The effect of sodium alginate (SA) on coagulation performance and floc characteristics with polyaluminum chloride (PAC) was evaluated in synthetic humic acid-kaolin water treatment. Coagulation performance and floc characteristics of PAC were investigated for comparison. The results showed that PAC plus SA exhibited certain synergistic effect on DOC (dissolved organic carbon) and turbidity removal. DOC removal was more enhanced by SA at low PAC doses than at higher ones, while turbidity removal was enhanced when PAC doses were larger than 1.5 mg/L The growth, breakage, regrowth and fractal nature of flocs were investigated using Mastersizer 2000, with the results suggesting that the aggregated flocs after PAC-SA (PAC dosed first) flocculation showed faster growth rate and with larger floc size compared with the flocs formed by PAC. Besides, PAC-SA gave the flocs with more open structure but better recovery ability after floc breakage compared with PAC. (C) 2012 Elsevier B.V. All rights reserved.