Design principles for a root culture bubble column bioreactor

A 15-liter, air-sparged column filled with high porosity (ϵ = 0.97) distillation column packings, which served as an inert support for the tissue, was used to cultivate three different Agrobacterium-transformed root lines: Solanum tuberosum and two lines of Hyoscyamus muticus. As the tissue grew, the specific growth rates and specific respiration rates declined by a factor of four over the 18- to 25-day cultivation periods.; Liquid mixing times were observed to steadily increase From 1.45 ± 0.45 minutes in a column with no roots to 5 hours at 204 g FW/L of Hyoscyamus muticus at 0.2 vvm gassing rate. As with Solanum tuberosum, the tissue respiration rate did not change with gas flow rate at any of the tissue concentrations.; Liquid mixing time was a strong function of gas flow rate at low solid phase holdup, similar to the root reactor. At 15% (v/v) the liquid mixing time of 127.2 ± 18.5 minutes measured at a gassing rate of 0.2 vvm was longer than mixing times measured for equivalent tissue concentrations in the root reactors, most likely due to reduced channeling on account of the more uniformly distributed solid phase.; Like the root reactor, gas disengagement measurements also suggested a significant static gas component in the rope ‘reactor’. The static gas holdup remained relatively constant with gassing rate. Gas phase residence time distributions suggested that the ‘true’ flowing (or dynamic) gas holdup was greater than suggested by the disengagement studies. This implies that the gas fraction that is stagnant under aerated conditions is not as great as suggested by the static holdup, which was measured after the gas supply was shut off.; The respiration rates measured for the root cultures in the bubble column reactor, along with known growth kinetics, allowed an independent calculation of the liquid-solid mass transfer coefficient (k_s). The values for ks based on measured respiration rates of S. tuberosum, hairy H. muticus, and hairless H. muticus, were 2.1 × 10−4 cm/s, 3.6 × 10−4 cm/s, and 1.07 × 10−3 cm/s, respectively. These calculations suggest that liquid-solid mass transfer is the limiting interfacial transport step, which is consistent with the liquid mixing and respiration studies carried out in the bubble column root reactors. (Abstract shortened by UMI.)...