The effect of surface-active solutes on water flow and contaminant transport in variably saturated porous media with capillary fringe effects
The effect of surface-active solutes on water flow and contaminant transport in variably saturated porous media with capillary fringe effects
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DOI：
10.1016/s0169-7722(01)00206-6
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发表时间：
2002-06-01
影响因子：
3.6
通讯作者：
Smith, JE
中科院分区：
文献类型：
--
作者：
Henry, EJ;Smith, JE
降低水的表面张力的有机污染物（表面活性剂）可以对通过多孔介质的不饱和流动产生影响，因为毛细压力依赖于表面张力。我们使用了一个中等规模的二维流动池（2.44 x 1.53 x 0.108 m），填充了细硅砂来研究表面活性剂引起的流动扰动。表面活性剂溶液（7% 1-丁醇和染料示踪剂）以恒定速率应用于位于无约束合成含水层上方土壤表面的点源上，该含水层具有环境地下水流量，毛细条纹约为55 cm。玻璃板允许视觉流动和运输观察。30个测量站分别由时域反射探头和现场测湿压头的张力计组成。当表面活性剂溶液在点源处施加时，观察到瞬态流动扰动与表面活性剂溶液的推进有关。在毛细条纹上方，表面活性剂溶液的推进形成了从点源辐射的可见排水锋。在到达毛细条纹后，由于空气进入压力的降低与表面活性剂引起的表面张力的降低成正比，导致毛细条纹在点源以下局部凹陷。最后，建立了新的毛细条纹高度。抑制毛细条纹的高度与初始毛细条纹的高度乘以表面活性剂溶液的相对表面张力成正比。表面活性剂在下沉毛管条纹中的水平运移，主要受周围地下水的驱动，导致沿下降梯度方向的楔形干燥锋的传播。通过比较表面活性剂与不含表面活性剂的实验中染料的迁移情况可知，由于表面活性剂诱导的排水降低了渗透区的储存容量，当污染物溶液中含有表面活性剂时，染料突破到地下水位的时间要快两倍以上。干燥锋的广泛传播和渗透带排水对污染物突破时间的影响表明，在含有表面活性有机污染物的系统或系统中，考虑表面张力对非饱和流动和运输的影响是很重要的，在这些系统中，表面活性剂被用于修复渗透带或无约束含水层。(C) 2002 Elsevier Science B.V.版权所有
Organic contaminants that decrease the surface tension of water (surfactants) can have an effect on unsaturated flow through porous media due to the dependence of capillary pressure on surface tension. We used an intermediate-scale 2D flow cell (2.44 x 1.53 x 0.108 m) packed with a fine silica sand to investigate surfactant-induced flow perturbations. Surfactant solution (7% 1-butanol and dye tracer) was applied at a constant rate at a point source located on the soil surface above an unconfined synthetic aquifer with ambient groundwater flow and a capillary fringe of similar to55 cm. A glass plate allowed for visual flow and transport observations. Thirty instrumentation stations consist of time domain reflectometry probes and tensiometers measured in-situ moisture content and pressure head, respectively. As surfactant solution was applied at the point source, a transient flow perturbation associated with the advance of the surfactant solution was observed. Above the top of the capillary fringe the advance of the surfactant solution caused a visible drainage front that radiated from the point source. Upon reaching the capillary fringe, the drainage front caused a localized depression of the capillary fringe below the point source because the air-entry pressure decreased in proportion to the decrease in surface tension caused by the surfactant. Eventually, a new capillary fringe height was established. The height of the depressed capillary fringe was proportional to height of the initial capillary fringe multiplied by the relative surface tension of the surfactant solution. The horizontal transport of surfactant in the depressed capillary fringe, driven primarily by the ambient groundwater flow, caused the propagation of a wedge-shaped drying front in the downgradient direction. Comparison of dye transport during the surfactant experiment to dye transport in an experiment without surfactant indicated that because surfactant-induced drainage decreased the storage capacity of the vadose zone, the dye breakthrough time to the water table was more than twice as fast when the contaminant solution contained surfactant. The extensive propagation of the drying front and the effect of vadose zone drainage on contaminant breakthrough time suggest the importance of considering surface tension effects on unsaturated flow and transport in systems containing surface-active organic contaminants or systems, where surfactants are used for remediation of the vadose zone or unconfined aquifers. (C) 2002 Elsevier Science B.V. All rights reserved.