Water treatment residual flocs are fractal-like aggregates made of many initial aggregates. We investigated in this study the coagulation dynamics for the humic-mineral-polyaluminium chloride (PACl) aggregates using small-angle light scattering techniques and the free-settling test. In contrast to reports in the literature, the presence of humic acid did not lead to a loose floc. Not only the time evolution of the coagulation dynamics, but also the final floc characteristics are only mildly affected by the humic acid. However, the strength of the formed floc does decline with humic acid, which leads to a turbid supernatant with high level of organics.

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