Physical and chemical effects of acoustic cavitation in selected ultrasonic cleaning applications

Abstract

Acoustic cavitation in a liquid medium generates several physical and chemical effects. The oscillation and collapse of cavitation bubbles, driven at low ultrasonic frequencies (e.g., 20 kHz), can generate strong shear forces, microjets, microstreaming and shockwaves. Such strong physical forces have been used in cleaning and flux improvement of ultrafiltration processes. These physical effects have also been shown to deactivate pathogens. The efficiency of deactivation of pathogens is not only dependent on ultrasonic experimental parameters, but also on the properties of the pathogens themselves. Bacteria with thick shell wall are found to be resistant to ultrasonic deactivation process. Some evidence does suggest that the chemical effects (radicals) of acoustic cavitation are also effective in deactivating pathogens. Another aspect of cleaning, namely, purification of water contaminated with organic and inorganic pollutants, has also been discussed in detail. Strong oxidising agents produced within acoustic cavitation bubbles could be used to degrade organic pollutants and convert toxic inorganic pollutants to less harmful substances. The effect of ultrasonic frequency and surface activity of solutes on the sonochemical degradation efficiency has also been discussed in this overview.

Inactivation of Staphylococcus aureus and Escherichia coli in milk by different processing sequences of ultrasound and heat

“…In particular, the sound wave with low frequency (20–100 kHz) and high intensity (10–1,000 W/cm 2 ) is referred as “power ultrasound.” Power ultrasound has the ability to generate acoustic cavitation, causing mechanical and sonochemical effects in the liquid (Kentish & Feng, ). The shear forces induced by cavitation could rub against cells and result in cell disruption and the formation of free radicals and hydrogen peroxide could cause cell oxidative damage (Yusof et al, ). These are considered as the major effects of ultrasound sterilization technique (Lacroix et al, ), and they can also produce some changes to food components during the processing (Aadil, Zeng, Han, & Sun, ; Abid et al, ).…”

Synergetic Effect of Ultrasound, the Heterogeneous Fenton Reaction and Photocatalysis by TiO2 Loaded on Nickel Foam on the Degradation of Pollutants

“…Consequently, NF increased the number of free radicals. Besides, due to adsorption-desorption in the gas-liquid boundary layer, the presence of NF increased the gas content in the solution, also strengthening the ultrasonic cavitation effect [23,24,25]. Under US, H 2 O 2 could produce OH• as the following Equations (2) and (3).…”

Ultrasound‐mediated therapies for the treatment of biofilms in chronic wounds: a review of present knowledge

“…The stable expansion and contraction of the MB are an important attribute of its associated biophysical effects; however, the effects of cavitation-enhanced gas exchange have been less investigated. During MB compression, there is an efflux of core gas into the local environment, followed by a net influx of gas upon expansion (Crum, 1984;Lentacker et al, 2014;Yusof et al, 2016). This is particularly important in regard to the use of nitric oxide microbubbles (NOMBs), since it shows that the MB has the capacity to deliver a locally concentrated therapeutic NO payload.…”