Transient behavior of biofilters: Start-up, carbon balances, and interactions between pollutants

The work describes the aerobic biodegradation of volatile organic compound (VOC) mixtures from effluent air streams in laboratory-scale compost based biofilters. A rapid start-up of the system (3-5 d) was observed and 82% of the carbon in the influent pollutant (methyl ethyl ketone) was recovered as carbon dioxide in the exhaust air after this period. Biofilter performance and carbon dioxide production were also investigated during and after 0.5-1-h step inputs of 2-10 g m(-3) of hexane, acetone, 1-propanol, and/or methyl isobutyl ketone (MIBK) during steady methyl ethyl ketone (MEK) treatment. Carbon dioxide patterns suggest that pulsed pollutants were first sorbed onto the packing material and subsequently degraded within 2-5 h. Hexane was not sorbed, and thus not degraded to a significant extent. Little effect was observed of the step inputs on the overall MEK removal process, mainly because the reactors were operated well below MEK breakthrough loading. However, the analysis of MEK profiles within the biofilter bed showed that significant inhibition did indeed occur. An even more important inhibition was observed between 1-propanol, MIBK, and acetone, when such a mixture was injected into the reactor. Practical design of biofilters should consider the possibility of reduced performances due to the presence of multiple VOCs in the waste air stream.