Kinetics Of Metal(s) Reduction In Biocathode Bioeletrochemical Systems

The increase of industrial activities and the associated waste production has intensified global environmental problems today. One of the most serious concerns is heavy metal pollution such as cobalt ions from lithium ion battery and chromium, copper and cadmium in electroplating wastewater. Conventional methods have been adopted to remove heavy metals including chemical method, physical-chemical process and bioremediation, which have disadvantages such as secondary pollution, extensive energy consumption and substandard effluent. Environmental friendly and cost-effective approaches are still in great need. Bioelectrochemical systems (BESs) normally divided into microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) which can convert organics in the anodes into chemicals and clean energy such as hydrogen, methane, and either electricity (MFCs) or at a low applied voltage (MECs). Biocathode MFCs or MECs, which use microorganisms as catalysts instead of the costly Pt catalyst has attracted much attention. Little information is available about biocathode BESs for efficient Co(II) reduction and sequential reduction of Cr(VI) in MFCs, Cu(II) in MFCs and Cd(II) in MECs.In this study,(1) Co(II) was successfully reduced and recovered from aqueous Co(Ⅱ) in biocathode MECs. The optimal operation conditions were applied voltage of0.2V, initial Co(II) concentration of40mg/L, temperature of35℃, with yields of0.502±0.005mol Co/mol COD and0.068±0.002mol CH4/mol COD. The apparent active energy required for Co(II) reduction in this biocathode MECs was26.7kJ/mol.(2) Sequential recovery of Cr(III) in biocathode MFCs (MFCscr), Cu in biocathode MFCs (MFCscu), and Cd in biocathode MECs (MECscd) was successfully achieved in this study. At an applied voltage of0.5V(MECscd), and an identical initial concentration of5mg/L, Cr(VI) in MFCscr, Cu(II) in MFCscu and Cd(II) in MECscd were reduced and recovered as Cr(III), Cu and Cd with yields of0.208±0.001mol Cr/mol COD,0.155±0.000mol Cu/mol COD,0.036±0.000mol Cd/mol COD, respectively.