Environmental Protection Technology Series
MICROSTRAINING AND DISINFECTION OF
COMBINED SEWER OVERFLOWS • PHASE III
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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EPA-670/2-74-049
August 19.74
MECROSTRAINING AND DISINFECTION OF
COMBINED SEWER OVERFLOWS - PHASE III
By
Michael B. Maher
Research Engineer
Crane Co.-Cochrane Environmental Systems
King of Prussia, Pa. 19406
Project S-800966
Program Element 1BB034
Project Officer
Richard Field
Storm and Combined Sewer Section CEdison, N.J.)
Advanced Waste Treatment Research Laboratory
National Environmental Research Center
Cincinnati, Ohio 45268
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
For sale by the Superintendent of Documents, U.S. Government
Printing Office, Washington, D.C. 20402
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REVIEW NOTICE
The National Environmental Research Center - Cincinnati
has reviewed this report and approved its publication.
Approval does not signify that the contents necessarily
reflect the views and policies of the U.S. Environmental
Protection Agency, nor does mention of trade names or
commercial products constitute endorsement or recommend-
ation for use.
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FOREWORD
Man and his environment must be protected from the ad-
verse effects of pesticides, radiation, noise and other forms
of pollution, and the unwise management of solid waste -
Efforts to protect the environment require a focus that recog-
nizes the interplay between the components of our physical en-
vironment—air, water, and land. The National Environmental
Research Centers provide this multidisciplinary focus through
programs engaged in
o studies on the effects of environmental contam-
inants on man and the biosphere, and
o a search for ways to prevent contamination and
to recycle valuable resources.
The pollution problems associated with combined sewer
overflows have been inherited by our cities because of lack
of foresight and have grown enormously in the past thirty
years. Huge volumes of untreated sewage and runoff contam-
inate our streams and estuaries after each heavy rainfall.
One of the most economical solutions to this problem is the
utilization of a microstrainer followed by high rate disin-
fection. The results of a pilot plant microstrainer with
high rate disinfection using both ozone and chlorine are
reported herein. This microstrainer was located at a com-
bined sewer overflow outfall in Philadelphia and was oper-
ated with and without polyelectrolyte addition.
A. W. Breideribach, Ph. D.
Director
National Environmental
Research Center, Cincinnati
111
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ABSTRACT
A microstrainer with a stainless steel screen having openings
of 23 microns reduced the suspended solids (SS) of the com-
bined sewer overflow from 50 to 300 mg/1 to 40 to 60 mg/1
operating at an average rate* of 38.4 m/hr (16 gpm/sq ft).
The addition of polyelectrolyte improved the overall perform-
ance of the microstrainer. The effluent SS was reduced to
an average of 23 mg/1 and the flow rates increased to an
average of 87-5 m/hr (36 gpm/sq ft).
The combined sewer served a residential area in Philadelphia
comprised of 4.5 hectares (11.2 acres). The average dry
weather flow was 91 cu m/day (24000 gpd). The average over-
flow rates encountered were about 70 times the average dry
weather flow.
An extensive coagulation study revealed that moderately
charged, high molecular weight,cationic polyelectrolytes
were the most suitable for this particular application. The
concentrations applied ranged from 0.25 to 1.5 mg/1.
Coliform reductions across the microstrainer were observed.
It was also found that microstrained effluent could be more
»
easily disinfected than the raw combined sewer overflow.
Chlorine and ozone were used for disinfection at low con-
tact times.
The capital cost of a microstrainer installation (based on
8.2 cu m/min hectare (1.96 cfs/acre) followed by a high rate
chlorine contact chamber is reported as $6o660/hectare
($24480/acre). When polyelectrolyte addition equipment is in-
cluded, the capital cost is $37250/hectare ($15030/acre).
Costs are in 1973 dollars.
This report, submitted in fulfillment of Project S-800966
(formerly 11023 FWT) is a continuation of the work previously
reported in EPA Reports 11023 EVO 06/70 and 11023 PWT 01/73.
* Based on the flow through the submerged screen area.
iv
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CONTENTS
Page
Foreword j_^
Abstract iv
List of Figures vi
List of Tables vii
Acknowledgements viii
Preamble ix
Sections
I Conclusions 1
II Recommendations 4
III Introduction 6
IV Experimental Equipment 9
V Sampling 19
VI Discussion of Results 29
VII Economics 63
VIII Operation & Maintenance 65
IX References 68
X Publications 69
XI Appendices 71
A. Coagulation Study 72
B. Table of Conversions 79
C. Disinfection Percent Removals 80
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FIGURES
Page
1. Isometric Drawing of a Microstrainer 10
2. Schematic Diagram of the Microstrainer and 11
Disinfection
3. Top View of Chlorination Chamber 13
4. Schematic Diagram of Chlorination Equipment 14
5. Schematic Diagram of Ozonation Equipment 16
6. Sampler with Plow Through Chamber 20
7. Outfall - 67th and Callowhill, Philadelphia, Pa. 30
8. Drainage Area - within 200 ft of Test Site 31
9. Rainfall Intensity - Philadelphia, Pa. 1903-1951 32
10. Hourly Variations, Sanitary Plow, 67th and 33
Callowhill Sts. Sewer
11. Cumulative Percent vs Particle Size 47
12. Percent Suspended Solids Removal vs Influent 53
Suspended Solids
13- Effluent Suspended Solids vs Influent Suspended 54
Solids
VI
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TABLES
Page
1. Laboratory Analysis 22
2. Hydrologic Data 34
3. Microstrainer Dynamic Performance Data 40
4. Particle Size Analysis 45
5. Microstrainer Removal Performance - 50
No Coagulant Addition
6. Microstrainer Removal Performance - 52
Coagulant Addition
7. Disinfection Results - Raw Combined 58
Sewer Overflow
8. Disinfection Results - Effluent 60
VI 1
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ACKNOWLEDGEMENTS
The work was supported by the U.S. Environmental Protection
Agency and performed for the City of Philadelphia Water De-
partment under Commissioner Carmen F. Guarino.
The overall planning and execution was under the general
direction of Richard Field, Chief, Storm and Combined Sewer
Section, Advanced Waste Treatment Research Laboratory, U.S.
EPA; George Carpenter, Project Leader, Chief of Philadelphia's
Water Pollution Control Plants; William Wankoff, Project
Engineer for the Philadelphia Water Department; William
Keilbaugh*, Manager of Crane-Cochrane's R & D Department;
George J. Grits, Technical Director of Crane-Cochrane; E.W.J.
Diaper, Marketing Manager, Municipal Department of Crane-
Cochrane; George Glover**, Sr. Research Engineer of Crane-
Cochrane 's R & D Department.
Thanks are extended to Martin Lozanoff and Edward Graves of
the City of Philadelphia's Northeast Water Pollution Labor-
atory who conducted all of the laboratory analyses, and also
to Richard Johnson under the supervision of Peter D'Amelio,
Philadelphia Water Department's Instrumentation Supervisor,
for assistance with instrumentation changes. Thanks are
also extended to Edward Szymala, former chemist for Crane-
Cochrane, who assisted in the laboratory and at the micro-
strainer site.
* Presently with Cyrus Rice, Division of NUS.
** Presently with Bechtel, San Francisco, California
Vlll
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PREAMBLE
This project was extended into Phase III to confirm the per-
formance of the microstrainer on combined sewer overflow
from Phases I and II, to obtain more high rate disinfection
data using both ozone and chlorine and to operate the micro-
strainer with coagulant addition.
In Phases I and II, the SS removal percentages were found
to be higher for higher influent SS concentrations. The
lower influent SS concentrations tended to produce some-
what lower effluent SS concentrations but eventually
approached a plateau. Therefore, it was proposed that the
program be extended to determine if coagulant addition
could be applied to reduce the residual SS problem. It was
also believed that the use of polymeric materials would per-
mit higher throughput rates due to agglomeration and en-
largement of the influent particulates.
Phase III was conducted basically in three parts: (1) The
pilot microstrainer and disinfection equipment were operated
as in Phase II; (2) a coagulation study was undertaken to de-
termine the most suitable coagulants; and (3)the microstrainer
and disinfection equipment were operated as in part (1) but
with coagulant addition.
IX
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SECTION I
CONCLUSIONS
1. Suspended solids (SS) removal performance tends to
confirm previous work (1) (2). Influent SS in the
combined sewer overflow were reduced from 50-300 mg/1
to 40-60 mg/1. The average SS removal in Phase III
was 70$. The microstrainer operated at an average
flow rate of 38.4 m/hr (16 gpm/sq ft). The flow rates
of 85.9 to 110.0 m/hr (35-45 gpm/aq ft) reported in
Phase II were never achieved in the Phase III study.
2. Polyelectrolyte addition improved the operating effi-
ciency of the microstrainer. SS removal increased to
78% and the average effluent SS was reduced to 23 mg/1.
The flow rate was also increased to an average of
87.5 m/hr (36 gpm/sq ft).
3. After an extensive laboratory coagulation study, mod-
erately charged, high molecular weight cationic poly-
electrolytes were found to be the most suitable for
this application. Betz 1150 and Atlasep 105C were
used in this study at initial concentrations ranging
from 0.25 to 1.5 mg/1.
4. A particle size analysis on the backwash showed that
the average size particle retained by the screen was
9.5 microns with polyelectrolyte addition and 3-9
microns without polyelectrolyte addition. It was also
found that the microstrainer removed particles as small
as 0.07 microns. The ratio of screen size to smallest
particle size removed was 330 to 1.
5. The total coliform content of the combined sewer over-
4 6
flow varied from 3' x 10 to 5 x 10 cells/100 ml. The
2
fecal coliform content also varied from 3 x 10 to
h
6 x 10 cells/100 ml. The 'microstrainer demonstrated
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the ability to remove an average of 77% total coli-
forms and 76% fecal conforms.
The microstralner reduced the organic material in the
combined sewer overflow. With polyelectrolyte addi-
tion, the volatile suspended solids (VSS) were re-
duced by 79$,total organic carbon (TOG) by 52% and
chemical oxygen demand (COD) by 57%- When no coagu-
lant was added, the VSS were reduced by 68%, TOG by
32% and COD by 37%-
The percent VSS/SS ranged from 30-55$ which is much
lower than the normal percent VSS/SS usually en -
countered in sewage treatment plant influents (60-85%)
and was indicative of the contribution of inorganics
in .storm runoff.
The microstrainer operated at a waste rate of approx-
imately 3% of the influent flow with a SS concentrarion
of about 700 to 1000 mg/1.
9. The microstrainer reduced the total phosphates by
without polyelectrolyte addition and by 2*4% with poly-
electrolyte addition.
10. Disinfection of microstrained effluent to below 200
fecal colif orms/100 ml was performed using short con-
tact times (3 minutes) with initial chlorine concen-
trations at as low as 2.6 mg/1 and initial ozone con-
centrations at as low as 3-8 mg/1. The untreated com-
bined sewer overflow was also successfully treated
with chlorine to below 200 fecal coliforms/100 ml at
an initial concentration as low as 5 mg/1 with 4
minutes of contact time. It was evident during this
study that with microstraining adequate disinfection
could be accomplished at much lower chlorine concen-
trations than the concentrations required for the raw
combined sewer overflow.
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11. The design criteria used for the construction of the
special, high mixing intensity, pilot size contact
chambers, appear to be appropriate and practicable
for full size units.
12. The special character of solids in combined sewer over-
flow (and stormwater) is vastly different from other
municipal and industrial wastewaters and from the pot-
able water sources to which a microstrainer is normally
applied. The high level (liquid) differentials across
the screen required to achieve the high flow rates
necessary to be practicable in stormwater service are
far beyond those conventionally used. Thus, empirical
relations and experience useful in conventional appli-
cations are misleading in the microstraining of com-
bined sewer overflows.
13. The capital cost of a microstrainer followed by high
rate chlorination would be $6o660/hectare ($21l480/acre)
in 1973 dollars. The operating costs would be
$0.012/cu m($Q046/1000 gal). These costs do not in-
clude engineering or land costs. The capital costs
for the microstrainer with polyelectrolyte
addition at 1 mg/1 decrease to ?37250/hectare ($150307
acre) since only half as many microstrainer units are
necessary. The operating costs would be $0.012/cu m
($0.045/1000 gal). Even with the additional costs 'for
polyelectrolyte addition, the microstrainer with high
rate chlorination is still practical and remains to be
the least expensive of the alternative methods con-
sidered (1), except for surface impounding when inex-
pensive land is available. All costs were based on
an overflow of 8.2 cu m/min hectare (1.96 cfs/acre).
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SECTION II
RECOMMENDATIONS
1. Microstrainers employed in storm flow service may be
operated at high differentials of about 6l cm (24 inches)
of water. At this differential and with similar solids
loadings as encountered in this study, flows of 36.0 to
60.0 m/hr (15-25 gpm/sq ft) can be obtained with an efflu-
ent quality of 40 mg/1 suspended solids. With poly-
electrolyte addition, performance can be improved to
obtain a throughput of 75-5 to 95-4 m/hr (30-40 gpm/sq ft)
with an effluent quality of 20 mg/1.
2. A full scale microstrainer with polyelectrolyte and
high rate chlorine treatment should be built and oper-
ated for storm flow to demonstrate improved stream
quality.
3. Polyelectrolyte evaluation should be monitored on
additional storms to extablish guidelines for mixing
intensities, contact times and maximum and minimum con-
centrations with a broader range of suspended solids
concentrations in the combined sewer overflow.
4. The influence of mixing intensity for disinfection of
wastewater should be recognized since a sizable savings
in capital cost may be realized with the substantial
decrease in contact time.
5. Because of the peak instantaneous capacity limitation
of the equipment, the benefit of flow equalization
especially within the sewers themselves should be eval-
uated prior to an actual design.
6. Based on the results (for this application), the dis-
infection equipment should be designed to be capable
of providing a maximum initial concentration of 6 mg/1
of chlorine and 9 mg/1 of ozone if necessary.
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7. More disinfection data should be collected on addi-
tional storms to continue to evaluate disinfection con-
centrations to meet low level coliform counts and to
determine the adequacy of contact times as short as 1.25
minutes.
8. Although it appeared from the jar tests and in the pilot
plant facility that adequate mixing and contact time had
been provided for flocculation, more research should be
undertaken to optimize these parameters.
9. For an actual microstrainer design, provisions should
be made to install polyelectrolyte equipment but care
should be taken to provide proper dilution^injection,
and mixing of the polyelectrolytes. When the feed to
the microstrainers is pumped, the polyelectrolyte
should be added to the pump suction, where possible, to
take advantage of the turbulent mixing provided.
10. Observations have indicated the benefit of increasing
the percent suspended solids removal by increasing the
polymer concentration; however, the balance between in-
creased polymer addition vs. efficiency and throughput
should be considered in operation of future facilities.
Care should also be taken to prevent polyelectrolyte
overfeeding which would foul the screen.
11. Handling methods of the microstrainer waste stream
should be investigated. The obvious solution would be
to discharge the waste stream to the interceptor during
microstrainer operation. However, if the interceptor
cannot accept this flow, this volume may have to be
stored and later slowly discharged to the interceptor
when It is less taxed.
12. It has been proposed that the microstrainer can be util-
ized as a tertiary treatment step for a nearby treatment
plant when not in storm service. (3)
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SECTION III
INTRODUCTION
PREVIOUS WORK
The original work covered the periods of January, 1969
through September, 1969 and June, 1971 through February,
1972 and was reported as EPA "Water Pollution Control Re-
search Series", Reports 11023 EVO 06/70 and 11023 IWT 01/73.
The previous work was performed at the same 4.5 hectare
(11.2 acre) drainage area served by a combined sewer in
a residential area of Philadelphia, Pa. A Crane-Glenfield
microstrainer was fitted first with 4.4 sq. m (47 sq ft.)
Mark "I" .(35 micron openings) screen and later with
Mark "0" (23 micron) screen. The SS content of
the storm overflow of the first two phases ranged from
20 to 700 mg/1. The flow rate through the microstrainer
ranged from 2.4 m/hr (1.0 gpm/sq ft) to 110.2 m/hr~
(45.0 gpm/sq ft) .In the latter part of Phase I, the Mark"I"
screen was replaced with Mark "0" screen and 4/5 of the
screen area was masked with plastic sheeting so that higher
velocities could be attained. The outlet weir level was
set initially for a 15-2 cm (6 in) maximum differential but
was later changed to 6l.o cm (24 in) in Phase I.
The SS removal ranged from 20 to 99+$ removal with the
higher removals generally occurring at the higher influent
SS levels. Coliform removal by the microstrainer were
observed; however, the results were not consistent. Or-
ganic removals as measured by TOG and COD ranged from
25 to 40$.
Disinfection using chlorine was employed on both the influ-
ent and effluent of the microstrainer. In Phase I bench
scale chlorination studies indicated that disinfection could
be accomplished in short contact periods with high velocity
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gradients. In Phase II, the high rate chlorine chambers
were installed to treat both the raw combined sewer over-
flow and the microstrainer effluent. With chlorine con-
tact times of only two minutes and initial concentrations
as low as 5 mg/1 of chlorine, total and fecal coliforms
6 5
were reduced from 10 cells/100 ml and 10 cells/100 ml
levels to under 10 cells/100 ml. Ozonation of the micro-
strainer effluent was also performed in cocurrent - counter-
current columns and four orders of magnitude bacterial kill
was obtained with an initial concentration as low as 4 mg/1
and a 12 minute contact time-
An economic study showed that microstraining with high rate
chlorine disinfection with high turbulent mixing was the
least expensive and the most compact of the other methods.
The other methods included screening, flotation, Bio-Disc,
activated carbon, primary clarification, separate sewers,
activated sludge and surface and sub-surface impoundments.
PRESENT WORK
The third phase of the work was conducted to confirm the
performance of the microstrainer and the disinfection re-
sults. Also, it was believed that the use of coagulants
would reduce the effluent solids level as well as increasing
throughput rates so provisions were made to add coagulant to
the microstrainer influent.
While the microstrainer operated without coagulant addi-
tion, a laboratory coagulant survey was conducted to deter-
mine the most suitable coagulants for this installation.
The coagulants which exhibited the best characteristics were
then used on a bench scale microstrainer before testing them
on the full scale pilot facility.
Disinfection of the raw combined sewer overflow and micro-
strainer effluent was performed in the two high rate chlo-
rine contact chambers which had been installed in Phase II.
7
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Ozone was also used to disinfect the microstrainer effluent
and was introduced with equipment borrowed from the
Philadelphia Water Department. The disinfection equipment
was automated so that samples could be taken even if the in-
stallation was unmanned during a storm event.
Project time and infrequency of rainfall permitted only
eight storm events where polyelectrolyte addition could be
evaluated; however, twenty-one storms were encountered when
the microstrainer operated without coagulant addition.
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SECTION IV
EXPERIMENTAL EQUIPMENT
Mierostrainer
The Microstrainer is a rotating drum filter. The type used
in this study was 1.68 m (5 ft) in diameter and 0.92 m (3 ft)
long and was covered by specially woven Mark,"©" stainless
steel wire fabric having nominal openings of 23 microns. 80%
of the screen area was blanked with three layers of poly-
ethylene sheets so that the effective area was 0.87 sq m
(9.-4 sq ft) .
The water entered the drum through the open end and flowed
radially through the drum into the outlet chamber depositing
SS on the inside of the drum screen. (Fig. 1). The drum
rotated continuously and passed the fouled screen under the
backwash jets which washed the solid material into a hopper
and then to waste. The deposited solids formed a mat which
become a much finer filter .than the screen itself and caused
a resistance which increased the liquid level differential
between the influent and effluent chambers. As the differ-
ential increased, the automatic speed controller increased
the drum speed from 2 rpm at idle -to 6.8 rpm at 6l cm (24
in) differential. The preferred mode of operation for this
application was to maintain a differential of 6l cm by use
of the reset-proportional band control. This gave an
effective submerged screen area of 0.72 sq m (7-8 sq ft).
The microstrainer ran at an idle speed of 2 rpm continuously
under an ultraviolet light. The ultraviolet light prevented
the formation of bacterial and other organic slimes which
would tend to clog the screen. City water was used for
backwash. At the onset of a storm when the overflow height
above the weir in the trough below the outfall reached 3 cm
(0.1 ft), an automatic level control started the disinfection
equipment, the automatic sampler controls and the feed pumps
in the trough,(Fig. 2).
9
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VARIABLE
DRIVE
DRIVE
PINION
WASHWATER
HOPPER
BACKWASH
SPRAYNOZZLE
HEADERS
RAW WATER
INLET
WASTE
OUTLET
PERIPHERAL
SEAL
PERIPHERAL
RACK ON DRUM
STRAINING
OCCURS OVER
ENTIRE
SUBMERGED
SECTION OF
MICROFABRIC
WATERLEVEL
IN TANK
Figure 1
Isometric Drawing of a Microstrainer
10
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TROUGH
EFFLUENT
CHLORINE
CHAMBER
1
INFLUENT
CHLORINE
CHAMBER
OZONE
COLUMN
OZONATOR
WEI
LEVEL
INDICATOR
POLYELECTROLYTE
SOLUTION
EFFLUENT ^S
~)
PUMP
EFI
— 4
^LUENT CHAMBER
^
MIC
1
;ROSTRAINER
DRUM
f i
t
M
1
PORTION OF SCREEN
IN SERVICE
^•EFFLUENT
SAMPLER
OUTFALL
FLOW
'RECORDER
INFLUENT
CHAMBER
INFLUENT
/SAMPLER
FLOW
RECORDER
INFLUENT
OVERFLOW
WEIR
Figure 2
Schematic Diagram of Microstrainer and Disinfection Systems
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The flow rate of combined sewer overflow to the microstralner
was controlled at a constant rate, predetermined by the selec-
tion of the number of pumps to be activated by the storm over-
flow level control. The flow rate through the microstrainer
was then independent of the combined sewer overflow rate and
was determined by the pump rate minus the flow over the over-
flow weir in the influent chamber.
Chlorine Disinfection Equipment
The clorine disinfection equipment consisted of two specially
designed chlorine contact chambers each equipped with a Shutte
and Koerting, variable area, rate of flow meter for the in-
flow measurement^ a Lapp, variable capacity, hypochlorite
metering pump; and a container of sodium hypochlorite solution.
The equipment was automatically operated at the onset of the
storm. Microstrained effluent was pumped to one of the
chambers while the other chamber was fed by a tap off the
microstrainer inlet line.
The contact chamber shown in Pig. 3 provided 4.25 minutes of
contact time at a flow rate of 41.5 cu m/hr (20 gpm). The
large number of baffles insured true plug flow so that full
residence time was utilized for chlorine contact. The high
liquid velocity of 0.82 m/sec (2.7 ft/sec) together with the
corrugated baffles resulted in a head loss of 3.7 cm (1.5 in)
over 14.5 meters (64 ft) of liquid travel.
Sample taps were located at 1/4, 1/2, 3/4 of the total
length of the chamber and at the outlet which provided samples
at 1.25, 2.25, 3.25 and 4.25 minutes contact time (Pig. 4).
Solenoid valves connected to timers were installed at cor-
responding taps 1, 3, and 4 on the effluent and tap 4 on the
influent so that disinfection samples could be obtained auto-
matically after 15 minutes of operation. These samples, for
bacteria analysis, were collected in sterile bottles contain-
ing several milliliters of sodium thiosulfate solution to
.12
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Figure 3
Top View of Chlorination Chamber
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ROTAMETER
TO OZONE
COLUMN
CHLORINE CONTACT
CHAMBER
SAMPLE TAPS
t T T f
PUMP
X-«-SOLENOID
T VALVES
f
D
SODIUM
HYPOCHLORITE
SOLUTION
EFFLUENT
-fi:
PUMP
CHLORINE CONTACT
CHAMBER
SAMPLE TAPS
r * t r
(^•SOLENOID VALVE
ROTAMETER
SAMPLE JARS-
MICROSTRAINED COMBINED
SEWER OVERFLOW
Figure 4
Schematic Diagram of Chlorination Equipment
RAW COMBINED
SEWER OVERFLOW
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quench the chlorine and were shaken vigorously, covered and
refrigerated.
All disinfections were performed at a constant flow rate of
41.5 cu m/hr (20 gpm) . Both the raw combined overflow and
the microstrainer effluent were treated simultaneously dur-
ing storm flow operation. A pre-selected chlorine concentration was
controlled by the setting of a positive displacement (Lapp)
pump and by the initial concentration of the hypochlorite
solution.
The chlorine solution concentrations were determined accord-
ing to the iodometric method in STANDARD METHODS (if). Chlo-
rine residuals were measured with the orthotolidine comparator
set. The samples were measured after collection. With the
short reaction time between the sample and the orthotolidine
reagent, the STANDARD METHODS (4) procedure indicates that
for practical purposes only free chlorine is measured.
Ozone Disinfection Equipment
A tube-type laboratory dzonator and a 3 m by 8.25 cm
(10 ft x 3-25 in) plexiglass cocurrent contact column
(Pig. 5) were borrowed from the Philadelphia Water Dept. to
perform the ozone disinfection study on the microstrained
effluent for Phase III. This set-up was chosen over the exist-
ing Trailigaz plate ozonator with cocurrent-countercurrent
columns which had been used in Phases I and II, because it
reached steady state much faster (5 minutes as opposed to
30-60 minutes). Also with the electrical facilities avail-
able; the system could be automated more easily.
Microstrained effluent was introduced to the cocurrent
column via a nozzle pointed down onto the porous stone dif-
fuser- This produced high turbulence and also supplied
the highest concentration of ozone to the incoming waste-
water. The column operated at 85-95 percent ozone absorption,
with a contact time of 3.3 minutes.
15
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OFF GAS
/"S
°2
CYLINDER
-••
*
2% KI /
SOLUTION /
I
OZONATOR
O
o
* • «
°2 -°3
MIXTURE
i
PL
(1
E
POROUS STONE DIFFUSER
Figure 5
Schematic Diagram of Ozonation Equipment
COLUMN
EFFLUENT
PLEXIGLASS COLUMN
(10T X 3-1/4" I.D.)
ROTAMETER
MICROSTRAINER
- EFFLUENT
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The initial ozone concentration was varied from 3-1 to 8.4 mg/1
and was dependent on the ozonator voltage, the gas flow rate,
the wastewater flow rate, and the percent absorption. The
concentration of the incoming gas and the off gas were deter-
mined by the iodometric method in STANDARD METHODS (4).
As in the chlorination set-up a sample of the ozonated efflu-
ent was taken after 15 minutes of operation for bacterial
analysis. Sodium thiosulfate was also used to quench any
ozone residual although no residual was ever found using
the orthotolidine method from STANDARD METHODS (4r ).
Polyelectrolyte Addition Equipment
The polyelectrolyte solutions were prepared every week at
0.15$ in a 135 liter (36 gal) plastic container. A Wallace
& Tiernan positive displacement pump was used to inject the
solution to about 0.04% before entering the microstrainer in-
fluent line (Pig. 2).
A Reynolds number of 1.6 x 10 was calculated for the micro-
strainer influent line showing turbulent conditions. The
polyelectrolyte was added 4.9 meters (16 ft) prior to com-
bined sewer overflow discharge point and had a. retention
time of 4.7 seconds. The pipe had four right angle bends
between the point of polyelectrolyte addition and the point
of discharge into the inlet chamber. The combined sewer
overflow entered the influent chamber to the microstrainer
drum and had a detention time of about 3-6 minutes (At maxi-
mum flow,, there was no overflow over the influent overflow weir.)
Unfortunately, the degree of mixing achieved was dependent
on the geometry of the system available and could not be
varied] however, visual observations of influent samples
taken at the opening of the drum showed coagulated particles
in suspension indicating good mixing in the chamber.
17
-------
It should be noted that for this Installation the poly-
electrolyte mixing occurred in the pipe line, in the influ-
ent chamber and inside the portion of the microstrainer drum
which was blocked off. In an actual installation where the
microstrainer is gravity fed, it would be sized for full
screen utilization; therefore, a suitable mixing and floccu-
lation chamber may have to be provided to insure good coagu-
lation. The polyelectrolyte would be fed after the bar
screens and would be mixed and detained in a baffled chamber.
The rate of coagulant addition would vary with flow and
would be injected by a variable speed positive displacement
pump which would be controlled by a signal from a measuring
device such as a flume. In a full size unit where the micro-
strainer is pump fed, it would be advantageous to add the
polyelectrolyte directly to the pump suction to take advant-
age of the turbulent mixing in the pump. It was impractical
at the pilot plant facility to add the polyelectrolyte to
the pump suction because of the geometry of the pilot plant
site; however, this would have been the preferred mode of
operation.
-------
SECTION V
SAMPLING
Sample bottles were washed with soap and water, rinsed
with methanol and thoroughly dried with hot air- After
each storm, the sampler tubes were flushed with hypochlo-
rite followed by a high velocity rinse with city water.
The bottles were then placed in the automatic vacuum
samplers (Pig. 6). The samplers each held 24 evacuated
bottles and once the reset timers activated the units,
took samples every two minutes. The influent reset timer
was set for two minutes to give sufficient volume of com-
bined sewer overflow in the influent chamber before sam-
pling was initiated.
At first, the influent sample was withdrawn through a
2.54 cm I.D. pipe (1.0 in) located 5-1 cm (2 in) axially
out from the inlet end of the drum and about 46 cm (18 in)
radially to the emerging side of the drum center. The
sample flow then went through a valve to the 24-7 liter
(6.5 gallon) flowthrough sample chamber.
Because of the low influent suspended solids results ob-
tained for July 11 and 15, 1973> the sampler equipment was
inspected and a clogged valve was discovered. As a result,
the influent sampler inlet housing was placed directly in
the influent chamber in approximately the same position as
the former sample inlet pipe. The effluent sample inlet
line was located in the center of the open screen panel
about 5 cm (2 in) from the floor and 5 cm (2 in) from the
screen and discharged to the 19 liter (5 gallon) effluent
sample chamber which contained the sampler housing. The
flow through the sampler chamber was about 19 liters/min
(5 gpm).
19
-------
1-0
o
Figure 6
Sampler with Flow Through Chamber
-------
Once the reset timers timed out, the samplers collected
discrete samples of approximately 300 ml each of the two
flows every two minutes for the duration of the storm and
stored them in refrigerated chambers. The samples were
then composited and sent to the Philadelphia Water Dept.
laboratory for analysis. The analyses are given in Table 1,
On three occasions effluent samples were composited in
groups over different periods of the storm.
The storm flow conditions of January 3, 30 and 31, 1974
were synthesized by opening fire hydrants on the street so
that more data could be obtained for polyelectrolyte addi-
tion.
21
-------
Table 1. LABORATORY ANALYSIS
Date Start-up
4/26/73 6:35 PM
4/27/73 12:05 PM
5/3/73 3:00 PM
5/9/73 4:00 PM
5/17/7^ 8:00 PM
5/20/73 12:00 N
5/27/73 12:15 AM
9:50 AM
2:45 PM
5/28/73 7:15 AM
6/22/73 8:25 PM
12:00 N
12:30 PM
Sample
INF
EFF
INF
EFF
INF
EFF
INF
EFF
INF
EFF
INF
EFF
INF
EFF
INF
EFF
INF
EFF
INF
EFF
INF
EFF
INF
EFF
INF
EFF
pH
6.7
6.9
6.7
6.9
7.2
7.1
6.9
7.1
6.7
7.0
6.9
6.9
6.9
7.0
7.1
7.1
6.9
7.1
7.2
7.2
7.5
8.0
6.9
7.0
6.9
6.9
Cond.
(mmhos)
39
81
63
160
147
237
60
128
140
140
62
89
134
181
128
147
119
272
45
64
420
527V
108
67V
520
710
ss
(mg/l)
22
9
291
89
260
50
176
48
72
50
132
54
155
28
97
38
70
77
174
58
256
39
293
48
238
47
vss
"(mg/D
11
8
84
26
64
22
52
6
48
40
71
27
48
13
36
14
41
9
40
14
111
20
123
15
101
17
22
-------
Table 1 (continued). LABORATORY ANALYSIS
T-P04 COD TOC TC/IOO
Img/1) (mg/1) (mg/1)
3.6
2.1
3.2
1.4
4.1
4.8
3.0
1.8
3.3
2.6
4.8
4.8
4.3
3.7
3.8
3.2
4.9
3.1
3.0
2.2
5.0
4.3
5.6
4.0
2.6
2.5
33
29
190
142
171
127
119
95
124
88
181
169
108
84
100
60
116
88
59201
96
284
220
224
64
196
48
9
7
55
3-4
32
28
26
20
34
26
46
38
28
26
22
14
29
21
16001
24
104
87
64
21
45
17
5
6
<1
12
1
11
46
34
25
< 8
< 8
30
21
20
22
7
26
9
9
53
19
41
13
35
55
.0
.0
.8
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
mi
10
5
PC/100
< 1
104* <1
10
10
10
10
10
5
3e-
c
4e
3
c-9
103
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
4
4
5i
?
2
4
2
4p
2
4s
2
5
4
5
5
5
4
1
<1
3
1
2
4
38
27
6
1
7
5
5
5
47
8
-------
Table 1 (continued). LABORATORY ANALYSIS
Date Start-up
6/29/73 5:00 AM
2:30 PM
7/11/73 3:00 PM
7/15/73 3:00 PM
8/1/73 6:30 PM
8/2/73 4:30 PM
10/2/73 5:00 PM
11/28/73 3:00 PM
12/5/73 11:00 PM
8:00 PM
12/13/73 10:45 PM
12/20/73 10:55 PM
12/26/73 6:45 PM
Sample
INF
EFF
INF
EFF
INF
EFF
INF
EFF
INF
EFF
INF
EFF
INF
EFF
INF
EFF-1
EFF-2
INF
EFF
INF
EFF
INF
EFF
INF
EFF
INF
EFF
PH
6.8
6.9
6.4
6.5
7.2
7.3
6.7
7.0
7.2
7.0
7.1
7.0
6.0
6.5
6.9
6.8
6.8
7.3
7.5
6.7
7.0
7.2
7.4
7.5
7.4
6.8
6.8
Cond.
(mmhos )
96
54V
48v
49
130
61V
279
79W
81
148
65
76
44
65
111
176
159
160
210
47
130
42
73
103
74
NR
NR
SS
(mg/1)
92
47
113
56
54
39
23X
19
154
63
78
26
53
19
204
68
30
108
38
171
36
84
5
65
15
86
28
vss
17
8
29
15
16
17 '
8
9
54
26
32
12
40
14
101
41
19
54
8
150
30
39
4
18
0
52
20
24
-------
Table 1. (continued) LABORATORY ANALYSIS
T-POj| COD
(mg/1) (mg/1)
2
1
2
2
1
2
0
1
4
4
2
1
1
0
2
1
0
3
1
2
2
2
1
3
2
0
0
.0
.6
.4
.9
.5
.5
.6
.6
.0
.4
.2
.8
.3
.75
.59
.51
.61
.0
.35
.77
.33
.21
.3
.0
.9
.88
.66
57
57
64
52
4
0
42
38
125
82
64
16
88
48
326
65
245
91
61
NR
NR
92
64
296
75
1600
800
TOC TC/100 ml
(mg/1)
22
19
30
18
15
15
12
15
39
26
22
16
31
18
71
18.5
22.5
38
26
45
22
32
21
67
27
28
17.6
16.
59.
18.
64.
89.
14.
62.
60.
45.
50.
26.
15.
NR
NR
NR
NR
NR
NR
NR
NR
NR
9.
9.
1.
4.
8.
0
0
0
0
0
0
0
0
0
0
0
0
7
0
3
0
0
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
5
4
4
4
4
4
3
3
4
4
5
5
5
3
6
5
5
NR
FC/100
14
74
71
51
15
15
5
6
32
7
18
7
NR
NR
NR
NR
NR
NR
NR
NR
NR
5
1
6
8
2
NR
.0 x
.0 x
.0 x
.0 x
.0 x
.0 x
.0 x
.0 x
.0 x
.0 x
.0 x
.0 x
.0 x
.3 x
.0 x
.0 x
.0 x
ml
3
103
4
io3
IO3
IO3
IO3
3
io5
IO3
IO5
IO4
IO4
25
-------
Table 1. ( Continued)
Date
1/3/74
1/30/74
1/31/74
Start-up Sample
10:30 AM INF
EFF-1
EFF-2
11:00 AM INF
EFF
11:00 AM INF-1
INF- 2
INF-3
EFF-1
EFF-2
EFF-3
pH
7.5
7.2
7.3
7.4
7.6
7.6
7.4
7.4
7.6
7.6
7.6
LABORATORY ANALYSIS
Cond.
(mmhos)
200
220
215
250
275
275
269
269
272
270
265
SS
68
45
56
72
4
44
53
69
10
5
4
vss
26
12
10
31
4
20
21
21
1
3
2
NR - No Results
Footnotes on page 28
26
-------
Table 1. (continued) LABORATORY ANALYSIS
T-POi| COD TOG ~TC/100 ml PC/100 ml
(me/1) (mg/ll fjng/l 'i .___
4.8 64 23.5 1.2 x 106 2.0 x 105
3.6 16 11 6.0 x 105 5.0 x 103
3.6 24 13 4.0 x 105 3.0 x 103
4.1 44 21 0 0
4.0 16 90 0
3.34 83 20 0 0
1.10 71 19 0 0
1.62 75 24 0 0
3.3 21 10 0 0
1.83 27 9 0 0
0.95 27 9 0 0
27
-------
FOOTNOTES: For Tables 1 and 5
a. Samples extraordinarily clear; not typical. Zero
colony for 0.01 ml sample.
b. Estimated, non-ideal colony count (ENICC) 18 organisms
per 0.1 ml sample.
c. ENICC - 115 org. per 0.1 ml
d. ENICC - 3 org. per 1.0 ml
e. Zero colony count per 0.1 ml
f. Zero colony count per 1.0 ml
g. ENICC - 10? org. per 0.01 ml and ENICC - 11 org. per
0.001 ml
h. Data for this and succeeding dates reflect sample
system changes.
1. ENICC - 80 org. per 0.0001 ml
j. ENICC - 17 org. per 0.001 ml
k. Grass in sample.
1. Suspect methanol contamination.
m. ENICC - 3 org. per 0.011 ml
n. ENICC - 8 org. per 0.011 ml
o. ENICC - 5 org. per 0.01 ml
p. ENICC - 7 org. per 0.01 ml
q. ENICC - 84 org. per 0.1
r. ENICC - 9 org. per 0.01 ml
s. ENICC - 9 org. per 1.0 ml
t. Zero colony per 0.01 ml
u. ENICC - 7 org. per 1.0 ml
v. Microstrainer effluent used in backwash system.
w. Backwash system plugged after 10 min. of operation;
backwash then switched to city water
x. Valve between influent chamber and influent sampler
found to be clogged with debris.
(A) Cells/100 ml x 105 TC Total coliform
(B) Cells/100 ml x 10 PC Fecal coliform
INC Increase
NR No Results
28
-------
SECTION VI
DISCUSSION OP RESULTS
Drainage Area - Rainfall and Runoff
The 4.5 hectare (11.2 acre) drainage area shown In Fig. 7
and Pig. 8 Is served by combined sewers. Rainfall Inten-
sity-return frequency curves for the drainage area were
furnished by the Philadelphia Water Dept. and are shown
in Pig. 9 The drainage area can be characterized by a
maximum calculated runoff coefficient of 61$ using the
rational method. The dry weather (sanitary) flow is shown
in Fig. 10
Table 2 shows the hydrologic characteristics measured for
the 27 storms for 1973 and 1974 (does not include the three
synthesized hydrant storms) during microstrainer operation.
Rainfall intensities were measured with a rain gauge located
about 100 meters from the test site. The rain gauge was a
15-4 cm (4.8 in) dual traverse, 6 hours universal rain gauge,
manufactured by Belfort Instrument Co.
The flow through the slot type regulator to the intercepting
sewer was approximately 55 cu m/hr (0.35 mgd) based on the
opening; however, at the end of June the slot regulator was
replaced by a fluidic regulator which diverted a constant
flow, under the storm conditions encountered, of 62 cu m/hr
(0.39 mgd) to the interceptor. This value was extrapolated
from a Philadelphia Water Dept. calibration curve for the
fluidic regulator. The excess combined sewage overflowed
into the concrete impoundment trough containing the three
pumps which fed the microstrainer. The remainder overflowed
a combination trapezoidal-rectangular weir to the creek.
The trough and weir arrangement impounded about 15 cu m
(4000 gallons)of combined sewer overflow.
29
-------
+144.5
Paved
Channel
+150.7 Intercepting
Figure 7
Outfall
67th & Callowhill
30
-------
Drainage Area -
Figure 8
within 200 ft of Test Site
-------
Note
Frequency Analysis by Method of
Extreme Values, After Gumbel
Return Period (Years)
0.1
1 1 1 1
10 15 20 30 40 50 60
Minutes
2 34
Hours
Figure 9
Rainfall Intensity - Philadelphia, Pennsylvania
1903-1951
32
-------
U)
U)
1800 -
1600 —
1400 -
1200
t-l
§
ffi
§, 1000
co
c
o
fO
O
Averaae Flow - 1000 aoh
8
8 10 midnight
10 noon 2 4
Hours of the Day
Figure 10
Hourly Variations, Sanitary Flow, 67th & Callowhill Sts. Sewer
(City of Philadelphia Data)
-------
Table 2. HYDROLOGIC DATA
Date
4/26/73
4/27/73
5/3 /73
5/9 /73
5/17/73
5/20/73
5/27/73
5/28/73
6/22/73
6/29/73
7/11/73
7/15/73
8/1 /73
8/2 /73
10/2 /73
11/28/73
12/5 /73
Start-up
time
6:35 PM
12:05 AM
3:00 PM
4:00 PM
6:00 AM
12:00 N
12:15 AM
9:50 AM
2:45 PM
7:15 AM
8:25 AM
12:00 N
12 : 3 0 PM
5:00 AM
2:30 PM
3:00 PM
3:00 PM
6:30 PM
4:30 PM
5:00 PM
3:00 PM
11:00 AM
8:00 PM
Rainfall*
(cm)
0.46
0.76
0.63
3.12
0.51
0.28
0.25
0.25
0.25
0.74
0.25
1.12
0.56
2.44
0.74
2.00
1.02
1.52
1.37
0.81
0.79
0.25
1.27
Max. storm
flow
(cu m/hr)
211.4
211.4
259.8
1359-4
211.4
211.4
211.4
141.9
211.4
209-5
141.9
178.4
110.9
322.3
390.0
167-5
677-3
481.3
209.5
209-5
141.9
198.5
5 Min.
intensity
(cm/mln)
1.22
3.05
6.10
36.58
0.91
1.52
0.61
0.91
0.61
2.74
0.61
2.44
1.22
5.49
4.57
6.10
1.83
7.37
6.60
3.05
3.05
0.91
5.18
10 Min.
intensity
(cm/fain)
1.22
1.98
3.51
35.05
0.91
1.07
0.61
0.76
0.61
1.83
0.61
2.44
0.91
5.08
2.79
5.08
1.52
6.35
4.83
2.59
3.05
0.76
3.51
34
-------
Table 2. (continued)
HYDROLOGIC DATA
Date
12/13/73
12/20/73
12/26/73
1/3 /74
1/30/74
1/31/74
Start-up
time
10
10
6
10
11
11
:45
:55
:45
:30
:00
:00
PM
PM
PM
AM
AM
AM
Rainfall* Max. storm
flow
(cm) ( p\i m/hr")
0.30
0.46
0.08
Fire
hydrant
Fire
hydrant
Fire
hydrant
141
209
211
209
199
209
-9
.5
.4
.5
.5
.5
5 Min.
intensity
(cm/nin)
1.22
2.44
.72
Fire
hydrant
Fire
hydrant
Fire
hydrant
10 Min.
intensity
(cm/fain)
1.07
1.52
.66
Fire
hydrant
Fire
hydrant
Fire
hydrant
* Total rainfall during microstrainer operation.
35
-------
The influent flow rate was continuously measured by a
venturi flow meter and recorded on a strip chart. The level
in the impoundment trough was also continuously monitored
with a bubbler tube system. The storm flows listed in Table 2
were equal to the maximum flow over the weir based on readings
from the level recorder, the flow pumped to the microstrainer
facility and the flow to the interceptor minus the dry weather
flow.
The average maximum storm flow encountered was 271 cu m/hr
(1.72 mgd) with a high of 1359-4 cu m/hr (8.6 mgd) and a low
of 110.9 cu m/hr (0.7 mgd).
Coagulation Study
Nineteen different polyelectrolytes were evaluated individ-
ually and in combination with inorganics and powdered coal.
A list of the coagulants used in the study follows:
Coagulants
A. Anionic Polyelectrolytes
1. Atlasep 2A2
2. Atlasep 3A3
3. Atlasep 4A4
4. Betz 1130
5. Hercofloc 8l6
6. Hercofloc 836
7. Hercofloc 822
B. Cationic Polyelectrolytes
1. Dow Purifloc C-31
2. Atlasep 105C
3- Betz 1150
4. Betz 1160
5. Betz 1170
6. Betz 1175
7. Betz 1190
8. Betz DK-522
36
-------
9. Hercofloc 810
10. Hercofloc 8l4
11. Hercofloc 828.1
C. Non-Ionic Polyelectrolytes
1. Dow Purlfloc N-ll
D. Inorganic Coagulants
1. Alum
2. Ferric Chloride
3. Lime
E. Organics
1. Powdered Coal
The polyelectrolytes and inorganic coagulant alone and in
combinations were screened in Craner-Cochrane' s laboratory
on a sample from the microstrainer influent chamber by jar
tests for various concentrations on liter samples of com-
bined sewer overflow using a gang stirrer. The samples were
fast or flash mixed for one minute followed by ten seconds
of slow mixing. The samples which exhibited the best coagu-
lation characteristics were then passed through a 10 cm
(4 in) high by 5 cm (2 in) diameter filter tube fitted with
a Mark "0" screen. The volume of the sample which passed
the test tube in 9 seconds was recorded. 100 ml of the
effluent was then passed through a 0.45 micron millipore
membrane filter .and the time was recorded. Examples of the
better results are shown in contrast to a background sample
of zero concentration of polyelectrolyte :
Type
Initial Cone
mg/1
1.5
4.0
3-0
0.0
Vol(ml)/9 sec
380
205
351
140
Millipore
Time(min/
100 mil
31
22
33
4
Atlasep 105C
Purifloc C-31
Betz 1150
Straight
The results of the coagulation study are given in the
Appendix. Atlasep 105C and Betz 1150 were chosen as the most
37
-------
suitable polymers to be employed at the microstrainer.
Both polymers exhibited large, strong floes, and increased
the throughput in the bench study as well as showing,
the best visual reduction of turbidity (best approach under
limited manpower conditions). Any residual polyelectrolyte
which passed through the Mark "0" screen along with the
very fine turbidity left in the solution would clog the
0.45 micron Millipore filter membrane. This resulted in
very slow rates through the filter membrane.
Atlasep 105C and Betz 1150 were then tried on the 23 cm
(9 in) I.D. by 23 cm (9 in) long, laboratory pilot micro-
strainer located at the test site. The influent to this
unit was the combined sewer overflow stored in a 20 cu m
(5000 gallon) covered steel tank located behind the
microstrainer building. It was impossible to duplicate
the dynamic conditions of the full scale microstrainer
with the small unit; however, the unit did exhibit good
coagulation in the inlet chamber resulting in an increase
of both turbidity reduction and throughput.
Based on these results, the full scale microstrainer at
the test site was operated with polyelectrolyte addition
for the last three months of Phase III beginning with the
storm of November 28, 1973 and ending on January 31» 1974.
Atlasep 105C was used during four different storm events at
an initial concentration of 1.5 mg/1. These storms occurred
on November 28, December 5 (two storms), and December 13,
1973. Betz 1150 was also used during four different storms-
December 20 and 26, 1973 and January 30 and 31, 1974. The
storms of January 30 and 31, 1974 were synthesized by open-
ing a fire hydrant.
Both coagulants were added to provide an initial concentra-
tion of 1.5 mg/1; however, during the hydrant induced storm of
January 31, 1974, the concentration was varied as follows:
0.25 mg/1, 0.5 mg/1, and 1.0 mg/1. As the concentration
38
-------
was Increased the percent removal increased but the through-
put decreased slightly. This is shown in Table 3.
In general, coagulant addition improved the performance of
the microstrainer by increasing both the throughput and the
.percent SS removal as well as consistently discharging an
effluent SS of less than 40 mg/1. A more thorough discus-
sion of coagulated vs uncoagulated conditions will be
presented later.
Throughput
The throughput across the microstrainer was dependent on the
influent flow rate, the influent suspended solids, the differ-
ential between the influent and effluent chambers, polymer
type and concentration, and the drum speed. Since the in-
flow, differential and the drum speed become constant once
the unit comes to equilibrium, the throughput is then depend-
ent on influent SS (size, shape, and concentration) which
would determine the porosity and thickness of the filter mat
on the screen. The throughput generally increased with time
since SS concentration decreased with the length of the
storm due to the initial flush phenomena. It should be noted
that the radial flow rates (throughput) listed in Table 3 are
average values based on the pump flow from the impoundment
trough minus the average value of the influent chamber over-
flow.
The average throughput for the microstrainer operating with-
out coagulant was 38.4 m/hr (16.0 gpm/sq ft) with a high of
56.4 m/hr (23.0 gpm/sq ft) and a low of 16.8 m/hr (6.8 gpm/
sq ft). The average throughput for operation with coagulant
was 87=5 m/hr (36.0 gpm/sq ft) with a high of 95-4 m/hr
(39.0 gpm/sq ft) and a low of 54.6 m/hr (22.3 gpm/sq ft).
In the Phase II Report (2), throughputs ranging from 85.6 to
110.0 m/hr (35-45 gpm/sq ft) were reported and were never
achieved in Phase III.
39
-------
Date
4/26/73
4/27/73
5/ 3/73
5/ 9/73
5/17/73
5/20/73
5/27/73
5/28/73
6/22/73
6/29/73
7/11/73
7/15/73
8/ 1/73
8/ 2/73
10/ 2/73
11/28/73
12/ 5/73
Start-up
time
-rf. ""=
6:35 PM
12:05 AM
3:00 PM
4:00 PM
8:00 AM
12:00 N
12.15 AM
9:50 AM
2 :45 PM
7:15 AM
8:25 AM
12:00 N
12:30 PM
5:00 AM
2:30 PM
3:00 PM
3:00 PM
6:30 PM
4:30 PM
5:00 PM
3:00 PM
11-rOO AM
8:00 PM
MS operation
(min)
45
45
24
48
45
45
30
30
30
32
48
48
48
48
45
54
52
30
48
35
20
25
30
Maximum
stormflow
Ccu m). ,
211.4
211.4
259.8
1359.4
211.4
211.4
211.4
141.9
211.4
209.5
141.9
178.4
110.9
322.3
209.5
390.0
167.5
677.3
481.3
209.5
209.5
141.9
198.5
Max imum
differential
(cm)
61.0
61.0
61.0
61.0
61.0
61.0
61.0
47.5
61.0
61.0
61.0
61.0
61.0
61.0
61.0
61.0
53.2
55.9
61.0
61.0
61.0
61.0
61.0
40
-------
Table 3. (continued) MICROSTRAINER DYNAMIC PERFORMANCE DATA
Maximum Throughput Flow through Coagulant Suspended
drum speed MS cone. solids
(rpm) m/hr (cu m) (mg/1) removal %
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.7
6.7
6.7
6.7
45,0
26.4
26.4
31.2
25.8
21.0
53.4
27.6
49.2
29.4
16.8
51.6
51.6
33.0-
36.0
46.2
45.0
54.0
42.6
56.4
54.6
95.4
95.4
32.6
19.1
19.1
22.6
18.7
15.2
38.7
20.0
35.6
21.3
12.2
37.4
37.4
23.9
26.1
33.5
32.6
39.0
30.9
40.9
39.6
69.1
69.1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1.5
1.5
1.5
59
69
80
73
31
59
82
61
INC
67
85
84
80
49
50
28
17
59
67
64
76
65
79
41
-------
Table 3. (continued) MICROSTRAINER DYNAMIC PERFORMANCE DATA
Date
12/13/73
12/20/73
12/26/73
I/ 3/74
1/30/74
1/31/74
Start-up
time
10:45 PM
10:55 PM
6:45 PM
10:30 AM
11:00 AM
11:00 AM
MS operation
(min)
30
25
15
6
45
45
Max imum
stormf low
(cu m)
141.9
209.5
211.4
209.5
199.5
209.5
Max imum
differential
(cm)
61.0
61.0
61.0
61.0
61.0
61.0
(a) Unit broke down after 1 sample was taken.
42
-------
Table 3. fnontinuedl MICROSTRAINER DYNAMIC PERFORMANCE DATA
Maximum Throughput Flow through Coagulant Suspended
drum speed MS cone. solids
(rpm) m/hr (cu m) (mg/1) removal %
6
6
6
6
6
6
.7
.7
.7
.7
.7
.7
95.
4
95.4
95.
(a)
75.
89.
91.
92.
4
5
4
1
4
69
69
69
69
54
64
66
67
.1
.1
.1
.1
.8
.7
.1
.0
1
1
1
1
1
0
0
.5
.5
.5
0
.5
.0
.5
.25
94
77
67
26
94
94
90
77
43
-------
A microscopic examination of backwash samples for both co-
agulated and uncoagulated conditions on separate occasions
showed that the average particle size retained by the Mark
"0" screen for the coagulated sample was larger, as was
expected. The backwash rate was 1.8 cu m/hr (8 gpm) and
the SS concentrations were 756 mg/1 for the coagulated
sample and 732 mg/1 for the uncoagulated sample. The co-
agulated backwash sample showed that 8% of the particles
were greater than 27 microns while the uncoagulated back-
wash sample showed only 3% of the particles were greater
than 27 microns. The average particle size retained for
the coagulated backwash sample was 9 = 5 microns and for
the uncoagulated sample, 3-9 microns. The particle size
analyses are given in Table 4 and a plot of cumulative per-
cent vs. particle size for both the coagulated and uncoagu-
lated backwash sample is shown in Fig. 11. Although this
data is based on two separate storm occurrences, micro-
scopic examinations had been made before on other storms
in preparation for particle size counting and had shown
the same basic particle size distributions.
It is not surprising that coagulation increased the through-
put. The mat of coagulated solids on the screen would not
be as compact due to larger void spaces and thus would allow
more liquid to pass through the screen. It should not be
inferred that coagulation will increase throughput in every
application; the increased throughput along with an increased
SS removal for this application -showed that the floe was
rigid in nature and able to withstand higher flow rates. In
other applications the floe may be more fragile depending on
the nature of the particles encountered and the coagulant
chosen; therefore, coagulation tests should be performed at
each installation.
44
-------
Table 4. BACKWASH PARTICLE SIZE ANALYSIS
Uncoagulated sample - January 3, 1974
Size ,
CMiprons)
0.07
0.14
0.7
3.0
7.0
14.0
27.0
41.0
61.0
109.0
136.0
Number
77
26
19
11
24
3
1
1
1
1
1
Coagulated samole
0.07
0.14
0.7
3.0
7.0
14.0
20.0
27.0
131
95
53
45
45
6
9
11
Percent Cumulative percent
by count
46.7
15.8
11.5
6.7
14.5
1.8
0.6
0.6
0.6
0.6
0.6
— December 26.
30.2
21.9
12.2
10.4
10.4
1.4
2.1
2.5
100.0
53.3
37.5
26.0
19.3
4.8
3.0
2.4
1.8
1.2
0.6
1973. Betz 1150 at 1.5 rn^/1
100.0
69.7
47.8
35.6
25.2
14.8
13.4
11.3
45
-------
Table 4. (continued) BACKLASH PARTICLE SIZE ANALYSIS
Size t
(Microns)
34
41
48
54
61
67
82
95
100
136
163
170
176
190
340
510
1190
1875
2900
Number
10
4
2
2
1
1
2
1
1
2
1
4
1
1
1
1
2
1
1
Percent
by o.nnnf.
2.3
0.9
0.5
0.5
0.2
0.2
0.5
0.2
0.2
0.5
0.2
0.9
0.2
0.2
0.2
0.2
0.5
0.2
0.2
Cumulative percent
8.8
6.5
5.6
5.1
4.6
4.4
4.2
3.7
3.5
3.3
2.8
2.6
1.7
1.5
1.3
1.1
0.9
0.4
0.2
46
-------
100
90--
80 -
70 --
EH 0
Iz; N
w 'H £D
O ra oU
ffi
W 'O
PM cu
H"S 50
> -P
H m
^40
1=) o
S X3
D cti
°~30
20
10 "
A COAGULATED 12/26/73 BETZ 1150 at 1.5 ppm
O UN COAGULATED 1/3/71*
0.1
1.0
10.0 100.0
SIZE, (Microns)
1000.0
Figure 11
Cumulative Percent vs. Particle Size
-------
Suspended Solids Removal
The suspended solids (SS) removal performance for the micro-
strainer on the uncoagulated influent is shown in Table 5.
The average percent removal was 70% for an average influent
SS of 159 mg/1. The average effluent SS concentration was
48 mg/1 with a range of 9 mg/1 to 89 mg/1. A plot of per-
cent solids removal vs. influent suspended solids (Pig. 12)
shows that there is a trend for the percent removal to in-
crease as the influent SS level increases which indicates
that the effluent SS level is fairly constant. Pig. 13
shows that the microstrained SS in the effluent was con-
sistently below 60 mg/1 regardless of the influent concen-
tration^ The lowest effluent concentrations were obtained
at the lower influent SS levels.
The addition of polyelectrolyte when compared to no addition
increased the percent removal of SS as well as giving a lower
effluent SS concentration (Table 6). The average influent
SS for this period decreased to 106 mg/1. The SS removal
achieved was 78% and the average effluent SS concentration
was 23 mg/1 with a range of 4-49 mg/1. Fig. 12 shows that
the percent removal did not follow any pattern with an in-
crease in influent solids concentration, but compositing
the samples may have reduced the marked difference between
influent and effluent SS concentrations and also the influ-
ent SS level was lower during the period when polyelectro-
lyte was being added. Pig. 13 indicates a trend toward an
increase in effluent solids with an increase in influent
solids; however, since two different polyelectrolytes were
used on only eight storms, it is difficult to draw any firm
conclusions. The Betz 1150 seemed to give the best effluent
quality, but it was added to a raw combined sewer overflow of
much lower SS levels (two of the flows were synthesized by a
hydrant). In general, the polyelectrolyte addition did give
a superior effluent quality while also markedly increasing the
48
-------
throughput. Further work is necessary to confirm these re-
sults .
Organic Solids and Total Phosphate Removals
The organic solids and total phosphate (T-PCO removals for
the coagulated and uncoagulated conditions of individual
storms are listed in Tables 5 and 6. A summary of average
values follows:
Uncoagulated
VSS COD TOG T-POj.
(mg/1) (mg/1) (mg/1 (mg/1')
Influent
Effluent
% Removal
50
16
68
133
84
37
38
26
32
3-33
2.84
15
Coagulated
Influent 58 154 40 2.58
Effluent 12 66 19 1.95
% Removal 79 57 52 24
The reduction of VSS closely parallels the reduction of total
SS as would be expected. It is interesting to note that the
percent VSS/SS ranges from 30-55% which is much lower than
the normal % VSS/SS of sewage treatment plant influents
(60-85%) and is indicative of the contribution of inorganics
in storm runoff. The lower removals of TOG,, COD, and T-PQ,
across the microstrainer (as compared to VSS) is attributed to the
suspended organic and inorganic material which is removed by the
screen since the microstrainer removes very little, if any dissolved
material and these parameters (TOC, COD and T-P04) include dis-
solved matter. The TOC and COD reduction increased by 20% with
polyelectrolyte addition. However, the substantial increase in
TOC and COD reduction with polyelectrolyte addition suggests that
some of the dissolved and colloidal material had coagulated; however,
this is speculative since dissolved solids were not measured.
49
-------
Table 5. MICROSTRAINER REMOVAL PERFORMANCE
Date of
storm
Start-up
time
SS
In
Out
Rem
mg/1 %
4/26/73
4/27/73
5/3 /73
5/9 /73
5/17/73h
5/20/73
5/27/73
5/28/73
6/22/73
6/29/73
7/11/73
7/15/73
8/1/73
8/2/73
10/2/73
1/3/74
See page
6
12
3
4
8
12
12
9
2
7
8
12
12
5
2
3
3
6
4
5
10
28
:35PM
:05AM
:OOPM
:OOPM
:OOPM
:OON
:15AM
:50AM
:45PMk
:15AM
:25AMV
:OON v
:30PMV
: OOAMV
:30AMV
: OOPMV
:OOPMW
:30PM
:30PM
:OOPM
:30AM
22
291
260
176
72
132
155
97
70
174
256
293
238
92
113
54
23X
154
78;
53
68
9
89
50
48
50
54
28
38
77
58
39
48
47
47
56
39
19
63
26
19
50
59
69
80
73
31
59
82
61
INC
67
85
84
80
49
50
28
17
59
67
64
26
vss
In
Out
Rem
mg/1 %
11
84
64
52
48
71
48
36
41
40
111
123
101
17
29
16
8
54
32
40
26
8
26;
22
6
40
27
13
14
9
14
20
15
17
8
15
17
9
26
12
14
11
27
69
66
88
17
62
73
61
78
65
82
88
83
53
48
INC
INC
52
62
65
58
T-PO^
In
4
Out Rem
mg/1 %
3.6
3.2
4.1
3.0
3.3
4.8
4.3
3.8
4.9
3.0
5.0
5.6
2.6
2.0
2.4
1.5
0.6
4.0
2.2
1.3
4.8
2.1
1.4
4.8
1.8
2.6
4.8
3.7
3.2
3.1
2.2
4.3
4.0
2.5
1.6
2.9
2.5
1.6
4.4
1.8
0.75
3.6
42
56
INC
40
21
0
14
16
37
361
14
29
4
20
INC
INC
INC
INC
18
42
25
for footnotes.
50
-------
Table 5. (continued) MICROSTRAINER REMOVAL PERFORMANCE
No coagulant addition
COD TOG TH (A)"m (B)
In Out Rem In Out Rem In Out Rem ' In Out Rem
mg/1 % mg/1 % % %
33 29 14 9 7 22 5.0 <0. la 98+ 6.0 0.9 > 85
224 64 71 64 21 67 41.0 13.0 68 2.0 0.27 86
196 48 76 45 17 62 35.0 5.5 84 4.6 1.0 78
57 57 0 22 19 14 16.0 5.9 63 1.4 .74 47
64 52 19 30 18 39 18.0 64.0 INC 0.71 5.1 INC
4 0 100 15 15 0 8.9 1.4 84 15.0 0.15 99
42 38 10 12 15 INC 6.2 6.0 3 0.5 0.6 INC
125 82 34 39 26 33 45.0 5.0 89 3.2 0.7 68
64 16 75 22 16 27 26.0 15.0 42 1x8 0.7 61
88 48 46 31 18 42 NR NR NR NR NR NR
64 20 69 24 12 50 12.0 5.0 58 20.0 0.4 98
51
-------
Table 6. MICROSTRAINER REMOVAL PERFORMANCE
Coagulant addition
Date of Start-up SS yss T-POi,
storm time In Out Rem In Out Rem In Out Rem
mg/1 % mg/1 % mg/1 %
11/28/73 3:OOPM 204 49 76 101 30 70 2.59 1.06 59
12/5 /73 11:00AM 108 38 65 54 8 85 3.0 1.35 55
8:OOPM 171 36 79 150 30 80 2.77 2.33 14
12/13/73 10:45PM 84 5 94 39 4 90 2.21 1.3 41
12/20/73 10:55PM 65 15 77 18 0 100 3.0 2.9 3
12/26/73 6:45PM 86 28 67 52 20 62 0.88 0.66 25
1/30/74 11:00AM 72 4 94 31 4 87 4.1 4.0 2
1/31/74 llsOOAM 55 6 89 21 2 90 2.0 2.0 0
(A) Cells/100 ml x 105
(B) Cells/100 ml x 104
52
-------
Table 6. (continued) MICROSTRAINER REMOVAL PERFORMANCE
COD TOC TC (A) FC (B)
In Out Rem In Out Rem In Out Rem In Out Rem
mq/1 % mg/1 % .
326 155 52 71 20.5 71 NR NR NR NR NR NR
91 61 33 38 26. 32 , NR NR NR NR NR NR
NR NR NR 45 22. 51 NR NR NR NR NR NR
92 64 30 32 21. 34 9.7 .09 99+ 50.0 0.13 99+
296 75 75 67 27. 60 13.0 4.0 69 60.0 8.0 87
1600 800 50 28 17.6 37 8.0 NR NR 2.0 NR NR
44 16 67 21 9- 57 0 0 0 0 0 0
76 25 67 21 9. 57 0 0 0 0 0 0
53
-------
un
100-
90-h
80-
70--
60--
K
K 40~-
PM
30-
20~-
10--
0
O
O
0
A A
O
O
o
o
o
o
o
H 1 1-
o
o o
o
o
o
o
o o
O NO POLYELECTROLYTE ADDITION
A POLYELECTROLYTE ADDITION
I—I—I—I—h
50 100 150 200 250
INFLUENT SUSPENDED SOLIDS (mg/1)
Figure 12
Percent Removal vs. Influent Suspended Solids
300
-------
en
ioo--
90—
80—
70"
CO '
o
H
O 60"
CO
Q
50
PL,
D 40
CO
EH
§30
w 20 — o
10
O
O
00
O
0 A
A
o
* A A
O
o
O
o
0
°
0
o
O NO POLYELECTROLYTE ADDITION
A POLYELECTROLYTE ADDITION
H 1 1 1 1 1 1 1 1 1 H-
50 100 150 200 250
INFLUENT SUSPENDED SOLIDS (mg/1)
Figure 13
Effluent Suspended Solids vs. Influent Suspended Solids
-------
Polyelectrolyte addition did not dramatically enhance phos-
phate removal. The phosphate removal probably resulted from
removal of the solid or adsorbed phosphates on the suspended
matter. The phosphate removal increased by 9% with poly-
electrolyte addition which paralleled the SS removal in-
crease of 8%.
Coliform Removal By A Microstrainer
Total coliform (TO) and fecal coliform (PC) counts were per-
formed on both the influent and effluent composite samples of
the microstrainer. The membrane filter technique in STANDARD
METHODS (4) was followed for coliform determinations. The
samples were macerated to reduce the possibility of clumping
and of isolating cells from the nutrient broth by a solids
barrier- Because the coliform levels in the combined sewer
overflow varied by as high as five orders of magnitude, it
was difficult to select a dilution range which would assure
an ideal colony count; therefore, the coliform counts
listed in Table 1 are often not ideal as can be seen by the
number of footnotes.
In 17 out of 22 storms, there was a reduction of fecal coli-
form across the microstrainer ranging from 21% to greater
than 99$3and in 20 out of 22 storms, there was a reduction
of total coliform ranging from 3% to greater than 99%
(Table 5).
Although the Mark "0" screen openings are 23 microns, the
formation of a mat of solids reduces the apertures substan-
tially. The particle size analysis on the backwash showed
that the microstrainer was able to remove particles as
small as 0.07 microns. In the membrane filter method a
known sample volume is passed through a 0.45 micron mem-
brane filter to retain coliforms; therefore, it is not sur-
prising that there was a coliform reduction across the screen
56
-------
Disinfection With Chlorine and Ozone
One of the primary functions of Phase III was to reinforce
previous data from Phase II that the microstrained effluent
was more amenable to disinfection using both chlorine (Clp)
in the form of sodium hypochlorite and ozone (0_) than the
raw combined sewer overflow and that disinfection could be
accomplished in short contact times.
The results listed in Tables 7 and 8 show that for the
seven storm events when Cl was added simultaneously to
both the influent and effluent that on five occasions a
greater coliform kill was obtained for the effluent sample and
at lower Cl? concentrations.
The results of Phase III show that by using the high rate C12
contact chamber both total and fecal coliform levels
of less than 200 FC/100 ml and 1000 TC/100 ml (Philadelphia
Water Dept. sewage treatment plant effluent standards) could
be achieved with initial Cl? concentrations as low as
5 mg/1 with 4.25 min. contact time for the raw combined
sewer overflow and as low as 2.6 mg/1 with 3.25 min. contact
time with the microstrained effluent. For design purposes
the recommended maximum chlorine concentrations that should
be provided would be 12 mg/1 for the raw combined sewer
overflow and 6 mg/1 for the microstrained effluent to insure
adequate chlorine disinfection. Higher Cl concentrations
are necessary for the raw combined sewer overflow because
of the higher Cl? demand and the larger amount and diameter
of protective solids.
On four occasions samples of chlorinated effluent were
collected after nnly 1.25 min. of contact time. In each
case the surviving FC levels were less than 10 organisms/
100 ml which was the same level achieved after 3-25 contact
time. The surviving TC levels were higher for 1.25 min.
contact time but still acceptable, especially at the lower
57
-------
Table 7. DISINFECTION RESULTS
Raw Combined Sewer Overflow
Date
6/22/73
6/29/73
7/11/73
7/15/73
8/1 /73
8/2 /73
Time TC
(1)
12:00 N 41.0
5:00 AM 16.0
2:30 PM(4) 18.0
18.0
18.0
3:00 PM 8.9
3:00 PM 6.2
6.2
6:30 PM 45.0
4:30 PM(5) 26.0
26.0
PC
(2)
2.0
1.4
0.71
0.71
0.71
15.0
0.5
0.5
3.2
1.8
1.8
Cl9 Cone.
^(mg/1)
5.0
12.0
12.0
12.0
12.0
5.0
9.0
9.0
,5.1
5.1
5.1
10/2 /73
5:00 PM
NR
NR
3.0
(1) Cells/100 ml x 105
(2) Cells/100 ml x 104
(3) Cells/100 ml
(4) Samples taken after 15, 20, and 25 min. of operation.
(5) Samples taken after 15 and 30 min. of operation.
TC Total Coliforms
FC Fecal Coliforms
RES Residual
NR No Results
Cl Chlorine
58
-------
Table 7. (continued) DISINFECTION RESULTS
Cl 2
(mg/1)
NR
NR
7.0
7.0
9.0
0.0
5.0
5.0
3.0
2.0
2.0
PH
8.6
7.1
7.3
7.2
7.3
8.6
6.8
6.9
7.4
7.2
7.3
Contact
time
(min)
4.25
4.25
4.25
4.25
1.25
4.25
4.25
4.25
4.25
4.25
4.25
Surviving
TC
if 3)
1500
500
100
230
140
134000
60000
56000
t 10
> 30000
6700
Surviving
FC
(3)
110
< 10
< 10
< 10
> 6000
6000
100
< 10
> 6000
200
1.5
NR
4.25
NR
NR
59
-------
Table 8. DISINFECTION RESULTS
Effluent
Date
6/22/73
6/29/73
7/11/73
7/15/73
8/1 /73
8/2 /73
10/2 /73
12/5 /73
Time
12:00
5:00
2:30
(4)
3:00
3:00
(5)
6:30
6:30
(5)
5:00
11:00
TC
(1)
N 13.0
AM 5.9
PM 64.0
64:0
64.0
PM 1.4
PM 6.0
6.0
PM 5.0
PM 15.0
15.0
EM NR
NR
AM NR
NR
FC G
(2)
0.27
0.74
5.1
5.1
5.1
0.15
0.6
0.6
0.7
0.7
0.7
NR
NR
NR
NR
12 cone .
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.6
5.6
5.6
2.6
2.6
2.7
2.7
Cl2 res.
..(me/1
NR
NR
1.7
1.7
1.7
3.0
1.5
1.5
4.0
0.0
1.5
1.5
1.5
1.5
1.0
)PH
8.4
7.2
7.8
7.7
7.6
9.7
7.0
7.2
7.2
7.3
7.2
NR
NR
NR
NR
Det.
time
4.25
4.25
4.25
4.25
1.25
4.25
4.25
4.25
4.25
4.25
4.25
1.25
3.25
1.25
3.25
12/20/73 10:55 AM 4.0 8.0 2.7 NR NR 1.25
(1) Cells/100 ml x 105
(2) Cells/100 ml x 104
(3) Cells/100 ml
(4) Samples taken after 15, 20, and 25 min. of operation.
(5) Samples taken after 15 and 30 min. of operation.
TC Total Coliforms
FC Fecal Coliforms
RES Residual
NR No Results
Cl Chlorine
Cone Initial concentration
60
-------
Table 8. (continued) DISINFECTION RESULTS
Surv
TC (3)
420
<100
100
20
160
18000
^ 10
20
5200
> 80000
4600
NR
2000
7000
170
Surv
FC (3)
<100
< 10
< 10
< 10
< 10
20
< 10
480
1300
120
< 10
80
< 10
Oo Cone.
NR
8.4
8.4
8.4
NR
NR
NR
NR
7.2
7.2
7.2
3.8
NR
3.1
NR
PH
NR
7.0
7.4
7.2
NR
NR
NR
NR
7.4
7.1
7.2
NR
NR
NR
NR
Det . time
(min)
NR
3.3
3.3
3.3
NR
NR
NR
NR
3.3
3.3
3.3
3.3
NR
3.3
NR
Surv
TC (3)
NR
2600
120
480
NR
NR
NR
NR
40
< 10
< 10
15000
NR
12000
NR
Surv
FC (3)
NR
50
60
30
NR
NR
NR
NR
< 10
10
10
< 10
NR
2850
NR
7000
3.1
NR
3.3
6100
250
61
-------
chlorine concentrations; however, in one instance when
5 mg/1 chlorine was added, the resulting surviving total
and fecal coliforms were above the acceptable limit. The
results indicate that with the proper chlorine concentration ade-
quate disinfection can be achieved in very short contact
times in a high velocity gradient chlorine contact chamber.
Disinfection results for the microstrained effluent using
ozone in a cocurrent column were obtained for seven storms
\
and are listed in Table 8. The ozone contact column had a
contact time of 3.3 minutes and the concentrations were
varied from 3.1 mg/1 to 8.4 mg/1., The results show that
total and fecal coliform levels of less than 200 FC/ 100 ml
and 1000 TC/100 ml could be achieved at the higher concen-
trations of 7-9 mg/1. Ozone would probably not be as suit-
able as chlorine for this application because of the some-
what higher capital and operating costs for 0 vs Cl^.
However, the use of ozone should not be overlooked
since the cost gap for chlorine vs ozone is already closing.
The concentrations necessary to meet disinfection require-
ments are higher for ozone than for chlorine because ozone
is a more powerful oxidant and reacts more vigorously with
the organics. For this reason ozone has many advantages
over chlorine such as the destruction of phenols whereas
when chlorine is used, the obnoxious chlorophenols are formed;
ozone is more effective in the reduction of color and odor;
ozone is a much better viricide; and also by the method of
application using air, an increased dissolved oxygen content
is imparted to the treated water.
62
-------
SECTION VII
ECONOMICS
The economics of Microstraining of combined sewer overflow
followed by high rate disinfection using chlorine was based
on a drainage area of 2.3 hectares (5-7 acres). The facility
would receive 8.2 cu m/min/hectare (1.96 cfs/acre) which was
equivalent to 28000 cu m/day (7.4 mgd). The costs are based
on treatment of 1.5 x 10 cu m/yr (3.85 x 10 gal/yr) Of
storm flow.
The costs are based on treatment with and without polyelec-
trolyte. With polyelectrolyte addition, two, 1.5 m (5 ft)
by 1.5 ni (5 ft) microstrainers are employed, rated at 97 m/hr
(40 gpm/sq ft). When no polyelectrolyte is used, four micro-
strainers are necessary since they are rated at one-half the
capacity, 48.5 m/hr (20 gpm/sq ft). All costs are in 1973
dollars.
Polyelectrolyte
Addition
Capital Costs
Material and Equipment
Microstrainer $42000.
Pumps & controls $ 4800.
Building $ 4100.
Grating & railing $ 1345-
Chamber $ 7985-
Wo Polyelectrolyte
Addition
Bar Screen $ 1700
Chlorine Equipment $ 1440,
Chamber $ 5870
Building & grating $ 1440.
Polyelectrolyte equipment $ 6000,
(inc. tank,pump, mixer,
and controls)
Mixing chamber $ 4000,
Installation $ 5000
Total Capital Cost $85680
63
$84000.
$ 9600.
$ 8200.
$ 2690-
$15970.
$ 1700.
$ 1440.
$ 5870.
$ 1440.
$ 0
$ 0
$ 8600.
$139510.
-------
Polyelectrolyte
Addition
Annual Operating Costs
Capital charge @ 10$ in- $ 8568.
stalled facility (less
land and engineering)
Utilities $ 300.
Maintenance and supplies $ 857.
%\% of installed facility
cost
Chlorine cost @$0.10/lb. $ 1900.
Clp gas % 6 mg/1
Polyelectrolyte cost
@$1.77/lb for 1 mg/1 $ 5600.
Total Operating Cost $17225.
No Polyelectrolyte
Addition
$13951.
$ 600.
$ 1395.
$ 1900.
0
$17846.
Summary
Capital Costs
$/hectare
$/acre
$/mgd
Operating Costs
$/hectare yr
$/acre yr
$71000 gal
37250
15030
11580
7490
3020
0.045
60660
24480
18850
7760
3130
0.046
64
-------
SECTION VIII
OPERATION AND MAINTENANCE OF THE MICROSTRAINER
During Phase III, the microstrainer operated continuously
with very few maintenance problems. For the entire 10 month
period, there was only one breakdo'wn which was caused by a
broken v-belt located between the electric motor and the
gear drive. The only other problems encounterd were due to
air leaks in the differential control system due to badly
worn copper tubing, an occasional fouled screen, clogged
backwash nozzles and the replacement of the sealing bands
which hadn't been replaced for three years.
It should be pointed out that the microstrainer was oper-
ated at a liquid differential of 24 inches and this was
only permissable because of the intermittent Cstorm) load conditions.
After three years of intermittent operation at the Philadelphia pilot
site all screen fabric remained in good condition as determined by
microscopic examination. The normal (dry^weather treatment) re-
commended, differential for continuous operation is 6 inches. The
microstrainer fabric will last indefinitely under a 6 inch differen-
tial depending on the particular application.
A full scale microstrainer facility for operation during
storm conditions would be housed and kept from freezing in
an insulated building. The facility would be automated. At
the onset of storm overflow the liquid level in the inlet
channel rises and actuates a level switch which starts the
microstrainer drum motor, the backwash jets, the bar screen
rake drive and turns on the UV lights. The microstrainer
unit would be automatically controlled by pneumatic measure-
ments of the differential head across the screen which would
be transmitted to a converter mechanism. This would control
the drum speed and would allow for variations in solids con-
centrations and flow while maintaining a constant differ-
ential of 24 inches.
After a storm, the program controls continue the operation
of the microstrainer, sump pumps and backwash ~pump until
65
-------
the chamber Is drained and the screen is cleaned and then
shuts them down. Because of the ease of start-up and the
very low residence volume of the microstrainer, unattended
operation can be accomplished with very simple controls.
The inlet chamber would be constructed with relief weirs
to enable bypassing excessive flows and the floor would be
sloped and valved for desludging and draining.
Although during the Phase III pilot study the microstrainer
ran continuously under an ultraviolet light and constant
backwash, under actual conditions the equipment would stand
idle during dry periods. To keep the microstrainer fabric
in condition to operate when needed, it must not be allowed
to remain full of raw sewage while not operating. The
settled solids foul the bottom of the screen and the dry
top portion may become too hardened and may be difficult to
backwash clean. The recommended procedure for combined
sewer overflow service is to drain the chamber, continue the
backwash of the slowly rotating drum using city water as
washwater for 15-30 minutes and then stop the drum and back-
wash water. For sustained dry periods the drum can be ro-
tated slowly for short periods at intervals under backwash
jets and the UV lights.
It is imperative that the microstrainer fabric be kept clean.
The backwash nozzles should be checked and cleaned when
necessary. If the raw combined sewer overflow is high in
manganese and iron, after a long period their respective
oxides may eventually build up and foul the screen. Screen
cleaning can be accomplished by turning off the backwash
jets and while allowing the drum to rotate slowly, a few
gallons of cleaning solution are sprinkled over the fouled
screen. The drum is then rotated for about 10 minutes in
this solution and then a high pressure backwash is applied.
The tank is then drained and the unit is ready for operation,
66
-------
Some of the cleaning solutions used are: sodium hypochlorite
for organic fouling (chlorine gas should never be used),
Jenolite solution (based on phosphoric acid) for the removal
of iron and manganese oxides, and hydrogen peroxide for
hardened clay-like materials.
In general, the microstrainer is an effective and economical
method of treatment. It can be operated with very little
maintenance, other than the normal lubrication and mainten-
ance associated with mechanical equipment. Running costs
are low, consisting mainly of the electricity required for
driving the motor, backwash pump and debris water pump.
67
-------
SECTION IX
REFERENCES
Cochrane Division - Crane Co. (Glover, G.E. and
Yatsuk, P.) "Microstraining and Disinfection of
Combined Sewer Overflows, "Water Pollution
Control Research Series", Report 11023 EVO 06/70
Cochrane Division - Crane Co. (Glover, G.E. and
Herbert, G.R.) "Microstraining and Disinfection of
Combined Sewer Overflows - Phase II", Water Pollu-
tion Control Research Series, Report 11023 FWT 01/73.
Rosenkranz, W. A., and Condon, F.J., "Technology
Improvements Related to Storm and Combined Sewer
Pollution Control", presented at the ASCE Meeting
on Water Resources Engineering, Atlanta, Georgia,
January, 1972.
APHA, STANDARD METHODS, 13th Edition, Dec., 1971,
American Public Health Association, Washington, D.C.
68
-------
SECTION X
PUBLICATIONS
The following publications and presentations have been
based upon the work reported herein and in the previous
Report EVO 11023 06/70 and PWT 11023 01/73.
1. Keilbaugh, W.A., Glover, G.E., and Yatsuk, P.,
"Microstraining and Disinfection of Combined Sewer
Overflows", Combined Sewer Overflow Seminar Papers,
EPA 11020—03/70, November, 1969, published by E.P.A.
2. Cochrane Division-Crane Co. (Glover, G.E. and Yatsuk,
P.), "Microstraining and Disinfection of Combined
Sewer Overflow", Water Pollution Control Research
Series #EVO 11023 06/70, published by E.P.A.
3. Diaper, E.W.J. and Glover, G.E., "Microstraining of
Combined Sewer Overflows", presented at 44th Annual
Meeting of Ohio Water Pollution Control Conference,
Cincinnati, Ohio,(1970).
4. Guarino, C., "Satellite Treatment Plants for Storm-
water Overflow", presented at the 8th Annual Confer-
ence of the Delaware River Basin Water Resources
Board, Buck Hill Palls, Pa.,(1970).
5. Diaper, E.W.J. and Glover, G.E., "Microstraining of
Combined Sewer Overflows", presented at 43rd Annual
National Conference of the Water Pollution Control
Federation, Boston, Ma.,(1970)
6. Glover, G.E., "Discussion of Problems of Obtaining Ad-
equate Sewage Disinfection", Proc Paper 8430. Journal
of San. Engr. Division of Am. Soc. of Civil Engineers.
(1972).
69
-------
7. Glover, G.E., "Application of Microstrainlng of Com-
bined Sewer Overflows", Combined Sewer Overflow Semi-
nar Papers, EPA-670/2-73-077, November, 1973, pub-
lished by E.P.A.
8. Glover, G.E., "High Rate Disinfection of Combined
Sewer Overflows", Ibid.
9. Diaper, E.W.J. "Microstraining and Disinfection of
Storm and Combined Sewers", presented at Technology
Transfer Seminar sponsored by the E.P.A., St. Charles
111 . ,(March 1973).
10. Diaper, E.W.J. "Combined Sewer Overflows", presented
at Technology Transfer Seminar sponsored by the E.P.A.
Newark, N.J.,(March 197*0 .
70
-------
SECTION XI
APPENDICES
Page
A. Coagulation Study 72
B. Table of Conversions 79
C. Disinfection Percent Removals 80
71
-------
APPENDIX A
COAGULATION STUDY
Membrane Refiltration Test
Date
7/16/73
7/16/73
7/16/73
7/16/73
7/16/73
7/16/73
7/16/73
Coagulant
type
Initial cone. Filter tube
(mg/1) vol(ml)/
9 sec.
7/13/73 200 mesh coal 50
100 mesh coal 50
7/16/73 straight
7/16/73 200 mesh coal
100 mesh coal
Dow C-31,
200 mesh coal
Dow C-31
100 mesh coal
Dow N-ll,
200 mesh coal
Dow N-ll
100 mesh coal
Atlasep 2A2
200 mesh coal
Atlasep 2A2
100 mesh coal
50
50
4
50
4
50
4
50
4
50
4
50
4
50
335
280
400
370
270
255
255
240
232
230
230
242
230
228
240
204
269
283
255
204
210
242
248
244
186
190
174
200
198
198
Millipore
time (min)/
100 ml
7.6
7-5
4.3
6.3
14.3
13.9
16.2
17 = 5
16.1
15.1
15-0
15.0
10.5
10.2
22.3
18.7
7-2
11.8
30.9
24.1
16.8
17.3
72
-------
APPENDIX A
COAGULATION STUDY
Membrane Refiltration Test
Date
Coagulant Initial cone
type (mg/1)
8/3/75 straight
8/3/73 alum 10
8/3/73 Atlasep 2A2
8/3/73 100 mesh coal 50
8/3/73 alum, 10
Atlasep 2A2 4
8/3/73 alum, 10
Atlasep 2A2 4
100 mesh coal 50
8/3/73 Atlasep 2A2 4
100 mesh coal 50
8/3/73 alum, 10
100 mesh coal 50
8/17/73 straight 0
8/17/73 Fed.
10
Filter tube Millipore
vol(ml)/ time (min)/
sec. 100 ml
185
182
144
140
138
80
74
70
126
120
114
60
30
42
40
50
50
68
74
74
78
72
70
110
105
115
80
73
78
19.2
20.0
16.1
16.8
61.1
69-1
15.1
19-2
60.0
49 = 5
54.6
53-5
25-6
24.2
33-3
33-3
32.1
35.5
23-7
21.5
73
-------
APPENDIX A
COAGULATION STUDY
Membrane Refiltration Test
Date Coagulant Initial cone
type (mg/1)
8/17/73 Atlasep 2A2
8/17/73 100 mesh coal 50
8/17/73
8/17/73
8/17/73
8/17/73
8/17/73
8/24/73
Atlasep 2A2
Fed ,
straight
10
10
Atlasep 2A2 , 4
100 mesh coal 50
Atlasep 2A2, 4
100 mesh coal 50
Dow C-31
10
100 mesh coal 50
8/17/73 Dow C-31, 4
100 mesh coal 50
0
8/24/73 100 mesh coal 50
Filter tube
-yol(ml)/
9 sec .
30
20
21
22
85
92
14
10
13
18
15
13
20
18
18
26
28
25
59
54
56
50
52
49
57
60
59
65
59
64
Mill
time
1
89.3
32.7
44.7.
39.1
48.5
90 +
12.0
13.1
5.3
5-3
5-3
6.0
16.5
19.0
100 ml
74
-------
Membrane
Date
8/24/73
8/24/73
8/24/73
8/24/73
8/24/73
8/24/73
8/24/73
8/24/73
8/24/73
8/24/73
APPENDIX A
COAGULATION STUDY
Refiltration Test
Coagulant Initial cone
type (mg/1)
Filter tube
vol(ml)/
9 sec.
Lime
Dow C-31
Atlasep 2A2
Lime,
Dow C-31
Lime,
Atlasep 2A2
Lime ,
100 mesh coal
Dow C-31,
100 mesh coal
Atlasep 2A2,
100 mesh coal
Dow C-31,
Lime,
100 mesh coal
Atlasep 2A2,
Lime,
100 mesh coal
10
4
4
10
4
10
4
10
50
4
50
4
4
10
50
4
10
50
64
60
70
60
58
58
37
25
22
43
57
57
40
29
24
60
65
65
68
64
67
45
29
23
64
61
62
46
41
38
Millipore
time (min)/
100 ml
24.5
9.0
90+
39-7
90+
50.5
9-5
90+
36.0
90 +
75
-------
APPENDIX A
COAGULATION STUDY
COAGULATION JAR TEST
Temperature = 22.5°C
30 second fast mix at 150 rpm followed by 60 second slow mix
at 10 rpm
Date
9/21/73
Coagulant
type
Atlasep 105C
9/21/73
Dow Purlfloc
C-31
9/21/73
Betz 1190
9/21/73
Betz 1160
Initial cone
(mg/1 )
0 = 5
1.0
1.5
2.0
2.5
0.5
1.0
1.5
2.0
2 = 5
3-0
4.0
0 = 5
1.0
1.5
2.0
2.5
5,5
11.0
16.5
22.0
27 = 5
0.5
1.0
1.5
2.0
2 = 5
Remarks
Medium sized floe
Large, ball-like floe
Large, ball-like floe
Overdosed, stuck to paddle
Overdosed, stuck to paddle
No floe formation
No floe formation
No floe formation
No floe formation
No floe formation
Very small, slow settling
Very small, slow settling
No floe formation
No floe formation
No floe formation
No floe formation
No floe formation
Small floe
Small floe
Small floe
Small floe
Small floe
Small floe
Fair floe
Large floe
Large floe
Large floe
76
-------
Date
9/24/73
Coagulant
type
Betz 1150
9/24/73 Betz 1170
9/24/73
Bttz DK-522
9/24/73 Betz 1190
9/24/73 Betz 1175
9/27/73
Betz 1110
APPENDIX A
COAGULATION STUDY
Initial cone.
(mg/1)
0.5
1.0
1.5
2.0
2.5
5-0
10.0
15.0
20.0
25.0
2.5
5.0
7-5
10.0
12.5
10.0
15.0
20.0
25.0
30.0
5.0
10.0
15.0
20.0
25.0
0.5
1.0
1.5
2.0
Remarks
No floe formation
No floe formation
Pair floe
Large floe
Large floe
No floe formation
No floe formation
No floe formation
No floe formation
No floe formation
Very small floe,no settling
Very small floc,no settling
Very small flocsno settling
Very small floc5no settling
Very small floc,no settling
Very small floc,no settling
Very small floc5no settling
Very small floc,-no settling
Very small floe,no settling
Very small floe,no settling
Medium floe, slow settling
Medium floe, slow settling
Medium floe, rapid settling
Medium floe, rapid settling
Medium floe, rapid settling
No floe formation
No floe formation
No floe formation
No floe formation
77
-------
APPENDIX A
COAGULATION STUDY
Date
9/24/73
9/24/73
Membrane
Date
9/25/73
9/25/73
9/25/73
9/25/73
9/25/73
Coagulant
type
Atlasep 2A2
Atlasep 4A4
Initial cone.
(mg/1)
0.5
1.0
1.5
2.0
2.5
0.5
1.0
1.5
2.0
Remarks
No floe formation
No floe formation
No floe formation
No floe formation
No floe formation
No floe formation
No floe formation
No floe formation
No floe formation
Refiltration Test
Coagulant
type
straight
Atlasep 105C
Betz 1150
Betz 1160
Betz 1175
Dow C-31
Initial cone
(mg/1)
0
1.0
1.5
2.5
3-0
3.0
3.5
15.0
20.0
4.0
4.5
Filter tube
vol/9 sec
(ml)
140
350
380
351
505
145
214
136
140
205
191
Millipore
time (min)/
100 ml
4.3
30+
30+
30+
30+
2.2
5.8
30.5
24.8
21.7
.15.4
78
-------
APPENDIX B
TABLE OP CONVERSIONS
Metric Unit
hectare
m
cm
cu m
sq m
cu m/hr
m/hr
Multiplier
2.47
3.28
2.54
264.20
10.76
0.00026
0.408
English Unit
acre
ft
in
gal
sq ft
mgd
gpm/sq ft
79
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APPENDIX C
DISINFECTION PERCENT REMOVALS
CD
O
Raw Combined Sewer Overflow
Date
6/22/73
b/29/73
6/29/73
7/11/73
7/15/73
8/1/73
8/2/73
Initial C19 cone
(mg/1)
5
12
12
12
12
5
9
9
5
5
5
Microstralned
Date
6/22/73
6/29/73
6/29/73
.0
.0
.0
.0
.0
.0
.0
.0
.1
.1
.1
Combined
Initial Cl? cone
(mg/lj
5
5
5
5
5
.0
.0
.0
.0
.0
Contact time
(rain)
4.25
4.25
4.25
4.25
1.25
4.25
4.25
4.25
4.25
4.25
4.25
Sewer Overflow
Contact time
(min)
4.25
4.25
4.25
4.25
1.25
Initial
TC(1)
41
16
18
18
18
8
6
6
45
26
26
.0
.0
.0
.0
.0
.9
.2
.2
.0
.0
.0
Initial
TC(1)
13
5
64
64
64
.0
• 9
.0
.0
.0
^Removal
99
99
99
99
99
84
90
90
99
98
99
.963
.969
.994
.987
.992
.944
.323
.968
.999
.846
.742
^Removal
99
99
99
99
99
.968
.983
.998
• 999
.998
Initial
FC(2)
2.
1.
0.
0.
0.
15.
0.
0.
3.
1.
1.
0
4
71
71
71
0
5
5
2
8
8
Initial
PC(2)
0.
0.
5-
5-
5..
27
74
1
1
1
^Removal
99-
99-
99-
99.
99.
96.
Inc
98.
99.
66.
98.
450
929
859
859
859
000
•
000
969
667
888
^Removal
96.
99.
99.
99-
99-
269
865
980
980
980
-------
00
APPENDIX C
DISINFECTION PERCENT REMOVALS
Microstrained Combined Sewer Overflow
Date Initial
(mg/
7/11/73
7/15/73
8/1/73
8/2/73
12/20/73
5
5
5
5
5
5
2
Date Initial
(mg/
6/29/73
6/29/73
8/1/73
8/2/73
12/20/73
(1) Cells/100
(2) Cells/100
8
8
8
7
7
7
3
Cip cone.
.0
.0
.0
.6
.6
.6
.7
0_ cone.
T }
.4
.4
.4
.2
.2
.2
.1
ml x 105
ml x 10 4
Contact time Initial
(min) TC(1)
4
4
4
4
4
4
1
.25
.25
.25
.25
.25
.25
.25
1.4
6- 0
6.0
• 5.0
15.0
15.0
4.0
Contact time Initial
(min) TC(1)
3
3
3
3
3
3
3
.3
.3
• 3
.3
.3
.3
.3
FC
C10
5-9
64.0
64.0
5.0
15.0
15.0
^Removal
87.
99.
99.
98.
94.
99.
98.
143
998
998
960
667
693
250
% Removal
99-
99-
99-
99-
99.
99-
4.0 98.
Fecal coliforms
Chlorine
559
998
992
992
999
999
475
Initial
FC(2)
0
0
0
0
0
0
8
.15
.6
.6
.7
.7
.7
.0
Initial
FC(2)
0
5
5
0
0
0
8
.74
.1
.1
.7
.7
.7
.0
^Removal
98.
99.
99.
93-
81.
98.
99.
667
833
833
143
429
286
988
^Removal
99.
99-
99.
99-
99.
99.
99.
324
882
941
857
857
857
688
TC Total coliforms
0,
Ozone
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA 670/2-74-049
3. RECIPIENT'S ACCESSIONING.
4. TITLE AND SUBTITLE
MICROSTRAINING AND DISINFECTION OF COMBINED SEWER
OVERFLOWS - PHASE III
5. REPORT DATE
Augl.1
6. PERF
1974; Truing Date
FORMING ORGANIZATION CODE
7. AUTHOR(S)
Michael B. Maher
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORG "\NIZATION NAME AND ADDRESS
Crane Co.-Cochrane Environmental Systems Division
800 Third Avenue
King of Prussia, Pennsylvania 19406
10. PROGRAM ELEMENT NO. pf£t 1BB034
ROAP: 21-ASY Task; 105
11. CONTRACT/GRANT NO.
S-800966
12. SPONSORING AG€NCY NAME AND ADDRESS
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
Supplements EPA reports 11023 EVO 06/70 and 11023 FWT 01/73 (PB-195 674 and
PB-219 879)
16. ABSTRACT A microstrainer reduced the SS of the combined sewer overflow from 50 to
300 mg/1 to 40 to 60 mg/1 operating at an average rate of 38.4 m/hr (16 gpm/sq,ft.)
Addition of polyelectrolyte improved the overall performance of the microstrainer.
The effluent SS was reduced to an average of 23 mg/1 and the flow rate increased to an
average of 87.5 m/hr, (36 gpm/sq.ft.) The combined sewer served a residential area in
Philadelphia composed of 4.5 hectares (11.2 acres). The average dry weather flow was
91 cu m/day (24,000 gpd). An extensive coagulation study revealed that cationic
polyelectrolytes were most suitable for this particular application. The concentra-
tions applied ranged from 0.25 to 1.5 mg/1. Coliform reductions across the micro-
strainer were observed. It was also found that microstrained effluent could be more
easily disinfected than raw combined sewer overflow. Chlorine and ozone were.used for
disinfection at low contact times. The capital cost of a microstrainer installation
followed by high rate chlorine contact chamber is reported as $60660/hectare
($24480/acre). When polyelectrolyte addition equipment is included, capital cost is
$37250/hectare ($15030/acre). Costs are in 1973 dollars.
This report, submitted in fulfillment of Project S-800966 (formerly 11023 FWT), is a
continuation of the work previously reported in EPA Reports 11023 EVO 06/70 and
11023 FWT 01/73.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Cost comparison, Polyelectrolytes,
Water quality, *Filtration, Coagu-
lation, Sewers, *0zone, *Chlorine,
^Surface water runoff
Water pollution con-
trol, *Microstraining
*Combined sewer over-
flow, *Storm runoff,
*Suspended solids
removal, *High rate
dis infection
13B
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNLIMITED
21. NO. OF PAGES
92
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
82
U.S. GOVERNMENT PRINTING OFFICE: 197't-657-581t/5301 Region No. 5-II
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