FERMENTERS

-Dr. Ekta Khare

Department of Microbiology
Institute of Biosciences & Biotechnology,
CSJM University, Kanpur
 Fermenters/Bioreactors
• A fermenter/bioreactor is a specially designed vessel
which is built to support the growth of high
concentration of microorganisms.
• It must be so designed that it is able to provide the
optimum environments or conditions that will allow
supporting the growth of the microorganisms.
• All bioreactors deal with heterogeneous systems
dealing with two or more phases, e.g., liquid, gas, solid.
• Therefore, optimal conditions for fermentation
necessitate efficient transfer of mass, heat and
momentum from one phase to the other.
 Fermenters
• A bioreactor consists of a complex system of
pipes, fittings, wires, and sensors.
• With the aid of on-line monitoring and diagnosis
tools, it is now possible to detect many things
that can go wrong during the process.
• Bioreactor operation mode is classified in: batch
processes, fed-batch and continuous processes.
• Normally these operations mode are used in
submerged or liquid fermentations or during cell
culture
 Fermenters
• The size of fermenters ranges from 1-2-liter
laboratory fermenters to 5,00,000 liters or,
occasionally, even more, fermenters of up to 1.2
million liters have been used.
• The size of the fermenter used depends on the process
and how it is operated.
• Generally, 20-25% of fermenter volume is left unfilled
with medium as “head space” to allow for splashing,
foaming and aeration.
• The fermenter design varies greatly depending on the
type and the fermentation for which it is used.
 The general requirements of the bioreactor
• The vessel should be robust and strong enough to withstand
the various treatments required such as exposure to high
heat, pressure and strong chemicals and washings and
cleanings.
• The vessel should be able to be sterilized and to maintain
stringent aseptic conditions over long periods of the actual
fermentation process.
• The vessel should be equipped with stirrers or mixers to
ensure mass transfer processes occur efficiently.
• It should have sensors to monitor and control the
fermentation process.
• It should be provided with inoculation point for aseptic
transfer in inoculum.
 ... The general requirements of the
bioreactor
• Sampling valve for withdrawing a sample for different
tests.
• Baffles should be provided in case of stirred fermenter
to prevent vertex formation.
• It should be provided with facility for intermittent
addition of an antifoam agent.
• In case of aerobic submerged fermentation, the tank
should be equipped with the aerating device.
• Provision for controlling temperature and pH of
fermentation medium.
• Main hole should be provided at the top for access
inside the fermenter for different purposes.
 Construction Material
• It is important to select a material for the body of the fermenter, which restricts the
chances of contamination.
• Moreover, it needs to be non-toxic and corrosion free.
• Glass is a material that provides a smooth surface inside the vessel, also non-toxic in
nature and corrosion-proof.
• Due to the transparency, it is easy to examine the inside of the vessel.
• However, it is difficult to handle glass as a pilot-scale fermenter.
• Another non-toxic, corrosion-proof material, stainless steel, was used.
• According to Americal Iron and Steel Institute, steel contains more than 4%
chromium is standardized as stainless steel.
• However, the minimum amount of chromium required to protect the steel from
corrosion depends on the corroding agent present in a specific environment.
• In a pilot-scale fermenter normally the steel contains around 10-13% of chromium.
• In many cases nickel is also mixed in high concentration with the chromium to make
the steel more corrosion resistant and it also provides engineering advantages.
• Now-a-days, stainless steel fermenters are mostly used for industrial production.
 Basic Feature of Fermenter Design
• The basic feature of bioreactor include agitation system, foam control,
oxygen delivering system, headspace volume, sampling port, temperature
and pH control system, sterilization system and lines for charging &
emptying the reactor.
 Agitator
(Impeller)
• The objectives of the impeller used in fermenters are bulk fluid and
gas mixing, air dispersion, heat transfer, oxygen transfer, suspension
of solid particles, maintain the uniform environment inside the
vessel, etc.
• Impellers involved in breaking the air bubbles produced in a liquid
medium.
• There are mainly three types of agitators used in industrial-scale
bioreactors
• Disc Turbine: It consists of a disc with a series of rectangular vanes
connected in a vertical plane around the disc.
• Vaned disc: In this case, the rectangular vanes are attached
vertically to the underside of a disc.
• Variable Pitch open turbine: This type of agitator lacks disc and the
vanes are directly connected to a center shaft.
 The aeration system (sparger)
• A sparger is a device that introduces air into the liquid medium in a fermenter.
• These are of three main types:
• Porous Sparger: It is made up of sintered glass, ceramics or metals’ and are
mostly used in laboratory-scale bioreactors.
• As it introduces air inside a liquid medium, bubbles formed are always 10 to
100 times larger than the pore size of the aerator.
• A major disadvantage of using porous sparger is that microbial growth may
occur on the pores which hamper the airflow.
• Orifice Sparger: Perforated pipes are used and attached below the impeller in
the form of a ring.
• The air holes are mostly drilled under the surface of the tubes.
• Orifice spargers were used to a limited extent in yeast manufacture, effluent
treatment and production of single-cell proteins.
• Nozzle Sparger: This is used in industrial-scale fermenters.
• It contains a single open or partially closed pipe as an air outlet.
• The pipe needs to be positioned below the impeller.
• The design helps to overcome troubles related to sparger blockage.
 Sparger

Sparger
 Baffles
• There are four baffles that are present inside
of an agitated vessel to prevent a vortex and
improve aeration efficiency.
• Baffles are made up of metal strips roughly
one-tenth of the vessel diameter and
attached to the wall.
• The agitation effect is slightly increased with
wider baffles but drops sharply with
narrower baffles.
• After installation of the baffle there a gap
between them and the vessel wall which
facilitates scouring action around the baffles
and minimizes microbial growth on the
baffles and the fermenter wall.
• Baffles are often attached to cooling coils to
increase the cooling capacity of the
fermenter.
 Stirrer glands and bearings
• These stirrer shafts play an important role to seal the openings of a
bioreactor.
• As a result, it restricts the entry of air from outside.
• There are several types of seals used for this purpose, which are
following:
• The Stuffing Box: The shaft is sealed by several layers of packing
rings of asbestos or cotton yarn which is pressed against the shaft
by gland follower.
• The Mechanical Seal: The seal is divided into two parts, first is the
stationary bearing housing and the second rotates on the shaft.
• These two parts are pressed together by springs.
• Magnetic Drives: This type of seals helps to counter the problem
originated by the impeller shaft which is going through the top or
bottom of the fermenter plate.
• The magnetic drive is made up of two magnets.
 Temperature Control
• During the fermentation process heat can be produced mainly in two
ways:
– microbial biochemical reactions
– mechanical agitation.
• In small scale production vessel the amount of produced heat is
negligible.
• Therefore, extra heat is provided by hot bath or internal heat coil or
heating jacket with a water circulation system or silicon heating jacket.
• The silicon heating jacket consists of silicon rubber mats with heating
wires and it is wrapped around the fermenter.
• In the case of pilot-scale fermenters, it is not possible to use silicon
jackets due to large size.
• In such cases, an internal heating coil is used for providing extra heat
while cold water circulation helps to remove excess heat.
 Foam control
• The problem often encounters in fermentation is foaming.
• When foaming becomes excessive, there is a danger that filters become wet
resulting in contamination, increasing pressure drop and decreasing gas flow.
• Foam can be controlled with mechanical foam breaker or the addition of
surface active chemical agents, called anti foaming agents.
• Mechanical foam breaker available is “turbosep”, in which foam is directed
over stationary turbine blades in a separator and the liquid is returned to
fermenter.
• Foam is also controlled by addition of oils.
• However, excessive oil additions may decrease the product formation.
• Antifoam oils may be
– synthetic, such as silicones or polyglycols, or
– natural, such as lard oil or soybean oil
• Either will substantially change the physical structure of foam, principally by
reducing surface elasticity.
• Industrial antifoam systems operate automatically from level-sensing devices.
 pH control sensors
• All types of fermenters are attached with a pH
control sensor which consists of a pH sensor
and a port to maintain the pH inside of the
fermenter.
• pH alteration can lead to death of the
organism which leads to product loss.
• Therefore, it is a crucial instrument for a
fermenter and needs to be checked regularly.
 Valves and steam traps
• Valves attached to fermenter are used to controlling the flow of liquids
and gases in a variety of ways.
• The different valves available are :
– gate valves,
– globe valves,
– piston valves,
– needle valves,
– plug valves,
– ball valves,
– butterfly valves,
– pinch valves,
– diaphragm valves,
– check valves,
– pressure control valves,
– safety valves
– steam traps
• Depending upon fermentation type and requirements these valves are
chosen in designing bioreactor with good productivity.
 Sampling port
• The sampling construction should be such
so that measures for preventing non-sterility
before and after the sampling be avoided.
• In the sites of the infection origin, sterilization should be performed promptly
with alcohol or steam.
• A bladder made of silicone or a similar material is placed into the sampling
pipe, and its end is stopped with a clamp.
• Thereby, it is sterilized together with the bioreactor vessel, and it remains in
such a state until the sampling.
• When sampling, the clamp is removed, and the bladder is also pulled down.
• With the sample's discharge, the pipe's end is immediately washed with
alcohol.
• Another drawback of this method is a hampered possibility of choosing the
sample's amount.
• Keofitt sampling device is available for sampling from bioreactor.
 Types of Fermenters
• Stirred Tank Bioreactor
• Airlift Bioreactor
• Bubble Column Bioreactors
• Fluidized Bed Bioreactor
• Packed Bed Bioreactor
• Photobioreactor
• Membrane Bioreactor
 Stirred Tank Bioreactors
• The stirred-tank bioreactor consists of a vessel, pipes, valves,
pumps, agitator, shaft, impeller and a motor.
• Sparger is mostly used to add air to the culture medium under
pressure.
• The impellers serve as a gas distributor throughout the fermentor
and also break down the larger bubbles for a uniform distribution.
• The motor power the bioreactor which helps in mixing cultures and
also there are sensors that can detect temperature, pH, dissolved
oxygen, glucose, lactic acid, ammonia, ammonium ion, and other
parameters in the culture medium.
• The typical decision variables are: type, size, location and the
number of impellers; sparger size and location.
• These determine the hydrodynamic pattern in the reactor, which in
turn influence mixing times, mass and heat transfer coefficients,
shear rates etc.
Stirred Tank Bioreactors
 Stirred Tank Bioreactor
• Advantages
• The efficient gas transfer to growing cells
• Good mixing of the contents
• Flexible operating conditions
• Commercial availability of the bioreactors.
• Disadvantages
• Their mechanic agitation produces shear stress which may
harm the cultured cells. but this can be overcome by changing
the shape and diameter of the impeller blade or adding
bovine serum albumin or dextran.
• Foaming can also cause a problem but again can be solved by
antifoaming agents.
 Airlift Bioreactor
• In airlift fermentor the liquid culture volume of the vessel is divided into
two interconnected zones by means of a baffle or draft tube.
• Only one of the two zones is sparged with air or other gas and this sparged
zone is known as the riser.
• The other zone that receives no gas is called down-comer.
• The bulk density of the gas-liquid dispersion in the gas-sparged riser tends
to be lower than the bulk density in the down-comer, consequently the
dispersion flows up in the riser zone and down-flow occurs in the down-
comer.
• Airlift fermentors are highly energy-efficient and are often used in large-
scale manufacture of biopharmaceutical proteins obtained from fragile
animal cells.
• Heat and mass transfer capabilities of airlift reactors are at least as good
as those of other systems, and airlift reactors are more effective in
suspending solids than are bubble column fermentors.
• All performance characteristics of airlift-fermentor are related ultimately
to the gas injection rate and the resulting rate of liquid circulation.
 Types of Air-lift Bioreactor
• Two types
– Internal loop reactor
• Internal-loop split reactor
• Internal loop concentric
tube reactor
– External loop reactor
 Air Bioreactor Advantages
Airlift Bioreactor Advantages
• It produces very little shear stress, less friction
• It requires fewer efforts to construct the
bioreactor.
• It is cost-efficient
• Less energy is required
Airlift Bioreactor Disadvantages
• High Pressure is required in this system
• No shaft is present which helps as a foam breaker
which creates a major drawback.
 Bubble Column Bioreactors
• It is simple to construct and operate.
• It consist of a cylindrical vessel with a ratio of 4:6 (height to
diameter).
• The upper section of the fermenter is often widened to
provide proper gas separation.
• The gas is spranger into liquid by the means of spranger
and hence, adequate level of mixing is obtained.
• The liquid phase can be delivered by batch or continuous
mode, which can either be countercurrent or concurrent.
• They have very low maintenance cost and very little space
for maintenance.
• It is widely used for waste water treatment, production of
enzymes, proteins and antibiotics.
 ... Bubble Column Bioreactors
Advantages
• It acquires good heat and
mass transfer
• Easy to operate
• Low maintenance
Disadvantages
• Bad mixing is a major
drawback which adversely
affects product conversion.
 Fluidized Bed Bioreactor
• A fluidized bed bioreactor is an immobilized cell reactor which is a
combination of stirred tank and packed bed continuous flow reactors.
• It can be explained as beds of regular molecules that are suspended in a
flowing liquid stream.
• This can be used for particles such as immobilized enzymes, immobilized
cells, and microbial flocs.
• It involves cell as biocatalysts including 3 phases – gas-liquid-solid.
• Usually fluidization is obtained either by external liquid recirculation or by
gas fed to the reactor.
• In the case of immobilized enzymes the usual situation is of two-phase
systems involving solid and liquid but the use of aerobic biocatalyst
necessitate introduction of gas (air) as the third phase.
• Basically the particles used in FBBs can be of three different types: (i) inert
core on which the biomass is created by cell attachment. (ii) Porous
particles in which the biocatalyst is entrapped.(iii) Cell aggregates/ flocs
(self-immobilization).
 ... Fluidized Bed Bioreactor
• Advantages of Fluidized
Bed Bioreactor
• It is used for wastewater
treatment and hydrogen
production.
• Disadvantages of Fluidized-
Bed Bioreactor
• It requires more energy in
order to achieve fluidization
in the bioreactor.
 Packed Bed Bioreactor
• A bed of solid particles, with biocatalysts or cells on or within the matrix of solids,
packed in a column constitutes a packed bed bioreactor.
• The solids used may be porous or non-porous gels, and they may be compressible or
rigid in nature.
• A nutrient broth flows continuously over the immobilised biocatalyst/ cells.
• The products obtained in the packed bed bioreactor are released into the fluid and
removed.
• While the flow of the fluid can be upward or downward, down flow under gravity is
preferred.
• One of the disadvantages of packed beds is the changed flow characteristic due to
alterations in the bed porosity during operation.
• While working with soft gels like alginates, carragenan etc the bed compaction which
generally occurs during fermentation results in high pressure drop across the bed.
• Packed beds arc generally used where substrate inhibition governs the rate of
reaction.
• Several modifications such as tapered beds to reduce the pressure drop across the
length of the reactor, inclined bed, horizontal bed, rotary horizontal reactors have
been tried with limited success.
Packed Bed Bioreactor
 Photobioreactor
• These are carried out either by exposing to sunlight or artificial illumination.
• Since artificial illumination is expensive, only the outdoor photo-bioreactors are
preferred.
• Certain important compounds are produced by employing photo-bioreactors e.g.,
p-carotene, asthaxanthin.
• They are made up of glass or more commonly transparent plastic. The array of
tubes or flat panels constitute light receiving systems (solar receivers).
• The culture can be circulated through the solar receivers by methods such as using
centrifugal pumps or airlift pumps.
• It is essential that the cells are in continuous circulation without forming
sediments.
• Further adequate penetration of sunlight should be maintained.
• The tubes should also be cooled to prevent rise in temperature.
• Photo-bioreactors are usually operated in a continuous mode at a temperature in
the range of 25-40°C.
• Microalgae and cyanobacteria are normally used.
• The organisms grow during day light while the products are produced during night.
 Photobioreactor
Advantages
• Contamination is lower.
• It can be space-saving as it
can be placed vertically,
horizontally or at an angle,
indoors or outdoors.
Disadvantages
• The control of PH and
temperature is quite
difficult.
• It is somewhere susceptible
to contamination.
 Membrane Bioreactor
• It consists of a biological reactor with suspended biomass and solids removal
by ultra- and microfiltration membranes.
• Membrane bioreactors successfully applied to various microbial
bioconversions such as alcoholic fermentation, solvents, organic acid
production, waste water treatment, etc.
• In membrane bioreactor the soluble enzyme and substrate are introduced on
one side of ultrafilter membrane by means of a pump.
• Product is forced out through the membrane.
• Membrane holds back the enzyme.
• Good mixing in the reactor can be achieved by using a stirrer.
• The most widely used membrane materials includes polysulfonte, polyamide
and cellulose acetate.
Advantages of Membrane Bioreactor
• The loss of the enzyme is minimized.
• Effluent quality is high
• The effluent is properly disinfected from all the pathogenic microbes.
 Membrane Bioreactor
Disadvantages of Membrane Bioreactor
• Quite costly and energy-consuming
• The aeration is limited
• Membrane pollution is also a drawback
 Questions
• Diagrammatically represent the design of basic fermenter/ stirred tank
bioreactor.
• Discuss in brief about the basic features of fermenter design.
• Write a short note on continuous stirred tank bioreactors.
• Write short note on
– Photobioreacters
– bubble column fermenter
– air-lift fermenter.
– Fludized bed reactor
– Packed bed reactor
– Impiller
– Spargers
– Baffels
• How many types of fermenters used in industries? Discuss their structure
and applications.
• What are the different components or parts of a typical fermenter and
their function.
• Write short note on antifoam agents, types and their function.