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Rapid sand filter
The rapid sand filter or rapid gravity filter is a type of filter used in the purification of water and is commonly used in municipal water treatment facilities.
Rapid sand filters use relatively coarse sand and other granular media to remove particles and impurities that have been trapped in a floc through the use of flocculation chemicals - typically salts of Aluminium or Iron. Water and flocculant flows through the filter medium under gravity or under pumped pressure and the flocculated material is trapped in the sand matrix.
Rapid sand filters must be cleaned frequently, often several times a day, by backwashing, which involves reversing the direction of the water. During backwashing, the bed is fluidized and care must be taken not to wash away the media.
The output from rapid sand filters requires further treatment before it is suitable for supply as drinking water (see Water purification). Unlike Slow sand filters, rapid sand filtration has very little effect on taste and smell unless activated carbon is included in the filter medium.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Rapid_sand_filter". A list of authors is available in Wikipedia.|