In general, the higher the shear stress is on membrane surface, the less the membrane fouling rate is as intuitively expected. However, randomness of the shear stress is also known as an important factor that can enhance antifouling effect of aeration. When shear stress was measured by particle velocimetry (Yeo, 2007), the membrane fouling rate measured by TMP increasing rate appeared linearly correlated with the standard deviation of surface shear stress (Fig. 1). This observation is in line with the earlier observation (Ueda, 1997) discussed here, where membrane fouling rates decreased as standard deviation of upflow velocity increased while average upflow velocity remained same. These observations are the theoretical foundation of so called “intermittent aeration” practiced in some commercial hollow fiber membrane processes.
Fig. 1. Effect of random shear stress on membrane surface in tightly held hollow fiber membranes (Yeo, 2007).
Â© Seong Hoon Yoon