Page 4 of 6 4. (a) When considering aeration of chemostats, describe the different steps that contribute to the overall

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Page 4 of 6
4. (a) When considering aeration of chemostats, describe the
different steps that
contribute to the overall oxygen transfer process. In each case,
identify the
parameters and / or factors that determine the transfer rate for
that step.

(b) A simple dynamic test was carried out to determine the oxygen
mass transfer
characteristics of a chemostat. Once the chemostat was at steady
state, the
air flow was switched off for a known amount of time, and then
restarted. The
dissolved oxygen concentration after restarting the air flow is
given in
Table Q4-1 below.
Table Q4-1 Dissolved O2 concentration upon restarting air
flow
Time [min] Dissolved O2 Concentration [g m−3]
1
1.50
3
3.62
5
5.47
7
6.34
9
6.77
11
7.33
13
7.66
15
7.70
∞
8.00
Given that: roverall = kLa'(CO2
∗ − CO2 ) − 1
YX O2⁄
rX
where roverall is in g m−3 min−1, determine the value of
kLa'.

(c) When working at laboratory scale, the oxygen transfer within a
Miniature
Stirred Bioreactor is said to be better than that within a standard
Erlenmeyer
flask. Why is this the case?