The main drawback of membrane bioreactors (MBR) systems is the fouling of the membrane, which is decreased and/or prevented through high liquid velocities or gas sparging. However, these two practices are based on rules of thumb or a trial-and-error approaches which are tedious, very time-consuming, do not necessarily provide optimal fouling control and they are not energy efficient. Therefore, dedicated experiments are needed to fully understand the hydrodynamics of it. Two types of MRB were studied: 1) Hollow Sheet (HS) and 2) Rotating Cross-Flow (RCF). Experimental velocity measurements were made for both systems and compared to CFD results. In general there was found a good agreement between experimental measurements and CFD results (error less than 20 %). Due to the fact the shear stress measurements were not perform, they were extracted from the CFD simulations, as the CFD simulation was validated against velocity data. The results of shear stress shows that the RCF system has larger (up to 10 times) shear values compared to hollow sheet (HS) systems. However, the shear stress in the RCF system is not homogeneously distributes, as for the HS system.