Colloid-Associated Groundwater Contaminant Transport in Homogeneous Saturated Porous Media: Mathematical and Numerical Modeling

Abstract

During the past two decades, significant efforts have been made to study contaminant transport in the presence of colloids. Several researchers reported that colloidal particles could enhance the migration of contaminants in groundwater by reducing retardation factor. When the colloidal particles are present in the aquifer, the subsurface system can be considered as a three-phase system with two solid phases and an aqueous phase. The interaction between contaminants, colloids, and solid matrix should be considered in assessing the fate and transport of the contaminant in the groundwater flow system. In this study, a one-dimensional numerical model is developed by employing a fully implicit finite difference method. This model is based on mass balance equations and mass partition mechanisms between the carriers and solid matrix, as well as between the carriers and contaminants in a saturated homogeneous porous medium. This phenomenon is presented by two approaches: equilibrium approach and fully kinetic first-order approach. The formulation of the model can be simplified by employing equilibrium partitioning of particles. However, contaminant transport can be predicted more accurately in realistic situations by kinetic modeling. To test the sensitivity of the model, the effect of the various chemical and physical coefficients on the migration of contaminant was investigated. The results of numerical modeling matched favorably with experimental data reported in the literature.

Impacts of Sediment Particle Grain Size and Mercury Speciation on Mercury Bioavailability Potential

“…While most of the Hg (∼47–96%) accumulated in the <45 μm fractions for the marine and river sediments, the majority of Hg in the terrestrial sediment was present in the sand-sized fraction (>45 μm). Colloidal nanophases in marine sediments have been proposed as an important vehicle for the transport of constituents, including Hg. − Hg in the colloidal nanophase may also be more bioavailable than in the larger size fractions, depending on its speciation …”

The impact of nanoparticle aggregation on their size exclusion during transport in porous media: One- and three-dimensional modelling investigations

“…The role of natural colloidal particles in the transport of solute contaminants has been demonstrated in many studies 16–19 . Being a colloid and having considerable capability for uptake of dissolved contaminants, NP aggregates once released into subsurface environments can crucially act as carriers of hazardous contaminants such as radionuclide, particularly if NP dispersions are purposefully injected into groundwater for the remediation of such pollutants 1,20,21 .…”

Colloidal transport of heavy metals in low‐advective‐velocity environmental systems: Reactive transport model on biogeochemical and hydrodynamic impacts

“…Due to their high specific surface areas, high reactive site densities, and high mobility in soils, the colloids facilitate the sorption and thus the transport of many contaminants in the subsurface, such as heavy metals, radionuclides, and organic compounds, which are otherwise immobile with limited solubility in the aqueous environment (Kretzschmar et al, 1999;Ryan & Elimelech, 1996;Thompson et al, 2006). Various researchers have studied the mobility of contaminants via colloidal particles, showing the facilitation of pollution transport in the subsurface systems (e.g., Benhabib et al, 2017;Cheng et al, 2016;de Jonge et al, 2004;Emerson et al, 2016;Ma et al, 2017;Sen et al, 2002aSen et al, , 2002bŠimůnek et al, 2006;Snousy et al, 2018;Zhuang et al, 2003), whereas others have demonstrated the adsorbed contaminants to be trapped among sediment grains, impeding pollution transport (e.g., Bekhit et al, 2006Bekhit et al, , 2009Ghiasi et al, 2020b;Kheirabadi et al, 2017;Peng et al, 2017;Sen & Khilar, 2006). Katzourakis and Chrysikopoulos (2015) developed a three-dimensional numerical model to investigate the simultaneous transport (co-transport) of dense colloids and viruses in porous media.…”