| Nowadays, anaerobic digestion technology has been considered as an important and effective method for food wastes treatment, which can not only decrease the quantity of food wastes but also produce clean biogas. However, the rapid accumulation of organic acids in the system would lead to the rapid drop of pH during the anaerobic digestion(AD) process, especially during the high-solids AD(HS-AD) process, which would inhibit the activity of methanogenic bacteria, reduce the efficiency of reaction system and even can stop the biogas production. Therefore, the regulation study of acidification during the high-solids anaerobic digestion from food wastes is of great importance.The pH adjustment during the HS-AD process from food wastes was indicated in this study, the impact of pH adjustment on methane generation during fermentation process was analyzed. By analyzing the changes of biogas generation, organic acids, amylase and other parameters during the AD process, the most appropriate mode of pH adjustment was obtained. Subsequently, the objective of this study was to improve the methanogens tolerance to butyric acids and thus enhancing the methanogens tolerance to organic acids, ultimately improving the methanogenesis capability of the HS-AD. Finally, the domesticated methanogenic sludge was used as the inoculation sludge to treat the food wastes in a horizontal anaerobic reactor by the HS-AD mode, the most appropriate substrate loading rate in the horizontal reactor was obtainedThe main results are as follows:pH adjustment could effectively solve the acid phenomenon during the HS-AD process from food wastes. Compared to the pH unadjusted group, the cumulative biogas yield, cumulative methane yield, methane content and TS removal rate of substrate in the pH adjusted groups were all increased. Among these groups, the adjustment group with pH 8 reached the maxima, which were 322.0 m L/g TS, 171.0 m L/g TS, 53.1% and 95.85%, respectively. Meanwhile, the extracellular amylase and protease in the group with pH 8 also reached the maxima, which were 1.18 U/m L and 2.73×10-3 U/m L, respectively. The concentration of coenzyme F420 in the group with pH 8 had two peaks, first peak value was 61.52 μmol/g TS at the 4th day, and second peak value was 101.29 μmol/g TS at the 16 th day, respectively.Methanogens were cultivated to tolerate acids by gradually increasing the concentration of butyrate in the anaerobic digestion system, then the food wastes were inoculated with the cultured sludge to carry out the HS-AD. The results indicated that the biogas and methane generation yields, final concentrations of organic acids and SCOD in different acid-tolerant cultured groups all represented a positive correlation with the adding concentration of sodium butyrate. Compared to the unacclimated group, cumulative methane production, cumulative methane yield, cumulative biogas yield and methane content of acid-tolerant domestication groups were all increased. Among these groups, group with domestication of 8 g/L sodium butyrate reached the maxima, which were 2044 m L, 101.8 m L/g TS, 228.0 m L/g TS and 44.7%, respectively. Meanwhile, the dehydrogenase, amylase, protease and coenzyme F420 in the group with domestication of 8 g/L sodium butyrate also reached the maxima, which were 321 TFμg/(m L?h), 1.0490 U/m L, 4.7972×10-3 U/m L and 20.77 μmol/g TS, respectively.Acid-tolerant domesticated methanogenic sludge was used as inoculum in the horizontal anaerobic reactor to dispose the food wastes by HS-AD. The substrate loading rate was initially set at 2 g TS/L·d. Then the substrate loading rate was increased to 5 g TS/L·d, 8 g TS/L·d, 11 g TS/L·d after the reaction system was stable. The results showed that the acid-tolerant domesticated sludge could deal with food wastes effectively. The most appropriate substrate loading rate of the horizontal anaerobic reactor was 8 g TS/L·d. At this time, average daily biogas production was 42 L, average biogas yield was 656 m L/g TS, average methane content was 58.8%, and average methane yield was 386 m L/g TS. |
