Design of a Fermentor

Design of a Fermentor


Fermentation can be defined as a metabolic process in which cheap raw materials such as sugar or carbohydrates are converted into economically important products like acids, gases and alcohols by micro-organism. This process is carried out in a equipment called as fermentor.

What is a Fermentor?

A Fermentor can be defined as a vessel in which sterile nutrient media and pure culture of micro-organism are mixed and fermentation process is carried out under aseptic and optimum condition.

Fermentor provides a sterile environment and optimum condition that are important for growth of micro-organisms and synthesis of desired product.

A fermentor should be constructed in such a way that it can make provisions for the below activities:

  • Sterilization
  • Temperature control
  • pH control
  • Foam control
  • Aeration and agitation
  • Sampling point
  • Inoculation points for micro-organisms, media and supplements
  • Drainage point for drainage of fermented media
  • Harvesting of product
  • Cleaning
  • Facility of providing hot, cold water and sterile compressed air.

Diagrammatic representation of Design of fermentor.

Design of Fermentor


Here one by one we will be studying major parts of fermentor and their function.

  1. Material used for fermentor
  2. Impellers
  3. Baffles
  4. Inoculation port
  5. Sparger
  6. Sampling point
  7. pH control device
  8. Temperature control system
  9. Foam control device
  10. Bottom drainage system

Here is a flow chart that shows major parts of fermentor.

Major parts of Fermentor

  1. Material used for fermentor

The material used for designing of a fermentor should have some important functions.

  • It should not be corrosive
  • It should not add any toxic substances to the fermentation media.
  • It should tolerate steam sterilization process.
  • It should be able to tolerate high pressure and resist pH changes.

The fermentor material used is also decided on type of fermentation process. For example, in case of Beer, Wine, Lactic acid fermentation, the fermentor tanks are made up of wooden material. Whereas material such as iron, copper, glass and stainless steel can be used in some cases. Most of the time, 304 and 316 stainless steel is used for designing of a fermentor and these fermentors are mostly coated with epoxy or glass lining.

A fermentor should provide the facility to control and monitor various parameters for a successful fermentation process.

2. Impellers

  • Impellers are an agitation device. They are mounted on the shaft and introduced in the fermentor through its lid.
  • They are made up of impeller blades and the position may vary according to its need.
  • These impellers or blades are attach to a motor on lid.
  • The important function of an impeller is to mix micro-organisms, media and oxygen uniformly.
  • Impeller blades reduce the size of air bubbles and distributes these air bubbles uniformly into the fermentation media.
  • Impellers also helps in breaking foam bubbles in the head space of fermentor. This foam formed during fermentation process can cause contamination problem and this problem is avoided by the use of impellers.

3. Baffles

  • Baffles are mounted on the walls of a fermentor.
  • The important function of baffles is to break the vortex formed during agitation process by the impellers.
  • If this vortex is not broken, the fermentation media may spill out of fermentor and this may result in contamination as well as can lead to different problems. So it is important to break the vortex formed by using a barrier.
  • Baffles acts as a barrier which break the vortex.

4. Inoculation Port

  • Inoculation port is a device from which fermentation media, inoculum and substrate are added in the fermentation tank.
  • Care should be taken that the port provides aseptic transfer.
  • The inoculation port should be easy to sterilize.

5. Spargers

  • A Sparger is an aeration system through which sterile air is introduced in the fermentation tank.
  • Spargers are located at the bottom of the fermentation tank.
  • Glass wool filters are used in a sparger for sterilization of air and other gases.
  • The sparger pipes contain small holes of about 5-10 mm. Through these small holes pressurized air is released in the aqueous fermentation media.
  • The air released is in the form of tiny air bubbles. These air bubbles helps in mixing of media.

6. Sampling point

  • Sampling point is used for time to time withdrawal of samples to monitor fermentation process and quality control.
  • This sampling point should provide aseptic withdrawal of sample.

7. pH Control device

  • The pH controlling device checks the pH of media at specific intervals of time and adjusts the pH to its optimum level by addition of acids or alkalis.
  • Maintaining pH to its optimum level is very important for growth of micro-organism to obtain a desired product.

8. Temperature control

  • Temperature control device generally contains a thermometer and cooling coils or jackets around fermentor.
  • During the fermentation process, various reactions take place in the fermentor. Heat is generated and released in the fermentation media. This increase in temperature is detrimental to the growth of micro-organisms, which may slow down the fermentation process.
  • So, it is necessary to control this rise in temperature. This is done by passing cool water through the coils or jackets present around fermentor.

9. Foam controlling device

  • A Foam controlling device is placed on the top of fermentor with a inlet into fermentor. This device contains a small tank containing anti-foaming agent.
  • Foam  is generated during fermentation. It is necessary to remove or neutralize this foam with the help of anti-foaming agents, lest the media may spill out of fermentor and lead into contamination and a mess.

10. Bottom drainage system

  • It is an aseptic outlet present at the bottom of fermentor for removal of fermented media and products formed.

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Fermentation Equipment and its Application

  • Fermentation can be defined as a metabolic process in which raw materials such as sugar or carbohydrates are converted into acids, gases and alcohols. Micro-organisms such as yeast and bacteria play a central role in the fermentation process.
  • Fermentation process requires a fermentor, substrate, inoculum and optimum conditions.
  • The equipment used to carry out fermentation is called a fermentor.
  • A fermentor can be defined as an equipment or a vessel in which fermentation process is carried out.
  • A fermentor is a complex machine. It is used to create optimum conditions that are necessary for the fermentation process.

 Design of a fermentor

  1. A fermentor should be large enough to allow creation of fermentor bacteria.
  2. The material used in the manufacture of a fermentor should be strong enough to tolerate the pressures of fermentation media and gases produced.
  3. The material should be non-corrosive.
  4. It should not contribute toxic ions or substances to the fermentation media, because these toxic ions can harm the growth of microbial culture.
  5. It should have an inlet for oxygen and outlet for carbon dioxide in case aerobic microbes are used for fermentation.
  6. It should be completely sealed from outside environment to avoid contamination.
  7. It should be easily sterilize.
  8. It should provide a facility to add anti-foaming agents as well as a temperature controlling system.
  9. A pH detecting system is also important. An outlet for the withdrawal of media for determination of pH as well as inlet for addition of acids and alkalis should be provided. It is important to maintain pH at optimum levels for growth of culture.
  10. The most important thing is that a fermentor should provide aseptic means of withdrawal of fermented product and introduction of culture samples.
  11. The fermentor facilitate the stirring of media so that inoculum and fermentation media mix properly. It also ensures that the gases required for growth of microbial culture are available to all microbes.

Types of Fermentors and its Uses

1. Laboratory Scale fermentor

  • It is the smallest type of fermentor.
  • Capacity of this fermentor is minimum one to two litres and maximum up to twelve to fifteen litres.
  • It is used for research and development purposes.
  • Laboratory scale fermentor is used for determination of optimum condition of growth and biosynthesis of micro-organism.

2. Pilot scale fermentor

  • Pilot scale fermentor are of intermediate size.
  • It is used in large scale studies of fermentation process.
  • The minimum size range is of 25 to 100 gallons that is 94 litres to 378 litres.
  • The maximum size range is 2000 gallons that is 7570 litres.

3. Industrial scale fermentor

  • Industrial fermentor is a large scale fermentor. It is used in industries for fermentation of industrially important product.
  • The minimum size range is 5000 gallons to 10,000 gallons that is 18927.06 litres to 37854.12 litres.
  • The maximum size range 10,0000 gallons that is 378541.18.

This was the overview of fermentor and important aspects that are considered under fermentation process but there are important aspects that are carried out during fermentation process.

  1. Media formulation
  2. Inoculum preparation
  3. Sterilization of nutrient media and preparation of media.
  4. Fermentation process
  5. Recovery
  6. Purification
  7. Waste disposal

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Introduction to Industrial Microbiology

Industrial microbiology is a branch of science that deals with the study and uses of micro-organism which have industrial and economic applications. In industrial microbiology, microbes classified, characterized are isolated from their natural environment. Further, these micro-organism are produced on a large-scale by use of a fermentor.

Fermenting tanks with yeast being used to brew beer. Photo by Kafziel

Modern Fermenting Tanks
Photo by Kafziel

The most important applications of industrial microbiology are using microbes to convert inexpensive raw materials into economically important products. Further, these products go through detection, analysis, assay, purification and recovery to make them safe and effective. The end products are valuable, but the microbes creating these products are equally important.

During the process of industrial fermentation, microbial cells produce extra-cellular as well as intra-cellular enzymes. These enzymes play an important role in fermentation, degradation and utilization of media components. Enzymes can be used as a product by itself and have many end use applications. For example, enzymes like amylase and proteases are used in a variety of products.
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Growth of a Bacterial Cell

Growth of a Bacterial Cell

It can be defined as orderly increase in  quantity of all cell components of a cell.The cell increases in its size,shape and weight and further undergoes cell division.The bacterial cell undergoes different growth phases.This growth phases of bacterial cell can be studied by plotting a growth curve.

As we know studying growth pattern of an individual bacterial cell is impossible due to its small size so here we use population of a bacterial cell for determining the growth curve. The population of a bacterial cell is obtained by innoculating  a small number of innoculum from old culture to a suitable  fresh culture media and growth of a cell is monitored at regular interval of time.The growth curve is plotted by using logarithm of cell number against time.

A bacterial cell undergoes four different growth phases and they are as follows:-

  1. Lag phase
  2. Log phase
  3. Stationary phase
  4. Death phase

Graphical representation of a growth phases of bacterial cell.

Growth Phases of Bacterial population

Growth Phases of Bacterial population

Where,On X axis L is equal to logarithm of number of cell.

On Y Axis T is equal to time in hours

Growth phases of a bacterial cell

1.Lag phase

Initially when we innoculate a old bacterial cell to a new fresh medium the bacterial cell does not carry out immediate cell division  and the inoculated population remains steady.As the bacterial cell get exposed to a new fresh medium these cells try to adjust in the new environment like present nutrients,pH,temperature as well as on other hand this cell synthesize amino-acids,protein,RNA,enzyme and intermediate metabolic products which are further necessary for growth and cell division .

The time of lag phase may vary from species to species due to various environmental factor.At the end of lag phase the bacterial cells starts to multiply and cells enter in logarithmic phase of growth.

2. Logarithmic phase

This log phase is also called as exponential growth phase.In this growth phase of bacterial all cell multiply and carry out cell division.Cell division in this growth phase is constant and maximum.Here the number of cells increases exponentially with time.In this growth phase all bacterial cells are small in size and biologically active as they are constantly dividing so in most of the biochemical and biological studies bacterial cells from this exponential growth phase are used.

If we plot a graph of logarithm of cell number against time on X axis it result in a straight line with positive slope.The multiplication rate and generation time of bacterial cell varies from species to species under different environmental condition.At the end of log phase the growth rate decrease that is generation time of cell increases .After the end of log phase the bacterial cell enters in stationary phase.

3.Stationary phase

As the cells enter in stationary phase the number of cells remain constant because generation time of cell is very low.It occurs due to various factors like depletion of nutrients, accumulation of toxic waste products,change in pH etc. Due to all this factors in this phase the growth rate is equal to death rate and the total number of cells till the end of stationary phase remains constant.

If we plot a graph of log of cell number against time a straight line parallel to X axis is formed with the end of this phase the death phase starts.

4. Death phase

In death phase of growth the bacterial cells starts to die.Here death rate is higher than the growth rate and the death rate increases to maximum at the end of death phase. There are various factors responsible for this phase like exhaustion of nutrients,accumulation of toxic waste products.drastic changes in pH etc.

If we plot a graph of log of number of cells against time on X axis a straight line with negative slope will be observed.Here with the death phase the bacterial growth curve end.

These are the growth phases of a bacterial cell.

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