Dependency of migration and reduction of mixed Cr2O72−, Cu2+ and Cd2+ on electric field, ion exchange membrane and metal concentration in microbial fuel cells

Metallurgical microbial fuel cells (MFCs) are holding great promise for metal waste and wastewater treatment with simultaneous metal recovery and separation, where ion exchange membranes (IEMs) are used as separators between the CH3COO− and PO43− filled anodes, and metal ions filled cathodes. How these ions migrate across the IEMs with simultaneous metal reduction on the cathodes, however, is not yet fully understood. Therefore, two proton exchange (N117 and N212), a cation exchange (CEM) and an anion exchange (AEM) membranes were studied to evaluate the suitability of IEMs as separators of MFCs for reduction of mixed Cr2O72−, Cu2+ and Cd2+ at each metals of either 10 mM or 1.0 mM, as a model for a wide variety of metals in practical electroplating and mining industries. It was found that circuit current directed reduction of more metals on the cathodes with less migration across the IEMs, compared to the more metal transport in the absence of circuit current. CEM was the most beneficial for less cross-over of Cr2O72− from one side, and CH3COO− and PO43− from the other side, despite slight more migration of Cu2+ and Cd2+ than that of AEM. A higher metal concentration with each of 10 mM led to more metal transport through the IEMs than that of 1.0 mM. This study demonstrates the dependency of migration and reduction of Cr2O72−, Cu2+ and Cd2+ on electric field, type of IEM and metal concentration, and thus provides a new insight into metallurgical MFCs for remediating Cr2O72−, Cu2+ and Cd2+ co-contamination with simultaneous metal recovery.