Kinetics And Mechanism Of Degradation Of Micro Pollutants By Reactive Bromine Species In Water Treatment

Personal care products and pharmaceutical are emerging micro pollutants which have potential risks of water environment safety and human health.Chlorination disinfection has limited removal capacity of PPCPs,advanced oxidation process such as UV/chlorine can remove PPCPs effectively.Br￣exists ubiquitously in natural water.It can transform to reactive bromine species during chlorine-based water treatment,including free bromine species（e.g.,HOBr、OBr￣、Br₂、Br OCl、Br₂O、Cl Br and Br₃￣etc.）and bromine radicals（RBS,e.g.,Br^·、Br₂^·￣、Br O^·and Cl Br^·￣etc.）.They enhance the degradation of PPCPs due to their high reactivity.In this study,degradation kinetics,products,pathways,the influence of water matrix,and disinfection byproducts of PPCPs by bromination process and UV/bromine process were examined.The transformation rules,reactivity and degradation pathways of reactive bromine species were explained.13 kinds of PPCPs were removed effectively by bromine alone,their apparent reaction rates with free bromine were between 10 M^-1s^-1～10³ M^-1s^-1.PPCPs of strong electron donating properties reacted more actively with free bromine.Higher p H value could render increment of OBr￣and decrement of other free bromine species,so that the degradation of most PPCPs were suppressed.However,the degradation rates of some PPCPs increased because their p Ka are higher than 7.The presence of natural organism matter（NOM）consumed free bromine,so the degradation of PPCPs decreased.Halogen ions enhanced the formation of free bromine species such as Br₂,Cl Br and Br₃￣,etc.They obsessed high reactivity and enhanced the degradation of most PPCPs.The existence of Br￣enhanced the degradation of PPCPs during chlorination of real water body.High concentration of HCO₃￣enhanced the degradation of some PPCPs due to promoting the formation of Br₂,Cl Br and Br₃￣.The presence of HCO₃￣enhanced the electrophilic substitution and oxidation process in the degradation of gemfibrozil and naproxen by bromine.21 PPCPs were removed effectively in UV/bromine process in which free bromine species,OH^·and bromine radicals were major reactive species.The second order rate constants of Br^·and PPCPs were determined between 10⁹ M^-1s^-1～10¹⁰ M^-1s^-1,and that of Br₂^·￣and PPCPs were determined between 10⁷ M^-1s^-1～10⁸ M^-1s^-1.Br^·was quenched under high p H condition but Br O^·can remain a certain concentration,therefore,RBS still contributed significantly to the degradation of PPCPs.Cl￣and Br￣promoted the degradation of some PPCPs via promoting the transformation of Br^·to Cl Br^·￣and Br₂^·￣.NOM and HCO₃￣quenched bromine radicals so that the degradation of PPCPs were decreased.In real water treatment,Br￣enhanced the degradation of PPCPs significantly via the formation of reactive bromine species in UV/chlorine process.Br O^·oxidized carbamazepine by electron transfer,and the main degradation products were hydroxylated products.