United States
- Environmental'Protection
Agency
July
1983
4lrEPA An {Emerging
Technology
Counter-
current
Aeration
A Promising
Process
Modification
For additional information contact:
EPA-OWPO(WH-547)
401 M Street, NW
Washington, DC 20460
(202)382-7370/7369
EPA Region 1
John F. Kennedy Federal Building
Boston, MA 02203
EPA Region 2
26 Federal Plaza
New York, NY 10278
EPA Region 3
6th & Walnut Streets
Philadelphia, PA 19106
EPA Region 4
345 Courtland Street, NE
Atlanta, GA 30308
EPA Region 5
230 South Dearborne Street
Chicago, IL 60604
EPA-MERL (489)
26 West St. Clair Street
Cincinnati, OH 45268
(513)684-7614
EPA Region 6
1201 Elm Street
Dallas, TX 75270
EPA Region 7
324 East 11th Street
Kansas City, MO 64106
EPA Region 8
1860 Lincoln Street
Denver, CO 80203
EPA Region 9
215 Fremont Street
San Francisco, CA 94105
EPA Region 10
1200 6th Avenue
Seattle, WA 98101
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Countercurrent Aeration - A Promising Process Modifier
Cost Consciousness
Protecting the environment and meeting required
wastewater discharge standards is becoming an
increasingly costly undertaking for communities.
New wastewater treatment plants are necessary to
meet the demands of community growth and to
replace old or inadequate plants, but new treatment
facilities can be very expensive. In addition to major
capital investment in equipment and construction,
the community must pay the operation (power,
chemicals, labor, sludge disposal) and maintenance
costs year after year. The process selection
decision, particularly for medium and small
communities, will have implications on the municipal
budget for the life of the plant and may even
determine whether the project is to be built at all.
Therefore, the consulting engineer, the public utility,
and the funding/regulatory agency must investigate
innovative technologies that may make treatment
plants less expensive and more efficient. Some
interesting, emerging technologies are variations or
modifications of standard wastewater treatment
techniques. Countercurrent aeration is just such a
technology. It is a modification of the aeration
system of the extended aeration activated sludge
process.
This fact sheet presents a capsule summary of the
Countercurrent aeration process to potential users
and to those professionals who evaluate,
recommend, and implement treatment process
alternatives.
Rotating Bridge
• Influent
.
,\
.
Return
Sludge Pumps'
, 4.X
Air Supply
Effluent
Figure 1 Process Plan View
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ttion
Description
Countercurrent aeration is based on research
performed in the Netherlands in the 1960s and .
developed into a full-scale treatment process by the
Schreiber Corporation in West Germany.
Aeration of the activated sludge is accomplished by
a diffuser grid suspended from a rotating bridge
which travels around the circular tank at an
approximate rate of 1 rpm. The term
"countercurrent" refers to the aeration system
movement in relation to the biomass. This is the
opposite of the fixed aeration situation found in
other diffused air processes (where the biomass
moves relative to the diffusers).
Process design of the countercurrent aeration plant
is similar to that used in conventional extended
aeration. Process layout for facilities up to
approximately 1.25 MGD is usually economical
using tankage as shown in Figure 1. This figure
illustrates one of the six configurations available in
the United States from the Schreiber Corporation.
Alternate tank arrangements can provide for
separate sludge thickening and digestion, as well
as denitrification.
Aeration Considerations
The aeration devices used in the process are
porous stone diffuser tubes which provide efficient
oxygen transfer. However, the rotation of the
diffuser system provides a horizontal component to
the bubble path. The longer bubble path, shown in
Figure 2, can result in higher oxygen transfer than
conventional systems.
Further process efficiency results from the reduced
oxygen requirement for mixing; the bridge rotates at
a rate sufficient to provide mixing before settling
occurs. The aeration system can usually be
designed for oxygen transfer requirements,
whereas higher mixing air requirements might have
governed for traditional extended aeration. The
design also allows for fewer diffusors and less air
piping than conventional systems.
Present Use
Over 500 countercurrent facilities are operational
worldwide but only ten are in the United States
(Table 1). However, several more are under
construction in this country. Since nearly all of the
Figure 2 Bubble Dispersion Pattern
plants are new, most of them are operating well
under capacity with resulting excellent performance.
At capacity, the process is expected to perform at
least as well as conventional extended aeration
activated sludge with lower energy costs.
Capital Costs •
A comparisdn of typicaJ construction costs for
countercurrent facilities with certain other activated ,
sludge processes is shown on Figure 3. The costs '
can be affected by, among other things,'site
conditions, industrial waste contributions, and final
effluent quality requirements. '
Location
Operating
Fredericksburgi PA*
Grand Island, NY i
Carlisle, PA
Cocoa, FL .
Mahanoy City, PA
Timber Pines, FL
Loudon, TN
Claiborne County, TN
Hampden Township, F
Size
, (MGD)
•;' •• '• ''•«.. .-.-;• ..
*>* Q.6 : •
0.2
(• -|]2', '•'
3.0
f >. - 1.0
••'•••* °-2
"•J • 'o5v '
A , , , 4.0
Tuskegee, AL i "; *'.: •' 'v V/2.0 ''
'Industrial system (poultry) -i 'i ,• >:. r-
'• ... -•'- m.'H-- \ .'v l!K fei.',=-: ,,.,ife'lii!i
Table 1 United States; Countercurrent Ae'fation'
Plants (January 1983)
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Flow (MGD)
Figure 3 Cost Curves
Oxygen Power
Transfer* Use
lbO2/hp/hr hp/MGD
Extended Aeration with Coarse
Bubble Diffusers
Oxidation Ditch
Mechanical Aerators
Extended Aeration with Fine
Bubble Diffusers
Countercurrent Aeration
'with clean water
3.0
3.4
3.6
5.0
6.0
83
73
69
49
41
Annual Costs
Operation and maintenance costs will be'similar to
other extended aeration processes with the
exception of power. Table 2 shows the dramatic
energy savings that can be achieved by using the
countercurrent aeration process (which also uses
the fine bubble diffusers).
Limitations
• Generally not cost-competitive for plant sizes '
under 150,000 gpd.
Observed Advantages
• Significant power savings over other activated
sludge processes.
• Requires less land than some other extended
aeration processes (e.g., oxidation ditch).
Process Considerations
• Concentric clarifier/aeration tanks possible up to
1.25 mgd.
• Careful tank construction and rotating equipment
placement required.
• Standard design may require some additions or
modifications for maximum operation flexibility
and safety.
Table 2 Power Use Comparison
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