Changes in interfacial tension of chlorinated solvents following flow through U.K. soils and shallow aquifer material

The interfacial tension (IFT) that arises at the interface between water and an immiscible organic liquid is a key parameter affecting the transport and subsequent fate of the organic liquid in water-saturated porous media. In this paper, data are presented that show how contact between a range of soil types and chlorinated hydrocarbon solvent (CHS) dense nonaqueous phase liquids (DNAPLs) can affect DNAPL/water IFT values. The soils examined are indicative of U.K. soil types and shallow aquifer materials. The solvents investigated were tetrachloroethylene (PCE) and trichloroethylene (TCE). Lab grade, recovered field DNAPL and industrial waste chlorinated solvent mixtures were used. The data from batch and column experiments invariably revealed that water/DNAPL IFT values change following contact with unsaturated soils. In the majority of cases, the IFT values increase following soil exposure. However, after contact with an organic-rich soil, the IFT of the lab grade solvents decreased. The experimental evidence suggests that these reductions are linked to the removal of organic material from the soil and its subsequent incorporation into the solvent IFT increases in the case of lab solvents are shown to be linked to the removal of stabilizers (added by the manufacturers to obviate degradation) that are removed by adsorption to soil mineral surfaces. Similarly, it is conjectured that adsorption of surface-active compounds from the industrial waste samples to soil surfaces is responsible for increases in the IFT in these samples. Finally, it was observed that invading CHSs are capable of dissolving and subsequently mobilizing in-situ soil contaminants. GC/MS analysis revealed these mobilized soil contaminants to be polyaromatic hydrocarbons and phthalate esters.     

Fluid and porous media property effects on dense nonaqueous phase liquid migration and contaminant mass flux

The effects of fluid and porous media properties on dense nonaqueous phase liquid (DNAPL) migration and associated contaminant mass flux generation were evaluated. Relationships between DNAPL mass and solute mass flux were generated by measuring steady-state mass flux following stepwise injection of perchloroethylene (PCE) into flow chambers packed with homogeneous porous media. The effects of fluid properties including density and interfacial tension (IFT), and media properties including grain size and wettability were evaluated by varying the density contrast and interfacial tension properties between PCE and water, and by varying the porous media mean grain diameter and wettability characteristics. Contaminant mass flux was found to increase as grain size decreased, suggesting enhanced lateral and vertical DNAPL spreading with higher fluid entry pressure. Mass flux showed a slight increase as the DNAPL approached neutral buoyancy, likely due to enhanced vertical spreading above the injection point. DNAPL spatial distribution and contaminant mass flux were only minimally affected by IFT and by intermediate-level wettability changes, but were dramatically affected by wettability reversal. The relationship between DNAPL loading and flux generation became more linear as grain size decreased and density contrast between fluids decreased. These results imply that capillary flow characteristics of the porous media and fluid properties will control mass flux generation from source zones.     

Degradation product partitioning in source zones containing chlorinated ethene dense non-aqueous-phase liquid

Abiotic and biotic reductive dechlorination with chlorinated ethene dense non-aqueous-phase liquid (DNAPL) source zones can lead to significant fluxes of complete and incomplete transformation products. Accurate assessment of in situ rates of transformation and the potential for product sequestration requires knowledge of the distribution of these products among the solid, aqueous, and organic liquid phases present within the source zone. Here we consider the fluid-fluid partitioning of two of the most common incomplete transformation products, cis-1,2-dichloroethene (cis-DCE) and vinyl chloride (VC). The distributions of cis-DCE and VC between the aqueous phase and tetrachloroethene (PCE) and trichloroethene (TCE) DNAPLs, respectively, were quantified at 22 °C for the environmentally relevant, dilute range. The results suggest that partition coefficients (concentration basis) for VC and cis-DCE are 70 ± 1 L(aq)/L(TCE?DNAPL) and 105 ± 1 L(aq)/L(PCE?DNAPL,) respectively. VC partitioning data (in the dilute region) were reasonably approximated using the Raoult's law analogy for liquid-liquid equilibrium. In contrast, data for the partitioning of cis-DCE were well described only when well-parametrized models for the excess Gibbs free energy were employed. In addition, available vapor-liquid and liquid-liquid data were employed with our measurements to assess the temperature dependence of the cis-DCE and VC partition coefficients. Overall, the results suggest that there is a strong thermodynamic driving force for the reversible sequestration of cis-DC and VC within DNAPL source zones. Implications of this partitioning include retardation during transport and underestimation of the transformation rates observed through analysis of aqueous-phase samples.     

Stable isotope evidence for biodegradation of chlorinated ethenes at a fractured bedrock site

Stable carbon isotope analysis of chlorinated ethenes and ethene was performed at a site contaminated with trichloroethene (TCE), a dense non-aqueous phase liquid (DNAPL). The site is located in fractured bedrock and had variable groundwater hydraulic gradients during the study due to a local excavation project. Previous attempts to biostimulate a pilot treatment area at the site resulted in the production of cis-1,2-dichloroethene (cis-DCE), the first product of reductive dechlorination of TCE. Cis-DCE concentrations accumulated however, and there was no appreciable production of the breakdown products from further reductive dechlorination, vinyl chloride (VC) and ethene (ETH). Consequently, the pilot treatment area was bioaugmented with a culture of KB-1, a natural microbial consortium known to completely reduce TCE to nontoxic ETH. Due to ongoing dissolution of TCE from DNAPL in the fractured bedrock, and to variable hydraulic gradients, concentration profiles of dissolved TCE and its degradation products cis-DCE, VC, and ETH could not convincingly confirm biodegradation of the chlorinated ethenes. Isotopic analysis of cis-DCE and VC, however, demonstrated that biodegradation was occurring in the pilot treatment area. The isotope values of cis-DCE and VC became significantly more enriched in 13C over the last two sampling dates (in one well from -17.6%o to -12.8%o and from -22.5%o to -18.2%o for cis-DCE and VC, respectively). Quantification of the extent of biodegradation in the pilot treatment area using the Rayleigh model indicated that, depending on the well, between 21.3% and 40.7% of the decrease in cis-DCE and between 15.2% and 36.7% of the decrease in VC concentrations can be attributed to the effects of biodegradation during this time period. Within each well, the isotope profile of TCE remained relatively constant due to the continuous input of undegraded TCE due to DNAPL dissolution.     

Density-modified displacement for DNAPL source zone remediation: density conversion and recovery in heterogeneous aquifer cells

Low interfacial tension (IFT) displacement (mobilization) of nonaqueous phase liquids (NAPLs) offers potential as an efficient remediation technology for contaminated aquifer source zones. However, displacement of dense NAPLs (DNAPLs) is problematic due to the tendency for downward migration and redistribution of the mobilized DNAPL. To overcome this limitation, a density-modified displacement method (DMD) was developed, which couples in situ density conversion of DNAPLs via alcohol partitioning with low IFT NAPL displacement and recovery. The objective of this work was to evaluate the DMD method for two representative DNAPLs, chlorobenzene (CB) and trichloroethene (TCE). Laboratory-scale experiments were conducted in a two-dimensional (2-D) cell, configured to represent a heterogeneous unconfined aquifer system containing low permeability lenses. After release and redistribution of either CB- or TCE-NAPL, the 2-D aquifer cells were flushed with a 6% (wt) n-butanol aqueous solution to achieve DNAPL to light NAPL conversion, followed by a low IFT surfactant solution consisting of 4% (4:1) Aerosol MA/Aerosol OT + 20% n-butanol + 500 mg/L CaCl2. Visual observations and experimental measurements demonstrated that in situ density conversion and immiscible displacement of both CB and TCE were successful. Effluent NAPL densities ranged from 0.96 to 0.90 g/mL for CB and from 0.95 to 0.92 g/mL for TCE, while aqueous phase densities remained above 0.96 g/L. Density conversion of CB and TCE was achieved after flushing with 1.2 and 4.9 pore vol of 6% n-butanol solution, respectively. Recoveries of 90% CB and 85% TCE were realized after flushing with 1.2 pore vol of the low IFT surfactant solution, which was followed by a 1 pore vol posttreatment water flood. Surfactant and n-butanol recoveries ranged from 75 to 96% based on effluent concentration data. The observed minimal mobilization during the n-butanol density conversion preflood and near complete mobilization during the low IFT displacement flood were consistent with total trapping number calculations. The results reported herein demonstrate the potential efficiency of the DMD technology as a means of DNAPL source zone restoration.     

Density-modified displacement for dense nonaqueous-phase liquid source-zone remediation: density conversion using a partitioning alcohol

Entrapped and pooled dense nonaqueous-phase liquids (DNAPLs) often persist in aquifers and serve as a long-term source of groundwater contamination. To address the problematic nature of DNAPL remediation, a surfactant-enhanced aquifer remediation (SEAR) technology, density-modified displacement (DMD), has been developed which significantly reduces the risk of downward migration of displaced DNAPLs. The DMD method is designed to accomplish DNAPL density conversion through the introduction of a partitioning alcohol, n-butanol (BuOH), in a predisplacement flood using conventional horizontal flushing schemes. Subsequent displacement and recovery of the resulting LNAPL is achieved by flushing with a low-interfacial tension surfactant solution. The objective of this study was to investigate density conversion of two representative DNAPLs, chlorobenzene (CB) and trichloroethene (TCE). A series of batch experiments was performed to assess changes in NAPL composition, density, and phase behavior as a function of BuOH mole fraction. Experimental results were used to develop contaminant/BuOH/water ternary phase diagrams and to elucidate regions of contrasting NAPL density. UNIQUAC calculations are presented to support measured compositional and phase behavior data. Density conversion of CB and TCE, relative to water, occurred at NAPL BuOH mole fractions of 0.38 and 0.50, respectively. Significant incorporation of water into the organic phase was observed at relatively high BuOH mole fractions and was shown to limit changes in NAPL composition and density. Interfacial tensions between CB-NAPL and TCE-NAPL and a 6% (by wt) BuOH aqueous solution were found to decrease with increasing NAPL BuOH mole fraction, although in both cases the measured values remained above 2.5 dyn/cm. Total trapping number calculations suggest that, in most aquifer formations, density conversion can be achieved without premature NAPL displacement using a 6% (by wt) BuOH aqueous solution.     

Experimental and numerical validation of the total trapping number for prediction of DNAPL mobilization

The total trapping number (N(T)), quantifying the balance of gravitational, viscous, and capillaryforces acting on an entrapped dense nonaqueous phase liquid (DNAPL) droplet was originally developed as a criterion to predict the onset and extent of residual DNAPL mobilization in porous media. The ability of this approach to predict mobilization behavior, however, has not been rigorously validated in multidimensional systems. In this work, experimental observations of residual tetrachloroethene (PCE) mobilization in rectangular columns are compared to predictions obtained using a multiphase compositional finite-element simulator that was modified to incorporate the dependence of entrapped residual,flow, and transport parameters on the total trapping number. Consistent with calculated NT values (1.21 x 10(-3)-1.10 x 10(-2)), residual PCE-DNAPL was mobilized immediately upon contact with a low-interfacial tension (IFT) surfactant solution and rapidly migrated downward to form a bank of mobile DNAPL. The numerical model accurately captured the onset and extent of PCE-DNAPL mobilization, the angle and migration of the DNAPL bank, the swept path of the surfactant solution, and cumulative PCE recovery. These findings demonstrate the utility of the total trapping number for prediction of DNAPL mobilization behavior during low-IFT flushing.     

In-situ control of DNAPL density using polyaphrons

Once spilled into soils, dense nonaqueous phase liquids (DNAPLs) such as chlorinated solvents migrate deep into the subsurface because of their high density. Their downward migration typically continues until capillary forces balance gravitational forces or until essentially impermeable strata are reached. Efforts to mobilize the DNAPL for remediation purposes risks driving the contaminants deeper, which has spurred research for modifying buoyancy forces in situ. In this paper, a novel means of controlling the density of a DNAPL phase using polyaphrons is presented. Polyaphrons are a class of high internal phase ratio emulsions (HIPREs) that have unusual properties such as indefinite stability and flow properties through porous media. They provide a means of selectively delivering a light organic phase liquid to the vicinity of the DNAPL phase. Upon destabilization of the polyaphron by a polyvalent cation, the light internal phase mixes with the DNAPL to produce a nonaqueous phase of lower density than the original contaminant. The negative buoyancy of the DNAPL can thus be reversed. This approach holds great promise for manipulating DNAPL densities prior to or during remediation treatments.     

Interfacial activity of phenolic-rich extracts from avocado fruit waste: Influence on the colloidal and oxidative stability of emulsions and nanoemulsions

The effects of phenolic-rich extracts from avocado peels (AP) and seeds (AS) on the colloidal and the lipid oxidative stability of oil-in-water (O/W) emulsions/nanoemulsions were evaluated. For this purpose, the interfacial tension (IFT) of avocado oil droplets in the presence of extracts and surfactants (low methoxyl pectin, LMP; Tween 80, T80), individually or combined, was assessed. Individually, T80 led to the lowest IFT values (4.25 ± 0.02 mN/m), followed by AS and AP extracts (9.27 ± 0.86 mN/m and 12.31 ± 0.10 mN/m, respectively) and LMP (14.88 ± 0.05 mN/m). Regarding particle size, the emulsions containing AP and AS extracts were smaller (1.45 ± 0.10 μm and 1.11 ± 0.03 μm, respectively), and stabler, than blank emulsions (4.05 ± 0.51 μm). Conversely, the extracts, especially AS extract, reduced the stability of nanoemulsions causing a 24-fold particle size increase. Nevertheless, AP and AS extracts reduced the formation of secondary oxidation products in emulsions/nanoemulsions. These findings provide novel insights into the potential use of avocado waste.     

Solvent release into a sandy aquifer. 2. Estimation of DNAPL mass based on a multiple-component dissolution model

A chlorinated solvent mixture (2.0 L of trichloroethylene, 0.5 L of chloroform, and 2.5 L of tetrachloroethylene) was released into a sandy aquifer to create a heterogeneously distributed DNAPL (dense nonaqueous-phase liquid) source. The dissolution and dissolved-phase plume development from this source were studied in detail along a cross-section downgradient of the source for a period of approximately 1 year. At the conclusion of the experiment, the site was excavated to map the actual distribution of solvent residuals in the subsurface. Multiple-component dissolution theory provides a tool for the estimation of the mass of a multiple-component DNAPL source present in the groundwater. Concentration ratios between the compounds change with time, and those changes can be used to estimate the mass of DNAPL upgradient of the monitoring point(s) or well(s). The method is independent of the dilution occurring in the groundwater and only requires observations of time series of the contaminants in one or more monitoring points. For the field experiment, the method was applied using the measured concentrations of individual sampling points, the depth-integrated concentrations, the area-integrated concentrations, and the effluent concentrations of the cell. The experiment showed that multiple-component dissolution theory may be a valuable tool for the estimation of the mass of multiple-component DNAPL residuals in the saturated zone.     

Destruction efficiencies and dynamics of reaction fronts associated with the permanganate oxidation of trichloroethylene

Although potassium permanganate (KMnO4) flushing is commonly used to destroy chlorinated solvents in groundwater, many of the problems associated with this treatment scheme have not been examined in detail. We conducted a KMnO4 flushing experiment in a large sand-filled flow tank (L x W x D = 180 cm x 60 cm x 90 cm) to remove TCE emplaced as a DNAPL in a source zone. The study was specifically designed to investigate cleanup progress and problems of pore plugging associated with the dynamics of the solid-phase reaction front (i.e., MnO2) using chemical and optical monitoring techniques. Ambient flow through the source zone formed a plume of dissolved TCE across the flow tank. The volume and concentration of TCE plume diminished with time because of the in situ oxidation of the DNAPL source. The migration velocity of the MnO2 reaction front decreased with time, suggesting that the kinetics of the DNAPL oxidation process became diffusion-controlled because of the pore plugging. A mass balance calculation indicated that only approximately 18% of the total applied KMnO4 (MnO4- = 1250 mg/ L) participated in the oxidation reaction to destroy approximately 41% of emplaced TCE. Evidently, the efficiency of KMnO4 flushing scheme diminished with time due to pore plugging by MnO2 and likely CO2, particularly in the TCE source zone. In addition, the excess KMnO4 used for flushing may cause secondary aquifer contamination. One needs to be concerned about the efficacy of KMnO4 flushing in the field applications. Development of a new approach that can provide both contaminant destruction and plugging/ MnO4- control is required.     

Reaction of nonaqueous phase TCE with permanganate

Oxidative treatment of trichloroethylene (TCE) in the form of dense nonaqueous-phase liquid (DNAPL) by potassium permanganate (KMnO4) was investigated in a series of batch tests. The study focused on understanding the fundamental mechanisms of oxidative removal of DNAPL TCE by permanganate oxidation. Dissolution experiment for DNAPL TCE has been performed as a control experiment in the absence of KMnO4. DNAPL TCE dissolved into the aqueous phase until it reached the saturation concentration of 1200 mg/L (9.16 x 10(-3) M) at 20 degrees C. The rate of dissolution of DNAPL TCE was proportional to the volume of the DNAPL. In the presence of KMnO4, the experimental results showed that the amount of TCE oxidized during the reaction was increased continuously as [MnO4-] decreased even though the rate decreased as [MnO4-] decreased. It was apparent that more DNAPL TCE was removed with a faster rate for higher initial permanganate concentration. At high permanganate concentration, the aqueous concentration of TCE was kept low and practically constant by the chemical reaction between aqueous TCE and MnO4-. However, as MnO4- was consumed in the system, the aqueous concentration started to increase until it reached solubility. From experimental observation, 1.56-1.78 mol of MnO4- was consumed per mole of TCE oxidized. Furthermore, 2.85-2.98 mol of Cl- was released to the solution per mole of TCE oxidized. Since the complete mineralization of TCE requires 2.0 mol of MnO4- and releases 3 mol of Cl- per mol of TCE oxidized, the observed stoichiometric factors indicated incomplete mineralization of TCE, but nearly complete dechlorination. Enhancement factor due to chemical reaction was quantified experimentally. The enhancement factor was shown to be a function of the molar ratio of MnO4- to TCE in the system, and hence varied during the reaction period.     

Assessment of degradation pathways in an aquifer with mixed chlorinated hydrocarbon contamination using stable isotope analysis

The demonstration of monitored natural attenuation (MNA) of chlorinated hydrocarbons in groundwater is typically conducted through the evaluation of concentration trends and parent-daughter product relationships along prevailing groundwater flow paths. Unfortunately, at sites contaminated by mixtures of chlorinated ethenes, ethanes, and methanes, the evaluation of MNA by using solely concentration data and parent-daughter relationships can result in erroneous conclusions regarding the degradation mechanisms that are truly active at the site, since many of the daughter products can be derived from multiple parent compounds. Stable carbon isotope analysis was used, in conjunction with concentration data, to clarify and confirm the active degradation pathways at a former waste solvent disposal site where at least 14 different chlorinated hydrocarbons have been detected in the groundwater. The isotope data indicate that TCE, initially believed to be present as a disposed product and/or a PCE dechlorination intermediate, is attributable to dehydrochlorination of 1,1,2,2-PCA. The isotope data further support that vinyl chloride and ethene in the site groundwater result from dichloroelimination of 1,1,2-trichlorethane and 1,2-dichloroethane, respectively, rather than from reductive dechlorination of the chlorinated ethenes PCE, TCE, or 1,2-DCE. The isotope data confirm that the chlorinated ethanes and chlorinated methanes are undergoing significant intrinsic degradation, whereas degradation of the chlorinated ethenes may be limited. In addition to the classical trend of enriched isotope values of the parent compounds with increasing distance associated to biodegradation, shifts of isotope ratios of degradation byproduct in the opposite direction due to mixing of isotopically light byproducts of biodegradation with compounds from the source are shown to be of high diagnostic value. These data underline the value of stable isotope analysis in confirming transformation processes at sites with complex mixtures of chlorinated compounds.     

Dehalorespiration model that incorporates the self-inhibition and biomass inactivation effects of high tetrachloroethene concentrations

In the vicinity of dense nonaqueous phase liquid (DNAPL) contaminant source zones, aqueous concentrations of tetrachloroethene (PCE) in groundwater may approach saturation levels. In this study, the ability of two PCE-respiring strains (Desulfuromonas michiganensis and Desulfitobacterium strain PCE1) to dechlorinate high concentrations of PCE was experimentally evaluated and depended on the initial biomass concentration. This suggests high PCE concentrations permanently inactivated a fraction of biomass, which, if sufficiently large, prevented dechlorination from proceeding. The toxic effects of PCE were incorporated into a model of dehalorespirer growth by adapting the transformation capacity concept previously applied to describe biomass inactivation by products of cometabolic TCE oxidation. The inactivation growth model was coupled to the Andrews substrate utilization model, which accounts for the self-inhibitory effects of PCE on dechlorination rates, and fit to the experimental data. The importance of incorporating biomass inactivation and self-inhibition effects when modeling reductive dechlorination of high PCE concentrations was demonstrated by comparing the goodness-of-fit of the Andrews biomass inactivation and three alternate models that do capture these factors. The new dehalorespiration model should improve our ability to predict contaminant removal in DNAPL source zones and determine the inoculum size needed to successfully implement bioaugmentation of DNAPL source zones.     

Biotransformation of Ni-substituted hydrous ferric oxide by an Fe(III)-reducing bacterium

The reductive biotransformation of a Ni(2+)-substituted (5 mol %) hydrous ferric oxide (NiHFO) by Shewanella putrefaciens, strain CN32, was investigated under anoxic conditions at circumneutral pH. Our objectives were to define the influence of Ni2+ substitution on the bioreducibility of the HFO and the biomineralization products formed and to identify biogeochemical factors controlling the phase distribution of Ni2+ during bioreduction. Incubations with CN32 and NiHFO were sampled after 14 and 32 d, and both aqueous chemistry and solid phases were characterized. By comparison of these results with a previous study (Fredrickson, J. K.; Zachara, J. M.; Kennedy, D. W.; Dong, H.; Onstott, T. C.; Hinman, N. W.; Li, S. W. Geochim. Cosmochim. Acta 1998, 62, 3239-3257), it was concluded that coprecipitated/sorbed Ni2+ inhibited the bioreduction of HFO through an undefined chemical mechanism. M?ssbauer spectroscopy allowed analysis of the residual HFO phase and the identity and approximate mass percent of biogenic mineral phases. The presence of AQDS, a soluble electron shuttle that obviates need for cell--oxide contact, was found to counteract the inhibiting effect of Ni2+. Nickel was generally mobilized during bioreduction in a trend that correlated with final pH, except in cases where PO4(3-) was present and vivianite precipitation occurred. CN32 promoted the formation of Ni(2+)-substituted magnetite (Fe2IIIFe(1-x)IINixIIO4) in media with AQDS but without PO4(3-). The formation of this biogenic coprecipitate, however, had little discernible impact on final aqueous Ni2+ concentrations. These results demonstrate that coprecipitated Ni can inhibit dissimilatory microbial reduction of amorphous iron oxide, but the presence of humic acids may facilitate the immobilization of Ni within the crystal structure of biogenic magnetite.     

Quantification of Spice Mixture Compositions by Electronic Nose: Part I. Experimental Design and Data Analysis Using Neural Networks

ABSTRACT: A quantitative procedure was developed to predict the composition of ternary ground spice mixtures using an electronic nose. Basil, cinnamon, and garlic were mixed in different compositions and presented to an e-nose. Nineteen training mixtures were used to build predictive models. Model performance was tested using 5 other mixtures. Three neural network structures—multilayer perceptron (MLP), MLP using principal component analysis as a preprocessor (PCA-MLP), and the time-delay neural network (TDNN)—were used for predictive model building. All 3 neural network models predicted the testing mixtures' compositions with a mean square error (MSE) equal or less than 0.0051 (in a fraction domain where sum of fractions = 1). The TDNN provided the smallest MSE.     

Effects of the nonionic surfactant tween 80 on microbial reductive dechlorination of chlorinated ethenes

Recent field studies have indicated synergistic effects of coupling microbial reductive dechlorination with physicochemical remediation (e.g., surfactant flushing) of dense nonaqueous phase liquid (DNAPL) source zones. This study explored chlorinated ethene (e.g., tetrachloroethene [PCE]) dechlorination in the presence of 50-5000 mg/L Tween 80, a nonionic surfactant employed in source zone remediation. Tween 80 did not inhibit dechlorination by four pure PCE-to-cis-1,2-dichloroethene (cis-DCE) or PCE-to-trichloroethene (TCE) dechlorinating cultures. In contrast, cis-DCE-dechlorinating Dehalococcoides isolates (strain BAV1 and strain FL2) failed to dechlorinate in the presence of Tween 80. Bio-Dechlor INOCULUM (BDI), a PCE-to-ethene dechlorinating consortium, produced cis-DCE in the presence of Tween 80, further suggesting that Tween 80 inhibits dechlorination by Dehalococcoides organisms. Quantitative real-time PCR analysis applied to BDI revealed that the number of Dehalococcoides cells decayed exponentially (R(2) = 0.85) according to the Chick-Watson disinfection model (pseudo first-order decay rate of 0.13+/-0.02 day(-1)) from an initial value of 6.6 +/-1.5 x 10(8) to 1.3+/-0.8 x 10(5) per mL of culture after 58 days of exposure to 250 mg/L Tween 80. Although Tween 80 exposure prevented ethene formation and reduced Dehalococcoides cell numbers, Dehalococcoides organisms remained viable, and dechlorination activity pist cis-DCE was recovered following the removal of Tween 80. These findings suggest that sequential Tween 80 flushing followed by microbial reductive dechlorination is a promising strategy for remediation of chlorinated ethene-impacted source zones.     

Approach to the quantification of milk mixtures by partial least-squares,principal component and multiple linear regression techniques

Four of the most widely employed multivariate calibration methods, partial least-squares regressions (PLS-1 and PLS-2), principal component regression (PCR) and multiple linear regression (MLR) were applied to predict the percentages of ternary mixtures of cow’s, ewe’s and goat’s milk based in the analysis of casein fraction by capillary electrophoresis. The prediction models were calculated by using three batches of 10 milk mixtures each prepared in three different seasons and were validated by applying them to the analysis of nine milk mixtures. All the models were good for the prediction of percentages of milk of each species. However, it was found that MLR led to more precise predictions than the other multivariate calibration methods with a root square error under 1.2%.     

Monitoring oxidation of chlorinated ethenes by permanganate in groundwater using stable isotopes: laboratory and field studies

Permanganate injection is increasingly applied for in situ destruction of chlorinated ethenes in groundwater. This laboratory and field study demonstrates the roles that carbon isotope analysis can play in the assessment of oxidation of trichloroethene (TCE) by permanganate. In laboratory experiments a strong carbon isotope fractionation was observed during oxidation of TCE with similar isotopic enrichment factors (-25.1 to -26.8 per thousand) for initial KMnO4 concentrations between 67 and 1,250 mg/L. At the field site, a single permanganate injection episode was conducted in a sandy aquifer contaminated with TCE as dense nonaqueous liquid (DNAPL). After injection, enriched delta13C values of up to +204% and elevated Cl- concentrations were observed at distances of up to 4 m from the injection point. Farther away, the Cl- increased without any change in delta13C of TCE suggesting that Cl- was not produced locally but migrated to the sampling point Except for the closest sampling location to the injection point, the delta13C rebounded to the initial 613C again, likely due to dissolution of DNAPL Isotope mass balance calculations made it possible to identify zones where TCE oxidation continued to occur during the rebound phase. The study indicates that delta13C values can be used to assess the dynamics between TCE oxidation and dissolution and to locate zones of oxidation of chlorinated ethenes that cannot be identified from the Cl- distribution alone.     

Experimental evaluation and mathematical modeling of microbially enhanced tetrachloroethene (PCE) dissolution

Experiments to assess metabolic reductive dechlorination (chlororespiration) at high concentration levels consistent with the presence of free-phase tetrachloroethene (PCE) were performed using three PCE-to-cis-1,2-dichloroethene (cis-DCE) dechlorinating pure cultures (Sulfurospirillum multivorans, Desulfuromonas michiganensis strain BB1, and Geobacter lovleyi strain SZ) and Desulfitobacterium sp. strain Viet1, a PCE-to-trichloroethene (TCE) dechlorinating isolate. Despite recent evidence suggesting bacterial PCE-to-cis-DCE dechlorination occurs at or near PCE saturation (0.9-1.2 mM), all cultures tested ceased dechlorinating at approximately 0.54 mM PCE. In the presence of PCE dense nonaqueous phase liquid (DNAPL), strains BB1 and SZ initially dechlorinated, but TCE and cis-DCE production ceased when aqueous PCE concentrations reached inhibitory levels. For S. multivorans, dechlorination proceeded at a rate sufficient to maintain PCE concentrations below inhibitory levels, resulting in continuous cis-DCE production and complete dissolution of the PCE DNAPL. A novel mathematical model, which accounts for loss of dechlorinating activity at inhibitory PCE concentrations, was developed to simultaneously describe PCE-DNAPL dissolution and reductive dechlorination kinetics. The model predicted that conditions corresponding to a bioavailability number (Bn) less than 1.25 x 10(-2) will lead to dissolution enhancement with the tested cultures, while conditions corresponding to a Bn greater than this threshold value can result in accumulation of PCE to inhibitory dissolved-phase levels, limiting PCE transformation and dissolution enhancement. These results suggest that microorganisms incapable of dechlorinating at high PCE concentrations can enhance the dissolution and transformation of PCE from free-phase DNAPL.