Unveiling the effects of reactor configurations on the performance of lignin removal in the ozone micro-nano-bubble system

Integrating the micro-nano-bubble (MNB) technology into the ozone (O3) system has been gaining popularity for endowing the ozonation process with prolonged bubble residence time and increased mass transfer rate. This paper reports the lignin removal performance of the O3 MNB system with different configurations in the secondary outlet and the baffle positions. The Eulerian-Eulerian Computational Fluid Dynamics-Population Balance Model (CFD-PBM) was employed to simulate the hydrodynamic conditions and mass transfer in the above-mentioned systems. The experimental data revealed that the MNB aeration led to high saturated concentrations of dissolved O3 (i.e., 9.24 mg/L) and dissolved oxygen (i.e., 28.73–32.84 mg/L), together with limited gaseous O3 emitted in the exhaust stream (i.e., 194.43 mg). Moreover, the efficiencies of the O3 MNB system to generate hydroxyl radicals and mineralize contaminants were 5.99 and 2.23 times higher than those in conventional macrobubble (MB) aeration, respectively. CFD analysis revealed that the system configuration influenced the distribution of MNB and the mass transfer process during pollutant removal. To verify the CFD results, the superior performances in lignin degradation (i.e., 85.46 %) and chemical oxygen demand (COD) removal (i.e., 84.35 %) were observed for the O3 MNB system after optimizing the secondary outlet and baffle configuration. This study highlights the high efficiency of the O3 MNB system in wastewater treatment and the feasibility of optimizing reactor design for large-scale use.