Photo-oxidation Degradation Processes And Mechanism Of Phthalic Acid Esters In Water

Phthalic acid esters(PAEs)are the most commnonly used plasticizer.Half of PAEs are environmental hormones,which have endocrine disruption character.The common used phthalates(dimethyl-,diethyl-,di-n-butyl-,di-n-octyl,butylbenzyl- and bis(2-ethylhexyl)-phthalates esters)have been included on the list of priority pollutants of the US Enviromental Protection Agency(EPA).The removal performances of PAEs(DMP,DEP,DBP and DEHP)in water were analyzed, by using the UV/H₂O₂/O3 combination processes.With the initial concentrations lmg/L,the removal efficiencies of PAEs reached more than 60%under the condition that the intensity of radiation and the dosage of H₂O₂ and O₃ were 200w,60mg/L and 3g/h during 15min.When the reaction time last to 60min,their removal efficiencies all reached more than 98%.The permanganate index just decreased from 67.7mg/L to 61.1mg/L during 60min,and it decreased to 14.4mg/L after 60h.In(C₀/C_t)and t of the degradation of PAEs follow the stair kinetic equations by using UV/H₂O₂/O₃ combination processes.The slopes of those lines were degradation rates.It was concluded that the halflife of the PAEs were DMP:7.571min, DEP:3.600min,DBP:4.470min,DEHP:9.664min,which were degraded by the UV/H₂O₂/O₃ combination processes.Four of the PAEs were determined in the representative water samples in JiangSu province in the fourth quarter of 2007,and the concentrations were from undetected to 15μg/L. For the real water samples,it has a good performance to remove PAEs in water by the UV/H₂O₂/O₃ combination processes.All of the PAEs' concentrations in surface water were under the limits of detection after 45min.During 180min,the permanganate index of the real water decreased from 4.47mg/L to 0.9412mg/L.The changes and reactions of DBP which is the most common and the highest concentration level in the real samples treated by the UV/H₂O₂/O₃ combination processes were studied.It was found that the intermediate products were monobutyl phthalate,dipropyl phthalate,DEP and methyl benzoate and the final product was benzoic acid.So the degradation mechanism and the possible degradation path of DBP were concluded,using the UV/H₂O₂/O₃ combination processes.The decrease of the permanganate index and the pH value were studied to prove the conclusion about the degradation mechanism and reaction course of DBP.The concentration level of benzoic acid in the real water samples was discussed when the degradation ended to evaluate whether the technology is safe or not.