Environmental Engineering Reference
In-Depth Information
N
KL
36.76 mg / L (0.3 d
1
)
ª
K
t
K t
º
0.3
t
2.76
t
D
n
0
e
e
e
e
n
a
¬
¼
NBOD
KK
2.76 d
1
0.3 d
1
a
n
0.3
t
2.76
t
D
4.483 e
e
NBOD
The DO deficit component resulting from SOD is computed as
2
SD
/
5.24
g
/ (m d) / 1 m
Kt
B
2.76
t
2.76
t
D
(1
e
)
1
e
1.90
1
e
SOD
1
K
2.76 d
a
The DO deficit component resulting from photosynthesis is computed as
PD
/
3/(md)/1m
g
2
D
(1
e
Kt
)
DS
1
e
2.76
t
1.087
1
e
2.76
t
Photo
K
2.76 d
1
a
The DO deficit component resulting from respiration is computed as
2
RD
/
2/(md)/1m
g
Kt
2.76
t
2.76
t
D
(1
e
)
DS
1
e
0.725
1
e
Re
s
1
K
2.76 d
a
The deficit components were computed and summed and then displayed in Fig. 9.11. The DO concentration
then was computed corresponding to the total DO deficit in Fig. 9.11 and the saturation DO concentration
at 20
ć
of 9.022 mg/L and the result is shown in Fig. 9.12. From Fig. 9.12 it is clear that the required DO
concentration of 5 mg/L cannot be met. Figure 9.12 also shows the computed DO concentration for the
case that does not consider the net photosynthetic DO production as part of the DO balance for waste-load
allocation as suggested by Fair et al. (1971, p. 649). For the case including photosynthesis the minimum
DO concentration is 3.94 mg/L, whereas for the case not including photosynthesis the minimum DO
concentration is 3.62 mg/L.
Fig. 9.11
Components of the dissolved oxygen deficit for the total dissolved oxygen balance example
Thus, it was decided to reduce the upstream NBOD concentration,
L
0
N
, until the 5 mg/L DO concentration
could be met. It was found that
L
0
N
must equal 20 mg/L in order to achieve the 5 mg/L DO requirement
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