Focusing on the improvement of removal efficiency of humic substances by coagulation, coagulation-flocculation processes were applied not only once but more than twice to the water being treated, and the effect of repeated coagulation was evaluated in jar-tests. With more than the critical dosage of PACl (15 mg/l), approximately 30% of color removal was attained in typical one-pass treatment, whilst maximum 65% removal was achieved by repeating the coagulation twice. Repeating coagulation enhances the coagulation process to achieve higher color removal efficiency, and can reduce the coagulant dosage.

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