FERMENTOR (Bioreactor)- stirred and airlift

FERMENTOR (Bioreactor)- stirred and airlift. By : Sumaiya Shaikh S19098.

What is a fermentor ?. A fermenter is an enclosed and sterilised vessel that maintains optimal conditions for the growth of a microorganism. The microorganism undergoes fermentation to produce large quantities of a desired metabolite for commercial use. They are systems or devices that supports a biologically active environment. They are vessels in which a chemical process is carried out which involves organisms or biochemically active substances derived from such organisms. They can be either aerobic or anaerobic. They are commonly cylindrical, ranging in size from liters to cubic meters, and are often made of stainless steel. They supply a homogeneous (same throughout) environment by constantly stirring the contents. They give the cells a controlled environment by ensuring the same temperature, pH, and oxygen levels..

Uses of fermentor. Fermenters are useful in the production of a broad range of products such as citric acid, lactic acid, vinegar, protease, lipase, amylase, cellulose, ethanol, glutamic acid, and streptomycin, all of which are used in the dairy, food and beverage, pulp and paper, and pharmaceutical industries, in biological wastewater treatment, and as industrial solvents.

Standard Fermentor components:. Probes and sensors are used to monitor condtions within the fermenter in order to maintain optimal levels of microbial growth Motorised stirring paddles function to distribute heat and materials evenly within the reaction chamber An external water jacket can be used to absorb excess heat and maintain a constant viable temperature An aerator can introduced compressed air into the chamber, while a defoamer can hinder the formation of foam Acid/base inlets allow for the regulation of pH levels within the chamber (formation of product may alter pH) Nutrient inlets and exhaust outlets allow for the introduction of sugars or the removal of metabolic wastes The necessary adjustments required for continued growth may differ between batch cultivation and continuous cultivation In both cases, conditions within the fermenter must remain aseptic to prevent contamination of the microorganism.

Batch Culture Fermentor. Fermentation is carried out in a closed fermenter, with nothing added or removed during the process (except venting of gas) Microorganisms and nutrients are left for a set period of time, during which the nutrient stock is depleted The advantage of a batch culture is that the fermenter can be used for different reactions with each separate use A disadvantage of a batch culture is that it results in significant periods of idle time between use, resulting in higher costs.

Example of Batch Culture Fermentor. The antibiotic penicillin can be mass produced via the use of deep-tank batch fermentation .Large industrial fermenters are constructed that have the capacity to hold thousands of litres . Penicillium mold is grown in the deep-tank batch fermenters following the addition of sugars and other key ingredients. The production process typically lasts 6 – 8 days, with the fermenter drained at the end of the fermentation cycle. Penicillin is separated from the solution and purified via downstream processing to improve its antibiotic potential.

Continuous Culture. Fermentation is carried out in an open fermenter, with nutrients added and product removed at a steady rate throughout This results in a continuous reaction with no idle time, reducing labour costs and increasing product yields A disadvantage of continuous culture is that there is a higher risk of contamination due to the constant adjustments Continuous fermentation is feasible only when the inoculated cells are genetically stable.

Example of Continuous Culture. Citric acid is mass produced by continuous fermenter systems from cultures of the fungus Aspergillus niger . Carbohydrates are continuously introduced into the fermenter in order to maintain the citric acid production. Iron (Fe2+ ions) is excluded from the mixture in order to slow the further conversion of citric acid within the Krebs cycle. As citric acid accumulates it is extracted as part of the medium that is being continuously withdrawn from the fermenter.

Stirred tank bioreactors. Stirred tank bioreactors (STBRs) are the reactors most widely employed for culturing of biological agents such as cells, enzymes, or antibodies. They are contactors where the well-mixed among phases is obtained mainly by internal mechanical agitation. The impeller must provide sufficiently rapid agitation to disperse all compounds and achieve an effectively homogeneous concentration inside the bioreactor..

The core component of the stirred tank bioreactor is the agitator or impeller, which performs a wide range of functions: heat and mass transfer, aeration, and mixing for homogenization. Two types of impellers are widely used in the conventional fermentation industry: axial and radial flow impellers. Over time, vast and valuable research endeavors have illustrated the transport phenomena of these impellers: oxygen transfer, heat transfer, power consumption, and fluid dynamics. These greatly facilitate the design, installation and optimization of these impellers in conventional fermentation, and so the standard stirred-tank bioreactor is used almost universally in the fermentation industry. Besides the impeller type, there are a number of geometric specifications important for the performance of the stirred tank reactor; these include the impeller off-bottom clearance, the impeller size, the baffles and their width, the sparger type and position, the ratio of liquid height to tank diameter and so on. For large-scale vessels, multiple impellers are often been installed in order to provide sufficient mixing and mass transfer..

Advantages and disadvantage of Stirred tank bioreactors:.

Airlift bioreactor. Airlift bioreactors are tower reactors for large-scale aerobic cultures where the mixing of the culture broth is done by the inserted gas via an airlift pump (Fig. 7.5). This pump injects compressed air at the bottom of the discharge pipe, which is immersed in the liquid. The compressed air mixes with the liquid, causing the gas–liquid mixture to be less dense than the rest of the liquid around it and therefore is displaced upwards through the discharge pipe by the surrounding liquid of higher density. Solids may be entrained in the flow and, if small enough to fit through the pipe, will be discharged with the rest of the flow at a shallower depth or above the surface. The only energy required is provided by compressed gas, which is prepared by a compressor..

Advantages and disadvantage of airlift bioreactor.

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