Removal of phosphorus and nitrogen from sewage by calcium and magnesium compounding agent

Key words:  sewage disposal  calcium and magnesium compound  phosphorus and nitrogen removal

Abstract:

Calcium-magnesium mixture agent was used for treating sewage with high nitrogen and phosphorus content, and phosphorus and nitrogen removal experiments were carried out. The mechanism of denitrification and phosphorus removal by calcium and magnesium compound was analyzed. And the dosages of NaOH and calcium and magnesium mixture agent were investigated, through which the optimized conditions were obtained. It is found when the mass concentration of NaOH, MgCl₂ and CaCl₂ is 150 mg/L, 60 mg/L, and 40 mg/L respectively, the removal rate of total phosphorus (TP), total nitrogen TN and NH₃-N reaches 90％ and 25％ after treatment. In the dynamic test, when the mass concentrations of NaOH, MgCl₂ and CaCl₂ is 105 mg/L and 48 mg/L, and 24 mg/L respectively, the removal rate of TP reaches 90％ and the removal rate of TN and NH₃-N is 30％. When Ca²⁺ and Mg²⁺ react with PO-₄, NH⁺₄ and other groups to form magnesium-ammonium-phosphate and hydroxyapatite precipitation, the phosphorus and the nitrogen in the sewage can be removed.