5382
001R99002
DEVELOPMENT OF AND APPLICATION OF THE SWIRL AND
HELICAL BEND DEVICES FOR COMBINED SEWER
OVERFLOW .ABATEMENT AND RUNOFF CONTROL
By
Richard Field, Chief
and
Richard P. Traver, Staff Engineer
Storm and Combined Sewer Section
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Edison, New Jersey 08S17
at
USEPA - Technology Transfer Seminar Series
on Combined Sewer Overflow
Assessment and Control Procedures
Tp-piTr'---!--.—I—I'—-- * - ' -r j_ , ,
_ ' ' '- ' -^''ton Agency
l< ;- s, ' ' , ^ . ' ' ^
Ciiict^o, I^VLIOU eOo04
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The Combined Sewer Problem
Overflow points are the built in inefficiencies of combined sewers.
Untreated overflows from combined sewers are a serious and substantial
u
Nationwide there are roughly 15,000 to 18,000 combined sewer overflow points.-
The 1977 Clean Water Act (PL95-217) critically fosters counter measures,
planning and construction for combined sewer overflow pollution. In
October 1978, EPA is to submit a report to Congress which in part is to es-
timate 1-hp mimber of years nec.sssa-rv, assuming an annual app-mp-n' afi nn nf $5
billion to correct CSO problems. This is strong indication—thatrcorigress
recognizes, and their willingness to support combined sewer overflow
pollution control.
Physical treatment alternatives are primarily applied for suspended
solids removal and their associated pollutants from wastestreams, and are
of particular importance to storm and combined sewer overflow treatment.
Physical treatment systems have demonstrated a capability to handle high
and variable influent concentrations and flowrates and operate independ-
ent of other treatment facilities, with the exception of treatment and
disposal of the sludge/solids residuals. Both the swirl and helical bend
units have demonstrated good treatment potential for highly variable.
combined sewer overflows.
The practice in the USA of designing regulators exclusively for
flowrate control or diversion of combined wastewaters to the treatment
plant and overflow to receiving waters must be reconsidered. Sewer
system management that emphasizes the dual function of combined sewer
overflow regulator facilities for improving overflow quality by concentrat-
ing wastewater solids to the sanitary interceptor' and diverting excess
storm flow to the outfall will pay significant dividends.
In 1971 a state-of-the-art report on regulators suggested a British
device using VQrtex_flow_patterns could regulate flow and simultaneously
remove solids. _This device would utilize the differences in inertia
between particles and liquid as well as gravitational forces to effect
solids-liquid separation.
Based on this concept, studies were conducted for EPA by the American
Public Works Association (for Lancaster. PA, EP_A^emp_nstration_granjt_jio_. _
S-802208) in conjunction with the LaSalle Hudrauli_c Laboratories, Quebec _
during 1972-1973 for swirl developement to suit American practice and
design optimization for greater solids removal. They produced a universal
design for the swirl regulator/concentrator which has been successfully
demonstrated in Syracuse, NY; and a large-scale 24 foot demonstration
unit in Lancaster, PA.
The dual functioning swirl flow regulator/solids separator has shown
outstanding potential for simultaneous quality and quantity control.
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IntegralParts of Swirl Regulator/Concentrator Desim
The swirl regulator/concentrator is of simple annular-shaped con-
struction and requires no moving parts. An isometric view of the final
form of the device is shown in Figure 1. Again, the swirl provides a
dual-function — regulating flow by a central circular weir spillway
while simultaneously treating combined wastewater by swirl action, which
imparts solids/liquid separation. Dry weather flows are diverted through
a cunette-like channel in the floor of the chamber into the bottom orifice
or foul underflow located near the clear water down shaft to the inter-
cepting sewer for subsequent treatment at the municipal plant. During
higher flow storm conditions, the low-volume concentrate (3-10% total
flow) is diverted via the same bottom orifice leading to the interceptor,
and the excess, relatively clear, high-volume supernatant overflows the
central circular weir into a downshaft for storage, treatment or discharge
to the stream. This device is capable of functioning efficiently over a
wide range of CSO rates and has the ability to separate settleable light
weight matter and floatable solids at a small fraction of the detention
time normally required for primary separation.
Figure 1. Isometric view of swirl regulator/concentrator
Legend: a - Inlet Ramp
b - Flow Deflector
c - Scum Ring
• d - Overflow Weir
a.- Spoilers
f - Floatables Trap
g - Foul Sewer Outlet
h - Floor Gutters
i - Dowrishaft . .. -
j'- Overflow Weir Plate__
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For an essentially static device to perform efficiently under varying
flowrates and suspended solids concentrations, special" attention.must be
given to the various elements within the chamber.
] ' The Inlet Ramp and Transition, .Sectjpji_siip_uld be designed to introduce^
' tne~Incommg flow at the bottom or tne chamber and allow solids to enter ;
at the lowest position possible. The inflow should be nonturbulent to I
prevent solids from being carried directly to the overflow weir along with'
the water and the floor of the ramp should be V-shape to allow for self
cleaning during periods of low flow.
The Flow Deflector is a verticle free standing wall that is an exten-
sion of the internal wall of the inlet ramp. It directs the flow around
the chamber, setting up the swirl or 'spiral hydraulic patterns, thereby
creating a longer particle path and a. greater change for solids separa-
tion.
The purpose of the Scum Ring^ is to prevent floating solids from over-
flowing. It should be extended a minimum of 6 inches below the level of
the overflow weir crest. The Overflow Weir and Weir Plate^ connects to a
Central Downshaft carrying the overflow liquid to discharge. Its underside
acts as a storage cap for floating solids that are directed beneath the
weir plate through the Floatables Trap. The verticle element of the weir
is extended below the weir plate a.minimum of 18 inches to retain and
store floatables. When the liquid level in the chamber decreases after
the rainfall, the floatables exit through the _foul sewer underflow._
The Spoilers are radial flow guides that extend from the downshaft
to the'scum ring and are vertically mounted onjthe weir plate, which break
"up the'turbulent vortex conditions that if allowed to exist would impede
proper function.
The Foul Sewer Outlet or Underflow is strategically located on the
floor of the. ^chamber which allows dry-weather flow and concentrated storm-
flow to exit via the interceptor to the municipal treatment plant. It
is placed at the point of maximum settleable solids concentration and is
designed to reduce the clogging problems that often incapacitate conven-
tional regulators.
Primary and Secondary Floor Gutters are designed for peak dry-weather
flow and are semi-circular in shape to prevent shoaling and solids deposi-
tion.
An Emergency Side Overflow Weir Assembly is present in the current
desing manuals. This allows the swirl to be overdriven to better than twice
its design flowrate(QD)and still maintain effective settleable solids removal
efficiencies. This is accomplished by short circuiting excess flow and
lint aini ng thp intpg-Hty nf thp rham'nA-r'g «;opa-r.ati"" f 1 nw paftP-r-r)<; , .
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Automated or Manually Actuated Flush RingAssemblies located around
the upper portion of the interior wall of the swirl chamber, and beneath '
the floatables trag_ allow fpr_ea_sy jzlean^up^operations following a CSO'
e-yent. . . .
Swirl device hydraulic models were developed using synthetic materials
simulating the particle size distribution and specific gravities of grit
and organics found in domestic sewage, CSO, and erosion ladden runoff that
resulted in a series of design curves relating anticipated performance to
"design flow and other pertinent design parameters.
A number of research reports and papers are available from the USEPA
Storm and Combined Sewer Section located in Edison, New Jersey.
Structurally, swirl regulator/concentrators, swirl degritters, and
swirl primary separators incorporate distinctly_different features. Some
of these differences are illustrated in Figure 2, The selected configur-
ation for each application was a result of consideration of hydraulic
principles and testing of a variety of physical models.
It is hoped that full-scale demonstrations of the degritter and
primary separator will be conducted and that complete technology transfer
documentation on the swirl concept will be accomplished. An amendment has
been added to the ongoing American Public Works Association grant for
additional work to include optimization of the swirl regulator/concentrator
design curves to cover smaller treatment inflow capacities than now exist
and to also prepare a swirl design textbook on all aspects of the device.
Verification of these design curves have been, or will be made, in
pilot and prototype facilities which will be discussed later. ^
Swirl cost curves shown in Figure 3 were developed on the basis
. of.jCapital costs experienced at Syracuse and full-scale costs estimated by
th-eAmerican Public Works Association study. It is assumed that isaintenance
and repair requirements will be similar for the swirl regulator independent
of size and that the person-hour requirements and associated costs will be
88 hours/year and $l,800/yearT~res^e~ctivelyT~ J
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'3 - Inlet Ramp
b • Flow Deflector
c - Scum Ring
d • Overflow V/eir and
•,Yeir Plats
a - Spoilers
I - Floataoles Trap
g - Foul Sawar Outlet
h - Floor Gutters
i - Downshart
(b) SMIRl. PRIMA3Y SEPARATOR
a - Inlet
b -
c - skirt
d - Gutters
• - Clear Effluent Outlet
f • 3affl»
g • Sludga Discharge
inlet
Deflector
Weir and '.Yeir Plates
Spoiler
e - Floor
f - Conical Hooper
Figure 2. Isometric configurations of swirl device in three applications
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10-
o
o
o
o
0
o
Note
a
o
Swirl Concentrator
rit Removal
Swirl Concentrator
90% Grit Removal
Swirl Concentrator
100% Grit Removal
Swirl Concentrator
90% Grit Removal
J_
50
150
200
100
Discharge - CFS
Figure 3. Estimated construction costs — swirl concentrator/regulator
Helical Bend Concentrator/Regulators have been modeled and design
criteria and comparative cost evaluations have been developed. Although
no demonstration projects have been implemented in the United States,
helical bends appear practical as in-line regulator devices commensurate
with, swirl.
The helical bend flow regulator is based on the concept of using
the secondary helical motion imparted to fluids at bends when a total
angle of approximately 60° is employed. Figure 4 illustrates the device.
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INLET
CHANNEL -OR
OVERFLOW
'.VE1R
OUTLET TO
STREAM
TRANSITION SECTION
15D
STRAIGHT
\ SECTION
5D
HELICAL
BEND 60°
NOTES:
1. Scum baffle is not shown.
2. Dry-weather flow shown in channel
,\\ OUTLET TO PLANT
Figure 4. Isometric view of helical bend regulator
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The polluted sewage is drawn to the inner wall. It then _____ _
passes to a_sjs:micircular chajmefTituated" at'a lowef~Tevel~l eliding to the
treatment plant. The proportion of the concentrated discharge will depend
on the particular design. The overflow passes over a side weir for dis-
charge to the receiving waters. Surface debris collects at the end of the
chamber and passes over a short flume to join the sewer conveying the flow
to the treatment plant.
The hydraulic model studies and the computer-mathematical simulation
of the helical bend combined sewer overflow regulator indicates that this
flash method of solids removal, without use of mechanical appurtenances,
can produce excellent efficiencies with reasonable size units in combined
sewer systems.
Model studies have confirmed the pattern of solids deposition in
the deeper channel portion of the helical bend, located along the inner
circumference of the bend section, and the ability of dry-weather flows
in this restricted deep channel to self-scour the deposited solids into the
foul sewer outlet.
The basic structural features of significance in the helical bend
model are: the inlet from the entrance sewer section to the device; the
transistion section from the inlet to the expanded cross section of the
straight-run section ahead of the bend; the overflow side weir and scum
board; and the foul outlet for the concentrated solids removal in the
secondary flow pattern, together with the means for controlling the amount
of this underflow going to the treatment works.
A design manual was developed which will enable engineers to utilize
the helical flow principal for solids removal from combined sewer flows
and to properly regulate the overflow of clarified wastewater to receiving
waters or points of retention and/or treatment.
A demonstration grant has been awarded to the Boston Water and Sewer
Commission to test the feasibility of using the swirl regulator/concentrator
and the helical bend regulator for removing pollutant loads from a separate
'storm sewer serving an urbanized area.
The comparative effectiveness of both units will be monitored by
splitting storm sewer effluent into two 10 cfs influent waste streams.
The foul concentrated sewer effluents for both devices will be drained
into a large receiving sanitary sewer having sufficient hydraulic capacity
and rate of flow to adequately transport without deposition the removed
solids to a treatment facility.
The proposed helical bend regulator is roughly fifty-feet long.
Swirls and helicals of the combined sewer overflow regulator variety
can be installed on separate storm drains before discharge and the re-
sultant concentrate can be stored in relatively small tanks as is shown
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in Figure 5, since concentrate flow is only a few percent of the total
flow. Stored concentrate can later be directed to the sanitary sewer
for subsequent treatment during low-flow or dry-weather periods, or if
capacity is available in the sanitary interceptor/treatment system, the
concentrate may be diverted to it without storage. This method of storm-
water control would be cheaper in many instances than building hugh holding
reservoirs for untreated runoff, and offers a feasible approach to the
treatment of separately sewered urban stormwater.
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STORM DRAIN
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JNTEHCEPTOR
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Figure 5. Swirl urban storm runoff pollution control device schematic
diagram
Site Selection and Design Philosophy __„„_.
The development and refinement of the swirl concentrator/regulator
has received major emphasis by the Storm and Combined Sewer Section. The
unit serves as a compact, static device for removing solids and particulate
material from combined and separate storm sewers during storm flow and for
primary treatment, erosion control and grit separation. A large scale
40 cfs 24 foot diameter swirl regulator/concentrator has just been com-
pleted and is on-line in Lancaster, Pennsylvania. A 10 cfs 12 foot
diameter swirl regulator was constructed in Syracuse, New York in June
1974 and evaluated. The performance of the device is good and extremely
economical providing the dual function of flow regulation and solids
separation. At the present time, the application of the swirl is being
implemented by such programs as the 108 Great Lakes Program, 201
Construction Grants Program and the 208 Areawide Waste Treatment Mana-
gement Program.
But what is the design application philosophy for sizing the swirl
for an actual site? __In _St. _Denis, France, a lOjneter diameter swirl
regulator has been constructed using' a. 10 year storm return period.
In other words, the swirl unit will reach design flow once every 10
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years—not very economical! The second problem with the French swirl
is that the pump for lifting the underflow from either a wet-weather
event or dry-weather flow are incapable of handling the heavy solids
loading.
A reasonable design philosophy for the sizing of_aswir_l_js.to-base
the design on percent of suspend'ed solids removed or percent of flow
treated at a specific site over a long- duration, for example, a-.year.
This means that a proposed location should have long term jqua_lity/
quantity data_j?or each overflow location. It then becomes an easy jLas
arrive"at a mass "loading curvs Tor each rainfall event. By making the
correct cost-benefit choice based on incremental removal versus storm
flowrate and hopefully receiving water impacts, design flow, which re-
lates to swirl chamber size, will readily fall out.
Now, let's come back to reality and how things really are I The
city engineer, consultant, or regional planning council will be lucky
if they have good raingauge data for the catchment area they wish to
apply swirl at, much less than quantity of overflows, or even number
of overflow occurrences.
A rough-cut approach, tp_ see what design flowi (QD) and resulting size
swirl would be applicable for a candidate site can~be made utilizing rain-
fall intensity records for the area in question.Following the determina-
tion of a "ballpark" QQ, and the decision to pursue swirl construction, it
is the responsibility of the consultant to make a characterization of the
subject catchment utilizing quantity/quality simulation models which are
available today in conjunction with some verification data. Only then can
a "cost-effective" decision be made as to what will be the actual design
flow.
An example of this rough-cut methodology can be cited with the ~
Detroit Water and Sewerage Department. An application:.is being pre-
pared for submission to the Region V 108 Great Lakes Program for the
construction of a swirl regulator/concentrator. Five good years of
raingauge data are available for the Schoolcraft Street catchment area.
402 events were recorded of which 115 were discounted as hayinp —
flows too small to trigger an overflow. This leaves us with 28f7 ev.eni-s _
over a 5 year period. Utilizing the simplistic equation Q=Cia, flow-
rates were determined for each rainfall intensity range and a tabulation
of those reoccurring events were tallied. With the desire to treat
approximately 70 percent of the overflow events, the rough-cut size was
determined to be 40 foot diameter based on a design flow of 100 cfs. This
results in having 41 out of 57 events per year at or below QQ. However,
with the ability to overdrive the swirl to at least twice its design
capacity or 200 cfs, and still effect a reasonable removal efficiency,
only 5 events per year are beyond the capabilities of the "rough-cut"
swirl treatment capacity. This particular case had an approximate
rainfall_intensity of .45 inch/hour and an approximate runoff coefficient
of .50. _Again,'this approach is only good enough to get a handle on
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what size facility would be needed. It is the consultant's responsibility
to make the decision on a final Qry after examining sufficient quantity/
quality data for the proposed site.
The following section will deal with brief descriptions of existing
installations which are utilizing the swirl as a regulator concentrator,
degritter, primary separator and erosion control device.
Syracuse, New York^ (Prototype Swirl Regulator/Concentrator)
A 12 foot diameter swirl combined sewer overlfow regulator was
installed at the West Newell Street outfall in Syracuse, New York.
Design flood flow to the swirl device was based on maximum carrying
capacity of the 24 inch diameter combined, .sewer inlet r .8.9 mgd -
and_a_design flow for quality control_(in accordance with scale model
investigations) of 6.8 mgd.
As mentioned earlier, tests indicate that the device is capable
of functioning efficiently over a wide range (10:1) of combined sewer
overflow rates, and can effectively separate suspended matter at a
small fraction of the detention time required for conventional sedi-
mentation or flotation [seconds to minutes as opposed to hours by
conventional tanks),
At least_50 percent removal of suspended solids and BODg were
obtained. ~~ Table__l_ further details suspended solids mass removal and
concentration reduction. The capital cost of the 6.8 mgd Syracuse
prototype was $55,000 or $8,100/mgd and $1,Odd/acre.
Table~ 11 Suspended solids removal
Storm No.
2-1974
3-1974
7-1974
10-1974
14-1374
1-1975
2-197.5
6-1973
12-1975
14-1975
15-1975
Swirl Concentrator [Conv. Reau later
Mass Loading
ka
Inf. Eff. fen.5
374 179 52
69 34 51
93 51 34
256 134 48
99 57 42
103" 24 77
463 1 67 64
112 62 45
250 163 33
83 43 42
117 21 82
Average SS
oer storm, ma/1
00 b
Inf. Err. Rem.
535 245 36
132 141 23
110 90 13
230 164 29
159 1 23 23
374 167 55
342 202 41
342 259 24
291 232 20
121 81 33
115 55 52
Mass Loading
ka
(V a '
Inf. Underflow Rem.
374 101 27
69 33 48
93 20 22 •
255 49 19
99 26 26 .
103 66 64 i
463 170 34-
112 31 27
250 48 19
83 14 17
117 72 61 L
apor the conventional regulator removal calculation, it is assumed that
the SS concentration of the foul underflow equals the SS concentration
of the inflow.
bQata reflecting negative SS removals at tail end of storms not included.
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However, it should be indicated 'at this point that the Syracuse
design closely matched full-pipe flood conditions and could be overly
safe for-pollution control; especially for larger outfalls. It is
entirely possible to further reduce capital costs to: $l,000/mgd
and $200 to $500/acre; in lieu of the thousands of dollars per mgd
and acre usually considered for combined sewer overflow control.
Denver, Colorado [Pilot Swirl Degritter}
A large 6 foot pilot swirl device designed as a grit_remoyal faci1ity.
was tested by the Metropolitan Denver Sanitary District.; Figure 6
exhibits a suggested swirl degritter layout for above-the-ground in-
stallations.
GS1T CHAM8S
INLET
/— WASH WATEH
/ OVBROW V»HR
SECTION A-A
Figure 6. Suggested Swirl Degritter Layout for Above-(he-Ground
' Installation with Inclined Screw Co
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It was found under testing performed on domestic sanitary waste-
water, at times spiked with 0.25mm dry blasting sand to simulate swirl
regulator foul concentrate concentration, that the swirl unit performed
well. The efficiency of removing grit particles was equal to that of
conventional grit removal devices. Scaled up detention times for full
size swirl units having volumes one tenth that of conventional tanks,
were as low as 20 seconds, whereas detention times of one minute and
greater are normal for conventional grit chambers.
The small size, high efficiency and absence of moving parts in the
basic swirl degritter unit offers economical and operational advantages
over conventional grit removal systems.
Toronto, Canada (Pilot Swirl Primary Separator)
A model study was conducted to determine if the swirl concentrator
principle could be used to provide primary treatment to sanitary sewage,
combined sewer overflow, and stormwater. In comparison, the swirl
regulator/concentrator provides a coarser pre-treatment. The design
was then tested on a pilot 12 foot diameter installation with real
sewage at Metropolitan Toronto's Humber wastewater treatment plant.
The studies provided proof of the applicability of the swirl principle
to the function of primary clarifications and verification the design that
was based on hydraulic model optimization. In a short detention period
solids are deposited by inertial and gravity action and agglomeration
mechanisms. Importantly, in storm flow treatment application, suspended
solids will be heavier due to high sewer transport velocities and, there-
fore, will tend to separate more readily which favors swirl separation
over sedimentation.
The basic advantages of the swirl clarification principle are that
it requires: (1) less land than conventional sedimentation, and (2) no
mechanical sludge collection of settled solids in the sludge hopper.
The latter advantage is partially achieved by providing a deep conical
hopper over the entire flood area, thus imposing an increase in costs.
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Annual operation_aiidjna,intenance_^:osts are_estimated to be
less witH~Ene swirl unit, about $5,000 TeTs for 5 mgd. In urban areas
where land is expensive the fact that swirl requires one-half or less the
surface area (according to overflow rates) could make it highly competitive.
The engineer must consider the costs of construction, operation and
maintenance, and land in a cost comparison figure. In the locations where
land is at a premium it is advisable to compare the costs of smaller
parallel swirl units with their lower operation and maintenance costs
against those of conventional tanks. . L
'R6cHester,'New York (Pilot Swirl Primary Separator and Swirl Degritter)
Pilot plant treatability studies were undertaken to delineate the
treatment alternatives available for control of combined sewer overflow
quality under the Monroe County, Division of Pure Waters, Rochester,
New York.
A major emphasis of the study was development of cost/benefit
comparisons of processes that would allow primary-level treatment efficien-
cies. These processes were compared relative to their response to treating
variable Duality confained sewer overflows. Treatment of the highly con-
centrated first-flush overflow was of particular importance.
The pilot facilities included a. swirl degritter^ and a swirl primary-
separator connected in series as shown in Figure 7, The swirl degritter
was 3 feet in diameter and approximately 4 feet in total depth. During
normal operations, the overflow from the degritter became the influent for
the swirl primary separator. Provisions were also made, however, to allow
the influent to bypass the degritter and go directly into the swirl
primary separator. The swirl primary separator was 6 feet in diameter and
approximately 6 feet in total depth including hopper.
Sflim. PRIMARY
SEPARATOR
CSQ
1NR.QV!
ErRUBJT
Figure 7. .Schematic Diagram of Swirl Pilot Facility in Rochester, NY
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The swirl devices were tested at flowrates ranging from 15 to 70 gpm.
Using Froude Law scaling relationships, these translate to flows of 0.2
and 1.0 mgd for a 15 foot diameter swirl primary separator and nominal
overflow rates of 1,245 to 5,705 gpd/ft, respectively. Mathematical
performance models were developed for each system relating suspended solids
removal rates to influent flcwrate [scaled by Froude number) and influent
concentration.
These performance equations were compared to the design curves of the
earlier development studies_for swirl devices. Taking differences of
particle size distributions'into account, the Rochester data generally
supports the design presented by the earlier work.
Lancaster, Pennsylvania (Prototype Swirl Regulator/Concentrator with
Prototype Degritter in Series for Foul Concentrate)^
The original swirl regulator/concentrator and degritter hydraulic
model studies were conducted for the Lancaster, Pennsylvania prototypes.
The prototype system as shown in Figure_8 is being supported by an EPA
demonstration grant. It is comprised of a 40 cfs, 24 foot main diameter
swirl combined sewer overflow regulator/concentrator with a smaller 2 cfs,
8 foot diameter swirl degritter in series to degrit the swirl regulator
foul underflow concentrate prior to its entry to the pumps feeding the
sanitary interceptor. Upstream gTit^ removal will prevent downstream pump-
ing problems, sewer siltation and deposition, and treatment pjroblems in the
Lancaster sewerage system. The relatively clear swirl regulator/coricentaT-~
tor overflow will receive disinfection and go directly to the Conestoga
River. This swirl system will serve a. drainage area of 215 acres.
Figure 8. DemonstTation System Flow Diagram Lancaster, PA
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The contractor's construction cost proposed for this system, which
also contains degritter and control housing, a pilot dicostrainer and
various appurtenances and research instrumentation is $669,000. The capital
cost of the swirl regulator alone was $50,200 or $l,946/mgd or $233/acre.
The Swirl Concentrator as an Erosion Control Device
Erosion-sedimentation causes the stripping of land, filling of surface
waters, and water pollution. Urbanization caused accelerated erosion rais-
ing sediment yields two to three orders of magnitude from 100 - 1000 •
ton/mi2/yr to 10,000 - 100,000 ton/mi /yr. At the present national rate
of urbanisation, i.e., 4,000 acre/day, erosion/sedimentation must be recog-
nized as a major environmental problem.
The swirl concentrator has also been adapted for the reduction of
erosion runoff sediment and other fine grained debris that results from
modern construction activities. Final design specifications are in manual
form. In conjunction with a. demonstration near Columbia, South Carolina
that tested the effectiveness of various soil stabilizers for erosion
control, a. swirl concentrator has been built, place in a highway runoff
channel and prepared for field testing.
A swirl concentrator with a 6 foot diameter was chosen for the test
for its practicality in installation. Both its size and weight were con-
sidered reansonable for manipulation by a 4-man team on the steep highway
.backs lopes_in the test area. Such a _swirl deviceican_jDe rapidly and
ecpnQmi.gaj.ly^ installed at points of erosion runoff by use of ""a" conventional
""cattle watering tank_fitted and equipped with a suitable inlet line, "
circuTar overflow weir, a foul sewer outlet and necessary interior
appurtenances. The total cost for the South Carolina 5.8 cfs unit was
$800 or a cost of $381/acre. This chamber can be readily disassembled,
moved to another site, and reinstalled for the treatment of erosion runoff
flows. If a permanent structure is desired, it can be fabricated out of
concrete.
The de-silted, or clarified effluent could be discharge 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 suitable points of erosion or for use
for other predetermined.purposes.
Closing Remarks
The swirl principal may be employed anywhere it is desirable to remove
solid particles from liquid flows. In the field' of water pollution control
this principle could relate to the degritting of sanitary and storm flows
and to primary separation, sludge thickening, and the final clarification
process. Because the swirl creates a defined mixing pattern it appears
feasible to apply a form of the swirl for the simultaneous enhancement of
chemical coagulation and disinfection while clarification of raw water for
_.pgt_ab_le useage or wastewater is taking p_lace_. The day has now dawned_upon
us where jvuge process, multimillion dollar, high structurally intensive
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recommendations for the treatment of our stormwater, combined sewer over-
flows and urban runoff can no longer be made. The swirl is one of the low
structurally cost-effective alternatives that is now available to be.broueh±_.
into our fight to protect and restore the Nation's receiving waters. ^_
f
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