Lecture 5

Question 1

system in which a biological conversion is effected. This definition applies to any conversion involving enzymes, micro organisms, and animal or plant cells

Answer 1

bioreactor

Question 2

• organisms are cultivated in a controlled manner
• materials are converted or transformed via specific reactions

Bioreactors are specifically designed to influence metabolic pathways

Answer 2

Bioreactors

Question 3

differ from conventional chemical reactors in that they support and control biological entities and must be designed to provide a higher degree of control over process upsets and contaminations, since the organisms are more sensitive and less stable than chemicals

Answer 3

bioreactors

Question 4

Bioreactions products are formed by three basic processes

Answer 4

1. processes in which the product is made by the cells
2. processes that produce a cell mass
3. biotransformations or enzymatic conversions: processes that modify a compound

Question 5

Bioreactions parameters

Answer 5

• controlled temperature
• optimum pH
• water availability
• gas evolution
• vitamins
• salts for nutrition
• sufficient substrate
• oxygen
• product and by-product removal

Question 6

potential entry for contaminants

Answer 6

valves
where stirrer shaft enters the vessel

Question 7

have a tendency to leak around the valve stem and accumulate broth solids in the closing mechanism

Answer 7

common valves

Question 8

valves are recommended for fermenter construction

Answer 8

pinch and diaphragm

Question 9

without repeated sterilisation cycles are use in valve closure

Answer 9

rubber or neoprene capable

Question 10

the gap between the rotating stirrer shaft and the fermenter body must be ______

Answer 10

sealed

Question 11

Inocula for larger fermentations are transferred from _______

Answer 11

smaller reactor

The simplest aseptic transfer method is to pressurise the inoculum vessel using sterile air: culture is effectively blown into the larger fermenter

Question 12

are fitted to the fermenters to allow removal of broth for analysis

Answer 12

sampling ports

Question 13

The majority of bioreactions are ______

Answer 13

batch wise

Question 14

Common steps of a batch-wise bioreaction

Answer 14

• sterilisation
• sterile culture medium is inoculated with microorganisms
• proper mixing keeps the differences in compositio and temperature at acceptable levels
• if needed, the medium is aerated to provide a continuous flow of oxygen. Gaseous by products formed, such as CO2 are removed
• an acid, alkalie or buffer solution us added if the ph needs to be controlled/modified
• to keep foaming to acceptable levels, antifoaming agents may be added when indicated by a foam sensor
• biomass concentration should remain high
• sterile conditions being maintained
• effective agitation so that the distribution of substances in the reaction is uniform
• temperature
• creation of the correct shear conditions - high may damage cells, low may lead to flocculation or growth on wall and stirrer

Question 15

Advantages of batch bioreactors

Answer 15

• reduced risk of contamination or cell mutation, due to a relatively brief growth period
• lower capital investment when compared to continuous processes for the same bioreactor volume
• more flexibility with varying product/biological systems

Question 16

Disadvantages of batch bioreactors

Answer 16

• Lower productivity levels due to time for filling, heating, sterilising, cooling, empty and clearning the reactor
• Greater expense incurred in preparing several subcultures for inoculation
• Higher costs for labour and/or process control for this non-stationary process

Question 17

Advantages of the continuous operations

Answer 17

• Increased potential for automating the process
• Reduced labour expense, due to automation
• Less time expended in emptying, filling and sterilising the reactor
• Reduced stress on instruments due to sterilisation

Question 18

Disadvantages of the continuous operations

Answer 18

• minimal flexibility since only slight variations in the process are possible (throughput, medium composition, oxygen concentration, temperature)
• Mandatory uniformity of raw material quality is necessary to ensure that the process remains continuous
• Higher investment costs in control and automation equipment, and increased expenses for continuous sterilisation of the medium

Question 19

Need adequate mixing and aeration

Answer 19

Aerobic bioreactor

characterised by the need of free oxygen

Question 20

Normally do no need gas sparging or agitation

Answer 20

Anaerobic bioreactor

lack of oxygen

Question 21

most common type of aerobic bioreactor

Answer 21

stirred tank bioreactor

Question 22

Mixing method mechanical agitation

Answer 22

• baffles are usually used to reduce vortexing
• application: free and immobilised enzyme reactors
• High shear forces may damage cells
• Requires high energy input

Question 23

• baffles are usually used to reduce vortexing
• application: free and immobilised enzyme reactors
• High shear forces may damage cells
• Requires high energy input

Answer 23

Mechanical agitation

Question 24

Mixing method: gas sparging

Answer 24

• simple design
• good heat and mass transfer
• low energy input

Gas-liquid mass tranfer coefficients depend largely on bubble diameter and gas hold up

Question 25

• simple design
• good heat and mass transfer
• low energy input

Gas-liquid mass tranfer coefficients depend largely on bubble diameter and gas hold up

Answer 25

Mixing method: gas sparging

Question 26

Mixing method: airlift

Answer 26

• compared to bubble column reactors, in an airlift reactors, there are two liquid steams: up flowing and down flowing steams
• Liquid circulates in an airlift reactors as a result of density difference between riser and downcomer

Question 27

• compared to bubble column reactors, in an airlift reactors, there are two liquid steams: up flowing and down flowing steams
• Liquid circulates in an airlift reactors as a result of density difference between riser and downcomer

Answer 27

Mixing method: airlift

Question 28

used with immobilised or particulate biocatalysts

Medium can be fed either at the top or bottom and forms a continuous liquid phase

Answer 28

packed bed bjocatalysts

Question 29

Another variation of the packed bed reactors. Liquid is sprayed onto the top of the packing and trickles down through the bed in small rivulets

Answer 29

Trickle bed reactor

Question 30

when the packed beds are operated in upflow mode the bed expands at high liquid flow rates due to upward motion of the particles

Answer 30

fluidised bed reactor

Question 31

have the following functions:
- homogenisation
- suspension of solids
- dispersion of gas-liquid mixtures
- aeration of liquid
- heat exchange

Answer 31

Stirred tank bioreactors

Question 32

Within each vessel the impeller is connected to an external motor which drives the stirrer system.

Should create high turbulence to maintain transfer rates but this an also generate considerable shear force

Answer 32

Stirred tank bioreactors

Question 33

flat vertical plates whose width is about 1/10 of the vessel diameter

Answer 33

baffles

Question 34

aid mixing and mass transfer by increasing turbulence and preventing vortex formation

Answer 34

baffles

Question 35

one of the advantages of this type of reactors are elimination of attrition effected generally encountered in mechanical agitated reactors

Answer 35

Airlift bioreactors

Question 36

Provide a much lower attrition of solid particles
Can be operated with smaller size particles without the drawbacks of clogging, high liquid pressure drop and bed compaction
Smaller particle size faciliates higher mass transfer rates and better mixing

Answer 36

Fluidised bed bioreactors

Question 37

used with attached biofilms especially in wastewater engineering
immobilised biocatalyst is packed in the column and fed with substrate either from top or from bottom
changed flow characteristic due to alterations in the bed porosity during operation

Answer 37

Packed Bed Bioreactors