Migration and transformation of phosphorus in waste activated sludge during ozonation

For phosphorus (P) recovery from waste activated sludge (WAS), the most important step is to release P into the solution. This study aimed to explore the migration and transformation of P in WAS during ozonation based on the Standards Measurements and Testing Program analysis. The results showed that WAS contained 7.10% P element and could be selected as potential substitution of phosphate rock. Inorganic phosphorus (IP) was the major P fraction in raw WAS (68.10%), and non-apatite inorganic phosphorus (NAIP) occupied 62.40% of IP. Ozonation facilitated the P application in agriculture as the bio-available P in the solid phase increased by 23.63% at ozone dosage 0.20 gO₃/gSS. The highest concentration of total phosphorus in liquid (TP_(L)) (40.68 mg/L) was achieved at ozone dosage 0.20 gO₃/gSS, and 89.62% of TP_(L) was PO₄^3--P, which was easy to be recovered by struvite precipitation. The contributions of different P fractions in solid phase to TP_(L) were related to ozone dosage. The analysis of P mass balance suggested that the optimum ozone dosage for P recovery was 0.15 O₃/gSS.