Toluene Degradation Rate Research Articles

Effects of nitrogen sources on toluene degradation by Pseudomonas putida BZ918

For effective toluene degradation, the effects of a nitrogen source were studied with Pseudomonas putida BZ912, which was isolated from crude oil contaminated soil and is capable of degrading VOC. Two nitrogen sources, ammonia and nitrate, showed different effects on specific growth rates (0.25 hr −1 and 0.12 hr −1 , respectively), biomass yields (0.56 vs. 0.39) and specific toluene degradation rates (0.51 hr −1 vs. 0.26 hr −1 ). Under the resting cell conditions, the cells pre-cultured in the ammonia-containing medium showed higher specific toluene degradation rate than that in nitrate-containing medium (0.045 hr −1 vs. 0.038 hr −1 ). Ammonia as a nitrogen source was effective for degradation in high toluene concentration because high cellular biomass was accomplished. Nitrate showed slow growth rate com- pared to ammonia. The resting cell conditions demonstrated that it was able to degrade toluene efficiently without in- creasing biomass. These conditions could be a solution for degrading VOC after high cellular biomass was obtained in a biofilter. By changing the nitrogen source and the growth conditions according to the toluene concentration, the control of cell biomass and the desired removal capacity were accomplished.

Mathematical Model for Photocatalytic Destruction of Organic Contaminants in Air

Photocatalytic oxidation (PCO) was investigated in a bench-scale reactor for the abatement of two airborne organic contaminants: toluene and ethanol. A mathematical model that includes the impacts of light intensity, initial contaminant concentration, catalyst thickness, and relative humidity (RH) on the degradation of organic contaminants in a photocatalytic reactor was developed to describe this process. The commercially available catalyst Degussa-PtTiO2 was selected to compare with the MTU-PtTiO2-350 catalyst, which was synthesized by the sol-gel process, platinized, and calcined at 350 °C. For toluene removal using the MTU-PtTiO2-350 catalyst, the degradation rate increased with increases in light intensity from 0.2 to 2.2 mW/cm2 and in catalyst thickness from 0.00037 to 0.00361 cm. However, further increases in light intensity and catalyst thickness had only slight effect on the toluene degradation rate. Increasing the initial concentration from 6.29 to 127.9 μg/L and the RH from 10 to 85% resulted in decreases in the toluene degradation rate. For ethanol removal using the MTU-PtTiO2- 350 catalyst, the degradation rate increased more rapidly with an increase in RH from 17 to 56%; the RH had little effect on the ethanol degradation rate while it further increased from 56% to 82%. We discuss applicability of the model to estimate the influence of process variables and to evaluate photocatalyst performance.

Interactions of hydrophobic and hydrophilic solvent component degradation in an air‐phase biotrickling filter reactor

AbstractInteractions amongst the degradation rates of toluene, xylenes, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), and n‐butyl acetate (n‐BA) were investigated. Experiments were performed in a biotrickling filter reactor packed with polypropylene Pall rings in a counter‐current air–water mode of operation. Under pseudo‐steady‐state conditions, the removal efficiency (RE) of the individual components in the middle of and at the effluent above the reactor bed was evaluated. By using a mixed microbial culture as the biocatalyst, the results revealed that an increased loading of toluene and xylene had a competitive effect on the RE of MIBK. After reaching a saturation point of the overall catabolic capacity of the biocatalyst, variations of RE were observed for the different components. This was most pronounced under conditions of overloading with the water‐soluble components mixture. Despite such variations, the system was able to efficiently degrade this complex pollutant mixture for a period of 1 yr. © 2006 American Institute of Chemical Engineers Environ Prog, 2006

Photocatalytic Degradation of Formaldehyde and Toluene Mixtures in Air with a Nitrogen-doped TiO2 Photocatalyst

Abstract Photocatalytic degradation in multiple contaminant system with a nitrogen-doped TiO2 visible-light photocatalyst was investigated. Formaldehyde and toluene were chosen as components of the contaminant. The degradation rate of toluene was depressed by coexisting formaldehyde, while that of formaldehyde was scarcely affected by coexisting toluene. This phenomenon is attributed to preferential adsorption of formaldehyde on the photocatalyst powder.

Kinetics of toluene degradation by toluene-oxidizing bacteria as a function of oxygen concentration, and the effect of nitrate

The kinetics of toluene degradation as a function of oxygen concentration were compared for six strains of toluene-oxidizing bacteria using initial rate assays. The effect of nitrate was also examined. Rates of degradation and the relative effect of oxygen on the degradation rate were correlated with the pathway for toluene oxidation. Strains which synthesize toluene dioxygenases, Pseudomonas putida F1, P. fluorescens CFS215, and Pseudomonas sp. strain W31, degraded toluene at significantly higher rates (151–166 nmol/mg per min) than strains synthesizing toluene monooxygenases, Burkholderia cepacia G4 (23 nmol/mg per min) and B. pickettii PKO1 (14 nmol/mg per min), or a methylmonooxygenase, P. putida PaW1 (12 nmol/mg per min). Rates declined 30–48% for the dioxygenase strains and 25% for PaW1 as the oxygen concentration was decreased from 240 to 50 μM, but declined less than 10% for G4 and PKO1. Nitrate enhanced toluene degradation by the denitrifying strains PKO1 and W31 at oxygen concentrations below 30 μM, but had no significant effect on any of the other strains. Biphasic kinetics were observed for all of the strains, with double-reciprocal plots of the data exhibiting an inflection point at a ‘critical oxygen concentration’ between 20 and 30 μM. Below this concentration, the rate of toluene degradation was inhibited to a greater extent than predicted by the kinetic data for higher oxygen concentrations. For the denitrifying strains PKO1 and W31, however, monophasic kinetics were observed when nitrate was provided as an alternative electron acceptor. These observations suggest that biphasic kinetics result when rates of toluene degradation are limited by the availability of electron acceptor at the critical oxygen concentration, and that this limitation is overcome by denitrifying strains able to respire nitrate. Taken together, our findings suggest that the synthesis of monooxygenases and the ability to denitrify represent independent adaptations for toluene utilization in low oxygen environments. Moreover, these data support the use of nitrate in mixed electron acceptor strategies for the bioremediation of contaminated aquifers, as well as the targeted use of monooxygenase and dioxygenase strains in settings in which their physiological traits can be best exploited.

A model study based on experiments on toluene removal under high load condition in biofilters

As a control measure for substrate inhibition phenomenon in biofilters caused by toxic gases with high concentration, an appropriate mathematical model is required to calculate gas concentrations at various positions within and outside biofilms. Thus validation of the Deshussess model, Devinny–Hodge model and Luong Model were carried out for high toluene load conditions, and the results were examined for their veracity. Calculated concentrations using the modified Deshussess model, which considers sorption volume of carriers, approximated to measurements. This appears to mean the contribution of porosity in inorganic ceramic carriers to the biological removal of toluene vapor. Since toluene removal capacities for high liquid concentrations, which were calculated using the Luong model, approximated to the measurements, the generality and usefulness of the Luong model in predicting the substrate elimination capacity in biofilters with substrate inhibition appear to be manifested. Simplified Devinny–Hodge model turned out to be not applicable to predicting gas concentration along longitudinal axis of biofilters with high gas load. Various model parameters, needed for modeling studies, including critical toluene load per unit biomass and time, maximum toluene degradation rate, half velocity toluene concentration, and maximum toluene concentration in liquid, above which biodegradation is inhibited, were experimentally determined.

Ethanol and toluene removal in a horizontal‐flow anaerobic immobilized biomass reactor in the presence of sulfate

In this study it is reported the operation of a horizontal-flow anaerobic immobilized biomass (HAIB) reactor under sulfate-reducing condition which was also exposed to different amounts of ethanol and toluene. The system was inoculated with sludge taken from up-flow anaerobic sludge blanket (UASB) reactors treating refuses from a poultry slaughterhouse. The HAIB reactor comprised of an immobilized biomass on polyurethane foam and ferrous and sodium sulfate solutions were used (91 and 550 mg/L, respectively), to promote a sulfate-reducing environment. Toluene was added at an initial concentration of 2.0 mg/L followed by an increased range of different amendments (5, 7, and 9 mg/L). Ethanol was added at an initial concentration of 170 mg/L followed by an increased range of 960 mg/L. The reactor was operated at 30(+/-2) degrees C with hydraulic detention time of 12 h. Organic matter removal efficiency was close to 90% with a maximum toluene degradation rate of 0.06 mg(toluene)/mg(vss)/d. Sulfate reduction was close to 99.9% for all-nutritional amendments. Biofilm microscopic characterization revealed a diversity of microbial morphologies and DGGE-profiling showed a variation of bacterial and sulfate reducing bacteria (SRB) populations, which were significantly associated with toluene amendments. Diversity of archaea remained unaltered during the different phases of this experiment. Thus, this study demonstrates that compact units of HAIB reactors, under sulfate reducing conditions, are a potential alternative for in situ aromatics bioremediation.

BTEX degradation in a cold-climate wetland system

A pilot-scale subsurface vertical-flow wetland system was constructed at the former BP Refinery in Casper, Wyoming in order to determine benzene, toluene, ethylbenzene and xylene (BTEX) degradation rates in a cold-climate application. The pilot system, consisting of 4 cells, each dosed at a nominal flow rate of 5.4 cubic metres per day, was operated between August and December 2002. The pilot tested the effects of wetland mulch and aeration on system performance. Areal rate constants (kA values) were calculated based on an assumed three tanks in series (3TIS). The presence of wetland sod and aeration both improved treatment performance. Mean kA values were 244 m/yr for cells without sod or aeration, and improved to 356 m/yr for cells with sod and aeration. Based on the results of the pilot system, a full-scale wetland system (capable of operating at 6,000 m3/day) was started up in May 2003. The full-scale system achieved permit compliance within one week of startup, but is currently being loaded at only 45% of the design hydraulic load, and 15% of the design BTEX mass load, resulting in a mean kA value of approximately 350 m/yr.

Degradation of toluene vapor in a hydrophobic polyethylene hollow fiber membrane bioreactor with Pseudomonas putida

A toluene degrading microorganism, Pseudomonas putida type A1, was isolated and enriched to treat toluene vapor in a hollow fiber membrane bioreactor. Prior to the membrane reactor experiments, a set of batch experiments using this microorganism was conducted to examine the effect of oxygen levels on the microbial activity. It was found that a low oxygen level does limit the degradation rate of toluene. A hydrophobic hollow fiber module was developed for biological degradation of toluene vapor with enhanced oxygen transfer capabilities. A hydrophobic polyethylene microfiltration hollow fiber membrane bioreactor showed that toluene removal efficiencies were consistently kept in the range of 86–97% at the loads of 0.85–4.3 kg Tol./m 3 day for 150 days. The result showed that a hollow fiber membrane bioreactor system would be a useful choice for treating air emissions containing volatile organic compounds (VOC).

VUV Photocatalytic Degradation of Toluene in the Gas Phase

Abstract The photocatalytic degradation rate of gaseous toluene under irradiation of vacuum ultraviolet (185 nm) was 2–3 times faster than that under irradiation of 254 nm. The 185-nm VUV photolysis was greatly improved by the presence of TiO2 photocatalyst.

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.

Microbial characterization of toluene-degrading denitrifying consortia obtained from terrestrial and marine ecosystems.

The degradation characteristics of toluene coupled to nitrate reduction were investigated in enrichment culture and the microbial communities of toluene-degrading denitrifying consortia were characterized by denaturing gradient gel electrophoresis (DGGE) technique. Anaerobic nitrate-reducing bacteria were enriched from oil-contaminated soil samples collected from terrestrial (rice field) and marine (tidal flat) ecosystems. Enriched consortia degraded toluene in the presence of nitrate as a terminal electron acceptor. The degradation rate of toluene was affected by the initial substrate concentration and co-existence of other hydrocarbons. The types of toluene-degrading denitrifying consortia depended on the type of ecosystem. The clone RS-7 obtained from the enriched consortium of the rice field was most closely related to a toluene-degrading and denitrifying bacterium, Azoarcus denitrificians (A. tolulyticus sp. nov.). The clone TS-11 detected in the tidal flat enriched consortium was affiliated to Thauera sp. strain S2 (T. aminoaromatica sp. nov.) that was able to degrade toluene under denitrifying conditions. This indicates that environmental factors greatly influence microbial communities obtained from terrestrial (rice field) and marine (tidal flat) ecosystems.

Anaerobic Biodegradation of Toluene Coupled to Sulfate Reduction in Oil-Contaminated Soils: Optimum Environmental Conditions for Field Applications

Degradation characteristics of toluene in enrichment culture were investigated in soil microcosms study and the optimum environmental conditions for anaerobic degradation of toluene coupled with sulfate reduction were determined for field site applications. Anaerobic sulfate-reducing bacteria were enriched from oil contaminated soil samples with toluene. Enriched consortia degraded toluene with sulfate as a terminal electron acceptor. The average degradation rate of toluene in enriched consortia ranged from 0.08 to 0.1 µmol g−1 day−1. Toluene degradation under sulfate-reducing condition was inhibited in the presence of molybdate alone or together with nitrate or fumarate, indicating that toluene is degraded directly by sulfate-reducing bacteria. Effects of initial toluene concentration, pH, temperature, and other hydrocarbons on toluene degradation were investigated. There is a trend of increasing rate of toluene degradation with increasing the initial mass up to 94 µmol of toluene. Toluene degradation did not affected by the presence of ethylbenzene and xylene, as a while, toluene was degraded in a slower rate in the presence of benzene. The sulfate-reducing bacteria in the enriched culture showed higher microbial activity at neutral (pH 6–8) and medium temperature (30–37°C) environments.

Degradation of benzene and toluene by a fluidized bed bioreactor including microbial consortium

A fluidized bed bioreactor including microbial consortium was used to remove benzene and toluene simultaneously. The microbial consortium was obtained from sewage treatment plant, and showed maximum benzene degradation rate of 45.2 mg/l·h·mg cell in 30 °C and pH 7.0, and maximum toluene degradation rate of 44.4 mg/l·h·mg cell in 30 °C and pH 8.0. The optimum operating condition of the fluidized bed bioreactor was 30 °C, pH 7.0 and 150 cm of liquid bed height. The average removal efficiency of benzene was 94% for inlet concentration of 53(±5) ppm benzene and that of toluene was 96% for an inlet concentration 48(±5) ppm toluene at 600 l/h of gas volumetric flow rate. The maximum removal capacity in the experimental condition was 22.3 g/m3·h for benzene and 16.3 g/ m3·h for toluene.

Analysis of microbial adaptation at enzyme level for enhancing biodegradation rate of BTX

Catechol was found to be a common intermediate in the degradation of benzene and toluene byAlcaligenes xyhsoxidans Y234, and the ring cleavage of the catechol mediated by catechol 1,2-dioxygenase was a rate-determining step. Since benzene induced higher level of catechol 1,2-dioxygenase than toluene, the cells pre-adapted to benzene showed higher degradation rate of benzene and toluene. The degradation rate ofm-xylene was also increased significantly when benzene-adapted cells were inoculated.m-Xylene was metabolized via 3-methyl catechol which was effectively cleaved by catechol 1,2-dioxygenase.

Degradation Characteristics of Toluene, Benzene, Ethylbenzene, and Xylene by Stenotrophomonas maltophilia T3-c

Stenotrophomonas maltophilia T3-c, isolated from a biofilter for the removal of benzene, toluene, ethylbenzene, and xylene (BTEX), could grow in a mineral salt medium containing toluene, benzene, or ethylbenzene as the sole source of carbon. The effect of environmental factors such as initial toluene mass, medium pH, and temperature on the degradation rate of toluene was investigated. The cosubstrate interactions in the BTEX mixture by the isolate were also studied. Within the range of initial toluene mass (from 23 to 70 μmol), an increased substrate concentration increased the specific degradation of toluene by S. maltophilia T3-c. The toluene degradation activity of S. maltophilia T3-c could be maintained at a broad pH range from 5 to 8. The rates at 20 and 40°C were 43 and 83%, respectively, of the rate at 30°C. The specific degradation rates of toluene, benzene, and ethylbenzene by strain T3-c were 2.38, 4.25, and 2.06 μmol/g-DCW/hr. While xylene could not be utilized as a growth substrate by S. maltophilia T3-c, the presence of toluene resulted in the cometabolic degradation of xylene. The specific degradation rate of toluene was increased by the presence of benzene, ethylbenzene, or xylene in binary mixtures. The presence of toluene or xylene in binary mixtures with benzene increased the specific degradation rate of benzene. The presence of ethylbenzene in binary mixtures with benzene inhibited benzene degradation. The presence of more than three kinds of substrates inhibited the specific degradation rate of benzene. All BTEX mixtures, except tri-mixtures of benzene, ethylbenzene, and xylene or mixtures of all four substrates, had little effect on the degradation of ethylbenzene by S. maltophilia T3-c. The utilization preference of the substrates by S. maltophilia T3-c was as follows: ethylbenzene was degraded fastest, followed by toluene and benzene. However, the specific degradation rates of substrates, in order, were benzene, toluene, and ethylbenzene.

Effect of ethanol on BTEX biodegradation kinetics: aerobic continuous culture experiments

The use of ethanol as an automotive fuel oxygenate represents potential economic and air-quality benefits. However, little is known about how ethanol may affect the natural attenuation of petroleum product releases. Chemostat experiments were conducted with four pure cultures (representing archetypes of the known aerobic toluene degradation pathways) to determine how ethanol affects benzene, toluene, ethylbenzene, and xylene (BTEX) biodegradation kinetics. In all cases, the presence of ethanol decreased the metabolic flux of toluene (measured as the rate of toluene degradation per cell). This negative effect was counteracted by an ethanol-supported increase in biomass, which is conducive to faster degradation rates. When the influent total organic carbon (TOC) of the toluene–ethanol mixture was kept constant, the metabolic flux of toluene was proportional to its relative contribution to the influent TOC. This empirical relationship was used to derive a mathematical model that simulated effluent benzene concentrations as a function of the influent mixed-substrate composition, the dilution rate, and Monod kinetic coefficients. Under carbon-limiting conditions (1 mg/L influent benzene), the data and model simulations showed an increase in benzene removal efficiency when ethanol was fed at low concentrations (ca. 1 mg/L) because its positive effect on cell growth outweighed its negative effect on the metabolic flux of benzene. High ethanol concentrations, however, had a negative effect, causing oxygen limitation and increasing effluent benzene concentrations to higher levels than when benzene was fed alone. The slower BTEX degradation rates expected at sites with high ethanol concentrations (e.g., at gasohol-contaminated sites) could result in longer BTEX plumes and a greater risk of exposure.

Photocatalytic degradation of volatile organic compounds at the gas–solid interface of a TiO 2 photocatalyst

In the present work, photocatalytic degradation of volatile organic compounds including gas-phase trichloroethylene (TCE), acetone, methanol and toluene over illuminated TiO 2 was closely examined in a batch photoreactor as a function of water vapor, molecular oxygen and reaction temperature. Water vapor enhanced the photocatalytic degradation rate of toluene, but was inhibitive for acetone, and, there was an optimum water vapor concentration in the TCE and methanol removal. In a nitrogen atmosphere, it showed lower photocatalytic degradation rate than in air and pure oxygen. Thus, it could be concluded that oxygen is an essential component in photocatalytic reactions by trapping photogenerated electrons on the semiconductor surface and by decreasing the recombination of electrons and holes. As for the influence of reaction temperature, it was found that photocatalytic degradation was more effective at a moderate temperature than at an elevated temperature for each compound.

Enhanced Toluene Degradation Under Chlorate-Reducing Conditions by Bioaugmentation of Sand Columns with Chlorate- and Toluene-Degrading Enrichments

Chlorate was examined as a potential electron acceptor for enhancing toluene degradation. Most chlorate respiring bacteria (CRB) use nitrate as an electron acceptor, and toluene is known to be degraded under denitrifying conditions. Therefore, it was hypothesized that there would be bacteria that could degrade toluene using chlorate as an electron acceptor, and that chlorate could be used to stimulate toluene degradation. Repeated tests and different approaches in batch tests failed to produce an enrichment capable of toluene degradation supported by chlorate reduction. However, the addition of chlorate increased the overall rate of toluene degradation in bioaugmented columns that were fed chlorate vs. a control column. Toluene removal at an influent toluene concentration of 11 mg/L was 93±5%, which was larger by a factor of 1.95 than toluene removal in a nonbioaugmented control column. Following the discontinued feed of chlorate, toluene removal decreased to 69±4%, demonstrating that chlorate could be used to produce a 1.36-fold increase in toluene removal.

Kinetic study for photocatalytic degradation of volatile organic compounds in air using thin film TiO2 photocatalyst

The present paper examined the kinetics of photocatalytic degradation of volatile organic compounds (VOCs) including gaseous trichloroethylene (TCE), acetone, methanol and toluene. Variable parameters were initial concentration of VOCs, water vapor content and photon flux of ultra-violet (UV) light. A batch photo-reactor was specifically designed for this work. The photocatalytic degradation rate increased with increasing the initial concentration of VOCs, but maintained almost constant beyond a certain concentration. It matched well with the Langmuir–Hinshelwood (L–H) kinetic model. For the influence of water vapor in a gas phase photocatalytic degradation rate, there was an optimum concentration of water vapor in the degradation of TCE and methanol. And, water vapor enhanced the photocatalytic degradation rate of toluene, whereas it inhibited that of acetone. As for the effect of photon flux, it was found that photocatalytic degradation occurs in two regimes with respect to photon flux.