The performance of biofilters inoculated with the fungus Scedosporium apiospermum was evaluated. This fungus was isolated from a biofilter which operated with toluene for more than 6 months. The experiments were performed in a 2.9 L reactor packed with vermiculite or with vermiculite-granular activated carbon as packing material. The initial moisture content of the support and the inlet concentration of toluene were 70% and 6 g/m 3 , respectively. As the pressure drop increased from 5-40 mm H 2 O a strong initial growth was observed. Stable operation was maintained for 20 days with a moisture content of 55% and a biomass of 33 mg biomass/g dry support. These conditions were achieved with intermittent addition of culture medium, which permitted a stable elimination capacity (EC) of 100 g/m 3 reactor h without clogging. Pressure drop across the bed and CO 2 production were related to toluene elimination. Measurement of toluene, at different levels of the biofilter, showed that the system attained higher local EC (200 g/m 3 r h) at the reactor outlet. These conditions were related to local humidity conditions. When the mineral medium was added periodically before the EC decreases, EC of approximately 258 g/m 3 r h were maintained with removal efficiencies of 98%. Under these conditions the average moisture content was 60% and 41 mg biomass/g dry support was produced. No sporulation was observed. Evaluation of bacterial content and activities showed that the toluene elimination was only due to S. apiospermum catabolism.

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A biofiltration system inoculated with the mold Paecilomyces variotii CBS115145 showed a toluene elimination capacity (EC) of around 250 g/m 3 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 O 2 /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 O 2 /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.Studies of biofiltration show that bacterial biofilms can degrade low concentrations of volatile organic compounds from off-gas streams (7,19). Recent work has demonstrated that biofilters containing fungi effectively eliminate volatile organic compounds, even under adverse environmental conditions such as low moisture content, low pH, and transient loadings (5,18,24,26,28). Previous results (9) have shown that a biofilter inoculated with a fungal strain (reported as Scedosporium apiospermum TB1 but recently reclassified as Paecilomyces variotii CBS115145) reached and maintained high elimination capacities (EC) of toluene (higher than 200 g/m 3 of biofilter/h, with a removal efficiency of 98%). The maximum EC of toluene, around 245 g/m 3 of biofilter/h, was obtained with the same strain growing on porous ceramic rings (1). The biofilter exhibited bacterial contamination, but fungal activity was responsible for about 70% of total removal. Woertz et al. Five metabolic pathways for toluene are known in bacteria (27). Toluene is initially hydroxylated on either the methyl group or the aromatic ring by an oxygenase. In fungi, initial hydroxylation on both molecular sites has also been reported. Some zygomycetes and deuteromycetes were shown to hydroxylate toluene at the aromatic ring, and the intermediates o-cresol and p-cresol were identified (21). Weber et al. (27) r...

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