Study On The Removal Of Diclofenac By Dielectric Barrier Discharge

In recent years, as a new-type pollutant, Pharmaceutical and Personal Care Products(PPCPs) have attracted more and more attention. PPCPs are a kind of micropollutant which contain pharmaceuticals, cosmetics, food additives and other personal care products and also their metabolites, and they have been detected in the ground water, surface water, drinking water, tap water, sea, sediments and the soils. Most PPCPs are deposited into the sewage as the original form or transformed form and then enter the sewage treatment plant. Although PPCPs enter the water environment at a very low concentration(ng/L～μg/L), but they can affect the water quality and potentially affect the safety of the drinking water's supply, the ecological environment and human health. Diclofenac was selected as the target contaminant, and the removal of the diclofenac by dielectric barrier discharge (DBD) plasma was carried out in this paper. The removal effect, the removal mechanism and the main factors that affect the removal of diclofenac by DBD were studied.Firstly, it was investigated the effect of the change of diclofenac initial concentration, the discharge time, the discharge output power intensity and diclofenac solution's initial pH on the removal efficiency of diclofenac, and then the best reaction conditions were determined. The conditions were:the diclofenac initial concentration was 20 mg/L, the discharge time was 10 min, the discharge output power intensity was 50 W, the diclofenac solution's initial pH was 6.15.Secondly, it was investigated the effect of the additives Fe2+, hydroxyl radical scavenge (Na2CO3) and NO3- on the removal efficiency of diclofenac. The result was that the addition of Fe2+ and NO3- had promoted the removal efficiency of diclofenac, but when the amount of Fe2+ added into the reaction system increased to a certain value the removal efficiency of diclofenac declined, and the best concentration of Fe2+ added into the reaction system was 20 mg/L. The removal efficiency of diclofenac had also increased when NO3- was added, but with the increasing amount of NO3- added into the reaction system the removal efficiency of diclofenac did not change obviously. The removal efficiency of diclofenac declined when the hydroxyl radical scavenge was added into the reaction system, because the hydroxyl radical was captured by Na2CO3 and then the amount of hydroxyl radical that reacted with diclofenac would reduced. Total organic carbon (TOC) declined at first but did not change with the discharge time increased. This was indicated that the macromolecule turned to small molecules during the discharge process, but now only part of the intermediate products had been mineralized into carbon dioxide and water. It needed more reaction time to completely mineralize organic material in the diclofenac sodium solution, and this maybe the reason that TOC remained unchanged.Finally, Liquid chromatography and mass spectrometry (LC-MS) was used to analyze the diclofenac degradation products, at the same time, pH had also been detected during the degradation process. And the volume of H2O2 produced during the discharge process was also detected. There were all four intermediate products and their m/z were 309.9,349.1,127.3 and 109.9 respectively. The trend of the pH during the discharge process was declining, and this was probably some organic acids had been produced during the degradation of diclofenac. With the discharge time increased, the amount of H2O2 produced during the process increased both in the distilled water and diclofenac solution. But the amount of H2O2 produced in the diclofenac solution was less than in the distilled water under the same discharge time.