Sand Filters

Sand filters are composed of layers of different grades of sand.

Sand filters are composed of layers of different grades of sand. When flocculated water is passed through a sand filter, the floc and other solids are precipitated out. Bacteria are also strained out. Sand filters may also contain a layer of carbon to filter out unpleasant tastes and odors. When sand filters become clogged with floc and organic material, they are backwashed or pressure washed. Backwashed water is run into settling tanks and disposed of as waste. In some countries, this wastewater may be used as a soil conditioner. Inadequate maintenance of sand filters has been the cause of occasional drinking water contamination. The American Water Works Association (AWWA) is a good source of information on sand filters.

A type of sand filter is sometimes used for the treatment of sewage. As the sand filter traps suspended particles, bacteria living in the sand assist in decomposing ammonia and nitrates into nitrogen gas.

Types of Sand Filters

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