BACKGROUND: The treatment of methane in bioreactors with an aqueous phase such as biofilters is limited by low methane water solubility. In the case of biotrickling filters (BTF), the continuous trickling water is a barrier to methane transfer. In a previous study, the use of non-ionic surfactants improved the performance of biofilters treating methane. RESULTS: Three BTFs treating methane were operated for 1 year under fixed operating conditions of methane concentration of 4.8 g m-3 and air flow rate of 0.25 m-3 h-1. Three kinds of packing material were tested and a non-ionic surfactant (Brij 35) was periodically added to the nutrient solution at a concentration of 0.5% w/w. Methane conversion was a function of the type of packing materials and the presence of Brij 35 in the nutrient solution. When Brij 35 was added, the methane conversion doubled with respect to the BTFs without surfactant. CONCLUSION: The addition of Brij 35 to the nutrient solution increased the performance of the BTF for the three packing materials tested. The non-ionic surfactant also affected the carbon dioxide production. The BTFs were stable when the packed bed was washed to remove the excess of biomass. Copyright (c) 2012 Society of Chemical Industry