Biomedical Engineering Reference
In-Depth Information
17.17.
Nitrate in groundwater is becomingmore of a problem. In addition tomeasures aiming
at applying lower loads of fertilizers, the need for effective treatment procedures is
increasing. One of the alternatives investigated is removal of nitrate by conversion to
gaseous N
2
using denitrifying bacteria immobilized in gel beads. Calculate the content
of an ideally mixed bioreactor treating 150 m
3
/h of groundwater. The concentration of
nitrate in the groundwater is 45 g/m
3
and the treated water contains 0.8 g/m
3
nitrate.
The load of gel beads in the reactor is 0.25 m
3
-gel/m
3
-reactionmixture. The diameter of
the gel beads is 2 mm, the diffusivity of nitrate inside the gel is 10
10
m
2
/s. Mass
transfer coefficient of nitrate in the reactor is 10
5
m/s. The kinetic constant are given
by
r
max
¼
0.5 g/(s m
3
-gel) and
K
m
¼
1g
$
m
3
.
17.18.
Invertase catalyzes the hydrolysis of sucrose to glucose and fructose (invert sugars).
The reaction follows Michaelis
e
Menten kinetics with
r
max
¼
10
4
mol
$
L
1
$
s
1
2
and
K
m
¼
0.001 mol/L. It is decided to carry out the reaction in a PFR packed with
particles immobilized invertase at 50% in volume fraction. The catalyst particles are
3.5 mm in diameter and the effective diffusivity of sucrose inside the particle is
0.2
10
9
m
2
/s. The available sucrose stream has a concentration of 350 g/L and we
need to produce 35 Mg invert sugar per day with 99% conversion. Compute the
amount of catalyst or volume of reactor required. Neglect the external mass transfer
effects.
17.19.
In
Table P17.19
, the oxygen-18 data were obtained from soil samples taken at different
depths in Ontario, Canada. Assuming that all the
18
O was laid down during the last
glacial age and that the transport of
18
O to the surface takes place by molecular
diffusion, estimate the number of years since the last glacial age from the data.
Independent measurements give by diffusivity of
18
O in soil as 2.64
10
10
m
2
/s.
TABLE P17.19
Depth from surface, m
0
3
6
9
12
18
21
24
18
O concentration ratio
0
0.35
0.65
0.83
0.94
1.00
1.00
1.00
17.20.
If disposal of industrial liquid wastes by incineration is to be a feasible process, it is
important that the toxic chemicals be completely decomposed into harmless
substances.
Table P17.20
shows the data for the burning of liquid droplets. What can
you learn from these data?
TABLE P17.20
Time, s
20
40
50
70
90
110
Droplet size,
m
m
9.7
8.8
8.4
7.1
5.6
4.0
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