5382
                                                        001R99002
                    DEVELOPMENT OF AND APPLICATION OF THE SWIRL AND
                        HELICAL BEND DEVICES FOR COMBINED SEWER
                         OVERFLOW .ABATEMENT AND RUNOFF CONTROL
                                          By

                                 Richard Field,  Chief
                                          and
                           Richard P.  Traver,  Staff  Engineer
                           Storm and Combined Sewer  Section
                      Municipal Environmental  Research  Laboratory
                         U.S.  Environmental  Protection  Agency
                               Edison,  New Jersey    08S17
                                         at
                      USEPA  - Technology Transfer Seminar Series
                            on Combined Sewer Overflow
                        Assessment and Control Procedures
                                                     Tp-piTr'---!--.—I—I'—-- * - ' -r  j_  , ,
                                                     _  	 '  '   '-  ' -^''ton Agency

                                                     l< ;- s, '  ' ,   ^   .  ' ' ^

                                                     Ciiict^o, I^VLIOU eOo04

-------

-------
 The Combined Sewer Problem

     Overflow points are  the built  in  inefficiencies of combined sewers.
 Untreated overflows from  combined sewers  are  a  serious and substantial
                        u                                     	
Nationwide there are roughly 15,000 to  18,000 combined sewer overflow points.-
The  1977 Clean Water Act  (PL95-217) critically  fosters counter measures,
planning and construction for combined  sewer overflow  pollution.   In
October 1978, EPA is to submit a report to Congress  which  in part is to es-
timate 1-hp mimber of years nec.sssa-rv, assuming  an  annual app-mp-n' afi nn nf $5
billion to correct CSO problems.  This  is strong indication—thatrcorigress
recognizes, and their willingness to support combined  sewer overflow
pollution control.

     Physical treatment alternatives are primarily applied for suspended
solids removal and their  associated pollutants  from wastestreams,  and are
of particular importance  to storm and combined  sewer overflow treatment.
Physical treatment systems have demonstrated a  capability  to handle high
and  variable influent concentrations and flowrates and operate independ-
ent   of other treatment  facilities, with the exception of treatment and
disposal of the sludge/solids residuals.  Both  the swirl and helical bend
units have demonstrated good treatment potential for highly variable.
combined sewer overflows.

     The practice in the  USA of designing regulators exclusively  for
flowrate control or diversion of combined wastewaters  to the treatment
plant and overflow to receiving waters must be  reconsidered.   Sewer
system management that emphasizes the dual function  of combined sewer
overflow regulator facilities for improving overflow quality by  concentrat-
ing wastewater solids to the sanitary interceptor' and diverting excess
storm flow to the outfall will pay significant dividends.
     In 1971 a state-of-the-art report on regulators suggested a  British
device using VQrtex_flow_patterns could regulate flow and simultaneously
remove solids.   _This	 device would utilize the differences in  inertia
between particles and liquid as well as gravitational forces to effect
solids-liquid separation.

     Based on this concept, studies were conducted for EPA by the American
Public Works Association (for Lancaster. PA,  EP_A^emp_nstration_granjt_jio_. _
S-802208)  in conjunction with the LaSalle Hudrauli_c Laboratories,  Quebec _
during 1972-1973 for swirl developement to suit American practice and
design optimization for greater solids removal.   They produced a universal
design for the  swirl regulator/concentrator which has been successfully
demonstrated in Syracuse, NY; and a large-scale 24 foot demonstration
unit in Lancaster, PA.

     The dual functioning swirl flow regulator/solids separator has shown
outstanding potential for simultaneous quality and quantity control.

-------
IntegralParts of Swirl Regulator/Concentrator Desim	

     The swirl regulator/concentrator is of simple annular-shaped  con-
struction and requires no moving parts.  An isometric view of  the  final
form of the device is shown in Figure 1.  Again, the swirl provides  a
dual-function — regulating flow by a central circular weir spillway
while simultaneously treating combined wastewater by swirl action, which
imparts solids/liquid separation.  Dry weather flows are diverted  through
a  cunette-like channel in the floor of the chamber into the bottom orifice
or foul underflow located near the clear water down shaft to the inter-
cepting sewer for subsequent treatment at the municipal plant.  During
higher flow storm conditions, the low-volume concentrate (3-10% total
flow) is diverted via the same bottom orifice leading to the interceptor,
and the excess, relatively clear, high-volume supernatant overflows  the
central circular weir into a downshaft for storage, treatment  or discharge
to the stream.  This device is capable of functioning efficiently  over a
wide range of CSO rates and has the ability to separate settleable light
weight matter and floatable solids at a small fraction of the  detention
time normally required for primary separation.
Figure 1.   Isometric view of swirl regulator/concentrator

Legend:   a - Inlet Ramp
        b - Flow Deflector
         c - Scum Ring
       •  d - Overflow Weir
         a.- Spoilers
         f - Floatables Trap
         g - Foul Sewer Outlet
        h - Floor Gutters
         i - Dowrishaft	. .. 	-
        j'- Overflow Weir Plate__

-------
       For an essentially static device  to perform efficiently under varying
  flowrates and suspended solids concentrations, special" attention.must  be
  given to the various elements within the chamber.
]	'  	 The Inlet Ramp and Transition, .Sectjpji_siip_uld be designed to introduce^
'  tne~Incommg flow at the bottom or tne chamber  and allow solids  to enter   ;
  at the lowest position possible.  The inflow should be  nonturbulent to     I
  prevent solids from being carried directly to the  overflow weir  along with'
  the water and the floor of the ramp should be V-shape to allow for self
  cleaning during periods of low flow.	

       The Flow Deflector is a verticle free standing wall that is an exten-
  sion of the internal wall of the inlet ramp.  It  directs the flow around
  the chamber, setting up the swirl or 'spiral hydraulic patterns,  thereby
  creating a longer particle path  and a. greater  change for solids separa-
  tion.

       The purpose of the Scum Ring^  is to prevent floating solids  from over-
  flowing.  It should be extended a minimum of 6  inches below the  level of
  the overflow weir crest.  The Overflow Weir and Weir Plate^ connects to a
  Central Downshaft carrying the overflow liquid  to  discharge.  Its underside
  acts as a storage cap for floating solids that  are directed beneath the
  weir plate through the Floatables Trap.  The verticle element of the weir
  is extended below the weir plate a.minimum of 18  inches to retain and
  store floatables.  When the liquid level in the chamber decreases after
  the rainfall, the floatables exit through the _foul sewer underflow._

       The Spoilers are radial flow guides that extend from the downshaft
  to the'scum ring and are vertically mounted onjthe weir plate, which break
  "up the'turbulent vortex conditions that if allowed to exist would  impede
  proper function.

       The Foul Sewer Outlet or Underflow is strategically located on the
  floor of the. ^chamber which allows dry-weather flow and  concentrated storm-
  flow to exit via the interceptor  to   the municipal  treatment plant.   It
  is placed at the point of maximum settleable  solids  concentration and  is
  designed to reduce the clogging problems that often  incapacitate conven-
  tional regulators.

       Primary and Secondary Floor Gutters are  designed for peak dry-weather
  flow and are semi-circular in shape to prevent shoaling and solids deposi-
  tion.

      An Emergency Side Overflow Weir Assembly is present in the current
desing manuals.  This allows the swirl to be overdriven to better  than  twice
its design flowrate(QD)and still maintain effective  settleable  solids removal
efficiencies.  This is accomplished by short circuiting excess  flow  and
  lint aini ng thp intpg-Hty nf thp rham'nA-r'g «;opa-r.ati""  f 1 nw  paftP-r-r)<; ,	.	

-------
      Automated or Manually Actuated Flush  RingAssemblies  located around
 the upper portion of the interior wall  of  the swirl  chamber,  and beneath  '
 the floatables trag_ allow fpr_ea_sy jzlean^up^operations  following a CSO'
 e-yent.	.	.	.

      Swirl device hydraulic models  were developed  using synthetic materials
 simulating the particle size distribution  and specific  gravities of grit
 and organics found in domestic sewage, CSO,  and erosion ladden  runoff that
 resulted in a series of design curves relating  anticipated performance to
"design  flow and other pertinent  design parameters.

      A  number of research reports and papers are available from the USEPA
 Storm and Combined Sewer Section located in  Edison,  New Jersey.
      Structurally, swirl regulator/concentrators, swirl degritters, and
 swirl primary separators incorporate distinctly_different  features.  Some
 of these differences are illustrated in  Figure  2,	 The selected  configur-
 ation for each application was a result  of consideration of hydraulic
 principles and testing of a variety of physical models.
      It is hoped that full-scale demonstrations of the degritter and
 primary separator will be conducted and that complete technology transfer
 documentation on the  swirl concept will be accomplished.   An amendment has
 been added to the ongoing American Public Works Association grant for
 additional work to include optimization of the swirl regulator/concentrator
 design curves to cover smaller treatment inflow capacities than now exist
 and to also prepare a swirl design textbook on all aspects of the device.

      Verification of  these design curves have been,  or will be made,  in
 pilot and prototype facilities which will be discussed later. 	^

      Swirl cost curves  shown  in	Figure 3   were developed on the basis
. of.jCapital costs experienced at Syracuse and full-scale costs  estimated by
 th-eAmerican Public Works  Association study.   It is assumed that isaintenance
 and repair requirements will be similar for the swirl regulator independent
 of size and that the  person-hour  requirements  and  associated costs  will be
 88 hours/year and $l,800/yearT~res^e~ctivelyT~    J

-------
                                                      '3 - Inlet Ramp
                                                      b • Flow Deflector
                                                      c - Scum Ring
                                                      d • Overflow V/eir and
                                                         •,Yeir Plats
                                                      a - Spoilers
                                                      I - Floataoles Trap
                                                      g - Foul Sawar Outlet
                                                      h - Floor Gutters
                                                      i  - Downshart
         (b)  SMIRl. PRIMA3Y SEPARATOR
              a - Inlet
              b -
              c - skirt
              d - Gutters
              • - Clear Effluent Outlet
              f • 3affl»
              g • Sludga Discharge
                                                 inlet
                                                 Deflector
                                                 Weir and '.Yeir Plates
                                                 Spoiler
                                              e - Floor
                                              f - Conical Hooper
Figure  2.   Isometric  configurations  of  swirl device  in three  applications

-------
       10-
     o
     o
     o
     o
     0
     o
                 Note
                 a
                 o
Swirl Concentrator
     rit Removal
                     Swirl Concentrator
                     90% Grit Removal
                                                         Swirl Concentrator
                                                         100% Grit Removal
                                                         Swirl Concentrator
                                                         90% Grit Removal
                                  J_
                     50
                         150
                                      200
                                 100

                             Discharge - CFS

Figure 3.  Estimated  construction costs  —  swirl concentrator/regulator
     Helical  Bend Concentrator/Regulators have been modeled and design
criteria and  comparative cost evaluations have been developed.   Although
no demonstration  projects have been  implemented in the United States,
helical bends appear practical as  in-line regulator devices  commensurate
with, swirl.

     The helical  bend flow regulator is  based on the concept of using
the secondary helical motion imparted to fluids at bends when a total
angle of approximately 60° is employed.   Figure 4 illustrates the device.

-------
                                                                      INLET
           CHANNEL -OR
           OVERFLOW
                             '.VE1R
  OUTLET TO
   STREAM
                                                           TRANSITION SECTION
                                                                 15D
                                        STRAIGHT
                                   \    SECTION
                                           5D
                             HELICAL
                             BEND 60°
                                      NOTES:
                                        1. Scum baffle is not shown.
                                        2. Dry-weather flow shown in channel
                     ,\\  OUTLET TO PLANT
Figure  4.   Isometric view of helical bend regulator

-------
	The polluted sewage is drawn to the inner wall.  It then     _____   _  	
 passes to a_sjs:micircular chajmefTituated" at'a lowef~Tevel~l eliding to the
 treatment plant.  The proportion of the concentrated discharge will depend
 on the particular design.  The overflow passes over a side weir for dis-
 charge to the receiving waters.  Surface debris collects at the end of the
 chamber and passes over a short flume to join the sewer conveying the flow
 to the treatment plant.

      The hydraulic model studies and the computer-mathematical simulation
 of the helical bend combined sewer overflow regulator indicates that this
 flash method of solids removal, without use of mechanical appurtenances,
 can produce excellent efficiencies with reasonable size units in combined
 sewer systems.

      Model studies have confirmed the pattern of solids deposition in
 the deeper channel portion of the helical bend,  located along the inner
 circumference of the bend section, and the ability of dry-weather flows
 in this restricted deep channel to self-scour the deposited solids into the
 foul sewer outlet.

      The basic structural features of significance in the helical bend
 model are:  the inlet from the entrance sewer section to the device;  the
 transistion section from the inlet to the expanded cross section of the
 straight-run section ahead of the bend; the overflow side weir and scum
 board; and the foul outlet for the concentrated solids removal in the
 secondary flow pattern, together with the means  for controlling the amount
 of this underflow going to the treatment works.

      A design manual was developed which will enable engineers to utilize
 the helical flow principal for solids removal from combined sewer flows
 and to properly regulate the overflow of clarified wastewater to receiving
 waters or points of retention and/or treatment.

      A demonstration grant has  been awarded to the Boston  Water and Sewer
 Commission to test the feasibility of using the  swirl  regulator/concentrator
 and the helical bend regulator  for removing pollutant  loads  from a separate
'storm sewer serving an urbanized area.

      The comparative effectiveness  of both  units  will be monitored by
 splitting storm sewer effluent  into two 10  cfs influent  waste  streams.
 The foul concentrated sewer effluents  for both devices will be drained
 into a large receiving sanitary sewer having sufficient  hydraulic  capacity
 and rate of flow to adequately  transport without  deposition the  removed
 solids to a treatment facility.

      The proposed helical  bend  regulator is  roughly  fifty-feet long.

      Swirls  and helicals  of the combined sewer overflow  regulator variety
 can be installed on separate  storm  drains before  discharge and the re-
 sultant concentrate can be  stored  in  relatively small tanks as is shown

-------
in Figure 5, since concentrate flow is only  a few percent  of the total
flow.  Stored concentrate can later be directed to the sanitary sewer
for subsequent treatment during low-flow or  dry-weather periods, or if
capacity is available in the sanitary interceptor/treatment  system, the
concentrate may be diverted to it without storage.  This method of storm-
water control would be cheaper in many instances than building  hugh holding
reservoirs for untreated runoff, and offers  a feasible approach to the
treatment of separately sewered urban stormwater.
i i!
< ,
(
1 l
SI/
5 i *
—
UJ
H-
<
3—
a
5i7
Sil
i o] r*— >•>
\ ZT ! . (
\ i >
< s I
- L= f
1 i
s >
M V
V ^^
§
OVBR-OVf



TREATMENT
PLAMT

^**^*^^


^ 	 r
*•«.
^





STORM DRAIN
NETY/OKK
\ SANITARY
JNTEHCEPTOR
~- SMALL CONCENTRATE

>

TANK


s S-.YIRL
CHAA13EH S
A"


" ~ j*^
/
X' \
\


^^

\
\






	 ,




"^^


Figure  5. Swirl urban storm runoff pollution control device schematic
           diagram
Site Selection and Design Philosophy __„„_.	

     The development and refinement of the swirl concentrator/regulator
has received major emphasis by the Storm and Combined Sewer Section.  The
unit serves as a compact, static device for removing solids and particulate
material from combined and separate storm sewers during storm flow and for
primary treatment, erosion control and grit separation.  A large scale
40 cfs 24 foot diameter swirl regulator/concentrator has just been com-
pleted and is on-line in Lancaster, Pennsylvania.   A 10 cfs 12 foot
diameter swirl regulator was constructed in Syracuse,  New York in June
1974 and evaluated.   The performance of the device is  good and extremely
economical providing the dual function of flow regulation and solids
separation.  At the present time,  the application  of the swirl is being
implemented by such programs as  the 108 Great Lakes Program,  201
Construction Grants Program and  the 208 Areawide Waste Treatment Mana-
gement Program.

     But what is  the design application philosophy for sizing the swirl	
for an actual site?  __In _St. _Denis,  France,  a lOjneter diameter swirl
regulator has been constructed using' a. 10 year storm return period.
In other words, the  swirl unit will reach design flow  once every 10

-------
 years—not very economical!  The second problem with the French swirl
 is that the pump for  lifting the underflow  from either a wet-weather
 event or dry-weather  flow are incapable of  handling the heavy solids
 loading.
	A reasonable design philosophy for the sizing of_aswir_l_js.to-base
  the design on percent of suspend'ed solids  removed or percent of flow
  treated at a specific site over a long- duration,  for example,  a-.year.
  This means that a proposed location should have  long term jqua_lity/
  quantity  data_j?or each  overflow location.   It  then becomes an easy jLas
  arrive"at a mass "loading curvs Tor each rainfall  event.   By making the
  correct cost-benefit choice based on incremental  removal  versus storm
  flowrate and hopefully  receiving water impacts,  design  flow,  which re-
  lates to swirl chamber  size, will readily  fall out.

      Now, let's come back to reality and how things  really  are I   The
  city engineer, consultant, or regional planning  council will  be lucky
  if they have good raingauge data for the catchment  area they  wish to
  apply swirl at, much less than quantity of overflows, or  even  number
  of overflow occurrences.
       A  rough-cut approach,  tp_ see what design  flowi (QD)  and resulting size
 swirl  would be applicable  for  a  candidate  site  can~be  made  utilizing rain-
 fall  intensity records  for the area in question.Following the determina-
 tion  of  a "ballpark" QQ, and the decision  to pursue  swirl construction,  it
 is  the responsibility of the consultant to make a  characterization of the
 subject  catchment utilizing  quantity/quality simulation models  which are
 available today in conjunction with some verification  data.   Only then can
 a "cost-effective" decision  be made as to what will  be the  actual design
 flow.

       An example of this rough-cut methodology can be  cited with  the  ~
 Detroit Water and Sewerage  Department.   An application:.is being  pre-
 pared for submission to the Region V 108 Great Lakes  Program for the
 construction of a swirl regulator/concentrator.  Five good years  of
 raingauge data are available for the Schoolcraft Street catchment  area.

       402 events were recorded of which  115 were discounted as hayinp    —
 flows too small to trigger  an overflow.   This leaves us with 28f7 ev.eni-s _
 over  a 5 year period.   Utilizing the simplistic equation Q=Cia,  flow-
 rates were determined for each rainfall  intensity range and a tabulation
 of those reoccurring events were tallied.   With the desire to treat
 approximately 70 percent of the overflow  events,  the rough-cut size was
 determined to be 40  foot diameter based  on a design flow of 100  cfs.  This
 results in having 41 out of 57 events per year at or below QQ.   However,
 with  the ability to  overdrive the swirl  to at least twice its design
 capacity or 200 cfs, and still effect a  reasonable removal  efficiency,
 only  5 events per year are beyond the capabilities of the "rough-cut"
 swirl treatment capacity.   This  particular case had an approximate
 rainfall_intensity of .45  inch/hour  and an approximate runoff coefficient
 of .50.   _Again,'this approach  is only good enough to get  a  handle on

-------
 what size  facility would be  needed.   It is  the consultant's responsibility
 to make  the  decision  on a  final Qry after examining sufficient quantity/
 quality  data for the  proposed  site.

     The following section will deal  with brief descriptions of existing
 installations which are utilizing  the swirl as a regulator concentrator,
 degritter, primary separator and erosion control device.

 Syracuse,  New York^ (Prototype  Swirl Regulator/Concentrator)

     A 12  foot diameter swirl  combined sewer overlfow regulator was
 installed  at the West Newell Street outfall in Syracuse,  New York.
 Design flood flow to  the swirl device  was based on maximum carrying
 capacity of  the 24 inch diameter combined, .sewer inlet r .8.9  mgd -
 and_a_design flow for quality  control_(in accordance  with  scale model
 investigations)  of 6.8 mgd.

     As  mentioned earlier, tests indicate that the device  is  capable
 of functioning efficiently over a wide range  (10:1) of combined sewer
 overflow rates,  and can effectively separate  suspended matter at a
 small fraction of the detention time  required for  conventional  sedi-
 mentation  or flotation [seconds to minutes  as  opposed to hours  by
 conventional tanks),

     At  least_50 percent removal of suspended  solids  and BODg were
 obtained. ~~ Table__l_ further  details suspended  solids  mass  removal and
 concentration reduction.   The capital  cost  of  the  6.8 mgd  Syracuse
 prototype  was $55,000 or $8,100/mgd and  $1,Odd/acre.

 Table~ 11    Suspended solids  removal
Storm No.
2-1974
3-1974
7-1974
10-1974
14-1374
1-1975
2-197.5
6-1973
12-1975
14-1975
15-1975
Swirl Concentrator [Conv. Reau later
Mass Loading
ka
Inf. Eff. fen.5
374 179 52
69 34 51
93 51 34
256 134 48
99 57 42
103" 24 77
463 1 67 64
112 62 45
250 163 33
83 43 42
117 21 82
Average SS
oer storm, ma/1
00 b
Inf. Err. Rem.
535 245 36
132 141 23
110 90 13
230 164 29
159 1 23 23
374 167 55
342 202 41
342 259 24
291 232 20
121 81 33
115 55 52
Mass Loading
ka
(V a '
Inf. Underflow Rem.
374 101 27
69 33 48
93 20 22 •
255 49 19
99 26 26 .
103 66 64 i
463 170 34-
112 31 27
250 48 19
83 14 17
117 72 61 L
apor the conventional regulator removal calculation,  it is assumed that
 the SS concentration of the foul underflow equals the SS concentration
 of the inflow.
bQata reflecting negative SS removals at tail end of storms not included.

-------
     However,  it  should be indicated 'at  this  point that the Syracuse
design closely matched full-pipe flood conditions and could be overly
safe for-pollution  control; especially for  larger outfalls.  It  is
entirely possible to further reduce capital costs to:  $l,000/mgd
and $200 to  $500/acre;  in lieu of the thousands of dollars per mgd
and acre usually  considered for combined sewer overflow control.

Denver, Colorado  [Pilot Swirl Degritter}

     A large 6 foot pilot swirl device designed as a grit_remoyal faci1ity.
was tested by the Metropolitan Denver Sanitary District.; Figure 6
exhibits a suggested swirl degritter  layout  for above-the-ground  in-
stallations.
     GS1T CHAM8S
                                  INLET
                                        /— WASH WATEH
                                        /   OVBROW V»HR
                                 SECTION A-A
            Figure 6.   Suggested Swirl Degritter Layout for Above-(he-Ground
                      '  Installation with Inclined Screw Co

-------
     It was found under testing performed on domestic sanitary waste-
water, at times spiked with 0.25mm dry blasting sand to simulate swirl
regulator foul concentrate concentration, that the swirl unit performed
well.  The efficiency of removing grit particles was equal to that of
conventional grit removal devices.  Scaled up detention times for full
size swirl units having volumes one tenth that of conventional tanks,
were as low as 20 seconds, whereas detention times of one minute and
greater are normal for conventional grit chambers.

     The small size, high efficiency and absence of moving parts in the
basic swirl degritter unit offers economical and operational advantages
over conventional grit removal systems.

Toronto, Canada (Pilot Swirl Primary Separator)

     A model study was conducted to determine if the swirl concentrator
principle could be used to provide primary treatment to sanitary sewage,
combined sewer overflow,  and stormwater.   In comparison,  the swirl
regulator/concentrator provides a coarser pre-treatment.   The design
was then tested on a pilot 12 foot diameter installation with real
sewage at Metropolitan Toronto's Humber wastewater treatment plant.

     The studies provided proof of the applicability of the swirl principle
to the function of primary clarifications and verification the design that
was based on hydraulic model optimization.   In a short detention period
solids are deposited by inertial and gravity action and agglomeration
mechanisms.   Importantly,  in storm flow treatment application,  suspended
solids will be heavier due to high sewer transport velocities and,  there-
fore, will tend to separate more readily which favors swirl separation
over sedimentation.

     The basic advantages  of the swirl clarification principle are that
it requires:   (1)  less land than conventional sedimentation,  and (2)  no
mechanical sludge collection of settled solids  in the sludge hopper.
The latter advantage is partially achieved  by providing a  deep conical
hopper over the entire flood area,  thus  imposing an increase in costs.

-------
     Annual operation_aiidjna,intenance_^:osts  are_estimated to be	
less witH~Ene swirl unit, about $5,000 TeTs  for 5 mgd.   In urban areas
where land is expensive the fact that swirl  requires  one-half or less  the
surface area  (according to overflow rates) could make it highly competitive.

     The engineer must consider the costs of construction,  operation and
maintenance, and land in a cost comparison figure.  In  the locations where
land is at a premium it is advisable to  compare the costs of smaller
parallel swirl units with their lower operation and maintenance costs
against those of conventional tanks.	    . L	
'R6cHester,'New York (Pilot  Swirl  Primary Separator and Swirl Degritter)
     Pilot plant treatability studies were undertaken to delineate  the
treatment alternatives available for control of combined sewer overflow
quality under the Monroe County, Division of Pure Waters, Rochester,
New York.

     A major emphasis of the study was development of cost/benefit
comparisons of processes that would allow primary-level treatment efficien-
cies.  These processes were compared relative to their response to  treating
variable Duality confained sewer overflows.  Treatment of the highly con-
centrated first-flush overflow was of particular importance.	
      The  pilot  facilities included a.  swirl  degritter^ and a swirl primary-
 separator connected in series as shown  in Figure 7,	The swirl  degritter
 was  3 feet in diameter and approximately 4  feet  in total depth.   During
 normal operations,  the overflow from  the degritter became the influent for
 the  swirl primary  separator.  Provisions were  also made,  however,  to allow
 the  influent to bypass the degritter  and go directly into the swirl
 primary separator.   The swirl primary separator  was  6 feet in diameter and
 approximately 6 feet in total depth including  hopper.
                                        Sflim. PRIMARY
                                         SEPARATOR
         CSQ
        1NR.QV!
                                                         ErRUBJT
 Figure 7.  .Schematic Diagram of Swirl Pilot Facility in Rochester, NY

-------
      The  swirl  devices were tested  at  flowrates  ranging from 15 to 70 gpm.
 Using Froude  Law  scaling relationships,  these  translate to flows of 0.2
 and  1.0 mgd for a 15  foot diameter  swirl primary separator and nominal
 overflow  rates  of 1,245 to 5,705 gpd/ft, respectively.   Mathematical
 performance models were developed for  each  system relating suspended solids
 removal rates to  influent flcwrate  [scaled  by  Froude  number)  and influent
 concentration.

      These  performance equations were  compared to the design  curves of the
 earlier development studies_for swirl  devices.   Taking  differences of
 particle  size distributions'into account, the  Rochester data  generally
 supports  the  design presented by the earlier work.

 Lancaster,  Pennsylvania (Prototype  Swirl Regulator/Concentrator with
 Prototype Degritter in Series for Foul Concentrate)^

      The  original  swirl regulator/concentrator and  degritter  hydraulic
 model studies were conducted for the Lancaster,  Pennsylvania  prototypes.
 The  prototype system as shown in Figure_8 is being  supported  by an EPA
 demonstration grant.  It is comprised of a  40  cfs,  24 foot  main diameter
 swirl combined  sewer overflow regulator/concentrator  with  a smaller 2  cfs,
 8  foot diameter swirl degritter in series to degrit the  swirl  regulator
 foul underflow  concentrate prior to its entry  to  the  pumps  feeding the
 sanitary  interceptor.  Upstream gTit^ removal will prevent  downstream pump-
 ing  problems, sewer siltation and deposition,  and treatment pjroblems in the
 Lancaster sewerage system.   The relatively  clear  swirl regulator/coricentaT-~
 tor  overflow  will receive disinfection and  go  directly to the  Conestoga
 River.  This  swirl system will serve a. drainage area  of  215 acres.
Figure 8.   DemonstTation System Flow  Diagram Lancaster,  PA

-------
       The contractor's construction cost proposed  for  this  system,  which
  also contains degritter and control housing, a pilot  dicostrainer  and
  various appurtenances and research instrumentation  is  $669,000.  The  capital
  cost of the swirl regulator alone was $50,200 or  $l,946/mgd  or $233/acre.

  The Swirl Concentrator as an Erosion Control Device

       Erosion-sedimentation causes the stripping of  land, filling of surface
  waters, and water pollution.  Urbanization caused accelerated  erosion rais-
  ing sediment yields two to three orders of magnitude  from  100  - 1000  •
  ton/mi2/yr  to 10,000 - 100,000 ton/mi /yr.  At the present  national  rate
  of urbanisation,  i.e., 4,000 acre/day, erosion/sedimentation must  be  recog-
  nized as a major environmental problem.

       The swirl concentrator has also been adapted for  the  reduction of
  erosion runoff sediment and other fine grained debris  that results from
  modern construction activities.  Final design specifications are in manual
  form.  In conjunction with a. demonstration near Columbia,  South Carolina
  that tested the effectiveness of various soil stabilizers  for  erosion
  control, a. swirl  concentrator has been built, place in a highway runoff
  channel and prepared for field testing.

       A swirl concentrator with a 6 foot diameter was chosen  for the test
  for its practicality in installation.   Both its size and weight were  con-
  sidered reansonable for manipulation by a 4-man team on the  steep highway
  .backs lopes_in the test area.  Such a _swirl deviceican_jDe rapidly and
  ecpnQmi.gaj.ly^ installed at points of erosion runoff by use of ""a" conventional
""cattle watering tank_fitted and equipped with a suitable inlet line,  "
  circuTar overflow weir,  a foul sewer outlet and necessary interior
  appurtenances.  The total cost for the South Carolina 5.8 cfs unit was
  $800 or a cost of $381/acre.  This chamber can be readily disassembled,
  moved to another  site,  and reinstalled for the treatment of erosion runoff
  flows.   If a permanent structure is  desired,  it can be fabricated out of
  concrete.

       The de-silted,  or clarified effluent could be discharge to drainage
  facilities  and disposed  of into receiving waters  or other points of disposal
  or use.   The collected solids  could  be discharged through the foul  sewer
  outlet and  entrained or  collected at  suitable points of erosion or  for use
  for other predetermined.purposes.

  Closing Remarks

       The swirl principal  may be employed anywhere  it is desirable to  remove
  solid particles from liquid  flows.   In the field' of water pollution control
  this principle  could relate  to the degritting of  sanitary and storm flows
  and to primary  separation,  sludge thickening,  and  the  final clarification
  process.  Because the swirl  creates a  defined mixing pattern  it appears
  feasible to  apply a  form  of  the swirl  for the simultaneous  enhancement of
  chemical coagulation and  disinfection  while  clarification of  raw water for
 _.pgt_ab_le useage or wastewater is  taking p_lace_.  The day has  now  dawned_upon
  us  where jvuge process, multimillion dollar, high structurally intensive

-------
                 recommendations for the treatment of our stormwater,  combined sewer over-
                 flows and urban runoff can no longer be made.   The swirl is one of the low
                 structurally cost-effective alternatives that  is now available to be.broueh±_.
                 into our fight to protect and restore the Nation's  receiving waters.       	^_
f

-------