A novel approach of synchronously recovering phosphorus as vivianite and volatile fatty acids during waste activated sludge and food waste co-fermentation: Performance and mechanisms

[Display omitted] •Efficient P and VFAs were synchronously recovered from WAS/FW co-fermentation.•83.09% of the TP in WAS was recovered as high-purity vivianite (93.90%).•The WAS/FW (30%) co-fermentation with pH uncontrolled generated the highest VFAs.•WAS/FW co-fermentation contributed to the release of Fe2+ and PO43− by lowering pH.•The flexible pH variation in WAS/FW reactor was favorable for microbial activity. This research proposed an innovative approach to synchronously enhance the recovery of phosphorus (P) as vivianite and volatile fatty acids (VFAs) during waste activated sludge (WAS) and food waste (FW) co-fermentation. A high performance was achieved under 30% FW addition and pH uncontrolled, which gained 83.09% of TP recovery as high-purity vivianite (93.90%), together with efficient VFAs production (7671 mg COD/L). The FW supplement could enhance VFAs production and subsequently lower pH to contribute to the release of Fe2+ and PO43−. Also, it could dampen disrupting effects of strong acidic pH on microbial cells (lowering LDH release). Moreover, the flexible pH variation caused by biological acidification could maintain relatively higher microbial activities (increasing enzymes’ activities), which was advantageous to the biological effects involved in Fe2+ and PO43 release and VFAs generation. Therefore, this research provide a promising and economic alternative to dispose of WAS and FW simultaneously for valuable resource recovery.