Feasibility Study of Constructed Wetland for Treatment of Municipal Wastewater
By Sandeep T. Tayade¹, Ajay R. Ojha², Rakesh Kumar³, and R. N. Singh 4
September 2005
Authors Designation
1, 2 = Project Fellow, National Environmental Engineering Research Institute (NEERI), Mumbai Zonal Laboratory
3 = Sr. Assistant Director, NEERI, Mumbai Zonal Laboratory
4 = Director, NEERI, Nehru Marg, Nagpur
The use of Constructed Wetlands to treat domestic wastewater is a rapidly emerging as a viable alternative in India. A pilot scale study was conducted to examine the feasibility of constructed wetland system for treatment of sewage at National Environmental Engineering Research Institute (NEERI), Mumbai. Treatment efficiency was evaluated for parameters such as BOD, N, P, TSS and Fecal Coliform. The results indicate high removal efficiencies particularly for BOD, TSS and FC. Wetland beds were prepared with locally available plants such as elephant grasses, cattails, etc and other similar species. Constructed wetland systems offer several potential advantages as a wastewater treatment process. These advantages include simple operation and maintenance, process stability under varying environmental conditions, lower construction and operating costs. The study deals with the performance of the constructed wetland for domestic wastewater and also the effectiveness of plant species.
Key words: Constructed wetland, biotechnology, elephant grasses, cattails
Introduction
The use of wetlands to treat effluent is not a new idea. Major interest has been developed in the concept of constructed wetlands for the treatment of point sources of pollution. Although wetlands in parts of the UK have been used for treating domestic wastewater since the Middle Ages, the catalyst for recent scientific studies has been the need to find low-cost, environmentally friendly techniques for wastewater (Gray and Biddlestone, 1995).
Constructed wetlands are artificial wastewater treatment system consisting of shallow (usually less than 1 m deep) ponds or channels, which have been planted with aquatic plants, and which rely upon natural microbial, biological, physical and chemical processes to treat wastewater. They typically have impervious clay or synthetic liners and engineered structures to control the flow direction, liquid detection time and water level. Depending on the type of system, they may or may not contain an inert porous media such as rock, gravel or sand (EPA/625/R-99/010, 2000).
Constructed wetlands are either free water surface (FWS) with shallow water depths or subsurface flow system (SFS) with water flowing laterally through the sand or gravel. Free water surface (FWS) typically consists of basin or channels, with some sort of surface barrier to prevent seepage, soil or another suitable medium to support the emergent vegetation and water at a relatively shallow depth flowing through the system. Figure 1 shows the type of constructed wetland.
The shallow water depth, low flow and presence of the plants stalks and litter regulate water flow and especially in long, narrow channels minimize short-circuiting. Subsurface flow system (SFS) is essentially horizontal trickling filters when they use rock media. In these systems, water level is below the ground, and flow through a sand or gravel bed (Luise Davis, 1994). Constructed wetlands are an effective and reliable water reclamation technology if they are properly designed, constructed, operated and maintained. They can remove most of pollutants associated with municipal and industrial wastewater and are usually designed to remove contaminants such as biochemical oxygen demand (BOD) and suspended solids (SS). Many of the treatment systems presently in operational conditions around the world have been designed to treat domestic wastewater and generally use the concepts originally reported by Professor R. Kickuth, who has had reed beds operating in Germany since from 1972 (Kickith, 1984; Cooper, 1990). These involved horizontal subsurface flow through an inert porous medium planted with suitable aquatic plants such asPhragmites australis.A two-year study of treatment system in Emmitsburg (Maryland) has consistently shows better than 70 % removal of BOD5 and 72% removal of suspended solids from domestic sewage wastewater at a loading rate of about 1600 m³/ ha-d corresponding to a retention time of about 4 - 6 days (EPA/625/1-88/022, 1988). Performance of wetlands system was found to be good even with limited plant coverage. The present study deals with the efficiency of constructed wetland setup in July 2001.
Materials and Methods
The pilot scale experiment is of subsurface flow system consisted of two experimental beds, 2 meter long, 1 meter wide and 0.30 meter deep. The sewage used in the experiment is the primary treated sewage collected from Lovegrove Pumping Station. An actual view of working constructed wetland with a media filtration is shown in Figure 2.
Constructed wetland is made of three component are:
- Inlet chamber; consists of crushed bricks and sand
- Treatment zone; consists of three layers viz., upper layer of crushed bricks; middle layer of sand and lower layer of stones
- Outlet zone; consists of three apertures
Plants species were collected from naturally occurring wetland region and transferred in the filled system and initially treated with tap water. Bed 1 is planted with Elephant grasses (Pennisetum purpureum) and Cattails (Typha latifolia) and bed 2 with Canny Lily (Canna indica) and Dwarf Palm (Cyperusspp). Theoretically, hydraulic loading rate and hydraulic retention time of the constructed wetland were 0.2614 m³/m²/day and 1.14 day respectively for both the beds.
Figure 2. Experimental Setup of Constructed Wetland - Bed 1 and Bed 2
The samples of influent and effluent were collected for a period of eight month, two samples a month and analyzed for parameters mention in Table 1.
| Parameters | Methods | Remarks |
| TSS (Total Suspended Solids) | SM 2540 D | Glass Fibre Filter Paper |
| Total Kjeldhal Nitrogen | SM 4500 NH3-E | |
| Phosphorus | SM 4500 P D | Spectrophotometer 108, Systronics |
| BOD (Biochemical Oxygen Demand | SM 5210 B | 3 Day BOD Test at 27oC |
| FC (Fecal Coliform) | SM 9215 D | Membrane Filter Method |
Results
The performance of both constructed wetland beds are mention in Table 2 and Table 3 respectively.
| Parameters | Ave. Concentration | Efficiency (%) | |
| Influent | Effluent | ||
| TSS (mg/l) | 144 | 25.00 | 83.00 |
| BOD (mg/l) | 152 | 23.00 | 85.00 |
| N (mg/l) | 24.0 | 9.40 | 60.00 |
| P (mg/l) | 2.80 | 1.50 | 46.00 |
| FC (colonies/100ml) | 4.5 x 107 | 1.7 x 106 | 96.00 |
| Parameters | Ave. Concentration | Efficiency (%) | |
| Influent | Effluent | ||
| TSS (mg/l) | 152 | 38.00 | 75.00 |
| BOD (mg/l) | 198 | 45.00 | 77.00 |
| N (mg/l) | 32.0 | 15.00 | 53.00 |
| P (mg/l) | 3.80 | 2.10 | 44.00 |
| FC (colonies/100ml) | 3.3 x 106 | 5.9 x 105 | 82.00 |
TSS concentrations were quite high in the influent wastewater and were dramatically reduced in the effluent water due to filtering action of both the constructed wetland. BOD removal of bed 1 is high as compare to bed 2 due to the microbial population and bacteria present on the root structure of the plant species. Similarly, nitrogen and phosphorus of bed 2 shows lower reduction as compare to the bed 1. FC shows the higher removal efficiency due to the plants species in bed 1. Over all, it is observed that the plants species (elephant grasses and cattails) present in bed 1 shows higher removal efficiency as compared to bed 2 (canny lily and draft palm). Hence, the plants of bed 1 are more effective for treatment of municipal wastewaters.
Conclusion
Constructed wetlands are an effective option for on-site wastewater treatment when properly designed, installed, and maintained. Sub surface flow constructed wetlands are found to be a viable tertiary treatment alternative for municipal wastewater. These systems are potentially good, low-cost, appropriate technology treatment for domestic wastewater in rural areas where land is inexpensive.
References
- Gray Kenneth Roy and Biddlestone Anthony Joseph; The university of Birmingham, „Engineered Reed Bed System For Wastewater Treatment” Trends of Biotechnology, 1995, pp 248-252.
- United States Environment Protection Agency; „Constructed Wetlands Treatment of Municipal Wastewater”, EPA/625/R-99/010, September 2000.
- Luise Davis; „A Handbook of constructed wetlands: A Guide to Creating Wetlands for Agricultural Wastewater, Domestic Wastewater, Coalmine Drainage and Stromwater in the Mid-Atlantic Region” Vol. 1 General Considerations, 1994.
- Cooper P.F; „European Design and Operating Guidelines for Reed Bed Treatment Systems” presented at conference on Use of Constructed Wetlands in Water Pollution Control, Cambridge, UK. 1990.
- Kickuth R; „Das Wurelraumverfahren in der Praxis”, 1984
- United States Environment Protection Agency; „Constructed Wetlands and Aquatic Plant Systems for Municipal Wastewater Treatment”, EPA/625/R-99/010, September 2000.
- APHA, „Standard Methods for the Examination of Water and Wastewater, 17thEdition, Washington D. C., 1989.
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