Ozonation of Non-Ionic Surfactants in Aqueous Solutions

Abstract

The effect of ozone on dilute aqueous solutions of a series of non-ionic surfactants of nonyl phenol ethoxylates, with n=4 to 30 ethylene oxide groups, dinonyl phenol ethoxylate and a polyethylene glycol were investigated. Assuming ozone concentration in solution to remain constant throughout the ozonation, the experiments showed first-order reactions with respect to surfactant concentration, as measured by the Wickbold method, and also with respect to COD & TOC. A linear relationship was established between the first-order reaction rate constants, and between n, the average number of ethylene oxide groups in the ethoxylate chain of the nonyl phenol ethoxylate series. The oxidation mechanism by ozone of non-ionic surfactant molecules is explained as mainly polyethoxylate chains' cleavage into shorter polyethylene glycols and to a smaller extent oxidation of the aromatic ring. High ozone doses do not convert the non-ionic surfactant completely to CO2 and H2O but smaller doses are sufficient to enhance biodegradation.