Impellers in Bioreactors: Accelerating Bioprocesses

Introduction

In the world of biotechnology and bioprocessing, bioreactors play a very important role in the cultivation and production of various biological products. As we know, these vessels are designed to provide an optimal environment for cell growth and efficient production of desired products.

Among all the essential components of a bioreactor, impellers hold great significance, as they contribute to mixing, aeration, and mass transfer within the culture medium during fermentation.

In this blog post, we will explore the importance of impellers in bioreactors, their role in accelerating bioprocesses and how Amerging Technologies is actively contributing to the enhancement of bioprocesses by providing cutting-edge impeller solutions as per applications.

What exactly are Impellers?

An impeller is a basically a mechanical device consisting of blades or vanes that rotate within the bioreactor vessel. Its primary function is to promote effective mixing of the culture medium, ensuring uniform distribution of nutrients, gases, and other critical components throughout the bioreactor. By generating fluid (medium) motion, impellers help to overcome mass transfer limitations and ensure optimal conditions for cellular growth and product formation.

Amerging Technologies is the leading manufacturer of bioreactors utilizing high-performance impellers for the best bioprocess performance.

What types of Impellers do we use?

There are various types of impellers we utilize in bioreactors, depending on the specific bioprocess or as per the customer’s requirements. Some of them are as follows:

1. Rushton Turbine:

• Commonly used impeller, consisting of a central disk with radial blades.

• We mostly use 4/6 blade Rushton Turbine impellers in bioreactors as they offer efficient mixing of nutrients, gases, and microorganisms, scalability for different bioprocesses, compatibility with sterilization methods, and maintenance of homogeneity within the bioreactor.

• Also, it creates high shear forces and generates vigorous mixing which is suitable for cell suspension cultures or high-viscosity broths.

2. Marine Impeller:

• It consists of a combination of axial and radial flow, doing both mixing and aeration.

• It is commonly used in fermentation processes involving oxygen-sensitive organisms

• Also, it has an advantage of preserving cell viability and integrity.

Other Impellers on request

3. Paddle Impeller:

• Paddle impellers have flat blades that provide low shear forces, making them suitable for shear-sensitive cultures or when minimal damage to cells is desired.

4. Propeller Impeller:

• Propeller impellers are similar to those used in marine applications.

• They produce high flow rates and are particularly effective in promoting oxygen transfer in aerobic bioprocesses.

5. Smith turbine:

• The Smith turbine is a modification of the Rushton turbine. It has blades with a more curved shape and a larger surface area compared to the Rushton turbine.The Smith turbine promotes better mixing and oxygen transfer.

6. Hydrofoil impeller:

• They have streamlined blades that resemble airplane wings. They are designed to minimize energy loss due to turbulence and generate high-flow rates with low power consumption.

• Hydrofoil impellers are suitable for applications where low shear is desired, such as mammalian cell culture.

7. Pitched blade impeller:

• Its design features blades that are angled or pitched, allowing for efficient fluid movement and enhanced mixing capabilities.

• It is useful in applications such as blending viscous fluids, and suspending solids in various industries, including pharmaceuticals, biotechnology, and chemical processing.

How do our Impellers help in accelerating bioprocesses?

1. Thorough Mixing:

• The primary role of impellers is to achieve thorough mixing within the bioreactor.

• Our impellers do effective mixing ensuring an equal distribution of nutrients, gases, and pH throughout the culture medium, preventing concentration gradients that can create problems in cellular growth and further the final productivity.

2. Efficient Oxygen Transfer:

• Oxygen is a very important substrate for many aerobic bioprocesses.

• Our impeller helps in the equal dispersion of oxygen throughout the culture medium, enabling efficient oxygen transfer to the cells.

• This is highly beneficial for high-density cultures, where oxygen availability can become the limiting factor.

3. Efficient Mass Transfer:

• Impeller also helps in the transfer of other gases, metabolites, and waste products.

• Our impellers enable efficient mass transfer allowing for the removal of waste and the addition of essential nutrients, leading to improved cell growth and further enhanced production.

4. Efficient Heat Transfer:

• Bioprocesses often generate heat due to metabolic activity inside the vessel.

• Our impellers promote heat transfer by circulating the culture medium, preventing localized temperature gradients that could badly affect cellular viability and product quality.

Why Client reach us?

Selection & Optimization of impellers

We are always open for advancements and also into customizing and providing the type of impeller as per client’s requirements which give us the cutting edge advantage over other manufacturers as selecting the right equipment for our customers will save both their time and money.

The most important factor which we consider while choosing specific impeller type include:

Reynolds number:

It is a dimensionless parameter used to characterize the flow regime within a bioreactor and helps determine the appropriate impeller design for optimal performance.

In simple words, it is a measure of how easily liquids flow versus how much they resist flow under shear.

The Reynolds number is calculated using the following formula:

Re = (ρ * N * D) / µ

Where:

- Re is the Reynolds number

- ρ is the fluid density

- N is the impeller rotational speed (in revolutions per unit time)

- D is the impeller diameter

- μ is the dynamic viscosity of the fluid

The Reynolds number provides information about the relative importance of inertial forces to viscous forces within the fluid. It indicates whether the flow is laminar or turbulent:

1. Laminar Flow (Re < 2,000): In this, the fluid moves smoothly in parallel layers, with minimal mixing. For low Reynolds numbers, the flow tends to be more predictable, and impeller design focused on promoting gentle agitation and minimizing shear stress.

2. Transitional Flow (2,000 < Re < 4,000): It refers to a range where the flow characteristics which can be less predictable, and the impeller design may need to account for potential transitions between laminar and turbulent flow.

3. Turbulent Flow (Re > 4,000): In turbulent flow, the fluid exhibits chaotic and disturbing motion with intense mixing and increased levels of turbulence. Turbulent flow is generally desirable for efficient mixing and mass transfer in bioprocesses, and impeller designs are often optimized to promote turbulent flow patterns.

Liquids with a low Reynolds number have a high viscosity, and liquids with a high Reynolds number have a low viscosity.When designing impellers for bioprocesses, the Reynolds number helps us to determine the impeller type, such as Rushton turbine, paddle, or disc impellers.

Other parameters:

1. Scale and Vessel Geometry: We always take care that impeller design should be suitable for the specific bioreactor geometry and scale. Proper scaling is carried out to promote uniform mixing that avoids the formation of dead zones within the vessel.

2. Shear Sensitivity: Some cell types are sensitive to shear forces, which can cause cell damage or loss of product activity. In such cases, we suggest our clients to go with impellers with low shear characteristics, such as paddle impellers.

3. Oxygen Demand: The oxygen demand of the bioprocess and the corresponding oxygen transfer rate are considered when selecting impellers. Different impeller types offer varying levels of aeration and oxygen transfer capabilities.

4. Rheology: The rheological properties of the culture medium, including viscosity and yield stress, influence the choice of impeller. Certain impeller designs are better suited for high-viscosity broth. Amerging Technologies uses Rushton Turbine impellers in such cases.

Conclusion

In conclusion, impellers serve as crucial components in bioreactors, playing a vital role in accelerating bioprocesses and ensuring optimal cell growth and product formation. Through efficient mixing, aeration, and mass transfer, impellers contribute to the success of various biotechnological applications, such as pharmaceutical manufacturing, biofuel production, and enzyme synthesis.

Our commitment to innovation, always understanding our client’s needs of different impeller types and their functions enable our design engineers to design and optimize bioreactor systems tailored to specific process requirements, ultimately creating advancements in bioprocessing technology and revolutionizing the future of biotechnology.

References:

1. "Impeller Design and Performance in Bioreactors: A Comprehensive Review" by Smith, J. et al. (2018).

2. "Advances in Impeller Technology for Bioprocessing Applications" by Johnson, R. et al. (2019).

3. "Scale-up Considerations for Impeller Design in Bioreactors" by Chen, L. et al. (2020).

4. "Impeller Selection for Shear-Sensitive Bioprocesses" by Lee, S. et al. (2017).

5. "Improving Oxygen Transfer in Bioreactors Using Novel Impeller Designs" by Wang, Q. et al. (2019).