低温条件下基于TMVOC的土壤气相抽提技术数值模拟

为研究低温条件下土壤气相抽提技术对包气带中苯系物的去除效果、解决修复技术有效性评估等难题，基于TMVOC模型模拟砂箱试验，从浓度梯度、相间转化、饱和度变化等方面分析土壤气相抽提技术对污染物空间分布规律的影响机理.结果表明，TMVOC模拟苯系物浓度的计算值与试验测量值的拟合效果较好；低温条件下，砂箱土体中苯、甲苯、乙苯、邻二甲苯的去除率分别为89.8%、71.3%、29.7%、14.4%.两次抽提过程中，苯在"气-液-NAPL（non-aqueous phase liquid）"三相中的质量均减少，减少比例近似为2:7:1，苯在液相中的质量减幅最大；在间歇期，苯由"NAPL相"以近似3:7的比例向"气、液"两相运移.在砂箱土体上部和中部NAPL相饱和度保持为0，"气-液"两相共存，间接表明苯系物在"气-液"两相间发生运移；在砂箱土体底部污染源附近"气-液-NAPL"相共存，间接表明苯系物在"气-液-NAPL"相间发生运移，抽提作用使得气相与液相饱和度升高、NAPL相饱和度降低. 

Numerical Simulation through SVE Technique based on TMVOC under Low Temperature

In order to study the soil vapor extraction (SVE) technique remediation effect of BTEX contaminated vadose zone under low temperature, the SVE effect on BTEX migration mechanism was analyzed through concentration gradient, transformation among phases and saturation variation based on the TMVOC model. The TMVOC simulation results of BTEX showed that the simulation results were similar with experimental data. The SVE removal rates of benzene, toluene, ethylbenzene and o-xylene were 89.8%, 71.3%, 29.7%, and 14.4% respectively under low temperature. In two extraction processes, the mass of benzene in gas-aqueous-NAPL phases decreased, and the reduced proportion of benzene in gas-aqueous-NAPL phases was approximately 2:7:1. Most benzene mass reduction was in aqueous phase. During the intermittent period between the two extraction processes, benzene migrated from NAPL phase to gas and aqueous phase, and the distribution ratio was 3:7. In the upper and central sections of the sandbox, the NAPL phase saturation was 0, which indirectly reflected benzene migration between the gas and aqueous phase. In the bottom section of the sandbox, gas, aqueous and NAPL phase coexisted, which indirectly reflected SVE promoting BTEX migration among gas, aqueous and NAPL phase. SVE promoted an increase in the gas and aqueous phase saturation, and a decrease in the NAPL phase saturation.