Bromate abatement with ultraviolet light-emitting diode/thiosulfate advanced reduction processes: Mechanisms,...

Area of Science:

• Environmental Chemistry
• Water Treatment Technologies
• Advanced Oxidation Processes

Background:

• Bromate is a carcinogenic byproduct of ozonation in water treatment.
• Conventional UV/sulfite advanced reduction processes (ARPs) are inefficient at acidic to neutral pH and use mercury lamps.
• There is a need for more efficient and sustainable methods for bromate removal.

Purpose of the Study:

• To investigate the efficacy of a UV-light emitting diode (UV-LED)-based ARP for bromate removal.
• To evaluate thiosulfate as a reducing agent with UV-LEDs at 265 nm and 280 nm.
• To compare the performance of UV-LED/thiosulfate with UV-LED/sulfite processes.

Main Methods:

• Utilized UV-LEDs emitting at 265 nm and 280 nm with thiosulfate and sulfite as reducing agents.
• Conducted experiments at pH 6.4 ± 0.1 to assess bromate degradation efficiency.
• Employed electron paramagnetic resonance and scavenging experiments to identify reactive species.
• Measured energy consumption (electrical energy per order).

Main Results:

• The UV-LED₂₆₅/thiosulfate process achieved 100% bromate removal at pH 6.4.
• This process followed a pseudo first-order rate constant of 1.3 × 10^-2 min^-1.
• UV-LED₂₆₅/sulfite achieved only 11.6% bromate degradation.
• Hydrated electrons and sulfite radicals were identified as key species in bromate degradation.
• Optimal performance was observed between pH 5.8-6.4.
• Higher thiosulfate doses increased removal efficiency.
• Chloride and bicarbonate ions interfered with the process.
• Energy consumption was comparable to existing UV/sulfite processes.

Conclusions:

• UV-LED/thiosulfate ARP is a highly effective method for bromate removal, particularly in acidic conditions.
• This process utilizes a sustainable UV radiation source and is compatible with acidic ozone-treated water.
• The findings demonstrate the potential of UV-LED technology for efficient and eco-friendly water treatment.