Comparative investigation of diclofenac degradation by Fe2+/chlorine and Fe2+/PMS processes

• The degradation of diclofenac by Fe 2+ /chlorine and Fe 2+ /PMS was compared. • Both radical species and Fe(Ⅳ) contribute to DCF degradation. • The degradation products and pathways were elucidated by LC/TOF/MS combined with DFT calculations. • Chlorinated DBPs could be decreased by prolonging Fe 2+ /chlorine oxidation. The degradation of diclofenac (DCF), a commonly used nonsteroidal anti-inflammatory drug, by Fe 2+ /chlorine and Fe 2+ /PMS processes was comparatively investigated. The influencing factors of pH, Fe 2+ and oxidant dosage on DCF degradation efficiency were evaluated and optimized. Typically, with an initial solution pH of 5, an Fe 2+ dosage of 70 μM, and a chlorine or PMS dosage of 70 μM, the degradation efficiency of DCF using the Fe 2+ /chlorine and Fe 2+ /PMS processes reached 94.2% and 79.7%, respectively, within 10 min. Quenching tests indicated the coexistence of •OH and RCS in the Fe 2+ /chlorine system, and both SO 4 ●– and •OH were identified in the Fe 2+ /PMS system. In addition, Fe(IV) was also identified to participate in DCF degradation in two systems based on the oxidation of PMSO to PMSO 2 . The degradation products and pathways of DCF were elucidated by LC/TOF/MS analysis and DFT calculations. It was assumed that the degradation pathway of DCF involves hydroxylation, dechlorination, decarboxylation, cleavage of the C-N bond, and chlorine substitution. In addition, trichloromethane (TCM), dichloroacetaldehyde (DCAL), dichloroacetonitrile (DCAN) and trichloronitromethane (TCNM) were also detected in the Fe 2+ /chlorine process, and these chlorinated DBPs initially increased and then decreased with prolonged reaction time, indicating that Fe 2+ /chlorine is capable of controlling DBPs formation. Finally, the acute and chronic toxicity of DCF and its degradation products were evaluated by the ECOSAR program.