PART 4 Flashcards
IMMOBILIZED CELL SYSTEMS
High cell concentrations
Cell reuse
Eliminates cell washout at high dilution rates
High volumetric productivities
May provide favorable microenvironment
Genetic stability
Protection from shear damage
MAJOR LIMITATION
Mass transfer (diffusional) resistance
ADVANTAGE OVER IMMOBILIZED ENZYMES
Whole cells provide cofactors, reducing power, energy that many enzymatic reactions require.
Types of Immbolization
Active Immbolization and Passive Immbolization
______________: similar to enzyme
immobilization. Entrapment and binding.
Active Immobilization
______________: Biofilm multilayer growth
on solid surfaces.
Passive Immobilization
Most widely used method of cell immobilization
Physical Entrapment
Various matrices
porous polymers (agar, alginate, carrageenan, polyacrylamide, chitosan, gelatin, collagen)
Physical Entrapment
- Porous metal screens
- Polyurethane
- Polystyrene
- Silica gel
- Cellulose triacetate
- Polymer Beads are also typically used
- Encapsulation
- Macroscopic membrane-based reactors (hollow fiber)
Methods of preparing polymer beads:
- Gelation of polymers
- Precipitation of polymers
- Ion exchange gelation
- Polycondensation
- Polymerization
- There is direct contact between nutrient and support materials
- High cell loadings
- Disadvantage: porous support materials causes intraparticle pore diffusion (at high cell densities) and hard to control microenvironmental conditions
- Selection of suitable support materials is highly based on adsorption capacity and strength of binding
Physical Adsorption
Widely used for enzymes but not for cells
In general, good support materials should be rigid and chemically inert, should bind cells firmly, high loading capacity
Covalent Binding
- Multilayer growth of cells on solid support surfaces
- Support materials can be biologically active or inert
- Common in waste water treatment and mold fermentations
Passive Immobilization: Biological Films
Diffusional Limitations
- Analysis similar to immobilized enzymes
- Damkohler number
- Effectiveness factor
- Thiele modulus
Immobilized-Bioreactors
- Packed-column
- Fluidized-bed
- Airlift
_____________: feed flows through a column packed with immobilized cells. Similar to a plug flow reactor. Can be recycle chamber.
Packed-column
_____________: feed flows up through a bed of immobilized cells, fluidizing the immobilized cell particles.
Fluidized-bed
_____________: air bubbles suspend the immobilized cell particles in a reactor.
Airlift
Solid-state Fermentations
- Fermentations of solid materials
- Low moisture levels or water activities
- Agricultural products or foods
- Smaller reactor volume
- Low contamination due to low moisture
- Easy product separation
- Energy efficiency
- Differentiated microbiological structures
Factors for Consideration in Reactor Design
- Heat Removal
- Foam Control
- Providing oxygen
- Sterilization
_____________: Cellular metabolism produces heat, removed by internal coils or reactor jackets.
Heat Removal
______________: Cellular metabolism produces compounds that promote foaming. Controlled by mechanical foam breakers and chemical additives.
Foam Control
______________: Cellular respiration requires oxygen. Sparged air, impeller makes smaller bubbles and increases residence time.
Providing Oxygen
______________: Single organism desired. Steam and filtering.
Sterilization
What Factors Limit Size of Reactors?
Ability to provide oxygen and remove heat.
Reactor Types
- Stirred-tank
- Bubble column
- Airlift
- Propeller Loop
- Jet Loop
- Good oxygen mass transfer
- High energy requirement for mixing
- Seal to maintain, keep sterile
Agitated tank
- Low shear environment
- No seal needed
- Restricted to low viscosity
- Less mixing than agitated tank
- Bubble coalescence limits upper air flow rate
Bubble Column
- Better mixing than bubble column with same low shear and energy requirements and lack of seal
- work with higher viscosity liquids than bubble columns
- Still less mixing than agitated tank
Loop reactors
__________ breaks bubbles into smaller ones to provide for better oxygen mass transfer
Impeller
_________ are typically glass, commercial fermentors are typically stainless-steel Heat removal/addition is typically by coils along the wall, or a water jacket around the tank.
Bench-top tanks
_________ prevents foaming problems, but can cause additional mass transfer resistance.
Antifoam
- volume of liquid in tank, does not include head space Seal for agitator shaft must not allow contamination.
“working volume”
_________ are used to augment mixing and gas dispersion.
Baffles
_____________: disc with 6 to 8 blades. Pumps fluid in a radial direction. Compartmentalization with multiple impellers on a shaft.
Rushton impellers
_____________: pumps liquid in a vertical direction. Lower energy for the same oxygen
Axial flow impeller
