BACKGROUND: Several sources such as the paper and pulp industry and waste treatment plants emit waste gases containing volatile organic sulfur compounds at elevated temperature. Since cooling the hot gases increases the operational cost of biological reactors, application of thermophilic microorganisms could be a cost-effective solution. The objectives of this study were to investigate the possibility of removal of dimethyl sulfide from waste gases under thermophilic conditions (52 degrees C) in a membrane bioreactor and to examine the long-term stability of the reactor at elevated temperature. The effects of operating conditions such as gas residence time, nutrient supply, temperature decrease and short-term shutdown on elimination capacity were investigated. RESULTS: A maximum elimination capacity of 54 g m(-3) h(-1) (0.108 g m(-2) h(-1)) was obtained at a mass loading rate of 64 g m(-3) h(-1) (0.128 g m(-2) h(-1)) with a removal efficiency of 84% at a gas residence time of 24 s. The long-term operation of the thermophilic membrane bioreactor was followed for 9 months. Although the removal efficiency decreased to 50% after 3 months of continuous operation, it recovered (>96%) after the excess biomass was removed by applying high-velocity liquid recirculation. CONCLUSION: This study demonstrated that the dimethyl sulfide removal is possible in a thermophilic membrane bioreactor with an elimination capacity of 54 g m(-3) h(-1) (0.108 g m(-2) h(-1)) at a gas residence time of 24 s. (C) 2008 Society of Chemical Industry.