Biodegradation of toluene by the new fungal isolates Paecilomyces variotii and Exophiala oligosperma

Two new fungal strains, namely Paecilomyces variotii and Exophiala oligosperma, were isolated on toluene as the sole carbon and energy source, mineralizing the substrate into carbon dioxide. Fungal strains isolated so far on such a pollutant and completely degrading it are very scarce. Both fungi degraded the pollutant over the pH range 3.9–6.9 and temperature range 23–40°C, but E. oligosperma was barely active at the highest temperature of 40°C. Fungal growth on alkylbenzenes at 40°C has not been reported before. Since the activity of the strains gradually decreased at pH values below 4.0, the use of nitrate instead of ammonium was tested. In the presence of toluene, nitrate was a suitable nitrogen source for the Exophiala strain, but not for the Paecilomyces strain. Nitrate rather than ammonium allowed the maintenance of a more constant pH.     

The removal of volatile ketone mixtures from air in biofilters

The work reported concerns the removal of mixtures of two ketones, methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK), which find wide application as industrial solvents, from effluent air streams in downward flow biofilters operating at relative humidities in excess of 95 percent. The inlet concentrations of the two pollutants were 300 mg m^–3 MEK and 330 mg m^–3 MIBK. Maximum elimination capacities achieved were 50 g m^–3h^–1 for MEK and 20 g m^–3h^–1 for MIBK. Marked interaction between the elimination of the two ketones was observed and established biophysical models for the kinetic analysis of biofilter operation proved inadequate as far as the complex processes involved in multi-component biodegradable vapour elimination were concerned. The complexity of such systems requires further definition and the development of appropriate models for process evaluation and design.     

Styrene degradation by <Emphasis Type="Italic">Pseudomonas</Emphasis> sp. SR-5 in biofilters with organic and inorganic packing materials

Pseudomonas sp. SR-5 was isolated as a styrene-degrading bacterium. In liquid culture containing 1% (v/v) styrene, more than 90% styrene was degraded in 53 h and the doubling time of SR-5 was 2 h. The removal of styrene gas was investigated in biofilters for 31 days using an organic packing material of peat and an inorganic packing material of ceramic inoculated with SR-5. The maximum-styrene-elimination capacities for peat and ceramic packing materials were 236 and 81 g m^–3 h^–1, respectively. The percentage of styrene converted to low molecular weight compounds including CO₂ in the peat and ceramic biofilters during a 10-day operation were estimated to be 90.4 and 36.7%, respectively. As the pressure drop in the peat bioflter at the end of experiment was significantly higher than that in ceramic biofilter, a biofilter using a mixture of peat and ceramic was tested. We determined that the maximum elimination capacity was 170 g m^–3 h^–1 and the production of low molecular weight compounds was 95% at a low pressure drop for this mixed packing material filter.     

Correlation of Biological Activity and Reactor Performance in Biofiltration of Toluene with the Fungus Paecilomyces variotii CBS115145

A biofiltration system inoculated with the mold Paecilomyces variotii CBS115145 showed a toluene elimination capacity (EC) of around 250 g/m³ of biofilter/h, which was higher than the values usually reported for bacteria. P. variotii assimilated m- and p-cresols but not the o isomer. Initial toluene hydroxylation occurred both on the methyl group and through the p-cresol pathway. These results were corroborated by detecting benzyl alcohol, benzaldehyde, and p-cresol as volatile intermediates. In liquid cultures with toluene as a substrate, the activity of toluene oxygenase (TO) was 5.6 nmol of O₂/min/mg of biomass, and that of benzyl alcohol dehydrogenase was 16.2 nmol of NADH/min/mg of protein. Toluene biodegradation determined from the TO activity in the biofilter depended on the biomass distribution and the substrate concentration. The specific enzymatic activity decreased from 6.3 to 1.9 nmol of O₂/min/mg of biomass along the reactor. Good agreement was found between the EC calculated from the TO activity and the EC measured on the biofilter. The results were confirmed by short-time biofiltration experiments. Average EC measured in different biofiltration experiments and EC calculated from the TO activity showed a linear relation, suggesting that in the biofilters, EC was limited by biological reaction. As the enzymatic activities of P. variotii were similar to those reported for bacteria, the high performance of the fungal biofilters can possibly be explained by the increased transfer of the hydrophobic compounds, including oxygen, from the gas phase to the mycelia, overcoming the transfer problems associated with the flat bacterial biofilms.     

Biofiltration of waste gases containing a mixture of formaldehyde and methanol

Several biofilters and biotrickling filters were used for the treatment of a mixture of formaldehyde and methanol; and their efficiencies were compared. Results obtained with three different inert filter bed materials (lava rock, perlite, activated carbon) suggested that the packing material had only little influence on the performance. The best results were obtained in a biotrickling filter packed with lava rock and fed a nutrient solution that was renewed weekly. A maximum formaldehyde elimination capacity of 180 g m^–3 h^–1 was reached, while the methanol elimination capacity rose occasionally to more than 600 g m^–3 h^–1. Formaldehyde degradation was affected by the inlet methanol concentration. Several combinations of load vs empty bed residence time (EBRTs of 71.9, 46.5, 30.0, 20.7 s) were studied, reaching a formaldehyde elimination capacity of 112 g m^–3 h^–1 with about 80% removal efficiency at the lowest EBRT (20.7 s).     

Stoichiometry of microbial continuous-flow purification of toluene-contaminated air

The applicability of a recently published modification of the chemostat, named titrostat, for microbial continuous-flow purification of toluene-contaminated air is discussed. This article describes the operative range and the toluene elimination efficiency of a 2-l titrostat running with a mixed bacterial culture dominated by two Acinetobacter species: A. calcoaceticus and A. radioresistens. The study focuses on the kinetics and stoichiometry of the process. Special attention is paid to the peculiarities of toluene as an unconventional growth substrate having high carbon and energy content. Removal productivity as high as 2.24 g l^–1 h^–1 with 99.9% elimination efficiency was observed at air flow rate 60 l h^–1, temperature 32°C, pH 6.2, toluene concentration in the inlet air 37.4 mg l^–1 and titrant solution containing NH₃ at 1.87 g l^–1. The maximum biomass yield from assimilated toluene, Y _s ^m=0.880±0.011, and a rate of substrate expenditures for cell maintenance, m _s=0.022±0.002 h^–1, were estimated.     

Simultaneous removal of benzene, toluene and xylenes mixture by a constructed microbial consortium during biofiltration

A bacterial consortium with complementary metabolic capabilities was formulated and specific removal rates were 0.14, 0.35, 0.04, and 0.39 h^–1 for benzene, toluene, o-xylene, and m,p-xylene, respectively. When immobilized on a porous peat moss biofilter, removal of all five (= BTX) components was observed with rates of 1.8–15.4 g m^–3 filter bed h^–1. Elimination capacities with respect to the inlet gas concentrations of BTX and airflow rates showed diffusive regimes in the tested concentration range of (0.1–5.3 g m^–3) and airflow (0.55–1.82 m³ m^–2 h^–1) except for o-xylene which reached its critical gas concentration at 0.3 g m^–3.     

Performance and macrokinetic analysis of biofiltration of toluene and p-xylene mixtures in a conventional biofilter packed with inert material

Interactions of toluene and p-xylene in air treatment biofilters packed with an inert filter media were studied. The effect of the inlet load of toluene, p-xylene and mixtures of both compounds on the biodegradation rate was analyzed in three lab-scale biofilters. A maximum elimination capacity (EC) of 26.5 and 40.3 g C m⁻³ h⁻¹ for an inlet load (IL) of 65.6 and 57.8 g C m⁻³ h⁻¹ was obtained for p-xylene and toluene biofilters, respectively. Inhibition of p-xylene biodegradation by the presence of toluene took place when the mixture was treated, whereas the presence of p-xylene had an enhancing effect on the toluene removal efficiency. Specific growth rates (μ) from 0.019 to 0.068 h⁻¹ were calculated in the mixed biofilter, where the highest values were similar to mixtures with lower p-xylene levels (IL_p-Xyl 8.84 ± 0.29 g C m⁻³ h⁻¹). Michaelis-Menten and Haldane type models were fitted to experimental EC for p-xylene and toluene biofilters, respectively.     

Microbial response and elimination capacity in biofilters subjected to high toluene loadings

Elimination capacity (EC) is frequently used as a performance and design criterion for vapor-phase biofilters without further verification of the microbial quantity and activity. This study was conducted to investigate how biofilters respond to high pollutant loadings and ultimately how this affects the EC of the biofilter. Two identical laboratory-scale biofilters were maintained at an initial toluene loading rate of 46 g m⁻³ h⁻¹ for a period of 24 days. After the initial biofilm development stage, the loading rates were increased to 91 g m⁻³ h⁻¹ and 137 g m⁻³ h⁻¹, respectively. Following a short period of pseudo-steady state, toluene removal efficiencies rapidly declined in both biofilters, with a concurrent decline in both critical and maximum ECs. The decline was mainly due to deterioration in the biodegradation activity of the biofilm and a decline in the toluene-degrading bacterial population within the biofilm phase. The findings imply that high toluene loadings accelerated the deterioration in overall performance due to a rapid accumulation of inactive biomass. As a result, care must be used when relying on EC values for biofilter design and operational purposes, since the values do not appropriately reflect the temporal changes in biodegradation activity and active biomass quantities that can occur in biofilters subjected to high inlet loadings.     

Elimination of hydrophobic volatile organic compounds in fungal biofilters: reducing start-up time using different carbon sources

Fungal biofilters have been recently studied as an alternative to the bacterial systems for the elimination of hydrophobic volatile organic compounds (VOC). Fungi foster reduced transport limitation of hydrophobic VOCs due to their hydrophobic surface and extended gas exchange area associated to the hyphal growth. Nevertheless, one of their principal drawbacks is their slow growth, which is critical in the start‐up of fungal biofilters. This work compares the use of different carbon sources (glycerol, 1‐hexanol, wheat bran, and n‐hexane) to reduce the start‐up period and sustain high n‐hexane elimination capacities (EC) in biofilters inoculated with Fusarium solani. Four parallel experiments were performed with the different media and the EC, the n‐hexane partition coefficient, the biomass production and the specific consumption rate were evaluated. Biofilters were operated with a residence time of 1.3 min and an inlet n‐hexane load of 325 g m⁻³_reactor h⁻¹. The time to attain maximum EC once gaseous n‐hexane was fed was reduced in the three experiments with alternate substrates, as compared to the 36 days needed with the control where only n‐hexane was added. The shortest adaptation period was 7 days when wheat bran was initially used obtaining a maximum EC of 160 g m⁻³_reactor h⁻¹ and a critical load of 55 g m⁻³_reactor h⁻¹. The results were also consistent with the pressure drop, the amount of biomass produced and its affinity for the gaseous n‐hexane, as represented by its partition coefficient. Biotechnol. Bioeng. 2011; 108:758–765. © 2010 Wiley Periodicals, Inc.     

Removal of toluene in waste gases using a biological trickling filter

The removal of toluene from waste gas was studied in a trickling biofilter. A high level of water recirculation (4.7 m h^–1) was maintained in order to keep the liquid phase concentration constant and to achieve a high degree of wetting. For loads in the range from 6 to 150 g m^–3 h^–1 the maximum volumetric removal rate (elimination capacity) was 35±10 g m^–3 h^–1, corresponding to a zero order removal rate of 0.11±0.03 g m^–2 h^–1 per unit of nominal surface area. The surface removal was zero order above the liquid phase concentrations of approximately 1.0 g m^–3, corresponding to inlet gas concentrations above 0.7–0.8 g m^–3. Below this concentration the surface removal was roughly of first order. The magnitude of the first order surface removal rate constant, k_1A , was estimated to be 0.08–0.27 m h^–1 (k_1A a=24–86 h^–1). Near-equilibrium conditions existed in the gas effluent, so mass transfer from gas to liquid was obviously relatively fast compared to the biological degradation. An analytical model based on a constant liquid phase concentration through the trickling filter column predicts the effluent gas concentration and the liquid phase concentration for a first and a zero order surface removal. The experimental results were in reasonable agreement with a very simple model valid for conditions with an overall removal governed by the biological degradation and independent of the gas/liquid mass transfer. The overall liquid mass transfer coefficient, K_La, was found to be a factor 6 higher in the system with biofilm compared to the system without. The difference may be explained by: 1. Difference in the wetting of the packing material, 2. Mass transfer occurring directly from the gas phase to the biofilm, and 3. Enlarged contact area between the gas phase and the biofilm due to a rough biofilm surface.     

Animal and worker exposure to dust and biological particles in animal care houses

An aerobiological study was performed to evaluate the potential exposure of animals and workers to dust constituents generated during routine animal house work. Different rooms of air conditioned (A, control) and passively ventilated (B, non-air conditioned) animal facilities were sampled, in order to evaluate total airborne culturable fungi and bacteria, fungal spore concentrations and particle levels. Airborne room particles were analyzed gravimetrically and for endotoxin content. All parameters, except for culturable fungi, were higher in facility B and statistically significant, with respect to those from the control facility A. Median values for airborne particle concentration, endotoxin and fungal spores in facility B were: 115 µg m^–3, 25 EU m^–3, and 2173 spores m^–3, respectively. Median values for facility A were: 66 µg m^–3, 9 EU m^–3, and 248 fungal spores m^–3. Broncheoalveolar lavage from rats kept in the rat room of B, presented median concentrations of total cells and lactate dehydrogenase, higher than those found in the control facility (4.4 × 10⁵ vs. 1.1 × 10⁵ and 2.7 UmL^-1 vs. 0.39 UmL^–1, respectively). Values of total and biological particles of both facilities, as well as the time spent in different rooms, showed that worker exposure was higher during cage washing. It was especially high in the passively ventilated facility (airborne particles 686 µg m^–3 3.5 h^–1 vs. 976 µg m^–3 3.5 h^–1, endotoxin 70 EU m^–3 3.5 h^–1 vs. 108 EU m^–3 3.5 h^–1). The type of basidiospores and ascospores found, as well as the significant correlation between particle levels and endotoxin contents suggests that wood chip bedding disturbance during cage washing is an important source for airborne biological particles. The changes in broncheoalveolar lavage components found in rats from these facilities and previously reported changes in pro-inflammatory cellular responses found in workers, indicate that these relatively low levels of exposure are enough to induce a biological response. Studies considering the composition of mixed organic dusts, would be needed to reevaluate current occupational standards.     

Mesophilic and thermophilic BTEX substrate interactions for a toluene-acclimatized biofilter

Benzene, toluene, ethylbenzene and xylene (BTEX) substrate interactions for a mesophilic (25°C) and thermophilic (50°C) toluene-acclimatized composted pine bark biofilter were investigated. Toluene, benzene, ethylbenzene, o-xylene, m-xylene and p-xylene removal efficiencies, both individually and in paired mixtures with toluene (1:1 ratio), were determined at a total loading rate of 18.1 g m^–3 h^–1 and retention time ranges of 0.5–3.0 min and 0.6–3.8 min for mesophilic and thermophilic biofilters, respectively. Overall, toluene degradation rates under mesophilic conditions were superior to degradation rates of individual BEX compounds. With the exception of p-xylene, higher removal efficiencies were achieved for individual BEX compounds compared to toluene under thermophilic conditions. Overall BEX compound degradation under mesophilic conditions was ranked as ethylbenzene >benzene >o-xylene >m-xylene >p-xylene. Under thermophilic conditions overall BEX compound degradation was ranked as benzene >o-xylene >ethylbenzene >m-xylene >p-xylene. With the exception of o-xylene, the presence of toluene in paired mixtures with BEX compounds resulted in enhanced removal efficiencies of BEX compounds, under both mesophilic and thermophilic conditions. A substrate interaction index was calculated to compare removal efficiencies at a retention time of 0.8 min (50 s). A reduction in toluene removal efficiencies (negative interaction) in the presence of individual BEX compounds was observed under mesophilic conditions, while enhanced toluene removal efficiency was achieved in the presence of other BEX compounds, with the exception of p-xylene under thermophilic conditions.     

Toluene degradation in a polyurethane biofilter at high loading

In the present study, toluene elimination in the polyurethane (PU) biofilter during long-term (145 day) operation was characterized, and assessed the effects of changing the inlet loading and space velocity (SV). A very high elimination capacity of 3.7 kg·m⁻³·h⁻¹ was obtained at an inlet loading of 4.0 kg·m^–3·h⁻¹ (inlet toluene concentration of 900 ppmv at a SV of 1,040 h⁻¹). Backwashing with irrigation and compressed air allowed maintenance of a pressure drop of < 80 mm H₂O·m⁻¹-filter at an SV of 830 h⁻¹ and an elimination efficiency of > 90% during the 145 day of operation. In conclusion, the PU biofilter can overcome the problems of clogging caused by excess biomass growth and of low treatment capacities of conventional biofilters.     

Removal of n-hexane by Fusarium solani with a gas-phase biofilter

A gas-phase biofilter inoculated with the fungus Fusarium solani, isolated from a consortium grown on hexane vapors, was used to degrade this compound. The biofilter, packed with perlite and operated with an empty bed residence time of 60 s, was supplied with hexane concentrations between 0.5 g m⁻³ and 11 g m⁻³. Biofilter performance was evaluated over 100 days of operation. Several strategies for supplying the nutritive mineral medium were assayed to maintain favorable conditions for the fungal growth and activity. The Fusarium system was able to sustain an average elimination capacity of 90 g m⁻³ _reactor h⁻¹ with a maximum of 130 g m⁻³ _reactor h⁻¹ . The mass transfer limitations due to high biomass development in the biofilter were confirmed in batch experiments. Bacterial contamination was observed, but experiments in the biofilter and in batch reactors using selective inhibitors and controlled pH confirmed the predominant role of the fungus. Results indicate that fungal biofilters can be an effective alternative to conventional abatement technologies for treating hydrophobic compounds.

     

Addressing biofilter limitations: A two-phase partitioning bioreactor process for the treatment of benzene and toluene contaminated gas streams

A two-phase partitioning bioreactor (TPPB) achievedsimultaneous and continuous removal and degradation of benzene and toluene froman air stream. The aqueous-organic system utilized n-hexadecane as the organicphase, and the organism Alcaligenes xylosoxidans Y234 in the aqueous phaseto achieve the degradation of benzene and toluene. The system, which operates asa well-mixed dispersion and is therefore resistant to substrate surges, was firstshown to be capable of utilizing toluene while operating at a loading capacity of 235 g m^-3 h^-1with an elimination capacity of 233 g m^-3 h^-1. It was also determined that to characterize TPPB performance in terms of elimination capacity thedefinition of elimination capacity must be extended to include the cell mass present, a readilycontrollable variable given the nature of the system. Based on this criterion, it wasestimated that for a cell concentration of 1 g l^-1 present in the TPPB, thepotential maximum toluene elimination capacity is 1290 g m^-3 h^-1 whichis substantially higher than any toluene elimination capacity achieved by biofiltersat a high removal efficiency. If no other factor were to limit the system, eliminationcapacities could be many times higher still, and are dependent on maintaining desiredcell concentrations above 1 g l^-1. The TPPB was then operated at nominalloading capacities of 63 g m^-3h^-1 (benzene) and 51 g m^-3 h^-1 (toluene) at a removal efficiency greater than 99% to demonstratedthe applicability of this system in dealing with two chemical species simultaneously. TPPBsystems therefore have been shown to be effective at removing gaseous organiccontaminants at high removal efficiencies while also possessing desirable operatingfeatures, such as providing and maintaining high cell concentrations throughout thereactor, and a capacity to effectively deal with high contaminant loadings.     

Influence of synthetic packing materials on the gas dispersion and biodegradation kinetics in fungal air biofilters

The biodegradation of toluene was studied in two lab-scale air biofilters operated in parallel, packed respectively with perlite granules (PEG) and polyurethane foam cubes (PUC) and inoculated with the same toluene-degrading fungus. Differences on the material pore size, from micrometres in PEG to millimetres in PUC, were responsible for distinct biomass growth patterns. A compact biofilm was formed around PEG, being the interstitial spaces progressively filled with biomass. Microbial growth concentrated at the core of PUC and the excess of biomass was washed-off, remaining the gas pressure drop comparatively low. Air dispersion in the bed was characterised by tracer studies and modelled as a series of completely stirred tanks (CSTR). The obtained number of CSTR (n) in the PEG packing increased from 33 to 86 along with the applied gas flow (equivalent to empty bed retention times from 48 to 12 s) and with operation time (up to 6 months). In the PUC bed, n varied between 9 and 13, indicating that a stronger and steadier gas dispersion was achieved. Michaelis–Menten half saturation constant (k _m) estimates ranged 71–113 mg m⁻³, depending on the experimental conditions, but such differences were not significant at a 95% confidence interval. The maximum volumetric elimination rate (r _m) varied from 23 to 50 g m⁻³ h⁻¹. Comparison between volumetric and biomass specific biodegradation activities indicated that toluene mass transfer was slower with PEG than with PUC as a consequence of a smaller biofilm surface and to the presence of larger zones of stagnant air.     

Acetone biodegradation in a trickle-bed biofilter

Laboratory scale-studies on acetone biodegradation in a trickle-bed biofilter were carried out using using two identically sized columns, one of which was packed with coconut fibre and the other with plexiglass chips. The columns were inoculated with two strains of bacteria: Burkholderia cepacia (syn. Pseudomonas cepacia) and Acinetobacter baumannii. The continuous process of air purification was carried out at incremental acetone concentrations from 0.3 to 2.5 g m⁻³ air and air flow-rates from 0.1 to 0.3 m³ h⁻¹. A maximum acetone elimination capacity of 95.8 g m⁻³ filter bed h⁻¹ was achieved at air flow-rate of 36 m h⁻¹.     

Continuous cultures of <Emphasis Type="Italic">Pseudomonas putida</Emphasis> mt-2 overcome catabolic function loss under real case operating conditions

The long-term performance and stability of Pseudomonas putida mt-2 cultures, a toluene-sensitive strain harboring the genes responsible for toluene biodegradation in the archetypal plasmid pWW0, was investigated in a chemostat bioreactor functioning under real case operating conditions. The process was operated at a dilution rate of 0.1 h⁻¹ under toluene loading rates of 259 ± 23 and 801 ± 78 g m⁻³ h⁻¹ (inlet toluene concentrations of 3.5 and 10.9 g m⁻³, respectively). Despite the deleterious effects of toluene and its degradation intermediates, the phenotype of this sensitive P. putida culture rapidly recovered from a 95% Tol⁻ population at day 4 to approx. 100% Tol⁺ cells from day 13 onward, sustaining elimination capacities of 232 ± 10 g m⁻³ h⁻¹ at 3.5 g Tol m⁻³ and 377 ± 13 g m⁻³ h⁻¹ at 10.9 g Tol m⁻³, which were comparable to those achieved by highly tolerant strains such as P. putida DOT T1E and P. putida F1 under identical experimental conditions. Only one type of Tol⁻ variant, harboring a TOL-like plasmid with a 38.5 kb deletion (containing the upper and meta operons for toluene biodegradation), was identified.     

Biotreatment of ammonia- and butanal-containing waste gases

The biological removal of ammonia and butanal in contaminated air was investigated by using, respectively, a laboratory-scale filter and a scrubber-filter combination. It was shown that ammonia can be removed with an elimination efficiency of 83% at a volumetric load of 100 m³·m^–2·h^–1 with 4–16 ppm of ammonia. During the experiment percolates were analysed for nitrate, nitrite, ammonium and pH. It was found that the nitrification in the biofilter could deteriorate due to an inhibition of Nitrobacter species, when the free ammonia concentration was rising in the percolate. It should be easy to control such inhibition through periodic analysis of the liquid phase by using a filter-scrubber combination. Such a combination was studied for butanol removal. Butanal was removed with an elimination efficiency of 80% by a scrubber-filter combination at a volumetric load of 100 m³·m^–2·h^–1 and a high butanal input concentration. Mixing the filter material with CaCO₃ and pH control of the liquid in the scrubber resulted in an increase of the elimination efficiency. These results, combined with previous results on the biofiltration of butanal and butyric acid, allow us to discuss the influence of odour compounds on the removal efficiency of such systems and methods for control. The results were used to construct a full-size system, which is described.