Q. What is Rapid Sand Filter?
A Rapid Sand Filter is a water treatment plant that includes provision for pre treating the water by coagulation and sedimentation for settlement of suspended solids before filtration with sterilization in the final process.
Rapid Sand Filter consists of layers of course sand with an effective size of 0.35 to 0.50 mm is used. The depth of sand layer is 0.60 to 0.75m. This sand is supported on a gravel layer of depth 0.45m in 5 to 6 layers. The effective size of gravel is 2 to 50 mm. Gravel is under by an under drainage system consisting CI central manifold with strainers & lateral.
Plan area of these tank s is 10 to 80 m2 or 6 x 8 m or 8 x 10 m. Rate of filtration of these filter is 3000 to 6000 Lit. /hrs/ m2. The cleaning of Rapid Sand Filter is effected by reversal flow. First air is passed at the rate of 600 - 900 lpm/ m2 at the pressure of 0.35 kg/cm2 for 5 minutes in the reverse direction. After this water is passed which removes the dirt by bubbling action. Water required for back wash 300 to 900 Lit. / hrs/ m2. Cleaning must be done after every 1 to 3 days.