Numerical study on kinetic/equilibrium behaviour of dissolution of toluene under variable subsurface conditions

doi:10.1080/19648189.2014.922902

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Numerical study on kinetic/equilibrium behaviour of dissolution of toluene under variable subsurface conditions

Journal Article•DOI•

Numerical study on kinetic/equilibrium behaviour of dissolution of toluene under variable subsurface conditions

M. Vasudevan¹, G. Suresh Kumar¹, Indumathi M. Nambi¹•Institutions (1)

Indian Institute of Technology Madras¹

21 Jul 2014-European Journal of Environmental and Civil Engineering (Taylor & Francis)-Vol. 18, Iss: 9, pp 1070-1093

TL;DR: In this article, numerically simulating dissolution and transport of toluene under the effect of sorption and biodegradation to understand their synergistic influence during the tailing phase, the authors found that influence of soil grain size and porosity are most significant in calculating the extent of mass transfer limitation.

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Abstract: Estimating the extent of kinetic/equilibrium behaviour of dissolution is essential for selecting remediation strategy for highly soluble aromatic constituents of petroleum present in the subsurface. Present study aims at numerically simulating dissolution and transport of toluene under the effect of sorption and biodegradation to understand their synergistic influence during the tailing phase. Subsurface conditions influencing mass transfer such as porous media properties, flow velocity and volumetric residual saturation of toluene entrapped in the pore space are varied and their impacts are assessed. The numerical results in terms of dimensionless numbers suggest that influence of soil grain size and porosity are most significant in calculating the extent of mass transfer limitation. Increases in the volumetric residual saturation results in prolonged near-equilibrium condition for dissolution especially for fine-grained porous media. Tailing is found to be prolonged for sand with low saturations and hig...

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Journal Article•DOI•

A critical review of the influence of groundwater level fluctuations and temperature on LNAPL contaminations in the context of climate change

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01 Feb 2022-Science of The Total Environment

TL;DR: In this paper , the authors synthesize and discuss the possible effects of the increase in temperature and groundwater level fluctuations on the behavior of light nonaqueous phase liquid and its components in a climate change context.

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15 citations

Journal Article•DOI•

Numerical studies on kinetics of sorption and dissolution and their interactions for estimating mass removal of toluene from entrapped soil pores

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M. Vasudevan¹, G. Suresh Kumar¹, Indumathi M. Nambi¹•Institutions (1)

Indian Institute of Technology Madras¹

01 Sep 2015-Arabian Journal of Geosciences

TL;DR: In this article, a comprehensive numerical model is presented for understanding the kinetic nature of dissolution and sorption of hydrophobic hydrocarbons and their interactions in order to estimate the rate and extent of mass removal from different phases.

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Abstract: When the non-aqueous phase liquid (NAPL) contaminant is entrapped in soil pores, their release to the subsurface environment is mainly limited by interphase mass transfer such as dissolution and sorption. Sorption onto the aquifer material plays an important role as a retardation mechanism in subsurface contaminant transport processes. Considering the heterogeneity associated with aquifer properties as well as contaminant source distribution, long-term contamination is an inevitable consequence of mass transfer limitation of residual mass from soil micropores. A comprehensive numerical model is presented in this study for understanding the kinetic nature of dissolution and sorption of hydrophobic hydrocarbons and their interactions in order to estimate the rate and extent of mass removal from different phases. The results showed that sorption by soils and sediments having different physicochemical properties generally follow non-linear behavior. It is observed from the study that sorption non-linearity can be effectively incorporated by the two-site kinetic model rather than combination of linear and non-linear sorption isotherms. Even though initial phase of mass transfer is dissolution-dominated, the extended tailing of concentration at higher pore volumes is controlled by non-equilibrium sorption, which is better explained by the two-site kinetic model.

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13 citations

Cites background from "Numerical study on kinetic/equilibr..."

...…Chennai-36, India e-mail: gskumar@iitm.ac.in I. M. Nambi EWRE Division, Department of Civil Engineering, Indian Institute of Technology Madras, Chennai-36, India e-mail: indunambi@iitm.ac.in and Darcy scale mass transfer (Miller et al. 1990; Nambi and Powers 2003; Vasudevan et al. 2014a, b)....
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...From the dissolution studies, it is observed that time required for mass transfer decreases as the flow velocity increases, resulting in more non-equilibrium condition with lesser Damkohler number (Vasudevan et al. 2014a, b)....
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Journal Article•DOI•

Numerical Modeling on Benzene Dissolution into Groundwater and Transport of Dissolved Benzene in a Saturated Fracture-Matrix System

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V. Renu¹, G. Suresh Kumar¹•Institutions (1)

Indian Institute of Technology Madras¹

26 May 2016-Environmental Processes

TL;DR: In this paper, an attempt has been made to numerically model the dissolution of benzene and to investigate the transport of aqueous phase benzene in a saturated fracture-matrix system under steady-state flow condition.

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Abstract: Dissolution from residual source zones of benzene poses serious threat to the groundwater quality. Proper understanding of fate and migration of dissolved benzene is a prerequisite for planning remediation strategies to reduce groundwater contamination. In the present study, an attempt has been made to numerically model the dissolution of benzene and to investigate the transport of aqueous phase benzene in a saturated fracture-matrix system under steady-state flow condition. In addition to dissolution mass transfer, advection, dispersion and matrix diffusion of aqueous benzene has been considered along the fracture. In the present numerical model, residual phase benzene is considered to be present along the entire length of the fracture and residual phase benzene is assumed to be immobile for the flow conditions considered in the analysis. Transport equations for fracture and rock-matrix are solved using implicit finite difference method. Transport equation for aqueous benzene within the fracture has been solved in a one-dimensional domain and transport equation for aqueous benzene within rock-matrix has been solved in a pseudo-two-dimensional domain. Sensitivity studies have been conducted to investigate the impact of variation of flow velocity, dispersivity, fracture aperture, inlet benzene concentration, rock-matrix diffusion coefficient, and half fracture spacing on transport of aqueous benzene concentration within the fracture. From the present study, it can be concluded that the addition of slow liquid benzene dissolution into aqueous phase influences the benzene breakthrough curves/profiles at different velocity, fracture aperture, initial benzene concentration, mass transfer rate, rock dispersivity and half fracture spacing.

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11 citations

Journal Article•DOI•

Numerical modelling on rate-limited dissolution mass transfer of entrapped petroleum hydrocarbons in a saturated sub-surface system

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M. Vasudevan¹, G. Suresh Kumar¹, Indumathi M. Nambi¹•Institutions (1)

Indian Institute of Technology Madras¹

02 Jan 2016-ISH Journal of Hydraulic Engineering

TL;DR: In this paper, the authors investigated dissolution characteristics of residual petroleum hydrocarbons resulting from both mobile and immobile domains under varying conditions of rate-limited diffusive mass transfer, longitudinal dispersivity and mean mobile fluid velocity in a saturated groundwater system.

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Abstract: Petroleum hydrocarbons generally referred to as light non-aqueous phase liquid (LNAPL) entrapped within a saturated subsurface geological formation can result in longer duration of contamination due to mass transfer limitations associated with heterogeneity of the system. Considering a part of the total pore volume as immobile is significant in capturing the behaviour of extended tailing by solute breakthrough profiles. In this context, the present numerical model investigates dissolution characteristics of residual petroleum hydrocarbons (LNAPL) resulting from both mobile and immobile domains under varying conditions of rate-limited diffusive mass transfer, longitudinal dispersivity and mean mobile fluid velocity in a saturated groundwater system. The numerical results suggest that the influence of residual LNAPL saturation on dissolution mass transfer coefficient is critical in comparison with mobile flow velocity and dispersivity. In addition, the rate-limited effect becomes predominant with significan...

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7 citations

Cites background from "Numerical study on kinetic/equilibr..."

...The effect of advective velocity in the mobile phase has significant impact on the dissolved concentration of toluene because of the increased dissolution rate, which enhances the transport (Vasudevan et al. 2014a)....
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...It is observed that when the velocity is 1.0 m/day, the Da value is less than 0.5 during the variation of Sh’, indicating mass transfer limited condition (Vasudevan et al. 2014a)....
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...…available for estimating dissolution mass transfer coefficient in terms of dimensionless parameters, and the most versatile one being developed by Nambi and Powers (2003) for a wide range of flow velocity and NAPL saturation (Prakash and Nambi 2012; Vasudevan et al. 2014a, 2014b) as given below....
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Journal Article•DOI•

Assessment of groundwater contamination risk by BTEX from residual fuel soil phase

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Victoria Zanello¹, Leonardo Scherger¹, Leonardo Scherger², Claudio Lexow¹•Institutions (2)

Universidad Nacional del Sur¹, National Scientific and Technical Research Council²

10 Feb 2021

TL;DR: In this paper, the authors assess the risk of groundwater contamination associated with BTEX dissolution from fuels as a residual phase using the HYDRUS 2D/3D simulation software.

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Abstract: The aim of this work is to assess the risk of groundwater contamination associated with BTEX dissolution from fuels as a residual phase. Numerical simulations of sixty scenarios were carried out with the software HYDRUS 2D/3D. Groundwater contamination risk was analyzed given the combination of different porous media textures (silt loam, sandy loam and clay), water fluxes (0.5%, 1% or 3% Rainfall), water table depths (1.5, 2.5, 5 or 8 m below ground surface) and biodegradation rate (active or null). Risk was calculated comparing leachate concentrations to the aquifer and limits established by an international guideline for human drinking water. In all cases, benzene and toluene had the highest mobility in the dissolved phase. Contrary, xylene and ethylbenzene tended to concentrate close to the source zone. These two compounds predominantly concentrated in the solid phase. Calculated risk was proportional to the water flux rate and inversely proportional to the unsaturated thickness. Without biodegradation, in fine-grained sediments risk was very high for shallow aquifers (> 1.5 m depth) and moderate or low for deeper aquifers. However, in sandy loam sediments risk was classified as very high for aquifers up to 8 m deep. When biodegradation was considered, leached concentrations were greatly reduced in the three textures. BTEX concentration in Bahia Blanca City´s aquifer showed acceptable agreement with simulated scenarios. The most sensitive parameters to model results were biodegradation > foc > water table depth > Ks. This study is important for assessing the risks and developing management strategies for fuel contaminated sites.

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6 citations

References

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Journal Article•DOI•

An experimental investigation of nonaqueous phase liquid dissolution in saturated subsurface systems: Transient mass transfer rates

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Susan E. Powers, Linda M. Abriola, Walter J. Weber

01 Oct 1992-Water Resources Research

TL;DR: In this paper, the authors focus on the experimental measurement and mathematical modeling of processes affecting the dissolution of nonaqueous phase liquids (NAPLs) entrapped in sandy porous media.

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Abstract: This work focuses on the experimental measurement and mathematical modeling of processes affecting the dissolution of nonaqueous phase liquids (NAPLs) entrapped in sandy porous media. Results of a series of laboratory-scale one-dimensional column dissolution experiments indicate that the length of time required to dissolve NAPLs and substantially reduce aqueous phase effluent concentrations is many times greater than predicted by equilibrium calculations. Experimental measurements clearly show an influence of both grain size and grain size distribution on the evolution of effluent concentrations. The longer cleaning times associated with coarse or graded media are attributed to the larger and more amorphous NAPL blobs associated with these media. A general correlation for transient dissolution rates is proposed which incorporates porous medium properties, Reynolds number, and volumetric fraction of NAPL. The model is calibrated with results from styrene dissolution experiments and is shown to adequately predict trichloroethylene dissolution rates in the same sandy media over the period of time required to dissolve the NAPL.

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523 citations

"Numerical study on kinetic/equilibr..." refers background or methods in this paper

...…the non-equilibrium nature of dissolution mass transfer, a first-order driving force model is employed here with a lumped mass transfer coefficient inclusive of the surface area parameter and a concentration gradient term (Nambi & Powers, 2003; Powers et al., 1994) as given in Equation (2)....
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...Many empirical correlations have been in practice for estimating dissolution mass transfer coefficient in terms of modified Sherwood number, which is being represented as a function of flow and NAPL properties for single compound from residually entrapped porous system with/without considering the effect of heterogeneity (Imhoff et al., 1994; Mayer & Miller, 1996; Nambi & Powers, 2003; Powers et al., 1994; Schaerlaekens et al., 2000)....
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...…which is being represented as a function of flow and NAPL properties for single compound from residually entrapped porous system with/without considering the effect of heterogeneity (Imhoff et al., 1994; Mayer & Miller, 1996; Nambi & Powers, 2003; Powers et al., 1994; Schaerlaekens et al., 2000)....
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...Powers et al. (1994) suggested that dissolution will be faster for relatively small spherical NAPL ganglia having larger interfacial areas for an equivalent NAPL saturation....
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...The correlation developed by Powers et al. (1994) is widely referred for uniform residual saturation in a homogeneous porous media, but is limited in application for similar saturation conditions....
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Journal Article•DOI•

An experimental study of complete dissolution of a nonaqueous phase liquid in saturated porous media

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Paul T. Imhoff, Peter R. Jaffé, George F. Pinder

01 Feb 1994-Water Resources Research

TL;DR: In this paper, the attenuation of gamma radiation was utilized to measure changing residual trichloroethylene (TCE) saturation in an otherwise water-saturated porous medium as clean water was flushed through the medium.

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Abstract: The attenuation of gamma radiation was utilized to measure changing residual trichloroethylene (TCE) saturation in an otherwise water-saturated porous medium as clean water was flushed through the medium. A front over which dissolution actively occurred was observed. Once developed, this front varied in length from ≈11 mm to ≈21 mm, lengthening as it moved through the porous medium. Gamma attenuation measurements and analyses of effluent water samples indicate that there was minimal if any transport of TCE as colloidal droplets. Even as trapped TCE ganglia decreased in size due to dissolution, there is no evidence that they became mobile and advected downgradient. An extraction of the porous medium at the completion of one experiment indicated that less than 0.002% of the original TCE mass remained, suggesting that minimal amounts of separate phase TCE remained trapped within the medium after flushing with 290 pore volumes. Mass transfer rate coefficients were computed and are shown to be a function of Darcy flux, TCE volumetric content, and distance into the region of residual TCE.

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366 citations

"Numerical study on kinetic/equilibr..." refers background in this paper

...The correlation by Imhoff et al. (1994) is incorporating the effect of dissolution fingering in terms of relative domain size, thereby suggesting the effect of contamination history on mass transfer coefficient, but it is substantially poor in predicting the dissolution breakthrough for laboratory…...
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...…which is being represented as a function of flow and NAPL properties for single compound from residually entrapped porous system with/without considering the effect of heterogeneity (Imhoff et al., 1994; Mayer & Miller, 1996; Nambi & Powers, 2003; Powers et al., 1994; Schaerlaekens et al., 2000)....
[...]
...Many empirical correlations have been in practice for estimating dissolution mass transfer coefficient in terms of modified Sherwood number, which is being represented as a function of flow and NAPL properties for single compound from residually entrapped porous system with/without considering the effect of heterogeneity (Imhoff et al., 1994; Mayer & Miller, 1996; Nambi & Powers, 2003; Powers et al., 1994; Schaerlaekens et al., 2000)....
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Journal Article•DOI•

Mass transfer from nonaqueous phase organic liquids in water-saturated porous media

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Jil T. Geller¹, James R. Hunt•Institutions (1)

Lawrence Berkeley National Laboratory¹

01 Apr 1993-Water Resources Research

TL;DR: Results of dissolution experiments with trapped nonaqueous phase liquids (NAPLs) are modeled by a mass transfer analysis and the fitted NAPL sphere diameters are consistent with the size of N APL ganglia observed by others and are the smallest at the largest flow velocity.

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Abstract: Results of dissolution experiments with trapped nonaqueous phase liquids (NAPLs) are modeled by a mass transfer analysis. The model represents the NAPL as isolated spheres that shrink with dissolution and uses a mass transfer coefficient correlation reported in the literature for dissolving spherical solids. The model accounts for the reduced permeability of a region of residual NAPL relative to the permeability of the surrounding clean media that causes the flowing water to partially bypass the residual NAPL. The dissolution experiments with toluene alone and a benzene-toluene mixture were conducted in a water-saturated column of homogeneous glass beads over a range of Darcy velocities from 0.5 to 10 m d(-1). The model could represent the observed effluent concentrations as the NAPL underwent complete dissolution. The changing pressure drop across the column was predicted following an initial period of NAPL reconfiguration. The fitted NAPL sphere diameters of 0.15 to 0.40 cm are consistent with the size of NAPL ganglia observed by others and are the smallest at the largest flow velocity.

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265 citations

"Numerical study on kinetic/equilibr..." refers background in this paper

...…coefficient by using empirical mass transfer relations, thereby enabling to link with the macro-scale Darcy flux (Chu, Kitanidis, & McCarty, 2007; Geller & Hunt, 1993; Imhoff, Jaffe, & Pinder, 1994; Kim and Chrysikopoulos, 1999; Liu, Tindall, Friedel, & Zhang, 2007; Mayer & Miller, 1996; Nambi &…...
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...In reality, the rate-limited dissolution is further complicated by the physical and biological processes of sorption and biodegradation, respectively (Clement, Gautam, Lee, Truex, & Davis, 2004; Geller & Hunt, 1993; Heyse, Augustijn, Rao, & Delfino, 2002)....
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Journal Article•DOI•

A review of NAPL source zone remediation efficiency and the mass flux approach.

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Kenichi Soga¹, Jwe Page¹, Tissa H. Illangasekare²•Institutions (2)

University of Cambridge¹, Colorado School of Mines²

05 Jul 2004-Journal of Hazardous Materials

TL;DR: The use of mass flux measurements (monitoring the concentration of contaminants in aqueous phase due to source zone NAPL-groundwater mass transfer) is introduced as a potential tool to assess the efficiency of technologies used in source zone remediation.

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252 citations

Journal Article•DOI•

A comparison of zero-order, first-order, and monod biotransformation models

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Barbara A. Bekins¹, Ean Warren¹, E. Michael Godsy¹•Institutions (1)

United States Geological Survey¹

01 Mar 1998-Ground Water

TL;DR: In this article, a series of numerical simulations comparing results of first-and zero-order rate approximations to Monod kinetics for a real data set illustrates that if concentrations observed in the field are higher than K{sub S, it may be better to model degradation using a zeroorder rate expression.

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Abstract: Under some conditions, a first-order kinetic model is a poor representation of biodegradation in contaminated aquifers. Although it is well known that the assumption of first-order kinetics is valid only when substrate concentration, S, is much less than the half-saturation constant, K{sub S}, this assumption is often made without verification of this condition. The authors present a formal error analysis showing that the relative error in the first-order approximation is S/K{sub S} and in the zero-order approximation the error is K{sub S}/S. They then examine the problems that arise when the first-order approximation is used outside the range for which it is valid. A series of numerical simulations comparing results of first- and zero-order rate approximations to Monod kinetics for a real data set illustrates that if concentrations observed in the field are higher than K{sub S}, it may be better to model degradation using a zero-order rate expression. Compared with Monod kinetics, extrapolation of a first-order rate to lower concentrations under-predicts the biotransformation potential, while extrapolation to higher concentrations may grossly over-predict the transformation rate. A summary of solubilities and Monod parameters for aerobic benzene, toluene, and xylene (BTX) degradation shows that the a priori assumption of first-order degradationmore » kinetics at sites contaminated with these compounds is not valid. In particular, out of six published values of K{sub S} for toluene, only one is greater than 2 mg/L, indicating that when toluene is present in concentrations greater than about a part per million, the assumption of first-order kinetics may be invalid. Finally, the authors apply an existing analytical solution for steady-state one-dimensional advective transport with Monod degradation kinetics to a field data set.« less

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201 citations