Response surface optimization of dissolved oxygen and nitrogen sources for the biodegradation of MTBE and BTEX

Response surface methodology (RSM) using central composite design was applied to obtain the optimal dissolved oxygen (DO) and nitrogen (N) concentrations for biodegrading MTBE (Methyl tert-butyl ether) and BTEX (benzene, ethylbenzene, toluene, p-xylene). Moreover, the effects of DO, N, and their interaction on the degradation process were evaluated. It was found that N, N², DO and DO² have significant effects on the efficiency of MTBE and BTEX removal. The removal efficiency when using biostimulation with bioaugmentation (BwB) is higher than with other processes, being greater than 82% at concentrations of 12 and 48 mg l⁻¹ for DO and N, respectively. However, it was also found that the interaction term of DO × N has no significant effect on the degradation processes.     

Degradation of BTEX compounds in liquid media and in peat biofilters

A mixed culture, enriched from Sphagnum peat moss, contaminated with gasoline vapours, degraded individual and mixed components of BTEX (benzene, toluene, ethylbenzene, xylene). Complete degradation of radiolabelled toluene by the mixed culture was observed in mineralisation studies. Individual isolates from a mixed culture containingPseudomonas maltophilia, P. testosteroni andP. putida biotype A exhibited contrasting BTEX degradation patterns. WhileP. putida biotype A degraded all of the BTEX compounds,P. maltophilia andP. testosteroni, appeared unable to degrade benzene and xylenes, respectively. When the peat, inoculated with the mixed culture, was used as a biofilter (6.2 cm diameter ×93 cm length) for degradation of toluene and ethylbenzene vapours, percentage removal efficiencies were 99 and 85, respectively. When the capacity of the biofilter to degrade a combination of BTEX compounds was evaluated, percentage removal efficiencies for toluene, ethylbenzene,p-xylene,o-xylene and benzene were 99, 85, 82, 80 and 78, respectively. The importance of using the mixed culture as an inoculum in the biofilter was established and also the relationship between contaminated vapour flow rate and percentage removal efficiency.     

Mesophilic and thermophilic BTEX substrate interactions for a toluene-acclimatized biofilter

Benzene, toluene, ethylbenzene and xylene (BTEX) substrate interactions for a mesophilic (25°C) and thermophilic (50°C) toluene-acclimatized composted pine bark biofilter were investigated. Toluene, benzene, ethylbenzene, o-xylene, m-xylene and p-xylene removal efficiencies, both individually and in paired mixtures with toluene (1:1 ratio), were determined at a total loading rate of 18.1 g m^–3 h^–1 and retention time ranges of 0.5–3.0 min and 0.6–3.8 min for mesophilic and thermophilic biofilters, respectively. Overall, toluene degradation rates under mesophilic conditions were superior to degradation rates of individual BEX compounds. With the exception of p-xylene, higher removal efficiencies were achieved for individual BEX compounds compared to toluene under thermophilic conditions. Overall BEX compound degradation under mesophilic conditions was ranked as ethylbenzene >benzene >o-xylene >m-xylene >p-xylene. Under thermophilic conditions overall BEX compound degradation was ranked as benzene >o-xylene >ethylbenzene >m-xylene >p-xylene. With the exception of o-xylene, the presence of toluene in paired mixtures with BEX compounds resulted in enhanced removal efficiencies of BEX compounds, under both mesophilic and thermophilic conditions. A substrate interaction index was calculated to compare removal efficiencies at a retention time of 0.8 min (50 s). A reduction in toluene removal efficiencies (negative interaction) in the presence of individual BEX compounds was observed under mesophilic conditions, while enhanced toluene removal efficiency was achieved in the presence of other BEX compounds, with the exception of p-xylene under thermophilic conditions.     

Bioremediation Assessment of a BTEX‐Contaminated Soil

The elimination of BTEX (benzene, toluene, ethylbenzene, o‐xylene) compounds from soil was studied. After 18 days at 20 °C, 21% of the initial total BTEX contamination (400 mg/kg soil) was lost due to sorption onto soil. Biodegradation decreased in the order ethylbenzene > toluene > benzene > o‐xylene. NPK fertilisation stimulated biodegradation, particularly that of benzene and toluene, significantly, and oleophilic fertilisation inhibited biodegradation. After 18 days, the residual contamination in the NPK‐fertilised, unfertilised and with oleophilic nutrients amended soil was 96, 166 and 196 mg total BTEX/kg soil, respectively. The presence of BTEX initially inhibited the biological activity of the soil (fluorescein diacetate hydrolysis) considerably. This short‐term, reversible inhibition was significantly higher in the unfertilised soil than in the fertilised soil.     

Bioremediation of benzene,toluene, ethylbenzene,xylenes-contaminated soil: a biopile pilot experiment

Aims: In this study, we evaluated the removal efficiency of fuel hydrocarbons from a jet fuel contaminated area using bioaugmentation treatment in biopile. Methods and Results: The hydrocarbon analysis of the sample revealed total hydrocarbons mainly constituted by benzene, toluene, ethylbenzene, xylenes (BTEX) and heavy aliphatic hydrocarbons. Enrichments of soil sample were performed with BTEX, pristane and fuel JP-5, respectively, selected hydrocarbon-degrading strains, namely Acinetobacter sp., Pseudomonas sp. and Rhodococcus sp. Three hundred litres of culture containing 10⁸ cell ml⁻¹ of each strain and nutrients sprayed on the biopile allowed a removal of 90% of total hydrocarbons in 15 days. Bioremediation process was monitored by observation of the respiration rate and the bacterial abundance and GC-MS analysis. Conclusions: The efficiency of the treatment in the biopile was considerable. The assessment of microbial activity during the experiment is necessary for interventions targeted to improve environmental parameters such as humidity, temperature, pH and nutrients for optimization of the bioremediation process. Significance and Impact of the Study: A better knowledge of microbial successions at oil-polluted sites is essential for environmental bioremediation. Data obtained in biopile study improve our understanding of processes occurring during oil pollution.     

Kinetics of BTEX biodegradation by a coculture of <Emphasis Type="Italic">Pseudomonas putida</Emphasis> and<Emphasis Type="Italic"> Pseudomonas fluorescens</Emphasis> under hypoxic conditions

Pseudomonas putida and Pseudomonas fluorescens present as a coculture were studied for their abilities to degrade benzene, toluene, ethylbenzene, and xylenes (collectively known as BTEX) under various growth conditions. The coculture effectively degraded various concentrations of BTEX as sole carbon sources. However, all BTEX compounds showed substrate inhibition to the bacteria, in terms of specific growth, degradation rate, and cell net yield. Cell growth was completely inhibited at 500mgl^–1 of benzene, 600mgl^–1 of o-xylene, and 1000mgl^–1 of toluene. Without aeration, aerobic biodegradation of BTEX required additional oxygen provided as hydrogen peroxide in the medium. Under hypoxic conditions, however, nitrate could be used as an alternative electron acceptor for BTEX biodegradation when oxygen was limited and denitrification took place in the culture. The carbon mass balance study confirmed that benzene and toluene were completely mineralized to CO₂ and H₂O without producing any identifiable intermediate metabolites.     

Biodegradation of benzene,toluene, ethylbenzene,and o-xylene by a coculture of Pseudomonas putida and Pseudomonas fluorescens immobilized in a fibrous-bed bioreactor

A fibrous-bed bioreactor containing the coculture of Pseudomonas putida and P. fluorescens immobilized in a fibrous matrix was developed to degrade benzene (B), toluene (T), ethylbenzene (E), and o-xylene (X) in synthetic waste streams. The kinetics of BTEX biodegradation by immobilized cells adapted in the fibrous-bed bioreactor and free cells grown in serum bottles were studied. In general, the BTEX biodegradation rate increased with increasing substrate concentration and then decreased after reaching a maximum, showing substrate-inhibition kinetics. However, for immobilized cells, the degradation rate was much higher than that of free cells. Compared to free cells, immobilized cells in the bioreactor tolerated higher concentrations (>1000 mg l⁻¹) of benzene and toluene, and gave at least 16-fold higher degradation rates for benzene, ethylbenzene, and o-xylene, and a 9-fold higher degradation rate for toluene. Complete and simultaneous degradation of BTEX mixture was achieved in the bioreactor under hypoxic conditions. Cells in the bioreactor were relatively insensitive to benzene toxicity; this insensitivity was attributed to adaptation of the cells in the bioreactor. Compared to the original seeding culture, the adapted cells from the fibrous-bed bioreactor had higher specific growth rate, benzene degradation rate, and cell yield when the benzene concentration was higher than 100 mg l⁻¹. Cells in the fibrous bed had a long, slim morphology, which is different from the normal short-rod shape found for suspended cells in solution.     

Determination of Mass Transfer Coefficients for A Mixture of Compost,Sugarcane Bagasse,and Granulated Activated Carbon as Packing Medium in Biofilter

ABSTRACT

A laboratory-scale biofilter unit packed with a mixture of compost, sugarcane bagasse, and granulated activated carbon (GAC) in the ratio of 55:30:15 by weight was used for a biofiltration study of air stream containing benzene, toluene, ethylbenzene, and o-xylene (BTEX). The effect of superficial velocity on mass transfer coefficient for the packing was studied by maintaining gas flow rates of 3, 4, 5, 6, and 8 L min^?1 for inlet concentrations of 0.1, 0.4, and 0.8 g m^?3 for each of benzene, toluene, ethylbenzene, and o-xylene. The maximum elimination capacity was found to be 20.92, 22.72, 20.73, and 18.94 g m^?3 h^?1 for BTEX, respectively, for stated flow rates. Removal efficiency of BTEX decreased from 99% to 71% for increasing inlet concentration from 0.1 to 0.8 g m^?3. Gas film mass transfer coefficient predicted by modified Onda's equation was within ±10% of the experimental values.     

Biodegradation of BTEX vapors in a silicone membrane bioreactor system

The biotreatment of complex mixtures of volatile organic compounds (VOCs) such as benzene, toluene, ethylbenzene, and xylene isomers (BTEX) has been investigated by many workers. However, the majority of the work has dealt with the treatment of aqueous or soil phase contamination. The biological treatment of gas and vapor phase sources of VOC wastes has recently received attention with increased usage of biofilters and bioscrubbers. Although these systems are relatively inexpensive, performance problems associated with biomass plugging, gas channeling, and support media acidification have limited their adoption. In this report we describe the development and evaluation of an alternative biotreatment system that allows rapid diffusion of both BTEX and oxygen through a silicone membrane to an active biofilm. The bioreactor system has a rapid liquid recycle, which facilitates nutrient medium mixing over the biofilm and allows for removal of sloughing cell mass. The system removed BTEX at rates up to 30 μg h⁻¹ cm⁻² of membrane area. BTEX removal efficiencies ranged from 75% to 99% depending on the BTEX concentration and vapor flowrate. Consequently, the system can be used for continuous removal and destruction of BTEX and other potential target VOCs in vapor phase streams. Journal of Industrial Microbiology & Biotechnology (2001) 26, 316–325. Received 14 August 2000/ Accepted in revised form 28 February 2001     

Thermophilic biodegradation of BTEX by two consortia of anaerobic bacteria

Two thermophilic anaerobic bacterial consortia (ALK-1 and LLNL-1), capable of degrading the aromatic fuel hydrocarbons, benzene, toluene, ethylbenzene, and the xylenes (BTEX compounds), were developed at 60 °C from the produced water of ARCO'S Kuparuk oil field at Alaska and the subsurface water at the Lawrence Livermore National Laboratory gasoline-spill site, respectively. Both consortia were found to grow at 45–75 °C on BTEX compounds as their sole carbon and energy sources with 50 °C being the optimal temperature. With 3.5 mg total BTEX added to sealed 50-ml serum bottles, which contained 30 ml mineral salts medium and the consortium, benzene, toluene, ethylbenze, m-xylene, and an unresolved mixture of o- and p-xylenes were biodegraded by 22%, 38%, 42%, 40%, and 38%, respectively, by ALK-1 after 14 days of incubation at 50 °C. Somewhat lower, but significant, percentages of the BTEX compounds also were biodegraded at 60 °C and 70 °C. The extent of biodegradation of these BTEX compounds by LLNL-1 at each of these three temperatures was slightly less than that achieved by ALK-1. Use of [ring-¹⁴C]toluene in the BTEX mixture incubated at 50 °C verified that 41% and 31% of the biodegraded toluene was metabolized within 14 days to water-soluble products by ALK-1 and LLNL-1, respectively. A small fraction of it was mineralized to ¹⁴CO₂. The use of [U-¹⁴C]benzene revealed that 2.6%–4.3% of the biodegraded benzene was metabolized at 50 °C to water-soluble products by the two consortia; however, no mineralization of the degraded [U-¹⁴C]benzene to ¹⁴CO₂ was observed. The biodegradation of BTEX at all three temperatures by both consortia was tightly coupled to sulfate reduction as well as H₂S generation. None was observed when sulfate was omitted from the serum bottles. This suggests that sulfate-reducing bacteria are most likely responsible for the observed thermophilic biodegradation of BTEX in both consortial cultures. Received: 12 July 1996 / Received revision: 31 December 1996 / Accepted: 31 January 1997     

Enhanced Anaerobic Biodegradation of Benzene-Toluene-Ethylbenzene-Xylene-Ethanol Mixtures in Bioaugmented Aquifer Columns

Methanogenic flowthrough aquifer columns were used to investigate the potential of bioaugmentation to enhance anaerobic benzene-toluene-ethylbenzene-xylene (BTEX) degradation in groundwater contaminated with ethanol-blended gasoline. Two different methanogenic consortia (enriched with benzene or toluene and o-xylene) were used as inocula. Toluene was the only hydrocarbon degraded within 3 years in columns that were not bioaugmented, although anaerobic toluene degradation was observed after only 2 years of acclimation. Significant benzene biodegradation (up to 88%) was observed only in a column bioaugmented with the benzene-enriched methanogenic consortium, and this removal efficiency was sustained for 1 year with no significant decrease in permeability due to bioaugmentation. Benzene removal was hindered by the presence of toluene, which is a more labile substrate under anaerobic conditions. Real-time quantitative PCR analysis showed that the highest numbers of bssA gene copies (coding for benzylsuccinate synthase) occurred in aquifer samples exhibiting the highest rate of toluene degradation, which suggests that this gene could be a useful biomarker for environmental forensic analysis of anaerobic toluene bioremediation potential. bssA continued to be detected in the columns 1 year after column feeding ceased, indicating the robustness of the added catabolic potential. Overall, these results suggest that anaerobic bioaugmentation might enhance the natural attenuation of BTEX in groundwater contaminated with ethanol-blended gasoline, although field trials would be needed to demonstrate its feasibility. This approach may be especially attractive for removing benzene, which is the most toxic and commonly the most persistent BTEX compound under anaerobic conditions.     

Enhanced anaerobic biodegradation of benzene-toluene-ethylbenzene-xylene-ethanol mixtures in bioaugmented aquifer columns

Methanogenic flowthrough aquifer columns were used to investigate the potential of bioaugmentation to enhance anaerobic benzene-toluene-ethylbenzene-xylene (BTEX) degradation in groundwater contaminated with ethanol-blended gasoline. Two different methanogenic consortia (enriched with benzene or toluene and o-xylene) were used as inocula. Toluene was the only hydrocarbon degraded within 3 years in columns that were not bioaugmented, although anaerobic toluene degradation was observed after only 2 years of acclimation. Significant benzene biodegradation (up to 88%) was observed only in a column bioaugmented with the benzene-enriched methanogenic consortium, and this removal efficiency was sustained for 1 year with no significant decrease in permeability due to bioaugmentation. Benzene removal was hindered by the presence of toluene, which is a more labile substrate under anaerobic conditions. Real-time quantitative PCR analysis showed that the highest numbers of bssA gene copies (coding for benzylsuccinate synthase) occurred in aquifer samples exhibiting the highest rate of toluene degradation, which suggests that this gene could be a useful biomarker for environmental forensic analysis of anaerobic toluene bioremediation potential. bssA continued to be detected in the columns 1 year after column feeding ceased, indicating the robustness of the added catabolic potential. Overall, these results suggest that anaerobic bioaugmentation might enhance the natural attenuation of BTEX in groundwater contaminated with ethanol-blended gasoline, although field trials would be needed to demonstrate its feasibility. This approach may be especially attractive for removing benzene, which is the most toxic and commonly the most persistent BTEX compound under anaerobic conditions.     

Substrate interactions during the biodegradation of BTEX and THF mixtures by Pseudomonas oleovorans DT4

The efficient tetrahydrofuran (THF)-degrading bacterium, Pseudomonas oleovorans DT4 was used to investigate the substrate interactions during the aerobic biotransformation of THF and BTEX mixtures. Benzene and toluene could be utilized as growth substrates by DT4, whereas cometabolism of m-xylene, p-xylene and ethylbenzene occurred with THF. In binary mixtures, THF degradation was delayed by xylene, ethylbenzene, toluene and benzene in descending order of inhibitory effects. Conversely, benzene (or toluene) degradation was greatly enhanced by THF leading to a higher degradation rate of 39.68 mg/(h g dry weight) and a shorter complete degradation time about 21 h, possibly because THF acted as an “energy generator”. Additionally, the induction experiments suggested that BTEX and THF degradation was initiated by independent and inducible enzymes. The transient intermediate hydroquinone was detected in benzene biodegradation with THF while catechol in the process without THF, suggesting that P. oleovorans DT4 possessed two distinguished benzene pathways.     

Metabolic diversity of aromatic hydrocarbon-degrading bacteria from a petroleum-contaminated aquifer

We characterized bacteria from contaminated aquifers for their ability to utilize aromatic hydrocarbons under hypoxic (oxygen-limiting) conditions (initial dissolved oxygen concentration about 2 mg/l) with nitrate as an alternate electron acceptor. This is relevant to current intense efforts to establish favorable conditions forin situ bioremediation. Using samples of granular activated carbon slurries from an operating groundwater treatment system, we isolated bacteria that are able to use benzene, toluene, ethylbenzene, orp-xylene as their sole source of carbon under aerobic or hypoxic-denitrifying conditions. Direct isolation on solid medium incubated aerobically or hypoxically with the substrate supplied as vapor yielded 10³ to 10⁵ bacteria ml^–1 of slurry supernatant, with numbers varying little with respect to isolation substrate or conditions. More than sixty bacterial isolates that varied in colony morphology were purified and characterized according to substrate utilization profiles and growth condition (i.e., aerobic vs. hypoxic) specificity. Strains with distinct characteristics were obtained using benzene compared with those isolated on toluene or ethylbenzene. In general, isolates obtained from direct selection on benzene minimal medium grew well under aerobic conditions but poorly under hypoxic conditions, whereas many ethylbenzene isolates grew well under both incubation conditions. We conclude that the conditions of isolation, rather than the substrate used, will influence the apparent characteristic substrate utilization range of the isolates obtained. Also, using an enrichment culture technique, we isolated a strain ofPseudomonas fluorescens, designated CFS215, which exhibited nitrate dependent degradation of aromatic hydrocarbons under hypoxic conditions.Abbreviations BTEX benzene, toluene, ethylbenzene, andp-xylene - HPLC high performance liquid chromatography - GAC granular activated carbon     

BTEX catabolism interactions in a toluene-acclimatized biofilter

BTEX substrate interactions for a toluene-acclimatized biofilter consortium were investigated. Benzene, ethylbenzene, o-xylene, m-xylene and p-xylene removal efficiencies were determined at a loading rate of 18.07 g m⁻³h⁻¹ and retention times of 0.5–3.0 min. This was also repeated for toluene in a 1:1 (m/m) ratio mixture (toluene: benzene, ethylbenzene, or xylene ) with each of the other compounds individually to obtain a final total loading of 18.07 g m⁻³h⁻¹. The results obtained were modelled using Michaelis–Menten kinetics and an explicit finite difference scheme to generate v _max and K _m parameters. The v _max/K _m ratio (a measure of the catalytic efficiency, or biodegradation capacity, of the reactor) was used to quantify substrate interactions occurring within the biofilter reactor without the need for free-cell suspended and monoculture experimentation. Toluene was found to enhance the catalytic efficiency of the reactor for p-xylene, while catabolism of all the other compounds was inhibited competitively by the presence of toluene. The toluene-acclimatized biofilter was also able to degrade all of the other BTEX compounds, even in the absence of toluene. The catalytic efficiency of the reactor for compounds other than toluene was in the order: ethylbenzene>benzene>o-xylene>m-xylene>p-xylene. The catalytic efficiency for toluene was reduced by the presence of all other tested BTEX compounds, with the greatest inhibitory effect being caused by the presence of benzene, while o-xylene and p-xylene caused the least inhibitory effect. This work illustrated that substrate interactions can be determined directly from biofilter reactor results without the need for free-cell and monoculture experimentation. Received: 13 April 2000 / Received revision: 20 July 2000 / Accepted: 27 July 2000     

Removal of BTEX compounds by industrial sludge microbes in batch systems: statistical analysis of main and interaction effects

Biodegradation is an effective technique to remediate polluted soil and groundwater. In the present experimental study, a mixed microbial culture obtained from the wastewater treatment sludge of a chemical industry was used to degrade liquid phase benzene, toluene, ethyl benzene, and xylene (BTEX), at individual initial concentrations varying between 15 and 75 mg/l. Experiments were conducted according to 2 ^k−1 fractional factorial design at the low (15 mg/l) and high (75 mg/l) levels of BTEX concentrations, to identify the main and interaction effects of parameters and their influence on biodegradation of individual BTEX compounds in mixtures. The individual removals varied between 16% and 75% when the concentrations of B, T, E, and X were sufficiently low in the mixture. However, both synergistic (removal of ethyl benzene) and antagonistic (removal of benzene) behavior were noticed when the concentrations of toluene and xylene was increased to higher levels. The individual removals were greater than 67% at their center point levels. The total BTEX removal values were later statistically analyzed and based on the Fischer’s variance ratio (F) and Probability values (P) it was observed that the main effects for total BTEX removal were significant than the squared and interaction effects.     

Temperature effects and substrate interactions during the aerobic biotransformation of BTEX mixtures by toluene-enriched consortia and Rhodococcus rhodochrous

A microbial consortium derived from a gasoline-contaminated aquifer was enriched on toluene (T) in a chemostat at 20 degrees C and was found to degrade benzene (B), ethylbenzene (E), and xylenes (X). Studies conducted to determine the optimal temperature for microbial activity revealed that cell growth and toluene degradation were maximized at 35 degrees C. A consortium enriched at 35 degrees C exhibited increased degradation rates of benzene, toluene, ethylbenzene, and xylenes in single-substrate experiments; in BTEX mixtures, enhanced benzene, toluene, and xylene degradation rates were observed, but ethylbenzene degradation rates decreased. Substrate degradation patterns over a range of BTEX concentrations (0 to 80 mg/L) for individual aromatics were found to differ significantly from patterns for aromatics in mixtures. Individually, toluene was degraded fastest, followed by benzene, ethylbenzene, and the xylenes. In BTEX mixtures, degradation followed the order of ethylbenzene, toluene, and benzene, with the xylenes degraded last. A pure culture isolated from the 35 degrees C-enriched consortium was identified as Rhodococcus rhodochrous. This culture was shown to degrade each of the BTEX compounds, individually and in mixtures, following the same degradation patterns as the mixed cultures. Additionally, R. rhodochrous was shown to utilize benzene, toluene, and ethylbenzene as primary carbon and energy sources. Studies conducted with the 35 degrees C-enriched consortium and R. rhodochrous to evaluate potential substrate interactions caused by the concurrent presence of multiple BTEX compounds revealed a range of substrate interaction patterns including no interaction, stimulation, competitive inhibition, noncompetitive inhibition, and cometabolism. In the case of the consortium, benzene and toluene degradation rates were slightly enhanced by the presence of o-xylene, whereas the presence of toluene, benzene, or ethylbenzene had a negative effect on xylene degradation rates. Ethylbenzene was shown to be the most potent inhibitor of BTEX degradation by both the mixed and pure cultures. Attempted quantification of these inhibition effects in the case of the consortium suggested a mixture of competitive and noncompetitive inhibition kinetics. Benzene, toluene, and the xylenes had a negligible effect on the biodegradation of ethylbenzene by both cultures. Cometabolism of o-, m-, and p-xylene was shown to be a positive substrate interaction.     

Biotreatment of groundwater contaminated with MTBE: interaction of common environmental co-contaminants

Contamination of groundwater with the gasoline additive methyl tert-butyl ether (MTBE) is often accompanied by many aromatic components such as benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene (BTEX). In this study, a laboratory-scale biotrickling filter for groundwater treatment inoculated with a microbial consortium degrading MTBE was studied. Individual or mixtures of BTEX compounds were transiently loaded in combination with MTBE. The results indicated that single BTEX compound or BTEX mixtures inhibited MTBE degradation to varying degrees, but none of them completely repressed the metabolic degradation in the biotrickling filter. Tert-butyl alcohol (TBA), a frequent co-contaminant of MTBE had no inhibitory effect on MTBE degradation. The bacterial consortium was stable and showed promising capabilities to remove TBA, ethylbenzene and toluene, and partially degraded benzene and xylenes without significant lag time. The study suggests that it is feasible to deploy a mixed bacterial consortia to degrade MTBE, BTEX and TBA at the same time.     

Kinetics of BTEX degradation in a packed-bed anaerobic reactor

The ever-increasing diversity of industrial activity is responsible for the discharge of compounds that are toxic or difficult to degrade into the environment. Some of the compounds found in surface and ground waters, usually deriving from the contamination of oil-based products, are benzene, toluene, ethylbenzene and xylenes (BTEX). To remove these compounds from contaminated water, a bench-scale horizontal-flow anaerobic immobilized biomass reactor, containing anaerobic biomass from various sources immobilized in polyurethane foam matrices, was employed to treat a synthetic substrate composed of protein, carbohydrates and BTEX solution in ethanol, as well as a BTEX solution in ethanol as the sole carbon source. The reactor removed up to 15.0 mg/l of each BTEX compound over a hydraulic detention time of 11.4 h. A first-order kinetic model fitted the experimental data well, showing correlation coefficients higher than 0.994. The apparent first-order coefficient values, , ranged from 8.4±1.5 day⁻¹ for benzene to 10.7±1.4 day⁻¹ for o-xylene in the presence of ethanol, protein and carbohydrates, and from 10.0±2.0 day⁻¹ for benzene to 13.0±1.7 day⁻¹ for o-xylene in the presence of ethanol. The BTEX degradation rates estimated here were 10- to 94-fold higher than those found in reports on microcosm studies.     

BTEX Exposures among Automobile Mechanics and Painters and Their Associated Health Risks

We measured the concentrations of benzene, toluene, ethylbenzene, and xylenes (BTEX) in the ambient air of automobile repair garages in Montreal, Canada, using the direct atmospheric pressure chemical ionization-tandem mass spectrometry (APCI-MS/MS) method. Among all the air samples analyzed, toluene was the most abundant BTEX-species (127–1101 μg/m³) followed by xylenes (50–323 μg/m³), ethylbenzene (11–65 μg/m³), and benzene (9.2–23 μg/m³). BTEX levels where ventilation was controlled simultaneously by both mechanical and natural systems were significantly less than levels at garages where only natural ventilation was used. Results suggest that multiple sources contribute to the occupational exposure of automobile mechanics and painters to the BTEX. Owing to the toxic effects of these chemicals, both chronic non-cancer hazard and integrated lifetime cancer risk due to the exposure of this occupational group were assessed. The levels of the BTEX measured at all the garages were less than the established limits for occupational exposure; still, benzene levels pose a potential cancer risk for the workers. At the prevailing levels of BTEX, they may not cause any chronic non-cancer problems for the workers.