Although the focus of this study is a solid-waste composting process, similar processes occur in bioremediation and solid-state fermentations. These processes occur in a matrix of organic particles and interconnected pores, and the pores are partially filled with air, aqueous solution, or a combination of the two. A multitude of microorganisms and their enzymes are responsible for the biodegradation process, resulting in a complex and poorly understood biochemical and microbial system. The byproducts of microbial activity, including heat and CO2 production, dynamically alter environmental conditions, leading to large temperature, moisture, and oxygen gradients in this matrix of organic particles (Finstein et al., 1985; Miller, 1991).
Each of these environmental conditions, as well as the substrate and microbial population, affect the substrate degradation rate. Several comprehensive models of degradation kinetics have been developed, including that of Finger et al. (1976), Haug (1980, 1993), Keener et al. (1992), Hamelers (1992), and Strombaugh and Nokes (1996). One way to structure such a comprehensive model is to determine degradation rates under one set of environmental conditions and then apply a series of corrective functions to account for the impacts of temperature, oxygen, moisture, etc., as illustrated in Equation :