Fermentation Off Gas

Fermentation Off Gas


Monitor the input and exhaust gases from fermentation vessels so that the fermentation process can be optimized.

Measuring the carbon dioxide (CO2) and oxygen (O2) concentrations. The measured carbon dioxide and oxygen are used to calculate the Carbon dioxide Evolution Rate (CER), Oxygen Uptake Rate (OUR) and the Respiratory Quotient (RQ) with a high degree of accuracy. These data may be used by operators or in feedback control to make process decisions. For example:

  • The OUR or CER may be used to determine when to transfer the seed tank or inoculate the fermentor.
  • OUR may be used to modify sparging air or agitation.
  • OUR may be used to determine if the culture has become contaminated.


Fermentation is one of the most important biochemical manufacturing processes. Fermentation processes
are utilized to manufacture pharmaceutical compounds, chemicals and biofuels (from both sugar and cellulosic
feed stocks). Fermentation is the term used by microbiologists to describe any process for the production
of a product by means of the mass culture of a microorganism.
The three main types of fermentation processes are batch, fed-batch and continuous. These processes are briefly described below:
Batch Fermentation
In a batch fermentation process, a sterilized nutrient solution in the fermentor is inoculated with microorganisms
and incubation is allowed to proceed with virtually no interaction. Typically, the only items added to the fermentor are oxygen, an antifoam agent and either an acid or base to control the pH.
Fed-batch Fermentation
If one adds some of the sterile nutrient to the fermentor, at well defined increments, while the fermentation
process is proceeding, one has created the fed-batch fermentation process.
Continuous Fermentation
As its name implies, in a continuous fermentation process sterile nutrient is added to the fermentor
continuously and an equal amount of converted product is removed from the fermentor.
The physical configuration within the fermentation vessel can be viewed as consisting of three phases:

  • Liquid phase: This phase contains all of the dissolved nutrients, substrates and metabolites.
  • Solid phase: This phase contains the individual cells, pellets, insoluble substrates and all precipitated products.
  • Gaseous phase: This phase is a region above the liquid and solid phases where gases are present

Installation notes

The MGA system can be configured to monitor the fermentors’ input and exhaust gases via a sample conditioning
and multiplexing valving system. In addition to measuring multiple points on one fermentor, a MGA system can use stream switching to analyze multiple fermentors. A typical fermentation configuration is illustrated
in Figure above. Gas sample lines from the feed and exhaust lines are pumped through a sample conditioning
system and stream selection manifold. The MGA data station controls the stream selection manifold to
determine which sample is sent to the MGA inlet. Calibration gas cylinders are also typically plumbed to the
stream selection manifold and controlled by the MGA data station. The MGA system is controlled by a data
station, and results are transmitted to the fermentation system controller, DCS or PLC using Modbus® RTU,
Modbus TCP/IP, OPC or Analog outputs.

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