Hydrodynamic Dispersion Coefficient Research Articles

Experimental and numerical study of bimolecular reactive transport in a single rough-wall fracture

In order to test the performance of the incomplete mixing model including the advection-dispersion-reaction equation (IM-ADRE) in simulating bimolecular reactive transport in fractured media, the laboratory-controlled experiments and numerical modeling were conducted in a single rough-wall fracture. Bimolecular reaction of aniline (AN) + 1, 2-napthoquinone-4-sulfonic acid (NQS) → 1, 2-naphthoquinone-4-aminobenzen (NQAB) was employed. Three different flow rates (0.15, 0.825 and 1.5 mL/s) and three fracture apertures (2, 3 and 4 mm) were considered in the experiment. The numerical simulation was analyzed and discussed based on the Péclet (Pe) number and Damköhler (Da) number. The results showed that although the spatial distribution of product concentration varied with the Pe number, the IM-ADRE model could simulate it well. The discrepancy between the simulated and measured peak product concentrations was less than 0.7%, which was far less than the value of 5% in previous study (Qian et al., 2015) produced by the IM-ADRE model used to modeling the reactive transport in porous media. This meant that the IM-ADRE model was effective for simulating and predicting the experimental results of bimolecular reactive transport in a single rough-wall fracture. Due to the instability of the product, the simulated value of the peak product concentration was always higher than the experimental value. Through further analysis of the model parameters, it was found that the hydrodynamic dispersion coefficient (D) changed significantly with the change of Pe number. The parameters m and β0 were linearly correlated with the Pe number. In addition, the IM-ADRE model was more sensitive to the parameters m and β0 but less sensitive to D.

Transport under advective trapping

Abstract

Effective dispersion coefficients for the upscaling of pore-scale mixing and reaction

We upscale reactive mixing using effective dispersion coefficients to capture the combined effect of pore-scale heterogeneity and molecular diffusion on the evolution of the mixing interface between two initially segregated dissolved species. Effective dispersion coefficients are defined in terms of the average spatial variance of the solute distribution evolving from a pointlike injection, that is, the transport Green function. We numerically investigate the temporal behavior of the longitudinal effective dispersion coefficients for two porous media of different pore-scale heterogeneity as measured by the statistics of the flow speed, and different Péclet numbers. We find that the effective dispersion coefficients evolve with time, or equivalently travel distance. As the solute samples the pore-scale flow heterogeneity due to advection and transverse diffusion, the effective dispersion coefficients evolve from the value of molecular diffusion to the corresponding hydrodynamic dispersion coefficients. Thus, at times smaller than the diffusion time over a characteristic pore length, the effective dispersion coefficients can be significantly smaller than the hydrodynamic dispersion coefficients. This difference can explain frequently observed mismatches between pore-scale reactive mixing data, and predictions using Darcy scale transport descriptions based on hydrodynamic dispersion coefficients that are constant in time. This suggests that the notion of incomplete mixing on the support scale can be quantified in terms of effective pore-scale dispersion coefficients. We use effective dispersion in order to approximate the transport Green function in terms of a Gaussian-shaped distribution that is characterized by the effective variance. This is approximation is termed dispersive lamella. Based on this representation, we study reactive mixing between two initially segregated solutes. The dispersive lamella approach accurately predicts the evolution of the product mass of an instantaneous bimolecular reaction obtained from direct numerical simulations. This demonstrates that effective dispersion is an accurate measure for width of the mixing interface between the two reacting species. These results shed some new light on pore-scale mixing, the notion of incomplete mixing, and its prediction and upscaling in terms of an effective mixing model.

Study of multispecies convection-dispersion transport equation with variable parameters

Multispecies pollutant migration is most natural phenomenon, frequently occurring in the polluted groundwater system and also evidently occurs in the nuclear repositories and sites having radioactive substances and chemical solvent. Modeling pollutant migration of reactive multispecies problem with variable transport parameters is quite a challenging issue, necessary for better sightedness of fate and transport of reactive solutes and their geochemical growth in the geological formations. At present most of the solutions for multispecies problem are corresponding to the constant parameters affecting the concentration distribution, not for variable transport parameters, because of the complexity of the modelled equation. This paper dealt with the comparative study of multispecies pollutant transport problem in porous structure to analyse the effect of spatially and temporally varying hydrodynamic dispersion coefficient and transport velocity terms in more general form. For mathematical elaboration, two-species transport problem is considered subjected to the concept of linear isotherm with both the parent and daughter species without using identical retardation factor and model is also incorporated with the first-order decay term under spatially varying initial conditions. Homotopy analysis method (HAM) is adopted to develop the series solution for the concentration segmentation of each species of the model. The advantage of this method is that it is capable to overcome the limitation of existing transform methods for some cases of complex modelled problems. The zeroth order deformation equation is derived by using HAM to generate the semi-analytical solution of the model under certain auxiliary linear operator. The impact of distinct retardation factor for different species and effect of diversity in dependency of modelled parameters over space and time are graphically depicted for both the species and illustrated that it has a valuable impact over multispecies pollutant migration. As there exist no analytical or numerical solution for such complex variable dependency of migration parameters over transport phenomenon, these solutions may be helpful to deliver a better significant about the concentration variation due to space and time dependent transport parameters, responsible for reactive multispecies migration, in more natural way.

Liquid phase nonpoint source pollution dispersion through conveyance structures to sustainable urban drainage system within different land covers

Liquid-phase nonpoint source pollution dispersion and removal on sustainable urban drainage systems (SUDS) is an important issue for urban pollution mitigation which remains a challenge, as current researches mostly focus on pollutants removal by settling. Nevertheless, most of liquid-phase pollutants behave as dissolved substances on overland flow and, therefore, they cannot be trapped, but uptake by biological mechanisms and adsorbed by green infrastructure media. Hence, dispersion of dissolved pollutant is of great importance for liquid-phase pollution removal, as it also increases contact with underlying media in the SUDS. This paper addresses the liquid-phase pollutant dispersion on conveyance structures within different materials, using experimental and modelling analysis. Hydrodynamic dispersion and flow velocity were analysed separately, or conjoint, using dispersivity, as it is a key factor for porous solute transport and removal. Therefore, the effect of different covers on pavements draining to, or as part of, SUDS with very shallow runoff was investigated. Four scenarios were performed in triplicate to measure the flow velocity and the conservative solute transport across longitudinal section of flume (experimental indoors self-contained setup) using electrolyte tracer under different flow discharges (32–1813 ml s−1) with 0.8, 4.4 and 13.2% slopes. For one scenario, free water flow on a smooth surface was performed and results were used as control. For the three remaining scenarios: sand roughness, stone and synthetic grass covers were investigated. The ratio of the dispersion coefficient and flow velocity (i.e. dispersivity factor) was also determined and compared with control. Finally, data were analysed considering flow regimes, using the dimensionless Reynolds and Froude numbers. Results showed that surface covers caused reduction in the flow velocity, from 1.2 to 7.7 fold. However, dispersivity factor can be increased from 3 to nearly 10 orders of magnitude for the three scenarios, compared to control, due to the dual effect on hydrodynamic dispersion coefficient and flow velocity. Results here presented should be helpful to better understand dissolved non-point source pollution dispersion and how different land covers can effect pollutant removal.

Soil infiltration and conservative solute transport characteristics with different viscosity of hydroxypropyl methyl cellulose

AbstractHydroxypropyl methyl cellulose (HPMC), a potential soil improver with the ability to hold water, has practical applicability in alleviating soil and water nutrient loss. By using Cl− as tracer ions, we evaluated the effects of different HPMC viscosities on soil water infiltration characteristics and conservative solute migration characteristics. Hydroxypropyl methyl cellulose with viscosities of 2 × 104, 6 × 104, 10 × 104, and 20 × 104 mPa s−1 was selected. Experimental results revealed that the cumulative infiltration amount, wetting front migration distance, and infiltration rate decreased significantly with increased HPMC viscosity. The addition of HPMC delayed the soil solute transport process, and HPMC with a higher viscosity caused greater soil solute transport delay. Both the convection‐dispersion equation (CDE) and the two‐region model (TRM) accurately simulated solute transport, but the simulation accuracy of the TRM was higher. Results of parametric fitting based on the TRM indicated that the average pore water velocity, hydrodynamic dispersion coefficient, and dispersion degree decrease with increased HPMC viscosity. The average pore water velocity decreased by 13.6–28.2% relative to the control group (CG). Compared with the CG, the water content ratio in movable water of HPMC groups changed irregularly with an increase in viscosity. The mass exchange coefficient increased significantly compared with the CG, with an irregular trend. These data will be useful in the application and promotion of HPMC as a soil improver.

Assessment and Prediction of Pore‐Scale Reactive Mixing From Experimental Conservative Transport Data

AbstractWe investigate the impact of pore‐scale heterogeneity on reactive mixing using experimental data from inert fluid‐fluid displacement in a quasi 2‐D porous medium. We interpret the invading and defending fluids as the conservative components A+C and B+C of the instantaneous irreversible bimolecular chemical reaction A+B→C and determine the reaction product C. We find strong growth of the reaction rate at short and intermediate times due to deformation of the mixing interface and heterogeneity‐induced increase of the mixing area. This behavior is captured by a dispersive lamella approach that quantifies the mixing dynamics at the interface in terms of temporally evolving effective dispersion coefficients. The latter capture the dominant controls on the evolution of the mixing interface, namely, advective heterogeneity and transverse mixing. Reactive transport formulations based on constant hydrodynamic dispersion coefficients are not able to describe the observed behavior due to the lack of complete mixing on the support scale, which is required for these approaches to hold. These results shed some new light on the origins of heterogeneity‐induced mixing and reaction dynamics in porous media and their systematic upscaling.

Hydrodynamic Dispersion in Porous Media and the Significance of Lagrangian Time and Space Scales

Transport in porous media is critical for many applications in the environment and in the chemical process industry. A key parameter for modeling this transport is the hydrodynamic dispersion coefficient for particles and scalars in a porous medium, which has been found to depend on properties of the medium structure, on the dispersing compound, and on the flow field characteristics. Previous studies have resulted in suggestions of different equation forms, showing the relationship between the hydrodynamic dispersion coefficient for various types of porous media in various flow regimes and the Peclet number. The Peclet number is calculated based on a Eulerian length scale, such as the diameter of the spheres in packed beds, or the pore diameter. However, the nature of hydrodynamic dispersion is Lagrangian, and it should take the molecular diffusion effects, as well as the convection effects, into account. This work shifts attention to the Lagrangian time and length scales for the definition of the Peclet number. It is focused on the dependence of the longitudinal hydrodynamic dispersion coefficient on the effective Lagrangian Peclet number by using a Lagrangian length scale and the effective molecular diffusivity. The lattice Boltzmann method (LBM) was employed to simulate flow in porous media that were constituted by packed spheres, and Lagrangian particle tracking (LPT) was used to track the movement of individual dispersing particles. It was found that the hydrodynamic dispersion coefficient linearly depends on the effective Lagrangian Peclet number for packed beds with different types of packing. This linear equation describing the dependence of the dispersion coefficient on the effective Lagrangian Peclet number is both simpler and more accurate than the one formed using the effective Eulerian Peclet number. In addition, the slope of the line is a characteristic coefficient for a given medium.

A mathematical model for column leaching of ion adsorption-type rare earth ores

Column leaching experiments with ion adsorption-type rare earth ores for different lixiviant concentrations and different column heights were carried out. A mathematical model of column leaching was constructed based on the experimental data. Two parameters (a and b) in the model were determined according to the following methodology: the ore column was divided into several units; each unit was treated with multiple leaching steps. The leaching process was simulated as a series of batch leaching experiments. Parameter a of the model was determined based on the selectivity coefficient of the balanced batch leaching experiment. Further, the influences of ammonium sulfate concentration, rare earth grade, column height, permeability coefficient, and hydrodynamic dispersion coefficient on the extraction were analyzed. Relationships between parameter b, the ammonium sulfate concentration, and the physical and mechanical properties of the ore column, were examined using dimensional analysis. It was determined that the optimal ammonium sulfate concentration for different column heights (2.5, 5.0, 7.5, and 10.0 cm) using the mathematical model were 5.9, 6.2, 7.3, and 7.7 g/L, respectively. The mathematical model can be used to estimate the breakthrough curve, leaching rate, and leaching period of rare earth ores, to achieve optimal extraction.

Preasymptotic Taylor dispersion: evolution from the initial condition

Although the process of hydrodynamic dispersion has been studied for many years, the description of solute spreading at early times has proved to be challenging. In particular, for some kinds of initial conditions, the solute evolution may exhibit a second moment that decreases (rather than increases, as is typically observed) in time. Most classical approaches would predict a negative effective hydrodynamic dispersion coefficient for such a situation. This creates some difficulties: not only does a negative dispersion coefficient lead to a violation of the second law of thermodynamics, but it also creates a mathematically ill-posed problem. We outline a set of four desirable qualities in a well-structured theory of unsteady dispersion as follows: (i) positivity of the dispersion coefficient, (ii) non-dependence upon initial conditions, (iii) superposability of solutions and (iv) convergence of solutions to classical asymptotic results. We use averaging to develop an upscaled result that adheres to these qualities. We find that the upscaled equation contains a source term that accounts for the relaxation of the initial configuration. This term decreases exponentially fast in time, leading to correct asymptotic behaviour while also accounting for the early-time solute dynamics. Analytical solutions are presented for both the effective dispersion coefficient and the source term, and we compare our upscaled results with averaged solutions obtained from numerical simulations; both averaged concentrations and spatial moments are compared. Error estimates are quantified, and we find good correspondence between the upscaled theory and the numerical results for all times.

Solute Dispersion of Organic Compounds on Undisturbed Soil Columns

Results of column tests performed on large undisturbed samples are presented, focusing on the behavior of the hydrodynamic dispersion coefficient ($$D_h$$). Tests were performed employing petroleum produced water from onshore facilities percolating sandy soils with different fine contents. To measure the organic content of the produced water, this work used the parameter TPH (total petroleum hydrocarbons). The obtained results show that the longitudinal dispersion coefficient ($$\alpha _L$$) varies with flow velocity ($$v_s$$) and that both the ratio between the hydrodynamic dispersion and diffusion coefficients ($$D_h/D$$) and $$\alpha _L$$ are approximately two orders of magnitude higher than the values normally found in the literature for the same type of soil. This is probably related to the fact that the organic compounds measured by TPH in the produced water are partially in dissolved form, but dispersed particles are also transported by water flow, increasing the experimental values of $$D_h$$.

Hydrodynamic Dispersion Coefficient of Urea in Silty Loam Soil

The modern theme of agriculture is not only to increase production but also to minimize undesirable environmental effects. Leaching of surface-applied fertilizer is the major source of groundwater pollution. Nitrogenous fertilizers are the most popular among the Indian farmers, which on leaching reach the groundwater in different forms (NH4-N, NO3-N, etc). NO3-N leaches faster than other types, remains in-reactive in groundwater, moves with the velocity of groundwater and contaminates it. Contamination arises when NO3-N accumulates in groundwater and consumed in high amount by humans and animals, may result in adverse health effects. For the study of contaminant transport phenomenon in porous medium, a general convection dispersion equation is used, in which dispersion coefficient is one of the primary parameters necessary to be determined for a particular soil. Keeping it in view a study was conducted to assess different available techniques to determine the dispersion coefficient with the help of soil columns having silty loam soil as soil medium. The value of the dispersion coefficient obtained for silty loam soil, by this method was equal to 0.00576 m2.

Simulating Zn, Cd and Ni Transport in Disturbed and Undisturbed Soil Columns: Comparison of Alternative Models

This study compared four solute transport models for three heavy metals, i.e. Zn, Cd and Ni, in two disturbed and undisturbed loamy soil columns. The models include convection–dispersion equation (CDE), mobile–immobile model (MIM), fractional advection–dispersion equation (FADE) and the continuous time random walk model (CTRW). The experiments were carried out for each metal at three initial concentrations (C0 = 50, 100 and 150 mg L−1) and three replications in both soil columns. The results indicated that CDE, MIM, FADE and CTRW, with r2 > 0.98 and RMSE Ni > Cd. The hydrodynamic dispersion coefficient (D) in the undisturbed soil was higher than the disturbed soil. The spreading parameter (β) of CTRW and the fractional differentiation orders (α) in FADE were approximately 1.0 and 1.7, respectively. Consequently, the heavy metal transport within both soil columns were anomalous or non-Fickian transport. However, CDE and MIM, which are based on Fickian diffusion law, were more appropriate for simulating heavy metal transport through two soil columns in comparison with CTRW and FADE.

Relationship between bed heterogeneity, chord length distribution, and longitudinal dispersion in particulate beds

We analyse a relationship between the bulk microstructure of randomly packed beds, which we quantify through chord length distribution (CLD) analysis of the interparticle void space, and the associated flow heterogeneity, as expressed by the longitudinal dispersion coefficient at a Péclet number of Pe = 10. A random collection of physically reconstructed packings is complemented with a systematic set of computer-generated packings of monosized spheres, for which the packing-generation algorithm has been carefully adjusted to realize a monotonic variation of the bed porosity and microstructural heterogeneity. The most relevant difference in the morphology between these computer-generated and the physically reconstructed packings are structural defects present in the real packings, such as particle oligomers and larger voids as well as contaminations and particle debris. These defects influence the pore space morphology and introduce additional structural heterogeneity. Hydrodynamic dispersion coefficients for all packings are derived by implementing the lattice-Boltzmann method to simulate fluid flow and a random-walk particle tracking technique to record the transport of passive, point-like tracers in the flow fields. We propose a morphological descriptor, σ/μ, based on statistical parameters of a CLD (standard deviation σ and mean chord length μ) that can be used to predict the dispersion coefficient in packed beds, independent from the underlying particle size distribution, packing-generation protocol, bed porosity, and the occurrence of structural defects.

Impact of Synthetic Porous Medium Geometric Properties on Solute Transport Using Direct 3D Pore-Scale Simulations

Transport processes in porous media have been traditionally studied through the parameterization of macroscale properties, by means of volume-averaging or upscaling methods over a representative elementary volume. The possibility of upscaling results from pore-scale simulations, to obtain volume-averaging properties useful for practical purpose, can enhance the understanding of transport effects that manifest at larger scales. Several studies have been carried out to investigate the impact of the geometric properties of porous media on transport processes for solute species. However, the range of pore-scale geometric properties, which can be investigated, is usually limited to the number of samples acquired from microcomputed tomography images of real porous media. The present study takes advantage of synthetic porous medium generation to propose a systematic analysis of the relationships between geometric features of the porous media and transport processes through direct simulations of fluid flow and advection-diffusion of a non-reactive solute. Numerical simulations are performed with the lattice Boltzmann method on synthetic media generated with a geostatistically based approach. Our findings suggest that the advective transport is primarily affected by the specific surface area and the mean curvature of the porous medium, while the effective diffusion coefficient scales as the inverse of the tortuosity squared. Finally, the possibility of estimating the hydrodynamic dispersion coefficient knowing only the geometric properties of porous media and the applied pressure gradient has been tested, within the range of tested porous media, against advection-diffusion simulations at low Reynolds (<10-1) and Peclet numbers ranging from 101 to 10-2.

Using a physical model to determine the hydrodynamic dispersion coefficient of a solution through a horizontal sand column

Miscible displacement can be understood as a physical process in a porous medium whereby two or more fluids fully dissolve into each other when a fluid mixes and goes into the pore space occupied by other fluids without the existence of an interface. A physical model was made in Can Tho University, which included an electrical current system connecting nine groups of four-electrode probes for measuring the electrical conductivity of a potassium chloride solution flowing through a horizontal sand column placed in a firm frame. The experiments were performed with different volumetric flow rates and three types of sand (fine, medium and coarse). The breakthrough curves were analysed, and then the hydrodynamic dispersion coefficients were calculated. The hydrodynamic dispersion coefficient was one of the hydraulic and solute transport parameters used to design a constructed subsurface flow wetland. The research proves that the flows were laminar, and that mechanical dispersions dominated over molecular diffusions and that the dispersions were large enough to cause combined mixing and flowing processes.

Contribution to the evaluation of solute transport properties in a karstic aquifer (Yucatan, Mexico)

In the process of solute transport, dispersivity and hydrodynamic dispersion coefficients are important factors that define the distribution and migration of dissolved salts in the aquifer. Tracer tests were carried out in wells located in the northeast coast of Yucatan, Mexico, whereby only the freshwater thickness of the aquifer was analyzed. Sodium chloride (NaCl) was used as a tracer. Groundwater flow velocity was estimated with the Drost dilution point method. To analyse the solute transport, the analytical model for instantaneous injection was chosen, which is derived from the advection–dispersion equation, and the dispersivity and longitudinal dispersion coefficients were determined. The results indicate that the longitudinal dispersivity and hydrodynamic dispersion of the aquifer vary from 2.56 to 2,500 m and between 1 × 10−3 and 1 × 10−2 m2/s, respectively. In the areas of Telchac Puerto, Dzilam Bravo and San Felipe, advection is the most important solute transport mechanism, while El Cuyo has lower velocity ranges than other locations in the study area and salts tend to disperse. Groundwater flow velocity varies between 3.1 × 10−7 and 8.65 × 10−5 m/s, associated with the flow in the karstic aquifer matrix, with maximum values ​​of 1.5 × 10−4 m/s, associated with the karstification of the aquifer. Groundwater flow velocity increases towards the coast, which is consistent with the fact that the aquifer discharges to the sea. It is observed that in the first 10 m of aquifer, the velocities are higher than those determined in deeper layers, up to an order of magnitude.

Hydrodynamic dispersion due to a variety of flow velocity profiles in a porous-walled microfluidic channel

A reduced-order model for the advective-dispersive mass transfer due to a variety of flow velocity profiles in a porous-walled microfluidic channel is developed in this study. The fluid flow in the microfluidic channel is described by a generalized class of the Poiseuille equation proposed by Amatore et al. (2009), which includes the bluntness parameter for exhibiting the level of bluntness of the velocity profile. This flow formulation represents all the traditional velocity profiles for the purely pressure-driven (Poiseuille) flow, the combined pressure-driven and electro-osmotic flows, and the purely electro-osmotic flow (EOF) in the microfluidic channel. The resulting reduced-order model delivers the mass transfer coefficients, including the hydrodynamic dispersion and the effective advection coefficients, which are functions of the Peclet number and the bluntness parameter. The results reveal that the hydrodynamic dispersion decreases when the flow varies from the pressure-driven to the electro-osmotic. In other words, the smaller the bluntness parameter the smaller the hydrodynamic dispersion. The diffusive, transient, and advective mass transfer regimes can be identified from the ratio of the hydrodynamic dispersion coefficient in the porous-walled microfluidic channel to the one in the nonporous-walled microfluidic channel. It is found that the mass transfer between the microfluidic channel and the porous medium should be included in determination of the hydrodynamic dispersion coefficient due to a variety of flow velocity profiles in a porous-walled microfluidic channel for the transient and the advective regimes. The results also show that the smaller the bluntness parameter the slower the mass transfer. Furthermore, the mass transfer in a porous-walled microfluidic channel is slower than the mass transfer in a nonporous-walled microfluidic channel.

The effect of pH and ionic strength on the transport of alumina nanofluids in water-saturated porous media

Alumina nanofluids are one of the most useful nanofluids, especially for increasing the thermal conductivity. Due to importance of porous media in the improvement of heat transfer, this study investigates the transport and retention of gamma alumina/water nanofluid in the water-saturated porous media. For this purpose, alumina nanofluids were introduced to the porous media consisting of water-saturated glass beads possessing various pH values (4, 7 and 10) and different ionic strengths (0.001 M of KCl, CaCl2, AlCl3, K2SO4, CaSO4, Al2(SO4)3, K2CO3 and CaCO3). Then the break through curve of each experiment was drawn and modeled by combining classical filtration theory with advection–dispersion equation. Single collector efficiency (η0) and attachment efficiency (α) were calculated by classical filtration theory. Also curve fitting of experiments and modeling was achieved by minimizing the sum of squared residuals, to calculate retardation factor (R) and hydrodynamic dispersion coefficient (D) of each experiment. According to the results, in general, increase in pH and ionic strength will enhance the removal rate coefficient, retardation factor and retention while decreasing the steady-state break through concentration and the hydrodynamic dispersion coefficient. The opposite of this rule was observed and analyzed for aluminum salts. The lowest retention of nanoparticles at 31.04% can be related to their transport in background solution with pH = 4 [α = $$3.87 \times 10^{ - 2}$$ , Katt = $$3.33 \times 10^{ - 3}$$ (min−1), R = 3.93, D = 0.91 (cm2 min−1)], and the highest retention in nanoparticle content of 94.29% was observed in background solution containing CaCO3 [α = $$14.33 \times 10^{ - 2}$$ , Katt = $$137.82 \times 10^{ - 3}$$ (min−1), R = 12.02, D = 0.62 (cm2 min−1)]. Therefore, chemistry of water plays an important role in transport and retention parameters. The classical filtration theory and the advection–dispersion model are able to perfectly model and quantify the parameters of the alumina nanofluid transport in saturated porous media.

Evaluation of Natural Zeolite as a Material for Permeable Reactive Barrier for Remediation of Zinc-Contaminated Groundwater Based on Column Study

The permeable reactive barrier (PRB) filled with natural zeolite plays the role of a reactive treatment zone for remediation of contaminated groundwater. Based on column lab experiments, the volume of remediated solution, the distribution (Kd) and retardation (Rd) coefficients were evaluated, confirming successful removal and retention of zinc from contaminated groundwater. The effect of hydrodynamic dispersion on zinc capturing by zeolite in PRB was evaluated by the hydrodynamic dispersion coefficient (DL) and retarded hydrodynamic dispersion coefficient (DLR) using the Brigham method. For different assumed distances of the barrier, the simulation of one-dimensional zinc concentration profile from the point source through the barrier has been modeled by a simple analytical pulse model. The results show that the flow rate has the most significant effect on the concentration profile, peaks, and broadening of curves. The residence contact time (τ) corresponding to higher Kd and Rd as well as lower DL and DLR values outcomes the optimal range of 6.2–9.4 min. This interval corresponds to the experimental performance at the bed length of 8 and 12 cm and flow rate in the range of 6.38–9.57 PV/h. The calculated minimum thickness and longevity confirm the successful application of zeolite as a material in PRB for remediation of zinc contaminated groundwater.