Evaluating iopamidol degradation performance and potential dual-wavelength synergy by UV-LED irradiation and UV-LED/chlorine treatment

Abstract

This study revealed the iopamidol degradation performance and the synergistic effect of dual-wavelength ultraviolet light-emitting diodes (UV-LEDs). It was found that the dual-wavelength irradiation (265 and 280 nm) can promote iopamidol degradation during both UV-LED alone and UV-LED/chlorine processes (p < 0.05). The effects of key experimental parameters including pH, chlorine dosage and water matrix during UV-LED/chlorine process were evaluated. Peak degradation rate was observed at pH 7.0 due to the combined effects of the quantum yield of aquatic chlorine photolysis (Φchlorine) and absorptivity of chlorine. The destruction pathways of iopamidol in the UV-LED/chlorine process were proposed by Ultra Performance Liquid Chromatography-Electrospray Ionization-mass spectrometry. Additionally, an opposite trend of iodinated trihalomethane (I-THM) formation during subsequent chlorination between Milli-Q and real waters with prolonging irradiation time was observed, while other detected disinfection by-product (DBP) formation showed the same variation in Milli-Q and real waters. The UV-LED/chlorine treatment using dual-wavelength can enhance iopamidol degradation significantly, but it also promoted I-THM formation in real water, indicating the need for evaluating DBPs before the application of UV-LED/chlorine process in drinking water treatment.