Dissolution enhancement of reactive chemical species by plasma-activated microbubbles jet in water

Plasma activated water (PAW) has emerged as a viable technique for sterilization process since it contains some long-lived reactive oxygen and nitrogen species along with some very short-lived but strong oxidation agents such as hydroxyl radical (OH^*) and superoxide anion (O₂ ⁻). However, the concentrations of the reactive species such as nitrite, nitrate, and ozone are often insufficient in water for sterilization, or only a small amount of PAW can be generated. In this study, we developed a state-of-the-art approach by combining microbubbles (MBs) and plasma technology in a water recirculation system to enhance the dissolution of reactive species in a large amount of water. The investigations included plasma absorbing power measurement, visualization of plasma-activated microbubbles (PAMBs) generation, bubble size distribution, and the concentration measurements of various reactive species in water, after the air plasma jet and the PAMBs jet treatments, respectively. The results revealed that the plasma absorbing power efficiency could reach up to 71.7% for both plasma jet and PAMBs jet cases, respectively. For the PAMBs jet, the mean equivalent diameter of the bubble was estimated to be 290 μm. The results of the concentrations of chemical species such as nitrite and ozone in PAMBs water could be increased up to twice as high as compared to PAW using the proposed device. Moreover, the concentration of nitrate in PAMBs water was found to be nearly three times greater than that in PAW. Thus, we found that employing the PAMBs jet can significantly increase the concentrations of chemical species in water, which could considerably widen the application. (paper)