Biomedical subjects

Michael D Annable

Publications and source records attributed to Michael D Annable.

16 recordsLinked to original sources

PubMed2006

Magnitude and directional measures of water and Cr(VI) fluxes by passive flux meter.

A new configuration of the passive fluxmeter (PFM) is presented that provides for simultaneous measurements of both the magnitude and the direction of ambient groundwater specific discharge qo and Cr(VI) mass flux J(Cr). The PFM is configured as a cylindrical unit with an interior divided into a center section and three outer sectors, each packed with a granular anion exchange resin having high sorption capacity for the Cr(VI) oxyanions CrO4(2-) and HCrO4-. The sorbent in the center section is preloaded with benzoate as the "resident" tracer. Laboratory experiments were conducted in which PFMs were placed in porous packed bed columns, through which was passed a measured volume of synthetic groundwater containing Cr(VI). During the deployment period, some of the resident tracer is depleted while the Cr(VI) is sorbed. The resin was then removed from the four sectors separately and extracted to determine the "captured" mass of Cr(VI) and the residual mass of the resident tracer in each. Cumulative specific discharge, q0t, values were assessed using the residual mass of benzoate retained in the center section. The direction of this discharge theta was ascertained from the mass distribution of benzoate intercepted and retained in the outer three sections of the PFM. Cumulative chromium fluxes, J(Cr)t, were quantified using the total Cr(VI) mass intercepted and retained on the PFM. Experiments produced an average measurement error for direction theta of 3 degrees +/- 14 degrees, while the average measurement errors for q0 and J(Cr) were, respectively, -8% +/- 15% and -12% +/- 23%. Results demonstrate the potential utility of the new PFM configuration for characterizing groundwater and contaminant fluxes.

Chromium↗

PubMed2006

Changes in air saturation and air-water interfacial area during surfactant-enhanced air sparging in saturated sand.

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.

Air↗

PubMed2006

DNAPL source depletion: linking architecture and flux response.

The relationship between dense non-aqueous phase liquid (DNAPL) mass reduction and contaminant mass flux was investigated experimentally in four model source zones. The flow cell design for the experiments featured a segmented extraction well that allowed for analysis of spatially resolved flux information. This flux information was coupled with image analysis of the NAPL spatial distribution to investigate the relationship between flux and the up-gradient NAPL architecture. Results indicate that in the systems studied, the relationship between DNAPL mass reduction and contaminant mass flux was primarily controlled by the NAPL architecture. A specific definition of NAPL architecture was employed where the source zone is resolved into a collection of streamtubes with spatial variability in NAPL saturation along each streamtube integrated and transformed into an effective NAPL content for each streamtube. The distribution of NAPL contents among the streamtubes (NAPL architecture) controlled dissolution dynamics. Two simplified models, a streamtube model and an effective Damkohler number model, were investigated for their ability to simulate dissolution dynamics.

Kinetics↗

PubMed2006

Effect of surface tension reduction on VOC removal during surfactant-enhanced air sparging.

In this study, the effect of decreased surface tension of water on the removal efficiency of a volatile organic compound (VOC) during air sparing was evaluated using a laboratory-scale, two-dimensional physical model packed with sand and water containing dissolved toluene as a representative VOC. Two sets of air sparging experiments were performed: the first at a surface tension of 69 dyne/cm with no surfactant applied, and with a toluene concentration of 110 mg/L; the second at a surface tension of 50 dyne/cm due to 110 mg/L of anionic surfactant, and 99 mg/L of toluene. Under the experimental conditions used in this study, the sparging influence zone estimated at the lower surface tension was about 2.5 times that estimated at the high surface tension. Also the rate of toluene removal by air sparging was found to be much faster at the lower surface tension. The sparging time required for 50% removal of the initial mass of toluene was 16.8 hours at 50 dyne/cm, which was much smaller than 82.5 hours measured at 69 dyne/cm. The final mass recoveries at low and high surface tensions were 92.1% and 56.6%, respectively. Therefore it was concluded that air sparging at reduced surface tension (surfactant-enhanced air sparging) greatly improved the removal efficiency of VOCs from the porous medium compared to conventional air sparging with no applied surfactant.

Air Pollutants↗

PubMed2005

Field demonstration of surfactant-enhanced solubilization of DNAPL at Dover Air Force Base, Delaware.

This study reports on a surfactant-based flood for tetrachloroethylene (PCE) removal from a control test cell at the Dover National Test Site. The surfactant formulation (sodium dihexyl sulfosuccinate (Aerosol-MA or AMA), isopropanol and calcium chloride) was able to achieve a high concentration of PCE in swollen micelles (supersolubilization) without vertical PCE migration. The hydraulic system included eight screened wells that were operated in both vertical circulation and line drive configurations. After 10 pore volumes of flushing, the overall PCE removal was 68% (65% of which corresponded to the surfactant flooding alone). In addition, the residual PCE saturation was reduced from 0.7% to 0.2%, and the concentration of PCE in the groundwater was reduced from 37-190 mg/L before the flushing to 7.3 mg/L after flooding. Recycling the surfactant solution reduced the required surfactant mass (and thus cost, and waste) by 90%. Close to 80% of the total PCE removal was obtained during the first five pore volumes which were operated in an upward vertical circulation flow scheme. No free oil phase was observed during the test. Further analysis of multilevel sampler data suggests that most of the trapped oil remaining in the cell was likely localized in secluded regions of the aquifer, which helps explain the lower PCE groundwater concentration after remedial activities. In summary, this field study demonstrated the feasibility of surfactant-enhanced remediation to reduce the mass in the source zone and significantly reduce the PCE aqueous concentration and therefore the risk associated with the contaminant plume.

2-Propanol↗

PubMed2005

Measured mass transfer coefficients in porous media using specific interfacial area.

Bulk and intrinsic mass transfer processes across interfaces between nonaqueous phase liquids (NAPLs) and water were studied in water-saturated columns. Columns packed with different grain sizes of sand were used to create various NAPL-water interfacial areas along with different NAPL saturations. The intrinsic mass transfer coefficients were estimated from the bulk mass transfer coefficients, and the specific interfacial areas were measured using tracer studies. The bulk mass transfer coefficients increased with increasing NAPL-water specific interfacial area as well as NAPL saturation and pore velocity and with decreasing grain sizes. Moreover, the bulk mass transfer coefficients were correlated with NAPL-water specific interfacial area rather than NAPL saturation and were more sensitive at high NAPL-water interfacial areas than at low interfacial areas. In contrast, the intrinsic mass transfer coefficients were nearly independent of specific interfacial area and NAPL saturation but dependent on pore velocity. Reduction of NAPL saturation by dissolution caused a linear decrease in the bulk mass transfer coefficients.

Chromatography, Gas↗

PubMed2005

Field-scale evaluation of the passive flux meter for simultaneous measurement of groundwater and contaminant fluxes.

A new method, passive flux meter (PFM), has been developed and field-tested for simultaneously measuring contaminant and groundwater fluxes in the saturated zone at hazardous waste sites. The PFM approach uses a sorptive permeable medium placed in either a borehole or monitoring well to intercept contaminated groundwater and release "resident" tracers. The sorbent pack is placed in a groundwater flow field for a specified exposure time and then recovered for extraction and analysis. By quantifying the mass fraction of resident tracers lost and the mass of contaminant sorbed, groundwater and contaminant fluxes are calculated. Here, we assessed the performance of PFMs at the Canadian Forces Base Borden field site in Ontario, Canada. Two field tests were conducted under imposed groundwater flow fields: (1) radial flow to a well and (2) linear flow in a test channel confined by sheet pile walls on three sides. Both tests demonstrate that the local fluxes measured by PFM and averaged overthe screen interval were within 15% of imposed groundwaterflow and within 30% of measured contaminant mass flux. Patterns in depth variations in groundwater and contaminant fluxes, determined by the PFM approach, allow for site characterization at a higher spatial resolution. These results support the PMF method as a potential innovative alternative for measuring groundwater and contaminant fluxes in screened wells.

Alcohols↗

PubMed2005

Characterization of pore scale NAPL morphology in homogeneous sands as a function of grain size and NAPL dissolution.

In this study, we investigate pore scale morphology of nonaqueous phase liquids (NAPLs) trapped in different pore sizes using tracer techniques. Specific interfacial area and saturation of NAPL trapped in homogeneous sands were measured using the interfacial and partitioning tracer techniques. The observed NAPL-water interfacial areas increased in a log-linear fashion with decreasing sand grain size, but showed no clear trend with residual NAPL saturation formed in the various grain sizes. The measured values were used to calculate the NAPL morphology index, which characterizes the spatial NAPL distribution within the pore space. The NAPL morphology indices, increased exponentially with decreasing grain size, indicating that the NAPL becomes smaller, but more blobs. For a fixed grain size, the specific interfacial area and saturation of the NAPL were measured following changes caused by dissolution using alcohol. The observed interfacial areas showed a decrease linearly as a function of the NAPL saturation.

Adsorption↗

PubMed2004

Surfactant-enhanced air sparging in saturated sand.

Air sparging as a subsurface remedial technique can be enhanced bythe addition of a surfactant. The effect of reduced surface tension of water on the extent of air intrusion and air saturation during air sparging in porous media was investigated. A sand column and a two-dimensional sand box were used for the experiments. The surface tension was controlled using an anionic surfactant, sodium dodecyl benzene sulfonate, and the concentration used was below the critical micelle concentration. Using the sand column, the air saturation was measured at different surface tensions and at different airflow rates. Initially water-saturated, the air saturation achieved in the column by air sparging at a surface tension of 3.42 x 10(-2) N/m was up to 5 times larger than that of water with no surfactant. Atthe same time, the rate at which the air saturation increased as a function of airflow rate was greater at reduced surface tensions. For box experiments with homogeneous sand, reduction of the surface tension caused a dramatic increase in the sparging area up to 5.2 times of that generated using water with no surfactant. A sand box experiment containing a vertical channel produced preferential flow of the air phase injected at the bottom of the channel when the surfactant was not applied. However, reducing the surface tension was found to promote airflow through the preferential channel and the finer sand surrounding the channel. These observations support the use of low concentration surfactants to improve air sparging swept zones.

Air↗

PubMed2004

Influence of residual surfactants on DNAPL characterization using partitioning tracers.

The partitioning tracer technique is among the DNAPL source-zone characterization methods being evaluated, while surfactant in-situ flushing is receiving attention as an innovative technology for enhanced source-zone cleanup. Here, we examine in batch and column experiments the magnitude of artifacts introduced in estimating DNAPL content when residual surfactants are present. The batch equilibrium tests, using residual surfactants ranging from 0.05 to 0.5 wt.%, showed that as the surfactant concentrations increased, the tracer partition coefficients decreased linearly for sodium hexadecyl diphenyl oxide disulfonate (DowFax 8390), increased linearly for polyoxyethylene (10) oleyl ether (Brij 97), and decreased slightly or exhibited no observable trend for sodium dihexyl sulfosuccinate (AMA 80). Results from column tests using clean sand with residual DowFax 8390 and Tetrachloroethylene (PCE) were consistent with those of batch tests. In the presence of DowFax 8390 (less than 0.5 wt.%), the PCE saturations were underestimated by up to 20%. Adsorbed surfactants on a loamy sand with positively charged oxides showed false indications of PCE saturation based on partitioning tracers in the absence of PCE. Using no surfactant (background soil) gave a false PCE saturation of 0.0004, while soil contacted by AMA 80, Brij 97, and DowFax 8390 gave false PCE saturations of 0.0024, 0.043, and 0.23, respectively.

Alkanesulfonic Acids↗

PubMed2004

Controlled release, blind test of DNAPL remediation by ethanol flushing.

A dense nonaqueous phase liquid (DNAPL) source zone was established within a sheet-pile isolated cell through a controlled release of perchloroethylene (PCE) to evaluate DNAPL remediation by in-situ cosolvent flushing. Ethanol was used as the cosolvent, and the main remedial mechanism was enhanced dissolution based on the phase behavior of the water-ethanol-PCE system. Based on the knowledge of the actual PCE volume introduced into the cell, it was estimated that 83 L of PCE were present at the start of the test. Over a 40-day period, 64% of the PCE was removed by flushing the cell with an alcohol solution of approximately 70% ethanol and 30% water. High removal efficiencies at the end of the test indicated that more PCE could have been removed had it been possible to continue the demonstration. The ethanol solution extracted from the cell was recycled during the test using activated carbon and air stripping treatment. Both of these treatment processes were successful in removing PCE for recycling purposes, with minimal impact on the ethanol content in the treated fluids. Results from pre- and post-flushing partitioning tracer tests overestimated the treatment performance. However, both of these tracer tests missed significant amounts of the PCE present, likely due to inaccessibility of the PCE. The tracer results suggest that some PCE was inaccessible to the ethanol solution which led to the inefficient PCE removal rates observed. The flux-averaged aqueous PCE concentrations measured in the post-flushing tracer test were reduced by a factor of 3 to 4 in the extraction wells that showed the highest PCE removal compared to those concentrations in the pre-flushing tracer test.

Environmental Pollutants↗

PubMed2003

Rate-limited solubilization of multicomponent nonaqueous-phase liquids by flushing with cosolvents and surfactants: modeling data from laboratory and field experiments.

The impact of rate-limited mass transfer on in-situ cosolvent and single-phase microemulsion flushing for the solubilization of multicomponent nonaqueous-phase liquids (NAPLs) was investigated. Laboratory and field data from both cosolvent and microemulsion flushing studies were modeled using a one-dimensional flow, enhanced-dissolution code. Transport of the flushing agents was described with a one-dimensional advection-dispersion model; more complex heterogeneities encountered at the field scale were characterized using the superposition of two solute transport equations. Cosolvent and microemulsion flushing solubilize NAPLs by different mechanisms. The modeling results presented here show that nonequilibrium effects influence both of these processes differently. Solubilization of individual constituents by cosolvents was limited by the rate of diffusion or transport of the component through the organic phase, while the rate-limiting step for microemulsification was independent of the NAPL constituent and was likely external to the organic phase. These data indicate that by accounting for field-scale hydrodynamic variability, laboratory-measured nonequilibrium parameters may be used to accurately predict field-scale nonequilibrium NAPL solubilization. Finally, the effects of field-scale media heterogeneity are likely to dominate those of weakly rate-limited dissolution, and accurate characterization of the former may be sufficient for adequate prediction of field-scale NAPL solubilization.

Diffusion↗

PubMed2003

Residual alcohol influence on NAPL saturation estimates based on partitioning tracers.

The influence of residual cosolvent on the partitioning tracer technique for estimating a nonaqueous phase liquid (NAPL) saturation in porous media was investigated. Batch equilibrium and column miscible displacement tests were used to evaluate the influence of residual alcohol cosolvents in the aqueous phase on partitioning and transport of alcohol tracers through sandy soil columns containing tetrachloroethylene (PCE). As the volume fraction of cosolvent alcohol (f(c)) increased ( f(c) < or = 0.1; 10 vol %), partition coefficients (K(nc)) for the alcohol tracers linearly decreased for residual cosolvent ethanol, linearly increased for residual cosolvent tert-butyl alcohol, and did not exhibit an evident change for residual cosolvent 2-propanol. These observations are consistent with measured changes in solubility (S(c)) of the alcohol tracers over the same range (f(c) < or = 0.1) of these residual cosolvent alcohols. Column miscible displacement tests using ethanol as a residual cosolvent ( f(c) < or = 0.1) exhibited earlier partitioning tracer breakthrough leading to an underestimation of NAPL saturation (S(n)) when constant, cosolvent-free partitioning coefficients were assumed. The underestimation magnitude increased with higher initial residual cosolvent alcohol in the columns. The S(n) underestimates were not significant but were 1-10% lower than the actual S(n) (0.18). The estimated partition coefficients based on column tests with residual cosolvent (K(col)) were consistently less than those based on batch tests. Column tests with low (0.5%) and high (15%) S(n) revealed that the residual cosolvent alcohol effect was different depending on the amount of NAPL in the column. Using ethanol for a cosolvent (10%) and 2,4-dimethyl-3-pentanol as a partitioning tracer, the S(n) values were underestimated by about 17% and 5%, respectively, in the low and high NAPL saturation columns.

Alcohols↗

PubMed2003

Degradation of perchloroethylene in cosolvent solutions by zero-valent iron.

Remediation of sites contaminated by chlorinated organic compounds is a significant priority in the environmental field. Subsequently, the addition of cosolvent solutions for in situ flushing of contaminated source zones has been successfully field tested. However, the treatment of effluent fluids in such cleanup efforts is an often overlooked component of this technology implementation. The purpose of this research was to evaluate the effectiveness of zero-valent iron (Fe(0)) in treating perchloroethylene (PCE) in an aqueous solution, and how the presence of a cosolvent (ethanol) and modification of the iron surface altered dechlorination. The modified iron surfaces included in this study were nickel-plated iron, acid-treated iron, and untreated iron surfaces. PCE dechlorination in the presence of each of the iron surfaces displayed pseudo first-order kinetics. The highest degradation rate of PCE occurred on the nickel-plated iron surface, 5.83 x 10(-3)h(-1), followed by the acid-treated iron, 4.92 x 10(-3)h(-1), and the untreated iron, 3.34 x 10(-3)h(-1). Dechlorination on each of the surfaces decreased with increasing cosolvent fractions. It was shown that as cosolvent fractions increased, PCE adsorption decreased and resulted in a concomitant decrease in PCE degradation rates.

Chromatography, High Pressure Liquid↗

PubMed2002

Controlled release, blind tests of DNAPL characterization using partitioning tracers.

The partitioning tracer technique for dense nonaqueous phase liquid (DNAPL) characterization was evaluated in an isolated test cell, in which controlled releases of perchloroethylene (PCE) had occurred. Four partitioning tracer tests were conducted, two using an inverted, double five-spot pumping pattern, and two using vertical circulation wells. Two of the four tests were conducted prior to remedial activities, and two were conducted after. Each test was conducted as a "blind test" where researchers conducting the partitioning tracer tests had no knowledge of the volume, method of release, nor resulting spatial distribution of DNAPL. Multiple partitioning tracers were used in each test, and the DNAPL volume estimates varied significantly within each test based on the different partitioning tracers. The tracers with large partitioning coefficients generally predicted a smaller volume of PCE than that expected based on the actual release volume. However, these predictions were made for low DNAPL saturations (average saturation was approximately 0.003), under conditions near the limits of the method's application. Furthermore, there were several factors that may have hindered prediction accuracy, including tracer degradation and remedial fluid interference.

Alcohols↗

PubMed2002

Mobilization and entry of DNAPL pools into finer sand media by cosolvents: two-dimensional chamber studies.

Two-dimensional chamber studies were conducted to determine qualitative and quantitative performance of cosolvents targeted at pooled dense non-aqueous phase liquid (DNAPL) (perchlorethylene, PCE) residing above a fine-grain capillary barrier. Downward mobilization of DNAPL, up gradient along an overriding cosolvent front, was observed. This produced significant pooling above a fine-grain layer that in some cases lead to entry into the capillary barrier beneath. Entry pressure calculations using physical and hydrogeologic parameters provided an excellent prediction of breakthrough of DNAPL into the capillary barrier. Calculations predict approximately 0.5 m of DNAPL would be necessary to enter a Beit Netofa clay, under extreme cosolvent flooding conditions (100% ethanol). Gradient injection of cosolvent did not appear to provide any benefit suggesting a rapid decrease in interfacial tension (IFT) compared to the rate of DNAPL solubilization. Use of a partitioning alcohol (tertiary butyl alcohol, TBA) resulted in DNAPL swelling and reduced entry into the capillary barrier. However, the trapping of flushing solution, containing PCE, could potentially lead to longer remediation times.

Benzenesulfonates↗