Modeling Composting Processes with Local Equilibrium and Local Non-Equilibrium Approaches for Water Exchange Terms

Abstract

A composting model including reactive transfers and biological reactions, and taking into account the drying phenomena, has been developed at the Darcy scale. The model is implemented under COMSOL Multiphysics® and different local equilibrium and non-local equilibrium approaches are evaluated to simulate drying phenomena. The two numerical approaches appear to be equivalent under conditions leading to local-equilibrium but the local non-equilibrium model has been preferred for the simulations because it allows for shorter calculation times and easier implementation. Tests carried out with this formulation point out the importance of drying in the control of organic matter biodegradation as well as its effect on gas composition. Therefore, the major conclusion of this study is that drying phenomena must be taken into account in composting models.

Keywords:

• Composting
• Drying
• Local non-equilibrium
• Modeling
• Porous media