| The process of material transfer and energy flow between microorganisms and the outside world is of great significance for the remediation of chromium pollution in water bodies.Both the interactions between microbial communities and the inorganic environment have great potential for environmental application.Direct or indirect use of microorganisms for environmental remediation is one of the most important research topics in environmental geochemistry.Based on the frontier of geology and environmental science,based on the synergistic effect between cyanobacteria and electric-producing bacteria and the principle of microbial mineralization,combined with the theory of microbial extracellular respiration,a method of cyanobacteria anode and jarosite cathode to enhance the efficiency of microbial chromium removal was proposed in this paper.To explore the effects of the above microbial metabolic processes and metabolites on the efficiency of chromium removal by MFC,evaluate the extent to which microbial activities improve the performance of MFC,and reveal the mechanism of cyanobacterial anode and jarosite cathode enhancing the efficiency of microbial chromium removal.Specific research contents are as follows:（1）Through simple device adjustment,cyanobacteria community was introduced into the MFC anode chamber,and a self-cycling MFC system for cyanobacteria anode was constructed,which effectively enhanced the ability of MFC anode to output electrons to the cathode,and improved the reduction and removal efficiency of Cr（Ⅵ）at the cathode.The polarization curve and power density curve show that compared with the ordinary MFC system,the cyanobacterial MFC has better electrochemical performance under light,the open-circuit potential increases from 477 m V to 648 m V,and the maximum power density increases from 3.87 W m-3 to 8.07 W m-3.The results of electrochemical tests showed that the cyanobacteria anode system had higher diffusion coefficient of anode substrate under light,and the charge transfer impedance of electrons formed by oxidation of substrate near the anode decreased from 13.3 kΩto1.35 kΩ,indicating that the synergistic effect of anodic algae and bacteria could effectively promote the efficiency of electron-producing microorganisms in the anode,and thus improve the electrochemical performance of the system.At the same time,the cyanobacterial anode MFC system can effectively treat Cr（Ⅵ）wastewater.The first-order kinetic constants of the cyanobacterial anode MFC system,ordinary MFC system and pure cyanobacterial control group for Cr（Ⅵ）removal under light were 0.2196 h-1,0.0607 h-1 and 0.0188 h-1,respectively.The Cr（Ⅵ）processing efficiency of cyanobacterial anode MFC system was increased by 3.6 times under light.In addition,three consecutive Cr（Ⅵ）cycle reduction experiments show that the system has a high recyclability and stability.（2）A new type of composite jarosite cathode electrocatalyst was prepared by a simple one-step complex method,which broke through the limit of single cathode material utilization at the cathode catalytic interface,effectively enhanced the utilization efficiency of electrons at the cathode catalytic interface of MFC,and improved the reduction and removal rate of Cr（Ⅵ）at the cathode.XRD and SEM show that jarosite supported by biochar can reduce the agglomeration of jarosite minerals,and make its average particle size smaller and more uniform dispersion.It is a good cathode electrocatalyst.The polarization curve and power density curve show that compared with ordinary MFC,the biochar-jarosite cathode MFC has better electrochemical performance.The open-circuit potential of the cathode MFC increases from 477 m V to 682.5 m V,the maximum power density increases from 3.87 W m-3 to12.11 W m-3,and the polarization phenomenon of the cathode is significantly weakened.The electrochemical test results show that the charge-transfer impedance of the cathode decreases from 2580Ωto 111Ω,and the double layer capacitance increases from 78.1μF to 228μF,which indicates that the composite material can effectively enhance the electron exchange capacity and electron holding capacity of the cathode,and thus improve the electrochemical performance of the system.At the same time,the biochar-jarosite cathode MFC system can efficiently treat Cr（Ⅵ）wastewater.The first-order kinetic constants of Cr（Ⅵ）removal by biochar-jarosite cathode MFC,jarosite cathode MFC,biochar MFC and ordinary MFC systems are 0.3846 h-1,0.2959 h-1,0.2382 h-1and 0.0625 h-1,respectively.Cr（Ⅵ）treatment efficiency of biochar-jarosite cathode MFC was increased by 5.2 times.In addition,three consecutive Cr（Ⅵ）cycle reduction experiments show that the system has a high recyclability and stability.（3）By coupling cyanobacterial anode and jarosite cathode to construct a joint MFC system,the anode electron output capacity and cathode electron consumption capacity of MFC were enhanced,and the reduction and removal rate of Cr（Ⅵ）at the cathode were improved.The polarization curve and power density curve show that the combined system has the best electrochemical performance compared with the cyanobacteria anode and pyrsite cathode MFC.The open-circuit potential is further increased to 713.0 m V,and the maximum power density is further increased to 14.70W m-3.The potential curve of the anode and cathode electrode shows that the polarization phenomenon of the anode and cathode of the combined system is significantly weakened.At the same time,the combined MFC system can efficiently treat Cr（Ⅵ）wastewater.The first-order kinetic constants of Cr（Ⅵ）removal were0.4480 h-1,0.3846 h-1,0.2196 h-1,0.0625 h-1 for the combined MFC,jarosite cathode MFC,cyanobacterial anode MFC and ordinary MFC,respectively.In this study,the interaction between microbial communities and the environmental effects of microbial mineralization products were explored,and the two parts of cyanobacteria anode system and pyrsite modified cathode system were studied specifically.The electrical output of the system was taken as the main evaluation index of MFC performance,and the electrochemical method was taken as the main method to improve the mechanism.Finally,the removal efficiency of Cr（Ⅵ）in the cathode chamber was used as the indicator of the extent to which the environmental properties of microorganisms were mined in MFC.The cyanobacteria-assisted anode system is a combination of algae and bacteria to improve the system efficiency from the perspective of synergistic effect between microorganisms,while the biogenic pyrsite modified cathode system is to improve the system efficiency from the perspective of biogenic environmental mineral catalyst.Finally,the two are coupled together to enhance the electrical output capacity of MFC and improve the remediation ability of Cr（Ⅵ）pollution in the MFC cathode chamber. |
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