Removal Characteristics Of Typical Endocrine Disrupting Chemicals By Ozonation

The reclamation of secondary effluent is one of the promising methods to solvewater shortage in China. However, endocrine disrupting chemicals （EDCs） have beenfrequently detected in the secondary effluent, posing potential threat to the safety ofits reuse. Ozonation has been reported as a powerful oxidation technology toeliminate EDCs. However, the research on EDCs ozonation in the secondary effluentis limited. Therefore, in this study, ozonation technology was used as a high efficienttechnology to remove EDCs in the secondary effluent. The objectives are toinvestigate the influence of various factors on EDCs ozonation efficiency, and toestablish the ozonation kinetics model in pure water and synthetic secondary effluent.In addition, the ozonation mechanism of EDCs is primarily discussed.The competitive ozonation kinetics experiments of phenol and five typical EDCs（E1, E2, EE2, E3and BPA） at different pH in pure water were conducted. Theexponential growth relationship between Rctand pH was revealed and the predictionmodels for ozonation kinetics of phenol and five typical EDCs in pure water wereestablished.By orthogonal experiments, it was found that the initial ozone and naturalorganic matter concentration significantly affected EE2degradation efficiency in thesynthetic secondary effluent. EE2degradation efficiency was found to be higher in thelower pH in the synthetic secondary effluent. The effects of various kinds of effluentorganic matters （EfOM） on the dissolved ozone （DO3） residual decay kinetics, OHgeneration and EDCs degradation efficiency were tested. The results showed that theEfOM that influenced DO3residual decay were listed in descending order of sodiumhumate, humic acid, NOM, bovine serum albumin, chicken serum albumin III,chicken serum albumin II, dextran, and sodium alginate. The H/C composition,UV254, UV258and UV280, Ex/Em=240/396and Ex/Em=345/436of EfOM werefound to be significantly correlated with DO3residual decay parameters. The lowerH/C value, higher UV254, UV258and UV280, and higher Ex/Em=240/396andEx/Em=345/436led to faster DO3residual decay. The functional group of o-aryl andcarbonyl in EfOM played an important role in DO3residual decay. The more o-aryland less carbonyl led to faster DO₃residual decay. The EfOM that influenced EDCsdegradation efficiency were listed in descending order of humus-like organic matters,protein-like organic matters, and polysaccharide-like organic matters. For thesynthetic secondary effluent in this study, when DO₃:TOC arrived at≥1.2or DO₃CT arrived at>2.5mg min L^-1,1μM five typical EDCs could be almost completelydegraded. In addition, the removal of UV280and FL1（Ex/Em=240/396） could beused as conventional surrogate parameters for assessing the removal of EDCs in thesynthetic secondary effluent during ozonation process. When UV280removal arrivedat>18%or FL1removal arrived at>40%,1μM five typical EDCs could be almostcompletely degraded.The results of quantum chemical calculation indicated that the phenolic hydroxylgroup of EDCs exerted great influence on the reaction between O₃, OH and EDCs.The phenolic hydroxyl group would be easily attacked by ozone molecule due to itshigh electron density. The electron of p-C atom to phenolic hydroxyl group would beeasily extracted by OH, producing unstable radicals in the structure of benzene ring.The o-atoms and m-C atoms to phenolic hydroxyl group would be easily attacked byaddition of OH, producing the intermediate products with the structure ofbenzenediol or pyrogallol and their transformation products （benzoquinone）.