Degradation of sulfamethoxazole by ionizing radiation: Kinetics and implications of additives

Sulfamethoxazole (SMX) is a widespread and persistent antibiotic pollutant in the aquatic environment. In this paper, SMX was degraded by gamma irradiation, and various influencing factors were explored. The experimental results revealed that after 1.5 kGy irradiation, 20 mg/L SMX could be completely decomposed. Kinetics studies suggested that the radiation-induced degradation process of SMX conformed first-order kinetic. The pH value had influence on the decomposition efficiency through changing the species of reactive radicals and the existing form of SMX molecules and their distribution. Additionally, the effect of inorganic anions (CO₃^2-, HCO₃^-, NO₃^-, SO₄^2-, Cl^-, HPO₄^2-) and organic matters (peptone, glucose, humic acid) on SMX degradation was evaluated, which had negative influence on SMX degradation. The degradation efficiency of SMX decreased in the effluent water of WWTP in comparison with that in deionized water, suggesting that the components in the effluent inhibited the radiation-induced decomposition of SMX. The mineralization of SMX by ionizing radiation was also evaluated. These results revealed that ionizing radiation is a promising technology to degrade SMX in aqueous solution as well as in wastewater.