Study On Recovery Of Heavy Metals In Wastewater By Microbial Fuel Cells With Simultaneous Electricity Production

Heavy metals in wastewater are harmful to human health and natural environment.As a valuable resource,heavy metals can be recovered by microbial fuel cell(MFC)with simultaneous electricity generation.Ion exchange membrane(IEM)is an important component of a double-chamber MFC,which becomes a key factor of heavy metal recovery due to its different ion transfer mechanisms influencing MFC performance.In this study,the artificial synthesis heavy metal wastewater containing Cr(VI),Cu(II)or their mixture was prepared to systematically investigate the effects of bipolar membrane(BP),cation exchange membrane(CMI),proton exchange membrane(Nafion)and anion exchange membrane(AMI)on electricity generation and heavy metal recovery by two-chamber MFCs,and the membrane fouling during the process was analyzed in detail.The results showed that AMI achieved the highest power generation,while Nafion was the lowest.The maximum power density of AMI was 530.8 m W/m~2,which was much higher than that of Nafion(52.3 m W/m~2).BP can effectively maintain the p H value and conductivity,followed by AMI and CMI,while Nafion caused anolyte become acidic,which inhibited the respiration of exoelectrogens and thus reduced the performance of MFC.The removal of heavy metals in MFC includes cathodic reduction,adsorption on IEM and transportation from cathode to anode.When treating wastewater containing Cr(VI),the total removal efficiencies by BP,AMI and CMI were all higher than 95%.The adsorption on AMI was as high as 91.1±0.7%,leading to a serious fouling on the membrane.BP obtained the highest reduction efficiency,which can be applied to recover single heavy metal anion.When treating wastewater containing Cu(II),the total removal efficiencies of CMI and AMI were both higher than 91%,while the total removal efficiency of BP was the lowest(32.5±2.6%).AMI exhibited lower adsorption efficiency(6.1±0.6%)and higher reduction efficiency(85.5±0.4%),which can be applied to recover single heavy metal cation.When treating wastewater containing mixed Cr(VI)and Cu(II),the coexistence of Cr(VI)and Cu(II)could promote the adsorption of ions on the membrane,but their competition reduced the total removal efficiency of heavy metals.CMI had high removal and reduction efficiencies of mixed heavy metals and can be applied to recover mixed heavy metal ions.The four IEMs were all contaminated by varying degrees of chemical fouling and biological fouling.When treating Cr(VI)wastewater,the adsorption efficiency of Cr(VI)on the AMI reached 91.1±0.7%,with more microorganisms covered on the AMI facing the anode,which causing serious fouling to the membrane.