Biodegradation of benzene, toluene; and other aromatic compounds by Pseudmonas sp. D8

Pseudmonas sp. D8 strain, which has the potential to utilize toluene as a sole carbon source, was isolated. At a concentration of 100 mg/l, this strain was found to efficiently degrade toluene and benzene (both individually and in mixture) in culture medium at 30°C and pH7. Following a two-hour lag phase, complete biodegradation of 100 mg/l toluene or benzene occurred within 6 to 8 hours. The addition of nitrate, phosphate, or sulfate at various concentrations were found to have significant influence on both toluene and benzene degradation. In addition, results show that the D8 strain has the ability to degrade monochlorophenols, nitrophenols, and phenol, but not aliphatic compounds. Inoculation of groundwater samples containing 100 mg/1 toluene or benzene with Pseudmonas sp. D8 resulted in rapid degradation within 24 33 hours.     

Biodegradation of toluene vapor in coir based upflow packed bed reactor by <Emphasis Type="Italic">Trichoderma asperellum</Emphasis> isolate

In the present study, a new biofiltration system involving a selective microbial strain isolated from aerated municipal sewage water attached with coir as packing material was developed for toluene degradation. The selected fungal isolate was identified as Trichoderma asperellum by 16S ribosomal RNA (16S rRNA) sequencing method, and pylogenetic tree was constructed using BLASTn search. Effect of various factors on growth and toluene degradation by newly isolated T. asperellum was studied in batch studies, and the optimum conditions were found to be pH 7.0, temperature 30 °C, and initial toluene concentration 1.5 (v/v)%. Continuous removal of gaseous toluene was monitored in upflow packed bed reactor (UFPBR) using T. asperellum. Effect of various parameters like column height, flow rate, and the inlet toluene concentration were studied to evaluate the performance of the biofilter. The maximum elimination capacity (257 g m^?3 h^?1) was obtained with the packing height of 100 cm with the empty bed residence time of 5 min. Under these optimum conditions, the T. asperellum showed better toluene removal efficiency. Kinetic models have been developed for toluene degradation by T. asperellum using macrokinetic approach of the plug flow model incorporated with Monod model.     

Biodegradation of benzene, toluene, and xylene (BTX) in liquid culture and in soil by Bacillus subtilis and Pseudomonas aeruginosa strains and a formulated bacterial consortium

Purpose

The major aromatic constituents of petroleum products viz. benzene, toluene, and mixture of xylenes (BTX) are responsible for environmental pollution and inflict serious public concern. Therefore, BTX biodegradation potential of individual as well as formulated bacterial consortium was evaluated. This study highlighted the role of hydrogen peroxide (H₂O₂), nitrate, and phosphate in stimulating the biodegradation of BTX compounds under hypoxic condition.

Materials and methods

The individual bacterium viz. Bacillus subtilis DM-04 and Pseudomonas aeruginosa M and NM strains and a consortium comprising of the above bacteria were inoculated to BTX-containing liquid medium and in soil. The bioremediation experiment was carried out for 120?h in BTX-containing liquid culture and for 90?days in BTX-contaminated soil. The kinetics of BTX degradation either in presence or absence of H₂O₂, nitrate, and phosphate was analyzed using biochemical and gas chromatographic (GC) technique.

Results

Bacterial consortium was found to be superior in degrading BTX either in soil or in liquid medium as compared to degradation of same compounds by individual strains of the consortium. The rate of BTX biodegradation was further enhanced when the liquid medium/soil was exogenously supplemented with 0.01?% (v/v) H₂O₂, phosphate, and nitrate_. The GC analysis of BTX biodegradation (90?days post-inoculation) in soil by bacterial consortium confirmed the preferential degradation of benzene compared to m-xylene and toluene.

Conclusions

It may be concluded that the bacterial consortium in the present study can degrade BTX compounds at a significantly higher rate as compared to the degradation of the same compounds by individual members of the consortium. Further, addition of H₂O₂ in the culture medium as an additional source of oxygen, and nitrate and phosphate as an alternative electron acceptor and macronutrient, respectively, significantly enhanced the rate of BTX biodegradation under oxygen-limited condition.     

Characterization of microbial consortia that reductively dechlorinate 4-chlorophenol and transform phenol to benzoate enriched from estuarine sediment of Lake Shinji

Monochlorophenols were degraded to benzoate via phenol by the initial dechlorination and the subsequent conversion of phenol to benzoate in anaerobic sediment samples of estuarine Lake Shinji under methanogenic conditions. To characterize bacteria that dechlorinate 4-chlorophenol and transform phenol to benzoate, we analyzed the microbial community structure of the enrichment culture with each 4-chlorophenol and phenol by the limiting dilution method with polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) of 16S rRNA gene. After serial dilution of the culture, the 4-chlorophenol-dechlorinating culture consisted of two dominant bacteria, one of which was most homologous with Dehalobacter sp. In the enriched culture with phenol, minor band homologous with Cryptanaerobacter phenolicass corresponded to the transformation activity.     

Relationship between the ATP content of subsurface material and the rate of biodegradation of alkylbenzenes and chlorobenzene

The rate of biotransformation of toluene in unconsolidated subsurface material from sites at Lula, Oklahoma, and Conroe, Texas, was compared to the ATP (adenosine triphosphate) content of these materials. The rate of toluene degradation decreased with decreasing ATP content. When ATP contents were at or less than 0.05 ng g⁻¹, biotransformation of toluene could not be detected (less than 1% of the initial concentration was degraded per week). At intermediate concentrations of ATP, 0.37 and 0.16 ngvg⁻¹, the rates of toluene degradation were 18 ± 4.5% and 25 ± 10% of the initial concentration per week. At ATP concentrations above 1 ng g⁻¹, the rates of toluene degradation exceeded 90% of the initial concentration per week. There was no simple relationship between ATP content and chlorobenzene degradation. Subsurface material that had been exposed to creosote wastes, and which degraded toluene rapidly, also degraded benzene, o-xylene, and m-xylene.     

Bacterial assisted phytoremediation for enhanced degradation of highly sulfonated diazo reactive dye

Purpose

Phytoremediation is the exploitation of plants and their rhizospheric microorganisms for pollutants treatment like textile dyes, which are toxic, carcinogenic and mutagenic from the effluent. The purpose of this work was to explore a naturally found plant and bacterial synergism to achieve an enhanced degradation of Remazol Black B dye (RBB).

Methods

In vitro cultures of Zinnia angustifolia were obtained by seed culture method. Enzymatic analysis of the plant roots and Exiguobacterium aestuarii strain ZaK cells was performed before and after decolorization of RBB. Metabolites of RBB formed after its degradation were analyzed using UV?CVis spectroscopy, high-performance liquid chromatography (HPLC), Fourier transform infrared (FTIR) and gas chromatography?Cmass spectrometry (GC-MS). Phytotoxicity studies were performed.

Results

The consortium ZE was found to be more efficient than individual plant and bacteria. Z. angustifolia roots showed significant induction in the activities of lignin peroxidase, laccase, DCIP reductase and tyrosinase during dye decolorization. E. aestuarii showed significant induction in the activities of veratryl alcohol oxidase, azo reductase and DCIP reductase. Analysis of metabolites revealed differential metabolism of RBB by plant, bacteria and consortium ZE. E. aestuarii and Z. angustifolia led to the formation of 3,6-diamino-4-hydroxynaphthalene-2-sulfonic acid, (ethylsulfonyl)benzene, and 3,4,6-trihydroxynaphthalene-2-sulfonic acid and propane-1-sulfonic acid, respectively, whereas consortium ZE produced 4-hydroxynaphthalene-2-sulfonic acid, naphthalene-2-sulfonic acid and 4-(methylsulfonyl)phenol. The phytotoxicity study revealed the nontoxic nature of the metabolites formed after dye degradation.

Conclusion

Consortium ZE was found to be more efficient and faster in the degradation of RBB when compared to degradation by Z. angustifoila and E. aestuarii individually.     

Altered toxicity of organic pollutants in water originated from simultaneous exposure to UV photolysis and CdSe/ZnS quantum dots

The paper reports unforeseen results of increased toxicity of water, subsequent to interactions between CdSe/ZnS quantum dots (QDs), phenol and toluene under UV irradiation. The consistent pattern of changes in measured toxicity (TU) was observed and correlated with degradation of phenol and/or toluene. Spearman rank coefficients (SRCs) for data pairs sum-parameters vs. TU were calculated. The highest correlation between toxicity and degradation by-products was observed for hydroquinone (0.86) and catechol (0.89). The presence of QDs in tested concentration range in the absence of UV has shown low toxicity and no interactions with phenol and/or toluene. The leak of constituent core and shell metal ions was observed. The minor differences in physical characteristics of tested QDs of the same chemical composition led to rather different degradation patterns of phenol and toluene, and the amount of leak of the metal ions as well.     

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 pmol), 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 degrees C were 43 and 83%, respectively, of the rate at 30 degrees C. The specific degradation rates of toluene, benzene, and ethylbenzene by strain T3-c were 2.38, 4.25, and 2.06 micromol/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.     

Determination of microbial activity in activated sewage sludge by dimethyl sulphoxide reduction

A method was developed to determine the dimethyl sulphoxide (DMSO) reduction rate in activated sewage sludge at nearly natural conditions. Linearity of microbially produced dimethyl sulphide with incubation time and sample size was shown. Apart from a fast, sensitive and highly reproducible automatic analysis of dimethyl sulphide, simultaneous determination of mineralisation, respiration and phenol degradation rates was possible. The DMSO reduction rate of samples taken from a municipal sewage plant ranged between 2 and 3 μmol/(g dry matter · h), respiration and mineralisation rates between 30 and 80 μmol/(g · h). Added¹³C₆-phenol was completely degradated after 96 h of incubation. A half-life of 14 h was calculated assuming first order decay. Dose response curves were obtained by incubating samples for 2, 6, 25, and 96 hours after addition of pentachlorophenol. At an incubation time of 6 h, the EC₅₀ values ranged from 20 mg/L (DMSO reduction) to 30 mg/L (phenol degradation) up to 180 mg/L (respiration and mineralisation). Increasing the incubation time to 96 h resulted in a lower EC₅₀ of 9 mg/L for DMSO reduction, whereas it increased to 500 mg/L for respiration and mineralisation.     

Biodegradation of dimethylphenols by bacteria with different ring-cleavage pathways of phenolic compounds

The biodegradation of 3,4, 2,4, 2,3, 2,6 and 3,5-di-methylphenol in combination with phenol andp-cresol by axenic and mixed cultures of bacteria was investigated. The strains, which degrade phenol andp-cresol through different catabolic pathways, were isolated from river water continuously polluted with phenolic compounds of leachate of oil shale semicoke ash heaps. The proper research of degradation of 2,4 and 3,4-di-methylphenol in multinutrient environments was performed. The degradation of phenolic compounds from mixtures indicated a flux of substrates into different catabolic pathways. Catechol 2,3-dioxygenase activity was induced by dimethylphenols inPseudomonas mendocina PC1, wheremeta cleavage pathway was functional during the degradation ofp-cresol. In the case of strains PC18 and PC24 ofP. fluorescens, the degradation ofp-cresol occurred via the protocatechuateortho pathway and the key enzyme of this pathway,p-cresol methylhydroxylase, was also induced by dimethylphenols. 2,4 and 3,4-dimethylphenols were converted into the dead-end products 4-hydroxy-3-methylbenzoic acid and 4-hydroxy-2-methylbenzoic acid. In the degradation of 3,4-dimethylphenol, the transient accumulation of 4-hydroxy-2-methylbenzaldehyde repressed the consumption of phenol from substrate mixtures. A mixed culture of strains with different catabolic types made it possible to overcome the incompatibilities at degradation of studied substrate mixtures.     

地下水中BTEX的原位生物修复研究进展

BTEX是苯、甲苯、乙苯和二甲苯的统称,存在于原油和石油产品中,其作为化工原料,广泛应用于农药、塑料及合成纤维等制造业.BTEX已成为地下水中普遍存在的污染物,自然衰减或生物修复工程已成功应用于地下水中BTEX的去除.自然衰减受BTEX污染的地下水具有良好的效果,但相比之下,生物修复工程更快、更有效.综述了在好氧和厌氧条件下,地下水中BTEX原位生物修复过程的微生物降解机制.     

Sorption and enhanced biodegradation of trace organics in a groundwater reclamation scheme— gloucester site, Ottawa, Canada

An inexpensive scheme to reclaim groundwaters contaminated by volatile organics at the Gloucester landfill site, near Ottawa, Canada, involved pumping of contaminated water into an conducted to evaluate the possible enhancement of biodegradation to improve this remedial measure.Batch experiments revealed that toluene (0.8–1.5 mg L⁻¹) was rapidly degraded aerobically while chloroform (1.2–1.0 mg L⁻¹) was recalcitrant under aerobic or anaerobic (denitrifying) conditions. Dynamic column experiments confirmed these findings. In column experiments, both chloroform and toluene were retarded relative to the pore water velocity, but to a far lesser extent than predicted by hydrophobic sorption theory. This discrepancy is attributed to the large particulate nature of the sorbent (sawdust) which prevented rapidly migrating organics from attaining an equilibrium partitioning with the bulk of this organic matter. Addition of acetate and nitrate at 20 mg L⁻¹ stimulated aerobic activity, but was inhibitory to toluene degradation. However, when nutrient addition ceased, enhanced toluene degradation was produced by the larger microbial population.In the field experiment, addition of acetate and nitrate to groundwater influent into the sawdust/sand pit may have stimulated benzene biodegradation, but had no apparent influence on volatile chlorinated hydrocarbon biodegradation. As in the column experiments, sorptive retardation was considerably less than predicted, due to a lack of equilibrium partitioning of organic solutes within the sawdust.Enhancing biodegradation in this remedial scheme was unsuccessful for a broad range of volatile organic compound types. Periodic nutrient addition to create variable environments for microbes appears to hold more promise for remediation than the continuous nutrient input scheme. This experience demonstrates the need for realistic field-scale experiments before translating laboratory studies into full-scale remedial operations.     

Aromatic hydrocarbons at urban,sub-urban,rural (8°52′N; 67°19′W) and remote sites in Venezuela

Using the novel on-line proton transfer reaction mass spectrometry (PTR-MS) technique, atmospheric concentrations of benzene, toluene, xylenes, and C₉-benzenes were measured in Caracas (urban), Altos de Pipe (sub-urban), Calabozo (rural) and Parupa (remote), during various campaigns in 1999 and 2000.Average daytime mixing ratios measured in Caracas are 1.1, 3.2, 3.7, and 2.7 nmol/mol for benzene, toluene, xylenes, and C₉-benzenes. At the sub-urban site, located only few km from Caracas, relatively low levels (∼20% of the levels measured in Caracas) of these aromatic hydrocarbons were observed.At the rural site during the dry season, higher concentrations of benzene (0.15 nmol/mol) were recorded, whereas those of toluene (0.08 nmol/mol) were lower during that time. The aromatic hydrocarbon ratios in the wet season (benzene: 0.08 nmol/mol; toluene: 0.09 nmol/mol) are consistent with an aged urban plume, whereas biomass burning emissions dominate during the dry season. From rural and urban [benzene]/[toluene] ratios a mean HO concentration of 2.6×10⁶ molecules/cm³ was estimated during the wet season. This value must be considered an overestimate because it does not account for background concentrations which are likely for benzene and toluene.At the remote “La Gran Sabana” region (Parupa) very low mixing ratios (0.031 and 0.015 nmol/mol for benzene and toluene) are showing the pristine region to be unaffected by local sources. From the [benzene]/[toluene] ratio we deduced, that “urban” air arriving from the coastline (350 km) is likely mixed with air containing some background of benzene and toluene.Urban emissions (automobiles) should be the major source of aromatic compounds, however, during the dry season biomass burning seems to make an important contribution.     

Measurements of aromatic hydrocarbon ratios and NOx concentrations in the rural troposphere: Observation of air mass photochemical aging and NOx removal

Measurements of the aromatic hydrocarbons (benzene, toluene, ethylbenzene and ortho(o)-xylene) at Niwot Ridge, Colorado have shown distinct correlations between the ratios of the concentrations of these compounds and the degree of direct urban influence. The major atmospheric removal mechanism of aromatic hydrocarbons is reaction with the hydroxyl radical, OH. This allows the decrease in the ratios of aromatic hydrocarbon concentrations to be related to the transport time and average OH number density within an air mass, if assumptions are made concerning background sources of aromatic hydrocarbons. Measured ratios of aromatic compounds at this site, along with ratios reported for several cities in the western United States, and estimates of transport times from these cities were used to calculate temporally and spatially averaged OH number densities. Hydroxyl radical number density estimates using toluene-, ethylbenzene-, and o-xylene-to-benzene ratios, were 1.2 ± 0.6 × 10⁶, 1.0 ±0.8 × 10₆ and 0.48 ± 0.8 × 10⁶ molecules cm⁻³, respectively. Considering the uncertainties in the assumptions used in the above estimates, we obtain a diurnal-average upper limit of 2.4 × 10⁶ molecules cm⁻³. The correlations between measured ratios are found to yield slopes consistent with those predicted by experimental OH rate constants for benzene, toluene and ethylbenzene, and approximately a factor of two different in the case of benzene, toluene and o-xylene. The ratio of NO_x: benzene was found to yield no correlation with toluene: benzene ratio for periods of westerly flow, but was well correlated with toluene: benzene ratio during periods of direct urban impact on the site (upslope easterly winds). The correlation of these ratios in urban plume air masses was consistent with NO₂ + OH + M being the major daytime removal mechanism of NO_x in the summertime.     

Performance evaluation of a continuous flow photocatalytic reactor for wastewater treatment

A novel photocatalytic reactor for wastewater treatment was designed and constructed. The main part of the reactor was an aluminum tube in which 12 stainless steel circular baffles and four quartz tube were placed inside of the reactor like shell and tube heat exchangers. Four UV–C lamps were housed within the space of the quartz tubes. Surface of the baffles was coated with TiO₂. A simple method was employed for TiO₂ immobilization, while the characterization of the supported photocatalyst was based on the results obtained through performing some common analytical methods such as X-ray diffraction (XRD), scanning electron microscope (SEM), and BET. Phenol was selected as a model pollutant. A solution of a known initial concentration (20, 60, and 100 ppmv) was introduced to the reactor. The reactor also has a recycle flow to make turbulent flow inside of the reactor. The selected recycle flow rate was 7?×?10^?5 m³.s^?1, while the flow rate of feed was 2.53?×?10^?7, 7.56?×?10^?7, and 1.26?×?10^?6 m³.s^?1, respectively. To evaluate performance of the reactor, response surface methodology was employed. A four-factor three-level Box–Behnken design was developed to evaluate the reactor performance for degradation of phenol. Effects of phenol inlet concentration (20–100 ppmv), pH (3–9), liquid flow rate (2.53?×?10^?7?1.26?×?10^?6 m³.s^?1), and TiO₂ loading (8.8–17.6 g.m^?2) were analyzed with this method. The adjusted R ² value (0.9936) was in close agreement with that of corresponding R ² value (0.9961). The maximum predicted degradation of phenol was 75.50 % at the optimum processing conditions (initial phenol concentration of 20 ppmv, pH?～?6.41, and flow rate of 2.53?×?10^?7 m³.s^?1 and catalyst loading of 17.6 g.m^?2). Experimental degradation of phenol determined at the optimum conditions was 73.7 %. XRD patterns and SEM images at the optimum conditions revealed that crystal size is approximately 25 nm and TiO₂ nanoparticles with visible agglomerates distribute densely and uniformly over the surface of stainless steel substrate. BET specific surface area of immobilized TiO₂ was 47.2 and 45.8 m² g^?1 before and after the experiments, respectively. Reduction in TOC content, after steady state condition, showed that maximum phenol decomposition occurred at neutral condition (pH?～?6). Figure

The schematic view of the experimental set-up     

Volatile organic compounds in roadside microenvironments of metropolitan Hong Kong

The characteristics and concentrations of volatile organic compounds (VOCs) in the roadside microenvironments of metropolitan Hong Kong were investigated. The VOC concentrations, especially toluene, benzene and chlorinated VOCs in Hong Kong were high when compared with those in most developed cities. The average and maximum concentration of toluene was 74.9 and 320.0 μg m⁻³, respectively. The respective values for benzene were 25.9 and 128.6 μg m⁻³. The chlorinated VOCs were dominated by trichloroethylene and tetrachloroethylene. The maximum concentrations of these two species reached 248.2 and 144.0 μg m⁻³, respectively. There were strong variations in the spatial fluctuation and characteristic of VOC concentrations. The highest VOC concentrations were found in the industrial district, which were followed by those in the commercial district, the central business district and finally the residential district. The highest concentrations of most VOC species, especially chlorinated VOC were found in the industrial and commercial districts. The average benzene/toluene ratio in Hong Kong was 0.5 suggesting that vehicular emission was the dominant VOC source in most areas of Hong Kong. There were strong deviations in benzene/toluene, benzene/ethylbenzene and benzene/(m+p-xylene) ratios in the commercial district, and highly chlorinated VOC in the industrial and commercial districts. These suggest that there were other benzene and VOC sources overlying on the high background VOC concentrations in these districts. The common usage of organic solvents in the building and construction industries, and in the small industries in the industrial and commercial districts were believed to be important sources of VOC in Hong Kong.