Bioreactors and Culture Techniques for Microbial Processes

Current bioreactors are grouped into either culture vessels and reactors using biocatalysts (e.g., immobilized enzymes/microorganisms) or plant and animal tissues. The latter is sometimes used to mean the bioreactor.

Table 1 shows a number of aerobic fermentation systems which are schematically classified into (i) internal mechanical agitation reactors, (ii) external circulation reactors, and (iii) bubble column and air-lift loop reactors. This classification is based on both agitation and aeration as it relates to oxygen supply. In this table, reactor 1 is often used at the industrial level and reactors (a)2, (b)2, (c)2, and (c)3, can be fitted with draught tubes to improve both mixing and oxygen supply efficiencies.

Culture techniques can be classified into batch, fed-batch, and continuous operation (Table 2). In batch processes, all the nutrients required for cell growth and product formation are present in the medium prior to cultivation. Oxygen is supplied by aeration. The cessation of growth reflects the exhaustion of the limiting substrate in the medium. For fed-batch processes, the usual fed-batch and the repeated fed-batch operations are listed in Table 2.

A fed-batch operation is that operation in which one or more nutrients are added continuously or intermittently to the initial medium after the start of cultivation or from the halfway point through the batch process. Details of fed-batch operation are summarized in Table 3. In the table the fed-batch operation is divided into two basic models, one without feedback control and the other with feedback control. Fed-batch processes have been utilized to avoid substrate inhibition, glucose effect, and catabolite repression, as well as for auxotrophic mutants.

Table 1. Classification of Aerobic Fermentation Systems

(a) Internal mechanical agitation reactors

1. Turbine-stirring installation

2. Stirred vessel with draft tube

3. Stirred vessel with suction tube

(b) External circulation reactors

1. Water jet aerator

2. Forced water jet aerator

3. Recycling aerator with fritted disc

(c) Bubble column and air-loop reactors

1. Bubble column with fritted disc

2. Bubble column with a draft tube for gyration flow

3. Air lift reactor

4. Pressure cycle reactor

5. Sieve plate cascade system

Table 2. Classification of Fermentation Processes
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