Efficiency of ozone micro nano bubbles in treating concentrated brine in zero discharge process of coking wastewater

In the Zero Liquid Discharge (ZLD) process of coking wastewater, mechanical vapor recompression (MVR) evaporation crystallization is employed to treat membrane-concentrated liquor, ultimately yielding highly saline concentrated wastewater, which is challenging to treat using conventional oxidation methods. Ozone micro nano bubble technology can enhance ozone mass transfer efficiency and augment its oxidation capability, making it a promising method for treating MVR-concentrated discharge. To verify the feasibility of engineering applications of this technology, this study focused on MVR-concentrated discharge and compared the ozone mass transfer rate and organic degradation efficiency between ozone micro nano bubbles and conventional macrobubbles. It analyzed the impact of salinity and organic concentration on the treatment efficiency of both ozone oxidation processes from technical and economic perspectives, thereby delineating the applicable scope of ozone micro nano bubble technology for high-salinity wastewater treatment. The results indicated that as the salinity increased from 0.1 mol/L to 1 mol/L, the ozone mass transfer coefficients for ozone micro nano bubbles and conventional macrobubbles increased by 0.13 and 0.09 times, respectively, with the ozone self-decomposition rate rising by 2.10 and 1.38 times, respectively. When treating high-salinity and high-organic wastewater (TOC 57.2-587.6 mg/L, conductivity 3.47-28.6 mS/cm), ozone micro nano bubble technology could enhance TOC removal rates by 0.50 to 3.76 times compared to conventional macrobubble technology, while reducing energy consumption per ton of water by up to 71%. When treating ultra-high salinity and ultra-high organic wastewater (TOC 5 626 mg/L, conductivity 164.3 mS/cm), the removal efficiency of micro nano bubbles tended to align with that of conventional macrobubbles, albeit with higher energy consumption per ton of water. The salinity and organic concentration of high-salinity wastewater significantly affect the treatment efficiency of ozone micro nano bubbles, and the appropriate ozone aeration method should be selected based on the wastewater characteristics in engineering applications