The Study On Degradation Of Phthalate Esters In Environment By Dielectric Barrier Discharge

Recently,the usage of phthalates?PAEs?has increased.Because of the weak van der Waals between the molecules,PAEs are easy to flow out in large quantities,then migrate into environment and cause some risks.Therefore,it is necessary not only to limit the emission of plasticizers from the source,but also to comprehensively treat the existing pollution.However,some traditional plasticizer treatment methods consumed large amounts of reagents or long time-consuming,even caused secondary pollution to the environment.Hence,the search for efficient and clean way is necessary.Discharge plasma technology,as a new technology based on the advanced oxidation principle developed in recent decades,has broad prospects for the removal of refractory organic micro-pollutants,and dielectric barrier discharge has been extensively studied as an effective discharge form.Based on this,this paper proposed to use dielectric barrier discharge plasma to degrade dimethyl phthalate?DMP?in water.A dielectric barrier discharge plasma system was developed,and DMP degradation efficiency and mechanism were explored.To improve DMP removal from water environment,dielectric barrier discharge coupled with sodium percarbonate was developed,and the detailed synergistic effects on DMP removal,active species formation,mineralization,and byproducts generation were discussed.Besides,the removal behavior of DMP in soil was preliminarily discussed.The main conclusions are as follows:1.A dielectric barrier discharge plasma system was developed.Experiments examined the effects of electrical,contaminant properties,etc.The results showed that DMP could be high-efficiently and rapidly eliminated by the dielectric barrier discharge plasma treatment.Under the condition of discharge voltage 16 kV,air flow rate 160 L/h,DMP initial concentration 30 mg/L,and pH value 5.95,DMP removal efficiency reached 79.1%after 60min's treatment.Appropriate increasing in discharge voltage and air flow rate could promote the degradation of DMP,but over-improvement would lead to a decline in energy efficiency.The initial concentration showed the opposite.Alkaline environment was conducive to the degradation of DMP.DMP removal process fitted well with the first-order kinetic model.2.The contribution degree and the action of different active substances on the degradation of DMP were investigated via various scavengers and direct determination.The results showed that DMP removal efficiency decreased to 75.1%,19.4%,1.5%,12.0%when sodium dihydrogen phosphate,p-benzoquinone,isopropanol,and triethylenediamine were added to the system,respectively.The contents of H₂O₂ and O₃ reached the highest values of2.33 mmol/L and 1.15 mg/L at 6 min and 10 min,respectively;and its content increased sharply first and then tended to balance with the treatment time prolonged.The degradation and mineralization of DMP were discussed by the changes of COD and UV-Vis during the reaction.In addition,EEM fluorescence,AFM,FT-IR and chromatography analysis were also used to speculate DMP degradation mechanism.O₃ and·OH attacked C-O,C-C,C=C bonds in DMP molecular structures,which initiated DMP degradation process and then generated some intermediates,such as MMP,PA,organic acids,and finally mineralized into CO₂ and H₂O.3.A dielectric barrier discharge coupled with sodium percarbonate was developed.DMP degradation efficacy and active species formation in such a synergistic system were discussed,and the synergistic mechanism was also analysed by comparing the differences between different systems.DMP degradation efficiency was improved to 98.1%after 60 min's treatment with 20 mg sodium percarbonate addition.Sodium percarbonate alone could hardly degrade DMP.Increased voltage could speed up the removal of DMP,making the degradation more thorough.Researches showed sodium percarbonate not only played an increasing role in H₂O₂ generation,but also provided an alkaline condition,which then benefitted ozone decomposition into OH radicals.Compared with single discharge system,more active species were generated in synergistic system.4.DMP degradation in soil environment was also explored in a dielectric barrier discharge plasma system.The effects of soil moisture,discharge voltage,and soil pH on the removal efficiency of DMP were investigated respectively.The contents of active substances and their effects were also discussed.DMP degradation efficiency reached 56.4%after 60min's treatment.The best treatment conditions were discharge voltage of 18 kV,pH of 7.00and soil moisture of 12%.Properly increasing the soil moisture content would accelerate the degradation of DMP,but high humidity would have adverse effects.