On the Kinetic Regimes in the Ozonation of Carbamazepine: The Influence of Ozone Concentration in Water Treatment

The removal of persistent pharmaceutical compounds such as carbamazepine (CBZ) by advanced oxidation processes (AOPs) remains a major challenge in water treatment, particularly in relation to understanding the operating conditions governing reaction kinetics and transformation pathways. In this context, this study aims to evaluate the effect of ozone concentration on the kinetics and mechanistic regimes of CBZ ozonation in aqueous solutions. Ozonation experiments were conducted in an aqueous solution at an initial CBZ concentration of 50.0 mg/L, using inlet ozone concentrations between 1.9 and 58.5 g/m3 under controlled conditions. CBZ degradation followed apparent pseudo-first-order kinetics under the studied conditions, with the corresponding apparent rate constant increasing linearly with the inlet ozone concentration. At ozone concentrations ≥ 15.7 g/m3, rapid CBZ removal was observed, together with high dissolved ozone levels, accelerated loss of aromaticity, and transient formation of colored oxidation intermediates, which were subsequently degraded. In contrast, low ozone concentrations led to ozone-limited kinetics and slower aromatic breakdown. The pH evolution revealed two distinct kinetic regimes, transitioning from oxidant-limited to reaction-controlled behaviour and stabilizing at pH 4.3. These findings may provide guidelines for optimizing ozone-based treatment processes. The insights gained may be applied to the design, scale-up, and operation of advanced and hybrid oxidation systems.