Abstract：The synthetic water containing humic acid and kaolin was treated using composite coagulant polyaluminum chloride and polydimethyldiallylammonium chloride (PAC-PDMDAAC) firstly. Then, the water treated by coagulation was filtrated using ultrafiltration membrane. The effect of coagulant dosage and pH on the water treatment efficiency was investigated. Disinfection was carried out for the water treated by coagulation or by combined coagulation- ultrafiltration processes using NaClO solution as disinfectant. The residual chlorine data was fitted using first-order chlorine decay model and the initial concentrations of fast reacting agents and slow reacting agents were obtained by calculating the residual chlorine data using the software AQUASIM. For the purpose of lowest concentration of precursors of disinfection by-products, there existed different coagulant dosages and pH for coagulation and coagulation- ultrafiltration processes. For the water treated by coagulation, the concentration of precursors of disinfection by-products was the lowest when the flocs size was small and the flocs size behaved a concentrated distribution. While for the water treated by coagulation- ultrafiltration, the concentration of precursors of disinfection by-products was the lowest when the flocs size distribution curve had two peaks and the volume percentage of flocs with larger particle size was higher.
