Filtration is the most common application in any water treatment facility or requirement. Filtration is primarily done to remove the foreign matter, suspended particles, odour etc.
Most water treatment plants like softener, RO, DM or ETP will use some of the filtration mechanisms in up stream or down stream depending on the requirement.
The filtration units are designed on Turbidity in raw water. Turbidity is a measure of presence of suspended matter. The surface waters like river etc. have high turbidity levels as compared to borewell waters.
If the turbidity levels are high ( Say more than 500 NTU ), then one must employ coagulation, sedimentation, clarification process before using filtration.
Different types of filters & their brief process, advantages are given below

Sand Filter

The sand filter comprises of multiple layers of sand put above one another in a pressure vessel. The coarse layer ( Pebbles ) are at the bottom & fine layer ( 16/32 fine sand ) is put on the top. The filtration happens in the top layer. The dirt gets accumulated in the filter bed & gradually pressure drop starts increasing in the bed.
The filters are backwashed in the reverse direction ( Upflow ) to remove the dirt accumulated on the top. This dirt is taken out of the filter through drain pipes.

Models : D – 300 to D – 2400 ( For flow rates upto 60 m3/hr )

Activated Carbon Filter

Activated carbon is one of the most widely used media for adsorption of impurities. It is used for de-chlorination, removal of organics and removal of odour. The supporting media ( Pebbles ) are put at the bottom & Carbon of specified grade is put as top layer.
The carbon filters also need backwash to loosen the bed similar to sand filters.

Model : C – 300 to C – 2400 ( For flow rates upto 60 m3 / hr )