CWs for On-Site Wastewater Treatment In line with the objectives of the original study, the results for TSSs, BOD, FCs, nitrogen and ammonia are discussed extensively below. The Ohio Environmental Protection Agency (OEPA) guidelines for discharge standards are shown in Table 4.1. Table 4.1: Surface discharge limits (maximum concentrations) (OEPA, 2001; Hoddinott, 2006) Pathogen FCs BOD5 TSSs Ammonia Phosphorous Concentration 2000 15 18 1.5 1 Unit Counts/100 ml mg l-1 mg l-1 mg l-1 mg l-1 41 The average BOD5 removal in the Czech case study CWs was 88%, and the average outflow concentration was 10.5 mg l-1, which are below the OEPA standards (Hoddinott, 2006). Moreover, the average COD removal was 75%, with an average outflow concentration of 53 mg l-1. COD removal was less than BOD removal because of the presence of non-biodegradable pollutants (Hoddinott, 2006); however, it was observed that BOD and COD removal was not affected by the seasons. TSS removal was recorded at an average of 84.3%, and effluent concentrations averaged 10.2 mg l-1, within the OEPA limit of 18 mg l-1. TP concentrations in the discharge in all the CWs were above 3mg l-1. The required concentration is <1mg l-1, a figure deemed to be unobtainable for home systems. From the observations, Phragmites increased TP removal to 97 from 50%. Mechanical technologies to remove phosphorus were not recommended because the study aimed to maintain simplicity and low costs for the CW project. Ammonia removal rates in the Czech CWs averaged 43%. Individual rates ranged from 9–73% in the CWs.There was no significant seasonal variation observed in the removal of ammonia (Hoddinott, 2006). Planted CWs were more effective at nitrogen removal than unplanted CWs, but the effluent concentrations were below the OEPA guidelines of 1.5mg l-1 in both cases. SSF CWs produced almost 100% removal of coliforms and other bacteria, which fulfills one of this study’s objectives. Seeding experiments using Salmonella showed removal rates of 95– 99.8% in winter and summer, which meet the OEPA standards. Planted CWs recorded a 90% removal of bacteria, Giardia, Cryptosporidium and enteric viruses (Hoddinott, 2006). In addition, the CWs proved efficient in the removal of Cryptosporidium oocysts through protozoan 42 predation, which has been unresponsive to ordinary chlorination treatment efforts (Hoddinott, 2006). In summary, the study showed that iron added to the substrate improved the degradation of nitrogen and phosphorus to almost 100%, and that Phragmites was the best species for vegetation, which goes to prove that the plants and substrate medium are essential to the CW pollutant removal process. 4.2.2. Use of VF CWs for On-Site Treatment of Domestic Wastewater: New Danish Guidelines The results from the review of a VF system that should achieve 95% BOD removal, 90% nitrification and 90% phosphorus removal, according to a new set of guidelines set by the Danish government (Brix & Arias, 2005), are discussed. It was discovered that filter sand that is too coarse results in water passing through too fast and, hence, lower nitrification rates. In addition, the bed depth should be less than 1 m, in accordance with the guidelines, since most of the removal actually takes place in the upper few centimeters (Brix & Arias, 2005). According to the study, if the hydraulics of a system are not up to standard, there is a risk that the wastewater will bypass the thin filters too quickly (Brix & Arias, 2005). Since the VF2 and VF3 systems were loaded by gravity, water was not effectively distributed over the surface beds, as is the case in a pump-loaded system. The two systems received greywater only, while VF1 received recirculated influent. Effluent recirculation resulted in lower effluent concentrations and, therefore, better performance. Due to the recirculation, the influent concentration decreased, albeit artificially, because of dilution by the recirculated effluent. Ammonium–nitrogen concentrations in sewage can be higher than 100 mg l-1, which is why recirculation is important for lowering concentrations. The new Danish guidelines require effluent concentrations of <40 mg l -1 for 43 BOD, <150 mg l-1 for COD and >2.5 m2 PE-1 for surface area. The need for a smaller area in the VF ensures efficient BOD removal and nitrification; however, systems with <2 m2 are efficient in BOD and TSS removal, especially in domestic wastewater. Table 4.2 shows the removal efficiencies for various parameters in the VF beds. Table 4.2: Performance data (mean±1 SD) for some single-household VF CWs (Brix & Arias, 2005) System Parameter VF1 (without TSS recirculation) BOD5 NH4–N NO2+ NO3–N TN TP VF1 (with 100% TSS recirculation) BOD5 NH4–N NO2+ NO3–N TN TP VF2 TSS BOD5 NH4–N NO2+ NO3–N TN TP VF3 TSS BOD5 NH4–N NO2+ NO3–N TN TP Inlet (mg l-1) 85±28 254±123 105±45 <0.1 125±51 17.2±7.0 68±22 100±35 45±13 0.13± 0.09 57 ±13 5.2± 1.7 88 ±8 507± 395 242 ±75 0.1± 0.1 350 ±5 20.6± 7.5 124± 135 320 ±139 18 ±22 0.5± 0.5 30± 23 4.6 ±3.6 Outflow (mg l-1) 8± 3 19± 4 23 ±17 40 ±13 72 ±28 13.0 ±6.6 3± 1 11 ±3 7± 1 36 ±4 44± 5 5.7 ±1.2 7± 5 7 ±2 59± 11 141 ±40 190 ±37 7.5± 4.8 4± 3 2 ±1 0.4 ±0.2 8.0± 2.6 9 ±3 4.5 ±2.6 Efficiency % 91 92 78 43 25 96 89 85 23 0 92 98 76 46 64 97 99 98 63 2 To summarise, system clogging was observed as a risk in such beds, but can be minimised by allowing wastewater to fully pass through the bed before loading the next dose of wastewater. Planted reeds also prevent clogging, but substrate texture also plays a big role. The rate of 44 oxygen transfer from the atmosphere and the aerated drainage layer to the bed medium should be high. The case study proved that all of the Danish guidelines could be met, yielding a good performance. 4.2.3. The Attenuation Capacity of CWs to Treat Domestic Wastewater in Ireland Based on the parameters measured in Chapter 3, the following measurements and analytical parameters from the case study, along with seasonal variations, can be discussed. Water balance: RB1’s mean inflow was 327.3 L d-1 and mean outflow 349.9 L d-1, while RB2’s mean inflow was 136.9 L d-1 and mean outflow 149.2 L d-1. Neither bed had any significant effect on incoming HLRs, acting to increase RB1 and RB2 winter flows by 6.4 and 7.2%, and summer flows by 0.5 and 1.7%, respectively (O'Luanaigh & Gill, nd). HRT: Results from two tracer studies performed at the end of the first sampling year and during the final sampling phase, show that RB1 had a HRT of 6.5 days, while RB2 had a HRT of 5 days. The results were similar to calculated nominal retention times, meaning that dead zones were largely absent. Organic matter removal: COD concentrations at the inlet and outlet showed similar removal rates of RB1 67% and RB2 55%. According to a temporal variation analysis, COD removal in both beds showed a steady performance increase with time. There was minimal seasonal influence on performance, meaning that temperatures did not necessarily affect reed bed function. 45 Nitrogen removal: TN removal in both beds was limited by slow rates of mineralisation and little nitrification because of the anoxic environment. Only about half of the organic nitrogen fraction was converted to ammonium–nitrogen. There was a slight declining trend over the first three years of operation. Ammonium–nitrogen constituted the highest fraction of TN concentrations at both the inlet and outlet of RB1 (O'Luanaigh & Gill, nd). Nitrogen removal was highest during the first year of operation; however, there was a decreasing trend through the three years. Seasonal influence was minimal. RB2 had 41% TN removal, despite effluent from the RBC being partially nitrified, and nutrient removal, and denitrification in particular, often being a key focus for tertiary treatment (O'Luanaigh & Gill, nd). Denitrification in the reed bed was compromised, however, by the inability of the RBC to mineralise all of the organic–nitrogen to ammonium–nitrogen, and then fully nitrify the effluent. Table 4.3: Average influent and effluent nitrogen loads from RB1 and RB2 ( O'Luanaigh & Gill, nd) COD mg/l g/d RB1 514 182 in RB2 195 61 out TN Org–N NH4–N TKN NO3–N mg/l g/d mg/l g/d mg/l g/d mg/l g/d mg/l g/d 105.5 38.6 26.5 10.1 74.9 27.5 101.4 37.6 3.9 1.0 NO2–N mg/l g/d 0.2 0 76.9 27.3 13.1 4.7 61.0 21.1 74.1 25.8 2.8 0.05 0 RB1 193 in RB2 107 out 32 92.8 15.6 25.0 4.1 22.1 4.0 47.1 8.1 37.9 5.1 7.8 2.4 15 63.9 9.2 20.7 2.6 32.5 4.4 26.7 3.9 4.7 0.9 11.8 1.8 1.5 Phosphorous removal: The removal of TP averaged out at 45%. Efficiency slightly decreased after the first year, and stabilised over the next 18 months. Summer removal rates were higher 46 than those of winter, which could be attributed to plant growth (plants accumulating biomass better in summer than winter). According to O'Luanaigh and Gill (nd), the temporal variations of phosphate–phosphorus effluent concentrations showed the same pattern as the influent values, and it appears that adhesion sites were still readily available after the 26 months of monitoring. Bacterial removal: The mean removal of TCs and Escherichia coli in RB1 was 98.5% (1.8 log units) and 96% (1.4 log units), respectively, while the mean removal rates for TCS and E. coli in RB2 were 1.3 log units and 1.7 log units, respectively. There was little seasonal or annual variation in either indicator organisms in RB1 and RB2. In addition, an analysis of samples from intermediate sampling points in the middle section of the reed bed showed an exponential decrease in the concentrations of both coliform species, with longitudinal distances of r2 = 0.947 (TCs) and r2 = 0.977 (E. coli).Table 4.4 shows the E. coli concentrations from the two Beds Table 4.4: Average influent and effluent E. coli concentrations from RB1 and RB2 (O'Luanaigh & Gill, nd) RB1 in RB1out RB2 in RB2 out E. coli concentration (MPN/100 ml) 7.44 x 105 2.80 x 104 1.10 x 104 2.39 x 102 Removal (log-unit) 1.4 1.7 Under HSSF CWs, in on-site wastewater treatment, the results showed that the system could achieve good hydraulic distribution using an aspect ratio of 3:1. According to the research, a common misconception is that such systems do not significantly reduce effluent HLR because of evapotranspiration. Tertiary treatment beds can be used to remove nitrogen, since they provide good environments for denitrification, especially if they are receiving nitrified effluent. There 47 was no significant TN removal in secondary beds receiving effluent from a septic tank. Both secondary and tertiary beds provided low TP removal during the first years of operation, a situation that was expected to deteriorate with time, if the sites for adsorption and precipitation became saturated. Plant uptake and harvesting did not have significant results on TP removal. 4.2.4. A Recirculating VF CW for the Treatment of Domestic Wastewater The general performance of the recirculating VF CW was assessed by comparing the quality of raw versus treated domestic wastewater, and by the conformity of the effluents to Israeli regulations for irrigation of the urban landscape (Sklarz, Gross, Yakirevich, & Soares, 2009). Figure 4.1 shows the results for the various parameters analysed. 48 Figure 4.1: Values of TSSs (a), COD (b) and BOD5 (c) in raw and treated domestic wastewater from planted and unplanted recirculating VF CWs using several RFRs (Sklarz, Gross, Yakirevich, & Soares, 2009) 49 With reference to the results presented in Figure 4.1, the unplanted systems were found, on average, to reduce TSSs by approximately 90%, from 90 to 10 mg l-1, BOD5 by 95%, from 120 to 5 mg l-1 and COD by 84%, from 270 to 40 mg l-1, using an RFR of 4.5 m3 h-1 and 12 hours of treatment. The ratio of COD to BOD5 increased from 2.25 to 8, apparently due to the favoured removal of biodegradable organic matter over less biodegradable organic matter (Sklarz, Gross, Yakirevich, & Soares, 2009). TSSs and BOD5 levels conform to Israeli regulations, at 10 mg l-1 each for urban landscape irrigation. It was observed that nitrification was efficient because the ammonia levels dropped from an average of 37 mg N l-1 in the raw domestic wastewater to 3 mg N l-1 in the effluent, followed by an increase in nitrate, from negligible levels to 25 mg N l-1 in the effluent; the transitory accumulation of nitrite was consistently low, at levels of 3 mg N l-1 (Sklarz, Gross, Yakirevich, & Soares, 2009). It is important to note that the maximum concentration of nitrogen for unrestricted irrigation, according to the Israeli recommendations, is 25 mgl-1 , but concentrations of over 50 mg l-1 are commonly used for fertilisation purposes in landscape irrigation and agricultural practices (Sklarz, Gross, Yakirevich, & Soares, 2009). Therefore, the results for TN removal conformed to the Israeli standards. When a peat layer was added, the observation was that the planted system continued to perform the same as before it was planted, but that the unplanted system deteriorated in terms of TSSs, COD and BOD removal. Moreover, ammonia was reduced to less than 5 mg N l-1. There were no changes in the transformation of nitrogen; however, small amounts of nitrite did accumulate, and nitrate accumulated up to about 25 mg N l-1. The decreasing performance in the unplanted system was likely due to the reduction in the RFR. When the RFR was increased, in order to test this theory, the effluent quality in the unplanted bed went back to the original, and remained high 50 even when the RFR was again decreased. This means that the sudden RFR reduction could have caused changes in the recirculating VF CW biofilm, which had acclimatised to working under high RFR conditions. These changes consisted of sloughing of the old biofilm, which may have increased solids and organic matter levels. After the second RFR reduction, the process did not repeat itself. According to the study (Sklarz, Gross, Yakirevich, & Soares, 2009), plants are thought to improve efficiency by taking up different components from the wastewater, enhancing oxygen transport, releasing enzymes and other agents that enhance degradation, and by providing a favourable environment for microbial population development; however, other studies have demonstrated that equal treatment efficiencies of wetlands can be achieved with and without plants (Sklarz, Gross, Yakirevich, & Soares, 2009). Additionally, due to the continuous recirculation in the recirculating VF CW, the planted area was small in relation to the amount of wastewater that was being treated and, hence, the role of plants in this case was limited (Sklarz, Gross, Yakirevich, & Soares, 2009). To summarise, recirculating VF CW effluents were overall of high quality – even when operated without the soil–plant component – and conformed to the Israeli regulations. The potential organic load capacity in this case was higher than that in previous studies. The contribution of the plant–soil component requires further study. Nitrogen was converted to nitrate with relatively small losses, and the nitrate in the effluents partially fulfilled the plant nutrient requirements, reducing the need for fertiliser, thereby providing environmental and economic benefits (Sklarz, Gross, Yakirevich, & Soares, 2009). 51 4.2.5. A Hybrid CW System for Decentralised Wastewater Treatment Analysis of the chemical and physiological parameters discussed in the methodology of the case study (Kinsley, Crolla, Rode, & Zytner, 2014) are here discussed in terms of absolute values and their reactions to seasonal variation. According to the study results, during the summer, the combined HF–VF system reduced BOD5 concentrations to virtually undetectable levels (<2 mg/l) at all HLRs (Figure 4.2); however, during the winter, the VF effluent concentrations increased from 3 to 9 mg/l with an increasing HLR. Average TSSs varied between 8 and 12 mg/l during the summer (Figure 4.3), and between 11 and 18 mg/l during the winter, with no significant differences between the HF and VF values (Kinsley, Crolla, Rode, & Zytner, 2014). The TSS values were not affected by increasing HLRs. 52 Figure 4.2: Changes in BOD5 with season and HLR (Q = 2.8 m3/d) (Kinsley, Crolla, Rode, & Zytner, 2014) 53 Figure 4.3: TSSs with season and HLR (Q = 2.8 m3/d) (Kinsley, Crolla, Rode, & Zytner, 2014) Without recycling, TN was reduced by only 19 and 24% during summer and winter, respectively; with recycling, the outlet TN ranged between 9.6 and 11.8 mg/l, with no significant differences observed, either between seasons or with an increased recycling ratio (Kinsley, Crolla, Rode, & Zytner, 2014). The more the recycle ratio was increased, the more TKN increased and nitrate decreased between summer and winter. This observation means that the more the flow was increased, the more the VF became saturated, leading to the reduced transfer of oxygen and decreased nitrification. In light of the study, it was observed that phosphorus was reduced to below 1.0 mg/l for the first 18 months of the study, after which TP concentrations increased; during this time, pH at the HF outlet remained above pH10 (Kinsley, Crolla, Rode, & Zytner, 2014). This indicates that the best removal mechanism for phosphorus was precipitation in a high-pH environment. Furthermore, the peat layer in the VF filter was effective at maintaining that high-pH environment at between pH7 and 8. The phosphorus attenuation of the material declined very quickly when highly- 54 soluble calcium was released from the surface of the blast-furnace slag (Kinsley, Crolla, Rode, & Zytner, 2014). For E. coli, during the summer, a total of 3.4 logs were removed, while during the winter, a total of 2.3 logs were removed (Kinsley, Crolla, Rode, & Zytner, 2014). Removal was not satisfactory, and the study suggests further treatment using ultraviolet light or chlorination, especially if the effluent is to be reused. The concentration standards required for E. coli in effluent that is to be reused for irrigation is <103 CFU/100 ml. This study demonstrated high removal rates for all physiological and chemical parameters; however, the system was affected by seasonal variation. Removals during winter were not as high as in the summer. 4.2.6. CW of Lepironia articulata for Household Greywater Treatment This study discussed the removal of BOD, COD, AN, TSSs and turbidity. Table 4.5 and figure 4.4 document water consumption in the household, showing that the washing machine produced the highest quantity of greywater, while the kitchen had the lowest. Table 4.5: Household water consumption in the case study (Wurochekke, Harun, Mohamed, & Kassima, 2014) Household activity Kitchen Bathroom Washing machine Quantity of greywater (m3/day) 5000 37000 136500 55 Removal Percentage 3% Washing machine 21% Bathroom Kitchen 76% Figure 4.4: Percentage removal of greywater produced by household activities (Wurochekke, Harun, Mohamed, & Kassima, 2014) The model produced the results shown in Table 4.6 for greywater loading discharged from the house. Table 4.6: Analytical results of greywater loading before treatment (Wurochekke, Harun, Mohamed, & Kassima, 2014) No. 1 2 3 Water volume (m3) 0.021 0.014 0.010 Time (s) 419 279 627 Flow rate x 10-5 (m3/s) 5.012 5.018 1.595 A preliminary analysis was conducted before treatment to determine the concentrations of the pollutants in the greywater. Table 4.7 records the results found during the morning and evening sampling times. Table 4.7: Preliminary results of raw greywater in the morning and evening (Wurochekke, Harun, Mohamed, & Kassima, 2014) 56 Sampling date Time/parameters BOD (mg/l) 05/03/2013 10.00 am 9.00 pm 17/03/2013 10.00 am 9.00 pm 271 60 309 167 COD (mg/l) TSSs (mg/l) AN (mg/l NH3–N) Turbidity (NTU) 807 705 1103 469 153 78 54 83 3.83 1.72 2.6 1.24 132 67.9 35.1 52.2 According to the study (Wurochekke, Harun, Mohamed, & Kassima, 2014), the mini-CW model provided a high removal performance of 81.42% BOD, 84.57% COD, 39.83% AN, 54.70% TSSs and 45.01% turbidity. The highest reductions in pollutants after treatment were BOD (81.42%) and COD (84.57%), signifying that the treatment system was capable of reducing the solid fraction of BOD and, thus, the remaining part after treatment was probably soluble (Wurochekke, Harun, Mohamed, & Kassima, 2014). The reduction in organic matter is significant, although COD was the most affected. The organic constituents decomposed and facilitated the growth of plants, with minerals being converted to protein, since they are able to remove organic compounds by the uptake of those organic compounds as carbohydrates and amino acids. In accordance with the study findings (Wurochekke, Harun, Mohamed, & Kassima, 2014), TSS reduction, on average, was 54.7%, which indicates some inefficiency because only physical sedimentation was used to remove the TSSs. AN reduction was low as well, being at 39.83%, on average, which could be attributed to the short treatment time. The ideal treatment time for AN reduction would have been eight days or longer, according to previous studies. Colour removal was low, and the study suggested further degradation. Turbidity removal showed the system to be inefficient, since the rate was low, at 45.01%. 57 The organic matter in the wastewater had high removal rates, although the system was generally inefficient at removing colour, turbidity, TSSs and AN due to various factors. The study would have been more efficient with adjustments to resolve these limiting factors. 4.2.7. CW System for Wastewater Treatment The study showed that VF CWs are most suitable when it comes to meeting high removal standards, such as 95% for BOD, 90% for TP and 90% nitrification. The VF bed for BOD removal and nitrification was very effective at high HLRs, even during winter. TSSs removal in the system was also very high. As reported by the authors (Farooqi, Basheer, & Chaudhari, 2008), a recycling rate of 1:1 (100% recycling) resulted in about 50% denitrification, which improved and stabilised the overall treatment performance of the system (Farooqi, Basheer, & Chaudhari, 2008). In addition, the removal of indicator bacteria in the system was about 2 logunits, although TP removal in the VF CWs was very limited, since it was not possible to acquire a sand bed medium with enough capacity to bind the phosphorus (Farooqi, Basheer, & Chaudhari, 2008). To combat this challenge, however, phosphorus removal can be obtained by simple precipitation with an aluminum compound in the sedimentation tank, prior to the CW (Farooqi, Basheer, & Chaudhari, 2008). The single-household system performance was monitored with and without recirculation, and the results proved that recirculation is essential in efficient pollutant removal. 58 4.2.8. Use of Macrophyte Plants, Sand and Gravel Materials in CW for Greywater Treatment To demonstrate that local macrophyte plants and natural substrates could successfully treat domestic wastewater, the results of studies based in West Java, Indonesia and Thailand and Costa Rica (Qomariyah, Ramelan, Sobriyah, & Setyono, 2017) are included in the Table 4.8. Table 4.8: Effectivenes of pollutant removal in CWs with natural substrates and local macrophytes (Qomariyah, Ramelan, Sobriyah, & Setyono, 2017) In agreement with the research findings, the treatment efficiency of BOD and COD varied between 76.03-99.4% and 78.89-98.46%, respectively, except for COD removal in the Thailand study, which varied between 42 and 83% (Qomariyah, Ramelan, Sobriyah, & Setyono, 2017) .The system in Thailand was still efficient because the influent concentrations of COD were low due to high degradation rates that occurred in the settling tank and the collection systems. The most recent study (Qomariyah, Ramelan, Sobriyah, & Setyono, 2017) showed inlet BOD concentrations of 496–850 mg/l, which were reduced to 2.19–17.2 mg/l, a value that was lower than the EPA guidelines of 30mg/l. According to (Qomariyah, Ramelan, Sobriyah, & Setyono, 59 2017), detergent in the wastewater was removed at an efficiency rate of 99.86%. Similarly, TSS removal through sedimentation and interception yielded results ranging from 95.47 to 99.56%, with an average of 98.06%. Outlet concentrations of TSSs were at 2–10 mg/l, which is below the EPA guideline and the Indonesian wastewater reuse standard. The Thailand study used both Canna and Heliconia (flowering plants) and gravel as the substrate, which resulted in TSS removals of 88–96% for both plants. The average removal of TCs in Indonesia and FCs in Costa Rica was 99.45 and 99.99%, respectively, which is a very high efficiency. As observed in the study, the Thai case produced a low removal of TP (6–35%) and TN (4–37%), unlike the other studies. Substrates that contain high calcium, aluminium and iron have high phosphorus, so that the high removal of phosphorus in the study might due to the high amount of iron-rich sand in the substrate used. Nutrient removal is not a wastewater reuse criterion; hence, if the treated effluent is to be used for irrigation, then nutrient removal is likely to become unnecessary (Qomariyah, Ramelan, Sobriyah, & Setyono, 2017). In the Costa Rica case, on the other hand, a longer HRT of 7.9 days was used, resulting in a level of treatment that exceeded the requirement of the local standards for wastewater reuse, in terms of BOD (average <10 mg/l) and FCs (average 122 cfu/100 ml), and with effective removal of E. coli (99.99%) (Qomariyah, Ramelan, Sobriyah, & Setyono, 2017). Sand, gravel, plant species and crushed rock are all materials that can be found locally, all yielding high performance in greywater treatment. Organic pollutants and pathogens have high removal rates in such systems and, therefore, the treated effluent can be reused for irrigation, for example. No energy is required to operate these CWs, therefore the systems are affordable. They are also a better alternative than conventional methods, as they can be employed as decentralised systems in developing countries. 60 4.2.9. Integrated CWs for Treating Domestic Wastewater The new integrated CW system in Glaslough is here compared to the mature integrated CW system in Dunhill, in relation to their nutrient removal perfomances and the impact of seasonal and annual changes. The two systems show impressive removal efficiencies of BOD and COD. Regarding the water quality data, ammonia–nitrogen, nitrate–nitrogen and MRP removal for the Glaslough system were high, at 99.0, 93.5 and 99.2%, respectively, whereas the Dunhill CW had removal efficiencies of 58, 80.8 and 34.0%, respectively (Scholz, 2011). In agreement with the study (Scholz, 2011), MRP and nitrate–nitrogen concentrations in the effluent increased gradually. In the Dunhill system, the decrease was attributed to an overload of the system. In the fourth year, the concentrations of the two parameters, as well as ammonia– nitrogen, were three times more than in the first three years. In the effluent, nitrate–nitrogen concentrations were higher than in the influent, suggesting that the nitrification process contributed to the transfer of some ammonia–nitrogen into nitrate–nitrogen. Both ammonia– nitrogen and nitrate–nitrogen, however, were released by the system. In both systems, according to the study (Scholz, 2011), effluent concentrations of COD and BOD were higher in summer and autumn than in spring and winter, but the removal efficiencies for these did not vary greatly in either system because of an increased Organic loading rate caused by increased evaporation and decreased precipitation (Scholz, 2011). Effluent concentrations of ammonia–nitrate, nitrate–nitrogen and MRP in the Glaslough system did not change significantly, but increased in the Dunhill system because of the higher HRTs provided by the sytem in Glaslough, which removed 99.2% more MRP than at Dunhill (Scholz, 2011). 61 The difference in the reduction of MRP between the systems could be because the subsoil and sediments in Glaslough did not reach saturation. Therefore, the results indicate that the integrated CW in Glaslough had a higher pollutant reduction capacity than did Dunhill. This is most likely due to overloading of the CW system at Dunhill. 4.2.10. Efficiency of Small CWs for Subsurface Treatment of Single-Family Domestic Effluent The 21 wetlands studied (Steer, Fraser, & Boddy, 2002) are numbered from one to 21 in Table 4.9, which shows their individual removal values for the relevant parameters from the study. 62 Table 4.9: System performance (Steer, Fraser, & Boddy, 2002) 63 According to Table 4.9a (which appears as 2a on the table) from the case study, the CWs individually reduced FCs from 82.7 to 99.9%, with the exception of CW 18, at 27.9%; however, overall FCs were reduced to 87.9±27.1% between the input and the output in these systems (Steer, Fraser, & Boddy, 2002). According to the study, the failure of that one system was attributed to a delay in planting the vegetation in the second cell, and a disrupted flow through the cell as a result of breaches in the clay liners, full blockage of the transfer pipes, or partial/full obstruction of the substrate (Steer, Fraser, & Boddy, 2002). The disruption of flow might have changed the retention time, hence reducing time available for protozoa to consume the FCs. In agreement with the study (Steer, Fraser, & Boddy, 2002), effluent was discharged from the polishing cell of these wetlands at levels below the EPA’s recommended 1000 counts/100 ml for 74% of the samples collected (Steer, Fraser, & Boddy, 2002). Two wetlands – CW18 and 19 – 64 failed to meet all the requirements on every occasion, while nine (CWs 1, 3, 7, 8, 9, 10, 11, 17, 21) met all the requirements for pollutant removal on every occasion. The systems that did not meet the guidelines were 15% less efficient at reducing loads than those that met the guidelines (Steer, Fraser, & Boddy, 2002). The data was unsuitable for determining seasonal effects. Furthermore, according to Table 4.9a (2a on the table), these CWs individually reduced TSSs, with efficiencies ranging from 25.0 to 89.1%, with the exception of CW 17 at -250%. In general, TSSs were reduced by 55.8±52.8% using the subsurface treatment CW process (Steer, Fraser, & Boddy, 2002); however, the negative efficiency at CW 17 resulted from remobilisation of the solids, failing because the overall effectiveness and longevity of the system was affected. Nevertheless, no observations could explain why the solids were remobilised (Steer, Fraser, & Boddy, 2002). Two systems (CW 4 and 12) failed to meet all the standards, but five systems (CW 5, 7, 11, 13, 15) did meet all the required standards. At total of 79% of the samples released TSSs below the recommended EPA level of 30 mg/l.The data was unsuitable for determining seasonal effects. According to Table 4.9b (2b on the table), BOD5 was reduced individually in the wetlands, from 70.9 to 95.9%, with the exception of CW 1 at 27.2%; overall these treatment wetlands reduced BOD5 by an average of 70.3±48.5% (Steer, Fraser, & Boddy, 2002). At total of 89% of the samples met EPA guidelines for BOD output at lower than 30 mg/l. CWs 16 and 18 failed to meet the EPA guidelines in all the samples. In addition, the samples that did not meet the standards had double the input loads of samples that did (Steer, Fraser, & Boddy, 2002). BOD reduction was 10% less in the winter, compared to summer, autumn and spring. 65 According to Table 4.9b (2b on the table), ammonia was the least efficiently reduced, by only 19.8–98.4% in that individual wetlands, and 56.5±31.3% in general, from input to output. Only 16% of the samples met the effluent guidelines, and all of the wetland samples failed to meet the EPA standard of 1.5 mg/l. CW 1 had the least ammonia reduction and the lowest input load due to aeration being performed prior to Cell 1. All the system samples failed to meet the guidelines on one or more occasion (Steer, Fraser, & Boddy, 2002). Treatment efficiency in the few systems that passed was 97%, with those that failed at only 53%. Ammonia reduction was 20% more efficient in autumn than winter, spring or summer, being most efficient in September and October. In agreement with the study’s findings (Steer, Fraser, & Boddy, 2002) , the CWs were individually capable of reducing 37.5–99.1% TP and 80.5±19.8% in general (Steer, Fraser, & Boddy, 2002). Three of the systems – CW 16, 17 and 18 – removed <50% TP. CW 16 failed to meet the standards on all occasions, while CW 7 and 8 met all the standards on every occasion. The EPA guidelines were exceeded by 50% of the systems. Reduction efficiency was high, at 94%, compared to 65% efficiency when it was not met (Steer, Fraser, & Boddy, 2002). The variable TP removal could not be attributed to substrate type, since all of the systems had the same substrate, nor to input loads or maintenance. Annual harvesting was not performed and, therefore, the decaying biomass could have provided another source of phosphorus. Phosphorous reduction in winter was 10% less than in summer and spring, and 20% less than in autumn. Table 4.10 shows the results for the various parameters analysed in the CWs related to initial concentrations, final concentrations and average reductions. 66 Table 4.10: Wetland data base summary (Steer, Fraser, & Boddy, 2002) Pathogen Samples (n) Fecal TSS BOD5 NH3 P 132 131 131 125 125 Average input cnts or mg/l 36410 55.4 104.7 47.7 8.36 SD input cnts or mg/l 63300 62.1 77 32.3 3.75 Average output cnts or mg/l 2150 18.8 13.7 18.4 1.71 SD output cnts or mg/l 5670 17.3 18.4 16.7 2.41 Average SD % % reduction reduction 87.9 55.8 70.3 56.5 80.5 27.1 52.8 48.5 31.3 19.8 In summary, the study showed that phosphorous, ammonia, and BOD removal were influenced by seasonal effects. Winter had the lowest BOD removal which was 10% less when compared to the other seasons spring, summer, and fall. Nevertheless, the system successfully reduced pollutants and improved water quality. 4.2.11. Reed bed CW system The results from the analysis of various parameters from this study are discussed, and compared to the Oman MECA Standard (A) in order to determine the effectiveness and efficiency of the system. Table 4.11 shows the removal efficiency for various components of a double-stage VF reed bed. 67 Table 4.11: Data for the treatment of effluent by the reed bed system (Haya Water, 2017; Oman Government, 2018) Parameter Raw Sewage (mg/ l ) Treated Effluent MECA Standard Removal (mg/ l) (A) Efficiency COD 1206 12.7 150 98.9 BOD 372.3 3.9 15 98.9 NH3–N 58.2 0.2 5 99.6 NO3–N - 32.9 50 (NO3) - TN 90.7 8.7 15 90.4 TP 11.3 0.1 30 99.1 TSSs 633.3 1.2 15 99.8 O&G 36 0.3 0.5 98.1 FCs - 117 200 per 100ml - VHO 22 <1 <1 per l 98 68 Excellent efficiency levels were obtained for the various parameters analysed, as follows: COD (98.9%), BOD (98.9%), ammonia–nitrogen (99.6%), TN (90.4%), TP (99.1%), TSSs (99.8%), O&G (98.1%) and VHO (98%). When compared to MECA Standard (A), due to the high efficiencies, the parameters are in compliance (Haya Water, 2017). Graph 4.1 shows a representation of treated effluent (mg/l) and the MECA Standard (A), as well as its removal efficiencies for all the above-mentioned parameters. Graph 4.1: Relationship between treated effluent, the MECA standard and removal efficiency (Haya Water, 2017; Oman Government, 2018) Relationship Between the Treated Effluent, its MECA Standard (A) and their Removal Efficiency 150 117 98.9 98.9 12.7 15 3.9 99.6 90.4 32.9 COD BOD 5 0.2 NH3-N 0 NO3-N Treated Effluent (mg/L) 99.1 99.8 98.1 15 1.2 TSS 0.5 0.3 O&G 98 30 15 8.7 TN 0.1 TP MECA Standard A 0 FC 0 VHO Removal Efficiency From Graph 4.1, it can be seen that the high levels of removal efficiencies for the solids (COD and BOD) mean that they can be easily removed from the treated effluent. Moreover, there are high levels of removal efficiencies recorded for ammonia–nitrogen, TN, TP, TSSs, O&G, FCs and VHO, which means that they comply entirely with the MECA standards (Haya Water, 2017). High levels of ammonia, nitrogen and phosphorus show that the soils through which the 69 effluent passed are highly nutritious. Moreover, the lack of nitrates in the TE sped up aeration and eutrophication. The lack of FCs in the TE means that the water quality, in terms of cleanliness, was very high. The design made the system highly efficient and effective. The system regulated the flow to maintain an optimal retention time for pollutant removal, while still reducing cost and size. The retention time depended on the type of wastewater being treated and, hence, it was observed that non-domestic wastewater took a longer time to be treated because it contained a heavier concentration of pollutants than domestic wastewater. Phragmites australis showed a relatively constant growth and high substrate levels, which contributed to the high efficiency of the system because the plant had high pollutant- and nutrient-absorption capacities. In summary, analysis of the chemical, physical and biological parameters in the Haya study showed that the system was highly efficient and effective, meaning that the system should be adopted, since it is advantageous in terms of size, cost and time. 4.3. Summary and Comparison A comparison is made between two related case studies that used different CW designs (HSSF) and (VF). Case study 1 “HSSF CW for On-Site Wastewater Treatment” (Hoddinott, 2006) and case study 2 “The use of VF CW for on-site treatment of domestic water: New Danish guidelines” (Brix & Arias, 2005) are compared, in terms of methodology and results. 70 Pretreatment for Case 1 required the use of a septic tank, which provided primary treatment by removing TSSs anaerobically, while maintaining regular pumping of the septic tank. Case 2 pretreatment also required the use of septic tanks, or chamber sedimentation tanks. Case 1, however, did not provide specific measurement requirements, as opposed to Case 2. The vegetation in Case 1 was recommend to be P. australis, the same as for Case 2, because it facilitates better bacterial growth and is quite tolerant of toxicity. In both cases, effluent recirculation was suggested at a rate of 50% for the purpose of enhancing denitrification. Case 1 recommended the use of gravel as the filtration medium, while Case 2 suggested the use of sand. Both cases, however, agreed that the bed should be lined using geotextile or gravel to prevent the filtration medium from entering the drainage layer. Both cases provided information on bed size and dimensions, but Case 1 was more detailed, even providing equations for calculating surface area and aspect ratio. Case 2, on the other hand, provided information regarding the distribution system, while Case 1 did not. From Table 4.2 in Case 2, the average removal efficiency for TSSs was 94%, while Case 1 recorded an average of 84.3% in the discussion of the results, which was well within the EPA standards, according to Table 4.1. BOD5 removal in Case 1 was 88%, while in Case 2, it was 94.5%. With reference to Table 4.1, COD, BOD, ammonia, coliforms and TSS removals were all within the stated OEPA standards for effluent concentrations (Hoddinott, 2006). TN removal in Case 1 averaged at 43%, while for Case 2 it was 43.75%. TP removal in Case 1 was 97%, using Phragmites, but in Case 2, the removal efficiency for the same averaged 22.75%. From this comparison, it can be concluded that the VF system is better at removing TSSs and BOD5. On the other hand, the HSSF system is better at TP removal. Both systems, however, had no significant difference in TN removal. 71 Chapter 5 CONCLUSION Single-household wastewater management is a challenge in most developing countries. It is difficult to find a system that is, at the same time, efficient, easy to operate and maintain, and low in cost. Nevertheless, water being a key element for the world’s survival, a sustainable solution is required for the problem. Effluent mismanagement is one of the factors that contributes to massive water pollution of water bodies and water courses, since the effluent is often discharged directly, without treatment. Water is essential to life and so it must be conserved and its quality maintained. CWs come in handy for single-family homes to manage and treat their own wastewater. The systems are convenient, since they do not necessarily require large pieces of land to be operated on. In the absence of adequate land, consumers might have to purchase manufactured systems that could be more costly, but such costs should be weighed against the effects pollution inflicts on the environment and public health. In addition, these systems are very easy to maintain and, therefore, are perfect for domestic use, wherein the consumers do not necessarily need extensive knowledge about the technicalities of the system. It is important for public awareness programs to be initiated to teach people about CWs, so that they can fully understand the benefits of such systems, and so will be more likely to adopt these systems in their homes. The methodologies discussed included information about flow type, design type, effluent recirculation, bed dimensions, aspect ratios, distribution, sealing, insulation, substrate media, 72 construction materials, vegetation, water balance, reuse criteria, influent/effluent quality, location, PEs, surface area needs, sampling and energy requirements. From assessment of all of this information, it was determined that the basic design for a single-household system should consist of pre-treatment (usually in a septic tank), which acts as the primary treatment, followed by secondary and tertiary treatments. This basic design was replicated throughout the case studies outlined in this report. Some systems had modifications or additions to the basic design, such as aeration and the use of technologically-advanced machines, such as the RBC. Results from the analysed samples showed removal efficiencies for both chemical and physiological parameters, such as COD, BOD5, TCs, TN, TKN, TP, FCs and TSSs. The efficiencies of the systems were also evaluated, in relation to how seasonal variations affected performance. Colder temperatures in winter seemed to slow down system functions in general, compared to times of warmer temperatures, in spring, autumn and summer. This phenomenon has been attributed to the death of plants during winter, slowing down the microbial function that is essential to pollutant removal through, for example, protozoan predation. System performance was also discussed, in relation to the role and capacity of vegetation to take up pollutants, the suitability of substrate media and the effects of HLRs and HRTs on the beds. Based on the research findings, the study “A Recirculating VF CW for the Treatment of Domestic Wastewater” was the best system assessed. The study’s efficiency was measured both by percentage removal of pollutants, and also by their conformity to the Israeli regulations, which makes the study very reliable. TSSs, BOD5 and COD removals were 90, 95 and 84%, respectively. These three parameters conformed to the Israeli standards. There was efficient nitrification as well, and there were very low nitrate and nitrite concentrations, also conforming 73 to the Israeli regulations. The soil-component ensured that ammonia removal was <5 mg N l-1, a value that is often difficult to achieve. In conclusion, single-household CWs are a good solution for wastewater management in singlefamily homes, as they are low cost, easy to operate and maintain, and highly effective. They should be adopted as a matter of public policy as part of the global effort to conserve, and maintain the quality of, water. 74 Chapter 6 RECOMMENDATIONS Based on the discussions reported here, a number of recommendations can be made:  CWs should be installed where large areas of land are available and the price is cheap  In the case of water surges, good-quality construction materials should be used in the building of CW systems. The following recommendations can be made for future work in Oman study:  A VF–HF hybrid design should be implemented in Oman to produce the most efficient and effective system for treating wastewater and ensuring easy and adequate cleaning of the sewage within the shortest amount of time.  To increase the number of CWs in Oman, companies similar to Haya Water should be encouraged to invest in CW projects. As a start, the Oman government could discount the cost of the pipes and chemicals used in such treatments.  It is recommended to implement Reed Bed Treatment Technology as a sustainable solution in Regional Governorates since there are huge empty areas.  Future studies should further address the details of water balance, energy balance and CW design parameters. 75 REFERENCES Brix , H., & Arias, C. A. (2005). 2. The use of vertical flow constructed wetlands for on-site treatment of domestic wastewater: New Danish guidelines. Ecological Engineering, 25(5), 491-500. Crawford, G., & Sandino, J. (2010). Energy efficiency in wastewater treatment in North America: A compendium of best practices and case studies of novel approaches. Retrieved from Water Environment Research Foundation.: https://www.nyserda.ny.gov//...Water-Wastewater.../north-american-drinking-water-u... Farooqi, I. H., Basheer, F., & Chaudhari , R. J. (2008). Constructed Wetland System (CWS) for Wastewater Treatment. Proceedings of Taal2007: The 12th World Lake Conference, 1004-1008. Haya Water (2017). Haya Water. Retrieved from: https://haya.om/en/Pages/Home.aspx [Accessed 17th of May 2018] Hoddinott, B. C. (2006). Horizontal Subsurface Flow Constructed Wetlands for On-Site Wastewater Treatment. Dayton, Ohio: Wright State University. Jhansi, S. C., & Mishra , S. K. (2013). Wastewater treatment and reuse: Sustainability options. Consilience: The Journal of Sustainable Development, 10(1), 1-15. Kinsley, C., Crolla, A., Rode, J., & Zytner, R. (2014). A Hybrid Constructed Wetland System for Decentralized Wastewater Treatment. Ontario: Ontario Rural Wastewater Centre. 76 Nelson , J., Bishay, F., Van Roodselaar, A., Ikonomou, M., & Law, F. C. (2007). The use of in vitro bioessays to quantify endocrine disrupting chemicals in municipal wastewater treatment plant effluents. The Science of the Total Environment, 374(1), 80-90. O'Luanaigh, N., & Gill, L. W. (nd). The attenuation capacity of constructed wetlands to treat domestic wastewater in Ireland. 1-8. Oman Government (2018). Ministry of Environment and Climate Affairs. Retrieved from meca.gov: https://meca.gov.om/en/module.php?module=decisions&page=2 [Accessed 17th of May 2018] Postel, S. L. (2000). Entering an era of water scarcity: The challenges ahead. Ecological Applications, 10(4), 941-948. Praewa, W. (2017). Sustainable Wastewater Treatment for Thailand. Retrieved from: https://minds.wisconsin.edu/bitstream/handle/.../MS_Thesis_Wongburi_Praewa.pdf?... [Accessed 20th of March 2018] Qomariyah, S., Ramelan, A., Sobriyah, & Setyono, P. (2017). Use of macrophyte plants, sand & gravel materials in constructed wetlands for greywater treatment. IOP Conference Series: Materials Science And Engineering, 176, 012018. Scholz, M. (2011). Integrated constructed wetlands for treating domestic wastewater. Wetland Case Studies, (2.1), 1-36. Secretariat, R. (2014). Renewables 2014 global status report. REN 21. Paris: Technical Report. 77 Sklarz, M. Y., Gross, A., Yakirevich, A., & Soares, M. M. (2009). A recirculating vertical flow constructed wetland for the treatment of domestic wastewater. Desalination, (246), 617624. Steer, D., Fraser, L., & Boddy, J. (2002). Efficiency of small constructed wetlands for subsurface treatment of single-family domestic effluent. Ecological Engineering, 18(4), 429-440. Vymazal, J., & Kropfelova, L. (2008). Types of constructed wetlands for wastewater treatment. Wastewater Treatment in Constructed Wetlands with Horizontal Sub-surface Flow, 121202. Wetzel, R. G. (1993). Micro-communities and micro-gradients: Linking nutrient regeneration, microbial mutualism, and high sustained aquatic primary production. Netherlands Journal of Aquatic Ecology, 27(1), 3-9. Wurochekke, A. A., Harun, N. A., Mohamed, R. M., & Kassima, A. H. (2014). Constructed Wetland of Lepironia Articulata for Household Greywater Treatment. APCBEE Procedia, (10) 103-109. 78
ENG 4 133 Bachelor Thesis German University of Technology in Oman (GUtech) Department of Engineering Title of the Thesis ASSESMENT AND REVIEW OF CONSTRUCTED WETLAND FOR MUNICIPAL WASTEWATER: SELECTED CASE STUDIES Course Coordinator: Dr.-Ing. Najah Al Mhanna Project Supervisor: Main supervisor: Dr.Hind Bargash Student Name: Al Hawra Al Ajmi Spring 2018 Approval of the Dean of the Faculty of Engineering and Computer Science Dr.-Ing. Najah Al Mhanna I certify that this Thesis satisfies the requirements of a Bachelors Thesis for the Degree of Bachelor of Engineering in Environmental Engineering. Dr.-Ing. Najah Al Mhanna Head, Department of Engineering I certify that I have read this Thesis and that it is my opinion that the Thesis is fully adequate in scope and quality as a Bachelors Thesis for the Degree of Bachelor of Environmental Engineering. Name Supervisor Examining Committee 1. Name 2. Name i Declaration: In accordance with the requirements of the degree of Bachelor of Engineering at German University of Technology in Oman, I present the following thesis titled “Assessment and review of constructed wetland for Municipal wastewater: selected case studies”. This work was performed under the supervision of Dr. Hind Bargash. I hereby declare that the work submitted in this thesis is my own and based on the results found solely by myself. Materials of work found by other researchers are clearly cited and listed in reference list. This thesis, neither in whole nor in part, has been previously submitted for any degree. The author confirms that the library may lend or copy this thesis upon request, for academic purposes. Name: Hawra Mohsin Al Ajmi Signature: ii ABSTRACT Municipals can be classified as small towns whose major wastewater effluents are composed of rainwater, domestic water and extremely small percentages of industrial water which are negligible because they do not really affect the constituents found in the wastewater. As a result, few municipal wastewater effluents contain heavy metals. The most common constituents required to be removed from the wastewater are BOD, COD, TSS, TKN, TP, FC, TC, N and Ammonia. This report aims to identify the various methodologies, designs, and innovations that can be used to treat municipal wastewater through constructed wetlands. The results of the various studies are as well presented to show the efficiency removal rates, designs, strategies, and cost parameters that can be adopted by municipalities to effectively treat wastewater in a way that barely intrudes on the ecosystem and the environment. The highest removal rates recorded among all studies were; 99.1% TP, 77% TKN, 98.9% COD, 98.9% BOD. 99.8% TSS, 90.4% TN, 99% TC, 99% FC, 95% nitrogen organic (NORG), 84% Ammonium-nitrogen (NH4 +-N), 79% nitrate-nitrogen (NO3—N), 99.6% Ammonia-nitrogen (NH3-N), 98% Viable helminths ova(VHO), 98.1% Oil &Grease (O&G) and 98% Escherichia coli (E. coli). The successful removal of such pollutants leads to wholesome integration of treated wastewater back to the environment via discharge into streams or rivers. Treated effluent can be collected and reused for purposes such as irrigation. Keywords: Municipal wastewater, effluent, removal rates, cost, efficiency, plants species i ‫الخالصة‬ ‫يمكن تصنيف البلديات على أنها بلدات صغيرة حيث تتكون مياه المجاري فيها من مياه األمطار والمخلفات المائية من االستخدامات‬ ‫المنزلية ونسبة مئوية متناهية في الصغر من المخلفات السائلة من االستخدامات الصناعية وهي النسبة التي ال تذكر إلنعدام تأثيرها‬ ‫الفعلي على المكونات الموجودة في مياه الصرف الصحي‪ .‬ونتيجة لذلك‪ ،‬فنسبة صغيرة للغاية من المخلفات السائلة للبلديات تحتوي‬ ‫على معادن ثقيلة‪ .‬وعلى خالف ندرة المعادن الثقيلة في هذه المخلفات فإن العناصر المطلوب إزالتها من مياه المجاري تتضمن‬ ‫الطلب البيولوجي الكيميائي على األكسجين و الطلب البيولوجي الكيميائي على األكسجين والمواد الصلبة العالقة الكلية و نتروجين‬ ‫كيلدال الكلي والفسفوروز الكلي والقولونيات البرازية والقولونيات الكلية والنيتروجين واألمونيا۔ يهدف هذا التقرير إلى تحديد‬ ‫مختلف المنهجيات والتصاميم والمبتكرات التي يمكن استخدامها في معالجة مياه المجاري البلدية من خالل األراضي الرطبة‬ ‫(األهوار) التي يتم إنشاؤها‪ .‬كما يستعرض التقرير الحالي نتائج الدراسات المختلفة إلظهار معدالت كفاءة إزالة الملوثات‬ ‫والتصاميم واالستراتيجيات ومعايير التكلفة التي يمكن للبلديات تبنيها والعمل بها لمعالجة مياه المجاري على نحو فعال بطريقة ال‬ ‫تكاد تتطفل على النظام البيئي والبيئة‪ .‬كانت أعلى معدالت اإلزالة المسجلة عبر كافة الدراسات على النحو التالي ‪ 99.1%.:‬من‬ ‫الفسفوروز الكلي و‪ %77‬من نتروجين كيلدال الكلي و‪ %98.9‬من الطلب الكيميائي على األكسجين و‪ %98.9‬من الطلب‬ ‫البيولوجي الكيميائي على األكسجين و‪ %99.8‬من المواد الصلبة العالقة الكلية و‪ %90.4‬من النيتروجين الكلي و‪ %99‬من‬ ‫القولونيات الكلية و‪ %99‬من القولونيات البرازية و‪ %95‬من النيتروجين العضوي و‪ %84‬من األمونيوم و‪ %79‬من نيترات‬ ‫النيتروجين و ‪ %99.6‬من نيتروجين األمونيا و‪ %98‬من الديدان الطفيلية و‪ %98.1‬من النفط والشحوم و‪ %98‬من اإلشريكية‬ ‫القولونية۔ ومع إزالة مثل هذه الملوثات بنجاح‪ ،‬يسهل دمج المياه المعالجة في البيئة من خالل إعادة تصريفها في الجداول واألنهار‬ ‫‪ .‬يُمكن تجميع مياه المجاري ال ُمعالجة وإعادة استخدامها ألغراض متنوعة مثل عمليات الري‪.‬‬ ‫الكلمات الداللية‪ :‬مياه املجاري البلدية فضالت‪,‬معدالت اإلزالة‪ ,‬التكلفة ‪,‬الكفاءة‬ ‫‪ii‬‬ ACKNOWLEDGMENT The completion of this study could not have been possible without the help, support and guidance of my beloved supervisor, the expertise Dr Hind Bargash, I would like to thank her for her constant contribution and patience throughout. It was truly a pleasure having her as my mentor. I would like to express my special gratitude towards my supportive family. My parents; Fatma AlAjmi and Mohsin Al-Ajmi, my siblings; Alaa, Alya and Mohammed and my uncle; Yassir AlAjmi for being by my side and believing in me, their constant motivation and encouragement was a reason for my accomplishment. Special thanks to my group members and partners Nujoom Al-Amri and Thuraya Al-Busaidi for assisting, advising and collaborating with me through this whole journey. Last but not least I would like to thank my friends who directly and indirectly supported me and helped me survive through the stress of accomplishing this study. iii TABLE OF CONTENTS ABSTRACT ..................................................................................................................................... i ‫ الخالصة‬............................................................................................................................................... ii ACKNOWLEDGMENT................................................................................................................ iii LIST OF FIGURES ..................................................................................................................... viii LIST OF TABLES ......................................................................................................................... ix LIST OF GRAPHS ........................................................................................................................ xi LIST OF ABBREVIATIONS ....................................................................................................... xii INTRODUCTION .......................................................................................................................... 1 1.1 Background ......................................................................................................................................... 1 1.2 Limitations of Constructed Wetlands ................................................................................................. 2 1.3 Problem Statement .............................................................................................................................. 3 1.4 Aim and Objectives............................................................................................................................. 4 LITERATURE REVIEW ............................................................................................................... 5 2.1. Domestic, Municipal and Industrial Wastewater ............................................................................... 5 2.2. Conventional Wastewater Treatment ............................................................................................... 6 2.2.1. Primary Treatment ...................................................................................................................... 7 2.2.2. Secondary Treatment .................................................................................................................. 7 2.2.3. Tertiary Treatment ...................................................................................................................... 8 2.3. Constructed Wetlands (CWs) ............................................................................................................. 8 iv 2.4. Main Benefits and Outcomes of CWs ................................................................................................ 9 2.5. Types of CWs .................................................................................................................................... 10 2.6. Components of CWs ........................................................................................................................ 10 2.6.1. Water ........................................................................................................................................ 10 2.6.2. Substrates, Sediments and Litter .............................................................................................. 11 2.6.3. Vegetation ................................................................................................................................. 11 2.6.4. Microorganisms ........................................................................................................................ 12 2.6.5. Animals...................................................................................................................................... 13 2.7. Literature Summary ......................................................................................................................... 13 METHODOLOGY ....................................................................................................................... 14 3.1 Overview ........................................................................................................................................... 14 3.2 Methodologies................................................................................................................................... 14 3.2.1 Performance and Cost Comparison of a FWS and a VSF Constructed Wetland System .......... 14 3.2.2 Horizontal Sub-Surface Flow and Hybrid Constructed Wetlands Systems for Wastewater Treatment ............................................................................................................................................ 16 3.2.3 Municipal Wastewater Treatment using Constructed Wetlands ................................................ 19 3.2.4 Efficiency of a Horizontal Sub-Surface Flow Constructed Wetland Treatment System in an Arid Area ............................................................................................................................................ 21 3.2.5 Feasibility of Using Constructed Treatment Wetlands for Municipal Wastewater Treatment in the Bogotá Savannah, Colombia ......................................................................................................... 23 3.2.6 Performance of Four Full-Scale Artificially Aerated Horizontal Flow Constructed Wetlands for Domestic Wastewater Treatment ........................................................................................................ 25 3.2.7 A review on the sustainability of constructed wetlands for wastewater treatment: Design and operation ............................................................................................................................................. 27 v 3.2.8 Constructed Wetlands as a Sustainable Solution for Wastewater Treatment in Small Villages 28 3.2.9 Municipal Wastewater Treatment using Vertical Flow Constructed Wetlands Planted with Canna, Phragmites and Cyprus ........................................................................................................... 29 3.2.10 Development of Constructed Wetlands in Performance Intensifications for Wastewater Treatment: A Nitrogen and Organic Matter Targeted Review ........................................................... 30 3.2.11. Reed bed CW system .............................................................................................................. 31 RESULTS AND DISCUSSION ................................................................................................... 36 4.1 Overview ........................................................................................................................................... 36 4.2 Results and discussions ..................................................................................................................... 36 4.2.1 Performance and Cost Comparison of a FWS and a VSF Constructed Wetland System .......... 36 4.2.2 Horizontal Sub-Surface Flow and Hybrid Constructed Wetlands Systems for Wastewater Treatment ............................................................................................................................................ 38 4.2.3 Municipal wastewater treatment using constructed wetlands .................................................... 43 4.2.4 Efficiency of a Horizontal Sub-Surface Flow Constructed Wetland Treatment System in an Arid Area ............................................................................................................................................ 44 4.2.5 Feasibility of using constructed treatment wetlands for municipal wastewater treatment in the Bogotá Savannah, Colombia ............................................................................................................... 47 4.2.6 Performance of Four Full-Scale Artificially Aerated Horizontal Flow Constructed Wetlands for Domestic Wastewater Treatment ........................................................................................................ 49 4.2.7 A review on the sustainability of constructed wetlands for wastewater treatment: Design and operation ............................................................................................................................................. 51 4.2.8 Constructed Wetlands as a Sustainable Solution for Wastewater Treatment in Small Villages 52 4.2.9 Municipal wastewater treatment using vertical flow constructed wetlands planted with Canna, Phragmites and Cyprus ....................................................................................................................... 56 vi 4.2.10 Development of constructed wetlands in performance intensifications for wastewater treatment: A nitrogen and organic matter targeted review .................................................................. 58 4.2.11. Reed bed CW system .............................................................................................................. 60 4.3 Summary and Comparison ...................................................................................................... 63 CONCLUSION ............................................................................................................................. 65 RECOMMENDATIONS .............................................................................................................. 67 REFERENCES ............................................................................................................................. 68 vii LIST OF FIGURES Figure 3.1: Flow diagram of Korestia facility (Gikas & Tsihrintzis, 2014). ................................ 21 Figure 3.2: The horizontal sub-surface flow constructed wetland treatment (HSF-CW) system layout (Albalawneh, Chang, Chou, & Naoum, 2016)................................................. 22 Figure 3.3: Site process flowsheets of aerated HSSF CW sites( Butterworth, et al., 2016). ........ 26 Figure 3.4 Design of VFCW (Abou-Elela & Hellal, 2012). ......................................................... 30 Figure 3.5: Description of the process for treated effluent (Haya Water, 2017). ......................... 33 Figure 3.6: Stage A (Haya Water, 2017) ...................................................................................... 34 Figure 3.7: Stage B (Haya Water, 2017)....................................................................................... 34 Figure 3.8: Photographs after both stages (Haya Water, 2017) .................................................... 35 Figure 4.1: Concentrations of COD, BOD and TSS in treated effluent (Abou-Elela & Hellal, 2012) ........................................................................................................................... 56 viii LIST OF TABLES Table 3.1: Design criteria for a double-stage VF reed bed after pre-treatment (septic tank) (Haya Water, 2017). .............................................................................................................. 32 Table 4.1: Capital and operating costs (€) for the two facilities( Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007)................................................................................ 37 Table 4.2: Treatment efficiency of vegetated beds of HSSF CWs—world wide experience(data from Australia, Austria, Brazil, Canada, Czech Republic, Denmark, Germany, India, Mexico, New Zealand, Poland, Slovenia, Sweden, USA and UK)( Vyzamal, 2005). 38 Table 4.3: Performance of on-site HF CW at Zitenice, Czech Republic during the period January 2003–September 2004( Vyzamal, 2005) .................................................................... 39 Table 4.5: Performance data from Oaklands Park VF-HF CW (August 1989–September 1991, numbers in mgl-1)( Vyzamal, 2005) ............................................................................ 41 Table 4.7: Treatment performance of a hybrid HF-VF constructed wetland at Darzlubie, Poland; concentrations in mgl-1 (Vyzamal, 2005)..................................................................... 42 Table 4.8: Construction cost of Korestia facility (Gikas & Tsihrintzis, 2014). ............................ 43 Table 4.9: BOD5, COD, TSS, FC, and P removal (Albalawneh, Chang, Chou, & Naoum, 2016) ..................................................................................................................................... 45 Table 4.10: Estimated percent removal of pollutants for the three treatment systems evaluated (Arias & Brown, 2009). .............................................................................................. 48 Table 4.11: Summer and winter ammonium inlet loadings and effluent concentrations (Butterworth, et al., 2016) ........................................................................................... 49 ix Table 4.13: Percentages of removal of biochemical oxygen demand(BOD), chemical oxygen demand(COD) and total suspended solids(TSS), during the second year of wetland operation (Solano, Soriano, & Ciria, 2004) ................................................................ 53 Table 4.15: Pathogen removal during the second year of wetland operation (Solano, Soriano, & Ciria, 2004) ................................................................................................................. 55 x LIST OF GRAPHS Graph 4.1: Relationship between treated effluent, the MECA standard and removal efficiency (Haya Water, 2017) (Oman Government, 2018) ....................................................... 61 xi LIST OF ABBREVIATIONS CW constructed wetlands HF horizontal flow VF vertical flow SSF sub-surface flow HSSF horizontal sub-surface flow VSSF vertical sub-surface flow FWS free water surface HRT hydraulic retention time HLR hydraulic loading rate P.e population equivalent BOD Biological oxygen demand COD chemical oxygen demand EC electrical conductivity TSS total suspended solids FC fecal coliforms TC total coliforms xii TKN total kjeldahl nitrogen TP total phosphorous TN total nitrogen TE treated effluent SF surface Flow RBC rotating biological conductor MECA Ministry of Environment and Climate Affairs xiii CHAPTER 1 INTRODUCTION 1.1 Background Water is one of the essentials that contribute primarily to the sustenance of life for living things. Water is “life”, meaning the existence of all inhabitants on Earth is dependent on this resource. Therefore, mankind must care to protect all water resources. Despite water being essential for life, sustenance water pollution has become a significant threat to water sources. Industrial wastes and exhaust fumes are the major contributors of water pollution across the globe, and the growth in industrial development across the world has caused more wastes to be released in the water bodies. The untreated waste discharged from single household, municipal and industrial activities into the water sources and land have endangered marine life, degraded the environment, and increased the risk of humans contracting water-borne diseases. (Postel, 2000). Water pollution control mechanisms must include public awareness, and the public need to be educated on the importance of preserving water resources by properly disposing wastes to prevent municipal, industrial and domestic wastewater. If the public understand the need to keep water safe, then the pollution of water and environmental degradation can be eluded. CW treatment systems for wastewater recycling is cost effective and can help those people struggling with the scarcity. The strategy of conserving water benefits the society and helps the environment and water utilities. 1 The concept of sustainability can be integrated into both human activities and the general human society (Praewa, 2017). If the human activities are less sustaining, there are adverse effects on the ecosystem which is essential for sustenance and support of human life. Present-day approaches have been designed to incorporate sustainability, environmental ethics and the participation of public efforts in creating developmental projects in the communities. Known and unknown water substances being added to the public water used in industries, households and for commercial purposes transforms the water into household, municipal and industrial wastewaters. CWs is a sustainable approach for municipal, single household and industrial wastewater treatment. These enhance the basis for water reclamation and reuse of most essential water resources management programs across the globe (Praewa, 2017). CWs are managed and engineered wetland systems that are gaining worldwide popularity in wastewater reclamation and treatment. Moreover, they naturally perform pollutant removing processes mediated by complex interactions between soil/gravel media, water, vegetation and their associated microbial assemblages and the environment to improve water quality viably. CWs are designed to exploit the physical, chemical, and biological treatment processes that are found in wetlands and provide a provision for organic material reduction, nutrients, metals, total suspended solids, pathogenic organisms and biological oxygen demand. CWs cost less and have easier operation and maintenance, and they proved to have a great potential for application in households, industries, and municipals wastewater treatment. 1.2 Limitations of Constructed Wetlands 2 CW systems have limitations that sabotage their effectiveness. In contrast with other conventional wastewater systems that accomplish the same purpose, they tend to occupy large pieces of land. CW system has an economic deficit, making it impossible for people who do not have money to buy more land, the ability to install a CW. Therefore, in some cases, constructing a wetland system is expensive (Jhansi & Mishra, 2013). Water treatment effectiveness is hindered because biological components in wastewater are in most cases sensitive to chemicals such that any water surges would affect the process of CW. Although the wetlands are designed to survive in very little amounts of water, they cannot survive completely in areas that are dry. Cold weather conditions weaken the effectiveness of the wetland system, and high temperatures that may be a result of dry periods and drought, also affects the performance of the system. Heavy rains also have an impact on the effectiveness of the constructed wetland systems, most especially during the spring season. The system effectiveness is dependent on many changing weather patterns; therefore, their effectiveness in the treatment process are gradually compromised (Crawford & Sandino , 2010). Applying constructed wetland systems for municipal, industrial and single household wastewaters is a new concept (Crawford & Sandino, 2010), and consequently, the technology to reinforce its effectiveness is not fully developed. Some ecological and environmental critiques believe that more should be done to realize full efficiency of the constructed design system. 1.3 Problem Statement Most developing countries have challenges regarding industrial, municipal and single household wastewater management because they have limitations in obtaining wastewater management technologies that are economical, usable and effective. The sole purpose of 3 wastewater management is to prevent the spread of diseases and infections that are caused by water contamination. Nutrients recovery, water reuse, and reclamation, including conserving water resources are other wastewater management objectives that most world organizations are working to attain. Changing from conventional wastewater management to more efficient and effective wastewater management should be embraced globally (Praewa, 2017). The discharges and effluents that emerge because of water pollution should be disposed of in a way to not spread diseases and infections to the members of the society. Stagnant, polluted water bodies give mosquitoes a good breeding site, placing people at very high risk of contracting malaria (Praewa, 2017). 1.4 Aim and Objectives The aim of this study is to provide an assessment of the various types of CW wastewater treatment systems, through a review of their design for use in municipals, and a discussion of their performance, in terms of onsite wastewater treatment, percentage removal of pollutants, water reuse criteria and influent/effluent quality. Using several study cases as examples. 4 CHAPTER 2 LITERATURE REVIEW 2.1. Domestic, Municipal and Industrial Wastewater In this day and age, the issue of municipal, industrial and domestic wastewater is of great concern because it can cause severe environmental problems and can also impact people in terms of their health. Studies have estimated that wastewater comprises 99% water, with the remaining 1% being a mixture of suspended and dissolved organic solids, detergents and chemicals (Secretariat, 2014). Sewage is wastewater that comprises household waste from toilets, sinks and showers/baths that is disposed of via sewers. Municipal wastewater includes input that ranges from, for example, shops, to restaurants and bars, and car washes (Secretariat, 2014). Frequently, pretreated industrial wastewater is included in with the municipal wastewater. A wide variety of processes result in the formation of industrial wastewater, including plastic manufacturing, wood pulping, petroleum refinement and food processing. According to Secretariat (2014), these different types of wastewater have varying compositions, containing for instance, different pathogens, bacteria and nutrients. Untreated wastewater components can be organised into three categories – physical, biological and chemical. Solid and inorganic constituents in wastewater comprise the physical components. The biological 5 components are bacteria, viruses, protozoa and other pathogens. Lastly, the chemical components include dissolved materials and organic matter, as well as nutrients and metals, which, in most cases, are heavy metals. In rare cases, wastewater might contain reusable resources for example, water, carbon and other nutrients that could be recovered. For effective effluent regulatory standards to be met, wastewater needs to undergo appropriate treatment in order to get rid of the pollutants and, according to Crawford & Sandino (2010), this process should be focused on the recovery of resources, so as to be self-sustaining. Advances in scientific knowledge, and a greater consciousness about the environment and water as a resource, have given rise to new and improved technologies and treatment systems that are effective in dealing with wastewater pollution and also in reducing the energy used in recycling wastewater; however, selection of the appropriate technology to solve a specific wastewater problem should be undertaken with great care. Generally, there are two types of wastewater treatment systems – conventional and sustainable CW. 2.2. Conventional Wastewater Treatment Conventional wastewater treatment comprises physical, chemical and biological processes, involving three stages, referred to as primary, secondary and tertiary treatments. 6 2.2.1. Primary Treatment This treatment is used in the removal and separation of particulate inorganic materials and solids, which would otherwise clog and destroy water pipes of the network. This type of treatment entails screening, grit removal and sedimentation. Screens are used to get rid of large debris, including plastics and cans. The grit chamber system is used to remove, settle, gravel- and sand-sized particles. According to Nelson et al. (2007), the wastewater is then moved into a quiescent basin, where it is temporarily retained so that the remaining heavier solids can settle to the bottom of the basin, while the lighter solids, including grease and oil, can accumulate on the surface. Finally, skimming and sedimentation processes are used to remove both the floating and settled pollutants. The liquid that remains is transferred to the secondary treatment. In this primary stage, 50% of the TSS and 30–40% of the BOD are removed (Nelson, Bishay, Van Roodselaar, Ikonomou, & Law, 2007). 2.2.2. Secondary Treatment Dissolved and biological matter is removed in the secondary treatment. According to Nelson et al. (2007), 90% of the organic matter in the wastewater is removed at this stage. The attached and suspended growth processes are the two most suitable conventional methods used in secondary treatment. In the attached growth process, algae, bacteria and other microorganisms are grown on the surface of the wastewater, resulting in the formation of biomass, which breaks down the organic waste. Trickling filters, bio-towers and rotating biological contactors are included in the attached growth 7 process unit. In the suspended growth process, the microbial growth is suspended in an aerated water mixture; however, activated sludge, in which a biomass of aerobic bacteria and other microorganisms is grown, is the most common type of suspended growth process. 2.2.3. Tertiary Treatment The tertiary treatment is more advanced, aimed at producing a better-quality, more purified effluent for discharge into estuaries and low-flow river ecosystems. Coagulation sedimentation, filtration, reverse osmosis and extended secondary biological treatments are some of the methods that are used in this stage. These methods remove nutrients and stabilise oxygen in oxygendemanding substances. The treated effluent can then be safely reused, recycled or discharged (Praewa, 2017). In most circumstances, a final disinfection process is needed before tertiary-treated wastewater can be discharged. Disinfectants can be added to kill off pathogens and microorganisms, and. chlorine and ultraviolet light are also commonly used. The treated water can then either be discharged into different water bodies, including recharging underground reserves, or used in agricultural irrigation (Praewa, 2017), as long as it meets the required standards. 2.3. Constructed Wetlands (CWs) CW systems for single-household, municipal, and industrial wastewater are designed in ways that imitate the natural processes at work in wetlands but include features that provide advantages over natural wetland processes. Such CWs incorporate chemical, biological and physical processes that 8 are used to remove the pollutants and enhance and improve the quality of the wastewater (Vymazal & Kropfelova, 2008). These design systems use aquatic macrophyte and microbial communities, and plant roots and their host minerals to effectively remove pollutants, which include nitrogen, metals and pathogenic organisms, among many others. In 1904, the first CW was built in Australia (Vymazal & Kropfelova, 2008). Despite this, technological advancement in the field has been slow (Vymazal & Kropfelova, 2008). As the number of CWs increases around the world, and the benefits and effectiveness of the system over conventional treatment systems become better understood, CWs are finding wider favor among ecologists, scientists and water and environmental engineers, and this is leading to their popularisation even among developing countries. 2.4. Main Benefits and Outcomes of CWs The CW is a beneficial wastewater system because, upon treatment, the water that is discharged can either be used for domestic activities or can be directly discharged into the environment. It is also beneficial to the end-users, as construction costs are minimal, and the costs of operation and maintenance are affordable. The operation and maintenance of CWs are periodic, unlike conventional water treatment systems, which in most cases require continuous, on-site labour (Crawford & Sandino, 2010). The CW system facilitates the recycling and reuse of water, thereby defraying the costs of installation, operation and maintenance. The CW system not only provides a habitat for wetland organisms but is also engineered in a way that finds favor with the public because of its many benefits. 9 2.5. Types of CWs There are various types of CWs that depend on the available landscape, including SF and SSF systems. SF CWs have shallow flow and lower velocity over the substrates, whilst SSF CWs have either VF or HF over the substrates. Hybrid CWs combine both VF and HF (Vymazal & Kropfelova, 2008). Each type of CW system has its benefits and drawbacks, and each differ in the treatment process used. SF CWs make use of plant stems, leaves and rhizomes to effectively treat wastewater. In dense vegetation, however, the process can be limited because there is not enough circulation of oxygen, which is vital for the organisms. In SSF CWs, roots are used in the treatment of effluents as water passes through a series of gravel beds. This process is considered to be superior to, and more effective than that used in SF CWs. 2.6. Components of CWs 2.6.1. Water Locations in which landforms predominantly direct surface water straight into shallow basins, or where impermeable subsurface layers hinder the ground from absorbing surface water, are the most likely places for wetlands to form naturally. Such conditions in a location can be engineered to create wetlands (Jhansi, & Mishra, 2013). Land can be structured in such a way that surface water is collected, and such basins can be sealed in order to retain the collected surface water. Once a landscape has been modified in this way, a wetland can be constructed. 10 In the construction of a wastewater wetland system, hydrology is among the most important factors to be considered. This is because it not only links all of the functions of the wetland, but it is also a key factor in the CWs failure or success in a given landscape. The hydrology of the CW is important in relation to the hydrology of other surface water in the area. Small, natural hydrological changes can promote significant effects in the CW, impacting on its utility. Through rainfall and evapotranspiration, there is substantial interaction between the wetland system and the atmosphere because of the wetland water is shallow and covers a large surface area. The hydrology, in most cases, is also affected by vegetation density in the wetland, which can obstruct the flow of water. 2.6.2. Substrates, Sediments and Litter Soil, sand, gravel and rock, as well as organic materials, such as compost, are used to make the substrates for the wastewater to flow over. Due to the high biological productivity and low water velocities in wetlands, it is possible to easily accumulate sediments and litter (i.e., organic matter). These substrates, sediments and litter are vitally importance because they support all of the living organisms that dwell in wetlands (Secretariat, 2014). For many contaminants in a wetland, the substrate acts as a sink. The substrate is also important because its permeability affects the movement of water passing through the CW. 2.6.3. Vegetation In any CW, the presence of both vascular and non-vascular plants is of vital importance (Praewa, 2017), vascular plants being the higher plants, whereas non-vascular plants are the algae. When algae undergo photosynthesis, they increase the dissolved oxygen content in the water, which 11 significantly affects the metals and nutrients present in the water. The presence of plants in a CW system, therefore, is very important, since they also penetrate the substrate structure, transferring oxygen into the substrate, a process that is not possible or achievable, even using diffusion. The presence of submerged leaves, stalks and litter is important in FWS wetlands in terms of attached microbial growth, wherein the leaves, stalks and litter themselves serve as substrates. Wastewater wetlands are mostly characterised by the absence of emergent plants, although natural wetland systems commonly include reeds, rushes and cattails. Cattails have the ability to survive and thrive under diverse environmental conditions, and they can produce massive annual biomass. Rushes –particularly bulrushes – are perennial, grass-like plants that are capable of growing and thriving in clumps. They tend to grow better in water that ranges from 5 cm to 3 m deep (Wetzel, 1993). Most bulrushes grow well in water that has a PH of 4–9. Reeds are tall, annual grasses with a perennial rhizome. Reeds are among the most widespread emergent aquatic plants. CWs that use reeds are at an advantage because the reeds have the ability to transfer oxygen into the substrate, thus improving the effectiveness of the system. 2.6.4. Microorganisms The functions of CWs are, in some way, controlled and regulated by the presence of microorganisms and their metabolic processes. Algae, protozoa, fungi and yeasts are examples of microorganisms that are found in wetlands. Microbial activity in the system is important because this is how nutrients are recycled. Microbial activity also affects the processing capacity of the 12 wetland because it can cause reduced conditions in the substrate. In CWs, microbial communities are affected by toxic chemicals, such as those found in pesticides (Wetzel, 1993). 2.6.5. Animals Certain vertebrates and invertebrates take up residence in CW systems. Insects and worms are (invertebrates) are significant contributors to the treatment process (Wetzel, 1993), making it safe and more effective. 2.7. Literature Summary CWs for municipal, industrial and domestic wastewater treatment can be designed in appropriate and specific ways to meet most intended purposes. Wetland systems can be engineered to take advantage of the various features of a site. CWs are an effective approach that can be employed in improving wastewater quality and allowing for its reclamation and reuse. Moreover, CW systems are of economic and thus they are globally applicable. CHAPTER 3 13 METHODOLOGY 3.1 Overview This section elaborates in detail the methodology employed in various CW projects as presented in a number of case studies. The CWs, although employ different designs, all serve municipal needs for wastewater treatment. This chapter explains the designs used, population equivalent served, the construction costs, operation and maintenance costs, size of the CW, and the overall methods used to treat municipal wastewater. 3.2 Methodologies 3.2.1 Performance and Cost Comparison of a FWS and a VSF Constructed Wetland System The study compares two CWs designs to define which is more appropriate for a municipal in terms of design considerations, construction cost, constituent removal performance, and operation and maintenance(O&M) costs(Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). Both CWs treat domestic wastewater from municipals. The first CW is an FWS CW found in Pompia, Crete, in South Greece, while the second is a VSF CW located in Gomati, Chalkidiki, in North Greece. The FWS CW is designed for a population of 1200 p.e., and its total construction cost is €305,000. The capital and O&M cost is €22.07 p.e.-1 yr-1 or €0.50 m-3 of influent. The design of the FWS system comprises a septic tank with three screen vault filters (up-flow reactor simulation), a FWS CW comprising a series of two basins with surface areas of 4300m2 and 1200m2, a chamber in each basin to regulate water level, small pumps and a pipeline system for recirculating effluent back into the inlet of the first basin, and a compost filter to control odor in the septic tank(Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). In the basins, the inflow is 14 distributed uniformly at the inlet of each of the two basins using manifolds. The plant species planted in the wetland areas are Phragmites australis and Arundo donax. The reeds were planted in the winter of 1999 and experienced speedy growth due to advantageous climatic conditions (Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). By the end of the year, the vegetation was dense and the plants had grown more than two meters in height. The basic parameters used in the FWS CW are the following: mean daily flow rate 144 m3 d-1, maximum daily flow rate, 216 m3 d-1; maximum hourly flow rate, 27.7 m3 h-1; retention time, 5-14 d(depending on the season of the year); sewage average temperature of 10°C in the winter and of 22°C in the summer(Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). The VSF CW is designed for a capacity of 1000 p.e., and its total construction cost is €410,850. The capital and O&M costs are €36.81 p.e.-1 yr-1 or €0.56 m-3 of influent. The VSF system comprises an inflow structure, a rotating disk screen with openings of 1 mm, a closed twin settling tank(48 m3 each chamber; dimensions 4 m x 6 m x 2.5 m), closed twin sludge digestionstabilization tank(48 m3 each chamber; dimensions 4 m x 6 m x 2.5 m), an open siphon tank(3.2 m3; dimensions 1.0 m x 4.2 m x 0.8 m) for intermittent wastewater feeding, a stage I VSF circular basin(4 cells, 640 m2, sand and gravel fill, 1 m deep), a stage II VSF circular basin(4 cells, 360 m2, sand and gravel fill, 1 m deep), a stage III rectangular HSF cell(800 m2, sand and gravel fill, 0.5 m deep) and a VSF circular basin(4 cells, 240 m2) which receives digested-stabilized sludge for drying and storage(Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). All the basins are planted with Phragmites australis. The HSF cell was not planted at the time of the study and was out of the wastewater stream. The VSF was planted and put into operation in May 2003. The wastewater flows from the inflow structure to the rotating disk screen and then to the settling tanks. From there, sludge is collected from the settling tank and pumped into the sludge digestion15 stabilization tank and then into the VSF sludge basins. From the VSF sludge basins, the leachate is pumped back to the siphon with wastewater from the settling tanks to feed the stage I VSF basin and then the stage II VSF basin. The effluent is then discharged into a stream. The basic parameters for the design are the following: mean daily flow of the system, 180 m3 d-1; maximum hourly flow, 28.5 m3 h-1, hydraulic loading rate, 36 m yr-1; organic loading rate, 196 kg ha-1 d-1(Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). Samples for the FWS system were frequently composed of the inflow, settling tank outflow and system outflow; while samples for the VSF system were often assembled from the inlet, settling tank outflow, siphon, stage I VSF outflow and stage II VSF outflow(Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). The monitoring period totaled 3 years from August 1999 to August 2003 for the FWS, while the monitoring period for the VSF was July 2003 to August 2004. The samples were analyzed for TKN, TP, TC, FC, TSS, COD, and BOD5. 3.2.2 Horizontal Sub-Surface Flow and Hybrid Constructed Wetlands Systems for Wastewater Treatment The purpose of the study is to discuss the methodologies and results of several case studies for HSSF and Hybrid CWs that are sampled regionally and are as follows: The HSSF System: The most widely used HSSF concept was developed in Germany by Kathe Seidel. The design comprises a four-sided cot imbedded with Phragmites australis and lined with an impermeable membrane. Wastewater is treated with mechanical methods before it is fed into the CW inlet. From the inlet, the wastewater is passed slowly through the filtration medium and is finally collected at the outlet. Another system was designed by Reinhard Kickuth to improve on the first by using 16 cohesive soils with a high content of clay. The full- scale municipal sewage treatment operation measured an area of 22ha and was located in Liebenburg-Othfresen. The system uses soil as its medium with a size of 2m2 p.e-1 for the vegetated beds. In Denmark, beds were built with an area of 3 and 5 m2 p.e-1. The systems are structured with minimum proportion and a subdivided inlet trench that was divided into two or more units. In contrast, in the United Kingdom, reed bed treatment systems designed with an area of 5 m2 p.e-1 were used. The substrate is composed of very course material to ensure sub-surface flow. The general equation used to determine the sizing of HSSF CWs is as follows: 𝐴ℎ = 𝑄𝑑 (𝑙𝑛𝐶𝑜 − 𝑙𝑛𝐶) … … … … … … … … … … … … … … … … … … … … … … . … . . … … (3.1) 𝐾𝐵𝑂𝐷 Where Ah is the surface flow of bed (m2), Qd is the average flow (m3 day-1), Cin is the influent BOD5 (mgl-1), Cout is the effluent BOD5 (mgl-1) and KBOD is the rate constant (mday-1). Typically, the HF CW has a filtration bed of a depth of about 0.6–0.8m and is planted with Phragmites to allow the roots of the plant species to penetrate the whole bed. The oxygen released from the roots and their rhizomes should be enough to satisfy the demand for physiological needs. In the soil zone below the Fe3+ reduction zone is where anaerobic respiration occurs through facultative or obligate anaerobes. In the flooded soils and sediments, acetic acid is the primary acid that is formed; however, over-production of the acid can result in very low pH levels. SS that are not removed during pre-treatment are removed through filtration and settlement, but removal of SS in the pre-treatment stage is ideal to prevent clogging of the substrate. Nitrogen removal is done through nitrification or denitrification while phosphorous is removed mainly by ligand exchange reactions(Vyzamal, 2005). 17 A case of an HF CW found in Zitenice, Czech Republic, was built in 1993 for a population of 4 p.e. The system was composed of a pre-treatment section made up of an advanced septic tank and built-in baffles. The retention time of the tank is 12 hours. The area of the bed is 18 m2, and the bed is filled with 1–4 mm of coarse sand as the filtration material. The facility was first planted with Phragmites australis and Typha latifolia, and then these were replaced by Iris pseudacorus and Iris sibirica in 2002. Another case study located in Spalene Porici, Czech Republic is presented. The facility was designed for a population of 700 p.e. and was built in 1992. The pre-treatment section comprised an Imhoff tank and local septic tanks. The sewerage system is combined with an average flow of 200 m3 day-1. The vegetated bed is then divided into four sections and has an area of 2500 m2. The four beds are equal in size and two of them are parallel to each other. The beds are filled with 0-16mm of gravel and the beds are planted with Phragmites australis and Phalaris arundinacea. In later years, P. australis takes over the other plant species and becomes dominant. Another case study located in Spalene Porici, Czech Republic is presented. The facility was designed for a population of 700 p.e. and was built in 1992. The pre-treatment section comprised an Imhoff tank and local septic tanks. The sewerage system is combined with an average flow of 200 m3 day-1. The vegetated bed is then divided into four sections and has an area of 2500 m2. The four beds are equal in size and two of them are parallel to each other. The beds are filled with 0-16mm of gravel and the beds are planted with Phragmites australis and Phalaris arundinacea. In later years, P. australis takes over the other plant species and becomes dominant. The Hybrid System(VF-HF): 18 In Oaklands Park, UK, a VF-HF system was built in 1987. The first stage is made up of six vertical beds with an area of 8m2 and planted with P. australis. The second stage is made up of three vertical beds with an area of 5m2 each and planted with P. australis, yellow flag and bulrushes. The third stage is a HF bed measuring an area of 8m2 and planted with yellow flag while the fourth is a 20m2 bed planted with bulrush, bur reed, and sweet flag. Another system known as the Colecott system designed for 60 p.e based on the original Seidel’s concept is presented. The system is made up of four VF beds in the first stage measuring a total area of 64m2, two VF beds in the second stage measuring 60m2, and one HF bed with an area of 60m2 as well in the third stage(Vyzamal, 2005). The Hybrid System(HF-VF): A case study in Poland shows that HF and VF constructed wetlands could also be combined in more than two stages(Vyzamal, 2005). The system in Darzlubie in Poland consists of a combination of HF bed measuring 1200m2, cascade of five alternate HF and VF beds (total are of 270m2), and HF(II) bed (500m2)(Vyzamal, 2005). After this point 50% of the flow is directed to two VF(II) beds(total area 500m2) and the final stage of the treatment system is a 1000m2 HF bed where the outflow from VF(II) and HF(II) are combined(Vyzamal, 2005). 3.2.3 Municipal Wastewater Treatment using Constructed Wetlands The case study describes and discusses the Korestia wastewater treatment plant located in the northern part of Kastoria, Northwest Greece, which focuses on expanding constructed wetland use as the preferred wastewater treatment system in small municipalities and settlements. The municipality of Korestia has an area of 12,228 ha. The population of Korestia at the time of the 19 CW was about 500 residents and practices mainly agriculture and livestock keeping. The entire project is designed to serve a population of 600 p.e. The system is a hybrid series consisting of three stages. The first stage is composed of three identical VF beds measuring a total area of 891 m2 or 1.5 m2/ p.e. The second stage is composed of two identical VF beds with a total surface area of 594 m2 or 1.0 m2/p.e. The third stage is composed of one HSF bed (added for denitrification) measuring a total surface area of 903 m2 or 1.5 m2/p.e. The total construction cost was 286,282 € or 477 €/p.e., while the operation cost came to 7,121 €/year, or 11.87 €/p.e./year. The wastewater discharge per p.e. was calculated as 150 L/d, and the total flow of wastewater was 90 m3/d(Gikas & Tsihrintzis, 2014). High-density polyethylene geomembrane (1 mm) was used to completely waterproof the beds to avoid leaching of the sewage water to groundwater. The geomembrane is protected on all sides using a special geotextile that prevents damage from a substrate material that may cause tearing and holes. The substrate used for the beds is porous inert material from a quarry or torrent deposits, and the porous media of the beds are as follows: 1st stage CWs have a depth of 0.90 m and consist of 3 layers from the bottom to the top: cobbles 0.2 m(diameter 20–40 mm), coarse gravel 0.2 m(diameter 5– 20 mm) and fine gravel 0.5 m(diameter 2–8 mm) 2nd stage CWs have a depth of 0.90 m and consists of 3 layers from bottom to top: cobbles 0.2 m(diameter 20–40 mm), fine gravel 0.3 m(diameter 3–8 mm) and river sand 0.4 m(diameter 0.2–4.0 mm); the 3rd stage CW is filled with 50 cm of gravel(diameter 18–30 mm)(Gikas & Tsihrintzis, 2014). Phragmites australis is the plant species used for all the beds. Two polyvinyl chloride pipes (PVC) route wastewater from Korestia village into the treatment facility and into a pump vault. The pump vault has two submerged pumps that operate alternately, first pumping the wastewater to the first stage VF beds by using electricity. The rest of the facility, 20 however, uses gravity. Each bed in the first CW stage receives an entire load of about 14 m3 during a two-day feeding phase and then rests for four days during which another basin is fed. The design parameter concentrations to be analyzed were BOD, TSS, TKN and TP(Gikas & Tsihrintzis, 2014). Figure 3.1 shows the flow diagram of Korestia facility. Figure 3.1: Flow diagram of Korestia facility (Gikas & Tsihrintzis, 2014). 3.2.4 Efficiency of a Horizontal Sub-Surface Flow Constructed Wetland Treatment System in an Arid Area The study was performed in Al-Samra Agricultural Research Station located in Central Jordan. The station is found 36 km downtown of Amman and has an elevation of 550 m above sea level. A benchmark project site was developed in 2008 for an HSF CW. Partially treated municipal wastewater was held in a 300 m3 pond and then directed into the HSF CW to be retreated. The treated effluent was then collected in another 150 m3 holding pond and used for the irrigation of forest trees. For this project, the system was made up of 17 HSSF CWs, and the mean hydraulic residence time was 2 days. The system was divided into two main categories. In the first category, there are a total of 9 beds with each measuring 9.5 m x 1.7 m x 0.8 m in terms of length, width, and height. The wetland media used is coarse volcanic tuff measuring 10–20 mm in diameter. Three of the beds had Phragmites australis, another three had the kenaf plant, and the last three had no vegetation and 21 were used as controls. The second category had 8 beds measuring 6.5 m x 2.5 m x 0.8 m in length, width and height. The wetland media used for four of the beds was coarse volcanic tuff 10–20 mm in diameter, while the other four beds were filled with fine volcanic tuff 4–8 mm in diameter. Two of the beds filled with fine media and two filled with coarse media were planted with reeds, while the rest had no vegetation and were used as controls. Each bed was outfitted with a tube in the middle to measure water temperature daily. All the beds had the same volume of 13 m3. The total HSF CW volume was 221m3, while the total surface area was 275m2. Figure 3.2 shows the HSFCW layout. Figure 3.2: The horizontal sub-surface flow constructed wetland treatment (HSF-CW) system layout (Albalawneh, Chang, Chou, & Naoum, 2016). The following abbreviations are used: Long bed(L), short bed(S), coarse media(C), and fine media(F), reeds(R), kenaf(K), and no vegetation(N)(Albalawneh, Chang, Chou, & Naoum, 2016). The influent and effluent were sampled and analyzed on a bimonthly basis for 18 months from November 2008 to August 2011. The chemical and biological characteristics of wastewater 22 focused on in this study are: BOD5, COD, TSS, FC and P. (Albalawneh, Chang, Chou, & Naoum, 2016). Removal efficiency(%) for each parameter of water quality was calculated based on mass flow difference between the effluent and influent relative to the influent(Albalawneh, Chang, Chou, & Naoum, 2016). 3.2.5 Feasibility of Using Constructed Treatment Wetlands for Municipal Wastewater Treatment in the Bogotá Savannah, Colombia A treatment wetland model for pollutant removal is developed using data from literature whose performance is then compared to a waste stabilization ponds and sequencing batch reactor to quantify its performance and sustainability(Arias & Brown, 2009). The three systems are compared in terms of cost and emergy. Two sites are used for the study. The first site is Tabio, and it is located 50 km northwest of Bogota and has a population of 14,000 with an average temperature of 14°C. The municipality was designed to treat 20 L/s of wastewater. In addition, the plant has an area of 3.4 ha and was constructed in 1992. The system consists of a screen, sedimentation tank, anaerobic basin, and two series of facultative lagoons each with two basins(Arias & Brown, 2009). The second site is at LaCalera, and it is located 30 km east of Bogota and hosts a sequencing batch reactor (SBR) that was constructed in 2002. It is designed with a flow of 36.5 L/s and for a population of 16,000. The system comprises a manual screen and sedimentation tank for primary treatment, two reactor tanks for secondary treatment, sludge digester, and sludge drying beds(Arias & Brown, 2009). A hypothetical CW treatment system is developed from the previously mentioned two actual designs, and its location is assumed to be Tabio. The system consists of screens, sedimentation tanks, an anaerobic basin, and a combination of modeled SSF and SF wetland units(Arias & 23 Brown, 2009). Data for wastewater was derived from raw wastewater quality data from Tabio and used to size the hypothetical system. The area of the plant was determined from the 3.4 ha of the plant, minus 2900 m2 taken up by the anaerobic basin, minus 30% of the extra area set aside for pre-treatment structures and open areas(Arias & Brown, 2009). The model was subject to a sensitivity analysis to determine the effect of the system configuration on the overall feasibility study, and this analysis was performed by estimating the pollutant removal and the cost for different area distributions between SSF and SF wetlands; the configuration used in this study was found at the point where maximum pollutant removal and minimum cost intersected(Arias & Brown, 2009). Effluent concentration in each unit was calculated using the following model: 𝐶𝑒 = 𝐶 ∗ + (𝐶𝑖 − 𝐶 ∗ ) exp ( −𝑘𝐴 ) … … … … … … … … … … … … … … … … … … … . … … … … . .3.2 0.0365𝑄 Where Ce is outlet concentration(mg/L),Ci is inlet concentration(mg/L),C* is background concentration(mg/L),A is wetland area(ha), Q is water flow rate(m3/day), and k is first-order areal rate constant(m/yr)(Arias & Brown, 2009). The net annual cost of treatment was estimated as the following: 𝑁𝑒𝑡 𝐴𝑛𝑛𝑢𝑎𝑙 𝐶𝑜𝑠𝑡 = 𝑂&𝑀 + 𝐶𝑜𝑛𝑠𝑡𝑟𝑢𝑐𝑡𝑖𝑜𝑛 𝐿𝑖𝑓𝑒𝑡𝑖𝑚𝑒 …………………………………………………(3.3) Where net annual cost, construction, and annual O&M were calculated in 2003 dollars, and lifetime refers to the facility design lifetime, which is assumed to be 25 years for the three systems(Arias & Brown, 2009). 24 3.2.6 Performance of Four Full-Scale Artificially Aerated Horizontal Flow Constructed Wetlands for Domestic Wastewater Treatment An evaluation of the recital of four full-scale aerated horizontal flow constructed wetlands was conducted to regulate the efficacy of the technology on sites receiving high and variable ammonia loading rates not yet described in the data(Butterworth et al., 2016). The typical HSSF system serves about 2000 PE. All aeration systems consist of 1.6 kW air blower, dispersal header and loops of perforated LDPE 12 mm piping with 2 mm holes (Butterworth, Richards, Jones, Jefferson, & et, 2016) drilled into it at 300 mm intervals placed on top of the impermeable liner covering the surface area of the bed floor(Butterworth et al., 2016). Sites A, B, and D are planted with P.Australis, while Site C is planted with T.latifolia. “Site A consists of a primary settling tank, a submerged aerated filter, and tertiary treatment is via two HSSF CWs with a separately combined sewer overflow(CSO) HSSF CW that receives the wastewater exceeding six times the dry weather flow”(Butterworth et al., 2016). Site A, in addition, obliges as a control site with side by side wetlands of equal size where the aeration of the test bed began 3 March 2011 and was left dormant in the control bed. The standard pass to respective bed was 46 m3/d, the resultant to standard hydraulic loadings was 0.46 m3/m2/d and the average inlet loadings to the bed through the trial were 12 gBOD/m2/d, 25 gTSS/m2/d and 9.1 g ammonium nitrogen(NH4+-N/m2/d)(Butterworth et al., 2016). Site B treatment is via an integral RBC which is followed by a combined wetland. The bed was retrofitted and has been operated with intermittent aeration. The mean flow of the bed is 45 m3/d, the mean hydraulic loading is 0.1 m3/m2/d and the average loadings to the bed during the trial are 11 gBOD/m2/d, 1 gTSS/m2/d and 1.6 gNH4 +-N/m2/d(Butterworth et al., 2016). 25 Site C comprises two fundamental RBCs and a collective tertiary reed bed and the driver for aeration at this site was the addition of an ammonia effluent consent at a site that was not originally designed to nitrify(Butterworth et al., 2016).“The average trickle to the bed is 248 m3/d, followingon in average hydraulic loadings of 0.4 m3/m2/d and average loadings to the bed during the trial were 8 g BOD/m2/d, 17 gTSS/m2/d, and 8.9 gNH4+-N/m2/d”(Butterworth et al., 2016). Site D is the only secondary bed consisting of a septic tank and a combined reed bed. The bed was refurbished in March 2010 and fitted with aeration on 30 March 2011, and because the consented flow is below 50 m3/d, this site had no flow measurement during the trial(Butterworth et al., 2016). Figure 3.3 shows all the site designs for sites A through D: Figure 3.3: Site process flowsheets of aerated HSSF CW sites( Butterworth, et al., 2016). Composite samples were unruffled fortnightly (every 15 min over 24 h) during the first year and monthly. “In this context, robustness is described as the ability of a treatment unit to produce consistent effluent quality under varying influent characteristics and differentiates from resilience, which is defined as the ability to return to normal after a dynamic event.”(Butterworth, et al., 2016). 26 Robustness index indicates the robustness of a process and is calculated by the following: 𝐺% 𝑇 𝑇50 𝑅𝐼 = [(1 − 100) × 𝑇90 ] + [𝑇 50 𝑔𝑜𝑎𝑙 𝐺% × 100]………………………………………………………..(3.4) Where RI is the robustness index, G% is the percentage time spent under Tgoal, T90 is the 90th percentile value(mgNH4+-N/L), T50 is the 50th percentile value(mgNH4+-N/L) and Tgoal is the treatment goal(mgNH4+-N/L)(Butterworth et al., 2016). 3.2.7 A review on the sustainability of constructed wetlands for wastewater treatment: Design and operation The study discusses various CW designs and parameters including plant species, substrate types, water depth, HRT, HLR and feeding mode to determine the most sustainable factors that ensure a CW is suitable, stable and sustainable. In agreement with the study(Wu et al., 2015), regarding plant selection, factors such as the tolerance of waterlogged anoxic, hyper-eutrophic conditions, and the capacity of pollutant absorption should be used to choose the most suitable plant. In addition, there are three types of plants used for vegetation that should be considered during plant selection: emergent plants, submerged plants, and floating plants. Plant tolerance to wastewater toxicity and environmental stress should be monitored to ensure proper and rapid growth. Plants can accumulate toxic components in the water; therefore, the capacity for a species to remove pollutants is another important factor. The substrate chosen for the CW is another critical factor since it provides a growing medium for the plants and facilitates movement of wastewater. Therefore, substrate selection should be considered in terms of capacity for pollutant sorption (through exchange, complexation, precipitation and adsorption) and hydraulic permeability(Wu et al., 2015). 27 HLR and HRT rates are essential for controlling wetlands, and their rates should be carefully regulated for performance efficiency. In addition, the design of the feeding mode of the influent (continuous, batch, intermittent) may be instrumental in influencing oxidation-reduction conditions and oxygen transfer and diffusion hence influencing removal rates(Wu et al., 2015). 3.2.8 Constructed Wetlands as a Sustainable Solution for Wastewater Treatment in Small Villages A pilot-scale SSF CW is constructed with the aim of removing pollutants from wastewater from small villages. The CW is located near Soria sewage treatment plant, North Spain, in a Mediterranean semi-arid area with minimum and maximum temperatures of 22 and 50°C. The system comprises two series with different HAR values of 150 and 75 mm day-1 and HRTs of 1.5 and 3 days, respectively. Each bed has an area of 40 m2, length to width ratio of 10:1, depth of 1 m, diameter gravel of 0.5–1 cm and gravel depth of 0.40 m. In addition, each bed is lined with impermeable plastic to prevent groundwater contamination. The inlet and outlet zones measure 1 m each and have large stones of diameter 5–10 cm, and each inlet has a PVC pipe at the top. The influent feeding the beds is collected from urban runoffs, domestic water, and a small manually controlled percentage between 1.5 and 3 from the industrial food processing industry. Each bed is fitted with two sampling tubes at the head and at the end. Typha sp. and Phragmites sp. are planted in the beds. Sampling began two months after establishment (June of the first year) and was performed every month during an 18-month period (up to November of the second year). Samples were tested for 28 BOD, COD, TSS, TC and FC bacteria and fecal streptococci bacteria and were analysed. (Solano, Soriano, & Ciria, 2004). Treatment efficiency was calculated by the following equation: 𝑅 = (1 − 𝐶𝑒 ⁄𝐶𝑖 )100……………………………………………………………...(3.5) Where Ci and Ce are the influent and effluent concentrations in mg l-1. 3.2.9 Municipal Wastewater Treatment using Vertical Flow Constructed Wetlands Planted with Canna, Phragmites and Cyprus A pilot-scale VF plant was developed to treat wastewater near a wastewater treatment plant in North Cairo, Egypt. The plant has a total surface area of 457.56 m2. The system series comprises a coarse screen, oil removal, primary settling tank, and a wetland basin. The influent flow rate is at 20 m3/day and the surface loading rate is between 26.2 kg BOD ha-1day-1 and 76.5 kg BOD ha1 day-1 with a detention time of 7.7 days(Abou-Elela & Hellal, 2012). The CW is fed influent using a submersible pump and a network of PVC pipes. The flow rate and pump runoff are controlled by use of SCADA software, and water flow is measured by electromagnetic flow(Abou-Elela & Hellal, 2012). All climatic parameters that can affect the hydro-balance are monitored. The beds are planted with Canna, P.australis and Cyprus papyrus and are used to estimate biomass, water content, and nutrient content when harvested. Figure 3.4 shows the design of the VFCW. 29 Figure 3.4 Design of VFCW (Abou-Elela & Hellal, 2012). Samples of wastewater were collected every week from the inlet and the outlet for about two years. The physio-chemical and biological analyses is performed for raw wastewater, treated wastewater, and harvested biomass to determine TC, Escherichia coli, and FC. All the analysis were carried out according to Standard Methods for the Examination of Water and Wastewater(APHA,2005) (Abou-Elela & Hellal, 2012). 3.2.10 Development of Constructed Wetlands in Performance Intensifications for Wastewater Treatment: A Nitrogen and Organic Matter Targeted Review The study proposes a number of operational strategies to improve the efficiency removal rates of CWs. The following operational strategies are proposed: 1. Effluent recirculation: A part of the effluent is extracted and then transferred back to the inflow of the system. 2. Artificial aeration: Involves aeration of CWs with compressed air. 3. Tidal operation: It is categorized by numerous serial overflow and channel sequences per day creating a repeat pattern of flooding and draining. 4. Drop aeration: Involves a multilevel (six) two layer drop aeration system which has been tested in two pilot scale VF CWs measuring an area of 0.75m2 each(Wu, Kuschk, Brix, Vymazal, & Dong, 2014). 5. Flow direction reciprocation: Involves altering the path of the current occasionally. 30 6. Earthworms: are introduced into SSF CWs to clean clogged substrates. 7. Bio-augmentation: involves the supplementation of microbes that possess favorable metabolic traits into wetland The following design strategies are proposed: 1. Circular-flow corridor CW: The system involves partial recirculation of wastewaters within the beds. 2. Towery hybrid system: comprises three stages. The first and the third stages are rectangular HSSF CWs while the second is a circular three-layer FWS CW. 3. Baffled SSF CW: incorporates sequential up and down flows by inserting vertical baffles along the wetland width which makes water flow up and down instead of horizontally. 4. Microbial fuel cell CWs: are made up of two chambers (one aerobic and the other anaerobic), where oxidation and reduction occur. A cathode electrode is placed on the aerobic side (near the plant roots) while an anode is placed on the anaerobic side (near the bottom of the microcosm) where electricity production is monitored. 3.2.11. Reed bed CW system Haya water company conducted a study to design, build, and operate a CW in Quriyat. The aim of the study was to evaluate the efficiency of a reed bed system as an alternative and sustainable treatment of domestic and partially non-domestic wastewater solution (Haya Water, 2017). The system used a double stage VF CW with an anoxic tank. The full study occurred for a year from 12 June 2016 to 12 July 2017. BOD, TSS, COD, O&G, VHO, TP, TN, and NH3-N were analyzed to determine the quality of treated effluent and whether it could be used for irrigation purposes, 31 their results were then compared with the regulations set by ministerial decision 145/1993 Standard(A) (Oman Government, 2018). The area of the reed bed was 1300 m2 designed to hold a capacity of 50 m3 of wastewater daily. The reed bed received influent from a balancing tank and the vegetation used was P.Australis. The reed bed was divided into two stages as illustrated in table 3.1. The filter used in stage 1 was >1 in size, and the filter material was a fine gravel of a thickness between 2-2.8mm and a depth of >30cm. The filter used in stage 2 was >1 in size, and the filter material thickness was between 0.25 and 0.4 mm and had a depth of greater than 30 cm. Table 3.1 demonstrates the design criteria of the reed bed: Table 3.1: Design criteria for a double-stage VF reed bed after pre-treatment (septic tank) (Haya Water, 2017). The two stages in the system were presented as stage A and stage B. Stage A had three basins, A1, A2, and A3; and stage B had two basins, B1 and B2. There were three tanks used; anoxic tank, buffer tank, and TE storage tank all alongside three pumps. The buffer tank acted as the measuring 32 can and was where the process began. The raw sewage was discharged into the anoxic tank from the buffer tank, and that’s where partial denitrification occurred. Stage A was the settlement stage where 50% TSS and 20% BOD were removed and it took 2 hours for wastewater to be pumped into each compartment. Partial denitrification also occurred in stage A. Wastewater was then pumped into stage B for biological treatment. Stage B was the aeration stage, because that’s where nitrification (ammonia converted to nitrate) and biological processes occurred. Also, 50% effluent recirculation to the anoxic tank was applied to allow for further denitrification (nitrate converted to nitrogen gas) (Haya Water, 2017). The rest of the effluent was discharged to the treated sewage effluent storage tank for disinfection. Figure 3.5 demonstrates the process of the wastewater effluent treatment. Figure 3.5: Description of the process for treated effluent (Haya Water, 2017). The figures below show the stages from its initiation at “stage A” and “stage B” and the two final figures represents the final product of Phragmites Australis plants after both stages (Haya Water, 2017). 33 Figure 3.6: Stage A (Haya Water, 2017) Figure 3.7: Stage B (Haya Water, 2017) 34 Figure 3.8: Photographs after both stages (Haya Water, 2017) 35 CHAPTER 4 RESULTS AND DISCUSSION 4.1 Overview This chapter provides a broadened interpretation of the results and gives feasible solutions based on the research regarding the presented methodologies discussed in Chapter 3. This section, in addition, provides a discussion of the results found in terms of their effects on the efficiencies and effectiveness of the CWs. At the end of the chapter, a comparison is made between two related case studies to sample the differences and similarities. 4.2 Results and discussions 4.2.1 Performance and Cost Comparison of a FWS and a VSF Constructed Wetland System As mentioned in the methodology’s objective, a comparative analysis in terms of removal efficiency and cost during the monitoring period of both systems are discussed in this section. In reference to the study’s results (Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007), the overall removal efficiencies showed that BOD, COD and TSS had an average removal of 94.4%, 96.1% and 95.5% in the FWS which were similar to the BOD and TSS removals of the VSF system recorded at 92% and 95%, while the COD was 89%. The FWS reduction for TKN and TP were 53% on average while for TC and FC they were 98.7% and 97.1% respectively. On the other hand, the VSF system recorded average TKN removal at 77% and average phosphorous removal at 62%(Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). The lower removal rates for COD in the VSF could be attributed to the newness of the design and the under developed 36 macrophytes. Moreover, another reason could be because the HSF basin was not operated during the study of the system(Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). The capital and operating costs for the two facilities are shown in table 4.1 as follows: Table 4.1: Capital and operating costs (€) for the two facilities( Tsihrintzis, Akratos, Gikas, Karamouzis, & Angelakis, 2007). Cost (€) Cost category FWS system Capital, including (construction cost) VAT 344,615 VSF system 410850 Construction cost per p.e 287.18 410.85 Net-present-value cost 25036 29848 Annual average O&M cost 1445 6960 O&M cost per p.e. per year 1.20 6.96 O&M cost per m3 per year 0.03 0.11 Total annual cost (capital and 26481 O&M) 36808 Total annual cost per p.e 36.81 22.07 Total annual cost per m3 of 0.50 influent 0.56 In summary of what has been observed, both systems proved to be effective in producing high effluent quality. The VSF somehow provided a better treatment at a lower area than the FWS at a higher design flow rate and lower temperatures of operation. However, the VSF, being more complex, is more susceptible to design, construction and operation and maintenance problems. When it comes to comparing the costs of both systems, the VSF system is slightly more expensive because of the higher use of concrete and pumps. The FWS system, in contrast, is simpler and less 37 expensive in capital and operational costs. Nonetheless, both systems are less expensive when compared to conventional treatment systems in the same area. If land availability is not an issue, the FWS would be preferable, but if the amount of land is an issue, the VSF should be used but with careful monitoring to avoid operation related problems. 4.2.2 Horizontal Sub-Surface Flow and Hybrid Constructed Wetlands Systems for Wastewater Treatment The results of the various case studies that have been discussed in Chapter 3 and are as follows: Table 4.2: Treatment efficiency of vegetated beds of HSSF CWs—world wide experience(data from Australia, Austria, Brazil, Canada, Czech Republic, Denmark, Germany, India, Mexico, New Zealand, Poland, Slovenia, Sweden, USA and UK)( Vyzamal, 2005). Parameter Inflow (mg l-1) Outflow (mg l-1) Efficiency (%) N BOD5 108 16.0 85 164 COD 284 72 75 131 TSS 107 18.1 83 158 TP 8.74 5.15 41 149 TN 46.6 26.9 42 137 NH4+-N 38.9 20.1 48 151 NO3—N 4.38 2.87 35 79 FC (CFU/100ml) 1.27 × 107 9.96 × 105 92 51 38 Table 4.3: Performance of on-site HF CW at Zitenice, Czech Republic during the period January 2003–September 2004( Vyzamal, 2005) Parameter Inflow (mg l-1) After pre- Outflow (mg l-1) Efficiency (%) treatment (mg l1 ) BOD5 373 73 9.7 97 COD 1118 182 37 97 TSS 639 44 9.1 99 TP 17.1 10.6 10.6 38 NH4+-N 59 62 51 14 NO3—N 0 0 2.9 - NORG 24.2 9.1 1.1 95 TN 85 72 55 35 Table 4.3 shows very high removal rates for organics (BOD5 and COD) both being at 97% and yielding very low removal rates for nutrients (TP, TN, NH4+-N, and NO3—N), all being below 38% and below. The highest removal rate exhibited is for TSS, which is almost at 100% efficiency, meaning that the system successfully eliminates the deferred objects. 39 Table 4.4: Treatment efficiency of HF CW at Spalene Porıcı, Czech Republic during the period November 1992–December 2002; Values in mgl−1, bacteria in log10 CFU/100ml, efficiency in % for chemical parameters, in log units for bacteria. Standard deviations in parentheses( Vyzamal, 2005) Parameter Inflow Outflow Efficiency BOD5 23.3 (43) 4.6(3.4) 80 COD 85 (147) 26.1(11.5) 69 TSS 91 (228) 9.5(8.0) 90 NH4+-N 11.6 (5.9) 9.4(5.0) 19 NO3—N 3.0 (2.9) 1.79(2.2) 40 TP 2.25 (1.25) 2.09(1.52) 7 TC 6.14 (6.47) 5.01(5.42) 1.1 FS 4.47 (4.64) 3.62 (4.03) 0.9 In table 4.4, fluctuations in inflow are high while fluctuations in outflow are steady. The inflow concentration of the organics is too low to be treated using conventional systems such as activated sludge because such systems would most likely fail(Vyzamal, 2005) According to table 4.5; the highest removals were of BOD5 and TSS. In comparison to the HF systems, the results of the Hybrid system show higher removals of nitrogen because of the presence of nitrification in the VF bed. The HF bed, in addition, successfully reduces nitrates produced in the VF bed. TP removals are however very low. 40 Table 4.5: Performance data from Oaklands Park VF-HF CW (August 1989–September 1991, numbers in mgl-1)( Vyzamal, 2005) Parameter Influent Effluent Stage 1 VF Stage 2 VF Stage 3 HF Stage 4 HF BOD5 285 57 14 15 7 TSS 169 53 17 11 9 NH4+ -N 50.5 29.2 14 15.4 11.1 NO2,3—N 1.7 10.2 22.5 10.0 7.2 Ortho P 22.7 18.3 16.9 14.5 11.9 Table 4.6: Performance of the VF–HF Colecott hybrid system; concentrations in mgl-1, efficiency in % (Vyzamal, 2005). Parameter Inflow VF1out VF2out Hfout Efficiency COD 462 210 66 47 89 BOD5 269 171 43 23 91 TSS 53 28 3 1 98 NH4+-N 45 28 16 7 84 NO3- -N 0.1 4.7 3.8 2.7 - NO2—N 0.1 0.2 0.1 0.1 - PO4 18 16 15 11 39 Similar to table 4.5, table 4.6 shows very high organics and TSS removals, while TP removal records the lowest value. TN removal is again higher in this system due to nitrification in the VF. 41 Table 4.7: Treatment performance of a hybrid HF-VF constructed wetland at Darzlubie, Poland; concentrations in mgl-1 (Vyzamal, 2005). Inflow Outflow Removal % BOD5 265 29.2 89 COD 574 68.9 88 TSS 308 55.5 82 TN 101 14.1 86 NH4+ -N 28.5 5.7 80 TP 5.0 1.0 80 Table 4.7 shows high removal rates for all components. The most efficient removals are for BOD5 and COD followed by TN. However, the system seems to be more effective in nutrient and TP removal than its counterpart, the VF-HF bed. In summary, HSSFs are the systems to use when the target is mainly to remove organics and suspended solids. Nitrogen and phosphorous usually have low removal rates in HSSFs (below 50%) for municipal wastewater, especially when systems are designed with an area of 5 m2 per PE. The removal of phosphorous is hindered by the low capacity of sorption of filtration materials, and the removal of nitrogen is hindered by the lack of oxygen in the filtration and hence low nitrification rates. In contrast, VF systems provide a good condition for nitrification, but no denitrification occurs in these systems. Therefore, a hybrid system is preferred, since it combines both the VF and HF systems to complement each other and to achieve higher removal rates, especially for nitrogen removal. 42 4.2.3 Municipal wastewater treatment using constructed wetlands According to Gikas & Tsihrintzis (2014) the initial design parameters concentration of the Korestia facility were 333 mg/L BOD, 350 mg/L TSS, 67 mg/L TKN and 8 mg/L TP. However, the expected concentrations of the effluent after treatment are: BOD <20 mg/L, SS <15 mg/L, TKN <6 mg/L and TP <4 mg/L(Gikas & Tsihrintzis, 2014). In addition, the constructions costs of the facility are presented in Table 4.8. Table 4.8: Construction cost of Korestia facility (Gikas & Tsihrintzis, 2014). COST (€) Inlet works, screening 29,623 First stage VF CWs 38,671 Second stage VF CWs 33,296 Third stage HSF CWs 33,162 Ancillary works (pipe network, siphon) 15,743 Electrical 19,586 Infrastructure and landscape restoration 27,164 Construction cost 197,245 Total construction cost (including professional 286,282 engineers’ and contractors’ fees Total construction cost / p.e. (€/p.e.) 477.13 Hybrid systems in European countries and in Greece similar to the one discussed operate at high efficiency in removing pollutants. From the results presented, it is proposed that the use of CWs for wastewater treatment should be adopted in small municipalities and settlements since the Korestia facility proves that it can be a preferable alternative to conventional systems because it 43 can be low in cost, effective in the use of CW technology, instrumental in the disposal and management of sludge, and can operate smoothly with minimal problems. 4.2.4 Efficiency of a Horizontal Sub-Surface Flow Constructed Wetland Treatment System in an Arid Area According to the study, the influent water was fed continuously to the beds while the HSF-CW had an overall mean influent flow of 28 m3 day-1. However, after the effluent passed through the beds, it effluent was reduced to 23 m3 day-1 with an overall loss of 17%(Albalawneh, Chang, Chou, & Naoum, 2016). Table 4.9 shows the performance of the HSF CW in the mass flow removals of BOD, COD, TSS and P and the FC count. 44 Table 4.9: BOD5, COD, TSS, FC, and P removal (Albalawneh, Chang, Chou, & Naoum, 2016) Parameter Long Beds Coarse media No plant Kenaf Short Beds Coarse media Reed No plant Group 1 Reed Short Beds Coarse Fine media media Fine media No plant Group 2 Reed Group 3 Group 4 BOD5 Mass 51 flow removal * efficiency (%) Number of 41 samples 56 66G1 37 62G2 50 67G3 50 59G4 42 41 22 22 22 22 40 40 COD Mass 42 flow removal * efficiency (%) Number of 38 samples 49 58 38 56 47 64 47 55 38 38 24 24 24 23 48 47 TSS Mass 56 flow removal* efficiency (%) Number of 53 samples 64 73 67 79 65 64 73 63 54 53 34 34 34 34 68 68 P Mass flow 38 removal * efficiency (%) Number of samples 53 46 64G1 35 61G2 58 75G3 49 67G4 54 53 34 34 34 34 68 68 FC Log 0.4 reduction * Number of samples 47 0.5 0.5 0.6 0.9 1.2 1.2 0.8 1.1G4 48 48 26 26 26 26 52 52 (1)*All the effluents were significantly(p<0.05)lower than the influent, for the same parameter; G1: significant differences (p<0.05)compared to others in group1, for the same parameter;G2: significant differences(p<0.05)compared to others in group 2,for the same parameter;G3: significant differences(p < 0.05)compared to others in group 3,for the same parameter;G4: significant differences(p < 0.05)compared to others in group 4,for the same parameter;(2) 1: Short coarse media =mean of(short bed, coarse media, no plant- beds) and(short bed, coarse media, reed-beds);2: Short fine media=mean of(short bed, fine media, no plant- beds) and(short bed, fine media, reed-beds)(Albalawneh, Chang, Chou, & Naoum, 2016). 45 Based on the studies observation, BOD5, COD, TSS and phosphorous demonstrated average efficiency removals of 55%, 51%, 67% and 55%, respectively. However, Albalawneh, Chang, Chou, & Naoum, (2016) also stated that HSF CW systems had different removal rates for BOD ranging from 37% under SCN conditions to 67% under SFR conditions; the removal efficiency for COD ranged from 38% under SCN conditions to 64% under SFR conditions(Albalawneh, Chang, Chou, & Naoum, 2016). Reed plants were more efficient in BOD removal than kenaf and unplanted beds, while COD removals among the three beds showed no significant difference. Bed dimensions did not affect BOD and COD removal. The fine media was more efficient than coarse media in BOD and COD removal, but the differences between their effluents were not significant. Pursuant to the study objectives, TSS removal efficiency ranged from 56% under LCN to 79% under SCR while the mean log reduction of FC ranged from 0.4 under LCN to 1.2 under SFN and SFR with a mean of 0.8(Albalawneh, Chang, Chou, & Naoum, 2016). Bed dimensions did not affect TSS and FC removal, and fine media showed lower FC concentration in the effluent than coarse media. There were no significant differences in FC removal regarding the vegetation type. Overall phosphorous removal was 55% and ranged from 35% in SCN conditions to 75% in SFR conditions. Fine media was more efficient in phosphorous removal than coarse media, and the mass flow of phosphorous in the reed bed was significantly lower than the flow in the kenaf and unplanted beds. The bed dimensions showed no significant differences in phosphorous removal. In conclusion, the system removed BOD, COD, P and TSS efficiently. The aspect ratios of the bed did not affect the removal significantly, but the plants, although efficient, consumed too much water and concentrated the effluent. The removal efficiencies were based on mass flow and not concentration due to the evaporation that concentrated the effluent because of the water losses. 46 Fine and coarse media without vegetation reduced water loss by 4% while improving pollutant removal. 4.2.5 Feasibility of using constructed treatment wetlands for municipal wastewater treatment in the Bogotá Savannah, Colombia According to the study(Arias & Brown, 2009), the economic analysis suggested that the net annual cost of the treatment wetland was US$ 14,672, compared to US$ 14,201 for the stabilization ponds and US$ 54,887 for the batch reactor. The key differences among these cost evaluations were the cost for the gravel media used in the CWTS (US$ 50,477 for the 0.4ha), along with the greater amount of excavation necessary for the WSP, resulting in an added US$ 48,706 of manual labor costs. Gravel being the costliest item for this CWTS implies that the potential of using this material in a large-scale SSF in this region is limited thus minimizing its use can result in great cost reduction, as illustrated with the sensitivity analysis. The main components in the SBR construction that lead to this increased cost were concrete and steel, in addition to a number of other necessary materials only needed for the construction of this system and not the other two(Arias & Brown, 2009). In contrast, the emergy evaluations show that the ponds have the lowest annual emergy flow(6.65+16sej/yr), followed by the constructed wetland(2.88E+17sej/yr) and the batch reactor(8.86E+17sej/yr). A sensitivity analysis showed that a ratio of SSF to SF wetland area of 1–4 yielded appropriate removal while maintaining construction costs as low as possible(Arias & Brown, 2009). The proposed hypothetical system has the potential of getting high removal efficiencies, especially of BOD and TSS as compared to the other two systems according to Table 4.10. The WSPs, however, recorded higher removal of E. coli than the CWTS, which can be attributed to higher storage volumes in the WSPs and hence higher detention times. The results for the CWTS 47 are based on results of an empirical model which is accurate, but parameters such as design and cost are crucial to consider when gauging the performance of a system. Table 4.10 demonstrates the comparison of the removal efficiencies for the three systems. Table 4.10: Estimated percent removal of pollutants for the three treatment systems evaluated (Arias & Brown, 2009). Constituent CWTS WSPs SBR SS 97 79 73 BOD 92 86 79 E. coli 98 99.5 84 TN 62 - - NH4 62 -8 - TP 47 -35 30 The study proves that a CW system should be adopted in Bogota. Due to the observations of the study, the CWTS had the highest performance for treatment, the most value for investment, and achieved the highest pollutant removal rates. Therefore, the system is preferred and can be used instead of conventional systems, especially when land is available. 48 4.2.6 Performance of Four Full-Scale Artificially Aerated Horizontal Flow Constructed Wetlands for Domestic Wastewater Treatment In agreement with the Butterworth et al findings, the competence of systems to yield ammonium effluent concentrations <3 mgNH4+-N/L was observed across all sites in systems receiving variable loadings between 0.1 and 13.0gNH4+-N/m2/d while potential pliability issues were detected in relation to spike loadings posited to be due to an insufficient nitrifying population within the beds(Butterworth et al., 2016). Nitrification was adequately efficient and constant across all loading rates. In addition, nitrification rates in aerated units increased linearly with increased loadings, while the non-aerated wetlands showed non-linear rates. There was no significant difference between effluent concentrations in tertiary beds A and B, except for the variations recorded upstream. According to Butterworth et al, achieving low effluent concentrations and the increased spread in the data at Site C compared to consistently low concentrations in Sites A and B means that the effluent data could not be categorized as statistically the same(Butterworth et al., 2016). Sites C and D, however, had statistically effluent concentrations. The nitrification rate is not the controlling factor when it comes to design. TSS reduction was significant in sites B through D, but site A showed no significant TSS reduction in both aerated and non-aerated beds. BOD concentrations in both influent and effluent were low in all sites. No significant difference in the median of effluent concentration was observed between the aerated bed and control bed in site A. BOD loading did not affect effluent concentration, and aeration did not enhance BOD removal. Table 4.11 shows the seasonal effects on the different sites Table 4.11: Summer and winter ammonium inlet loadings and effluent concentrations (Butterworth, et al., 2016) 49 Season Site Loading (gNH4+-N/m2/d) Median mean max Outlet Concentration (mgNH4+N/L) Median mean max n Summer Site A 2.0 (aerated) 0.3 11.5 0.1 0.02 1.4 19 Site A 2.0 (controlled) 0.3 11.5 6.5 0.03 20.6 19 Site B 0.08 0.02 1.9 0.1 0.01 1.5 20 Site C 0.04 0.01 0.07 0.2 0.04 0.3 5 Site D n/a n/a n/a 0.5 0.1 2.6 11 Site A 2.8 (aerated) 0.07 12.5 0.1 0.02 0.6 23 Site A 2.8 (controlled) 0.07 12.5 8.4 0.1 22.1 23 Site B 0.2 0.02 10.9 0.2 0.02 15.0 22 Site C 4.3 0.4 11.9 0.9 0.2 5.3 29 Site D n/a n/a n/a 1.2 0.1 13.3 20 Winter For the aerated wetlands, seasonal impacts show a small decrease of ammonium in the effluent, and this effect is concurrent with the increased HLR that can be attributed to heavy rainfall and hence less residence time in the bed. As observed from table 4.11, sites C and D had an increase in median outlet concentrations during winter in the aerated beds as opposed to summer. In site A (aerated bed), the mean effluent ammonium remained the same during both summer and winter. In contrast, in site A(non-aerated), there were higher mean outlet concentrations in winter when the temperature decreased. Conclusively, the study shows that the system was able to produce nitrified products that were down to 3mgNH4+-N/l in both the secondary and tertiary stages of the system. There was, however, 50 limited resilience to spike loads in all the systems. The system was proved to be highly efficient in ammonia removal for sites that were small in size and could receive high but variable rates of flow. 4.2.7 A review on the sustainability of constructed wetlands for wastewater treatment: Design and operation FWS and SSF CWs mainly use emergent plants. FWS CWs use P. australis, T.latofllia, Cyprus papyrus, Scirpus validus and T.domingensis as the most common emergent plant species. On the other hand, SSF CWs commonly use P. australis and Typha spp. In terms of plant tolerance to toxicity in wastewater, T.latifolia was stressed by ammonia concentrations of about 160–170 mg/L, while S.validus was the most tolerant. In a range of 20.5–82.4 mg/L concentration, Scirpus actus is the least tolerant to ammonia(Wu et al., 2015). Concentrations of up to 400 mg/L showed that Zornia latifolia had the highest tolerance to ammonia. High COD levels can disrupt the metabolism of P. australis. Arundo donax and Sarcoconia fruticose have the highest tolerance to salinity. Typha angustata had the highest tolerance for Cr, while P. australis has the highest tolerance for antibiotics. Wetland plants had a major role in the removal of carbamazepine, sulfonamides and trimethoprim when cast-off in CW sewage handlings; however, E. acicularis had an excellent ability to accumulate metals from water such as In, Ag, Pb, Cu, Cd, and Zn(Wu et al., 2015). According to Wu et al., (2015), phosphorous removal can be enhanced using gravel, sand, clay, calcite, marble, vermiculite, slag, fly ash, bentonite, dolomite, limestone, shell, zeolite, wollastonite, activated carbon, and lightweight aggregates; however, sand, gravel and rock are poor candidates for longterm phosphorus storage(Wu et al., 2015). 51 A higher HLR facilitates faster flow of wastewater through the bed, reducing the optimal time for contact. Increased HRT, on the other hand, allows for better microbial growth and hence better removals for TN and ammonium (Wu et al., 2015). Results of studies conducted show that the batch feeding mode obtained better performance than continuous in terms of providing oxidising conditions. Also, CW with the batch feeding mode showed higher ammonium removal efficiency (95.2%) than continuous systems (80.4%) (Wu et al., 2015). On the other hand, the intermitted feeding mode had higher nitrogen removal in CW than in continuous feeding mode. However, continuously fed systems showed a better sulphate removal than intermitted systems (Wu et al., 2015). Summarily, the study has been observed to majorly focus on CW design factors which have proved to be very essential to the success and sustainability of a CW project. 4.2.8 Constructed Wetlands as a Sustainable Solution for Wastewater Treatment in Small Villages The section discusses the removal rates for BOD, COD, TSS, TC, FC, and FS in relation to their HAR rates during the first and second year of wetland operation as observed in the tables 4.124.15 below. 52 Table 4.12: Biochemical oxygen demand(BOD), chemical oxygen demand(COD) and total suspended solids(TSS) removals during the first year of wetland operation (Solano, Soriano, & Ciria, 2004). Species HAR, mmday-1 BOD removal % Summer autumn COD removal % Summer autumn TSS removal % Summer autumn Cattail 150 75 86 81 71 76 78 76 64 69 87 90 88 90 Reed 150 75 77 85 NS 68 77 NS 68 77 NS 50 73 NS 87 91 NS 70 93 NS N S, values in these columns were not significantly different (probability α=0.05). HAR-hydraulic application rate (Solano, Soriano, & Ciria, 2004). Table 4.13: Percentages of removal of biochemical oxygen demand(BOD), chemical oxygen demand(COD) and total suspended solids(TSS), during the second year of wetland operation (Solano, Soriano, & Ciria, 2004) Species HAR, BOD removal % mmday-1 S S A W COD removal % S S A W TSS removal % S S A W Cattail 150 75 70b 70b 83b 75b 63 92a 83b 64 68c 77b 77b 88a 50b 51b 76a 67a 58b 85a 94a 93a 69b 81 69b 88 Reed 150 75 74b 84a 83b 63c 63 48d 93a 90a 90 87a NS 68b 85a 52b 54b 77a 69a 64b 90a 75b 91b 67b 83 83a 82 NS Values in columns with different letters indicate significant differences (probability α=0.05). N S, values in these columns were not significantly different (probability α=0.05). HAR, hydraulic application rate. During the first year, there was no significant relationship between the parameters that were measured and the HAR. During the second year, the reed beds with the lowest HAR had 53 significantly higher removal rates. The behavior of the beds with cattails was unclear since some of the plants died in autumn and summer in the bed that had the highest HAR. In the first year, there were no seasonal differences found in removal performance of BOD, COD, and TSS because the sampling period for the year ranged from June to November and the planting had been done two months earlier in April. In the second year, lower BOD removals were observed during winter which is generally attributed to microbial functions being limited by low oxygen levels. Therefore, the low BOD removals might have been a result of the lack of above ground biomass since the plants were harvested in autumn and hence led to lower the oxygen levels in the root zone. However, regarding the COD and TSS, there were no significant differences for percentage removals for that sampling season and the rest of the year. In reference to the study’s results, the performance shown by both plants at removing BOD, COD and TSS was similar and even higher; between 63 and 93% for BOD, 50 and 88% for COD and 58 and 93% for TSS when compared to performance of other authors between 65 and 91% for BOD, 48 and 75% for COD and 58 and 88% for TSS (Solano, Soriano, & Ciria, 2004). Table 4.14: Pathogen removal during the first year of wetland operation (Solano, Soriano, & Ciria, 2004) Species HAR, mmday-1 Total coliforms Faecal coliforms Faecal streptococci removal % removal % removal % Summer autumn Summer autumn Summer autumn Cattail 150 75 85 85 89 91 93 98 98 99 85 93 92 86 Reed 150 75 99 99 NS 93 98 NS 87 91 NS 97 99 NS 85 93 NS 90 93 NS N S, values in these columns were not significantly different (probability α= 0.05). HAR-hydraulic application rate (Solano, Soriano, & Ciria, 2004). 54 Table 4.15: Pathogen removal during the second year of wetland operation (Solano, Soriano, & Ciria, 2004) Species HAR, Total coliforms Fecal mmday-1 removal % removal % S S A W S S coliforms Fecal streptococci removal % A W S S A W Cattail 150 75 62b 80a 80b 81b 65b 75b 91a 98a 78a 85a 69b 93a 71b 50b 93a 85a 33b 43a 62b7 71b 41b 6a 84a 50a Reed 150 75 40b 82a 75b 82b 40c 59b 97a 91a 81a 85a 77b 93a 86b 43b 92a 76a 51a 58a 62b 85a 74b 49b 80a 66a Values in columns with different letters indicate significant differences (probability α=0.05). HAR, hydraulic application rate. TC, FC, and FS removals varied widely according to the tables presented. HAR did not significantly affect the removal of these parameters in the first year; however, in the second year, the bed that had the lowest HAR of 75 mmday-1 and the longest retention time of 3 days (both for cattail and reed beds) had the best removal rates. There was little effect of seasonal variation in the first year on removals, but in the second-year, summer and autumn had the best removals. In addition, there was maximum plant growth in the second year. However, when the two vegetative cycles are compared, the first year had higher removals than the second year, and this could be attributed to a deficiency of oxygen in the root zones during the second year. Summarily, both reed beds had high removals of chemical and physiological parameters. However, only winter showed a slight lower removal rates which was because of the lower oxygen levels in the root zone. The beds with the lowest HAR rates were the most suitable for efficient removals. In conclusion, the results obtained being satisfying proved that the system can be a suitable 55 treatment for small villages, however, it would be required to have a previous pretreatment for the removal of heavy metals, grit and floatable materials(Solano, Soriano, & Ciria, 2004). 4.2.9 Municipal wastewater treatment using vertical flow constructed wetlands planted with Canna, Phragmites and Cyprus During the study period, the organic loading rate of VFCW’s influent samples varied between 185 and 335(mg/L) for COD and between 59 and 175(mg/L) for BOD, while the average concentrations of TSS, NH4+-N, TKN and TP were 94, 16.7, 30.7 and 3.15(mg/L) respectively. The average bacterial indicators counts were 2.8×107 MPN/100 ml for TC, 2.3×106 MPN/100 ml for FC and 2.4×106 MPN/100 ml for E. coli (Abou-Elela & Hellal, 2012). As reported by Abou-Elela & Hellal, (2012), the average removal efficiencies for COD, BOD, and TSS in the final effluent were 88%, 90%, and 92% respectively, which could be attributed to the presence of diverse plant species, quick removal of settleable organics and fast degradation of organic compounds. Their corresponding residual values were 30.60, 13.20, and 8.50(mg/L). Figure 4.1 represents the COD, BOD, and TSS concentrations in the treated effluent. Figure 4.1: Concentrations of COD, BOD and TSS in treated effluent (Abou-Elela & Hellal, 2012) 56 Both nitrification and denitrification occurred during the two-year operation. Ammonia concentration decreased from 18.3 to 7.9(mg/L), while nitrate absorption in the waste increased from 0.12 to 0.52(mg/L). TKN removal was observed along the monitoring period. According to the study, the TKN removal efficiencies varied between 31% and 70% with an average percentage removal of 53%. The average TKN removal efficiencies throughout this study were within the removal range reported in other studies of constructed wetlands (Abou-Elela & Hellal, 2012). Phosphorous removal averaged at 62% with a concentration of between 0.4 and 2 mg/l in the treated wastewater (Abou-Elela & Hellal, 2012). The high removal rate is attributed to a long contact time that is 7.7 days and the use of three different species of plants on the same basis, leading to an increase in phosphorous removal. According to Abou-Elela & Hellal, (2012), the concentrations of the bacterial indicators in the TE were 2.6×103 MPN/100 ml for TC, 1.25×103 MPN/100 ml for FC and 1.1×103 MPN/100 ml for E. coli with an average removal efficiency ranging from 94% to 99.99%. These efficiencies can be clarified by the large concentration of oxygen in the VFCW. The high temperatures of 25–30°C in the VF CW caused an aerobic environment which led to higher removal rates. Biomass harvesting for P. australis and Canna was conducted after 12 months of project operation, but Cyprus was not harvested because it was too short. The yield for dry biomass of P. australis was 3.26 kg/m2, while the same for Canna was 4.83 kg/m2. Canna uptake for nitrogen and phosphorous was 68.1 g/m2 and 32.55 g/m2, respectively. For Phragmites, the uptake was 48.6 gN/m2 for nitrogen and 28.91 gP/m2 for phosphorous (Abou-Elela & Hellal, 2012). The results show that Canna had better uptake rates than Phragmites, and this effect can be attributed to the roots of Canna being more widely distributed in the reed bed. In contrast, in reference to the study, 57 Cyprus proved much more efficient at nitrogen removal, phosphorous removal, and the removal of heavy metals than the other two species. In terms of bacterial analysis, it was indicated that canna was more effective in the removal of microorganisms. However, according to Abou-Elela & Hellal(2012) in the TE, the residual bacterial counts showed a slight exceed (103 MPN/100ml) to the permissible limits stated in national regulatory standards of wastewater reuse in restricted irrigation(ECP501,2005). Conclusively, the presence of a diverse species of plants ensured that there were higher removal rates of BOD, COD, TSS, N, and TP because they provide more effective and efficient distribution of the root system, and hence, a more diverse habitat for microbes. In addition, the physio-chemical characteristics of treated wastewater were in compliance to the national regulatory for treated wastewater reuse in restricted irrigation. However, the TE would require a slight disinfection to eliminate the residual pathogens. In conclusion, the quality of treated effluent proved that the use of VFCW is an effective technology for wastewater treatment and could be used for irrigation purposes in rural areas and small communities. 4.2.10 Development of constructed wetlands in performance intensifications for wastewater treatment: A nitrogen and organic matter targeted review The following results are observed for the proposed operational strategies: 1. Effluent recirculation improves the effluent quality by enhancing aerobic microbial activity without significantly modifying the whole system operation. 58 2. Artificial aeration improves the poor oxygen transfer rates observed in traditional HSSFs and improves the removal of organic matter, E.coli, and ammonium. Artificial aeration, however, does not have a significant influence on phosphorous removal. 3. According to the research, the tidal operation also solves oxygen transfer limitations in tidal CWs and improves nitrogen removal by enhancing alternate aerobic and anaerobic environments(Wu, Kuschk, Brix, Vymazal, & Dong, 2014). 4. Drop aeration shows the increase of BOD5 removal load from 8.1 to 14.2 g/m2 within five days. The system has low capital costs, high HLR, high pollutant removal efficiencies, easy maintenance, low operation costs, and minimal clogging. 5. Flow direction reciprocation shows better pollutant removal efficiencies, higher microorganisms populations and hence lower organic compound accumulation and minimal clogging. 6. The study results explain that earthworm integration in SSF CWs reduces clogging, enhances break down large quantities of organic matter, enhances density and biomass of wetland plants and hence improving nitrogen and phosphorus uptake, and reduces sludge production in VFCWs, hence reducing sludge maintenance costs(Wu, Kuschk, Brix, Vymazal, & Dong, 2014). 7. Bio-augmentation accelerates degradation of pollutants such as pesticides and heavy metals by shortening adaptation period and hence accelerating the suitable habitat conditions for microbial growth. The following are results observed for the innovative strategies proposed in the study: 59 1. Circular flow corridor CW enhances TN removal, dilutes inflow water to reduce the toxicity effect on plants and delays clogging of media while improving P removal. The system is cost effective. 2. Towery hybrid CW enhances N removal by improving nitrification and denitrification rates. Average percentage removal efficiencies for TSS, COD, NH4 –N, TN, and TP are 89, 85, 83, 83, and 64%, respectively. 3. Baffled SSF CW enhances pollutant removal. The unit, recorded percentage removal rates of 74, 84, and 99% were higher than the conventional CW; which yielded results of 55, 70, and 96% using HRTs of 2, 3, and 5 days, respectively. 4. Microbial fuel cell yields the results that CWs enhanced pollutant removal and simultaneously generated power. 4.2.11. Reed bed CW system The results of the study were compared with the MECA standard (A) to determine effectiveness and efficiency (Oman Government, 2018). Table 4.16 shows the removal efficiency for various components of a double stage vertical flow reed bed. 60 Table 4.16: Data for the treatment of effluent by the reed bed system (Haya Water, 2017; Oman Government, 2018) Parameter Raw Sewage Treated MECA Standard Removal (mg/L) Effluent(mg/L) (A) Efficiency COD 1206 12.7 150 98.9 BOD 372.3 3.9 15 98.9 NH3-N 58.2 0.2 5 99.6 NO3-N - 32.9 50 (NO3) - TN 90.7 8.7 15 90.4 TP 11.3 0.1 30 99.1 TSS 633.3 1.2 15 99.8 O&G 36 0.3 0.5 98.1 FC - 117 200 per 100ml - VHO 22 <1 <1 per L 98 The Haya water CW showed removals of COD (98.9%), BOD (98.9%), NH3-N (99.6%), TN (90.4%), TP (99.1%), TSS (99.8%), O&G (98.1%) and VHO(98%). The results for all the parameters being excellent in treatment efficiency, showed compliance to the MECA standard (A) (Oman Government, 2018). Graph 4.1 shows a representation of Treated Effluent(mg/L) and the MECA Standard(A) as well as the removal efficiencies for all the above-mentioned parameters. Graph 4.1: Relationship between treated effluent, the MECA standard and removal efficiency (Haya Water, 2017) (Oman Government, 2018) 61 Relationship Between the Treated Effluent, its MECA Standard (A) and their Removal Efficiency 150 117 98.9 98.9 12.7 15 3.9 BOD 99.6 99.1 90.4 32.9 COD 5 0.2 NH3-N 0 NO3-N Treated Effluent (mg/L) 99.8 98.1 15 1.2 TSS 0.5 0.3 O&G 98 30 15 8.7 0.1 TP TN MECA Standard A 0 FC 0 VHO Removal Efficiency The graph shows the high removal of COD and BOD, meaning that the solids can easily be removed from the wastewater. In addition, the high removals for TN, TP, VHO, FC, TSS, O&G, and NH3-N mean that the effluent concentrations were in compliance with MECA standards (Haya Water, 2017). On the other hand, the high percentages of ammonia, phosphorous, and nitrogen show that the soils in which the effluent was passing through were highly nutritious. The absence of nitrate in the treated effluent catalyzed the process of eutrophication and aeration. Also, the absence of FC showed that the treated effluent was very clean. The design chosen was used to ensure the effectiveness and efficiency of the system. Moreover, it reduced the cost and size at the same time while regulating the flow to optimize retention time for efficient pollutant removal. However, the retention time was determined based on the type of effluent being treated. Domestic wastewater took less time to treat since it had less pollutant concentration than the non-domestic wastewater. 62 The plants used (Phragmites Austrails) in the system showed high treatment efficiency since the species chosen had relatively constant growth and high substrate levels. Conclusively, the system after an analysis of physical, biological, and chemical parameters, yielded high removal efficiencies that complied with MECA Standards (A), proving that it was an effective and viable solution to treatment. 4.3 Summary and Comparison For the comparison, two HSSF case studies, referred to as case 1” Horizontal Sub-Surface Flow and Hybrid Constructed Wetlands Systems for Wastewater Treatment” (Vyzamal, 2005) and case 2 “Efficiency of a Horizontal Sub-Surface Flow Constructed Wetland Treatment System in an Arid Area” (Albalawneh, Chang, Chou, & Naoum, 2016). are compared in terms of methodology and results. In case 1, the HSSF CW methodology is analyzed against case 2 HSSF CW methodology. Case 1 used P. australis as its principle wetland vegetation while case 2 used P. australis, kenaf plant and no vegetation in the control beds. Case 1 summarized the typical or general HSSF CWs designs and parameters used all over the world in regions that are not arid while case 2 focused on a project located in Al Samra Agricultural Research Station in Central Jordan which is majorly an arid area. The substrate media used in case 1 is soil and coarse substrate while case 2 uses coarse volcanic tuff and fine volcanic tuff. The biggest area used for reed beds is 5m2 in case 1 while case 2 uses an average area of 16.25m2. In case study 1 the removal efficiencies were based on the concentration, however in case number 2 the removal efficiencies were based on mass flow. The results of the two cases can be compared in terms of performance efficiency rates presented in percentage. With reference to table 4.2, the 63 removal of BOD in case 1 is at 85%, while that for case 2 is 55%. COD removal in case 1 is higher than in case 2 since it is at 75% for case 1 and 51% in case 2. Similarly, TSS in case 2 being at 67% is lower than TSS removal in case 1 being at 83%. Perhaps, the lower removal rates of case 2 could be attributed to harsh climatic conditions since the area is arid, which is unlike the areas discussed in case 1. Another reason could be that case 2 was based on mass flow and not concentration (because evaporation caused water losses and concentrated the effluents). In addition, the use of kenaf plants could have yielded lower removal rates in case 2. 64 CHAPTER 5 CONCLUSION Water is one of the most important elements and it is essential to the survival of not only the human race but whole world with all its living inhabitants. Unfortunately, the human race has made water pollution a global crisis, a state of affairs which threatens the possibility of survival. Often, effluents from our towns in sewage collection systems are discharged directly into water bodies and water courses without any treatment effort. In some cases, efforts for treatment are made using conventional treatment methods that are almost always expensive to construct, operate, and maintain and at the same time may not be as effective or efficient in wastewater treatment. Hence, the introduction of CWs as a cost effective and more efficient alternative for wastewater treatment in comparison to conventional treatment methods has been proposed. CWs are cheaper to construct, easier to operate and maintain, and according to this report it has been proved that they are much more efficient than other systems. Apart from water conservation efforts, constructed wetlands assist in animal conservation efforts especially for the species that live in water bodies. By controlling direct discharge of harmful effluents into large water bodies and improving water quality, water species have a greater chance of survival. However, CWs can be a disadvantage in some cases in terms of land since some require large land areas. Moreover, they can also allow for mosquito breeding which is a threat to human health. The review of CWs for municipal wastewater using case studies has been the main objective of this report. The main aspects discussed throughout the whole report have been water quality, design type, and reuse criteria. More specifically, the methodology section explores all possible methods used in construction and design of CWs for municipal wastewater management. 65 Parameters such as location, PE, pre-treatment, secondary treatment, tertiary treatment, flow design, surface area, aspect ratio, bed dimensions, energy requirements, loading rates, loading designs, aeration, retention times, construction materials, substrate media, distribution layer design, vegetation, and sampling methods are discussed and specified according to treatment demand. From the samples, an array of chemical and physiological parameters is analyzed whose results are then discussed in relation to efficiency of removal, conformation to set standards and reuse criteria. The parameters include COD, BOD5, TSS, FC, TC, TN, TP, bacteria (E.coli) and in few cases some heavy metals. The results are as well discussed in regard to seasonal variations and their effects on the removal efficiencies for the pathogens. Moreover, the role of plant species used in vegetation is discussed in terms their contribution to pollutant removal. It has been established in almost all cases that planted CWs are more efficient than unplanted CWs and that the most common and effective plant species are Typha spp. and Phragmites. Based on the research findings the study “Feasibility of using constructed treatment wetlands for municipal wastewater treatment in the Bogotá Savannah, Colombia” is the best case study. Although the model discussed is hypothetical, comparing it to real and existing models makes it relevant and reliable. The CWTS model shows among the highest COD, SS, and E.coli removals ranging from 92%–98%. TN, NH4, and TP removals are also higher than the other two systems used for comparison. The study shows that it is cost-effective and highly efficient. Summarily, CWs have proved to be an efficient and cost effective alternative to conventional wastewater treatment, even in developing countries. 66 CHAPTER 6 RECOMMENDATIONS In light of the details discussed in the report, the following general recommendations can be made for future works: • A proper recommendation would entail considering the building mechanisms of constructed wetlands that would not have to incur large operation and maintenance costs. • The rate of water surges in the wetlands bed need to be controlled to avoid the efficiency of the system in the pollutant removal rates. For the Oman study, the following recommendations can be made for future work: • A VF-HF design should be implemented in Oman because it is easier to clean and can be maintained within a very short time while being very effective and efficient. • Other companies such as Haya should be encouraged by the government to invest in similar projects to increase the number of CWs for wastewater treatment. Therefore, the government can introduce discounts on the materials used for construction. • It is recommended to implement reed bed treatment technology as a sustainable solution in regional governorates since there are large empty areas. • Water balance, energy balance and design parameters should be considered more in the studies. 67 REFERENCES Abou-Elela, S. I., & Hellal, M. S. (2012). Municipal Wastewater Treatment using Vertical Flow Constructed Wetlands Planted with Canna, Phragmites and Cyprus. Ecological Engineering 47, 209-213. Albalawneh, A., Chang, T. K., Chou, C. S., & Naoum, S. (2016). Efficiency of a horizontal subsurface flow constrcuted wetland treatment system in an arid area. Water 8, 1-14. Arias, M. E., & Brown, M. T. (2009). Feasibility of using constructed wetlands for municipal wastewater treatment in the Bogota Savannah, Colombia. Ecological Engineering 35, 1070-1078. Butterworth, E., Richards, A., Jones, M., Jefferson, B., & et. (2016). Performance of Four FullScale Artificially Aerated Horizontal Flow Constructed Wetlands for Domestic Wastewater Treatment. Water 8, 1-15. Crawford, G., & Sandino , J. (2010). Energy efficiency in wastewater treatment in North America: a compendium of best practices and case studies of novel approaches. Retrieved from Water Environment Research Foundation: https://www.nyserda.ny.gov/-/...Water- Wastewater.../north-american-drinking-water-u Gikas , G. D., & Tsihrintzis, V. A. (2014). Municipal wastewater treatment using constructed wetlands. Water Utility Journal 8, 57-65. Haya Water. (2017). Haya Water. Retrieved from: https://haya.om/en/Pages/Home.aspx Accessed 1st June 2018 68 Jhansi, S. C., & Mishra , S. K. (2013). Wastewater treatment and reuse: Sustainability options. Consilience: The Journal of Sustainable Development 10(1), 1-15 Nelson, J., Bishay, F., Van Roodselaar, A., Ikonomou, M., & Law, F. C. (2007). The use of in vitro bioassays to quantify endocrine disrupting chemicals in municipal wastewatertreatment plant effluents.. The science of the Total Environment, 374(1), 80-90. Oman Government. (2018). Ministry of Environment and Climate Affairs. Retrieved from meca.gov: https://meca.gov.om/en/module.php?module=decisions&page=2 [Accessed 17th May 2018] Postel, S. L. (2000). Entering an era of water scarcity: the challenges ahead . Ecological Applications 10(4), 941-948. Praewa, W. (2017). Sustainable Wastewater Treatment for Thailand. Retrieved from: https://minds.wisconsin.edu/bitstream/handle/.../MS_Thesis_Wongburi_Praewa.pdf?...[A ccessed 20th March 2018] Secretariat, R. (2014). Renewables 2014 global status report. REN21. Paris: Tech Rep. Solano, M. L., Soriano, P., & Ciria, M. P. (2004). Constructed Wetlands as a Sustainable Solution for Wastewater Treatment in Small Villages. Biosystems Engineering 87 (1), 109-118. Tsihrintzis, V. A., Akratos, C. S., Gikas, G. D., Karamouzis, D., & Angelakis, A. N. (2007). Performance and Cost Comparison of a FWS and a VSF Constructed Wetland System. Environmental Technology 28, 621-628. 69 Vymazal , J., & Kropfelova, L. (2008). Types of constructed wetlands for wastewater treatment. Wastewater Treatment in Constructed Wetlands with Horizontal Sub-Surface Flow,, 121202. Vymazal, J. (2005). Horizontal sub-surface flow and hybrid constructed wetlands systems for wastewater treatment. Ecological Engineering, 478-490. Wetzel, R. G. (1993). Micro-communities and micro-gradients: Linking nutrient regeneration, microbial mutualism, and high sustained aquatic primary production. Netherland Jounal Aquatic Ecology 27 (1) , 3-9. Wu, H., Zhang, J., Ngo, H. H., Guo, W., Hu, Z., Liang, S., & Liu, H. (2015). A review on the sustainability of constructed wetlands for wastewater treatment: Design and operation. Bioresource Technology 175, 594-601. 70

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