HRT exerts a profound influence on the hydraulic conditions and contact time among different reactants within the reactor. proposed that a short HRT is favorable for aerobic microbial granulation.Nevertheless, a very short cycle time would suppress the growth of suspended solids due to frequent washout of the suspended material. cultivated aerobic granules at four different HRTs (2, 6, 12, and 24 h) and reported the differences in the characteristics of aerobic granules formed.