Biochemical Engineering Fundamentals, Part 1 - Bailey J., Ollis D. 1989

Transport phenomena in biotechnological systems
Non-Newtonian fluids
Solutions of macromolecular compounds

Certain microorganisms secrete Polysaccharides and related Biopolymers, as well as their derivatives, such as xanthan, polyalginic acid, and pullulan, into the medium. Xanthan is widely used to provide the necessary viscosity to Food Products and to stabilize Suspensions, and in the future, it may also be used in oilfield development. The secreted biopolymers impart non-Newtonian fluid properties to the culture broth; typically, The behavior of such liquid media is described by equation (8.92) at n < 1 (pseudoplastic behavior).

In a batch process, the variation of biopolymer concentration over time causes The properties of the liquid medium, and consequently the transport phenomena parameters (mass and Heat transfer), to also change over time. Since transport coefficients in the equations describing non-Newtonian fluid behavior are typically expressed in terms of the power-law model parameters n and η0, it is natural to attempt to find a specific relationship between the biopolymer concentration and these rheological parameters.

For xanthan, this relationship is expressed by the equation

Class="center">η₀ = A ⋅ [Р]^B      (8.97)

Here B ≈ 2.5, and [Р] is the polymer concentration.

During the synthesis of certain extracellular biopolymers, the power-law index n and viscosity η0 change over time According to the following equation:

ln η₀(t) = C + D ⋅ n(t)      (8.98)

If the dependence of [Р] on t is known from a biological kinetic model, equations (8.97) and (8.98) make it straightforward to describe the relationships n(t) and η₀[Р(t)] as well. The latter, in turn, can be used to calculate heat and Mass transfer coefficients, as well as mixing parameters and power consumption [39, 40].