Reactive Transport: A Review of Basic Concepts with Emphasis on Biochemical Processes

Abstract

Reactive transport (RT) couples bio-geo-chemical reactions and transport. RT is important to understand numerous scientific questions and solve some engineering problems. RT is highly multidisciplinary, which hinders the development of a body of knowledge shared by RT modelers and developers. The goal of this paper is to review the basic conceptual issues shared by all RT problems, so as to facilitate advance along the current frontier: biochemical reactions. To this end, we review the basic equations to point that chemical systems are controlled by the set of equilibrium reactions, which are easy to model, but whose rate is controlled by mixing. Since mixing is not properly represented by the standard advection-dispersion equation (ADE), we conclude that this equation is poor for RT. This leads us to review alternative transport formulations, and the methods to solve RT problems using both the ADE and alternative equations. Since equilibrium is easy, difficulties arise for kinetic reactions, which is especially true for biochemistry, where numerous frontiers are open (how to represent microbial communities, impact of genomics, effect of biofilms on flow and transport, etc.). We conclude with the basic 10 issues that we consider fundamental for any conceptually sound RT effort.

Modeling the Organic Carbon Oxidation and Redox Sequence Under the Partial‐Equilibrium Approach: A Discussion by Means of a Semi‐Analytical Solution

“…As discussed in a recent review by Carrera et al. (2022) the advection dispersion equation is a poor representation of transport in such domains. This has been acknowledged for conservative transport but is even more relevant for reactive transport and, particularly, for organic carbon oxidation.…”

Towards Understanding Factors Affecting Arsenic, Chromium, and Vanadium Mobility in the Subsurface

“…Macroscale models can be formulated either by posing the model phenomenologically, such that they have a form that is similar to the corresponding microscale model, or they can be derived by direct averaging of microscale equations. Although the former approach is encountered often enough to be considered standard [ 114 , 134 , 137 , 189 ], the latter approach can result in models that are consistent across scales. Careful averaging from the microscale to the macroscale provides a verifiable link between scales that can allow one to check any assumptions or approximations that have been used to derive and close the model at the macroscale [ 113 , 119 , 157 ].…”

“…The use of phenomenological macroscale continuum models has led to well-documented modeling error [ 114 , 117 , 130 , 135 , 137 , 155 , 157 , 177 , 189 ], and some in the literature to question whether continuum models are viable for reactive transport [ 114 , 158 ]. To illustrate the sources of error, we will describe the commonly used macroscale ADRE, which has been phenomenologically posed, followed by a discussion of modeling error that results from this approach.…”

“…The next generation of macroscale simulators requires a reactive transport model that only requires knowledge of the current state of the system, as well as accessible medium parameters. Vigorous work on these issues is underway in the geochemical modeling community [ 116 , 118 , 134 , 155 , 185 , 189 ].…”

Modeling Mixing in Stratified Heterogeneous Media: The Role of Water Velocity Discretization in Phase Space Formulation

“…In contrast to dispersion, mixing is a direct cause of chemical reactions (Cirpka and Valocchi 2007;Rezaei et al 2005;De Simoni et al 2005Soler-Sagarra et al 2022;Tartakovsky et al 2008;Cirpka 2002;Herrera et al 2017). The ADE employs Fick's law (Fick 1855) to characterize both processes and must, therefore, be considered inadequate for reactive transport (Carrera et al 2022). A new formulation is needed to reproduce advection, dispersion and mixing (de Dreuzy et al 2012;de Dreuzy and Carrera 2016).…”