Bio Reactor Engineering

8/12/2019 Bio Reactor Engineering

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Bioreactor Engineering


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1. Bioreactor configurations

2. Bioreactor operation modes

3. Practical considerations for

bioreactor design

Outline of Lecture


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Bioreactor:device, usually a vessel, used to direct the activity of a

biological catalyst to achieve a desired chemical transformation.

Product

Bioreactor

Recycle

Product

separation & purification

Nutrients tank

Waste

Input

Pre-filtration

Fermenter:type of bioreactor

in which the biocatalyst is a

living cell.

What is a bioreactor?


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1. Aerobic bioreactor:Need

adequate mixing and

aeration

2. Anaerobic bioreactor:no

need for sparging oragitation

Challenges in Bioreactor Design


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Bioreactor Configurations- 1. Stirred tank

Mixing method: Mechanical

agitation

Baffles are usually used to

reduce vortexing

Applications: free and

immobilized enzyme

reactions

High shear forces may

damage cells

Require high energy input


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Bioreactor Configurations- 2. Bubble column

Mixing method: Gas

sparging

Simple design

Good heat and mass

transferLow energy input

Gas-liquid mass transfer

coefficients depend largelyon bubble diameter and gas

hold-up.


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Bioreactor Configurations- 3. Airlift reactor

Mixing method: airlift

Compared to bubble

column reactors, in an

airlift reactors, thereare two liquid steams:

up-flowing and down-

flowing steams. Liquid

circulates in an airliftreactor as a resutl of

density difference

between riser and

downcomer.


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Bioreactor Configurations- 4. Packed-bed reactor

Packed-bedreactors are used

with immobilized

or particulate

biocatalysts.

Medium can be

fed either at the

top or bottom and

forms a

continuous liquid

phase.


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Bioreactor Configurations- 5. Trickle-bed reactor

The trickle-bedreactor is another

variation of the

packed bed

reactors.

Liquid is sprayed

onto the top of the

packing and

trickles down

through the bed in

small rivulets.

f


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Bioreactor Configurations- 6. Fluidized bed reactor

When the packed beds

are operated in upflow

mode, the bed expands

at high liquid flow ratesdue to upward motion

of the particles.

i O i d


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Bioreactor Operation Modes-1. Batch Operation

A batch bioreactor

is normally

equipped with an

agitator to mix the

reactant, and the

pH of the reactantis maintained by

employing either

buffer solution or a

pH controller

Sm

Ss

CK

Cr

dt

dCr

max

trCCC

CK ss

s

sm max0

0ln Change of

Cs with time,

t

Batch

operation with

stirring

A foam breaker may be installed to disperse foam

Bi O i M d


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Bioreactor Operation Modes-2. Plug-flow mode

In a plug-flowreactor, the

substrate enters

one end of a

cylindrical tubewith is packed with

immobilized

enzyme and the

product steam

leaves at the otherend.

trCCC

CK ss

s

sm max0

0ln

F, Cs0 F, Cs

t = 0F

V

An ideal plug-flow reactor can

approximate the long tube,

packed-bed and hollow fiber or

multistaged reactor

Residence

time

Continuous

operation without

stirring

V

Bi t O ti M d


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Bioreactor Operation Modes-3. Continuous stirred-tank

A continuous

stirred-tank reactor

(CSTR) is an ideal

reactor which is

based on the

assumption thatthe reactants are

well mixed.Continuous

operation with

stirring

F, Cs0

F, Cs

V

Bi t O ti M d


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Bioreactor Operation Modes-3. Continuous stirred-tank reactor-Con.

dt

dC

VVrFCFC

s

sss

0

F, Cs0

F, Cs

V

Mass balance of substrate:

onAccumulatinConsumptioOutput-Input

0dt

dCsSteady state:

Michaelis-

Menten rate:Sm

S

CK

Crr

max

0

max

0

sm

s

ss CK

Cr

VFCFC

Bi t O ti M d


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Bioreactor Operation Modes-3. Continuous stirred-tank reactor-Con.

ss

sms

CC

CrKC

0

max

F, Cs0

F, Cs

V

Mass balance of substrate:

0max0

sm

sss

CK

CrVFCFC

smsss

CKCC

Cr

V

F

0

max

1

V

F

f


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kcal

YCVq

1

Heat production rate:

q : heat production rate, kcal/ls

V: reactor liquid volume, l

: specific growth rate,s-1

C: biomass concentration (g/l)

Ykcal: a yield coefficient given as

grams of cells formed per kcal energy

released,g cells/kcal

Heat load: Heat load is determined by energy balances

Practical Issues for Bioreactors- Temperature Control (Heat Load)

Popular

method


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Practical Issues for Bioreactors-Temperature control (heat transfer)

Heat transfer surface area:1. Low in (a) external jacket and (b) external coil for small reactors2. High in (c) internal helical coil and (d) internal baffle coil for large reactors

3. Easily adjustable in (e) a separate external heat exchange unit

Difficult to clean

Easily fouled by cellgrowth on the

surface

No cleaning problem

Sterility

requirement

Shear forces

imposed on cells De letion of

f


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1. Biological reactions almost invariably are three-phase reactions

(gas-liquid-solid). Effective mass transfer between phases is oftencrucial. For example, for aerobic fermentation, the supply of

oxygen is critical.

HPCgAA

*

gAAlA CCKJ *

The equation governing the oxygen transfer rate is:

Agitation:

Mechanical stirring (for small reactors, and/or viscous liquids,

low reaction heat)

Air-driven agitation (for large reactors and/or high reaction heat)

Practical Issues for Bioreactors-Agitation (gas transfer)

P ti l I f Bi t


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1. Mechanical foam

breaker (a

supplementaryimpeller)

2. Chemical antifoam

agents (mayreduce the rate of

oxygen transfer)

Practical Issues for Bioreactors- Foaming removal

P ti l I f Bi t


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1. Aseptic operation (3-5% of fermentations in

an industrial plant are lost due to failure of

sterilization.

2. Construction materials (glass for small

bioreactors, e.g., < 30 liters and corrosion-resistant stainless steel for large reactors)

3. Sparage design (three designs: porous, orifice

and nozzle)

4. Evaporation control due to dry air input

Practical Issues for Bioreactors- Other issues


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Summary of Lecture

1. Bioreactor configurations

2. Bioreactor operation modes

3. Practical considerations for

bioreactor design

Documents

Bio Reactor Engineering