David A. Bruce, Ph.D. -- Research Activities

Sonochemical Reactions and Remediation Technologies
Sonochemical oxidation has been investigated as an environmentally benign process for removing CH2Cl2, CCl4, TCE, and a variety of other organic contaminants from waste water streams. In general, the destruction of organic compounds in water occurs through oxidation reactions involving hydroxyl radicals. Production of these radicals in water systems typically requires the addition of strong oxidizing agents, such as hydrogen peroxide, or high temperatures and pressures, such as with supercritical water oxidation (SCWO). Sonochemical techniques, such as ultrasound or hydrodynamic processing, produce an oxidative environment via cavitation that yields localized microbubbles or supercritical regions in the aqueous phase. With ultrasonic techniques, however, the formation of these supercritical regions does not necessitate the temperature and pressure of the bulk solution to increase much beyond ambient conditions.

The chemical effects of ultrasound are due to the phenomenon of acoustic cavitation, which involves the formation and subsequent collapse of microbubbles from acoustical wave-induced compression/rarefaction. The lifetime of a given microbubble is on the order of microseconds, and bubble collapse generates pockets of supercritical water by producing regions with intense, highly localized heating and high local pressure. During the momentary transition, these "micro-regions" are believed to reach temperatures as high as 5000° C and pressures of 500 atmospheres, even when the bulk liquid average temperature and pressure are maintained near ambient values. This type of cavitation in water has been shown to generate an assortment of highly reactive species, including OH•, H•, and H2O2• radicals. These radical species are what initiate the destruction of dissolved organic pollutants.

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