United States
                                                             Environmental Protection
                                                             Agency
                                                                                       July
                                                                                       1983
that BAF will be the most cost-effective alternative,
but a detailed cost analysis of the alternatives has
yet to be performed. Cost estimates for the project
at Spanish Fork have indicated that BAF could
save between 10 and 20 percent on the
construction costs and between 20 and 40 percent
on the operating costs. Although it is too early to
present direct dollar comparisons for BAF systems
versus conventional technology, BAF has certain
features which should reduce costs:

• Land requirements one-fifth to one-tenth of
  conventional systems.
• No secondary clarifier  or filter required.

« Single source of sludge.
• Simplicity of operation.

The items listed above demonstrate areas where
potential cost savings may be realized with a BAF
system. However, actual cost savings will depend
on individual operating conditions and on further
development and refinement of operating
techniques with this emerging treatment technology.
                                               SEPA  An  Emerging
                                                             Technology
                                                                  i
                                                             The  Biological
                                                             Aerated
                                                             Filter

                                                             A  Promising
                                                             Biological
                                                             Process
For additional information contact:
 EPA-OWPO(WH-547)
 401 M Street, SW
 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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The Biological Aerated Filter  - A  Promising  Biological  P
The Need for Innovative Technology
Effective wastewater treatment as a means of
protecting our nation's streams continues to be an
issue which warrants thorough consideration. As a
result of today's spiraling construction and energy
costs, the task of providing satisfactory wastewater
treatment facilities is becoming increasingly
complex. Thus, community officials and consulting
engineers are faced with the need to modify
existing treatment plants or build new facilities that
are affordable, yet meet the treatment needs of the
community. Although this is a critical problem for
small municipalities, it is not unique to them. The
problem is universal, affecting large and small
communities alike.

Meeting wastewater treatment goals in today's
economic climate calls for a departure from the
established, or conventional, treatment alternatives.
New and innovative concepts are needed to
increase benefits while decreasing costs to the
               community. An example of this innovative
               technology approach is the Biological Aerated Filter.
               The BAF system is a relatively new advancement
               in biological wastewater treatment which shows
               potential for producing a high quality treated effluent
               at costs (capital and O&M) lower than those of
               conventional treatment alternatives.

               The Process
               The Biological Aerated Filter (BAF) is a down flow,
               high rate, fixed film, biological  wastewater treatment
               system. The process is capable of removing both
               soluble and suspended organic material frofrTthe
               wastewater. Figure 1 is a schematic of a.BAF '.
               system. Primary effluent is introduced to the BAF
               and flows downward through a packed bed 6f
               granular media. The media provides a surface for
               the growth of microorganisms  which assimilate the
               organic matter in the wastewater. Air is introduced
               directly into the packed bed, countercurrent to the
               wastewater flow, roughly five feet below 'the top of
    To Primary
     Clarlfier
                         ' Primary Effluent
              Dirty Backwash Water
      )„        I   __       Process Air
      Compressor I—>r	
               '    j       Air Scour
         «          |	(Backwash)
                                             ! Active Biological
                                                 and
                                             Solids Removal
                                                 Zone    ;
    Polishing Zone
ill  I  f I  III
                     Granular
                      Media
Backwash Water
  Feed Tank
                                                                    Treated Effluent
Rgure .1  Biological Aerated Filter

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pcess
     the bed. This provides oxygen for biological growth.
     BOD absorption/oxidation and solids filtration are
     accomplished in the upper portion of the bed. The
     bed volume below the level of air injection is
     undisturbed and serves as a polishing zone for the
     removal of suspended solids. This may eliminate
     the need for a separate secondary clarifier.

     Excess biological growth and trapped suspended
     solids are removed from the bed by periodic
     backwashing of the entire media with treated
     effluent. Air is introduced to the bottom of the bed
     during the backwash cycle to scour excess solids
     from the media. The dirty backwash water is
     removed from the BAF system by siphon and
     returned to the primary clarifier.


     Operational Experience
     The BAF system was developed and is patented by
     OTV of Paris, France. EIMCO in Salt Lake City,
     Utah, has exclusive marketing rights for the
     patented BAF system in the United States. The
     present BAF design technology and expected
     performance is based on OTV pilot plant studies,
     results from  a full scale 0.5 MGD system built at
     LeHavre, France, in 1978, and recent EIMCO pilot
     work in Salt  Lake City. The facility at LeHavre was
     built to treat  primary effluent and provide high
     quality water for industrial use. It has been reported
     that this plant has consistently produced effluent
     BOD5 and suspended solids of less than 10 mg/l.

     While most of the operating experiences with  the
     BAF process have occurred in France, pilot tests
     have recently been conducted in Asheville, North
     Carolina and Park City, Utah and are currently
     being run at Spanish Fork, Utah and Salt Lake City,
     Utah. These tests were and are being conducted
     with domestic wastewater after primary clarification.
     OTV has conducted pilot plant tests on industrial
     wastewater sources. However, high strength
     wastewaters require recycling of treated effluent to
     reduce BAF influent concentrations to acceptable
     levels.

     Typical design parameters of the BAF are
     summarized in Table 1. Specific ranges and values
     for organic loading rates for BOD removal and
     nitrification have been developed by the
   Effluent Quality

    BOD5

    Suspended Solids

    Dissolved Oxygen

   Removal Efficiency

    BOD5

    Suspended Solids

   Bed Depth

   Organic Loading Rate



   ^Detention Time

   Sludge Production


   Air flow
 10-20 mg/l

 10-20 mg/l

 0.5-2.0 mg/l



 80-96 percent  '

 85-96 percent

 5-6 feet
                 •V
140-350 Ib. BODs/day
lOOOcu. ft. of
media volume

30-80 minutes

0.4-0.7 lb./lb. BOD5
removed

2-5 scfm/ft2
 Table 1  Typical BAF Design Ranges

 manufacturer. These loading tables are proprietary
 and are not available for public distribution. Present
 design of BAF systems is based on limited
 research and development and operational
 experience. The Salt Lake City project is being run
 by the University of  Utah and is a demonstration
 project supported by EPA- ORD to obtain third
 party information and tb study process feasibility
1 and optimization.      :

 Advantages
 The BAF system is capable of producing a high
 quality treated effluent, equal to or better than 20
 mg/l BOD5 and 20 mg/l suspended solids for most
 domestic wastewaters. The process can also be
 operated to achieve high levels of nitrification,
 although this operatingi mode will require lower
 loading  rates and a  larger system for the same
 flow. Since filtration  is  achieved in the lower portion
 of the filter, the BAF system eliminates the need for
 a secondary clarifier and filter in cases where an
 effluent  with low suspemded solids is required. This
 can substantially reduce the capital and operating

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costs. Another feature of the process is the reduced
land requirement. The system requires substantially
less space than most conventional systems
(approximately one-fifth the area for conventional
activated sludge systems). EIMCO markets the
BAF process in modules which makes staged
construction of the project very practical for small to
medium sized facilities. A BAF module assembly
marketed by EIMCO is shown in Figure 2. One
additional feature of the process is that the operator
does not have to be concerned with  as many
operating parameters as with most conventional
systems such as activated sludge. This allows the
system to be micro-processor controlled, thus
simplifying operation.

Limitations
One of the major limitations of the BAF process is
the lack of full-scale operational experience in the
United States. Caution must be used for design
situations that deviate significantly from OTV's and
ElMCO's data base. The BAF process does not
lend itself to retrofitting into an existing treatment
system except for combining it with an existing
primary clarifier. There is little benefit to
combining the BAF process with an existing
trickling filter or activated sludge system. For large
BAF systems (greater than 10 MGD), the
economies of scale are not as favorable as other
systems because as the size of the project
increases, the unit costs per volume do not reduce
at the rate that they do for systems such as
oxidation ditches, aerated lagoons, and others. The
suppliers of the BAF system are currently marketing
only systems capable of handling flows equal to or
greater than 0.5  MGD. Thus, the BAF process may
not be suitable for flows under 0.5 MGD.

Costs
Since the BAF system is relatively new in the
United States, reliable cost information is currently
not available. In the project at Park City, it appears
                    Media -
                               Backwash Water Over
                                Pressure Protection
        Backwash Water Inlet
              Backwash
               Water
               Siphon
       Backwash    N.
     Water Channel
                                                                                           Manhole

                                                                                         Effluent
                                                                          Backwash Air
                                                                  Process Air
                                                                    Header
                                                  -Underdrain
                                                    Nozzles
 Figure 2  BAF Module Assembly

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