The robustness of ANAMMOX process under the transient oxytetracycline (OTC) shock

•The ANAMMOX performance under transient OTC stress was investigated.•The factors influencing the stability were evaluated.•The changes in sludge characteristics were provided.•The indicators for robustness and recovery performance were addressed. The effect of transient oxytetracycline (OTC) shock on the stability of anaerobic ammonium oxidation (ANAMMOX) process was evaluated in the present study. The shock test was implemented with 155–1731mgL−1 OTC, lasting for 1 to 3-fold hydraulic retention times, under the nitrogen loading rate (NLR) of 6.72 and 13.4kgm−3d−1. The response of the process was divided into shock and recovery stage and the performance under the stress was indicated by stability index and granule characteristic. In the shock period, nitrogen removal rate (NRR) was ranged from 12.1 to 12.1–4.04kgm−3d−1. The specific ANAMMOX activity (SAA) and heme c content, were respectively reduced by 1.4% and 17.6–29.4%. Foremost, the OTC shock was restorable and the recovery lasted for 4–353h. The robustness of ANAMMOX process was dependent on OTC level, duration of shock and NLR applied.