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Michael D Annable – 1st expert on this subject based on the ideXlab platform
surfactant enhanced Air Sparging with viscosity control for heterogeneous aquifersHydrogeology Journal, 2019Co-Authors: Hobin Kwon, Jaekyeong Choi, Michael D AnnableAbstract:
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 SpargingJournal of Contaminant Hydrology, 2018Co-Authors: Jaekyeong Choi, Hobin Kwon, Michael D AnnableAbstract:
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 experimentsJournal of Contaminant Hydrology, 2015Co-Authors: Michael D AnnableAbstract:
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.
Washington J Braida – 2nd expert on this subject based on the ideXlab platform
Air Sparging effectiveness laboratory characterization of Air channel mass transfer zone for voc volatilizationJournal of Hazardous Materials, 2001Co-Authors: Washington J BraidaAbstract:
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 columnsJournal of Contaminant Hydrology, 2000Co-Authors: Washington J BraidaAbstract:
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 – 3rd expert on this subject based on the ideXlab platform
remediation of dnapl source zones in groundwater using Air SpargingLand Contamination & Reclamation, 2004Co-Authors: Krishna R Reddy, Luesgald TekolaAbstract:
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 waterGround Water Monitoring and Remediation, 1999Co-Authors: Jeffrey A Adams, Krishna R ReddyAbstract:
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 SpargingGeotechnical and Geological Engineering, 1998Co-Authors: Robin Semer, Jeffrey A Adams, Krishna R ReddyAbstract:
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.