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

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−. [Display omitted] •SO4•− concentration was significantly decreased in the presence of Cl−.•HO• and Cl• concentrations were firstly increased then decreased with increasing Cl− concentrations.•The inhibitory effects of bicarbonate and DOM were more significant in the presence of Cl−.•Cl2•− played a critical role for HO• formation during radical transformation.•A model was established to predict the degradation rate constants of 34 micropollutants.