A mathematical model that incorporates mass transfer process and biofilm reactions is presented to predict the performance of a trickle-bed air biofilter (TBAB) for treating isopropyl alcohol (IPA) and acetone (ACE) mixtures. The model consists of a set of mass balance equations for IPA, ACE and oxygen in the bulk gas phase and within the biofilm. The effluent gas phase IPA and ACE concentrations predicted by the present model were in good agreement with the measured data available in a previous study. The important parameters were evaluated by sensitivity analysis to determine their respective effects on model performance. Four parameters were identified that strongly influenced model performance: surface area of the biofilm per unit volume of packing material (A(S)), empty-bed residence time (EBRT), maximum specific growth rate of microorganism (mu(m)), and microbial yield coefficient (Y). Practical applications of the model to derive the performance equation of TBAB for treating different inlet IPA and ACE concentrations were also demonstrated. (C) 2003 Elsevier Ltd. All rights reserved.