Subsurface contaminant transport in the presence of colloids: Effect of nonlinear and nonequilibrium interactions

Abstract

The effect of kinetic nonlinear sorption of contaminants in the presence of colloids is the focus of this study. Different sorption isotherms are considered where contaminant sorption and colloid deposition are assumed to be linear or nonlinear (Freundlich), and contaminant attachment to mobile and immobile colloids is assumed to follow either linear or Langmuir isotherms. Varying combinations accounting for different possibilities are used to investigate effects of different isotherms on contaminant transport. Two‐dimensional numerical simulations in homogenous media show that the effect of colloids on nonlinearly sorbing contaminant is altered from facilitation to retardation depending on the Freundlich exponent and concentration value. One finding from the study indicates that incorporating the colloid effect on contaminant transport does not necessarily represent a conservative assumption. The study shows that ignoring the fact that colloids have limited sites and describing contaminant attachment to colloids by linear isotherms may lead to inaccurate results. In addition, it is found that assuming colloids are linearly deposited on the solid matrix is a conservative assumption in the applications that focus on peak concentration arrival. However, when small contaminant concentrations are of concern (i.e., early arrival is the quantity of interest), assuming nonlinear colloidal deposition becomes the critical scenario.