Influence of mixing proportion on the solid-state anaerobic co-digestion of distillerʹs grains and food waste

The solid-state anaerobic co-digestion (AC) of distillerʹs grains (DG) and food waste (FW) for biogas production was investigated. The effects of different DG/FW (TS) ratios (10/1, 8/1, 6/1, 4/1, 1/0, and 0/1) were examined. Co-digestion with the above DG/FW ratios was found to be superior to that of mono-digestion. The AC of DG and FW had a good synergistic effect of the lower range of propionate/acetate ratio and VFA/alkalinity ratio. No methane was produced when the propionate/acetate ratio was >0.1 ± 0.01, but this inhibition was reversible. When the propionate/acetate ratio was <0.08 ± 0.01, methane production began to recover. When the volatile fatty acids (VFA)/alkalinity ratios were <0.9 ± 0.05, the AC of the influents successfully proceeded in a stable manner. However, when the VFA/alkalinity and propionate/acetate ratios were >1.25 ± 0.21 and 0.1 ± 0.01, respectively, the AC system reached an acidification crisis and failed. Therefore, the propionate/acetate and VFA/alkalinity ratios may be used as important indices for controlling anaerobic digestion (AD).