Dependency of simultaneous Cr(VI), Cu(II) and Cd(II) reduction on the cathodes of microbial electrolysis cells self-driven by microbial fuel cells

Microbial fuel cells (MFCs) using either Cr(VI) (MFCsCr) or Cu(II) (MFCsCu) as a final electron acceptor, are stacked to self-drive microbial electrolysis cells (MECs) using Cd(II) (MECsCd) as an electron acceptor for simultaneous reduction of Cr(VI) in MFCsCr, Cu(II) in MFCsCuand Cd(II) in MECsCdwith no external energy consumption. Titanium sheet (TS) and carbon rod (CR) as the cathodes of MECsCdare assessed for efficient system performance. MFCsCrand MFCsCuin series is superior to the parallel configuration, and higher Cd(II) reduction along with simultaneous Cr(VI) and Cu(II) reduction supports TS function as a good cathode material. Conversely, CR can not entirely proceed Cd(II) reduction in MECsCddespite of more Cr(VI) and Cu(II) reduction in the same serial configuration than either system alone. While a decrease in cathode volume in both MFCsCrand MFCsCuwith serial connection benefits to reduction of Cr(VI) in MFCsCrand Cu(II) in MFCsCu, Cd(II) reduction in MECsCdis substantially enhanced under a decrease in cathode volume in individual MFCsCrand serially connected with volume-unchanged MFCsCu. This study demonstrates simultaneous Cr(VI), Cu(II) and Cd(II) recovery from MFCsCr-MFCsCu-MECsCdself-driven system is feasible, and TS as the cathodes of MECsCdis critical for efficient system performance.