One-dimensional Transport Model Research Articles

Analysis of 1D Contaminant Migration through Saturated Soil Media Underlying Aquifer Using FDM

AbstractFinite-difference method (FDM) has been adapted herein to solve a one-dimensional (1D) contaminant transport model to predict contaminant migration through soil in waste landfill underlying an aquifer. Providing an effective engineered barrier, which will separate the waste from groundwater, can minimize the potential contamination in the groundwater system. In this paper, a solution technique has been developed using FDM for the analysis of 1D contaminant transport in a layer of finite thickness. The present study considers the effects of advection, dispersion/diffusion, geochemical reactions, and decay in a single model with a finite quantity of pollutant in the landfill and transport of contaminants toward groundwater beneath the clay deposit/liner. The computer program CONTAMINATE-1D-FM has been developed using the proposed solution technique to analyze the contaminant migration. The short-term and long-term effects of different factors influencing groundwater contamination have been presented...

Estimation of transport parameters of phenolic compounds and inorganic contaminants through composite landfill liners using one-dimensional mass transport model

One-dimensional (1D) advection–dispersion transport modeling was conducted as a conceptual approach for the estimation of the transport parameters of fourteen different phenolic compounds (phenol, 2-CP, 2-MP, 3-MP, 4-MP, 2-NP, 4-NP, 2,4-DNP, 2,4-DCP, 2,6-DCP, 2,4,5-TCP, 2,4,6-TCP, 2,3,4,6-TeCP, PCP) and three different inorganic contaminants (Cu, Zn, Fe) migrating downward through the several liner systems. Four identical pilot-scale landfill reactors (0.25 m 3) with different composite liners (R1: 0.10 + 0.10 m of compacted clay liner (CCL), L e = 0.20 m, k e = 1 × 10 −8 m/s, R2: 0.002-m-thick damaged high-density polyethylene (HDPE) geomembrane overlying 0.10 + 0.10 m of CCL, L e = 0.20 m, k e = 1 × 10 −8 m/s, R3: 0.002-m-thick damaged HDPE geomembrane overlying a 0.02-m-thick bentonite layer encapsulated between 0.10 + 0.10 m CCL, L e = 0.22 m, k e = 1 × 10 −8 m/s, R4: 0.002-m-thick damaged HDPE geomembrane overlying a 0.02-m-thick zeolite layer encapsulated between 0.10 + 0.10 m CCL, L e = 0.22 m, k e = 4.24 × 10 −7 m/s) were simultaneously run for a period of about 540 days to investigate the nature of diffusive and advective transport of the selected organic and inorganic contaminants. The results of 1D transport model showed that the highest molecular diffusion coefficients, ranging from 4.77 × 10 −10 to 10.67 × 10 −10 m 2/s, were estimated for phenol (R4), 2-MP (R1), 2,4-DNP (R2), 2,4-DCP (R1), 2,6-DCP (R2), 2,4,5-TCP (R2) and 2,3,4,6-TeCP (R1). For all reactors, dispersion coefficients of Cu, ranging from 3.47 × 10 −6 m 2/s to 5.37 × 10 −2 m 2/s, was determined to be higher than others obtained for Zn and Fe. Average molecular diffusion coefficients of phenolic compounds were estimated to be about 5.64 × 10 −10 m 2/s, 5.37 × 10 −10 m 2/s, 2.69 × 10 −10 m 2/s and 3.29 × 10 −10 m 2/s for R1, R2, R3 and R4 systems, respectively. The findings of this study clearly indicated that about 35–50% of transport of phenolic compounds to the groundwater is believed to be prevented with the use of zeolite and bentonite materials in landfill liner systems.

Numerical modeling of diffusion for volatile organic compounds through composite landfill liner systems

Mass flux of solute exiting a landfill liner system is a valuable indicator for evaluating the performance of the Municipal Solid Waste (MSW) landfill liner systems. For the volatile organic compounds, such as toluene, the diffusion occurring inevitably in the intact landfill liner systems can transport toluene through the liner system and finally contaminate the outer groundwater. The diffusion of toluene, through four different municipal solid waste landfill liner systems, i.e., Subtitle D composite liner system, composite liner system with a Geosynthetic Clay Liner (GCL) instead of low permeability compacted soil, Wisconsin NR500 liner system, and a proposed four-component composite liner system that is a combination of the GCL composite liner system and the Subtitle D liner (with a 61 cm (2 feet) or 91.5 cm (3 feet) thick compacted clay liner), were evaluated in terms of mass flux. A one-dimensional block-centered numerical model of the diffusive transport through the four intact liner systems was developed for this purpose. The comparison of mass flux shows that the proposed four-component composite liner system outperforms the other liner systems based on mass flux and can be a preferable alternative for a MSW composite liner system.

Management of Groundwater Quality in Sodic Soils using Semi-analytical One-dimensional Solute Transport Model

A semi-analytical one-dimensional solute transport model to manage and predict groundwater quality was tested for its application in Golewala, Punjab. The model being semi-discrete and continuous in time has significant computational advantage over the existing ones, especially for long-term predictions. The model was tested for transport of soluble Ca + Mg, CO3 and HCO3 and EC in soil profile with respect to time under barren soil. The results showed that the model can be used to predict the status of total salt concentration at different depths with time and to manage ground water quality in sodic soils.

Numerical Investigation of the Quench Behavior of ${\rm Bi}_{2}{\rm Sr}_{2}{\rm CaCu}_{2}{\rm O}_{x}$ Wire

The quench behavior of Bi2Sr2CaCu2Ox (Bi2212) wire is investigated through numerical simulations. This work is part of the U.S. Very High Field Superconducting Magnet Collaboration (VHFSMC). Numerical simulations are carried out using a one-dimensional computational model of thermal transport in Bi2212 composite wires. A quench is simulated by introducing heat in a section of the wire, and the voltage and temperature are monitored as function of time and position. The quench energy, normal zone propagation velocity, and spatial distribution of temperature are calculated for varying transport current and applied magnetic field. The relevance of these simulations in defining criteria for experimental measurements is discussed.

Solution of a nonsymmetric algebraic Riccati equation from a one-dimensional multistate transport model

For the steady-state solution of a differential equation from a one-dimensional multistate model in transport theory, we shall derive and study a nonsymmetric algebraic Riccati equation B− – XF− – F+X + XB+X = 0, where F± ≡ (I – F)D± and B± ≡ BD± with positive diagonal matrices D± and possibly low-ranked matrices F and B. We prove the existence of the minimal positive solution X* under a set of physically reasonable assumptions and study its numerical computation by fixed-point iteration, Newton’s method and the doubling algorithm. We shall also study several special cases. For example when B and F are low ranked then X*=Γ∘(∑i=14UiViT) with low-ranked Ui and Vi that can be computed using more efficient iterative processes. Numerical examples will be given to illustrate our theoretical results.

Investigating the redox sensitivity of para-toluenesulfonamide (p-TSA) in groundwater

The groundwater downstream of a former sewage irrigation farm in Berlin is contaminated with ammonium (NH4 +) and para-toluenesulfonamide (p-TSA), besides other anthropogenic pollutants. In the field, in situ removal of NH4 + by gaseous oxygen (O2) and air injection is currently being tested. A laboratory column experiment using aquifer material and groundwater from the site was performed to determine whether this remediation technology is also feasible to reduce high p-TSA concentrations in the anoxic groundwater. First, the column was operated under anoxic conditions. Later, compressed air was introduced into the system to simulate oxic conditions. Samples were collected from the column outlet before and after the addition of compressed air. The experiment revealed that whereas p-TSA was not removed under anoxic conditions, it was almost fully eliminated under oxic conditions. Results were modelled using a transient one-dimensional solute transport model. The degradation rate constants for p-TSA increased from 2.8E−06 to 7.5E−05 s–1 as a result of microbial adaption to the change of redox conditions. Results show that O2 injection into an anoxic aquifer is a successful strategy for p-TSA remediation.

Groundwater Recharge through Vertisols: Irrigated Cropland vs. Natural Land, Israel

Land use change from natural ecosystems to cropland influences groundwater recharge, including water quantity and quality. Soil core samples (0–11‐m depth) from six boreholes beneath irrigated cropland and two boreholes beneath natural ecosystems, in Vertisols, were analyzed for particle size distribution, water content, and water‐extractable Cl− Chloride mass balance and numerical, one‐dimensional unsaturated flow and transport modeling were used to assess average and transient recharge fluxes and to test matrix vs. preferential flow hypotheses. Water contents under irrigated cropland were significantly higher than under natural land with similar particle size distributions. Pore‐water Cl− concentrations in deep vadose zones (>3 m) under irrigated cropland (900–2000 mg L−1) were similar to recent local groundwater Cl− and significantly lower than pore‐water Cl− in deep vadose zones under natural land (3000–6000 mg L−1). Calibrated models' recharge rates through the soil matrix were much higher under irrigated cropland (90–230 mm yr−1) than natural ecosystems (1–3 mm yr−1) and were consistent with groundwater‐balance estimates of average recharge (110–160 mm yr−1). In contrast, matrix recharge rates under natural ecosystems were considerably lower than those based groundwater balance (50–80 mm yr−1). While matrix unsaturated flow under irrigated cropland explains vadose zone and groundwater observations, under natural ecosystems preferential flow paths are required to support observations. Plowing and irrigation prevent development of crack networks and promote matrix percolation through the clay, which flushes salts from previously immobile vadose zone pore water. These phenomena may be applicable to similar land use changes in Vertisols globally.

One-Dimensional Surface Flow and Solute Transport Model for Basin Irrigation in Traditional Surface Application of Fertilizer

A basis of contrast for advanced basin fertigation method can be provided by simulating the one-dimensional surface flow and solute transport process of basin irrigation in traditional surface application of fertilizer. A nonuniform distribution field of water flow velocity and solute concentration along the basin and its arbitrary cross section were constructed on the basis of vertical linear and logarithmic law in turbulence theory and continuous equation of incompressible hydrodynamics. A one-dimensional surface flow and solute transport model for basin irrigation in traditional surface application of fertilizer was proposed. At the same time, validation of the proposed model was carried out by using the results of typical basin irrigation tests. Results show that the proposed model can efficiently simulate the water flow and solute transport processes of basin irrigation, and exhibits good potential in conservation of water and solute quantity. Thus, the proposed model provides a research numerical to...

Minority carrier transport length of electrodeposited Cu2O in ZnO/Cu2O heterojunction solar cells

The minority carrier transport length is a critical parameter limiting the performance of inexpensive Cu2O–ZnO photovoltaic devices. In this letter, this length is estimated to be ∼430 nm for electrochemically deposited Cu2O by linking the cell’s carrier generation profile with back and front incident photon-to-electron conversion efficiency measurements to a one-dimensional transport model. This critical length explains the losses typically presented by these devices and appears to correlate well with the microcrystalline film structure. The consequences of the magnitude of the length on device design with the aim of improving solar cell performance are described.

Mathematical modeling of two-phase flow and transport in an immobilized-cell photobioreactor

A one-dimensional two-phase flow and transport model is presented for a packed bed photobioreactor with transparent gel granules containing immobilized photosynthetic bacterial cells. The inherently coupled two-phase flow and mass transport, along with the biochemical reactions occurring in the photobioreactor are taken into account. The source term in the species conservation equation of the substrate is derived from a local transport model for a single gel granule. Model predictions of the glucose consumption efficiency and hydrogen production rate are in good agreement with experimental data. The results show that the photoinhibition of immobilized cells appears at incident light intensities higher than 6000 lux. It is the most suitable for photo-hydrogen production under neutral conditions and 30 °C of the influent substrate solution. Moreover, a high influent substrate solution flow rate results in a large hydrogen production rate due to the improved substrate transport from the bulk solution to gel granules.

Modelling long term corrosion behaviour of copper canisters in KBS-3 repository

The well known KBS-3 repository design involves the disposal of spent fuel in copper canisters in a deep geological repository sealed with clay based buffer and backfill materials. A one-dimensional reactive transport model has been developed to predict the evolution of the general corrosion behaviour of the copper canisters by the initially trapped O2 and by sulphide ions. Various sources of sulphide are considered, including the microbial reduction of sulphate, the dissolution of pyrite impurities and the ground water itself. The model has been used to simulate the evolution of the canister corrosion behaviour for various scenarios, including both the Olkiluoto and Forsmark proposed repository locations, the vertical and horizontal KBS-3 design variants, increased ground water sulphide or chloride concentrations, different microbial scenarios, different rates of repository saturation, and with and without the dissolution of pyrite. Following a brief description of the model, the results of these and other simulations are described.

The effects of flocculation and bed erodibility on modeling cohesive sediment resuspension

[1] Flocculation and bed erodibility are two main processes causing the transport of cohesive sediments to be more complicated than typical noncohesive sediments. Earlier flocculation models assume a constant fractal dimension and/or a constant floc yield strength. However, recent studies have shown that considering both the fractal dimension and the floc yield strength to be variable is critical to the prediction of temporal evolution of floc size. Due to consolidation, it is also well established that critical bed shear stress of a mud bed cannot be parameterized as a constant. This study further investigates how flocculation models with different degrees of complexity and bed erodibility can affect the resulting cohesive sediment resuspension driven by tidal flows. A one-dimensional vertical numerical model for sediment transport is revised to incorporate modules for flocculation and bed erodibility. Model results are compared with data measured in the Ems/Dollard estuary. Model study suggests that it is important to incorporate variable critical shear stress in order to properly model the supply of sediment from the bed. When flocculation is neglected or incorporated incompletely, numerical model predicts nearly zero sediment concentration during slack water and very steep concentration gradient, which are inconsistent with the observed data. When the fractal dimension and the floc yield strength are both considered to be variable, the numerical model predicts much smaller settling velocity and hence captures the more well-mixed condition consistent with field observations.

Frequency Dependence of Alternating Current Electrospray Ionization Mass Spectrometry

The novel effects resulting from the entrainment of low mobility ions during alternating current (ac) electrospray ionization are examined through mass spectrometry and voltage/current measurements. Curious phenomena such as pH modulation at high frequencies (>150 kHz) of an applied ac electric field are revealed and explained using simple mechanistic arguments. Current measurements are utilized to supplement these observations, and a simplified one-dimensional transient diffusion model for charge transport is used to arrive at a scaling law that provides better insight into the ac electrospray ionization process. Moreover, because of the different pathway for ion formation in comparison to direct current (dc) electrospray, ac electrospray (at frequencies >250 kHz) is shown to reduce the effects of ionization suppression in a mixture of two molecules with different surface activities.

Modeling Two-Phase Water Transport in Hydrophobic Diffusion Media for PEM Fuel Cells

The prevailing method for modeling water transport in hydrophobic fuel cell diffusion media employs the same two-phase generalization of Darcy’s law widely used for analyzing the movement of oil and water through soil and porous rock. Recent experiments, however, have identified certain problems when the same approach is applied to the nonwoven carbon papers used in fuel cell diffusion media. These problems could be addressed by generalizing the Darcy formulation still more, but significant challenges, such as measuring the relevant material properties, still remain. Instead, this paper proposes a simpler model adapted specifically for fuel cells. Based on analysis of published experiments, the proposed one-dimensional model for heat and two-phase water transport assumes a uniform liquid pore saturation wherever the diffusion medium is wet and neglects the capillary pressure gradients required to transport water in liquid form. In addition to the properties for dry transport, the two-phase water transport model requires just one additional material parameter—the ratio of dry to wet effective gas diffusion coefficients—which can be measured by straightforward limiting current methods. Example half-cell solutions for a Toray diffusion medium show how the proposed model can reproduce changes in oxygen transport resistance observed in limiting current experiments.

Transport and Bacterial Interactions of Three Bacterial Strains in Saturated Column Experiments

The impact of bacteria-solid and bacteria-bacteria interactions on the transport of Klebsiella oxytoca, Burkholderia cepacia G4PR1, and Pseudomonas sp. #5 was investigated in saturated sand column experiments (L = 114 mm; ø = 33 mm) under constant water velocities (∼ 5 cm · h(-1)). Bacterial strains were injected into the columns as pulses either individually, simultaneously, or successively. A one-dimensional mathematical model for advective-dispersive transport and for irreversible and reversible bacterial kinetic sorption was used to analyze the bacterial breakthrough curves. Different sorption parameters were obtained for each strain in each of the three experimental setups. In the presence of other bacteria, sorption parameters for B. cepacia G4PR1 remained similar to results from individual experiments, indicating the presence of other bacteria generally had a lesser influence on its migration than for the other bacteria. K. oxytoca is more competitive for the sorption sites when simultaneously injected with the other bacteria. Ps. sp. #5 generally yielded the greatest detachment rates and the least affinity to attach to the sand, indicative of its mobility in groundwater systems. The results of this study clearly indicate both bacteria-solid and bacteria-bacteria interactions influence the migration of bacteria. A more complete understanding of such interactions is necessary to determine potential migration in groundwater systems.

A field and reactive transport model study of arsenic in a basaltic rock aquifer

Abstract The use of geothermal energy as a source for electricity and district heating has increased over recent decades. Dissolved As can be an important constituent of the geothermal fluids brought to the Earth’s surface. Here the field application of laboratory measured adsorption coefficients of aqueous As species on basaltic glass surfaces is discussed. The mobility of As species in the basaltic aquifer in the Nesjavellir geothermal system, Iceland was modelled by the one-dimensional (1D) reactive transport model PHREEQC ver. 2, constrained by a long time series of field measurements with the chemical composition of geothermal effluent fluids, pH, Eh and, occasionally, Fe- and As-dissolved species measurements. Di-, tri- and tetrathioarsenic species ( As ( OH ) S 2 2 - , AsS 3 H 2− , AsS 3 3 - and As ( SH ) 4 - ) were the dominant form of dissolved As in geothermal waters exiting the power plant (2.556 μM total As) but converted to some extent to arsenite (H 3 AsO 3 ) and arsenate HAsO 4 2 - oxyanions coinciding with rapid oxidation of S 2 - to S 2 O 3 2 - and finally to SO 4 2 - during surface runoff before feeding into a basaltic lava field with a total As concentration of 0.882 μM following dilution with other surface waters. A continuous 25-a data set monitoring groundwater chemistry along a cross section of warm springs on the Lake Thingvallavatn shoreline allowed calibration of the 1D model. Furthermore, a series of ground water wells located in the basaltic lava field, provided access along the line of flow of the geothermal effluent waters towards the lake. The conservative ion Cl − moved through the basaltic lava field (4100 m) in less than10 a but As was retarded considerably due to surface reactions and has entered a groundwater well 850 m down the flow path as arsenate in accordance to the prediction of the 1D model. The 1D model predicted a complete breakthrough of arsenate in the year 2100. In a reduced system arsenite should be retained for about 1 ka.

Thermophysical Optimization of Specialized Concrete Pavement Materials for Collection of Surface Heat Energy and Applications for Shallow Heat Storage

Great potential exists to use pavement structures to collect or store solar energy for heating and cooling of adjacent buildings, for example, airport terminals and shopping malls. Therefore, pavement materials comprising both conventional and unconventional concrete mixtures with a wide range of densities, thermal conductivities, specific heat capacities, and thermal diffusivities were investigated. The thermophysical properties were then used as inputs to a one-dimensional transient heat transport model to evaluate temperature changes at various depths at which heat might be abstracted or stored. Results indicated that a high diffusivity pavement (e.g., one that incorporated high conductive aggregates or metallic fibers, or both) could significantly enhance heat transfer as well as reduce thermal stresses across the concrete slab. However, a low diffusivity concrete could induce a more stable temperature at shallower depths and enable easier heat storage in the pavement, which would help to reduce the risk of damage caused by freeze–thaw cycling in cold regions.

TRANSPORT MODEL FOR ADSORPTION-DESORPTION OF ARSENIC ON IRON HYDROXIDE UNDER REDOX CONDITION

Arsenic contamination of groundwater has been rising as a critical issue to be solved. In this study, one-dimensional transport model for arsenic behavior with microbiological redox mechanism was developed. This model defined five reductive-bacterial groups and two oxidative-bacterial groups to model reductive sequence and oxidizing process. Microbial growth was assumed to follow Monod type kinetics. The numerical simulation model includes the chemical species in the bio-, mobile- and matrix phases. This model can describe the mass transport, bacteria mediated bio-chemical reducing processes, iron precipitation and Fe-As adsorption and desorption process. The simulation results can reproduce the results of soil column experiment, and validity of the model was confirmed.

Development and validation of a size-resolved particle dry deposition scheme for application in aerosol transport models

Abstract. A size-resolved particle dry deposition scheme is developed for inclusion in large-scale air quality and climate models where the size distribution and fate of atmospheric aerosols is of concern. The "resistance" structure is similar to what is proposed by Zhang et al. (2001), while a new "surface" deposition velocity (or surface resistance) is derived by simplification of a one-dimensional aerosol transport model (Petroff et al., 2008b, 2009). Compared to Zhang et al.'s model, the present model accounts for the leaf size, shape and area index as well as the height of the vegetation canopy. Consequently, it is more sensitive to the change of land covers, particularly in the accumulation mode (0.1–1 micron). A drift velocity is included to account for the phoretic effects related to temperature and humidity gradients close to liquid and solid water surfaces. An extended comparison of this model with experimental evidence is performed over typical land covers such as bare ground, grass, coniferous forest, liquid and solid water surfaces and highlights its adequate prediction. The predictions of the present model differ from Zhang et al.'s model in the fine mode, where the latter tends to over-estimate in a significant way the particle deposition, as measured by various investigators or predicted by the present model. The present development is thought to be useful to modellers of the atmospheric aerosol who need an adequate parameterization of aerosol dry removal to the earth surface, described here by 26 land covers. An open source code is available in Fortran90.