Study On Oxidative Degradation Of Sulfanilamide By Peracetic Acid And Activated Peracetic Acid

Various types of antibiotics have played an important role in the treatment of rare diseases.However,the extensive use of the antibiotics has resulted in environmental pollution problems of serious concern.Due to their bioaccumulation and environmental persistence,the antibiotics have been found in rivers,lakes,seawater,and even in food.The increase in drug resistance caused by sulfonamide antibiotics and the possible emergence of superbugs also have emerged as an issue that cannot be ignored.Therefore,it is of great significance to develop an efficient method to remove sulfonamide antibiotics.In this thesis,peracetic acid（PAA）,a common municipal sewage disinfectant,was used for the direct oxidation degradation of sulfamethoxazole（SMX）.Moreover,the effect of benzoquinone（BQ）as a constituent humic acids（HAs）commonly existing in practical natural waters on oxidation of sulfonamide antibiotics by PAA was also checked.The main contents were as follows.（1）Direct oxidation of SMX by PAA and its reaction mechanism:The oxidant PAA was first prepared by using hydrogen peroxide and acetic acid,and then the direct oxidation of SMX by PAA was investigated.It was found that a complete oxidation of SMX by PAA can be achieved within 240 min at initial p H value of 7when the concentrations of PAA and SMX were 10 m M and 20μM,respectively.The degradation rate of SMX by PAA was 0018 min^-1,360 times that by hydrogen peroxide.Quenching experiment by methanol indicates that SMX oxidation was mainly ascribed to PAA oxidation effect.Thus,SMX oxidation rate was linearly fastened with the increase of PAA concentrations.In the wide p H range of 3-11,p H 7was most favorable to SMX oxidation since SMX is in the form of anion（SMX^-）while PAA exists in the form of molecule.Effect of common anions on SMX degradation was then assessed.It was found that Br^-promoted SMX oxidation,while Cl^-and HA depressed SMX oxidation.It is because Br^-can react with PAA to produce HBr O with higher oxidation capacity,while Cl^-and HA consumed PAA.PAA can also efficiently oxidize other sulfonamide antibiotics.Based on the liquid chromatography-mass spectrometry（LC-MS）results,possible reaction pathways of SMX oxidation by PAA were proposed.（2）Process and mechanism study of BQ promoted PAA oxidation of SMX:BQ is a constituent of HAs,therefore,effect of BQ on oxidation process and efficiency of SMX by PAA was investigated.It was found that BQ remarkably promoted SMX oxidation by PAA at the basic p H values.When concentrations of SMX,PAA and BQ were 20μM,10 m M and 1 m M,36%degradation of SMX by PAA alone was obtained in 90 min,while SMX can be completely degraded in 90 min in the BQ/PAA system.The degradation rate of SMX was increased from 0.04 min^-1for the BQ/PAA system to 0.005 min^-1for PAA alone.The enhancement effect of BQ originates from the formed semiquinone radicals（SQ·）from oxidation of BQ under the basic p H conditions.SQ·can donate electrons to PPA,inducing its activation to generate organic radicals（e.g.,CH₃COOO·,CH₃COO·）and realizing enhanced oxidation of SMX.Effect of main reaction conditions on SMX oxidation was further investigated.It was demonstrated that increasing PAA or BQ concentrations can fasten SMX degradation.In the wide initial p H range of 5-11,the best degradation of SMX was achieved in the BQ/PAA system at initial p H 9,and too high or too low p H values did not facilitate SMX oxidation.HAs and inorganic anions exhibited negligible effect on SMX degradation in the BQ/PAA system,indicating that the BQ/PAA system has a strong anti-interference capability to these compounds,and shows good potential in treatment and remediation of natural waters.LC-MS analysis was conducted to identify oxidation products of SMX in the BQ/PAA system and possible degradation pathways for SMX oxidation were proposed accordingly.The main reactive sites of SMX for oxidation by organic radicals in the BQ/PAA system are amino groups and N-S bond in SMX molecules.