Fermentation

Bio Reactors (Fermentation tank): Function, Designs and types!

A bioreactor is a device in which a substrate of low value is utilized by living cells or enzymes to generate a product of higher value. Bioreactors arc extensively used for food processing, fermentation, waste treatment, etc. On the basis of the agent used, bioreactors are grouped into the following two broad classes: (i) those based on living cells and, (ii) those employing enzymes. But in terms of process requirements, they are of the following types: (i) aerobic, (ii) anaerobic, (iii) solid state, and (iv) immobilized cell bioreactors. 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. Chemical engineering principles are employed for design and operation of bioreactors. But, in general, theoretical explanation usually lags behind technical realization. A bio Reactor should provide for the following: (i) agitation (for mixing of cells and medium), (ii) aeration (aerobic fermenters; for O2 supply), (iii) regulation of factors like temperature, pH, pressure, aeration, nutrient feeding, liquid level, etc., (ivsterilization and maintenance of sterility, and (v) ) withdrawal of cells/medium (for continuous fermenters). Modern fermenters are usually integrated with computers for efficient process monitoring, data acquisition, etc.

• It should provide a controlled environment for optimum biomass/product yields.
• It should permit aseptic fermentation for a number of days reliably and dependably, and meet the requirements of containment regulations. Containment involves prevention of escape of viable cells from a fermenter or downstream processing equipment into the environment
• It should provide adequate mixing and aeration for optimum growth and production, without damaging the microorganisms/cells. The above two points (items 2 and 3) are perhaps the most important of all.
• The power consumption should be minimum.
• It should provide easy and dependable temperature control.
• Facility for sampling should be provided.
• It should have a system for monitoring and regulating pH of the fermentation broth.
• Evaporation losses should be as low as possible.
• It should require a minimum of labour in maintenance, cleaning, operating and harvesting operations
• It should be suitable for a range of fermentation processes. But this range may often be restricted by the containment regulations.
• It should have smooth internal surfaces, and joints should be welded wherever possible.
• The pilot scale and production stage fermenters should have similar geometry to facilitate scale-up.
• It should be contrasted using the cheapest materials that afford satisfactory results.
• There should be adequate service provisions for individual plants.