Abstract
In the present work, a novel packed bed external loop pneumatically agitated airlift bioreactor with an internal gas distributor (perforated plate) between two rolls of packing in the riser was designed and built. This novel approach combines advantages of packed bed and external loop airlift bioreactors. The main objective of this research work was to characterize the hydrodynamic performance of this novel reactor through a non-intrusive flow visualization technique called electrical resistance tomography (ERT). The tomography images, which were generated using a linear back projection algorithm, were employed to explore the effects of different design parameters and operating conditions. These include the effect of the two packing in the riser and the internal gas distributor (perforated plate) installed between the two packing. Other parameters investigated include the effect of sparger configuration, gas flow rate, and liquid height in the bioreactor on the different hydrodynamic parameters such as gas holdup, mixing time, and liquid circulation velocity. Results showed that the gas holdup and mixing time increased in the presence of the gas distributor, while the riser superficial liquid velocity was decreased. Furthermore, gas holdup and mixing time increased, superficial liquid velocity decreased when decreasing liquid height in the reactor, and when using packing or gas distributor between two packings in the riser. These results can be used to improve mixing characteristics in external loop airlift bioreactors for wider range of applications.
Highlights
The effect of gas flow rate, bioreactor liquid height, sparger configuration and bioreactor configuration on gas holdup, mixing time and liquid superficial velocity will be discussed in this chapter
A novel external loop airlift bioreactor was designed by installing an internal gas distributor between two packings in the riser
The lower gas flow rate resulted in the formation of smaller number of bubbles, which contributed to a lower gas holdup
Summary
Biotechnology research has been advanced both on laboratory and on industrial scale. A large variety of microorganisms are being genetically engineered for possible use in production processes. When the sparging aeration system is used in the bioreactors, the dissolved carbon dioxide can transfer from liquid medium to rising bubbles and leave the culture system through exit gas. An airlift fermentor differs from bubble column bioreactor because of its fluid flow characteristics by the introduction of a draft tube which improves circulation and provides better mass and heat transfer efficiencies and more uniform shear conditions. Airlift bioreactors have been extensively used in biotechnology industries in recent years in a variety of arrangements and applications This includes commercial manufacture of pharmaceuticals, enzymes, fragrances, dyes and antibiotics (Sarkar et al, 2008; Zhang et al, 2005; Al-Qodah and Lafi, 2001). Analyses and description of the behaviour of airlift bioreactors usually involve the use of parameters such as gas holdup, liquid velocity, mass. The liquid velocity affects turbulence, the gas-liquid mass transfer, and the shear forces (Mohanty et al, 2007; Zhang et al, 2005; Hwang and Cheng, 1997)
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