Three-phase CFD simulation coupled with population balance equations of anaerobic syntrophic acidogenesis and methanogenesis reactions in a continuous stirred bioreactor

•CFD was applied to simulate a stirred continuous bioreactor for anaerobic digestion.•A simulation based on CFD coupled with PBE of syntrophic reactions was described.•Hydrodynamics behavior and concentration profiles of species (VFAs) were predicted.•The simulation was in good agreement with the experimental propionate concentration.

Anaerobic digestion is a sequential complex biochemical process that involves a series of reactions that are mediated by several different groups of anaerobic microorganisms. In many anaerobic digesters, syntrophic reactions are regarded as steps that limit the rate of the process. This research describes a simulation based on three-dimensional computational fluid dynamics (CFD) coupled with population balance equations (PBE) of syntrophic (acetogenesis and methanogenesis) reactions in a continuous stirred reactor. The commercial software FLUENT 6.3 was employed to solve the governing equations. A model of Eulerian multiphase and k−εk−ε turbulence (RNG) was formulated to simulate reaction zone hydrodynamics in the reactor with various influent concentrations of volatile fatty acids (VFAs) and hydraulic retention times (HRT). Concentration profiles of VFAs in the three-phase system displayed a heterogeneous flow pattern. Simulation results indicate that VFAs were degraded efficiently and the model was found to be in good agreement with results of experiments, especially at low concentrations of influent VFAs.