Degradation kinetics and mechanism of penicillin G in aqueous matrices by ionizing radiation

The gamma radiation induced-degradation of a β-lactam antibiotic, penicillin G was investigated in aqueous solution. Special attention was paid to the effects of the organic substances such as peptone and glucose on penicillin G degradation, which can be found in the wastewater of the factories producing antibiotics. Results showed that gamma radiation was effective to degrade and deactivate penicillin G in pure water. With the initial concentrations of 0.27   mM, 1.34   mM and 2.68   mM, a complete removal of penicillin G could be achieved at the adsorbed doses of 2.5   kGy, 10   kGy and 20   kGy, respectively. Penicilloic acid from the β-lactam ring cleavage and a series of fragment compounds such as thiazolidine and penicillic acid were identified during gamma irradiation-induced degradation of penicillin G. Addition of Fe 2+ was efficient to enhance the mineralization. The TOC removal efficiency of penicillin G was 21.7% using gamma irradiation alone at 10   kGy, which increased to 56.4% with 1.0   mM Fe 2+ addition. The gamma radiation-induced degradation of penicillin G was inhibited in the presence of peptone and glucose and the inhibitive effect increased with increasing their concentrations. The rate constant, k of the pseudo first-order kinetics decreased by 74% and 64% in the presence of 1.0   g/L of peptone and glucose, respectively, and by 96% and 89% in the presence of 10   g/L of peptone and glucose, respectively. The ratio of k / k 0 was increased by 1.3 times with H 2 O 2 addition and by 3 times with Fe 2+ addition, in the presence of 10   g/L of glucose. Adding Fe 2+ was effective to improve the ionizing radiation induced degradation of penicillin G antibiotic in the glucose-containing wastewater.