Simultaneous recovery of vivianite and produce short-chain fatty acids from waste activated sludge using potassium ferrate as pre-oxidation treatment

Recovery resources from waste active sludge (WAS) is an effective way to alleviate the predicament of WAS disposal, and it is also conducive to the carbon neutralization of wastewater treatment systems. This study discussed the strategy of WAS anaerobic fermentation after pre-oxidation with potassium ferrate (K₂FeO₄, PF), which can simultaneously recover vivianite and enhance SCFAs production. The results showed that PF pre-oxidation considerably shortened the fermentation time of SCFAs to 2 days, and the main Fe–P mineral was vivianite. The optimal PF dosage of 0.06 g Fe (VI)/g TSS for pre-oxidation WAS resulted in the maximum SCFAs production and vivianite recovery rate of 3698.2 ± 118.98 mg COD/g VSS and 32.39%, respectively. The mechanism analysis showed that the oxidizing properties of PF significantly accelerated the disintegration of tight EPS, release of protein and sludge acidification efficiency. Moreover, the PF strengthened the transfer of P to the solid phase, forming the Fe–P mineral and unsaturated coordination state of phosphate group. Then the key microorganism Geobacter reduced the Fe³⁺ in Fe–P state to Fe²⁺ and combined unsaturated phosphate to form vivianite. This study provides an alternative method for resource recovery and environmentally friendly disposal of WAS and contributes to the carbon neutrality of urban water systems.