Effect Of Ion Exchange Membrane On Recovery Of Mixed Cd(?), Cu(?) And Cr(?) In Bioelectrochemical Systems

Bioelectrochemial systems (BESs) is divided into microbial fuel cells (MFCs) and microbial electrolysis cells (MECs), both of which can convert chemical energy in organics or inorganic matter into clear energy (electricity, hydrogen and so on). Typical MFCs is composed of cathode and anode chambers, and separator of membrane. Reduction of heavy metals on the cathodes can provide an effective strategy for simultaneous heavy metal recovery in the cahtodes and organic wastes treatment in the anodes of BESs. While multiple heavy metals including Cr(?), Cu(?) and Cd(?) have been individually or mixed explored in BESs using anion exchange membrane (AEM), cation exchange membrane (CEM), various types of Nafion membrane, or bipolar membrane, systematically exploring effects of different ion exchange membranes on recovery of mixed metals of Cr(?), Cu(?) and Cd(?) in BESs is scarcely reported. In this study, membranes of one CEM, one AEM and two types of Nafion were used in BESs for recovering mixed Cr(?), Cu(?) and Cd(?). Results in this study will provide a strategy for effective recovery of mixed Cr(VI), Cu(?) and Cd(?) on the cathodes with simultaneous organics treatment on the anodes of BESs(1) All the four membranes exhibited higher metal transport under open circuit conditions (OCCs) than that in closed circuit conditions (CCCs). Nafion 212 achieved the most metal transport than the rest three membranes under OCCs, reaching a Cu(?) transport of 29.1 ± 0.2% in an initial each metals of 10 mM at an operation time of 96 h,5.3 times as high as that in CCCs. (2) A decrease in initial metal concentrations similarly increased metal transport through all of the four membranes. AEM achieved the highest metal transport, reaching a Cr(VI) transport of 5.8 ± 0.8% in an initial each metals of 1.0 mM at an operation time of 96 h,1.9 times as high as that in 10 mM. (3) All of the four membranes exhibited higher transport of anions in the anodes to the cathodes in OCCs than those in CCCs, reaching the highest CH3COO- transport for AEM, as high as 1.3 times of that in CCCs. (4) Membrane performance decreased with the prolonged operation time, from an initial 360 mW/m2 to 30 mW/m2 at 90 days, a decrease of 78.9%. EIS(Electrochemical impedance spectroscopy) analysis demonstrated the increase in internal resistance, from an initial 2.4 ? to 19 ?, as high as 6.2 times of the new ones. Membrane rinse restored some degree of membrane performance, reaching the best for Nafion 212 with a 95% of the initial power density.