Efficacy and mechanism of the artificial sweetener saccharin degradation by thermally activated persulfate in aquatic environments†

Artificial sweeteners, which potentially pose threats to ecosystems, are prevalent emerging contaminants in aquatic environments. This study explored the efficacy and mechanism underlying the degradation of saccharin by thermally activated persulfate treatment (thermal/persulfate) for the first time. Saccharin degradation followed pseudo-first-order kinetics, with a k_obs value of 0.023 min⁻¹ under the following conditions: [saccharin]₀ = 5 mg L⁻¹, [persulfate]₀ = 100 mg L⁻¹, temperature = 70 °C and solution pH = 7.0. Optimal saccharin degradation occurred under neutral and weakly acidic pH conditions (pH 7 and 5), and the calculated apparent activation energy of saccharin was 113.3 kJ mol⁻¹. The results from the scavenger experiments and electron paramagnetic resonance identification revealed that SO₄˙⁻ and ·OH were the predominant radical species involved in saccharin degradation, with ·OH likely playing the major role. HCO₃⁻, NO₃⁻, and dissolved organic matter competed with saccharin for free radicals, decreasing the saccharin degradation rate; however, Cl⁻ had a positive effect. Saccharin degradation involved monohydroxylation and dihydroxylation and produced TP1 and TP2, respectively. During treatment, 35% TOC reduction was achieved, and the Microtox® toxicity initially increased and then decreased, suggesting that saccharin and its transformation byproducts undergo mineralization and detoxification. The saccharin degradation rate was lower in actual water matrices than in deionized water. In conclusion, this work comprehensively investigated the degradation of saccharin by thermally activated persulfate treatment for future applications in water/wastewater treatment.