CONTENTS-
Abstract
Introduction
Material and Methods
Results and Discussion
Suitability of the Method
Conclusions
References

Stresses to lakes arise from easily identifiable point sources such as municipal and industrial wastewaters, non-point sources such as urban and agricultures runoff within a lake's watershed. Major degrading factors include excessive eutrophication due to nutrients and organic matter loading from domestic wastewater. Thus, it is necessary to take a step for management and restoration of lakes. Looking for a problem, a pilot scale study based on phyto-treatment concept was setup in National Environmental Engineering Research Institute (NEERI) laboratory, Mumbai. Treatment efficiency of subsurface phytophil system were evaluated for pollutant parameters such as total suspended solids (TSS), biochemical oxygen demand (BOD), nitrogen (N), phosphorus (P) and fecal coliform (FC). The results indicate high removal efficiencies particularly for BOD, TSS and FC. Wetland bed was prepared with locally available plants such as elephant grass and cattails. This technology offers several advantages such as simple operation, maintenance, economically and environmentally sound treatment of wastewater as well as for aquatic habitants.

Lakes and their surrounding watersheds are unique and valuable ecosystems for both people and nature. Lakes are critical "storage tanks" for freshwater.  More than 90% of all available   freshwater is contained in lakes and reservoirs (Shiklomanov, I. 1993). Lakes provide human beings with services that include water for irrigation, drinking, industry, and dilution of pollutants, hydroelectric power, transportation, recreation, fish, and aesthetic enjoyment (Postel, 1997). These services are impaired by exploitation of lakes and their catchment area   (Hasler, 1947). Because human effects on lakes are growing, concern increases that lake ecosystem services are in jeopardy (Naiman et al. 1995). These concerns parallel those for the sustainability of services from many ecosystems and the biosphere itself (Arrow et al., 1995).

Reservoirs are constructed for the purposes of flood control and power generation too. Accordingly, it is difficult to focus on a single issue when considering the long-term use and protection of these important and finite water resources .

The drainage basin is the logical management unit for lakes and reservoirs because the drainage basin is (i) the source of water, (ii) the place where it is used, and (iii) where human activities impact both water quantity and quality, Activities that generate pollutants (e.g., urbanisation, industrialisation, agricultural production) are similar in both lake and reservoir drainage basins, whether from point or non-point pollution sources. Point sources are ‘pipeline' discharges of pollutants to receiving waters, e.g. domestic sewage discharges or industrial waste effluents from factories or plants. They are relatively easy to identify and isolate. In contrast, non-point pollution results from storm runoff or snowmelt, which transports polluting materials diffusely and over land in urban and agricultural areas to rivers, lakes and reservoirs. Thus, non-point source pollution is closely tied to precipitation and runoff events, and less predictable and more variable in nature. Because of their diffuse nature, non-point pollutant sources are also more difficult to identify and deal with.

Of particular importance in addressing lake and reservoir problems is the need to consider an “ecosystem approach”. Here, rather than adopting the sectoral approach that focuses on a single water use, the ecosystem approach considers both human water needs within the larger context of the drainage basin and environmental water needs or ecological requirements. This approach, therefore, is a prudent means of balancing the water needs for economic development and environmental protection.

Water quality problems typically involve water pollution issues. Major water pollutants include a variety of organic and inorganic chemicals such as heavy metals and industrial compounds. They can affect human health and/or interfere with industrial or agricultural water use. If the level of a pollutant in the water supply exceeds an acceptable level for a given water use (e.g., domestic or industrial water supply), the water is considered unsafe or too degraded for that use. Solutions to lake and reservoir pollution problems, therefore, usually focus on reduction of pollution at the source and/or treatment of the polluted water prior to use.

Virtually all lake and reservoir water problems are related either to issues of (1) quantity – there is too little or too much water, or (2) quality – the water is too degraded (polluted) for drinking water supply, agricultural irrigation and/or industrial or other purposes. The problem of too little water results either from limited precipitation or excessive water usage. In contrast, the problem of too much water is typically manifested as floods. Solutions to these problems, therefore, usually involve developing larger water supplies or reducing current water uses, respectively.

Considering a problem of pollutants in lakes or reservoirs, a pilot scale study of phytophil system was developed in National Environmental Engineering Research Institute (NEERI), Mumbai Zonal Laboratory for treatment of wastewater reaching lakes or runoff water.

Phytophil Technology is one such technological solution, which can be easily implemented in nearby lakes and/ water bodies. The system is based on filterable wetland being utilised for a wide variety of applications throughout the world. This treatment system reflects phenomena observed in natural marshland settings. They act as filters for removal of organic matter (carbon, nitrogen and phosphorous), suspended solids, and pathogenic organisms.

The filterable wetland is sown with aquatic plants where wastewater flows in horizontal outflow zone. This zone is designed in such a manner that it mainly removes BOD and also phosphorous and oxidises nitrogen.

The technology can be utilised for municipalities, industries and even for municipal landfills (USEPA, 2000). The technology works on gravity, without a need for any chemical and major pumping. It provides greater flexibility with regard to loads and desired outputs.

The pilot scale study of phytophil system consisted of single bed whose dimensions are 2 m long, 1 m wide and 0.30 m deep. The municipal wastewater used in the experiment was primary treated sewage collected from Lovegrove pumping station. An actual view of working constructed wetland with a media filtration is shown in Fig1.

The treatment system has three components:

Plants species were collected from naturally occurring wetland region and transferred in the filled bed and initially treated with fresh water. Treatment bed was planted with elephant grasses ( Pennisetum purpureum ) and cattails ( Typha latifolia ). Hydraulic loading rate and hydraulic retention time of the treatment bed were 0.25 m 3 /m 2 /day and 2 day respectively.

The samples of influent and effluent were collected for a period of eight months, twice samples a month and analysed for parameters mentioned in Table 1.

SM- Standard methods(APHA, 1998)

The results of the study are presented in Table 2 .

Table 2 : Efficiency of the Treatment Bed

These are an average of 16 samples

Suspended Solids Removal

TSS concentrations were quite high in the influent wastewater and was   dramatically reduced in the effluent water due to filtering action of the treatment media present in the bed. Most of the suspended solids are removed through sedimentation and filtration, as vegetation obstructs the flow and reduces velocities. In most of the applications, a sedimentation pond is added upstream of the treatment bed to promote the removal of larger suspended particles and to minimise chances of clogging the bed. The pond can also dilute the raw influent if it is considered too strong. These processes remove a significant portion of the BOD, nutrients (mostly nitrogen and phosphorus) and pathogens. Ideally, however, wastewater reaching the bed should not have any floatables and grits, which are likely to clog the system quickly and reduce the HRT.

Biochemical Oxygen Demand Removal

BOD removal of bed is high in influent (152 mg/l) and reduces to 23 mg/l in treatment zone due to the microbial population and bacteria present on the root structure of the plant species. Wastewater is aerobically degraded by bacterial biofilm that is attached to the plants. In treatment bed, the aquatic plants supply oxygen to the wetland floor through their roots, thereby promoting the aerobic digestion of organic material. Some anaerobic degradation of organic material also occurs in the bottom sediments. Wetlands provide a diversified micro-environment, which plays an important role in pollutant processing. Various processes occur within the water column, on the plants, in the wetland substrate and in concentrated areas of microbial activity known as biofilms. Biofilms are formed as bacteria and microorganisms attach themselves to the plant roots and the substrate matrix to form a biological filter from the water surface to the wetland floor. As wastewater passes through the thick growth of plants, it is exposed to this living biofilm, which provides a treatment process similar to that found in conventional sewage treatment plants.

Nitrogen And Phosphorous Removal

Similarly, nitrogen and phosphorus of bed shows lower reduction as compared to TSS and BOD. Treatment systems promote the process of nitrification / denitrification, which removes nitrogen from the wastewater. In simple terms, bacteria in the wastewater   (Nitrosomonas) oxidises ammonia to nitrite in an aerobic reaction. The nitrite is then oxidised aerobically by another bacteria (Nitrobacter) forming nitrate. De-nitrification occurs as nitrate is reduced to gaseous forms under anaerobic conditions in the litter layer of the wetland substrate. This reaction is catalysed by the denitrifying bacteria Pseudomonas spp. and other bacteria. Wetland plants play an important role in nitrogen removal by providing biofilm attachment points and by supplying oxygen for nitrification in the root zone. Phosphorous removal in wetlands is based mainly on the phosphorous cycle and can involve a number of processes such as adsorption, filtration, sedimentation, complexation/precipitation and assimilation/uptake. Nutrients reaching lakes during rains, if made to pass through the phytophil system, can be removed to a large extent.

Pathogens Removal

Pathogens of concern in aquatic treatment systems are parasites, bacteria and viruses. Because it is impractical to monitor all pathogens, indicator organisms such as fecal coliform (E. Coli) are used to measure the removal efficiency of a treatment system. These indicators are used because they are easy to monitor.

Fecal Coliform shows   higher removal efficiency compared to other pollutant parameters. Coliform removal is achieved through a combination of natural die-off, temperature, sunlight (ultraviolet light), water chemistry, predatation and sedimentation. Despite the presence of water, a wetland is a hostile place for pathogens. A proportion of bacteria are removed by sedimentation, especially those attached to particles. Biofilm filtering removes some of the pathogens by direct contact. Predation occurs as the wetland provides a habitat for a variety of microorganisms, some of which are pathogen predators such as zooplankton. The shallow water columns found in wetlands allow the penetration of ultra-violet light from sunlight, which also destroys pathogens.

Phytophil Technology can be implemented with a pond or other treatment system, which can remove grit or large floating material, setup nearby lakes or water bodies. Advantages of this system include flood protection and flow control, water quality improvement, landscape and recreational amenity and provision of wildlife habitat. Phytophil wetland planning should not overlook the need for long-term maintenance. Additional vegetation planting may be required to speed plant coverage, replace damaged plants or to try more suitable varieties. Perimeter fencing may be required. Maintenance may be needed to control the spread of undesired plant species. Inlets and outlets can become blocked with debris, which will require periodic removal. Inlet and outlet structures should be inspected weekly. Most importantly, if the wetland functions well as a sediment and nutrient trap, it may eventually require dredging to remove accumulated materials. Thus, vehicular access to the site must be provided for maintenance and possibly dredging equipment. Before implementation, it is necessary to monitor the pollutant load and fluctuation of wastewater flow to decide the area for treatment zone. Figure 2 depicts the different element of phytophil treatment for lakes or water bodies.

These elements are :

•  Inlet zone/pond – to trap sand, to silt-sized particles and improve water quality. This module can have some secondary benefits, including landscape aesthetics and flow attenuation.

•  Phytophil treatment system an area of plants such as rushes, reeds and sedges – to improve water quality through the trapping of fine particles and soluble pollutants. This module can have some secondary benefits, including wildlife habitat and flow attenuation.

•  Lake/island – to provide passive recreation, landscape enhancement and wildlife habitat. Depending on the outlet structure, lakes can significantly attenuate flow. Lakes can also provide water quality benefits, but this function can be compromised if the lake attracts large populations of wildlife, which can degrade water quality.

•  Flood retarding basin – to protect downstream areas from flooding and to control stream hydrology. This module can provide more open space within the urban landscape. Treatment modules located in flood retarding basins can benefit from the extra hydrologic control provided by the basin.

•  High flow by pass – pipeline or channel should be made for high flow during rainy season.

Phytophil tecnology is an effective option for on-site wastewater treatment when properly designed, installed, and maintained. This treatment system can be a viable secondary as well as tertiary treatment alternative for municipal wastewater.   These systems are potentially good, low-cost and appropriate technology for domestic wastewater treatment in areas where land is inexpensive.

APHA, (1998) “Standard Methods for the Examination of Water and Wastewater, 20 th Edition, Washington D. C.

Arrow, K., B. Bolin, R. Costanza, P. Dasgupta, C. Folke, C.S. Holling, B. Jansson, S. Levin, K. Maler, C. Perrings, and D. Pimentel. (1995). Economic growth, carrying capacity, and the environment. Science 268: 520-521.

Hasler, A.D. (1947). Eutrophication of lakes by domestic drainage. Ecology 28: 383-395.

Igor Shiklomanov, (1993) "World Fresh Water Resources," in Water in Crisis: A Guide to the World's Fresh Water Resources, Peter H. Gleick, ed. Oxford University Press, New York, , Table 2.8, p. 20. .

Naiman, R.J., J.J. Magnuson, D.M. McKnight, and J.A. Stanford. (1995). The freshwater imperative. Island Press, Washington, D.C., USA.

Postel, D.M., S.R. Carpenter, D.L. Christensen, K.L. Cottingham, J.R. Hodgson, J.F. Kitchell, and D.E. Schindler. (1997). Seasonal effects of variable recruitment of a dominant piscivore on food web structure. Limnology and Oceanography, in press.

United States Environment Protection Agency (USEPA);(2000). “Constructed Wetlands and Aquatic Plant Systems for Municipal Wastewater Treatment”, EPA/625/R-99/010.

* National Environmental Engineering Research Institute (NEERI),
Mumbai Zonal Laboratory, 89/B, Dr. A. B. Road,
Worli. Mumbai-400 018. India.

** National Environmental Engineering Research Institute (NEERI),
Nehru Marg, Nagpur-440 020. India.

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