This article discusses the fundamental behavior of kaolin, humic acid, and aluminum in the primary coagulant PAC, which were included together or separately in three simulated natural surface waters, in direct sand filtration. According to the bench scale experiment, the treatment of water containing humic acid with or without kaolin was found to be much more complex than that of turbid waters. With the filtration of water containing both the materials, at most 31 % of humic acid was removed at a pH level of 7, and 78 % at a pH level of 5 corresponding to a suitable coagulation pH level, with the additions of 25 mg/l of PAC and 0.15 mg/l of an organic polymer. A strong correlation was also noted to exist between the behaviors of humic acid and aluminum.

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