Abstract
For collection of rainwater for potable purposes, a vertical flow multimedia roof water filter was developed and tested for hydraulic efficiency and pollutant removal efficiency to meet drinking water standards. Along with sand and gravel, three forms of charcoals, which act as adsorbents, viz, (coconut) shell charcoal, wood charcoal and anthracite were tested as filter media. Along with these, three types of circular shaped screens made up of nylon, aluminium and non-woven coir-sisal fabric were also tested. Four different filling volume ratios, viz., 1:1:1, 3:2:1, 2:1:3 and 1:3:2 were employed. The quality of the inlet water was studies by collecting and analysing roof water samples from two sites each in Tamil Nadu and Kerala. The multimedia vertical filters were found to be effective in removing TS, K and PO4 2, normalizing pH and reducing EC. It also showed good efficiency in removing nitrate. However, the removal percentage of Fe 2+ , Na + and Ca 2+ were low, while that of Mg 2+ showed –ve value. To compare different filter combinations, a new parameter, UPI (Universal Performance Index), which represents the weighted average of the hydraulic efficiency and quality improving efficiencies, giving extra weight to the latter, has been developed. Statistical analysis of UPI values for roof water filters showed that the proportion P3 (1:2:3), media M3 (anthracite) and screen S2 (aluminium mesh) were found to be the best. P1M3S2 (gravel-anthracite-sand in 1:1:1 proportion separated by aluminium meshes) emerged the best filter combination. The economic analysis of the developed filter system showed acceptable values for financial viability criteria including the Net Present Value, Internal Rate of Return and Benefit-Cost Ratio.
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