Removal Of Chlorinated Hydrocarbons From Groundwater Based On Electrochemical Techniques

Chlorinated hydrocarbons are widely used as industrial feedstocks and solvents,and their leakage can not only damage the ozone layer but also have a cumulative impact on human health and the ecological environment.Both domestic and international studies have found chlorinated hydrocarbons in the groundwater of some industrial parks,where the coexistence of carbon tetrachloride?CT,CCl₄?,chloroform?CF,CHCl₃?,dichloromethane?DCM,CH₂Cl₂?and chloroethylene is common.In this paper,trichloro ethylene?TCE,C₂HCl₃?was firstly removed by electro-oxidation,then electro-reduction and electro-oxidation were carried out for CT and DCM,respectively,and DCM was finally removed by electro-activated persulfate technology.All four studies have achieved high removal results,the main conclusions are as follows:?1?Due to the higher oxidation activity of Ti electrode compared to Ti/RuO₂-IrO₂,Fe and TiO₂ electrodes,the removal of C₂HCl₃ was better when Ti electrode was used as anode material.The removal efficiency of C₂HCl₃ essentially increased with cell voltage,temperature and concentration of the electrolyte?Na2SO4?in solution,and it decreased with pH and the initial concentration of the contaminant.The assay showed that the?OH generated by this process that was mainly involved in C₂HCl₃ oxidative removal,with the removal rate of C₂HCl₃?10 mg/L?reaching approximately 97.31%at 180 min.?2?CCl₄ is difficult to remove in an electro-oxidative atmosphere,whereas it can be removed rapidly in an electro-reductive atmosphere with Fe electrode as cathode,with a removal rate of about 97.05%at 180 min.Higher initial concentrations of contaminants and pH reduced the removal efficiency of CCl₄,and it was mainly H?that exerted a dechlorination and hydrogenation effect on CCl₄ in the electro-reduction atmosphere.The main chloroplastic products of CCl₄ are CHCl₃ and CH2Cl2,where CHCl3 is removed by continued electrical reduction and CH2Cl2accumulates in reducing atmosphere.?3?Under the electro-oxidation atmosphere,the removal rate of CH₂Cl₂ is positively correlated with cell voltage,reaction temperature and electrolyte?K₂SO₄?concentration,and the initial pH of 7 is more favorable for the final removal of CH₂Cl₂.The removal rate of CH₂Cl₂?10 mg/L?in 240 min was 93.8%when the optimal parameter of energy efficiency was selected.?4?CH₂Cl₂ was oxidized by K₂S₂O₈ alone at temperatures above 30°C for initial removal,and the 180 min removal rate of CH2Cl2?10 mg/L?was 20.7%.The removal efficiency of CH₂Cl₂ by electro-activated persulfate systems increased with increasing cell voltage,while the removal of CH2Cl2 was inhibited by increasing initial concentration of contaminants and initial pH,and it was also favored by higher temperatures,with a removal rate of about 48.7%for 180 min at 15°C.The?OH and SO₄^-?in the electro-activated persulfate system can oxidatively dechlorinate CH₂Cl₂ at high speed,which is more efficient than the single oxidation effect,and it can greatly adapt to the groundwater temperature environment.