REVERSE BANK FILTRATION FOR CLEANING WATER IN A REMOTE VILLAGE IN SOUTH INDIA

This study sought to remove E.coli and Total Coliform bacteria contamination from the village water supply in Nersa, Karnataka, India by using a reverse bank filter (BF). Reverse bank filtration uses natural processes to clean water, including filtration through layers of sand and gravel and a bioactive layer, known as collimation layer or Schmutzdecke, that forms on top of the filter. The origin of the village water supply is a mountain spring. After initial testing of water quality in the village and an exploration of alluvial deposits suitable for filter construction, two pilot filters were constructed in 300 L plastic tanks. The hydraulic properties of these experimental filters were tested by conducting a conservative tracer test and the using the method of moments to determine filter properties, such as pore volume and residence time. Additionally, the filters ability to remove bacteria and the benefit of adding granular activated carbon (GAC) were evaluated. The test results indicate that local alluvial deposits are suitable for filter construction and that bacteria removal is not improved by the addition of this type of GAC. A full-scale filter system was then constructed including a flow regulating tank, gravel ascending flow pre-filter, and BF filter (5 m by 7 m by 2 m). Although limited data exists, this system successfully reduced turbidity and E.coli. Replication of a BF filter technology in the larger study area requires locating other spring fed rivers. Precipitation and air temperature data combined with normalized distribution vegetation index (NDVI) was used in an exploratory analysis of spring locations in the context of a digital elevation model. This study showed that reverse bank filtration can be part of a clean and affordable water supply system for rural villages in mountainous terrain in India