Vinyl Chloride Concentrations Research Articles

Degradation of vinyl chloride (VC) by the sulfite/UV advanced reduction process (ARP): Effects of process variables and a kinetic model

Vinyl chloride (VC) poses a threat to humans and environment due to its toxicity and carcinogenicity. In this study, an advanced reduction process (ARP) that combines sulfite with UV light was developed to destroy VC. The degradation of VC followed pseudo-first-order decay kinetics and the effects of several experimental factors on the degradation rate constant were investigated. The largest rate constant was observed at pH9, but complete dechlorination was obtained at pH11. Higher sulfite dose and light intensity were found to increase the rate constant linearly. The rate constant had a little drop when the initial VC concentration was below 1.5mg/L and then was approximately constant between 1.5mg/L and 3.1mg/L. A degradation mechanism was proposed to describe reactions between VC and the reactive species that were produced by the photolysis of sulfite. A kinetic model that described major reactions in the system was developed and was able to explain the dependence of the rate constant on the experimental factors examined. This study may provide a new treatment technology for the removal of a variety of halogenated contaminants.

The effect of A-site substitution by Sr, Mg and Ce on the catalytic performance of LaMnO3 catalysts for the oxidation of vinyl chloride emission

Catalytic oxidation of vinyl chloride (VC) emission was carried out over LaMnO3 and La0.8A0.2MnO3 (A=Sr, Mg and Ce) perovskite oxides synthesized via co-precipitation method. Numerous characterization techniques were performed to investigate the relationship between the catalytic performance and its physicochemical properties. It was found that the partial substitution of lanthanum by cerium and magnesium had a positive effect on the catalytic performance for VC oxidation, whereas strontium involved a negative effect. Under the reaction conditions (VC concentration=1000ppm, GHSV=15,000h−1), the overall catalyst ranking in terms of the catalytic activity from the best to the worst performance was La0.8Ce0.2MnO3>La0.8Mg0.2MnO3>LaMnO3>La0.8Sr0.2MnO3 with regard to the temperature of T50 and T90. The Ce-doped perovskite catalyst showed the optimum catalytic performance due to its higher specific surface area and its ability to promote the low-temperature reducibility. Moreover, as the active species, the increased surface adsorbed oxygen was also responsible for the enhancement of the catalytic performance.

Simplified Analysis of Chlorinated Ethenes in Water Samples by Gas Chromatography with Flame Ionization Detection

Chlorinated ethenes are among the most common environmental contaminants and are known or suspected carcinogens. This class of compounds includes perchloroethene (PCE), trichloroethene (TCE), and their breakdown products, including dichloroethene (DCE) isomers and vinyl chloride (VC). Engineers and scientists must be able to measure concentrations of these chemicals in water samples to assess site contamination, monitor clean-up progress, and test possible remediation technologies. Gas chromatography with flame ionization detection (GC/FID) is a common method for measuring these contaminants in environmental samples. In this study, we tested the hypothesis that FID response factors are equal for all chlorinated ethene compounds. The rationale for the investigation was that if the hypothesis is correct, a single calibration curve can be used for GC/FID analysis of all chlorinated ethene compounds, saving time and money during sample analysis. Based on our measurements, a single calibration curve (FID response versus mass of analyte injected) is applicable to analysis of PCE, TCE, and all three DCE isomers (r2=0.990, n=50 measurements), allowing for simplified quantification of those chemicals. However, the apparent FID response factor for VC was lower by ∼40%, indicating that a separate calibration curve would need to be used to accurately estimate the VC concentration in water samples. The difference in the apparent VC response factor is caused predominantly by losses of VC to volatilization during the analysis.

Modeling the kinetics of the extraction of vinyl chloride from polyvinyl chloride

Literature data was used to construct a model for predicting the amount of vinyl chloride in various liquid food products. The model predicts the vinyl chloride content in such products at different temperatures and for different contents of the monomer in the polymer. Flow of the liquid counter to the direction of the polymer increases the rate at which vinyl chloride is extracted.

Robustness of an aerobic metabolically vinyl chloride degrading bacterial enrichment culture

Degradation of the lower chlorinated ethenes is crucial to the application of natural attenuation or in situ bioremediation on chlorinated ethene contaminated sites. Recently, within mixtures of several chloroethenes as they can occur in contaminated groundwater inhibiting effects on aerobic chloroethene degradation have been shown. The current study demonstrated that metabolic vinyl chloride (VC) degradation by an enrichment culture originating from groundwater was not affected by an equimolar concentration (50 μM) of cis-1,2-dichloroethene (cDCE). Only cDCE concentrations at a ratio of 2.4:1 (initial cDCE to VC concentration) caused minor inhibition of VC degradation. Furthermore, the degradation of VC was not affected by the presence of trans-1,2-dichloroethene (tDCE), 1,1-dichloroethene (1,1-DCE), trichloroethene (TCE), and tetrachloroethene (PCE) in equimolar concentrations (50 μM). Only cDCE and tDCE were cometabolically degraded in small amounts. The VC-degrading culture demonstrated a broad pH tolerance from 5 to 9 with an optimum between 6 and 7. Results also showed that the culture could degrade VC concentrations up to 1,800 μM (110 mg/L).

Atmospheric-Pressure Radio-Frequency Discharge for Degradation of Vinyl Chloride With $\hbox{Pt}/\hbox{Al}_{2}\hbox{O}_{3}$ Catalyst

This study investigates the application of a radio-frequency-powered plasma with a Pt/γ-Al2O3 catalyst to decompose the chlorinated volatile organic compound of vinyl chloride (VC) in air. The use of an atmospheric-pressure plasma jet is explored as an innovative technology for the treatment of VC. The effects of some major system parameters such as input power (PWI), plasma energy density, initial concentration of VC (C0), and space velocity (SV) of the catalyst on the plateau temperature (TP) of a reactor and conversions of VC (XVC) are studied and elucidated. The results show that the effectiveness of the plasma-assisted catalysis is evident as indicated by the increase of XVC and the rate constant. At a PWI of 250 W without a catalyst, the values of XVC were 14% and 5.4% for C0 = 200 and 450 ppmv, respectively. In the presence of the Pt/γ-Al2O3 catalyst with an SV of 17 400 h-1, the values of XVC for C0 = 200 and 450 ppmv increased to 49% and 39%, respectively. Note that the values of TP were 550 K and 430 K without and with the Pt/γ-Al2O3 catalyst at an SV of 17 400 h-1 and a PWI of 250 W. The proposed kinetic models describe the relationships of C/C0 with the major parameters for the plasma and plasma-assisted catalytic degradation of VC, showing good agreement with the experimental data. The information obtained is useful for the operation, design, and analysis of plasma devices.

Assessing chlorinated ethene degradation in a large scale contaminant plume by dual carbon–chlorine isotope analysis and quantitative PCR

The fate of chlorinated ethenes in a large contaminant plume originating from a tetrachloroethene (PCE) source in a sandy aquifer in Denmark was investigated using novel methods including compound-specific carbon and chlorine isotope analysis and quantitative real-time polymerase chain reaction (qPCR) methods targeting Dehaloccocoides sp. and vcrA genes. Redox conditions were characterized as well based on concentrations of dissolved redox sensitive compounds and sulfur isotopes in SO 4 2−. In the first 400 m downgradient of the source, the plume was confined to the upper 20 m of the aquifer. Further downgradient it widened in vertical direction due to diverging groundwater flow reaching a depth of up to 50 m. As the plume dipped downward and moved away from the source, O 2 and NO 3 − decreased to below detection levels, while dissolved Fe 2+ and SO 4 2− increased above detectable concentrations, likely due to pyrite oxidation as confirmed by the depleted sulfur isotope signature of SO 4 2−. In the same zone, PCE and trichloroethene (TCE) disappeared and cis-1,2-dichloroethene (cDCE) became the dominant chlorinated ethene. PCE and TCE were likely transformed by reductive dechlorination rather than abiotic reduction by pyrite as indicated by the formation of cDCE and stable carbon isotope data. TCE and cDCE showed carbon isotope trends typical for reductive dechlorination with an initial depletion of 13C in the daughter products followed by an enrichment of 13C as degradation proceeded. At 1000 m downgradient of the source, cDCE was the dominant chlorinated ethene and had reached the source δ 13C value confirming that cDCE was not affected by abiotic or biotic degradation. Further downgradient (up to 1900 m), cDCE became enriched in 13C by up to 8‰ demonstrating its further transformation while vinylchloride (VC) concentrations remained low (< 1 μg/L) and ethene was not observed. The correlated shift of carbon and chlorine isotope ratios of cDCE by 8 and 3.9‰, respectively, the detection of Dehaloccocides sp genes, and strongly reducing conditions in this zone provide strong evidence for reductive dechlorination of cDCE. The significant enrichment of 13C in VC indicates that VC was transformed further, although the mechanism could not be determined. The transformation of cDCE was the rate limiting step as no accumulation of VC occurred. In summary, the study demonstrates that carbon–chlorine isotope analysis and qPCR combined with traditional approaches can be used to gain detailed insight into the processes that control the fate of chlorinated ethenes in large scale plumes.

Development of a procedure for the gas-chromatographic determination of vinyl chloride and 1,2-dichloroethane in blood with the use of headspace analysis

A procedure for the determination of the weight concentrations of vinyl chloride and 1,2-dichloroethane in blood over the range of 0.1–2.0 μg/cm3 was developed. The procedure is based on a static version of gas-chromatographic headspace analysis. The determination was performed on a column packed with a Chromaton N-AW-DMCS sorbent with 15 wt % Apiezon L using flame-ionization detection. The relative error of the procedure was no higher than 20%.

Field assessment of carboxymethyl cellulose stabilized iron nanoparticles for in situ destruction of chlorinated solvents in source zones

This study pilot-tested carboxymethyl cellulose (CMC) stabilized zero-valent iron (ZVI) nanoparticles (with a trace amount of Pd catalyst) for in situ destruction of chlorinated ethenes such as perchloroethylene (PCE) and trichloroethylene (TCE) and polychlorinated biphenyls (PCBs) that had been in groundwater for decades. The test site was located in a well-characterized secondary source zone of PCBs and chlorinated ethenes. Four test wells were installed along the groundwater flow direction (spaced 5 ft apart), including one injection well (IW), one up-gradient monitoring well (MW-3) and two down-gradient monitoring wells (MW-1 and MW-2). Stabilized nanoparticle suspension was prepared on-site and injected into the 50-ft deep, unconfined aquifer. Approximately 150 gallons of 0.2 g/L Fe–Pd (CMC = 0.1 wt%, Pd/Fe = 0.1 wt%) was gravity-fed through IW-1 over a 4-h period (Injection #1). One month later, another 150 gallons of 1.0 g/L Fe–Pd (CMC = 0.6 wt%, Pd/Fe = 0.1 wt%) was injected into IW-1 at an injection pressure <5 psi (Injection #2). When benchmarked against the tracer, approximately 37.4% and 70.0% of the injected Fe was detected in MW-1 during injection #1 and #2, respectively, confirming the soil mobility of the nanoparticles through the aquifer, and higher mobility of the particles was observed when the injection was performed under higher pressure. Rapid degradation of PCE and TCE was observed in both MW-1 and MW-2 following each injection, with the maximum degradation being observed during the first week of the injections. The chlorinated ethenes concentrations gradually returned to their pre-injection levels after ∼2 weeks, indicating exhaustion of the ZVI's reducing power. However, the injection of CMC-stabilized nanoparticle and the abiotic reductive dechlorination process appeared to have boosted a long-term in situ biological dechlorination thereafter, which was evidenced by the fact that PCE and TCE concentrations showed further reduction after two weeks. After 596 days from the first injection, the total chlorinated ethenes concentration decreased by about 40% and 61% in MW-1 and MW-2, respectively. No significant long-term reduction of PCB 1242 was observed in MW-1, but a reduction of 87% was evident in MW-2. During the 596 days of testing, the total concentrations of cis-DCE (dichloroethylene) and VC (vinyl chloride) decreased by 20% and 38% in MW-1 and MW-2, respectively. However, the combined fraction of cis-DCE and VC in the total chlorinated ethenes (PCE, TCE, cis-DCE and VC) increased from 73% to 98% and from 62% to 98%, respectively, which supports the notion that biological dechlorination of PCE and TCE was active. It is proposed that CMC-stabilized ZVI-Pd nanoparticles facilitated the early stage rapid abiotic degradation. Over the long run, the existing biological degradation process was boosted with CMC as the carbon source and hydrogen from the abiotic/biotic processes as the electron donor, resulting in the sustained enhanced destruction of the chlorinated organic chlorinated ethenes in the subsurface.

Inhibition of aerobic metabolic cis-1,2-di-chloroethene biodegradation by other chloroethenes

The presence of other chloroethenes influences aerobic metabolic biodegradation of cis-1,2-dichloroethene ( cDCE). A new metabolically cDCE degrading enrichment culture was identified as also being capable of degrading vinyl chloride (VC), but not 1,1 -dichloroethene (1,1DCE), trans-1,2-dichloroethene ( tDCE), trichloroethene (TCE), or tetrachloroethene (PCE). The fastest degradation of cDCE was observed in the absence of any other chloroethene. In the presence of a second chloroethene (40–90 μM), the rate of cDCE (60 μM) degradation decreased in the following order: cDCE (+PCE) > cDCE (+ tDCE) > cDCE (+VC)> cDCE (+1,1DCE) ≈ cDCE (+TCE). With increasing concentrations of VC, ranging from 10 to 110 μM, the rate of cDCE (60 μM) degradation decreased. This study demonstrates that the inhibiting effects of chloroethene mixtures have to be considered during laboratory studies and bioremediation approaches based on metabolic cDCE degradation.

The Use of Multizone Models to Estimate an Airborne Chemical Contaminant Generation and Decay Profile: Occupational Exposures of Hairdressers to Vinyl Chloride in Hairspray During the 1960s and 1970s

Vinyl chloride (VC) was used as a propellant in a limited percentage of aerosol hairspray products in the United States from approximately 1967 to 1973. The question has arisen whether occupational exposures of hairdressers to VC-containing hairsprays in hair salons were sufficient to increase the risk for developing hepatic angiosarcoma (HAS). Transient two-zone and steady-state three-zone models were used to estimate the historical airborne concentration of VC for individual hairdressers using hairspray as well as estimated contributions from other hairdressers in the same salon. Concentrations of VC were modeled for small, medium, and large salons, as well as a representative home salon. Model inputs were determined using published literature, and variability in these inputs was also considered using Monte Carlo techniques. The 95th percentile for the daily time-weighted average exposure for small, medium, and large salons, assuming a market-share fraction of VC-containing hairspray use from the Monte Carlo analysis, was about 0.3 ppm, and for the home salon scenario was 0.1 ppm. The 95th percentile value for the cumulative lifetime exposure of the hairdressers was 2.8 ppm-years for the home salon scenario and 2.0 ppm-years for the small, medium, and large salon scenarios. If using the assumption that all hairsprays used in a salon contained VC, the 95th percentile of the theoretical lifetime cumulative dose was estimated to be 52-79 ppm-years. Estimated lifetime doses were all below the threshold dose for HAS of about 300 to 500 ppm-years reported in the published epidemiology literature.

Assessment of air pollutant emissions from the Akrotiri landfill site (Chania, Greece)

Air pollutants emitted from landfills affect air quality, contribute to the greenhouse effect and may cause serious problems to human health under certain circumstances. The current study was focused on the determination of air emissions from the Akrotiri landfill site which is located in the Akrotiri area (Chania, Greece). The landfill consists of two phases, phase A (first phase) which is currently closed (operational between 2003 and 2007) and phase B (second phase, operation between 2007 and (foreseen) 2013). Three different emission models (the EPA LandGEM model, the triangular model and the stoichiometric model) were used for the quantification of emissions. The LandGEM 3.02 software was further adopted and used in conjunction with the long-term dispersion model ISC3-LT for the evaluation of the dispersion of gaseous chemical components from the landfill. The emission and meteorological conditions under which the models were applied were based on the worst-case emission scenario. Furthermore, the concentration of hydrogen sulfide, vinyl chloride and benzene were determined in and around the landfill site. The concentrations of hydrogen sulfide and benzene were calculated to be far below the limit value proposed by the World Health Organization (WHO) for human health safety. However, the vinyl chloride concentrations were above the WHO reference lifetime exposure health criteria for the phase B area.

SET‐LRP of vinyl chloride initiated with CHBr3 and catalyzed by Cu(0)‐wire/TREN in DMSO at 25 °C

AbstractThe single‐electron transfer living radical polymerization (SET‐LRP) of vinyl chloride (VC) initiated with CHBr3 in dimethylsulfoxide (DMSO) at 25 °C was investigated using Cu(0) powder and Cu(0) wire as the catalyst. It was determined that living kinetics and high conversion are achieved only through the proper calibration of the ratio between Cu(0) and TREN and the concentration of VC in DMSO. For both Cu(0) powder and Cu(0) wire, optimum conversion was achieved with higher levels of TREN than reported in earlier preliminary reports and under more dilute conditions. Using these conditions, 85+% conversion of VC could be achieved with Cu(0) powder and wire to produce white poly(vinyl chloride) (PVC) with Mn = 20,000 and Mw/Mn = 1.4–1.6 in 360 min. The use of Cu(0) wire provides the most effective catalytic system for the LRP of PVC allowing for simple removal and recycling of the catalyst. In the Cu(0) wire‐catalyzed SET‐LRP of VC, the consumption of Cu(0) was monitored as a function of conversion. From these studies, it is evident that the catalyst can be recycled extensively before significant exchange of Cu(0) into Cu(II)X2 and change in catalyst surface area is observed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 164–172, 2010

Spatial and Temporal Distributions of Geobacter lovleyi and Dehalococcoides spp. during Bioenhanced PCE-NAPL Dissolution

The spatial and temporal distributions of multiple reductively dechlorinating bacteria were simultaneously assessed in a one-dimensional sand column containing a tetrachloroethene (PCE) nonaqueous phase liquid (NAPL) source and associated plume zones. The column was uniformly inoculated with a PCE-to-ethene dechlorinating microbial consortium that contained Dehalococcoides spp., Dehalobacter spp., and Geobacter lovleyi strain SZ. Geobacter and Dehalococcoides populations grew and colonized the column material, including the mixed-NAPL (0.25 mol/mol PCE in hexadecane) source zone. In contrast, Dehalobacter cells did not colonize the porous column material, and planktonic Dehalobacter cell titers remained below the detection limit of ca. 2.6 x 10(2) cells/mL throughout the experiment. Significant PCE dechlorination was observed and resulted in bioenhanced NAPL dissolution up to 21-fold (maximum) and 5.2-fold (cumulative) relative to abiotic dissolution. cis-1,2-Dichloroethene (cis-DCE) wasthe primary dechlorination product although vinyl chloride (VC) was also formed throughout the experiment. Ethene production occurred after significant depletion of PCE from the NAPL and when cis-DCE concentrations dropped below 6 microM. Data obtained after increasing the column residence time from 1.1 to 2.8 days and introducing a VC pulse to the column indicated that both the residence time and cis-DCE inhibition limited significant VC and ethene production. Although both Geobacter and Dehalococcoides cells were present and active in the mixed-NAPL source zone and plume region, Geobacter cell numbers were typically more than 1 order of magnitude higher than Dehalococcoides cell numbers, which is consistent with the production of predominantly cis-DCE. Analysis of both liquid- and solid-phase samples indicated that Geobacter cells grew and remained attached to the porous medium within the source zone but were largely planktonic in the plume region. In contrast Dehalococcoides cell were attached throughoutthecolumn,and Dehalococcoides cell titers increased by 1 to 2 orders of magnitude over the length of the column, correlating to increases in VC concentrations. The results from this study highlight that bioenhanced dissolution is governed by a complex interplay between resident dechlorinators, contaminant concentrations, and other aquifer-specific characteristics (e.g., hydrology).

Bioremediation of a former dry cleaner using potassium lactate

AbstractChlorinated solvents were released to the surficial groundwater underneath a former dry cleaning building, resulting in a groundwater plume consisting of high concentrations of trichloroethene (TCE) and cis‐1,2‐dichloroethene (cis‐1,2‐DCE) and low concentrations of tetrachloroethene (PCE) and vinyl chloride. The initial remedial action included chemical oxidation via injection of 14,400 gallons of Fenton's Reagent in March 2002, and an additional 14,760 gallons in April 2002. A sharp reduction of contaminant concentrations in groundwater was observed the following month; however, rebound of contaminant concentrations was evident as early as October 2002. A source area of PCE‐impacted soils was excavated in June 2004. Following the excavation, Golder Associates Inc. (2007) implemented a biostimulation plan by injecting 55 gallons of potassium lactate (PURASAL® HiPure P) in September 2005, and again in February 2006. Comparing the preinjection and postinjection site conditions, the potassium lactate treatments were successful in accomplishing a 40 to 70 percent reduction in mass within four months following the second injection. Elevated vinyl chloride concentrations have persisted through both injection events; however, significant vinyl chloride reduction has been observed in one well with the highest total organic carbon (TOC) concentrations following each injection. © 2008 Wiley Periodicals, Inc.

Biodegradation potential and bacterial diversity of a petrochemical wastewater treatment plant in Iran

An activated sludge treatment was evaluated for its effectiveness in cleaning up a petrochemical wastewater in Iran. For assessing biodegradation potential of activated sludge, seven characteristics of wastewater (temperature, pH, dissolved oxygen, chemical oxygen demand, concentrations of ethylene dichloride, vinyl chloride, and total hydrocarbons) were monitored during six months. It was shown that dominant pollutants in order of magnitude were normal-alkanes (C 10–C 21), aromatics, and polycyclic hydrocarbons. The activated sludge treatment revealed maximum reduction of 89%, 99%, 92%, and 80% in COD, ethylene dichloride, vinyl chloride and total hydrocarbons concentrations, respectively. Preliminary screening of culturable petrochemical-degrading microorganisms of the activated sludge resulted in the collection of 67 bacterial and one mold species. Bacterial strains mainly belonged to Pseudomonas, Flavobacterium, Comamonas, Cytophaga, Acidovorax, Sphingomonas, Bacillus and Acinetobacter genera. The isolated mold was identified as Trichoderma sp.

Remediation of TCE-contaminated groundwater by a permeable reactive barrier filled with plant mulch (Biowall)

A pilot-scale permeable reactive barrier filled with plant mulch was installed at Altus Air Force Base in Oklahoma, USA to treat trichloroethylene (TCE) contamination in groundwater emanating from a landfill. The barrier was constructed in June 2002. It was 139 meters long, 7 meters deep, and 0.5 meters wide. The barrier is also called a Biowall because one of the mechanisms for removal of TCE is anaerobic biodegradation. This study aimed at evaluating the performance of the pilot-scale Biowall after its installation. Data from over four years' monitoring indicated that the Biowall greatly changed geochemistry in the study area and stimulated TCE removal. The concentration of TCE in the Biowall and downgradient of the Biowall was greatly reduced as compared to that in ground water upgradient of the Biowall, while the concentration of cis-DCE in the Biowall and downgradient of the Biowall was much higher than that observed upgradient of the Biowall. Over time, the concentration of vinyl chloride in the Biowall and downgradient of the Biowall increased. Dehalococcoides DNA was detected within and downgradient of the Biowall, corresponding to the observation that vinyl chloride was produced at these locations. Results from a tracer study indicated that the regional groundwater flow pattern ultimately determined the flow direction in the area around the Biowall. The natural groundwater velocity was estimated at an average of 0.060 ± 0.015 m/d.

Assessment of a groundwater contamination with vinyl chloride (VC) and precursor volatile organic compounds (VOC) by use of a geographical information system (GIS)

Regarding the health effects of volatile organic compounds (VOC) and their decomposition products (particularly vinyl chloride (VC)) under chronic low-dose exposure, VOC groundwater contaminations are seen to be an ongoing public health issue. This article presents results of a long-term investigation surveying VOC and VC groundwater contamination upstream of a large groundwater works in Cologne, Germany. For 10 years a contaminated aquifer has been monitored for different VOC and for VC. In total, 255 samples have been taken to assess both the 3-dimensional distribution and the temporal dynamics of the contaminants. VOC and VC precursor substances have been measured by means of pentane-liquid-liquid-extraction, GC and ECD, VC by means of derivatisation to 1,2 dibromochloroethane, GC, ECD, and by purge and trap technique and GC-MS-coupling. For spatial analysis all test results and additional hydrogeological attribute data have been transferred to a GIS. The spatial VOC distribution has been assessed by use of kriging interpolation indicating a decrease of the initial contaminants in time. A cluster analysis allowed to distinguish several independent contaminations within the large contamination area. The VC contamination was increasing. Anaerobic microbial dechlorination of VOC and subsequent VC accumulation were seen to be as credible from several indications (VC presence, downstream change of tetra/trichloroethylene-ratio and anaerobic conditions in the aquifer, high Fe(2+)- and Mn(2+)-concentrations). There was no statistically significant vertical differentiation of VOC and VC concentrations. The VOC load within the different water protection zones of the waterworks could be assessed.

In situ reductive dechlorination of chlorinated ethenes in high nitrate groundwater

In situ bioremediation using carbohydrate was evaluated as an in situ treatment alternative for trichloroethene (TCE) and cis-1,2-dichloroethene (cDCE) in groundwater containing high nitrate concentrations. Upon addition of carbohydrate to groundwater, sequential reduction of electron acceptors was observed, where nitrate was reduced early in the pilot test, followed by sulfate and TCE. Reduction of cDCE to vinyl chloride and ethene occurred in conjunction with increased iron and manganese, and increased methane concentrations, approximately 7 months into the evaluation period, following depletion of nitrate and sulfate. TCE, cDCE, and vinyl chloride concentrations decreased from approximately 500 to >10 μg/L within 21 months of operation.

Trichloroethylene Removal from Groundwater in Flow-Through Columns Simulating a Permeable Reactive Barrier Constructed with Plant Mulch

Groundwater contaminated with TCE is commonly treated with a permeable reactive barrier (PRB) constructed with zero-valence iron. The cost of iron has driven a search for less costly alternatives, and composted plant mulch has been used as an alternative at several sites. A column study was conducted that simulated conditions in a PRB at Altus Air Force Base, Oklahoma. The reactive matrix was 50% (v/v) shredded tree mulch, 10% cotton gin trash, and 40% sand. The mean residence time of groundwater in the columns was 17 days. The estimated retardation factor for TCE was 12. TCE was supplied at concentrations near 20 microM. Over 793 days of operation, concentrations of TCE in the column effluents varied from 0.1% to 2% of the column influents. Concentrations of cis-DCE, vinyl chloride, ethylene, ethane, and acetylene could account for 1% of the TCE that was removed; however, up to 56% of 13C added as [1,2-13C] TCE in the column influents was recovered as 13C in carbon dioxide. After 383 and 793 d of operation, approximately one-half of the TCE removal was associated with abiotic reactions with FeS that accumulated in the reactive matrix.