Degradation kinetics and mechanism of β-lactam antibiotics by the activation of H₂O₂ and Na₂S₂O₈ under UV-254 nm irradiation

Graphical abstract: - Highlights: • Removal efficiency was comparable at different UV fluence rates but same fluence. • Reducing pH to 3 or 2 did not inhibit the removal of nitrobenzene by UV/S₂O₈²⁻. • 1.84 × 10⁻¹⁴ M [HO^• ]_ss and 3.10 × 10⁻¹³ M [SO₄^{• −}]_ss in UV/S₂O₈²⁻ were estimated. • HO^• reacted faster with the β-lactams than SO₄^{• −} but sharing similar byproducts. • Transformation pathways included hydroxylation, hydrolysis and decarboxylation. - Abstract: The extensive production and usage of antibiotics have led to an increasing occurrence of antibiotic residuals in various aquatic compartments, presenting a significant threat to both ecosystem and human health. This study investigated the degradation of selected β-lactam antibiotics (penicillins: ampicillin, penicillin V, and piperacillin; cephalosporin: cephalothin) by UV-254 nm activated H₂O₂ and S₂O₈²⁻ photochemical processes. The UV irradiation alone resulted in various degrees of direct photolysis of the antibiotics; while the addition of the oxidants improved significantly the removal efficiency. The steady-state radical concentrations were estimated, revealing a non-negligible contribution of hydroxyl radicals in the UV/S₂O₈²⁻ system. Mineralization of the β-lactams could be achieved at high UV fluence, with a slow formation of SO₄²⁻ and a much lower elimination of total organic carbon (TOC). The transformation mechanisms were also investigated showing the main reaction pathways of hydroxylation (+16 Da) at the aromatic ring and/or the sulfur atom, hydrolysis (+18 Da) at the β-lactam ring and decarboxylation (–44 Da) for the three penicillins. Oxidation of amine group was also observed for ampicillin. This study suggests that UV/H₂O₂ and UV/S₂O₈²⁻ advanced oxidation processes (AOPs) are capable of degrading β-lactam antibiotics decreasing consequently the antibiotic activity of treated waters