Study On The Removal Of Trichloroethylene From Soil And Groundwater By Sodium Percarbonate And Sodium Persulfate Double Oxidation System

With the rapid development of economy,environmental pollution has become an increasingly serious problem.Pollutants such as heavy metals pollutants,volatile organic pollutants and persistent organic pollutants are discharged into the environment,causing serious pollution to soil and groundwater.Trichlorethylene（TCE）has become one of the common pollutants in soil and groundwater,posing a major threat to human health and the environment.Therefore,it is urgent to remediate TCE-contaminated soil and groundwater.This paper took TCE as research object,and mainly studied the effect and influencing factors of citric acid（CA）-Fe²⁺catalyzed sodium percarbonate（SPC）single oxidation system,sodium persulfate（PS）single oxidation system,and SPC-PS double oxidation system to remove TCE from groundwater under neutral conditions.The free radicals and their contributions in the double oxidation system were determined by free radical scavenging experiments.The soil box simulation experiment of SPC-PS double oxidation system to remove TCE from soil and groundwater was carried out,in order to provide theoretical basis and technical support for the application of SPC-PS double oxidation system to actual TCE contaminated site remediation projects.The main conclusions are as follows:1.The experimental results of SPC and PS single oxidation systems showed that the chelating agent CA could improve the degradation rate of TCE in SPC and PS systems.The degradation process of TCE by SPC and PS single oxidation system conformed to the pseudo-first-order kinetic model.Considering the impact of chemicals on soil and groundwater environment and economic factors,the optimal molar ratio of SPC/CA/Fe²⁺/TCE was 15:3:6:1,and the degradation rate of TCE was 96.5%after the reaction was carried out for 180 min at a temperature of 20℃and p H of 7.The optimum molar ratio of PS/CA/Fe²⁺/TCE was 24:6:12:1,and the degradation rate of TCE was 60.4%after the reaction was carried out for 180min at a temperature of 20℃and p H of 7.The concentrations of SPC,PS,CA,and Fe²⁺all had an impact on the degradation of TCE,and too low or too high dosages of chemicals were not conducive to the degradation of TCE.2.The experimental results of the SPC-PS double oxidation system showed that the CA-Fe²⁺catalyzed SPC-PS double oxidation system could significantly increase the degradation rate of TCE in groundwater.Different ratios of SPC/PS affected the final degradation rate of TCE.The optimal molar ratio of SPC/PS/CA/Fe²⁺/TCE was 10:8:5:10:1,and the degradation rate of TCE after 180 minutes of reaction was 98.5%at a temperature of 20℃and p H of 7.And the reaction conformed to the pseudo-first-order kinetic model.The p H had a certain influence on the degradation of TCE,and the degradation rate of TCE decreased gradually with the increased of p H.When the concentration of common anions（HCO₃^-,Cl^-）in groundwater was low,the inhibitory effect on the removal of TCE in groundwater by the SPC-PS double oxidation system was small,and when the concentration of HCO₃^-,Cl^-was high,the inhibition effect on the degradation of TCE was obvious.SO₄^2-,NO₃^-had little effect on the degradation of TCE.The free radical scavenging experiment determined that the active free radicals in the SPC-PS oxidation system were HO·,SO₄·^-,O₂·^-,and HO·played a dominant role in the degradation of TCE.3.The results of the poisoning experiment showed that after 30 days of natural aging in the soil poisoning experiment,the soil at different points was polluted to varying degrees,and the pollution degree of the lower layer of soil was higher than that of the upper layer,indicating that TCE migrated downward under the action of gravity.The most polluted point was the lower soil at point C of the pollution source in the center of the soil box,with the highest concentration reaching 595.4 mg/kg.Groundwater was also seriously polluted,and the concentration of TCE in groundwater was 8796.5μg/L.4.The in-situ chemical oxidation technology of SPC-PS double oxidation system was used to remediate TCE polluted soil and groundwater.In the first 14 days of restoration,the concentration of TCE in the groundwater changed irregularly,and then the concentration of TCE decreased gradually.On the 42nd day,the concentration of TCE in groundwater decreased to 454μg/L,and then the degradation of TCE was relatively slow.By the 62nd day,the TCE concentration in the groundwater was reduced to 48μg/L,reaching the restoration target.The concentration of the lower soil at point C of the pollution source gradually increased in the initial stage of remediation,and the concentration of TCE began to decrease on the 6th day,and the concentration of TCE in the soil of the other points gradually decreased with the progress of oxidation.After 62 days of oxidation,the concentration of TCE in the soil at each sampling point reached the restoration target.GC-MS was used to detect the soil and groundwater during the remediation process.It was detected that a small amount of chloroform and dichloromethane were generated during the TCE degradation process,and no other intermediate products were detected.The p H of the groundwater did not change much during the remediation process,indicating that the SPC-PS double oxidation system had little impact on the soil and groundwater environment,and had a good application prospect.