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.     

Comparison of Different Packing Materials for the Biofiltration of Air Toxics

Abstract

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.     

Multiple microbial activities for volatile organic compounds reduction by biofiltration

In the northeast of Italy, high volatile organic carbon (VOC) emissions originate from small-medium companies producing furniture. In these conditions it is difficult to propose a single, efficient, and economic system to reduce pollution. Among the various choices, the biofiltration method could be a good solution, because microbial populations possess multiple VOC degradation potentials used to oxidize these compounds to CO2. Starting from the air emissions of a typical industrial wood-painting plant, a series of experiments studied in vitro microbial degradation of each individual VOC. Isolated strains were then added to a laboratory-scale biofiltration apparatus filled with an organic matrix, and the different VOC behavior demonstrated the potential of single and/or synergic microbial removal actions. When a single substrate was fed, the removal efficiency of a Pseudomonas aeruginosa inoculated reactor was 1.1, 1.17, and 0.33 g m(-3) hr(-1), respectively, for xylene, toluene, and ethoxy propyl acetate. A VOC mixture composed of butyl acetate, ethyl acetate, diacetin alcohol, ethoxy propanol acetate, methyl ethyl ketone, methyl isobutyl ketone, toluene, and xylene was then fed into a 2-m(3) reactor treating 100 m3 hr(-1) of contaminated air. The reactor was filled with the same mixture of organic matrix, enriched with all of the isolated strains together. During reactor study, different VOC loading rates were used, and the behavior was evaluated continuously. After a short acclimation period, the removal efficiency was > 65% at VOC load of 150-200 g m(-3) hr(-1). Quantification of removal efficiencies and VOC speciation confirmed the relationship among removal efficiencies, compound biodegradability, and the dynamic transport of each mixture component within the organic matrix. Samples of the fixed bed were withdrawn at different intervals and the heterogeneous microbial community evaluated for both total and differential compound counts.     

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.     

Backfitting Electrostatic Precipitators: Gas Velocity and Reliability Considerations

Abstract

The kinetic behavior of the toluene biofiltration process was investigated in this research. Toluene was used as a model compound for less water-soluble gas pollutants. The limiting factor in the overall toluene biofiltration process was determined by analyzing the effectiveness factor of the biofilm along the biofilter. Experiments were conducted in three laboratory-scale biofilters packed with mixtures of chaff/compost, D.E. (diatomaceous earth)/compost and GAC (granular activated carbon)/compost, respectively. A mathematical model previously proposed was verified in this study as being applicable to these biofilters packed with different filter materials. Both the experimental and theoretical results confirmed that the biodegradation rate along the biofilter followed the zero order, fractional order to first order kinetics as toluene concentration decreased. Moreover, at higher toluene concentration, biodegradation rate and mass flux of toluene were lower near the bottom of the biofilter due to substrate inhibition. Analysis of the effectiveness factor indicated that biofiltration of a less soluble compound such as toluene should not be operated at high gas flow rates (low gas residence times) due to the mass transfer limitation of such a system. At an approximate constant inlet toluene concentration of 0.9 g/m³, the toluene removal efficiency in these three biofilters would drop below 90% when the gas residence time decreased to 2.5, 2.5, and 2.0 min, respectively.     

Evaluation of Trickle Bed Air Biofilter Performance as a Function of Inlet VOC Concentration and Loading,and Biomass Control

ABSTRACT

The 1990 Amendments to the Clean Air Act have stimulated strong interest in the use of biofiltration for the economical, engineered control of volatile organic compounds (VOCs) in effluent air streams. Trickle bed air biofilters (TBABs) are especially applicable for treating VOCs at high loadings. For long-term, stable operation of highly loaded TBABs, removal of excess accumulated bio-mass is essential. Our previous research demonstrated that suitable biomass control for TBABs was achievable by periodic backwashing of the biofilter medium. Backwashing was performed by fluidizing the pelletized biological attachment medium with warm water to about a 40% bed expansion. This paper presents an evaluation of the impact of backwashing on the performance of four such TBABs highly loaded with toluene. The inlet VOC concentrations studied were 250 and 500 ppmv toluene, and the loadings were 4.1 and 6.2 kg COD/m³ day (55 and 83 g toluene/m³ hr). Loading is defined as kg of chemical oxygen demand per cubic meter of medium per day. Performance deterioration at the higher loading was apparently due to a reduction of the specific surface of the attached biofilm resulting from the accumulation of excess biomass. For a toluene loading of 4.1 kg COD/m³ day, it was demonstrated that the long-term performance of biofilters with either inlet concentration could be maintained at over 99.9% VOC removal by employing a backwashing strategy consisting of a frequency of every other day and a duration of 1 hr.     

Exceedances of the National Ambient Air Quality Standard for Ozone Occurring at a “Pristine” Area Site

Abstract

This paper presents a comparative study of the biodegradation of three aromatic volatile compounds in a compost-based biofilter: toluene, xylene, and 1,2,4-trimethyl-benzene, used in the course of this work for the first time in the field of biofiltration. Hence, three identical biofiltration units have been operated at the laboratory scale. During the experiments, nitrogen (as urea) was supplied at various concentrations to each reactor, via irrigated nutrient solutions. A comparative analysis of the results showed that the biodegradability scale followed the degree of substitution around the aromatic ring: toluene > xylene > trimethylbenzene, with 95, 80, and 70% maximum conversions, respectively. In addition, and despite the different removal levels achieved in the three biore-actors, it was established that from a reaction viewpoint, the degradation of the three compounds seemed to follow similar metabolic pathways involving methylcatechol isomers. Finally, by varying the nitrogen input concentrations in the three reactors, three degradation regimes have been highlighted: an N-limitation regime and an N-optimum regime, common to the three solvents, and an N-excess regime, favorable to the colonization of the filter beds by nitrifying species, which particularly affected the xylene and trimethylbenzene biodegradation.     

Control of Organic Emissions from Surface Coating Operations

ABSTRACT

Step tracer tests were carried out on lab-scale biofilters to determine the residence time distributions (RTDs) of gases passing through two types of biofilters: a standard biofilter with vertical gas flow and a modified biofilter with horizontal gas flow. Results were used to define the flow patterns in the reactors. “Non-ideal flow” indicates that the flow reactors did not behave like either type of ideal reactor: the perfectly stirred reactor [often called a "continuously stirred tank reactor" (CSTR)] or the plug-flow reactor.

The horizontal biofilter with back-mixing was able to accommodate a shorter residence time without the usual requirement of greater biofilter surface area for increased biofiltration efficiency. Experimental results indicated that the first bed of the modified biofilter behaved like two CSTRs in series, while the second bed may be represented by two or three CSTRs in series. Because of the flow baffles used in the horizontal biofilter system, its performance was more similar to completely mixed systems, and hence, it could not be modeled as a plug-flow reactor. For the standard biofilter, the number of CSTRs was found to be between 2 and 9 depending on the airflow rate. In terms of NH₃ removal efficiency and elimination capacity, the standard biofilter was not as good as the modified system; moreover, the second bed of the modified biofilter exhibited greater removal efficiency than the first bed. The elimination rate increased as biofilter load increased. An opposite trend was exhibited with respect to removal efficiency.     

Assessment of volatile organic compound removal by indoor plants—a novel experimental setup

Indoor plants can remove volatile organic compounds (VOCs) from the air. The majority of knowledge comes from laboratory studies where results cannot directly be transferred to real-life settings. The aim of this study was to develop an experimental test system to assess VOC removal by indoor plants which allows for an improved real-life simulation. Parameters such as relative humidity, air exchange rate and VOC concentration are controlled and can be varied to simulate different real-life settings. For example, toluene diffusion through a needle gave concentrations in the range of 0.10–2.35 μg/L with deviations from theoretical values of 3.2–10.5 %. Overall, the system proved to be functional for the assessment of VOC removal by indoor plants with Hedera helix reaching a toluene removal rate of up to 66.5 μg/m²/h. The mode of toluene exposure (semi-dynamic or dynamic) had a significant influence on the removal rate obtained by H. helix.     

Performance Characteristics of a Regenerative Catalytic Oxidizer for Treating VOC-Contaminated Airstreams

ABSTRACT

A pilot apparatus of a regenerative catalytic oxidizer (RCO) equipped with two electrical heaters and two 20-cm i.d. × 200-cm height regenerative beds was used to treat methyl ethyl ketone (MEK) and toluene, respectively, in an airstream. The regenerative beds were packed with gravel (approximate particle size 1.25 cm, specific area 205 m²/m³, and specific heat capacity 840 J/kg °C) as a solid regenerative material and K-type thermal couples for measuring solid and gas temperatures, respectively. The catalyst bed temperature was kept around 400 °C and the gas superficial velocity was operated at 0.234 m/sec. This investigation measured and analyzed distributions of solid and gas temperatures with operating time and variations of volatile organic compound (VOC) concentrations in the regenerative beds. The overall VOC removal efficiency exceeded 98% for MEK and 95% for toluene. Degradation of VOCs will exist for MEK on the surface of solid material (gravel) in the temperature range of 330-400 °C, but toluene does not exhibit this phenomenon.     

Fungal biofilters for toluene biofiltration: evaluation of the performance with four packing materials under different operating conditions

Packing materials play a key role in the performance of bioreactors for waste gas treatment and particularly in biofilter applications. In this work, the performance of four differently packed biofilters operated in parallel for the treatment of relatively high inlet concentration of toluene was studied. The reactors were compared for determining the suitability of coconut fiber, digested sludge compost from a waste water treatment plant, peat and pine leaves as packing materials for biofiltration of toluene. A deep characterisation of materials was carried out. Biological activity and packing capabilities related to toluene removal were determined throughout 240 days of operation under different conditions of nutrients addition and watering regime. Also, biofilters recovering after a short shutdown was investigated. Nutrient addition resulted in improved removal efficiencies (RE) and elimination capacities (EC) of biofilters reaching maximum ECs between 75 and 95 g m(-3)h(-1) of toluene. In the first 80 days, the pH decreased progressively within the reactors, causing a population change from bacteria to fungi, which were the predominant decontaminant microorganisms thereafter. All reactors were found to recover the RE rapidly after a 5 days shutdown and, in a maximum of 7 days, all reactors had been completely recuperated. These results point out that fungal biofilters are a suitable choice to treat high loads of toluene. In general, coconut fiber and compost biofilters exhibited a better performance in terms of elimination capacity and long-term stability.     

An Improved Model for Analyzing the Performance of Photocatalytic Oxidation Reactors in Removing Volatile Organic Compounds and Its Application

Abstract

An improved photocatalytic oxidation (PCO) reactor model was developed to analyze the removal of volatile organic compounds (VOCs) in indoor air. One new parameter, the average total removing factor K _t, together with the other two parameters, the number of mass transfer units NTU_m and the fractional conversion e, are found to be the main parameters influencing the photooxidation performance of PCO reactors. Three new parameters, the ideal reaction number of mass transfer units, NTU_m,ir; the ideal reaction fractional conversion, ε_ir; and the reaction effectiveness, η, also are defined. These concepts are helpful to the structural design and optimization for PCO reactors. The application of the model in designing a plate-type PCO reactor is demonstrated. This study shows that the present model is an effective tool for designing PCO reactors and for evaluating VOC removal performance of available PCO reactors.     

A hybrid biological process of indoor air treatment for toluene removal

Bioprocesses, such as biofiltration, are commonly used to treat industrial effluents containing volatile organic compounds (VOCs) at low concentrations. Nevertheless, the use of biofiltration for indoor air pollution (IAP) treatment requires adjustments depending on specific indoor environments. Therefore, this study focuses on the convenience of a hybrid biological process for IAP treatment. A biofiltration reactor using a green waste compost was combined with an adsorption column filled with activated carbon (AC). This system treated a toluene-micropolluted effluent (concentration between 17 and 52 µg/m³), exhibiting concentration peaks close to 733 µg/m³ for a few hours per day. High removal efficiency was obtained despite changes in toluene inlet load (from 4.2 × 10^?3 to 0.20 g/m³/hr), which proves the hybrid system’s effectiveness. In fact, during unexpected concentration changes, the efficiency of the biofilter is greatly decreased, but the adsorption column maintains the high efficiency of the entire process (removal efficiency [RE] close to 100%). Moreover, the adsorption column after biofiltration is able to deal with the problem of the emission of particles and/or microorganisms from the biofilter.

ImplicationsIndoor air pollution is nowadays recognized as a major environmental and health issue. This original study investigates the performance of a hybrid biological process combining a biofilter and an adsorption column for removal of indoor VOCs, specifically toluene.     

Degradation of toluene,xylene, and trimethylbenzene vapors by biofiltration: a comparison

This paper presents a comparative study of the biodegradation of three aromatic volatile compounds in a compost-based biofilter: toluene, xylene, and 1,2,4-trimethylbenzene, used in the course of this work for the first time in the field of biofiltration. Hence, three identical biofiltration units have been operated at the laboratory scale. During the experiments, nitrogen (as urea) was supplied at various concentrations to each reactor, via irrigated nutrient solutions. A comparative analysis of the results showed that the biodegradability scale followed the degree of substitution around the aromatic ring: toluene > xylene > trimethylbenzene, with 95, 80, and 70% maximum conversions, respectively. In addition, and despite the different removal levels achieved in the three bioreactors, it was established that from a reaction viewpoint, the degradation of the three compounds seemed to follow similar metabolic pathways involving methylcatechol isomers. Finally, by varying the nitrogen input concentrations in the three reactors, three degradation regimes have been highlighted: an N-limitation regime and an N-optimum regime, common to the three solvents, and an N-excess regime, favorable to the colonization of the filter beds by nitrifying species, which particularly affected the xylene and trimethylbenzene biodegradation.     

错流式生物滴滤床净化甲苯废气

采用焦化厂污泥为菌源驯化甲苯降解菌，接种错流式生物滴滤床，净化含甲苯废气。研究了生物滴滤床的挂膜启动和长期运行情况，填料和营养液对滴滤床去除能力的影响，并对长期运行的压降进行了观察分析。反应器挂膜启动需要6 d时间，稳定运行的平均去除效率为95％，单位体积最大去除负荷为251 g/(m³·h)。结果表明，采用错流式生物滴滤床可以有效去除甲苯废气；以比表面积大的生物陶粒作为填料以及定期适量更换营养液，均有助于提高生物滴滤床的去除能力；错流式生物滴滤床具有压降小、气液分布均匀的特点。     

Development and performance of an alternative biofilter system

Step tracer tests were carried out on lab-scale biofilters to determine the residence time distributions (RTDs) of gases passing through two types of biofilters: a standard biofilter with vertical gas flow and a modified biofilter with horizontal gas flow. Results were used to define the flow patterns in the reactors. "Non-ideal flow" indicates that the flow reactors did not behave like either type of ideal reactor: the perfectly stirred reactor [often called a "continuously stirred tank reactor" (CSTR)] or the plug-flow reactor. The horizontal biofilter with back-mixing was able to accommodate a shorter residence time without the usual requirement of greater biofilter surface area for increased biofiltration efficiency. Experimental results indicated that the first bed of the modified biofilter behaved like two CSTRs in series, while the second bed may be represented by two or three CSTRs in series. Because of the flow baffles used in the horizontal biofilter system, its performance was more similar to completely mixed systems, and hence, it could not be modeled as a plug-flow reactor. For the standard biofilter, the number of CSTRs was found to be between 2 and 9 depending on the airflow rate. In terms of NH3 removal efficiency and elimination capacity, the standard biofilter was not as good as the modified system; moreover, the second bed of the modified biofilter exhibited greater removal efficiency than the first bed. The elimination rate increased as biofilter load increased. An opposite trend was exhibited with respect to removal efficiency.     

Biotrickling filtration of airborne styrene: A comparison of filtration media

This study compares the performances of fern and plastic chips as packing media for the biofiltration of a styrene-laden waste gas stream emitted in a plant for the manufacture of plastic door plates. Fern chips (with a specific surface area of 1090 m² m^?3) and plastic chips (with a specific surface area of 610 m² m^?3) were packed into a pilot-scale biotrickling filter with a total medium volume of 50 L for the performance test. Field waste gas with styrene concentrations in the range of 161–2390 mg Am^?3 at 28–30 °C) was introduced to the bed and a fixed empty-bed retention time (EBRT) of 21 sec, a volumetric gas flow rate of 8.57 m³ hr^?1, and superficial gas velocity of 53.6 m hr^?1 were maintained throughout the experimental period. Nutrients containing metal salts, nitrogen, phosphorus, and milk were supplemented to the filters for maintaining the microbial activities. Results reveal that the biotrickling filter developed in this study had the highest styrene monomer (SM) elimination capacities (170 g m^?3 hr^?1 for fern-chip packing and 300 g m^?3 hr^?1 for plastic-chip packing) among those cited in the literature. The plastic medium is a favorable substitute for endangered fern chips. The thermal-setting nature of plastic chips limits their recycle and reuse as raw materials, and the study provides an opportunity for the utilization of the materials.

Implications: Biotreatment of contaminants in air streams offers an inexpensive and efficient alternative to conventional technologies. Biofiltration has a great potential for the degradation of gas-borne styrene and total hydrocarbon (THC) removal efficiency of around 80%. The objective of this research was to compare the performances of fern chips and a kind of plastic chips as packing media for biofiltration of the styrene-laden waste gas stream emitted from cutting operations of stripes of premixed unsaturated polyester (UP) and styrene paste before hot-pressing operations for making plastic door plates. From a practical point of view, the plastic medium can be a good substitute medium for fern chips, which has been declared as a protected plant. This study provides an experimentally verified model for the design and operation of such biotreatment systems.     

An improved model for analyzing the performance of photocatalytic oxidation reactors in removing volatile organic compounds and its application

An improved photocatalytic oxidation (PCO) reactor model was developed to analyze the removal of volatile organic compounds (VOCs) in indoor air. One new parameter, the average total removing factor Kt, together with the other two parameters, the number of mass transfer units NTUm and the fractional conversion epsilon, are found to be the main parameters influencing the photooxidation performance of PCO reactors. Three new parameters, the ideal reaction number of mass transfer units, NTUm,ir; the ideal reaction fractional conversion, epsilonir; and the reaction effectiveness, eta, also are defined. These concepts are helpful to the structural design and optimization for PCO reactors. The application of the model in designing a plate-type PCO reactor is demonstrated. This study shows that the present model is an effective tool for designing PCO reactors and for evaluating VOC removal performance of available PCO reactors.     

Isovaleraldehyde elimination by UV/TiO2 photocatalysis: comparative study of the process at different reactors configurations and scales

A proposal for scaling-up the photocatalytic reactors is described and applied to the coated catalytic walls with a thin layer of titanium dioxide under the near ultraviolet (UV) irradiation. In this context, the photocatalytic degradation of isovaleraldehyde in gas phase is studied. In fact, the removal capacity is compared at different continuous reactors: a photocatalytic cylindrical reactor, planar reactor, and pilot unit. Results show that laboratory results can be useful for reactor design and scale-up. The flowrate increases lead to the removal capacity increases also. For example, with pilot unit, when flowrate extends four times, the degradation rate varies from 0.14 to 0.38 g h^?1 m_cat ^?2. The influence of UV intensity is also studied. When this parameter increases, zboth degradation rate and overall mineralization are enhanced. Moreover, the effects of inlet concentration, flowrate, geometries, and size of reactors on the removal capacity are also studied.     

Effect of Substrate Henry’s Constant on Biofilter Performance

Abstract

Butanol, ether, toluene, and hexane, which have Henry's constants ranging from 0.0005 to 53, were used to investigate the effects of substrate solubility or availability on the removal of volatile organic compounds (VOCs) in trickle-bed biofilters. Results from this study suggest that, although removal of a VOC generally increases with a decrease in its Henry's constant, an optimal Henry's constant range for biofiltration may exist. For the treatment of VOCs with high Henry's constant values, such as hexane and toluene, the transfer of VOCs between the vapor and liquid phases or between the vapor phase and the biofilm is a rate-determining step. However, oxygen (O₂) transfer may become a rate-limiting step in treating VOCs with low Henry's constants, such as butanol, especially at high organic loadings. The results demonstrated that in a gas-phase aerobic biofilter, nitrate can serve both as a growth-controlling nutrient and as an electron acceptor in a biofilm for the respiration of VOCs with low Henry's constants. Microbial communities within the biofilters were examined using denaturing gradient gel electrophoresis to provide a more complete picture of the effect of O₂ limitation and denitrification on biofilter performance.