EPA-600/2-77-069a
August 1977
Environmental Protection Technology Series
,.j, ^r iffiSS.^
'V -,' ^V ;f}>v -*'
.-C ",\' ^^C * , , 'f'1*?'
SCREENING/FLOTATION TREATMENT OF
COMBINED SEWER OVERFLOWS
Volume I Bench Scale and
Pilot Plant Investigations
X'Wvi.^.-.-.Aj
H
Municipal Environmenta! Research Laboratory
Office of Research and Development
U,S. Environmenta! Protection Agency
Cincinnati, Ohio 45268
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-77-069a
August 1977
SCREENING/FLOTATION TREATMENT OF
COMBINED SEWER OVERFLOWS
Volume 1 - Bench Scale and Pilot Plant
Investigations
by
Mahendra K. Gupta, Donald G. Mason,
Michael J. Clark, Thomas L. Meinholz,
Charles A. Hansen and Anthony Geinopolos
Envirex Inc.
A Rexnord Company
Environmental Sciences Division
Milwaukee, Wisconsin 53201
EPA Contract No. 14-12-40
Project Officers
Anthony N. Tafuri
Storm and Combined Sewer Section
Wastewater Research Division
Municipal Environmental Research Laboratory (Cincinnati)
Edison, New Jersey 08817
and
Clifford Risley
Region V
U.S. Environmental Protection Agency
Chicago, Illinois 60606
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Municipal Environmental Research ^
Laboratory, U.S. Environmental Protection Agency, and approved for publication.
Approval does not signify that the contents necessarily reflect the_views and
policies of the U.S. Environmental Protection Agency, nor does mention of
trade names or commercial products constitute endorsement or recommendation
for use.
11
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FOREWORD
The Environmental Protection Agency was created because of Increasing public
and government concern about the dangers of pollution to the health and
welfareof the American people. Noxious air, foul water, and spoiled land
are tragic testimony to the deterioration of our natural environment The
complexity of that environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development Is that necessary first step in problem solution
and it involves defining the problems, measuring its impact, and searching
for solutions. The Municipal Environmental Research Laboratory develops new
and improved technology and systems for the prevention, treatment and
management of wastewater and solid and hazardous waste pollutant discharges
from municipal and community sources, for the preservation and treatment of
public drinking water supplies, and to minimize the adverse economic, social,
health, and aesthetic effects of pollution. This publication is one of the
products of that research; a most vital communications link between the
researcher and the user community.
The study contained herein documents bench scale and pilot plant Investiga-
J«HnLS??UCted u° dfe!op and ftnPr°ve a treatment system (screening/flotation)
for handling combined sewer overflows. It was found that a screening/
flotation treatment system is an effective method of reducing the pollution
caused by combined sewer overflows. Hwnunon
Francis T. Mayo
Director
Municipal Environmental
Research Laboratory
iii
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ABSTRACT
This report documents bench scale and pilot plant studies conducted to develop
and improve a treatment system for combined sewer overflows. The processes
of chemical oxidation, screening, dlssolved-air flotation and disinfection
were evaluated in the laboratory. It was determined that chemical oxidation
was not feasible. The majority of the pollutants were of a particulate nature,
which Indicated solids/liquid separation processes could provide effective
treatment. Screening/flotation and sequential screening were the solids/
liquid separation processes Investigated on ,a demonstration basis.
A 5 mgd screening (one drum screen) and dissolved-air flotation demonstration
test facility was designed and installed at the Hawley Road CSO outfall in
Milwaukee, Wisconsin. The treatment system was operated successfully on 55
combined sewer overflows during 1969 and 1970 and on 8 overflow events during
the 1971-1972 season. It was concluded that screening/flotation is an effec-
tive method of reducing pollution caused by combined sewer overflows. The
overall pollutant removals measured in terms of suspended solids, volatile
suspended solids, BOD and COD ranged between 60-75%.
A 5 mgd sequential screening (three drum screens in series) demonstration
test facility was also designed and installed at the Hawley Road CSO outfall
in Milwaukee. The screening system was operated during 1971 on 21 combined
sewer overflows. The overall pollutant removals measured In terms of suspen-
ded solids, volatile suspended solids, BOD, COD and TOC were about 301.
Addition of chemical flocculants or variation in hydraulic and solids loadings
did not effect significant improvement In the removal efficiencies. It was
concluded that the use of three screens in series did not show any advantage
over a single screen.
Subsequent field work, based upon bench scale testing, was concentrated on
Improving or upgrading the performance of the'screening/flotation demonstra-
tion system. Effluent flow pressurization mode of operation and powdered
activated carbon were Investigated for improving performance, and the results
obtained showed no apparent improvement.
Investigation of microscreenlng (22 micron) for polishing flotation effluent
Indicated that overall partlculate removal efficiency of an additional 5 to
10% could be achieved.
This report was submitted as partial fulfillment of contract number U-12-AO
under the sponsorship of the U.S. Environmental Protection Agency. This
report covers a period from October 1967 to March 1975.
Iv
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TABLE OF CONTENTS
ABSTRACT
LIST OF TABLES
LIST OF FIGURES
ACKNOWLEDGEMENTS '
SECTION I - CONCLUSIONS
SECTION II - RECOMMENDATIONS
SECTION III - INTRODUCTION
SECTION IV - LITERATURE SEARCH
Characteristics_of Combined Sewer Overflows
Removal of Solids by Screening
DIssolved-Air Flotation
Disinfection of Combined Sewer Overflows
Ultraviolet Light Disinfection
Disinfection by Chemicals
Summary Remarks
SECTION V - SITE SELECTION AND PRELIMINARY INVESTIGATIONS
Site Selection
Preliminary Investigations
Conclusions - Preliminary Investigations
SECTION VI - DESIGN AND CONSTRUCTION OF THE 5 MGD SCREENING/
FLOTATION DEMONSTRATION FACILITY
Design of Screen
Floatation System Design
Design of Supporting System
Operation Methods and Test Plan
Methods and Operational Procedures
Sampling Procedures
Test Plan
PAGE
I y
ix
xiil
xfv
7
11
13
15
15
16
17
19
19
23
33
34
39
40
43
43
43
46
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TABLE OF CONTENTS (CONTINUED)
PAGE
SECTION VII - SCREENING/FLOTATION OPERATING RESULTS
(1969-1970) AND DISCUSSION
Characterization of Raw Waste
Results of the Screening Operation
Operation of the Flotation System
Operational Difficulties
Disinfection of Combined Overflows
Conceptual Design
Pumping System
Screening System
Flotation System
Economic Considerations
SECTION VIII - DESIGN AND CONSTRUCTION OF THE 5 MGD
SEQUENTIAL SCREENING DEMONSTRATION FACILITY
Location of Site
Treatment System Components
Design of the Screening System
Design of Supporting Systems
SECTION IX - SEQUENTIAL SCREENING OPERATING RESULTS (1971) AND
DISCUSSION
Operational Methods and Procedures
Sampling Procedures
Test Plan
Raw Wastewater Quality
Operation of the Sequential Screening System
Bench Scale Screening Tests
Operation of the Backwash System
Disinfection of Combined Sewer Overflows
SECTION X -
INVESTIGATIONS CONDUCTED FOR UPGRADING SCREENING/
FLOTATION PERFORMANCE
Screening/Flotation Using Effluent Pressurization and
Microscreening of Flotation Effluent
Test Plan
Coarse Screening
Dissolved-Air Flotation Operation
Flotation Effluent Screening
Microscreening of Raw CSO
Powdered Activated Carbon Addition
48
54
56
66
67
67
69
70
72
77
81
81
81
84
87
91
91
91
92
93
96
103
108
108
110
111
118
119
121
125
125
130
vi
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TABLE OF CONTENTS (CONTINUED)
SECTION XI - REFERENCES
SECTION XI I - APPENDICES
APPENDIX A - CHEMICAL OXIDATION STUDIES
LITERATURE SEARCH
Hydrogen Peroxide
Ozone
Oxidation by Chlorine
Oxidation by Oxy-Acids and their Salts
Electro-Chemical Oxidation
Combination of Oxidants
PAGE
142
LABORATORY INVESTI GAT IONS
General Test Procedures
Special Test Procedures
Oxidants
Ozone Oxidation System
with Various Chemical
RESULTS AND DISCUSSION
Oxidation with Hydrogen Peroxide
Oxidation with Chlorine
Oxidation with Combined System of Hydrogen
Peroxide and Chlorine
Oxidation with Ozone
Oxidation with Gamma Radiation
«
SUMMARY AND CONCLUSIONS
REFERENCES - APPENDIX A
APPENDIX B - BENCH SCALE STUDIES FOR UPGRADING
FLOTATION TREATED COMBINED SEWER
OVERFLOWS
INTRODUCTION
Scope of Work
Test Procedures
RESULTS AND EVALUATIONS
Operation of the Field Treatment System
During 1972
Evaluation of Various Processes for Upgrading
Flotation Effluents
High Rate Filtration
Microscreening
Carbon-Flotation Tests
147
149
152
154
155
155
156
156
156
159
161
161
164
167
167
173
173
175
178
178
179
184
184
184
187
187
187
VI I
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TABLE OF CONTENTS - APPENDIX B (CONTINUED)
PAGE
Ozone Oxidation 195
Removal of Total Phosphates 195
DISCUSSION 199
SUMMARY AND CONCLUSIONS 201
REFERENCES - APPENDIX B 203
APPENDIX C - ANALYTICAL PROCEDURES 204
Analytical Instruments and Apparatus 204
Analytical Procedures and Analyses 204
APPENDIX D - BNECH SCALE TEST PROCEDURES 20?
Dissolved-Air Flotation Test Procedure 207
Microscreening Test Procedure 209
APPENDIX E - DEMONSTRATION SYSTEM, OPERATING DATA 212
AND STATISTICAL PROCEDURES
OPERATING DATA 212
Screening/Flotation System 212
1969-1970 Data 212
1971-1972 Data 238
1973 Data 246
1974 Data 254
Sequential Screening System 264
1971 Data
Microscreening System 272
Flotation Effluent Treatment (1973) 273
Raw CSO Treatment (1973) 275
STATISTICAL PROCEDURES 277
APPENDIX F - ENGLISH UNITS AND CONVERSION TO METRIC 280
UNITS
VI I I
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LIST OF TABLES
Table
1
2
3
4
5
6
7
8
3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
2k
25
26
27
28
29
30
31
32
33
34
Quality of Combined Sewer Overflows
Characteristics of Combined Overflow - Hawley Road Site
Summary of Preliminary Screening Data
Summary of Preliminary Flotation Data
Preliminary Screening/Flotation Data
Preliminary Disinfection Data
Variable Combinations Utilized For Flotation Testing
Summary of First Flush Data
Summary of Data At Intervals of Greater Than 4 Days
Between Overflows
Summary of Extended Overflow Data
Particulate & Dissolved Relationships
Pollutant Removals by Screening
Pollutant Removals by Screening/Flotation
Summary of Particulate and Dissolved Organic Removal
Efficiencies
Effect of Pressurized Flow Rate on Solids Removal
Comparison of The Effect of Overflow Rate on Removal
Efficiencies
Summary of Disinfection Data
Operating Cost Estimates
Summary of Overflow Occurrence Data - 1971
Summary of Raw Water Quality Data - 1969-1971
Dissolved and Volatile Fractions in Combined
Operating Conditions For The Series Screening
Sewer Overflows
System
Summary of Overall Pollutant Removals Across The Screening
System
Summary of Pollutant Removals on Various Screens
Variation in Hydraulic & Solid Loadings on The Screens
Wet Sieve Analysis Results on Storm 71-*2 Raw Overflow
Comparison of Bench Scale and Full Scale Screening Data
Comparison of Pollutant Removal Efficiencies of 23 and
63 Micron Screens
Summary of Disinfection Data With Chlorine
Combined Sewer Overflow Characteristics - 1969-1973
Summary of Screened Water Quality - 1973
Pollutant Removals by Screening During Extended Overflows
Pollutant Removals by Screening/Flotation System in Split
Flow 6 Effluent Pressurization at Low Overflow Rates
Screening/Flotation Effluent Quality - 1969-1973
Page
10
26
27
30
31
32
50
53
53
55
57
60
62
65
68
80
94
95
97
98
99
100
102
103
105
106
109
120
119
122
123
124
ix
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List of Tables - (Continued)
Table Page
* ....HI ^....
35 Summary of Operating Conditions, Microscreening Flotation 126
Effluent
36 Summary of Wastewater Characteristics, Mlcroscreen 127
Treatment of Flotation Effluent
37 Summary of Pollutant Removals by Microscreening of 128
Flotation Effluent
38 Summary of Operating Conditions For Microscreening 129
Raw CSO
39 Summary of Influent and Effluent Characteristics For 131
The Microscreening of Raw CSO
40 Comparison of Removal Efficiencies 132
41 Average Operational Parameters For Dlssolved-Alr 134
Flotation Process - 1974
42 Combined Sewer Overflow Quality Characteristics - 1971-1974 135
43 Screened Effluent Quality Characteristics and Percent 136
Removals by The Screening Process - 1971-1974
44 Percent Removals by The Dissolved-Air Flotation Process - 138
1971-1974
45 Final Effluent Quality Characteristics and Percent Removals 139
by The Screening/Dissolved-AIr Flotation P-ocess -
1971-1974
A-1 Laboratory Analysis of Combined Sewer Samples Utilized 157
For Chemical Oxidation Study
A-2 Results of Chemical Oxidation With Hydrogen Peroxide 162
A-3 Effect of UV Light and Cobalt on Hydrogen Peroxide Oxidation 163
A-4 Chlorine Oxidation Tests 165
A-5 Light Catalyzed Chlorine Oxidation 166
A-6 Oxidation With Combined Hydrogen Peroxide and Chlorine 168
A-7 Summary 0 Oxidation Tests 169
A-8 Summary 0^ Oxidation and Air Flotation Tests 171
A-9 Summary Disinfection Data - All Spring Storms 172
A-10 Summary of Oxidation of Combined Overflows With Various 174
Oxidants and Combinations
B-1 Hawley Road Field Data - 1972 185
B-2 Summary of Raw Water Quality Data - 1969-1972 186
B-3 Results of The Mixed-Media Filtration Tests 188
B-4 Upgrading of Flotation Effluents by Microscreening 189
1 B-5 Bench Scale Flotation Tests For The Evaluation of Effluent 191
Recycle Mode of Dissolved Air Flotation (Without Activated
Carbon)
B-6 Carbon Flotation Treatment. - Storm No. 1972-1 193
B-7 Carbon Flotation Treatment - Storm No. 1972-2 194
B-8 Carbon Flotation Treatment - Storm No. 1972-3 195
B-9 Carbon Flotation Treatment - Storm No. 1972-4 197
B-10 Ozonation Tests 198
B-11 Results of Total Phosphate Analysis 200
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List of Tables - (Continued)
Table
E-1
E-2
E-3
E-4
E-5
E-6
E-7
E-8
E-9
E-10
E-11
E-12
E-13
E-14
E-15
E-16
E-17
E-18
E-19
E-20
E-21
E-22
E-23
E-24
E-25
E-26
E-27
E-28
E-29
E-30
1971 Data
in Percent
1971 Data - High
Operational Data
Raw Waste Characteristics - First Flushes - 1969-1970 Data
Raw Waste Characteristics - Extended Overflows - 1969 Data
Screened Water Quality - First Flushes - 1969-1970 Data
Screened Water Quality - Extended Overflow - 1969 Data
Effluent Water Quality - First Flushes - 1969 - 1970 Data
Effluent Water Quality - Extended Overflow - 1969 Data
Dissolved COD and TOC Data - 1970 Data
Screen Backwash & Floated Scum Quality - 1969 Data
Screen Backwash & Floated Scum Quality - 1970 Data
First Flush Evaluations - 1969-1970 .
First Flush Removals in Percent - 1969-1970
Extended Overflow Removals in Percent - 1969 Data
Suspended Solids Mass Balance - 1969 Data
Screening/Flotation Pilot Unit Operational Data - 1971-1972
Raw Waste Characteristics Extended Overflows - 1971-1972 Data
Screened Water Quality Extended Overflow, 1971-1972 Data
Effluent Water Quality - Extended Overflow 1971-1972 Data-
Low Overflow Rates
Effluent Water Quality - Extended Overflow 1971-1972 Data -
High Overflow Rates
Floated Scum Qaulity
Extended Overflow Removals
Overflow Rates
Extended Overflow Removals in Percent 1971-1972 Data -
Low Overflow Rates
Screening/Flotation Pilot Unit Operational Data - 1973
Raw Waste Characteristics Extended Overflows - 1973 Data
Screened Water Quality Extended Overflow - 1973 Data
Effluent Water Quality Extended Overflow, 1973 Data -
Low Overflow Rates
Effluent Water Quality - Extended Overflow - 1973. Data -
High Overflow Rates
Floated Scum Quality 1973 Data
Extended Overflow Removals in Percent - 1973 Data -
High Overflow Rates
Extended Overflow Removals in Percent - 1973 Data -
Low Overflow Rates
1974 - Run
1974 - Run
197*» - Run
1974 - Run
1974 - Run
197*» - Run
1971* - Run
1974 - Run
197*» - Run
E-31
E-32
E-33
E-3*»
E-35
E-36
E-37
E-38
E-39
Operational
Operational
Operational
Operational
Operational
Operational
Operational
Operational
Operational
Resul ts
Results
Results
Resul ts
Results
Results
Resul ts
Results
Results
No.
No.
No.
No.
No.
No.
No.
No.
No.
1
2
3
4
5
6
7
8
9
Page
211
215
216
218
219
221
222
225
226
228
229
231
232
235
237
238
239
240
242
243
244
245
246
247
248
249
250
251
252
253
254
255
/ii>6
257
258
259
260
261
XI
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List of Tables - (Continued)
Table Page
E-40 Operational Results - 1974 - Run No. 10 262
E-41 Operating Conditions For The Series Screening System 263
E-42 Raw V/aste Characteristics 265
E-43 Screened Water Quality - Drum Screen 1 (20 Mesh) 267
E-44 Screened Water Quality - Drum Screen 2 (100 Mesh) 268
E-45 Screened Water Quality - Drum Screen 3 (230 Mesh) 269
E-46 Screen Backwash Quality 271
E-47 Operating Conditions For The Microscreening System 272
E-48 Microscreening Treatment of Flotation Effluent - 273
(Raw Waste Characteristics}
E-49 MIcroscreened Water Quality - (Flotation Effluent 274
Treatment)
E-50 Microscreening Treatment of Raw CSO - (Raw Waste 275
Characteristics)
E-51 Microscreened Water Quality - (Raw CSO Treatment) 27&
xii
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LIST OF FIGURES
NO.
1 Relationship of frequency of combined sewer overflows
to interceptor capacity
2 Project drainage area
3 Relationship of runoff coefficient to perviousness
k Relation between water depth and flow in Hawley Road sewer
5 Typical interceptor device
6 Comparison Tyler mesh to size of opening
7 Scale drawing of demonstration system
8 Demonstration system
9 Screening system
10 Screening system
11 Flotation system
12 Flotation tank
13 Hawley Road outfall
14 Interior views of the control shack
15 Relationship between flow in .sewer and suspended solids
16 Suspended solids removal-screen Ing/flotation
17 Baffle arrangement for overflow rate tests
18 Recommended screen arrangement
19 Recommended screening/flotation arrangement
20 Overall system configuration
21 Schematic flow sheet for sequential screening treatment
system
22 Sequential screening demonstration system
23 Sequential screening demonstration system
2k Open end of the screen
25 Liquid level electrical probes
26 Screening system
27 Raw feed system
28 Interior view of the control shack
29 Bench scale screening data
30 Modifications to d5ssolved-air flotation system
31 Schematic flow diagram for sequential screening system
32 Dissolved-air flotation & microscreening operation modes
A-l Human tolerance for ozone
A-2 Ozone absorption systems
A-3 Schematic of ozone test apparatus
B-1 Screening/flotation flow diagram
B-2 Schematic of ozone test apparatus
D-1 Microscreen bench test apparatus
PAGE
21
22
24
25
28
35
36
37
38
41
42
44
45
52
58
63
73
76
78
82
83
83
85
85
86
88
89
107
112
in
115
150
153
160
180
183
210
XI I I
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ACKNOWLEDGEMEN'
Many personnel from the Environmental Sciences Division of Envirex, Inc.,
Milwaukee, Wisconsin contributed to the successful completion of this study.
Bench scale testing and studies for feasibility and to obtain basic
design and operating data were performed by Donald G. Mason, Mahendra
Gupta, Richard E. Wullschleger and Melvin Teske.
K.
Mechanical design and supervision of fabrication, construction and in-
stallation of the initial screening/flotation and sequential screening
systems as well as subsequent modifications was carried out by the
Design and Construction section headed by Joseph E. Milanowski.
Field operation of the Hawley Road pilot demonstration systems during
over one hundred storm events, quickly responded to at all hours of the
day and night, was performed by such dedicated individuals as Donald G.
Mason, Mahendra K. Gupta, Frank Toman and Thomas L. Meinholz.
Timely completion of the laboratory analyses for the inevitable on-
slaught of samples resulting from each overflow treated was consistently
achieved by Richard E. Wullschleger and his laboratory staff.
This document is a compilation and condensation of several individual
reports previously prepared for EPA by various authors including Donald
G. Mason (Sections IV - VII and Appendix A), Mahendra K. Gupta (Sections
IV - X and Appendix B) and Michael J. Clark, Thomas L, Meinholz and
Charles A. Hansen (Section X, Powdered Activated Carbon Add! t ion) . This
document, Volume I, was compiled, condensed and edited by Anthony
Geinopolos using the individual reports prepared by the above listed
authors.
The cooperation of the City of Milwaukee in making the Hawley Road site
available for these studies is duly acknowledged.
The bench scale study reported in Appendix B, Application of Activated Car-
bon Addition, was performed under the sponsorship of the Wisconsin Department
of Natural Resources.
Deep appreciation is extended to the U.S. Environmental Protection Agency,
especially Project Officers Stephen Poloncsik and Clifford Risley of Region
V and Messrs. Anthony Tafuri and Richard Field, Chief, Storm and Combined
Sewer Section, Edison, N.J., Frank Condon and William Rosenkranz, Washington,
D.C. for their continued aid and helpful advice during the project.
XIV
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SECTION I
CONCLUSIONS
1. Screening/Flotation Treatment
a. A screening/flotation treatment system is an effective method of re-
ducing the pollution caused by combined sewer overflows.
b. The combined .sewer overflows monitored had the following characteris-
tics in mg/1 at the 95% confidence level.
BOD 49+JO
COD 161+19
Suspended Solids 16^±2^
Volatile Suspended Solids 90+J4
Total Nitrogen 5.5+0.8
c. Approximately 20% of the overflows monitored exhibited first flushes
of the following characteristics in mg/1 at the 95% confidence level.
BOD 186+40
COD 581+92
Suspended Solids 522+J50
Volatile Suspended Solids 308+83
Total Nitrogen 17.6+3-1
When present these first flushes persisted for 20 to 70 minutes.
d. All first flushes occurred at a time interval of greater than 4 days
between overflows.
e. It was demonstrated that a screening/flotation system could achieve
the following percent removal efficiencies based on the raw waste
characteristics encountered (Hydraulic Loading: Screen 40 gpm/sq ft,
Flotation 2.75 gpm/sq ft).
Without Chemical With Chemical
Flocculant Addition Flocculant Addition
BOD
COD
Suspended Solids
Volatile Suspended Solids
Hi t;rogen
35+8
41+8
43+7
48+J1
29+14
60+J1
57+11
71+9
71+9
24+9
f. The chemical flocculant addition required to achieve the above stated
-------
removals was 20 mg/1 ferric chloride and 4 mg/1 of a cationic polyelec-
trolyte.
g. An operating pressure of 50 psig and a pressurized flow rate of 20%
of the raw waste flow provided sufficient air bubbles for proper
flotation tank operation.
h. The average volume of waste residual solids (i.e. screen backwash
and floated scum) was 1.75% of the raw flow.
I. The average removal efficiencies for the screening/flotation system
decreased (as shown below in percent removals) when the hydraulic over-
flow rate was increased from "2.75 to 3-75 gpm/sq ft.
Low Overflow Rate High Overflow Rate
BOD 59 52
COD 57 5^
Suspended Solids 70 61
Volatile Suspended Solids 71 64
j. Utilizing a 50 mesh (297 u) screen at a hydraulic loading of 40 gpnr>
per sq ft of screen. The percent removal efficiencies for screening
alone were observed to be:
BOD 27+5
COD 26 +_ 5
Suspended Solids 27 +_ 5
Volatile Suspended Solids 34 +_ 5
k. The screening/flotation system provides sufficient detention time
(~15 min.) for effective chlorlnation.
1. Because of the intermittent operation and remote location of
combined sewer overflew treatment systems, completely automated oper-
ation is required.
m. The use of a 50 mesh (297 y) screen eliminated the need for
bottom sludge scrapers.
n. It was not always possible to obtain optimum chemical flocculant
addition due to widely varying raw waste characteristics.
o. Bench scale tests showed that the effluent quality of screening/
flotation treatment of combined sewer overflows could be upgraded
significantly by using filtration, microscreening, powdered act-
ivated carbon and coagulants and the effluent recycle mode of dis-
solved-alr flotation. However, when applied on the 5 mgd screening/
flotation facility at the Hawley Road site, it was observed that,
(l) No apparent differences in removal efficiencies were obtained
-------
2.
as a result of using effluent recycle mode of pressurized
flow as opposed to the split flow mode using chemicals.
(2) Suspended solids levels in the flotation effluent were re-
duced by 5-10% by microscreening based on raw effluent quality.
(3) The improvement in performance due to activated carbon addition
was not readily apparent, and any improvement achieved did not
appear to warrant the additional carbon costs incurred.
The sequential screening treatment system investigated was much less
effective than the screening/flotation treatment system in handling
combined sewer overflows. In fact, it was concluded that the use of
three screens in series did not show any advantage over a single screen.
It was found that the screening system could achieve the following
percent removal efficiencies based on the raw waste characteristics
encountered (hydraulic loadings: 15-i»5 gpm/sq ft).
Suspended Sol ids
Volatile Suspended Solids
BOD
COD
TOC
Without Chemical
Flocculant Addition
28+8
32 +_ 11
28 +_ 7
30 + 9
25 + 12
With Chemical
Flocculant Addition
22 +_ 1A
31 + 17
16 + 15
10 +_ 7
12 + 17
The microscreening of raw CSO removed only about 35-57% of the sus-
pended solids present in the overflows monitored during the 1973 season
and no improvement in the effluent quality was achieved via micro-
screening compared to screening/dissolved-air flotation treatment.
Chemical oxidation bench scale studies indicated that chemical oxid-
ation of combined sewer overflow is not technically or economically
feasible. Chlorine, hydrogen peroxide and ozone, singly and in comb-
ination were the oxidants investigated.
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SECTION I I
1.
2.
3.
RECOMMENDATIONS
Screening/flotation should be utilized to reduce the pollution from
combined sewer overflows where treatment is the preferred alternative.
Basic design and operating procedures have been outlined in this report
and may be used in applying screening/flotation treatment full scale
in handling combined sewer overflows.
There is a need for an investigation to determine and evaluate various
sludge disposal alternatives for handling the residual sludges arising
from screening/flotation and from other CSO treatment alternatives.
It is estimated that the Hawley Road test facility could be operated
about \% of the time for treating combined sewer overflows. This low
magnitude of operating time Is typical for facilities designed for
treating only CSO. Consideration should be given to adapting CSO
treatment processes, such as screening/flotation, for dual treatment
of dry and wet weather flows.
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SECTION II I
INTRODUCTION
During recent years combined sewer overflow has been recognized as a sig-
nificant pollution problem. Immediate reaction was to separate the sewer
systems. It was found, however, that this solution was expensive and some-
times impossible. Furthermore, it has aiso been shown that stormwater could
carry a large pollutional load, therefore, tending to reduce the effect-
iveness of sewer separation. As research to find a solution to the combined
sewer problem began, it became apparent that no one solution would solve
all the problems associated with combined overflows. The ultimate solution
depends upon successful application of many different approaches which may
include separation of sewers, holding tanks, and treatment systems.
The Environmental Protection Agency (EPA) has not only established combined
sewer overflow (CSO) as a problem but has fostered technology research,
development and demonstration to counteract it. This project illustrates
well-the continued efforts of EPA for the advancement of approaches for
combined sewer overflow control and treatment. For example, from 1967
through 1974, EPA awarded grants and contracts for the bench scale in-
vestigation, pilot plant demonstration development and full scale install-
ation of screening/flotation as a combined sewer overflow treatment method.
This volume, Volume I, covers the bench scale investigations and pilot plant
demonstration development of screening/flotation as a CSO treatment method
under EPA Contract No. 1*4-12-40. In a separate document, Volume II, Is
covered the full scale screening/flotation operation conducted under EPA
Grant No. S800744 (formerly 11023FWS).
Initially, the technical approach in this project (EPA Contract No. 14-12-40)
was screening and chemical oxidation of combined overflows. Early during
the study it was determined that chemical oxidation was not feasible and this
approach was abandoned. A summary of the work done on chemical oxidation
may be seen in Appendix A. During the investigation of chemical oxidation,
however, a promising alternative was uncovered. It was discovered that the
pollutants in combined sewer overflow consisted mainly of particulate matter.
This clearly indicated that an efficient solids/liquid separation process
should provide a high degree of treatment for combined overflows. The work
scope of EPA Contract No. 14-12-40 was modified to allow study of a screening/
dissolved-air flotation system. Later, after evaluating the system for a
short time, it became apparent that a more detailed study of the screening
process could provide important additional information and the contract was
amended to include those studies. Still later, promising improvements of
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the screening/flotation treatment method were investigated, as a part of
the contract, on a bench scale and pilot demonstration basis.
In effect, the total work performed under EPA Contract No. 14-12-40 in-
cluded the following:
1. Literature search, site arrangements, preliminary investigations
2. Design and construction of a 5 MGD screening/flotation system
3. Operation of the screening/flotation system
4. Design and construction of a 5 MGD series screening system
5. Operation of the series screening system
6. Upgrading screening/flotation performance by:
a. Using flotation effluent pressurized flow as
opposed to split flow pressurization
b. Microscreening of flotation effluent
c. Powdered activated carbon addition
7. System disassembly and restoration of demonstration site
This report. Volume I, summarizes the work performed to date on I terns 1
through 6, listed above.
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SECTION IV
LITERATURE SEARCH
It Is assumed that the following process elements will be utilized to accom-
plish the treatment of combined sewer overflows.
A. Solids/liquid separation
1. Screening
2. Dissolved-Air Flotation
B. Disinfection of the waste flow
A search of the existing literature was made to determine the characteristics
of combined sewer overflow, and to obtain pertinent information on the above
mentioned process elements.
CHARACTERISTICS OF COMBINED SEWER OVERFLOWS
More than 1400 U.S. communities serving 50 million people have what is known
as combined sewer systems which provide one collection system for both sani-
tary sewage and stormwater runoff (1). During dry weather the flow in such
a system consists mainly of sanitary sewage and is normally intercepted by
the interceptor systems before it reaches the outfall, where it otherwise
would be discharged to a lake or river. As long as the capacity of the
interceptor system exceeds the flow in the combined sewer, the flow is
directed to the sewage treatment plant for purification.
During a storm, the flow In the combined sewer can increase from 50 to 100
times the normal dry weather flow (2). Normal interceptor capacities are
between 1.5 and 5.0 times the dry weather flow (hereinafter abbreviated DWF)
(2) (3) (A), This would mean that at norma1 interceptor capacities, the inter-
ceptors would be from 97.3 to 99.0% efficient in collecting and transporting
the sanitary sewage to the treatment plant. These efficiencies are very mis-
leading, since during periods of high stormwater runoff, it is possible to
have up to 36% of the sanitary sewage bypassing the interceptor system and
being discharged untreated into the receiving waters (5). This discharge of
untreated combined overflows could cause severe pollution problems if the
water is reused a relatively short distance downstream as a water supply or
for recreational activities.
The pollution caused by combined sewer discharge ?s directly related to the
frequency of storm runoff exceeding the interceptor capacity. Three
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Independent Investigators (5)(6) (7) report that the normal dry weather flow Is
approximately equivalent to a rainfall intensity of about 0.01 inch/hour.
With Interceptor capacities of 1.5 to 5 times the dry weather flow, rainfall
Intensities greater than 0.015 to 0.05 inch/hour would be necessary to cause
combined overflow which would go untreated. Palmer (6), Johnson (7), and
McKee (5) studies the rainfall records of Detroit, Washington, D.C. and Boston.
The results of their findings showing the number of combined overflows per
month for given Interceptor capacities may be seen in Figure 1. With an
Interceptor capacity of 5 times (DWF), the number of overflows per month was
between four and six. This indicates the extent of possible pollution of
the receiving body of water.
The pollutional effect of combined sewer overflows will, of course, be deter-
mined not only by the frequency.of overflows, but also by the quality of the
overflow. The most important and commonly discussed pollutional parameters
associated with combined sewer overflows are suspended solids, BOD, and col I-
form count. To establish a basis for comparison, the average raw (primarily
domestic) sewage contains 200-300 mg/1 suspended solids (0(8) (9), (50-60% of
these suspended solids are settleable), 100-300 mg/1 BOD (1)(8)(9) and con-
form counts of 43-150 x 104 per ml (9) (10).
Assuming pure stormwater to be essentially unpolluted, it would be expected
that the BOD, suspended solids, and coliform counts of combined sewer overflow
to be substantially lower than those of raw sewage. This assumption could
result in considerable error when estimating the quality of combined sewer
overflows. A limited amount of data has been obtained which indicates the
-------
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a
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o
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-------
Table 1. QUALITY OF COMBINED SEWER OVERFLOWS
Source
reference
number
(6)
(14)
(13)
(13)
(13)
(12)
(11)
(11)
BOD,
mg/1
50
100
59
92
121
40 to
260
220 to
614
Suspended
sol ids,
mg/1
250
544
203
129
436
150
130 to
930
168 to
426
COL 1 FORM,
per ml
x 103
43
300
.5
180
2.3 to
24
2.1
Discuss ion
Detroit, Michigan
Buffalo, New York
(Bi rd Avenue)
San Francisco, California
(Average value)
Chicago, 1 1 1 inois
Buffalo, New York
(Bai ley Avenue)
Average values
Toronto, Ontario, Canada
( Eg 1 in ton Aven ue )
Wei land, Ontario. Canada
(Burgar Street)
10
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overflows. The survey indicated those uses most affected were commercial
(fishing), recreational (swimming), and public health (water supplies). The
main pollutant affecting these water uses is pathogenic bacterial contamina-
tion (measured by coliform density) (1) (5) (15) (16). Table 1 shows the range
of coliform counts to vary from 0.5x!03 to 300x!03/m1 In combined sewer over-
flows. The suspended solids concentration of combined overflow can be quite
large. Table 1 shows a range of suspended solids in combined overflows of
129-930 mg/1. The values shown in Table 1 are averages. The initial peak of
suspended solids can be higher (11) (15) (1*0. Romer and Klashman (16) pre-
sented graphs which illustrate how suspended solids in combined overflows vary
as the flow increases. They reported that, in general, the suspended solids
concentration and the flow reach a maximum value at approximately the same
time. The suspended solids theti begin to fall off rapidly. Stegmaier (17)
has shown that the main increase in solids is of inorganic nature. Initially,
the BOD exerted by the solids will probably be quite large, since the settled
organic material will be resuspended before the inorganics. Hence, the BOD
of combined sewer overflows wi11 initially be quite high with a large portion
of the BOD in the particulate form. This would seem to indicate some sort of
mechanical separation may be very effective in removing BOD during the first
flushes of a storm. Later, as the storm progresses the BOD would be expected
to decrease to levels much lower than those of raw sewage. The ratio of
dissolved to particulate BOD will increase and mechanical separation will
probably become less efficient in removing BOD.
REMOVAL OF SOLIDS BY SCREENING
Bar screens with openings of 1/2 to 1-1/2 inches are used extensively in
sewage treatment plants throughout the United States (18). The amount of
solids removed by these coarse type screens ranges from 0.5 to 6 cubic feet
of wet solids per million gallons of sewage (19)(20). On a dry weight basis,
this represents 9 to 48 pounds of dry solids per million gallons of sewage
(19)(20) or a removal of about 1-6 ppm from the sewage flow. Since raw sewage
contains 200-300 ppm (1)(8)(9) suspended solids, bar screens remove only a
small fraction of the solids, i.e. 0.5 to 2%. This fact is not surprising,
since the primary purpose of bar screens is to remove large and/or floating
solids to protect pumps and other treatment devices downstream of the bar
screens (8)(18).
In general, the approach velocity in the screening channel should not fa)I
below a self-cleaning value (about 1.25 fpm) or should it r{se to values high
enough to force the screenings through the bars (about 3 fps) (8) (18). Head-
losses through the bar racks can be formulated as an orifice loss (8).
h - g(w/b)I|/3 hu sine
where:
h = loss of head in feet
w = maximum width of the bars facing the flow
b = minimum width of the clean openings between pairs of bars
velocity head (in feet) of the water as it approached the rack
the angle of the rack with the horizontal
bar shape factor
6
$
11
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Values for g are 2.42 for sharp-edged rectangular bars, 1.79 for circular
bars, and 0.76 for tear-drop shaped bars (8). Headless through bar racks
Is generally held below one foot by periodic cleaning of the bars. This
cleaning can be accomplished manually or mechanically (8).
Fine screens of 1/16 fnch to 1/32 Inch openings have been used in a number of
locations (19) (20(21)(22) to treat municipal wastes. This size of screen will
removed 2-20% of the suspended solids in raw sewage (9)(18)(19) (20) (21) (22).
Openings of 1/16 inch correspond to a sieve size (Tyler series) of 12 to 20
mesh. Use of standard wire sizes finer than these meshes tend to blind be-
cause of the build-up of animal fats and greases on the screen (23). It has
been reported by Peterson (23), however, that the use of new synthetic mater-
ials for screens has greatly reduced the blinding tendency and allows greases
to be discharged from the top of the screens. He also reports meshes as fine
as 300 have been used when filtering raw sewage. The allowable rates of
filtration, with these extremely fine mesh screens, however, were not reported.
The results of screening raw sewage through a 300 mesh screen showed a reduc-
tion In suspended solids from 196-101 mg/1 or a k8.$% removal (23). This
removal rate is approximately equal to the rates obtained by primary sedimen-
tation of raw sewage (8) (18).
As the openings in .the screen are reduced, the headless increases and screen
blinding becomes very important. This necessitates automatic mechanical
cleaning, which is generally accomplished by backwashing the screen with jets
of water and/or air. Headlosses through fine screens can be calculated from
an orifice type equation.
where:
Q = CA/2g~h
0, = flow (cfs)
A = area (sq ft)(actual open area)
g s gravity constant (32 ft/sec )
C = screen coefficient
h s headless through the screen (feet)
Screen coefficients (C) vary with the size of the screen openings. Values are
generally between 0.3 to 0.6 for 2 to 60 mesh screens. Headlosses through
fine mesh screens are generally held below 2.5 feet (8) by varying the
frequency of cleaning.
There is a very limited mention found in the literature on screening of
combined sewer overflows. Stegmaier (17) and Romer and Klashman (16), however,
have shown that a large portion of the suspended solids in combined sewer over-
flows can be attributed to inorganic materials. This tends to indicate that
fine screening of combined sewer overflows may show a higher percentage of re-
moval of suspended solids than is obtainable when screening raw sewage. Bou-
cher and Evans (2k) have discussed the microstraining process and its applica-
tions in removal of suspended material. They have indicated that miscoscreen-
ing can be effectively and economically used in polishing of sewage effluents.
The Metropolitan Sanitary District of Chicago is reported to be using micro-
strainers for its Hanover Water Reclamation Faci 1 ity. (25). A study by Kefl-
baugh e_t §1 (26) reported up to 98? of suspended solids were removed from a
12
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combined sewer overflow by using a nominal 23 micron aperture microstrainer
screen. However, most of the data published towards the use of microstrainers
in waste treatment has been of investigational nature only, and significantly
more data is needed to substantiate such findings.
DISSOLVED-AIR FLOTATION
An active use of dissolved-air flotation (DAF) in the waste treatment area
has only been made in the last two decades, but the use of air-bubbles to
change the apparent specific gravity of suspended matter in water has been
practiced for nearly a century in the mining industry for the processing of
ores. Selective adsorption was accomplished by the use of flotation agents.
Chase (27) and Rohlich (29) have discussed the developmental background of
dissolved-air flotation. The process as it is used now is an outgrowth of
air flotation methods used in the recovery of paper fibers. The fiber recov-
ery was achieved by the adsorption of an air bubble on the fiber. The floated
material formed a scum and was collected by a suitable mechanism. The pres- .
ence of alum and glue addition aided the separation of fiber by the flotation
process. Dissolved-air flotation utilizes a much smaller diameter bubble
(less than 100 microns) than that used in the mining industry. It is clear
from the above discussion that the removal of suspended matter is accomplished
when there exists sufficient adsorption forces between the air bubble and
sol id particle.
Geinopolos and Katz (29) have discussed solids-liquid separation by dissolved-
air flotation as compared to sedimentation and have indicated that a waste
could be treatable by either sedimentation or flotation, but higher separation
rates and solids concentration may be possible by dissolved-air flotation.
This results in smaller basins, smaller sludge volumes and higher water re-
coveries for treatment by flotation processes as compared to sedimentation.
The mechanism and driving forces involved in the flotation process are similar
to those encountered in sedimentation. Stoke's Law illustrates the mechanism
by the following equation:
V/he re:
V
g
D
u =
V -
Particle separation velocity, ft/sec
Gravity constant, ft/sec
Diameter of particle, ft
Density of particle, Ib/cu ft
Density of liquid, Ib/cu ft
Viscosity of liquid, Ib/ft/sec
In the flotation process, the density of the air-solid combination ?s less
than the suspending medium and value of V becomes negative, causing an upward
particle velocity. Also, the effect of the air-bubble is to increase the
difference in densities between the particle and suspended medium, which in
turn increases the solids separation rate.
13
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Van Vuuren et_ aj_ (30) has reported the use of oxygen produced by algal photo-
synthesis to accomplish flotation. He also cited the applicability of dis-
persed air flotation In conjunction with chemical precipitation in advanced
treatment of wastes (31). Chase (27) has described the types of dissolved-
air flotation processes used for waste treatment. These include pressure and
vacuum types. However, pressure type applications in waste handling far out-
number those for vacuum flotation, primarily because of inherent flexibility
in a pressurized system. The vacuum process is limited by the amount of
reduced pressure that can be effectively used. Geinopolos and Katz (29) state
that the process elements of dissolved-air flotation are:
(l) Flow pressurization
(2) Air Introduction
(3) Air solution
(4) Pressure reduction and bubble formation
(5) Bubble/solids attachment
(6) Solids/liquid separation
(7) Separated solids removal
The literature described variations in the flow pressurizing process (27) (28)
(32) (33). These include: total pressurization, in which the entire volume of
raw waste is 'pressurized, split flow, in which a portion of the raw waste is
pressurized and later blended with the remaining raw waste stream; and efflu-
ent pressurization, in which a portion of basin effluent is pressurized and
later blended with the entire volume of raw v/aste.
The dissolved-air flotation process has been applied to remove suspended
matter from many industrial wastes such as: paper wastes (35), refinery
wastes (28)(36), laundry wastes (37), soap wastes (38), machine shop wastes
(39), automobile wastes (40), and others (27)(28) prior to discharge in a
receiving body of water or resue. Vrablic (34) in his discussion of the fun-
damental principles of dissolved-air flotation mentions that hydrophobic
solids will float much more easily than wi11 hydrophilic ones. In an inves-
tigation of the kinetics of removal of organic matter by activated sludge,
Rohlich and Katz (41) demonstrated that activated sludge floe can be separated
from water by dissolved-air flotation. Ettelt (42) has also shown that
dissolved-air flotation can be successfully employed for activated sludge
thickening. There have been several other reports on the use of dissolved-
atr flotation for dewatering of aerobic biological solids (43)(44)(45)(46).
Proper performance of a flotation unit is dependent upon sufficient air bub-
ble/solids attachment to effect good flotation. Batch laboratory flotation
tests as described by Eckenfelder (47) have been used to estimate the flota-
tion characteristics of wastes for the purposes of design. Howe (48),. in a
mathematical derivation of flotation cell design also recommended that consid-
erable experimentation with each different waste precede the use of his equa-
tions in determining the exact criteria for flotation cells. For sludge
thickening application, air/solids ratio has been used to relate laboratory
data to prototype facilities. A ratio of 0.03-0.10 is considered optimum for
most sludges (34)(4g). However, air/solids ratio for clarification alone is
generally not critical. Truck mounted continuous flow, pilot scale units are
used widely to obtain design information. Primary variables for flotation de-
sign are operating pressure, pressurized flow to raw waste flow ratio, reten-
14
-------
tion period and the combined particle/air bubble rise rate. Generally, the
effluent suspended solids decrease and the concentration of solids In the
floated sludge increase with increasing retention period. For clarification,
a detention period of 15 to 30 minutes Is normally considered adequate in the
flotation zone. Rise rates of 1.0 to 3.0 gpm/sq ft (0.13-0.39 feet/minute)
are commonly employed. The amount of pressurized flow usually varies from
15 to 50?o of raw waste flow for separation. The recycle amount and detention
period are higher for thickening application depending upon feed solids con-
centration. The process pressure may vary from 30 to 70 psig, with 40 psig
considered normal. Air requirements range from 0.5 to 1.0 cu ft of standard
air per one hundred gallons of pressurized flow (32). The air and liquid
are mixed under pressure in a retention tank with a detention time of 1 to 3
minutes.
Addition of chemicals may be employed depending upon the nature of the waste
and the degree of treatment required. Chemicals such as alum, lime and ferric
chloride are usually used in the chemical treatment of a wastewater. The
purpose of chemical treatment is to precipitate and coagulate colloidal and
finely suspended particles to form large suspended floe particles. This in-
creases the separation rate of the solids by flotation. Recent efforts to
improve flotation efficiency by chemical addition have involved use of synthe-
tic organic polyelectrolytes. Generally these polymers have been found to
Improve solids capture (clarification), to increase the concentration of solids
in the float and to Increase the capacity of flotation equipment (50,51,52).
An apparent advantage of polyelectrolytes is the elimination of a separate
flocculation tank, since the floe particles are formed in an extremely short
period of time. Cationic polyelectrolytes have been successfully employed
as flotation aids for thickening applications (^6) (53). The results indicate
that desired float concentrations may be achieved with high solids loadings
when polymers are utilized. Bench scale procedures are normally employed for
determining the dosage and effectiveness of a particular polymer application
In dlssolved-alr flotation.
DISINFECTION OF COMBINED SEWER OVERFLOWS
Disinfection may be defined as destroying those bacteria that cause Infection
or disease. Sterilization, achieved for example at 250°F and 15 psi for 15
minutes, is defined as the destruction of all living organisms (54). Methods
commonly used for disinfection include heat, ultraviolet light, and chemical
addition. Chemicals which have been used include chlorine, bromine, iodine,
potassium permanganate and ozone (8). The various methods and chemicals used
for disinfection which appear applicable to this project are discussed below.
Ultraviolet Light Disinfection
The effect of radiation on bacteria has been studied in detail, and the re-
lationship between wave length and germicidal effect is well known. The
optimum wave length is 2600 angstrom, hence, low pressure mercury vapor lamps
with their high output at 2537 angstrom are effective bactericidal agents
(55). Light of this wave length falls in the ultraviolet section of the
light spectrum. To Insure disinfection, the water should be relatively
15
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free of suspended matter which might shade the organisms against the light
(8). Time and exposure intensity must also be adequate to insure disinfection.
One hundred microwatts per square centimeter of 2537 angstrom light will pro-
duce high bacteria kills at contact times of less than one minute (55)(56).
Use of ultraviolet light for disinfection has found limited application,
probably because other methods of disinfection are more economical (8).
Disinfection by Chemicals
it is widely employed for
may be regulated to
Chlorine has proven so economical and efficient that
its bactericidal action. The chlorination of wastes
accomplish various degrees of bactericidal action. Chlorine is a bacterio-
static agent when applied in small concentrations (2 mg/1), to prevent an
Increase in the bacterial population. Chlorine is a disinfecting agent when
applied in larger amounts (10 mg/1) to destroy fhose bacteria that cause
Infection or disease. Chlorine may be, but seldom is, applied in amounts so
large (2000 mg/1) as to be a sterilizing agent (i.e. to destroy all living
organisms (5*0.
Forms of chlorine which may be used for disinfection and other purposes include
gaseous or liquid chlorine, chlorinated lime, calcium hypochlorite, sodium
hypochlorite, chlorinated copperas, and chloramines. Chloramines, however,
are a slower acting and less active form of disinfectant. Liquid or gaseous
chlorine Is the most commonly utilized form.
The efficiency of disinfection using chlorine or other disinfecting agents
Is dependent on (a) the contact time, (b) the type and concentration of
microorganisms, (c) the pH and temperature of the water, (d) the presence of
interfering substances, (e) and the degree of protection afforded organisms
from the disinfecting solution by materials in which they may be imbedded.
Generally, a chlorine dosage, sufficient to give a 0.5 ppm residual after a
15 minute contact time, is considered adequate for disinfection (5*0. The
actual amount of chlorine added to obtain this residual will vary with the
waste being chlorinated. Fair and Geyer (8) give values of 6 to 2l\ mg/1 for
raw sewage.
Camp (10) indicates screening and chlorination of combined sewer overflows
would be an effective and inexpensive way of treating these flows. Chlorine
dosages were estimated to range from 1.6 to 8.5 ppm.
Symons (57) found the chlorine demand for Buffalo sewage during periods of
combined overflow to range from 6 to 7 mg/1. Considering the possible
quantities of combined sewer overflow, this represents quite a substantial
chlorine dosage, and will require chlorine feeders operating over a very
wide range of flows.
Iodine and bromine were also found to be effective in disinfecting sewage, but
required higher dosages (4-9 times) compared to chlorine (58). Fluorine was
found to be so reactive that it was difficult to store and apply (58).
16
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Potassium permanganate has been used to disinfect water supplies (59)(60), and
is an effective disinfectant at relatively low dosages (59). Use of potassium
permanganate has not been widespread. This is probably due to one or more
of the following disadvantages of potassium permanganate disinfection when
compared to chlorine disinfection.
1. KMNQ^ imparts a purple color to the water which must be removed
before use (62).
2. Most effective pH for KMNO^ is 5-9 which is below the pH of
many water sources.
3« Potassium permanganate is not a good post-treatment disinfectant
because of the color and pH criteria.
Ozone is a very effective disinfectant. This fact is well known and has been
proven over a period of 60 to 80 years (35)(46)(61)(62) (63). Ozone is used
extensively in Europe, especially in France (62). Disinfection by ozone fol-
lows a slightly different pattern when compared to chlorine. Generally, with
increasing chlorine dosage the number of bacteria progressively decrease,
while with ozone little reduction is noticed until a critical dosage is
reached. At this critical value the bacterial population rapidly reduces (35).
Unlike chlorine, the disinfecting action of ozone is little affected by temper-
ature changes or pH. Ozone acts rapidly and is almost 'instantaneous, where
chlorine needs time to be effective (35)(61).
The reason ozone is not utilized to the same extent as chlorine is probably
twofold, i.e., cost and inability to carry an ozone residual for any length
of time. Hann (62) states that, in general, if disinfection is the sole
objective, ozone is more expensive than chlorine. This is largely due to the
sophisticated and expensive equipment required for on-site ozone generation.
When using ozone as a disinfectant, the inability to carry an ozone residual
for significant periods is cited as a disadvantage (35).
When using ozone, proper precautions must be taken in applying the ozone to
insure disinfection (62). The water should be low in turbidity, the ozone
demand must be satisfied, and there must be a residual of free ozone in the
water for a definite period of time. This usually is from 0.1 to 0.2 ppm
ozone residual for 1 to 5 minutes (35)(62).
SUMMARY REMARKS
The material contained in this literature search was compiled in an effort
to uncover the known process elements applicable to the treatment of wastes
similar to combined sewer overflows. The information gained from this litera-
ture search will be used as a guideline for laboratory and bench scale tests
to determine what combination(s) of the various process elements is (are)
best suited to the design, fabrication, and operation of a prototype combined
sewer overflow treatment unit.
17
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I
Although a literature search is technically concerned only with the reporting
of data found in published form, some of this data, for one reason or another
can be eliminated from further consideration without the benefit of labora-
tory testing. As a result, this report comprises a certain number of
engineering judgments and/or evaluations. Such judgments, however, have been
made only where the material available or the investigator's experience have
justified making them. That data which appeared to have genuine value to
the completion of this project has been carried forward to the laboratory
studies portion of the project.
Significant observations from the literature search are summarized below:
1. The flow in combined sewers can increase 50 to 100 times the
dry weather flow.
2. Normal interceptor capacities are between 1.5 to 5.0 times
the dry weather flow.
3- Up to 36% of the sanitary sewage can bypass the interceptor system
during heavy storms.
4. Rainfall intensity greater than 0.015 to 0.05 inches per hour
is generally sufficient to cause combined sewer overflow.
5. Limited data indicate pure storm water can be quite polluted.
6. The majority of the solids settled in the sewer system during dry
weather are not resuspended until the capacity of the interceptor
system is exceeded.
7. It was indicated that the main water usages affected by combined
sewer overflow were commercial fishing, swimming, and public
water supply due to bacterial contamination.
18
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SECTION V
SITE SELECTION AND PRELIMINARY INVESTIGATIONS
SITE SELECTION
A search was conducted to select a suitable demonstration site for the instal-
lation and operation of a demonstration treatment unit. The City of
Milwaukee, as an available source of combined sewer overflow, was solicited
in regard to participating in the demonstration of the proposed treatment
system. The City of Milwaukee responded favorably by offering both access to
a combined sewer as well as providing sufficient land to install the demon-
stration equipment. In addition, the City Engineer's Office was made avail-
able for consultation and aid in selecting the most beneficial demonstration
site.
Six potential sites were investigated.
of Milwaukee as follows:
These sites were located in the City
1. The Edgewood Avenue site, consisting of a 72" combined sewer discharg-
ing into the Milwaukee River.
2. The 27th Street site (south end of viaduct), consisting of a 48"
combined sewer discharging into the Menomonee River.
3. The East Kane Place site, consisting of a 72" combined sewer discharg-
ing into the Milwaukee River.
k. The Bay Street site, consisting of a 90 inch diameter combined sewer
discharging into Lake Michigan.
5. The Russell Avenue site, consisting of a 90 inch diameter combined
sewer discharging into Lake Michigan.
6. The Hawley Road site, consisting of an 8'6" by 5'0" combined box
sewer discharging into the Menomonee River.
The potential sites were appraised and evaluated from the standpoint of
availability for project duration, access to sewer flow, access to utility
sources, space limitations, extent of structural and/or topographical
modifications, proximity to residential or developed areas, drainage area
covered, and the socio-economic nature of the drainage area.
By inspection, the Edgewood Avenue, 27th Street, and East Kane Place loca-
tions were eliminated as potential demonstration sites. The Edgewood Avenue
and 27th Street sites were inaccessible and limited in space. The East Kane
Pi. site was located in a residential and developed area. In fact, the site
19
-------
consisted of a city-owned lot, located between two residences, which were
about thirty feet apart.
The Bay Street, Russell Avenue, and Hawley Road locations were further inves-
tigated as potential demonstration sites. Maps of the respective combined
sewer areas were obtained from the City Engineer's Office in which the
drainage area covered and the socio-economic nature of the drainage area
were delineated. The areas drained by ea.ch of these three sites is pre-
dominantly residential with some local business and industrial activity. ,
The drainage areas covered by the three potential sites were as follows:
Bay Street
Russell Avenue
Hawley Road
385 acres
465 acres
495 acres
The Bay Street location was eliminated because an investigation revealed
that It would be difficult and impractical to impound the flow in the sewer
to provide the necessary raw sewage pump suction conditions.
The Russell Avenue site was eliminated because of a restrictive time limit
placed by Milwaukee County authorities upon the use of the site for project
purposes. It was .felt that the site may not be available for the full dura-
tion of the project.
Since the Hawley Road site appeared to be the most desirable location for a
demonstration unit, additional information was obtained on this sewer and
the area served.
As mentioned above, the total area served by this sewer is 495 acres. The
area is located on the western edge of the Milwaukee City limits. Figure 2
presents a street map of the City of Milwaukee. The outlined portion depicts
the drainage area served by the Hawley Road sewer. The drainage area was
studied using recent (1970) aerial photos. It was determined that approxi-
mately k2% of the area was impervious, i.e., roof tops, streets and parking
lots. This value Is within the range presented in the literature (8) for
North American cities In areas of 1 and 2 family dwellings. The relationship
between runoff coefficient and pervlousness Is presented in Figure 3. The
data In Figure 3 Is based on the City of Milwaukee runoff curves. It may be
seen (Figure 3) that the runoff coefficient for the Hawley Road drainage
area Is 0.40. While it Is recognized that the runoff coefficient can vary as
the storm progresses (8), no attempt was made to refine the runoff coefficient
since an exact number was not critical to this project. The aerial photo-
graph Indicated that the area is a completely developed residential area of
one of the older sections of the city. There is very little open area present
such as parks or fields. All dwellings are of the one and two family variety.
Population density based on number of dwellings per acre and assuming four
persons per family was estimated at 35 persons per acre. There are some small
shops such as jewelry, hardware, etc. No industrial manufacturing facilities
are located within the drainage area served by the Hawley Road sewer. The
one industry which is within the drainage area is Topp Oil and Supply Company.
20
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LOCATION OF UWIT
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They are involved with blending various oils and apparently do not actually
process any oil at this site. A discussion with personnel at the Milwaukee
Sewage Treatment Plant revealed that Topp Oil did not discharge any signifi-
cant pollutional load into the sewage system.
The combined sewer outfall serving the Hawley Road drainage area is rectan-
gular in cross section, 8.5 ft wide and 5 ft high- The relationship between
water depth and flow rate is shown, in Figure k. It may be seen from the
figure that the sewer has a capacity well in excess of 100 MGD. Because of
the location of the sewer and the rectangular shape, a retaining structure
was easily added to impound
ing periods of low rainfall
high retaining structure Is
flow, a volume of about 100
normal overflow has stopped.
tips up as a result of water
the flow. This allowed long test runs even dur-
intensity. Calculations show that if a 3 foot
placed at the combined sewer outfall to retain the
000 gallons can be retained for evaluation after
The retaining structure is a movable dam which
pressure if the sewer begins to surcharge. In
the normal untipped position the dam does not seal the sewer completely and
this insures that the sewer will always be dry prior to any overflow. At a
treatment rate of 5 MGD, this reservoir would allow an additional one half
hour operation of the demonstration system. In actual operation an additional
operating time of only 15-20 minutes has been realized. It should be noted
that the length of operation reported herein includes this 15-20 minute stor-
age factor and hence the duration of overflow is shorter jthan the length, of
run by this time period. The Hawley Road Sewer is fed by two interceptor de-
vices. These interceptor devices are of the sump type. A sketch of the
interceptor device utilized is shown In Figure 5.
Since the Hawley Road Sewer and adjacent land met all the requirements
necessary to successfully complete the demonstration phase of this contract,
arrangements were completed with the City of Milwaukee in February of 1963
to allow use of the sewer and land for this project.
PRELIMINARY INVESTIGATIONS
After the site selection was finalized, 14 overflows were monitored to obtain
information on overflow characteristics, and to provide raw overflow for
subsequent laboratory testing. Results of the laboratory testing program
were then utilized to design the demonstration system. Table 2 presents a
summary of the data collected prior to system design. As was expected, the
range of values is quite large. Suspended solids values from 2153 to 65 mg/1
were observed, and COD values ranged between 1410 and 52 mg/1. The dissolved
organic fraction of the overflows as measured by COD was only 4 to 25% of the
total organic load present in the combined overflow. This indicated that an
efficient solids/liquid separation system should provide high removals of.
pollutants from the raw waste. Coliform density also varied widely from 440
to 26,000 per mi Hi liter.
Laboratory testing which was performed included screen ing ^ chemical oxidation,
flotation and disinfection* Chemical oxidation proved impractical for use 'in
treating combined sewer overflow. Complete details of oxidants utilized,
reaction times and efficiency may be seen in Appendix A.
23
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A summary of the preliminary screening data 5s presented in Table 3. Various
mesh sizes from 50 to AOO (297-37 y openings) were Investigated. The majority
of the tests were run on a 50 mesh-297 y opening screen. The laboratory
test consisted of pouring the sample through the screen into a beaker. The
sample was poured gently to avoid breakup of any particles, and in all tests
a mat of solids was not allowed to form on the screen. This eliminated the
filtering action which could have resulted if a layer of solids was allowed to
form on the screen. It was anticipated that in actual field operation the
screens would operate partially blinded and hence the removal rates would
probably be higher in the field when compared in the laboratory analysis shown
In Table 3. All screen mesh sizes mentioned in this report are Tyler series
mesh. Relationship of opening size to mesh size Is presented in Figure 6.
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28
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Based on the data of Table 3, average removal of suspended solids was 18.6%
for a 50 mesh screen, 32% for 100 to 200 mesh screen, and 51 % for a ^00 mesh
screen. An exception to these figures may be seen in the data from 12/217
67 in Table 3. For this test a 120 mesh screen was utilized and the raw
waste was flocculated with 1 mg/1 of Reten A-l polyelectrolyte. Removals of
COD and suspended solids from this test were 56% and 55% respectively. These
removals were significantly higher than those obtained on the same waste (no
polymer) using a 200 mesh screen, i.e., COD removal and 26% suspended solids
removal (Table 3). These results indicate that flocculation prior to screen-
ing can improve the efficiency of the screens. More detailed data, however,
is needed to verify these results.
Tables k and 5 present the results of the laboratory flotation testing.
Table k indicates those flotation tests which were run on raw overflow and
Table 5 those tests run on screened overflow. The results shown in Table k
indicated extremely high removals of COD and suspended solids may be obtained
using flotation alone in conjunction with polyelectrolyte addition. Bench
scale flotation testing was performed using a standard procedure which is
detailed in Appendix D. Removals of 73 to 95% COD and 38 to 97% suspended
solids were obtained. In Table 5 data on screening/flotation are presented.
All the experiments except 5/20/68 were performed without the addition of
flocculating chemicals. Based on the data presented in Table 5, suspended
solids removals of h\% to 72%, BOD removals of 40% to 62% and COD removals of
42% to 72% were predicted at the 90% confidence level. By.comparing the two
experiments on the overflow of 5/20/63, the effect of chemical flocculant
addition may be seen. Addition of 10 mg/1 C-31, a cationic polyelectrolyte,
caused an increase in suspended solids removal from 61 to 81%, while the BOD
and COD removals increased from 56 and 28% to 63 and k6% respectively.
A summary of preliminary disinfection data collected during the preliminary
sampling period is presented in Table 6. Data from ozone and chlorine dis-
infection are shown. In general, ozone disinfection was not as reliable as
chlorine. Ozone demand for these waters was quite high, and since ozone is
extremely reactive, a residual ozone concentration could not be obtained
except at extremely high dosages (approximately 60 mg/1 or greater).
Inability to obtain small residual ozone concentrations for a short period
of time resulted in the relatively poor E. Coli removals.
Chlorine disinfection on the other hand provided improved disinfection at a
dosage of 10 mg/1. Since chlorine is less reactive compared to ozone, some
chlorine residual could generally be attained. Disinfection efficiency was
better than ozone, but in some tests (April 28, 1968) with high coliform
densities, the effluent had significant coliform indicating incomplete disin-
fection. It appears from this data, as the coliform density increases,
higher chlorine dosages will be required.
29
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CONCLUSIONS PRELIMINARY INVESTIGATIONS
The following conclusions can be made based on the data taken during the
preliminary investigations.
1. Combined Sewer overflow from the Hawley Road sewer contains
primarily particulate pollution.
2. Chemical oxidation is not technically feasible for combined over-
f1ows.
3. Screening/dissolved-air flotation is a relatively effective method
for treating combined overflow.
k. Addition of chemical flocculents greatly increases the removal
efficiency of dissolved-air flotation.
5,
Disinfection with chlorine was found to be more reliable than
with ozone.
33
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SECTION VI
DESIGN AND CONSTRUCTION OF THE 5 MGD SCREENING/FLOTATION
DEMONSTRATION FACILITY
The results of the preliminary sampling and laboratory analysis were utilized
in the design of a 5 MGD demonstration treatment facility incorporating
screening and dissolved-ai r flotation. This section of the report describes
the design criteria utilized, and the features of the demonstration system.
A flow sheet for the system is shown in Figure 7 and a photograph of the over-
all system is shown ?n Figure 8.
DESIGN OF SCREEN
The design of the demonstration unit involved three basic areas, I.e. ,
screen design, flotation tank design and integration of all system com-
ponents. Based on removal efficiencies obtained in the preliminary sampling
phase, a screen mesh of 50 (297u openings) was selected. This mesh gave
fairly good removal of pollutants (20-302) and allowed high flow rates (50
gpm/sq ft) at reasonable headlosses. The screen ts an open ended drum into
which the raw waste flows after passing a 1/2" bar rack. The purpose of the
bar rack Is to remove large objects which may clog the screened solids re-
moval system or damage the screen material, which Is 306 stainless steel.
The water passes through the screen media and into a screened water chamber
directly below the drum. The drum rotates and carries the removed solids
to the spray water cleaning system where they are flushed from the screen.
Those solids which will not adhere to the screen media are picked up by 4
angle iron sections which act similar to a roto-dip feeder and are thus
removed from the flow. Screened water is used for backflushtng the screen.
The drum rotation and spray water cleaning are controlled by liquid level
switches located in the screen chamber. The switches are set to actuate
at a headless of 6" of water through the screen. The solids which are
flushed from the screen along with the spray water are collected in a hopper
inside the drum. This hopper is connected to a drain pipe which forms the
main axis of the drum. The slurry is then routed to waste. Detailed photo-
graphs of the screening system are shown in Figures 9 and 10. These photo-
graphs show the screen, internal hopper, float switches, and drive system.
The basic screen is fabricated from mild carbon steel. The screen backing
material (Figure 9) is a perforated metal plate which has proven to be
adequate support for the screen. Hole size for the backing material is 3/V
x 3/4" on 7/8" centers. This provides 73% open area and only a minimum of
flow restriction. Rotation speed is controlled by a variable speed drive,
which is positioned manually. Rotation speed range is 0.5 - 5 rpm. The
screened water is sealed from the raw waste by compressing a tube between
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Figure 9. Screening system
37
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Figure 10. Screening system
38
-------
the end of the drum and a stationary ring. The sealing arrangement allows
operation at a maximum headless of about 12". Any excess headloss will
allow some unscreened water to enter the screened water chamber and a
possible raw waste overflow from the bar screen chamber. During some runs
with extremely heavy solids loads, the headloss capacity of the screen has
been exceeded. These instances will be discussed in a later section of this
report.
The drum screen is an 8 sided drum with an effective diameter of 7i feet.
The length of the drum is 6 feet. The 8 panels have dimensions of 3' wids
by 6' long. Total screen area is -1M» sq ft. The wetted screen area was a
minimum of 72 sq ft and a maximum of 90 sq ft depending upon the head loss
across the screen.
FLOTATION SYSTEM DESIGN
The dissolved air flotation basin design was based on the criteria utilized
by the American Petroleum Institute (API)(64). The major design parameters
are overflow rate, detention time, horizontal velocity and depth to width
ratio. The design procedures were modified slightly to allow the high
flexibility required in a project of this nature.
The basic principle of dissolved air flotation (OAF) is to produce extremely
small air bubbles (<\00p) which can be attached to the particulate matter
in a wastewater and cause flotation and removal of the particulate matter.
To provide these fine air bubbles a liquid stream is mixed with air under
pressure. The pressure is then released through a weir type diaphragm valve
to form the bubbles. The bubble laden stream is then mixed with the re-
maining wastewater to be clarified in a contained mixing zone within the
DAF tank. This mixing zone has a detention time of approximately 60 seconds.
The bubbles attach to the solids in this mixing zone. The bubble formation
system is termed the pressurized flow system. Generally, the source of
pressurized flow is the process effluent or another relatively solids free
stream. In this project the screened water was used as the source of press-
urized flow. The advantages to this approach eliminate an increase in
hydraulic loading on the DAF tank and provides a simplified plumbing system.
Because of the possible presence of a significant amount of solids in the
pressurized flow stream, a pressure tank without packing material was util-
ized. This avoided the potential clogging problems associated with a
pressure tank packed with some form of tower packing to increase the air
water interface. The type of pressurizatIon utilized in this project has
been termed sidestream-pressurization.
The following discussion will delineate the process steps occurring in the
flotation tank. Screened water is pumped into the pressure tank. Air is
mixed with the water at the inlet to the pressure tank. Water level in the
tank is controlled by a liquid level float switch. A slight excess of air
is always added. If the water level becomes too low the air stream is
vented to atmosphere to allow the water level to rise. Hence, the water
level in the pressure tank is positively controlled. There is a de-
flector baffle in the tank which spreads the incoming water and promotes a
39
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large air water interface for good air solution. The pressure in the tank
Is controlled by an air operated weir valve; this valve provides the proper
back pressure as well as the required shearing action to form the small
bubbles. This valve is controlled by a pneumatic controller. Once the
pressure has been released and the bubbles formed, the bubble laden stream
Is mixed with the remainder of the screened water flow. A 60 second mixing
chamber is provided in the tank prior to entering the flotation zone. This
allows time for bubble/solid attachment. When flocculating chemicals are
utilized they may be added either to the raw flow or to the pressurized flow
after the pressure has been reduced. Generally polyelectrolyte type flocc-
ulants, which require little or no flocculation period are added in the
pressurized flow stream. Once the pressurized stream and remaining raw waste
have been mixed, they enter the flotation zoie of the tank where separation
occurs. A skimming system skims the floated scum into three separate scum
troughs, which convey the scum to ultimate disposal. Generally the solids
concentration of the scum is 1-2% solids on a dry weight basis. This con-
centration flows easily by gravity and does not require screw conveying.
Figures 11 and 12 show various details of the flotation system.
The design of the DAF system was such that a wide range of selected var-
iables could be evaluated in order to be able to recommend design procedures
specific to combined sewer overflow. The following range of variables is
possible with the demonstration system.
Flow rate 1500 - kkOO gpm
Surface loading 2-10 gpm/sq ft
Horizontal velocity 1.30 - 3.75 ft/min
Pressurized flow rate.300 - 1100 gpm
Operating pressure AO * 70 psig
Detention time 1 - kk minutes
In addition to the above flexibility, the flotation tank can be divJded down
the center. This in effect forms two separate flotation tanks. The leigths
of these tanks can be controlled by appropriate baffles. This then allows
the evaluation of two separate overflow rates on the same storm, thus
allowing direct comparison of the overflow rate variable and elimination of
all other possible Interacting variables. The tank was divided as des-
cribed above at the start of the 1970 storm period (April, 1970). The
final as-built dimensions of the flotation tank were 18 feet wide, 8i feet
water depth, and a 65' long flotation zone.
DESIGN OF SUPPORTING SYSTEMS
The appurtenant equipment and tasks necessary to provide a functional de-
monstrating system included site preparation, construction of a manhole and
pumping sump, selection of the necessary flow metering equipment, and design
of suitable electrical and pneumatic control systems.
As may be seen in Figure 8, the system was located under an existing highway
bridge which provided overhead protection. Site preparation involved laying
a concrete slab to provide support for the system tankage. A manhole was
-------
PRESSURE TANK, CONTROL SHACK, AND SCREEN SYSTEM
PRESSURE TANK AND PRESSURE REDUCTION VALVE
Figure 11. Flotation system
-------
HEAD END OF FLOTATION TANK
OVERHEAD COLLECTOR AND EFFLUENT STRUCTURE
Figure 12. Flotation tank
-------
constructed as well as a pumping sump, directly in the combined sewer.
A dam was also provided in the sewer to allow impoundment of a limited
quantity of overflow for subsequent treatment. This dam was designed to
tip under the hydraul i-c pressure of the overflow to prevent surcharging
the sewer. A photograph of the outfall is shown in Figure 13.
Flow metering equipment is provided to measure the influent flow rate, the
volume of screen backwash water and the volume of floated scum. All other
process flows could be obtained by adding or subtracting the proper measured
values. The raw flow and screen backwash are measured via venturi meters
connected to differential pressure gauges which both record and totalize
the flows. The floated scum is measured with an open channel float type
meter, which records and totalizes the flow of floated scum.
The electrical control panel provides all necessary controls for 100%
automatic operation with manual overrides on all systems. Operational modes
will be discussed in a later section of this report. A Merchants Police
alarm is connected to the system so that personnel will be alerted when the
system goes into operation. The system is always (2k hours per day, 7 days
per week) ready to operate, and hence, the maximum possible number of over-
flows can be monitored. Photographs of the control shack are shown in
figure 14.
OPERATION METHODS AND TEST PLAN
Methods and Operational Procedures
The demonstration system previously described was put into operation in May
of 1969. Data reported in Section VII represent data taken during the
.period May, 1969 through November, 1970. During this period 55 overflows were
treated with the demonstration system. The system Is put into operation
automatically when a float switch in the sewer senses an overflow. The
pressurized flow system is immediately put into operation and the raw feed
pump begins to prime. All runs were started with the tank approximately 80%
full of water. The water in the tank was that left from the previous run.
The raw feed pump generally primed in about 12-15 minutes. When primed the
raw pump is activated, and the flow meters, chemical feeder (if utilized),
skimmers and all other auxiliary equipment are put Into operation. At the
end of the run the system shuts down automatically. All variables are then
selected for the next run and the controls positioned. Variables associated
with tank operation include pressurized flow rate, operating pressure, scum
removal cycle, raw flow rate, and chemical dosage.
SAMPLING PROCEDURES
Sampling began when the raw pump primed. Raw waste and screened water
sample collection was started immediately. Effluent sample collection was
delayed for 15 minutes to allow purging of the water in the tank from the
previous run. This procedure insured collection of representative effluent
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samples. Screen backwash and floated scum samples were taken during screen
backwash and scum removal periods.
Sampling during 1969 runs was manual. Equal volumes of raw waste were taken
every ten minutes. Screened water and effluent samples were taken continu-
ously at a rate producing about 2.5 gallons of sample per hour. Screen
backwash and floated scum were composited in equal volumes.
An automatic sampling system was put into operation for all 1970 runs. The
system consists of two timers connected through the proper valving, to
automatically composite the raw waste, screen water and effluent samples.
The first timer controls the sample taking frequency (0-30 minutes). The
second timer controls the duration of sampling time (0-60 seconds). The sam-
pling valves are air operated weir valves. The automatic system has proven
much superior to the manual methods, since the chance for human error has been
eliminated and the operator is free to monitor the remainder of the system.
In general, samples were composited every 5 minutes with the automatic system.
Floated scum and screen backwash sample taking was not automated due to the
problems associated with intermittent flows and heavy solids concentrations in
these process streams. The samples were refrigerated immediately after the
run. Analyses were then started within 0-8 hours. Sample analysis procedures
are discussed in Appendix C.
TEST PLAN
Variables associated with the operation of the demonstration system include
hydraulic overflow rate (gpm/sq ft of tank area), pressurized flow rate,
operating pressure, addition of chemical flocculants, and the floated scum
removal cycle. During the first few runs it was determined that values
for operating pressure and the removal cycle for floated scum were not
critical. A test plan was then initiated with pressurized flow rate,
hydraulic overflow rate, and addition of chemical flocculants as the three
variables. Eight possible combinations of these variables are shown in
Table 7. It was planned to obtain 7 to 8 runs for each variable combin-
ation requiring 56 to 6A separate runs. The demonstration system was
operated on 55 combined sewer overflows. All variable combinations of
Table 7 were fully evaluated except Numbers 3 and k. These combinations
were abandoned based on the results obtained from combinations 1 and 2
which indicated higher overflow rates without chemicals was not feasible.
-------
Table 7. VARIABLE COMBINATIONS UTILIZED
FOR FLOTATION TESTING
Combination
1
2
3
4
5
6
7
8
Pressurized
flow as
% of total
flow
14-20
21-30
14-20
21-30
14-20
21-30
14-20
21-30
Overflow rate,
gpm/sq ft
2.5
2.5
3.8
3.8
2.5
2.5
3.8
3.8
Chemical
flocculants
No
No
No
No
Yes
Yes
Yes
Yes
-------
SECTION VII
SCREENING/FLOTATION OPERATING RESULTS (1969-1970) AND DISCUSSION
suspended solids con-
days of a previous over-
CHARACTERIZATION OF RAW WASTE
As was expected, the quality of the combined sewer overflow from the Hawley
sewer varied widely. In 12 of the 55 overflows reported herein, extremely
high poHutional values were observed. These first flushes persisted for
20 to 70 minutes. A summary of the first flush data may be seen in Table
8. The range of the data presented is at the 35% confidence level. First
flush occurence appears to be associated with the length of time between
overflows and the intensity of the overflow. The
centration for those overflows occurring within k
flow were calculated to be 151-^29 mg/1 while the suspended solids for those
overflows occurring at an interval larger tnan h days were found to be 3*»9
+_ 80 mg/1. Comparison of the COD data at intervals shorter than k days and
longer than k days produced CODs of ]kk +_ 21 and 39*» +. 72 mg/1 respectively.
These values are at the 95% confidence level. All the data was tabulated
as a function of the interval between overflows. (Table E-10, Appendix E.)
This data indicates that essentially all overflows which exhibited the first
flush phenomenon occurred at intervals of k days or longer between overflows.
However, all overflows occurring at an interval of greater than 4 days did
not exhibit the first flush phenomenon. Table 9 illustrates this point. All
overflows which occurred at intervals of greater than k days are presented
in Table 9 along with data on rainfall intensity and total rainfall. A
total of 23 overflows occurred at intervals of greater than k days between
overflows. Of these 23 overflows only 12 exhibited the first flush pheno-
menon. It may be concluded from this data that the length of time between
overflows is related to the occurrence of first flushes and there are
obviously other variables which strongly influence this phenomenon. These
variables could include: the dry weather flow variation, the intensity of
rainfall and runoff and the sewer system interceptor capacity. Furthermore
the data presented herein may be biased by the 12-15 minutes which was
required to prime the raw pump for the treatment system in that extremely
short time flushes would not have been detected.
A satisfactory method for measuring the rate of flow in the sewer has not
been developed. Development of a method has been complicated due to the
presence of the dam, which was placed in the sewer to impound the flow.
This dam backs water up past one of the two interceptor devices feeding
the Hawley Road sewer. This makes single point gauging impossible. Another
complication which arises is the fact that the dam Is not stationary. As
-------
Table 8. SUMMARY OF FIRST FLUSH DATA3
(95% Confidence Level Range)
Analysis
COD
BOD
Total sol ids
Total volatile sol ids
Suspended solids
Volatile suspended solids
Total nitrogen
Ortho phosphate
PH
Coli form density
Concentration, mg/1
581 ± 92
186 ± 40
861 ± 117
489 ± 83
522 ± 150
308 ± 83
17.6 ± 3.1
2,7 ± 1.0
7.0 ±0.1
142 ± 108 x 103 per ml
a. Data represents 12 overflows
49
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Table 9. SUMMARY OF DATA AT INTERVALS OF
GREATER THAN 4 DAYS BETWEEN OVERFLOWS
Run
no.
691
695
6911
6912
691 4
6916
6919
702
708
7011
7013
7022
6918
6922
6923
6925
6928
707
7010
7014
7017
7019
7020
Days
between
overflows
18
15
8
5
6
12
24
26
9
14
12
19
11
17
6
11
19
7
11
6
8
18
15
Fi rst
flush
occurrence
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
No
No
No
No
No
No
Average
rainfal 1
In tens i ty ,
in/hr
0.13
0.32
0.40
0.70
0.35
0.40
1.2
0.17
0.84
0.17
0.80
0.10
1.6
0.3
0.5
0.1
0.4
0.11
0.18
0.36
0.15
0.24
Total
rainfall
inches
0.42
0.25
0.50
1.00
0.17
0.10
0.10
0.3
0.14
0.25
0.20;
0.15
0.45
0.10
0.5
0.17
0.12
0.30
0.33
0.22
0.30
0.23
0.25
50
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the flow increases the dam tips to prevent sewer surcharge. This causes
large fluctuations in water level. Down stream of the dam the sewer has a
dog leg and extreme turbulence has been observed at the mouth of the sewer.
Because of the above discussed difficulties reliable data on the total
flow rate in the sewer was not obtained. However, lack of total flow data
does not in any way influence the operation of the demonstration system.
Data on rainfall was obtained routinely and runoff rate estimates were made
using the rational method. These runoff rates were then plotted against the
suspended solids in the overflow. A result of this plot is presented in
Figure 15. It appears from Figure 15 that there was no relationship between
flow rate in the sewer and the suspended solids in the overflow. This is as
expected, since once the sewer system and drainage basin has been thoroughly
flushed, the rate of flow should not have a significant effect on overflow
quality. However, since actual sewer flow rates were not obtained, a
positive conclusion cannot be made.
After the flushes had passed (if they were present), the characteristics of
the overflow became remarkably stable, considering the large variations
present in the first flushes. The end of the first flushes was determined
by visual observation of the raw combined overflow. The screen backwash
ran continuously during periods when high suspended solids were present in
the raw feed. Thus when the screen backwash pump began cycling the end of
the first flushes was indicated. The exact length of the first flushes
was not recorded. A summary of all data other than first flushes (termed
extended overflows) is presented in Table 10. The data of Table 10 show
a relatively small range of values at the 95% confidence level. The data
compared well to data from other research on combined sewer overflow (6)
(11) (12)(13)(14)(65)(66). The pollutant levels in the extended overflow
are about what is expected from a very weak domestic sewage. One major
difference is the BOD value of 49 mg/1. This is quite low compared to the
COD value of 161 mg/1. Generally, the BOD:COD ratio of domestic sewage is
in the range of 0.6 (67). The dissolved solids in combined overflow is
also quite low. Total dissolved solids (TDS) based on the data of Table 10,
is 212 mg/1. Milwaukee tap water is about 160 mg/1. This represents only
about 42 mg/1 TDS increase as compared to ~700 mg/1 usually added when water
is used and discarded as domestic sewage (8).
Of particular interest to this project is the amount of organic material
present in the dissolved state. Table 11 presents data on this relation-
ship. The amount of dissolved COD ranges from 30 to 38% of the total COD.
The dissolved TOC ranges from 26 to 42% of the
are somewhat higher than those obtained in the
of 4-25%. The cause of this difference is not
portion of the overflow will not be removed in
system, unless it is chemically precipitated.
efficiencies will be expected as the dissolved
increases.
total TOC. These values
preliminary sampling phase
known. The dissolved
the screening/flotation
Hence, lower removal
fraction of the waste
A discussion of the results of the operation of the demonstration unit
follows. A discussion is divided into three phases: screening operation,
51
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Table 10. SUMMARY OF EXTENDED OVERFLOW DATA
(95% confidence level range)
Analysis
COD
BOD
Total solids
Total volatile solids
Suspended solids
Volatile suspended solids
Tota1 nit rogen
PH
Coliform density per ml
Concentration, rng/1
161 ± 19
49 ± 10
378 ± 46
185 ± 23
166 ± 26
90 ± 14
5.5 ± 0.8
7.2 ± 0.1
62.5 ± 27 x 103
a. Data represents 44 overflows
Table 11. PARTICIPATE & DISSOLVED RELATIONSHIPS
(95% confidence level)
Relationship
Dissolved COD/Total COD
Dissolved TOC/Total TOC
Dissolved TOC/Di ssol ved COD
Total TOC/Total COD
No. of
samples
34
13
14
17
95% Confidence level
0.34 ± 0.04
0.34 ± 0.08
0.36 ± 0.02
0.33 ± 0.05
53
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flotation tank operation and disinfection. Because of the wide range
of pollutional values obtained In the raw waste, the removals through
various processing steps are presented as percentage removals. Absolute
effluent water quality data may be seen in Appendix E, Tables E-6 and E-7.
Absolute effluent quality can also be estimated by applying the observed
percentage removal figures (Table 12 and 13) to the raw overflow water
quality presented in Tables 9 and 10.
RESULTS OF THE SCREENING OPERATION
Table 12 presents a summary of the data on removal of pollutants by
screening alone. A listing of all data collected is presented in Appendix
E, Tables E-4, E-5 and E-6, Generally, the percent removals during the
first flush were in the range of 30 to kQ%. The confidence band is wide due
to the relatively small number of first flush overflow occurrences. During
the first flushes a mat of solids sometimes covered the entire screen. This
mat acted as a fine filter medium and undoubtedly, increased the removal
efficiencies as compared to a clean screen. Unfortunately the headloss
Increased greatly as the mat formed and in runs 695, 6911, 6912, 6914, 6916
and 702, the headloss capacity of the screen was exceeded for brief periods
of time. Examination of these runs Indicated that the screen was removing
about 200 mg/1 of suspended solids which was equivalent to 4,9 pounds of
dry solids per minute. Based on screen rotation speed and area, this amounts
to a solids loading of approximately 1.2 pounds of dry solids removed per
100 sq ft of screen area. This number represents the critical level of
solids loading at which a headloss of 14 inches will be exceeded.
This value of solids loading is specific for a 14 inch headloss across the
screen. The loading could possibly be increased by increasing the allowable
headloss differential. This could, however, cause a decrease in removal
efficiencies by forcing more solids through the screen and/or cause a break
up of solids which could affect the efficiency of the flotation process.
The hydraulic flow rate was in the range of 40-45 gpm/sq ft.
depending upon solids loading, could probably be increased.
This rate
The design of the screening system should be based on both hydraulic flow
rate and solids loading rate. Either of these variables could control
screen design depending upon waste characteristics.
During the extended overflows and after the first flushes had passed,
removal efficiencies dropped to the 20 to 30 percent levels (Table 12).
The probable cause of this decrease is that essentially no solids mat
formed during extended overflows, and hence, no added filtering action was
obtained.
The screen was backwashed with water from the screened water chamber via
a pressurizing pump. Spray nozzles with 1/4" diameter orifices were used
to effectively distribute the water oveT the screen media. Washing was
54
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Table 12. .POLLUTANT REMOVALS BY SCREENING
(35% confidence level)
Pollutant
COD
BOD
Suspended sol ids
Volatile suspended solids
Removal during
first flushes, %a
39 ± 15
33 ± 17
36 ± 16
>
37 ± 18
Removal during ,
extended overflows. %
26
27
27
34
± 5
±5
±5
± 5
a. Represents 8 overflows
b. Represents k6 overflows
(See pages 5^-55 for discussion).
55
-------
performed from outside the screen drum. Some problems were encountered
with nozzle plugging due to an inefficient seal on the drum screen. The seal
has been improved significantly, but it is still recommended that an in-
line small hydraulic cyclone be utilized on future designs to eliminate
any operational problems. The volume of screen water required is approx-
imately 100 gallons per minute. Continuous washing of the screen would
therefore require about 3% of the raw waste flow. Actual spray wash
requirements were in the range of 0.7 to 1.0 percent of the raw flow, since
the screen wash did not run continuously during operation. Screen wash
quality was in the range of 500 to 3000 mg/1 suspended solids (Appendix E -
Table E-90). Good media cleaning was always obtained and no permanent
media blinding was experienced. In general, operation of the screen was
very satisfactory.
OPERATION OF THE FLOTATION SYSTEM
Overall contaminant removals using the screening and flotation systems are
presented in Table 13. A 1isting of al1 data is presented in Appendix E,
Tables E-12 and E-13- During the first flushes, removals of BOD and COD
were in the range of 55 to 65 percent,while suspended solids removals were
70 to 75 percent. Removals of nitrogen were significantly lower at about
kf> percent. In those first flush runs where flocculating chemicals were
added the optimum chemical dosage was generally not obtained, since the
pollutant levels were significantly higher compared to extended overflows.
This difficulty illustrates the need for some type of control system which
would automatically adjust the chemical dosage depending upon the raw feed
water quality.
Removals during extended overflows were generally lower than during first
flushes. Removals also varied widely Hepending upon whether flocculating
chemicals were utilized. Table 13 presents various pollutant removal
efficiencies for three different categories, i.e., without chemical
flocculant addition, with polyelectrolyte (Dow C-31) and clay addition,
and with polyelectrolyte (Dow C-31) and ferric chloride addition.
Figure 16 presents a probability plot of suspended solids removal for the
1969 data. The slope of the probability line shows a distinct change at
about 50% removal. This change in slope indicates some operating variable
was affecting the removal rates and caused a change in the normal dis-
tribution of the data. This change was chemical flocculant addition.
Examination of the data more closely indicated 10 of \k runs without
chemical addition were below 52% suspended solids removal, while 10 of 13
runs with chemical addition were above 52% removal. Removals of volatile
suspended solids show trends similar to suspended solids removals.
The effect of optimizing the chemical treatment scheme is clearly illus-
trated in Table 13. Suspended solids and volatile suspended solids
removals increased significantly by varying the chemical addition from
polyelectrolyte and clay (1969 data) to polyelectrolyte and ferric chloride
56
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58
-------
(1970 data). The chemical dosage required to provide consistent removals
was found to be 20 mg/1 ferric chloride and 4 mg/1 polyelectrolyte. The
ferric chloride is added to the raw waste water flow prior to screening
and the polyelectrolyte is added to the pressurized flow stream prior to
mixing with the remainder of the screened waste flow.
The BOD and COD data also indicate increased removals when chemical
flocculants were added. An exception to this observation is the COD
removal data with and without chemicals for the 1969 overflows (Table 13).
It is felt that the small decrease in COD removals was due to an increase
in the dissolved organic fraction of the raw combined overflow. During
late summer and fall leaves and other decaying organic material can cause a
substantial amount of organic material to be converted to the dissolved state.
This was very evident In run number 6919 as the appearance of raw waste after
filtering was quite yellow. Run numbers 6928, 6929 and 6930 also had a very
high dissolved fraction. This increase in dissolved organics resulted in
the small decrease noted when chemical flocculants were added, since dis-
solved organic removals can be accomplished only by precipitation.
Apparently, the dissolved organic material was not exerted as BOD (5)
possibly due to unacclimated organisms and BOD removals were therefore not
affected to the same degree as COD removals.
A summary of removal efficiencies for particulate organic material is
presented in Table 14. It .may be seen that during the 1969 runs, numbers
6923 through 6929, particulate COD removal ranged from a high of 96% to a
low of 34%. It is obvious from the spread of the data that effective
coagulation was not always being achieved. During the 1970 runs (700 Series)
particulate COD removals were much more consistent reflecting the improved
chemical treatment system, I «e. , ferric chloride and polyelectrolyte
addition. The average particulate COD removal efficiency for the 1970 data
was 76+8% at the 95% confidence level. This value compared closely to the
suspended solids removals for the 1970 data of 7H9% (Table 13) thus
indicating that effective chemical treatment was generally obtained during
the 1970 overflows. There are, however, some overflows (7012, 7014, 7015,
7023) where the particulate COD removals were below the 95% confidence range.
This further illustrates the need for some type control system for metering
the chemical addition.
Removal of dissolved organic compounds can only be obtained by precipitation
of the material or absorption on the flocculated particles obtained when
polyelectrolyte or other flocculating chemicals were added to the raw waste
stream. Removal of dissolved COD for those runs, where data is available,
is presented in Table 14. As expected, removal of dissolved COD was
erratic and ranged from no removal to a high of 43% removal. Generally, the
removals were in the range of 20 to 25%. Other chemical flocculants may
give slightly improved removals, but 20-30% removal of dissolved organics
?s all that can be expected in a screening/flotation system.
It has been determined from laboratory studies that a flocculation period
may further improve the removal efficiency of the flotation process.
An important variable in the operation of a d?ssplved-air flotation system
59
-------
Table 14. SUMMARY OF PARTICULATE AND DISSOLVED
ORGANIC REMOVAL EFFICIENCIES
Run
tt
6923
6924
6925
6926
6927
6928
6929
704
705
706
707
708
709
7011
7012
7013
7014
7015
7016
7018
7019
7020
7021
7022
7023
7024
7025
C-31,
mg/1
6.0
0
0
2.7
0
3.0
3.0
6.0
6.0
6.0
6.0
6.0
4.2
5.3
3.9
4.6
3.5
4.5
4.5
4.5
4.5
3.8
3.8
°'5b
0.5°
0.5b
4.0
a. Overflow rate ^2.5
b. Herco floe
810 used
Chemical dosage
Fed,,
mg/1
0
0
0
0
0
0
0
0
0
0
0
o
30
17
16
16
21
21
21
21
21
18
18
15
15
25
25
gpm/sq ft
for these overflows
Clay,
mg/1
6
0
6
0
0
0
3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
' 0
Particulate
COD
removal ,
%
54
34
86
33
73
57
39
63
95
95
74
85
88
87
53
80
42
50
93
87
77
81
91
88
48
78
69
Dissolved
COD
removal ,
%
+2
+ 14
+25
+22
+23
+23
+23
+ 11
0
-2
+ 10
-3
+20
+27
-19
+30
+31
+29
+4
+8
+33
+40
+24
+43
+21
-3
+22
60
-------
Is the volume of pressurized flow required to supply sufficient air bubbles
for proper process operation. For a given volume of liquid, the number
of bubbles and their size will be a function of the operating pressure.
Generally the greater the pressure, the larger the volumes of air dissolved
and the smaller the size of the bubbles. There is of course a limit to
the benefit to be gained by increasing operating pressure. Pressurized
flow volumes generally .utilized are in the range of 15~50% of the raw waste
flow. Table 1k presents a comparison of pressurized flow ratios utilized.
Rates from 13 to 22% of the raw flow were considered low values while rates
from 23 to kk% were considered high values; The data Is further segregated
into those runs with and without chemical, flpcculant addition. A compar-
ison of means test (68) was performed on the high and low pressurized flow
values of Table 15. The procedure for performing this test may be seen
in Appendix E. The results of this comparison indicated there was no
statistically significant difference between suspended solids removals for
low or high pressurized flow whether or not chemical flocculants were
utilized.
It appears, considering all data, that a pressurized flow value of 20% of
the raw flow will be sufficient for dissolved-air flotation operation on
combined sewer overflow. A slight increase in pressurized flow may be
required if the improved efficiencies predicted in the laboratory are
obtained in the field, since a larger volume of solids will require
floating. Air requirements based on a 20% pressurized flow system would
be 1.4 SCFM per million gallons per day of raw flow capacity. An oper-
ating pressure of 50 psig provides sufficient air solution and a small
enough bubble size to be effective without requiring excessive pressure
drops at the pressure reduction value.
Another variable which can significantly affect the removal efficiencies
.of a dissolved air flotation system is the overflow rate, i.e., gpm/ sq ft
of tank area. Removal data presented In Table 13 were all at the over-
flow rate of approximately 2.5 gpm/sq ft.
To allow for a study of higher overflow rates, the flotation tank of the
demonstration system was partitioned as shown in Figure 17 for all 1970
runs. All process elements up to the point of entering the flotation
zone were identical to the 1969 runs. A longitudinal baffle was placed
the entire length of the tank. This had the effect of producing two
separate flotation zones. Lateral baffles were then placed at one-half
the length of the tank on side one and at two-thirds the length of the
tank on side two. Effluent samples were taken just as the water flowed
under these baffles to insure collection of a sample representative of
the portion of the tank being utilized. The unshaded area of Figure 17
represents the unused portion of the tank. The raw flow as It enters
the flotation zone is split into equal volumes. Since the effective
length of each side of the tank is different, two overflow rates are thus
obtained on the same storm. This completely eliminates the effect of any
interacting variables like pressurized flow, chemical addition, and the
differences inherent in any two combined overflows, allowing direct
determination of the effect of overflow rate.
61
-------
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63
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Data taken on direct comparison of overflow rates are presented in Table
16. The data indicates removal efficiencies decrease as the overflow rate
Is increased. Data from each run is presented, as well as average values
for low and high overflow rates along with the 95% confidence range. By
comparing the mean values, removal efficiency decreased approximately
5-14% as the overflow rate increases from "2.5 to 3.75 gpm/sq ft. A
paired comparison test (Appendix E) was also run on the data of Table 16.
The results of this test indicated that there was a difference in the low
and high overflow rate data. Confidence levels at which the difference
was significant are as follows: COD - 90%, BOD - 95%, suspended solids
99% and volatile suspended solids - 95%. It is anticipated that at
higher overflow rates the decrease in removal efficiencies will be even
greater.
Of considerable importance in the operation of a screening/flotation system
is the volume of residual solids produced during operation. Volumes of
floated scum generated during operation of the demonstration unit ranged
from 0.75 to 1.41 percent of the raw flow at the 95% confidence level.
Scum concentration was generally in the range of 1 to 2% solids on a dry
weight basis (Appendix E, Table E-9). The floated scum and screen wash-
water from this project are disposed of via an interception sewer which
directs them to the sewage treatment plant for ultimate disposal. Since
gravity flow is utilized it is desirable to limit the sludge concentration
to about 2% as this concentration easily flows by gravity. Higher con-
centrations can be obtained by skimming the floated scum blanket at less
frequent intervals. Sludge concentrations as high as k% solids have been
obtained in this manner. Obviously the higher the concentrations, the
smaller the volume of sludge produced for ultimate disposal. For this
reason it is felt that in full scale operations sludge volumes will be
somewhat less than those obtained during this study. Another factor,
which will offset this reduction in scum volume, is the addition of more
effective chemical flocculants. As the chemical flocculant addition is
optimized, the volume of scum will increase due to the additional chemicals
added and the higher efficiency of solids capture.
Ultimate solids disposal will dictate the desired solids concentration in
the floated scum and, hence, the volume of scum which requires disposal.
If scum is disposed of by way of an interceptor sewer a solids content in
the range of 1-2% will be desirable. This should result in an average
scum plus screen wash volume of 1.75 percent of the raw flow. If disposal
Is by tanker truck or solids dewatering at the site, a high solids con-
centration is desired (4%), and the volume should be less than 1 percent
of the raw flow.
During the operation of the demonstration system some settled sludge was
noticed. The amounts of settled sludge were, however, extremely small,
with one exception. Runs number 691 and 692 were made without using the
drum screen. Upon draining the tank after run number 692, about 4-6" of
settled material was discovered. This consisted of grit, twigs and other
material which could not be floated. Later in the year the tank was again
drained after 13 additional runs which were all made with the screen in
service. Settled sludge volume amounted to only 2-3 inches at this
64
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-------
draining. This clearly demonstrates the value of the screen In removing
heavy participate matter which cannot be floated in the flotation tank.
The tank was again drained at the end of the 1969 season and sludge volumes
were again only 2-3 inches. It may be concluded that bottom skimming
systems are not required when screening precedes flotation. If, however,
applications arise where flotation is used alone, it is imperative that
some type of bottom skimming be provided or large sludge blankets will form
which will eventually scour into the effluent.
Material balances for suspended solids were made for almost all runs. The
tabulated data may be seen In Table E-l*», Appendix E. The balance of solids
in and solids out of the system generally totaled within about 25%. In
some cases, however, the error was higher. The probable reasons for the
material bal?nce errors are believed to result from scum sampling and
collection procedures. At the end of a run, the floated scum blanket which
remained on the tank was lost with respect to material balances. Generally
this scum was skimmed off after the run when the scum meter was not total-
izing. It was also difficult to obtain a representative sample of scum,
since scum was scraped intermittently and the solids concentration could
vary widely from the beginning to the end of the skimming cycle. Scum
samples were taken manually and if other operating problems arose, a scum
sample from every skimming cycle may not have been obtained. Because of
the sampling procedures it is felt that scum suspended solids concentrations
were not representative. Since suspended solids in the scum could account
for a significant portion of the solids balances, it is felt that these
errors contributed to a large extent In the material balance discrepancies.
OPERATIONAL DIFFICULTIES
Difficulties were also experienced with the raw flow meter totalizer. The
units on the totalizer were 30,000 gallons per count and thus could not be
read accurately. The totalizer has subsequently been changed and thus
this problem eliminated. Another possible source of material balance error
is the fluctuating concentration of the raw overflow. Limited data has
been collected to indicate that the pollutant concentration can vary
significantly during an overflow. This variation could introduce errors
in the material balance.
The following discussion will be limited to those problems which were encoun-
tered and the method of solution. Some difficulties were encountered with the
float switches utilized in the. system. These switches are the reed type which
are activated by a sliding float. They required frequent cleaning, once per
week, as sand would work its way between the float and the shaft and cause
the float to become inoperable. Replacement of this type of switch with a
conductivity type should solve this problem.
Difficulties were also encountered with the back pressure control valve on
the pressurized flow system. This problem resulted from excess moisture
In the compressed air. All problems were in the positioner for the valve
which accepts a 0-20 psi control pressure and positions the valve accordingly
66
-------
The positioner was utilized only because of the design flexibility required in
a demonstration system. In the full scale applications when the pressurized
flow rates are known, valve positioners will not be required and the problems
incurred will be eliminated.
A minimum amount of difficulty was experienced with the chemical metering
pump, but this was a result of improper materials selection and the
difficulties were easily eliminated. As may be concluded from the above
discussion, the operation problems encountered were minimal and this attests
to the soundness of the system design.
DISINFECTION OF COMBINED OVERFLOWS
Another important aspect in the treatment of combined sewer overflows 5s
adequate disinfection. The screening/flotation system provides sufficient
detention time (12-20 minutes) to obtain the necessary chlorine contact time.
The system also is flexible in that various points of chlorine addition are
available depending upon process needs. A summary of the disinfection data
taken during the project is presented in Table 17. Hypochlorite salts were
utilized as a source of chlorine. Dosage was held essentially constant at 10
mg/1. It was noticed, however, that the strength of the ch-lorine stock
solution could decrease rapidly depending upon environmental conditions. .
Therefore, some of the storms could have had dosages less than 10 mg/1. In
general, relatively good disinfection was obtained. A trend seems to exist
in Table 17 which indicates that as the coliform density increases the
absolute coliform density in the effluent also increases. Nevertheless
good disinfection can be obtained in conjunction with the operation of a
screening/flotation system.
CONCEPTUAL DESIGN
This portion of the report deals with the design concepts necessary to
utilize a screening/flotation system on a full scale basis for treating
combined sewer overflow. It is not the intention of this discussion to
provide specific answers to all design details. Sufficient information
will be presented to form a basis for process design. Various engineering
considerations and/or judgements must be provided to produce the final
overall system design.
The overall system can be divided into various subsystems and these
subsystems are listed and discussed below:
1> Pumping system
a. Self cleaning bar screen
b. Pump pit
c. Variable rate pumping system
2. Screening/flotation system
a. Drum screens
67
-------
Table 17. SUMMARY OF DISINFECTION DATA
Run
no.
695
696
697
698
699
6910
6911
6912
6913
6919
6920
6921
6922
703
704
706
707
708
Chlorine
dosage,
mg/1
10
10
10
8
10
10
10
10
10
10
10
10
10
10
10
10
10
10
Point
of
addition3
PF
PF
PF
PF
PF
PF
PF
PF
PF
EFF
EFF
EFF
EFF
INF
INF
INF
INF
INF
Detention
time,
min
20
20
20
20
20
20
20
20
20
10
10
10
10
21
21
21
21
21
Influent
Col Iform pep
100 ml x 10-*
36
5,7
1.3
7.8
6.2
19
20
65
38
310
160
55
82
270
1 2.2
0.7
3^0
110
Effluent
Col i form
per 100 ml
<100
<4
<4
<4
2
<2
10
<5000
<5000
60,000
40,000
<7
15,000
<1000
<100
200
3800
18,000
a. PF - Chlorine added in pressurized flow line
EFF « Chlorine added to effluent from flotation basin
INF - Chlorine added to raw waste prior to bar screen
Note: Samples were dechlorinated when necessary using Na_SO .
68
-------
b. Pressurized flow system
c. Sludge collection
d. System tankage
e. Flocculators
Solids slurry storage
a. Mixers
b. Transfer system
c. Dewatering (if required)
Chemical addition
a. Chemical storage
b. Mixing system
c. Metering pumps
d. Disinfection
PUMPING SYSTEM
The pumping system is obviously a vital subsystem in the overall treat-
ment concept. It is envisioned that a sump will-be utilized to provide
the necessary pump suction conditions. A self cleaning bar screen will
be utilized just up stream of the sump to remove large objects which will
not pass the pumps and/or could cause problems down stream in the treat-
ment system in such areas as the drum screens or sludge removal systems.
Bar spacing is recommended at 1/2" as this value proved adequate in the
demonstration system. A medium duty bar screen will have sufficient
strength to handle the imposed solids loading.
The pumping system must be able to handle the variable rates which will
be encountered during operation. The pumps therefore must be controlled
automatically to vary the pumpage as the raw flow varies. There are
numerous pumping system configurations of this type which have been
employed in the past for storm water pumping, municipal waste'treatment
and industrial processing. Many pump manufacturers offer package pumping
systems (69) which would meet the required design considerations. There-
fore no detailed information on pump station design will be presented herein.
It should be noted however that open type screw pumps seem to be ideally
suited to combined sewer overflow treatment systems, since they can provide
variable flow rate from a constant speed motor. Since any system must be
designed for a specific hydraulic flow rate, an overflow structure should
be provided for the pumping system. Considerations involved in overflow
design should include utilization of the sewer system for maximum storage
of raw overflow. This will provide a damping effect on t'le raw flow rate,
and minimize control problems in the treatment system. Proper design of
the overflow will provide satisfactory treatment system operation with a
minimum of excess overflows. Provisions should also be made for sump
cleaning, since large volumes of gravel and grit are anticipated. Overall
pump system design should provide for ease of cleaning and maintaining the
69
-------
pumps. No problems were encountered during operation of the demonstration
system with regard to feed pumps. The demonstration system, however,
had only a single feed pump and the flow rate did not vary during operation.
Since the screening/flotation system can function at overflow rates higher
than the design value, the pumping system should be designed with this
fact in mind and sufficient capacity should be provided. A pumping
capacity of one and one-half the flotation design capacity should be
provided, since the flotation unit can handle this additional volume for
short periods with only moderate decrease in removal efficiencies.
It may be possible in some applications to utilize gravity flow. In this
case only sluice gates will be required to direct the raw flow to the
various screening/flotation modules. The gates .should be automatically
positioned to provide proper control. Consideration of head loss across
the screen becomes more critical when contemplating a gravity feed design.
It may also be possible in some applications to utilize gravity feed and
effluent pumping. This approach should provide the most maintenance free
pumping system since the effluent water will be low in suspended solids.
When gravity feed systems are utilized, a sump or stilling basin will
still be required to provide proper hydraulic control, and the bar screen
is also required for system protection. Grit accumulations are expected
to be greater in the gravity flow systems, since turbulance from the pump'
suction will not be present.
SCREENING SYSTEM
The screening syrtem consists of basically two sections, the drum screen
and the backwashlng system. The critical design parameters associated
with the drum screen include hydraulic loading, solids loading, and head
loss capability. The hydraulic loading is a function of the wetted screen
area. This area varies only slightly as the head loss across the screen
Increases during operation. The hydraulic loading is not affected by
rotation speed. Generally a drum screen can operate with up to 70% of
the screen surface submerged. Higher submergence is not recommended due
to possible flooding of the backwash water removal hopper. Hydraulic
loading in the range of 25-45 gpm/sq ft of screen area was utilized in
the demonstration system for a 50 mesh, 297y opening, screen media.
A hydraulic loading of 40 gpm/ft and a screen size of 50 mesh are
recommended at this time.
Drum rotation speed controls the solids loading on the screen. It was
found during this study that a solids loading of 1.2 pounds of dry solids
removed per 100 sq ft of screen media produced a head loss of about 13 inches
of water. Drum rotation speeds were in the range of 1 to 5 rpm. Solids
loading may be calculated with the following equation:
70
-------
where:
L = Solids loading per 100 sq ft
R = Screen removal efficiency (%)
F = Feed solids into screen (Ibs per mln)
r - Drum rotation speed rpm
A = Total surface area of screen
As may be seen from the equation, solids loading is directly proportional
to solids removal efficiency and inversely proportional to drum rotation
speed. A removal efficiency (R) of 35% is recommended based on the results
obtained in the demonstration unit. Drum rotation speeds of 2 to 12 rpm
are also recommended.
It is apparent that selection of drum area is controlled by two criteria;
hydraulic loading and solids loading. Either of these two variables may
control the screen area requirements. If a solids loading of 1.2 Ibs per
100 sq ft is utilized, resulting head losses will be in the range of 12 to
1A inches of water. Higher head losses and subsequently ^higher solids
loadings may be possible without a significant effect on 'process efficiency.
The inside of the drum should be fitted with an angle iron system (similar
to a roto-dip feeder), which will pick up any solids which will not adhere
to the screen media and would not be carried up to the spray washing
system.
The screen cleaning system consists of a pump, a header system and spray
nozzles. A hopper inside the drum collects the material as it is flushed
from the screen. Required screen wash water rates amount to 15 gpm per
foot of drum length. This volume is sufficient to clean a completely
blinded screen. The spray nozzles utilized should provide a low mechanical
pressure on the screen media, but still provide good washing capability.
The nozzles should have as large an opening as possible consistent with
a good spray pattern. The nozzles utilized on the demonstration uni.t had
egg shaped openings with the smallest dimensions being I/A of an inch.
They were positioned about 12" from the drum surface and provided excellent
cleaning capability. They exerted an average pressure of less than 1 psi
on the media.
Some problems were encountered with nozzle plugging due to an inefficient
seal between the raw and screened water. Plugging occurred mostly from
gravel or grit with some plugging due to string and twigs. The drum seal
has subsequently been improved, but to eliminate a possible plugging problem,
a small wet cyclone (six inch diameter) should be utilized to trap any
material which could cause plugging. The dirty wat.er discharge from the
cyclone should be routed back through the screen.
It is recommended that screen rotation be continuous. This eliminates
71
-------
rapid change In head loss when the clean screen enters the water, which
could result in an incomplete washing cycle. If the drum were stationary,
the portion of media not in contact with the flow would initially be clean.
As the head loss reached the limit of the backwash actuating system and
the drum was activated, it would rotate only until sufficient clean screen
area was wetted to reduce the head loss to normal values and the washing
system would then be deactivated. This could leave portions of the screen
unwashed and cause rapid head loss fluctuations. When the rotation is
continuous, a solids layer gradually builds up over the entire drum surface.
The back wash system is then activated and cleans the entire screen before
deactivating. It is recommended that the spray water cleaning system be
activated by monitoring differential pressure, i.e. head loss across the
screen. Conductivity probes can be utilized, and there are a number of
commercially available, inexpensive units on the market. The system
probes are mounted in the tank at the desired differential elevation. When
the water contacts both probes, a relay is tripped which can be used to
activate the backwash pump. The relay remains closed until the water level
is below the lower probe. The differential chosen should be about 50-60?
of the expected head loss across the screen, i.e. for a 2' head loss the
spray system should activate at 1 to 1.2 foot of head loss. This prevents
the screen from becoming completely blinded prior to activation of the
back wash system. The lower probe should be set two to three inches higher
than the head loss level when the screen is completely clean. This will
prevent unnecessarily long back wash cycles.
The media utilized in the demonstration system was type 30A stainless steel.
This media proved adequate. Because of the near neutral pH encountered in
the demonstration runs (6.8 - 7-5), brass screen which is considerably less
expensive could be utilized. During the two years of operation reported
herein some bacterial growth on the screen has been experienced. It was
found that a rinsing with chlorine solution would remove these growths.
The control of the feed water flow into the drum screen is extremely
important. The possibility exists, with this highly variable raw waste,
that the head loss capacity of the screen may be exceeded during the heavy
solids loading peaks. The system should therefore have an automatic by-
pass feature, which will allow relief of the screen if the head loss
capacity is exceeded. The water which is bypassed during these times can
be routed to the flotation zone. It is also recommended that a head loss
capacity of 2k inches of water be provided.
Figure 18 presents a sketch of the recommended screen configuration. This
sketch illustrates the important features of the screen tnstallation which
have been discussed above.
FLOTATION SYSTEM
The design of the flotation system requires the consideration of the follow-
ing components: pressurized flow system, flotation basin and scum removal
72
-------
BACKWASH
HEADER
LIFTING FLIGHTS
FOR SOLIDS NOT
ADHERING TO SCREEN
SCREEN BACKWASH HEADER
BACKWASH
CTUATORS
A A A A
SCREENED
SOLIDS
HOPPER
SCREENED SOLIDS DISCHARGE
FEED
CHANNEL
SCREENED WATER
Figure 18. Recommended screen arrangement
73
-------
system. Details on design recommendations will be discussed in this section
along with a proposed system arrangement.
The pressurized flow system is the heart of the dissolved air flotation
process. It includes a pump, air solution tank, pressure reduction valve,
source of compressed air and suitable control systems.
The pressurized flow system should be designed to provide a volume equal
to 30% of the raw flow rate into the system. This should provide an
adequate margin of safety since testing at the demonstration site indicated
20% was sufficient. The recommended design operating pressure is 50 psig.
The air solution tank should provide maximum air water interface to obtain %
higher air solution. Some air solution tanks are packed with a tower packing
to provide this interface. For treatment of combined overflows, however,
a packless tank is recommended. A packed tank would be very susceptible
to plugging due to the solids present in the waste stream. Packless tanks
are generally fitted with an internal baffle to promote air water interface.
Nominal detention time in the tank is generally in the range of one minute.
The tank should also have some method of controlling the water level, since
only about 20% of the tank volume is filled during operation.
The pressure in the system is controlled via an adjustable valve. Weir
type valves have been utilized successfully. The valve is positioned by
way of a pneumatic controller which allows automatic control of the system
pressure. The valve, besides providing pressure control, provides the
necessary shear forces to promote proper bubble formation.
The sizing of the flotation basin is based mainly on the American Petroleum
Institute (API) standards (6k). Based on operation of the demonstration
system, some modifications have been made to this procedure. The API design
criteria are listed below as follows:
L - 1.2 FV, ^
n t
Where: L = effective tank length (ft)
V = rate of rise of particles (fpm)
V. = horizontal velocity in tank (fpm)
n
d = effective tank depth (ft)
F = (0.026 V. /Vj + 0.995
h t
V. maximum = 15 V or 3 fpm
tn (tank detention) = 10 minutes minimum
d (depth of tank) =0.3 to 0.5 of tank width
minimum depth = 3'
-------
The particle
rate, i .e. ,
rise rate can also be expressed as a surface loading
where S. = surface loading gpm/sq ft and V is in fpm
The demonstration system design was based on the API procedures listed
above. A particle rise rate of 0.4 fpm (S = 3 gpm/sq ft) was utilized
based on laboratory tests. The tank was also designed to allow changing
the overflow rate. It is obvious from the above discussion that the
particle rate of rise is critical in the flotation basin sizing. It may
also be seen that the horizontal velocity will be at the maximum value
(3 fpm) for all rise rates in excess of 0.2 fpm. The particle rise rate
is dependent upon particle diameter to the second power and the apparent
difference in density of the particle bubble combination and suspending
fluid to the first power. Little can be done to control the latter, but
the particle size can be significantly affected by proper chemical addition
and flocculating procedures. Rise rates as great as 5 fpm have been
obtained in the laboratory, indicating large floe particles can be developed.
It Is recommended that the above discussed procedures be utilized to size
the flotation basin, A
should be uti 1 i zed.
particle rise rate of 0.45 (S, = 3.3 gpm/sq ft)
Overhead skimmers are provided to remove the floated
are sometimes utilized on flotation systems to remove
may possibly settle. If screening (50 mesh or finer)
system, bottom skimming is not recommended since the
settled sludge expected can be removed while draining
storms. If, however, flotation is utilized without
skimming will be required. Removal of scum should be
cycle or the sensing of a sludge blanket. This will
removed only when required and hold to a minimum the
scum which will require ultimate disposal.
scum. Bottom skimmers
any sludge which
is uti1ized in the
smal1 amount of
the tank between
screening, bottom
controlled by a timed
allow sludge to be
volume of floated
The recommended general arrangement for the screening/flotation system
is presented in Figure 19. It is felt that this configuration will meet
all process requirements and be the most economical system.
The additional subsystems required to complete the treatment system are
sludge storage and the chemical storage and feeder units. A possible
overall site arrangement including these subsystems is shown in Figure 20.
Sludge storage should be sufficient to handle 2% of the raw flow for the
design storm period. This should provide sufficient storage volume,
however, the ultimate sludge disposal method may dictate the desired
storage volume. Sludge disposal alternatives available include tanker
trucking, providing a truck mounted vacuum filter to reduce the slurry
to a cake for hauling, or disposal by pumping to an interceptor sewer
for transporting to the sewage treatment plant. If the latter method is
used, the interceptor obviously must not have possible overflow points
75
-------
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in its course to the sewage treatment plant. If disposal via interceptor is
utilized, a sludge pump will be required and essentially no solids storage
pit will be necessary. On the other hand, if it is not feasible to pump
solids into the interceptor during a storm, they may be stored at the site
and pumped to the interceptor after the storm has passed. Regardless of
which method is selected, proper attention should be given to the problems
associated with handling sewage solids slurries.
The chemical treatment module (Figure 20) should provide for storage of
flocculating chemicals (ferric chloride and a polyelectrolyte) as well as
chlorine. A sufficient supply of chemicals consistent with the requirements
of the system should be provided. Estimated chemical dosages are: ferric
chloride - 20-25 mg/1, polyelectrolyte - 5 mg/1, and chlorine - 10-15 mg/1.
The chemical treatment module also houses the proper feeder systems to accur-
ately dispense the chemicals into the wastewater flow.
The entire system detailed in Figure 20 should be automated 100%. This will
allow remote monitoring and control of the treatment facility at a central
location. However, the maintenance involved with automatic systems which are
used intermittently will have to be tolerated. It is felt that this mainten-
ance will not be of such a magnitude to negate the advantages of automation.
ECONOMIC CONSIDERATIONS
There are many factors which must be considered when estimating the capital
costs of a combined sewer treatment facility. The basic areas of considera-
tion for a screening/flotation system are listed below:
1. Screening/flotation system including
self cleaning bar screen
variable rate pumping system
solids storage and disposal
instrumentation
control building
erection costs
2. Sewer interconnection (i.e. combining a number of overflow points
to reduce the number of treatment sites) and outfall facilities
3. Land costs
k. Special design problems
foundations (soil problems)
ground water
special construction techniques
freezing problems
5. Engineering costs and fees
The total installed cost for the demonstration facility was approximately
$90,000 (1968) or $18,000 per MGD capacity for the 5 MGD plant. It should be
noted that the demonstration system did not have a self cleaning bar screen,
a variable rate pumping system, or solids storage facilities which would in-
crease the cost per MGD capacity. On the other hand, the demonstration
system was of all steel construction and only 5 MGD capacity. A larger cap-
77
-------
AUTOMATICALLY CLEANED
BAR SCREEN
INFLUENT
SEWERS
PUMPING SYSTEM
FLOTATION TANKS
UJ
iti
cj
to
a:
a
to
<
ca
ca
<
ca
ca
a:
o
z:
o:
SOLIDS
SLURRY
STORAGE
uf
u.
UJ
UJ
>-
CHEMICAL
STORAGE
AND
PUMPING
SYSTEM
Figure 20. Overall system configuration
78
-------
acity and concrete construction are expected to decrease the cost per MGD
capaci ty.
Based on the above generalized information, the cost of providing a screening/
flotation system to treat the entire Hawley Road drainage area (^500 acres) is
presented below. It was assumed that the design storm was the once in 5 year
storm. From Milwaukee rainfall records this intensity is approximately 1.0
inch per hour for the estimated time of concentration of the drainage area of
100 to 110 minutes. This amounts to an overflow rate of approximately 120
MG. Allowing a 33% surge factor for this peak storm results in a design cap-
acity of 90 MGD. The following costs are estimated for this system capacity.
1. Screening/flotation system
2. Sewer interconnection and outfall facilities
3. Land costs (1.5 acres § $100,000/acre)
4. Special design problems
5. Engineering costs and fees
Total
Cost/MGD
Cost/acre
$1,350,000
65,000
150,000
90,000
240,000
$1,895,000
$ 21,056
3,828
$.
A detailed design and cost estimate for a midwest city indicated a system
cost of $22,000 per MGD capacity which compares favorably with the above es-
timate for the Hawley Road drainage 'basin.
The operating costs for a screening/flotation system include power, chemicals,
and maintenance. Table 18 presents a summary of the estimate operating costs.
The total operating cost is 3-09^/1000 gallons of treated overflow. The
majority of this cost is for chemical addition, i.e. 2.5K/1000 gallons.
These costs are based on operation of the demonstration system at Hawley Road
and are not expected to vary significantly with plant size.
79
-------
Table 18. OPERATING COST ESTIMATES
Item
Power
FeCl3a
Polyelectrolyte3
Chlorine3
Laborb
Partsb
Quantity Unit cost
15 KW/MGD 1.5*/KWH
20 mg/1 ^.SC/lb
k mg/1 35
-------
SECTION VI I I
DESIGN AND CONSTRUCTION OF THE 5 MGD SEQUENTIAL
SCREENING DEMONSTRATION FACILITY
LOCATION OF THE SITE
The location of the site for the sequential screening treatment system is the
same as the site for screening/flotation system, i.e. The Hawley Road Site.
A detailed description of this site has been included in Section V of this
report on screening/flotation treatment of combined sewer overflows. Briefly,
the total drainage area served by this sewer is *65 acres consisting predom-
inantly of developed residential housing. Of this drainage area, h2% w^as
determined to be impervious. There is very light commercial usage and no
heavy industry within this area. The drainage area contributing to Hawley
Road combined sewer overflow is shown in Figure 2.
TREATMENT SYSTEM COMPONENTS
A flow schematic of the 5 mgd sequential screening treatment system utilized
is shown in Figure 21. Also, two photographs of the overall treatment system
are shown in Figures 22 and 23. The treatment process consists of passing the
raw combined sewer overflow, sequentially, through a series of screens of
varying size openings. The raw waste is first passed through a 1/2" bar rack.
The purpose of this bar rack Is to remove lerge objects which may clog or
damage the finer mesh drum screens. The flow then passes through a series of
three drum screens, with openings varying from coarse to fine. The coarse,
medium and fine screen openings selected for this study were: 20 mesh (8^1
microns), 100 mesh (1^9 microns) and 230 mesh (63 microns) respectively. The
drum screens are contained in basins of steel construction and are cleaned
with spray backwash nozzles. The water utilized for the spray backwash ing is
the screened effluent from the respective drum screens. The captured solids
from each screen are discharged to a sanitary sewer located at the site.
The treated effluent is discharged directly to the Menomonee River.
The series screening system is designed for a maximum hydraulic capacity of 5
MGD. The system can be operated either in parallel or in series with the
screening/dissolved-air flotation treatment facility. Provisions are made for
adding flocculant aids and disinfectant to the waste flow at various points
as shown in Figure 21. The entire system has been automated for start up,
sampling and flow monitoring with the exception of backwash waste sampling.
81
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DESIGN OF THE SCREENING SYSTEM
The screening system consists of basically two sections, the drum screens and
the backwashing system. The entire design of the screening system was based
upon the data generated and the experience gained from the operation of the
existing screening/flotation treatment facility. The critical design para-
meters associated with the design of the drum screens include solids loading,
hydraulic loading, and head loss capability. A solids loading of 1.4 lbs/100
sq ft was selected. Drum rotation speeds were in the range of 1 to 7 rpm.
As mentioned earlier, the screen openings selected for the three drum screens
were: 20 mesh, 100 mesh and 230 mesh. These openings allowed high hydraulic
through-put rates of the order of 50 gpm/sq ft for 20 mesh screen and up to
30 gpm/sq ft for the finer screens at reasonable headlosses. A maximum
headloss capability of 2k inches and a maximum screen surface submergence of
75% were provided in the design of all the three drum screens. The screen
material utilized was 316 stainless steel in square weave mesh. The backwash
pumps were sized to provide minimum screen wash water rates of 15 gpm per
foot of drum length. The nozzles utilized were spaced 6" apart and were de-
signed to exert an average pressure of less than 1 psi on the media.
Each screen is an open ended drum into which the waste water flows (Figures
18 and 24). The water passes through the screen media and into a screened
water chamber directly below the drum. The drum rotates and carries the re-
moved solids on top of a hopper into which the solids fall by gravity or are
flushed from the screen by a spray water cleaning system (Figure 18.) Those
solids which will not adhere to the screen media are picked up by angle iron
sections which act similar to a trough or a roto-dip feeder and are thus
removed from the flow. Screened water from each drum screen is used for the
backwashing of the respective screen. The spray water cleaning is controlled
by liquid level electrical probes located In the screen chamber. The probes
are set to actuate at a headloss of 12" of water through the screen (Figure
25). The resultant solids slurry is then routed to a sanitary sewer.
More photographs of the screening system showing the screens, the drives and
the backwashing systems are shown in Figure 26. The basic screen is fab-
ricated from mild carbon steel. The screen backing material is a perforated
metal plate 3/4" x 3/4" on 7/8" centers. This provides 73% open area and
only a minimum of flow restriction. The rotation of the drum screens is
continuous. The drum rotation speed Is controlled by a variable speed drive
which is positioned manually. The screened water was initially sealed from
the raw waste by a single lip extruded rubber seal fastened between the end
of the drum and a stationary ring. However, sealing problems were immed-
iately apparent during the monitoring of the first overflow with the above
described seals. It was found that the rubber seals buckled and overturned
backwards from the water pressure. This in turn caused leakage of the in-
fluent water into the screened water compartment. A new seal design was
then Incorporated for all the three screens. The new seal was an X-shaped ex-
truded plastic which could be compressed between the end of the drum and the
stationary ring. The seal was also wired to the stationary ring at 12"
intervals to hold it in place. This arrangement eliminated all leakage prob-
lems and provided an excellent sealing between the influent and the screened
water.
84
-------
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Figure 26. Screening system
86
-------
The backwashing system consists of a pump, a header system and spray nozzles.
The nozzles utilized for the demonstration unit had egg-shaped openings with
the smallest dimensions being 1/4 of an inch. They were positioned about
12" from the drum surface at 6" intervals and provided excellent cleaning
capability. To eliminate possible plugging problems of the nozzles, the
screened water utilized for the backwashing is passed through a small, wet
cyclone (6" diameter) for the coarse screen and through 1/16" mesh strainers
for the medium and fine screens. Such provisions can trap any large materials
that may overflow into the screened water chamber when the headless capability
on the upstream screen is exceeded.
As indicated earlier, the maximum headless handling capability of the drum
screens is 2V. Any excess headless will allow some unscreened water to enter
the screened water chamber. The overflow on the coarse and the medium mesh
screens will only act as the influent to the downstream screen, but if the
headloss capability is exceeded on the third and the finest screen (230 mesh)
the overflow mixes with the final effluent affecting its quality. During
some runs with extremely heavy solids loads, the headloss capacity of the
screens was exceeded, which will be discussed later.
The drum screens as installed are 12 sided drums with effective diameters of
8 ft. The length of the coarse screen is 4.5 ft and of the other two finer
screens is 7 ft. The 8 panels for each screen are 2 ft wide and run through
the length of the drum screens. The maximum wetted screen areas for the
three screens are: 76 sq ft for the coarse screen and 123 sq ft each for
the medium and fine screens.
DESIGN OF SUPPORTING SYSTEMS
The appurtenant equipment and tasks necessary to provide a functional demon-
stration system included site preparation, construction of a manhole and
pumping sump, selection of the necessary flow metering equipment and chemical
feed system, and design of suitable electrical and pneumatic control systems.
The site location and the retaining structure to allow a limited impoundment
of the flow have been discussed earlier. Site preparations involved laying
a concrete slab to provide support for the system tankage. A manhole was
constructed as well as a pumping sump, directly in the combined sewer. A
centrifugal pump was selected for transporting the CSO from the sump to the
demonstration unit. A vacuum pump was also provided to prime the raw feed
pump. Photographs of the raw pumping system and the influent channel of
the treatment unit are shown in Figure 27. Flow metering equipment is pro-
vided to measure the influent flow rate and the volumes of screen backwash
water for the three drum screens. Both these flows are measured via venturi
meters connected to differential pressure gauges which both record and total-
ize the flows. A positive displacement, triple head chemical metering pump
is provided to add flocculating chemicals and disinfectant. The electrical
control panel is equipped with all necessary controls for 100% automatic
operation with manual overrides on all systems. Photographs of the control
shack housing the control panel, flow meters, chemical pump and the vacuum
pump are shown in Figure 28.
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A transfer pump and a pneumatic flow rate controller are provided to trans-
fer the flotation treated effluent to the sequential screening system. In-
fluent channel wall between adjacent drum screens can be removed to provide
maximum flexibility in operational modes. The test plan, operation modes,
and sampling procedures will be discussed later. A merchant police alarm
is connected to the system so that personnel will be alerted when the system
goes into operation. The system is always (2k hours per day, 7 days per
week) ready to operate; and hence, the maximum possible number of overflows
can be monitored.
90
-------
SECTION IX
SEQUENTIAL SCREENING OPERATING RESULTS (1970
AND DISCUSSION
OPERATIONAL METHODS AND PROCEDURES
The demonstration system previously described in Section VII I was put into
operation in early October, 1970. However, drum screen sealing problems (al-
so discussed in Section VIII) necessitated a new design of the seals. This
problem coupled with dry weather did not permit any further operation of the
screening facility during the remainder of the 1970 operational season. Data
reported herein was taken during the 1971 operational season between May and
October. During this period 21 overflows were monitored with the screening
system. The system was put into operation automatically when a conductivity
probe in the sewer sensed an overflow. The drum screens were immediately
put into operation as the raw feed pump began to prime. The raw feed pump
was generally primed in about 7-10 minutes. On priming, the raw pump is
activated and the flow meters and the chemical feeder (if utilized), along
with the sampling system and the backwashing system (operates only when the
headless across the screen reaches a pre-set level), were placed into opera-
tion. At the end of the overflow, the system shut down automatically. The
screened water chambers were then drained out manually through the backwash
pumps. The controls were subsequently positioned for regulating desired
variables for the next run. The variables associated with the screening
operation include raw flow rate, drum screen speeds, backwashing rates and
chemical dosages.
SAMPLING PROCEDURES
The sampling system consisted of two timers connected through the proper
valving, to automatically composite the raw waste and the screened effluent
samples. The first timer controlled the sample taking frequency (0-30 min-
utes). The second timer controlled the duration of sampling time (0-60 sec-
onds). Generally, the samples were composited every five minutes with the
automatic system throughout the duration of the overflow. The sampling
valves were air operated weir valves.
Sampling began after the raw pump was primed. The first samples of the raw
and screened effluents were collected only after a minimum of 5 minutes of
system operation had elapsed. The time interval was sufficient for filling
water in the screening chambers and insured collection of representative ef-
fluent samples. Screen backwash samples from the various screens were col-
91
-------
lected manually during the backwash periods. These samples were riot auto-
mated due to the problems associated with intermittent flows and heavy solids
concentrations in these process streams.
Separate samples of the composited final effluent were normally taken out at
the end of each overflow for total coliform analysis. These samples were
placed in bottles containing excess sodium thiosulfate to allow purging of
any residual disinfectant (chlorine). Later in the study, it was felt that
the coliform count results from the composite samples may not be truly rep-
resentative of the actual disinfection efficiency due to any disinfection pro-
vided by the residual disinfectant during the period of sample collection.
To overcome this problem, two types of effluent samples, instant and com-
posite, were analyzed for total col{forms. The instant sample referred to a
grab sample of the screened effluent while the composite sample referred to '
the one which was taken at the end of the overflow from the composited
(through the duration of the storm) final effluent. Both these samples were
then placed in bottles containing sodium thiosulfate to purge any residual
chlorine. All samples were refrigerated immediately after each run. Analyses
were then started within 0-8 hours. Sample analysis procedures are dis-
cussed in Appendix C.
TEST PLAN
The variables that needed to be evaluated and optimized for the operation of
the sequential screening facility include: screen openings, screen media,
sequential arrangement of screens, hydraulic loading rates, solids loading
rates, backwashing rates and addition of chemical flocculants. During the
first operational season the test plan was designed to study only the hydrau-
lic and the solids loading rates by assuming the other variables. Also,
Initially, the sequential screening system was operated in parallel to the
screening/flotation system and the following flow routing path and design
parameters were selected:
Flow Routing Path: Raw -* Bar Screen -* Coarse Screen -* Medium
Screen-* Fine Screen
Screen Media:
Bar Screen Openings:
Coarse Screen Size:
Medium Screen Size:
Fine Screen Size:
Chemical Flocculant Addition:
Backwash Rates:
316 stainless steel
1/2 inch
20 mesh (841 micron)
100 mesh (]^^ micron)
230 mesh (63 micron)
None
As needed
The variations in the hydraulic loading rates could be achieved by varying
the flow rates and in solids loading rates by varying the drum speed rotation
and/or by blanking out portions of the drum screening areas. It was planned
to obtain 5 to 6 runs for each variable combinations of the test conditions
at high and low values.
However, from the operation of the first few runs, it became apparent that it
92
-------
was not possible to operate the field unit under pre-set conditions for vary-
ing the solids loadings because of the variability of the CSO quality. Also,
the particulate pollutant removals on the screens were significantly lower
than expected. Therefore, the test plan was modified to provide the best
possible test conditions that may improve the final effluent quality. These
changes in the test conditions included: lowering of the raw flow rates to
decrease the hydraulic loadings, increasing the drum rotation speed and pro-
viding maximum available screening surface area to decrease the solids load-
ings and adding cationic polymer flocculants at different treatment points.
These conditions were changed in the field whenever possible to provide max-
imum information with the limited number of overflows occuring during the
1371 operational season.
RAW WASTEWATER QUALITY
A total of 21 overflows were monitored on the sequential screening system
during the 1971 operational season. As expected, the quality of the com-
bined sewer overflow from the Hawley Road sewer varied widely (Table E-16,
Appendix E). However, the extremely high pollutant loaded first flushes, re-
ported in an earlier report on screening/flotation treatment (70), were not
distinguished separately. Instead, each overflow was counted as a separate
event over the entire length of the system operation. This change was made
to reduce the number of samples for laboratory analysis since it was felt
that sufficient data had already been collected in previous years to define
the raw wastewater characteristics. The overflow duration generally ranged
between 30 and 140 minutes for any one storm. A summary of the overflow
occurrence data is shown in Table 19. The interval between successive ovei
flows ranged widely from 0.5 days to 3^ days. No specific relationship could
be established between the amount of particulate matter in the CSO (as shown
by the suspended solids) and the period between successive overflows. Data
on rainfall was obtained routinely and is shown for most storms in Table 19.
The rainfall data on a few storms was missed because of minor maintenance
problems with the raingauge. No attempt was made to measure the rate of flow
in the sewer because of the following two reasons as pointed out in an earlier
report on screening/flotation treatment (70):
1. It is difficult to measure the flow in the Hawley Road sewer under
prevailing conditions as described previously on page 51.
2. Such measurement does not influence the operation of the demonstra-
tion system.
A summary of the characteristics of the combined sewer overflow quality is
presented in Table 20. The data is included not only for the 1971 operation-
al season but also has been compared with the past two years of data. All
data is presented at 95? confidence level. The pollutant levels for this year
generally fall in between the first flush and the extended overflow pollutant
levels recorded during the two previous years. This is expected since the
first flushes and the extended overflows were not separated out for the 1971
season. The detailed analyses and the operational parameters for each over-
93
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Table 19. SUMMARY OF OVERFLOW
OCCURRENCE DATA - 1971
Over-
flow
no.
71-1
71-2
71-3
71-4
71-5
71-6
71-7
71-8
71-9
71-10
71-11
71-12
71-13
71-14
71-15
71-16
71-17
71-18
71-19
71-20
71-21
Days
between
overflows
8
9
1
6
1
1
2
16
11
14
8
4
0.5
6
2
34
2
6
16
13
Duration
of
overflow,
min.
30
59
30
32
107
57
143
64
70
50
85
57
46
83
35
37
55
49
95
54
120
Suspended
solids,
mg/1
172
206
1,025
322
560
437
78
556
330
886
313
188
229
138
303
580
1,074
336
349
293
204
Average
rainfall
intensity,
in/hr.
0.50
0.60
1.00
0.35
2.00
0.90
0.25
1.40
0.36
0.10
0.12
0.75
1.10
0.65
0.04
3.70
0.09
0.09
0.14
0.67
0.10
Note:
Average rainfall intensities for overflows Nos. 71-9 71-10
71-11, 71-15, 71-17, 71-18, 71-19, and 71-21 estimated from'
data obtained from local weather burea.
-------
Table 20. SUMMARY OF RAW WATER QUALITY DATA - (1969-1970)
Coiistituent Concentration
at 95% confidence level
Analysis
pH
Total Solids, mg/1
Total volatile solids, mg/1
Suspended solids, mg/1
Vol. suspended solids, mg/1
TOG, mg/1
COD, mg/1
BOD, mg/1
Dissolved TOC/Total TOG
Dissolved COD/Total COD
Total Nitrogen, mg/1
Ortho Phosphate, mg/1
Coliform density per ml
1971 1969-70
Season a First flushes3
7.2 ± 0.1
605 ± 151
156 ± 73
435 ± 129
146 ± 46
73 ± 27
209 ± 86
64 ± 32
0.36 ± 0.05
6.3 ± 1.9
0.86 ± 0.37
75.5 ± 69 x
103
7.0 ± 0.1
861 + 117
489 ± 83
522 ± 150
308 ± 83
581 ± 92
186 ± 40
17.6 ± 3.1
2.7 ,± 1.0
142 ± 108 x
103
1969-70
Extended
overflows c
7.2 ± 0.1
378 ± 46
185 ± 23
166 ± 26
90 ± 14
.
161 ± 19
49 ± 10
0.34 ± 0.04
5.5 ± 0.8
1.0 ± 0.24
62.5 ± 27 x
103
a. Data represents 21 overflows
b. Data represents 12 overflows
c. Data represents 44 overflows
95
-------
flow are incl
there is a wi
concentration
The dissolved
dissolved sol
of Table 20,
the MIIwaukee
uded in Appendix E (Tables E-41 and E-42). It can be seen that
de variation in the waste water quality. The participate matter
measured as suspended solids varied between 78 and 1074 mg/1.
^solids content of the CSO is again quite low. The TDS (Total
ids) based on the difference of total solids and suspended solids
is 170 mg/1. This value is very similar to the TDS content of
tap water and represents a very insignificant change.
Of particular interest to this project are the volatile and the dissolved
organic fractions in the combined sewer overflows. Table 21 presents data on
these relationships for 1969-1971 operational seasons.
The dissolved COD or TOC fraction is In close agreement for the three year
data and ranges between 30 to 41* of the total COD or TOC. The dissolved
organic material will not be removed by the screening process and will in-
fluence the removal efficiencies of COD and TOC. The volatile fraction in
the particulate matter has been found to be significantly lower for the 1971
season. It can be seen from Table 21 that the VSS/SS fraction for this year
is only 2$% as compared to 57% for the two previous seasons. Thin layers of
fine cementous material were observed on th^-Inside walls of the screening
chambers at the end of overflow runs. These may have been a result of the
washings from the new lining of the sewers in the drainage area during the
spring of 1971. The resultant effect of this fine cementous material would
be to decrease the volatile fraction of the particulate matter. This fine
material will not be removed on the drum screens and will again tend to
lower the removal efficiencies.
OPERATION OF THE SEQUENTIAL SCREENING SYSTEM (FIELD TESTS)
The sequential screening system was operated on a total of 21 overflows A
summary of the operating conditions for the three screens is presented in
Table 22. A detailed listing of complete data Is included in Appendix E,
Tables E-41 to E-46. The feed flow rates to the screening system varied
between 1800 and 3300 gpm. The resulting hydraulic loadings ranged between
li and 43 gpm/sq ft based on the maximum wetted surface areas of the screens
The drum rotation speeds varied in the range of 1 to 7 rpm. Of the 21 over-
flows _mon I to red on the screening system, 15 were operated without any floc-
culating chemicals while a cationic polyelectrolyte (Nalco 607) was added to
the^remaining 6 overflows. Chlorine was added to 13 of the overflows for
disinfecting the waste waters. The chlorine dosages ranged between 5 and 17
mg/1. . ' '
The summaries of the pollutant removal efficiencies across the screening
system (1 to 3 screens in series) are tabulated in Tables 23 and 24. These
removals are presented as percentage removals because of the wide range of
pollutional values obtained in the raw waste. Absolute effluent water qual-
ity data may be seen in Appendix E, Tables E-43, E-44, and E-45. The absolute
values can also be estimated by applying the observed percentage removal
numbers (Tables 22 and 23) to the raw overflow water quality presented in
Tab 1e 20.
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Table 23. SUMMARY OF OVERALL POLLUTANT REMOVALS
ACROSS THE SCREENING SYSTEM3
Percent removals at 95% confidence level
Analysis
Suspended solids
Volatile suspended solids
TOG
COD
BOD
Without chemical
flocculants
28 ± 8
32 ± 11
25 ± 12
30 ± 9
28 ± 7
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Q
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31 ± 17
12 ± 17
10 ± 7
16 ± 15
a. Three screens in series 841m, 149 y, 63y
b. Represents 15 runs
c. Represents 6 runs with cationic polyelectrolyte Nalco 607
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Generally, the overall percent removals across the screening system was In
the range of 30% without the addition of any chemical flocculants. The per-
cent removals were lower for the runs with chemical flocculants. The reason
for such a decrease in the removal efficiencies are not known. However, a
good comparison cannot be made as only six runs were made with chemical
flocculant addition and the range of removals was quite large. Table 2k
presents a summary of the progressive removals through the screening system
in various stages. The percent removals on the coarse drum screen (84ly)
were extremely low because of the relatively large openings. The removals on
the coarse and medium screens in series were only slightly (M5%) improved.
The improvement in pollutant removals was of the order of 5% only when all
the three screens were In series. Since the success of a mechanical separation
process such as screening Is dependent largely upon the particle size dis-
tribution in the raw waste, It was indicated that the poor performance of the
screening system may have been a result of the particle size distribution
in the combined sewer overflows. This necessitated the need to develop in-
formation regarding the particle size distribution of CSO in order to improve
the pollutant removal efficiencies via the screening process.
In an effort to improve upon the efficiency of the screening system, several
measures were undertaken during the operation of various runs. Specific
measures that were tried were:
1. Reductions in hydraulic loadings and solids loadings by changing
the raw flow rate and drum speeds.
2. Thorough inspection of the sampler system, the drum screen panels
and other mechanical and electrical .co-ponents and controls that
could affect the performance of the system.
3. Bench scale tests to provide detailed information on screening
removal efficiencies as well as comparison with the field data.
4. Addition of chemical flocculants in the field as well as bench
scale evaluation of promising chemical flocculants that will
provide a quick floe to be removed on the screens.
The variation in the feed flow rates and the drum rotation speeds for all the
21 overflows is prs^ented in Table 22. The resultant hydraulic and solid
loadings are shown in Table 25. The hydraulic loading varied between 15 to
45 gpm/sq ft. The solids loadings, calculated for the entire duration of the
overflow were generally less than the design solids loading of 1.4 lbs/100
sq ft. However, the solids loadings exceeded the design values many times
during the Initial stages of several overflows. This Is expected because of
the variation in the raw water quality over the duration of an overflow. No
significant increase in removal efficiencies was attained due to the change in
the hydraulic and solids loadings.
During the initial phase of the screening operation,' it was thought that the
poor performance of the screening system might have been a cause of some
mechanical operational problem such as leaks, sampling system and other minor
maintenance problems. A thorough inspection of the screen panels, sampler
101
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location and operational controls was made to eliminate any possibly problem
areas. However, no significant areas of concern were found although some
modifications in the sampler system and its locations were made to insure col-
lection of truly representative samples.
A chemical flocculant Dow C-31 was added in runs 71-09 and Nalco 607 was added
in runs 71-17 through 71-21 at a dosage of 5 mg/.l. Both the above polymers
are cationic in nature. Dow C-31 had earlier been used at the Hawley Road
facility for screening/flotation treatment (70). The polyelectrolyte Nalco
607 was selected based on initial bench scale studies with various polymers.
The polymers were added in the raw waste for runf 71-09, 71-17, 71-18 and 71-
19 and in the effluent from screens #2 for runs 71-20 and 71-21. Addition of
these polymers at the two separate locations did not provide any improvement
in the removal efficiencies (Table 24) of the screening system. However, it
should be noted that a specific flocculation period was not provided and
effective flocculation may not have occurred. Additional qualitative bench
scale tests on raw combined sewer overflow samples from runs 71-19 and 71-20
indicated two promising flocculants in Magnifloc 905-N (non-ionic) and Atlas
105C (cationic). Both these polymers can provide an excellent floe. Unfor-
tunately, field testing of these flocculants could not be possible due to the
shutdown of the treatment facility with the onset of cold weather. However,
it is recommended that these promising chemical flocculants be evaluated in
future field screening tests and consideration be given to the provision of
proper flocculation period prior to screening.
BENCH SCALE SCREENING TESTS
In an effort to obtain more detailed information on the removal efficiency
utilizing screens with various size openings, a series of bench scale tests
were performed. Results of the wet sieve analysis performed on the raw over-
flow from Storm No. 71-12 are shown in Table 26.
Table 26. WET SIEVE ANALYSIS RESULTS
STORM 71-12 RAW OVERFLOW
ON
Screen opening
20 mesh (841 p)
100 mesh (149 p)
200 mesh (84 y)
400 mesh (37y)
Filtrate from 400 mesh
Weight retained, gins
0.0151
0.0193
0.0071
0.0322
0.6680
% retained, by weight
2.0
2.6
1.0
4.3
90.1
103
-------
It can be seen from this table that only a total of 10% of the participate
matter by weight was retained on various screens up to 400 mesh (37 microns).
This indicates that 90% of the particulate matter by weight was finer than
37 microns for this particular overflow event. Side-by-side data with
field testing was obtained on storms 71-15, 71-16 and 71-20. A comparison
of this data is presented in Table 27.
Removals of volatile suspended solids and.TOC generally agreed, however, sus-
pended solids removals were all significantly higher in the laboratory tests
as compared to the full scale systems. It is not known what was causing this
difference, but it may have been the sampling techniques or the inherent
differences between the bench scale and the full scale systems. In any
event, additional side-by-side bench scale testing is recommended for future
field screening tests. This will allow proper scale up factors to be deter-
mined and the reliable bench scale testing technique to be developed.
In an effort to improve upon the screening efficiency, finer micronic screens
[finer than 230 mesh (63y)] were utilized in bench scale tests. A comparison
of the screening efficiencies of the 63 micron square weave screen with the
23 micron twill weave screen is shown in Table 28, Both these screens were
in stainless steel media. It can be seen from this table that the pollutant
removal efficiencies for 63 micron screen were in the range of 20 to 40%
while the corresponding removal efficiencies were in the range of 55 to 30%
for 23 micron screen. An exception in the removal efficiencies is evident for
run no. 71~20 where the highest suspended solids removal was only 37% and the
volatile suspended solids and TOC removals were extremely poor. This obser-
vation shows the high degree of variability that can be generally expected in
the particle size distribution in combined sewer overflows. However, in most
overflows greater than 50% of the particulate matter was found to be in a
particle size range of 20 to 60 microns. Figure 29 presents a plot of sus-
pended solids removal against screen size opening. It may be seen in this
figure that a significant increase in removal efficiency was obtained at
screen openings of 18 to 23 microns. Since the success of a mechanical se-
paration process such as screening is dependent to a great extent upon the
particle size distribution in the raw waste, it appears that decreasing the
size of opening on the third drum the series screening system will provide a
significant increase in the removal efficiencies. It is also apparent from
the full scale and bench scale data that three screens in series hold no ad-
vantage over a single screen. It may be necessary, however, to use a roughing
screen to protect the very fine mesh (small opening) screens required for
high removal of contaminants from combined sewer overflows.
Most of the screening media utilized during the bench scale and field tests
was made of stainless steel. However, a wide variety of plastic media screens
made in nylon and polyester are available now at $4/sq ft. Plastic media
screens are significantly cheaper (approximately by a factor of 5-8) than the
stainless steel media screens in comparable screen openings. Moreover, the
square weave stainless steel media is very susceptible to damage because of
the thin wire size utilized in its weaving. Plastic media screens are com-
parably stronger in square weave. Samples of the plastic media screens were
not received in time to evaluate their application feasibility on the Hawley
104
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Road CSO. It Is therefore recommended that these screens be evaluated be-
fore making a final selection of the micronic screen for the treatment of
combined sewer overflows.
OPERATION OF THE BACKWASH SYSTEM
The screens were backwashed with waters from respective screened effluent
chambers via separate pressurizing pumps. Spray nozzles with 1/4" diameter
orifices were used to effectively distribute the water over the screen media.
Washing was performad from outside the screen drums. The total screen
water utilized varied between 100-130 gpm. With the installation of 1/16"
strainers on the backwashing waters, almost no nozzle plugging problems were
experienced. However, it was felt that the amount of screen water volume can
be further reduced by placing the spray nozzles closer to the drum screens.
Currently the spray headers are approximately 12" from the drum screens. It
Is felt that a distance of 4 to 6" should provide sufficient spray backwashing
at 30-50 gpm. At this rate, the spray wash requirements would amount to only
1 to 2% of the raw waste flow when continuous washing of the screens is
provided. The actual spray wash utilized with intermittent washings (only
when screens were blinded) were in the range of 0.5 to 2% of the raw flow.
Screen wash quality ranged between 500 to 9,000 mg/1 suspended solids. A
listing of the screen wash volumes and quality data is presented in Appendix
E, Tables E-41 and E-46.
DISINFECTION OF COMBINED SEWER OVERFLOV/S
A summary of the disinfection data utilizing chlorine is presented in Table
29. A total of 13 overflows were treated with chlorine. Calcium hypochlorite
was utilized as a source of chlorine. The range of chlorine dosages used was
5 to 17 mg/1. It was found that the sequential screening system provided
adequate detention time (^5-10 minutes) for effective disinfection when chlo-
rine was introduced in the raw overflow. Based on the results shown in Table
29, a dosage of 7.5 to 10 mg/1 was considered sufficient for effective disin-
fection. Results of only one overflow (No. 71-12) were significantly poorer
where a high number of coltforms was recorded in the screened effluent in
spite of the use of a chlorine dose of 10.3 mg/1. The reason for this poor
disinfection may have been due to some error in the handli ng of the effluent
sample. Nevertheless it was concluded that good disinfection can be obtained
in conjunction with the operation of a sequential screening system.
108
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Table 29. SUMMARY OF DISINFECTION DATA WITH CHLORINE
Storm no.
71-5
71-6
71-7
71-9
7i-ai
71-12
71-13
71-14
71-15
71-16
71-19
71-20
71-21
Chlorine dosage,
mq/1
7.5
7.5
7.5
7.5
5.0
10.3
11.0
11.0
15.0
17.0
9.0
6.7
10.0
Total coliforms, no. /ml
Influent
31,000
115,000
6,000
490
3,600
6,500
34,000
140
380,000
128,000
5,700
9,000
21,000
Effluent
54
<1
<1
0
<50
2,178
6
3
3
2
<1
100
<1
109
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SECTION X
INVESTIGATIONS CONDUCTED FOR UPGRADING
SCREENING/FLOTATION PERFORMANCE
Previous work performed and described in preceding sections of this report
has shown that:
1. Screening/flotation is an effective method for reducing pollution
caused by combined sewer overflows. The overall pollutant removals
achieved, measured in terms of suspended solids, volatile suspended
solids, BOD and COD, ranged between 60% and 75%.
2. Sequential screening was not as effective as screening/flotation in
reducing pollution caused by combined sewer overflows. The percen-
tage removals attained by sequential screening were about 30% for
the contaminant parameters of suspended solids, volatile suspended
solids, BOD, COD and TOC. It was concluded that the use of three
screens in series did not show any advantage over the use of a sin-
gle screen.
Bench scale investigations were then investigated in an effort to improve
the observed pollutant removal efficiencies. For example,
1. Bench scale investigations showed that a significant increase in
pollutant removal efficiencies could be obtained by using screening
material which had openings of 18 to 23 microns.
2. Also, laboratory bench scale tests using various dissolved-air flo-
tation treatment modes indicated that the quality of the treated
effluent in the effluent recycle mode of operation was significantly
better than that using the split flow mode of operation.
3. Moreover, bench scale tests demonstrated that powdered activated
carbon, when used in conjunction with dissolved air flotation in the
effluent recycle mode, provided excellent removals of both particu-
late and soluble organic pollutants.
The bench scale investigations alluded to in Item No. 1, above, were performed
and described as a part of the work reported previously in Section IX.
The laboratory studies referred to above in I tern Nos. 2 and 3 were performed
separately as part of a larger study conducted to compare and evaluate the
feasibility of various means for upgrading flotation treated combined sewer
overflows. A detailed account of these feasibility studies is documented in
110
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Appendix B.
Based on the bench scale findings described above, additional work was per-
formed at the Hawley Road site utilizing the 5 mgd demonstration systems to
evaluate the following modifications and additions on the upgrading of
screening/flotation performance.
1. Screening/flotation system operation after conversion of flotation
system to effl.uent pressurization.
2. Conversion of the third drum screen on the sequential screening
system to accommodate a 18-23 micron opening synthetic media screen
and the operation of the screening system on both the flotation
effluents and raw CSO's.
3. Conducting separate field tests using powdered activated carbon and
coagulants with the screening/flotation system as modified under
I tern 1, above.
The following discussion summarizes and documents the work performed in the
upgrading investigation.
SCREENING/FLOTATION USING EFFLUENT PRESSURIZATION AND MlCROSCREENING OF
FLOTATION EFFLUENT
The original system design at Hawley Road utilized screened, raw wastewater as
the source of liquid stream for pressurization. The advantage of this initial
approach was to decrease the hydraulic loading on the DAF tank and thereby
reduce the tank surface area requirements. The bench scale tests performed
indicated that the use of the treated effluent as the pressurized flow source
enhanced suspended solids removals. To utilize DAF effluent as the liquid
stream source for pressurization, an 8 inch pipe was installed along the out-
side of the flotation tank from the effluent trough to the existing liquid
stream manifcld inside the screened water tank. A schematic representation of
these modifications is shown in Figure 30. A slope of 1/8 inches per foot
permitted gravity flow of the effluent to the header manifold. Appropriate
valves at this juncture permitted the choice of either screened water or DAF
effluent as the liquid stream source for pressurization.
The second modification for upgrading the effluent quality from the DAF unit
involved the microscreening of the flotation effluent. No modifications were
required to transfer the DAF effluent to the screening system as the necessary
equipment was already installed. The modifications necessary to the screening
system are discussed below.
The original treatment process consisted of passing the waste flow sequential-
ly through a series of screens of varying size openings. A representation is
shown in Figure 31. A raw feed pump delivered the waste stream from a sump in
the sewer to the screening system. The raw waste passed through a 1/2 inch
bar rack, to remove large objects which may clog ,or damage the finer mesh
111
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drum screens. The flow was then channeled through a series of three drum
screens. The drum screens were contained in basins of steel construction
and were cleaned with spray backwash nozzles. The water utilized for the
spray backwashing was the screened effluent from the respective drum basins.
The captured solids from each screen were discharged to a sanitary sewer
located at the site. The treated effluent was discharged to the Menomonee
River. A transfer pump and a pneumatic flow rate controller was also pro-
vided to transfer flotation treated effluent to the sequential screening
system. In addition, the influent channel walls between adjacent drum
screens could be removed to provide maximum flexibility in operational modes.
The stainless steel screens originally used ranged from 20 mesh (8A1 microns)
to 230 mesh (63 microns). As a result of the laboratory bench scale testing
with various fine screen medias, a nylon media was selected for the micro-
screening tests. The selected screen was a 3^3 x 66 mesh, plain reverse dutch
weave type media and had nominal pore openings of 22 microns. The media,
designated NY-76-k, was supplied by the TET-KRESSILK Co. This media was sup-
ported by and retained on 18 x 2k inch high density polyethylene grid panels.
These panels, in turn, were clamped onto the screen drum by mild steel re-
taining bars. Additional cross braces were added to support the panels' end
points. A total of 5^ grid panels were used to cover the third drum screen.
The total exposed microscreen area was 98.5 sq ft. No further alteration was
needed except for the removal of the old screening media, the additional
cross braces, and the grinding of a few rough weld burrs, to adapt the drum to
accept the microscreen media. The backwash spray header was lowered to pro-
vide better spray penetration through the finer mesh screen.
Initial sequential screening results had shown no appreciable advantage in
passing the process stream through progressively finer screens, however, the
coarse, 20 mesh screen was retained in the process scheme to protect the
delicate nature of the microscreen cloth. The influent channel baffle in
the second screen chamber was removed allowing the waste stream to bypass
that chamber and flow directly from the roughing screen (20 mesh) to the mi-
croscreen drum.
While existing metering and recording equipment provided influent and backwash
flow rates and volumes, a differential pressure recording meter was installed
to measure the inches of water headless across the microscreen.
The process versatility of the two systems is apparent. Each system had the
capability of independent operation, that is, separate raw pump controls,
metering and measuring devices. In addition, a transfer pump system allowed
the effluent from either system to be transferred to the inlet of the other
treatment system. A process sheet illustrating these flow schemes is shown in
Figure 32.
The modification of the existing split flow flotation system to one with
effluent pressurization and the conversion of the third drum of the series
screening system to a microscreen (22 micron opening) was completed in the
early summer of 1973. Both systems were then put into automatic startup op-
eration. The two systems were initially run in series to evaluate both the
performance of effluent pressurization and of the microscreen polishing of
-------
1
Illl
Ill
P ST
20
P L=
MICRO
SCREEN
" hhl-LULNI
TRANSFER
SYSTEM
OPERATION OF THE TREATMENT SYSTEMS IN SERIES
20y
MICRO-
SCREEN
'EFFLUENT
RAW J |
CSfl *[_\
sssa
1 5°
-^MESH
r-jSCREEN
D-
D-
-0
-0
DISSOLVE D-AIR
FLOTATION
*-EFFLUENT
OPERATION OF THE TREATMENT SYSTEM IN PARALLEL
Figure 32. Dissolved-air flotation
6 mfcroscreening operation modes
115
-------
flotation effluent. The parameters associated with this mode of operation
included overflow rates, chemical dosages, percent recycle rates and effluent
quality. Midway into the operation season, the micro screening testing was
extended to include direct screening of raw CSO, and the results of this
testing will be reported later in this section. The flotation unit was then
operated parallel to the screening system to provide a comparison of process
methods while also accumulating more data on the effect of effluent press-
urization on effluent quality. A brief description of the operating methods
of each of the treatment systems follows.
The flotation system was put into operation automatically when a pressure
switch in the sewer sensed an overflow. The pressurized flpw system was then
immediately put into operation and the raw feed pump began to prime. All
runs were started with the tank full of water from the pre/'ous run. The raw
pump generally primed in about 7-12 minutes. When primed, the raw pump was
activated, and the flow meters, chemical feeder, skimmers and all other
auxiliary equipment were put into operation. The transfer pump and a pneu-
matic flow rate controller automatically transferred the flotation treated
effluent to the screening system. At the end of the run, the system shut down
automatically. Process variables were then selected for the next run and the
controls positioned accordingly. .Variables associated with the tank operation
included the pressurized flow rates, injection air pressure, overflow rates,
and chemical dosages. ,..-,.
Although the microscreening system had automatic startup capabi1ities, it was
put into operation manually in order to observe and control any excessive
headlosses across tne screens that might occur. By switching the transfer
pump and pneumatic flow controller to an automatic mode, the drum screens,
sampling system, flow meters and the backwash system (operated only when
headless across the screen reached a preset level) were put into operation.
At the end of the overflow, the system shut down automatically. When treat-
ing raw CSO, the system was manually switched to the automatic mode whereby
the drum screens were immediately put into operation and the raw feed pump
began to prime (generally in about 7 to 10 minutes). On priming, the raw
pump and the above mentioned support systems were all activated. At the end
of the overflow, the system shut down automatically. The controls were then
positioned for regulating the desired variables for the next run. The varia-
bles associated with the screening operation included raw flow rate, drum
screen speeds, backwashing rates and headloss across the screens.
The flotation system sampling began automatically when the raw pump primed.
Raw waste and screened water sample collection was started immediately. Ef-
fluent sample collection was delayed for one tank detention period to allow
purging of the water in the tank from the previous run. This procedure insured
collection of representative effluent samples. Screen backwash and floated
scum samples were taken during screen backwash and scum removal periods.
The automatic sampling system consisted of two timers connected through the
proper valving, to automatically composite the raw waste, screen water and
effluent samples. The first timer controlled the sample taking frequency (0-
30 minutes). The second timer controlled the duration of sampling time (0-60
seconds). The samplinq valves were air operated weir valves. In general,
116
-------
samples were comppsited every 5 minutes with the automatic system. Floated
scum and screen backwash sample taking was not automated due to the problems
associated with intermittent flows and heavy solids concentrations in these
process streams. The samples were refrigerated immediately after the run.
Analyses were then started within 0-8 hours.
The screening system was automatically sampled in a similar manner. Gen-
erally, the samples were composited every five minutes with the automatic
system throughout the duration of the overflow. The first samples of the raw
and the screened effluent were collected after a minimum of 5 minutes of
system operation had elapsed to allow purging of any waste remaining^from
previous tests, After collection, the samples were handled as described above.
To define the removal efficiencies of each process, it was proposed to run
the same schedule of analytical tests as described in Sections VII and IX
with the following exceptions.
1. Total and dissolved TOC in place of COD analysis.
2. Effluents from the coarse screen (50 mesh) to be analyzed only
for suspended solids, volatile suspended solids and TOC.
3, Total phosphorus in place of ortho phosphates.
A listing of the analysis schedule Is presented below.
ANALYSIS SCHEDULE
Raw Coarse Fine Flotation Screen Flotation
waste screen screen eff 1 uen_t_ backwash sludges
f w i u 7 »* *
pH
Total solids
Total volatile solids
Suspended sol ids
Total organic carbon
Dissolved organic carbon
BOD
Total organic nitrogen
Total phosphorus
Total col I form
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
X X
X X
X
X
X
X
X
X
X
X
X
X
117
-------
Sample analysts procedures are discussed in Appendix C.
Test Plaji
The variables associated with the operation of the flotation system included
hydraulic overflow rate (gpm/sq ft of tank area), pressurized flow rate,
operating pressures, the addition of chemical flocculants, and the floated
scum volumes. To investigate effluent pressurization as a method of improv-
ing the quality of effluent produced by the DAF unit, test conditions were
selected to provide a common basis for comparisons between the modes of
pressurized flow (i.e. split flow and effluent recycle). These test con-
ditions were determined by the previous testing performed (Sections VI and
VII), and were as follows:
pressurized flow (split flow)
operating pressure
overflow rate
Chemical dosages
20% raw flow
40-50-psig
3-3 gpm/sq ft
25 mg/l FeClj
4 mg/l polyelectrolyte, cat ionic
(C31 or equivalent)
It was planned to closely adhere to these test conditions while evaluating the
effluent recycle mode of pressurized flow. The pressurized flow and the oper-
ating pressure could be adequately controlled to maintain these conditions.
Because the flotation tank was divided into two separate areas, two overflow
rates were obtainable concurrently. Therefore the raw flow rate was adjusted
to obtain overflow rates which would be close to the optimum overflow rate of
3.3 gpm/sq ft. Previous studies had shown that at equivalent dosage rates,
Nalco 607 was a satisfactory substitute for the cationlc polyelectrolytes
(C31) which was used previously.
The operational parameters monitored for the screening system included the
hydraulic and solids loading rates, drum rotational speed, headlosses across
the drum and the volumes of backwash required. Because the effluent from the
flotation unit was automatically transferred to the screening system, the
hydraulic loading rate was fixed. The solids loading rate and the attendant
headlosses across the screen could be varied by adjusting the rotational
speed speed of the drum. During the operating season this test plan was
expanded to include the direct microscreening of raw CSO. During these test
runs, the raw flow rate was varied to allow variations in the hydraulic load-
Ing rates.
A total of 10 overflow events were monitored at the Hawley Road test facili-
ties during the 1973 operating season. The detailed analyses of the charac-
teristics for each of these overflows is presented in Tables E-41 and E-42
In Appendix E. Each overflow was counted as a separate event over the entire
length of the storm duration. No distinction was made between the first
flush and the extended durations due to the short durations of most storms
during the operational periods.
Consistent with previous observations, Appendix E. there was a wide variation
118
-------
in the raw CSO wastewater characteristics. The suspended solids concentra-
tions of the raw CSO ranged from 39 to 276 mg/1 during the 1973 operating
season. Similar variations appear in the other pollutant parameters. A
summary of the actual raw water quality concentrations sampled by each of -
the treatment systems is shown in Table 30. For comparison, previously re-
ported (71) raw CSO characteristics are also presented. The ranges of data
shown is at the 95? confidence level.
It can be readily seen that the pollutant levels of the raw wastewater for
the 1973 season were, in general, lower than the corresponding pollutant
levels of previous seasons. For example, influent suspended solids to the
flotation system were only 146 ± 60 mg/1 as compared to 2kk'± 51 mg/1 obtained
during the 1969, 1970, and 1971 seasons. The suspended solids to the screen-
ing system were only 97 ± 80 mg/1.
The results of the screening/flotation unit operation are divided into the
following two sections: coarse screening, and dissolved air flotation.
Coarse Screening
The raw flow entered the 50 mesh (297 micron) opening drum screen via a 1/2
inch opening bar rack. The bar screen removed the gross particulates and the
50 mesh screen removed most of the settleable particulates'prior to flotation
treatment. Complete results of the screening treatment are listed in Appen-
dix E, Table E-17. A summary of the screened water quality is shown in Table
31. .......
Table 31. SUMMARY OF 50 MESH SCREENED WATER QUALITY - 1973
(95% confidence level)
Ana lysis
Total sol]ds
Total volatile solids
Suspended solids
Suspended volatile solids
TOC
BOD
Con cen t ra t i on, mg/1
269 ± 85
110 ± 37
126 ± 57
kk ± 14
36 ± 15
36 ± 17
Particulate matter, as measured by suspended solids, ranged from 45 to 276
mg/1.
119
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A summary of the pollutant removals effected by the 50 mesh drum screen is
presented in Table 32. For comparative purposes, removal rates obtained
in previous operations are also shown. In general, removals by the drum
screen during the 1973 season were lower than those obtained in past per-
formances. The percent removals for various pol1utants were in the range of
15 to 28%. No significant leaks in the drum screen were found that may have
caused the lower removal efficiencies during 1973 operations, and the lower
removal efficiencies could only be a result of a difference in particle size
distribution of the particulate matter.
The backwash volumes ranged between 0 to 2.7? of the raw flow and averaged
0.8% for all runs during 1973. Some blinding problems were experienced on
the screen media during prolonged dry weather periods. Such blinding could
have been a result of microorganism growth and the screens were kept cleaned
with periodic washes with sodium hypochlorite and/or dilute acid solutions.
Dissolved-Aif Flotation Operation
As mentioned earlier, during 1973, the operation of the dissolved-air flota-
tion system was conducted in the effluent pressurization mode compared to the
split flow mode of pressurization during previous years. A complete listing
of the operational parameters is included in Appendix E, Table E-23. Briefly,
the surface hydraulic loading rates ranged between 2.7 and 3.9 gpm/sq ft on
the low overflow rate side of the flotation tank to between 4.0 and 7.8 gpm/
sq ft on the high overflow rate side. The pressurization flow ranged between
400 to 650 gpm representing 27 to 33% of the raw flow. Chemical treatment
consisted of the addition of ferric chloride and Nalco 607, a cationic polymer.
The average dosages of these chemicals based on the raw flow were 25 and 4
mg/1 respectively.
A summary of the pollutant removal efficiencies of the screening/flotation
system in terms of percent removals is presented in Table 33' A summary of
the effluent quality from the flotation unit is presented in Table 34. Also
presented are the comparative removals achieved by the system during the years
1969 through 1972, during which years the unit was operated in the split flow
mode of pressurized flow. Comparing the percent removal efficiencies, there
is no apparent difference in the overall system performance via the two modes
of operation. For example, the suspended solids reductions In the effluent
recycle mode ranged from 48 to 76% compared to 48 to 80% for the split flow
mode of operation. Similarly, the percent removals of various other pollu-
tant parameters were comparable for the two modes of operation. However,
when the effluent quality data shown in Table 34 is compared for the two oper-
ation modes, the results are quite different. It can be readily seen that
the quality of the DAF effluent during 1973 (using effluent pressurization)
is significantly better than previous years (when split flow mode of pressur-
ization was used). Since the concentration of pollutants during 1973 was
generally lower than in previous years, and only 9 runs were made in effluent
pressurization mode, it would appear that additional data is required to sat-
isfactorily evaluate the performance of the effluent pressurization compared
to split flow pressurization.
121
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The mechanical operation of the screening/flotation system in general was
excellent and no overflows were missed due to any mechanical problems.
Maintenance was minimal and the system could be run with minimum supervision.
Flotation Effluent Screening
A listing of the operating conditions for the five test runs where the DAF
effluents were processed through the 22 micron nylon microscreen is presented
in Table 35 and in Appendix E, Table E-^7. The influent flow to the micro-
screen (the entire flow from flotation unit) varied from 1687 to 2385 gpm.
These flows corresponded to hydraulic loading rates of 27 to 37 gpm/sq ft.
The solids loading rates, based on the suspended solids removed on the screen,
were extremely low and varied between 0.16 and 1.68 lbs/100 sq ft.- This
loading is based on pounds of suspended solids in the flotation effluents per
100 square feet of wetted screen area.
The headloss across the screen generally varied between 12.5 to 13.5 inches
of water. During run 73"5, however, th headloss briefly exceeded 1A.5 inches
and a portion bypassed the screening chamber via an overflow weir.
this headloss exceeded 9 inches of water differential, the backwash
activated, indicating that the backwashing on the microscreen was
100% of the operational time. The backwashing volume pumped
during these runs ranged between 3.^-^.0% of the raw flow.
of water
Whenever
pump was
kept "on"
The results of the microscreen ing operation for the five storm events inves-
tigated are presented in Table 36. The influent concentrations were arrived
at by averaging the results of the high and low overflow rate flotation
effluents. Also, a summary of the percentage pollutant removals is presented
in Table 37. The percent pollutant removals on the screen are presented
both based on raw CSO as well as flotation treated effluent qualities. It
can be seen that the microscreen i ng unit removed approximately 20 to A0%
(Table 37) of pollutants based on the influent quality coming into the micro-
screen. However, the incremental improvement tn effluent quality due to
microscreening over and above the flotation treatment was only 5 to 12% for
suspended ard volatile suspended solids while no improvement was recorded in
TOC removals.
Based on these low incremental improvements in effluent quality, it was de-
cided to curtail efforts to upgrade DAF effluent by microscreening and instead
activities were directed towards evaluation of the, use of the microscreening
unit for the treatment of raw CSO.
MICROSCREENING OF RAW CSO
The necessary valving modifications were made to the microscreening system to
allow treatment of the raw CSO instead of the flotation treated effluents.
Five raw combined sewer overflows of the 1973 season were treated by the
microscreening unit. A summary of the operational parameters for these five
storms is shown in Table 38 and in Appendix E, Table E-^7- The hydraulic
loading rates ranged between 13 and 27.5 gpm/sq ft. The solids loading rates
125
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were again quite low as shown in the table. A summary of the influent and
effluent water quality data is presented in Table 39 and in Tables E-50 and
E-51, Appendix E. It can be seen that the particulate concentrations in
these five storms were extremely low. The suspended solids at 97 ± 80 mg/1 at
the 35% confidence limits were unusually low and contributed to the low solids
loadings on the microscreen. The percentage pollutant removals on the micro-
screen are shown in Table 40. Also, presented in this table are the corres-
ponding treatment efficiencies via the screening/flotation unit in the efflu-
ent recycle mode of operation. It can be seen that the mean pollutant re-
movals via microscreening ranged between 35 to 57% for various parameters at
the 35% confidence limits. The corresponding pollutant removal via flotation
treatment were consistently better than microscreening and ranged between
50 to 67%.
POWDERED ACTIVATED CARBO.'I ADDITION
The Hawley Road screening/flotation treatment facility was operated for ten
overflow events from August 2, 197A to October 29, 197*», The purpose of this
effort was to determine the effect on screening/flotation effluent quality of
using the addition of powdered activated carbon and chemical coagulants. The
flotation unit was operated using the effluent recycle pressurization mode,
The chemicals were added in the following order and at the following location
points: alum and polymer in the screen chamber effluent followed by the acti-
vated carbon in the flocculator.
The following schedule of analytical tests was performed on each sample:
PH
Suspended solids (SS)
Volatile suspended solids (VSS)
Total solids (TS)
Total volatile solids (TVS)
Biological oxygen demand (BOD)
Total organic carbon (TOC)
Soluble organic carbon (SOC)
Total phosphorus
Sample analyses procedures are given in Appendix C.
The variables associated with the operation of the flotation system include
the hydraulic overflow rate, pressurized flow rate, operating pressure, and
the addition of chemical flocculants. To investigate powdered activated car-
bon addition as a method of improving the quality of effluent produced by the
dissolved-air flotation unit, test conditions were selected on the basis of
previous studies and the bench scale testing. The desired conditions were:
1.
2.
3.
pressurized flow (effluent recycle)
25% of raw flow
operating pressure
overflow rate
chemical dosages
40-50 psig
3-3 gpm/sq ft
40 mg/1 Alum
0.5 - 1.0 mg/1 Betz 1160
40 mg/1 Carbon
130
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It was planned to closely adhere to these conditions while evaluating the
process with the addition of carbon. The pressurized flow and the operating
pressure could be easily controlled to maintain these conditions. The chem-
ical feed pumps were set for the desired dosages and functioned well except
for a couple of instances when pump problems caused addition rates less than
desired. For previous studies at the Hawley Road site, the flotation tank
was divided into two modules. This allowed for the simultaneous study of a
high overflow rate and a low overflow rate. For this study, however, the
divisions were removed resulting in one flotation zone and one overflow rate.
It was intended to run the facility at a flow rate of 3 MGD, however, it was
found that the drum screen could not handle the flow at this rate. Therefore,
the site was run at the highest rate possible that would not hydraulically
overload the drum screen.
The means and ranges for the operating conditions during the ten runs in 1974
are given in Table 41. The operating conditions are given on a run-by-run
basts in Appendix E, Tables E-31 through E-40.
A total of 10 overflow events were monitored at the Hawley Road facility
during the 197*1 operations. The quality characteristics of the combined
sewer overflows on a run-by-run basis are presented in Appendix E, Tables
E-31 to E-40. A summary of the combined sewer overflow quality concentrations
is presented in Table 42. For comparison, previously reported combined sewer
overflow quality characteristics are also presented. The ranges given for the
means are at the 95 % confidence level.
It can be seen that the pollutional concentrations of the combined sewer
overflows for 1974 have increased when compared to the concentrations found
in 1973, Except for the suspended solids concentrations, they have also shown
a slight increase compared to the concentrations found in 1971"72.
The ranges given at the 95 percent level of confidence are all greater than
those found in 1973 or 1971~72. This indicates that the quality concentra-
tions found in 1974, in addition to being higher on the average, were much
more variable than those encountered in 1971-72 and 1973. This high varia-
tion in concentration in conjunction with the low sample number (10) made it
difficult to show significant statistical differences between the means for
1974 and the means from 1971-72 or 1973-
The increase in the mean pollutional concentrations of the combined sewer
overflows also affected the removal calculations (effluent concentrations in-
creased but percent removals also increased) which will be discussed later in
this section.
The screened overflow quality characteristics are given on a run-by-run basis
in Appendix E, Tables E-31 to E-40. The mean quality characteristics of the
screened combined sewer overflows in 1971-72, 1973, and 1974 are given in
Table 43. Also presented are the pollutional percent removals achieved by
the .screen in 1971-72, 1973, and 1974. As with the raw overflow, the screened
overflow was of a higher pollutional concentration than in 1973. The percent
removals for 1973 and 1974, however, were similar. The mean concentrations
133
-------
Table 41. AVERAGE OPERATIONAL PARAMETERS FOR
DISSOLVED-AIR FLOTATION PROCESS - 1974
Flow rate
Raw, gpm
Recycle, gpm
Tota1, gpm
Recycle rate, percent
Hydraulic overflow rate
Raw, gpm/sq ft
Total, gpm/sq ft
Chemical dosages
Alum, mg/1
Carbon, mg/1
Polyelectrolyte, mg/l
Mean
1866
540
2406
29
2.38
3.10
35
50
0.9
Range
1362-2205
400-700
1987-2705
21-46
1.74-2.83
2.5.6-3.46
18-63
26-94
0.11-1.7
134
-------
Table 42. COMBINED SEWER OVERFLOW QUALITY CHARACTERISTICS
(1971-1974) (mg/1) (952 confidence level)
Parameter
SS
VSS
TS
TVS
BOD
TOC
SOC
Total phosphorus
1971-72
230±97
75 ±28
347±100
158+79
34+18
45±15
1973
--.'
129 ±62
52±21
255±75
108±36
42±19
39±17
17±7
0.99+0.51
1974
* ^ /
162±101
87 ±68
^09+195
213±108
74±64
58 ±42
25±10
1.47+0.73
135
-------
Table 43. SCREENED EFFLUENT QUALITY CHARACTERISTICS (mg/1)
AND PERCENT REMOVALS BY THE SCREENING PROCESS - (1971-1974)
(952 confidence level)
Parameter
SS
VSS
TS
TVS
BOD
TOC
SOC
Parameter
SS
VSS
BOD
TOC
SOC
1971-72
204±118
71±4l
493±220
227±68
23±16
39±15
1971-72
12
18
28
9
1973
126±58
44±15
269±85
110±37
37±17
36±15
Percent Removal
1973
13
22
15
11
1974
132±57
68±35
322±134
173±68
51 ±26
46±20
23±10
1974
16
14
15
13
17
136
-------
were^compared among the t.hree different study, periods and no statistically
significant differences were found. The mean percent removals were also
compared among the three periods and again no statistically significant
differences (increase or reduction) were found.
As discussed previously, in 1974 the operation of the dissolved-a?r flota-
tion system was conducted in the effluent pressurization mode with the addi-
tion of alum, polyelectrolyte, and powdered activated carbon. In 1973, the
system was operated in the effluent pressurization mode with the addition of
ferric chloride and polyelectrolyte, and in 1971-72, in the split flow
pressurization mode with the addition of ferric chloride and polyelectrolyte.
The average 1974 operating conditions are given in Table 41. The raw flow
rate averaged 1.87 MGD with a range of 1.36 to 2.21 MGD. The recycle rate
averaged 0.54 MGD and ranged from 0.40 to 0.70 MGD« This resulted in an
average recycle rate of 28.9 percent of the raw flow and a range of 21.4 to
45.9 percent. The hydraulic overflow rate averaged 2.95 gpm/sq ft with a
range^of 2.56 to 3.46 gpm/sq ft. The chemical treatment consisted of the
addition of alum, average dosage of 35 mg/1; powdered activated carbon,
average dosage of 50 mg/1; and polyelectrolyte (Betz 1160), average dosage of
0.9 mg/1.
A summary of the pollutional percent removals achieved by the dissolved-air
flotation unit is presented in Table 44. Also presented are the comparative
removals achieved by the system during, the testing periods in 1971-72 and
1973. Statistical comparison of the percent removal efficiencies again re-
vealed no significant differences among the three periods of study.
The final effluent quality characteristics from screening/flotation are given
on a run-by-run basis in Appendix E, Tables E-31 to E-40. The mean quality
characteristics of the final effluent, and the mean percent removals achieved
by the overall system are given in Table 45 for 1971-72, 1973, and 1974.
It can be seen from Table 45 that the quality of the effluent in 1974 is sim-
ilar to the effluent quality in 1971-72, but less than the quality achieved
by the screening/dissolved-air flotation process in 1973. On the other hand,
the pollutional percent removals for 1974 are also similar to those achieved'
in 1971-72 but they are better than the percent removals attained in 1973.
The increase in percent removals and in effluent concentrations is attributed
to the increase In the raw quality concentrations in 1974 compared to 1973.
The high pollutional concentrations in the raw combined sewer overflows in
1974 led to better percent removals than in 1973, but these increased percent
removals did not result in improved final effluent quality over the quality
achieved in 1973. In fact, the quality of the effluent decreased in 1974.
Comparing 1973 to 1974, the average effluent SS increased from 22 to 37 mg/1,
the total solids increased from 208 to 321 mg/1, the BOD increased from 20 to
28 mg/1, and the TOC increased from 25 to 33 mg/1. Statistical analyses
indicated that these changes were not significant at the 95 percent confidence
level, but the overall pattern does indicate that an actual increase did
occur. The lack of statistical significance is probably due to the low num-
ber of observations made (8 or 9 samples for the given parameters in 1973 and
137
-------
Table 44. PERCENT REMOVALS BY THE DISSOLVED-AIR
FLOTATION PROCESS - (1971-1974)
Parameter
SS
VSS
BOD
TOC
SOC
Percent Removals
1971-72. 1973
59 49
49 49
43 41
49 31
1974
54
47
56
37
32
138
-------
Table 45. FINAL EFFLUENT QUALITY CHARACTERISTICS
AND PERCENT REMOVALS BY THE
SCREENING/DISSOLVED-AIR FLOTATION PROCESS-0971-197*)
Parameter
SS
VSS
TS
TVS
BOD
TOC
SOC
Total Phosphorus
1971-72
87+38
39±18
40U154
191 ±78
13+8
20 ±9
1973
5 2 ±22
21 ±7
. 208+66
91 ±40
20 ±8
25±15
15+9
0.47+0.19
1974
58+37
35 ±29
321+130
172 ±63
28+27
33±25
16±8
0.52+0.37
Percent Removals
Parameter
SS
VSS
BOD
TOC
SOC
Total Phosphorus
1971-72
58
48
59
52
1973
54
60
46
35
16
47
1974
60
56
65
45
38
65
Note: Intervals given are at the 95 percent level of confidence,
139
-------
3 samples in 1974).
Statistical comparison of the 1971-72 and 1974 means, both effluent concen-
trations and percent removals, showed no significant differences. No
patterns were obvious from observation of the data either, because of some
percent removals improving while the concentration in the effluent also
increased. Better SS, VSS, and BOD percent removals were achieved in 1974
than in 1971-72 while the percent removal of TOC was better in 1971-72. In
197*», the final effluent SS, VSS, total solids, and total volatile solids
concentrations were lower than those found in 1971-72, but the final effluent
BOD^and TOC concentrations were higher than in 1971-72. Therefore, no sig-
nificant improvement in the efficiency of the screening/dissolved-air flo-
tation process can be shown due to the change from split flow pressurization
with ferric chloride and polyelectrolyte addition (1971-72) to effluent
recycle pressurization with alum, powdered activated carbon, and polyelect-
rolyte addition (197*0-
The percent removals of soluble organic carbon (SOC) and total phosphorus
do show marked improvements in 1974 when compared to 1973. The improvement
in the SOC percent removal is statistically significant at the 95 percent
level of confidence. The effluent concentrations of both total phosphorus
and SOC, however, were higher in 1974 than 1973, but the increase in the
average SOC concentration, 1 mg/1, is very slight compared to the increases
observed for the other quality parameters.
The effectiveness or. noneffectiveness of the powdered activated carbon addi-
tion is not clearly shown by the results from the study. There was a signifi-
cant improvement in the percent removal of SOC and a corresponding increase
in the percent removal of TOC, but at the same time, the average effluent
concentration of TOC increased from 25 to 33 mg/1 and the SOC concentration
increased from 15 to 16 mg/1. The corresponding increases in the raw flow
were: TOC, 39 to 58 mg/1, and SOC, 17 to 25 mg/1. It does appear that the
addition of powdered activated carbon did improve the percent removal of the
soluble portion of the total organic carbon, and this improved removal did
prevent the effluent SOC concentration from increasing as much as the efflu-
ent concentrations of the other parameters when the combined sewer overflow
pollutional strength increased in 1974. However, the improvement of the SOC
percent removal, 16 to 38 percent, cannot be entirely attributed to the
addition of the powdered activated carbon. The percent removals of many of
the other parameters also increased; apparently because of the increased
concentrations of the parameters In the raw overflow. For this reason, it is
difficult to make a judgement on the magnitude to which the powdered acti-
vated carbon was responsible for the improvement in the percent removal of
SOC by the screening/dissolved-air flotation process.
The same problem also affects the improvement in the percent removal of total
phosphorus in 1974 when compared to 1973. How much of the improved removal
is due to the addition of alum, and how much is a consequence of increased
phosphorus concentrations in the raw combined sewer overflows? It appears
that the addition of alum helped in improving the percent removal of phos-
phorus, 47 to 65 percent, but the improvement cannot be quantified from the
data available.
140
-------
During the course of the study In 1374, one run at the Hawley Road facility
was conducted without the addition of carbon (Run Ho. 7, Table E-37, Appendix
E. The intention was to compare this run with the others for which carbon
was added. The very low pollutional strength of the overflow (SS: k2 mg/1;
BOD: 15 mg/1; and TOC: 18 mg/1), however, made comparisons on a percent
removal basis difficult. The effluent concentrations (SS: 29 mg/1; BOD:. 14
mg/1; and TOC: 13 mg/1) rray indicate the minimum effluent concentrations
that can be practically achieved by the screening/dissolved-air flotation
process.
Any consideration of the use of pov/dered activated carbon to improve the
treatment efficiency of the screening/dissolved-air flotation process must
take into account the increased costs that are required to achieve the im-
proved efficiency. The use of alum and polyelectrolyte (Betz 1160) as the
chemical flocculants resulted in a chemical cost of 3.94
-------
SECTION XI
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(4) Palmer, C.L.. WPCF Journal 35:2:162 (1963).
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(6) Palmer, C.L., Sewage and Industrial Wastes 22:2:154 (1950).
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& Sons, Inc., New York, (1961).
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(September 15, 1954).
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sented at the Air Utilization Institute, University of Wisconsin, (Apr? 1
15, 1958).
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Recovery", P roceed i ngs of t^he 1 Oth I ndust r t a 1 Waste Conference , Purdue
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of Adsorption by Activated Sludge", Biological Treatment and Sewage and
Industrial Wastes by McCabe, J. and Eckenfelder, W.W., Volume T, p. 6<3,
Reinhold, New York, (1956).
Ettelt, G.A., "Activated Sludge Thickening by Dlssolved-Ai r Flotation",
Proceedings 19th Purdue Industrial Waste Conference, p . 2 1 0 , (1 964).
Katz, V/. J., Public Works 39:12:114 (1958).
Uurwitz, E. and Katz, W.J., Wastes Engineering 30:12:730 (1959).
Ettelt, G.A. and Kennedy, T.J., WPCF Journal 38:2:248 (1966).
Katz, W.J., and Geinopolos, A., WPCF Journal 39:6:946 (1967).
Eckenfelder, W.W., Jr., Indus trial Wate. r ^ Po i lj_u itj pn_ _Cqn t TO <_] i_, McGraw-Hill,
New York,.?. 275, (1966) .
Howe, R.H.L., "Mathematical Interpretation of Flotation for Solid-
Liquid Separation", B ? o 1 og i ca 1 T rea tmen t : ojF _Sewe rage |_ _and_ _Ltl4uAt_r_Lil
Wastes, Reinhold Publishing Company, 2nd Edition, 1958.
Eckenfelder, W.W. , Jr., et al ., "Dissolved-Ai r Flotation of Biological
S 1 udges" , Biological Treatment of Sewag_e_and_ lndjjsj:rial Wastes ,
Reinhold, New York, p. 251-253,Tl953f.
Ga rwood , J . , E f f 1
7 : 380 ( 1 967) .
Mogelnicki, S.J., "Experiences in Polymer Application to Several Solids-
Liquid Separation Processes", proceed i_ng_s 1 [Oth Sanitary jnjj nee_r_'nT£
Conference, University of I 11 inois, Tfufletin 65, 115:47" f 113610 .
"The Use of Organic Polyelectrolyte for Operational Improvement of
Waste Treatment Processes", Report prepared by City of Cleveland, Ohio,
for FWPCA, Grant No. V/PRD 102-01-68, (May, 1969).
Braithwaite, R.L., Water and Sewage Works 111:12:547 (1964).
"Chlorinatfon of Sewage and Industrial Wastes", Manua 1 of Pract ? ce No .
4^, Federation of Sewage and Industrial Wastes Association, (1951).
Koller, L.R. Ultraviolet Radiation, John Wiley & Sons, Inc., New York,
0952).
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Symons, R.S., Sewage Works Journal 13:2:249 (1941).
144
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McKee, J.E., et^ aj_., WPCF Journal 32:8:795 (i960).
Cleasby, J.L. , et al.t Journal AWWA 56:4:466 (1964).
Cherry, A.K., Journal AWWA 54:5:417 (1962).
Hann, V.A., Journal AWWA 48:10:1316 (1956).
Hann, V.A., Journal AWWA 35:5:585 (1943).
Powell, M.P., e^aj_., Journal AWWA 44:12:1144 (1952).
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Petroleum Insti tute, (1969).
Christensen, Ralph, Private communication, EPA Project No. 11030 FOB,
Detroit, Michigan, FWQA Chicago, I 11 inois, (1969).
Gannon J. and Stueck, L., "Current Developments in Separate vs. Com-
bined Storm and Sanitary Sewage Collection and Treatment", presented
42nd Michigan WPCF Conference, June, (1967).
Eckenfelder, W.W. Jr., Principles of Biological Oxidation. Pergamon
Press, New York, (1966).
Bennett, C.A. and Franklin, N.L., Statistical Analysis in Chemistry
and the Chemical Industry. John Wiley and Sons, London, (195"4~)~
Bulletin 720B "Variable Capacity Pumping Systems", Aurora Pump Com-
pany, Aurora, I 11inois.
Mason, D.G. and Gupta, M.K., "Screening/Flotation Treatment of Com-
bined Sewer Overflows", USEPA Report No. 11020 FDC-01/72, (January 1972).
Hansen, C.A., Agnew, R.W. and Murray, D.L., "Quality Characteristics
of Combined Sewer Overflows and Urban Stormwater Runoff", presented
at the 45th Annual Central States V/ater Pollution Control Association
Meeting, Milwaukee, Wisconsin, (June 15, 1972).
145
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SECTION XI I - APPENDICES
APPENDIX A - CHEMICAL OXIDATION STUDIES
LITERATURE SEARCH
Removal of organic contaminants from combined sewer overflows cannot be
effectively and economically accomplished by conventional biologixal oxidation
methods (Al) (A2) for the following reasons:
A. Large and highly variable flows.
B. Intermittent operation would be required because of the nature
of the flows, and this has a very detrimental effect on biological
oxidation systems (A3)(A4)(A5).
C. Removal of the solids produced would require a large number of
sedimentation tanks (because of high flows) which would be used only
periodically.
Use of chemical oxidation on combined overflows has the potential advantage
of effective destruction of biological organisms and the removal of organic
contaminants without the production of residual waste concentrates. Some of
the technical difficulties connected with the successful treatment of wastes
by chemical oxidation include the relatively dilute concentrations of organic
materials present, the unknown composition of a wide range of possible organic
compounds present, and the continually changing concentrations and composition
present in a combined wastewater flow such as the one which this project 5s
concerned.
These difficulties necessitate the use of gross parameters ?n evaluating the
effectiveness of a given chemical oxidant. Such parameters would include know-
ing the chemical oxygen demand of the waste (COD) and the concentration of the
oxidizing properties in the chemical being utilized. Having this information,
the oxidation efficiency (A6) can be calculated as shown below:
Oxidation Efficiency - ACOD
Available Oxidation Equivalents x 100
Where: ACOD = change in COD brought about by the oxidation process (in
milligrams of 02 per liter)
And: Available Oxidation Equivalents = amount of chemical oxidation
equivalents available from the oxidant used (in milligrams of 0,
per liter)
-------
Taking into account the variation in organic concentration and volume of the
waste flow to be treated under this contract, the "ideal" oxidant should have
the following characteristics:
A. It must be nonspecific in its attack on organic materials.
B. Its required contact and retention time should not be excessive
(30 minutes or less).
C. It should be easy to handle and dispense.
D. It should effectively oxidize the organic materials at the prevailing
pH of the waste.
E. Jt should not produce any secondary pollutants which are difficult to
remove from the waste flow.
From the literature (A6) it was found that six types of oxidation systems
offer various degrees of potential for the treatment of organic impurities
in wastewater. These systems are:
A. Oxidation by oxidants containing active oxygen.
B. Accelerated molecular oxygen oxidation.
C. Catalytic oxidation of adsorbed organlcs.
D. Oxidation by chlorine and its derivatives.
E. Oxidation by oxy-acids and their salts.
F. Electrochemical oxidation.
Of the six oxidation systems mentioned, only systems A, D, E, and F appear to
have potential for treating combined sewer overflows. These systems will be
discussed in detail below.
Hydrogen Peroxide
Considerable work has been done regarding the application of hydrogen peroxide
(H20_) as an oxidizing agent in the treatment of wastewater containing organic
impurities (A6)(A?)(A8)(A9)(A10) (A11) (A12).
In aqueous media, hydrogen peroxide decomposes to form the *OH radical. This
radical is one of the strongest oxidants known in aqueous systems. However,
hydrogen peroxide does not, when used alone, oxidize organic materials within
a practical reaction time. The system requires a multivalent iron salt as a
catalyst.
The principle reactions involved in a hydrogen peroxide iron salt system are
as follows: (A11)(A12)
.+
-I-,-.!,!,
Fe+
Fe
H
2.
-» Fe + OH + 'OH
-------
Considering reactions 1 and 2 above, the iron salt acts truly as a catalyst
i.e., it is not utilized during the reactions. Reaction.!; is the rate 1 imU'-
Ing reaction. Once the ferrous ion is formed, reaction 2 is extremely rapid
(A11)(A12). The production of *OH~radicals via reactions 1 and 2 using fer^-
r!c salts requires two to three hours at 65°C (A6). By using ferrous salts,
the production of *OH~radicals is essentially immediate, but the iron salt; !!
no longer performs as a true catalyst, since it is not reproduced at the same
rate at which it is being utilized. There are other reactions associated ; ;
with the H,0 --iron salt system which compete with the organic material being
oxidized for the "OH~ radical. The following
petition for 'OH~ radicals (All)(A12).
3. FE+++ "OH +
reactions illustrate the com-;
5.
6.
'OH
2 2 2
Hence, only an unknown portion of the *OH radicals produced are available to
oxidize the organic substrate.
The efficient production of 'OH radicals requires a specific pH range of 3
to 5 (A6)(A7) (A10) (All). Above or below this specific pH range, production
of "OH radicals is greatly reduced. During the reactions, an excess of H
Ions are formed (A9) so the pH will normally stabilize in the optimum range.
Elsenhauer (A?) found that the initial pH of an ABS solution could be as
high as 11, before it would significantly affect pH stabilization in the 3
to 4 pH range. The pH of the system can also be lowered to the specific
range by use of acid (All).
The reactions between 'OH radicals and specific organic substrates were sum-
marized by Busch (A12) after review of a number of papers on the subject.
Since the waste to be oxidized under this contract contains many different
types of organic substrates tn unknown proportions, these specific equations
were not directly applicable and hence were not reproduced herein.
Use of the hydrogen peroxide method of oxidizing organic wastes has been
experimentally evaluated. Davidson found that phenols could be chemically
oxidized (90% complete) to carbon dioxide and water in ten minutes (A9).
Etsenhauer demonstrated that in dilute aqueous solutions of phenol, the
reaction efficiency was considerably increased In the presence of air-avail-
able oxygen (A7)
Eisenhauer also found that the reaction between a hydrogen peroxide- ferrous
salt combination and Acrylonitri le Butadiene Styrene Polymers was rapid and
80 to 902 of the ABS was destroyed in the first ten minutes. Further ABS
removals were obtained at slower reaction rates, with a .99^ ABS removal
effected after fifteen to twenty hours. The optimum reaction pH level was
found to be from 3-0 to 3-5. The optimum concentrations of the reactants
-------
were six moles of ferrous salt per mole of ABS, and nine moles of 1^2 per
mole of ABS. Multiple Incremental additions of the ferrous salt will decrease
the reaction time required (All).
Applying this information to a treatment of laundry wastes containing ABS,
Eisenhauer obtained ABS reductions in excess of 90%, both with the raw waste
and with effluent from a pretreatment process in which the detergent builders
were precipitated. For a laundry waste containing 50 to 80 parts per million
ABS, it was found that chemical costs ranged from $0.^5 to $0.70 per 1,000
gallons for the effluent pretreated with ferric sulfate. This includes the
cost of ferrous sulfate, ferric sulfate, sulfurlc acid, and hydrogen peroxide
Bishop <3t aj_ (All) used hydrogen peroxide-iron salt systems to oxidize refrac-
tory organics in municipal wastewaters previously subjected to secondary bio-
logical treatment. Significant conclusions from this paper (All) are present-
ed below.
1. The hydrogen peroxide-iron salt systems in various wastewaters
oxidize a significant portion (=70%; of the organics refractory
to biological oxidation.
2. The oxidation process involves free radical ('Otj) oxidation and
auto-oxidation and is effective only in the .pH range of 3 to k.
3. Oxidation efficiencies of 60% for the ferric ion systems and 30 to
51% for the ferrous systems were reported.
No data were found in the existing literature where hydrogen peroxide was used
to oxidize raw sewage or combined sewer overflow. Since the H202 systems did
oxidize the refractory organics present in sewage, there should be no problem
oxidizing the organics in combined sewer overflow. The important problems
associated with the use of this oxidation system for combined sewer overflow
include:
1. The restricted pH range will require lowering of the pH of the com-.
bined sewer flow.
2. Materials used for construction will have to be able to withstand the
pH of the system. This will require the use of stainless steel, or
rubber coated mild carbon steel.
3. Removal of the ferric hydroxide formed during the reaction will re-
quire a flocculation and settling period.
A. The pH will have to be readjusted to near neutral before the effluent
is discharged.
149
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Ozone
The use of ozone as an oxidant for water and waste treatment is described in
the literature (A6) (A13) (AU) (A15) (A16) (A17) (A18) (A19) (A20) (A21). Ozone is a
blue gas under normal conditions. It contains three atoms of oxygen (0,) and
Is heavier than air or oxygen. Ozone is one of the most powerful oxidants
known (A13). The oxidizing power of ozone is exceeded only by fluorine and
compounds such as oxygen difluoride, atomic oxygen, and the hydroxyl radical
(A22). In high concentrations, ozone is toxic (A13)(A14). Figure A-1 shows
the human tolerance for ozone at various concentrations and exposure times.
Source; Prolonged Ozone Inhalation, Its Effects On
Visual Parameters, J. M. Langewerf, Aerospace
Medicine, 36, June 1963-
10,000
1000
a.
a.
z
o
LU
o
o
o
LU
1
o
100
10
NON-TOXIC
NON SYMPTOMATIC
REGION
0.1
0.1
FATAL REGION
3ERMANENT
TOXIC
S. REGION
fEMPORARY
TOXIC
REGION
REGION
10 100
EXPOSURE TIME, MINUTES
Figure A-1. Human 'tolerance for ozone
150
1000
10,000
-------
The area between the symptomatic line and irritant line of Figure A-1 is a
nontoxic region. The threshold odor level of ozone is 0.01 to 0.02 ppm which
is well below the toxic region as shown in Figure A-1 (A13). Exposed persons
are thus given a warning of ozone's presence.
Ozone can be produced in a number of ways. Among these are silent electric
discharge, electrochemically, and chemically (A22). Use of silent electric
discharge is the principal upon which most laboratory and large scale ozoni-
zers depend (A13)(A22). Production of ozone by this method requires the use
of cold, clean air or oxygen. Basic equipment necessary include an air fan,
equipment for filtering and drying the air and an ozonizer (A14), When
applying the ozone to water, some type of diffuser system and a contact tank
wjll also be needed (AH). Ozonizers produce ozone by passing the dried air
between two concentric electrodes separated by a dielectric. High frequen-
cies ^(500 cps to 1000 cps) and high voltages (4000 to 30,000 volts) are
utilized. Some oxygen in the air passing through the ozonizer is broken into
charged oxygen atoms, which recombine to form 0_. Ozonizers operating on air
under pressure produce far greater quantities of ozone in higher concentrations
than those operating in air at atmospheric pressures (A13)(A17). Commercial
ozonators produce ozone concentrations of 1 to k percent by weight in air (A1?)
(A23). Power consumption is 9.5 to 11.5 KWH per pound of ozone produced (A23).
Ozone is very corrosive and hence the materials used in the piping system
carrying ozonated air must be carefully chosen. Porcelain has been used with
success, as have aluminum, stainless steel, pressboard, oak, vinyl plastic and
glass (A14)(A24). Polyvinyl chloride (PVC) has been used but there is a pos-
sibility that this material decomposes ozone (A14).
The exact oxidation mechanism of ozone on organic materials is not thoroughly
understood. Ozone decomposition may be a source of 'OH radicals or the 0, it-
self may be the actual oxidant (A6)(A21). Ozone is known, however, to be3an
effective oxidant (A1?)(A18)(A21). The exact oxidation products and intermed-
iates resulting from ozone oxidation have not been defined. Evans and Ryckman
(A18) , when ozonating secondary sewage treatment plant effluents have found
that ozone readily oxidized ABS to Intermediate compounds which were not de-
tected by an ABS analysis. These intermediates actually caused an increase in
BOD and COD values of the partially ozonated waste, and in fact destroyed the
biological inertness of the ABS. Increased ozonation of this partially
ozonated waste then caused a decrease in BOD and COD of the waste, apparently
due to oxidation of some of the organic carbon to C0_ and H_0.
Andrews (A16) was recently granted a patent on a new method of treating raw
sewage. The method Involves removal of the solids from raw sewage by a com-
bination of settling, screening, and centrifuglng. The resulting liquor,
essentially free of solids and containing the soluble BOD fraction of the raw
sewage, is ozonated to oxidize the BOD. The effluent from ozone treatment is
filtered before discharging into the receiving stream.
The patent claims this treatment method produces a clear, colorless effluent,
free from bacteria, and containing a high quantity of dissolved oxygen. How-
ever, no reference is made to ozone dosages required and BOD effluent content.
15!
-------
Miller (A21) reports use of ozone to control sewer odors at sewage lift sta-
tions. He states ozone addition reduced the raw sewage BOD from 120 to 32-
39 mg/1. Septic conditions in flat sewers disappeared and the plant influ-
ent contained 2 to 4 mg/1 of dissolved oxygen. No mention was made of the
quantities of ozone added. The ozone was injected directly into the pump
wet wells for conventional lift stations and into the air compressors
supplying air for the pneumatic-ejector type lift stations.
March and Panula (A15) reported on a study where raw sewage was ozonated.
They report that the BOD of the sewage which was ozonated decreased from 400
to 300 mg/1. Application rate was 6 mg/1 of ozone actually absorbed by the
sewage. This indicates that 1 mg of 0_ will' oxidize about 16 mg of BOD which
seems quite high. The amount of 0, applied during this study was greater
than the amount actually utilized.-1 Absorption efficiencies averaged 22.6%.
Hence, the actual ozone dosage was about 26 mg/1. March and Panula (A15) in-
dicate that the biggest problem in full-scale ozone treatment is efficient
use of the ozone being produced. They suggest collecting the unabsorbed
ozone and reapplying it to the sewage to obtain better absorption efficien-
cies. It should be noted that a simple diffusion system was used during this
study with a 3i foot depth of liquid over the diffusers. Bubble size was on
the order of 0.01 inches in diameter.
O'Donovan (A1*f) stresses the importance of mixing techniques when introducing
ozone into water. He stresses small bubble diameter and turbulence to be im-
portant In obtaining good 0, absorption efficiencies. Two types of absorp-
tion systems which-have been used are illustrated in Figure A-2 (AH) (A25)
Campbell (A25) reports 90% utilization of ozone when using a partial-ejection
system.
The use of ozone to oxidize combined sewer overflow appears to hold considera-
ble promise. Ozone has many of the characteristics of the "ideal oxidant" as
previously discussed. It is apparently nonspecific in its oxidation of or-
ganic material (A21), the necessary contact time is less than 30 minutes (A14)
(A25), it oxidizes at the prevailing pH of the waste (A25), and is not diffi-
cult to dispense (AlA). Some disadvantages involved with the use of ozone
include precipitation of iron and manganese when present in concentrations
greater than 0.2 mg/1 Fe and 0.1 mg/1 Mn, inability to carry an ozone residual
for significant periods, and inability to store ozone requires ozonators at
each application site. Recently, however, Matheson Inc. has announced it had
a process which will allow storage of ozone which could eliminate this latter
disadvantage.
Oxidation by Chlorine
Chlorine or its derivatives are added to most municipal water supplied in the
United States to kill micro-organisms. Green and Stumpf (A26) have shown
that chlorine compounds react with certain enzymes which are essential to the
metabolic process of living cells and that death results from the inactivation
of these enzymes. Dosages required for disinfection are low, 0.2 to 2 mg/1
(Al).
Use of chlorine to reduce the BOD of sewage has been practiced. Four kinds of
152
-------
INJECTOR
OZONIZED AIR
PUMP
CONTACT TANK
III
^
*
JL
(
>
**" (} ^ OZON
FLOW
PATRIAL-INJECTION
(A)
MIXER
RAW WATER
TURBULENCE
CHAMBER
OZONIZED AIR
OZONIZED WATER
KERAG SYSTEM
(B)
Figure A-2. Ozone absorption systems
153
-------
reactions could be involved in reducing BOD by chlorination (A1)(A27).
1. Direct oxidation of organic materials.
2. Substitution of chlorine for hydrogen which produces compounds
which have a bactericidal power.
3. Substitution of chlorine for hydrogen which produces compounds
which are no longer biologically degradable.
A. Addition of chlorine to unsaturated .compounds forming nonbiode-
gradable substances.
Griffin and Chamberlin (A28) have shown that chlorination of sewage does re-
sult in a reduction of BOD. After an 18 hour contact period, about 35% of the
BOD had been removed from screened raw sewage at a 200 mg/1 chlorine dosage.
Increasing the dosage had little effect on further removals.
Although chlorine and its derivatives do oxidize many of the organic chemicals
contained in municipal wastewaters, they do not usually convert them to the
readily acceptable forms of carbon dioxide and water (A6) . Instead, the reac-
tion of chlorine wlj:h organics may produce molecules having considerable taste
and odor, and complex compounds which serve as secondary pollutants may also
be formed. The addition of stoichiometric amounts of chlorine will not effect
oxidation of the organics, and a large chlorine residual may remain in the
treated waste (A6) (A28) . Since oxidation by chlorine is far less effective
than by active-oxygen elements and since the unknown by-products of chlorine
oxidation may be toxic, chlorine and its derivatives are not considered to be
good prospects for removal of large amounts of organic pollutants from waste-
waters by oxidation (A6).
A method of making chlorine more reactive could, however, make the use of
chlorine more attractive. Use of ultraviolet radiation to catalyze the oxida-
tion of organic material by chlorine has been suggested (A29) . No specific
data on such a process was found in the literature, but the process will be
investigated during the laboratory phase of this study.
Oxidation by Oxy-Acids and Their Salts
The'oxy-acid oxidants are usually added to aqueous systems as the salt of the
oxy-acld. Important oxy-acid salts with high oxidation potentials include
potassium permanganate (KMNO^), sodium ferrate (NaFeO.) and potassium ferrate
(KgFeO^). The oxidation potentials of the oxy-acids are strongly dependent
upon the acidity of the aqueous system, with the potential increasing as the
acidity increases (A6) .
Potassium permanganate (KMNO.) is used as an oxidant to disinfect water sup-
plies (A1)(A30) and as an oxidizing agent in the permanganate oxygen demand
test (A31). However, references in the literature report only limited oxida-
tion of organics with KMNO^, and a residual permanganate persists in the
154
-------
water for more than twenty-four hours (A30)(A3l). Vosloo (A32) reports that
the permanganate concentration necessary for maximum oxidation should be
about twice the concentration of permanganate which will be utilized. The use
of potassium permanganate would therefore require removal of the excess MNO.-
ion as a part of the treatment process, and this would greatly increase the
salt load in the aqueous system (A6). The potential for using KMNO,
oxidant in this project is not at all promising, and hence, KMNO^
will not be considered.
^ as an
oxidation
Although ferrate salts such as potassium ferrate (iCFeO.) are not commercially
produced, their high oxidation potentials (A33) and the coagulating properties
of their oxidation products, a highly insoluble ferric hydroxide, make the
ferrates a potentially attractive group of oxidants for treatment of waste-
waters (A6).
Exploratory laboratory tests using K2FeO. to treat filtered municipal secon-
dary effluents in dosages supplying approximately 100 milligrams per liter of
available oxygen showed the combination of ferrate oxidation and coagulation
to b0 nearly as effective as the previously discussed H_0_ - iron salt system
for removing organic materials from wastewaters (A6). The ferrate salts, how-
ever, also possess the same disadvantages as the H-O- iron salt system, (see
previous discussion on hydrogen peroxide oxidation! and these disadvantages
must be considered when attempting to use the ferrate salts as oxidants in
this project.
E1ectro-Chemi ca1 Ox i da t ? on
Any material that increases the electrical conductivity of an aqueous solution
may enter into a chemical reaction at the surface of electrodes placed in the
solution (A27). Interest in electrochemistry as a possible technique for pur-
ifying municipal wastewaters is based on the fact that many organic chemicals
take part in such electrode reactions, often resulting in the complete de-
gradation of complex organic molecules to carbon dioxide, water and other
oxides. After reviewing a recent study on electrochemical oxidation (A3^), it
was concluded that electrochemical oxidation did not hold potential for treat-
ing combined sewer overflows for the following reasons:
1. High operating and maintenance costs.
2. Formation of precipitates which would have to be removed from
the waste flow.
3. Long reaction times are necessary ~ 2 to 5 hours.
Combination ..of. Oxidants
Although no specific data were found in the literature about combining vari-
ous oxidants, a combination of ozone and H20_ or other combinations may pro-
duce an effective oxidation system. For this reason, various combinations of
oxidants will be evaluated during the laboratory phase of this project.
155
-------
LABORATORY INVESTIGATIONS
General Test Procedures
The literature search indicated that the oxidants with the highest potential
success were ozone, hydrogen peroxide, and chlorine. During the laboratory
investigation phase the above mentioned oxidants as well as various oxidant
combinations were evaluated.
Samples of seven separate combined sewer overflows from the demonstration site
at Hawley Road were collected during the Fall of 1967. These samples were
analyzed in the laboratory within twenty-four hours of their collection for
BOD, COD, dissolved COD, total solids, suspended solids, volatile suspended
solids, coliform density and pH. The data from these analyses has been re-
ported and discussed in the main body of this report. Since the likelihood
of getting sufficient and frequent combined overflows during the fall and
winter seasons in Milwaukee is small, it was decided to freeze some combined
overflow samples and use them for chemical oxidation evaluation during dry
weather. Therefore, about twenty liters of combined overflow samples from
three separate -storms were frozen in individual containers having volumes of
from 100 to 200 mi Hi liters. The laboratory analysis of the three storm sam-
ples frozen for chemical oxidation studies is shown in Table A-1. During
dry periods, samples were thawed as needed. Samples were mixed thoroughly in
a Waring blender after thawing to provide a colloidal system characteristic
of the original unfrozen raw sample. Whenever a sample without the particu-
late matter was needed for oxidation of the dissolved organic matter, the
thawed sample was not mixed. Instead, the supernatant was filtered through an
SS-597 filter paper and mill{pore filter discs to obtain a dissolved sample.
Standard Methods (A35) procedures were employed for various analyses in the
laboratory and are discussed in Appendix C.
Special Test Procedures with Various Chemical Oxidants
Chlorine and hydrogen peroxide oxidations were performed with and without
ultraviolet (UV) light. Chlorine was applied in the form of calcium hypo-
chlorlte solution (HTH) and a 0.75% stock solution was utilized for hydrogen
peroxide oxidation. Procedures for determination of oxidant dosages and re-
siduals are discussed in Appendix C. Cobalt in the form of CoCl *6 H20 was
utilized In a number of tests to determine If It helped to catalyze oxidation
reactions of H20_ and chlorine. The apparatus consisted of an eight inch dia-
meter flat bottomed dish on a magnetic stlrrer under a protective hood cover.
A 300 ml aliquot of raw waste was used. For tests performed with ultraviolet
light, the UV lamp was suspended above the water surface with ring stands at
three and six inch heights. The two UV lamps utilized were a single bulb
Sperti sun lamp and a double bulb G.E. germicidal lamp. Samples were taken at
various intervals during the oxidation period for COD analysis.
Some difficulty was encountered in measuring the COD after oxidation with var-
ious oxidants. Contrary to expectations, some samples exhibited an increase
In COD after oxidation. This observation could have been caused by the break
156
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157
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down of organic material which prior to oxidation was not measured by the COD
tests. The increase may also have been caused by the excess oxidant remain-
ing (the reaction kinetics were not known and exact amounts of oxidants could
not be utilized). Since it was desirable to know if the COD was increasing
due to partial oxidation, the excess oxidants were removed prior to analyzing
for COD. Several trial and error procedures were investigated for the removal
of these excess oxidants. It was planned that excess oxidant would be re-
moved after oxidation tests by adding a small excess of sodium sulfite.
After the addition of sodium sulftte, the sample was aerated until a galvanic
cell oxygen analyzer indicated the presence of dissolved oxygen in the sample.
Also, investigations were undertaken to study the effect of excess oxidants
and chemicals on the COD test results. Theoretically, the reaction between.
hydrogen peroxide and hexavalent chromium In a COD test may proceed as
fo11ows:
8H+ =
2Cr
2K [ORP = +0.65].
EQ. I
Then 1 mg
0.4? mg COD
Similarly, the reaction between sodium sulfite and dichromate may proceed
as follows:
3Na2S03 + K2Cr207' -f 8H
Then 1 mg Na2SO « 0.12? mg/COD
+ 2Cr+3 +
+ 2K ..... EQ II
Experimentally it was found that the COD exerted by hydrogen peroxide solution
decreased with Increasing strength of H_02 solution as follows:
Concentration of
H202 Solution
50
100
150
200
250
Ratio of mg COD/mg HLO-
0.42
0.41
0.39
0.38
0.37
The reason for such observation can be attributed to the redox relationships
of hydrogen peroxide, since H_02 can also react with the trlvalent chromium
produced as follows:
2Cr
*3
6H
« 6H20
* [ORP
EQ III
Thus hydrogen peroxide solution was found to exert a significant COD value and
this was a factor in the increased COD results of hydrogen peroxide treated
samples.
Also, sodium sulfite was experimentally found to have a chemical oxygen demand
158
-------
of 0.09 mg per mg of Na^SO,.
calculated value of 0.127 and
of sodium sulfite utilized in
This is approximately 70% of the theoretically
is not significant in light of the small amounts
these studies.
When calcium hypochlorite was used as an oxidant, the sulfite was added in
increments until a spot test with ortho-tolidine indicated that there was no
more free chlorine. The sample was then aerated until a galvanic cell oxygen
analyzer indicated the presence of dissolved oxygen in the sample. Experimen-
tally it had been found that a 715 mg/1 calcium hypochlorite solution exerted
a nominal COD of 9 mg/1 which could possibly be the result of experimental
errors. This experimental observation is also supported by possible theoreti-
cal reaction between chlorine and hexavalent chromium, as:
3CI
,- + lOCr
+3
17H20
[ORP = -.H],
.E0_ IV
The negative oxidation-reduction potential indicates that the above reaction
should proceed to the left and therefore, theoretically the reaction should
not take place. This leads to the conclusion that no COD should be exerted
by the chlorine solution.
Somewhat contradictory results were obtained when COD tests were performed on
samples from stormwater oxidation tests, whereas the COD of calcium hypo-
chlorite solution was negligible and the COD of oxidized sodium sulfite was
very small, in most cases the COD values of chlorinated waste samples which
were dechlorinated with sodium sulfite and aerated were 5 to 35% higher than
the samples which were not dechlorinated. Because of this difference, an
alternate method of dechlorlnation was also used: the sample was acidified
to a pH of one and stripped of chlorine by aeration. Unfortunately, the
stripping process was extremely slow, often requiring several hours. In some
cases, not all the chlorine was removed by the time the COD analyses were
performed. In general, the COD values obtained by acidification and strip-
ping were lower than the values obtained by sulfite treatment. The exact
cause of this difference in values is not known.
Ozone Oxidation System
Ozone was purchased by the bottle and used in a pressure tank system. A
schematic of the apparatus utilized is shown in Figure A-3. Ozone was sup-
plied dissolved in 'Freon 13' under high pressure in stainless steel cylin-
ders. Since ozone has a half life of approximately three days at room tem-
perature it was necessary to keep the ozone cylinder packed in dry ice. A
three mole-percent vapor phase concentration was utilized for oxidation stud-
ies. To maintain a constant ozone concentration supply, ozone was utilized
in the vapor phase. This was achieved by inverting the ozone bottle and con-
verting the liquid ozone to vapor phase by passing it through a vaporizing
coi 1.
Ozone was mixed with the waste at elevated pressures in the range of 40 to 80
psig. This pressure charged stream was then placed in a graduated cylinder
for the required reaction time. Samples were air-stripped to remove excess
159
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ozone remaining after the reaction time. Pressurization of waste could be
total or partial. When the entire waste was pressurized, it was called total
pressurization. If only a portion of the waste was pressurized, the amount
was calculated as a percentage of the nonpressurized portion, and was called
a recycle system. Use of a pressure tank system enabled large amounts of
ozone to be dissolved and when the pressure was released the extremely small
air-ozone bubbles stayed in contact with the liquid much longer than the
coarse bubbles produced from diffuser type systems. Such a system was util-
ized because the literature search indicated that the ozone contact time is
critical and greatly affects efficient use of ozone. Titrations for ozone
determination were performed in accordance with Standard Methods (A35).
RESULTS AND DISCUSSION
Oxidation with Hydrogen Peroxide
Results of chemical oxidation with hydrogen peroxide are presented in Tables
A-2 and A-3. Hydrogen peroxide requires a catalyst to oxidize effectively
within reaction times of one hour or less. Table A-2 shows the results of the
tests performed using iron as a catalyst. Oxidation tests were run on the
dissolved fraction of the overflow (Tests 1 through 7) as well as the over-
flow after screening through a 50 mesh screen (Tests 8 and 9).
Tests 1 through 7 (Table A-2) indicated that a substantial portion of the
dissolved COD can be oxidized in 15 minutes and the oxidation efficiencies
were in the range of those reported in the literature. When the effluent
from the 50 mesh screen (Tests 8 and 9) was oxidized with the hydrogen perox-
ide - iron salt system, the oxidation efficiencies were lower than those ob-
tained when oxidizing only dissolved COD. This indicated the importance of
removing a major portion of the solids prior to oxidation, since particulate
matter is more difficult to oxidize than dissolved organic matter.
Use of hydrogen peroxide-iron salt system does not appear feasible. Ferrous
iron seems to work well, but relatively large concentrations are required (on
the order of 60 to 100 mg/1 as Fe ). This system requires strict pH control
(3 to A) and a neutralization and settling period to remove the iron precipi-
tate which is formed. Organic removal efficiencies are in the 30 to 50%
range for dissolved organics and were reduced to about 14% when particulate
organics were present. In an attempt to more efficiently utilize the hydrogen
peroxide, other catalysts were evaluated which would not be as restrictive as
ferrous salts.
The literature indicated that hydrogen peroxide is decomposed by ultraviolet
light. Also Test 7 (Table A-2) indicated that cobalt may help catalyze a hy-
drogen peroxide system. Therefore, tests were run with both these catalysts
to study any improvements in the efficiency of hyd rogen peroxide oxidation
system. The results of these tests are shown in Table A-3. It is seen that
the use of either or both cobalt and ultraviolet light along with hydrogen
peroxide did not produce consistent results. From tests 1 and 2 (Table A-3)
161
-------
Table A-2. RESULTS OF CHEMICAL OXIDATION OF COMBINED
SEWER OVERFLOW WITH HYDROGEN PEROXIDE
Test
no.
. 1
2
3
4
5
6a
7b
8
9
Ava liable
°2
50
100
100
100
100
100
100
150
300
COD
Initial
54
67
54
54
65
65
65
216
216
Final
50
30
41
33
37
42
31
186
185
Percent
reduction
7
55
24
39
43
35
52
14
14
Oxidation
efficiency,
%
8
37
13
21
28
23
34
20
10
Filtered
prior to
analysis
No
Yes
No
Yes
Yes
Yes
Yes
No
No
a. Aerated during the oxidation
b. Cobalt added during the oxidation
Notes: 1. In Tests 1 through 7 only the dissolved COD was oxidized, i.e.,
all solids removed prior to oxidation. Tests 8 and 9 were
run on combined overflow after screening through a 50 mesh
screen.
2. All oxidations were for 15 minutes at room temperature.
162
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it Is clear that reaction time has an important bearing on COD reductions in
the treatment of storm waters with hydrogen perioxide.' In Test 1, when a hy-
drogen peroxide dosage of 110 mg/1 as 0_ was utilized, a 33% reduction in COD
was obtained in 15 minutes; the COD reduction reduced to 19% in 30 minutes
and even became negative at the end of the 90 minute reaction time. A possi-
ble explanation for the increase in COD in a certain initial reaction time
may be the partial oxidation of large molecular weight organic compounds in
the raw storm samples to smaller intermediate compounds which exhibited an
increase in COD. Increased oxidation at a h'igher reaction time may then
cause a decrease in COD of these samples, apparently, due to the oxidation of
some of the organic carbon to CO and H_0. Similar explanations have been
mentioned in literature for ozone oxidation (A18). When UV light was used as
a catalyst, results were contradictory as shown in Tests 2, 7, 11, 12, 13 and
14 (Table A-3). Test 2 showed negative COD reductions for all reaction times
between 15 to 90 minutes while Tests 7 and 11 to 14 showed COD reduction be-
tween 6 to 47% for reaction times of 15 and 30 minutes. Similar contradic-
tions in results were shown when cobalt was used as a catalyst either inde-
pendently or in combination with UV light (Tests 3 to 6, Table A-3).
The results presented in Tables A-2 and A-3 clearly indicated that a hydrogen
peroxide reaction system was not technically feasible for treating combined
sewer overflows. Thus work on such a system was abandoned.
Oxidation with Chlorine
Results of chlorine oxidation with and without ultraviolet light are present-
ed In Tables A-4 and A~5. Oxidation with chlorine and no ultraviolet light
resulted in a reduction of COD of about 20 to 25% at available chlorine do-
sages of 280 to 560 mg/1 (Table A-4). The amount of chlorine destroyed was
about 25% and hence a large chlorine residual remained after the oxidation.
Reducing the chlorine dosage to 56 mg/1, reduced the percent COD oxidized to
only 8% (Test 3, Table A-4). These results indicate that chlorine is not an
effective oxidant for combined sewer overflows. This conclusion is supported
by the literature search.
Oxidation with chlorine and ultraviolet light in the 2800 to 3200 8 range was
not significantly different from those oxidations where ultraviolet light was
not used (Table A-4). The reason for these low oxidation efficiencies may
have been due to the long wave length light which was used i.e. 2800 to 3200
A or the low ultraviolet output of the lamp which was used for the reactions.
A review of the research conducted by Midwest Research Institute (A36) indi-
cated that lower wave lengths were more effective. Therefore, a lower UV
light wave length of 2587 A was used for further experiments. This wave
length would also provide good disinfection. The results of these experiments
are shown in Table A-5. It should be noted that for light catalyzed oxida-
tions to be effective, relatively clear solutions were required. Therefore,
the results of the screening step could have a pronounced influence on the
efficiency of light catalyzed oxidations.
From the results shown in Table A-5, it is seen that COD reductions of 10% to
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50% can be expected depending upon light intensity, chlorine dosage and reac-
tion time. The amount of chlorine required is extremely large. Approximate-
ly 7 to 10 mg of chlorine is required per mg of COD oxidized. Hence, for a
200 mg/1 COD waste, 1400 to 2000 mg/1 of chlorine would be consumed. This al-
so results in high chlorine residuals in the effluent. With the use of an
ultraviolet light catalyst, organic removal does increase to the 25 to 50%
level compared to 10-25% level without the catalyst, but large chlorine re-
siduals are still present in the reactor effluent. This fact, coupled with
relatively long reaction times (30 to 60 minutes)" and poor light penetration
when the waste is turbid appear to eliminate the possibility of using light
catalyzed chlorine to oxidize combined sewer overflows,
Oxidation with Combined System of Hydrogen Peroxide and Chlorine
Results of oxidation with the combined system of hydrogen peroxide and chlo-
rine with and without ultraviolet light catalyst are shown in Table A-6. The
results of these tests were extremely discouraging as inconsistent and nega-
tive reductions in COD were observed. The importance of reaction time was
again demonstrated (Tests 1 to 4, Table A-6) in the use of the combination of
these oxidants for the treatment of storm wastes. These results were similar
to the ones discussed earlier for oxidation by hydrogen peroxide alone. A
small positive COD reduction was shown when reaction time was very small (in-
stantaneous sample, Tests 3 ^nd 4, Table A-6). For higher reaction times up
to 60 minutes negative COD reductions were obtained. Also the use of UV light
as a catalyst did not show any improvement in results (Tests 2, 3 and k com-
pared to 1, Table A-6). Hence, investigations in this area were terminated.
Oxidation with Ozone
The result of the ozone oxidations are shown in Table A-7. Using total pres-
surization at 40 psig, Tests 1 and 2 show the difference in COD reductions
for raw and filtered storm water samples. The higher COD reduction of 46% ex-
hibited for raw waste sample (Test 2, Table A-7) was probably due to the flo-
tation of some of the suspended matter as well as the higher solids content of
the raw waste sample. When a 20% recycle system was used with the 10 mg/1 do-
sage of polymer C-31 on raw sample (Test 4) the COD reduction was extremely
high at 36%. The reason for such a high reduction was probably the floccula-
tion of the suspended matter with the C-31 flocculant and the flotation of
floe on the surface. Tests 5 and 6 (Table A-7) show the effect of reaction
time of ozone at two different operating pressures of 40 and 70 psig. It was
shown that COD reductions increased from 27 to 52% when the reaction time was
increased from 1 to 20 minutes at 40 psig. There was no significant improve-
ment in COD reductions when the operating pressure was increased to 70 psig.
Therefore, a pressure of 40 psig was utilized for all future tests. The ozone
dosage utilized.for all the tests discussed above was 40 mg/1. When a 30 mg/
1 ozone dosage was utilized the COD reduction was 32% (Test A-7) for a reac-
tion time of five minutes as compared to 43% COD reduction shown for 40 mg/1
for corresponding conditions (Test A-5). This means that higher ozone dosages
result in improved COD reductions. When ozone was applied in combination
167
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with other oxidants (such as C12 and H20 ) or catalysts (such as Co and Ni)
(Tests 8 through 18), no significant improvement in COD reductions could be
obtained in most cases either with dissolved or raw storm water samples.
However, in one case where ozone was used with both chlorine and hydrogen per-
oxide (Test 10), the COD reductions were observed to be significantly improved
at 70%, However, this efficiency was only for the dissolved organic fraction
and would be reduced significantly if particulate organic materials are pre-
sent. The use of all three oxidants at their respective dosages (Test 10,
Table A-7) would result in extremely high (>$1.00/1000 gal.) operating costs.
Two benefits which are possible when using a pressure tank system are the
possibility of floating some of the lighter organic solids, and the probabil-
ity that the heavier grit particles will settle. These benefits can greatly
increase the removal efficiencies of the treatment system. From the results
shown in Table A-7, ozone appears to be the best oxidant among the ones eval-
uated In this study because it:
1. Provides the best oxidation.
2. Requires reasonable reaction time.
3- Can be used in a pressure system allowing effective Introduction of
ozone.
It should be noted that all the tests shown in Table A-7 were obtained with
overflow samples which had earlier been collected and frozen. Therefore, it
was not possible to run disinfection tests because of the adverse effect that
freezing has on the coliform organisms. Hence, further experiments were
planned to study disinfection efficiency and BOD and COD removals using ozone
treatment and fresh overflows.
The results of these experiments are shown in Tables A-8 and A-9. A recycle
system was utilized and a value of 10% recycle was used to keep the ozone do-
sage in 10 to kQ mg/1 range on all overflows except the April 3 overflow
(Tables A-8 and A-9). Since some flotation and/or sedimentation occurs, air
flotation tests were run as a control to determine how much removal was due
to oxidation and how much to sedimentation and/or flotation.
Comparing the suspended solids removals (Table A-8) indicates little differ-
ence between ozone treatment and air flotation. This points out that little
if any particulate matter is oxidized. These results are consistent with
the oxidation results obtained with the frozen overflows. The, BOD removal
was generally better with the ozone treatment compared to air flotation (Ta-
ble A-8). The COD removals, however, followed the opposite trend. Overall
removal rates with screening and ozone treatment or flotation are in the
range of 50 to 80% for the first flushes and ^5-65% for the normal overflows
providing means are available to remove settled and floated solids.
The amount of disinfection obtained with ozone and chlorine is shown in Table
A-9. At relatively high ozone dosages good disinfection is obtained. When
the dosage is dropped below 10 mg/1 disinfection becomes very poor. Chlorine,
however, will give good disinfection at a 10 mg/1 dosage over a wide range of
coliform concentrations. These results indicate that ozone may not be satis-
\
170
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171
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Table A-9. SUMMARY DISINFECTION DATA - ALLJPRING STORMS
Date
4/3
4/3
4/17
4/20
4/23
4/28
4/28
Type3
FF
EO
EO
EO
EO
FF
EO
E. Coli,
per ml
1388
421
1280
1850
6000
32000
26000
°3
dosage,
mg/1
80
59
40
, "-30 ;.;.
<10 ,
<10
<10
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in
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per ml
21
4
74
;, I?
3200
"9500
13700
. ;;e|. '::.
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mg/1
Id
10
10
10
10
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effluent,
per ml
__ -;'"
--
0.5
1 ^
2 '/
20
8
a. FF - First flush
EO - Extended overflow
172
-------
factory for disinfection because of its high costs and nonattainment of
residual ozone for a sufficient period.
Oxidation with Gamma Radiation
Use of gamma radiation for oxidizing organlcs was indicated in the literature
(A38)(A39). Tests were run on gamma irradiation of combined overflow using a
cobalt source. The results of preliminary tests on these were discouraging
and investigations into this area were terminated.
SUMMARY AND CONCLUSIONS
Table A-10 presents a summary of the various oxidants and oxidation systems
utilized. Hydrogen peroxide, chlorine, and ozone were evaluated both alone
and in combination. Various catalysts were also utilized including ferrous
iron, nickel and cobalt. The best system was a mixture of all three oxidants,
which provided up to 70% oxidation of the dissolved fraction of a combined
sewer overflow. Any single oxidant did not produce greater than 50% oxidation
of the dissolved fraction. When screened overflow was utilized, the highest
oxidation percentage was A0%, hence particulate matter was oxidized only to
a very limited extent. This indicates that an efficient solids/liquid sep-
aration system must be utilized prior to chemical oxidation. Even if this is
done, a removal efficiency of only about 40% In the chemical oxidation stage
could be economically realized. Therefore chemical oxidation of combined
sewer overflows does not appear to be justified.
The following conclusions can be made based on the chemical oxidation studies
performed.
1. Chemical oxidation of combined sewer overflow is not technically
feas ible.
2. Ozone was the best oxidant evaluated in this study.
3. Oxidation with chlorine requires extremely high concentrations of
chlorine and results in a high chlorine residual in the effluent.
A. Particulate matter is extremely difficult to oxidize.
5. A combination of oxidants can provide increased oxidation of
organic material.
173
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REFERENCES - APPENDIX A <
A1. Fair, G. and Geyer, J.t Water Supply and Waste Disposal, John Wiley and
Sons, Inc., New York (1961 ) « '
A2. Eckenfelder, R.B. and O'Connor, D., Biological Waste Treatment, Pergamon
Press (1961). -
A3. Laboon, J.F., Sewage Works Journal 7:9:911 (1935).
A4. Bolenlus, R.H., Sewage and Industrial Wastes 22:3:365 (1950).
A5. Mills, E.V., e±a]_., The Surveyor 104:79 (1945).
A6« Summary Report, Advanced Waste Treatment Research, U.S. Department of
Health, Education and Welfare, Public Health Service Publication No.
999-WP-24, p. 69 (1965).
A7. Eisenhauer, H.R. , "The Chemical Removal of Aklyl benzene sulfonates from
Wastewater Effluents", Presented before the Division of Water and Waste
Chemistry, American Chemical Society, Los Angeles, California (1963).
A8. Busch, A.W., et a]_. , API Project for Research on Refinery Wastes
(NonbiologicaT'Treatrnent) Progress Report No. 2. Rice University, p. 11,
'"
A9. Davidson, C.A. and Busch, A.W. , "Catalyzed Chemical Oxidation of Phenol
in Aqueous Solution", Presented at 31st Midyear Meeting of API Division
of Refining, Houston, Texas (1966).
A10. Eisenhauer, H.R. , WPCF Journal, 36:9:1116 (1964).
A11. Bishop, D.F., e£al., "Hydrogen Peroxide Catalytic Oxidation of Refrac-
tory Organics 7n"Hunicipal Wastewaters", Presented at the 148th National
Meeting of the American Chemical Society (September 2, 1964).
A12. Busch, A.W. , ejt aj_. , API Project for Research on Refinery Wastes. Prog-
ress Report NoT 3, Rfce University (June 22, 1964).
A13. Connell, G.F., "Application of Ozone", Refrigeration Service Engineers
Society, Chicago, Illinois (1966)
A14. 0' Donovan, D.C., Journal AWWA 57:9:1167 (1965).
A15. Marsh, G.R. and Panula, G.H., Water and Sewage Works 112:10:372 (1965).
A16. U.S. Patent No. 3,276,994, issued to C.W. Andrews.
A17. Sease, W.S. and Connell, G.F., Plant Engineering 20:11:486 (1966).
175
-------
A18. Evans, F.L. and Ryckman, D.W., "Ozonated Treatment of Wastes Containing
ABS", Proceedings 18th Industrial Waste Conference, Purdue University,
p. 141 (1963).
A19. Buecher, C.A. and Ryckman, D.W., "Reduction of Foaming of ABS by
Ozonation", Proceedings 18th Industrial Waste Conference, Purdue
University, p. 141 (1963).
A20. Tyoer R.G., et al., Sewage and Industrial Wastes 23:9:1151 (1951).
A21. Miller, F.K., Water and Wastes Engineering 3:12:52 (1966).
»
A22. Moeller, T., Inorganic Chemistry, John Wiley and Sons, Inc., New York,
P. 485 (1957).
A23. "Welsback Ozone Equipment", Bulletin 109 (September 1966).
A24. Schevchenko, E.T., "Tests of a Semi-Industrial Apparatus for Ozonization
for Dnieper Water", Chemical Abstracts, Volume 65, 5220, 1966, Ozoni rov.
Vody i Vybor Rats (1965) (Russian).
A25. Campbell, R.M., Journal of the Institute of Water Engineers, 17:333
(1963).
A26. Green, D.E. and Stumpf, P.K., Journal AWWA 38:11:1301 (1946).
A27. Snow, W.B., Sewage and Industrial Wastes 24:6:689 (1952).
A28. Griffin, A.E., and Chamberlin, N.S., Sewage Works Journal 17:4:730
(1945).
A29. Private Communication, Mr. Carl Brunner, Taft Sanitary Engineering Cen-
ter, Cincinnati, Ohio (November 14, 1967).
A30. Sptker, R.G. and Skrinde, R.T., Journal AWWA 57:4:472 (1965).
A31. Burtle, J. and Buswell, A.M., Sewage Works Journal 7:9:839 (1935).
A32. Vosloo, P.B.. Sewage Works Journal 20:1:171 (1948).
A33. Gould, E.S., Inorganic Reactions and Structure, Henry Holt'and Company,
New York (1956).
A34. Miller, H.C. and Knipe, W., Report AWTR-13, U.S. Department of Health,
Education and Welfare, Public Health Service (1965).
A35. American Public Health Association, Standard Methods for the Examination
of Water and Waste Water - 12th Edition, APHA, New York (1964).
A36. Meiners, A.F., et_ aK, "An Investigation of Light Catalyzed Chlorine
Oxidation for Treatment of Waste Water", Advanced Waste Treatment Re-
search Laboratory, FWQA, Repprt #TWRC-3.
176
-------
A37- Sawyer, C.M. , Chemistry for Sanitary Engineers, McGraw-Hill Publishing
.Company, p. 28? (I960). ' :
A38. Touhell, C.J., et^ aj_. , WPCF Journal
(1969).
A39. Ballantine, L.A. , et^ aJN , "The Practicality of Using Atomic Radiation
for Was tewater Treatment", WPCF Journal k\:$:kk7 (March, ^^6^) .
Ml
-------
APPENDIX B
BENCH SCALE STUDIES FOR THE UPGRADING OF FLOTATION
TREATED COMBINED SEWER OVERFLOWS
INTRODUCTION
The problem of combined sewer overflows (CSO) has been recognized as a signif-
icant pollutional problem in recent years (Bl). Several programs have been
Initiated by the federal and state governments to develop methods of coping
with this problem. Among the various projects undertaken by the Environmental
Protection Agency (EPA), a research and development contract was awarded to
the Environmental Sciences Division of Envlrex Inc. (A Rexnord Company - pre-
viously, Rex Chainbelt Inc.) to develop an effective and economical method of
treatment for combined sewer overflows. Subsequently, a 5 mgd demonstration
test facility was designed and installed by Envirex at the Hawley Road CSO
outfall in Milwaukee utilizing the unit processes of screening and dissolved-
air flotation (82). The treatment system was operated successfully on 55
combined sewer overflows during 1969 and 1970. It was concluded that screen-
ing/flotation is an effective method of reducing pollution caused by combined
sewer overflows. The overall pollutant removals measured in terms of suspen-
ded solids, volatile suspended solids, BOD and COD ranged between 60-75%.
However, this performance of the demonstration system did not meet the pro-
posed requirements of the Wisconsin Department of Natural Resources with re-
gard to the removals of BOD and suspended solids for intermittently operated
treatment facilities in the Milwaukee River Drainage Basin. These require-
ments called for a minimum removal of 80% of the raw BOD and suspended solids
and were similar to the "secondary treatment" requirements for the physically-
chemically treated wastewaters.
A proposal was prepared by the Environmental Sciences Division of Envirex Inc.
to the Wisconsin Department of Natural Resources to supplement the existing
evaluation program to include laboratory bench scale investigations to up-
grade the quality of the effluent from the screening/flotation process. The
objectives of the proposed evaluatory work were:
1. To determine the technical and economic feasibility of upgrading
the quality of the effluent from the screening/dissolved-air
flotation process to a level comparable to that produced by
secondary treatment as interpreted by the Wisconsin Department of
Natural Resources.
2. To supplement the programmed analytical determinations to include
provisions for determining the total phosphorus content of pert-
inent field and bench scale test samples.
178
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Scope of Work
11 was anticipated_'_that__ the unit treatment processes having potentia1 for
accomplishing the desired results were:f) high-rate filtration, 2) micro-
screening, 3) powdered activated carbon treatment in conjunction with
dissolved-air flotation (both in split flow and effluent recycle modes) and,
4) ozone oxidation. Initially, the intent of the program was to investigate
the application of these processes on the effluents obtained from the field
operation of the screening/flotation facility at Hawley Road. Since the 1971
operating season did not provide a sufficient number of rainfall events to
complete the contract requirements, the cooperative research agreement was
extended into the 1972 operational season. The conduct of the originally con-
ceived prograriThowever, was contingent upon the anticipated continuation of
the EPA-Contract 14-12-40, which, at that time, expired on March 31, 1972.
However, the renewal of Contract 14-12-40 could not be authorized in time for
operations during 1972. A proposal was then made to the Wisconsin Department
of Natural Resources to modify the work scope of the existing Rex-DNR program.
Under the terms of the amended contract, the work scope called for the react-
ivation of the Hawley Road site and the field operation of the screening/flo-
tation system. It was anticipated that the allocated funds were sufficient
to operate the treatment system on four separate overflows. Three of the four
overflows were to be operated under optimum test conditions as determined by
the EPA Contract 14-12-40 (B2). The effluent from these three overflows were
to be subjected to the above mentioned bench scale evaluations for the upgrad-
ing of this effluent. The fourth overflow event was to investigate the use
of powdered activated carbon on an actual combined sewer overflow run if the
laboratory tests showed promise.
A review of the test data was made at the end of the three overflow events
by the personnel of the Wisconsin Department of Natural Resources and Envirex
Inc. It was mutually decided that the remaining funds in the contract (after
allocations for shutdown of the site and writing of the final report) be
utilized to conduct additional bench scale effluent recycle flotation tests,
involving the use of alum, polyelectrolyte and activated carbon on a selected
overflow that may be more polluted than normal. It was al so decided that no
additional field flotation, filtration, microscreening and ozone oxidation
tests be conducted on the last overflow sample.
Test Procedures
The field operation of the demonstration system was in accordance with the
optimum treatment conditions determined by previous work performed under EPA
Contract 14-12-40. A description of the Hawley Road'site, and the design and
operation details of the treatment system have been previously described and
discussed in the main body of this report (Sections V and VI). A process
schematic of the treatment system utilized is shown in Figure B-1.
A listing of the optimum operational conditions utilized for the field oper-
ation of the screening/flotation system, as determined previous work performed
in EPA Contract 14-12-40 is as follows (B2):
179
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SCREEN BACKWASH SYSTE
CHEMICAL
ADDITION
CSO
SOURCE
1/2" BAR
RACK
DRUM SCREEN
50 MESH
TO INTERCEPTOR SEWER
SCREENED EFFLUENT
SCREENED
SOLIDS
DISCHARGE
FLOATED
SCUM
DISCHARGE
EFFLUENT
. TO
RECEIVING
STREAM
FLOTATION ZONE
AND
CHLORINE CONTACT
MIXING
ZONE
CHLORINE AND
CHEMICAL .
FLOCCULANT
ADDITION
PRESSURE
REDUCTION
AIR
SOLUTIO
SYSTEM
AIR
DISSOLVE
TANK
c
AIR COMPRESSOR
Figure B-1. Screening/flotation flow diagram
180
-------
Screening
Hydraulic throughput rate
Drum rotation speed
Maximum available headless
Submergence
Dissolved-air flotation (DAF)
Pressurized flow
Operation pressure
Overflow rate
Chemical dosages
40 - 50 gpm/sq ft
4 - 5 rpm
12 - 14 in. water
50 - 63%
20% raw flow
50 psi
3.3 gpm/sq ft
20 tng/1 FeCK
4 mg/1 cationic polyelectro-
lyte (C-31)
Composite samples of the effluent were collected from the field operation of
the screening/flotation system via an automatic sampling system which compo-
sited the samples every five minutes throughout the duration of the overflow.
At times, however, some grab samples or manually composited samples were also
collected whenever a large amount of sample was required for evaluations such
as high rate filtration. The samples were refrigerated immediately after the
run. Generally, the collected samples were subjected to various bench scale
and analytical evaluations at the Envi rex laboratories within 0-15 hours
depending upon the time of the occurrence of an overflow. A description of
the sample analysis procedures is presented in Appendix C. A brief descrip-
tion of the methods and procedures utilized for the bench scale evaluations
is given below:
High Rate
Fi 1tratl_on_ -
6
The filtration tests were
in gravel, 12 in sand and
conducted on a dual media
18 In anthracite. A 1 inch
_
filter consisting of
diameter glass column was utilized for the polishing of the flotation efflu-
ents. The filtration rate utilized was 5 gpm/sq ft. The field effluent sam-
ples were kept mixed either manually or by aeration In order to feed represen-
tative influent to the filtration column. Generally, the filtration tests
were conducted for a period of 4-6 hours. Composite filter effluent ^samples
were collected at every 1/2 to 1 hour intervals and analyzed for various
pertinent constituents such as BOD, suspended solids, TOC and turbidity.
Hicroscreening - The microscreening tests were conducted with various types
of screens made of stainless steel, nylon and polyester. The microscreening
test assembly consisted of a screen holder to hold a 1.75 in. diameter screen,
sealed between two 0-rings. A long cylindrical tube, which was threaded to
fit the screen holder was placed on top of the screen to permit water heads
up to 15 inches. The openings of the various screens utilized for the tests
varied between 15 and 23 microns.
Carbon- Flotation Treatment - These tests were conducted to investigate the
181
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potential of utilizing powdered activated carbon in conjunction with
flocculating chemicals and dissolved-air flotation for the treatment of com-
bined sewer overflows. The objective was to evaluate the improvement in the
effluent quality when activated carbon was added to the raw CSO for the adsor-
ption of the soluble organics. Control tests (without carbon) were also con-
ducted to compare the bench scale effluent qualities with or without the
addition of carbon.
Bench scale flotation tests with and without carbon were conducted in two
different modes of dissolved-alr flotation. These modes of DAF are split
flow pressurization and effluent recycle pressurization.
The split flow mode of pressurization Is that type of DAF where a portion 6f
the raw flow is pressurized at a suitable pressure and ts mixed with air.
Since the raw flow is split in two parts, this mode of DAF can be easily sim-
ulated in the laboratory tests. However, the same Is not true for the
effluent pressurization mode of DAF where a portion of the treated effluent
Is recycled and pressurized and mixed with air under pressure.
The effluent recycle mode of DAF or the effluent pressurization concept can
be well simulated In the laboratory by a technique developed by Rexnord Inc.
called the "Developed Recycle" technique. The procedure consists of utiliz-
ing tap water in desired proportion for Initial pressurization. The pressur-
ized flow Is thefn mixed with the chemically flocculated raw waste and the
particulate matter Is floated in a 1-liter graduated cylinder. The flotation
effluent obtained from this first cycle of flotation is next pressurized In
a second cycle of flotation in place of the tap water. The resulting
effluent from the second cycle is considered to correspond closely to the
expected flotation effluent in the field via effluent pressurization.
Ozone Treatment - Ozone utilized for the laboratory tests was supplied dis-
solved in 'freon 13' under high pressure In stainless steel cylinders. Since
ozone has a half life of approximately three days at room temperature, it was
necessary to keep the ozone cylinder packed in dry ice. To maintain a con-
stant ozone concentration supply, ozone was utilized in the vapor phase.
This was achieved by Inverting the ozone bottle and converting the liquid
ozone to the vapor phase by passing it through a vaporizing coil. A five
mole-percent vapor phase concentration was utilized for Oj oxidation studies.
A schematic of the apparatus utilized for the ozone treatment tests is shown
In Figure B-2.
A gas bulb was utilized as the contact chamber between ozone and wastewater
sample. The procedure utilized for the ozone oxidation tests was as follows:
The gas bulb (capacity 275 ml) was filled with the wastewater samp.-le. Next,
ozone was passed into the bulb replacing a desired amount of the sample. The
ozone-waste sample mixture was allowed to remain in the gas bulb for the de-
sired reaction time. At the end of the contact time, a small volume of the
mixture was taken out for TOC analysis. The remaining mixture was then
treated with potassium Iodide and sulfurlc acid and titrated with sodium
thlosulfate for ozone determination in accordance with Standard Methods (B3).
182
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RESULTS AND EVALUATIONS
The results of the total DNR program undertaken during the years 1971 and
1972 can be divided into two distinct areas as per the objectives, i.e.,
1. The upgrading of the field treated effluents.
2. The determination of the total phosphorus content in the raw and
and flotation effluent.
The tests conducted to achieve these objectives are discussed as follows:
Operation of the Field Treatment System During 1972"
The field treatment system at Hawley Road was operated on three separate
overflow events during 1972. Mechanical operation of the treatment facility
was excellent. The raw ar>d flotation treated effluent qualities along with
the pertinent test conditions for the three overflows are shown in Table B-1.
The raw CSO analyses for the 4th overflow sample, collected for the bench
flotation tests, are also included in the same table. Comparing the results
shown In this table to the previous data collected at Hawley Road (Table B-2)
with regard to the CSO quality, it was found that:
a. The pollutant content of the raw wastewater during these storms was
significantly lower than the corresponding quality during previous
seasons. For example, suspended solids for 1972 ranged between
105-181 mg/1 compared to a 95% confidence value of 435 ± 129 mg/1
for the 1971 season.
b. The soluble TOC/total TOC fraction during 1972 was higher than in
previous years. It ranged between 0.3 - 0.6 compared to previous
year's 95% confidence value of 0.32 ± 0.15.
c. The pollutant removals in the flotation effluent for most parameters
ranged between 60-95% for the storms #2 and 3 and were comparable to
the effluent quality during previous years. However, the removals
for storm #1 were comparably lower at 35-57% but can be justified
in the wake of the higher soluble organic carbon fraction (60%) in
the raw wastewater for this storm.
Evaluation of Various Processes for the Upgrading of Flotation Effluents
The results of the various bench scale tests conducted on the field flotation
effluents or raw samples are described In the following subsections:
1. High rate filtration
2. Mfcroscreening
3. Flotation tests with and without activated carbon
4. Ozone oxidation
184
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Table B-2. SUMMARY OF RAW WATER QUALITY DATA
(1969 to 1971)
Constituent concentration
at 35% confidence level
1969-70
Analysis
pH
Total solids, mg/1
Total volatile solids, mg/1
Suspended solids, mg/1
Volatile suspended solids,
mg/1
TOC, mg/1
COD, mg/1
BOD, mg/1
Dissolved TOC/total TOC
Dissolved COD/total COD
Total nitrogen, mg/1
Ortho phosphate, mg/1
Coliform density, per ml
a. Data represents 21 overflows
b. Data represents 12 overflows
c. Data represents 44 overflows
1971 1969-70
Season First flushes'3
7.2 ±
605 ±
156 ±
435 ±
146 ±
73 ±
209 ±
64 ±
0.36 ±
6.3 ±
0.86 ±
75.5 ±
*
0. 1
151
73
129
46
27
86
32
0.05
1.9
0.37
69 x 103
7.0 ± 0.1
861 ± 117
489 ± 83
522 ± 150
308 ± 83
581 ± 92
186 ± 40
17.6 ± 3.1
2.7 ± 1.0
142 ± 108 x 103
extended
overflows
7.2
378
185
166
90
-
161
49
-
0.34
5.5 ±
1 .0 ±
± 0,. 1
± k6
± 23
± 26
± 14
± 19
± 10
± 0.04
0.8
0.24
62.5 ± 27
x
103
186
-------
High Rate Filtration - Bench scale filtration tests were performed on flo-
tation effluents from three separate overflow events. The results of these
tests are shown in Table B-3* From these results it can be seen that mixed
media filtration does an excellent job in removing the particulate matter
from the flotation effluents. The suspended solids removals ranged between
85 to 98 % for the bench scale test results shown in Table B-3.' However, as
expected, no significant reduction
Microscreening - The results of the mlcroscreening tests on the flotation
effluents for various pollutant parameters are shown in Table B-4. These
tests were conducted on the field flotation effluents in both the 1971 and
1972 operational seasons.
Various screen media of 316 stainless steel, polyester and nylon were utilized
for these tests in varying opening sizes between 15 to 23 microns. The weave
of the polyester and nylon media was square weave type while the stainless
steel media was of Dutch twill weave type. It can be seen from the results
shown in Table B-4 that the percent pollutant removal on the mlcroscreens
varied over a wide range, between negative removals to greater than 90%. The
reason for such a variation can be attributed to the variation, in the size of
the particulate matter in CSO. It can be seen from these results that con-
sistently approximately 15 to 35 mg/1 of the particulate matter passed through
the microscreens and therefore Is considered to be finer than 15-23 micron
size. While this finer particulate matter could not be removed by the micro-
screens employed, it Is interesting to note that similar particulate matter
was removed by mixed media filtration. Also, it was indicated that twill
weave stainless steel media provided somewhat better particulate removals
compared to square weave plastic media but at significantly reduced through-
put rates.
Flotation Tests With and Without Activated Carbon - Bench scale flotation tests
were undertaken In the laboratory on raw composite CSO samples 1971-5 and
1971-6 to evaluate the effect of utilizing effluent recycle mode of pressuri-
zation as compared to split flow mode of pressurization. The results of these
tests are shown in Table B-5 along with the test conditions utilized. Both
these tests were conducted without the addition of activated carbon. From
the results shown in Table B-5, it can be clearly seen'that a significant in-
crease in the effluent quality can be achieved via effluent pressurization as
compared to the split flow pressurization. It was found that approximately
50 to 60% increase in the removals of the particulate matter could be achieved
in the laboratory via pressurization of only 20% of the treated effluent In-
stead of the raw CSO.
Also, bench scale flotation tests were conducted in conjunction with powdered
activated carbon and flocculating chemicals. Pulverized filtrasorb 400
(Manufactured by Calgon Corp.) was utilized for the evaluations during storm
numbers 1972-1 and 1972-2 while the powdered activated carbon grade Nuchar
C-115WG (manufactured by Westvaco Corp.) was uti1ized during storm numbers
1972-3 and 1972-4. Initially, the chemical flocculant combination of FeCl,
and a cationic polyelectrolyte (Nalco 607) was utilized for the bench scale
187
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evaluations since this combination was found to be suitable for the field
tests at the Hawley Road site. Later, several other flocculant chemical com-
binations were tried as the above combination was indicated to be unsuitable.
The various tests undertaken and the subsequent developments will be discussed.
in their respective chronological order in the following sections.
The results of the tests conducted on the raw waste from storm no. 1972-1
are shown in Table B-6. Three tests were conducted at varying contact times
and carbon dosages in the split flow mode of DAF. The effluent quality ob-
tained via these tests was considerably lower. Based on the results of these
tests it was indicated that:
1. The flocculant combination of FeCK and a cationic polyelectrolyte
may not provide good flocculation In conjunction with powdered
activated carbon.
2. Split flow mode of DAF may not be suitable when used in conjunction
with powdered activated carbon treatment.
Several flocculant chemical combinations were investigated in 100ml graduated
cylinder bench tests to find the combination that would provide suitable floc-
cu ation of the raw waste in conjunction with carbon. Various cationic, ant-
onic and non-tonic polymers along with alum or Fed, were evaluated. A com-
bination of alum and Atlas 105C, a cationic polymer? was concluded to be the
best flocculant chemical combination. This chemical combination along with
powdered activated carbon was utilized for the DAF tests on raw CSO samples
from Storm No. 1972-2. An effluent pressurization mode of DAF was utilized
during these tests. The results of these tests are shown in Table B-7. It
can be seen that an excellent removal of the pollutants was achieved during
these tests. The TOC concentration of the effluents from the three tests was
12 mg/1 as compared to a raw content of 59 mg/1. However, no appreciable im-
provement In the effluent quality was shown because of either an increase in
the activated carbon dosage or in the contact time prior to the addition of
the flocculating chemicals. It was also found that greater than 60% removal
was achieved in the dissolved organic pollutants, based on the soluble TOC
concentrations of the raw and effl uent samples (assuming all the TOC in the
effluent was in the soluble form).
it was also indicated that probably an excess of various chemicals had been
utilized during these tests and that further reductions in these dosages may
be possible.
The above mentioned changes were incorporated in the carbon flotation tests
on Storm No. 1972-3. Also, direct comparative tests were conducted for split
flow and effluent recycle modes of DAF for the various test conditions evalua-
ted during the earlier storms. The results of these tests are shown in Table
B-8. It was again confirmed that the effluent quality in the affluent recycle
mode of DAF tests was significantly superior to the corresponding quality in
the split flow mode of DAF (test Nos. 4 and 5 compared to Nos. 1 and 2 respec-
tively). Also, it was confirmed that the flocculant combination of alum and
Atlas 105C provided a better effluent quality compared to the ferric chloride
192
-------
Table B-6. CARBON FLOTATION TREATMENT - STORM NQ. 1972-1
Raw waste analysis:
Suspended solids, mg/1
TOC, mg/1
Soluble TOC, mg/1
105
27
16
FLOTATION TESTS
Test no.
Test conditions:
Mode of DAF treatment
Carbon (Filtrasorb 400)
Dosage, mg/1
Carbon contact time prior to
flocculant addition, mJn
FeCl., mg/1
NalcC 607, mg/1
Flocculatlon time, min
Flotation data:
Split flow rate, %
Pressure, psi
Flotation time, min
Scum volume, ga1/1000 gal.
Sludge volume, gal./IOOO gal
Effluent quality:
Suspended solids, mg/1
TOC, mg/1
Split flow
100
0
25
5
10
20
45
5
15
10
156
72
Split flow
too
45
25
5
10
20
45
5
35
5
23
23
Split flow
50
60
25
5
10
20
45
5
25
<10
118
56
193
-------
Table B-7. CARBON FLOTATION TREATMENT - STORM NO. 1972-2
Raw waste analysis:
Suspended solids,
TOC, mg/1
BOD, mg/1
Soluble TOC, mg/1
mg/1
160
59
69
32
FLOTATION TESTS
Test no.
Test conditions:
Mode of DAF treatment
Carbon (Filtrasorb 400)
Dosage, mg/1
Carbon contact time prior
to flocculant addition,
min
Alum, mg/1
Atlas 105C, mg/1
Flocculation time, min
le rate,
min
Effluent
recycle
50
60
50
3.5
2.5
Flotation data:
Effluent recycle
Pressure, psi
Flotation time, mm
Rise rate, fpm
Scum volume, gal./IOOO gal.
Sludge volume, gal./1000 gal.
Effluent quality:
Suspended solids, mg/1
TOC, mg/1
BOD, mg/1
25
45
5
<1
20
Trace
8
12
5
Effluent
recycle
100
60
50
2.5
2.5
25
45
5
<1
32
Trace
12
11.5
3
Effluent
recycle
50
5
50
2.5
2.5
25
45
5
1.0
15
Trace
11
12
5
194
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and Nalco 607 combination (test No. k compared to No.' 3). = The results shown
In test Nos. 4 to 7 again indicated that the effect of increased carbon con-
tact time prior to flocculation was insignificant. A carbon dosage of 50mg/1
at minimum carbon contact time was considered to provide the optimum results
with regard to the effluent quality.
However, it was also noted that the effluent quality in the effluent recycle
mode of DAF without the addition of carbon (test No. k) was quite favorable
when compared to the corresponding quality with carbon (test no. 5). The
addition of 50 mg/1 carbon would add approximately 5C/1000 gal. to the treat-
ment cost of the system. Therefore, additional comparative tests with and
without carbon were recommended at this stage to further explore the effect
of carbon addition, since the high removal of soluble organics from the raw
waste without the addition of carbon are questionable. Also, ft was pointed
out that since alum was being utilized as a'flocculant, significant removal
of the total phosphorus content may be possible via the use of a suitable
alum dosage. These considerations were further evaluated on an additional
overflow sample (Storm No. 1972-4). The results of these tests are shown in
Table B-9. The results showed some improvements in the effluent quality by
increasing the alum dosage from 40 to 100 mg/1 (test No. 2 compared to No. 1).
The total phosphate removals exceeded 85% in all cases but were significantly
better at 95% in Test No. 2 at the increased alum dosage of 100 mg/1 without
the use of powdered carbon. Again, the effect of the addition of 50 mg/1
carbon was very marginal (test Nos. 1 and 2 compared to Nos. 3 and 4). Such
high removals of soluble organics without the addition of carbon were again
questioned but no additional bench scale or field tests could be conducted
because of limited funds. The static nature of bench scale tests may have
contributed to the high removals of soluble TOC. No firm conclusions with
regard to the use of activated carbon in conjunction with flotation could be
made without additional tests under dynamic field operating conditions.
Ozone Oxidation - Bench scale ozone oxidation tests were performed on 3 raw
and 3 field flotation effluent samples. These samples did not correspond to
the operation of the treatment system during 1972 and instead were obtained
during the system operation of 1971. The tests were conducted on filtered
and unflltered samples to evaluate the oxidation of soluble and particulate
organic matter. The results of these tests are shown in Table B-10. It can
be seen that extremely poor oxidation of the organic matter was achieved (as
measured by influent and effluent TOC concentrations) with ozone dosages as
high as 30 mg/1. The reaction with ozone is expected to be instantaneous,
but, no improvement in the effluent TOC values was indicated by increasing
the ozone contact time. Therefore, it was concluded that ozone treatment of
CSO was technically unfeasible.
Removal of Total Phosphates
Analyses of the total phosphate concentrations were conducted on the raw and
flotation effluent samples for both the 1971 and 1972 operational seasons.
Also, phosphorus analyses were made for the bench scale test samples of
196
-------
Table B-9. CARBON FLOTATION TREATMENT - STORM NO. 1972-4
Raw waste analysis:
Suspended solids, mg/1
TOG, mg/1
BOD, rag/1
Total phosphate as P, mg/1
Turbidity, ftu
PH
Soluble TOC, rag/I
157
60
54
1.47
70
7.5
30
Test no.
FLOTATION TESTS (all in effluent recycle mode)
1 2 3
Test conditions:
Carbon (Nuchar 115) Dosage, mg/1 0
Carbon contact time prior to
flocculant addition, min. 0
Alum, mg/1 40
Atlas 105C, mg/1 0.75
Flocculation time, min. 10
Flotation data:
Effluent recycle, % 25
Pressure, psi 45
Flotation time, min. 8
Rise rate, tpm 2.4
Scum volume, gal/1000 gal. 20
Sludge volume, gal/1000 gal. Trace
Effluent quality:
Snsnended solids, mg/1 5
TOC, mg/1 ' 15
BOD, mg/1 8
Total phosphate as P, mg/1 0.24
Turbidity, ftu 4.3
pH 7.1
0
0
100
0.75
10
25
45
8
2.4
20
Trace
<1
12
5
0.07
1.0
6.7
.50
0 ,
40
0.75
10
25
45
8
2.0
25
Trace
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198
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Storm No. 1972-A as discussed earlier. The results of all these tests are
shown in Table B-11. It can be seen that generally, the removal of total
phosphates varied between 40 and 75% for the field flotation effluents. Sig-
nificant improvement in these removals (up to 95%) were achieved, however,
during the bench scale tests on Storm No. 1972-4 by the addition of alum as a
flocculant as discussed earlier for carbon-flotation test results. Therefore,
it is recommended that the addition of alum as a flocculant be evaluated in
field flotation tests to confirm the improved removals of phosphorus on a
full scale basis.
DISCUSSION
The bench scale tests conducted during this study have unquestionably demon-
strated that the effluent quality currently obtained via the screening/flo-
tation treatment of combined sewer overflows can be improved. Both micro-
screening and mixed media filtration can contribute towards a significant
improvement of the treated effluents with regard to the particulate matter.
However, neither of these unit processes can remove any of the soluble or
dissolved pollutants that are present in the raw combined sewer overflows.
Moreover, it has been indicated that approximately 15~35 mg/1 of the partic-
ulate matter present in the flotation effluents is finer than 15-20 microns
and therefore passes through the corresponding screen openings. Filtration
results, however, were found to be significantly better than microscreening,
as measured by the filtrate suspended solids because of the very complex
mechanism of filtration, whereby the removed solids may form a mat and help
to remove the remaining finer particulates.
Assuming that the particulate matter can be effectively removed via a suitable
size microscreen or mixed media filtration, significant improvement in the
overall removals cannot be attained without some reduction of the soluble or-
ganic pollutants. Theoretically, this could be achieved by adsorption on
activated carbon or oxidation via chemical oxidants such as ozone. The re-
sults of the ozone oxidation tests were concluded to be technically unfeas-
ible. However, it was found through the various tests conducted during the
carbon-flotation experiments that a significant reduction (greater than 60%)
in the soluble organics (as measured by TOC) along with an excellent removal
of particulates, can be achieved via dissolved-air flotation in the effluent
recycle mode of operation. The addition of powdered activated carbon provid-
ed only marginal improvement in the effluent quality. This may have been a
result of the static nature of bench scale tests. The high removals of solu-
ble organtcs seen in the bench scale flotation tests without carbon may not
be sustained in field tests. Therefore, it is recommended that additional
bench and field flotation tests in conjunction with powdered activated carbon
be conducted to confirm the findings of the results of this study.
A new chemical flocculant combination consisting of alum and a cationic poly-
mer Atlas 105C was found to provide the best results. The addition of alum
also helped in providing more than 90% reduction of total phosphates. Thus,
the various advantages that can be achieved through the use of effluent re-
cycle mode of dissolved-air flotation in .conjunction with alum and a cationic
199
-------
Table B-11. RESULTS OF TOTAL PHOSPHATE ANALYSIS
A. Results
Overflow
no.
1971-1
1971-2
1971-3
1971-4
1971-5
1971-6
1972-1
1972-2
1972-3
B. Bench
of field operation
Raw
0.68
0.19
0.77
1.23
1.62
0.58
0.74
1.88
1.84
scale test results
Effluent without
of the flotation system.
Total phosphate as P, mg/1
High overflow rate
mg/1 % removal
-<-
0.13 31.5
0.23 70.0
1.24
0.79 51.3
0.35 39.7
for conditions shown in
Low overflow rate
mg/1 %
0.17
0.10
0.19
0.80
0.75
0.34
0.35
0.73
0.46
Table B-9.
remova 1
75.0
47.5
75.4
35.0
53.7
41.5
47.2
61.1
75.0
Effluent with 50 mg/1
ca rbon ca rbon
Overflow Alum % Alum % Alum
no. Raw 40 mg/1 removal 100 mg/1 removal 40 mg/1
% Alum
removal 100 mg/1
y
'b
removal
1972-4 1.47 0.24 83.8 0.07 95.2 0.09 93.8 0.23 84.4
200
-------
polymer are:
1. Significant Improvement of the flotation treated effluents with
regard to both the participates and the soluble organic pollutants.
2. No addi tjonal uni t processes are requi red to achieve these improve-
ments. .,-. -. . - ..^*-...~. .,. -. ;, , ,.,. ^ "--^
3. No significant increase in the chemical costs were observed by
changing to the new flocculant combination. The operating costs v
have been concluded to be approximately 3.U/1000 gal. In an earlier
study (B2). . ':
4. Significant reduction in the phosphorus content of the treated
effluents.
Based on these advantages, it was recommended that the above described
treatment system be utilized for the treatment of combined sewer overflows
at the Hawley Road test facility to confirm the findings of the bench scale
tests. It is anticipated that if the field tests are successful, the above
findings can be implemented in full-scale screening/flotation systems.
It should also be noted that the above recommended modifications with regard
to effluent recycling have been approved by U.S. EPA for the Hawley Road
test facility. The modified treatment system will then be operated on a
1imited number of combined sewer overflows. The test program, however,
does not include any evaluation of the powdered activated carbon-flotation
concept. Therefore, it is recommended that separate field tests with pow-
dered activated carbon be conducted to confirm the findings of the bench
scale results. Such an evaluation would involve the operation of the treat-
ment system on six or more overflow events and can be conducted under the in-
dependent sponsorship of the Wisconsin Department of Natural Resources.
SUMMARY AND CONCLUSIONS
This report documents the results of a test program undertaken to upgrade the
quality of the effluent from an existing screening/flotation system in Mil-
waukee, Wisconsin for the treatment of combined sewer overflows. The unit
treatment processes investigated to accomplish the above objective were:
1) high-rate filtration, 2) microscreening, 3) powdered activated carbon in
conjunction with dlssolved-a?r flotation (both in split flow and effluent
recycle modes, and 4) ozone oxidation.
The results of the bench scale tests have demonstrated that the effluent
quality currently obtained via the screening/flotation treatment of combined
sewer overflows can be improved significantly. Both microscreening and
mixed media filtration were found to provide high quality effluents with re-
gard to particulate matter; with filtration treatment providing consistently
higher removals than microscreening. However, neither of these processes
could remove any of the soluble organ Ics present in the raw waste. The re-
201
-------
moval of the soluble organics via ozone oxidation was not successful. How-.
ever, a significant (>60%) reduction in the soluble organics was achieved
along with excellent removal of particulate matter via powdered activated
carbon and flotation treatment. Such treatment required the operation of,,-.
dissolved-air flotation in the effluent recycle mode. Also, the use of a new
flocculant combination consisting of alum and a cationic polymer (Atlas 105C)
was found to be necessary for achieving the improved effluent quality via ;
carbon addition. It was also noted that the effluent quality in the effluent
recycle mode of DAF was significantly better than the split flow mode of DAF
and compared favorably with that achieved with carbon addition.
The following conclusions can be made based upon the upgrading study per-
formed:
1.
2.
3.
5.
6.
7.
8.
The effluent quality currently obtained via the screening/flotation
treatment of combined, sewer overflows can be upgraded significantly.
Both mixed media filtration and microscreening were found to be
effective means of removing the particulate matter in the flotation
effluents. However, neither of these processes can remove any
soluble organic fraction present in the treated effluents.
Approximately 20-30 mg/1 of the suspended solids
effluents were finer than 15-20 micron size.
in the flotation
Filtration treatment of the flotation effluents provided better
removals of the particulate matter compared to microscreening.
Flotation treatment of the raw CSO in the effluent recycle mode of
dissolved-air flotation provided better effluent quality compared
to filtration or microscreening of split flow treated flotation
effluents. However, the most optimum results were achieved via a
new flocculant combination of alum and Atlas 105C (polymer) as
compared to the previously used FeCl, and cationic polymer com-
bination.
The field test results showed a total phosphate removal of 40-75%.
These removals could, however, be upgraded to greater than 30% by
using the alum-polymer combination during bench scale tests.
Powdered activated carbon, when used in conjunction with DAF in the
effluent recycle mode, provided excellent removals of both particu-
late and soluble organic pollutants. These removals, however,
were not significantly better than the effluent quality achieved
during the bench test results without the use of activated carbon.
Ozone treatment of CSO's did not provide any significant removal of
organic pollutants.
it was recommended that the existing flotation system should be modified to an
effluent recycle type of system and additional field tests should be conducted
with and without the addition of powdered activated carbon.
202
-------
REFERENCES - APPENDIX B
B1. Pollution of Stormwater and Overflows from Combined Sewer Systems..:-.
' A Preliminary Appraisal, USPHS, November, 1964.
B2. Mason, D.G. and Gupta, M.K. "Screening/Flotation Treatment of Combined
Sewer Overflows'^ USEPA Report No. 11020FDC-01/72, January 1972.
B3. Standard Methods for the Examination of Water and Waste Water - 13th
Ed? tion, American Public Health Association, New York, 1971.
203
-------
APPENDIX C "
ANALYTICAL PROCEDURES
ANALYTICAL INSTRUMENTS AND APPARATUS , .
pH Meter: Beckman.Model s H-2 and SS-2 ,
Beckman Instruments Incorporated
Fullerton, CA
Incubator: Model 1483
Precision Scientific Co.
Chicago, IL
Conductivity Bridge: Model RC16B2
Industrial Instruments Inc.
Cedar Grove, NJ
BOD Incubator: Labi Ine No. 3554B and No. 3555 Incubators
Lab-Line Instruments, Inc.
Mel rose Park, IL
Analytical Balance: Type H5 and Type HI 0
Mettler Instruments Corp.
HIghtstorm, NJ
Ozone Cylinder: Vaporising Coll and Regulator
Matheson Company, Inc.
East Rutherford, NJ
Spectrophotometer: Coleman Model 14
Coleman Instrument Co.
May wood, IL
TOC Analyzer: Beckman Model 951 Total Carbon Analyzer
Beckman Instrument Co.
Fullerton, CA . . .
ANALYTICAL PROCEDURES AND ANALYSES
The following analyses were performed according to Standard Methods for the
Examination of Water & Wastewater. (SM) 12th and 13th Editions, 1965 and T971
respectively, and Methods for Chemical Analysis of Water and Wastes (MCA),
204
-------
Water Quality Office, U.S. Environmental Protection Agency, 1971. The page
numbers of the analytical procedures used and the references are noted with
each analysis.
Sol ids - Total
Sol ids - Total
Volatile
SM_, 13th Ed., p. 535; MCA, p. 280; Evaporation to dry-
ness at 103°C.
SM_, 13th Ed., p. 292 and 536; MCA, p. 282; Residue and
dish ignited at 500°C.
Solids - Suspended SM. 12th Ed., p. 424; Filtration through asbestos mat in
Sol ids - Volatile
Suspended
gooch crucible; dried at 103°C.
SM_, 12th Ed., p. 425; Residue and filter from the sus-
pended solids analyses are tgnited at 600°C. The filter
from the suspended solids test is transferred to a tared
crucible and charred before ignition.
Biochemical Oxygen SM, 13th Ed., p. 489; Conventional 5 day procedure. DO
Demand (BOD)
Chemical Oxygen
Demand (COD)
Phosphate - Ortho
Phosphate - Total
measured by either YSI probe or Winkler method
SM, 13th Ed., p. 495; MCA, p. 19.
SM, 12th Ed., p. 231; Amino naphthol sulfonic acid (ANS)
procedure.
MCA, p. 242 and SM, 12th Ed., p. 231; Sample is digested
with persulfate "{MCA method) and phosphate measured by
ANS procedure (SM)V"
Nitrogen - Kjeldahl SM_, 13th Ed., p. 244; MCA_," p. 149; Digestion of sample
followed by distillation and titration. Measures both
organic N and NH,.
Chloride SM, 12th Ed., Method A, p. 86, A 0.423N standard silver
nitrate tltrant was used instead of 0.0141N because of
high chloride content In raw storm H20, thus giving a
more detailed endpoint.
Chlorine, Total Available - SjM, 12th Ed., Method A, p. 91.
Ozone
Concentration
Coliform -
Bacteria Count
SM, 12th Ed., Method A, p. 220; The titration procedure
stated was followed, but the sample collection and ozone
absorption techniques are those as specified by the
Matheson Company (Matheson Gas Data Book).
SM, 13th Ed., p. 679; Membrane filter procedure. The
millipore filter technique described Jn "Techniques for
Microbiological Analysis (ADM-40)", Millipore Filter Corp.,
Bedford, MA, p. 22 was used. Where necessary, samples
were dechlorlnated using
205
-------
Analysis for Soluble (Dissolved) Matter
The analysts for soluble matter, i.e., TOC or BOD, was obtained by filtering
the sample through a millipore filter (0.^5 y and then performing the
appropriate analysis on the filtrate. If the sample contained gross amounts
of solids which would rapidly blind the millipore filter disc, the sample was
preflltered through SS-597 filter paper. The filtrate from this prefi1tration
was then filtered through the mi Hi pore disc as described above.
206
-------
APPENDIX D
BENCH SCALE TEST PROCEDURES
DISSOLVED-AIR FLOTATION TEST PROCEDURE
A copy of the Instructions for performing dissolved-air flotation tests is
attached. This sheet described the test as normally used in the REX Chainbelt
Process Laboratory. This procedure was modified at times during the chemical
oxidation tests by using different detention times and by using ozone instead
of normal air as the source of bubbles.
The rate of separation of the suspended sol ids from a waste is useful in the
design of industrial .waste treatment equipment. Rate of separation data may
be conveniently obtained in the laboratory from treatment tests performed on
the waste in question. The treatment process which wil1 be considered are
dissolved-air flotation and sedimentation. Generally, the procedure used in
obtaining rate-of-separation data is to observe the solids/liquid Interface
and to record its travel with time.
A. Dissolved-Air Flotation
In the tests using dissolved-air flotation, the rate of rise of the
major portion of the solids Is recorded. At times the solids-liquid
Interface may be vague and good judgment may have to be exercised In
following this interface. Care should be taken to avoid following
the interface formed by the air bubbles along. In general, this
interface Tags behind the solids-liquid interface;
A suggested procedure for the performance of laboratory flotation
tests and the equipment needed is as follows:
1. Equipment
a. Flotation pressure cell
b. Graduated cylinder of one liter capacity containing
an effluent sampling arm
c. Tire pump or source of compressed air
d. Gooch crucibles for suspended solids determinations
e. Stop watch
2. Flotation Test Procedure
a. Record waste temperature, pH, operating pressure,
recycle rate, and flotation detention time
207
-------
b. Record rate of separation data. The form shown below Is
suggested in obtaining the rate of separation data.
The ultimate data desired is the position of the interface at various inter-
vals throughout the test. The column below labeled "volume" is used as a
convenient means of obtaining the position of the interface at any given
time. For example, in the hypothetical case shown below, a liter graduate
was used in the test. At the beginning of the test, the solids-liquid inter-
face is at the bottom of the graduate or at zero volume. As flotation
progresses, the solids-liquid Interface moves progressively up the height of
the graduate. The position of the Interface at any given time may be conven-
iently obtained using the appropriate graduation mark on the liter cylinder
as a reference. After the flotation test, the graduation marks may be
converted to the feet of height by actual measurement.
Time Volume POI (Position of Interface)
(tnln) (ml) (feet)
00 0
1 100 0.115
2 350 0.411
3 500 0.589
4 650 0.766
5 800 0.946
6 950 1.222
7 950 1.222
8 950 1.222
The data obtained are plotted using Time as the abscissa and POI in feet as
the ordinate.
I
POI
(ft)
TIME (minutes)
The slope of the straight line portion of the curve
represents the rate of particle rise.
During flotation it should be noted whether settling
of solids took place. Note observation.
208
-------
c. Record the floated .^cum.volume obtained immediately
befpre ;pbtaining a sample of the.effluent..
d. Obtain sample of effluent five minutes after flotation
is started, for the appropriate analyses. Repeat the,
flotation and obtain another sample of effluent for ,
analysis after an eight minute detention period.
e. If possible, a small portion of the floated scum should be
analyzed for total sol ids content. , -.
MlCROSCREENING TEST PROCEDURE : - : , -. : ,
The mlcroscreening bench test apparatus consisted of a plexiglass vessel
threaded to accept a screen media holder. A precision relieving, air
regulator supplied air pressure to the liquid above the microscreening media
simulating constant liquid heads of 1.5 inches to 61.5 inches of water. A
sketch of the apparatus is shown in Figure D-l. The sample is poured in the
inverted sample reservoir. The filter media with the microscreening material
is threaded on the sample reservoir. Air pressure is applied to simulate
the desired liquid head. The entire apparatus is then inverted. The sample
will bubble out of the sample reservoir until the liquid covers the spout
end of the reservoir. In all tests, the throughput rate through the media
must be less than the flow out of the reservoir. By varying the pore size
of screens, by media selection and varying the head of water pressure
applied, no problem was experienced in obtaining the flow required. By
measuring the volume of filtrate collected per unit time, throughput rates
could be calculated. The filtrate was also analyzed for suspended solids so
that removal rates could be calculated.
209
-------
AIR
REGULATOR
\
2" PVC CAP
2" PLEXIGLAS TUBE
PVC REDUCER
(glued in place)
STEEL WASHER
RUBBER SEAL
MICROSCREEN
MEDIA
MEDIA HOLDER
RUBBER SEAL
§
2" x H" PVC
REDUCER
Figure D-l. MIcroscreen bench test apparatus
210
-------
APPENDIX £
OPERATING DATA AND STATISTICAL PROCEDURES
OPERATING DATA - SCREENING/FLOTATION SYSTEM
Table E-1. OPERATIONAL DATA - 1969
Run
no.
691
692
693
694
695
696
S97
698
699
63 10
6911
6912
6913
6914
6915
6916
6917
6918
6919
6920
6921
6922
6923
6924
-i925
6926
6927
6928
6929
6930
Duration,
Date
6/4/69
6/4/69
6/7/69
6/7/69
6/22/69
6/25/69
6/26/69
6/27/69
6/29/69
7/2/69
7/1 1/69
7/16/69
7/17/69
7/23/69
7/26/69
8/7/69
8/9/69
8/11/69
9/4/69
9/5/69
9/6/69
9/23/69
9/29/69
9/29/69
10/10/69
10/10/69
10/12/69
10/31/69
11/2/69
11/3/69
min
123
70
103
30
75
110
150
105
50
180
75
35
60
75
40
50
150
65
35
90
60
65
180
47
65
243
75
55
45
110
Raw
waste,
gal .
378000
189000
302400
88200
201600
340200
44100°
277200
151200
554400
226800
100800
163800
226800
100800
138600
395640
190680
100800
277200
176400
201600
453600
143640
176400
705600
226800
163800
1 1 3400
327600
Screen
wash,
gal .
0
0
1600
800
2000
<600
600
600
<600
<600
800
3200
1200
5200
<600
4800
3600
<600
1200
600
<600
600
600
<600
<600
8400
1200
2400
1800
1800
Floated
scum,
gal.
6200
3450
3400
900
1900
3500
6250
6700
850
4400
2100
4oo
700
1200
450
200
1700
460
450
1850
540
700
2200
310
3850
1700
750
600
250
1150
Overflow
rate,
gpm/sq ft
2.63
2.31
2.51
2.51
2.30
2.64
2.51
2.26
2.58
2.63
2.58
2.46
2.33
2.58
2.15
2. .37
2.25
2.51
2.46
2.63
2.51
2.65
2.15
2.61
2.32
2.48
2.58
2.55
1.76
2.55
211
-------
Table E-1. (Continued)
OPERATIONAL DATA - 19&9
Chemical
Run
no.
691
692
693
694
695
696
697
698
699
6910
6911
6912
6913
6914
6915
6916
6917
69)8
6919
6920
6921
6922
6923
6924
6925
6926
6927
6928
6929
6930
Rainfall
Inches
0.42
0.17
0.20
0.10
0.25
0.50
1.75
0.50
1.00
1.50
0.27
0.12
0.45
0.17
0.40
0.10
0.30
0.45
0.10
0.05
0.20
0.14
0.70
0.17
0.40
0.12
0.10
0.50
In/hr
0.13
0.68
0.15
0.10
0.32
0.50
1.17
0.40
0.70
2.30
0.40
1.50
0.45
0.35
0.35
0.40
0.10
1.60,
1.20
2.10
1.20
0.30
0.15
0.15
0.10
0.30
Operating
pressure,
psig
50
40
50
50
50
50
50
50
60
60
60
55
50
60
60
60 :
60
60
60
60
50
50
50
50
50
60
50
50
50
50
Pressurized
flow rate ,
qpm
600
650
850
850
900 '-
900
900
600
700
700
475
600
900
400
400
450
600
450
800
650
500
500
500
500
800
400
550
550
550
550
add!
C-31
mg/1
«MX»MMM
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
5
0
3
3
3
3
3
5
0
0
3
0
2.5
2.5
5
tion
Cl,
mg/J
0-
d
0 '
o:
10
0
10
8
10
10
10
10
10
0
0
0
0
0
0
0
o :
o :
0
0
0
0
0
0
0
0
212
-------
Table E-1. (Continued)
OPERATIONAL DATA - 1970
Run
no.
701
703
704
705
706
707
708
709
7010
7011
7012
7013
7014
7015
7016
7017
7018
7019
7020
7021
7022
7023
7024
7025
Date
VI 3/70
4/9/70
5/11/70
5/12/70
5/15/70
5/22/70
5/31/70
6/1/70
6/12/70
6/26/70
6/26/70
7/8/70
7/14/70
7/15/70
7/19/70
7/27/70
7/31/70
8/18/70
9/2/70
9/3/70
10/23/70
10/26/70
10/27/70
10/31/70
Duration,
min
90.7
47.6
49.7
138.6
52.3
73.7
90.1
90
44.1
75.1
68
49.5
40
49.8
97.2
66.6
34.1
36.4
51.8
95.6
38
64.5
149.1
95
Raw
waste,
gal.
252000
126000
119700
286020
117180
153720
186480
178920
95760
142380
143640
131040
133560
1 1 8440
217980
147420
75600
10200
152700
229320
1 1 8440
153720
322560
241920
Screen
wash',
gal.
1200
4800
360
60
0
1380
3960
420
120
3300
460
2820
1080
480
60
0
240
1740
0
0
2160
0
60
4260
Floated
scum,
gal .
1050
500
300
500
250
350
1000
2050
1300
1900
1700
1000
1000
500
1600
1050
150
100
600
1150
200
500
750
600
Overflow rate,
dom/so ft
High
4.75
4.52
4.16
3.53
3.83
3.56
3.54
3.40
3.71
3.24
3.61
4.52
5.71
4.06
3.83
3.79
3.79
4.79
5.08
4.10
5.33
4.07
3.75
4.35
Low
3.56
3.39
3.09
2.65
2.87
2.67
2.65
2.55
2.78
2.43
2.7.1
3.39
4.28
3.05
2.88
2.84
2.84
3.59
3.81
3.Q8
4.00
3 f
.06,
-_ n «
2.81
3.27
213
-------
Table E-1 (Continued)
OPERATIONAL DATA - 1970
Chemical
Run
no.
701
703
704
705
706
707
708
709
7010
7011
7012
7013
7014
7015
7016
7017
7018
7019
7020
7021
7022
7023
7024
7025
Rainfall
Inches
0.7
0.3
0.07
0.57
0.25
0.28
0.14
0.5
0.33
0.25
0.10
0.20
0.22
0.10
0.25
0.30
0.45
0.23
0.25
0.35
0.15
0.70
0.40
0.32
In/hr
..
0.17
0.09
0.23
0.33
0.36
0.84
1.11
0.11
0.17
0.09
0.80
0.18
0.13
0.13
0.36
2.25
0.15
0.24
0.18
0.10
0.35
0.10
Operating
pressure,
psig
50
50
50
50
50
50
50
50
50
50
60
50
55
50
50
50
50
50
50
50
50
50
50
50
Pressurized
flow rate,
gpm
800
600
900
900
900
450
450
550
550
450
350
600
950
450
450
450
450
550
550
550
600
600
600
600
add! tion.
C-31
0
0
6
6
6
6
6
4.2
4.6
5.3
3.9
4.6
3.5
4.5
4.5
4.5
4.5
3.8
3.8
3.8
0.5a
0.5a
0.5a
4
mg/1
l^eCl3
0
0
0
0
0
0
0
30
29
17
16
16
21
21
21
21
21
17.5
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225
-------
Table E-9. SCREEN BACK WASH & FLOATED SCUM QUALITY 1969 DATA
(mg/1 except pH)
Run
#
693
694
695
696
697
698
699
6910
6911
6912
6913
6914
6915
6916
6917
6918
6919
6920
6921
6922
6923
6924
6925
6926
6927
6928
6929
6930
£"
^ M
__
6.8
6.8
--
7.8
7.1
6.5
7.0
7.2
7.0
6.9
6.6
6.8
7-1
--
7.1
7.2
7.4
--
6.8
7.2
7.3
Screen
Total
Solids
__
1688
643
__
296
1443
2542
2192
1865
--
__
3638
1776
__
2303
2431
--
4185
890
--
__
2901
_-
1600
1623
1322
Back Wash Qual I ty
Total
Volatile
Solids
»
1388
538
220
_
1025
1814
1450
1100
2486
1406
_
1830
1813
__
2533
694
__
.«
972
1236
1244
1048
Suspended
Solids3
__
1554
543
183
1371
2434
1909
1500
«
3366
1435
1746
2298
> *
3872
715
f
2843
^ ^
1330
1253
1019
a. Calculated based on dissolved solids in raw waste
226
-------
Table E-9. (Continued)
SCREEN BACK WASH 6 FLOATED SCUM QUALITY 1969 DATA
(mg/1 except pH)
Floated Scum Qual } ty
Run
#
693
63k
695
696
697
698
699
6910
6911
6912
6913
6914
6915
6916
6917
6918
6919
6920
6921
6922
6923
6924
6925
6926
6927
6928
6929
6930
£1L
6,8
7.2
7.1
7.2
7.5
--
7.3
6.6
7.0
7.0
7.0
6.6
6.8
7.0
6.8
7.0
6.9
7.0
6.9
7.1
7.5
7.3
7.0
6.8
6.8
7.0
Total
Solids
2395
4005
584
686
385
1439
36860
14282
19081
11131
3705
22627
4687
7694
13650
12168
3111
2291
13228
6699
2508
11361
1705
3268
7027
2804
Total
Volatile
Solids
1520
2390
330
332
202
647
19958
7550
10700
6919
2244
13403
3163
3544
8450
6644
1408
1848
8082
3471
1097
5002
1132
2100
5045
2020
Suspended
Solids3
2004
3879
484
613
272
--
1367
36720
13999
18716
10852
3624
22355
4346
7608
13093
12035
3087
1978
13053
6610
2100
11303
1492
2998
6657
2501
a. Calculated based on dissolved solids in raw waste.
227
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-------
Table E-11. FIRST FLUSH EVALUATIONS (RAW COMBINED SEWER OVERLFOW QUALITY)
(1969-1970)
Days Since
Last Run
Overflow No.
0 703
0 692
0 694
0 6924
o 6930
0 705
0 709
0 7012
697
698
6913
6920
6921
6926
6927
7015
7021
7024
2 699
I 6911
I 706
I 704
I 706
I 7023
3 693
3 696
COD
206
220
173
125
217
199
168
117
66
47
223
127
114
95
94
191
90
178
59
185
140
141
140
169
241
87
BOD
mg/1
91
43
31
65
35
37
49
7
7
31
25
29
36
_
25
54
28
58
28
67
17
Suspended
Sol ! ds
mg/1
218
365
158
129
87
316
148
119
57
176
114
102
141
56
140
118
1.71
148
104
149
109
149
107
169
88
Volatile
Suspended
Solids
mg/1
88
145
80
66
66
193
86
81
26
29
120
62
64
65
45
85
63
125
43
78
75
39
75
73
117
46
229
-------
FIRST FLUSH EVALUATIONS
Table E-11. (Continued)
(RAW COMBINED SEWER OVERFLOW QUALITY)
(1969-1970)
Days Since
Last
Overflow
3
3
3
7
3
4
5
5
6
6
6
8
8
11
11
11
12
13
14
15
17
17
18
19
19
2k
26
Run
No.
6915
6925
7016
7018
7025
6910
6912
7014
6914
6923
707
6911
708
6918
6925
7013
6916
7011
7020
695
6922
7019
691
6928
7022
6919
702
COD
118
195
130
244
139
78
472
191
574
163
211
920
512
137
118
649
531
390
153
615
248
286
676
334
372
642
617
BOD
mg/1
«»*»
70
66
12
10.1
18
61
101
180
160
37
39
330
89
212
53
180
113
172
124
145
170
224
Suspended
Solids
mg/1
116
87
135
337
123
208
496
232
554
104
228
1180
431
192
70
479
405
232
466
538
165
264
642
180
415
312
582
Volatile
Suspended
Solids
mg/1
62
63
95
183
103
66
253
139
322
68
146
678
247
82
22
289
310
156
204
310
117
164
391
138
273
244
228
230
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234
-------
Table E-14. SUSPENDED SOLIDS MASS BALANCE - 1969 DATA
Run
No.
691
692
693
695
696
697
698
699
6910
6911
6912
6913
6915
6917
6920
6921
6922
6923
6924
6925
6926
6927
6928
6929
6930
Pounds
SS
In
353
575
426
282
250
706
132
187
961
522
417
240
97
343
263
150
277
393
154
103
829
106
246
82
238
Pounds
SS
Out
372
337
146
157
163
499
141
111
650
362
181
88
46
124
79
64
94
184
80
54
203
41
122
45
146
Pounds
SS Left
in Tank
80
145
39
63
39
92
42
59
94
86
48
43
37
25
23
29
37
33
45
25
23
15
60
32
36
Pounds
SS
Screen Wash
0
0
26
_
16
51
15
43
12
19
4
199
13
19
15
Pounds
SS
Scum
-..»_
58
63
14
31
15
50
84
47
109
15
62
191
13
12
239
17
68
160
11
15
17
25
Balance
% (A)
-28
+ 16
+57
- 9
+ 14
+ 12
-50
+ 9
+ 17
- 5
+22
- 6
- 1
+26
-16
+29
+41
-17
+ 8
-43
+29
+37
+ 14
-37
+ 7
a. (+) Excess solids in; (-) Excess solids out.
235
-------
Table E-14. (Continued)
SUSPENDED SOLIDS MASS BALANCE - 1970 DATA
Run
No.
701
703
704
705
706
707
708
709
7011
7012
7013
7014
7015
7016
7018
7019
7021
7022
7023
7024
7025
Pounds
SS
In
316
228
108
750
145
291
667
220
274
142
481
257
138
244
211
224
225
408
137
458
247
Pounds"
SS
Out
211
151
48
154
38
120
181
44
74
76
158
83
84
40
29
60
68
60
80
179
89
Pounds
SS Left
In Tank
68
100
33
43 '
26
63
80
20
43
43
100 ;,
50
57
15
31
48
24
41
42
44
30
Pounds
SS
Screen Wash
14
67
'.'.'
"
--
36
--
38
81
__ .
54
--
..
5
54
28
--
--
--
Pounds
SS
Scum
21
18 -
17
144
17
32
173
463
175
215
107
48
63
181
21
2
154
40
53
24
120
Balance
* (A)
f 1
-47
+ 9
+55
+44
+14
+35
-157
-36
-135
+ 13
+30
-48
f 1
+36
+35
- 9
+65
-28
+46
+ 3
a. (+) Excess solids In; (-) Excess solids out.
236
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241
-------
Table E-20. FLOATED SCUM QUALITY - 1971 DATA
(mg/1 except pH and col I form)
Floated Scum Qaulity
Run
71-2
71-3
71-4
71-5
71-6
PH
7.35
7.55
7.45
7.12
Total
solids
26152
28009
29290
Total
volati le
solids
4733
4731
_-
6608
Suspended
solids3
26050
27951
29144
a. Calculated based on dissolved solids in raw waste.
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Table E-28. FLOATED SCUM QUALITY - 1973 DATA
(mg/1 except pH and col?form)
Floated Scum Quality
Run
73-1
73-2
73-3
73-4
73-5
73-6
73-7
73-8
73-9
73-10
Total
solids
34500
15700
258500
8539
16600
37996
14857
10298
15845
Total
volatile
sol ids
9760
5550
6400
2672
; 6895
12613
5881
4415
6940
Suspended
solids
15581
258364
8419
16442
37823
14770
.10181
4 t , .
' "'> * V f:~ s,»< - ; v. \"'.' . /
a. Calculated based on dissolved solids in raw waste.
O O K>
~' o t a/ -6- -'"! -K. V* . i o
J"J1 C^1 ' ' r?n f"J O' **U !; -^"!
.<"'!
250'
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252
-------
Table E-31. OPERATIONAL RESULTS FOR HAWLEY
ROAD TREATMENT FACILITY ;
Run No. "'
Date >
Duration of Run, min.
Total Volume Treated, cu m (gal.)
Recycle Rate, %
Flow Rates, 1/min (gpm)
Raw
Recycle
Total
Overflow Rate, 1/mln/sq m (gpm/sq ft)
Raw , -''.-"' "' ' ?'
Total , ;' :
Chemical Dosages, mg/1
Alum ;
Carbon
Betz 1160
1
August 2, 1974
:88.8 :
458 (120,960)
45.9
5155 (1362)
2366 (625)
7521 (1987)
71 (1.75)
104 (2.55)
,94
1.4'
Percent Removal
Qual i ty Parameters ..-,,
pH .' %. ;:-;
SS, mg/1
VSS,mg/l
TS, mg/1 , '1? '-.:
TVS, nig/1
BOD, mg/1
TOC, rn'g/1 * S :
SOC, nig/1
Total ,P, mg/1 as P .
j(-i eeneu
, Raw Effluent
. *
96 72
321 ; 24ov
-21 -23/v
12 14
r i rid i
Effluent
~
17
; 365
-, 10
11
ro.33
"^» # ''i
Screen Flotation
*"
25.0 76.3 ?
'' i;.-
J 25%J2 ^52.0^
>-? < ^
(9.5) r? '56.5^
3^i8 I ' ;(8.3)
: ; .! o
1 >' S i *. .
; (rU6) I ^46. 7 i
Total
82.2
(13.7)
52.3
31.5
8.3
45.9
Note: Numbers in parentheses represent an increas,e in conqentra'tion.
ry, ;,».,, f.rf
** ^-1 »r
fit "t- !*ri E.«^ ->"»
I t { } I
pv% fVi ^v> /*₯> grvt
,^< ..« ^ ,-; ,^-i
O C
-------
Table E-32. OPERATIONAL RESULTS FOR HAWLEY
ROAD TREATMENT FACILITY
Run No.
Date
Duration
Total Volume Treated, cu m (gal.)
Recycle Rate, %
Flow Rates, l/m!n (gpm)
Raw
Recycle
Total
Overflow Rate, 1/min/sq m (gpm/sq ft)
Raw
Total
Chemical Dosages, mg/1
Alum
Carbon
Betz 1160
Quality Parameters
PH
SS, mg/1
VSS, mg/1
TS, mg/1
TVS, mg/1
BOD, mg/1
TOC, mg/1
SOC, mg/1
Total P, mg/1 as P
Raw
7.35
134
84
333
175
34
29
26
'1.66
Screened
Effluent
7.35
124
77
280
169
29
29
28
0.72
Final
Effluent
7.25
34
9
519
233
6
10
9
0.19
2
August 10, 1974
70
486 (128,520)
34.0
6949 (1836)
2366 (625)
9315 (2461)
96 (2.35)
129 (3.16)
30
46
1.7
Percent Removal
Screen
7.4
8.3
15.9
3.4
14.7
0.0
(7.6)
56.6
Flotation
72.5
88.3
(85.3)
(37-8)
79-3
65.5
67.8
73.6
Total
74.6
89.2
(55.8)
(33.0
82.3
65'. 5
6 5". 3
88.5
Note: Numbers In parentheses represent an Increase in concentration.
254
-------
Table E-33- OPERATIONAL RESULTS FOR HAWLEY
ROAD TREATMENT FACILITY
Run No.
Date
Duration of Run, min.
Total Volume Treated, cu m (gal.)
Recycle Rate, %
Flow Rates, 1/min (gpm)
Raw
Recyc 1 e
Total
Overflow Rate, 1/min/sq m (gpm/sq ft)
Raw
Total
Chemical Dosages, mg/1
Alum
Carbon
Betz 1160
,: Screened Final
Quality Parameters Raw Effluent Effluent
PH " ,.,.^2 7:o g;g
SS, mg/1 .. , 131 183 30
VSS, mg/1 . 43 62 8
TS, mg/1 \ 612 443 398
TVS, mg/1, .... 189 . v ,. 153 139
BOD, mg/1 . ' " 64 ." 55 22
TOC, mg/1 . 36 48 20
SOC, mg/1 12 8 , 11
Total P, mg/1 as P 1.02 ,,.1.25 0..19
3
August 16, 1974
140
963 (254,520)
30.3
6881 (1818)
2082 (550)
8963 (2368)
95 (2.33)
124 (3.04)
63
60
0.45
Percent Removal
Screen Flotation
(39*6) 83.6
(44.1) 87.0
27.6 10.1
19.0 9.1
14.0 60.0
(33.3) 58. 3:
33.3 (37.5)
(22.5), 84.8
Total
77.0
81.3
34.9
26.4
., 65,6
44.4
8-3
81 .3
Note": Numbers in 'parenth'eses* rep'resen't" an "increase in concent ration. "
.; '''.'' ,'-" "..--'.'.-";..' ~! ' ~: ?, &'?'"">'" I ''£> J i". -\i f S1O T,! 5 i ,:fif':,; ;'3"l«" Hi 7 "SSuKiu'/l :;?*i
-------
Table E-34. OPERATIONAL RESULTS FOR HAWLEY
ROAD TREATMENT FACILITY
Run No.
Date
Duration of Run, min.
Total Volume Treated, cu m
Recycle Rate, %
Flow Rates, 1/min. (gpm)
Raw
Recycle
Total
Overflow Rate, 1/min/sq m
Raw
Total
Chemical Dosages, mg/1
Alum
Carbon
Betz 1160
Quality Parameters Raw
PH 6.95
SS, mg/1 57
VSS, mg/1 19
TS, mg/1 180
TVS, mg/1 * 147
BODJ mg/1 ' : 26
TOC, -mg/1 22
SOC, mg/1 " 14
Total P, mg/1 as P 1.19
(gal.)
(gpm/sq ft)
Effluent Effluent
5.85 6.30
68 48
17 20
226 200
187 187
23 1 0
19 11
"'- 12 7
vi'isi ?Jo.2i
4
August 26, 1974
63 '
496 (131,040)
23.9
7911 (2090)
1892 (500)
9803 (2590)
109 (2.68)
135 (3.32)
57
43
0.43
Pe rcen t Remova 1
Screen Flotation Total
(19.2) 29.4 15.7
10.5 (17.6) (5.2)
(25.5) 11.5 (11. i)
(27.2) 0.0 (27.2)
11.5 56.5 61.5
13.6 42.1 50.0
14.2 41.6 50.0
(35.2) 86\9 82.3 '
Note: Numbers in parentheses represent an increase in concentration.
256
-------
Table E-35. OPERATIONAL RESULTS FOR HAWLEY
ROAD TREATMENT FACILITY
Run No.
Date
Duration of Run, min.
Total Volume Treated, cu m (gal.)
Recycle Rate, %
Flow Rates, 1/min (gpm)
Raw
Recycle
Total
Overflow Rate, 1/min/sq m (gpm/sq ft)
Raw
Total
Chemical Dosages, mg/1
Alum
Carbon
Betz 1160
Quality Parameters
PH
SS, mg/1
VSS, mg/1
TS, mg/1
TVS, mg/1
BOD, mg/1
TOC, mg/l
SOC, mg/1
Total P, mg/1 as P
Screened
Raw Effluent
7.1
254
130
822
340
90
84
37
1.92
7.1
320
170
759
312
92
86
48
1.91
Final
Effluent
7.1
70
34
664
271
18
41
25
0.53
5 ;
September 12, 1974
105
763 (201,600)
26.1
7244 (1914)
1892 (500)
9136 (2414)
100 (2.45)
126 (3.09)
.45
42
0.54
Percent Removal
Screen Flotation
(26.0)
(30.8)
7-7 -
8.2
(2.2)
(2.4)
(29.7)
0.5
78.1
80.0
12.5
13.1
80.4
52.3
47.9
72.2
Total
72.4
73.8
19.2
20.3
80.0
51.2
32.4
72.4
Note: Numbers in parentheses represent an increase in concentration.
257
-------
Table E-36. OPERATIONAL RESULTS FOR HAWLEY
ROAD TREATMENT FACILITY
Run No.
Date
Duration of Run, mfn.
Total Volume Treated, cu m
Recycle Rate, %
Flow Rates, 1/min. (gpm)
Raw
Recycle
Total
Overflow Rate, 1/min/sq m
Raw
Tota 1
Chemical Dosages, mg/1
Alum
Carbon
Betz 1160
Quality Parameters Raw
PH 6.7
SS, mg/1 168
VSS, mg/1 48
TS, mg/1 373
TVS, mg/1 259
BOD, mg/1 62
TOC, mg/1 56
SOC, mg/1 36
Total P, mg/1 as P 1.7
6
September 28, 1974
(gal.)
(gpm/sq ft)
Screened
Effluent
6.4
146
56
282
183
44
54
23
1.1
Final
Effluent
6.95
15
4
169
149
10
15
11
0.2
1249
6609
1892
8501
91
117
147
(330,088)
28.6
(1746)
(500)
(2246)
(2.23)
(2.87)
45.8
45.8
0.95
Percent Removal
Screen
13.1
(16.7)
24.4
29.3
. 29.0
3.6
36.1
35.3
Flotation Total
89.7 91
92.8 91
40.1 54
18.6 42
77.3 83
72.2 73
52.2 69
81.8 88
.1
.7
.7
.5
.9
.2
.4
.2
Note: Numbers in parentheses represent an increase in "concentration.
258
-------
Table E-37. OPERATIONAL RESULTS FOR HAWLEY
ROAD TREATMENT FACILITY
Run No.
Date
Duration
Total Volume Treated, cu m (gal.)
Recycle Rate, %
Flow Rates, 1/min (gpm)
Raw
Recycle
Total
Overflow Rate, 1/min/sq m (gpm/sq ft)
Raw
Total
October 6, 1974
100
900 (236,400)
26.8
7055 (1864)
1892 (500)
8947 (2364)
97 (2.39)
123 (3.03)
Chemical Dosages, mg/1
Alum
Carbon
Betz 1160
Quality Parameters
pH
SS, mg/1
VSS, mg/1
TS, mg/1
TVS, mg/1
BOD, mg/1
TOC, mg/1
SOC, mg/1
Total P, mg/1 as P
Raw
6.8
42
19
114
32
'15
18
; 1 3
.6.44
Screened
Effluent
6.4
49
25
117
17
15
20
10
0.25
Final
Effluent
6.2
29
15
93
47
' 14
!3
1 0
0.25
13 (pump malfunctioned)
0
1.1
Percent Removal
Screen
(16.7)
(21.6)
(2.6)
' 47.0
0.0
11.1
23.1
(4.5)
Flotation
40.8
40.0
20.5
(176.0)
6.7
35.0
0.0
%5:.6":
Total
31 .6
21.0
18.4
(46.9)
6-7
27.8
23.1
43". 2
Note: Numbers in parentheses represent an increase in concentration.
259
-------
Table E-38. OPERATIONAL RESULTS FOR HAWLEY
ROAD TREATMENT FACILITY
Run No.
Date
Duration of Run, min.
Total Volume Treated, cu m
Recycle Rate, %
Flow Rates, l/mln (gpm)
Raw
Recycle
Total
Overflow Rate, l/mln/sq
Raw
Total
Chemical Dosages, mg/1
Alum
Carbon
Betz 1160
Quality Parameters
PH
SS, mg/1
VSS, mg/1
TS, mg/1
TVS, mg/1
BOD, mg/1
TOC, mg/1
SOC, mg/1
Total P, mg/1 as P 0
m
Raw
6.7
74
42
152
84
37
33
17
.35
(gal.)
(gpm/sq ft)
Screened
Effluent
6.6
91
50
156
86
33
40
17
0.92
8
October 13, 1974
135
1002 (264,600)
35.6
Final
Effluent
6.7
59
33
131
66
20
28
13
0.54
7434
2650
10084
102
139
0
(1964)
(700)
(2664)
(2.51)
(3.41)
33
43
.74
Percent Removal
Screen
(22.4)
(19.0)
(2.6)
(2.3)
(2.7)
(21.2)
0.0
(8.2)
Flotation
35.1
34.0
16.0
23.2
47.3
45.0
23-5
- ,41.3
Tota 1
20.2
21.4,
13.3;
21.4
45.9.
33.0
23-5
36,4
Note: Numbers in parentheses represent an increase in concentration.-
260
-------
Table E-39- OPERATIONAL RESULTS FOR HAWLEY
ROAD TREATMENT FACILITY
Run No.
Date
Duration of Run, min.
Total Volume Treated, cu m (gal.)
Recycle Rate, %
Flow Rates, 1/mfn (gpm)
Raw
Recycle
Total
Overflow Rate, 1/min/sq m (gpm/sq ft)
Raw
Total
9
October 29, 1974
100
857 (226,480)
21.4
7059 (1865)
1514 (400)
8573 (2265)
97 (2.39)
118 (2.90)
Chemical Dor ,s, mg/1
Alum
Carbon
Betz 1160
Quality Parameters
PH
SS, mg/1
VSS, mg/1
TS, mg/1
TVS, mg/1
BOD, mg/1
TOC, mg/1
SOC, mg/1
Total P, mg/1 as P
Raw
6.8
523
303
885
503
318
213
53
4.04
Screened
Effluent
6.8
170
100
456
274
135
96
44
2.18
Final
Effluent
6.7
170
106
402
282
118
114
39
1.66
18.5 (pump malfunctioned)
25.6
1.23
Percent Removal
Screen
67.5
66.9
48.4
45.5
57.5
54.9
16.9
46.0
Flotation
0.0
(6.0)
11.8
(2,9)
12.6
(20.8)
11.3
23.8
Total
67.5
65.0
54.5
43.9
62.8
46.4
26.4
58.9
Note: Numbers in parentheses represent an increase in concentration.
261
-------
.Table E40. OPERATIONAL RESULTS FOR HAWLEY
ROAD TREATMENT FACILITY
Run No.
Date
Duration of Run, min.
Total Volume Treated, cu m
Recycle Rate, %
Flow Rates, 1/min (gpm)
Raw
Recycle
Total
Overflow Rate, 1/min/sq
Raw
Total
Chemical Dosages, mg/1
Alum
Carbon
Betz 1160
Qua 1 1 ty Pa rameters
pH
SS, mg/1
VSS, mg/1
TS, mg/1
TVS, mg/1 : I-
BOD, mg/1
TOC, mg/1
soc, mg/i :;
Total P, mg/1 as P-.;: 1
;.; ':;; ; "
m
(gal.)
(gpm/sq ft)
10
October 29, 1974
104
106 (281,320)
22.7
8346 (2205)
1892 (500)
10238 (2705)
115 (2.82)
141 (3.46)
21.7 (pump malfunctioned);
46.8
0.11 (pump malfunctioned)
Raw
6.7
140
95
296
192
74
69
.34
,.27
Screened
Effluent
6.8
102
58
260 ,
;; 180
57
54
; :; 27 :>
' ''i jiviijS ;:
,.. , . ., : :.: ...
Final
Effluent
7.0
82
68
- 273 ,
173
36
49
21 ;
?.'&$$':
-- ' ._. . -:l
Percent Removal
Screen Flotation Total
''."."-
27.1 19.6
38.9 (17.2)
12.1 ,; (5.0)=
/ ;6,25: '', 3,;9r
23.0 36.0;
21.7 9.2
: 20.5; ;;:; 22.2
; ;- :;7-^| ? 2^6
' - '- ;;>_-:/r i'-,-
41.4
28.4 ;
7.7
9.8
51.3 '
28.9
38,2
34U
!
Note: Numbers in parentheses represent an increase in concentration.
:,) '> o ,
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STATISTICAL PROCEDURES
The following statistical procedures were utilized
Estimate of a Mean Value
x = x ± ts
where: x - estimated mean value
x = mean of n values
t = student "t" value at n-1 degrees of freedom for some
confidence level
s = standard deviation of the data points
n » number of pieces of data
Comparison of Means Test
1. Perform "F" test
2
S2
If: F < F go to step 2
If: F > F go to step 3
Ft = Table "F" value
F = calculated "F" value
si = standard deviation of first set of data
82 = standard deviation of second set of data
2. Comparison of means "t" test when:
2 2
i = 02
E(x2)2 - ((Ex2)2/n)
- 2
277
-------
X1 " X2
Degrees of freedom (DF) = n- + n_ - 2
Read "t" table at t and DF to find confidence level at which a difference
exists.
3. Comparison of means "t" test when
2 J. 2
i 7* 02
Si?
Sx2 =
Complete DF (v) from:
Sx2,))2
where: v. - N. - 1
v, - N2 - 2
X1 * X2
/Sx2 *- Sx!
Read "t" table at t and DF to find confidence level at which a difference
exists
Paired Comparison Test
1. Calculate S.
where S . »/S(dJ - I)2
d - -
and d == x - y
d. =« x - y
n = number of pairs of data
x & y » data pai r
7< & y^ s average of each set of data
278
-------
2. Calculate t;
where t
Compare calculated "t" to table "t" to determine If there is a
significant difference in the two sets of data.
t t ' *;
Confidence Range
The Confidence Range was calculated by:
Range = x ± ts/ /n-1
where x = mean value
t = value from "t" table at desired confidence range
and degrees of freedom
s = standard deviation
n = number of pieces of data.
279
-------
APPENDIX F
ENGLISH UNITS AND CONVERSION TO METRIC UNITS
English Unit
acre
acre - feet
cubic feet
cubic feet
cubic feet/
minute
cubic feet/
second
cubic inches
cubic yards
feet
gal Ion
gallon/minute
gallons per day
per square foot
horsepower
inches
pounds
mi 1 1 ion gal Ions/
day
square feet
square inches
tons (short)
(2,000 Ibs)
tons (long)
(2,240 Ibs)
yard
NOTE: Multiply
factor to
.
Abbreviation
ac
ac ft
cu ft
cu ft
cfm
cfs
cu in
cu yd
ft
gal .
gpm
gpd/sf
hp
in
1b
mgd
sq ft
sq in
ST
LT
yd
the value of the
get the value of
Conversion
Factor By
0.405
1233.5
0.028
28.32
0.028
1.7
16.39
0.7646
0.3048
3.785
0.0631
0.0407
0.7457
2.54
0.454
3,785
0.0929
6.452
0.907
0.016
0.9144
English Unit
Metric Unit
hectares
cubic meters
cubic meters
liters
cubic meters/
minute
cubic meters/
minute
cubic centi-
meters
cubic meters
meters
1 iters
1 iters/second
cubic meters
per day per
square meter
ki lowatts
centimeters
ki log rams
cubic meters/
day
square meters
square centi-
meters
metric tons
(1000 kilo-
grams)
metric tons
(1000 kilo-
grams)
meters
by the indicated
Abbreviation
ha
cu m
cu m
L
cu m/min
cu m/min
cu cm
cu m
m
L
L/sec
3 2
m/m /day
kw
cm
kg
cu m/day
sq m
sq cm
kkg
kkg
m
conversion
the corresponding Metric Unit.
280
M
^^Bi
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
i. REPORT NO.
EPA-600/2-77-069a
3. RECIPIENT'S ACCESSION>NO.
4. TITLE AND SUBTITLE
SCREENING/FLOTATION TREATMENT OF COMBINED SEWER
OVERFLOWS
Volume 1 - Bench Scale and Pilot Plant Investigations
5. REPORT DATE
August 1977 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
7.AUTHOR Guptaj Mahendra K>> Masonj Donald G.5 Clark,
Michael J., Meinholz, Thomas L., Hahsen, Charles A.
and Geinopoloa.,
8. PERFORMING ORGANIZATION REPORT NO
ana ueinopoIPS, Ant-hnny.
I. PERFORMING ORGANIZATION NlAME AND ADDRESS
Environmental Sciences Division
JEnvirex Inc. (A Rexnord Company)
5103 West Beloit Road
Milwaukee. Wisconsin
1O. PROGRAM ELEMENT NO.
1BC611
11. CONTRACT/GRANT NO.
EPA Contract No. 14-12-40
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research LaboratoryCin.,OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Dhin
13. TYPE OF REPORT AND PERIOD COVERED
Final 10/67-3/75
14. SPONSORING AGENCY CODE
EPA/600/14
UPPLEMENTARY NOTES
Project Officer: Anthony N. Tafuri (201) 321-6679, FTS 340-6679.
16. ABSTRACT ' ~~ ~
This report documents bench scale and pilot plant studies conducted to develop and
improve a treatment system for combined sewer overflows. The majority of pollutants
were of a particulate nature, which indicated solids/liquid separation processes
could provide effective treatment.
Screening/flotation and sequential screening treatment processes were investigated
on a 5 mgd demonstration basis. It was concluded that screening/flotation is an
effectxve method of reducing pollution caused by combined sewer overflows and the
overall pollutant removals ranged between 60% - 75%. On the other hand, sequential
screening was not as effective a treatment method as indicated by overall pollutant
removals of about 30%. Moreover, it was concluded that the use of three screens in
series did not show any advantage over a single screen.
Effluent flow pressurization mode of operation and powdered activated carbon were
investigated for improving the performance of screening/flotation treatment, and
the results obtained showed no apparent improvement. Also, investigation of
microscreening (22 micron) for polishing flotation effluent indicated that overall
particulate removal efficiency of an additional 5% to 10% could be achieved
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
*Combined sewers, ^Overflowssewers,
*Waste treatmentsewage treatment,
Sewage, Waste water
Combined sewer overflows,
Screening/flotation
treatment, Sequential
screening treatment,
Physical/chemical treat-
ment, Laboratory studies
13 B
8. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)'
UNCLASSIFIED
21. NO. OF PAGES
295
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
281
* U.S. GOVERNMENT PRINTING OFFICE : 1977 0-241-037/66
-------
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