A new solid support membrane aerated biofilm reactor was designed for the synthesis of enantiopure (S)-styrene oxide utilizing Pseudomonas sp. strain VLBI20 Delta C growing in a biofilm as biocatalyst In analogy to traditional packed bed systems, maximizing the volumetric oxygen mass transfer capability (k(1)a) was identified as the most critical issue enabling a consistent productivity, as this parameter was shown to directly influence biofilm growth and biotransformation performance. A microporous ceramic unit was identified as an ideal microenvironment for biofilm growth and for efficient oxygen transfer A uniform and dense biofilm developed on this matrix. Due to this dual function, the reactor configuration could be significantly simplified by eliminating additional packing materials, as used in traditional packed bed reactors Up to now, a maximum productivity of 28L(aq)(-1) was achieved by integrating an in situ substrate feed and an in situ product recovery technique based on a silicone membrane. The system was stable for more than 30 days before it was actively terminated. Biotechnol. Bioeng 2010, 106 516-527. (C) 2010 Wiley Periodicals, Inc.