Bioproduction of Volatile Fatty Acids from Excess Municipal Sludge by Multistage Countercurrent Fermentation

A novel anaerobic fermentation process-multistage countercurrent fermentation was applied to improve the bioproduction of volatile fatty acids (VFAs) from excess municipal sludge. Results showed that the total VFAs concentration and the total VFAs yield reached (10.5±0.5) g/L and 0.20 gVFAs/gVS(Volatile solid) using this novel process. Comparing with the conventional anaerobic fermentation, the concentration and yield of total VFAs increased by 31% and by 54%, respectively. Moreover, removal ratio of organic solids also increased by 37% and it was 50% at the end of multistage countercurrent fermentation. We further investigated the mechanism of VFAs production. Results revealed that this novel process could reduce the inhibitory effect of VFAs on the acid-forming microorganisms, and the total VFAs yield and the removal ratio of organic solids respectively depended on the first stage and the third stage of this novel process. Therefore, the multistage countercurrent fermentation can efficiently improve the bioproduction of VFAs from excess municipal sludge, and relatively enhance the removal ratio of organic solids.