The short- and long-term effects of Mn2+ on the performance of anaerobic ammonium oxidation (anammox) granules were investigated in the present study. Anammox activity was determined at various Mn2+ concentrations in batch assays, and the 50% inhibition concentration value was determined to be 7.33 mg L-1. However, no obvious deterioration of reactor performance was observed during the 150-day continuous-flow operation, and the nitrogen removal efficiency of the test reactor (R-1) fluctuated between 91% and 92% as the Mn2+ concentration was increased from 1 to 200 mg L-1. Additionally, the specific anammox activity, heme c content and the amounts of extracellular polymeric substances in the anammox biomass increased and then subsequently decreased. The results demonstrated that short-term exposure to Mn2+ has a negative effect on anammox biomass, but the biomass could tolerate Mn2+ stress after acclimation to a high concentration of 200 mg L-1 at the end of the continuous-flow experiment. (C) 2017 Elsevier Ltd. All rights reserved.