Impact of nitrite on the formation of trichloronitromethane during the UV-LED/chlorine process

Abstract

A UV-LED at a fixed wavelength is increasingly employed in the UV/chlorine process to degrade contaminants of emerging concern. However, degradation of contaminants and formation of disinfection by-products (DBPs) in post-chlorination would be significantly altered in the presence of nitrite because of the generation of reactive nitrogen species (RNS). As nitrite has a maximum absorption at ∼350 nm, its impact on the performance of the UV-LED₃₆₅/chlorine process and subsequent formation of DBPs was investigated. The presence of nitrite in the UV₃₆₅ irradiation process accelerated the degradation of bisphenol A (BPA), while slightly inhibiting the degradation of BPA in the UV₃₆₅/chlorine process; nitrite in UV₃₆₅ and UV₃₆₅/chlorine processes resulted in the non-negligible formation of trichloronitromethane (TCNM). The concentration of generated DBPs and the corresponding cytotoxicity and genotoxicity all changed because of the presence of nitrite; the concentrations of nitrite, pH, and UV fluence were important factors for the formation of TCNM during the UV₃₆₅/chlorine/nitrite process. Therefore, the impact of nitrite on the TCNM formation in the UV-LED₃₆₅/chlorine process is worth noting.