U

total bioreactor length

Fig. 11.4. Two main mixing directions in continuous SSF bioreactors

The amount of flow dispersion will depend on the design and operation of the bioreactor and the mixer and on the number of mixers used. It may be assumed to be roughly proportional to the sum of mixing lengths divided by total bioreactor length (see Fig. 11.4). For example, in a CSSFB composed of a single long belt carrying fermenting solids from inlet to outlet, the bed might not be mixed at all or it may be mixed occasionally so that sum of mixing lengths is negligible compared with total belt length. On the other hand, in a CSSFB composed of a rotating drum with curved baffles, the mixing length may be equal to total bioreactor length, leading to a wide residence time distribution.

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