The trade-off between nitrogen removal and current generation in an air-cathode bioelectrochemically assisted osmotic membrane bioreactor

One of the key challenges for the application of an osmotic membrane bioreactor (OMBR) is low nitrogen removal efficiency. Herein, a novel integrated configuration by combining a single-chamber air-cathode bioelectrochemical system (BES) with an OMBR was proposed to facilitate nitrogen removal due to simultaneous nitrification and denitrification in the bioreactor, and carbon source trade-off between nitrogen removal and current generation were also investigated under different hydraulic retention times (HRTs) and draw solute (DS) concentrations. By applying sodium acetate as DS, the supplementary carbon source from reverse-fluxed solute promoted nitrogen removal (i.e., total nitrogen removal efficiency of 93.08 ± 0.93%) and current generation (i.e., current density of 110.67 ± 4.99 A/m3). Sequencing analyses revealed that nitrifying bacteria (62.7%), denitrifying bacteria (33.82%), and electrochemically-active bacteria (EAB, 4.31%) were abundant in the bioreactor. Both a long HRT or a high DS concentration improved nitrogen removal, but promoted the carbon source competition among denitrifying bacteria, EAB, and other heterotrophic bacteria. Cost balance of 0.32–1.13 $USD/kgCOD or 3.60–9.03 $USD/kgN was obtained, and a lower DS concentration was more cost-saving for the system operation. Those results have demonstrated that the proposed system could be an alternative approach for simultaneous enhancement of nitrogen removal and current generation.