Degradation of Pharmaceuticals and Metabolite in Synthetic Human Urine by UV, UV/H₂O₂, and UV/PDS

To minimize environmental pharmaceutical micropollutants, treatment of human urine could be an efficient approach due to the high pharmaceutical concentration and toxic potential excreted in urine. This study investigated the degradation kinetics and mechanisms of sulfamethoxazole (SMX), trimethoprim (TMP) and N₄-acetyl-sulfamethoxazole (acetyl-SMX) in synthetic fresh and hydrolyzed human urines by low-pressure UV, and UV combined with H₂O₂ and peroxydisulfate (PDS). The objective was to compare the two advanced oxidation processes (AOPs) and assess the impact of urine matrices. All three compounds reacted quickly in the AOPs, exhibiting rate constants of (6.09–8.53) × 10⁹ M^–1·s^–1 with hydroxyl radical, and (2.35–16.1) × 10⁹ M^–1·s^–1 with sulfate radical. In fresh urine matrix, the pharmaceuticals’ indirect photolysis was significantly suppressed by the scavenging effect of urine citrate and urea. In hydrolyzed urine matrix, the indirect photolysis was strongly affected by inorganic urine constituents. Chloride had no apparent impact on UV/H₂O₂, but significantly raised the hydroxyl radical concentration in UV/PDS. Carbonate species reacted with hydroxyl or sulfate radical to generate carbonate radical, which degraded SMX and TMP, primarily due to the presence of aromatic amino group(s) (k = 2.68 × 10⁸ and 3.45 × 10⁷ M^–1·s^–1) but reacted slowly with acetyl-SMX. Ammonia reacted with hydroxyl or sulfate radical to generate reactive nitrogen species that could react appreciably only with SMX. Kinetic simulation of radical concentrations, along with products analysis, helped elucidate the major reactive species in the pharmaceuticals’ degradation. Overall, the AOPs’ performance was higher in the hydrolyzed urine than fresh urine matrix with UV/PDS better than UV/H₂O₂, and varied significantly depending on pharmaceutical’s structure.