EPA-600/2-76-271
December 1976
Environmental Protection Technology Series
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1, Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4, Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to develop and
demonstrate instrumentation, equipment, and methodology to repair or prevent
environmental degradation from point and non-point sources of pollution. This
work provides the new or improved technology required for the control and
treatment of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-76-271
December 1976
THE SWIRL CONCENTRATOR FOR EROSION RUNOFF TREATMENT
By
Richard H. Sullivan, American Public Works Association
Morris M. Cohn, Consultant
James E. Ure, Alexander Potter Associates
F. E. Parkinson, LaSalle Hydraulic Laboratory, Ltd.
Paul E. Zielinski, Clemson University
Contract Number 68-03-0272
Project Officer
Richard Field
Storm and Combined Sewer Section
Wastewater Research Division
Municipal Environmental Research Laboratory (Cincinnati)
Edison, New Jersey 08817
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S.ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
The Municipal Environmental Research Laboratory —
Cincinnati, has reviewed this report and approved its
publication. Approval does not signify that the contents
necessarily reflect the views and policies of the U.S.
Environmental Protection Agency, nor does mention of trade
names or commercial products constitute endorsement or
recommendation for use.
11
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FOREWORD
The Environmental Protection Agency was created because of
increasing public and government concern about the dangers of
pollution to the health and welfare of the American people.
Noxious air, foul water, and spoiled land are tragic testimony to the
deterioration of our natural environment. The complexity of that
environment and the interplay between its components require a
concentrated and integrated attack on the problem.
Research and development is that necessary first step in
problem solution and it involves defining the problem, measuring its
impact, and searching for solutions. The Municipal Environmental
Research Laboratory develops new and improved technology and
systems for the prevention, treatment, and management of
wastewater and solid and hazardous waste pollutant discharges from
municipal and community sources, for the preservation and
treatment of public drinking water supplies, and to minimize the
adverse economic, social, health, and aesthetic effects of pollution.
This publication is one of the products of that research; a most vital
communications link between the researcher and the user
community.
As part of these activities, the study described here investigated
the applicability of a swirl concentrator chamber to perform the
function of concentrating erosion products from stormwater runoff.
Francis T. Mayo
Director
Municipal Environmental
Research Laboratory
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ABSTRACT
A device for the partial removal of erosion
products in stormwater runoff has been developed.
The swirl concentrator as an erosion control device
has been designed to concentrate the heavier soils
from large flows. The concentrated underflow of
up to 14 percent of the flow can be directed to a
forebay or settling basin.
The device is circular and for small watersheds
a simple stock watering tank could be used with
only minor modifications.
The design of the swirl concentrator as an
erosion control device is based upon a hydraulic
model study and research previously sponsored by
the City of Lancaster, Pennsylvania and the U.S.
Environmental Protection Agency into the
mechanics of secondary motion flow-fields as
developed in the swirl concentrator.
This report is submitted by the American
Public Works Association in partial fulfillment of
the contract 68-03-0272 between USEPA and
APWA Research Foundation.
iv
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CONTENTS
Page No.
Chapter I Overview, Conclusions and Recommendations 1
Chapter II The Study 6
Chapter III Design Factors for Swirl Erosion Runoff Treatment Prototypes 13
Chapter IV Glossary of Pertinent Terms 31
Chapter V Appendix — LaSalle Hydraulic Laboratory Report 32
TABLES
1 Sieve Analysis 24
2 Swirl Efficiency Analysis 26
3 Modifications Tested in Model and Results 45
4 Comparable Recovery Rates for Sloping and Horizontal
Chamber Floors 62
5 Percent Suggested Recovery in Model 69
FIGURES
1 Schematic View, Swirl Concentrator as an Erosion
Runoff Treatment Facility 3
2 Flow Diagram 4
3 Model Layout 9
4 Original Layout for Test No. 1 10
a Plan and Elevation 10
b Photos, Original Layout and Original Layout with Inlet Baffle 11
5 Prototype Particle Sizes Represented by Gilsonite — 1.06 14
6 Recovery Rates on Model as Function of Particle Settling
Velocity and Discharge with 5 Percent Draw-off 15
7 Recovery Rates on Model as Function of Particle Settling
Velocity and Discharge with 10 Percent Draw-off 16
8 Recovery Rates on Model as Function of Particle Settling
Velocity and Discharge with 14 Percent Draw-off . 17
9 Predicted Prototype Recovery Rates with 5 Percent Draw-off 18
10 Predicted Prototype Recovery Rates with 10 Percent Draw-off 19
1.1 Predicted Prototype Recovery Rates with 14 Percent Draw-off 20
12 General Design Dimensions, Scale — 1:4 .21
13 Prototype Particle Sizes Represented by Petrothene — SG 1.01 25
14 Standard Stock Watering Tank 29
15 Gradation Curve for Gilsonite Used in Model 34
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FIGURES (Continued)
Page No.
16 Prototype Settling Velocities Simulated by Gilsonite - SG 1.06 35
17 Gradation Curve for Petrothene Used in Model 37
18 Prototype Settling Velocities Simulated by Petrothene-SG 1.01 38
19 Prototype Particle Sizes Represented by Petrothene - SG 1.01 . 39
20 Range of Prototype Grit Particle Sizes (SG 2.65) Simulated,
Respectively, by Gilsonite, Petrothene and Petrothene Dust 40
21 Settling Velocity Distributions for Petrothene Dust and
Stormwater Runoff 41
22 Settling Velocity Distributions for Shredded Petrothene X
and Stormwater Runoff 42
23 Settling Velocity Distribution for Gilsonite and
Stormwater Runoff 43
24 Model Layout for Tests 2 to 13, Modification 1 47
a Plan and Elevation . . 47
b Photos, Uneven Flow Spoilers Stuck on the 50.8 cm (20 in.)
Weir Disk and Modification 1, Tested with a 3 I/sec
(0.8 gal/sec) Discharge . 48
25 Photos, Deposit of Petrothene Found After 3 I/sec (0.8 gal/sec) Test 49
26 Influence of Inlet Deflector on Recovery Rate 0.50 m (20 in.) $
Weir Disk 5 Percent Draw-off, Modification 11 50
27 Model Layout for Tests 14 to 16, Modification 2 '51
28 Model Layout for Tests 17 to 19, Modifications 53
29 Photos, Inlet Baffle, Modification 3 54
30 Model Layout for Tests 20 to 22, Modification 4 55
31 Photos, Details, Modification 4 56
32 Model Layout for Tests 23 to 3 ^Modifications 5, 6, and 7 57
33 Model Layout for Tests 3 2 to 3 5, Modifications 58
34 Model Layout for Tests 36 to 38, Modification 9 59
35 Photos, Details, Modification 7 60
36 Influence of Weir — Chamber Diameter Ratio 61
37 Model Layout for Tests 39 to 41, Modification 10 63
38 Model Layout for Tests 42 to 59 and 69 to 107, Modification 11 64
39 Influence of Chamber Floor Slope 65
40 Influence of Continuous Underflow Draw-off, Modification 11 66
41 Model Layout for Tests 60 to 68, Modification 12 67
42 Influence of Inlet Size 68
43 Suggested Recovery Curves for Gilsonite and Petrothene in
Model with 5 Percent Draw-off 70
44 Suggested Recover Curves for Gilsonite and Petrothene in
Model with 10 Percent Draw-off 71
45 Suggested Recovery Curves for Gilsonite and Petrothene in
Model with 14 Percent Draw-off 72
46 Retention Times for Prototype 73
VI
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ACKNOWLEDGEMENTS
The American Public Works Association is
deeply indebted to the following persons and their
organizations for the services they have rendered to
the APWA Research Foundation in carrying out
this study for the U. S. Environmental Protection
Agency.
PROJECT DIRECTOR
Richard H. Sullivan
CONSULTANTS
Dr. Morris M. Cohn, P.E., Consulting Engineer
Paul B. Zielinski, P.E.
ALEXANDER POTTER ASSOCIATES, CONSULTING ENGINEERS
Morris H. Klegerman, P.E.
James E. Ure, P.E.
LA SALLE HYDRAULIC LABORATORY, LTD.
F. E. Parkinson
George Galina
U. S. ENVIRONMENTAL PROTECTION AGENCY
Richard Field, P.E., Project Officer, Chief, Storm & Combined
Sewer Section (Edison, New Jersey)
VII
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AMERICAN PUBLIC WORKS ASSOCIATION
Board of Directors
Ray W. Burgess, President
John J. Roark, Vice President
Herbert A. Goetsch, Immediate Past President
Robert D. Bugher, Executive Director
Joseph F. Casazza
John T. Carroll
William B. Drake
Lambert C. Minis
James J. McDonough
Robert D. Obering
Robert C. Esterbrooks
James E. McCarty
Kenneth A. Meng
Frank R. Bowerman
N. W. Diakiw
Rear Admiral A. R. Marschall
APWA RESEARCH FOUNDATION
Board of Trustees
Samuel S, Baxter, Chairman
Ross L. Clark, Vice Chairman
Robert D. Bugher, Secretary-Treasurer
Richard H. Sullivan, General Manager
John F. Collins
Jean L. DeSpain
William B. Drake
Richard Fenton
William C. Gribble, Jr.
Erwin F. Hensch
John A. Lambie
Harold L. Michael
vm
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CHAPTER I
OVERVIEW, CONCLUSIONS AND RECOMMENDATIONS
Overview of the Study Project
The discharge of erosion runoff solids and
other debris into receiving waters represents a
source of water pollution of significant
proportion. Numerous points of construction
and reconstruction which involve disturbance
of the native soil and earth-moving operations
make control of erosion and treatment of
such runoff stormwaters an important factor
in protecting the nation's water resources,
eliminating damage to reservoirs and other
water areas, and preventing impairment of the
natural beauty of the land.
The recent level of such construction as
subdivision housing and highway projects may
continue and increase in the future, adding
further reason for invoking the principle of
control and treatment of erosion wastewaters.
Study of the application of the swirl
solids-liquid separator for the removal of
suspended solids contained in stonnwater
erosion flows is a natural consequence of the
proven ability of such secondary-flow
patterns in similar hydraulic devices to
remove substantial amounts of solids from
combined sewer overflows during wet-weather
flow incidents; to classify and separate grit
from sanitary and combined sewer
wastewaters; and to achieve clarification, or
primary treatment, of wastewaters in
treatment plants. These solids-removal uses of
swirl chambers have been demonstrated in a
series of sequential hydraulic and
mathematical model studies carried out as
parts of previous investigations by the
American Public Works Association (APWA)
Research Foundation for, and on behalf of,
the U.S.Environmental Protection Agency
(USEPA) and other involved entities. These
reports include:
• The Swirl Concentrator as a Combined
Sewer Overflow Regulator Facility,
EPA-R2-72-008
• Relationship Between Diameter and
Height for the Design of a Swirl
Concentrator as a Combined Sewer
Overflow Regulator, EPA-670/2-74-039
• The Swirl Concentrator as a Grit
Separator Device, EPA-670/2-74-026
« Helical Bend Combined Sewer Overflow
Regulator, EPA-600/2-7 5-062
These studies were, in particular, directed
toward solution of point pollution problems.
In addition, studies are being conducted
by Onondaga County, Syracuse, New York,
USEPA Grant No. S-802400 - swirl overflow
regulator, full-scale prototype; Metropolitan
Toronto, Ontario, USEPA Grant No.
S-803157; - swn-i primary separator, pilot;
Metropolitan Sewer District No. 1, Denver,
Colorado, USEPA Grant No. S-803157 -
swirl degritter, pilot; Monroe County Pure
Waters Agency, Rochester, New York,
USEPA Grant No. Y-005141, swirl primary
separator and degritter, pilots; The University
of Wisconsin, Milwaukee, project, grit and
floatables; and Clemson University, South
Carolina, project, aquiculture wastes.
The study of the applicability and
capability of modified swirl concentrator
chamber facilities to serve a related
solids-removal function for nonpoint
pollution control resulted from the successful
demonstrations of these direct uses in sewer
systems. The utilization of the swirl
secondary-flow pattern to alleviate a nonpoint
drainage pollution problem is, therefore, a
"fourth-generation" approach to a related
resources protection need. The simplicity of
the model swirl device studied, and of the
proposed prototype units for actual field
installations, should offer a workable
opportunity to apply this hydraulic principle
for the correction of a major source of water
and land resources despoilation.
The final result of the model erosion
treatment studies undertaken by the APWA
Research Foundation at the LaSalle Hydraulic
Laboratoiy at LaSalle, Quebec, has been to
provide the basis of an economical, effective
swirl device which can utilize a relatively
inexpensive standard cattle watering tank,
properly modified, fitted, and equipped, for
the purpose of removing adequate amounts of
earthen material contained in
nonpoint-stormwater erosion runoff flows.
The use of a conventional, purchasable basin
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or tank which can be installed at a point to
intercept and treat erosion waters offers the
added advantage that this unit can be
removed with minimum effort and expense,
transferred to another location and reinstalled
to handle such flows at any other point of
erosion. This flexibility makes the swirl device
useful during construction work, and
removable and reusable in connection with
other similar projects. It, therefore, falls into
the category of a construction "tool" which
contractors or governmental or private field
crews can use to meet temporary needs.
The development and demonstration of
the performance of the model swirl erosion
runoff treatment unit involved the use of a
0.9-m (3 ft) scaled -laboratory hydraulic
model made of Plexiglas® fitted with a pipe
inlet, a 15.24-cm (6 in) control circular
overflow pipe and spill weir for clarified
storm erosion water, a foul sewer outlet, and
other investigative internal appurtenances.
Facilities were provided for the measured
introduction of small particles of Petrothene®
and Gilsonite® specific gravity 1.01 and 1.06
respectively, into the incoming water stream
to simulate grit and other solids material in
erosion runoff, and for collection and
evaluation of solids discharged through the
foul sewer outlet and contained in the
clarified overflow.
A series of twelve modifications were
made in the internal structure of the swirl
model. A cycle of 62 exhaustive performance
tests was carried in the swirl chamber,
covering liquid flow and solids separation
phenomena under these modifications. After
investigation of all of the variations in the
model, the studies were finalized in terms of
the optimum configuration and ratio of sizes
and locations of the variable components.
Original studies of performance with a sloping
bottom floor were discontinued and
subsequent findings were based on a flat-floor
configuration. This made it possible to
translate design criteria in terms of use of
standard cattle watering tanks as the "shell"
of prototype swirl chambers for treating
erosion storm flows.
The effect of continuous draw-off of
collected grit material, via the swirl
concentrator chamber foul sewer outlet, on
solids recovery demonstrated the beneficial
effects of such removal on entrained solids.
The hydraulic studies served as the basis for
the evolvement of suggested recovery rate or
performance curves, influenced by foul
material draw-off and particle settling
velocities. General design dimensions were
ascertained for actual prototype installations;
designing engineers will be provided with the
structural, and appurtenant design criteria and
step-by-step instructions on how to utilize the
study curves to determine and predict swirl
removal performance levels.
Figure 1, Schematic View, Swirl
Concentrator as an Erosion Runoff Treatment
Facility, shows the essential features of the
device. ;
The essential features, as indicated on
Figure 1 include:
a) a round outer shell
b) a flat floor
c) an internally supported clear water
overflow weir with a bottom discharge
d) a concentrate discharge take-off to a
settling basin
e) a baffled inlet to insure the development
of the swirl flow field
f) flow spoilers to improve the efficiency of
the circular discharge weir.
Figure 2, Flow Diagram, indicates the
basic assumptions concerning the use of the
device. A permanent installation will require a
flow-splitting diversion device, where multiple
units are used, and bar screens to protect the
units from coarse debris. A settling pond or
other facility will be required to handle the 5
to 14 percent concentrated' underflow from
the swirl assembly. The clarified flow may be
run into a detention pond or directly into
receiving water, based upon the degree of
protection against erosion solids required by
receiving water quality standards.
Conclusions
The following conclusions can be drawn
from the studies carried out at the LaSalle
Hydraulic Laboratory, LaSalle, Quebec, on
the applicability and capability of the swirl
concentrator for the treatment of surface
erosion runoff.
• A properly designed and proportioned
swirl concentrator chamber can perform an
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LEGEND
a — Inlet
b — Flow Deflector
c — Spoilers
d—Overflow Weir
e-Weir Plate
f — Overflow (clear)
g — Underflow (solids)
h —Floor
FIGURE 1 SCHEMATIC VIEW, SWIRL CONCENTRATOR AS
AN EROSION RUNOFF TREATMENT FACILITY
effective job of removing erosion particles
from stormwater runoff, and thereby
markedly reduce the effects of soil erosion
and the impact of such earth solids on
contiguous land and surface waters which are
the recipients of the erosion materials.
• Such a swirl device can be rapidly and
economically installed at points of erosion
runoff by use of a standard or conventional
cattle watering tank having a 3.66-m (12 ft)
diameter 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 appurtenances. Such a
chamber could be readily disassembled,
moved to another site, and reinstalled for the
treatment of erosion runoff flows.
• The desilted, or clarified effluent could
be discharged to drainage facilities and
disposed of into receiving waters or other
points of disposal or use. The collected matter
could be discharged through the foul sewer
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UNDERFLOW
DRAINAGE
AREA
SOLIDS
LAGOON
OR
FOREBAY
RETENTION POND
OR
RECEIVING WATER
OVERFLOW
SWIRL
CONCENTRATOR
PIPE
OR DITCH
FIGURE 2 FLOW DIAGRAM
outlet and entrained or collected at suitable
points for return to the point or points of
erosion or for use for other predetermined
purposes.
• An inlet baffle, extending from the
inlet to a point tangent to the overflow weir,
can double the solids removal effectiveness' of
the swirl chamber.
• The retention of floatable materials in
the chamber, by means of a concentric skirt,
is not feasible; however, floatables from
nonpoint runoff are not anticipated to be a
problem.
• A weir-to-chamber diameter ratio ,of
2:3 will produce the optimum clarification
efficiency in the swirl clarification device.
• Continuous draw-off of the collected
erosion material through the foul sewer
opening in the bottom of the swirl chamber
enhances the solids removal efficiency of the
unit.
• An inlet pipe-to-chamber diameter
ratio of 1:6 will produce effective grit solids
removal efficiencies for low, intermediate,
and high rates of erosion runoff discharges.
• Use of standard cattle watering tanks
for the swirl chamber will be simplified if the
chamber bottom is left flat, rather than being
sloped to the point of foul sewer outlet. If
higher degrees of erosion runoff clarification
are desired, and if the cost of installing a
sloping floor in the swirl cattle watering
chamber is merited, increases in efficiency
may be achieved, ranging from 10 to 25
percent for maximum and minimum discharge
rates, respectively.
• Based on the hydraulic;model studies,
practicable prototype design: criteria have
been developed and a step-by-step design
procedure utilizing rational design curves and
detailed sketches has evolved.
Recommendations
The erosion of soil and other native or
indigenous materials at points ;of unprotected
land areas, such as at general construction
sites, housing developments,1 and highway
location and relocation projects, can be
damaging to the nation's land and water
resources. Various means should be instituted
to prevent the washing or scouring of such
materials and the disturbance of sites, and the
damaging of environmental aesthetics. When
erosion has occurred, or is occurring, it is
beneficial to intercept the disturbed soil
material and to make provision for its return
to the eroded areas, or to make provision for
its use for other purposes. Treatment of
erosion runoff waters will prevent obvious
and visible water pollution conditions and
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prevent heavy siltation of reservoirs, streams,
and lake areas.
The ability of a simple swirl chamber
constructed of a standard cattle watering tank
to be moved and reinstalled at other sites — as
demonstrated by hydraulic model studies
carried out under this investigation project at
the LaSalle Hydraulic Laboratory — should
promote its utilization for erosion runoff
treatment.
« It is recommended that erosion runoff
treatment units of the swirl type be installed
at a number of sites in accordance with
prototype design recommendations. These
prototype units should be placed under
technical study to ascertain their solids
removal efficiency under practical field
conditions.
• Any modifications in basic design, or
in the size and location of appurtenant parts
of the swirl device, should be researched to
compare findings with other installations in
the first prototype group and to establish
standards for future utilization of this simple
treatment device.
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CHAPTER II
THE STUDY
Because of the potential impact of
erosion runoff on water quality and soil
conservation and current concern over
corrective actions that will prevent such
conditions, APWA, under contract to the
US EPA, has conducted a study of the
applicability of the simple, economical swirl
concentrator principle to the problem of
removing erosion products from stormwater
runoff.
The hydraulic model studies1'4 were
carried out at the LaSalle Hydraulic
Laboratory, where all of the previous
investigations of the swirl concentrator were
performed for APWA-USEPA research
projects. The research swirl facilities which
were utilized in the previous studies of
combined sewer overflow regulation and
clarification,1-2 removal of grit from
wastewater flows,3 and the primary treatment
of wastewaters4 were modified for this study.
Full utilization was made of the
principles that were developed during the
preceding swirl chamber investigations.1"4
Background data developed by Beak
Consultants, Ltd., Rexdale, Ontario, Canada,
on the nature of wastewater solids and the
choice of solids materials that will simulate
field conditions in laboratory studies, were
the basis for the choice of Petrothene and
Gilsonite for the erosion solids studies.
The principle involved in the swirl unit
for the erosion runoff studies was to produce
swirl-action secondary-flow patterns in a
rotational-velocity chamber which will
separate solids from liquids in erosion runoff
wastewaters. The deposited solids would be
removed from the bottom of the chamber
through a foul sewer connection; the clarified
liquid would be discharged over a central
weir, through a shaft. Monitoring of the solids
contained in the bottom draw-off and in the
clarified effluent would be performed by
trapping and measuring these solids; the
recovery efficiency would be determined by
comparing the bottom material with the total
solids injected into the inflow to the swirl
concentration chambers by means of a
feeding device.
The model previously fabricated for other
swirl studies was used; it was modified to
simulate, by scale-up procedures, a
commercial cattle watering tank which would
constitute the proposed field prototype
installation. The 0.9-m (3 ft) diameter model
was, therefore, on a scale of 1:4 with the
3.66-m (12 ft) cattle watering tanks available
in the commercial market. Inlet facilities,
interior appurtenant units, a bottom solids
draw-off connection, and an overflow weir
and downdraft effluent pipe were installed.
The bottom of the model was first tested with
a 1:15 concrete floor slope. The floor was
later made flat, to represent the bottom of
the commercial cattle watering tank proposed
as a prototype unit that would be 0.9 m (3 ft)
deep.
The Plexiglas outer shell of the swirl
chamber was 13 mm (0.5 in) thick. In the
center of the cylinder, an imbedded polyvinyl
chloride (PVC) pipe, 15.2-cm (6 in) inside
diameter, was installed to serve as the
downdraft outlet for the clarified erosion
water that would spill over the circular weir
supported by the vertical pipe structure. The
weir was maintained at a height of 0.61 m (2
ft) over the swirl concentrator chamber
bottom during the entire series of tests
performed with the unit.
The inlet pipe for the chamber was 15.2
cm (6 in) in diameter, set at a slope of
1:1,000. The test solids introduced into the
swirl concentrator chamber, with water
supplied from a constant-level tank in the
laboratory's supply system, were injected into
the inlet pipe by means of a vibrating feeder
upstream from the swirl chamber. The rates
of flow tested during the course of the studies
of chamber modifications were 3, 5, and 7
I/sec (0.8, 1.3, and 1.8 gal/sec). These flows,
respectively, represented the following
erosion water flows in the proposed
prototype:
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3
0.8
96
25
0.096
3.39
1289.2
2.19
5
1.3
160
42
0.160
5.65
13815.3
3.65
7
1.8)
224
59)
0.224
7.91)
19341.4
5.11)
3
0.8
96
2.19
54.2
5
1.3
160
3.85
32.5
7
1.8)
224
5.11)
23.2
Model Q I/sec
(Model Q gal/sec
Prototype Q I/sec
(Prototype Q gal/sec
Prototype Q m3/sec
(Prototype Q ft3/sec
Prototype Q m3/day
(Prototype Q mgd
The prototype unit, 3.66 m (12 ft) in
diameter, with an effective depth of 61 cm
(24 in) from the floor to the crest or lip of-
the overflow weir, will serve as a "flash"
solids separator. The overflow pipe would be
0.67 m (2.2 ft) in diameter. The overflow
liquid would experience short detention times
in the chamber, as shown by the following
data:
Model Q I/sec
(Model Q gal/sec
Prototype Q I/sec
(Prototype Q mgd
Prototype sec
detention
Grit Simulation in the Model Studies
To carry out meaningful studies of swirl
concentrator chamber efficiencies in the
removal ;of the type of soil solids contained in
erosion runoff wastewaters, it was necessary
to determine the type of laboratory test
materials which would best simulate actual
field conditions.
Gilsonite was chosen for laboratory
studies because it simulated the major range
of grit material that would be encountered in
prototype operation. The Gilsonite had a
specific gravity of 1.06. Its gradation sizes, or
particle sizes, were determined and settling
velocities corresponding to these sizes for the
model and prototype at 1:4 scale were
ascertained in accordance with techniques
described in the literature, and based on
irregularly shaped particles. For the range of
prototype settling velocities simulated by the
Gilsonite test material, the study was able to
determine the particle sizes for the type of
grit that would be contained in actual erosion
runoff, with a specific gravity of 2.65.
Because of the relatively large particle sizes
which the Gilsonite simulated, it was
determined that shredded Petrothene, with a
specific gravity of 1.01, would best represent
actual prototype grit in the laboratory model
studies, and that Petrothene dust, which had a
grain size range of 0.5 to 3 mm (.02 to .12
in), should be studied because it had lower
settling velocities than shredded Petrothene.
Because of the ease in handling the
Petrothene, this material was chosen as the
simulating material in subsequent tests carried
out for the purpose of exploring modified
swirl chamber configurations and appurtenant
structural formats that would achieve the best
possible solids recovery performance. The
same type of settling velocity studies made
with Gilsonite were repeated for the
Petrothene particles. Families of curves to
define these characteristics were evolved from'
these study procedures. The work carried out
by Beak Consultants, Ltd.,5 in connection
with previous studies of swirl units for other
applications was utilized in the erosion
clarification studies. The final result was the
development of settling velocity distribution
curves that would predict the ability of
prototype installations to recover erosion
solids, based on extrapolation of model tests
solids at a 1:4 scale, when scaled in
accordance with Froude's Law.
Some of the laboratory Petrothene dust
particles, and the silts and clays that will be
contained in erosion runoff waters in actual
field operations were found to lie in the
general range of colloids. The short-time
detention of erosion runoff in a swirl
concentrator could not possibly achieve
removal of such fine solids and the studies
made no pretention of being able to
accomplish their removal.
Model Test Procedures
The tests of solids separation in the
model were carried out under steady-state
flows, despite the fact that any field
prototype would be subjected to a wide range
of flow rates during the course of any storm
event. A liter (0.26 gal) of the test solids was
added to the incoming flow over a 5 minute
period and the model was operated for 10
minutes after the cessation of the injection
period. The solids retained in the swirl
chamber, the amount collected in the settling
-------
basin used to capture and gauge the effluent
overflow, and the material entrained in the
foul sewer settling tower were measured.
Efficiencies of solids recovery were
computed.
These efficiency determinations made it
necessary to provide wells or basins for
collecting the slurry discharge from the foul
sewer and the clear water overflow from the
swirl chamber. Flow was gauged in the clear
effluent overflow collecting basin by means of
a calibrated V-notch weir. The foul sewer
settling tower was equipped with a discharge
line that could be adjusted in height to
modify the withdrawal of underflow from the
swirl chamber at predetermined rates. Figure
3, Model Layout, shows the details of the test
unit and its gauging and control facilities.
Brief tests of solids recoveries under three
variations of flow rates, utilizing the original
model layout, as shown in Figure 4, Original
Layout for Test No. 1, with a flat disc weir,
showed that the flow pattern induced in the
unit was an unstable vortex, rather than a true
swirl, at even the lowest flow rate. A baffle
was installed to overcome this vortex action,
extending from the inlet pipe to the periphery
of the overflow weir, but the vortex flow
pattern persisted. Flow spoilers were installed
on the flat disc weir, shaped irregularly to
produce better flow distribution in four
quadrants of the weir. Solids recovery rates
were uniformly high - approximately 95
percent — with Gilsonite. The use of the flow
deflector or baffle was found to enhance
solids recovery. This baffle was used in all
subsequent model tests.
Extended series of twelve structural
modifications were made in the swirl
chamber's internal facilities, and a total of 62
specific tests were conducted, involving
different flow rates, changes in foul sewer
draw-off rates, and the use of different
laboratory model solids — Gilsonite, shredded
Petrothene and Petrothene dust. The various
structural changes or configurations, the type
of solids injected into the incoming flow, the
rate of draw-off, and the solids recoveries
achieved are tabulated in the full report of the
LaSalle Hydraulic Laboratory, contained in
Chapter V.
Various modifications were tested in the
model. In all of the modifications, except
one, the inlet size was 15.2 cm x 15.2 cm (6
in x 6 in). The modifications produced
varying solids recovery efficiencies, ranging
from a high of 99.5 percent to a low of 42
percent for a model flow rate of 3 I/sec (0.78
gal/sec); from 95 percent to 25 percent for
model flows of 5 I/sec (1.3 gal/sec); and from
95 percent to 12 percent under flows of 7 I/sec
(1.8 gal/sec). The highest consistency in solids
recovery occurred at the lowest hydraulic
loading rate. Gilsonite recoveries were generally
higher than for the smaller and lighter Petro-
thene materials. The use of an inlet baffle and
flow spoilers was found to improve solids
recovery.
Chapter V describes the model test
procedures, the nature of the model
modifications and the recovery levels. It
explains the influence of the weir crest and
the spiral flow.guide on shredded Petrothene
recovery; the effect of a concentric skirt for
collecting floatable solids in the swirl chamber
on solids separation; the influence of weir
diameter on solids recovery; the effect of
chamber floor slope on chamber efficiency;
the influence of continuous underflow
draw-off on solids separation; and the
influence of inlet size on swirl chamber
performance. Similar studies were carried out
with Petrothene dust, used to simulate the
smaller solids particles which will enter actual
prototype swirl chambers in the form of
native silts and clays carried with heavier
eroded materials by storm runoff waters.
As a result of the complex series of
studies with model structural modifications,
while handling the three types of simulated
test solids at the three rates of flow applied to
the laboratory model, the LaSalle Laboratory
evolved rational estimates of solids recoveries
in the model and developed a design
procedure. Two examples of the design
procedure are contained in Chapter III.
-------
Foul outflow Foul solids
settling tower rscovery screen
Chamber cylinder 13 mm (O.S in.)
plexiglass -914 mm (36 in ) dia
Clear outflow settling basin
P 1'Vi H V f h
i /
/I
Clear water overflow outlet
pipe 102 mm (4 in ) plexiglass
Discharge returned to
pumping station
r\
Calibrated V-notch weir
////////A/////////////////////////////
Clear outflow settling basin
Foul outlet
discharge
control
Butterfly control
valve
PVC Supply pipe
Small water supply
for solids injection
Water supply from
pumping station
Foul Outlet
discharge control
Chamber cylinder 13 mm (0.5 in )
plexiglass - 914 mm (36 in.) dia
PVC
Supply
pipe
Foul outflow
settling tower
Butterfly
control valve
Clear water overflow pipe
102 mm (4 in) plexiglass
Foul solids
recovery screen
ELEVATION
Section A-A
FIGURE 3 MODEL LAYOUT
-------
0.91 m 0 Chamber
(36 in)
INLET
15.2 cm x 15.2 cm
(6 in x 6 in)
270
FOUL OUTLET
320°
0.50 m Weir
(20 In)
PLAN
To Overflow Tank
FOUL OUTLET
ELEVATION
Section A-A
FIGURE 4a ORIGINAL LAYOUT FOR TEST NO. 1
10
-------
ORIGINAL LAYOUT
ORIGINAL LAYOUT WITH INLET BAFFLE
FIGURE 4b ORIGINAL LAYOUT FOR TEST NO. 1
11
-------
REFERENCES
1. The Swirl Concentrator as a Combined
Sewer Overflow Regulator Facility,
EPA-R2-72-008, September 1972.
2. Relationship Between Diameter and
Height for the Design of a Swirl Concentrator
as a Combined Sewer Overflow Regulator,
EPA-670/2-74-039, July 1974.
3. The Swirl Concentrator as a Grit
Separator Device, EPA-670/2-74-026, June
1974.
4. Swirl Concentrator as a Primary
Treatment Facility, Draft Report, 1976, EPA
Grant No. 803157.
5. Physical and Settling Characteristics of
Particles in Storm and Sanitary Wastewater,
EPA-670/2-75-011, April 1975.
12
-------
CHAPTER III
DESIGN FACTORS FOR
SWIRL EROSION RUNOFF TREATMENT PROTOTYPES
This section on design makes frequent
reference to the following listed Figures:
5 Prototype Particle Sizes Represented
by Gilsonite - SG 1.06
6 Recovery Rates in Model as Function
of Particle Settling Velocity and
Discharge with 5 percent Draw-off
7 Recovery Rates in Model as Function
of Particle Settling Velocity and
Discharge with 10 percent Draw-off
8 Recovery Rates in Model as Function
of Particle Settling Velocity and
Discharge with 14 percent Draw-off
9 Predicted Prototype Recovery Rates
with 5 percent Draw-off
10 Predicted Prototype Recovery Rates
with 10 percent Draw-off
11 Predicted Prototype Recovery Rates
with 14 percent Draw-off
12 General Design Dimensions
The procedure described in this section is
relevant to a fixed prototype size whose scale
is imposed by the use of a standard or
conventional 3.66-m (12 ft) diameter cattle
watering tank as the swirl chamber. The fixed
scale of 1:4 determines the dimensions of the
whole structure as they appear in Figure 12,
General Design Dimensions.
Under operating conditions, it is assumed
that the user has a situation in which the
prototype discharge, Qp, is known, as well as
the prototype particle settling velocity v , of
the materials to be removed from the flow.
1. Enter Figure 9 (5 percent draw-off)
where the expected discharge appears on
the abscissa
2. Move up in the graph until the given
particle settling velocity curve (or particle
size) is found
3. Check whether or not this intersection
gives an acceptable rate of recovery
4. If the recovery is not high enough, try
Figures 10 or 11 in which draw-off is
increased, respectively, to 10 and 14
percent of the inflow
5. If conditions are still not acceptable, even
with the larger draw-off rates, then
reduce the expected discharge per unit by
5/2
providing multiple swirl chambers
6. If this gives too many standard 3.66-m
(12 ft) units, try larger chambers, making
reference directly to Figures 6, 7, and 8,
the recovery curves for the 0.914-m (3 ft)
diameter model
7. Select an approximate new chamber
diameter, Dn and divide this by the
model diameter to find the new scale:
l/\n = 0.9l4/Dn m = 3/Dn ft
Where:
Xra = scale factor
Next, calculate:
new discharge scale = l/Xn"
new settling velocity scale = 1 /\n n
8. Multiply:
2pxl/A,j5/2 = Qm model discharge
vsp x \l\n '/2 = vsm model particle
settling velocity
9. Go into Figures 6, 7, or 8 with these
model values, interpolating as necessary
between the discharge curves, to find the
corresponding recovery
10. If the recovery is too low, try
progressively larger chambers, each time
following the procedure in steps 7,8, and
9 above until a satisfactory recovery rate
is obtained
11. Use Figure 12 to find the dimensions of
the new chamber. Since the chamber
shown on the figure is the standard
3.66-m (12 ft) unit studied at scale 1:4,
each dimension must be multiplied by the
factor Xn/4
For purposes of illustrating the procedure
for the application of this swirl unit to the
problem of soil erosion, two examples will be
given. The first is based upon an engineering
approach where a permanent facility is to be
designed for a required level of efficiency.
The second example is for the case where a
developer must provide temporary facilities at
a construction site.
Permanent Erosion Control Facility
For a permanent erosion control facility
the use of the swirl concentrator may be
envisioned as an auxiliary treatment device
13
-------
7.0 (2.76) ^
6.0 (2.36) ..
5.0 (1.97) -
4.0 (1.57)
3.0(1.18)
2.0 (.787)
1.0
RANGE OF PROTOTYPE
GRIT SETTLING VELOCITY
REPRESENTED BY
GILSONITEAT
SCALE 1/4
0.5
| (.20)
E
o
f:
O
LU
o
0.1
(.04)
PROTOTYPE
"GRIT PARTICLE
SIZES
SIMULATED
BY GILSONITE
0.01
(.004)
0.01 (.0004)
1.2 (.05)
PARTICLE DIAMETER, mm (in )
FIGURE 5 PROTOTYPE PARTICLE SIZES REPRESENTED BY
GILSONITE-SG 1.06
14
-------
100
90
0.07
(.03)
PARTICLE SETTLING VELOCITY, cm/sec (in/sec)
FIGURE 6 RECOVERY RATES ON MODEL AS FUNCTION OF PARTICLE SETTLING
VELOCITY AND DISCHARGE WlTH 5 PERCENT DRAW-OFF
15
-------
100
10
0
0.07
(.03)
PARTICLE SETTLING VELOCITY, cm/sec (in/sec)
FIGURE 7 RECOVERY RATES ON MODEL AS FUNCTION OF PARTICLE SETTLING
VELOCITY AND DISCHARGE WITH 10 PERCENT DRAW-OFF
16
-------
Qm = 3 I/sec
(0.79 gal/sec)
Qm = 5 I/sec
(1.3 gal/sec)
0.07
(0.03)
0.2 0.5
(.08) (2.0)
PARTICLE SETTLING VELOCITY, cm/sec (in/sec)
FIGURE 8 RECOVERY RATES ON MODEL AS FUNCTION OF PARTICLE SETTLING
VELOCITY AND DISCHARGE WITH 14 PERCENT DRAW-OFF
17
-------
o
DC
HI
a.
>
cc
\u
O
o
ui
cc
100
so
60
40
CL
0
I/sec
(gal/sec)
Qpm3/sec _l
(ft3/sec)
I n
PARTICLE SETTLING VELOCITY
PROTOTYPE GRIT PARTICLE
Qpm3/day
(mgd)
_L
PROTOTYPE DISCHARGE
I I I L_
_L
2.5'
(.07)
L
3
(.08)
1_
3.5
(.10)
4
(.11)
5
(.14)
6
(.17)
l_
7
(.2)
8 9
(.23) (.25)
[_
_L
1.7 2
(6,435) (7,570)
2.5 3 3.5 4
(9,463) (11,355) (13,248) (15,140)
5 6
(18,925) (22,710)
FIGURE 9 PREDICTED PROTOTYPE RECOVERY RATES
WITH 5 PERCENT DRAW-OFF
18
-------
100
I-
Z
LU
o
cc
LU
a.
>
CC
LU
o
o
LU
DC
PROTOTYPE GRIT PARTICLE
Qp I/sec
(gal/sec!
>
200 jSf^ 250
(52.8) - (66)
PROTOTYPE DISCHARGE
Q m3/sec
{ft3 /sec)
Qp m3/day
(mgd)
1 1
2.5 3
(.07) (.08)
, ,
1.7 2
(6.435) (7,57).
1 1
3.5 4
(.10) (.11)
I
2.5
(9,463)
5
(.14)
I
3
(11,355)
I
3.5
I.
6
(.17)
1
4
(13,248X15,140)
1 I
7 8
(.2) (.23)
I
5
(18,925)
I
9
(.25)
I
6
(22,710)
FIGURE 10 PREDICTED PROTOTYPE RECOVERY RATES
WITH 10 PERCENT DRAW-OFF
3.6 m (12 ft) Diameter Chamber
19
-------
100
I r-|
PARTICLE SETTLING VELOCITY
PROTOTYPE GRIT PARTICLE
(gal/sec)
200 ^ 250
(52.8)
-------
Four Flow Spoilers
0.86 m (34 in ) long
-PIPE
0.61 m (2 ft)
INLET
0.61 m x 0.61 m
(2 ft x 2 ft)
A
J
ELEVATION
Section A-A
TO DISCHARGE
TANK
OUTLET °-10 •" W in )
Foul Outlet discharge
adjusting device
FIGURE 12 GENERAL DESIGN DIMENSIONS
SCALE: 1/4
21
-------
installed ahead of a stormwater
retention-detention facility. The primary
purpose of the unit would be to concentrate
the larger soil particles in order to retard the
siltation of the retention facility or
downstream receiving waters. To this end, the
concentrated underflow could be directed to
a readily cleaned auxiliary sediment trap
where conventional equipment, such as a
backhoe, Gradall,® or even a bucket loader —
assuming that the area could be dewatered —
could be used to remove the collected soil.
Such a facility would minimize the total
maintenance cost and improve the efficiency
of the major storage facility or receiving
waters.
The design procedure is developed in
accordance with the various elements
normally required for a complete system.
These elements are:
Hydrological Considerations
Solids Analysis
Swirl Unit Design
Efficiency Computation
Assessment of Retention Volumes
Other Design Considerations and Details
A typical site situation is shown in Figure
2, Flow Diagram. This plan shows a large drain-
age area with a stormwater retention facility.
The swirl unit and soil collection pond
intercept this flow ahead of the retention
facility ponds. It is assumed that all runoff
from the basin is detained on the property and
passed through the swirl unit or units.
For purposes of determining the quantity
of runoff to be expected from the drainage
area, any of a number of methods, can be
used. In references to a recent survey
conducted by APWA6 rainfall runoff
predictions in practice are based primarily on
unit hydrographs and the Rational Method. In
general, maximum erosion will occur under
conditions of peak runoff. The peak storm
which may cause maximum erosion may
never occur during a given interval of interest
in design for erosion runoff control. Common
design practice for drainage structures is based
on a rainfall intensity which occurs
frequently. A commonly used rainfall
intensity is a 10-year recurrence interval,
although in many cases the choice of a design
rainfall is determined for a specific project by
the requirements of the local or state public
agency having jurisdiction.
As an example, let it be assumed that a
80.9 hectare (200 acre) drainage basin is
selected. For this watershed, the time of
concentration is found to be 45 minutes.
Assuming that it is desired to find the peak
runoff at a time when equilibrium conditions
are established for this site, the duration of
the storm is taken as the time of
concentration. From a duration-intensity
relation established for this site, it is
determined that the intensity is 1.27 cm/hr
(0.5 in/hr). Further information on the site
indicates that 20 percent of the basin is
occupied by buildings for which a runoff
coefficient of 0.9 is selected; 15 percent is
roadways with a runoff coefficient of 0.9; and
the remainder is grassed yard areas for which
a runoff coefficient of 0.3 is assumed. An
average coefficient for this site can be
calculated as:
(40 ac + 30 ac) x 0.9 + 130 ac x 0.3
Cave •= 200 ;
Cave =0.51
The peak runoff calculated for this storm,
using the Rational Method, is:
Q = CiA
Q = 0.51 (1.27 cm/hr) 80.9 ha - 52.4
cm-ha/hr
-52.4x27.8= 1,460 I/sec
Q =0.51 (0.5 in/hr) (200 ac) = 51
ft3 /sec
This flow will be used later as the inflow
to the swirl erosion control facility. More
accurate predictions of the proper intensity of
rainfall upon which to predict the most severe
eroding rainfall to be handled by this erosion
control device can only be obtained after
several field experiences have been evaluated.
Any method used prior to the time of
verification can only be subjective and is
highly dependent upon local conditions. In
many areas of the country, more accurate
information is available for the prediction of
times of concentration and peak rainfall
intensities.
A second part of the hydrologic analysis
required to design an erosion control facility
involves an estimate of the peak volume of
22
-------
runoff for a given storm. This volume will be
used to size the retention pond and the soil
collector pond. Obviously, the high-intensity,
short-duration storm may contribute a high
flow rate for a short period, but it would
represent only a portion of the total volume
of runoff that could be expected from a
storm of longer duration. With reference to a
set of intensity-duration curves, it was
observed that for the same recurrence
frequency that was used in the determination
of the. peak flow rates, a storm of longer
duration of 4 hours would yield an intensity
of 1.02 cm/hr (0.4 in/hr). The peak rate of
flow for this storm can be estimated in the
same manner as previously:
Q = 0.51 (1.02 cm/hr) 80.9 ha = 42.1
cm-ha/hr
= 42.1 x27.8 = 1170 I/sec
<2 = CiA = 0.51 (0.4 in/hr) 200 ac
= 40.8 ft3 /sec
The use of the Rational Method C factor
will result in an estimate of a larger flow than
would ordinarily be anticipated for all but the
most intense storms.
Perhaps the most accurate method for
determining the volume of runoff would be to
integrate the area on a hydrograph
determined for this watershed. For the
determination of this volume, the use of a
unit hydrograph would be advantageous.
Various other methods are also available
for computing the storage volume necessary
to hold the total runoff. Using one of these
methods, assume the resultant volume is
8,420 m3 (297,226 ft3). This yields a larger
volume than that associated with the
short-duration, higher-intensity storm.
The final hydrologic determination deals
with an annual estimate of the total quantity
of sediment to be expected. This volume will
be used to estimate the total amount of
settleable solids to be collected in the two
ponds. Reference to a chart of expected
annual rainfall in the project area, will provide
the annual precipitation rate. It is probably
not necessary to reduce these values for
precipitation occurring as snowfall for the
purpose of this estimate. Assume that this
value is 76.2 cm (30 in) per year. It is also
assumed that the area of the two retention
ponds is small compared to the total area,
although this fact may not always be true.
The runoff volume per year is then:
V = 0.51 (76.2 ) x
x 80.9 ha
10,000m2
x— - - - 3 14,000 m3/yr
ha
1 ft
V= 0.51 (30in/yr)x -
12 in
ft2
x 200 ac x 43,500 —
ac
= 11,1 00,000 ft3 /yr = 4 1 1 ,000 yd3 /yr
In summary, these three calculated
quantities will be used in the following
manner:
a. The peak runoff rate will be used to size
the swirl concentrator erosion control
device or devices, the main drainage
trench conducting flow to the device and
any inlet conduit that must be used.
b. The single storm volume will be used to
size the two retention basins.
c. The annual storm runoff volume will be
used to estimate the quantity of
settleable material which will accumulate
in the retention basins. This represents
material for which storage capacity must
be provided within the pond, or the
volume of material which must be
removed.
Solids Analysis
The next step in the design procedure is
to determine the quantity, type and size of
material that is likely to be found in
stormwater runoff at this site. Table 1 , Sieve
Analysis, presents an analysis of a sample of
storm runoff from an erosion site which was
sieved and separated into groups having
similar specific gravities. Such an analysis is
used to determine the type and specific
gravities of the material present, thus enabling
a reasonable estimate of the type and
quantity of material that can be removed in a
swirl erosion control unit. This example
should be viewed as merely an indication of
the type of investigation that should be
conducted. There may be many sites for
23
-------
TABLE 1
SIEVE ANALYSIS
Sieve Size
10
20
60
100
120
200
PAN
Size
mm (in)
2.00 (.08 )
0.84 (.03 }
0.25 ( .01)
0.149(.006)
0.125(.005)
0.074(.003)
Material
Retained
gm (oz)
4.0(0.14)
6.5(0.23)
39.0(1.4 )
100.5(3.5 )
77.0(2.7 )
44.0(1.5 )
79.0(2.8 )
Percent
Retained
1.14
1.86
11.14
28.71
22.00
12.57
22.57
TOTAL
Percent Retained
According to SG
SG/2.65 SG/1,20 SG/1.01
1.04
1.06
8.64
23.61
21.00
12.07
22.57
90.59
2.0
5.0
# * * #
1.0
0.5
8.5
0.1
0.2
# * * #
0.5
0.1
_ _ _
0.9
which more elaborate and complete analyses
may be desirable.
Assuming that it is desirable to remove as
much settleable material as possible in the
swirl unit, the smallest particle that is
predicted from the model studies to be
removed is a grit particle, specific gravity
2.65, 43 microns in diameter, having a settling
velocity of 0.14 cm/sec (0.055 in/sec) as
shown in Figure 11. A design incorporating
the removal of this size of grit particle will
also remove larger size particles of lighter
weight. For example, with reference to Figure
5, a particle of specific gravity 2.65 and a
settling velocity of 0.14 cm/sec (0.055 in/sec)
is 0.045 mm (.002 in) in diameter. For the
same settling velocity a particle of SG 1.20
with a diameter of 0.14 mm (0.006 in) will
settle at the same rate as a particle having a
SG of 1.01 (organic material) with a diameter
of 0.6 mm (0.02 in). Similar settling velocities
can be obtained from Figure 13, Prototype
Particle Sizes Represented by Petrothene —
SG. 1.01. Particle sizes larger in diameter than
those quoted are expected to be removed. In
the sieve analysis shown in Table 1, the
material expected to be removed in part by
the swirl concentrator is shown in the specific
gravity columns at the right side of the table
above the asterisk marks, considering that the
settling velocity is 0.14 cm/sec (0.055 in/sec)
for a particle having an SG of 2.65.
Hydrometer analysis using pan material,
or 22.5 percent of the total sample, showed:
Percent particle size greater than 0.052
mm (0.002 in)- 16.0%
Percent particle size less than 0.052 mm
(0.002 in) - 6.57 %
From design data, using a particle settling
velocity of 0.14 cm/sec (0.055 in/sec) it was
determined that the following percent of
material will be subject to removal in the swirl
chamber:
SG2.65 90.59-6.57 = 84.02%
SG 1.20 8.5 - 1.5 = 7.0 %
SG 1.01 0.9 -0.6 = 0.3 %
(These quantities are shown in the table as the
percent in each SG column above the asterisk)
Total material subject to removal by swirl
concentrator - 91.33%
Total material not subject to removal —
8.67%
The removable material percent shown
here will be multiplied by the recovery
efficiencies of the chamber from the design
curves, Figures 9, 10, or 11.
Swirl Unit Design
From an earlier section it had been
determined that the peak design runoff flow
rate is 1,460 I/sec (51 ft3/sec). With reference
to Figure 11, it is seen that for a
12-foot-diameter chamber, the highest
efficiency is obtained when the flow rate does
not exceed 96 I/sec (3.4 ft3/sec). Dividing the
flow by a factor of 15 would give 97 I/sec
(3.4 ft3/sec) as the design flow for each of the
chambers, and this flow in Figure 11 is at the
left end of the curve, at the highest possible
removal efficiency for this particle size. The
use of 15 chambers would also mean that
24
-------
1 !
I SETTLING VELOCITY, cm/sec (in./sec) 1
—
2.5 (1)
,
—
0.2 ^
1
0.1
—
.0121
t
RANGE OF PROTO-
TYPE GRIT SET-
TLING VELOCITY
REPRESENTED BY
PETROTHENE
AT SCALE 1/4
' (.08)
i
(.04)
RANGE OF PROTO-
TYPE GRIT SET-
TLING VELOCITY
REPRESENTED BY
PETROTHENE
AT SCALE 1/4
(.0047)
£L (.004)
PROTOTYPE
PARTICLE SIZES
SIMULATED BY
— PETROTHENE DUST
0.12 mm < d < 0.5 mm
— (.008in
-------
higher intensity storms could still be handled
by these chambers with only a small
reduction in efficiency. In fact, the design
runoff could be more than doubled in each
chamber. It should be noted that if the
14-percent draw-off rate is excessive for the
volume of storage desired, Figures 9 and 10
should be used with smaller draw-off rates
and corresponding reductions in efficiencies.
Efficiency Computation
Using the efficiencies given in Figure 11
and the percent of each size material given in
Table 1, the efficiency of the 3.65-m (12 ft)
diameter chamber can be determined, as
shown in Table 2, Swirl Efficiency Analysis.
For specific gravities less than 2.65, an
equivalent particle size for that particle can be
obtained from Figure 5. As an example with
reference to Table 2, a particle for specific
gravity of 1.20 is taken as 0.25 mm (0.01 in).
In Figure 5, find this size along the abscissa;
go vertically upward to the curve marked SG
1.20, then left or horizontally to the curve
marked SG 2.65, then downward to the
abscissa. The values read, settling velocity is
0.5 cm/sec (0.19 in/sec) for a SG 1.20 and
particle size 0.25 mm (0.01 in); an equivalent
particle of SG 2.65 having this settling
velocity is a particle of 0.082 mm (0.003 in).
Refer back to Figure 11 for this size particle
of 82 microns and settling velocity of 0.5
cm/sec (0.019 in/sec). For a flow rate of 97
I/sec (3.4 ft3/sec), this yields an efficiency of
69 percent. This procedure is continued for
other particle sizes. It is seen that an
efficiency of 68.76 percent is predicted for
this material if a set of 15 swirl concentrators
were used.
Alternate Chamber Design Investigation
The design discharge, Q is 1,460 I/sec (51
ft3/sec). With reference to Figure 8, the
smallest particle shown is one having a settling
TABLE 2
SWIRL EFFICIENCY ANALYSIS
Sieve
Size
10
20
60
100
120
200
HYD
COL. 1
Particle
Size mm(in)
2.00 (.08 )
0.84 (.03 )
0.25 (.01 )
0.149(.006)
0.125(.005)
0.074(.003)
0.052(.002)
COL. 2
Percent
Retained
SG 2.65
1.04
1.66
8.64
23.61
21.00
12.07
16.00
COL. 3
Percent
Eff. from
Fig. 11
100
100
92
82
79
69
59
COL. 3
= 1 x2
100
1.04
1.66
7.95
19.36
16.59
8.32
9.44
COL. 4
Percent
Retained
SG 1 .20
2.0
5.0
1.0
0.5
COL. 5
Percent
Eff. from
Fig. 11 &5
— .—
69
56
COL. 6
= 4x5
1.38
2.8
64.36
4.18
Sieve
Size
10
20
60
100
120
200
HYD
COL. 7
Percent
Retained
SG1.01
0.1
0.2
0.5
0.1
COL. 8
Percent
Eff. from
Fig. 5 & 11
60
COL. 9
= 7X8
0.1
0.12
'.,
•
'
.
Total percent of removal material removed in
swirl unit = 64.36% + 4.18% + 0.22%
= 68.76%
Total percent of settleable material removed
by swirl concentrator
= 68.76% x 91.3% = 62.7%
0.22
26
-------
velocity of 0.07 cm/sec (0.03 in/sec). For
other draw-off rates, Figure 6 or 7 could be
used for 5 percent or 10 percent draw-off,
respectively. Figure 8 was selected since the
best recovery occurred with a draw-off of 14
percent. Assume that four prototype
chambers will be used, each having a diameter
of 6.4 m (21 ft). This sets the model scale at:
X = Lp/Lm = 6.4 m/0.914 m (21 ft/3ft) = 7
From the Froude Law the velocities of
settlement can be related as:
vsp/vsm = VLjT^ = ^fT = 2-65
The model discharge is also found from
the Froude Law as:
= 129.64
1
1.29.64
= 2.811/s
Referring now to Figure 8, the discharge
line for 2.81 I/sec (0.74 gal/sec) must be
interpolated between the 3 I/sec (0.80
gal/sec) line and zero at 100 percent recovery.
Assume it crosses the 0.07 cm/sec (0.03
in/sec) settling velocity line at about 60
percent recovery.
This model settling velocity corresponds
to a prototype settling velocity of:
0.07 cm/sec x 2.65 = 0.185 cm/sec (0.073
in/sec)
From Figure 5, this gives a particle size of
0.05 mm (0.002 in) for SG = 2.65 material.
Another approach to selecting the
chamber size would be to decide to use 3 I/sec
(.106 ft3/sec) in either Figures 6, 7, or 8 as
the required rate of recovery curve. Working
with Froude's Law, the scale can be found:
• O IO = i''4OU x -— =1217
- Upl
-------
the firm of Beak Consultants, Ltd.5 Among
figures quoted for suspended solids in
stormwater, these settleable solids vary from
0 to 7,640 mg/1, with an average of 687 mg/1.
The concentration of solids can vary widely
and is depending upon the character and the
use of the land from which the storm flow is
generated. Using an average value of 700 mg/1,
an estimate of the settleable solids per storm
is:
1
mg
V = 8,420 m3 x 1,000 — x 700 -~
kg
x
•= 3.68m3 (130ft3)
1,000,000 1,600kg
On an annual basis the volume of
settleable solids is:
V = 314,000 m3xl, 000-^r x 700 —
kg
m
m
1,000,000 g 1,600kg
= 137m3 (4,841ft3)
Assume that 100 percent of all settleable
solids will be retained in the ponds.
Temporary Facility at Construction Site
Another application of the swirl separator
is as a temporary facility for erosion control
at a construction site. For this purpose the
foul sewer underflow, conveying most of the
settleable solids, would discharge into a soil
collector pond and the overflow would
discharge into a drainage ditch or channel or
flow directly into a watercourse. For this
purpose, the conventional cattle watering
tank, with a diameter of 3.65 m (12 ft) and
height of 0.91 m (3.0 ft), could be used after
modification to meet the design details shown
in Figure 12. Figure 14, Standard Stock
Watering Tank, shows a typical unit.
The riser pipe, shown in Figure 12 as 0.67
m (2.2 ft), could be changed to 0.61 m (2.0
ft) to utilize standard size pipe. The clarified
overflow outlet could be attached directly to
the underside of the chamber and could be
made rectangular in shape. Dimensions of
0.61 m (2.0 ft) wide and 0.22 m (0.75 ft)
high would provide a waterway having an area
equivalent to the riser pipe. The underflow or
foul outlet could likewise be made in
rectangular or square shape, attached to the
bottom of the box. The outlet should
probably be at least 0.15 cm (0.06 in) square
to prevent problems with clogging. The outlet
could terminate at the outside wall of the
chamber, with a 0.15 cm (0.06 in) standard
pipe flange for attaching the pipe to convey
flow to the soil collection pond.
Assume the following conditions:
Site area tributary to chamber is 3.12 ha (8
ac)
Runoff coefficient C is 0.4
Time of concentration is 15 min
Rainfall intensity is 6.35 cm/hr (2.5 in/hr)
For
Q = CiA:
= 0.4 x 6.35 cm/hr x 3.12 ha
= 8 cm-ha/hr
= 8 x 27.8 = 222.4 I/sec
Q = 0.4 x 2.5 in/hr x 8.0 ac
= 8 ft3/sec
From Figures 9, 10, and 11, it is apparent
that the largest allowable flow through one
chamber is 222.4 I/sec (8.0 ft3/sec).
Therefore, under the above assumed
conditions the largest site that can be served
by one chamber is 3.12 hectares (8.0 ac). The
greatest recovery of solids will occur if a
14-percent draw-off (Figure 11) is used rather
than 10-percent (Figure 10) or 5-percent
(Figure 9).
From Figure 11, the percentage of
various size solids to be recovered will be as
follows:
Size Solids
mm
0.35
0.30
0.25
0.18
0.16
in
0.014
0.012
0.009
0.007
0.006
Percentage
Recovery
85
73
53
37
31
A 14-percent draw-off means that this
percentage of the peak flow will pass through
the underflow outlet to the soil collection
pond. This amounts to 0.14 x 222.4 I/sec (8
ft3/sec) = 32 I/sec (1.1 ft3/sec). The head or
depth of water above the underflow outlet
will be 0.61 m (2.0 ft) when the outlet weir
28
-------
FIGURE 14 STANDARD STOCK WATERING TANK
starts overflowing. At peak flow this head
may increase to 0.76 m (2.5 ft). Approximate
hydraulic computations indicate that this
head is too small to permit use of a 0.10-m,
(0.33 ft) diameter underflow outlet. If an
outlet pipe 0.15 m (0.5 ft) in diameter is
used, the head is sufficient to force the flow
through about 15 m (50 ft) of outlet.
To meet the recovery performance shown
in Figure 11 it is necessary to keep the
underflow to about 32 I/sec (1.1 ft3/sec). To
prevent decreasing the rate of underflow due
to backwater, the maximum water level in the
soil collection pond should be below the top
of the underflow pipe. The most practical
way of regulating the underflow rate would
be to provide a shear gate at the outlet pipe
and to determine the actual setting of the gate
from measurements of the volume in the
collection pond during actual storm
conditions.
A further design consideration is the
volume of the soil erosion collection pond.
Obviously, the foul sewer discharge from the
swirl chamber underflow will outlet into the
pond, and clear effluent will overflow to the
selected drainage ditch or the designated
watercourse during a storm period. However,
whenever the rate of flow into the swirl
chamber is not sufficient to fill the chamber
to the overflow weir crest, all of the storm
runoff will discharge through the foul sewer
into the soil collection pond. Thus, the rate of
flow into the pond will vary from 0 to 32
I/sec (1.1 ft3/sec). Hence, if it is desired to
provide storage for all underflow in a 4-hr
storm the required storage would be 32 I/sec
(1.1 ft3/sec) x 4 x 60 x 60, or 447 m3
(15,800 cu ft). This would require a pond 1.2
m (4 ft) deep and 18.9 m (62 ft) square. If a
2-hr detention time is considered adequate to
settle out the suspended solids, then the
29
-------
depth could be reduced to 0.61 m (2 ft) or
the surface dimensions of the pond reduced.
An overflow weir should be provided to pass
32 I/sec (1.1 ft3/sec) when the pond becomes
filled to the designed depth.
The chief advantage of such a temporary
construction swirl separator is that it is
portable and has no mechanical parts. Thus,
the chamber could be moved about on the
construction site, as required, or moved to
other sites. Multiple units could be used to
meet requirements of larger sites or to remove
higher percentages of suspended solids.
REFERENCES
6. Practices in Detention of Urban
Stormwater Runoff, APWA Special Report
No. 43, Table 8, p. 33.
30
-------
CHAPTER IV
GLOSSARY OF PERTINENT TERMS
Cattle Watering Tank — A standard,
commercially available tank or tub used on
farms, ranches and stock feeding lots for
dispensing drinking water for cattle and other
livestock.
Concentric Skirt — A vertical sheet or
panel, constructed in circular form concentric
with the outer diameter and the overflow
downdraft pipe in a swirl chamber for the
purpose of separating flow zones and acting as
a suppressant of any short-circuiting of flow
patterns or the overflow of floating solids
with the effluent.
Depth of Chamber — The vertical
distance between the bottom of the swirl
chamber and the crest or lip of the overflow
weir, or the level of the flat weir disc; the
depth of the chamber to the overflow level.
Erosion — The washing or scouring action
of stormwater on the land, resulting in the
displacement and movement of grit, silt and
other indigenous solids with the wastewater
flow; the type of solids which are intended to
be removed from the flow by the swirl
concentrator chamber.
Flat Weir Disk - The flat circular plate
that extends around the overflow pipe in the
swirl chamber, to a predetermined diameter,
over which the clarified effluent flows on its
way to the overflow opening.
Flow Spoiler — Vertical energy
dissipating baffle or plate installed on the weir
disc or elsewhere in the swirl concentrator
chamber for the purpose of preventing
excessive flow disturbances and dampening
the development of free vortex flow patterns
and other undesired flow conditions in the
chamber.
Foul Sewer — A sewer line, from the
bottom of the swirl concentrator chamber to
some point of discharge to an interceptor
sewer, a catchment basin or other point of
solids disposal, installed for the purpose of
drawing off the solids slurry retained in the
swirl chamber due to the recovery efficiency
of the device.
Gilsonite® — A test material used in the
swirl studies to simulate the grit material that
will be contained in erosion runoff flows into
prototype units in the field; solids having a
specific gravity of 1.06 and a size range of 0.5
to 3 mm.
Grit — Solids carried by erosion runoff
waters which, because of their size, >0.2 mm
(0.008 in), and specific gravity, 2.65, settle
readily in a swirl concentrator chamber.
Inlet Baffle — A structural plate installed
from the inlet to the overflow weir for the
purpose of producing or inducing the desired
flow pattern in a swirl chamber; a device to
serve as a guide for the incoming flow and to
place it in circulatory action to take full
advantage of the swirl secondary flow pattern
in the chamber.
Petrothene® — A synthetic plastic
material which, in shredded or dust form, has
a specific gravity of 1.01 and was used in the
study to simulate the lighter silts and clays
which may be. contained in erosion runoff
wastewater to be treated by prototype field
units.
Prototype — A full-scale version of the
laboratory test model, designed to handle
erosion runoff in actual practice; in this
study, a scaled-up replica of the laboratory
model of a size that would be four times
larger than the model itself; in this study, one
prototype proposed for actual field use on a
temporary basis would be a conventional,
commercial cattle or stock watering tank.
Recovery — The percentage of solids
introduced into a swirl concentrator chamber
that will be retained as settled material in the
bottom of the chamber and drawn off
through the foul sewer; solids carried over
with the clarified effluent are not considered
as part of the recovery in the current studies.
Swirl Concentrator Chamber — A
cylindrical tank or chamber, in which the
shape, method of inflow and overflow, and
internal appurtenant structures induce a
swirl-type flow pattern which produces the
desired separation of solids from the liquid
flow.
Underflow — The slurry, containing the
recovered solids, which is withdrawn from the
bottom of the swirl concentrator chamber;
the converse of the clarified overflow; the
erosion solids which the prototype swirl
chamber is intended to recover and, thus,
prevent from causing environmental pollution,
loss of soil cover, and downstream siltation.
31
-------
CHAPTER V
APPENDIX
(LaSalle Hydraulic Laboratory Report)
Previous research has been carried out on
the Swirl Concentrator, covering its
application as a stormwater regulator, a grit
separation device, and a primary settling
chamber. The present study was undertaken
to investigate the application of the swirl
solids separation principle to the treatment of
erosion runoff. The same model used in
previous studies was utilized, with
modifications that would accommodate larger
flows and demonstrate the capabilities of a
prototype device that would be simple,
sturdy, moveable, and easy to operate.
Since the object of the study was to
develop a design that would remove grit
particles whose size and gradation would
depend on the nature of the watershed area
and its indigenous soils, three kinds of solid
materials were used in the model to allow
interpretation and interpolation of results.
Scaling up was accomplished to provide
recovery rates for various sizes of prototype
particles as a function of discharge rates.
The principle in the swirl separation of
erosion soil solids from runoff waters covered
a controlled combination of solids settling
with rotational liquid velocity, induced by
means of spill over an overflow weir, the slope
of the chamber floor and a bottom foul draw-
off. Modifications were innovated and
investigated in order to obtain optimum
removal of the solids. The foul outlet was
provided during construction of the model
and a continuous underflow was drawn off
during all tests at predetermined rates.
The basic layout was evolved from the
laboratory's previous experience with the
swirl combined sewer overflow regulator
configuration and based on the desire to use
standard cattle watering tanks in actual field
installations. These commercial tanks are 3.66
m (12 ft) diameter and 0.91 m (3 ft) deep;
they would provide the basic shell of an
economical swirl chamber. The inlet, circular
weir, clear effluent overflow, and foul outlet
could be added at moderate cost.
Description of the Model
The central part of the hydraulic test
model was the separation chamber, which
took the form of a vertical Plexiglas cylinder
with 1:15 cement floor slope in the first stage
of the tests, as shown on Figure 3 and Figure
4, contained in Chapter II of this report. The
floor slope was later eliminated and the
chamber floor was made flat, level with the
inlet floor elevation. A spiral flow guide
encircling the foul outlet was embedded in
the floor for some tests of the research series.
In the center of the cylinder an
embedded poly vinyl chloride (PVC) pipe,
15.2 cm (6 in) inside diameter, provided the
support for the circular weir and the outlet
which discharges the clear effluent overflow
spilling over the weir. The elevation of the
weir was maintained constant at 15.2 cm (6
in) above the inlet floor level during the entire
series of tests.
Inflow to the chamber was supplied
through PVC pipe, 15.2-cm (6 in) diameter
set at a slope of 1:1,000. A vibrating solids
injection system was placed in this supply
line, 2:14 m (9 ft) upstream of the chamber.
Water supply for the model was obtained
through a pipe directly connected to the
constant level tank in one of the laboratory's
permanent pumping stations.
The overflow effluent through the central
outlet pipe was conducted to a large settling
basin equipped with a calibrated V-notch
weir. A point gauge in a manometer pot was
used to read the level in the basin,
determining the discharge going over the
V-notch weir.
A flexible 2.5 cm- (1 in) diameter tygon
tube was placed inside the cylinder beneath
the floor of the test chamber to collect the
foul flow. The foul flow was withdrawn from
the bottom of the cylinder, and conducted to
a solids settling tower fitted with an
adjustable level outlet pipe which could be
raised or lowered at will to control the rate of
discharge drawn off through the foul outlet.
32
-------
The suggested use of a conventional cattle
watering tank as the prototype swirl chamber
established the model scale of 1:4. This meant
that the prototype unit would have to be
operating with a 61 cm (24 in) square duct
entering a 3.66-m (12 ft) diameter chamber,
based on the first step of the study. Later, the
square duct inlet was reduced to 0.40 cm
(0.16 in) while the chamber remained
unchanged.
The selected discharges (Qm) to be tested
were respectively, 3, 5, and 7 I/sec (0.8, 1.3,
and 1.8 gal/sec) in the model. When
transposed at the prototype scale (Qp), these
values represented the following flows:
QP
QP
QP
I/sec
I/sec
m3/sec
ft3/sec
mgd
3
96
0.1
3.4
2.2
5
160
0.16
5.6
3.6
7
224
0.2
7.9
5.1
The 3.66 m (12 ft) prototype size
chamber, with the weir crest or lip 61 cm (24
in) above the horizontal floor and a central
overflow pipe of 67.3 cm-(26.5 in) diameter,
would give, respectively, the following
detention times:
Qm I/sec
(ft3 /sec)
Qp I/sec
(ft3 /sec)
Detention (sec)
Prototype
3
(0.1)
96
(3.4)
54.2
5
(0.2)
160
(5.6)
32.5
7
(0.2)
224
(7.9)
23.2
Grit Simulation in the Model
The amount and composition of the
erosion runoff depends essentially on
topography and the nature of the soil of the
watershed area. The nature of the soil
particles which are to be removed from the
runoff flow in a proposed prototype structure
is not precisely known.
According to their grain sizes, soil
particles are classified as sand, silt, and clay.
Following is a list of the generally accepted
soil classifications, according to grain size:
Coarse Sand
Medium Sand
Fine
Silt
4.8-2.0 mm
2.0-0.4 mm
0.4-0.05 mm
0.05-0.005 mm
(0.19-0.08 in)
(0.08 - 0.02 in)
(0.02-0.002 in)
(0.002 - 0.0002 in)
Clay Smaller than
0.005 mm (0.0002 in)
Colloidal clay Smaller than
0.001 mm or M (0.00004 in)
To ascertain the range of simulation used
in the model, the approach involved
determination of the kind of solids which
could be represented by the materials
commonly used in the laboratory for such
solids simulation.
Gilsonite - SG 1.06
0.5 mm (0.02 in) > d > 3 mm (0.12 in)
The Gilsonite used in these tests had a
gradation curve as shown in Figure 15,
Gradation Curve for Gilsonite Used in Model.
Figure 16, Prototype Settling Velocities
Simulated by Gilsonite — SG 1.06, shows the
settling velocity corresponding to various
particle sizes for the model and prototype at
scale 1:4, determined according to the
approach described by Larras.7 This work is
based on irregularly shaped particles such as
were used in the model studies.
A family of curves for different specific
gravities was presented in Figure 5. For the
range of prototype settling velocities
simulated by the Gilsonite in Figure 15, it is
possible, in Figure 5, to find the particle sizes
for specific gravity 2.65 corresponding to
erosion runoff components.
As an example, in Figure 16 the finest
Gilsonite particle of 0.5 mm (0.02 in) (No. 35
sieve) simulates, at 1:4 scale, a settling
velocity of 1 cm/sec (0.4 in/sec). Using this
value in Figure 5, grit solids with specific
gravity 2.65 would have a particle size of 0.14
mm (0.0055 in). However, given the relatively
large particle sizes represented by the
Gilsonite, shredded Petrothene X - SG 1.01
was judged more adequate for testing of
further improvements in the swirl chamber
structure.
Shredded Petrothene X - SG 1.01
0.5 mm (0.02 in) > d > 3.0 mm (0.12 in)
Gilsonite, at prototype scale 1:4, left a
zone of fine grit not represented. Petrothene
X, with particle sizes ranging from 0.5 to 3
33
-------
3 4
U.S. STANDARD SIEVE NUMBERS
6 8 10 16 20 30 40 50 70 100 140
100
90
6 4
(.24) (.16)
0.6 0.4
.02) (.01)
0.2
(.008)
0.1
(.004)
Fine
GRAVEL
Coarse
UI-SMIIM ii^-c uu mm \in
Medium
;
Fine
SAND
FIGURE 15 GRADATION CURVE FOR GILSONITE USED IN MODEL1
1Tho Helical Bend Combined Sewer Overflow Regulator, USEPA Report, EPA-600/2-75-062, December 1975,
Figure 8, p. 18.
34
-------
10 (3.9)
7.2 (2.8)
5(2)
4(1.6)
3 (1.2)
2 (.8)
o
< 1 (.4)
c
u
=l/4
1.06
I.03 0.1 0.2 0.3 0.5 1.0 2.0. 3.0 5 10
012) (.04) (.08) (.12) .2) U) (.8) (1,2) (2) (4)
PARTICLE SIZE, mm (in)
FIGURE 16 PROTOTYPE SETTLING VELOCITIES SIMULATED BY
GILSONITE - SG 1.06
35
-------
mm (0.02 to 0.12 in), was selected to fill this
void; its gradation curve is shown in Figure
17, Gradation Curve for Petrothene Used in
Model.
The same procedure described earlier for
Gilsonite was followed to define the settling
velocities of the particles simulated by
Petrothene X at scale 1:4 as shown in Figure
18, Prototype Settling Velocities Simulated
by Petrothene - SG 1.01. Similarly, the
prototype particle sizes can be found in
Figure 19, Prototype Particle Sizes
Represented by Petrothene.
Following an example through this
procedure again, the finest particle in the
model, 0.5 mm (0.02 in) at scale 1:4, gives a
prototype settling velocity of 0.2 cm/sec (0.4
in/sec) in Figure 7. Using this value in Figure
8, it can be determined that the smallest
particle simulated at specific gravity 2.65 is
0.052 mm (0.004 in), or down to the lower
end of the fine sand range.
Due to its relative ease of handling and
the wide range of recovery rates it simulated,
this material was selected for testing of
improvements in the swirl chamber structure.
Petrothene Dust - SG 1.01
d< 1.0 mm (0.04 in)
As shown in Figure 8, Petrothene with
grain size 0.5 - 3.0 mm (0.02 - 0.12 in) does
not cover the prototype silt range. It was
therefore evident that a new kind of material
with lower settling velocity had to be found:.
Settling column tests performed by T. W;.
Beak Consultants, in connection with
previous swirl studies,2 defined the size of the
dust particles in the range of 120 to 500
microns. Use of these values in Figures 18 and
19, and utilizing the same procedure
described earlier, indicates that the finest
prototype size represented at specific gravity
2.65 is 0.012 mm (12 microns), covering 95
percent of the silt range (50 to 0.5 microns),
Since only one scale for the prototype
was being considered (X = 1:4), all results
could be presented more simply as shown in
Figure 20, Range of Prototype Grit Particle
Sizes (SG 2.65) Simulated, Respectively, by
Gilsonite, Petrothene, and Petrothene Dust.
The figure shows directly the prototype
particle sizes at specific gravity 2.65
(ordinate) as a function of the model particle
sizes (abscissa). This figure also has the
advantage of showing either overlaps or gaps,
if any, existing in the simulation.
Settling Velocity Distributions for Gilsonite,
Petrothene, Petrothene Dust, and Stormwater
Runoff
Settling velocity distribution for
Petrothene dust, carried out by T.W. Beak
Consultants, is represented in Figure 21,
Settling Velocity Distributions for Petrothene
Dust and Stormwater Runoff. Also delineated
in Figure 21 is the curve for the settling
velocity distribution of solids in Stormwater
runoff. Both of these curves were taken
directly from the Beak report.
Above the model curve for Petrothene
dust in Figure 21, a second curve has been
drawn, giving the settling velocity distribution
at prototype scale 1:4 represented by the
model material, when transposed according to
Froude's Law. The same procedure was
followed for Petrothene [0.5 - 3 mm (0.02 -
0.12 in)] and Gilsonite [0.5 - 3 mm (0.02 -
0.12 in)] and the results are plotted
respectively in Figure 22, Settling Velocity
Distributions for Shredded Petrothene X and
Stormwater Runoff, and in Figure 23,
Settling Velocity Distributions for Gilsonite
and Stormwater Runoff. The extrapolated
Stormwater runoff curve from Beak was also
traced in the figure.
Model Simulation of Prototype Runoff
Examination of Figures 21, 22, and 23
shows clearly that the model particle
simulation is several orders of magnitude
away from the settling velocities given in the
Beak Consultants, Ltd., runoff sample.
Further analysis .of the curve for runoff in
Figure 21, shows it to have a median settling
velocity considerably less than 0.01 cm/sec
(0.004 in/sec), meaning that the particles
were at least as fine as silt, and probably in
the clay sizes range.
Samples like these fall into the class of
colloidal turbid water which might require at
least days of quiescent settling to be clarified.
It is evident, therefore, that there should be
no pretention of trying to remove these fine
particles in the swirl concentrator.
36
-------
U.S. STANDARD SIEVE NUMBERS
6 4
(.24) (.016)
0.6 0.4
(.02) (.02)
0.2
(.008)
GRAIN SIZE IN mm (in )
100
34 6 8 tO /6 2O 3O 4O SO 7O IOO 140
0.1
(.004)
Fine
GRAVEL
Coarse
Medium
Fine
SAND
FIGURE 17 GRADATION CURVE FOR PETROTHEIS1E USED IN MODEL
37
-------
1b0 SETTLING VELOCITY, cm/sec (in /sec)
2.5(1)
t
_i.
(.4)
75
(.2)
.2 ^
1
J
1
RANGE OF PROTOTYPE
SETTLING VELOCITY
REPRESENTED BY
PETROTHENE AT
SCALE I/4
(.08)
I
(.04)
RANGE OF PROTOTYPE
SETTLING VELOCITY
REPRESENTED BY
PETROTHENE DUST
AT SCALE I/4
'0.012 (.0047)
.01 (.004)
.001 (.OC
103)
>
/
'
/
/
/
/
/
/
/
t
>
f
0
/
//
7 /
/ /
/
/
/
PETR
/
/
/
' /
/
1
1
t
/
/
/
I
'
OTHENE
DUST
12 (.0047) |
/
/
/
/
/
1
J
'
/
/
/
/
/
/
/
f
/
.
S
f
/
Jr
r
SHREDDED
PETROTHENE
X
/
/
'
s
s
s
,»
t
1/4
1.01
01 0.1 0.5 1 3 10
03) (.004) (.02) (.04) (.12) (.4)
PARTICLE SIZE IN mm (in,)
FIGURE 18 PROTOTYPE SETTLING VELOCITIES SIMULATED BY
PETROTHEIME-SG 1.01
38
-------
"o
c
SETTLING VELOCITY, cm/sec (
2.5 (1)
0.2
0.1
0121
L
RANGE OF
PROTOTYPE GRIT
SETTLING VELOCITY
REPRESENTED BY
PETROTHENE
AT SCALE 1/4
'(.08)
(.04)
RANGE OF
PROTOTYPE GRIT
SETTLING VELOCITY
REPRESENTED BY
PETROTHENE
AT SCALE 1/4
(.0047)
ML (.004)
C
.(
001
PROTOTYPE
PARTICLE SIZES
SIMULATED BY
PETROTHENE DUST
).12 mm < :d < 0.5 mm
D08in
'/
/ /
^ — f
r~/~?
//
/
/
~-L
PROTOTYPE
PARTICLE SIZEJ
SIMULATED BY
^ PETROTHENE
).5 mm
-------
l.U.d'H
0.5 (.02)
0.4 (.016;
0.3 (.012)
0.2 (.008)
¥
J 0.1 (.004)
N 0.08 (.0031)
W
ill
> 0.06 (.0024)
H
|2 0.05 (.002)
O
0- 0.04 (.0016)
0.03 (.001 2)
0.02 (.0008)
0.012 (.0005
0.01 (.0004
j
t
•\
0.57
RANGE OF
PARTICLES
GILSONITE
0.22 (.009)
; ,
r i
RANGE
PROT
REP
SG
3 mrr
l-\7
OF PR
OTYF
RESE
1.06
. <
in E
:NTED
rf<0.5r
^<.02i
TYPE
Y
UPMFi^
/
y^
/
/
f
•'RANGE OF
/PROTOTYPE
/PARTICLES REPRE-
SENTED BY i y
PETROTHENE ]/
DUST y/|
0.5 mm
IE D
/
UST
3Y
nm
n)
/
S
/
/
J
/
/
/
/
PE
/
/
TR
l/
OT
N?
<£s
<£s
^
SILSONITE
HENE X in
cp
mm (in)
b/
0Y
I
/
.S
I .12 .15 .2 .3 .4 .5 .6 .7 .8 .9 1.0 1.5 2 2.5 3
^v ^5 ^^ ^^ *^ ^3 £)f ^i ^^ ^3 ^^ ^^ ^^ ^— ^^
^s ^^ ^5 ^5 ^5 v:* ^* ^^ Cl?' ^S N^J x^ ' ^^J ^^
MODEL SIZE IN mm (in)
FIGURE 20 RANGE OF PROTOTYPE GRIT PARTICLE SIZES (SG 2.65) SIMULATED,
RESPECTIVELY, BY GILSONITE, PETROTHENE and PETROTHENE DUST
40
-------
0.3
(.12)
0.2
(.08)
8 0-1
IE (>04)
~^ 0.08
JB (.031)
"E
o
O
o
Ul
0.06
(.024)
0.05
(.02)
0.04
(M6)
a
<= 0.03
H (.012)
LU
CO
0.02
(.008)
0.01
(.004)
.Median, settling Velocity
for Petrothene Dust
SG I.Ot
Model Petrothene Dust1
d < 1 mm
Velocity distribution of
Solids in Stormwater
Runoff2
10 2O 4O 50 60 80 90 95
PERCENT LESS THAN OR EQUAL TO
98 99 99.5
nd Settling Characteristics of Particulates in Storm and Sanitary Wastewater. USEPA Report
-670/2-75-011 April 1975 — Figure 12, p. 21
Physical and Settling Characteristics of Particulates in Storm and Sanitary Wastewater. USEPA Reoort
ErA-670/2-7 5-011 April 1975 — Figure 3, p. 9! '
FIGURE 21 SETTLING VELOCITY DISTRIBUTIONS FOR PETROTHENE DUST
AND STORMWATER RUNOFF
41
-------
4.0
(1.6)
3.0
(1.2)
2.0
(.8)
u
o
o
tu
1.0
(.4)
0.8
(.31)
* 0.6
§ (.24)
UJ 0.4
w (.16)
0.3
(.12)
0.02
(.08)
Median .Settling Velocity,
for Shredded Petrpthene
SG-1.011
Model :
shredded
Petrotihene SG l.0;l
0.5-3mm(.02-.12in.)2>.
Stormwater Runoff.
10 20 30 40 50 60 70 80 90 95
PERCENT LESS THAN OR EQUAL TO
98 99 99.5
1 Physical and Settling Characteristics of Participates in Storm and Sanitary Wastewater, EPA 670/2-75-011
April 1975 - Figure 7, p. 16'
Physical and Settling Characteristics of Particulates in Storm and Sanitary Wastewater, EPA 670/2-75-011
April 1975 — Figure 3, p. 9
FIGURE 22 SETTLING VELOCITY DISTRIBUTIONS FOR
SHREDDED PETROTHENE X® AND
STORMWATER RUNOFF
42
-------
o
-I
u
8.0
(3.1)
6.0
(2.4)
5.0
(2)
4.0
(1.6)
3.0
(1.2)
2.0
(.8)
o
o
111
e>
i? 1.0
jJ (.4)
III 0.8
(.31)
0.6
(.24)
0.5
(.2)
0.4
(.16)
0.3
(.12)
Median-.
Settling, .yeto
-------
Model-to-prototype particle transposition
will, therefore, be based on the individual
particle sizes as portrayed in Figure 20.
Testing Procedure
Although use of the swirl concentrator
for erosion runoff clarification would
normally involve a continuously varying
discharge over a storm hydrograph,
steady-state discharges were used for testing
purposes. For each individual test a
steady-state discharge was set running in the
model until equilibrium conditions were
established. A mixture containing one liter
(0.26 gal) of Gilsonite or Petrothene was
injected into the supply pipe, using the same
vibrating rate for all tests. The full liter (0.26
gal) was added over a period of 5 minutes and
the model was allowed to run 10 minutes
after the end of soils injection.
The amount of material found on the
bottom of the chamber was measured
separately. The same procedure was followed
for material floating in the effluent overflow
settling basin. The remaining portion
deposited in the settling basin was found by
subtraction, assuming no material was lost.
The recovery rate was taken as the
percentage represented by the amount
measured on the bottom of the chamber, as
compared to the total found in the chamber
and deposited in the effluent overflow settling
basin.
Settleable Solids Recovery Results
In discussing settleable solids for the
purpose of this study, reference is made to
the recovery rates for Gilsonite and shredded
Petrothene X, both with a particle size range of
0.5 mm < d < 3 mm (0.02 in < d < 0.12 in)
and Petrothene dust with a size range of 0.12
mm < d < 0.5 mm (0.005 in < d < 0.02 in).
As described, Gilsonite and Petrothene, both
shredded or dust, were considered as
representing grit material over the ranges
defined in Figure 19. The different steps
followed in the model testing are recorded in
Table 3, Modifications Tested in. Model and
Results.
Tests Carried Out With Gilsonite - SG 1.06
Brief tests carried out with the original
model layout, including a flatwise weir 0.50
m (11.6 ft) diameter, as shown in Figure 4,
Original Layout for Test No. 1, covered three
selected discharges. They showed that the
flow pattern established in the swirl chamber
was an unstable vortex even when the smallest
discharge 3 I/sec (0.8 gal./sec) ;was used. Due
to these special conditions prevailing in the
chamber, no solids injection was made; hence,
no volumetric measurement was taken.
To eliminate the vortex flow pattern, a
baffle extending from the inlet to the
periphery of the weir was tested, as shown in
Figure 4b, Original Layout With-Inlet Baffle.
This did not completely still the vortex, so
flow spoilers were installed on the flat disc
weir. These flow spoilers were cut unevenly to
obtain a better distribution of flow over the
four quadrants of the weir. This format is
shown in Figure 24a, Model Layout for Tests
2 to 13 - Modification 1.
Tests carried out with Gilsonite and the
deflector were unable to show any further
improvements since recovery rates were
almost constant around 95 percent. They
proved, however, that the presence of a
deflector at the inlet end was very useful in
increasing the efficiency rate, particularly for
high-flow conditions. After the model had
been improved using Petrothene X, 0.5 — 3
mm (0.02 — 0.12 in), Gilsonite tests were
resumed with different rates of draw-off.
Table 3, Modifications Tested in Model and
Results, shows quantitative results for those
tests. Slight deposits of Petrothene remained
in the chamber after the tests, as shown in
Figure 25, Deposit of Petrothene Found After
3 I/sec (0.8 gal/sec) Test.
Tests Carried out with Shredded Petrothene X
SG 1.01 - 0.5 mm < d <3 mm (0.02 in
-------
TABLE 3
MODIFICATIONS TESTED IN MODEL AND RESULTS
Mod.
No.
Fig. Weir
No. 6
cm (in)
Inlet
Baffle
Draw-off
(Percent)
Percent Recovery vs Discharge Recovery
3 I/sec ... 5 I/sec 7 I/sec Fig.
(0.8 aal/sec) (1.3 aal/sec) (1.8 aal/sec)
18 20
Flat weir disc; 4 uneven flow spoilers; 1/15 floor slope;
15.2 cm x 15.2 cm (6 in x 6 in) inlet size;
material used —
Gilsonite 0.5 mm < d< 3 mm (.02 in < d < .12 in) SG 1.06
1 13 20
1 13 20
No
Yes
5
5
95
96
90
95
76
95
Flat weir disc; 4 uneven flow spoilers; 1/15 floor slope;
15.2 cm x 15.2 cm (6 in x 6 in) inlet size;
material used - shredded Petrothene X 0.5 mm < d <3 mm
(.02 in < d < .12 in) SG 1.01
1 13
1 13
20
20
No
Yes
5
5
42
86
17
52
8
22
14
14
21
Circular weir with lip 5.1 cm (2 in) high; 4 even flow spoilers;
1/15 floor slope; 15.2 cm x 15.2 cm (6 in x 6 in) inlet size;
shredded Petrothene X 0.5 mm < d < 3 mm (.02 in < d < .12 in) SG 1.01;
spiral flow guide 2.5 cm (1 in) high encircling foul outlet
2
3
4
15
16
17
20
20
20
Yes
Spiral flow
Yes
Spiral flow
Yes
5
guide
5
guide
5
0.87 m (2
7.6 cm (3
71
.85
76
in)
79
ft)
high
high.
43
, open
42
open at
48
23
at oul inlet
23
foul outlet
25
Circular weir with lip 5.1 cm (2 in) high; 4 even flow spoilers;
1/15 floor slope; shredded Petrothene 0.5 mm < d < 3 mm
(.02 in < d < .12 in) SG 1.01; concentric skirt 60.5 cm (24 in) 0
immerse 0.5 m (1.64 in) no spiral flow guide; 15.2 cm x 15.2 cm
(6 in x 6 in) inlet size
Yes
65
35
18
Circular weir with lip 5.7 cm (2.25 in) high; 4 even low spoilers; flat
floor; shredded Petrothene 0.5 mm < d < 3 mm (.02 in < d < .12 in)
SG 1.01; no skirt, no spiral low guide;
15.2 x 15.2 cm (6 in x 6 in) inlet size.
45
-------
TABLE 3 (Continued)
Mod. Fig.
No. No.
11
11
23
23
Weir
e
cm(in)
24
24
Inlet
Baffle
Yes
Yes
Draw-off Percent Recovery vs Discharge Recovery
(Percent)
3 I/sec 5 I/sec 7 I/sec Fig.
(0.8 gal/sec) (1.3 gal/sec) (1.8 gal/sec)
14
20
81 54 31
84 56
25
25
12
26 24
Circular weir with lip 5.7 cm (2.25 in) high; 4 even flow spoilers;
horizontal floor; 10.2 cm x 10.2 cm (4 in x 4 in) inlet size;
shredded Petrothene 0.5 mm
-------
Four Flow Spoilers
of uneven length
INLET
15.24 a 15.24cm
(6inx 6in)
Four Flow Spoilers
of uneven length
To Overflow Tank
FOUL OUTLET
ELEVATION
Section A-A
FIGURE 24 a MODEL LAYOUT FOR TESTS 2 to 13
MODIFICATION 1
47
-------
UNEVEN FLOW SPOILERS STUCK ON THE 50.8 cm (20 in ) WEIR DISK
(Modification 1)
MODIFICATION 1 TESTED WITH A 3 I/sec (0.8 gal/sec) DISCHARGE
FIGURE 24 b MODEL LAYOUT FOR TESTS 2 to 13
MODIFICATION 1
48
-------
DEPOSIT OF PETROTHENE FOUND AT INLET AFTER 3 I/sec (0.8 gps)
DEPOSIT OF PETROTHENE FOUND IN THE CHAMBER BOTTOM
AFTER 3 I/sec (0.8 gal/sec) TEST
FIGURE 25 DEPOSIT OF PETROTHENE FOUND AFTER
3 I/sec (0.8 gal/sec) TEST
49
-------
Qm I/sec 0
(gal/sec)
Qp I/sec L_
gal/sec
°P
Q
ft3/sec
mgd
DISCHARGE
J_
50
(13.2)
100
(2.64)
150
(39.6)
200
(52.8)
250
(66)
Tests carried out with Inlet Deflector
— Tests carried out without Inlet Deflector
MATERIAL USED : Ground Petrothene X-nominal SG 1.01
Grain sizes 0.5 - 3 mm irregular shapes
FIGURE 26 INFLUENCE OF INLET DEFLECTOR ON RECOVERY RATE
0.50 m (20 in.) 0 WEIR DISK, 5 PERCENT DRAW-OFF - MODIFICATION 11
50
-------
15.24 cm x 15.24cm
(6inx 6 in)
(1 in)
FOUL OUTLET
TO OVERFLOW TANK
INLET
BAFFLE
FLOW SPOILERS
OF SAME LENGTH
BOTTOM
SPIRAL
FLOW
GUIDE
FIGURE 27 MODEL LAYOUT FOR TESTS 14 to 16
MODIFICATION 2
51
-------
the foul outlet, also shown in Figure 27,
Modification 2. The purpose of this
device was to help concentrate a part of
the flow around the central overflow pipe
where weak velocities prevailed, and to
reduce the solids deposits on the chamber
bottom during normal operation of the
model.
Results as shown in Table 3, when
compared to previous values for Stage 1,
indicated an 18-percent drop of
efficiency for small 3 I/sec (0.8 gal/sec)
and intermediate 5 I/sec (1.3 gal/sec)
flows. Values for the high flow 7 I/sec
(1.8 gal/sec) remained unchanged.
Modifications 3 and 4 included the same
spiral flow guide with different heights;
both were open at the four outlet. As
shown in Figure 28, Model Layout for
Tests 17 to 19, Modifications 3, the
height of the spiral flow guide was 2.2 cm
(0.87 in) above the chamber floor at the
foul outlet. This is shown in Figure 29,
Inlet Baffle, Modification 3. It was raised
to 7.6 cm (3.0 in) as shown in Figure 30,
Model Layout for Tests 20 to 22,
Modification 4; and in Figure 31, Details,
Modification 4. Results showed a slight
improvement with respect to
Modification 2, but the best efficiency
rate was still 8 percent below the values
obtained in Stage 1, with no special flow
guide, and deposits of solids at the small
flow were still not eliminated. This device
was discarded in the ensuing tests for this
reason.
2. Influence of a Concentric Skirt
for Collecting Floatables —
Modifications 5, 6, and 7
The configuration for these tests is shown
in Figure 32, Model Layout for Tests 23 to
31, Modifications 5, 6, and 7. These stages
dealt with the influence of a concentric skirt,
61.0 cm (24.0 in) in diameter, designed to
retain floatables when set at different
immersion depths.
The bottom of the skirt was successively
placed 1.25 cm (0.5 in) Modification 5; 2.5
cm (1.0 in) Modification 6; and 5.0 cm (2^0
in) Modification 7; below the water level in
the chamber. Weir diameter and inlet baffle"
conditions were similar to those • previously
used in Modifications-2, 3, and 4.
Addition of the skirt resulted in • a
decrease of about 30 percent in the recovery
rate. The reduction in efficiency seemed to
increase with the immersion depth, but the
scattered results obtained failed to define a
specific trend. The poorest results were those
obtained with the 5.0 cm (2.0 in) immersion
depth, Modification 7, and intermediate
discharge 5 I/sec (1.3 gal/sec).
Therefore, the use of the skirt was
discarded in subsequent tests and floatables
were allowed to discharge with the overflow
effluent.
3. Influence of Weir Diameter —
Modifications 8 and 9
These modifications are shown in Figures
24a and 24b, Model Layout for tests 2 to 13;
Figure 33, Model Layout for Tests 32 to 35,
Modification 8; and Figure 34, Model Layout
for Tests 36 to 38, Modification 9.
Smaller diameter weirs provide a wider
area between the weir lip and the chamber
wall than do larger weirs. This reduces the
upward velocity component, giving a better
opportunity for the simulated erosion runoff
particles in suspension to settle.
On the other hand, the distance from the
central overflow pipe to the weir lip or crest is
reduced in proportion when smaller weirs are
used and, consequently, the time allowed for
particles in suspension under the weir to settle
is shortened. On the basis that an optimum
size must exist, decision was made to test two
additional weirs: one had a weir with a 61 cm-
(24 in) diameter, Modification 8, shown in
Figure 33, Model Layout for Tests 32 to 35.
The other provided a weir with a 71 cm-(28
in) diameter. Figure 34, Model Layout for
Tests 36 to 38, Modification 9; and Figure 35,
Details - Modification 7; show this change.
Results, as plotted in Figure 36, Influence
of Weir-Chamber Diameter Ratio, show that
the differences in efficiency are smaller
between the small and intermediate weirs
than when the largest weir is utilized. They
show also that the maximum was reached
when a weir of 61 cm (24 in) was used.
Subsequent tests were, therefore, carried
out with a weir-chamber diameter ratio of
2:3.
52
-------
15.24 cm x 15.24cm
(6 in x 6 in)
2.54 cm
(1 in.)
FOUL, OUTLET
TO OVERFLOW TANK
INLET
BAFFLE
FLOW SPOILERS
OF SAME LENGTH
BOTTOM
SPIRAL
FLOW
GUIDE
FIGURE 28 MODEL LAYOUT FOR TESTS 17-19
MODIFICATIONS
53
-------
Modification 2: 50.3 cm (20 in ) diameter weir. Inlet Baffle and bottom.
Spiral Flow Guide 2.5 cm (1 in } high closed at foul outlet.
Modification 3: 50.3 cm (20 in ) diameter weir. Inlet Baffle and bottom.
Spiral Flow Guide 2.2 cm (0.87 in ) high open at foul
outlet.
FIGURE 29 INLET BAFFLE, MODIFICATION 3
54
-------
15.24 cm x 15.24 cm
(6 in x 6 in) ,
FOUL OUTLET
TO OVERFLOW TANK
INLET
BAFFLE
FLOW SPOILERS
OF SAME LENGTH
2.54cm
(1 in)
BOTTOM
SPIRAL
FLOW
GUIDE
FIGURE 30 MODEL LAYOUT FOR TESTS 20 to 22
MODIFICATION 4
55
-------
.^____i^H
Modification 4: View of the bottom spiral. Flow Guide 7.5 cm (3 in
high at foul outlet.
Modification 4: 50.3 cm (20 in ) diameter weir. Inlet Baffle and bottom.
Spiral Flow Guide 7.5 cm (3 in ) high open at foul outlet.
FIGURE 31 DETAILS, MODIFICATION 4
56
-------
INLET
15.24 cm x 15.24cm
(6 in x 6 in)
FOUR FLOW SPOILERS
OF SAME LENGTH
Variable immersion
of Skirt End
FOUL OUTLET
54 cm (1 in.)
TO OVERFLOW TANK
ELEVATION
Section A-A
FIGURE 32 MODEL LAYOUT FOR TESTS 23 to 31
MODIFICATIONS 5, 6 and 7
57
-------
FOUR FLOW SPOILERS
OF SAME LENGTH
INLET
15.24 cm x 15.24cm
(6 in x 6 in)
TO OVERFLOW TANK
FOUL OUTLET
2.54 cm (1 in )
Section A-A
FIGURE 33 MODEL LAYOUT FOR TESTS 32 to 35
MODIFICATION 8
58
-------
FOUR FLOW SPOILERS
OF SAME LENGTH
INLET
15.24 cm x 15.24cm
(6 in x 6 in)
FOUL OUTLET
2.54 cm (1 in )
TO OVERFLOW TANK
ELEVATION
Section A-A
FIGURE 34 MODEL LAYOUT FOR TESTS 36 to 38
MODIFICATION 9
59
-------
61 cm (24 in.) diameter weir and inlet baffle
71 cm (28 in ) diameter weir and inlet baffle
FIGURE 35 DETAILS, MODIFICATION 7
60
-------
Q
Op
90
80
70
g 60
cc
LLJ
> 50
UJ
8 40
UJ
CC
30
20 -
10
I/sec
(gal/sec)
I/sec
_
O
Op ft3 /sec
mgd
\
\
\
\
\
\
\
\
1
(.26)
2
(.53)
Discharge
-i : 1 L
3
(.8)
5
(1.3)
6
(1.6)
7
(1.8)
8
(2.1)
50
IOO
150
200
i
250
0 = 0.51 m (20in)D3/D =0.555 Mod. I • —•
0 = 0.61 m (24ln) D3/D = 0.667 Mod. 8 Q— D
0 = 0.71 m (28in) Dg/D = 0.78 Mod. 9 O -•——O
Material Used = Ground Petrothene X nominal SG 1.01
Grain Sizes 0.5-3 mm (0.2-12 in ) irregular shapes
FIGURE 36 INFLUENCE OF WEIR - CHAMBER DIAMETER RATIO
(All tests carried out with inlet baffle)
1:15 CHAMBER FLOOR SLOPE AND 5 PERCENT DRAW-OFF
61
-------
4. Influence of the Chamber Floor Slope —
Modification 10
These modifications are shown in Figure
37, Model Layout for Tests 39 to 4,1,
Modification 10; and in Figure 38, Model
Layout for Tests 42 to 59 and 69 to 107,
Modification 11.
Since cattle watering tanks are suggested
as an economical way to construct these swirl
chamber units, studies were undertaken to
test the effect on the recovery rate produced
by a flat chamber floor. Both the 51 cm- (20
in) and 61 cm- (24 in) diameter weirs wete
tested with 5 percent draw-off. Only results
relevant to the second weir are presented in
Figure 3 9, Influence of Chamber Floor Slope.
It shows that a flat floor is not as efficient.
Recovery rates decreased, as indicated by
Table 4, Comparable Recovery Rates for
Sloping and Horizontal Chamber Floors.
Table 4 indicates that the 61 cm- (24 in)
diameter weir had smaller losses, and yielded
better recovery rates for intermediate and
high discharges when the floor slope was
eliminated. Therefore, this weir diameter
should be considered for design purposes with
either a flat chamber bottom or with the 1:15
sloping floor.
TABLE 4
COMPARABLE RECOVERY RATES
FOR SLOPING AND HORIZONTAL
CHAMBER FLOORS
Recovery Rates (Percent)
at Rate of Flow
Model discharge
I/sec {ft3/sec) 3(0.11) 5(0.18) 7(0.25)
A. Tests of recovery rates performed with a 51 cm
(20 in) <£ Weir:
slope of 1/15 86 52 22
horizontal floor 66 37 15
absolute loss 20 15 7
relative loss 23 29 31
B. Tests of recovery rates performed with a 61 cm
(24 in) Weir:
slope of 1/15 87 54 20
horizontal floor 66 44 23
absolute loss 21 10 3'
relative loss 24 19 11
5. Influence of Continuous Underflow
Draw-Off, Modification 11
This configuration is shown in Figure 38,
Model Layout for Tests 42 to 59 and 69 to
107, Modification 11. Although the
preceeding tests were all carried out with a 5
percent continuous underflow, additional
tests were performed at increased draw-off
rates. The rates selected were 10 and 20
percent of the discharge.
The foul outlet pipe was unable to pass
the-l,400-cm3/sec (85.4 in3/sec) required for
the 7 I/sec (1.8 gal/sec) discharge at the 20
percent draw-off rate. The maximum rate
evacuated was 14 percent; therefore, the same
rate was applied respectively to 3 and 5 I/sec
(0.8 and 1.3 gal/sec) discharges.
Results, as plotted in Figure 40, Influence
of Continuous Underflow Draw-off,
Modification 11, show that the efficiency
increased with the draw-off. This
phenomenon seemed more pronounced for
small discharges 3,I/sec (0.8 gal/sec) than for a
high 7 I/sec (1.8 gal/sec) rate.
Of importance is the fact that deposits of
solids on the bottom of the swirl chamber
disappeared gradually as the underflow
draw-off rate was increased.
6. Influence of Inlet Size Modification 12
Conditions represented by Figure .41,
Model Layout for Tests 60 to 68,
Modification 12, were similar to those for
Modification 11, except that the square inlet
pipe was reduced to 10.1 cm (4 in) instead of
the 15.2 cm (6 in) previously used. Trie same
draw-off, representing 5 percent of the total
discharge, was maintained so the results
would be directly comparable.
The recovery rate for the two sizes of
pipe inlets are shown in Figure 42, Influence
of Inlet Size. Although the same inlet baffle
was used, Figure 41 shows that efficiency of
the swirl chamber dropped significantly when
the inlet velocity was increased.
Consequently, the 15.2 cm x 15.2 cm (6 in x
6 in) inlet was installed in! the model for
further tests.
Tests Carried Out with Petrothene
'Dust - SG 1.01
0.12 mm < d < 0.5 mm (0.005 < d < 0.2 in)
After the model had been set up for
62
-------
FLOW SPOILERS
OF SAME LENGTH
INLET
15.24 cm x 15.24cm
(6 in x 6in)
270 —
FOUL OUTLET
INLET
BAFFLE
WEIR UP 5cm
(2 in )'
ELEVATION
Section A-A
TO OVERFLOW TANK
2.54 cm
(1 in)
FOUL OUTLET
FIGURE 37 MODEL LAYOUT FOR TESTS 39 TO 41
MODIFICATION 10
63
-------
FOUR FLOW SPOILERS
OF SAME LENGTH
INLET
15.24 cm x 15.24cm
(6 in x6in)
TO OVERFLOW TANK
FOUL OUTLET
2.54cm (1 in.)
Section A-A
FIGURE 38 MODEL LAYOUT FOR TESTS 42 TO 59
AND 69 TO 107
MODIFICATION 11
64
-------
100
90
80
70
60
50
40
30
20
10
Qm I/sec C
(gal/sec)
Q I/sec
Q ft3 /sec
P
Q mgd
\
\
\ \
\ \
\ \
\ \
\ ~
\ *
\ \
\ \
\ \
\ \
\ \
\ \
\ \
\ ^
n\
i
D123456789
(.26) (.53) (.8) (1.1) (1.3) (1.6) (1.8) (2.1) (2.4)
DISCHARGE
i i i i i
0 50 IOO I50 200 250
I i i i i i ill
0123456789
1 | l 1 1 1
01 23456
0.61 m (24 in) Weir Diameter
n— • •— D Horizontal Chamber floor Mod. II
Material used - Shredded Petrothene X nominal SG = 1.01
Grain Size 0.5 - 3mm irregular slopes
FIGURE 39 INFLUENCE OF CHAMBER FLOOR SLOPE
(All tests carried out with inlet baffle
and 5 percent Draw-off)
65
-------
80
70
H-
0 60
•CC
LU
CL
> 50
LU
8 40
LU
CC
30
20
i r\
IU
\"
-.
~ .'.
- < . \\
•v \ •'•-
\. \\-.
\. \ o
\y ^ \~|
N. \ M^
\\\
\.NN\
^V » \
>VX\
\>°\
*\
Discharge
i i i i i i i
Q,,, I/sec 0 1 23 4 5 6 7 8
°P
Qp
Qp
(gal/sec) (.26) (.53) (.8) (1.1) (1.3) (1.6) (1.8) (2.1)
I I I i I
I/sec 0 50 100 150 200 250
1 1 1 I I i i 1 1
cfs 0 1 2 34 5 6 7 89
1 1 | 1 II
mgdO 1 2 3 4 5 6
A— —A 1 n °/ " " / d U/nir ^
0 d 14% " " ( 15.2 x 15.2 cm (6x6 in))
Material Used: Shredded Petrothene X nominal SG 1.01
Grain Sizes 0.5 - 3 mm irregular shapes
FIGURE 40 INFLUENCE OF CONTINUOUS
UNDERFLOW DRAW-OFF
MODIFICATION 11
66
-------
FOUR FLOW SPOILERS
OF SAME LENGTH
- INLET
10.2 cm x 10.2 cm
(4 in x4 in)
TO OVERFLOW TANK
FOUL OUTLET
2.54cm (1 in )
Section A-A
FIGURE 41 MODEL LAYOUT FOR TESTS 60 to 68
MODIFICATION 12 - SG 2.65
67
-------
80
70
2 60
01
O
DC
uj 50
cc
% 40
O
0
LU
cc 30
20
10
0
I/sec
(gal/sec)
N •.
X°N\
x x\
NNN *\
N ^S.
"^^
I
1 | , i | i | 1
1 234 5678
(.26) (.53) (.8) (1.1) (1.3) (1.6) (1.8) (2.1)
Discharge
i ill i
0 I/sec 0 50 100 150 200 250
QP
QP
ft3/sec 0 ',2 3, 4 ,5 6, 7 |8 9|
mgd c
) 1 2 3 4 5 6
15.2 cm x 15.2 cm (6 in x 6 in) INLET SIZE. Mod. 11-5% Draw off
O-„.-._._o 10.1 cm x 10.1 cm (4 in x 4 in) INLET SIZE. Mod. 12-5% Draw off
Material used: shredded Petrothene x nominal SG — 1.01
Grain sizes: 0.5 - 3 mm (.02- .12 in)
irregular shapes
FIGURE 42 INFLUENCE OF INLET SIZE
68
-------
optimum recovery, a new series of tests was
carried out with Petrothene dust. The
configuration corresponding to Modification
1, Figure 23, was used, namely a 15.2 cm x
15.2 cm (6 in x 6 in) square inlet, and a 0.61
m (2 ft) diameter weir with 5.7 cm (2.25 in)
lip. The crest of the lip was set at the same
elevation as the inlet crown; the flat chamber
floor was retained.
The series of tests involved the use of the
three respective discharges — 3,5, and 7 I/sec
(0.8, 1.3, and 1.8 gal/sec) in the model with
varying draw-off rates (5, 10, and 14 percent).
This total of nine additional tests completed
the data necessary to prepare the curves in
Figures 43, 44, and 45, Suggested Recovery
Curves for Gilsonite and Petrothene in Model
with 5 percent, 10 percent, and 14 percent
Draw-off, respectively.
Predicted Prototype Grit Recovery
As mentioned, the recovery curves
attained for the Gilsonite and Petrothene in
the model studies are as shown in Figures 43,
44, and 45.
For the three model discharges used in
the tests, the corresponding recovery rates are
given in Table 5, Percent Suggested Recovery
in Model.
The recovery rates have been expressed as,
a function of the particle settling velocity, to
provide for more effective use of the curves.
Plotting according to this method gave the
curves represented in Figures 6, 7, and 8.
The advantage of this method of
presentation is that it allows a precise
interpolation for particle settling velocities
lying within the range of the materials used.
For example, to find the recovery rate
corresponding to a particle whose settling
velocity is 0.5 cm/sec (0.2 in/sec) with 10
percent draw-off, the values can be found in
Figure 33 on the vertical 0.5 cm/sec (0.2
in/sec) at the respective intersections with the
3, 5, and 7 I/sec (0.8, 1.3, and 1.8 gal/sec)
discharges. Results are 66, 42, and 21 percent,
respectively.
The final steps in calculating the
predicted prototype recoveries are as follows:
a. For a given model particle settling
velocity in either Figure 6, 7, or 8. To
find the recovery rate for a given
discharge.
b. Multiply the particle_settling velocity by
the velocity scale, ^/ 4 = 2, to find the
particle settling velocity in the prototype.
c. Use Figure 5 with this prototype particle
settling velocity and find the
corresponding grit size for SG 2.65.
d. Multiply the given discharge in (a), above,
by the discharge scale 4s/2 = 32 to find
the prototype discharge.
e. Plot the grit particle size (c) as a function
of discharge (d) and recovery rate (a) in
Figures 9, 10, or 11.
An example can be followed through this
procedure: in Figure 8, take the particle
settling velocity of 0.8 cm/sec (0.3 in/sec)
with a model discharge of 5 I/sec (1.3 gal/sec).
This shows a recovery rate of 54 percent.
These particles in the prototype would have a
settling velocity of 2 x 0.8 =1.6 cm/sec (0.63
in/sec). In Figure 5, this gives a grit particle
size of 0.16 mm (0.006 in) or 160/u.
Multiplying the model discharge of 5 I/sec
(1.3 gal/sec) by 32 gives 160 I/sec (42.2
gal/sec). The particle size, discharge, and
recovery rate then define one point in Figure
.11, as shown.
A network of points was calculated for
each of the draw-off rates to give the families
of curves in Figures 9, 10, 11.
TABLE 5
PERCENT SUGGESTED RECOVERY IN MODEL
Discharge
model
I/sec qal/sec
3 (0.8)
5 (1.3)
7 (1.8)
Gilsonite
Draw-off
5% 10% 14%
99.5 99.5 99.5
89 93 95
67 75 84
Shredded Petrothene
Draw-off
5% 10% 14%
66 73 81
44 50 54
23 27 31
Petrothene Dust
Draw-off
5% 10% 14%
46 52 56
25 28.5 33
12 14 18
69
-------
100
90
80
70
Z 60
LU
O
DC
S 50
cc
LU
> 40
o
LU
or
30
20
10
Q_
p
QL
I/sec 0
gal/sec
I/sec
ft3/sec o
mcjd o
Model
J I
Discharge
Gilsonite
0.5 - 3 mm
(.02-.12 in)
Petrothene x
0.5 - 3 mm
.02 -.12 in)
Petrothene Dust
0.12 — 0.5 mm
(.005 - .02 in)
1
(.26)
2
(.53)
3
(.8)
4
(1.1)
5
(1.3)
6
(1.6)
7
(1.8)
8
(2.1)
50
100
150
200
I
250
I
PROTOTYPE
' DISCHARGE
(SCALE 1/4)
15.2 cm x 15.2 cm (6 in x 6 in ) INLET SIZE - INLET DEFLECTOR
FIGURE 43 SUGGESTED RECOVERY CURVES FOR
GILSONITE AND PETROTHENE IN MODEL
WITH 5 PERCENT DRAW-OFF
70
-------
o
cc
8
m
100
90
80
70
60
50
40
30
20
10
felLSONITE
0.5-3 mm
(.02-.12 in)
SHREDDED
PETROTHENE 'X
0.5-3 mm
(.02-.12 in)
PETROTHENE
DUST
0.12-0.5 mm
(.005 - .02 in)
Qm I/sec
(gal/sec)
I
I
I
1
(.26)
2
(.53)
3
(.8)
4
(1.1)
5
(1.3)
6
(1.6)
7
(1.8)
8
(2.1)
9
(2.4)
DISCHARGE MODEL
DISCHARGE PROTOTYPE SCALE I/4
Qp I/sec 0
2p ft3/sec
1_
T> mgd 0
I
I
50
I
IOO
150
_L
200
I
I
I
I
I
_L
J_
I
8
250
L_
123456
15.2 cm x 15.2 cm (6 in x 6 in.) INLET SIZE - INLET DEFLECTOR
FIGURE 44 SUGGESTED RECOVERY CURVES FOR
GILSONITE AND PETROTHENE IN MODEL
WITH 10 PERCENT DRAW-OFF
71
-------
100
90
80
70
Z 60
in
o
cc
ui en
a. 5O
CC
ui
> 40
O
u
LU
tt 30
20
10
0
I/sec 0
(gal/sec)
I
I
I
I
j_
1
,26)
2
(.53)
3
(.8)
4
(1.1)
5
(1.3)
6
(1.6)
GILSONITE
0.5-3 mm
(.02-.12 in)
SHREDDED
PETROTHENE
0.5-3 mm
(.02-.12 in)
PETROTHENE
DUST
0.12-0.5 mm
(.005 - .02 in)
7
(1.8)
8
(2.1)
DISCHARGE MODEL
DISCHARGE PROTOTYPE SCALE
9
(2.4)
I/4
Qp I/sec 0
Qp ft3/sec 0
Q p m g d
I
50
JL
IOO
ISO
_L
I
I
I
200
I
I
_L
_L
8
250
I
0123456
15.2 cm x 15.2 cm (6 in. x 6 in ) INLET SIZE - INLET DEFLECTOR
FIGURE 45 SUGGESTED RECOVERY CURVES FOR
GILSONITE AND PETROTHENE IN MODEL
WITH 14 PERCENT DRAW-OFF
72
-------
After the range of discharge of normal
operation for the prototype had been
determined, computations were carried out to
determine the corresponding retention time.
The approach followed was to take the whole
volume of the chamber up to the circular weir
lip rest level and to subtract the volume of
both the weir and central overflow pipe. The
results of this computation are presented in
Figure 46, Retention Times for Prototype.
REFERENCES
7. Hydraulique et Granulats, Jean Larras,
Eurolles, Paris, 1972, 256 pp.
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
EPA-600/2-76-271
3. RECIPIENT'S ACCESSION- NO.
. TITLE AND SUBTITLE
THE SWIRL CONCENTRATOR FOR EROSION
RUNOFF TREATMENT
5. REPORT DATE
December 1976 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
, AUTHOR(S)
Richard H. Sullivan, Morris M. Cohn, James E. Ure,
F. E. Parkinson, and Paul E. Zielinski
8. PERFORMING ORGANIZATI
REPOR
PERFORMING ORG'VNIZATION NAME AND ADDRESS
American Public Works Association
1313 East 60th Street
Chicago, Illinois 60637
10. PROGRAM ELEMENT NO.
1BC611
11. CONTRACT/GRANT NO.
68-03-0272
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory - cin.,
Office of Research and Development
U.S. Environmental Protection Agency \
Cincinnati, Ohio 45268
OH
13. TYPE OF REPORT AND PERIOD COVERED
FINAL
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES i
Supplement to "The Swirl Concentrator as a Combined Sewer Overflow Regulator Facility,"
EPA-R2-72-008, September 1972 (NTIS PB-214 687). USEPA Project Officer: Richard Field,
16. ABSTRACT Telephone: 201-548-3347.
A device for the partial removal of erosion products in stormwater runoff has been developed. The
swirl concentrator as an erosion control device has been designed to concentrate the heavier soils from
large flows. The concentrated underflow of up to 14 percent of the flow can be directed to a forebay
or settling basin.
The device is circular and for small watersheds a simple stock watering tank could be used with
only minor modifications.
The design of the swirl concentrator as an erosion control device is based upon a hydraulic model
study and research previously sponsored by the City of Lancaster, Pennsylvania and the U.S.
Environmental Protection Agency into the mechanics of secondary motion flow^fields as developed in
the swirl concentrator.
This report is submitted by the American Public Works Association in partial fulfillment of the
contract 68-03-0272 between USEPA and APWA Research Foundation.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS , C. COS AT I Field/Group
Overflows
Design
Flow rate
Swirling—separation
Waste treatment
*Erosion control
Soil erosion
*Solids separation
* Swirl concentrator
Overflow quantity
Overflow quality
Stormwaterl runoff
13b
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
82
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
74
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