Simultaneous removal of organic matter and nitrogen compounds by partitioned aeration in a 226 L-scale microbial fuel cell

Abstract

Although microbial fuel cells (MFCs) have been widely studied as wastewater treatment technologies that convert organic matter to electricity, there are few reports of large-scale MFCs that treat both organic matter and nitrogen compounds. In this study, a 226 L reactor equipped with 27 MFC units was partially aerated at 10% of its total volume. The MFC unit consists of a cylindrical air core covered with a carbon-based air cathode, an anion exchange membrane, and a graphite non-woven fabric anode. The air-cathode MFC with 13 L min⁻¹ aeration rate produced a current density of 0.0012–0.15 A m⁻² with 40 to >93% biological oxygen demand (BOD) removal to have an effluent BOD of <5–36 mg L⁻¹ at a hydraulic retention time (HRT) of 12–47 h. Meanwhile, 55 ± 17% of the total nitrogen (TN) was removed, resulting in 9.7 ± 3.8 mg L⁻¹ TN in the effluent, although the TN removal was limited at ≥20 °C. The mono-exponential regression for BOD and TN (≥20 °C) estimated that an HRT of 21 h could meet the Japanese effluent quality standards of BOD and TN. Calculation of the total energy recovered via current generation and energy consumed by aeration suggested an energy consumption of 0.22 kW h m⁻³. Decreasing the aeration rate and HRT in the reactor would further reduce energy consumption and increase energy production.