# Bioprocess Engineering Questions and Answers – Comparison of Batch and Continuous Culture in Industrial Processes

This set of Bioprocess Engineering Questions and Answers for Campus interviews focuses on “Comparison of Batch and Continuous Culture in Industrial Processes”.

1. What is the unit of Rbatch, where Rbatch is the output of the culture?
a) g biomass dm-3 h
b) g biomass dm-3h-1
c) g biomass dm h-1
d) g biomass dm-1 h-1

Explanation: From the following equation:
Rbatch = (xmax – xo) / (ti – tii)
Rbatch is the output of the culture, unit is g biomass dm-3h-1.

2. What does tii represents in the equation of the productivity of a batch culture?
a) The organism is growing at μmax
b) Includes acceleration phase
c) The organism is not growing at μmax
d) Includes the stationary phase

Explanation: The tii is the time during which the organism is not growing at μmax and includes the lag phase, the deceleration phase and the periods of batching, sterilizing and harvesting.

3. “The productivity of the continuous culture must be greater than the batch”.
a) True
b) False

Explanation: The productivity in batch culture is at its maximum only towards the end of the process.
For a continuous culture operating at the optimum dilution rate, under steady – state conditions, the productivity will be constant and always maximum. Thus, the productivity of the continuous culture must be greater than the batch.

4. The product formation is transient in continuous culture.
a) True
b) False

Explanation: In batch fermentation, the demands of the culture vary during the fermentation- at the beginning, the oxygen demand is low but towards the end the demand is high, due to the high biomass and the increased viscosity of the broth. Also, the amount of cooling required will increase during the process, as will the degree of pH control. In a continuous process oxygen demand, cooling requirements and pH control should remain constant. Thus, the use of continuous culture should allow for the easier introduction of process automation.

5. What do you mean by the term “Back mutation”?
a) Mutant to wild type
b) Mutant from wild type
c) Mutant from normal type
d) Mutant forward from wild type

Explanation: Mutation can occur in two directions; mutation from wild type to mutant is called a forward mutation, and mutation from mutant to wild type is called a back mutation or reversion. Reverse mutation from the aberrant state of a gene back to its normal, or wild type, state can result in a number of possible molecular changes at the protein level. True reversion is the reversal of the original nucleotide change.
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6. The production of alcohol by continuous culture is feasible, why?
a) Due to protein degeneration
b) By-product of mass generation
c) By-product of energy generation
d) Due to Strain degeneration

Explanation: The problem of strain degeneration has limited application of large scale continuous culture to biomass and, to a lesser extent, potable and industrial alcohol. The production of alcohol by continuous culture is feasible because it is a byproduct of energy generation and thus, is not a drain on the resources of the organism.

7. The adoption of continuous culture is difficult for which type of systems?
a) Microbial
b) Animal
c) Plant
d) Bacterial

Explanation: The adoption of continuous culture for animal cell products is even more complex than for microbial systems. Furthermore, it is difficult to monitor the genetic stability of cells which are immobilized in a large scale reactor system. Thus, large scale animal cell products are still produced by batch methods.

8. The terms “Concentrated effluent” and “Diluted effluent” are used in internal feedback systems.
a) True
b) False

Explanation: In internal feedback systems, effluent is removed from the vessel in two streams:
1) Filtered stream
2) Unfiltered stream
Filtered stream serves the purpose of feedback, whereas, Unfiltered stream is utilised for product harvesting.

In external feedback systems, Effluent from fermenter is fed through a separator.
Two effluent streams are: 1) Concentrated stream
2) Diluted stream
Wherein, Concentrated stream serves as feedback and Diluted is used for product harvesting.

9. What is the source of “Whey”?
a) Rice
b) Wheat
c) Soya
d) Milk

Explanation: Whey is the liquid remaining after milk has been curdled and strained. It is a byproduct of the manufacture of cheese or casein and has several commercial uses. Sweet whey is a byproduct produced during the manufacture of rennet types of hard cheese, like Cheddar or Swiss cheese. Acid whey (also known as sour whey) is a byproduct produced during the making of acid types of dairy products, such as cottage cheese or strained yogurt.

10. Continuous culture provides a higher degree of control than a batch culture.
a) True
b) False

Explanation: Continuous culture provides a higher degree of control than a batch culture. Growth rates can be regulated and maintained for extended periods. By varying the dilution rate, biomass concentration can be controlled. Secondary metabolite production can be sustained simultaneously along with growth. In steady state continuous culture, mixed cultures can be maintained using chemostat cultures – unlike in a batch process where one organism usually outgrows another.

11. Turn – over rate is high in which type of process?
a) Continuous
b) Batch
c) Semi-batch
d) Semi-continuous

Explanation: In continuous culture, The turn- over rate (conversion of the substance to desired product) is high and in batch culture it is less, as, Nutrients in the fermenter in batch culture is utilized in relatively slow rate compared to the continuous culture.

12. Small size fermenter is required in continuous culture.
a) True
b) False

Explanation: Smaller size fermenter is required in continuous culture since the yield is very high.

13. Which of the following is not an advantage of continuous culture over batch culture?
a) More control on the growth and production
b) Turnover rate will be high
c) Washing step is required
d) More closer to the natural environment

Explanation: No such washing step is required since continuous addition of nutrients and microbes are performed.

14. In penicillin production process, batch fermentation is used.
a) True
b) False

Explanation: The antibiotic penicillin can be mass produced via the use of deep-tank batch fermentation. Penicillium mold is grown in the deep-tank batch fermenters following the addition of sugars and other key ingredients. The production process typically lasts 6 – 8 days, with the fermenter drained at the end of the fermentation cycle. Penicillin is separated from the solution and purified via downstream processing to improve its antibiotic potential.

15. In Citric acid production, batch fermentation is used.
a) True
b) False

Explanation: Citric acid (citrate) is widely used as a flavour enhancer, a preservative in manufactured foods and an antioxidant. It is produced as an intermediate of the Krebs cycle under aerobic conditions. Citric acid is mass produced by continuous fermenter systems from cultures of the fungus Aspergillus niger. Carbohydrates are continuously introduced into the fermenter in order to maintain the citric acid production. Iron (Fe2+ ions) is excluded from the mixture in order to slow the further conversion of citric acid within the Krebs cycle. As citric acid accumulates it is extracted as part of the medium that is being continuously withdrawn from the fermenter.

Sanfoundry Global Education & Learning Series – Bioprocess Engineering.

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