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1.
Water Res ; 190: 116778, 2021 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-33387950

RESUMO

Determining robust values for the air-water or NAPL-water interfacial adsorption coefficient, KIA, is key to characterizing and modeling PFAS transport and fate in several environmental systems. Direct, high-resolution measurements of surfactant adsorption at the fluid-fluid interface were aggregated from the literature. This data set was used to examine the accuracy and applicability of Γ and KIA measurements determined for three PFAS from transport experiments and surface-tension data. The transport-measured Γ and KIA data were observed to be fully consistent with the directly-measured data. Specifically, Γ values for the two methods were entirely coincident in the region of overlapping concentrations, which spanned ~4 orders-of-magnitude. Furthermore, the two data sets adhered to an identical Γ-C profile. These results conclusively demonstrate the accuracy of the transport-measured values. Γ and KIA values determined from the application of the Gibbs adsorption equation to measured surface-tension data were fully consistent with the directly-measured and transport-measured data sets, demonstrating their applicability for representing PFAS transport in environmental systems. The directly-measured data were used to examine the concentration dependency of KIA values, absent the potential confounding effects associated with the use of surface-tension or transport-measured data. The directly-measured data clearly demonstrate that KIA attains a constant, maximum limit at lower concentrations. Two separate analyses of the transport-measured data both produced observations of constant KIA values at lower concentrations, consistent with the directly-measured data. These outcomes are discussed in terms of surface activities, relative surface coverages, and critical concentrations.


Assuntos
Fluorcarbonetos , Água , Adsorção , Tensão Superficial , Tensoativos
2.
Chemosphere ; 2632021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-33184521

RESUMO

The interfacial tracer test (ITT) conducted via aqueous miscible-displacement column experiments is one of a few methods available to measure air-water interfacial areas for porous media. The primary objective of this study was to examine the robustness of air-water interfacial area measurements obtained with interfacial tracer tests, and to examine the overall validity of the method. The potential occurrence and impact of surfactant-induced flow was investigated, as was measurement replication. The column and the effluent samples were weighed during the tests to monitor for potential changes in water saturation and flux. Minimal changes in water saturation and flux were observed for experiments wherein steady flow conditions were maintained using a vacuum-chamber system. The air-water interfacial areas measured with the miscible-displacement method completely matched interfacial areas measured with methods that are not influenced by surfactant-induced flow. This successful benchmarking was observed for all three media tested, and over a range of saturations. A mathematical model explicitly accounting for nonlinear and rate-limited adsorption of surfactant at the solid-water and air-water interfaces as well as the influence of changes in surface tension on matric potentials and flow was used to simulate the tracer tests. The independently-predicted simulations provided excellent matches to the measured data, and revealed that the use of the vacuum system minimized the occurrence of surfactant-induced flow and its associated effects. These results in total unequivocally demonstrate that the miscible-displacement ITT method produced accurate and robust measurements of air-water interfacial area under the extant conditions.


Assuntos
Ar/análise , Água/química , Adsorção , Benchmarking , Modelos Teóricos , Fenômenos Físicos , Porosidade , Tensão Superficial , Tensoativos/química
3.
Chemosphere ; 263: 128193, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-33297158

RESUMO

The interfacial tracer test (ITT) conducted via aqueous miscible-displacement column experiments is one of a few methods available to measure air-water interfacial areas for porous media. The primary objective of this study was to examine the robustness of air-water interfacial area measurements obtained with interfacial tracer tests, and to examine the overall validity of the method. The potential occurrence and impact of surfactant-induced flow was investigated, as was measurement replication. The column and the effluent samples were weighed during the tests to monitor for potential changes in water saturation and flux. Minimal changes in water saturation and flux were observed for experiments wherein steady flow conditions were maintained using a vacuum-chamber system. The air-water interfacial areas measured with the miscible-displacement method completely matched interfacial areas measured with methods that are not influenced by surfactant-induced flow. This successful benchmarking was observed for all three media tested, and over a range of saturations. A mathematical model explicitly accounting for nonlinear and rate-limited adsorption of surfactant at the solid-water and air-water interfaces as well as the influence of changes in surface tension on matric potentials and flow was used to simulate the tracer tests. The independently-predicted simulations provided excellent matches to the measured data, and revealed that the use of the vacuum system minimized the occurrence of surfactant-induced flow and its associated effects. These results in total unequivocally demonstrate that the miscible-displacement ITT method produced accurate and robust measurements of air-water interfacial area under the extant conditions.


Assuntos
Benchmarking , Água , Modelos Teóricos , Porosidade , Tensão Superficial
4.
Water Resour Res ; 56(2)2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-33223573

RESUMO

Per- and Polyfluoroalkyl Substances (PFAS) are emerging contaminants of critical concern. As surfactants, PFAS tend to accumulate at air-water interfaces and may stay in the vadose zone for long times before contaminating groundwater. Yet not well understood, the extent of retention in the vadose zone has critical implications for risk management and remediation strategies. We present the first mathematical model that accounts for surfactant-induced flow and solid-phase and air-water interfacial adsorption. We apply the model to simulate PFOS (a PFAS compound of primary concern) transport in the vadose zone at a model fire-training area site impacted by Aqueous Film-Forming Foam (AFFF). Air-water interfacial adsorption is shown to have a significant impact-amplified by the low water content due to gravity drainage-total retardation factors range from 233 to 1355 for the sand and 146 to 792 for the soil used in the study. The simulations illustrate it can take several decades or longer for PFOS to reach groundwater. Counterintuitively, the lower water content in the sand-due to stronger drainage and weaker capillary retention-leads to retardation factors greater than for the soil. Also, most PFOS is adsorbed at air-water interfaces with only 1-2% in the aqueous phase. The implications include 1) fine-texture materials could have lower retardation factors than sand due to higher retained water content, 2) soil PFAS concentrations are likely to be orders of magnitude higher than those in groundwater at source zones. Both implications are consistent with recent field observations at hundreds of AFFF-impacted sites.

5.
Water Resour Res ; 20(1)2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-33184520

RESUMO

This study investigates the accuracy and reproducibility of air-water interfacial areas measured with high-resolution synchrotron x-ray microtomography (XMT). Columns packed with one of two relatively coarse-grained monodisperse granular media, glass beads or a well-sorted quartz sand, were imaged over several years, encompassing changes in acquisition equipment, improved image quality, and enhancements to image acquisition and processing software. For the glass beads, the specific solid surface area (SSSA-XMT) of 31.6 ±1 cm-1 determined from direct analysis of the segmented solid-phase image data is statistically identical to the independently calculated geometric specific solid surface area (GSSA, 32 ±1 cm-1) and to the measured SSSA (28 ±3 cm-1) obtained with the N2BET method (NBET). The maximum specific air-water interfacial area (Amax) is 27.4 (±2) cm-1, which compares very well to the SSSA-XMT, GSSA, and SSSA-NBET values. For the sand, the SSSA-XMT (111 ±2 cm-1) and GSSA (113 ±1 cm-1) are similar. The mean Amax is 96 ±5 cm-1, which compares well to both the SSSA and the GSSA values. The XMT-SSSA values deviated from the GSSA values by 7-16% for the first four experiments, but were essentially identical for the later experiments. This indicates that enhancements in image acquisition and processing improved data accuracy. The Amax values ranged from 74 cm-1 to 101 cm-1, with a coefficient of variation (COV) of 9%. The maximum capillary interfacial area ranged from 12 cm-1 to 19 cm-1, for a COV of 10%. The COVs for both decreased to 5-6% for the latter five experiments. These results demonstrate that XMT imaging provides accurate and reproducible measurements of total and capillary interfacial areas.

6.
Environ Pollut ; : 115917, 2020 Oct 23.
Artigo em Inglês | MEDLINE | ID: mdl-33143983

RESUMO

The objective of this study is to compare the consistency between column and batch experiment methods for measuring solid-phase sorption coefficients and isotherms for per and polyfluoroalkyl substances (PFAS). Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are used as representative PFAS, and experiments are conducted with three natural porous media with differing geochemical properties. Column-derived sorption isotherms are generated by conducting multiple experiments with different input concentrations (multi-C0 method) or employing elution-front integration wherein the entire isotherm is determined from a single breakthrough curve (BTC) elution front. The isotherms generated with the multi-C0 column method compared remarkably well to the batch isotherms over an aqueous concentration range of 3-4 orders of magnitude. Specifically, the 95% confidence intervals for the individual isotherm variables overlapped, producing statistically identical regressions. The elution-front integration isotherms generally agreed with the batch isotherms, but exhibited noise and systematic deviation at lower concentrations in some cases. All data sets were well described by the Freundlich isotherm model. Freundlich N values ranged from 0.75 to 0.81 for PFOS and was 0.87 for PFOA and are consistent with values reported in the literature for different geomedia. The results of this study indicate that column and batch experiments can measure consistent sorption isotherms and sorption coefficients for PFOS and PFOA when robust experimental setup and data analysis are implemented.

7.
J Contam Hydrol ; 235: 103716, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32977295

RESUMO

A simple one-dimensional heterogeneous-source model was used to simulate dissolution of organic liquid that was non-uniformly distributed in physically heterogeneous porous media. The permeability field was depicted as a pseudo-homogeneous medium. The source zone was discretized into multiple domains representing different organic-liquid configurations and hydraulic accessibilities, each with a different representative upscaled mass transfer rate coefficient that is temporally variable. This simplified approach represents a system where minimal information is available regarding system heterogeneities. All factors that influence dissolution were incorporated into the calibrated mass transfer terms. The mass transfer terms were calibrated for each zone separately. The one-dimensional, heterogeneous-source model adequately simulated the multi-stage dissolution behavior observed for column-scale systems that were packed with different natural soils, as well as for flow-cell systems wherein the source zone consisted of both a residual zone and pool. The results indicate that the model adequately simulated the presence of multiple organic-liquid zones in porous media with different configurations and hydraulic accessibilities, which accounts for the non-ideal dissolution behavior observed. The calibrated mass transfer terms for each source type were consistent with those obtained for systems that contained only one of either source type.

8.
Sci Total Environ ; 740: 140017, 2020 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-32927568

RESUMO

Per- and polyfluoroalkyl substances (PFAS) are contaminants of critical concern due to their persistence, widespread distribution in the environment, and potential human-health impacts. In this work, published studies of PFAS concentrations in soils were compiled from the literature. These data were combined with results obtained from a large curated database of PFAS soil concentrations for contaminated sites. In aggregate, the compiled data set comprises >30,000 samples collected from >2500 sites distributed throughout the world. Data were collected for three types of sites- background sites, primary-source sites (fire-training areas, manufacturing plants), and secondary-source sites (biosolids application, irrigation water use). The aggregated soil-survey reports comprise samples collected from all continents, and from a large variety of locations in both urban and rural regions. PFAS were present in soil at almost every site tested. Low but measurable concentrations were observed even in remote regions far from potential PFOS sources. Concentrations reported for PFAS-contaminated sites were generally orders-of-magnitude greater than background levels, particularly for PFOS. Maximum reported PFOS concentrations ranged upwards of several hundred mg/kg. Analysis of depth profiles indicates significant retention of PFAS in the vadose zone over decadal timeframes and the occurrence of leaching to groundwater. It is noteworthy that soil concentrations reported for PFAS at contaminated sites are often orders-of-magnitude higher than typical groundwater concentrations. The results of this study demonstrate that PFAS are present in soils across the globe, and indicate that soil is a significant reservoir for PFAS. A critical question of concern is the long-term migration potential to surface water, groundwater, and the atmosphere. This warrants increased focus on the transport and fate behavior of PFAS in soil and the vadose zone, in regards to both research and site investigations.

9.
Environ Sci Technol ; 54(19): 11876-11885, 2020 Oct 06.
Artigo em Inglês | MEDLINE | ID: mdl-32972138

RESUMO

The objective of this research was to investigate the retention and transport behavior of GenX in five natural porous media with similar median grain diameters but different geochemical properties. Surface tensions were measured to characterize surface activity. Miscible-displacement experiments were conducted under saturated conditions to characterize the magnitude of solid-phase adsorption, while unsaturated-flow experiments were conducted to examine the impact of air-water interfacial adsorption on retention and transport. The results from surface-tension measurements showed that the impact of solution composition is greater for the ammonium form of GenX than for the acid form, due to the presence of the NH4 counterion. The breakthrough curves for the experiments conducted under saturated conditions were asymmetrical, and a solute-transport model employing a two-domain representation of nonlinear, rate-limited sorption provided reasonable simulations of the measured data. The magnitudes of solid-phase adsorption were relatively small, with the highest adsorption associated with the medium containing the greatest amount of metal oxides. The breakthrough curves for the experiments conducted under unsaturated conditions exhibited greater retardation due to the impact of adsorption at the air-water interface. The contributions of air-water interfacial adsorption to GenX retention ranged from ∼24% to ∼100%. The overall magnitudes of retardation were relatively low, with retardation factors < ∼3, indicating that GenX has significant migration potential in soil and the vadose zone. To our knowledge, the results presented herein represent the first reported data for solid-water and air-water interfacial adsorption of GenX by soil. These data should prove useful for assessing the transport and fate behavior of GenX in soil and groundwater.

10.
Environ Pollut ; 263(Pt A): 114446, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32283452

RESUMO

As a result of metal mining activities in Pakistan, toxic heavy metals (HMs) such as chromium (Cr) and lead (Pb) often enter the soil ecosystem, accumulate in food crops and cause serious human health and environmental issues. Therefore, this study examined the efficacy of biochar for contaminated soil remediation. Poplar wood biochar (PWB) and sugarcane bagasse biochar (SCBB) were amended to mine-contaminated agricultural soil at 3% and 7% (wt/wt) application rates. Lactuca sativa (Lettuce) was cultivated in these soils in a greenhouse, and uptake of HMs (Cr and Pb) as well as biomass produced were measured. Subsequently, health risks were estimated from uptake data. When amended at 7%, both biochars significantly (P<0.01) reduced plant uptake of Cr and Pb in amended soil with significant (P<0.01) increase in biomass of lettuce as compared to the control. Risk assessment results showed that both biochars decreased the daily intake of metals (DIM) and associated health risk due to consumption of lettuce as compared to the control. The Pb human health risk index (HRI) for adults and children significantly (P<0.01) decreased with sugarcane bagasse biochar applied at 7% rate relative to other treatments (including the control). Relative to controls, the SCBB and PWB reduced Cr and Pb uptake in lettuce by 69%, 73.7%, respectively, and Pb by 57% and 47.4%, respectively. For both amendments, HRI values for Cr were within safe limits for adults and children. HRI values for Pb were not within safe limits except for the sugarcane bagasse biochar applied at 7%. Results of the study indicated that application of SCBB at 7% rate to mine impacted agricultural soil effectively increased plant biomass and reduced bioaccumulation, DIM and associated HRI of Cr and Pb as compared to other treatments and the control.


Assuntos
Metais Pesados/análise , Saccharum , Poluentes do Solo/análise , Adulto , Celulose , Carvão Vegetal , Criança , Cromo , Ecossistema , Humanos , Chumbo , Alface , Paquistão , Solo , Madeira/química
11.
Chemosphere ; 250: 126305, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32135438

RESUMO

The aqueous-based interfacial tracer method employing miscible-displacement tests is one method available for measuring air-water interfacial areas. One potential limitation to the method is the impact of tracer-induced drainage on the system. The objective of this study was to investigate the efficacy of a low-concentration tracer test method for measuring air-water interfacial area. Tracer concentrations and analytical methods were selected that allowed the use of tracer input concentrations that were below the threshold of tracer-induced drainage. Multiple tracer tests were conducted at different water saturations. Interfacial areas increased from 34.8 to 101 cm-1 with the decrease in saturation from 0.86 to 0.62. The method produced relatively robust measurements of air-water interfacial area, with coefficients of variation ranging from 6 to 26%. A variably saturated flow and transport model that accounts for the effects of tracer on interfacial tension, and the retention of tracer at the air-water and solid-water interfaces, was used to test for potential tracer-induced drainage. The simulations showed that the use of low tracer-input concentrations eliminated this phenomenon. This is consistent with the measured data for effluent-sample masses, which exhibited minimal change during the tests, and with the observation that the interfacial areas obtained with the low-concentration-tracer method were consistent with values measured with two methods that are not influenced by tracer-induced drainage. These results demonstrate that the low-concentration miscible-displacement tracer test method is an effective approach for measuring air-water interfacial areas in porous media.


Assuntos
Monitoramento Ambiental/métodos , Porosidade , Tensão Superficial , Água
12.
Sci Total Environ ; 713: 136744, 2020 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-32019053

RESUMO

There is great interest in the transport behavior of PFAS in the vadose zone, and the impact of leaching on groundwater contamination. Air-water interfacial adsorption is an important process for PFAS retention in unsaturated porous media, and it is influenced by many factors including solution conditions such as ionic strength. The present study employed miscible-displacement column experiments to investigate the impact of ionic strength and pH on perfluorooctanoic acid (PFOA) retardation and transport under dynamic water-flow conditions. The results showed that retardation under unsaturated conditions was affected significantly by changes in ionic strength, whereas there was minimal impact for saturated conditions. This indicates that air-water interfacial adsorption, which was a major source of retardation, was influenced significantly by changes in ionic strength while they had a minor impact on solid-phase adsorption. The impact of changes in ionic strength on the magnitude of air-water interfacial adsorption observed for the column experiments was consistent with measured surface-tension data. The impact of changes in pH was less significant compared to that of ionic strength for transport under unsaturated conditions. These results illustrate the influence of solution chemistry on PFAS adsorption and transport under unsaturated conditions. This solution-dependent behavior should be considered when characterizing PFAS transport in soils and the vadose zone.

13.
J Hazard Mater ; 392: 122328, 2020 06 15.
Artigo em Inglês | MEDLINE | ID: mdl-32092655

RESUMO

The performance of trichloroethene (TCE) removal was initially investigated in sodium persulfate (SPS) or potassium monopersulfate triple salt (PMS) oxidative environment by reduced graphene oxide (rGO) supported nZVI (nZVI-rGO) catalyst and further the role of sulphur by anchoring nano FeS on nZVI-rGO (FeS@nZVI-rGO) was evaluated. The high usage of oxidants and stability of FeS@nZVI-rGO catalyst were significantly improved due to the insoluble nature of this innovative catalyst by involvement of nano FeS which limited the rapid iron loss caused by the corrosion of active sites and mitigated rapid oxidants decomposition in FeS@nZVI-rGO/SPS and FeS@nZVI-rGO/PMS systems. The tests for target contaminant removal showed that over 95 % TCE could be removed at 100 mg L-1 FeS@nZVI-rGO and 1.2 mM SPS or 0.3 mM PMS dosages, in which over 85 % TCE could be dechlorinated. The reactive oxygen radicals (ROSs) generation mechanisms and their contribution to TCE removal were investigated through radical scavenge tests in both systems, indicating that both HO and SO4- were the major ROSs rather than O2-. In conclusion, this study revealed the well function and fundamental mechanism of this innovative catalyst by anchoring nano FeS and worth of further demonstration of this technique in TCE contaminated groundwater remediation application.

14.
Water Res ; 168: 115179, 2020 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-31639593

RESUMO

The transport of per- and poly-fluoroalkyl substances (PFAS) in the vadose zone is complicated by the fact that multiple mass-transfer processes can contribute to their retention and retardation. In addition, PFAS transport at some sites can be further complicated by the presence of organic immiscible liquids (OIL). Mass-transfer processes are inherently rate limited and, therefore, have the potential to cause nonideal transport of PFAS. The objectives of this research were to: (1) develop a solute-transport model that explicitly accounts for multiple retention processes, including adsorption at air-water and OIL-water interfaces, adsorption by the solid phase, and diffusive mass-transfer between advective and nonadvective domains, and (2) apply the model to measured transport data to delineate which processes are rate limited and contribute to observed nonideal transport. Breakthrough curves for transport of two PFAS and one hydrocarbon surfactant in sand obtained from prior miscible-displacement experiments exhibited nonideal transport. The multiprocess model effectively simulated the measured transport data. The results of the analyses indicate that adsorption at the air-water and OIL-water interface can generally be treated as effectively instantaneous for transport in porous media. The rate limitations associated with solid-phase adsorption and diffusive mass transfer between advective and nonadvective domains were of greater significance.


Assuntos
Fluorcarbonetos , Adsorção , Porosidade , Dióxido de Silício , Água
15.
Chem Eng J ; 362: 243-250, 2019 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-31588180

RESUMO

This study investigated the reductive initiation for the depletion of highly oxidized/perhalogenated pollutants, specifically the degradation of carbon tetrachloride (CT) was induced by adding methanol (MeOH) into a ferrous ion (Fe(II)) activated calcium peroxide (CaO2) system. The results indicated that CT could be completely degraded within 20 min at CaO2/Fe(II)/MeOH/CT molar ratio of 30/40/10/1 in this system. Scavenging tests suggested that both superoxide radical anion (O2 •-) and carbon dioxide radical anion (CO2 •-) were predominant reactive species responsible for CT destruction. Hydroxymethyl radicals (•CH2OH), an intermediate in the transformation of MeOH, could also initiate CT degradation by reducing C-Cl bond. GC/MS analysis identified CHCl3, C2Cl4, and C2Cl6 as the intermediates accompanied by CT destruction, and a reduction mechanism for CT degradation was proposed accordingly. In addition, the impact of solution matrix and initial solution pH were evaluated, and the results showed that Cl-, NO3 -, and HCO3 - had adverse effects on CT degradation. Moreover, the alkaline condition was unfavorable to CT depletion. In conclusion, the results obtained in the actual groundwater tests encouragingly demonstrated that the CaO2/Fe(II)/MeOH process is a highly promising technique for the remediation of CT-contaminated groundwater.

16.
Environ Pollut ; 254(Pt B): 113102, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31491699

RESUMO

Per- and poly-fluoroalkyl substances (PFAS) have attracted considerable concern due to their widespread occurrence in the environment and potential human health risks. Given the complexity of PFAS retention in multi-phase systems, it would be useful for characterization and modeling purposes to be able to readily determine the relative significance of the individual retention processes for a given PFAS and set of subsurface conditions. A quantitative-structure/property-relationship (QSPR) analysis was conducted for adsorption of PFAS by soils, sediments, and granular activated carbon (GAC), and integrated with a prior analysis conducted for adsorption to air-water and oil-water interfaces. The results demonstrated that a model employing molar volume provided reasonable predictions of organic-carbon normalized soil/sediment adsorption coefficients (log Koc), GAC-adsorption coefficients (log Kd), and air/oil-water interfacial adsorption coefficients (log Ki) for PFAS. The relative magnitudes of solid-water and air/oil-water interfacial adsorption were compared as a function of controlling variables. A nomograph was developed that provides a first-order determination of the relative significance of these interfacial adsorption processes in multi-phase porous-media systems.


Assuntos
Fluorcarbonetos/química , Poluentes Químicos da Água/química , Adsorção , Carvão Vegetal/química , Sedimentos Geológicos/química , Humanos , Modelos Químicos , Porosidade , Solo/química , Água/química
17.
Environ Sci Technol ; 53(18): 10654-10664, 2019 Sep 17.
Artigo em Inglês | MEDLINE | ID: mdl-31464435

RESUMO

The objective of this research was to examine the influence of nonideal sorption/desorption on the transport of polyfluorinated alkyl substances (PFASs) in soil, with a specific focus on characterizing and quantifying potential extended, mass-transfer-limited elution behavior. Perfluorooctane sulfonic acid (PFOS) was used as a representative PFAS, and miscible-displacement experiments were conducted with two soils comprising contrasting geochemical properties. The influence of nonlinear, rate-limited, hysteretic, and irreversible sorption/desorption on transport was investigated through experiments and model simulations. The breakthrough curves measured for PFOS transport in the two soils were asymmetrical and exhibited extensive elution tailing, indicating that sorption/desorption was significantly nonideal. The widely used two-domain sorption kinetics model could not fully simulate the observed transport behavior, whereas a multirate model employing a continuous distribution of sorption domains was successful. The overall results indicated that sorption/desorption was significantly rate-limited and that nonlinear, hysteretic, and irreversible sorption/desorption had minimal impact on PFOS transport. Comparison of PFOS transport data to data reported for two hydrophobic organic contaminants (HOCs) showed that the HOCs exhibited much more extensive elution tailing, likely reflecting differences in sorption/desorption mechanisms. The projected influence of rate-limited sorption/desorption on PFOS transport at the field scale was investigated through simulation. The results of the study suggest that rate-limited sorption/desorption may affect the field-scale transport of PFOS and other PFAS for systems influenced by transient or short-residence-time conditions and in some cases could possibly increase the amount of flushing required to reduce PFOS concentrations to levels below those associated with human-health concerns.


Assuntos
Fluorcarbonetos , Poluentes do Solo , Adsorção , Ácidos Alcanossulfônicos , Humanos , Solo
18.
Water Res ; 161: 17-26, 2019 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-31174056

RESUMO

The objective of this research is to examine the influence of surfactant and solution composition on PFAS adsorption at fluid-fluid interfaces. Surface tensions were measured for select PFAS, as well as a representative hydrocarbon surfactant. These data are supplemented with data sets collected from the literature. The influence of surfactant headgroup charge, specifically for zwitterionic PFAS, was investigated. The impacts of surfactant counterion for ionic PFAS and the influence of headgroup size for nonionic PFAS were also investigated. In addition, the influence of solution ion composition, ionic strength, and pH was examined. The impact of co-solutes, specifically ethanol, humic acid, and trichloroethene, was also examined, as well as the behavior of PFAS mixtures and fluorocarbon-hydrocarbon surfactant mixtures. The data were interpreted within the framework of a QSPR model recently developed to predict fluid-fluid interfacial adsorption coefficients (Ki) of PFAS. The results demonstrate that all of the factors investigated have some degree of impact on Ki values. Thus, the composition of soil-pore water and groundwater is likely to affect the magnitude of PFAS adsorption at air-water and organic liquid-water interfaces. However, the influence on Ki of most of the factors investigated is small for lower PFAS concentrations (less than ∼1-10 mg/L). Hence, their impacts on fluid-fluid interfacial adsorption are likely to be relatively minor at the low PFAS concentrations representative of many environmental systems, especially compared to the impact of other factors such as fluid saturations, porous-medium properties, and PFAS molecular structure. The results of this study indicate that the revised QSPR model provides reasonable first-order predictions of Ki for a wide range of PFAS in environmental systems.


Assuntos
Fluorcarbonetos , Água Subterrânea , Adsorção , Tensão Superficial , Tensoativos
19.
Environ Pollut ; 252(Pt A): 777-783, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31200203

RESUMO

Solvent stabilizer 1,4-dioxane, an emerging recalcitrant groundwater contaminant, was commonly added to chlorinated solvents such as trichloroethene (TCE), and the impact of co-disposal on contaminant transport processes remains uncertain. A series of batch equilibrium experiments was conducted with variations of 1,4-dioxane and TCE composition to evaluate aqueous dissolution of the two components and their sorption to aquifer sediments. The solubility of TCE increased with increasing amounts of 1,4-dioxane, indicating that 1,4-dioxane acts as a cosolvent causing solubility enhancement of co-contaminants. The solubilization results compared favorably with predictions using the log-linear cosolvency model. Equilibrium sorption coefficients (Kd and Kf) were also measured for different 1,4-dioxane and TCE compositions, and the findings indicate that both contaminants adsorb to aquifer sediments and TCE Kd values increased with increasing organic matter content. However, the Kd for TCE decreased with increases in 1,4-dioxane concentration, which was attributed to cosolvency impacts on TCE solubility. These findings further advance our understanding of the mass-transfer processes controlling groundwater plumes containing 1,4-dioxane, and also have implications for the remediation of 1,4-dioxane contamination.


Assuntos
Dioxanos/análise , Dioxanos/química , Água Subterrânea/química , Tricloroetileno/análise , Tricloroetileno/química , Poluentes Químicos da Água/análise , Adsorção , Solubilidade , Solventes/análise
20.
J Hazard Mater ; 368: 506-513, 2019 04 15.
Artigo em Inglês | MEDLINE | ID: mdl-30710779

RESUMO

Two carboxylic acids (formic acid (FA) and citric acid (CIT)) enhanced the Fenton process using Fe(II)-activated calcium peroxide (CP) to develop a hydroxyl (HO) and carbon dioxide radical (CO2-) coexistence process for the simultaneous redox-based degradation of three chlorinated hydrocarbons (CHs), namely carbon tetrachloride (CT), tetrachloroethene (PCE), and trichloroethene (TCE), was investigated. The experimental results showed that CT removal was increased while PCE and TCE degradation were decreased with the addition of FA to the Fe(II)/CP system. However, addition of CIT to the Fe(II)/CP/FA system enhanced the removal efficiency of all three contaminants. For example, 81.7%, 79.4%, and 96.1% of CT, PCE, and TCE, respectively, were removed simultaneously under the optimal molar ratio of 12/12/12/12/1 of CIT/CP/Fe(II)/FA/CHs. Mechanism study confirmed the specific roles of HO and secondarily generated CO2- radical. PCE and TCE were degraded oxidatively by HO while CT was degraded via reductive dechlorination by CO2-. Carbonate reduced PCE and TCE degradation in actual groundwater as it consumed reactive oxygen species, whereas humic acid and neutral pH had minimal impact on contaminant removal. These results can help us better understand the synergistic effects of carboxylic acids in the modified Fenton process for the redox degradation of refractory chlorinated hydrocarbons.

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