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, R_ct , 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, R_ct was a constant value for the majority of the reaction. Therefore, R_ct corresponds to the ratio of the √OH concentration to the O₃ concentration in a given water (i.e. R_ct = [√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 R_ct .