| The usage of lithium ion batteries (LIBs) has rapidly increased because nowadays, they are widely used as electrochemical power sources. One of the most serious concerns is heavy metals such as copper and cobalt ions. Conventional methods have been adopted to remove heavy metals including chemical method and electrodeposition, which have disadvantages such as secondary pollution, extensive energy consumption and substandard effluent. Bioelectrochemical systems (BESs) is normally divided into microbial fuel cells (MFCs) and microbial electrolysis cells (MECs). Self-driven MFCs-MECs system is truly environmental friendly for wastes and wastewaters treatment due to zero external energy consumption. In this study, MECs driven by MFCs was introduced for complete Cu(Ⅱ), Co(Ⅱ) and Li(Ⅰ) separation and recovery, which not only extracted energy from wastewaters through the anodes of MFCs and MEC, and in situ utilized the energy of MFC to power MEC, and thus avoided the need for external energy input in MECs, but also achieved simultaneous and complete separation of Cu(Ⅱ), Co(Ⅱ) and Li(Ⅰ) each other. In this study:(1) System performance was heavily dependent on the cathode material of MEC and cathode volumes in both MEC and MFC. Ions of Co(Ⅱ) were efficiently reduced using either TS or SSM, and CR cannot proceed this occurrence. While smaller cathode volumes in MFCs achieved appreciable Co(Ⅱ) reduction of 41.4±3.8% on the CR cathode, the highest Co(Ⅱ) reduction using TS (45.0±0.3%) and SSM (39.7±3.6%) was obtained under smaller cathode volumes in both MFCs and MECs. Sequential MFCs and MECs operation efficiently reduced Cu(Ⅱ) and Co(Ⅱ), achieving 100% and 65.3 - 72.0%, respectively with either TS or SSM. These results demonstrate cathode material of MECs and cathode volumes in both MECs and MFCs were critical for efficient Co(Ⅱ) reduction in MECs driven by MFCs. SSM was an excellent cathode material under the condition of MFCs 13 mL-MECs 13 mL.(2) Under continuous flow conditions, self-driven MFCs-MECs can achieve complete separation of Cu(Ⅱ), Co(II) and Li(Ⅰ) each other, with removal rates of 1.10 ± 0.04 mg/(L-h) for Cu(Ⅱ) in MFCs,1.01 ± 0.03 mg/(L·h) for Co(Ⅱ) in MECs and most of Li(Ⅰ) remained in effluents (HRT of 9 h and with #60 mesh size). A higher influent metal concentration of 50 mg/L Cu(Ⅱ),50 mg/L Co(Ⅱ) and 15 mg/L Li(Ⅰ) improved Cu(Ⅱ) and Co(Ⅱ) removal rates, copper and cobalt yields, and operational efficiencies including cathodic coulombic efficiencies (CEs) and anodic CEs in MFCs and MECs, as well as overall system efficiencies. However, Cu(Ⅱ), Co(Ⅱ) and Li(Ⅰ) were not able to be separated each other. A longer HRT of 12 h slightly improved Cu(II) and Co(Ⅱ) removal rates, but product yield and operational efficiencies decreased in addition to the uncomplete separation of Cu(Ⅱ), Co(Ⅱ) and Li(Ⅰ) each other. These results demonstrate mesh size of SSM as MEC cathodes, HRT and influent metal concentration were critical for complete separation of Cu(Ⅱ), Co(Ⅱ) and Li(Ⅰ) each other in self-driven MFCs-MECs under continuous flow conditions.(3) Various materials of CR, TS, SSM and copper sheet (CuS) were individually used as the cathodes of MFCs for Cu(Ⅱ) reduction over time. After 12 cycle operation (72 h), power density for CR decreased about 55% whereas Cu(Ⅱ) removal increased to 76%. In contrast and at cycle 12, TS and SSM had maximum power densities of 3.13 W/m3 and 6.46 W/m3, respectively, about 76% (TS) and 245% (SSM) improvements, compared to the controls with no copper-deposited. Different from CR, TS and SSM, CuS was heavily corroded even at cycle 1 and Cu(Ⅱ) removal was thus remarkably decreased. As a consequence, SSM as the cathodes of MFCs was an alternsative candidate for efficient Cu(Ⅱ) removal and electricity generation in MFCs for a comparatively long term operation. |
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