The presence of chlortetracycline (CTC) in swine wastewater poses a threat to anaerobic treatment and ecological safety. This study investigated the concentration-dependent effects of CTC on methanogenesis, microbial properties, and antibiotic resistance genes in an anaerobic ceramic membrane bioreactor (AnCMBR). Batch assays identified a biological inhibition threshold at 50 mg/L CTC. During long-term operation, CTC at 10 mg/L (after a brief adaptation) increased methane yield by 28%, while 50 mg/L CTC inhibited methanogenesis and reduced COD removal from 97% to 86%. High-level CTC raised antibiotic resistance gene abundance and decreased acute toxicity removal from 68% to 46%. Biodegradation dominated CTC removal, but its contribution declined from 42% to 19% as CTC increased, lowering overall removal from 60% to 30%. Metagenomic analysis revealed that low-level CTC upregulated hydrolysis/fermentation-related genes (e.g., enolase, phosphoglycerate mutase, pyruvate kinase), enhancing substrate supply for methanogenesis. In contrast, high-level CTC markedly enriched Spirochaetes (from 3% to 66%), suppressed key methanogenic genes involved in methyl-CoM reductase and downstream acetyl-CoA metabolism, while preserving acetoclastic pathway genes (acsS1.2, ackA, pta), collectively shifting the pathway toward acetoclastic methanogenesis. Notably, the AnCMBR maintained stable filtration performance, with the transmembrane pressure remaining below 6.5 kPa over 160 days. These findings demonstrate that low CTC levels can be tolerated after acclimation, whereas high CTC stress severely impairs methanogenesis, detoxification, and biosafety.
Zhang et al. (Sat,) studied this question.