Characteristics of high-solids anaerobic co-fermentation for converting food waste and excess sludge to biogas

Evaluation of high-solids anaerobic co-fermentation of food waste and excess sludge was conducted in laboratory scale, which operated at mesophilic (35℃±1℃) and high-solids (12% total solids) conditions. The effects of mixing ratios on biogas conversion and rate-limiting steps of high-solids anaerobic co-fermentation were discussed. Results showed that compared with other mixing ratios, a mixture ratio of 30:30 could obviously enhance the anaerobic efficiency of biogas production, and the cumulative biogas yield, cumulative methane yield, biodegradability as well as VS removal rate increased to 612 mL/gVS, 327 mL/gVS, 76.9% and 63.6%, respectively. Moreover, it was found that volatile fatty acids were mainly inhibition factor of multi-food waste case. The biogas production rate exhibited a rapid increase in earlier 5 days of co-fermentation, but the content of methane was still below 60% throughout the high-solids anaerobic co-fermentation. As far as the case of multi-sewage sludge, the peaks of biogas production rate were obtained from the 10th to the 25th day. It was also observed that methane content rapidly increased to 50% in earlier five days and then stabilized at approximately 70%.