Catalytic nano-ozonation for the removal of pharmaceutical micropollutants

Ozonation is increasingly implemented for micropollutant removal in wastewater treatment. However, its efficiency is constrained by the high ozone demand imposed by complex effluent matrices with elevated DOC concentrations. Although ozone nanobubbles (NBs) have emerged as a process intensification strategy, systematic comparisons with conventional microbubble (MB) systems under realistic wastewater conditions remain limited. This paper evaluates the effect of ozone-NBs combined with different oxidation processes to enhance micropollutant removal in a real tertiary effluent (DOC: 50 mg/L), a highly demanding wastewater matrix. The effluent was spiked with 15 cytostatic compounds and treated using four oxidation schemes (O 3 , O 3 /UVA, O 3 /H 2 O 2 , and O 3 /UVA/H 2 O 2 ) and three bubble configurations (MBs, NBs, hybrid MB/NB system). NB-assisted ozonation improved removal efficiencies compared with conventional MB-based ozonation while reducing the ozone dose required to achieve 80% removal by one to two orders of magnitude for several compounds. The incorporation of UVA irradiation and H 2 O 2 improved the degradation of ozone-resistant compounds, including cyclophosphamide, ifosfamide, azathioprine, bicalutamide, and prednisone. NB–O 3 /UVA/H 2 O 2 system exhibited the highest performance, achieving an average micropollutant removal of up to 83%. Notably, low ozone doses (0.3 mg O 3 /mg DOC) yielded removal efficiencies above 75%, outperforming conventional MB-based treatments, which typically achieve ~50% removal at higher ozone dosages. These results suggest that NB-assisted ozonation enhances the reduction in the applied ozone dose required to achieve a given removal by alleviating gas–liquid mass-transfer limitations and promoting radical-mediated oxidation. This strategy reduces ozone consumption while improving the removal of persistent micropollutants, supporting the development of quaternary wastewater treatment technologies.