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

Synergistic effects of ozone (O3) and peroxymonosulfate (PMS, HSO5xe213; ) for isothiazolinone biocides degradation was studied. The synergistic ozonation process (O3/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 (Rct,center dot R) for the O3/PMS process was 24.6 times that of ozonation alone. Calculated second-order rate constants for the reactions between isothiazolinone biocides and xfffc; (kSO4 center dot-,MIT and kSO4 center dot-,CMIT) were 8.15 x 109 and 4.49 x 109 Mxe213; 1 sxe213; 1, respectively. Relative contributions of O3, hydroxyl radical (center dot OH) and oxidation to MIT and CMIT removal were estimated, which were 15%, 45%, and 40% for O3, center dot OH and oxidation to MIT, and 1%, 67%, and 32% for O3, center dot OH and xfffc; oxidation to CMIT at pH 7.0, respectively. Factors influencing the O3/PMS process, namely the solution pH, chloride ions (Clxe213; ), and bicarbonate (HCO3xe213; ), were evaluated. Increasing the solution pH markedly accelerated O3 decay and center dot OH and xfffc; formation, thus weakening the relative contribution of O3 oxidation while enhancing that of center dot OH and xfffc; . Clxe213; had a negligible effect on MIT and CMIT degradation. Under the dual effect of bicarbonate (HCO3xe213; ) 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 O3 and O3/PMS processes for MIT and CMIT degradation in different water matrices was compared.

Automated summary

The synergistic effects of ozone and peroxymonosulfate on the degradation of isothiazolinone biocides were studied. The results showed that the synergistic ozonation process significantly improved the degradation efficiency, mainly through the involvement of hydroxyl radicals and oxidation. Solution pH, chloride ions, and bicarbonate were found to influence the process.