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residual dry substrate)

Fig. 25.1. (a) Strategy of operation of an intermittently-mixed forcefully-aerated bioreactor, as modelled in the case study. (b) In Fig. 25.2 the solid and gas phases are represented in the manner as shown in the diagram on the right.

Instead of assuming that the solids and air are in thermal and moisture equilibrium, as was done in Chap. 24, the model uses the balance equations, which have driving force equations for heat and mass transfer, to calculate the changes in the dry solids and liquid water, thereby allowing calculation of the water content of the solid phase. Note that the water content of the solid phase in turn affects the rate of evaporation to the gas phase. Given the water content and the temperature of the solid, the model calculates the water activity of the solid. The water activity of the solid, along with its temperature, affects growth. The model calculates and combines fractional growth rates in the same manner as was done in Eqs. (22.1), (22.2), and (22.3) in Sect. 22.2.

Gas phase energy balance (Tg)

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