Kinetics and mechanisms of sulfate radical oxidation of β-lactam antibiotics in water

The quantitative removal of contaminant antibiotic activity from waters intended for reuse is one of the biggest problems facing water utilities today. As conventional water treatments are not sufficient, advanced Oxidation and Reduction Processes (AO/RPs) are being considered for additional remediation. In support of the potential use of sulfate radical based AO/RPs, we have determined the reaction rate constants for the sulfate radical with a large library of β-lactam antibiotics. The SO4- reactivity with the five-member ring species was found to have an extrapolated zero ionic strength average rate constant of (1.6 ± 0.9) × 109 M−1 s−1, slightly slower than for the six-member antibiotics at (2.1 ± 0.6) × 109 M−1 s−1. Transient spectral studies indicated that the majority of these radicals reacted at the five- or six-member rings adjacent to the β-lactam core, predominately at the sulfur atom and the double bond, respectively. As these oxidations occur next to the β-lactam moiety, rather than at the peripheral aromatic rings observed for hydroxyl radical reaction, sulfate radical remediation through the use of added persulfate might result in more efficient antibiotic activity removal than when using a traditional AO/RP treatment.