Rapid Gravity Sand Filters
The rapid gravity sand filter is a type of filter 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 flocs flows through the filter medium under gravity pressure and the flocculated material are trapped in the sand matrix. Rapid filters are usually built open with the water passing down the filter but by gravity. It has a filter rate of 4 – 8 m3/m2/hr. The tank is made of concrete with a depth of 3.0 to 3.5m. Coarse sand of size 0.4 to 1.5mm is used as the filter medium.
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