[Sulfate Reduction and Microbial Community of Autotrophic Biocathode in Response to Externally Applied Voltage]

The removal efficiencies of environmental pollutants in a microbial electrolysis system (MES) with a biocathode are highly affected by the externally applied voltage. Although the cathode biofilm plays a key role in the pollution removal, its response to the applied voltage is still unknown. A two-chambered MES with a biocathode was constructed to study the impact of the different applied voltages (0.4, 0.5, 0.6, 0.7, and 0.8 V) on the sulfate reduction, extracellular polymer formation, and cathodic bacterial community. The results show that the current output and coulomb and COD removals of the MES are positively correlated with the applied voltage ranging from 0.4 to 0.8 V. The sulfate reduction rate first increases and then decreases with increasing voltage in the MES. The maximum sulfate reductive rate[78.9 g·(m³·d)^-1] and maximum S^2- production (31.9 mg·L^-1±2.2 mg·L^-1) were achieved at 0.7 V. The highest electron recovery efficiencies of the MES are 41.8%; hydrogen production may be a pathway leading to electron loss. The polysaccharide and protein contents of the cathode biofilm increase with increasing voltage. The cathode biomass at 0.8 V is 70% higher than that at 0.4 V. The high throughput sequencing results show that Proteobacteria and Dsulfovibrio are dominant in the cathodic microbial community at the phylum and genus levels, respectively. The relative abundance of Desulfovibrio shows little variation with the increasing voltage, indicating that Desulfovibrio is of advantage for using the cathode as electron donor for the respiratory metabolism. With the increasing voltage, the distribution of Desulfovibrio at species level indicates that the changes of Desulfovibriox magneticus RS-1 and s_unclassified_g_Desulfovibrio are contrary.