Bioreactor height

The effective bioreactor height influences the circulation path, which has many hydrodynamic implications as implied by the liquid circulation velocity defined by Blenke (1979)  

The bioreactor height is often presented in the form of the riser aspect ratio (Ar/i/r). The effect of riser aspect ratio is expected to depend on the gas flow and gas circulation rate. An increase in the riser aspect ratio does not significantly change the liquid circulation velocity. Therefore, the circulation path length and circulation time increases with increasing riser aspect ratio, which allows the gas phase to achieve its equilibrium bubble diameter more efficiently. 

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Pressure drops of 1 m of water per meter of bioreactor or higher could quickly put a limit on bioreactor height. These pressure drops need to be carefully considered in the design of the aeration equipment for packed bed bioreactors. If pressure drop is a problem and infi equent mixing can be tolerated, then this mixing can be used to limit the pressure drop [127]. 

The easiest way to use the Da number is to identify a temperature which must not be exceeded within the bioreactor during the fermentation and to rearrange the equation to be explicit in H. Allowable bioreactor heights can then be calculated if an assumption is made about how Vz varies as H increases. Note that this approach predicts that there are no Hmits on height if the ratio Vz/H is maintained constant, although this is likely to lead quickly to unacceptably high pressure drops as scale increases [142]. More knowledge about the effects of pressure drop on packed bed operation is therefore required before this approach can be used effectively. 

The bioreactor height can be defined in two ways. The first definition is often termed the effective bioreactor height and is defined as the distance between the base and the bottom of the gas separator. The second is the unaerated iiquid height, which is defined as the distance from the base to the fluid surface prior to aeration. These definitions are shown in Figure 8.6 for the internal-loop and extemal-ioop airiift bioreactors. 

The area ratio effects on the liquid-phase mass transfer coefficient are more difficult to predict. Area ratio effects are usually studied by keeping the bioreactor volume equal, which requires the effective bioreactor height to be adjusted. As the height is increased, the interfacial solute gas concentration increases as well, which decreases the gas solubility and, in turn, the liquid-phase mass transfer coefficient. In addition, an increase in the area ratio decreases the liquid circulation rate, which increases gas holdup, but may decrease surface renewal. The greater height also raises the pressure drop and power consumption, which increases surface renewal and the liquid-phase mass transfer coefficient. The extent of these effects is dependent on the operational scale and power level, and it is hard to predict which will dominate. 

Bioreactor with the assumption of tank diameter is equal to the height of the liquid (/), = H). Assume steady-state condition, no cell accumulation and no death rate ... 

If substrate inhibition exists, a well-mixed bioreactor is desirable. Mixing in three-phase fluidized bed bioreactors can be increased by adding an external recycle loop, by inserting a draft tube in the reactor, or by decreasing the height to diameter ratio. 

Frmdamentally, air-lift bioreactors are a modification of the bubble colunms that generate air-flow for medium circulation unidirectionally by having at least two columns—a raiser column and a downer column. They are either a draft tube or an external loop bioreactor. The bubbles sparged into a draft tube generate upward flow and medium pours into the annular space between the draft tube and bioreactor vessel and flows downwards. An essential design feature to consider is the bioreactor ratio of the height (H) to the diameter (D). Values of H/D of five or more are needed for sufficient mixing (18). Efficiency of medium circulation depends on the rate of aeration and on the ratio of the cross-sectional area of the draft tube to the total... 

Consider an idealized simple case of a Michaelis-Menten type bioreaction taking place in a vertical cylindrical packed-bed bioreactor containing immobilized enzyme particles. The effects of mass transfer within and outside the enzyme particles are assumed to be negligible. The reaction rate per dilfcrential packed height (m) and per unit horizontal cross-sectional area of the bed (m ) is given as (cf. Equation 3.28) ... 

For scale-up of inoculum conditions of hairy root cultivation, a 1-L bioreactor (working volume of 800 mL) was used. This bioreactor had a height/diameter aspect ratio of 7.14. The bubble bioreactors had no internal mechanical agitation parts. The supplied aeration rate was 0.1 wm at the bottom by sparger. Each bioreactor was inoculated with 0.2-2.0 % (w/v) g fresh weight of hairy roots and cultured for 32 d. 

These bioreactors are characterized by their large height-to-diameter ratio and by an internal concentric cylinder, as shown in Figure 9.7. In the lower central region, there is a tube that injects gas inside the bioreactor. The pressurized gas stream generates bubbles that result in a low-density region inside the central tube. When these bubbles ascend, the liquid is... 

Fig. 4. Schematic diagram of a concentric-tube airlift bioreactor (with working volume of 1.0 1). 1 Reactor column 2 inner draft tube (with its height of 15 cm) 3 sparger B bottom clearance (2.5 cm) d diameter of draft tube (4.5 cm) D reactor diameter (7.0 cm) H column height (40 cm)...

The reciprocating bioreactor is a slim cylindrical vessel with a height/ diameter ratio of the order of 4 to 5 (Brauer and Sucker, 1979). The reactor contains a package of sieve plates attached to five rods. In the reactor of Brauer and Sucker (1979), the plate spacing is 42 mm, the diameter of the holes in the plates is 12 mm, and the hole spacing is 29 mm. This element undergoes a reciprocating motion up and down the reactor with an amplitude of 100 mm. 

The aerobic bioreactor is a tank measuring 32 m in diameter by 6 m in height, which gives a useful volume of about 5000 m. It has four ABS pumps, each with a power of 45 kW, by means of which the content of the reactor is constantly recirculated at a rate of 1400 m /h per pump, with the objective, obtaming perfect homogenization inside the reactor. 

Air or oxygen sparged into the bioreactor at the bottom drives circulation to keep cells in suspension, instead of a mechanical stirring device. To improve circulation and oxygen input and minimize cell damage, the height to diameter ratio is normally high in airlift fermenters (Handa et al, 1987). 

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