Instrumentation and Process Control Fermentation systems must be

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, p. H 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. p. H 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 Sensors which operate on samples which are continuously withdrawn from the fermenter, e. g. exhaust-gas analyzers. 3.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. p. H, 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– load cells, – agitator shaft power and speed meters, and – external sensors used to analyze samples regularly withdrawn from the bioreactor.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

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