Turbidity removal by an upflow pellet-floc formation process

Abstract

An innovative fluidized pellet-floc bed clarifier with very high upflow velocity of 30 and 40 cm./min. or very short hydraulic detention time of 5 and 3.8 minutes, was developed. The raw synthetic water of 50 NTU turbidity was treated using polyaluminum chloride coagulant and anionic polymer flocculant. Chemical dosages consisted of PACl dosage of 1, 2, 3, 4 mg./l. and polymer dosage of 0.1, 0.2, 0.3 mg./l. including paddle agitating speed of 5, 10, 15 rpm. Were determined for this study. Clarification by pellet-floc formation process was achieved by uneven-external forces given onto the surface of strong floc-aggregates in order to deform, shrink and compact the floc aggregates, resulting in exudation of liquid from the floc aggregates and producing high-density pellet flocs. Thus, good quality water of less than 3 NTU could be produced in this very high upflow rate clarifier. Excess pellet flocs were continuously drawn off from the clarifier to a sludge concentrator. The sludge drawoff rate was kept constant at 15% of the inflow rate.