Up - Bioreactors

Question 1

[Bioreactors] What 2 main types of bioreactors are there?

Answer 1

Surface and submerse reactors - depends on the gas supply

Question 2

[Bioreactors] Give two examples of surface bioreactors, their advantages and disadvantages

Answer 2

Shake flask:
+ Cheap, simple
- Small volume, no control

Wave/bag:
+ Sensitive cells, presterilized, easy and cheap for high sterility demands
- Medium volumes, limited mixing rate

Question 3

[Bioreactors] Give four examples of submerse bioreactors

Answer 3

Bubble column/airlift reactor: Only gas flow from bottom/force around

Jet/Jet-loop reactor: Mixing with liquid (added gas) flow/force around

Stir-tank/propeller reactor: Mechanical mixing by stirrer/propeller (less force)

Perfusion reactor: Cell are immobilized in matrix/recaptured and media exchanged

Question 4

[Bioreactors] What are the advantages and disadvantages with the four types of submerse reactors?

Answer 4

Bubble:
+ Cheap, sensitive cells
- Low oxygen transfer, high risk of foam

Jet:
+ Cheap, oxygen transfer
- High risk of foam, sensitive cells

Stir:
+ Well mixed, high oxygen transfer, high cell densities, easy control, multiple scales
- Sensitive cells, expensive (maintanence, operation)

Perfusion:
+ Very high cell densities, remove product/inhibitor continously, single use variants
- Very technical, tight packing can make oxygen diffusion limiting (combat with high flow rate), diluted products

Question 5

[Bioreactors] Give three examples of photobioreactors, their advantages and disadvantages

Answer 5

Flat panel (vertical, mixing by bubbles) and horizontal tubes (mix by gas flow):
+ Good light penetration (thin, mixing), sensitive cells, better control (temperature etc.)
- Risk of foam, biofouling (grow on support), oxygen build-up

Open ponds (e.g. raceway ponds mixing by paddle wheels):
+ Large scale
- Risk of contaminants, evaporation of water

Question 6

[Bioreactor] What cultivation equipment can be used for animal cells?

Answer 6

SMALL
(Roller) flasks: Gentle mixing and surface growth
+ Surface growth (anchorage), cheap, simple, disposable
- Low cell and product concentration, medium composition changes with growth

MEDIUM
Spinner flasks: Suspension/microcarrier cultures. Propeller allows for gentle mixing.
+ Continuous stirring, easier environmental adjustment, possible for larger volumes (need more flasks however)
- Low cell and product concentration (compared to microorganisms)

LARGE
Wave-reactor
Perfusion
Hollow fiber (like perfusion)

Question 7

[Photobioreactors] What are some important design criteria for growth in photobioreactors? (7)

Answer 7

Surface-to-volume ratio (s/v): Amount of light per unit volume > important for light penetration. Make sure not to have too long light path.

Orientation and inclination: Orientation to the sun/light source. Importance is to get the light to the reactor.

Oxygen accumulation: Oxygen toxic  necessary to degas to release the oxygen. Also need more CO2.

Mixing: Transport cell into the light/dark zone

Temperature control: Solar energy will heat things > cooling or organisms that tolerate the variations in temperature

Supply of CO2: Needed if residence time of bubbles is insufficient for complete absorption. Open ponds often work themselves out.

Materials: Glass, plastics

Question 8

[Bioreactors] How can one control the feed in continous processes?

Answer 8

Four different manners:
- Chemostat: Constant feed rate and the growth is controlled by a limiting substrate (metabolic controlled)
- Turbidostat: Feed rate controlled by optical density
- pH-auxostat: Feed rate controlled by pH
- Nutristat: Feed rate controlled by a certain nutrient concentration

Question 9

[Bioreactors] What is “chemostat” synonomous with?

Answer 9

Continous process