Photodegradation of sulfonamides in UV/ozone, UV/oxidant, and UV/ ozone/oxidant systems: comparison in terms of mineralization efficiency and power consumption.

UV/O₃, UV/H₂O₂, UV/Na₂S₂O₈, UV/O3/H₂O₂, and UV/UV/Na₂S₂O₈ systems were used to mineralize sulfamethoxazole (SMX) and sulfathiazole (STZ). The effects of pH and salinity on sulfonamide mineralization were determined. The mineralization of sulfonamides exhibited pseudo-firstorder kinetics. At pH 5, the pseudo-first-order rate constants (k) of SMX in the UV/O₃, UV/H₂O₂, UV/Na₂S₂O₈, UV/O₃/H₂O₂, and UV/O₃/Na₂S₂O₈ systems were 0.0193, 0.0011, 0.0022, 0.0172, and 0.0925 min^-1, respectively, and those of STZ were 0.0238, 0.0011, 0.0031, 0.0201, and 0.0536 min^-1, respectively. At pH 5, adding Na2S2O8 to the UV/O3 system promoted sulfonamide mineralization, whereas adding H₂O₂to the UV/O₃ system inhibited it. At pH 9, adding Na₂S₂O₈ or H₂O₂ to the UV/ O₃ system promoted sulfonamide mineralization. The highest efficiency of mineralization for both SMX and STZ was achieved using the UV/O₃/Na₂S₂O₈ system and the efficiency followed the order pH 5 > pH 7 > pH 9. In the UV/O₃/Na₂S₂O₈ system at pH 9, adding 0.62 mM salinity reduced the k value of SMX from 0.0224 to 0.0181 min^-1 and that of STZ from 0.0322 to 0.0233 min^-1 . In the UV/O₃/ H₂O₂ system at pH 9, adding 0.62 mM salinity reduced the k value of SMX from 0.0137 to 0.0065 min^-1 and that of STZ from 0.0159 to 0.0072 min^-1 . The figure-of-merit electrical energy per order was used to estimate the electrical energy efficiencies of the systems. At pH 5, the UV/O₃/Na₂S₂O₈ system exhibited the highest energy efficiency for SMX mineralization whereas the UV/Na₂S₂O₈system did so for STZ mineralization. The highest energy efficiency system varied with the parent compound. [ABSTRACT FROM AUTHOR]