Reductive Dechlorination Of Tetrachloroethylene Research Articles

Fate & transport of vinyl chloride in soil vapor

AbstractVinyl chloride (VC) is a common risk driver in vapor intrusion (VI) studies. At many sites, initial screening shows potential indoor air impacts for VC at unacceptable levels. During follow‐up site characterization, however, the VI pathway for VC is rarely if ever found to be complete. This paper sets forth a conceptual model for understanding these results and summarizes data from several field sites to illustrate the concepts. VC can be formed under anaerobic conditions via reductive dechlorination of tetrachloroethylene or trichloroethylene. The ultimate fate of any VC that is produced depends on the amount of available oxygen. If sufficient oxygen is available, VC will readily undergo aerobic biodegradation. Data are presented for multiple field sites to illustrate the fate and transport of VC. The sites are drawn from various regions of the United States and cover a range of conditions. At these sites, VC was detected at relatively high concentrations in groundwater. It may also have been detected in deeper soil gas, but generally was fully attenuated before reaching shallow soil depths. Indoor air results were consistently non‐detect. The behavior is also discussed for sites with very shallow groundwater, where VC was found in some subslab soil gas samples but not in the overlying indoor air.

Dynamics of chlorinated aliphatic hydrocarbons in the Chalk aquifer of northern France

The Chalk aquifer used for drinking-water production in the southwest of the Lille European Metropolis is threatened by the presence of chlorinated aliphatic hydrocarbons (CHCs), their concentrations in groundwater regularly exceeding the regulatory limits for drinking water in France. This hinders its use for drinking-water production. Understanding the dynamics and spatial distribution of CHC in the aquifer is a key factor for resource sustainability. For that purpose, an intensive monitoring was undertaken in several well fields and at different depths over eight years. To assess a possible migration and/or degradation of the compounds, the water column in several wells was sampled at various depths with passive samplers. Furthermore, CHC degradation mechanisms were investigated with compound-specific carbon-isotope analysis. The CHC concentrations and their distributions in the area depend on past and current industrial activity, causing plumes emphasized by pumping in the wells, such plumes being multi-source with no identified origin in most wells. In the south area of Les Ansereuilles, reductive dechlorination of tetrachloroethylene from a former industrial laundry highly impacted the surrounding area with its main degradation product cis-1,2-dichloroethylene. The same area is also affected by tetrachlroroethylene from several industrial laundries, textile factories and dyeing industries with also an anaerobic degradation. In the northern part of Les Ansereuilles, tetrachloroethylene, trichloroethane, trichloroethylene and 1,1-dichloroethylene were found as primary products, whereas cis-1,2-dichloroethylene appears to be an anaerobic degradation product of TCE. The other well fields (Houplin-Ancoisne, Seclin and Emmerin) are less impacted by CHC pollution, and it was shown that no CHC degradation occurred in the wells. However, the stratification of CHCs in the well-water columns, their constant concentration values over time caused by the large amount of available CHCs, and the minor degradation occurring in wells are of concern for water operators in the future.

Reductive dechlorination of tetrachloroethylene by bimetallic catalysts on hematite in the presence of hydrogen gas

Reductive dechlorination of tetrachloroethylene by bimetallic catalysts on hematite in the presence of hydrogen gas

Impacts of microbial community composition on isotope fractionation during reductive dechlorination of tetrachloroethylene

Isotope fractionation has been used with increasing frequency as a tool to quantify degradation of chlorinated aliphatic pollutants in the environment. The objective of this research was to determine if the electron donor present in enrichment cultures prepared from uncontaminated sediments influenced the extent of isotope fractionation of tetrachloroethylene (PCE), either directly, or through its influence on microbial community composition. Two PCE-degrading enrichment cultures were prepared from Duck Pond (DP) sediment and were incubated with formate (DPF) or H(2) (DPH) as electron donor. DPF and DPH were significantly different in both product distribution and extent of isotope fractionation. Chemical and isotope analyses indicated that electron donors did not directly affect the product distribution or the extent of isotope fractionation for PCE reductive dechlorination. Instead, restriction fragment length polymorphism (RFLP) and sequence analysis of the 16S rRNA clone libraries of DPF and DPH identified distinct microbial communities in each enrichment culture, suggesting that differences in microbial communities were responsible for distinct product distributions and isotope fractionation between the two cultures. A dominant species identified only in DPH was closely related to known dehalogenating species (Sulfurospirillum multivorans and Sulfurospirillum halorespirans) and may be responsible for PCE degradation in DPH. Our study suggests that different dechlorinators exist at the same site and can be preferentially stimulated by different electron donors, especially over the long-term (i.e., years), typical of in-situ ground water remediation.

Concentration effect of copper loading on the reductive dechlorination of tetrachloroethylene by zerovalent silicon

The dechlorination of tetrachloroethylene (PCE) by zerovalent silicon (Si(0)) in the presence of low concentration of Cu(II) ion was investigated under anaerobic conditions. The mass loadings of Cu(II) in the Si(0)-H(2)O system were in the range 0.06-3 wt% (0.02-1 mM). In addition, the X-ray photoelectron spectroscopy (XPS) and electron probe microanalysis (EPMA) were used to characterize the change in chemical species and distribution patterns of metals, respectively. Results showed that the pre-incubation time of 3 d was needed to activate the reactive sites of Si(0) before the dechlorination of PCE. Addition of low concentration of Cu(II) at 0.06 wt% significantly enhanced the dechlorination of PCE, while high concentration of Cu(II) would occupy the reactive sites of Si(0), and subsequently decreased the dechlorination efficiency and rate of PCE. The pseudo first-order rate constant (k(obs)) for PCE dechlorination by 0.06 wt% Cu/Si was 0.028 h(-1), which was 2.8 times higher than that by Si(0) alone. However, the k(obs) for PCE dechlorination decreased to 0.0016 h(-1) when the loading of Cu(II) increased to 3 wt%. The EPMA results showed that the distribution of 0.06 wt% Cu on the Si(0) surface was homogeneous without any aggregation, which means that the maximum rate constant was observed before the total coverage of the active sites on the reductive metal by the catalytic metal layer. The surface coverage of Cu to Si(0) can theoretically calculate by estimation of the lowest energy fcc(111) crystallographic orientation. The calculated surface coverage of 0.06 wt% Cu onto Si(0) was approximately 43%, which is consistent with the experimental results obtained in this study.

Reductive Dechlorination of Tetrachloroethylene by Green Rusts Modified with Copper

Reductive dechlorination of tetrachloroethylene (PCE) by green rust modified with copper (GR(Cu)) was investigated using a batch reactor system. Four different forms of GRs (GR-Cl, GR-SO4, GR-CO3, and GR-F) were synthesized by partial air oxidation of Fe(OH)2 and used in reductive dechlorination. The addition of Cu(II) into GRs produced 100-nm particles on the surface of GRs, which were considered to be metallic Cu and transformed a portion of GR to magnetite. Concentration of Fe(II) in the liquid phase increased and concentration of Fe(II) in the solid phase decreased during the modification process and the extent of these changes was dependent on the amount of Cu(II) added. The most reactive of the modified GRs was GR-F(Cu), which reacted with PCE at a rate that was 80 times faster than that of GR-Cl(Cu). The rate of PCE degradation by GR-F(Cu) was strongly dependent on pH with higher rates at higher pH over the range of pH 7.5–11. Increasing concentrations of Cu(II) over the range of 0 to 5 mM increased rate constants. The rate of dechlorination of PCE by GR-F(Cu) showed surface saturation behavior with respect to PCE concentration.

The Relative Contributions of Abiotic and Microbial Processes to the Transformation of Tetrachloroethylene and Trichloroethylene in Anaerobic Microcosms

Reductive dechlorination of tetrachloroethylene (PCE) and trichloroethylene (TCE) was studied in well-defined microcosms prepared with aquifer materials from three locations. Electron donors and terminal electron acceptors were added to both stimulate microbial activity and generate reactive minerals via microbial iron and sulfate reduction. The relative importance of abiotic and microbial PCE and TCE reductive dechlorination was then assessed by analysis of reaction products and kinetics and, in some cases, by stable carbon isotope fractionation. The predominant PCE and TCE transformation pathway in most microcosms was microbial reductive dechlorination. Rates of abiotic transformation were similar in magnitude to those for microbial reductive dechlorination in only a few cases where the activity of dechlorinating bacteria was low. Comparison of geochemical conditions with abiotic product recoveries showed thatthe greatest extent of abiotic reductive dechlorination occurred under iron- and sulfate-reducing conditions. Under these two geochemical conditions, high concentrations of Fe(II) and S(-II) solid species were present, suggesting the involvement of Fe(II) and S(-II) minerals in abiotic reductive dechlorination. Both abiotic and microbial dechlorination of PCE and TCE took place under almost all microcosm conditions; the relative rates of the two processes under field conditions will depend on factors such as the abundance of dechlorinating bacteria, soil properties, and the mass loading of reactive minerals.

COMPLETE DECHLORINATION OF TETRACHLOROETHYLENE BY USE OF AN ANAEROBIC CLOSTRIDIUM BIFERMENTANS DPH‐1 AND ZERO‐VALENT IRON

A laboratory test was conducted to examine the combined effect of an anaerobic Clostridium bifermentans DPH‐1 and addition of zero‐valent iron (Fe0) on the reductive dechlorination of tetrachloroethylene (PCE). In addition, the dechlorination of cis‐1,2‐dichloroethylene (cDCE) produced from PCE was examined using Fe0. The cDCE produced was completely dechlorinated to non‐toxic end products, mostly, ethylene by a subsequent chemical reductive process. Production of ethylene was dramatically increased with increase of initial cDCE concentration in the range of 10.3 µM to 928 µM (1.0–90 mg l−1) and the velocity constant was calculated to be 0.38 day−1. On the other hand, the combined use of strain DPH‐1 and Fe0 showed the most significant effect on the initial PCE dechlorination, but cohesion of Fe0 was found to inhibit the dechlorination rate of PCE. It is thought that phosphoric acid iron contained in a medium forms film on the surface of iron particle, so oxidation of iron is inhibited.

Reductive Dechlorination of Tetrachloroethylene and Trichloroethylene by Mackinawite (FeS) in the Presence of Metals: Reaction Rates

Reductive dechlorination by mackinawite (FeS) is an important transformation pathway for chloroethylenes in anoxic environments. Yet, the impact of metals on reductive dechlorination is not well understood, despite their frequent cooccurrence with chloroethylenes. Fe(II), Co(II), Ni(II), and Hg(II) were evaluated for their impact on the dechlorination rates of PCE and TCE by FeS. Compared with unamended FeS batches, the dechlorination rates of both chloroethylenes decreased by addition of 0.01 M Fe(II). Relative to 0.01 M Fe(II)-added FeS batches, the dechlorination rates increased in FeS batches amended with 0.01 M of Co(II) and Hg(II), whereas the rates decreased in 0.01 M Ni(II)-added batches. While significantly impacting the dechlorination rates, the amended metals were quantitatively sequestered by FeS mainly because of formation of metal sulfides. Comparison of the dechlorination rates between metal-added FeS batches and metal sulfide batches suggests that discrete metal sulfides do not form in metal-added FeS batches. The observed exceptionally high reactivity of CoS suggests that it may be useful in reactive permeable barrier applications because of its stability in anoxic waters. The dechlorination rates of PCE and TCE significantly varied with Fe(ll) amendment concentrations (Fe(II)0), indicating the presence of different types of solid-bound Fe phases with Fe(II)o.

Reductive dechlorination of tetrachloroethylene in soils by Fe(II)-based degradative solidification/stabilization.

Fe(II)-based degradative solidification/stabilization (DS/S) is a modification of conventional solidification/stabilization (S/S) that uses Fe(II) as a reducing agent for chlorinated organics while immobilizing inorganic contaminants. Feasibility of the Fe(II)-based DS/S technology in treating soils contaminated with tetrachloroethylene (PCE) was tested in this study. The results of the PCE degradation experiments conducted in the presence of a humic acid suggest that natural organic matter would not significantly interfere with the degradative reaction by the Fe(II)-containing reactive species in DS/S systems. Solid-phase degradation experiments showed that the DS/S technology could effectively treat PCE in soils without substantial production of chlorinated intermediates. A pseudo-first-order rate law reasonably described degradation kinetics. The half-lives of PCE ranged from 13 to 335 days, which are within time spans allowable for typical in-situ DS/S application. Trichloroethylene (TCE) was the only chlorinated product observed in the solid-phase experiments, and its presence was generally transitory with the amount being less than 7% of the initial amount of PCE on a molar basis. A surface reaction appears to control observed PCE degradation kinetics rather than mass transfer to the reactive surface.

Efficient dechlorination of tetrachloroethylene in soil slurry by combined use of an anaerobic Desulfitobacterium sp. strain Y-51 and zero-valent iron

A laboratory test was conducted to examine the combined effect of bioaugmentation of an anaerobic bacterial Desulfitobacterium sp. strain Y-51 and addition of zero-valent iron (Fe 0) on the reductive dechlorination of tetrachloroethylene (PCE) in a non-sterile soil slurry. Introduction of a strain Y-51 culture in soil (3 mg vss (volatile suspended solids)/kg soil) containing PCE (at 60 μmol/kg soil) led to complete conversion of PCE to cis-1,2-dichloroethylene ( cis-DCE) within 40 d. Treatments of the same soil slurry with Fe 0 (0.1–1.0%) resulted in extended PCE dechlorination to ethylene (ETH) and ethane (ETA). The combined use of a strain Y-51 culture and Fe 0 showed effective dechlorination of PCE than did the individual use. The cis-DCE produced from biological PCE dechlorination by strain Y-51 was totally converted to non-chlorinated end products by the following chemical reduction by Fe 0. Furthermore, anaerobic corrosion of Fe 0 was found to stimulate the biological reductive dechlorination of PCE by keeping proper levels of pH and oxidation-reduction potential (ORP) and by producing cathodic hydrogen, which might be used as an electron donor for respiratory PCE dechlorination. These findings suggest that the combined use of bacterial strain Y-51 and Fe 0 is effective for practical treatment of PCE and other chlorinated ethylenes in contaminated sites.

Efficient Dechlorination of Tetrachloroethylene in Soil Slurry by Combined Use of an Anaerobic Desulfitobacterium sp. Strain Y-51 and Zero-Valent Iron.

A laboratory test was conducted to examine the combined effect of bioaugmentation of an anaerobic bacterial Desulfitobacterium sp. strain Y-51 and addition of zero-valent iron (Fe0) on the reductive dechlorination of tetrachloroethylene (PCE) in a non-sterile soil slurry. Introduction of a strain Y-51 culture in soil (3 mg vss (volatile suspended solids)/kg soil) containing PCE (at 60 micromol/kg soil) led to complete conversion of PCE to cis-1,2-dichloroethylene (cis-DCE) within 40 d. Treatments of the same soil slurry with Fe0 (0.1-1.0%) resulted in extended PCE dechlorination to ethylene (ETH) and ethane (ETA). The combined use of a strain Y-51 culture and Fe0 showed effective dechlorination of PCE than did the individual use. The cis-DCE produced from biological PCE dechlorination by strain Y-51 was totally converted to non-chlorinated end products by the following chemical reduction by Fe0. Furthermore, anaerobic corrosion of Fe0 was found to stimulate the biological reductive dechlorination of PCE by keeping proper levels of pH and oxidation-reduction potential (ORP) and by producing cathodic hydrogen, which might be used as an electron donor for respiratory PCE dechlorination. These findings suggest that the combined use of bacterial strain Y-51 and Fe0 is effective for practical treatment of PCE and other chlorinated ethylenes in contaminated sites.

Reductive Dechlorination of Tetrachloroethylene by Fe(II) in Cement Slurries

Fe(II) is a potentially effective reductant for treating chlorinated organics in soils by degradative solidification/stabilization (DS/S) process. DS/S is a modification of conventional S/S that promotes degradation of organic contaminants while immobilizing inorganic contaminants. In this study, degradation of tetrachloroethylene (PCE) by Fe(II) in the presence of cement hydration products was characterized by using batch slurry reactors. Cement has been found to catalyze or participate in the PCE degradation reactions over the pH range investigated (10.6−13.8), and the degradation kinetics can generally be described by a pseudo-first-order rate law. PCE degradation rate was greatest at pH ∼12.1 with a half-life of 4.1 days when [PCE]0 = 0.245 mM and [Fe(II)]0 = 39.2 mM. Under this condition, 98% of the PCE initially present in the system transformed to nonchlorinated products (acetylene, ethylene, ethane) with acetylene being predominant, implying that elimination pathways were favored in the cement systems at high pH. Production of chlorinated intermediates was minimal in Fe(II)/cement systems. Addition of Fe(III) to Fe(II)/cement systems increased PCE degradation rates by factors of ∼2 to 3, suggesting Fe(II)-Fe(III) (hydr)oxides might have been reactive agents. Three hypotheses for the reaction mechanisms are discussed.

Reductive Dechlorination of Tetrachloroethylene by Soil Sulfate-Reducing Microbes under Various Electron Donor Conditions

Biotransformation of tetrachloroethylene (PCE) by soil sulfate-reducing bacteria was investigated using acetate, lactate and methanol as electron donors. Results show that the effectiveness of biotransformation of PCE by soil sulfate-reducing bacterial is dependent upon the type of electron donor used.

Reductive Dechlorination of Tetrachloroethylene and Trichloroethylene Catalyzed by Vitamin B12 in Homogeneous and Heterogeneous Systems

The reduction of tetrachloroethylene (PCE) and trichloroethylene (TCE) catalyzed by vitamin B{sub 12} was examined in homogeneous and heterogeneous (B{sub 12} bound to agarose) batch systems using titanium(III) citrate as the bulk reductant. The solution and surface-mediated reaction rates at similar B{sub 12} loadings were comparable, indicating that binding vitamin B{sub 12} to a surface did not lower catalytic activity. No loss in PCE reducing activity was observed with repeated usage of surface-bound vitamin B{sub 12}. Carbon mass recoveries were 81-84% for PCE reduction and 89% for TCE reduction, relative to controls. In addition to sequential hydrogenolysis, a second competing reaction mechanism for the reduction of PCE and TCE by B{sub 12}, reductive {beta}-elimination, is proposed to account for the observation of acetylene as a significant reaction intermediate. Reductive {beta}-elimination should be considered as a potential pathway in other reactive systems involving the reduction of vicinal polyhaloethenes. Surface-bound catalysts such as vitamin B{sub 12} may have utility in the engineered degradation of aqueous phase chlorinated ethenes. 19 refs., 6 figs., 1 tab.

Role of Methanogenic and Sulfate-Reducing Bacteria in the Reductive Dechlorination of Tetrachloroethylene in Mixed Culture

Tetrachloroethylene (perchloroethylene, PCE) is widely used in many industries and particularly as a degreasing and dry-cleaning solvent. It is commonly found as a groundwater contaminant and because of its carcinogenic properties is considered a pollutant, which must be eliminated by proper treatment. This research examines the role of a mixed culture in PCE dechlorination at high concentration from an ecological point of view. The respective role of sulfate-reducing and methaogenic bacteria in tetrachloroethylene cechlorination is studied. 19 refs., 5 figs., 2 tabs.