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 UV 254 /H 2 0 2 treatment. Second-order rate constants for reactions of the parabens with ozone and (OH)-O-center dot were k(O3) = 10(7) - 10(8) M-1 s(-1) and k(center dot OH) = (2.3 - 4.3)x 10(9) M-1 s(-1) at pH 7. Species-specific k os 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(UV) = (2.4 - 7.2)x 10(-4) cm(2) 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 gO(3)/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.