PART 2 - Transport Phenomena in Bioprocess System Flashcards
Determination of Oxygen Transfer rates
Several phases are involved in the bioprocesses: the substrates, nutrients, and products must be transferred from one phase to the other therefore, _____________________ may often become the limiting step of the overall process rate and be a relevant factor in scale-up.
mass transfer between phases
__________________ is used to improve mass transfer and also to ensure homogeneous distribution of the nutrients in the liquid phase.
This is true in both aerobic (Oxygen) and anaerobic (methane/CO2) systems.
Mixing, by aeration and agitation,
Oxygen is one of the most important nutrients for aerobic cells that need ____________________ in the broth for maintenance, growth and production of bioproducts.
oxygen dissolved
Due to its low solubility in broths, which are usually aqueous solutions (approximately 9 ppm at 25Β°C and 1 atm in pure water), oxygen must be ______________________ (air or oxygen) with the purpose of achieving acceptable productivities, independent of the physical operational modes (batch, semibatch, and continuous cultures).
continuously supplied by a gas phase
Frequently, in aerated bioreactors, the critical limiting factor to providing the optimal environment is the:
oxygen transfer rate (OTR)
Generally speaking, the experimental data can be accurately fitted to obtain the relations corresponding to ____.
Since the dimensionless groups are dimensionally consistent, the correlations can be computed and stated using a variety of techniques, including the __________________________.
ππΏ
Buckingham Pi theory
What are the factors influencing Oxygen Transfer Rate
- Interfacial Area
- Mass Transfer Coefficient
- Concentration Gradient
Three dimensionless numbers play a significant role in the mass transfer process:
(1) Sherwood Number,
(2) Schmidt Number, and
(3) Grashof Number.
The mass-transfer coefficient ππΏ is dependent on the: (2)
- vesselβs geometrical configuration and
- the physical properties of the fluids
This is a dimensionless number that represents the ratio of the convective mass transfer rate to the diffusive mass transfer rate. It is defined as:
Sherwood Number (Sh)
Sherwood Number
In bioprocessing applications especially during aeration, l will be equivalent to the _______________________.
diameter of the air bubbles.
A high Sherwood number indicates that ____________ is the dominant mode of mass transfer, while a low Sherwood number indicates that ____________ is the dominant mode.
convection
diffusion
This describes the relationship between mass diffusivity over momentum diffusivity or vice versa.
Hence, this dimensionless number is most applicable to cases that simultaneously involve mass and momentum diffusion and can be expressed as:
The Schmidt number (Sc)
In bioprocessing applications, the Schmidt number is often used to design and optimize processes that involve mass transfer, such as aeration, fermentation, and filtration.
For example, this number is used to determine the ___________________________________.
rate of oxygen transfer from the air to a culture of cells in a fermenter.
A _______Schmidt number indicates that momentum transfer is more important than mass transfer, while a ________ Schmidt number indicates that mass transfer is more important than momentum transfer.
In general, the Schmidt number is a useful tool for understanding and predicting the behavior of mass transfer processes in bioprocessing.
high
low
This number is mostly associated with the cases involving free (natural) convection.
It gives the dominance of the buoyancy force over the viscous forces and can be mathematically given as
Grashof Number
In bioprocessing, the ______________ is used to characterize the flow of fluids in bioreactors and other vessels.
Grashof number
A low Grashof number indicates that the flow is _________, while a high Grashof number indicates that the flow is __________.
_______________ flow is generally more effective at mixing fluids, which can be important for bioprocesses that require good mixing, such as fermentation.
laminar
turbulent
Turbulent
____________________________ is a measure of how quickly an organism consumes oxygen.
It is typically measured in units of milliliters of oxygen per minute per gram of body weight (ml O2/min/g BW).
The Oxygen-Absorption Rate (OAR), also known as Respiration Rate or Metabolic Rate,
Oxygen-absorption rate per unit volume q/v can be estimated by:
When selecting a method for OTR, several factors must be taken into account, mainly:
(i) The bioreactor type and its mechanical design,
(ii) The aeration and mixing of the system
(iii) The flow characteristics of gas and liquid phases,
(iv) The composition of the fermentation medium,
(v) The type of microorganism and its morphology, due to the possible effect on measurements.
Whatever the method used for the experimental determination of ππΏπ , data generation is basically the _______: the measured variable (usually oxygen concentration) is compared to the value predicted by a mathematical model that includes ππΏπ as a parameter.
same
All the models are a simplified description of the system and, therefore, ππΏπ is not a property of the system, but a parameter of the model adopted. A few of the processes are listed as follows:
- Dynamic Gassing Out Technique
- Direct Measurement
- Dynamic Technique
- Sodium Sulfite Oxidation Method
- Hydrogen Peroxide Method
________ came up with the ___________________________________ in 1979.
This technique monitors the change in the oxygen concentration, while an oxygen-rich liquid is deoxygenated by passing nitrogen through it.
Vanβt Riet
dynamic gassing out technique
Dynamic Gassing Out Technique
This is usually used to measure the concentration.
Polarographic electrode
A ______________________ is a type of electrochemical sensor that is used to measure the concentration of dissolved oxygen (DO) in a liquid.
It works by inducing an electrochemical reaction with the dissolved oxygen, and the resulting electrical signal is ________________ to the DO concentration.
polarographic sensor
proportional
In this technique, a _______________________________ is used to estimate the oxygen concentration in the gas stream entering and leaving the fermenter.
If the inlet flow rate of oxygen is Qin and the outlet flow rate of oxygen is Qout, then the residual rate of uptake of oxygen (q) can be estimated as follows:
gaseous oxygen analyzer
__________________________________ used the ______________________ to estimate the ππΏπ value for the oxygen transfer during an actual fermentation process with real culture medium and microorganisms.
The present method is implemented in a microorganism-rich aerated batch fermenter over which the oxygen material balance is applied.
Taguchi and Humphrey
Dynamic Technique
The _____________________________ method (________ et al., 1944) is based on the oxidation of sodium sulfite to sodium sulfate in the presence of catalyst (Cu++ or Co++) as
sodium sulfite oxidation
Cooper
This method due to _________ (1988) is, like the sulfite method, a chemical method. However, it has several advantages compared with the sulfite method. In the ________________ method, the transfer of oxygen from the liquid to the gas phase is measured.
Oxygen is generated by the enzyme-catalyzed decomposition of hydrogen peroxide:
Hickman
hydrogen peroxide
