Bio Reactor Engineering
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Transcript of Bio Reactor Engineering
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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