Sand Filter

Sand filters are used world over for water treatment. These filters are used in various industries for cleaning water. In sewage units, sand filters are used as a final polishing stage. In sand filters the residual suspended materials and bacteria are trapped by the sand. The sand filter also provides physical matrix for bacterial decomposition of nitrogenous material like ammonia and nitrates, into nitrogen gas. For different application there are different types of sand filters. Usually there are three types of sand filters used:

• Rapid (gravity) sand filters
• Upflow sand filters
• Slow sand filters

Rapid sand filters and upflow sand filters uses flocculant chemicals to work effectively, whereas, in slow sand filters pathogens can be removed efficiently with improved taste and odor. In this filter no chemical is required for disinfecting or purifying the water.

In sand filters activated carbon is used for removing bad taste and odor. After some period, sand filters become clogged with floc. To deal with this the filter is backwashed or pressure washed for removing the floc. The backwash is passed into the settling tank in which floc gets settled which is later disposed of as waste material. The supernatant water is again return to the treatment process or they are discharged as waste stream.

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