An improvement over the single media filters is multi-media filters. The improved filter bed action based on innovative use and selection of filter media has lead to this improvement. Compared to the conventional sand filter multi-media filter allows delivery of high quality filtered water at a much faster rate.
The conventional sand filter consists of lighter and finer sand particles at the top of the filter bed, while the heavier and coarser sand particles remain at the bottom after backwashing. The top few inches of the filter bed is the place where the filtration takes place.
The multi-media filter is radically different from the sand filter. The multi-media filter bed is upside down compared to the sand filter bed. Coarser but lighter particles remain at the top while the finer and heavier particles remain at the bottom of the bed. Selection of a suitable media leads to the innovative design. There are many advantages offered by the configuration. In this method the entire bed acts as a filter, rather than the top few inches. The complete bed traps turbidity and hence the filter can hold far more solids filtered from the water before backwashing is required.
The filter bed consists of three layers of filter media. The total bed depth is generally 26 to 40 inches. In a three layer filter, the large, lighter weight particles of anthracite coal form the topmost layer. The middle layer is made up of heavier and smaller particles of calcined aluminum silicate or sand. The bottom layer is made up of heavier garnet.
In small communities of
Kerala flats this filter is used to cleanse the water for drinking purposes. In spite of the heavy rainfall in Kerala, it is important that everybody saves water and utilizes it judiciously.
