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Bioreactors and Fermenters

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Course Objectives

This lesson will discuss bioreactors including basic operations, typical instrumentation configurations and calibration methods

We will discuss the basic operation of a Bioreactor/Fermenter

We will discuss some of the instrumentation applicable to a client bioreactor

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Bioreactor Basics

Bioreactors are specialized tanks used for growing cells

Bioreactors are used in many different processes from brewing beverages to developing pharmaceutical products

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Bioreactor Basics

A bioreactor is a tank that maintains a nutrient level necessary for cell growth, as well as providing an environment that meets the temperature, pH and oxygen levels that are needed for the process

The steps in the bioreactor process (fermentation) are as follows:

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Bioreactor Basics

Batch Fermentation: A sterilized nutrient solution in the bioreactor is inoculated with microorganisms, and incubation begins. At this stage nothing is added to the process except oxygen, an antifoaming agent, and acids or bases to control the pH level. The biomass concentration at this point generally changes constantly as a result of the metabolism of the cells

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Bioreactor Basics

After inoculation of the sterile nutrient solution with microorganisms, four typical phases of growth occur

Lag Phase: During this phase, there is a physiochemical equilibration between the microorganism and the environment which follows the inoculation where there is very little growth

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Bioreactor Basics

Log Phase: Towards the end of the lag phase, cells have adapted to the new conditions of growth. The growth of the cell mass now approaches a doubling of cell number per unit of time for bacteria and yeast, or a doubling of biomass per unit of time for filamentous organisms such as fungi

As long as there exists an excess of substrate, growth rate of the cell mass remains constant during this phase

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Bioreactor Basics

Stationary Phase: When the substrate has been metabolized or toxic substances have formed, growth rate begins to slow down or completely stop. The biomass increases gradually, or remains constant during this phase, however composition of the cells may change

Due to lysis (destruction of the cell membrane) new substrates are released which may serve as energy sources for the slow growth of survivors.

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Bioreactor Basics

Death Phase: During the Death Phase, the energy reserves of the cells are exhausted. Cells are now dying at an exponential rate

During most processes, the fermentation is interrupted somewhere between the log phase and the death phase

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Bioreactor Basics

Fed Batch Fermentation: In the fed batch fermentation process, the substrate is added in increments as fermentation progresses. The critical elements of the nutrient solution are added in small concentrations at the beginning of the fermentation, and these substances continue to be added in small doses during the production phase

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Bioreactor Basics

Continuous Fermentation: Sterile nutrient solution is added to the bioreactor continuously and an equivalent amount of converted nutrient solution with microorganisms is simultaneously taken out of the system

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Bioreactor Basics

Microbial Fermentation is a three phase system. Phase 1: The liquid phase contains dissolved

nutrients, substrates and metabolites. Phase 2: The solid phase consists of individual

cells, pellets, insoluble substrates, or precipitated metabolic products.

Phase 3: The gaseous phase provides a reservoir for oxygen supply and CO2 removal.

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Bioreactor Basics Stirring and Mixing is crucial for the transfer of

energy, nutrients, substrate and metabolites. For the three phases, mixing brings about the

following: Dispersion of air in the nutrient solution. Homogenization to equalize the temperature and

concentration of nutrients. Suspension of microorganisms and solid nutrients. Dispersion of immiscible liquids.

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Bioreactor Basics

One of the most critical factors in the fermentor operation is provision for adequate gas exchange.

Oxygen is the most important substrate for microbial metabolism, and carbon dioxide is the most important gaseous metabolic product.

The mass transfer of oxygen to a liquid is characterized by the oxygen transfer rate or the volumetric oxygen transfer coefficient. These values are a critical parameter of the bioreactor process.

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Bioreactor Basics

For optimal yield, the fermentation process must be carried out at constant temperature.

Finally, sterilization of the cultures at all stages is crucial to the process.

Factors that affect the sterilization of the cultures include the composition of the culture medium, the pH value, and the size of the suspended particles.

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Bioreactor Basics

It is for all of the stages of the bioreactor/fermentation process mentioned above, that instruments that monitor agitation, temperature, pH and DO2 (dissolved oxygen) content are all critical to the success of the process.

The next section covers the instrumentation involved in a typical Bioreactor.

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Bioreactor Instrumentation

The exact instrumentation configuration is different from one bioreactor to the next, but all bioreactors contain a similar set of instrumentation.

Bioreactors contain a number of temperature measuring devices measuring many parameters including the following (Actual usage vary from one bioreactor to another):

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Bioreactor Instrumentation Tank Temperature Jacket Temperature Inoculums Temperature Media Temperature Titrant Temperature Sample Temperature Harvest Temperature CIP Steam Temperature Agitator Steam Temperature

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Bioreactor Instrumentation

Bioreactors contain analytical measurement instruments including one or more pH transmitters and one or more DO2 transmitters.

Bioreactors contain air flow measurement instruments measuring Sparge Gas, O2, CO2 and Headspace Air flow into the tank.

Bioreactors have a number of pressure measuring devices including pressure gauges and pressure transmitters measuring many parameters including the following:

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Bioreactor Instrumentation

Tank Pressure Media Pressure Steam Pressure Compressed Air Pressure

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Bioreactor Instrumentation

Bioreactors typically have a level sensing device of some type.

Bioreactors have a speed sensing instrument attached to the agitator motor to monitor the amount of agitation.

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Summary

This lesson covered the basics of the fermentation process, and the basic functioning of a bioreactor including a discussion of the critical parameters.

The instrumentation used in a typical bioreactor system were discussed.

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Where to Get More Information There are many possible sources of

information about this subject including white papers on the fermentation process, discussion with scientists and engineers at client sites, and Manuals and Standard Operating Procedures for the actual Bioreactor system being worked on.