Performance and metagenomics analysis of anaerobic digestion of food waste with adding biochar supported nano zero-valent iron under mesophilic and thermophilic condition

A large amount of food waste (FW) brings environmental pollution and sanitation problems. Anaerobic digestion (AD) is an effective technology to treat FW and generate biogas energy. This study investigated the effect of biochar supported nano zero-valent iron (BC-nZVI) on AD performance of FW. Results showed that the cumulative methane yield (CMY) increased by 21.52%-54.90% and the lag time decreased significantly with BC-nZVI. Under mesophilic and thermophilic condition, the peak of CMY was achieved at 178.82 +/- 5.27 mL/g VS and 193.01 +/- 6.81 mL/g VS with 5 g/L BC-nZVI, respectively. Besides, BC-nZVI stimulated hydrolysis process and reduced the inhibition of NH4+-N and volatile fatty acids accumulation, and it could improve the system stability. Structural equation model analysis indicated that digestion time, BC-nZVI, NH4+-N, temperature and total volatile fatty acid had significant effects on CMY, explaining 92.20% of its total variation. The metagenomic analysis of key microorganisms and related metabolism pathways involved in AD system was further investigated. The results suggested that BC-nZVI contributed to strengthen methanogenesis through enriching the various predominant methanogenic pathways and activating most enzymes related to methane metabolism. BC-nZVI could improve the AD system function and provided a better AD performance by shifting the microbial communities and altering functional genes. This study provided a theoretical basis for BC-nZVI applications and improvements in AD process of FW.