Airlift bioreactors are used for cell culturing, pallet form fermentation, and immobilized enzyme reactions. Typically, airlift bioreactors are used when the desired reactants and/or final products are in a gaseous state and for aerobic cell cultures.
An airlift bioreactor works by agitating the contents of the bioreactor pneumatically using gas. The gas used for agitation can act to either, introduce new molecules to the mixture inside of the bioreactor, or remove specific metabolic molecules produced by microorganisms. Airlift bioreactors have a built-in bubble column designed to release gas into the bioreactor. Gas is usually injected into the bubble column at the bottom of the bioreactor. Mixing occurs as the bubbles rise through the bubble column to the top of the bioreactor.
Simple diagram of an airlift bioreactor
The pattern of fluid circulation inside airlift bioreactors can be customized through the design of its bubble column and shape. There are two separate channels within an airlift bioreactor: one channel for gas/liquid up-flow and one channel for gas/liquid down-flow. Both channels create a closed gas/liquid circuit. The mechanism for removing gaseous substances at the top of the bioreactor is called the gas separator.
There are two types of airlift bioreactors: external loop vessels and baffled vessels. External loop vessels have distinct and separate conduits for circulation of gases and liquids. Baffled vessels draw upon spider diffraction techniques to customize gas and liquid through the bioreactor flow by including channels, vanes, and/or other methods of obstruction. Baffled vessels allow for greater control of gas and liquid circulation patterns within bioreactors through the creation of customized bubble disengagement and gas/liquid flow rates.
The primary advantage of airlift bioreactors over other bioreactors is due to the nature of how the contents inside airlift bioreactors are mixed. They have no focal points of energy dissipation and have homogenous shear and stress forces throughout the entire bioreactor. This makes airlift bioreactors ideal for culturing shear-sensitive cells.
Textile materials with leather-like properties were produced by growing the fungus Rizopus delemar, fed with bread waste, in an airlift bioreactor.
An airlift reactor containing fungal pellets of Asergillus niger KP was used to remove selenite from wastewater and convert it into selenium nanoparticles. Selenite, considered the most toxic of the selenium species, is found in wastewater from agricultural and industrial activities. Fungal pellets are a densely packed form of the hairy region of fungal hyphae.
Biodesulfurization was demonstrated in an airlift bioreactor in which the sulfur-oxidizing bacteria Thioalkalivibrio versutus was used to convert harmful hydrogen sulfide, a common poisonous gas found in natural gas, biogas, and industrial waste to sulfur. The bacteria remove sulfide from sulfide-contaminated sources, oxidize the sulfide, and eliminate it in the form of sulfur.
The removal of gas-phase trichloroethylene (TCE), a volatile organic compound (VOC), by Rhodococcus opacus bacteria was demonstrated in an airlift bioreactor. The performance of the system was predicted by an artificial neural network (ANN)-based model using the Levenberg-Marquardt (LM) back propagation algorithm, and optimized biological topology is 3:12:1.
CellMaker airlift bioreactors, developed by Cellexus International, are available in 8L and 50L sizes and are designed for cell lines such as E. Coli, Pichia, yeast, algae, and bacteriophage.
Spira is an airlift photobioreactor designed by Rob Russell while in the Product Design course at University of Leeds. Spira keeps air flowing through it to optimize the growth of spirulina, a type of microalgae. The device was designed for individuals to grow and harvest the nutrient-rich microalgae daily, which could increase its health benefits and allow people to decrease the amount of food they consume from land- and water-intensive farming. Growing spirulina in the bioreactor also converts carbon dioxide into oxygen through photosynthesis, which may provide air purification benefits in the home.
Companies in the airlift bioreactor market include the following:
Shree Biocare
Knik Technology
Rotech
Solida Biotech
Zeta GmBH
