Degradation Of Aquatic Sulfadiazine By Persulfate Activated With Zero Valent Iron

Sulfonamides have made great contributions to the prevention and treatment of human and animal diseases in the past.But in recent years,the abuse of sulfonamide antibiotics in humans,farming,and agriculture has attracted more attetion for the detection of sulfonamide drugs in water environment.Sulfonamide antibiotics not only have shown various adverse effects towards human health,but also showed potential harm to the ecological environment by increasing antibiotic resistance of pathogenic bacteria.Therefore,it is necessary to develop efficient and economical technologies to remove aquatic sulfonamides.Fe⁰/persulfate（PS）system was used to degrade the sulfadiazine in this research.Firstly,we studied the effect of initial pH value on the degradation efficiency of sulfadiazine in the Fe⁰/PS system,obtaining the persudo first-order reaction rate constants through batch experiments.Increasing initial pH value decreased the corrosion of Fe⁰,which inhibited k_obsbs value and the removal of sulfadiazine.But the pH value of the solution ranging from 5.0-9.0showed little effect on the final degradation of sulfadiazine.Effects of solvent parameters on the degradation of sulfadiazine by Fe⁰/PS were carried out under neutral conditions.The ratio of Fe⁰:PS was optimised to 1:1.The excessive amount of zero valent iron consumed active oxidants and inhibited the degradation of sulfadiazine.Meanwhile,excessive persulfate could not accelerate the removal of pollutants for the limitation of zero valent iron loading.With concentrations of zero valent iron or persulfate,increasing concentration of pollutants also reduced the removal efficiency due to the production of oxidizing active substances in reaction process.Common aquatic materials including sulfate,nitrate,chloride,perchlorate,and HA all showed negative effects on SDZ degradation by Fe⁰/PS following a trend of Cl-<ClO₄-<SO₄^2-<NO₃^-<HCO₃-<HA.The dominating reactive oxygen species（ROS）in the Fe⁰/PS system was indified as·SO₄-by chemical quenching experiments and electron spin resonance（EPR）spectrum.Besides,strongly negative effects of 1,10-phenanthroline and ethylenediaminetetraacetic acid（EDTA）on SDZ degradation in the Fe⁰/PS process proved that·SO₄^-was not generated by an one-step reaction between Fe⁰and PS but via the indirect oxidation of Fe（II）by PS.The optimation of sulfadiazine was calculated by density functional theory,and the charge distribution of atoms in SDZ was obtained.Then Fukui function value of atoms in SDZ was calculated,and the active site of sulfadiazine attacted by·SO₄-was found at S-N bond,S-C bond,-NH₂ group,and some C and N atoms in SDZ.Finally,the degradation intermediates of sulfadiazine were obtained by mass spectrometry,and four degradation pathways of sulfadiazine in the Fe^0/PS system were deduced.Three degradation pathways of sulfadiazine were classical transformation pathways based on·SO₄-,and the fourth degradation pathway was dominated by the attack of few·OH.