AWWA WQTC62379

Up to now, the initial phase of ozone decomposition has largely been ignored by the scientific community. In drinking water it is typically called "instantaneous ozone demand" and is considered an inherent inefficiency of ozonation. In this paper we time-resolve ozone demand by utilizing a continuous quench flow system, which allows measurements starting 350 milliseconds after ozone addition. It is shown that the initial phase displays very high HO· exposure ([HO·dt/]O₃dt ~10^-6), indicating that many oxidation processes and therefore product formation during this phase are HO·-based - i.e. akin to an advanced oxidation process (AOP). It is further shown that the rapid ozone decomposition and very high HO· yields may be partly explained by the direct reaction of ozone with amino and phenolic moieties of the natural organic matter (NOM). Finally, the halogenation (HOCl, HOBr) of amine-containing lake Zurich water minimizes HO· exposure significantly, confirming that this may represent an important mechanism in the Cl₂-NH₃ process for minimization of bromate during ozonation of bromide containing waters. Includes 12 references, figures.