Glycine-assisted phosphorus release and recovery from waste-activated sludge†

This study reports a sustainable and green method for phosphorus (P) extraction and recovery from waste activated sludge (WAS) using glycine as a P-extraction agent. Glycine showed an extraordinary ability to induce P release from waste-activated sludge at a rate of 8.7 mg P per L per h without being consumed. The P-extraction rate was linearly related to the mixed liquor suspended solid concentration and was not affected by the temperature in the range of 25–35 °C. After extraction, the released P was recovered via calcium precipitation, resulting in high P-content (48%, as phosphate) products (dominated by amorphous calcium phosphate). An unparallel advantage of the method is the high recyclability of glycine. Repetitive experiments showed <10% glycine loss over four P-extraction–P-recovery–glycine-reuse cycles. Additionally, extremely low heavy metal contents were observed in the P-recovery products in comparison to the acid/alkali-assisted P extraction, indicating its environmental friendliness as a sustainable strategy for P recovery from WAS.