Biocathodic nitrous oxide removal in bioelectrochemical systems

Anthropogenic nitrous oxide (N2O) emissions represent up to 40% of the global N2O emission and are constantly increasing. Mitigation of these emissions is warranted since N2O is a strong greenhouse gas and important ozone-depleting compound. Until now, only physicochemical technologies have been applied to mitigate point sources of N2O, and no biological treatment technology has been developed so far. In this study, a bioelectrochemical system (BES) with an autotrophic denitrifying biocathode was considered for the removal of N2O. The high N2O removal rates obtained ranged between 0.76 and 1.83 kg N m–3 net cathodic compartment (NCC) d–1 and were proportional to the current production, resulting in cathodic coulombic efficiencies near 100%. Furthermore, our experiments suggested the active involvement of microorganisms as the catalyst for the reduction of N2O to N2, and the optimal cathode potential ranged from −200 to 0 mV vs standard hydrogen electrode (SHE) in order to obtain high conversion rates. Successful operation of the system for more than 115 days with N2O as the sole cathodic electron acceptor strongly indicated that N2O respiration yielded enough energy to maintain the biological process. To our knowledge, this study provides for the first time proof of concept of biocathodic N2O removal at long-term without the need for high temperatures and expensive catalysts