Effect of sludge retention time on the removal of fluoroquinolone antibiotics in wastewater treatment of activated sludge

In this study, the effect of the sludge retention time (SRT) (SRT = 15 d, 20 d, 30 d) on the removal of three typical fluoroquinolone antibiotics (norfloxacin (NOR), ofloxacin (OFL), ciprofloxacin (CIP)) and the role of microorganisms in the process was investigated. The removals of fluoroquinolone antibiotics were mainly removed by adsorption under all three sludge retention times, with average removal rates of 82.87 %, 62.53 % and 70.06 %, respectively. When the initial antibiotic concentration was higher than 3 mg/L, the biomass, total extracellular polymeric substance (EPS) and PN/PS showed a decreasing trend, and the sludge activity decreased. In the sequencing batch bioreactor, the removal efficiency of OFL increased from 59.24 % to 72.99 % as the SRT increased from 15 to 30 days. In addition, prolongation of SRT increased the diversity of active microorganisms while the relative abundance of K-strategic bacteria (Nitrospira, Glutamicibacter) increased under low food-to-microorganism (F/M) ratio conditions, which played a key role in the removal of fluoroquinolone antibiotics. Biodegradation removal increased from 7.89 % to 22.18 % and adsorption/biodegradation ratio decreased from 6.51 to 2.03.