In this paper a mechanistic model is presented for the estimation of temperature variations, moisture requirements, and elimination capacity of a waste air biofilter. The model considers diffusion and biodegradation of the pollutant in the biofilm, heat generation due to the bioreaction, and water evaporation from the solid media due to heat generation. Mass and energy balances were employed to derive the equations of the model. The equations were solved numerically using the finite volume method. The model was used to describe a set of experimental data for methane removal in a bench-scale biofilter. The model showed that an increase in elimination capacity caused a temperature rise in the biofilter. The model also showed that the air temperature and humidity increased along the height of the biofilter in the direction of airflow. The rate of increase in air humidity was higher in the first segment of the biofilter, indicating higher moisture requirement in this segment. A stoichiometric approach was adopted to estimate carbon dioxide production in the biofilter. The model predictions were in good agreement with the experimental data.