In this study, the anammox consortium was found to adapt to the wastewater containing dissolved oxygen (DO), as the DO was gr\adually increased. Batch tests indicated the maximum aerobic ammonium oxidizing activity of the consortium was 1.38 mmolNH(4)(+) -N(g VSS)(-1) day(-1), which played key roles in the oxygen consumption process; the maximum anaerobic ammonium oxidizing activity was slightly decreased after long-term oxygen exposure, but only from 21.23 mmolNH(4)(+)-N(g VSS)(-1) day(-1) to 20.23 mmolNH(4)(+)-N(g VSS)(-1) day(-1). Microbiological community analysis identified two strains similar to Nitrosomonas eutropha were responsible for oxygen consumption. which were able to exist in the autotrophic anaerobic condition for long periods and protect anammox bacteria Planctomycetales from the influence of oxygen. Microbiological composition analysis showed Nitrosomonas and Planctomycetales approximately accounted for 10% and 70% of the bacteria, respectively. The possibility of cultivation anammox consortium in presence of DO will lead to substantial savings of energy and resource in the industrial application. (c) 2008 Elsevier Ltd. All rights reserved.