Based on the model proposed by De Visscher and Van Cleemput for methane oxidation in landfill cover soils, a simulation model for biofiltration of toluene-contaminated air has been developed for biofilters with substrate inhibition. A convenient way to optimize biofilter performance was developed assuming Haldane kinetics. It was calculated that for a typical oilsands operation emitting 200 ton of toluene annually, 90% of the toluene can be removed by a 740 m(3) biofilter, if the waste gas sent to the biofilter has a toluene concentration of 2.25 g m(-3). The optimal initial concentration increases with increasing target efficiency. (C) 2008 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.