Transcript Slide 1

Bioreactor Design and Operation
- Overview of bioreactors
- Modified batch and continuous reactors
- Immobilized cell system
- Operation consideration
- Scale up/down
- Bioreactor Instrumentation and control
- Sterilization
Bioreactor Design and Operation
- Fermentation processes
- solid state: water content: 40~ 80%, mostly mold
fermentation on agriculture products and food:
rice, wheat, barley, corn and soybean.
e.g.rotary drum fermentator
- submerged system: water content > 95%
e.g. bacteria, yeast.
Bioreactor Design and Operation
- Overview of bioreactors for submerged system
- Classification:
operation modes:
- batch: stirred tank
- continuous: chemostat, fluidized-bed
- modified types of the above modes:
fed-batch, chemostat with recycle,
multi-stage continuous reactors
Oxygen supply:
- aerobic: airlift
- anaerobic
Form of biocatalyst:
- free cell (enzyme)
- immobilized cell (enzyme)
packed-bed, membrane reactor
Industrial Bioreactor
Glacial Lakes Energy in Watertown, South Dakota
47+ million gallon per year ethanol production .
World's Largest Industrial Fermenter (Chem. Eng. News,10-Apr-78)
The fermenter is 200' high and 25 ft diam.
Requirements for Cultivation Methods
• Biomass concentration which must remain high
• Sterile conditions being maintained
• Effective agitation so that the distribution of
substances in the reaction is uniform
• Heat removal
• Creation of the correct shear conditions - high
may damage cells, low may lead to flocculation
or growth on wall and stirrer
Most bioprocesses in industry are batch:
• Even though the cell mass formation rate is higher in
chemostat, it can only benefit the growth-associated
products but not to secondary products which are
repressed by growth (more efficient in batch).
• Genetic instability - chemostat will place strong selection
pressure for the most rapidly growing cells .
• Operability and reliability – in chemostat, instrument
failure more likely in long term, sterility.
• Flexibility in batch.
• lower capital expenditure in batch.
Disadvantages of batch reactors:
• an increased non-productive time required due to
sterilising, filling and cooling.
• the frequency of sterilisation is increased causing greater
stress on instruments.
Chemostat with cell recycle
- To keep the cell concentration higher than the normal
steady-state level in a chemostat.
- To increase the cell and product yield.
- For low-product-value processes: e.g. waste treatment.
fuel ethanol
,
X1, S
v
Chemostat with cell recycle
Cell mass balance (qp=0, kd ≈0, X0=0, Monod equation is applied):
where µ=µnet=µg-kd
A chemostat can be operated at dilution rates higher than
the specific growth rate when cell recycle is used.
Chemostat with cell recycle
Chemostat with Cell Recycle
Mass balance on growth-limiting substrate (qp=0, kd ≈0, X0=0,
Monod equation is applied):
1
FS0  FS  V g X1
dS
FS  (1   ) FS  V
dt
M
Y
X /S
At steady state, dS/dt  0,
X1 
D
g
M
Y
X /S
(S0  S )
Since  g  [1   (1  C )]D,
M
Y
X1 
X /S
(S0  S )
1    C
K s D(1    C )
S
 m  D(1    C )
M
Y
K s D(1    C )
, X1 
[S0 
]
[1   (1  C )]
 m  D(1    C )
X /S
Chemostat with cell recycle
recycle
µm=1.00h-1, S0=2.0g/l, Ks=0.01 g/l, Yx/s=0.5 g/g,
concentration factor C=2.0 and recycle ratio α=0.5