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  • Question
  • In a glucose-yeast extract medium, Lactococcus lactis has a maximum specific growth rate (um) of 1.23 h-1. What would be the specific growth rate of this organism at steady state in a 4 litre reactor being fed at 2 litres per hour?


  • Options
  • A. 0.5 h-1
  • B. 1.2 h-1
  • C. 2.4 h-1
  • D. 4 h-1

  • Correct Answer
  • 0.5 h-1 


  • Fermentation Reactors problems


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    • 1. Two continuous bioreactors containing the same organisms, fed with the same feed at the same dilution rate were compared. Reactor 1 started with an initial concentration of glucose of 10 g.l-1, while reactor 2 contained 0.1 g.l-1 of glucose at the start of the process then at steady state

    • Options
    • A. the concentration of glucose in reactor 1 would be greater than that in reactor 2
    • B. the concentration of glucose in reactor 1 would be equal to reactor 2
    • C. the concentration of glucose in reactor 1 would always be zero.
    • D. the concentration of glucose in reactor 1 would be less than that in reactor 2
    • Discuss
    • 2. Which of the following is not correct with regards to continuous cultures?

    • Options
    • A. The major industrial scale application of continuous cultures is in waste water treatment
    • B. Mutation and contamination present a major risk to the operation of continuous cultures for the production of metabolites
    • C. The continuous cultures is very useful for the production of pharmaceuticals
    • D. Continuous cultures have an advantage that they do not need to shut down as regularly as batch culture reactor
    • Discuss
    • 3. In fed batch bioreactor modelling, the rate of change in the bioreactor volume is assumed to be equal to

    • Options
    • A. flow rate
    • B. initial volume
    • C. volume of solids in the reactor
    • D. none of these
    • Discuss
    • 4. In a plug flow reactor, the highest concentration of substrates is exposed to the cells that

    • Options
    • A. are near the effluent or exit of the reactor
    • B. are in the mid way along the reactor
    • C. are located near entrance of feed
    • D. are near the wall of the reactor
    • Discuss
    • 5. Pseudo-steady state in a continuous reactor refers to a reactor in which

    • Options
    • A. Pseudomonads are being cultured
    • B. concentration oscillate around a mean value
    • C. concentration increase with time
    • D. concentration decrease with time
    • Discuss
    • 6. The toxicity of organic acids to cells

    • Options
    • A. enhances as the pH falls
    • B. reduces as the pH falls
    • C. is not affected by pH
    • D. is highest at pH 7.0
    • Discuss
    • 7. A microorganism which is subjected to the Crabtree effect is most likely to

    • Options
    • A. ferment in the presence of low concentrations of sugar and dissolved oxygen
    • B. respire in the presence of low sugar and high dissolved oxygen concentrations
    • C. ferment in the presence of high concentrations of sugar and dissolved oxygen
    • D. respire in the presence of high sugar and low dissolved oxygen concentrations
    • Discuss
    • 8. Production of organic acids in batch culture is generally growth associated phase followed by non-growth associated production. The probable reason for this is that

    • Options
    • A. organic acids uncouple catabolism from anabolism
    • B. biomass yields increase as the fermentation proceeds
    • C. organic acids are secondary metabolites
    • D. high concentrations of organic acid promote the growth of the microbial population
    • Discuss
    • 9. In an activated sludge process, the biomass is recycled to

    • Options
    • A. increase the efficiency of the process
    • B. reduce sludge volumes
    • C. increase the concentration of cells
    • D. all of the above
    • Discuss
    • 10. Continuous culture has an advantage over to a batch cultures as

    • Options
    • A. continuous reactors do not need to be shut down and cleaned as regularly as a batch reactor
    • B. most downstream and upstream processes are continuous in nature and thus the operation of continuous bioreactor can be better integrated into the overall manufacturing process
    • C. cells can be maintained at a constant physiological state simply by setting the dilution rate
    • D. all of the above
    • Discuss


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