Degradation of cyclophosphamide and 5-fluorouracil in water using UV and UV/H₂O₂: Kinetics investigation, pathways and energetic analysis

The photodegradation of cyclophosphamide (CP) and 5-fluorouracil (5FU) in water was investigated by low-pressure UV and UV/H₂O₂ processes. The degradation effect of the two cytostatic drugs (CSDs) can be expressed using a pseudo first-order kinetic model in both UV and UV/H₂O₂ process. Their photodegradation effect in direct UV system significantly increases with the addition of H₂O₂ due to HO generation. At low H₂O₂ dose, the degradation efficiency of CSDs increases with oxidant concentration; however, excess H₂O₂ at higher dose reacts with HO and inhibits CSDs degradation. The optimal H₂O₂ dose is 0.2 mM for both CSDs degradation based on the electrical energy analysis. The photodegradation effect of CSDs decreases in the presence of NOM, HCO₃^- or Cl^-, and increases with NO₃^-. Treated water (TW) from a water treatment plant and secondary effluent (SE) from a wastewater treatment plant was employed as natural waters to evaluate the potential application of UV/H₂O₂. High concentration of alkalinity, NOM and Cl^- in SE decreases the degradation efficiency of CSDs significantly. Transformation by-products of CSDs were detected to propose their potential degradation pathways.