Study On The Efficiency And Mechanism Of Pollutant Removal By Electrocoagulation System Based On Bipolar Electrodes

Electrocoagulation has the advantages of high efficiency,wide range of pollutants removal,simple equipment operation and maintenance,easy to realize automation and so on.It has become an effective method for the treatment of suspended particles,soluble inorganic pollutants and organic pollutants in wastewater.However,the immature design of the electric flocculation reactor and the high energy consumption and treatment cost seriously limit its large-scale practical application.Therefore,it is very important to optimize the design of the electrocoagulation reactor to reduce energy consumption and improve efficiency for promoting the large-scale application of the electrocoagulation system.In this paper,a new type of electrocoagulation system based on bipolar electrode is constructed,and its basic characteristics,application performance and related mechanisms are studied.The main research contents are as follows:First,in view of the complicated operation and maintenance of the reactor caused by the wire/ohm connection of the sacrificial electrode in the electrocoagulation system,a new electrocoagulation system with graphite plate electrode as the driving electrode and sacrificial iron/aluminum electrode as the bipolar electrode was constructed.The redox reaction on bipolar Fe/Al electrode is driven by electric field,which eliminates the wire/ohm connection problem of sacrificial electrode.The effects of the placement angle(0,45,90),the number(one,two,three)and the geometry(rectangular,H-type,T-type)on the performance of bipolar iron/aluminum electrodes were discussed.The simulation results based on COMSOL multiphysics software show the effects of different placement angles and different number of bipolar electrodes on the distribution of current and electric field in the solution.The results show that electrochemical dissolution rate of bipolar Fe/Al depends more on its geometry than on its electrochemical parameters,which provides theoretical reference and potential application mode for large-scale application of the system.Second,based on the construction of an electrocoagulation reactor with twodimensional electrode system and bipolar electrode,the performance for treating actual municipal wastewater was discussed.The effects of different combinations of bipolar iron/aluminum electrodes placed horizontally on the removal efficiency of turbidity,total organic carbon(TOC),total nitrogen and total phosphorus were analyzed.The resultsshow that application of two bipolar Fe/Al electrodes can increase the TOC removal rate by 22.7%,and the total phosphorus removal rate by 1.9 times.Specially,the energy consumption of TOC removal process is reduced by 53.9%,and that of total phosphorus removal process is reduced by 75.3%.The application of bipolar electrode in electrocoagulation system not only improves the efficiency of pollutant treatment,but also reduces the energy consumption.It has theoretical significance for optimizing the design of electroflocculation reactor and promoting its practical application.Third,a novel system of electrocoagulation coupling electro-Fenton based on bipolar iron electrode was constructed to remove the antibiotic sulfonamide.Humic acid,a natural organic compound,was used as chelating agent to complexate with Fe(II)/Fe(III)to inhibit the formation rate of insoluble iron hydroxide precipitation in the system.The three-dimensional fluorescence spectrum(FEEM)of humic acid in solution and Fourier infrared spectrum(FTIR)of humic acid in sediment were studied.The results show that the structure of humic acid is stable in the electrocoagulation/electro-Fenton coupling system.The intermediate products produced during the oxidative degradation process of sulfanilamide were determined by liquid chromatography-mass spectrometry(LC-MS/MS),and the possible oxidative degradation path of sulfanilamide in the electrocoagulation/electricFenton coupling system based on bipolar iron electrode was given.Based on bipolar iron electrode,the electrocoagulation coupling electro-Fenton system constructed in this paper shows the excellent performance and potential application value for degrading the refractory organic pollutants,and provides practical basis for optimizing the design of electrocoagulation reactor and promoting its large-scale application.