BACKGROUND: Two-phase partitioning bioreactors (TPPBs) are considered as a new technology for xenobiotic degradation in gaseous effluents. However, there is still a need for more knowledge on how to design and scale up TPPBs. The partitioning of the two phases remains a misunderstood method of research. In particular, the impact of pollutant (isopropylbenzene), biomass and surfactant extract needs to be better evaluated. RESULTS: An adapted scale-down apparatus has been developed in order to quantify the speed of phase partitioning (SPP) into a plug flow section. First, it was shown that isopropylbenzene (IPB) does not destabilise the system more significantly. Second, respectively 0.5 g L-1 and 0.05 g L-1 of biomass and surfactant extract, separately or in mixture, were sufficient to ensure the stability of the two-phase system. Finally, a 100 m(3) limit of scaling-up was suggested on the basis of the circulation time comparison. CONCLUSION: The scaling up of an aqueous-silicone oil TPPB was found to be definitely conceivable when the presence of biotic compounds were considered. However, further considerations are needed to verify our assumptions, in particular by taking into account the velocity field pattern in full-scale bioreactors and reproduce it in laboratory-scale apparatus. (C) 2010 Society of Chemical Industry