The effect of non-ionic surfactants on the biofiltration of methane (CH4) was analyzed. Two biofilters (BF) treating CH4 were operated for one year at fixed CH4 concentration of 4.8 gm(-3) and air flow rate of 0.25 m(-3) h(-1). Three polyoxyethylenes (Brijs), and 3 mono polyoxyethylenesorbitans (Tweens) were added to the nutrient solution at a concentration of 0.5% (w/w). Without surfactant, CH4 conversion had an average level of 35%, with Brijs the CH4 conversion varied between 38% and 46%, and with Tweens between 43% and 48%. The non-ionic surfactants decreased the biomass accumulation in the packed bed due to their detergent character. Biofilters were operated in a range of nitrogen concentration in the nutrient solution from 0.5 to 2 gN L-1 using Tween 20 at a concentration of 0.5% (w/w). The ECmax observed in this study, 45 g m(-3) h(-1), occurred when the nitrogen concentration was 1 gN L-1. (C) 2011 Published by Elsevier Ltd.