Incorporation of death kinetics into a 2-dimensional dynamic heat transfer model for solid state fermentation

Dynamic two‐dimensional modelling was used in a theoretical analysis of the overheating problem in solid‐state fermentation within a packed‐bed bioreactor. The model described the growth and death of the fungus Rhizopus oligosporus as functions of temperature; the generation of metabolic heat; and the transfer of heat within the packed‐bed by conduction and convection. The model predicted that convection was the dominant heat transfer mechanism under the design and operational parameters applied. Significant death occurred in the upper region of the bed where the highest temperatures were reached. The temperature rise at the top of the bed could be minimized by using high superficial air velocities or low inlet air temperatures. The most effective strategy for a column with a bed height: bed diameter ratio of 1:1 or less was to use a high superficial air velocity

The investigation of transient multidimensional heat transfer in solid state fermentation

A mathematical model is presented which predicts the temperature profiles for solid state fermentation in a packed bed in two dimensions, radial and axial. Heat transfer within the bed occurs by conduction through the solid material and convection by the air used for aeration. The temperature at the wall of the reactor is fixed at 298 K. Simulations with the model indicate that the air velocity and air temperature will significantly influence the temperature and biomass concentration profiles. The effect of the bioreactor geometry is also discussed. This fundamental model of solid state fermentation can be used to predict the effects of a range of parameters and can be used a a tool to aid scale-up to large bioreactors

Hexahedral modular bioreactor for solid state bioprocesses

The design of a modular bioreactor for solid state fermentation is a promising development because it keeps the homogeneity of the bed at optimal levels. This study determines the optimum geometry of elementary modules of hexahedral bioreactors subjected to constant volume. The bioreactors have a square section and do not need an external cooling system, because the optimization limits the temperature of the bed to 35 C. The geometric optimization followed the Constructal principle of minimum heat resistance. The numerical simulations take into account the following parameters: inlet air temperature and velocity, and module volume. Once the elementary module has been selected, the total volume of the bioreactor can be calculated

Evaluating strategies for overcoming overheating problems during solid-state fermentation in packed bed bioreactors

Normal operation of packed bed bioreactors used for solid-state fermentation involves a static bed aerated from the bottom throughout the fermentation. This leads to axial temperature profiles with the highest temperature, sometimes over 20 degrees C higher than the inlet air temperature, occurring at the top of the bed. An axial heat transfer model was used to explore two strategies designed to prevent the temperature reaching undesirable levels, namely periodic reversal of the direction of airflow, and periodic mixing. Simulations were done for the growth of Aspergillus niger on a starchy substrate. The bed was assumed to be wide enough such that the radial heat transfer could be ignored. With hourly air reversal or mixing events, the maximum temperature predicted during the fermentation is higher than the maximum temperature predicted for normal operation. Increasing the frequency of air reversals leads to temperatures close to the maximum for growth in the middle of the bed. However, for a 0.345 m high bed and a superficial air velocity of 0.0236 m s(-1), mixing 10-60 times per hour can lead to lower maximum temperatures in the column compared to normal operation, because the frequent mixing distributes the benefits of the effective cooling at the bottom of the column throughout the bed. The degree of reduction in maximum temperature increases with increasing specific growth rate of the microorganism. Modelling is a useful tool in guiding experimental programs for the design and scale-up of bioreactors for solid-state fermentation, since it can be used to identify promising strategies and eliminate unfruitful strategies. (C) 1999 Elsevier Science S.A. All rights reserved