Hydroxyl Radical/Ozone Ratios During Ozonation Processes. I. The RctConcept

Abstract The ozonation of model systems and several natural waters was examined in bench-scale batch experiments. In addition to measuring the concentration of ozone (O3), the rate of depletion of an in situ hydroxyl radical probe compound was monitored, thus providing information on the transient steady-state concentration of hydroxyl radicals (√OH). A new parameter, Rct , representing the ratio of the √OH-exposure to the O3-exposure was calculated as a function of reaction time. For most waters tested, including pH-buffered model systems and natural waters, Rct was a constant value for the majority of the reaction. Therefore, Rct corresponds to the ratio of the √OH concentration to the O3 concentration in a given water (i.e. Rct = [√OH]/[O3]). For a given water source, the degradation of a micropollutant (e.g. atrazine) via O3 and √OH reaction pathways can be predicted by the O3 reaction kinetics and Rct .