Comparative analysis of para-nitrophenol degradation and DBPs formation in the UV/chlor(am)ine/Fe(Ⅲ) systems

Para-nitrophenol (PNP), a highly toxic compound widely detected in water bodies, was investigated as the target contaminant during the UV/chlor(am)ine/Fe(III) processes to evaluate its degradation kinetics model, and disinfection byproducts (DBPs) formation and pathways. The incorporation of Fe(III) introduced a oxidation-reduction cycle of Fe(II) and Fe(III), which can generate additional hydroxyl radicals, reactive chlorine species, and reactive nitrogen species, thereby accelerating PNP degradation by 21.85 % in the UV/chlorine system and 31.08 % in the UV/chloramine system. PNP degradation followed pseudo-first-order kinetics, with observed rate constants ( k obs ) calculated as 0.0938 and 0.0604 min −1 , in the UV/chlorine/Fe(III) and UV/chloramine/Fe(III) systems, respectively. Radical quenching experiments confirmed the dominant reactive species in each system, supporting the mechanistic interpretation. In the UV/chlorine/Fe(III) system, DBP yields ranked as follows: Halonitromethanes (HNMs) > trihalomethanes (THMs) > haloacetamides (HAcAms) > haloacetonitriles (HANs), while the order was HNMs > THMs > HANs > HAcAms, in the UV/chloramine/Fe(III) system. Factors influencing DBP formation, including Fe(III) dosage, initial pH, and chlor(am)ine dosage, were systematically investigated. The cytotoxicity index (CTI) contributions of each DBP in the UV/chlor(am)ine/Fe(III) systems were ranked as follows: HNMs > HANs > THMs > HAcAms. Based on detected transformation products (TPs) and radical contribution analysis, plausible pathways for PNP transformation and DBPs formation were proposed. These findings provide valuable insights into PNP degradation behavior and the mechanisms of DBPs formation in the UV/chlor(am)ine/Fe(III) systems, supporting their future practical applications.