Microbial mechanism underlying the effect of biochar supported nano zero-valent iron on the anaerobic digestion of food waste

Anaerobic digestion (AD) is one of the effective methods to treat the food waste (FW). In this study, biochar supported nano zero-valent iron (BC-nZVI) was prepared by carbon thermal reduction process. The effects of concentrations (1, 2 and 3 g/L) of BC-nZVI on methane production, microorganisms and metabolic mechanism during the AD of food waste were investigated. The results showed that 1 g/L of BC-nZVI was the best concentration for methane production. The cumulative methane production was enhanced by 29.54% at BC-nZVI 1 g/L. Microbial community analysis showed that BC-nZVI mainly increased the abundances of hydrolytic bacteria (including Bacteroidetes_vadinHA17 , Proteiniphilum , Syntrophobacter ) and acetoclast ( Methanosaeta ). Further exploration of the mechanism using PICRUSt2 version based on 16 S rRNA gene sequence analysis indicated that the addition of BC-nZVI promoted the abundances of enzymes related to methane metabolism such as the phosphate acetyltransferase and the methyl-coenzyme M reductase alpha subunit, which made the AD system stable.