Fenton's Oxidation Kinetics, Pathway, and Toxicity Evaluation of Diethyl Phthalate in Aqueous Solution
A comprehensive study of the chemical oxidation degradation of diethyl phthalate (DEP) was conducted through Fenton processes. Effects of various operating parameters that considerably affect DEP decomposition were investigated, including solution pH, H2O2, Fe2+, and DEP concentration. The removal efficiency of DEP achieved 98% under reaction conditions of pH value of 3.0, concentration of 0.3 mM of Fe2+, and 6.0 mM of H2O2 after 170 min. In general, DEP degradation in Fenton process was found to occur in two stages, with an extremely fast stage and then a slow one, as a result of change of H2O2 and Fe2+ initial concentration. Based on the pseudo-steady-state hypothesis of hydroxyl radical formed by the Fenton reaction, a kinetic model for DEP degradation has been proposed which describes the effect of decomposition byproducts on the oxidation reaction. The experiment results also were in good agreement with Behnajady-Modirshahla-Ghanbery (BMG) kinetic model. During the degradation process, seven degradation intermediates of DEP were detected out by means of GC/MS, including ethyl 2-hydroxybenzoate, ethyl 3-hydroxybenzoate, phthalic anhydride, benzoic acid ethyl ester, malonic acid, oxalic acid, and acetic acid. Probable degradation pathway of DEP by the Fenton reaction was also proposed. Inhibitory effects of DEP and intermediate products were investigated in aqueous solution with Photobacterium phosphoreum. Findings indicated that the solution was not completely detoxified even if DEP completely disappeared, further post-treatment was recommended. All these observations have significant potential applications and require further investigation.