UV/solar photo-degradation of furaltadone in homogeneous and heterogeneous phases: Intensification with persulfate

Previous studies on removal of the pharmaceutical drug Furaltadone (FTD) in water have not shown to be totally efficient or are very expensive. In this study, sulfate radicals derived from persulfate anions activated with different irradiation sources (UVA, UVC and solar light) and combined with H₂O₂ and/or TiO₂ have been tested in homogeneous and heterogeneous phases under different operation modes and reaction systems. In homogeneous phase, UV produces a slow mineralization (k = 0.0013 min⁻¹). The combined processes are faster (k_UV/H2O2 = 0.0185 min⁻¹, k_UV/PS = 0.0206 min⁻¹) with the best performance for the UV/PS system yielding nearly 80% of mineralization in half an hour. The overall process (UV/H₂O₂/PS) does not show synergy and mineralization is even slower (k_UV/H2O2/PS = 0.015 min⁻¹) due to the production of a high amount of radicals favouring unproductive reactions (scavenger effect). A mineralization mechanism is proposed involving formation of 5hydroxymethylene-2(5H)-furanone and NO as the main intermediates. In heterogeneous phase (UVA/TiO₂/PS), the holes play an important role changing the mineralization mechanism. The main intermediates formed were C₁₂H₁₇N₄O₄ and C₁₁H₁₄N₃O₄, which rapidly were degraded to form C₈H₁₅O₃N₃, C₄H₁₀NO and C₅H₁₀NO. An economic study of operation costs has been made for selected processes: UVC/PS, UVA/TiO₂/PS and Solar/TiO₂/PS. The Solar/TiO₂/PS process has the lowest operation costs due to the use of solar energy. However, it would need an additional stage to recover the catalyst. Finally, a loss of 27% in efficiency during mineralization was found after 5 cycles, but the catalyst recovers its initial performance after regeneration at 500 °C.