Two-stage biofilters (using perlite and granular activated carbon, GAC, as packing materials) were used for the removal of several linear, branched, and cyclic C(5)-C(8)saturated aliphatic hydrocarbons from air, both as individual chemicals and in mixtures. The acclimation of biofilters from styrene to n-heptane was complete in 14-18 days. The substrate switch resulted in significant changes in pH and microbial composition of biofilters. Subsequent experiments were conducted under steady state conditions at a constant EBRT of 123 s and near-neutral pH, assuring the predominantly bacterial (as opposed to fungal) biofilter population. n-Heptane was removed with consistently high, 87-100%, removal efficiencies (RE) for up to 16 g x m(-3) x h(-1) critical substrate loads in the perlite biofilter, while n-hexane and n-pentane exhibited significantly lower RE under similar conditions. The REs for iso-octane and cyclohexane were less than 10% under similar loads; n-heptane biodegradation was consistently ca. 10% lower in the presence of iso-octane than in its absence. The GAC biofilter showed a significantly lower efficiency than the perlite biofilter (the critical load, yielding RE > 90%, was only 5 g x m(-3) x h(-1) for n-heptane). Evidence obtained indicates that the rate limiting step for mixed culture biofiltration of aliphatic hydrocarbon mixtures is biodegradation rather than mass transfer.

Institute of Chemical Technology Department of Fermentation Chemistry and Bioengineering Prague Czech Republic

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