Pharmaceutical degradation by ozone nanobubbles: degradation kinetics and matrix-dependent effects

This study investigated the degradation performance of ozone nanobubbles against five representative pharmaceuticals: ibuprofen (IBU), metronidazole (MTZ), sulfamethoxazole (SMX), naproxen (NPX), and carbamazepine (CBZ) under various operational and water matrix conditions. Results show that molecular structure governed their degradation by ozonation. SMX, NPX, CBZ, and MTZ were completely degraded at a low ozone dose (1.5 mg/L). By contrast, IBU showed greater resistance, requiring 5.5 mg/L, and was therefore selected for further investigation. Evaluation of operational and water-matrix conditions showed that increasing ozone concentration from 1.5 to 5.5 mg/L improved degradation but reduced ozone utilisation efficiency, while IBU degradation was enhanced at neutral pH within the investigated range of pH 3 to 7. Background organic matter from humic acid promoted IBU degradation at low DOC (0.5–1.5 mg/L) but inhibited the degradation at higher DOC (3.5–6 mg/L). In comparison with conventional bubbles, ozone nanobubbles exhibited a 2.8-fold higher ozone mass transfer coefficient (0.17 vs 0.06 min −1 ), maintained a higher attainable saturation concentration of dissolved ozone, and achieved a 1.4-fold greater IBU degradation rate constant at the same dissolved ozone concentration. Under a more complex matrix simulated by humic acid at 3.5 mg/L DOC, ozone nanobubbles maintained the superior IBU and colour degradation compared with conventional bubbles. Findings from this study highlight the benefits of ozone nanobubbles over traditional ozone bubbles and their prospective use in advanced water and wastewater treatment for pharmaceutical abatement.