Utilization of Copper (II) Wastewater for Enhancing the Treatment of Chromium (VI) Wastewater in Microbial Fuel Cells

The effect of copper (II) wastewater addition on the treatment of chromium (VI) wastewater in dual-chamber microbial fuel cells (MFCs) was investigated for different Cr(VI)/Cu(II) concentration ratios (2:1, 1:1, 1:2, 1:4) and external resistances (10, 500, 1 000, 2 000 Ω). The results demonstrated that the addition of Cu(II) and Cr(VI) into the cathode chamber of MFCs could enhance the Cr(VI) removal efficiency. The Cr(VI) removal efficiency increased with the increase in the Cr(VI)/Cu(II) concentration ratio. The Cu(II) on the Cr(VI) removal efficiencies increased with the decrease of external resistance. The highest Cr(VI) removal efficiency achieved was 91.00% in MFC at the Cr(VI)/Cu(II) concentration ratio of 1:4 and external resistance of 10 Ω, which was 132.57% higher than the MFC with Cr(VI) only (39.13%). The scanning electron microscopy with coupled energy dispersive spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS) analyses of the cathode electrode at the end of the experiments indicated that Cr(VI) reduced to non-conductive Cr(III) deposits (Cr₂O₃) on the cathode electrode, resulting in cathode deactivation which blocked the electron transfer. However, the addition of Cu(II) could improve the electrical conductivity of the cathode due to its conductive reduzates (copper and Cu₂O) on the cathode which could reduce the cathode deactivation and subsequently enhance the Cr(VI) removal efficiency.