title: Hydroxyl radical formation in batch and continuous flow ultrasonic systems.
abstract: The creation of free radicals by ultrasonic cavitation is the main mechanism that leads to chemical degradation of target pollutants and the process is considered an alternative advanced oxidation technology. The goal of this study was to compare the effects of batch and continuous flow ultrasonic systems on the formation of hydroxyl radicals. Ultrasonic batch experiments were conducted in two reactors (small and large) using a standard 20kHz catenoidal titanium horn at varying amplitudes and sonication times. The effect of saturating gas was also investigated by introducing helium and air at 1Lmin(-1) into the larger 100mL reactor. In the continuous flow system, the experiments were conducted with a 20kHz, 3.3kW ultrasonic systems using a titanium "donut" horn at varying volumetric flow rates and amplitudes. Formation of hydroxyl radicals was determined using terephthalic acid dosimetry measurements. At the same energy densities, higher hydroxyl radical concentrations were formed in the batch system than in the continuous flow system. Sonication time appeared to be the main factor that influenced the results in batch and continuous flow systems. The two gases (helium and air) did not increase the hydroxyl radical formation at any amplitude or sonication time tested.
authors.affiliation: Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, IA 50011-3080, USA; Department of Energy, Power Engineering and Environment, Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Ivana Lucica 5, HR-10000 Zagreb, Croatia; Department of Civil, Construction and Environmental Engineering, Iowa State University, Ames, IA 50011-3232, USA.
authors.forename: Hrvoje
authors.initials: H
authors.lastname: Juretic
authors.affiliation: Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, IA 50011-3080, USA.
authors.forename: Melissa
authors.initials: M
authors.lastname: Montalbo-Lomboy
authors.affiliation: Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, IA 50011-3080, USA; Department of Civil, Construction and Environmental Engineering, Iowa State University, Ames, IA 50011-3232, USA; Department of Food Science and Human Nutrition, Iowa State University, Ames, IA 50011-3080, USA.
authors.forename: J Hans
authors.initials: JH
authors.lastname: van Leeuwen
authors.affiliation: Department of Civil and Environmental Engineering, Urban Water Research Center, University of California, Irvine, Irvine, CA 92697-2175, USA.
authors.forename: William J
authors.initials: WJ
authors.lastname: Cooper
authors.affiliation: Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, IA 50011-3080, USA. Electronic address: dgrewell@iastate.edu.
authors.forename: David
authors.initials: D
authors.lastname: Grewell
keywords: Batch; Continuous flow; Donut horn; Hydroxyl radical; Terephthalate dosimetry; Ultrasonication