Photodegradation of Nitrogenous Disinfection Byproducts by Far-UVC Light at 222 nm

Krypton chloride (KrCl*) excimer lamps emitting far-UVC 222 nm light have emerged as a promising alternative technology to conventional low-pressure UV (LPUV) lamps emitting at 254 nm. Herein, the suitability of 222 nm for the photodegradation of 12 haloacetonitrile and haloacetamide disinfection byproducts (DBPs) was investigated. Photolysis of all these nitrogenous DBPs is significantly enhanced at 222 nm, compared to 254 nm. The photolysis rate constants (k _222 nm = 7.96 × 10³ - 1.60 × 10⁶ cm²·Einstein^-1) and quantum yields (Φ_222 nm = 0.049-14.43) are 3-56 and 1.2-4.5 times greater, respectively. The photolysis rate of haloacetamides is faster than that of haloacetonitriles and increases with the number of halogens on DBPs. Bromo-DBPs feature much faster photodegradation than chloro-DBPs within the same structural class. The photolysis rates at 222 nm strongly correlate with DBP molar absorption coefficients (ε) and the energy gap between the highest occupied and the lowest unoccupied orbitals (E _HOMO - E _LUMO), indicating the importance of light absorption and photoexcitation. Nitrate and natural organic matter in water cast considerable light-screening effects but also generate reactive species that play a role in the degradation of DBPs at 222 nm. These findings are useful for further developing far-UVC-based technology to mitigate water contamination.