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，颗粒在饱和砂和砾石中的迁移和保留是一个关键过程;例如，颗粒结合的污染物的河床去除、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化地下递送以及保护饮用水供应免受致病病原体源的影响。 目前还没有足够的能力来预测这些颗粒在环境条件下观察到的复杂的传输行为。 因此，缺乏支持上述环境系统优化设计的理论。 目前，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基本机制和过程。 拟议的研究旨在确定所观察到的复杂的胶体运输行为是否会出现从负责颗粒附着的表面异质性的孔隙尺度表示。 拟议的调查涉及平行实验和模拟孔隙（微观模型）和网络（填充砂柱）规模。 该研究将为研究人员和从业人员提供一个变革性的平台，以进行颗粒传输的机械预测，从而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学，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运输和转化中的作用。保留胶体的非对数线性分布、低浓度的延伸拖尾、阻塞和熟化）。 基于经验的连续尺度速率常数和比例因子的对流-弥散方程来描述，并在有限的程度上预测，所观察到的复杂的传输行为。 尽管这些描述是机制的非常有用的指标，但只有在更基本的水平上识别和参数化潜在的物理化学机制/过程，才有可能实现真正的预测能力。 孔尺度（纳米级）的胶体表面相互作用是充分证明发挥深远的影响胶体输运行为在连续尺度（列和字段）。 本研究的目的是确定是否可以预测的连续尺度的速率常数和缩放因子，以及是否会出现所观察到的复杂的连续尺度的行为，从表面异质性的孔隙尺度表示和网络尺度表示的包装结构。 这项调查涉及平行的实验和模拟在孔隙（微观模型）和连续（列）尺度。 耦合孔隙尺度力/扭矩平衡模拟将进行孔隙/颗粒网络模拟，以开发连续尺度速率常数和标度因子的机理预测。 新的方法将被用来代表负责胶体附着到大体积排斥表面在孔隙尺度的表面异质性。 拟议的研究还将利用和扩展最近对连续体（网络）尺度上拓扑结构影响的理解，其中将探索分子（扩散驱动）和粒子（湍流驱动）传输行为之间的过渡。

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.