Effect of Ultrasonic Frequency on the Performance and Cleaning of UF Membranes Used in Sea Water Desalination Pretreatment

Abstract

This study aims to evaluate the impact of ultrasound (US) on the performance and cleaning of ultrafiltration membranes (UF) used in the pretreatment of sea water desalination plants. The effects of ultrasonic frequency on flux and fouling during the ultrafiltration process to saline solutions contaminated with Humic Acid (HA) were investigated. Ultrasonic application had a strong impact on the normal ultrafiltration process, especially at low frequency. The estimated increase in the flux were 67% and 38% when applying ultrasonic irradiation on dead end flat sheet ultrafiltration cell at 300 W and frequencies of 28 kHz and 40 kHz, respectively, but there was no significant increase in the flux at the upper frequency 100kHz where the flux nearly identical to that was obtained by stirring only. Upon ultrasonic application, total filtration resistance and reverse resistance, which include concentration polarization and cake layer, were sufficiently reduced as revealed by the quantitative resistance analysis using resistance in series model. The flux recovery ratio was increased to 72% when 28 kHz frequency was applied during mechanical and chemical cleaning. Ultrasonic enhancement factor (E_US) was higher by 11% in the online application of US on UF process than that of cleaning process. The application of ultrasound is an effective and promising way to enhance the ultrafiltration and cleaning of fouled membranes used in the pre-treatment of the seawater desalination process.

Keywords: ultrasound frequency, ultrafiltration, pretreatment, desalination of sea water