Theoretical and experimental formation of low chlorinated dibenzo-p-dioxins and dibenzofurans in the Fenton oxidation of chlorophenol solutions

• Published in: Chemosphere (Oxford) 2016-10, Vol.161, p.136-144
• Main Authors: Fernández-Castro, Pablo, San Román, M. Fresnedo, Ortiz, Inmaculada
• Format: Article
• Language: English
• Subjects: 2-Chlorophenol; Benzofurans; Chlorophenols - chemistry; Dibenzo-p-dioxins; Dibenzofurans; Dibenzofurans, Polychlorinated - chemistry; Fenton oxidation; Halogenation; Hydrogen Peroxide - chemistry; Iron - chemistry; Models, Chemical; Oxidation-Reduction; Polychlorinated Dibenzodioxins - chemistry; Reaction mechanism; Solutions; Temperature
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2016.07.011

The formation of chlorinated and non-chlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) has been experimentally investigated after the Fenton oxidation of 2-chlorophenol (2-CP, 15.56 mM) aqueous solutions by assessing the influence of iron concentration (0.09–2.88 mM), hydrogen peroxide dose (40.44–202.20 mM), temperature (20–70 °C) and chloride concentration (0–56.35 mM). The presence of chloride in the medium together with room temperature and substoichiometric Fenton conditions (40.44 mM H2O2) led to an increase in total PCDD/Fs concentration from less than 1 ng L−1 to 2 μg L−1. Results showed a dominance of the dichlorinated species (DCDD/Fs) in the homologue profile of total PCDD/Fs reaching values up to 1.5 μg L−1. Furthermore, the products distribution exhibited a gradual decrease in the homologue concentration as the chlorination degree increased from di-to octachloro-substituted positions. Considering the characteristics of the reaction medium, the experimental results, and the information gathered in bibliography with regard to the generation of active radicals from 2-chlorophenol, a mechanism describing the formation of low chlorinated PCDD/Fs in a Fenton oxidizing aqueous system has been proposed. [Display omitted] •Fenton oxidation reports fast degradation kinetics of aqueous 2-CP solutions.•Complete mineralization of CP is not reached especially under substoichiometric conditions.•The formation of minor byproducts such as PCDD/Fs are observed.•High concentrations of DCDD and DCDF have been detected.•A mechanism for the formation of low chlorinated PCDD/Fs in aqueous oxidation media is proposed.