CFD modeling of hydrodynamic characteristics of slug bubble flow in a flat sheet membrane bioreactor

It has previously been shown experimentally that the use of intermittent slug bubbling through the periodic introduction of large bubbles is an effective strategy to control fouling in MBRs. As the current set of experimental results is limited, a numerical study on the properties of a single bubble rising in an industrial flat sheet MBR was undertaken. A three-dimensional simulation with the volume of fluid (VOF) method was implemented. The predicted bubble is of a typical spherical cap shape which is consistent with experimental observation. The variation of the predicted shear stress on the membrane surface also shows good agreement with previous electrochemical results. Compared with the film region, the shear stresses in the wake region of the bubble were more intense and covered a much larger area. Additionally, the dominant component of shear stress is parallel with the bubble rising direction. For a fixed 100 mL bubble, the averaged shear stress attains a maximum value when the gap between the membranes is around 8 mm. With increasing activated sludge viscosity, the averaged shear stress increased only slightly. A brief review of CFD modeling and associated experimental work on two-phase flow in various membrane modules is included.