Abstract: Liquid is purified by passing it through a bed containing disc-shaped buoyant media beads having grooved surfaces. Such beads are formed from a polymeric pellets. The pellets are passed through a scarifier to roughen their surfaces. Pellets are also passed through a rolling mill which grooves the pellets and compresses them into disc-like shapes.

Abstract: Liquid is purified by passing it through a bed containing disc-shaped buoyant media beads having grooved surfaces. Such beads are formed from a polymeric pellets. The pellets are passed through a scarifier to roughen their surfaces. Pellets are also passed through a rolling mill which grooves the pellets and compresses them into disc-like shapes.

Abstract: A multi-bed filtration system includes an upstream filter bed in series with a downstream filter bed of nonbuoyant media. Also included is a system for periodically backwashing the nonbuoyant filter bed. Coagulant-treated water is passed through the upstream filter bed, followed by the downward flow of water through the downstream filter bed. Thereafter, the downward flow of water through the downstream filter bed is periodically interrupted. During these interruptions, a limited amount of water is introduced upwardly through the downstream filter bed by the backwashing system. Such backwashing frees coagulated solids within the bed, causing the solids to move upwardly through the bed. The solids ultimately collect in a zone above the surface of the bed. When normal filtration recommences, water passes through the deck of solids in the zone prior to entering the nonbuoyant filter bed.