Modeling and analysis of particle behavior in fluidized bed bioreactors during non-Newtonian sewage treatment

The stability of biofilms attached to support particles plays a crucial role in fluidized bed bioreactors (FBBRs) when treating non-Newtonian sewage. Biofilm instability is governed by particle-particle (P-P) and particle-wall (P-W) collisions. This paper presents a numerical study of particle behavior in a FBBR using a combined approach of computational fluid dynamics (CFD) and discrete element method (DEM) tailored for non-Newtonian flow systems. Following validation, the CFD-DEM model is utilized to quantify the FBBR performance regarding bed expansion, void fraction distribution, and P-P/W interactions. The impacts of three variables are examined, including sewage superficial velocity and two rheological properties, i.e., sewage temperature and solid concentration. The results reveal that increasing sewage superficial velocity and sewage solid concentration or decreasing sewage temperature, leads to a transition in particle flow from symmetrical to asymmetrical in the radial direction, along with a circulating flow at the lower part of the bed. The relationships between the variables and the bed expansion, uniformity, and P-P/W interactions are also established, identifying optimum conditions to enhance bed uniformity and reduce P-P/W interactions. Overall, the findings demonstrate the value of the CFD-DEM model for understanding, designing, and optimizing FBBRs.