Enhancing short-chain fatty acids production from waste activated sludge anaerobic fermentation with addition of red mud: Performance and mechanisms

Red mud (RM) as hazardous waste produced from aluminum refining industry has threatened the environment and human health. In this study, RM was added into the fermenter to promote short chain fatty acids (SCFAs) production from waste activated sludge (WAS) anaerobic fermentation. Results showed that the addition of RM could effectively improve the SCFAs production, especially, acetic acid. In particular, the production of total SCFAs and acetic acid in 20 g/L RM added fermenter were 1108.1 mg COD/L and 415.5 mg COD/L, which were 116.0% and 1308.0% higher than that in control fermenter. Batch experiment revealed that RM could enhance the hydrolysis and acidification process. Further study indicated that the activity of enzyme related to hydrolysis- acidification, abundance of fermentative bacteria for SCFAs production and functional metabolism genome were all improved with the addition of RM. The potential mechanism maybe that the RM promoted the hydrolysis- acidification process with the contained varies Fe(III) oxides as electron acceptor, and the produced Fe2+ 2 + could serve as necessary trace elements to synthesize enzyme and then stimulate the expression of enzyme genes.