Theory: Different types of Bioreactor
Bioreactor: Bioreactor is a vessel, which is used to carry out one or more biochemical reactions to convert raw materials to products through the action of biocatalyst, enzyme microorganisms, cells of animal or plants. The raw material could be an organic compound e.g sugar or an inorganic chemical eg., CO2 or even complex material such as meat, animal manure or waste stream. The product of conversion may be biomass (e.g, Bakers yeast growth associated primary metabolites (eg. Ethanol, Citric acid) or non growth associated metabolites (Antibiotics, bioactive compounds for plants) etc. These products may be extra cellular or intracellular as well. A large number of bioreactor designs are therefore needed to accommodate great diversity of substrate product and biocatalyst. Cultivation of the cells or biocatalyst is done in a perfectly mixed (submerged) mode or non mixed mode (surface) or via solid state cultivation.
Stirred tank Reactors: These are the vessels with four baffles, round sparger for aeration (if required) and contain flat blade turbine impeller for agitation. These reactors are operated with the modified designs of impellers for the cultivation of shear sensitive plant or animal cells. Such typical impeller designs include setric impeller helical impeller & marine impeller etc.
Bubble column Reactor: This type of reactor consists of long cylindrical column with or without horizontal perforated plates. Aeration and agitation is effected by sparging gas from the base via perforated pipe/plates or sintered glass. These reactors are particularly useful for hairy root culture of the plant cells.
Air lift reactor: In an air lift reactors the fluid volume is divided by providing a draft tube in the reactor. Sparging is done either inside or outside the draft tube. The sparger zone (having less density) is known as riser and the zone receiving no gas (having high relative density) is known as down comer. This density difference between the two zones leads to circulation of broth and keep the heterogeneous cell mass under homogenous conditions. No power is consumed for agitation in this type of the reactor and so they are regarded as highly energy efficient system. These reactors are suitable for bacteria yeast fungi and particularly for animal and / or plant cells however, these can be not be applied to viscous systems.
Fluidized bed reactor: In this an up flowing liquid stream is used to suspend or fluidize dense solid particles. It is more or less equivalent to bubble column except that cross section area is expanded near the top to reduce super facial velocity of fluidizing liquid to a value below that needed to keep the solids or gas to produce gas – liquid – solid fluidized bed Typical application of these reactor is in waste treatment.
Packed bed bioreactors: A bed of solid particles usually with compressing walls constitute packed bed. Biocatalyst is supported in porous or non porous bed. The particle may be randomly shaped wood chips or rocks or sphere cubes Fluid comprising of dissolved nutrient and substrate flows through the solid bed. The Flow rate and in term the residence time of substrate is manipulated to increase or decrease substrate contact with the bed (microorganisms).
Photo bioreactors: Photobioreactors are used for photosynthetic culture of cyano bacteria, micro algae and plants. Due to high dependence on light, these types of reactors should have high surface to volume ratio and this greatly affects the design of the bioreactor. These reactors are generally open to atmosphere e.g. ponds, lagoon etc. In ponds and lagoons plastic lined channels are used. The culture is mixed and circulated by a paddle wheel. Closed photo bioreactors are also in use now which are made up of glass / plastic tubing which are arranged in a ladder configuration. Instead of tubes a conventional vessel with low surface to volume ratio may be illuminated by optical fibers to convey light inside from an external source.
Rotary Drum Reactors: In this, the drum is filled with 40% of its volume and rotated by means of rollers. It is particularly suitable for the cultivation of the plant cell cultures.
Mist Bioreactor: This is suitable for hairy root cultivation of plant cells. Static root mass is contained in a chamber that is mostly empty. Nutrients are supplied as mist of fine droplets suspended in circulating air currents that penetrates the spaces between the roots.
Solid State Reactor: The substrates of solid state fermentation are solid having little or no water. Small particles with large surface to volume ratio are preferred. Small heaps may be prepared to do this effectively. Deep bed requires forced aeration with moistened air. Aeration may vary widely. Occasional turning and mixing improves oxygen transfer. Solid state process generally use mixed culture. The product formed is extracted from the bed by solvent extraction.