The present work provides the kinetic background for understanding product formation during ozonation of organic contaminants under water treatment conditions. The steady state [HO.]/[O_3] ratio during continuous ozonation of several U.S. surface water was found to have a fairly constant value, averaging (1.3 +- 0.4) x 10~(-7). The rate constant for reaction of Ho radicals with nuatural DOC was estimated to be (3.8 +- 2.1) x 10~4 L (mg DOC)~(-1) s~(-1), a value that is similar to that found earlier in Swiss surface waters. The [HO]/[O_3] ratios can be used to estimate the relative importance of the HO versus direct O_3 reaction pathways, with the help of previously measured HO and O_3 reaction rate constants.
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