Advances in Computational Fluid Dynamics modeling of anaerobic digestion process for renewable energy production: A review

Anaerobic digestion is a widely used process for organic waste treatment and biogas production. It is a complex process involving four main biochemical reactions, four microbial groups, and hydrodynamics phenomena. Research focuses on the development of numerical models based on mass transfer and biochemical reaction kinetics, adapted to a specific waste. However, parameters such as mass transfer, fluid rheology, and temperature strongly influence the physicochemical and biological reactions. These parameters are considered in computational fluid dynamic models. In this paper, we present a critical analysis of advances in computational fluid dynamic modeling of anaerobic digesters. This review addresses the work contributions, the technologies of bioreactors as well as the meshing approaches in order to model the mechanical mixing. A detailed analysis is also presented on the evaluation of the effects of waste rheology and total solid content on the flow. Specific studies on biofilm, high anaerobic digesters, multiphase studies, coupling of biochemical and computational fluid dynamic models, turbulence modeling are addressed in this review. In conclusion, computational fluid dynamic models provide a local description of the process and constitute a promising tool to design anaerobic digestion units and optimization the anaerobic digestion process (reduction of dead zone, fluid homogenization, etc.). Thermal modeling is mainly useful in cold countries or those experiencing significant temperature variations. Few studies concern the coupling of biochemical and computational fluid dynamic models, allowing to consider both the bio-physicochemical aspects and the flow field. Future research should focus on microbiological aspects, as well as the full integration of biochemical reactions in computational fluid dynamic models.