Effect of norfloxacin on performance, microbial enzymatic activity and microbial community of a sequencing batch reactor

Abstract

Abstract The performance, microbial community and enzymatic activity of a sequencing batch reactor have been assessed under norfloxacin stress. The COD removal was restrained at 5-30 mg/L norfloxacin, whereas there was a slight inhibition on the NH 4 + -N removal at 30 mg/L norfloxacin. The effluent NO 3 − kept an increasing trend under norfloxacin stress. The oxygen uptake rate, nitrifying rate and denitrifying rate of activated sludge maintained the decreasing trend with the increase of norfloxacin concentration from 0 to 30 mg/L. The variation tendencies of microbial enzymatic activity interrelated with nitrogen transformation was similar to the corresponding nitrifying rate and denitrifying rate under norfloxacin stress. The existence of norfloxacin promoted the extracellular polymeric substances (EPS) production, reactive oxygen species generation and lactate dehydrogenase release of microorganisms in activated sludge due to the potential biotoxicity of norfloxacin. The protein and polysaccharide contents of loosely bound EPS (LB-EPS) and tightly bound EPS (LB-EPS) maintained an increasing trend with the increase of norfloxacin concentration. The chemical composition of EPS was also impacted under norfloxacin stress. The microbial diversity and richness displayed some distinct differences at different norfloxacin concentrations.