US Salinity Laboratory, USDA, ARS, Riverside, CA, USA.
J Contam Hydrol. 2012 Sep;138-139:83-92. doi: 10.1016/j.jconhyd.2012.06.007. Epub 2012 Jul 7.
Experiments were designed to better understand the causes and implications of colloid and microorganism retention hysteresis with transients in solution ionic strength (IS). Saturated packed column experiments were conducted using two sizes of carboxyl modified latex (CML) microspheres (0.1 and 1.1 μm) and microorganisms (coliphage φX174 and E. coli D21g) under various transient solution chemistry conditions, and 360 μm Ottawa sand that was subject to different levels of cleaning, namely, a salt cleaning procedure that removed clay particles, and a salt+acid cleaning procedure that removed clay and reduced microscopic heterogeneities due to metal oxides and surface roughness. Comparison of results from the salt and salt+acid treated sand indicated that microscopic heterogeneity was a major contributor to colloid retention hysteresis. The influence of this heterogeneity increased with IS and decreasing colloid/microbe size on salt treated sand. These trends were not consistent with calculated mean interaction energies (the secondary minima), but could be explained by the size of the electrostatic zone of influence (ZOI) near microscopic heterogeneities. In particular, the depth of local minima in the interaction energy has been predicted to increase with a decrease in the ZOI when the colloid size and/or the Debye length decreased (IS increased). The adhesive interaction was therefore largely irreversible for smaller sized 0.1 μm CML colloids, whereas it was reversible for larger 1.1 μm CML colloids. Similarly, the larger E. coli D21g exhibited greater reversibility in retention than φX174. However, direct comparison of CML colloids and microbes was not possible due to differences in size, shape, and surface properties. Retention and release behavior of CML colloids on salt+acid treated sand was much more consistent with mean interaction energies due to reduction in microscopic heterogeneities.
实验旨在更好地理解溶液离子强度（IS）瞬变时胶体和微生物滞留滞后的原因和影响。使用两种大小的羧基改性乳胶（CML）微球（0.1 和 1.1 μm）和微生物（噬菌体 φX174 和大肠杆菌 D21g）在各种瞬变溶液化学条件下进行了饱和填充柱实验，并对不同清洁程度的 360 μm 渥太华砂进行了实验，即去除粘土颗粒的盐清洁程序，以及去除粘土和由于金属氧化物和表面粗糙度而降低微观非均质性的盐+酸清洁程序。盐处理砂和盐+酸处理砂的结果比较表明，微观非均质性是胶体滞留滞后的主要原因。这种非均质性的影响随着 IS 的增加和胶体/微生物尺寸的减小而增加。这些趋势与计算得出的平均相互作用能（二级最小值）不一致，但可以用微观非均质性附近的静电影响区（ZOI）的大小来解释。特别是，当胶体尺寸和/或德拜长度减小（IS 增加）时，预计局部相互作用能最小值的深度会随着 ZOI 的减小而增加。因此，对于较小尺寸的 0.1 μm CML 胶体，粘附相互作用在很大程度上是不可逆的，而对于较大尺寸的 1.1 μm CML 胶体则是可逆的。同样，较大的大肠杆菌 D21g 比 φX174 在保留方面表现出更大的可逆性。然而，由于尺寸、形状和表面特性的差异，无法直接比较 CML 胶体和微生物。由于微观非均质性的减少，CML 胶体在盐+酸处理砂上的保留和释放行为与平均相互作用能更为一致。
