Far-UVC\n222 nm Treatment: Effects of Nitrate/Nitrite\non Disinfection Byproduct Formation Potential

Irradiation at far\nultraviolet C (far-UVC) 222 nm by krypton chloride\n(KrCl*) excilamps can enhance microbial disinfection and micropollutant\nphotolysis/oxidation. However, nitrate/nitrite, which absorbs strongly\nat 222 nm, may affect the formation of disinfection byproducts (DBPs).\nHerein, we evaluated model organic matter and real water samples and\nobserved a substantial increase in the formation potential for trichloronitromethane\n(chloropicrin) (TCNM-FP), a nitrogenous DBP, by nitrate or nitrite\nafter irradiation at 222 nm. At a disinfection dose of 100 mJ·cm<sup>–2</sup>, TCNM-FP of humic acids and fulvic acids increased\nfrom ∼0.4 to 25 and 43 μg·L<sup>–1</sup>,\nrespectively, by the presence of 10 mg-N·L<sup>–1</sup> nitrate. For the effect of nitrate concentration, the TCNM-FP peak\nwas observed at 5–10 mg-N·L<sup>–1</sup>. Stronger\nfluence caused a greater increase of TCNM-FP. Similarly, the increase\nof TCNM-FP was also observed for wastewater and drinking water samples\ncontaining nitrate. Pretreatment using ozonation and coagulation,\nflocculation, and filtration or the addition of H<sub>2</sub>O<sub>2</sub> can effectively control TCNM-FP. The formation potential\nof other DBPs was minorly affected by irradiation at 222 nm regardless\nof whether nitrate/nitrite was present. Overall, far-UVC 222 nm treatment\nposes the risk of increasing TCNM-FP of waters containing nitrate\nor nitrite at environmentally relevant concentrations and the mitigation\nstrategies merit further research.