In the present work a biocatalytic membrane reactor operating in water phase while extracting the water unstable reaction product in organic phase by water-in-oil droplet formation via membrane emulsification has been optimized and tested. The performance of the system as a function of pH, temperature, residence time, and immobilized enzyme amount has been investigated with identification of optimal parameter values for best system performance. In addition to optimal reaction conditions practical aspects such as energy and chemical consumptions have been taken into account. Therefore experiments to test the process efficiency at temperature and pH different from the ideal ones have been performed. The stability of the catalytic process has been evaluated on a lab scale showing no activity decay for more than three days of continuous operation with a constant production of oleuropein aglycon of about 9 g/m(2) h. The suitability of the system for the conversion of oleuropein present in olive mill waste water (OMWW) has also been proved. (C) 2011 Elsevier B. V. All rights reserved.