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(Designs and features of industrial fermenters), Continuous fermentation
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Continuous fermentation
- Open system
- Continuation of the process - no idle time
- Continuously nutrients added
- More control on growth of microbes and products
- Turnover rate is higher
- Nutrients utilize in high rate
- Microbes maintained in exponential growth rate
- Products are extracted from the overflow of fermenter
- No cleaning steps required
- Smaller size of fermenter
- Limited application
- Production of primary metabolites, organic acids
- Nutrients added and product removed at steady rate
- Higher risk of contamination due to constant adjustment
- Feasible only when inoculated cells are genetically stable
Batch fermentation
- Closed system - initial limited amount of nutrient
- Process is stopped once product is formed
- Nutrients are added only once
- Less control over the microbes growth and products
- Turnover rate is less
- Nutrients are utilize in slow rate
- Microbes undergoes the growth rate
- End product are isolated
- Fermenter is cleaned end of each process
- Larger size fermenter
- Huge application in industrial production
- Production of secondary metabolites - antibiotics
- Nothing added or removed during the process
- MO and nutrients are left for a set period of time
- Stirrer tank reactor
- Bubble column reactor
- Air fit reactor
- Sterile air - Provide operation free from contamination
- Temperature controller - Maintain specific temperature
- Sparger & baffle - Provide adequate mixing and aeration& allow dissolved oxygen
- pH controller - Control pH pf the culture
- Sample inlet - Allow feeding of nutrient solutions and reagents
- Provide access points for inoculation and sampling
- Baffles
- Metal strips roughly 1/10 of vessel diameter and attached radially to the wall
- To prevent a vortex & improve aeration efficiency
- 4 baffles are normally incorporated into agitated vessels of all sizes
- Attached radially to the wall of bioreactor - 4-8 baffles are incorporated
Glass
- smooth & non-toxic
- round or flat bottom
- no alkali release
- borosilicate glass
-corrosion proof
- visibility - useful for examination
- serializable by autoclave
- top and bottom portions attached by flanges
- not suitable for large scale
- fragility
SS
- steels with >4% chromium
- corrosion resistance
-strength & durability
- internally coated with glass or epoxy for more resistance
- composition altered - accordingly used for specific purposes
- Eg, American Iron & Steel Institurte (AISI)
- AISI-316: 18% Cr, 10% Ni, 2--2.5% Molybdenum
- AISI-304: 18.5% Cr, 10% Ni [Brewing equipement]
- Acid fermentation required SS with 3-4% Molybdenum to withstand the pH conditions
- Laboratory fermenter - 1-15L
- Pilot plant fermenter - 50-100L
- Industrial fermenter - 5000/10000 gallons
- Temperature
- Adequate provision for temperature control
- Heat - produced by microbial activity and mechanical agitation
- The heat may need to be removed or added to the system
- Thermastatically controlled bath / internal heating coils - used supply heat
- Heating jacket / silicone heating jacket - circulate water to removed heat
- Aeration
- Provide: Sufficient oxygen for metabolite requirements & Uniform suspension of microbial cells
- 2 types: Fine bubble aerator & Mecahnical agitation - fungal & actinomycete
- Aerobic - presence of oxygen; Anaerobe - absence of oxygen
- Oxygen is essential for metabolic requirement of MO
- Sparger introduce air into the liquid contents in a fermenter:
- Porous sparger - porous. Eg. Sintered glass, ceramic bubble size is 10-100x larger than aerator block.
- Orifices sparger - air holes were drilled on the under surface of the tubes through which air is passed on the contents. Air is passed through rings - ring sparger
- Nozzle sparger - open or partially closed pope through which air is supplied into the fermenter. Similar to orifice sparger
- Agitation
- by using agitator
- Agitation is required to achieve a number of mixing objectives:
- Uniform suspension of microbial cells in homogeneous nutrient medium
- Bulk fluid and gas-phase mixing
- Air depression
- Oxygen transfer
- Heat transfer
- Suspension of solid particles
- Maintaining of solid particles
- Maintaining a uniform environment throughout the vessel contents
- Agitators classify into:
- Disc turbines - consist of disc with a series of rectangular vaned set in a vertical plane around the circumference
- Vaned disc - a series of rectangular vanes attached vertically to the underside.
- Air from the sparger hits the underside of the disc, displaced towards the vanes where the air bubbles are breaking into smaller bubble
- Open turbines of variable pitch
- Propeller - The vanes of variable pitch open turbine and the blades of a marine propeller are attached directly to a boss on the agitator shaft
- pH control
- Essential in acid fermentation - citric acid, acetic acid..
- Glass reference electrodes tips should be covered properly to indicate the pH of the fermenter accurately
- Sealing should be perfect for the electrodes with the fermenter
- Large scale industrial level - used pH sensors
- Sufficient strength & durability
- periodic maintenance is vital
- Foam control
- Aeration and agitation of liquid medium can cause the production of foam
- Proteolytic bacteria - bacteria that degrade protein to peptide, can cause particularly serious foam probelms
- Problems:
- It will rise in the head space of the tank and be forced from the tank along with the spent air which often causes contamination of the fermentation. Environmental hazard may develop.
- Limiting gas exchange between the medium and the atmosphere of the head space
- Siphoning will develop and loss of contents of fermenter - serious consequences if pathogenic in nature
- Foam control method:
- Using a defined medium & modification in parameters - stirring speed & air supply rate
- Addition of anti-foaming agents: Inert antifoam & Mechanical antifoaming devices
- Inert antifoams - silicones & suplhonates
- Made of crude organic materials
- Animal and vege oils are often used - soybean oil, corn oil, linseed, cotton seed
- Long-chain alcohol - octadecanol, stearyl, ester
- Mechanical antifoaming devices: Disc, propeller hollow cones attached to agitator shaft
- Antiseptic & Maintenance of aseptic conditions
- It is essential that the fermenter design meets the requirement of degree of aseptic and containment
- Degree depends on the specific fermentation process
- It will be necessary to be able to sterilize, keep sterile of the fermenter and its contents throughout a complete growth cycle.
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