The Mechanism Of High Salinity Wastewater Treatment By A New Advanced Oxidation Technology Based On Ce(?)/Ce(?) Cycling

Traditional biological and physical methods have great disadvantages in dealing with saline wastewater.Advanced oxidation processes(AOPs)as new technologies for the pollutants treatment are widely used in sewage treatment.Howerver,it always produce a variety of toxic and even carcinogenic adsorbable organic halogen(AOX),resulting in secondary pollution.The Ce(?) /Ce(?)-based advanced oxidation technology has great potential,however,there are no related studies about the effects of salinity on cerium-induced degradation of organic pollutants,and the mechanism of Ce(?) for saline wastewater treatment is still unclear.Therefore,investigations on the mechanism of Ce(?) /Ce(?)degradation of saline wastewater is meaningful.In this thesis,an azo dye-Acid Orange 7(AO7)and 2,4,6-trichlorophenol(TCP)were selected as the model nonbiodegradable substrate in wastewater.The kinetics,reaction mechanism and degradation products for Ce(?) ,Ce(?) /Cl-,UV/Ce(?) ,UV/Ce(?) /Cl-,Ce(?)/UV and Ce(?)/UV/Cl-systems were studied.The effects of pollutant concentration,pH value and chloride ion concentration were also investigated.(1)Degradation of AO7 by Ce(?) systemCe(?) has strong oxidation capacity,and it can directly oxidize pollutants under acidic conditions.The decolorization rate of AO7 was found to be positively correlated with Ce(?) concentration,but chloride ion inhibited the AO7 degradation rate.In UV/Ce(?) system,the decolorization rate of AO7 was 45% within 30 min,but in UV/Ce(?) /Cl-system only about 80% AO7 was removed within 50 min.Obviously,the AO7 decolorization rate decreased with an increase in chloride ion concentration from 0 to 300 mmol/L.In the present study,the decolorization rate of acid orange 7(AO7)in four cerium(?) system process were investigated as a function of a wide range of salinity and pH.Relatively low pH was favorable for Ce(?) catalytic degradation,and the decoloration rate decreased rapidly along with increasing pH.Fluorescent probe technology suggested hydroxyl radicals were generated in UV/Ce(?) process,but not in UV/Ce(?) /Cl-system.More importantly,no adsorbable organic halogen(AOX)were generated with the increasing content of chloride ion present in the solution.This phenomenon can be explained by Ce(?) and Cl-will form an unstable complexes: H2 Ce Cl6.(2)Degradation of TCP by Ce(?) systemIt is found that there were differences between degradations of TCP and AO7 with Ce(?) -related systems.In the dark,Ce(?) can effectively degrade TCP,but its degradation would be inhibited by chloride.However,under UV irradiation,the degradation rate of TCP had a different trend in UV/Ce(?) /Cl-system: chloride ion can promote the TCP degradation.In UV/Ce(?) system nearly about 70% TCP was removed within 150 min,but in UV/Ce(?) /Cl-system,TCP was completely decomposed with the presence of 300 mmol/L chloride.In addition,UV/Ce(?) /Cl-system only produced a small amount of HO?,but HO? is not the active substance of the system.The mineralization rate and AOX removal rate of TCP in the UV/Ce(I V)/Cl-system were significantly less than those in the Ce(?) /UV system.GC-MS data indicated that less low-molecular-weight compounds were detected in UV/Ce(?) /Clthan Ce(?) /UV.It suggested that UV/Ce(I V)/Cl-was only efficient in destructing TCP molecule,but Ce(?) /UV can lead to degradation of TCP and its byproducts.