Reaction kinetics and degradation efficiency of halogenated methylparabens during ozonation and UV/H2O2 treatment of drinking water and wastewater effluent

Abstract

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 UV254/H2O2 treatment. Second-order rate constants for reactions of the parabens with ozone and •OH were kO3 = 107 – 108 M−1 s−1 and k•OH = (2.3 – 4.3)× 109 M−1 s−1 at pH 7. Species-specific kO3 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 [kUV = (2.4 − 7.2)× 10−4 cm2 mJ−1] 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 gO3/gDOC for > 97% degradation. During UV/H2O2 treatment with 10 mg L−1 H2O2, the degradation levels were > 90% at a UV fluence of 2000 mJ cm−2, 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/H2O2 were effective in controlling parabens and their halogenated products during advanced water treatment.