The KrCl* excimer lamp emitting at far-UVC 222 nm is a promising disinfection technology for water and wastewater treatment, especially for viruses. Additional advantages of the KrCl* excimer light source include the absence of mercury and no harm to exposed human tissues, compared to the conventional low-pressure mercury ultraviolet (LPUV) lamps which emit primarily at 254 nm. Recently, KrCl* excimer lamps have also emerged as a powerful tool for UV-based advanced oxidation processes and direct photolysis of organic micropollutants (OMPs) in water. However, the fundamental photochemical properties at 222 nm are still largely unknown for common OMPs. To address this knowledge gap, we conducted a screening of 46 OMPs of different structural characteristics to identify their direct photolysis rates, molar extinction coefficients, and quantum yields at 222 nm, and compared the photochemical properties with those at 254 nm from LPUV. Generally, the fluence-normalized photolysis rate constant obtained at far-UVC 222 nm was 1.2–64.2 times higher than that under LPUV for most OMPs, whether they feature higher or lower absorbance at 222 nm than at 254 nm. The quantum yields of OMPs at 222 nm, measured based on the loss of parent compounds by direct photolysis, varied in the range of 0.015–0.85 depending on the compound structures. Notably, simple and non-nitrogenous aromatic compounds often absorb light more strongly at 222 nm, but their quantum yields at 222 nm were lower than those at 254 nm. However, most nitrogenous aromatic OMPs feature higher quantum yields at 222 nm albeit their weaker light absorbance at this wavelength than at 254 nm. Lastly, KrCl*-222 nm was less effective than LPUV in photolyzing a small group of OMPs, including four sulfonamides, enrofloxacin, 9-anthracenecarboxylic acid, and 1,4-benzoquinone, owing to their absorbance peaks at 254 nm. Results of this study shed new light on the direct photolysis behaviors of OMPs at far-UVC 222 nm and indicate the need of further research in this area.

Direct photolysis of organic micropollutants by KrCl* excimer lamps at far-UVC 222 nm

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