Molecular Ozonation of Alkylphenol Ethoxylates in Aqueous Systems

Nonylphenol ethoxylates (NPEOs) and octylphenol ethoxylates (OPEOs) are common wastewater contaminants. In this study the oxidation of NPEOs and OPEOs by molecular ozone was evaluated in five aqueous matrices including ultrapure water, tap water, wastewater influent, wastewater effluent, and hospital influent. Ozonation followed second order reaction kinetics, and the rate constants for OPEO and NPEO oxidation were determined to be 1.3 x102 and 3.6 x 102 M-1s-1, respectively. Reaction kinetics were not affected by pH in the acidic range or by the ethoxylate chain length. However, reaction kinetic constants were negatively correlated to the dissolved organic matter content of the matrix. During the course of the reaction, hydroxylated alkylphenol ethoxylates metabolite formation was observed. The slow reaction rates and observation of structurally similar metabolites suggest that molecular ozone in itself would not be a suitable treatment process for removing NPEOs and OPEOs from contaminated water.