Airlift types

As this trend levels off with larger columns, it is recommended that values estimated for a 60 cm column are used. If heat transfer is a problem, then heat transfer coils within the column, or even an external heat exchanger, may become necessary when operating a large, industrial bubble column-type fermentor. Scale-up of an internal loop airlift-type fermentor can be achieved in the same way as for bubble column-type fermentors for external loop airhfts see Section 7.7. 

A two-litre airlift type fermenter was also applied to the scaled-up culturing in the same conditions as the RDF. However, the shoot formation frequency was below 30%. Tanaka [28] reported that Catharanthus roseus cells were damaged by hydrodynamic stress when cultured in a jar fermenter but not when cultured in a RDF. The low... 

In the preliminary experiment for MAFF clone 1 in liquid culture using a 100 ml flask, the ratio of UC to DT tended to increase with the increase of rotation rates. In the case of Cephaelis ipecacuanha (section 1.4.2), the frequency of adventitious shoot formation on intemodal segments was 83.7% when cultured in a RDF, whereas it is below 30% when cultured in an airlift type fermenter. The inhibition of shoot formation might be related with the hydrodynamic stress produced by aeration and/or rotation. Therefore, a RDF was chosen for P. somniferum cultures because the production of DT seemed to be associated with the codeine formation. Since moderate growth and alkaloid accumulation and proliferation of DT were observed in WP medium, DT was cultured using WP liquid medium. 

A third type of bioremediation involves the use of a bioreactor in a dedicated treatment area. The contaminated soil is excavated, slurried with water, and treated in the reactor. The horizontal drum and airlift-type reactors are usually operated in the batch mode but may also be operated in a continuous mode. Because there is considerable control over the operating conditions, treatment often is quick and effective. Contaminated groundwater and effluent also may be treated in either fixed-film or stirred-tank bioreactors. However, bioreactors are still in the developmental stages and further research is required to optimize their efficiency and cost effectiveness (Wilson and Jones 1993). 

Jamrack, W. D. and Walker, H. A. Improvements in or relating to Airlift Type Mixer-Settler Apparatus. U.K. Patent Spedfication 774,554 (application 1954). 

Nonmechanical, airlift type used fa- acid eggs and jet pumps... 

Static bath mode. Feed enters at one end of the dmm and the floats exit from the other end. The sink product is removed continuously from the rotating dmm through the use of lifters attached to the dmm which empty into a launder as they move to the top. A modification of the simple dmm separator is the two-compartment dmm separator which allows a two-stage separation. In the cone-type separator (up to 6.1 m in dia and 450 t/h) feed is introduced at the top. The medium in the cone is kept in suspension by gentle agitation. The sink product is removed from the bottom of the cone either directly or by airlift in the center of the cone. The maximum particle size that can be separated is limited to 10 cm. Other separators include the Drewboy bath and the Norwaltbath (2). 

Loop bioreactor a modified type of airlift system in which a pump transports the air and liquid through the vessel. 

In applications of airlift bioreactor there are various types of fermenter. The most common airlift bioreactors are pressure cycle, internal and external loop bioreactors. 

A modified type of airlift system widi gas and liquid flow patterns in which a pump transports the ah and liquid through die vessel. Here, an external loop is used, with a mechanical pump to remove the liquid. Gas and circulated liquid are injected into the tower through a nozzle. Figure 6.2 shows an airlift bioreactor diat operates widi an external recirculation pump. 

Reactor type Slurry bubble colunrn Slurry bubble column Slurry airlift reactor... 

There are a wide variety of three-phase fluidized bioreactor designs possible. The conventional reactor, shown in Fig. 9, is fluidized by both gas and liquid entering at the bottom of the reactor and leaving at the top and is the most common type of three-phase fluidized bed bioreactor. This reactor may be configured to operate with little axial liquid mixing or in a well-mixed mode by adding a recycle stream. The airlift reactor or draft tube fluidized bed reactor, Fig. 10, is also frequently used. In this reactor, gas is injected at the bottom of a draft tube placed in the center of the... 

Biomass containment in continuously operated bioreactors is an essential prerequisite for the feasibility of practical industrial-scale dye biodegradation. Biofilm airlift reactors have demonstrated excellent performance for their ability to control mixing, interphase mass transfer and biofilm detachment rate. Further studies are required to further exploit the potential of this type of reactors with either aggregated cells or biofilm supported on granular carriers. 

In some respects, airlift reactors (airlifts) can be regarded as modifications ofthe bubble column. Airlift reactors have separate channels for upward and downward fluid flows, whereas the bubble column has no such separate channels. Thus, fluid mixing in bubble columns is more random than in airlift reactors. There are two major types of airlift reactors, namely, the internal loop (IL) and the external loop (EL). 

The IL airlift reactor shown in Figure 7.11a is a modification of the bubble column equipped with a draft tube (a concentric cylindrical partition) that divides the column into two sections of roughly equal sectional areas. These are the central riser for upward fluid flow and the annular downcomer for downward fluid flow. Gas is sparged at the bottom of the draft tube. In another type of IL airlift, the gas is sparged at the bottom of the annular space, which acts as the riser, while the central draft tube serves as the downcomer. 

Two major types of fermentors are widely used in industry. The stirred tank, with or without aeration (e.g., air sparging) is most widely used for aerobic and anaerobic fermentations, respectively. The bubble column (tower fermentor) and its modifications, such as airlifts, are used only for aerobic fermentations, especially of a large scale. The important operating variables of the sparged (aerated)... 

Aerated stirred tanks, bubble columns, and airlifts are usually used for aerobic fermentations. One criterion of scaling-up aerated stirred tank fermentor is k a, approximate values of which can be estimated by Equation 7.36a or b. For the turbulent range, a general correlation for k a in aerated stirred fermentors is of the following type [3] ... 

Several different bioreactor configurations have been described for use in cell culture and fermentation applications. These include stirred tanks, airlift, and hoUow-fiber systems. The majority of bioreactor systems in use for cell culture applications are still of the stirred-tank type. These systems have been used for batch, fed-batch, and perfusion operations. It would not be possible to adequately cover the field of stirred-tank scale-up in the space available here. Instead, this section will touch briefly on the important issues in bioreactor scale-up. For detailed methodologies on stirred-tank bioreactor scale-up, the reader is referred to several review papers on the topic [20,27,28]. 

Until now, bioreactors of various types have been developed. These include loop-fluidized bed [14], spin filter, continuously stirred turbine, hollow fiber, stirred tank, airlift, rotating drum, and photo bioreactors [1]. Bioreactor modifications include the substitution of a marine impeller in place of a flat-bladed turbine, and the use of a single, large, flat paddle or blade, and a newly designed membrane stirrer for bubble-free aeration [13, 15-18]. Kim et al. [19] developed a hybrid reactor with a cell-lift impeller and a sintered stainless steel sparger for Thalictrum rugosum cell cultures, and cell densities of up to 31 g L1 were obtained by perfusion without any problems with mixing or loss of cell viability the specific berberine productivity was comparable to that in shake flasks. Su and Humphrey [20] conducted a perfusion cultivation in a stirred tank bio-... 

As microcarriers provide a good surface area for attachment per unit volume, various types have been routinely used to grow anchorage-dependent cell lines in bioreactors primarily used for suspension cultures. Airlift reactors can also be operated using microcarriers. Wang et al. reported the use of a fluidized-bed... 

Fig. 6 Various types of animal cell bioreactors (A) roller bottle (B) rotating disk (C) stirred tank with a marine impeller (D) tank with a pulsating agitator (E) stirred tank with a spin filter (F) airlift (G) fluidized bed and (H) hollow fiber. (View this art in color at WWW. dekker. com.)...

The split-cylinder IL airlift reactor (not shown in the figure) has a vertical flat partition which divides the column into two halves which act as the riser and downcomer sections. In these IL airlift reactors, as the gas holdup in the downcomer is smaller than that in the riser, the liquid will circulate through the riser and downcomer sections due to differences in the bulk densities of the liquid-gas mixtures in the two sections. The overall values of kLo for a well-designed IL airlift reactor of both the draft tube and split-cylinder types, are approximately equal to those of bubble columns of similar dimensions. 

In bubble columns, agitation of the liquid phase, and hence suspension of the catalyst is effected by the gas flow. The gas is often recycled to cause more turbulence and thus better mixing. Circulation of the liquid is often required to obtain a more uniform suspension. This can either be induced by the gas flow (airlift loop reactor) or by use of an external pump. In the latter instance it is possible to return the slurry to the reactor at a high flow rate through an ejector (Venturi tube). The local under-pressure causes the gas to be drawn into the passing stream, thus affording very efficient mixing. This type of reactor is called a Jet-loop or Venturi reactor. 

---