The short-term effects of Cu(II) on the Anaerobic Ammonium Oxidation (Anammox) process were evaluated using batch tests. The IC50 of Cu(II) on Anammox mixed culture was 12.9 mg L-1. The long-term effects of Cu(II) on the Anammox process were examined in two upflow anaerobic sludge blanket reactors, a test reactor (R-1) and a control reactor (R-0). The performance of R-1 was strongly inhibited by Cu(II) at a concentration of 5 mg L-1 with a specific Anammox activity of 0.9 mg TN g(-1) volatile suspended solids h(-1), which corresponded to a 94% loss in activity. Without Cu(II) addition, the recovery phase of R-1 was consistent with the typical characteristics seen in an Anammox process startup, with a good fit to both the modified Boltzmann model (R-2 = 0.9860) and the modified Stover-Kincannon model (R-2 = 0.9701). Maintaining the influent Cu(II) at a low level of no more than 4 mg L-1 was necessary for preventing the copper inhibition. (C) 2013 Elsevier B.V. All rights reserved.