Long-Term Inhibition of the Antibiotic Oxytetracycline on an Upflow Low-Matrix Anammox Biofilter

Abstract

The long-term effects of the antibiotic oxytetracycline (OTC) on the process of anaerobic ammonium oxidation (anammox) were studied in an upflow low-matrix anammox biofilter. When OTC was increased to 40 mg/L, the nitrogen removal rate (NRR) reduced from 0.536 to 0.395 kg/(m³·day), and then decreased further with OTC concentration. Although extracellular polymeric substances (EPS) increased from 36.3 to 177.6 mg/g of suspended solids, this was insufficient to resist the toxicity of OTC to anaerobic ammonia-oxidizing bacteria (AAOB). The total nitrogen removal efficiency decreased from the initial 85.2% to 17.3%, and the relative abundance of AAOB decreased from 16.40% to 9.35%. When the OTC concentration exceeded 40 mg/L, some microorganisms died, which led to a decrease in EPS, but an increase in soluble microbial products. The relative abundance of AAOB decreased from 16.40% to 4.6% when the OTC concentration reached 90 mg/L, and remained at 4.8% when OTC was no longer added. The anammox process could not be recovered during the four generation cycles after OTC addition ceased. The IC₅₀ of OTC toward the NRR of the anammox process was calculated to be approximately 10.47 mg/L.