AWWA JAW51659

Runoff can rapidly change coagulant demand and produce water that is difficultto treat by conventional coagulation processes. In cases in which alkalinity dropped below about 30 mg/L as CaCO3, adding supplemental OH- (using lime or sodium hydroxide) - and thereby markedly increasing alkalinity before adding coagulant - sharply reduced turbidity after sedimentation but increased coagulant demand. Coagulant demand was a linear function of increased alkalinity and raw water dissolved organic carbon, and it was not strongly influenced by turbidity or calcium concentration below about a pH of 7.8. Includes 26 references, tables, figures.