Exploring the influence of air resistance on the hollow fiber membrane process in water treatment based on ultrasonic...

In water treatment with membrane filtration process, a lot of factors such as process design, operation, and fouling affect membrane flux. But it is often neglected the flux decline which attribute to air resistance. In this study, it has been observed that air resistance caused by air trapped initially at startup as well as the release of air from the permeating liquid has an adverse effect on the membrane filtration and backwash process in water treatment. In the study, a new in-situ monitoring method, ultrasonic phased array (UPA), was used to investigate the distribution of released air in the hollow fiber membrane module. The operation parameters such as backwash interval, duration and strength were investigated. A strategy was also proposed to mitigate the adverse effects of air resistance. The results showed that UPA can successfully monitor the distribution of released air, which has a good positive correlation with air sound pressure reflection R¯_air. The released air is mainly distributed far away from the outlet, while as the backwash interval and strength increase, the range of released air distribution gradually expands. We also found the optimal operating parameters for the minimum released air volume that the backwash interval is 90 min and the backwash duration is 60 s. Besides, the air resistance has a good positive correlation with released air. Moreover, the released air migration results show that air dispersion and redissolution are beneficial to reduce the air resistance in the backwash process. In summary, the optimal operation can mitigate the air resistance in the variable membrane filtration mode in water treatment.