Abstract
Problem statement: Understanding the mechanisms that control the transport and fate of colloidal particles in subsurface environments is a crucial issue faced by several researchers in the last years. In many cases, natural colloids have been shown to play a major role in the spreading of strongly sorbing contaminants, while manufactured micro-and nanoparticles, which are nowadays widely spread in the subsurface, can be toxic themselves. On the other hand, in recent years studies have been addressed to the use of highly reactive micro-and nanoparticle suspensions for the remediation of contaminated aquifers. Provide the set of partial-differential model equations and its numerical solution for the colloid transport under transient hydrochemical conditions, that have been previously shown to be extremely important in micro-and nanoparticle transport in porous media. Approach: This study presented a novel colloid transport model, called MNM1D (Micro-and Nanoparticle transport Model in porous media in 1D geometry), able to simulate the colloid behavior in porous media in the presence of both constant and transient hydrochemical parameters (namely ionic strength). The model accounts for attachment and detachment phenomena, that can be modeled with one or two linear and/or langmuirian interaction sites. The governing equations were solved using a finite-differences approach, herein presented and discussed in details. Results: Both qualitative and quantitative comparisons with results of well-established colloid transport models, based both on analytical and numerical solutions of the colloid transport equation, were performed. The MNM1D results were found to be in good agreement with these solutions. Conclusion: The shown good agreement between MNM1D and the other models indicated that this code can represent in the future a useful tool for the simulation of colloidal transport in groundwater under transient hydrochemical conditions.
Highlights
Micro- and nanoparticles, both natural and anthropogenic are widely spread in the subsurface[1,2]
The present study illustrates the MNM1D code (Micro-and Nanoparticle transport Model in porous media), an innovative colloid transport model developed by the authors of this study[12], able to simulate colloid deposition and release in saturated porous media during transients of ionic strength
An application of the MNM1D code for the solution of the inverse problem was presented by the researchers[12], where it was applied for fitting a set of laboratory tests run in transient ionic strength conditions
Summary
Micro- and nanoparticles, both natural (clays, oxides, bacteria) and anthropogenic (coatings, paints, chemical reactants) are widely spread in the subsurface[1,2]. In recent years studies have been addressed to the use of highly reactive micro- and nanoparticle suspensions for the remediation of contaminated aquifers[7]. As millimetric zerovalent iron is known to degrade a large number of organic compounds[8], in the last years studies focused on the use of colloidal suspensions of nanoscale iron particles, that are known to have a specific area (and reaction kinetics) orders of magnitude higher than millimetric iron[9,10,11]. The dependence of attachment/detachment coefficients on salt concentration is explicitly embedded into the model. The model validation through both analytical (Stanmod) and numerical (Hydrus1D) solutions is reported
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