Interactive effects between tetracycline and nitrosifying sludge microbiota in a nitritation membrane bioreactor

Nitritation-related processes are often applied for the treatment of wastewater that contains high concentrations of both ammonium and antibiotics. Nonetheless, the interactions between antibiotics removal and nitritation performance are not well-known so far. Herein, two parallel lab-scale nitritation membrane bioreactors (MBRs) were operated without (reactor R1) and with (reactor R2) tetracycline (TC) for 380 days to reveal the interactive effects between TC and nitrosifying sludge microbiota. The nitritation MBR exhibited excellent removal efficiencies on TC (87.6-100%) at the environmentally relevant TC concentration (≤ 1 mg/L) but poor removal at higher TC concentration (i.e., 10 mg/L). Furthermore, batch tests indicated that adsorption was the primary TC removal route by nitrosifying sludge, although biodegradation could be strengthened after long-term exposure to TC. Initial TC removal by both adsorption and biodegradation decreased in the presence of ammonia. Meanwhile, although activity of ammonia oxidizing bacteria (AOB) was likely inhibited by high TC dosage (10 mg/L), the presence of TC did not markedly attenuate the nitritation performance and the membrane permeability. The results of 16S rRNA sequencing showed that AOB affiliated to Nitrosomonadaceae were enriched (24.2-44.5%) in the MBR. The AOB was resistant to TC at low dosage (≤ 10 μg/L), but their relative abundance was significantly decreased at a higher dosage of 100 μg/L TC and then recovered with a further elevated TC to 10 mg/L, indicating an acclimation of AOB to long-term TC exposure. Additionally, the analysis of TC resistance genes (tet) suggested that the recovery of AOB abundance was likely linked to an increase of tet(G) and the occurrence of tet(O) at 10 mg/L TC.