Instrumentation and Process Control

• Fermentation systems must be efficiently controlled in order to optimize productivity and product yield, and ensure reproducibility.

• The key physical and chemical parameters involved are largely depend on– a. the bioreactor,– b. its mode of operation– c. microorganism being used.

• They are primarily – aeration, – mixing, – temperature, – pH and – foam control.

Control and maintenance at optimum levels inside the reactor is mediated by sensors (or electrodes), along with compatible control systems and data logging

• Samples can be taken off-line for various analysis, such as – cell counts – determination of DNA, – determination of RNA; – determination of lipids, – determination of specific proteins, – determination of carbohydrates and – other key metabolites and substrates.

There are three main classes of sensor:

1. Sensors which penetrate into the interior of the fermenter, e.g. pH electrodes, dissolved-oxygen electrodes.

2. Sensors which operate on samples which are continuously withdrawn from the fermenter, e.g. exhaust-gas analyzers.

3. Sensors which do not come into contact with the fermentation broth or gases, e.g. tachometers, load cells.

• Internal sensors

– are in or above the fermentation medium ( e.g. pH, oxygen, foam, redox, medium analysis and pressure probes).– should be steam sterilizable and robust.

• Some sensors do not come into direct contact with any internal component of the bioreactor and do not need sterilization; for example, – load cells, – agitator shaft power and speed meters, and – external sensors used to analyze samples regularly withdrawn from

the bioreactor.

• It is also possible to characterize a sensor in relation to its application for process control. These are of three types:-

– 1. In-line sensor.

– 2. On-line sensor.

– 3. Off-line sensor.

Characteristics of ideal sensor or Criteria for selection or evaluation

• When evaluating sensors to use in measurement and control it is important to consider – response time, – gain,– sensitivity, – accuracy, – ease and speed of calibration,– stability, – reliability, – output signal (continuous or discontinuous),– materials of construction, – robustness, – sterilization,– maintenance, – availability to purchase and – cost

The Sensors used in bioprocess fermenter monitoring and control

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