Transcription

United Nations Human Settlements ProgrammeCONSTRUCTED WETLANDS MANUALCONSTRUCTEDWETLANDS MANUAL

United Nations Human Settlements ProgrammeCONSTRUCTEDWETLANDS MANUAL2008

Copyright United Nations Human Settlements Programme (UN-HABITAT), 2008All rights reserved. The material in this publication may be reproduced in whole or in partor in any form for education or non-profit uses without special permission from the copyrightholder, provided acknowledgment of the source is made. UN-HABITAT would appreciatereceiving a copy of any publication which uses this publication as a source.CitationUN-HABITAT, 2008. Constructed Wetlands Manual. UN-HABITAT Water for AsianCities Programme Nepal, Kathmandu.United Nations Human SettlementsProgramme (UN-HABITAT)P.O. Box30030, Nairobi 00100, KenyaTel(254-20) 7621234Fax(254-20) itat.orgHS Number: HS/980/08EISBN Number: (Volume) 978-92-1-131963-7Constructed Wetlands ManualiiDisclaimer: The designations employed and the presentation of the material in this publicationdo not imply the expression of any opinion whatsoever on the part of the Secretariat of theUnited Nations concerning the legal status of any country, territory, city or area, or of itsauthorities or concerning delimitation of its frontiers or boundaries or regarding its economicsystem or degree of development. The analysis, conclusions and recommendations of thereport do not necessarily reflect the views of the United Nations Human SettlementsProgramme (UN-HABITAT), the Governing Council of UNHABITAT or its MemberStates.April, 2008

forewordIn a rapidly urbanizing world, poor environmental sanitation has emerged as a majorchallenge, threatening the health and livelihoods particularly of the poor. It is also nowclear, that if business continues as usual, the sanitation related MDG to halve by 2015, theproportion of people without sustainable access to basic sanitation will not be met.Mere provision of toilets is not enough to ensure good environmental sanitation. Excretafrom toilets needs to be transported and disposed of safely without creating an environmentalhealth hazard. While in the large cities of industrialized countries this is usually achievedthrough centralized wastewater management systems with advanced treatment technologies,such systems tend to be expensive and difficult to operate.Smaller, decentralized, wastewater management and treatment systems such as constructedwetlands can be a viable alternative for many urban areas in developing countries. Constructedwetlands are relatively inexpensive to build where land is affordable and can be easilyoperated and maintained even by the community.This manual, drawing upon a number of examples in Nepal, provides basic guidance on thedesign, construction and operation and maintenance of constructed wetlands and alsoindicates situations where this may not be a feasible alternative.I believe that the experiences and the case studies described in this manual can serve asuseful reference material for municipal officials and water and sanitation professionals andhope that it will stimulate local action for affordable and simple wastewater managementsystems and technologies.Anna Kajumulo TibaijukaExecutive Director, UN-HABITATConstructed Wetlands Manualiii

Constructed Wetlands Manualiv

PrefaceWith support from the Water and Sanitation Trust fund, UN-HABITAT is implementing the WaterFor Asian Cities Programme (WAC) which is currently operational in India, People’s Republic ofChina, Nepal, Lao PDR and Vietnam and is being extended to Cambodia, Indonesia and Pakistan.With the overarching goal of creating an enabling environment for pro-poor investments in cities,the WAC programme is demonstrating innovative approaches for improving access to water andsanitation for the poor. These pilot and demonstration projects usually aim to tackle difficult waterand environmental sanitation problems through practical community based approaches. One suchproblem confronting the rapidly urbanizing cities in Asia is the safe treatment and disposal ofwastewater. Conventional solutions using advanced technologies are simply not affordable or are toocomplex to maintain in most small and medium sized towns.Under the WAC’s “normative” work programme, lessons learnt through pilot projects are documentedfor wider dissemination. This publication on the design, construction, operation and maintenance ofconstructed wetlands was prepared under the WAC programme on the basis of experiences in Nepaland in recognition of the need for a viable alternative to conventional wastewater treatment anddisposal technologies. It should however be noted that constructed wetlands have their limitationsthe unavailability or the cost of land can make them unviable; and climatological aspects andwastewater parameters can affect their proper functioning.The preparation of the manual was coordinated by Dr. Roshan Shrestha, Chief Technical Adviser,WAC, Nepal. The WAC programme also appreciates the contribution of Mr. Shirish Singh, Dr. GuenterLangergraber and Dr. Elif Asuman Korkusuz of the University of Natural Resources and AppliedSciences Vienna in the development of this manual.vConstructed Wetlands ManualAndre DzikusChiefWater and Sanitation Section IIWater, Sanitation and Infrastructure BranchUnited Nations Human Settlements Programme (UN-HABITAT)

Constructed Wetlands Manualvi

Contentsiiiforewordvpreface1chapter ONE introduction3chapter TWO what is a constructed wetland?72.1 Advantages of constructed wetlands52.2 Limitations of constructed wetlands5chapter THREE configurations of constructed wetland3.1 Horizontal Flow (HF)73.2 Vertical Flow (VF)83.3 Hybrid9chapter FOUR how does a constructed wetland function15chapter FIVE design of constructed wetland5.1 Preliminary treatment15vii5.2 Primary treatment5.2.1 Septic Tank5.2.2 Anaerobic Baffle Reactor (Improved septic tank)1616175.3 Sizing of the wetland5.3.1 Sizing based on equation5.3.2 Sizing based on specific area requirement per Population Equivalent181820Constructed Wetlands Manual11

3547Constructed Wetlands Manualviii535.4 Depth5.4.1 HF wetland5.4.2 VF wetland2121225.5 Bed cross section area (only for HF wetland)225.6 Media selection5.6.1 HF wetland5.6.2 VF wetland5.7 Bed Slope232324245.8 Sealing of the bed255.9 Inlet and outlet structures5.9.1 Inlets5.9.2 Outlet2626325.10 Vegetation33chapter SIX construction of constructed wetland6.1 Basin Construction356.2 Lining of the basinPermeability test35366.3 Substrate filling6.3.1 HF wetland6.3.2 VF wetlandSand suitability test373737386.4 Inlet and Outlet Structures396.5 Planting vegetation406.6 Water level management for the growth of vegetation41chapter SEVEN operation and maintenance7.1 Start-up477.2 Routine operation7.2.1 Adjustment of water levels7.2.2 Maintenance of flow uniformity7.2.3 Vegetation management7.2.4 Odor Control7.2.5 Maintenance of berms (Walls)4748484850517.3 Long-term operations51chapter EIGHT constructed wetland for sludge drying

chapter NINE case studies9.1 Hospital wastewater treatment (Dhulikhel Hospital)9.1.1 Technical description9.1.2 Performance9.1.3 Operation and maintenance9.1.4 Costs55555758589.2 Combined laboratory and domestic wastewatertreatment and reuse (ENPHO)9.2.1 Technical description9.2.2 Performance9.2.3 Operation and maintenance9.2.4 Costs58585959619.3 Institutional wastewater treatment (Kathmandu University)9.3.1 Technical description9.3.2 Performance9.3.3 Operation and maintenance9.3.4 Costs61616264649.4 Municipal wastewater treatment (Sunga)9.4.1 Technical description9.4.2 Performance9.4.3 Operation and maintenance9.4.4 Costs64646667679.5 Grey water treatment (Private residence)9.5.1 Technical description9.5.2 Performance9.5.3 Operation and maintenance9.5.4 Costs67676969699.6 Septage and landfill leachate treatment (Pokhara)9.6.1 Technical description9.6.2 Costs70707173references77Annex - A: How to treat raw sewage with constructed wetlands: An overview of theFrench systemsixConstructed Wetlands Manual55

TablesTable 1Table 2Table 3Table 4Table 5Table 6Table 7Table 8Table 9Table 10Table 11Table 12Table 13Major International ConferencesPollutant Removal Mechanisms in Constructed WetlandsBasic design criteria for two-compartment septic tankBasic design criteria for an anaerobic baffle reactorFortnightly O & M action listTwo-monthly O & M action listYearly O & M action listTechnical description of Dhulikhel Hospital Constructed WetlandTechnical description of ENPHO Constructed WetlandTechnical description of Kathmandu University Constructed WetlandTechnical description of Sunga Constructed WetlandAverage concentrations of pollutants at SungaTechnical description of Constructed Wetland at Private Residence5121618515252565962656768FiguresFigure 1Figure 2Figure 3Figure 4Figure 5Figure 6Figure 7Figure 8Figure 9Figure 10Figure 11Figure 12Constructed Wetlands ManualxImproved sanitation coverage in 2002Components of a constructed wetlandSchematic cross- section of a horizontal flow constructed wetlandSchematic cross- section of a vertical flow constructed wetlandPollutant removal mechanismOxygen transfer from rootsNitrogen transformations in a constructed wetlandSchematic cross- section of a two-compartment septic tankSchematic cross- section of an up flow anaerobic baffle reactorKBOD for HF plotted against Temperature for substrate depth 40 cm and porosity 40%KBOD for VF plotted against Temperature for substrate depth 70 cm and porosity 30%Specific area requirement per PE for HF and VF wetland fordifferent specific wastewater dischargesFigure 13 Substrate arrangement in a HF wetlandFigure 14 Substrate arrangement in a VF wetlandFigure 15 Substrate arrangement in a VF wetlandFigure 16 Outlet devicesFigure 17 Typical grain size distributionFigure 18 Sand suitability testFigure 19 The effect of wetland layout configuration on effective flow distributionFigure 20 Results of sand suitability testFigure 21 Technique for planting rhizome cuttingsFigure 22 Substrate profile for sludge drying bedFigure 23 Schematic representation of constructed wetland at Dhulikhel HospitalFigure 24 Performance of constructed wetland at Dhulikhel Hospital from 1997 to 2006Figure 25 Schematic representation of constructed wetland at ENPHOFigure 26 Performance of constructed wetland at ENPHO from 2002 to 2006Figure 27 Schematic representation of constructed wetland at SungaFigure 28 Performance of constructed wetland at Kathmandu University from 2001 to 2006Figure 29 Schematic representation of constructed wetland at Kathmandu UniversityFigure 30 Performance of constructed wetland at Sunga from August 2006 to August 2007Figure 31 Schematic representation of constructed wetland at private residenceFigure 32 Performance of constructed wetland at private residence from May 1998 to May 2000Figure 33 Schematic representation of septage and landfill leachate treatment 96061636466676970

ONEintroductionALMOST all of the world’s major cities have gone in to the 21st Century facing anenvironmental crisis. The world’s cities not only face the challenge of supplying adequatesanitation facilities to its residents (Figure 1), but must also ensure that the available waterresources are not contaminated. The discharge of untreated wastewater is a major contributorto deteriorating health conditions and pollution of nearby water bodies. The problem isexpected to increase due to rapid pace of urban growth, unless measures are taken to controland treat effluents.The approach of centralized, water-based sewer systems was applied to attain considerablepublic health improvement in urban areas of industrialized countries. However, the cost ofsuch a sewer-based system is enormous and is unaffordable to many of the developingcountries. Centralized systems require conventional (intensive) treatment systems, whichare technologically complex and financially expensive, so many communities of thedeveloping countries cannot afford the construction and operation of conventional treatmentsystems. For these communities, alternative natural treatment systems, which are simple1Percentage of populationusing improved sanitationLess than 50%50% to 75%76% to 90%91% to 100%Insufficient dataFIGURE 1Improved sanitation coverage in 2002 (WHO/UNICEF, 2004) FIGURE 1Constructed Wetlands Manualchapter

in the construction and operation, yet inexpensive and environmentally friendly, seem tobe appropriate.Constructed Wetlands (CWs) are a natural, low-cost, eco-technological biological wastewatertreatment technology designed to mimic processes found in natural wetland ecosystems,which is now standing as the potential alternative or supplementary systems for thetreatment of wastewater.This manual is not a plea to implement constructed wetlands for wastewater treatment butaims at providing a comprehensive description of the issues related to wastewater treatmentthrough constructed wetlands. This manual has been prepared as a general guide to thedesign, construction, operation and maintenance of constructed wetlands for the treatmentof domestic wastewater as well as introduction to the design of constructed wetland forsludge drying.Chapter 2 presents an introduction of the constructed wetlands and its development.Chapter 3 describes the configurations of constructed wetlands and gives insight of thehorizontal and vertical flow constructed wetlands. Chapter 4 aims at providing an overviewof working principle of constructed wetlands and describes the removal mechanisms ofspecific pollutants. Chapter 5 illustrates the various aspects to be considered during thedesign of a subsurface flow constructed wetland. The constructional aspects of the wetlandare illustrated with pictures in Chapter 6. Chapter 7 states the operation and maintenanceof wetlands for smooth functioning and Chapter 8 gives an introduction on the design ofconstructed wetlands for sludge drying. Six case studie