The influence of different humic substances and linear alkylbenzene sulfonate on chemical treatment of a synthetic wastewater was investigated at pH=6-6.5. In soft water, humus significantly inhibited particle destabilization. The additional coagulant dosages needed for efficient coagulation corresponded to the dosages required for humus removal from pure solutions. Adsorption of humus onto precipitated hydroxide was regarded as being the major mechanism of interaction here. In hard water, high concentrations of humus seemed to impair aggregation of microflocs. This was attributed to the formation of soluble calcium humate complexes in raw water that may adsorb more slowly on precipitated hydroxide than dissolved humus. Precipitation of phosphate was not affected by humus in a definite way. A clear influence of LAS on coagulation was not found.

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