The Research About Remediation Of Volatile Organic Contaminant By Thermal Enhanced Soil Vapor Extraction

The volatile organic compound (VOC) in soil is a potential hazard that requires priority control. The target contaminants in this research is BTEX, include benzene, toluene, chlorobenzene, ethybenzene, ditoluene (o-xylene, p-xylene, m-xylene). The paper primarily focuses on studying the treatment effect of thermal enhanced soil vapor extraction (SVE) on BTEX in soil, carrying out thermal remediation experiments for BTEX and aiming at exploring a fast and efficient technology for remediation of BTEX-contaminated soil.This paper includes the following contents:(1) the nature property of the soil on site contaminated by BTEX;(2) the study of the repair process of BTEX through SVE technology;(3) the feasibility study of heat enhanced SVE—thermal desorption trial;(4) the research on thermal enhanced SVE.Analysis results of soil samples contained BTEX demonstrate that the content of BTEX in the soil is significantly high. In addition, the clay soil with high density and organic material (7%) may affect the removal efficiency of SVE.The results of SVE experiment show that the optimized pumping rate is6L/min for the thermal enhanced SVE trial; the removal efficiency on BTEX pollutants is in the following sequence:benzene> toluene> chlorobenzene> ethylbenzene> m, p-xylene> o-xylene. Such sequence clarifies that chemicals with higher molecular weight and boiling point are more difficult to be removed by SVE. The removal efficiency in different soil layers is also different. Removal efficiency is higher near extraction points and surface layer because of the formation of "preferential flow" within clayey soil.The results of thermal desorption trial indicate that:the BTEX pollutants in the soil could be removed effectively through heating; Heating target temperature range for the next step test could be set at60-80℃; Conclusion is drawn based on first-order decay model that the higher the temperature, the greater the first-order decay constant K and the higher the pollutants molecular weight, the smaller the K value.The experiment results of thermal enhanced SVE research indicate that:the temperature at the central and the edge location rises faster as the increase of heating source power. Also, higher the power of heating source causes smaller fluctuation range of the temperature in the center but greater fluctuation range of the temperature along edges. On the other hand, higher temperate increases the removal rate of organic matters in soil and thus is the preferable condition for BTEX removal. Three power scales (100W,200W,400W) are set in the study; The heating time under the three power level to achieve the removal efficiency more than90%are168.5h,122.5h and104h respectively and the corresponding energy consumption are29.45KW.h,33.5KW.h and48.8KW.h. That is to say, power has direct impact on time length required for repair. Engineering application should choose a power level in accordance with practical requirement and condition.