Enhanced resistance to ciprofloxacin stress in integrated floating film activated sludge system filled with surface-modified carriers for simultaneous nitrification and denitrification

Abstract

While the effectiveness of integrated floating film activated sludge (IFFAS) system filled with surface-modified carriers has been demonstrated in promoting simultaneous nitrification and denitrification (SND) performance, the effect of antibiotic stress on this system remains unexplored. Herein, this study investigated the stress response of SND in IFFAS under short- and long-term exposure to ciprofloxacin (CIP), a commonly used antibiotic. Results indicated the significantly higher semi-inhibitory concentration of CIP in the IFFAS system with modified carriers (36.54 mg/L) than that in IFFAS with conventional high density polyethylene (HDPE) carriers (28.77 mg/L). IFFAS system with modified carriers exhibited improved resistance to CIP toxicity compared to IFFAS using HDPE carriers or conventional activated sludge under long-term exposure to CIP concentrations from 50 to 3000 μg/L. The surface-modified carriers demonstrated a multifaceted strategy to mitigate the inhibitory effects of CIP, such as enhancing production of extracellular polymeric substances (EPS) to serve as a potential protective barrier against CIP toxicity, the less suppression of key enzyme activities involved in nitrogen removal, as well as inducing the upregulation of antibiotic resistance genes (ARGs) (qepA, qnrB/C) and the integrase gene (intI1) to enhance target prevention and efflux pumping mechanisms for resistance to CIP. These findings collectively underscored the efficacy of modified carriers in attenuating CIP toxicity within the SND system.

Graphical abstract

Keywords

Simultaneous nitrification and denitrification (SND) / Ciprofloxacin / Modified carrier / Resistance / Extracellular polymeric substances (EPS)

Highlight

	● Modified carriers promoted SND resistance to CIP stress with IC50 of 36.54 mg/L.
	● Modified carriers induced more EPS to trap CIP to mitigate the toxicity.
	● Activities of AMO, NXR, NAR, and NIR were less suppressed on modified carriers.
	● Target preventing and efflux pumping were the main mechanisms to resist CIP.

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