Does Water Content or Flow Rate Control Colloid Transport in Unsaturated Porous Media?
Does Water Content or Flow Rate Control Colloid Transport in Unsaturated Porous Media?
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DOI：
10.1021/es404705d
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发表时间：
2014-04-01
影响因子：
11.4
通讯作者：
Harsh, James B.
中科院分区：
文献类型：
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作者：
Knappenberger, Thorsten;Flury, Markus;Harsh, James B.
可移动的胶体在污染物在土壤中的运移中起着重要的作用：许多污染物以胶体形式存在，胶体可以促进其他不可移动的污染物的运移。在非饱和土壤中，除其他因素外，胶体运移受含水量和流速的影响。我们的目的是确定水含量或流速对胶体运输更重要。在不同含水量(有效含水饱和度s -e为0.1 ~ 1.0,s -e = (theta - theta(r))/(theta(s) - theta(r)))和流速（孔隙水速度nu为5和10 cm/min）的稳态流动条件下，通过带负电荷的聚苯乙烯胶体（直径为220 nm）通过非饱和填砂柱。在我们的实验中，含水量是主要因素。胶体输运随含水量的降低而降低，当含水量低于临界含水量（S-e < 0.1）时，胶体输运受到抑制，胶体在水膜中被拉伸。钟摆环和水膜厚度的计算表明，只有当钟摆环相互连接时，胶体才能运动。在二次能最小值处，流速影响胶体的保留，流速越大，捕获的胶体越少。这些结果证实了水含量和流速对非饱和多孔介质中胶体运移的重要性，并突出了水含量的主导作用。
Mobile colloids can play an important role in contaminant transport in soils: many contaminants exist in colloidal form, and colloids can facilitate transport of otherwise immobile contaminants. In unsaturated soils, colloid transport is, among other factors, affected by water content and flow rate. Our objective was to determine whether water content or flow rate is more important for colloid transport. We passed negatively charged polystyrene colloids (220 nm diameter) through unsaturated sand-filled columns under steady-state flow at different water contents (effective water saturations S-e ranging from 0.1 to 1.0, with S-e = (theta - theta(r))/(theta(s) - theta(r))) and flow rates (pore water velocities nu of 5 and 10 cm/min). Water content was the dominant factor in our experiments. Colloid transport decreased with decreasing water content, and below a critical water content (S-e < 0.1), colloid transport was inhibited, and colloids were strained in water films. Pendular ring and water film thickness calculations indicated that colloids can move only when pendular rings are interconnected. The flow rate affected retention of colloids in the secondary energy minimum, with less colloids being trapped when the flow rate increased. These results confirm the importance of both water content and flow rate for colloid transport in unsaturated porous media and highlight the dominant role of water content.