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

Bioprocess Engineering ,Basic Concepts, -Michael L Bioprocess Engineering ,Basic Concepts, -Michael L. Shuler , Fikret Kargi, Second Edition

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 Sensors which operate on samples which are continuously withdrawn from the fermenter, e.g. exhaust-gas analyzers. 3.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. Principles of Fermentation Technology,- Peter F. Stanbury, Allen Whitaker, Stephen J. Hall, Second Edition

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for example, load cells, agitator shaft power and speed meters, and external sensors used to analyze samples regularly withdrawn from the bioreactor.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. Principles of Fermentation Technology,- Peter F. Stanbury, Allen Whitaker, Stephen J. Hall, Second Edition

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 Principles of Fermentation Technology,- Peter F. Stanbury, Allen Whitaker, Stephen J. Hall, Second Edition

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