CN5172 Biochemical Engineering
Quiz 2 (27 October 2021)

Q1. Blood taken from patients infected with Covid-19 must be decontaminated
before disposal. Every 3.15L of blood must be decontaminated in 15s at 121mC.
At this temperature, deactivation of the Covid-19 viruses follows first order
kinetics with a deactivation constant, k = 0.098 s-1. Decontamination efficiency
is such that only 1 virus will remain viable if decontamination is carried out
continuously for a day. The blood contains approximately 5.5 x 109 viral
particles/cm3.
Your initial calculations indicate that a plug flow sterilizer (5cm diameter, 46m
length) will accomplish the job. A colleague, however, suggests the use of an
existing SIP (steam-in-place) continuously stirred tank bioreactor of the same
volume. Quantitatively convince your colleague that his suggestion does not
make sense.
(20 marks)


Q2. Examococcus kaicheerios is cultivated in a 20m3 bioreactor equipped with two
sets of standard flat-blade turbine impeller at 30mC. The bioreactor is aerated
and agitated at 0.25VVM and 60rpm, respectively using air with CL* = 7.8
gO2/m3. At 30mC, the specific oxygen consumption rate of E. kaicheerios is
3.384 x 10-4 gO2/gdcw-s.

For the flat-blade turbine impeller used:

where Pg/V = gassed power per unit volume (W/m3)
V = volume of liquid (m3)
Vs = nominal (superficial) air velocity based on empty cross-
sectional area of vessel (m/s)
= oxygen transfer coefficient (s-1)

The fermentation is conducted in the minimal medium:
Glucose (50g/L), NH4NO3 (20g/L), KH2PO4 (0.5g/L), MgSO4 (0.1g/L).
E. kaicheerios has a partial mass composition (%) of: C, 50; N, 10; P, 4; S, 1.
The cell yield coefficient on nitrogen is 0.4gdcw/g, and that on glucose is
0.3gdcw/g.
Determine the steady state cell concentration in gdcw/L.
State all necessary assumptions.
(30 marks)



066.07.03 )(102 s
g
L VV
P
xak -=
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