Bioreactors discontinuous

Bioreactors are operated in discontinuous mode, with a sequential or continuous feed of the substrate (fed-batch operation) or in continuous mode. The choice of the operating mode depends mainly on the reaction characteristics ... 

Discontinuous agitation of rotating drum bioreactors has been used in a few studies [152, 153]. In the work of de Reu et al. [152], when the temperature within the bed exceeded a setpoint, a one-minute agitation regime was initiated, with rotation alternately clockwise and counterclockwise at 4-6 rpm. In different fermentations adequate temperature control was achieved with mixing events being initiated at intervals from as short as 9 min to as long as 142 min. 

Figure 3 Fermentation modes for recombinant bacteria, yeast, and animal cells. On the left-hand side, the feed streams and harvesting streams are schematically shown for the batch, fed-batch, and continuous cultivation of microorganisms. On the right-hand side, the product concentration and the cell density are shown. For batch and fed-batch a discontinuous product concentration profile is obtained. With constitutive expression of a product, the product concentration is dependent on the cell density. Product is present in the culture supernatant during the whole production cycle and thus more susceptible to degradation. When the product formation is induction controlled, the production concentration raises sharply after addition of the inductor. The residence time of the product in the bioreactor is reduced. For continuous culture a constant product concentration profile is maintained over the entire production cycle. The residence time of the product in the bioreactor depends on the harvesting time and is shortest tor all fermentation modes when harvesting is continuously performed. Changing the mode of production can highly influence the composition of feed for preparative chromatography.

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