Solubilization and stabilization for prolonged reactivity of ozone using micro-nano bubbles and ozone-saturated solvent: A promising enhancement for ozonation

The enhanced ozonation treatment by a combination of micro-nano bubbles (MNBs) and ozone-saturated solvent (e.g. acetic acid (HAc)) was investigated. The solubility, decomposition rate of ozone, and reactive oxygen species (ROSs) in various concentrations of HAc with/without MNBs were examined, and these synergetic effects were verified by the enhanced removal of p-chlorophenol (4-CP). The results showed that MNBs promoted the solubility and mass transfer coefficient (K(L)a) of ozone in both deionized (DI) water and HAc solution by 2.03-2.26 and 2.30-3.68 times respectively compared with normal millibubbles. Addition of a certain amount (0.5-5%) of HAc can further benefit the ozonation process. The ozone solubility was about four times larger in 5% HAc solution compared with that in DI water (0%), while the former K(L)a was 3.91-fold higher. The average half-lives of ozone were prolonged by 1.39-3.52 times in 0.5-5% HAc solutions to water alone. This was attributed to the inhibited chain reaction by scavenging the hydroxyl radical ((OH)-O-center dot) in the presence of HAc and thus retarded (OH)-O-center dot-catalyzed ozonolysis. The detection of ROSs showed that the concentrations of hydrogen peroxide (H2O2) and (OH)-O-center dot were up to 39.53 +/- 4.10 and 70.17 +/- 3.09 mu g/L in the hybrid system. The ROSs led to that 48.15-77.55% of 4-CP were removed by ozonation with MNBs in 30 min, and 9.50-29.40 percent improvements were achieved in the HAc solutions than in the DI water. These results indicate that the combination of ozone with MNBs and HAc could enhance the removal of 4-CP effectively. This study illustrated the solubilization and stabilization effect for prolonged reactivity of ozone using MNBs and ozone-saturated solvent together.