Continuous ozonation of pharmaceuticals in hospital wastewater using a coiled flow inverter reactor

The widespread use of pharmaceuticals due to population growth has led to their persistent occurrence in aquatic environments, with hospital wastewater (HWW) representing a particularly concentrated and complex source. Ozonation is an effective advanced oxidation process for pharmaceutical degradation, but its practical application is often limited by high ozone generation cost, low solubility in water, and the need for large, energy-intensive contactors. Process intensification through miniaturized, and compact reactors offer a promising strategy for on-site, targeted treatment of HWW. Here, we developed a novel continuous ozonation system integrating a coiled flow inverter (CFI) reactor and evaluated its performance for removing four representative pharmaceuticals (Ketorolac tromethamine, Sulfathiazole, Tetracycline hydrochloride, and triamterene) from both aqueous solutions and HWW. Reactor hydrodynamics were systematically investigated across liquid flow rates (5-50 mL/min), initial pharmaceutical concentrations (10-50 mg/L) and solution pH (2-12). An optimum flow rate of 10 mL/min was identified, enabling stable degradation within ~10 minutes, half the time required for conventional batch ozonation. Under these optimised conditions, intensified gas-liquid contact facilitated rapid pharmaceutical degradation, consistently achieving >80% removal. The non-linear exponential decay model (R 2 > 0.99) accurately described the degradation kinetics of all pharmaceuticals, with apparent rate constants of 0.86 to 2.00 min⁻¹, capturing rapid initial oxidation followed by stabilisation under continuous CFI-assisted ozonation. Radical-scavenging experiments confirmed hydroxyl-radical-mediated oxidation. When applied to spiked HWW, the system maintained high removal efficiencies (66-98%) despite matrix complexity, demonstrating robustness and practical suitability for real-world wastewater treatment. This study highlights the potential of CFI-based continuous ozonation as an efficient, scalable, and sustainable solution for hospital wastewater treatment.