Treatment of water contaminated with dimethyl phthalate by Fenton, photo-Fenton and ultraviolet/hydrogen peroxide processes.

摘要

This study showed that the application of hydrogen peroxide (H₂ O₂) alone was not sufficient to oxidize Dimethyl phthalate (DMP) in water. Fenton process was found to be effective in removing DMP from pure water and seemed to follow a pseudo-first order reaction, however, it did not show any removal of DMP when the water was spiked with appreciable amount of methanol. The results indicated that increasing the concentration of Fe2+ caused an increase in the removal of DMP from pure water by Fenton process, while, increasing the initial concentration of H ₂O₂, did not always lead to improving the efficiency of the Fenton process. A high temperature and a pH value of 3 to 4 were found to be best for achieving an efficient removal of DMP from pure water. The study also showed that DMP could be partially degraded by direct photolysis (i.e. UV light only), and that a great enhancement of the removal efficiency was achieved when the action of UV light was combined with the action of Fenton's reagent (i.e. photo-Fenton).; On the other hand, the UV/H₂O₂ process was found to be effective in removing DMP from the pure and methanol-spiked water and the DMP removal seemed to be a pseudo first-order reaction. Similar to Fenton, the high temperature and low pH resulted in enhancing the removal efficiency of DMP by the UV/H₂O₂ process. Lower removal rate of DMP was observed when the initial concentration of DMP (i.e. DMP_i) was increased. It was concluded that an optimum molar ratio between DMP _i, H₂O₂ and Fe2+ must be determined in order to obtain the best removal efficiency. The efficiency of Fenton process dropped down drastically when DMP was spiked into local groundwater rather than pure water. However, the efficiency of UV/H₂O₂ dropped only slightly under the same conditions. Due to its many advantages, UV/H₂O₂ process was selected in this study to be the suitable oxidation process for the removal of DMP from water. The optimum conditions required to reach a considerable treatment efficiency of more than 97% of the 0.1 mM DMP at neutral pH value, were: H₂O₂ of 2.0 mM; UV exposure time of 30.6 minutes; and temperature of 33.6°C.