Fluidized‐bed fermenters: A steady‐state analysis

Abstract

A new mathematical model is presented model is presented for use in the design and optimization of fluidized-bed fermenters. Unlike previous models, the biomass particle size is not a required input parameter, but is predicted as a consequence of the process by which the fermenter reaches a steady state. Both tower fermenters and supported-film bioreactors are included in the analysis. The differences between them are explained as a consequence of the different effects of added biomass on the particle settling velocity and the tendency of a fluidized bed to stratify. A detailed qualitative treatment of solids mixing allows the model to predict the varying biomass concentration through a tower fermenter and the more constant concentration in the supported film reactor. Other features of this analysis are the inclusion of an axial dispersion term to allow for different liquid mixing conditions, and the introduction of a variable transformation that eliminates the need for a computer solution. A sample design problem is included.

Bioreactor Performance: Process Design Methods

“…6.38. Increasing Xr has the effect of minimizing Sex and also of making Sex less sensitive or more stable with respect to variations in the flow rate of constant-volume reactors with residence times considerably below the washout value (Andrews, 1971 illustrating how the critical dilution rate depends on the degree of feedback r, the number of stages N, and the concentration of limiting substrate. Toda and Dunn (1982) emphasized that a combination of a backmix and a plug flow fermenter with recycle streams provides better performance than does a single CSTR for the continuous production of a substance that depends on the maturity of growing cells (see Equ.…”

“…Bioreactor Performance: Process Design Methods unified model approach, that is, non-steady-state loading (fluctuations in Sin and v z ), dual-substrate limitation (e.g., Reuss and Buchholz, 1979), the effect of additional biomass on particle-settling velocity (which is different for, e.g., tower fermenter and fixed bed reactors), and some practical considerations (bed expansion, clogging, wall effects, and shearing). The use of non-monosized support particles is recommended as an alternative to a tapered tower fermenter, as normally a fixed bed bioreactor is superior due to almost constant cell concentrations throughout the bed (Andrews, 1982).…”

Adsorption With Biological Growth

“…Furthermore, as suggested by Andrews (1979), it is often more convenient to consider mass balance in biodegradation in terms of the transfer and reaction of the equivalent organic carbon. Both Eqs.…”

“…A slightly more accurate method was suggested by Andrews (1979). The former information can be obtained in different ways.…”

Prediction of average biofilm density and performance of a spherical bioparticle under substrate inhibition

“…This performance evaluation always requires biofilm density and thickness in the biofilm reactor, since overall reaction rate is critically dependent on these parameters (Karel et al, 1985;Andrews, 1982). In the literature, it has generally been assumed that the biofilm density is constant and independent of biofilm thickness (Grady, 1983;Livingston and Chase, 1989;Vos et al, 1990).…”