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Journal ArticleDOI

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

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.
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...
Citations
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Journal ArticleDOI
TL;DR: In this article, the fate and transport of toluene, a light nonaqueous-phase liquids (LNAPLs) in the subsurface region under dynamic groundwater table conditions were investigated.
Abstract: The focus of this study was to investigate the fate and transport of toluene, a light nonaqueous-phase liquids (LNAPLs) in the subsurface region under dynamic groundwater table conditions. ...

39 citations


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

  • ...Dynamic 77 nature of groundwater table causes significant spreading of pooled LNAPL in smear zone, 78 which considerably increases the LNAPL-water interphase area and resulted in accelerated 79 dissolution (Mobile et al. 2012; Vasudevan et al. 2014)....

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  • ...This in turn significantly 332 increases dissolved phase concentration load to receiving groundwater and vapor 333 contamination to unsaturated pore air (Dobson et al. 2007; Vasudevan et al. 2014)....

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Journal ArticleDOI
TL;DR: Results compared to previous numerical studies suggest the presence of small scale dissolution fingering created perpendicular to the horizontal dissolution front, mainly triggered by heterogeneities in the medium structure and the local NAPL residual saturation.

26 citations


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

  • ...Petroleum hydrocarbon dissolution is often described in terms of mass transfer at the NAPL/water interface assuming local equilibrium (Seagren et al., 1999; Sulaymon and Gzar, 2011) or rate limited mass transfer (Miller et al., 1990; Imhoff et al., 1994; Vasudevan et al., 2014)....

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Journal ArticleDOI
TL;DR: In this paper, the authors proposed that India's soil-water systems provide a vital source of freshwater and sustain the drinking water supply for the world's second-largest population, however, groundwater within the large geogra...
Abstract: India’s soil-water systems provide a vital source of freshwater and sustain the drinking water supply for the world’s second-largest population. However, groundwater within the large geogra...

24 citations

Journal ArticleDOI
TL;DR: Variations in groundwater flow regimes due to direct draining/pumping and surrounding climatic variabilities may significantly affect the spatial and temporal distribution of hydrocarbon co-... as mentioned in this paper.
Abstract: Variations in groundwater flow regimes due to direct draining/pumping and surrounding climatic variabilities may significantly affect the spatial and temporal distribution of hydrocarbon co...

24 citations

Journal ArticleDOI
TL;DR: In this article, 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.

15 citations

References
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Journal ArticleDOI
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.
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.

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 ArticleDOI
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.
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.

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)....

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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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Journal ArticleDOI
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.
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.

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 ArticleDOI
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.

252 citations

Journal ArticleDOI
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.
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

201 citations