Research on the enhanced treatment of organic matter in drinking water plant based on micro-nano bubble ozone aeration

To improve the organic matter removal efficiency of important process stages such as raw water coagulation and pre/post ozone treatment in water plants, a comparative study was conducted on the ozone mass transfer efficiency under two aeration modes, i.e., micro-nano bubble (MNBs) aeration and ordinary aeration disc aeration. A small-scale experiment was conducted to investigate the impact of MNBs on the coagulation effect of raw water in water plants and study the removal efficiency of organic matter and algae in the pre and post-ozone treatment process stages under two aeration modes. The results showed that the number of nanobubbles produced by the microbubble generator in this study was 1.2×10⁶ mL⁻¹. Therefore, MNBs ozone (MNBs-O₃) had a longer residence time in water, and the utilization rate of MNBs-O₃ gradually increased within 20 minutes, while the ordinary aeration tray showed a trend of first increasing and then rapidly decreasing. When 12.5% of MNBs water was added to the raw water, the adsorption of hydrophobic organic compounds and the generation of hydroxyl radicals by MNBs could significantly improve the coagulation and precipitation effect of the raw water, and the decrease in UV₂₅₄ could reach more than 15%. The longer residence time also made it easier for MNBs-O₃ to convert large organic molecules into small molecules during the pre-ozone process. The molecular weight distribution results showed that 110 kDa peak disappeared and new peaks appeared in the parts less than 1 Da. The removal efficiency of BOD₅ was about 15% (much lower than 50% of ordinary aeration discs), and there was no significant change in TOC and UV₂₅₄. During the post-ozone process, BOD₅ of MNBs-O₃ group increased by 40%, and TOC increased by 36%, while UV₂₅₄ first increased and then decreased. The above results indicate that MNBs-O₃ can decompose aromatic organic compounds into oxygen-containing chain-like organic compounds during the pre-ozone process, and some large molecule organic compounds can be degraded into small molecules, which is helpful for the treatment of subsequent process stages. While during the post-ozone process, MNBs-O₃ can further improve the treatment efficiency of residual recalcitrant organic compounds in water. In addition, under the conditions of this study, the reduction rate of algae by MNBs-O₃ could reach 25% and MNBs-O₃ treatment did not increase the bromate concentration in water, and its efficiency could be further improved through the air flotation function of MNBs in the future. Although replacing ordinary aeration discs with MNBs increases electricity consumption by about 30%, MNBs significantly shorten the intake time and reduce O₃ usage. In summary, this study establishes a theoretical basis for the application of MNBs in raw water coagulation and pre/post-ozone treatment processes.