Agitation and Aeration MCQs

Question 1

The dynamic technique is based on the

Accepted Answer

oxygen material balance in an aerated batch fermenter during the growth of microorganisms

Answer

change of the oxygen concentration

Answer

oxidation of the sodium sulfite to sodium sulfate

Answer

oxygen material balance in a fermenter

Question 2

The addition of antifoams to an aerated bioreactor will decrease oxygen transfer rates because antifoams

Accepted Answer

All of the above answers

Answer

increase the tendency of bubbles to coalesce

Answer

tend to accumulate in the gas liquid interface

Answer

reduce the surface tension of the liquid

Question 3

During fermentation, the saturation concentration of oxygen was reduced from 7 ppm. to 1 ppm. Which one of the following conclusions can be drawn?

Accepted Answer

No conclusion can be drawn

Answer

Microbial growth is oxygen limited since the oxygen concentration is lesser than the saturation concentration

Answer

Microbial growth is not oxygen limited since the oxygen concentration is lesser than the saturation concentration

Answer

Experimental error leads to the reduction

Question 4

If the stirrer speed is too slow, bubbles will accumulate and coalescese under the impeller. This phenomenon is known as a

Accepted Answer

flooded impeller

Answer

coalesced impeller

Answer

river impeller

Answer

dry impeller

Question 5

The maximum solubility of the alkane in the medium is 5 ppm. If the actual dissolved concentration of the alkane in the medium is 1 ppm. what conclusion may be drawn?

Accepted Answer

No conclusion on the growth rate can be withdrawn

Answer

The growth rate is limited by the rate of mass transfer of the alkane into the fermentation medium

Answer

The growth rate is limited by the intrinsic kinetic properties of the cells and not by mass transfer

Answer

The growth rate is neither mass transfer nor kinetically limited

Question 6

Reynolds (Rei) number for the impeller is given by (where Di, stirrer diameter; N, stirrer speed, ρ, density of fluid and μ, viscosity of fluid)

Accepted Answer

Di2Nρ/μ

Answer

DiVρ/μ

Answer

Di2Vρ/μ

Answer

DiNρ /μ

Question 7

The advantage of axial flow impellers over radial flow impellers is that axial flow impellers

Accepted Answer

provide better lift of solids

Answer

provide high shear conditions

Answer

provide low shear conditions

Answer

are cheaper to build

Question 8

Larger propellers turn at the speed of

Accepted Answer

400 to 800 rpm

Answer

20 to 150 rpm

Answer

150 to 300 rpm

Answer

1150 rpm

Question 9

A microbial population in a suspension culture will only be limited by oxygen availability if the dissolved oxygen

Accepted Answer

concentration is less than the critical concentration

Answer

concentration is greater than the critical concentration

Answer

levels are greater than the saturation concentration of oxygen

Answer

levels are equal to saturation oxygen level