Micro-Nanobubble Ozonation Coupled with H2O2 for Enhanced Treatment of Coking Reverse Osmosis Concentrate

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.