The anammox granules with Fe and Fe3O4 as cores were successfully obtained in anaerobic continuously stirred tank reactors (CSTR) in this study. The sizes [d(0.5)] of Fe-anammox and Fe3O4-anammox granules successively arrived to 417.3 mu m and 988.5 mu m on the 39th and 72nd day, corresponding to the specific anammox activity (SAA) of 0.24 and 0.239 kgN kgVSS(-1) d(-1), respectively. The SAA of blank-anammox granule was stable (about 0.20 kgN kgVSS(-1) d(-1)) in the whole study. The anammox granulation mechanisms of common anammox granule (blank-anammox granule) and Fe-anammox/Fe3O4-anammox granule were extracellular polymers (ECP) bonding model and ion-bonding model, respectively. Results showed that the optimal oxidation-reduction potential (ORP) of anammox bacteria was 209 mV. The reasonable concentration of Fe2+ and Fe3+ was beneficial to the granulation and activity of anammox bacteria by maintaining high ORP and gathering acylhomoserine lactones (AHLs). The quorum sensing (QS) material of anammox bacteria was identified as N-dodecanoyl homoserine lactone by LC-MS. (C) 2014 Elsevier Ltd. All rights reserved.