A Study On Catalytic Characteristics And Mechanism Of Metal Coagulants During Ozonation

Aiming at the enhanced treatment of dissolved wastewater treatment plant effluent organic matter,hybrid ozonation-coagulation（HOC）process was established by combining coagulation and ozonation together.Through the investigation of the removal performance of the HOC process for EfOM（effluent organic matter）and IBP（ibuprofen）,the active sites on the surface of the hydrolysed species for the generation of reactive oxygen species were identified,and the intermediate reactive oxygen species during the HOC process,such as superoxide,were detected to directly elucidate the mechanism of the HOC process.The results would provide theoretical basis for the safety control of reclaimed water.Using AlCl₃·6H₂O,preformed Al₁₃3 and FeCl₃,the HOC removal performance for IBP in ultrapure water and DOC,UV₂₅₄,color in the WWTP（wasterwater treatment plant）effluent were investitaged.The results showed that the metal coagulants can be used as catalysts to promote the decomposition of ozone to produce hydroxyl radicals.Thus,the HOC process can achieve efficient removal of dissolved organic matter in WWTP effluent.Compared with AlCl₃·6H₂O,preformed Al₁₃ and FeCl₃ exhibited higher organic matter removal performance during the HOC process.FeCl₃-HOC process and Al₁₃-HOC process have similar removal performance.The effect of phosphate on the removal performance of the HOC process was investigated to determine the catalytic active sites on the surfaces of the hydrolysed species of the coagulants.The result showed that phosphate can lead to the substitution of hydroxyl groups on the catalyst surface and inhibit the effect of HOC process significantly.This phenomenon revealed that hydroxyl groups on the surface of hydrolysed Al species were the active sites for the generation of reactive oxygen species involving hydroxyl radicals.The result of FTIR further indicated that the surface hydroxyl groups were the active reaction sites for the HOC process.Based on the results of X-ray photoelectron spectroscopy,the hydroxyl groups were the main component of oxygen-containing groups on the surface of metal coagulants.In order to explore the generation and occurrence of typical reactive oxygen species in the HOC process,NBD-Cl and pCBA were used as probes to determine the generation of superoxide radical and hydroxyl radical respectively,and then,the occurrence was also analysed.The results clearly indicated that the content of·O₂^-during HOC process was higher than that of ozonation alone,which revealed that metal coagulants can promote the decomposition of ozone.Additionally,most of the generated·O₂^-in the Al₁₃-HOC was adsorbed on the surface of preformed Al₁₃ at different pH values.However,a considerably lower proportion of adsorbed·O₂^-was observed on the surface of in situ formed Al species from AlCl₃·6H₂O or FeCl₃compared with that on the surface of preformed Al₁₃.The HOC process can generate more hydroxyl radicals than ozonation alone.Thus,it can achieve efficient removal of organic pollutants.Furthermore,low proportions of adsorbed·OH were found on the surfaces of preformed Al₁₃,AlCl₃·6H₂O and FeCl₃ indicating that the·OH oxidation for the removal of organic pollutants occurred primarily in the aqueous phase.