Formation Of Halogenated By-products In Co²⁺ Activated Peroxymonosulfate Oxidation Process

Sulfate radicals(SO4·-)generated by Co2+ catalyzed activation of peroxymonosulfate(PMS)are highly oxidative and applied to degrade various organic pollutants.Due to the strong oxidizing property,sulfate radical(SO4·-)can easily transformed halides to reactive halogen species such as X·,X2·-,XOH·-,X2,and XOH.It was revealed in this research halide ions could be transformed in this process to reactive halogen species which react with phenols subsequently,leading to the formation of halophenols and halogenated disinfection by-products.It is well accepted that Co2+ was the best catalyst for peroxymonosulfate(PMS)activation to generate SO4·-.Phenol was added as a model compound to mimic the reactivity of natural organic matter(NOM).This study focused on the transformation of halides in Co2+/PMS oxidation process.It was revealed that Br-was efficiently transformed to reactive bromine species(RBS)including free bromine and bromine radicals(Br·,Br2·-,etc.)in Co2+/PMS system.RBS thus generated resulted in the bromination of phenol and formation of brominated DBPs(Br-DBPs)including bromoform and bromoacetic acids.Br-DBPs were further degraded by excessive SO4·-and transformed to bromated ultimately.Free bromine was also formed in the absence of Co2+,free bromine was incorporated to phenol sequentially and leading to Br-DBPs as well.However,Br-DBPs could not be further transformed in the absence of SO4·-.The kinds and quantity of chlorinated disinfection by-products increased with the increasing of Cl-/Br-,the yields of Br-DBPs had a trend of gradual decrease.Transformation of organic chlorine and chlorphenols(CPs)in Co2+/PMS oxidation processes were also explored in this study.It was revealed that the degradation of CPs follow the first-order kinetic reaction equation in Co2+/PMS oxidation process.Degration of CPs was expected to result in the formation of halogen intermediates and products which were analyzed by HPLC/MS.The formation of the DBPs in the system of PMS and Co2+/PMS system were deeply discussed.In the presence of Br-,Co2+/PMS system generated more species and lower yields of DBPs than PMS system.Moreover,with the increase of the chlorine substituents,the yields of Br-DBPs decreased gradually and the quantity of chlorinated disinfection by-products increased by degrees.In summary,the chlorine substituents followed the transformation of organic chlorine?inorganic chlorine?organic chlorine in Co2+/PMS system.The findings of this research can provide valuable information in assessing the feasibility of SO4·-based oxidation technologies in real practice.