The rheological behaviors of the anaerobic granular sludge (AGS) in a spiral symmetry stream anaerobic bioreactor (SSSAB) were investigated. Shear-thinning behavior, thixotropic behavior, concentration–viscosity behavior and temperature–viscosity behavior were evaluated based on the constitutive equation of the AGS. The results indicated that the Herschel–Bulkley model was able to adequately describe the constitutive relation of AGS in the SSSAB. The AGS also showed shear-thinning behavior as well as thixotropic behavior. The critical shear rate and network strength of the AGS were 61.8 s−1 and 497.0 W m−3, respectively. The relationship between the apparent viscosity and the sludge concentration was illustrated and explained by the Woodcock formula. The relationship between apparent viscosity of the AGS and temperature could be modeled using the Arrhenius equation. The AGS was significantly thermo-sensitive and its mean energy of activation was 14.640 kJ mol−1. Notably, it was necessary to consider such behaviors in the hydrodynamic modeling of SSSAB in which shear condition, sludge concentration and temperature were in non-uniform distribution.

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