Study On Degradation Of Antibiotic Sulfadimethoxine In Water By UV/PS (Persulfate) Process

Antibiotics are widely used in various fields to treat human and animal infectious diseases and promote the growth of animals and plants.According to official statistics,its consumption increased by 65%between 2000 and2015.Among them,sulfamethazine（SDM）,a typical sulfonamide antibiotic,is widely used in animal husbandry.Researchers have detected it in many lakes,surface water and drinking water.The continuous enrichment of residual antibiotics in water will affect the balance of ecosystem and human health,and seriously cause disability,teratogenesis and mutation.However,traditional wastewater treatment processes can not effectively treat antibiotic wastewater,and advanced oxidation processes（AOPs）came into being.In recent years,AOPs technology based on UV activated different oxidants has attracted people’s attention.Among them,UV/persulfate（PS）process is used to degrade antibiotics because of its high redox potential of sulfate radical（SO₄^-·）,selectivity and no secondary pollution.This study takes SDM as the experimental object,and the main research contents are as follows:（1）In terms of molecular structure characteristics,HOMO/LUMO orbitals,average local ionization energy（ALIE）,Fukui function and spectrum of SDM molecular structure were analyzed based on density functional theory.The results are as follows:the HOMO/LUMO orbital data shows that N8,C10,C14,C12,C15 and C16 are the most likely active sites to be attacked by free radicals;ALIE data shows that Cl4 and Cl0 are most likely to react,and H29,H27 and H28 are also more likely to participate in the reaction;Fukui function data shows that N8,C10,C15 and C16 are the most vulnerable to electrophilic attack,and H28,H29,H33,C13 and C19 are the most vulnerable to nucleophilic attack.（2）In terms of the kinetics and influencing factors of UV/PS process degradation of SDM,the effects of PS concentration,UV light intensity,solution p H,background anion and real water on the degradation process were investigated,the response surface optimization experiment was carried out,the optimal reaction conditions were obtained and verified,and the electrical energy efficiency in the degradation process was evaluated.The results are as follows:UV/PS process can promote the degradation of SDM,and the reaction rate constant increases with the increase of UV light intensity and PS concentration;acidic conditions are conducive to the degradation of SDM;HCO₃^-、Cl^-,NO₃^-,SO₄^2-,and CO₃^2-can promote the degradation of SDM;compared with pure water,the removal rate of SDM in actual water is significantly reduced,and the removal rate under the best reaction conditions can reach 99.9%;the change of electric energy consumed by the reaction is negatively correlated with the change of UV light intensity and PS concentration.（3）In terms of the mechanism and risk assessment of UV/PS process degradation of SDM,the intermediate products generated in the degradation process were identified and their degradation paths were predicted based on ultra-high resolution liquid chromatography tandem mass spectrometry;the fragmentation mechanism was deduced by mass frontier software;carry out the acute toxicity experiment of luminescent bacteria,analyze the toxicity changes in the whole degradation process,and evaluate the ecological risk in the reaction process;molecular docking technique was used to investigate and clarify the mechanism of toxic effect.The results are as follows:eight intermediates were identified by ultra-high resolution liquid chromatography tandem mass spectrometry;amino oxidation,hydroxylation and bond breaking reactions occurred in the degradation process,and the reaction sites were in good agreement with the results of quantitative calculation;the toxicity data of SDM produced in the process of acute degradation showed that the toxicity of SDM was higher than that of SDM produced in the process of acute degradation;molecular docking results showed that SDM,Pr235（the least toxic intermediate）,and Pr356（the most toxic intermediate）were linked with luciferase of vibrio harveyi,vibrio fischeri,and bacillus cereus luciferase by hydrogen bonding,carbon-hydrogen bonding,Pi-Sigma bonding,Pi-Alkyl bonding,Pi-sulfur bonding,Pi-Pi T-shaped and van der Waals.