Prediction of Carbon BTEX Adsorption Capacity Using Field Monitoring Data

The need for predicting adsorption capacity for benzene, toluene, ethylbenzene, and xylenes (BTEX) onto granular-activated carbon (GAC) is a problem commonly associated with petroleum-spill remediation. In this study, monitoring data are compiled from operational records of ground-water pump and treat remediation sites where GAC adsorption is utilized as a primary treatment mechanism for BTEX. The monitoring data are reduced to adsorbed and equilibrium concentrations from which Freundlich isotherms and various linear and multivariate models are calibrated for prediction of BTEX capacity on GAC. The models are employed by themselves and with Ideal Adsorbed Solution Theory to predict capacity for total BTEX and benzene. Several models are selected based on prediction ability and are tested with independent data. Two simple models, a multivariate model and a Freundlich isotherm, are recommended. Complex empirical models and Ideal Adsorbed Solution Theory did not perform as well as the selected models and were rejected. From the Freundlich isotherm, new Freundlich constants are reported that describe adsorption of total BTEX on GAC from gasoline-contaminated ground water.     

Modeling of Aqueous BTEX Adsorption in Column and Multistage Adsorbers

Theoretical and experimental investigations have been conducted on the adsorption characteristics of benzene, toluene, ethylbenzene, and xylene (BTEX) by macroreticular resins. A theoretical model is proposed for describing the BTEX breakthrough curves of the adsorption column. The column adsorption model contains two model parameters, τ and K, that are conveniently estimated using the observed breakthrough data. The model was tested for benzene adsorption with a flow rate between 12 and 30 mL∕min, inlet concentration between 200 and 500 mg∕L, and temperature between 30 and 60°C. Excellent fit of the model to the measured data was obtained. The proposed model hence offers a convenient means for accurate predictions of the adsorption capacity and breakthrough point of a column BTEX adsorption process. Also developed are the mass balance equations representing countercurrent multistage adsorption process. The countercurrent multistage adsorption process has been shown to save a significant amount of adsorption resin in achieving the same BTEX removal as the single-stage process. Experimental tests for a two-stage example verify that up to 60% of the Ambersorb resin can be saved over a single-stage process.     

Opioid-receptor subtype agonist-induced enhancements of sucrose intake are dependent upon sucrose concentration

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 degrees 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 degrees C on BTEX compounds as their sole carbon and energy sources with 50 degrees 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 degrees C. Somewhat lower, but significant, percentages of the BTEX compounds also were biodegraded at 60 degrees C and 70 degrees 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 degrees 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 degrees 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.     

Effect of Uncertain Hydraulic Conductivity on the Simulated Fate and Transport of BTEX Compounds at a Field Site

Monte Carlo simulations were conducted to investigate the effect of uncertain hydraulic conductivity (K) on the natural attenuation of BTEX compounds (benzene, toluene, ethyl benzene, and xylenes) through aerobic respiration, denitrification, Fe(III) and sulfate reductions, and methanogenesis observed at a field site on Hill Air Force Base, Utah. First, the uncertainty in the ln?K field was represented by multiple realizations of spatially correlated random fields. The simulated BTEX plumes resulting from a light nonaqueous phase liquid source were analyzed for mass distributions and the relationships among various factors such as dissolved BTEX mass, plume spreading, and depletions of electron acceptors or productions of Fe2+ and methane. Second, additional K realizations with the same mean but different variances and correlation lengths were used to determine how the model responds to varying degrees of uncertainty in the K field. The methodology and insights are of general interest and applicable to fuel-hydrocarbon natural-attenuation sites.     

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.     

Permeation of BTEX through Unaged and Aged HDPE Geomembranes

The effects of aging of high-density polyethylene (HDPE) geomembranes on the diffusion and partitioning of a group of volatile organic compounds (VOCs) are examined. Two different 1.5?mm thick HDPE geomembranes were aged in the laboratory at 85°C by immersing in a synthetic leachate for up to 32?months. The results of partitioning and diffusion tests performed at room temperature on both unaged and aged geomembranes using a dilute aqueous solution containing four VOCs commonly found in landfill leachates [benzene, toluene, ethylbenzene, and xylenes (BTEX)] are reported. The diffusion and partitioning coefficients decreased with increased aging. The calculated permeation coefficients decreased by 36–62% after aging the geomembrane for about 10–32?months. This decrease in diffusion, partitioning, and permeation coefficients is related to the increase in geomembrane crystallinity during aging. A relationship between partitioning, diffusion, and permeation coefficients with the geomembrane crystallinity is established and could potentially be used to evaluate the migration of VOCs through HDPE geomembranes. Aging of HDPE geomembrane did not increase diffusive transport of organic contaminants.     

BTEX Extraction from Clay Soil Using Prefabricated Vertical Drains

A pilot scale field test was conducted to demonstrate the feasibility of using prefabricated vertical drains (PVDs) for in-situ point extraction of benzene, toluene, ethylbenzene, and xylene (BTEX) under vacuum. Results indicated the achievement of an average flow rate of 16.7 mL∕s for the five PVD systems. Grab samples from the effluent indicated an increase in retrieved BTEX concentration with time. Maximum retrieved concentrations in a 2-day period were ～0.4 mg∕L for benzene, 0.27 mg∕L for toluene, 0.19 mg∕L for ethylbenzene, and 0.025 mg∕L for xylene. Based on the limited results of the pilot scale test, a full-scale remediation of the site using the PVDs system is deemed feasible.     

A chromosomally based tod-luxCDABE whole-cell reporter for benzene, toluene, ethybenzene, and xylene (BTEX) sensing

A tod-luxCDABE fusion was constructed and introduced into the chromosome of Pseudomonas putida F1, yielding the strain TVA8. This strain was used to examine the induction of the tod operon when exposed to benzene, toluene, ethylbenzene, and xylene (BTEX) compounds and aqueous solutions of JP-4 jet fuel constituents. Since this system contained the complete lux cassette (luxCDABE), bacterial bioluminescence in response to putative chemical inducers of the tod operon was measured on-line in whole cells without added aldehyde substrate. There was an increasing response to toluene concentrations from 30 micrograms/liter to 50 mg/liter, which began to saturate at higher concentrations. The detection limit was 30 micrograms/liter. There was a significant light response to benzene, m- and p-xylenes, phenol, and water-soluble JP-4 jet fuel components, but there was no bioluminescence response upon exposure to o-xylene. The transposon insertion was stable and had no negative effect on cell growth.     

Bioremediation of Mixed Wastes (BTEX, TPH, TCE, and cis-DCE) Contaminated Water

Together with industrialization, more sites have become contaminated with mixed wastes of organics. Contamination of groundwater with benzene, toluene, ethylbenzene, and three isomers of xylene (BTEX) and chlorinated aliphatic hydrocarbons (CAHs) allows for the application of aerobic bioremediation to achieve mineralization of both types of compounds. In this study, the aerobic bioremoval of mixtures of these compounds [BTEX, BTEX/trichloroethylene (TCE), BTEX/cis-1,1-dichloroethylene (cis-DCE), BTEX/total petroleum hydrocarbons (TPH)/TCE, and toluene and ortho-xylene (ToX/TCE] was assessed under different environmental conditions (pH and temperature) by using indigenous microorganisms isolated from potentially contaminated regional sites. The highest TPH bioremoval efficiencies (<50%) occurred at 25°C and under neutral or alkaline conditions. TCE was cometabolized with toluene and o-xylene provided as growth substrates, and the highest bioremoval efficiency occurred at ToX/TCE, and pH and temperature impacted the mineralization of compounds. This study would help enhance the applicability of bioremediation technology to the mixed-wastes contaminated sites.     

Statistical Analysis of BTEX Surface Soil Regulatory Guidance Values

Residential surface soil regulatory guidance values (RGVs) specify the threshold at which soil contamination requires action. Usually, these are risk-based values based on child ingestion, inhalation, and dermal exposure. Benzene, toluene, ethylbenzene, and xylenes (BTEX) are among the five most commonly regulated soil contaminants in the United States and worldwide. More than 100 regulatory jurisdictions have established surface soil RGVs for BTEX compounds. Analysis of these values indicates that they vary by several orders of magnitude and appear to fit a lognormal random variable model with values well dispersed across the number spans. The RGVs applied to benzene are statistically distinct from those applied to TEX contamination, but the TEX values appear to be statistically indistinguishable. The magnitude of difference between TEX RGVs of different jurisdictions appears to be more significant than differences in the T, E, and X values specified by any one jurisdiction. Although value distributions are dominated by randomness, some contain clusters of points that are unlikely to be random and may represent consensus on appropriate values. Where “consensus clusters” exist, they should be identified and explored. The mechanistic explanations for cluster values may yield methods of reducing RGV variability.     

BTEX在改性泥炭上的低温吸附与解吸

为探讨砂金矿山开采中伴生泥炭的环保利用新途径,研究了地下水中BTEX在改性泥炭上的吸附与解吸行为.试验结果表明:BTEX在改性泥炭上吸附与解吸均呈现非线性,可用Freundlich模型描述,吸附常数Kf、泥炭与水标化分配系数Koc顺序为二甲苯＞乙笨＞甲笨＞笨,这与上述化合物的辛醉与水分配系数Kow变化一致;BTEX在改...     

Effects of Ethanol versus MTBE on Benzene, Toluene, Ethylbenzene, and Xylene Natural Attenuation in Aquifer Columns

The increased use of ethanol as a replacement for the gasoline oxygenate, methyl tert-butyl ether (MTBE), may lead to indirect impacts related to natural attenuation of benzene, toluene, ethylbenzene, and the three isomers of xylene (BTEX compounds). Ethanol could enhance dissolved BTEX mobility by exerting a cosolvent effect that decreases sorption-related retardation. This effect, however, is concentration dependent and was not observed when ethanol was added continuously (at 1%) with BTEX to sterile aquifer columns. Nevertheless, a significant decrease in BTEX retardation was observed with 50% ethanol, suggesting that neat ethanol spills in bulk terminals could facilitate the migration of pre-existing contamination. MTBE (25 mg/L influent) was not degraded in biologically active columns, and it did not affect BTEX degradation. Ethanol (2 g/L influent), on the other hand, was degraded rapidly and exerted a high demand for nutrients and electron acceptors that could otherwise have been used for BTEX degradation. Ethanol also increased the microbial concentration near the column inlet by one order of magnitude relative to columns fed BTEX alone or with MTBE. However, 16S-ribosomal ribonucleic acid sequence analyses of dominant denaturing gradient gel electrophoresis bands identified fewer species that are known to degrade BTEX when ethanol was present. Overall, the preferential degradation of ethanol and the accompanying depletion of oxygen and other electron acceptors hindered BTEX biodegradation, which suggests that ethanol could increase the length of BTEX plumes.     

Effect of BTEX on Degradation of MTBE and TBA by Mixed Bacterial Consortium

Methyl tert-butyl ether (MTBE) contamination in groundwater often coexists with benzene, toluene, ethylbenzene, and xylene (BTEX) near the source of the plume. Tertiary butyl alcohol (TBA) is a prevalent intermediate of MTBE degradation. Therefore, there is a significant potential for interference of MTBE and TBA degradation by the presence of BTEX whether treatment is in situ or ex situ. In this study, the effect of BTEX on the degradation of MTBE and TBA was examined using a mixed bacterial culture enriched on MTBE and BTEX. In batch studies, the presence of BTEX did not have a significant effect on MTBE degradation, but did have a slight effect on TBA degradation. Under continuous flow conditions, all compounds degraded simultaneously. Normalizing rates to the MTBE loading to the reactor indicates that BTEX may assist in the development of the biomass for TBA and overall MTBE degradation. Using denaturing gradient gel electrophoresis, several diverse organisms were identified, two of which showed very high similarity with PM1, a known MTBE degrader.     

Long-Term AS∕SVE for Petroleum Removal in Low-Permeability Piedmont Saprolite

A 3.5-year pilot test of air sparging∕soil vapor extraction (AS∕SVE) was carried out to determine whether the heterogeneity of the Piedmont saprolite would allow adequate soil vapor velocities and effective vapor-phase extraction rates for petroleum hydrocarbon (PHC) remediation. The objectives were to compare: (1) the effectiveness of pulsed SVE versus pulsed AS∕SVE operation; (2) benzene, toluene, ethylbenzene, and xylene (BTEX) versus PHC removal; and (3) biological versus physical removal of PHC. Stack exhaust gas, SVE wells, and soil vapor probes were monitored for total combustible hydrocarbons (TCH), BTEX, O2, CO2, temperature, and flow rate using handheld meters and gas chromatography. The majority of contaminant recovered was removed from the vadose zone via SVE. BTEX and TCH were both effectively removed from the more-permeable and highly contaminated unsaturated-saturated zone interface. Bioremediation accounted for 23% of total removal. Overall, the AS∕SVE system physically removed an estimated 18,800 kg of PHC and 5,300 g of BTEX with an average rate of 70 kg d?1 and 0.4 g d?1, respectively, which was consistent with other AS∕SVE studies in sandy media.     

Temperature Effects of Trickle-Bed Biofilter for Treating BTEX Vapors

Effects of temperature change in the range of 15–50°C on the performance of a trickle-bed biofilter for treating benzene, toluene, ethylbenzene and o-xylene (BTEX) vapors in air streams were investigated. In the steady-state condition, the BTEX removal efficiency increased as the operating temperature increased in the range of 15–30°C. However, an opposite trend was observed between 30 and 50°C. The trickle-bed biofilter appears to be an effective treatment process in the temperature range of 25–35°C. The microscopic observations showed that the morphologies of the leading microorganisms within the first-stage biofilm were rod-shaped bacteria in association with filaments, bacilli, and cocci at 15, 30, and 50°C, respectively. A theoretical evaluation on the temperature coefficient (θ) indicated that the temperature effects on the performance of a trickle-bed biofilter are more significant under lower BTEX loading rates. Furthermore, the mean θ value for a trickle-bed biofilter was equal to 1.021, which is in the typical range of some commonly used aerobic processes (1.0–1.10).     

Co-Occurrence of MTBE and Benzene, Toluene, Ethylbenzene, and Xylene Compounds at Marinas in Large Reservoir

Methyl tert-butyl ether (MTBE) is released into the environment as one of some gasoline components, not as a pure compound. Benzene, toluene, ethylbenzene, and xylene (BTEX) compounds are major volatile constituents found in gasoline and are water soluble and mobile. This study focused on the occurrence of MTBE with BTEX compounds in several marinas in Lake Texoma, which is a large reservoir located on the Oklahoma and Texas border. During a monitoring period from June 1999 to July 2001, MTBE and BTEX were detected in 28 and 5% of samples analyzed, respectively. Methyl tert-butyl ether co-occurred with BTEX compounds in 15% of lake water samples when detectable MTBE was present. The relatively low co-occurrence (15%) of MTBE with BTEX compounds is primarily due to the volume percentage in gasoline mixtures and physicochemical properties such as water solubility and Henry’s law constant. Toluene was the most commonly co-occurring BTEX with MTBE. Values of the ratios of the BTEX concentration to the MTBE concentration generally increase with depth of water.     

顶空气相色谱法测定水中苯系物

利用HP-FFAP毛细管柱分离苯系物,项空气相色谱法测定水中苯系物.讨论了顶空试样体积、平衡温度、平衡时间、氯化钠用量等因素对测定的影响.该方法实现了水中苯、甲苯、乙苯、对二甲苯、间二甲苯、邻二甲苯、苯乙烯等各组分的完全分离,方法的检出限在1.3 ～1.6 μg/L,RSD为1.57％ ～2.35％ （n =6）,加标回收率为99.0％ ～102％（n=6）.本方法可用水中苯系物的测定.     

Control of Incinerator Organics by Fluidized Bed Activated Carbon Adsorber

Adsorption on activated carbon of organic compounds from a particle-free and low temperature gas stream has been investigated previously. However, the adsorption processes in a fluidized bed adsorber of particles interfacing with high temperature flue gas has rarely been studied. The major objective of the work was to demonstrate the performance of a fluidized activated carbon adsorber for removal of organic compounds [polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene, and xylene (BTEX)] and particulate from flue gas of an incinerator at selected fluidized velocities, fixed bed heights, and bed temperatures. The particle-size distribution of particulate prior to and after flowing through the fluidized adsorption bed were also analyzed. The results indicate that the fluidized bed activated carbon adsorber has a high removal efficiency of PAHs and BTEX. Three evaluated parameters show different effects on PAHs, BTEX, and particles. That the fluidized bed activated carbon adsorber has the ability to filter coarse particles due to the inertia collision is also identified.     

Treatment of MTBE-Contaminated Water in Fluidized Bed Bioreactor

Methyl tertiary-butyl ether (MTBE) biodegradation was evaluated in a laboratory-scale granular activated carbon (GAC)-based fluidized bed bioreactor system. The reactor was operated in seven distinct phases during which the MTBE loading rate, hydraulic retention time, cocontaminant loading [butyl, toluene, ethylbenzene, and xylene (BTEX) and tertiary-butyl alcohol (TBA)] and temperature were varied. The reactor was able to treat MTBE to less than 20 ug/L at 25°C and total organic carbon (TOC) loading rates between 0.01 and 1.1 kg/m3 of expanded GAC bed per day (kg/m3?day). Net biomass yield in the reactor under high loading conditions was approximately 0.55 g of total suspended solids (TSS) per gram of TOC consumed. This high yield under the higher loading rates necessitated that biomass be removed from the reactor to control bed expansion. At a loading rate of 1.5 kg/m3?day, MTBE effluents exceeded 20 ug/L. Reactor performance decreased as the reactor temperature was reduced from 25 to 15°C, but even at the lower temperatures MTBE removal efficiency exceeded 99%. Methyl tertiary-butyl ether treatment efficiency was not affected by the addition of TBA or BTEX under the conditions evaluated. Results of this study demonstrate that fluid bed bioreactors inoculated with an appropriate microbial culture can efficiently treat MTBE-contaminated water.     

Estimation of Koc values for deuterated benzene, toluene, and ethylbenzene, and application to ground water contamination studies

Sorption partition coefficients between water and organic carbon (Koc) for deuterated benzene, toluene, and ethylbenzene have been estimated by measuring values of the octanol-water partition coefficient (Kow) and HPLC retention factors (k1), which correlate closely to values of Koc. Measured values of log Kow for non-deuterated and deuterated toluene are 2.77 (+/- 0.02) and 2.78 (+/- 0.04), respectively, indicating that within experimental error, log Koc for deuterated and non-deuterated toluene are the same. The HPLC method provides greater precision, and yields values of delta log Koc (= log Koc [deuterated]-log Koc [non-deuterated]) of -0.021 (+/- 0.001) for benzene, -0.028 (+/- 0.002) for toluene, and -0.035 (+/- 0.003) for ethylbenzene. The small values of delta log Koc demonstrates that deuterated compounds are excellent tracers for the hydrologic behavior of ground water contaminants.