Selection, Scale-Up Operation, and Control of Bioreactors Flashcards
Factors for Consideration in Reactor Design
➢ Heat Removal
➢Foam Control
➢ Providing Oxygen
➢ Sterilization
What factors limit the size of reactors?
Ability to provide oxygen and remove heat.
Reactor types include:
➢ Stirred-Tank
➢ Bubble Column
➢ Airlift
➢ Propeller Loop
➢ Jet Loop
Reactor types comparison: Agitated Tanks
➢ Good oxygen mass transfer
➢ High energy requirement for mixing
➢ Seal to maintain and keep sterile.
Reactor types comparison: Bubble Column
➢ Low shear environment
➢ No seal needed
➢ Restricted to low viscosity
➢ Less mixing than agitated tank
➢ Bubble coalescence limits upper air flow rate.
Reactor types comparison: Loop reactors
➢ Better mixing than bubble column with the same low shear and energy requirements and lack of seal.
➢Work with higher viscosity liquids
than bubble columns.
➢Still less mixing than agitated tanks
It breaks bubbles into smaller ones to provide for better oxygen mass transfer
Impeller
Comparison between bench-top tanks and commercial fermenters
Bench-top tanks are typically glass, commercial fermenters are typically stainless steel.
Heat removal/addition is typically done by
coils along the wall, or a water jacket around the tank.
It prevents foaming problems but can cause additional mass transfer resistance.
Antifoam
What is “working volume”?
volume of liquid in tank; does not
include head space.
Seals for _________________ must not allow contamination
agitator shaft
These are used to augment mixing and gas dispersion.
Baffles
Types of impellers
➢ Rushton Impellers
➢ Axial Flow Impeller
Rushton impellers are:
➢ Disc with 6 to 8 blades.
➢ Pumps fluid in a radial direction.
➢ Compartmentalization with multiple
impellers on a shaft.
Axial flow impellers are:
➢ Pumps liquid in a vertical direction.
➢ Lower energy for the same oxygen
mass transfer.
➢ Lower shear rates.
Transfer rate at steady state is determined by the _____________
➢ slowest rate
➢ OTR is not the rate at which OUR = OTR you
provide air to the reactor. You will actually provide much more oxygen to the reactor than is transferred to the cells.
Oxygen Profile 1-6
- Bulk gas phase oxygen concentration.
- Transfer across stagnant gas layer.
- Partitioning into the liquid phase (C* at saturation).
- Transfer across stagnant liquid layer.
- Bulk liquid concentration ( ).
- Transfer across stagnant liquid layer to cell.
Experimental Determination of O2 Mass Transfer
➢ The previous correlation offers design estimates.
➢ Medium components, temperature, and pressure can
affect volumetric transfer coefficient and oxygen
solubility.
➢ Simple experiments can be done to measure volumetric
transfer coefficient.
➢ Unsteady state, steady state, dynamic and sulfite are
methods to measure volumetric transfer coefficient.
Unsteady State Method
○ Fill the reactor with medium only – no cells.
○ Measure DO concentration in
the medium.
○ Remove oxygen from the
medium by sparging with N2.
○ Introduce air, and record the
increase in DO.
Steady State Method
○ Requires an oxygen gas
analyzer for the effluent air.
○ Perform an O2 mass balance to
obtain OUR.
Dynamic Method
○ Utilizes a fermentor with actively
growing cells.
○ Requires only a DO meter.
○ The air to the fermentor is shut
off, and the DO decreases due
to consumption by the
microorganisms. The air is then
turned on, and the DO increases.
Scale -Up
○ Empirical
○ Make the controlling regime the same in the small scale as in the large scale
Scale-Up Criterion
○ Power Input: Oxygen Transfer Rate
○ Liquid Circulation Rate
: Mixing Time
○ Tip Speed: Shear
○ Reynolds Number: Geometry
COMMON ON-LINE INSTRUMENTATION
➢ pH
➢ Temperature
➢ Dissolved oxygen
➢ Foam
➢ Flow Rates
➢ Level
➢ Off-gas composition
○ Carbon dioxide
○ Oxygen gas
○ Volatile Organic Compounds
_______________ control is generally not as sophisticated as chemical production process control due to a lack of on-line sensors.
Fermentation process
Why is there a lack of on-line sensors?
Each probe into the fermentor increases the probability of contamination, difficult to sterilize
some probes, probe fouling, probe placement
(gradients within the fermentor).
What does sterilization mean?
The absence of detectable, viable
organisms.
Sterilization is probabilistic: some
portion of the population is more
resistant to sterilizing agents than
other portions.
What does disinfection mean?
Reduction in the amount of detectable, viable organisms.
Methods of Sterilization
➢ Filter
➢ Heating
➢ Radiation
➢ Chemical
Filter is for:
➢ Heat-sensitive liquids and gases
➢ Most common for gases - ΔP
important.
Heating is:
➢ Most common for liquids and
equipment.
➢ Typically steam at 121°C is used.
➢ Time and T are both important.
➢ Risk degrading medium components.
Radiation is commonly used for:
Surfaces
Chemicals are often used for:
Risk toxic residues
Fluids and process equipment (filtration equipment,
reactors, etc) can be sterilized by
➢ heat
➢ microfiltration
➢ radiation
➢ chemical agents
➢ UV light.
Nature of the Problem: Chemostat
A faster growing contaminating
organism can outgrow the desired
organism and cause washout of the
desired organism.
Nature of the Problem: Batch
The product can be biologicaly
contaminated (could be lethal) or the purity profile could be significantly affected.
For continuous sterilization, there is:
High temperature, short exposure time.
For batch sterilization, it cannot:
Cannot count the cooling and heating periods for sterilization.
This is a common method for specific agents.
Thermal sterilization
It is common for the insides of equipment that cannot be heat-sterilized or steam-sterilized.
Ethylene Oxide
Media that cannot be heat-sterilized (heat-labile vitamins,
proteins, sugars) must be filter-sterilized using filters with
narrow pore-size distributions.
Commonly used to sterilize filtration equipment.
Weak (3%) sodium hypochlorite solution
Sanitize means:
To clean with the purpose of
removing possible biological and
nonbiological
health.
Disinfect means:
To greatly reduce the number of living organisms.
Sterilize means:
To eliminate al viable organisms
present (often bioprocesses).
