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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