Impacts of exogenous C6-HSL on the enhanced cometabolic removal of sulfadiazine by enriched nitrifying sludge

Abstract

The antibiotics in the wastewater could be effectively removed by the cometabolism of nitrifying sludge mediated by ammonia monooxygenase (AMO). The effects of quorum sensing (QS) system regulated by N-acyl homoserine lactones (AHLs) on the performance and functional microorganisms in wastewater treatment have also been increasingly reported, yet few studies report the impacts of AHLs on the cometabolic removal of antibiotics by nitrifying bacteria. In this study, N-hexanoyl-L-homoserine lactone (C6-HSL) and sulfadiazine (SDZ) were selected, and a series of batch tests were implemented to study the cometabolic degradation of SDZ by enriched nitrifying sludge and the responses of the sludge under different concentrations of exogenous C6-HSL (0.1, 0.5 and 1 μM). The results indicated C6-HSL enhanced the cometabolic removal of SDZ by nitrifying sludge, with the highest removal efficiency of 84.60 % achieved with 1 μM C6-HSL. The extracellular polymeric substances (EPS) increased by 50.8 %–139.5 %，and a positive correlation between the increase of protein content in EPS and the concentration of C6-HSL was established. C6-HSL also brought an increase in cellular adenosine triphosphate content, which increased by 51.8 % with 1 μM C6-HSL. Moreover, C6-HSL up-regulated the amoA gene and enhanced AMO activity, which led to the sufficient degradation of SDZ.