Evaluation of Productivity of Zymotis Solid-State Bioreactor Based on Total Reactor Volume

David A. Mitchell¹*, Oscar F. von Meien², Luiz Fernando L. Luz Jr.² and Nadia Krieger<sup>3

1</sup>Departamento de Bioquímica, Universidade Federal do Paraná, Cx. P. 19046, Curitiba 81531-990, Paraná, Brazil
²Departamento de Engenharia Química, Universidade Federal do Paraná, Cx. P. 19011, Curitiba 81531-990, Paraná, Brazil
³Departamento de Química, Universidade Federal do Paraná, Cx. P. 19081, Curitiba 81531-990, Paraná, Brazil

Article history:
Received: January 14, 2002
Accepted: February 10, 2002

Key words:
Zymotis bioreactor, packed-bed bioreactors, volumetric productivity, solid-state fermentation, modeling, large scale cultivation, heat transfer

Summary:
In this work a method of analyzing the performance of solid-state fermentation bioreactors is described. The method is used to investigate the optimal value for the spacing between the cooling plates of the Zymotis bioreactor, using simulated fermentation data supplied by a mathematical model. The Zymotis bioreactor has good potential for those solid-state fermentation processes in which the substrate bed must remain static. The current work addresses two design parameters introduced by the presence of the internal heat transfer plates: the width of the heat transfer plate, which is governed by the amount of heat to be removed and the pressure drop of the cooling water, and the spacing between these heat transfer plates. In order to analyze the performance of the bioreactor a productivity term is introduced that takes into account the volume occupied within the bioreactor by the heat transfer plates. As part of this analysis, it is shown that, for logistic growth kinetics, the time at which the biomass reaches 90 % of its maximum possible value is a good estimate of the optimum harvesting time for maximizing productivity. Application of the productivity analysis to the simulated fermentation results suggests that, with typical fast growing fungi (
μ = 0.324 h^–1), the optimal spacing between heat transfer plates is of the order of 6 cm. The general applicability of this approach to evaluate the productivity of solid-state bioreactors is demonstrated. 

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