Constructed Wetlands in Nepal: Chronicle, Continuance and Challenges Roshan R. Shrestha and Prajwal Shrestha Environment and Public Health Organization (ENPHO), P.O.Box – 4102, Kathmandu Nepal. (Email:
[email protected])
ABSTRACT Constructed Wetland (CW) for treatment of wastewater was introduced in Nepal on 1997 from a hospital. Now, there are 12 sub-surface flow constructed wetland system in operation for treatment of gray water, wastewater and fecal sludge. Recently, government has decided to install CW system at 8 small towns for treatment of municipal wastewater. On the basis of past six year experience on CW, ENPHO found high pollutant removal efficiency as more than 95 percent of major pollutants such as suspended solids, organic pollutants, ammonia-nitrogen. At three sites, the treated wastewater is being reused for toilet flushing, irrigation and cleaning vehicles. This paper analyses the pros and cons of CWs in Nepal for the treatment and reuse of wastewater from various sources and recommends measured to expand the use of this technology in Nepal for water conservation and protection of water bodies in a sustainable manner. KEY WORDS: appropriate technology, constructed wetland, reuse, wastewater treatment
INTRODUCTION Problems associated with the lack of clean drinking water and polluted water bodies are common to many cities in developing countries. During the recently concluded World Summit on Sustainable Development in Johannesburg, commitments were made to halve the proportion of people without the access to sanitation and safe drinking water by 2015 and several countries and organizations announced millions of dollars in investment for water and sanitation projects (UNEP, 2003). Although these commitments from the global community are indeed welcome, money alone will not solve the problem. There are many examples where money has gone down the drain and expensive treatment plants remain unutilized. What is needed is investment in appropriate technologies, which are simple, inexpensive and effective. CONSTRUCTED WETLANDS IN NEPAL Environment and Public Health Organization (ENPHO), a national non-governmental organization, has introduced constructed wetland (CW) technology as a low cost and effective option for wastewater treatment and recycling in Nepal. In 1997, the first CW was built at the Dhulikhel Hospital under design and technical supervision of a Ph.D. Scholar (one of the authors of this paper) from University of Agricultural Sciences (BOKU), Vienna, Austria. Following the successful demonstration of CW technology in
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Dhulikhel Hospital, this technology has been replicated at several places (Shrestha et al, 2000 and Shrestha et al., 2003). Now, there are 12 sub-surface flow constructed wetland systems in operation for treatment of greywater, wastewater and fecal sludge (Table 1). Table 1 : List of Constructed Wetlands in Nepal SN 1 2 3 4 5 6 7
Place Dhulikhel Hospital Private house, Kathmandu Kathamndu Metropolitan City Malpi-International School SKM P.R.S. Hospital Kathmandu University Staff Quarter of M. Marsyangdi Hydro Electric Power
Date of Operation
Q m3/d
July, 1997
40
April, 1998 August, 1998 August, 2000
0.5
Dec. 2000
15
2001
40
40 25
CW configuration HFB followed by VFB VFB SDB followed by VFB HFB followed by VFB HFB followed by VFB HFB followed by VFB
Size of the CW S. Tank - 10 m3, HFB - 140 m2, VFB - 121 m2 S. Tank - 0.5 m3, VFB- 6 m2 S. Tank - 40 m3, SDB - 225 m2, VFB - 362 m2 S. Tank - 25 m3, HFB - 136 m2, VFB - 231 m2 S. Tank - 10 m3, HFB - 72 m2, VFB - 69 m2 S. Tank - 40 m m3, HFB 290 m2, VFB - 338 m2
S. Tank - 13 m3, HFB - 148 m2, VFB - 150 m2 8 S. Tank - 500 liters & VFB ENPHO Laboratory Aug, 2002 1.5 VFB 18 m2 9 HFB followed S. Tank 7 m3 HFB - 50 m2 by VFB and VFB - 150 m2 m2 Kapan Monastery July, 2003 17 10 Septage and Not started HFB - 1180 m2, VFB - 1500 Landfill leachate in full SDB followed m2 and 7 SDB each of 235 treatment, Pokhara operation 115 by HFB & VFB m2 11 Private house, S. Tank - 0.5 m3, VFB - 6 0.5 Kathmandu Aug, 2002 VFB m2 12 Shuvatara School May, 2004 VFB S. Tank 4 m3 - VFB – 95 m2 HFB – Horizontal Flow Bed; VFB- Vertical Flow Bed; S. Tank : Settlement Tank; SDB – Sludge Drying Bed April, 2002
26
HFB followed by VFB
Photo : CW of Dhulikhel Hospital and Fecal Sludge and Landfill Leachate in Pokhara
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Treatment Efficiency of CW in Nepal On the basis of past six years experience in Nepal, pollutant removal efficiency of CW found quite high (Table 2). For example, effluent quality in terms of BOD and COD level in all CWs were obtained within permissible limit specified by European Norms (Önorm, 1995) irrespective of the area occupied by CW. However, poor performance in removal of ammonia was observed due to high hydraulic loading like in Dhulikhel Hospital (CW 1) and ENPHO laboratory (CW 6). Initially ammonia removal was as good as other CWs in CW 1 when hydraulic loading was 15 to 20 m3, it reduces with increase in hydraulic loading (Figure 1). Table 2 : Efficiency of CWs (ENPHO, 2004) 1 1997 40 261 380 24.7 93.5 349 14 95.9 680 49.5 92.7 52
Date of Operation Q m3/d Size of the Bed (m2) Before Treatment TSS (mg/L) After Treatment TSS (mg/L) TSS Removal (%) BOD Before Treatment (mg/L) BOD After Treatment (mg/L) BOD Removal (%) COD Before Treatment (mg/L) COD After Treatment (mg/L) COD Removal (%) N-NH3 Before Treatment (mg/L)
2 1998 0.5 6 357 4.6 98.0 311 4 98.0 564 25 94.0 20
Constructed Wetlands 3 4 5 2000 2000 2001 20 15 20 376 141 587 232 400 208 6.5 8 26.7 97.2 97.0 87.2 340 322 304 1.3 9 6 99.6 98.0 97.9 480 938 580 14.5 62 38.5 97.0 94.0 93.4 30 61 70
6 2002 1.5 18 141 12.5 87.0 426 17 95.0 682 78 88.0 116
7 2003 10 150 356 2 99.4 525 2 99.7 1032 19 98.1 88
N-NH3 After Treatment (mg/L) 17 1.0 0.9 1.8 0.3 70 3.9 N-NH3 Removal (%) 68 91 97 96 99.6 40 96 1 : Dhulikhel Hospital; 2 : Single house grey water; 3: Malpi School; 4: SKM Hospital; 5: Kathmandu University; 6: ENPHO laboratory; 7 : Kapan Monastry
Figure 1 : Efficiency of Dhulikhel Hospital CW (CW- 1) Pollution removal rate of Dulikhel Hospital CW (1997-2003) 45
100
30 60
m3/day
removal (%)
80
40 15 20
0
0 1997
1998 TSS
1999 NH3-N
2000 BOD5
2001 COD
2002
2003
Q (m3/day)
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. RECOGNITION OF CW AND NEW SYSTEMS UNDER CONSTRUCTION Past seven years experience on CW in Nepal made able to recognize this technology as one of the options for treatment of wastewater in Nepal. It is well reflected in Draft National Hygiene & Sanitation Policy 2004 which stressed for promotion of this technology in small towns and communities (MPPW, 2004). Similarly, this technology became an integral component of Urban Environment Improvement Program. This program is intending to improve environment of eight small towns of the country implementing under the loan of Asian Development Bank (ADB). In addition, ADB has recently approved a demonstration project to build a community scale CW at Thimi municipality for the treatment of municipal wastewater and ENPHO has designed several CWs for treatment of wastewater from a hospital, two communities and one pharmaceutical. MAJOR CHALLENGES Country has still lack of strong legislation to control discharge of municipal wastewater, therefore wastewater treatment facilities are still not prioritized by the government and concerned agencies. Land requirement, initial capital investment and difficult in availability of proper filter media in some places make difficult to convince that it is a low cost technology. This is a low maintenance system, but people often think it is a no maintenance system. Therefore, sometimes there is carelessness in taking care of simple operation and maintenance requirements such as security, checking for blockage in the pipes, and harvesting the plants. There is a lack of comprehensive scientific investigation on operational CW for future replication with cost effective design. REFERENCES
ENPHO, 2004. Constructed Wetlands in Nepal. ENPHO Magazine, World Water Day Issue. MPPW, 2004. National Hygiene and Sanitation Policy 2004 (Draft). Ministry of Physical Planning & Works. HMG Shrestha, R.R., Harberl R., Laber, J, Manandhar R., and Mader J, 2000 Application of Constructed Wetlands for Wastewater Treatment in Nepal, Wat. Sci. Tech. Vol 44 (11-12), 375-380. Shrestha R. R., Tuladhar B and Shrestha P. (2003). Experience With Application of Constructed Wetlands for Wastewater Treatment and Reuse in Nepal. ENPHO Magazine 2003, pp. 40 to 47. Önorm, 1995, ÖN B 2505 Bepflanzte Bodenfilter (Pflanzenklaranglagen) – Anwendung, Bemessung, Bau und Betrieb, Abfallwritschaft. Jhg. 47, H11/12, 300-309. UNEP, 2003, World Environment Day – WED 2003 Website.
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