BACKGROUND: Methanol is a major pollutant emitted in Canada. Methanol is toxic to humans and it is associated with environmental problems such as smog generation. Biofiltration is a treatment method of considerable interest for controlling methanol emissions, because of its characteristics: no production of hazardous wastes, low energy consumption and low operating costs. The present study analyzed the effects of porous and non-porous packing materials, the nitrogen concentration in nutrient solution and the methanol inlet load on biofilter performance and biofilm characteristics. RESULTS: The biofilter packed with porous material presented a removal efficiency up to 95%, which was higher than the 35% removal efficiency with the non-porous material. Inlet load (IL) influenced the biomass and carbon dioxide production rates. The critical inlet load (ILcrit) occurred at 80 g m(-3) h(-1). The cellular densities of methylotrophs and non-methylotrophs were affected by all operating variables examined. CONCLUSION: Biofiltration can be applied for controlling methanol emissions with high removal efficiency. The cellular density of methylotrophs is correlated with the performance of the biofilter. (C) 2008 Society of Chemical Industry.