Release of phosphorus from sewage sludge during ozonation and removal by magnesium ammonium phosphate

The release rule of phosphorus from sewage sludge during ozonation and removal by the magnesium ammonium phosphate (MAP) method were investigated. The results showed that the concentrations of total phosphorus in aqueous phase (TP_(A)) and orthophosphate (PO₄^3--P) in ozonized sludge supernatant rose obviously with increasing ozone dose when ozone dose was below 61.2 mg O₃/gSS then almost kept constant. The TP_(A) and PO₄^3--P contents in the ozonized sludge supernatant were 70.9 and 63.3 mg/L when ozone dose was 61.2 mg O₃/gSS, respectively. Total phosphorus in the sludge solid (TP_(S)) was mostly distributed in inorganic phosphorus (IP) (more than 81.5% of TP_(S)), and non-apatite inorganic phosphorus (NAIP) was the major component of IP in the sludge (more than 78.7% of IP) during ozonation. The release contribution (RC) of IP to TP_(A) accounted for over 73.9%. The optimized conditions for the removal of phosphorus from ozonized sludge supernatant were set at an initial Mg²⁺/PO₄^3--P molar ratio of 1.8, pH 9.5, and reaction time of 5 min, under which the removal efficiencies of TP_(A) and PO₄^3--P were 43.1 and 52.2%, respectively.