Environmental Engineering Reference
In-Depth Information
detect an ammonia toxicity problem the un-ionized ammonia amount must be computed as
NH N
0.94412(1
4
U
(9.30)
x
10 )
0.0559
Where
U
= the concentration of un-ionized ammonia in mg/L, and NH
4
N = the concentration of total
ammonia nitrogen in mg/L, and
2729.92
x
0.09018
pH
T
273.16
where pH = the pH of the water in standard units.
In the late 1990s, the USEPA (1998, 1999a) developed new criteria for ammonia toxicity on the basis
of detailed toxicity studies of many key fish species. Different criteria were developed for acute toxicity
and chronic toxicity, the presence or absence of salomonid fish, and the presence or absence of juvenile
fish. The new criteria are for total ammonia with the conversion from un-ionized ammonia to total ammonia
built into the criteria. These new USEPA standards have been incorporated into many State standards, such
as those for Illinois.
Acute toxicity
—The one hour average concentration of total ammonia nitrogen (NH
4
+
+ NH
3
) does
not exceed, more than once in three years on average, the Criterion Maximum Concentration (CMC) that
is calculated as follows:
Salmonid fish are present:
0.275
39.0
CMC
(9.31)
110
7.204
pH
110
pH
7.204
Salmonid fish are absent:
0.411
58.4
CMC
(9.32)
110
7.204
pH
110
pH
7.204
Chronic toxicity
—The thirty-day average concentration of total ammonia nitrogen (in mg/L) does not
exceed, more than once in three years on average, the Criterion Continuous Concentration (CCC) calculated
as follows:
Early life stages are present:
0.0577
2.487
ª
º
0.028( 25
T
)
CCC
u
min(2.85,1.45
u
10
)
(9.33)
«
»
7.688
pH
pH
7.688
110
110
¬
¼
Early life stages are absent
ª
0.0577
2.487
º
CCC
u
1.45
u
10
0.028(25
T
)
(9.34)
«
»
7.688
pH
pH
7.688
110
110
¬
¼
The 1999 update also included consideration of the 4-day average where the highest 4-day average
within the 30-day period should not exceed 2.5 CCC.
Figure 9.19 shows a comparison of the new CMC standard and the old State of Illinois standard of
0.04 mg/L of un-ionized ammonia converted to the total ammonia concentration via Eq. (9.30) for three
different pH levels. Except for temperatures less than 3
ć
for a pH of 7, the new CMC standard is
substantially less restrictive than the old State of Illinois standard. This example shows that through
scientific research industry and municipalities can face reduced restrictions while still meeting the goals
of the CWA.
The lower 51-km long reach of Salt Creek in the western suburbs of Chicago, U.S. presents an
interesting example of the effects of ammonia toxicity on the aquatic community. During dry weather
this reach of Salt Creek is a classic effluent dominated stream as it receives the effluent of 11 wastewater
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