Ozonation is widely applied for refractory wastewater treatment, but its practical engineering is often limited by poor ozone mass transfer and low ozone utilization. In this study, micro-nano bubbles (MNBs) technology was employed to improve ozone delivery, and the performance of an O3-MNBs system for treating coking reverse osmosis concentrate (ROC) was systematically compared with the conventional millimeter-sized ozone bubbles (O3-MBs) system. To further promote oxidation, hydrogen peroxide (H2O2) was introduced, forming an O3-MNBs/H2O2 system. Results showed that O3-MNBs (D50 = 36 μm) achieved a volumetric mass transfer coefficient 2.5 times higher than O3-MBs. Under optimized conditions (pH: 7–9, ozone dosage: 10 mg/(L·min), temperature: 20–30 °C), COD removal in the O3-MNBs system reached 34.9 ± 1.2%, nearly twice that of the O3-MBs system, while the O/C ratio decreased by approximately 50% (4.7 ± 0.2), indicating enhanced ozone utilization efficiency. The addition of H2O2 further increased COD removal to 52.1 ± 2.9% and reduced the O/C ratio to 2.9 ± 0.2, reflecting strong synergistic effects. Moreover, the integration of MNBs and H2O2 effectively reduced energy consumption per unit of pollutant removed. Overall, the O3-MNBs-based technology enhances organic pollutant degradation, ozone utilization and energy efficiency, offering a promising strategy for high-salinity refractory wastewater treatment.
Guo et al. (Fri,) studied this question.