Collaborative Research: Nano- and micro-particle transport prediction in subsurface media: The role of heterogeneity and structure

在许多水质环境中，颗粒在饱和沙子和砾石中的传输和保持是一个关键过程；例如，颗粒结合污染物的流床去除，使用河岸过滤的低能量饮用水处理，用于污染物清除的新型纳米颗粒或细菌的工程地下输送，以及保护饮用水供应免受致病病原体来源的影响。目前还没有足够的能力来预测在环境条件下观察到的这些颗粒的复杂输运行为。因此，缺乏支持上述环境系统优化设计的理论支持。目前的数学模型可以描述但不能预测这些行为，因为到目前为止，这些模型还不能代表环境条件下颗粒附着到表面的潜在机制和过程。这项拟议的研究旨在确定所观察到的复杂的胶体传输行为是否会从导致颗粒附着的表面非均质性的孔隙尺度表示中出现。拟议的研究包括在孔隙(微观模型)和网络(填充砂柱)尺度上的并行实验和模拟。这项研究将为研究人员和从业者提供一个变革性的平台，以执行粒子传输的机械预测，以设计环境问题的解决方案。其他更广泛的影响包括初中和高中生物、化学和地球科学教师参加为期六周的暑期实习，在那里他们进行实地和实验室经验，研究颗粒在微量元素迁移和转化中的作用。目前缺乏预测环境条件下观察到的胶体复杂迁移行为的能力(例如，滞留胶体的非线性对数线性剖面、低浓度的加长尾矿、堵塞和成熟)。在平流-弥散方程中使用了基于经验的连续介质尺度速率常数和标度因子来描述和有限地预测观测到的复杂输运行为。虽然这些描述是非常有用的机制指标，但真正的预测能力只有在更基本的水平上识别和参数化基本的物理化学机制/过程时才可能实现。孔尺度(纳米尺度)胶体-表面相互作用在连续介质尺度(柱和场)对胶体传输行为产生了深远的影响。这项研究的目的是从表面非均质性的孔隙尺度表示和堆积结构的网络尺度表示，确定是否可以预测连续介质的速率常数和标度因子，以及是否会出现观察到的复杂的连续介质尺度行为。这项研究涉及孔(微观模型)和连续体(柱)尺度的平行实验和模拟。孔隙尺度力/扭矩耦合模拟将应用于孔隙/颗粒网络模拟，以发展对连续介质尺度速率常数和尺度因子的机理预测。新的方法将被用来表示在孔隙尺度上胶体附着到整体排斥表面的表面不均一性。拟议的研究还将利用和扩展最近在连续统(网络)尺度上对拓扑影响的理解，其中将探索分子(扩散驱动)和粒子(轨迹驱动)传输行为之间的转变。

Many water quality contexts exist in which particle transport and retention in saturated sands and gravels is a critical process; e.g., streambed removal of particle-bound contaminants, low energy drinking water treatment using riverbank filtration, engineered subsurface delivery of novel nanoparticles or bacteria for contaminant cleanup, and protection of drinking water supplies from disease-causing pathogen sources. There is yet insufficient capability to predict the observed complex transport behaviors of these particles under environmental conditions. Consequently, the theory to support optimized design of the above environmental systems is lacking. Mathematical models currently can describe but not predict these behaviors because, as yet, the models do not represent the underlying mechanisms and processes for particle attachment to surfaces under environmental conditions. The proposed research aims to determine whether observed complex colloid transport behaviors will emerge from pore-scale representation of the surface heterogeneity responsible for particle attachment. The proposed investigations involve parallel experiments and simulations at pore (micromodel) and network (packed sand column) scales. The research will provide for a transformative platform for researchers and practitioners to perform mechanistic prediction of particle transport for design of solutions to environmental problems. Additional broader impacts include engagement of middle and high school biology, chemistry, and earth science teachers in six-week long summer internships where they undertake field and laboratory experiences examining the role of particles in trace element transport and transformation.The capability to predict the observed complex transport behaviors of colloids under environmental conditions (e.g., non log-linear profiles of retained colloids, extended tailing of low concentrations, blocking, and ripening) is currently lacking. Empirically based continuum-scale rate constants and scaling factors are employed in the advection-dispersion equation to describe, and to a limited extent predict, the observed complex transport behaviors. Whereas these descriptions are extremely useful indicators of mechanisms, true predictive capability will be possible only if the underlying physicochemical mechanisms/processes are identified and parameterized at a more fundamental level. Pore scale (nanoscale) colloid-surface interactions are well-demonstrated to exert profound influences on colloid transport behaviors at the continuum scale (column and field). This research aims to determine whether the continuum-scale rate constants and scaling factors can be predicted, and the whether the observed complex continuum-scale behavior will emerge, from pore-scale representation of surface heterogeneity and network-scale representation of packing structure. This investigation involves parallel experiments and simulations at pore (micromodel) and continuum (column) scales. Coupled pore scale force/torque balance simulations will be conducted to pore/grain network simulations in order to develop mechanistic prediction of continuum scale rate constants and scaling factors. New approaches will be used to represent surface heterogeneity responsible for colloid attachment to bulk repulsive surfaces at the pore scale. The proposed research will also capitalize on, and extend, recent understanding of influences of topology at the continuum (network) scale where the transition between molecular (diffusion-driven) and particle (trajectory-driven) transport behaviors will be explored.