The physical characteristics of denitrifying granular sludge and their granulation mechanism were investigated in two denitrifying reactors (R1 and R2). The results showed that the denitrifying granular sludge was streamlined in shape with the aspect ratio (AR) of 0.62 +/- 0.05, large in size with the diameter of 2.39 +/- 0.05 mm, and fast in settlement with the average settling velocity (VS) of 126.36 +/- 13.32 m/h at the nitrate loading rate (NLR) of 35.14 +/- 0.38 kg/(m(3) d). The dominance of denitrifying granular sludge with good settleability was attributed to the enhanced growth of granular sludge by extracellular polymers (EPS) and the shaping of granular sludge by shear force. (C) 2013 Elsevier Ltd. All rights reserved.