Lecture 5 Flashcards
system in which a biological conversion is effected. This definition applies to any conversion involving enzymes, micro organisms, and animal or plant cells
bioreactor
- organisms are cultivated in a controlled manner
- materials are converted or transformed via specific reactions
Bioreactors are specifically designed to influence metabolic pathways
Bioreactors
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
bioreactors
Bioreactions products are formed by three basic processes
- processes in which the product is made by the cells
- processes that produce a cell mass
- biotransformations or enzymatic conversions: processes that modify a compound
Bioreactions parameters
- controlled temperature
- optimum pH
- water availability
- gas evolution
- vitamins
- salts for nutrition
- sufficient substrate
- oxygen
- product and by-product removal
potential entry for contaminants
valves
where stirrer shaft enters the vessel
have a tendency to leak around the valve stem and accumulate broth solids in the closing mechanism
common valves
valves are recommended for fermenter construction
pinch and diaphragm
without repeated sterilisation cycles are use in valve closure
rubber or neoprene capable
the gap between the rotating stirrer shaft and the fermenter body must be ______
sealed
Inocula for larger fermentations are transferred from _______
smaller reactor
The simplest aseptic transfer method is to pressurise the inoculum vessel using sterile air: culture is effectively blown into the larger fermenter
are fitted to the fermenters to allow removal of broth for analysis
sampling ports
The majority of bioreactions are ______
batch wise
Common steps of a batch-wise bioreaction
- 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
Advantages of batch bioreactors
- 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
Disadvantages of batch bioreactors
- 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
Advantages of the continuous operations
- 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
Disadvantages of the continuous operations
- 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
Need adequate mixing and aeration
Aerobic bioreactor
characterised by the need of free oxygen
Normally do no need gas sparging or agitation
Anaerobic bioreactor
lack of oxygen
most common type of aerobic bioreactor
stirred tank bioreactor
Mixing method mechanical agitation
- baffles are usually used to reduce vortexing
- application: free and immobilised enzyme reactors
- High shear forces may damage cells
- Requires high energy input
- baffles are usually used to reduce vortexing
- application: free and immobilised enzyme reactors
- High shear forces may damage cells
- Requires high energy input
Mechanical agitation
Mixing method: gas sparging
- simple design
- good heat and mass transfer
- low energy input
Gas-liquid mass tranfer coefficients depend largely on bubble diameter and gas hold up
- simple design
- good heat and mass transfer
- low energy input
Gas-liquid mass tranfer coefficients depend largely on bubble diameter and gas hold up
Mixing method: gas sparging
Mixing method: airlift
- 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
- 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
Mixing method: airlift
used with immobilised or particulate biocatalysts
Medium can be fed either at the top or bottom and forms a continuous liquid phase
packed bed bjocatalysts
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
Trickle bed reactor
when the packed beds are operated in upflow mode the bed expands at high liquid flow rates due to upward motion of the particles
fluidised bed reactor
have the following functions:
- homogenisation
- suspension of solids
- dispersion of gas-liquid mixtures
- aeration of liquid
- heat exchange
Stirred tank bioreactors
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
Stirred tank bioreactors
flat vertical plates whose width is about 1/10 of the vessel diameter
baffles
aid mixing and mass transfer by increasing turbulence and preventing vortex formation
baffles
one of the advantages of this type of reactors are elimination of attrition effected generally encountered in mechanical agitated reactors
Airlift bioreactors
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
Fluidised bed bioreactors
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
Packed Bed Bioreactors
