TREATING HIGH-TURBIDITY WATER USING FULL-SCALE FLOC BLANKET CLARIFIERS

摘要

The dynamic responses of the blanket in full-scale flat-bottom type floc blanket clarifiers of PingTsan Water Works, Taiwan Water Supply Corporation, were monitored when the coagulant (polyaluminum chloride , PACl) was subjected to a step-change in dosage. The blankets in the clarifiers were easily washed out with the conventional coagulation-clarification process (the “single -stage process”), which seriously threatened drinking water quality. The PingTsan Water Works adopted a pre-treatment stage before the single -stage process to enhance the treatment efficiency. We monitored on November 9-10, 2000 the performance of this full-scale “two-stage process” to treat the high-turbidity storm water. The two-stage process produced stable blanket and quality clarified water that was insensitive to the variation of raw water turbidity or of the PACl dose. rnPilot tests were conducted on October 6-7, 2001, to demonstrate the performance differences to deal with high-turbidity storm waters between the single-stage and the two-stage processes. The single-stage process produced unstable blanket to PACl change. Not only the produced blanket was easily washed out when the PACl dose was step-decreased, it recovered very slowly when the dosage resumed its original value. The yielded blanket by two-stage was less readily deteriorated with insufficient coagulant dose, and was more easily recovered when more coagula nt was supplied. Applying two-stage process for achieving the same effluent quality could considerably reduce the total PACl dosage.