The altered effects of chloride on the treatment efficiency of SO4·−-based AOPs by other background water constituents

A significant loss of the treatment efficiency induced by Cl − is a well-recognized drawback of the SO 4 ·− -based AOPs and various mathematical model have been established to achieve quantitative prediction of the treatment efficiency of SO 4 ·− -based AOPs at different levels of Cl − . However, the background water constituents (e.g., ammonia and dissolved organic matter (DOM)) complicate the chemistry of Cl − /SO 4 ·− system and disable these models. This study shows that the degradation of sulfamethoxazole and bisphenol A by Co 2+ /PMS process decreased with dosing Cl − at fresh water level, due to the shifted distribution of reactive species from SO 4 ·− to Cl 2 ·− , ClO · and HOCl. Besides quenching radicals, HOCl also contributed to pollutant degradation. Though ammonia alone negligibly influence the Co 2+ /PMS process, ammonia reacts with the in situ formed HOCl in the Cl − /SO 4 ·− process rapidly along with the generation of chloramine which mainly severed as radical scavenger rather than oxidant. Consequently, more severe efficiency loss of the SO 4 ·− -based AOPs occur in the copresence of ammonia and Cl − . Unexpectedly, the efficiency loss was alleviated after dosing DOM, which was attributed to the suppressed formation of chloramine. The occurrence of chlorate and disinfection by-products are not concerns in the Co 2+ /PMS process when Cl − coexists with ammonia and DOM, because of the decreased formation of HOCl. These results enhance our understanding of the complex chemistry of SO 4 ·− -based AOPs in real water and promote the progress of SO 4 ·− -based AOPs towards the niche applications in water treatment.