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Water samples collected from early March 2001 to the end of April 2002 at the branch of Pearl River around the Guangzhou City were analyzed for its micro-polluted characteristics. The coagulation behavior of polyaluminum chlorides(PACls) was then examined focusing on the effect of primary water quality and speciation distribution. The results showed that PACIs exhibit better coagulation efficiency than alum in accordance with the different speciation. The turbidity removal property of PACIs is evidently better than alum at low dosage. While in neutral zone (about 6.5-7.5). the turbidity removal of PACIs decreases owing to the restabilization of particles at higher dosage. The organic matters in raw water exhibit marked influence on coagulation. In acidic zone, organic matters complex with polymer species and promote the formation of floes. With an increase in pH. the complexation of organics with polymer species gradually decreases, and the removal of organics mainly depends on adsorption. The effect evidently improved with the raise of B value. [ABSTRACT FROM AUTHOR]