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

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.