United States September
Environmental Pratectior 1983
Agency
• It should require less operator's time than the
cqnVentional activated" sludge process.
• At flows less than 5.0 MGD, the combined
system costs (capital and O & M) for SBR are
expected to be lower than conventional activated
sludge.
• At flows between 0.1 and 5.0 MGD, the SBR
capital and O & M costs are competitive with
oxidation ditch systems.
• Proper selection of aeration modes will prevent
filamentous organism growth.
The potential limitations of the SBR process are:
• There is currently only one system in the U.S.
with operational experience.
• Scum accumulation was a problem at Culver
because the secondary clarifiers were not
equipped with skimmers.
• Sequencing of multiple tanks and operating
cycles may be complex; however, this was not .
problem at Culver where the operator reported
ease of operation.
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 Dearbome. 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
4>EPA An Emerging
Technology
Sequencing
Batch
Reactors
i
A Project
Assessment
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Sequencing Batch Reactors - A Project Assessment of
Background
Cost considerations are playing an
increasingly important role in a community's
selection of a wastewater treatment technology. For
this reason, consulting engineers are seeking
innovative ways to reduce both capital and
operation and maintenance expenses to meet their
client's needs. One such technology worthy of
consideration is the Sequencing Batch Reactor
(SBR). The purpose of this fact sheet is to
introduce this technology to potential users.
Batch treatment utilizing activated sludge is not
new. The first activated sludge batch systems were
developed and patented in the early 1900s.
However, lack of convenient and effective control
systems rather than process-related deficiencies
limited their use. Only recent developments in
hardware such as electronic and mechanical timers,
solenoids, and microprocessors have overcome
these problems and rendered this technology a
viable candidate for the treatment of municipal
wastewaters.
The Process
SBR technology is the treatment of wastewater on
a batch basis and is no more than an activated
sludge system which operates in time rather than in
space, i.e., all steps of the process take place, one
after the other, in the same tank instead of moving
to a second tank for the continuation of the
treatment. Typical SBR operation (Figure 1)
involves filling a tank with raw wastewater or
primary effluent, aerating the wastewater to convert
the organics into microbial mass, providing a period
for settling, discharging the treated effluent, and a
period identified as IDLE that represents the time
after discharging the tank and before refilling. For
most projects, a multiple tank system is required.
This configuration allows incoming flow to be
switched to one tank while the other is going
through the aeration, clarification, and discharge
functions. A key element in the SBR process is that
a tank is never completely emptied, but rather a
portion of settled solids is left in the tank for the
next cycle. The remaining portion of this residue
(sludge) is wasted. The fraction wasted will depend
upon the desired sludge age.
Inf
uent
\ *««'"";%'*» ?-/
, A v^^A>-^>y^s^^>s^OLK
Effluent
\
^
Fill (4 Hr.)
Aeration (6 Hr.)
Settle (6 Hr.)
^ Discharge (4 Hr.)
•*• Waste Sludge (4 Hr.)
Figure 1 Typical SBR Operation for One Cycle
The retention of sludge within the tank establishes
a population of microorganisms uniquely suited to
treating the waste. During the process, the
microorganisms are subject to periods of high and
low oxygen and high and low food availability. This
condition develops a population of organisms which
is very efficient at treating the particular wastewater.
This selection process is similar to that found in
staged reactor activated sludge systems.
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I'
n Promising Process Modification
Demonstration Plant
An existing continuous-flow activated sludge
treatment plant owned and operated by the town of
Culver, Indiana was selected by the U.S.
Environmental Protection Agency as the first
full-scale demonstration site for SBR technology
beginning in 1979. The retrofit plant in Culver is the
only SBR plant currently treating domestic
wastewater in the United States. The demonstration
project was operated by the town of Culver in
cooperative agreement with the University of Notre
Dame. Other SBR projects are in design or
construction phases in Grundy Center, Iowa;
Sabula, Iowa; LeClaire, Iowa; and Poolesville,
Maryland.
The Culver plant serves a population of
approximately 2,500 people. Flow to the plant is
typically 0.3 to 0.4 MGD; however, infiltration to the
sewers causes occasional periods of high flows
(0.8 to 0.9 MGD). A simplified flow schematic of the
Culver plant is shown in Figure 2. Raw wastewater
passes through a bar screen, comminuter, grit
chamber, and a primary clarifier. Two aeration
tanks were converted 'to SBR reactors. The existing
secondary clarifiers were not required for SBR
operation. The existing chlorine contact tank was
replaced by a specially designed chlorination box
for disinfection of the treated effluent prior to
discharge to a stream. While the SBR at Culver
treated primary effluent, raw wastewater can be
treated directly in the SBR.
Operating experiences for the Culver SBR system
have shown it to provide very good removal
efficiencies for BOD arid suspended solids.
Performance data are summarized in Table 1.
When operated to achieve biological nitrogen
removal, the SBR system removed approximately
90% of the influent inorganic nitrogen.
At Culver, phosphorus was removed chemically by
adding either alum or ferric chloride. The system at
Culver was not stressed with respect to organic
loading and as a result, the organic removal
limitation for the SBR was not determined. The
amount of time that the SBR operates in a mixing
Bar Screen
Comminuter
Raw Wastewater
oar ocreen s***™**^.
•/////-O
Grit Chamber
Chlorination
SBR Tank No. 1
SBR Tank No. 2
f Stream Discharge
Primary
Clarifier
L>» Waste Sludge to
! Sludge Handling System
Figure 2 Culver Plant Flow Schematic
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Raw
Wastewater
(mg/i)
Rnal
Effluent
(mg/l)
Percent
Removal
Operational Strategy: BOD removal
BOD5
TSS
NH4-N-^|
plus U
NOX-N— 1
TP
160
130
24.4
6.3
9.5
8.0
16.6
0.45
94
94
32
93
Operational Strategy: Nutrient Removal
BOD5
TSS
NH4-N-1
plus K-
NOX-N-I
TP
170
150
22
6.5
10.5
5.5
2.4
0.75
94
, 96
89
88
Table 1 Performance Data
mode or aeration mode is more important to
system design and operation than either sludge age
or loading.
Cost Comparisons - Capital
Based on current projections (1983 dollars), SBR
capital costs are estimated to parallel closely the
capital costs for oxidation ditch systems in the 0.1
to 5.0 MGD range. Between flows of 0.5 to 5.0
MGD the SBR capital costs are lower than the
costs for conventional activated sludge. These
comparisons are summarized in Figure 3. The data
was generated via EPA's Computer Assisted
Procedures for the Design and Evaluation of
Wastewater Treatment Facilities (CAPDET)
program
Operation & Maintenance
Computer estimates show the SBR process to have
O & M costs equivalent to oxidation ditch systems
between flows of 0.1 to 5.0 MGD. These same
estimates show the SBR to have lower O & M
costs than activated sludge between flows of 0.5 to
5.0 MGD (see Figure 3). This data was also
generated via EPA's CAPDET program. Operating
the SBR under a nutrient removal strategy would
5.0
&
•s 1.0
£ 0.5
CAPITAL COSTS
TOTAL ANNUAL O & M COSTS
0.5 1.0
Flow, MGD
Figure 3 Cost Comparison Curves
require more energy because of the higher
'dissolved oxygen needed for nitrification vs.
organics removal only. These increased energy
requirements would lead to higher O&M costs for
the SBR as well as other conventional activated
sludge systems.
Summary
The SBR process offers the following advantages:
• It has the flexibility to be operated either as a
labor-intensive, low energy, high sludge yield
system, or as a minimal labor, high energy, low
sludge yield system.
• It is well suited for systems with a wide range of
flow and/or organic loadings.
• It can achieve high BOD and suspended solids
reductions and can be operated with or without
nutrient removal.
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