Optimization and kinetics of nutrient removal from wastewater by chemical precipitation of struvite

Nutrient removal by the precipitation of struvite from synthetic municipal wastewater was tested. Response surface methodology with the Box-Behnken experimental design was employed to determine the optimal phosphorus removal efficiency with the influencing process variables of pH, temperature, magnesium to phosphorus molar ratio, mixing speed (rpm), and organic contents. Under the values of pH, temperature, Mg to P ratio, mixing, and organic content of 9.86, 26.5 degrees C, 1.64, 80 rpm, and 1,020 mg sugar/l, respectively, optimum phosphorus (PO4-P) removal efficiency of 90.1% was obtained. Results of analysis of variance indicated that the quadratic model predicts the responses adequately with the five factors that coded the process variables. The effects the factors have on the amount of PO4-P removal were ranked (with their relative scores) in the descending order of pH (11.8), Mg:P ratio (6.2), organic content (2.4), mixing speed (1.1), and temperature (0.5), where the ranking quantifications were according to the respective coefficients of the factors in the quadratic model equation. Removal of nitrogen (NH4-N) was limited by equal molar amount of PO4-P removed and thus the remaining NH4-N must be subsequently treated using usual nitrogen removal processes.