A multimedia filter is used to reduce the level of suspended solids (turbidity) in process water. Suspended solids can consist of small particles such as silt, clay, grit, organic matter, algae and other microorganisms. The filtration degree of a multi-media filter depends heavily on the selection of the filtration media and flow (velocity) through the filter.
A typical multimedia filter setup contains three layers of filling. Those are anthracite, sand and gravel.
The anthracite traps the courser dirt particles to prevent the formation of a layer cake on top of the filter bed.
The smaller particles get trapped in the sand layer. With a low fluid velocity, particle will adhere to the sand with a cohesive bonding.
The gravel allows the water to flow evenly to the bottom diffusors and out of the filter media.
This filter package allows the entire filter bed to function longer between backwashes. A well operated filter removes particles down to 15-20 microns. With use of a coagulant addition it can filter particles down to 5-10 microns.
Multimedia filters is designed in vertical or horizontal shape depending on filter capacity, with manual or automatic valves used in operation and backwashing the filter.
Automatic filter backwashing can be done via a differential pressure switch and control system.
