Infrasonic pulsing for foulant removal in crossflow microfiltration

In this study, a novel technique called infrasonic pulsing was used to remove foulant cake and improve flux through microfiltration membranes. The technique consists of applying pressure pulses on the permeate side, with frequencies on the order of 1-10 Hz. We present a model of the infrasonic pulsing process and show that it is able to describe the net permeate flux behavior for experiments with an inorganic (talc) suspension and a biological (yeast) suspension using a flat polymeric membrane. We also discuss how the net permeate flux depends on the cake formation time constant and the infrasonic frequency, duty cycle, and amplitude. It is shown that infrasonic pulsing results in up to a four-fold improvement in the net flux for the talc system and up to a three-fold improvement for the yeast system. The net flux was found to be independent of frequency (between 3.5 and 12.5 Hz) for talc, due to the relatively large value of the time constant for cake growth (nearly 500 s), and it decreased as the duration of the pulses was increased. However, in experiments with yeast, the net flux was found to increase as the pulse frequency increased, due to a much smaller value of the time constant for cake growth (about 4 s), and it also decreased as the duration of the pulses was increased. It is proposed that the infrasonic pulses cause rapid vibrations of the membrane which lift a portion of the foulant cake off its surface. (C) 2000 Elsevier Science B.V. All rights reserved.