New insights into antibiotic stimulation of methane production during anaerobic digestion

Residual antibiotics in swine wastewater pose a critical challenge for stable anaerobic digestion (AD). This study offers fresh insights into the anaerobic treatment of swine wastewater. The results showed that the presence of three typical antibiotics (sulfamethoxazole (SMX), oxytetracycline (OTC) and ciprofloxacin (CIP)) in swine wastewater could promote methane production by stimulating the production and conversion of ethanol. Among them, SMX exhibited the strongest methane promotion effect, with the cumulative methane production increasing from 138.47 to 2204.19 mL/g VS. According to the microbial community structure, antibiotics could promote the growth of Corynebacterium, Lutispora and hydrogenotrophic methanogens (Methanosassiliicoccus, Methanobrevibacter, and Methanobacterium), but inhibit the enrichment of acetoclastic methanogen (Methanosaeta). The relative abundance of Methanosaeta decreased from 2.93-19.80% to 0.52-2.58% under antibiotic stress. Furthermore, there were significant differences in the influence of different antibiotic types on methanogenic pathways. Specifically, OTC and CIP promoted the acetoclastic and hydrogenotrophic pathways, respectively, to enhance methane production. However, SMX could promote both acetoclastic and hydrogenotrophic pathways.