Trichloroethylene Degradation Rate Research Articles

Influence of pH on persulfate oxidation of TCE at ambient temperatures

In situ chemical oxidation (ISCO) is a technology used for groundwater remediation. This laboratory study investigated the use of the oxidant sodium persulfate for the chemical oxidation of trichloroethylene (TCE) at near ambient temperatures (10, 20 and 30 °C) to determine the influence of pH (pH = 4, 7 and 9) on the reaction rate (i.e., pseudo-first-order rate constants) over the range of temperatures utilized. TCE solutions (60 mg l −1; 0.46 mM) were prepared in phosphate buffered RO water and a fixed persulfate/TCE molar ratio of 50/1 was employed in all tests. Half-lives of TCE degradation at 10, 20 and 30 °C (pH 7) were 115.5, 35.0 and 5.5 h, respectively. Maximum TCE degradation occurred at pH 7. Lowering system pH resulted in a greater decrease in TCE degradation rates than increasing system pH. Radical scavenging tests used to identify predominant radical species suggested that the sulfate radical ( SO 4 - ) predominates under acidic conditions and the hydroxyl radical ( OH) predominates under basic conditions. In a side by side comparison of TCE degradation in a groundwater vs. unbuffered RO water it was demonstrated that when the system pH is buffered to near neutral pH conditions due to the presence of natural occurring groundwater constituents that the TCE degradation rate is higher than in unbuffered RO water where the system pH dropped from 5.9 to 2.8. The results of this study suggest that in a field application of ISCO, pH should be monitored and adjusted to near neutral if necessary.

The effect of salinity conditions on kinetics of trichloroethylene biodegradation by toluene-oxidizing cultures

This study investigates the effect of salt (NaCl) conditions on the biodegradations of trichloroethylene (TCE) by mixed cultures enriched on toluene. Two cultures were separately cultivated in this investigation, involving culture LHTO4, cultivated with freshwater and culture HHTO4, cultivated with 3.5% (w/v) NaCl solution. Batch tests were conducted to elucidate the degradations of toluene, TCE and a mixture of toluene and TCE by cultures LHTO4 at salinities of 0, 2 and 3.5% and by HHTO4 at salinity of 3.5%. The measurements were analyzed with microbial kinetics. The results show that for culture LHTO4 in the resting cells, when the transient salinities increased from 0 to 3.5%, the maximum specific rate of TCE degradation, kTCE, declined from 2.28 to 1.45d−1, and the observed TCE transformation capacity, Tc,obs, decreased from 0.060 to 0.036mgTCE/mgVSS. In the presence of toluene, TCE degradation was more inhibited by toluene (inhibition coefficients, KI,TOL were 0.8, 2.2, and 0.96mg/L for salinity 0, 2, and 3.5%, respectively) than toluene degradation was by TCE (KI,TCE were 14, 5.8, and 1000mg/L for salinity 0, 2, and 3.5%, respectively). Under long-term salinity stress, the culture HHTO4 maintained its capacity to utilize toluene but lost its effectiveness in the cometabolic transformation of TCE: kTCE fell to 0.25d−1 and Tc,obs dropped to 0.024mgTCE/mgVSS. This work reveals that the degradation of TCE by toluene-oxidizing cultures under saline conditions can be best described by the chosen kinetic equations and experimentally estimated constants, which can thus be used to lay a foundation for the rational design of biological processes to remove TCE from saline solutions.

Flux-based assessment at a manufacturing site contaminated with trichloroethylene

Groundwater and contaminant fluxes were measured, using the passive flux meter (PFM) technique, in wells along a longitudinal transect passing approximately through the centerline of a trichloroethylene (TCE) plume at a former manufacturing plant located in the Midwestern US. Two distinct zones of hydraulic conductivity were identified from the measured groundwater fluxes; a 6-m-thick upper zone (∼7 m to 13 m below the ground surface or bgs) with a geometric mean Darcy flux ( q 0) of 2 cm/day, and a lower zone (∼13 m to 16.5 m bgs) with a q 0 ∼ 15 cm/day; this important hydrogeologic feature significantly impacts any remediation technology used at the site. The flux-averaged TCE concentrations estimated from the PFM results compared well with existing groundwater monitoring data. It was estimated that at least 800 kg of TCE was present in the source zone. The TCE mass discharge across the source control plane (85 m × 38 m) was used to estimate the “source strength” (∼365 g/day), while mass discharges across multiple down-gradient control planes were used to estimate the plume-averaged, TCE degradation rate constant (0.52 year − 1 ). This is close to the rate estimated using the conventional centerline approach (0.78 year − 1 ). The mass discharge approach provides a more robust and representative estimate than the centerline approach since the latter uses only data from wells along the plume centerline while the former uses all wells in the plume.

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 (γ-Fe 2O 3) to the more hydrated goethite (α-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 3O 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.

Development and mathematical modeling of a two-stage reactor system for trichloroethylene degradation using Methylosinus trichosporium OB3b

A two-stage reactor system was developed for the continuous degradation of gas-phase trichloroethylene (TCE). Methylosinus trichosporium OB3b was immobilized on activated carbon in a TCE degradation reactor, trickling biofilter (TBF). The TBF was coupled with a continuous stirred tank reactor (CSTR) to allow recirculation of microbial cells from/to the TBF for the reactivation of inactivated cells during TCE degradation. The mass transfer aspect of the TBF was analyzed, and mass transfer coefficient of 3.9 h(-1) was estimated. The loss of soluble methane monooxygenase (sMMO) activity was modeled based on a material balance on the CSTR and TBF, and transformation capacity (T (c)) was determined to be 20.2 micromol mg(-1). Maximum TCE degradation rate of 525 mg 1(-1) d(-1) was obtained and reactor has been stably operated for more than 270 days.

有機塩素化合物の分解に適する硫黄含有鉄粉の特性

Batch dechlorination experiments with a shaken electrolytic solution and soils were carried out to identify iron powders suitable for degradation of chlorinated organic compounds and investigate the effects of operational factors on the reaction rate. Reduced or water atomized iron powders with varying contents of sulfur, manganese, and silicon were used. 50 mL of the electrolytic solution and 5 g of iron powder were added to a 100 mL vial glass bottle for the degradation tests of water, and 40 g of dry sand and iron powder adjusted for the water content in soil were used in the dechlorination tests of soils contaminated by trichloroethylene (TCE). The TCE concentration was measured by the headspace GC/MS analysis method. A correlation was observed between the degradation rates of the electrolytic solution and the results of the soil tests. The degradation rate of TCE in water was enhanced by higher concentrations of sulfur and silicon and lower concentrations of manganese. EPMA analysis of the iron powders with high concentrations of sulfur verified that FeS precipitates in iron powders with lower manganese concentrations, whereas MnS precipitates in powders with higher manganese concentrations. Because degradation of TCE takes place at the local electrode on the surface of the iron powder with FeS forming the cathode, the increase in the dechlorination reaction rate seen under the above-mentioned conditions was attributed to the fact that the electrical conductivity of FeS is higher that of MnS. The dechlorination rates of TCE per unit mass of iron powder were constant and independent of the iron powder content in the soil. On the other hand, the overall degradation rate of TCE increased with the water content in the soil.

Abiotic Degradation of Trichloroethylene under Thermal Remediation Conditions

The degradation of trichloroethylene (TCE) to carbon dioxide (CO2) and chloride (Cl-) has been reported to occur during thermal remediation of subsurface environments. The effects of solid-phase composition and oxygen content on the chemical reactivity of TCE were evaluated in sealed ampules that were incubated at 22 and 120 degrees C for periods ranging from 4 to 40 days. For all treatments, no more than 15% of the initial amount of TCE was degraded, resulting in the formation of several non-chlorinated products including Cl-, CO2, carbon monoxide, glycolate, and formate. First-order rate coefficients for TCE disappearance ranged from 1.2 to 6.2 x 10(-3) day(-1) at 120 degrees C and were not dependent upon oxygen content orthe presence of Ottawa sand. However, the rate of TCE disappearance at 120 degrees C increased by more than 1 order-of-magnitude (1.6 to 5.3 x 10(-2) day(-1)), corresponding to a half-life of 13-44 days in ampules containing 1% (wt) goethite and Ottawa sand. These results indicate that the rate of TCE degradation in heated, three-phase systems is relatively insensitive to oxygen content, but may increase substantially in the presence of iron bearing minerals.

Visible light mediated photocatalytic degradation of gaseous trichloroethylene and dimethyl sulfide on modified titanium dioxide

This paper reports the potential of four modified TiO2 photocatalysts to degrade gaseous volatile organic compounds under visible light irradiation. Two modified photocatalysts were prepared by sensitizing TiO2 Degussa P25 with CdS and eosin Y, respectively. Two other photocatalysts were S-doped TiO2. One was prepared through a recently described sol–gel method (S-doped TiO2-SG), whereas a new type was synthesized by a physical mixture method (S-doped TiO2-PM).All modified photocatalysts showed a shift in UV–vis absorbance towards higher wavelengths, up to λ=620nm. Photocatalytic activity under near-UV and visible light irradiation was systematically investigated through the degradation of gaseous trichloroethylene (TCE) and dimethyl sulfide (DMS) in a batch reactor. Although TiO2 Degussa P25 showed 1.3–6.6 times higher TCE degradation rates than modified photocatalysts under near-UV irradiation, no significant activity was observed at λ>400nm. In contrast, modified catalysts showed photocatalytic activity under both blue (400–540nm) and yellow light (480–720nm) irradiation, with S-doped TiO2-PM and S-doped TiO2-SG giving the highest TCE degradation rates, respectively. Under daylight irradiation (400–720nm), S-doped TiO2-PM yielded the highest activity towards both TCE and DMS degradation, exemplified by removal efficiencies higher than 99% within 110min of irradiation at concentrations up to 537ppmv.

Preparation, structural characterization and photocatalytic activity of mesoporous Ti-silicates

This paper focuses on structural and photocatalytic properties of ordered mesoporous Ti-silicates, prepared by both impregnation (IMP) and coprecipitation (CP) methods. Catalyst characterization was carried out by inductively coupled plasma analysis, nitrogen adsorption–desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX). Photocatalytic activity was evaluated for gaseous trichloroethylene (TCE) decomposition in a batch reactor under near-UV irradiation.Both the Ti incorporation method (IMP or CP) and TiO2 content (4.7–35.0wt.%) had large effects on structural characteristics and photocatalytic activity of Ti-silicates, whereas no important effects were observed with respect to calcination temperature (200–600°C). At all conditions, TiO2 was present as pure anatase crystallites with particle diameters in IMP catalysts of 4.4–7.0nm, being clearly smaller than those in CP ones (12.0–19.6nm). The ordered structure of the silica was at least partially preserved up to a TiO2 content of 25wt.% (CP) and 33wt.% (IMP). With increasing TiO2 content, specific surface area (SSA 376–805m2g−1) of both CP and IMP catalysts decreased. Similar trends were observed for pore volumes (0.6–1.2mLg−1) and pore diameters (4.5–7.5nm) in IMP catalysts. Initial photocatalytic TCE degradation rate constants (0.014–0.202min−1) obtained with CP catalysts increased systematically with TiO2 contents up to 35wt.%, while in IMP ones, they levelled off at TiO2 contents above 17wt.%. TCE degradation rates obtained with CP catalysts were up to a factor of six higher than those measured applying the IMP method. This may be explained by a different TiO2 localization in the silica structure. During IMP preparation, TiO2 is mostly incorporated within the silica mesopores, whereas during CP synthesis, it is mainly localized on the external silica surface.

Oxidative Degradation and Toxicity Reduction of Trichloroethylene (TCE) in Water Using TiO2/Solar Light: Comparative Study of TiO2 Slurry and Immobilized Systems

A solar–driven, photocatalyzed degradation system using TiO2 slurry and immobilized systems was constructed and applied to the degradation of trichloroethylene (TCE) contaminated water using TiO2 with solar light. The experiments were carried out under constant weather conditions on a sunny day. Solar photocatalytic treatment efficiency of the solar light/TiO2 slurry system was compared with that of the solar light/TiO2 immobilized system. The operation of the solar light/TiO2 slurry and immobilized systems showed 100% (TiO2 slurry system), 80% (TiO2 immobilized system) degradation of the TCE after 6 h, with a chloride production yield of approximately 89% (TiO2 slurry system), 72% (TiO2 immobilized system). The oxidants such as H2O2 and S2O8 2 – in the TiO2 slurry and immobilized systems increased TCE degradation rate by suppressing the electron/hole recombination process. The degradation rate and relative toxicity reduction of TCE followed the order of solar light/TiO2 slurry+ S2 O8 2 –> solar light/TiO2 slurry+ H2 O2> solar light/TiO2 immobilized+ S2 O8 2 – > solar light/TiO2 slurry> solar light/TiO2 immobilized+ H2 O2> solar light/TiO2 immobilized. Finally, following to the toxicity result, the acute toxicity was reduced by below toxicity endpoint (EC50 concentration) following the treatment. It means that many of the metabolites of TCE reduction are less toxic to Vibrio fischeri than the parent compound. Based on these results, TCE can be efficiently and safely treated in a solar–driven, photocatalyzed degradation system.

The effect of salinity on trichloroethylene co-metabolism by mixed cultures enriched on phenol

This work examines the effects of salinity on the biodegradation of trichloroethylene (TCE) by four chemostat-cultivated cultures: LHPO-3, LHPO-6, HHPO-3 and HHPO-6, all of which had been enriched on phenol but grown under different conditions. Cultures LHPO-3 (with hydraulic retention time [HRT] of 3.1 days) and LHPO-6 (6.5-day HRT) were cultivated with fresh water, whereas cultures HHPO-3 (3.3-day HRT) and HHPO-6 (6.1-day HRT) were cultivated with seawater. Batch tests of TCE degradation by the four bacterial consortia in the absence of phenol were undertaken in solutions with salinities in the range 0–3.28% (w/v). Moreover, the effect of adding phenol on TCE degradation by LHPO-3 in 1.64% salinity solution was investigated. The results showed that the observed bacterial yields for the cultures LHPO-3, LHPO-6, HHPO-3 and HHPO-6 were 0.66, 0.47, 0.58 and 0.33 mg volatile suspended solids/mg phenol, respectively. In the absence of phenol, the extents of TCE degradation by cultures LHPO-3 and LHPO-6 increased with salinity stress, reaching 0.052 mg TCE/mg VSS for LHPO-3 and 0.033 mg TCE/mg VSS for LHPO-6, and then declined as salinity increased further. The tolerance of TCE degradation to salinity for culture LHPO-3 was around 3.28% and that for LHPO-6 was 1.64–2.33%. In the presence of phenol, the rate and extent of TCE degradation by LHPO-3 were enhanced when an optimal dosage of phenol of 10 mg phenol/mg TCE was applied. Degradation of TCE by cultures HHPO-3 and HHPO-6 was not observed.

Recovery of trichloroethylene removal efficiency through short-term toluene feeding in a biofilter enriched withPseudomonas putida F1

Trichloroethylene (TCE) is an environmental contaminant provoking genetic mutation and damages to liver and central nerve system even at low concentrations. A practical scheme is reported using toluene as a primary substrate to revitalize the biofilter column for an extended period of TCE degradation. The rate of trichloroethylene (TCE) degradation byPseudomonas putida F1 at 25°C decreased exponentially with time, without toluene feeding to a biofilter column (11 cm I.D.×95 cm height). The rate of decrease was 2.5 times faster at a TCE concentration of 970 μg/L compared to a TCE concentration of 110 μg/L. The TCE itself was not toxic to the cells, but the metabolic intermediates of the TCE degradation were apparently responsible for the decrease in the TCE degradation rate. A short-term (2 h) supply of toluene (2,200 μg/L) at an empty bed residence time (EBRT) of 6.4 min recovered the relative column activity by 43% when the TCE removal efficiency at the time of toluene feeding was 58%. The recovery of the TCE removal efficiency increased at higher incoming toluene concentrations and longer toluene supply durations according to the Monod type of kinetic expression. A longer duration (1.4∼2.4 times) of toluene supply increased the recovery of the TCE removal efficieny by 20% for the same toluene load.

Effect of cyclodextrins on iron-mediated dechlorination of trichloroethylene — A proposed new mechanism

This paper evaluates the possibility of using cyclodextrins (CDs) as solubility-enhancing agents that could be employed to increase the rate of the mass delivery of trichloroethylene (TCE) to an iron wall where dechlorination will occur. Dechlorination of TCE by zero-valent iron was performed in the absence and in the presence of CDs in batch (static) and column (dynamic) systems. The presence of CDs slowed the overall degradation of TCE. The effect of various concentrations of different CDs on the rate of TCE degradation was evaluated, and it was found that as the CD concentration increased, reaction rate decreased. However, the overall decrease in reaction rate could not be explained solely on the basis of TCE:CD host-guest complexation. A novel mechanism involving CD binding to the iron surface, in addition to TCE:CD complexation, was proposed, and this enabled satisfactory interpretation of the kinetic data. A central feature of the proposal is that Fe:CD binding impedes electron transfer from the underlying iron metal to the TCE molecule. The overall rate of TCE degradation by zero-valent Fe in the presence of CDs is governed by several factors: the extent of binding of CD with the iron surface, the binding constant between CD and TCE, and the degradation of complexed TCE (TCE:CD), where CD is, in turn, associated with the iron surface. It appeared that CD binding to the iron surface depends largely on the type of substituent groups present in the β-CD derivatives as well as their degree of substitution. Association constants for the Fe:CD interaction were determined. The new hypothesis explained well both batch and column data, and the magnitude of Fe:CD binding constants was found to be similar in the two systems. Key words: cyclodextrin, trichloroethylene, zero-valent iron, reductive dechlorination.

High-frequency, high-power ultrasonic chemical reactors

A novel high-frequency (612 kHz), high-power (4 kW), pilot-plant scale sonochemical reactor was developed and used to study the degradation of organic chemical pollutants in aqueous solutions. The degradation rates of trichloroethylene, dichloromethane, and phenol were found to exceed those of similar frequency, small-scale bench reactors by factors ranging from 2.5 to 7. In addition, there is linear dependence between the observed sonolytic rate constants and the applied power density. The addition of ozone during sonication did not affect the first-order degradation rate constants for phenol degradation compared to the linear combination of sonication and ozonation. However, enhancement in the degradation rates of the total organic carbon (TOC) were observed. The enhanced reactivity of sonolysis coupled with ozonation is due to the sonolytic formation of hydrogen peroxide in water, which in turn reacts with ozone to form a highly reactive ozonide intermediate, dihydrogen trioxide, that reacts in a similar fashion to hydroxyl radical. However, its lifetime in aqueous solution is found to be substantially longer, and thus it is more likely to react with refractory organic compound fragments.

Biofiltration of Trichloroethylene-Contaminated Air: A Pilot Study

This project demonstrated the biofiltration of a trichloroethylene (TCE)-contaminated airstream generated by air stripping groundwater obtained from several wells located at the Anniston Army Depot, Anniston, AL. The effects of several critical process variables were investigated to evaluate technical and economic feasibility, define operating limits and preferred operating conditions, and develop design information for a full-scale biofilter system. Long-term operation of the demonstration biofilter system was conducted to evaluate the performance and reliability of the system under variable weather conditions. Propane was used as the primary substrate necessary to induce the production of a nonspecific oxygenase. Results indicated that the process scheme used to introduce propane into the biofiltration system had a significant impact on the observed TCE removal efficiency. TCE degradation rates were dependent on the inlet contaminant concentration as well as on the loading rate. No microbial inhibition was observed at inlet TCE concentrations as high as 87 parts per million on a volume basis.

Microemulsion and solution approaches to nanoparticle iron production for degradation of trichloroethylene

Abstract In this study, nanoscale iron particles were synthesized using the microemulsion method and the properties were compared with the particles produced by the solution method. The nanoparticles were characterized by using the transmission electron microscope (TEM) and powder X-ray diffraction (XRD) . The water-in-oil (w/o) microemulsion system was made up of n-octane, cetyltrimethyl-ammonium bromide (CTAB), butanol and water, and was characterized by measuring the conductivity of the solution and interfacial tension between the surfactant solution and the n-octane. The conductivity of the microemulsion system increased from about 10 μs cm −1 to over thousands of μs cm −1 with the addition of water. Interfacial tension between the n-octane and the CTAB aqueous solution was reduced to less than 6 dyn cm −1 with the addition of butanol, a co-surfactant used in this study. The average diameter of synthesized iron nanoparticles using the microemulsion method was less than 10 nm, which was much smaller than the particles produced by the solution method. The performance of the nanoiron produced in the laboratory was studied by dechlorinating trichloroethylene (TCE), a dense non-aqueous phase liquid (DNAPL) and listed as a priority pollutant by the US EPA. The degradation rate of TCE by the nano iron particles produced in the laboratory was quantified and compared with a commercially available nano iron product.

Study on the gas-phase photolytic and photocatalytic oxidation of trichloroethylene

Direct sampling mass spectrometer was used to study photolytic and photocatalytic oxidation of trichloroethylene (TCE) in gas-phase. The experiments were conducted under UV lamps with 365 nm (black lamp) and 253.7 nm (germicidal lamp) dominant wavelength, respectively, in the presence or absence of TiO 2. Concentrations of TCE and CO 2 were detected quantitatively. Mass spectrograph peaks of the documented intermediates and products were detected on-line during the process of photolysis and photocatalysis of TCE. The results indicated that TCE could be directly photodegraded under the irradiation of germicidal lamp, but black lamp could hardly work on TCE by photolysis. This photolytic degradation rate of TCE was much quicker than that of photocatalysis for the same irradiation intensity of germicidal lamp. The products and intermediates detected showed that both photolysis and photocatalysis of TCE were dominated by a free-radical-offence mechanism.

Characterization and Performance of Granular Iron as Reactive Media for TCE degradation by Permeable Reactive Barriers

The application of Permeable Reactive Barriers (PRBs), an innovative clean-up technology for in-situ groundwater remediation, represents an effective alternative to traditional pump-and-treat systems and has raised strong interest during recent years. From recent statistics of the Italian Water Research Institute (IRSA), trichloroethylene (TCE) from industrial activities is the most widespread contaminant in groundwater. The goal of the research was to test the suitability and performance of a high purity granular iron reactive medium for TCE degradation by PRBs. The suitability was evaluated based on chemical and physical characteristics of the material and the performance of the granular iron, in terms of TCE removal efficiency, was evaluated by column tests.The experimental results showed that the characteristics of the granular iron are suitable for application as a reactive medium, since the hydraulic conductivity values were fully consistent with those reported in the literature, and the leaching tests indicated a reduced release of heavy metals. The overall removal efficiency of TCE was higher than 97% in all the tests performed at the flow rate of 0.25 cm3 min-1 (corresponding to a groundwater flow velocity of 0.37 m d-1) both for the 100% iron and the iron-sand columns. Moreover, TCE degradation around 60% was observed even in the first section of the columns fortypical groundwater flow velocity. The TCE reduction in the outlet stream was confirmed by the assessment of chlorine mass balance and by the absence of any reaction intermediate detected by GC-MS.Finally, the concentration profiles in the columns were not in agreement with those expected for a chemistry-controlled kinetic regime. This suggests that TCE degradation rate may have been limited by precipitation phenomena, hindering the contaminant transport to the iron surface.

Kinetic Study of Trichloroethylene Biodegradation by Methylosinus trichosporium OB3b PP358 lmmobilized in a Fibrous-Bed Bioreactor

Biodegradation of trichloroethylene (TCE) by resting cells of methanotrophic Methylosinus trichosporium OB3b PP358, which constitutively expresses soluble methane monooxygenase (sMMO), was studied in a fibrous-bed bioreactor operated in the recycle batch mode. Cells were grown on methane as the substrate with aeration, and then used to degrade TCE through the cometabolism with sMMO in the absence of methane. Complete biodegradation of TCE was verified with the TCE and chloride ion mass balance. In general, concentration of up to ~12 mg/l, and followed the first-order reaction kinetics. TCE transformation was inhibited in the presence of methane or methanol. Without the energy source and after being exposed to TCE for an extended period, cells gradually lost most of their capability in degrading TCE, which was attributed to reduced sMMO enzyme activity due to lack of NADH and cell death caused by TCE toxicity and oxygen starvation. However, the reactor was able to recover its TCE degradation ability after rejuvenating and regrowing cells with methane and air. Compared to free cell and other immobilized cell systems, the cells immobilized in the fibrous-bed bioreactor not only showed a much higher TCE degradation rate (up to 84.77 mg/(1 day) or ~32 times of that from free cells), but also had a better tolerance to TCE (22.6 mg/l or ~11 times higher than that with free cells). With periodical rejuvenation, the bioreactor could be used for long-term treatment of TCE-contaminated water.

Effect of sorption and desorption resistance on aerobic trichloroethylene biodegradation in soils

Biodegradation of trichloroethylene (TCE) by toluene-degrading bacteria was measured under aerobic conditions in aqueous and soil-slurry batch microcosms. For soil-phase experiments, a freshly contaminated soil and a soil containing only the desorption-resistant fraction of TCE were tested. In both cases, presence of soil resulted in biodegradation rates substantially lower than those determined in the absence of soil. In aqueous-phase experiments, an appreciable increase in the rate and extent of TCE biodegradation was observed in microcosms when toluene was added multiple times. The TCE degradation rates were clearly correlated with toluene dioxygenase (TOD) enzyme activity over time, thus providing an indication of the cometabolic pathway employed by the microbial population. In soil-slurry experiments containing freshly contaminated soil, a TCE degradation rate of approximately 150 microg TCE/kg/h was observed during the first 39-h period, and then the TCE degradation rate slowed considerably to 0.59 and 0.84 microg TCE/kg/h for microcosms receiving one and two additions of toluene, respectively. The TCE degradation rates in soil-slurry microcosms containing the desorption-resistant fraction of TCE-contaminated soil were approximately 0.27 and 0.32 microg TCE/kg/h in microcosms receiving one and two additions of toluene, respectively. It is clear from these results that mass transfer into the aqueous phase limited bioavailability of TCE in the contaminated soil.