Smaller bioreactors can efficiently distribute oxygen and remove carbon dioxide without nebulizers. However, these measures do not apply to larger bioreactors, as the lower surface area to volume ratio leads to carbon dioxide accumulation and prevents oxygen penetration. Therefore, nebulizers are necessary for the introduction of oxygen and the removal of carbon dioxide.
Systems with micro and large nebulizers are often useful because they can meet different process needs. For example, large nebulizers produce larger bubbles that effectively remove dissolved CO 2 from the solution, but large bubbles require vigorous agitation to break them down and release oxygen.
While this may work well for cold-tolerant cell lines, stirring can damage more delicate mammalian cells. In these cases, a lower-powered macro-distributor can be used first to remove CO 2 and then a micro-distributor in series to produce smaller bubbles that deliver oxygen more efficiently.
The Challenge: Bubble Characteristics Determine O2 Transport and CO 2 Vapor Extraction Rates
Bubble formation and size significantly affect how oxygen is dispersed throughout the bioreactor. Bubble characteristics are significantly influenced by pore size and distribution, distributor material, flow rate, liquid and gas properties, and pressure. For example, micro sprayers produce smaller, spherical bubbles, while larger sprayers produce slightly larger and less uniformly shaped bubbles.
Micro spargers produce micron-sized and spherical bubbles, and surface tension is the dominant force as they pass through the bioreactor. They, therefore, have a long residence time in the reactor, which improves oxygen transfer, but is not suitable for removing carbon dioxide from the culture.
Large nebulizers produce bubbles with an average diameter of 1-4 mm, where surface tension and buoyancy in the broth combine to influence their shape and movement. These bubbles have a shorter residence time but are less likely to dissolve than smaller bubbles. However, micro spargers may also produce larger asymmetric bubbles, with inertial forces governing their behavior. These bubbles can easily burst without dissolving or stripping CO2.
The shape and size of the bubbles determine the amount of shear stress the cell will experience, the effectiveness of stripping CO 2 from the system, and the rate of total oxygen transfer to the cell. Therefore, it is important to optimize the bioreactor nebulizer to ensure that the oxygen bubbles are uniform in size and distribution and do not damage the cells.
Solution: Use strict production quality control of the HENGKO bioreactor sparger
HENGKO has more than twenty years of experience developing and producing sintered sparger. Our stainless steel sparger are the result of dozens of engineers who have often improved the production method to produce this high-quality product with uniform pores and, thus, uniform bubble size released into the bioreactor. Our porous spargers are recommended for use with low-flow mass flow controllers.
How to use: The low-flow mass flow controller slowly introduces oxygen into the porous sparger. The spargers does not immediately release gas. Instead, the pressure gradually increases until a critical point is reached, at which point the bubbles are gently released into the bioreactor.
Using this sparging method, the oxygen mass flow rate can be adjusted to control the release rate of the bubbles into the bioreactor. The holes in the sparger are small enough that bubbles will form predictably. Therefore, this bioreactor sparging technology is scalable across vessel sizes, with an oxygen transfer rate proportional to the gas flow rate.
Questions Guide About
What is meant by sparger?
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What is the use of sparger in bioreactor explain its types?
Where is the sparger located in bioreactor?
Which type of sparger is mostly used in large scale fermentation?
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