Transcript CEN 551 - DAV College For Girls, Yamunanagar

Microbial biotechnological processing
Types of
Fermentation
Performance
Process
Design
Fermenter Design
Optimisation
Construction
Configuration
Bio reactor
Control

Vessel or tank in which whole cells or cellfree enzymes transform raw materials into
desirable biochemical products and/or
less undesirable by-products

Also termed a Bioreactor

Factors to consider when
designing a fermenter
› Aseptic and regulatory
capability, long-term reliability
› Adequate aeration and
agitation
› Low power consumption
› Temperature and pH controls
› Sampling facilities
(14 L fermenter shown is a
copyright of New Brunswick
Scientific)
The basic function of a fermenter is to
provide a suitable environment in which
an organism can efficiently produce a
target product that may be
- gene of interest
- cell biomass,
- a metabolite,
- bioconversion product.
closed and open.
› A closed system implies that all the nutrient components are
added at the beginning of the fermentation process and, as
a result, the growth rate of the contained organisms will
eventually proceed to zero either due to diminishing nutrients
or accumulation of toxic waste products. A modification of
the batch process is the fed batch system. Here, volumes of
nutrients may be added to augment depletion of nutrients.
Overall, the system, however, remains closed .
› In contrast to the above type, in the open system, organisms
and nutrients
fermenter.
can
continuously
enter
and
leave
the
What it should be capable of:
 Biomass concentration must remain high
 Maintain sterile conditions
 Efficient power consumption
 Effective agitation
 Heat removal
 Sampling facilities
Fermenters range from simple stirred tanks to
complex integrated systems involving varying
levels of computer input.
 Fermenter design involves sciences like
Microbiology, Biochemistry, Chemical
Engineering, Mechanical Engineering,
Economics, Fermentation technology.
 There are 3 groups of bioreactor currently
used for industrial productions;
- non-stirred, non-aerated (Beer and wine)
- non-stirred, aerated (Biomass, eg Pruteen)
- stirred, aerated
(Antibiotics)

› All materials must be corrosion resistant to prevent
trace metal contamination of the process
› Materials must be non-toxic so that slight dissolution of
the material or components do not inhibit culture
growth
› Materials of the fermenter must withstand repeated
sterilization with high pressure steam
› Fermenter stirrer system and entry ports be sufficiently
robust not to be deformed under mechanical stress
› Visual inspection of the medium and culture is
advantageous, transparent materials should be used

A microbial fermentation can be viewed as a
three-phase system, involving liquid-solid, gas-solid,
and gas-liquid reactions.

The liquid phase contains dissolved nutrients,
dissolved substrates and dissolved metabolites.
The solid phase consists of individual cells, pellets,
insoluble substrates, or precipitated metabolic
products.
The gaseous phase provides a reservoir for oxygen
supply and for CO2 removal.


› Fermenter should be designed to exclude entrance
of contaminating organisms as well as containing
the desired organisms
› Culture volume should remain constant,
› Dissolved oxygen level must be maintained above
critical levels of aeration and culture agitation for
aerobic organisms
› Parameters such as temperature and pH must be
controlled, and the culture volume must be well
mixed.
› Therefore a need for control exists

Intensive properties
- temperature, concentration, pressure, specific heat

Extensive properties
- mass, volume, entropy and energy

Mass and energy levels should be balanced at the start
and finish of fermentations.

Combining this with determination of thermodynamic
properties and rate equations we can build computer
and mathematical models to control processes.
1. Bioreactor size - to provide required production
capacity
2. Mass transfer - to provide nutrients to cells, well
dispersed, adequate oxygen etc
3. Control systems
(a) temperature, pH, etc.
(b) sterilisation/ aseptic operation
(c) proper sampling
(d) heat transfer - example sterilisation of media
4. Requirement for asepsis / containment
 The inoculum is the starter culture that is
injected into the fermenter
› It must be of sufficient size for optimal growth
kinetics
 Since the production fermenter in industrial
fermentations is so large, the inoculum
volume has to be quite large
- A seed fermenter is usually required to produce
the inoculum volume
-The seed fermenter’s purpose is not to produce
product but to prepare inoculum


In situ batch sterilization of liquid medium. In this
process, the fermenter vessel containing medium is
heated using steam and held at the sterilization
temperature for a period of time; cooling water is
then used to bring the temperature back to normal
operating conditions
Temperature control during reactor operation.
Metabolic activity of cells generates heat. Some
microorganisms need extreme temperature
conditions (e.g. thermophilic microorganisms)
Heat transfer configurations for bioreactors: jacketed
vessel, external coil, internal helical coil, internal
baffle-type coil, and external heat exchanger.



External jacket and coil give low heat transfer area. Thus,
they are rarely used for industrial scale.
Internal coils are frequently used in production vessel; the
coils can be operated with liquid velocity and give relatively
large heat transfer area. But the coil interfere with the mixing
in the vessel and make cleaning of the reactor difficult.
Another problem is film growth of cells on the heat transfer
surface.
External heat exchanger unit is independent of the reactor,
easy to scale up, and provide best heat transfer capability.
However, conditions of sterility must be met, the cells must be
able to withstand the shear forces imposed during pumping,
and in aerobic fermentation, the residence time in the heat
exchanger must be small enough to ensure the medium does
not become depleted of oxygen.
Batch and Chemostat .
 Batch: changing conditions - transient (S,
X, growth rate), high initial substrate,
different phases of growth.
 Chemostat: steady-state, constant low
concentration of substrate, constant
growth rate that can be set by setting the
dilution rate (i.e. the feed flow rate) .
 Chemostat more efficient.
 Batch more common.

 Productivity
 Flexibility
 Control
 Genetic
stability
 Operability
 Economics
 Regulatory
 Productivity:
rate of product
per time per volume.
Chemostat better for growth
associated products. Wasted
time in batch process.
 Flexibility: ability to make more
than one product with the
same reactor. Batch better.
 Control: maintaining the same
conditions for all of the product
produced.
 Genetic
stability: maintaining the
organism with the desired
characteristics. Chemostat selects
for fast growing mutants that may
have the desired characteristics.
 Operability: maintaining a sterile
system. Batch better.
 Regulatory: validating the process.
Initially, many process batch, too
expensive to re validate after
clinical trials.
Fermentations of solid materials
 Low moisture levels
 Agricultural products or foods
 Smaller reactor volume
 Low contamination due to low
moisture
 Easy product separation
 Energy efficiency
 Differentiated microbiological
structures

In contrast to submerged
fermentation, SSF is the cultivation of
microorganisms under controlled
conditions in the absence of free
water.
 Examples of SSF include industrial
enzymes, fuels and nutrient enriched
animal feeds.

Stanbury, P.F., A. Whitaker, and S. J. Hall,
Principles of Fermentation Technology,
2nd ed., Butterworth Heinemann, Oxford,
2000.