Anaerobic biodegradation of ceftriaxone: Transformation pathways, toxicity assessment, and microbial mechanisms

The overuse of ceftriaxone has resulted in its widespread occurrence in aquatic environments, posing ecological and health risks. An anaerobic membrane bioreactor (AnMBR) was operated for 128 days to systematically investigate the anaerobic microbial transformation of CTX. The AnMBR exhibited stable and efficient performance, maintaining chemical oxygen demand removal above 90% and achieving an average CTX removal efficiency of 65.0 ± 15.2%. Several potential degradation pathways are proposed, involving β-lactam ring hydrolysis, C-S bond cleavage, and decarboxylation reactions. Toxicity assessments using ADMETlab 3.0 platform reveal that although most TPs showed reduced ecotoxicity and dermal toxicity compared to the parent compound, several intermediates exhibited elevated risks of nephrotoxicity and genotoxicity. Metagenomic analysis indicates that long-term CTX exposure reshaped the microbial community, enriching methanogens such as Methanothrix soehngenii and Methanosarcina mazei, though these taxa might not directly participate in CTX degradation. Several archaeal and bacterial MAGs carrying functional genes, including lactam hydrolase, thioesterase, and decarboxylase, were identified, suggesting a collaborative and functionally diverse microbial network involved in CTX transformation. This study offers mechanistic insights and technical foundations for advancing anaerobic biotechnologies in the treatment of antibiotic-contaminated wastewater, while highlighting the need for ongoing monitoring of potential long-term risks associated with TPs.