Bioelectrochemical anoxic ammonium nitrogen removal by an MFC driven single chamber microbial electrolysis cell.

Nitrogen removal from wastewater is an indispensable but highly energy-demanding process, and thus more energy-saving treatment processes are required. Here, we investigated the performance of bioelectrochemical ammonium nitrogen (NH-N) removal from real domestic wastewater without energy-intensive aeration by a single chamber microbial electrolysis cell (MEC) that was electrically powered by a double chamber microbial fuel cell (MFC). Anoxic NH-N oxidation and total nitrogen (TN) removal rates were determined at various applied voltages (0-1.2 V), provided by the MFC. The MEC achieved a NH-N oxidation rate of 151 ± 42 g NH-N m d and TN removal rate of 95 ± 42 g-TN m d without aeration at the applied voltage of 0.8 V (the anode potential E = +0.633 ± 0.218 V vs. SHE). These removal rates were much higher than the previously reported values and conventional biological nitrogen removal processes. Open and closed-circuit MEC batch experiments confirmed that anoxic NH-N oxidation was an electrochemically mediated biological process (that is, an anode acted as an electron acceptor) and denitrification occurred simultaneously without NO and NO accumulation. Moreover, ex-situN tracer experiment and microbial community analysis revealed that anammox and heterotrophic denitrification mainly contributed to the TN removal. Thus, the bioelectrochemical anodic NH-N oxidation was coupled with anammox and denitrification in this MFC-assisted MEC system. Taken together, our MFC-driven single chamber MEC could be a high rate energy-saving nitrogen removal process without external carbon and energy input and high energy-demanding aeration.