Photosonolysis of TCA, TCE, and PCE in Flow-Through Reactor System

Photosonolysis of 1,1,1-trichloroethane (TCA), trichloroethylene (TCE), and tetrachloroethylene (PCE) in water was investigated using a cup-horn, flow-through reactor system. Water containing titanium dioxide was deliberately contaminated with a mixture of volatile organic compound (VOC)—TCA, TCE, and PCE—and individual VOC. These solutions were irradiated with ultraviolet light (UV) and ultrasonic waves (US), independently and concurrently (UVUS). The values of the first-order degradation rate constant and the removal efficiency for the VOC were evaluated for the UV, US, and UVUS treatments. The results showed that the concurrent use of UV and US increased the VOC degradation rate and removal efficiency beyond the additive effect of UV and US, suggesting that the UVUS effect on the decomposition of the VOC is synergistic under certain conditions. TCE and PCE were more readily degraded than TCA, suggesting that double-bond cleavage is one of the initial degradation pathways. With the reactor specifications used, the photosonolysis process can produce water meeting the drinking water standard (MCLs of 5 μg∕L) for TCE and PCE with a removal efficiency of approximately 90%.     

Apparent first-order kinetics in the transformation of 1,1,1-trichloroethane in groundwater following a transient release

A transient release of 1,1,1-trichloroethane (TCA) to an otherwise uncontaminated aquifer at a manufacturing facility presented a useful opportunity to validate the results of previous laboratory and field studies on TCA transformation in groundwater. Abiotic TCA transformation to 1,1-dichloroethylene (DCE) and acetic acid at the site exhibited first-order kinetics with half-life of 2.9 years 15 degrees C. Degradation effects were seen to overwhelm chemical retardation effects on the DCE/TCA concentration ratio in groundwater. The kinetic data was sufficient to date the release to within one week of when it actually occurred. A kinetic approach may be applicable to dating the releases on other contaminated sites where a single transient release is indicated. The transformation of dissolved TCA in groundwater with a half-life of several years can be expected at many contaminated sites.     

The role of cytokines in bacterial pneumonia: an inflammatory balancing act

The effect of 2 mM ethanol, a concentration indicative of daily alcohol consumption, was investigated on trichloroethylene (TRI) metabolism in perfused Wistar rat liver. The study consisted of two parts: The first part studied TRI administration with or without ethanol. In the second study chloral hydrate (CH), an intermediate in TRI metabolism, was administered in the absence or presence of ethanol to phenobarbital (PB) treated or non-PB-treated rats. The concentrations of the metabolites, total trichloroethanol (TCE), and trichloroacetic acid (TCA) were measured by gas chromatography and intracellular reduced pyridine nucleotides by surface fluorometry. In the first study, ethanol infusion significantly increased the TCE/TCA ratio, TCE production rate, and percentage of reduced pyridine nucleotides, and decreased TCA production rate without an associated change in the sum of TCE and TCA formation rates. In the second study, ethanol infusion in the absence or presence of PB produced similar significant increases in the TCE/TCA ratio, TCE production rate, and percentage of reduced pyridine nucleotides, accompanied by a decrease in TCA formation. The observed shift in TRI metabolism in the presence of ethanol, from oxidation to TCA to reduction to TCE, suggests that alcohol exerts alterations in hepatic intracellular oxidation-reduction (redox) states.     

Effects of Seepage Velocity and Temperature on the Dechlorination of Chlorinated Aliphatic Hydrocarbons

The influence of seepage velocity and groundwater temperature on the dechlorination rates of trichloroethylene (TCE) and tetrachloroethylene (PCE) by zero-valent iron (Fe0) were investigated by running laboratory column tests at seepage velocities ranging from 31 to 1,884?m/year at temperatures of 10 and 23°C. By increasing the seepage velocity from 31 to 1,884?m/year at 10°C, there were approximately seven- and nine-fold increases in the normalized dechlorination rate constants (SA) of TCE and PCE, respectively. Similarly, a four-fold increase in the SA of TCE and PCE was also observed at 23°C when increasing the seepage velocity from 103 to 1,183?m/year. Raising the groundwater temperature from 10 to 23°C at a given seepage velocity resulted in 2.7 and 1.1 times increases in the TCE SA and PCE SA, respectively. With the application of the Arrhenius equation, activation energies of 70.3?kJ/mol for TCE and 38.6?kJ/mol for PCE dechlorination were determined, indicating domination of the electron transfer process over the mass transfer as a major rate-limiting step of the dechlorination reactions by Fe0.     

Photochemical Destruction of Tetrachloroethylene and Trichloroethylene from the Exhaust of an Air Stripper

A novel pilot-scale photochemical reactor is utilized to carry out vapor-phase tetrachloroethylene (PCE) and trichloroethylene (TCE) destruction experiments from the exhaust of a groundwater remediation air stripper. The cylindrical-shaped stainless steel photochemical reactor has an inner diameter of 32?cm and a length of 105?cm. Low-pressure mercury ultraviolet (UV) lamps are used as the photochemical energy source to initiate the destruction reaction within the reactor. A cylindrical-shaped air stripper with a volume of 15.7?L is constructed and utilized for transferring the contaminant from the aqueous phase to the vapor phase. Experiments are conducted using the air stripper to determine phase-transfer characteristics of PCE and TCE. The results show good contaminant phase transfer using clean airflow rates of 1.5 and 3.0?L/min. Next, groundwater remediation experiments are conducted with the air stripper exhaust flowing into the photochemical reactor for contaminant destruction. The first experiment use distilled water contaminated with dissolved PCE, the second experiment use distilled water contaminated with dissolved TCE, and the third experiment use distilled water contaminated with both dissolved PCE and TCE. All three experiments show excellent contaminant destruction efficiencies. This study demonstrates that the photochemical reactor should be included as part of an overall air-stripping PCE/TCE groundwater remediation scheme for complete contaminant destruction.     

Comparison of Potassium Permanganate and Hydrogen Peroxide as Chemical Oxidants for Organically Contaminated Soils

Laboratory experiments were completed to compare the treatment efficiency of KMnO4 with H2O2 (alone or with amendments) for sand and silty clay soil contaminated with either a mixture of volatile organic compounds (VOCs) [trichloroethylene (TCE), tetrachloroethene (PCE), and 1,1,1-trichloroethane (TCA)] or semivolatile organic compounds (SVOCs) (naphthalene, phenanthrene, and pyrene). The relatively treatment effects of soil type, oxidant loading rate and dosing, and reaction period, as well as the use of surfactant or iron amendments and pH adjustment were examined using batch experiments with contaminated soil slurries. When KMnO4 was applied to low organic carbon, acidic, or alkaline soils, at loading rates of 15–20 g∕kg it was found to degrade consistently 90% or more of the alkene VOCs (TCE and PCE) and 99% of the polyaromatic SVOCs (naphthalene, pyrene, and phenanthrene). H2O2 was more sensitive to contaminant and soil type and VOC treatment efficiencies were somewhat lower as compared with KMnO4 under comparable conditions, particularly with the sandy soil and even when supplemental iron was added. In clay soil, H2O2 with iron addition degraded over 90% of the SVOCs present compared with near zero in sandy soil, unless the pH was depressed to pH 3 and iron amendments were increased, whereby the treatment efficiency in the sandy soil was increased slightly. With both H2O2 and KMnO4, treatment efficiency increased to varying degrees as the oxidant loading rate (g∕kg) and reaction time (h) were increased. Multiple oxidant additions or surfactant addition were not found to have any significant effect on VOC treatment efficiency. Also, very limited TCA treatment was observed with either H2O2 or KMnO4.     

Transition metal doping effect and high catalytic activity of CeO2–TiO2 for chlorinated VOCs degradation

A series of transition metals (Fe, Co, Ni, Cu, Cr and Mn)-doped CeO₂–TiO₂ catalysts were prepared by the sol–gel method and applied for the catalytic removal of 1,2-dichloroethane (DCE) as a model for chlorinated VOCs (CVOCs). The various characterization methods including X-ray diffraction (XRD), N₂ adsorption–desorption, UV-Raman, NH₃ temperature-programmed desorption (NH₃-TPD) and H₂ temperature-programmed reduction (H₂-TPR) were utilized to investigate the physicochemical properties of the catalysts. The results show that doping Fe, Co, Ni or Mn can obviously promote the activity of CeO₂–TiO₂ mixed oxides for DCE degradation, which is related to their improved texture properties, acid sites (especially for strong acidity) and low-temperature reducibility. Particularly, CeTi–Fe doped with moderate Fe exhibits excellent activity for 1,2-dichloroethane (DCE) degradation, giving a T_90% value as low as 250 °C. More importantly, only trace chlorinated byproducts were produced during the low-temperature degradation of various CVOCs (dichloromethane (DCM), trichloroethylene (TCE) and chlorobenzene (CB)) over CeTi–Fe1/9 catalyst with high durability.     

Electrospray analysis of biological samples for trace amounts of trichloroacetic acid, dichloroacetic acid, and monochloroacetic acid

Trichloroethylene (TCE) has been identified as a widespread groundwater contaminant. Trichloroacetic acid (TCA) and dichloroacetic acid (DCA) are toxicologically relevant metabolites of TCE that produce tumors in B6C3F1 mice. A sensitive method for measuring these metabolites in plasma has been developed to obtain pharmacokinetic data from TCE exposure. This is particularly important because DCA is more potent at producing hepatoproliferative lesions than TCA. At present, it is unclear whether DCA is produced by humans. Existing gas chromatographic methods cannot detect DCA at low nanogram-per-milliliter levels. A Finnigan TSQ 700 mass spectrometer (MS) with electrospray ionization was used to measure TCA, DCA, and monochloroacetic acid (MCA) in plasma. The MS was operated in negative ion tandem MS mode. The limit of detection for TCA and DCA was 4 ng/ml, and the limit of detection for MCA was 25 ng/mL. Plasma samples from human subjects exposed to 100 ppm TCE for 4 h contained TCA at concentrations as high as 10 micrograms/mL. DCA concentrations were less than 5 ng/mL, and MCA was not detected (less than 25 ng/mL).     

Effect of Carbon Source on PCE Dehalogenation

A laboratory study using the upflow anaerobic sludge blanket reactor for treating high-strength wastewater containing tetrachloroethene (PCE) was carried out to study the effect of carbon source, recycle, and shock loading on dehalogenation of PCE and process performance. The PCE was dehalogenated to trichloroethylene, cis-1,2-dichloroethylene, vinyl chloride, and ethylene. During the study on the effect of carbon source, the PCE and COD removal up to 97% and biogas production of 0.518–0.47 m3∕kg CODrem with methane content up to 66% were achieved under steady-state operating conditions. An increase in the influent COD from 2,000 to 4,000 mg∕L did not show any improvement in the PCE removal. Recycling of effluent at 50% showed the decrease in COD removal and increase in the effluent concentration of dichloroethylene and vinyl chlorides. Around 1–3.5% of influent PCE stripping to biogas was observed. It was observed that methanol has the stimulatory effect on the dehalogenation of PCE. A shock loading study showed that the upflow anaerobic sludge blanket reactor could assimilate 1.5–2 times the original PCE concentration (50 mg∕L) without much effect on the process performance.     

Experimental Investigation of the Interaction of Soil Air Permeability and Soil Vapor Extraction

Soil vapor extraction column experiments were performed to investigate contaminant removal and its interaction with soil air permeability. Water, TCE, and PCE, and a mixture of TCE and PCE were used as contaminants. Three gradations of Ottawa sand were used at relative densities of 0.60 and 1.0:?medium, fine, and uniform. Soil air permeability was found to increase linearly with time by 25–150?% to a maximum value when the contaminant was completely removed. The largest increase in soil air permeability was found for fine and/or dense samples. The experimental data were used in a previously developed model by Farhan in 1998 and Farhan et al. in 2001 to predict column behavior. In general, the model predictions were in good agreement with the experimental results. They revealed that the assumption of local equilibrium between the pore air and contaminants is valid for a wide range of pore velocities (2.0–9.2 cm/s).     

Remediation of TCE-Contaminated Groundwater in a Sandy Aquifer Using Pulsed Air Sparging: Laboratory and Numerical Studies

The objective of this study was to investigate, through laboratory and numerical investigations, the effectiveness of a pulsed air sparging system for remediation of groundwater contaminated with trichloroethylene (TCE) in a sandy aquifer. In laboratory experiments, air was pulsed into TCE source zone on a daily basis in order to remediate TCE-contaminated groundwater. Most dissolved TCE was removed at the end of experiments although its concentrations fluctuated due to the air pulsing. The measured gaseous phase TCE concentration increased whereas the aqueous phase TCE concentration decreased during air sparging pulses. Experimental data were assessed by using a numerical code STOMP (subsurface transport over multiphases) with some modification based on the TCE dissolution kinetics. The unmeasured residual TCE mass was predicted through numerical simulations. Results show that aqueous concentrations for TCE are still much higher than the maximum contaminant level in spite of successful removal of 95% of residual TCE. It may imply that it would be more appropriate to apply air sparging combined with other remediation technologies such as bioremediation for remediation of TCE-contaminated groundwater.     

Biodegradation of PCE in a Hybrid Membrane Aerated Biofilm Reactor

A continuous flow flat sheet hybrid membrane aerated biofilm reactor (MABR) was used to treat a synthetic wastewater containing perchloroethylene (PCE); 1.25–2.5?g chemical oxygen demand (COD)/L of glucose was also added to the synthetic wastewater as a source of COD representative of a real wastewater. The reactor was able to biodegrade 70?mg?L?1 of PCE in 9?h without the accumulation of any intermediate compounds, resulting in a removal rate of 247?mmol of PCE?h?1?m?3 in a reactor with a specific membrane area of 4.048?m2?m?3. MABRs have never been used before for PCE degradation, and this rate is one of the highest volumetric PCE degradation rates reported in the literature. COD removal was also good and varied from 85 to 92%. Since very few volatile fatty acids accumulated in the system, most of the residual COD was attributed to soluble microbial products as reported by previous researchers. A mass balance on chloride during this study showed that only 72–81% of it could be accounted for. It is probable that some of the chlorinated ethenes were adsorbed onto the biofilm or that aerobic intermediates of low-chlorinated compounds such as trichloroethanol, dichloroacetyl, and chloroacetaldehyde were produced in the system. Nevertheless the chloride mass balance in this work compares well with the literature. Due to their high PCE and COD removal rates, hybrid MABRs have the potential to be used for a number of refractory organics which require combined anaerobic/aerobic biological treatment for degradation.     

Simultaneous and Sequential Photosonolysis of TCE and PCE

Aqueous solutions of trichloroethylene (TCE) and tetrachloroethylene (PCE) were treated in a flow-through reactor equipped with ultrasound and ultraviolet light sources. The reactor was operated as sonolysis (US), photolysis (UV), and simultaneous photosonolysis (UV/US) reactors; then as US, UV, and sequential UV/US reactors with the installation of a partition in the reactor. The reactor without the partition was simulated by using one continuously stirred-tank-reactor (1-CSTR) model, and the reactor with the partition was simulated by using the sequential CSTR model. Through model calibration, the decomposition rate constants and reactor efficiencies for the removal of TCE and PCE were evaluated. The results suggest that the combined effect of UV and US on the decomposition of TCE and PCE is synergistic in both the simultaneous and sequential UV/US modes, that the rate constants of sonolysis and photolysis are greater with the sequential combination than with the simultaneous combination, and that overall efficiency is higher for the reactor with the partition than for the one without it.     

Aromatase cytochrome P450 transcripts are detected in fractured human bone but not in normal skeletal tissue

Dichloroacetic acid (DCA) and trichloroacetic acid (TCA) are metabolites of the industrial solvent and environmental contaminant trichloroethylene (TCE), as well as contaminants of chlorinated drinking water. Human exposure to these chemicals is of concern as all three have been shown to increase liver tumor incidence in mice. Differences in dose-response curves, progression to cancer, and postexposure regression of lesions suggest that TCA and DCA work through different mechanisms. The purpose of this study was to further characterize the proliferative hepatocellular lesions promoted by TCA and DCA using biomarkers of cell growth, differentiation, and metabolism in liver sections to better delineate the distinctions in the mechanism of the two chloroacetates. Fifteen-day-old female mice were initiated with 25 mg/kg N-methyl-N-nitrosourea. The initiated mice were administered DCA or TCA (20.0 mmol/L) in drinking water from age 49 days until euthanasia at age 413 days. The pathologic assessment showed that the foci of altered hepatocytes and tumors occurring in the animals promoted with DCA were eosinophilic and positive immunohistochemically for TGF-alpha, c-jun, c-myc, CYP 2E1, CYP 4A1, and glutathione S-transferase-pi (GST-pi). The DCA lesions also were essentially negative for c-fos and TGF-beta, but nontumor hepatocytes were consistently TGF-beta-positive. In contrast, tumors promoted by TCA were predominantly basophilic, lacked GST-pi, and stained variably; usually, more than 50% of the tumor hepatocytes were essentially negative for the other biomarkers. This study demonstrates some striking differences in certain molecular biomarkers of cell growth, differentiation, and metabolism between DCA and TCA. The results also suggest some potential growth signal transduction pathways that may contribute to the DCA promotion of tumors, further support the premise that these two chloroacetates promote hepatocarcinogenesis in different ways, and provide a rational basis for a similar comparison with TCE. Such a comparison should give some insight as to whether DCA, TCA, or both are playing a significant role in the murine liver carcinogenesis of the parent compound, TCE.     

Biodegradation of Tetrachloroethene by Chitin Fermentation Products in a Continuous Flow Column System

The ability of chitin fermentation products to promote tetrachloroethene (PCE) reduction was evaluated in a continuous-flow column system to identify how different electron donors affect reductive dechlorination. Natural chitin fermentation products were initially used to support PCE reduction. Acetate (3.5?mM) was the dominant fermentation product, followed by propionate (0.1?mM), butyrate (0.1?mM), and hydrogen (100?nM). After chlorinated ethene concentration profiles reached pseudo steady state, the ability of individual fermentation products (acetate, acetate+propionate, propionate, or formate) to support PCE reduction was evaluated. None of the fermentation products tested stimulated dechlorination as well as the suite generated from chitin (kPCE = 6.9?day?1); however, acetate-stimulated PCE dechlorination the best (kPCE = 5.3?day?1), followed by formate (kPCE = 2.4?day?1), acetate+propionate (kPCE = 1.8?day?1), and propionate (kPCE = 1.2?day?1). Similar trends were observed for the PCE daughter products trichloroethene and dichloroethene. Free energies of individual fatty acid reactions were calculated and shown to be useful predictors of dechlorination performance, except for the case of acetate+propionate. Hence, acetate is the dominant fatty acid controlling dechlorination in the chitin-enhanced system, propionate appears to have an inhibitory effect when present with acetate alone, and other unidentified nutrients produced during chitin fermentation likely contribute to dechlorination activity as well.     

Feasibility of Amending Slurry Walls with Zero-Valent Iron

Rapid degradation of aqueous trichloroethylene (TCE) was observed in batch experiments conducted with soil∕bentonite slurry wall materials amended with the addition of zero-valent iron. The first-order TCE decay constants for soil∕bentonite∕iron mixtures, when normalized to the available iron surface area, were approximately 1–2 orders of magnitude higher than observed in batch experiments with pure iron systems. Permeability tests indicated an increase in SB hydraulic conductivity roughly proportional to the amount of iron added. Based on the observed reaction rates and the assumption of sustained long-term performance, significantly less than one percent added iron would be required to reduce the diffusive flux of TCE across an installed slurry wall by over 10 orders of magnitude. However, the release of hydrogen gas was noted as a potential problem for low permeability systems containing zero-valent iron.     

Differences in phenotype and cell replicative behavior of hepatic tumors induced by dichloroacetate (DCA) and trichloroacetate (TCA)

Dichloroacetate (DCA) and trichloroacetate (TCA) are two hepatocarcinogenic by-products of water chlorination. To compare the effects of DCA and TCA on cell replication in the nodules and tumors they induce, male B6C3F1 mice were administered 2.0 g/L DCA or TCA in their drinking water for 38 or 50 weeks, respectively. The pretreated mice were then given water containing 0, 0.02, 0.5, 1.0, or 2.0 g/L DCA or TCA for two additional weeks to determine whether cell proliferation in the normal liver or tumors that had been induced by DCA or TCA was dependent on continued treatment. Prior to sacrifice the mice were subcutaneously implanted with mini-osmotic pumps to label DNA in dividing cells with 5-bromo-2'-deoxyuridine (BrdU). Serial sections of nodules/tumors and normal liver were stained immunohistochemically for BrdU, the oncoproteins c-Jun and c-Fos, and hematoxylin and eosin (H & E); or with Periodic acid-Schiff (PAS) stain, BrdU, and H & E, respectively. DCA and TCA transiently stimulated the division of normal hepatocytes relative to rates observed in the livers of control mice. However, at 40 and 52 weeks of treatment, replication of normal hepatocytes was substantially inhibited by DCA and TCA, respectively. Cell division within DCA-induced lesions that were identified macroscopically was significantly higher with increasing dose of DCA administered in the last 2 weeks of the experiment. DCA-induced lesions were found to display immunoreactivity to anti-c-Jun and anti-c-Fos antibodies, were predominantly basophilic, and contained very little glycogen relative to surrounding hepatocytes. In contrast, rates of cell division within TCA-induced altered hepatic foci and tumors were very high and appeared to be independent of continued treatment. TCA-induced lesions did not display immunoreactivity to either c-Jun or c-Fos antibodies. Results from this study suggest that the mechanisms by which DCA and TCA induce hepatocarcinogenesis in the male B6C3F1 mouse differ.     

Evaluation of Granular Surfactant-Modified/Zeolite Zero Valent Iron Pellets As a Reactive Material for Perchloroethylene Reduction

The use of permeable reactive barriers (PRBs) for groundwater remediation is based on two distinct mechanisms: sorption and transformation. With sorption as the main mechanism, contaminants sorb on the PRB materials and are retarded. With transformation as the main mechanism, the contaminants react with the PRB materials and then converted to less toxic or innocuous substances. In this study, we tested surfactant-modified zeolite/zero valent iron (SMZ/ZVI) pellets as a PRB material to retard and degrade perchloroethylene (PCE), utilizing both sorption and transformation processes. Batch PCE kinetic studies showed instantaneous PCE removal from the aqueous phase due to sorption and subsequent removal with time due to reduction. The separation of sorption from reduction can be used to obtain both the PCE distribution coefficient (Kd) and the pseudofirst-order reduction rate constant (μobs) from a single batch experiment. The calculated Kd and μobs values are 3.0 and 0.5?L/kg and 0.14 and 0.05?h?1 for SMZ/ZVI and Z/ZVI pellets, respectively. Column experiments were performed at linear flow velocities of 0.07, 0.14, and 0.20?cm/min. The results were modeled using the one-dimensional advection–dispersion equation with linear sorption and first-order transformation. The Kd values were 2.3±0.4 and 0.5±0.1?L/kg for SMZ/ZVI and Z/ZVI pellets, respectively, in agreement with those of the batch study. The PCE transformation constants varied between 0.077 and 0.199?h?1 for the SMZ/ZVI pellets and between 0.037 and 0.144?h?1 for the Z/ZVI pellets, indicating that an enhanced transformation of PCE occurred with the sorbing SMZ/ZVI pellets. The PCE reduction rates were faster at slower flow rates, indicating that the reduction was not a mass-transfer-limited process.     

Physical Properties of Vegetable Oil and Chlorinated Ethene Mixtures

Laboratory experiments were conducted to investigate the abiotic interactions of soybean oil (SoyOil) and chlorinated ethene (CE) nonaqueous phase liquids (NAPLs). The mixed NAPL density and interfacial tension behaved ideally, as predicted by the volume ratio. The mixed NAPL viscosity increased exponentially from that of the pure CE to that of pure SoyOil as the volume fraction increased. The measured contact angle was highly variable and was unpredictable as a function of the volume composition of the mixed NAPL. The physical property effects indicate that the mobilization of residual CE NAPLs because of SoyOil injection is unlikely. Equilibrium dissolution of CEs from the NAPL mixtures behaved linearly as a function of the mole fraction. Dissolved SoyOil in simulated groundwater enhanced the dissolution of trichloroethene (TCE) during flow tests, increasing the effluent TCE concentration from 141?to?202?mg/L. The ready intermingling of the CE dense nonaqueous phase liquids (DNAPLs) and SoyOil indicate that such interactions may be significant at sites where vegetable oil is injected into DNAPL source areas to enhance in situ anaerobic bioremediation.