Radical chemistry and PPCP degradation in the UV/peroxydisulfate process in the presence of chloride at freshwater levels

Chloride (Cl) affects the sulfate radical (SO4 center dot-)-based advanced oxidation processes for application. This study investigated the effects of Cl at freshwater levels (5-1000 mu M) on radical chemistry and pharmaceuticals and personal care products (PPCPs) degradation in a UV/peroxydisulfate (UV/PDS) process. By using radical probes and a kinetic model, SO4 center dot- was converted to chlorine radical (Cl-center dot), and Cl-center dot was subsequently transformed to hydroxyl radical (HO center dot). The SO(4)(center dot-)concentration monotonically decreased by 56.8-91.7% at 5-1000 mu M Cl at pH 7, and that of HO center dot increased by 127-419%. Cl-center dot/Cl-2(center dot) formation was less prevalent at <= 100 mu M Cl, but Cl-2(center dot) was notable at 1000 mu M Cl. Increasing pH promoted the transformation from SO4 center dot- to HO center dot and drove the conversion from Cl-center dot/Cl-2(center dot) to HO center dot, resulting in less Cl-center dot/Cl-2(center dot) at pH 10. Increasing Cl from 10 to 1000 mu M decreased the pseudo-first-order rate constants (k 's) of 18 PPCPs from 1.6% to 93.9% but increased the k ' s of 5 other PPCPs by 2.5-33.4%, compared to those without Cl. Cl (1000 mu M) primarily transformed SO4 center dot- to HO center dot and Cl-center dot with the conversion ratios of 89.8% and 0.7%, respectively. Therefore, the contributions of HO center dot increased from 16-65.9% to 83.6-99.5%, and those of SO4 center dot- decreased from 10.2-62.6% to < 8.6%, as Cl rose from 10 to 1000 mu M. This study demonstrated that at freshwater levels, Cl primarily drove the conversion from SO4 center dot- to HO center dot, emphasizing the importance of HO center dot in PPCP degradation in the UV/PDS process.

Automated summary

This study investigated the effects of chloride on the transformation between SO4 center dot- and HO center dot in the UV/PDS process, finding that the impact on PPCP degradation varied depending on the concentration of chloride.