Gravity granular media filtration is also known as "Rapid gravity" filtration due to their high filtration rates. The major advantage of gravity filters against pressure filters is that they are always open to inspection and hence remedial measures. The general configuration of filter bed is Silica sand and Anthracite coal supported by graded gravel/pebble media. Normally the filter boxes are constructed in concrete. Clarification units normally precede filters. Filters act as polishing units to achieve effluent turbidity less than 1 NTU. However when the influent turbidity is low, direct filtration units are also practiced.

The duel media filters work on the principal of "in depth" penetration against "surface filtration" phenomenon of rapid sand filters. Our founders had patented crushed coconut shell media as an alternative to coal media in duel media filters. The filtration rate of duel media filters is two to three times that of single media filtration. The terminal headloss (pressure drop) in filter beds is 2.0m to 2.5m. The service cycle is from 24 hr to 72hr.The exhausted filter beds are cleaned by using "hard (water) wash" and "air scour".

We have specialization of controlling the rate of filtration by non-mechanical hydraulic means. We design the filter operation based on "Influent flow splitting system" or "Variable declining rate arrangement". Both the system eliminates the maintenance prone "Rate of flow controllers". The battery of filter beds can be operated manually or else can be fully automated. We have a vast experience in application of granular media filters. We have designed more than 200 filter beds which are operating satisfactorily.