Photodegradation performance and mechanism of sulfadiazine in Fe(III)-EDDS-activated persulfate system.

In order to overcome the shortcomings in the traditional Fenton process, Fe(III)-EDDS-activated persulfate advanced oxidation process under irradiation is carried out as a promising technology. The photodegradation of sulfadiazine (SD) in Fe(III)-EDDS-activated persulfate system was investigated in this paper. The results showed that SD could be effectively degraded in Fe(III)-EDDS/S2O82-/hv system. The effects of Fe(III):EDDS molar ratio, the concentration of Fe(III)-EDDS, and the concentration of S2O82- on SD degradation were explored. At neutral pH, when Fe(III):EDDS = 1:1, Fe(III)-EDDS = 0.1 mM, S2O82- = 1.5 mM, the best SD degradation was achieved. The experiment of external influence factors showed that the degradation of SD could be obviously inhibited by the presence of CO32-, SO42-, whereas the degradation of SD was almost unaffected by the addition ofCl-. The degradation of SD could be slightly inhibited by the presence of humic acid and NO3-. The effect of pH on SD degradation was investigated, and SD could be degraded effectively in the pH range of 3-9. ESR proved that 1O2, ·OH, SO4-, and O2- were produced in the process. SO4- and ·OH were identified as the main radicals while O2·- also played non-ignorable role. Eleven intermediate products of SD were analysed. The C = N, S-N, and S-C bonds of SD were attacked by radicals firstly, leading to a series of reactions that eventually resulted in the destruction of SD molecules and the formation of small organic molecules.