Bioreactors Mixed by the Motion of the Bioreactor Body

It is also possible to obtain some mixing within the substrate bed through movement of the whole bioreactor body (Fig. 9.6). A rocking-drum bioreactor of 1.3 L holding volume was used by Barstow et al. (1988), Ryoo et al. (1991), and Sargantanis et al. (1993) in studies of bioreactor control strategies. The bioreactor consists of three concentric drums, an inner, a middle, and an outer drum (Fig. 9.6(a)). The inner drum and the middle drum are perforated, and the substrate bed is held, loosely packed, between these two drums. Air is introduced inside the inner drum. It passes through the perforations into the bed, through the bed and through the perforations in the middle drum to the space between the middle drum and the outer drum where it then moves to the air outlet. Water can be dripped

Horizontal Drum Perforat Bioreactor

Fig. 9.6. Bioreactors in which the mixing action is provided by the motion of the bioreactor body. (a) The rocking-drum bioreactor. The substrate bed is held between the inner and middle drums, which are both perforated in the manner shown on the right in the exploded view of the middle drum. The diagram on the right also shows how the mixing action is provided by the forwards and backwards turning of the middle drum. (b) A drum in which a stationary pipe remains within the bed as the drum body rotates

Fig. 9.6. Bioreactors in which the mixing action is provided by the motion of the bioreactor body. (a) The rocking-drum bioreactor. The substrate bed is held between the inner and middle drums, which are both perforated in the manner shown on the right in the exploded view of the middle drum. The diagram on the right also shows how the mixing action is provided by the forwards and backwards turning of the middle drum. (b) A drum in which a stationary pipe remains within the bed as the drum body rotates through the perforations in the inner drum, moving by gravity through the bed. The two outer drums rotate in relation to the inner drum, this causing a mixing action within the bed. The name "rocking drum" arises because the rotation occurs with three-quarter turns in a clockwise-counterclockwise sequence, at a rate of 1 revolution every 5 minutes. At the scale of 1.3 L, good control is achieved, with the substrate bed temperature being controlled within ± 1°C of the set point of 37°C. However, it is questionable whether this bioreactor will be effective at large scale. Certainly, the mixing action generated by the relative motion of the inner and middle drums will be inefficient at large scale.

Schutyser et al. (2003a) used a 28-L drum bioreactor (30 cm internal diameter and 40 cm length) in which the air line entered at the central axis but then passed through the bed in a U-shaped tube, which had several small holes in the horizontal section that passed through the center of the bed (Fig. 9.6(b)). Mixing action was provided by the rotation of the drum. They used discontinuous mixing. However, from the point of view of good aeration, continuous mixing would be better.

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