Advanced oxidation of five contaminants in water by UV/TiO2: Reaction kinetics and byproducts identification

Abstract

The extent and kinetics of degradation of 1,4 dioxane, n-nitrosodimethylamine (NDMA), tris-2-chloroethyl phosphate (TCEP), gemfibrozil, and 17β estradiol in a prepared aqueous matrix by means of UV/TiO2 (ultraviolet light/titanium dioxide) oxidation was evaluated. Degussa P25 TiO2 was employed as a photocatalyst excited by UV light in a 1 L water-jacketed batch photoreactor. The rate of degradation was modeled using a pseudo-first order rate model and the Langmuir-Hinshelwood rate model with a high correlation. Degradation rate constants were found to be maximum at pH 5.0 and 1.5 g L−1 TiO2 dose. For these conditions first order rate constants, values were as follows: 0.29 min−1 for 1,4 dioxane, 0.50 min−1 for NDMA, 0.12 min−1 for TCEP, 0.61 min−1 for gemfibrozil, and 0.53 min−1 for 17β estradiol. While for the Langmuir-Hinshelwood rate model, the following constants were found: 0.11 Lmg−1 and 2.81 mgL−1 min−1 for 1,4 dioxane, 0.12 Lmg−1 and 4.35 mgL−1 min−1 for NDMA, 0.06 Lmg−1 and 1.79 mgL−1 min−1 for TCEP, 0.21 Lmg−1 and 3.27 mgL−1 min−1 for gemfibrozil, and 0.15 Lmg−1 and 3.43 mgL−1 min−1 for 17β estradiol. In addition, specific byproducts of degradation were identified using GC/MS analysis. The results obtained from the kinetics analysis showed that UV/TiO2 oxidation is a promising process for treating trace organic contaminants in water, but further research is needed to better understand how to incorporate these findings into pilot and full-scale designs. The toxicity of oxidation byproducts, and their potential for interacting with other compounds should be considered in the treatment of contaminated waters using the UV/TiO2 oxidation process.