Experimental Study On Removal Of Trichloroethylene From Soil By Thermally Enhanced Soil Vapor Extraction

With the rapid development of modern industry,the pollution of chlorinated hydrocarbon organic compounds to soil and groundwater is becoming more and more serious.At present,the technology of thermally enhanced soil vapor extraction is the most widely used and effective remediation technology of soil pollution.In this paper,trichloroethylene(TCE)was used as the research object to carry out the experiment of temperature distribution of soil and the experiment of the influence of heat strengthening on the permeability of soil.The law of heat distribution and the mechanism of heat transfer in soil were studied,and the effect of heat strengthening on the permeability of soil was revealed.At the same time,we designed the experiment of TCE migration in soil under the condition of thermal enhanced SVE,and explored the migration rule of TCE in soil under the condition of normal temperature and thermal enhanced and the mechanism of thermal enhanced.The conclusion is as follows:(1)By monitoring the temperature change of soil with different water content,the distribution rule and transmission mechanism of heat in soil can be revealed.The results show that the heat flux density near the heat source in soil is higher than that far away from the heat source.The heat transfer of soil will increase with the increase of heat source temperature,and this effect will decrease with the increase of heat source temperature.Appropriate amount of soil moisture can enhance the heat conduction ability of soil,but it can reduce the heating rate of soil.(2)Through monitoring the change of vacuum degree in the soil with different water content under the condition of heating extraction,the influence of heat strengthening on the change of soil permeability under the action of extraction was analyzed,It is found that Under the condition of extraction,the air permeability of air dried soil and wet soil will quickly improve and then keep stable.Under the condition of extraction,the optimization degree of dry soil and wet soil permeability increases with the increase of heating temperature.However,under the condition of heating extraction,the air permeability of dry soil becomes worse after reaching a stable state,but this phenomenon does not appear in wet soil.This shows that the main effect of heating on the permeability of wet soil is to change the soil moisture content,while that of dry soil is to change the particle size.(3)Through the establishment of normal temperature SVE system and 120 ℃thermally enhanced SVE system,the remediation effect of soil under the conditions of normal temperature and 120℃ thermally enhanced extraction,the migration rule of gas-phase TCE in soil and the mechanism of heat strengthened were explored.The results showed that the removal efficiency of TCE in soil was 99.99% at room temperature and 120℃.and 120℃ heating could improve the removal rate of TCE in the soil,make the extraction earlier and increase the remediation scope of the soil.In addition,the gas phase TCE in the soil only migrates downward in the static state,while TCE migrates upward and upward to the extraction well in the extraction process by the extraction well.The effect of heat strengthening on the gas phase TCE migration in the gas phase extraction process is mainly reflected in the influence on the volatile rate of TCE and the change of soil permeability.