Communication Dans Un Congrès Année : 2021

Scale-down methodology to study the effect of fluid dynamic stress and oxygen gradients on filamentous fungal fermentations producing cellulases

Résumé

Most processes for the biological conversion of ligno-cellulosic biomass (LCB) to bio-products require the use of enzymes called cellulases, especially for the production of second generation ethanol. The technoeconomic evaluations of this process demonstrate that reducing the cost of cellulases is a prerequisite to bring the ethanol cost to values close to that of ethanol produced from starch. One of the most efficient organisms for the production of these enzymes is the filamentous fungus Trichoderma reesei, mainly thanks to its high secretion capacity. Scaling-up fermentation processes using this microorganism is very challenging because of the complex links that exist between the process conditions, the morphology of fungi and its performances. Actually, the filamentous morphology induces an increase of the viscosity that strongly reduces the rate of oxygen mass transfer. To ensure a sufficient rate, the power input has to be increased, which results in a reduction of the mycelial structures. So, scaling-up this process is complicated as the fungal morphology impacts process parameters, whereas process conditions affect in return the morphology and possibly the process productivity. The goal of this work was to develop a scale-down approach at lab-scale to mimic hydrodynamic conditions of industrial bioreactors and to study their impact on T. reesei growth and cellulase production. Cultures in bioreactors using a wide range of agitation conditions, were firstly undertaken to better understand the impact of the fluid dynamic stress on Trichoderma reesei rheology, morphology, and productivity and also the link between these different parameters. Dissolved oxygen gradients observed in large-scale bioreactors were then simulated by two scale-down systems: A two-compartments system with two stirred-reactors and, a single-compartment-system. The fungus was exposed to anaerobic conditions for the same duration and the kinetics of cellulases production were compared with a “control” with a constant dissolved oxygen concentration. The two different scale down approaches showed very different results indicating that the impact of the oxygen starvation on the physiology of the fungus is complex and depends on the distribution of the residence times of the microorganisms in the aerated or non-aerated zones.The results of this work illustrate how the economic success of using filamentous fungus at industrial scale will largely be dependent on microbial capabilities and process considerations.

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Dates et versions

hal-03482240 , version 1 (15-12-2021)

Identifiants

  • HAL Id : hal-03482240 , version 1

Citer

Fadhel Ben Chaabane, Tamiris Goncalves-Roque, Catherine Béal, Alvin W. Nienow, Frédéric Augier. Scale-down methodology to study the effect of fluid dynamic stress and oxygen gradients on filamentous fungal fermentations producing cellulases. International Symposium on Mixing in Industrial Processes ISMIP10, Nov 2021, Kobe, Japan. pp.O-153. ⟨hal-03482240⟩
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