Synergistic effects of ozone/peroxymonosulfate for isothiazolinone biocides degradation: Kinetics, synergistic performance and influencing factors.

Synergistic effects of ozone (O) and peroxymonosulfate (PMS, HSO) for isothiazolinone biocides degradation was studied. The synergistic ozonation process (O/PMS) increased the efficiency of methyl-isothiazolinone (MIT) and chloro-methyl-isothiazolinone (CMIT) degradation to 91.0% and 81.8%, respectively, within 90 s at pH 7.0. This is 30.6% and 62.5% higher than the corresponding ozonation efficiency, respectively. Total radical formation value (R) for the O/PMS process was 24.6 times that of ozonation alone. Calculated second-order rate constants for the reactions between isothiazolinone biocides and (k and k) were 8.15 × 10 and 4.49 × 10 M s, respectively. Relative contributions of O, hydroxyl radical (OH) and oxidation to MIT and CMIT removal were estimated, which were 15%, 45%, and 40% for O, OH and oxidation to MIT, and 1%, 67%, and 32% for O, OH and oxidation to CMIT at pH 7.0, respectively. Factors influencing the O/PMS process, namely the solution pH, chloride ions (Cl), and bicarbonate (HCO), were evaluated. Increasing the solution pH markedly accelerated O decay and OH and formation, thus weakening the relative contribution of O oxidation while enhancing that of OH and . Cl had a negligible effect on MIT and CMIT degradation. Under the dual effect of bicarbonate (HCO) as inhibitor and promoter, low concentrations (1-2 mM) of bicarbonate weakly promoted MIT and CMIT degradation, while high concentrations (10-20 mM) induced strong inhibition. Lastly, oxidation performance of O and O/PMS processes for MIT and CMIT degradation in different water matrices was compared.