Shear stress generated by radial flow impellers at bioreactor integrated membranes

Abstract

The study reveals the hydrodynamics at the surface of a submerged tubular membrane module integrated in a stirred membrane bioreactor. The reactor is equipped with a conventional six flat-blade impeller imposing radial circulation across the membrane interface. Simulation and computer visualization of “real” flow using a Reynolds-averaged Navier-Stokes model and CFD methodology are employed. A variety of model solutions at various mixing intensity are obtained and the mixing conditions are assessed by delineation of the near-wall zones and identification of the zones' shear rate and shear stress values. Shear rate non-uniformity along the surface of the tubular module is visualized. Shear stress values as high as 160 Pa at the membrane module lower section and as low as 0.6 Pa at the module upper section has been determined. Referring to reported data for shear stress near flat plate stirred filtration cells and external narrow-channel cross-flow systems, the mixing conditions are expected to allow enhanced access of the retentate fluid to the membrane surface, as well as possible low membrane fouling potential related to microfiltration practice.