Electrochemical Reduction of Nitrite to Ammonia for Use in a Bioreactor

Abstract

One novel means of biofuel production requires the reduction of nitrite ions to produce ammonia (which serves as an electron source for genetically-modified, carbon dioxide-fixing bacteria). The feasibility of this process depends on the performance of both the electrochemical reactor and a coupled bioreactor. We report on characterization of the electrochemical process involving nitrite reduction to ammonia in buffered electrolytes in the pH range between 6.0 and 8.0. A limiting current plateau was observed and determined to be due to flux of phosphate buffer (the primary source of protons) to the electrode surface. Importantly to the development of a sustainable process, current efficiencies of nitrite reduction to ammonia of 100% on both nickel and glassy carbon electrodes are possible. A divided flow-by porous electrode cell was designed as a proof of principle by coupling it to the bioreactor. It was observed that the overpotential of glassy carbon cathode decreased by ∼500 mV over 10 days which would correspond to 24% decrease in power requirements for the electrochemical reactor.