ORBIT e.V.

Oxygen and temperature kinetics of aerobic solid-state Biodegradation

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Rates of decomposition are of critical interest to operators of most biodegradation processes, since they determine the length of time the process must continue to achieve a particular extent of decomposition. While the goals of the decomposition process vary widely, ranging from reduction of odors or contaminants to production of high valueadded products, most of these goals are impacted by the rate processes that occur. In the short term biodegradation kinetics affect process control requirements (insuring adequate oxygen supply, etc., and in the longer term they affect facility size, throughput, and thus capital costs and payback time on investments.

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 [1]:

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