BACKGROUND: Kinetic parameters used for modelling air biofilters are commonly determined by growing microorganisms in suspended cultures. However, they are not representative of phenomena occurring in a biofilm. There is need for new methods for calculating the true kinetics of pollutant degradation in an air biofilter. RESULTS: An experimental method for calculating the kinetic parameters of a microbial consortium which degrades methanol in an air treatment biofilter was developed. The kinetic parameters were calculated by taking biomass from biofilters packed with clay spheres or compost pellets. The kinetic runs were carried out in batch bioreactors at a constant temperature of 25 degrees C. The results obtained show that the maximum specific growth rate of microorganisms developed in the biofilter packed with clay spheres was twice as high as that packed with compost pellets; 0.233 h(-1) for clay spheres and 0.129 h(-1) for compost pellets. For both biofilters, the specific methanol biodegradation increased with methanol concentration in the biofilm, whereas carbon dioxide production was not a function of this parameter. CONCLUSION: Results show that for both biofilters, the Monad model fitted to the specific growth rate and the microbial consortium did not include any inhibition over the entire range of methanol concentrations tested. (C) 2009 Society of Chemical Industry