Remediation of Pollutants using Ultrasound Induced Cavitation: “Nanostars in a Jar”

Wastewater treatment is becoming a worldwide concern due to new and tighter environmental regulations, and the increasing need for fresh water for the exponentially growing population. Major contributing factors are the increase in the presence of emerging contaminants (EC) such as pharmaceuticals, pesticides, microplastics and industrial chemicals, and the ineffective removal of these ECs by existing wastewater treatment processes. Alternative methods such as ultrasound is been investigated as an advanced oxidation process to enhance degradation of ECs. Irradiation of ultrasound in solution can generate acoustic cavitation that leads to the creation of reactive free radicals and conditions to facilitate applications such as degradation of pollutants, synthesis of polymers as well as nanomaterials such as metal colloids, metal nano-composites and hollow shelled micro/nano-spheres. These ultrasonic effects stem from the creation of cavitation bubbles as the sound waves propagate through a liquid medium. Liken to “a star in a jar”, these cavitation bubbles can emit light (sonoluminescence) and undergo violent collapses to generate extreme temperatures (> 5000 k), pressures (> 1000 atm) and jet velocities (up to 120 m/s has been reported). It is these remarkable conditions which create the unusual physical and chemical effects that we observe. However, to capitalise on these effects, one needs to understand the mechanisms behind the physical and chemical conditions created, and the importance of solution and sonication conditions used. This presentation will provide fundamental background on the mechanism behind ultrasound enhanced degradation, importance of solution and sonication conditions, and some case studies on the application of ultrasound in degradation of emerging pollutants such as pharmaceuticals.