利用典型双重介质物理模拟实验和有限差分方法揭示隙宽和孔隙度对TCE(三氯乙烯)挥发的定性影响,并分析根据4种经验模型计算的有效扩散系数及其对应的挥发通量的差异,同时推算非水溶相(Napl)TCE对挥发的贡献.发现由3~5mm砂石构成的透水块(P5)搭建而成含1条隙宽3mm垂向裂隙(F3)的双重介质P5F3在Napl泄漏后快速进入地下水后,“气-土”界面气相挥发通量较由2~3mm砂石构成的透水块(P3)搭建而成含1条隙宽1mm的垂向裂隙(F1)的双重介质P3F1小.将泄漏源区域附近分为源上游区、泄漏源(裂隙)区和源下游区,并比较水溶相TCE在各区域对应“气-土”界面上方挥发通量,通量大小排序是“裂隙区”>“源下游区”>“源上游区”;裂隙隙宽与孔隙块体长度比是1:150与1:50时,裂隙中水溶相TCE挥发通量分别占整体的3%与5%;Bartelt-Hunt模型对应的有效扩散系数计算的界面通量最大,最小的是Currie模型.Napl相TCE泄漏在含裂隙孔隙介质包气带中,且包气带厚度较小,Napl相TCE挥发对其关键界面通量的贡献远大于水溶相TCE;根据空气罩内气相TCE浓度与数值计算的水溶相挥发浓度之差可知该贡献可达78%以上.
Abstract
Trichloroethylene (TCE), a common chlorinated hydrocarbon and volatile organic compound (VOC), poses significant risks to environmental and human health. Its volatilization and diffusion in fractured porous media are complex and difficult to characterize. The volatilization behavior of TCE at the air-soil interface of complex dual media remains poorly understood experimentally. Simulation experiments of NAPL-phase TCE leakage in dual-media systems, combined with finite difference numerical technique, were used to qualitatively assess the influences of fracture and pore structure geometry on TCE volatilization and diffusion. The diffusional fluxes of TCE volatizedfrom the aqueous phase, calculated using effective diffusion coefficients (De) obtained from four empiricalandsemi-empirical models, werecompared. In addition, the contribution of volatilization fluxes of TCE from the non-aqueous phase liquid (NAPL)was also analyzed. We find the volatilization flux of TCE at the air-soil interface of the complex structure P5F3 constructed with permeable blocks made of 3~5mm gravel (P5) and a 3mm-aperture vertical fracture (F3) was lower than thatof structure P3F1. Comparison the TCE diffusional flux volatilized from the aqueous phase at the air-soil interface over the upstream-source, source, and downstream-source regions, thehighest vapor flux was estimated overfracture region, followed by the downstream-source region, with the upstream-source region showing the lowest flux. TCE vapor diffusional flux from aqueous phaseoverfracture region accounts for 3% and 5% of the total fluxover entire regionwhenthe ratio of fracture width to permeable block length is 1:150 and 1:50, respectively. The interface diffusional fluxbased on De from the Bartelt-Hunt model is the largest, while that from the Currie model is the smallest. The amount of vapor TCE volatized from Napl-phaseis significantly greater than that fromaqueous phase, the former may account for more than 78% of total gas-phase TCE, based on the discrepancy between the gas-phase TCE concentration measured under the sealed air chamber in the lab and the value estimated numerically from the aqueous phase alone.
关键词
含裂隙孔隙介质 /
挥发性有机物(VOC) /
双重介质 /
三氯乙烯(TCE) /
挥发通量 /
实验研究
Key words
fractured porous media /
volatile organic compounds (VOC) /
dual media /
trichloroethylene (TCE) /
volatilization flux /
experimental study
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基金
国家重点研发计划项目(2024YFC3712702,2020YFC1807102);国家自然科学基金资助项目(42207106)
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