Airlift bioreactors

Figure 19.1 shows an airlift bioreactor contains external loop which is made of Pyrex glass. The bioreactor was fed with sweet cheese sterilized and deprotenized whey. The cell suspension was aseptically transferred to the bioreactor. Airlift bioreactor was operated at working volume of 7 liters that included 10% pre-culture. The regulation system allows for temperature control at 30 1°C foam-level and pH controlled by addition of antifoam and ammonia, respectively. The set-point fixed at pH 5.0 0.1. The system was aerated with filtered air at a different flow rate of 0.1, 0.4, and 0.8 vvm that was controlled using an aeration pump controller Each run was achieved in duplicates the average values of lactose, ethanol, and biomass concentrations were calculated and monitored with respect to time. 

M. Y. Chisti, Airlift Bioreactors, Elsevier AppHed Science, New York, 1989. 

Airlift pressure cycle bioreactor the gas is circulated by means of pressurised air. 

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. 

The gas is circulated by means of pressurised air. In airlift bioreactors, circulation is caused by die motion of injected gas through a central tube, with fluid recirculation through the annulus between die tube and the tower or vice versa. Figure 6.1 shows an airlift bioreactor widi an internal loop cycle of fluid flow. 

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. 

Fig. 6.2. Airlift bioreactor with external recirculation pump.

The inoculate was prepared in 250 ml flasks containing 100 ml of growth medium, which is inoculated with 10 ml of spore suspension. The mixture was shaken at 250 rpm and the temperature was controlled at 26 °C for 48 h. Then, 110 ml of resulting mycelia suspension is used to inoculate a 1000 ml broth in the airlift fermenter. The sterilised media are slowly pumped into the bioreactor at a flow rate of about lOOmlh-1 until 2 1 working volume is fully utilised. Aeration rates of 0.5, 1 and 2vvm (1,2 and 4 1 air/min) are used.6,7 Samples were taken at 24 hour intervals and evaluated for biomass, sugars and antibiotic concentrations. 

Glasgow LA, Jones GT, Erickson LE (1989) Hydrodynamic characterization of airlift bioreactor operation. In Two-Phase Flows, Tapie, Tawan... 

The aims of the present work were to culture H. pluvialis in the airlift bioreactor in order to examine the effect of superficial gas velocities on growth of H. pluvialis. 

Figure 1 shows that high superficial gas velocity in the airlift bioreactor obviously inhibited growth of H. pluvialis. In this study, the best superficial gas velocity for growth of H. pluvialis was found at the lower limit of the experiment (0.4 cm s ), which providing the maximum cell density and maximum specific growth rate of 77x10 cells mL (2.79 g L of... 

Figure 1 Growth curve ofH. pluvialis at different superficial gas velocities (Ug=0.4,2, 2.5, 3 cm s" ) in 3L airlift bioreactor (Aa/Ar=3.2).

This work demonstrated that an airlift system was suitable for the cultivation of Haematococcus pluvialis, one of the most effective microorganisms that could produce high potential antioxidant carotenoid, astaxanthin. Aeration was shown to be crucial for a proper growth of the alga in the airlift bioreactor, but it must be maintained at low level, and the most appropriate superficial velocity was found to be at the lower limit of the pump, i.e. 0.4 cm s". ... 

L airlift bioreactor respectively [130]. The slow growth rate of plant cells leads to a high possibility of contamination during the cell culture, thereby increasing the production cost. Thus, efforts have been made towards alternative hosts, like engineering microbes to produce Taxol. 

Navia-Osorio, A., Garden, H., Cusido, R.M. et al. (2002) Production of paclitaxel and baccatin III in a 20-L airlift bioreactor by a cell suspension of Taxus wallichiana. Planta Medica, 68, 336-340. 

The draft-tube airlift bioreactor was studied using water-in-kerosene microemulsions [263], The effect of draft tube area vs. the top-section area on various parameters was studied. The effect of gas flow rates on recirculation and gas carry over due to incomplete gas disengagement were studied [264], Additionally, the effect of riser to downcomer volume was also studied. The effect of W/O ratio and viscosity was tested on gas hold-up and mass transfer coefficient [265], One limitation of these studies was the use of plain water as the aqueous phase in the cold model. The absence of biocatalyst or any fermentation broth from the experiments makes these results of little value. The effect of the parameters studied will greatly depend on the change in viscosity, hold-up, phase distribution caused due to the presence of biocatalyst, such as IGTS8, due to production of biosurfactants, etc., by the biocatalyst. Thus, further work including biocatalyst is necessary to truly assess the utility of the draft-tube airlift bioreactor for biodesulfurization. 

Recent reports on other forms of reactors are also available. Immobilized cell bioreactors, upflow sludge blanket reactors, draft-tube airlift reactor and other have been suggested. Each of these reactors has its own pros and cons and the advantages need to be evaluated with the whole process in mind. Further work is necessary in this area. Several process schemes have been considered and evaluated with the batch reactor design as the core BDS reactor ... 

Mehrnia, M. R. Towfighi, J. Bonakdarpour, B., and Akbarnejad, M. M., Gas hold-up and oxygen transfer in a draft-tube airlift bioreactor with petroleum-based liquids. Biochemical Engineering Journal, 2005. 22(2) pp. 105-110. 

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... 

Figure 10. Airlift or draft-tube three-phase fluidized bed bioreactor.

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