The effects of zero-valent iron (ZVI) and ferroferric oxide (Fe3O4) on anammox activity and granulation in anaerobic continuously stirred tank reactors (CSTR)

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 μm and 988.5 μm 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.