Mechanical Agitators And Airlift Fermenters Biology Essay

A fermenter is a vas in which high graduated table agitation is carried out. There are 3 chief stairss involved in the agitation procedure. They are upstream processing, the agitation procedure itself and downstream processing.

Fermenters have several parts. Each portion has its ain usage and importance. The most of import portion though is the fomenter which brings about commixture of the contents contained in the fermenter vas.

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Based on the type of mixer nowadays in the fermenter vas we have automatically agitated fermenters and airlift fermenters. When we compared the 2 it was found that each type of fermenter has its ain advantages and disadvantages and a little alteration in the desing of the fermenter can take to better commixture and reduced mortality rates of the micro-organisms that are used in the agitation procedure.


A fermenter is a vas in which big graduated table agitation is carried out. It provides the right ambiance with all the appropriate conditions for the full agitation procedure to take topographic point. The agitation procedure is made up of 3 stairss. They are as follows:

Upstream processing: this involves sterilization of the fermenter vas, strain choice, isolation, saving, media readying, innoculum readying, debut of the media into the fermenter ( which occupies about 70-80 % of the volume of the fermenter vas ) and add-on of the innoculum to the fermenter.

Agitation itself: where the selected strain utilises the substrate and foods to bring forth the rough signifier of the coveted merchandise

Downstream processing: this includes stairss such as separation of the biomass from the supernatant fluid by centrifugation, filtration ( by vaccum ) , cell break, protein purification, freeze-drying and merchandise recovery.

There are several parts in a fermenter. These in general include: the fermenter vas itself ( which can either be made from pyrex glass or chromium steel steel depending on its capacity ) , the H2O recess and mercantile establishment, the outer chilling jacket ( which is filled with either tap H2O of refrigerated H2O ) , internal chilling spirals ( these are needed for big fermenters in order to guarantee efficient heat transportation ) , a motor ( to drive the impeller ) , velocity accountant, mechanical seal, a stirring shaft, baffle home bases ( to bring forth axial liquid flow and prevent vortexing ) , sparger, sparger ring, air filter, extra recess, air exhaust mercantile establishment, a froth ledgeman, a pH accountant, steam recess and a harvest mercantile establishment. They are shown in the diagram below:

These are used for the mass production of commercially of import substances such as antibiotics, monoclonal antibodies, etc.. There are several considerations which go into the pick of fermenter that is to be used. For illustration, size of the reactor required for optimum production, treating conditions prevailing inside the fermenter, manner of operation ( i.e. batch, fed-batch or uninterrupted ) , mass energy balance, heat transportation, mass transportation, commixture, aeration, cost effectivity etc.. The type of fermemter used depends upon the merchandise that is being produced.

Most importance is given to the appropriate proviso of equal commixture and aeration in the design of a fermenter since most agitation procedures are oxygen-requiring i.e. aerobic.

What is blending?

This is a physical operation that is carried out in all fermenters. It reduces the non-uniformity in a fluid. This is done by the riddance of gradients of concentration, temperature and other such belongingss. This procedure is achieved by substituting substances between different parts of the fermenter. This brings about unvarying mingling of the constituents that are present in the assorted parts of the fermenter. If the system is homogeneous so the assorted physical every bit good as chemical belongingss of that system will be more or less homogeneous.

The undermentioned stairss are involved in commixture:

Mixing of soluble constituents e.g. sugars

Dispersion of air in the signifier of gas bubbles throughout the liquid

Care of suspension of solid atoms such as cells

Dispersion of non-miscible liquids in the signifier of a suspension of all right droplets of as emulsions

Promotion of heat transportation.

Mixing is of premier importance in a bioprocess operation. In order to bring forth an optimum environment for agitation to happen, the cells which are present in the fermenter must hold entree to all the necessary substrates and foods in order to bring forth the coveted terminal merchandise. Such an environment can merely be produced when the contents that have been filled into the fermenter are uniformly assorted, if the contents of the fermenter are non assorted decently so zones of alimentary depletion will happen in parts of the fermenter. It is besides of import to keep a unvarying biomass suspension since substrate concentration can make zero in parts where the cells stay out of suspension.

Another of import facet of commixture is that it produces heat transportation. This is of import since it is necessary to keep a peculiar temperature during agitation for industry of the coveted merchandise. Cooling spirals incorporating H2O are present around the fermenter in order to take up any extra heat that is given of during agitation. The rate at which heat gets transferred from the medium in the fermenter to the chilling H2O is straight dependent on the blending status prevalent in the fermenter vas. And, the effectivity of the commixture in bend depends upon the rheological belongingss of the civilization fluid.

Blending can be attained in several ways. Depending upon the type of blending equipment nowadays in the fermenter they are divided into 2 types. They are automatically agitated and airlift fermenters.

Mechanically agitated fermenters:

A good illustration of this type of fermenter is the moved armored combat vehicle fermenter. They can be of 2 types depending on where they are being used. When used in the research lab they are little and are made of pyrex glass. When used on an industrial graduated table they are big and made of unstained steel. These are the most normally used assortment of fermenters for industrial intents. They provide low capital and operating costs. Their tallness to diameter ratio can be varied depending upon the heat removal specifications.

The basic operating rule of the moved armored combat vehicle bioreactor is reasonably simple to understand. In this fermenter the medium along with the innoculum are introduced into the vas from the top. The air supply required for the agitation procedure to take topographic point is provided from the underside of the fermenter. The air bubbles that are produced by the air supply are disrupted with the aid of the fomenter that is present in the fermenter. The fomenters besides produce turbulency. The turbulency so produced AIDSs in the O control and besides appropriate mass transportation. There are several types of fomenters that can be used in the moved armored combat vehicle fermenter. A few illustrations are four blade phonograph record turbine, pitched blade phonograph record turbine, ground tackle, coiling thread type fomenter, curved blade phonograph record turbine, pitched blade paddle and so on.

Pitched blade phonograph record turbine curved blade phonograph record turbine coiling thread

Anchor Four blade high efficiency impeller

Pitched blade paddle impeller

Among these the most normally used fomenter in the moved armored combat vehicle bioreactor is the four blade phonograph record turbine, although now there are several new designs with 12-18 blades and besides concave bladed fomenters. These have the ability to better hydrokineticss.

This fermenter apart from holding fomenters is besides provided with baffles that are by and large attached to the walls of the fermenter. The presence of these baffles AIDSs in the bar of vortex formation which could do a hinderance in the commixture procedure. The figure of baffles present scopes from four to eight in figure.

The waste gases that are produced during the agitation procedure are removed from the top the the fermenter and the merchandise that is formed flows in the downward way and is cod through a drain tubing that is present at the underside of the fermenter.

Airlift fermenters:

These fermenters are besides known as tower reactors. An airlift fermenter can be described as being a bubble column with a draught tubing. There are several types of airlift fermenters presently in usage.

In a typical airlift fermenter the air is fed in through a sparger pealing which is located at the underside of the cardinal draft tubing. This cardinal draft tubing controls the medium and besides the circulation of air. This air so flows in the upward way and the waste gases that are produced are removed from the top of the fermenter. The liquid that is present in the fermenter contains the coveted merchandise. It flows downwards and is drained at the underside of the vas through a tubing.

The heat money changer for this type of a fermenter can either be present internally of can be present as an external cringle. The airlift external cringle fermenters are by and large used for batch operations. These types of reactors use induced in order to direct the air and liquid throughout the vas. This type of a fermenter consists of a riser and a external down-comer which are attached to the chief vas at the top and bottom severally. the waste gases that are produced during the class of the agitation procedure are removed from the top of the vas and the liquid descends to the underside through the down-comer and is collected from the underside of the vas.

Figure 5 shows a cut-away position, that is, the vas

and downcomer are really taller than shown for the

peculiar diameter drawn.

Comparison between comparative virtues of airlift and automatically agitated fermenters:

Airlift fermenters have several advantages over the more commercially used stirrted armored combat vehicle fermenters which make usage of mechanical fomenters. These fermenters have a simple designs with no traveling parts or fomenters. They have a lower care cost as compared to automatically agitated fermenters. They besides have a lesser hazard of defects in design and are much simpler to sterilise. The shear rate that is produced by airlift is much lesser when compared to that which is produced by mechanical fomenters. These fermenters ( airlift ) can be used for both works and animate being cells, hence are more flexible in their usage in footings of the cells being used. The efficiency of airlift in gas-phase detachment is higher than in the automatically agitated fermenters. These fermenters besides have a well controlled flow and have good commixture efficiency rates. They besides provide good defined abode times for all stages. There is an increased mass-transfer achieved in airlift fermenters due to the enhanced O solubility that is achieved in these big armored combat vehicles owing to the greater force per unit area in the vas.

When compared to automatically agitated fermenters, really big volume armored combat vehicles of airlift fermenters can be maintained with easiness and it has besides been shown that these big armored combat vehicles have a greater merchandise end product. The efficiency of heat transportation is besides greater in airlift fermenters.

There are besides certain disadvantages of airlift fermenters. The chief disadvantage of these fermenters is that a high initial capital investing has to be made due to the big graduated table of procedures. Besides, these fermenters need greater air throughput and much higher operating force per unit areas when compared to the conventional automatically agitated agitators. Another point to be noted that can work as a disadvantage is the fact that airlift fermenters require low clash with an optimum hydraulic diameter for the riser and downcomer to work suitably but, there are no such issues involved with the automatically agitated fermenters. These fermenters besides have a lower efficiency of gas compaction when compared to the automatically agitated fermenters. It is besides hard to keep consistent degrees of substrate, food and O in such fermenters since the beings are conctantly go arounding through the fermenter and there are invariably altering conditions within the fermenter vas. When frothing occurs these fermenters are inefficient in keeping gas/liquid separation where as automatically agitated fermenters have a good ability to undertake foam formation and can therefore keep gas/liquid separation. The above mentioned disadvantages can nevertheless be overcome be a few alterations in design such as addition in the figure of provender points. This would take to the riddance of the hazard of the being undergoing uninterrupted rhythms of high growing followed by famishment which leads to the production of unsought byproducts, low output of the coveted merchandise and high mortality rates of the being being used in the agitation procedure. Apart from that alteration in design, multiple entry points must besides be provided for O. Most of this O must be supplied from the underside of the vas since it would help in the circulation of the fluid throughout the fermenter vas. This alteration besides reduces mortality rates of the being being used in the agitation procedure.

Mechanically agitated fermenters besides have their ain advantages. They have low initial capital investing and besides low operating costs. The usage of mechanical fomenters reduces the hazard of taint of the contents of the fermenter vas and besides prevent cell mutant from happening. This is chiefly due to the fact that the cells have a brief period of growing in these fermenters. Mechanically agitated fermenters besides provide high transition rates of the growing material nowadays in the vas. Flexibility of pick in mechanical agitatior provides options of working with assorted biological systems. The usage of a mechanical fomenter besides allows the use of cell growing rate, this is to state that they aid in increasing cell growing rate. But, the drawback of this use is that it besides increases care costs by a certain sum.

In such systems changing degrees of dilution can be used. This AIDSs in the production of secondary metabolites. As opposed to the airlift fermenters, consisten degrees of O, food and substrate can be maintained in automatically agitated fermenters. Besides, degrees of major components such as foods can be maintained in these fermenters. Further, these fermenters already have multiple feed points for foods every bit good as air flow included in their design as compared to the airlift fermenters which have merely one provender point for food and merely one provender point for the air in the commonly used designs of airlift fermentrs. They therefore have an advantage over airlift fermenters in footings of mortality rates of the being being used in the agitation procedure.


We see above that both airlift fermenters and automatically agitated fermenters have their ain advantages and disadvantages. A few alteration in the design of both can do them much more efficient in their working. We notice that really few alterations have to be made in the design of either type of fermenter and we can accomplish greater efficiency in their commixture abilities. This increased efficiency in blending would take to a more efficient agitation procedure and therefore better quality of the merchandise being manufactured.


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