Fouling mechanisms of an end-free submerged membrane (Yonsei End Free;YEF) module under different filtration modes

Abstract

This study investigated effects of the concentration of ball clay suspensions and different filtration modes on the fouling of a submerged module (YEF; Yonsei End Free). In a crossflow filtration mode, short filtration time could reduce the membrane fouling at the one-minute stop duration. In order to see the effect of the stop duration on the increase in transmembrane pressure (TMP), the stop duration was increased to 0.75, 1.5 and 3 minutes while the suction time was set at 15 minutes in a dead-end filtration mode. The overall TMP increasing rate of 1.5-minute duration mode was twice less than that of 0.75-minute stop duration. Whereas, the TMP increasing rates of 1.5-minute stop duration and 3-minute stop duration were quite similar. Thus, the stop duration of 1.5 minutes was chosen for further experiments. To account for different individual fouling mechanisms, three fouling models were tested. The blocking model could fit the experimental data well in whole cycle period for both crossflow and dead-end filtration modes. The gel resistance of the crossflow filtration was 1.7 times higher than that of dead-end filtration suggesting that the gel formed on the surface of membrane tends to be taken off along with cake when the aeration restarted after the pause. On the other hand, the cake resistance of dead-end filtration was 5.9 times higher than that of crossflow filtration. Irreversible fouling was mainly caused by blockage of fine fraction of the ball clay particles.