Oxidation of Aqueous Pollutants Using Ultrasound: Salt-Induced Enhancement

Ultrasound can be used to oxidize aqueous pollutants; however, due to economic reasons, higher oxidation/destruction rates are needed. This study reports enhancements of reaction rates by the addition of sodium chloride salt. Using 20 kHz ultrasound, large salt-induced enhancements are observed6-fold for chlorobenzene, 7-fold for p-ethylphenol, and 3-fold for phenol oxidation. The reaction rate enhancements are proportional to the diethyl ether−water partitioning coefficient of the pollutants. It appears that the majority of oxidation reactions occur in the bubble−bulk interface region. The addition of salt increases the ionic strength of the aqueous phase which drives the organic pollutants toward the bubble−bulk interface. A first order reaction rate equation is proposed which can represent the observed enhancement with a good accuracy. A new sonochemical-waste-oxidation process is proposed utilizing the salt-induced enhancement.