CFD modelling of the hydrodynamics in a filtration unit with rotating membranes

Membrane BioReactor (MBR) is a commonly used technology in wastewater treatment; however, fouling is the main drawback of MBR. Grundfos proposes a system that splits the technology into two parts: the biological tank and the membrane system. The latter rotates to decrease and mitigate the fouling. This paper evaluates two membrane configurations, a central and eccentric axis. The shear stress profile in a single rotating membrane was obtained through CFD modelling with different operating conditions that show that an increasing TSS or angular velocity causes an increment in the shear stress over the membrane surface. Additionally, based on the CFD results and empirical correlations, a factor α used to determine the shear stress for non-Newtonian fluids was calculated in order to predict the behavior for central and eccentric placement configuration MBRs. The velocity profile in a wagon of 36 membranes was obtained from CFD simulations, where it was evident that eccentric placement is the best option since it reduces the dead zones and increases the shear stress, which helps reduce fouling.