Methane Production By Co-Digestion Of Sewage Sludge And Food Waste

Biogas production and VS removal efficiency of sole sewage suldge fermentation are relatively low, because of the low organic matters, C/N ratio and slow biodegradation of sewage sludge. An effective way to imporve the biogas yield of sole sewage sludge digestion was co-digestion with food waste. Food waste contains abundant nutrient elements and organic matters, which was readily biodegraded. Co-digestion of sewage sludge and food waste could balance nutrient and trace elements of substrate, improve the buffering capacity of the process, and thus increase methane yield, shorten the fermentation cycle, improve the removal efficiencies of organic matters and capacity utilization.In this study, effects of vegetable oil content on the co-digestion of sewage sludge and food waste were investigated in batch experiments. At the vegetable oil contents of 0-50%, gas production, methane yield and metabolites variation were examined to obtain the optimal oil content. Results showed that at the vegatable oil contents of 0-30%, methane yield increased with the oil content, and methane yield and VS removal efficiency were highest at the vegetable oil content of 30%, with the values of 471.8 ml/g-VS and 64.6% respectively, which were 64.5% and 17.0% higher than those without vegetable oil addition. At the vegetable oil contents of 40%-50%, methane yield was obviously inhibited. Co-digestion could effectively resist the inhibition of oil on methane production.Effects of low-temperature heat-pretreatment combined co-digestion of sewage sludge and food waste were investigated in batch experiments. Results showed that the organic matters were released to liquid phase and the methane production rate increased after the substrate was heat-pretreated under low-temperature. The methane yields and methane production rate increased with the temperature and pretreatment time. After the mixture of sewage sludge and food waste was heat-pretreated under 70? for 30 min, methane yield of 220.3ml/g-VS was obtained, which was 1.1 times higher than that of sole sewage sludge digestion without heat-pretreatment. Considering the cost and the fermentation efficiency, the parameters of 70? and 30 min were recommended to be used in engineering application.Lab-scale experiments were conducted using CSTRs to investigate the fermentation of dewatered sludge and the co-digestion of dewatered sludge and food waste. Results showed that the average methane yield of 37.8ml/g-VS was obtained from sole dewatered sludge digestion. After low-temperature heat-pretreament, the methane yield of dewatered sludge increased by 14.2%. The average methane yield of co-digestion was 172.1ml/g-VS, which was 3.6 times higher than that of sole dewatered sludge digestion. After low-temperature heat-pretreament, the average methane yield of co-digestion was 211.7ml/g-VS, which was 18.7% higher than that of co-digestion without pretreatment. Co-digestion of dewatered sludge and food waste was an efficient and economical fermentation process.A CSTR with the volum of 2m~3 was used in the pilot-scale experiment on co-digestion of dewatered sludge and food waste. Results showed that during the start-up phase of co-digestion of dewatered sludge and food waste, the value of pH and ORP and the concertration of total alkalinity remained stable, the concertrtion of NH4+-N increased, and should be strickly controled.