Irtfftffw WATER POLLUTION CONTROL RESEARCH SERIES • 11023 EVO 06/70
ATE
Microstraining and Disinfection
of
Combined Sewer Overflows
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WATER POLLUTION CONTROL RESEARCH SERIES
The Water Pollution Control Research Reports descriLe the results and progress
in the control and abatement of pollution of our Nation’s waters. They provide
a central source of infonration on the research, development and demonstration
activities of the Federal Water Quality Administration, Department of the
Interior, througn in-house research and grants and contracts with the Federal,
State, and local agencies, research institutions, and industrial or_anizations.
Triplicate tear-out abstract cards are placed inside the back cover to facili-
tate Information retrieval. Space is provided on the card for the user’s
accession number and for additional key words. The abstracts utilize the
WRSIC system.
Water Pollution Control Research Reports will be distributed to requesters as
supplies permit. Requests should be sent to the Project Reports System,
Off,ce of Research and Development, Department of the Interior, Federal Water
Quality Administration, Washington, D.C. 20242.
Previously Issued reports on the Storm and Combined Sewer Pollution Control
Program:
11020 --- 12/67 Problems of Combined Sewer Facilities and Overflows,
1967, (WP-20-ll)
11030 OtIS 0l 69 Water Pollution Aspects of Urban Runoff, (WP-20-15)
11020 EXV 07/69 Strainer/Filter Treatment of Combined Sewer Overflows,
(WP—20- 16)
11020 FKI 01/70 Dissolved Air Flotation Treatment of Combined Sewer
Overflows, (WP-20-1 7)
11020 DIH 06/69 In woved Sealants for Infiltration Control, (WP-20-18)
11020 DES 06/69 Selected Urban Storm Water Runoff Abstracts, (WP-20-21)
11020 DIG 08/69 Polymers for Sewer Flow Control, (WP-20-22)
11020 EKO 10/69 Combined Sewer Separation Using Pressure Sewers, (ORD-4)
11020 --- 10/69 Crazed Resin Filtration of Combined Sewer Overflows, (DAST-4)
11023 FDD 03/70 Rotary Vibratory Fine Screening of Combined Sewer Overflows,
(DAST—5)
11020 --- 06/69 Sewer Infiltration Reduction by Zone Pumping, (DAST-9)
11020 DGZ 10/69 DesIgn of a Combined Sewer Fluidic Regulator, (DAST-l3)
11023 DPI 08/69 RapId-Flow Filter for Sewer Overflows
11020 --- 08/70 CombIned Sewer Overflow Seminar Papers
11020 DWF 12/69 Control of Pollution by Underwater Storage
11024 --- 06/70 Combined Sewer Overflow Abatement Technology
11034 FKL 07/70 Storm Water Poll u ti on from Urban Land Acti vi ty
11024 FKN 11/69 Storm Pollution and Abatement from Combined Sewer Overflows-
Bucyrus, Ohio, (DAST-32)
11024 DMS 05/70 Engineering Investigation of Sewer Overflow Problem - Roanoke,
Virginia
11000 --- 01/70 Storm and Combined Sewer Demonstration Projects - January 1970
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MICROSTRAINING AND DISINFECTION
OF
COMBINED SEWER OVERFLOWS
by
Cochrane Division, Crane Co.
King of Prussia, Pa.
for the
FEDERAL WATER QUALITY ADMINISTRATION
U.S. DEPARTMENT OF THE INTERIOR
Program Number 11023 EVO
Contract Number 14-12-136
June 1970
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FWQA Review Notice
This report has been reviewed by the Federal
Water Quality Administration and approved for
publication. Approval does not signify that
the contents necessarily reflect the views and
policies of the Federal Water Quality Adminis-
tration, nor does mention of trade names or
commercial products constitute endorsement or
recommendation for use.
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ABSTRACT
Microstraining(C), using a Microstrainer screen of a nominal aperture
size of 23 microns, removes up to 98% of the suspended solids from a
combined sewer overflow. The sewer, which has an average sanitary
sewage flow of 1,000 gph, serves a residential area of 11 acres in the
City of Philadelphia. The maximum combined sewer flow recorded during
rainstorms in one year of operation has been 11.3 cfs (304,000 gph).
Volatile suspended solids removals with the 23-micron Microstrainer
screen have averaged 68% and 71% during different test periods.
BOD removals and coliform bacteria concentrations in the Microstrained
effluents have varied widely. Postulations as to the effects of Micro-
straining on both actual concentrations and on the measurement tech-
niques are given.
Results to date indicate that there is a slightly better kill of coliform
group bacteria with chlorine than with ozone in the Microstrainer
effluents when both are used at an initial nominal concentration of 5 ppm,
with 5 to 12 minutes detention time. However, chlorine has been applied
at slightly higher levels and with better control than the ozone, and it
has not been possible to optimize requirements for these chemical feeds.
Limited tests indicate that higher dosages of chlorine for shorter contact
times may be the most efficient and economical approach.
Preliminary estimates of the costs of treatment for a combined sewer via
the Microstraining process, using tentatively-established Microstrainer
throughput rates, show that the capital costs per acre of drainage for a
full—scale plant in a similar area would be approximately $10,200 for
Microstraining alone, $11,200 for Microstraining plus chlorination, and
$19 ,800 for Microstraining plus ozonation. The first two cost figures
compare favorably with other techniques that have been proposed. For
example: the costs associated with construction of separate storm and
sanitary sewers have, in several cases, been estimated to range be-
tween $20,000 and $23,000 per acre. Of eight other currently—proposed
schemes, whose costs we have roughly estimated, only surface im-
poundment (where aesthetically acceptable and where low—cost land is
available) appears competitive.
(C) Copyrighted Trade Name - Crane Co., Glenfield & Kennedy Div.
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More reliable cost estimates for Microstraining could be derived through
additional investigation at the higher throughput rates. Such investiga—
tion was begun during the latter part of the program. We have also
performed preliminary calculations which show that installations ten or
more times as large may produce per acre costs 20% to 30% lower than
these estimates.
Moreover, if the market for Microstrainers were to increase substantial-
ly, it is probable that lower production costs would result in savings to
users.
This work has been conducted with the cooperation of the City of
Philadelphia in fulfillment of Contract No. 14-12-136 between the
Federal Water Quality Administration and the Cochrane Division of
Crane Co.
Key Words: Microstraining, combined sewer overflows, solids
removal, ozonation, chlorination, BOD removal,
treatment costs.
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CONTENTS
SECTION Page
I Results and Conclusions 1
II Recommendations 5
III Introduction 7
IV Experimental Equipment and Test Site 11
Microstrainer 11
Chemical Equipment 12
Test Site 15
Operation 18
Sampling 20
Submerged Screen Area 20
V Rainfall and Runoff 21
VI Combined Sewer Overflow Quality 25
VII Microstraining Results 37
Total Suspended Solids 37
BOD
Fecal and Total Coliform
Sampling and Analysis
VIII Chlorination and Ozonation
IX Economics 53
Projected Capital Cost of High Rate Micro—
strainer—High Rate and Chlorination Facility 53
Capital Cost of Combined Sewer Overflow
Treatment Schemes 58
Annual Costs of Combined Storm Sewer Over-
flow Facilities 6 #
X Problems Encountered 71
XI Acknowledgements 73
XII References 75
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FIGURES
Page
1 Equipment Installation-Schematic 13
2 Treatment Equipment Air Preparation
and Ozone Generator
3 Outfall 67th & Callowhill i6
4 Drainage Area
5 Collection Sump From Overflow End 19
6 Rainfall Intensity 1903—1951 22
7 Maximum Storm Run-Off Vs Rainfall Intensity 23
8 Hourly Variations, Sanitary Flow, 67th &
Callowhill Sts. Sewer 2 4
9 Influence of Run—Off Rate on Suspended Solids 28
10 Suspended Solids Reduction-Mark I Screen 38
11 Suspended Solids Reduction—Mark 0 Screen 39
12 Suspended Solids Reduction—Mark 0 Screen,
Reduced Area 1 O
13 Volatile Suspended Solids Removal—Microstrainer
14 BOD Removals—Microstrainer
15 Microstrainer—Chlorination Capital Costs 5 )4
16 Proposed Schemes for Treatment of Combined
Sewer Overflows 60
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TABLES
Page
1 Suspended Solids and BOD, Microstrainer
Influent, Effluent 26
2 Fecal Coliform 29
3 Volatile Suspended Solids, Microstrainer 33
4 Total Coliform
5 Total Coliform, Final Effluent Average Values 50
6 Capital Cost of Combined Sewer Overflow
Treatment Schemes 55
7 Estimated Operating Costs of Proposed Combined
Sewer Overflow Treatment Facilities 66
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SECTION I
RESULTS AND CONCLUSIONS
The preliminary information developed in this work indicates that treat-
ment of combined sewer overflows via Microstraining can furnish a high
degree of solids removal at a per-acre cost of approximately 40% to
50% of the cost of sewer separation in cities where separation has been
considered( 1 ), such as Washington, D.C., Philadelphia and Chicago.
Treatment of an actual overflow in a residential area of Philadelphia has
produced solids removals of up to 98%. Limited data for a fine Mark
‘0” (23 micron) screen, under relatively high throughput conditions,
show removal figures ranging from 78% to 98%, with an average of 91%.
Figures for a larger number of tests made with lower throughputs show a
solids removal range of 62% to 96%, with an average of 80%.
Volatile suspended solids removals have roughly paralleled the experi-
ence with total suspended solids. These removals for the Mark “I” (35
micron) screen averaged 47% and, for three modes of operation using the
Mark “0” screen, have averaged 68%, 71% and 71%.
Bacteriological mea surement changes across the Microstrainer screens
exhibit anomalies, with both reductions and increases in total and fecal
coliform counts. Further large reductions in total coliform count can, of
course, be achieved with chlorine or ozone. Our results, with both
ozone and chlorine, although again anomalous in some instances, indi-
cate a slightly better performance with chlorine at the concentrations
used. However, chlorine has been used at a 5 ppm feed rate, the
chlorine detention times usually being 5 and 10 minutes; while the ozone,
whose detention period was about 12 minutes, was used at 3.8 ppm.
Average values for total residual coliform after treatment were 166 1000,
129,000 and 619,000 per 100 mirespectively. These values for fecal
coliform were 41,000, 81,000 and 42,000. We attribute the seemingly
better performance of the chlorine to a more positive mode of chlorine
addition and a higher feed rate than has been possible with the ozone.
In some work, carried Out near the end of the program, 15 ppm of
chlorine with only 2 minutes detention produced greater bacterial kills
than the lower concentration with longer detention.
Several possible explanations for the apparent increases across the
Microstrainer have been postulated:
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1. Natural predators for bacteria are largely removed by Microstrain—
ing and are thus not present in large numbers on the discharge side.
2. Large clumps of bacteria are broken up into numerous smaller clumps
or singlets by passage through the screen.
3. The bacterial food su 9 ply is made more available (more surface area
is produced on the escaping solids) by the screening process, and
growth kinetics are enhanced. This is perhaps reflected in some of
the BOD 5 measurements in which increases were observed across
the Microstrainer.
BOD removals across the Microstrainer have been difficult to
measure. In those cases where reductions have been recorded
across the Mark “0” screen, the average reduction has been 65%.
However, in 8 of 17 measurements made while this screen was in
service, increases in BOD were shown.
Analytical results from the City of Philadelphia Water Department’s
Research and Development Group(2) indicate that, in one set of samples
taken at the end of the program, predators were absent from the Micro-
strainer effluent, while present in the influent, and this may be a factor.
However, the third explanation may also be important, and we believe
that such effects of the Microstraining process can be desirable in the
treatment of stormwater:
1. Smaller particles will have less tendency to occlude bacteria. They
are thus more vulnerable to attack from ozone or chlorine.
2. If the BOD is exerted over a shorter time period, downstream effects
will be less persistent.
The special characteristics of stormwater overflow are vastly different
from characteristics of other municipal waste waters, and they will
require a different treatment approach. Foremost among these special
characteristics are perhaps the high instantaneous flow rates and the
fact that the treatment facility must operate for only relatively short
time periods, usually following relatively long idle periods.
Two very different treatment schemes show the lowest costs. A small,
full-flow, unattended plant consisting of a Microstrainer operating at
a high rate, together with a chlorination chamber of low detention time,
can satisfy the space, flow rate, and quality limitations in the majority
of instances, at capital and operating costs significantly lower than
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most other proposed schemes. A surface impounding basin located at
an existing outfall, with low-rate repumping to a sewage plant, has
been reported practical in one case(s), and it should be in other
locations where low-cost land is available at the outfall and impound-
ment is aesthetically permissible.
“PretreatmenlY’ of the Microstrainer influent by means of a heavy-solids
trap and a bar screen are recommended for full-scale installations.
Estimates for installed capital costs for various types of installations
based on a drainage area similar to the one used in this work are:
1. Bar screening and Microstraining $10 , 200 per acre
2. Bar screening, Microstraining and
chlorination @5—20 ppm $11,200 per acre
3. Bar screening, Microstraining and
ozonation @ 5 ppm $19 / 800 per acre
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SECTION II
RECOMMENDATIONS
1. In order to bring more realism to studies of this type, regulatory
agencies should define acceptable effluent qualities for several
typical combined sewer overflow situations.
2. The performance of a Microstrainer at the high flow rates reported
herein should be confirmed by additional work, and extended to
determine the maximum and the optimum flow rates for solids re-
moval, should they exist. This investigation should also provide
information on the effects of Microstraining on bacterial concen-
trations and growth characteristics, and develop routine mea sure-
ment techniques that meaningfully reflect these changes.
3. The low-residence, high-chlorine—dose bacterial kill should be
confirmed by additional work.
4. The ozonation work should be continued, to optimize ozone use
in this application.
5. Where ozone is chosen for disinfection of the Microstrainer effluent
in a full-scale plant, oxygen should be used on a once-through
basis in place of air.
6. A full—scale, in—line Microstrainer and chlorination facility, with-
out an impounding basin, should be built as a demonstration plant.
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SECTION III
INTRODUCTION
The pollution problems associated with combined sewer overflows in our
cities have multiplied and grown enormously over the past 20 to 30 years.
The increased concentration and growth of urban activities have brought
this about, and these problems have been subjected to much technical
arid economic study. The studies have been intensified and broadened,
particularly over the past 15 years or so, because of increased public
awareness of the severity of the overall problem of pollution of our
streams and coastal waters.
Exact figures are difficult to obtain—-and they are certainly variable
over a wide range in relation to such factors as sewer design and ser-
vice, time of day, intensity and frequency of rainfall and character of
the drainage area-—but the contribution to pollution of the combined
overflows is of considerable magnitude. An example is data reported
from Buffalo, N.Y. (1), which indicated that one—third of the city’s
annual production of sewage solids overflowed without treatment,
although only 2% to 3% of the sewage volume actually overflowed. And,
in a special three—year study conducted at Northampton in England , it
was estimated that the overflow loads of suspended solids, COD, and
BOD discharged in a year of average rainfall would be respectively 132,
62, and 35 times the daily dry-weather load, with an overflow setting of
three times the dry—weather flow. Further, work accomplished at
Detroit, Mich. (5) is reported to show that bacterial contamination effects
in the receiving stream persist for several days after discharge has
ceased, and the duration of effects increases with an increase in storm
intensity.
Heavy debris and sludge deposits in receiving streams below sewer out-
falls are common, and are considered to be long-term contributors to
pollution, because only their surface layers are readily accessible to
natural purification processes.
Among the possible solutions to the problem that have been proposed,
and in some cases implemented, are separate and parallel storm and
sanitary systems, separate sanitary systems piped within larger storm
sewers, retention tanks for combined sewer overflows, in-system
storage for peak flows, control of runoff by modifying the surface of the
drainage area, various treatment processes, and combinations of these.
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The costs of sewer separation for the entire country have been variously
estimated at 25 to 30 billion dollarsG 1 -) and higher(6), depending on the
factors considered in arriving at the estimates. And many municipalities
indicate that the practical possibility of changing all combined sewers
to separate is remote(7).
In a more recent estimation, it is suggested that street refuse can pre-
sent a significant pollution load (8)• There is thus a growing body of
opinion that the quality of separated urban stormwater is such that this
separated stormwater should be treated in some manner prior to dis-
charge into natural waters.
It now seems obvious that, for a variety of reasons, the concept of
separate storm and sanitary systems is not, at least by itself, the an-
swer to the problem. Rather, conclusions from information gathered in
an extensive survey( ) point out that different solutions and combina-
tions of solutions will be required in different localities, depending upon
local circumstances. These circumstances include not only the discharge
systems, rainfall, areal characteristics, etc. , but also the desired
character of the effluents as they relate to the receiving stream or body
of water.
This work has consisted of the design, installation, operation, and
evaluation of Microstraining equipment, and of ozonation and chlorina-
tion at a typical combined sewer overflow. Operation has not been
extensive enough to permit complete evaluations; however, information
available permits preliminary conclusions regarding Microstrainer
operation on this type of combined sewer overflow.
Initially, the Microstrainer was fitted with a Mark “I” screen. Results
indicating effluents of intermediate quality were obtained from nine
suitable rainfalls occurring within a 6—month period.
A finer, Mark “0”, screen was then fitted to the Microstrainer. Effluent
qualities, with respect to removals of total and volatile suspended
solids, increased measurably.
After an additional eight usable rainfalls, the Microstrainer controls
were altered to produce a pre-established constant differential head
across the Microstrainer screen. Results from six sets of samples
during three different rainfalls indicated still further improvement in
suspended solids removals.
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Finally, the differential head was increased well above the normal level
noted above, by blanking off much of the screen area. This reduction
in screen area amounts to about 80%, and has resulted in high suspend-
ed solids removals. These results are most significant because they
suggest that much higher hydraulic loadings, with attendant lower
capital costs, give better results.
These last tests, although few in number, indicate that the Microstrainer
Mark 110 11 screen in this service is superior to the Mark “I” coarser
screen, and that the Mark 11011 performs well at a higher hydraulic load-
ing. No evidence of screen plugging has been observed at any time.
The work reported here should provide a basis for the use of additional
tools for combatting a complex pollution problem.
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SECTION IV
EXPERIMENTAL
EQUIPMENT AND TEST SITE
Microstrainer
The test system uses Microstraining for the removal of suspended solids
and associated impurities, followed by ozonation or chlorination for
disinfection. The Microstrainer is a drum filter 5 feet in diameter by
3 feet long, with a specially woven wire fabric of stainless steel as the
filter medium. In this work, two different types of screen have been
employed; the Mark “I (nominal aperture 35 microns), and the Mark IIQ II
(23 microns). In operation, the drum is submerged in the flowing water
to approximately two—thirds of its depth. Raw water enters through the
upstream end of the drum and flows radially outwards through the micro—
fabric, leaving suspended solids deposited on the inside of the mesh.
The drum rotates continuously, at variable speeds, carrying the dirty
fabric out of the water and under backwashing jets mounted across the
top of the drum.
In general, drum rotation should be as slow as possible, consistent
with throughput and an acceptable differential head across the micro—
fabric. This is because of the filtering advantage usually provided by
the initial buildup of a layer of solids on the microfabric. The controlled
variability of drum rotational speed thus becomes a key feature of the
Microstraining process, and the speed is controlled by the differential
head best suited to the circumstances involved.
Intercepted solids are flushed into a receiving trough fitted inside the
drum with its top edge above the water level. In a full—scale project,
these solids would be returned to the interceptor sewer for disposal to
the nearest sewage treatment plant.
Inasmuch as ultraviolet radiation can inhibit the formation of bacterial
and other organic slimes, which tend to foul the Microstrainer fabric,
the Crane—Glenfield Microstrainer is equipped with an ultraviolet
irradiation source. This source is positioned over the revolving drum
parallel to the backwash jet headers, and it is designed to avoid the
production of ozone, Ozone, produced from oxygen in air, can be
deleterious to the microfabric.
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Microstrainers of this type have been employed since 1945 for the
filtration of municipal and industrial water supplies, and more recently
for utertiary treatment of sewage eff1uents( ).
Chemical Equipment
After water passes through the Microstrainer, it is collected in a 1,200—
gallon storage tank, for ozonation or chlorination. Ozone is generated
in an Otto* Plate Type (Model 3—63) Ozonizer. This ozone generator has
15 plate—type elements, and is rated at 300 grams of ozone per hour, at
a concentration of 20 grams per cubic meter of air, for a maximum power
load of 7 kw. Energy to the high—voltage electrodes is variable from
7,000 to 15,000 volts. The maximum cooling water needed is 11 gallons
per minute at 15—foot head. Air drying equipment consists of a refriger-
ator and desiccator. Electrical control panels are also provided. The
air is supplied by a 1/2 hp blower and is filtered. It is cooled to 2
to 50 C, and desiccated in silica—gel columns to a dew point of -40° C.
The concentration of ozone in air, and the amount of ozone introduced
into the water, can be varied by adjusting the air flow and the voltage
to the ozone generator.
In the CEO Otto system that is used (Figures 1 and 2), ozonized air is
mixed with the water in injectors powered by pumps. Two pump injector
sets are used, each set supplying one of two contact columns connected
in series. The water and ozonized air mixtures travel down through
centrally—located pipes in the columns, and then pass upward through
the columns. The water overflows at a point about 12 inches from the
tops of the columns, and the air, with some residual ozone exhausts at
the tops of the columns. The overall gas—liquid flow is counter current,
with the water in the first column being initially contacted with ozone
exhausted from the second column. The water from the first column is
then pumped to the second, where it is contacted with full strength
ozonized air. The treated water is discharged through a sampling tank
to the surface stream.
The columns are 17 feet high by 12 inches in diameter with the central
downpipes 1—1/2 inches in diameter.
*Supp]J.ed by La Compagni.e des Eaux et de l’Ozone
(CEO) of Paris, France.
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Ozonized Air
Rota meter
Inj ector _..
Vent
i 1IIIL. Chlorinator
H
L J
Level
Chlorine Contact-
Storage Tank
Microstrainer
2nd Oz Injection
Contact Contact Pump Measuring
Column Column Weir
Equipment Installation—Schematic
Figure 1
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Treatment Equipment, Air Preparation and Ozone Generator-
Left, Ozone Contact Columns-Center, Microstrainer-Right
Figure 2
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This system can be described as a combination co-current and counter
current contactor, since within the columns the gas and water flow in
the same direction, but the sequence of passage of liquid through
successive absorbers is counter current to the gas sequence.
In an actual plant, where operation is intermittent, it would seem
desirable from a capital cost standpoint to use an oxygen, rather than
an air, supply to the ozonizer. Using oxygen, the concentration of
ozone generated is twice that with air. Thus the ozone generator size
can be halved.
We suggest that oxygen would be used on a once-through basis, with no
oxygen recycle, thus also eliminating the need for desiccation equipment.
Chlorination equipment supplied for the plant was a small gas chlorina-
tor*. Originally, water was treated by means of this system, and
attempts were made to retain the chlorinated effluent for varying periods
of time. However, the short duration of very many of the usable rain-
storms created metering and regulation problems. This, coupled with
the need for a supply of water for relatively long periods of time f or
operation of the ozonator, forced a change in the method of chlorine
treatment. Manual addition of a solution of sodium hypochiorite to
samples of Microstrainer effluent from the holding tank was adopted.
Close control of chlorine addition was then possible, and the residual
chlorine, after chosen retention times, was destroyed by the addition
of thiosulfate prior to refrigerated storage while awaiting analysis.
Test Site
The test site is located on the western side of Philadelphia on a sewer
outfall which enters a tributary stream of Cobbs Creek, flowing eventual-
ly into the Delaware River. The outfall serves an area of approximately
11. 2 acres, principally dwelling houses with paved roads and sidewalks
(Figures 3 and 4). Dry—weather flow in the sewer averages 1 , 000 gallons
per hour, and at the setting employed during the tests, the interceptor
will collect up to three times this flow. In Figure 3, the dotted lines
define sub—drainage areas, and the solid lines connecting the small
circles (manholes) are the sewer lines. The outfall, which is 24 inches
in diameter with a theoretical capacity of about 37 cfs, is located at
*Wallace and Tiernan
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Outfall
67th & Caflowhill
Figure 3
+144.5
Paved
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I
.
H
I.
y
Drainage Area
Figure 4
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elevation 148, about 3 feet below the 150.7 foot intercepting elevation.
Overflows normally take place when storms in the area exceed a rate of
0.1 inch per hour, which occurs approximately 40 times a year, mostly
during the spring and summer. However, our plant requires 0.2 to 0.3
inch per hour for about 1 hour to produce sufficient overflow for a test
run. The rate of overflow can reach as much as 1 million gallons per
hour during a storm of 6 inches per hour, which is attained on an aver-
age of once every 5 years.
The sewer overflow was modified to incorporate a collection sump
(Figure 5) from which the storm water runoff is pumped into the test
installation. Rate of overflow is measured by means of a weir at the
sump outlet, and is continuously recorded. A baffle wall in front of
the weir prevents surges of water from upsetting the measurement of
flow rate.
Two Microstrainer supply pumps are installed between the baffle wall
and the measuring weir, one having a maximum flow capacity of 13,000
gph, and the other 5,000 gph. These pumps have been used both togeth-
er and separately, to supply water at rates of 5,000 and 18,000 gph,
with some intermediate and lower rates, depending on the supply heads
available. Intakes to the pumps are protected by a screen with 1/2 inch
square openings.
Operation
As water enters the collection sump, the level rises, starting the float-
actuated pump(s) and initiating a timer connected to the sampling de-
vices inside the test installation.
The rate of flow to the Microstrainer is recorded continuously. The
pumped flow from the sump, together with the measured and recorded
weir overflow, yield a measure of the total storm overflow. (The
interceptor continues to carry an additional three times mean dry-
weather flow.)
As water enters the Microstrainer drum, head loss through the fabric
increases, and by means of a differential pressure transmitter and servo
system, the drum speed is increased. The effluent flow rate from the
Microstrainer is measured and recorded. Water for backwashing is
drawn from the downstream side of the strainer by means of a small
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Treatment Building in Right Background
Figure 5
Collection Sump From Overflow End
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pump (40 psig discharge), kept supplied during dry periods from a
storage tank containing city water. The Microstrainer thus commences
its filtering action at the beginning of a storm, passing strained water
into the collection tank. Water may be stored here for further tests or
bypassed and returned to the stream.
Sampling
Composite samples of the raw and strained water are extracted automat-
ically by two N-Con Surveyor Model Samplers and stored in refrigerated
containers, from which they are collected and tested by the Philadelphia
Water Department. The raw, or influent, sample is taken from the
Microstrainer inlet chamber, and the effluent sample is withdrawn from
a point in close proximity to the discharge side of the screen. A time
delay mechanism delays the beginning of the sampling operation for
8 minutes after the supply pumps are actuated, in order to permit the
accumulation of enough water in the inlet and outlet chambers of the
Microstrainer for the samplers to operate. The samplers were adjusted
to withdraw portions of the flows at a fixed rate every 6 minutes. The
time lag between influent and effluent sample withdrawals is approxi-
mately 5 seconds. Ozonation and chlorination are carried Out as soon
as possible, and further samples are taken before and after this chem-
ical treatment.
The Philadelphia Water Department performs the laboratory analysis of
samples, maintains the recording rain gauge and cleans the outfall
sewer after each overflow.
Submerged Screen Area
The fraction of the drum submerged was calculated from the water level
inside the drum. For unattended tests, the level inside the drum was
calculated from the differential pressure record.
The area of screen on the drum, when none is blanked off, is 47 square
feet. In the beginning of the project the maximum drum submergence
observed was 74%, or 35 square feet of microfabric. On 7/23/69, the
outlet weir was lowered so that any differential would yield a lower level
inside the drum and, therefore, reduce submergence. The area of the
screen was later reduced to approximately 9.4 square feet. At the
resulting higher differential, the submergence obtained was 78%, or
7. 4 square feet of submerged microfabric.
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SECTION V
RAINFALL AND RUNOFF
Rainfall Intensity—Return Frequency curves for the City of Philadelphia,
as furnished by the City Water Department, are shown in Figure 6.
Figure 7 shows the rainfall intensities and durations that we have meas-
ured at a rain gauge* located in our test drainage area, about 100 yards
from the test site, along with calculated corresponding runoff coeffi-
cients. Total flows are measured by a weir mounted at the discharge of
the combined sewer trough, plus the metered quantities that are pumped
to the Microstrainer. The normal sanitary flow (Figure 8) expected dur-
ing the same period is subtracted and the pre-calibrated portion that
flows into the interceptor through a drop” weir preceding the outfall is
added. In relation to the higher total flows, this constitutes a minor
correction, since the drop weir is set to accept only three times the
average dry—weather flow (1,000 gallons per hour).
In 1969, 40 of 45 storms produced overflows in the order of 0.81 to 8.12
cfs, with rain intensities ranging from .12 to 3.3 inches per hour. It
can be seen that the highest rainfall recorded during our work has been
about 3.3 inches per hour for 10 minutes, but that the highest runoff co-
efficients (0.8) do not coincide with these periods. We also have shown,
for some points in Figure 7, the intervals in days since the previous
rainfall. These figures do not appear to be adequate for interpretation
of the differences in the runoff coefficients.
The highest flow at which the combined sewer discharged into its
receiving sump was thus approximately 300 ,000 gallons per hour (or
about 11 cfs) for about 0.4 hours. The corresponding runoff coefficient
was calculated at 0.5. The 11—acre area involved has an impervious-
ness factor of 61%.
*4.8 inch dual traverse, 6 hours,
Universal Rain Gage, Belfort Instrument Co.
21
-------
Note: Frequency Analysis by Method
of Extreme Values, After
Gumbel
Return Period (Years)
00
Minutes Duration
Rainfall Intensity 1903—1951
Philadelphia, Pennsylvania
Figure 6
0
s - I
1)
0. 4
C l )
a)
0
I- . ’
>1
—I
U)
a)
-4
-4
CD
15.0
10.0
8.0
6.0
4.0
2.0
1.0
0.8
0.6
0.4
0. 2
5 10 15 20
180 240
22
-------
Run-Off Coefficient
0 2
0 . 10
No. + Maximum Intensity Over 5 Mm
No.* Maximum Intensity Over 10 Mm
0+ —‘-Days Since Last Storm
3
-l
(U
‘-4
(U
i)
14
C)
C. ’ )
‘-I
‘-I
(U
4 - I
14
0
( I D
—I
(U
0 5.0
Maximum Storm Run-Off Vs
Rain Fall Intensity (City of Philadelphia Data)
Figure 7
1.0 0.8 0.6
0.4
5*
1+
1* 1+
*
1+
1.0 2.0 3.0 4.0
Rain Fall Intensity Inches/Hour
23
-------
1800
1600
1400 —
s - I
1200
0
iooo_ Average Flow - 1000 GPH
U)
0
— 0
600 —
400 —
200 —
0 I I • I • I I • I
2 4 6 8 10 noon 2 4 6 8 10 mIdnight
Hours of the Day
Hourly Variations, Sanitary Flow, 67th & Callowhill Sts. Sewer
(City of Philadelphia Data)
Figure 8
-------
SECTION VI
COMBINED SEWER OVERFLOW QUALITY
As expected, our data show that within the capabilities of the samplers,
the quality of the overflow tends to change with both the quantity and
the duration of the rainfall. For example: in Table 1, for the storm of
7/23/69, it is seen that the suspended solids concentration of the
Microstrainer influent was 55 ppm during the early storm period,
increasing to 97 ppm at a second sampling, and then falling to a lower
21 ppm nearer the end of the last period. The same phenomena are
shown for the storm of 7/28/69. Figure 9, which combines elements of
both time and rainfall intensity, illustrates the relationship between
overflow rate and suspended solids concentration, over a larger number
of storms for which data are available. From this limited information
there appears to be a direct relationship, but these data were accmu-
lated over relatively short periods; and it would seem that, with high
runoff intensities for longer periods, this relationship will not hold.
Unfortunately, data for prolonged high flows are not available.
Fecal coliform analyses are generally higher at the beginning or toward
the middle of a storm, and lower at the conclusion (Table 2). BOD
results tend to follow the same course as the total suspended solids
and volatile suspended solids for 7/28/69 and 9/3/69 (Table 3).
25
-------
TABLE 1
SUSPENDED SOLIDS AND BOD, MICROSTRAINER INFLUENT, EFFLUENT
Suspended Solids, mg/i BOD, mg/i
Date In Out % Reduction In Out %Reductlon
MARK “I SCREEN
12—3—68 104 57 45 21 18 14
1—23—69 71 62 13 17 82+(1) Incr
4—11—69 202 90 55 36 23 36
4—18—69 223 150 33 29 22 28
4—19—69 457 251 45 27 20 26
4—21—69 115 71 38 40 12 70
5—9—69 108 44 59 39 18 54
5—19—69 173 89 49 43 26 53
5—20-69 372 139 63 44 252+(1) mar
Average 203 106 44 33 20 —
MARK U0 SCREEN
6—15—69 107 71 34 20 9 55
6—18—69 103 17 84 112 38 66
6—23—69 159 48 70 11 15 Incr
6—25—69 157 24 85 38 6 84
7—7—69 118 49 58 30 48 Incr
7—23—69 55 29 47 41 3 93
7—23—69 97 43 56 135 7 95
7—23—69 21 17 19 5 4 20
Average 102 37 57 49 16
-------
TABLE 1 (continued)
SUSPENDED SOLIDS AND BOD, MICROSTRAINER INFLUENT, EFFLUENT
Suspended Solids, mg/i BOD, mg/i
Date In Out - % Reduction In Out % Reduction
MARK “0” SCREEN
Control change, maximum
differential increaded
7—28—69 175 66 62 8 6 25
7—28—69 498 55 89 385+(1) 76 80
7—28—69 288 72 75 13 210+(1) Incr
7—29—69 139 50 64 14 16 Incr
7—29—69 189 17 91 260 370+(1) Incr
8—4—69 163 6 96 438+(1) 584+(1) Incr
Average 242 44 80 74 33 —
MARK “0” SCREEN
Filter Area Reduced
9—3—69 111 2 98 135 740+0-) Incr
9—3—69 419 17 96 740+(1) 208 72
9—3—69 69 15 78 13 45 Incr
0- )Dissolved 2 in all dilutions was entirely depleted
before the end of the five days and are not included
in average.
-------
0
Thousands of Gallons Per Hour
Influence of r -Off Rate on S ispenc ed Solids
Fig ire 9
400
30
SS=60 + 1.17 (GPH1n 1000)
60 + 355 (cfs/acre)
-4
0
0
0
0
10
0
200
300
28
-------
TABLE 2
PECAL COLIFORM( 1 )
After Chlorination After Ozonation Residual 03, ppm
Date In Out 5 ppm-5min 5 ppm-iD mm 3.8 ppm
MARK 11111 SCREEN
12—3—68 330 655
1—23—69 1,300 900
4—11—69 510 670 5
4—18—69 1,610 1,630
1’) 4—19—69 1,460 1,940
4—21—69 690 5,700
5—9—69 9,000 8,800 100 670 140
110
5—19—69 28,000 28,000
1,500 2,500 33 1.9
5—20—69 3,000 4,800 0.2 1.3
2,100 3,000 0.3
( 1 )Thousands per 100 ml
-------
TABLE 2 (continued)
FECAL C0LIF0RM
After Chlorination After Ozonation Residual 03. ppm
Date In Out 5 pm-5rn1n Spprn-lOrnin 3.8 pp
MARK “0” SCREEN
6—15—69 13,400 6,200 77,000(2) 58 32,000(2) 1.6
— — 23,000(2) —
6—18—69 4,400 2,600 77 0 44 1.9
— — 23 —
6—23—69 100 2,800 63 22 200 0.6
— — 57 —
6—25—69 6,700 590 91 8.4 5,700 1.3
— — 2,800 —
7—7—69 27,000 30,000 — — — —
11,000 0 1 6.8 —
— — 4.3 —
7—23—69 2,200 2,700 — — — —
3,700 810 — — — —
2,800 1,100 0.1 25 0.6 0
1 Thousancis per 100 ml
( 2 )Values not used in calculation of averages
-------
TABLE 2 (continued)
FECAL COLIFORM( 1 )
After Chlorination After Ozonation Residual 03, ppm
Date In Out 5 ppm—5 mm 5 ppm-lU mm 3.8 ppm
MARK ‘0 SCREEN
Controls changed to produce fixed relation between
differential and drum speed. Maximum differential
increased
7—28—69 240 190
120 0
H 11 0.5 5.4 0.6 0.3
1.8
0 76 25 7
2.6
25 31 17
19
7—29—69 5 90
110 120
8—4—69 200 18 0 0 2.3 0.6
25
1 Thousands per 100 ml
-------
TABLE 2 (continued)
FECAL COLIFORM( 1 )
After Chlorination After Ozonation Residual 03. ppm
Date In Out 5 ppm-5 mm 5 ppm-lU mm 3.8 ppm
SCREEN FILTERING AREA REDUCED
9—3—69 5,200 3,900
7,300 6,000
2,600 3,800
L)
( 1 )Thousands per 100 ml
-------
TABLE 3
VOLATILE SUSPENDED I MICROSTRAINER
mg/i
Date - In Out % Reduction
MARK ‘I’ 1 SCREEN
12—3—69 60 60 0
1—23—69 33 27 18
4—11—69 41 21 49
4—18—69 63 38 40
4—19—69 111 52 53
4—21—69 44 22 50
5—9—69 51 21 59
5—9—69 69 27 61
5—19—69 79 38 52
5—19—69 42 20 52
5—20—69 90 30 67
5—20—69 42 17 60
Average 60 31 47
-------
TABLE 3 (continued)
VOLATILE SUSPENDED SOLIDS, MICROSTRAINER
mg/i
Date In Out % Reduction
MARK “0” SCREEN
6—15—69 34 12 65
6—18—69 35 4 89
6—23—69 31 12 61
6—25—69 81 8 90
7—7—69 53 28 47
7—23—69 21 7 67
7—23—69 39 13 67
7—23—69 9 4 56
Average 38 11 68
MARK 0” SCREEN - Controls Changed
7—28—69 37 9 76
7—28—69 63 13 79
7—28—69 48 22 46
7—29—69 44 19 57
7—29—69 38 9 76
8—4—69 54 3 94
Average 47 12 71
-------
TABLE 3 (continued)
VOLATILE SUSPENDED I MICROSTRAINER
mci/i
Date In Out — -. % Reduction
MARK IOh1 SCREEN - Area Reduced
9—3—69 21 9 57
9—3—69 42 7 83
9—3—69 18 5 72
Average 27 7 71
L )
-------
SECTION VII
MICROSTRAINING RESULTS
Total Suspended Solids
As initially installed, the Microstrainer was fitted with the Mark “I”
screen, with a nominal aperture size of 35 microns. As work progressed,
it became evident that the backwash jets, in conjunction with slime pre-
vention by means of ultraviolet light, would prevent plugging and foul-
ing of the screen, and that the influents that were received could be
more than adequately handled. Accordingly, after about 6 months of
operation, the finer Mark “0” screen was installed, to determine if
increased quality of the effluent could be realized without pluggage.
Furthermore, after an additional 2 months of operation, the Micro—
strainer controls were altered to provide a drum speed more closely
related to differential head. And finally, 80% of the filter screen area
was blanked off by inserting plastic film inside the screen. At the
same time, the backwash jets normally serving the blanked—off area
were turned off.
These last—named steps were taken to increase the Microstrainer
hydraulic loading and to determine the effects of this increase on the
quality of the effluent. An increase in hydraulic rating would corre-
spondingly reduce capital cost of a full-scale installation.
As can be seen in Table 1 and Figures 10, 11 and 12, the removals of
total suspended solids ranged from 13% to 98%, the higher values being
characteristic of the Mark “0 screen and better—regulated drum speeds.
Although the data are scattered, regressions are shown for suspended
solids in the feed vs % reduction of suspended solids, in Figure 10 and
11. These illustrate the improvement in performance gained through the
use of the Mark “0” screen, and also show the tendency for increased
removal efficiency with an increase in the influent suspended solids
concentration. For the amount of data acquired, straight line regres-
sions offered a reasonable fit.
The results for removal of volatile suspended solids are shown in
Table 3 and Figure 13. These results parallel those for total suspended
solids, about an average value of 71% removal for the Mark “0’ screen
and the higher differentials.
37
-------
80
0
70
0
( I D
t 60
w
a)
0 .
50
CID
C
o 0
4 -J
o40—
0
20 y = 35.4 + .044 (ss feed)
I I I
100 200 300 400 500
Suspended Solids in Feed, ppm
Suspended Solids Reduction
Mark I Screen
Figure 10
-------
I I I i I i
100 200
Suspended
300
Solids in Feed, mg/i
Suspended Solids Reduction
Mark 0 Screen
Figure 11
y = 48.0 + .113 (ss feed)
I I
400 500
0
x x
U)
0
0
(1)
a)
U)
0
•1-’
0
- c i
a)
0
0 ’
x
100
90
80
70
60
50
40
30
20
10
U
a
D
a
0
x
Mark 0 Screen
Mark 0 With Control Change
x
600
-------
100 4
80
c i )
ci
a
60
0
C)
4:—
0 40
30 —
20
10
100 200 300 400 500 600
Suspended Solids in Feed, mg/i
Suspended Solids Reduction
Mark 0 Screen, Reduced Area
Figure 12
-------
Ma ;’k I
Mark 0
Mark 0
Control
Change
Volatile Suspended Solids Removal Microstra,iner
Fiquro 13
Mark 0
Reduced
Area
4:-
H
100
90
80
70
0
1::
40
30
20
10
0
34
Av Level Effluent
mo/i
12
3 Dec 68 Jan Mar May July 3 Sept 69
7
-------
BOD
Removals of BOD are scattered (Table 1, Figure 14).
It is postulated that the volatile suspended solids that pass the screens
are in a much more finely divided form. It is further suggested that the
resulting increased surface area of these solids may serve as a more
rapid and more efficient growth medium for bacteria. It is thus probable
that downstream effects, after Microstraining, will be less persistent,
particularly in view of the major reduction in volatile suspended solids.
Moreover, it appears certain that post-treatment with chlorine or ozone,
if practiced, should produce markedly better disinfection, considering
the reduction in the number of larger particles that tend to occlude
organisms, protecting them from the action of these treatments.
Fecal and Total Coliform
As shown in Tables 2 and 4, both fecal and total coliform bacteria
analyses quite frequently show increases in concentrations in the
Microstrainer effluent. This phenomenon has previously been noted by
Boucher(lO). Clearly, no net “removal” of these organisms can be
claimed on the basis of these results. However, several postulations
have been made for these observed increases:
1. Natural predators are largely removed by Microstraining and are
thus not present in large numbers on the discharge side.
2. Large clumps of material rich in bacteria are fragmented into
numerous smaller particles by passing through the screen.
3. The bacterial food supply is similarly made more available by the
screening process, and the growth rate during the 5—day mea sure—
ment period is enhanced.
As related above, we have tended to accept the last-named postulation,
but it must be emphasized that the question has not been resolved. A
complicating factor is the report from the Philadelphia Research Group
that on one occasion predators (paramecia) were absent from the Micro—
strainer discharge sample, while they were present in the influent
sample. These last results were obtained at the end of the program,
and confirmation was not possible.
42
-------
Mark I Mark 0
500%* +470%*I
Mark 0 Mark 0
Control Change Reduced Area
I
a)
E
0
0
0
+100
+ 50
0
— 50
—100
Av Level Effluent 0
mg/i
16 33
20
*Oxygen Depleted
(1) Do Not Include * Data
Mar
May
BOD Removals - Microstrainer
Figure 14
Sept
-------
TABLE 4
TOTAL C0LIFORM 1 )
After Chlorination
Out 5 oom—5 mm 5 oom—10 mm
After Ozonation Residual 03, ppm
3.8 oom
Date In
MARK hhIU SCREEN
3
6
800
12—3—68
666
740
—
1—23—69
1,607
1,280
—
4—11—69
720
840
—
4—18—69
2,600
2,970
—
4—19—69
2,310
2,380
4—21—69
1,310
9,800
5—9—69
10,300
8,500
330
580
5—19—69
5—20—69
100,000
8,700
2,700
5,200
93,000
4,000
3,600
6,700
—
33
0.2
0.4
760
1.9
1.3
( 1 )Thousand per 100 ml
-------
TABLE 4 (continued)
TOTAL COLIFORM ’)
After Chlorination After Ozonatlon Residual 03, ppm
Date ±n_ Out 5ppm-5 mm 5 ppm-lU mm 3.8 ppm
MARK “0” SCREEN
6—15—69 19,900 8,600 98,000(2) 130 60,000(2) 1.6
— — 36,000(2) —
6—18—69 8,600 5,900 290 0 100 1.9
— — 120 —
6—23—69 1,200 14,000 240 79 500 0.6
— — 220 —
6—25—69 10,000 860 150 18 7,600 1.3
— — 3,900 —
7—7—69 28,000 11,000 5.1 100 18 —
— — 13 —
7—23—69 1,800 1,100 0.2 110 4.8 0
Thousand per 100 ml
(2)vaiues not used in calculation of averages
-------
TABLE 4 (continued)
TOTAL COLIFORM 1
After Chlorination After Ozonation Residual 03, ppm
Date In Out S ppm—S mm 5 ppm-lU mm 3.8 ppm
MARK 0 II SCREEN
Controls changed to produce fixed relation between
differential and drum speed. Maximum differential
increased
7—28—69 170 0 330 200 30
8
44 11 0.8 12 0.5 0.3
5.4
78 200
31 100
23
7—29—69 130 330
150 230
8—4—69 15 8 0 0 3.8 0.6
32
(1)
Thousands per 100 ml
-------
TABLE 4 (continued)
TOTAL COLIFORM( 1 )
After Chlorination After Ozonation Residual 03. ppm
Date In Out 5 ppm—5 miri 5 ppm-lU mm 3.8 ppm
SCREEN FILTERING AREA REDUCED
9—3—69 12,000 16,000
20,000 13,000
12,000 20,000
Thousands per 100 ml
-------
Sampling and Analysis
Early in the program, when apparent inconsistencies were observed in
the SOD and bacterial results, the sampling and analysis procedures
were reviewed by project personnel. COD analyses were also performed
on several samples by the City Northeast Laboratory Group, during this
early period, and these measurements confirmed the SOD results. The
sampling location for the discharge side of the Microstrainer was
ultimately changed to a point about 1 to 2 inches from the screen, and
close attention was paid to sample handling and analysis procedures.
As noted above, these apparent inconsistencies were not eliminated and
the postulations concerning BOD and coliform test results are made as
possible explanations.
It should be emphasized that suspended and volatile solids analyses
from the same samples were not inconsistent, and these latter results
lend support to sample validity.
Nonetheless, it must be recognized that these problem areas, intensified
by the intermittent operation involved, do exist. And special care is
required to validate performance.
L 3
-------
SECTION VIII
CHLORINATION AND OZONATION
Average total coliform concentrations for the final effluents in all of our
work, under varying conditions imposed on the Microstrainer, using
5 ppm of chlorine for 5 and 10 minute retention times, were 166,000 per
100 ml and 129 ,000 per 100 ml, respectively. For fecal coliform con-
centrations, these values, in the same order, were 41,000 and 81,000.
Similar results for ozone at a concentration of 3.8 ppm and a detention
time of about 12 minutes were 619,000 and 42,000. The corresponding
total coliform results for the Microstrainer effluent (prior to chemical
treatment) ranged from zero (in one instance) to a high of 93,000,000,
and the fecal coliform counts ranged from zero to 30 , 000 1000.
Ozone, of course, is more desirable for color removal, or in those cases
where a less stable, less persistent chemical residual is needed
(chioramines may be both persistent and toxic to fish in the receiving
water).
Higher chemical feed and/or longer detention times are needed for a
more complete bacterial kill. In this treatment situation it is obvious
that the former is more economical because of the increased cost of
storage for detention. Whether additional disinfection time would be
available in the outfall line and receiving water downstream of an
actual plant of this type would depend on individual circumstances.
Table 5 gives average values of coliform concentrations in the final
effluent.
Time has permitted a limited amount of investigation of larger dosages
of chemicals and shorter detention times, and some results with
chlorine* indicate that greater bacterial kills may be attained in this
way. For example: in one test on different portions of the same sample,
total coliform counts were 110,000 per 100 ml for 10 ppm dosage and
2 minutes reaction time, and 7 , 500 per 100 ml for 15 ppm and 2 minutes.
*These last—acquired results are not listed in any of the Tables.
-------
TABLE 5
TOTAL COLIFORM, FINAL EFFLUENT
AVERAGE VALUES
(Thousands per 100 ml)
CHLORINATION (5 ppm) OZONATION (3.8 ppm)
5 mm 10 mm
166 129 619
FECAL COLIFORM, FINAL EFFLUENT
AVERAGE VALUES
(Thousands per 100 ml)
CHLORINATION (5 ppm) OZONATION (5 ppm)
5 mm io mm
41 81 42
50
-------
It is suggested that short detention times may be much more effective
for effluents from the small—aperture Microstrainer screen, because of
the fine state of subdivision of the particulate matter, which escapes
the straining process. Organisms are less likely to be shielded from
chemical attack by occlusion than in the larger particulates character-
istic of many other processes.
51
-------
SECTION IX
ECONOMICS
The best solution for the combined-sewer—overflow problem appears to
vary with individual circumstances( ). Among the determining circum-
stances are the character of the existing collection system, nature of
the receiving water, population density, rainfall, land use factors (i.e.,
residential, commercial, industrial), topography, and size of the catch—
merit area.
In many cases, it would appear that large land areas required for holding
basins are not available. And in some cases, the prospect of retaining
large volumes of combined sewage for discharge at low rates to the
sewer system and a disposal plant would appear unattractive from both
aesthetic and practical standpoints.
Large detention basins, such as have been mentioned for Columbus,
Ohio, and Boston, Mass. (6), will presumably sometimes be employed
where huge overflow volumes are involved. But in instances where
large amounts of land are not available, or ultimate disposal is difficult,
or where the local environment is not suitable for detention-tank
installation, the Microstrainer should be considered.
In this connection, a recent publication(U) points out that 25% of the
catchment areas in Washington, D.C., are 25 acres or less in size,
and that a similar survey of Milwaukee, Wis. , revealed that 50% of
these areas are of 25 acres or less. There is no intent to imply that
the use of Microstraining should be limited to the smaller areas, but
these figures illustrate the number of smaller subdivisions of a drainage
basin that might be handled locally.
The cost analysis below illustrates approximate costs for Microstrain—
ing, and for other suggested processes, in a drainage area of the type
used in this program.
Projected Capital Cost of High-Rate Microstrainer
and Chlorination Facility
To help illustrate the applicability of the Microstraining and chemical
disinfectant techniques for combined sewer overflows, projected costs
of a facility have been developed. Figure 15 and Table 6 show capital
53
-------
6
Capacity of Facility - Cu Ft Per Sec
Microstrainer—Chiorination Capital Costs
Figure 15
o Microstrainer & Controls
o Microstrainer Installation & Bldg
Microstrainer Installed
120 Sec Chlorination Facility
(Basis — 45 gpm/ft 2 submerged screen)
rJ)
4
3
2
1
0
50 100
51
-------
TABLE 6
CAPITAL COST OF COMBINED SEWER OVERFLOW TREATMENT SCHEMES
(10 mgd plants)
Scheme
No. Train of Steps in Scheme
Capital Cost of
Treatment Step
S oer mad
Capital Cost of Scheme
Less Land and Engineering
$ per mgd $ per cfs $ per acre
1 Separate storm sewer, no treat-
ment of storm water.
2 Surface impounding basin, low
rate repumping station.
Sewage plant addition.
3 Sub—surface impounding basin,
low rate repumping station.
4 Equalizing basin (5 mm)
Primary clarifier
High rate “Bio-Disc ‘ , including
secondary clarifier
Conventional chlorine contact
5 Equalizing basin (5 mm)
Primary clarifier
High rate aeration
Secondary clarifier
Conventional chlorine contact
1,000(1)
6,000(2,3)
25,000(2,4)
1,000(2,3) 33,000
1,000(1)
6,000 (2,3)
25,000(2,4)
4,000(3,5)
1,000(2,3)
‘ 31
ND*
ND
ND
ND
17,000
5, 100
ND
19 , 500
11,000
3,300
ND
12,500
21,400
24,000
23,000
6 , 500
ND
25,000
42,000
47,000
37,000
*Not Determined
-------
TABLE 6 (continued)
CAPITAL COST OF COMBINED SEWER OVERFLOW TREATMENT SCHEMES
(10 mgd plants)
Scheme
No. Train of Steps in Scheme
Capital Cost of
Treatment Step
$ per mqd
Capital Cost of Scheme
Less Land and Engineering
$ per mgd $ per cfs $ per acre
6 Equalizing basin
Wet cyclone
Dissolved air flotation
Conventional chlorine contact
1, 000 (1)
2,500(6)
6,650—11,650(7)
1,000(2,9) 10—15,000
7—10,000
13—19,000
7 Equalizing basin
Fine screen
Dissolved air
Conventional chlorine contact
1, 000 (1)
1,350(8)
6,650—11,650(7)
1,000(2,9)
9—14,000
6— 9,000
12—18,000
8 Primary clarifier
Carbon and polymer feeders
Carbon re-activation furnace
Conventional chlorine contact
9 Bar screen and 45 gpm/ft 2
Microstrainer
2—minute chlorine contact
chamber with hypochlorite
feeder
6,000(2,3)
1,000(1)
4,000(8)
1,000(2,3) 12,000
7,950(9)
7,800
15,500
900(9)
8,850 5,700 11,200
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TABLE 6 (continued)
CAPITAL COST OF COMBINED SEWER OVERFLOW TREATMENT SCHEMES
(10 mgd plants)
Capital Cost of Capital Cost of Scheme
Scheme Treatment Step Less Land and Engineering
No. Train of Steps in Scheme $ per mgd $ per mgd $ per cfs $ per acre
10 Bar screen and 45 gpm/ft 2
Microstrainer 7 1950(9)
2—minute ozone contact
chamber with once-thru
oxygen fed ozone generator 7,700(9) 15,650 10,100 19,800
‘Ji
(1) Estimate
(2) Pre-publication copy of FWQA Contract Report 14-12-462.
(3) Assumption that conventional sewage equipment might have a stormwater capacity three times
its rated capacity in normal sewage service.
(4) Private communication: W. Torpey, regarding minimum anticipated relative cost of high rate
to conventional biological equipment; i.e. , one-fifth of cost on a maximum flow capacity
basis.
(5) R. Smith, “Cost of Conventional and Advanced Treatment of Waste Water”, JWPCF, v40n9,
September 1968.
(6) O.F. Tangle and R.J. Brinson, ‘Wet Cyclones”, Chem Engr, June 1955.
(7) D.G. Mason, “The Use of Screening/Dissolved Air Flotation for Treating Combined Sewer
Overflow “, FWQA Combined Sewer Overflow Seminar, Edison, New Jersey, November 5, 1969.
(8) Manufacturers’ quotations.
(9) This work.
-------
costs for such facilities. These costs are based on the assumption that
the Microstrainer will treat 45 gpm (0. 1 cfs) of the overflow water under
consideration, per square foot of submerged screen area. Further, they
are based on the assumption that an adequate bacterial kill can be
accomplished in a suitably configured detention chamber of only 2
minutes residence time. The observations recorded in earlier sections
of this report indicate that these assumptions are reasonable.
To make this scheme as generally applicable as possible, the head loss
of the water flow through the entire facility is limited to 4 feet. Two
feet of the loss will occur in the Microstraining and inlet section con-
taining the bar screen. The provision for 2 feet head loss in the
chlorination section is to insure adequate turbulent mixing. Since it is
anticipated that the overflow facility will not be sized large enough to
treat the once—in—ten-year storm, provision has been made to bypass
a flow equal to the Microstrainer capacity while the Microstrainer is in
operation. Thus the facility can accept twice the design capacity,
treat half and bypass the remainder, without interfering with operation.
Design in an actual case would depend on local hydrology.
The dollar benefit to society from the reduction of pollution by combined
sewer overflows has not been established. The assignment of such a
benefit value is beyond the scope of this work. Thus, the cost of
Microstraining treatment of combined sewer overflows cannot be com-
pared to the value of the benefit. However, the estimated cost of
Microstraining can be compared to the approximate costs of other
methods of treatment.
Capital Cost of Combined Sewer
Overflow Treatment Schemes
At a recent symposiumV2) on treatment of combined sewer overflows,
some nine treatment schemes were discussed. These schemes Consist-
ed of combinations and modifications of 12 basic treatment steps. To
compare the costs of these schemes, approximate costs have been
developed for the individual steps. Further, the capital costs of the
treatment steps have been expressed in terms of dollars per unit of
capacity, in combined-sewer—overflow service. At the present stage
of knowledge regarding both the effluent quality required and the
capabilities of these techniques in this service, some broad assump-
tions had to be made.
5B
-------
Figures l6a through l6i show schematically the treatment schemes under
consideration. Table 6 lists the steps required in each scheme, and
the estimated price per mgd of capacity. As noted in the references to
this table, conventional sewage treatment processes such as primary
clarification, trickling filter, conventional chlorination, etc. , have
been assumed to be capable of treating three times their nominal sewage
service capacity when used in combined-sewer-overflow service.
Advanced biological treatment processes such as rotary Bin-Disc, ultra-
high—rate activated sludge, etc. , have been assumed to have a capacity
such that the capital cost per unit of overflow capacity will be one-
fifth that of comparable conventional biological equipment per unit of
conventional sewage capacity.
The advanced non—biological treatment processes such as fine screens,
wet cyclones, etc. , have been developed from manufacturers’ reported
costs.
All reported costs were scaled to 1969 dollars and then to 10 mgd of
nominal capacity. This scaling of the conventional steps of sewage
treatment to 10 mgd nominal sewage capacity, together with the
assumption that equipment with 10 mgd. nominal sewage capacity is
capable of 30 mgd combined-sewer-overflow capacity, introduced an
inconsistency. The error favors the conventional equipment, since the
comparison on a dollar cost—per-mgd capacity is made from a base of
30 mgd in case of conventional equipment and 10 mgd for the advanced
treatment equipment. In general, all of the assumptions made favor
the conventional and advanced biological steps.
The capital costs as noted in Table 6 include equipment procurement,
equipment installation, and building, but do not include land or engi-
neering fees. The land required for the various schemes covers a very
wide range, from 0. 03 acre per acre of drainage area in the case of
surface impounding (Scheme 2) to less than 0.0002 acre per acre of
drainage area in the case of Microstraining-chiOriflatiOn (Scheme 9).
The capital costs of combined sewer overflow treatment facilities shown
in Table 6 were developed on a dollar per mgd basis and converted to
dollars per cfs basis (1 mgd — 1 . 54 cfs) , and also to dollars per acre of
drainage area on the assumption that 1.96 cfs was an adequate provi—
sion for overflow from an acre of drainage area.
59
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C l )
0
0
z
Proposed Schemes For Treatment of Combined Sewer Overflows
Figure 16a—16c
Scheme 1 — Separate Storm Sewer — No Treatment
(a)
Surface Impounding
Ba sin
Scheme 2 - Surface Impounding — Dry Weather
Repumpi; to Sewace Plant
(b)
Sub-surface
impounding basin
>
Scheme 3 - Sub-surface Impounding — Dry Weather
Repumping to Sewage Plant
(c)
6o
-------
Primar\
C lar:Lfier
Sc ondar\
Disinfection
C ham her
4 -. Primary Clarification + Hi rate Rotary
Bio—Disc + Disinfection
Chamber
C l )
01
C-)
cx
z
Scheme 5 -.
Primary Clarification + Hi—rate Aeration ±
Secondary Clarification and Disinfection
(e)
Disinfect i oh
Chamber
Scheme 6 — Wet Cyclone + Dissolved Air Flotation
and Disinfection
(f)
Proposed Schemes For Treatment of Combined Sewer Overflows
Figure 16d—16f
6
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em e
I-il—rate Microstraining + Low Residence
Chlorination
Hi- rate Microstraininq + Low Residence
Ozonation
(I)
Proposed Schemes For Treatment of Combined Sewer Overflov.’ s
Ficure 16g- -16i
s-.
Scheme 7
Chamber
Fine Screen + Dissolved Air Flotation
and Dlsi.ifcuiio
Carnox to
Scheme 8 Powdered Carbon Primary Clarifier +
Carbon Reactivation
Hi-rate
Mi rostiainer
Sc he in e
9-
Low Residence
Disinfection Chamber
10-
62
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The cost of surface impounding reported by Bannister at $6,500 per
acre for a 95—acre drainage area was not scaled to a 10 mgd base.
This surface impounding facility at Chippewa Falls, Wis., made use of
a fortunate set of circumstances, such as available, very-low—cost
land adjacent to the drainage area, an existing interceptor of sufficient
size, and sufficient excess treatment capacity in the sewage plant. It
might be noted here that a land acquisition cost of $30,000 per acre
would add $1,000 per acre drained to the cost of this type of treatment
facility. And, a recent check in Philadelphia indicates that some river-
front land is currently valued at upwards of $100 ,000 per acre. The
costs of separation of sewers (Scheme 1) and of sub—surface impounding
(Scheme 3) were not reduced to the l0-mgd base.
The cost of the Microstrainer and low—residence—time chlorination
facility was developed from base costs. Figure 15 shows the cost per
cfs of design capacity. This figure also illustrates an economy that
should be realized as plant size is increased. As previously noted,
this facility includes provision for bypassing excess flow equal to the
design flow.
The Microstraining—chiorination scheme is, as shown on Table 6, the
most economical on—site treatment scheme on the basis of capital cost.
As will be seen in a later section, it is also one of the most economical
on the basis of operating cost.
c3
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Annual Costs of Combined Storm
Sewer Overflow Facilities
To arrive at uniform annual costs, some broad assumptions are made:
1. Where the overflow is to be treated at the overflow point, the
elevation of the overflow is such that water will flow through
a gravity-type plant and then to the receiving stream without
repumping.
2. Rain occurs as 30 to 40 events per year producing overflow.
3. Rainfall volumes reaching a treatment facility total 90,000
cubic feet per year per acre (equivalent to 40 inches of rain
at a runoff coefficient of 0. 6).
4. Where a combined—sewer—overflow impounding basin is used,
it is so located with respect to the sewage treatment plant,
and is served by an existing interceptor of such size, that
50 feet of head is required for pumping from a surface basin
and 200 feet of head for pumping from a sub—surface basin.
5. Annual capital charges are based upon amortizing, on a straight—
line basis, the installed cost of the facility (less land) over 20
years, and upon interest charges at the annual rate of 5% of
first cost. That is, the annual capital charge is the installed
cost of the facility divided by 10.
6. Oxidant dosages of 5 ppm chlorine or 5 ppm ozone are used,
except in Scheme 9, where 15 ppm of chlorine is used.
7. The flow—rate capacities of the various treatment steps are as
cited in the previous section on Capital Costs.
8. Maintenance supplies, replacement parts, and maintenance labor,
in addition to operator labor listed elsewhere, will amount to 1%
of the capital cost per year.
The basis for the costs shown in Table 7 are:
$
acre -yr
Cost of pumping total flow to
50 feet head (@60% eff @ 1c /kwh) 1.80
o4
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Cost of pumping total flow to
200 feet head (@60% eff @ l /kwh) 7.20
Cost of pumping 3% waste flow to
50 feet (@ 60% eff @ l /kwh) .06
Cost of pumping 25% aeration flow to
60 psig (@ 60% eff @ l /kwh) 1.20
Cost of 1 horse power Continuous drive
(@ lc /kwh) 8.25
Cost of 1 ppm Chlorine
(@42 / available Cl 2 ) 2.40
Cost of ozone, 1 ppm
($5.20/ from 02 @ l9 /%) 30.00
Cost of 1 ppm polymer
(@50 /41) 2.80
Cost of one visit
(8—man hr @ $4.00/hr) 4.10
The power Costs do not include demand Changes which might
be an additional 15% for infrequent demands. Power costs
for ozone generation are included in oxidant Cost.
The operating costs for the several schemes as shown in Table 7 are
strongly influenced by the method of treating capital costs and mainte-
nance costs. The costs of electric power, labor and chemicals are
almost negligible, although high on a cents per 1 ,000 gallons basis,
when spread over approximately 675,000 gallons per acre-year of com-
bined sewer overflow.
The labor costs are based upon weekly or twice-weekly visits of
operators, or in the case of the Microstrainer, a visit after each of the
estimated 40 rain events per year.
Several of the treatment steps; e.g. , dissolved air flotation, activated
sludge, etc., normally require a startup period of at least 30 minutes.
No impounding capacity has been provided prior to these steps, nor
have power and other costs been included to operate these treatment
65
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TABLE 7
ESTIMATED OPERATING COSTS OF PROPOSED
COMBINED SEWER OVERFLOW TREATMENT FACILITIES
Maintenance
Supplies and
Replacement
Parts at Total Capital
Capital 1% of Oper Plus
Scheme at 10% Capital and O&M
No. Description per year Cost Cost Labor Oxidant Other Maint Total
1 Separate storm sewer 2,300 70* 70 2,370
2 Surface impounch nt 650 65 2 pump 160 227 877
3 Sub—surface impound-
ment 2,500 250 8 pump 258 2,758
4 Primary clarifier —
“Bio—Disc” secondary
clarification 4,200 420 8 disc 208 12 648 4,848
5 Primary clarification —
high rate aeration
clarification 4,700 470 13 blower 416 12 911 5,611
* Lower figure used for sewer maintenance
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TABLE 7 (continued)
ESTIMATED OPERATING COSTS OF PROPOSED
COMBINED SEWER OVERFLOW TREATMENT FACILITIES
Maintenance
Supplies and
Replacement
Parts at Total Capital
Capital 1% of Oper Plus
Scheme at 10% Capital and O&M
No. Description per year Cost Cost Labor Oxidant Other Maint Total
6 Cyclone-dissolved air
flotation 1,600 160 1 corn— 208 12 382 1,982
pre s s or
1 pump
7 Screen and dissolved
air flotation 1,500 150 1 corn— 208 12 Poly— 375 1,875
pressor mer 3
1 pump
8 Primary clarification -
powdered carbon and
regeneration 1,550 155 8 misci 416 12 Carbon
74 665 2,215
9 Microstraifliflg
chlorination 1,050 105 8 drum 160 36 309 1,359
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TABLE 7 (continued)
ESTIMATED OPERATING COSTS OF PROPOSED
COMBINED SEWER OVERFLOW TREATMENT FACILITIES
Maintenance
Supplies and
Replacement
Parts at Total Capital
Capital 1% of Oper Plus
Scheme at 10% Capital and O&M
No. Description per year - Cost Cost Labor Oxidant Other Maint Total
10 Microstrainlng—
ozonation 1,980 198 8 drum 160 150 516 2,496
Cx)
All values dollars per acre-year (based on a single
10 mgd, 7.8 acre installation).
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steps continuously, since it is anticipated that these treatment steps
would be adapted to intermittent service.
In contrast to all the other treatment schemes whose annual costs were
developed from estimates of labor requirements, from calculated power
and chemical requirements, etc., the Microstrainer-2 minute chlorination
(at 15 ppm) scheme costs were developed from a detailed design and
actual operating experience under storm conditions. In Schemes 1
through 8, the cost of a conventional chlorination chamber with a nominal
10 mgd capacity, operating on 30 mgd of storm water with a 5 ppm
chlorine dose, is used.
These costs are, by the nature of the available data, quite crude. They
are, however, considered sufficiently accurate to rank the several schemes
according to their attractiveness in combined—sewer—overflow service.
It should be noted that these annual costs have been estimated for a
single plant. Multiple installations in any given general locality would
incur lower “per plant” labor and maintenance costs.
69
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SECTION X
PROBLEMS ENCOUNTERED
Longer trough retention times were needed for extended operation periods.
The l3,000—gph pump was too large for the lighter rainfalls and lower
flows into the retaining trough. A second, smaller pump was added.
Drains became clogged, which caused solids buildups near pump inlets.
Direct sewer flow into the Microstrainer by gravity, with in-line bar
screening, would eliminate the need for a surge facility and/or supply
pumps. The bar screen can be manually or automatically operated.
The sewer overflow regulator at high sewer flows was found to be forced
open to a larger—than—normal setting. This condition sometimes pre-
vented small storms from flowing to the retention trough. Debris block-
ed the regulator at times and false startups would follow. Improved
sewer overflow regulators are needed.
The air drying system for the Microstrainer controls on drum rate and
differential head required frequent attention and maintenance. Electrical
instrumentation can be substituted for air—operated controls.
The chlorination unit was not used due to operating problems. The use
of gaseous chlorine is undesirable and presents problems in storage.
Liquid sodium hypochlorite was used on bench samples at the test site.
The sodium hypochlorite is easily stored and handled.
Operation of the ozone equipment was hampered by a refrigeration unit
failure. The refrigeration unit is part of the air preparation system
providing moisture—free air to the ozone generator. Injection nozzles
must be sized and calibrated according to liquid flow rate, to insure a
proper mixture of air—ozone and water.
The use of oxygen on a once-through basis, in place of the air, would
eliminate the need for an air preparation system. The ozone generator
would operate under pressure, with the water flow by gravity.
Composite samplers were employed to obtain samples of the raw and
Microstrained water. This type of sampling is not so representative of
variations within a storm. More information about a storm could be
71
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obtained if samples were taken and stored individually. The low suction-
lift capability of the samplers hindered their operation.
It can be seen that some of these problems are unique to an installation
that is intended for investigative work. Still others would apply as well
to operation of a full—scale plant of this type. For example: air—
operated controls for the Microstrainer are standard and have good
operating records for continuously—operated Microstrainers. Also,
ozonators operated on air are widely and satisfactorily used in municipal
water treatment applications.
72
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SECTION XI
ACKNOWLEDGE MENTS
This work was carried Out and the report prepared by G.E. Glover,
Research Engineer, and P.M. Yatsuk, Associate Engineer, under the
general direction of W.A. Keilbaugh, Manager of Research and
Development.
The Cochrane Division of Crane Co. is greatly indebted to Mr. Allyn
Richardson, Project Officer, FWQA, Boston, Mass., and Mr. Darwin
Wright, Project Manager, FWQA, Storm and Combined Sewer Pollution
Control Branch, Washington, D.C., for their assistance and coopera-
tion in this program.
The cooperation of the City of Philadelphia Water Department, Mr. S.
Baxter, Commissioner, their Water Pollution Control Division under
Mr. C.F. Guarino, the Research and Development Group under Mr. J.
V. Radzuil and the Analytical Group at the Northeast Laboratories under
G. Carpenter, are gratefully acknowledged.
Plant design and its early operation were carried out by Messrs E.W.J.
Diaper, Manager of Municipal Water and Waste Treatment and Mr.J.D.
Reilly, both of the Cochrane Division, Crane Co.
This program is sponsored by the FWQA of the U . S. Department of the
Interior under Contract No. 14—12-136.
STATEMENT OF INVENTION
The Cochrane Division, Crane Co., does hereby certify that to the best
of its knowledge and belief, no inventions have resulted from perform-
ance under this contract.
73
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SECTION XII
REFERENCES
(1) “Pollutional Effects of Stormwater and Overflows From Combined
Sewer Systems”, U.S. Dept. of Health, Education and Welfare,
PHS Pub. No. 1246, November 1964.
(2) City of Philadelphia Data.
(3) Bannister, A.W., Chippewa Falls, Wis., FWQA Combined Sewer
Overflow Seminar, Edison, N.J., November 4—5, 1969.
(4) Davidson, R.N. and Gameson, A. L. H., “Field Studies on the
Flow and Composition of Storm Sewage”, Symposium on Storm
Sewage Overflows, Institute of Civil Engineers, William Clowes
& Sons, Ltd., London, 1967.
(5) Burrn, R.J., “The Bacteriological Effect of Combined Sewer Over-
flows on the Detroit River”, J. Water Pollution Control Federation,
1967, 39 (March) 410—425.
(6) Bacon, V.W., Leland, R., and Sosewitz, B., “Separation of
Sewage From Storm Water”, Symposium on Storm Sewage Overflows,
Institution of Civil Engineers, 1967, William Clowes & Sons,
Ltd., London.
(7) “Problems of Combined Sewer Facilities and Overflows”, WP-20--ll,
American Public Works Association — Research Foundation, for the
U.S. Dept. of Interior, Fed. Water Quality Administration.
(8) ‘Water Pollution Aspects of Urban Runoff; The Causes and
Remedies of Water Pollution From Surface Drainage of Urban J reas”,
WP—20—l5, Am. Public Works Association - Research Foundation,
for the U.S. Dept. of Interior, Fed. Water Quality Administration.
(9) Lynam, B., Ettelt, G., and McA.loon, T., “Tertiary Treatment at
Metro Chicago by Means of Sand Filtration and Microstrainers”,
J. Water Pollution Control Federation, Vol. 41, No. 2, Part 1,
February 1969.
75
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(10) Boucher, P.L., “Microstraining and Ozonation of Water and Waste
Water “, 22nd Purdue Industrial Waste Conference, May 1967.
(11) Tucker, L.S., “Sewered Drainage Catchments in Major Cities U
ASCE Urban Water Resources Research Program, Tech. Memorandum
No. 10, Am. Society of Civil Engineers, New York, N.Y.,
March 1969.
(12) FWQA Combined Sewer Overflow Seminar, Edison, N.J.,
November 4—5, 1969.
76
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BIBLIOGRAPHIC: ACCESSION NO.
Cochrane Division, Crane Co., Microstralning and Disinfection of
Combined Sewer Overflows. F’WQA Program Number 11023 EVO.
June 1970.
ABSTRACT KEY WORDS:
M icrostraining(C) , usIng a Microstrainer screen of a nominal aper— MICROSTRAINING
tore of 23 microns, removed up 1098% of the suspended solids from a
combined sewer overflow, The sewer, in a residential area of Philadel— COMBINED SEWER OVERFLOWS
phia, has alt average dwf of 1,000 gph. The maximum combined sewer
flow during rainstorms in one year of operation was 304,000 gph SOLIDS REMOVAL
(II. 3 cfs).
Volatile suspended solids removals with the above screen have OZONATION
averaged 68% and 71% during different test periods.
Results indicated that there was a slightly better kill of coilforin CHLORINATION
group bacteria with chlorine than with ozone in the Microstrainer efflu-
ents when both were used at an initial nominal concentration of S ppm, SOD REMLNAL
with 5 to 12 minutes detention time. However, chlorine seas applied at
slightly higher levels and with better control than ozone. TREATMENT COSTS
Preliminary estimates of the costs of treatment via Microstraining.
using tentatively—established throughput rates, show that the capital
costs per acre of drainage would be approximately $10,200 for Micro—
straining alone, $11,200 for Microstralnirig plus chlorination, and
$29,800 for Microstraining plus ozonatiOn.
Of eight other cuinentiy—proposed schemes, whose costs were
estimated, Only surface Impoundment (where aesthetically acceptable
and where low cost land is available) appears competitive.
(C)Copyrighted Trade Name—Crane Co. , Gienfleid & Kennedy Div.
BIBLIOGRAPHIC: ACCESSION NO.
Cochrarie Division, Crane Co. . Microstraifling sod Disinfection of
Combined Sewer Overflows. F’WQA Program Number 11023 EVO,
June 1970.
ABSTRACT KEY WORDS:
Microstraining . using a Microstrainer screen of a nominal aper— MICROSTRAINING
ture of 23 microns, removed up to 98% of the suspended solids from a
combined sewer overflow. The sewer, ins residential area of Philadel— COMBINED SEWER OVERFLOW’S
phia, has an average dwf of 1,000 gph. The maximum combined sewer
flow during rainstorms in one year of operation was 304,000 gph SOLIDS REMOVAL
(11.3 cfs).
Volatile suspended solids rem0v 1s with the shove screen have OZONATION
averaged 68% and 71% durIng different test periods.
Results indicated that there was a slightly better kill of cohform CHLORINATION
group bacteria with chlorine than with ozone In the Minrostralner efflu—
erits when both were used at an initial nominal concentration of 5 ppm, BOD REMOVAL
with 5 to 12 minutes detention time. However, chlorine was applied at
slightly higher levels and with better control than ozone. TREATMENT COSTS
Preliminary estimates Of the costs of treatment via Microstraining,
using tentatively—established throughput rates, show that the capital
costs per acre of drainage would be approximately $10,200 for Micro—
straining alone, $11, 200 for Microstraining plus chlorination, and
$19,800 for Microstrairung plus ozonation.
Of eIght other currently—proposed schemes, whose costs were
estimated, only surface Impoundment (where aesthetically acceptable
and where low cost land is available) appears competitive.
(C)Copyrlghted Trade Name—Crane Co., Gienfieid & Xennedy Div.
BIBLIOGRAPHIC: ACCESSION NO,
Cochrane Division, Crane Co. , Microstralning and Disinfection of
Combined Sewer Overflows, FWQA Program Number 11023 EVO,
June 3970.
ABSTRACT KEY WORDS:
Microstraining , using a 6 :icrostrainer screen of a nominal aper— MOCROSTRAINING
ture of 23 microns, removed up to 98% of the suspended solids from a
combined sewer overflow. The sewer, in a residential area of Pliiladel— COMBINED SEWER OVERFLOWS
phia, has an average dwf of 1,000 gph. The maximum combined sewer
flow during rainstorms in one year of operation was 304,000 gp O SOLIDS REMOVAL
(11.3 cfs).
Volatile suspended solids removals with the above screen have OZONATZON
averaged 68% and 71% dOng different test periods.
Results indicated that there was a slightly better kill of coilform CHLORINATION
group bacteria with chlorine than with ozone in the }dicrosttaifler efflu-
ents when both were used at an Initial nominal concentration of S ppm, BOD REMOVAL
with S to 12 minutes detention time. However, chlorine was applied at
slightly higher levels and with better control than ozone. TREATMENT COSTS
Preliminary estimates of the costs of treatment via Microstrsifling,
using tentatively—established throughput rates, show that the capital
costs per acre of drainage woulo be approximately $10,200 for Micro—
straining alone, $11,200 for Microstrainlng plus chlorination, and
$19 .800 for Mjcrostrainiflg plus ozoristion,
Of eight other currently—proposed schemes, whose costs were
estimated, only surface Impoundment (where aesthetically acceptable
end where low cost land is available) appears competitive.
(C)Copyrlghted Trade Name-Crane Co.. Glenfield & Kennedy Div.
-------
Accession Number I 2 1
[ _J
[
Subject
Feld & Group
05D
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
j Organization
Cochrane Division,
Crane
Co., King of Prussia,
Pa.
Title
MICROSTRAINING AND DISINFECTION OF COMBINED SEWER OVERFLOWS
Glover, George E
Yatsuk, Peter M
22 Citation
FWQA Contract 14—12—136, 75 p, June 30, 1970
23 1 Descriptors (Starred First)
*Sewers, *Storm runoff, *Filtratjon, *Water pollution control, *Cost comparisons,
Water Quality, Ozone, Chlorine, Biochemical oxygen demand
25 ldrv,tifiers (Starred First)
*Microstraining, *Combined sewer overflow, *Suspended solids removal
Microstraining , using a Microstrainer screen of a nominal aperture of 23 microns,
removed up to 98% of the suspended solids from a combined sewer overflow. The sewer,
in a residential area of Philadelphia, has an average dwf of 1,000 gph. The maximum
combined sewer flow during rainstorms in one year of operation was 304,000 gph (11.3 cfs).
Volatile suspended solids removals with the above screen have averaged 68% and
71% during different test periods.
Results indicated that there was a slightly better kill of coliform group bacteria with
chlorine than with ozone in the Microstrainer effluents when both were used at an initial
nominal concentration of 5 ppm, with 5 to 12 minutes detention time. However, chlorine
was applied at slightly higher levels and with better control than ozone.
Preliminary estimates of the costs of treatment via Microstraining, using tentatively—
established throughput rates, show that the capital costs per acre of drainage would be
approximately $10,200 for Microstraining alone, $11 , 200 for Microstraining plus chlorination
and $19 ,800 for Microstraining plus ozonation.
Of eight other currently—proposed schemes, whose costs were estimated, only surface
impoundment (where aesthetically acceptable and where low cost land is available) appears
competitive.
Abstract
(C)copyrighted Trade Name — Crane Co., Glenfield & Kennedy Div.
Absiractor
Authors
WR- 102 (REV. OCT. S5SI
eR S IC
In gjtution
Cochrane Division, Crane Co.
SEND TO: WATER RESOURCES SCIENTIFIC INFORMATION CENTE
U.S. DEPARTMENTOFTHENTERIOR
WASHINGTON, 0. C. 20240
* U .S. GOVERNMENT PRnOTONG OFFICE 1970 0 - 404-964
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