Growth processes in bioreactors with external sources of biomass: Application of structured, continuum models

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Abstract
Batch, fed‐batch, and single‐stage CSTR bioreactors operate without external sources of biomass after they have been inoculated. However, other kinds of bioreactors, such as the second and subsequent reactors in a cascade of CSTRs, operate with continuous introduction of biomass from one or more external sources. The biomass in a bioreactor with an external source is not homogeneous with respect to past history of environmental conditions, and growth of this biomass is not balanced (steady‐state) growth even when the bioreactor operates in steady state. So‐called unstructured models of growth, which assume biomass to lack any internal structure or to have an invariant internal state, can give only a first approximation to the growth rate behavior of the biomass in a bioreactor with an external source of biomass. Structured models, which endow biomass with a changeable internal structure, are required to obtain more accurate predictions of growth rate behavior in such reactors. Introduction of structure is not sufficient for improved accuracy, however, and the fact that biomasses from different sources are remain segregated from one another must also be accounted for by any structured growth model used. This article presents, among others, the systems of different equations that result from application of the notions to the reactors of a cascade of CSTRs.