Effect of Nitrate Concentration on the Coupling Process of Electricity Generation and Nitrate Removal in Biocathode Microbial Fuel Cells

The effect of nitrate (NO3−-N) concentration in catholyte on electricity generation and pollutant removal was investigated in biocathode microbial fuel cells (BMFCs). Results indicated that the NO3−-N removal rate and output voltage could be promoted with increasing NO3−-N concentrations, but both of them would be inhibited when the NO3−-N concentrations was more than 100.0 mg/L. The maximum NO3−-N removal rate and the maximum output voltage was 0.833 mg/(L/h) and 406 mV, respectively, when the initial NO3−-N concentration was 100.0 mg/L. Based on the Han–Levenspiel model, the kinetics of NO3−-N removal and output voltage were established in which the maximum NO3−-N removal rate was 1.06 mg/(L/h), and the maximum output voltage was 478 mV. Moreover, NO3−-N concentrations had a great impact on the coupling of electricity generation and NO3−-N removal, which indicated that electricity generation was closely related to the NO3−-N removal. In addition, it was found that the community structure in the cathode biofilm by high-throughput sequencing changed at different NO3−-N biofilm as measured by the main functional microbial genus responsible for removing NO3−-N, which remained as denitrifying Proteobacteria.