Water free anaerobic co-digestion of vegetable processing waste with cattle slurry for methane production at high total solid content

• Water free co-digestion of vegetable processing waste and cattle slurry is feasible.
• The maximal methane production was obtained at conditions of 35% of V% and 40% of I%.
• The optimum condition was 35% of V% and 30% of I%.
• Total solid content (TS%) at the optimum condition reached up to 8.6%.
• T80 for the optimum condition was 42.9% shorter than that of the maximal CH4 yield.

The increase of vegetable planting area lead to the large amounts of VPW (vegetable processing wastes). Effects of V% (VPW proportion) and I% (inoculum proportion) on water free anaerobic co-digestion of VPW with CS (cattle slurry) for methane production was investigated. The results showed that the total methane production was increased from 141.2 L/kg VS (volatile solids) to 186.8 L/kg VS with V% increasing from 17% to 35%. When V%, I% and TS% (total solids content) were 35%, 40% and 7.9%, respectively, the maximal methane production of 186.8 L/kg VS was obtained. However, the optimal conditions were 35% of V% and 30% of I%, the methane production was 170.8 L/kg VS, the maximal methane production was only 9.4% higher than that of the optimal conditions, the TS% of the optimal condition was 8.6% and higher than that of the maximal methane production, the reductions of TS% and VS% for this condition were 29.5% and 49.2%, respectively, and the T80 for this condition was 42.9% shorter than that of the maximal methane production. The results indicate VPW can be co-digested with CS without water addition.