DESIGN OF FERMENTERS AND TYPES OF FERMENTERS

BY: SHREELAKSHMI S NAIR

FERMENTORS:

Fermenter is a system which provide controlled environmental conditions for the growth of microbes to obtain a desirable metabolite by preventing the entry of contaminants. Sterility is maintained by steam. Steam is maintained at 121 degree for a period of time and all the unwanted microbes are killed.

In designing a fermenter, following points must be considered

1. The fermenter vessel must be able to work aseptically for a number of days.
2. Evaporation loss should be less
3. It must allow nutrient and reagent feed.
4. Proper aeration and agitation should be provided.
5. Temperature and pH control should be provided.
6. Power consumption must be low.
7. It should facilitate the growth wide range of microbes.

PARTS OF FERMENTOR:

1. Impellers: Mixes the nutrient media so that each and every cell gets equal amount of nutrients, It also prevents the settling down of nutrients. This impeller is connected to the motor.
2. Temperature Sensor and pH sensor: Microbes grow only at a particular temperature and pH.Hence a sensor is provided at the top side of fermenter to keep a track on it.
3. Water jacket: Helps in cooling down of the fermenter when the temperature rises. Water jacket provides the circulation of water which controls water. The reactors are covered with water jacket.
4. Sparger: It is hollow plate which consist of two plates in which the top one contains holes on it. Oxygen passes to the lower plate which moves to the upper plate from where it comes out in the form of bubble .This bubble is broken by impeller releasing oxygen.
5. Baffles: It helps in preventing vortex formation. Vortex formation prevents efficient mixing of nutrients hence it’s important to have baffles.

TYPES OF FERMENTER

1. Air lift Fermenter: Volume of the culture will be divided into two sections with the help of baffle. Only of the two section will be sparged with air or any other gas and this region where it is sparged is called riser. The other section is known as down-corner. Successive cycles of low and high pressure are created during growth medium circulation. Hence it is also called pressure cycle fermenter. It can be used for continuous process. It doesn’t require agitation and it’s cost effective.

• Continuous Stirred Tank Bioreactor: It consists of a cylindrical vessel which is occupied with a motor driven central shaft which supports one or more impellers. Shaft is present at the bottom of the bioreactor. The air provided to the culture medium is through the spranger.Advantages of stirred tank reactors are that they provide efficient gas transfer for the growing cells.

• Bubble Column Fermenter: 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.

• Fluidized Bed Fermenter: This type of reactor is used to carry out multiphase reactions. The fluid is passed through a solid material at high velocities to suspend the solids. It provides excellent mixing, increased mass transfer and enlarged surface area which increases the efficiency. Removal of heat and exchange if gases are easy. It requires more pumping power and also chances for erosion of internal components are more.

• Hollow Fiber Membrane Fermenter: This fermenters are commonly used for suspension cell. Acyclic polymer or polysulphone fibers are used. Nutrients and oxygen from the intercapilary stream moves across the membrane into the extra capillary space. The product accumulates on the extra capillary site and thus can be harvested at considerably high concentration.it consist of a cylindrical vessel which consist of individual fibers which are held together in a shell and tube heat exchange arrangement.it allows simultaneous separation of cell from extra cellular product no wash out required because cells are trapped. High productivity per unit of volume is obtained due to high cell density.in this type of reactors diffusion may cause limitation in growth and accumulation of toxic products in fiber are observed.

• Fixed Bed Fermenter: It is generally used for connecting an immobilized bio catalyst cell for enzyme with the substrate solution. The vessel is packed with a bed of immobilized enzyme particles. The substrate solutions is added from one side and the product is recovered from the other end. It is difficult to maintain pH and gaseous reactant.

• Tray Fermenter: Generally its made up of wooden or plastic metal tray which are widely used for traditional solid state fermentation the substrate in trays area arranged one above the other so that steam sterilization of the substrate allow aeration by air, moistures applied to the substrate by double flow nozzle with water and air and forced aerator by a blower and can be carried out automatically.
• Dialysis Unit Fermenter: It allows toxic waste metabolite or end product to diffuse away from the microbial culture and permits new substrate to diffuse through the membrane towards the culture.
• Deep Jet Fermenter (High Pressure Consuming Bioreactor): The fermenter medium is circulated by pumps gas dissolution and the liquid movement. The gas mixed with high power jet of liquid is injected into the fermenter. Better gas dissolution is obtained in this design but it also leaves involvers more power consumption.

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