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FE 462 BIOCHEMICAL ENGINEERING. Cell Kinetics and Fermenter Design. Bioreactors. Bioreactors. Bioreactors. Bioreactors. Bioreactors. Bioreactors. Bioreactors. Stirred Tank Ferment e rs.
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FE 462 BIOCHEMICAL ENGINEERING Cell Kinetics and Fermenter Design
Stirred Tank Fermenters A bioreactor is a device within whichbiochemicaltransformations are caused by the action of enzymes orliving cells. The bioreactor is frequently called a fermenter whetherthe transformation is carried out by living cells or in vivo cellularcomponents (enzymes). For a large-scale operation the stirred-tank fermenter (STF) is themost widely used design in industrial fermentation. It can beemployed for both aerobic or anaerobic fermentation of a wide rangeof cells including microbial, animal, and plant cells.
Kinetics of Substrate Utilization, Product Formation, and Biomass Production in Cell Cultures It is difficult to obtain useful kinetic information on microbial populations from reactors that have spatially no uniform conditions. Hence it is desirable to study kinetics in reactors that are well mixed. Ideal Batch Reactor Many biochemical processes involve batch growth of cell populations. After seeding a liquid medium with an inoculum of living cells, nothing (except possibly some gas) is added to the culture or removed from it as growth proceeds. Typically in such reactor, the concentrations of nutrients cells, and products vary with time as growth proceeds. Glucose Product Cell biomass Time
Kinetics of Substrate Utilization, Product Formation, and Biomass Production in Cell Cultures A material balance on moles of component i;
The Ideal Continuous Flow Stirred Tank Reactor (CSTR) The diagram of this process is shown in fig.2, which is a schematic diagram of completely mixed stirred tank reactor. Such configurations for cultivation of cells are frequently called chemostats.
Continuous Fermentor Flow rate1 = Flow rate2 Pump 1 Pump 2 Feedstock vessel (sterile) Collection vessel
Pro and cons of chemostat • (+) • Excellent experimental tool because µ is defined • (-) • Low biomass and product concentration • Loss of biomass in outflow • Relatively prone to be contaminated compare to batch or fed batch reactors • Microbial selection for non-producing mutants
Characteristics of Continuous (Chemostat) Fermentors • Input rate = output rate (volume = const.) • Flow rate is selected to give steady state growth (growth rate = dilution rate) • Dilution rate > Growth rate culture washes out • Dilution rate < Growth rate culture overgrows • Dilution rate = Growth rate steady state culture • Stable chemostat cultures can operate continuously for weeks or months.
The Ideal Continuous Flow Stirred Tank Reactor (CSTR) For biomass
The Ideal Continuous Flow Stirred Tank Reactor (CSTR) For Substrate
The Ideal Continuous Flow Stirred Tank Reactor (CSTR) For Product
The Ideal Continuous Flow Stirred Tank Reactor (CSTR) Example-
The Ideal Continuous Flow Stirred Tank Reactor (CSTR) Solution Intercept Slope
The Ideal Continuous Flow Stirred Tank Reactor (CSTR) Solution
MULTIPLE FERMENTERS CONNECTED IN SERIES A question arises frequently whether it may be more efficient to usemultiple fermenters connected in series instead of one large fermenter. Choosing the optimum fermenter system for maximum productivity depends on the shape of the l/rx versus Cx curve andthe process requirement, such as the final conversion.
Cell Recycling For the continuous operation of a PFF or CSTF, cells are dischargedwith the outlet stream which limits the productivity of fermenters.The productivity can be improved by recycling the cells from theoutlet stream to the fermenter.
Considerations in selecting industrial fermenters are: • Nature of substrate solid, liquid, suspended slurry, • water-immiscible oils • 2. Flow behaviour (rheology), broth viscosity and type of fluid • (e.g. Newtonian, viscoelastic, pseudoplastic, Bingham plastic). • 3. Nature and amount of suspended solids in broth. • 4. Whether fermentation is aerobic or anaerobic, and O2 demand. • 5. Mixing requirements. • 6. Heat-transfer needs. • 7. Shear tolerance of microorganism, substrate and product. • 8. Sterility requirements. • 9. Process kinetics, batch or continuous operation, single-stage or • multistage fermentation. • 10. Desired process flexibility. • 11. Capital and operational costs. • 12. Local technological capability and potential for • technology transfer.
Types of submerged-culture fermenter. (A) Stirred-tank fermenter. (B) Bubble column. (C) Internal-loop airlift fermenter. (D) External-loop airlift fermenter. (E) Fluidized-bed fermenter. (F) Trickle-bed fermenter
Bubble Column Although simple, it is not widely used because of its poor performance relative to other systems. It is not suitable for very viscous broths or those containing large amounts of solids. Airlift Fermenters In the internal-loop design, the aerated riser and the unaerated downcomer are contained in the same shell. In the external-loop configuration, the riser and the downcomer are separate tubes that are linked near the top and the bottom not suitable for viscous broths. Their ability to suspend solids and transfer O2 and heat is good. The hydrodynamic shear is low.
Air lift reactors: In such reactors, circulation is caused by the motion of injected gas through a central tube with fluid recirculating through the annulus between the tube and the tower or vice versa.
Fluidized-bed Fermenter Fresh or recirculated liquid is continuously pumped into the bottom of the vessel, at a velocity that is sufficient to fluidize the solids or maintain them in suspension. Trickle-bed Fermenter a cylindrical vessel packed with support material (e.g. woodchips, rocks, plastic structures). A liquid nutrient broth is sprayed onto the top of the support material, and trickles down the bed. Air may flow up the bed, countercurrent to the liquid flow. These fermenters are used in vinegar production, as well as in other processes.
Solid-state Fermentations • Substrate Characteristics • Water Activity • Typically, solid-state fermentations are carried out with little or no free water. • Excessive moisture tends to aggregate the substrate particles, and hence aeration is made difficult. • For example steamed rice, a common substrate, becomes sticky when the moisture level exceeds 30–35% w/w. • The low-moisture environment of many solid-state fermentations favours yeasts and fungi.( mostly to produce extracellular enzyme by mold on cereals) • During fermentation, the water activity is controlled by aeration with humidified air and, sometimes, by intermittent spraying with water.
Advantages of SSF( solid state fermentation) • Small fermentor volume, lower capital and operating cost • Lower chance of contamination due to low water • Easy product seperation • Energy efficient Disadvantages of SSF( solid state fermentation) • Heterogenous structure due to poor mixing so difficulty in controlling pH, DO, temperature)
Bubble Column Although simple, it is not widely used because of its poor performance relative to other systems. It is not suitable for very viscous broths or those containing large amounts of solids. Airlift Fermenters In the internal-loop design, the aerated riser and the unaerated downcomer are contained in the same shell. In the external-loop configuration, the riser and the downcomer are separate tubes that are linked near the top and the bottom not suitable for viscous broths. Their ability to suspend solids and transfer O2 and heat is good. The hydrodynamic shear is low.
Oxygen Demand Submerged cultures are most commonly aerated by bubbling with sterile air. in small fermenters, the maximum aeration rate ≤ 1VVM ( 1 VVM-volume of air per unit volume of broth per minute). In large bubble columns and stirred vessels, the max superficial aeration velocity < 0.1 m s−1. ( Q/A)
