Avishek Bhattacharjee
M.Sc Biotehnology 3rd sem
Bioprocess Engineering
Institute of Genetic Engineering
Kolkata, india
A Bioreactor is basically a device in which the organisms are cultivated and
motivated to form the desired product’s. It is a containment system designated
to give right environment for optimal growth and metabolic activity of the organism
1. At every step of the development of a biotechnological process, bioreactor is
invariably used.
2. The sizes of the bioreactor can vary over several orders of magnitudes. The
microbial cell (few mm3), shake flask ( 100-1000 ml), laboratory fermenter ( 1 –
50 L), pilot scale (0.3 – 10 m3) to plant scale ( 2 – 500 m3) are all examples of
bioreactors.
3. Whatever may be the size of the bioreactor, the conditions in the bioreactor have
to be favorable so that living microorganisms can exhibit their activity (specific
biochemical and microbial reactions) under defined conditions.
4. This results in a series of
special features in the
reaction engineering of biocatalytic processes. The
reaction rate, cell growth,
and process stability depend
on the environmental
conditions in the bioreactor.
5. There are several unique
aspects of biotechnological
processes, which require
special consideration in
design of bioreactors.
Requirements of bioreactors
(a) The design and construction of biochemical reactors must preclude foreign
contamination(sterility). Furthermore, aseptic conditions should be maintained
during the fermentation and ensure containment.
(b) Optimal mixing with low, uniform shear,
(c) Adequate mass transfer (oxygen),
(d) Clearly defined flow conditions,
(e) Feeding of substrate with prevention of under or overdosing,
(f) Suspension of solids,
(g) Gentle heat transfer,
(h) Compliance with design requirements such as: ability to be sterilized;
simple construction; simple measuring, control, regulating techniques; scale
up; flexibility; long term stability; compatibility with up- downstream
processes; antifoaming measures.
Bioreactor design is a relatively complex engineering task, which is studied in the
discipline of biochemical engineering. Under optimum conditions, the microorganisms
or cells are able to perform their desired function with a 100 percent rate of
success.[citation needed] The bioreactor's environmental conditions like gas (i.e., air,
oxygen, nitrogen, carbon dioxide) flow rates, temperature, pH and dissolved oxygen
levels, and agitation speed/circulation rate need to be closely monitored and controlled.
Most industrial bioreactor manufacturers use vessels, sensors and a control system
networked together.
A proper bioreactor should have the following configurations:
 Heat and oxygen transfer configuration
· Sterilization procedures
· Foam control
· Fast and thorough cleaning system
· Proper monitoring and control system
Traditional design is open cylindrical or rectangular vessels made from wood or stone.
Most fermentations are now performed in close system to avoid contamination.
 It should be constructed from non-toxic, corrosion-resistant materials. Small
fermentation vessels of a few liters capacity are constructed from glass and/or
stainless steel.
Based on the designs of the bioreactors, they can be grouped into the
following types
1. Continuous stirred tank bioreactors
2. Bubble column bioreactors
3. Airlift bioreactors
4. Fluidized bed bioreactors
5. Packed bed bioreactors
6. Photo bioreactors
1.Batch Bioreactor
Various aspects of batch reactors are being
utilized in chemical and metal processing
industries.
The basic concept of batch reactor is to be
considered that the molar or mass reactions
are restricted in a variable temperatures,
stirring and PH. However the inflow and out
flow of the reaction products will remain
constant in same close door open vessels,
reaction containers or in small conical flasks.
High-pressure reactor. This reactor is generally
used in polymer synthesis, where the process
of polymerization requires high-pressure
reactions. In high-pressure reactors, the
pressure gauge is varied between 1.5 Atm. to
10 Atm. To design a high-pressure reactor,
special types of stainless steels are used.
2.FED BATCH FERMENTOR
A Fed batch reactor has similar operational conditions as to a
batch reactor. It has additional features for continuous
addition or removal of one or more components / streams for
reactions. Additionally for better yields and selectivity, gradual
addition or removal in semi batch reactor assists in controlling
temperature particularly when the net reaction is highly
exothermic. Thus, the use of a semi batch reactor intrinsically
permits more stable and safer operation than a batch operation.
Fed batch reactors are mostly used in critical reactions and
rarely used in wastewater treatments.
3.CONTINUOUS FERMENTER
Continuous fermentation is an open system
.It involves the removal of culture medium
continuously and replacement of this with
a fresh sterile medium in a bioreactor. Both
addition and removal are done at the same
Rate so that the working volume remains
Constant.
Practical Issues for Bioreactors
A)Heat Transfer Configurations:
The primary heat transfer configurations in fermentation vessels are:
i. External jackets
ii. Internal coils
iii. External surface heat exchanger
B)Agitation (gas transfer
Mixing should produce homogeneous conditions and promote
a) Nutrient transfer
b) Gas transfer
c) Heat transfer
Heat transfer is necessary during both sterilization and for temperature
maintenance during operation.
C) Foaming removal
Mechanical foam breaker (a supplementary impeller)
Chemical antifoam agents (may reduce the rate of oxygen transfer)
D)- Mass transfer:
Transfer of nutrients from the aqueous phase into the microbial
cells during fermentation is relatively straightforward as the
nutrients are normally provided in excess.
Transport of Nutrients
The performance of the reactor is affected if the rate of the
transport of the limiting nutrients is slower than the rate of
utilization by the cells.
Efficiency of the bioprocess could be increased by increasing the
rate of transport of a limiting nutrient.
Transport of Oxygen
Compressed air entering a fermenter is usually stripped of
moisture and any oil vapors that may originate from the
compressor.
To prevent the risk of contamination, gases introduced into the
fermenter should be passed through a sterile filter.