Ozonation and ozone-based advanced oxidation processes have been shown to be effective in the oxidation of several pharmaceutically active compounds (PhACs) routinely detected in surface waters. Under typical operating conditions of these processes, most of the parent compound oxidized is expected to lead to the formation of transformation products (TPs). For a target ozone exposure, the resulting hydroxyl radical exposure depends on the water matrix or process chosen (e.g. peroxone) which in turn may influence the degradation pathway and the TPs formed. This study was undertaken to examine the expected impact that varying ozone and hydroxyl radical exposures may have on TP formation from the oxidation of PhACs during typical drinking water ozonation. Two representative PhACs were selected for the study. Carbamazepine was chosen to represent PhACs with a fast reaction rate with ozone (kO3 > 104 M−1 s−1) and bezafibrate was chosen to represent PhACs with a slow to moderate reaction rate with ozone (kO3 < 104 M−1 s−1). The results show that under varying ozone and hydroxyl exposure scenarios examined, the major oxidation pathway for the parent compound was dominated by reaction with ozone for carbamazepine while for bezafibrate it varied.

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