Comparison of UV-LED/chlorine and UV/chlorine Processes on the Removal of 2-Isopropyl-3-ethoxypyrazine, 2-Isobutyl-3-Methoxypyrazine, and 2,4,6-Trichloroanisole

This study focuses on the removal of taste and odor compounds―2-isopropyl-3-methoxypyrazine (IPMP), 2-isobutyl-3-methoxypyrazine (IBMP), and 2,4,6-trichloroanisole (TCA)―using advanced ultraviolet light-emitting diode/chlorine (UV-LED/Cl2) and UV/Cl2 processes. UV-LED technology offers several advantages over conventional UV lamps, including higher efficiency, longer lifespan, and the elimination of mercury. In this study, UV-LEDs with wavelengths of 255 nm and 285 nm were compared with conventional UV technology at 254 nm to evaluate the degradation efficiency of the target compounds under varying UV doses. The results showed that IPMP degradation reached 88%, 84%, and 92% for UV-LED at 255 nm, UV-LED at 285 nm, and UV at 254 nm, at an initial concentration of 200 ng/L. Similarly, the IBMP removal rates were 75%, 73%, and 76%, and the TCA removal rates were 66%, 49%, and 76%, for UV-LED 255 nm, UV-LED 285 nm, and UV 254 nm, respectively. UV 254 nm demonstrated the highest efficiency for all compounds, and UV-LED 255 nm showed comparable performance. In contrast, UV-LED 285 nm exhibited the lowest efficiency owing to its limited absorption in the UV range for chlorine photolysis. Moreover, a higher pH of 9 resulted in faster degradation rates compared with neutral pH 7 for both UV-LED 255 nm and 285 nm. For UV-LED at 255 nm, the degradation rate constants for IPMP, IBMP, and TCA were respectively 0.0021, 0.0016, and 0.0011 cm²/mJ at pH 9, compared with 0.0020, 0.0041, and 0.0009 cm²/mJ at pH 7. Reactive chlorine species, such as Cl·, Cl₂·^-, and ClO· contributed 37.5% to TCA removal, 20.3% to IPMP, and 18.8% to IBMP. In conclusion, this study tested the applicability of UV-LED/Cl₂ in water treatment and demonstrated that UV-LED/Cl₂ is an effective method for the removal of taste and odor compounds.