Enhancing biogas generation performance from food wastes by high-solids thermophilic anaerobic digestion: Effect of pH adjustment

• Biogas generation performance was significantly enhanced by pH adjustment.
• Maximal methane yield of 171.0 ml g−1 TS was achieved at the group of pH 8.0.
• Enzyme activities were explored and they reached the maxima at the group of pH 8.0.
• High TS, VS removal rates of substrate were achieved with the pH adjustment mode.

Anaerobic digestion has been considered as a promising disposal technology for food wastes treatment, which can not only decrease the quantity of food wastes but also produce clean biogas. However, organic acids were generated during the high solids anaerobic digestion (HS-AD) process, which would cause severe acidification and methanogenesis inhibition. The influence of pH adjustment on biogas generation from food wastes during HS-AD was investigated in this study. The results indicated that the cumulative biogas yield, cumulative methane yield and methane content in the group with pH of 8 reached their maxima of 322.0 ml g−1 TS, 171.0 ml g−1 TS and 53.1%, which were 1.49, 7.57 and 5.06 times higher than pH uncontrolled group, respectively. Besides, amylase and protease enzyme activity also reached maxima of 1.18 U ml−1 and 2.73 × 10−3 U ml−1, respectively. The concentration of coenzyme F420 at the group with pH of 8 had two peaks, first peak value was 61.52 μmol g−1 TS at the 4th day, and second peak value was 101.29 μmol g−1 TS at the 16th day, respectively. The TS, VS removal rates of total and substrate also reached maxima of 52.07%, 63.46% and 90.92%, 95.85%, which were all higher than pH uncontrolled group.