Reaction kinetics and degradation efficiency of halogenated methylparabens during ozonation and UV/HO treatment of drinking water and wastewater effluent.

This study investigated the reaction kinetics and degradation efficiency of methylparaben and its halogenated products (Cl-, Br-, Cl,Cl-, Br,Cl-, and Br,Br-methylparabens) during ozonation and UV/HO treatment. Second-order rate constants for reactions of the parabens with ozone and OH were [Formula: see text] = 10 - 10 M s and [Formula: see text] = (2.3 - 4.3)× 10 M s at pH 7. Species-specific [Formula: see text] values of the protonated and deprotonated parabens were closely related to phenol ring substituent effects via quantitative structure-activity relationships with other substituted phenols. The UV photolysis rate of the parabens [k = (2.4 - 7.2)× 10 cm mJ] depended on the halogenation state of the paraben and solution pH, from which species-specific quantum yields were also determined. In simulated treatments of drinking water and wastewater effluent, the parabens were efficiently eliminated during ozonation, requiring a specific ozone dose of > 0.26 gO/gDOC for > 97% degradation. During UV/HO treatment with 10 mg L HO, the degradation levels were > 90% at a UV fluence of 2000 mJ cm, except for Cl,Cl-methylparaben. Kinetic models based on the obtained reaction kinetic parameters could successfully predict the degradation levels of the parabens. Overall, ozonation and UV/HO were effective in controlling parabens and their halogenated products during advanced water treatment.