Experimental and statistical study of an in-situ ultrasound (US)-assisted ultrafiltration process: Application to fouling control in skimmed milk filtration

Abstract

In the present work, in-situ ultrasound was employed as an innovative technique for fouling control and membrane cleaning in ultrafiltration of skimmed milk solution. A response surface methodology (RSM) was used to examine the influence of operational parameters, including US power and frequency, solid concentration, and feed flow rate, on the performance of the US-assisted ultrafiltration process. The experiments were conducted without US irradiation initially, and the results were compared to those obtained through US-assisted filtration. Filtration performance was found to improve at higher levels of power and feed flow rate and at lower levels of US frequency and solid concentration. The total mass of permeate, permeate flux, and mass of particles retained on the membrane were determined for each run. The permeate flux was improved using US by >67 % at the optimum conditions of 100 w, 28 kHz, 0.5 wt%, 1 L/min). A novel synchrotron X-ray high contrast imaging technique available at the Canadian Light Source (CLS) was employed for real-time visualization of US-generated bubbles and its influence on fouling control. It was observed that the number and size of the microbubbles increased as the US power enhanced from 50 W to 100 W. Under the influence of the US frequency, significantly larger bubbles were created at 20 kHz, while microbubbles' size decreased when the frequency changed to 40 kHz. A non-phenomenological mathematical model was also developed to predict US-assisted ultrafiltration performance under the defined factor levels.