Insights into the transformations, antimicrobial activity, and degradation efficiency of a representative carbapenem antibiotic by high-frequency ultrasound hybridized with the (photo)Fenton process

Carbapenems are potent antibiotics that reach sewage systems and then the environment, causing negative impacts. Thus, research on degrading processes to limit the carbapenem discharge in sewage systems is needed. Herein, fundamental aspects of high-frequency ultrasound alone and hybridized with the (photo)Fenton process to deal with a representative carbapenem antibiotic (meropenem, MERO) in water were considered. Initially, the action of ultrasound alone (at 578 kHz) on MERO in distilled water was tested for degradation, resulting in a partial removal (∼53 % after 120 min) and a moderate pseudo-first-order-kinetics (k: 6.3 × 10^-3 min^-1). Then, to enhance the MERO elimination ferrous ions were added to the ultrasound system, forming the sono-Fenton process. The increase in the ferrous ions concentration from 0 to 5 mg L^-1 augmented the rate of MERO degradation (k changed from 6.3 to 15.7 × 10^-3 min^-1) and diminished the electric energy consumption from 1.22 to 0.49 kWh L^-1. Afterward, the MERO treatment by the hybridized sono-photo-Fenton process (i.e., ultrasound combined with Fe²⁺ and UVA light) was evaluated, showing that the degradation efficiency was higher than by the sono-Fenton or photolysis (indeed, a synergistic index of 1.11 was obtained). Moreover, the sono-photo-Fenton process decreased the antimicrobial activity (against Staphylococcus aureus) after 30 min of treatment, indicating that the by-products did not have antimicrobial activity. The structures of primary by-products, at 50 % of MERO degradation, were elucidated through Fukui indices and LC-MS, finding that the pyrroline ring, β-lactam core, and thioether group on MERO were susceptible to the attacks of generated hydroxyl radicals (HO) and the primary transformations occurred on such moieties of the antibiotic. Finally, the treatment of MERO in synthetic hospital wastewater by the action of the sono-photo-Fenton process was assessed, degrading 36 % of MERO at 60 min of treatment. The results from this research indicated that the hybridized processes could be an alternative to be used in niche applications for treating carbapenem antibiotics even in complex matrices, transforming them into less problematic compounds.