Effects of Tetracycline on Nitrification: Nitrogen Removal Performance and the Microbial Community

To investigate the effect of tetracycline on the nitrogen removal performance, extracellular polymeric substances (EPSs), and microbial community composition, four sequencing batch reactors (SBRs) were operated at tetracycline concentrations of 0 mg L⁻¹, 5 mg L⁻¹, 20 mg L⁻¹, and 35 mg L⁻¹ (R_CK, R₅, R₂₀, and R₃₅, respectively). The results showed that nitrogen removal decreased with increasing tetracycline concentration. However, the production of EPSs was significantly increased. More importantly, tetracycline significantly altered the microbial community structure in the nitrification process. Specifically, tetracycline exposure significantly decreased the abundance of both Nitrosomonas and Nitrospira. Additionally, Nitrosomonas has a stronger resistance to tetracycline than Nitrospira, resulting in a nitrite accumulation in ammonia oxidation at tetracycline concentrations of 5 mg L⁻¹ and 20 mg L⁻¹. This work provides useful information for an advanced understanding of the tetracycline pollution in biological nitrogen process.