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

Synergistic effects of ozone (O 3 ) and peroxymonosulfate (PMS, HSO 5 − ) for isothiazolinone biocides degradation was studied. The synergistic ozonation process (O 3 /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 ct, R ) for the O 3 /PMS process was 24.6 times that of ozonation alone. Calculated second-order rate constants for the reactions between isothiazolinone biocides and ( k SO4 -,MIT and k SO4 -,CMIT ) were 8.15 × 10 9 and 4.49 × 10 9  M −1  s −1 , respectively. Relative contributions of O 3 , hydroxyl radical ( OH) and oxidation to MIT and CMIT removal were estimated, which were 15%, 45%, and 40% for O 3 , OH and oxidation to MIT, and 1%, 67%, and 32% for O 3 , OH and oxidation to CMIT at pH 7.0, respectively. Factors influencing the O 3 /PMS process, namely the solution pH, chloride ions (Cl − ), and bicarbonate (HCO 3 − ), were evaluated. Increasing the solution pH markedly accelerated O 3 decay and OH and formation, thus weakening the relative contribution of O 3 oxidation while enhancing that of OH and . Cl − had a negligible effect on MIT and CMIT degradation. Under the dual effect of bicarbonate (HCO 3 − ) 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 3 and O 3 /PMS processes for MIT and CMIT degradation in different water matrices was compared.