Kinetic modelling and synergistic impact evaluation for the anaerobic co-digestion of distillers' grains and food waste by ethanol pre-fermentation.

The anaerobic digestion of food waste (FW) often leads to acidification inhibition owing to rapid biodegradation, resulting in system instability. In this study, distillers' grains (DG) and food waste were mixed in accordance with volatile solid (VS) ratios of 0.9:0.1, 0.85:0.15, 0.8:0.2, and 0.7:0.3. The experimental groups adopted yeast to conduct ethanol pre-fermentation and then inoculated sludge to perform anaerobic digestion, while the control groups conducted anaerobic digestion without pre-treatment. Results showed that the experimental groups had lower propionic acid concentrations; higher alkalinities, pH values and methane production rates and shorter stagnation periods than the control groups regardless of the mixing ratio. Specifically, at the DG/FW ratio of 0.7:0.3, compared with the control group, the propionic acid concentration was reduced by 59.6%, the alkalinity was increased by 41.7%. Even under high organic loading, the propionic acid and VFA did not accumulate in the system after ethanol pre-fermentation, and the anaerobic digestion system remained stable. At DG/FW ratios of 0.9:0.1 and 0.85:0.15, a synergistic effect was observed during the co-digestion of DG and FW. And, the synergistic effect of EP was relatively high, especially when the DG/FW ratio was 0.9:0.1, and methane yield increased by 26.8%.