Tao Yang,Xiujuan Kong,Ge Zeng,Maoju Jiang,Linqian An,Peng Su,Qixiao Lv,Jun Ma,Juan Li
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 - .
The electrochemical technology provides a practical and viable solution to the global water scarcity issue, but it has an inherent challenge of generating toxic halogenated byproducts in treatment of saline wastewater. Our study reveals an unexpected discovery: the presence of a trace amount of Br– not only enhanced the electrochemical oxidation of organic compounds with electron-rich groups but also significantly reduced the formation of halogenated byproducts. For example, in the presence of 20 μM Br–, the oxidation rate of phenol increased from 0.156 to 0.563 min–1, and the concentration of total organic halogen decreased from 59.2 to 8.6 μM. Through probe experiments, direct electron transfer and HO• were ruled out as major contributors; transient absorption spectroscopy (TAS) and computational kinetic models revealed that trace Br– triggers a shift in the dominant reactive species from Cl2•– to Br2•–, which plays a key role in pollutant removal. Both TAS and electron paramagnetic resonance identified signals unique to the phenoxyl and carbon-centered radicals in the Br2•–-dominated system, indicating distinct reaction mechanisms compared to those involving Cl2•–. Kinetic isotope experiments and density functional theory calculations confirmed that the interaction between Br2•– and phenolic pollutants follows a hydrogen atom abstraction pathway, whereas Cl2•– predominantly engages pollutants through radical adduct formation. These insights significantly enhance our understanding of bromine radical-involved oxidation processes and have crucial implications for optimizing electrochemical treatment systems for saline wastewater.
Ziying Wang,Yisheng Shao,Naiyun Gao,Bin Xu,Na An,Xian Lu
Applying the highly oxidative sulfate radical ( SO 4 - · ) to pollutant degradation may cause it to react with the coexisting bromide (Br − ) to form undesired byproducts. This study investigated the transformation of Br − during the degradation process of a contaminant (diethyl phthalate (DEP)) via heat-activated persulfate (PS). Dibromoacetonitrile and bromoform formed with Br − and natural organic matter (NOM) in the solution, while only bromoform was detected without NOM. The formation of these brominated disinfection byproducts (Br-DBPs) can be ascribed to the reactions between the phenolic groups of DEP degradation intermediates or NOM and reactive bromine species (free bromine and radical bromine) generated through the oxidation of Br − by SO 4 - · . Br-DBPs were degraded by excessive SO 4 - · , which indicates that organic bromine is a temporary phase during the turnover of Br − . The time-dependent formation of organic and inorganic bromines suggests that Br − may have cycled several times between organic and inorganic forms before eventually turning into bromate. The bromate formation showed a lag phase before continuously increasing. Generally, increasing the temperature, PS dosage, and Br − and organic matter (DEP and NOM) concentrations increased the maximum concentration of Br-DBPs. Additionally, these reaction parameters facilitated bromate formation except for organic matter, whose inhibitory effect is probably due to the consumption of reactive species by organic matter and the generated superoxide anion. The total organic carbon concentration of the solution exhibited a relatively quick reduction followed by a slow decrease. These results highlight the potential risks of PS activation technologies and can help prevent such risks in actual practice.
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