A Numerical Model with Finite Difference Schemes for Multi-Species Solute Transport in Porous Media

A precise forecast of contaminant and solute transport has an inevitable role in the management of water resources. In accordance with this purpose, in this paper, a novel one-dimensional numerical model for the transport of a decay chain through homogeneous porous media is proposed. To develop the suggested model, two different schemes of the finite difference method, namely the Lax-Wendroff scheme and Fourth-Order scheme, are used. The verification and validation of the established model are examined by the analytical results of three multi-species solute dispersion problems with three- and four-chain members. The total mean square error, L2- and L∞-norms are applied to assess the results. Although analyses show that both schemes provided reliable results, the numerical results of the Lax-Wendroff scheme are more accurate.

Influence of Clay on Solute Transport in Saturated Homogeneous Mixed Media

In this study, four homogeneous porous media (HPM1-HPM4), consisting of distinct proportions of sand-sized and clay-sized solid beads, were prepared and used as single fracture infills. Flow and nonreactive solute transport experiments in HPM1-HPM4 under three flow rates were conducted, and the measured breakthrough curves (BTCs) were quantified using conventional advection-dispersion equation (ADE), mobile-immobile model (MIM), and continuous time random walk (CTRW) model with truncated power law transition time distribution. The measured BTCs showed stronger non-Fickian behaviour in HPM2-HPM4 (which had clay) than in HPM1 (which had no clay), implying that clay enhanced the non-Fickian transport. As the fraction of clay increased, the global error of ADE fits also increased, affirming the inefficiency of ADE in capturing the clay-induced non-Fickian behaviour. MIM and CTRW performed better in capturing the non-Fickian behaviour. Nonetheless, CTRW’s performance was robust. 12.5% and 25% of clay in HPM2 and HPM3, respectively, decreased the flowing fluid region and increased the solute exchange rate between the flowing and stagnant fluid regions in MIM. For CTRW, the power law exponent ( β CTRW ) values were 1.96, 1.75, and 1.63 in HPM1-HPM3, respectively, implying enhanced non-Fickian behaviour. However, for HPM4, whose clay fraction was 50%, the β CTRW value was 1.87, implying a deviation in the trend of non-Fickian enhancement with increasing clay fraction. This deviation indicated that non-Fickian behaviour enhancement depended on the fraction of clay present. Moreover, increasing flow rate enhanced the non-Fickian transport based on β CTRW .

A critical evaluation of short columns for estimating the attachment efficiency of engineered nanomaterials in natural soils

Short, saturated packed columns are used frequently to estimate the attachment efficiency (α) of engineered nanomaterials (ENMs) in relatively homogeneous porous media, but a combined experimental and theoretical approach to...

Mobility, Degradation, and Uptake of Indaziflam under Greenhouse Conditions

The objectives of this study were to evaluate the leaching, degradation, uptake, and mass balance of indaziflam, as well as its potential to produce phytotoxicity effects on young pecan trees. Pecan trees were planted in pots with homogeneous porous media (sandy loam soil), preferential flow channels open to the soil surface, and shallow tillage at the soil surface. Pots were treated with indaziflam at two application rates of 25 and 50 g a.i./ha in 2014 and 2015. Each pecan tree was irrigated with 7 L of water every 2 weeks during the growing season. An irrigation volume of 2 L was used to maximize indaziflam retention time in the soil from Dec. 2015 until the end of the trees’ dormant stage. In 2014, leachate samples were collected after each irrigation for quantifying indaziflam mobility. Soil samples were collected at depths of 0 to 12 and 12 to 24 cm after 45, 90, and 135 days of indaziflam application, and leaf samples were collected at the end of the growing season to quantify mobility and uptake. Indaziflam was detected in leachate samples, and the leaf indaziflam content increased with increasing application rate. Indaziflam and its breakdown products were detected at both sampling depths. Mass recovery and half-life values for indaziflam in the soil ranged from 38% to 68% and 63 to 99 days, respectively. No phytotoxicity effects were observed from increasing application rate and retention time of indaziflam in the soil. Most of the applied indaziflam was retained in the soil at shallow depth.

Transport of aggregating nanoparticles in porous media

<p> </p><p>A   novel   mathematical   model   was   developed   to   describe   the   transport   of nanoparticles in water saturated, homogeneous porous media with uniform flow. The model accounts for the simultaneous migration and aggregation of nanoparticles. The nanoparticles can  be found suspended  in the  aqueous phase  or attached  reversibly and/or   irreversibly   onto   the   solid   matrix.   The  Derjaguin-Landau-Verwey-Overbeek (DLVO)  theory   was   used   to   account   for   possible   repulsive   interactions   between aggregates allowing for both reaction-limited aggregation (RLA), and diffusion-limited aggregation (DLA) cases to be considered.   The governing coupled partial differential equations were solved initially by employing adaptive operator splitting methods, which decoupled   the   reactive   transport   and   aggregation   into   distinct   physical   processes. Subsequently, the resulting equations were treated individually with proper use of either a finite difference scheme or a specialized ordinary differential equations solver. The results from various model simulations showed that the transport of nanoparticles inporous media is substantially different than the transport of conventional biocolloids. In particular,   aggregation   was   shown   to   either   decrease   or   increase   nano particle attachment   onto   the   solid   matrix   and   to   yield  either  early   or  retarded  breakthrough. Finally,   useful   conclusions   were   drawn   regarding   the   particle   distribution   density   at various points in time and space.</p>