Combined discrete particle and continuum model predicting solid‐state fermentation in a drum fermentor

Abstract

The development of mathematical models facilitates industrial (large-scale) application of solid-state fermentation (SSF). In this study, a two-phase model of a drum fermentor is developed that consists of a discrete particle model (solid phase) and a continuum model (gas phase). The continuum model describes the distribution of air in the bed injected via an aeration pipe. The discrete particle model describes the solid phase. In previous work, mixing during SSF was predicted with the discrete particle model, although mixing simulations were not carried out in the current work. Heat and mass transfer between the two phases and biomass growth were implemented in the two-phase model. Validation experiments were conducted in a 28-dm3 drum fermentor. In this fermentor, sufficient aeration was provided to control the temperatures near the optimum value for growth during the first 45-50 hours. Several simulations were also conducted for different fermentor scales. Forced aeration via a single pipe in the drum fermentors did not provide homogeneous cooling in the substrate bed. Due to large temperature gradients, biomass yield decreased severely with increasing size of the fermentor. Improvement of air distribution would be required to avoid the need for frequent mixing events, during which growth is hampered. From these results, it was concluded that the two-phase model developed is a powerful tool to investigate design and scale-up of aerated (mixed) SSF fermentors.

Estimation of Transfer Coefficients for SSF Bioreactors

“…The value of h b will depend on whether the bed is mixed or not, with h b increasing as the intensity of mixing increases (Oostra et al 2000). They estimated h b as: was determined experimentally for moist oats (Schutyser et al 2004). However, it is often not a simple matter to determine h b and, instead of doing this, the overall heat transfer coefficient for transfer from the bed to the outside is often determined experimentally (see Sect.…”

Model-based Control of Enzyme Yield in Solid-state Fermentation

“…Mitchell et al [8] and Sangsurasak and Mitchell [12], for instance, presented a model taking into account the two-dimensional heat transfer and evaporation in the SSF, enabling to predict drying properly during fermentation. Von Meien and Mitchell [13] and Schutyser et al [14] proposed two-phases models to predict temperature and moisture gradients in packed bed bioreactors for SSF, which in addition allows to represent water transfer from the solid phase to the gas phase.…”

“…The model used in this contribution is motivated by the approaches presented in [13,14] and considers a fermentative system composed of the thermophilic fungus Myceliophthora thermophila I-1D3b cultivated in a mixture of sugar cane bagasse and wheat bran (7:3 dry weights) [5]. The bioreactor was supposed to operate as packed bed bioreactor without mixing during the whole fermentation.…”

Two-phase and two-dimensional model describing heat and water transfer during solid-state fermentation within a packed-bed bioreactor

“…Von Meien and Mitchell [37] were the first to suggest a heterogeneous two-phase model in SSF to predict temperature and moisture gradients in an intermittently stirred bioreactor with forced aeration, using the same approach applied for heat and mass transfer during grain drying in deep fixed beds; see for instance [38]. Two-phase models have also been applied by Schutyser et al [39]. Although two-phase models require the always difficult to obtain fluid-to-particle information to be implemented, these models are more realistic and are the only ones able to represent properly water transfer from solid-to gas-phase.…”