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Up to now, the initial phase of ozone decomposition has largely been ignored by the scientific community. In drinkingwater it is typically called "instantaneous ozone demand" and is considered an inherent inefficiency of ozonation. Inthis paper we time-resolve ozone demand by utilizing a continuous quench flow system, which allows measurementsstarting 350 milliseconds after ozone addition. It is shown that the initial phase displays very high HO exposure([HOdt/]Osub3/subdt ~10sup-6/sup), indicating that many oxidation processes and therefore product formation during this phase areHO-based - i.e. akin to an advanced oxidation process (AOP). It is further shown that the rapid ozone decomposition and very high HO yieldsmay be partly explained by the direct reaction of ozone with amino and phenolic moieties of the natural organic matter (NOM). Finally, thehalogenation (HOCl, HOBr) of amine-containing lake Zurich water minimizes HO exposure significantly, confirmingthat this may represent an important mechanism in the Clsub2/sub-NHsub3/sub process for minimization of bromate during ozonationof bromide containing waters. Includes 12 references, figures.

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Edition: Vol. - No. Published: 11/01/2005 Number of Pages: 6