Removal of saccharin by UV/persulfate process: Degradation kinetics, mechanism and DBPs formation

Abstract

As a widely used artificial sweetener, saccharin (SAC) has received extensive attention due to its widespread detection in aquatic environment and potential risk to human health. In this study, the SAC removal by UV-activated persulfate (PS) was comprehensively examined. The results demonstrated that SAC could be eliminated effectively through UV/PS oxidation and its removal behavior can be well described by pseudo-first-order kinetic model. The introduction of different scavengers manifested that sulfate radicals (SO4−∙) were identified to be the major reactive radicals under acidic and neutral conditions, while hydroxyl radicals (HO∙) were determined to be the dominant species under alkaline environments. The reaction rates of SAC with SO4−∙ and HO∙ were calculated to be 1.48 × 108 and 1.56 × 109 M−1 s−1, respectively. The degradation rate constant was positively related to PS dosage (0.21–2.52 mM). The degradation decelerated with the increase of pH from 4.0 to 8.0 and slightly accelerated at pH 9.0. The introduction of Cl− posed a positive impact, while the presence of HCO3−, Br− and humic acid overall retarded SAC removal. Low concentrations of NO3− promoted the degradation, whereas the high levels of NO3− exerted a negative effect. The SAC degradation by UV/PS was mainly initiated through the hydroxylation of the benzene ring, cleavage of C-N bonds, decarboxylation and denitrogenation. The SAC removal in real water matrices by UV/PS treatment was still relatively efficient. Of note, the increased yield of trichloromethane, dichloroacetic acid, trichloroacetic acid and dichloroacetonitrile was found due to chlorination after UV/PS pretreatment.