Trace Br- Inhibits Halogenated Byproduct Formation in Saline Wastewater Electrochemical Treatment.
Environ Sci Technol
; 58(27): 12212-12224, 2024 Jul 09.
Article
em En
| MEDLINE
| ID: mdl-38916044
ABSTRACT
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 Cl2â¢- to Br2â¢-, 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 Br2â¢--dominated system, indicating distinct reaction mechanisms compared to those involving Cl2â¢-. Kinetic isotope experiments and density functional theory calculations confirmed that the interaction between Br2â¢- and phenolic pollutants follows a hydrogen atom abstraction pathway, whereas Cl2â¢- 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.
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Águas Residuárias
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En
Ano de publicação:
2024
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Article