Performance and mechanisms of citric acid improving biotransformation of waste activated sludge into short-chain fatty acids.

[Display omitted] • Citric acid (CA) exhibits dose-dependent effects on the SCFAs promotion. • CA is mainly converted to acetic acid in the anaerobic fermentation system. • CA removes multivalent cations from extracellular polymeric substances (EPS). • CA facilitates WAS hydrolysis by disrupting EPS and microbial cells. • Microbial functional traits related to SCFAs production are regulated by CA. Numerous effective chemical strategies have been explored for short-chain fatty acids (SCFAs) production from waste activated sludge (WAS), but many technologies have been questioned due to the chemical residues. This study proposed a citric acid (CA) treatment strategy for improving SCFAs production from WAS. The optimum SCFAs yield reached 384.4 mg COD/g VSS with 0.08 g CA/g TSS addition. Meanwhile, CA biodegradation occurred and its contribution to the yield of total SCFAs, especially acetic acid, cannot be ignored. Intensive exploration indicated the sludge decomposition, the biodegradability of fermentation substrates, as well as the abundance of fermenting microorganisms were definitely enhanced in the existence of CA. The optimization of SCFAs production techniques based on this study deserved further study. This study comprehensively revealed the performance and mechanisms of CA enhancing biotransformation of WAS into SCFAs and the findings promotes the research of carbon resource recovery from sludge. [ABSTRACT FROM AUTHOR]