Volatile Fatty Acids Production From Sewage Sludge By Anaerobic Countercurrent Fermentation

A novel anaerobic fermentation process—multistage countercurrent fermentation was used to improve the production of volatile fatty acid from sewage sludge. With the control of fermentation parameters in the whole processes, the optimal conditions for the VFAs production from the sludge fermentation were investigated. The microbial community structure in sludge samples was analyzed by Fluorescence In Situ Hybridization(FISH). Results were shown as follows:(1) By this process, the highest concentration of volatile fatty acids(VFAs) and total VFAs yield reached 10.5±0.5 g/L and 0.20 g/gVS, respectively. Comparing with the conventional anaerobic process, the concentration and yield of total VFAs increased 31% and 54%, respectively. The further investigation showed the utilization of substrate was also enhanced by this process, and the ratio of substrate degradation reached 50% which increased by 37%. The results indicated that the new process could reduce the inhibitory effect of the products on the production of VFAs during fermentation. Moreover, the yield of VFAs and the decomposition of substrate were depended on the first stage and the third stage of this novel process;(2) The effects of substrate concentration on bioproduction of Volatile Fatty Acids (VFAs) from sewage sludge by multistage countercurrent fermentation process were studied. Results showed that the concentrations of substrate have significant effects on bioproduction of VFAs by this process. The concentration and yield of total volatile fatty acids reached 20 g/L and 0.20 g/gVS, respectively when VS was 100 g/L. The process was of great superiority during fermentation with high concentrations of substrate. The results indicated that the process could reduce the inhibitory effect of the products on the production of volatile fatty acids during the fermentation when the concentrations of substrate were high;(3) The effects of sludge retention time (SRT) on bioproduction of VFAs from sewage sludge by multistage countercurrent fermentation process was studied. The results indicated that it was not conducive to the bioproduction of VFAs when SRT was long or short during multistage countercurrent fermentation. The VFAs production and decomposition of substrate were best when SRT was 9 days;(4) Based on the optimal conditions and substrate obtained in the former experiments, we analyzed the differences of microbial community structure between multistage countercurrent fermentation and conventional anaerobic fermentation by fluorescence in situ hybridization (FISH). The mechanism of improving the production of volatile fatty acid from sewage sludge by multistage countercurrent fermentation was explored through the analysis of microbial community structure.