A comparison of simultaneous organic carbon and nitrogen removal in microbial fuel cells and microbial electrolysis cells

• Simultaneous COD and ammonium removal was achieved in MFC and MEC.
• Under optimal conditions COD removal was near complete in both systems.
• An ammonium removal rate of 0.38 g/L/day was achieved in MFC.
• Ammonium removal in MEC (0.1 g/L/day) required microaerobic conditions.

This study demonstrates simultaneous carbon and nitrogen removal in laboratory-scale continuous flow microbial fuel cell (MFC) and microbial electrolysis cell (MEC) and provides side-by side comparison of these bioelectrochemical systems. The maximum organic carbon removal rates in MFC and MEC tests were similar at 5.1 g L−1 d−1 and 4.16 g L−1 d−1, respectively, with a near 100% carbon removal efficiency at an organic load of 3.3 g L−1 d−1. An ammonium removal efficiency of 30–55% with near-zero nitrite and nitrate concentrations was observed in the MFC operated at an optimal external resistance, while open-circuit MFC operation resulted in a reduced carbon and ammonium removal of 53% and 21%, respectively. In the MEC ammonium removal was limited to 7–12% under anaerobic conditions, while micro-aerobic conditions increased the removal efficiency to 31%. Also, at zero applied voltage both carbon and ammonium removal efficiencies were reduced to 42% and 4%, respectively. Based on the observed performance under different operating conditions, it was concluded that simultaneous carbon and nitrogen removal was facilitated by concurrent anaerobic and aerobic biotransformation pathways at the anode and cathode, which balanced bioelectrochemical nitrification and denitrification reactions.