Enhanced Treatment Of Heavy Metal Wastewater Using Conductive-based Polycrystalline Catalytic Electrode Coupled In Bioelectrochemical System

Bioelectrochemical system（BES）is a green wastewater treatment technology that can simultaneously achieve pollutant degradation and electrical energy output.The BES will spontaneously generate bioelectric energy in the process of treating organic pollutants,and the electric energy can be directly used for the recovery of heavy metal ions.However,BES still has some problems in the field of heavy metal wastewater treatment,such as low recovery efficiency of heavy metal ions,poor effluent quality,weak power generation performance of the system and high wastewater treatment costs.The choice of cathode material is the key to solving these problems.In this project,the Catalytic Electrodes was developed and technically coupled with the Microbial Fuel Cell（MFC）to construct the BES.The system has significant advantages as follows:（1）The recovery efficiency of heavy metal ions and the effluent quality have been effectively improved;（2）The electricity-generating performance of the system was enhanced using highly electrochemically catalytically active electrodes;（3）Inexpensive transition metal catalysts promote the reduction of wastewater treatment costs and economy.In the process of trying to improve the performance of BES in the treatment of heavy metal wastewater,the multifunctional electrodes were actively explored in this study.The catalytic membrane electrode not only acts as the cathode to maintain the power output of the system,but also acts as a filter medium to improve the quality of the effluent,and finally realizes the removal of organic pollutants,large particle pollutants and heavy metal ion pollutants.The self-generated electric field in the MFC can effectively reduce the surface contamination of the membrane electrode,prolong the stable operation time,and maximize the economic benefits.In this study,different catalytic electrodes were prepared from the selection of catalysts.The effect of catalytic electrodes on BES wastewater treatment performance and electricity generation performance was investigated,and the removal mechanisms and reduction paths of different types of pollutants were explored.The autogenous electroflocculation technology is tried to increase the removal efficiency of pollutants.Taking the practical application of BES as the research end point to achieve the expected goals of reducing system operating costs,expanding wastewater treatment scale,and improving effluent quality.The specific research results are as follows:（1）The carbon fiber cloth was used as the base,the mixed solution of polyvinylidene fluoride（PVDF）,polyvinylpyrrolidone（PVP）,iron powder and dimethylformamide（DMF）was used as the casting solution,and the Fe/PVDF catalytic electrode was prepared by the phase inversion method.The Fe/PVDF catalytic electrode was sequentially treated with hydrochloric acid solution and potassium permanganate solution to realize the in-situ synthesis of manganese dioxide（Mn O₂）on the surface of the catalytic electrode,and finally the Mn O₂/Fe/PVDF catalytic membrane electrode was obtained.With the catalytic membrane electrode as the system cathode and filter medium,the microelectrolysis and electroflocculation process was introduced into the coupled BES using an aluminum anode,and almost complete removal of copper ions was achieved（removal efficiency>99.9%）.The removal efficiencies of the system for pollutants such as TOC,COD,NH₄⁺-N,and TP can reach 98.2%,97.9%,94.5%,and 94.9%,respectively.The open circuit voltage of the system can reach 1.4 V,which confirms that the catalytic membrane electrode can significantly improve the power generation capacity of BES.During the experiment,the maximum power density of the system can reach 2250 m W m^-3,corresponding to a current density of 10.65 m A m^-2.The antifouling performance of the catalytic electrode under the action of an electric field was improved by 30%compared with the control group.（2）The carbon fiber cloth was used as substrate,graphene oxide,metal-organic framework HKUST-1 and Mn O₂-Fe₃O₄ nanoparticles as catalyst,PVDF and PVP as binder and pore-forming agent,GO/HKUST-1/Mn O₂-Fe₃O₄/PVDF catalytic membrane electrode was prepared.In the electrochemical performance test,the catalytic electrode exhibited excellent electrochemical redox catalytic activity.The coupling system formed by the electrode and MFC has very excellent performance in treating mixed heavy metal wastewater.The removal efficiencies of Cu²⁺,Zn²⁺,Cr₂O₇^2-,Ni²⁺in the synthetic mixed heavy metal wastewater(ion concentration:Cu²⁺,200 mg L^-1;Zn²⁺,200 mg L^-1;Cr₂O₇^2-,50 mg L^-1;Ni²⁺,30 mg L^-1)reached 99.9%,99.9%,99.7%,and 99.8%,respectively.It also has obvious advantages for the removal of other pollutants in wastewater（removal efficiency:COD,95.3%;NH₄⁺-N,99.9%;TP,95.9%）.The catalytic membrane electrode has excellent antifouling performance,the system runs continuously for 60 days without obvious blockage,and the maximum power can reach 1600 m W m^-3.（3）Mn/Mo/Co catalytic electrodes were prepared by loading cobalt,molybdenum,and manganese onto stainless steel mesh by electrodeposition,high calcination,and electrospinning.From the electrochemical analysis results,the three metal element catalysts can greatly improve the electrochemical performance of the electrode,which not only reduces the charge transfer resistance of the electrode,but also promotes the occurrence of the electro-redox reaction.In the process of using BES to treat silver-containing wastewater,the catalytic electrode can increase the removal efficiency of silver ions to 100%.During the electroreduction process,the silver is clearly visible on the electrode surface.The BES can achieve a maximum power density of 1008.2 m W m^-3 at a current density of 5.5 A m^-2,and the energy efficiency of silver ion recovery is 27.8 kg k Wh^-1.The application of BES in practical engineering is explored by combining the inflow mode of the actual wastewater treatment.In this process,the recovery efficiency of silver ions can still reach 90.2%,indicating that BES has good engineering application prospects.