PARTICLE-SIZE AND CHEMICAL EFFECTS ON CONTACT FILTRATION PERFORMANCE

This work involves a laboratory-scale investigation of the effects of suspended particle size and coagulant type on the performance of contact or in-line direct filtration (no flocculation). Dilute monodisperse and polydisperse suspensions of polystyrene particles (0.27-, 1.24-, 1.32-, and 10-mum diameters) were applied to shallow beds of 0.4-mm glass-bead filter media after destabilization with either cationic polymer or calcium chloride. The particle removal and head-loss results show dramatic effects of particle size on filtration performance. Submicron particles significantly improve the removal of larger particles in mixed size suspensions and also dominate head-loss development. Head-loss development is typically linear with time and for mixed suspensions is the same as, or somewhat lower than, head loss for monodisperse suspensions of the smaller-sized particle. Polymer destabilization generally causes more head loss than calcium chloride destabilization for a similar extent of particle deposition.