Synthesis of granular activated carbon/zero valent iron composites for simultaneous adsorption/dechlorination of trichloroethylene

The coupling adsorption and degradation of trichloroethylene (TCE) through dechlorination using synthetic granular activated carbon and zerovalent iron (GAC-ZVI) composites was studied. The GAC-ZVI composites were prepared from aqueous Fe²⁺ solutions by impregnation with and without the use of a PEG dispersant and then heated at 105 °C or 700 °C under a stream of N₂. Pseudo-first-order rate constant data on the removal of TCE demonstrates that the adsorption kinetics of GAC is similar to those of GAC-ZVI composites. However, the usage of GAC-ZVI composites liberated a greater amount of Cl than when ZVI was used alone. The highest degree of reductive dechlorination of TCE was achieved using a GAC-ZVI700P composite (synthesized using PEG under 700 °C). A modified Langmuir-Hinshelwood rate law was employed to depict the behavior of Cl liberation. As a result, a zero-order Cl liberation reaction was observed and the desorption limited TCE degradation rate constant decreased as the composite dosage was increased. The GAC-ZVI composites can be employed as a reactive GAC that is not subject to the limitations of using GAC and ZVI separately.     

Intrinsic bioremediation of trichloroethylene and chlorobenzene: field and laboratory studies.

Activities at a former fire training area at Robins Air Force Base in Georgia, USA resulted in contamination of groundwater with a mixture of trichloroethylene (TCE) and chlorobenzene (CB). Results from the field investigation suggest that intrinsic bioremediation process is occurring, which caused the decrease in TCE and CB concentrations, and increase in TCE degradation byproducts [e.g., dichloroethylene isomers (DCEs), vinyl chloride (VC)] concentrations. Contaminated groundwater samples collected from this site were used to conduct microbial enumeration tests, and used as the inocula for microcosm establishment. Results from the microbial enumeration study indicate that methanogenesis was the dominant biodegradation pattern within the source and mid-plume areas, and the aerobic biodegradation process dominated the downgradient area. Laboratory microcosm experiments were conducted to evaluate the feasibility of using CB as the primary substrate to enhance the intrinsic biodegradation of TCE. Microcosm results suggest that CB can serve as the primary substrate (electron donor), and enhance TCE biodegradation to less-chlorinated compounds under both aerobic cometabolism and reductive dechlorination conditions.     

Effects of ferrous ions on the reductive dechlorination of trichloroethylene by zero-valent iron

The surface characteristics of zero-valent iron (ZVI) and the efficiency of reductive dechlorination of trichloroethylene (TCE) in the presence of ferrous ions were studied. The experimental results indicated that the acid-washing of a metallic iron sample enhanced the efficiency of TCE degradation by ZVI. This occurred because acid-washing changed the conformation of oxides on the surface of iron from maghemite (gamma-Fe(2)O(3)) to the more hydrated goethite (alpha-FeOOH), as was confirmed by XPS analysis. However, when ferrous ions were simultaneous with TCE in water, the TCE degradation rate decreased as the concentration of ferrous ion increased. This was due to the formation of passive precipitates of ferrous hydroxide, including maghemite and magnetite (Fe(3)O(4)), that coated on the surface of acid-washed ZVI, which as a result inhibited the electron transfer and catalytic hydrogenation mechanisms. On the other hand, in an Fe(0)-TCE system without the acid-washing pretreatment of ZVI, ferrous ions were adsorbed into the maghemite lattice which was then converted to semiconductive magnetite. Thus, the electrons were transferred from the iron surface and passed through the precipitates, allowing for the reductive dechlorination of TCE.     

Benzene and toluene biodegradation down gradient of a zero-valent iron permeable reactive barrier

This study simulated benzene and toluene biodegradation down gradient of a zero-valent iron permeable reactive barrier (ZVI PRB) that reduces trichloroethylene (TCE). The effects of elevated pH (10.5) and the presence of a common TCE dechlorination by product [cis-1,2-dichloroethene (cis-1,2-DCE)] on benzene and toluene biodegradation were evaluated in batch experiments. The data suggest that alkaline pH (pH 10.5), often observed down gradient of ZVI PRBs, inhibits Fe(III)-mediated biotransformation of both benzene and toluene. Removal was reduced by 43% for benzene and 26% for toluene as compared to the controls. The effect of the addition of cis-1,2-DCE on benzene and toluene biodegradation was positive and resulted in removal that was greater than or equal to the controls. These results suggest that, at least for cis-1,2-DCE, its formation may not be toxic to iron-reducing benzene and toluene degrading bacteria; however, for microbial benzene and toluene removal down gradient of a ZVI PRB, it may be necessary to provide pH control, especially in the case of a biological PRB that is downstream from a ZVI PRB.     

Removal of trichloroethylene in reduced soil columns

A continuous soil column experiment was conducted to investigate reductive dechlorination of trichloroethylene (TCE) in soil system reductively manipulated by three types of reductants (Fe(II), dithionite, and Fe(II) + dithionite (combined treatment of Fe(II) and dithionite)). The soil column reduced by Fe(II) + dithionite has the greatest bed volumes (51.8) treated to breakthrough indicating that the combined treatment of Fe(II) and dithionite is more effective for the reductive dechlorination of TCE in the reduced soil column than the separate treatment of Fe(II) or dithionite. The measured bed volumes to breakthrough in control and treated soil columns were similar to the estimated bed volumes based on the result of batch kinetic experiment, differing by a factor of 0.96-1.02. The relative concentration of bromide (non-reactive tracer) reached the approximate value of 1 between 0.87 and 1.03 bed volume. C2 hydrocarbons (acetylene, ethylene, and ethane) were observed as transformation products in the effluents of soil columns treated by the reductants. However, no chlorinated intermediates were observed at the concentrations above detection limits throughout the experiment. Chloride was observed in the effluents of soil columns reduced by dithionite and Fe(II) + dithionite.     

The cooperative electrochemical oxidation of chlorophenols in anode-cathode compartments

By using a self-made carbon/polytetrafluoroethylene (C/PTFE) O2-fed as the cathode and Ti/IrO2/RuO2 as the anode, the degradation of three organic compounds (phenol, 4-chlorophenol, and 2,4-dichlorophenol) was investigated in the diaphragm (with terylene as diaphragm material) electrolysis device by electrochemical oxidation process. The result indicated that the concentration of hydrogen peroxide (H2O2) was 8.3 mg/L, and hydroxyl radical (HO) was determined in the cathodic compartment by electron spin resonance spectrum (ESR). The removal efficiency for organic compounds reached about 90% after 120 min, conforming to the sequence of phenol, 4-chlorophenol, and 2,4-dichlorophenol. And the dechlorination degree of 4-chlorophenol exceeded 90% after 80 min. For H2O2, HO existed in the catholyte and reduction dechlorination at the cathode, the mineralization of organics in the cathodic compartment was better than that in the anodic compartment. The degradation of organics was supposed to be cooperative oxidation by direct or indirect electrochemical oxidation at the anode and H2O2, HO produced by oxygen reduction at the cathode. High-performance liquid chromatography (HPLC) allowed identifying phenol as the dechlorination product of 4-chlorophenol in the cathodic compartment, and hydroquinone, 4-chlorocatechol, benzoquinone, maleic, fumaric, oxalic, and formic acids as the main oxidation intermediates in the cathodic and anodic compartments. A reaction scheme involving all these intermediates was proposed.     

Evaluating chlorine isotope effects from isotope ratios and mass spectra of polychlorinated molecules

Compound-specific chlorine isotope analysis receives much interest to assess the fate of chlorinated hydrocarbons in contaminated environments. This paper provides a theoretical basis to calculate isotope ratios and quantify isotope fractionation from ion-current ratios of molecular- and fragment-ion multiplets. Because both (35)Cl and (37)Cl are of high abundance, polychlorinated hydrocarbons consist of molecules containing different numbers of (37)Cl denoted as isotopologues. We show that, during reactions, the changes in isotopologue ratios are proportional to changes in the isotope ratio assuming a nonselective isotope distribution in the initial compound. This proportionality extents even to fragments formed in the ion source of a mass spectrometer such as C 2Cl 2 (double dechlorinated fragment of perchloroethylene, PCE). Fractionation factors and kinetic isotope effects (KIE) may, therefore, be evaluated from isotope, isotopologue or even fragment ratios according to conventional simple equations. The proportionality is exact with symmetric molecules such as dichloroethylene (DCE) and PCE, whereas it is approximately true with molecules containing nonreactive positions such as trichloroethylene (TCE). If in the latter case isotope ratios are derived from dechlorinated fragments, e.g., C 2HCl 2, it is important that fragmentation in the ion source affect all molecular positions alike, as otherwise isotopic changes in reactive positions may be underrepresented.     

Application of surfactant enhanced permanganate oxidation and bidegradation of trichloroethylene in groundwater

The industrial solvent trichloroethylene (TCE) is among the most ubiquitous chlorinated solvents found in groundwater contamination. The main objectives of this study were to evaluate the feasibility of using non-ionic surfactant Simple Green™ (SG) to enhance the oxidative dechlorination of TCE by potassium permanganate (KMnO₄) employing a continuous stir batch reactor system (CSBR) and column experiments. The effect of using surfactant SG to enhance the biodegradation of TCE via aerobic cometabolism was also examined. Results from CSBR experiments revealed that combination of KMnO₄ with surfactant SG significantly enhanced contaminant removal, particularly when the surfactant SG concentrated at its CMC. TCE degradation rates ranged from 74.1% to 85.7% without addition of surfactant SG while TCE degradation rates increased to ranging from 83.8% to 96.3% with presence of 0.1 wt% SG. Furthermore, results from column experiments showed that TCE was degraded from 38.1 μM to 6.2 μM in equivalent to 83.7% of TCE oxidation during first 560 min reaction. This study has also demonstrated that the addition of surfactant SG is a feasible method to enhance bioremediation efficiency for TCE contaminated groundwater. The complete TCE degradation was detected after 75 days of incubation with both 0.01 and 0.1 wt% of surfactant SG addition. Results revealed that surfactant enhanced chemical oxidation and bioremediation technology is one of feasible approaches to clean up TCE contaminated groundwater.     

Degradation of DCE and TCE by Fe–Ni nanoparticles immobilised polysulphone matrix

The reduction of dichloroethane (DCE) and trichloroethylene (TCE) by bimetallic iron–nickel (Fe–Ni) nanoparticles has been studied in this study. The reduction mechanism involves hydrodechlorination at the iron–nickel interface. The Fe–Ni nanoparticles have been synthesised by the chemical reduction method and immobilised on to a polysulphone matrix. The as-synthesised nanoparticles and Fe–Ni immobilied polysulphone support have been characterised to establish the particle size of the nanoparticles, which are of the order of 36–41?nm, and the physical characteristics of the immobilised support. Batch experiments have been performed using gas chromatography-mass spectrometry to study the degradation of DCE and TCE. The studies have shown that the bimetallic system is quite effective in the dechlorination of DCE and TCE. Also, the stability of the nanoparticles in the matrix has been explored with respect to its suitability for use in the degradation of chlorinated hydrocarbons.     

Detection of low levels of trichloroethylene vapor with Raman spectrometry

The response of a novel fiber-optic Raman probe to low levels of trichloroethylene (TCE) vapors is characterized. The detection limit of the current probe for TCE vapor is 34 mg/L, and the probe exhibits a fully reversible response. The probe uses an organic-polymer, low-density polyethylene to concentrate TCE vapors in the optical path of the fiber-optic Raman spectrometer. The relative standard deviation for measurement of 677 mg/L of TCE in the vapor is 0.3%.     

Reactivity of Fe(II)/cement systems in dechlorinating chlorinated ethylenes

Ferrous iron (Fe(II)) in combination with Portland cement is effective in reductively dechlorinating chlorinated organics and can be used to achieve immobilization and degradation of contaminants simultaneously. Reactivities of chlorinated ethylenes (perchloroethylene (PCE), trichloroethylene (TCE), 1,1-dichloroethylene (1,1-DCE), vinyl chloride (VC)) in Fe(II)/cement systems were characterized using batch slurry reactors. Reduction kinetics of the chlorinated ethylenes were sufficiently fast to be utilized for the proposed treatment scheme, and were described by a pseudo-first-order rate law. The order of reactivity of the chlorinated ethylenes was TCE>1,1-DCE>PCE>VC. Reduction of TCE and PCE mainly yielded acetylene, implying that the transformation of the two compounds occurred principally via reductive beta-elimination pathways. Transformation of 1,1-DCE and VC gave rise to primarily ethylene, implying that major degradation pathways were a reductive alpha-elimination for the former and a hydrogenolysis for the latter. The reactivity of the Fe(II)/cement systems in dechlorinating TCE was proportional to Fe(II) dose when the Fe(II)/cement mass ratio varied between 5.6 and 22.3%. The Fe(II)/cement systems with a higher Fe(II) loading were less extensively affected by pH in reductive reactions for TCE than in the previous experiments with PCE or chlorinated methanes. Amendment of Fe(II)/cement systems with Fe(III) addition was found effective in increasing the reactivity in the previous study, but the current findings indicated that the extent to which the reaction rate increased by the amendment might be dependent on the source of the cement and/or the compounds tested.     

Enhanced dissolution of TCE in NAPL by TCE-degrading bacteria in wetland soils

The influence of trichloroethene (TCE) dechlorinating mixed cultures in dissolution of TCE in nonaqueous phase liquid (NAPL) via biodegradation was observed. Experiments were conducted in batch reactor system with and without marsh soils under 10 and 20 degrees C for 2 months. The dissolution phenomenon in biotic reactors containing mixed cultures was showed temporal increases compared to abiotic reactors treated with biocide. Effective NAPL-water transfer rate (K(m)) calculated in this study showed more than four times higher in biotic reactors than that in abiotic reactors. The results might be attributed to the biologically enhanced dissolution process via dechlorination in reactors. Temperature would be a factor to determine the dissolution rate by controlling bacterial activity. The TCE dechlorination occurred even in an interface of TCE-NAPL that demonstrated no previous TCE biodegradation, suggesting that microbes may be useful in developing source-zone bioremediation system. In conclusion, dechlorinating mixed culture could enhance dissolution in NAPL that may be useful in the application of source zone bioremediation.     

Resonance-enhanced multiphoton ionization for real-time monitoring of trichloroethylene formed by degradation of tetrachloroethylene using zero-valent zinc

Resonance-enhanced multiphoton ionization (REMPI) is investigated as a potential technique for real-time monitoring of selected volatile organochloride compounds (VOCs). In a proof-of-concept experiment, the progress of the reductive-degradation of tetrachloroethylene (PCE) to trichloroethylene (TCE) by zero-valent zinc was monitored by REMPI measurements performed in the headspace above the PCE solution. Two-photon resonant REMPI spectra of TCE and PCE were recorded over the wavelength range 305-320 nm. The concentrations of PCE and TCE in the headspace were monitored by measurement of the ionization signal with 315.64- and 310.48-nm excitation for PCE and TCE, respectively. Calibration curves yielded a linear range of more than 2 orders of magnitude for both compounds. The REMPI headspace results agreed well with the solution-phase results from gas chromatography analysis, which was used for independent verification of the progress of the reaction.     

Boosting sensitivity of organic vapor detection with silicone block polyimide polymers

We demonstrate that silicone block polyimide polymers have an unusually high sensitivity to nonpolar organic vapors, including chlorinated organic solvent vapors. When 0.18-5.34-microm-thick films of silicone block polyimide polymers were deposited onto 10-MHz thickness shear mode (TSM) oscillators, these films were implemented to detect parts-per-billion concentrations of trichloroethylene (TCE) with a detection sensitivity of 0.5-23.5 Hz per 500 ppb of vapor. With a film thickness of 3.4 microm (91.5-kHz frequency shift upon film deposition), optimized for the minimal sensor noise of 0.04 Hz, the calculated detection limit of sensor response (S/N = 3) was 3 ppb of TCE. Detection limits for other chlorinated organic solvent vapors, such as perchloroethylene (PCE), cis-1,2-dichloroethylene (DCE), trans-1,2-DCE, 1,1-DCE, and vinyl chloride (VC) were 0.6, 6, 6, 11, and 13 ppb, respectively. Assuming only the mass-loading response when deposited onto the TSM devices, silicone block polyimide polymers have partition coefficients of over 200 000 to parts-per-billion concentrations of TCE that make them at least 100 times more sensitive than other known polymers for TCE detection. We observed that unlike conventional polyimides, water sensitivity of the new hybrid polyimides is suppressed because of the silicone soft block. Water sensitivity is comparable with the sensor response to nonpolar organic vapors. The high sensitivity and long-term stability of these sensor materials make them attractive for ultrasensitive practical sensors.     

Electrically induced reduction of trichloroethene in clay

Chlorinated compounds such as trichloroethene (TCE) are recalcitrant contaminants commonly detected in soil and groundwater. Contemporary remedies such as electron donor amendment tend to be less or ineffective in treating chlorinated compounds in matrix of lower permeability, such as clay. In this study, electrically induced reduction (EIR) was tested by inserting electrodes in saturated clay containing 122.49–125.43 mg TCE kg^?1. Weak electric potentials (E) of 6, 9, and 12 V m^?1 were applied, and up to 97% of TCE were depleted during the study period. Corresponding increases in chloride concentrations was observed during TCE depletion, indicating a reductive dechlorination pathway. No migration of TCE was observed between the two electrodes, neither were intermediate compounds such as dichloroethene (DCE) or vinyl chloride (VC). Results were also tested against a mathematical equation we previously established for field applications. Electrically induced reduction may offer a novel method for in situ degradation of chlorinated contaminants, especially in low-permeable media such as clay.     

Feasibility of bioremediation of trichloroethylene contaminated sites by nitrifying bacteria through cometabolism with ammonia.

The autotrophic ammonia-oxidizing bacteria (Nitrosomonas sp.) are able to dechlorinate trichloroethylene (TCE) through cometabolism using ammonia (NH(3)) as a growth substrate. Cometabolic kinetics models suggest that TCE is a potent competitive inhibitor of NH(3) oxidation because it competes with NH(3) for oxidation by the enzyme of ammonia monooxygenase (AMO). In this study, an enriched culture of nitrifying bacteria was used to investigate the efficiencies of cometabolism of TCE by AMO. In addition, the relationships among specific growth substrate (NH(3)) utilization rate (qNH(3)), specific nongrowth substrate (TCE) cometabolic rate (qTCE), NH(3) and TCE concentrations, and NH(3)/TCE and TCE/NH(3) ratios were also analyzed. We found that the relationships between qNH(3) and NH(3) for the systems with and without TCE followed the Alvarez-Cohen competitive inhibition model and Monod model, respectively. Our results demonstrate that TCE could be cometabolized in a nitrification system when sufficient oxygen and NH(3)200 microg/l) were also found to show inhibitory effects towards NH(3) oxidation in enriched nitrifying culture. We also found that the NH(3)/TCE ratio rather than TCE concentrations alone exhibited strong correlation with qNH(3), much the same as the Ely activity recovery model presented. Our results suggest that the relationship between qTCE and TCE concentrations followed the Oldenhuis enzyme inactivation model for systems without NH(3).     

Synthetic spectra: a tool for correlation spectroscopy

We show that computer-generated diffractive optical elements can be used to synthesize the infrared spectra of important compounds, and we describe a modified phase-retrieval algorithm useful for the design of elements of this type. In particular, we present the results of calculations of diffractive elements that are capable of synthesizing portions of the infrared spectra of gaseous hydrogen fluoride (HF) and trichloroethylene (TCE). Further, we propose a new type of correlation spectrometer that uses these diffractive elements rather than reference cells for the production of reference spectra. Storage of a large number of diffractive elements, each producing a synthetic spectrum corresponding to a different target compound, in compact-disk-like format will allow a spectrometer of this type to rapidly determine the composition of unknown samples. Other advantages of the proposed correlation spectrometer are also discussed.     

Unbiased high-throughput screening of reactive metabolites on the linear ion trap mass spectrometer using polarity switch and mass tag triggered data-dependent acquisition

Constant neutral loss (CNL) and precursor ion (PI) scan have been widely used for the in vitro screening of glutathione conjugates derived from reactive metabolites, but these two methods are only applicable to triple quadrupole or hybrid triple quadrupole mass spectrometers. Additionally, the success of CNL and PI scanning largely depends on structure and CID fragmentation pathways of GSH conjugates. In the present study, a highly efficient methodology has been developed as an alternative approach for high-throughput screening and structural characterization of reactive metabolites using the linear ion trap mass spectrometer. In microsomal incubations, a mixture of glutathione [GSH, gamma-glutamyl-cystein-glycin] and the stable-isotope labeled compound [GSX, gamma-glutamyl-cystein-glycin-(13)C2-(15)N] was used to trap reactive metabolites, resulting in formation of both labeled and unlabeled conjugates at a given isotopic ratio. A mass difference of 3.0 Da between the natural and labeled GSH conjugate (mass tag) at a fixed isotopic ratio constitutes a unique mass pattern that can selectively trigger the data-dependent MS(2) scan of both isotopic partner ions, respectively. In order to eliminate the response bias of GSH adducts in the positive and negative mode, a polarity switch is executed between the mass tag-triggered data dependent MS(2) scan, and thus ESI- and ESI+ MS(2) spectra of both labeled and nonlabeled GSH conjugates are obtained in a single LC-MS run. Unambiguous identification of glutathione adducts was readily achieved with great confidence by MS(2) spectra of both labeled and unlabeled conjugates. Reliability of this method was vigorously validated using several model compounds that are known to form reactive metabolites. This approach is not based on the appearance of a particular product ion such as MH(+) - 129 and anion at m/z 272, whose formation can be structure-dependent and sensitive to the collision energy level; therefore, the present method can be suitable for unbiased screening of any reactive metabolites, regardless of their CID fragmentation pathways. Additionally, this methodology can potentially be applied to triple quadrupole or hybrid triple quadrupole mass spectrometers.     

Remediation of TCE contaminated soils by in situ EK-Fenton process

The treatment performance and cost analysis of in situ electrokinetic (EK)-Fenton process for oxidation of trichloroethylene (TCE) in soils were evaluated in this work. In all experiments, an electric gradient of 1V/cm, de-ionized water as the cathode reservoir fluid and a treatment time of 10 days were employed. Treatment efficiencies of TCE were evaluated in terms of the electrode material, soil type, catalyst type, and catalyst dosage and granular size if applicable. Test results show that graphite electrodes are superior to stainless steel electrodes. It was found that the soil with a higher content of organic matter would result in a lower treatment efficiency (e.g. a sandy loam is less efficient than a loamy sand). Experimental results show that the type of catalyst and its dosage would markedly affect the reaction mechanisms (i.e. "destruction" and "removal") and the treatment efficiency. Aside from FeSO4, scrap iron powder (SIP) in the form of a permeable reactive wall was also found to be an effective catalyst for Fenton reaction to oxidize TCE. In general, the smaller the granular size of SIP, the lower the overall treatment efficiency and the greater the destruction efficiency. When a greater quantity of SIP was used, a decrease of the overall treatment efficiency and an increase of percent destruction of TCE were found. Experimental results have shown that the quantity of electro-osmotic (EO) flow decreased as the quantity of SIP increased. It has been verified that the treatment performances are closely related to the corresponding EO permeability. Results of the cost analysis have indicated that the EK-Fenton process employed in this work is very cost-effective with respect to TCE destruction.     

Cometabolic degradation of TCE in enriched nitrifying batch systems

The aim of this study was to evaluate the effect of the trace pollutant trichloroethylene (TCE) on the nitrification process and to assess its cometabolic degradation. Nitrification was accomplished in batch suspended growth systems containing an enriched nitrifier culture. The presence of TCE resulted in both the inhibition of specific oxygen uptake rate (SOUR) and specific ammonium utilization rate (qNH(4)-N). In both SOUR and qNH(4)-N a 50% decrease was observed in a TCE concentration range of 1000-2000 ppb. TCE was cometabolically degraded by this enriched nitrifier culture. The cometabolic degradation of TCE was found to be dependent on initial TCE concentration. The results may be applicable in the treatment of TCE containing industrial wastewaters and contaminated groundwaters and soils.