Fe(III)-enhanced degradation of para-nitrophenol in a UV/monochloramine system: Mechanism and toxicity analysis

Para-nitrophenol (PNP) is widely used in agricultural production and dye synthesis but poses a threat to human health and ecological security when it enters aquatic environments. This study aimed to investigate PNP degradation in the UV/monochloramine system in the presence of Fe(III) (i.e., UV/NH₂Cl/Fe(III) system). Results revealed that PNP degradation after 10 min in the UV/NH₂Cl/Fe(III) system (45.67%) exhibited higher performance compared to that in the UV/NH₂Cl system (14.59%). Besides, the degradation efficiency of PNP was enhanced with moderate increases in NH₂Cl and Fe(III) concentrations, whereas it declined with increasing pH and initial PNP concentrations. Notably, a Fe(II)/Fe(III) redox cycle was established in the UV/NH₂Cl/Fe(III) system, synergistically driven by Fe(III) and NH₂Cl through UV irradiation. This cycle facilitated the continuous generation of reactive species, thereby enhancing their contribution to PNP degradation (75.17%). The possible degradation pathways of PNP were subsequently proposed. Moreover, toxicity evolution and energy consumption analyses were conducted to evaluate the ecological risks and economic feasibility of the system. Overall, this study provides a comprehensive understanding of the PNP degradation mechanisms in the UV/NH₂Cl/Fe(III) system and demonstrates its potential as an eco-friendly and cost-effective technology for the removal of organic pollutants in wastewater.