Benzene, Toluene, Ethylbenzene And O-xylene Research Articles

Sulfonation of Divinylbenzene Adsorbents Packed in a Micro Sampler to Extract Airborne Organic Compounds

ABSTRACT In this work, sulfonated divinylbenzene (SDVB) adsorbents, with the 60–80 mesh diameter, were packed inside a 22-gauge stainless steel needle to fabricate a sulfonated needle trap sampler (SNTS), which is a micro sampler. An analysis of Fourier-transform infrared spectroscopy (FTIR) scanning data, thermal gravimetric analysis (TGA) data, and scanning electron microscopice (SEM) observations, confirmed the physiochemical characteristics of sulfonated DVB adsorbent resins. A gas mixture of approximately 20 ppm of ethanol, methyl ethyl ketone (MEK), benzene, toluene, ethylbenzene and o-xylene (BTEX) was prepared to evaluate the sampling efficacies of the SNTS. The results reveal that, in 1–2 h, SNTS adsorbed increased 92–116% more methanol and 12–20% more MEK than NTS. The SNTS adsorbed 4–15% less BTEX than the NTS. The tested SNTS exhibited remarkable adsorption capacities of methanol, which emitted in a metal frame manufacturing plant. The SNTS is recommended as an alternative passive sampler to the active adsorbent tubes.

Ultrasound-assisted heterogeneous activation of persulfate and peroxymonosulfate by asphaltenes for the degradation of BTEX in water

This study investigated – for the first time – the simultaneous degradation of benzene, toluene, ethylbenzene and o-xylene (BTEX) by persulfate (PS) and peroxymonosulfate (PMS) activated by asphaltenes (Asph) under ultrasound (US) irradiation. Advantageous properties such as high thermal stability, low production cost and extensive availability make asphaltenes as an appealing carbonaceous material for heterogeneous catalysis. The application of asphaltenes in PS/US increased the degradation of BTEXs from 31%, 34%, 35%, 32%–78%, 94%, 98% and 98%, while the removal of these compounds in PMS/US system was improved from 26%, 27%, 24%, 20%–76%, 91%, 97%, 97%, respectively. PS and PMS activation followed a typical sulfate-radical based advanced oxidation processes. In terms of activation of PS and PMS, the particles of asphaltenes intensified formation of reactive radicals by creating additional centers of cavitational events. Moreover, owing to π–π stacking interaction between asphaltenes and sp2-hybridized systems of BTEX, the contaminants undergo adsorption on the surface of asphaltenes and subsequent oxidation by formed radicals. The radical route of BTEX degradation in both PS/US/Asph and PMS/US/Asph systems was mainly contributed by sulfate (SO4•−) and hydroxyl radicals (HO•) and coexisting superoxide radical anions (O2•−) played a minor role.

Monitoring of volatile organic compounds in ambient air of Taldykorgan, Kazakhstan

The pollution of ambient air is one of the main sources of risk to human health in the world. There is a direct relationship between the level of air pollution and risk of the development of cancer, cardiovascular, respiratory and other diseases. Benzene, toluene, ethylbenzene and o-xylene (BTEX) are one of the most toxic volatile organic compounds. The aim of this study was to quantify BTEX in air of Taldykorgan, Kazakhstan using solid-phase microextraction followed by gas chromatography with mass-spectrometric detection. In different sampling seasons, average concentrations of four BTEX analytes varied from 7.5 to 27 µg/m3, from 15 to 250 µg/m3, from 2.4 to 12.8 µg/m3 and from 2.6 to 21 µg/m3, respectively. The highest concentrations of TEX were detected in autumn, while the highest concentrations of benzene were observed in winter. Toluene-to-benzene ratios in almost all measurements were above 1 indicating that the traffic emissions are the main source of air pollution with BTEX.

Development of A Fiber-Packed In-Tube Extraction Device and Its Application in BTEX Analysis

Abstract A fiber-packed in-tube extraction device was developed with heat-resistant fibers coated with molecularly imprinted polymer as adsorbent for concentration detection of volatile organic compounds (VOCs). The coated fibers were longitudinally packed into a filling chamber. The inner diameter of the filling chamber was 3 mm and its length was 2.5 cm. The filling chamber was connected to gas chromatography port by a stainless needle. The device was heated by an external heater consisting of the heating wire surrounded outside of the filling chamber to gasify the analytes in the adsorbent. The prepared fiber-packed in-tube extraction device was used to analyze benzene, toluene, ethylbenzene and o-xylene (BTEX) in gas sample coupled with gas chromatography. The result showed that the device had better permeability. The extraction time for 150 mL of gas sample was 1.2 min. The linear detection range, recovery, limit of detection (LOD) and limit of quantification (LOQ) were also evaluated for the promising method. The linear detection ranges for BTEX were all 1–300 μg L−1, with the correlation coefficients of greater than 0.9936. The LODs and LOQs of the analytes were in the range of 0.02–0.03 μg L−1 and 0.03–0.05 μg L−1, respectively. The recoveries of BTEX were 90.3%, 94.3%, 98.7% and 103.3%, respectively.

Novel highly-integrated mems based solid state detectors for analytical gas chromatography

In this work, a novel detector of gaseous analytes for monitoring of low levels of BTEX (benzene, toluene, ethylbenzene and o-xylene) is discussed. The detector is based on SnO2 thin (30nm) films functionalized with gold-palladium (9:1 molar ratio) bimetal nanoparticles. The detector consists of four independent sensing elements thermally activated by an internal heater. The performance of Au/Pd@SnO2 sensing elements was evaluated in comparison with some other gas sensitive materials, such as: pure SnO2, SnO2 decorated with gold (Au), and SnO2 decorated with palladium (Pd) nanoparticles. The superiority of the gas sensing performance of the Au/Pd@SnO2 nanocomposite structure was demonstrated based on its response to low concentrations (12.5-500 ppb) of benzene or toluene. A more complex analysis of gaseous mixtures with different concentrations (0.3–20ppb) of BTEX mixture was accomplished by incorporating the novel detector into the portable gas chromatograph (GC) PAC R1120. High sensitivity of the detector in combination with fast response and recovery time allowed us to obtain fine gas chromatograms and to perform a complete analysis of a gas sample in less than 11min. Ultra-low concentrations of BTEX components at sub-ppb level (0.3 ppb) were identified and detected by the GC analysis. Besides the experimental data, the theoretical validation of the detector’s high performance was provided based on high catalytic activity of Au/Pd nanoparticles and electronic interaction of bimetal nanoclusters with SnO2 support.

Идентификация и определение органических загрязнителей в воздухе города Астана с использованием твердофазной микроэкстракции

Solid-phase microextraction in combination with gas chromatography and mass-spectrometry (GC-MS) was used for determination of benzene, toluene, ethylbenzene and o-xylene (BTEX), polycyclic aromatic hydrocarbons (PAH), and for identification of volatile organic compounds (VOCs) in ambient air of the city of Astana, Kazakhstan. The screening of the samples showed the presence of mono- and polycyclic aromatic hydrocarbons, alkanes, alkenes, phenols, and benzaldehydes. The concentrations of naphthalene were 5-7 times higher than the permissible value, it was detected in all studied air samples. Average concentration of naphthalene was 18.4 μg/m3, acenaphthylene – 0.54 μg/m3, acenaphthene – 1.63 μg/m3, fluorene – 0.79 μg/m3, anthracene – 3.27 μg/m3, phenanthrene – 0.22 μg/m3, fluorantene – 0.74 μg/m3, pyrene – 0.73 μg/m3. Average concentrations of BTEX in the studied samples were 31.1, 84.9, 10.8 and 11.6 μg/m3, respectively. Based on the statistical analysis of the concentrations of BTEX and PAH, the main source of city air pollution with them was assumed to be vehicle emissions.

Adsorption of Benzene, Toluene, Ethylbenzene and o-Xylene by Carbon-Based Adsorbents

This study explored the possibility of applying different carbon-based adsorbents for removal of benzene, toluene, ethylbenzene and o-xylene (BTEX) from indoor air in static and dynamic modes. To determine BTEX removal effectiveness, the approach based on solid-phase microextraction (SPME) in combination with gas chromatography – mass spectrometry (GC-MS) was used. In static mode, removal effectiveness of BTEX from indoor air using different carbon-based adsorbents (shungite, walnut shell, saxaul, apricot pits, activated charcoal, Tenax, carbon black) varied from 80% to 100%. Optimal preparation conditions for shungite-based adsorbent are no activation and addition of NaOH at 1:0.8 ratio. Shungite-based adsorbent was not able to remove BTEX from polluted indoor air at the flow rate 300 mL/min corresponding to the linear flow rate 25 cm/s, a minimum value for most commercial air purification systems. At the flow rate 75 mL/min (6.25 cm/s), a saturation time of shungite-based adsorbent made up 368 min for benzene and 437 min for toluene. At this flow rate, BTEX adsorption capacities of the shungitebased adsorbent were 0.3, 2.1, 0.2 and 0.3 μg/g, respectively. Compared to shungite, activated charcoal allowed the complete removal of BTEX at both flow rates in the whole studied time frame. Thus, shungite-based adsorbents are not recommended for BTEX removal from air because of much greater efficiencies of classic activated charcoal adsorbents. Applied methodology based on SPME-GC-MS allowed simple, fast and inexpensive collection of data and can be recommended as the analytical for developing new adsorbents and systems for air purification.

Carbon nanospheres covalently modified with polydimethylsiloxane on a porous sol–gel support for use in headspace solid-phase fiber microextraction of BTEX

Carbon nanospheres were covalently modified with hydroxy-terminated poly(dimethylsiloxane) to give a new sorbent (referred to as CNS-PDMS). It was applied as the extraction phase in a sol–gel based solid-phase microextraction fiber for benzene, toluene, ethylbenzene and o-xylene (BTEX). Due to the unique properties of CNS and the performance of the sol–gel coating technology, this fiber possesses a porous surface, a long operational lifespan (at least 200 times), and high thermal stability (up to 350°C). Its extraction capability is higher than that of commercial polydimethylsiloxane (PDMS) and polydimethylsiloxane/divinylbenzene (PDMS/DVB) fibers. Following desorption, the BTEX were quantified by GC with FID detection. The detection limits (at an S/N ratio of 3) range from 1 to 10 pg mL−1, and the limits of quantification (at an SNR of 10) are between 3 and 30 pg mL−1. The repeatability of a single fiber (for n = 5) is between 3.9 and 6.3%, and the fiber-to-fiber reproducibility (for n = 3) ranges from 5.3 to 8.2%, respectively. The relative recoveries in the real water samples ranged from 92.5% to 99.5%. The results demonstrate that the method is highly effective for analyzing BTEX in water samples.

Quantification of benzene, toluene, ethylbenzene and o-xylene in internal combustion engine exhaust with time-weighted average solid phase microextraction and gas chromatography mass spectrometry

A new and simple method for benzene, toluene, ethylbenzene and o-xylene (BTEX) quantification in vehicle exhaust was developed based on diffusion-controlled extraction onto a retracted solid-phase microextraction (SPME) fiber coating. The rationale was to develop a method based on existing and proven SPME technology that is feasible for field adaptation in developing countries. Passive sampling with SPME fiber retracted into the needle extracted nearly two orders of magnitude less mass (n) compared with exposed fiber (outside of needle) and sampling was in a time weighted-averaging (TWA) mode. Both the sampling time (t) and fiber retraction depth (Z) were adjusted to quantify a wider range of Cgas. Extraction and quantification is conducted in a non-equilibrium mode. Effects of Cgas, t, Z and T were tested. In addition, contribution of n extracted by metallic surfaces of needle assembly without SPME coating was studied. Effects of sample storage time on n loss was studied. Retracted TWA–SPME extractions followed the theoretical model. Extracted n of BTEX was proportional to Cgas, t, Dg, T and inversely proportional to Z. Method detection limits were 1.8, 2.7, 2.1 and 5.2mgm−3 (0.51, 0.83, 0.66 and 1.62ppm) for BTEX, respectively. The contribution of extraction onto metallic surfaces was reproducible and influenced by Cgas and t and less so by T and by the Z. The new method was applied to measure BTEX in the exhaust gas of a Ford Crown Victoria 1995 and compared with a whole gas and direct injection method.

A non-ionic surfactant-mediated sol–gel coating for solid-phase microextraction of benzene, toluene, ethylbenzene and o-xylene in water samples using a gas chromatography-flame ionization detector

In this study, sol–gel hybrid organic–inorganic materials were prepared in the presence of polyethyleneoxide (PEO) non-ionic surfactants (Triton X-100), which act as co-porogenic agents. For the first time, non-ionic surfactant mediated sol–gel coatings were evaluated by analyzing benzene, toluene, ethylbenzene and o-xylene (BTEX) in the aqueous samples. Two different fiber coatings were prepared including: un-modified poly(dimethylsiloxane) (PDMS) coating prepared from PDMS in the absence of Triton X-100 as a non-ionic surfactant (PDMS-no TX100), and modified PDMS coating prepared from this polymer in the presence of Triton X-100 as a porogenic agent and conditioned at a higher temperature than decomposition temperature of a non-ionic surfactant (PDMS-TX100). After the analytical procedure was optimized, the dynamic linear range obtained using PDMS-TX100 and PDMS-no TX100 fibers was 4–200 000 and 100–200 000 pg mL−1 and the limits of detection (S/N = 3) were 1–3 and 30–300 pg mL−1, respectively. The relative standard deviations (RSDs) for one fiber (repeatability) (n = 5) were from 3.1 up to 6.2% and between fibers or batch to batch (reproducibility) (n = 3) in the range of 4.2–7.7% for three fibers. The developed method was successfully applied to the real water samples while the relative recovery percentages obtained for the spiked water samples at 20 pg mL−1 of each analyte were from 94.41 to 104.05%.

Gaseous and Particle‐bound VOC Products of Combustion Extracted by Needle Trap Samplers

AbstractGaseous benzene, toluene, ethylbenzene and o‐xylene (BTEX) were extracted by using the divinylbenzene (DVB) particles (mesh sizes 60–80, 80–100 and 100–120) as sorbents packed in passive needle trap samplers (NTS). This study performed feasibility tests of these self‐designed DVB‐NTS as diffusive time‐weighted average (TWA) samplers and compared extraction efficiency with that of 100 mm polydimethylsiloxane‐solid phase microextration (PDMS‐SPME) fiber for sampling gaseous and particle‐bound volatile organic compounds (VOCs) from burning mosquito coils. Experimental results indicated that extraction rate of NTS is a reliable index in extracting VOCs. Additionally, comparisons of the NTS in extracting BTEX mass showed the NTS packed with the smallest diameters of adsorbent particles (100–120 mesh DVB) were the most effective. The mass of gaseous BTEX extracted by 100 μm PDMS‐SPME fiber were substantially lower than that extracted by DVB‐NTS of all meshes for the 30‐min TWA sampling of burning mosquito coils, and NTS packed with 100–120 mesh DVB adsorbed BTEX 50–120 ng BTEX. Particles clogging inside the packed phase of NTS inhibited VOC extraction performance after 3–5 samplings of burning particles, especially NTS packed with small‐diameter adsorbents.

A solid phase microextraction coating based on ionic liquid sol–gel technique for determination of benzene, toluene, ethylbenzene and o-xylene in water samples using gas chromatography flame ionization detector

Ionic liquid mediated sol–gel sorbents for head-space solid phase microextraction (HS-SPME) were developed for the extraction of benzene, toluene, ethylbenzene and o-xylene (BTEX) compounds from water samples in ultra-trace levels. The analytes were subsequently analyzed with gas chromatography coupled to flame ionization detector (GC-FID). Three different coating fibers were prepared including: poly(dimethylsiloxane) (PDMS), coating prepared from poly(dimethylsiloxane) in the presence of ionic liquid as co-solvent and conditioned at a higher temperature than decomposition temperature of ionic liquid (PDMS-IL-HT) and coating prepared from poly(dimethylsiloxane) in the presence of ionic liquid as co-solvent and conditioned at a lower temperature than decomposition temperature of ionic liquid (PDMS-IL-LT). Prepared fibers demonstrate many advantages such as high thermal and chemical stabilities due to the chemical bonding of the coatings with the silanol groups on the fused-silica surface fiber. These fibers have shown long life time up to 180 extractions. The scanning electron micrographs of the fibers surfaces revealed that addition of ionic liquid into the sol solution during the sol–gel process increases the fiber coating thickness, affects the form of fiber structure and also leaves high pores in the fiber surface that cause high surface area and therefore increases sample capacity of the fibers. The important parameters that affect the extraction efficiency are desorption temperature and time, sample volume, extraction temperature, extraction time, stirring speed and salt effect. Therefore these factors were investigated and optimized. Under optimal conditions, the dynamic linear range with PDMS-IL-HT, PDMS and PDMS-IL-LT fibers were 0.3–200,000; 50–200,000 and 170–150,000pgmL−1 and the detection limits (S/N=3) were 0.1–2 and 15–200 and 50–500pgmL−1, and limit of quantifications (S/N=10) were 0.3–8 and 50–700 and 170–1800, respectively. The relative standard deviations (RSD) for one fiber (repeatability) (n=5), were obtained from 3.1 up to 5.4% and between fibers or batch to batch (reproducibility) (n=3) in the range of 3.8–8.5% for three fibers. The developed method was successfully applied to the real water samples while the relative recovery percentages obtained for the spiked water samples at 20pgmL−1 were from 91.2 to 103.3%.

Modelling and kinetic aspects of a BTEX contaminated air-treating biofilter

In this study, the overall performance of a biofilter was evaluated in terms of its elimination capacity by using 3-D mesh techniques. The overall results indicate that the agreement between experimental data and model predictions is excellent for benzene, toluene, ethylbenzene and o-xylene (BTEX). In this study, the maximum removal rate (r max) values for BTEX were 0.0117, 0.0126, 0.0081 and 0.0146 g m–3 h–1, and the half-saturation constant (KS ) values were calculated to be 0.269, 0.297, 0.156 and 0.394 g m–3, respectively. For this system, the coefficients of determination (r 2) of BTEX compounds were greater than 0.97. The BTEX concentration profiles along the depth were also determined using a convection–diffusion reactor (CDR) model. The sums of squares of the errors (SSEs) of BTEX were 0.0078, 0.0059, 0.0129 and 0.0269, respectively, with r 2 values greater than 0.99 for all four compounds at low concentrations.

Application of ultrasound-assisted emulsification microextraction for determination of benzene, toluene, ethylbenzene and o-xylene in water samples by gas chromatography

An ultrasound-assisted emulsification microextraction procedure has been developed for determination of benzene, toluene, ethylbenzene and o-xylene (BTEXs) in water samples by gas chromatography–flame ionization detection system (GC–FID). The method is based on the dispersion of microvolumes of an organic solvent in the aqueous phase and subsequent extraction of target analytes into the fine droplets of the organic phase. After centrifugation, the sedimented phase is separated and directly injected to the GC system. The effects of experimental parameters such as type and volume of organic solvent, sonication and extraction times, salt effect and centrifugation time were evaluated and optimized. Under the optimum conditions a relatively broad dynamic linear range of 0.01–20μgmL−1 and a good linearity (R2) ranging from 0.9986 to 0.9998 were obtained for all the target analytes. The repeatability and reproducibility for 2μgmL−1 of each analyte (n=5) were in the range of 1.58–5.75% and 2.54–5.89%, respectively. The limit of detection (S/N=3) and preconcentration factor were in the range of 0.4–2μgL−1 and 653–835, respectively. Finally, the purposed method has been successfully applied to the determination of BTEX compounds in different water samples and good spiked recoveries over the range of 94–99% were obtained.

A novel solid-phase microextraction using coated fiber based sol–gel technique using poly(ethylene glycol) grafted multi-walled carbon nanotubes for determination of benzene, toluene, ethylbenzene and o-xylene in water samples with gas chromatography-flam ionization detector

In this study, poly(ethylene glycol) (PEG) grafted onto multi-walled carbon nanotubes (PEG-g-MWCNTs) were synthesized by the covalent functionalization of MWCNTs with hydroxyl-terminated PEG chains. For the first time, functionalized product of PEG-g-MWCNTs was used as selective stationary phase to prepare the sol–gel solid-phase microextraction (SPME) fiber in combination with gas chromatography-flame ionization detector (GC-FID) for the determination of ultra-trace levels of benzene, toluene, ethylbenzene and o-xylene (BTEX) in real water samples. The PEG-g-MWCNTs were characterized by Fourier transform infrared spectra and also thermo-gravimetric analysis, which verified that PEG chains were grafted onto the surface of the MWCNTs. The scanning electron micrographs of the fiber surface revealed a highly porous structure which greatly increases the surface area for PEG-g-MWCNTs sol–gel coating. This fiber demonstrated many inherent advantages, the main being the strong anchoring of the coating to the fused silica resulting from chemical bonding with the silanol groups on the fused-silica fiber surface. The new PEG-g-MWCNTs sol–gel fiber is simple to prepare, robust, with high thermal stability and long lifetime, up to 200 extractions. Important parameters influencing the extraction efficiency such as desorption temperature and time, extraction temperature, extraction time, stirring speed and salt effect were investigated and optimized. Under the optimal conditions, the method detection limits (S/N = 3) were in the range of 0.6–3 pg mL −1 and the limits of quantification (S/N = 10) between 2 and 10 pg mL −1. The relative standard deviations (RSDs) for one fiber (repeatability) ( n = 5) were obtained from 4.40 up to 5.75% and between fibers or batch to batch ( n = 3) (reproducibility) in the range of 4.31–6.55%. The developed method was successfully applied to real water samples while the relative recovery percentages obtained for the spiked water samples at 20 pg mL −1 were from 90.21 to 101.90%.

Comparative study of direct immersion and headspace single drop microextraction techniques for BTEX determination in water samples using GC-FID

In the present work the determination of benzene, toluene, ethylbenzene and o-xylene (BTEX) in environmental sample solutions using gas chromatography with flame ionisation detection (GC-FID) combined with three different sampling techniques, such as; direct single drop microextraction (DI-SDME), headspace single drop microextraction (HS-SDME) and ultrasonic assisted HS-SDME, were compared. In all of these techniques, for the determination of BTEX, the experimental parameters such as organic solvent effect, extraction time, agitation speed and salting effect were optimised. At their optimised conditions of operation the detection limits, times of extraction and precision for the three techniques are established. A detailed comparison of the analytical performance characteristics of these techniques for final GC-FID determination of BTEX in water samples was given. The technique provided a linear range of 50–20000 ng mL–1 for DI-SDME and 10–20000 ng mL–1 for HS-SDME methods, good repeatability (RSDs <4.72–7.74% for DI-SDME and 1.80–7.05% for HS-SDME (n = 5), good linearity (r ≥ 0.9978) and limits of detection (LODs) in the range of 0.006–10 ng mL−1 for DI-SDME, 0.1–3 ng mL–1 for HS-SDME methods (S/N = 3). Then the optimised techniques were also applied to real samples (river and waste waters) containing BTEX and similar precision (RSD < 8.2, n = 3) was obtained.

Model for a solid‐liquid airlift two‐phase partitioning bioscrubber for the treatment of BTEX

AbstractBACKGROUND: Airlift solid–liquid two‐phase partitioning bioreactors (SL‐TPPBs) have been shown to be effective for the treatment of gas streams containing benzene, toluene, ethylbenzene and o‐xylene (BTEX). The airlift SL‐TPPB is a low‐energy system that utilizes a sequestering phase of solid silicone rubber beads (10%v/v) that will uptake and release large amounts of BTEX in order to maintain equilibrium conditions within the system. This increases mass transfer from the gas phase during dynamic loading periods and improves degradation performance. This study discusses the development and analysis of a steady‐state, tanks‐in‐series mathematical model, arising from mass balances on BTEX and oxygen in the gas, aqueous and polymer phases to predict the performance of the airlift SL‐TPPB over various gas flow rates and BTEX loadings.RESULTS: An estimability analysis on model parameters determined that the parameters to which model output is most sensitive are those that affect biological activity, which were targeted for estimation. The developed tanks‐in‐series model was able to predict the removal of BTEX components and dissolved oxygen concentrations over various inlet loadings (20, 60 and 100 mg L−1 h−1) and gas flow rates (2,3 and 4 L min−1) that resulted in a range of system performance from effective BTEX treatment to oxygen limiting conditions.CONCLUSIONS: The model developed, with estimated parameters, provides a valuable tool to determine operating conditions that will result in favourable performance of the airlift SL‐TPPB. Copyright © 2009 Society of Chemical Industry

Biodegradation of BTEX compounds in a biofilm reactor—Modeling and simulation

In this study the biodegradation process of toxic compounds such as benzene, toluene ethylbenzene and o-xylene (BTEX), present in petrochemical effluents is described by a phenomenological model expressed through a single differential equation which allows the description of the concentration profile through a fixed bed biofilm reactor. The mechanisms which control the mass transfer, such as the effects of dispersion, convection and reaction in the liquid phase, and of diffusion and reaction within the biofilm, are considered in this model. The reaction in the biofilm is described by Michaelis–Menten kinetics. The Finite Volume Method (FVM) is used in the discretization of the differential equation of the phenomenological model, an algorithm being developed for the numerical simulation of the biodegradation process of BTEX compounds under different operational conditions. The computational algorithm developed was validated by comparing the results of the numerical simulation of the biodegradation process of BTX compounds with experimental data provided in the literature. The results obtained through the simulations showed that the parameters evaluated in this study influenced the biodegradation of BTEX compounds, and that the mathematical model and the numerical methodology adopted can be used as an efficient tool for predicting the dynamic and stationary behavior of the biodegradation process.

Model for a solid–liquid stirred tank two-phase partitioning bioscrubber for the treatment of BTEX

A dynamic mathematical model has been developed to predict the performance of a stirred tank, solid–liquid two-phase partitioning bioreactor (SL-TPPB) for the treatment of benzene, toluene, ethylbenzene and o-xylene (BTEX) contaminated gases. The SL-TPPB system consists of an aqueous phase containing a bacterial consortium and a solid phase of silicone rubber beads (10%; v/v) with a high affinity for BTEX compounds. The silicone rubber beads serve to sequester and release BTEX according to thermodynamic equilibrium, which increases mass transfer from the gas phase and reduces aqueous phase concentrations of these toxic compounds during fluctuating inlet loadings. The model was developed from mass balances on BTEX components in the gas, aqueous and polymer phases, and biomass in the aqueous phase. Dynamic experimental data from this system were used to fit model parameters and to assess the accuracy of the model. A detailed estimability analysis of model parameters and initial conditions was completed to identify uncertain parameters that are most influential for the model predictions and to determine the parameters and initial conditions that should be targeted for estimation using the dynamic data. It was found that the developed model, with estimated parameters and initial conditions, has the ability to predict experimental off-gas BTEX concentrations with reasonable accuracy, which are the outputs of greatest importance.

Response of a solid–liquid two-phase partitioning bioreactor to transient BTEX loadings

A two-phase partitioning bioreactor (TPPB) consisting of an aqueous phase containing a bacterial consortium and a polymeric phase of silicone rubber pellets (solid volume fraction 0.1) was used to treat a gaseous waste stream containing benzene, toluene, ethylbenzene and o-xylene (BTEX). The function of the solid polymer phase was to absorb/desorb the gaseous volatile organic compounds providing a buffering effect to protect the cells from high transient loadings and to sequester the BTEX for subsequent degradation. The TPPB was subjected to high and fluctuating inlet loadings of BTEX in the form of 4 h step changes of 2, 4, 6 and 10 times the nominal inlet loading of 60 g m −3 h −1 total BTEX in approximately equal amounts, and removal efficiencies and elimination capacities were determined. It was found that overall removal efficiencies of greater than 95% can be achieved while obtaining overall elimination capacities of up to 282 g m −3 h −1 during transient operation and TPPB operation succumbs to toxic substrate levels between step changes of 6 and 10 times the nominal loading value (360–600 g m −3 h −1). BTEX concentrations in the aqueous phase and the polymer phase of the TPPB were monitored throughout the imposed step changes to determine the extent to which the sequestering phase can buffer the aqueous phase from BTEX. With the polymer phase comprising only 10% of the total working volume of the reactor, the polymer beads accounted for up to 93%, 91% and 70% of the total BTEX present in the working volume for step changes of 2, 4 and 6 times the nominal loading, respectively.