Coagulation is widely applied in water treatment processes, and good coagulation performance is important in providing high quality drinking water. Due to the restriction in research methods, there is lack of researches on the effect of source water quality as well as the morphologic change and composition of coagulants on coagulation process. A series of coagulation tests were conducted using the source water from a waterworks in a southern city, and the preparation and application of new composite reagents were conducted aiming at poor coagulation effect. The results indicated that the Al_(13) had significant advantages in the turbidity removal compared with polyalumium chloride commonly used in waterworks. But too high concentration of organic matter in the source water could decrease the coagulation performance of Al13. Compared with turbidity removal, the removal of organic matter needed more coagulants. HCA, a kind of cationic organic flocculant, was combined with the inorganic coagulant, which could significantly enhance the electricity neutralization capacity of the composite reagents. In the case of ensuring low dosage,the removal rate of organic matter could effectively be increased,the floc size during the balance was increased, and the settleability of flocs was improved.
