Environmental Engineering Reference
In-Depth Information
w) Define TEC, MEC, and PEC.
x) Which pollutants are highly likely to adsorb to sediments?
y) List the advantages and disadvantages of the methods to remediate contaminated sediments.
2. a) For a river assume dissolved oxygen is lost to CBOD decay and sediment oxygen demand and it
is replaced by atmospheric reaeration. Derive the equation for the stream critical time.
b) Determine the critical deficit for K a = 0.8 day -1 , K d = 0.2 day -1 , S B = 2 mg/day/L, D 0 = 1.5 mg/L,
and L 0 = 10 mg/L.
3. The Red River of the North in the vicinity of Fargo, North Dakota, receives wastewater flow from
the Fargo Wastewater Treatment Plant (WWTP) and the Moorhead, Minnesota, WWTP. The population of
Fargo was 73,000 in 1990 and at that time the WWTP was operating at full capacity of 0.42 m 3 /s. By 2000
the population of Fargo had grown to 90,600, and the need for capacity expansion at the WWTP was
obvious. Develop a Streeter-Phelps model of the Red River of the North to examine capacity expansion
issues for the Fargo WWTP.
In the modeling the Red River of the North will be divided into 3 reaches as follows (note: data from
Wesolowski (1994)).
Length
(km)
Velocity
(m/s)
Depth
(m)
Reach
Slope
Comments
1.136×10 -4
1
19.0
0.131
0.73
Moorhead WWTP to Fargo WWTP
1.345×10 -4
2
11.9
0.165
0.73
Fargo WWTP to Sheyenne River
0.785×10 -4
3
18.7
0.131
0.98
Sheyenne River to end of study area
For the trial condition the following flows and characteristics should be considered.
Discharge (m 3 /s)
Flow Source
BOD (mg/L)
DO (mg/L)
Upstream inflow
1.42
1.5
8.0
Moorhead WWTP
0.14
15.0
6.5
Fargo WWTP
1.07
25.0
5.0
Sheyenne River
0.45
5.7
8.5
The flow for the Fargo WWTP represents a capacity expansion to 1.14 m 3 /s more than doubling the
current capacity. The BOD concentrations for the WWTPs represent the current permit limits for a 7-day
average. The upstream inflow on the Red River is substantially higher than the 7-day, 10-year low flow
of 0.31 m 3 /s and the flow of the Sheyenne River is double the 7-day, 10-year low flow of 0.23 m 3 /s.
Step 1
Determine and plot the dissolved oxygen (DO) and BOD trajectories throughout the study reach. Can the
North Dakota state DO standard of 5 mg/L be maintained with the new higher flow from the Fargo WWTP?
Temperature = 24.2 ć , K d = 0.2 day -1 at 20 ć , and K a is computed using the Tsivoglu and Neal (1976)
equation.
Step 2
If the DO concentration does not meet the state standard, determine the allowable BOD discharge from
the Fargo WWTP for the trial conditions.
Step 3
Determine and plot the DO trajectory throughout the study reach if the Langbein and Durum (1967)
equation is used to determine K a .
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