Decentralised wastewatermanagement using constructedwetlands in Nepal

The paper describesthe importance ofsmall scaledecentralizedwastewater treatmentusing reed bedtreatment systems inNepal with exampleswhere the systemprovides good qualityand cost effectiveservices.

December 2008

WaterAid’s mission is toovercome poverty byenabling the world’spoorest people to gainaccess to safe water,sanitation and hygieneeducation.

WaterAid/Marco Betti

Environment management is asignificant challenge in developingcountries mainly due to lack ofstrong legislation to controlwastewater and institutionalcapacity for integrated planning andmanagement. This paper describesthe importance of small scaledecentralized wastewater treatmentusing reed bed treatment systems(RBTS) in Nepal. It shows howpublic/community participation cansupport small scale constructionwork while ensuring checks onquality and price of construction. Itincludes examples where thissystem provides good quality, low-cost services.

Environmental Public HealthOrganisation (ENPHO) withtechnical support of a Nepali Ph.DScholor from University of NaturalResource and Applied Life SciencesVienna introduced the system inNepal through research and thenby designing and constructing apilot-scale wastewater treatmentsystem in Dulikhel Hospital in1997. Since then this has beenfollowed by 13 such systems atvarious institutions (e.g. hospitals,schools, university, and monastery)and individual households. Thesystem is found to be highlyeffective in removing pollutants

Abstract

WaterAid/ Marco Betti

such as suspended particles,ammonia-nitrogen, BOD, COD andpathogens.

With the experience of designingthe system and more than eightyears of monitoring and

Krishna Lal Shrestha,Chairman,

Sunga waste watertreatment plant,

Thimee

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Haphazard disposal of untreated wastewaterfrom households as well as institutions andindustry is causing severe deterioration ofwater bodies in many urban areas in thedeveloping world. Most cities do not haveadequate systems for the collection andtreatment of wastewater and this is usuallynot considered to be a priority forinvestment. It is estimated that in developingcountries, 300 million urban residents, 34%of them in South Asia, have no access tosanitation (WaterAid Nepal, 2006).Approximately two-thirds of the populationin the developing world has no hygienicmeans of disposing of excreta and an evengreater number lack adequate means ofdisposing of wastewater. This is a majorpublic health risk as it can lead to outbreaksof diseases such as diarrhoea, cholera, andtyphoid.

Although urbanisation is a relatively newphenomenon in Nepal, with only about 15%of the population living in urban areas, therate of urbanisation is very high. This rapidurbanisation is haphazard and so exertsimmense pressure on the urban environment.Municipal managers often lack the expertiseand resources to deal with this issue. As a

Introduction

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evaluation of the system, the challenge wasto upscale this technology to a communityscale. To overcome this challenge acommunity scale wastewater treatmentsystem was designed for Madhaypur ThimiMunicipality, a first of its kind in Nepal. Asthe local people in Madhaypur ThimiMunicipality showed interest in wastewatertreatment, ENPHO with support of theAsian Development Bank (ADB), UN-HABITAT and WaterAid Nepal (WAN)

result, urban sanitation has become a majorchallenge for municipalities and small townsin Nepal. Most of the urban and semi-urbanareas of the country rely on on-site sanitationfacilities such as pit latrines, pour flushtoilets and septic tanks. It is estimated thatonly about 12% of urban households areconnected to the sewer system andwastewater treatment is virtually non-existent. Almost all the wastewater isdischarged into nearby rivers without anytreatment. The total wastewater produced inthe country is estimated to be 370 millionlitres per day (MLD). The installed capacity ofwastewater treatment plants is only 37 MLD(10% of total demand) and functioningwastewater treatment plants account for 17.5MLD, or 5% of total demand (Nyachhyon,2006).

constructed a wastewater treatment systemin Sunga area. The treatment plant has thecapacity to treat 50m3 of wastewater perday. The local community has formed acommittee for construction and futureO&M of the RBTS. This RBTS will set avaluable precedent for other larger systemsin other parts of the country as well assystems envisaged under national urbandevelopment projects in Nepal, such as theUrban Environment Improvement Project.

Krishna Shrestha, Caretaker,Sunga waste water treatmentplant, Thimee

WaterAid/ Marco Betti

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The problem of wastewater management isparticularly severe in Kathmandu Valley,which has five municipalities and is thelargest urban centre in the country. In the1980s four wastewater treatment plantswere built in Kathmandu Valley, one inSundarighat, Lalitpur to treat wastewaterfrom the core areas of Kathmandu, anotherin Balkumari, Lalitpur to treat wastewaterfrom the city of Lalitpur and one each inthe Sallaghari and Hanumanghat areas ofBhaktapur. These treatment plants arebased on simple lagoon systems, wherewastewater is treated through naturalprocesses such as sedimentation andbiological degradation in a series of largelagoons. Although these plants aretechnically very simple with no mechanisedparts, they are still not functioning wellbecause of poor operation andmaintenance and mismanagement. In 2002another wastewater treatment plant thatuses a more complicated oxidation ditchtechnology has been constructed atGuhyeshwori. Although this plant ispartially functioning the cost of operationis very high and its sustainability isquestionable.

Overall the wastewater generated by abouttwo million only residents in KathmanduValley has severely deteriorated the waterquality in the Bagmati river, particularly in theurban stretches. This primarily affects thepoor people who live near the river and aremore exposed to the pollution.

The issues that arise from this prevailingposition can be summarised as follows:

As wastewater management is not apriority for most people or thegovernment, simple and cost effectivesystems are necessary to ensure thatthey are managed in a sustainablemanner.

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A simple and effective operation andmaintenance system is essential for operating awastewater treatment system.Centralised wastewater management systemsare difficult to operate because of thedifficulties in maintaining the long sewernetworks and treatment plant.

In the late 1990s, in an attempt to try and deal withsome of these difficulties, a new low-cost, lowtechnology process was introduced, by whichwetlands are constructed and wastewater treated inthem. In this paper, the constructed wetlands processis presented, and its implementation in Nepaldescribed. Some case studies provide particulardetails and then some commentary discusses thechallenges involved and the way ahead.

Constructed wetland atKathmandu University

ENPHO/ Dr.Roshan Raj Shrestha

44

Constructed Wetlands (CW) is abiological wastewater treatmenttechnology designed to mimicprocesses found in naturalwetland ecosystems. Thesesystems use wetland plants,soils and their associated micro-organisms to removecontaminants from wastewater.Application of constructedwetlands for the treatment ofmunicipal, industrial andagricultural wastewater as wellas storm water started in the1950s and they have been usedin different configurations,scales and designs. CWs arereceiving increasing worldwideattention for wastewatertreatment and recycling due tothe following major advantages:

use of natural processessimple construction (can beconstructed with localmaterials)simple operation andmaintenancecost-effectiveness (lowconstruction and operationcosts)process stability.

Research studies have shown that wetlandsystems have great potential in controllingwater pollution from domestic, industrial andnon-point source contaminants. As it hasbeen widely recognised as a simple, effective,reliable and economical technologycompared to several other conventionalsystems, it can be a useful technology fordeveloping countries.

Constructed wetlandwastewater treatment system

There are various types of constructedwetland systems for treating wastewaterbased on the type of plants used, type ofmedia used and flow dynamics. The mostcommon type of constructed wetlandsystem used in Nepal is the sub-surfaceflow system, which is also known as theReed Bed Treatment System (RBTS). Thebasic features of RBTS include a bed of

FIGURE 2 VERTICAL FLOW CONSTRUCTED WETLAND

FIGURE 1 HORIZONTAL FLOW CONSTRUCTED WETLAND

Source: Cooper et al., 1996

Source: Shrestha, 1999

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TABLE 1 POLLUTANT REMOVAL MECHANISMS IN CONSTRUCTED WETLANDS

uniformly graded sand or gravel with plantssuch as reeds growing on it. The mostcommon type of plant used in Nepal isPhragmites karka. The depth of media istypically 0.3-0.6 m. Wastewater is evenlydistributed on the bed and flows through iteither horizontally or vertically. As thewastewater flows through the bed of sandand reeds, it gets treated through naturalprocesses like mechanical filtering,chemical transformations and biologicalconsumption of pollutants in wastewater.As RBTS uses simple natural processes, itis effective yet inexpensive and simple tooperate.

As noted above, the RBTS can be of twotypes: vertical flow (VF), where thewastewater flows vertically from the top tothe bottom of the bed, and horizontal flow(HF), where the wastewater flows from one

end of the bed to another. VF beds are fedintermittently in a large batch flooding theentire surface. After a while the bed drainscompletely free, allowing air to refill the bed.This kind of feeding leads to good oxygentransfer and hence better removal ofpollutants. VF systems also require less landarea (1-2 m2/person) than HF systems, whichneed 5-10 m2/person for secondarytreatment. A typical VF system can removethe BOD5 of up to 96%; the HF system canremove only up to 65%. In recent years, acombination of the two (hybrid system) hasbecome popular due to the higher efficiencyof organic removal.

Constructed wetlands remove pollutants fromwastewater through various physical,chemical and biological mechanisms. Some ofthe main pollutant removal mechanisms inconstructed wetlands are presented in Table 1.

Wastewater constituents Removal mechanism

Suspended solids SedimentationFiltration

Soluble organics Aerobic microbial degradationAnaerobic microbial degradation

Phosphorous Matrix sorptionPlant uptake

Nitrogen Ammonification followed by microbial nitrificationDenitrificationPlant uptakeMatrix adsorptionAmmonia volatilisation (mostly in SF system)

Metals Adsorption and cation exchangeComplexationPrecipitationPlant uptakeMicrobial oxidation/reduction

Pathogens SedimentationFiltrationNatural die-offPredationUV irradiation (SF system)Excretion of antibiotics from roots of macrophytes

Source: Cooper et al., 1996

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In Nepal, the Environment and PublicHealth Organization (ENPHO) with technicalsupport from a Nepali Ph.D Scholar fromUniversity of Natural Resource and AppliedLife Sciences Vienna introduced CW forwastewater treatment in 1997 byconstructing the first plant at DhulikhelHospital (Shrestha, 1999). Since then, theinterest in this technology has beengrowing and more than a dozenconstructed wetlands have beenestablished for various applications suchas the treatment of hospital wastewater,grey water, septage, landfill leachate,institutional wastewater and municipalwastewater. The first constructed wetland

Constructed wetlands in Nepal

treatment plant in Dhulikhel was designedto treat 10 m3/day of wastewater but it issuccessfully treating more than four timesthat amount. (Shrestha et. al, 2000)

Satisfied with the performance of thetreatment plant, the hospital is nowexpanding the capacity of the plant.Recently, ENPHO with support from theAsian Development Bank (ADB), UN-HABITAT, WaterAid Nepal, Madhyapur ThimiMunicipality and the local people haveestablished the first community-basedwastewater treatment system in Nepalusing this technology. The UrbanEnvironment Improvement Project (UEIP)

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TABLE 2 CONSTRUCTED WETLANDS IN NEPAL

SN Location Type of TreatmentWastewater Capacity

1 Dhulikhel Hospital Hospital Designed for10 m3/daybut treating40 m3/day

2 Private house at Dallu Grey water 0.5 m3/day

3 Kathmandu Metropolitan City Septage 40 m3/day

4 Malpi International School Institutional 25 m3/day

5 Sushma Koirala Memorial Hospital 15 m3/dayPlastic & ReconstructiveSurgery Hospital

6 Kathmandu University Institutional 40 m3/day

7 Staff Quarter of Middle Domestic 26 m3/dayMarshyangdi Hydro ElectricPower Station

8 ENPHO Laboratory Domestic and 1 m3/daylaboratory

9 Kapan Monastery Institutional 17 m3/day

10 Septage and Landfill Septage and Septage:Leachate Treatment Plant landfill 75 m3 and

leachate Leachate:40 m3

11 Sunga Municipal 25 m3/day

Source: Shrestha and Shrestha, 2004

77

The experience with constructed wetlands overthe last decade has clearly shown that thissimple and cost effective system can be used totreat various types of wastewater ranging fromgrey water to leachate and septage. However, inspite of the enormous potential for the use ofCW for wastewater treatment, there are somechallenges in the promotion of this technologyin Nepal, which are as follows:

Due to the lack of awareness of CWtechnology, it is often difficult to convincepeople that it will workAlthough the cost of the technology isrelatively low, it is still difficult toconvince people to invest in a treatmentplant instead of just discharging effluentinto the river

Challenges

Although CW technology uses locallyavailable materials, in some placesspecified types of sand and gravel orreeds may not be readily availableThis is a low maintenance system, butpeople often think it is a nomaintenance system. This sometimesleads to carelessness in taking care ofsimple operation and maintenancerequirements such as checking forblockage in the pipes, harvesting theplants etc.Wastewater treatment is not a priorityfor city governments, privateindustrialists or institutions, due to thelack of strong legislation andstandards.

which is being implemented in eight urbancentres with the assistance ADB is now inthe process of constructing 18 more plantsin these towns. A list of operating CWs inNepal is given in Table 2. (Shrestha andShrestha, 2004)

In general, the performance of the CWshas been excellent. Regular monitoring ofthe systems shows high pollutant removalefficiency achieving close to 100%removal of total coliforms and organicpollutants. The pollutant removal rates insix different constructed wetlands areshown in Table 3.

TABLE 3 TREATMENT EFFICIENCY OF CONSTRUCTED WETLANDS IN NEPAL

Location TSS BOD5 COD NH4Removal Removal Removal RemovalRate (%) Rate (%) Rate (%) Rate (%)

Dhulikhel Hospital 98.6 98.9 83.7 57

Dallu House 98.6 99.5 96.8 97

Malpi School 99.1 99.5 99.5 98

SKM Hospital 98.1 99.2 95.4 98

Kathmandu University 97.9 98.9 99.1 99

ENPHO 92.1 99.7 97.8 91

Source: Shrestha et.al., 2003

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BOX 1 DHULIKHEL HOSPITAL ESTABLISHES THE FIRST CONSTRUCTED WETLAND IN NEPAL (SHRESTHA AND SHRESTHA, 2004)

In 1997, Dhulikhel Hospital, a community-based hospitallocated in Dhulikhel Municipality, set up the firstconstructed wetland wastewater treatment system inNepal to treat all the wastewater generated in thehospital and ensure that the people living around thehospital have access to clean treated water for irrigation.The system was designed by the Environment and PublicHealth Organisation (ENPHO) with technical support fromthe University of Natural Resources and Applied LifeScience (BOKU), in Austria. As this was the firstexperiment with constructed wetlands in Nepal, thesystem was designed using fairly conservativeassumptions and plenty of safety margin to ensure thatthe treated water would be of acceptable quality. As aresult, although the volume of wastewater has increasedmore than fourfold, the treatment system is stilloperating effectively today. The treatment system wasoriginally designed to treat 10 m3 of wastewater per day,but it is currently treating about 40 m3 per day as thecapacity of the hospital has increased significantly overthe past 10 years.

The constructed wetland at Dhulikhel Hospital has asedimentation tank of 10 m3 capacity for pre-treatmentfollowed by a horizontal flow bed then a vertical flow bed.The horizontal flow bed has a surface area of 140 m2 and isfilled with 0.6 m sand and gravel. Similarly, the verticalflow bed has an area of 120 m2 and is filled with 1.05 m ofsand and gravel. Both the beds are planted with local

reeds of the species Phragmitis Karka. Initial tests donein 1997 showed that the plant was able to remove 98% oftotal suspended solids (TSS), 98% of BOD5, 96% of CODand 99.9% of total coliforms. It also removed 80% of theammonia nitrogen and 54% of phosphate. Follow-upmonitoring in 2003 showed that the plant was stillremoving 96% of BOD5 and 93% of TSS and COD.

The Hospital as well as the local people are very satisfiedwith the performance of the treatment system and thesystem has become a showpiece for the Hospital. Manyresearchers, students, journalists and other peopleregularly visit the Hospital to see the constructed wetlandin action and learn from it. The Hospital is now in theprocess of expanding the system.

BOX 2 GREYWATER RECYCLING AT THE HOUSEHOLD LEVEL USING CONSTRUCTED WETLAND

Dr Roshan Raj Shrestha's family has a simple house builton about 135 m2 of land in Dallu, ward 15 of KathmanduMetropolitan City. At first glance, the house does not lookmuch different from the other houses in theneighbourhood. But it is very special because it is thefirst house in Nepal that treats and recycles its wastewater to reduce water consumption as well as waterpollution. In 1998, Dr Shrestha, who pioneered the use ofConstructed Wetlands in Nepal, demonstrated how thistechnology could be applied to treat grey water at thehousehold level, significantly reducing water demand andwater pollution in a cost effective manner. In a city wherethe water demand is more than twice the supply and thedischarge of untreated wastewater has significantlydeteriorated the local rivers, this system hasdemonstrated how each family can make a difference.

The system consists of a 0.5 m3 water tank that has beenconverted into a settlement tank followed by a feedingtank and a small vertical flow reed bed with an area of only6 m2. The system is good enough to treat all the greywater generated in the house with seven members and

Greywater recycling at theDhulikhel Hospital

Dr. Roshan Raj Shrestha

Greywater recycling at thehousehold level usingconstructed wetland (EcoHome at Chhauni, Kathmandu)

the treated water is used for non-consumptive uses suchas flushing, gardening and washing. Tests done on thetreated water showed that the system was able to remove97% of the TSS, 98% of the BOD5, 98% of ammonianitrogen and 99.9% of the total coliform. Dr Shrestha pointsout that the system required an investment of only aboutRs. 35,000 (US$500) and the family is able to save about400 litres of water per day.

Dr. Roshan Raj Shrestha

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BOX 3 COMMUNITY-BASED WASTEWATER MANAGEMENT

Located in Madhyapur Thimi Municipality, Sunga Toleis the owner of the first community-based wastewatertreatment plant in Nepal. Madhyapur Thimi is an oldNewar community in the Kathmandu Valley, which isbelieved to have been settled in the 7th century.Situated on elevated land area at an altitude of 1325 m,the municipality covers a total area of 11.47 sq km andhad a population of 47,751 in 2001. As the town wasdesignated as a municipality only in 1996, majorinfrastructure developments like the sewerage system,water supply and road network are all still in theplanning phase. Sanitation improvement is one of themost urgent issues the city needs to address, withmore than 50% of the population still lacking propersanitation facilities. Though a part of the municipalitywas connected to sewers in the 1990s and thewastewater was supposed to be treated throughoxidation ponds the work remained incomplete becauseof a lack of funds.

At the request of the Municipality, in 2005, ENPHO, withsupport from ADB, UN-HABITAT and WaterAid Nepal,initiated the construction of a community-basedwastewater treatment plant at Siddhikali, where therewas an outfall of a large sewer line and wasteland.However, after the construction began, a few people raisedobjections to the plant saying that it would pollute thelocal area. Even though a lot of effort was made to convincethe local people and they were taken on observation visitsto existing treatment plants, they refused to allow theconstruction to proceed. This meant that, although mostof the local people supported the project, the objectionsof a few led to the failure of the initiative in Siddhikali,thus demonstrating the need for extensive communitymobilisation.

Although disappointed by the initial setback, ENPHO andthe municipality were delighted when the people of Sungainvited them to build the treatment plant in theirneighbourhood instead. With the support of the localcommunity, a new system was soon designed and builton steep terrain, which was previously a waste dumpingsite next to a school at Sunga. Now the site has a beautifulgarden and a model treatment plant that provides alearning ground for students as well as professionals.

The constructed wetland at Sunga consists of a coarsescreen and a grit chamber for preliminary treatment, a 42m3 anaerobic baffle reactor (ABR) for primary treatment,horizontal flow followed by vertical flow reed beds forsecondary treatment and two sludge drying beds fortreating sludge. The total area of the constructed wetlandis 375 m2. The treatment plant has a capacity to treatwastewater from 200 households, but it is currently treatingwastewater from 80 households. The plant receives anaverage daily flow of 10 m3 of very high-strength wastewater(average BOD5 of raw wastewater is 1,775 mg/l). Monitoringof the performance of the system over its first year ofoperation shows that it removes organic pollutants highlyefficiently (up to 98% TSS, 97% BOD5 and 96% COD). Itwas also found that the ABR was very effective in removingorganic pollutants and could remove up to 74% TSS, 77%BOD5 and 77% COD (Singh et al., 2007).

The total cost of the treatment plant was Rs. 2.5 millionand the municipality has agreed to provide Rs. 50,000per year for operation and maintenance costs.

The total construction cost of the wetland amounted toNRs. 1,800,000 (US$ 26,000) at NRs. 2,900 (US$ 40) perm2 of the wetland. The average O&M cost of the wetland isabout NRs. 20,000 (US$ 290) per year.

Sunga, wastewater treatmentplant, Thimee

WaterAid/ Marco Betti

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BOX 4 TREATMENT OF LANDFILL LEACHATE AND SEPTAGE

Leachate from landfill sites and septage from septic tanksare known to have very high concentrations of pollutants.As more and more cities construct landfills to managetheir waste, there is a need to treat the leachate theygenerate. Often a simple pond is constructed at thebottom of the landfill to collect the leachate, which isthen either recirculated back into the landfill, as in thecase of the Sisdol Landfill in Kathmandu, treated or sentdirectly to the river. The experience from Sisdol showsthat recirculation has not been effective in treating thelandfill and direct discharge in the river can causesignificant pollution downstream.

Septic tanks have been widely promoted as a means ofon-site sanitation. In urban areas, many houses orinstitutions have septic tanks to partially treat thewastewater they generate. But these have to beperiodically cleaned, which generates large quantitiesof highly concentrated faecal sludge or septage. Severalmunicipalities and small private companies operateseptic tank cleaning services. However, in the absence oftreatment systems, the highly contaminated sludge issimply dumped in rivers, resulting in heavy pollution.

Pokhara Sub-Metropolitan City is a major tourist hub inwestern Nepal. The city is spread over an area of 55 sq.km. and had a population of 156,312 in 2001. In 2003,the Asian Development Bank supported PokharaEnvironmental Improvement Programme to build a

sanitary landfill site for the city as part of the SecondTourism Infrastructure Development Project. There was aneed for a simple and cost effective system for treatingthe leachate as well as the sludge produced by cleaningof septic tanks in the city. It was estimated that the citygenerated 12,000 m3 of faecal sludge and 15,600 m3 ofmunicipal waste every year, all of which would becollected and brought to the site. In response, a specialwetland was built at the site which consisted of sevensludge drying beds occupying a total area of 1645 m2,where the faecal sludge is initially treated. Each day,sludge is spread on a separate sludge drying bed,resulting in a weekly feeding cycle. The dry sludge isremoved and composed while the leachate from thesludge drying beds, as well as the leachate from thelandfill, is fed into a feeding tank and then to twocompartmental horizontal flow and four compartmentalvertical flow constructed wetlands. The plant is designedto treat 35 m3 of septage and 40 m3 of landfill leachateper day.

The treatment plant at Pokhara is the largest constructedwetland in Nepal and it was built at a cost of Rs. 6 million(US$ 85,700). The effectiveness of the treatment planthas not yet been monitored as it is still not fullyoperational. However, as experiences from other countrieshave shown that constructed wetlands can be used totreat faecal sludge, the treatment plant built in Pokharacan be a model for other cities if it is operated properly.

Wastewater treatment plant inPokhara Sub-Metropolitan city

ENPHO/ Dr.Roshan Raj Shrestha

Source: Shrestha R R, 2005

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The following steps should be taken to furtherpromote decentralised wastewatermanagement through constructed wetlands:

As this technology is still relatively new,there is need for continuous research anddevelopment to test the viability of thissystem under various conditions,including applicability for different typesof wastewater, effectiveness underdifferent climatic conditions, and the useof different materials and plants. Theperformance of existing constructedwetlands should be carefully monitoredand additional research is required tooptimise design and minimiseconstruction cost.Pilot projects should be conducted toexperiment with the use of thistechnology for industrial sites that

The way ahead produce wastewater with a high organiccontent, such as slaughterhouses, dairies,breweries and food processing industries.Although constructed wetlands are lowmaintenance systems people often thinkthey are no maintenance system, resulting inpoor performance due to simple problemssuch as clogging of pipes. Therefore, allsystems need to be regularly monitored andproper systems for operation andmaintenance should be established.Local governments, as well asinternational organisations involved in thewater and wastewater sector, shouldpromote this technology by building localcapacity and scaling up its application.Professionals and organisations involved inpromoting CW technology should be givenopportunities to conduct experiments,improve their skills, network with oneanother and disseminate their findings.

Constructed wetland at Kapan,Kathmandu

ENPHO/ Dr. Roshan Raj Shrestha

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