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Design of Solid-State Fermentation Systems for Polymer Hydrolytic Extracellular Enzyme Production by Filamentous Fungi
Published on: June 6, 2025
Improved performance in viscous mycelial fermentations by agitator retrofitting.
B C Buckland1, K Gbewonyo, D Dimasi
1Merck Sharp and Dohme Research Laboratories, P.O. Box 2000, Rahway, New Jersey 07065.
Biotechnology and Bioengineering
|May 1, 1988
Summary
Replacing standard impellers with larger axial-flow hydrofoil impellers significantly boosts oxygen transfer in viscous fermentations. Reducing broth viscosity through water addition also enhances oxygen transfer, suggesting improved mixing is key.
Area of Science:
- Biochemical Engineering
- Fermentation Technology
- Rheology
Background:
- Viscous mycelial broths pose challenges for oxygen transfer in industrial fermentation.
- Standard Rushton turbines may be suboptimal for achieving efficient oxygen transfer in such systems.
Purpose of the Study:
- To evaluate the impact of impeller type on oxygen transfer efficiency in pilot-scale viscous fermentations.
- To investigate the role of broth rheology and viscosity on oxygen transfer.
Main Methods:
- Comparison of radial flow Rushton turbines with axial-flow Prochem hydrofoil impellers.
- Rheological characterization of Streptomyces and Norcardia broths.
- Assessment of oxygen transfer coefficient (K(L)a) under varying conditions, including water addition.
Main Results:
- Larger diameter axial-flow hydrofoil impellers significantly improved oxygen transfer efficiency compared to Rushton turbines.
- The Streptomyces broth exhibited highly shear-thinning behavior.
- Water addition to reduce viscosity in Norcardia broth substantially increased the oxygen transfer coefficient (K(L)a).
Conclusions:
- Impeller design and viscosity modification are critical factors for enhancing oxygen transfer in viscous mycelial fermentations.
- Improved bulk mixing, driven by impeller type and reduced viscosity, is the primary mechanism for increased oxygen transfer.
- A model based on Bajpai and Reuss concepts explains performance enhancement through an enlarged well-mixed micromixer region.
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