Photodegradation of sulfonamides in uv/ozone, uv/oxidant, and uv/ ozone/oxidant systems: Comparison in terms of mineralization efficiencand power consumption

Abstract

UV/O3, UV/H2 O2, UV/Na2 S2 O8, UV/O3 /H2 O2, and UV/O3 /Na2 S2 O8 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-first-order kinetics. At pH 5, the pseudo-first-order rate constants (k) of SMX in the UV/O3, UV/H2 O2, UV/Na2 S2 O8, UV/O3 /H2 O2, and UV/O3 /Na2 S2 O8 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 Na2 S2 O8 to the UV/O3 system promoted sulfonamide mineralization, whereas adding H2 O2 to the UV/O3 system inhibited it. At pH 9, adding Na2 S2 O8 or H2 O2 to the UV/ O3 system promoted sulfonamide mineralization. The highest efficiency of mineralization for both SMX and STZ was achieved using the UV/O3 /Na2 S2 O8 system and the efficiency followed the order pH 5 > pH 7 > pH 9. In the UV/O3 /Na2 S2 O8 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 / H2 O2 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 /Na2 S2 O8 system exhibited the highest energy efficiency for SMX mineralization whereas the UV/Na2 S2 O8 system did so for STZ mineralization. The highest energy efficiency system varied with the parent compound.