Mechanistic features of ultrasonic desorption of aromatic pollutants

This study attempts to identify the physical mechanism of ultrasonic desorption of aromatic pollutants. Specifically, an attempt is made to discriminate between the contributions made by the various physical effects of ultrasound and cavitation that generate high convection in the medium towards enhancement in desorption of pollutants. Two model adsorbents (activated charcoal and Amberlite XAD-4) and three aromatic pollutants (viz. phenol, p-cresol and nitrobenzene) have been chosen. The experimental techniques adopted in this study alter the characteristics of the cavitation phenomenon in the medium. The approach is to couple experimental results with simulations of cavitation bubble dynamics. Qualitative comparison between experimental and simulations results reveals that microturbulence generated by cavitation bubble plays insignificant role in enhancement of desorption. On the other hand, acoustic waves emitted by cavitation bubbles mostly contribute to enhancement of the desorption process. This is due to high pressure amplitude and discrete nature of the waves that create intense yet intermittent and chaotic convection in the medium. The experimental/modeling framework presented in this thesis could be extended to any other set of pollutant-adsorbent.

► An attempt to discern the physical mechanism of ultrasonic desorption.
► Model adsorbents—Amberlite XAD-4 resin, activated charcoal.
► Distinction among components of convection generated by ultrasound and cavitation.
► Micro-convection of oscillatory nature and high amplitude intermittent shock waves.
► Shock waves emitted by cavitation bubbles contribute mainly to desorption.