33. Ultrasound

The use of ultrasound for the remediation of polluted sites and soils has been studied at the research and development stage for some ten years.

Two main applications for ultrasound have now been identified: use on soil to improve the accessibility of pollutants, and use on water to destroy organic pollutants present in the dissolved phase.

• Principle

  Ultrasonic waves are pressure waves with frequencies between 20 kHz and 2 MHz (for the applications described below). These waves cause compression cycles – in the medium in which they propagate.

  Under the effect of an ultrasonic wave, a cavitation bubble is formed and increases in size during compression cycles – depression. When it reaches its resonance size, the cavitation bubble implodes (figure