EPA-670/2-75-011
April 1975
Environmental Protection Technology Series
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EPA-670/2-75-011
April 1975
PHYSICAL AND SETTLING CHARACTERISTICS OF
PARTICIPATES IN STORM AND SANITARY WASTEWATERS
by
Robert J. Dalrymple
Stephen L. Hodd
David C. Morin
Beak Consultants Limited
Rexdale, Ontario, Canada
Contract No. 63-03-0272
Program Element No. 1BB034
Project Officer
Richard Field
Storm and Combined Sewer Section (Edison, N.J.)
Advanced Waste Treatment,Research Laboratory
National Environmental Research Center
Cincinnati, Ohio 45268
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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REVIEW NOTICE
The National Environmental Research Center — 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.
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FOREWORD
Man and his environment must be protected
from the adverse effects of pesticides, radiation,
noise and other forms of pollution, and the unwise
. management of solid waste. Efforts to protect the
environment require a focus that recognizes the
interplay between the components of our physical
environment - air, water, and land. The National
Environmental Research Centers provide this
multidisciplinary focus through programs engaged
in
• studies on the effects of environmental
contaminants on man and the biosphere,
and
» a search for ways to prevent
contamination and to recycle valuable
resources
The studies by the American Public Works
Association of the use of secondary motions for
the separation of solids from liquid flow fields has
required precise definition of settleable solids in
stormwater, combined sewer overflows, and
sanitary sewage. Solid characteristics such as
particle shape, size, and settling velocity determine
the design and efficiency of solids removal.
Information on solid characteristics has not
been researched to an appreciable degree. There is
need for better definition of solids to facilitate
design of physical treatment methods.
This report by Beak Consultants, Limited,
covers studies conducted for solids, and the search
for solids which could be used in a hydraulic model
to simulate sewage solids.
The wide range of information which has been
reported highlights the need for studies of this type
to more precisely define the solids in the various
flows to be treated.
A. W. Breidenbach, Ph.D.
Director
National Environmental Research Center
Cincinnati
in
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ABSTRACT
An investigation was conducted, as part of model studies
utilizing a swirl concentrator as a primary separator, helical
combined sewer overflow regulator, and related studies, to
characterize the properties of solids in sanitary sewage,
combined sewer overflows, and stormwater runoff. To
effectuate this study, material suitable for monitoring
removal efficiencies in hydraulic models of the swirl
concentrator unit has been developed.
The approach taken by Beak Consultants, Ltd., serving as
a subcontractor to the American Public Works Association in
the simulation sewage studies, was to match as closely as
possible the settling characteristics of solids in three types of
sewage and/or urban runoff with a well-defined, uniform
artificial test material. An Amberlite anion exchange resin
(IRA-93), when ground and sieved to between 74 and 149
microns, was found to closely simulate the settling
characteristics of domestic sewage. This material is of
uniform density and appears to react according to Stokes'
law for spherical particles at this size range. Arizona Road
Dust, between 10 and 20 microns, was found to exhibit a
similar settling velocity distribution.
Importantly, as background information for the selection
of synthesized solids, the settling characteristics (including
size and specific gravity distribution) of a few samples of
sanitary sewage, combined sewer overflow, and stormwater
were determined. These values will be useful for future
determinations of physical treatment process design and
associated treatability.
This report on these studies recommends that either or
both of these materials be used in the scale-model efficiency
trials.
This report was submitted in partial fulfillment of
Contract 68-03-0272 between the U.S. Environmental
Protection Agency and the American Public Works
Association.
IV
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AMERICAN PUBLIC WORKS ASSOCIATION
Board of Directors
Herbert A. Goetsch, President
Ray W. Burgess, Vice President
Erwin F. Hensch, Immediate Past President
Jean V. Arpin
John T. Carroll
Donald S. Frady
Lambert C. Mims
James J. McDohough
Robert D. Obering
John J. Roark
James E. McCarty
Robert D. Bugher, Executive Director
Kenneth A. Meng
Wesley E. Gilbertson
Frank R. Bowerman
A.R. Marschall
APWA RESEARCH FOUNDATION
Board of Trustees
Samuel S. Baxter, Chairman
Milton Pikarsky, Vice-Chairman
Fred J. Benson John A. Lambie
Ross L. Clark James E. McCarty
John F. Collins D. Grant Mickle
W. C. Gribble Marc C. Stragier
Robert D. Bugher, Secretary-Treasurer
Richard H. Sullivan, General Manager
Martin Manning, Director of Research
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CONTENTS
Page
Section I Overview, Findings and Recommendations 1
Section II Review of Physical and Chemical Characteristics of
Suspended Solids in Sanitary Sewage, Combined Overflows,
and Stormwater Runoff 13
Section III Settling Velocity Relationships of Sanitary Sewage and Stormwater Runoff . . 13
Section IV Simulated Sewage 16
Section V References 27
Section VI Appendices
Appendix A — Laboratory Methods Used by Beak Personnel 29
Appendix B — Preparation of Amberlite IRA-93 Solid Particles ...'.... 31
Appendix C - Monitoring Procedure for Efficiency Trials 32
TABLES
1. Particle Size Distribution of Suspended Solids in Sanitary Sewage 5
2. Solids Classification by Concentration in Sanitary Sewage 6
3. Particle Size Distribution of Volatile Suspended Solids in Sanitary Sewage .... 7
4. Particle Size Distribution of Suspended Solids in Combined Sewer Overflows ... 7
5. Solids Concentrations in Combined Sewer Overflows 9
6. Particle Size Distributions of Solids - Selected City Composites 11
7. Physical Characteristics of Simulated Sewage Materials 18
8. Efficiency Program Monitoring Program Conditions 32
FIGURES
1. Particle Size Distributions of Some Waste Stream Solids 4
2. Settling Velocity Distribution of Solids in Sanitary Sewage 14
3. Settling Velocity Distribution by Weight of Solids in Stormwater Runoff . ... 15
4. Settling Velocity Distribution of Solids in Sanitary Sewage After Application
Application of Model Scale Factor • 17
5. Settling Velocity vs Particle Size for IRA-93 Anion Exchange Resin 1.9
6. Settling Velocity vs. Particle Size for XAD-2, Non-Ionic Resin 20
7. Settling Velocity vs Particle Size for Shredded Petrothene X-l 01 20
8. Settling Velocity Distribution for 50-100 Mesh IRA-93, 149-297 Microns ... 22
9. Settling Velocity Distribution for 200-400 Mesh IRA-93, 38-74 Microns .... 22
10. Settling Velocity Distribution for 2100-200 Mesh IRA-93, 74-149
Microns and Comparison With Sanitary Sewage (after
application of Model Scale Factor) 24
11. Efficiency Monitoring Material IRA-93, 74-149 Microns . 25
12. Efficiency Monitoring Material Ira-93, 74-149 Microns (Wet Sieved) 25
13. Settling Velocity Distribution for Arizona Road Dust (10-20 Microns) 26
14. Settling Velocity Distribution for Petrothene Dust «1000 Microns) 26
VI
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ACKNOWLEDGMENTS
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
Dr. Paul Zielinski
ALEXANDER POTTER ASSOCIATES
CONSULTING ENGINEERS
Morris H. Klegerman
James E. Ure
T.W. BEAK, CONSULTANTS, LTD.
Stephen L. Hodd
David C. Morin
Robert J. Dalrymple
APWA STAFF
Lois Borton Cecelia Smith
Shirley Olinger Oleta Ward
U.S. ENVIRONMENTAL PROTECTION AGENCY
Richard Field, Project Officer
Chief, Storm and Combined Sewer Section (Edison, N.J.)
Advanced Waste Treatment Research Laboratory
Cincinnati, Ohio 45268
VII
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SECTION I
OVERVIEW, FINDINGS AND RECOMMENDATIONS
The research study reported here has
resulted in the identification of an artificial
material which may be used to represent the
settling velocity characteristics of raw sanitary
sewage flows and combined sewer overflows.
This material has generally proved suitable for
monitoring the solids removal efficiency of a
model swirl concentrator being evaluated
under the current contract. The development
and evaluation of this material is the principal
result of an intensive search and study which
has resulted in several significant laboratory
determinations.
A literature review of the 'settling
characteristics of combined sewer overflows
provided little information as to settling
velocities of the suspended matter to be
expected. Settling column tests on primary
sewage in Philadelphia, Pa., disclosed that the
median settling velocity of the suspended
solids was 0.054 cm/sec (0.106 ft/sec).
Attention was then directed to the selection
of artificial materials with settling velocities
approaching this parameter. Settling column
studies on a variety of solid particles indicated
that Amberlite IRA-93, anion exchange resin
with a specific gravity of 1.04, possessed
lower settling velocities than all other
materials evaluated. Amberlite IRA-93, in its
commercially available state, still did not have
sufficiently low settling velocities to
accurately simulate the action of sewage
solids. Therefore, the resin was pulverized,
classified according to particle size, and
further settling column tests were conducted.
Settling velocities for that portion passing
through 100-mesh and retained on 200-mesh
(74-145^) provided results compatible with
the desired range.
FINDINGS AND RECOMMENDATIONS
Based on results of studies of simulated
sewage solids materials, it is recommended
that the 'hydraulics prototype studies being
conducted at the LaSalle Hydraulics
Laboratory to develop and determine swir!
concentrator removal efficiency proceed with
the use of the proper size range of Amberlite
IRA-93, Anion Exchange Resin and Arizona
Road Dust. Both of these materials exhibit
settling velocities in the desired ranges.
However, the high cost and reported
unavailability of the Arizona Road Dust have
resulted in the use of the IRA-93 in initial
monitoring tests.
The apparent improvement in settling
characteristics after storage due to
agglomeration of small particles should be the
subject of additional study to define the
effects of storage on settling characteristics
and to determine the overall feasibility of this
form of pretreatmeht. In addition, combined
sewer overflows should be tested to determine
if there is a like improvement in settling
characteristics after storage.
THE STUDY
This research study was performed by
Beak Consultants Limited, as a subcontractor
to the American Public Works Association,
(APWA), in connection with U.S.
Environmental Protection Agency (EPA)
Contract No. 68-03-0272. This contract was
dated April 26, 1973 and is entitled
Development of a Swirl Primary Separator
and a Helical Combined Sewer Overflow Dual
Functioning Regulator and Separator. The
overall objective of this contract is the
development and evaluation of a solids
separation device to provide primary
treatment of combined sewer overflows and
stormwater runoff. The swirl separator, in
addition, has applicability as a primary
clarification unit at a wastewater treatment
plant for handling dry-weather sanitary
sewage.
Importantly, as background informatior
for the selection of synthesized solids, the
settling characteristics (including size anc
specified gravity distribution) of sanitarj
sewage, combined sewer overflow, anc
stormwater were determined. These value
will be useful for future determinations o
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physical treatment process design and associated
treatability.
APWA has conducted hydraulic and
mathematical model studies to develop the
basic design and determine the efficiency of
the unit. In conjunction with the hydraulic
studies, a mathematical model has been
developed to predict particle flqw in the swirl
concentrator. To preclude the utilization of
actual sewage particulates in hydraulic studies
and to facilitate computer simulation, Beak
Consultants conducted a study to select a
commercially available material to simulate
the solids fractions in sanitary sewage,
stormwater runoff, and combined sewer
overflows and subsequently to monitor the
efficiency of the swirl concentrator in
removing the suspended particulates
represented by the chosen solids material.
The scope of study included a literature
search to define the properties and
concentration of solids by sizes in combined
sewer overflows and sanitary sewage.
Sampling and analysis of sanitary sewage
provided further information regarding
settling characteristics in relation to particle
size. Having gained knowledge of the settling
velocities of suspended sewage solids, an
evaluation of artificial materials to simulate
sewage solids was undertaken. This report
presents findings of the literature search, data
obtained from sewage sampling, and results of
the tests conducted to select a material which
would represent the range of settling
velocities characteristic of sanitary sewage
solids particles.
The final phase of Beak's study covered a
monitoring program to measure suspended
solids removal efficiency of the swirl
concentrator model at LaSalle Hydraulic
Laboratory. The detailed results of the
monitoring program will be submitted with
the report on the model development.
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SECTION II
REVIEW OF PHYSICAL AND CHEMICAL CHARACTERISTICS
OF SUSPENDED SOLIDS IN SANITARY SEWAGE,
COMBINED SEWER OVERFLOWS, AND STORMWATER RUNOFF
The following section presents the results
of the literature review conducted to
characterize sanitary sewage, combined sewer
overflows and stormwater runoff in terms of
their suspended solids content and physical
and chemical characteristics. In some cases,
investigators reported very similar results,
especially for sanitary sewage. However, the
inconsistency and variability of solids
properties from a study in one city to that in
another was most obvious. For example, these
flows cannot be characterized by single
average concentrations of suspended solids
and volatile content, or by a single particle
size distribution. Rather, a wide range of
individual physical and chemical parameters, is
required to realistically represent the solids
contained in sanitary sewage, combined sewer
overflows and stormwater runoff.
SANITARY SEWAGE
An evaluation of the literature covering
the characterization of solids in sanitary
sewage emphasizes the variability of the
physical and chemical properties of these
solids. These properties are influenced by
such factors as range of flow rate, time of day
and contribution of industrial wastes to the
total flow. Variation of solids properties in
sewage from one geographical location to
another is also evident.
Particle Size Distribution and Density
Several investigators1'2'3'4 separated the
insoluble particulate solids in sewage, into
t.hre,e classifications: (a) settleable; (b)
supracolloidal; and (c) colloidal solids.
Generally the separation, technique involved:
(a) a sedimentation or quiescent settling step
to determine settleable solids; (b) a
centrifugal step to determine supracolloidal
solids; and (c) a candle filtration3.
high-pressure membrane filtration,1 >2 or.
supercentrifugation4 to determine-colloidal
solids. Rickert and Hunter4 report ideal size
limits of > 100 microns, 1 to 100 microns and
1 millimicron to 1 micron for, respectively,
the settleable fraction, supracolloidal fraction
and colloidal fraction. Work by Rudolfs and
Balmat5 confirmed that the limits had been
attained for the first two fractions. However,
electron microscopy studies on secondary
effluent4 indicated that the colloidal fraction
was in the range 0.2 to 1.0 micron. Table 1,
Particle Size Distribution of Suspended Solids
in Sanitary Sewage, shows the results of these
investigations in terms of percent of solids in
each size range. It can be seen that the split is
approximately 45 percent settleable, 35
percent supracolloidal and 20 percent
colloidal. This figure of 45 percent settleable
solids coincides quite closely with accepted
primary' treatment efficiency of 50 to 60
percent removal of total suspended solids, as
reported in the Water Pollution Control
Federation's Sewage Treatment Plant Design,
1967. This . distribution is presented
graphically in Figure 1, Particle Size
Distributions of Some Waste Stream Solids. A
straight line is drawn using only two data
points. The dotted portion of the line
represents an extrapolation.
A sieve analysis of particle size was
carried out on raw sanitary sewage from
Lancaster City, Pa., by Meridian Engineers of
Philadelphia, Pa.6 This analysis shown in
Table 1, covered sizes greater than 149
microns, and showed that only 13 percent of
the solids were greater than 149 microns in
size. This result would seem to indicate that
some sewages can contain a high percentage
of fine solids if it is assumed that the
remainder passed through the 149 micron
sieve. Solids were retained on five sieves only,
indicating a rather narrow particle size range.
In addition to the sieve analysis, specific
gravity measurements of the suspended solids
were carried out, using a mineralogical
sink-float procedure in benzene-acetylene
tetrabromide solution. This analysis showed a
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10,000
I.OOO
IOO
o
LEGEND
— — Extrapolated Results
Sanitary Stw H»
RtftrcncM \i ,4,7
001
9999
Percent by weight
FIGURE 1 PARTICLE SIZE DISTRIBUTIONS OF SOME WASTE STREAM SOLIDS
4
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TABLE 1
PARTICLE SIZE DISTRIBUTION OF SUSPENDED SOLIDS
IN SANITARY SEWAGE
SOURCE OF FIGURES PARTICLE SIZE RANGE DISTRIBUTION
(microns) (percent)
Hunter & Heukelekian1 >100(Settleable) 49.4
(average of two studies) 1 - lOO(Supracolloidal) 31.4
a) Winter-Spring 1959 0.2 - 1.0 (Colloidal) 19.2
b) Fall-Winter 1959-1960
Heukelekian & Balmat2
Meridian Engineers6 *
Painter, Viney & Bywaters7
* Note: Remainder passed No. 200 mesh
>100
1 - 100
0.2- 1.0
> 1,190 (0.047 in.)
590- 1,190
420 - 590
210-420
< 149
>100
1 - 100
0.2 - 1.0
47.0
34.0
19.0
4.42
1.38
3.46
3.09
86.9
37.1
44.8
18.1
range of specific gravities from 0.80 to 1.60
percent were in the specific gravity range 0.80
to 1.25.
It is reasonable to postulate that particle
size can be affected by two main factors: flow
rate and industrial wastewater contribution.
High flow rates in sewer lines can cause
agglomerates to break up, thus producing
more fine solids. Industrial wastes can provide
a variety of particle sizes, dependent on types
of waste involved.
Total and Settleable Suspended Solids
Table 2, Solids Classification by
'Concentrations in Sanitary Sewage, shows
actual solids concentrations found in the
various studies reviewed. Settleable solids range
from 37 percent to 65 percent of the
suspended solids concentration.
No correlation was found between
concentrations of Settleable, solids in
milliliters per liter (mill) and milligrams per
liter (mg/l). Settleable solids are measured
. volumetrically, percentagewise, by quiescent
settling of a one liter sample for one hour in
an Imhoff cone. The cone is graduated in
milliliters and, after one hour, the volume of
settled solids is recorded to give settleable
solids in mill. A sample of at least one liter is
settled quiescently in a cylindrical glass
container for one hour. Suspended solids in
the supernatant liquor are determined before
and after to determine settleable solids
gravimetrically (in mg/l). See Appendix A.
Actual levels of suspended and settleable
solids can be affected by time of day at which
the sample was obtained, by the contribution
of industrial flows, and the amount of inflow,
infiltration or sand among other factors. Peak
flow periods of the day such as morning
(preparation for work) and late afternoon
(cleaning up after work) are characterized by
high solids loads. Large input flows of an
industrial effluent containing high solids levels
also will result in increased solids
concentrations.
Insoluble Oil Fraction
The insoluble oil fraction or total.grease
in sewage was reported by several sources.
Hunter and Heukelekian1 found that
approximately 25 mg/l of grease were
contributed by the particulate matter to the
raw sewage. The settleable solids fraction,
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TABLE 2
SOLIDS CLASSIFICATION BY CONCENTRATIONS IN SANITARY SEWAGE
Settleable Solids
Volumetric
ml/1
Avg. Max.
3.3
6.7
6.1
10.6
2.4
4.8
7.0 2.5
Sources of Figures
(Reference No.)
Hunter and Heukelekian1
a) Winter-Spring 1959
b) Fall-Winter 1959-1960
Rickcrt and Hunter4
Spring 1967
Meridian Engineers6
Lancaster, Pa.
Painter, Vincy & Bywaters7
Imhoff, Muller & Thistlethwayte8
Fair, Geyer, Okun9
Portland, Oregon14
Roy F. Wcston, Inc.15
Washington, D.C.
Engineering-Science, Inc.
San Francisco16
a) Selby Street
b) Laguna Street
City of Los Angeles
Hyperion Treatment Plant
City of Philadelphia
Northeast Water
Pollution Control Plant
City of New Orleans
City of Phoenix
Fair and Geyer, 1954
contributed the most to this total. The City
of Los Angeles reported a total grease
concentration of 52 mg/1 at its Hyperion
Treatment Plant. Grease and floatables
concentrations in dry-weather flow at two
locations in San Francisco1 6 averaged 45 mg/1
and 2.9 mg/1 respectively.
Organic Content as a Function of Particle Size
It can be determined from the data in
Table 2 that the organic content of the
suspended solids in sewage, measured as
volatile suspended solids, ranges from 70 to
85 percent of the suspended solids (ss)
concentration. In terms of particle size
fractions, approximately the same
distribution occurs as for total ss. Several
sources'-2'3'4 reported that of the total
volatile ss, approximate contributions by the
settleable, supracolloidal and colloidal
13.2
8.9
3.0
3 I
mg/I
Avg.
69
75
74
240
310
140
95
Total
Suspended Solids
mg/I
Max. Min.
Avg.
145
146
162
188
647
480
235
129
Volatile
Suspended So/ids
mg/I
Avg. Max. Min.
258
236
83
58
208
174
180
244 50
176 260 90
209
194
255
272
186
255
295
120
125
125
340
170
161 230
148
162
212
130
62
54
fractions are respectively 50, 30 and 20
percent. The results are shown in Table 3,
Particle Size Distribution of Volatile
Suspended Solids in Sanitary Sewage.
COMBINED SEWER OVERFLOWS
As" was found for sanitary sewage, a
similar variability of solids properties was
observed in different combined sewer
overflows investigated. In addition to those
solids normally found in sanitary sewage,
combined sewer overflows contain solids
washed into the sewer system from urban
roadway and land areas. Since overflows
occur as a result of elevated flow rate,
scouring of solids deposits in lines may take
place. Scouring loosens and mixes the solids
which may accumulate between storm events
and contributes additional grit and sand to
the solids load. A. first flush phenomenon may
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TABLE 3
PARTICLE SIZE DISTRIBUTION OF VOLATILE SUSPENDED SOLIDS
IN SANITARY SEWAGE
Source of Figures
Hunter & Heukelekian1
a) Winter-Spring 1959
b) Fall-Winter 1959-1960
Heukelekian & Balmat2
Painter & Viney3
Rickert & Hunter4
MOO Microns
%Settleable
46.5
53.0
45
48
48
occur. This results in increased contaminant
concentration levels during the initial stages
of a storm event. An intense, widespread
storm and smaller drainage area increases the
possibility of a first flush occurrence. As the
storm continues, contaminant concentrations
tend to decrease. This solids level at the end
of a storm and after first flush may be lower
than dry-weather flow solids concentrations.
Particle Size Distribution and Density
The Envirogenics Company1 ° carried out '
an extensive study of the .physical and
chemical properties of combined sewer
overflow solids collected in San Francisco
from April 1969 to May 1970 using a
screening technique. The samples obtained
represented several storms and in all cases the
overflow was sampled as close to the
beginning of the storm as possible and at
specific time intervals thereafter. A total of
60 combined sewage composite samples were
analyzed for a number of parameters,
including a qualitative description of physical
appearance.
In addition to fecal material, paper, food
particles and cigarette butts contributed by
sanitary sewage; leaves, twigs, string, rags and
plastic-materials, most coming from street
washings; were observed. Particle size
distribution analyses were successfully
accomplished for 47 samples. Overall average
results are reported in Table 4, Particle Size
Distribution of Suspended Solids in
Combined Sewer Overflows. The cumulative
particle size distribution of the samples is
presented graphically in Figure 1. The
sanitary sewage graph is included for purpose
of comparison. For the combined sewer
1 - 100 Microns 0.2 - 1.0 Micron
% Supracolloidal % Colloidal
35.0
30.2
35
31
35
18.5
16.8
20
21
17
overflows, 27.0 percent of the solids are
greater than 100 microns in size, which is
comparable to the character of sanitary
sewage solids.
An extrapolation of the combined sewer
overflow graph is shown by the dotted
portion. There is an indication that a greater
percentage of ss in range 1 to 100 microns
was found in combined sewer overflows than
in sanitary sewage — 50 percent compared
with 35 percent respectively. It must be
TABLE4
PARTICLE SIZE DISTRIBUTION OF SUSPENDED
SOLIDS IN COMBINED SEWER OVERFLOWS
Source of Figures
Envirogenics Co.1 °
San Francisco, Cal.
Meridian Engineers6 *
Lancaster, Pa.
Size Range
(microns)
>3,327
991-3,327
295-991
74-295
<74
>9,525
4,760-9,525
2,000-4,760
1,190-2,000
590-1,190
420-590
210-420
149-210
74-149
44-74
<44**
Distribution
(percent)
5.1
8.8
15.9
21.8
48.3
1.77
1.06
1.40
1.88
3.10
2.78
7.01
5.19
20.1
23.8
31.91
* The material tested represents those solids retained in a
catch basin. Sampling took place the week following the storm
event. Thus, results are not directly applicable to all solids in
combined sewer overflows. The particle si/es could be higher
than in the actual flow as some fractions of the smaller si/e
ranges could have been carried through the basin.
** Not measured
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pointed out, however, that the method of
analysis was not designed to provide an
accurate distribution below 74 microns,
which was the smallest mesh sieve used. For
the same reason, no reliable comparison of
the fraction less than one micron can be
made.
Meridian Engineers 6 carried out particle
size analysis and density measurements of
solids in catch basins. Since sampling occurred
after the storm event, the solids collected are
considered to have been hydraulically
classified. Therefore, the size classification is
not representative of the total combined
sewer overflow. The results of this analysis are
shown in Table 4, and graphically in Figure 1.
A total of 68.1 percent of the suspended
material was retained on a sieve size as small as
44 microns. It must be assumed that the
remaining 31.9 percent of the solids was less
than 44 microns in size.
A much larger range of discrete sizes of
particles was obtained from the combined
sewer overflow than for raw sanitary sewage
in 'the Meridian study (compare the entries on
Table 4 with those on Table 1).
The specific weight of the combined
overflow solids was measured using the same
procedure as Meridian used for the raw
sanitary sewage solids. A relatively wide range
of specific weights was reported ranging from
less than 0.80 g/cc to 2.60 g/cc. In the size
range of 2,000 microns and higher, all particle
specific weights were in the range 1.05 g/cc to
1.25 g/cc. However, as size range decreased to
149 microns, the full range of specific weights
was encountered, with by far the greatest
percentage being in the range 1.25 g/cc to
2.60 g/cc. This would tend to indicate that
the particles of moderate size (149-2,000
microns) have the highest specific weight.
This particle size lies within the range of some
silica-sands grit. Since a similar analysis on
raw sanitary sewage indicated a complete lack
of solids in the specific weight range of 1.60
g/cc to 2.60 g/cc, it could be reasonably
concluded that these denser particles were
washed into the system from urban roadways,
land areas, and by infiltration. The overall
implication of the analyses of particle size and
density is that combined sewer overflows
contain larger amounts of solids of various
sizes and densities than those found in
sanitary sewage.
Additional estimates of particle size range
of combined sewer overflows can be extracted
from studies of treatment methods involving
screening or filtration through specific size
mesh screens. A study '' reported ss removal
efficiencies of 36+ 16 percent for first flushes
and 27 ± 5 percent for extended overflows in
Milwaukee, Wisconsin, using a screen of mesh
size 50 (297 micron openings). Such higher
removal for first flushes probably results from
the formation of a solids mat on the screen
due to the presence of initial high ss.
However, for extended overflows, the
indication is that roughly 27 percent of the
solids is larger than 297 microns in size. This
compares favorably with the particle size
distribution previously cited.1? The drum
screen consisted of a rotating straining
element enveloped with replaceable wire mesh
plates. Rotating on its horizontal, axis, the
straining element accepted incoming gravity'
flow while partially submerged inside an open
chamber. As the drum turned, a jet spray
washed off debris trapped on the mesh screen
into a waste collector above the fluid level.
Two sizes of screen were used - 841 micron
openings (20 mesh) and 420 micron openings
(40 mesh). Removal of ss averaged 19 percent
for the larger screen and 25 percent for the
smaller screen. These results were also
comparable to some of the particle size
distributions reported in Figure 1. This study
was extended to include monitoring of
settleable solids removal by the two screen
sizes. Removal by both screens was in the
order of 55 to 60 percent. Thus it can be
assumed that a large portion of settleable
solids was smaller than 420 microns in size.
Total and Settleable Suspended Solids
Table 5, Solids Concentrations in
Combined Sewer Overflows, shows total
suspended and settleable solids concentrations
found in the various combined sewer
overflows from different geographical
locations. Just as was found for sanitary
sewage, settleable solids in combined
overflows range quite widely in terms of
portion of suspended solids; from 37 to 87
percent based on mean values. For the most
-------
TABLE 5
SOLIDS CONCENTRATIONS IN COMBINED SEWER OVERFLOWS
3.1
Source of Figures
(Reference No.)
Envirogenics Company1 °
Rex Chainbelt, Inc.1'
a) Extended
overflows
b) First flushes
(95% confidence level for a & b)
Hydrotechnic Corporation1 2
a) Spring Storms (1971)
b) Summer and Fall Storms (1970) 5.26
Envirogenics Company13
Winter 1968-1969
a) Start of Storm
b) 3 hrs. after start
c) 12-18 hrs. after start
Symposium on Storm and
Combined Sewer Overflows'"
Portland, Oregon
Milwaukee, Wisconsin
a) Extended
overflows
b) First flushes
(95% confidence level)
Detroit, Michigan
a) 1968 Avg. of daily
grab samples - 59 Loc.
b) 1969 Avg. of daily
grab samples - 59 Loc.
Bucyrus, Ohio - 3 sewer locations1 4
Engineering Science, Inc.' 6
San Francisco, Selby St.
Laguna St.
Benzie and Courchaine1 8
Detroit, Michigan (1964)
Burm et al1 9
Detroit, Michigan (1965)
Dunbar and Henry2 °
Buffalo, New York
Buffalo, New York
Buffalo, New York
Detroit, Michigan
Toronto, Ontario
Toronto, Ontario
Welland, Ontario
Weibel et al2'
Cincinnati, Ohio (1962-1963)
Total
Settleable Solids Suspended Solids
ml /I mg/1 mg/1
Avg. Max. Min.
2.58 14 0.05
6.98 14.0 1.5
5.26 19.0 0.2
Avg. Max. Min Avg.
67.6
166
±26
522
±150
411
234
178.2 488 28 230.5
77.3 142 0 106.3
112.2 210 28 145.5
Max.
426
976
1.560
502
186
241
Min.
4
177
28
56
47
30
Volatile
Suspended
mg/1
Avg. Max.
52.2 373
14
±90
308
±83
166.2 311
91.7 186
99.5 221
Solids
Min.
4
51
26
26
5.0 1.5
146
133-
174
330-
848
325 70
90
58-
87
221-
495
166 57
1.350 53
145 <0.3
40 2.0
238
1.067 27
656
533
430
477
150
274
250
1 .005
2.440
990
1 .050
1.260
483
1.398
804
1,220
544
436
930
580
426
70
20 182
90 238
120 228
24
53
23
117
172
158
126
130
17
168
440
570
640
886
264
452
70
80
70
4
28
210 1,200
53 290
-------
part, however, combined sewer -overflows
contain a greater percentage of settleable
solids than does sanitary sewage. For values
found, total suspended solids concentrations
range from 4 mg/1 to 2,400 mg/1 and
settleable solids from zero to 1,380 mg/1.
These minima and maxima values do not
necessarily correspond to the same samples.
The type of storm that causes the
overflow can affect solids concentrations
greatly. De Filippi and Shih17 found that
post peak ss concentrations in overflows from
long, intense storms are reduced to
approximately one-third of the comparable
values for a short, intense storm. They
concluded that solids characteristics of
overflows from consecutive storms are
probably similar to those from long-duration,
low-intensity storms. In the case of their
study, they found that the quantity of waste
materials contributed by the initial first flush
of a storm is proportional to the dry-weather
period between storms. Dry-weather flow and
quality characteristics were reported to be
similar in both combined sewer systems and
sanitary sewage systems during dry weather.
However, the quantity of waste materials
contributed by the iitial first flush of a storm
is affected by several factors including
antecedent dry period, intensity of storm,
sewer system configuration, soil
characteristics in the area, street cleaning
practices and land use in the drainage area.
Insoluble Oil Fraction
Several investigators report results of oil
and grease analysis of combined sewer
overflow samples. Engineering Science Inc.16
performed studies on combined sewer
overflows at two locations in San Francisco
resulting from several storms. Samples were
-obtained throughout the course of each
overflow at time periods ranging from ten
minutes to almost three hours between
samples. Sampling was most frequent (i.e. —
smaller time periods between samples) during
the first few hours of the overflow. Combined
results from the two locations showed a range
of 0.4 to 120.5 mg/1 of grease, using
liquid-liquid extraction with hexane as the
solvent following acidification and gentle
heating of the sample. Floatable solids were
also collected, using a Teflon-coated Flotation
Funnel following mixing to create a
homogeneous sample. Concentration ranged
from 0.4 to 44.6 mg/1.
Extensive analysis of combined sewer
overflows for parameters including oil and
grease was undertaken by the Detroit Metro
Water Department14 (Section 6). Daily grab
samples from 59 different locations were
analyzed. The average oil and grease
concentration of these daily grab samples
ranged from 11 to 2,775 mg/1 for the various
locations in 1968, and from 13 to 689 mg/1 in
1969.
Organic Content
Table 5, shows the volatile ss'
concentrations in several combined sewer
overflows. A relatively wide range of organic
content is portrayed. Actual average
concentrations range from 51 mg/1 to 495
mg/1, which is similar to sanitary sewer flows
with an average range of 1:10 and the
maximum twice the average. Minimum and
maximum values reported are 1 mg/1 and
1,280 mg/1, respectively. There is also
evidence .of a wide range of organic content in
terms of percentage of total ss. Using average,
concentrations as a basis, the content ranges
from 25 percent21 to 86 percent.13
Unfortunately, none of the investigators
reported analysis of size range fractions for
organic content. Thus, an estimate of organic
content as a function of particle size cannot
be made.
However, volatile content of settleable
solids was reported by some observers. Burm
et.al.19 reported that volatile settleable solids
ranged from 30 to 50 percent of total
settleable solids. Engineering Science, Inc.16
reported a wider range - from 15 to 70
percent. Most results however are well below
50 percent.
URBAN STORMWATER
Urban stormwater includes either
overland sheet flow or storm flow in the
separate storm sewered or unsewered drainage
system. In most cases, separate storm-sewer
flows are quite large over a short period of
time and are not tributary to wastewater
treatment system. As a result, large quantities
10
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of relatively heavily contaminated wastewater
are diverted to natural watercourses with no
form of treatment to reduce the pollution
load. In this respect, and in some others,
urban stormwater and untreated combined
sewer overflows may be similar. However, a
close examination of physical and chemical
properties reveals important differences,
especially with respect to ss with which this
report is primarily concerned.
Several investigators previously cited have
conducted studies of separate stormwater
concurrently with combined sewer overflow
investigations, so that a comparison between
the two discharges could be made. The results
of these comparisons will be discussed.
Particle Size Distribution
The URS Corporation23 conducted an
extensive investigation of street surface
contaminants which are washed into both
combined and separate sewers during a storm
event. Sections of streets in several cities were
.washed down with water. The washings were
collected and analyzed. Solid materials were
• extracted and dry-sieved for particle size
• distribution covering ten individual ranges
from less than 4 microns to greater than
4,800 microns. The results are shown in Table
6, Particle Size Distribution of Solids —
Selected City Composites. The percentage in
each size range was averaged for the five ckies
under investigation to produce an overall
distribution. This provides a very rough
estimate. The average distribution is presented
graphically in Figure 1. It is somewhat
different from those for combined sewer
overflows and indicates that solids particle
sizes are larger in separate storm runoff.
Total and Settleable Suspended Solids
De Fillipi and Shih1 7 observed that total
suspended solids and settleable solids
concentrations were much higher in
stormwater runoff than in combined sewer
overflows during their study in Washington,
D. C. Suspended solids ranged from 130 to
11,280 nig/1, with an average concentration of
1,697 mg/1. Settleable solids ranged from zero
to 7,640 mg/1, with an average of 687 mg/1.
Volatile ss concentrations, however, were
lower in stormwater runoff than in combined
sewer overflows.
Benzie and Courchaine18 and Burm
et.al.1 9 also observed higher ss concentrations
in stormwater runoff. Both of these studies
compared combined sewer overflows in
Detroit, Michigan, with stormwater runoff in
Ann Arbor, Michigan. The latter study19
showed that stormwater runoff was higher in
all solids parameters studied: ss, volatile ss,
settleable solids and volatile settleable solids.
PARTICLE
SIZE
RANGE
(microns)
>4,800
2,000-4,800
840-2,000
246-840
104-246
43-104
30-43
14-30
4-14
<4
Milwaukee
12.0
12.1
40.8
20.8
5.5
1.3
4.2
2.0
1.2
0.5
TABLE 6
PARTICLE SIZE DISTRIBUTION OF SOLIDS
- SELECTED CITY COMPOSITES -
DISTRIBUTION (PERCENT BY WEIGHT)
Bucyrus Baltimore Atlanta
10.1
7.3
20.9
15.5
20.3
13.3
•7.9
4.7
17.4,
4.6
6.0
22.3
20.3
11.5
10.1
4.4.
2.6
0.9
14.8
6.6
30.9
29.5
10.1
5.1
1.8
0.9
0.3
Tulsa
37.1
9.4
16.7
17.1
12.0
3.7
3.0
0.9
0.1
Source: URS Research Company (23)
11
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Average concentrations for the four
parameters were 2,080, 218, 1,590, and 140
nig/1, respectively. In physical appearance, the
stormwater runoff was brownish and muddy
while the combined sewer overflow was less
turbid and darker in color. Geomorphological
differences between the two study areas were
the primary cause of the differences. Ann
Arbor has a more rolling topography and is
subject to a higher degree of scouring and
erosion. The soil has a much looser texture
than the primarily clay soil found in Detroit.
The settleable solids ranged from 70 to 90
percent of the total ss in both cases.
Wiebel et al.2' investigated urban land
runoff in Cincinnati, Ohio. Their results were
much different than other studies. Average ss
ranged from 5 to 1,200 mg/1, with a weighted
average of 210 mg/1. Volatile content was
approximately 25 percent of the ss
concentration. Settling for 20 minutes
reduced ss 27 to 53 percent and volatile ss 17
and 50 percent. Soderlund and Lehtinen22
reported similar low ss (129 mg/13 average)
and volatile ss (51 mg/1 average) in urban
stormwater runoff from Stockholm, Sweden.
A study24 in Tulsa, Oklahoma, showed
that stormwater runoff in this location
contained an average ss concentration of 367
mg/1. Concentrations ranged from 84 to 2,052
mg/1. These results fall between the high levels
first cited and the low levels just described.
An o'verview of these investigations
indicates that there is a wide variety in the
solids characteristics of separate stormwater
runoff. These properties are primarily a
function of land use, along with soil and
topographical features.
SETTLING VELOCITY
Specific information concerning settling
velocities of solids in sanitary sewage,
stormwater and combined sewer overflows
was not available in the literature. However,
general design specifications for conventional
primary clarifiers supplied some basic data.
These clarifiers are designed to remove
virtually 100 percent of settleable solids while
operating with overflow rates that may range
from 60,0-900 gal/sq ft/day. This range of
overflow rates is equivalent to a settling
velocity range of 0.028 to 0.043 cm/sec
(0.0009 to 0.0014 ft/sec). Thus, the settling
velocities of settleable solids should be larger
than these figures. In practice 37 to 65
percent of the total ss are settleable and
should be removed by primary clarification.
Arrangements were made to conduct settling
column tests of sanitary sewage and combined
sewer overflow in Philadelphia to confirm
settling velocities.
Settling Velocities of Erosion Solids
As previously stated, the types of solids
to be found in stormwater runoff are affected
by-the type of soil found in the area that is
tributary to the storm-sewer system: The
erosion of land areas can be the prime
contributor of solids to stormwater. As
mentioned in an APWA publication, Hazen2 s
reported that settling velocities of soil
materials can _range from 0.015 cm/sec
(0.0005 ft/sec) for silt 10 microns in size, to
0.33 ft/sec for coarse sand, 1,000 microns
in size. The relatively large range of settling
velocities indicates that the effectiveness of a
solids separation device for treatment of
stormwater will be dependent on the type of
particles in the waste stream. If the runoff
contains fine and coarse sand, 40 microns and
greater in size, separation should be
efficiently accomplished. However, silt and
clay materials present a much more difficult
separation problem.
12
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SECTION III
SETTLING VELOCITY RELATIONSHIPS OF SANITARY SEWAGE
AND STORMWATER RUNOFF
The review of solids characteristics
(Section II) provided minimal information
regarding the settling characteristics of the ss
fraction in the waste streams studied. Settling
velocity is an important factor in determining
performance of a swirl concentrator as a
solids separation device. The purpose of this
study, to establish settling velocity
relationships for sanitary sewage, stormwater,
and combined sewer overflows was two-fold.
Initially, the laboratory settling column tests
provided an indication of the settling
characteristics to be expected. Secondly,
particle settling velocities provided a target
for selection of a material to simulate the
sewage ss.
At the time of the preparation of this
report a suitable sample of combined sewer
overflows has not been available for settling
column analysis. The stormwater runoff
sample obtained in Toronto, Canada, at the
Sherwood Park Storm Sewer Outfall,
contained a low concentration of ss compared
to reported averages from other sources. More
important, however, was the low settleable
solids portion of the ss in the sample. The
results of settling column studies on this
sample are reported.
SANITARY SEWAGE
Sanitary sewage sampling was conducted
by Beak personnel at the Northeast Water
Pollution Control Plant in Philadelphia, Pa.
Three samples of sewage were collected at
different times during the day following grit
removal, and settling column tests were
performed on each sample. Although the
three samples contained different
concentrations of ss and percent settleable
solids, their settling characteristics were found
to be sufficiently comparable so that the
results for each could be combined. The ss
and percent settleable solids in the samples
after one hour of settling were as follows:
Sample No. 1 - 495 mg/1; 84% settleable
Sample No. 2 - 220 mg/1; 64% settleable
Sample No. 3 - 437 mg/1; 63% settleable
The range of settling velocities observed in
sanitary sewage tested is presented graphically
in Figure 2, Settling Velocity Distribution of
Solids in Sanitary Sewage. The median
settling velocity observed was 0.054 cm/sec
(0.0017 ft/sec). The next section of the
report indicates that the type of simulated
solids used by previous researchers had
settling velocities significantly greater than
sanitary sewage, and hence would not be
suited to this study.
URBAN STORMWATER
The settling column test procedure is
described in detail in Appendix 1, together
with all other test procedures used by Beak
Laboratory staff.
The stormwater runoff sample was
collected in late afternoon and stored
overnight at 4° C (39° F) to ensure a
minimum of biological activity. The following
morning settling column tests were performed
on a portion of the sample; the other portion
remained in storage for future testing. The
first test is referred to as Run 1. The initial ss
concentration was 337 mg/1 and settleable
solids after one hour were 20 percent of this
value. Complete results are presented
graphically in Figure 3, Settling Velocity
Distribution by weight of Solids in
Stormwater Runoff. Figure 3 shows that
settling velocities were approximately an
order of magnitude below those observed in
sanitary sewage. In fact, in Run 1, 78 percent
of the solids in the stormwater have settling
velocities less than 0.01 cm/sec (0.00033
ft/sec) compared with only 31 percent for
sanitary sewage. This indicates that'the solids
in the sample were probably coarse clays and
silt and perhaps not representative of many
soil types.
The remaining portion of stormwater
runoff was kept at 4° C (39° F) for six days
and then tested with the settling column so
that the effect of storage could be
determined. The testing of this sample is
referred to as Run 2. The initial suspended
13
-------
T)
C3
O
d>
~~.
U
u
o
I
Percent less than or equal to
FIGURE 2 SETTLING VELOCITY DISTRIBUTION
OF SOLIDS IN SANITARY SEWAGE
solids concentration was 323 mg/1, similar to
that in Run 1. However, settleable solids after
one hour were only 13 percent of the initial.
Surprisingly, as the-results for Run 2 indicate
in Figure 3, the settling characteristics were
improved by aging in storage. In Run 2 only
57 percent of the solids in the stormwater had
settling velocities less than 0.01 cm/sec
(0.00033 ft/sec).
This observation would seem to indicate
an error in the measurement of settleable
solids for Run 2'since with improved settling
characteristics more solids should settle in one
hour. The test could not be repeated due to
exhaustion of the sample. For both Runs 1
and 2, the sample was tested at its storage
temperature. During the test period the
temperature rose from 5° C to 12° C (41° F
to 54° F). As the samples were obtained in
March, a winter month, it was decided to run
the test at a low temperature rather than at an
indoor ambient temperature.
The improvement in settling
characteristics after storage is apparently due
14
-------
ft/sec cm/sec
33
x 10-3
S3
•3
o
BO
98 9»
Percent less than or equal to
FIGURE 3 SETTLING VELOCITY DISTRIBUTION
BY WEIGHT OF SOLIDS IN STORMWATER
RUNOFF
to agglomeration of small particles since the
agglomeration phenomenon was also observed
during one-hour tube settling tests. This.
observation, although based only on a few
settling column tests, does suggest that
storage prior to sedimentation may increase
the removal rate and hence decrease the
concentration of ss in stormwater runoff.
Further study appears warranted to precisely
define the effects of storage on settling
characteristics and to determine the overall
feasibility of this form of pretreatment and to
determine if inprovement also occurs with
combined sewer overflows.
15
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SECTION IV
SIMULATED SEWAGE
MATERIALS USED IN
PREVIOUS STUDIES
Several different materials have been used
in the past to simulate the ss contained in
sewage flows. Investigators have generally
used mixtures of different materials in an
attempt to simulate grit, fine and coarse ss,
bed material and floating or surface solids
separately. The properties of these different
fractions differ in terms of settling
characteristics. The theoretical settling
velocity of a material in an aqueous medium
is a function of the specific weight of the
particles as well as of their size and shape.
This function is the familiar Stokes' law
relationship, which is shown below for
spherical particles. Stokes' law is valid only
for particles when the Reynolds number is
less than 1.
( 7s -Tw )
where:
V.
D
= fall velocity
= sphere diameter
7S = specific weight of sphere
7W = specific weight of fluid
(JL = fluid viscosity
In previous studies of simulated materials for
use with swirl separators, the size and specific
weight of the specific fraction of solids in
sewage was estimated and the settling velocity
calculated. Then the scale factor of the model
that was being tested was applied to
determine the required size and specific
weight of the test materials to be used to
simulate the sewage solids. From this size and
specific weight, a settling velocity was
calculated. Knowing the size and specific
weight desired enabled researchers to select a
material with properties close to those
required. As will be discussed later, Beak
chose to approach the simulation problem
from a different point of view.
Smisson2 6 used a specifically prepared
mixture of hardwood sawdust for the ss, and
perspex filings for the floatables. The mixture
had a specific gravity of 1.19, with individual
particles being fibrous in shape. Equivalent
sphere sizes ranged from 200 to 600 microns,
with theoretical settling velocities ranging
from 0.25 to 0.75 cm/sec (0.1 to 0.3 in/sec).
Prus-Chacinski and Wielgorski2 7 also used
perspex shavings to simulate the surface or
floatable material. However, a mixture of
graduated coal dust (100 to 1,000-micron
particle size range) and polystyrene 0.16 to
0.32 cm (1/16 to 1/8-inch) diameter and
average relative density 1.05 was used to
simulate, respectively, the bed material and
suspended load.
Ackers, Harrison and Brewer2 8 likewise
used a mixture of three materials to represent
grit, coarse ss and floating solids. Bakelite
particles of specific gravity 1.42 and about
500 microns diameter were used to simulate
grit. The size and specific gravity of the
coarser fraction of solids were assumed to be
2.54 cm (one inch) in diameter and 1.005.
respectively. Particles of this size and specific
gravity were determined to have a settling
velocity of 6.1 cm/sec (0.2 ft/sec). The model
scale was applied and the desirable settling
velocity of the test material was determined
to be 1.77 cm/sec (0.058 ft/sec). Polystyrene
particles 1,250 microns in size, with a settling
velocity of 1.98 cm/sec (0.065 ft/sec), were
used. Following a similar method of
assumption, the desirable rise velocity of the
floatables in the model work was calculated
to be 1.77 cm/sec (0.058 ft/sec). Polythene
particles 2,000 microns in size, with a
calculated rise velocity of 2.13 cm/sec (0.07
ft/sec) were selected for use in that study.
Other materials which have been used to
simulate the solids fraction of sewage include
repulped newspaper, nylon thread, asbestos
fibers, calcium carbonate floe, river silts,
coarse clays, polyethylene beads and
size-classified road dust. Beak examined many
of these materials for their applicability as
simulated sewage solids, but only polystyrene
beads, a shredded polyethylene material and
size-classified road dust (Arizona Road Dust)
were selected for further study.
DESCRIPTION AND RESULTS OF STUDY
Settling velocity data from Beak's
Philadelphia study of raw sanitary sewage
16
-------
provided the basis for consideration of
simulated sewage materials. The . median
settling velocity of primary sewage was
determined to be 0.054 cm/sec (.002 ft/sec).
Before the settling velocities determined
could be applied to the selection of a material
to simulate the solids load, the scale factor of
the swirl concentrator model developed by
LaSalle Hydraulic Laboratory had to be taken
into consideration. The model work was done
with Froude number scaling, and as a result,
settling velocity of sewage must be reduced
by the square root of the model scale factor.
In this way, removal efficiencies in the
one-twelfth scale model should be comparable
to removal efficiencies using actual sewage in
the full-scale prototype.
The distribution of settling velocities was
altered by multiplying the settling velocity at
each percentage by l'/V12,-since the scale
factor of the model is 12. This new frequency
distribution, shown in Figure 4, Settling
Velocity Distribution of Solids in Sanitary
Sewage After Application of Model Scale
Factor, represents the desired settling velocity
distribution of the ideal test material. It was
ft /sec, cm/sec
"" ..... ! '
.033
x 10-3
•OOt
FIGURE 4
39 « S> (B » «S 90. •« SB
Percent less than or equal to
SETTLING VELOCITY DISTRIBUTION
OF SOLIDS IN SANITARY SEWAGE AFTER
APPLICATION OF MODEL SCALE FACTOR
17
-------
observed that the required median settling
velocity range is 0.016 — 0.02 cm/sec'
(.0005-.0007 ft/sec).
Having established this range of settling
velocity, numerous materials were evaluated
for suitability as simulated sewage solids with
terminal settling velocities in the desired
range. Where particle size permitted, each
simulated sewage material was examined for
the relationship between settling velocity and
particle size by the use of tube settling tests.
In this test, individual particles were sized and
settling time over a known tube depth was
measured. These screening tests, when
performed in replicate, provided a basis for
the selection of the particle size range
required for each prospective simulated solid.
Other factors considered during selection of
solid materials included cost, availability and
uniformity of particle characteristics.
Table 7, Physical Characteristics of
Simulated Sewage Materials, presents
information regarding materials given
consideration as simulated sewage solids.
Several materials, including IRA-93, IRA-401,
XAD-2, DOWEX 21K resins and shredded
Petrothene were examined as they were
received by Beak, i.e. in large particle sizes.
The IRA-401 and DOWEX 21K are gel-type
resins and are easily broken into irregularly
shaped pieces. Particle uniformity was one of
the selection factors and due to this physical
instability, these resins were eliminated from
further consideration. The remaining resins,
IRA-93 and XAD-2, are macro-reticular-type
resins which are physically more stable.
IRA-93 resin is a polystyrene based
copolymer which is extremely stable both
chemically and physically. The manufacturer
states that in aqueous medium the resin is
TABLE 7
PHYSICAL CHARACTERISTICS OF SIMULATED SEWAGE MATERIALS
Material
Manufacturer
Amberlite Anion Rohm and Haas
Exchange Resin
Type
IRA-93
Specific Size Range Settling Velocity
Gravity (Microns) Range (cm/sec)
1.04 200-1,000 0.15-1.5
149-297
Non-ionic Resin Rohm and Haas
Dowcx Anion Dow Chemical
Exchange Resin
Ari/.ona Road Donaldson Co.,Inc.
Dust Minneapolis, Mn.
IRA-401
XAD-2
21K
1.06
1.03
1.06
2.65
Petrothene
X10I
U.S. Industrial
Chemicals
Shredded 1.01
Dust
74-149
38-74
300-1,400
200-1,000
200-1,000
10-20
700-3,000
<0.02:2%
0.02-0. 1 :42%
> 0.1:56%
<0.01:24%
0.01-0,05:53%
>0.05:23%
>0.01:68%
0.01-0.05 :30%
>0.05:2%
0.2-2.4
0.1-1.0
0.15-2.0
0.01-0.05 :77%
> 0.05:5%
0.3-1.7
100-1,000 <0.01 :II7r
0.01-0.05 :20%
> 0.05 :69%
-------
electrically neutral and therefore should not
be electrically attracted to the swirl
concentrator model cpnstruction material.
The resin absorbs moisture from the dry to
the wet state rapidly. Laboratory tests have
indicated an immeasurable amount of swelling
as the resin becomes wet. In addition, swelling
due to ion exchange should be negligible at
the neutral pH of the hydraulic model test
water. Swelling of about 20 percent
maximum may occur within five minutes.
Figure 5, Settling Velocity vs. Particle
Size for IRA-93 Exchange Resin and Figure 6,
Settling Velocity vs Particle Size for XAD-2
Non-Ionic Resin, show the results of tube
settling tests of individual particles.
Both resins were tested in their
commercially available particle size range. The
shredded Petrothene, also physically stable,
was likewise tested for settling rate as a
function of particle size. The results are
shown in Figure 7, Settling Velocity vs.
ft/sec cm/sec
330
x I0'3
FIGURE 5
Percent less than or equal to
SETTLING VELOCITY VS PARTICLE SIZE
FOR IRA-93 ANION EXCHANGE RESIN
19
-------
.
•*?9T5™™ .1J1 ""TT if 1; * .,.,.. ( ,1 i>f^l| JililHL • 1 )' '„ jjf ^ .. - »^-+ ' ^,_,^.,.,.V-^a.»S,^.ljL,i™™«".'!^.,««J4" :"-t - -%ai4*=-I'..-dMf:- njuriSMS* =Vf J«w»-M»f:: ^ -V,*lt^^(sKa!iJMhjTpl- "
- „ —. *«. - .,-,...- - — ^^ """ '
(oas/y puB oas/uio) X;
20
-------
Particle Size for Shredded Petrothene —
X-101. In each figure, the ideal Stokes' law
relationship between particle size and settling
velocity for spherical shaped particles is
included. For the spherically shaped resins,
the experimental points are in close
agreement with theory. However, there is
more scatter and less agreement for shredded
Petrothene. Experimental settling velocities
are less than those predicted by theory. This
is. due to the irregular shape of the shredded
particles, which results in an increased drag
force. It was obvious from these figures that a
much smaller particle size was necessary to
obtain settling velocities in the desired range.
This posed the problem of determining a
method of reducing the size of the
particulates. At this point it was necessary to
rule out further study with XAD-2 non-ionic
resin. Amberlite IRA-93 was selected for
particle size reduction due to the results of
tube settling tests presented in Figure 5 and
its cost advantage over XAD-2. IRA-93 costs
$85 per cubic foot wheres XAD-2 costs $92
per cubic foot. Extrapolation of the ideal
Stokes' law line shown in Figure 5 indicated
that the particle size range required to give
settling velocities in the range 0.016-0.02
cm/sec(0.04-0.05 in/sec) was 80-100 microns.
Pulverization of the IRA-93 resin was
established as the practical means of obtaining
the desired particle sizes. The resin was
pulverized with a rotary mill pulverizer by a
Toronto laboratory. It was decided to test the
pulverized resin in three size ranges — 50-100
mesh (149-297 microns); 100-200 mesh
(74-149 microns); and 200-400 mesh (38-74
microns) — so that the theoretical range
would be well bracketed to allow for possible
non-ideal behavior. As a result of
pulverization, the particles in these three size
ranges are non-spherical in shape.
Pulverizing could not be used for
Petrothene, however, since the heat evolved in
the pulverizing step is sufficient to melt the
plastic material. Fortunately, a by-product of
the shredding operation was available for use.
Petrothene is commercially available in
approximately 4 mm cubical pieces. LaSalle
Hydraulic Laboratories had this larger
material shredded to obtain the smaller size
shredded Petrothene. The Petrothene dust, a
by-product of shredding, has much smaller
particles than the shredded fraction.
The ideal Stokes' law line shown in
Figure 7 predicted that particle sizes in the
range 170 to 200 microns would be1 required
for settling velocities in the range 0.016 to
0.02 cm/sec (0.04-0.05 in/sec).
However, indications were that the
irregular shape of the Petrothene dust
particles resulted in lower settling velocities
than theory predicted. This meant that the
ideal theoretical size range might have
provided lower settling velocities than those
desired. Thus it was decided to continue
settling studies on Petrothene dust in a
mixture of several size ranges below 1,000
microns in particle size to provide, as for
IRA-93, a large bracketing for non-ideal
behavior.
A third material in the desired settling
velocity range was obtained. This was the
specially size-classified Arizona Road Dust.
Settling velocity distributions for each size
fraction were available from a member of the
project team, General Electric in Philadelphia,
Pa. From these curves, a size range 10 to 20
microns was selected for study by Beak. This
material is very expensive at $100 per pound
and therefore only the one size range was
studied.
SETTLING COLUMN STUDIES
As a result of screening tests, three
materials were selected for further settling
velocity analysis. These were the ground
IRA-93 in three size ranges; the Petrothene
dust; and the 10-20 micron-size Arizona Road
Dust. The settling column tests were used
because tube settling of individual particles
was not practical at the small sizes involved.
All materials tested in the settling column
were tested at an initial concentration of
approximately 200 mg/1.
Amberlite, IRA-93
A settling velocity distribution curve for
each size range tested was prepared. Figure 8,
Settling Velocity Distribution for 50-100
Mesh IRA-93, 149-297 microns, indicates that
this size range is too small. The median
settling velocity is 0.1 cm/sec (.003ft/sec),
which is greater than that required for
simulation. These results are also in close
agreement with theory.
21
-------
(oas/y pue oas/uio)
22
-------
Figure 9, Settling Velocity Distribution
for 200-400 Mesh IRA-93, 38-74 microns,
indicates that this size range is too small. The
median settling velocity is 0.001 cm/sec
(0.0004 in/sec), which is lower than that
required for simulation. These results are also
in close agreement with theory.
Figure 10, Settling Velocity Distribution
for 100-200 Mesh IRA-93, 74-149 microns,
indicated that this material was in the desired
range. The median settling velocity for the
three runs varied from 0.0215 to 0.037
cm/sec (.0007-.0012 ft/sec), which was
slightly higher than the ideal requirement of
0.016 cm/sec C-OOOSfVsec). The range of
settling velocities observed was in close
agreement with that predicted by Stokes' law
for spherical particles of 1.04 specific gravity.
This theoretical range is 0.012 to 0.05 cm/sec
(.0004-..002 ft/s-ec). The pulverized IRA-93
resin appeared to behave according to Stokes'
law and therefore would lend itself readily to
mathematical modeling of the settling
characteristics of the swirl separator.
The difference between the three batches
was due to the fact that the material tested in
each case was the product of a different
sieving and pulverizing batch. The sieving
was done manually. This indicated the need
to regulate the pulverizing and sieving
procedure so that the same material could be
obtained in each batch.
A procedure for pulverizing and sieving
the IRA-93 resin was developed in order to
produce a consistently uniform sample. A
detailed description of this procedure is
included in Appendix B.
The study of simulated sewage solids
resulted in the selection of Amberlite IRA-93
resin, 100-200 mesh particle size range, as the
material with which to monitor the efficiency
of the swirl concentrator model developed by
the LaSalle Hydraulic Laboratory. Figure 11,
Efficiency Monitoring Material, IRA-93,
74-149 Microns; and 12, Efficiency
Monitoring Material, IRA-93, 74-149 Microns,
Wet Sieved; present settling velocity
distribution curves for two typical samples of
IRA-93 used in the swirl concentrator
monitoring program. The sample shown in
Figure 12 was wet sieved to provide a
comparison to the dry-sieving procedure
previously mentioned. The median settling
velocity for the wet-sieved resin is slightly
higher than for the dry-sieved material,
indicating that wet sieving may have removed
a higher percentage of the very fine particles.
Arizona Road Dust
Figure 13, Settling Velocity Distribution
for Arizona Road Dust, 10-20 microns,
indicates that this material has a median
settling velocity of 0.023 cm/sec (0.06
in/sec), which is close to the desired range.
This material is also considered to be an
excellent material for use as simulated sewage
solids but its high cost, $100 per pound, in
comparison to that of IRA-93, $85 per cu ft
or about $ 12 per pound, reduces its practical
application to the monitoring program in
which larger quantities will be required.
Petrothene Dust
Figure 14, Settling Velocity Distribution
.for Petrothene Dust (< 1,000 microns),
indicates that settling velocities obtained were
not in the desired range. Problems were
encountered in wetting the surface of
particles of this size so that they would not
float on the surface of the water. The smaller
the particles, the more difficult this
procedure. This test indicated that much
smaller particles would be required to obtain
the required settling velocities. Particle size
analysis of the dust showed that less than 15
percent of the dust would be suitable. This
dust is difficult to obtain in quantity, so
further work with Petrothene was abandoned.
The overall summary of the study of
simulated sewage is presented in Table 7. This
table presents results of screening tests and
settling column tests conducted on simulated
sewage solids.
In addition to the development of a
material to simulate sewage solids. Beak
designed a program by which solids removal
efficiency could be studied on the hydraulic
model of the swirl concentrator as a primary
settling device. The procedure is described in
Appendix C.
23
-------
* 10-
Percent less than or equal to
FIGURE 10 SETTLING VELOCITY DISTRIBUTION FOR 50-100 MESH
IRA-93, 74-149 MICRONS AND COMPARISON WITH
SANITARY SEWAGE (after application of model scale factor)
24
-------
(oas/»j pue Das/mo)
25
-------
(oas/jj puB oas/uio) Xj
i^.,»sUJ>4»i».' i&l L44 ^4™ ^
(oas/jj pue oas/uio)
26
-------
SECTION V
REFERENCES
1. J. V. Hunter, H. Heukelekian, "The
Composition of Domestic Sewage
Fractions," Journal of Water Pollution
Control Federation, 37:8:1, 142-151,
163, August 1965.
2. H. Heukelekian, J. Balmat, "Chemical
Composition of the Particulate Fractions
of Domestic Sewage," Sewage and
Industrial Wastes, 31:4:413, April 1956.
3. H. A. Painter, M. Viney, "Composition of
a Domestic Sewage," Journal of
Biochemical and Microbiological
Technology and Engineering, 1:143,
1959.
4. D. A. Rickert, J. V. Hunter, "General
Nature of Soluble and Particulate
Orga.nics in Sewage and Secondary
Effluent," Water Research, 5:421-435,
1971.-
5. W. Rudolfs, J. Balmat, "Colloids in
Sewage I-Separation of Sewage Colloids
With the Aid of the Electron Microscope,
Sewage and Industrial Wastes, 24:3:247,
March 1952.
6. J. Krantz, D. L. Russell, P.E., Lancaster
Silo Project: Particle Sizing and Density
Study, Preliminary Report, Meridian
Engineers, Philadelphia, Pennsylvania,
January 1973.
7. H. A. Painter, M. Viney, A. By waters,
"Composition of Sewage and Sewage
Effluents," Journal, Institute of Sewage
Purification.
8. K. Imhoff, W. J. Muller, D. K. B.
Thistlethwayte, Disposal of Sewage and
Other Wdterborne Wastes, Ann Arbor
Science Publishers, Incorporated Ann
Arbor, Michigan, 1971.
9. G. M. Fair, J. C. Geyer, D. A. Okun,
Water and Wastewater Engineering, John
Wiley and Sons, Incorporated, New York,
New York, 1968.
10. In-Sewer Fixed Screening of Combined
Sewer Overflows by Envirogenics
Company, Environmental Protection
Agency, Water Quality Office, Water
Pollution Control Research Series, 11024
FKJ 10/70, U. S. Government Printing
Office, Washington, D.C.
11. Screening/Flotation Treatment of
Combined Sewer Overflows by The
Ecology Division, Rex Chainbelt,
Incorporated, Environmental Protection
Agency, Office of Research and
Monitoring, Water Pollution Control
Series, 11020 FDC 01/72, U. S.
Government Printing Office, Washington,
D.C.
12. R! Nebolsine,-P. J. Harvey, C. Fan, High
Rate Filtration of Combined Sewer
Overflows, Hydrotechnic Corporation,
Environmental Protection Agency, Office
of Research and Monitoring, Water
Pollution Control Research Series, 11023
EYI 04/72, U. S. Government Printing
Office, Washington, D.C.
13 Urban Storm Runoff and Combined
Sewer Overflow Pollution, Sacramento,
California by Envirogenics Company,
Environmental Protection Agency, Water
Pollution Research Series, 11024 FKM
12/71, U. S. Government Printing Office,
Washington D.C.
14. Combined Sewer Overflow Abatement
Technology, A Compilation of papers
presented at the Environmental
Protection Agency Symposium on Storm
and Combined Sewer Overflows, June
1970, Chicago, Illinois. Environmental
Protection Agency, Department of the
Interior, Water Pollution Control
Research Series 11024 06/70, U.S.
Government Printing Office, Washington
D.C.
15 Combined Sewer Overflow Abatement
Alternatives, Washington, D.C., by Roy
F. Weston, Incorporated, Environmental
Protection Agency, Water Quality Office,
Water Pollution Control Research Series,
11024 EXF 08/70, U.S. Government
Printing Office, Washington, D.C.
16. Characterization and Treatment of
Combined Sewer Overflows by
Engineering-Science Incorporated,
Environmental Protection Agency,
Division of Research and Training Grants,
EPA Grant WPD-113-01-66, November
1967.
27
-------
17. J. A. DeFillippi, C. S. Shih,
"Characteristics of Separated Storm ^nd
Combined Sewer Flows," Journal of
Water Pollution Control Federation,
40:112, 1968.
18. W. J. Benzie, R. J. Courchaine,
"Discharges From Separate Storm Sewers
and Combined Sewers," Journal, Water
Pollution Control Federation, 38:410,
1966.
19. R. J. Burm, D. F. Krawczyk, GG. L.
Harlow, "Chemical and Physical
Comparison of Combined and Separate
Sewer Discharges, Journal, Water
Pollution Control Federation, 40:112,
1968.
20. D. D. Dunbar, J. G. F. Henry, "Pollution
Control Measures for Stormwaters and
Combined Sewer Overflows," Journal,
Water Pollution Control Federation,
38:1:9, January 1966.
21. S. R. Weibel, R. J. Anderson, and R. L.
Woodward, "Urban Land Runoff as a
Factor in Stream Pollution," Journal,
. Water Pollution Control Federation,
36:914,1964.
22. G. Soderlund, H. Lehtinen, Comparison
of Discharges from Urban Stormwater
Runoff, Mixed Storm Overflow and
Treated Sewage, Advances in Water
Pollution Research, Proceedings of the
6th International Conference, Jerusalem,
1972, S. H. Jenkins (ed.), Pergamon Press
Limited, 1973.
23. J. D. Sartor and G. B. Boyd, Water
Pollution Aspects of Street Surface
Contaminants, URS Research Company,
Environmental Protection Agency, Office
of Research and Monitoring,
Environmental Protection Technology
Series, EPA-R2-72-081, November 1972,
U. S. Government Printing Office,
Washington, D.C.
24. Storm Water Pollution from Urban Land
Activity, by AVCO Economic Systems
Corporation. Environmental Protection
Agency, Department of the Interior,
Water Pollution Control Research Serie's,
11034 FKL 07/60, U.S. Government
Printing Office. Washington, D.C.
25. Detention of Urban Stormwater Runoff,
American Public Works Association
Special Report 43, 1974.
26. B. Smisson, Design, Construction and
Performance of Vortex Overflows,
Symposium on Storm Sewage Overflow,
Institution of Civil Engineers, London,
1967.
27. T. M. Prus-Chacinski, J. W. Wielogorski,
Secondary Motions Applied to Storm
Sewer Overflows, Symposium on Storm
Sewage Overflow, Institution of Civil
Engineers, London, 1967.
28. P. Ackers, A. J.M. Harrison, A. J.
Drewer, Laboratory Studies of Storm
Overflows With Unsteady Flow,
Symposium on Storm Sewage Overflow,
Institution of Civil Engineers, London
1967.
29. A Standard Method of Examination of
Wastewater, U.S. Environmental Protection
Agency
30. J. Happel and B.J. Byrne, Motion of a
Sphere and Fluid in a Cylindrical Tube,
Ind. Eng. Chem. 46, p.l 181 (1954).
31. Gordon M. Fair and John C. Geyer, Water
Supply and Waste-Water Disposal, John
Wiley Sons, Inc., New York, 95 pp (1954).
28
-------
SECTION VI
APPENDIX A
LABORATORY METHODS USED BY BEAK PERSONNEL
SETTLING COLUMN TEST
Procedure
The test column consists of a 6-foot,
8-inch diameter, Plexiglas® cylinder with
sampling ports at 1-foot increments. The
bottom of the cylinder is fitted with a
watertight base, 12-inch diameter, to give a
stable base during the test run.
A 15-gallon sample was collected and the
settling test run immediately to prevent any
changes in the sample. The most important
variable was temperature and, where possible,
the test should be performed before any great
change occurs. In most cases it is not practical
(or meaningful) to attempt to adjust the
sample temperature to that of the ambient
temperature where the test is being
performed. The temperature of the sample in
the column was recorded at the start and the
finish of the test run. The samples were mixed
thoroughly and dumped into the test column
as quickly as possible. To assure thorough
mixing in the column, a handmade plunger
was used to agitate the contents throughout
the depth of the column. The timer is then
started and the column is sampled in sequence
within 30 seconds at each port. Starting from
the top of the column, the ports sampled are
at the 0.305, 0.61,0.91, 1.22, 1.52. and 1:67
meter levels. (1,2,3,4,5, and 5.5 foot)
These time zero samples are averaged to
provide the initial ss of the sample in the
column. The column is then sampled from
each port at convenient time intervals. The
time intervals were: 10, 20, 40, 60, 80, and
120 minutes.
The samples withdrawn from each sample
port (except the bottom one) were collected
in small containers (approximately 500 ml) to
be analyzed for ss. Care must be taken to
flush out each sample port before the sample
is taken. The filter paper used for this analysis
was Whitman GF-C® or equivalent.
The depth of liquid in the column should
be recorded initially and after each set of
samples has been removed. It is more
convenient to measure all depths from the top
of the column.
The percent settleable solids was
determined on the large sample collected for
the settling test. This was done by filling a
graduated cylinder (1,000 ml) with the
sample and allowing the sample to stand for
one hour. After 60 minutes a sample is
withdrawn from the center of the cylinder for
ss determination.
Interpretation of Results
Using the ss results from the above
procedure, the percent of initial ss is
calculated for each sample. Each sample is
associated with a specific port, time and
liquid level. The quantity z/t is calculated
where z is the distance down the column from
the surface of the sample and t is the time at
which the sample was taken. This quantity is
converted to a settling velocity in cm/sec.
Percent of initial ss is then plotted against 2It
resulting in a distribution of settling velocities
of the ss in the sample. When interpreted by a'
slightly different method, the percent removal
of ss can be evaluated as a function of
overflow rate and detention time. This is used
for the design of a primary clarifier.
SETTLEABLE SOLIDS (BY WEIGHT)
The settleable solids after one hour
quiescent settling analysis was conducted
according to Standard Methods, Edition
13,29 with one change. The glass vessel used
had a diameter of 6 cm (2.4 in.) as opposed to
the required 9 cm (3.5 in.). The minimum
settling depth of 20 cm (7.8 in.) was
observed. In all other respects Beak's method
was identical to that in Standard Methods.
A study by Happel and Byrne30 has
indicated that wall effects are negligible for
settling in columns 6-9.cm (2.4-3.5 in.). The
wall effect is given by the expression:
Vi
D_ =
1 _
1/2
29
-------
where:
V°o
the settling velocity in
column of diameter D
the settling velocity in
an infinite diameter
medium
d = the particle size
For the size of material we investigated it
is apparent that d is infinitely small and Vn is
DLJ
v
unity when D equals 6 cm.
30
-------
APPENDIX B
PREPARATION OF AMBERLITEIRA-93 SOLID PARTICLES
Amberlite IRA-93 is an anion exchange
resin manufactured by Rohm and Haas,
Philadelphia, Pa. IRA-93 is a macroreticular
exchange resin that is a crosslinked copolymer
based on polystyrene. Preparation of the resin
for use in solids removal efficiency
evaluations was as follows:
1. The resin was pulverized utilizing an
IRL Bleuler R-28 Rotary Mill. This
unit is a ring pulverizer with a 125 ml
ring container. Tests revealed that a
grindtime of 1.5 minutes resulted in
the greatest quantity of particles in
the desired size range.
2. After being pulverized, the resin
particles were size classified using
U.S. standard sieves and a mechanical
shaker. The sieve series employed was
30, 50, 100 and 200 mesh sieves.
Sieving time used was 20 minutes.
Material retained on 200 mesh was
then wet sieved by placing the 200
mesh screen under a flowing water
tap for 15 minutes. The purpose of
the wet-sieving was to remove the
extremely fine particles. The resin
solids were then dried and considered
ready for use.
31
-------
APPENDIX C
MONITORING PROCEDURE FOR EFFICIENCY TRIALS
Bl-AK. established a monitoring program
to determine the efficiency of the swirl
concentrator model in removing suspended
solids material. The program was based on the
principle of monitoring the steady-state
condition. The monitoring of the efficiency
trials was performed in the following manner.
I. A pro-measured quantity of prepared
rosin was added to the inlet at
specific time intervals depending on
the flowrate through the model. The
intervals were considered to be short
compared to the detention time of
the system hence representative of a
continuous injection. The samples
were added by a premeasured leveled
spoon.
2. In order to permit steady-state
conditions to develop in the swirl
concentrator, a period of time equal
to 4 detention times was permitted
to lapse before outlet samples were
collected. It was determined
experimentally that after 4 detention
times the overflow concentration
approached 98 percent of the final
steady state concentrations.
3. The overflow sample was a composite
sample of 10 subsamples taken at
equal intervals during the stea.dy-state
period.
4. The concentration of suspended
solids of the overflow composite was
measured and compared to the
average suspended solids
concentration of the inlet after
correction for background
concentration of the water supply.
The overall program is described in
Table 8, Efficiency Trials Monitoring
Program Conditions. The percent
removal efficiency was calculated as:
% Removal =
100 (l -
Cone, out
\
Cone, added — Cone, background
TABLE 8
EFFICIENCY PROGRAM MONITORING PROGRAM CONDITIONS
Flow Detention
Q Time t
(l*/sec) (min)
O.I
0.3
0.5
0.75
1.0
37.5
12.5
7.5
5.0
3.75
4 t
(min)
Inject
One
Spoon
Every
Sec
Sampling
Period
(min)
Take
Sample
Every
Sec
Amount
of
Sample
(ml)
150
50
30
20
15
300
100
60
40
30
150-240
50-80
30-48
20-32
15-24
600
200
120
80
60
100
100
100
100
100
Number Total
of Sample
Samples Volume
(ml)
10
10
10
10
10
1,000
1,000
1,000
1,000
1,000
I spoon of resin weighs 1.13 grams
32
-------
TECHNICAL REPORT DATA
(Please read Ins&uctions on the reverse before completing)
1. REPORT NO.
EPA-670/2-75-011
2.
3. RECIPIENT'S ACCESSION«NO.
4. TITLE AND SUBTITLE
PHYSICAL AND SETTLING CHARACTERISTICS OF PARTICULATES
IN STORM AND SANITARY WASTEWATERS
5. REPORT DATE
April 1975; Issuing Date
6. PERFORMING ORGANIZATION CODE
. AUTHOR(S)
Robert J. Dairymple, Stephen L. Hodd, David C. Morin
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
AMERICAN PUBLIC WORKS ASSOCIATION
1313 East 60th Street
Chicago, Illinois 60637
10. PROGRAM ELEMENT NO.
1BB034; ROAP 21-ASY; Task 107
11. CONTRACT/SKAGCKNO.
68-03-0272
12. SPONSORING AGENCY NAME AND ADDRESS
National Environmental Research Center
Office of Research Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
An investigation was conducted, as part of model studies utilizing a swirl concentrator as a primary separator, helical
combined sewer overflow regulator, and related studies, to characterize the properties of solids in sanitary sewage, combined
sewer overflows, and stormwater runoff. To effectuate this study, material suitable for monitoring removal efficiencies in
hydraulic models of the swirl concentrator unit has been developed.
The approach taken by Beak Consultants, Ltd., serving as a subcontractor to the American Public Works Association in the
simulation sewage studies, was to match as closely as possible the settling characteristics of solids in three types of sewage and/or
urban runoff with a well-defined, uniform artificial test material. An Amberlite Anion Exchange Resin (IRA-93), when ground
and sieved to between 74 and 149 microns, was found to closely simulate the settling characteristics of domestic sewage. This
material is of uniform density and appears to react according to Stokes' law for spherical particles at this size range. Arizona
Road Dust, between 10 and 20 microns, was found to exhibit a similar settling velocity distribution to that of the colloidal (or
semi-colloidal) components of sanitary sewage flow.
Importantly, as background information for the selection of synthesized solids, the settling characteristics (including size
and specific gravity distribution) of sanitary sewage, combined sewer overflow and stormwater were determined. These-values
will be useful for future determinations of physical treatment process design and associated treatability.
This report on these studies recommends that either or both of these materials be used in the scale-model efficiency trials.
This report was submitted in partial fulfillment of Contract 68-03-0272 between the U.S. Environmental Protection Agency
and the American Public Works Association, entitled Development of a Swtrl Primary Separator-and a Helical Combined
Sewer Overflow Dual Functioning Regulator and Separator.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Regulations
Overflows
Hydraulic models
Combined sewers
Waste treatment
'Solids separation
Overflow quality
Particulate size
Particulate density
Settling velocity
13B
13. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
41
20. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
U.S. GOVERNMENT PRINTING OFFICE: 1978— 757-14O/138S
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