Fate of typical organic halogen compounds in the coexistence of endogenic chlorine atoms and exogenic X

The transformation of halogenated organics in advanced oxidation processes (AOPs) has been extensively investigated. However, we currently know little about the fate of halogenated pollutants in the presence of exogenic halides (Cl- or Br-). Herein, the degradability, mineralization rate, and accumulation capacity of adsorbable organic halogen (AOX) for chlorophenols (2-chlorophenol (2-CP), 3-chlorophenol (3-CP), 4-chlorophenol (4-CP), and 2,4,6-trichlorophenol (TCP)) were compared in the Fe2+/persulfate (PS) process with the addition of exogenic halides. Results indicate that exogenic X- can lead to a decrease in chlorophenols degradation and mineralization rate, undesirable accumulation of AOX, and generation of halogenated by-products which are more toxic than precursor chlorophenols. Results of kinetics modeling show that Cl2•- plays more important role than SO4•- with an addition of Cl-, while SO4•-, Br2•-, and Br2 are responsible for the effect of Br-. As well, the effect of endogenic chlorine atoms on chlorophenols reveals that the degradability and AOX formation potential of 3-CP are highest while that of TCP are the lowest. This study demonstrates the significant influence of endogenic chlorine atoms and exogenic X- on the fate of typical organic halogen compounds. Consequently, the X- level and position/number of halogen atoms should be considered simultaneously when treating organohalogen compounds.