Effect of nano zero-valent iron on the anaerobic digestion of food waste: Performance and mechanism

•Addition of nZVI improve the methane production and the stability of AD system.•nZVI did not significantly contribute to the hydrolysis and acidification stages, but promoted the methanogenic stag.•The corrosion hydrogen production efficiency of nZVI during AD first increased and then decreased with the increase of nZVI addition.•nZVI addition results in the increase of hydrogenotrophic methanogens and DIET- associated methanogens. Food waste (FW) is prone to accumulate volatile fatty acids (VFAs) during anaerobic digestion (AD). In this study, nano zero-valent iron (nZVI) was used to enhance AD system stability and improve methane production efficiency. Results showed that nZVI facilitated the AD obviously. The highest cumulative methane production of 195.63 ± 5.38 mL/g VS was obtained at the nZVI dosage of 1.0 g/L, which was 22.6 % higher than that of the control. The appropriate addition of nZVI mainly strengthened the methanogenic stage of AD of FW, reduced the accumulation of VFAs and alleviated the pH fluctuation of the system. The corrosion hydrogen production efficiency of nZVI during AD first increased and then decreased with the increase of nZVI addition. Microbial community analysis demonstrated that the addition of nZVI mainly increased the abundance of hydrotropic methanogens and DIET-associated methanogens, and promoted the growth of bacteria in a symbiotic relationship with methanogens. In summary, the nZVI addition supplied a promising approach to improve the methane production efficiency from AD of FW.