EPA-60Q/2-77-0533
May 1977 Environmental Protection Technology Series
HANDLING AND DISPOSAL OF
SLUDGES FROM COMBINED SEWER
OVERFLOW TREATMENT
Phase I • Characterization
Mtnite^i EBTh-wmintit
Offks of Rwwrch
IB t
-------
EPA-600/2-77-053a
May 1977
HANDLING AND DISPOSAL OF SLUDGES
FROM COMBINED SEWER OVERFLOW TREATMENT
Phase I - Characterization
by
M. K. Gupta, E. Bellinger, S. Vanderah
C. Hansen and M. Clark
Environmental Sciences Division, Envirex Inc.
Milwaukee, Wisconsin 53201
Contract No. 68-03-02^2
Project Officer
Anthony N. Tafurl
Storm and Combined Sewer Section
Wastewater Research Division
Municipal Environmental Research Laboratory (Cincinnati)
Edison, New Jersey OB817
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
-------
DISCLAIMER
This report has been reviewed fay the Hunlclpa! 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.
II
-------
FOREWORD
The Environmental Protection Agency was created because of Increasing public
and government concern about the dangers of pollution to the health and
welfare of the American people. Noxious afr, foul water, and spoiled land
are tragic testimony to the deterioration of our natural environment. The
complexity of the 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 problem, 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.
This report discusses the results of a characterization and treatment
feasibility test program for the handling and disposal of the residual sludges
from combined sewer overflow treatment systems.
Francis T. Mayo, Director
Municipal Environmental Research
Laboratory
ili
-------
ABSTRACT
This report summarizes the results of a characterization and treatment test
program undertaken to develop optimum means of handling and disposal of
residual sludges from combined sewer overflow (CSO) treatment systems. Desk
top engineering reviews were also conducted to gather, analyze and evaluate
pertinent Information relating to pump/ bleed back of the treatment residuals to
the dry-leather sludge handling/treatment and disposal facilities.
The results Indicate that j: he volumes and characteristics of the residuals
produced from CSO treatment vary widely. For the residuals evaluated In this
study, the volumes ranged from less than ]% to 6$ of the raw volume treated
and contained O.!2| to 111 suspended solids. The volatile content of these
sludges varied between 25% and 63& with biological treatment residuals showing
the highest volatile content and fuel values. The heavy metal and pesticide
concentrations of the various sludges were observed to be significant and are
presented .
It was concluded that the pump/bleedback of CSO treatment residuals may not
be practical for an entire city because of the possibility of hydraulic and/or
solids overloading of the dry-weather treatment facilities and other adverse
effects. However, controlled pump/bleedback on a selective basis may be
feasible. For low solids content residuals (storage, screen backwash, waste
activated sludge, etc.), gravity or flotation thickening were concluded to
be the optimum steps for the removal of the major water portion while centrl-
fugatton and vacuum filtration were concluded to be the optimum dewatering
techniques for the high solids content residuals (settled storage treatment
sludge, flotation scum and other thickened sludges) prior to their ultimate
disposal by Incineration or landfill. As a result of the findings and conclu-
sions of this initial study, the USEPA is now involved In a followup study to:
1. Evaluate on a pilot scale basis the process treatment systems of
thickening followed by centrlfugation or vacuum filtration for
handling and disposing of CSO treatment sludges, as well as
stabilization methods such as anaerobic digestion.
2.
oc geson.
Develop capital and operating costs for the above mentioned
treatment systems.
3. Evaluate alternative methods for ultimate disposal of storm
generated residuals and assess the potential Impacts of such
handling and disposal.
This report covers a period from March, 1973 to February, 1975 and was sub-
mitted In partial fulfillment of Contract No. 68-03-02^2 by the Environmental
Sciences Division of EnvFrex Inc., under the sponsorship of the U.S.
Environmental Protection Agency.
Iv
-------
CONTENTS
Page
Abstract fv
List of Tables vt
List of Figures fx "
Ac know1edgroen t s x II
Sections
1 FINDINGS AND CONCLUSIONS 1
II RECOMMENDATIONS 5
III INTRODUCTION 6
IV SAMPLING, TEST METHODS AND PROCEDURES 9
V CHARACTERIZATION OF CSO SLUDGES \k
VI BENCH-SCALE THICKENING TESTS AND EVALUATIONS 25
VII PUMPBACK/BLEEDBACK CONCEPT AND ITS APPLICABILITY 96
VIII DISCUSSION 125
IX REFERENCES 127
Appendices
A SITE DESCRIPTIONS 131
B ANALYTICAL PROCEDURES
C COST DATA
-------
LIST OF TABLES
Number Page_
1 List of CSO Treatment Projects from which Sludge Samples
were Procured 8
2 Sludge Volumes Produced per Storm Event for Various CSO
Treatment Methods 15
3 Characteristics of CSO Sludges from Physical or Storage/
Settling Type Treatment 18
k Characteristics of CSO Sludges from Physical/Chemical
Type Treatment 19
5 Characteristics of CSO Sludges from Biological Treatment 20
6 Average PCB and Pesticides Concentrations In CSO Sludges 23
7 Average Heavy Metal Concentrations in CSO Sludges 24
8 Centrifuge Testing Results for Milwaukee, VII, Humboldt
Avenue, Storage/Settling Sludge 35
9 .Centrifuge Testing Results for Cambridge, MA, Storage/
SettlIng Sludge 36
10 Summary of Area and Cost Requirements for Storage/
Settling Treatment Residuals Under Optimum
Treatment Conditions 37
11 Centrifuge Testing Results for Racine, Wt, Screening/
Dtssolved-Alr Flotation Sludge *3
12 Vacuum Filtration Testing Results for Racine, Wl»
Screenlng/Dlssolved-Alr Flotation Sludge ^5
13 Centrifuge Testing Results for Milwaukee, Wl, Hawley
Road, Dtssolved-Alr Flotation Sludge 51
\k Vacuum Filtration Testing Results for Milwaukee', Wl,
Hawley Road, Disso)ved-Alr Flotation Sludge 52
15 Centrifuge Testing Results for San Francisco, CA,
DIssoIved-Air Flotation Sludge 5°
16 Vacuum Filtration Testing Results for San Francisco, CA
Dissolved-Air Flotation Sludge 59
17 Summary of Area and Cost Requirements for Physical/
Chemical Sludges Under Optimum Treatment Conditions ^°
VI
-------
LIST OF TABLES (continued)
Number
18 Centrifuge Testing Results for Kenosha, Wl, Contact
Stabilization Sludge 68
19 Vacuum Filtration Testing Results for Kenosha, Wl
Contact Stabilization Sludge 69
20 Centrifuge Testing Results for New Providence, NJ,
Wet-Weather Trickling Filtration Secondary Sludge 79
21 Centrifuge Testing Results for New Providence, NJ,
Wet-Weather Trickling Filtration Secondary Sludge 80
22 Vacuum Filtration Testing Results for New Providence, NJ
Wet-Weather Trickling Filtration Primary Sludge 82
23 Vacuum Filtration Testing Results for New Providence, NJ
Wet-Weather Trickling Filtration Secondary Sludge 83
24 Centrifuge Testing Results for New Providence, NJ, Dry-
Weather Primary Sludge 9'
25 Centrifuge Testing Results for New Providence, NJ, Dry-
Weather Secondary Sludge 92
26 Vacuum Filtration Testing Results for New Providence,NJ,
Dry-Weather Primary Sludge 93
27 Vacuum Filtration Testing Results for New Providence, NJ,
Dry-Weather Secondary Sludge 9*1
28 Summary of Area and Cost Requirements for Wet-Weather
Biological Sludges Under Optimum Treatment Conditions 95
29 Velocities Required to Prevent Solids Deposition 99
30 Toxic Limit for Metals In Raw Sewage Subject to Sludge
Digestion 102
31 Distribution of Metals Through the Activated Sludge
Process (Continuous Dosage) '°3
32 Heavy Metal Concentration in the Sludges Resulting
From Combined Sewer Overflow Treatment 105
33 Summary of Solids Increases at Dry-Weather Treatment
Plants for Pump/Bleedback of CSO Produced Sludges
from 1.25 cm of Runoff 123
B-1 Effect of Exposure of Pesticides to Mercury and Copper 151
C-I Assumptions for Development of Cost Data 171
C-2 Hutnboldt Avenue - Summary of Performance, Cost and
Space Requirements 172
vll
-------
LIST OF TABLES (continued)
Number Page
C-3 Details of Operating Cost Estimates for Humboldt Avenue,
Milwaukee, Wl 173
C-4 Cambridge, MA - Surmary of Performance, Cost and Space
Requirements
C-5 Details of Operating Cost Estimates for Cambridge, MA 175
C-6 Racine, Wl - Summary of Performance, Cost and Space
Requirements 176
C-7 Details of Operating Cost Estimates for Racine, Wl 177
C-8 Hawley Road, Milwaukee, Wl - Summary of Performance,
Cost and Space Requirements 173
C-9 Details of Operating Cost Estimates for Hawley Road,
Milwaukee, Wl 179
C-10 San Francisco, CA - Summary of Performance, Cost and
Space Requirements 180
C~ll Details of Operating Cost Estimates for San Francisco, CA 181
C-12 Kenosha, Wi - Summary of Performance, Cost and Space
Requirements 182
C-13 Details of Operating Cost Estimates for Kenosha, Wl 183
t-\k New Providence, NJ - Summary of Performance, Cost and
Space Requirements )8*t
C-15 Details of Operating Cost Estimates for New Providence, RI 185
C-16 New Providence, NJ - Summary of Performance, Cost and
Space Requirements 186
C-17 Details of Operating Cost Estimates for New Providence, RI 187
VIII
-------
LIST OF FIGURES
Ijumber
1 Humboldt Avenue, Milwaukee, Wl - Bench scale
dewatering tests 26
2 Cambridge, MA - Bench scale dewatering tests 27
3 Flux concentration curve for Milwaukee {Humboldt
Avenue) (storage/settling) sludge 29
k Flux concentration curve for Cambridge (storage/
settling) sludge 30
5 Flotation thickening results for Milwaukee (Humboldt
Ave.) Wl, storage/settling sludge - without chemicals 31
6 Flotation thickening results for Milwaukee, Wl,
(Humboldt Ave.} storage/settling sludge - with
chemicals (230% recycle rate) 32
7 Flotation thickening results for Cambridge, MA,
storage/settling sludge - without chemicals 33
8 Flotation thickening results for Cambridge, MA,
storage/settling sludge - with chemicals 34
3 Racine, Wl - Bench scale dewatering tests 39
10 Flux concentration curve for Racine, Wl, screening/
dlssolved-a!r flotation sludge - without chemicals 40
11 Flotation thickening results for Racine, Wl, screening/
dissolved-air flotation sludge 41
12 Flotation thickening results for Racine, Wl, screening/
dissolved-alr flotation sludge after pre-gravlty
thickening to 6.9$ solids 42
13 Milwaukee, Wl, (Hawley Road) - Bench scale dewatering
tests 46
14 Flux concentration curve for Milwaukee, Wl, (Hawley
Road) - dlssolved-atr flotation sludge, without chemicals 47
Ix
-------
LIST OF FIGURES (continued)
Number
1i> Flux concentration curve for Milwaukee, Wl, (Hawley
Road) - Dlssolved-alr flotation sludge with chemicals *»8
16 Flotation thickening results for Milwaukee, Wl,
(Hawley Road) - DIssolved-atr flotation sludge (all
tests at 3901 recycle rate for thickening) 50
17 San Francisco, CA, Bench scale dewaterlng tests S3
18 Flux concentration curve for San Francisco, CA, -
Dlssolved-alr flotation sludge (with chemicals) Sk
19 Flotation thickening results for San Francisco, CA, -
Dlssolved-alr flotation sludge - without chemicals 55
20 Flotation thickening results for San Francisco, CA, -
Dlssolved-alr flotation sludge - with chemicals
(all tests at 370? recycle rate for thickening) 56
21 Kenosha, Wl, - Bench scale dewaterlng tests 62
22 Flux concentration curve for Kenosha, Wl, - Contact
stabilization sludge * without chemicals 63
23 Flux concentration curve for Kenosha, Wl - Contact stab-
ilization sludge - with DOW C-31 polymer, H-12 kg/m ton 6k
2k Flotation thickening test results for Kenosha, Wl, -
Contact stabilization sludge - without chemicals &5
25 Flotation thickening test results for Kenosha, Wl, -
Contact stabilization sludge - with Atlasep 3A3
polymer at 1901 recycle rate 66
26 New Providence, NJ, - Bench scale dewaterlng tests
(wet-weather) 71
27 Flux concentration curve for New Providence, NJ, -
Wet-weather trickling filtration primary sludge -
without chemicals 72
28 Flux concentration curve for New Providence, NJ,
Wet-weather trickling filtration primary sludge with
chemicals (333 kg/m ton of lime and 5.0 kg/m ton of
magnlfloc 837A polymer) 73
29 Flux concentration curve for New Providence, NJ, wet-
weather secondary sludge (without chemicals)' Jk
-------
LIST OF FIGURES (continued)
Number Page
30 Flux concentration curve for New Providence, NJ, wet-
weather secondary sludge (with 105 kg/m ton ferric
chloride and 2 kg/m ton magnlfloc 905N polymer) 75
31 Flotation thickening test results for New Providence,
NJ, wet-weather primary sludge 76
32 Flotation thickening test results for New Providence,
NJ, wet-weather secondary sludge (without chemicals) 77
33 Flotation thickening results for New Providence, NJ,
wet-weather secondary sludge (with chemicals) 78
3*» New Providence, NJ, - Bench scale dewatering tests
(dry-weather) 34
35 Flux concentration curve for New Providence, NJ, -
Dry-weather primary sludge 35
36 Flux concentration curve for New Providence, NJ, Dry-
weather secondary sludge gg
37 Flotation thickening test results for New Providence,
NJ, Dry-weather primary sludge 87
38 Flotation thickening test results for New Providence,
NJ, Dry-weather secondary sludge (without chemicals) 88
39 Flotation thickening test results for New Providence,
NJ, Dry-weather secondary sludge (with chemicals) 89
40 Graphs depicting the Increase in hydraulic loading
and solids loading during pumpback/bleedback to the
treatment plant 98
41 Response of system to metal dosage 101
42 Comparison of the requirements of on-site treatment of
wet-weather sludges vs. pump/bleedback to the dry-
'. weather treatment plant '^
B-l Centrifugal force vs. RPM for Dynac Model CT-136Q
centrifugalIon 163
B-2 RPM versus speed control setting 164
XI
-------
ACKNOWLEDGEMENTS
This Investigation was carried out by the Environmental Sciences Division of
Envfrex Inc. Many people contributed to the success and timely completion
of this project. Messrs. Richard WulIschleger, Ernest Bellinger and Mahendra
Gupta participated In the bench scale treatment feasibility work. The
laboratory analyses were conducted by various personnel of Envlrex's process
laboratory under the supervision of Richard WulIschleger, The evaluation of
the collected data was conducted by a team of engineering personnel led by
Mahendra Gupta, Project Manager, and Anthony Gelnopolos, Project Director.
Other members of the engineering evaluation team were Steve Vanderah, Ernest
Bellinger, Charles Hansen, and Michael Clark.
The various CSO treatment facilities operators, engineers, supervisors,
contractors, administrators and regional EPA officers were most helpful In
providing the sludge samples, past data and other necessary Information
throughout the conduct of this study. It Is Impossible to mention all those
who have contributed to the success of this project. However, special mention
must be made for the support of the project by the U.S. Environmental
Protection Agency and the wilting assistance and helpful advice of the
Project Officer, Mr^ Anthony Tafurl and Mr. Richard Field, Chief, Storm and
Combined Sewer Section, EPA, Edison, New Jersey.
XI
-------
SECTION I
FINDINGS AND CONCLUSIONS
1. Raw CSO Sludge Characteristics
a. The sludge volumes produced from the treatment of combined sewer over-
flows varied from less than \% to 6| of the raw flow volume treated.
b. The solids concentration of the sludge residuals from CSO treatment
varied widely, ranging from 0.121 to 111 total suspended solids. The
wide range observed Is attributed to the CSO treatment method used
and treatment plant operation,
c. The volatile content of the sludge solids varied between 25% and 63%
for the sludges obtained from the treatment types investigated.
Biological treatment sludges showed the highest volatile sol Ids
fraction (about 604)f whereas that for sludges from physical/chemical
treatment showed only 251 to kQ% volatile fraction.
d. As might be expected, the biological sludges with higher volatile
solids also showed higher fuel values compared to other sludge types.
The average fuel value of biological sludges was 3515 cal/gm
(6331* BTU/lb) compared to an average of 2032 cal/gm (3662 BTU/lb)
for other sludges.
e. Pesticide and PCB concentrations In the residual sludges investigated
were observed to be significant. Generally, the PCB concentrations
were higher than those for pp'DDD, pp'DDT and dleldrln. The
Cottage Farm (Cambridge, MA) storage treatment sludge generally
showed the higher pesticide concentrations In this study. The range
of PCB and pesticide values for the various sites Investigated were:
PCB non-detectable to 6570 pg/kg drf sol Ids
pp'DDD non-detectable to 225 wg/kg dry solids
pp'DDT non-detectable to 170 pg/kg dry solids
Dfeldrfn non-detectable to 192 pg/kg dry solfds
f. Heavy metal (Zn, Pb, Cr, Cu, Hg, and Ni) concentrations In the residual
sludges were also significant, and varied widely for the sludges
Investigated, Cambridge, HA sludge again showed generally higher
heavy metal concentration of the sludges Investigated. The range of
heavy metal concentrations for the various sites Investigated were:
-------
Zinc 697-715^ mg/kg dry solids
lead l64-2Mi8 mg/kg dry sol Ids
Copper 200-2^5^ mg/kg dry solids
Nickel 83- 995 mg/kg dry solids
Chromium 52-2^71 mg/kg dry solids
Mercury 0.01-100.5 mg/kg dry solids
2. Disposal of CSO Sludges by Pump/bleedback to Dry-Weather Treatment
Facilities
a. From the results of a desk-top analysis it does not appear practical
In the cases studied to pump/bleedback CSO treatment residuals from
an entire city's combined sewers to an existing dry-weather treatment
facility because of the possibility of exceeding the hydraulic and/or
solids handling capacities of such facilities. Addition of sludge
handling facilities or controlled pump/bleedback of CSO treatment
residuals from a ppjrtton, of a city's combined sewer area would be
possible.
In some cases on-slte treatment of wet-weather flow sludges may be
practical, particularly when the dry-weather treatment facilities are
at or near design capacity. However> before any one alternate Is
decided upon, site-specific analysis should be performed.
b. In the cases studied, pump/bleedback of CSO treatment residuals may
produce only marginal hydraul1c overload Ings (10-20% or less) of the
dry-weather treatment capacity when the pump/bleedback is spread over
a period of 24 hours or greater.
However, the solids loadings (assuming complete transport and no
solids settling fn the sewer), may Increase as much as 3^0%, when the
pump/bleedback Is spread over a 2k hour period (for treatment residual
concentrations greater than }% solids). The Impact of such discharge
will be proportionately less when the pump/bleedback is spread over
periods greater than 2k hours.
Tolerable solids loadings may result from the pump/bleedback of such
low solids CSO treatment residuals as centrates, supernatants, and
filtrates from auxiliary CSO sludge dewatering treatments as gravity
or flotation thickening, centrlfugatlon, and vacuum filtration.
c. Pump/bleedback of the retained contents of storage treatment basins
may produce hydraulic and solids overloadlngs^of 1001 or higher
of the dry-weather treatment facilities when spread over a 2k hour
period.
d. The overload effect of pump/bleedback of CSO treatment residuals may
produce shock toads (hydraulic, solids, toxic heavy metal levels,
PCB and pesticides, low volatile solids, etc.) which may adversely
-------
affect dry-weather treatment operation and performance (primary,
secondary and sludge handling and disposal).
e. Any reduction In the treatment efficiency of the dry-weather
facUftles due to pump/bleed back, although small In terms of concen-
tration, can add significant pollutant load in terms of mass loading
on the receiving water body. Furthermore, even assuming no reduction
In treatment efficiency, at least some fraction of the pumped-back/
bled-back residuals would be discharged to the receiving water as
a carryover in the treated effluent. This Is a disadvantage of the
pump/bleedback concept that must be considered In Its evaluation.
3. Dewaterlng of CSO Treatment Sludges
a. Retained contents of the storage treatment at the end of an overflow
must be concentrated via conventional techniques such as sedimentation,
prior to further thickening of the residuals. The supernatant way then
be either discharged to the receiving waterbody or dry-weather sewage
treatment facilities (if permissible hydraulIcatly).
Centrifugal ton was found to be the optimum dewatering process for the
on-slte treatment of Milwaukee, WI and Cambridge, MA (storage treat-
ment) sludges, based on performance, area and cost considerations.
b. A combination of gravity thickening and centrlfugation provided
optimum treatment for most CSO sludges evaluated during this study.
This combination was most effective for less concentrated combined
screen backwash and flotation scum residuals such as for Racine,
Wi. For more concentrated residuals, such as for flotation scums
at Hilwaukeeand San Francisco, direct centrlfugatlon and vacuum
filtration were effective.
c. Basket type centrifuges were Indicated to be better suited for
dlssolved-alr flotation sludges (Racine and San Francisco) and
biological treatment residuals (Kenosha and New Providence) because
of poor scrollabllity of these sludges.
d. Vacuum filtration in combination with gravity or flotation thickening
provided optimum dewatering performance for alum treated dissolved-
air flotation (San Francisco) sludge and the biological sludges.
However, based on area and cost requirements, the results of gravity
or flotation thickening plus centrifugation were comparable to vacuum
filtration.
e. No significant differences in dewatering characteristics were apparent
for the wet and dry-weather sludge samples obtained from the primary
and secondary clarlflers at New Providence, NJ, although the raw
sludge residuals were significantly different inherently.
-------
Considerations for Ultimate Disposal by Incineration
a. As previously statedr the fuel values obtained for the CSO treatment
sludges investigated varied significantly with biological sludges
having the highest values.
b. The calculated heat requirements for the Incineration of the dewatered
CSO sludges showed that a significant amount of auxiliary heat
would be required to sustain combustion.
-------
SECTION II
RECOMMENDATIONS
1. The treatment processes of thickening followed by centrlfugatlon should
be further utilized on a full scale basis to demonstrate the effectiveness
of this treatment combination for the handling and disposal of CSO sludges.
2. Develop basic design criteria and operating characteristics of the
thlckenlng-centrlfugatlon dewaterlng system In a form that can be trans--
lated into actual practice with minimum delay.
3. Develop capital and operating costs for the demonstrated treatment system.
4. Evaluate, on a nationwide basis, the extent of the wet-weather flow sludge
problem with respect to quantities generated, characteristics and facility
and cost requirements for handling and disposal of the CSO sludges.
5. Evaluate the "shock load" effect of CSO treatment residuals on dry-
weather treatment plant operation and performance.
6. Evaluate alternative methods for ultimate disposal of raw CSO sludges
and treated CSO sludges.
7. Investigate the feasibility of land treatment/disposal of raw CSO,
-------
SECTION Ml
INTRODUCTION
The pollutlonal contribution of combined sewer overflows Is of national
Importance. The magnitude of the problem fs Illustrated by the fact that more
than 1,300 United States communities serving 25.8 million people have combined
sewer systems (I). Sufficient Information has been accumulated to confirm that
the combined sewer overflow problem Is of major Importance and Is growing
worse with Increasing urbanization, economic expansion, and water demands (2).
Various methods for dealing with combined sewer overflows have been proposed.
These methods pertain to the segregation of sewers, enlargement of Interceptors
and storage and treatment of combined sewer overflows. Among the various
treatment methods are the physical, physical-chemical and biological treatment
systems. Many of these concepts have been demonstrated or are planned for
demonstration by the USEPA O^.S). As with most wastewater treatment
processes, treatment of combined sewer overflows by the above processes results
(n residuals, which contain. In the concentrated form, objectionable contami-
nants present In the raw combined sewer overflows.
Sludge handling and disposal of the residual sludges from combined sewer
overflow treatment has been generally neglected, thus far, In favor of the
problems associated with the treatment of the combined sewer overflow Itself.
Optimum handling and disposal of these residuals must be considered an Integral
part of CSO treatment because It significantly affects the efficiency and cost
of the total waste treatment system. Surprisingly, there Is little information
available In the literature concerning the characteristics, methods of disposal
and economics of the sludge and Its dispensation* EPA has recognized the need
for defining the problems and establishing treatment procedures for handling
and disposing of residual sludges from combined sewer overflow treatment.
During 1973, USEPA awarded a contract (No. 68-03-0242) to Envlrex Inc. to
Investigate Phase I (Characterization) of a two phase program whose total
project objectives for both Phase I and Phase II are:
I. Characterize the residual sludges arising from the treatment
(physical, physical-chemical, and biological) of combined sewer
overflows (Phase I).
2, Develop and demonstrate a process treatment system for handling and
disposing of the sludges arising from treatment of combined sewer
overflows (Phase II).
3, Develop capital and operating costs for the treatment systems
developed and demonstrated (Phase II).
-------
This report Incorporates the results of the characterization and feasibility
investigations undertaken In Phase I of the above mentioned project.
The first and most difficult step In the ultimate disposal of sludge is the
removal of the water normally associated with the sludges. In general, the
less water associated with the sludge solids, the less costly the subsequent
steps of ultimate disposal. The various steps leading to the ultimate
disposal of the sludges arising from conventional dry-weather treatment are:
I) thickening by sedimentation or flotation, 2) digestion of thickened sludges,
3) dewaterlng by centrlfugatlon or vacuum f11tratlon and k) ultimate disposal
by incineration and/or landfill. Digestion of the sludge residuals Is
generally practiced after step one and the digested sludge may or may not be
dewatered prior to ultimate disposal. Although information regarding the
handling and disposal of sludges arising from combined sewer overflow
treatment Is lacking, It Is Indicated that the procedures used for handling
conventional waste treatment sludges should be applicable. Therefore, the
unit treatment processes of gravity thickening, flotation thickening, centri-,
fugatlon, vacuum filtration and incineration were evaluated for the handling
and disposal of CSO treatment residuals.
The specific objectives of this project were met through the performance of
the following work tasks;
1. Desk top reviews evaluating a non-conventional method for handling
combined sewer overflow residues by pumping back or bleeding back
the residual sludges or stored overflows to the deriving sewerage
system.
2, Field surveys conducted at selected EPA combined sewer overflow
treatment sites to acquire and evaluate differences In sludge
characteristics attributable to treatment process differences. In
addition, bench scale Investigations were conducted on residual
sludges using conventional methods for handling combined sewer
overflow residues,
3. Derivation, development, evaluation, and comparison of alternative
process flow sheets for the handling and disposal of the sludges
arising from the treatment of combined sewer overflows.
Several EPA demonstration projects were contacted for the procurement of the
residual samples. Suitable samples were obtained from eight treatment sites
In seven cities across the nation. A listing of the sites from which the
samples were procured is shown In Table 1. Detailed descriptions of the dry
and wet weather treatment facilities listed In Table 1 are presented In
Appendix A. The ensuing sections of this report delineate the sampling
procedures, test methods, treatabllity test results, desk top reviews,
engineering evaluations and proposed recommendations.
-------
Table 1, LIST OF CSO TREATMENT PROJECTS
FROM WHICH SLUDGE SAMPLES WERE PROCURED
LocatIon
CD
I. Hmbotdt Ave.
Milwaukee, Wl
2. Cottage Farm
Cambridge, MA
3. Philadelphia, PA
4. Racine, Wl
5. Hawley Road
Milwaukee, Wl
6. Baker Street
San Francisco, CA
7. Kenosha, WI
8. Hew Providence,
NJa
Ma t ur e_ of _ proce s s
Physical treatment
Physical treatment
Physical treatment
Physical/chemical
treatment
Physical/chemical
treatment
Physical/chemical
treatment
Biological treatment
Type of treatment
Storage/settlIng
Storage/settl Ing
Microscreen Ing
Screen!ng/dIssolved-
atr flotation
Screenfng/dIssoived-
alr flotation
SampJ I n_g_jy 1 n t
Storage tank
Storage tank
Screen backwash
Combined screen backwash
S flotation scum
Flotation scum
D!sso!ved-atr flotation Flotation scum
Contact stabilization
activated sludge
Biological treatment Trickling filtration
StabH Ization tank
Primary clarlfler;
secondary clarlfJer
a. Both wet-weather and dry-weather treatment sludge samples were procured.
-------
SECTION IV
SAMPLING, TEST METHODS AND PROCEDURES
SAMPLE COLLECTION
As mentioned previously, sludge samples were collected from eight treatment
sites In seven U.S. cities. All samples were collected manually. Only one
sample was obtained from each site for characterization and testing. Each of
these samples was composited manually from several grab samples collected
during the operation of the treatment facility. Most of the feasibility tests
were conducted on site except for two sites where samples had to be air
freighted to Milwaukee because of scheduling difficulties. These arrangements
generally necessitated a sludge aging period of k to 36 hours after which
the feasibility tests could be started. Laboratory analyses requiring
Immediate attention, such as BODg and coliforms, were undertaken Immediately
while samples were refrigerated for other less critical analyses. Separate
special samples were also preserved immediately In glass bottles having
teflon lined stoppers for pesticides and PCB analyses.
Every effort was made to utilize uniform sampling and testing procedures for
various sludge samples; yet certain special handling procedures had to be
adopted for Individual sludge samples because of their Inherent differences.
The following details the Individual sample collections for the various sites
visited.
I. Humboldt Avenue, HiIwaukee, Wt - This detentlon-chlorlnatlon
treatmentrac11Ity produces the entire contents of the storage basin as
the treatment residuals. During overflow periods, the tank contents
are mixed with only one of the seven rotary mixers to dispense chlorine
and to enable the detention tank to act as a settling basin. After the
overflow has subsided, all mixers are activated to resuspend settled
solids and the pumpback of the tank contents to the sewer commences.
Thus, large volumes of relatively dilute residuals are produced that
must be disposed of In a satisfactory manner. A 0.9 cu m (ZkQ gal.)
sample of the resuspended contents of the storage tank was collected for
the storm event of March 3, 1971*.
it was observed that the collected waste settled very poorly and the
supernatant was very turbid. This may have been due to the fact that the
tank contents were mixed overnight and any floe present was sheared. The
suspended solids concentration of this sample was only 181 mg/1 and
further concentration of the solids present via sedimentation was deemed
necessary prior to undertaking any thickening tests. To facilitate
-------
faster settling the waste was treated with 25 mg/1 of ferric chloride
and flocculated for two minutes, The waste was then allowed to settle for
one hour before the supernatant was removed. Approximately two gallons
of settled sludge was collected from the original sample. This chemically
clarified and settled sludge was utilized In the bench testing and
laboratory analyses.
2j, Cjgttage Farm , Cambridge , MA - This detention-ehlorlnation facility
produces" 1 aVge" volumes of reta i ned residuals which are normally returned
to the dry-weather treatment facility. No mixing provisions are available
In the detention tank. This necessitates manual hosing down of the residual
solids from the bottom of the tank after the supernatant has been pumped
out. Two separate samples of this residual sludge were collected on February
20 and Harch 21, 197*t.
3» PJlUjjelj^Ma^ PA_ " This pilot scale demonstration facility utilizes
mTc^scTeeTmTg™ Treatmen t of combined sewer overflows. No suitable sludge
sample could be collected during the contract period. However, a backwash
waste sample was obtained manually by flushing Callowhlll Street between
Edgemore and 6th Streets with fire hydrant water on two occasions
(January 30 and 31 » 197^}, Also, a small backwash sample from an earlier
overflow (January 27, 1 97^) was collected. Comparison of the manually
flushed and actual storm samples Indicated that there were significant
differences In their characteristics. Therefore, It was felt that any
results derived from the thickening testing of the collected sample would
not truly represent the sludges from mlcroscreenlng treatment of CSO.
Hence any results obtained from bench tests at this site were omitted
from this report.
k, Racine, W I - The sludge at this site is generated by a screening/
dTssolved-atF flotation system. Because of the nature of this system,
two sludges are generated. The first of these Is the backwash from the
screening process. The second sludge Is the scum produced from the dlssolved-
alr flotation process. At this site residual solids from both sources are
piped to a common tank and eventually returned to the sewer when sufficiently
low flows are experienced. Since Jt was not physically possible to obtain
separate representative samples of the screen backwash and floated scum at
this site (due to the closed pipes carrying the two residuals), a 0.15 cu m
(40 gal.) sample of the combined residuals was obtained from the holding tank,
Due to the dilute nature of this sample It was deemed necessary to provide
further concentration of the solids present via sedimentation prior to under-
taking any thickening tests. The collected sample showed good amenability
to settling and the residual solids could be concentrated to approximately
121 of the original volume within 30 minutes of sedimentation. However,
this reduced volume of recovered sludge was not sufficient to conduct all
bench- thicken ing tests. Therefore, another larger sample was collected from
the holding tank from the next storm event during September 1973. To
facilitate collection of a large concentrated sample, the combined contents
of the holding tank were allowed to settle In the same tank at the treatment
site. A Q.08 cu m (20 gal.) sample of the concentrated sludge having a
solids content of 2.722 was then drawn off for thickening tests.
10
-------
5 . Haw I ey Road , M 1 1 way tee , W 1 - This site also has a screen I ng/dlssolved-
air flotation pilot demonstration system with a treatment capacity of
18,925 cu m/day (5 mgd). During the storm event of July 21, 1973, only
the dlssolved-aJr flotation scum was obtained since the screen backwash
system did not require activation. Several grab samples collected manually
during ttie operation of the treatment facility were manually composited to
one 0.15 cu m (kO gal.) sample for characterization and thickening tests.
6. flaker Street f San Francisco r CA - The dlssolved-alr flotation process
Is used for the treatment of CIO at this site. Flexibility exists to per-
mit recycling of either the treated effluent or raw Influent stream for
air saturation under pressure. The chemical feed systems are provided
for adding alum, polyelectrolyte, caustic and sodium hypochlorlte solutions.
A 0.15 cu m (kQ gal.) grab sample of the floated scum was obtained on
February 12, 197^ for characterization and laboratory thickening tests.
The treatment facility was operated In the effluent recycle mode of
operation using alum, caustic and polyelectrolyte during this storm event. •
7 . .Kgnojs ha j, W I - A biological type treatment system using the contact
stabf'l I zat Ion process (modified conventional activated sludge process)
fs utilized at this site for the treatment of CSO. The system Is designed
to treat 75,700 cu m/day (20 mgd) of combined sewer overflow. The
clarification and solids handling facilities are shared with the dry-
weather treatment plant to obtain optimum use of the equipment. During
dry-weather, waste activated sludge Is discharged through the stabilization
tank to maintain a supply of viable stabilized sludge ready for use at all
times. During an overflow, this stabilized sludge Is mixed with the raw
waste and aerated In the contact tank for a period of 15-30 minutes after
which the solids are settled In a final clarifler and returned to the
stabilization tank. During a storm event, all solids removed from the
raw waste or biologically produced are retained within the system, I.e.
in the contact tank, stabilization tank or clarlfier.
A 0.15 cu m (kQ gal.) sludge sample was obtained from the aerated stabili-
zation tank Immediately after the overflow stopped on August 9, 1973«
This point of sampling represented the most practical sampling point for
obtaining a representative sample of the residual waste solids.
8 . New P rov I d ence, N J - This facility Is designed for the treatment of
domes t 1 c wa s t ewa t er w 1 t h a high amount of stormwater Infiltrate during
wet-weather periods. However, because of the biological nature of the
treatment system (trickling filtration), the biota Is kept alive by
continuous operation during dry-weather periods. Due to the dual use of
this trickling filter facility, two sludge samples were collected, one
during dry-weather and one during wet-weather, Samples of the final
clarifler and primary clarifler sludge were collected during both the dry
and wet-weather periods.
The primary sludge was sampled from the sludge discharge line from the
primary clarifler. About 0,13 cu m (35 gal.) was collected for the dry-
weather sample and about 0.08 cu m (20 gal.) was collected for the wet-
11
-------
weather sample. The final clarifler sample was withdrawn from the end
of the sludge line, where It mtxes with the flow at the head end of the
plant. About 0.13 cu m (35 gal.) was collected during the dry-weather
period for on-slte tests while about 0.08 cu m (20 gal.) was collected
during the wet weather event for characterization and bench tests.
ANALYTICAL PROCEDURES
Analytical procedures were conducted In accordace with Standard Methods
the Examination of Water and Wastewater (6) and EPA's H^yo"dV^pT^Chenfl"ca
Analysis^ of Water and WasJtesT '(7l"T Beta 11 s are presented InAppend"! x 8»
SLUDGE THICKENING BENCH TEST PROCEDURES
The bench tests consisted of gravity thickening, dtssolved-air flotation
thickening, centrifuge dcwaterlng, and vacuum filtration. Appendix B
contains detailed descriptions of the sludge thickening bench scale testing
procedures. A brief description of these tests Is presented below:
K §£ayl t y. T h I c ken Ing - These tests were conducted In one liter graduated
cyTi nd e r is , The c y fl n de r s were filled with sludge to the 1000 ml mark
and allowed to settle for at least one hour. During this time readings
of the position of the Interface were taken and recorded along with the
elapsed time. This test was then repeated using a variety of sludge
concentrations, Fol lowing these tests, various flocculating chemicals
were screened to determine the optimum chemical and dosage for floe
formation. The chemical was then added to the sludge at the predetermined
dosage and another set of sett! Ing tests were conducted to define the
effects of chemical f locculation. The data derived was then analyzed by
a combination of the Coe and Clevenger (8) and Manclnl (9) methods to
define design parameters for a gravity thickener.
2. Dissolved -Air Flotation Thickening - The basic equipment used In these
tests was a graduated^ cylinder /stopwatch, and pressurized flow source.
To conduct the test a predetermined amount of sludge was placed in the
graduated cylinder and pressurized flow was Introduced Into the sludge
until the total volume reached 1000 ml. The position of the Interface
was then recorded along with the time of the reading* This test was con-
ducted with different amounts of sludge so that the optimum recycle rate
could be determined. Once determined, a series of tests were conducted
to determine the optimum chemical dosage. The test yielding the bast
estimated scum concentration and rate of rise was then selected.
3. Centrifuge pewaterlng - Chemically untreated and/or treated sludge
was" centrlfuged" foF"vaFlous times at different "G" (gravitational) forces.
The resultant centrate was decanted off, measured, and analyzed for
suspended solids. The sludge depth was then measured and penetrability
was determined via a glass rod. From the data recorded, cake solids, cake
quantity, and optimum spin time and speed were determined.
12
-------
k. Vacuum Ft ItratIon - Allquots of the sludge with different chemical
dosages were filtered! through a Whatman filter paper held In a Buchner
funnel. The volume of the filtrate and the elapsed time were recorded
as the test progressed. The specific cake resistance was then calculated
to determine the optimum chemical dosage. The filter paper was replaced
with filter cloth, A variety of cloths were screened to determine which
cloth would best discharge the cake. This cloth was then applied to the
filter leaf and placed In approximately two liters of chemically treated
sludge for a specified pickup time. The leaf was rotated out of the
sludge and held upside down for the specified drying time. The filtrate
was then volumetrteal1y measured and both the filtrate and cake were
analyzed for solids. The data was then tabulated to determine the optimum
conditions for vacuum filtration.
13
-------
SECTION V
CHARACTERIZATION OF CSO SLUDCES
The characterization of CSO sludges Is presented according to the following
groupings based on the type of treatment process utilized at the various sites.
A. Physical Treatment and/or Storage/Settling
1. Milwaukee, Wl (storage/settling)
2, Cambridge, MA (storage/settling)
3. Philadelphia, PA (mkroscreenlng)
8, Physical/Chemical Treatment
1. Racine, Wl (screenlng/dlssolved-air flotation)
2, Milwaukee, Wl (screenlng/dlssolved-atr flotation)
3* San Francisco, CA (dissolved-air flotation)
C. Biological Treatment
1. Kenosha, Wl (contact stabilization)
2. New Providence, MJ (trickling filtration)
A discussion of the volumes produced and the sludge characteristics emanating
from these groups Is presented In the following sections. The sludge quantity
and quality data are based on the laboratory analyses of one grab or manual
composite sample from each site. The analyses were performed on the raw
samples prior to the conduct of the sludge treatment feasibility tests.
SLUDGE VOLUMES
The sludge volumes produced per storm event at each site and the estimated
volumes of sludge that would result from the treatment of the entire combined
sewer area for the respective cities are presented In Table 2. The volumes
shown represent average values and were derived from the past data obtained
at these sites. Estimates of the average residual sludge volumes produced
per unit of raw combined sewer overflow treated are also shown In this table
for the various treatment types investigated. Comparative available sludge
volume data for high rate filtration treatment of CSO are also Included
from the Cleveland, OH study (10).
-------
Table 2. SLUDGE VOLUMES PRODUCED PER STORM
EVENT FOR VARIOUS CSO TREATMENT METHODS
Contributing areas, 00 Ac
Site
Humboldt Ave. , Mtlw. Wl
Cambridge, HA
Philadelphia, PA
Racine, Ul
Hawley Road, HI IK. wl
San Francisco, CA
Kenosha, Wl
Hew Providence, HJ
Primary - W (
Secondary - W
Primary - W
Secondary-DW
Cleveland, OH
Type of To
Treatment Site
Storago/setti
HH .2
0.
Sol ids content
of the
residual sludqe
t
0.015 (l.74)c
0.016 <4.4)c
0 70
0.84d
3.65e
2,25
0.83
0.12
2.50
0.38
0.46
,01 to 1.0
a. Based on past data from various sites.
b. There are no contributing storm sewers. The system treats sanitary sewaqe with excessive storm water Infiltrate,
c. Reduced volune of concentrated solids achieved by settling of solids In the holdlno tank. It Is assumed that only settled solids will require further
handling and thickening and the supernatant can be discharged to the receiving water.
d. Floated scun plus screen backwash water.
e. Floated scum only,
f. Sludge production In gallons produced per day,
q. Combined residuals from primary and secondary clarlflers
h. During an average run only 57.5* of CSO from contributing areas Is treated by the wet-weather demonstration system
I. WW m wet-weather; DW - dry^«ather Ac „ 0-W5 ha. qa, . 0.003785 cu m
-------
As seen in Table 2, the volumes of residual sludges produced from the
treatment of CSO vary from 0.2 percent to 6.8 percent of the raw flow treated.
Among the various types of CSO treatment resfduals evaluated during this
study, the storage/settling treatment produced the least amounts of residuals
as a percentage of raw CSO flow treated for further thickening when It Is
assumed that the settled supernatant Is discharged to the receiving water.
Sludge volumes produced by dlssolved-alr flotation treatment alone were less
than II of the raw CSO treated {San Francisco and Hawley Road, Milwaukee),
however, the addition of screen backwash water to the flotation sludges
Increased the residual volume to 4.8$ of the raw CSO flow (Racine), The solids
content of the flotation sludges dropped from approximately 3$ to 0,8% due
to the dilution by screen backwash water. Thus, when screening Is used with
dtssolved-atr flotation, the screen backwash water can account for nearly 801
or more of the sludge volume. Therefore, It Is Indicated that any possible
sludge handling method for the CSO sTudge should Include separation of the
screen backwash water and the floated sludge. Since the backwash ts generally
low In solids, It could possibly be bled back to the sewer and treated with
the raw flow at the dry-weather treatment facilities, If such added hydraulic
and sot ids loadings can be accommodated. Sludge handling would then b$
concerned with less than 201 of the volume that is due to the floated sludge,
which Is about 2-4% solids. This sludge could be thickened by gravity
settling or flotation and then further concentrated by centrlfugatfon or
vacuum filtration before final disposal.
Because comprehensive rainfall monitoring was conducted as part of the Racine
project (II), the sludge production can also be related to the rainfall amounts.
It was found that an average rainfall amount of 0.25 cm (O.tO In.) must fall
In the combined sewer area before overflow will begin* After overflow does
begin, each additional 0.25 cm (0.10 in.) of rainfall will produce an average
overflow of 17,922 cu m (4,735,000 gal.) for the subject area having a
composite average coefficient of runoff (c) value of 0.65. Using 0.048 cu m
(12.7 gal.) of sludge produced per unit volume of CSO treated reveals that
every 0.25 cm (O.I In.) of rainfall after the first 0.25 cm (0.1 In,) will
produce 957 cu m (226,000 gal.) of CSO sludge for the Racine study area.
Among the biological typesof CSO treatment processes Investigated, the contact
stabilization at Kenosha, Wl produced 3-5% of the raw CSO treated through
the system as the residual sludge volume. This percentage was calculated
from the data obtained from the Kenosha stormwater project report (12). The
report showed that during an average run, 13,248 cu m (3.5 miUlon gal.) of
CSO was treated removing 3,977 kg (8,760 Ibs) of suspended solids and produced
another 663 kg (1,460 Ibs) of solids. Using these numbers and an average
solids concentration of 1% (the solids concentration of one grab sample
obtained during this study was 8,300 mg/l), the residual sludge volume was
calculated to be 464 cu m (122,600 gal.) or 3.51 of the raw CSO, Comparatively,
the average sludge volume from the dry-weather plant operation at Kenosha
is indicated to be approximately l«ll of the average raw flow treated through
the plant (13). (This percentage Includes both the primary as well as the
waste activated sludge.) On a mass basis, it is indicated that an average
of 15,193 kg (33,500 Ibs) of solids are produced per day from the primary
and secondary facilities. The average dry-weather flow through the plant
during this period (1974-75) was 83,280 cu m/day (22 mgd). Using these
16
-------
numbers, the amount of residual solids produced from 13,24s cu m (3.5 million
gal.) of dry-weather flow would be 2417 kg (5329 Ibs) of solids. Thus, It
is indicated that the residual solids produced during dry-weather treatment
are approximately 521 of the solids produced during wet-weather treatment at
Kenosha, Wl. The tower production of solids during dry-weather treatment Is
expected because of the weaker solids concentration of the influent waste during
dry-weather flow. Average Influent suspended solids concentration during dry-
weather flow varied between 125 and ISO mg/1 during 1970 to 1975 compared to
a weighted mean average of 332 mg/1 during 1972 for the wet-weather treatment.
The residual sludge volume from the primary and secondary clarlflers was
calculated to be 6,8$ of the raw CSO from the trickling filtration treatment
at New Providence, NJ (H,15). The comparative dry-weather residual sludge
was estimated to be 4,61 of the influent flow and was again found to be less
than the wet-weather sludge production.
in order to compare the sludge volume production from various types of CSO
treatment, some data was made available to this study from another EPA pilot
demonstration project (10) In which high-rate deep-bed filtration was utilized
for the treatment of CSO. It was Indicated that an average of 4.0? of raw
CSO was produced as residual sludge (backwash wastewater) from this type of
treatment. The solids content of this wastewater varied from approximately
10,000 mg/I after 1-2 minutes of backwashing to less than 100 mg/1 after
approximately 5 minutes of backwashing.
SLUDGE CHARACTERISTICS
The characteristics of the CSO sludges obtained from this study are presented
In Tables 3~5« The solids content of the sludge samples varied widely. The
holding tanks produced sludges of 1.7%, 4.41 and 11.0% solids after sedimen-
tation; the screening up to 0.71, dlssolved-air flotation 2.251 (San Francisco)
and 3.651 (Hawley Road, Milwaukee), screening/dissolved-air flotation 0.842
(Racine), and biological treatment 0.12 to 2.51 for trickling filtration
(New Providence) and 0.831 for contact stabilization (Kenosha).
The volatile fraction of the sludge suspended solids varied from 25? to 63?.
Biological treatment sludges showed the highest volatile fraction, about 60?»
while physical and physical/chemical treatment sludges showed only a 25? to
481 volatile fraction.
The BOD, TOC, DOC (dissolved organic carbon), total phosphorus and TKN (total
Kjeldahl nitrogen) concentrations also varied widely. The highest concentra-
tions were found in the sludge sample obtained from Cambridge, MA.
The soluble nitorgen forms, amnonla, nitrites, and nitrates, were low In
concentration for all sites except the New Providence secondary sludge which
was very high In ammonia concentration.
It may be noted that the suspended solids value for Cambridge, MA shown In
Table 3 at 111 solids is significantly higher than the corresponding value
17
-------
Table 3. CHARACTERISTICS OF CSO SLUDGES FROM
PHYSICAL OR STORAGE/SETTLING TYPE TREATMENT
Sites
Parameter
Total SoUds
Suspended Sol ids
Total Volatile Sol ids
Volatile Suspended Solids
BODj
TOC
Dissolved Organic Carbon
Total Phosphorus (as P)
Total Kjeldahl Nitrogen
( as N)
Ammonia (as N)
N02 (as N)
N03 (as H)
Density
PH
Total Coliforms
Fecal Co!I forms
Fuel Value
PCB»s
pp1 ODD
pp' DOT
Dleldrln
Zinc
Lead
Copper
Nickel
Chromium
Mercury
Units Milwaukee3
mg/1 18
mg/1 17
mg/1 9
mg/1 8
mg/1 2
mg/1 1
mg/1
,900
,400
,150
,425
,200
,250
55
mg/1 109.1
mg/1
mg/1
mg/1
mg/l
gm/cm
—
#/100 ml
#/100 ml
cal/gm (BTU/lb)
Mg/kg. dry
pg/kg. dry
pg/kg. dry
yg/kg. dry
mg/kg. dry
mg/kg. dry
mg/kg. dry
mg/kg. dry
mg/kg. dry
mg/kg. dry
56
4.1
0.15
1.7
1.015
6.4
—
—
—
47
ND
ND
20
799
2,063
201
159
243
2.7
Cambridge3 Philadelphia.
126,900
110,000
57,500
4 1, 400
12,000
16,200
949
293.4
28
3.2
0.4
0.5
1.06
5.7
210,000,000
2,800,000
2721 (4903)
6,570
NO
170
58
946
1,261
757
126
260
0.01
8,660
7,000
2,520
1,755
—
1,032
**<••
11.5
46
—
—
—
1.05
7.4
_~
—
1971 (3227)
ND
ND
ND
ND
1,189
2,448
200
289
52
2.1
ND = None detected.
3 = After settling of holding tank contents.
18
-------
Table 4. CHARACTERISTICS OF CSO SLUDGES FROM
PHYSICAL/CHEMICAL TYPE TREATMENT
Sites
Parameter
Total Solids
Suspended Solids
Total Volatile Solids
Volatile Suspended Solids
BOOg
TOC
Dissolved Organic Carbon
Total Phosphorus (as P)
Total Kjeldahl Nitrogen
(as N)
Ammonia (as N)
N02 (as N)
NQ3 (as N)
Density
pH
Total Col i forms
Fecal Conforms
Fuel Value
RGB's
pp1 ODD
pp1 DDT
Dleidrln
Zinc
Lead
Copper
Nickel
Chromium
Mercury
Units Racine Milwaukee3 San Franc isco-£
mg/1
mg/1
mg/l
mg/1
mg/1
mg/1
mg/I
mg/1
mg/1
mg/1
mg/1
mg/1
gm/cm-*
»_
#/100
I/10Q
cal/gra
pg/kg.
pg/kg.
yg/kg.
yg/kg.
mg/kg.
mg/kg.
rag/kg .
mg/kg.
mg/kg.
mg/kg.
ml
ml
!BTU/II
dry
dry
dry
dry
dry
dry
dry
dry
dry
dry
9,769
8,433
3,596
3,340
1,100
260
60
39.2
112
6.3
<0. 1
<0. 1
1.01
6.9
40,000 6
1 ,400
«'•$»>
603
ND
ND
24
1,638
1,023
481
215
215
2.3
42,700
41,900
11,350
10,570
3,200
6,050
340
149
517
12.5
<0.1
1.07
7.2
,400,000
220,000
775
225
TR
9
855
164
248
173
150
2.1
24,000
22,500
9,400
8,850
1,000
1,600
67
166
375
7.5
0.02
0.1
1.014
5.2
6,300,000
17,000
»> '$?<.>
29
96
192
/uB
1,583
36?
<83
1,667
3-9
ND = None Detected TR * Trace (<0.2 pg/1 on wet basis)
a » Floated sludge only
19
-------
Table 5. CHARACTERISTICS OF CSL SLUDGES
FROM BIOLOGICAL TREATMENT
New Providence
Wet- Weather Sludges
Parameter
Total Solids
Suspended Solids
Total Volatile Solids
Volatile Suspended
Solids
BOD 5
TOC
Dissolved Organic Carbon
Total Phosphorus (as P)
Total Kjeldahl Nitrogen
(as N)
Ammonia (as N)
N02 (as N)
N03 (as N)
Density
PH
Total Col 1 forms
Fecal Coliforms
Fuel Value
PCB's
pp1 ODD
pp1 DDT
Dleldrln
Zinc
Lead
Copper
Nickel
Chromium
Mercury
Units Kenosha
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
gni/cm
—
if/lOQ ml
#/100 ml
pg/kg. dry
pg/kg. dry
pg/kg. dry
pg/kg. dry
mg/kg. dry
mg/kg. dry
mg/kg. dry
mg/kg. dry
mg/kg. dry
mi/kg, dry
8,527
8,300
5,003
5,225
1,700
3,400
29
194
492
2k
0.055
0.065
7.9
1,200,000
79,000
>) 3'1lf!
93
TR
88
7,154
528
1,454
528
1,278
2.6
Primary
2,010
1,215
1,120
780
728
700
220
22
65
9
0.02
Secondary
25,500
25,070
15,500
14,770
11,200
13,000
710
436
6
180
0.02
0.11 0.09
1.005 1-013
6.9
44,000,000
3,400,000
,o) 3|io
ND
ND
ND
697
<498
995
995
746
100.5
"""*
1,300,000,000
1,000,000
3.583
--
— —
„-
1,294
353
1,020
784
2,471
-«-
TR « Trace (<0.2 jig/1 on wet basis)
20
-------
Table 5. (continued)
CHARACTERISTICS OF CSO SLUDGES
FROM BIOLOGICAL TREATMENT
New Providence
Parameter
Total Solids
Suspended Solids
Total Volatile Sol Ids
Volatile Suspended Solids
BODg
TOC
Dissolved Organic Carbon
Total Phosphorus (as P)
Total Kjeldahl Nitrogen
(as N)
Ammonia (as N)
N02 (as N)
N03 (as N)
Density
PH
Total Coliforms
Fecal Collforms
Fuel Value
PCB's
pp1 DDD
pp1 DDT
Dieldrin
Zinc
Lead
Copper
Nickel
Chromium
Mercury
Units
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
§m/on3
—
1/100 ml
1/100 ml
eallft!)?ib)
pg/kg. dry
yg/kg. dry
ug/kg. dry
pg/kg. dry
mg/kg. dry
mg/kg. dry
mg/kg. dry
mg/kg. dry
mg/kg. dry
mg/kg. dry
Dry-Weather
Primary
4.168
3,840
3,205
3,200
1,600
—
92
40.7
214
38
<0.01
0.03
1.006
6.7
20,000,000
2,000,000
"•tli22)
ND
1,750
878
3,000
1,288
240
600
480
347
6.2
Sludges
Secondary
4,930
4,620
3,638
3,610
2,950
—
54
92.7
277
25
0.019
0.01
1.005
6.7
8,500,000
1,000,000
-_
—
__
—
1,744
304
953
913
2,049
21.5
21
-------
for the same site in Table 2 at k,k%. These two values represent two
separate grab samples. The first sample showed a solids value of k,k%,
however, enough sample was not available for detailed analysts. Therefore,
a second sample in larger volume was obtained from this site. This sample
was analyzed for various constituents and was found to have the significantly
higher solids concentration, The lower value was used In Table 2 comparisons
because It was judged to be more representative of the residual solids
concentrations based on communfeat Ions wfth the plant personnel (15).
The sludge densities ranged from 1.005 to 1.0 gm/cm^ for the various sludges
analyzed with an average value of J.026 gm/otK. The storage/settling type
sludges had density values of 1.015 gm/cm3 and 1,06 gm/cm^ for Milwaukee and
Cambridge sites. The physical/chemical treatment sludges had densities
ranging between 1.01 to 1.07 gm/cm*.
The pH of the sludge samples collected ranged from 5.2 to 7.9. The low value
of 5.2 was found In San Francisco where alum was being used.
As would be expected with higher volatile solids, the biological sludges also
had the greatest fuel values among the sludges evaluated. The biological
sludges had an average fuel value of 3>515 cal/gm (633^ BTU/lb) while the
other sludges produced an average fuel value of 2,032 cal/gm (3662 BTU/lb),
It can also be noted that the fuel value for the primary and secondary sludges
for dry as well as wet-weather treatment at New Providence, NJ were quite
close, ranging between 3500 to 4500 cal/gm (6307 to 8109 BTU/lb).
As can be seen In Table 5, the various constituents such as suspended solids,
volatile suspended solids, BODj and TOC showed significantly higher concen-
trations in the secondary wet-weather sludge compared to the dry-weather
sludge for New Providence. This Increase In wet-weather solids may be
attributed In some part to the synthesis of dissolved organic matter present
In the sewer Infiltrate resulting In higher solids from the secondary
clarifier. The weaker suspended solids In the primary wet-weather sludge
may be a result of the dilution of the Influent sewage solids by the
Infiltrate.
The results of the PCB and pesticide analyses are summarized In Table 6,
Among the PCB's and pesticides analyzed for the various sludges, the PCB's
were generally of the highest concentrations. The Cambridge sludge showed
the highest concentrations of PCB's and pp'DDT while the Milwaukee (Hawley
Road) sludge had the highest concentration of pp'DDD and the San Francisco
sludge had the highest concentration of diatdrln. The significantly higher
PCB value at Cambridge may have been a result of pollutant buildup in combined
sewers and incomplete flushing of the tank residuals at the end of previous
storm events.
22
-------
Table 6. AVERAGE PCB AND PESTICIDE
CONCENTRATIONS IN CSO SLUDGES
Parameter
PCB
pp'DDD
pp'DDT
Dieldrin
Average
(yg/kg dry)
*»07a
^3
kk
1*3
Range
ND-6570
ND-225
ND-170
MD-1 92
Site o? hlglest
concentration
Cambridge
Milwaukee
Cambridge
San Francisco
3. Represents the average PCB value without Cambridge data. When
Cambridge PCB value Is used, the average PCB value becomes 13^7 wg/kg
dry solids, which Is significantly higher than all other sludge
sample values.
NO » none detected.
The heavy metals concentrations analyzed for various sludges are summarized
in Table 7. Zinc was usually found to be the heavy metal of the highest
concentration with the concentration of lead also being high. The secondary
wet-weather sludge from New Providence and the sludge from Kenosha were
both found to be high in heavy metal concentration. At New Providence,
increased heavy metai loadings may be a result of the leaching of these
metals In the groundwater Infiltrate. Comparing the average heavy metal
values obtained during this study for wet-weather sludges with the 33 dry-
weather plant sludge average (17), It Is seen that the dry-weather values are
significantly higher than the wet-weather values. The higher heavy metal
values In dry-weather sludges may be a result of accumulations of these
pollutants In sludge blankets over a longer period compared to shorter
wet-weather treatment durations.
23
-------
Table 7. AVERAGE HEAVY METAL
CONCENTRATIONS IN CSO SLUDGES
Parameter
Zinc
Lead
Copper
Nickel
Chromium
Mercury
a. Represe
fag/kg dry)
1,700
1,100
636
372
787
2.2
Range
697-7 15*
1 6ft-2M8
200-1*154
83- 995
52-2471
0.01-100.5
Sfte of highest
concentration
Kenosha
Philadelphia
Kenosha
New Providence
New Providence
New Providence
Average 33
dry -weather pi
sludges, mg/kg
4,210
2,750
1,590
680
1,860
10
ant
dry
nts average mercury concentration without New Providence data.
When this data Is used, the average mercury value becomes 14.5 mg/kg
dry sol ids.
b. See Reference I?.
24
-------
SECTION VI
BENCH-SCALE THICKENING TESTS AND EVALUATIONS
The results of the bench-scale dewatering tests on the sludge samples
procured from the various CSO treatment facilities mentioned earlier
are discussed for each site In the three subsections below. Along with
the technical feasibility evaluations, economic analyses of the de-
watering techniques were also developed for each site. A complete listing ,
of the cost data and the assumptions made to develop these data are pre-
sented in Appendix C. Cost data represent the latest available, December,
1974 prices for capital equipment and updated published cost data (18,19)
to December 137^ prices. Since the CSO treatment systems at Philadelphia,
Milwaukee, (Hawley Road), and San Francisco were pilot scale studies and
did not treat the entire overflow from the sewer outfall drainage area,
these sites were scaled up to the entire flow for the respective technical
and economic evaluations that follow.
A. PHYSICAL TREATMENT AND/OR STORAGE/SETTLING
Three samples of the treatment residuals were obtained under this category
of CSO treatment. Two of these samples were procured from storage
treatment sites in Milwaukee, Wl, and Cambridge, HA, The third sample
was the backwash waste from the pilot mlcroscreenlng unit in Philadelphia,
PA. The detained contents (CSO) from storage basins were very dilute
compared to conventional sludges. For disposal, these residuals can
either be pumped or bled back to the dry-weather sewage treatment facilities
or dewatered on-slte. A discussion of the pump/bleedback concept of such
residuals Is presented In Section VI1 of this report. For on-slte treat-
ment, It Is imperative that such residuals be concentrated via conventional-
techniques prior to their thickening treatment. Therefore, for the sludge
treatabllity studies herein, only the clarified sludge residuals were
evaluated. As mentioned earlier, In Section IV, because of the special
handling required for the procurement of these three sludge samples, only
limited amounts of residuals were available for the dewatertng tests.
Accordingly, only gravity, flotation and centrlfugatlon thickening tests
were conducted on these samples.
MI Iwaukee, Wl, and Cambridge, MA
Figures 1 and 2 show the treatment schematics of the bench-scale dewatering
techniques Investigated at Milwaukee and Cambridge, respectively. The
Milwaukee CSO sample was first treated with 25 mg/l ferric chloride and
25
-------
KJ
cso
COMPLETELY
MIXED
HOLDING TANK
CONTENTS
FeCl
25 m
SEDIMENTATION
r
C-ftl POLYMER (DOW CHEMICAL CO.)
3.0 to 5.7 kg/m ton
SOLID!
FLOTATION
THICKENING
SEDIMENTATION
SOLID!
GRAVITY
THICKENING
SEDIMENTATION
1.
SOLID!
CEN1KIFUGATION
C - 41 POLYMER
3.5 kg/n ton
Figure I, Humboldt Avenue, Milwaukee, Wt - bench scale dewaterlng tests
-------
STORAGE
SEDIMENTATION
77/7/777.
11% SLUDGE SOLIDS
STORM I
STORM 2
GRAVITY
THICKENING
ATLASEP I05C POLYMER
0.18 kg/m ton
CENTRJFUGATION
ATLASEP I05C POLYMER
"0.5? kg/m ton
FLOTATION
THICKENING
Figure 2. Cambridge, MA - Bench scale dewaterlng tests
-------
settled In the laboratory prior to the thfckenfng tests as shown In Figure I.
The Cambridge CSO was settled In the detention tank Itself and two
separate samples were used for the thickening tests as shown In Figure 2.
Bench-scale tests consisted of gravity, flotation, and centrlfugatlon
thickening.
The average quantities of sludge requiring dewaterlng treatment for the two
sites were calculated to be approximately 131 cu m (34,700 gal.) and 68 cu m
(18,000 gal.) on a per storm event basis (Table 2). The chemical clarifi-
cation of Milwaukee (Humbotdt Avenue) tank contents produced a residual
with 1.74% solids while the sedimented residue samples obtained from Cam-
bridge showed 4.4% and 111 solids for two separate samples. The flux con-
centration curves (see Appendix B for details of curve construction) for
the gravity thickening tests for Milwaukee and Cambridge samples are shown
In Figures 3 and 4. From these curves, it can be seen that for Milwaukee,
the sludge could be concentrated to 6% solids at an allowable mass loading
rate of approximately 45 kg/sq m/day (9 Ibs/sq ft/day). The corresponding
concentration level achieved for the Cambridge sludge was 141 solids with
the more concentrated raw sample at 160 kg/sq m/day (32 Ibs/sq ft/day)
without any chemicals* The results of the flotation thickening tests for
the two sites are shown in Figures 5 through 8. It was found essential to
use flocculating chemicals (cationic polyelectrolytes such as Atlasep
105C and Dow C-41) to aid flotation. Optimum flotation thickening results
were achieved at recycle rates between 300 and 600% and polyelcctrolyte
dosages between 1 and 3 kg/m ton (2 to 6 Ibs/ton). Scum solids concen-
trations of 11 to 14% for Milwaukee and 6 to 8% for Cambridge sample (with
the 4.4% solids raw sample) at the above mentioned optimum chemical dosages
and recycle rates were achieved. The results of the centrifuge tests for
the two storage tank residuals are presented in Tables 8 and 9. Again
optimum results were achieved with the aid of the catlontc polyelectrolyte,
Dow C-41. Optimum solids recoveries were achieved at gravitational force
between 700 and 1,000 G and spin time between 60 and 120 seconds. Cake
solids between 30 and 35% could easily be achieved for both sludges under
optimum conditions.
A summary of the estimated area and cost requirements of various dewatertng
techniques under optimum treatment conditions for the two storage/settling
type treatment sites is shown in Table 10. The total annual costs shown in
this table include the amortized capital costs, operating costs and the
cost of hauling the ultimate treatment residuals to a landfill area, it Is
also assumed that the dewatered supernatant liquid can be discharged
to the dry-weather treatment facilities. Additional details of the cost
estimates are presented in Appendix C. For comparison, vacuum filtration
treatment costs are also included bas&d on engineering judgment and filter
performance for other sludges evaluated In this study. Examination of
Table 10 shows that centrlfugatlon was the optimum dewaterlng process based
on performance, area and cost requirements for both the storage treatment
sites evaluated In this study.
Philadelphia, PA
As mentioned earlier, the backwash wastewaters produced from the micro-
28
-------
U3
500
(102.5)
5 (82.0)
300
(61.5)
200
o
100
(20.5)
FLUX CONCENTRATION CURVE
.TANGENT TO THE FLUX CONCENTRATION CURVE AT THE SELECTED
SLUDGE CONCENTRATION SHOWS THE ALLOWABLE MASS LOADING
RATE FOR GRAVITY THICKENING
I 2 3 k 5 6
SLUDGE CONCENTRATJON, I
Figure 3. Flux concentration curve for Milwaukee (Humboldt Ave.) (storage/settling) sludge
-------
flj
"O
tr
VI
500
(102.5)
400
(82.0)
£ 300
~ (61.5)
«B
|
cr
Irt
-x,
01
VI
ts>
200
(41.0)
100
(20.5)
FLUX CONCENTRATION CURVE
TANGENT TO THE FLUX CONCENTRATION
CURVE AT THE SELECTED SLUDGE CON-
CENTRATION SHOWS THE ALLOWABLE
MASS LOADING RATE FOR
GRAVITY THICKENING
10
12
Figure k.
2468
SLUDGE CONCENTRATION, %
Flux concentration curve for Cambridge (storage/settling) sludge
14
-------
I"
er
«n
0)
"O
G
or
i9
Z
2
§
I/I
400
(82.0)
350
(71.75)
300
(61.5)
250
(51.25)
200
150
(30.75)
100
(20.5)
50
(10.25)
RECYCLE
RATE 0
751 RECYCLE RATE
10
12
16
ESTIMATED SCUM CONCENTRATION, %
Figure 5. Flotation thickening results for Milwaukee (Humboldt Ave.)
Wl, storage/settling sludge - without chemicals
31
-------
350 -
(71,75)
300
(61.50)
250
(51.25)
m
200
5 (41-0)
a-
in
150
(30.75)
D*
Ifl
100
-------
itOO
(82.0)
350
(71.75)
300
(61.5)
m
T3
-------
400
(82.0)
350
(71.75)
300
(61.50)
>-
10
250
(51.25)
200
(41.0)
01
JO
-g
0-
tfl
O)
„• 150
5 (30.45)
0
<
3
100
(20.25)
50
(10.25)
5001 RECYCLE RATE
ATLASEP 105C POLYMER 1.1 kg/m ton
5401 RECYCLE RATE
ATLASEP IOSC POLYHER 2.3 kg/m ton
5701 RECYCLE RATE
ATUSEP 105C POLYMER
0.6 kg/m ton
5701 RECYCLE RATE WITHOUT
POLYHER
10
ESTIMATED SCUM CONCENTRATION, I
Figure 8. Flotation thickening results for Cambridge, MA
storage/settling sludge - with chemicals
-------
Table 8. CENTRIFUGE TESTING RESULTS FOR
MILWAUKEE, Wl, HUMBOLDT AVENUE, STORAGE/SETTLING SLUDGE
Vn
Test
Ho.
1
2
3
k
5
6
7
6
9
10
It
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
Appl led G
force^ G's
1,000
1,000
1,000
1,000
700
700
700
700
400
400
400
400
1,000
1,000
1,000
1,000
800
800
300
800
£00
600
600
600
400
400
400
400
Time,
sec
120
90
60
30
120
90
60
30
120
90
60
30
120
90
60
30
120
90
60
30
120
90
60
30
120
go
60
30
Feed
solids,
_ma/t_
17,400
17,400
17,400
17,400
17,400
17,400
17,400
17,400
17,400
I7»*00
17,400
I7,4oo
17,400
17,400
17,400
17,400
17,400
17,400
17,400
17,400
17,400
17,400
17,400
17,400
17,400
17,400
17,400
17,400
Chemical
none
none
none
none
rone
none
none
none
none
none
none
none
C-41
C-41
C-41
C-41
C-41
C-41
C-41
C-41
C-41
C-41
C-41
C-4»
C-41
C-41
C-41
C-41
Dosaqe,
Centrate
solids.
kg /a ton mg/l
none
none
none
none
none
none
none
none
none
nan«
none
none
3.4
3.4
3.4
3.4
3.4
3.4
3.4
3.4
3.4
3.4
3.4
3-4
3.4
3.4
3.4
3.4
238
228
288
524
190
230
324
570
326
401
605
3,200
119
119
107
121
84
114
84
89
90
151
155
134
106
120
128
129
Centrate
volume,
ml
67
70
69
68
67
68
69
68
69
69
66
64
71
72
71
70
71
71
74
73
74
71
71
69
63
69
69
68
Sludge
Penetration, depth,
cm cffl
0.75 .45
0.8
0.85
1.1
0.8
0.95
.0
.45
-55
.65
.75
CS
0^4
0 4
0.45
1.6
0.6
0,4
0.45
!.3
.4
.5
.6
.6
.6
.45
.45
.55
.65
.75
.9
.4
35
.6
.6
6
.3
.4
.3
0.5 1.4
0.65 1.5
0.65 1.6
0.9 1.55
0.65 1.6
0.7 1.65
1.6 1.6
1 8 .8
Cake
solids,
%
16.1
25. 8
21.4
18.1
1C. I
18.4
21.4
1B.I
21.4
21 3
14 1
10. 0
32.4
43-2
32 4
25.9
32.5
32 4
13.0
64.9
13-0
32.4
32.3
21.6
21.6
21.6
21 6
18.5
Penetration, Recovery
*
50
42
44
31
30
41
31
0
0
0
0
0
71
70
72
0
63
69
67
0
64
57
60
0
59
57
0
0
*
98.6
98.6
98.3
96-9
98.9
98.6
96 3
96 7
98.1
97-6
96.5
81.6
99-3
99.3
9S-3
99.3
99-5
99.3
99-3
99.4
99.4
99.1
99-1
99-2
39 3
99 3
99.2
99.2
Corrected
, recovery.
*
31.9
90.4
90.5
86 1
S2.2
90.1
ev
0°
°l
°*
0?
oa
95-9
95- »
SS.O
Od
95-0
S5.6
95-5
0s
SS.O
93.6
94.1
o3
94.1
93.6
<£
oa
Indicates full penetration of the test rod through the thickened studqe and hence poor performance under the corresponding test conditions.
See Appendix B for procedure.
-------
Table 9. CENTRIFUGE TESTING RESULTS FOR
CAMBRIDGE, HA, STORAGE/SETTLING SLUDGE
Test
(to.
1
2
3
It
$
6
7
8
3
Itt
11
12
13
Hi
15
16
1
2
3
k
5
6
7
6
9
10
11
12
13
14
15
16
Appl led G
Force., S's
1,000
1,000
1 ,000
1,000
800
too
fioo
600
600
600
600
600
1)00
wo
400
4oo
1,000
1,000
1 ,000
»,000
800
sou
BOO
600
600
ooo
600
600
1)00
WO
400
400
Spin time
_ sec _
120
90
60
30
120
90
60
30
120
90
60
30
120
30
60
30
S20
90
60
30
120
90
60
30
120
90
60
30
120
3D
60
30
feed
, solids, C
-ma/1
110,000
no, ooo
110,000
110,000
110,000
110,000
HO, 000
110,000
110,000
110,000
110.000
110,000
110,000
110,000
110,000
110,000
110,000
110,000
HO, 000
110,000
110,000
U 0,000
110,000
110,000
110,000
110,000
110,000
110,000
110,000
110,000
110,000
HO, 000
henlcal ,
Mlasep
nona
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
1Q5C
I05C
105C
lose
105C
lose
105C
lose
I05C
I05C
lose
105C
lose
lose
lose
)05C
Dosage,
ka/rn ton
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
0.18
0.18
0.18
0.18
0.18
0.18
0.18
0.18
0.18
0 IB
0.18
0.18
0.18
0.18
0.18
0.18
Centrate
solids,
IW» /I
912
987
975
2.183
766
812
1,943
2,733
,249
,616
,433
3,000
,566
,363
,683
3,066
515
585
510
310
500
610
735
845
780
720
735
965
830
670
855
1 ,290
Centnte
vo I uw ,
ml
42
43
43
46
48
47
46
45
43
45
47
46
42
39
40
41
49
50
49
46
47
51
49
43
44
44
46
43
47
43
17
34
Penetrat Ion,
C-1
1.0
1.0
1.15
0.35
0.45
0.35
0.45
0.40
0.6
0 7
0.7
0,75
0.8
0.65
0.95
1.3
0.55
0.4
0,45
0.55
O.J
0.4
0.55
0.55
0.55
0.45
0.5
0.65
0.5
0.55
0.85
1.0
Sludge
dapth,
cm
3.8
3.75
3-6
3.3
3-25
3.5
3. 35
3.45
3.05
3-6
3.55
3.G
3.85
4.2
4.2
4.S
3.2
3.25
3-4
3-55
3.4
3-45
3.35
3-55
3 6
4.05
3.65
3.9
3.8
4.15
4-7
4.5
Cake
solids,
%
24-9
25-6
25.6
2D.I
30.4
29.3
23.1
27-1
25-6
27-2
29.2
28.0
24,8
22.8
23.4
13- 3
31-6
32.9
31.6
28.3
29.4
34.2
31.&
30.4
26.5
26.5
28.3
25.6
29-3
25-7
11.6
20.0
'enetration
%
74
73
68
89
86
90
87
88
85
81
80
79
79
86
76
71
83
88
87
84
9<
88
84
84
85
89
86
S3
87
87
62
78
Recovery ,
J
SI. 7
91.0
91.1
80.2
93.0
92.6
82.3
75 2
88. 6
85.3
87.0
72.7
85.8
87.4
B4.7
72.1
95-3
94.7
92.6
91,7
94.7
94.4
93-3
92.3
32-9
93. 4
93-3
91.2
92.4
93-9
92.2
88.3
Corrected
recovery
(V
D8
88
87
79
91
9)
81
74
86
83
B4
70
aj
85
81
70
93
93
91
89
93
92
91
90
90
91
91
89
90
91
90
C6
-------
Table 10. SUMMARY OF AREA AND COST REQUIREMENTS FOR STORAGE/SETTLING
TREATMENT RESIDUALS UNDER OPTIMUM TREATMENT CONDITIONS
S i te
Gravity
thickening'*
Flotation
thickening"5
Centrlfugationb
Vacuum
filtrationb
Humboldt Avenue
Sludge
solids,
1
6
14
32
30C
Area
sq ft (sq m)
710 (66)
452 (42)
32 (3)
140 (13)
Total
annual
cost,3 $/yr
57,600
39,600
21,300
26,700
Cambridge
Slylge ' Total
solids, Area annual
% sq ft'
\k 1260
7 365
34 32
30C 140
(sq m) cost , $/yr
(117) 37,900
(34) 72,300
(3) 22,700
(13) 31,000 •
Capital costs amortized for 20 year equipment life and 10% Interest rate. For details
of cost estimates, see Appendix C,
All tests conducted after concentration of storage tank contents with sedimentation
c Comparative data based on assumptions of 95% solids recovery and yield of 15 kg/sq m/hr
(3 lbs/sq ft/hr).
All costs based on December, 197^ prices.
-------
screening treatment of CSO are quite dilute In nature and pre-concentration
of these wastes Is necessary prior to any dewatertng. Because of the many
difficulties experienced In collecting a suitable sludge sample from this
site, a synthetic waste sample was produced for bench-scale dewaterlng tests
by flushing the site drainage area with fire hydrant water. It was hoped
that the waste sample produced would be similar to the actual screen back-
wash waste. However, only an extremely limited amount of concentrated
sludge sample could be generated by the hydrant flushing and the data ob-
tained was highly questionable. It was felt that any conclusions derived
from such data would not be meaningful and may be misleading. Therefore,
It was decided to omit the data from the treatment feasibility tests for
this site. However, evaluations were conducted on the pump/bleedback
concept for this wastewater, and are presented In Section VII of this report.
B. PHYSICAL/CHEMICAL TREATMENT
Three samples of residuals were obtained under this category of CSO treatment.
Two of these samples were procured from screenlng/dlssolved-alr flotation
treatment facilities In Milwaukee and Racine, Wl. The third sample was
obtained from the dissolved-alr flotation treatment facility In San Francisco,
CA.
Racine, Wl
Two separate samples of the combined screen backwash and flotation scum
from the sludge holding tank were obtained In Racine. A schematic of the
various dewater ing tests conducted on these samples Is shown In Figure 9-
The average quantity of the residuals (both floated scum and screen back-
wash) requiring handling and/or treatment on a per storm basis for the
Racine facility Is estimated to be 458 cu m (121,000 gal.) at a suspended
solids concentration of 8,430 mg/1 (Table 2), The flux concentration
curve for the gravity thickening tests for Racine sludge Is shown In Figure
10. The sludge settled extremely well with and without chemicals. Using
the Coe and Clevenger (8) and Manclni (9) method of gravity thickening
analysis, underflow concentrations greater than 151 solids could be expected
at extremely high solid loading rates In excess of 2,000 kg/sq m/day
(400 Ibs/sq ft/day).
The results of the flotation thickening tests are shown In Figures 11 and 12.
Addition of 0.2 kg/m ton (0.4 Ibs/ton), of Atlasep IAI polymer helped to
produce better flotation thickening results* Solids concentrations of up
to 8% could be estimated for the thickened scum, However, due to the dilute
nature of the sludge, when a sample was gravity thickened first to about 1%
solids and then flotation thickened, solids concentrations of 15 to 13%
could be achieved. Optimum recycle rates were between 300 and kQQ% and
mass loading rates of 200-250 kg/sq m/day (40-50 Ibs/sq ft/day) could be
successfully utilized,
The results of the centrifuge tests for Racine sludge are presented in Table
11. Several samples were tested for centrlfugatlon at various feed solid
levels shown In the table. Generally, the tests showed amenability of the
38
-------
ATLASEP IAJ POLYMER
0.7 kg/m ton
LIME
VACUUM
FILTRATION
GRAVITY
THICKENING
ATLASEP 1A1
POLYMER
0.9 kg/ra ton
CENTRIFU6ATION
SCREENING
FLOTATION
BACKWASH
r WASTE
HOLDING / SETTLING
CENTRIFUGATIQN
STORM 2
FLOTATION
THICKENING
FLOATED
SCUM
CENTRIFUGATION
A
GRAVITY
THICKENING
CENTRIFUGATION
i
i
r"i f\-t
\f
URAVI IT
THICKENING
FLOTATION
THICKENING
ATLASEP IAI
POLYMER
o.2 kg/ra ton
STORM I
Figure 9. Racine, Wl - Bench scale dewaterlng tests
-------
3000
(6t5.0)
2500
(512.5)
0!
TJ
2000
£ (410.0)
IA
JO
I
g-
M
X.
1500
(307.5)
1000
3 (205.0)
CO
500
002.5)
FLM CONCENTRATION CURVE
TANGENT TO THI FLUX CON-
CENTRATION CURVE AT THE
SELECTED SLUDGE CONCEN-
TRATION SHOWS THE ALLOW-
ABLE MASS LOADING RATE
FOR GRAVITY THICKENING
8 12
SLUDGE CONCENTRATION, %
20
Figure 10. Flux concentration curve for Racine, Wl,
screening/ dtssolved-alr flotation sludge - without chemicals
-------
350
(71.75)
300
•o
ut
250
£(51.25)
200
cr
i/i
"X,
en
o ISO
2(30.75)
o
2 ioo
(20.5)
50
(10.25)
951 RECYCLE
RATE; NO
CHEMICALS
270% RECYCLE RATE
NO CHEMICALS
380* RECYCLE RATE
NO CHEMICALS
370% RECYCLE RATE
0.2 kg/m ton ATLASEP
IAI POLYMER
8
ESTIMATED SCUM CONCENTRATION, %
iO
Figure 11, Flotation thickening results
for Racfnc, Wl, screenfng/dIssolved-afr flotation sludge
-------
400
(82.0)
350
(71.75)
300
(61.5)
m
•a
cr 250
•5(51.25)
-S 200}-
1 (41. (
cr
O)
<3 I5C
1(30.75)
1
IOC
(20.5)
5C-
(10.25)
12
1801 RECYCLE RATE
NO CHEMICALS
a
400*. RECYCLE RATE
NO CHEMICALS
\k 16 18 20
ESTIMATED SCUM CONCENTRATION, I
22
Figure 12. Flotation thickening results for Racine, Wl, screening/dissolved-
atr flotation sludge after pre-gravlty thickening to 6.9% solids
-------
Table 11. CENTRIFUGE TESTING RESULTS FOR
RACINE, VI, SCREENING/DISSQLVED-AIR FLOTATION SLUDGE
Test
fb.
1
2
3
4
5
&
7
&
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
Applied S
force,;'G'_3"
400
400
400
750
750
750
1 ,000
1,000
1,000
400
400
400
750
750
750
1,000
1,000
1,000
400
750
1,000
400
750
1,000
400
750
1,000
400
750
1,000
400
750
1 ,000
400
750
1 ,000
400
750
1,000
400
750
1,000
Spin time,
sec
60
90
120
60
90
120
60
90
120
60
90
120
60
90
120
60
90
120
60
60
60
120
120
120
60
60
Go
60
60
60
120
120
120
120
120
120
60
60
60
120
120
120
Feed
solids,
8,433
8,433
8,433
8,433
8,433
3,433
8,433
8,433
8,433
75,400
75,400
75,400
75,400
75,400
75,400
75,400
75,400
75,400
75,400
75,400
75.400
75,400
75,400
75,400"
27,200
27,200
27,200
27,200
27,200
27,200
27,200
27,200
27,200
27,200
27,200
27,200
32,000
32,200
32,000
32,000
32,000
32,000
Chemical
none
none
none
none
nona
nona
none
none
none
none
none
nona
none
none
none
none
none
none
905-K
905-H
90S-N
90S N
905-N
905-N
none
none
none
1-4-1
1-A-l
1-A-l
none
none
none
1-A-l
1-A-l
-A-l
-A-l
-A-l
-A-l
-A-l
-A-l
-A-l
Dosage,
l J
98 8
99- 1
QQ ]
yy * '
98.6
98.8
92.9
98.9
98 8
99.0
98 4
98.8
99.0
96 k
95-2
99.2
99.2
99-2
77.6
88.3
99-5
9B.8
98 8
99 0
91 -9
gC.S
98.3
99- 1
99.2
99-2
98.9
99.2
39-1
99.0
99-1
99 2
Corrected
recovery,
t
oa
oa
oa
oa
SP
Qa
93
94
95
94
95
96
37
95
57
97
97
98
97
98
98
71
80
87
84
92
95
05
90
90
90
93
96
94
97
97
97
97
97
a. Denotes poor icrollabllfty of the thickened sludge. See Appendix B for procedure.
-------
sludge to centrifugal: I on. Addition of chemical flocculants aided cent r If u-
gatlon but did not provide very significant Improvement In the results.
Sludge samples without prior gravity thickening showed high cake solids
(20-301) but the scrollabl Hty of this sludge was found to be poor, Indicating
that a basket type centrifuge would be required for direct sludge centrlfuga-
tlon as opposed to a scroll type centrifuge. However, when the raw sludge
wasgravity thickened prior to centrlfugatlon, cake sot Ids as high as 30 to
351 could be achieved for a scroll type centrifuge. Optimum solids recover-
ies were achieved at gravitational forces between 600 and 1,000 6 and
spin time between 60 and 120 seconds.
Vacuum filtration test results for Racine sludge are presented In Table 12.
Buchner Funnel tests Indicated that lime at a dosage of 147 kg/nt ton
(294 Ibs/ton) In conjunction with an Ionic polyelectrolyte, Atlasep IAI, at
a dosage of 0.7 kg/m ton (1.4 Ibs/ton) provided optimum results for vacuum
filtration on sedlmented sludge samples with a feed solids concentration
of approximately 3%. Optimum cake solids (20 to 25%) with good cake dis-
charge characteristics were observed with either a 4/1 satin multlfilament
or a 7/1 satin monofilament cloth. Optimum yield rates were between 14 to
18 kg/sq m/hr (2.9 to 3.7 Ibs/sq ft/hr) at a submergence of 37.51. It was
also observed that sludge may be free draining and therefore amenable to
dewatering via gravity draining. In this regard, one liter of sludge
treated with 1.1 kg/m ton (2.2 Ibs/ton) (At was poured on to an open weave
filter cloth (1/1 plain weave, saran, monofilament 30x25 threads per inch).
After gravity drain of several seconds the cloth was wrapped around the
dewatered sludge to form a ball. The sludge ball was then compressed by
hand to further dewater the sludge. The filtrate volume was 910 ml. Cake
solids were 24.61 and filtrate suspended solids were 405 mg/1. No problem
was encountered with discharge from the cloth media. This Indicates that
a gravity drain-compression or filter press type dewatering may be
applicable for such CSO sludges.
Mi Iwaukee, WI (H aw1ey Road}
A sludge sample of the floated scum without any screen backwash water was
obtained from the Hawley Road treatment facility for bench-scale tests. A
schematic of the various bench-scale dewatering tests conducted on'thls
sample Is shown In Figure 13. Hawley Road is only a small demonstration
treatment facility and treats less than 41 of the CSO at Its outfall loca-
tion. Based on published data (20) it Is indicated that the flotation
scum volumes requiring handling and/or treatment would be approximately
0.71 of the raw CSO volume treated and are comparable to the corresponding
residual sludge volumes for Racine and San Francisco flotation scum
volumes as discussed in Section V. The flux concentration curves for the
gravity thickening tests for this sludge are shown In Figures 14 and 15.
The sludge was found to be amenable to gravity thickening and underflow
solids concentrations of 8 to 101 could be achieved. Addition of floccula-
ting chemicals aided in the gravity thickening by providing improved mass
loading rates (from 200 to 300 kg/day/sq m (40 to 60 Ibs/sq ft/day) @10I
solids) as shown In the flux curves. Optimum chemical was found to be a
catlonic polyelectrolyte, Dow C-4lt at a dosage of 4 to 5 kg/m ton (8 to !0
Ibs/ton).
44
-------
Table 12. VACUUM FILTRATION TESTING RESULTS FOR RACINE, Wl,
SCREENING/DISSOLVED-AIR FLOTATION SLUDGE
Feed Solids Concentration - 27,200 mg/l
Chen lea
il dosage, cycle
ka^a ton
IAI
1.1
I.I
1.1
0
0.49
0.49
0.49
0.49
0.49
0.43
0.74
0.74
0.74
0.74
0.74
1.1
CaO
0
0
0
0
0
0
0
110
110
no
147
147
147
147
147
0
time.
nln
4
2
1-3
2
2
2
4
2
1.3
4
3
4
6
3
4
3
Pickup
t I roe,
sec
90
45
30
45
45
45
90
45
30
90
65
90
100
65
90
90
Dry
time,
sec
100
45
30
45
45
Ii5
100
45
30
100
75
100
130
75
100
100
.Submergence,
*
37.5
37.5
37,5
37.5
37,5
37.5
37.5
37.5
37.5
37.5
37.5
37.5
37.5
37.5
37-5
37.5
Yield,
kfl/hr/m
_-
—
7.09
—
8.38
3-55
18.4
26.7
16.8
11.2
14.2
14.8
17.0
21.0
Loading,
kg/in
—
_.
0.24
—
0.28
0.24
0.61
0.59
1.12
0.56
0.94
1.48
0.85
1.40
Cake
solids,
I
—
..
20.8
*
18.0
25.0
21.5
18.5
21.2
49.0
23.9
21.4
23.2
21.6
Filtrate
solids,
—
_.
8,550
—
405
187
74
13
6
25
16
11
1,400
2,090
Filtrate
Vpl UltMS •
PI
910
540
820
170
345
250
365
260
220
370
250
325
380
460
480
Type of cloth
2X2 twill multl-
f f lament olef In
2X2 twill nultl-
fl lament oleftn
2 X 1 twill saran
mono f I lament
2 X 1 twill saran
monofl lament
2 X 1 twill saran
monof 1 lament
4X1 satin nylon
multlf 1 lament
4X1 satin nylon
multlf 1 lament
4 X 1 satin nylon
multlf I lament
4X1 satin nylon
aiultl filament
4X1 satin nylon
nultlf (lament
4 X 1 satin nylon
mult! f I lament
4 X 1 satin nylon
multif 1 lament
Satin polypropylene
Satin polypropylene
Satin polypropylene
Cake
Discharge
characteristics
No cake
^
No cake
No cake
Good thin
No cake
Fair
Fair
Excellent
Excel lent
Excel lent
Excellent
Excel lent
Excellent
Excellent
Ho cake
-------
SCREENING
'DISSQLVED-AIR
FLOTATION
ATLASEP SCUM
3A3 3.65*
POLYMER SOLIDS
I kg/m ton
FLOTATION
THICKENING
GRAVITY
THICKENING
GRAVITY
THICKENING
ATLASEP 3A3 POLYMER
0.2 kg/m ton
CFNTRI FIXATION
CENTRIFUGATION
ATLASEP 3A3 POLYMER
0.76 kg/m ton
AND
LIME 95 kg/m ton
VACUUM
FILTRATION
Figure 13* Milwaukee, Wl (Hawley Road) * bench scale dewaterfng tests
-------
fll
•o
500
(102.5)
400
(82.0)
J» 300
Z, (61.5
m
•o
cr
in
100
(20.5;
FLUX CONCENTRATION CURVE
TANGENT TO THE FLUX CONCENTRATION CURVE AT
THE SELECTED SLUDGE CONCENTRATION SHOWS
THE ALLOWABLE MASS LOADING RATE FOR GRAVITY
THICKENING
246
SLUDGE CONCENTRATION, I
10
12
Figure Ik. Flux concentration curve for Milwaukee, WI (Hawley Road), dissolved-air
flotation sludge, without chemicals
-------
co
500
(102.5)
cr
M
5 300
- (61.5)
<0
"O
IT
H 20°
•* (M.O)
C3
O
_J
CO
100
(20.5)
Figure 15*
FLUX CONCENTRATION CURVE WITH
DOW C-41 POLYMER
TANGENT TO THE FLUX CONCENTRATION CURVE AT
THE SELECTED SLUDGE CONCENTRATION SHOWS THE
ALLOWABLE MASS LOADING RATE FOR GRAVITY
THICKENING
to 5 kg/m ton
10
12
SLUDGE CONCENTRATION,
Flux concentration curve for Milwaukee, Wl , (Haw ley Road) dtssolved-alr
flotation sludge with chemicals
-------
The results of flotation thickening tests are shown In Figure 16. Without
the aid of any chemicals, scum concentrations of up to 15% could be expected
at a solids loading rate of approximately 75 kg/sq in/day (15 Ibs/sq ft/day).
However, use of an an Ionic polyelectrolyte, Atlasep 3A3, provided a scum
concentration of 10-11% at significantly higher loading rates of the order
of 250-350 kg/sq m/day (50-70 Ibs/sq ft/day). Optimum recycle rates tanged
between 350 and 400%.
Centrlfugatlon test results are shown in Table 13' Again, prior gravity
thickening and chemical addition (0.2 kg/m ton, Atlasep 3A3) helped to pro-
vide Improved cake solids. Raw scum yielded a cake solids concentration in
the range of 19 to 23% while chemically treated and 5edImented sludge
(feed concentration 9-10% solids) yielded cake solids of approximately 22
to 30% upon centrlfugatlon. Optimum solids recoveries were achieved at
gravitational forces between 700 and 1,000 G and spin time between 60 and
120 seconds.
Vacuum filtration tests on this sludge were conducted on gravity thickened
samples having a feed solids concentration of 10.31* The test results are
shown in Table 14. Buchner Funnel tests showed that a chemical combination
of lime (35 kg/m ton) and Atlasep 3A3 (0.8 kg/m ton) provided optimum test
results. Cake solids of up to 30% were achieved under optimum chemical
conditions. Optimum yield rates of 50 kg/sq m/hr (10 Ibs/sq ft/hr) were
achieved at 37*51 submergence.
San Franc tsco, CA
A treatment schematic of the various bench soale tests conducted on the
San Francisco sludge sample is shown in Figure 17- The grab sample ob-
tained for bench tests had a suspended solids concentration of 2.251
as compared to the flotation scum sample for Hawley Road at 3*651
solids. The flux concentration curve for the gravity thickening tests
for this, sludge Is shown in Figure IS. The results showed generally poor
settling characteristics. Chemical coagulants were necessary for any
meaningful gravity thickening results. Even with the aid of chemical
coagulants (up to 12 teg/m ten of Atlasep 105C, a catIonic polyelectrolyte),
the sludge was thlckeded only to a level of 2 to 3% solids at low mass
loading-rates of 50 to 70 kg/sq in/day (10-14 Ibs/sq ft/day). At
significantly reduced loading rates of the order of 10 to 20 kg/sq m/day
(2 or 4 Ibs/sq ft/day); thickening up to 4* solids may be possible* it
was indicated that such poor performance for gravity thickening may be
due to the alum treatment of CSO utilized at this treatment facility.
The results of flotation thickening tests are shown In Figures 19 and 20.
Scum concentrations of up to 5 to 6% solid could be achieved at mass
loading rates between 50 to 100 kg/sq m/day (10-20 Ibs/sq ft/day) and
recycle rates between 350 and 450%. With the aid of Atlasep 105C
(0.4 to 0.5 kg/to ton dosage), maximum concentration of only 7*5% solids
was possible at similar mass loadings and recycle rates, (it should be
noted that the Atlasep 105C polymer used here has since been discontinued
for production by the manufacturer but any equivalent polymer should
provide comparable performance). Centrifuge test data for the
-------
400
(82.0)
350
(71.75)
300
(61.5)
09
-a
250
5" (51.25)
(A
_a
6 200
cr (41.0)
"1 I5°
§ (30.75)
Q
5
£ 100
2 (20.5)
50
(10.25)
NO CHEMICAL
1.0 kg/m ton
ATUASEP JA3
POLYHER
0.3 kg/m ton
^ATLASEP 3A3
POLYMER
V
0.5 kg/m ton ATLASEP 3A3
POLYMER
68 10 12 14 16
ESTIMATED SCUM CONCENTRATION, *
Figure 16. Flotation thickening results
for Milwaukee, Wl, Hawley Road., dlssolved-afr -flotation sludge
(all tests at 390? recycle rate for thickening)
50
-------
Table 13. CENTRIFUGE TESTING RESULTS FOR
MILWAUKEE, Wl, HAWLEY ROAD, DISSOLVED-AJR FLOTATION SLUDGE
Test
No,
1
2
3
k
5
6
7
8
9
10
11
12
13
111
15
16
17
18
Appl led r,
force, "G's"
400
400
400
400
700
700
700
700
1,000
1.000
1,000
1,000
700
7flO
700
1,000
1,000
1 ,000
Spin time
sec
30
60
20
120
30
60
90
120
30
60
30
120
30
75
120
30
75
120
Feed
solids,
tng/1
36,540
36,5*0
36,5*0
36.5*0
36,5*0
36,5*0
36,5*0
36,5*0
36,5*0
36,5*0
36,5*0
36,540
99,200
93,200
99,200
99,200
99,2000
99,2000
Dosage,
Chemical kq/m ton
none
none
none
none
none
none
none
none
none
none
none
none
fttlasep 3A3
Atlasep 3A3
Atlasep 3A3
AtJasep 3AJ
Atlasep 3A3
Atlasep 3A3
rx>ne
none
none
none
none
none
none
none
nono
none
none
none
0.20
0.20
0.20
0.20
o.an
0.20
Central*
solids,
mq/t
5.475
310
210
208
776
?f
17!
16]
204
142
153
13*
365
332
298
t,770
424
465
Generate
volume,
ml
51.5
51.3
62.3
62.0
58.8
6t.O
60.8
62.5
58.3
62.0
63. 0
63.3
*2.0
*8.0
50.5
45.0
48. o
50.0
Penetration,
en
2.1
2.1
1.6
1.4
2.2
1.4
1.3
1.1
2.0
1.3
1.1
1.0
3-2
1-7
t.3
2.8
1.8
1.6
Sludtie
depth,
en
2.1
2.1
1 .1
2.1
2.3
2.4
1.-5
1.7
2.3
1.9
2.0
1.7
3.9
3.3
3.3
3,°
3 *
1.2
Cake
sol Ids,
?•
15.6
17.4
21.4
21.1
16 5
19.6
n.2
21,9
16.°
21.1
22.8
23.*
22 *
27.5
30.3
24.5
27.5
2°. 7
Penetration,
*
r>
0
14
34
4
41
3*
31
U
31
*4
45
18
54
fil
30
46
S"
Recovery ,
?;
85.0
P9.4
<)9.5
99. S
97.8
10.7
99.6
91.6
99.5
93.7
9?. 7
HP 7
99.1
19.7
«9.7
98.2
99.6
oq.g
Corrected
recovery,
J
o.oa
o.oa
31 ?
ST 6
70. n
91 2
89.4
88.6
31.7
88.7
9K3
"2.0
83.5
33-8
94. 1
87.1
-------
Table 14. VACUUM FILTRATION TESTING RESULTS
MILWAUKEE, Wl, HAWLEY ROAD, DISSOLVED-AIR FLOTATION SLUDGE
Feed solids cbneentratldn 10.3*
Chemical
do$aqes kq/m ton
0. 26 35
0.76 95*
0.3b 95
0.3B 9S
Cycle
time,
mln
5
4
*
"
Pickup
time,
sec
75
90
90
90
Dry
time,
sec
150
100
100
100
Submer-
aonee,
t
25
37.5
37.5
37.5
Ylelrf,
kg/hr/m
37.1
so.'s
50.2
*"'"
Loadlnq,
kq/ra
3.03
3.38
3.34
3.33
Cake
solids,
35.7
30.4
31.1
31.7
Filtrate
solids,
raq/1
232
463
3.501
—
Filtrate
volume,
ml
235
197
200
—
Type of cloth
2x2 twill olefln
inul tlfllament
2x2 twtll olefm
multif i lament
2x1 plain poly-
propylene mono-
f I lament
2x2 twill olefln
nul 1 1 f 1 lament
Cake
Discharge
character-
istics
Excel 1 ent
Excel lent
Excellent
Excellent
-------
cso
DISSOLVED-
AIR
FLOTATION
_S£UM
2.251
SOLIDS
GRAVITY
THICKENING
ATLASEP IOSC POLYMER
3.25 kg/m ton
FLOTATION
THICKENING
.LIME
M»0 kg/m ton
VACUUM
FILTRATJOH
ITLASEP I05C POLYMER
0.5 kg/m ton
CENTRIFUGATION
Figure I?. San Francisco, CA, - bench scale dowatering tests
53
-------
250
(51.25)
200
(kl.Q]
a*
tn
m
150
(30.75)
<0
1
cr
C9
3E
a
100
(20.5
50
(10.25
FLUX CONCENTRATION CURVE
TANGENT TO THE CONCENTRATION CURVE AT THE
SELECTED SLUDGE CONCENTRATION SHOWS THE
ALLOWABLE MASS LOADING RATE FOR GRAVITY
THICKENING
Figure 18.
1.0 2.0
SLUDGE CONCENTRATION,*
3.0
Flux concentration curve for San Francisco, CA, dlssolved-aJr flotation sludge
(with chemicals)
-------
kQQ \-
(82.0)
350 .
(71.75)
300
(61.5)
O"
lit
Ifl
£ 250
~ (51.25)
i
0- 200
(M.O)
Ol
(9
150
(30.75)
100
(20.5)
50
(10.25)
2851 RECYCLE RATE
RECYCLE RATE
370* RECYCLE RATE
6 8 10 12 14 16
ESTIMATED SCUM CONCENTRATION, %
Figure 19. Flotation thickening results for San Francisco, CA
dlssolved-alr flotation sludge - without chemicals
55
-------
350
(71.75)
300
(61.5)
-3 250
5 (51.55)
cr
w
CD
1
(T
CD
200
150
(30.75)
< 100
-• (20.5)
VI
50
(10.25)
ATLASEP I05q
POLYMER
0.3 kg/m ton
t
\
ATLASEP 105C
POLYMER
O.^t kg/m ton
-ATLASEP 105C
POLYMER
0.5 kg/m ton
ESTIMATED SCUM CONCENTRATION, %
Figure 20. Flotation thickening results for San Francisco, CA
dfssolved-alr flotation sludge - with chemicals
(all tests at 3701 recycle rate for thickening)
-------
San Francisco sample is presented In Table 15. Without chemical treat-
ment, the sludge showed poor scrollabilIty characteristics and could be
concentrated only to about J-B% solids. However, concentrations up,,to
111 solids were achieved when chemical treatment with Atlasep 105C
(0.5 kg/m ton) was utilized. It was Indicated that the chemically treated
sludge could be treated with both the scroll and basket type centrifuges.
Marked Improvement tn the centrate clarity was also achieved with chemical
clarification.
The results of the vacuum filtration tests are shown in Table 16. iuchner
Funnel tests indicated that best filtration results were obtained with
large dosages of lime (350 to ^50 kg/m ton) Instead of the catlonlc poly-
electrolyte, Atlasep 105C that had shown optimum results for other dewaterlng
techniques. A 3 x 1 twill weave filter media provided the best cake discharge
characteristics with lime treatment. The loading and yield rates shown
In Table 16 are based on dry weight of sludge solids. Cake solids of approx--
Imately 181 for a yield of 15 to 20 kg/sq m/hr (3 to *i Ibs/sq ft/hr) were
achieved for the thickened sludge.
Trea tmen t Cos t s f orPhys_Ica 1 /Chem ica 1 CSO S1_udg_es_
A summary of the estimated area and cost requirements of various dewaterfng
techniques under optimum treatment conditions for Physical/Chemical CSO
sludges is shown In Table 17. As mentioned earlier for storage treatment
the total costs shown include the amortization of capital costs and the
hauling cost of the ultimate treatment residuals from the site along with
other operating costs such as labor, chemical, maintenance, power, etc.
Details of these cost estimates and the assumptions made to arrive at them
are presented In Appendix C. it Is evident that generally centrlfugatlon
alone or In combination with gravity thickening are the optimum dewatering
steps based on performance, area and cost requirements. For Racine and San
Francisco, basket type centrifuges were considered for cost calculations
based on the results of the feasibility tests. It Is Interesting to note
that the total cost of gravity or flotation thickening Is significantly more
than centrlfugatlon or vacuum filtration even when the latter are In
combination with the former. The reason for such a difference stems from
the hauling cost of the ultimate treatment residuals, which are significantly
larger in volume for gravity thickening and flotation thickening compared to
the residual volumes after centrifugatfon or vacuum filtration. For San
Francisco, the cost results of centrlfugatlon and vacuum filtration are close;
while vacuum filtration edges out centrlfugatlon in thickened solids
performance. This may be due to the nature of the raw sludge because of the
use of alum treatment at San Francisco, compared to ferric chloride treatment
at Racine and Milwaukee (Hawley Road).
C. BIOLOGICAL TREATMENT
Sludge samples from two sites using biological treatment were procured. Both
these sites are operated during wet-weather as well as dry-weather. A wet-
weather sludge sample was procured from Kenosha, Wl where the contact stabili-
zation activated sludge process Is utilized, Four sludge samples were procured
57
-------
Table 15. CENTRIFUGE TESTING RESULTS FOR
SAN FRANCISCO, CA, D1SSQLVED-AIR FLOTATION SLUDGE
Ho.
1
6
7
8
10
11
12
13
£ i*
15
16
17
18
19
20
21
22
23
24
25
26
27
28
Applied fi
force, 'Vs"
400
600
800
1 ,.000
600
800
1,000
400
600
800
1,000
400
700
1,000
400
700
1,000
400
700
1,000
400
700
1 ,000
Spin time,
sec
30
60
60
60
90
90
90
120
120
120
120
30
30
30
60
60
60
90
90
90
120
120
120
Feed
sol Ids,
2,25
2.25
2.25
2.25
2.25
2.25
2.25
2.25
2.25
2.25
2.25
2.25
2.25
2.25
2,25
2,25
2.25
2.25
2.25
2.25 '
2.25
2,25
2.25
Chemical
none
nona
none
none
none
none
none
none
none
none
non«
lose
lose
lose
lose
lose
105C
105C
I05C
I05C
I05C
105C
105C
Dosage,
kg/m ton
none
none
none
none
none
none
none
none
none
none
none
0.53
0.53
0.53
0.53
0.53
0.53
0.52
0.52
0.53
0.53
0.53
0.53
Centrate
solids,
jng/1
—
6,925
4,825
3,260
3,690
2,260
1,500
1,460
2,275
1,350
1,025
89
51
72
67
98
66
80
73
56
82
132
33
Centrata
vo 1 use ,
ml
--
59.5
58.0
57.8
55-5
56.0
56.5
56.5
55.0
56,0
57.5
53.0
54,8
55.8
55.0
58.2
58.3
55-2
58.8
59,2
59.0
59.8
59-8
Penetration,
cm
--
3
2.8
2.7
3.0
2.8
2.68
2.73
2.73
2.6J
2.6
3.05
2.85
2.63
2.8
1.3
1.3
2.75
0.85
1.5
1.1
0.8
1.2
Sludge
depth,
cm
..
3
2.8
2.7
3.0
2.8
2.68
2.73
2.73
2.63
2.6
3.05
2.85
2.63
2.8
2.53
2.38
2.75
2.5
2.35
2.63
2.53
2.35
Cake
solids,
I
„
8.2
8.3
8,3
7.6
8.2
8,7
8.7
7.8
8.5
9.3
7.6
8.3
8.8
8.4
10.0
10.1
8.5
10.4
10.6
10.5
11.0
1K1
Penetration,
*
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
48
43
0
64
35
58
68
48
Recovery,
—
69.2
78.5
85.7
83.6
89.9
93.3
93.7
89.8
94.0
95.4
99.6
99.7*
99.6
99.7
99.5
99.7
99-6
99.6
99.7
99.6
99.4
99.8
Corrected
recovery,
%
Oa
-------
Table 16. VACUUM FILTRATION TESTING RESULTS FOR SAM FRANCISCO,
CAt D1SSOLVED-AJR FLOTATION SLUDGE
vo
Feed solids concentration: 2,251
Cheralcal
105-C
I05-C
CaO
CaO
CaO
CaO
CaO
CaO
Dosage,
kglm ton
0.66
0.66
356
444
444
444
444
M4
Cycle
time,
nln
5
8
7.8
8
5
3
2
3
Pickup
time,
»ec
75
175
170
170
no
65
44
44
Dry
time,
sec
150
195
190
190
122
73
48
D2
Submergence,
t
25
37.5
37.5
37.5
37.5
37.5
37.5
25
Yield,
kg/hr/m2
__
—
— ,
U.4
14.7
19-3
21
13-5
Load 1 ng ,
hfl/m2
__
—
—
1.48
1.23
0.96
0.70
0.67
Cake
sal Ids,
>
Mo Cake
23.3
24.J
18.2
18,0
18,1
18 k
18.7
Filtrate
sol Ids,
mg/ \
147
62
77
123
134
110
146
108
Filtrate
vo 1 uwe ,
580
530
255
680
520
405
300
310
Type of
cloth
3X1 twill
3X1 twill
3X1 twill
3X1 twill
3X1 twill
3X1 twill
3X1 twill
3*1 t*lll
Cake
Discharge
characteristics
Poor
Poor
Good
Very Good
Very Good
Very Good
Very Good
Very Hood
-------
Table !?. SUHMARY OF AREA AND COST REQUIREMENTS FOR PHYSICAL/CHEMICAL
SLUDGES UNDER OPTIMUM TREATMENT CONDITIONS
Site
Racine
Kawley Road
San Francisco
Sludge
solids, Area
Gravity
thickening
Flotation
thickening
Centrifugal Ion
Vacuum
filtration
% sq ft
10 172
13b MOO
20 194
33b 205
nb 325
(sq mi
(IS)
030)
(18)
(19)
(50)
Total Sludge
annual solids, Area
cost , S/yr t Iq Ft tsq HI)
W.800 10 312 (29)
63,800 13 797 (7*)
56,900 23 21,5 (2)
3MOO 30b 3^5 (32)
Wt.JOO 36b te tt2)
Total Sludge
annual solids,
cost , S/yr *
71,500 k
69,200 6
39,800 11
38,100
1(1,300 18
Area
1,959 (182)
172 (16)
32 (3)
129 (12)
Total
annual
cost , $/yr
^5,000
40.500
2^,600
23,900
a. Capital costs aoortlzed for 20 year equipment life and 10% Interest rate. For details of cost estimates, See Appendix C.
b. These tests conducted on gravity thickened sludge.
All costs based on December, 1974 prices.
-------
front the primary and secondary clariflers at New Providence, NJ where
trickling filtration treatment Is utilized during both the wet and dry-
weather treatment periods.
Kenosha, Wl
A treatment schematic of the bench scale dewaterlng techniques Investi-
gated at Kenosha is shown In Figure 21. The average quantity of sludge
requiring handling and/or treatment on a per storm basis was estimated to
be k6k cu m (122,600 gal.) at a suspended solids concentration of 0.8 to
1.0% solids. These values are based on published data (12) and analytical
results obtained during this study. The flux concentration curves for the
gravity thickening tests are shown In Figures 22 and 23. These curves
represent the test data without chemicals and with chemicals respectively.
As can be seen from these curves, this sludge showed poor amenability to
gravity thickening both with and without chemical aids. Sludge concentra-
tions of less than 2% solids could be achieved at low solids loadings 10-
20 kg/sq m/day (2-4 Ibs/sq ft/day). Such performance of a biological
sludge is similar to gravity thickening performance of conventional dry-
weather biological sludges.
The flotation thickening test results are shown in Figures 24 and 25.
Optimum recycle rate was found to be approximately 2001. Chemical dosage
tests were conducted using Dow C-31, a cat Ionic polyelectrolyte and
Atlasep 3A3, an an Ionic polyelectrolyte based on chemical screening tests.
The cationfc polymer, C-31, produced optimum results and concentrations of
k to 51 solids could be achieved at mass loading rates of 50-100 kg/sq m/day
(10-20 Ibs/sq ft/day).
Data on the centrifugatIon tests for the Kenosha sludge sample is shown in
Table 18. Bench test procedure for a scroll type centrifuge indicated poor
scroll ability as evidenced by the zero resistance to penetration of the
centrifuged sludge in all tests. Chemical aids did not provide any improve-
ment in test results both in terms of cake solids, cent rate clarity or
scrollablllty of the centrifuged sludge. Therefore, It was concluded that
scroll type centrifuge would not be applicable to the biological sludge at
Kenosha. However, a basket type centrifuge Is expected to produce positive
results as evidenced by the cake solids up to $% for centrifuged sludge
(test no. 8) under optimum test conditions of 1000G and 120 seconds deten-
tion time. A combination of flotation thickening and centrifugatlon did
not provide any improvement in the test results for a scroll type centrifuge.
The results of vacuum filtration tests are shown in Table 19. Because of
the dilute nature of the raw sludge, all filtration tests were conducted
after flotation thickening of the raw sludge to a level of 3.1* solids.
Chemical dosage screening tests on a Buchner Funnel showed that a chemical
combination of 160 kg/m ton (220 Ibs/ton) ferric chloride and 128 kg/m ton/
(256 Ibs/ton) lime provided optimum filtration results of the various filter
media investigated, best cake discharge characteristics were obtained with
the 4/1 satin nylon multlfilament cloth. Cake solids of up to 15% for a
yield of approximately 18 kg/sq m/hr (3.6 Ibs/sq ft/hr) were achieved under
optimum test conditions.
61
-------
DOW C-31 POLYMER
12 kg/m ton
GRAVITY
THICKENING
ATLASEP 3A3 POLYMER
5.4 kg/m ton
FLOTATION
THICKENING
CENTRIFUGATION
ATLASEP 3A3 POLYMEJ_
S.b kg/m ton
FLOTATION
THICKENING
DOW C-31 POLYMER
7«8 kg/m ton
CENTRIFUGATION
ATLASEP 3A3 POLYMER Fed 160 kg/m ton
kg/m ton ^ and LIME, 128 kg/m ton
FLOTATION
THICKENING
VACUUM
FILTRATION
Figure 21, Kenosha, Wl - Bench-Scale Dewaterlng Tests
62
-------
II)
"X,
lit
TO
•a
250
(51.25)
200
(41.0)
ISO
(30.75)
100
S" (20.5)
50
o
I (10.25)
C/}
<
FLUX CONCENTRATION CURVE
TANGENT TO THE FLUX CONCENTRATION
CURVE AT THE SELECTED SLUDGE CON-
CENTRATION SHOWS THE ALLOWABLE
MASS LOADING RATE FOR GRAVITY
THICKENING
0.25
0.5 0.75 1.0
SLUDGE CONCENTRATION, *
1.25
Figure 22,
Flux concentration curve for Kenosha, Wl, contact stabilization sludge
(without chemicals)
-------
HJ
TJ
flj
•a
o-
Ul
en
a
<
o
250
(51.25)
200
(41.0)
150
(30.75)
FLUX CONCENTRATION CURVE
TANGENT TO FLUX CONCENTRATION CURVE
AT THE SELECTED SLUDGE CONCENTRATION
SHOWS THE ALLOWABLE MASS LOADING RATE
FOR GRAVITY THICKENING
0.25
0.5 0.75 1.0
SLUDGE CONCENTRATION, I
1.5
1.75
Figure 23. Flux concentration curve for Kenosha, Wl, contact stabilization sludge
(with DOW C-31 polymer, M-12 kg/m ton)
-------
m
•a
or
«n
a
•a
ex
V)
o»
a
<
o
<
350
(71.75)
300
(61.5)
250
(51.25
200
(41.0
ISO
(30.75)
100
(20.5)
50
(10.25)
1*00* RECYCLE RATE
1901 RECYCLE RATE
*
\
\
1002 •
RECYCLE RATE \
280* RECYCLE RATE
\
\
\
1_
012345
ESTIMATED SCUM CONCENTRATION, I
Figure 2k. Flotation thickening test results for Kenosha, Wl,
contact stabilization sludge (without chemicals)
65
-------
~* 300
£ (61.5)
•a
or
<£ 250
£ (51.25)
m
IA
X,
O»
200
150
§ (30.75)
too
(20.5)
50
(10.25)
ATLASEP 3A3 §.*» kg/n ton
ATUSEP 3A3 ».l kg/ra ton
ATLASEP 3A3 3.7 kg/m ton
ATLASEP 3A3 2.2 kg/m ton
01 2 3
-------
a
•o
4-1
14-
o-
"N.
I/I
B3
•o
cr
ui
en
a
<
o
350
(71.75)
300
(61.55
250
(51.25)
. 200
(41.0)
150
(30.75)
100
(20.5)
50
(10,25)
DOW C-3J POLYMER
kg/m ton
DOW O3I POLYMER
2,8 kg/m ton
DOW C-31 POLYMER-
ID.6 kg/m ton
DOW C-3I POLYMER
I6.2 kg/m ton
01 23 k 5
ESTIMATED SCUM CONCENTRATION, %
Figure 25 (contd.) Flotation thickening test results for Kenosha, W!
contact stabilization sludge (with DOW C-31 polymer at 190% recycle rate)
-------
Table 19. VACUUM FILTRATION TESTING RESULTS FOR KENOSHA,
Wl, CONTACT STABILIZATION SLUDGE
Feed solids concentration: 3. I
Chemical
ka/m
FeClj
60
60
60
60
60
60
60
6D
60
60
60
60
dosage,
ton
CaO
128
128
128
128
128
128
128
128
128
(28
128
128
_
Cycle time,
win
j,
3
k
k
3
k
3
4
3
k
3
3
Pickup time,
sec
60
45
60
60
45
60
45
90
65
£0
45
45
Dry time.
sec
120
90
120
120
90
120
90
120
75
!20
90
90
Submergence,
J
25
25
25
25
25
25
25
25
37.5
25
25
25
Yield,
kg/hr/m2
14.3
18,0
15.8
. 15.6
18.0
13.1
18.2
17.1
19.8
14.2
11.2
17.6
Loading
kq/m2
0.98
0.88
1 07
1.02
O.CC
0.88
0,93
1.12
0.98
0.93
0.93
0.88
t
Take sol i
*
14.3
15.16
14.8?
IS.?*!
15 16
16.55
14.28
13-33
It. 89
13- ?S
13.09
15". 36
Filtrate
ds, solids.
rmj/1
3,850
1,560
88
60
82
12
45
—
—
10
—
—
Filtrate
volume,
ml
310
220
428
460
360
290
235
295
270
240
200
210
Type of cloth
2x2 twill olefln
multl f 1 1 arrant
2x2 twill olefln
mul ti filament
Napped 1x5 olefln
spun staple
Napped 1x5 olefln
spun staple
Napped 1x5 olefln
spun staple
1x4 satin nylon
mul 1 1 f I lament
1x4 satin nylon
multlfllasnent
1x4 satin nylon
mul 1 1 f I lament
1x4 satin nylon
mul t If I lament
1x4 satfn nylon
mul ttf t lament
1x4 satin nylon
CHI 1 1 1 f 1 1 amen t
1x4 satin nylon
mul t 1 f I laraent
Cake
Discharge
character-
istics
Poor
Poor
Poor
Poor
Poor
Good
•
Excel lent
Good
Good
Excel lent
Good
Good
-------
Table 18. CENTRIFUGE TESTING RESULTS FOR KEHOSHA,
Wl, CONTACT STABILIZATION SLUDGE
oo
Test
Ho,
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Applied G
force, "G's"
400
750
1,000
1,000
750
400
750
1,000
1,000
750
750
400
400
750
1,000
1,000
750
4oo
750
1 ,000
1 ,000
400
400
1,000
Spin
time,
sec
60
60
60
90
90
120
120
120
120
120
120
120
60
60
60
90
90
120
120
120
120
120
120
120
Feed
solids,
jng/l
8,413
8,413
8,413
8,413
8,413
8,413
8,413
8,413
8,413
8,413
8,413
8,411
25,850
25,850
25,850
25,850
28,850
25,850
25,850
25,850
25,850
25,850
25,850
25,850
Chemical
none
none
none
none
none
none
none
none
C3I
C3J
C3t
C3I
none
none
none
none
none
none
none
none
C3I
C3I
C31
C31
Dosage,
kg/m ton
none
none
none
none
none
none
none
none
12.05
12,05
7,01
12.05
none
none
none
none
none
none
none
none
7.81
7.81
7.81
11.72
Cent rate
soltds,
mg/1
..
—
—
134
132
140
54
96
79
90
77
—
-»
12,900
14,725
12,195
7,790
107
7,350
206
160
Generate
volume,
nil
_„
68.3
64,0
64.0
62.5
70.8
63.0
64.0
68.0
67.2
44.5
64.8
—
61.5
67-5
52. 5
57.2
60.5
53.5
43.0
45.8
44.5
40.0
41,5
Penetration,
CO
7.C
2.2
1.9
7.9
1.9
9.75
1.84
1.75
1.5
1.65
3.84
1.9
8.5
7-25
6.5
5.68
5.97
4.9
6,78
4.4
3.73
7.02
7-65
7.5
Sludge
depth,
cm
7.8
2.2
1.9
7-9
1-9
9.75
1.84
1-75
1.5
1.65
3.84
l.g
8.5
7.25
6.5
5.68
5.97
4.9
6.78
4.4
3.73
7.02
7-65
7.5
Cake
soltds ,
%
„_
—
__
5.6
5.2
—
5.7
8.9
8.0
2.)
6.1
5.6
—
—
—
6.2
6.0
—
6.0
6.0
6.6
5-2
5-5
5.8
Penetration,
i
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Q
0
0
0
0
0
0
Recovery,
%
—
—
98.4
98.4
..
98.3
99.3
98.8
99.0
98.9
99.1
—
—
--
49.6
42.5
—
52.4
69.6
99.6
71.3
99-2
99.4
Corrected
recovery ,
^
O3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
a. Denotes poor scrollabllIty of the thickened slydge. See Appendix B for procedure.
-------
Table 19, VACUUM FILTRATION TESTING RESULTS FOR KENOSHA,
Wlf CONTACT STABILIZATION SLUDGE
Feed solids concentration:
Chemical dosage.
kd/flt i
FaCt 3
£0
60
60
60
60
60
60
60
60
60
60
£0
PP
CaO
128
128
123
128
128
128
128
128
128
126
128
128
Cycle time,
rnlri
4
3
4
4
3
4
3
4
3
4
3
3
Pickup time,
sec
60
45
60
60
45
60
45
90
65
60
45
45
Dry time,
sec
120
90
120
120
90
120
90
12C
75
f20
90
90
Submerge nee,
25
25
25
25
25
25
25
25
37.5
25
25
25
Yield,
kg/hr/m2
14.3
18.0
15.8
15.6
18.0
13.1
18.2
17.1
19.8
14.2
11.2
17.6
Loading
kq/m2
0.38
0.88
1 07
1,02
0.08
0.88
0.93
1.12
0.98
0,93
0.93
0.88
fake solids,
14.9 3
15.16 1
14.85
13. ?4
15.16
16 55
14.28
13.33
11.89
!3.?5
13.09
I ?-36
Filtrate
sot fds,
mq/1
,850
,560
88
60
82
<*2
45
--
—
10
~
—
Filtrate
volume,
ml
J10
220
1(28
460
360
290
235
295
270
240
200
210
Type of cloth
2x2 twill olefln
cult If 1 lamnt
2x2 twill olefln
multl filament
Napped 1x5 olefln
spun staple
Napped 1x5 olefln
spun staple
Napped 1x5 olefln
spun staple
1x4 satin nylon
multlf Mament
1x4 satin nylon
mul tlfl lament
1x4 satfn nylon
mutt) Filament
1x4 satin nylon
multlf Mament
1x4 satin nyJon
multlf Hament
1x4 satin nylon
multlf (lament
1x4 satin nylon
myltlf I lament
Cake
Discharge
character-
istics
Poor
Poor
Poor
Poor
Poor
Good
Excel lent
Good
Good
Excel lent
Good
Good
-------
New Providence,NJ
This treatment facility utilizes trickling filters for the treatment of
dry-weather flow as welt as large quantities of polluted water during
wet-weather periods generated by Infiltration to the sewer system. De-
watering tests were conducted on separate sludge samples from the primary
and secondary clarlfler during both the wet and dry-weather periods.
Vtej^eatherSljjdge Samples - A schematic of the dewaterlng techniques
Tnvestlgatecfon wet-weather samples Is shown In Figure 26. The total
quantity of the primary sludge during wet-weather Is 735 cu m (194,200
gal.) per storm event based on mass balance for a measured sludge con-
centration of 0.121 solids. However, this low solid strength for a
primary sludge probably stems from the unique clartfier operation situa-
tion at New Providence whereby a fixed amount of sludge produced per day
Is sent out for separate treatment and therefore, sludge blanket and
strength do not build up In a conventional manner. If this underflow is
compared to a convwntioaa! situation, assuming 4| solids (21,22),
approximately 22 cu m (5,800 gal.) of sludge would be produced. The
quantity of sludge produced from secondary clarlfler was estimated at
approximately 62 cu m (16,380 gal.) per storm event. The measured solids
concentration of the secondary sludge sample procured was 2.51.
The flux concentration curves for the gravity thickening tests for the
primary and secondary samples are shown in Figures 27 through 30. The
dilute primary sludge sample showed amenability to gravity thickening.
With the help of flocculating chemicals (lime and anionic polymer), up to
8% solids could be expected at mass loading rates of 500 kg/sq m/day
(100 Ibs/sq ft/day). Without chemical aids, the results were significantly
poorer. Comparitively, the secondary sludge showed poor amenability
to gravity thickening as solids concentrations of only 2 to 3% were
achieved with or without chemical aids at low loading rates of less than
20 kg/sq m/day (*» Ibs/sq ft/day).
The flotation thickening test results are shown in Figures 31 through 33-
For primary sludge, again chemicals aided in superior performance and
solids concentrations similar to gravity thickening (up to 81) were
achieved at mass loading rates of the order of 250 kg/sq m/day
(50 Ibs/sq ft/day). The optimum recycle rates were generally less
than 160%. For secondary clanfler sludge, the flotation thickening
performance was significantly better than gravity thickening as solid
concentrations up to 5% without chemicals and up to 61 with chemicals
were achieved. With chemical aids (lime and Hagnifloc anionic polyelec-
trolyte 837-A), these concentrations were achieved at significantly higher
loading rates of 250 to 350 kg/sq m/day (50 to 10 Ibs/sq ft/day)
compared to lower loading rates of less than 50 kg/sq m/day (10 Ibs/
sq ft/day) without chemicals. The optimum recycle rates were between 250
and 3001,
The results of centrifugation tests for the primary and secondary sludge
samples are shown in Tables 20 and 21 respectively. The results show
poor amenability to centrifugation for the primary sludge sample. Cake
70
-------
I—IWE AND MAGNIFLOC 837* POLYMER
GRAVITY
THICKENING
LIME AND MASNIFLOC 837A POLYMER
FLOTATJON
THICKENING
.LIME AND MAONIFLOC 837A POLYMER
CENTRIFUGATION
GRAVITY
THICKENING
r- FERRIC CHLORIDE AND LIME
VACUUM
FILTRATION
SECONDARY
LARIFIER
r~ FERRIC CHLORIDE AMD MAGNIFLOC 905N POLYMER
GRAVITY
THICKENING
FLOTATION
THICKENING
LIME AND HAGNIFLOC 837A POLYMER
CENTRIFUGATION
FERRIC CHLORIDE AND MAGNIFLOC
N POLYMER
f
GRAVITY
THICKENING
VACUUM
FILTRATION
FERRIC CHLORIDE AND
905 N POLYMER FERRIC CHLORIDE AND LIME
Figure 26, New Providence, NJ - bench scale dewaterfng tests (wet-weather)
71
-------
250
(51.25)
^ 200
m (*H.O)
cr
in
"« 150
- (30.75)
n
1 100
o- (20.5)
(3
2, 50
3 (10.25)
to
FLUX CONCENTRATION CURVE
TANGENT TO THE FLUX CONCENTRA-
TION CURVE AT THE SELECTED
SLUDGE CONCENTRATION SHOWS THE
ALLOWABLE MASS LOADING RATE FOR
GRAVITY THICKENING
SLUDGE CONCENTRATION, %
Figure 27. Flux concentration curve for New Providence, NJ,
wet-weather trickling filtration primary sludge (without chemicals)
-------
I/I
v>
-Q
(V
I
«T
§
500
(102.5)
400
(82.0)
300
(61.5)
200
100
(20.5)
0
(0)
FLUX CONCENTRATION CURVE
TANGENT TO THE FLUX CONCENTRATION
CURVE AT THE SELECTED SLUDGE CON-
CENTRATION SHOWS THE ALLOWABLE
MASS LOADING RATE FOR GRAVITY
THICKENING
1.0
2.0
3.0
4.0
5-0
6.0
7.0
8.0
SLUDGE CONCENTRATION, *
Figure 28. Flux concentration curve for New Providence, NJ» wet-weather trickling filtration primary
sludge with chemicals (333 kg/m ton of lime and 5«0 kg/rn ton of magnifloc 837A polymer)
-------
FlUX CONCENTRATION CURVE
TANGENT TO THE FLUX CONCENTRATION CURVE
AT THE SELECTED SLUDSE CONCENTRATION
SHOWS THE ALLOWABLE MASS LOADING RATE
FOR GRAVITY THICKENING
0
SLUDGE CONCENTRATION, %
Figure 2g. Flux concentration curve for New Providence, NJ, wet-weather
secondary sludge (without chemicals)
-------
--4
VJ1
-------
a
-a
•0
C
(82.0)
350
(71.75)
300
(61.5)
250
(51.25)
200
(41.0)
150
. (30.75)
(9
Z
o
<
o
100
(20.5)
50
(10.25)
95% RECYCLE RATE
1.0 kg/m ton
MAGNIFLOC 837A
POLYMER AND 192
kg/m ton LIME
,1'
A
HO CHEMICALS
1601 RECYCLE RATE
901 RECYCLE RATE
1.1 kg/m ton HAGNiFLOC 837A
POLYMER AND 288 kg/m ton LIKE
i RECYCLE RATE, 0.5
kg/m ton MAGNIFLQC 837A
POLYMER AND 96 kg/m ton
LIME
2468
ESTIMATED SCUH CONCENTRATION, %
10
Figure 31« Flotation thickening test results for
New Providence, NJ, wet-weather primary sludge
76
-------
350
(71.75)
<6,.5>
30°
250
^(51.25)
X
n
•o
«*-
O"
200
5(41.0)
I50_
e(3i.7S)
O"
M
100.
I (20.5)
o
00
5C-
(JO. 25)
280% RECYCLE RATE
RECYCLE
RATE •
RECYCLE RATE
ESTIMATED SCUM CONCENTRATION, *
Figure 32. Flotation thickening test results for New Providence, NJ,
wet-weather secondary sludge (without chemicals)
77
-------
kOQ
(82.0)
350
(71.75)
300
(6.JS)
250
(51.25)
fr
T3
4*
o- 200
»•»•*
(9
•a
1 150
y (30.75!
ID
cj
- 100
| (20.5)
_l
t/l
50
(10.25)
0
DMA
L
"
-
a
-
-
GNIFLOC 837A POLYMER 0.3 kg/m ton
IME 5.9 kg/m ton
.
M
;
\l MAGNIFLOC 837A POLYMER 0.6 kg/m ton
\ LIME 12.5 kg/m ton
I
1
^ |[j,
i 1
• \
D * i
i |
*
* MAGNIFLOC 837A POLYMER 0.5 kg/m ton
LIME 9.8 kg/m ton
a
Figure 33*
k 5 6 7 8
ESTIMATED SCUM CONCENTRATION, %
Flotation thickening results for New Providence, NJ, wet-
weather secondary sludge (with chemicals)
78
-------
Table 20. CENTRIFUGE TESTING RESULTS FOR NEW PROVIDENCE, NJ,
WET-WEATHER TRICKLING FILTRATION PRIMARY SLUDGE
Test
No,
10
11
12
13
14
15
16
17
18
19
20
21
22
2J
24
25
26
27
28
29
30
31
32
33
Applied E
force, "G's"
1,000
1,000
1,000
1,000
700
700
700
700
400
400
400
400
1,000
1,000
1 ,000
1 ,000
700
700
700
700
400
400
400
400
Spin
time,
sec
30
60
go
120
30
60
90
120
30
60
90
120
30
60
90
120
30
60
90
120
30
60
90
120
Feed
solids,
rog/1
1,200
1,200
1,200
1,200
1,200
1,200
1,200
1,200
1 ,200
1 ,200
1,200
1 ,200
1,200
1,200
1 ,200
1 ,200
1 ,200
1,200
1,200
1,200
1,200
1 ,200
1 ,200
1 ,200
Chemical
none
none
none
none
none
none
none
none
none
none
none
none
837A+CaO
837A+CaO
8J7A+C8Q
837A+CaO
837A+CaO
837A+CaO
837A+CaO
837A+CaO
B37A+CaO
837A+CaO
83?A+CaO
337A+CaO
Dosage,
kg/a ton
none
none
none
none
none
none
none
none
none
none
none
none
13.4+2,670
13.4+2,670
13.4+2,670
13.4+2,670
13.4+2,670
13.4+2,670
13.4+2,670
13.4+2,670
13.4+2,670
13.4+2,670
13.4+2,670
13.4+2,670
Centrate
solids.
mp/l
313
206
208
222
550
338
234
3*o
992
516
449
545
320
325
361
200
207
216
215
212
237
187
162
178
Centrate
vo 1 ufne ,
ml
69
70
70
70
67
69
69
70
69
68
68
67
68
69
67
68
66
68
69
69
66
67
f?
68
Penetrations,
en
0.55
0.6
0.55
0.4
0.7
0.95
0.85
0.65
1.2
0.85
1.0
0.95
0.4
0,45
0.25
0.35
0.4
0.5
0.4
0.5
0.5
0.55
0.55
0.55
Sludae
depth.
cm
1.5
1.15
1.3
1.35
1-75
1.35
1.6
1.4
1.45
1.5
1.6
1.55
1.75
1.65
1.6
1.5
1-5
1.45
1.3
1.0
1.45
1.55
1.55
1-5
Cake
solids,
I
1.14
1.51
1.51
1.49
0.66
1.11
1.23
1.32
0.36
0.78
0,85
0.68
0,97
1.13
0.82
1.09
0.85
1.08
1.25
1.26
1.00
0.97
1.31
1.11
Penetration,
I
63
48
58
70
60
30
47
54
17
43
38
39
77
73
84
77
73
66
6?
50
66
65
65
63
Recovery,
8
73.9
82.8
82.6
81.5
54.1
71.8
80.5
71.6
17.3
57.0
62.5
54.5
73.3
72.9
69.9
83.3
82.7
82.0
82.0
82.3
80.2
84 k
86,5
85.1
Corrected
recovery,
*
70.6
76.9
78,1
78,6
51.4
63.6
74,6
67.2
14.5
52.4
56.7
4g.6
71.4
70.6
68.7
81.1
80.0
78,6
79.0
76.7
7*. 9
ao.s
82.8
81 3
-------
Table 21. CENTRIFUGE TESTING RESULTS FOR NEW PROVIDENCE, NJf
WET-WEATHER TRICKLING FILTRATION SECONDARY SLUDGE
oo
o
Test
'to.
,
2
3
4
5
6
7
a
3
34
35
36
37
36
39
to
ill
42
43
44
"•5
Applied f,
force, fi's
1,000
1,000
1,000
700
700
700
400
'(00
400
1,000
1,000
f ,000
1,000
700
700
700
700
-400
400
400
400
Spin
time.
sec
60
90
120
60
90
120
60
90
120
30
60
90
120
30
60
90
120
30
60
90
120
Feed
sol ids,
_mg/l _
25,000
25,000
25,000
25,000
25,000
25,000
25,000
25,000
25,000
25,000
25,000
25,000
25,000
25,000
25,000
25,000
25,000
25,000
25,000
25,000
25,000
Chemical
none
none
none
none
none
none
none
none
none
FeC I +S05N
FeC 1 JW05M
FeCK+gosn
FeCl |+905:i
FeCU+905N
FeCI^+905'J
Fed ?+905«
FeCU+?05N
FeCI^+IOSN
FeCI,+905H
FeCK+905N
FeCI*+?05H
nosatie.
k<]/ra ton
none
none
none
none
none
none
none
none
none
1458+40
1 458+40
»4 53+40
1458+40
14 53+40
!453+liO
1458+40
1458+40
1*58+40
1458+40
1458+40
) 4 53+40
Centrate
So3 ids.
rag/1
008
52S
658
1,300
1,050
637
1 ,4Qu
840
850
174
184
136
169
23)
165
ISO
137
252
119
157
187
Centrate
volume,
ml
38
43
44
38
39
41
33
35
36
43
46
43
50
39
44
43
44
37
34
40
4j
Penetration,
era
4.45
3.7
3-3
4.65
4.65
3.65
4,95
4.65
4.4
1.65
1.35
1.65
1-75
2.25
1.8
2.3
2.1
3-0
2.6
2.65
. 2-45
Sludne
denth.
cm
4.45
3.9
3-8
4.65
4.65
4.1
4.95
4.65
4.4
3 9
3-25
3.4!,
3.3
4.3
3.8
3.6
3-65
4.3
3. 95
4.05
3.9
fake
solids.
IV
b.o
5.8
6.0
4.9
5.1
5-4
4-3
4.6
4-7
s. a
6.4
7.2
7.5
5.2
6.0
b.u
6.0
4 9
4.6
5.3
5.0
Penetration,
>
0
5
16
0
0
11
0
0
0
58
40
52
47
48
53
39
42
30
34
34
37
Recovery ,
S
34.0
92. 4
97-3
34.4
95. E
97-4
94.0
36.6
96.6
99-3
99.2
99-4
99.3
99.0
99-3
99.2
99.4
98.9
99-5
99-3
25.2
Corrected
recovery.
?
oa
72.3
80.8
od
o3
7S.O
°a
o!
cP
93.9
90.5
93-1
92.1
91.9
93-1
90.4
91.2
87.7
89.4
&9-J
39.3
Denotes poor thlckanlnn performance for a scroll type centrlfune. See Appendix. 8 for procedure.
-------
solids of only 2% or less were achieved even with the aid of chemicals.
For the secondary sludge, cake solids of approximately 1.5% were achieved
with the aid of chemicals (ferric chloride and Magnlfloc nonionic poly-
electrolyte). Both samples showed poor scroll ability and hence basket
type centrifuge will be necessary for such sludges. No centrffugation
tests were run on gravity thickened primary sludge samples. Based on the
results of various other sludges evaluated in this study, it is Indicated
that significantly better centrifugation results on gravity thickened
sludges can be expected.
The vacuum filtration tests on both the primary and secondary sludge samples
were conducted on pre-sedimented samples. The feed solids concentrations
after sedimentation were 2.5% and 3.2% for the two samples respectively.
The test results are shown In Tables 22 and 23 respectively. Based on the
results of the Buchner Funnel tests, a combination of ferric chloride and
lime showed best filtration results for both sludge samples. Best cake dis-
charge characteristics were obtained with multifilament polypropylene fil-
ter cloth. Cake solids of nearly 281 were achieved for the primary sludge,
while solids concentrations of only 16 to 18% were achieved for the secon-
dary sludge samples under optimum test conditions. The optimum filter
yields for the two samples were approximately 18 kg/sq m/hr (3.5 Ibs/sq ft/
hr).
DryWeather Sludge Samples - A schematic of the dewateflng techniques in-
vestigated on the dry-weather sludge samples from the primary and secondary
clarlflers Is shown In Figure 3^. The present quantities of sludge being
discharged from primary and secondary clarlflers are 68 cu m (26,150 gal.)
per day respectively (Table 2). As mentioned earlier, these quantities are
presently discharged without regard to the sludge strength. Both sludge
samples procured for dewatering tests showed low solids concentrations of
0.38 and 0.46 respectively.
The flux concentration curves for the gravity thickening tests on the two
samples are shown In Figures 35 and 36. Both these curves represent the
test data without the addition of any flocculating chemicals, it was
found that flocculating chemicals did not provide any Improvement In the
gravity thickening performance. For primary sludge, solid concentrations
of only 2 to 3% were achieved at mass loading rates between 30 and 50
kg/sq m/day (6-10 Ibs/sq ft/day). These values compared to approximately
8% solids at mass loading rates up to 100 kg/sq m/day (100 Ibs/sq ft/day)
for wet-weather primary sludge. The results were poorer for secondary
sludge samples where a solids concentration of only 1% or less could be
expected at solids loadings below 20 kg/sq m/day (k Ibs/sq ft/day). The
dry-weather secondary sludge results were quite similar to the poor gravity
thickening results for the wet-weather secondary sludge discussed earlier.
The results of flotation thickening tests are shown In Figures 37 through
39. For primary sludge, scum concentrations of greater than 5% solids
could be expected at a mass loading rate of 65 kg/sq m/day (13 Ibs/sq ft/day)
with the use of 15.6 kg/m ton (31 Ibs/ton) of Dow C-31 polyelectrolyte and
at a recycle rate of 2301. However, for secondary sludge, use of chemicals
did not aid in flotation thickening as shown by a comparison of Figures 3d
81
-------
Table 22. VACUUM FILTRATION TESTING RESULTS FOR NEW PROVIDENCE, NJ»
WET-WEATHER TRICKLING FILTRATION PRIMARY SLUDGE
Feed Solids Concentration - 2.5%
CO
NJ Chemical
dosage,
kg/ra ton
Feel, CaO
*
54 160
54 160
54 160
54 160
54 16Q
Cycle
time.
mln
4
f,
2*
3
4
Pickup
time,
sec
£0
132
30
66
ae
Dry
time.
sec
120
148
60
73
98
Submergence
*
25
37.5
25
37.5
37.5
Yield, ,
kg/hr/m
13.35
11
17.7
18.2
17.1
Loading,
kg/a
0.89
1.10
0.59
0.91
1. 14
Cake
solids,
*
27.4
26.9
27-5
27.8
25.7
Fl It rate
solids,
mg/1
116
174
82
92
85
Filtrate
volume,
ml
420
570
265
430
550
Type of cloth
multl fl lament
polypropylene
nultl filament
polypropylene
multl filament
polyp ropy lane
mult! filament
polypropylene
nultl fl lament
polypropylene
Cake
Discharge
characteristics
Good
Good
Good
Good
Good
-------
Table 23. VACUUM FILTRATION TESTING RESULTS FOR NEW PROVIDENCE, NJ»
WET-WEATHER TRICKLING FILTRATION SECONDARY SLUDGE
Feed Solids Concentration - 31,500 mg/I
Chemical
dosage,
kg/m ton
Fed,
3
85
85
85
85
85
85
CaO
^
25k
254
254
254
254
254
Cycle
time.
min
4
k
6
2
3
5
Piekup
time,
see
60
88
132
45
66
110
Ory
tlme.
sec
120
98
146
50
73
122
Submergence
4
25
37.5
37.5
37.5
25
25
Vleld,
kg/hr/m
18.45
24,45
16.9
39-6
34.8
21.84
Loading,
kg/a*
1.23
U63
1.69
1.32
1.74
1.82
Cake
sol Ids,
'4
18.5
15.7
16.5
13.8
15.0
13.5
Fl let-ate
solids,
ma/I
231
184
IBS
546
44J
478
Filtrate
volume,
ml
460
sto
600
265
360
360
Type of cloth
mulclf 1 lament
polypropylene
raultlf Hament
polypropylene
mult If (lament
polypropylene
multlf i lament
polypropylene
mult 1 f 1 lament
polypropylene
mul tlf llanent
polypropylene
Cake
Discharge
characteristics
Good
Good
Good
Good
Good
Good
-------
PRIMARY
CLARIFIER
GRAVITY
THICKENING
FLOTATION
THICKENING
GRAVITY
THICKENING
GRAVITY
THICKENING
t
^
nnu r_ii Dm vuc
t
t
2.3 kg/m ton
CENTRIFUGATION
FERRIC CHLORIDE
"ton S LIME 58 kg
VACUUM
FILTRATION
SECONDARY
CLARIFIER
GRAVITY
THICKENING
FLOTATION
THICKENING
FERRIC CHLORIDE 2(6 kg/m ton
.CENTRIFUGATION
GRAVITY
THICKENING
FERRIC CHLORIDE
733 kg/m ton
VACUUM
FILTRATION
Figure
New Providence, NJ - bench scale dewaterlng tests (dry-weather)
-------
250
(51.25)
00
a
•o
Ml
-Q
-o
cr
M
"%.
O»
cs
z
a
o
200
(41.0)
ISO
(30.75)
100
(20.5)
50
(10.25)
FLUX CONCENTRATION CURVE
TANGENT TO THE FLUX COHGEMTRATIOM CURVE AT THE
SELECTED SLUDGE CONCENTRATION SHOWS THE ALLOWABLE
MASS LOADINS RATE FOR GRAVITY THICKENING
0 1.0 2.0 3.0 4.0 5.0
SLUDGE CONCENTRATION, %
Figure 35. Flux concentration curve for New Providence, NJ, dry-weather primary sludge
-------
oo
cr>
m
"0
cr
in
U»
-Q
ID
i
cr
in
cn
a
<
o
FLUX CONCENTRATION CURVE
TANGENT TO THE FLUX CONCENTRATION CURVE
AT THE SELECTED SLUDGE CONCENTRATION
SHOWS THE ALLOWABLE MASS LOADING RATE FOR
GRAVITY THICKENING
1.0 2.0 3.0
SLUDGE CONCENTRATION, %
Figure 36. Flux concentration curve for New Providence, NJ, dry-weather secondary sludge
-------
o*
Ifl
in
.a
n
•0
or
M
kOQ
(82.0)
350
(71.75)
300
(61.5)
250
(51.25)
200
(kl.Q)
i 150
5 (30.75)
100
(20.5)
50
(10.25)
225% RECYCLE RATE
OOW C-3t POLYMER 10. ^ kg/m ton
NO CHEMICALS
1501 RECYCLE RATE
230% RECYCLE RATE
DOW POLYMER C-31 15.6 kg/m
ton
Figure 37-
23^56
ESTIMATED SCUM CONCENTRATION, I
Flotation thickening test results for New Providence,
NJ, dry-weather primary sludge
87
-------
400
(92,0)
350
(71.75)
300
•>: (61.5)
10
•a
cr
< 250
£ (51.25)
>»
1
V
M
U)
200
(41.0)
ca
150
S (30.75)
V)
too
(20.51
50
(10.25)
301 RECYCLE RATE
951 RECYCLE RATE
65% RECYCLE RATE
2901 RECYCLE RATE
10
12
ESTIMATED SCUM CONCENTRATION, I
Figure 38. Flotation thickening test results for New Providence, NJ(
dry-weather secondary sludge (without chemicals)
-------
350
(71.75)
300
(61.5)!
-g
250
^ (51.25)1
tr
w
Irt
5 200
m
-Q
S"
C3
O
<
o
in
150
(30,75)
100
(20.5)
50
(10,25)
\ZO% RECYCLE RATE
DOW C-31 POLYMER 8.2 kg/m ton
Figure 39.
I 2 J k 5
ESTIMATED SCUM CONCENTRATION, I
Flotation thickening test results for New Providence, NJ,
dry-weather secondary sludge (with chemicals)
89
-------
and 39. Scum concentrations as high as 8 to 101 solids could be achieved
without use of any chemical aids at mass loading rates between 50 and 100
kg/sq m/day (10-20 Ibs/sq ft/day). The optimum recycle rates varied
between 200 and 300% for the two samples. Again, the dry-weather flota-
tion thickening results were similar to the wet-weather thickening results.
Centrifugatlon test results are shown In Tables 2k and 25 for the two
samples. For the primary sludge sample, these tests were conducted on a
presedltnented sample at a feed solids concentration of 1.8%. Optimum
results were shown without the use of flocculating chemicals and cake solids
up to 13% were achieved under optimum test conditions (700 to 1000 G and
60 to 120 seconds spin time). These results are In sharp contrast to the
primary sludge samples during wet-weather, and confirm the earlier statement
for the primary wet-weather sludge sample whereby it was indicated that
significantly improved centrifuge performance may be expected for pre-
thlckened sludge samples. The tests on the secondary sludge samples were
conducted without pre-thicken Ing. Generally poorer results were shown as
cake solids of only 2% or less were achieved. However, this performance
may again be attributed to the dilute nature of the raw sample and signifi-
cantly improved results can be expected on pre-thlckened samples.
The vacuum filtration tests on both the primary and secondary dry-weather
sludge samples were conducted on pre-thickened samples, similar to the
wet-weather filtration tests. The feed solids concentrations after sedimen-
tation of the raw samples were 2.61 and I.3% respectively. The test results
are shown in Tables 26 and 27. A chemical combination of lime and ferric
chloride again provided optimum filtration results similar to the wet-
weather sludge filtration tests. Best cake discharge characteristics were
achieved with a 3 x 1, 1001 olefln mult!filament filter cloth for both the
sludges. Cake solids of 20 to 22% for primary sludge and 12 to 141 for
secondary sludge were achieved under optimum conditions. The optimum
filter yields varied between 13 and 35 kg/sq m/hr (2.6 and 7 Ibs/sq ft/hr)
for primary sludge and between 10 to 15 kg/sq m/hr (2-3 Ibs/sq ft/hr) for
the secondary sludge. These results are very similar to the corresponding
results for wet-weather sludges and indicate amenability to dual (dry/wet)
treatment of sludges,
Treatment Costs for Biological CSO Sludgei (Wet-Weather)
A summary of the estimated area and cost requirements of the various de-
watering techniques for wet-weather biological treatment sludges is shown
in Table 28. Again, the total costs Include amortized capital, operating
and hauling costs of ultimate residuals as shown in Appendix C. it is
evident that for biological sludges, generally, vacuum filtration dewatertng
in combination with gravity or flotation thickening provided most effective
and economic method of handling such sludges. However, the economic results
for centrlfugatlon In combination with gravity or flotation thickening
were quite close to the corresponding costs for vacuum filtration. Because
of the poor scrollability of biological sludges, cost estimates for centrif-
uges were based on basket type centrifuge units. A more detailed discussion
of the overall sludge treatment needs is made in Section VItI of this report
after discussion of the bleed back concept in Section VII.
90
-------
Table 2k. CENTRIFUGE TESTING RESULTS FOR
NEW PROVIDENCE, MJ, DRY-WEATHER PRIMARY SLUDGE
Test
No.
!
2
3
4
S
6
7
8
9
10
1)
12
13
14
IS
16
17
18
-IS
20
Applied S
force, '6'i'
1 ,000
1 ,000
1 ,000
1 ,000
1,000
7DO
700
700
700
wo
400
400
700
700
700
700
400
400
400
<|OQ
Spin
time,
sec
120
120
90
60
30
120
go
60
30
120
go
60
120
go
60
30
120
90
60
30
Feed
solids,
mg/1
17,500
17,500
17,500
17,500
17,500
17,500
17,500
17,500
17,500
17,500
17,500
17,500
17,500
»7,500
17,500
17,500
17,500
17,500
17,500
47,500
Chemical
None
C31
C31
C31
C31
C31
C31
C31
C31
C31
C3I
C31
FeCI3
FeCI,
FeClf
F«Cl|
FeCI*
FeCI^
FeClf
FeCIl
Centrata
Dosage, solids,
kg/in ton mg/l
(tone
2.29
2.29
2.29
2.29
2.29
2.29
2.29
2.29
2.29
2.29
2.29
5.?
5.7
5.7
5.7
5.7
5.7
5.7
5.7
31k
267
146
264
WO
132
188
246
510
200
290
250
94
130
122
158
156
146
292
142
Generate
volume, Penetration,
ml cm
65 2.45
65 0.9
63
64
61
65 t
64
61
62
63
64
61
63 (
60 (
61
57
58
57
50
57
.05
.0
.4
>-9
.2
,0
.45
,1
.4
.9
.75
).85
.1
.3
• 3
.45
.65
.3
Sludge
depth
cm
2 45
1.75
1 75
2.0
2.25
1.8
2.0
2,0
2.35
2.0
2.05
2.30
2.05
2.4
2.2
2.3
2.05
2.5
2.45
3-35
Sludge
depth
cm
2 45
1.75
1 75
2.0
2.25
1.8
2.0
2,0
2.35
2.0
2.05
2.30
2.05
2.4
2.2
2.3
2.05
2.5
2.45
3-35
Cake
solids.
*
12.9
13.0
10.9
11.8
9.2
13.0
11.8
9.3
9,8
10.8
11, S
9.3
10,9
C.7
9 3
7-2
7.7
7.2
5.2
7 2
Penttrat Ion,
*
40
48
40
50
37
50
40
50
38
45
29
15
63
64
48
54
42
33
3
43
Recovery,
4
98
98
99
9C
97
99
99
99
97
S9
96
99
99
99
99
99
99
99
98
99
Corrected
recovery,
1
go
91
90
91
88
92
90
92
88
90
87
82
95
95
92
92
90
69
76
91
-------
Table 25. CENTRIFUGE TESTING RESULTS FOR
NEW PROVIDENCE, NJ, DRY-WEATHER SECONDARY SLUDGE
Test Applied <5
Ho. force, "G's"
21
22
23
2E|
25
26
27
28
29
30
31
32
33
35
36
37
,000
,000
,000
,000
,000
,000
,000
,000
,000
,000
,000
,000
,000
,000
,000
,000
,000
38 700
39 700
40 700
41 700
42 1(00
43 400
44 400
45 400
Spin
time.
sec
120
120
90
60
1ZO
90
60
30
120
120
60
30
30
120
90
60
30
120
90
60
30
120
90
60
30
Feed
solids.
Dosage
Generate
sol ids,
% Chemical kg/m ton raq/1
4,620
4,620
4,620
4,620
4,620
4,P20
4,620
4,620
4,620
4,620
4,620
4,620
ii,620
4,620
4,620
4,620
4,620
4,62^
4,620
it, 620
4,620
4,620
4,620
li,620
4,620
None
Fed 3
Fed,
Fed;
Fed:
Fed*
Fed:*
Fed:
C-313
Fed,
Fed,
Fed:
Fed*
Fed:
Fed,
Fed*
Fed,
Fed,
Fed,
Fed*
Fen,
Fen;
Fed;
Fed;
Fed*
Hone
21.6
21.6
21.6
500
500
500
500
12.9
216
216
216
1,080
216
216
216
216
21f
?I6
21*
216
216
2lf
2IC
216
334
128
116
98
120
74
130
ioa
325
194
175
228
112
92
104
IOC
134
114
128
162
320
164
198
192
396
Centrate
volume,
ml
53
54
53
51
59
52
52
49
55
62
59
57
44
54
53
52
47
53
52
49
44
50
46
47
33
Pene fat Ion t
cm
2.75
2
2.5
3-1
1.05
1.25
2.15
3-05
3.0
1.35
2.1
3-3
3.5
1.25
2.05
2.45
3-55
l.'i
1.60
3.95
2^15
3.65
3-9
5-3
Sludge
depth,
cm
2.75
3.0
2.85
3.1
2.0
2.85
3.05
3-05
3.0
2.8
2.85
3.3
3.5
2.85
3.1
3.2
3-55
3-05
3 4
3 45
4.0
3.4
3.65
3-9
5.3
Corrected
solids, Penetration, Recovery, recovery,
t % % *
.5
.6
.5
.4
.1
.5
.5
.3
.6
.6
.1
.8
.1
.6
.5
.5
.2
.5
.5
.3
.1
,k
.2
.2
0.8
0
33
12
0
62
56
20
0
0
52
26
0
0
56
34
25
0
54
44-
13
0
37
0
0
0
93
96
97
98
97
9E
97
98
93
96
96
95
98
98
98
98
97
90
n "
96
93
96
96
96
91
0
86
78
0
92
92
83
0
0
90
83
0
0
92
58
85
0
92
39
78
C
87
0
0
0
-------
Table 27. VACUUM FILTRATION TESTINS RESULTS FOR
NEW PROVIDENCE, MJ, DRY-WEATHER SECONDARY SLUDGE
Feed Solids Concentration - 1.91
Chemical dosage,
kg/m ton r,,.,.
620
620
620
733
733
56?
56?
567
567
56?
CaO
0
0
0
0
0
212
212
212
212
212
time,
mln
5
5
3
5
t,
5
4
3
2
3.5
P I ckup
time,
sec
110
75
45
75
60
75
60
45
30
30
Orv
*" r
time,
sec
122
150
90
150
120
ISO
120
90
GO
120
Submergence,
37-5
25
25
25
25
25
25
25
i5
14
, Yield,
kg/hr/m
7.48
7,38
9.92
7-09
7.66
6.23
8.73
15.16
16.86
11.46
Loading
kg/in
0.62
0.61
0.49
0.59
0.51
0.52
0.58
0.78
0.56
0.66
Cake
, solids,
*
9.8
10.3
10.1
11.5
13.2
12.6
12.8
13.6
12.9
13.8
I7! 1 1 rate
solids,
67
41
47
37
21
166
79
51
73
45
Fl 1 1 rate
vo\ ume ,
ml
430
360
240
400
285
355
335
445
340
365
i»_», _.
UUK0
Type of cloth Discharge
characteristic-;
3 X 1 twill olefln
100% imiltlfl lament
3 X 1 twill olefln
100% multl fi lament
3 X I twill olefln
1003; multl filament
3 X 1 twill olefln
100% mult If I lament
3 X 1 twill olefln
100% rajl tl filament
} X 1 twill olefln
100% multlfllament
3 X 1 twill olefln
100% multlfllament
3 X \ t*m olefln
100% multlfllament
3X1 twill olefln
100% multlfnament
3 X 1 twill olefln
100% multl filament
Poor
Good
Fair
Good
Good
Good
Good
dooti
Good
Good
-------
Table 28. SUMMARY OF AREA AND COST REQUIREMENTS FOR
WET-WEATHER BIOLOGICAL SLUDGES UNDER OPTIMUM TREATMENT CONDITIONS
Site.
Kcnosha,
U1
Sludge Toti
sol Ids, Area , a no
S stj ft
Gravity
Thickening 1 1593
Flotation
ThlcKenlng 3 W3
Centrifuge*!™ 9 205
Vacuum
Filtration 15 61%
(sq m) cost"
(US) 520
Ci3) 186
(19) 90
(57) 79
^"rfmary sludge
5l
uat
. J/yr
,700
,600
,100
,800
Sludge
solids,
*
8
6
13b
27. 5b
Area ,
172
151
205
323
{sq m)
£16)
(.4)
(19)
(30)
Total
annual
cost , $/yr
21
32
24
18
,100
,500
,300
,600
Secondary sludge
Sludge
sallds> Area,
X sq ft Uq m)
-------
Table 26. VACUUM FILTRATION TESTING RESULTS FOR
NEW PROVIDENCE, NJ, DRY-WEATHER PRIMARY SLUDGE
Feed Solids Concentration - 2.6%
Chemical dotage, Cyc)(.
Fed
206
206
206
303
15*1
CaO
58
58
38
58
58
I IIIIC ,
inin
5
2
2
2
2
Pickup
y * _—
1 1 ina ,
sec
75
30
30
30
30
Dry
fci —^
Cl BiO ,
sec
150
60
60
60
60
CithnwB vfi^ftf-m. V t m. 1 A
aUDmeryftneCp t le |af „
I kg/hr/ni
25
25
25
25
25
18.5
33.8
34.08
28.04
12.54
Cake
1 n*A t n« urn 1 t AT:
UDAui "9 * **" ' * *"* f
ki/m *
1.55 22.8
1.13 20.1
1.13 21.5
0.93 14.5
0.41 17.2
Filtrate
„ _ I * j_
sol ids ,
73
84
68
263
117
Filtrate
vol ume ,
nl
830
470
555
175
330
Type of cloth
3 X 1 twill olefln
100% rtiultiflUment
3 X 1 twill olafln
1002 multlfilnment
3 X 1 twill olefin
100% multl fl lament
3 X 1 Mill olafln
100% multlfl lament
3 X 1 twill olefln
100% multlfi lament
Cake
Discharge
cha rtcte r 1 $ 1 1 cs
Blinds
Poor
Good
Poor
Good
-------
SECTION VII
PUMPBACK/BLEEDBACK CONCEPT AND ITS APPLICABILITY
The determination of the efficiency of various sludge thickening and dewater-
Ing techniques for treating the sludges arising from combined sewer overflow
treatment processes has been the main thrust of this research activity.
However, the feasibility of actually pumping back or bleeding back these
on-slte sludges to existing dry-weather treatment facilities must also be
considered. By controlled pumpback or bleedback of the CSO treatment
residuals, additional cost of the on-site sludge treatment facilities may be
avoided or minimized. At the dry-weather treatment plant, the diluted
sludge can then be removed In the grit removal, primary sedimentation, or
secondary treatment processes and become part of the treatment plant sludge.
In cases where the combined sewer overflow treatment facilities are located on
the grounds of the municipal wastewater treatment plant, the question that
has to be resolved Is whether the existing sludge handling facilities (perhaps
with unused capacity) can be used for the combined sewer overflow treatment
sludges, or If separate facilities of a different type have to be constructed.
A typical mode of operation of a pumpback or a bleedback system would consist
of monitoring Instrumentation that would measure the flow rate and solids
handling capacity at the treatment plant and feed this information back to
the sludge holding facilities. When the capacity at the treatment plant is
sufficient, the tanks automatically drain, or are pumped If necessary, to
the interceptor sewer. Any significant increase In the flow rate at the
treatment plant due to a rainfall or any other cause would be sensed and the
sludge draining would cease.
LOADING ON THE DRY-WEATHER PLANT
When the sludge enters the sewerage system it will be diluted significantly
by the dry-weather flow. The resultant Increase In suspended solids concen-
tration at the dry-weather plant will be a function of the 1) concentration
of the sludge Itself, 2) the amount and rate of sludge draining, 3) the dry-
weather sewage suspended solids concentration, and k} the dry-weather flowrate.
The primary effect on the treatment plant once the sludge has reached the
treatment plant will be measured by 1) the change In hydraulic loading,*
2) the change in grit and solids loading, and 35 the effect of slug loadings
of toxic materials such as heavy metals or pesticides on the treatment pro-
cesses (especially biological). The secondary effect on the treatment plant
-------
Is I) the Increased sludge production which must be handled by the existing
solids handling facilities and 2). the possibility of any disruption of the
digestion process due to any slugs of heavy metals or pesticides or even
grit if it were to get past the grit chambers into the primary sedimentation
tanks.
To Illustrate the puntpback/bleedback concept a hypothetical example Is
presented. Listed below are the criteria for a typical city, assuming that
some type of combined sewer overflow treatment facility exists along with
a conventional activated sludge treatment plant for dry-weather flow.
Sewered population 100,000 persons
Treatment plant design capacity 94,625 cu m/day (25 mgd)
Average dally flow 75,700 cu m/day (20 mgd)
Gross digestion volume 7400 cu m (300,000 ft3}
Sewered area 4050 ha (10,000 acres)
Combined sewer area 2025 ha (5000 acres)
Overflow from a 2.5 cm (1.0 in) rain 246yQ25 cu m (65 million
Sludge produced (assuming 200 mg/1 solids gallons)
removed) 49,485 kg (109,000 Ibs)
Sludge volume at 2$ concentration 2460 cu M (0,65 million
ga11ons)
* Assuming approximately 501 of the rainfall results In overflow.
If the 2460 cu m (0.65 million gal.) were bled'back to the treatment plant at
a constant rate over a 24 hour period, .this would be an average increase in
flow rate of only 3*25%. However, the average Increase in solids loading
would ,be 3381. Figure 40 contains two graphs, the top shows a typical dry
weather diurnal flow pattern with the additional flow due to the bleedback
also shown. The bottom graph shows the dry-weather solids loading and the
solids loading due to bleedback. A constant raw suspended solids value of
200 mg/1 was used in determining the dry-weather solids loading.
The significant fact in Figure 40 is that although the Increase in hydraulic
loading at the dry-weather treatment plant fs negligible, the solids loading
Is significant. Based on the hypothetical data used to calculate the graphs
In Figure 40, the average suspended solids concentration In the raw flow
during the period of bleedback would be 870 mg/1. If this concentration would
cause significant solids deposition in the sewerage system, or If the added
solids would be In excess of what the dry-weather plant facilities could
handle, then bleedback would not be feasible. It may be possible to increase
the duration of bleedback to reduce the rate of solids loading but there are
limits on this time because of possible problems with sludge septlcity, odors,
necessity of aeration, and reduced amenability to certain thickening processes.
The possibility of settling occurring In the sewerage system during pump/bleed-
back will obv.lously depend on the hydraulic situation In the sewer to which the
97
-------
GRAPH DEPICTING INCREASE IN FLOW DURING PUMPBACK/BLEEDBACK
94,625
(25)
87,055
(23)
79,^85
71 .915
09)
64,345
3 (17)
56,785
(15)
r- ——i
DRY-WEATHER FLOW PLUS
PUMPBACK BLEEDBACK
ORY-WEATHER FLOW ONLY
47.7
(105)
43.6
(95)
39.1
(85)
13.6L
(30)
4.5
(10)
SRAPH DEPICTING INCREASE IN SOLIDS LOADING DURING PUMPBACK/
BLEEDBACK
SOLIDS LOADING DURING BLEEDBACK
DRY-WEATHER SOLIDS LOADING
8 10
8 10 M
Figure 40. Graphs depleting the Increase fn hydraulic loading (top) and
solids loading (bottom) during pumpback/bleedback to the treatment plant
-------
produced sludge Is pumped or bled. it Is common practice for most sewers to
be designed with a velocity of at least 0.6 cm/s (2 fps) to prevent solids
deposition. However, In larger Interceptor sewers at low flow, velocities
can go below 0.6 cm/s (2 fps). In addition, particles having specific
gravities significantly greater than 1.0 and with relatively large diameters
require velocities In excess of 0.6 cm/s (2 fps) to prevent settling. The
velocity required to keep a particle in suspension Is a function of both
particle specific gravity and diameter as designated below (23).
/
Required velocity » / -s- g (s-1) Dg
where: 8 » dtmenslonless empirical constant
f « friction factor (0.025 for a full pipe)
g « acceleration due to gravity
s - specific gravity
Dg «* particle diameter to b© transported
It should be noted that required velocities to keep a particle In suspension
change 1) with a change in diameter at a constant specific gravity and 2) with
a change in specific gravity at a constant diameter. In many cases velocities
of greater than 0,6 cm/s (2 fps) can be required, and these Instances may
arise with sludge being drained back to the sewerage system. Actual velocities
required to keep materials in suspension have been determined. Table 29 has
been developed by the American Society of Civil Engineers and contains the
various velocities required to prevent deposition of materials, some of which
may be analogous to sludge being pumped or bledback (23,24)
Table 29. VELOCITIES REQUIRED TO PREVENT SOLIDS DEPOSITION
water transporting
Clear water colloidal silts
Material
Fine sand, non-colloidal
Sandy loam, non-colloidal
Slit loam, non-colloidal
Alluvial silts, non-colloidal
Ordinary firm loam
Fine gravel
Stiff clay, very colloidal
Alluvial silts, colloidal
m/s
0.457
O.S33
0.609
0.609
0.762
0.762
1.14
1.14
f/s
1.50
1.75
2.00
2.00
2.50
2.50
3.75
3.75
m/s
0.762
0.762
0.914
1.067
1.067
1.524
1.524
1.524
f/s
2.50
2.50
3.00
2.50
3.50
5.00
5.00
5.00
Even if the excess solids passed through the sewerage system and settled in
primary sedimentation, and a concentration of 5% were achieved, It Is doubtful
99
-------
that this amount of sludge could be removed. At 5% this would amount to a
volume of 980 cu m (35,000 ft3), and tf pumped to the digester in a 2k hour
period this would displace over 101 of the digester contents. This does not
Include the additional solids that may be produced In secondary treatment by
conversion of the soluble BOD associated with the purnp/bleedback into btomass.
Furthermore, as pointed out earlier in this report, the volatile percentage of
the sludges produced at these combined sewer overflow treatment sites appears
to be below 60%. This means that the digestion of this material will probably
be very inefficient and have a minimum impact on reducing the putresclblllty
of the sludge.
Obviously, the hypothetical example discussed here is applicable only to
itself. Each application will be unique and must be studied as such. In
some applications the combined sewer area may be a smaller portion of the
total area and the additional solids loading would not be a significant
addition, or perhaps in some applications the primary removal and sludge
handling facilities may be sufficient to handle the increased load. It should
also be remembered that even If the present sludge handling facilities at the
dry-weather treatment plant are of insufficient capacity, it may be more
economical from a capital and operating cost perspective to build additional
facilities at the dry-weather plant rather than at the combined sewer overflow
treatment site.
TOXICITY CONSIDERATIONS
Toxtcity to a biological treatment system as a result of pumpback/bteedback
of sludges produced from combined sewer overflow treatment must also be
considered. The primary concern is the heavy metals and pesticides which are
concentrated in the sludge, it Is difficult to determine what the specific
limiting values of certain heavy metals entering a sewage treatment plant
would be. The toxicity can be reduced by other chemicals which may precipitate
the metals, form organo-metallic compounds, or by combining with other metals
to have an antagonistic effect. Conversely the toxlctty may be increased by
other cations having a synerglstlc effect (25,26).
Many articles on the subject of metal toxicity to biological treatment
processes have appeared In the literature. Since most data were developed in
laboratory tests, some for continuous operations and some for batch, there is
a variance In reported values. It has been reported (25) that for sewage
treatment bacteria (as found in the activated sludge process) silver and nickel
are the most toxic to sewage bacteria, with no bacterial growth occurring
above 25 mg/l of either element. Copper and chromium were found to have no
effect on sewage bacteria in concentrations lower than 25 mg/l, but were
highly toxic at 100 mg/l. Zinc toxicity was considered moderate, with no
toxicity effects at less than 100 mg/l concentrations.
Barth, et al (27) conducted extensive laboratory tests simulating an activated
sludge plant. Reductions In aerobic treatment efficiency on a continuous
dose basis were found at the levels listed below, it was also concluded that
the activated sludge process could tolerate, with only about a 5^ decrease In
efficiency, concentrations of chromium, copper, nickel and zinc up to 10 mg/l,
either singly or In combination. An Interesting finding of this study was
100
-------
that although the threshold levels (those concentrations at which an effect
on treatment can be noticed) may be low, e.g. 1-2 rog/J, there Is a plateau
effect being realized for a manifold Increase In concentration. Figure 4!
Illustrates this point.
Metal
Hexavalent chromium
Copper
Nickel
Zinc
Concentration tn
influent sewage
10 mg/1
I mg/1
1-2.5 mg/1
5-JQ mg/1
o
ui —
500 mg/1
75 mg/1
>50 -<200 mg/l
160 mg/1
101
-------
TABLE 31. DISTRIBUTION OF METALS THROUGH THE ACTIVATED SLUDGE PROCESS
(CONTINUOUS DOSAGE)
o
UJ
Outlet
of metal
fPH
Primary sludge
Excess activated sludge
Final effluent
Metal unaccounted for
Average efficiency of process in
removing metal
Range of observations
Cr (VI)
(15 rog/0
2.k
27
56
15
kk
18-58
Cu
(10 mg/1)
9
55
25
15
75
50-80
Ni
(10 rng/l)
2.5
15
72
11
28
12-76
Zn
(10 mg/1)
14
63
11
12
80
74-97
-------
Other reported metal toxicity levels to the activated sludge process from
various studies Include 10 mg/1 for nickel (28) and 16.0 mg/1 for nickel
(NISOij), 0,40 mg/l for copper (CuSOl^), and 0.23 mg/1 for chromium (CrCla) (29).
Although chromium has been the subject of many toxtcfty studies (-30,31,32), a
wide range of values have been reported at the maximum allovable limits, e.g.
up to 250 mg/l. However, It Is agreed that reduced chromium has little effect
on treatment and that hexavalent chromium Is toxic, but at much higher concen-
trations than the other common heavy metals.
A notable effect reported (n most studies Is the Inhibition of nitrification
by the heavy metals. Values In the range of 1-2 mg/1 of metals, even though
not toxic, may completely stop nit IfIcation. This could have an important
effect on any breakpoint chlorlnatlon step that would follow final settling
or the oxygen demand on the receiving body of water when nitrification begins.
Just as Important and perhaps even more critical than the effect of the heavy
metals on treatment Is the effect on digestion. Limits of 1 mg/1 for copper,
cyanide, and chromium, and 2.5 mg/1 for zinc and nickel have been recommended
as maximum concentrations for raw sewage subject to sludge digestion (33).
Table 30 illustrates the various reported maximum limits for raw sewages
subjected to sludge digestion.
Table 30. TOXIC LIMIT FOR METALS IN RAW SIWAGE
SUBJECT TO SLUDGE DIGESTION (34)
Reference No,**
Metal , mg/1
Chromium
Cyanide
Copper
Iron
Zinc
Nickel
1
5.0
2.0
1,0
5.0
2
5.0
1.0
1.0
5.0
3° % 56789
0.05 1.0 1.5
0 0.1 1-1.6
0.30 0.2 1.0 0.7
0.3 0.3 >5.0
2.0
a. See Reference 3^* for references,
b. For streams and sewers.
Various sources (32,3^,35) have noted that heavy metals in the feed to a
digester will concentrate In the digested sludge, It appears that when
concentrations approach the 1000 mg/l level of heavy metals, digester failure
may be realized. The Barth study (27) mentioned earlier traced the fate of
heavy metals through the activated sludge process and the results are summar-
ized In Table 31.
102
-------
TABLE 31. DISTRIBUTION OF METALS THRQUSH THE ACTIVATED SLUDGE PROCESS
(CONTINUOUS DOSAGE)
Outlet
Percent
of metal
fed
Primary sludge
Excess activated sludge
Final effluent
Metal unaccounted for
Average efficiency of process fn
removing metal
Range of observations
Cr (VI)
(15 mg/1)
i.k
27
56
15
W
18-58
Cu
(10 mg/1)
9
55
25
15
75
50-80
Nf
(10 mg/1)
2.5
15
72
1!
28
12-76
Zn
(10 mg/1)
14
63
1)
!2
80
7A-97
-------
This same study listed the highest allowable dosages for raw feed to
anaerobic digestion as follows:
Primary Primary and
Metal sludge secondary siudge
Hexavalent chromium >50 mg/1 >§0 mg/1
Copper 10 mg/1 5 mg/1
Nickel HO mg/1 >10 mg/1
Zinc 10 rng/1 10 mg/1
One of the most Important conclusions relative to the question of the feasi-
bility of bleeding combined sewer overflow treatment sludges containing heavy
metals back to the treatment plant Is the fact that if a digester fails, it
completely fails. Unlike the activated sludge process which can have a
reduction In efficiency caused by the presence of metals, the anaerobic
digestion process will continue to operate at very close to normal efficiencies
until the critical level has been reached at which point digester failure
wi 11 occur•
Table 32 has been developed showing the concentrations of certain heavy metals
in the sludges resulting from treatment at the various combined sewer overflow
sites. As seen by the data in Table 32 some of the sludges do contain heavy
metals In excess of the toxic concentrations discussed earlier, if these
sludges are bled back to the treatment plant resulting In a significant concen-
tration dilution, the toxlclty dangers are greatly reduced. However, It must
also be realized that the above sludge samples only represent one event from
each site and are not truly representative of a complete year of operation.
In addition, the synergistic effect of these various metals cannot be fully
predicted nor can the effect of the possible shock loading on the biological
treatment process be predicted without the use of empirical methods. These
types of methods are strongly recommended when the concept of sludge pump/
bleedback Is being considered.
Therefore, it Is Indicated that It may be more feasible to thicken and dewater
the sludge on site rather than pump/bleedback these residuals to the treat-
ment plant. However, the problem of ultimate disposal remains. If It Is
found that a sludge can be brought up to a 201 solids concentration, the trans-
portation costs of conveying this sludge to a place of ultimate disposal will
be greatly reduced. However, this Is based on the assumption that the sludge
can be disposed of without any form of digestion. If digestion of some type
Is required (e.g. anaerobic digestion, heat treatment, wet oxidation) then the
logistics of concentrating the solids, foJlowed by transport to a digestion
process, followed by further dewaterIng become questionable. Therefore, on the
following pages the combined sewer overflow treatment site studies are analyzed
for the feasibility of on-slte treatment of the residual sludges resulting
from treatment as compared to solids pump/bleedback or other alternatives.
-------
Table 32. HEAVY METAL CONCENTRATIONS IN THE SLUDGES
RESULTING FROM COMBINED SEWER OVERFLOW TREATMENT
Site
Racine, Ul
Kan ley Road,
>IIlw. , Wl
O
vn San Francisco,
Cal rfornia
Philadelphia,
Pennsylvania
tenosha, Wl
Hew Providence,
New Jersey
Humboldt Ave.
Hilw., Wl
Cambridge,
Hassachu setts
Type of
treatment
Screenlnq /Dis-
solved Air
Flotation
Screen liKj/Dl s-
solved AI f
Flotation
Dissolved Air
Flotation
Screening
Contact Sta-
btl izatlon
TMekl ing
Filter
Storage Tank
w/Htxtng
Storage
Type of
sludge
Backwash and
Float
Float
Backwash
Return
Activated
Primary
Sed Imentat ion
Secondary
Clarification
From Set tl inn
Test
Settled in
Tank
Tota 1
solids Zinc
9769 16.0 1638
42700 36.5 855
2400 17 708
8660 10.3 Hfi9
0527 61 7154
2010 1,4 694
25500 33 I2<"<
18900 15.1 79S
126.100 120 49?
Lead Copper
fnq/1 raq/kq roq/1 rag/kq
10.0 1023 4.7 481
7 164 10.2 248
38 1583 8.9 367
2!. 2 2448 1.73 200
4-5 528 12.4 1454
"1 *4g8 2 ngs
9 353 26 in20
39 ZOf-3 3.8 201
160 1261 it- 757
MIckel
ma/1
2.1
7.4
<2
2.5
4.5
2
20
3
1/1
215
173
«83
283
528
995
784
159
126
Chromium Hercufy
"9/1
2.1
6.4
40
0.45
10.9
1.5
63
4.6
33
mg/ko mq/l
215 0.022
ISO 0.09
1667 0.093
52 0.018
1278 0.022
746 0",202
2471
24J O.OJ1
26(1 1.55
mq/kq
2.3
2.1
3.9
2.1
2.6
100
2.7
0.01
-------
PHYSICAL TREATMENT
Milwaukee. WI - Storage
The Hymboldt Avenue storage tank In Milwaukee serves approximately 231 ha
(570 acres) out of a total of 1000 ha (17,300 acres) of combined sewer area
In the city. The unit Is designed to handle a 1.3 cm (0.5 In.) rainfall
utilizing 1§,l4Q cu m (4 million gal.) of storage. Thus, scaling up the
storage volume for the entire combined sewer area for a unit rainfall anal-
ysis (2.54 cm [1.0 In.]), a total storage volume of 912,185 cu m (241 million
gal.) would be required (36,37). Since this type of detention tank Is
equipped with mixers, the raw suspended solids concentration Is usually the
same as the pump/bleedback concentration. However, when the storage tank has
Its capacity exceeded, the mixers are not operated and the tank functions
similar to a sedimentation basin. When this occurs It becomes possible for
the pump/bleedback concentration to be higher than the raw discharge. The
average raw flow concentration of suspended solids at Humboldt Avenue is
estimated from operating records to be 192 mg/1.
The metropolitan Milwaukee area Is served by two sewage treatment plants—the
Jones Island Plant and the South Shore Plant. The Jones Island Plant is the
major plant and handles- almost alt of the city's combined sewer areas and
therefore, will be the subject of this feasibility analysis. The treatment
consists of primary screening (Instead of primary sedimentation) followed by
the conventional .activated sludge process, and chlorlnation. Primary sludge
(screenings) Is Incinerated. The waste activated sludge is gravity thickened,
vacuum filtered, and then processed Into fertilizer (Milorganlte). Data from
1970-1973 Indicated that the plant had an average daily flow of 650,263 cu m/
day (I7t«8 mgd) with average raw flow concentrations of 236 mg/1 suspended
solids, (153,517 kg/day [338,143 Ibs/day]), and 232 mg/1 IOD, (151,565 kg/day
1333,845 Ibs/day]).
Examining the concept of pump/bleedback of the contents of holding tanks
serving the entire combined sewer area over various durations of time, the
following percentage Increases in hydraulic loading and solids loading
would result,
Percentage Increases
Bleedback duratIon HydrauTIe Jpad^Ing^ Sol tds loadTIng
6 hrs 561 456
12 hrs 281 229
24 hrs 140 114
48 hrs 70 57
72 hrs 47 38
96 hrs 35 28
The Jones Island Plant can handle approximately 757,000 cu m/day (200 mgd),
therefore, the shortest duration of time In which the tank contents could be
pumped or bledback would be 96 hours. The sludge handling capacity at the
plant Is 199 metric tons per day (220 tons/day), and the facilities run near
106
-------
design capacity at all times. If the 96 hour pump/faleedback duration was
used the Increase In solids loading during this period would be 281.
Obviously the only way this additional solids loading could be handled Is
by constructing additional solids handling facilities for this excess material.
As part of this study a sample of the mixed contents In the storage tank was
taken and allowed to settle (see Section IV). The initial sample had a sus-
pended solids concentration of 181 mg/1 and the settled sludge compacted to
17^00 mg/1, occupying 0.91 of the original volume, resulting In a SVI of
50 ml/gm. If the solids were allowed to settle In this manner and the super-
natant pumped or bledback to the treatment plant, the hydraulic loading on
the dry-weather treatment plant would be almost Identical to that described
earlier for pump/faleedback of the entire contents. However, if the superna-
tant had a suspended solids concentration of 35 mg/1, as found in the settling
tests, the Increase In solids loading would be as follows:
8leedback duration % Increase In sol Ids loading
6 hrs 83
12 hrs 42
24 hrs 21
48 hrs 11
72 hrs 7
96 hrs 5
From this data It would appear that pump/bleedback to the dry-weather treat-
ment plant of the supernatant from settling would be possible from a solids
loading consideration over a period of more than two days. However, the
limiting factor In this case would be the hydraulic loading.
The settled sludge at a solids concentration of 1.741 would constitute a
volume of 8,213 cu m (2.17 rail lion gal.) resulting from a rainfall of 2.54 cm
0.0 In.). Direct hauling of this volume of sludge would appear to be both
very expensive {at 2.64c/liter [I0«/gal.] this would amount to $217,000) and
loglstically be Impractical. Therefore a further solids concentration step
would be required.
It was found from the bench scale testing (Section VI) that centrifugal ion was
the optimum dewaterlng method. It Is estimated that a settled sludge of 1,741
can be increased to 301 solids through centrlfugatton with polymer addition.
The centrate quality should have a suspended solids concentration of
approximately 110 mg/1 and the volume of centrate would be 7,835 cu m (207
million gal.). If this material were to be bledback, the Increase in solids
and hydraulic loading would not be significant. The solids at a 301 concen-
tration from the centrifuge will amount to a volume of 363 cu m (96,000 gal.)
which can be directly hauled to ultimate disposal at a reasonable cost,
probably less than $10,000 as opposed to the $217,000 cost of hauling the
raw sludge.
A unique consideration for Milwaukee Is the fact that their waste activated
sludge is converted to a commercial fertilizer known as Mllorganlte. Thus,
even If the sewerage system and solids handling facilities were adequate to
107
-------
handle the solids being bledback, the affect on the feritlzer production
process may be the most significant.
Cambr Idge,, HA - Detent Jon
The detention tank used to treat combined sewer overflows in Cambridge, MA
known as the Cottage Farm facility. Is actually a combination storage/
chiortnation and "rough1' sedimentation tank. The total holding volume of the
facility Is approximately 4,920 cu m (1.3 million gal.) with the storage/
chlorination tanks having a volume of 4,550 cu m (1.2 mil lion gal.). The
facility was designed to handle an average of 22 overflows per year ranging
from 1,514 to 302,800 cu m (0,4 to 80 million gal.) with an average overflow
volume of 23,845 cu m (6.3 million gal.) and a total of 151 of the overflow
being retained (12). The design criteria used In choosing the 15% total cap-
ture Is not fully understood. During actual testing of the facility the
average overflow was 33,308 cu m (8.8 million gal.).
The detention facility receives overflow from a combined sewer area of 13,500
ha (33,333 acres); however, there are many overflow polhts from this system
in addition to that discharging Into the detention facility. There are only
an additional 1,270 ha (3,136 acres) of combined sewers present which are not
connected in any way to the Cambridge overflow facility. Thus, there are a
total of 14,770 ha (3&»47Q acres) of combined sewered area out of a total of
105,624 ha (259,911 acres) of sewered area In the metropolitan area.
However, many of the combined sewers are In the process of being separated.
Using the unit rainfall analysis, 2.54 cm (1.0 In.) of rainfall will result
In an overflow volume (assuming 50% of the rainfall results In overflow) of
1.87 million cu rn (495.3 mil 1 ion gal.). Extrapolating on the 154 retention
volume used in the demonstration system, the resulting holding volume would
be 280,000 cu m (74.3 million gal.) and the bypass volume would be 1.59
million cu m (421,0 mil 1 Ion gal.). During the actual overflow period when
the sludge samples were taken and analyzed as part of this study, the raw
flow had a suspended solid* concentration of 165 mg/l and the effluent concen-
tration was 93 mg/l. Tr~ settled sludge had a concentration of 4,4%, Thus
If the same removal efficiencies and sludge concentrations are applied to
the unit rainfall analysis, a total of 161,191 kg (355,046 Ibs) of sol Ids
would be produced and 3,671 cu m (968,000 gal.) of sludge at a 4.41 concen-
tration would result. It must also be noted that this hypothetical example
Is based on the allowance that 1.59 million cu m (421 million gal.) of overflow
be discharged to the receiving body of water after chlorination, and the
suspended solids concentrations would be about 100 mg/1 in the effluent.
There are two treatment plants, the Deer island and Nut island plants, serving
the entire 105,624 ha (259,911 acre) metropolitan area (3W« However, the
Cottage Fai*m facility drains to an Interceptor sewer leading to the Deer
Island treatment plant. This plant has an average design capacity of
l»298,255 cu m/day (343 mgd), with a maximum 24 hour capacity of 2,172,590 cu m/
day (574 mgd). Treatment consists of screening and grit removal (located at
discrete headworks where the feeding sewers terminate), pre-chlorlnation,
pre-aeration, primary sedimentation, and post chlorination. Sludge treatment
consists of gravity thickening, anaerobic digestion and ocean disposal.
108
-------
The sludge handling capacity Is 1,514 cu m/day (0.4 mgd). During 1973 the
average dally flow to the Deer Island Treatment Plant was 1,298,255 cu m/day
(343 mgd} and the average dally sludge production was 1,200 cu m/day (0.3 mgd}
or 8*1,600 N (188,000 Ifas).
Examining the feasibility of pump/bleedback as opposed to on-slte treatment
of the sludge, It Is obvious that the existing plant could easily handle the
additional hydraulic loading of 280,000 cu m (74.3 million gal.) In a period
of 2k to 48 hours. The excess sludge handling capacity is approximately
18,160 kg/day (40,000 Ib/day). Thus pump/bleed back of the tank contents at
the rate of 18,160 kg/day (40,000 Its/day) would take approximately nine days.
Pump/bleed back at the rate of 22,700 kg/day (50,000 Ibs/day} and 27,240 kg/day
(60,000 Ibs/day) would reduce the required time to seven days and six days,
respectively. For overflows having lower solids concentrations the pump/
bleed back concept would take proportionately less time.
From the above calculations, It appears that the concept of sludge pump/
b feedback to the dry-weather* treatment plant may be feasible; however, It
must be noted again that only \$% of the total overflow Is retained and of
the 85% of the overflow still discharging to the receiving body of water, the
suspended solids concentration would be approximately 100 mg/l. It was also
assumed that the solids being pumped or bledback were held In suspension In
the sewerage system and did not settle out before reaching the treatment plant.
Although It has just been shown that pump/bleedback from this type of system
may be feasible In Cambridge from a hydraulic and solids loading standpoint,
the practicality of sludge pump/bleedback has not been examined. The Deer
Island treatment plant has a raw sludge volatile solids percentage of 70.4
and a digested sludge volatile percentage of 47.7. The volatile percentage
of the sludge analyzed from the Cottage Farm facility was 37*6 while the sus-
pended solids content of the settled sludge on the bottom of the detention
tank was 4.4%.
Another significant concern when studying the possibility of sludge pump/
bleedback that Is especially significant In the case of Cambridge Is the
heavy metal concentrations. With the exception of mercury, the heavy metal
concentrations are very high, and In some cases an order of magnitude higher
than the concentrations found at other sites. Below are the heavy metal and
analytical results:
b_as j s , mg/ 1 Dry basis, mg/kg
Zinc 120
Lead 160 j,26l
Copper 96 757
Nickel 16 126
Chromium 33 260
««rcury 1.55 0.0!
log
-------
Even If a 1:100 dilution were to occur during pump/bleedback, the synergtstic
effect of the heavy metals may upset treatment or digestion. Also If a
majority of the heavy metals were found to be in the partlculate form, then
the high concentrations would be very dangerous to digestion.
Centrlfugatlon of the settled sludge was found from the laboratory tests to be
the most optimum method of dewaterlng with an expected solids concentration of
201 at 901 recovery and a sludge volume reduction of 891. Thus, If the settled
sludge produced from the treatment of a 2»5^» cm (1.0 In.) rain, which Is
calculated to be 2,671 cu m (968,000 gal.) at a k,k% solids concentration,
were subjected to centrffugatlon, this would result In a centrate volume of
3,267 cu m (861,500 gal.) at approximately 2,500 mg/1 suspended solids concen-
tration of 20$ suspended solids. Assuming that ocean disposal of sludge is
permitted there would be two apparent alternative methods of solids handling.
These would be 1) sludge pump/bleedback to the sewerage system and treatment
plant or 2) direct disposal from the treatment site to the ocean. The only
way the second choice would be considered the most attractive alternative would
be If It was felt that pump/bleedback to the sewerage system would cause
severe solids deposition or If the bledback sludge would receive no benefit
by going through digestion and enly reduce the effective digestion volume
available for the normal treatment plant sludge.
If ocean disposal Is not permissible It will be necessary for not only the
sludge from the detention facilities but also the sludges from the dry~weather
treatment plant to be disposed of on land In some form. Therefore it would
be necessary to take the digested sludge now being transferred to sea and put
this sludge through a further dewaterlng step(s) before finally disposing of
it on the land. Again there are two alternatives If ocean disposal Is not
permitted. These are 1) sludge pump/bleedback to the sewerage system and
treatment plant with the sludge being thickened, digested, dewatered and
disposed of with the normal treatment plant sludge and 2} on site sludge
Centrlfugatlon followed by disposal with the centrate bledback to the sewerage
system. The objectives to the first alternatives are the same as In the
previous cases. However, assuming pump/bleedback Is feasible, the comparison
between the two alternatives Is whether It Is more economical to re-thicken,
digest, and dewater the sludge at the treatment plant or to centrifuge the
sludge at the detention tanks and dispose of It. Also, If the sludge
were to be sent back to the dry-weather treatment plant there ts the
possibility that some of the grit would not be removed by the existing grit
facilities and therefore additional classification equipment may be required.
It Is estimated that the operating costs for Centrlfugatlon would be 84^/cu m
(Q.32$/gal.) or 2$/kg (Q,9U/lb). This cost does not Include amortization of
the capital equipment costs. The operating cost would then have to be com-
pared to the handling costs at the treatment plant and the lesser chosen.
This type of comparison assumes, however, that land disposal of the centrl-
fuged sludge (at 37% volatile solids) would be permissible without any diges-
tion or oxidation step such as lime stabilization. It Is estimated that the
land disposal costs of the dewatered sludge would be approximately the same
for both alternatives. Some recent land (or alternative) disposal method
costs are listed below (39).
110
-------
Cost range _
Method $/kg "" l/lb
Pipeline to land 0.55 - 2.20 0.25 - 1.0
Trench to land 2.20 - 0.50 1.0 - 2.5
Rail to land 3.30 - 11.0 1.5 - 5-0
Drying 3-3 - 5-5 1.5 - 5.0
Compost 0.55 - 1.1 0.25 - 0.5
Incineration 4.4 - 5.5 2.0 - 2.5
Ph I \ adel phi a , PA - Scr een_| ng
Studying the feasibility of on site treatment compared to sludgepump/bleedback-
for the treatment system being tested in Philadelphia requires a great deal of
data synthesis since the flow capacity and drainage area of the study site Is
so small compared to the large combined sewer area in the City of Philadelphia.
The 23 ji micro screen ing unit In operation has an average design capacity of
iOOO 1/mln/sq m (25 gpm/ft2) and serves an area of 4.5 ha (11.1 acres). The
entire sewered area of metropolitan Philadelphia is §2,600 ha (228,600 acres)
with the combined sewer area being 64,800 ha (160,000 acres). Using a unit
rainfall analysis (1.0 inch [2.54 cml) with the assumption that half of the
rainfall results In overflow, the total overflow volume treated would be
8,221,020 cu m (2,172 million gal.). From actual operating data (40) it is
estimated that a backwash sludge volume of 520,000 cu m (137 million gal.)
would be produced at a suspended solids concentration of 2,000 mg/1 resulting
in a dry solids production of 1,045,000 kg (2,300,000 Ibs).
The metropolitan Philadelphia area is served by three sewage treatment plants—
the Northeast, Southeast and Southwest plants. The Northeast plant, which has
secondary treatment, has a design capacity of 662,375 cu m/day (175 mgd) and
in 1972 the average daily flow was 681,300 cu m/day (180 mgd). The sludge
from the plant is digested and then barged to sea for ultimate disposal*
During 1972 the average daily sludge production was 2,157 cu m/day (0,57 mgd)
with an average suspended solids concentration of 4.4? (94,962 kg £209,167 lb]).
The other two treatment plants consist of only primary treatment with a
cumulative design flow rate of 1,029,520 cu m/day (272 mgd), and an actual
cumulative flow rate of 991,670 cu m/day (262 mgd) during 1972. The sludge
from the Southeast plant Is piped to the Southwest plant where it is digested,
centrifuged, and then lagooned prior to barging. During 1972 the cumulative
sludge production was 3t255 cu m/day (0.86 mgd), with an average suspended
solids concentration of 5.41 (175,850 kg [387,310 Ibs]). The combined solids
handling capacity of the plant is estimated to be about 20% higher than
actually used in 1972. However, there presently exists a restriction against
increasing the amount of sludge barged to sea, which in effect means that
any additional sludge produced by the City of Philadelphia will have to be
disposed of by an alternate means.
Studying the feasibility of sludge pump/bleedback to the Philadelphia treatment
plants for digestion purposes, with alternate disposal being other than to the
Ul
-------
ocean, the increases In daily solids production are as follows for various
putnp/b leedback periods:
Purop/Bleedback duration
days %increase in solids
1 385
3 12?
5 76
7 54
9 42
It would appear that the shortest pump/bleedback duration possible, with a
slight overload on the dry-weather treatment plant, would be at least nine
days. This length of time would allow the possibility of odoriferous con-
ditions to occur and the solids would surely settle out In the backwash
holding tank (unless some means of aeration were Implemented). The settling
of the solids would have no significant effect (other than a higher pump/
bleedback concentration when the bottom sludge was being removed) provided
that provisions for the removal of the sludge were made.
Once the sludge Is digested at the treatment plant, the sludge in excess of
the present dally production must be split off and disposed of in some other
manner than ocean disposal. Regardless of the alternate type of disposal
chosen some type of dewatering step will most likely be utilized to minimize
disposal transportation costs. It Is calculated for Philadelphia's annual
rainfall of about 102 cm (40 In.) that the weight of sludge produced from
combined sewer overflow treatment by microscreenlng would be approximately
381 of the total annual sludge produced by the existing treatment plants.
Even if only half the annual overflow In the CSO area were treated, the
weight of sludge would still be 191 of "Philadelphia's annual production.
Since these additional dewatering facilities will be required either at the
combined sewer overflow sites themselves or on the grounds of the conventional
treatment plants, the major factors in deciding where the solids handling
facilities should be located would be the effect of the extra sol Ids on the
dry-weather plant (primary sedimentation sludge removal facilities), the ne-
cessity of digestion, and the cost of many separate sludge handling facilities
compared to one or two facilities located at the dry-weather treatment plants.
The obvious effect on the dry-weather treatment plant Is the increased solids
loading resulting tn an increased sludge volume which must be handled, thus
reducing the effective processing time for the conventional plant dry-weather
sludges. In the case of the combined sewer overflow sludge at the Philadelphia
test site, as Is the case for most sites, the volatile percentage of the
suspended solids was very low (25%). From this fact It can be seen that
conventional aerobic or anaerobic digestion will have little effect on reducing
the volatile content of this sludge. Thus, pumping or bleeding the sludge
back to the treatment plant will only displace volume tn the digesters and
reduce the effective digestion period of the conventional plant solids.
112
-------
One method of reducing the volume of wet weather sludge that would utilize
dry-weather sludge digestion facilities would be to degrit the wet weather
sludge prior to digestion, By degr!ttlngf much of the Inert material (that
not amenable to digestion) could be separated prior to digestion, thus greatly
reducing the ultimate volume of wet weather sludge to be handled. Obviously,
the optimum location for degrftttng this sludge would be at the wet weather
treatment site ItseJf, prior to pump/bleedback Into the sewerage system.
However, in actual application it would have to be determined If the highly
Inert wet weather sludge were discharged into the sewerage system and diluted,
would the inert material In fact be removed by the conventional grit removal
facilities at the dry-weather plant.
Regarding the matter of cost, It Is obvious In the case of solids handling
that the larger the capacity of the facility, the lower the unit cost will be.
However, in this particular case, if it Is assured that digestion is not
required for the combined sewer overflow produced sludges, it would stilt be
necessary to increase the sizes of the digestion equipment at the conventional
treatment plant unless degrlttlng facilities were constructed, since the
combined sewer overflow sludge would be mixed with the conventional plant
solids. If on-slte treatment of the solids were utilized, only thickening
and centrlfugatlon or vacuum filtration would be required. The solids could
then be transported to ultimate disposal.
The thickening process could serve a dual function by acting as a holding tank
(or vice versa), thus reducing the flow rate to the dewaterlng process and
resulting in a smaller capacity unit. Also, an economic study could be
performed to determine if a centrally located dewatering facility, with the
sludges from the combined sewer overflow sites being pumped to this site,
could be constructed and operated at a lower cost than discrete on-slte units.
Thus for the case of Philadelphia, a 1a-ge city with a high percentage of its
drainage area being served by combined sewers, a pump/bleedback of solids
produced from combined sewer overflow treatment does not appear to be the
obvious solution for handling the wet weather sludges. The optimum solution
can only be determined by comparing the specific costs of on-slte treatment
facilities versus the facilities needed for pump/bleedback. Figure 42
Illustrates the requirements of either alternative.
PHYSICAL CHEMICAL TREATHiNT
Racine, WJ|__^. Screentn^/Dissolved-AIr Flotation
The combined sewer overflow facilities In Racine, Wl from which sludge samples
were obtained for this study utilize the screenlng/dlssolved-alr flotation
process. The facilities consist of two adjacent but separate treatment plants
having capacities of 166,540 cu m/day (44 mgd) and 52,990 cu m/day (14 mgd)
for a combined capacity of 219,530 cu m/day '(58 mgd}. The units serve a
combined sewer area of 190 ha (470 acres) and are designed to handle a 1.27
cm/hr (0.5 in./hr) rainfall. The floated scum from the flotation units plus
the screen backwash Is retained In holding tanks until after the level In the
interceptor sewer leading to the treatment plant drops to such a level that
the tanks can be bled into the interceptor.
113
-------
Alternate 1
OH-SITE TREATMENT
Alternate 2
PUHP/8LEEDBACK
CSO SLUDGE
Holding Facility (Thickener)
Aeration
Centr Ifugatlon
_. ^_
*2
Stabilization (e.g. lime)
Ultimate Disposal
CSO SLUDGE
I
Holding Facility
4,
Aeration
Degr!tt1ngJ
V
Pump/Bleed back
I
Expansion of Primary Sedimentation
and Sludge Removal Facilities
Increase Digester Facilities
Ultimate Disposal
1. Depending on the design rate of the centrlfugatlon facility.
2. May or may not be needed, depending on regulations.
3. Degrlttlng facilities only required In one of the two locations shown,
Figure 42. Comparison of the requirements of
on-slte treatment of wet weather sludges versus
pump/bleedback to the dry-weather treatment plant
-------
The existing dry-weather treatment plant serving the City of Racine consists
of full primary treatment rated at 87,055 cu m/day (23 mgd) and secondary
treatment (activated sJudge) rated at 45,420 cu m/day (12 mgd). During the
calendar year of 1973 the average daily flow was 91,597 cu m/day (24.2 mgd).
Waste activated sludge Is returned to the primary sedimentation tanks where
It is settled out with the primary sludge and this sludge Is then anaerobic-
ally digested and vacuum filtered. The sludge Is then disposed of at a land-
fill site. The total volume of the two stage digestion system Is 7,570 cu m
(2 mg). In 1973 an average of 341 cu m/day (90,090 gal./day) of sludge at a
solids concentration of 7-48% resulting In 25,450 kg/day (56,080 Ib/day) of
dry solids was produced.
Scaling up the screening/dissolved air flotation units to treat the entire
combined sewer overflow area (284 ha [701 acres]) for a 2,54 cm (1.0 In.)
rainfall, the volume of overflow Is estimated to be 35,957 cu m (9.5 million
ga 1.).
From operating experience at the combined sewer overflow treatment sites In
1972 and 1973 U is estimated that 1,798 cu m (0.4? million gal.) of sludge
at a suspended solids concentration of 8,400 mg/1 would be produced. It
should be noted that the low solids concentration is caused by mixing the
floated scum and screen backwash. The floated scum alone can be expected to
have a solids concentration of 2.4$; however, the dilute screen backwash
(<3000 mg/1) causes the resultant sludge In the holding tanks to be of very
tow solids concentration.
Examining the feasibility of sludge pump/bleedback In Racine, it is obvious
that the 1,798 cu m (0.47 million gal.) of sludge at a concentration of
8,400 mg/1 could be handled by the dry-weather plant over a one to two day
period with no significant increase In flow. However, at the present time
the average daily flow to the treatment plant Is greater than design, so even
though the flow would be a small percentage increase, It would be flow above
the capacity of the plant. From a solids loading standpoint, the bleedback
of 14,982 kg (33,000 Ibs) of solids would represent the following percentage
Increase:
1 Increase
Pump/Bleed back Period, days j_n sol Ids
1 59
2 29
3 20
4 15
5 12
6 10
From the above data it would appear that sludge pump/bleedback would be
feasible over a period of greater than two days. However, at the present
time the digestion and solids handling capacity of the Racine treatment plant
Is rated at 22,700 kg/day (50,000 Ibs/day). Therefore, the plant is already
operating above capacity and theoretically could not handle any more solids,
thus necessitating on-sfte treatment of the solids. However, the Racine
treatment plant Is scheduled to undergo expansion in the near future and the
possibility of utilizing sludge pump/bleedback of the combined sewer overflow
115
-------
sludge would be greatly improved If the new solids handling faculties had
the capacity to handle these extra solids.
Making a rough economic comparison of the costs (capital and operating) of
building additional solids handling facilities at the existing dry-weather
plant versus building a centralized wet-weather sludge facility, the data gen-
erated by Burd (21) in 1968 can be used. Although these costs are outdated,
they are valid for use in making a relative comparison assuming equal escala-
tion of all costs. The additional dry-weather sludge handling facilities
(including thickening, digestion, dewatering and landftiling) are estimated to
have an annual capital and operating cost of l.l-5«5e/kg dry solids ($10-50/
ton) with an average cost of 2.8
-------
directly to a landfill site. However, as seen by the Philadelphia discussion
earlier, If a final study were being performed to decide which alternative
would be optimum, serious consideration would have to be given to the volume
and weight of sol ids In the backwash.
The sewage treatment facilities in Milwaukee were described earlier In this
section, and of course apply to this analysis also. In summary, the average
dally flow at the treatment plant is 651,020 cu m/day (172 mgd) with a dally
solids loading of 153,517 kg/day (338,1^3 lb/day} and the waste activated
sludge from secondary treatment Is ultimately marketed as fertilizer.
Using the unit rainfall analysis as the basis for comparison, it Is calculated
that a 2.5*» cm (1,0 In.) rainfall over the 7|000 ha (17,300 acres) of combined
sewer area would result In a treated overflow volume of 885,690 cu m (23*»
million gal.). From this It Is estimated that the flotation process would
produce about 3,200 cu m (0.85 million gal.) of sludge at a solids concentra-
tion of 3-651 for a total dry weight of 116,919 kg (257,630 Ibs). The
calculated increase in solids loading at the Jones island treatment plant
for various pump/bleedback durations would be as follows:
Pump/bleedback period I Increase
days _ __ In sol Ids
1 76
2 38
3 25
k 19
5 15
6 13
7 II
Based on the premises that the sludge could be transported to the treatment
plant In the sewerage system without settling, and that the solids could
be removed at the treatment plant, then the slight excess capacity for solids
handling at the Jones Island treatment plant would make pump/bleedback
feasible over approximately a four day period. Again It Is noted that the
screen backwash has not been considered.
However, the logistic feasibility of pumping or bleeding back this sludge
becomes questionable when It Is considered that the sludge has already
achieved a solids concentration of 3.651 in the flotation process. It appears
to be somewhat a wasted effort to dilute these solids in the sewerage system
and then use space In the gravity thickener at the Jones Island treatment
plant to re-thicken these solids to their original state. It should also
be noted that the Jones Island treatment plant utilizes grit chambers followed
by screening, rather than primary sedimentation, and the solids pumped or bled
back that were removed In screening would be subjected to Incineration, The
fuel value of the floated scum at Hawley Road was determined to be 1,65A
cal/gm (2996 BTU's/lb), which is not especially good for Incineration purposes.
However, if upon further study It was found that the pumped or bledback sludge
going to and being removed in the final clarlfiers contained significant
concentrations of nitrogen and phosphorus, then the sludge may prove
117
-------
advantageous in the production of MHorganite. However, again tt Is found
that the volatile sol Ids percentage of the sludges Is on the low side, 321,
and this casts doubt upon the quality of this material as a fertilizer, it
also Indicated that the sludge may have a high grit content and therefore
expansion of the existing grit removal facilities would probably be required
If the sludge were to go to the dry-weather plant.
The type of on-slte treatment chosen as best In the laboratory testing was
direct centrlfugatton of the floated scum. The bench scale tests indicated
that a 20% cake solids could be achieved, with a centrate suspended solids
concentration of 200 mg/1 through centrifugatlon. The cake solids would have
to be hauled to a land site for ultimate disposal.
San Franc i sco , CA - j>j sjolji/ed-Alr^ Flotat ton
The combined sewer overflow prototype unit In San Francisco Is similar to
those found in Racine and Milwaukee, Wt with the exception that screening
does not precede flotation. The test unit serves an area of 68 ha (168 acres)
while the entire drainage area of the city (all of which is served by combined
sewers) Is 12,150 ha (30,000 acres). Applying the unit rainfall analysis
an estimated overflow volume of 1,5^0,500 cu m (kOJ million gal.) would be
produced. Estimating the volume and solids concentration of the sludge
produced for this test site was very difficult. The grab sample taken of
the floated scum during this project had a suspended solids concentration of
2.25%, however, operating data from the San Francisco sites Indicates that a
float concentration of 1000-2000 mg/l can be expected. Also, the combined
sewer overflow at the San Francisco site has a very low average raw suspended
solids concentration and thus the net suspended solids removals are only in
the range of 20 mg/l .
For a volume of 1,5^0,500 cu m (40? million gal.) this 20 mg/l would amount
to 30,821 kg (67,800 Ibs) of solids. At a concentration of 1,000 mg/l this
would be a volume of 30,772 cu m (8 million gal.) and at a 2.25% concentration
the volume would be 1 ,363 cu m (0.36 mill ion gal .),
The metropolitan San Francisco area Is served by three separate primary
sewage treatment plants with a total design capacity of 1,135,500 cu m/day
(300 mgd). An estimated 57,000 kg (125,000 Ibs) of solids are gravity
thickened, anae rob J ca 1 1 y digested, and vacuum filtered (to a solids concen-
tration of >25%) before being disposed of In a landfill or used as a soil
conditioner, the volume of slydge produced from combined sewer overflow
sites (1,363 or 30,772 cu m fO.36 to 8 million gal.]) could be pumped or bled-
back to the treatment plants without any hydraulic problems. Although the
present solids handling facilities at San Francisco are running at capacity,
pump/bleedback of the 30,831 kg (67,880 Ibs) of solids over a two to three
day period would only Increase the loading on the solids handling facilities
by a matter of about 151. However, an especially Important aspect of pump/
bleedback which must be considered in the case of San Francisco Is the solids
removal efficiencies being achieved at the treatment plant. In San Fran-
cisco, the weighted average removal of suspended solids Is approximately
501. Assuming these removal efficiencies held true during periods of sludge
pump/bleedback, then half of the solids which were removed at the combined
118
-------
sower overflow facilities would escape In the effluent from the dry-weather
treatment plant.
Ironically, although the hydraulic and solids loadings appear to be feasible
In the case of the San Francisco test site, the low suspended solids removals
achieved at the dry-weather treatment plant would make solids oump/bleedback
Impossible. Thus for San Francisco it would appear that on-slte treatment Is
necessary In order to make the effort put Into treating the combined sewer
overflow worthwhile. The on-slte treatment process found to be best for
San Francisco consisted of thickening followed by vacuum filtration. Since
the solids produced from the treatment of the combined overflow must be stored
on-site until the flow rate In the sewer decreases If pump/bleedback Is going
to be utilized, the thickener requirements are not really an extra cost.
However, If the concentration of the flotation scum can be consistently In
the vicinity of 21 rather than 1,000-2,000 mg/1, the size of the holding tank
could be greatly reduced. It Is estimated that utilizing vacuum filtration on
the floated scum in excess of 21, a cake of 18% solids could be achieved.
This would result In net volume of
-------
be examined as the source of these solids. This ts due to the fact that the
contact stabilization process does not utilize any primary sedimentation,
therefore at! solfds, both participate matter and solubles converted Into
blomass, settle out tn the final clarffter as part of the sludge blanket,
This slyd§e !s then returned to the stablUzatfon tank as part of the waste
sludge. The excess solids produced as a result of the treatment of the com-
bined sewer overflow will either cause an Increase In the blanket depth of
the final clarlfier necessitating an Increase In the flow rate to the stabil-
ization tank, or cause the sludge blanket, and thus the sludge pumped to the
stabilization tank, to have a higher solids concentration.
The entire sewered area of Kenosha Is 3,735 ha (9,222 acres) of which 539 ha
(1,331 acres) are combined, Assuming the excess flow can be conveyed to the
treatment plant and that adequate combined sewer overflow treatment facilities
can be constructed, It Is estimated that a 2.54 cm (1,0 In.) rainfall would
result In an excess flow volume of €8,130 cu tn (18 mg). From actual operating
data in Kenosha (36) it is estimated that the treatment of this volume would
produce 23,BSD kg (53,530 Ibs) of solids which constitutes a volume of 2,384
cu m (630,000 gal*} at a concentration of 1%. Also, the sample of the sludge
analyzed as part of this study had a relatively high volatile solfds percent
(63.0), thus necessitating digestion before going to land disposal.
The alternatives available in the case of Kenosha are not really whether pump/
bleedback Is feasible or not, but rather whether the existing form of sludge
handling should be expanded and utilized or whether an alternate method should
be employed for sludge handling. This Is the case for centrally located wet
weather systems as opposed to satellite treatment systems which face the pump/
bleedback question. Therefore, there appears to be three actual alternatives;
1} enlarge as necessary the existing flotation thickening, digestion, and de-
watering facilities, 2) build completely separate thickening and dewaterlng
facilities (assuming digestion Is not required) or 3) use soffit of th* existing
sludg* handling facilities and also construe! som§ additional ntw facllltUt.
Assuming chat this excess sludge must be subjected to digestion, and based on
the fact that the existing digesters are already at capacity, It appears
obvious that additional digesters would be required. However, 1972 operating
data from the Kenosha treatment plant indicated that the flotation thickeners
were only operated at an average dally loading of 20 kg/day/sq m (4,1 lb/day/
ft ) (J3). If It Is estimated that loadings of up to 100 kg/day/sq m (20 Ibs/
day/ft2) are possible (13), then the existing thickeners could easily handle
the additional solids within two days. Thus, only additional digesters would
be needed since the filter press facilities are also capable of handling the
excess sol Ids.
If digestion is not required, It would appear from the bench scale testing
done that thickening followed by vacuum filtration or centrlfugatlon would
be the optimum combination to utilize. With either procedure a cake solids
concentration of at least 151 should b« attainable. This would reduce the
volume of sludge to be ultimately disposed of from 2,384 cu m (630,000 gal.)
down to approximately 159 cu m (42,000 gal.). Again, as In the case above,
the existing flotation equipment could be utilized with new dewaterlng
facilities provided. It should be noted here that if the thickened solids
120
-------
could go straight to dewatering prior to disposal, the feasibility of
utilizing the excess filter press capacity for dewatering the undigested
sludge should be tested and the results compared to those obtained In the
tests for dewatertng undigested sludge by means of vacuum filtration and
centrtfugatton. Another aspect of the Kenosha system which could possibly
render digestion unnecessary Is the fact that the stabilization tank also
serves as an aerobic digester. Therefore, if the excess solids produced as a
result of combined sewer overflow treatment were withdrawn front the stabili-
zation tank over a period of more than two days ft can be expected that a
significant destruction In the volatile solids concentration may occur.
The alternative of building alt new facilities does not seem practical In any
situation. The fact that excess capacity is available In the existing
flotation thickeners, coupled with the amenability of biological sludges to
flotation thickening, makes the use of these facilities Imperative. The only
decision to be made, If In fact complete combined sewer overflow treatment
were carried out In Kenosha, would be whether to expand the existing digestion
facilities or to build separate mechanical dewatering facilities (vacuum
filtration or centrffugatlon) or to use the existing filter press facilities
if possible. From an economic standpoint, it appears possible In Kenosha
If satisfactory digestion were accomplished In the stabilization tank, that the
existing flotation thickeners and filter press would be sufficient to handle
the extra wet weather solids and no new facilities would be required.
New Providence, NJ- TricklingFilter
Of all the combined sewer overflow sites studies, the trickling filter system
tested in New Providence was the most unique since the concept of solids
bleedback Is utilized as part of the normal mode of operation for this
installation. As discussed in detail in Appendix A the two trickling filters
which normally run In serial'during normal flow periods are converted to
parallel oparatton during periods of high flow. Tha solids settling In the
final clarlfler are recyclad to the primary sedimentation tank where they
settle out with the primary solids. This combined sludge Is then drained to
a sewer which flows to a larger sewage treatment plant downstream.
Apparently the downstream treatment plant has the capacity to remove and
handle the solids produced at the New Providence facility.
This facility does not really treat combined sewer overflow, but actually
handles the high flows caused by Inffltratlpn Into the sanitary sewers'
Therefore, since the present plant can handle the high flows experienced
during rainfall periods, It Is not forecasted that any appreciable Increase
In flow can be expected In future years. Thus, it Is not applicable in this
case to compare on-sfte treatment versus bleedback since the existing form
of bleedback appears to be functioning as planned and will continue to be
used In the future. If this type of arrangement were to be utilized at
another site not being able to discharge the excess solids to another
treatment facility, feasibility studies for the optimum means of on-slte
thickening, digestion and dewatering would be required. However, these
feasibility studies would be conducted In the same manner as those normally
associated with dry-weather treatment plants.
121
-------
SUMMARY
After reviewing the eight combined sewer overflow sites which were part of
this study for the feasibility of utilizing pump/bleedback of treatment pro-
duced solids as compared to on-slte treatment, it is apparent that no specific
conclusions can be drawn for all cases, but instead each case must be studied
on an Individual basis. In general. It does not appear possible to pump or
bleedback the solids produced from the treatment of an entire combined sewered
city to the dry-weather treatment plant. This Is due primarily to the possi-
bility of solids settling in the existing sewerage system and to the over-
loading of the dry-weather treatment plant sludge handling facilities. Also,
in cases of combined sewer overflow storage, It may not be possible from a
hydraulic consideration to pump or bleedback the entire stored contents to
the dry-weather treatment plant. These facts become especially critical when
the dry-weather plants under study are near design capacity for either
hydraulic or solids handling facilities. If only a portion of a city's
drainage area is served by combined sewers, then controlled pump/bleedback of
the combined sewer overflow treatment produced sludges may be possible.
In most cases where on-slte treatment of the sludges produced from combined
sewer overflow treatment is utilized, the hydraulic and solids loadings
resulting from "the pump/bleedback of centrates, supernatants, and filtrates
from sludge thickening and dewaterlng processes such as flotation, centrifu-
gatlort, or vacuum filtration will be possible. However, in many cases pump/
bleedback of the concentrated sludges has been shown to be a problem. Table
33 summarizes the Increase in solids loading on dry-weather treatment plants
resulting from the treatment of 1.2 cm (0.5 In.) of runoff. The amounts of
sludge were determined from the data generated at the existing combined sewer
overflow treatment demonstration systems. The figure only represents those
sites where satellite treatment was tested.
A very important consideration which can easily be overlooked when comparing
the concept of pump/bleedback versus on-site treatment Is the efficiency of
removal at the existing dry-weather treatment plant. It Is not possible to
accurately estimate, without actual field testing, what effect pump/bleedback
will have on the percentage removals at the dry-weather treatment plants.
However, even if it is assumed that the percentage removals obtained during
normal operating periods hold true during the pump/bleedback periods when the
flow rates increase, the percentage of contaminants ending up in the receiving
body can still be significant. For example, If a combined sewer overflow
treatment site achieves 70% removal of suspended solids and these solids are
pumped or bled back to a treatment plant achieving 801 removal of suspended
solids, the net removal of the combined sewer overflow treatment site is:
(0.70) x (0.80) - 0.56 or 56t
This can greatly Increase the true cost of combined sewer overflow treatment
when studied on a cost per mass removal basis.
Another example analogous to the above would be the effect of pump/bleedback
which caused effluent quality to decrease only a slight amount. Using the City
of Milwaukee as an example, if pump/bleedback raised the average raw flow rate
122
-------
Table 33. SUMMARY OF SOLIDS INCREASES AT DRY-WEATHER
TREATMENT PLANTS FOR PUMP/BLEEDBACK OF CSO PRODUCED
SLUDGES FROM 1.25 cm (0,5 in.) OF RUNOFF
Milwaukee,
Pump/
Bleed back
duration,
days
0,5
1.0
2.0
3-0
4.0
5.0
6.0
7.0
8.0
9.0
Milwaukee, Wl
storage
(total contents)
? increase
229
114
57
38
28
23
19
16
14
12
storage
(only settled
sludge)
? Increase
42
21
11
7
5
Cambridge, MA
Storage
? increase
294
138
60
3*
21
14
8
5
Philadelphia, PA
mlcroscreenlng
1 Increase
770
385
193
127
97
76
63
54
48
42
Racine, Wl
S/DAF
% Increase
118
59
29
20
15
12
10
9
7
6
Milwaukee, Wf
OAF only
"1 Increase
152
76
38
25
19
15
13
11
10
8
-------
fay 101 for a period of 3 days and the average effluent suspended solids con-
centration Increased by only 2 mg/l, the following additional loading of
solids would enter the receiving body of water:
651,020 cu m/day [172 mgd]} (1.1) (3 days) (2 mg/1) (constants) -
(4300 kg (9500 Ibs])
Thus, over a three day period the Increase of 2 mg/1 In effluent concentration
would have an actual Increase loading to the receiving body of water of
^300 kg (9500 Ibs) which 5s significant.
Other Important considerations that must be made when studying the concept of
pump/bleedback are 1) the possibility of toxlcity of heavy metals or other
elements to the associated dry-weather treatment plant biological processes
2) the need and practicality of subjecting the combined sewer overflow solids,
which appear to have a low volatile percentage to digestion, and 3) the possi-
bility of overloading the grit removal and primary sludge removal facilities,
thus necessitating additional degritting facilities either at the head end
of the treatment plant or at the overflow treatment site Itself,
Although this section has analyzed the feasibility of pump/bleedback of CSO
sludges versus on-slte treatment, its purpose has only been to demonstrate
the voluminous ramifications (specifically for the requirement of additional
faculties) and problems resulting from either alternative. Specific answers
to determine the best method for each municipality requires a thorough
economic study of aH the alternatives available. No general recommendations
can be made.
-------
SECTION VI11
DISCUSSION
The characterization data presented In Section V of this report has unquestion-
ably demonstrated the magnitude of the problem posed by the sludge residuals
generated as a result of combined sewer overflow treatment. The data has shown
that the volumes and characteristics of these residuals vary widely. The
pump/bleedback of the entire amount of residuals to dry-weather treatment
facilities does not seem to be a promising method of disposing these residuals
as discussed In Section VII. However, partial pump/bleedback In specific
situations may be possible, Therefore, on-slte handling and treatment of these
residuals Is necessary for a satisfactory solution to this Important problem.
The treatablllty test results (Section VI) have demonstrated that several
dewaterlng techniques may be applicable for the on-slte thickening of the
various residuals.
Dilute sludges such as the retained contents of storage/settling treatment or
screen backwashes require a concentration step before any thickening treatment
may be utilized. Therefore, for CSO treatment sites employing a combination
of storage and screenIng/dIssolved-atr flotation treatment, perhaps a more
logical and economical step would be to keep the dilute tank residuals and
screen backwash separated from the concentrated residuals such as settled
solids or flotation scum. After concentration of the dilute residuals by
sedimentation with or without chemicals, the clarified supernatant may be
best discharged to the sanitary sewer or the receiving body of water while
the clarified sludge can then be combined with flotation scum and further
dewatered by smaller size dewaterlng equipment. It Is estimated that such a
modification of keeping the dilute wastes separated from already concentrated
wastes, for example, In Racine, WI, may provide as much as 301 to 40! reduc-
tion in the total cost of sludge treatment estimated earlier. Furthermore,
.in any actual system, the presence of grit or inorganic matter is expected
to be significant and separate means of removing grit may be required in any
CSO residual handling treatment facility.
From the treatment feasibility test results, generally It was shown that
centrlfugatlon or vacuum filtration were both applicable for dewaterlng
after sludge thickening by gravity or flotation thickening. However, when
overall results were compared based on performance, cost and area requirements,
centrlfugation was found to be the optimum dewatering method for all physical
and physical/chemical residuals except alum treated San Francisco sludge and
the biological sludges. Centrtfugation alone or in combination with gravity
or flotation thickening offers several other advantages that must be kept In
mind In the final selection of an optimum dewaterlng step at any specific CSO
treatment site:
125
-------
I. Centrifugation is quick to start up and shot down In the field for
Intermittent uses tn line with unpredictable timing of CSO occurrences,
2. The process Is less sensitive to flow and concentration changes and
can be geared for various applications tn a short time. This can
provide optimum utilization of the equipment even during dry-weather
periods.
3. It can be automated to reduce labor costs. Savings In chemical costs
are also possible because chemical conditioning is not required In
all cases as for vacuum filtration. Furthermore, the power costs
for equipment operation are also lower compared to vacuum filtration.
*t, Centrlfugatlon requires less space and because of Its compactness can
be easily mounted on portable equipment which may then be utilized
at a number of CSO outfall treatment locations tn a metropolitan area.
Because of the above advantages and only limited number of sites that utilize
biological treatment for combined sewer overflows, it is recommended that
additional development work be continued on centrifugalIon treatment of CSO
sludges with and without gravity or flotation thickening. The centrifuge
equipment, both scroll and basket type units, should be evaluated at several
CSO treatment locations. This may best be accomplished by using a portable
treatment unit and utilizing it for a 6 to 8 week period at each site. The
costs developed during this study should be re-evaluated and demonstrated
based upon the operational data developed in Phase II. Furthermore, the
organtcs making up the volatile solids tn the CSO sludges may be far more
putrescible than digested sludges and most probably will require stabilization
prior to ultimate land disposal. On-site digestion facilities such as anaer-
obic digestion are not considered to be appropriate for CSO sludges because
of the quick on-off characteristics of CSO treatment. However, stabilization
by other methods such as I line stabilization may be appropriate and necessary
prior to the ultimate disposal of the CSO sludges. These ultimate disposal
considerations should be investigated and evaluated In detail in Phase il.
However, it should be noted that the ultimate choice of such sludge treatment
concepts is expected to be site specific. The selection of the final treat-
ment method must be based on treatabllity tests at the specific sites
under consideration since no one method of handling and/or treatment would
be applicable to every situation.
126
-------
SECTION IX
REFERENCES
1. "U.S. Department of Health, Education and Welfare, Pub!Ic Health Service,
1962 Inventory of Municipal Waste Faculties", PHS Publication 1065,
Washington, D.C., 1962.
2. "Pollutlonal Effects of Stormwater and Overflows from Combined Sewer
Systems", U.S. Dept. of Health, Education and Welfare, PHS Publication No.
1246, 1964.
3. "Storm and Combined Sewer Demonstration Projects", Water Pollution
Control Series, US EPA Report No. EPA 11202—01/70, EPA, Washington,
D.C., January 1970.
4. Field, R. and Struzesk!, E. J., Jr., "Management and Control of Combined
Sewer Overflows", JWPCF, 44:7, July 1972.
5. "Combined Sewer Overflow Seminar Papers", US EPA Report No. EPA-67Q/2-
73-077, GPO 1.23/2:670/2-73-077* EPA, Cincinnati, OH, November 1973.
6. Standard Methods for the Examination of Water and^ Wastewater » 13th Ed.,
American Public Health Association Inc., NY, 1971.
7. "Methods for Chemical Analysis of Water and Wastes", US EPA Report No.
EPA-16020—07/71, NTIS-PB211968, US EPA, Cincinnati, OH, 1971.
8. Coe, H. S. and Clevenge.r, G. H,, "Methods of Determining the Capacity of
Slime—Settling Tanks", Trans. Are.Inst. Mining Mfg.Engineers, 55:356,
1916.
9. Manclnl, J. L., "Gravity Clarlfler and thickener Design", Proceedings 17th
Purdue industrial Wastes Conference, p, 262-277, 1964.
10. Nebolslne, R., Harvey, P, J. and Fan, Chi Yuan, "High Rate Filtration
of Combined Sewer Overflows11, US EPA Report No. EPA 11023EY/04/72,
NTIS-PB 211144, April 1972.
11. Clark, M.J., et al., "Screen!ng/D!ssoIved-AJr Flotation Treatment as an
Alternate to Combined Sewer Overflows", unpublished EPA Report, EPA
Contract No. S800744 (11023 FWS).
127
-------
12* Agnew, R, W.» et al., "Biological Treatment of Combined Sewer Overflow at
Kenosha, Wisconsin", US EPA Report No. EPA-S70/2-75-QI9, NTIS-PB 242 126,
April 1975,
J3. Selln, 6,, Past operating data for Kenosha, Wisconsin Water Pollution
Control Plant for 1970-1975| Private communications.
14. Homack, P., Zippier, K. L.t and Herkert, E. C., "Utilization of Trickling
Filters for Dual Treatment of Dry and Wet-Weather Flows", US EPA Report
No. EPA-670/2-73-Q71» NTIS-PB 23135VAS, 1973-
15, Tragno, Frank, Plant Superintendent, Borough of New Providence, NJ;
Private communications.
16, Weiss, M.» Director Environmental Planning and Monahan, F. L., District
Supervisor, The Commonwealth of Massachusetts, Boston, MA; private
communications regarding Cottage Farm Storrawater Treatment Station at
Cambridge, MA.
17. Salotto, B, V,» Grossman, E. and Farrell, J. B., "Elemental Analysis of
Wastewater Sludges from 33 Wastewater Treatment Plants In the United
States", US EPA Report No. EPA-902/9~74~Q02, NTIS-PB 239 868, May 1974.
18. decker, H. C. and Nichols, T. M., "Capital and Operating Costs of
Pollution Control Equipment Modules, Volume II; Data Manual", US EPA
Report No. EPA-R§-73-023b, NTIS-PB 22k 536/AS, 1973.
19. "Process Design Manual for Sludge Treatment and Disposal", US EPA
Technology Transfer Report No. EPA 625/1-74-006, US EPA, Washington,
D.C., October, 1974.
20. Mason, D, G. and Gupta, M. K., "Screening/Flotation Treatment of Combined
Sewer Overflows", US EPA Report No, EPA-11020 FOC01/72, GPO, January 1972.
21. Burd, R. S., "Study of Sludge Handling and Disposal", US EPA Report No.
17010—05/68, NTIS-PB 179 514, May 1968.
22. "Sewage Treatment Plant Design", WPCF Manual of Practice $8 (ASCE Manual
of Engineering Practice No. 36), 1967.
23, "Design and Construction of Sanitary and Storm Sewers", WPCF Manual of
Practice No. 9, American Society of Civil Engineers and the Water Pollution
control Federation, 1969.
24. "Handbook of Hydraulics", King and Brater, McGraw-Hill Book Company,
5th Ed., 1963.
25. Poon, C., and Bhayanl, K. H., •'Metal Toxlclty to Sewage Organisms",
JASCE - Sanitary Engineering Division, 97'.SA2:16l» 1971,
J28
-------
26. Kugelman, t. J., and McCarty, P. L., "Cation Toxictty and Stimulation In
Anaerobic Waste Treatment", JWPCF. 37:1:97, 1965.
27. Barth, E., et al.» "Summary Report on the Effect of Heavy Metals on the
Biological Treatment Processes", JWPCF, 37:1:86, 1965.
28. Hill, H., "Effect on Activated Sludge Process, Nickel", Sewage and
Industrial Wastes, 22:2:272, 1950.
29. Sheets, W. D., 'Toxiclty of Hetal-FJnlshlng Wastes", Sewage and Industrial
Wastes, 29:12:1380, 1957.
30. Moore, W. A., et al., "The Effect of Chromium on the Activated Sludge
Process of Sewage Treatment", Proceedings of the 55th Industrial Waste
Conference, Purdue University, May I960.
31. Jenkins, S. H,, and Hewitt, C. W., "Chromium Wastes, Effects on Activated
Sludge", Sewage and Industrial Wastes, 14:5:1358, 1942.
32. Vryburg, R», "Effect of Chromium Wastes on Sewage Plant Processes",
Sewage and Industrial Wastes. 25:2:2*10, 1953.
33. Nemerow, N. L., TheorIesand Practices of Industrfa I Waste Treatment,
Add I son-Wesley PublIsh1ng Company, Inc., 1963»
3k, Rudgal, H. T., "Effects of Copper-Bearing Wastes on Sludge Digestion"
Sewage and I ndustr la I Wastes, 18:6:1130, 1946
35- Wlschmeyer, W. J., and Chapman, J. T., "Nickel, Effects of Sludge
Digestion", Sewage and Industrial Wastes, 19:5:790, 1947.
36. Lager, J, A., and Smith, W. G., "Urban Stormwater Management and
Technology: As Assessment", US EPA Report No. EPA 670/2-74-040, NT1S-
PB 240 867/AS, 1974.
37« "A Comprehensive Plan for the Milwaukee Watershed", Southeastern Regional
Planning Commission, Waukesha, Wl.
38. "Fifty-Fourth Annual Report" Commonwealth of Massachusetts, Metropolitan
District Commission, Sewerage Division, January 1974,
39. Bernard, H., "Alternative Methods for Sludge Movement", Proceedings of
the National Conference on Municipal Sludge Managemsnt, June 11-13, 1974,
Plttsburg, PA, p, II.
40. Maher, M., "Mtcrostralnlng and Disinfection of Combined Sewer Overflows -
Phase III", US EPA Report No. EPA-670/2-74-049, NTIS-PB 235 771/AS, 1974.
129
-------
41. "Milwaukee Waste Water Treatment facilities", Descriptive literature
prepared by the Sewerage Commission of the City of Milwaukee, 1968.
42. City of Milwaukee, Wl, and Consoer, Townsend and Associates, Chicago, IL,
"Detention Tank for Combined Sewer Overflow, Milwaukee, Wl, Demonstration
Project", USEPA Report No. EPA-6QQ/2-75-071» December 1975.
43. "Combined Sewer Detention and Chlorlnatlon Station, Boston, Massachusetts",
Unpublished USEPA r.eport, USEPA Grant No. 112Q2FAT, 1973.
44. Coates, G. K., "Water Pollution Control Department, Racfne, Wl",
Thirty-sixth annual report for 1973.
45. "San Francisco Master Plan for Wastewater Management", preliminary
comprehensive report, San Francisco Department of Public Works, September
15, 1971.
46. Bursztynsky, T, A., et al.» "Treatment of Combined Sewer Overflows by
DIssolved-AIr Flotation", USiPA report No. EPA600/2-7S-OQ3, NTIS,
September 1975.
47. "1972 Annual Report of Kenosha Water Utility", Kenosha, Wl, Water
Pollution Control Division, 1972.
48. Armour, J. A, and Byrke, J, A., "Method for Separating Polychlorlnated
Blphenyls from DDT and Its Analogs", JADAC, 53'-763» 1970.
49. Young, S.J.V., and Burke, J.A., "Micro Scale Alkali Treatment for Use In
Pesticide Residue Confirmation and Sample Cleanup", Bulletin of
Environmental Contamination and Toxicology, 7-'60, 1972*
50, Lamberton, J.G., Claeys, R.R., "Large, Inexpensive Oven Used to
Decontaminate Glassware for Environmental Pesticide Analysis", JADAC,
55:898, 1972.
51. Hall, E.T., "Variations of Florlsil Activity, Method to Increase
Retention Properties and Improve Recovery and Elutlon Patterns of
Insecticides", JADAC, p. 1349, 1971.
52. "Method for Polychlorlnated Biphenyls (PCi's) In Industrial Effluents11,
USEPA, National Environmental Research Center, Analytical Duality
Control Laboratory, Cincinnati, OH, 1973.
53. Katz, W.J. and Gelnopolos, A*, "Sludge Thickening by Dissolved-Alr
Flotation", JWPCF, 39:6:946-957, June 1967.
54. Veslllnd, A., "Estimation of Sludge Centrifuge Performance", JASCE -
Sanitary Engineering Division, 96:3:805-818, March 1970.
55. Douglas, G. and Mason, D.G., "Vacuum Filtration-Bench Scale Test
Procedures", Rexnord Inc. Internal research report, October, 1970.
130
-------
APPENDIX A
SITE DESCRIPTIONS
j. HUMBOLDT AVE., MILWAUKEE, Wl
pry-Weait her Trea tment
Two dry-weather treatment plants serve the 60,704 ha. (149,888 ac.) area within
the limits of the Milwaukee Metropolitan Sewerage District. The older of
these plants (Jones Island) serves 16,155 ha (39,888 ac) and provides secon-
dary treatment for flows up to 757,000 cu m/day (200 mgd). The South Shore
plant has primary treatment and Is capable of treating a 1,211,200 cu m/day
(320 mgd) flow. New secondary treatment facilities capable of treating
454,200 cu m/day (120 mgd) were completed at the South Shore plant Jn 1974.
Following Is a brief description of each of these plants (41).
Jones Island Treatment Plant - All sewage entering the Jones Island plant is
passed through mechanically cleaned bar screens to remove the coarse contents
such as garbage, rags, and wood from the raw wastewater flow. The screened
sewage then enters degritting chambers where the velocity is reduced to
approximately one foot per second. There are eight grit chambers 2.4x2,4x27.4m
(8x8x90 ft) long. The flow Is regulated by individually controlled gates
placed at Inlet and outlet points.
The sewage flows from the grit chambers to the fine screen house. The sewage
passes through a series of rotary drums having 0.24 cm(3/32 in.) slots, con-
tinuous across the face of the drum. Solids too large to pass through these
slots are brushed off of the drums and on to a belt conveyor. The screenings
are then conveyed to a collection hopper and pneumatically ejected to the in-
cinerator building where they are Incinerated along with the coarse screen-
ings and grit. Approximately 54,400 wet kg (60 wet tons) of these materials
are incinerated each day.
Screened sewage flows from the fine screen house into mixing channels where
controlled columns of activated sludge are applied. Mixing with air continues
In feed channels until this mixture reaches the aeration tanks where biological
treatment takes place. The aeration tanks have ridge and furrow type aeration
and provides two way reverse flow. The aeration tanks are designed to aerate
the mixed liquor for an average period of six hours.
Activated sludge Is removed by quiescent settling. Both Dorr and Tow-Bro
type clarlflers are used for final sedimentation. The settled sludge is with-
drawn from the bottom of the clarlfiers and the effluent is discharged to Lake
Michigan.
131
-------
A portion of the sludge Is returned to the Incoming sewage for seeding. The
remaining increment is conditioned with ferric chioride and dewatered by vacuum
filtration on any of 24 vacuum filters at the plant. The filter cake has a
moisture content of about 831.
After vacuum filtration, the sludge is conveyed to an Indirect-direct counter-
flow rotary drum type dryer. These dryers reduce the moisture content of the
sludge to about 5?« The dried solids are then crushed and screened and sold
as fertllizer.
Sou.tjl ffiore Treatment PJ,an^ ~ The sewage enters the South Shore Plant through
2.54"~cin 0 m.") mech an lea 1 fy cleaned bar screens. Solids removed from the
screens are hand-fed to hammermfll type grinders and returned to sewage flow.
After screening the sewage flows Into the grit basins. Flow through the grit
basins proceeds at about 0.3048 m/sec. (1.0 fps), The grit is removed from
the chambers and washed. Cleaned grit is stored and hauled away by truck to
a sanitary landfill or an incineration site. The organ Ics washed from the
grit are returned to the sewage flow.
The sewage then flows to the distribution chambers from which ft is routed to
the settling basins. The sixteen tanks provide a, detention period of 3 hours
at 227,100 cu m/day (60 mgd). When the secondary treatment plant is added
and the flow is upgraded to 454,200 cu m/day (120 mgd) the settling period
will be 1.5 hours. Straight line mechanical sludge collectors convey the
sludge to cross collectors which, In turn deposit the sludge in a vault. The
effluent overflows from the settling tanks and is dispersed to Lake Michigan.
Sludge from the vault or directly from the hoppers, Is pumped by four posi-
tive displacement pumps to the digestion tanks. The total volume of the di-
gestion tanks is 44,800 cu m (1,600,000 cu ft). The sludge temperature Is
maintained at 29.% to 32.2 °C (85° to 90 F) by heaters which can burn either
natural gas or digester gas.
Sludge flows from the digesters by gravity and Is pumped to four lagoons.
The lagoons are approximately 118.9 m square (390 ft square) with a minimum
depth of 4.6 m (15 ft) and have a total capacity between 224,000 and 280,000
cu m (8 and 10 mil lion cu ft). They are estimated to be adequate for 20
years without removal of sludge.
Wet^-WeatherTreatment
Humboldt Avenue, Mtjwaukee, Wl (42} - The detention tank at Humboldt Avenue
receives tne~comblnecTsewer overf 1 ow from a 205 ha (570 ac). drainage area
containing approximately 33-8 km (21 miles) of combined sewers and represent-
ing 1/27 of the combined sewer area in Milwaukee. The area Is residential
and commercial In character and contains primarily combined sewers with a
few separate storm sewers Intercepted within the project area. Two relief
sewers which traverse the area and the Milwaukee Sewerage Commission's Inter-
cepting sewer remove from the system a substantial amount of the total combined
sewage generated within the study area before It reaches the detention tank,
132
-------
Flow to the tank Is by gravity, through a 198 cm (78 in.) sewer. Upon enter-
Ing the tank Inlet channel, the flow passes through a mechanically cleaned
3.8 cm (1.5 In.) bar screen. All solid material retained on the screen are
deposited In a 2,25 cu m (3 cu yd) portable refuse container.
Seven rotary mixers are located within the tank. Only one of these seven
mixers Is equipped with a two-speed motor drive and ts operated at low speed
prior to and during periods of tank overflow to distribute chlorine for
disinfection. Facilities for pre and post-chlor Ination of the C$0 are
provided. The pre-chlorlnation diffuser header Is located just ahead of the
tank Inlet and runs across the Inlet channel. The post-chlortnatlon diffuser
distributes chlorine across the entire 22.9 m (75 ft) width of the tank at a
point about 3.7 m (12 ft) above the tank floor and 53.9 m (177 ft) from the
overflow weir.
Combined sewer overflows In excess of the tank capacity (3.9 million gal.) ,
[14761.5 cu m] during periods of overflow are discharged from the tank to the
Milwaukee River. After the overflow has subsided, all mixers are activated
to resuspend settled solids. The resuspended tank contents are then pumped to
the Jones Island Treatment Plant.
2. CAMBRIDGE, MA
Dry-Weather Treatment
There are two dry-weather treatment plants serving a 165 ha (407.5 ac.) drain-
age area. These plants are the Deere Island Treatment Plant, 1,298,255 cu m/
day (343 mgd) and the Nut Island Treatment Plant, 1,286,900 cu m/day (340 mgd).
The following Is a description "of these plants (§8).
Deere Island[Treatment Plant - This treatment plant has been In operation
since June~,TT06B and serves 22 communities with a population of approximately
1,400,000. Seven pumping stations are located throughout the contributing area,
The facilities Include three remote headworks which are connected to the main
pumping facility by two deep rock tunnels. The tunnel from the Ward Street
and Columbus Part Headworks is approximately 11.3 km (7 miles) long. An
additional facility, the Wlnthrop Terminal Facility, located on the main
plant site, provides sewerage service for local areas and Is connected
directly to the Deere Island Plant through a separate direct pump discharge.
Each headworks provides screening and grit removal for the sewage flowing
through the headworks.
Treatment at the Deere Island Plant starts with pre-chlorlnatlon and pre-
aeratton. The pre-searat!on tankes place In two channels, each 121.9x6x4.3 m
(400 x 20 x 14 ft), with a detention time of 10 minutes. The flow then passes
to the sedimentation tanks which have a detention time of 60 minutes. The
effluent Is then post-chlorinated and discharged through two marine outfalls
located In approximately 15.2 m (50 ft) of water In Boston Harbor.
133
-------
The treatment of raw sludge Is accomplished by separate sludge thickening
prior to high rate dfgestfon. Three primary digesters, equipped with fixed
cover, Internal heaters, and draft tube mixers, have a sludge reclrculatlon
system via a common manifold. A fourth digester, equipped wtth a fixed
cover and separate liquid raclrculatlon system, serves as a storage tank, •
receiving all primary digested solids and overflow to allow controlled dis-
charge of digested material to the sea during periods of outgoing tides,
Nutisland Treatment Plant - The Nut Island Plant has been treating waste
from 21 cTt'lesTand towns with a population of 775,000 since 1962.
The treatment processes Include pre-chlorlnatlon, coarse screening and grit
removal for Incineration, pre-aeratlon of the effluent for 20 minutes, pri-
mary sedimentation, and post-chlor I nation of plant effluent prior to
discharge through a 152.4 cm (60 In.) outfall pipe some 1,828,8 m (6,000 ft)
off shore In deep tidal water.
The treatment of raw sludge Is accomplished by modified high rate digestion.
Two primary tanks, which have fixed covers, and one primary tank with a
floating cover are equipped to provide continuous reclrculatlon of the tank
contents. A secondary digestion tank of the same capacity is equipped with
a floating cover and supernatant drawoff. The digested sludge Is disposed
of through a 30.5 cm (12 In.) submarine pipe line which extends a distance
of 6.8 km (4.2 miles) from the treatment plant Into deep tidal water on the
south side of President Road.
Gas produced by the digestion process Is the principal source of fuel for
all plant power and heating purposes. One or more of the six waste gas
burners, provided for burning excess gas, are In continuous use.
Wet-Weather _Treatment
Cottage Farm, Cambridge^ MA (43) - The Cottage Farm Combined Sewer Detention
and CnforTnat1oh Sta11on Is 1ocated on the north bank of the Charles River
just upstream of the Boston University (B.U.) Bridge In Cambridge, MA. The
Cottage Farm Station diverts, stores and treats excess CSO which cannot
be carried to Deere Island Sewage Treatment Plant from the communities In the
Charles River sewer system. It Is one element of the Metropolitan District
Commission's comprehensive sewage system expansion program to reduce pollu-
tion In the Charles River basin.
The outfall from the facility Is located so as to provide effective discharge
and mixing of the effluent with the river water. Flows up to 2,1 times the
1986 dry weather flow, or 552,610 cu m/day (146 mgd) can be carried to the
Ward Street Headworks, and from there to the Deere Island Sewage Treatment
Plant. Flows In excess of 552,610 cu m/day (146 wgd) are diverted to the
Cottage Farm Detention and Chlorlnatlon Station. The design capacity,
882,283 cu m/day (223 mgd), of the Cottage Farm Facility was established by
the capacity and need for diversion of the Charles River Sewer System at the
B.U. Bridge, Any overflows from these systems are discharged through relief
outlets Into the rlvar basin,
134
-------
During a rainstorm, when the relief sewers contributing flows to the Cottage
Farm Station reach their Individual downstream capacity, they become sur-
charged. The flow enters the Inlet channel to the plant and activates the
plant when the flow depth reaches 35.6 cm (14 In.). As the flow enters the
plant. It is directed to three channels, each designed for 454,200 cu m/day
(120 mgd). In the channel, the flow passes through a coarse bar screen
followed by a fine bar screen. The coarse bar screen has openings of 8.9
cm (3.5 In.) and the fine bar screen has an opening of 1.3 cm (0.5 in.). Both
of these screens are mechanically cleaned.
From the screen chambers, the flow enters the wet wells from where It Is pumped
Into one of the discharge channels. Chlorine is added at the discharge side
of the pumps. From the discharge channel, the flow Is divided Into six
diversion channels which distribute the flow into six detention tanks. Flows
in excess of the detention tank's capacity discharge into the Charles River
Basin through a 243-8 cm (96 in.) outfall.
After an activation, the detention tanks are dewatered by gravity through a
pipe In cfte bottom of each tank and drained oack to the North Charles Relief
Sewer. The residual waste Is ultimately disposed of at the Deere Island
Treatment Plant, The screen channel Is cleaned by reefrculating the chlori-
nated flow retained In the first detention tank to the inlet structure and
then back through the channels Into the wet well from where It Is pumped to
the North Charles Relief Sewer. The detention tanks, pump discharge channel,
wet well, and screen room are then manually washed by a maintenance crew.
3. RACINE, Wl
Dry-Weather Treatment (44)
The treatment of wastewater at Racine, Wl Is accomplished by a full primary
treatment, a 45,420 cu m/day (12 mgd) secondary treatment plant, chlorlnatlon,
sludge digestion and vacuum filtration. The average flow to the plant for
1970, 1971, and 1972 was 79,257.9 cu m/day (20.94 mgd).
The wastewater flows through a mechanically cleaned bar screen to four
commlnutors, each rated 45,420 cu m/day (12 mgd). The wastewater then flows
to the degrlttlng chambers which consist of three grit channels. Two of these
are 2.9 m (9-5 ft) wide and 12.2 m (40 ft) long and the third Is 5.9 m
(19.5 ft) wide and 12.2 m (40 ft) long. All channels have a flow depth of
0.9 m (3 ft) and are provided with mechanical scrapers. The grit is removed
from the grit basins by the scrapers. A screw type cross conveyor and screw
type grit washer remove and further cleanse the grit for satisfactory disposal
as fill materials. Four primary clariflers, each 10.5 (34.5 ft) wide and
41.8 m (137.3 ft) long can hold a total of 4,920.5 cu m (1,300,000 gal.).
Mechanical scrapers push the sludge to hoppers from where It Is sent to
digesters. Clarified effluent flows over weirs to the secondary plant. The
sludge from the primary treatment goes to a 3,785 cu m (1,000,000 gal.)
primary digester. A gas reclrculatlon system Is provided for mixing of the;,
sludge, and a heat exhcnager Is provided for heating the sludge. The . .
temperature Is maintained at 35°C (95°F). During this process methane gas
135
-------
Is produced and utilized as a fuel supply for the engines and bo tiers.
After primary digestion, the sludge Is pumped to the secondary digesters.
The total volume of the secondary digesters Is 3»?85 cu m (1,000,000 gal«).
The digested sludge is then pumped to the vacuum filtration system.
Secondary treatment consists of an activated sludge type treatment system
utilizing the Kraus process. Four aeration tanks having a total volume of
8,516 cu m (2,250,000 gal.) handle an average of 3.797 cy m/day (12 mgd) of
settled wastewater. The tanks can be operated In several alternate modes.
Settled wastewater can be Introduced Into the tanks, together with return
activated sludge. The contents are then mixed with atr provided through
dlffyser tubes. This air also serves as a supply of oxygen for the micro-
organisms. The resulting mixed liquor Is transferred from the aeration tanks
to two final settling tanks each having a volume of 1,892.5 cu m (500,000
gal.) and a detention time of 2 hours, The effluent Is conveyed to a
chlorine contact tank prior to discharge Into Lake Michigan.
The residual sludge from the various operations is dewatered by vacuum filtra-
tion. Two 3m (10 ft) by 3m (10 ft) vacuum filters are utilized. Each filter
has its own conditioning tank where chemicals are added to aid coagulation and
improve f I Iterabll ity. Chemicals utilized are lime and ferric chloride. The
filter cake Is disposed of, by truck, to a land fill site.
WetWea the r T rea tmenjt 1J )
The entire combined sewer system for the City of Racine covers 28k ha. (700
ac.) of the central city. Two satellite treatment plant units are provided
at the (CSO) outfalls to treat a maximum flow of 219,500 cu m/day (58 mgd
from a contributing area of 190 ha. (469 ac.), or 67 percent of the entire
combined sewer area.
The treatment units consist of two basic operations: screening followed by
dissolved-alr flotation. The CSO enters the site wet well and passes through
a mechanically cleaned bar screen to a spiral screw pump. The pump discharges
Into a channel leading to the drum screen. The screen employed to remove
suspended matter In the flow has 297 micron openings (50 mesh). When headless
through the screens become excessive, backwash water Is pumped from the screen
chamber and sprayed on the outer surface of the screens to flush solids from
the inner surface. These solids along with the backwash are collected In a
hopper and flow by gravity to a screw conveyor which delivers them to the
sludge tank, where they are held until the overflow event Js over.
The CSO then flows to the flotation tanks where it is blended with air
saturated pressurized flow. The floated sludge is periodically skimmed
from the top of the tanks and deposited In the screw conveyor which
delivers it to the sludge tank.
This system does not employ effluent recycle for air mixing and pressurization,
Instead, approximately 20 percent of the raw flow Is pressurized for this
purpose. Ferric chlorine and polymer are added to the raw CSO to facilitate
the coagulation of particulate matter before flotation. Ferric chloride is
136
-------
added In the wet well ahead of the spiral screw pump-. Polymer Is added In the
drum screen effluent channel. Chlorine Is also added In the drum screen
effluent channel for disinfection purposes.
The sludge holding tanks are drained back to the city sewer system when the
water level In the sewer has decreased to the point where the tank contents
can be drained without causing an overflow at a point farther downstream In
the Interceptor sewer.
*». HAWLEY ROAD, MILWAUKEE, WI
Dry-Weather Treatment
The dry-weather treatment plant for Milwaukee, WI has been previously described
in conjunction with the Humboldt Avenue detention and chlorination facility..
Wet-WeatherTreatment_(20)
The Hawley Road screenIng/dissolved-atr flotation system is a 18,900 eu m/day
(5 mgd) pilot demonstration treatment facility. The combined sewer area
served Is 200 fta {^95 ac.) and Is a completely developed residential area
In one of the older sections of thectty. The treatment site is located at
one of 110 combined s.ewer overflow points in the Milwaukee area. The entire
combined sewer area in the City of Milwaukee Is 70 sq km (27 sq ml).
The demonstration unit consists ot two basic operations; screening followed
by dissolved-air flotation. The CSO passes through a bar screen and then en-
ters the drum screen. 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 cleaning system where they are flushed into
a hopper inside the screen and washed to a drain pipe that discharges to
the city sewer system.
The screened CSO then flows to the head end of the flotation tank where it
Is mixed with the air saturated pressurized flow coming from the pressurfzatfcn
tank. A port top of the flotation tank effluent or the raw CSO can be used as
the source of pressurized flow. The floated scum Is scrapped off the flotation
tanks and flows by gravity to the cfty sewer system.
Provisions are also made In the system for the addition of ferric chloride
and polymer to the flow before it enters the flotation tank similar to the
Racine CSO treatment system described earlier.
137
-------
5. SAK FRANCISCO, CA
Dry-Weat her .TgeatmentjtjHjj^
The San Francisco Bay metropolitan district has a total drainage area of
11,340 ha (28,000 ac) of which 9,720 ha (24,000 ac) drains to public sewer
systems while the remainder drains to private sewer systems. Sanitary flows
from both public and private sewers are treated at one of the three waste
treatment plants In the Bay area. The domestic and industrial flows are
estimated to be 138 million cu m (36.5 billion gal.) per year while the storm-
water runoff Is estimated to be 33 million cu ro (8.8 billion gal.) per year.
Of this total flowof 171 million cu m (45.3 billion gal.) per year, only 149
million cu m (39-3 billion gal.) can be handled through the dry-weather treat-
ment facilities. The remainder of 22 million cu m (6 billion gal.) per year
Is discharged to the San Francisco Bay as combined sewer overflow. A brief
description of the three dry-weather treatment plants serving San Francisco
area follows:
North PointPlant - The plant serves a tributary area of 3037 ha (7500 ac.)
of combinqS"res!den11a1. commercial and industrial land uses. The treatment
consists OT pro and post-cmor mat ion, pre-aeratlon and primary sedimentation.
The treatment capacity of the plant is 246,025 cu m/day (65 mgd). Any flows
In excess,,of the plant capacity are bypassed via upstream diversion structures
to the San Francisco Bay without any treatment.
Primary settling takes place In six combination pre-aeratlon - sedimentation
tanks. Total detention time including pre-aeratlon at the design flow
capacity of 246,025 cu m/day (65 mgd) Is two hours. Under normal conditions
all six tanks are In operation. About once a year each tank is taken out
of service for maintenance and repair.
The North Point Plant does not Include facilities for treatment of sludge,
Sludge Is pumped to the Southeast Plant at an average flow of 3217*3 cu m/day
(850,000 gpd) and a solids concentration of about I percent.
RIchmond-Sunset Plant - The plant serves a tributary area of 4236.3 ha
TTOj45Q ac)» most of which is residential. The plant provides primary treat-
ment for a peak wet-weather flow of 264,950 cu m/day (70 mgd). The treat-
ment capacity of the plant Is 264,950 cu m/day (70 mgd). Any flows In excess
of the plant capacity are bypassed at two separate points. The treatment
consists of primary sedimentation and effluent chlorlnatlon prior to
discharge to the Pacific Ocean. The residual solids are first stabilized
In aerobic digestion tanks and then conditioned by elutrlatlon and coagula-
tion addition prior to dewaterlng by vacuum filtration. The stabilized-
filtered sludge is then used as a soil conditioner. At the .present tlmer
the average raw sludge flow to the digesters Is 378.5 cu m/day (100,000 gpd)
at a solids concentration of 2.0-2.5 percent. Present cake production is
approximately 1088.4 m tons (1200 tons) of dry solids per year at an
average solids concentration of 251.
138
-------
Southeast Plant - This plant serves nearly kOkB ha. (10,000 ac.) of heavy
ind us t r l¥n *«f "areas of San Francisco and approximately 810 ha. (2000 ac)
of San Mateo counties. The treatment consists of primary sedimentation and
effluent chlorinatlon. The residual solids from both the North Point as well
as the Southeast plants are processed at this facility through gravity
thickeners, digesters and vacuum filters after elutriatlon and chemical
conditioning. Approximately 19,000 m tons (21,000 tons) of sludge cake is
produced per year from this plant at an average solids concentration of 28%.
Wet-Weather Treatment (*t6)
The wet-weather treatment system, called the "Baker Street Plant", Is a
dlssoived-alr flotation system and Is used for the treatment of CSO in
San Francisco, CA. The treatment facility receives the drainage from 68 ha.
(168 ac.) and has a hydraulic capacity of 9,084 cu m/day (24 mgd). The
facility Is comprised of two "modules" of 4,5^2 cu m/day (12 mgd) capacity
and each Is capable of operation independent of the other. Each module has
the following key components: flotation tank equipped with sludge and scum
removal systems; recycle system piped to permit Intake of recycle flow from
either the flotation tank at a point just under the effluent launder or from
the raw influent stream; chemical feed systems for handling alum, caustic,
polyelectrolyte, and sodium hypochlorlte solutions; solids handling system
providing for the air lifting of solids for subsequent gravity flow to a
solids sump and the ultimate transfer of solids to the city sewer system.
From storm generated flows, the treatment system can receive up to 9,084 cu m/
day (24 mgd); anything in excess of this flow is bypassed to the Bay. The
Influent flows through a bar screen and a magnetic flow meter before It Is
split and fed Into the two flotation tanks. The effluent from these tanks
Is discharged into San Francisco Bay.
The system Is designed such that the water needed for air saturation can be
split from the influent stream or taken as recycle from the flotation tank.
This water Is pumped by a recycle pump Into a pressurization tank. At the
recycle pump, air Is Introduced Into the stream by an air compressor.
In the pressurization tank, air-water interface Is provided to obtain high
rates of air solution. The pressure In the tank Is maintained at the desired
level by a downstream pressure reduction valve. Nominal detention time In the
tank Is generally about one minute. The pressurized flow is then blended
with the raw flow In a mixing zone at the Influent end of each flotation tank.
Independent chemical feed systems, consisting of tankage, pumpage and alterna-
tive chemical introduction points, are provided. Feed pH is automatically
adjusted to desired levels using caustic. Other chemicals that are utilized
are alum and polyelectrolyte to aid In solids flocculatlon and separation,
There are two sources of sludge in this system: the solids that are floated
and the solids that settle to the bottom of the flotation tanks. The floated
solids are skimmed off the flotation tanks during operation and flow fay gravity
139
-------
to a solids sump. Any settled sot Ids at the bottom of the tank are washed to
a corner of the tank and pumped to the solids sump. These accumulated solids
ore then pumped to a city sewage pumping station.
6. KENQSHA, Wl
Dry-Weather Treatment
The dry-weather treatment facilities consist of primary sedimentation with a
maximum design capacity of 113,500 cu m/day (30 mgd) followed fay a 87,055
cu m/day (23 mgd} conventional activated sludge system and chlorlnatlon. Raw
sewage enters the plant by gravity from a 183 cm (82 In.) diameter Intercep-
tor sewer. Flows In excess of the plant capacity are diverted by a hydraulic
control gate.
The raw sewage entering the plant Is pumped through two grit removal facili-
ties which operate In parallel, The discharge from the grit chamber flows by
gravity to 6 primary settling basins which have a total surface area of
2,303 sq m (24,760 sq ft) and a volume of 7,213 cu m (257,600 cu ft). The
maximum hydraulic capacity of the facility is rated at 113,500 cu m/day (30
mgd), resulting in surface overflow rates of k$tj cu m/day/sq m (1,212 gpd/
sq ft) and a detention time of 1.54 hours. Effluent from primary sedimenta-
tion Is conveyed to the mixed liquor aeration tanks where It is mixed with
return activated sludge (RAS). There are four mixed liquor tanks having a
total volume of 13,328 cu m (476,000 cu ft) and an aeration time of 3.72
hours at a maximum design capacity of 87,055 cu m/day (23 mgd)« The mixed
liquor from the aeration tanks flows to three 25.9 m (85 ft) diameter final
clarlflers, having a total surface area of 1,581 sq m (17.020 sq ft). The
surface overflow rate at maximum flow Is 5S«1 cu m/day/sq m (1,350 gpd/sq ft)
and the detention time (not Including RAS) Is 1,32 hours. The waste acti-
vated sludge (WAS) from the final clarlfier Is thickened by means of two
dlssolved-air flotation units having a total capacity of 8,080 kg (20,000 Ib)
of solids per day.
The effluent after final clarification Is chlorinated In a contact tank having
a volume of 605.6 cu m (160,000 gal.). At a flow of 113,550 cu m/day (30. mgd)
the detention time in this tank Is 7»7 minutes plus an additional 7.3 minutes
In the discharge conduit to Lake Michigan*
Wet-Weather Treatment (12)
The process for treating combined sewer overflows at the Kenosha demonstra-
tion site Is contact stabl 1 tzatlon. The main difference between the demon-
stration project and normal contact stabilization plant is the periodic usage
of the system. Due to this, provisions for borrowing waste activated sludge
from the dry-weather plant were made. This provision was never utilized
because there was always sufficient volume of sludge In the stabilization
tank, prior to system deployment, to provide a sufficient reaeration time
during operation.
-------
The original grit basins had a maximum hydraulic capacity of 34,056 cu rn/day
(9 mgd) and would not be able to handle a higher loading. In order to pro-
vide more grit removal capacity, an unused mixing and floceulation basin
was converted Into a grit basin. The new grit basin Is conveniently located
between the pump room and the site for the contact stabilization tanks.
The modified tank Is designed to handle a flow of 75,700 cu m/day (20 mgd)
at a velocity of 0.06 m per second (0.2 fps). The floor of the tank is sloped
so that all extremities drain to the middle 6m (20 ft) of the.west walK At
this location a telescoping valve and a screen well are installed to drain
the tank after a run. The deposited grit on the floor of the tank is flushed
to the west wall where It Is suction pumped to a truck and hauled to a land-
fill site,
The contact and stabilization tanks are located on a structure" which is divided
by concrete walls Into four compartments. Two contact tanks arc designed to
handle a maximum flow of 75,700 cu m/day (20 mgd) and a stabilized sludge
flow of 11,355 cu m/day (3 mgd} for a 15 minute contact perfcrd. This
requires a volume of approximately 946 cu m (250,000 gal.). The contact tanks
have a volume of 620.7 and 30*1.5 cu m (164,000 and 80,465 gal.)t with a
combined volume of 925.3 cu m (244,456 gal.).
Aeration is supplied to the contact tank by means of a fixed air disperser
system located along the bottom of the northern wall of the contact tank.
The dlspersers are supplied by the existing blower system and are capable
of delivering up to 106.4 cu m/min (3,800 cfm) of air.
The stabilization tank is also divided into two tanks so that various stabili-
zation times may be studied. "Both tanks are identical, having a volume of
1,386 cu m (366,329 gal.) each. One tank may be filled without filling the
other. This allows for a short stabilization time if desired. The two tanks
are connected by permanent openings In the concrete wall divider 2.19 m (7.17
ft) above the floor of the tank. After this height Is reached, both tanks
must be filled simultaneously.
Aeration for the stabilization tanks is provided by 8 mechanical surface
aerators, four In each tank. The aerators are 50 horsepower each and have
a total design transfer rate of 454 kg (1,000 Ib) per hour.
Two 37*850 cu m/day (10 mgd) pumps are provided to transfer the stabilized
sludge to the contact tanks. This combined capacity allows up to 75,700
cu m/day (20 mgd) of stabilization sludge to be transferred, which is equal
to 100 percent of the combined sewer flow. A 1,892.5 cu m/day (0.5 mgd)
pump is also needed during dry-weather to transfer unused stabilized sludge
to the existing thickeners. All three pumps are located on a concrete plat-
form between the contact and stabilization tanks.
The clarifier is designed for use during both dry-weather flow and over-
flow conditions. During dry-weather, the mixed liquor from the existing
plant is fed to the new clarifier for sedimentation. The settled sludge
from the clarifier is pumped back into the existing plants sludge return
system. The clarifier doubled the existing plant's ciarfficatfon area.
141
-------
The entire biosorptlon process Is completely automated and fs directed from
a rnatn control board. The main control board receives and sends Information
from and to all operations of the process. The information regulates all
flow rates which In turn determine contact times, mixed liquor concentrations,
stabilization times, air supply rates, and settling times. This Is done by
setting all variable flows as a percentage of the raw sewage flow.
During dry-weather the only activity performed by the wet-weather facilityi
is to store waste activated sludge In the stabilization tank for a set period
of time before going on to the existing thickener. The rate of wasted sludge
flow from the existing treatment plant to the stabilization tank Is manually
set at the main control board. By allowing the tank to fill to the desired
volume and then settling the flow out of the tank equal to 100 percent of
the flow Into the tank, a constant stabilization detention time Is achieved.
7. NEW PROVIDENCE, NJ
Dry and Wet-Weather Treatment
The, dual,fuse of treatment plants, using wet-weather facilities to treat dry-
weather flows, is demonstrated well in New Providence. Unlike the other
sites, the New Providence area has a totally separated sewer system. High
infiltrptyon/lnflow conditions during periods of wet-weather may Increase
flows to rates as high as 10 times the dry-weather flow. To treat these flow
variations while maintaining high levels of treatment, a unique trickling
filter operation has been Installed.
The plant is designed to handle a dry-weather flow of 1892 cu m/dav (Q»5 mgd)
and wet-weather flows of up to a maximum of 22,710 cu m/day (6 mgd). The
treatment facilities Include primary clarification, trickling filtration,
secondary clarification, and post chlorlnatlon. Residual sludges up to
5,678 cu m/day (1.5 mgd) are pumped to the city of Summit, NJ solids handling
facilities under a "Pumping Rights" agreement.
Two commlnutors are provided at the inlet facilities for shredding the
coarser solids In the raw sewage. The raw sewage Is pumped by low lift
pumps (three at 18,925 cu m/day (5 mgd) each) to the primary settling reser*
voir, a 1,608.6 cu m (425,000 gal-.) tank which provides the first phase of
treatment at the facility. The clarlfler has a two fold function: It removes
organlcs, Inorganics, scum, grease and oil from the flow and the large volume
of the tank allows equalization of flow to the treatment plant. The sludge
from this tank Is pumped dally to the City of Summit during a period of about
three hours.
One of the two filters Is a plastic media filter 11 m (36 ft) In diameter and
4.4 m (14.3 ft) deep. The primary tank effluent plus the reclrculated flows
are distributed on the filter by a pair of distributor arms which rotate by
virtue of the liquid head created In the center column to which the rotating
arms are attached.
142
-------
During dry-weather operation, the effluent from the plastic media filter
Is pumped to the high rate rock trickling filter. The rock filter Is 19.8 m
(65 ft) In diameter, 1.8 m (6 ft) deep and Is constructed of concrete. From
here the effluent flows to the final clarlfler.
The final clarlfler Is 21m (70 ft) In diameter and has a sldewall depth of
2.4m ( 8 ft). The bottom scraper arras operate at about 2 revolutions per
hour. During periods of dry-weather, reclrculatlon pumps with a capacity of
3,028 cu m/day (0.8 mgd) provide the minimum hydraulic loadings for the
trickling filters. The sludge at the bottom of the final clarlfler flows,
by gravity, to the Inlet of the plant.
The unique feature of this plant Is Its ability to operate under a wide
range of hydraulic loadings. During dry-weather the.plant operates In
series with the plastic filter being the lead filter. During periods of
wet-weather, when the flow increases above 10,598 cu m/day (2.8 mgd), auto-
matic transfer to parallel operation takes place and is maintained until
flow drops to the series range. A portion of the total filter flow Is then
conveyed to the plastic media filter and the remainder to the rock trickling
filter. The effluents from the two filters are combined and conveyed to
the final clarlfier. When In parallel operation, the second stage and reclr-
culation pumps are automatically turned off.
The flow to each filter can be varied, either on a preset ratio basis or a
preset constant flow basis. These operations can be controlled as follows:
An adjustable preset constant flow to the plastic filter can be maintained
automatically by the control circuit. Under this mode of operation, a constant
flow Is applied to the plastic media trickling filter with any excess flow
discharged onto the rock media trickling filter. Similarly, an adjustable
preset constant flow can be maintained to the rock media trickling filter with
any excess flow applied to the plastic media trickling filter. In addition,
a constant ratio of flow can be maintained between the plastic media trickling
filter and the rock media trickling filter. This ratio can be set between 0.2
and 4.0, I.e., If the Indicator Is set at 1.0, It would Indicate that both
filters—the plastic and the rock—would be receiving the same flow. If the
total filter flow exceeds 17,033 cu m/day (4.5 mgd), the raw sewage pumps
which pump to Summit at a constant rate of 5,6?8 cu m/day (1.5 mgd) are
automatically turned off. When the wet-weather flow decreases to 11,355 cu m/
day (3 mgd), the Summit pumps are automatically turned back on. At a flow
rate of 7,750 cu m/day (2 mgd), the secondary treatment system will switch
automatically from parallel to series operation, resulting In the turning
on of the second stage and reclrculatlon pumps.
Under the foregoing conditions, an extreme amount of flexibility Is provided
In the operation of the plant for the treatment of both dry-weather and
wet-weather flows.
143
-------
APPENDIX B
ANALYTICAL PROCEDURES
The following analyses were performed according to Standard Methods for the
Examination of Water and Wastewatar, 13th Edition, 1971 (SH) (6) and Methods
for Chemical Analysts of Water and Wastes, 1971, EPA Water Quality Office
(WQp), Cincinnati, Ohio (7).
pH
Total Solids
Total Volatile Solids
; ,(t
Suspended; So1 Ids
Volatile Suspended Solids
BOD
TOC
Total Phosphate
Kjeldahl Nitrogen
Nitrate
Nitrltt
Metals Zn, Pb» Cu» Nl, Cr
Mercury
Density
Heat Value
Pesticides and PCB's
Soluble Parameters
WQ0, p. 230
WQO, p. 280
WQJJ, p. 282
WQO, p. 278
WQO, p. 282
SH, p. 489
WQj), p, 221
WQp, p. 239
WQ.O, p. 149
Sit, p. 458
WQP, p, 1S5
Digestion - WO.O, p. 8§ '®
recommended by the manufacturer for the
Instrument used (Perkins-Elmer Model 403)«
Digestion - Nitric acid reflux procedure (see
below). Analysis: Perkin-Elmer Mercury
Analysis System Operating Directions 303-3119.
Pycnometer method (wide mouth pycnometer)
Instructions for 1241 and 1242 Adtobatle Colori-
meters, Manual Ho, 142, Parr Instrument
Company, Molina, IL
Details of the pesticide analytical procedure
are Included later In this appendix.
Samples were filtered through 0.45 micron
membrane filters to remove suspended solids
In preparation for measurement of soluble
parameters.
-------
HI trie acid reflux(digest!on procedure forjnercury - A suitable sample volume
was placed In a 250 ml round bottom flask and 10 ml of concentrated nftrlc
acid was added. The flask was then connected to a reflux condensor (about
60 cm In length) and heated with a heating mantle causing the acid to reflex
gently* The mixture was heated for two hours before allowing It to cool
at room temperature. The cooled mixture was washed down In the column with
about 60-70 ml of distilled water. The sample was then filtered through
Whatman No. 42 paper to remove Insoluble material and the filtrate was made
up to 100 ml with distilled water. A suitable aliquot was then analyzed
for mercury.
PESTICIDE ANALYSIS
Introduction
The method described here was used for the extraction and Isolation of organo-
chlorlne pesticides and certain polychlorlnated blphenyl (PCS) mixtures
from stormwater and combined sewer overflow sludges. This method Is based on
EPA approved procedures with slight modifications to adapt It to CSO sludges.
The limit of detection was 1 jig/1 for Arochlor related PCB's and the follow-
ing organochlorlne pesticides: BHC, llndane, heptachlor, aldrln, heptachlor
epoxlde, dieldrln, endrln, Captan, DDE, DDD, DDT, methoxychlor , endosulfan,
dlchloran, mi rex, pentachloronltrobenzyene and trlfluralln,
The selected cleanup procedures permitted the analyst to eliminate certain
anticipated interferences and allowed for separation of analogs of Arochlor
11254, #1260, #1262, #4465, from organochlorlne pesticide.
Summary
PCB's and organochlorln* pesticides ware eooxtracted either by liquid-liquid
extraction or for samples of high solids by mixing with anhydrous NiaSOi)
and soxhlet extraction. A combination of the standard Florlsel column
cleanup and silicic acid column chromatography were employed to separate
PCB's from organochtorlne pesticides (48). Identification was made with a
gas chromatograph equipped with an electron capture detector through the use
of two or more unlike columns. Further confirmation by chemical modification
using a mlcroscale alkali treatment was used as recommended In the literature
(49).
Interferences
1. All glassware, solvents, reagents, and sampling hardware must be
demonstrated to be free of Interferences under the conditions of analysis.
Therefore,all glassware was fired at 230°C after tamberton et al. (50).
2. Organochlorlne pesticides and PCB's are mutually interfering. The
silicic acid column cannot separate Arochlors #1221, #1242, 11248,
#5442 and #5460 completely from DDT and Its analogs. (Early elutlng
peaks from the Arochlors may occur in the polar eluate). For this reason
the use of the chemical modification confIrmatlng technique was utilized
as recommended in the literature (49).
145
-------
Apparatus
!. Gas chromatograph equipped with recorder
2, Detector, Electron Capture
3. Gas chromatograph columns
Two unlike columns of non-polar and semi polar type suitable for
pesticide analysis (e.g. glass 1/4" x 6 ft packed with 10%
DC200 sillcone fluid on 80-100 mesh Anakron ABC.)
k. 500 ml Kuderma-Denlsh glassware (Kontes K-570000)
5. Chromatographlc column 400 x 22 mm(Kontes K-420550, 0-4) with adapter,
hose connector type (Kontes K-185030}
6. Separating funnel 250 ml (Kontes K-633Q30)
7. Evaporative Concentrator (Kontes K-569250)
8. Concentrator tube (Kontes K-570050) graduated In 0,1 ml to 1 ml
i • \
3. Separatory funnels (125 ml, 1000 ml with Teflon Stopcocks)
10. Volumetric flask 250 ml
11. FlorlsIl-PR Grade (60-100 mesh) prepared after the method of Hall
12. Silicic acid, Malllckrodt 100 mesh
13. Glass Wool - hexane extracted
M. Centrifuge tubes 40 ml Pyrex
15. Soxhlet Extractor, 250 ml
16. Magnetic stlrrer with teflon control bar, hexane extracted
17' 1 gallon sample bottles, with teflon caps
18, 10 ml transfer pipette
19. Celite 5^5 washed
20. Air regulator
146
-------
Reagents, Solvents, andStandards
1. Sodium chloride ACS saturated solution
2. Sodium sulfate ACS granular anhydrous, conditioned for k hrs at *tOO°C
3. Diethyl ether - nanograde
4. Hexane, acetonitrlle, methanol, methylene chloride, petroleum ether
(BR 30-60°C) - pesticide grade
5. Standards - appropriate organochlortne and arochlors for elements in
question
Calibration
1. Gas chromatograph conditions were considered acceptable when response to
heptechlor epoxide was iO% of full scale for < 1 ng (nanogram) Injection
(full scale - 1 x I0~9 amp). Detector response for quantitative work was
kept in the demonstrated linear range.
2. Standards were injected frequently as a check on detector and column sta-
bility.
Sample Preparation
1, Adjusted pH to near 7.0.
2. If the solids content of the combined sewer overflow sample was high (as
with sludges and some Influent samples), liquid-liquid partition was not
possible due to emulsion formation. Under these conditions the sample
aliquot was centrifuged and the supernatant treated as detailed in the
extraction section below. The solids were combined with anhydrous NajSO^
and extracted as discussed below.
3. For a sensitivity of 1 pg/ltsample aliquots were between 50 to 100 ml.
Extraction
1. Two methods of extraction could be employed depending on the nature of the
sample. Unless the sample appeared to be low In solids and organIcs, such
as a well treated effluent sample, it was necessary to separate the solids
from the liquid and extract each separately. The extracts could then be
combined and concentrated as a single extract.
2, Liquid - liquid extraction was employed for samples of low solids and or-
ganic content. The procedure used for liquid-liquid extraction Is de-
scribed as follows:
147
-------
Place an aliquot of the sample In a one liter separatory funnel and
make the column up to 500 ml using distilled water. Add 30 ml of
methylene chloride In hexane (V:V) and shake vigorously for two minutes.
Allow the phases to separate and drain the water layer Into a clean
Erlenmeyer flask. Pass the organic layer through a 3-V column of anhy-
drous Na2SQjL and collect in a 500 ml K-D flask. Return the water phase
to the separatory funnel and rinse the Erlenmeyer with a second 30 ml
volume of solvent. Add the solvent to the separatory funnel and com-
plete the extraction procedure. The water phase should be extracted with
three 30 ml aliquots of solvent. Concentrate the extract on a water
bath to 5 ml.
3» If an emulsion was formed between the water and solvent phases, It was
necessary to remove the solids using the following procedure:
Place suitable aliquots of the high solids content sample In clean
(hexane washed) glass centrifuge tubes. Decant the supernatant Into a
one liter funnel and extract the pesticides as outlined In item 2 above.
Remove as much of the centrifuge cake as Is possible with a glass rod
and combine It with hexane washed anhydrous sodium sulfate in a large
mortar and pestle. Work the sample to free flowing dry state by contin-
uously adding small amounts of anhydrous sodium sulfate. Add a small
amount of sodium sulfate to the centrifuge tube to dry any remaining
sample and aid in removing It. Combine all the dried sample and pour it
into a glass Soxhlet extraction thimble. To prevent the dried sample
from packing too tightly, layer glass beads at about 1 Inch Intervals in
the extraction thimble. Place the filled thimble In a soxhlet apparatus
by pouring them through the filled extraction thimble. Extract the
sample for 6 to 8 hours. Take the extract just to dryness on a water
bath In a K-D assembly, cool and wash the K-D assembly with hexane and
adjust sample to 5 ml.
k. The concentrate was analyzed quantitatively to determine:
a. If organochlorine pesticides were present
b. If PCB's were present
c. Combination of a and b
d. If elemental sulfur was present
e. If response was too complex to determine a, b, or c
5. If a, determined organochlorine pesticides.
6. If b, determined PCB's
7. If c, compared peaks obtained to standard arochlors and determined which
Arochlors were present. If Arochlor peaks were analogs of #125^ and
11260, the PCB's were separated from DDT and its analogs by the comfalna-
natlon of Florlsll column and silicic acid column technique. If other
Arochlor analogs were present, further confirmation with the micro-alkali
technique was employed.
8. If d» remove sulfur.
-------
9. If e, the applicable separation procedures described below were followed.
Cleanup and Separation Procedures
(!) Acetonitrlle Partition for removal of fats and oils, (note; not
all pesticides are quantitatively recovered by this procedure.
Efficiency of partitioning for pesticides of Interest should be
demonstrated).
Transfer the 5 ml concentrated extract to a 125 ml separatory
funnel and add enough hexane washings to bring volume to 15 ml.
Extract the sample with four 30 ml portions of hexane saturated
acetonltrtle by shaking vigorously for one minute. Combine and
transfer the acetonltrtle phases to a one liter separatory
funnel and add 650 ml of distilled water. Add kQ ml of satur-
ated sodium chloride solution. Mix thoroughly and extract with
two 100 ml portions of hexane, Combine the hexane extracts In
a one liter separatory funnel and wash with two 100 ml portions
of water. Discard the water layer, pass the hexane layer through
a 3"^ Inch sodium sulfate column Into a K-D flask and rinse the
funnel and column with three 10 ml portions of hexane. Concen-
trate the hexane extracts to 6-10 ml and analyze via GLC unless
further cleanup is required.
(II) Sulfur Interference - Elemental sulfur Is encountered In most
sediment samples, marine algae and some industrial wastes. The
solubility of sulfur In various solvents Is very similar to the
organochlorlne and organophosphate pesticides; therefore, the
sulfur Interference follows along with the pesticides through
the normal extraction and cleanup techniques. The sulfur will
be quite evident In gas chromatograms obtained from electron
capture detectors, flame photometric detectors operated in the
sulfur or phosphorus mode, and Coulson electrolytic conducti-
vity detectors. If the gas chromatograph is operated at the
normal conditions for pesticide analysis, the sulfur Inter-
ference can completely mask the region from the solvent peak
through aldrln.
This technique eliminates sulfur by the formation of copper
sulflde on the surface of the, copper. There are two critical
steps that must be followed to remove all the sulfur: (1) all
oxides must be removed to give copper a shiny, bright appear-
ance that would make It highly reactive; (II) the sample ex-
tract must be vigorously agitated with the reactive copper for
at least one minute (46).
It will probably be necessary to treat both the 61 and 151
Florisll eluates with copper If sulfur crystallizes out upon
concentration of the 6% eluate.
Certain pesticides will also be degraded by this technique, such
-------
as the organophosphates, chlorobenzilate and heptachlor (see
Table B-l}. However, these pesticides are not likely to be
found in routine sediment samples because they are readily de-
graded In the aquatic environment.
If the presence of sulfur is Indicated by an exploratory Injec-
tion from the final extract concentrate (presumably 5 ml) Into
the gas chromatograph, proceed with removal as follows:
a. Under a nitrogen stream at ambient temperature, concentrate
the extract in the concentrator tube to exactly 1.0 ml.
b. If the sulfur concentration Is such that crystallization
occurs, carefully transfer, by syringe, 500 yl of the
supernatant extract (or a lesser volume if sulfur deposit
is too heavy) Into a glass-stoppered, 12 ml graduated,
conical centrifuge tube. Add 500 \i\ of iso-octone,
c. Add 2 yg of bright copper powder, stopper and mix vigor-
ously one minute on a Vortex Genie mixer,
NOTE: The copper powder as received from the supplier must
be treated for removal of surface oxides with 6N HN03-
After about 30 seconds of exposure, decant off acid,
rinse several times with distilled water and finally
with acetone. Dry under a nitrogen stream.
d. Carefully transfer 500 yl of the supernatant-treated ex-
tract Into a 10 ml graduated evaporation concentrator tube.
An exploratory Injection Into the gas chromatograph at this
point will provide Information as to whether further quan-
titative dilution of the extract Is required.
NOTE: If the volume transfers given above areffollowed,
a final extract volume of 1.0 ml wilt be of equal
sample concentration to a 4 ml concentrate of the
Florlsfl cleanup fraction.
(ill) Florlsll Column Cleanup - Place a charge of activated Florlsil
(the weight of the charge Is determined by Its Laurie Acid
Value, see Hall (51)) in the Chromaflex column and settle by
gentle tapping. Add a 1 cm layer of anhydrous sodium sulfate
and pass 50-60 ml of petroleum ether through the column. When
the petroleum ether Is about 5 mm from the sodium sulfate,
transfer the sample extract by decantatlon and petroleum ether
washings to the column and elute with the following mixed
ethers at 5 ml/minute. (NOTE; For both column chromatography
procedures the elutlon rate fs important. To quickly adjust this
rate the lower part of a broken 25 ml burette equipped with teflon
stopcock placed between the chromaflex column and the receiving
vessel Is most useful in making repetitive low adjustments without
losing eluate.). Collect each eluate in a 500 ml K-D flask.
150
-------
Table 8-1. EFFECT OF EXPOSURE OF PESTICIDES TO HERCURY AND COPPER
Compound
BHC
LIndane
Heptachlor
Aldrln
Heptachlor Epoxlde
pp'-ODE
Dieldrih
Endrin
DDT
Chlorobenzllate
Arochlor 125*
Halathion, dlazlnon,
ParathIon, Ethlon,
TrithIon-
Percentage Recovery Based on Mean
of Duplicate Tests
Mercury
81.2
75.7
39.8
95.5
69.1
92.1
.79.1
90.8
79.8
7.1
97 .1
0
Copper
98.1
9*. 8
5.*
83.3
96.6
102,9
9%.9
89.3
85.1
0
10%.3
0
Note: If the mlcroaikalf dehydrochlorlnation procedure is used, elemental
• sulfur is removed.
151
-------
To the first elutton (61 etuate) add 200 ml of 61 ethyl ether In
petroleum ether (V/V); second elution, 200 ml 151 ethyl ether In
petroleum ether. Most pesticides of interest will be in these
eluates. Refer to Reference 52 for more details.
61 Eluate
Aldrin Heptachlor Strobane
BHC Heptachlor epoxide Toxaphene
Chlorodane Lindane Treflurolin
ODD Methoxyehlor PCB's
DDE Mi rex
DDT Pentachlornltrobenzene
151 Eluate
Endosulfan I Dechloran
Endrin Phtholate
Dieldrin
Concentrate the eluates and analyze by GLC.
(1v) Stltctc Acid Column Separation Procedure
A. SJHcIc Acid Preparation
a. Celtte 545 must be oven dried and free of electron
capturing substances (acid washed).
b. Silicic Acid - Oven dry for a minimum of seven hours
at 130 C to remove water. Cool the silicic acid and
weigh into a glass stopper bottle and add 3% water.
Stopper bottle and shake well. Allow 15 hours for
equilibrium to occur. Determine separation achieved
by loading 40 yg of Arochlor 11254 and pp 'DDT In
hexane on the column. Inadequate separation will
mean readjustment of the water content of the silicic
acid In recommended increments of 0,51. More water
Is required when tht PCB elutes In the polar solvent
with pp 'DDE; less water when pp 'DDE elutes In the
petroleum ether portion. Standardization is required
for each new lot of silicic acid purchased. Once a
batch of silicic acid is hydrated activity remains
for about 5 days.
B. Column Preparation - Weigh 5 g of celite and 20 g of
silicic acid and combine in a 250 ml beaker. Immedi-
ately slurry with 80 ml of petroleum ether. Transfer
the slurry to the chromatographic column, keeping the
stopcock open. Stir the slurry In the colunn to remove
air bubbles, then apply air pressure to form the petroleum
ether through the column. Do not allow the column to
152
-------
crack or go dry and close the stopcock when air pressure
Is not being applied. Stop the flow when the petroleum
ether level Is 3 mm above the surface of the silicic
acid. The adsorbent at this point should be firm and
not loose shape If tapped.
C. Elutlon Patterns - Large amounts of PCB's or pesticides
placed on the column will result in incomplete separa-
tion. The extracted sample placed on the column should
contain no polar solvents and be < 5 ml in volume.
Place a 250 ml volumetric flask beneath the column and
carefully add a suitable aliquot of the 6| florist I
eluate, taking care not to disturb the surface of the
silicic acid. Apply slight air pressure until the sol-
vent level is each 3 mm from the surface of the silicic
acid. Carefully position the 250 nil separatory funnel
containing 250 ml of petroleum ether on the column and •
allow the petroleum ether to run down the sides of the
column until the space above the silicic acid is one
half full. Apply air pressure and adjust the flow rate
to 5 ml/minute. When exactly 250 ml are collected, re-
place the volumetric flask with a 500 ml K-D flask and
elute @ 5 ml/mln with 200 ml of methylene chloride, hex-
ane and acetonltrtle (80:19:1, V/V) to recover the pest-
icides, Quantitatively transfer the petroleum ether
eluate cental rtg the PCB's to a 500 ml K-D and concen-
trate both eluates to 5 ml. Analyze vfa GLC. NOTE: the
separation between the PCB's and pp 'DDE is very narrow;
great care should be exercised In adjusting the elutlon
flow rate and volume of the petroleum ether portion.
Petrojeum Ether Eluate
Aldrin
Arochlors
#1260
112589 #1262
Hexach lorbenzene
Polar Eluate (Acetoni tri le, Methylene Chloride, Hexane)
Arochlors #l221a Endrin
#U*»2a Heptachlor
H]2kBa Heptachlor epoxlde
BHC Lindane
pp ' DOE Toxaphene
pp'DDT
pp'DDD
a. These Arochlors divide between the two eluates. The
earliest eluating peaks may occur In the polar eluate.
153
-------
Confirmation Techniques - Qualitative confirmation by
comparing relative retention time (RRT) of the consti-
tuents on two or more unlike columns Is suggested as a
minimum criteria for Identification after appropriate
cleanup and column chromatography.
If an Arochlor analog which does not completely occur In
the petroleum ether eluate Is suspected»the alkali-de-
chlorlnatlon procedure Is strongly recommended (see
Young et al (49)), In any event such confirmatlonal
techniques add greatly to the reliability of the residue
analysis In the absence of more sophisticated mass spec-
troscopy Instrumentation.
BENCH SCALE TEST METHODS
Gray!ty Sjudge Th S cken i ng
The bench scale tests described herein can be used to determine whether
sludge is amenable to thickening by gravity sedimentation with or without
chemical aids. Data obtained using,this procedure can be used for design
of gravity thickening equipment. An example of thickener design using
the Coe £ Clevenger (8) and Hancini (9) methods is presented.
Procedure-
I. Obtain a sample of the sludge at the concentration typical
of the expected sludge concentration,
2. Obtain a sample of this sludge for analyses (suspended solids
and total solids),
3. Measure and record in centimeters the distance between the JOO ml
and 1,000 ml marks on a 1 liter graduated cylinder.
k. Fill the cylinder with sludge to the 1,000 ml mark,
5. Start the stopwatch.
6. Record the position of the Interface (In ml) with respect to
time (in minutes). Continue recording at 2-10 min. Intervals
(or more frequently if necessary) for 2 hours or until no
further settling or compaction occurs,
7. During the above (step 6) set aside the remaining sludge sample and
allow It to settle for approximately 2 hours,- After that time
decant off the supernatant and save It for dilution water. Heasure
the total volume of supernatant and the total volume of settled
-------
sludge and record. Obtain a sample of the settled sludge (250-300 ml)
for analyses, (suspended solids, total solids, and specific gravity)
8. Conduct settling rate tests at several concentrations between the
original (Cj) and the settled sludge (Cf) concentrations. These
concentrations are obtained by appropriate dilutions of the settled
sludge with the supernatant. These dilutions should cover the com-
plete range between Cj and C,. Recommended values are obtained by
using the concentrations of C = Cf-r{Cf-C|); where T1 Is an arbi-
trary factor value of which can be selected to provide suitable con-
centrations between Cj and Cf. For example T1 can have values such
as 0-25, 0.5 and 0.75. The proper dilutions can then be made using
the following equations.
The Initial sludge concentration, Cl, can be expressed as:
I V.
where Ci = solids concentration of the original sludge
Cg * solids concentration of the supernatant (assumed = 0)
C-: = solids concentration of the settled sludge
Vj = total volume of sludge before settling - V + V,
V " volume of the supernatant
V- » final sludge volume after settling
or
One liter of sludge of the desired concentration Is obtained using the
following equation:
MfCf + MsCs - 1000 C
Where M^. « ml of settled sludge
H «• ml ~of supernatant
C » desired concentration
or
MfCf » 1000 (Cf-r (Cf-C,)J
Substituting for C. and simplifying Hf ** 1000
155
-------
Add Mf ml of settled sludge to a 1 liter graduated cylinder. Fill to the
100Q ml mark using the supernatant. Mix thoroughly, start the stopwatch and
record the position of the Interface with respect to time. These tests can
be run for a shorter period of time because only the Initial settling rate
Is of Importance and the later compaction rate Is not needed. Repeat for
ail values of r. After settling, mix thoroughly and obtain a sample for
suspended sol Ids.
Graytty Thicken ing Wi th Chemicals - Chemical addition may Improve thickening
or Ted linen ta7ibrT~prope~rt I esof a s 1 udge by forming a floe and Increasing the
settling rate. The Initial step in testing with chemicals is to screen
numerous chemicals for effectiveness. Among chemicals that can be screen*=J
are FeClj, Hme, alum, and polyelectrolytes (catlonfc, nonionic and anionlc).
Screening tests are normally conducted in 100ml graduated cylinders using
various dosages of chemicals and combI nations of chemicals. The test of
effectiveness In these screening tests Is the visual observation of floe
formation. After selection of the chemical or chemicals, settling rate
tests are conducted in 1 liter graduated cylinders at a wide range of chemical
dosages. A graph of the settling rate versus chemical dosage generally yields
a curve of the following form.
Settl Ing
Rate
Chemical Dosage
The optimum chemical dosage Is at or near the break point of the curve, I.e.
the point at which additional chemical Increases the settling rate only
slightly or not at all, A complete set of settling tests as described In
the previous section is then conducted using chemicals at the optimum
dosage. It should be noted that the chemical dosage used In these tests
must be on a weight-weight basis, I.e. gm of chemical per kg of dry sludge
solids. Correct amounts of chemical (in mg/l) to use at the various sludge
dilutions can be determined using the following equation:
D - D.
where 0 » chemical dosage at the test sludge concentration
mg/l
D, « optimum chemical dosage with sludge at the
Initial concentration, mg/l
156
-------
The dosages calculated in the above manner are those that are used on the
sludge samples after mixing the settled sludge with the supernatant.
Chemicals are added after the sludge fs nixed to the desired concentration.
The chemical Is mixed with the sludge, flocculated If necessary and settled
as described previously. The same mix time and flocculatlon time must be
used for the entire series.
Data Ana tysjjs -
I. Plot the data obtained from the settling tests, I.e. position of the
Interface In ml versus time In minutes. Each graph will have the
following configuration:
Position
of the
interface
Time
The settling rate Is the linear portion of the curve. Determine
the settling rate in ml/mln and convert to meters/hr using the
following:
S - 6.67 x Id**1* LS
where S. « settling rate, m/hr
L • distance between 100 and 1000 ml mark, cm
$2 • settling rate, mi/min (slope of the settling curve
1 1 near section)
2. Plot the settling rate (m/hr) versus the sludge concentration (mg/1)
on graph paper If necessary.
3. Construct a flux concentration curve from the settling rate curve
i.e. mass loading In kg/day/sq m versus mg/1 suspended solids
G - 0.024 (Sj) (C)
where G ™ mass loading, kg/day/sq m
S, » settling rate, at the tested concentration m/hr
C ° sludge concentration, mg/1
157
-------
(Mass Loading)
kg/day/m2
Sludge Concentration (mg/1
5.
Construction of a tangent to the curve from the desired underflow
concentration (point a) will intersect the Y axis at the maximum
mass loading (point b).
From the mass loading rate obtained above the minimum required sur
face area for thickening may be determined
A - 1.44 x 10~3
where A = surface area required for thickening, sn m
Cj= feed sludge concentration, mg/1 suspended solids
-------
where A « surface area required for clarification, sq m
Q_ «» effluent flow rate, 1/mln
S. « settling rate at the feed sludge concentration, m/hr
DISSOLVED-AIR FLOTATION SLUDGE THICKENING
It has been Indicated that dtssolved-alr flotation may be used as a method
of thickening sludge to a higher solids concentration In relatively shorter
periods of time than other gravity thickening methods. Flotation may be
applied to the concentration of sewage plant sludges as well as Industrial
waste sludges.
Bench scale studies are Invaluable In determining the amenability of dissolved-
air flotation to sludge thickening and In obtaining certain basic process
and equipment design data. Set forth below Is a test procedure for conducting
sludge thickening tests using dlssolved-alr flotation (53).
Final effluent or primary effluent should be used as a source of pressurized
flow. If another source Is used as pressurized flow, the source should be
Indicated.
The rate of solids separation will be obtained by performing actual tests
using the appropriate experimental apparatus. As a part of these tests, the
following data should be obtained:
a. Floated sludge volume
b. Settled sludge volume
c. Flotation detention time
d. Volume of waste sludge used
e. Volume of pressurized flow used
f. Concentration of combined flow
The test conducted to obtain the above data should be performed In one liter
graduates. Obtain the vertical distance between the 100 ml mark and the 1,000
ml mark In Inches or other convenient units and record.
Experimental Procedure
1. Rate of solids separation test:
The rate of solids separation of the major portion of the waste sludge
solids Is obtained by observing the solids-liquid Interface during
flotation and recording Its upward travel with time. This test should
be performed In a one-liter graduate.
2, Waste sludge volume:
The amount of waste sludge to be placed Into the one-liter graduate
for thickening will vary with the Initial waste sludge solids concentration
159
-------
and with the ratio of pressurized flow volume/waste sludge volume to be
used
Let the amount of waste sludge to be placed Into the one-lfter graduate
for the test be calculated as follows:
V
" 2Y +" 1
where X «• volume of waste sludge to be placed In graduate, ml
Y = percentage waste sludge solids concentration
V « total volume of waste sludge and pressurized flow (usually
1000 ml)
For example, assume the waste sludge to be thickened has a solids concentra-
tion of 18. From the equation above, the amount of waste sludge to be
placed In the graduate Is 333 ml, when V - 1000 ml.
The weight of the sludge In the graduate should be obtained and recorded.
The weight of the sludge may be obtained by first determining the graduate
tare (weight of empty graduate) on a laboratory beam balance. Record the
graduate tare. Then, similarly obtain the weight of graduate containing
the sludge to be thickened. Obtain the sludge weight by difference and
record. The sludge In the graduate Is now ready for the addition of
pressurized flow.
3. Pressurized flow
The flotation pressure cell Is filled approximately cnree-quarters full
with relatively solids-free water. The cell cover Is secured, and air Is
injected Into the cell using compressed air or a tire pump until a pressure
of bQ psig is attained. The cell Is then shaken vigorously for about 30
seconds to facilitate solution of air In the pressurized flow source. Open
the discharge valve located on the pressure cell and fill the attached
rubber tubing with air-charged flow. Check the quality of the air bubbles
formed. The rubber tubing Is then inserted Into the graduate (all the way
down to the bottom of the graduate) containing the waste sludge to be
thickened. The pet-cock on the pressure cell Is again opened and the press-
urized flow Is allowed to enter the graduate at the bottom and mix with the
waste sludge. Pressurized flow Is added until the combined volume Is
1000 ml. Move the tubing up and down In the cylinder to assure complete
mixing. It Is Important that the pressure of *iO psig be maintained during
the release of pressurized flow Into the graduate.
Determine the total weight of the contents of the graduate and record It.
Also determine weight of pressurized flow used by calculation and record It.
160
-------
4. Rate of solids separation data
At the beginning of the test, the solfds-Uqufd Interface 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 rate of rise of the major portion of the solids Is recorded.
At times the sol Ids-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 alone. In
general, this Interface lags behind the solfds-IIqufd Interface.
The form which may be used In obtaining the rate of separation Is suggested
by the followl-ng example. The flotation detention time should be 60 minutes.
Time Volume POI (Position of Interface)
(mln) (ml) (ft) .
00 0
0.5 170 0.207
1.0 320 0.379
1.5 430 0.504
2.0 540 0.628
3.0 620 0.718
4.0 655 0.756
5.0 680 0.784
10.0 750 0.865
15.0 780 0.889
20.0 795 0,917
30.0 810 0.934
40.0 850 0.980
50.0 865 0.995
60.0 870 1.000
The ultimate data desired Is the position of the Interface at various time
Intervals throughout the test. The column above 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 above, the position
of the Interface at any given time may be conveniently obtained using the
appropriate graduation mark on the liter cylinder as a reference. After the
flotation test, the graduation marks may be converted to meters of height
by actual measurement.
5. Analyses of data
The data derived from the bench testing Is then used to estimate the scum
concentration at various mass loading rates. This data Is then graphically
plotted. Optimum overflow rates are then selected from this plot for the
design of d!ssolved~alr flotation thickeners.
161
-------
CENTRIFUGE TEST PROCEDURE
The purpose of this test is to determine the dewaterfng characteristics of
sludge by centrffugatlon. Data obtained Include the effects of centrifugal
force, the effect of residence time, estimates of solids recovery, sludge
concentration and sludge consistency. Procedures were developed by
Vestllnd (5M.
Procedure
Approximately 2-k liters of sludge are required to run a complete test series.
If the sludge contains large or stringy materials ft should be prescreened
on a coarse screen to avoid erroneous results,
1. Mix the screened sludge well and obtain a sample.
2. Place 75 ml of sludge Into each of the centrifuge tubes. NOTE:
It is important that balanced amounts of samples be placed in
opposite centrifuge tubes. Sample sizes other than 75 ml may be
used but the amount must be the same In opposing centrifuge tubes.
3. Place In the centrifuge and spin for a predetermined time at the
required centrifugal force. Suggestions for spin time are 30 seconds,
60 seconds, 90 seconds and 120 seconds. Suggested centrifugal forces
are 400 g, 600 g» 800 g and 1000 g. The step by step procedure for
this test using the Dynac (manufacturer of the centrifuge) Model
CT-13&0 centrifuge Is as follows:
a. Place the filled centrifuge tubes In the head,
b. Turn the timer dial clockwise to the "hold" setting.
c. Determine the rpm required to obtain the desired centrifugal
force using Figure 8-1.
d. From Figure B-2 determine the setting on the speed control
which will yield the required rpm with the number of centrifuge
tubes used.
e. Close and lock the centrifuge cover.
f. QulcKiy turn the speed control knob clockwise to the required
setting simultaneously starting the stopwatch.
g. At the end of the predetermined spin time turn the speed
control knob counter-clockwise to zero and Immediately apply
the brake until the head stops.
k» Record the sludge depth on a data sheet.
162
-------
1500
1000
goo
800
700
o
Of
o
soo
%00
300
200
1000 2000
REVOLUTIONS PER MINUTE
3000
Figure B-l. Centrifugal force vs. RPH for
Dynac Model CT-1360 centrlfufe
163
-------
2500 •-
2000
ac
Cd
Ul
a.
o 150Q--
1000 ._
500 •-
2 CENTRIFUGE TUBES
(75 ml per tube)
CENTRIFUGE TUBES
(75 ml per tube)
30 40 50 60
SPEED CONTROL SETTING
Ffgure B-2. RPH vs. speed control setting
70
80
-------
5. Pour off the centrate from the tubes Into a graduated cylInder.
Record the centrate appearance and the total volume. Mix well and
obtain a sample of the centrate.
6, Determine the consistency of the sludge using the glass rod (^ mm x
kO mm, 13 gm weight). Position the tip of the rod at the sludge
surface. Drop the rod from this position, measure and record the
depth which Is penetrates.
7. Repeat steps 2 through 6 for all test conditions,
8. If chemical conditioning Is desired, determine a suitable chemical
dosage for floe formation. Dose each sludge sample with the same
chemical dosage Immediately prior to each centrlfugatfon condition
utilizing the same mixing time, degree of agitation and holding
time for each test. Repeat steps 2 through 7 for these tests.
Data Analysis
I, Estimate the percent solids recovery for each test utilizing the
following equation;
Cf - C x 100
I Recovery * §
Cf
where C. *» suspended solids concentration In the feed sludge (mg/l)
C » suspended solids concentration In the centrate (mg/1)
2. Estimate the sludge solids concentration using the following equations
vv=
where C * final sludge suspended solids concentratldn (mg/1)
5
C- - feed sludge suspended solids concentration (mg/l)
C =» suspended solids concentration In the centrate (mg/l)
V, a total feed sludge volume centrlfuged (ml)
V » total volume of centrate decanted (ml)
This parameter Is only an Indicator of the relative compactabllIty
of the feed sludge at various operating conditions.
Calculate the sludge penetrability to determine a correction factor
for solids recovery using;
165
-------
d-d
s P_
100
where P » sludge penetrability
d » depth of sludge after eentrifuglng
d = depth of penetration of the glass rod
The factor P Is the percentage of the total sludge depth not
penetrated by the glass rod.
k. Plot the recovery and penetrability versus the centrifugal force
(x gravity) at constant spin times on log probability paper as
below:
Percent
Recovery
Penetrability
Centrifugal force (g)
The data should plot as straight lines.
Estimate of Prototype Operation
At a constant centrifugal force read the recovery at one of the spin times,
Also read the penetrability at the same spin time. An estimate of the
recovery is then determined from the following equation.
Recovery in Percent
0.1
x 100
VACUUH FILTRATION TESTS
Buchner Funnel Test Prpcedu£e
The Buchner funnel test is conducted to determine the optimum chemical
dosage for filter leaf tests (55).
I. Moisten filter paper (Whatman #4) and place it in the Bucnner Funnel.
Apply a vacuum to obtain a seal. Empty water collected In filtrate
receiver.
166
-------
2. Analyze the sludge to be filtered for solids content.
3. Measure a volume of sludge that will provide a 3 mm to 6 mm thtck
cake.
4. Select the conditioning chemicals to be utilized and add a predeter-
mined amount to the sludge to be conditioned. This should be reported
as kg chemical/ton sludge dry solids.
5. Agitate the volumetric flask vigorously and allow the sludge to sit
tws minutes. Always agitate the sludge approximately the same amount
for any one test serFes.
6. Add the sludge to the funnel and quickly apply vacuum. As soon as
vacuum is applied, start the stopwatch. A vacuum reservoir may be
needed to hold a constant vacuum,
7, Take filtrate volume readings with respect to time.
8. Continue the test until the cake cracks, or no filtrate is deposited
for a one minute interval. Usually five minutes Is sufficient. Be
sure the cake edqes do not shrink from the sides of the Buchner funnel.
If it does, tap the edges of the cake to maintain a seal,
9, Sample cake for total solids,
10. Record filtrate temoerature, vacuum level, and cake thickness.
11, Plot a curve of time/volume filtrate vs. volume filtrate and record
the slope of the curve. The slope recorded should include only the
linear portion of the curve.
a = 2PA2b/pw
*)
where a = specific resistance in sec /gm
P = vacuum level in gm/sq cm
A = area of Buchner funnel in sq cm
b = slope of t/v vs. v curve in sec/cm
p = viscosity in Poise
u => l/[Ct/ (100-Ci)) - (Cf/ (100-Cf))]
Ci - initial sludge moisture (%)
Cf = moisture concentration in cake (I)
12. Repeat steps 1 through 12 for several dosages of the same chemical.
13. Plot specific resistance vs. chemical dosage. The minimum point
obtained on the carve Is the optimum chemical dosage for the
chemical tested.
167
-------
F>1ter HedI a Se 1act Ion Test Pfocedure
]. Select a cloth for testing !n accordance with Information available
on chemical and physical conditions, sludge type and properties,
and parameter qualities desired.
2, Moisten the cloth and place It ,1n a Buchner funnel. Apply a vacuum
to obtain a seal.
3. Analyze sludge sample for solids content,
4, Measure a volume of sludge equivalent to a cake thickness of 3 mm
to 6 mm.
5. Condition the sludge with the optimum chemical dosage determined
from the Buchner Funnel test as described tn that test procedure*
£. Add the sludge to the Buchner Funnel, Apply-a vacuum of about 50 cm
Kg and start the stopwatch.
7. Measure the time to collect 100 cc of filtrate, 150 cc of filtrate,
and 200 cc of filtrate* Discontinue test after 5 minutes.
8, Remove the cloth and measure cake thickness.
9. Note cake release as follows;
excellent - cake peels off medium tn pteces with slight amount
of spatula aid.
fair - cake must be taken off medium piece by ptece with
spatula.
poor - cake will not come off medium even with maximum
spatula use. Some solids left on medium.
10. Analyze the cake for solids content and the filtrate for suspended
solids.
11. Wash the filter cloth on both sides with an Intense water spray for
5 seconds.
12. Determine if any soltds are deposited In the cloth Interstices by
eye or microscopic evaluation.
13- Rtpeat steps 1 to 12 three times utilizing the same sample medium.
14, Run a standard test on the sludge at optimum chemical dosage using
#4 Whatman filter paper and a 50 cm Kg vacuum.
168
-------
Vacuum Filter Leaf Test Procedure
i. Condition approximately 20 liters of sludge according to Buchner
Funnel test results.
2. Place cloth selected from media screening test on the filter leaf
and attach leaf hose to filtrate receiver.
3. Crimp the hose connecting the leaf to the vacuum source and set
vacuum to desired level with the bleeder valve.
k. Immerse the leaf In the sludge so that the surface of the leaf Is
two to three inches below the sludge level. Release the hose and
start the stopwatch simultaneously.
5. Keep the leaf submerged for a predetermined pickup time obtained
from preliminary tests. For thin sludges, move the leaf slowly
In a horizontal plane with a circular wrist movement at a rate of
approximately 6 rpm. In thick sludges, the leaf should remain
stationary. Keep thin sludges mixed with a small mixer. Thick
sludges should bs thoroughly mixed prior to the test.
6. At the end of the pickup time, the leaf Is rotated out of the bucket.
7. The leaf Is then held with the cake upward for the duration of
the drying cycle. At the end of this time, vacuum Is released.
Adjust the vacuum as much as needed during the dry time to maintain
vacuum level. Allow all filtrate to drain from the hose to the
filtrate receiver.
8. Remove the cake from the fitter leaf by blowing Into leaf hose and
dislodging It with a spatula. Analyze the cake for total solids,
Note cake discharge and thickness.
9. Analyze filtrate for suspended solids, and record the filtrate volume,
10. Analyze solids content of remaining sludge. Two to four tests may
be run on the same sample.
ProUmlnary Jestj ng - in initial test, submerge test leafs for various
pertods^of time aria not* at what time cake sloughing takes place, I.e. sludge
will no longer build up uniformly, but falls off when leaf Is removed from
bucket. This Is the maximum pickup time. The minimum pickup time Is the
time required to produce a cake thick enough to discharge.
Utilizing the maximum pickup time determined above, perform a leaf test and
allow the cake to dry until It cracks or shrinks away from the edges of
the leaf. This represents the maximum drying time. Run the remainder of the
leaf tests according to steps 1-11 in the range of these established pickup
and drying times.
169
-------
Flocculatton Test Procedure
I. Measure 50 ml to 100 ml Into a 100 ml graduated cylinder and add a
predetermined dosage of the chemical selected.
2. Invert the cylinder three times, keeping the palm on the top of the
cylinder. (This Is rapid mix.)
3. Add any additional chemicals In the order desired and repeat step 2.
4. Gently swirl the graduated cylinder with the wrist for a predetermined
time Interval. Observe the floe formation.
5* Repeat steps 1 to 4 for various chemical dosages, and compare the
graduated cylinders visually to determine optimum chemical dosage.
Floe size, supernatant clarity, and rate of floe formation all
help In determining the optimum chemical dosage.
6, Utilize any other chemicals desirable.
t.
170
-------
APPENDIX C. COST DATA
Table C-I. ASSUMPTIONS FOR DEVELOPMENT OF COST DATA
1. Use a maximum sludge treatment time of 2^ hours.
2. Assume 50 combined sewer overflows per year,
3- Capital costs for flotation thickening, centrlfugatlon and vacuum
filtration include $3,000 for a pump. Gravity flow assumed for
gravity thickeners.
k. Power costs - assume motors running at 751 of full toad current. Use
5. Assume $6,000 for chemical feed system.
6. Chemical costs - polymer ; $1.75/lb.
lime : $9.00/100 Ibs.
ferric chloride: $6.5/100 .Ibs.
7- Assume 31 of Initial capital Investment for vacuum filters to be the
annual maintenance required. Also assume 0.5 man hours per shift for
operator attention.
8. Area estimates are for equipment only,
9. Assume $0.10 per gallon for hauling costs.
10. Labor costs based on §6 per man hour.
U. All costs are based-on December, 197^ prices.
171
-------
Table C-2. HUMBOLDT AVENUE - SUMMARY OF PERFORMANCE, COST AND SPACE REQUIREMENTS
Initial residual sludge volume: 34,700 gal.
Initial residua) sludge concentration; 1.741 sol ids
N)
Performance
Dewaterlng
process
Gravity
thickening
Flotation
thickening
Centrifugation
Vacuum
filtration6
Sludge
I
solids
6.0
14.0
32,4
30.0
Process
effluent
mg/1
870C
522d
84
870
Residual volume
Sludge
gal .
10,063
4,313
1,864
2,013
Process
effluent
gal ,
24,637
30,387
32,836
32,687
Cost
Capital
$
57,000
111,000
65,000
63,000
Operating
$/year
590
4,960
4,360
8,650
Dewatered
sludge
haul ing
cost
$/year
50,315'
21 ,565
9,350
10,065
Total
annual
costb
$/yea_r-
57,600
39,563
21,345
26,702
Area
sg ft
707
450
35
143
a. Bench tests done on the basis of sedimentation prior to dewaterlng. To convert storage basin Into
settling basin would be a capital expenditure of $516,000; $3,096 operating cost for a total annual
amortized cost of $63,705.
b. Including amortization costs for a 20 year equipment life, 10% Interest rate.
c. Based on 35% removal.
d. * Based on 37% removal.
e. Estimated values based on vacuum filter performance under similar conditions found in this study
(3#/ft/hr, 951 recovery).
-------
Table O3. DETAILS OF OPERATING COST ESTIMATES
FOR HUMBOLDT AVENUE, MILWAUKEE, Wl
Operating Costs ($/Year)
Dewatering Operating Maintenance Chemical Pcawer Total
Method
Gravity Thickening
Flotation Thickening
Centrlfugation
Vacuum Filtration
Labor
0
1,800
1,200
2,400
570
2,220
1,300
2,040
Costs
0
0
1,520
4,000
Costs
20
940
340
210
590
4,960
4,360
8,650
173
-------
Table C-4. CAMBRIDGE, MA - SUMMARY OF PERFORMANCE, COST AND SPACE REQUIREMENTS
Initial residual sludge volume: 17|850gal.a
Intttal residual sludge concentration: 4.4$ solids and 11% solids
DewaterIng
process
Gravity
thickening
Flotation
thickening
CentrifugalIon
Vacuum ..
filtration
Performance
Sludge Process
% effluent
sol Ids mg/1
Res Idua1 voIurae
Process
Sludge effluent
gal. gal.
Dewatered
sludge
___^_^ . hauling
CapitalOperating cost
$ $/year $/year
Cost
14.0 2,200° 5,610 12,240
77,100
801
30.0 2,200 2,618 15,232
68,000 9,954
7.2 1,320 10,908 6,942 109,000 4,935 54,540
34.2 610 2,424 15,426 65^000 2,955 12,120
Total
annual
cost** Area
$/year sq ft
28,050 37,907 1,256
72,278 370
22,710 35
13,090 31,031
143
a. Based on mass balance of average conditions.
b. Including amortization costs for a 20 year equipment life, ]Q% Interest rate.
c. Performed on a grab sample from Storm I at 11% solids,
d. Assume 95% capture.
e. Based on 37% caputre.
f. Estimated values based on vacuum filter perofrmance under similar conditions found In this study
(3#/ft2/hr; 95* recovery).
-------
Table C-5. DETAILS OF OPERATIHG COST ESTIMATES
FOR CAMBRIDGE. MA
0{3eratjng Costs ($/Ye_a_r_)
Dewaterthg
Method
Gravity Thickening
Flotation Thickening
Centrifugatfon
Vacuum Filtration
Operating
Labor
0
1,800
1,200
3,600
Maintenance
771
2,060
1,300
2,040
Chemical
Costs
0
325
115
4,000
Power
Costs
30
750
340
314
Total
801
4,935
2,355
9,954
175
-------
Table C-6. RACINE, Wl - SUMMARY OF PERFORMANCE
COST AND SPACE REQUIREMENTS
Initial residual sludge volume: 121,000 gal.a
initial residual sludge concentration: 8,430 mg/1
Dewaterlng
process
Performance
Sludge Process
% effluent,
solids mg/1
Residual volume
Sludge,
gal.
Process
effluent,
gal .
Dewatered
sludge
Cost
Capital,
$
Operating,
$/year
haul ing
cost,
$/year
Total
annua 1
costb,
$/year
Gravity
thickening
19
Centrlfugatlon 20
Gravity 32,9
thickening &
centrlfugatlon
Gravity 23.2
thickening £
vacuum flit.
Gravity 13.2
thickening &
flotation
thickening
1,321
1,821
676
10,200 110,800 29,300
5,100 115,900 158,000
3,100 117,900 105,300
313 51,000 5*1,755 177
12,790 25,500
4,544 15,500
7,728 113,272 162,700
56,8*19 200
32,413 205
4,397 116,603 97,300 10,663 21,985 44,077 320
6,064 38,640 63,815 1,404
a. Based on a mass balance of average conditions.
b. Including amortization costs for a 20 year equipment life, lot interest rate.
c. Assume 35% removal.
d. Basket centrifuge recommended since sludge not scrotable.
e. Assume 97% removal.
-------
Table C-7. DETAILS OF OPERATING COST ESTIMATES
FOR RACINE, Wl
Dewatering
jtethod
Gravity Thickening
Centrifugation
Gravity Thickening
and Centrifugatlon
Operating Costs ($/year)
Operating Maintenance Chemical Power
Labor
0
7,200
1 ,800
Gravity Thickening
and Vaccum Filtration 3,600
Gravity. Thickening
and Flotation
Thickening
Maintenance Chemical
Costs
3
293
,160
0
0
1,800
1,813
2,333
2,961
*,396
372
Total
Cos t_s _
20 313
2,J»30 '2,790
931 *
334 10,663
931 6,064
177
-------
Table C-8, HAWUY ROAD, MILWAUKEE, Wl - SUMMARY OF PERFORMANCE,
COST AND SPACE REQUIREMENTS
Initial residual sludge volume: 36,675 gal.a
initial residual sludge concentration; 3.65% solids
oo
Performance
Sludge
Dewatertng %
process solids
Gravity
thickening 10
Flotation
thickening 13
Centrlfugatton 23.4
Gravity
thickening &
vacuum
filtration 35.7
Gravity
thickening 6 30.3
centrlfugatlon
Process
effluent,
mg/1
1 ,825d
l,095e
134
2,056
2,123
Residua! volume
Sludge,
gal .
13,386
10,297
5,721
3,750
4,418
Process
effluent,
gal .
23,289
26,378
30,954
32,925
32,257
Capital ,
$
35,600
102,300
65,000
103,600
100,600
Dewatered
sludge
Operating,
$/year
376
5,682
3,606
10,333
4,179
hauling
cost,
$/year
66,930
51 ,485
28,605
18,750
22,090
Total
annual
costb
$/year
71,489
69,183
39,856
41 ,252
38,085
Area,
sg ft
314
796
20
457
349
a. Scaled to entire outfall volume.
b. Including amortization costs for a 20 year equipment life, 10| Interest rate.
c. Ocwaterlng units sized based on treating entire outfall CSO of 36,675 GPD.
d. Assume 95% removal.
e. Use 97% removal.
-------
Table C~9. DETAILS OF OPERATING COST ESTIMATES
FOR HAWLEY ROAD, MILWAUKEE, Wt
Opera 11 ng Costs ($/Year)
Dewatering Operating Maintenance Chemical Power Total
Method Labor Costs Costs
Gravity Thickening 0 356 0 20 376
Flotation Thickening 1,800 2,046 1,026 810 5,682
Centrifugation 1,800 1,300 0 506 3,506
Gravity Thickening
and Vacuum Filtration 3,600 2,596 ^,003 33^ 10,333
Gravity Thickening
and Centrifiliation 1,800 1,656 197 526 J»,179
179
-------
Table C-10. SAN FRANCISCO, CA - SUHMARY OF PERFORMANCE,
COST AMD SPACE REQUIREMENTS
Initial residual sludge volume: 14,550 gal.a
Initial residua) sludge concentration; 2.25% solids
oo
o
Performance
Oewaterlng
process
Gravity
thickening
Flotation
thickening
Centrlfugatlon
Vacuum filtration
Sludge,
1
sol ids
4.5
6.1
11.1
18.2
Process
effluent,
mg/1
I,125C
675d
33
123
Residual volume
Sludge,
gal.
7,275
5,367
2,949
U699
effluent,
pal .
7,275
9,183
11,601
12,751
Dewatered
sludge
Cost
Capital,
$
67,500
85,000
65,000
62,000
Operating,
$/year
735
3,728
2,196
7,600
haul Ing
cost,
$/year
36,375
26,835
14,745
8,995
Total
annual
cost?
$/year
45,039
40,547
24,576
23,878
Area,
sg ft
1,963
170
35
128
a. Based on mass balance.
b, including amortization costs for a 20 year equipment life, 10% interest rate.
c. Assume 951 removal.
d. Based on 971 removal.
-------
TableC-li. DETAILS OF OPERATING COST ESTIMATES
FOR SAN FRANCISCO, CA
Operati ng Cos ts_($/Year)
Dewaterlng Operating Maintenance Chemical Power Total
Methods Labor Costs Costs
Gravity Thickening
Flotation Thickening
Centrifugation
Vacuum FlItratlon
0
1,800
600
1,800
675
1,580
1,300
1,860
0
6k
127
3,731
60
28/i
169
209
735
3,728
2,196
7,600
181
-------
oa
fo
Table C-12. KENOSHA, Wl - SUMMARY OF PERFORMANCE,
COST *ND SPACE REQUIREMENTS
Initial residual sludge volume; 122,500 gal,a
Initial residual si udge concentration: 8,300 mg/1
Performance
Residual volume
Process
Cost
Dewaterfng
process
Gravity
thickening
Flotation
thickening
Centrlfugatlon
Sludge Process
% effluent Sludge effluent Capital Operating cost
sol Ids mg/1 gal. gal. $ $/year
Dewaterfng
sludge Total
hauling annual
1.0
3.1
8.9
Flotation
thickening £ 6.6
centrlfugatlon
Flotation
thickening
& vacuum
filtration
15.2
— 101,675 20,825 87,700 2,010
2k3c 32,798 89J02 117,000 8,843
5* 11,42*1 111,076 170,000 13,030
356 15,^05 107,095 182,000 17,116
331 6,689 115,811 185,000 24,631
cost , Area
$/year sq ft
508,375 520,686 1,590
163,990 186,576 465
57,120 90,118 200
77,025 115,401 500
33,445 79,806 608
a. Based on a mass balance.
b. Including amortization costs for a 20 year equipment life, JQ| Interest rate.
c. Based on 971 removal.
d. Based on basket centrifuge since zero corrected recovery Indicates that the cake Is not scrollable.
-------
Table C-l3. DETAILS OF OPERATING COST ESTIMATES
FOR KENOSHA, Wl
Operating Costs (_$/Y_e_a_r)
Dewatering Operating Maintenance Chemical Power Total
Method Labor ____________ Costs Costs _
Gravity Thickening 0 877 1»°73 60 2,010
Flotation Thickening 1,800 2,320 k,Qlk 709 8,8^3
Centrifugation 7,200 3,^00 0 2,^30 13,030
Flotation Thickening
and Centrifugation 2,700 3,560 9,809 1,0^7 17,116
Flotation Thickening
and Vacuum Filtration 5,^00 i|,750 13,^58 1,023 24,631
183
-------
Table C-14. NEW PROVIDENCE, NJ - SUMMARY OF PERFORMANCE,
COST AND SPACE REQUIREMENTS
Wet-Weather, Primary Clarifler Sludge
Initial residual sludge volume; 195,000 gal.
Initial residual sludge concentration: 0.12% solids
CO
Performance
Sludge Process
Dewaterlng % effluent
process solids
Gravity ,
thickening0 8.0 2,000
Flotation ,
thickening 5.9 1,200
Gravity
thickening & 13.0 170
centr If ugat ion
Gravity
fv±±9 27*5 2,082
& vacuum
filtration
Residual volume
Process
Sludge effluent,
gal . gal .
3,000 192,000
3,970 191,000
1,750 193,250
85f 195,000
Cost
Cap I tal
$ ,
41 ,300
76,000
100,300
109,300
Operating
$/year
1,273
3,624
3,737
5,298
Dewaterlng
sludge
haul i ng
cost,
I/year
15,000
20,000
8,750
425
Total
annual
costb,
$/year
21,124
32,500
24,268
18,561
Area,
sq ft
177
150
200
320
a. Based on mass balance.
b. Including amortization costs for a 20 year equipment life, 10% interest rate.
c. Assume 95% removal. d. Based on 97% removal.
e. Assume prethlckenlng to 4% solids prior to assumed centrifuge performance based on dry weather
sludge data.
f. Done on 1% sample.
-------
Table C-l 5. DETAILS OF OPERATING COST ESTIMATES
FOR NEW PROVIDENCE, NJ
Wet Weather Primary Clarlfier Sludge
Oje racing Costs ($/Year)
Dewaterlng Operating Ma I ntenance Chemical Power Total
Method Labor Costs Costs
Gravity Thickening 0 *f!3 gJ»Q 20 '
Flotation Thickening 1,800 1,520 0 30^ 3,62*»
Gravity Thickening 1,200 1,593 WO \Qk 3,737
and Centrifugal ion
Gravity Thickening
and Vacuum
Filtration 1,200 2,^53 1,573 72 5,298
185
-------
Table C-16. NEW PROVIDENCE, NJ - SUMMARY OF PERFORMANCE,
COST AND SPACE REQUIREMENTS
Wet-Weather, Final Clartfler Sludge
Initial residual sludge volume: 15,995 gal.
Initial residual sludge concentration: 2.5% solids
oo
Performance
Dewater Ing
process
Gravity
thickening
Flotation ,
thickening
Centrlfugatlon
Gravity
thickening &
vacuum
filtration
Sludge
%
solids
4.0
4.6
7.5
18.5
Process
effluent
mg/1
1 ,250C
750e
169
1,481
Residual volume
Sludge
gal .
9,997
8,693
5,332
2,161
Process
effluent,
_jal «
5,998
7,302
10,663
13,834
Capital Operating
$ $
69,000 1 ,848
99,300 4,512
71,000 4,297
121,000 10,299
Dewatered
sludge
hau 1 1 ng
cost
$/year
49,985
43,465
26,660
10,805
Total
annual
costb»
$/year
59,938
59,721
39,297
35,317
Area.
sq ft
737
780
50
586
a. Based on mass batanca
b. Including amortization costs for a 20 year equipment life, 10% Interest rate.
c. Assume 95% removal.
d. feed solids to flotation thickener - 32,300 mg/1 suspended solids.
e. Use 97% removal.
-------
Table C-17.DETAILS OF OPERATING COST ESTIMATES
FOR NEW PROVIDENCE, NJ
Wet-Weather - Final Clarlffer Sludge
Operating costs
Operating roan-
hours required
Dewaterlng method at $6/hr
Flotation thickening
Gravity thickening
Centrlfugatlon
Gravity thickening
1,800
0
1,200
1,200
Chemical
Maintenance cost
1,986
690
1,420
2,570
0
1,148
1,3*1
6,422
Power
cost
806
10
336
107
Total
cost
4 .592
1,848
4,297
10,299
and vacuum filtration
187
------- |