Numerical Analyses on Contaminant Transport Using a Dual Reactive Domain Model

Abstract

An advection-dispersion equation (ADE) describes contaminant transport in porous media. An ADE can cover equilibrium phenomena of interest, which includes sorption, decay, and chemical reactions. Among these phenomena, sorption mechanism is described by several types of sorption isotherm. If sorption isotherm is linear, the solution of the ADE can be easily obtained. However, if sorption isotherm is non-linear, like Langmuir model or non-linear Freundlich molel, the coefficients of resultant differential equation become non-linear. In this case, there is no analytic solution. Dual reactive domain model (DRDM) is a combined model of linear and Langmuir models, so it can cover linear and non-linear characteristics of sorption behavior. In this article, we present numerical analyses of ADE using a DRDM. The simulation results reveal that even if sorption data may be fitted well using linear or non-linear isotherms, the characteristics of contaminant transport by applying the two are quite different from each other. To be concrete, the retardation effect of linear isotherm is different from that of the DRDM. As the non-linearity of sorption isotherm increases, the difference of retardation effects of the two cases becomes large. Even if we use a DRDM to simulate contaminant transport, which shows a linear or non-linear sorption behavior, we can get pretty similar simulation results. Although the transport of contaminant is very sensitive to sorption models used, using a DRDM can reduce the uncertainty due to the selection of sorption model. Therefore, we recommend a DRDM as a sorption model to more accurately describe the transport of contaminant.