L.R. Chevalier, Ph.D., P.E., D-WRE, BCEE, F-ASCE
Curriculum for Sustainability at Southern Illinois University Carbondale
Based on
Chevalier, L.R., 2010, Impact of Wastewater Effluent on Rivers and the Use of
Reclaimed Wastewater Supplies, Center for Sustainable Engineering,
http://www.csengin.org/library.htm
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Investigate the basic operations of a waste water
treatment facility
Find sources of information on the characteristics and
per capita generation of wastewater
Review the basic calculations for the input parameters
of the DO Sag model (Streeter-Phelps)
Evaluate the impact of releasing wastewater effluent
into a river using the DO sag model
Identify the issues involved with the direct and
indirect use of treated wastewater as a municipal
water supply source
Tour a water reclamation (waste water treatment)
facility
 Draw a schematic of the facility and describe the
treatment objective of each unit process. Include an
estimate of the daily flow as well as the facility’s
capacity.
 Use a technical resource to describe five major
characteristics of wastewater. Develop a glossary that
defines the terms reported.
 Identify two by-products of wastewater treatment.
What are the characteristics and uses of these byproducts? Can these by-products be reduced or used
commercially?
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District of Columbia Water and Sewer Authority
Largest advanced wastewater treatment plant in the world
 Capacity of 370 million gallons per day (MGD)
 Peak capacity of 1.076 billion gallons per day and
 Covers 150 acres.
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To collect wastewater
 1,800 miles of sanitary and combined sewers
 22 flow-metering stations,
 9 off-site wastewater pumping stations, and 16 stormwater pumping
stations
 Separate sanitary and storm sewers serve approximately two-thirds of
the District of Columbia
 In older portions of the system, such as the District's downtown area,
combined sanitary and storm sewer systems are prevalent.
3500
3000
2500
Population
P  P0 e
 kt
2000
1500
1000
500
0
0
1
2
3
4
5
Time (days)
Activity: Determine which curve is for k= 0.5 day-1. What is the rate constant for the
other curve? Discuss how you arrived at your answer. The initial population for this
example is 150.
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1st container
 2 L container with a
concentration of
 100 mg/L.
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
Determine the mass
(mg) of the contaminant
in the container by
multiplying the
concentration by the
volume
(100 mg/L)(2L) = 200 mg
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2nd container
 0.5 L
 500 mg/L.

The mass of the contaminant in this
container
 (500 mg/L)(0.5 L) = 250 mg

Mix the two containers.
 Total volume of water = 2 L + 0.5 L = 2.5 L
 Total mass of contaminant = 200 mg + 250 mg =
450 mg

The final concentration uses these
combined calculations, noting that
concentration is mass divided by volume:
 Final concentration = 450mg/2.5 L = 180 mg/L
Q1 C1
Q3 C3
Q2 C2
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One stream is flowing at a rate of 0.5 L/s with a
concentration of 2000 mg/L.
he other stream is flowing at a rate of 1.5 L/s
with a concentration of 200 mg/L.
We will now consider the calculations needed
to determine the concentration in the
combined stream.
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
Mass flux: mass/time [M/T]
For the first stream
 (0.5 L/s)(2000 mg/L) = 1000 mg/s
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For the second stream
 (1.5 L/s)(200 mg/L) = 300 mg/s
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Mass Flux for the combined streams
 (M/T)1 + (M/T)2 = (M/T)3
 1000 mg/s + 300 mg/s = 1300 mg/s
Q1 C1
Q3 C3
Q2 C2

Add the flows
 Q1+Q2 = Q3
 0.5 L/s + 1.5 L/s = 2.0 L/s
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Final concentration
 (1300 mg/s) ÷ (2.0 L/s) = 650 mg/L
Q1 C1
Q3 C3
Q2 C2
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Dissolved oxygen (DO) in river water is the
source of oxygen used by aquatic life.
DO sag model is used to evaluate whether
wastewater effluent released into a stream
will cause the dissolved oxygen in the stream
to go below levels needed for a healthy
stream.
The evaluation starts by considering the river
water at the point of the effluent discharge.
EFFLUENT FROM A WATER RECLAMATION PLANT
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Calculate the initial dissolved oxygen in a
stream at the point of wastewater effluent
release
Using the subscript “s” for the stream, “eff”
for the effluent and “t” for total
 (QsCs + QeffCeff )/Qt = Ct
 where Qt = Qs + Qeff
Activity: Find a reference for the dissolved oxygen
concentrations needed for different species of river fish and
other aquatic life. Discuss whether there is more biodiversity at
higher or lower dissolved oxygen concentrations.
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
D = DOsat – DOt
Da = DOsat – DOinitial
Activity: Find a reference for dissolved oxygen concentrations
for a range of water temperatures above freezing and below
boiling. Discuss the reason why the dissolved oxygen
concentration changes. Would you expect the same trend for
other dissolved gases or dissolved solids? Justify your answer.
𝑘𝑑 𝐿𝑎
𝐷=
𝑒 −𝑘 𝑑 𝑡 − 𝑒 −𝑘 𝑟 𝑡 + 𝐷𝑎 𝑒 −𝑘 𝑟 𝑡
𝑘𝑟 − 𝑘𝑑
10
DO sat
Dissolved Oxygen (mg/L)
9
8
D
7
6
5
4
3
2
1
0
0
1
2
3
4
Time (day)
5
6
7
8
BOD is the Biochemical Oxygen Demand
Reported as a concentratrion
 (QsBODs+QeffBODeff )/Qt = BODt = La
10
DO sat
9
Dissolved Oxygen (mg/L)
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
8
D
7
𝑘𝑑 𝐿𝑎
𝐷=
𝑒 −𝑘 𝑑 𝑡 − 𝑒 −𝑘 𝑟 𝑡 + 𝐷𝑎 𝑒 −𝑘 𝑟 𝑡
𝑘𝑟 − 𝑘𝑑
6
5
4
3
2
1
0
0
1
2
3
4
Time (day)
5
6
7
8
kr ,rate of reaeration or reoxygenation of the stream
kd ,rate of deoxygenation.
Rate constants are dependent on the system under
investigation and on temperature.
10
DO sat
9
Dissolved Oxygen (mg/L)
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
8
D
7
𝑘𝑑 𝐿𝑎
𝐷=
𝑒 −𝑘 𝑑 𝑡 − 𝑒 −𝑘 𝑟 𝑡 + 𝐷𝑎 𝑒 −𝑘 𝑟 𝑡
𝑘𝑟 − 𝑘𝑑
6
5
4
3
2
1
0
0
1
2
3
4
Time (day)
5
6
7
8
1
𝑘𝑟
𝑘𝑟 − 𝑘𝑑
𝑡𝑐 =
𝑙𝑛
1 − 𝐷𝑎
𝑘𝑟 − 𝑘𝑑
𝑘𝑑
𝑘𝑑 𝐿𝑎
10
DO sat
Dissolved Oxygen (mg/L)
9
8
7
6
5
4
Mimimum dissolved oxygen, DOmin
Maximum deficit, Dmax
Critical time, tc
3
2
1
0
0
1
2
3
4
Time (day)
5
6
7
8
Dissolved Oxygen (mg/L)
10
9
8
7
6
5
4
3
2
1
0
DO sat
DOsat -Da
DOmin
0
1
2
3
4
5
6
7
8
Time (day)
Activity: There are a number of input parameters for the DO sag model.
To understand the impact or sensitivity of a given parameter on a system
under study, investigate a range of values of one parameter while keeping
all other values constant. Generate a graph that shows how this value
impacts the minimum DO or tc. Discuss what values of the model can be
controlled by the operation of the treatment plant.
In this exercise, you have investigated the
fundamental aspects of wastewater treatment,
and the impact of effluent release into a river.
 As the demands of water supplies increase, and
in some regions of the world critically scarce, the
direct reuse of waste water is a discussion of
value.
 In fact, wastewater treatment is being
recognized as water reclamation in many
discussions.
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Activity. Read Babcock et al, 2004, Chen and Wang, 2009,
Shoenberger and Sorgini 2009. Discuss their findings and
the how it relates to the issue of water sustainability. Find
additional papers that discuss the issue.

Environmental Protection Agency, Sustainable Infrastructure for
Water and Wastewater,
 http://www.epa.gov/waterinfrastructure/bettermanagement_energy.
html
Babcock, R.W., McNair, D.A., Edling, L.A. Nagato, H., 2004,
Evaluation of a system for residential treatment and reuse of
wastewater, J. Environmental Engineering-ASCE, 130(7):766-773.
 Chen, R., Wang, X.C, 2009, Cost-benefit evaluation of a
decentralized water system for wastewater reuse and
environmental protection, Water Science Technology, 59(8):15151522.
 Shoenberger, P., Sorgini, L., 2009, Solving potable water shortages
with wastewater reclamation, Water and Wastes Digest,
http://www.wwdmag.com/Solving-Potable-Water-Shortage-withWastewater-Reclamation--article7591.
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BOD, biochemical oxygen demand
Da, initial oxygen deficit
DO, dissolved oxygen
DOsat, saturated dissolved oxygen
k, rate constant
L, liter
La, biochemical oxygen demand at point of sewage discharge
M, mass
mg, milligram
Q, flow
s, second
t, time