Degradation of octylphenol and nonylphenol by ozone - Part II: Indirect reaction

The indirect reaction of octylphenol (OP) and nonylphenol (NP) with hydroxyl radicals ((OH)-O-center dot) during ozonation was investigated at pH values ranging from 6 to 9. A parameter R-ct. representing the ratio of the (OH)-O-center dot-exposure to the ozone-exposure, was measured using a method involving a low concentration of p-chlorobenzoic acid as a (OH)-O-center dot-probe compound during the ozonation. By assuming that R-ct is a constant value at a given pH, the second order rate constants of the alkylphenol reaction with hydroxyl radicals were determined as 1.4(+/- 0.2) x 10(10) and 1.1(+/- 0.2) x 10(10) M-1 s(-1) for OP and NP, respectively. The proportions of each alkylphenol degraded by direct molecular ozone reaction and indirect hydroxyl radical reaction were predicted at different pH values. The contribution of indirect (OH)-O-center dot reactions with each AP was found to represent over 50% of the total degradation for pH approximate to 7, and the contribution increases substantially with pH > 7. (c) 2007 Elsevier Ltd. All rights reserved.