A variety of media types and membrane filters is available today, each suited to specific waste streams. Media filters Media filters can be used to remove residual suspended solids and free oil. When operated properly and with appropriate pretreatment, media filters should deliver long run times, efficient backwashing without media loss and consistent high-quality effluent. Flow through the filter can be under pressure or by gravity. Current technologies include sand filters, clustered filters, automatic valveless gravity filters, multimedia and mixed-media filters, walnut shell media filters, activated carbon filters and precoat filters.
Sand filters are the oldest and most common types of media filters.
They trap particles as water flows via gravity through a bed of sand into an underdrain. Sand filters capture all types of suspended solids down to between 5 microns and 10 microns or less. They also remove oils efficiently. Sand filters differ mainly in their backwashing method. Traveling bridge sand filters backwash media cells using a scouring mechanism mounted on a bridge.