Degradation mechanism and kinetic modeling for UV/peroxydisulfate treatment of penicillin antibiotics

Abstract

The widespread occurrence of penicillin antibiotics (PENs) in natural environment has raised increasing concerns due to their potential to induce antibiotic-genes. In this study, the degradation of PENs by UV/peroxodisulfate (PDS) process was investigated to determine the reaction kinetics, transformation mechanism and energy efficiency. The second-order rate constants for sulfate radical (SO4−) and hydroxyl radical (HO) with PENs, including, pencillin G (PG), amoxicillin (AMX) and carbenicillin (CBN), were determined to be (3.90–9.32) × 109 M−1·s−1 and (6.67–9.86) × 109 M−1·s−1, respectively. A pseudo steady-state kinetic model was employed and successfully predicted the degradation of PENs in ultrapure water. The modeling results revealed that both direct and indirect photolysis contributed to PENs degradation, and the contribution of indirect photolysis increased with the increase of PDS dosage. SO4− was the major contributor to PENs indirect photolysis. The effect of pH and water matrices, including HCO3−, Cl− and natural organic matter were evaluated and modeled. Combined with the modeling results, the derived radicals and excited species were likely generated and involved in the overall degradation of PENs. Based on the developed model, we gave a roughly calculation of electrical energy per order (EE/O) to evaluate the energy efficiency of PDS treatment processes. Finally, the transformation product analysis indicated that the thioether sulfur on the five-membered ring and the side chain, e.g., benzene ring on PG and CBN were the reactive sites for SO4−, while the primary amine was another reactive site for SO4− on AMX.