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AWWA WQTC62589
- Ozonation of Thiocarbamate and Urea Herbicides, Triazines and Benzenes on EPA Drinking Water Contaminant Candidate List
- Conference Proceeding by American Water Works Association, 11/01/2005
- Publisher: AWWA
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The objective of this research was to determine the rate constants and treatability for tenchemicals on the US Environmental Protection Agency (USEPA) Contaminant Candidate List (including thiocarbamate and ureaherbicides, triazines and substituted benzene compounds) using ozone alone and ozone/H<sub>2</sub>O<sub>2</sub> advanced oxidation processes (AOP).Ozonation and AOPs are recognized to be effective treatment processes to achievedegradation of contaminants in drinking water. The knowledge of the reaction kinetics ofozonation and AOPs on emerging contaminants such as those on the ContaminantCandidate List (CCL) is essential to the USEPA's regulatory strategies for thesechemicals. Second-order rate constants of the direct reactions (k<sub>O3,M</sub>) for three CCLchemicals and the constants of the indirect reactions (k<sub>OH</sub>) for ten CCL chemicals weremeasured. Initial chemical concentrations were about 0.5-1 uM and ozone doses appliedranged from 1.8 to 4.4 ppm, within the range of drinking water treatment doses. Themolar ratios of H<sub>2</sub>O<sub>2</sub>/O<sub>3</sub> were about 1-10 for ozone doses of 0.5-5 ppm.Results show both urea herbicides (diuron and linuron) and RDX have slow directreactions with ozone, which can be explained by the presence of multiple electro-withdrawingsubstituted groups (Cl and NO<sub>2</sub>) in their structures. On the other hand, therates of indirect OH radical reactions varied. Terbicil, thiocarbamate (EPTC andmolinate) and urea (diuron and linuron) herbicides, and nitrobenzene all are highlyreactive toward OH radicals demonstrated by k<sub>OH</sub> on the order of 109 and higher.Prometon and dinitrotoluenes show medium reactivity, while RDX is relatively unreactivetoward OH radicals.Therefore, ozonation at low pH, which involves mainly the direct ozone reaction, is notefficient for treating urea herbicides and RDX. AOPs, such as ozonation at high pH andthe O<sub>3</sub>/H<sub>2</sub>O<sub>2</sub> process, will be highly efficient for the removal of terbicil, thethiocarbamates, the ureas, prometon and nitrobenzene. Of importance, only RDX can notbe effectively treated by either ozonation or the O<sub>3</sub>/H<sub>2</sub<O<sub>2</sub> AOP. Includes 13 references, tables, figures.
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