Colloid-Filtration Theory for Vadose-Zone Systems

渗流区系统的胶体过滤理论

• 批准号: 0409174
• 负责人: James Saiers
• 金额: --
• 依托单位: Yale University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-08-01 至 2008-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0409174&HistoricalAwards=false
• 关键词: Colloid; Filtration; Theory; Vadose; Zone

0409174SaiersKnowledge of processes that govern the transport of colloid-sized particles through thevadose zone is required to predict the movement of sorbing contaminants within soils, to assessthe risks associated with the entry of pathogenic microbes into drinking-water aquifers, and toestimate the time scales for soil illuviation and soil-profile development. Colloid deposition atair-water and solid-water interfaces plays an important role in controlling the transport rates andporewater concentrations of colloids in the vadose zone. Despite the importance of colloids invadose-zone processes, a theory suitable for predicting colloid deposition in unsaturated porousmedia does not exist.The focus of this proposed research is to take steps towards filling this gap in knowledgeby defining, in a quantitative way, the fundamental relationships between colloid-depositionkinetics at air-water and solid-water interfaces and the physical properties of the soil-water-colloidsystem. These relationships will be derived through analysis of a suite of pore-scalesimulations of water flow and advective-diffusive colloid transport through partially saturatedvoid spaces. Modern models for air-water configuration in variably saturated porous media willbe used to specify the geometry of the porewater domains for which the pore-scale simulationsof colloid transport will be conducted. Regression analysis of the results of the flow-and-transportsimulations is expected to yield power-law equations that express the rate of colloidcollisions with air-water and solid-water interfaces as functions of fluid-flow velocity, colloidsize and density, porous-medium texture, and capillary pressure (which controls watersaturation). Except for the need to account for the presence of the air phase, the proposedapproach for deriving the power-law equations for colloid-interface collision rates isconceptually similar to published approaches used to formulate the colloid-filtration equationsfor water-saturated porous media.Predictions of colloid-deposition kinetics made with the power-law equations will becompared with measurements of colloid deposition made in laboratory column experiments. Inthese experiments, the sensitivity of colloid-deposition rates to variations in colloid diameter,grain-size, grain-size distribution, porewater velocity, and capillary pressure will be examined.Comparison of measured and predicted deposition rates will reveal deficiencies in the newtheory and help direct its refinement.Findings from this study will advance current knowledge of mass-transport processes inpartially saturated geologic materials and substantially improve our understanding of key mass-transferreactions that affect porewater concentrations of colloids within the vadose zone. Thisproposed research represents a first attempt at deriving and testing a colloid-filtration theory forunsaturated porous media that is needed to make quantitative inferences regarding colloidmobility in the vadose zone. Such a theory should make an important contribution towardsaddressing critical water-quality issues of national concern that are related to the movement ofmicrobial pathogens and colloid-associated contaminants through near-surface environments.

0409174Saiers 需要了解控制胶体大小的颗粒通过渗流区运输的过程，以预测土壤内吸附污染物的运动，评估与病原微生物进入饮用水含水层相关的风险，并估计土壤浸蚀和土壤剖面发展的时间尺度。空气-水和固体-水界面上的胶体沉积对于控制包气带中胶体的传输速率和孔隙水浓度起着重要作用。尽管胶体侵入区过程很重要，但适合预测不饱和多孔介质中胶体沉积的理论并不存在。这项研究的重点是通过定量定义空气-水和固-水界面的胶体沉积动力学与土壤-水-胶体系统的物理性质之间的基本关系，采取措施填补这一知识空白。这些关系将通过对水流和通过部分饱和空隙空间的平流扩散胶体传输的一系列孔隙尺度模拟进行分析而得出。不同饱和多孔介质中空气-水结构的现代模型将用于指定孔隙水域的几何形状，并对其进行胶体传输的孔隙尺度模拟。对流动和传输模拟结果的回归分析预计会产生幂律方程，将胶体与空气-水和固体-水界面的碰撞速率表示为流体流速、胶体尺寸和密度、多孔介质结构和毛细管压力（控制水饱和度）的函数。除了需要考虑空气相的存在之外，所提出的用于推导胶体界面碰撞率幂律方程的方法在概念上类似于用于制定水饱和多孔介质的胶体过滤方程的已发表方法。使用幂律方程对胶体沉积动力学的预测将与实验室柱实验中进行的胶体沉积测量进行比较。在这些实验中，将检查胶体沉积速率对胶体直径、粒度、粒度分布、孔隙水速度和毛细管压力变化的敏感性。测量的沉积速率和预测的沉积速率的比较将揭示新理论的缺陷，并有助于指导其完善。这项研究的结果将推进当前对部分饱和地质材料和地质材料中质量传输过程的认识。 大大提高了我们对影响包气区内胶体孔隙水浓度的关键传质反应的理解。这项拟议的研究代表了推导和测试不饱和多孔介质胶体过滤理论的首次尝试，该理论需要对渗流区的胶体流动性进行定量推断。这样的理论应该为解决国家关注的关键水质问题做出重要贡献，这些问题与微生物病原体和胶体相关污染物通过近地表环境的移动有关。