Bromine radicals and hydroxyl radicals efficiently degrade emerging organic contaminants in the UVA photolysis of bromine process
Bromine (HOBr and OBr - ) can be rapidly formed in chlorine-involved processes in the presence of bromide (Br - ), and it significantly affects chlorine chemistry. The activation of chlorine by ultraviolet light A via light emitting diode (UVA-LED) is promising for disinfection and removal of organic contaminants in water treatment, while the bromine behavior therein remains unclear. In this study, the activation of bromine by UVA-LED (UVA-LED/bromine) was investigated to understand the bromine chemistry by selecting ibuprofen (IBP) and benzoic acid (BA) as the representatives. Bromine was readily decomposed into Br - and bromate by UVA photolysis with Br - being the major product. The apparent quantum yield of HOBr (0.589 ± 0.017 mol Einstein −1 ) and OBr - (0.0190 ± 0.0015 mol Einstein −1 ) kept stable at bromine concentrations of 20 – 200 μM, while it decreased as pH increased from 6.0 to 10.0. IBP and BA were rapidly degraded by the UVA-LED/bromine process under different conditions, and it could be well simulated by a kinetic model. Reactive bromine species (RBS, mainly Br• and Br 2 •- ) instead of hydroxyl radical (•OH) contributed predominantly therein. The efficiency of the UVA-LED/bromine process decreased in real waters, mainly due to negative effects of background constituents such as chloride, bicarbonate, and humic acid, as evidenced by both experiments and kinetic modeling. Brominated disinfection byproducts (DBPs) were generated during IBP and BA degradation, while their concentrations were within the regulation limit of drinking water. The results advance the bromine chemistry, and shed light on the UVA-LED photolyzed chlorine process in the presence of Br - .
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