| Raw water temperatures in Ontario drop below 5.0°C for several months during the year. Bench scale experiments were conducted using jar test apparatus to examine the effect of raw water temperatures on the treatment efficiency of the coagulation/flocculation (CF) process, using alum as the primary coagulant, and a cationic polymer Magnafloc LT-22 as a coagulant aid, over a temperature range of 1.0--22.0°C. Temperature adversely affected alum coagulation, with residual turbidity increasing with reducing temperatures. The adverse effect on residual turbidity was partly compensated by increasing alum and Magnafloc LT-22 dosages.;Test results at about 3.5°C suggest that polyaluminum chloride (PACl) blend (Sumaclear-750) may be a better primary coagulant than alum for the CF process at low temperatures. Residual turbidity levels similar to or lower than that observed with alum were obtained with the PACl blend at about one-fourth of the dosage level with alum. |
