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

Abstract

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 (KLa) 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 KLa 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) in the presence of HAc and thus retarded OH-catalyzed ozonolysis. The detection of ROSs showed that the concentrations of hydrogen peroxide (H2O2) and OH were up to 39.53 ± 4.10 and 70.17 ± 3.09 μg/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.