AFRL-ML-TY-TP-2004-4522 Screening of Fungi for Biodegradation of Volatile Organic Compounds

Many industrial practices and waste treatment operations produce gas streams containing volatile organic compounds (VOCs) that require treatment. Although biological treatment has been applied successfully to treat many waste gases, the literature contains numerous reports of diminished treatment performance under conditions of excessive drying or low pH in biofilter beds. Use of fungi in biofilter treatment systems may mitigate these effects. Recent research indicates that some fungal species are able to tolerate low pH conditions and low moisture environments. Although many fungal species have been tested for their ability to degrade nonvolatile compounds, relatively few accounts of fungal degradation of VOCs have appeared in the literature to date. In the studies described herein, five fungal species, Exophiala lecanii-corni, Mucor rouxii (ATCC 44260), Phanerochaete chrysosporium (ATCC 24725), Cladosporium sphaerospermum (ATCC 200384), and Cladosporium resinae (ATCC 34066) were screened for their ability to degrade compounds commonly found in paint spray booth off-gases. Fungal cultures inoculated on to ceramic support media were provided VOCs as their sole carbon and energy sources. Compounds tested included aromatic hydrocarbons (benzene, p-xylene), ketones (methyl ethyl ketone), and an organic acid (n-butyl acetate). Experiments were conducted using a variety of pH values ranging from 3.5 to 6.5. Fungal ability to degrade each VOC was determined by observing presence or absence of visible growth on the ceramic support media during a 30-day test period. Results indicate that Exophiala lecanii-corni and Cladosporium sphaerospermum can readily utilize n-butyl acetate, methyl ethyl ketone, benzene, and p-xylene as their sole carbon and energy source. Phanerochaete chrysosporium was able to degrade n-butyl acetate, methyl ethyl ketone, and benzene but not p-xylene under the conditions tested. Cladosporium resinae was able to degrade n-butyl acetate and methyl ethyl ketone but not benzene or p-xylene under the conditions tested. Mucor rouxii was able to use n-butyl acetate as a sole carbon and energy source; however, it was unable to utilize any of the other VOCs tested under the conditions imposed. Maximum growth for most of the tested fungi was observed at a pH value of approximately 5.0. Results of these screening studies reveal that not only are several fungal species capable of degrading the compounds tested, they also suggest that the experimental methods described herein may be of use in conducting further screening studies for candidate microorganisms.