Nonequilibrium and Multicomponent Transport Models

This chapter considers the use of the convection-dispersion equation (CDE) for two more challenging albeit unrelated problems of nonequilibrium and multicomponent transport. The physical nonequilibrium concept is based on convective-dispersive transport in a mobile region of the liquid phase and diffusive solute transfer between the mobile and immobile regions. The concept behind physical nonequilibrium models is that differences between regions of the liquid phase lead to mostly lateral gradients in the solute concentration resulting in a diffusive type solute transfer process. Multicomponent models have been formulated to solve the simultaneous transport of many species. Typically, these models include not only the previously discussed single species CDE but also equilibrium or kinetic descriptions for chemical processes in the aqueous and adsorbed phases. The chapter reviews the formulation of all relevant processes and variables to solve multicomponent transport problems, and contains a case study of reclaiming a sodic soil by furrow irrigation.