Computational Fluid Dynamics applied to Anaerobic Digesters

Anaerobic digestion is one of the most widespread technologies for sludge treatment, the by-product of wastewater treatment, in which a methane-rich biogas stream is produced. When scaled-up, transport phenomena become more important and the relation between full-scale flow patterns and biogas yield is still not well understood. Since the digester sludge behaves as a non-Newtonian fluid, ensuring homogeneous properties in the whole full-scale digester becomes a challenge and recent literature suggest that it might be not optimal for biogas production.

Computational Fluid Dynamics (CFD) modelling techniques allows us to develop a more in-depth understanding of full-scale systems by studying its flow field. Additionally, it enables for the first time to simultaneously study the interaction between (bio)chemical reactions and hydrodynamics. In the first part of the project, a sludge rheological mimicking fluid (Carbopol) will be used to study in-depth the mechanisms of energy dissipation in general non-Newtonian fluids. In the second part, a full-scale CFD model will be built to study the flow behaviour of an existing cylindrical digester in a Water Resource Recovery Facility (WRRF).

Within this project, special attention is paid to

1. Properly calibrating and evaluating all CFD submodels (density, viscosity, type of turbulence, etc.) for a hydrofoil mechanical mixer.
2. Evaluate the CFD model performance by comparing the results with Particle Image Velocimetry (PIV) hydrodynamic data at different locations around the impeller.

An important outcome of this project is to assess the quality of the data and to give quantitative reasons for CFD submodel selection. The project will work with OpenFOAM® (an open-source CFD toolbox) and all the results will be available in the UGent project repository (on GitHub) that will allow the users to valorise code.