Improved ultrasonic cleaning of membranes with tandem frequency excitation

In water purification membrane fouling is the most common problem that decresases efficiency in the purification process. In this work we propose a simple method to remove the particles deposited on the membrane surface by applying two different ultrasound frequencies in tandem. First a high ultrasound frequency, here 220 kHz, is used to create microscopic bubbles that are immediately after excited with a lower ultrasound frequency, e.g., 28 kHz. High speed video of the bare membrane shows the higher number of bubbles after the application of the high ultrasound frequency, as opposed to applying only a low ultrasound frequency. The method is then evaluated by recording the flux delivered and the transmembrane pressure (TMP) in this small scale experiment. The results show that after the application of the tandem frequency the transmembrane pressure is restored to the value of the non fouled membrane.