Phosphate recovery from swine wastewater by struvite precipitation and process optimization using response surface methodology

Abstract

This study investigated the recovery of phosphate (P) as struvite from swine wastewater. In this study, the influence of pH, Mg:P molar ratio, Ca and CO3 2– was studied. The optimum pH for achieving high P recovery efficiency was found as 9.5. The purity of struvite precipitates is decreased from 84.5% to 69.7%. At Mg:P molar ratio of 3:1, the maximum P recovery efficiency achieved was 95%. The presence of Ca ions in swine wastewater inhibited the formation of struvite. The existence of CO3 2– is also preventing the recovery of P as struvite. Moreover, optimization and interaction between the factors were performed using Box-Behnken design of response surface methodology. A model was developed, and optimized conditions for achieving high P recovery efficiency was found as pH is 9.5, Mg:P molar ratio is 3.21, Ca: Mg molar ratio is 1.93, CO3 2–:P molar ratio is 3.49. An economic evaluation showed that the cost to recover P as struvite was 2.06 $/m3.