Concentration-dependent chloride effect on radical distribution and micropollutant degradation in the sulfate...

This study quantitatively evaluated the effect of chloride (Cl^-) on the radical distribution and micropollutant degradation in the UV/peroxydisulfate AOP using both experimental and modeling approaches. Results showed that SO₄^•- was significantly scavenged by Cl^- at environmentally relevant concentrations (1-5000 mg/L). With increasing Cl^- concentrations from 1 to 5000 mg/L, Cl^- transformed SO₄^•- to HO^• and then to Cl₂^•-. The critical role of Cl₂^•- as a precursor of HO^• in the radical transformation was highlighted. The inhibitory effects of bicarbonate and dissolved organic matter (DOM) on micropollutant degradation was more significant in the presence of Cl^- than that in the absence of Cl^-, mainly due to the consumption of Cl₂^•- by bicarbonate and DOM. Using the model-predicted radical concentrations in the UV/peroxydisulfate process in the presence of different concentrations of Cl^-, the degradation rate constants of 34 micropollutants and the contributions of each radical to the degradation were predicted and compared. The findings improved the fundamental understanding of the Cl^- effect on radical transformation and micropollutant degradation in the SO₄^•--based AOPs. The model enables to foresee whether a SO₄^•--based AOP is effective for the degradation of a certain micropollutant in the water with known concentrations of Cl^-.