Understanding the kinetics of antibiotic mixture biotransformation and microbial interactions in an anaerobic...

The increase of antibiotics in aquatic environments, along with the emergence of antibiotic-resistant bacteria, highlights the improvement of wastewater treatment technologies. This study investigates a plug-flow structured anaerobic fixed-bed reactor (PF-AnFBR) for removal nine antibiotics representing different classes-an approach rarely explored in anaerobic systems. By integrating spatially resolved sampling along the reactor bed with advanced kinetic modeling, the study provides the first mechanistic evaluation of antibiotic mixture removal in a PF-AnFBR. COD removal remained high (COD > 97%) despite the presence of antibiotics, and significant removal was observed for trimethoprim (100%), sulfamethoxazole (83.3%), and enrofloxacin (81.3%). The first-order model accurately described COD removal, while the reversible biotransformation model (RevBio) successfully captured antibiotic fate (NRMSE < 3.5%), revealing class-specific mechanisms: fluoroquinolones dominated by adsorption (high K_D and k_sor), sulfonamides exhibiting reversible biotransformation, and trimethoprim characterized by highly irreversible biotransformation. Microbial community and KEGG-based functional analyses identified key taxa (e.g., Pseudomonas, Lactivibrio, Syntrophorhabdus, Methanothrix) and metabolic pathways (ABC transporters, cytochrome P450 enzymes) responsible for antibiotic transformation. By coupling reactor hydrodynamics, kinetic modeling, and microbial ecology, this study provides novel mechanistic insight into the removal of complex antibiotic mixtures in anaerobic fixed-bed reactors and supports PF-AnFBR as a robust technology for decentralized wastewater treatment.