EPA
TECHNOLOGY
TRANSFER
SWIRL DEVICE
FOR
REGULATING
AND PREPARED BY
TREATING U.S.
COMBINED ENVIRONMENTAL
SEWER PROTECTION
OVERFLOWS AGENCY
-------
-------
EPA
TECHNOLOGY
TRANSFER
SWIRL DEVICE
FOR
REGULATING
AND
TREATING
COMBINED
SEWER
PREPARED BY
U.S.
ENVIRONMENTAL
PROTECTION
OVERFLOWS AGENCY
EPA-625/2-77-012
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Prototype Swirl Primary Separator
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Untreated storm overflows from combined
(storm and sanitary) sewers are a substantial
water pollution source during wet-weather pe-
riods. There are roughly 15,000 to 18,000 combined
sewer overflow points in the USA that emanate
from 40 to 80 percent of the total organic load in
municipalities during wet-weather flow periods.
It has been estimated that, on a national level, the
expenditure for combined sewer overflow pollu-
tion abatement would be $25 billion.
In considering wet-weather water pollution
abatement, attention must first be directed to
control of the existing combined sewerage system
and replacement (or stricter maintenance) of
faulty regulators. Consulting and municipal en-
gineers will agree that regulator mechanical fail-
ures and blockages persist at the overflow or diver-
sion points resulting in unnecessary by-passing,
which is also a problem during dry weather. Mal-
functioning overflow structures, both of the static
and dynamic varieties, are major contributors to
the overall water pollution problem.
The practice in the USA of designing regulators
exclusively for flow-rate control or diversion of
combined wastewaters to the treatment plant
and overflow to receiving waters must be recon-
sidered. Sewer system management that em-
phasizes the dual function of combined sewer over-
flow regulator facilities for improving overflow
quality will pay significant dividends. The dual
function is concentration of wastewater solids to
the sanitary interceptor, and diversion of excess
storm flow to the outfall. A new phrase has been
coined, the "two Q's," to represent both the quan-
titative and qualitative aspects of overflow regula-
tion. Regulators and their appurtenant facilities
should be recognized as devices which have the
responsibility of controlling both quantity and
quality of overflow to receiving waters, in the in-
terest of more effective pollution control.
An intensive study to develop a new type of
combined sewer overflow regulator device, called
swirl, was conducted under the general supervi-
sion of the U.S. Environmental Protection Agency's
Storm and Combined Sewer Technology Program,
Municipal Environmental Research Laboratory,
Cincinnati, Ohio. The design of this device was
based on hydraulic and mathematical modeling to
optimize its configuration. This report describes
the results of a full-scale prototype swirl unit that
controlled real overflows in the city of Syracuse,
New York, and discusses other areas of operation.
The prototype evaluation project is jointly spon-
sored by EPA and Onondaga County, New York,
under ongoing EPA Demonstration Grant No.
S-802400.
Swirl Hydraulic Model in Operation
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LEGEND
a Inlet Lamp
b Flow deflector
c Scum ring "" " i'' ~"^
|_d Qyerflow vve/r anc/ wej£ plate
floatables trap
_ Foul sewer outlet
h Floor gutters
i Downshaft
INFLOW
Isometric View of Swirl Regulator/Separator
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ELEMENTS OF THE SWIRL REGULATOR/SEPARATOR
The swirl flow regulator/separator is of simple
annular-shaped construction and requires no mov-
ing parts. An essentially static device performing
under such variable conditions requires careful
design of its internal elements, as shown in the
isometric drawing.
(a) Inlet ramp. The inlet ramp should be de-
signed to introduce the incoming flow at the bot-
tom of the chamber, while preventing problemat-
ical surcharges on the collector sewer immedi-
ately upstream. Introducing the inflow at the
chamber floor will allow the solids to enter at as
low a position that is possible. It is essential that
this ramp and its entry port introduce the flow tan-
gentially so that the "long path" maximizing the
solids separation in the chamber may be devel-
oped.
(b) Flow deflector. The flow deflector is a verti-
cal, free-standing wall which is a straight line ex-
tension of the interior wall of the entrance ramp.
Its location is important because it directs flow
which is completing its first revolution in the
chamber to strike and be deflected inwards, form-
ing an interior water mass which makes a second
revolution in the chamber, thus creating the "long
path."
(c) Scum ring. The purpose of the scum ring is to
prevent floating solids from overflowing.
(d) Overflow weir and weir plate. The weir
plate is a horizontal circular plate that connects
the overflow weir to a central downshaft which
carries the overflow liquid to discharge. Its under-
side acts as a storage cap for floating solids directed
beneath the weir plate through the floatables trap.
The vertical element of the weir is extended
below the weir plate to retain and store floatables.
(e) Spoilers. Spoilers reduce rotational energy of
the liquid above the weir plate and between the
scum ring and weir, thus increasing the overflow
capacity of the downshaft and improving the sep-
aration efficiency.
(f) Floatables trap. This trap is a surface flow de-
flector which extends across the outer rotating flow
mass, directing floating materials into a channel
crossing the weir plate to a vertical vortex cylinder
located at the wall of the overflow downshaft. The
floating material is then drawn down beneath
the weir plate by the vortex and dispersed under
the plate around the downshaft.
(g) Foul sewer outlet. This outlet is the exit ori-
fice designed to direct peak dry-weather flow and
separated combined sewage solids in the form of
a concentrated slurry to the interceptor.
(h) Primary floor gutter. The primary floor gutter
is the peak dry-weather flow channel connecting
the inlet ramp to the foul sewer outlet, avoiding
dry-weather solids deposition.
(i) Downshaft. During higher-flow storm condi-
tions, the low-volume concentrate is diverted to
the intercepter via the foul sewer outlet, and the
excess relatively clear, high-volume supernatant
overflows the center circular weir into the down-
shaft for storage, treatment, or discharge to the
receiving stream.
The swirl device is capable of functioning ef-
ficiently over a wide range of combined sewer
overflow rules and has the ability to separate settle-
able light-weight organic matter and floatable
solids at a small fraction of the detention time
required for primary separation—seconds to min-
utes as opposed to hours.
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SYRACUSE PROTOTYPE
A 3.6 m (12 ft) diameter swirl combined sewer
overflow regulator was installed at West Newell
Street in Syracuse, New York. Preconstruction
inspections at the test site confirmed that full-pipe
flow conditions occurred during normal springtime
overflows from the 54-acre tributary area. Design
flood flow to the swirl device was based on maxi-
mum carrying capacity of the 24-inch diameter
combined sewer—8.9 mgd—and a design flow for
quality control, in accordance with scale model
investigations of 6.8 mgd.
An ideal installation would not require a pump.
Unfortunately, however, it was not possible to
avoid pumping at the test site. The Syracuse swirl
prototype did not fit between the hydraulic gradi-
ents of the combined sewer inlet and the inter-
ceptor receiving the foul concentrate flow. Without
a pump, dry-weather flow would have caused a
standing depth of about 0.9 m (3 ft) of sewage in the
swirl chamber, resulting in solids accumulation
and a possible septicity condition between storms.
A submersible pump that operates during dry
weather was therefore installed downstream of
the outlet.
!l. .„..,....,, JJ
Profile of Syracuse Swirl Regulator
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Overflow Operation
The facility was designed for immediate re-
sponse to an overflow condition. A flowmeter on
the 0.3 m (12 in) foul sewer outlet line measures
dry-weather flow and the foul concentrate to the
interceptor during wet-weather flow. The average
dry-weather flow range is approximately 1.3 to 2.0
cu m/min (0.50 to 0.75 mgd).
Since the downstream capacity of the inter-
ceptor is 3.4 cu m/min (1.3 mgd), maximum flow is
reached. Flow in excess of 3.4 cu m/min (1.3 mgd)
will be forced over the central overflow weir
where it is measured by another flowmeter,
disinfected, and discharged to the receiving
stream.
When the overflow subsides, the pump reac-
tivates and lowers the water level in the swirl
chamber to allow free gravity flow in the floor gut-
ter to prevent solids from settling. Scour velocity is
maintained between storms. Sampling is per-
formed at the inlet and outfall locations at 15- or 5-
minute intervals during overflow events.
Coarse Floatables Removal
The coarse floatables/scum removal mecha-
nism has worked satisfactorily. During overflows,
floatables are contained by the scum ring fc) in the
outer ring of the chamber, and forced into the
floatables trap (f) and under the weir plate for wet-
weather containment by the swirl action. These
pollutants are subsequently drawn down and re-
moved to the foul sewer during dry weather.
SWIRL REGULATOR
SYRACUSE PROTOTYPE
Wet Weather Operation
Dry Weather Operation
Floatables Entrapment During
Wet Weather Operation
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Maintenance
As the period between storms increases, more
frequent maintenance will be required because
of solids build-up during dry-weather flow. Periodic
pump clogging also occurs from the accumulation
of debris during overflow when the pump is not
operating.
Manual hosing of the chamber walls and floor
was necessary after each overflow. As an overflow
subsided, the flow-through time in the swirl in-
creased from 23 seconds at maximum flow to 9
minutes at minimum flow. This resulted in shoal-
ing of soljds on the chamber floor. Subsequent dry-
weather flowrates and velocities were not great
enough to carry accumulated solids to the floor
gutter and through the foul sewer outlet. Automatic
washdown facilities can eliminate the need for
manual hosedown, and thus reduce maintenance.
The frequency of swirl chamber cleaning is ap-
proximately once per month.
Estimated manpower requirements for the
swirl at West Newell Street are 48 hr/yr (4 hr/
cloggingx 12 clogs/yr) for submersible (single-vaned
impeller) pump cleaning, and 40 hr/yr (4 hr/over-
flow x 10 overflows/yr) for chamber cleaning,
totalling 88 hr/yr. Cost-wise, maintenance
amounts to $1,800/yr.
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SOLIDS SEPARATION EFFICIENCIES
Hydraulic Model
Based on laboratory hydraulic model studies,
suspended solids (SS) removal efficiency for the
swirl treating combined sewer overflows should
be approximately 65 percent. Particle removal ef-
fectiveness was determined to be a function of
effective diameter and specific gravity (or settling
velocity). For grit with specific gravity of 2.65 and
greater than 0.3 mm, removals were over 90 per-
cent; removals decreased to less than 40 percent
for 0.1 mm (0.04 in) grit. For settleable organics
with specific gravity of 1.20, and larger than 1.0
mm, efficiency ranged from 80 to 100 percent; and
for 0.3 mm particles, efficiencies decreased to less
than 20 percent.
Prototype
Relatively good SS removal efficiencies were
determined over the entire storm flow range of
the Syracuse prototype (Table 1). Total mass loading
and concentration removal efficiencies ranged
from 33 to 82 percent and 18 to 55 percent, respec-
tively, with flowrates from 0.54 cu m/min (0.2
mgd) to 20.5 cu m/min (7.6 mgd). Figures 1 and 2
illustrate the total SS mass removals with respect
to time and storm flowrate. The shaded areas be-
tween curves indicate a trend of higher removals
at storm onset when concentrations are generally
higher, and again near the end of the storm when
flowrates drop.
Table I
SUSPENDED SOLIDS REMOVAL
Swirl Concentrator
Conventignal Regulator
Average SS
„ per storm, mg/ 1
Mass Loading
kg
Inf.
Eff.
Rem.b
Inf.
Eff.
Rem.b
Inf.
Mass Loading
kg
Underflow
Rem.a
Jlf- -2-1974
•I- 3'1974
Kt_Z-1974
•lpplO-1974
Rret4-1974
•p£ 1-1975
•r-i-1975
6-1975
•^-12-1975
||fl4-1975
535
182
110
230
159
374
342
342
291
121
115
345
141
90
164
123
167
202
259
232
81
55
36
23
18
29
23
55
41
24
20
33
52
374
69
93
256
99
103
463
112
250
83
117
179
34
61
134
57
24
167
62
168
48
21
52 *
51
34
48
42
77
64
45
,33
42
82
374
,69
93
256
99
103
463
112
250
83
117
101
33
20
49
26
66
. 170 "
31
48
14
72
27
48
22
19
26
64
37
28
19
17
62
fgrjthe conventional regulator removal calculation, it is assumed that the SS concentration of the foul underflow equals the
^S^concentrat/on of the inflow, , , ,
Sa^re/Tect/ngjiegat/ve SS removals at tail end of storms not included.
- -4
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3.96-,
•o
&0
CO
en
c
I
u.
2.64-
7.32-
STORM #1 3/24/75
TOTAL SUSPENDED SOLIDS
o MASS LOADING (INFLUENT)
AMASS LOADING (EFFLUENT)
— FLOW
77:00 72:00 73:00 74:00 75:00 76:00 77:00 78:00
TIME, hrs
Figure 1. Swirl Regulator Suspended Solids Removal, Syracuse, N.Y., Storm #1.
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5.88-n
4.74-
•& 4.20 A
I 3.7 2722
< r-
3
7874-
907-
I I I I I
STORM #2 4/3/75
TOTAL SUSPENDED SOLIDS
O MASS LOADING (INFLUENT)
A MASS LOADING (EFFLUENT)
—FLOW
7:00 8:00 9:00 70:00 77:00 72:00 73:00 74:00 75:00 76:00 77:00
TIME, hrs
Figure2. Swirl Regulator Suspended Solids Removal, Syracuse, N. Y., Storm #2.
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Figure 3 further reveals the trend of greater SS
mass loading reduction as the SS influent concen-
trations increase. Suspended solids influent con-
centrations greater than 250 mg/I generally re-
sulted in removals of better than 50 percent of the
total mass loading to the swirl.
Care must be taken in evaluating swirl solids
treatability since under dry-weather flow condi-
tions, all regulators are designed to divert the en-
tire flow volume and associated solids to the inter-
cepting sewer until a predetermined overflow
rate is reached. This diversion to the interceptor
continues at a maximum throughout the storm.
However, the swirl has the added advantage of
concentrating solids as well as conventionally
diverting flow during overflow events. This con-
centrating effect is evidenced by removal effi-
ciencies in terms of SS concentrations varying
from 18 to 55 percent (Table 1), as previously stated;
whereas conventional regulators are assumed not
to concentrate solids at all (zero percent removal)
(Table 1, footnote a).
If the swirl regulator was replaced by a con-
ventional flow regulator, the net mass loading
reductions (attributable to the SS conventionally
going to the intercepted underflow) would have
ranged from 17 to 64 percent (Table 1) as compared
to a more effective range of 33 to 82 percent (Table
1) for the swirl. This may be a better way to com-
pare the effectiveness of the swirl to conventional
combined sewer overflow regulators since con-
ventional devices will remove the solids associated
with the flow diverted for treatment.
5!
Z
7200-
7700-
7000-
900-
800-
700-
600-
500-
400-
300-
200-
700-
o STORM #6 6/5/75
A STORM #2 4/3/75
X STORM #1 3/24/75
XXX
70
20 30 40 50 60
MASS REMOVAL, %
70
80
90
700
Figures. Swirl Regulator Suspended Solids Influent Concentration
vs Percent Mass Loading Removal, Syracuse, N. Y.
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For low-flow storms, approaching the maxi-
mum dry-weather capacity of the interceptor, the
advantages of swirl concentration are reduced as
would be expected based on the physical principle
of mass balance involved. In other words, as the
ratios of "inflow to foul outlet underflow" or "weir
overflow to foul outlet underflow" decrease, the
SS removal advantage from swirl concentrating
also decreases. This is because the intercepted hy-
draulic loading to underflow becomes more signif-
icant in the net mass loading calculation of the
hypothetical conventional regulator. This phenom-
enon is exemplified by the SS total (of the swirl)
compared to SS net (of the conventional regulator)
mass loading removals of Storm No. 1-1975 (Table 1),
where the hydraulic loadings to the swirl were low,
approaching dry-weather conditions.
Many outfalls are designed to pass 20,100 and
even 1,000 times average dry-weather flow as op-
posed to West Newell Street which, at best, passes
only 10 times average dry-weather flow. For these
cases, the swirl concentrating effect will exhibit
distinct advantages over conventional regulators
for SS removal.
BOD REMOVAL
Prototype analyses indicated BOD5 removals of
50 to 82 percent for mass loading, and 29 to 79 per-
cent in terms of concentration (Table 2). Figures 4
and 5 indicate the trend for BOD5 total mass load-
ings removal for the swirl prototype. Figure 6 in-
dicates higher removals at higher BOD5 influent
concentrations.
Table 2
BOD5 REMOVAL
X%«r -'
jptorm #
Ife975
Mass Loading, kg
Influent
26,545
3,565
12,329
Effluent
4,644
1,040
6,164
Rem. (%)
82
71
50
"."• ; ^ Average BOD5 ^
" per storm, mg/l
Influent
314 "
165
*99
^^i^~,,, ^ -^.^^^.E^.a^^^^-^^^^ag
v. y». -, "•<
Effluent
65
^
70
Rem. (%) a
79
, " " 32 j:
— J-L.^7
-------
J 0
5 0.076-
= 0.752-
P« 0.229-
£ 2 0.305-
907-^
V
£
3.96-1
|
CO
.1
s 7.32-1
2.64-
§
0-
es
in
680-
^.-^
454-
5
2 227~
5TORM #7 3/24/75
5 DAY BOD
o M/ASS LOADING (INFLUENT)
A MASS LOADING (EFFLUENT)
ROW
0-.
77:00 72:00 73:00 74:00 75:00 76:00 77:00 78:00 79:00
TlME,hrs
Figure4. BOD5 Removals, Syracuse, N.Y., Storm #1.
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3*
o-
S-S 0.254
5 28 -
J.ZO
3.96-
CO
7
1 2.64 -
3
u
•V
O 7.32-
0-
_,? 0.508-
907-
680-
5
O 5^
^
^t
0
I I I I I
STORM #2 4/3/75
5 DAY BOD
o MASS LOADING
(INFLUENT)
LOADING
(EFFLUENT)
—FLOW
7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00
TIME, hrs
Figure 5. fiODs Removals, Syracuse, N. Y., Storm #2.
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500 -
O
iu
U
I
u.
Z
I
I
400-
300 -
200 -
700
O STORM #2 4/3/75
X SrORM #7 3/4/75
STORM #7 6/21/74
40 60 80
MASS REMOVAL, %
FigureG. Swirl Regulator BODS Influent Concentrations vs. Percent Mass Loading
Removal, Syracuse, N.Y.
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Costs for the swirl prototype at West Newell
Street (designed to remove 90 percent grit, With-
out pumping) were $55,000 capital ($8,100/mgd or
$1,000/acre) and $2,000/yr operation and main-
tenance. In addition, $13,000 in capital costs were
incurred for pumping. If an automatic pipe and
nozzle washdown were installed, it would cost
an additional $3,500 (estimated).
Swirl cost curves (Figure 7) were developed on
the basis of capital costs experienced at Syracuse
and full-scale costs estimated for another study. It
is assumed that swirl regulator maintenance
requirements are independent of size and that the
person-hour requirements and associated costs
will be 88 hr/yr and $1,800/yr, respectively, as pre-
viously stated.
The West Newell Street design closely matches
full-pipe flood conditions which could be overly safe
for pollution control, especially for larger outfalls.
It is entirely possible to reduce capital costs to
$2,000/mgd and to $200-500/acre.
70-
6-
4-
2-
LEGEND
O EPA-600/2-75-062
A SWIRL PROTOTYPE, SYRACUSE
(AS BUILT, WITHOUT PUMPING)
0 SWIRL PROTOTYPE, SYRACUSE
(PRO1ECTEDFOR100% GRIT REMOVAL)
100% GRIT REMOVAL
90% GRIT REMOVAL
32.4 64.5 96.9 129.0
DESIGN FLOW RATE, mgd
Figure 7. Estimated Construction Cost Curves — Swirl Regulator
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Aside from their use as flow regulator/sepa-
rators, modified swirl devices have been con-
sidered, developed or demonstrated for grit re-
moval and primary treatment of combined sewer
overflows and municipal wastewater as well as
for erosion control and separate urban stormwater
pollution abatement.
THE SWIRL CONCENTRATOR
AS A GRIT SEPARATOR DEVICE
The ability of the swirl flow pattern to effective-
ly remove solids of particular sizes or specific grav-
ities was noted during previous studies as discussed
earlier. A swirl configuration and associated flow
pattern was developed and adapted to effectively
remove grit from either the underflow from the
swirl combined sewer overflow regulator or from
domestic sanitary sewage under EPA Grant No.
S-802219 with the city of Lancaster, Pennsylvania.
Hydraulic model development was performed by
LaSalle Hydraulic Laboratory, Ltd., LaSalle, Quebec,
Canada.
Recently a large pilot swirl concentrator de-
signed as a grit removal facility was tested by the
Metropolitan Denver Sanitary District No. 1 under
EPA Grant No. S-803157. It was found that under the
physical arrangements in Denver and testing with
domestic sanitary wastewater ("spiked" with
0.25 mm dry blasting sand to simulate wet-
weather flow concentrations), the swirl unit per-
formed well. The efficiency of removing grit par-
ticles with specific gravity of 2.65 and sizes greater
than 0.2 mm was equal to that of conventional grit
removal devices. The small size, high efficiency,
and absence of mechanical equipment in a swirl
grit chamber facility offers economic advantages
over conventional systems.
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INLET
GRIT
CHAMBER
WASHWATER
OVERFLOW WEIR
GRIT WASHER
WASHWATER
OUTLET
ADJUSTABLE
WEIR
GRIT WASHER
AND ELEVATOR
SECTION A-A
Grit Chamber /Above Ground With Inclined Screw Conveyor — General Layout Plan
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THE SWIRL CONCENTRATOR
AS A PRIMARY SEPARATOR
In the interest of removing a greater fraction of
suspended solids than the swirl regulator/separator
does, a study was conducted to determine if the
basic swirl concentrator principle could be used to
provide primary treatment to combined sewer
overflows and municipal wastewaters com-
parable to conventional sedimentation. Again, a
hydraulic model with synthetic wastewater was
used to arrive at an optimized configuration and a
design basis. The design was then tested under
actual wet- and dry-weather flow conditions using
a large scale, 0.79 cu m/min (0.3 mgd) pilot con-
structed in Toronto, Canada under EPA Grant No.
S-803157. These studies indicated that the device
closely matched the treatment efficiency of con-
ventional primary sedimentation at an overflow
rate of 65.2 m3/m2 day (1600 gpd/sq ft) which is 2.67
times conventional design. Figure 8 gives a com-
parison of time to achieve treatment between
the swirl and the conventional system at Toronto.
Its height and diameter are equal, thus providing a
relatively deep structure which enhances sludge
thickening.
The relatively high overflow rates or lower
detention times used with swirl concentrator
design at various levels of suspended solids removal
make the device potentially less costly to construct
with less space required, thus enhancing its use in
wastewater plant expansion and combined
sewer overflow treatment. Its static sludge and
scum collection system enhances appeal because
of lower operation and maintenance costs.
60-
50-
40-
30-
20-
10-
0
x= CONVENTIONAL
• = SWIRL
0
60
TIME, in minutes
720
Figure 8. Comparison of Time to Achieve Primary Treatment — Swirl vs. Conventional Sedimentation
— Toronto, Canada
-------
•Y
Swirl Prototype Primary Separator, Toronto, Canada
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THE SWIRL CONCENTRATOR AS
AN EROSION CONTROL DEVICE
Soil erosion and resulting sediment are major
problems. A properly designed and proportioned
swirl concentrator chamber as developed under
EPA Contract No. 68-03-0272 with the American
Public Works Association, Chicago, Illinois, and
LaSalle Hydraulic Laboratory, Ltd., LaSalle, Quebec,
Canada, can perform an effective job of removing
soil erosion particles from stormwater runoff at
construction or other vulnerable sites. This swirl
device can be rapidly and economically installed
at points of erosion runoff by use of a conventional
cattle watering tank having a 3.66 m (12 ft) dia-
meter and a 0.9 m (3 ft) depth, fitted and equipped
with a suitable inlet line, a circular overflow weir,
a foul sewer outlet, and necessary interior ap-
purtenances. Such a chamber could be readily
disassembled, moved to another site, and rein-
stalled for the treatment of erosion runoff flows. If
a permanent structure is desired, it can be fab-
ricated out of concrete.
The de-silted or clarified effluent could be dis-
charged to drainage facilities and disposed of into
receiving waters or other points of disposal or use.
The collected solids could be discharged through the
foul sewer outlet and entrained or collected at suit-
able points for return to the point or points of ero-
sion for use for other predetermined purposes. See
Figure 9.
CONSTRUCTION
SITE
DRAINAGE
AREA
SOLIDS
LACOON
OR
FOREBAY
DETENTION POND
OR
RECEIVING WATER
OVERFLOW
PIPE
OR DITCH
SWIRL
CONCENTRATOR
Figure 9. Swirl Erosion Control Device—Schematic.
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THE SWIRL CONCENTRATOR AS
URBAN STORMWATER RUNOFF
POLLUTION CONTROL DEVICE
Swirls similar to the combined sewer overflow
regulator variety can be installed on separate
storm drains before discharge and the resultant
concentrate can be stored in relatively small
tanks since concentrate flow is only a few percent
of total flow. Stored concentrate can later be di-
rected to the sanitary sewer for subsequent treat-
ment during low-flow or dry-weather periods, or
if capacity is available in the sanitary system, the
concentrate may be diverted to it without storage
(see Figure 10). This method of stormwater control
would be cheaper in many instances than building
huge holding reservoirs and it offers a feasible ap-
proach to the treatment of separately sewered
urban stormwater.
TREATMENT
PLANT
. SANITARY
INTERCEPTOR,
—SMALL CONCENTRATE
TANK
STORM DRAIN
NETWORK
X X
Figure 10. Swirl Urban Stormwater Run-Off Pollution Control Device—Schematic.
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For further information:
The following detailed project reports are avail-
able from the National Technical Information Ser-
vice, Springfield, Virginia 22151.
EPA-600/2-75-062, "The Helical Bend Combined
Sewer Overflow Regulator."
EPA-670/2-74-026, "The Swirl Concentrator as a
Grit Separator Device."
EPA-670/2-74-039, "Relationship Between Diam-
eter and Heights for the Design of a Swirl
Concentrator as a Combined Sewer Overflow
Regulator."
This capsule report was prepared by Richard Field
and Hugh Masters, U.S. Environmental Protection
Agency, Storm and Combined Sewer Sect/on, Ed/-
son, New Jersey.
U.S. GOVERNMENT PRINTING OFFICE: 1977-758-905
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