This work reports on the separation of biohydrogen using a hollow-fiber PDMS membrane. The performance of the module was evaluated using binary CO2/H-2 (35-65 vol.% H-2 content) and ternary CO2/H-2/H2S mixtures (50 vol.% H-2, 50 vol%"CO2, 25-175 ppm H2S) and the effect of recovery and gas composition (with special focus on hydrogen sulfide content) was revealed. H2S is a potential impurity of the raw gas coming from steady-state, dark fermentative hydrogen producing bioreactors. The results indicated that H2S could have a concentration-dependent impact on membrane behavior and affected the obtainable CO2/H-2 selectivity. The outcomes were thoroughly compared to other relevant gas separation reports found in the literature. Evaluating the impacts of trace-level substances present in the gaseous mixture containing biohydrogen may help to design effective purification system based on membrane technology for the hydrogen economy. (C) 2015 Elsevier B.V. All rights reserved.