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

Abstract

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...

Identification ofPaecilomyces variotiiin Clinical Samples and Settings

“…Additionally, P. formosus has also been isolated from toluene gas biofilters. However, these isolates were misidentified as P. sinensis and P. variotii, and the correct name for these isolates is P. formosus (14,16,37). The extremotolerant nature is suggested to contribute to the pathogenic potential of fungi.…”

Phenomenological model of fungal biofilters for the abatement of hydrophobic VOCs

“…The better than expected behavior of the bacterial biofilm can be possibly due to the better kinetic properties of bacteria (García-Peña et al, 2005).…”

A comparative analysis of microflora during biofilm development on grape seeds exposed to methanol in a biofilter

“…Most microbial studies of biofilters have led to the characterization of species (e.g., bacteria, filamentous fungi, and yeasts) that exhibit interesting physiological capabilities in VOC degradation (Lipski et al 1998;Juteau et al 1999;Devinny et al 1999;Zilli et al 2000;Wacket 2003;García-Peña et al 2005). Some reports characterized the microorganisms responsible for VOC degradation, such as Pseudomonas, and possible degradation pathways (Cho et al 2000;Bordel et al 2007;Diaz et al 2007).…”