The Efficacy And Mechanism For The Field-induced Electro-fenton Degradation Of Dimethyl Arsenic

Organic arsenic is a common pollutant and the methyl arsenic in organic arsenic to pollute the water environment has been widely reported.The common methyl arsenic includes monomethyl arsenic（MMA）and dimethyl arsenic（DMA）and so on.Dimethyl arsenic is very difficult to be removed by traditional oxidation or flocculation,and the removal efficiency of methyl arsenic from adsorbent is much lower than that of inorganic arsenic.With the development of advanced oxidation technology,the electro-Fenton method has attracted much attention due to the advantages of in situ producing H₂O₂ and its high utilization rate.In this study,the double cathode induced electro-Fenton reaction system was constructed by improving the Fe²⁺dosage in the electro-Fenton reaction and the effects of the system on DMA removal and mechanism were emphatically discussed.First,comparative study of hydrogen peroxide（H₂O₂）generated by cathodes of single and double activated carbon fibers was carried out.When the pH was between 2 and 3,the amount of H₂O₂ generated by the double cathode was almost twice than that produced by the single cathode under the same conditions.The productive process of the hydrogen peroxide（H₂O₂）electrochemically generated by single and double cathode under different current densities was compared.The results show that the H₂O₂ efficiency from double cathode was higher than that from single cathode under same current densities.In the experiment,an induction-induced Fenton system with an iron bar as the sensing anode,a RuO₂/Ti network as the anode and two activated carbon fibers as the double cathode was further constructed.Taking dimethyl arsenic（DMA）as a characteristic contaminant,the research investigated the effects of initial pH,current density and initial concentration of reactants on the removal efficiency of DMA.The results showed that when the initial pH value,current density and initial concentration of dimethyl arsenic（DMA）was 3,2mA/cm² and 5 mg/L,respectively,the dimethyl arsenic（DMA）removal rate of 94.4%was achieved after 240 minutes of induction electro-Fenton reaction.A series of methods,including XRD,SEM,TEM,FTIR,XPS and HPLC-ICP-MS and so on,were used to characterize the hydroxyl complexes flocs of iron.The results showed that there were DMA,MMA,As（III）and As（V）in the flocs,demonstrating that the DMA and its degradation products from the aqueous solution were removed by the adsorption.In the double-cathode electro-Fenton system,the released Fe²⁺from the induced iron electrode interacted with the hydrogen peroxide（H₂O₂）produced by the cathode to generate the hydroxyl radical to degrade dimethyl arsenic（DMA）into monomeric arsenic（MMA）,As（III）and As（V）.At the same time,the dimethyl arsenic（DMA）,monomeric arsenic（MMA）,As（III）and As（V）were adsorbed on the interface of the iron hydroxyl complex from the hydrolysis of ferric ion to thereby realize the efficient removal of dimethyl arsenic.Based on the above research,a continuous flow process with the DMA removal through the double cathode electro-Fenton system was constructed.The results showed that the removal of DMA reached the desired effect with residence time of 4 hours in the continuous flow process.The effect of humic acid on the process was investigated,indicating that with the increase of humic acid concentration,the removal rate of DMA decreased gradually.This study shows that the removal of DMA through the double cathode electro-Fenton system can achieve the desired results,which provides an effective treatment method for the removal of DMA in drinking water.This study also offers the theoretical basis and technical support for the removal of methyl arsenic in water supply engineering,and has practical application value.