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Michael D Annable - One of the best experts on this subject based on the ideXlab platform.

  • surfactant enhanced Air Sparging with viscosity control for heterogeneous aquifers
    Hydrogeology Journal, 2019
    Co-Authors: Hobin Kwon, Jaekyeong Choi, Michael D Annable
    Abstract:

    The effects of surface-tension and/or viscosity changes in groundwater on the remedial performance of Air Sparging for heterogeneous aquifers were investigated. The study used a one-dimensional (1-D) column and a two-dimensional (2-D) flow-chamber aquifer model. To introduce a heterogeneous setting, the middle part of the model was packed with a finer soil [LKZ, low hydraulic conductivity (K) zone]. Fluorescein sodium salt was used at 200 mg/L for all experiments as a surrogate contaminant. For the 1-D column experiments, the rate of fluorescence decay in the LKZ during surfactant-enhanced Air Sparging (SEAS) was significantly higher than during the standard Air sparing (AS) process without additives; the area of fluorescence loss, measured after 17 h of Air Sparging (including ozone), was double and triple that of the conventional AS process, for SEAS without thickener (SEAS1) and SEAS with thickener (SEAS2), respectively. Experimental results using the 2-D chamber also confirmed the enhanced Air intrusion into the LKZ during the SEAS process. The Air fluxes through the LKZ increased by 47 and 103% for the SEAS1 and SEAS2 compared to AS, respectively; and 79 and 90% of fluorescence disappeared in the LKZ during ozone injection for SEAS1 and SEAS2, respectively, whereas only 10% disappeared for AS during the 3-h experimental period. The findings of this study indicate that the AS process, at low surface tension and increased groundwater viscosity may be a viable alternative to the conventional AS process for aquifers of heterogeneous hydrogeological formations.

  • effect of increased groundwater viscosity on the remedial performance of surfactant enhanced Air Sparging
    Journal of Contaminant Hydrology, 2018
    Co-Authors: Jaekyeong Choi, Hobin Kwon, Michael D Annable
    Abstract:

    Abstract The effect of groundwater viscosity control on the performance of surfactant-enhanced Air Sparging (SEAS) was investigated using 1- and 2-dimensional (1-D and 2-D) bench-scale physical models. The viscosity of groundwater was controlled by a thickener, sodium carboxymethylcellulose (SCMC), while an anionic surfactant, sodium dodecylbenzene sulfonate (SDBS), was used to control the surface tension of groundwater. When resident DI water was displaced with a SCMC solution (500 mg/L), a SDBS solution (200 mg/L), and a solution with both SCMC (500 mg/L) and SDBS (200 mg/L), the Air saturation for sand-packed columns achieved by Air Sparging increased by 9.5%, 128%, and 154%, respectively, (compared to that of the DI water-saturated column). When the resident water contained SCMC, the minimum Air pressure necessary for Air Sparging processes increased, which is considered to be responsible for the increased Air saturation. The extent of the Sparging influence zone achieved during the Air Sparging process using the 2-D model was also affected by viscosity control. Larger Sparging influence zones (de-saturated zone due to Air injection) were observed for the Air Sparging processes using the 2-D model initially saturated with high-viscosity solutions, than those without a thickener in the aqueous solution. The enhanced Air saturations using SCMC for the 1-D Air Sparging experiment improved the degradative performance of gaseous oxidation agent (ozone) during Air Sparging, as measured by the disappearance of fluorescence (fluorescein sodium salt). Based on the experimental evidence generated in this study, the addition of a thickener in the aqueous solution prior to Air Sparging increased the degree of Air saturation and the Sparging influence zone, and enhanced the remedial potential of SEAS for contaminated aquifers.

  • changes in Air flow patterns using surfactants and thickeners during Air Sparging bench scale experiments
    Journal of Contaminant Hydrology, 2015
    Co-Authors: Michael D Annable
    Abstract:

    Abstract Air injected into an aquifer during Air Sparging normally flows upward according to the pressure gradients and buoyancy, and the direction of Air flow depends on the natural hydrogeologic setting. In this study, a new method for controlling Air flow paths in the saturated zone during Air Sparging processes is presented. Two hydrodynamic parameters, viscosity and surface tension of the aqueous phase in the aquifer, were altered using appropriate water-soluble reagents distributed before initiating Air Sparging. Increased viscosity retarded the travel velocity of the Air front during Air Sparging by modifying the viscosity ratio. Using a one-dimensional column packed with water-saturated sand, the velocity of Air intrusion into the saturated region under a constant pressure gradient was inversely proportional to the viscosity of the aqueous solution. The Air flow direction, and thus the Air flux distribution was measured using gaseous flux meters placed at the sand surface during Air Sparging experiments using both two-, and three-dimensional physical models. Air flow was found to be influenced by the presence of an aqueous patch of high viscosity or suppressed surface tension in the aquifer. Air flow was selective through the low-surface tension (46.5 dyn/cm) region, whereas an aqueous patch of high viscosity (2.77 cP) was as an effective Air flow barrier. Formation of a low-surface tension region in the target contaminated zone in the aquifer, before the Air Sparging process is inaugurated, may induce Air flow through the target zone maximizing the contaminant removal efficiency of the injected Air. In contrast, a region with high viscosity in the Air Sparging influence zone may minimize Air flow through the region prohibiting the region from de-saturating.

  • laboratory evaluation of surfactant enhanced Air Sparging for perchloroethene source mass depletion from sand
    Journal of Environmental Science and Health Part A-toxic\ hazardous Substances & Environmental Engineering, 2009
    Co-Authors: Michael D Annable
    Abstract:

    Surfactant-enhanced Air Sparging (SEAS) was evaluated in this laboratory-scale study to assess: (i) the removal efficiency of volatile contaminant from an aquifer model contrasted to conventional Air Sparging; and (ii) the effect of mass removal of dense non-aqueous phase liquid (DNAPL) during Air Sparging on the changes in aqueous flux of dissolved DNAPL. We conducted Sparging experiments to remove perchloroethene (PCE) sources from laboratory flow chambers packed with sand. PCE was emplaced in rectangular zones at three locations within the flow chamber. The resident water was supplemented with the anionic surfactant, sodium dodecylbenzene sulfonate (SDBS), to reduce the surface tension of water, and then sparged with nitrogen gas at a constant flow rate of 0.12 L/min. It was found that SEAS was significantly more efficient than conventional Air Sparging for removing PCE. For SEAS, about 78% and 75% of total PCE mass was depleted from the flow chamber at a surface tension of 52.2 dynes/cm (350 mg/L SDBS...

  • changes in Air saturation and Air water interfacial area during surfactant enhanced Air Sparging in saturated sand
    Journal of Contaminant Hydrology, 2006
    Co-Authors: Kyongmin Choi, Jiwon Moon, Michael D Annable
    Abstract:

    Abstract Reduction in the surface tension of groundwater, prior to Air Sparging for removal of volatile organic contaminant from aquifer, can greatly enhance the Air content and the extent of influence when Air Sparging is implemented. However, detailed information on the functional relationship between water saturation, Air–water contact area induced by Air Sparging and the surface tension of water has not been available. In this study, the influence of adding water-soluble anionic surfactant (sodium dodecyl benzene sulfonate) into groundwater before Air Sparging on the Air–water interfacial area and water saturation was investigated using a laboratory-scale sand packed column. It was found that water saturation decreases with decreasing surface tension of water until it reaches a point where this trend is reversed so that water saturation increases with further decrease in the surface tension. The lowest water saturation of 0.58 was achieved at a surface tension of 45.4 dyn/cm, which is considered as the optimum surface tension for maximum de-saturation for the initially water-saturated sand used in this study. The Air–water contact area generated in the sand column due to Air Sparging was measured using a gaseous interfacial tracer, n -decane, and was found to monotonically increase with decreasing water saturation. The results of this study provide useful design information for surfactant-enhanced Air Sparging removal of volatile contaminants from aquifers.

Washington J Braida - One of the best experts on this subject based on the ideXlab platform.

  • Air Sparging effectiveness laboratory characterization of Air channel mass transfer zone for voc volatilization
    Journal of Hazardous Materials, 2001
    Co-Authors: Washington J Braida
    Abstract:

    Abstract Air Sparging in conjunction with soil vapor extraction is one of many technologies currently being applied for the remediation of groundwater contaminated with volatile organic compounds (VOCs). Mass transfer at the Air–water interface during Air Sparging is affected by various soil and VOC properties. In this study with a single Air-channel apparatus, mass transfer of VOCs was shown to occur within a thin layer of saturated porous media next to the Air channel. In this zone, the VOCs were found to rapidly deplete during Air Sparging resulting in a steep concentration gradient while the VOC concentration outside the zone remained fAirly constant. The sizes of the mass transfer zone were found to range from 17 to 41 mm or 70 d 50 and 215 d 50 ( d 50 =mean particle size) for low organic carbon content media (

  • modeling of Air Sparging of voc contaminated soil columns
    Journal of Contaminant Hydrology, 2000
    Co-Authors: Washington J Braida
    Abstract:

    Abstract Air Sparging is a remediation technology currently being applied for the restoration of sites contaminated with volatile organic compounds (VOCs). Attempts have been made by various researchers to model the fate of VOCs in the gas and liquid phase during Air Sparging. In this study, a radial diffusion model with an Air–water mass transfer boundary condition was developed and applied for the prediction of VOC volatilization from Air Sparging of contaminated soil columns. The approach taken was to use various parameters such as mass transfer coefficients and tortuosity factors determined previously in separate experiments using a single Air channel apparatus and applying these parameters to a complex system with many Air channels. Incorporated in the model, is the concept of mass transfer zone (MTZ) where diffusion of VOCs in this zone was impacted by the volatilization of VOCs at the Air–water interface but with negligible impact outside the zone. The model predicted fAirly well the change in the VOC concentrations in the exhaust Air, the final average aqueous VOC concentration, and the total mass removed. The predicted mass removal was within 1% to 20% of the actual experimental mass removed. The results of the model seemed to suggest that Air-sparged soil columns may be modeled as a composite of individual Air channels surrounded by a MTZ. For a given Air flow rate and Air saturation, the VOC removal was found to be inversely proportional to the radius of the Air channel. The approach taken provided conceptual insights on mass transfer processes during Air Sparging operations.

Krishna R Reddy - One of the best experts on this subject based on the ideXlab platform.

  • remediation of dnapl source zones in groundwater using Air Sparging
    Land Contamination & Reclamation, 2004
    Co-Authors: Krishna R Reddy, Luesgald Tekola
    Abstract:

    Air Sparging has shown to be a promising remediation technique for the treatment of saturated soils and groundwater contaminated by volatile organic compounds (VOCs). These compounds include non-aqueous phase liquids (NAPLs) that are typically classified by their density with respect to water; light NAPLs, or LNAPLs, are less dense, and dense NAPLs, or DNAPLs, are denser than water. Although Air Sparging is promising, the remedial efficiency of the process may vary considerably depending on the subsurface conditions that exist at the site and the system variables that are used. Source zones of free-phase (pure liquid) DNAPL may be particularly difficult to remediate, since the contaminant tends to form small globules that become trapped within the soil matrix. The present investigation was performed to evaluate and compare the spatial effects of different Air injection rates on the remediation of DNAPL source zones, and to determine the effect of groundwater flow on the removal of DNAPL source zones during Air injection. Five laboratory experiments were conducted using a two-dimensional (2D) physical aquifer simulation apparatus containing homogeneous sand that was artificially contaminated with a DNAPL. The first three tests each used a progressively higher rate of Air injection without groundwater flow, while the last two tests were performed using two different rates of Air injection with groundwater flow, due to an identical 0.01 hydraulic gradient. The results showed that DNAPL source zones were effectively removed by Air Sparging, because the injected Air increased volatilisation, dissolution and diffusion. Compared to the tests with lower Airflow, the increased rate of Airflow substantially enhanced removal because the additional Air provided a greater interfacial area for DNAPL mass transfer. Using Air Sparging under groundwater flow conditions also resulted in an increased rate of contaminant removal, but this was partially due to undesirable off-site lateral contaminant migration, which occurred due to groundwater flow. Consequently, when groundwater flow was occurring, it was beneficial to use a higher Airflow rate for two main reasons: (1) because the greater amount of Air saturation provides faster removal, and (2) because the greater Air saturation reduces the hydraulic conductivity of the sand, thereby hindering groundwater flow and lateral contaminant migration.

  • laboratory study of Air Sparging of tce contaminated saturated soils and ground water
    Ground Water Monitoring and Remediation, 1999
    Co-Authors: Jeffrey A Adams, Krishna R Reddy
    Abstract:

    Air Sparging has proven to be an effective remediation technique for treating saturated soils and ground water contaminated by volatile organic compounds (VOCs). Since little is known about the system variables and mass transfer mechanisms important to Air Sparging, several researchers have recently performed laboratory investigations to study such issues. This paper presents the results of column experiments performed to investigate the behavior of dense nonaqueous phase liquids (DNAPLs), specifically trichloroethylene (TCE), during Air Sparging. The specific objectives of the study were (1) to compare the removal of dissolved TCE with the removal of dissolved light nonaqueous phase liquids (LNAPLs), such as benzene or toluene; (2) to determine the effect of injected Air-flow rate on dissolved TCE removal; (3) to determine the effect of initial dissolved TCE concentration on removal efficiency; and (4) to determine the differences in removal between dissolved and pure-chase TCE. The test results showed that (1) the removal of dissolved TCE was similar to that of dissolved LNAPL; (2) increased Air-injection rates led to increased TCE removal at lower ranges of Air injection, but further increases at higher ranges of Air injection did not increase the rate of removal, indicating a threshold removal rate had beenmore » reached; (3) increased initial concentration of dissolved TCE resulted in similar rates of removal; and (4) the removal pf pure-phase TCE was difficult using a low Air-injection rate, but higher Air-injection rates led to easier removal.« less

  • technical note an experimental investigation of Air flow patterns in saturated soils during Air Sparging
    Geotechnical and Geological Engineering, 1998
    Co-Authors: Robin Semer, Jeffrey A Adams, Krishna R Reddy
    Abstract:

    Air Sparging is an emerging method used to remediate saturated soils and groundwater that have been contaminated with volatile organic compounds (VOCs). During Air Sparging, Air is injected into the subsurface below the lowest known depth of contamination. Due to buoyancy, the injected Air will rise through the zone of contamination. Through a variety of mechanisms, including volatilization and biodegradation, the Air will serve to remove or help degrade the contaminants. The contaminant-laden Air will continue to rise towards the ground surface, eventually reaching the vadose zone, where the vapours are collected and treated using a soil vapour extraction (SVE) system.

  • system effects on benzene removal from saturated soils and ground water using Air Sparging
    Journal of Environmental Engineering, 1998
    Co-Authors: Krishna R Reddy, Jeffrey A Adams
    Abstract:

    This paper presents the results of a laboratory investigation performed to study the role of various Air Sparging system parameters on the removal of benzene from saturated soils and ground water. A series of one-dimensional column experiments was conducted with predetermined contaminant concentrations and predetermined injected Air flow rates and pressures to investigate the effects of: (1) the soil type; (2) the use of pulsed Air injection; and (3) the synergistic effects of co-contaminants on Air Sparging removal efficiency. This study demonstrated that the grain size of the soils affects the Air Sparging removal efficiency. A threshold value exists for effective particle size (D10), which is equal to 0.2 mm; above this threshold value, the rate of removal is linearly proportional to the D10 value; while below this value, there is a drastic increase in the time required for contaminant removal. Additionally, it was demonstrated that pulsed Air injection did not offer any appreciable advantages over con...

  • mechanisms controlling toluene removal from saturated soils during in situ Air Sparging
    Journal of Hazardous Materials, 1998
    Co-Authors: Robin Semer, Krishna R Reddy
    Abstract:

    In situ Air Sparging is an effective method for removing volatile organic compounds from saturated soils and groundwater. Removal efficiency levels as high as 98% are often reported, and the remediation time is significantly less than that required for conventional pump and treat technology. However, predictions of the time required for contaminant mass removal by Air Sparging have been approximate at best due to a lack of understanding of the relative importance of the various mechanisms that are responsible for this contaminant removal. Volatilization is considered the most dominant mass transfer mechanism during the Air Sparging process. Dissolution, desorption and biodegradation are the other major mechanisms that determine the rate at which contaminants are partitioned into different phases or transformed into nonhazardous substances. Additionally, advection, dispersion and diffusion are the transport mechanisms that dictate the overall contaminant removal efficiency. This paper first describes these different mechanisms along with the factors that affect these mechanisms. Then, experimental data is presented for toluene removal from Ottawa sand and fine gravel by means of Air Sparging. The tests performed included batch tests to characterize the adsorption characteristics of toluene on the Ottawa sand, and Air Sparging column tests on both the sand and the gravel to provide information on the effects of soil type and injected Air flow rate on the overall Air Sparging remedial efficiency. These test results are assessed in light of the mechanisms affecting contaminant removal during Air Sparging.

Ann-sofi Jönsson - One of the best experts on this subject based on the ideXlab platform.

Ronald W Falta - One of the best experts on this subject based on the ideXlab platform.

  • numerical modeling of kinetic interphase mass transfer during Air Sparging using a dual media approach
    Water Resources Research, 2000
    Co-Authors: Ronald W Falta
    Abstract:

    A dual-media multiphase flow approach is proposed for modeling the local interphase mass transfer that occurs during in situ Air Sparging. The method is applied to two- or three-phase flow in porous media to simulate the small gas channels that form during Air Sparging, allowing resolution of the local diffusive mass transfer of contaminants between the flowing gas phase and nearby stagnant liquid-filled zones. This approach provides a good match with laboratory column experiments in which dissolved trichloroethylene (TCE) is removed by Air Sparging, and it is shown that the simulation results are very sensitive to the nature of the local mass transfer regime. The numerical model is then applied to hypothetical field Air-Sparging cases involving either a dissolved plume of TCE or a TCE nonaqueous phase liquid source. In these simulations the local mass transfer appears to play a much smaller role than in the laboratory-scale tests, and significant deviations from local equilibrium simulations only occur when the mass transfer rates are reduced below the calibrated laboratory-scale values.

  • numerical simulation of Air Sparging for remediation of napl contamination
    Ground Water, 1997
    Co-Authors: John E Mccray, Ronald W Falta
    Abstract:

    A numerical simulation study of Air Sparging for the removal of nonaqueous phase liquids (NAPLs) from the subsurface is presented. These simulations were performed using the T2VOC integrated finite-difference, multiphase-flow, contaminant transport code. The code is used to model two-dimensional Air Sparging experiments from Ji et al. (1993) which include both homogeneous and heterogeneous permeability distributions. The model predicts the experimental gas plume shape and behavior very well. Field-scale simulations using a radially symmetric, cylindrical mesh are then used to model hypothetical DNAPL and LNAPL spills and Air Sparging remediation performance in various hydrogeologic settings. Both homogeneous and heterogeneous systems are considered. The results of the study indicate that the Sparging-induced gas pressure increase, or ``positive pressure,`` measured at steady state below the water table, closely corresponds to both the subsurface gas distribution and the effective zone of contaminant reduction. Because this positive pressure is easily measured in the field with a simple monitoring device, it can be used to realistically define the Sparging radius of influence.

  • Field-scale model for Air Sparging performance assessment and design
    1996
    Co-Authors: Gretchen L. Hein, John S. Gierke, Hutzler, Ronald W Falta
    Abstract:

    Air Sparging has been used as an in situ technique to remove VOCs from contaminated groundwater: Air is injected into the groundwater from an injection well, and the VOC partitions into the Air phase and rises to the unsaturated zone, where another technique, such as soil vapor extraction, is used to remove the gases from the vadose zone. A computer model that accurately describes the process is needed. This project comprises model development and laboratory experiments, conducted independently. The model will be tested using the laboratory data. Only preliminary results are available. Preliminary laboratory column tests have been conducted along with some modeling to simulate the removal of a single VOC from a soil column. Comparison show that a finite element code is able to predict removal of methane and TCE. To determine if the Air flow pattern in Air Sparging is predictable, experiments were done in a large-scale reactor and compared to numerical simulations.

  • defining the Air Sparging radius of influence for groundwater remediation
    Journal of Contaminant Hydrology, 1996
    Co-Authors: John E Mccray, Ronald W Falta
    Abstract:

    A theoretical study of Air Sparging for the removal of volatile organic compounds (VOCs) from groundwater is presented. A simple relationship is developed between the observed subsurface pressure increase due to Sparging and the gas saturation at that location, thus providing a quantitative measure of the Sparging radius of influence. Multiphase numerical simulations using a radially symmetric cylindrical geometry are used to confirm this relation, and to relate the injected gas radius of influence to the zone of VOC cleanup during Sparging. These simulations also illustrate the transient and steady-state behavior of Air Sparging systems in both homogeneous and heterogeneous systems.