Biomedical Engineering Reference
In-Depth Information
12.23. For the activated sludge unit shown in
Fig. P12.23
, the specific growth rate constants of
cells are given by
1h
1
,
K
S
¼
m
max
¼
0.01 g/L, YF
X/S
¼
0.50 g-X/g-S,
k
d
¼
0.05/h, and the
feed conditions are
Q
¼
500 L/h,
R
¼
0.4,
y
s
¼
0.1,
X
e
¼
0,
V
¼
1500 L, and
S
0
¼
1g/L.
(a) Calculate the substrate concentration (
S
) in the reactor at steady state.
(b) Calculate the cell concentration(s) in the reactor.
(c) Calculate
X
R
and
S
R
in the recycle stream.
12.24. Wastewater containing terephthalic acid (TA) is treated using two aerobic sludge tanks
in series. The first tank was 12 L in size and the second was 24 L. It is determined to
reduce the TA concentration from 5 g-COD/L to below 0.1 g-COD/L. The Monod
growth parameters are given by
m
max
¼
1.61/day and
K
S
¼
0.25 g/L. The results of the
experiments were reported in the following manner:
DðS
0
SÞ
¼
0:16
X
Tank
1
:
þ 0:62
S
DðS
0
SÞ
¼
0:3
X
S
þ 5:4
Design a CSTR sludge system to handle a wastewater flow of 1000 m
3
/day with
a loading of 5.6 kg-COD/m
3
.
12.25. An industrial waste with an inlet BOD
5
of 0.8 g/L must be treated to reduce the exit
BOD
5
level to no greater than 0.02 g/L. The inlet flow rate is 400 m
3
/h. Kinetic
parameters have been estimated for waste as
Tank
2
:
0.20 h
1
;
K
S
¼
m
max
¼
0.05 g-BOD
5
/L,
0.005 h
1
. A waste treatment unit of 3200 m
3
is
available. Assume a recycle ratio of 0.40 and
X
e
¼
YF
X/S
¼
0.50 g-CS600/g-BOD
5
,
k
d
¼
0. If you operate the concentrator at
2, find
S
and determine if sufficient BOD
5
removal is attained in a well-mixed
activated sludge process to meet specifications. What will be
X
(or CS600) and the
sludge production rate from this process?
12.26. Consider a well-mixed waste treatment system (
Fig. P12.26
). The system is operated
with a reactor of 1000 L and flow rate of 100 L/h. The separator concentrates biomass
by a factor of 2. The recycle ratio is 0.7. The kinetic parameters are
c
R
¼
0.5 h
1
;
m
max
¼
K
S
¼
0.2 g/L, YF
X/S
¼
0.50 g-X/g-S,
k
d
¼
0.05/h. What is the exit substrate
concentration for
S
0
¼
1 g/L?
Q
,
S
0
(1 -
y
s
)
Q
X
,
S
Waste water
Effluent
S
e
,
X
e
(1 +
R
)
Q
V, X, S
Air
RQ
S
R
,
Settling
Tan k
X
R
Activated sludge reactor
(
R + y
s
)
Q
S
R
=
S
X
R
y
s
Q, S
R
,
X
R
Excess sludge
FIGURE P12.23
A schematic of an activated sludge unit.
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