United States
Environmental Protection
Agency
Municipal Environmental
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-84-151 Oct. 1984
Project Summary
Swirl and Helical Bend
Regulator/Concentrator for
Storm and Combined Sewer
Overflow Control
William C. Pisano, Daniel J. Con nick, and Gerald L Aronson
Swirl and helical bend devices were
'studied for 3 years at Lancaster, PA.
and West Roxbury in Boston, MA. At
Lancaster, the study included:
e a full-scale swirl regulator/solids
concentrator (SRC) for combined
sewer overflow (CSO) control (24-
ft (7.3-m) diameter) and
• a swirl degritter for SRC foul
underflow (8-ft (2.4-m) diameter).
At West Roxbury:
e a pilot-scale SRC for separate
urban stormwatertreatment(10.5-
ft (3.2-m) diameter) and
• a pilot-scale helical bend regulator/
solids concentrator (HBRC) for
separate urban stormwater treat-
ment (60-ft (18.3-m) long).
Data from the Lancaster facility indi-
cated that the SRC is an efficient treat-
ment device to remove heavier or "f irst-
flush"-related suspended solids and
grit. Treatment efficiencies usually
exceeded 60% for flows exceeding 20
cfs (666 L/s). The swirl degritter did not
function properly.
At West Roxbury, efficiencies are low
for both units and do not appear to be
related to flowrate.
This Project Summary was developed
by EPA's Municipal Environmental
Research Laboratory. Cincinnati, OH,
to announce key findings of the
research project that is Mfy document-
ed in a separate report of the same title
(see Project Report ordering informa-
tion at back).
Introduction
Untreated storm overflows from
combined (storm and sanitary) sewers
are a substantial source of water
pollution during wet-weather periods. In
U.S. municipalities, 40% to 80% of the
total organic load during wet-weather
flow periods emanates from roughly
15,000 to 18,000 CSO points. On a
national level, the cost to abate CSO
pollution has been estimated to be $30
billion. In considering wet-weather
water pollution abatement, attention
must first be directed to control of the
existing combined sewerage system
and replacement (or stricter maintenance)
of faulty ' regulators. Consulting and
municipal engineers will agree that the
regulator mechanical failures and
blockages that persist at the overflow or
diversion points result in unnecessary
bypassing; this is also a problem during
dry weather. Malfunctioning overflow
structures, both of the static and dynamic
varieties, are also major contributors to
the overall water pollution problem.
In the interest of more effective
pollution control, regulators and their
appurtenant facilities should be
recognized as devices having the
responsibility of controlling both quantity
and quality-trie two "Q's"—of overflow to
receiving waters. The U.S. practice of
-------
designing regulators exclusively for flow-
rate control or for diversion of combined
wastewaters to the treatment plant and
overflow to receiving waters should be
reconsidered. Sewer system manage-
ment that emphasizes the dual functions
of CSO regulator facilities for improving
overflow quality-thai of concentrating
wastewater solids to the sanitary
interceptor and diverting excess storm
flow to the outfall-will pay significant
dividends.
SRC's and HBRC's (isometric views.
Figure 1), which operate as flow regula-
tors and simultaneously remove floatable,
settleable solids and their associated
pollutants from wastestreams, are partic-
ularly important for CSO control.
With separate sewers, stormwater
discharges also impose pollution
problems especially when they have
industrial and sanitary cross connec-
tions, as many of them do. Swirls similar
to the CSO regulator can be installed on
separate storm drains before discharge,
and the resultant concentrate can be
stored in relatively small tanks since
concentrate flow is only a few percent of
total flow. Stored concentrate can later be
directed to the sanitary sewer for subse-
quent treatment during low-flow or dry-
weather periods, or if capacity is available
in the sanitary system, the concentrate
may be diverted to it without storage. This
latter method of stormwater control
would be cheaper in many instances than
building huge holding reservoirs, and it
offers a feasible approach to the
treatment of separately sewered urban
stormwater.
Lancaster Facility
The concept at the Lancaster, PA,
project (Figure 2) called for a prototype
SRC to receive the combined sewage; the
foul outlet flow to be controlled and
directed to a second, smaller swirl device
for grit removal; and the relatively clear
overflow from the SRC to be discharged to
the Conestoga River. The swirl degritter
was included to prevent excessive wear
caused by grit in the raw sewage pumps,
which are downstream of the degritter
clear effluent.
The design flows, Qd, are:
• SRC = 40 cfs (1133 L/s) with a
surcharge capacity for limited treat-
ment of 90 cfs (2549 L/s);
• swirl degritter = 1.2 cfs (34 L/s); and
• foul sewer underflow (regulated by a
Hydrobrake at 3% of Old|) = 1.2 cfs (34
L/s).
The SRC controls CSO from the 215-
acre (88.5-ha) Stevens Avenue drainage
area (one of the city's six overflow points
to the Conestoga River). During wet
weather, sewage enters the SRC and is
directed along the floor gutters to the foul
underflow and then to the Stevens
Avenue pumping station.
The goal of the Lancaster project was to
demonstrate a full-scale prototype CSO
SRC for simultaneous hydraulic control
(flow splitting) and treatability of
settleable and floatable matter.
Inlet
Channel for
Overflow
r- Scum Baffle
\ \ r Weir
Transition
Section
Outlet to
Stream
Straight
\. Section
Helical
Bend 60°
Outlet to
Sewer
Isometric View of
Helical Bend Regulator
Emergency
Concentrate
' Return to
Sewer
to Stream
Section
* Concentrate
Return to
Sewer
~ Emergency
Weir
Plan
Swirl Concentrator
Effluent to Stream or
Additional Treatment
Figure 1. Hulical bend and swirl concentrator.
2
-------
Swirl Degritter^
Screw ConveyorV
Swirl Degritter Effluent
Discostrainer
To StevensAve.
Pumping Station Dry Weath~
Bypass
Concentrated (Foul) Underflow
Swirl Concentrator
Emergency Overflow Weir
Combined Sewer
Diversion Chamber
Sluice Gate
*• Swirl Unit Bypass
Control Building
Flow Meter
Hydrobrake
Swirl Unit Influent
Emergency Overflow Trough
Swirl Concentrator Effluent
To Conestoga
River
Figure 2. Lancaster Swirl Project facilities layout.
West Roxbury Facility
The SRC and HBRC were operated
side-by-side for comparative evaluation
at West Roxbury. The Qd are:
• SRCandHBRC = 6cfs(170L/s)with
surcharge capacities of 12 cfs (340
L/s) for limited treatment; and
• foul sewer underflow (regulated by a
Hydrobrake at 3% of Qd\ = 0.18 cfs
(5.1 L/s).
At the West Roxbury facility (Figure 3),
stormwater runoff from 160 acres (65 ha)
of separately sewered drainage area
enters the site through an 87-in. (2.2-m)
reinforced concrete pipe (RCP) that
connects into a 120-in. (3.05-m) conduit
discharging to the Charles River 1000ft
(305-m) downstream. Separate storm
drainage is diverted by gravity into the
site and to the two units. Flow is split
evenly to each of the two units by motor-
driven, bottom-opening sluice gates.
Clear water discharge from the SRC and
HBRC drains by gravity into the 120-in.
RCP. The foul sewer concentrated under-
flows drain from the units and are
discharged by gravity into the foul sump
tank. Discharge in the foul sewer under-
flow is limited to 3% of Qd. The goal of the
West Roxbury project was to demonstrate
a pilot SRC and HBRC for treating settle-
able solids and floatables in separate
urban stormwater runoff.
Results and Conclusions
Lancaster Facility
Data from the evaluation period (1980-
1981) indicated that the SRC is an
efficient treatment device to remove
heavier or "first-flush"-related suspend-
ed solids. Treatment efficiencies exceeded
60% for flows exceeding 20 cfs (566 L/s).
Special cross-sectional samplers
capable of taking complete vertical
"slices" of flow over an entire pipe cross
section in an automatic discrete mode
were developed and installed in the 36-
in. (0.91-m) influent conduit to the SRC
and in the T2:'n. (30.4-cm) line to the
swirl degritter to obtain representative
suspended solids samples to the SRC and
the swirl degritter. The new cross-
sectional sampler and a Manning model
6000* sequential sampler were used
during four storm events. An analysis of
the data indicated that suspended solids
of samples collected by the new sampler
were 6 to 7 ti mes more co ncentrated than
samples collected (at the same instant) by
the Manning sampler during the first 10
minutes of the storm's peak "first flush."
Concentration factors reduced to 2 to 4
for samples collected mid-event and then
down to 1.5 to 2.0 for end-of-event
samples.
The set of SRC influent suspended
solids concentration factors cited above
were used to reassess the seemingly poor
efficiency performance of an event
monitored in the fall of 1980 (before
special cross-sectional samplers were
installed) and an event monitored in 1978
during the initial evaluation period. With
the use of these factors, both events
showed good suspended solids removal
efficiency.
A summary of the SRC suspended
solids removals for five events monitored
with the cross-sectional samplers is
presented in Table 1. The removal and
efficiency percentages associated with
the indicated estimated flows are also
presented. Removal is defined as the
percentage of the influent mass
contained in the foul underflow line.
Efficiency is defined as the removal
'Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use.
-------
27 in. Sanitary Trunk Sewer
Figure 3. Swirl/Helical Bend site plan. W. Roxbury Project.
Table 1.
Summary of Swirl Regulator/
Concentrator Performance
Date of Event
Estimated
Flow Rate
Icfsl
Removal Efficiency
9/10/80
10/2/80
5/10/81
7/2/81
7/20/81 pm
18
7
50
7
2
20
a
6
55
20
5
46
70
50
52
46
80
12
23
35
76
86
41
83
62
39
47
24
5
5
5
10
73
78
11
80
minus the percentage of inflow contained
in the foul underflow line. These results
were derived primarily by inspection of
raw data. Overall flow-weighted removal
and efficiency calculations are not given
because of the approximate nature
of flow measurements. Flowmeters
continuously malfunctioned during the
course of the project. It appears that the
SRC provided significant suspended
solids removal near design flow
conditions. As expected, efficiency
deteriorated at lower flow rates because
of the flow splitting phenomenon. In most
cases, efficiency exceeded 60% for flows
of about 20 cfs (566 L/s) or greater. As
anticipated, most of the suspended solids
were settleable inorganic grit. The SRC
appears to provide the degree of
treatment that it was originally designed
for, i.e., 90% removal of settleable
material (defined as grit having an
effective diameter of 0.35 mm and a
specific gravity of 2.65) at design flow (40
cfs (1133 L/s).
Evaluation results for the swirl degritter
are inconclusive. The unit rarely
functioned correctly because of blockage
problems. Visual observation, however,
indicated adequate grit removal when the
device did function.
West Roxbury Facility
Table 2 summarizes the suspended
.solids performance data for the SRC and
HBRC. Treatment efficiencies for both
ranged from approximately 5% to 35%
and do not appear to be related to
flowrate. The SRC had been sized to
provide 80% removal of grit (2.65 specific
gravity, 0.35 mm effective diameter) and
other settleable solids with equal or
greater settling velocity; the HBRC had
-------
Table 2.
Summary: West Roxb
ury Evalu-
tion; Suspended Solids Removal
and Efficiency Rates
Date
Flow
cfs
Removal
%
Efficiency
%
Swirl Concentrator
6/29/80
7/29/80
10/3/80
10/25/80
6/9/81
6/22/81
8/4/81
2.0
3.0
6.0
3.0
0.8
3.0
2.2
2.0
6.0
12.0
21.0
35.3
36.0
29.7
34.0
27.0
27.0
33.0
9.5
5.8
8.2
27.5
32.0
21.4
2.75
19.0
16.0
William C. Pisano, Daniel J. Connick, and Gerald L Aronson are with Environ-
mental Design & Planning, Inc., Hanover, MA 02339.
Richard Field is the EPA Project Officer (see below).
The complete report, entitled "Swirl and Helical Bend Regulator/Concentrator for
Storm and Combined Sewer Overflow Control," (Order No. PB 85-102 523;
Cost: $28.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Storm and Combined Sewer Program
Municipal Environmental Research Laboratory — Cincinnati
U.S. Environmental Protection Agency
Edison, NJ 08837
21.0
5.5
5.7
Helical Bend
6/29/80
7/29/80
10/3/80
10/25/80
6/9/81
6/22/81
8/4/80
1.5
2.5
4.5
2.5
.8
.8
2.0
6.0
12.3
6.0
23.0
36.5
16.0
36.5
41.2
50.5
25.5
31.0
10.0
12.9
6.0
26.5
10.4
26.5
10.0
19.3
13.5
27.0
8.0
8.9
1 cfs = 28.2 Us
been sizfed to provide 90% removal of grit
(at design flows of 6 cfs (170 L/s)for both
SRC and HBRC units). Apparently both
units are able to achieve a low degree of
primary-type suspended solids removal
for separate stormwater. It is speculated,
however, that a significant fraction of the
suspended solids had lower settling
velocities than those the units were
designed for—negatively affecting both
removal and efficiency.
The full report was submitted in fulfill-
ment of Grant Nos. S-805975 and S-
802219 under the sponsorship of the
U.S. Environmental Protection Agency.
*USGPO: 1984-559-111-10717
-------
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES PAI
EPA
PERMIT No G-35
Official Business
Penalty for Private Use $300
i-CU W TlLl
<•< -. '* I c N v ;
4 '< Itt\
5 D t A R
. I
N S
j L
y =
3^,-i
------- |