Effects of biochar supported nano zero-valent iron with different carbon/iron ratios on two-phase anaerobic digestion of food waste

[Display omitted] •BC/nZVI with carbon/iron of 3:1 was found to be optimum for this system.•VFAs concentration was increased by 31.4% in acidogenic phase with BC/nZVI added.•The addition of BC/nZVI enhanced cumulative methane production by 24.8%.•BC/nZVI promoted the abundance of Methanothrix in methanogenic phase.•BC/nZVI stimulated methanogenesis through the acetoclastic methanogenic pathway. The promotion effects of biochar supported nano zero-valent iron (BC/nZVI) with different carbon/iron ratios on two-phase anaerobic digestion (AD) of food waste (FW) were studied. Results suggested that when the carbon/iron ratio was 3:1 AD system showed the best performance, with the concentration of volatile fatty acids (VFAs) in acidogenic phase (AP) and the cumulative methane production in methanogenic phase (MP) increased by 31.4% and 24.8%, respectively. Metagenomic analysis demonstrated that BC/nZVI increased the relative abundance of Defluviitoga in AP, and promoted the growth of Methanothrix in MP. Metabolic pathway analysis in AP indicated that BC/nZVI mainly promoted the abundances of acetate kinase and butyrate kinase to enhance acid production. Methane metabolism pathway analysis in MP revealed that BC/nZVI increased methane production by promoting the module of M00357 and activating related enzymes. The results of this sutdy showed that BC/nZVI promoted AD of FW mainly through acetoclastic methanogenic pathway.