Knowledge of particle deposition and transport in saturated porous media is of significant importance for various engineered applications and environmental concerns. Surface physical and chemical heterogeneities play a critical role in particle deposition because they can increase attachment in the primary minima of Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energy profile by reducing the repulsive energy barrier. We present a comprehensive review showing that surface heterogeneity can alter particle deposition through multiple additional mechanisms such as increasing attachment at secondary minima at concave locations and detachment from primary minima at nanoscale convex asperities. The pore-scale deposition mechanisms due to surface heterogeneity can cause anomalous particle retention and transport behaviors at continuum scales such as equilibrium sorption and nonmonotonic retention profiles. To accurately determine the particle transport in porous media at continuum scales requires future research: (1) improving existing techniques to accurately measure and represent surface heterogeneities and determine attachment and detachment; (2) using statistic models to characterize variations of attachment and detachment with surface heterogeneity; (3) using Lagrangian/Eulerian approach to thoroughly understand pore-scale retention mechanisms in porous media, and incorporating them into continuum equations to simulate particle transport at continuum scales.

This study used polystyrene latex colloids as model microplastic particles (MPs) and systematically investigated their retention and transport in glass bead-packed columns. Different pore volumes (PVs) of MP influent suspension were first injected into the columns at different ionic strengths (ISs). The breakthrough curves (BTCs) were obtained by measuring the MP concentrations of the effluents. Column dissection was then implemented to obtain retention profiles (RPs) of the MPs by measuring the concentration of attached MPs at different column depths. The results showed that the variation in the concentrations of retained MPs with depth changed from monotonic to non-monotonic with the increase in the PV of the injected influent suspension and solution IS. The non-monotonic retention was attributed to blocking of MPs and transfer of these colloids among collectors in the down-gradient direction. The BTCs were well simulated by the convection-diffusion equation including two types of first-order kinetic deposition (i.e., reversible and irreversible attachment). However, this model could not well simulate the non-monotonic retention profiles due to the fact that the transfer of colloids among collectors was not considered. The results in this study are critical to developing models to simulate the fate and transport of MPs in porous media such as soil.