Wei Zhang - Impact of dissolved organic matter on colloid transport in the vadose zone: Deterministic approximation of transport deposition coefficients from polymeric coating characteristics

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  Publication Details (including relevant citation   information): Morales, Verónica L., Zhang, Wei, Gao,   Bin, Lion, Leonard W., Bisogni Jr., James J., McDonough, Brendan   A., Steenhuis, Tammo S., Water Research,   2011, 45 (4), pp 1691-1701

  Abstract: Although numerous studies have been   conducted to discern colloid transport and stability processes,   the mechanistic understanding of how dissolved organic matter   (DOM) affects colloid fate in unsaturated soils (i.e., the vadose   zone) remains unclear. This study aims to bridge the gap between   the physicochemical responses of colloid complexes and porous   media interfaces to solution chemistry, and the effect these   changes have on colloid transport and fate. Measurements of   adsorbed layer thickness, density, and charge of DOM-colloid   complexes and transport experiments with tandem internal process   visualization were conducted for key constituents of DOM, humic   (HA) and fulvic acids (FA), at acidic, neutral and basic pH and   two CaCl2 concentrations. Polymeric characteristics reveal that,   of the two tested DOM constituents, only HA electrosterically   stabilizes colloids. This stabilization is highly dependent on   solution pH which controls DOM polymer adsorption affinity, and   on the presence of Ca+2 which promotes charge neutralization and   inter-particle bridging. Transport experiments indicate that HA   improved colloid transport significantly, while FA only   marginally affected transport despite having a large effect on   particle charge. A transport model with deposition and   pore-exclusion parameters fit experimental breakthrough curves   well. Trends in deposition coefficients are correlated to the   changes in colloid surface potential for bare colloids, but must   include adsorbed layer thickness and density for sterically   stabilized colloids. Additionally, internal process observations   with bright field microscopy reveal that, under optimal   conditions for retention, experiments with FA or no DOM promoted   colloid retention at solid-water interfaces, while experiments   with HA enhanced colloid retention at air-water interfaces,   presumably due to partitioning of HA at the air-water interface   and/or increased hydrophobic characteristics of HA-colloid   complexes.

  Address (URL): http://www.sciencedirect.com/science/article/pii/S0043135410007359