Fermentor

Fermentor
Design of fermentor
types of fermentor
airlift fermentor
stirred tank fermentor
photobioreactor
packed bed reactor
bubble column reactor

1. FERMENTOR/BIOREACTOR

2. Fermentor A fermentor (bioreactor) is a closed vessel with adequate arrangement for aeration, agitation, temperature and pH control, and drain or overflow vent. A fermentor is used for commercial production in fermentation industries. De Beeze and Liebmann (1944) used the first large scale (above 20 litre capacity) fermentor for the production of yeast.  Chain Weizmann (1914-1918) developed a fermentor for the production of acetone.

3. Design A bioreactor should provide for the following: (i) Agitation (for mixing of cells and medium), (ii) Aeration (aerobic fermentors ); for O 2  supply, (iii) Regulation of factors like temperature, pH, pressure, aeration, nutrient feeding, liquid level etc., (iv) Sterilization and maintenance of sterility, and (v) Withdrawal of cells/medium (for continuous fermentors ).

4. The size of fermentors ranges from 1-2 litre laboratory fementors to 5,00,000 litre or, occasionally, even more, fermentors of upto 1.2 million litres have been used.  

5. FACTORS TO DESIGN A FERMENTER The vessel should be well equipped to maintain aseptic conditions inside it for a number of days. Aeration and agitation are important for the production of biological metabolites. However, controlled agitation is required to prevent any damage to the cells. It should be less expensive in terms of power consumption. Temperature is an important environmental factor required for microbial growth. Therefore, a temperature control system is required. Optimum pH is important for the growth of the organism; therefore, the fermenter must be equipped with a pH controller .

6. The fermentation of a huge culture is a time-consuming process. It needs to be contamination-free until the process is complete. Apart from that, it is also important to monitor the growth rate of the organism. Therefore, an aseptic sampling system is needed to design a fermenter. The fermenter vessel should be designed properly to minimize the labor involved in cleaning, harvesting, etc. It should be designed in such a way that it reduces evaporation. The vessel needs to be equipped with a smooth internal surface to support adequate mixing.

7. DESIGN OF FERMENTER Hence design of a fermenter is important in the process of fermentation. Construction material Agitator Stirrer Sparger Baffles Temperature control pH control

8. Construction material It is important to select a material for the body of the fermenter, which restricts the chances of contamination. It needs to be non-toxic and corrosion free.  Glass is a material that provides a smooth surface inside the vessel and also non-toxic in nature and used in small scale production. 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 

9. Inoculation Port Inoculation port is a device from which fermentation media, inoculum and substrate are added in the fermentation tank. Sampling point Sampling point is used for time to time withdrawal of samples to monitor fermentation process and quality control. Bottom drainage port It is an aseptic outlet present at the bottom of fermentor for removal of fermented media and products formed.

10. Agitator or Impeller The impeller used in fermenters are bulk fluid and gas mixing, air dispersion, heat transfer, oxygen transfer, suspension of solid particles and maintain the uniform environment inside the vessel. Air bubbles often cause problems inside the fermenter. Impellers involved in breaking the air bubbles produced in a liquid medium . There are mainly three types of agitators used in industrial-scale bioreactors namely disc turbine, vaned disc and pitch open turbine.

11. Stirrer The stirrer shafts play an important role to seal the openings of a bioreactor. As a result, it restricts the entry of air from outside. One type of seal used in both small and large scale fermenter is 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. Steam condensate is used to lubricate and cool the seals during operation and provides protection against the contamination.

12. Sparger A sparger is a device that introduces air into the liquid medium in a fermenter. There are three main types of fermenter used in industrial-scale bioreactors such as 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 are formed Orifice Sparger :  These are used in small stirred fermenters where 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. Nozzle Sparger :  This is used in industrial-scale fermenters. The main characteristic of this kind of sparger is that it contains a single open or partially closed pipe as an air outlet .

13. 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. Baffles are often attached to cooling coils to increase the cooling capacity of the fermenter.

14. Temperature control During the fermentation process heat can be produced mainly in two ways, firstly microbial biochemical reactions and secondly mechanical agitation. A temperature control helps to control the temperature at the optimum level by removing or providing heat. The 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.

15. pH control 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. Foam control 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.

16. Foam checking probe pH checking probe

17. Cooling Jacket: The fermenter is fitted externally with a cooling jacket through which steam (for sterilization) or cooling water (for cooling) is run. Use of Computer in Fermenter Computers are used to model fermentation processes in industrial fermenters. Integration of computers into fermentation systems is based on the computers capacity for process monitoring, data acquisition, data storage, and error-detection

18. TYPES OF FERMENTOR Following are the types of fermenter Airlift Fermenter Continuous Stirred Tank Bioreactors Photo-Bioreactors Bubble Column Fermenter Fluidized Bed Bioreactors Packed Bed Bioreactors

19. Airlift Fermenter The simple type Used for continuous culture In airlift fermenter the liquid culture volume of the vessel is divided into two interconnected zones by means of a baffle or draft tube . Draft tubes promote better mass transfer and mixing O ne of the two zones is sparged with air or other gas T his sparged zone is known as the riser . The other zone that receives no gas is called down-comer . Mainly two types- internal loop and external loop

20. Suited for aerobic culture and fermentation Production of beer, yeast and SCP Used for Waste water treatment For production of Proteins from cells

21. Continuous Stirred Tank Bioreactors Common model in chemical and environmental engineering A continuous stirred tank bioreactor consists of a cylindrical vessel with motor driven central shaft that supports one or more agitators (impellers ). The mixing device promote efficient mixing The shaft is fitted at the bottom of the bioreactor. The number of impellers is variable and depends on the size of the bioreactor i.e., height to diameter ratio, referred to as aspect ratio.

22. Several types of impellers (Rustom disc, concave bladed, marine propeller etc.) are in use. The air is added to the culture medium under pressure through a device called sparger. The sparger may be a ring with many holes or a tube with a single orifice. The sparger along with impellers (agitators) enables better gas distribution system throughout the vessel. The bubbles generated by sparger are broken down to smaller ones by impellers and dispersed throughout the medium. This enables the creation of a uniform and homogeneous environment throughout the bioreactor.

23. Suited also for anaerobic process Used for waste water treatment Biogas production Pharmaceutical products

24. Photo-Bioreactors: These are the bioreactors specialized for fermentation that can be carried out either by exposing to sunlight or artificial illumination . Mainly employed for the cultivation of photosynthetic organisms Provide controlled supply of environmental conditions Has two types – open system and closed system Open system are usually outdoor reactors/ open pond reactors build in large area Closed system are indoor reactors with artificial setup

25. Certain important compounds are produced by employing photo-bioreactors e.g., p-carotene, asthaxanthin . Used for growing algae and cyanobacteria Bioplastic production Waste water remediation Nutraceutical and pharmaceutical product production Biofuel production

26. Bubble Column Fermenter Generate and control gas-liquid chemical reactions Bubble column fermenter is usually cylindrical with an aspect (height to diameter) ratio of 4-6. Gas is sparged at the base of the column through perforated pipes,perforated plates,or sintered glass or metal micro-porous spargers. O2 transfer,mixing and other performance factors are influenced mainly by the gas flow rate and the properties of the fluid.

27. Used for chemical processes Production of alcohols and fuels Also used as algal bioreator

28. Bubble Column Fermenter

29. Fluidized bed bioreactor is comparable to bubble column bioreactor except the top position is expanded to reduce the velocity of the fluid. The design of the fluidized bioreactors (expanded top and narrow reaction column) is such that the solids are retained in the reactor while the liquid flows out. These bioreactors are suitable for use to carry out reactions involving fluid suspended biocatalysts such as immobilized enzymes, immobilized cells, and microbial floc k s. Fluidized Bed Bioreactors:

30. For an efficient operation of fluidized beds, gas is spared to create a suitable gas-liquid-solid fluid bed. It is also necessary to ensure that the suspended solid particles are not too light or too dense (too light ones may float whereas to dense ones may settle at the bottom), and they are in a good suspended state. Recycling of the liquid is important to maintain continuous contact between the reaction contents and biocatalysts. This enable good efficiency of bioprocessing.

31. Packed Bed Bioreactors: A bed of solid particles, with biocatalysts 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 immobilized biocatalyst. 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.