Microbial electrolysis drives ammonium removal from saline wastewater through marine anammox bacteria

Currently, ammonium removal from saline wastewater still poses a challenge to conventional biological nitrogen removal process. Herein, the conversion of NH4+-N to N2 was successfully driven by marine anammox bacteria (MAB) in a single chamber microbial electrolytic cell (MEC) using NH4+-N as the sole substrate. Compared with no ammonium removal in the abiotic reactor with applied voltage (0–1.5 V), the maximum ammonium and total nitrogen removal rate (ARR and TNRR) of 55 and 50 g/m3•d were obtained at the voltage of 1.1 V, which were 78 % and 76 % higher than that of 0.5 V, respectively. At the voltage ≥ 1.1 V, the accumulation of NO2–-N and NO3–-N was observed in the MEC, and the nitrifying bacteria Nitrosmonas and Nitrospira were detected on the anode surface with the relative abundances of 0.84 % and 0.21 %, respectively. It was proved that the production of NO2–-N and NO3–-N was an electrochemical biological process by electroactive nitrifying bacteria. Candidatus Scalindua was the main functional genus for ammonium removal at anode biofilm with the relative abundance of 19.27 %. Therefore, ammonium was successfully removed by integrating anodic anammox and anodic nitrification. Applied voltage increased the microbial diversities at anode surface and promoted the formation of electrode biofilm. These findings indicated a promising saline wastewater treatment by employing salt-tolerant MAB for ammonium removal.