PART 4 Flashcards
(36 cards)
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