Formation of Hydroxyl Radicals by Collapsing Ozone Microbubbles under Strongly Acidic Conditions

Abstract

Hydroxyl radicals are strong oxidants in aqueous solution, reacting rapidly with a wide range of dissolved compounds. In contrast, ozone is a highly selective oxidant. Understanding the process by which ozone is transformed into hydroxyl radicals is important in the treatment of wastewater and drinking water. We use electron spin-resonance spectroscopy to demonstrate that when microbubbles of ozone in strongly acidic aqueous solution collapse, the ozone progressively decomposes and large quantities of hydroxyl radicals are generated. Moreover, the degradation of polyvinyl alcohol, which is ozone resistant, was also observed during the collapse of the microbubbles. These findings indicate that ozone microbubbles are potentially useful in future water-treatment applications.

Removal of residual pesticides in vegetables using ozone microbubbles

“…Thus, in lettuce, both the treatments of the decompression type and the gas-water circulation type removed residual FT effectively, and the decompression type was more effective than the gas-water circulation type. The dissolved O3 in the solutions of OMB treatments generates hydroxyl radicals that are highly effective at decomposing organic molecules like the residual FT (Sumikura et al, 2007;Takahashi et al, 2007b), and hydroxyl radicals are generated by the collapse of OMB in solutions (Chu et al, 2008a). The decompression type would have generated a high enough concentration of dissolved O3 to produce a large amount of hydroxyl radicals.…”

“…Microbubbles (MB) are less than 50 μm in diameter and have special properties such as generation of free radicals, self-pressurization and negative charge, and their use in the field of food science and agriculture is attracting attention (Sumikura et al, 2007;Takahashi et al, 2007b). Millibubbles generated by using an air pump are 2-3 mm in diameter, rapidly rise in water and burst at the water surface.…”

Microbubble enhanced ozonation process for advanced treatment of wastewater produced in acrylic fiber manufacturing industry

“…The pH in aqueous solutions also influences the zeta potential of microbubbles. The results of previous researchers [11,27] revealed that zeta potential of microbubbles of ozone is negative over a wide range of pH conditions [32]. In general, the bubbles' zeta potentials are positive in the highly acidic solutions.…”

Cu(II)-catalyzed THM formation during water chlorination and monochloramination: A comparison study

“…3, without Cu(II), no ESR signal was detected in monochloramination of HA (Insert a). Right after the addition of Cu(II), a strong ESR signal of • OH [21] appeared (Insert c). The • OH signal was also detected in the catalytic chlorination (Insert b), exhibiting a comparatively weaker intensity, however.…”