Chlorotetracycline-driven modulation of substrate utilization and metabolic traits in sludge anaerobic fermentation for optimized methane production

Anaerobic digestion (AD) is a highly efficient and promising method for treating waste activated sludge (WAS). Nevertheless, the presence of chlortetracycline (CTC) in WAS introduced uncertainty into the AD process. This study revealed that   the cumulative methane yield was increased by 27.5 % with the CTC concentration at 50 mg/kg dry sludge by enhancing hydrolysis, acidification and methanogenesis during which specific microbial communities were enriched and related functional genes were enhanced. Subsequent investigations found   the accumulation of extracellular polymeric substances (EPS) was improved and methane-producing microorganisms (e.g., Bacteroidetes and Euryarchaeota ) were also enriched under CTC exposure. Metagenomic analysis further elucidated that   CTC significantly increased functional genes related to bacterial secretion system and metabolism of organic matter for methane production (e.g., pyruvate metabolism and methane metabolism). This study shed light on the substantial impact of CTC on the AD of WAS and provided a promising strategy for improvements in anaerobic fermentation.