Focusing on low biogas yields in the anaerobic co-digestion of waste activated sludge and food waste, the enhancing effects and mechanisms of microscale zero valent iron (mZVI) on anaerobic co-digestion was investigated. The results indicated that the addition of mZVI enhanced the methanogenesis stage of co-digestion but had no significant effect on the solubilization, hydrolysis, and acidification stages. With a dosage of 10 g·L-1 mZVI, the cumulative methane yield (based on VS) within 15 days reached 238.68 mL·g-1, which was 20.05% higher than the control group. The mechanism analysis showed that mZVI promoted electron transport system (ETS) activity (based on INTF/TS), which increased to 21.50 mg·(g·h)-1 with 10 g·L-1 mZVI compared to 13.43 mg·(g·h)-1 in the control group. Furthermore, mZVI enhanced direct interspecies electron transfer (DIET) between specific bacteria and methanogens. Microbial community analysis demonstrated that the abundance of DIET-related microorganisms, such as Syntrophomonas, Methanosarcina, and Methanobacterium, was higher in presence of mZVI.
Keywords: anaerobic co-digestion; direct interspecies electron transfer (DIET); food waste; microbial community; microscale zero valent iron (mZVI); waste activated sludge.