Removal Of Di-(2-ethylhexyl) Phthalate From Aqueous Solution By UV/Peroxymonosulfate And Ozone:Influencing Factors And Reaction Pathways

The hazardous potential of phthalate esters ?PAEs?-type plasticizer is becoming an issue of great concern due to the wide application of these compounds in many plastic products. Despite the endocrine disrupting effectsand the environmental occurrences of PAEs derivatives in aquatic systems, little study on their degradation mechanism data is available regarding theireffects. Further more, PAE-typeplasticizers are continuslly released into the water environment, whereas the elimination efficiency was quite limited in wastewater treatment plants. Therefore, to enhance the removal performance of such plasticizer and reduce potential risk to the ecosystem, it is necessary to adopt appropriate tertiary treatment process. This investigation will provide insight into the degradation mechanisms and useful information for assessing thepotentialecologicalriskof PAE-typeplasticizers, and willcontribute to a better understanding of advance oxidation processin aqueous solution to remove PAE-type plasticizers. Concrete workconsists of the following five aspects:?1? Study of factors on DEHP degradation under UV/PMS systemOur study focuses on the effects of the concentration of PMS and DEHP,temperature, pH value, humic acid and some common ions like Fe²⁺, Co²⁺, NO3-and HCO3-, and the results showed their effects: ?In UV/PMS system, the degradation rate increased with the ration of PMS and DEHP increasing,however, when the concentration of DEHP increased from 10 to 100 mg/L, due to the low solubility of DEHP, the degradation rate would be inhibited; ?Heating would increase the degradation rate, and was an important factor; ?The acid condition was more suitable for DEHP degradation; ?Also, the study investigated the effects of Fe²⁺, Co²⁺, NO3+, HCO3+ and HA, the results showed the acceleration of these ions, while HA had aninhibiting effect on DEHP degradation in UV/PMS system.?2? Study of factors on DEHP degradation under ozone systemTo investigate theefficiency of ozone system in degrading DEHP, our studyfocuses on the effects of temperature and pH value, the result showed that in ozone system, heating would accelerate the degradation rate. In addition, at different pH condition, the kapp value was also different, when pH value was 11,indicating the increasing pH would accelerate the degradation rate.?3? Study on degradation mechanism under UV/PMS and ozone systemThe structure identifications of the oxidation products wereperformed based on the analysis of the TIC and the corresponding MS/MS spectra. A total of seven products were detected. In UV/PMS system, DEHP had three transformation pathways involving the hydroxylation of benzene ring, the cleavage of the ester bond and the breaking of the side chain of DEHP. A total of four products were detected in ozone system. In ozone system, DEHP had two transformation pathways involving the cleavage of the ester bond and the breaking of the side chain of DEHP. Both the UV/PMS and the ozone system were based on the attack of free radicals and the word of direct oxidation. In UV/PMS system, HO' would attack the position where the FED2HOMO+FED2LUMO value were highest in DEHP, and would be added into the benzene ring, while in ozone system, it would not happen. In the products in ozone system would be found in UV/PMS system, suggesting HO'- contribute more than SO₄^·-.