Combining solar photo-Fenton and magnetic activated carbon for enhanced antibiotic degradation and antibacterial activity inhibition: Application in a flow mode reactor

Antibiotic contamination in aquatic environments poses a serious risk to public health and contributes to the emergence of antimicrobial resistance. In this study, a magnetic powder activated carbon derived from pulp and paper mill sludge, combined with Fe magnetic nanoparticles (PAC-Fe), was synthesized via a one-step activation and magnetization strategy for application in a flow mode heterogeneous solar photo-Fenton system. The PAC-Fe was applied for the degradation of sulfamethoxazole (SMX) and trimethoprim (TMP) in surface water at natural pH, under natural solar irradiation. The system achieved 91 % ± 2 % removal of SMX and complete removal of TMP, after 180 min of irradiation with the degradation kinetics fitted to the BMG model. The results indicate that the hydroxyl radical (HO•) drives the degradation pathway. In ultrapure water, TMP degradation occurred mainly in solution, while SMX transformation occurred primarily on the catalyst surface. In surface water, the participation of HO• was still evident, although the dominant reaction zone could not be distinguished. The PAC-Fe catalyst exhibited satisfactory magnetic properties, enabling easy post-treatment separation and potential reuse. Transformation products (TPs) were identified for both antibiotics, one for SMX and five for TMP, mostly resulting from hydroxylation and demethylation pathways. ECOSAR predictions indicated that several of the TPs showed increased chronic toxicity. Yet, the treatment led to complete elimination of antibacterial activity for all tested bacterial strains after degradation of SMX and TMP. These results confirm the viability of PAC-Fe-based solar photo-Fenton treatment for efficient removal of antibiotics at environmentally relevant concentrations in complex water matrices.