Diffusion of TCE Through Soil-Bentonite Slurry Walls

Diffusion experiments performed using both a dissolved solution of trichloroethylene (TCE) and a pool of free phase TCE adjacent to a simulated soil-bentonite (SB) wall are described. These tests examine a multi-layer system that includes both contaminated sand and a SB barrier. Results obtained from experiments with dissolved TCE as the primary source are shown to be consistent with those obtained with free-phase TCE as the source of contaminant. Diffusion and sorption coefficients of a soil-bentonite slurry wall are reported to be 3.5 × 10^?10 m ² /s and 0 cm ³ /g, respectively. These diffusion and sorption coefficients were used to evaluate the effectiveness of a hypothetical SB slurry wall located adjacent to a TCE spill.     

Betula pendula: A Promising Candidate for Phytoremediation of TCE in Northern Climates

Betula pendula (Silver birch) trees growing on two contaminated sites were evaluated to assess their capacity to phytoscreen and phytoremediate chlorinated aliphatic compounds and heavy metals. Both locations are industrially-contaminated properties in central Sweden. The first was the site of a trichloroethylene (TCE) spill in the 1980s while the second was polluted with heavy metals by burning industrial wastes. In both cases, sap and sapwood from Silver birch trees were collected and analyzed for either chlorinated aliphatic compounds or heavy metals. These results were compared to analyses of the surface soil, vadose zone pore air and groundwater. Silver birch demonstrated the potential to phytoscreen and possibly phytoremediate TCE and related compounds, but it did not demonstrate the ability to effectively phytoextract heavy metals when compared with hyperaccumulator plants. The capacity of Silver birch to phytoremediate TCE appears comparable to tree species that have been employed in field-scale TCE phytoremediation efforts, such as Populus spp. and Eucalyptus sideroxylon rosea.     

Kinetic analysis of the inhibitory effect of trichloroethylene (TCE) on nitrification in cometabolic degradation

In this study, the inhibitory effect of TCE on nitrification process was investigated with an enriched nitrifier culture. TCE was found to be a competitive inhibitor of ammonia oxidation and the inhibition constant (K _I ) was determined as 666–802 μg/l. The TCE affinity for the AMO enzyme was significantly higher than ammonium. The effect of TCE on ammonium utilization was evaluated with linearized plots of Monod equation (e.g., Lineweaver–Burk, Hanes–Woolf and Eadie–Hofstee plots) and non-linear least square regression (NLSR). No significant differences were found among these data evaluation methods in terms of kinetic parameters obtained.     

Aquifer Protist Response and the Potential for TCE Bioremediation with Burkholderia cepacia G4 PR1

Abstract Bacterivorous protists have been recovered from pristine and contaminated aquifer environments, but the ecological role of these organisms in bioremediation strategies has not been well defined. Burkholderia cepacia G4 PR1 constitutively expresses a toluene ortho-monooxygenase (tom) due to a secondary transposition of a Tn5 transposable element in a trichloroethylene (TCE) degradative plasmid (TOM). Groundwater and sediment from a potential site for a TCE bioremediation field demonstration were used in laboratory microcosms to test the survival of this organism. In nonsterile aquifer sediment slurries, the bacterium was eliminated in a logrithmic decay concomitant with an increase in bacterivorous protists. A half-life for the organism calculated from extinction coefficients increased logarithmically with increasing inoculation density above 1 × 10⁶ PR1 ml⁻¹. For inoculation densities below this level, the half-life of PR1 increased exponentially with decreasing inoculation density. The lowest half-lives corresponded to densities of bacteria that stimulate response of bacterivores. In a column system designed to incorporate aquifer flow, repeated addition of PR1 resulted in a buildup of bacterivore populations and reduced half-life of the bacterium. Addition of TCE and growth substrate in the eluent resulted in prolonged survival of PR1 and apparent mineralization of TCE. The results indicate significant but predictable losses due to native bacterivores would occur within and beyond a treatment zone where PR1 would be added to the aquifer, and mineralization of TCE in contaminated groundwater might be possible with repeated inoculation and addition of nutrients. Received: November 1999; Accepted: February 2000; Online Publication: 28 August 2000     

Aerobic,phenol-induced TCE degradation in completely mixed,continuous-culture reactors

BothPseudomonas putida F1 and a mixed culture were used to study TCE degradation in continuous culture under aerobic, non-methanotrophic conditions. TCE mass balance studies were performed with continuous culture reactors to determine the total percent removed in the reactors, and to quantify the percent removed by air stripping and biodegradation. Adsorption of TCE to biomass was assumed to be negligible. This research demonstrated the feasibility of treating TCE-contaminated water under aerobic, non-methanotrophic conditions with a mixed-culture, continuous-flow system.Initially glucose and acetate were fed as primary substrates. Pnenol, which has been shown to induce TCE-degrading enzymes, was fed at a much lower concentration (20mg/L). Little degradation of TCE was observed when acetate and glucose were the primary substrates. After omitting glucose and acetate from the feed and increasing the phenol concentration to 50mg/L, TCE biotransformation was observed at a significant level (46%). When the phenol concentration in the feed was increased to 420mg/L, 85% of the incoming TCE was estimated to have been biodegraded. Under the same conditions, phenol utilization by the mixed culture was greater than that ofP. putida F1, and TCE degradation by the mixed culture (85%) exceeded that ofP. putida F1 (55%). The estimated percent-of-TCE biodegraded by the mixed culture was consistently greater than 80% when phenol was fed at 420mg/L. Biodegradation of TCE was also observed in mixed-culture, batch experiments.     

Transpiration and metabolisation of TCE by willow plants – a pot experiment

Willows were grown in glass cylinders filled with compost above water-saturated quartz sand, to trace the fate of TCE in water and plant biomass. The experiment was repeated once with the same plants in two consecutive years. TCE was added in nominal concentrations of 0, 144, 288, and 721 mg l^?1. Unplanted cylinders were set-up and spiked with nominal concentrations of 721 mg l^?1 TCE in the second year. Additionally, ¹³C-enriched TCE solution (δ¹³C = 110.3 ‰) was used. Periodically, TCE content and metabolites were analyzed in water and plant biomass. The presence of TCE-degrading microorganisms was monitored via the measurement of the isotopic ratio of carbon (¹³C/¹²C) in TCE, and the abundance of ¹³C-labeled microbial PLFAs (phospholipid fatty acids). More than 98% of TCE was lost via evapotranspiration from the planted pots within one month after adding TCE. Transpiration accounted to 94 to 78% of the total evapotranspiration loss. Almost 1% of TCE was metabolized in the shoots, whereby trichloroacetic acid (TCAA) and dichloroacetic acid (DCAA) were dominant metabolites; less trichloroethanol (TCOH) and TCE accumulated in plant tissues. Microbial degradation was ruled out by δ¹³C measurements of water and PLFAs. TCE had no detected influence on plant stress status as determined by chlorophyll-fluorescence and gas exchange.     

Development and characterization of DehaloR^2, a novel anaerobic microbial consortium performing rapid dechlorination of TCE to ethene

A novel anaerobic consortium, named DehaloR^2, that performs rapid and complete reductive dechlorination of trichloroethene (TCE) to ethene is described. DehaloR^2 was developed from estuarine sediment from the Back River of the Chesapeake Bay and has been stably maintained in the laboratory for over 2 years. Initial sediment microcosms showed incomplete reduction of TCE to DCE with a ratio of trans- to cis- isomers of 1.67. However, complete reduction to ethene was achieved within 10 days after transfer of the consortium to sediment-free media and was accompanied by a shift to cis-DCE as the prevailing intermediate metabolite. The microbial community shifted from dominance of the Proteobacterial phylum in the sediment to Firmicutes and Chloroflexi in DehaloR^2, containing the genera Acetobacterium, Clostridium, and the dechlorinators Dehalococcoides. Also present were Spirochaetes, possible acetogens, and Geobacter which encompass previously described dechlorinators. Rates of TCE to ethene reductive dechlorination reached 2.83 mM Cl⁻ d⁻¹ in batch bottles with a Dehalococcoides sp. density of 1.54E+11 gene copies per liter, comparing favorably to other enrichment cultures described in the literature and identifying DehaloR^2 as a promising consortium for use in bioremediation of chlorinated ethene-impacted environments.     

Dual augmentation for aerobic bioremediation of MTBE and TCE pollution in heavy metal-contaminated soil

In this work we isolated from soil and characterized several bacterial strains capable of either resisting high concentrations of heavy metals (Cd²⁺ or Hg²⁺ or Pb²⁺) or degrading the common soil and groundwater pollutants MTBE (methyl-tert-butyl ether) or TCE (trichloroethylene). We then used soil microcosms exposed to MTBE (50 mg/l) or TCE (50 mg/l) in the presence of one heavy metal (Cd 10 ppm or Hg 5 ppm or Pb 50 or 100 ppm) and two bacterial isolates at a time, a degrader plus a metal-resistant strain. Some of these two-membered consortia showed degradation efficiencies well higher (49–182% higher) than those expected under the conditions employed, demonstrating the occurrence of a synergetic relationship between the strains used. Our results show the efficacy of the dual augmentation strategy for MTBE and TCE bioremediation in the presence of heavy metals.     

Correlation of TCE cometabolism with growth characteristics on aromatic substrates in toluene-degrading bacteria

We have constructed a bacterial library consisting of 97 strains of toluene-degrading bacteria from soil and activated sludge samples for examining their physiological properties in terms of cometabolism of TCE. Large variation of TCE degradation ability was observed in Gram-positive and Gram-negative strains, as well as diverse patterns of availability of aromatics as a growth substrate. No clear correlation was observed between the number of available substrates for growth and TCE degradation ability. However, the growth on some of the aromatics showed positive or negative correlations with TCE degradation ability. Kendall correlation constants (tau) for the growth on cumene, m-xylene, p-xylene, and m-cresol with TCE degradation ability were statistically significant (P < 0.001): their values were −0.44, −0.31, −0.26, 0.37, respectively. Among 12 of aromatics, only m-cresol showed positive correlation with TCE degradation ability. These findings would be useful for enrichment and isolation of the microbes that have TCE-cometabolism ability, which is a selective disadvantage through the toxicity or competitive inhibition against growth substrates.     

Dynamics of reductive TCE dechlorination in two distinct H<Subscript>2</Subscript> supply scenarios and at various temperatures

Anaerobic microbial dechlorination of trichloroethene (TCE) by a mixed, Dehalococcoides containing culture was investigated at different temperatures (4–60 °C) using propionate and lactate as a slow- and fast-releasing hydrogen (H₂) source, respectively. Distinct temperature-dependent dynamics of substrate fermentation and H₂ levels could explain observed patterns of dechlorination. While varying the temperature caused changes in rate, the overall pattern of dechlorination was characteristic of the supplied electron donor. Feeding cultures with a rapidly fermentable substrate such as lactate generally resulted in high H₂ concentrations and fast and complete dechlorination accompanied by rapid methanogenesis. In contrast, low H₂ release rates resulting from fermentation of propionate were associated with 2 to 3−fold longer time frames necessary for complete dechlorination at intermediate temperatures (15–30 °C). A lag-phase prior to dechlorination of cis-dichloroethene (cDCE), together with a characteristic build-up of H₂ and methane, was consistently observed at slow H₂ supply. At temperatures of 10 °C and lower, the system remained in this lag phase and no dechlorination past cDCE was observed within the experimental time frame. However, when lactate was the substrate, complete dechlorination of TCE occurred within 74 days at 10 °C, accompanied by methane production. The choice of fermentable substrate decisively influenced the rate and degree of dechlorination at an electron donor/TCE ratio as high as 666:1. Temperature-dependent H₂ levels resulting from fermentation of different substrates could be satisfactorily explained through thermodynamic calculations of the Gibbs free energy yield assuming a constant metabolic energy threshold of −20 kJ/(mol reaction).     

An integrated model for assessing the risk of TCE groundwater contamination to human receptors and surface water ecosystems

The practical implementation of the European Water Framework Directive has resulted in an increased focus on the hyporheic zone. In this paper, an integrated model was developed for evaluating the impact of point sources in groundwater on human health and surface water ecosystems. This was accomplished by coupling the system dynamics-based decision support system CARO-PLUS to the aquatic ecosystem model AQUATOX using an analytical volatilization model for the stream. The model was applied to a case study where a trichloroethylene (TCE)-contaminated groundwater plume is discharging to a stream. The TCE source will not be depleted for many decades; however, measured and predicted TCE concentrations in surface water were found to be below human health risk management targets. Volatilization rapidly attenuates TCE concentrations in surface water. Thus, only a 30-m stream reach fails to meet surface water quality criteria. An ecological risk assessment found that the TCE contamination did not impact the stream ecosystem. Uncertainty assessment revealed hydraulic conductivity to be the most important site-specific parameter. These results indicate that contaminant plumes with μg L^?1 concentrations of TCE entering surface water systems may not pose a significant risk.     

Use of Fenton's Reagent for the Degradation of TCE in Aqueous Systems and Soil Slurries

Fenton's reaction is comprised of hydrogen peroxide (H₂O₂) catalyzed by iron, producing the hydroxyl radical (·OH), a strong oxidant. ·OH in turn may react with H₂O₂ and iron and is capable of destroying a wide range of organic contaminants. In this laboratory study, Fenton's reaction was observed in aqueous and soil slurry systems using trichloroethylene (TCE) as the target contaminant, with the goal of maximizing TCE degradation while minimizing H₂O₂ degradation. Fenton's reaction triggers a complex matrix of reactions involving ·OH, H₂O₂, iron, TCE, and soil organics. In soil slurries with a high fraction of organic carbon (f_OC), iron tends to sorb to soil organics and/or particles. In aqueous systems the optimal ratio of H₂O₂:Fe²⁺:TCE to degrade TCE in a timely fashion, minimize costs, and minimize H₂O₂ degradation is 300?mg/L: 25?mg/L: 60?mg/L (19:1:1 molar ratio), while soil slurries with a f_OC up to approximately 1% and a soil:water ratio of 1:5 (weight ratio) require about ten times the amount of H₂O₂, the optimal ratio being 3000?mg/L: 5?mg/L: 60?mg/L (190:0.2:1 molar ratio). TCE degradation rates were observed to decrease in soil slurries with higher f_OC because of competition by soil organic matter, which appears to act as a sink for ·OH. H₂O₂ degradation rates tended to increase in soil slurries with higher f_OC, most likely due to increased demand for ·OH by soil organics, increased available iron and other oxidation processes.     

Effect of trichloroethylene (TCE) and toluene concentrations on TCE and toluene biodegradation and the population density of TCE and toluene degraders in soil.

Toluene is one of several cosubstrates able to support the cometabolism of trichloroethylene (TCE) by soil microbial communities. Indigenous microbial populations in soil degraded TCE in the presence, but not the absence, of toluene after a 60- to 80-h lag period. Initial populations of toluene and TCE degraders ranged from 0.2 x 10(3) to 4 x 10(3) cells per g of soil and increased by more than 4 orders of magnitude after the addition of 20 micrograms of toluene and 1 microgram of TCE per ml of soil solution. The numbers of TCE and toluene degraders and the percent removal of TCE increased with an increase in initial toluene concentration. As the initial TCE concentration was increased from 1 to 20 micrograms/ml, the numbers of toluene and TCE degraders and the rate of toluene degradation decreased, and no TCE degradation occurred. No toluene or TCE degradation occurred at a TCE concentration of 50 micrograms/ml.     

TCE degradation in a methanotrophic attached-film bioreactor

Trichloroethene was degraded in expanded-bed bioreactors operated with mixed-culture methanotrophic attached films. Biomass concentrations of 8 to 75 g volatile solids (VS) per liter static bed (L(sb)) were observed. Batch TCE degradation rates at 35 degrees C followed the Michaelis-Menten model, and a maximum TCE degradation rate (q(max)) of 10.6 mg TCE/gVS . day and a half velocity coefficient (K(S)) of 2.8 mg TCE/L were predicted. Continuous-flow kinetics also followed the Michaelis-Menten model, but other parameters may be limiting, such as dissolved copper and dissolved methane-q(max) and K(S) were 2.9 mg TCE/gVS . day and 1.5 mg TCE/L, respectively, at low copper concentrations (0.003 to 0.006 mg Cu/L). The maximum rates decreased substantially with small increases in dissolved copper. Methane consumption during continuous-flow operation varied from 23 to 1200 g CH(4)/g TCE degraded. Increasing the influent dissolved methane concentration from 0.01 mg/L to 5.4 mg/L reduced the TCE degradation rate by nearly an order of magnitude at 21 degrees C. Exposure of biofilms to 1.4 mg/L tetrachloroethene (PCE) at 35 degrees C resulted in the loss of methane utilization ability. Tests with methanotrophs grown on granular activated carbon indicated that lower effluent TCE concentrations could be obtained. The low efficiencies of TCE removal and low degradation rates obtained at 35 degrees C suggest that additional improvements will be necessary to make methanotrophic TCE treatment attractive. (c) 1993 John Wiley & Sons, Inc.     

Enhanced biotransformation of TCE using plant terpenoids in contaminated groundwater

Aims:  To examine plant terpenoids as inducers of TCE (trichloroethylene) biotransformation by an indigenous microbial community originating from a plume of TCE-contaminated groundwater.
Methods and Results:  One-litre microcosms of groundwater were spiked with 100 μmol 1⁻¹ of TCE and amended weekly for 16 weeks with 20 μl 1⁻¹ of the following plant monoterpenes: linalool, pulegone, R-(+) carvone, S-(−) carvone, farnesol, cumene. Yeast extract-amended and unamended control treatments were also prepared. The addition of R-carvone and S-carvone, linalool and cumene resulted in the biotransformation of upwards of 88% of the TCE, significantly more than the unamendment control (61%). The aforementioned group of terpenes also significantly ( P  < 0·05) allowed more TCE to be degraded than the remaining two terpenes (farnesol and pulegone), and the yeast extract treatment which biotransformed 74–75% of the TCE. The microbial community profile was monitored by denaturing gradient gel electrophoresis and demonstrated much greater similarities between the microbial communities in terpene-amended treatments than in the yeast extract or unamended controls.
Conclusions:  TCE biotransformation can be significantly enhanced through the addition of selected plant terpenoids.
Significance and Impact of the Study:  Plant terpenoid and nutrient supplementation to groundwater might provide an environmentally benign means of enhancing the rate of in situ TCE bioremediation.     

Analysis of the rate-limiting step of an anaerobic biotrickling filter removing TCE vapors

A detailed analysis of a biotrickling filter treating trichloroethene (TCE) vapors anaerobically is presented and discussed. The biotrickling filter relies on mixed cultures containing bacteria from the genus Dehalococcoides that reductively dechlorinate TCE to ethene. After about 200 days of steady operation, as biomass in the packed bed increased, a partial loss in treatment performance was observed which prompted the present investigations. Analysis of TCE and of its degradation metabolites in the gas phase and in the trickling liquid combined with the calculation of global effectiveness factors revealed that significant mass transfer limitations existed. Depending on the conditions, either the gas film or the liquid film limited the removal of TCE. These findings were confirmed by the determination of gas and liquid films mass transfer coefficients. In all cases, removal of TCE was greater without trickling of liquid. The most plausible reason for the onset of mass transfer limitations was the decrease in the specific interfacial area brought by important biomass growth over time. Overall, this study illustrates how complex kinetic and transport limitations can vary with the operating conditions in biotrickling filters.