Find an Article

Thursday, May 5, 2011

Basics & Working of a Fermentor

Industrial processes require large vessels for fermentation which can hold huge amounts of nutritive media. These vessels are called fermenters, Industrial fermenters are designed to provide best possible growth conditions and also conditions that aid in good biosynthesis of product by microbes.

Important features of a Fermentor
  1. The vessel must be strong enough to withstand the pressures of large volumes of liquid medium.
  2. The fermentor should be made up of a material that must not corrode  & shouldnt contribute toxic ions to the medium.
  3. In aerobic fermentation process, oxygen  has to be supplied to the medium by a process called aeration.
  4. The carbon-dioxidde formed during fermentation has to be flushed out of the fermentor.
  5. The contents of the fermentor has to be stirred for a number of reasons such as equal distribution of nutrients throughout the medium, prevention of microbial cells from settling down, etc
  6. As the fermentation process proceeds along with stirring and aeration, there will be foam formation, so there should be a method to detect and control the foam formation. Foam affects product yield and also the growth of microbes.
  7. During the growth of micro-organisms, fermentator must be maintained at a predetermined temperature. so temperature control is required. Optimal Temperature is essential for the growth of microbes.
  8. The fermentor should contains aseptic means of drawing culture from the fermentor and also aseptic means of injecting nutrients and other to the fermentor.
  9. There must be a drain at the bottom of the fermentor through which the completed fermentation broth can be removed.
  10. A mechanism should be there for monitoring pH of the medium during fermentation.
Construction of Fermentor
  1. Fermentors are available in differnet sizes. The sizes are usually stated based on the total volume capacity of the fermentor. However actual operating volume of fermentor is always less than that of the total volume capacity of fermentor. There is a space above the liquid called spathe head space which allows for splashing, foaming and aeration.
  2. Small laboratory fermentors will have total volume capacity of 1-2 Lts  and medium fermentors will have volume capacity of 12-15 Ltrs. Pilot scale fermentors are in the range of 2.5 - 100 Ltrs and some times even more than that. Very large fermentors will have total  volume capacity up to 1,00,000 gallons are also in use.
  3. The material used for making fermentor construction depends on the size, small laboratory fermentors are made of glass, while large ones are made up of stainless steel.
  4. An impeller is mounted to a shaft through a bearing in the lid of the fermentor and is driven by a mortar beneath the fermentor. The impeller is fitted with impeller blades, The heights of the impeller blades are adjustable. when rotated at high speed, vigorous stirring and agitation of the medium are achieved.
  5. Stirring creates circular movements of the medium. Baffles attached to sides of the fermentor wall helps in proper mixing of the medium and microbial cells.
  6. Majority of the fermentation process are aerobic. The sparger is located at the bottom of the fermentation tank so impeller disperses air from the sparger.
  7. Actively metabolising cultures generate heat, thus can increase temperature of the medium above the optimum growth temperatures. In small fermentors this is achieved by passing cold water through jacketed walls or through coils which runs inside the tank.

Working of a Fermentor

This video has been taken during my training session at Biozeen