Investigating the performance and mechanism of nitrogen gas fixation and conversion to ammonia based on biocathode bioelectrochemistry system

Background Nowadays, microbial electrochemistry is widely used to produce valuable products (CH4, CH3CH2OH, CH3COOH, etc.) from carbon dioxide. Meanwhile, given that low-value nitrogen (N-2) is abundantly available as a feedstock for chemicals, thus ammonia (NH3) synthesis using bioelectrochemistry is still a promising technology. However, considering N-2 stability and ammonium (NH4+) adsorption with a proton exchange membrane, developing suitable microbial systems for NH3 synthesis still faces challenges. Based on this, we developed a single-chamber biocathode bioelectrochemical system for efficient NH3 production. Results For the reaction system that we constructed, NH4+ production reached 6.31 mg L-1 within 10 days, and NH4+ production was positively correlated with current density. A C2H2 reduction assay further verified the activity of nitrogenase enzyme. Microbial community analysis revealed that Clostridia plays a crucial role in the N-2 fixation process, and the synergistic interaction between different microorganisms favors electron transfer and an increase in NH3 production. Conclusions The results of a series of experiments have proved that this green and economical method can be used to efficiently generate NH4+. This reaction system not only utilizes the advantages of obtaining electrons for reduction reaction, but also improves electron transfer and avoids the shortcomings of NH4+ adsorption. Additionally, this in-depth study of N-2 fixation mechanism provides a theoretical reference for other applications of bioelectrochemical systems. (c) 2022 Society of Chemical Industry (SCI).