Improved Rapid Sand Filter for Performance Enhancement

Filtration is process in which water is purified by passing through sand media. In India rapid sand filters are used conventionally for filtration. Sand media having characteristics as effective size (E. S.0.35-0.60mm), uniformity coefficient (U. C. - 1.3-1.7), specific gravity- 2.67, limiting head loss- 1.8-3.0m, depth of sand- 60cm, depth of gravel support-40 cm, etc. The advantages of rapid sand filter are easy operation, less space requirement, more filtration rate, more output and easy backwashing. Along with some advantages there are some drawbacks in rapid sand filter. Due to improper backwashing mud ball formation is a major problem shown in filter media. At the time of backwashing process stratification of sand media takes place. Sand grains having small size come at top layer. It reduces porosity at top layer which results in maximum removal at top layer. Thereforeheadloss increases in shorter run time which affects filtration process. To overcome these problems researchers have tried for capping of rapid sand filter. Capping is process in which upper sand bed layer of few cm is replaced with capping material. Some materials suitable for capping are anthracite coal, PVC granules, Polypropylene bids, and bituminous coal etc. In the present work conventional rapid sand filter and capped rapid sand filter are compared.