Effect of Ultrasonication on Membrane Structure and Flux Recovery for Whey Ultrafiltration

Abstract

In this study, the effect of ultrasound irradiation on the flux recovery and fouling mitigation for the membranes made of the polysulfone by the phase inversion method were investigated. Two ultrasound irradiation regimes, including inside and outside the module, were chosen for this study. The experiments were conducted to investigate the effect of ultrasound irradiation on the membrane structure and cleaning. The ultrasound was irradiated in the frequency of 20 kHz and at the intensity of 25.5-127.4 W/cm2. When the membranes were irradiated directly out of the module, they may be damaged and the large holes were formed due to remaining in direct acoustic cavitation area. The flux recovery for the whey ultrafiltration process was increased with the increase of the irradiation time and the ultrasound intensity. The released energy which is the result of the cavitation threshold of bubbles indirectly may clean the foulant. During 60 min ultrasound irradiation, the flux recoveries were between 83-91% for membranes. At the probe distance of 1 cm from the module and after 20 min, the destruction or cracks in the membrane may be happened. The FE-SEM showed that the adjacent holes were connected and the crack was formed. The results for using the ultrasound for cleaning the fouled membranes showed that in the long distances, a large number of cavitation bubbles collapses before they reach to the membrane and in short distance, due to higher energy density, the produced acoustic and turbulence stream are increased and the membrane may be damaged.