• • High upflow velocity (3.00–6.30 m·h−1) under stepwise OLR increase (0.300–1.000 kg COD·m−3·d−1) achieved PSB granulation within ~60 d, yielding average granule size of 285.58 μm and SVI of 22.73 mL·g−1, indicating superior settleability and potential for efficient biomass retention in continuous-flow reactors.
• • Hydraulic shear stress specifically induced secretion of hydrophobic tryptophan-like proteins and humic acids in EPS, which are critical for cell adhesion and granule structural integrity, as confirmed by 3D-EEM analysis.
• • High upflow velocity enriched functional microbial populations, particularly Xanthobacteraceae, known for stress tolerance and EPS production, enhancing system stability and granule compactness under high organic loading.
• • The synergistic control of hydraulic selection and organic loading offers a practical operational strategy to overcome PSB washout, enabling stable treatment of high-strength organic wastewater (COD up to 3000 mg·L−1) with resource recovery potential.