The granulation of Anammox sludge plays an important role in improving the efficiency of high-rate Anammox bioreactors. The present study involved the use of anaerobic granular sludge to start up the Anammox process to accomplish granulation in Anammox reactor. The accumulation of nitrogen gas and subsequent slugging behavior were observed in the upflow Anammox granular sludge bed (AGSB) reactor, resulting in deteriorated effluent quality. Based on shear force analysis of the gas column under the quasi-steady state, the liquid-induced shear force was increased by progressively shortening of hydraulic residence time (HRT) and implementing effluent recycling. it appeared to be the right strategy to eradicate the slugging behavior which disappeared completely when HRT was shortened to 1.10 h with liquid upflow velocity of 1.30 cm min(-1). The application of high shear stress enhanced the nitrogen removal performance to 15.40 kg-N m(-3) d(-1). Thus the amendments in the liquid-induced shear force by shortening HRT may be an appropriate strategy to overcome slugging behavior of the Anammox reactor. (C) 2009 Elsevier B.V. All rights reserved.