Optimization of simultaneous removal of phosphorus and humic substances from reject water by calcium phosphate precipitation

This paper is concerned with the optimization of simultaneous removal of phosphorus (P) and humic substances (HS) from wastewater by calcium phosphate precipitation. Separate and combined effects of the concentration of HS, pH and Ca/P mole ratio (Ca/P) on P and HS removal were analyzed by using the response surface methodology. The composition of harvested precipitates was analyzed by X-ray diffraction. The results proved the simultaneous removal of P and HS. And the existence of HS reduced the P removal efficiency. The pH had the most significant effect on the removal efficiency of P, while Ca/P and the concentration of HS were the two predominant factors that affected the removal efficiency of HS. In the three-factors-combined-response experiment, the combined effect of Ca/P and the concentration of HS had the most significant effect to HS removal. Increasing pH reduced the effect of HS on P removal. Meanwhile, the crystallinity of the precipitate was enhanced, while the purity was reduced.