Enhanced flupyradifurone removal by nanobubble ozonation: Extra ozone activation beyond mass transfer compresses risk-relevant windows

Nanobubble ozonation (NB-O 3 ) is often assumed to enhance pollutant abatement mainly by improving ozone mass transfer, but its ability to provide additional oxidation benefits under comparable ozone exposure for representative pesticides is unclear. We compared conventional bubble ozonation (CB-O 3 ) with NB-O 3 for flupyradifurone (FPF) removal performance, examining whether the superiority of the latter involves additional ozone activation beyond enhanced mass transfer. Upon switching from CB-O 3 to NB-O 3 , the apparent first-order rate constant for FPF removal and dissolved organic carbon removal efficiency at 30 min increased from 0.083 to 0.112 min −1 and from 17.6% to 48.5%, respectively. Under matched bulk ozone exposure, NB-O 3 exhibited ·OH/ozone exposure ( R ct ) 41.2% higher than that observed for the paired conventional bubbling control. DMPO-·OH and TEMP- 1 O 2 signals were 39.3% and 21.1% higher, respectively. This evidence suggests an additional activation gain beyond mass transfer. Compared with CB-O 3 , NB-O 3 reduced the exposure windows of the key transformation products TP1, TP2, and TP6 by 57.9%, 39.0%, and 26.9%, respectively, shortening the cumulative window of intermediates retaining the pharmacophore/chloropyridinyl fragment by 43.1%. After 30 min, the luminescent-bacteria inhibition rate and auxiliary normalized composite risk index decreased to 18.4% and 0.53, respectively. The total disinfection byproduct formation potential and ΣN-DBP formation potential after chlorination were 23.3% and 32.0% lower than those under CB-O 3 . The advantage persisted in buffered matrices and real waters. NB-O 3 improved FPF control through better ozone transfer, additional activation, and shortened risk-relevant intermediate residence.