Natural pyrite activated peroxydisulfate enhanced short-chain fatty acids production from anaerobic fermentation of waste activated sludge: Performance and mechanisms

Peroxydisulfate (PDS) additive has been proven as an effective strategy to enhance short-chain fatty acids (SCFAs) production from waste activated sludge (WAS), which can achieve dual objectives of waste disposal and resource recovery. However, the high cost of PDS limits its large-scale application in sludge treatment. This study explored the feasibility of using natural pyrite (FeS 2 ) as an activator for PDS to enhance its capacity for promoting SCFAs production while reducing the required dosage. Compared to sole PDS (1 mM/g volatile suspended solids (VSS)), FeS 2 /PDS co-treatment (0.5 mM/g VSS PDS + 0.6 mM/g VSS FeS 2 ) obviously increased the maximum SCFAs production from 4589.5 mg COD/L to 5951.3 mg COD/L, accompanied with an enhanced proportion of acetate from 62.0 % to 75.2 %. Mechanism exploration revealed that FeS 2 /PDS enhanced the generation of hydroxyl radicals (•OH) and sulfate radicals (SO 4 •− ), thereby promoting WAS solubilization and hydrolysis. The detectable soluble chemical oxygen demand within the supernatant after 4 days of co-treatment fermentation was 5.3-fold higher than that in the single FeS 2 test and 2.0-fold higher than that in the single PDS test. Meanwhile, the activities of key enzymes, including protease, α-glucosidase, acetate kinase, and butyrate kinase, were also significantly enhanced after the FeS 2 /PDS treatment, accompanied with an increase in the abundance of hydrolytic and acidogenic microorganisms such as Acinetobacter , Clostridium_sensu_stricto , and Fonticella . Besides, FeS 2 /PDS co-treatment improved the dewaterability (42.7 % reduction in capillary suction time) and reduced operation cost (37.9 % decrease), as compared to the sole PDS (1 mM/g VSS) treatment. These findings suggest that FeS 2 /PDS co-treatment is a promising and cost-effective technique to enhance WAS anaerobic fermentation.