Air-cathode desalination cells for simultaneous wastewater treatment, brackish water desalination, and power generation

There is a growing need for low-energy desalination technologies to treat brackish water due to increasing water and energy constraints. This study investigates the use of an air cathode microbial desalination cell (AMDC) for simultaneous wastewater treatment, brackish water desalination, and electricity generation. The AMDC consisted of three chambers—anode, desalination, and cathode—with volumes of 2833 mL, 1416 mL, and 2833 mL, respectively. An anion exchange membrane (AEM) and a cation exchange membrane (CEM) separated the anode–desalination and desalination–cathode chambers, respectively. Both the anode and cathode electrodes were graphite plates (90 mm × 90 mm × 3 mm). The cathode chamber was aerated using an air pump. Four batch runs were conducted with varying synthetic anolyte COD concentrations and total dissolved solids (TDS) levels in the desalination chamber. In Run 1, the AMDC operated for 19 days in open-circuit voltage (OCV) mode to reach steady state, followed by 11 days in closed-circuit voltage (CCV) mode. The polarization curve for this run showed a peak power density of 5.8 mW/m² and a current density of 24 mA/m², with an internal resistance of 643 Ω. In Runs 2–4 the AMDC was operated in CCV mode using an external resistance of 500 Ω to evaluate electricity generation, anolyte COD removal, and brackish water TDS reduction. Run 3 showed the highest performance, with a peak current density of 25.06 mA/m², a power density of 5.087 mW/m², and a maximum COD removal efficiency of 45.04%. Coulombic efficiency (CE), defined as the fraction of electrons recovered as current from the substrate, was 1.6%, 3.3%, and 3.99% for Runs 2, 3, and 4, respectively. The highest TDS removal efficiency (27.7%) was also observed in Run 3.