Enhanced oxidation of aromatic hydrocarbons by ozone micro-nano bubble water: Mechanism and influencing factors

Aromatic hydrocarbons are common contaminants in groundwater, which could threat human health through multiple ways and have low degradation rates. Micro-nano bubble ozonation has been developed as a novel technology to oxidize organic contaminants effectively. Since most technologies such as dissolved air flotation (DAF) could only produce ozone micro-nano bubble water (OMBW) instead of independent ozone micro-nano bubbles, the comparison between OMBW and ozonated water (OW) had more significant implications. This study investigated the oxidation rate of four aromatic hydrocarbons (AHs) including toluene, ethylbenzene, o-xylene and p-xylene by both OW and OMBW at the same dissolved ozone concentration through a series of batch experiments. Results showed that the oxidation rate of AHs by OMBW was 13.6–22.6% higher than that by OW when solution pH was 8, which was mainly caused by the promoted contact between AHs and OH·at the micro-nano bubble interface. This conclusion was also validated by the faster increase of reaction rate between OH·and AHs for OMBW when solution pH increased from 5 to 9, leading to the increase of OH·utilization rate in alkaline environment. The inhibition effect by anions (Cl-, SO42- and HCO3-) as well as dissolved organic matter, and the promotion effect by Mg2+ were both magnified in OMBW, which was also caused by the interfacial effect of micro-nano bubble. This study was critical to our understanding of the removal behavior of organic contaminants by OMBW, and it would also guide the design of more efficient oxidation technologies based on micro-nano bubbles.