Hydrodynamics and permeability of aerobic granular sludge: The effect of intragranular characteristics and hydraulic conditions

Aerobic granulation technology has been widely investigated for its efficient treatment of municipal and industrial wastewater. The efficiency and stability, which are affected by the permeability and forces on granule surface, are both crucial to its full scale application. In this work, the structural and hydrodynamic characteristics of the granules were investigated using experimental approach and numerical simulations. Aerobic granule was considered to be a porosity sphere composed of smaller particles. Mixture model in FLUENT was used for gas-liquid two-phase flow simulation, and the phase resistance was calculated using schiller-naumann function. The influence of gas holdup and granule size on the surface force was simulated and the results show that the shear stress increases with the gas holdup, while the granule size has little effect on the surface force. Using the computational fluid dynamics (CFD) numerical model, it was demonstrated that the convection path lines for the granules colored by the velocity magnitude increase with the Reynolds number and the primary particle diameter. The model also indicated that improving the permeability of a granule can reduce the total pressure on the granule surface, but it has less effect on the strain rate. In addition, a new simulation was developed to evaluate the fluid collection efficiency, which proved to be in good agreement with the results determined by formulas and experiments. (C) 2016 Elsevier B.V. All rights reserved.