•A continuous self-circulating up-flow granular sludge bed process was introduced.•Accurate self-circulating multiple times and O2 supply were driven only by aeration.•High up-flow velocity of 7–16 m/h contributed to particle formation and stability.•HRT of 10 h and DO of 0–0.3 mg/L were optimized for higher OLR and energy savings.•Self-circulation driven by aeration is key factor regulating nitrogen removal. Aerobic granular sludge (AGS) capable of nitrogen and phosphorus removal is mainly limited to the applications in sequencing batch reactors. This study introduced an innovative continuous self-circulating up-flow fluidized bed process (Zier process) using separate aeration. The process was composed of an anoxic column (Zier-A), aeration column (Zier-OO) and aerobic column (Zier-O), and was used to treat actual municipal sewage continuously for 170 days. The process achieved self-circulation of 20–32 times and an up-flow velocity within the reactor of 7–16 m/h which were accurately controlled with only separate aeration. The larger proportion of self-circulating multiple times contributed to particle formation and stability, providing hydraulic shear conditions, and screened the precipitation performance of the granular sludge (GS). Meanwhile, the dissolved oxygen (DO) of Zier-O was controlled at 0.1–0.3 mg/L, and the DO of Zier-A input water was zero. The accurate oxygen supply enhanced simultaneous nitrification and denitrification (SND) as well as short-cut nitrification and denitrification in Zier-O and improved the COD utilization rate and the nitrogen removal rate in Zier-A. The COD treatment capacity reached 2.46 kg-COD/(m³·d). With a hydraulic retention time of 10 h, the process consistently ensured that the average concentrations of ammonia nitrogen and total nitrogen in the effluent were maintained below 5 and 15 mg/L, respectively. Moreover, the process maintained the shape and stability of GS, the median diameter of GS ranged between 300–1210 μm, the percentage of mass with particle size distribution < 200 μm at a height of 150 cm within Zier-A and Zier-O accounted for as low as 0.04%–0.05%, and showed good settling performance. The suspended solids in effluent can be maintained at 50–80 mg/L. Overall, the unique structural setting and control method of the Zier process provide another approach for the application of continuous AGS treatment for municipal sewage. Display omitted