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Shafieiyoun S, Thomson NR. Intra-NAPL diffusion and dissolution of a MGP NAPL exposed to persulfate in a flow-through system. JOURNAL OF HAZARDOUS MATERIALS 2019; 365:366-374. [PMID: 30448549 DOI: 10.1016/j.jhazmat.2018.10.096] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2018] [Revised: 10/30/2018] [Accepted: 10/31/2018] [Indexed: 06/09/2023]
Abstract
Intra-NAPL diffusion is a critical process that can influence NAPL/water mass transfer. A series of physical model experiments was performed to investigate the role of intra-NAPL diffusion on the transient dissolution of a complex multicomponent NAPL subjected to persulfate treatment. To support these observations, a diffusion-based model was developed and calibrated using the experimental data. The experimental results indicated that while persulfate was able to completely degrade dissolved phase components, mass loss after ∼410 pore volumes of persulfate flushing was less than the no-treatment system. Intra-NAPL diffusion limitations were not observed in the physical model experiments. A comparison of experimental and simulated results indicated that processes related to persulfate/NAPL interactions restricted mass transfer, and yielded multicomponent mass transfer rate coefficients that were ∼30% of those estimated from an equivalent water-flushing experiment. Simulation results showed that a combination of NAPL composition and geometry, and interphase mass transfer rate can yield intra-NAPL diffusion limitations. Remedial technologies that rely on the aggressive flushing of reagents into NAPL zones may give rise to intra-NAPL diffusion limitations, which will directly affect treatment efficiency.
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Affiliation(s)
- Saeid Shafieiyoun
- Department of Civil and Environmental Engineering, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, N2L 3G1, Canada.
| | - Neil R Thomson
- Department of Civil and Environmental Engineering, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, N2L 3G1, Canada
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2
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Shafieiyoun S, Thomson NR. The role of intra-NAPL diffusion on mass transfer from MGP residuals. JOURNAL OF CONTAMINANT HYDROLOGY 2018; 213:49-61. [PMID: 29776661 DOI: 10.1016/j.jconhyd.2018.04.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2017] [Revised: 03/15/2018] [Accepted: 04/20/2018] [Indexed: 06/08/2023]
Abstract
An experimental and computational study was performed to investigate the role of multi-component intra-NAPL diffusion on NAPL-water mass transfer. Molecular weight and the NAPL component concentrations were determined to be the most important parameters affecting intra-NAPL diffusion coefficients. Four NAPLs with different viscosities but the same quantified mass were simulated. For a spherical NAPL body, a combination of NAPL properties and interphase mass transfer rate can result in internal diffusion limitations. When the main intra-NAPL diffusion coefficients are in the range of self-diffusion coefficients (10-5 to 10-6 cm2/s), dissolution is not limited by internal diffusion except for high mass transfer rate coefficients (>180 cm/day). For a complex and relatively high viscous NAPL (>50 g/(cm s)), smaller intra-NAPL diffusion coefficients (<10-8) are expected and even low mass transfer rate coefficients (~6 cm/day) can result in diffusion-limited dissolution.
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Affiliation(s)
- Saeid Shafieiyoun
- Department of Civil and Environmental Engineering, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada.
| | - Neil R Thomson
- Department of Civil and Environmental Engineering, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada
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3
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Trellu C, Miltner A, Gallo R, Huguenot D, van Hullebusch ED, Esposito G, Oturan MA, Kästner M. Characteristics of PAH tar oil contaminated soils-Black particles, resins and implications for treatment strategies. JOURNAL OF HAZARDOUS MATERIALS 2017; 327:206-215. [PMID: 28068645 DOI: 10.1016/j.jhazmat.2016.12.062] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Revised: 12/24/2016] [Accepted: 12/30/2016] [Indexed: 06/06/2023]
Abstract
Tar oil contamination is a major environmental concern due to health impacts of polycyclic aromatic hydrocarbons (PAH) and the difficulty of reaching acceptable remediation end-points. Six tar oil-contaminated soils with different industrial histories were compared to investigate contamination characteristics by black particles. Here we provide a simple method tested on 6 soils to visualize and identify large amounts of black particles (BP) as either solid aggregates of resinified and weathered tar oil or various wood/coke/coal-like materials derived from the contamination history. These materials contain 2-10 times higher PAH concentrations than the average soil and were dominantly found in the sand fraction containing 42-86% of the total PAH. The PAH contamination in the different granulometric fractions was directly proportional to the respective total organic carbon content, since the PAH were associated to the carbonaceous particulate materials. Significantly lower (bio)availability of PAH associated to these carbonaceous phases is widely recognized, thus limiting the efficiency of remediation techniques. We provide a conceptual model of the limited mass transfer of PAH from resinated tar oil phases to the water phase and emphasize the options to physically separate BP based on their lower bulk density and slower settling velocity.
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Affiliation(s)
- Clément Trellu
- Université Paris-Est, Laboratoire Géomatériaux et Environnement (EA 4508), UPEM, 77454 Marne-la-Vallée, France; Department of Environmental Biotechnology, Helmholtz-Centre for Environmental Research - UFZ, Permoserstr. 15, 04318 Leipzig, Germany
| | - Anja Miltner
- Department of Environmental Biotechnology, Helmholtz-Centre for Environmental Research - UFZ, Permoserstr. 15, 04318 Leipzig, Germany
| | - Rosita Gallo
- University of Cassino and Southern Lazio, Department of Civil and Mechanical Engineering, Via Di Biasio, 43, 03043 Cassino, FR, Italy; Department of Environmental Biotechnology, Helmholtz-Centre for Environmental Research - UFZ, Permoserstr. 15, 04318 Leipzig, Germany
| | - David Huguenot
- Université Paris-Est, Laboratoire Géomatériaux et Environnement (EA 4508), UPEM, 77454 Marne-la-Vallée, France
| | - Eric D van Hullebusch
- Université Paris-Est, Laboratoire Géomatériaux et Environnement (EA 4508), UPEM, 77454 Marne-la-Vallée, France
| | - Giovanni Esposito
- University of Cassino and Southern Lazio, Department of Civil and Mechanical Engineering, Via Di Biasio, 43, 03043 Cassino, FR, Italy
| | - Mehmet A Oturan
- Université Paris-Est, Laboratoire Géomatériaux et Environnement (EA 4508), UPEM, 77454 Marne-la-Vallée, France
| | - Matthias Kästner
- Department of Environmental Biotechnology, Helmholtz-Centre for Environmental Research - UFZ, Permoserstr. 15, 04318 Leipzig, Germany.
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4
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Ranc B, Faure P, Croze V, Simonnot MO. Selection of oxidant doses for in situ chemical oxidation of soils contaminated by polycyclic aromatic hydrocarbons (PAHs): A review. JOURNAL OF HAZARDOUS MATERIALS 2016; 312:280-297. [PMID: 27043880 DOI: 10.1016/j.jhazmat.2016.03.068] [Citation(s) in RCA: 76] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2015] [Revised: 03/23/2016] [Accepted: 03/25/2016] [Indexed: 06/05/2023]
Abstract
In situ chemical oxidation (ISCO) is a promising alternative to thermal desorption for the remediation of soils contaminated with organic compounds such as polycyclic aromatic hydrocarbons (PAHs). For field application, one major issue is the selection of the optimal doses of the oxidizing solution, i.e. the oxidant and appropriate catalysts and/or additives. Despite an extensive scientific literature on ISCO, this choice is very difficult because many parameters differ from one study to another. The present review identifies the critical factors that must be taken into account to enable comparison of these various contributions. For example, spiked soils and aged, polluted soils cannot be compared; PAHs freshly spiked into a soil are fully available for degradation unlike a complex mixture of pollutants trapped in a soil for many years. Another notable example is the high diversity of oxidation conditions employed during batch experiments, although these affect the representativeness of the system. Finally, in this review a methodology is also proposed based on a combination of the stoichiometric oxidant demand of the organic pollutants and the design of experiments (DOE) in order to allow a better comparison of the various studies so far reported.
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Affiliation(s)
- B Ranc
- Université de Lorraine, Laboratoire Interdisciplinaire des Environnements Continentaux, UMR 7360, Site Aiguillette, 54506 Vandœuvre-lès-Nancy cedex, France; CNRS, Laboratoire Interdisciplinaire des Environnements Continentaux, UMR 7360, Site Aiguillettes, 54506 Vandœuvre-lès-Nancy cedex, France; ICF Environnement, 14 à 30 rue Alexandre, 92635 Gennevilliers, France; Université de Lorraine, Laboratoire Réactions et Génie des Procédés, UMR 7274, 1 rue Grandville, 54001 Nancy cedex, France; CNRS, Laboratoire Réactions et Génie des Procédés, UMR 7274, 1 rue Grandville, 54001 Nancy cedex, France
| | - P Faure
- Université de Lorraine, Laboratoire Interdisciplinaire des Environnements Continentaux, UMR 7360, Site Aiguillette, 54506 Vandœuvre-lès-Nancy cedex, France; CNRS, Laboratoire Interdisciplinaire des Environnements Continentaux, UMR 7360, Site Aiguillettes, 54506 Vandœuvre-lès-Nancy cedex, France
| | - V Croze
- ICF Environnement, 14 à 30 rue Alexandre, 92635 Gennevilliers, France
| | - M O Simonnot
- Université de Lorraine, Laboratoire Réactions et Génie des Procédés, UMR 7274, 1 rue Grandville, 54001 Nancy cedex, France; CNRS, Laboratoire Réactions et Génie des Procédés, UMR 7274, 1 rue Grandville, 54001 Nancy cedex, France.
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5
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Fu J, Suuberg EM. Thermochemical and Vapor Pressure Behavior of Anthracene and Brominated Anthracene Mixtures. FLUID PHASE EQUILIBRIA 2013; 342:10.1016/j.fluid.2012.12.036. [PMID: 24319314 PMCID: PMC3848959 DOI: 10.1016/j.fluid.2012.12.036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The present work concerns the thermochemical and vapor pressure behavior of the anthracene (1) + 2-bromoanthracene (2) and anthracene (1) + 9-bromoanthracene (3) systems. Solid-liquid equilibrium temperature and differential scanning calorimetry studies indicate the existence of a minimum melting solid state near an equilibrium temperature of 477.65 K at x1 = 0.74 for the (1) + (2) system. Additionally, solid-vapor equilibrium studies for the (1) + (2) system show that the vapor pressure of the mixtures depends on composition, but does not follow ideal Raoult's law behaviour. The (1) + (3) system behaves differently from the (1) + (2) system. The (1) + (3) system has a solid solution like phase diagram. The system consists of two phases, an anthracene like phase and a 9-bromoanthracene like phase, while (1) + (2) mixtures only form a single phase. Moreover, experimental studies of the two systems suggest that the (1) + (2) system is in a thermodynamically lower energy state than the (1) + (3) system.
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Affiliation(s)
- Jinxia Fu
- Brown University Department of Chemistry, Providence, RI USA 02912
| | - Eric M. Suuberg
- Brown University School of Engineering, Providence, RI USA 02912
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6
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Rice JW, Fu J, Suuberg EM. Thermodynamics of Multicomponent PAH Mixtures and Development of Tar-Like Behavior. Ind Eng Chem Res 2011; 50:3613-3620. [PMID: 21442010 DOI: 10.1021/ie102325d] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This study explores the solid/liquid phase behavior of mixtures of polycyclic aromatic hydrocarbons (PAHs), exploring the transition from non-ideal solid mixtures to a relatively ideal liquid behavior characteristic of "tars". PAH mixtures have been studied using differential scanning calorimetry, melting point analysis and Knudsen effusion. Mixtures of anthracene, pyrene and fluoranthene show behavior that is consistent with other binary PAH mixtures; that is, the initially solid mixture exhibits a significant melting point depression, relative to the pure components, and in a certain range of composition, solid azeotrope behavior on vaporization. As the number of distinct PAH species is increased (by adding in benzo[a]pyrene, phenanthrene, fluorene and chrysene) this behavior gradually gives way to liquid phase character at even room temperature, and the vaporization behavior approaches that crudely predictable from ideal mixture theory.
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Affiliation(s)
- James W Rice
- Brown University School of Engineering, 182 Hope Street Box D, Providence, RI USA 02912
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7
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Singh M, Rai RN, Rai US. Some Physicochemical and Thermal Studies on Organic Analog of a Nonmetal-Nonmetal Monotectic Alloy; 2-Cyanoacetamide–4-chloronitrobenzene System. ACTA ACUST UNITED AC 2011. [DOI: 10.4236/ajac.2011.28111] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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8
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Luning Prak DJ, Waddle AN. Solubilization of Nitroaromatic Compounds from Multi-Component Mixtures into Nonionic Surfactant Micellar Solutions. SEP SCI TECHNOL 2010. [DOI: 10.1080/01496391003607381] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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9
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Chen X, Jawitz JW. Convergence of DNAPL source strength functions with site age. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2009; 43:9374-9379. [PMID: 19928794 DOI: 10.1021/es902108z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Dissolution of dense nonaqueous phase liquid (DNAPL) source zones can be accurately predicted based on appropriate characterization of the source zone architecture, which controls the rate of mass discharge or source strength function. However, the architecture changes temporally as the source zone mass is depleted by dissolution. To generalize comparisons between contaminated sites with different porewater velocities or contaminant solubilities, site age is defined in terms of the fraction of contaminant mass that has been eluted from the source zone by aqueous dissolution. Here changes in DNAPL architecture during dissolution of a source zone were measured by light transmission visualization in laboratory flow chambers. Architectures measured at ages corresponding to initial conditions, 20, 50, and 90% mass removal were used in an equilibrium streamtube (EST) model to accurately predict subsequent dissolution. It is shown both experimentally and theoretically that as DNAPL contaminated sites age, fractional reductions in contaminant discharge and mass converge to become equal, regardless of the initial architecture. This behavior is a consequence of convergence from log-normal to exponential behavior. Analysis of errors in dissolution predictions suggests that the age of many contaminated sites is likely sufficient that architecture and source strength function characterization may not be necessary as it can be assumed with reasonable accuracy that future dissolution will follow an exponential decay model.
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Affiliation(s)
- X Chen
- Soil and Water Science Department, University of Florida, Gainesville, Florida 32611, USA
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10
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Birak PS, Miller CT. Dense non-aqueous phase liquids at former manufactured gas plants: challenges to modeling and remediation. JOURNAL OF CONTAMINANT HYDROLOGY 2009; 105:81-98. [PMID: 19176266 PMCID: PMC2742311 DOI: 10.1016/j.jconhyd.2008.12.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2008] [Revised: 11/29/2008] [Accepted: 12/07/2008] [Indexed: 05/20/2023]
Abstract
The remediation of dense non-aqueous phase liquids (DNAPLs) in porous media continues to be one of the most challenging problems facing environmental scientists and engineers. Of all the environmentally relevant DNAPLs, tars in the subsurface at former manufactured gas plants (FMGPs) pose one of the biggest challenges due to their complex chemical composition and tendency to alter wettability. To further our understanding of these complex materials, we consulted historic documentation to evaluate the impact of gas manufacturing on the composition and physicochemical nature of the resulting tars. In the recent literature, most work to date has been focused in a relatively narrow portion of the expected range of tar materials, which has yielded a bias toward samples of relatively low viscosity and density. In this work, we consider the dissolution and movement of tars in the subsurface, models used to predict these phenomena, and approaches used for remediation. We also explore the open issues and detail important gaps in our fundamental understanding of these extraordinarily complex systems that must be resolved to reach a mature level of understanding.
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Affiliation(s)
- P S Birak
- Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, NC 27599-7431, USA.
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11
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McColl CM, Johnson GR, Brusseau ML. Evaporative mass transfer behavior of a complex immiscible liquid. CHEMOSPHERE 2008; 73:607-13. [PMID: 18614196 PMCID: PMC2886807 DOI: 10.1016/j.chemosphere.2008.05.051] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2008] [Revised: 05/20/2008] [Accepted: 05/21/2008] [Indexed: 05/04/2023]
Abstract
A series of laboratory experiments was conducted with a multiple-component immiscible liquid, collected from the Picillo Farm Superfund Site in Rhode Island, to examine liquid-vapor mass-transfer behavior. The immiscible liquid, which comprises solvents, oils, pesticides, PCBs, paint sludges, explosives, and other compounds, was characterized using gas chromatography and gas chromatography/mass spectrometry to determine mole fractions of selected constituents. Batch experiments were conducted to evaluate equilibrium phase-partitioning behavior. Two sets of air-stripping column studies were conducted to examine the mass-transfer dynamics of five selected target compounds present in the immiscible-liquid mixture. One set of column experiments was designed to represent a system with free-phase immiscible liquid present; the other was designed to represent a system with a residual phase of immiscible liquid. Initial elution behavior of all target components generally appeared to be ideal for both systems, as the initial vapor-phase concentrations were similar to vapor-phase concentrations measured for the batch experiment and those estimated using Raoult's law (incorporating the immiscible-liquid composition data). Later-stage removal of 1,2-dichlorobenzene appeared to be rate limited for the columns containing free-phase immiscible liquid and no porous medium. Conversely, evaporative mass transfer appeared to be ideal throughout the experiment conducted with immiscible liquid distributed relatively uniformly as a residual phase within a sandy porous medium.
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Affiliation(s)
- Colleen M McColl
- Department of Soil, Water, and Environmental Science, The University of Arizona, Tucson, AZ 85721, United States
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12
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Brown DG, Gupta L, Kim TH, Keith Moo-Young H, Coleman AJ. Comparative assessment of coal tars obtained from 10 former manufactured gas plant sites in the eastern United States. CHEMOSPHERE 2006; 65:1562-9. [PMID: 16698063 DOI: 10.1016/j.chemosphere.2006.03.068] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2005] [Revised: 03/27/2006] [Accepted: 03/29/2006] [Indexed: 05/09/2023]
Abstract
A comparative analysis was performed on eleven coal tars obtained from former manufactured gas plant sites in the eastern United States. Bulk properties analyzed included percent ash, Karl Fisher water content, viscosity and average molecular weight. Chemical properties included monocyclic- and polycyclic-aromatic hydrocarbon (PAH) concentrations, alkylated aromatic concentrations, and concentrations of aliphatic and aromatic fractions. It was found that there was at least an order-of-magnitude variation in all properties measured between the eleven coal tars. Additionally, two coal tars obtained from the same manufactured gas plant site had very different properties, highlighting that there can be wide variations in coal tar properties from different samples obtained from the same site. Similarities were also observed between the coal tars. The relative chemical distributions were similar for all coal tars, and the coal tars predominantly consisted of PAHs, with naphthalene being the single-most prevalent compound. The C(9-22) aromatic fraction, an indicator of all PAHs up to a molecular weight of approximately 276 gmole(-1), showed a strong power-law relationship with the coal tar average molecular weight (MW (ct)). And the concentrations of individual PAHs decreased linearly as MW (ct) increased up to ca. 1000 gmole(-1), above which they remained low and variable. Implications of these properties and their variation with MW (ct) on groundwater quality are discussed. Ultimately, while these similarities do allow generalities to be made about coal tars, the wide range of coal tar bulk and chemical properties reported here highlights the complex nature of coal tars.
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Affiliation(s)
- Derick G Brown
- Department of Civil and Environmental Engineering, Lehigh University, 13 East Packer Avenue, Bethlehem, PA 18015, USA.
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Benhabib K, Simonnot MO, Sardin M. PAHs and organic matter partitioning and mass transfer from coal tar particles to water. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2006; 40:6038-43. [PMID: 17051797 DOI: 10.1021/es0600431] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
The coal tar found in contaminated soils of former manufactured gas plants and coking plants acts as a long-term source of PAHs. Organic carbon and PAH transfer from coal tar particles to water was investigated with closed-looped laboratory column experiments run at various particle sizes and temperatures. Two models were derived. The first one represented the extraction process at equilibrium and was based on a linear partitioning of TOC and PAHs between coal tar and water. The partition coefficient was derived as well as the mass of extractable organic matter in the particles. The second model dealt with mass transfer. Particle diffusion was the limiting step; organic matter diffusivity in the coal tar was then computed in the different conditions. A good consistency was obtained between experimental and computed results. Hence, the modeling of PAH migration in contaminated soils at the field scale requires taking into account coal tar as the source-term for PAH release.
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Affiliation(s)
- Karim Benhabib
- LSGC- Laboratory of Chemical Engineering Science, CNRS-INPL, Nancy, France
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14
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Ming Y, Russell LM. Thermodynamic equilibrium of organic-electrolyte mixtures in aerosol particles. AIChE J 2006. [DOI: 10.1002/aic.690480619] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Roy JW, Smith JE, Gillham RW. Laboratory evidence of natural remobilization of multicomponent DNAPL pools due to dissolution. JOURNAL OF CONTAMINANT HYDROLOGY 2004; 74:145-161. [PMID: 15358491 DOI: 10.1016/j.jconhyd.2004.02.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2003] [Revised: 01/26/2004] [Accepted: 02/06/2004] [Indexed: 05/24/2023]
Abstract
Mixtures of dense non-aqueous phase liquids (DNAPLs) trapped in the subsurface can act as long-term sources of contamination by dissolving into flowing groundwater. In general, the components of higher solubility are removed more quickly, thus altering the composition of the remaining DNAPL, and possibly leading to changes in its physical properties. Through the development of a simple compositional model, Roy et al. [J. Contam. Hydrol. 2002 (59) 163] showed that preferential dissolution of a mixed DNAPL could potentially result in changes in density and interfacial tension that could subsequently lead to remobilization of an initially static DNAPL pool. The laboratory experiments presented in this next paper provide a proof-of-concept for the previously presented theory, demonstrating and quantifying this process of remobilization. In addition, the experiments provide a data set for evaluation of the model presented by Roy et al. [J. Contam. Hydrol. 2002 (59) 163]. In the four experiments, a DNAPL pool comprised of tetrachloroethene and benzene was created as an open pool overlying glass beads within a water-saturated 2-D flow box. Experiments included rectangular and triangular pools. In each of the experiments, remobilization (as breakthrough) was observed more than 2 weeks after formation of the initial pool. During each experiment, the pool height declined as mass was lost by dissolution, while sampling indicated a decrease in the mole fraction of benzene, the more soluble component. Small protuberances formed along the bottom of the pool as its composition changed with time and the displacement pressure was achieved for various pore throats. Eventually one of the protuberances extended further, forming a finger (breakthrough). In general, the pool emptied as the finger proceeded further into the beads. It was also shown theoretically and experimentally that remobilization will occur sooner for pools with a triangular (pointing down), rather than rectangular, shape. The experimental results were simulated using the model developed by Roy et al. [J. Contam. Hydrol. 2002 (59) 163]. The model matched the observations well, suggesting that it accurately represents the primary mechanisms involved with natural remobilization under the conditions of the study.
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Affiliation(s)
- J W Roy
- Department of Earth Sciences, University of Waterloo, Waterloo, ON, N2L 3G1, Canada.
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16
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Chrysikopoulos CV, Vogler ET. Acoustically enhanced multicomponent NAPL ganglia dissolution in water saturated packed columns. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2004; 38:2940-2945. [PMID: 15212271 DOI: 10.1021/es034665n] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The impact of acoustic pressure waves on multicomponent nonaqueous phase liquid (NAPL) ganglia dissolution in water saturated columns packed with glass beads was investigated. Laboratory data from dissolution experiments with two and three component NAPL mixtures suggested that acoustic waves significantly enhance ganglia dissolution due to the imposed oscillatory interstitial water velocity. The dissolution enhancement was shown to be directly proportional to the acoustic wave frequency. Furthermore, it was demonstrated that the greatest dissolution enhancement in the presence of acoustic waves is associated with the component of the NAPL mixture having the smallest equilibrium aqueous solubility. Finally, square shaped acoustic waves were shown to lead to greater NAPL dissolution enhancement compared to sinusoidal and triangular acoustic waves. The results of this study suggested that aquifer remediation using acoustic waves is a promising method particularly for aquifers contaminated with NAPLs containing components with very low equilibrium aqueous solubilities.
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17
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Roy JW, Smith JE, Gillham RW. Natural remobilization of multicomponent DNAPL pools due to dissolution. JOURNAL OF CONTAMINANT HYDROLOGY 2002; 59:163-186. [PMID: 12487412 DOI: 10.1016/s0169-7722(02)00056-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Mixtures of dense nonaqueous phase liquids (DNAPLs) trapped in the subsurface can act as long-term sources of contamination by dissolving into flowing groundwater. If the components have different solubilities then dissolution will alter the composition of the remaining DNAPL. We theorized that a multicomponent DNAPL pool may become mobile due to the natural dissolution process. In this study, we focused on two scenarios: (1) a DNAPL losing light component(s), with the potential for downward migration; and (2) a DNAPL losing dense component(s), with the potential for upward migration following transformation into a less dense than water nonaqueous phase liquid (LNAPL). We considered three binary mixtures of common groundwater contaminants: benzene and tetrachloroethylene (PCE), PCE and dichloromethane (DCM), and DCM and toluene. A number of physical properties that control the retention and transport of DNAPL in porous media were measured for the mixtures, namely: density, interfacial tension, effective solubility, and viscosity. All properties except density exhibited nonlinear relationships with changing molar ratio of the DNAPL. To illustrate the potential for natural remobilization, we modelled the following two primary mechanisms: the reduction in pool height as mass is lost by dissolution, and the changes in fluid properties with changing molar ratio of the DNAPL. The first mechanism always reduces the capillary pressure in the pool, while the second mechanism may increase the capillary pressure or alter the direction of the driving force. The difference between the rate of change of each determines whether the potential for remobilization increases or decreases. Static conditions and horizontal layering were assumed along with a one-dimensional, compositional modelling approach. Our results indicated that for initial benzene/PCE ratios greater than 25:75, the change in density was sufficiently faster than the decline in pool height to promote DNAPL breakthrough into the adjacent porous medium. In contrast, there was no potential for natural remobilization of a PCE-DCM mixture, primarily because the densities of the components are not sufficiently different. Dissolution of a DCM-toluene mixture decreased the density, reducing the tendency for downward displacement. However, the ultimate transformation from a DNAPL to an LNAPL may induce upward displacement. These results suggest that at sites with DNAPL pools containing a mix of components of sufficiently different densities and relative solubilities, natural remobilization may be an active mechanism, with implications for site evaluation and remediation.
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Affiliation(s)
- J W Roy
- Department of Earth Sciences, University of Waterloo, Waterloo, ON, Canada N2L 3G1.
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Prak DJL, Pritchard PH. Solubilization of polycyclic aromatic hydrocarbon mixtures in micellar nonionic surfactant solutions. WATER RESEARCH 2002; 36:3463-3472. [PMID: 12230191 DOI: 10.1016/s0043-1354(02)00070-2] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
This study sought to examine the solubilization of mixtures of the polycyclic aromatic hydrocarbons (PAHs) in solutions of the nonionic surfactants: Tween 20, Tween 80, Triton X 100, Brij 35, and Brij 58. When pyrene (PYR), fluoranthene (FLA), and phenanthrene (PHE) were solubilized from two-PAH mixtures, the PAH concentrations and molar solubilization ratios deviated very little from those as found in the single-PAH systems. When these PAHs were solubilized from the three-PAH mixtures, however, not all three PAHs reached their single-PAH solubilities. When the PAHs were added sequentially to surfactant solution, the PAH added last reached its single-PAH solubility, while the concentration of other two PAHs were lowered by 14-45%. When the PAHs were added simultaneously to the surfactant solution, the composition of the solid phase influenced which PAH reached its single-PAH solubility. For solids containing equal mole fractions of all three PAHs, FLA and PHE dissolved in surfactant solution to a lesser extent than the single-PAH systems. In similar systems containing no surfactant, only FLA solubility decreased. As the mole fraction of a PAH in the solid phase increased, its solubility in the micelle phase (and in the aqueous phase) increased up to the solubility limit. Based on these studies, both PAH-PAH interactions and micelle-PAH interactions should be taken into account when predicting the concentrations of PAH mixtures in micellar surfactant solutions. This should be done because PAH-PAH interactions can influence aqueous solubility, while micelle-PAH interactions can affect the distribution of PAHs in the micellar phase, which may change as the mixture composition changes.
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