Pore Scale Variation in Retardation Factor as a Cause of Nonideal Reactive Breakthrough Curves: 2. Pore Network Analysis

Adsorption of solutes in porous media is typically represented as an equilibrium process. The adsorption process is determined by the concentration of the solute in the fluid next to the solid grain in individual pores. The concentration near the solid surface is different from the average concentration within the pore due to the development of concentration gradients within the pore space. Simulations with pore network models are usually based on the average concentration in individual pore throats. To advance the realism of such models, we develop a relationship between pore-scale adsorption coefficients and corresponding coarse-grained adsorption parameters. A numerical scheme is proposed: firstly the solute transport within a single pore is simulated undergoing equilibrium adsorption at the pore wall, and secondly flux-averaged concentration breakthrough curves are obtained. By fitting the breakthrough curves, the coarse-grained adsorption parameters are determined from the pore-scale hydraulic and adsorption parameters.

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Parameter Determination for Chloride and Tritium Transport in Undisturbed Lysimeters during Steady Flow

Hydrology Research ◽

10.2166/nh.1992.0007 ◽

1992 ◽

Vol 23 (2) ◽

pp. 89-104 ◽

Cited By ~ 30

Author(s):

Ole H. Jacobsen ◽

Feike J. Leij ◽

Martinus Th. van Genuchten

Keyword(s):

Experimental Data ◽

Unsaturated Flow ◽

Transport Model ◽

Time Moment ◽

Breakthrough Curves ◽

Coarse Sand ◽

Retardation Factor ◽

Parameter Determination ◽

Model Parameters ◽

Water Fraction

Breakthrough curves of Cl and 3H2O were obtained during steady unsaturated flow in five lysimeters containing an undisturbed coarse sand (Orthic Haplohumod). The experimental data were analyzed in terms of the classical two-parameter convection-dispersion equation and a four-parameter two-region type physical nonequilibrium solute transport model. Model parameters were obtained by both curve fitting and time moment analysis. The four-parameter model provided a much better fit to the data for three soil columns, but performed only slightly better for the two remaining columns. The retardation factor for Cl was about 10 % less than for 3H2O, indicating some anion exclusion. For the four-parameter model the average immobile water fraction was 0.14 and the Peclet numbers of the mobile region varied between 50 and 200. Time moments analysis proved to be a useful tool for quantifying the break through curve (BTC) although the moments were found to be sensitive to experimental scattering in the measured data at larger times. Also, fitted parameters described the experimental data better than moment generated parameter values.

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Transport of Microorganisms in the Underground – Processes, Experiments and Simulation Models

Water Science & Technology ◽

10.2166/wst.1991.0080 ◽

1991 ◽

Vol 24 (2) ◽

pp. 309-314 ◽

Cited By ~ 16

Author(s):

G. Teutsch ◽

K. Herbold-Paschke ◽

D. Tougianidou ◽

T. Hahn ◽

K. Botzenhart

Keyword(s):

Simulation Models ◽

Mass Conservation ◽

Breakthrough Curves ◽

Conservation Equation ◽

Retardation Factor ◽

Natural Systems ◽

Laboratory Setup ◽

Preliminary Model ◽

Sand And Gravel ◽

Mass Conservation Equation

In this paper the major processes governing the persistence and underground transport of viruses and bacteria are reviewed in respect to their importance under naturally occurring conditions. In general, the simulation of the governing processes is based on the macroscopic mass-conservation equation with the addition of some filter and/or retardation factor and a decay coefficient, representing the natural “die-off” of the microorganisms. More advanced concepts try to incorporate growth and decay coefficients together with deposition and declogging factors. At present, none of the reported concepts has been seriously validated. Due to the complexity of natural systems and the pathogenic properties of some of the microorganisms, experiments under controlled laboratory conditions are required. A laboratory setup is presented in which a great variety of natural conditions can be simulated. This comprises a set of 1 metre columns and an 8 metre stainless-steel flume with 24 sampling ports. The columns are easily filled and conditioned and therefore used to study the effects of different soil-microorganism combinations under various environmental conditions. In the artificial flume natural underground conditions are simulated using sand and gravel aquifer material from the river Neckar alluvium. A first set of results from the laboratory experiments is presented together with preliminary model simulations. The large variety of observed breakthrough curves and recovery for the bacteria and viruses under investigation demonstrates the great uncertainty encountered in microbiological risk assessment.

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The impact of porosity on organic matter cycling in a two-dimensional porous medium

10.5194/egusphere-egu21-9432 ◽

2021 ◽

Author(s):

Hanbang Zou ◽

Pelle Ohlsson ◽

Edith Hammer

Keyword(s):

Porous Medium ◽

Organic Matter ◽

Carbon Sequestration ◽

Soil Carbon ◽

Pore Network ◽

Pore Scale ◽

Decomposition Of Organic Matter ◽

Organic Matter Cycling ◽

The Impact

Carbon sequestration has been a popular research topic in recent years as the rapid elevation of carbon emission has significantly impacted our climate. Apart from carbon capture and storage in e.g. oil reservoirs, soil carbon sequestration offers a long term and safe solution for the environment and human beings. The net soil carbon budget is determined by the balance between terrestrial ecosystem sink and sources of respiration to atmospheric carbon dioxide. Carbon can be long term stored as organic matters in the soil whereas it can be released from the decomposition of organic matter. The complex pore networks in the soil are believed to be able to "protect" microbial-derived organic matter from decomposition. Therefore, it is important to understand how soil structure impacts organic matter cycling at the pore scale. However, there are limited experimental studies on understanding the mechanism of physical stabilization of organic matter. Hence, my project plan is to create a heterogeneous microfluidic porous microenvironment to mimic the complex soil pore network which allows us to investigate the ability of organisms to access spaces starting from an initial ecophysiological precondition to changes of spatial accessibility mediated by interactions with the microbial community.Microfluidics is a powerful tool that enables studies of fundamental physics, rapid measurements and real-time visualisation in a complex spatial microstructure that can be designed and controlled. Many complex processes can now be visualized enabled by the development of microfluidics and photolithography, such as microbial dynamics in pore-scale soil systems and pore network modification mimicking different soil environments &#8211; earlier considered impossible to achieve experimentally. The microfluidic channel used in this project contains a random distribution of cylindrical pillars of different sizes so as to mimic the variations found in real soil. The randomness in the design creates various spatial availability for microbes (preferential flow paths with dead-end or continuous flow) as an invasion of liquids proceeds into the pore with the lowest capillary entry pressure. In order to study the impact of different porosity in isolation of varying heterogeneity of the porous medium, different pore size chips that use the same randomly generated pore network is created. Those chips have the same location of the pillars, but the relative size of each pillar is scaled. The experiments will be carried out using sterile cultures of fluorescent bacteria, fungi and protists, synthetic communities of combinations of these, or a whole soil community inoculum. We will quantify the consumption of organic matter from the different areas via fluorescent substrates, and the bio-/necromass produced. We hypothesise that lower porosity will reduce the net decomposition of organic matter as the narrower pore throat limits the access, and that net decomposition rate at the main preferential path will be higher than inside branches

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DETERMINATION OF TRANSPORT PARAMETERS FOR SOLUTES IN SALT-TREATED SOIL COLUMNS

IRAQI JOURNAL OF AGRICULTURAL SCIENCES ◽

10.36103/ijas.v48i1.436 ◽

2017 ◽

Vol 48 (1) ◽

Author(s):

Bahia & Naser

Keyword(s):

Sodium Chloride ◽

Calcium Chloride ◽

Peclet Number ◽

Dispersion Coefficient ◽

Breakthrough Curves ◽

Retardation Factor ◽

Transport Parameters ◽

Péclet Number ◽

Mixed Salts ◽

Sodium And Potassium

A laboratory experiment was carried out at the Department of Soil Sciences and Water Resources, College of Agriculture, University of Baghdad. Silty clay soil was treated with three salt solutions (NaCl, CaCl2 and mixed NaCl–CaCl2). Homogeneously packed soil columns (10 cm, 40 cm) were leached six times using tap water. Effluent samples were collected to determine ion concentration Cl-, Ca++, Na+, K+ and Mg++. Breakthrough curves were used to estimate solute transport parameters (retardation factor, peclet number) using an analytical solution of convection-dispersion equation (CDE) by CXTFIT program. The results showed that relative concentration of chloride was increased rapidly with calcium chloride, which increased sodium leaching rate at starting of breakthrough curve. Sodium chloride increased water requirements for calcium displacement. Results indicated a good fitting of convection-dispersion equation with breakthrough curves data. The best-fit were used to calculate peclet number, retardation factor and dispersion coefficient. When soil was treated with calcium chloride, Peclet number of chloride was increased from 3.13 to 6.48, while it has been decreased for calcium, sodium and potassium. Sodium chloride decreased peclet numbers of chloride, calcium and sodium. Also mixed salts increased sodium peclet number from 1.01 to 9.02. Results showed, calcium chloride decreased retardation factor of chloride from 1.59 to 0.50, while it has been increased from 1.39, 1.58 to 175.00, 493.36 for each of sodium and potassium, respectively. Retardation factor of calcium was decreased when soil was treated with sodium chloride or mixed salts. Dispersion coefficient was decreased for chloride, and increased for calcium and magnesium. When soil was treated with calcium chloride, dispersion coefficients have been increased from 24.29, 25.56 to 40.51, 40.89 cm2hr-1 for sodium and potassium, respectively.

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Pore-scale Mixing and the Evolution from Anomalous to Normal Hydrodynamic Dispersion

10.5194/egusphere-egu21-13655 ◽

2021 ◽

Author(s):

Marco Dentz ◽

Alexandre Puyguiraud ◽

Philippe Gouze

Keyword(s):

Porous Media ◽

Large Scale ◽

Molecular Diffusion ◽

Pore Space ◽

Breakthrough Curves ◽

Heterogeneous Porous Media ◽

Hydrodynamic Dispersion ◽

Pore Scale ◽

Sandstone Sample ◽

Flow Variability

Transport of dissolved substances through porous media is determined by the complexity of the pore space and diffusive mass transfer within and between pores. The interplay of diffusive pore-scale mixing and spatial flow variability are key for the understanding of transport and reaction phenomena in porous media. We study the interplay of pore-scale mixing and network-scale advection through heterogeneous porous media, and its role for the evolution and asymptotic behavior of hydrodynamic dispersion. In a Lagrangian framework, we identify three fundamental mechanisms of pore-scale mixing that determine large scale particle motion: (i) The smoothing of intra-pore velocity contrasts, (ii) the increase of the tortuosity of particle paths, and (iii) the setting of a maximum time for particle transitions. Based on these mechanisms, we derive an upscaled approach that predicts anomalous and normal hydrodynamic dispersion based on the characteristic pore length, Eulerian velocity distribution and P&#233;clet number. The theoretical developments are supported and validated by direct numerical flow and transport simulations in a three-dimensional digitized Berea sandstone sample obtained using X-Ray microtomography. Solute breakthrough curves, are characterized by an intermediate power-law behavior and exponential cut-off, which reflect pore-scale velocity variability and intra-pore solute mixing. Similarly, dispersion evolves from molecular diffusion at early times to asymptotic hydrodynamics dispersion via an intermediate superdiffusive regime. The theory captures the full evolution form anomalous to normal transport behavior at different P&#233;clet numbers as well as the P&#233;clet-dependence of asymptotic dispersion. It sheds light on hydrodynamic dispersion behaviors as a consequence of the interaction between pore-scale mixing and Eulerian flow variability.&#160;

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