A comparison on phosphorus release and struvite recovery from waste activated sludge by different treatment methods

Enhancing phosphorus (P) recovery from P-rich waste activated sludge is economically effective for sustainable development and long-term food security. It is the first step for struvite recovery to find a new way to release phosphorus fully from the waste activated sludge. In this study, food-processing wastewater was found to contribute to phosphorus-rich activated sludge, which was suitable for the recovery of phosphorus in comparison with sewage sludge. In addition, six sludge treatment methods were examined resulting in significant differences on the release and recovery performance of phosphorus and nitrogen. Enzymatic hydrolysis (EH) pre-treatment showed better phosphorus release while thermal hydrolysis (TH) pre-treatment was beneficial for nitrogen release. Anaerobic fermentation (AF) after sludge pre-treatment significantly increased the accumulation of ammonia nitrogen (around 34% of sludge total nitrogen, TN) and orthophosphate (around 68% of sludge total phosphorus, TP) in the hydrolysate for struvite recovery. The highest P recovery rate was obtained using a combined EH-AF (67.98% of sludge TP). Although non-pretreated AF and free nitrous acid hydrolysis (FNAH)-AF could also achieve comparable release of phosphorus and nitrogen, the purity of struvite obtained by EH, TH, EH -AF and TH-AF was better than the former. This study provides important information on the effects of different sludge treatment methods to the release of nitrogen and phosphorus to guide the application.