Enhanced degradation of para-nitrophenol during the UV/chlorine process with the addition of Fe(III): Performance, reaction mechanisms, and DBPs formation

Abstract

Para-nitrophenol (PNP) enters aquatic environments through wastewater discharge, potentially threatening ecological security and public health. This work investigated the enhanced degradation of PNP in wastewater during the UV/chlorine process with the addition of Fe(III) (UV/chlorine/Fe(III)). The UV/chlorine/Fe(III) process (61.85 %) exhibited higher performance in PNP degradation in 10 min compared to the UV/chlorine process (40.00 %) because the synergistic effect of Fe(III) and free chlorine enhanced hydroxyl radicals (OH) and reactive chlorine species (RCSs) production. Furthermore, OH and RCSs were identified as the primary contributors to degrade PNP during the UV/chlorine/Fe(III) process, and their corresponding contributions accounted for 40.09 % and 37.10 %, respectively. Besides, the degradation efficiencies of PNP were promoted by increasing the dosages of Fe(III) and free chlorine and declined by increasing pH and PNP concentration. Also, Cl− could promote PNP degradation, while SO42− and HCO3− inhibited it. Then, the reaction mechanisms of PNP degradation during the UV/chlorine/Fe(III) process were proposed based on the identified transformation products (TPs) and the density functional theory (DFT) calculation. Meanwhile, PNP, TPs, and other possible intermediate products presented different ecotoxicity. Finally, the formation and toxicity of disinfection by-products (DBPs) with different Fe(III) concentrations, chlorine dosages, initial pHs, and PNP concentrations were explored. Overall, the obtained findings can provide deep insights into the mechanisms of PNP degradation and a new approach to enhancing PNP degradation in wastewater.