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

-------
  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

-------
 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

-------
 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

-------
                                      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

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            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

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            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

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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

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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%

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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

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                                                                       .






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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

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(oas/y pue oas/uio)
                   22

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    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

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* 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

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                     25

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(oas/jj pue oas/uio)
                            26

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                                  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

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 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

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                                      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

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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

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                                     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

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                                    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

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                                           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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