v>EPA
United States
Environmental Protection
Agency
Office of Water
Washington, D.C.
EPA 932-F-99-073
September 1999
Waste water
Technology Fact Sheet
Sequencing Batch Reactors
DESCRIPTION
The sequencing batch reactor (SBR) is a fill-and-
draw activated sludge system for wastewater
treatment. In this system, wastewater is added to a
single "batch" reactor, treated to remove
undesirable components, and then discharged.
Equalization, aeration, and clarification can all be
achieved using a single batch reactor. To optimize
the performance of the system, two or more batch
reactors are used in a predetermined sequence of
operations. SBR systems have been successfully
used to treat both municipal and industrial
wastewater. They are uniquely suited for
wastewater treatment applications characterized by
low or intermittent flow conditions.
Fill-and-draw batch processes similar to the SBR
are not a recent development as commonly thought.
Between 1914 and 1920, several full-scale fill-and-
draw systems were in operation. Interest in SBRs
was revived in the late 1950s and early 1960s, with
the development of new equipment and technology.
Improvements in aeration devices and controls have
allowed SBRs to successfully compete with
conventional activated sludge systems.
The unit processes of the SBR and conventional
activated sludge systems are the same. A 1983 U.S.
EPA report, summarized this by stating that "the
SBR is no more than an activated sludge system
which operates in time rather than in space." The
difference between the two technologies is that the
SBR performs equalization, biological treatment,
and secondary clarification in a single tank using a
timed control sequence. This type of reactor does,
in some cases, also perform primary clarification. In
a conventional activated sludge system, these unit
processes would be accomplished by using separate
tanks.
A modified version of the SBR is the Intermittent
Cycle Extended Aeration System (ICEAS). In the
ICEAS system, influent wastewater flows into the
reactor on a continuous basis. As such, this is not
a true batch reactor, as is the conventional SBR. A
baffle wall may be used in the ICEAS to buffer this
continuous inflow. The design configurations of the
ICEAS and the SBR are otherwise very similar.
Description of a Wastewater Treatment Plant
Using an SBR
A typical process flow schematic for a municipal
wastewater treatment plant using an SBR is shown
in Figure 1. Influent wastewater generally passes
through screens and grit removal prior to the SBR.
The wastewater then enters a partially filled reactor,
containing biomass, which is acclimated to the
wastewater constituents during preceding cycles.
Once the reactor is full, it behaves like a
conventional activated sludge system, but without a
continuous influent or effluent flow. The aeration
and mixing is discontinued after the biological
reactions are complete, the biomass settles, and the
treated supernatant is removed. Excess biomass is
wasted at any time during the cycle. Frequent
wasting results in holding the mass ratio of influent
substrate to biomass nearly constant from cycle to
cycle. Continuous flow systems hold the mass ratio
of influent substrate to biomass constant by
adjusting return activated sludge flowrates
continually as influent flowrates, characteristics, and
settling tank underflow concentrations vary. After
the SBR, the "batch" of wastewater may flow to an
equalization basin where the wastewater flowrate to
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additional unit processed can be is controlled at a
determined rate. In some cases the wastewater is
filtered to remove additional solids and then
disinfected.
As illustrated in Figure 1, the solids handling system
may consist of a thickener and an aerobic digester.
With SBRs there is no need for return activated
sludge (RAS) pumps and primary sludge (PS)
pumps like those associated with conventional
activated sludge systems. With the SBR, there is
typically only one sludge to handle. The need for
gravity thickeners prior to digestion is determined
TO SOLIDS HANDLING,
DISPOSAL, OR
BENEFICIAL REUSE
SCREENING/ SBR EQUALIZATION FILTRATION DISINFECTION
GRINDING
Source: Parsons Engineering Science, 1999.
FIGURE 1 PROCESS FLOW DIAGRAM
FOR A TYPICAL SBR
on a case by case basis depending on the
characteristics of the sludge.
An SBR serves as an equalization basin when the
vessel is filling with wastewater, enabling the system
to tolerate peak flows or peak loads in the influent
and to equalize them in the batch reactor. In many
conventional activated sludge systems, separate
equalization is needed to protects the biological
system from peak flows, which may wash out the
biomass, or peak loads, which may upset the
treatment process.
It should also be noted that primary clarifiers are
typically not required for municipal wastewater
applications prior to an SBR. In most conventional
activated sludge wastewater treatment plants,
primary clarifiers are used prior to the biological
system. However, primary clarifiers may be
recommended by the SBR manufacturer if the total
suspended solids (TSS) or biochemical oxygen
demand (BOD) are greater than 400 to 500 mg/L.
Historic data should be evaluated and the SBR
manufacturer consulted to determine whether
primary clarifiers or equalization are recommended
prior to an SBR for municipal and industrial
applications.
Equalization may be required after the SBR,
depending on the downstream process. If
equalization is not used prior to filtration, the filters
need to be sized in order to receive the batch of
wastewater from the SBR, resulting in a large
surface area required for filtration. Sizing filters to
accept these "batch" flows is usually not feasible,
which is why equalization is used between an SBR
and downstream filtration. Separate equalization
following the biological system is generally not
required for most conventional activated sludge
systems, because the flow is on a continuous and
more constant basis.
APPLICABILITY
SBRs are typically used at flowrates of 5 MOD or
less. The more sophisticated operation required at
larger SBR plants tends to discourage the use of
these plants for large flowrates.
As these systems have a relatively small footprint,
they are useful for areas where the available land is
limited. In addition, cycles within the system can be
easily modified for nutrient removal in the future, if
it becomes necessary. This makes SBRs extremely
flexible to adapt to regulatory changes for effluent
parameters such as nutrient removal. SBRs are also
very cost effective if treatment beyond biological
treatment is required, such as filtration.
ADVANTAGES AND DISADVANTAGES
Some advantages and disadvantages of SBRs are
listed below:
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Advantages
• Equalization, primary clarification (in most
cases), biological treatment, and secondary
clarification can be achieved in a single reactor
vessel.
• Operating flexibility and control.
• Minimal footprint.
• Potential capital cost savings by eliminating
clarifiers and other equipment.
Disadvantages
• A higher level of sophistication is required
(compared to conventional systems), especially
for larger systems, of timing units and controls.
• Higher level of maintenance (compared to
conventional systems) associated with more
sophisticated controls, automated switches, and
automated valves.
• Potential of discharging floating or settled sludge
during the DRAW or decant phase with some
SBR configurations.
• Potential plugging of aeration devices during
selected operating cycles, depending on the
aeration system used by the manufacturer.
• Potential requirement for equalization after the
SBR, depending on the downstream processes.
DESIGN CRITERIA
For any wastewater treatment plant design, the first
step is to determine the anticipated influent
characteristics of the wastewater and the effluent
requirements for the proposed system. These
influent parameters typically include design flow,
maximum daily flow BOD5, TSS, pH, alkalinity,
wastewater temperature, total Kjeldahl nitrogen
(TKN), ammonia-nitrogen (NH3-N), and total
phosphorus (TP). For industrial and domestic
wastewater, other site specific parameters may also
be required.
The state regulatory agency should be contacted to
determine the effluent requirements of the proposed
plant. These effluent discharge parameters will be
dictated by the state in the National Pollutant
Discharge Elimination System (NPDES) permit.
The parameters typically permitted for municipal
systems are flowrate, BOD5, TSS, and Fecal
Coliform. In addition, many states are moving
toward requiring nutrient removal. Therefore, total
nitrogen (TN), TKN, NH3-N, or TP may also be
required. It is imperative to establish effluent
requirements because they will impact the operating
sequence of the SBR. For example, if there is a
nutrient requirement and NH3-N or TKN is
required, then nitrification will be necessary. If
there is a TN limit, then nitrification and
denitrification will be necessary.
Once the influent and effluent characteristics of the
system are determined, the engineer will typically
consult SBR manufacturers for a recommended
design. Based on these parameters, and other site
specific parameters such as temperature, key design
parameters are selected for the system. An example
of these parameters for a wastewater system loading
is listed in Table 1.
TABLE 1 KEY DESIGN PARAMETERS
FOR A CONVENTIONAL LOAD
Municipal Industrial
Food to Mass (F:M) 0.15 - 0.4/day 0.15-
0.6/day
Treatment Cycle
Duration
4.0 hours
4.0-24
hours
Typically Low Water 2,000-2,500 2,000-4,000
Level Mixed Liquor rng/L rng/L
Suspended Solids
Hydraulic Retention 6-14 hours varies
Time
Source: AquaSBR Design Manual, 1995.
Once the key design parameters are determined, the
number of cycles per day, number of basins, decant
volume, reactor size, and detention times can be
calculated. Additionally, the aeration equipment,
decanter, and associated piping can then be sized.
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Other site specific information is needed to size the
aeration equipment, such as site elevation above
mean sea level, wastewater temperature, and total
dissolved solids concentration.
The operation of an SBR is based on the fill-and-
draw principle, which consists of the following five
basic steps: Idle, Fill, React, Settle, and Draw.
More than one operating strategy is possible during
most of these steps. For industrial wastewater
applications, treatability studies are typically
required to determine the optimum operating
sequence. For most municipal wastewater
treatment plants, treatability studies are not required
to determine the operating sequence because
municipal wastewater flowrates and characteristic
variations are usually predictable and most
municipal designers will follow conservative design
approaches.
The Idle step occurs between the Draw and the Fill
steps, during which treated effluent is removed and
influent wastewater is added. The length of the Idle
step varies depending on the influent flowrate and
the operating strategy. Equalization is achieved
during this step if variable idle times are used.
Mixing to condition the biomass and sludge wasting
can also be performed during the Idle step,
depending on the operating strategy.
Influent wastewater is added to the reactor during
the Fill step. The following three variations are
used for the Fill step and any or all of them may be
used depending on the operating strategy: static fill,
mixed fill, and aerated fill. During static fill, influent
wastewater is added to the biomass already present
in the SBR. Static fill is characterized by no mixing
or aeration, meaning that there will be a high
substrate (food) concentration when mixing begins.
A high food to microorganisms (F:M) ratio creates
an environment favorable to floe forming organisms
versus filamentous organisms, which provides good
settling characteristics for the sludge. Additionally,
static fill conditions favor organisms that produce
internal storage products during high substrate
conditions, a requirement for biological phosphorus
removal. Static fill may be compared to using
"selector" compartments in a conventional activated
sludge system to control the F:M ratio.
Mixed fill is classified by mixing influent organics
with the biomass, which initiates biological
reactions. During mixed fill, bacteria biologically
degrade the organics and use residual oxygen or
alternative electron acceptors, such as nitrate-
nitrogen. In this environment, denitrification may
occur under these anoxic conditions. Denitrification
is the biological conversion of nitrate-nitrogen to
nitrogen gas. An anoxic condition is defined as an
environment in which oxygen is not present and
nitrate-nitrogen is used by the microorganisms as
the electron acceptor. In a conventional biological
nutrient removal (BNR) activated sludge system,
mixed fill is comparable to the anoxic zone which is
used for denitrification. Anaerobic conditions can
also be achieved during the mixed fill phase. After
the microorganisms use the nitrate-nitrogen, sulfate
becomes the electron acceptor. Anaerobic
conditions are characterized by the lack of oxygen
and sulfate as the electron acceptor.
Aerated Fill is classified by aerating the contents of
the reactor to begin the aerobic reactions completed
in the React step. Aerated Fill can reduce the
aeration time required in the React step.
The biological reactions are completed in the React
step, in which mixed react and aerated react modes
are available. During aerated react, the aerobic
reactions initialized during aerated fill are completed
and nitrification can be achieved. Nitrification is the
conversion of ammonia-nitrogen to nitrite-nitrogen
and ultimately to nitrate-nitrogen. If the mixed react
mode is selected, anoxic conditions can be attained
to achieve denitrification. Anaerobic conditions can
also be achieved in the mixed react mode for
phosphorus removal.
Settle is typically provided under quiescent
conditions in the SBR. In some cases, gentle mixing
during the initial stages of settling may result in a
clearer effluent and a more concentrated settled
sludge. In an SBR, there are no influent or effluent
currents to interfere with the settling process as in a
conventional activated sludge system.
The Draw step uses a decanter to remove the
treated effluent, which is the primary distinguishing
factor between different SBR manufacturers. In
general, there are floating decanters and fixed
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decanters. Floating decanters offer several
advantages over fixed decanters as described in the
Tank and Equipment Description Section.
Construction
Construction of SBR systems can typically require
a smaller footprint than conventional activated
sludge systems because the SBR often eliminates the
need for primary clarifiers. The SBR never requires
secondary clarifiers. The size of the SBR tanks
themselves will be site specific, however the SBR
system is advantageous if space is limited at the
proposed site. A few case studies are presented in
Table 2 to provide general sizing estimates at
different flowrates. Sizing of these systems is site
specific and these case studies do not reflect every
system at that size.
TABLE 2 CASE STUDIES FOR SEVERAL
SBR INSTALLATIONS
Flow
(MGD)
0.012
0.10
1.2
1.0
1.4
1.46
2.0
4.25
5.2
Reactors
No.
1
2
2
2
2
2
2
4
4
Size
(feet)
18x12
24x24
80x80
58x58
69x69
78x78
82x82
104x80
87x87
Volume
(MG)
0.021
0.069
0.908
0.479
0.678
0.910
0.958
1.556
1.359
Blowers
No.
1
3
3
3
3
4
3
5
5
Size
(HP)
15
7.5
125
40
60
40
75
200
125
Note: These case studies and sizing estimates were provided
by Aqua-Aerobic Systems, Inc. and are site specific to
individual treatment systems.
The actual construction of the SBR tank and
equipment may be comparable or simpler than a
conventional activated sludge system. For
Biological Nutrient Removal (BNR) plants, an SBR
eliminates the need for return activated sludge
(RAS) pumps and pipes. It may also eliminate the
need for internal Mixed Liquor Suspended Solid
(MLSS) recirculation, if this is being used in a
conventional BNR system to return nitrate-nitrogen.
The control system of an SBR operation is more
complex than a conventional activated sludge
system and includes automatic switches, automatic
valves, and instrumentation. These controls are
very sophisticated in larger systems. The SBR
manufacturers indicate that most SBR installations
in the United States are used for smaller wastewater
systems of less than two million gallons per day
(MGD) and some references recommend SBRs only
for small communities where land is limited. This is
not always the case, however, as the largest SBR in
the world is currently a 10 MGD system in the
United Arab Emirates.
Tank and Equipment Description
The SBR system consists of a tank, aeration and
mixing equipment, a decanter, and a control system.
The central features of the SBR system include the
control unit and the automatic switches and valves
that sequence and time the different operations.
SBR manufacturers should be consulted for
recommendations on tanks and equipment. It is
typical to use a complete SBR system recommended
and supplied by a single SBR manufacturer. It is
possible, however, for an engineer to design an SBR
system, as all required tanks, equipment, and
controls are available through different
manufacturers. This is not typical of SBR
installation because of the level of sophistication of
the instrumentation and controls associated with
these systems.
The SBR tank is typically constructed with steel or
concrete. For industrial applications, steel tanks
coated for corrosion control are most common
while concrete tanks are the most common for
municipal treatment of domestic wastewater. For
mixing and aeration, jet aeration systems are typical
as they allow mixing either with or without aeration,
but other aeration and mixing systems are also used.
Positive displacement blowers are typically used for
SBR design to handle wastewater level variations in
the reactor.
As previously mentioned, the decanter is the
primary piece of equipment that distinguishes
different SBR manufacturers. Types of decanters
include floating and fixed. Floating decanters offer
the advantage of maintaining the inlet orifice slightly
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below the water surface to minimize the removal of
solids in the effluent removed during the DRAW
step. Floating decanters also offer the operating
flexibility to vary fill-and-draw volumes. Fixed
decanters are built into the side of the basin and can
be used if the Settle step is extended. Extending the
Settle step minimizes the chance that solids in the
wastewater will float over the fixed decanter. In
some cases, fixed decanters are less expensive and
can be designed to allow the operator to lower or
raise the level of the decanter. Fixed decanters do
not offer the operating flexibility of the floating
decanters.
Health and Safety
Safely should be the primary concern in every
design and system operation. A properly designed
and operated system will minimize potential health
and safety concerns. Manuals such as the Manual of
Practice (MOP) No. 8, Design of Municipal
Wastewater Treatment Plants, and MOP No. 11,
Operation of Municipal Wastewater Treatment
Plants should be consulted to minimize these risks.
Other appropriate industrial wastewater treatment
manuals, federal regulations, and state regulations
should also be consulted for the design and
operation of wastewater treatment systems.
PERFORMANCE
The performance of SBRs is typically comparable to
conventional activated sludge systems and depends
on system design and site specific criteria.
Depending on their mode of operation, SBRs can
achieve good BOD and nutrient removal. For
SBRs, the BOD removal efficiency is generally 85
to 95 percent.
SBR manufacturers will typically provide a process
guarantee to produce an effluent of less than:
• lOmg/LBOD
• 10 mg/L TSS
• 5-8 mg/L TN
• 1-2 mg/L TP
OPERATION AND MAINTENANCE
The SBR typically eliminates the need for separate
primary and secondary clarifiers in most municipal
systems, which reduces operations and maintenance
requirements. In addition, RAS pumps are not
required. In conventional biological nutrient
removal systems, anoxic basins, anoxic zone mixers,
toxic basins, toxic basin aeration equipment, and
internal MLSS nitrate-nitrogen recirculation pumps
may be necessary. With the SBR, this can be
accomplished in one reactor using aeration/mixing
equipment, which will minimize operation and
maintenance requirements otherwise be needed for
clarifiers and pumps.
Since the heart of the SBR system is the controls,
automatic valves, and automatic switches, these
systems may require more maintenance than a
conventional activated sludge system. An increased
level of sophistication usually equates to more items
that can fail or require maintenance. The level of
sophistication may be very advanced in larger SBR
wastewater treatment plants requiring a higher level
of maintenance on the automatic valves and
switches.
Significant operating flexibility is associated with
SBR systems. An SBR can be set up to simulate
any conventional activated sludge process, including
BNR systems. For example, holding times in the
Aerated React mode of an SBR can be varied to
achieve simulation of a contact stabilization system
with a typical hydraulic retention time (HRT) of 3.5
to 7 hours or, on the other end of the spectrum, an
extended aeration treatment system with a typical
HRT of 18 to 36 hours. For a BNR plant, the
aerated react mode (oxic conditions) and the mixed
react modes (anoxic conditions) can be alternated to
achieve nitrification and denitrification. The mixed
fill mode and mixed react mode can be used to
achieve denitrification using anoxic conditions. In
addition, these modes can ultimately be used to
achieve an anaerobic condition where phosphorus
removal can occur. Conventional activated sludge
systems typically require additional tank volume to
achieve such flexibility. SBRs operate in time rather
than in space and the number of cycles per day can
be varied to control desired effluent limits, offering
additional flexibility with an SBR.
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COSTS
This section includes some general guidelines as
well as some general cost estimates for planning
purposes. It should be remembered that capital and
construction cost estimates are site-specific.
Budget level cost estimates presented in Table 3 are
based on projects that occurred from 1995 to 1998.
Budget level costs include such as the blowers,
diffusers, electrically operated valves, mixers, sludge
pumps, decanters, and the control panel. All costs
have been updated to March 1998 costs, using an
ENR construction cost index of 5875 from the
March 1998 Engineering News Record, rounded off
to the nearest thousand dollars.
TABLE 3 SBR EQUIPMENT COSTS
BASED ON DIFFERENT PROJECTS
Design Flowrate
(MGD)
Budget Level
Equipment Costs ($)
0.012
0.015
1.0
1.4
1.46
2.0
4.25
94,000
137,000
339,000
405,000
405,000
564,000
1,170,000
Source: Aqua Aerobics Manufacturer Information, 1998.
In Table 4, provided a range of equipment costs for
different design flowrates is provided.
TABLE 4 BUDGET LEVEL EQUIPMENT
COSTS BASED ON DIFFERENT FLOW
RATES
Design Flowrate
(MGD)
Budget Level Equipment
Costs ($)
1
5
10
15
20
150,000-350,000
459,000 - 730,000
1,089,000-1,370,000
2,200,000
2,100,000-3,000,000
Note: Budget level cost estimates provided by Babcock King -
Wilkinson, L.P., August 1998.
Again the equipment cost items provided do not
include the cost for the tanks, sitework,
excavation/backfill, installation, contractor's
overhead and profit, or legal, administrative,
contingency, and engineering services. These items
must be included to calculate the overall
construction costs of an SBR system. Costs for
other treatment processes, such as screening,
equalization, filtration, disinfection, or aerobic
digestion, may be included if required.
The ranges of construction costs for a complete,
installed SBR wastewater treatment system are
presented in Table 5. The variances in the estimates
are due to the type of sludge handling facilities and
the differences in newly constructed plants versus
systems that use existing plant facilities. As such, in
some cases these estimates include other processes
required in an SBR wastewater treatment plant.
TABLE 5 INSTALLED COST PER
GALLON OF WASTEWATER TREATED
Design Flowrate
(MGD)
Budget Level
Equipment Cost
($/gallon)
0.5-1.0
1.1 -1.5
1.5-2.0
1.96-5.00
1.83-2.69
1.65-3.29
Note: Installed cost estimates obtained from Aqua-Aerobics
Systems, Inc., August 1998.
There is typically an economy of scale associated
with construction costs for wastewater treatment,
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meaning that larger treatment plants can usually be
constructed at a lower cost per gallon than smaller
systems. The use of common wall construction for
larger treatment systems, which can be used for
square or rectangular SBR reactors, results in this
economy of scale.
Operations and Maintenance (O&M) costs
associated with an SBR system may be similar to a
conventional activated sludge system. Typical cost
items associated with wastewater treatment systems
include labor, overhead, supplies, maintenance,
operating administration, utilities, chemicals, safety
and training, laboratory testing, and solids handling.
Labor and maintenance requirements may be
reduced in SBRs because clarifiers, clarification
equipment, and RAS pumps may not be necessary.
On the other hand, the maintenance requirements
for the automatic valves and switches that control
the sequencing may be more intensive than for a
conventional activated sludge system. O&M costs
are site specific and may range from $800 to $2,000
dollars per million gallons treated.
REFERENCES
1. AquaSBR Design Manual. Mikkelson, K. A.
of Aqua-Aerobic Systems. Copyright 1995.
2. Arora, Madan L. Technical Evaluation of
Sequencing Batch Reactors. Prepared for
U.S. EPA. U.S. EPA Contract No. 68-03-
1821.
7. Metcalf & Eddy, Inc. Wastewater
Engineering: Treatment, Disposal, Reuse.
3rd edition. New York: McGrawHill.
8. Parsons Engineering Science, Inc. Basis of
Design Report - Urgent Extensions to
Moray Sewer Treatment Works, Abu Dhabi,
UAE, 1992.
9. Norcross, K.L., Sequencing Batch Reactors
- An Overview. Technical Paper published
in the IAWPRC 1992 (0273-1221/92).
Wat. Sci. Tech., Vol. 26, No. 9-11, pp.
2523 - 2526.
10. Peavy, Rowe, and Tchobanoglous:
Environmental Engineering. New York:
McGraw-Hill, Inc.
11. U.S. EPA. Innovative and Alternative
Technology Assessment Manual,
EPA/430/9-78-009. Cincinnati, Ohio, 1980.
12. U.S. EPA. EPA Design Manual, Summary
Report Sequencing Batch Reactors.
EPA/625/8-86/011, August 1986.
13. Manual of Practice (MOP) No. 8, Design of
Municipal Wastewater Treatment Plants,
14. Manual of Practice (MOP) No. 11,
Operation of Municipal Wastewater
Treatment Plants.
Engineering News-Record. A publication of
the McGraw Hill Companies, March 30,
1998.
Irvine, Robert L. Technology Assessment of
Sequencing Batch Reactors. Prepared for
U.S. EPA. U.S. EPA Contract No. 68-03-
3055.
Liu, Liptak, and Bouis. Environmental
Engineer's Handbook, 2nd edition. New
York: Lewis Publishers.
Manufacturers Information. Aqua-
Aerobics, Babcock King-Wilkinson, L.P.,
Fluidyne, and Jet Tech Systems, 1998.
ADDITIONAL INFORMATION
Brad Holtsinger, Chief Operator
City of Stockbridge WWTP
4545 North Henry Boulevard
Stockbridge, GA 30281
Gary Hooder, Operator
Martinsburg WWTP
133 East Allegheny
Martinsburg, PA 16662-1112
Mitchell Meadows, Lead Operator
13 00 Recker Highway
Auburndale, FL 33823
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Teresa Schnoor, Administrator
Antrim TWP
P.O.Box 130
Greencastle, PA 17225
Charles Sherrod, Chief Operator
Blountstown WWTP
125 West Central Avenue
Blountstown, FL 32424
The mention of trade names or commercial products
does not constitute endorsement or recommendation
for use by the U.S. Environmental Protection
Agency.
For more information contact:
Municipal Technology Branch
U.S. EPA
Mail Code 4204
401 M St., S.W.
Washington, D.C., 20460
IMTB
Exceience fh compliance through optftnal technical sotrtroru:
MUNICIPAL TECHNOLOGY
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