Coupling computational fluid dynamics and kinetic models using a compartmental model applied to a full-scale...

Area of Science:

• Environmental Engineering
• Biochemical Engineering
• Renewable Energy Systems

Background:

• Anaerobic digestion is vital for climate change mitigation but lacks full-scale hydrodynamic and biokinetic interaction studies.
• Understanding these interactions is crucial for optimizing biogas production and digester efficiency.

Purpose of the Study:

• To develop and validate a Compartmental Model (CM) for full-scale agricultural anaerobic digesters.
• To investigate the interplay between hydrodynamics and biokinetics, including the impact of mechanical agitation.
• To provide a computationally efficient alternative to Computational Fluid Dynamics (CFD) for digester modeling.

Main Methods:

• Developed a Compartmental Model (CM) by dividing a full-scale digester into compartments based on CFD velocity fields.
• Validated the CM's hydrodynamic component by comparing Residence Time Distribution (RTD) with CFD simulations.
• Integrated Anaerobic Digestion Model No. 1 (ADM1) into the CM to simulate biokinetic processes over time and space.

Main Results:

• The CM accurately predicted RTD, offering a faster alternative to CFD for hydrodynamic analysis.
• Highest biological activity (58.9% of CH4 production) occurred in the 26.8% reactor volume near the inlet, indicating high acidification risk.
• Simulations showed that systems without mechanical mixing produced more methane (CH4) but had a higher risk of acidification compared to agitated systems.

Conclusions:

• The developed CM is a powerful, computationally efficient tool for analyzing full-scale anaerobic digesters.
• The inlet region is critical for digester performance and requires careful monitoring to prevent acidification.
• Mechanical agitation influences both RTD and CH4 production, with trade-offs between yield and operational stability.