Removal of suspended solids by coagulation and foam separation using surface-active protein

By using several kinds of surface-active proteins as a chemical agent that combined collector with frother, removal of suspended substances by coagulation and foam separation with dispersed air was examined. Milk casein showed the greatest capability of suspension removal, and coagulating flocs formed by clay particles and iron hydroxide were almost perfectly recovered in foam generated from the liquid, even in the case of freshwater and seawater suspension at neutral pH. In contrast, the removal efficiency was extremely low using sodium dodecyl sulfate (SDS). Casein had a much greater capability for removing solids than SDS as a result of the high adsorptive activity of casein on the floc. For municipal wastewater treatment, the removal efficiency of turbidity and suspended solids was over 98% with the condition of iron coagulant (FeCl3) 20 mg-Fe/L and casein 3 mg/L and pH 5–6. Moreover, this method proved to be an effective treatment for polluted saline water (salinity 1.5%), and the suspended solids were almost perfectly recovered in foam. Here, we show a new method for quickly removing (within 7 min) suspended solids from polluted wastewater utilizing casein and bubbles.