Nitrifying sludge system is a promising alternative for the removal of numerous antibiotics, however the impacts of combined exposure of antibiotics on nitrifying sludge system remain poorly understood. In this study, the impacts of individual and combined exposure of sulfamethoxazole (SMX) and cephalexin (CFX) on nitrifying sludge performance were investigated. Nine sequencing batch reactors were operated for 21 days under three concentration gradients (0.2, 2, and 10 mg/L). The results demonstrated a significant, dose-dependent decline in nitrification efficiency: ammonium nitrogen (NH4⁺–N) removal rates decreased to 73% and 61.2% under 10 mg/L individual and combined exposures, respectively ( p 92% reduction in amoA relative abundance. Antibiotic degradation efficiency also declined dramatically under the combined exposure of high antibiotic concentrations due to the inhibition of AOB, although resistant heterotrophs known to efficiently degrade antibiotics were enriched. The propagation of antibiotic resistance genes (ARGs) was caused by both horizontal gene transfer and the enrichment of potential hosts. Overall, this study elucidates the influence mechanism of combined antibiotic stress on nitrifying sludge systems.
Zhu et al. (Sat,) studied this question.
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