l.r. chevalier, ph.d., p.e., d-wre, bcee, f-asce curriculum for sustainability at southern illinois...
Post on 21-Dec-2015
217 views
TRANSCRIPT
Impact of Wastewater Effluent on Rivers and the Use of Reclaimed Water Supplies
L.R. Chevalier, Ph.D., P.E., D-WRE, BCEE, F-ASCE
Curriculum for Sustainability at Southern Illinois University CarbondaleBased onChevalier, 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
Objectives
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
Initial Activities
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 facilityβs 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 by-products? Can these by-products be reduced or used commercially?
Virtual Tour: District of Columbia 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.
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.
Blue Plains Wastewater Treatment Plant
O Street Pumping Facility
Virtual Tour
Elmhurt, IL WWTP
Background: Growth Rate Models
ktePP 0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.50
500
1000
1500
2000
2500
3000
3500
Time (days)
Popula
tion
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.
Background: Mixing
1st container 2 L container with a
concentration of 100 mg/L.
Determine the mass (mg) of the contaminant in the container by multiplying the concentration by the volume
(100 mg/L)(2L) = 200 mg
Background: Mixing
2nd container 0.5 L 500 mg/L.
The mass of the contaminant in this container (500 mg/L)(0.5 L) = 250 mg
Background: Mixing
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
Background: Mixing
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.
Q1 C1
Q2 C2
Q3 C3
Background: Mixing
Mass flux: mass/time [M/T] For the first stream
(0.5 L/s)(2000 mg/L) = 1000 mg/s For the second stream
(1.5 L/s)(200 mg/L) = 300 mg/s Mass Flux for the combined streams
(M/T)1 + (M/T)2 = (M/T)3
1000 mg/s + 300 mg/s = 1300 mg/sQ1 C1
Q2 C2
Q3 C3
Background: Mixing
Add the flows Q1+Q2 = Q3
0.5 L/s + 1.5 L/s = 2.0 L/s Final concentration
(1300 mg/s) Γ· (2.0 L/s) = 650 mg/L
Q1 C1
Q2 C2
Q3 C3
DO Sag Model
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.
DO Sag Model
EFFLUENT FROM A WATER RECLAMATION PLANT
DO Sag Model
Calculate the initial dissolved oxygen in a stream at the point of wastewater effluent release
Using the subscript βsβ for the stream, βeffβ for the effluent and βtβ for total (QsCs + QeffCeff)/Qt = Ct
where Qt = Qs + Qeff
DO Sag Model
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.
Dissolved Oxygen Deficit, D
D = DOsat β DOt
Da = DOsat β 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.
DO Sag Model
π·= πππΏπππ βππαΊπβπππ‘ βπβπππ‘α»+π·ππβπππ‘
0 1 2 3 4 5 6 7 80
1
2
3
4
5
6
7
8
9
10
Time (day)
Dis
solv
ed O
xygen (
mg/L
)
DO sat
D
Ultimate BOD, La
BOD is the Biochemical Oxygen Demand Reported as a concentratrion
(QsBODs+QeffBODeff)/Qt = BODt = La
π·= πππΏπππ β ππαΊπβπππ‘ β πβπππ‘α»+ π·ππβπππ‘
0 1 2 3 4 5 6 7 80
1
2
3
4
5
6
7
8
9
10
Time (day)
Dis
solv
ed O
xygen (
mg/L
)
DO sat
D
Rate Constants, k
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.
0 1 2 3 4 5 6 7 80
1
2
3
4
5
6
7
8
9
10
Time (day)
Dis
solv
ed O
xygen (
mg/L
)
DO sat
D π·= πππΏπππ β ππαΊπβπππ‘ β πβπππ‘α»+ π·ππβπππ‘
Critical time, tc
π‘π= 1ππβππππαππππα1βπ·πππβπππππΏπ α
0 1 2 3 4 5 6 7 80
1
2
3
4
5
6
7
8
9
10
Time (day)
Dis
solv
ed O
xygen (
mg/L
)
DO sat
Mimimum dissolved oxygen, DOmin
Maximum deficit, Dmax
Critical time, tc
Spreadsheet Model
Spreadsheet Model
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.
0 1 2 3 4 5 6 7 80123456789
10
Time (day)
Dis
solv
ed O
xygen (
mg/L
)
DO sat
DOmin
DOsat -Da
Question of Sustainability 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.
Question of Sustainability
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.
References
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):1515-1522.
Shoenberger, P., Sorgini, L., 2009, Solving potable water shortages with wastewater reclamation, Water and Wastes Digest, http://www.wwdmag.com/Solving-Potable-Water-Shortage-with-Wastewater-Reclamation--article7591.
Nomenclature
BOD, biochemical oxygen demandDa, initial oxygen deficitDO, dissolved oxygenDOsat, saturated dissolved oxygenk, rate constantL, literLa, biochemical oxygen demand at point of sewage dischargeM, massmg, milligramQ, flow s, secondt, time