Study On The Simultaneous Generation Of Electricity And Recovery Of Heavy Metals By Shewanella Putrefaciens

With the speeding up of industrialization,heavy metal pollutions are becoming more and more serious,which are not only destroying the natural environment,but also threatening to human health.Thus,their management has attracted extensive attentions worldwide.In this field,treatment for water heavy metal pollutions is essential.However,present methods are limited by high energy consumption,high costs and secondary pollution.Therefore,in this work,a microbial treatment method based on Shewanella putrefaciens（S.putrefaciens）was proposed,which is a novel approach with low energy consumption,low costs and environmental friendliness.Firstly,the removal rate of Co²⁺by S.putrefaciens from water solution was studied.The removal rate was characterized to be 58.37±6.45%by ICP under the optimal conditions.In addition,the recovered product was characterized by FTIR,XRD,TEM and XPS,and identified as Co（Ⅱ）/Co（Ⅲ）PO₄@EPS.Then,its catalytic capacity for the reductive degradation of4-nitrophenol（4-NP）was investigated.The results show that the recovered heavy metal products can effectively catalyze the reduction of 4-NP by Na BH₄,that 86.47%4-NP can be catalytically transformed 100μL 2mg·L^-1 Co（Ⅱ）/Co（Ⅲ）PO₄@EPS within 18 min.Hence the material is hopeful to be practically used.Furthermore,S.putrefaciens was applied for simulated wastewater treatment,and the removal rates of Co²⁺,Mn²⁺and Ni²⁺reached 62.44±3.13%,71.59±2.71%and 67.64±2.44%,respectively.Moreover,the products recovered from simulated wastewater showed much better catalytic ability,that the conversion rate of 4-NP reached 86.94%within 80 s,more than the rate of Co（Ⅱ）/Co（Ⅲ）PO₄@EPS in 18 min.According to the TEM observation of product structure,the improvement of Co²⁺treatment effect and catalytic performance were attributed to the formation of nanoscale recovered products in bacterial cells.Subsequently,this work built a double-room microbial fuel cell based on S.Putrefaciens,and its power generation was studied.The results show that the maximum output voltage of the device is 371.6 m V,and the corresponding maximum power is 1.436 W·m^-2.The coulomb efficiency was calculated to be 22.02%in combination with the change of Chemical Oxygen Demand（COD）value and the output voltage.Further,fluorescence microscopy and electrochemical characterization techniques were used to explore the behavior of S.putrefaciens and the change of electrochemical properties of the battery in the reaction process.The results demonstrate that electrical activity of S.putrefaciens was accompanied by the generation of electroactive extracellular polymers,which promoted the electron transfer between the cell and the electrode and contributed to the electrical output.Moreover,this study investigated the electrical activity of S.putrefaciens in the anode region.It is inferred from the results that,at the beginning of the reaction,S.putrefaciens generated electrons by metabolizing substrates and formed electrically active films on the electrode to promote electron transfer.As the reaction continued,the biofilm on the electrode tended to mature and the battery voltage output tended to be stable.However,when the activity of S.putrefaciens decreased,the internal impedance of the cell increased rapidly,impeding the output of power.Finally,combining the abilities of power generation and Co²⁺recovery of S.putrefaciens,this study designed a bifunctional microbial fuel cell to simultaneous generate electricity and recover heavy metal based on S.Putrefaciens.Although the introduction of Co²⁺adversely affected S.Putrefaciens,the maximum output voltage of the device still reached 364.5 m V,and the corresponding maximum output power was 1.38 W·m^-2.Meanwhile,the coulomb efficiency increased to 38.45%due to the reduction of total COD variation.The removal rate of Co²⁺by S.Putrefaciens.was 39.86%,and Co（Ⅱ）/Co（Ⅲ）PO₄@EPS recovered in the anode area also improves the electrochemical performance of microbial fuel cell.In addition,pollution ions(Cu²⁺)commonly found in industrial wastewater were added to the cathode solution in this study,which was recovered by the electric energy generated by S.Putrefaciens.Cyan solid products were successfully recovered from the cathode and were identified as Cu₂（OH）₂CO₃containing Cu（0）by XPS characterization.In this study,the microbial fuel cell based on S.Putrefaciens can realize both goals of electricity generation and heavy metal recovery simultaneous,providing a novel approach with lower consumption,low cost and environmental friendliness for the treatment of heavy metals in water.It also provides a reference for further research.