Geoscience Reference
In-Depth Information
■
EXAMPLE 19.7
Problem:
Calculate the oxygen deficit in a stream after pollution. Use the following equation and
parameters for a stream to calculate the oxygen deficit (
D
) in the stream after pollution.
Parameters:
Pollution enters stream at point
X
.
t
= 2.13.
L
a
= 22 mg/L (pollution in stream at point
X
).
D
a
= 2 mg/L.
k
1
= 0.280/day (base e).
k
2
= 0.550/day (base e).
Note:
To convert log base e to base 10, divide by 2.31.
Solution:
kL
kk
e
×
−
(
)
+
1
2
a
−
kt
−
kt
−
kt
D
=
−
e
De
1
2
2
a
1
0 280
.
×
22
(
)
+
−
0 280
.
×
213
.
−
0 550
.
×
2
13
−
0 550
.
×
213
.
D
=
e
−
e
2
e
0 550
.
−
0 280
.
616
0 270
.
.
(
)
+×
(
)
−
0 258
.
−
0 510
.
−
0 510
.
=
×
10
−
10
210
=
22 805520
.
×
( .
−
0 3090
.
)
+
(
203090
×
.
)
=
22 81
.
×
0 243
.
+
0 6180
.
= 6.16 mg/L
■
EXAMPLE 19.8
Problem:
Calculate deoxygenation constant
k
1
for a domestic sewage with BOD
5
of 135 mg/L and
BOD
21
of 400 mg/L.
Solution:
BOD
135
400
1
−
log
1
−
−
log
1
−
=
−
log.
066
5
0 1804
5
.
400
k
=
=
=
=
0.361/day
1
t
5
Biochemical oxygen demand occurs in two different phases (see Figure 19.2). The first phase is
carbonaceous BOD
(CBOD), when mainly the organic or carbonaceous material is broken down.
The second phase is the
nitrogenous BOD
phase. Here, nitrogen compounds are decomposed,
which requires oxygen. This is of particular concern when conducting tests for discharge permit
compliance, especially if nitrification is known to occur.
The Streeter-Phelps equation provides a rough estimate of the ecological conditions in a stream.
Small variations in the stream may cause the DO to be higher or lower than the equation indicates;
however, this equation may be used in several different ways. As mentioned, the quantity of the
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