Experimental Study On The Remediation Of Volatile Chlorinated Hydrocarbons Polluted Low Permeability Vadose Zone Soil By Thermal Oxidation Soil Vapor Extraction

In the organic polluted soil,volatile chlorinated hydrocarbons?VCHs?pollution is widespread.Soil vapor extraction?SVE?is often used to repair the VCHs polluted soil,but for the low permeability vadose zone soil,the effect of conventional SVE is poor.This paper is based on a chemical site restoration project in Northeast China,aiming at the low permeability aeration zone soil polluted by VCHs 1,2-dichloroethane?1,2-DCA?,a thermal oxidation SVE system was designed.The heat conduction heating and oxidation-adsorption coupling method were used to strengthen the SVE technology for indoor simulation experiment,and the removal rule of target remediation pollutants under different conditions was studied.Through the research of this paper,the main results and conclusions are as follows:?1?The soil type of the aeration zone in the study area is mainly silty clay,with an average moisture content of 24.27%,a bulk density of 1.24 g/cm³,and a porosity of51.73%.It is mainly composed of clay and amorphous minerals,accounting for 63%.The soil particle size is mainly distributed in the range of 10.00-50.00?m,with an average organic content of 8.75%.The main pollutants are petrochemical organic compounds,and the main pollutants exceeding the standard are 1,2-DCA,its highest content is 11.40 mg/kg,and the coexisting pollutants are trichloroethylene?TCE?and p-dichlorobenzene?PDB?.?2?In the SVE experiment,the effects of different moisture content,extraction rate and organic matter content on the removal efficiency of 1,2-DCA were investigated.On this basis,the removal rule of 1,2-DCA at different sampling locations was analyzed.Under the conditions of 15%moisture content,2.26%organic matter content,5L/min extraction rate,6.0 cm from the sampling point to the extraction well and 12.5±1.0 cm sampling depth,the removal rate of 1,2-DCA can reach the maximum average value of80.57%.Under the set experimental conditions,the influence of the increase of moisture content on the removal of 1,2-DCA is bidirectional,that is,increase first and then decrease;the increase of extraction rate can effectively improve the removal rate;the increase of organic matter content can inhibit the increase of removal rate;with the increase of sampling depth,the removal rate of 1,2-DCA increases first and then decreases;with the increase of distance from extraction well,the time for the removal rate to reach the stable period increases,but at the later stage of the stable period,the removal rate of each point has little change.?3?In the heat conduction enhanced SVE experiment,heat is transferred by conduction fluid,and the removal rule of organic matter with the change of moisture content and temperature was analyzed at different sampling distance.For 1,2-DCA,the best experimental conditions are that the temperature of the central heating well is 80?,the water content is 5%,and the sampling point is 3.0 cm away from the central well,the average removal rate can reach 95.48%,which is 42.92%higher than that of the normal temperature SVE experiment.The increase of the temperature of the central heating well can effectively improve the removal rate of 1,2-DCA;however,the increase of the water content does not have a simple linear correlation with the peak value corresponding to the temperature of each sampling point in different wells;the further away from the central well,the lower the removal rate of 1,2-DCA.For the three coexisting organic compounds,1,2-DCA,TCE and PDB,the water content is set to25%,the best experimental conditions are still under the conditions of 80?central heating well temperature and 3.0cm from the sampling point to the central well.The average removal rates of 1,2-DCA,TCE and PDB in stable period were 92.05%,89.96%and 63.07%,respectively.Temperature still plays an important role in the removal of organic matter,and it is also affected by water content and organic matter properties.?4?In the experiment of thermal oxidation SVE,through heating conduction fluid and preparing adsorption oxidation material with volcanic slag as substrate,the effect of temperature,particle size of volcanic slag,type of oxidant and the proportion of adding on 1,2-DCA gas removal was investigated.The temperature rise of central heating well can obviously increase the concentration of extracted gas;when the temperature of the central heating well is 80?,0.1⁰.25 mm size volcanic slag prepared by 20%Na₂S₂O₈ has the best adsorption and oxidation effect on the gas phase1,2-DCA.