Effect of zero-valent iron addition on the biogas fermentation of food waste after anaerobic preservation

To solve the problem of acidification during high-load anaerobic digestion of food waste, the effects of adding Fe 0 on acidified fermentation system were investigated. Four adding Fe 0 groups and four control groups were set under different inoculum-to-substrate ratios (ISRs) of 1.00, 0.80, 0.65, and 0.50. Results showed that adding Fe 0 significantly increased methane production, except for the over-acidification group under ISR= 0.5. As for the control groups, the pH of system decreased to below 5.8 with the decrease of ISR, which led to the instability of the system and the stop of gas production. Compared with the control groups, pH recovered faster and the concentration of volatile fatty acids was lower with Fe 0 addition under the same ISR. Moreover, in the Fe 0 group under ISR= 0.65, the pH recovery effect was the most obvious and microbial-community analysis showed that the relative abundance of Clostridium increased by 14.9%. As a result, the best recovery effect was obtained by adding Fe 0 under ISR= 0.65, and the cumulative CH 4 yield increased by 77.3% compared with the control group. Therefore, adding Fe 0 to the acidified fermentation system can effectively alleviate acidification and thus increase methane production when ISR > 0.5.