The purpose of this study is to investigate the nitrogen removal performance of the anaerobic ammonium oxidation (Anammox) process and the microbial community that enables the Anammox system to function well at ambient temperatures. A reactor with a novel spiral structure was used as the gas-solid separator. The reactor was fed with synthetic inorganic wastewater composed mainly of NH(4)(+)-N and NO(2)(-)-N, and operated for 92 days. Stable nitrogen removal rates (NRR) of 16.3 and 17.5 kg-N m(-3) d(-1) were obtained at operating temperatures of 33 +/- 1 and 23 +/- 2 degrees C, respectively. To our knowledge, such a high NRR at ambient temperatures has not been reported previously. In addition, the experiments presented herein confirm that high influent NO(2)(-)-N concentration of 460 mg L(-1) did not noticeably inhibit the Anammox activity. Furthermore, the freshwater Anammox bacterium KU2, which was identified as the dominant bacterial species in the consortium by 16S rRNA gene analysis, is considered to be responsible for the stable nitrogen removal performance at ambient temperatures. (C) 2010 Elsevier Ltd. All rights reserved.