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.     

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.     

Treatment of waste gas containing diethyldisulphide (DEDS) in a bench scale biofilter

Waste gas containing diethyldisulphide (DEDS) is generated from various industries including pulp and paper, refinery, rayon and molasses based distilleries, etc. DEDS has odour threshold detection with an average concentration of 10(-9)mg/m(3) at 25 degrees C. DEDS is toxic to bacteria, fungus and also to mammals when exposed for a long period. Waste gas containing DEDS require proper treatment prior to discharge into the environment. DEDS containing waste gas was treated in a biofilter, packed with compost along with wooden chips and enriched with DEDS degrading microorganisms. The biofilter could remove DEDS to the extent of 94+/-5% at a loading of 1.60 g/m(3)/h with an empty bed retention time of 150s. At optimal operating conditions, the average moisture content required by the biofilter was in the range of 60-65%. The biodegradative products of DEDS were thiosulphate and sulphate.     

Low and high acetate amendments are equally as effective at promoting complete dechlorination of trichloroethylene (TCE)

Experiments with trichloroethylene-contaminated aquifer material demonstrated that TCE, cis-DCE, and VC were completely degraded with concurrent Fe(III) or Fe(III) and sulfate reduction when acetate was amended at stoichiometric concentration; competing TEAPs did not inhibit ethene production. Adding 10× more acetate did not increase the rate or extent of TCE reduction, but only increased methane production. Enrichment cultures demonstrated that ~90 μM TCE or ~22 μM VC was degraded primarily to ethene within 20 days with concurrent Fe(III) or Fe(III) + sulfate reduction. The dechlorination rates were comparable between the low and high acetate concentrations (0.36 vs 0.34 day^?1, respectively), with a slightly slower rate in the 10× acetate amended incubations. Methane accumulated to 13.5 (±0.5) μmol/tube in the TCE-degrading incubations with 10× acetate, and only 1.4 (±0.1) μmol/tube with low acetate concentration. Methane accumulated to 16 (±1.5) μmol/tube in VC-degrading enrichment with 10× acetate and 2 (±0.1) μmol/tube with stoichiometric acetate. The estimated fraction of electrons distributed to methanogenesis increased substantially when excessive acetate was added. Quantitative PCR analysis indicated that 10× acetate did not enhance Dehalococcoides biomass but rather increased the methanogen abundance by nearly one order of magnitude compared to that with stoichiometric acetate. The data suggest that adding low levels of substrate may be equally if not more effective as high concentrations, without producing excessive methane. This has implications for field remediation efforts, in that adding excess electron donor may not benefit the reactions of interest, which in turn will increase treatment costs without direct benefit to the stakeholders.     

Development and operation of a trickling biofilter system for continuous treatment of gas-phase trichloroethylene

A parallel trickling biofilter (TBF) system that consists of two TBFs units in parallel, one for biodegradation of trichloroethylene (TCE) and the other for reactivation of an inactivated biofilm, was developed and operated for continuous treatment of gas-phase TCE by Burkholderia cepacia G4. For inlet loadings below 8.6 mg TCE l^–1 d^–1, complete removal of TCE was achieved. The maximal TCE elimination capacity was 17 mg l^–1 d^–1.     

Experiments and three phase modelling of a biofilter for the removal of toluene and trichloroethylene

Volatile organic compounds, namely, toluene, trichloroethylene, styrene, etc., disposed off by electronics and polymer industries, are very harmful. The treatment of VOC laden air through biochemical route is one of the potential options for reduction of their concentration in parts per million or parts per billion level. Under the present investigation, a 0.05-m diameter and 0.58-m high trickle bed biofilter has been studied for the removal of VOCs namely toluene and trichloroethylene from a simulated air–VOC mixture using pure strain of Pseudomonas putida (NCIM2650) in immobilized form. Inlet concentrations of VOCs have been varied in two ranges, the lower being 0.20–2.00 g/m³ and higher being 10–20 g/m³, respectively. The Monod type rate kinetics of removal of VOCs has been determined. A three-phase deterministic mathematical model has been developed taking the simultaneous reaction kinetics and interphase (gas to liquid to biofilm) mass transfer rate of VOCs into consideration. Experimentally determined kinetic parameters and mass transfer coefficients calculated using standard correlations have been used. Concentrations have been simulated for all the three phases. Simulated results based on the model have been compared with the experimental ones for both gas and liquid phases satisfactorily. The mathematical model validated through the successful comparison with experimental data may be utilized for the prediction of performance of biofilters undergoing removal of different VOCs in any further investigation and may be utilized for the scale-up of the system to industrial scale.     

Selection of trichloroethene (TCE) degrading bacteria that resist inactivation by TCE

Two isoprene (2-methyl-1,3-butadiene) utilizing bacteria, Alcaligenes denitrificans ssp. xylosoxidans JE 75 and Rhodococcus erythropolis JE 77, were identified as highly efficient cooxidizers of TCE, cis- and transdichloroethene, 1,1-dichloroethene and vinylchloride. Isoprene grown cells eliminate chloride from TCE in stoichiometric amounts and tolerate high concentrations of TCE.     

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.     

Enhanced sulfate reduction and trichloroethylene (TCE) biodegradation in a UASB reactor operated with a sludge developed from hydrothermal vents sediments: Process and microbial ecology

Most Trichloroethylene (TCE) biodegradation reports refer to methanogenic conditions, however, in this work, enhanced sulfidogenesis and TCE biodegradation were achieved in an upflow anaerobic sludge blanket (UASB) reactor in which a completely sulfidogenic sludge, from hydrothermal vents sediments, was developed. The work was divided in three stages, (i) sludge development and sulfate reducing activity (SRA) evaluation, (ii) TCE biodegradation and (iii) SRA evaluation after TCE biodegradation. For (i) SR was 98 ± 0.1%, 84% as sulfide (H₂S, 1200 ± 28 mg/L), sulfate reducing activity (SRA) was 188 ± 50 mg COD H₂S/g VSS*d. For (ii) The reactor reached 74% of TCE removal, concentrations of vinyl chloride of 16 ± 0.3 μM (5% of the TCE added) and ethene 202 ± 81 μM (67% of the TCE added), SRA of 161 ± 7 mg COD H₂S/g VSS*d, 68% of sulfide (H₂S) production and 93% of COD removal. For (iii) SRA was of 248 ± 22 mg COD H₂S/g VSS*d demonstrating no adverse effects due to TCE.Among the genera of the microorganisms identified in the sludge during TCE biodegradation were: Dehalobacter, Desulfotomaculum, Sulfospirillum, Desulfitobacterium, Desulfovibrio and Clostridium. To the best of our knowledge, this is the first report using a sulfidogenic UASB reactor to biodegrade TCE. The overall conclusions of this work are that the reactor is efficient on both, sulfate and TCE biodegradation and it could be used to decontaminate wastewater containing organic solvents and relatively high concentrations of sulfate.     

Biocatalytic dechlorination of trichloroethylene with bio-palladium in a pilot-scale membrane reactor

Trichloroethylene (TCE) is a toxic and recalcitrant groundwater pollutant. An innovative technology using microbial produced Pd(0) nanoparticles for the remediation of TCE contaminated groundwater was developed. The nanoscale bio-Pd particles were precipitated on the biomass of Shewanella oneidensis and hydrogen gas, formate, or formic acid were used as hydrogen donors. Ethane turned out to be the only organic degradation product and no intermediate chlorinated reaction products were detected. Subsequently bio-Pd was implemented in a plate membrane reactor (MR) for the treatment of water containing TCE. In a continuous MR system, containing 50 mg L(-1) bio-Pd, removal rates up to 2,515 mg TCE day(-1) g(-1) Pd were achieved with H(2) gas as hydrogen donor. The measured chloride mass balance confirmed the removal rates. This work shows that a complete, efficient and rapid removal of TCE was achieved with bio-Pd and that a MR system containing bio-Pd and supplied with hydrogen gas offers an alternative for the current remediation technologies of water contaminated with TCE.     

Autotrophic denitrification by nitrate-dependent Fe(II) oxidation in a continuous up-flow biofilter

A continuous-upflow biofilter packed with sponge iron was constructed for nitrate removal under an anaerobic atmosphere. Microbacterium sp. W5, a nitrate reducing and Fe(II) oxidizing strain, was added to the biofilter as an inoculum. The best results were achieved when NO₃ ^?-N concentration was 30 mg/L and Fe²⁺ was 800 mg/L. Nitrite in influent would inhibit nitrate removal and aqueous Fe²⁺ resulted in encrustation. Fe(II)EDTA would prevent cells from encrustation and the maximum nitrogen removal efficiency was about 90 % with Fe(II)EDTA level of 1100 mg/L. Nitrate reduction followed first-order reaction kinetics. Characteristics of biofilms were analyzed by X-ray fluorescence spectroscopy.     

Demonstration of efficient trichloroethylene biodegradation in a hollow‐fiber membrane bioreactor

Rapid cometabolism of trichloroethylene (TCE) by pure cultures of Methylosinus trichosporium OB3b PP358 was demonstrated in a two‐stage hollow‐fiber membrane bioreactor over the course of 3 weeks. PP358 was grown in a continuous‐flow chemostat and circulated through the shell of a hollow‐fiber membrane module (HFMM), while TCE contaminated water (160 to 1450 μg/L) was pumped through the fiber lumen (fiber interior). In parallel‐flow HFMM biological experiments, 82% to 89% of the influent TCE was removed from the lumen (5.1‐min residence time) with 99% of the transferred TCE undergoing biodegradation. Biological experiments in a larger capacity baffled radial‐flow HFMM resulted in 66% to 99% TCE transferred and 93% to 96% TCE biodegradation at lumen residence times of between 1.5 and 3.7 min. Biodegradation was maintained throughout the experiments at pseudo‐first‐order biodegradation rate constants of 0.41 to 2.8 L/mg TSS/day. Best‐fit computer modeling of the baffled radial‐flow biological process estimated mass transfer coefficients as large as 2.7 × 10⁻² cm/min. The computer model was also shown to simulate the experimental results quite well. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 62: 681–692, 1999.     

Phreatophyte influence on reductive dechlorination in a shallow aquifer contaminated with trichloroethene (TCE)

Phytoremediation uses the natural ability of plants to degrade contaminants in groundwater. A field demonstration designed to remediate aerobic shallow ground‐water contaminated with trichloroethene began in April 1996 with the planting of cottonwood trees, a short‐rotation woody crop, over an approximately 0.2‐ha area at the Naval Air Station, Fort Worth, Texas. The project was developed to demonstrate capture of contaminated groundwater and degradation of contaminants by phreatophytes. Analyses from samples of groundwater collected from July 1997 to June 1998 indicate that tree roots have the potential to create anaerobic conditions in the groundwater that will facilitate degradation of trichloroethene by microbially mediated reductive dechlorination. Organic matter from root exudates and decay of tree roots probably stimulate microbial activity, consuming dissolved oxygen. Dissolved oxygen concentrations, which varied across the site, were smallest near a mature cottonwood tree (about 20 years of age and 60 meters southwest of the cottonwood plantings) where degradation products of trichloroethene were measured. Oxidation     

Acetone biodegradation in a trickle-bed biofilter

Laboratory scale-studies on acetone biodegradation in a trickle-bed biofilter were carried out using using two identically sized columns, one of which was packed with coconut fibre and the other with plexiglass chips. The columns were inoculated with two strains of bacteria: Burkholderia cepacia (syn. Pseudomonas cepacia) and Acinetobacter baumannii. The continuous process of air purification was carried out at incremental acetone concentrations from 0.3 to 2.5 g m⁻³ air and air flow-rates from 0.1 to 0.3 m³ h⁻¹. A maximum acetone elimination capacity of 95.8 g m⁻³ filter bed h⁻¹ was achieved at air flow-rate of 36 m h⁻¹.     

Biodegradation of ethanol vapour in a biofilter

Biofiltration is a cost effective air pollution control technology for volatile organic compounds. Biofiltration of ethanol vapour from air stream was evaluated in this study. Experimental investigations were conducted on a laboratory scale biofilter, containing mixture of compost and polystyrene inert particles as the filter materials. Mixed consortium of activated sludge was used as a inoculum. The continuous performance of biofilter for ethanol removal was monitored for different concentrations and flow rates. The removal efficiencies decreased at higher concentrations and higher gas flow rates. A maximum elimination capacity of 195 g m^х h^у was achieved. The response of biofilter to shut down and restart-up operation showed that the biofilm has got a good stability.     

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.