Nonequilibrium Transport and Transport-Controlled Reactions

多孔介质非常重要，不仅因为它们含有大部分可获得的淡水，而且还因为它们的生物学意义，例如，暗水带（河流或河口以下）。稀释和生化反应控制着地下、海滩或河床沉积物、地下水补给盆地等地的水质。例如，从一个源发出的污染物羽流通过稀释和羽流内部或边缘的化学反应而逐渐减少。工程原位修复项目的成功往往取决于化学输送和添加剂混合的有效性，这些添加剂刺激原生微生物分解污染物。对反应物的混合同样重要的可能是去除反应产物，如果它们残留下来，会抑制反应，因为它们对微生物有害。许多在环境过程研究中很重要的生化反应与输送过程（如平流、扩散和水固区之间的质量交换）相比是非常快的。在多孔介质中混合是非常缓慢的，因此通常是控制速率的机制。在实际应用中感兴趣的尺度上的反应速率通常由地质构造内的输运和混合速率控制，而不是由在小型和完全混合的反应器中测量的速率控制。数值输运-反应模拟模型在描述场尺度过程方面是无价的，但人们普遍担心它们的有效性，它们用来描述反应动力学的数学表达式和参数的物理意义，或者这些表达式或参数可以转移到其他地点的程度，或者缩放到不同大小的地点。这项研究是对运输限制反应基本原理的重要重新检查，以确定潜在的机制，并深入了解常用数学表达式的适用性，参数的适当值以及规模效应的重要性。现有的方法被重新审视，新的方法被提出和测试。提出了一种新的方法，其前提是现有的参数如色散系数或传质系数不充分，有时不适合描述由水文输运控制的反应动力学。需要考虑、测量和研究相对于尺度变化的替代量。一种方法与现有的方法截然不同，它基于混合势的严格推导，这种方法量化了运输控制的反应并确定了它们的速率。关键问题包括：在实地进行哪些实际测试，如何解释结果，实际可行的准确性或可靠性，以及风险评估的影响。通过检查最近完成的实地研究和实验中的具体问题以及进行实验室实验和详细的数值模拟，评估各种方法的适用性。

Porous media are extremely important, not only because they contain most of accessible freshwater, but also because of their biological significance, e.g., hyporheic zones (below rivers or estuaries). Dilution and biochemical reactions control the quality of water in the subsurface, in the sediment of beaches or riverbeds, at groundwater recharge basins, etc. For example, a contaminant plume emanating from a source is gradually diminished through dilution and through chemical reactions in the interior or at the edges of the plume. The success of projects of engineered in-situ remediation often depends on the effectiveness of chemical delivery and mixing of additives, which stimulate native microorganisms to break down contaminants. Equally important to the mixing of reactants may be the removal of reaction products which, if they remain, inhibit reactions because they are deleterious to the microorganisms. Many biochemical reactions that are important in the study of environmental processes are very fast in comparison to transport processes, like advection, diffusion, and mass exchange between aqueous and solid zones. Mixing in porous media is very slow and, thus, is usually the mechanism that controls rates. Reaction rates at scales of interest in practical applications are usually controlled by the rates of transport and mixing within geologic formations, rather than by the rates measured in small and completely mixed reactors. Numerical transport-reaction simulation models are invaluable in describing field-scale processes but there are widespread concerns about their effectiveness, the physical significance of the mathematical expressions and parameters that they employ to describe reaction kinetics, or the extent that these expressions or parameters can be transferred to other sites, or be scaled to sites of different size. This research is a critical reexamination of the fundamentals of transport-limited reactions in order to identify underlying mechanisms and to develop insights into the applicability of commonly used mathematical expressions, appropriate values of parameters, and the importance of scale effects. Existing approaches are revisited and novel approaches are proposed and tested. A new approach is proposed based on the premise that existing parameters like dispersion coefficients or mass-transfer coefficients are inadequate, and occasionally ill-suited, for describing the kinetics of reactions that are controlled by hydrologic transport. Alternative quantities need to be considered, measured, and studied with respect to changes in scale. One approach, which constitutes a drastic departure from available procedures, is based on a rigorous derivation of mixing potentials, which quantify transport-controlled reactions and determine their rates. Critical questions include: what practical tests to perform in the field, how to interpret the results, what accuracy or reliability are practically feasible, and risk-assessment implications. The applicability of various approached is evaluated by examining specific problems from recently completed field studies and experiments and by performing laboratory experiments and detailed numerical simulations.