Enhancing simultaneous electrosynthesis of CO2 and nitrogen removal in microbial fuel cell (MFC) cathode compartment by adding Fe–C/biochar compound substrates

A denitrifying microbial fuel cell (MFC) based on CO2 regulation and Fe–C/biochar compound substrate supplementation was constructed to investigate the MFC performance, CO2 fixation and microbial mechanism under different experimental conditions. The results showed that the addition of CO2 and Fe–C/biochar compound substrate improved the electricity generation (397.8 mV, 88.3 mW/m2), denitrification rate and organic carbon removal performance (93.5%) of the system by promoting the generation of soluble microbial products (SMP), extracellular polymeric substances (EPS), volatile fatty acids (VFAs), polyhydroxyalkanoate (PHA) and glycogen in the cathode reactors. Microbial community analysis and metagenomic results revealed that both CO2 and Fe–C/biochar compound substrates constitute a degree of positive feedback to denitrification and carbon fixation. Nevertheless, there were a large number of exoelectrogenic bacteria (Geobacter) attached to the biochar which merely had positive correlation with heterotrophic denitrifiers (Sulfurimonas and Methylophilus). Thermomonas and Thiobacillus were positively correlated with carbon felt rather than Fe–C.