Study On Fouling Mechanism And Fouling Control Of Electrode In Capacitive Deionization Desalination System

Capacitive deionization(CDI)as a new type of desalination technology has broad application prospects for water treatment due to its low energy consumption,convenient operation,and low environmental impact.However,the actual water body is a complex system that contains not only inorganic ions that can be efficiently removed by CDI,but also organic ions and inorganic ions that may cause CDI fouling and scaling.Therefore,this paper selected natural organic matter and iron ion to study the fouling and scaling in CDI system.The paper examined the effect of natural organic matter(Humic acid and Bovine serum albumin)on CDI performance.Through batch experiments,organic matter reduced the desalination performance of CDI system by 60%,and the increase of organic matter concentration further reduced the desalination performance of CDI.Combined with the distribution of organic matter in the CDI system,the decrease in CDI performance was mainly due to the irreversible adsorption of organic matter on the electrode.The desorption amount only accounted for less than 20% of the adsorption amount,which caused the accumulation of organic matter on the CDI electrode.Meanwhile,through pore size structure,electrochemical impedance spectroscopy and cyclic voltammetry analysis,the organic matter attached to the electrode caused the reduction of electrode adsorption sites,the increase in the resistance of the CDI system and the decrease in the capacitance of the CDI system,thus hindering the diffusion and accumulation of ions in the CDI system,resulting in decreased CDI desalination performance.During the operation of CDI,iron ions migrate to the negative electrode of CDI under the action of electric field and caused scaling on the negative electrode.The results of Raman spectroscopy,X-ray photoelectron spectroscopy and X-ray diffraction showed that the main component of iron scale on negative electrode was ferric oxide,which was the product of the reaction of iron ion with oxygen in water.Combining with the transformation law of iron ions in the CDI system,the iron scale produced could not be effectively removed during the discharge phase,which was tightly combined on the electrode,causing the scale fouling of the CDI system.The results of electrochemical analysis showed that the deposition of iron scale increased the resistance of the CDI system by about 26%,hinder the migration of ions in the pore of the electrode and the formation of electric double layer,resulting in the decrease of desalination performance and charge efficiency of CDI system.In addition,when there were organic compounds in the water,the scaling amount of iron ions on the CDI electrode decreased,and the drop amount even reached 70%,which was due to the formation of iron-containing flocs caused by the coagulation between organic matter and iron ions.However,the adsorption of organic matter on the electrode led to a more serious decline in the performance of CDI.According to the previous research on CDI organic fouling,powdered activated carbon(PAC)was used as a pretreatment to alleviate the organic fouling of CDI.PAC removed organic matter that could be adsorbed by the electrode in the water in advance,reduced the accumulation of organic matter in the CDI system(the amount of deposition was reduced by 40%),and alleviated the organic fouling of CDI.Meanwhile,the effect of PAC entering the CDI system on the performance of the CDI system was investigated.The results of organic matter removal and electrochemical analysis showed that compared with the removal of PAC,entering the CDI system could further reduce the accumulation of organic matter on the electrode and enhance the migration of ions in the system,thereby improving the performance of the CDI system.In addition,by comparing different types of PAC,the PAC with the same material as the CDI electrode had the best mitigation effect on organic fouling,because the removal of organic matter was affected by surface functional groups.In addition,the mitigation effect of ion exchange membranes on iron ions scale was affected by the initial concentration of iron ions.At low concentrations,it could effectively alleviate the scaling fouling of iron ions by preventing the scaling of iron ions on the electrode.However,at high concentrations,due to the adsorption of iron flocs in the solution by the anion exchange membrane,the CDI system deposited more iron ions,which intensified the degradation of CDI performance.This paper systematically studied the organic fouling and scaling fouling in the CDI system,and used PAC pretreatment to alleviate organic fouling of CDI system,providing technical support for the stable operation of CDI.