Sand filter

Encyclopedia : S : SA : SAN : Sand filter

A sand filter is a basic tool of water purification. Passing flocculated water through a sand filter strains out the floc and the particles trapped within it. The medium of the filter is sand of varying grades. As water flows through the sand, impurities such as solids, precipitates, turbidity and in some cases even bacterial particles are filtered out. Where taste and odour may be a problem (organo-leptic impacts), the sand filter may include a layer of activated carbon to remove the taste and odour. Sand filters become clogged with floc after a period in use and they are then backwashed or pressure washed to remove the floc. This backwash water is run into special settling tanks so that the floc can precipitate out and is then disposed of as waste material. In some countries this may be used as a soil conditioner. Inadequate filter maintenance has been the cause of occasional drinking water contamination. A good source of information is the American Water Works Association (AWWA).

A different type of sand filter is sometimes used for sewage treatment as well. The sand traps suspended material and bacteria living in the sand decompose ammonia and nitrates into nitrogen gas.

From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.