Air Biofilter Research Articles

Fungi growing on aromatic hydrocarbons: biotechnology's unexpected encounter with biohazard?

The biodegradation of aromatic hydrocarbons by fungi has traditionally been considered to be of a cometabolic nature. Recently, however, an increasing number of fungi isolated from air biofilters exposed to hydrocarbon-polluted gas streams have been shown to assimilate volatile aromatic hydrocarbons as the sole source of carbon and energy. The biosystematics, ecology, and metabolism of such fungi are reviewed here, based in part on re-evaluation of a collection of published hydrocarbon-degrading isolates obtained from authors around the world. Incorrect or outdated identifications in original publications are corrected by ribosomal DNA sequence analysis. The data show that many volatile-hydrocarbon-degrading strains are closely related to, or in some cases clearly conspecific with, the very restricted number of human-pathogenic fungal species causing severe mycoses, especially neurological infections, in immunocompetent individuals. Neurochemistry features a distinctive array of phenolic and aliphatic compounds that are related to molecules involved in the metabolism of aromatic hydrocarbons. Hence, there may be physiological connections between hydrocarbon assimilation and certain patterns of mammalian infection.

Back-propagation neural network for performance prediction in trickling bed air biofilter

Experimental studies were carried out with a laboratory-scale biotrickling filter to treat a gaseous stream contaminated with benzene, toluene and xylene (BTX) operated in a continuous mode. The biotrickling filter initially acclimatised with toluene was used to treat BTX compound individually at loading rates ranging from 7.2 g/m³hr to 62.2 g/m³hr, operated in a sequential mode. The results showed removal efficiencies as high as 100% when operated with toluene as the sole carbon source. An application of the back-propagation neural network to this experimental data is presented in this paper. The performance parameters namely, elimination capacity and removal efficiency were predicted from the experimental observation by selecting the appropriate network topology. The sensitive internal parameters of the network were selected using the 2(k–1) fractional factorial design. The neural-network-based model was found to be an efficient data-driven tool to predict the performance of a biotrickling filter.

Removal of Methyl Isobutyl Ketone From Contaminated Air by Trickle-Bed Air Biofilter

A laboratory-scale trickle-bed air biofilter was evaluated for the removal of methyl isobutyl ketone (MIBK) from a waste gas stream. Six-millimeter (6 mm) Celite pellets (R-635) were used as the biological attachment medium. Effects of MIBK volumetric loading rates on removal efficiency, biofilter reacclimation, biomass growth, and removal kinetics were studied under three different operating conditions, namely, backwashing and two intermittent periods (off chemical—no MIBK input; and off flow-no flow input). Backwashing of the biofilter once a week with full-medium fluidization removed the excess biomass and attained stable long-term performance with over 99% removal efficiency for loading rates less than 3.26 kg chemical oxygen demand (COD) ∕ m3 day . The two intermittent periods could also sustain high removal efficiency for loading rates up to 1.09 kg COD∕ m3 day without any backwashing. The recovery time increased with an increase in loading rates. Furthermore, the intermittent operations required a ...

Behavior of trickle‐bed air biofilter for toluene removal: Effect of non‐use periods

AbstractA laboratory‐scale trickle bed air biofilter (TBAB) packed with synthetic, inorganic media for microbial attachment was used for toluene removal from an air stream. Three experimental strategies—including backwashing as the active biomass control and two non‐use periods (starvation, which represents a period without toluene loading, and stagnant, which reflects no flow)—were considered in this study. The non‐use periods can be considered as another means of biomass control for low VOC loadings (0.70 and 1.41 kg COD/m3·day), whereas at high VOC loading (>3.52 kg COD/m3·day) backwashing is deemed essential to remove the excess biomass accumulation in the biofilter. As the toluene loading rate was increased, a considerably longer reacclimation period was unavoidable for biofilter performance to reach the 99% removal for all experimental strategies (backwashing, starvation, and stagnant). Because the biofilter response was strongly dependent on the active biomass in the system, biofilter response after the non‐use periods was significantly different from that after backwashing. © 2005 American Institute of Chemical Engineers Environ Prog, 2005

Hydrodynamic characterization of a trickle bed air biofilter

This paper reports the effect of superficial liquid mass flow rate and bed void fraction on the pressure drop, dynamic liquid hold-up, mean liquid residence time and biofilm wetting, in a co-current down-flow xylene-removing trickle bed air biofilter (TBAB). The gas–liquid pressure drop increased with liquid mass flow rate and it also increased with diminishing bed void fraction, the effect being larger at bed void fraction of 0.41. Dynamic liquid hold-up was higher with increasing liquid mass flow rate, and showed a maximum when the bed void fraction was 0.69. The same pattern was observed for the mean liquid residence time and the wetting efficiency. Liquid residence time distribution curves indicate stagnant regions, channeling, and recirculation within the TBAB, whose effects were larger at a bed void fraction of 0.41. A maximum elimination capacity of 30 g/m 3 h, with 78% removal efficiency, was reached when the bed void fraction was 0.8 and the liquid mass rate 14.1 kg/m 2 s. An average minimum elimination capacity of 6 g/m 3 h was observed at a bed void fraction of 0.41. Xylene isomers were preferentially removed in the order of o > m > p. © 2005 Elsevier B.V. All rights reserved.

Impact of interchanging VOCs on the performance of trickle bed air biofilter

Abstract Trickle bed air biofilters (TBABs) were evaluated under conditions of an interchange of the feed volatile organic compounds (VOCs). Two aromatic compounds (toluene and styrene) and two oxygenated compounds (methyl ethyl ketone and methyl isobutyl ketone) were interchanged as single solutes. The results obtained revealed that the biofilter provided high removal efficiency within the critical loading, which was previously defined in the non-interchanging VOC-fed biofilters. The biofilter recovered easily to the 99% removal after interchanging to oxygenated compounds, regardless of the immediately preceding compound fed to each biofilter, but for aromatic compounds, a longer reacclimation period was required. The biofilter response after interchange of feed VOCs depended on the physicochemical property of feed VOCs as well as the biomass retained in the biofilter prior to interchanging VOC. Using high EBRT at the critical loading (which corresponds to high inlet concentration), problems related to oxygen limitation within the biofilm may have appeared. It was noticed that a smaller ratio of COD/N and a larger ratio of CO 2 /COD were encountered after an interchange of the feed VOCs.

Evaluation of Trickle-Bed Air Biofilter Performance under Periodic Stressed Operating Conditions as a Function of Styrene Loading

Trickle-bed air biofilters (TBABs) are suitable for treating volatile organic compounds (VOCs) at a significantly high practical loading because of their controlled environmental conditions. The application of TBAB for treating styrene-contaminated air under periodic backwashing and cyclical nonuse periods at a styrene loading of 0.64–3.17 kg chemical oxygen demand (COD)/m3·day was the main focus of this study. Consistent long-term efficient performance of TBAB strongly depended on biomass control. A periodic in situ upflow with nutrient solution under media fluidization, that is, backwashing, was approached in this study. Two different nonuse periods were employed to simulate a shutdown for equipment repair or during weekends and holidays. The first is a starvation period without styrene loading, and the second is a stagnant period, which reflects no flow passing through the biofilter. For styrene loadings up to 1.9 kg COD/m3·day, removal efficiencies consistently above 99% were achieved by conducting a coordinated biomass control strategy, that is, backwashing for 1 hr once per week. Under cyclical nonuse periods for styrene loadings up to 1.27 kg COD/m3·day, stable long-term performance of the biofilter was maintained at more than 99% removal without employing back-washing. No substantial impact of nonuse periods on the biofilter performance was revealed. However, a coordinated biomass control by backwashing subsequently was unavoidable for attaining consistently high removal efficiency at a styrene loading of 3.17 kg COD/m3·day. As styrene loading was increased, reacclimation of the biofilter to reach the 99% removal efficiency following back-washing or the nonuse periods was delayed. After the nonuse periods, the response of the biofilter was a strong function of the biomass in the bed. No significant difference between the effects of the two different nonuse periods on TBAB performance was observed during the study period.

A Model for the Biofiltration of Butyl Acetate and Xylene Mixtures by a Trickle-Bed Air Biofilter

A mathematical model that incorporates the rates of the mass transfer process and the biofilm reaction is presented to predict the performance of a trickle-bed air biofilter (TBAB) for treating butyl acetate and xylene mixtures. A thorough understanding of the factors that influence these rates is necessary before the practical application of a TBAB for treating many kinds of pure and mixed volatile organic compounds (VOC) in the air stream. The model presented consists of a set of mass balance equations for butyl acetate, xylene and oxygen in the bulk gas phase and within the biofilm. The butyl acetate and xylene concentration profiles of the gas phase predicted by the model were in good agreement with the measured data documented in a previous study. The most relevant parameters were evaluated in a sensitivity analysis to determine their respective effects on the model performance. Four parameters were identified to strongly influence the model performance, the surface area of the biofilm per volume unit of the packing material (AS), the empty-bed residence time (EBRT), the maximum specific growth rate of the microorganism (μm), and the microbial yield coefficient (Y). The practical application of the model to derive the performance equation is also presented and discussed. This equation makes it possible to simultaneously obtain a relatively high VOC removal efficiency and to minimize the capital cost.

Evaluation of trickle-bed air biofilter performance for MEK removal

A lab-scale trickle-bed air biofilter (TBAB) was operated to evaluate the removal of methyl ethyl ketone (MEK) from waste gas. Three biomass control strategies were investigated, namely, backwashing and two non-use periods (starvation and stagnant). Five volumetric loading rates from 0.70 to 7.04 kg COD/m 3 day were employed. Backwashing once a week removed the excess biomass and obtained long-term, stable performance over 99% removal efficiency for loading rates less than 5.63 kg COD/m 3 day. The two non-use periods could also sustain 99% removal efficiency and could be employed as another means of biomass control for loading rates up to 3.52 kg COD/m 3 day. The non-use periods did not delay the recovery when the loading rate did not exceed 3.52 kg COD/m 3 day. The pseudo-first-order removal rate constant decreased with increase in volumetric loading rate. The effect of non-use periods on removal rate showed apparent transition from positive to negative with the increase in loading rate.

Fungal biocatalysts in the biofiltration of VOC-polluted air

Gas-phase biofilters used for the treatment of waste gases were originally packed with compost or other natural filter beds containing indigenous microorganisms. Over the past decade much effort has been made to develop new carrier materials, more performant biocatalysts and new types of bioreactors. Elimination capacities reached nowadays are 5 to 10 times higher than those originally reported with conventional compost biofilters. With the recently developed inert filter beds, inoculation is a prerequisite for successful start-up and operation. Either non-defined mixed cultures or pure bacterial cultures have originally been used. The search for efficient fungal biocatalysts started only a few years ago, mainly for the biofiltration of waste gases containing hydrophobic compounds, such as styrene, α-pinene, benzene, or alkylbenzenes. In this review, recently isolated new fungal strains able to degrade alkylbenzenes and other related volatile organic pollutants are described, as well as their major characteristics and their use as biocatalysts in gas-phase biofilters for air pollution control. In biofiltration, the most extensively studied organism belongs to the genus Exophiala, although strains of Scedosporium, Paecilomyces, Cladosporium, Cladophialophora, and white-rot fungi are all potential candidates for use in biofilters. Encouraging results were obtained in most of the cases in which some of those organisms were present in gas-phase biofilters. They allow reaching high elimination capacities and are resistant to low pH values and to reduce moisture content.

Characterization and Selection of Materials for Air Biofiltration in Fluidized Beds

A methodology is described for the selection of the best material to employ in a fluidized biofilter applied to volatil organic compounds (VOC) treatment. Two different supports were considered: one natural, scrap wood, and one synthetic, polyurethane foam. In a first part, the main objective was to establish the fluidizability of the selected solids. Particles of increasing moisture content were tested in rigs equipped with different air distribution technologies. Maps of flow regimes were drawn by varying air velocity and bed height. In the second part, the sorption capacities of the selected materials were evaluated at different humidity levels for a soluble organic compound (ethanol) and an insoluble one (toluene). Their ability for supporting viable microorganisms was then measured. Fine particles with 45% moisture content fluidized with the tuyere distributor in channeling and slugging regimes, whereas the conical distributor generated a spouted bed regime. Coarse wood particles with 45% moisture commonly used in fixed bed biofilters were considered as less suitable due to limitations borne by their fluidization regimes. Finally polyurethane foam filled with Agar gel could not endure the mechanical stress to which particles are subjected in fluidized beds. It was shown that a 45% moisture content was optimum to ensure transfer for both soluble and hydrophobic compounds. Considering the biological criterion, it appeared that a 45% humidity level was sufficient to ensure biomass growth and biodegradation of pollutants on fine scrap wood particles.

Biofiltration of Butyl Acetate and Xylene Mixtures Using a Trickle‐Bed Air Biofilter

AbstractButyl acetate and xylene mixtures are commonly encountered from the manufacture of semi‐conductor or opto‐electronic apparatuses. The release of these substances into the ambient air may have a negative effect on the air quality. This study attempts to employ a trickle‐bed air biofilter for treating butyl acetate and xylene mixtures under different gas flow rates and influent concentrations. Almost complete VOC removal could be attained with influent carbon loadings of BA (butyl acetate) and X (xylene) below 40 and 15 g/m3h, respectively. As the influent carbon loadings of BA and X were increased up to 150 and 110 g/m3h, removal efficiencies higher than 80 % were achieved. Therefore, the trickle‐bed air biofilter (TBAB) appeared efficient in the control of emissions containing mixtures of butyl acetate and xylene with low to medium carbon loadings. The removal efficiencies of butyl acetate were higher than those of xylene, indicating that butyl acetate was the substrate preferred in the utilization of butyl acetate and xylene mixtures by the microorganisms. Carbon recoveries of 98–101 % were achieved, demonstrating the accuracy of results. The carbon mass rate of the liquid effluent was approximately two to three orders of magnitude less than that of the CO2 effluent, indicating that the dissolved VOCs and their derivatives in the leachate were present in a negligible amount in the reactor. Applicable operating conditions of the TBAB unit for treating BA and X mixtures were suggested.

A model for treating toluene and acetone mixtures by a trickle-bed air biofilter

A mathematical model that incorporates mass transfer process and biofilm reactions is presented to predict the performance of a trickle-bed air biofilter (TBAB) for treating toluene (T) and acetone (ACE) mixtures. The model consists of a set of mass balance equations for T, ACE and oxygen in the bulk gas phase and within the biofilm. The gas phase T and ACE concentrations predicted by the model were in good agreement with the measured data available in a previous study. The important parameters were evaluated in the sensitivity analysis to determine their respective effects on the model performance. Four parameters were identified as strongly influencing the model performance, the surface area of the biofilm per unit volume of packing material (A S), the empty-bed residence time (EBRT), the maximum specific growth rate of microorganism (μ m), and the microbial yield coefficient (Y). A practical application of the model to derive the performance equation of TBAB is also given.

Biofiltration of butyl acetate by a trickle-bed air biofilter

The performance of a trickle-bed air biofilter (TBAB) for treating butyl acetate (BA) vapour was evaluated under different influent concentrations and gas flow rates. Almost complete BA removal could be achieved for influent carbon loading between 12 and 177 g m −3 h −1 . The TBAB appeared to be efficient for controlling BA emission under these carbon loading conditions. The applicable conditions of TBAB were thus suggested. A mathematical model that incorporates mass transfer process and biofilm reactions was presented to predict the performance of TBAB for BA removal. The effluent gas phase BA concentrations predicted by the model were in good agreement with the measured data. In a sensitivity analysis, three parameters were identified to strongly influence the model performance, the surface area of the biofilm per unit volume of packing material ( A S ), the empty-bed residence time (EBRT), and the microbial yield coefficient on BA ( Y B ). A practical application of the model to derive the performance equation of TBAB is also given.

A model for treating isopropyl alcohol and acetone mixtures in a trickle-bed air biofilter

A mathematical model that incorporates mass transfer process and biofilm reactions is presented to predict the performance of a trickle-bed air biofilter (TBAB) for treating isopropyl alcohol (IPA) and acetone (ACE) mixtures. The model consists of a set of mass balance equations for IPA, ACE and oxygen in the bulk gas phase and within the biofilm. The effluent gas phase IPA and ACE concentrations predicted by the present model were in good agreement with the measured data available in a previous study. The important parameters were evaluated by sensitivity analysis to determine their respective effects on model performance. Four parameters were identified that strongly influenced model performance: surface area of the biofilm per unit volume of packing material ( A S), empty-bed residence time (EBRT), maximum specific growth rate of microorganism ( μ m), and microbial yield coefficient ( Y). Practical applications of the model to derive the performance equation of TBAB for treating different inlet IPA and ACE concentrations were also demonstrated.

Biofiltration for the Treatment of Complex Mixtures of VOC – Influence of the Packing Material

AbstractCurrently air biofiltration is largely considered for the removal of Volatile Organic Compounds (VOC) from polluted airstreams. In order to select a suitable packing material for the treatment of VOC polluted air and better understand the influence of the packing material properties upon the removal efficiency, a mixture of eleven VOC was treated in two down‐flow biofilter units packed with either peat or Granular Activated Carbon (GAC) and functioned under similar operating conditions for 92 days. Using the peat biofilter under steady‐state conditions achieved a removal efficiency of 90% greater than the 80% achieved using the GAC filter. Moreover, in both cases, a stratification of the abatement along the column was observed but it differed according to the type of the packing material used. For the peat biofilter, elimination of oxygenated compounds occurred in the first 50 cm of the column, whereas aromatic and halogenated compounds were treated in the segments closer to the outlet. In contrast, with GAC, the removal of oxygenated and aromatic compounds took place along the height of the column. For the removal of microorganisms fixed on peat and activated carbon particles, the crushing with an ultra‐turrax was the most efficient dispersing method, compared to agitation with a vortex and ultrasound. The counting of microorganisms using three culture media [Luria Bertoni (LB); Plate Count Agar (PCA); Tryptic Soy Agar, tenfold diluted (TSA 1/10)] demonstrated that the TSA 1/10 was likely most suitable for the recovery of the peat biofilter microflora (TSA 1/10: 5.6 × 109 CFU/g of dry peat, PCA: 1.5 × 109 CFU/g of dry peat, LB: 0.3 × 109 CFU/g of dry peat) probably due to the dominance of oligotrophic bacteria, whereas for the activated carbon biofilter there was no significant difference (PCA: 4.4 × 109; LB: 4.2 × 109; TSA 1/10: 4.5 × 109 CFU/g of dry activated carbon) between these media suggesting that oligotrophic and zymogeneous bacteria are likely in the same proportion.The results illustrated that even the removal efficiency is associated with the pollutant properties; it was assumed that the sorptive properties of GAC could modify the VOC degradation mechanisms and then entail a real reduction of the removal efficiency.

Biofiltration of isopropyl alcohol and acetone mixtures by a trickle-bed air biofilter

The performance of a trickle-bed air biofilter (TBAB) treating isopropyl alcohol (IPA) and acetone (ACE) mixtures was investigated under different gas flow rates and influent concentrations. In pseudo-steady-state conditions, the elimination capacities of IPA and ACE increased but the removal efficiencies decreased with increased influent carbon loading. The removal efficiencies of IPA were higher than those of ACE, indicating that IPA is a preferred substrate in the IPA and ACE mixtures. More than 90% removal efficiencies were achieved with influent carbon loadings of IPA and ACE below 80 and 53 g/m 3·h, respectively. The TBAB appears efficient for controlling mixed IPA and ACE emission with low to medium carbon loadings. Applicable operating conditions of TBAB for treating mixed IPA and ACE emission were suggested.

Biofiltration of isopropyl alcohol by a trickle-bed air biofilter.

The performance of trickle-bed air biofilter (TBAB) for the removal of isopropyl alcohol (IPA) was evaluated in concentrations varying from 100 to 500 ppmv and at empty-bed residence time (EBRT) varying from 20 to 90 s. Nearly complete IPA removal could be achieved for influent carbon loading between 6 and 88 g/m3 x h. The TBAB appears efficient for controlling IPA emission under low-to-high carbon loading conditions. Carbon recoveries of 95-99% were achieved demonstrating the accuracy of results. Applicable operating conditions of TBAB for controlling IPA emission were suggested.

Biofiltration of toluene and acetone mixtures by a trickle-bed air biofilter

Toluene and acetone mixtures are commonly encountered from the manufacture of semi-conductor or opto-electronic apparatus. This study attempts to employ a trickle-bed air biofilter (TBAB) for treating toluene and acetone mixtures under different gas flow rates and influent concentrations. In the pseudo-steady-states, the elimination capacities of toluene and acetone increased but the removal efficiencies decreased with the increase of influent carbon loading. The removal efficiencies of toluene were higher than those of acetone, indicating that toluene is a preferred substrate in the mixtures. Greater than 90% removal efficiencies were achieved with influent carbon loadings of toluene and acetone below 125 and 15 g/m3 h, respectively. The TBAB appears efficient for controlling toluene and acetone mixture with medium toluene and low acetone loadings. Applicable operating conditions of TBAB for treating mixed toluene and acetone emission are suggested.

Biofiltration of 1,1,1-trichloroethane by a trickle-bed air biofilter.

The performance of a trickle-bed air biofilter (TBAB) in the removal of 1,1,1-trichloroethane (TCLE) was evaluated in concentrations varying from 0.025 to 0.049 g/m3 and at empty-bed residence time (EBRT) varying from 20 to 90 s. Nearly complete TCLE removal could be achieved for influent carbon loading between 0.98 and 5.88 g/m3 h. The TBAB appeared efficient for controlling TCLE emission under low-carbon-loading conditions. Carbon recoveries higher than 95% were achieved, demonstrating the accuracy of results. The carbon mass rate of the liquid effluent was approximately two orders of magnitude less than that of the effluent CO2, indicating that dissolved TCLE and its derivatives in leachate were present in negligible amounts in the TBAB.