Membrane cleaning with ultrasonically driven bubbles

Abstract

A laboratory filtration plant for drinking water treatment is constructed to study the conditions for purely mechanical in situ cleaning of fouled polymeric membranes by the application of ultrasound. The filtration is done by suction of water with defined constant contamination through a membrane module, a stack of five pairs of flat-sheet ultrafiltration membranes. The short cleaning cycle to remove the cake layer from the membranes includes backwashing, the application of ultrasound and air flushing. A special geometry for sound irradiation of the membranes parallel to their surfaces is chosen. Two frequencies, 35kHz and 130kHz, and different driving powers are tested for their cleaning effectiveness. No cleaning is found for 35kHz, whereas good cleaning results are obtained for 130kHz, with an optimum cleaning effectiveness at moderate driving powers. Acoustic and optic measurements in space and time as well as analytical considerations and numerical calculations reveal the reasons and confirm the experimental results. The sound field is measured in high resolution and bubble structures are high-speed imaged on their nucleation sites as well as during their cleaning work at the membrane surface. The microscopic inspection of the membrane surface after cleaning shows distinct cleaning types in the cake layer that are related to specific bubble behaviour on the membrane. The membrane integrity and permeate quality are checked on-line by particle counting and turbidity measurement of the permeate. No signs of membrane damage or irreversible membrane degradation in permeability are detected and an excellent water permeate quality is retained.

How does ultrasonic cavitation remove dental bacterial biofilm?

“…Similar bubble behaviour was observed by Reuter et al [26] where they explain that the bubble is held to the surface via the secondary Bjerknes force and moves across the surface erratically via self-propelling forces, which result from its non-spherical oscillation driven by the pressure wave. Once cavitation bubbles were at a certain distance away from the scaler (approximately 4 mm measured from high speed images), they stopped moving forward on the surface and therefore Fig.…”

“…Individual bubbles appeared to travel underneath the translucent part of the biofilm without disrupting the biofilm surface and emerged out of the biofilm at another location (start of supplementary video b). Reuter et al [26] also observed a cavitating bubble cleaning a cake layer, which went underneath the surface contaminant to dislodge it from the surface, and it appears that the cavitation bubbles clean in a similar manner when disrupting bacterial biofilm.…”

Review on Membranes for the Filtration of Aqueous Based Solution: Oil in Water Emulsion

“…A short cleaning cycle to get rid of some cake formation on the layer of the membrane includes backwashing, air flushing and ultrasound. For NF membrane, a report suggested hydrochloric acid as a best cleaning agent at concentration of 0.20% w/w [154].…”

Microbubble dynamics in a viscous compressible liquid near a rigid boundary

“…Microbubble dynamics are associated cavitation damage to pumps, turbines and propellers Lauterborn & Kurz 2010), as well as applications in biomedical ultrasonics (Coussios & Roy 2007;Curtiss et al 2013;Wang et al 2015b;Vyas et al 2016Vyas et al , 2017, sonochemistry (Suslick 1990;Blake 1999) and cavitation cleaning (Ohl et al 2006;Reuter et a. 2017).…”