Biochemical Reactor

A wide range of antibiotics, vitamins, amino acids, fine chemicals, and foodstuffs are manufactured biochemically. Detoxification of industrial and domestic waste water is also carried by biochemical means. The heart of a biochemical process is the reactor. In a bioreactor, the transformation of raw materials into desired products is carried out by the enzyme systems, living microorganisms or by isolated enzymes. The reaction products are formed by three basic processes, namely

1. The product is produced by the cells either as extracelluar or intra-cellular. Examples of the former include alcohols or citric acid production, and examples of the latter are metabolite or enzyme production.

2. Production of cell mass, like baker's yeast or single-cell proteins for food industries.

3. Biotransformations, where the cell catalyzes the conversion via dehydrogenation, oxidation, hydrogenation, amination, or isomer-ization. Steroids, antibiotics, or prostaglandins are produced by this approach.

The type of reactor depends on the nature of the process (including reaction kinetics), operating conditions (namely, mode of operation and gas liquid flow patterns), and physical and chemical properties of the substrates and the microbe. A plethora of biochemical reactors are available commercially, from which the most suited one could be selected based on certain selection criteria. Chapters 11 and 12 deals in more detail agitated and tower reactors, respectively.

In general the special features required by a biochemical reactor are reliable sterilization and ease of maintenance of sterility, rapid mixing (homo-genization) of reactor contents, sufficient and economical oxygen supply to the bioculture (aeration), good removal of heat of reaction, efficient retention of the bioculture in the reactor, permitting a high cell concentration, and sophisticated level of instrumentation to maintain constant operating conditions. Good mixing is achieved by proper design of stirrer, revolutions per minute (rpm), and stirrer motor. Oxygen flow rate and correct design of gas distributor in the reactor can ensure high gas-to-liquid mass transfer rate. Reactors are provided with jacket and cooling coils to rapidly remove the exothermic heat generated during the reaction, so that enzymes or the organisms are not exposed to excessive temperatures. As microorganisms are very sensitive to medium pH, reliable process control is very essential in bioreactors.

Biochemical rectors are made of stainless steel to maintain sterile conditions. Simple geometric shape, minimum number of flanges, welds and measuring and sampling nozzles, elimination of dead zones, and minimum surface roughness are also very essential for sterile operation. Valves are flush bottom diaphragm valves to avoid dead pockets and facilitate ease of sterilization.

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