2lecture Types 1

8/7/2019 2lecture Types 1

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TYPES - I

P.V.S.YUGANDHAR

M.Tech (Biotech)


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` A bioreactor is a reactor system used for the

culture of LIVING CELLS. They vary in size and

complexity from a 10 ml volume in a test tube to

computer controlled fermenters with liquidvolumes greater than 100 m3. They similarly vary

in cost from a few cents to a few million dollars.

P.V.S.YUGANDHAR

M.Tech (Biotech)


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` Standing Cultures

` Shake flasks

` Mechanically stirred bioreactors

` Bubble driven bioreactors

P.V.S.YUGANDHAR

M.Tech (Biotech)


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Airlift bioreactors

` Packed bed and trickle flow

bioreactors

` Fluidized bed bioreactors

P.V.S.YUGANDHAR

M.Tech (Biotech)


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` Standing cultures - T flasks

` T-flasks used in the small scale culture ofanimal cells are another example of a

standing culture. T-flasks are normallyincubated horizontally to increase the surfacearea for oxygen transfer.

` The surface aeration rate in standing cultures

can be increased by using large volumeflasks.

P.V.S.YUGANDHAR

M.Tech (Biotech)


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P.V.S.YUGANDHAR M.Tech (Biotech)


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` Fernback flasks----

Have larger surface areaThe following photograph shows a 3 litre

"Fernback" flask containing 1 litre of mediumand a 250 ml Erlenmeyer flask containing 100ml of medium. Note how the former has a

large surface area.Large Pyrex flasks are used for the smallscale production of fermented products. Oneexample is Kombucha tea which is a tea

brewed by mixture of yeasts and acetic acidbacteria.

P.V.S.YUGANDHARM.Tech (Biotech)


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` Shake flasks are commonly used for smallscale cell cultivation. Through continuousshaking of the culture fluid, higher oxygentransfer rates can be achieved as compared tostanding cultures. Shaking continually breaks

the liquid surface and thus provides a greatersurface area for oxygen transfer. Increasedrates of oxygen transfer are also achieved byentrainment of oxygen bubbles at the surfaceof the liquid.



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` For liquid volumes greater than 3 liters, air

sparging is required for effective oxygentransfer. The introduction of bubbles into theculture fluid by sparging, leads to a dramaticincrease in the oxygen transfer area.

` Agitation is used to break up bubbles and thusfurther increase kLa. Sparged fermenters

required significantly lower agitation speeds foraeration efficiencies comparable to thoseachieved in non-sparged fermenters. Air-sparged fermenters can have liquid volumes ofgreater than 500,000 liters.



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` Sparging without mechanical agitation canalso be used for aeration and agitation. Two

classes of bubble driven bioreactors are

bubble column fermenters and airlift

fermenters.` Bubble driven bioreactors are commonly used

in the culture of shear sensitive organisms

such as moulds and plant cells.



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Airlift fermenters are howevermore expensive to construct than

bubble column reactors.An airlift fermenter differs frombubble column bioreactors by thepresence of a draft tube whichprovides

>better mass and heat transferefficiencies

>more uniform shear conditions.



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`An airlift fermenter differs from a bubblecolumn bioreactor by the presence of a draft

tube. The main functions of the draft tubeare to:` Increase mixing through the reactorThe

draft tube enhances axial mixing throughoutthe whole reactor

` Reduce bubble coalescence.This presumably occurs due to circulatory

effect that the draft tube induces in thereactor. Circulation occurs in one directionand hence the bubbles also travel in one

direction.Small bubbles lead to an increased surface

area for oxygen transfer.`



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` Equalize shear forces throughout the reactor.This is believed to be the major reason whyairlift bioreactors have higher productivities

than stirred tank reactors.



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2lecture Types 1