PART 5 Flashcards
Oxygen Mass Transfer
- 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 (Cl)
- Transfer across stagnant liquid layer to cell
- Transfer rate at steady state is determined by the slowest rate (just like on a highway).
- As we have seen before, for an oxygen-transfer rate limited process or at steady state:
Oxygen mass transfer
____________ is not the rate at which you provide air to the reactor. You will actually provide air more oxygen to the reactor than is transferred to the cells.
OTR
oxygen transfer rate
OUR = OTR
Correlations can be used to predict the ____________.
volumetric transfer coefficient kla
The previous correlation offer design estimates.
____________, ____________, and ____________ can affect kla and oxygen solubility.
Medium components, temperature, and pressure
Simple experiments can be done to measure kla.
____________, ____________, ____________ and ____________ to measure kla.
Unsteady state, steady state, dynamic and sulfite methods
Fill the reactor with medium only - no cells. Measure the DO concentration in the medium. Remove oxygen from the medium by sparging with N₂. Introduce air, and record the increase in DO
Unsteady Method
Requires an oxygen gas analyzer for the effluent air. Perform an O₂ mass balance to obtain OUR.
Difficulty in both methods - C* is a function of pressure (height of liquid and high pressure aeration gas).
Steady-State Method
Utilizes a fermentor with actively growing cells.
Requires only a DO meter.
Dynamic Method
The air to the ____________ is shut off, and the ____________ due to ____________ . The air is then turned on, and the the ____________.
fermentor
DO decreases
consumption by the microorganisms
DO increases
Empirical
Make the controlling regime the same on the small scale as on the large scale.
Scale-up
SCALE-UP CRITERION
Power input - OTR
Liquid circulation rate - mixing time
Tip speed - shear
Reynolds number - geometry
- Cannot scale by all of these. If we scale by one of these, the other parameters are not constant between the small and large scale.
- Each can have an effect on culture behavior.
SCALE-UP CRITERION
________ by requiring characteristic times to be constant between the small and large scale.
Scale-up
Common On-line Instrumentation
- pH
- Temperature
- Dissolved oxygen
- Foam
- Flow rates
- Level
- Off-gas composition (CO2, O2, VOCs)
_________________ is generally not as sophisticated as chemical production process control due to a lack of on-line sensors.
Fermentation process control
Each probe into the ______________ increases the _____________ , difficult to sterilize some probes, probe fouling, probe placement (gradients within the fermentor).
fermentor
probability of contamination
Form a group of three and describe 5 control loops based on the most common instrumentation.
Typical Fermentor Control Schemes
Identify the measured variable, and the controlled variable - specifying what is the final control element (ie. valve, pump, etc.)
Typical Fermentor Control Schemes
______________= the absence of detectable, viable organisms.
Sterilization
______________= reduction in the amount to detectable, viable organisms.
Disinfection
______________: some portion of the the population is more resistant to sterilizing agents than other portions.
Sterilization is probabilistic
Methods of sterilization
- Filter P important.
- Heat
- Radiation
- Chemical
______________: Heat sensitive liquids and gases. Most common for gases - P important.
Filter
