Inhibition of norfloxacin on anaerobic digestion: Focusing on the recoverability and shifted microbial communities

Antibacterial properties of norfloxacin (NOR) could cause adverse impact on engineered biological process. In this study, the objective was to investigate the inhibitory effects of NOR on anaerobic digestion focusing on the recoverability and microbial community changes. The effects of different concentrations of NOR on anaerobic digestion were studied with three continuous feed cycles. Results showed that NOR seriously inhibited the methane production with an 50% inhibitory concentration (IC 50 ) of 0.41 mM. In addition, with extending of exposure time, inhibitory effect increasingly strengthened and the IC 50 values decreased to 0.16 mM and 0.07 mM in the second and third feeding cycle, respectively. However, when the inhibitor in supernatant was removed, the performance recovered and the relative methane yield increased by 9 times from 25.38 mL/g VS to 257.05 mL/g VS. The transformation of NOR showed that the degradation of NOR in the anaerobic digestion was difficult and the recovery was due to the removal of NOR. The microbial analysis revealed that the inhibition of NOR on bacteria of Candidatus _ Cloacimonas , Petrimonas , Ercella , Sphaerochaeta and hydrogenotrophic methanogens of Methanoculleus and Methanobacterium was recoverable when NOR was removed. However, it was irreversible for acetoclastic methanogen of Methanosaeta . These findings provided comprehensive understanding on the characteristics of NOR inhibition and also provided feasible strategy to recover the NOR inhibited anaerobic digestion.