Ammonium recovery from biocatalytic calcification reactor effluent by struvite precipitation

Abstract

Chemical precipitation is a suitable method for the recovery and removal of ammonium in water and a fertilizer known as MAP (magnesium ammonium phosphate; MgNH4PO4.6H2O; struvite) is obtained. Additionally, the advantage of this method is that environmental conditions do not have any effect compared to biological methods. In this study, the recovery of ammonium (Cmean=348 mg NH4+/L ± 38.1; n=25) occurred after the hydrolysis of urea in the biocatalytic calcification reactor (BCR) effluent and it precipitated as struvite. The effects of operating parameters, such as different phosphate and magnesium sources, Mg2+:NH4+:PO43-molar ratio, pH value, mixing speed-time, and fertilizer effect, were examined. The precipitates were characterized by X-ray diffraction and scanning electron micrograph. The optimum molar ratio of Mg2+:NH4+:PO43− was determined as 1.25:1:1. Studies using different pH ranges (7-10) and this molar ratio showed that the ammonium recovery of approximately 96% was reached at a pH value of 9.36. It was seen that the rapid mixing (200 rpm) of 30-s period and the slow mixing (30 rpm) of 2-min period were sufficient for MAP precipitation. Struvite that was obtained after precipitation was used as a fertilizer and it was observed to have a positive effect on plant growth.