A rotating flat-sheet membrane bioreactor (RFMBR) was employed to start up anammox process, in comparison with a conventional membrane bioreactor (CMBR). The anammox process was successfully started up within around 16 days in both bioreactors. The particle image velocimetry (PIV) analysis showed a larger velocity gradient and a stronger shear stress on membrane surface in RFMBR than in CMBR. At the end of the experiment, the mean particle size of anammox granules achieved 899 mu m in RFMBR, while the value reached 809 mu m in CMBR, and the trans-membrane pressure (TMP) reached 4 and 16 kPa in RFMBR and CMBR, respectively. Furthermore, the scanning electron microscope (SEM) observation of the biofilm formed on membranes illustrated that a much thinner biofilm with the thickness of 35 mu m was formed in RFMBR, compared to the value of 120 mu m in CMBR. Crown Copyright (c) 2012 Published by Elsevier B.V. All rights reserved.