PART 2 - Transport Phenomena in Bioprocess System

Question 1

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.

Answer 1

mass transfer between phases

Question 2

__________________ 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.

Answer 2

Mixing, by aeration and agitation,

Question 3

Oxygen is one of the most important nutrients for aerobic cells that need ____________________ in the broth for maintenance, growth and production of bioproducts.

Answer 3

oxygen dissolved

Question 4

Due to its low solubility in broths, which are usually aqueous solutions (approximately 9 ppm at 25°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).

Answer 4

continuously supplied by a gas phase

Question 5

Frequently, in aerated bioreactors, the critical limiting factor to providing the optimal environment is the:

Answer 5

oxygen transfer rate (OTR)

Question 5

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 __________________________.

Answer 5

𝑘𝐿
Buckingham Pi theory

Question 6

What are the factors influencing Oxygen Transfer Rate

Answer 6

1. Interfacial Area
2. Mass Transfer Coefficient
3. Concentration Gradient

Question 6

Three dimensionless numbers play a significant role in the mass transfer process:

Answer 6

(1) Sherwood Number,
(2) Schmidt Number, and
(3) Grashof Number.

Question 7

The mass-transfer coefficient 𝑘𝐿 is dependent on the: (2)

Answer 7

• vessel’s geometrical configuration and
• the physical properties of the fluids

Question 8

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:

Answer 8

Sherwood Number (Sh)

Question 9

Sherwood Number

In bioprocessing applications especially during aeration, l will be equivalent to the _______________________.

Answer 9

diameter of the air bubbles.

Question 10

A high Sherwood number indicates that ____________ is the dominant mode of mass transfer, while a low Sherwood number indicates that ____________ is the dominant mode.

Answer 10

convection
diffusion

Question 11

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:

Answer 11

The Schmidt number (Sc)

Question 11

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 ___________________________________.

Answer 11

rate of oxygen transfer from the air to a culture of cells in a fermenter.

Question 12

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.

Answer 12

high
low

Question 13

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

Answer 13

Grashof Number

Question 14

In bioprocessing, the ______________ is used to characterize the flow of fluids in bioreactors and other vessels.

Answer 14

Grashof number

Question 15

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.

Answer 15

laminar
turbulent

Turbulent

Question 16

____________________________ 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).

Answer 16

The Oxygen-Absorption Rate (OAR), also known as Respiration Rate or Metabolic Rate,

Question 17

Oxygen-absorption rate per unit volume q/v can be estimated by:

Question 18

When selecting a method for OTR, several factors must be taken into account, mainly:

Answer 18

(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.

Question 19

Whatever the method used for the experimental determination of 𝑘𝐿𝑎 , data generation is basically the _______: the measured variable (usually oxygen concentration) is compared to the value predicted by a mathematical model that includes 𝑘𝐿𝑎 as a parameter.

Answer 19

same

Question 20

All the models are a simplified description of the system and, therefore, 𝑘𝐿𝑎 is not a property of the system, but a parameter of the model adopted. A few of the processes are listed as follows:

Answer 20

1. Dynamic Gassing Out Technique
2. Direct Measurement
3. Dynamic Technique
4. Sodium Sulfite Oxidation Method
5. Hydrogen Peroxide Method

Question 21

________ 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.

Answer 21

Van’t Riet

dynamic gassing out technique

Question 22

Dynamic Gassing Out Technique

This is usually used to measure the concentration.

Answer 22

Polarographic electrode

Question 23

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.

Answer 23

polarographic sensor

proportional

Question 24

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:

Answer 24

gaseous oxygen analyzer

Question 25

__________________________________ used the ______________________ to estimate the 𝑘𝐿𝑎 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.

Answer 25

Taguchi and Humphrey

Dynamic Technique

Question 26

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

Answer 26

sodium sulfite oxidation
Cooper

Question 27

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:

Answer 27

Hickman
hydrogen peroxide