Activation of sulfite by FeS for anaerobic fermentation enhancement of waste activated sludge: Performance and mechanisms

Maximizing resource recovery by improving the anaerobic treatment efficiency of waste activated sludge (WAS) is critical to reducing carbon emissions. In this study, a concept of “co-treating” WAS with sulfite-laden wastes (sulfite) and mackinawite (FeS) was proposed to improve the anaerobic fermentation performance of WAS. Experimental results showed that the maximal short-chain fatty acids (SCFAs) yield of 2461.4 mg COD/L and corresponding acetate proportion (55.9 %) were obtained with a sulfite/FeS ratio of 0.8 at 500 mg S/L sulfite . It was found that •OH, SO 4 •- , . O 2 , and 1 O 2 free radicals produced by FeS/sulfite pretreatment could decompose the sludge flocs significantly, resulting in reduced particle size and viable cell ratio, thereby providing more available organics for SCFAs production. Mechanism investigations revealed that FeS/sulfite pretreatment enhanced the production of SCFAs by increasing key hydrolytic enzymes, improving the abundance of microorganisms related to hydrolysis and acidification and altering the functional traits of the corresponding microbes. FeS/sulfite pretreatment also facilitated the conversion of propionate and butyrate acid to acetate during anaerobic fermentation, probably due to FeS/sulfite-induced iron reduction and sulfate reduction. The GC–MS results suggested that FeS/sulfite pretreatment promoted the quality of the fermentation mixture by decreasing the refractory compounds. This work provided a practical approach to the final disposal of WAS with added economic and environmental value.