Pollutant Transformation And Molecular Biology Analysis In An Anaerobic Process Using Electrode As The Electron Acceptor

Fermentative hydrogen production, as a process for clean energy recovery from organic wastewater, is limited by its low hydrogen yields due to the incomplete conversion of substrate, with most of the fermentation products being volatile fatty acids (VFAs). Thus, further recovery of the energy from the VFAs is expected.In this work, microbial fuel cell (MFC) was applied to recover energy in the form of electricity from mixed VFA of acetate, propionate and butyrate. Response surface methodology was adopted to investigate the relative contribution and possible interactions of the three components of VFAs. Research found that anode biofilm was established quickly after the operation of MFCs. A stable electricity generation was demonstrated in MFCs after the enrichment of electrochemically active bacteria. MFCs also showed good wastewater treatment performance. No VFAs were detected at the end of the electricity generation cycle. COD degradation followed the apparent first-order kinetics. The coulombic efficiency achieved by these MFCs was only 20-39%, which was possibly attributed to the competitive utilization of electrons by oxygen diffused through the air-cathode or the respiration of non-electrochemically active bacteria. Acetate was found to be the most appropriate substrate for electricity generation. Higher power density and coulombic efficiency could be obtained when acetate was the predominant fraction of the mixed VFAs. Antagonistic effect appeared in mixed VFAs. Propionate with a proportion below 12% showed a positive impact on the power density, while more than 17% of propionate caused a decrease. A decrease in power density was observed when butyrate exceeded 24%. Compared with power density, response of coulombic efficiency towards VFAs compositions was relatively smooth. A high coulombic efficiency (＞36%) could be achieved when acetate accounted for 60-67% of the mixed VFAs. Changes in propionate proportion within the examined range did not cause much variation in coulombic efficiency. A drastic drop in coulombic efficiency occurred when the proportion of butyrate exceeded 26%. The DGGE profiles showed that the bacterial communities of the anode biofilm were different from those of the inoculum sludge. Proteobacteria (Beta-. Delta-) and Bacteroidetes were predominant in the VFAs-fed MFCs. Shift in microbial community structures were observed when different compositions of VFA mixtures were used as the electron donor. DGGE profiles were clustered to three major groups which were consistent with the substrate compositions. The overall electron recovery efficiency can be increased from 15.7% to 27.4% if fermentative hydrogen production and MFC processes are integrated.