Measuring CO₂ and O₂ in Bioreactors

Accurate measuring of oxygen (O₂) and carbon dioxide (CO₂) is critical for a number of processes across a number of industries. From healthcare and veterinary medicine to landfills and even restaurants, the measurement and analyzation of CO₂ and/or O₂ ensures medical machines, food packaging, and more are safe, healthy, and up to standards. Today, we’re going to focus on the importance of measuring these two gases in bioreactors and how to obtain an accurate reading of both.

What is a bioreactor?

Before understanding how to measure CO₂ and O₂ in a bioreactor, it’s first important to understand what a bioreactor is and what it’s used for. A bioreactor, or sometimes referred to as a fermentor, is a vessel that supports a biologically active environment to grow a number of organisms including yeast, bacteria, fungi, and more. The process can either be aerobic, meaning results are produced utilizing oxygen, or anaerobic, meaning there is no presence of oxygen.

The apparatus is able to do this by controlling pH levels, temperature, and airflow. The size and shape can vary slightly depending on its use, but they are typically made of stainless steel and are cylindrical.

So, how does it differ from a fermentor? It doesn’t! The two essentially refer to the same thing but commonly used interchangeably, depending on what the apparatus is being used for. The word bioreactor is frequently used when referring to the cultivation of mammalian cells, but can also be used generically. The term fermentor is more commonly used among scientists who cultivate fungi, bacteria, or yeast.

If this all sounds a bit vague, that’s because it is! There are a variety of types of bioreactors that are widely used across industries for hundreds of different purposes. A few common uses for bioreactors are for fermentation of alcohol, food processing and packaging, waste treatment, production of pharmaceuticals and vaccines, and more. We’ll discuss the role of bioreactors in these processes a bit later.

Regardless of its use, size, or shape, in order for a bioreactor to properly function, it must contain the following parts:

    • Agitator: The agitator mixes the contents of the bioreactor together to keep the cells in a homogenous condition.
    • Baffle: The baffle is used to not only improve aeration efficiency but also to prevent a vortex from forming.
    • Sparger: The sparger’s job is to provide and distribute oxygen to the cells.
    • Jacket: The jacket, similar to what we use a jacket for, allows the bioreactor to remain at a controlled temperature.

Below is a diagram of a typical bioreactor or fermentor and its parts:

diagram of a typical bioreactor or fermentor and its parts

[Image: ScienceDirect.com]

Examples of bioreactor applications
To help you understand the purpose and importance of measuring CO₂ and O₂ in bioreactors and fermenters, we wanted to share a few common examples with you. As we mentioned, bioreactors are used for hundreds of purposes, so keep in mind that this is not a complete list!

  • Fermenting alcohol
    If you’ve ever visited a brewery or winery, you’ve most likely seen those large, stainless-steel cylinders that the alcohol is produced in. Those are bioreactors! While you only taste the end-product, there’s a lot going on inside those fermentors, and a lot of it depends on the levels of O₂ and CO₂ in each. When brewing beer, ethanol (also known as alcohol) is the desired outcome. In order to produce the alcohol, oxygen must be absent, and in order to produce the carbonation, CO₂ is needed. The lack of oxygen and the right amount of carbon dioxide is crucial, so accurate measurements of each are necessary.
  • Sewage treatment
    In order to turn sewage and wastewater into something usable, bioreactors are used to develop bacteria that nullify toxins in the water so that it can be recycled into usable water and biosolids. In order to achieve this, the bioreactor must have a constant supply of oxygen. To ensure that enough oxygen is being provided to the bioreactor, the measurement of oxygen levels at all times is critical.
  • Vaccine production
    As we find ourselves in the midst of a global pandemic, vaccine production is more important now than ever. Interestingly enough, vaccines are typically produced by injecting viruses into chicken eggs! While this method is still used, bioreactors are now being used to experiment with mammalian cell-based vaccine production. To ensure the cells are thriving in the right environment, measuring levels of certain components including temperature, pH, and most importantly, oxygen, is of the utmost importance.

The role of oxygen in bioreactors

So, what do oxygen and carbon dioxide have to do with bioreactors? Why should we care about the levels of each in these vessels? One of the most crucial purposes of a bioreactor is to provide dissolved oxygen to the cells through aeration. Typically, the oxygen is transferred into the bioreactor or fermentor through the sparger. As we mentioned before, bioreactors can be used regardless of whether or not a process is aerobic or anaerobic, so understanding which it is and the level of oxygen needed to complete the process is critical.

If oxygen levels are too low, the growth of the cells will slow down, which could lead to a lesser quality of the final results. On the other hand, if there is too much dissolved oxygen in the fermentor, you risk not only wasting energy, but these higher levels can lead to cell mutations or worse, cell death. Whether the levels of oxygen are too high or too low, you run the risk of less accurate results, regardless of the application.

The purpose of carbon dioxide in bioreactors

Carbon dioxide is produced through respiration (did you know? when you exhale, you’re producing carbon dioxide!), from the burning of organic or carbon compounds, and through fermentation to make products like yeast or alcohol. When conducting a chemical process in a bioreactor, the levels of carbon dioxide need to be properly monitored and analyzed.

Similarly to oxygen, there needs to be a proper amount of carbon dioxide in the bioreactor in order for cells or organisms to properly grow and reproduce. The amount of dissolved carbon dioxide, like oxygen, has a major impact on the growth, liveliness, and production of cells.

How is O₂ measured in bioreactors?

Regardless of the application or where the O₂ is being measured, oxygen are measured in parts-per-million (PPM). In order to determine the measurement of each gas, an analyzer is required.

Why Alpha Omega Instruments?

For 25 years, Alpha Omega Instruments (AOI) has manufactured only the highest quality products in our industry. We offer a number of instruments that can help you measure O₂ levels in a bioreactor, regardless of the application. Our products have become known for their reliability, precision, and cost-effective pricing, and we’re committed to pairing you with an O₂ analyzer that will provide you with the best possible outcomes.

Depending on your needs, we offer a number of instruments to assist you with measuring O₂ in bioreactors:

So, whether you’re an expert at measuring CO₂ and O₂ in bioreactors or are just getting started, AOI has the right instrument for you. Regardless of your industry or application, measuring CO₂ and O₂ in fermenters is critical to receiving high-quality and desired outcomes.

Not sure which instrument is right for you? Contact us today and we’ll pair you up with the right instrument for you and your project.