Removal Of Toluene Vapors Research Articles

Removal of toluene in a biotrickling filter in the presence of methanol vapors: Experimental study, mathematical modeling, and kinetic parameters optimization

The performance of biotrickling filters (BTFs) has been significantly affected during the co-treatment of volatile organic compounds (VOCs) with different hydrophilicities. Removal of toluene vapor as a hydrophobic compound in the absence and presence of methanol as a hydrophilic pollutant was studied in a BTF. The inlet loading ranges were 18−36 g.m−3.h−1 for toluene and 0−225 g.m−3.h−1 for methanol at constant empty bed residence time (EBRT) of 60 s. The removal efficiency of toluene (RET) varied from 30 to 80 %, while RE of methanol (REM) remained almost constant at > 90 % within different phases of experiments due to the unlimited solubility in water. A comprehensive dynamic mathematical model consisting of mass transfer through gas, liquid, and biofilm phases with the kinetic of biodegradation in the BTF and accumulation of methanol in liquid was developed. The interaction parameters were optimized by genetic algorithm and validated by experimental data. Sensitivity analysis on the optimized parameters showed that biofilm thickness and methanol interaction parameter had the most effects on RET as 45 % and 38 %, respectively. Model simulation showed that 43–90 % of biofilm depth was active for toluene degradation at different inlet gas-phase concentrations, indicating a diffusion-limited condition in the process. In contrast, all depth of biofilm was fully active for methanol degradation, showing a kinetic-limited regime dominant for methanol removal in the BTF under all operating conditions. Results showed that the developed model could effectively predict the dynamics of VOCs removals along with the determination of kinetic constants.

Removal of toluene vapor in the absence and presence of a quorum-sensing molecule in a biotrickling filter and microbial composition shift

Toluene is highly toxic and mutagenic, and it is generally used as an industrial solvent. Thus, toluene removal from air is necessary. To solve the problem of reducing high toluene concentrations with a short gas retention time (GRT), a quorum-sensing molecule [N-(3-oxododecanoyl)-L-homoserine lactone] (OHL) was added to a biotrickling filter (BTF). In this study, a BTF was used to treat synthetic and natural waste gases containing toluene. An extensive analysis was performed to understand the removal efficiency, removal characteristics, and bacterial community of the BTF. The addition of 20 μM OHL to the BTF significantly improved toluene removal, and more than 99.2% toluene removal was achieved at a GRT of 0.5 min when natural waste gas containing toluene (590–1020 ppm or 2.21–3.83 g m−3) was introduced. The maximum inlet load for toluene was 337.9 g m−3 h−1. Moreover, the BTF exhibited satisfactory adaptability to shock loading and shutdown operations. Pseudomonadaceae (33.0%) and Comamonadaceae (26.3%) were predominant bacteria in the system after a 98-day operation. These bacteria were responsible for toluene degradation. The optimal moisture content and low pressure drop for system operations demonstrated that the BTF was energy and cost efficient. Therefore, processing through a BTF with OHL is a favorable technique for toluene treatment.

Removal of toluene vapors from the polluted air with modified natural zeolite and titanium dioxide nanoparticles.

Toluene is a colorless and flammab1le liquid with the same solubilizing capacity as benzene that is in many cases used as an alternative to benzene, because of the uncertainty of being carcinogens. Workers can be exposed to toluene by breathing the chemical. To avoid inhalation and dermal effects caused by exposure to toluene, solutions such as adsorption, thermal oxidation, membrane separation and photocatalytic processes are applied. In this study, removal of toluene vapors with modified natural zeolite and titanium dioxide nanoparticles was discussed. The natural zeolite was modified using chemical and thermal methods. The samples characterized by Brunauer-Emmet-Teller, Barrett-Joyner-Halenda, X-ray diffraction and scanning electron microscopy tests. After stabilization of TiO2 nanoparticles, the removal efficiency for the toluene vapors at a concentration of 50, 150 and 300 ppm were evaluated using a dynamic system. The results showed that the zeolite has a very porous surface and after modifying the context its specific surface area increased 2.54 times. The results of the adsorption capacity calculation and photocatalytic process showed that modified zeolite samples-TiO2 bed has greater efficiency in the adsorption capacity and better photocatalytic activity than a Ze-TiO2 bed. Ze-TiO2 bed was able to remove 26% of toluene vapors at the concentration of 50 ppm and inlet flow rate of 1 L/m, which was 1.26 times more than a bed Ze-TiO2. According to the results of this study, while modifying the natural zeolite increased desirable properties such as specific surface area and Si/Al ratio, but in comparison with similar studies with synthetic bed such as zeolite Y and ZSM-5, could not achieve desired results in a photocatalytic activity for its application in industry. However, because of its abundance in the world and Iran and therefore low cost of preparation and also due to its unique characteristics, it is recommended that more studies to be done about modifying and its application in photocatalytic processes.

Application of Glycyrrhiza glabra root as a novel adsorbent in the removal of toluene vapors: equilibrium, kinetic, and thermodynamic study.

The aim of this paper is to investigate the removal of toluene from gaseous solution through Glycyrrhiza glabra root (GGR) as a waste material. The batch adsorption experiments were conducted at various conditions including contact time, adsorbate concentration, humidity, and temperature. The adsorption capacity was increased by raising the sorbent humidity up to 50 percent. The adsorption of toluene was also increased over contact time by 12 h when the sorbent was saturated. The pseudo-second-order kinetic model and Freundlich model fitted the adsorption data better than other kinetic and isotherm models, respectively. The Dubinin-Radushkevich (D-R) isotherm also showed that the sorption by GGR was physical in nature. The results of the thermodynamic analysis illustrated that the adsorption process is exothermic. GGR as a novel adsorbent has not previously been used for the adsorption of pollutants.

Modeling of a foamed emulsion bioreactor: I. Model development and experimental validation

Recently, a new type of bioreactor for air pollution control referred to as the foamed emulsion bioreactor (FEBR) has been developed. The process relies on the emulsion of an organic phase with a suspension of an actively growing culture of pollutant-degrading microorganisms, made into a foam with the air undergoing treatment. In the current paper, a diffusion and reaction model of the FEBR is presented and discussed. The model considers the fate of the volatile pollutant in the emulsion that constitutes the liquid films of the FEBR. Oxygen limitation as well as substrate inhibition were included in the biokinetic relationships. The removal of toluene vapors served for the validation of the model. All the model parameters were determined by independent experiments or taken from the literature. The model predictions were found to be in good agreement with the experimental data and the model provided useful insights on the phenomena occurring in the FEBR. Model parametric sensitivity studies and further discussion of the factors that limit the performance of the FEBR are presented in Part 2 of this paper.

Comparison of Different Packing Materials for the Biofiltration of Air Toxics

Four different biofilter packing materials (two porous ceramics, perlite, and open pore polyurethane foam) were compared for the removal of toluene vapors. The focus was on evaluating performance at relatively short gas retention time (13.5 and 27 sec). The reactors were initially operated as biotrickling filters with continuous feeding and trickling of a nutrient solution. After significant plugging of the biotrickling filter beds with biomass was observed, the operation mode was switched to biofiltration with only periodic supply of mineral nutrients. This resulted in stable conditions, which allowed detailed investigations over >6 months. The reactor packed with cattle bone Porcelite (CBP), a ceramic material containing some macronutrients and micronutrients, exhibited the highest performance. The critical load (i.e., load at which 95% removal occurred) was 29 g m−3 hr−1 at a gas retention time of 13.5 sec and 66 g m−3 hr−1 at a gas retention time of 27 sec. After the long-term experiment, the packing materials were taken from the reactors and examined. The reactors were divided into three sections, top, middle, and bottom, to determine whether spatial differentiation of biomass occurred. The assays included a double-staining technique to count total and live microorganisms and determination of moisture, protein, and dry weight contents. Microbial community analysis was also conducted by denaturing gradient gel electrophoresis. The results showed that most reactors had a significant fraction of inactive biomass. Comparatively, the CBP biofilter held significantly higher densities of active biomass, which may be the reason for the higher toluene removal performance. The analyses suggest that favorable material properties and the nutrients slowly released by the CBP provided better environmental conditions for the process culture.

Removal of Toluene Vapor with Dispersed Activated Carbon

This work considers the mechanisms of mass transfer in a process of dispersed sorbent injection. During experiments, an air supply was dosed with toluene vapor, at partial pressures between 4 and 15 Pa. Powdered activated carbon (PAC) was added to remove the toluene from the air, and the resulting mixture was passed through a 3-m-long, tubular, aluminum test section. Toluene concentrations were measured at seven axial locations within the test section. Comparing the measurements with mathematical models indicated the importance of adsorption kinetics. At reduced toluene inlet concentrations the PAC removed a slightly bigger fraction of toluene from the air stream. This fraction increased with PAC concentration. The effect on removal of varying the air temperature between 25 and 85°C was small. Alternative models incorporating either pore diffusion or surface diffusion were fitted to the results. The quality of the fits was fair only, but sufficient to show that the pore diffusivity that gave the best fit was far larger than would be expected from the Knudsen diffusivity in the pores. That is, surface diffusion was an important part of the intraparticle mass transfer.

Influence of mixing and water addition on the removal rate of toluene vapors in a biofilter.

The effects of successive mixing (homogenization) of packing material (peat), with or without water addition, on the removal of toluene vapors in a biofilter were studied. Over a period of 50 days, an increase in the Elimination Capacity (EC) of approximately 240% was obtained by successive mixing and water additions. After each mixing, a high EC of toluene was maintained only for a short period of 3-4 days. After this time, decreased biofilter performance was observed, probably associated with the development of dried and/or clogged zones. In the long-term experiments, an attenuation of the EC recovery was observed after successive mixing. In this case, an increase of 110% over 4 months of experiment was obtained. The global reduction of EC over time could be explained by the colonization of the biofilter by filamentous fungi which was facilitated by the mixing of the packing material. The most frequently observed fungi were identified as Scedosporium sp. and Cladosporium sp.

Biofiltration of toluene vapor under steady-state and transient conditions: Theory and experimental results

Removal of toluene vapor from airstreams was studied in a vapor phase biological reactor known as a biofilter. The reactor was packed with a mixture of peal and perlite particles on which a mixed microbial population (consortium) was immobilized and formed a biolayer. The reactor was operated over a period of 11 months under various inlet-airstream toluene concentrations and flow rates of the contaminated airstream. Except at start-up, no supplemental nutrients were provided to the column, which remained active and never exhibited any significant pressure drop build-up. The process was modeled with general mass balance equations which take into account reaction, mass transfer, and adsorption of the pollutant onto the packing material. The model equations were solved numerically and the predicted concentration profiles agreed very well with the experimental data, for both steady-state and transient operation. Predicted concentration profiles for the biofilm indicate that toluene gets depleted before oxygen in a thin layer of the order of 35 μm. This finding is opposite to what has been reported for hydrophilic solvents where oxygen is depleted before the contaminant in the biolayer. The model equations have been used in parameter sensitivity studies that have revealed the parameters which need to be accurately known for predicting the performance of a biofilter.

Biofiltration of toluene vapor under steady-state and transient conditions: Theory and experimental results

Removal of toluene vapor from airstreams was studied in a vapor phase biological reactor known as a biofilter. The reactor was packed with a mixture of peal and perlite particles on which a mixed microbial population (consortium) was immobilized and formed a biolayer. The reactor was operated over a period of 11 months under various inlet-airstream toluene concentrations and flow rates of the contaminated airstream. Except at start-up, no supplemental nutrients were provided to the column, which remained active and never exhibited any significant pressure drop build-up. The process was modeled with general mass balance equations which take into account reaction, mass transfer, and adsorption of the pollutant onto the packing material. The model equations were solved numerically and the predicted concentration profiles agreed very well with the experimental data, for both steady-state and transient operation. Predicted concentration profiles for the biofilm indicate that toluene gets depleted before oxygen in a thin layer of the order of 35 μm. This finding is opposite to what has been reported for hydrophilic solvents where oxygen is depleted before the contaminant in the biolayer. The model equations have been used in parameter sensitivity studies that have revealed the parameters which need to be accurately known for predicting the performance of a biofilter.