CFD Simulation of Integrated Physical and Biological Processes for Anaerobic Digestion

An extensive investigation of anaerobic methane fermentation requires identifying the relationship between physical environment and biological process. A computational fluid dynamics (CFD) based mathematical model was developed to characterize mixing and heat transfer coupled with biochemical reaction kinetics for anaerobic methane fermentation. The transient biological process was solved based on steady physical process, in which a computational cell was physically treated as an individual bioreactor with its own residence time and temperature. The CFD method was validated against two experiments available from the literature. An examination of mixing in a complete-mix digester indicates that the methane production remains almost unchanged while the energy efficiency decreases with increasing mixing power. A quantitative analysis of heat transfer in the digestion process of a plug-flow digester demonstrates that the energy output increases nonlinearly with the increase in heating energy within a limited temperature range. The CFD simulation platform is generic and may be applicable to the study of biohydrogen fermentation and other bioenergy sources.