Abstract
Power ultrasonics (> 100 kHz), through acoustic cavitation, efficiently splits water to generate reactive oxygen species (ROS: center dot OH, O, HO2 center dot, O-3 and H2O2). As a result, water sonolysis is considered as an alternative advanced oxidation process for water treatment. In this process, the type of dissolved gases plays a crucial role in controlling the rate of ROS generation by affecting the sonoactivity and the size of active bubbles in the reacting medium. Maximizing the amount of oxidative radicals is important to develop sonochemical reactors for wastewater treatment. The purpose of this study is to determine the effect of some noble saturating gases (Ar, Xe, and He) on the sonochemical activity and the size distribution of active bubbles for the production of ROS in the sonicated water over a range of ultrasound frequency (213, 355 and 515 kHz) and acoustic intensity (1-2 W/cm(2)). An advanced acoustic cavitation model for reactive bubbles is adopted. The size distribution of active bubbles and the peak of ROS production are in the sequence Xe > Ar > He at all frequencies and intensities. The increase in ultrasonic frequency from 213 to 515 kHz narrows the spectrum of active bubbles and causes the optimal radii (giving the maximal molar yield) to be lower for all gases. In terms of size distribution and maximum ROS generation, the usage of argon is about as efficient as that of xenon. The use of helium, however, is less efficient regarding the active bubble size distribution (narrowest ranges), the optimal radii (smallest), and the maximum ROS generation (lowest).