What Modeling Work Says about Rotating Drum Bioreactors Without Axial Mixing

Mitchell et al. (2002a) developed a model to describe the operation of rotating-drum bioreactors that have large length to diameter ratios, for example, similar to the 11 m long by 1 m diameter rotating-drum bioreactors reported by Ziffer (1998), and that have end-to-end aeration. In such bioreactors, axial mixing may make a relatively small contribution, and in the model of Mitchell et al. (2002a) there was no axial mixing in either the substrate bed or the air phase.

In this model the bioreactor wall is not recognized as a separate subsystem (Fig. 23.8). A water balance is not done because it is assumed that water is periodically added to the bed in order to maintain a sufficiently high water activity so as not to limit growth. The model equations are partial differential equations, since both time and axial distance are independent variables. The partial differential equations are converted into ordinary differential equations by orthogonal collocation.

i

k SURROUNDINGS

of air without axial dispersion

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