Continuous Culture

An-Ping Zeng; Jibin Sun

doi:10.1128/9781555816827.ch49

Chapter 49 : Continuous Culture

Authors: An-Ping Zeng, Jibin Sun

Content Type: Reference

Publication Year: 2010

Category: Applied and Industrial Microbiology

Book DOI: 10.1128/9781555816827

Chapter DOI: 10.1128/9781555816827.ch49

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Abstract:

The major applications of continuous culture are, however, still found in fundamental studies and process optimization at laboratory scale. This chapter provides a brief introduction to the general concept and theory of different types of continuous culture. The design and operation of equipment and experiments are discussed from an application point of view. Depending on the control parameter and the operation mode, continuous culture can be classified into four general types. The general concept and theory of four types of continuous culture are described in a detailed manner. A chemostat is usually started as a batch culture. The specific growth rate of a chemostat culture can be determined from a material balance for biomass: net increase in biomass = biomass in incoming medium + growth - output - death. Generally speaking, auxostats have the following advantages over conventional chemostats. First, auxostats permit stable operation in the “high-gain” areas near the maximum growth rate. Second, they reach steady state more rapidly at high dilution rates than the open-loop chemostat. Third, population selection pressures in an auxostat lead to cultures that grow rapidly. Finally, it is possible to design a dual set point auxostat that controls two growth parameters simultaneously. Nutrient reservoirs for continuous culture should have ports for feeding, addition and/or mixing of heat-labile nutrients and substrate, venting, and sparging of the medium. In particular, recent developments in implementing continuous culture in microfluidics or microdevices are worth mentioning and are briefly summarized in this chapter.

Citation: Zeng A, Sun J. 2010. Continuous Culture, p 685-699. In Baltz R, Demain A, Davies J, Bull A, Junker B, Katz L, Lynd L, Masurekar P, Reeves C, Zhao H (ed), Manual of Industrial Microbiology and Biotechnology, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555816827.ch49

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Continuous Culture

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FIGURE 1

Schematic diagram of four types of continuous culture.

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FIGURE 1

Schematic diagram of four types of continuous culture.

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FIGURE 2

Steady-state values of biomass and growth-limiting substrate concentration in a chemostat according to equations 9 and 10. Parameters: μmax = 1.0 h-1; Ks = 0.01 g/liter;

= 0.5 g/g.

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FIGURE 2

Steady-state values of biomass and growth-limiting substrate concentration in a chemostat according to equations 9 and 10. Parameters: μmax = 1.0 h-1; Ks = 0.01 g/liter; = 0.5 g/g.

/content/10.1128/9781555816827.ch49.ch49fig03

FIGURE 3

Typical profiles and reasons for continuous cultures deviating from chemostat behavior. The biomass curve of a corresponding chemostat culture (see Fig. 2 ) is also shown for comparison. (A) Effect of wall growth. K is the amount of growing biomass attached to the reactor surface per unit volume of culture. (B) Effect of imperfect mixing. (C) Effect of maintenance metabolism. ms is the maintenance requirement for substrate (g/g • h). (D) Effect of growth inhibition by product(s) and/or substrate.

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FIGURE 3

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FIGURE 4

Steady-state limiting-nutrient concentration, S̅, and dilution rate, D, as functions of biomass concentration in a turbidostat culture. Growth parameters are as given in the legend to Fig. 2 .

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FIGURE 4

Steady-state limiting-nutrient concentration, S̅, and dilution rate, D, as functions of biomass concentration in a turbidostat culture. Growth parameters are as given in the legend to Fig. 2 .

/content/10.1128/9781555816827.ch49.ch49fig05

FIGURE 5

A typical setup of a bench-scale continuous-culture system. The feeding rate and the culture volume are controlled by a weight control unit.

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FIGURE 5

A typical setup of a bench-scale continuous-culture system. The feeding rate and the culture volume are controlled by a weight control unit.

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FIGURE 6

Diagram of a drip tube.

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FIGURE 6

Diagram of a drip tube.

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FIGURE 7

Control scheme for the reactor volume of a continuous culture that uses a liquid level controller backed up by an effluent gas system. (Modified from reference 66 .)

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FIGURE 7

Control scheme for the reactor volume of a continuous culture that uses a liquid level controller backed up by an effluent gas system. (Modified from reference 66 .)

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FIGURE 8

Schematic diagram of a back-flushing configuration for a cell recycle reactor with membrane microfiltration. The permeate in the reservoir is back-flushed through the membrane module by using pressurized nitrogen gas or air and controlled by a timer.

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FIGURE 8

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FIGURE 9

Transient behavior of a steady state after step changes in a continuous culture operated at a constant dilution rate. The culture is subjected to metabolic overflow and growth inhibition by substrate and products. The substrate concentration in the feed (y 0) is increased from (A) 0.334 to 0.550 (in dimensionless units), (B) 0.334 to 0.400, and (C) 0.334 to 0.335. The relative time is numerically equal to the number of reactor volume exchanges (residence times) ( 64 ).

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FIGURE 9

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FIGURE 10

Steady-state concentrations of biomass (A), substrate in reactor (B), and product (C) in a continuous culture at a constant feed substrate concentration but varied dilution rates (dimensionless feed substrate concentration, y 0 = 0.2). This culture is subject to metabolic overflow and growth inhibition by product. Multiple steady states are found in a given range of dilution rates. Depending on the operation mode, different steady states can be obtained under identical operation conditions ( 64 ).

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FIGURE 10

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