Oxidation of Disinfection Byproducts and Algae-related Odorants by UV/H2O2

This research involved an investigation of the application and reaction mechanisms of UV/H2O2 for the simultaneous removal of regulated halogenated disinfection byproducts (DBPs) and odorous aldehydic algal byproducts in the presence of geosmin and 2methylisoborneol, which are earthy-musty odorants that commonly occur in drinking water. UV/H2O2 is an expensive advanced oxidation process that is used to successfully control geosmin and 2-methylisoborneol. The aqueous oxidation of odorous aldehydes and halogenated DPBs were compared to that of the earthy-musty odorants and the changes to the sensory properties of the drinking water were examined. Geosmin, 2-methylisoborneol, heptadienal, decadienal, and nonadienal, hexanal, and the two most prevalent classes of DBPs, trihalomethanes (THMs) and haloacetic acids (HAAs) were oxidized by UV photolysis alone and the UV/H2O2 process with 6 mg/L H2O2 and realistic ng/l to μg/L concentrations of the test compounds. The di-, and tri-brominated THMs and HAAs were substantially (80-99%) removed by direct UV photolysis mechanism at the same UV/H2O2 dose required for removing 95% of geosmin and 65% of 2-methylisoborneol with faster reaction rates for the more bromine substituted compounds. The C-Br bond cleavage is the first step of brominated HAAs degradation by UV photolysis, and followed by either of two second steps: reaction with oxygen producing peroxyl radical or interaction with water molecule causing O-H insertion/H-Br elimination. Trichloromethane and mono-, di-, and tri-chlorinated HAAs were not substantially removed under the same conditions used for the brominated compounds. The principal removal mechanism was by the reaction with hydroxyl radical for the UV/H2O2 process. The second order reaction rate constants were on the order of 10 10 M s with faster reaction rates