Effects of carbon-nitrogen ratio on electricity generation, pollutant removal and microbial community structure of single-chamber MFCs in high salinity wastewater

Abstract

In this study, five sets of single-chambered air cathode microbial fuel cells (MFC) were constructed. The effect of the carbon-nitrogen ratio on electricity generation and pollutant removal was discussed and the dominant strains in electrode biofilms were analyzed by high-throughput sequencing. The results showed that in terms of electricity generation performance, the increase of the carbon-nitrogen ratio was beneficial to the energy output at the carbon-nitrogen ratio of 3∶1, 4∶1, 5∶1, 6∶1 and 7∶1. When the carbon-nitrogen ratio was 7∶1, the open circuit voltage, internal resistance and maximum power density were 765 mV, 78.4 Ω and 7.33 W·m−3, respectively. Single-chamber MFCs could achieve simultaneous nitrification and denitrification, and the best removal effect of pollutants occurred at the carbon-nitrogen ratio of 4∶1, the corresponding removal rates of COD, ${\rm{NH}}_4^ + $ -N and TN were (86.17± 2.4)%, (96.98±1.8)% and (96.64±1.8)%, respectively. Microbial sequencing results showed that Thauera was the core genus of single-chamber MFC. With the increase of carbon- nitrogen ratio, the abundances of heterotrophic nitrification microorganisms in the cathode biofilms were 35.72%, 46.90%, 40.17%, 35.63% and 21.38 % in turns. The abundances of aerobic denitrifying bacteria were 35.72%, 52.60%, 49.59%, 45.08% and 21.38%, respectively. It is speculated that the heterotrophic nitrification-aerobic denitrification was the main pathway for nitrogen removal.