Struvite precipitation potential for nutrient recovery from anaerobically treated wastes

Geochemical equilibrium speciation modeling was used to determine optimum c onditions for precipitation of magnesium ammonium phosphate, or struvite, f or the recovery of nutrients from an aerobically digested wastes. Despite a wide range of pH values with the potential to precipitate struvite, the op timum pH was determined to be 9.0. Bench experiments conducted on effluent from an anaerobic sequencing batch reactor (ASBR) treating swine wastes ach ieved a maximum of 88% ammonia removal at a pH of 9.5 with added magnesium and phosphate to achieve an ammonium magnesium: phosphate molar ratio of 1: 1.25:1. Struvite precipitation was performed on a continuous basis in a pil ot-scale ASBR treating swine wastes. Through the addition of supplemental m agnesium and phosphate, the ammonia concentration was reduced from 1500 mg/ L as nitrogen to less than 10 mg/L. The supernatant from the struvite preci pitation clarifier was recycled to the feed of the ASBR without adverse imp act, simulating on-farm effluent reuse as flush water.