Basic Features Design and Operating Variables for Group III Bioreactors

The basic design features have already been presented in Sect. 3.3.1. Some possible design variations include (Fig. 8.1):

• the inclusion of baffles (or, more correctly, "lifters");

• periodic reversal of the direction of rotation;

• use of drum cross-sections that are not circular;

• inclination of the drum axis to the horizontal.

Design variables for both baffled rotating-drum and stirred-drum bioreactors include (Fig. 8.2):

• the length and diameter of the bioreactor. Note that the geometric proportions can vary over quite a wide range;

• the inclination of the central axis of the bioreactor to the horizontal;

• the size and shape of the mixing device within a stirred-drum and the number, size, and shape of baffles in a baffled rotating-drum;

• the design of the inlet and outlet of the aeration system, which will affect the gas flow patterns in the headspace;

• the presence or absence of an external water jacket. Note that for a rotating drum this will increase the weight to be rotated and also will require a rotating water seal on the inlet and outlet water lines;

• whether internal features such as baffles or paddles are designed to aid in cooling;

• the design of the system for the addition of water or other additives to the bed during the process;

• in continuous operation, the design of the substrate inlet and outlet.

Rotating Drum Bioreactors
Fig. 8.1. Basic features of (a) rotating-drum bioreactors and (b) stirred-drum bioreactors

Design: number of air inlets, location, format

Operating: inlet air

• temperature

Design: geometric proportions (length and diameter)

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