PART 4

Question 1

IMMOBILIZED CELL SYSTEMS

Answer 1

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

Question 2

MAJOR LIMITATION

Answer 2

Mass transfer (diffusional) resistance

Question 3

ADVANTAGE OVER IMMOBILIZED ENZYMES

Answer 3

Whole cells provide cofactors, reducing power, energy that many enzymatic reactions require.

Question 4

Types of Immbolization

Answer 4

Active Immbolization and Passive Immbolization

Question 5

______________: similar to enzyme
immobilization. Entrapment and binding.

Answer 5

Active Immobilization

Question 6

______________: Biofilm multilayer growth
on solid surfaces.

Answer 6

Passive Immobilization

Question 7

Most widely used method of cell immobilization

Answer 7

Physical Entrapment

Question 8

Various matrices

Answer 8

porous polymers (agar, alginate, carrageenan, polyacrylamide, chitosan, gelatin, collagen)

Question 9

Physical Entrapment

Answer 9

• Porous metal screens
• Polyurethane
• Polystyrene
• Silica gel
• Cellulose triacetate
• Polymer Beads are also typically used
• Encapsulation
• Macroscopic membrane-based reactors (hollow fiber)

Question 10

Methods of preparing polymer beads:

Answer 10

• Gelation of polymers
• Precipitation of polymers
• Ion exchange gelation
• Polycondensation
• Polymerization

Question 11

• 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

Answer 11

Physical Adsorption

Question 12

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

Answer 12

Covalent Binding

Question 13

• Multilayer growth of cells on solid support surfaces
• Support materials can be biologically active or inert
• Common in waste water treatment and mold fermentations

Answer 13

Passive Immobilization: Biological Films

Question 14

Diffusional Limitations

Answer 14

• Analysis similar to immobilized enzymes
• Damkohler number
• Effectiveness factor
• Thiele modulus

Question 15

Immobilized-Bioreactors

Answer 15

• Packed-column
• Fluidized-bed
• Airlift

Question 16

_____________: feed flows through a column packed with immobilized cells. Similar to a plug flow reactor. Can be recycle chamber.

Answer 16

Packed-column

Question 17

_____________: feed flows up through a bed of immobilized cells, fluidizing the immobilized cell particles.

Answer 17

Fluidized-bed

Question 18

_____________: air bubbles suspend the immobilized cell particles in a reactor.

Answer 18

Airlift

Question 19

Solid-state Fermentations

Answer 19

• 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

Question 20

Factors for Consideration in Reactor Design

Answer 20

• Heat Removal
• Foam Control
• Providing oxygen
• Sterilization

Question 21

_____________: Cellular metabolism produces heat, removed by internal coils or reactor jackets.

Answer 21

Heat Removal

Question 22

______________: Cellular metabolism produces compounds that promote foaming. Controlled by mechanical foam breakers and chemical additives.

Answer 22

Foam Control

Question 23

______________: Cellular respiration requires oxygen. Sparged air, impeller makes smaller bubbles and increases residence time.

Answer 23

Providing Oxygen

Question 24

______________: Single organism desired. Steam and filtering.

Answer 24

Sterilization

Question 25

What Factors Limit Size of Reactors?

Answer 25

Ability to provide oxygen and remove heat.

Question 26

Reactor Types

Answer 26

1. Stirred-tank 2. Bubble column 3. Airlift 4. Propeller Loop 5. Jet Loop

Question 27

* Good oxygen mass transfer * High energy requirement for mixing * Seal to maintain, keep sterile

Answer 27

Agitated tank

Question 28

* Low shear environment * No seal needed * Restricted to low viscosity * Less mixing than agitated tank * Bubble coalescence limits upper air flow rate

Answer 28

Bubble Column

Question 29

* 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

Answer 29

Loop reactors

Question 30

__________ breaks bubbles into smaller ones to provide for better oxygen mass transfer

Answer 30

Impeller

Question 31

_________ 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.

Answer 31

Bench-top tanks

Question 32

_________ prevents foaming problems, but can cause additional mass transfer resistance.

Answer 32

Antifoam

Question 33

- volume of liquid in tank, does not include head space Seal for agitator shaft must not allow contamination.

Answer 33

"working volume"

Question 34

_________ are used to augment mixing and gas dispersion.

Answer 34

Baffles

Question 35

_____________: disc with 6 to 8 blades. Pumps fluid in a radial direction. Compartmentalization with multiple impellers on a shaft.

Answer 35

Rushton impellers

Question 36

_____________: pumps liquid in a vertical direction. Lower energy for the same oxygen

Answer 36

Axial flow impeller