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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