Industrial design of bioreactors

By

Dr. Jitender Kumar

Bubble column bioreactors�

• The bubble column is employed in numerous chemical, biomedical and biochemical industries.
• They are easy in construction, simple maintenance and operate at a low cost.
• They have a cylindrical shape with a ratio of 4:6 (height: diameter ratio) and at the base of the column, air and gas are introduced through perforated pipes or plates or a metal micro porous sparger.
• The rate of flow of gas or air is monitored to ensure proper mixing or transfer of O2 is accomplished.

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Features of Bubble column bioreactors �

• The aspect ratio for height-to-diameter is usually between 4-6.
• Gas is supplied at the bottom by perforated pipes or plates , or metal spargers with porous materials.
• Oxygen transfer, mixing , and other performance parameters are affected mostly by the gas flow rate as well as the rheological characteristics of the gas.
• Mixing and mass transfer could be improved by putting perforated plates, or baffles with vertical sides within the vessel.
• Doesn’t contain any draft tubes.

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Mechanisms of Bubble column bioreactors �

• In the bubble column bioreactor the gas or air is introduced into the bottom of the column by perforated pipes, plates, or through metal micro porous spargers.
• The flow rate of gas or air affects the performance factors for O2 transfer mixing.
• The bubble column bioreactors can be equipped with perforated plates for improved the efficiency.
• The reactants are compressed by a finely dispersed catalyst , and so create the product using the process of fermentation.

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Advantages of Bubble column bioreactors �

• Efficient mixing without cell damage.
• High volumetric efficiency.
• Outstanding heat management.
• Greater utilization of the plate’s area as well as flow distribution.
• Self-regulating.

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Disadvantages of Bubble column bioreactors �

• Inefficient as compared to other bioreactors in terms of agitation, aeration etc.
• Doesn’t have draft tube.
• A higher consumption of catalyst make the process costly.
• Installation costs are higher, and the design is difficult to create.

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Applications of Bubble column bioreactors �

• The reactor is used extensively for the cultivation of heat-sensitive organisms. e.g. plant cells and mould.
• Cell damage can be minimum.
• Chemical and pharmaceutical production.

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Packed Bed fermenters�

• A packed bed bioreactor consist of solid particles, with biocatalysts on or within the matrix of solids, packed in a column constitutes .
• The solids used may be porous or non- porous gels, and they may be compressible or rigid in nature.
• A nutrient broth flows continuously over the immobilized biocatalyst.
• The products obtained in the packed bed bioreactor are released into the fluid and removed.

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Features of Packed Bed Reactors�

• A bed of particles are confined in the reactor. The biocatalyst (or cell) is immobilized on the solids which may be rigid or macro porous particles.
• A fluid containing nutrients flows through the bed to provide the needs of the immobilized biocatalyst. Metabolites and products are released into the fluid and removed in the outflow.
• The flow can be upward or downward. If upward fluid is used, the velocity can not exceed the minimum fluidization velocity.

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Advantages of Packed Bed Reactors�

• Higher conversion per unit mass of catalyst than other catalytic reactors
• Low operating cost.
• Continuous operation.
• No moving parts to wear out.
• Catalyst stays in the reactor .
• Reaction mixture/catalyst separation is easy
• Design is simple to use and maintenance.
• Effective at high temperatures and pressures.

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Disadvantages of Packed Bed Reactors�

• Undesired heat gradients.
• Difficult to treat large volume flow.
• Poor temperature control.
• Difficult to clean.
• Difficult to replace catalyst.
• Undesirable side reactions.

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Application of Packed Bed Reactors�

• These are used with immobilized enzymes or particulate biocatalysts.
• High conservation per weight of catalyst than other catalytic reactors thus mostly preferred bioreactor.
• Used is waste water and effluent treatment processes.

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Fluidized Bed Bioreactor�

• Fluidized bed bioreactor is comparable to bubble column bioreactor except the top position is expanded to reduce the velocity of the fluid.
• The design of the fluidized bioreactors (expanded top and narrow reaction column) is such that the solids are retained in the reactor while the liquid flows out.
• These bioreactors are suitable for use to carry out reactions involving fluid suspended biocatalysts such as immobilized enzymes, immobilized cells, and microbial flocks.

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Features of Fluidized Bed Bioreactor�

• Suitable for reactions involving a fluid-suspended particulate biocatalyst such as immobilized enzyme and cell particles.
• Similar to the bubble column reactor except that the top section is expanded to reduce the superficial velocity of the fluidizing liquid to a level below that needed to keep the solids in suspension.
• Consequently, the solids sediment in the expanded zone and drop back, hence the solids are retained in the reactor whereas the liquid flows out.
• The properties include:
• Extremely high surface area contact between fluid and solid per unit bed volume.
• High relative velocities between the fluid and the dispersed solid phase and High levels of intermixing of the particulate phase.

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Mechanism of Fluidized Bed Bioreactor�

• For an efficient operation of fluidized beds, gas is spared to create a suitable gas-liquid-solid fluid bed.
• It is also necessary to ensure that the suspended solid particles are not too light or too dense (too light ones may float whereas to dense ones may settle at the bottom), and they are in a good suspended state.
• Recycling of the liquid is important to maintain continuous contact between the reaction contents and biocatalysts.
• This enable good efficiency of bioprocessing.

Advantages of Fluidized Bed Bioreactor�

• Uniform particle mixing.
• Uniform temperature gradients.
• Ability to operate reactor in continuous state.
• Most effective in sewage works treatment processes.
• Useful byproducts can be produced and utilized.

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Disadvantages of Fluidized Bed Bioreactor�

• Increased reactor vessel size leads to handling and storage issues.
• Pumping requirements and pressure drop.
• Extensive chemical analysis.
• Lack of mixing and aeration.
• Erosion of Internal components
• Pressure loss scenarios

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Application of Fluidized Bed Bioreactor�

• These reactors can utilize high density of particles and reduce bulk fluid density.
• Fluidized beds are used as a technical process which has the ability to promote high levels of mixing between gases and solids.
• In a fluidized bed bioreactor the basic properties of solids can be utilized, indispensable to modern process and chemical engineering
• The food processing industry: fluidized beds are used to accelerate freezing in some individually quick frozen (IQF) tunnel freezers.
• The fluid used in fluidized beds may also contain a fluid of catalytic type.
• Fluidized beds are also used for efficient bulk drying of materials.

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Refrences

• Principles of fermentation technology by Stan bury and Whittaker
• Industrial Microbiology by Prescott and Dunn.
• Fermentation technology by Frazier.

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• Thanks