Engineering Questions with Answers - Multiple Choice Questions
MCQs on Antibiotics – Fermentors or Bioreactors
Six types of bioreactors are, Continuous Stirred Tank Bioreactors, Bubble Column Bioreactors, Airlift Bioreactors, Fluidized Bed Bioreactors, Packed Bed Bioreactors and ____________
a) Hollow fibre reactor
b) General purpose reactor
c) Assembly reactor
d) Photo bioreactor
Explanation: Bioreactors are the vessels used in bioprocess technology for production of bio-products. There are mainly six types of bioreactors. The six types are: Continuous Stirred Tank Bioreactors, Bubble Column Bioreactors, Airlift Bioreactors, Fluidized Bed Bioreactors, Packed Bed Bioreactors and Photo-Bioreactors.
How much fraction is the diameter of impeller than the diameter of the vessel in a stirred tank bioreactor?
Explanation: Optimisation is required in every step of bio-production. Similarly optimisation is required in vessel and its accessories sizes. The diameter of the impeller is generally 1/3 rd of the vessel diameter.
Sparger in stirred tank bioreactor helps in ________________
a) Proper gas distribution
b) Proper mixing of medium
c) Measuring temperature of medium
d) Better sterility
Explanation: A device known as the sparger is used to sparge in air inside a stirred tank reactor or a short stirred tank reactor. There are different kinds of sparger available. It can be ring with many holes, a tube with single orifice. Spargers and impellers enables better gas distribution throughout the vessel.
. Impellers in stirred tank bioreactors helps in ________________
a) Breaking down large bubbles into smaller ones
b) Mixing of medium contents
d) Homogenisation, mixing, breaking bubbles
Explanation: Bioreactors are cylindrical vessels with a motor driven shaft that supports one or more impellers or agitators. The bubbles which are generated by the sparger are bigger and has to be broken down to smaller bubbles by the use of impellers. This leads to a uniform and homogeneous environment throughout the bioreactor.
What is the aspect ratio of bubble column bioreactors?
Explanation: Air or gas sparged inside a bioreactor such an ad bubble column reactor through the use of perforated pipes or plates are called spargers. The flow rate of the air/gas influences the some factors —O2 transfer, mixing. The bubble column bioreactors may be fitted with perforated plates to improve its performance. The vessel used for bubble column bioreactors is usually cylindrical and has an aspect ratio of 4-6 (i.e., height to diameter ratio).
Which of the following is a characteristic for airlift bioreactors?
a) More efficient than bubble column reactors
b) Less efficient than bubble column reactors
c) Equally efficient as bubble column reactors
d) Not at all efficient
Explanation: Airlift bioreactors are more efficient than bubble columns. This is particularly true for denser suspension of microorganisms. The mixing of the contents is better than the bubble column than any other bioreactor.
There are three types of airlift bioreactors.
Explanation: Internal loop bioreactor creates an internal liquid circulation channel. It has a single container and has a central draft tube that creates interior liquid circulation channel. External loop airlift bioreactor has an external loop where the liquid circulate through separate independent channels.
. Two-stage airlift bioreactors are used for the temperature dependent formation of products.
Explanation: In two-stage airlift bioreactors growing cells from one bioreactor (maintained at temperature 30℃) are pumped into another bioreactor (at temperature 42°C). Since the temperature cannot be abruptly very quickly increased from 30℃ to 42℃ there is a necessity for the two-stages.
What is the most important thing one should remember while working with fluidized bed reactor?
a) Gas dispersion
b) Medium pH
d) Weight of solid particles
Explanation: For an efficient operation of fluidized beds, gas is sparged to create a suitable and optimised gas-liquid-solid fluid bed. It is necessary to keep in mind that the suspended solid particles are not too light or too dense (too light ones may float whereas to dense ones may settle at the bottom), and they should stay in a good suspended state.
. Why packed bed bioreactors are good?
a) Does not allow accumulation of products
b) Allow ease in pH controlling
c) Allow proper gas distribution
d) Less concentration of enzymes or cells required because of immobilisation
Explanation: It’s a difficult task to control the pH of packed bed bioreactors by the adding acid or alkali because of poor mixing. These bioreactors are preferred for bioprocessing technology involving product-inhibited reactions since the packed bed bioreactors does not allow accumulation of the products.
Which microbes are used in photobioreactors?
Explanation: Photo-bioreactors are operated in a continuous mode at a temperature range of 25-40℃. Microalgae and cyanobacteria are used for this bioprocess most of the times. The organisms will be growing during day light while the products are produced during night
What is the value of μmf / μf for fluidized bed fermenter?
a) 0.02 – 0.5
Explanation: The substrate tends to make lumps which adhere to the inner wall of the fermenter. This phenomenon causes an increase in the value of μmf. Thus, μmf / μf is actually estimated to be 0.02-0.5.
. What may cause foaming in a bioreactor?
a) A decrease in agitation
b) The formation of large stable bubbles
c) The formation of small unstable bubbles
d) The breaking of large unstable bubbles
Explanation: Large weak foam bubbles are easily broken by mechanical forces (i.e., agitation) and may form new tiny bubbles which are much more stable. Tiny bubbles has higher surface area to volume ratio which gives more mass transfer.
How does impeller speed affect bubble size?
a) As impeller speed increases, the bubble size increases
b) As impeller speed increases, bubble size stays consistent
c) As impeller speed increases, bubble size becomes inconsistent
d) As impeller speed increases, the bubble size decreases
Explanation: As impeller speed increases shear and turbulence increases, this decreases the bubble size. Large bubbles impedes in proper mixing of media. But smaller bubbles will give better mass transfer.
In a chemostat operating under steady state, a bacterial culture can be grown at dilution rate higher than the maximum growth rate by _________
a) Partial cell recycling
b) Using sub optimal temperature
c) pH cycling
d) Substrate feed rate cycling
Explanation: D = F/V
Dilution rate is the rate with which substrate is added to a continuous system and products are removed from the system. When dilution rate is higher than maximum growth rate wash out condition occurs in which the cell concentrations progressively decreases. Only way of culturing biomass in the case of wash out is by partially recycling the cells, which were removed from the system.