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ADVANCED OXIDATION PROCESSES IN THE TREATMENT OF CONTAMINANT CANDIDATE LIST (CCL) COMPOUNDS
Citation:
PELLER, J. R., M. ELOVITZ, AND K. VINODGOPAL. ADVANCED OXIDATION PROCESSES IN THE TREATMENT OF CONTAMINANT CANDIDATE LIST (CCL) COMPOUNDS. Presented at SETAC NORTH AMERICA 28th ANNUAL MEETING, MILWAUKEE, WI, November 11 - 15, 2007.
Description:
The current (2nd) Contaminant Candidate List was completed in 2005 by the United States EPA as an update to the Safe Drinking Water Act. The list of 42 chemical contaminants spans a wide array of classes, from pesticides to pharmaceuticals to elements, all of which are anticipated or known to be present in public water supplies. One focus of the EPA, in relation to the CCL, is to conduct research on these contaminants to determine the most useful means for remediation. Gaining most recent attention are the Advanced Oxidation Processes (AOPs), techniques that generate the hydroxyl radical, a strong, relatively nonselective oxidant, in aqueous environments. In reactions with most organic compounds, the hydroxyl radical effectively oxidizes the compounds by addition of the OH, by electron transfer or by hydrogen abstraction. Further hydroxyl radical reactions typically take place with the oxidized intermediates, and complete oxidation to form carbon dioxide and water often is the result with longer time exposures. The efficiency of these reactions, or the rate at which the hydroxyl radical reacts with the contaminant, is essential knowledge to assess the effectiveness of the AOPs. The best means to determine these reaction rates involves the technique of pulse radiolysis, where high energy radiation is used to form hydroxyl radicals and short timescale detection methods are implemented. Rate constant determinations were performed for sixteen of the chemicals listed on the CCL using pulse radiolysis techniques at the Radiation Laboratory on the campus of the University of Notre Dame. All of the tested compounds reacted with the hydroxyl radical, and in most cases, the UV spectrum of the reactive intermediate (transient) was readily detected. With the compounds that did not display a measurable UV absorption, competition kinetics experiments were conducted to measure the rate constants. In all cases, solutions were pre-saturated with nitrous oxide gas to ensure that only the hydroxyl radical reaction took place and typical calculated rate constants fell in the 2-6 x 109 M-1s-1 range. Absolute rate constants for all 16 compounds are reported and chemical structures are linked to reactions rates for an evaluation of the potential of Advanced Oxidation Processes.