A study of synergistic oxidation between ozone and chlorine on benzalkonium chloride degradation: Reactive species and degradation pathway

Ozonation and chlorination are widely used for disinfection or micropollutant elimination in water treatment or reclamation fields. It was found in this study that the presence of free chlorine increased the production of reactive species significantly during ozonation of dodecylbenzyldimethylammonium chloride (DDBAC, quaternary ammonium compound). DDBAC hardly underwent degradation by the chlorination process. However, the removal of DDBAC by ozonation after 10 min increased from 22% to 92%, when the dosage of free chlorine increased from 0 to 112 mg/L. pH affected the synergistic effect of ozone/chlorine oxidation of DDBAC. The promotion effect of free chlorine was greater at acidic conditions than that at basic conditions. The radical quenching experiments suggested that various reactive species formed during ozone/chlorine oxidation of DDBAC. The contributions of ozone, reactive species that could or could not be quenched by tBuOH were 8%, 78% and 13%, respectively. In the mixed system of DDBAC and pCBA, the degradation percentage of DDBAC and pCBA after 15 min increased from 31.0% and 13.1% to 53.8% and 28.3% with the presence of chlorine, respectively. Based on the steady-state concentration assumption, the steady-state concentration of center dot OH during ozone/chlorine oxidation of DDBAC was 2.3 times higher than that during the sole ozonation process, being 7.5 x 10(-14) M and 3.3 x 10(-14) M, respectively. Ten oxidation products were identified by HPLC-MS/MS during ozone/chlorine oxidation of DDBAC. Three degradation mechanisms were observed: the hydrogen abstraction of the alkyl chain by hydroxyl radical; the cleavage of the benzyl-nitrogen bond of DDBAC; and the addition of hydroxyl radical on the aromatic ring or the alkyl chain.