5LECTURE STR-2

8/7/2019 5LECTURE STR-2

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P.V.S.YUGANDHAR M.Tech (


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Temperature control system

pH control system

Cleaning and sterilization facilities

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


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Temperature probesHeat transfer systemTypically the heat transfer system will

use a "jacket" to transfer heat in or out ofthe reactor. The jacket is a shell whichsurrounds part of the reactor. The liquidin the jacket does not come in directcontact with the fermentation fluid.



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The jacket will typically be modified toencourage turbulence in the jacket andthus increase the heat transfer efficiency.An alternative to using jackets are coils.

Coils have a much higher heat transferefficiency than jackets. However coils takeup valuable reactor volume and can bedifficult to clean and sterilize.

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


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In pilot and production scale reactors,

heating is typically only required

during the initial stages and finalstages of the fermentation as most

processes which occur during a

fermentation process, including the biological reactions (eg. growth)

chemical reactions

mixing

Which are exothermic



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The pH control system consists of

a pH probe

alkali delivery systemacid delivery system

The pH probe is typically steam

sterilizable.



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Small scale reactors are taken apartand then cleaned before being re-

assembled, filled and then sterilizedin an autoclave.

However, reactors with volumesgreater than 5 litres cannot be placedin an autoclave and sterilized. Thesereactors must be cleaned and

sterilized "in place". This process isreferred to "Clean in Place" and"Sterilize in Place". The commonlyused acronyms for these processes

are CIP and SIP.P.V.S.YUGANDHAR M.Tech ( Biotech)


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CIP and SIP involves the complete

cleaning and sterilization of notonly the fermenter but also alllines linked to the internal

components of the reactor.S

team,cleaning and sterilizingchemicals, spray balls and highpressure pumps are used in these

processes. The process is usuallyautomated to minimize thepossibility of human error.



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Sterilization of the inlet air is undertaken to

prevent contaminating organisms fromentering the reactor. The exit air on the

other hand is sterilized to not only keep

contaminants from entering but also to

prevent organisms in the reactor from

contaminating the air.

A common method of sterilizing the inlet

and exit air is filtration. For small reactors

(with volumes less than 5 litres), disk

shaped hydrophobic Teflon membranes

housed in a polypropylene housing is used.

are used. Teflon is tough, reusable and does

not readily block.P.V.S.YUGANDHAR M.Tech ( Biotech)


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For larger laboratory scale fermenters(up to 1000 litres), pleated membrane

filters housed in polypropylenecartridges are used.

Sterilization of the inlet and exit air inlarge bioreactors (> 10,000 litres) canpresent a major design problem.Large scale membrane filtration is a

very expensive process. Heat

sterilization is alternative option.Steam can be used to sterilize the air.With older style compressors, it waspossible to use the heat generated by

the air compression process toP.V.S.YUGANDHAR M.Tech ( Biotech)


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A compressor forces the air intothe reactor. The compressor willneed to generate sufficientpressure to force the air through

the filter, sparger holes and intothe liquid.

Air compressors used for large

scale bioreactors typicallyproduce air at 250 kPa. The airshould be dry and oil free so as tonot block the inlet air filter orcontaminate the medium.P.V.S.YUGANDHAR M.Tech ( Biotech)


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During sterilization the concept of

"maintaining positive pressure"will often be used. Maintainingpositive pressure means thatduring sterilization, cooling andfilling and if appropriate, thefermentation process, air must bepumped into the reactor.

Maintaining positive pressuremeans that during sterilization,cooling and filling and if

appropriate, the fermentationP.V.S.YUGANDHAR M.Tech ( Biotech)


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The air sparger breaks the incoming air

into small bubbles.Various designs can be used such asporous materials made of glass or metal.However, the most commonly used type of

sparger used in modern bioreactors is thesparge ring:A sparge ring consists of a hollow tube in

which small holes have been drilled. Asparge ring is easier to clean than porous

materials and is less likely to block duringa fermentation.

The sparge ring must be located below theagitator and be approximately the same

diameter as the impeller.


Sparger -- Oxygen delivery system -


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P.V.S.YUGANDHAR M.Tech

( Biotech)


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P.V.S.YUGANDHAR M.Tech

( Biotech)


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