Mineralization of Poly(vinyl alcohol) by Ozone Microbubbles under a Wide Range of pH Conditions

Poly(vinyl alcohol) (PVA) is a well-known recalcitrant pollutant that threatens ecological systems and human health. In this study, ozone-microbubble treatment was evaluated as a physicochemical method to mineralize PVA in solution for wastewater treatment. Microbubbles are very small bubbles (<50 μm in diameter) and shrink in water because of the rapid dissolution of the interior gas. Ozone microbubbles were generated by a hybrid microbubble generator in PVA solutions with pH conditions of 2, 7, and 10. Ordinary ozone bubbling was also performed as control tests. The change in the total-organic-carbon content was measured to evaluate the efficiency of the system for wastewater treatment. Ordinary ozone bubbling was not able to mineralize aqueous PVA solutions under nonalkaline conditions, and approximately 30% of the total organic carbon remained at pH 2 and 7. Conversely, ozone microbubbles effectively mineralized PVA in aqueous solution to almost 0% in total organic carbon regardless of the pH condition. Effective mineralization of PVA, a recalcitrant organic chemical, demonstrates the potential of ozone-microbubble systems for physicochemical wastewater treatment.