Bioelectrochemically enhanced autotrophic Feammox for ammonium removal via the Fe(ii)/Fe(iii) cycle

Abstract

Autotrophic anaerobic ammonium oxidation coupled to Fe(III) reduction (Feammox) is a potential technology for removing ammonium from low-C/N wastewater, but it requires a continuous supply of Fe(III) source. To reduce the supply, a microbial electrolysis cell (MEC) was employed to allow iron recycling in Feammox under different voltages (0.2 V, 0.6 V, and 1.0 V). Results showed that the optimal voltage was 0.6 V, with a maximum efficiency for ammonium oxidation of 71%. The ammonium oxidation rate achieved 2.5 ± 0.1 mg N L⁻¹ per day, which was 3 times that of conventional Feammox. Cyclic voltammetry confirmed that ammonium oxidation and iron redox occurred on the anode. The bacterial population had a unique evolutionary direction at 0.6 V, with Geobacteraceae becoming the dominant family. Positive interactions between nitrogen-related bacteria and iron-related bacteria enhanced the autotrophic Feammox process. This study will further advance Feammox in the treatment of ammonium-containing wastewater.