Practical and Theoretical Aspects of Engineering Modeling of Anaerobic Digestion for Livestock Waste Utilization Systems

Abstract

ABSTRACT MATHEMATICAL representation and engineering modeling of methane fermentation are essential to the understanding and application of anaerobic digestion systems for waste management in animal production operations. The most important parameter necessary in determining the economic feasibility and practical application of these systems is the energy yield which can be expected from a given waste type and amount. Biological processes are quite difficult to represent mathematically due to the wide range of behavior encountered in bacterial cultures. These factors have made steady-state predictions the state-of-the-art. It is important, however, to recognize that steady-state predictions are of little value in practical terms, because these processes never operate at steady-state. When fermentation systems fail, they are not at steady-state. Failure, by definition, is a dynamic or transient state. Models which predict steady-state conditions are therefore of limited value when studying the dynamic conditions encountered in animal production operations. The practical and theoretical aspects of developing a validated dynamic, computer-based, predictive model of methane fermentation for all four major animal wastes are described. The development of a model of this type, which is useful in engineering, required much innovation and application of techniques and concepts from the disciplines of microbiology and biochemistry.