Biodegradation modeling is gaining more attention as a useful tool for predicting the attenuation of organic contaminants in groundwater. In this paper we compare two conceptual models. The first approximates biodegradation with an instantaneous reaction between the organics and oxygen. The advantage of this model is its simplicity and minimal biotransformation data requirements. Inherent in this model is the assumption that biodegradation in groundwater is oxygen transport limited. The second conceptual model utilizes a dual substrate Monod kinetic relationship to calculate biodegradation. While theoretically more accurate, the model suffers from being numerically more complex to implement. The kinetic model also requires more biotransformation data for each organic contaminant than the instantaneous reaction model. The analysis presented in this paper is intended to determine the requirements that must be placed on a system's Damköhler number to guarantee that reaction mechanisms are not kinetically limited. Results indicate that the instantaneous reaction is an adequate assumption when nondimensionalized reaction rates are large
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