Hydroxyl radical rate constants: comparing UV/H 2 O 2 and pulse radiolysis for environmental pollutants Michael S. Elovitz, Hilla Shemer, Julie R. Peller, K. Vinodgopal, Mano Sivaganesan and Karl G. Linden ABSTRACT Michael S. Elovitz Mano Sivaganesan Water Supply & Water Resources Division U.S. EPA, Cincinnati, OH 45268, USA Hilla Shemer Rabin Desalination Laboratory, Department of Chemical Engineering, Grand Water Research Institute, Technion, Haifa 32000, Israel Julie R. Peller K. Vinodgopal Department of Chemistry, Indiana University Northwest, Marram Hall/3400 Broadway, Gary, IN 46408, USA Karl G. Linden (corresponding author) Department of Civil, Environmental, and Architectural Engineering, University of Colorado at Boulder, Boulder, CO 80309, USA Tel.: +1 (303) 492-4798 Fax: +1 (303) 492-7317 E-mail: karl.linden@colorado.edu The objective of this study was to measure hydroxyl radical reaction rates using both UV/H 2 O 2 and pulse radiolysis techniques for 10 US EPA Contaminant Candidate List compounds (2,6- and 2,4-DNT, EPTC, prometon, linuron, diuron, RDX, molinate, nitrobenzene, and terbacil). The rate constants determined using these techniques were compared to each other and to values reported in the literature. Difference factors between k OH obtained using UV/H 2 O 2 and pulse radiolysis ranged from 1.1 to 4.7. It was shown that even small differences in hydroxyl radical rate constants values can result in fairly large differences (up to 50%) when trying to predict removals of pollutants in an advanced oxidation process. Key words | competition kinetics, contaminant candidate list, oxidation, photolysis, ultraviolet (UV) irradiation INTRODUCTION The US EPA Contaminant Candidate List (CCL) specifies unregulated priority contaminants and pathogens for the Agency’s drinking water program. The CCL comprises several different classes of chemical compounds, and it is widely recognized that no single treatment technology can be applicable to all of them. For example, granular activated carbon adsorption may be very effective for removing hydrophobic compounds, but this method works poorly for very volatile or water soluble compounds. Furthermore, traditional methods all have known drawbacks. Activated carbon adsorption and air stripping are common water treatment technologies that merely transfer the organic pollutant from one phase to another. Biological treatment of wastewater is able to degrade many organic pollutants but is usually only economical for relatively high strength wastewaters and biodegradable compounds (Nacheva et al. 2000; Zhou et al. 2006). In contrast, advanced oxidation processes (AOPs) are generally applicable for destroying a broad spectrum of chemicals. Over the past 25 years there has been a growing awareness that the treatment of many pollutants by AOPs can be both efficient and economical. AOPs represent those technologies which bring about enhanced oxidative degra- dation of pollutants in aqueous solution by the generation of highly reactive intermediates (e.g., the hydroxyl radical) via several methods. In some, an external energy source is used such as ultraviolet (UV) irradiation or radiolysis, and in others the process is driven by chemical energy (e.g., O 3 /H 2 O 2 , Fe 2 þ /H 2 O 2 ). AOPs can complement or even replace conventional treatment processes since they are able to treat and destroy organic (Beltran et al. 1998; Bose et al. 1998; Acero et al. 2000; Shemer & Linden 2007) and doi: 10.2166/aqua.2008.102 391 Q IWA Publishing 2008 Journal of Water Supply: Research and Technology—AQUA | 57.6 | 2008 Downloaded from https://iwaponline.com/aqua/article-pdf/57/6/391/401283/391.pdf by guest on 15 June 2020