Ozonation kinetics of six dichlorophenol isomers

This paper investigates the kinetics of reactions between dichlorophenol (DCP) isomers and dissolved ozone in solutions of pH varying from 2 to 6 at 5 to 35°C. A DCP can exist as dichlorophenol molecules and dichlorophenoxide anions in the aqueous solution, and both forms are reactive toward ozone. The overall reaction is second order requiring two moles of ozone for conversion of each mole of DCP. The ozonation rate of 2,6-DCP is the fastest and that of 3,4-DCP is the slowest at an identical condition. The Arrhenius equation is applicable to correlate temperature effects; the activation energy ranges from 46.5 to 55.3 kJ/mol. The reaction rate increases very rapidly as the acidity decreases, and the overall rate constant is greater than 1000000 M-1.s-1 in solutions with pH of 5 or larger at 25°C. The results of this study suggest that DCPs can be removed rapidly from wastewaters by ozone treatment.