The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform
Christine Stumpp - One of the best experts on this subject based on the ideXlab platform.
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Analytical transport modelling of metabolites formed in dual-porosity media.
Environmental science and pollution research international, 2016Co-Authors: Bastian Knorr, Piotr Maloszewski, Christine StumppAbstract:Contaminants like nitroaromatic compounds can be degraded in the subsurface to similar or even more toxic metabolites. Degradation or transformation rates are dependent on physical, chemical and biological properties which can be different in sedimentological layers or other heterogeneous structures of aquifers. Sediments with low hydraulic conductivity can even consist of Immobile Water. These regions are only accessible by diffusion. Most modelling approaches accounting for Immobile Water regions focused on the mathematical description of the transport and decay of the parent compound. The objective of this study was to develop an analytical model to quantify the transport and formation of a metabolite in dual-porosity media describing the exchange between mobile and Immobile Water regions based on the metabolite’s diffusion coefficient. Column experiments with a well-defined Immobile Water region were performed under anoxic conditions at three different Water flow velocities. The model compound 4-Cl-nitrobenzene was reduced to 4-Cl-aniline (4-Cl-An) by surface-bound Fe (II) species within the Immobile Water region. Transport and formation of the metabolite were quantified with a modified solution of the single fissure dispersion model assuming additionally for the region with Immobile Water first-order metabolite production, irreversible sorption and an instantaneous equilibrium sorption. The number of unknown fitting parameters was reduced to two (sorption rate and retardation factor) by stepwise parameter estimation using tracer and parent compound data. Experimental results of the metabolite for each Water flow velocity were successfully described with a first-order production term (λ prod = 1.51 ± 0.08 h−1), retardation factor (R im = 2.94 ± 0.45) and first-order irreversible sorption rate (K im = 0.39 ± 0.16 h−1) within the Immobile Water region. Model results supported that 4-Cl-An was formed within the Immobile Water region. 4-Cl-An sorbed instantaneously onto the clay matrix while a fraction was irreversibly sorbed. Experimental results and the provided analytical solution help to improve the understanding about reactive transport and the formation of metabolites in dual-porosity media.
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Quantifying the impact of Immobile Water regions on the fate of nitroaromatic compounds in dual-porosity media.
Journal of contaminant hydrology, 2016Co-Authors: Bastian Knorr, Piotr Maloszewski, Christine StumppAbstract:Abstract Nitroaromatic compounds (NACs) are reduced by structural or surface bound Fe (II) species under anaerobic conditions in the subsurface. This reaction preferentially occurs on clay minerals which are mainly present in areas with low hydraulic conductivity containing nearly Immobile Water. Diffusion is the dominating transport process in these zones. Due to the complexity in such heterogeneous systems, the mathematical prediction of reactive solute transport taking into account diffusive mass exchange into Immobile Water regions still remains challenging. Therefore, the influence of Immobile Water regions on the fate of 4-Cl-Nitrobenzene (4-Cl-Nb) was quantified in dual-porosity column experiments at three different mean transit times under saturated anaerobic conditions in the presence of soluble Fe (II). A multi-tracer approach and a Single Fissure Dispersion Model (SFDM) were used to estimate input parameter to further model the transport of 4-Cl-Nb. Reactive solute transport of 4-Cl-Nb was quantified considering instantaneous sorption on to the clay matrix and a reduction within the Immobile Water region following first-order kinetics. The experimental results indicated that sorption onto the clay matrix enhanced the mass exchange of 4-Cl-Nb into Immobile Water region compared to nonreactive solutes. At the same time the abiotic reduction of 4-Cl-Nb limited the process of back diffusion to mobile Water regions. Fitted retardation factors (Rim = 4.62 ± 0.68) and decay rates (k = 1.51 ± 0.08 h− 1) were independent on tested flow velocities. Findings of this study can advance the understanding on the fate of NACs in the subsurface which is essential for prediction of reactive solute transport at field scale.
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Diffusive mass exchange of non-reactive substances in dual-porosity porous systems – column experiments under saturated conditions
Hydrological Processes, 2015Co-Authors: Bastian Knorr, Piotr Maloszewski, Florian Krämer, Christine StumppAbstract:Diffusive mass exchange into Immobile Water regions within heterogeneous porous aquifers influences the fate of solutes. The percentage of Immobile Water is often unidentified in natural aquifers though. Hence, the mathematical prediction of solute transport in such heterogeneous aquifers remains challenging. The objective of this study was to find a simple analytical model approach that allows quantifying properties of mobile and Immobile Water regions and the portion of Immobile Water in a porous system. Therefore, the Single Fissure Dispersion Model (SFDM), which takes into account diffusive mass exchange between mobile and Immobile Water zones, was applied to model transport in well-defined saturated dual-porosity column experiments. Direct and indirect model validation was performed by running experiments at different flow velocities and using conservative tracer with different molecular diffusion coefficients. In another column setup, Immobile Water regions were randomly distributed to test the model applicability and to determine the portion of Immobile Water. In all setups, the tracer concentration curves showed differences in normalized maximum peak concentration, tailing and mass recovery according to their diffusion coefficients. These findings were more pronounced at lower flow rates (larger flow times) indicating the dependency of diffusive mass exchange into Immobile Water regions on tracers' molecular diffusion coefficients. The SFDM simulated all data with high model efficiency. Successful model validation supported the physical meaning of fitted model parameters. This study showed that the SFDM, developed for fissured aquifers, is applicable in porous media and can be used to determine porosity and volume of regions with Immobile Water. Copyright © 2015 John Wiley & Sons, Ltd.
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Changes in Water table level influence solute transport in uniform porous media
Hydrological Processes, 2014Co-Authors: Franziska Anna Rühle, Nadine Zentner, Christine StumppAbstract:Changes in the Water table level result in variable Water saturation and variable hydrological fluxes at the interface between the unsaturated and saturated zone. This may influence the transport and fate of contaminants in the subsurface. The objective of this study was to examine the impact of a decreasing and an increasing Water table on solute transport. We conducted tracer experiments at downward flow conditions in laboratory columns filled with two different uniform porous media under static and transient flow conditions either increasing or decreasing the Water table. Tracer breakthrough curves were simulated using a mobile–Immobile transport model. The resulting transport parameters were compared to identify dominant transport processes. Changes in the Water table level affected dispersivities and mobile Water fractions depending on the direction of Water table movement and the grain size of the porous media. In fine glass beads, the Water flow velocity was similar to the decline rate of the Water table, and the mobile Water fraction was decreased compared with steady-state saturated conditions. However, Immobile Water was negligible. In coarse glass beads, Water flow was faster because of fingered flow in the unsaturated part, and the mobile Water fraction was smaller than in the fine material. Here, a rising Water table led to an even smaller mobile Water fraction and increased solute spreading because of diffusive interaction with Immobile Water. We conclude that changes of the Water table need to be considered to correctly simulate transport in the subsurface at the transition of the unsaturated–saturated zone. Copyright © 2014 John Wiley & Sons, Ltd.
Rajesh Srivastava - One of the best experts on this subject based on the ideXlab platform.
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Effect of Immobile Water content on contaminant transport in unsaturated zone
Journal of Hydro-environment Research, 2007Co-Authors: Suresh A. Kartha, Rajesh SrivastavaAbstract:Abstract The effect of Immobile Water content on contaminant advection and dispersion in unsaturated porous media has been studied using a formulation which assumes that even in the Immobile liquid zone, there occurs minor liquid flow. An approach is proposed for computing this liquid velocity. One dimensional numerical simulation is carried out to study the effect of Immobile Water content on the time of appearance of contaminant at the bottom of an unsaturated column. The numerical model developed is verified using analytical solutions for simple advective-dispersive cases. From the simulations, it was observed that increase in the Immobile Water content leads to quicker appearance of contaminant.
Indumathi M. Nambi - One of the best experts on this subject based on the ideXlab platform.
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Numerical Modeling of the Effect of Immobile Water Content on Nitrate Transport in an Unsaturated Porous System
Data mining and knowledge engineering, 2013Co-Authors: M. Berlin, G. Suresh Kumar, Indumathi M. NambiAbstract:Nitrate originating from wasteWater applied onagricultural sites, is one of the most common pollutants ingroundWater. It causes a prime risk for human health during theconsumption of nitrate contaminated groundWater. In this presentstudy, a numerical model is developed to understand and forecast thefate and transport of nitrogen species in an unsaturated porous media.In addition, the concept of mobile-Immobile Water content in anunsaturated zone is incorporated in the one-dimensional numericalmodel for nitrogen species transport. The mass transfer of contaminantin mobile-Immobile zone is effectively carried out to predict theconcentration of nitrogen species in unsaturated zone. The numericalresults of Water flow and contaminant transport model in unsaturatedzone developed for this study have been validated with the availableanalytical/numerical solution. Results indicate that the Immobile Watercontent plays a predominant role in nitrogen species transport in anunsaturated zone. The simulation results also suggest that nitrogenspecies concentration travels to a low depth in mobile Water zonecompared to the Immobile Water content due to the exchange ofcontaminant mass from mobile phase to Immobile phase. Moreover,the numerical results suggest that the mass transfer rate is aninfluencing parameter in the movement of ammonium nitrogen andnitrate nitrogen concentration in an unsaturated zone.
Thomas C Voice - One of the best experts on this subject based on the ideXlab platform.
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effects of degree of Water saturation on dispersivity and Immobile Water in sandy soil columns
Journal of Contaminant Hydrology, 1997Co-Authors: Munjed A Maraqa, Roger B Wallace, Thomas C VoiceAbstract:Abstract Three natural nonaggregated soil samples, with similar grain-size distributions, have been used to determine the dispersive behavior of porous media under steady, saturated and unsaturated flow conditions. Tritium was used as a tracer and was found to have no sorption on the solid matrix. Generated breakthrough curves (BTCs) for the unsaturated experiments were symmetrical with no evidence of tailing. The unsaturated experiments for two of the soils were adequately described by considering all the Water in the pore volume as mobile. However, about 10% of the pore Water, independent of the degree of saturation, was found to be Immobile in the case of the third soil during unsaturated flow. For this soil, there was no mass transfer between the two Water regions, indicating that the Immobile Water is essentially isolated from the flowing Water fraction. For all three soils, dispersivity under unsaturated conditions was found to be higher, independent of the degree of Water saturation, than the value determined for the saturated experiments. This is inconsistent with what would be expected from the simple bundle-of-capillary-tubes model and does not agree well with a more sophisticated conceptualization of the porous medium. The data, however, clearly indicate a wider range in pore-Water velocities when these soils are desaturated.
Bastian Knorr - One of the best experts on this subject based on the ideXlab platform.
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Analytical transport modelling of metabolites formed in dual-porosity media.
Environmental science and pollution research international, 2016Co-Authors: Bastian Knorr, Piotr Maloszewski, Christine StumppAbstract:Contaminants like nitroaromatic compounds can be degraded in the subsurface to similar or even more toxic metabolites. Degradation or transformation rates are dependent on physical, chemical and biological properties which can be different in sedimentological layers or other heterogeneous structures of aquifers. Sediments with low hydraulic conductivity can even consist of Immobile Water. These regions are only accessible by diffusion. Most modelling approaches accounting for Immobile Water regions focused on the mathematical description of the transport and decay of the parent compound. The objective of this study was to develop an analytical model to quantify the transport and formation of a metabolite in dual-porosity media describing the exchange between mobile and Immobile Water regions based on the metabolite’s diffusion coefficient. Column experiments with a well-defined Immobile Water region were performed under anoxic conditions at three different Water flow velocities. The model compound 4-Cl-nitrobenzene was reduced to 4-Cl-aniline (4-Cl-An) by surface-bound Fe (II) species within the Immobile Water region. Transport and formation of the metabolite were quantified with a modified solution of the single fissure dispersion model assuming additionally for the region with Immobile Water first-order metabolite production, irreversible sorption and an instantaneous equilibrium sorption. The number of unknown fitting parameters was reduced to two (sorption rate and retardation factor) by stepwise parameter estimation using tracer and parent compound data. Experimental results of the metabolite for each Water flow velocity were successfully described with a first-order production term (λ prod = 1.51 ± 0.08 h−1), retardation factor (R im = 2.94 ± 0.45) and first-order irreversible sorption rate (K im = 0.39 ± 0.16 h−1) within the Immobile Water region. Model results supported that 4-Cl-An was formed within the Immobile Water region. 4-Cl-An sorbed instantaneously onto the clay matrix while a fraction was irreversibly sorbed. Experimental results and the provided analytical solution help to improve the understanding about reactive transport and the formation of metabolites in dual-porosity media.
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Quantifying the impact of Immobile Water regions on the fate of nitroaromatic compounds in dual-porosity media.
Journal of contaminant hydrology, 2016Co-Authors: Bastian Knorr, Piotr Maloszewski, Christine StumppAbstract:Abstract Nitroaromatic compounds (NACs) are reduced by structural or surface bound Fe (II) species under anaerobic conditions in the subsurface. This reaction preferentially occurs on clay minerals which are mainly present in areas with low hydraulic conductivity containing nearly Immobile Water. Diffusion is the dominating transport process in these zones. Due to the complexity in such heterogeneous systems, the mathematical prediction of reactive solute transport taking into account diffusive mass exchange into Immobile Water regions still remains challenging. Therefore, the influence of Immobile Water regions on the fate of 4-Cl-Nitrobenzene (4-Cl-Nb) was quantified in dual-porosity column experiments at three different mean transit times under saturated anaerobic conditions in the presence of soluble Fe (II). A multi-tracer approach and a Single Fissure Dispersion Model (SFDM) were used to estimate input parameter to further model the transport of 4-Cl-Nb. Reactive solute transport of 4-Cl-Nb was quantified considering instantaneous sorption on to the clay matrix and a reduction within the Immobile Water region following first-order kinetics. The experimental results indicated that sorption onto the clay matrix enhanced the mass exchange of 4-Cl-Nb into Immobile Water region compared to nonreactive solutes. At the same time the abiotic reduction of 4-Cl-Nb limited the process of back diffusion to mobile Water regions. Fitted retardation factors (Rim = 4.62 ± 0.68) and decay rates (k = 1.51 ± 0.08 h− 1) were independent on tested flow velocities. Findings of this study can advance the understanding on the fate of NACs in the subsurface which is essential for prediction of reactive solute transport at field scale.
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Diffusive mass exchange of non-reactive substances in dual-porosity porous systems – column experiments under saturated conditions
Hydrological Processes, 2015Co-Authors: Bastian Knorr, Piotr Maloszewski, Florian Krämer, Christine StumppAbstract:Diffusive mass exchange into Immobile Water regions within heterogeneous porous aquifers influences the fate of solutes. The percentage of Immobile Water is often unidentified in natural aquifers though. Hence, the mathematical prediction of solute transport in such heterogeneous aquifers remains challenging. The objective of this study was to find a simple analytical model approach that allows quantifying properties of mobile and Immobile Water regions and the portion of Immobile Water in a porous system. Therefore, the Single Fissure Dispersion Model (SFDM), which takes into account diffusive mass exchange between mobile and Immobile Water zones, was applied to model transport in well-defined saturated dual-porosity column experiments. Direct and indirect model validation was performed by running experiments at different flow velocities and using conservative tracer with different molecular diffusion coefficients. In another column setup, Immobile Water regions were randomly distributed to test the model applicability and to determine the portion of Immobile Water. In all setups, the tracer concentration curves showed differences in normalized maximum peak concentration, tailing and mass recovery according to their diffusion coefficients. These findings were more pronounced at lower flow rates (larger flow times) indicating the dependency of diffusive mass exchange into Immobile Water regions on tracers' molecular diffusion coefficients. The SFDM simulated all data with high model efficiency. Successful model validation supported the physical meaning of fitted model parameters. This study showed that the SFDM, developed for fissured aquifers, is applicable in porous media and can be used to determine porosity and volume of regions with Immobile Water. Copyright © 2015 John Wiley & Sons, Ltd.
