Study of Impact of Filter Media Configuration on Clogging in Storm Water Harvester

Abstract

Due to rapid urbanization, there is a change in hydrology of the area. Urban storm water is a source of pollution for receiving waters. Various pollutants in urban waters include suspended solids,nutrients such as phosphorous and nitrogen, oil and surfactants, metals such as (cadmium, chromium, copper, nickel, iron, lead, manganese, sodium and zinc,) organic matter and micro organisms. Studies suggest that majority of these pollutants are associated with TSS. These pollutants have aimplication on receiving waters. Urban watersheds are different. Whereas demand for water is more, at the same time there is reduced infiltration due to impermeable surfaces. There is rapid and huge withdrawal of water to cater to the domestic needs which is approximately 130 lpcd.  This rapid withdrawal coupled with reduced infiltration is responsible for declining water table. In the last two decades water has declined at the rate of 50 to 100 cms per year in the states of Haryana and Punjab. Rice is also sown in adjoining areas which needs huge amount of water for irrigation needs. It needs 150cm of water majority of which is  met by pumping out ground water. So there is a need to harvest storm water.  There are two types of WSUD technologies to harvest storm water, filtration based  andnon filtration based(Department of swan and river trust,2007). The objective of these strategies is to check storm water flows and pollutants by retarding, reducing, removing, or preventing urban stormwater runoff quantity and pollutants from reaching receiving waters (Strecker et al., 2001). Filtration based technologies are considered to be superior to non filtration based technologies (Fletcher et al., 2004).. But clogging is alimitation of these filtration based technologies. Storm water harvesters although effective in removing TSS face a problem of maintenance and longevity issues (Warnaaretal,1999). Clogging has also been observed in Laboratory based studies for stormwater treatment using soil based filter media Hatt et al. (2008) and gravel stormwater filters (Siriwardene et al., 2007) .Clogging is defined as reduction in hydraulic conductivity due to physical, chemical or biological processes. Clogging develops due to deposition of sediments in pores of filter media. (Lindse et al,1992 ) found that 37 percent of 207 storm water harvesters clogged in first two years of operation.

(Barret and taylor ,2004)have also reported of numerous infiltration system failures due to clogging.Main advantage of these infiltration systems is that they can be engineered for site-specific requirements, such as with regard to the aims of treatment, water quality standardsat  end-use, site specific pollutant characteristics and available space.  There are three types of clogging: Physical, chemical and biological.however physical clogging has been found to be more predominant and chief cause of clogging (Siriwardene,2008).It is concluded that physical clogging is a limitation in storm water harvesters and need to be studied in detail. The study has been done in laboratory  to mimics  storm water harvesting  by passing synthetic storm water to predict clogging. Study has been done to predict the time period of clogging and to suggest measures to enhance the clogging period.