Energy recovery from corn straw-based biochar@MIL-88A(Fe)-mediated anaerobic digestion of waste activated sludge under norfloxacin: Metabolism and antibiotic resistance gene fates.

Norfloxacin (NOR), a commonly detected antibiotic in waste activated sludge (WAS), remains understudied in anaerobic digestion (AD). This study investigated the effect of NOR on WAS AD, with corn straw-based biochar modified with MIL-88A(Fe) (BM) added to enhance energy recovery during digestion. Accumulated methane production was inhibited by 41.86 % in the BM-mediated digestion system under 1 mg/L NOR. Moreover, NOR induced the build-up of volatile fatty acids (VFAs), hindering methanogenic pathways subsequently. Microbial community structure was altered, with an enrichment of bacteria responsible for NOR degradation and a 13.20 % reduction in the abundance of hydrogenotrophic methanogens under antibiotic stress. Methanogenesis was inhibited with the expression of related genes and enzymes suppressed. The high enzymatic activities of cytochrome P-450 (CYP450) and acetate kinase contributed to the high NOR biodegradation efficiency (88.79 %). Twelve typical antibiotic resistant genes (ARGs) types, including multidrug, aminoglycoside, macrolides (MLs), etc., were examined in the AD system. The total abundance of ARGs type and subtype increased under NOR addition, implying ARGs removal was inhibited by NOR stress. Resistance to NOR exposure was primarily associated with antibiotic efflux and alterations in antibiotic target. Horizontal gene transfer (HGT) and vertical gene transfer (VGT) were the mechanistic routes for ARG evolution, with HGT inhibited and VGT promoted following NOR addition. The dominant genus Acinetobacter was the potential host for nearly all ARGs. This study advanced understanding of the impact of NOR on WAS digestion with BM mediation, providing new insights for optimizing WAS digestion.