Fermentors air-lift

The use of air lift fermentors has been advocated as a means of overcoming the sensitivity to shear while still maintaining adequate oxygen and mixing characteristics (24). Scale-up of such fermentors has shown mixed results in that the productivity has either decreased (22-25) or increased (24) in going to larger sizes. The hydrodynamics of such systems are extremely complex to model. Some work on modeling of air lift systems for microbial fermentations has been carried out (26-29) however, none of the models so far proposed has been tested with plant cell systems. 

Transfer in an Air Lift Fermentor. Doctoral dissertation, Massachusetts Institute of Technology, 1973. 

The air-life fermentor consists of two concentric columns. The outer column has a conical bottom section with a perforated plate acting as a gas distributor. The inner column is positioned over this plate. Compressed air, enriched with CO2, is used to lift a suspension of mineral and bacterial culture in medium through this inner column. The suspension then falls to the reservoir and is air-lifted up the column again. The air-lift fermentor provides a good supply of oxygen and is able to keep high pulp densities (25%) of ore fully suspended in the medium. An illustrative example is provided by the work of Helle and Onken (47). Pachucas operate in a similar fashion to the air-lift fermentor, but there is no inner column. Air enters at the conical base of the reactor, aerates the medium, and suspends and circulates the mineral particles. Pachucas are useful reactors for building up culture stocks. 

In order to study in situ ethanol production and recovery, Tsao et al. [18] conducted ethanol fermentation in an air-lift loop fermentor with a side arm (ALSA) using CO2 to strip ethanol from the fermentor. Analogous to the traditional air-lift fermentor, the ALSA consists of an inner tube that enhances the mixing and mass transfer characteristics (see Fig. 3 for fermentor configuration... 

Recently, Lubbert and Larson (1990) analyzed the local mixing behavior in bubble columns and in air-lift fermentors utilizing a heat pulse-probe experiment. They considered the spreading of an originally narrowly distributed clump along the principle flow direction. Based on theory, the width of the spreading cloud (i.e. standard deviation) can be described by ... 

New types of fermentor have been developed such as the air lift fermentor where a stream of air effects mixing and aeration or systems where the cells are immobilised in foams and the growth medium is allowed to percolate through, removing the product from the cell matrix. 

Y ou are studying dispersion in a small air-lift fermentor. This ferment or is 1.6 m tall, with a 10-cm diameter. Air and pure water are fed into the bottom at superficial velocities of 11 and 0.78 cm/sec under these conditions the gas bubbles occupy 45% of the column volume. You continuously add 15 cm /min of 1-M NaCl solution near the top of the column. You find by conductance that the salt concentration halfway down the column is 2.32-10 M. What is the dispersion coefficient Answer 54 cm /sec. 

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