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The use of complex living organisms, process variation, and lack of real-time measurements of key parameters are some of the challenges involved in automating a bioprocess. This article explains an indirect approach to monitoring and controlling a fermentation process.
The automation of chemical processes began in the continuous petrochemical industries in the mid-20th century. University process-control courses and commercial automation products focused primarily on continuous linear processes running under steady-state conditions.
In the past few decades, batch and discrete manufacturing operations have started to benefit from automatic control. As a result, both vendor software and undergraduate courses have been challenged to integrate the unique requirements of these types of processes.
Most commercial bioprocesses are batch operations that are not continuous, linear, or steady-state. Automating them is significantly more complex than implementing a few proportional-integral-derivative (PID) controllers. This article examines some of the unique characteristics of bioprocesses, as well as a few selected measurement, modeling, and control techniques that are useful in automating them.
What is a bioprocess?
A bioprocess is a process in which the desired product (or its precursor) - for instance, antibiotics such as penicillin or proteins such as insulin - is produced by living biological material (e.g., fungal cells, E. coli bacteria, yeast, or mammalian cells) in a bioreactor (with various supporting unit operations). Most bioprocesses consist of three or four general phases that are conducted as a sequence of batch steps:
1. growing the living biological material
2. using the living biological material to make a desired product
3. separating the desired product from process materials and then purifying it
4. in some cases, modifying the product via chemical reaction before final purification.
Given the large diversity of biological processes, there are exceptions to the above paradigm. Sometimes the cell mass itself is the desired product, such as when it is used as a protein food supplement. In other cases, it is the activity of living cells that is important, such as the degradation of matter in waste-treatment systems.
Figure 1 shows some of the equipment involved in typical commercial bioprocesses. Note the use of unit operations such as fermentation and chromatography separations that are not commonly found in continuous processing industries. Figure 2 provides more detail on the components...