Dual-wavelength synergy and mechanism analysis of ultraviolet light-emitting diode (UV-LED)/H2O2 process for pesticide wastewater treatment

Ultraviolet light-emitting diode (UV-LED), as a new UV source, can be used to activate H2O2. The effect of wavelength on the removal of hexazinone and the potential dual-wavelength synergy was investigated. The degradation efficiency of hexazinone (kH, 6.45 × 10−5 m2 J−1) was the highest at 265 nm in single-wavelength UV-LED/H2O2 process, with the lowest energy consumption (EEO, 1.00 kWh m3 order−1), which was due to the strong absorption of H2O2 and the generation of large amount of HO at 265 nm. The increase in the number of photons under dual-wavelength UV-LED irradiation (265 and 280 nm) accelerated the photolysis of H2O2 to HO, resulting in the dual-wavelength synergy of pollutant degradation (increased by 14.18%) in UV-LED/H2O2 process. Besides, the UV-LED/H2O2 process had high degradation efficiency and energy saving in acidic, neutral and weakly alkaline environment (pH = 4.0–9.0), and exhibited dual-wavelength synergy (increased by 5.30–17.69%), but not in strongly alkaline condition (pH = 10.0). The UV-LED/H2O2 process had a certain ability to reduce the interference of coexisting substances, such as anions, humic acid, turbidity and polystyrene microplastics. Finally, the analysis of degradation pathway and biotoxicity of hexazinone and its intermediates indicated that UV-LED/H2O2 process was eco-friendly. The dual-wavelength UV-LED/H2O2 process provides a new strategy and insight for the efficient degradation of pollutants and energy conservation.