Biocathode MECs Driven By MECs For Cu(Ⅱ) And Co(Ⅱ) Recovery And Inhibitor Effects

Copper and cobalt are extensively used in microelectronic fields such as lithium ion batteries. Recovery of copper and cobalt from spent lithium ion batteries is thus one of the primary objectives in recycling these wastes due to the shortage of natural ores and environmental considerations. Previous tests have primarily examined Cu(Ⅱ) and Co(Ⅱ) removals in microbial electrolysis cells (MECs) with abiotic cathodes and driven by microbial fuel cell (MFCs). However, Cu(Ⅱ) and Co(Ⅱ) removal rates in this system were still slow. Therefore, it is necessary to develop a new self-driven system of biocathode MECs driven by MFCs for efficient Cu(Ⅱ) and Co(v) removal. Electron transfer mechanisms in biocathodes particularly relationships among cathode electrode, electrochemically active microorganism, and final electron acceptor are still unclear. Considering the potentially substantial effects of either initial Cu(Ⅱ) concentrations or inhibitors of rotenone and 2,4-dinitrophenol (2,4-DNP) on system performance of Cu(Ⅱ)-reduced biocathode MFCs, either changes in initial Cu(II) concentration or addition of rotenone and 2,4-DNP are expected to clarify the relationships among cathode electrode, electrochemically active microorganism, and final electron acceptor of Cu(Ⅱ), based on the isolated bacteria. Main results include:(1) Biocathodes MECs driven by MFCs enhanced removal rates of 6.0±0.2 mg/(L-h) for Cu(Ⅱ) at an initial concentration of 50 mg/L and 5.3 ± 0.4 mg/(L-h) for Co(II) at an initial 40 mg/L,1.7 and 3.3 times as high as those in MECs with abiotic cathodes driven by MFCs. Higher Cu(Ⅱ) concentrations and smaller working volumes in the cathodes of MFCs further improved removal rates of Cu(Ⅱ) (115.7 mg/(L-h)) and Co(Ⅱ) (6.4 mg/(L-h)) with concomitantly achieving hydrogen generation (0.05 ± 0.00 mol/mol COD). Bacterial community on the biocathodes was mainly composed of Proteobacteria (67.9%), Firmicutes (14.0%), Bacleroidetes (6.1%), Tenericutes (2.5%), Lentisphaerae (1.4%), and Synergistetes (1.0%). This study provides a beneficial attempt to achieve simultaneous enhanced Cu(Ⅱ) and Co(Ⅱ) removal, and efficient Cu(Ⅱ) and Co(Ⅱ) wastewaters treatment without any external energy consumption.(2) Four electrochemically active bacteria were isolated from mixed-culture Cu(II)-reduced biocathode MFCs, identified and tentatively termed as tenotrophomonas maltophilia JY1, Citrobacter sp. JY3, Pseudomonas aeruginosa JY5 and Stenotrophomonas sp. JY6. Either increase in initial Cu(Ⅱ) concentration or addition of inhibitors (rotenone or 2,4-DNP) had no effects on circuit current and Cu(Ⅱ) reduction rate for both Stenotrophomonas maltophilia JY1 and Pseudomonas aeruginosa JY5. This result illustrated the irrelevance of these two bacteria to the electron transfer between cathode electrode and final electron acceptor of Cu(Ⅱ). The addition of each inhibitor (rotenone or 2,4-DNP) could not lead to the decrease in circuit current and Cu(Ⅱ) reduction for Citrobacter sp. JY3, implying there was no involvement of intracellular electron transfer into the electron transfer between cathode electrode and electron acceptor of Cu(Ⅱ). However, for Stenotrophomonas sp. JY6, intracellular electron transfer was closely related with electron transfer between cathode electrode and electron acceptor of Cu(Ⅱ). These results demonstrated the dependency of relationships among cathode electrode, bacteria and electron acceptor of Cu(Ⅱ) on the isolated bacteria from mixed-culture Cu(Ⅱ)-reduced biocathode MFCs.