Energy-saving by recovery of value-added materials from complex dispersions by using semi-permeable membranes has been proved world-wide. The effect is related to fundamental knowledge of fluid flow and mass transfer in complex fluids close to membrane interfaces. Innovative biotechnologies for value-added products such as exopolysaccharides or antioxidants benefit by such explorations in preserving the biological activity of the target components. The paper presents a solution of theoretical model of a stirred tank reactor (STR) Biostat equipped with membrane immersed in a non-Newtonian model solution of exopolysaccharide, e.g. glucomannan and biomass. CFD methodology is employed to reveal original data on shear deformation rates and shear stress at the membrane interface, as well as to predict the average mass transfer coefficient related to the boundary layer at the membrane surface based on the flow information obtained. The results are compared with similar data reported for conventional systems with different impeller and systems with external membranes.