Acidic hydrothermal pretreatment enhances anaerobic digestion of spiramycin fermentation residue while reducing antibiotic resistance risks

To enhance the anaerobic valorization of spiramycin fermentation residue (SFR) while reducing the potential for antibiotic resistance dissemination, this study coupled acidic hydrothermal pretreatment with mesophilic anaerobic digestion and systematically evaluated methane production, organic matter transformation, microbial communities, antibiotic resistance genes (ARGs), and mobile genetic elements (MGEs). Acidic hydrothermal pretreatment advanced the methane production peak by approximately 4–6 d and increased the 30-d cumulative methane yield from 350 to 480 ml/g VS, corresponding to an increase of 37.14%. In the Pret group, the peak volatile fatty acid (VFA) concentration and acetate proportion reached 591 mg/L and 74.7%, respectively. Pretreatment also promoted the release and subsequent degradation of extracellular polymeric substance (EPS) proteins and polysaccharides and reshaped the fluorescence composition of dissolved organic matter (DOM). Microbial community analysis showed that pretreatment altered bacterial and archaeal succession and increased the relative dominance of acetoclastic methanogens such as Methanothrix . Over 30 d, ARGs and MGEs in the Pret group decreased by 95.23% and 99.66%, respectively, and their final abundances were 99.44% and 99.52% lower than those in CK. Overall, acidic hydrothermal pretreatment enhanced SFR anaerobic energy recovery and resistance-risk control by promoting organic matter release and transformation, reshaping microbial communities, and concurrently reducing ARGs and MGEs.