Understanding acoustic cavitation for sonolytic degradation of p- cresol as a model contaminant Rajesh Balachandran a , Zach Patterson a , Pierre Deymier a , Shane A. Snyder b , Manish Keswani a, * a Materials Science and Engineering,1235 E James E Rogers Way, University of Arizona, Tucson, AZ 85721, USA b Chemical and Environmental Engineering,1133 E James E Rogers Way, University of Arizona, Tucson, AZ 85721, USA highlights graphical abstract  Examined acoustic cavitation using hydrophone and chro- noamperometry measurements.  Stable cavitation prevalent at 1 MHz while transient cavitation dominant at 37 kHz.  Higher generation rate of OH  at 1 MHz than at 37 kHz.  p-cresol degradation rate faster at 1 MHz compared to 37 kHz.  Addition of H 2 O 2 or Cu 2þ /H 2 O 2 significantly improved the p-cresol degradation rate. article info Article history: Received 10 October 2014 Received in revised form 10 November 2015 Accepted 17 December 2015 Available online 4 January 2016 Handling Editor: Min Jang Keywords: Sonolysis Fenton's reagent p-cresol Acoustic cavitation Hydroxyl radicals abstract Many modern techniques exist for the degradation of organic pollutants in water. Numerous treatment processes which utilize the formation of hydroxyl radicals for oxidation of pollutants have been studied thoroughly. In this study, a three pronged approach has been used to characterize and understand the effect of two distinct acoustic frequencies (37 kHz and 1 MHz) on cavitation behavior. Correlation of this behavior with sonolysis of a target phenol pollutant is described. Hydroxyl radical capture, hydrophone, and microelectrode studies in this work show that megasonic frequencies are more effective for gen- eration of hydroxyl radicals and stable cavitation events than ultrasonic frequencies. UV absorption and fluorescence measurements confirm that the combination of ultrasonic sonolysis with a Fenton reagent achieved complete degradation of p-cresol at 50 mg/L in about 30 min. Cost estimates have been made for different sonication processes and compared with traditional advanced oxidation processes. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Sonolysis is one of the techniques used for the degradation of organics in water (Gonzalez-Garcia et al., 2010; Chowdhury and Viraraghavan, 2009). As an acoustic pressure wave from a trans- ducer propagates through the aqueous medium, the oscillation between high and low pressure causes cavitation bubbles to form, oscillate and subsequently collapse (Awad et al., 2010). Cavitation events are described as either stable or transient, and both cases generate highly localized temperature (thousands of Kelvin) and * Corresponding author. E-mail address: manishk@email.arizona.edu (M. Keswani). Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere http://dx.doi.org/10.1016/j.chemosphere.2015.12.066 0045-6535/© 2015 Elsevier Ltd. All rights reserved. Chemosphere 147 (2016) 52e59