Coagulation and sedimentation in chemical precipitation of wastewaters

The influence of different pollutants on coagulation and sedimentation in chemical treatment for tertiary phosphate removal was investigated in a model system. Phosphorus content and alkalinity resembled that of an effluent from biological treatment. Several pollutants inhibited coagulation and sedimentation. This was in some cases attributed to electrostatic stabilization due to adsorption of anionic species, while certain pollutants seemed to stabilize the precipitated particles sterically. At very low pollutant additions an increase of the sedimentation rate was observed in some cases, which also mainly could be rationalized by the same mechanism.