Phosphorus recovery from synthetic swine wastewater by chemical precipitation using response surface methodology.

With synthetic swine wastewater, central composite design using response surface methodology was employed to investigate the effects of pH value and concentrations of ammonium, phosphate, magnesium and calcium on phosphorous recovery. P recovery efficiency with the range of 53-99% was observed in the experimental runs. Results showed that magnesium ammonium phosphate were the only crystals, mixed with amorphous calcium precipitates, in the deposits. According to the regression quadratic model, the linear and quadratic terms of PO(4)(3-)-P and Mg had significant effects on the P recovery amount. With regard to the interaction terms, pH x NH(4)(+)-N, PO(4)(3-)-P x Mg, PO(4)(3-)-P x Ca and Mg x Ca showed significant influences. A maximum P recovery amount of 299.25 mg/L was achieved at optimized conditions with pH 9.7, NH(4)(+)-N 456 mg/L, PO(4)(3-)-P 300 mg/L, Mg(2+) 264 mg/L and Ca(2+) 59 mg/L, respectively.