Photo-Ozonation of Multiclass Pharmaceuticals in Model Water: Kinetic Comparison of UV-C, O3 and UV/O3 Under Selected pH Conditions

The removal of four representative pharmaceuticals—sulfamethoxazole (SMX), carbamazepine (CBZ), diclofenac (DCF) and ibuprofen (IBU)—was investigated in a model aqueous solution using UV-C photolysis, ozonation and a hybrid UV/O3 process. UV-C and UV/O3 experiments were conducted at initial pH 3, ~6 and 8, whereas single ozonation was applied at pH ~6 as a near-neutral reference. The processes were compared in terms of removal efficiency, apparent pseudo-first-order kinetics and kinetic enhancement. UV-C photolysis showed pronounced compound selectivity, with efficient removal of DCF and SMX but limited transformation of CBZ and IBU. Ozonation markedly improved the removal of ozone-reactive compounds, particularly CBZ and DCF. Under near-neutral conditions, UV/O3 provided high removal efficiencies for all target compounds after 30 min. Kinetic analysis showed that UV/O3 enhancement was compound-specific: apparent synergy was observed for CBZ and IBU, with SF values of 1.43 and 1.24, respectively, whereas SMX showed a subadditive response. DCF was rapidly removed under UV/O3 but was excluded from the main SF comparison because its concentration approached the lowest calibrated concentration level. These results indicate that UV/O3 is especially useful for poorly UV-susceptible pharmaceuticals.