Harvesting electricity from benzene and ammonium-contaminated groundwater using a microbial fuel cell with an aerated cathode

Abstract

Groundwater contaminated with benzene and ammonium was continuously treated using a microbial fuel cell (MFC) with an aerated cathode and a control without aeration at the cathode. Benzene (∼15 mg L⁻¹) was completely removed in the MFC of which 80% disappeared at the anoxic anode. Ammonium (∼20 mg L⁻¹) was oxidized to nitrate at the cathode, which was not directly linked to electricity generation. The maximum power density was 316 mW m⁻³ NAC at a current density of 0.99 A m⁻³ normalized by the net anodic compartment (NAC). Coulombic and energy efficiencies of 14% and 4% were obtained based on the anodic benzene degradation. The control reactor failed to generate electricity, and can be regarded as a mesocosm in which granular graphite was colonized by benzene degraders with a lower benzene removal efficiency compared to the MFC. The dominance of phylotypes affiliated to Chlorobiaceae, Rhodocyclaceae and Comamonadaceae was revealed by 16S rRNA illumina sequencing in the control and the MFC anode, presumably associated with benzene degradation. Ammonium oxidation at the cathode of the MFC was mainly carried out by phylotypes belonging to the Nitrosomonadales and Nitrospirales. Compound specific isotope analysis (CSIA) indicated that benzene degradation was initially activated by monohydroxylation with molecular oxygen. The intermediates of the benzene degradation pathway were subsequently oxidized accompanied by transferring electrons to the anode, leading to current production. This study provided valuable insights into the application of MFCs to treat groundwater contaminated with petroleum hydrocarbons (e.g. benzene) and ammonium.