Improving electroautotrophic ammonium production from nitrogen gas by simultaneous carbon dioxide fixation in a dual−chamber microbial electrolysis cell

Abstract

Microbial electrosynthesis is a promising technology for high-value added products generation from organic and inorganic waste. In this work, autotrophic dual−chamber microbial electrolysis cells (MECs) were set up for N2 fixation at −0.9 V vs Ag/AgCl (sat. KCl) cathodic potential under ambient conditions. Higher NH4+ production yield (average value of 0.35 µmol h−1 cm−2, normalized to cathode surface area) and higher faradaic efficiency (FE, 20.25%) were obtained with intermittent addition of N2 and CO2, while the yield and FE were only 0.018 µmol h−1 cm−2 and 4.21% in the absence of CO2. Furthermore, cyclic voltammograms (CV) explained the bioelectrochemical behavior of N2 reduction was coupled with CO2 reduction in the autotrophic MECs. Microbial community analysis and functional prediction in the cathodic chamber revealed that Xanthobacter and Hydrogenophaga played as producers for N2 and CO2 fixation and Pannonibacter acting as a decomposer for converting organic nitrogen to ammonium. This work not only provided an optional bioelectrocatalytic method for N2 fixation with negative CO2-emissions but also revealed the mechanism of simultaneous fixation of N2 and CO2 via Calvin cycle in autotrophic MECs.