Effect of water constituents on the degradation of sulfaclozine in the three systems: UV/TiO2, UV/K2S2O8, and UV/TiO2/K2S2O8

Bicarbonate, phosphate, chloride ions, and humic substances are among the constituents most widely present in natural waters. These non-target constituents can greatly affect the efficiency of advanced oxidation processes used for water decontamination due to their capacity to interfere with the adsorption of the target compounds on the surface of TiO₂, absorb photons, scavenge hydroxyl radicals (·OH), and generate photochemical reactive intermediates. In this work, the effect of these constituents on the degradation of sulfaclozine (SCL) was monitored in three different AOPs systems: UV/TiO₂, UV/K₂S₂O₈, and UV/TiO₂/K₂S₂O₈. It was shown that bicarbonate (HCO₃^-) and phosphate (HPO₄^2-) ions enhanced the degradation of SCL in UV/TiO₂ and UV/TiO₂/K₂S₂O₈ systems whereas the addition of humic substances influenced these rates with a much smaller extent. On the other hand, the degradation rate of SCL in the UV/K₂S₂O₈ system was not affected by the presence of HCO₃^- and HPO₄^2- but was inhibited in the presence of humic substances. In addition, the different mechanisms that can take place in the presence of these constituents were discussed and the degradation rate enhancement in presence of HCO₃^- and HPO₄^2- was attributed to the formation of new reactive species such as carbonate (CO₃^·-) and hydroxyl (·OH) radicals activated by TiO₂ holes (h⁺). In the presence of chloride (Cl^-) and nitrate (NO₃^-) ions, an enhancement of SCL adsorption on the surface of TiO₂ was observed. Finally, a comparative study of the degradation of SCL in river water and ultrapure water was reported.