Acute exposure effects of tetracycline, ampicillin, sulfamethoxazole, and their mixture on nutrient removal and microbial communities in the activated sludge of air-scouring and reciprocation membrane bioreactors

The fate of antibiotics, their effects on non-target species, and the spread of antibiotic resistance in wastewater treatment systems have been of concern in recent years. Despite its importance, the effects of these antibiotics on biological nutrient removal in WWTPs have not been completely elucidated. To evaluate the effects of antimi-crobial compounds on nutrient removal performance and microbiome, batch experiments were performed using activated sludge samples taken from two distinct membrane bioreactor systems (reciprocation MBR vs. air-scouring MBR). We exposed the activated sludge to 0 mg/L, 0.1 mg/L, and 1.0 mg/L of tetracycline (TET), ampicillin (AMP), sulfamethoxazole (SUL), and their mixture. The mixture of antibiotics significantly decreased ammonia removal efficiency in the reciprocation MBR (rMBR) and air-scouring MBR (AS MBR) by 5% and 12%, respectively. A significant reduction (p < 0.05) in the amoA-AOB gene was observed in AS MBR, while this gene remained unaffected in the rMBR. Interestingly, the gene abundance of amoA from comammox Nitrospira increased from 2.8 x 108 gene copies per gram sludge (0 mg/L) to 5.0 x 108 gene copies per gram sludge (1.0 mg/L) in the setup with antibiotics in the mixture. Correlation analysis of the relative abundance of prevalent taxa and antibiotic concentrations showed that the microbial communities of the AS MBR were more susceptible to TET and MXD antibiotics than the rMBR microbiome.