A novel funnel-shaped internals was proposed to enhance the stability and pollutant removal performance of an aerobic granular process by optimizing granule size distribution. Results showed up to 68.3 +/- 1.4% of granules in novel reactor ( R1) were situated in optimal size range ( 700-1900 mu m) compared to less than 29.7 +/- 1.1% in conventional reactor ( R2), and overgrowth of large granules was effectively suppressed without requiring additional energy. Consequently, higher total nitrogen ( TN) removal ( 81.6 +/- 2.1%) achieved in R1 than in R2 ( 48.1 +/- 2.7%). Hydraulic analysis revealed the existence of selectively assigning hydraulic pressure in R1. The total shear rate ( tau(total)) on large granules was 3.07 +/- 0.14 times higher than that of R2, while tau(total) of small granules in R1 was 70.7 +/- 4.6% in R2. Furthermore, large granules in R1 with intact extracellular polymeric substances ( EPS) outer layer structure entrapped hydroxyapatite at center, which formed a core structure and further enhanced the stability of aerobic granules. (C) 2016 Elsevier Ltd. All rights reserved.