Understanding roles of humic substance and protein on iron phosphate transformation during anaerobic fermentation of waste activated sludge.

Effects of fulvic acid (FA) and bovine serum albumin (BSA) on the transformation of ferric phosphate (FePO) during anaerobic fermentation of waste activated sludge were investigated. Both FA and BSA promoted phosphorus (P) release from FePO. A higher P release efficiency was achieved with FA addition compared with BSA at the same dose although BSA promoted iron (Fe) reduction more effectively. Both FA and BSA contributed to the enrichment of vivianite but hindered P re-precipitation with other ions, and FA affected more significantly. Microbial analysis revealed that FA contributed to the enrichment of iron-reducing bacteria (IRB) transporting electrons indirectly and increased the bioavailable Fe(III) via siderophores; BSA provided more electron donors, thereby enriched IRB transferring electrons directly to Fe(III). This study provides an in-depth understanding of Fe and P transformations in sludge bearing iron-phosphorus compounds and it is of practical value for P recovery as vivianite.