EPA-60Q/2-77-053c
December 1977
HANDLING AND DISPOSAL OF SLUDGES FROM
COMBINED SEWER OVERFLOW TREATMENT
Phase IN ~ Treatabillty Studies
by
R. Qsantowskl, A. Geinopolos, R. E. WulIschleger, M. J. Clark
Envirex Inc., Environmental Sciences Division
Milwaukee, Wisconsin 53214
Contract No. 68-03-0242
Project Officer
Anthony N. Tafuri
Storm and Combined Sewer Section
Wastewater Research Division
Municipal Environmental Research Laboratory (Cincinnati)
Edison, New Jersey 08817
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publi-
cation. 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.
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FOREWORD
The Environmental Protection Agency was created because of increasing public
and government concern about the dangers of pollution to the health and
welfare of the American peopler. Noxious air, foul water, and spoiled land
are tragic testimony to the deterioration of our natural environment. The
complexity of that environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is that necessary first step In problem solution
and it involves defining the problems, measuring its impact, and searching
for solutions. The Municipal Environmental Research Laboratory, develops
new and improved technology and systems for the prevention, treatment, and
management of wastewater and solid and hazardous waste pollutant discharges
from municipal and community sources, for the preservation and treatment of
public drinking water supplies, and to minimize the adverse economic, social,
health, and aesthetic effects of pollution. This publication is one of the
products of that research; a most vita! communications fink between the
researcher and the user community.
This report documents the results of an ongoing project Initiated to
evaluate the handling and disposal of combined sewer overflow (CSO) treat-
ment residuals by thickening-centrifugation.
Francis T. Mayo, Director
Municipal Environmental
Research Laboratory
iif
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ABSTRACT
This report documents the results of a project initiated to evaluate
the handling and disposal of combined sewer overflow (CSO) treatment
residuals. Bench scale thickening and pilot and full-scale centrlfugatlon
dewatering tests were performed at dry-weather and CSO treatment sites In
Kenosha, Racine, and Milwaukee, Wisconsin. CSO sludge at Kenosha is biolog-
ically generated; that at Milwaukee is physical in nature; and the Racine
CSO residuals are of physical-chemical origin. In addition, bench scale
anaerobic digestion studies were conducted to determine the effect of CSO
sludges on the anaerobic digestion stabilization process.
The results obtained from this project indicated that the dewatering of CSO
sludges appears feasible when the sludges are first degritted, where
required, and thickened prior to centrifugatIon. Under optimum centrifuge
operating conditions, thickened sludges were dewatered to cake concentrations
varying from 14.01 to 321 solids v/i th solids recoveries ranging from 80|
to 991. Similarly, the dry-weather sludges for the test sites were dewatered
to haulable cakes. Horeover, at Kenosha, the dewaterlng characteristics of
wet-dry weather sludge mixtures were similar to those for CSO sludge alone.
The bench scale anaerobic digestion studies showed that no significant
adverse effect was realized by adding CSO generated sludges to dry-weather
digesters at feed rates similar to that expected from a typical storm event.
Preliminary economic estimates indicate that first investment capital costs
for thicken Ing-centrifigation of CSO sludges ranged from 0.31 to 2.92
million dollars with annual costs of $^9,500 to $659,300 per year when
handling *».Q to 36.5 tons dry sludge per day. These cost ranges were
developed respectively, for the cities of Racine, Wl (population - 90,700;
CSO area - 702 acres), and Milwaukee, Wl {population - 670,00, CSO area -
16,800 acres).
The report recommends that a full-scale CSO sludge dewaterlng facility
employing degrittlng, thickening, and centrifygation should be developed as
a demonstration site for a further evaluation of the treatment of CSO
residuals.
This report was submitted In fulfillment of Contract No. 68-03-02^2 by the
Environmental Sciences Division of Envirex Inc. under the sponsorship of
the U.S. Environmental Protection Agency, Work for this report covers a
period from August, 1975 to September, 1976.
i v
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TABLE OF CONTENTS
Abstract iv
Table of Contents v
List of Tables vi i
List of Figures . x
Acknowledgments xiv
Section
I Conclusions 1
II Recommendations 7
Ml Introduction 8
IV Discussion of Results 9
Sludge Thickening 10
Sludge Dewaterlng 12
Heavy Metals Data 19
Digester Study Data 2!
V Description of the CSO Test Sites Investigated 2*1
Milwaukee, Wisconsin 2k
Racine, Wisconsin 26
Kenosha, Wisconsin 29
VI Sampling, Testing and Evaluation Procedures 33
Bench Scale Thickening Tests 33
Centrifuge Dewataring Tests 35
Heavy Hetals Testing 48
Bench Anaerobic Digestion Studies 48
VII Results of Sludge Thickening - Centrtfugation Studies 52
Conducted in Kenosha, Wisconsin
Flotation Thickening Tests 56
Centrifuge Dewaterlng Tests 57
Effect of Centrifugation on Heavy Metal Distribution jg
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TABLE OF CONTENTS (continued)
Section
VIII Results of Sludge Thlckening-Centrlfugation Studies 86
Conducted in Milwaukee, Wisconsin
Bench Scale Clarification Teats 88
Centrifuge Dewatering Tests 89
Effect of Centrifugal ion on Heavy Metals Distribution !0°
IX Results of Sludge Thickening - Centrifugatlon Studies
Conducted in Racine, W! scons in
Bench Scale Gravity Thickening Tests
Centrifuge Dewatering Tests
Effect of Centrlfugatlon on Heavy Metals Distribution 12°
X Results of Anaerobic Digestion Studies 126
Results Obtained Using Kenosha, Wisconsin Dry and
Wet-Weather Sludges 126
Results Obtained Using Racine, Wisconsin Wet-Weather 135
Sludge
XI Design Criteria and Economic Considerations
• Kenosha, Wisconsin
Milwaukee, Wi scons in 148
Racine, Wisconsin 155
XII References I6l
XII! Appendices
Appendix A - Kenosha, Wisconsin Centrifuge Test Data 163
Appendix B - Milwaukee, Wisconsin Centrifuge Test Data 197
Appendix C - Racine, Wisconsin Centrifuge Test Data 219
Appendix D - Bench Scale Anaerobic Digestion Test Data 239
and Calculations
Appendix E - Glossary of Terms 253
VI
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LIST OF TABLES
Table
Number Page No.
I Research Site Descriptions, Space, And Cost 6
Requirements
2 Comparison of Results - Bench Scale Flotation
Thickening Tests - Kenosha, Wisconsin 11
3 Comparison of Optimum Operating Parameters
Centrifuge Dewatering Tests - Kenosha, Wisconsin 1*t
k Comparison of Optimum Operating Parameters Centri-
fuge Dewatering Tests - Racine, Wisconsin 17
5 Test Site Average Total Volatile Solid Sludge
Concent ra 15 ons 1S
6 Comparison of Quality of Combined Sewage For
Various Cities 55
7 Results of 121.9 cm (48 in.) Basket Centrifuge
Tests Using Wet-Weather, Thickened WAS Sludge
From Kenosha, Wisconsin 68
8 Results of 121.9 cm (48 in.) Basket Centrifuge
Tests Using Dry-Weather, Thickened WAS and
Primary Sludges From Kenosha, Wisconsin 69
9 Results of 121.9 cm (48 In.) Basket Centrifuge
Tests Using a Mixture of Wet-Weather/Dry-
Weather Thickened Sludge From Kenosha, Wisconsin 7*J
10 Heavy Metal Concentrations for Centrifuge Tests
Using Kenosha Dry-Weather Sludge (Thickened WAS) 30
11 Heavy Metal Concentrations for Centrifuge Tests
Using Kenosha CSO Sludge SO
12 Effect of Centrlfugation on the Distribution of
Heavy Metals (Based on One Liter of Feed Sludge)
(All Values In mg) 82
vil
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LIST OF TABLES (continued)
Table
Number Page_Hp.
13 Heavy Metal Concentrations for Centrifuge Tests
Using Kenosha CSO/Dry-Weather Sludge Combination 83
14 Heavy Metal Mass Balances for the 121.9 cm (48 in.)
Basket Centrifuge Tests, Kenosha CSO/Dry-Weather
Sludge Combination °^
15 Results of the Thickened Sludge Solids Analysis -
Milwaukee Wet-Weather Sludge 37
16 Results of the Thickened Sludge Subnatant Sieve
Analysis - Milwaukee Wet-Weather Sludge 37
17 Results of Bench Scale Clarification Tests
Milwaukee, Wisconsin 90
18 Results of 12U9 cm (48 In.) Basket Centrifuge
Test Using Wet-Weather, Thickened Sludge Super-
natant From the Milwaukee Humboldt Avenue Site 9'
19 Results of 30.5 cm (12 in.) Basket Centrifuge
Test Using Wet-Weather Thickened Sludge From
Milwaukee - Humboldt Avenue Site 92
20 Results of the Decanter Centrifuge Tests Using
Dry-Weather Sludge - Milwaukee South Shore Water
Pollution Control Plant 93
21 Heavy Metal Concentrations for Centrifuge Tests
Using Milwaukee Wet-Weather Sludge 100
22 Heavy Metal Concentrations for Centrifuge Tests
Using Milwaukee Dry-Weather Sludge (Primary) 103
23 Results of the Decanter Centrifuge Tests Using
Dry-Weather Sludge - Racine Water Pollution Control
Plant 110
2k Results of the Decanter Centrifuge Tests Using
Wet-Weather Sludge - Racine Wet-Weather Site No. I 117
25 Heavy Meta! Concentrations for Centrifuge Tests
Using Racine Dry-Weather Sludge 124
26 Heavy Metal Concentrations for Centrifuge Tests
Using Racine Wet-Weather Sludge 124
vt 11
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LIST OF TABLES (continued)
Table
Number^ Page No.
27 Honitoring Parameters for Control and Variant
Laboratory Digesters (Kenosha Sludges) 128
28 T-Statfstic Test Results (Kenosha Study) (5%
Significance Level) '31
29 Distribution of Heavy Metals in Kenosha Sludge 136
30 Monitoring Parameters for Control and Variant
Laboratory Digesters (Racfne Wet-Weather Sludge) 138
31 Concentration of Heavy Hetals in Feed, and Digester
Sludges Using Racine CSO Sludge for Simulated Wet-
Weather Feed. (Concentrations in mg Metal/kg Dry
Solids)
32 Kenosha, Wl - Summary of Cost and Space Require-
ments '
33 Economic Evaluation Assumptions
3k Milwaukee, Wl - Summary of Cost and Space
Requirements 152
35 Racine, W! - Summary of Cost and Space Require-
ments '57
IX
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UST OF FIGURES
Figure
Number Page No.
1 Schematic diagram of the Milwaukee, Wisconsin CSO
demonstration storage facility 25
2 Schematic of Racine CSO treatment facility 27
3 Relationship between the Kenosha, Wl CSO demonstra-
tion treatment system and the conventional treatment
plant 30
4 Envtrex 30.5 cm (12 In.) basket centrifuge and pump
package 36
5 Envlrex 30.5 cm (12 In.) basket centrifuge - front
view 37
6 Sample 30.5 cm (12 In.) Basket Test Data Sheet 39
7 Envirex mobile centrifuge van's 121.9 cm (48 In.)
basket centrifuge 41
8 Envlrex 121.9 cm (48 In.) basket centrifuge - front
view 42
9 Forward and rear side views of the Envlrex centrifuge
van 43
10 Schematic diagram of a decanter centrifuge 45
. 1! Envlrex mobile centrifuge van's decanter centrifuge 46
12 Laboratory scale anaerobic digesters 49
13 Flotation thickening tests run 1 - Kenosha dry-
weather WAS 58
14 Flotation thickening tests run 2 - Kenosha dry
weather WAS 59
15 Flotation thickening tests run 3 - Kenosha wet-weather
WAS 60
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LIST OF FIGURES (continued)
Figure
Number _Page No.
16 Flotation thickening tests run 4 - Kenosha wet- and
dry-weather UAS combination *>'
17 30.5 cm (12 in.) Basket centrifuge tests on Kenosha
dry-weather sludges (without chemicals) ^3
18 30,5 cm (12 in.) Basket centrifuge tests on Kenosha
dry-weather sludges (without chemicals) '34
tg 30,5 cm (12 in.) Basket centrifuge tests on Kenosha
dry-weather thickened WAS alone (with polymer and
feed rate =3.0 kg/hr) 65
20 30,5 cm (12 f'n.) Basket centrifuge tests on Kenosha
combined dry-weather sludges (with polymer and feed
rate = 4.6 kq/hr) 66
21 Relationship between cake concentration and solids
feed rate [121.9 cm (48 fn.) basket centrifuge tests -
Kenosha sIudges j 7'
22 Relationship between solids recovery and solids feed
rate [121.9 cm (48 In.) basket centrifuge tests -
Kenosha sludges] ™
23 Relationship between cake concentration and solids
feed rate 121,9 cm (48 in.) basket centrifuge
tests-Kenosha wet-weather/dry-weather sludge coffibina-
tion 76
2k Relationship between solids recovery and solids feed
rate 121.9 cm (48 In.) basket centrifuge tests - Kenosha
wet~weather/dry-weather sludge combination 77
25 Cake concentration and solids recovery vs. polymer
dosage 121.9 cm (43 in.) basket centrifuge tests -
Kenosha wet-weather/dry-weather sludge concentration 79
26 Bar graph of cake solids and recovery vs. test runs
dry-weather sludge, Milwaukee, Wl 94
27 Cake solids and recovery vs. feed rate (kg/hr) dry-
weather sludge, Milwaukee, Wl 95
23 Cake solids vs. feed rate (kg/hr) dry-weather sludge,
Hilwaukee, Wt 97
xf
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LIST OF FIGURES (continued)
Figure
Number Page No.
29 Recovery vs. feed rate (kg/hr) dry-weather sludge,
MiIwaukee, Wl 93
30 Cake solids and recovery vs. differential speed (An)
dry-weather sludge, Milwaukee, Wl 99
31 Cake solids and recovery vs. polymer dosage dry-
weather sludge, Milwaukee, Wl 101
32 Flux concentration curve for dry-weather sludge,
Racine, Wl 106
33 Flux concentration curve for wet-weather sludge
Racine, Wl 107
3^t Flux concentration curve for wet-weather/dry-weather
sludge combination, Racine, Wl 108
35 Bar graph of cake solJjls and recovery vs. test runs,
dry-weather sludge, Racine, Wl 111
36 Cake solids vs. feed rate, dry-weather sludge, Racine
Wl 112
37 Recovery vs. feed rate (kg/hr) dry-weather sludge,
Racine, Wl 113
38 Cake solids and recovery vs. polymer dosage (kg/metric
ton) dry-weather sludge, Racine, Ml 115
39 Cake solids and recovery vs. differential speed (An),
rpm, dry-weather sludge, Racine, V/l 116
^»0 Bar graph of cake solids and recovery vs. test runs
wet-weather sludge, Racine, W! 1|8
41 Cake solids and recovery vs. feed rate wet-weather
sludge, Racine, Wl 119
^2 Cake solids and recovery vs. feed rate wet-weather
sludge, Racine, Wl 121
^3 Cake solids and recovery vs. differential speed wet-
weather sludge, Racine, Wl 122
XI I
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LIST OF FIGURES (continued)
Figure
Number Page Mo.
kk Cake solids and recovery vs. polymer dosage wet-
weather sludge, Racfne, Wt 123
& Effect of wet-weather sludge on anaerobic digestion -
Kenosha study (control digester minus test digester
pH and total gas product? on values) 1 30
& Effect of wet-weather sludge on anaerobic digestion -
46b Kenosha study (control digester minus test digester
CH and COCH values) 132
k7 Total gas production of control and variant digesters
48 Thickening-dewatering schematic Kenosha CSO sludge 146
49 Solids dewatering schematic Kenosha wet-weather/dry-
weather sludge combination 149
50 Dewatering schematic Milwaukee CSO sludge 153
51 Dewatering schematic Racine CSO sludge 558
xf i i
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ACKNOWLEDGMENTS
EnvJrex Inc. acknowledges the cooperation and support of the Environmental
Protection Agency. The assistance given by Project Officer, Anthony Tafurl,
and Richard Field, Chief of the Storm and Combined Sewer Section, Municipal
Environmental Research Laboratory (Cincinnati), USEPA, Edison, New Jersey
was received with much appreciation.
Special thanks are also extended to Ken Tappendorf, John Schlintz, and Joe
Grinker of the Milwaukee Sewerage Commission for their enthusiastic coopera-
tion in making the Milwaukee field test sites available for this project.
Stan Budrys and Jim Gursky of the City of Racine Water Pollution Control
Department provided much assistance for this project's use of the Racine
facilfties.
Gerald Selin of the Water Pollution Control Division of the City of Kenosha
is also gratefully acknowledged for his help and cooperation during the
experimental testing conducted on the grounds of that city's water pollution
control plant.
The authors also wish to express their grateful appreciation to the many
Envlrex personnel who contributed to the success of this project. Collection
of the field data was performed in part by Project Engineers, Ernest
Bollinger and Jerry Jordan. Chemist Rick Fulk helped in the evaluation of
the bench scale anaerobic djgester data. All of the many analyses were
performed by the very capable personnel of the Environmental Sciences
Division laboratory.
Finally, the authors would like to extend a sincere thank you to all of the
many other people who added their valuable comments and criticisms and by
doing so, helped to successfully complete the project.
XIV
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SECTION I
CONCLUSIONS
I. Characteristics of the Sludges Tested
a. The solids concentrations observed for the combined sewer overflow
(CSO) untblckened sludges were as follows;
Storage-Sedimentation (Milwaukee) - 0.02-0, HI
Screening/Flotation (Racine) - 0.05-0.1%
Biological (Kenosha) - 1.37-1.391
b. The raw CSO sludges derived from physical treatment (Milwaukee) and
from physical-chemical treatment (Racine) were similar in that they
contained more grit and were more dilute than their dry-weather
counterparts.
The solids content of the settled sludge from storage-sedimentation
(Milwaukee) was appreciably lower than that expected (2.51-5.01)
(5) from storage-sedimentation treatment of CSO, indicating that
dewatering of individual CSO sludges should be investigated
individually on their own merits.
c. The raw CSO sludge derived from biological treatment (Kenosha) was
similar tn nature to that of Its dry-weather counterpart.
d. The heavy metal (Zn, Pb, NI, Cu, Cr, Hg, Cd) data generated In this
study were quite variable between test sites. The dry-weather and
wet-weather range of heavy metal centrifuge feed concentrations are
presented below:
Dry-weather sludge Wet-weather sJudge
concentration range concentration range
mg_ me t_a 1 /kg soj _j_dI s_ mg metal /kg sol ids
Zinc HtSO-3681 710-3125
Lead 522-6900 410-1563
Nickel J40-H5 333-1563
Copper 600-1565 250-2170
Chromium 755-7600 110-3281
Mercury 0.975-W2 1.30-15.63
Cadmium kj 50
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The study concluded that the heavy metals appear to be solids
related with only slight concentrations observed In the soluble
portion of the sample. Therefore, heavy metal removal was
directly related to solids removal.
2, Sludge Thickening
Sludge thickening fs the first step In the thlckenlng-dewaterlng of CSO
sludges and removes the major portion of the liquid associated with the
raw sludge.
In this study, thickening was Investigated using bench-scale techniques.
The results obtained from testing the sludges from the various test sites
are summarized below,
a. Milwaukee (Storage-Sedimentation)
(I) The dilute (0.21 solids) sludge could be further concentrated
(to about 1.33! solids) by gravity thickening using chemicals
(ferric chloride and'polymer),
(2) Because of the dilute (0.2% solids) nature of the CSO sludge
obtained, the possibility of bleed/pump-back of the sludge to
the dry-weather plant was investigated by clarification testing
to determine the effect of bleed/pump-back on dry-weather
primary treatment.
The conclusions reached from the bench scale clarification tests
conducted on the Milwaukee physical wet-weather sludge, dry-
weather wastewater, and combinations of the two indicated that
the settling characteristics of the three wastes were similar.
Typical effluent solids ranged from 12-16 mg/1 for Influent
concentrations of 2QQ-%75mg/l« Chemical treatment Included
ferric chloride and polymer.
b. Racine (physleal-chemical)
The Racine physleal-chemical CSO sludge can be gravity thickened to
as high as H.0 percent solfds. This compares to gravity thickening
results of 3-0 percent for dry-weather sludge and ^.0-5.0 percent
for wet-weather/dry-weather sludge combinations.
c. Kenosha (biological)
The bench scale flotation thickening tests conducted on the Kenosha
biological sludges indicated that flotation thickening of the dry-
weather sludge, wet-weather sludge and the wet-weather/dry-weather
combined sludge was feasible and produced similar results. The
expected float concentrations and thickener loadings for these
sludges would be similar to current full-scale practice at the
Kenosha Water Pollution Control Plant [4.0% solids at 50 kg/m2/day
(10 Ib/ft2/day)].
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3. Centrifuge Sludge DewaterJng (pJJot and full-scale)
The following conclusions were drawn from the centrifuge dewaterlng
tests performed at the test sites.
a. Milwaukee (storage-sedimentation)
(I) It does not appear practical to dewater the gravity settled
Milwaukee CSO physical sludge without pretreatment. The dilute
sludge generated at this site contains significant amounts of
grit and widely dispersed organic solids. Attempts were.made
to dewater the gritty sludge, but the basket centrifuge and feed
Unes continuously clogged. One of the runs completed using the
30.5 cm (12 In.) basket centrifuge to dewater the degritted
dilute sludge yielded results of 28,4 percent cake and 82 percent
solids recovery. Based on this result and those obtained In
Phase I (I), it can be concluded that the Milwaukee wet-weather
sludge Is amenable to basket centrifuge dewatering provided the
sludge Is degritted and gravity thickened to about 2 percent
sol Ids content.
(2) The Milwaukee dry-weather primary sludge can be dewatered to a
haulable cake using a decanter centrifuge. Typical cake concen-
trations between 14.5"17«0 percent solids were achieved with
solids recoveries of 80-95 percent. Polymer requirements are
estimated at 0.88-1.24 kg/metric ton (1.76-2.48 Ib/ton).
b. Racine (physical-chemical)
(0 The Racine wet-weather physical-chemical sludge generated fs
quite similar to the Milwaukee physical CSO sludge produced.
The thickened sludge is very dilute and contains large amounts
of gritty material. Several dewatering runs were conducted
with the dilute screened CSO sludge using a decanter centrifuge.
For an optimum run, values of 32 percent cake solids and 92
percent solids recovery were obtained. Polymer requirements are
estimated at 0.96 kg/metric ton (1.92 Ib/ton). Based on the
findings obtained, it can be concluded that the dilute sludge
dewaters quite wet). The results of this research, in addition
to the data generated In Phase I (1), indicate that centrifuge
dewaterlng the CSO sludge would be feasible provided degrfttlng
and gravity thickening steps preceded centrifugalIon.
(2) The Racine dry-weather sludge (primary and thickened WAS) can be
dewatered to 30 percent haulable cakes with 99 percent suspended
solids recoveries using a decanter centrifuge. An expected polymer
dosage of 1.2 kg/metric ton (2.4 Ib/ton) would be required.
c. Kenosha (biological)
Under optimum conditions, the Kenosha CSO biological sludge can be
dewatered without polymer, to a 14.0 percent cake solids
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concentration with a basket centrifuge. The expected suspended
solids recovery Is 94.5 percent. Similarly, for dry-weather sludge,
an optimum cake of 17-5 percent was obtained with a corresponding
solids recovery of 93*5 percent. The dewaterlng characteristics of
the wet-dry weather sludge mixtures were similar to those obtained
for the CSO sludge alone, that is, optimum cake concentrations of
14 percent with solids recoveries In excess of 95 percent.
4. Bench Scale Anaerobic Digestion Study
The conclusions drawn from the tests performed on two laboratory diges-
ters (test and control) are presented below.
a. Kenosha (biological)
(1) Kenosha CSO sludge added to a laboratory test digester In an
amount representing the CSO solids generated by a 1,27 cm
(0.5 In.) and a 2.54 cm (I In.) rainfall had no statistically
significant effect (951 confidence level) in'digester gas
production, methane production, pH, and CQ2/CHlj ratio when
compared to a second laboratory digester fed dry-weather
sludge only, at a similar organic loading. The sludge represent-
ing the 1.27 cm (0.5 In.) rainfall was fed to the digester over
a period of two days; the sludge representing the 2.54 cm
(1 In.) storm was added in one day,
(2) When the laboratory test digester was fed Kenosha CSO sludge
exclusively for ten days, total gas production and methane
production was significantly lower (951 confidence level) than
that of the control digester fed dry-weather sludge at a similar
organic loading. The C02/CHi| ratio was not statistically
different. Volatile acid concentrations and the volatile acid/
alkalinity ratio remained low. The efficiency of the wet-weather
digester in terms of volume of gas produced per weight of
volatile solids destroyed was higher than for the control
digester.
b. Racine (physical-chemical)
(1) The laboratory digester fed Racine CSO sludge in an amount
representing the solids produced by a 2.54 cm (1 In.) rainfall
(added in one day) produced less gas than the laboratory fed
dry-weather sludge digester at a similar organic loading. The
difference was statistically significant at the 95 percent
confidence level but not at the 99 percent confidence level.
(2) In the Racine tests a decrease in total gas production was the
only evidence of a detrimental effect of Racine CSO sludge on
the laboratory digester performance. Volatile acid concentra-
tions and the volatile acld/alkalfnlty ratio remained low. The
volume of gas produced per weight of volatile solids destroyed
was similar for both digesters. The decrease In gas production
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after the Racine wet-weather sludge was fed to the laboratory
digester is not attributable to the heavy-metal concentrations In
the wet-weather sludge,
5. Costs for Thickening-Centrifuge Dewatering of Sludges
It is emphasized that the costs presented are given as a first approximation.
If a detailed economic evaluation fs necessary or desired, the individual
site must be examined separately with respect to locale, rainfall patterns,
type and location of treatment system, sludge characteristics, etc. Then
equipment and installation costs should be established from vendors and con-
tractors.
As a part of this study, annual costs which include both capital and O&M
costs have been developed for each site. The capital expenditures Include
the necessary equipment to provide a dewatered sludge. Examples of capital
costs Include sludge pumping costs, thickening costs (CSO sludge only), and
centrifugation costs. Degrittlng costs have also been developed as
necessary. Amortization is based upon a 20 year term and 6 percent cost of
money. Zero salvage value has been assumed. The estimated costs for the
sites investigated are shown in Table 1.
The costs generated were derived according to dry solids handling capacity.
Wet-weather sludge volumes are those generated from a 1.27 cm (0,5 In.)
rainfall on the CSO area, assuming a two day bleed/pump-back to the
treatment facility.
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TABLE I. RESEARCH SJTE DESCRIPTIONS, SPACE, AND COST REQUIREMENTS
Dry solids handled (ton/dayT Treatment space required (ft2)
Site
Kenosha
N! Iwaukee
Racine
CSO Dry- Wet- Dry- Wet-
area weather weather Mixture: weather weather Mixture:
(acres) sludge sludge dry-wet sludge sludge dry/wet
1,331 20.8 5.5
16,800 54.5 35.6
702 39.7 4.0
26.3
1,700 2,200 4,200
3,100 7,600
1,000 1,700
Site
Kenosha
Ml Iwaukee
Racine
Capital costs (mil lion $)
Dry- Wet-
weather weather Mixture:
sludge sludge dry /wet
1.12 0.95 2.19
1.90 2.92
1.64 0.31
Annual costs t$/yr)
Dry-
weather
sludje
219,900
488,400
408,900
Wet-
weather Mixture;
sludge dry /wet
114,000 345,500
659,300
49,500
NOTE; acres x 0.405 ** hectares
ft2 x 0.00929 - m2
ton x 0.907 a metric ton
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SECTION II
RECOMMENDATIONS
It Is recommended that a full-scale demonstration Installation be constructed
to further evaluate the application of the dewaterfng treatment train for
disposal of combined sewer overflow treatment sludges.
The dewatering treatment train recommended would be comprised of degrtttfng
(where required), thickening and centrlfugation.
In selecting degritting equipment, the swirl concentrator design should be
considered along with conventional grit removal equipment.
Thickening equipment may be either of the gravity or flotation type
depending on the CSO sludge to be treated.
Similarly, centrlfugation equipment may be either of the basket or decanter
type, as appropriate.
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SECTION I II
INTRODUCTION
The discharge of untreated sanitary and stormwater overflows from combined
sewer systems to receiving waters during and after heavy rains has been
found to be one of the most significant causes of water quality
deterioration. These storm generated discharges constitute a very high
degree of pollutlonal loading to watercourses as measured by the usual
standards of biochemical oxygen demand, solids, colJform organisms, and
nutrients. Various alternatives have been advanced for dealing with the
problems created by these discharges. Most of these alternatives Include
some form of treatment for the combined sewer overflow (CSO).
As with most wastewater treatment processes, treatment of CSO will result in
residuals which contain, in concentrated form, the objectionable contami-
nants present in the raw CSO, The handling and disposal of these residual
sludges from CSO treatment systems have been generally neglected, thus far,
in favor of developing methods of treatment for the CSO Itself, However,
sludge handling and disposal should be considered an Integral part of any
CSO treatment system because it will significantly affect the overall
efficiency and cost of the system. Despite these possible Impacts there
is Itttle Information available In the literature concerning the character-
istics, methods of disposal, and economic impact of handling CSO sludges.
The United States Environmental Protection Agency (EPA) has recognized this
need for defining the problems and establishing handling and disposal
techniques for residual sludges from CSO treatment. In 1973, the EPA
awarded Contract No. 68-03-02^2 to Envirex Inc. to conduct a feasibility
study (Phase I) of a program whose overall project objectives were:
1. Characterize the residual sludges arising from the treatment of
CSO.
2. Develop and demonstrate systems for handling and disposing of the
sludges arising from the treatment of CSO.
3. Develop capital and operating costs for the handling and disposal
systems developed and demonstrated.
The feasibility study (Phase () was completed in February, 1975 (1).
Conclusions drawn from the work performed indicated that thickening-
centrifugation and thickening-vacuum filtration were the applicable
dewatering methods.
-------
A second Phase, completed in February 1976, documented the results of an
assessment of the effort that the United States will have to exert in the
area of sludge handling and disposal if, in fact, full-scale treatment of
combined sewer overflows is to become a reality. Evaluation of the effect
of bleed/pump-back of CSO sludge on the hydraulic,'solids and/or organic
loadings to the dry-weather plant Indicated that overloading would occur
in most instances. Disregarding grit accumulation in sewers plus other
transport problems, it was established that solids loadings to the secondary
clarifier were limiting and required 8-22 day bleed/pump-back periods.
There may also be a toxic danger to dry-weather treatment plant biological
processes.
This report documents the activities for Phase III of the overall project.
The objectives of the third phase were to:
1. Demonstrate and evaluate, on a pilot-scale, the effectiveness of
thickenlng-centrifugation as a method for the handling and disposal
of CSO sludges.
2. Demonstrate and evaluate, on a bench-scale basis, the effectiveness
of anaerobic digestion of an appropriate CSO sludge.
3. Develop basic design criteria and operating characteristics for the
thickening-centrlfugation dewatering system In a form that can be
translated into actual practice.
4. Develop capital and operating costs for the thickening-centrifuga-
tion dewatering system.
These objectives were met through the use of a mobile centrifuge sludge
dewatering van which was taken to three selected CSO treatment sites. At
the sites, the CSO sludges were thickened and then dewatered using either
a 30.5 cm (12 in.) or a 121.9 cm (48 in.) basket centrifuge or a decanter
centrifuge, all of which are on the mobile van. A bench-scale anaerobic
digestion system was also constructed and operated to evaluate anaerobic
digestion of CSO sludges.
In addition, for each CSO treatment site visited, the city's dry-weather
treatment plant sludge was also tested using the thickenlng-centrifugation
process. These data allowed comparisons to be made between the use of
thickening-centrlfugation for dewatering CSO generated sludges and the
sludges generated by municipal sewage treatment plants.
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SECTION IV
DISCUSSION OF RESULTS
Future sections of this report will Individually cover in relatively great
detail the results of the work performed In the field and in the laboratory
with regard to:
t. The character and nature of the sludges derived from physical,
physical-chemfcal and biological treatment of CSO.
2. The thickening/centrifugation dewatering characteristics of the
CSO sludges, the dry-weather sludges and combinations of the two.
3. The heavy metal contents of the CSO sludges, the dry-weather
sludges and combinations of the too,
4. The effect of loading dry-weather anaerobic digesters wfth CSO
siudges.
In this section, the detailed information has been sifted and carried forward
to summarize pertinent technical and design information which will be needed
in subsequent evaluation and to bring out the similarities and differences
observed between the sludges as they affect operation, performance and design.
The discussion which follows includes the following Items:
1. Selection of thickening method and centrifugation equipment to be
used for the sludges tested.
2. Optimum ooerating parameters for thickening and centrifugation as
well as operating problems observed and means for their solution.
3- Similarities and differences observed between the sludges Investi-
gated with regard to character, dewaterability, heavy metal content
and effect on anaerobic digestion.
SLUDGE THICKErthIG
Bio I og i ca 1 51 udges - Kenosha,_J,-/j_
The bench scale flotation thickening results on the Kenosha biological
sludges yielded pood sludqe concentrations at low to moderate loadinqs. A
comparison of results for the three sludges tested is presented on the follow-
ing page In Table 2,
10
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TABLE 2. COMPARISON OF RESULTS - BENCH SCALE FLOTATION
THICKENING TESTS - KENQSHA, WISCONSIN
Es 11 mated'"!oad j ngs *aT~fr% so 11 d s
_ „ ,
Sludge type kg/m /day Ib/ft /day
Dry-v/eather WAS MS.9-73.4 10-15
v/et-weather WAS 53-8 11
Wet-weather/dry-weather 44.0 9
comb i n a 11 on WAS
The data indicate that a flotation thickener may be operated at the solids
loadinas shown above to yield a floated sludqe concentration of 4 percent
solids. The use of higher solids loadings to the flotation thickener will
result !n lower concentrations of thickened sludge. The data further demon-
strate that the loadings to the thickener to obtain a 4 percent sludge
v/ou!d be slightly less for the wet-weather/dry-weather sludge combination
vhen compared to either the dry-weather or wet-weather individual sludges.
This lower toadlnq rate however, is so minimal that it should not adversely
affect the economics of thickening the combined sludges on a full-scale.
-The bench scale results are consistent with the data generated in the Phase I
Heport (1), In Phase I, a wet-weather sludge concentration of 4.0 to 5.0
percent solids was achieved at mass loading rates of 5Q~100 kg/tn^/day (10-
20 Ibs/ft2/day). Presently, the tsenosha V/ater Pollution Control Plant's
full-scale flotation thickeners operate at a solids loading of 50 kg/m^/day
(10 Ib/ft2/day) which also compares well to the bench scale thickening results.
Physical Sludges - Hjjwaukee,__W|_
The results of the bench scale clarification tests conducted on the Milwaukee
sludges and wastewater Indicated that excellent effluent quality could be
obtained with chemical addition. The low effluent suspended solids (14-16
mg/1) of the Humboldt Avenue wet-weather supernatant makes it feasible for
discharge to the receiving body or return to the municipal sewer.
Slightly better effluent solids results were obtained for both the South
Shore dry-weather wastewater and the mixture of wet-weather sludge and dry-
weather wastewater. This occurred even though the dry-weather raw waste
"suspended solids were higher than the wet-weather sludge. Based on the data
presented In Table 1?» Section VIII, settling characteristics of the three
wastes tested were quite similar. No adverse effects were observed in any of
the parameters tested which indicated interferences in settling by the addi-
tion of wet-weather sludge to the dry-weather wastewater.
The residual wet-weather sludge volume that would be obtained through chemi-
cal clarification (15-20 ml/1) (J5-20 gal./1000 gal.) could then be con-
sidered for dewatering with basket centrifuges provided it had been pre-
11
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viously pretreated to remove grit, rags, sticks, and other materials which
would Interfere with the centrifugalIon process.
Phase I (I) showed that the sludge concentration following clarification was
1.7*» percent solids. This volume of sludge, which represents only about 0.9
percent of the total CSO generated (1) could be evaluated for degrlttlng
after clarification. The economic advantages of degrtttlng only this small
percentage of flow with a swirl concentrator or similar unit are most attrac-
tive. This alternative Is discussed more thoroughly In the Section XI,
economic evaluation.
Physical-Chemical Sludges - Racine, Wl
The bench scale gravity thickening tests conducted on the Racine physical-
chemical sludges demonstrated that significant differences In settling ,
characteristics exist between the dry-weather and wet-weather sludges. The
dry-weather sludge thickened to 3-0 percent at a mass loading of 1650 kg/m2/
day (338 Ib/ft2/day). Presently, the Racine Water Pollution Control Plant
Is obtaining an 8.9 percent sludge by returning waste activated sludge to the
primary settling basins for thickening.
The Racine wet-weather sludge was gravity thickened to an underflow sludge
concentration of 14.0 percent solids. This value compares favorably to an
earlier report (1). Therefore, as a result of thickening, sludge volume
through the CSO system could be substantially reduced. However, pumping
problems could result because of the viscous and gritty nature of the sludge.
This fact should be kept In mind In any future design considerations. Pre-
treatment requirements for thJs sludge will be discussed more thoroughly
later In this section.
The wet-weather/dry-weather sludge combination thickened to 4.0-5.0 percent
solJds at mass loadings of 610-885 kg/m2/day (125-181 Ib/ft2/day). This
concentration Is slightly higher than that of the "dry-weather only" sludge.
The increased concentration is due primarily to the presence of the wet-
weather sludge. The settling characteristics of this sludge mixture Indicated
that no adverse effects would occur by the bleedback of wet-weather sludge
to the dry-weather plant.
It is Important to note that the bench scale mass loading rates obtained are
appreciably higher than typical full-scale design gravity thickener loadings.
Therefore, although the above data are useful for comparative purposes, It
should not be used as full-scale design criteria.
SLUDGE DEWATERING
BiologicalSludges - Kenosha, WJ
The results of the Kenosha biological sludge centrlfugation studies Indicated
that the dewaterlng characteristics of the wet-weather sludge, dry-weather
12
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sludge, and wet-weather/dry-weather sludge combination were quite similar.
Table 3 was constructed to list the optimum operating parameters for the
three types of sludges tested. The wet-weather/dry-weather sludge mixture
is shown for operational parameters both with and without polymer.
The overall optimum full-scale dewatering parameters for the three biological
sludges stud-led reveal some Important characteristics as shown in Table 3-
One of these pertinent facts Is that the dry-weather sludge dewatered to a
slightly higher cake (17-5 percent) and had a slightly higher process rate
(144 kg/hr) (317 Ib/hr) as compared to those sludges containing all or part
CSO sludge.
Comparing the results of the full-scale 121.9 cm (48 in.) basket centrifuge
tests with those of the 30«5 cm (12 In.) basket centrifuge tests shows that
they are very similar. The preliminary work with the small basket centrifuge
Indicated that an optimum dry-weather sludge (primary plus thickened WAS)
feed rate would be 4.0 kg/mln (8.8 Ib/min). This rate would produce a cake
concentration of 14.0 percent solids and a SS recovery of 94 percent. During
the full-scale centrifuge testing, the optimum feed rate was 3.6 kg/mln (8.0
)b/min) With a resultant cake concentration of 17-5 percent solids and 93.5
percent SS recovery. In fact, the full scale testing of dry-weather sludge
indicated that the optimum feed rate may be higher than 3-6 kg/mfn (8.0 lb/
min). It was planned to Include greater feed rates than 3-6 kg/min (8.0 lb/
min), but this was not achieved because the feed solids concentrations were
less than expected at the time of the tests.
The results of the full-scale CSO sludge testing were similar to the results
of the small basket centrifuge testing of dry-weather thickened WAS. This
would be expected because both are biological sludges. The results of the
30.5 cm (12 In.) centrifuge testing of dry-weather thickened WAS showed an
optimum feed rate of 2.6 kg/mln (5.7 Ib/mln), producing a cake concentration
of 11.5 percent solids and a solids recovery of 96 percent. For the 121.3 cm
(48 In,) basket centrifuge testing of the CSO sludge, the optimum feed rate
was 2,4 kg/min (5.3 Ib/mtn) and it resulted In a 14.0 percent cake concentra-
tion and a SS recovery of 94,5 percent. The higher cake concentration for the
sludge fs attributed to more Inert solids In the sludge. The presence of these
Inert solids In the sludge would be expected to produce better dewatering
characteristics.
The full-scale CSO sludge centrlfugation tests yielded better cake results
tHarr the-bench s-ea-le GSB- s-J-udtje—dewatering-study conducted in the Phase I
(1). The optimum Phase 1 cake soiids obtained was 8.9 percent with a 99-3
percent recovery. The lower cake solids value obtained in Phase I would be
expected due to the scale down factors In the lab centrifuge.
The optimum operating parameters for the CSO/dry-weather sludge combination
are also compared in Table 3» The results were obtained using the full-
scale 121.9 cm (48 In.) basket centrifuge. For the sludge containing no
polymer, the optimum feed rate was 1.97 kg/min (4.34 Ib/min), yielding a cake
concentration of 14,3 percent and a suspended solids recovery of 94,6 percent,
At this loading, 99 kg (218 lb) of sludge could be processed per hour. For
13
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TABLE 3. COMPARISON OF OPTIMUM OPERATING PARAMETERS
CENTRIFUGE OEWATERING TESTS - KENOSHA, WISCONSIN
Feed rate, kg/m!n (ibs/imn)
Cake concentration, % solids
SS recovery, %
Average feed cone,, I solids
Feed rate, 1/mln (gpm)
Feed time, minutes
No. of cycles/hour
kg(!bs) processed/hour0
CSO sludge
2.4 (5.3)
14.0
94.5
2.95
81 (21.4)
13
3.3
103 (227)
Dry-weather
s 1 udge
3.6 (7-9)
17.5
93.5
3.24
111 (29.3)
10
4.0
144 (317)
Wet/dry-weather
sludge mixture -
no jsolymer
1.97 (4.34)
14.3
94.6
3.64
54.1 (14.3)
25
2.0
99 (218)
Wet/dry-weather3
sludge mixture -
polymer addition
2.58 (5.69)
14.8
97-8
4.27
61 (16.0)
22
2.2
126 (277)
Polymer dosage: 1.4 kg/metric ton (2.81 Ib/ton)
Cycles/hour =• 60/(feed time+ 5) where 5 minutes are added for the sklramfng
cycle and desludglng the centrifuge.
Kg processed/hr = 1/roin x feed time x kg/1 concentration of feed x cycles/hr.
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the runs conducted with polymer, an optimum feed rate of 2.58 kg/mln (5-69
Ib/mln) was obtained. This loading rate-resulted In a cake concentration of
14.8 percent solids with a corresponding solids capture of 97.8 percent and
a processing capacity of 126 kg (277 lb) oer hour.
Based on these results, It can be concluded that polymer addition to the CSO/
dry-weather sludge would be advantageous to Increase overall solids capture.
In conclusion, the Kenosha CSO sludge tested is a biological sludge and thus,
very homogeneous In nature. Because of pretreatment steps, the primary forms
of non-volatile solids such as grit have been removed. The remainder of the
non-volatHe solids, such as bacterial cell mass did not Interfere In the
thickening or dewaterlng of the sludge. From the bench scale tests performed,
the results indicated that the flotability of the CSO sludge and the wet-
weather/dry-weather sludge combination are similar to the dry-weather sludge.
Similarily, no significant adverse effects were observed in the dewatertng
characteristics of the proportioned wet-weather/dry-weather sludge or the
CSO sludge when the results are compared to those obtained for the dry-weather
sludge. At this site, It appears quite feasible to dewater any of the three
types of sludges studied using the centrlfugatlon process.
Physical Sludges - HMwaukee, Wl
The Milwaukee wet-weather sludge Is physically generated and, unlike the
Kenosha sludge, It Is heterogeneous by nature. The principal forms of the
non-volatile solids are gritty material which Interferes in the centrlfuga-
tlon process. This was well documented at the Humboldt Avenue wet-weather
site where gritty sludge was fed to the full-scale 121.9 cm (48 in.) basket
centrifuge. Alt of the runs attempted had to be terminated because of ex-
cessive vibration and machine clogging. To prevent machine damage, It was
decided to centrifuge only the sludge supernatant. On-site experience Indi-
cates that the sludge must be degritted prior to centrlfuging. Methods of
degrltttng the sludge concentrate line only, such as swirl concentration,
will be further developed In Section XI.
The results of the Milwaukee 30.5 cm (12.in.) basket centrifuge tests show
that the sludge supernatant dewatered quite well with polymer, with values'
of 28.4 percent for cake and 82 percent solids recovery obtained. These re-
sults are quite encouraging, considering that the basket centrifuge was
operating well below Its optimum design solids loading, which was not obtain-
able because of the low feed solids of the sludge supernatant. In the Phase I
report (I), the Humboldt Avenue sludge was chemically thickened to 1.74 per-
cent solids, and dewatered using a bench scale centrifuge. The average cake
concentration was 2k.3 percent solids for 28 runs. In several of the runs,
cakes In excess of 30 percent were obtained, with a maximum concentration of
64.9 percent. All of the solids recoveries were excellent, consistently In
the 95 percent or above range. Based on these study results,It appears that
centrlfugatlon would be feasible providing the wet-weather sludge was pre-
viously degritted and thickened. This approach is discussed In the economic
evaluation section of this report (Section XI),
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The Milwaukee South Shore dry-weather primary sludge dewatered very well
using the decanter centrifuge. Some pertinent discussion with regard to the
dewatering characteristics of that sludge are presented below:
1. The sludge can be dewatered to a 16.7 to 26.2 percent cake without
the aid of polymer. The corresponding recovery range ts 4 1 to
53 percent.
2. With polymer addition, the sludge can he dewatered to cake concen-
trations as high as 20.1 percent with a corresponding recovery of
31 percent. A maximum recovery of 98 percent was achieved with a
corresponding cake of 13.2 percent solids.
3. At feed rates between 118-203 kg/hr (260-450 Ib/hr) and a feed con-
centration of 4.5-5 percent T.S., optimal conditions were obtained
at a differential speed of 15 RPM, a polymer dosage of .88-1.24 kg/
metric ton (1. 76-2. 48 Ib/ton) and pool radius settings of 101 and
103 mm. At these settings, cake concentrations between 14,5-17 per-
cent solids were obtained with recoveries of 80-95 percent.
4. Good results were also obtained at a poo! depth of 103 mm with a
slightly higher polymer dosage of 2.06-2.88 kg/metric ton (4.12-
5.76 Ib/ton) and a differential speed of 23 RPM. Cake concentrations
of 13.2 and 16.3 percent solids were achieved with corresponding
recoveries of 98 and 96 percent.
The results obtained from the study indicate that the scrol labil Ity of the
South Shore dry-weather primary sludge is good.
The results of the Milwaukee study have shown that the optimum wet-weather
dewatering method would be basket centrlfugation because of the extremely
low feed solids concentrations present. It Is conceivable, however, that at
other CSO sedimentation applications where higher solids contents are obtain-
able, the use of a decanter centrifuge may be more practical.
The feed concentration of the dry-weather sludge (*^5 percent solids) required
the use of the decanter centrifuge, since the volume of solids generated is
high and would result in very short cycle times If the basket centrifuge
were used.
The dry-weather wastewater Is degHtted as a pretreatment operation at the
South Shore Water Pollution Control Plant. Although this removes the princi-
pal source of the non-volatile solids from the wastewater, some Inorganic
fines remain and are concentrated in the primary sludge. However, this did
not present a problem in dewatering the sludge. One problem that did de-
velop was that the foot valve on the feed intake to the centrifuge had to be
cleaned after every run due to accumulations of rags and other objectionable
materials. If the centrifuge were Installed on a permanent basis, a mechani-
cal cleaning device should be Installed on the feed line Intake, Also, pro-
visions should be made for a back flush system.
16
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-Sludges - Racine,. VM
A comparison of results for the Racine dry-weather and wet-weather optimum
dewaterlng characteristics using the decanter centrifuge has been prepared
and is shown below in Table 4,
TABLE *». COMPARISON OF OPTIMUM OPERATING PARAMETERS
CENTRIFUGE DEWATEJUNG TESTS - RACINE, WISCONSIN
Feed rate, kg/hr (ib/hr)
Cake concentration, % solids
SS recovery, % so! ids
Average feed concentration, 1 sol ids
Feed rate, l/min (gpra)
Polymer dosage, kg/metric ton
Dry-weather
sludge
336 (7*»0)
30.8
99-0
9.73
57.5 (15.2)
1.2 (2.k)
CSO
18.0 (39.6)
32.1
92.4
0.46
65.1 (17.2)
0.96 (1.92)
(Ib/ton)
The results of the full-scale dewatering tests on the dry-weather sludge in-
dicated that the optimum feed rate to the decanter centrifuge Is 336 kg/hr
(7^0 Ib/hr). This feed rate produces a cake concentration of 30.8 percent
solids with a suspended solids recovery of 99.0 percent.
For the wet-weather sludge, an optimum cake concentration of 32.1 percent
solids was obtained with a suspended solids recovery of 92,*t percent. The
feed rate to the machine was 18.0 kg/hr (39.6 Ib/hr). The data comparison
shows that the optimum wet-weather cake concentration and suspended solids
recovery is quite similar to the optimum dry-weather sludge. This is im-
portant to note since the decanter centrifuge was operating well below Its
design loading rate for the wet-weather sludge. Higher loading rates were not
possible due to the dfluteness of the feed sludge. It can be expected that
the optimum cake for a more concentrated wet-weather feed sludge would be
considerably higher in a practical design.
The excellent dewatering results obtained, coupled with the bench scale
thickening data suggests that the Ractne wet-weather sludge is very amenable
to thicken!ng-dewaterlng. Indeed, a true thickening step with some grit re-
moval would be required prior to centrifugation.
The Racine screening/dissolved air flotation wet-weather sludge Is a physical-
chemical sludge and is therefore very similar to the Milwaukee CSO sludge in
its origin. Grit and coarse material, removed in the screening process are
17
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discharged to the holding tank where It Is mixed with the floated sludge.
This sludge Is heterogeneous In nature, unlike the very homogenous wet-
weather biological sludge encountered at Kenosha. As such, the principal
form of the non-volatile solids Is Inorganic grit and sand. To better
Illustrate this. Table 5 was prepared which compares the average percent
total volatile solids at each of the dry-weather and wet-weather sites
tested.
As shown In the table, average dry-weather total volatile solids were In
excess of 55 percent for all of the test sites. As expected, wet-weather
average volatile solids were lower than the dry-weather, ranging from 37-1
percent to 50.8 percent, ft Is important to note, however, the pattern of the
CSO sludge volatile solids concentration that was extabllshed. For example,
the purely physical sludge at the M!Iwaukee-Humboldt Avenue CSO site had the
lowest concentration of volatile solids. As previously discussed, the sludge
at this «fte contains significant amounts of non-volatile sol Ids in the form
of Inorgai, irlt and sand.
TABLE 5. TEST SITE AVERAGE TOTAL
VOLATILE SOLID SLUDGE CONCENTRATIONS
Average Average
dry-weather wet-weather
total volatile total volatile
Tes t s i te
Kenosha
Hi Iwaukee
Racine
solids, %
63.6
62.2
56.4
solids, %
50.8
37.1
49.3
Of the wet-weather sludges tested, the Kenosha sludge had the highest con-
centration of volatile solids. This sludge Is derived frora biological
treatment, and as such, the principal forms of the non-volatile solids (grit,
sand, and other inorganics) have been removed, resulting in a very homo-
geneous sludge.
The Racine physical-chemical CSO sludge fell between the Milwaukee and
Kenosha sludges In volatile solids concentration. The principal form of
the non-volatile solids was the inorganic grit generated in the screening
backwash process»
In conducting the full-scale Racine dewatering tests, screening of the
thickened sludge was required to prevent clogging and damage to the decanter
centrifuge. The sludge samples for volatile solids were taken from the feed
line to the centrifuge and therefore definite amounts of non-volatile solids
-------
riad been removed from the sludge sample. It can be assumed that the volatile
solids concentration of the raw sludge would have been slightly lower If
some non-volatile material had not been removed. In any full-scale permanent
operation, grit removal would be a required pretreatment classification step
to remove objectionable Inorganic solids and other foreign matter. The
economic advantages of degrJttjng only the sludge or concentrate line instead
of the entire flow are fully developed In the Section XI, economic evaluation.
HEAVY METALS DATA
Biological S_l_udges ~ Kenosha, Wl_
The results of the Kenosha heavy metals data show several similarities that
exist between the three types of sludges that were tested from the Water
Pollution Control Plant. A discussion of heavy metal results for the dry-
weather sludge, the wet-weather sludge, and the dry-weather/wet-weather
comblnation sludge is presented below:
1. The highest metal concentrations obtained In all three sludges were
for zinc, copper, and chromium.
2. Hercury remained the least concentrated of the heavy metals In all
cases.
3. The metal concentrations at the Kenosha Water Pollution Control
Plant vary significantly with time and also the type of sludge being
tested. For example, the dry-weather feed sludge had a zinc concen-
tration of 3681 mg/kg which compares with the CSO sludge value of
2690 mg/kg. The zinc value for the dry-weather combination sludge,
however, was 7520 mg/kg. The combination sludge sample was taken
approximately one year after the dry-weather and CSO sludge samples,
and zinc concentration had more than doubled. SlmHar comparisons
were also observed for most of the other heavy metals.
4. The bulk of the heavy metals appear to be in the insoluble state.
This is shown by the high concentrations of heavy metal in the
sludge solids.
The combined dry-weather/wet-weather sludge was the only sludge dosed with
polymer. While no major differences were noted in the metal concentrations
of the skimmings or cake, centrate quality Improved for zinc, lead, copper,
chromium and mercury with the addition of polymer. The polymer dosage was
1.1 kq/metric ton (2,2 Ib/ton). Dependent on the quality of centrate re-
quired, polymer addition could be advantageous for the reduction in concen-
tration of certain trace metals. Any reduction in toxic metals (boron,
cadmium, cobalt, chromium, copper, mercury, nickel, lead and zinc) is impor-
tant to point out due to the hazardous health effects of metal toxlcity to
plants, man and animals.
19
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Phys|ca1 Sludges - Milwaukee, Wl
The distribution of heavy metals In the Milwaukee sludges followed a pattern
previously established for the Kenosha sludges. That Is, the highest metal
concentrations observed were for z!nc and chromium, while mercury again
proved to be the met a] least concentrated in the sludges.
Also, as with the Kenosha sludges, metals were concentrated in the solid
portion of the sludge. Reported values for feed, cent rate, skimmings and
cake were often of the same magnitude for the wet-weather and dry-weather
sludges.
For the Milwaukee wet-weather sludge, metal concentration comparisons are
possible for samples with and without polymer addition. At dosages of 1.0
kg/metric ton (2,0 Ib/ton) the results In Table 21, Section VIII show that
metals In the ceotrate are consistently lower for the samples In which
polymer was added. Polymer addition on the Kenosha wet-weather/dry-weather
sludge also improved the quality of the centrate with regard to heavy metal
reduction.
The comparison of the Hilwaukee wet-weather and dry-weather sludges demon-
strates some definite metal distribution patterns. For example, concen-
trations of lead, nickel, copper, and mercury are consistently lower for the
feed, centrate, and cake of the dry-weather sludge. This pattern was not
demonstrated tn the Kenosha sludge, and Is probably the result of local In-
dustrial activity.
Physical -Chemical Sludges -
The Racine heavy metals data that are presented In Tables 25 and 26, Section
IX were relatively comparable to the metal concentrations observed in the
Kenosha and Milwaukee sludges. It is Important to note, however, that over-
all concentrations of the Racine wet-weather sludge metals were slightly less
than either of the corresponding wet-weather sites at Kenosha or Milwaukee.
Future discussion will show that CSO sludge -metal concentrations are ap-
parently quite variable with time and therefore great difficulty occurs In-
attempting to characterize parameter trends. This variation also exists for
the Milwaukee sludge, and to a somewhat lesser extent, the Kenosha sludge.
The comparison of the Racine wet-weather sludge to the dry-weather sludge
shows that concentrations of zinc, lead, copper, chromium, and mercury are
higher for the dry-weather sludge. This pattern of consistently higher
heavy metals In the dry-weather sludge samples was also demonstrated at the
Kenosha Water Pollution Control Plant, but not for the Milwaukee samples.
The soluble metal analyses conducted verified that only minimal amounts of
heavy metals exist In the soluble state for the Racine sludges. As with the
Kenosha and Milwaukee sludges, dry weight trace metals were frequently of
the same magnitude for the feed, centrate, and cake. This Indicates that the
20
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metals are solids related, concentrating In the solid portion of the sludge.
The cadmium analyses that were performed on the Racine .sludges verified that
cake cadmium concentrations were moderate, ranging from l*f mg/kg for the CSQ
sludge to 31 mg/kg for the dry-weather sludge,
In conclusion, the heavy metal concentrations from the three study sites can
be quite variable. However, some important trends and similarities have been
established from analysis of the data.
DIGESTER STUDY DATA
The digesters were operated at the same hydraulic loading (20 day hydraulic
retention time) during the dry-weather feeding for both the Kenosha and Racine
CSO digester tests. The volatile sol ids loading in the Racine tests was about
22^ higher than In the Kenosha tests, however. During the control period,
the Racine test digesters produced about 39% more gas than the Kenosha test
digesters. The ratio of gas produced to volatile solids destroyed was only
about 11% higher for the Racine digesters, however. During both studies, the
standard deviation values for dally gas production during the control period
were similar (0.5 to 0.6 I/day). In the Kenosha study, the difference in
dally gas production between the two digesters averaged 0.015 I/day with a
standard deviation of 0.79 I/day during the initial control period. During
the Racine control period, the average difference between the two digesters
averaged 0,11 I/day with a standard deviation of 0.35 I/day.
After the addition of CSO sludge to the regular feed sludge to simulate the
solids resulting from a 2.5^ cm (1 In.) rainfall, the day-to-day gas pro-
duction of the digesters in both studies became more variable (standard de-
viations of the mean value for each digester increased).
In order to slmllate the addition of CSO solids resulting from a 2.5k cm
(1 in.) rainfall fed to the digester in one day, the volatile solids loading
to the digesters in the Kenosha tests was increased fay 601, The volatile
solids loading to the digesters In the Racine tests was Increased by only 26%
to simulate the same rainfall conditions. In the Kenosha tests, the differ-
ence in gas production between the control and wet-weather digesters was not
statistically significant at the 95S confidence level. In the Racine tests,
the difference was significant at the 95% confidence level but not at the 991
confidence level. The only period during the Kenosha tests when the differ-
ence In digester gas production was statistically different at the 951 confi-
dence level was Period 13 when the wet-weather digester was fed Kenosha CSO
sludge exclusively for a period of ten days. It Is quite unlikely that a
sewage treatment plant digester would be fed exclusively with CSO sludge.
The statistically lower gas production after feeding CSO sludge to the wet-
weather digester in the Racine tests cannot be attributed to the presence
of toxic heavy metals. The simulated wet-weather sludge fed to the test di-
gester contained lower concentrations of zinc, nickel, copper, chromium, iron
and cadmium than the dry-weather sludge fed to the control digester. Although
21
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the lead concentration in the wet-weather feed was higher, the concentration
of 'lead was less than half the geometric mean value found in the sludges fed
to digesters at 33 sewage plants by the EPA (13).
In spite of the lower gas production of the test digester after being fed
Racine CSO sludge, the volatile acid/alka!Inlty ratio of the digesting sludge
was less than 0,01 the day after the wet-weather feeding and was 0.13 the
fourth day after the wet-weather feeding. "These values are well below the
0,3 to 0,4 ratio which Indicates that the digester may be approaching upset
(MOP 16).
Summary
1. in general, the dewaterlng treatment train for handling CSO treat"
ment sludges would be comprised of degritting where required,
thickening (gravity or flotation, with or without chemicals) and
centrlfugatlon (basket or decanter, with or without chemicals).
a. The raw and thickened CSO sludges derived from physical treat-
ment (Milwaukee) and from physical-chemical treatment (Racine)
were similar In that they contained significantly more grit
than their dry-weather counterparts. The grit does not adversely
affect the gravity thickening process. However, to prevent
excessive machine wear and pluggage, degritting would be required
prior to any further dewatering by centrlfugatlon.
b. The raw and thickened CSO sludge derived from biological treat-
ment was similar in nature to that of Its dry-weather counter-
part and pretreatment prior to thickening Is not indicated.
c. The dilute physical CSO sludge (Milwaukee) investigated may be
futher thickened by gravity with chemicals.
The physical-chemical CSO sludge (Racine, screening/dissolved
air flotation) may be further thickened by gravity without
chemIca1s.
The biologicai CSO sludge (Kenosha, contact stabilization) may
be further thickened by flotation without chemicals.
d. Further dewatering of the Milwaukee thickened sludge (from
physical CSO treatment) may be obtained using a basket centrifuge
with the aid of polymer.
The Racine thickened sludge (from physical-chemical CSO treat-
ment) may be further dewatered using a decanter centrifuge with
the aid of polymer.
The Kenosha sludge (from biological CSO treatment) may be
dewatered using a basket centrifuge without chemicals.
22
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2. In general, the dewatering train for handling dry-weather treatment
sludges would be comprised of thickening, where required (gravity
or flotation, with or without chemicals) and centrifugal Ion (basket
or decanter, with or without chemicals),
a. The Milwaukee (South Shore Plant) dry-weather primary sludge can
be dewatered to a haulable cake using a decanter centrifuge with
the aid of polymer.
b. The Racine dry-weather sludge (primary plus activated) can be
dewatered to a haulable cake using a decanter centrifuge with
the aid of polymer.
c. The dewatering characteristics of dry-weather biological sludge
and combinations of dry-and wet-weather biological sludges were
similar to those for the CSO biological sludge alone. Satisfac-
tory results were obtained using flotation thickening and basket
centrlfuging without the aid of chemicals.
3. The heavy metal concentrations were quite variable between the test
sites investigated. However, the heavy metals present appear to be
solids related with only slight concentrations observed In the
soluble metal portion of the sample. Therefore, heavy metal removal
was directly related to solids removal.
kt The bench scale anaerobic digestion studies showed that no signifi-
cant adverse effect was realized by adding CSO generated sludges to
dry-weather digesters. If the CSO sludge is generated by physical
or physical-chemical treatment, prior discussion suggests that
sludge degritting will be necessary.
23
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SECTION V
DESCRIPTION OF THE CSO TEST SITES INVESTIGATED
Three CSO treatment plants were selected as study sites for thickenlng-cen-
trifugation dewaterlng of CSO sludges. The sites are located in Kenosha,
Wisconsin; Racine, Wisconsin; and Hllwaukee, Wisconsin.
The selection of the test sites was based on a desire to study the CSO
sludges produced by three different CSO treatment processes; a physical pro-
cess, a physical/chemical process, and a biological process. In Milwaukee,
a physical process Is employed. The raw CSO Is held In a storage facility
and then bled back to the sewer system when the CSO event is over. Sedimen-
tation is the only removal mechanism utilized. In Racine, a physical/chemi-
cal treatment system is operated, which consists of screening followed by
dfssolved-air flotation. A biological treatment process, contact stabiliza-
tion, is the method employed In Kenosha to treat CSO.
As mentioned previously, each test site city's dry-weather treatment plant
sludge was also studied in addition to the city's CSO sludge. This made it
possible to compare the dewatering characteristics of each city's CSO sludge
and the sludge being generated at the dry-weather treatment plant. Follow-
ing is a description of all the project test sites.
MILWAUKEE, WISCONSIN
CSO Treatment,Jacj 111y
The Milwaukee CSO physical treatment facility is a storage tank, A schematic
of the facility is shown in Figure I.
The capacity of the storage tank is 15.1^0 m3 (4 million gal.). Flows are
directed to the tank by gravity through a 198 cm (78 In.) sewer. Upon
entering the tank inlet channel, the flow passes through a mechanically
cleaned 3.8 cm (1.5 in.) bar screen. All materials retained on the screen
are deposited In a portable refuse container.
Only one of seven rotary mixers in the tank is operated during a CSO event.
It is used to disperse chlorine. Therefore, during this period the deten-
tion tank acts as a settling basin. When the CSO volume exceeds the
15,1^0 m3 (4 million gal.) capacity of the tank, the excess overflow begins
to discharge from the effluent end of the tank.
After the overflow has subsided, all seven mixers are activated to re-
suspend the settled solids. When this has been completed, the contents of
the tank are pumped back to the sewer.
2k
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OVERFLOW WEIR (DEPTH OF FLOW MEASURED)
BAFFLE WALL
(POSTCHLORINATION DIFFUSER
MIXER
(TYPICAL)
\
210'
BAFFLI
3ft" x 60" SLUICE GATES
72" INLET SEWER INVERT ELEV. 3-6
COMBINED SEWAGE PUMPS
1ft" COMBINED SEWAGE
TO M.I.S. SEWER
96" EFFLUENT SEWER
SLOPE TO RIVER
EFFLUENT SAMPLER
METIRS - ,025ft x In.
METERS - 0.305 x ft
TANK LIQUID LEVEL BUBBLER
BAFFLE WALL
78" BYPASS SEWER
TO RIVER
INVERT ELEV. 3.3
BAR
SCREEN
PRECHLORlNATION
DIFFUSER
Figure 1. Schematic diagram of the Milwaukee, Wisconsin
CSO demonstration storage facility.
-------
Facilities for pre- and post-chlor!nation of the CSO -are also provided. The
pre-chlorlnatfon dtffuser Fs located In the tank inlet channel. The post-
chlorination diffuser distributes chlorine across the entire width of the
tank at a point about 3-66 m (12 ft.) above the tank floor and 53.95 m
(177 ft.) from the effluent overflow weir.
As described, ft is obvious that the facility does not produce a residual
CSO sludge that could be used for testing centrifuge dewaterlng. Therefore,
for this project, the operation of the tank was changed. Overall operation
during a CSO event remained the same but during pumpback of the tank's con-
tents to the sewer, the mixers were not turned on. This resulted in the
supernatant being pumped to the sewer and a residual settled sludge remain-
ing In the bottom of the tank. This settled sludge was treated as the CSO
sludge produced at the Milwaukee CSO treatment facility.
Dry-Weathe^ Sewage Treatment Fact Uty
Two dry-weather treatment facilities serve the Milwaukee Metropolitan Sewerage
District. The older of these plants is the Jones Island plant. It utilizes
fine screening In lieu of primary sedimentation and provides secondary treat'-
ment for flows up to 757,000 m3/day (200 ragd). The South Shore plant is the
newer of the two. It has conventional primary treatment and is capable of
treating 1.2 million m3/day (320 mgd flow). New conventional secondary
treatment facilities capable of treating ^5'*,000 mB/day (120 mgd) were
completed at the plant in 197^.
For this study, the South Shore plant was selected as the site from which
Milwaukee's dry-weather sludge would be obtained.
RACINE, WISCONSIN
C50_ Treatment F_ac II ? t i es
The Racine CSO physical-chemical treatment facilities (there are two separate-
ly located treatment systems are designed for a total flow of 219,500 m3/day (58
mgd). A schematic of one of the units is given in Figure 2. Treatment con-
sists of two basic unit operations; screening followed by dissolved-air
flotation.
The raw CSO enters the site wetwell and then passes through a mechanically
cleaned bar screen to a spiral screw pump. The pump discharges Into a
channel leading to the drum screen Influent channel. The screens employed
to remove suspended matter In the CSO have 297 micron openings (50 mesh).
When headloss through the screens becomes excessive, backwash water Is
drawn from the screen effluent chamber by a backwash water pump and sprayed
on the outer surfaces of the screens to flush solids from the Inner surface.
These solids, along with the backwash water, are collected In a hopper and
then flow by gravity to a screw conveyor which delivers them to the sludge
holding tanks where they remain until the CSO event Is over.
The screened CSO then flows to the flotation tanks where It is blended with
26
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INTERCEPTOR SEWER
SLUDGE
AFTER
STORH
SLUDGE HOLDING
TANKS
Figure 2. Schematic of Racine CSO treatment facility.
-------
air-saturated pressurized ftow. The system does not employ effluent recycle.
Instead, approximately 20 percent of the raw flow is pressurized. The floated
sludge is periodically skimmed from the top of the tanks and is deposited In
the screw conveyor which delivers it to the sludge holding tanks.
Ferric chloride and polymer are added to the CSO to facilitate the coagula-
tion of partlculate matter before flotation. Ferric chloride Is added In the
wetwell 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 CSO sludge produced by the system (screen backwash water and floated
sludge) is drained back to the city sewer system when the water leve5! In the
sewer has decreased to the point where the tank contents can be drained with-
out causing an overflow at a point farther downstream in the Interceptor
sewer.
Dry-WeatherSewage Treatment Fac11Ity
The conventional treatment of dry-weather wastewater In Racine Is accomplished
by a 79,500 m3/day (21 mgd) primary treatment plant, a 45,^00 m3/day (12 mgd)
secondary treatment plant, chlorlnatlon, sludge digestion and vacuum filtra-
tion. The average flow to the plant is 79,500 m3/day (21 mgd).
The wastewater flows through a mechanically cleaned bar screen and then to
four commlnutors. Each commlnutor has a rated capacity of 45,^00 m3/day (12
mgd). After comminution, the wastewater flows to the grit chambers. The
settled grit is removed from the chambers by scrapers. A screw conveyor and
screw type grit washer remove and further cleanse the grit for satisfactory
disposal as a fill material. The wastewater then flows to four primary
sedimentation tanks with a total surface area of 1760 m2 (18,9^7 ft.2} and
a total volume of 4,920 m3 (1,300,000 gal.}. At the average flow rate of
79,500 m3 (21 mgd), this results in a surface overflow rate of ^5 m3/mVday
(I,108 gal./ft.2/day) and a detention time of I.k% hours.
The primary effluent then flows to secondary treatment which consists of an
activated sludge process. There are two mixed liquor aeration tanks with a
total volume of 8,500 m3 (2,250,000 gal.). The aeration tanks can be
operated In several alternate modes. The wastewater can be introduced Into
both tanks, together with return activated sludge. The first aeration tank
can also be utilized as a sJudge reaeration tank for the contact stabiliza-
tion process, or as a nitrification tank for the Kraus process. For both of
these processes, all of the primary effluent Is Introduced Into the second
aeration tank.
After aeration the mixed liquor flows to two final clarfflers. Each clarifler
has a volume of 1,893 ra3 (500,000 gal.) and a detention time of 2 hours.
The surface overflow rate is 43m3/niz/day (1,060 gal./ft. /day). The clarified
effluent Is then transported to a chlorine contact chamber for disinfection
prior to discharge.
28
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The waste activated sludge generated by secondary treatment is returned to
the primary sedimentation tanks where It is settled out with the primary
sludge. This sludge is then pumped to two-stage anaerobic digestion. The
total volume of the digestion system is 7»570 m3 (2 million gal.) and an
average of 3^1 m3/day (90,000 gal./day) of sludge at a solids concentration
of 7.5 percent or 25,5^7 kg/day (56,270 Ibs/day) dry sludge are handled.
The digested solids are then dewatered by vacuum filtration. Two 3ro (10 ft.)
by 3m (10 ft.) vacuum filters are utilized. Each filter has its own condi-
tioning tank where chemicals are added to aid fn coagulation and to Improve
f5Iterabi1ity. The chemicals used are lime and ferric chloride. The re-
sulting filter cake is disposed of at a landfill site.
KENOSHA, WISCONSIN
CSOTreatment Fac i U ty
The CSO treatment system in Kenosha Is unique in that it fs located adjacent
to the existing conventional dry-weather treatment plant. In fact, since
the system utilizes biological treatment it depends on the dry-weather plant
as a source of active biomass. Figure 3 presents a schematic of the CSO
contact stabilization process, the dry-weather treatment plant, and the
interconnections between the two.
The CSO treatment facility has a design capacity of 75,700 m3/day (20 mgd).
It consists of a grit chamber, mixed liquor contact tank, sludge stabiliza-
tion tank and final clarifler. The grtt chamber Is designed to handle a
flow of 75,700 m3/day (20 mgd) with a flow-through velocity of 0.06 m/sec
(0.2 ft./sec). Any deposited grit on the floor of the tank Js flushed to
the west wall where It is suction pumped to a truck and hauled to a landfill
site.
The contact and stabilization tanks, are located in one large concrete basin
which is divided by concrete walls into four compartments, two contact tanks
and two sludge stabilization tanks. The contact tanks are designed to
handle a maximum flow of 75.700 m3/day (20 mgd) and a sludge flow of 11,355
m3/day (3 rogd) with a 15 minute contact period. This requires a volume of
approximately $k6 m3 (250,000 gal.). The two contact compartments have
volumes of 621 m3 (16^,000 gal.) and 305 m3 (80,^65 gal.) for a combined
volume of 926 m3 (2^,465 gal.).
The stabilization tank also has two compartments which can be used separately
or together so that the sludge stabilization times can be varied. Both tanks
are identical, having a volume of 1,38? ""3 (366,329 gal.) each. Two
37,850 m3/day (10 mgd) pumps are provided to transfer the stabilized sludge
to the contact tanks during system operation. A 1,893 m3/day (0.5 mgd) pump
is also provided to transfer unused, stabilized sludge to the dry-weather
treatment plant's flotation thickeners during periods of dry weather.
The final clarifier is designed on a settling rate of 3 m/hr (10 ft./hr.).
•29
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ADMI MISTRATI ON £
LAB BUILDING
GARAGE
PRESENT MIXING
BASIN
WET-WEATHER
GRIT BASIM
WET-WEATHER
ELECTRICAL
UBSTATION
CHLORINE
BUILDING
CHLORINE \
CONTACT TANK
so-----
GRIT
TANK
DIGESTERS (3)
PUMP
BUILDING
FINAL EFFCUENT
Figure 3« Relationship between the Kenosha, W|
CSO demonstration treatment system and
the conventional treatment plant.
30
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The design overflow rate is 72.7 mS/m^/day (1,790 gal./ft.2/day). At a
flow rate of 75t700 m3/day (20 mgd), this requires a 42.7 m (140 ft.)
diameter clarifier which has a surface area of J ,430 m2 (15,394 ft.2) and
a volume of 5,230 ro3 (1,381,75** gal,). The clarfffer Is designed for use
during both dry-weather flow and CSO conditions. During dry-weather, the
mixed liquor from the dry-weather plant is fed to the clarlfrer and the
settled sludge Is pumped back Into the dry-weather plant's sludge return
system. During CSO conditions, the mixed liquor from the contact tank is
fed to the clarifier and the settled sludge is pumped to the sludge
stabilization tanks.
During a CSO event, raw sewage flows In excess of the dry-weather plant's
capacity of 87,055 m3/day (23 mgd) are pumped to the CSO treatment facility.
After passing through the grit chamber, the raw flow goes to the contact
tanks. Before entering the contact tanks, the raw CSO Is mixed with
stabilized sludge which is pumped from the stabilization tanks. After
fO to 15 minutes of aeration in the contact tanks, the mixed liquor flows
to the final clarifier. After settling Is achieved the effluent flows to
the dry-weather treatment plant's chlorinatfon facilities. The settled
sludge is pumped back to the sludge stabilization tanks.
After a CSO event has ended, all of the solids produced by the contact
stabilization process are fed to the dry-weather treatment plant's sludge
handling facilities.
During dry-weather conditions, the only activity within the CSO treatment
system Is a constant flow of waste activated sludge from the dry-weather
plant to the stabilization tanks. The waste activated sludge is then pumped
from the stabilization tanks to the dry-weather plant's handling facilities.
This procedure Insures the availability of an active biomass in the stabili-
zation tanks when a CSO event occurs.
Dry-Weather Sewage Treatment^ FacIIIty
The raw sewage entering the plant during dry-weather Is pumped through two
grit removal chambers which operate In parallel. The discharge from the grit
chambers flows by gravity to six primary sedimentation basins which have a
total surface area of 2,300 m2 (24,760 ft.2) and a volume of 7,295 m3
(257,600 ft.3). The maximum hydraulic capacity of the tanks Is 113,500
m3/day (30 mgd), resulting in surface overflow rates of 49.3 m3/m2/day (1212
ga!,/ft.2/day) and a detention time of 1.54 hours. The effluent from the
primary tanks flows to the mixed liquor aeration tanks where it is mixed
with return activated sludge. There are four aeration tanks having a total
volume of 13,430 m3 (476,000 ft.3). The aeration time in these tanks Is
3.72 hours at a maximum design capacity of 87,055 mVday (23 mgd). The
mixed liquor then flows to three 25.9 m (85 ft.) diameter final clarifiers
having a total surface area of 1,531 m2 (17,020 ft.2). At a flow rate of
87,055 m3/day (23 mgd), the surface overflow rate Is 54.9 m3/m2/day (1,350
ga1./ft.2/day) and the detention time is 1.32 hours. The effluent is then
chlorinated and discharged.
31
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The waste activated sludge, approximately "$}k m /day (83,000 gal./day) at
a solids concentration of 1.5 percent Is flotation thickened to about a
k percent solids concentration before going to anaerobic digestion. The
dally loading on the digesters, primary and waste activated sludge combined,
is 189 m3 (50,000 gpd) resulting In a dry solids weight of 11,035 kg/day
(24,307 Ibs/day). The digested sludge Is then further dewatered by means
of a filter press which produces a cake of approximately 35 percent solids
for disposal.
32
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SECTION VI
SAMPLING, TESTING, AND EVALUATION PROCEDURE
At each of the six sites (3 dry-weather treatment plants and 3 CSO treatment
facilities) utilized for this project, the following investigations were
carried out;
1, Bench scale thickening tests, either flotation or, gravity,
depending on the method In use at the site being considered
(at Milwaukee, bench scale sedimentation tests were
performed).
2. Centrifuge dewaterlng of the thickened sludge using either
the J21.9 cm (48 In.) basket centrifuge or the decanter
centrifuge on the mobile centrifuge van.
3. Auxiliary centrifuge dewatering of the thickened sludge
using a 30.5 cm (12 In.) basket centrifuge to augment
the data obtained during the full scale centrifuge
testing, when necessary.
4, Heavy metals analysis of composite samples of feed,
centrate, skimmings (for basket centrifuge runs only),
and cake taken during centrifuge testing.
In addition to the preceding tests, bench scale anaerobic digestion studies
were also conducted using dry-weather sludges and CSO sludges as the feed
source. The anaerobic digestion studies were conducted for sludges
obtained from Racine and Kenosha, Wl.
BENCH SCALE SLUDQE THICKENING TESTS
One of the conclusions drawn from Phase I (I) of this project was "a
combination of gravity thickening and centrifugatlon provided optimum
treatment for most CSO sludges evaluated , . . .". Therefore, one of the
objectives of this Phase 111 study was to evaluate the thlckening-
centrlfugation process for handling CSO sludges on a pilot scale.
The three sites selected for this project (Milwaukee, Racine, and Kenosha)
all contain built-in sedimentation or thickening processes. Kenosha provides
for flotation thickening of the waste activated sludge as ft Is wasted from
the CSO treatment facility's sludge stabilization tank, in Milwaukee,
33
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gravity sedimentation of the solids Is actually the treatment process
employed. At the Racine site, gravity thickening of the CSO treatment
residuals can be achieved In the sludge storage tank.
Since the sedimentation or thickening processes at the sites are built Into
the actual operation of the systems, the respective sedimentation/thickening
characteristics of the sludges were evaluated on a bench scale basis. In the
case of Kenosha, where the thickening unit handles both the dry-weather and
CSO sludges, the results of the bench scale tests were also compared to the
recorded operational data for the flotation thickener.
For the Racine and Kenosha sites, three sets of bench sca-le thickening tests
were conducted. The first was for the CSO sludge; the second for the corre-
sponding dry-weather sludge; and, the third for a mixture of the CSO sludge
and the dry-weather sludge. The mixture of the CSO sludge and the dry-weather
sludge for each site was calculated as follows:
1. The volume of CSO sludge generated by a 1.27 cm (0.5 In.) rain
over the city's combined sewer area was calculated based on
complete CSO treatment using the prevailing CSO treatment
process.
2. This CSO sludge volume was then fed to the dry-weather
treatment plant over 48 hours and the daily flow calculated.
3. From dry-weather plant records, the daily flow of dry-
weather sludge was obtained. The CSO sludge, liters/day
(gpd), divided by the dry-weather sludge, liters/day (gpd),
then gave a ratio of CSO sludge to dry-weather sludge over
the 48 hours of CSO sludge faleedback.
4. The calculated ratio was then used to prepare the mixture
of CSO sludge and dry-weather sludge for the bench scale
thickening tests.
The procedures used for conducting the bench scale thickening tests, both
gravity and flotation, were identical to those used in Phase I of this
project (1).
Using the data obtained; the solids rise or settling rates, the corresponding
overflow rates, the estimated final sludge concentrations, and the mass
loadings were calculated. Plots were then made of the point of sludge inter-
face versus time, and the mass loading versus the estimated final sludge
concentration. From these plots, comparisons of the thickening properties
of the three sludges were made and conclusions drawn about the differences
between the thickening characteristics of the city's CSO sludge and the city's
dry-weather sludge; and, the change In the dry-weather sludge thickening
characteristics as CSO sludges are Introduced Into the sludge mass.
34
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CENTRIFUGE DEWATERING TESTS
As with the thickening studies, the centrifuge dewatering studies were
conducted for the CSO sludge and dry-weather treatment plant sludge for
each city. Full scale centrlfugtng of an appropriate combination of dry-
weather and CSO sludges were also conducted at Kenosha. Full scale
centrifuge tests using dry-weather CSO sludge combinations in
HiIwaukee and Racine were not conducted because the sludges had to be
obtained from two different locations in the city, the site of the CSO
treatment facility and the site of the dry-weather sewage treatment plant.
Three centrifuge procedures were used during the course of this project to
evaluate dewatering of the CSO sludges and dry-weather sludges In the three
cities. Full scale centrifugation tests were achieved by either using a
121.9 cm (48 in.) basket centrifuge or a decanter centrifuge. Both of these
centrifuges were available on the mobile centrifuge van. The third centrifuge
procedure utilized a 30.5 cm (12 in.) basket centrifuge. This smaller
centrifuge was used when necessary, to establish the optimum operating ranges
before the larger 121.9 cm (48 In.) basket centrifuge was used, and to obtain
data to supplement that generated by the 121.9 cm (48 in.) basket centrifuge
tests. The selection of whether to use the decanter centrifuge or the basket
centrifuges was dependent on sludge concentration. Basket application is
generally restricted to sludges of less than 3% concentration. However, for
purposes of comparison between the test sites' dry-weather sludge and the wet-
weather sludge, only one type of centrifuge was used at both locations where
possible. Thus, only the basket centrifuges (121.9 cm and 30.5 cm) were used
at the Kenosha test site. At the Racine sites, the decanter centrifuge was
used for both the wet-and dry-weather sludges. In Milwaukee, however, the
dry-weather sludge was amenable to decanter application, while the wet-
weather sludge was not. Therefore, the basket centrifuge was used In lieu
of the decanter on the Milwaukee wet-weather sludge.
30.5 cm (12 In.) Basket Centrifuge Tests
Basket centrifuge tests are conducted using either the 30.5 cm (12 In.) or
121.9 cm (48 In.) basket centrifuge. In most cases, It was desirable to
conduct tests with the 30.5 cm (12 in.) basket to optimize performance and
then operate the 121.9 cm (48 in.) full scale unit to duplicate the
established, optimized mode of operation, in addition, In some cases, the
logistics of sample source or volume; power available; or centrifuge van site
accessibility made the 30.5 cm (12 in.) basket test work the primary source
of data. The use of the 30.5 cm (12 In.) basket also supplied valuable data
to supplemnt the results of the full scale basket centrifuge work. An
illustration of the 30,5 cm (12 in.) basket centrifuge and its companion
pump package Is shown in Figure 4, A section view of this centrifuge is
presented in Figure 5.
The independent test parameters for basket centrifugation are the feed rate
In kg/hr (Ibs/hr) (analyzed as total solids and then corrected for dissolved
solids); and, the polymer dose rate (if used) In kg/met, ton (Ibs/ton) of
feed solids. The dependent variables to be observed are the resultant cycle
35
-------
Figure k, Envlrex 30.5 cm (12 In.) basket centrifuge
and pump package.
-------
-FEED
BASKET
CENTRATE
DISCHARGE
Figure 5. 30,5 cm (12 In.) basket centrifuge-sect Ion view
37
-------
time In minutes; skimming volumes and concentration; the cake concentration;
and the centrate quality In mg/1 suspended solids.
To assure that all of the necessary variables were monitored for each of the
30.5 era (12 In.) basket centrifuge tests, data recording sheets were developed.
A sample data sheet is shown In Figure 6. The feed samples were analyzed for
total solids and total volatile solids; the centrate samples for total solids,
total volatile solids, suspended solids, and volatile suspended solids; and
the cake samples for total solids and total volatile solids. All analyses were
conducted according to "Standard Methods" (2),
Basket centrifuge operation can be best described as a batch-continuous
process where 50 to 90 percent of the time may be available for continuous
sludge feed, A specific volume, 5.7 liters (1.5 gal.) In the 30.5 cm (12 in.)
basket is available for sludge cake accumulation as the feed and dewaterlng
cycle progresses. Once the dewatered cake occupies this volume, the feed
cycle is complete and the feed flow is stopped.
At the beginning of a test, the feed pump and polymer addition pump (If
polymer is used) are calibrated at the desired rate. While the feed rate is
being set, a sample of the feed sludge Is obtained from the sludge container.
When the pumps are set, the run Is started by turning on the centrifuge and
allowing It to accelerate up to a constant speed. At Its design speed, the
30,5 cm (12 In.) basket centrifuge produces .a force of 1300 "G's" at the
outer wall. Once constant speed is reached, the feed pump and the polymer
pump are turned on and sludge feeding begins. At this point, timing of the
run also starts.
When centrate begins flowing from the centrate outlet, the time Is recorded.
This time fs used to determine the exact feed rate: 5.7 liters (1.5 gal.)/
time until centrate discharge beings « pumping rate. If polymer Is being
added, the polymer pumping rate must be subtracted from this calculated rate
to obtain the actual sludge feed rate.
A centrate sample Is taken approximately 2 minutes after centrate discharge
begins and every 2 minutes thereafter, until the test has ended. This
interval can be Increased If a low feed rate is being used and a very long
cycle time is expected. The end of the feed cycle is established by visual
monitoring of the centrate quality. A sudden deterioration of the centrate
quality indicates the end of the test. The time of this deterioration of
effluent quality Is recorded on the data sheet. Without polymer, centrate
suspended solids may be In the 1000 to 2000 jng/l range In the intltlal stages
of the feed cycle and deteriorate to *|QOQ to 6000 mg/} in 15 to 30 minutes.
With polymer, the Intltal centrate may be as low as 100 mg/1. If Initial
centrate without polymer Is In the 3000 mg/1 or greater range, it would
Indicate a difficult to dewater sludge and then polymer may have to be used
to achieve satisfactory solids recovery.
When the feed cycle has ended, the skimming device is advanced into the cake
wall to remove any partially thickened cake, normally the last portion of
the feed flow which has not been exposed to the 1300 "6" force long enough for
38
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" 30.S^CCTTlMETER (12 INCH) BASKET CENTRIFUGE
DATA StfEET
Date
srte
Sludge Type
Run No.
Time of Centrate Discharge
Time of Solids Breakover
Time Cycle Ended
Pump Feed Rate
Chemical Addition
Type
Feed Rate of Chemical
Chemical Solution Concentration
Volume of Skimmings
Samples
DESCRIPTION TIME OF SAMPLE
Feed
Centrate J
Centrate 2
Centrate 3
Centrate 4
Centrate 5
Skimmings
Cake 1
Cake 2
SKETCH OF FINAL CAKE CONDITION
Recorded By;
Figure 6. Sample 30.5 cm (12 in) Basket Test Data Sheet
39
-------
dewatering. The skimming volume Is usually In the 0.1 to 5.0 percent range
of the complete volume processed In the batch cycle. The actual volume of
skimmings Is noted on the data sheet and a sample of the skimmings Is taken
for analysis.
After skimming Is completed, the basket Is decelerated to a complete stop.
The 30.5 cm (12 In.) basket centrifuge does not Include mechanical provisions
for sludge removal. Thus, two cake samples are carefully scooped out from
mid-depth of the basket at two points, 180 degrees apart. Once these samples
are obtained, the basket Is cleaned out, all pump lines are cleaned with
water, and the pumps are reset for the next test.
The evaluation of the test results Is based on the cake concentration and
solids recoveries achieved for the varying feed rates and polymer addition
rates. Plots of cake concentration versus feed rate and solids recovery
versus feed rate can be developed and from the plots an optimum feed rate
can be selected for a desired cake concentration and/or solids recovery rate.
After selection of the feed rate, similar plots can be developed for varying
polymer dosages at a constant feed rate,and, then, an optimum polymer dosage
selected. Comparisons among these plots for the different sludges studied
also gives an indication of the suitability of the different sludges for
basket centrifuge dewatering.
For overall sizing, the optimum feed rate Is adjusted for the cycle time plus
skim time plus plow time (desludging) plus acceleration time (this total is
usually assumed to be 5 minutes per cycle) and an overall kg/hr (Ibs/hr) and
average llters/hr (gal./hr) production rate Is established.
121.9 cm (MS in.) Basket Centrifuge Tests
Basket centrifuge tests using the full scale 121.9 cm (48 in.) basket
centrifuge are conducted in a manner similar to the 30.5 cm (12 In.) basket
centrifuge tests. The independent variables are again the feed rate and the
rate of polymer addition (If used) and the dependent variables are the
centrate quality, cake concentrations, volume and concentration of the
skimmings, and the cycle time. The 121.9 cm (48 in.) basket centrifuge is
shown on the mobile centrifuge van in Figure 7. A section view of this
centrifuge is presented In Figure 8.
Upon arrival at the test site, the van must be placed In a position such that
it is no more than 22.9 m (75 ft) from a source of electrical power, 440 volt,
3 phase, 150 amperes} the sludge source; and, a water source. The location of
the van should also be on concrete or asphalt since this will make it easier
to level and facilitate cleanup operations. Once the van has been placed at
the selected location, the front and back outriggers are set up and the van
is leveled. It is critical to have the van as level as possible to prevent
excessive vibration during testing. At this time, the power is also
connected to the van, the 10.2 cm (4 in.) suction hoses can be put together
and placed in the sludge source, and the 2.54 cm (1 In.) water hose can be
connected to the water source. The physical set up of the van Is now
complete. Illustrations of the mobile centrifuge van are shown in Figure 9.
-------
Figure 7. Envtrex mobile centrifuge van's
121.9 cm (48 In.) basket centrifuge.
-------
HYDRAULIC
MOTOR
LINEAR
SKIMMER
POLYMER
FEED
EFFLUENT
DISCHARGE
FEED LINE
Figure 8, 121,0 cm (48 In.) basket centrifuge - section view
-------
Jt?
Figure 9- Forward and rear side views of
the Envirex centrifuge van.
-------
The 121.9 cm (48 In.) basket centrifuge was then operated for testing using
the detailed procedures provided by the manufacturer.
Decanter Centrifuge Tests
Decanter centrifuges are horizontal, cylindrical-conical, solid bowl
machines. In a typical unit, Figure 10, sludge Is fed through a stationary
feed tube along the centerline of the bowl through the hub of the screw
conveyor. The screw conveyor Is mounted Inside the rotating conical bowl.
It usually rotates at a lower speed than the bowl. Sludge leaves the end of
the feed tube. Is accelerated, passes through the ports In the conveyor
shaft, and Is distributed to the periphery of the bowl. Solids settle
through the liquid pool, are compacted by centrifugal force against the walls
of the bowl, and are conveyed by the screw conveyor to the drying or beach
area of the bowl. The beach area Is an inclined section of the bowl where
further dewaterJng occurs before the solids are discharged. Separated
liquid Is discharged continuously over adjustable weirs at the opposite end
of the bowl (3). The decanter centrifuge on the mobile centrifuge van Is
shown In Figure It.
The setup of the centrifuge van for use of the decanter centrifuge Is the
same as previously presented for use of the 121.9 cm (48 In.) basket
centrifuge.
Once the setup has been completed, the following steps are taken before the
decanter testing begins.
1. Select a desired pool depth by adjusting pool radius disc.
2. Hake sure the bowl rotates freely by hand In a clockwise
direction,
3. Hake sure the decanter's cover Is securely closed.
4. Turn "decanter drive" on and slowly crank the varldrlve
up to the selected speed.
5. Select a direction of rotation for the decanter conveyor
motor.
a) forward; conveyor rotates In the same direction
as the bowl: differential speed (An) * (bowl
speed-conveyor speed)/159.5
b) off; conveyor does not rotate: An = bowl
speed/159.5
c) reverse: conveyor rotates In the direction
opposite the bowl: An » (bowl speed-conveyor
speed)/159.5
-------
FEED
OUTLET FOR LIQUID PHASE
OUTLET FOR SOLIDS PHASE
Figure 10- Schematic diagram of a decanter centrifuge.
-------
Figure a Envlrex mobile centrrfug* van's decanter centrifuge-
-------
6, Torn "decanter conveyor" on and slowly crank the varldrlve
up to the desired speed.
7. Make sure that the valves of the feed lines are open so that
the sludge goes only to the decanter centrifuge.
8. Turn the sludge pump on. The flow rate should have been
set during Initial setup and can be checked by monitoring
the cake and centrate flows with a 37.9 liter (10 gat.)
bucket and a stopwatch.
The operation of the decanter centrifuge Is continuous and therefore, sludge
pumping, centrate discharge, and cake discharge are continuous. After 30
minutes of testing one set of conditions, the machine variables can be
changed to begin testing a new set of conditions. Feed rates can be
monitored during operation by using a 37.9 liter (10 gal.) bucket and stop-
watch to determine the cake and centrate flow rates.
Each test will produce 9 samples. Samples of the feed, centrate, and cake
are normally taken after equilibrium of each run. Feed and cake samples
were analyzed for total solids and total volatile solids, and the centrate
samples were analyzed for total solids, total volatile solids, suspended
solids, and volatile suspended solids.
Evaluation of the data obtained from the decanter centrifuge testing is more
complex than for the 121.9 cm (*»8 in.) basket centrifuge because there are
five independent variables that can affect the solids recoveries and the cake
concentrations achieved. These are the bowl speed, the differential speed,
the pool radius, the feed rate, and polymer addition (If used). To evaluate
these independent variables, the test procedures are set so that all of the
variables are fixed except for one and that one is varied from one extreme
to another and the results plotted. For example, fix al I the variables
except for the feed rate. Then, make three runs at 37«9f 75.8, and 113.7
llters/min (10, 20, and 30 gpra). From these 3 tests select an optimum feed
rate and keep It constant with all the other variables except for the
differential speed. Make 3 more runs at 6, 16, and 26 rpm and again plot
the results. Continue this process until all of the independent variables
have been studied. In this manner, the optimum conditions for decanter
operation can be developed for each sludge tested while the number of tests
are kept at a minimum. Comparisons among these developed optimums for each
sludge tested can^also be usedjtp determine the sludges amenability to the
decanter centrifuge dewatering process.
A system of parameter plots (*0 were also used for the evaluation of the data
developed during the decanter centrifuge testing. These plots were used In
an attempt to develop optimums that indicate the relationship of each of the
Independent variables on the dependent variable, either solids recovery or
cake concentration.
Finally, the optimum conditions developed for each sludge tested are used for
the overall sizing of decanter centrifuges for the dewatering of CSO sludges
and dry-weather treatment plant sludges.
-------
In addition to the standard evaluations performed for the centrifuge tests,
heavy metals determinations were also performed. This Involved heavy metal
analyses of the centrifuge feed sludge, the centrate, the skimmings, and the
cake for both the dry-weather sludge dewaterlng tests and the CSO sludge
dewaterlng tests In each city visited. The heavy metals evaluated were zinc,
lead, copper, nickel, chromium, and mercury.
The samples used for the heavy metal analyses were obtained by the following
procedure.
1. For each condition at one site, CSO sludge or dry-weather
sludge, several days were required to complete the necessary
centrifuge tests. One of these days was selected as the day
the samples would be obtained for the heavy metals analyses.
2. For one day of centrifuge testing, an average of ft-10
Individual tests were usually conducted. Samples were taken
for heavy metal analyses from the visually determined optimum
runs from that day. All of these discrete samples were
transported back to the laboratory.
3. At the laboratory, the Individual samples were composited
by equal volume Into feed, centrate, skimmings, and cake
samples.
k. The four composite samples were then analyzed for zinc,
lead, copper, nickel, chromium, and mercury. The analyses
were conducted according to the procedures given In the
literature (6)(7).
Evaluation of the heavy roetals data consisted of an Individual determination
of the heavy metals through the centrifuge dewaterlng process. Two separate
determinations, CSO sludge and dry-weather sludge, were performed for each
of the three cities visited for the project.
BENCH SCALE ANAEROBIC DIGESTION STUDIES
The objective of this study was to evaluate the short and long term effect of
feeding sludge containing storm generated solids to bench scale anaerobic
digesters on an Intermittent basis under controlled laboratory conditions.
The two digesters used In this study were Intended to simulate high rate,
single stage anaerobic digesters operated in the mesophlltc temperature range
with Intermittent (once dally) feeding and withdrawal. The digesters were
operated according to the guidelines presented In the literature (8)(9).
The bench scale digesters (See Figure 12) consisted of 20 liter (5,3 gal.)
plastic carboys fitted with teflon paddle agitators and a glass tube for
adding and withdrawing sludge. The agitators were operated at 35 rpm using
-------
DAYTON MODEL 3MIOI 35 R.P.M. GEARED MOTOR
RUBBER HOSE
COUPLING
10 MM ID STAIN-
7 MM SHAFT
LESS STEEL SHAFT
GUIDE
GLASS "T" FOR
GAS ANALYSIS
FEED TUBE
(15 MM ID)
THERMOMETER
TEFLON BLADE
STIRRER
COLLECTION BOTTLE
DIGESTER
DIGESTER
COLLECTION BOTTLE
(CALIBRATED)
LEVELING
CYLINDER
(1 LITER)
WITH OVERFLOW
Figure 12- Laboratory scale anaerobic digesters.
-------
constant speed motors (Dayton Model 3M101), Stainless steel tubes were used
as guides for the agitator shafts. Each tube extended from 5 cm (2 tn.)
below the sludge surface to about 7 cm (2.76 In.) above the top of the carboy.
The sludge forced Into the shaft guide by the pressure In the digester acted
as an effective seal. The lower end of the glass tubes used to add and with-
draw sludge were located near the path of an agitator paddle In the lower
half of each digester. The upper end of the glass tube was positioned so
that the pressure In the digester kept the sludge level near the top of the
tube. The suction end of a hand-operated bilge pump was attached to the tube
to withdraw sludge. Sludge was added by reversing the position of the btlge
pump and pumping the sludge into the digester. Sludge could be withdrawn and
added without allowing the addition of undesirable amounts of air. The upper
end of each glass tube was sealed with a rubber stopper except during the
dally sludge transfer operations.
Gas produced by the digesting sludge was collected In 20 liter (5.3 gal.)
calibrated collecting bottles over a 5% brine solution acidified with 2 ml
HjiSOii (conc)/l. The displaced brine solution was passed through a one liter
leveling cylinder and collected In a 15 liter (*f.O gal.) plastic container.
The outlet tube from the leveling cylinder was positioned so that a slight
positive pressure [approximately 6 cm (2.36 In.) water pressure] was main-
tained In the digesters. Thermometers were used to measure the temperature
of the gas In the headspace of each digester and In each collection bottle.
Samples of gas for analysis were withdrawn from a rubber hose atop each gas
collection bottle using a 5 ml syringe. After taking the dally gas samples
and measurements, the excess gas was vented from the top of each collection
bottle while replacing the displaced brine solution by siphon. The two
digesters were placed In the same 80 liter (21.2 gal.) water bath controlled
by a Precision Scientific Porta-Temp heater-agitator.
The digesters were started using digester sludge from the test site sewage
treatment plants. The sludge was transported under nitrogen and transferred
to the bench-scale digesters with a minimum amount of exposure to air.
Thereafter, the digesters were maintained with dally feedings of primary and
secondary sludges from the respective plants. Sludge volumes of 18 liters
(4.8 gal.) were maintained in each digester by withdrawing an equivalent
volume of sludge before each feeding. The digesters were fed with dry-weather
sludge at loadings similar to those used at the test sites for a period of at
least two weeks. Wbren monitoring showed that the two digesters were operating
In a similar manner, one of the digesters was fed wet-weather sludge at a
loading similar to that which would be used at the sewage plant after a typical
storm. The other digester was fed dry-weather sludge at the same organic
loading as the wet-weather digester. After one or two days of wet-weather
feed, dry-weather sludge and dry-weather loading rates were again used for
both digesters.
The feed sludge and the digesting sludge were routinely analyzed for pH value,
total solids, volatile solids and alkalinity. The volatile acid concentration
of the digesting sludge was also measured. Dally gas production, gas
composition and rate of methane production were routinely monitored. Total
and soluble concentrations of mercury, lead, zinc, nickel, chromium, copper
and cadmium In the feed and digesting sludges were analyzed. Analyses for pH,
50
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total solids, volatile solids, volatile acfds, and alkalinity were performed
as specified fn Standard Methods (2). Metals, with the exception of mercury,
were determined by atomic absorption spectrophotometry after digestion with
nitric and hydrochloric acid using procedures described fn Standard Methods
(2). Mercury was digested In a closed system and analyzed by ftameless atomic
absorption (6). Gas composition was measured by gas chromatography using a
thermal conductivity detector. A series column consisting of a 30 cm x 6 mm
(11.8 In. x .21* In.) 10 copper column packed with 70/80 mesh silica gel and a
305 cm x 6 mm (120 In. x .2^ In.) 10 copper column packed with 80/100 mesh
5A Molecular Sieve was used (10). Typical chromatograph operating conditions
weret 40 ec/mln carrier gas (He) flow rate, 25°C column temperature, *»0°C
detector temperature and 150 ma filament current. QuantHat Ion was performed
by comparing sample Injections with known standards of nitrogen, oxygen,
methane and carbon dioxide.
The experimental design was based on the paired t-statlstlc (ll) utilizing a
control and a variable digester operated under Identical conditions except
that storm generated soltds were Included In the sludge fed to the variable
digester. It was felt that paired t-distrlbutlon (control digester parameter
versus variable digester parameter) would generate the most useful data for
Interpreting the long range effects of storm generated solids on a microbio-
logical process of large variance such as anaerobic digestion. The long range
effects were evaluated using the 95 percent confidence Interval (assuming
normal distribution) on the statistics generated during a background period
when both digesters were fed dry-weather sludge at dry-weather rates before
wet-weather sludge was added to either digester.
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SECTION VII
RESULTS OF SLUDGE THICKENING-CENTRIFUGATIGN
STUDIES CONDUCTED IN KENOSHA, WISCONSIN
As discussed In Section V, the Kenosha CSO treatment system is located on the
grounds of the city's dry-weather treatment plant and the system shares the
sludge handling facilities of the dry-weather plant. The original dry-
weather test procedure for the project was to obtain sludges for centrifuge
dewaterlng which consisted of primary and flotation thickened waste acti-
vated sludge. Dry-weather conditions were assumed to exist after 5 days
without a CSO event. Wet-weather sludge was also obtained from the flota-
tion thickeners. Detention times through the Kenosha treatment plant were
calculated to Insure that true CSO sludge was being used for the dewaterlng
tests. The length of time that the CSO sludge continued to discharge from
the flotation thickeners was dependent on the duration of the CSO event.
The flotation thickening characteristics of the wet-and-dry weather sludges
were evaluated by obtaining samples of the two sludges prior to the thicken-
ing unit and running separate bench scale flotation thickening tests. After
completing all of these tests using the dry-weather sludge and the CSO
sludge, an appropriate combination of the two sludges was also tested for
its thlckenlng-centrifugatlon characteristics.
The Kenosha site, however, presented a problem in the area of obtaining a
CSO sludge produced by the biological treatment process. When the first
preliminary visit was made to the Kenosha Water Pollution Control Plant, it
was discovered that the contact stabilization process used for treating CSO
was not in operation due to equipment problems. Discussions with the plant
superintendent revealed that both of the sludge transfer pumps had been
removed because of shaft and bearing breakdowns and that some of the aera-
tion equipment used In the stabilization tanks was Inoperative, Further
discussions with the superintendent and city water utility manager indicated
that because of the high cost of the repairs required and the uncertainty
of what role the treatment system would have In a plan for complete CSO
abatement as ordered by EPA, the necessary repairs were not expected to be
made until late 1976 at the earliest. Obviously, to meet the objectives
of the project, It became Imperative to develop an alternative plan for
studying the thicken Ing-centrifugatIon process for dewaterlng a CSO sludge
generated by a biological treatment process.
The alternative decided upon was to use the dry-weather treatment plant's
conventional activated sludge process to produce a sludge as similar as
possible to the sludge produced by the contact stabilization process.
52
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During a CSO event, the CSO treatment facility receives the flows in excess
of the dry-weather plant's capacity. Therefore, both treatment systems re-
ceive the same raw flow. The contact stabilization process is a modifica-
tion of the activated sludge process and it was, therefore, assumed that
the two processes wil! produce a very similar biological sludge if they
receive essentially the same influent. The major difference between the two
treatment systems Is that the raw flow to the dry-weather plant undergoes
primary treatment before going to the activated sludge process while the flow
to the contact stabilization process does not receive primary treatment.
Therefore, In order to assume that the dry-weather plant's conventional
activated sludge process will produce a sludge similar to the contact stabi-
lization process during a CSO event, the effects of the dry-weather plant's
primary treatment would have to be minimized.
An Investigation of the Kenosha treatment plant's records Indicated that
primary treatment achieves an average suspended solids (SS) removal of 42
percent. The raw sewage averages 127 mg/1 SS and the primary effluent 7k
mg/1 SS. If the conventional activated sludge process Is to be considered
as the biologi-cal CSO treatment process, this primary effluent would have to
be considered as the raw CSO. A SS concentration of only Ik mg/1 would not
be typical of a raw CSO. Therefore, the SS concentration of the flow going
to the activated siudge process would have to be increased, if possible.
A major CSO event occurred In Kenosha on August 28-29, 1975. During this
event, all six of the primary sedimentation tanks were in operation. Samples
of the primary effluent were taken every hour for six hours beginning at
10;00 AH on August 29. This, however, was about 10.5 hours after the CSO
event began. The results were as follows:
Primary effluent SS
Sampie concent rat ton (mg/1)
10:00 AM 58
1UQQ 62
12:00 80
1:00 PM 66
2:00 72
3:00 70
It can be seen that all of the results are similar to the average primary
effluent SS concentration and no perceptible increase occurred due to the
CSO event. However, because any "first flush" effects may have been missed
during the first 10.5 hours, It was decided to conduct further sampling of
the primary effluent during CSO events. It was also decided that during the
next major CSO event which was sampled, one of the six primary sedimentation
tanks would be taken out of service in order to Increase the primary effluent
SS concentration.
The next sampling program was carried out during the CSO event that occurred
53
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In Kenosha on October 24, 1975. A primary effluent sample was obtained at
5:30 PM, 1.5 hours after the event began; and at 7:30 PM. During the
sampHng, one primary sedimentation tank was out of service. The results
were:
Primary Effluent SS
Sample
5:30 PM 151
7:30 PM \5I*
The dual effects of the high plant flow during the CSO event and the removal
of one sedimentation tank from service, apparently resulted In a primary
effluent concentration that was 106 percent greater than the average. These
excess solids, then, would be carried to the activated sludge process and
their presence In the secondary sludge would make tt similar to the sludge
produced by the contact stabilization method of CSO treatment.
The next step was to remove two of the six primary sedimentation tanks
from service during a major CSO event In order to further increase the pri-
mary effluent SS concentration. However, when this was discussed with the
plant superintendent, he stated that he did not want this done. He said
that having one primary sedimentation tank out of service had resulted in a
significant increase in the SS concentration of the plant's final effluent,
This seems to indicate a solids overload on the secondary treatment plant
and that excess solids should also be present in the secondary sludge. For
this reason, CSO sludge for Kenosha was obtained from the activated sludge
process after a major CSO event occurred while one primary sedimentation tank
was out of operation.
Table 6 gives the ranges of SS concentration found for raw CSO for various
U.S. cities (5). The average of 152 mg/J found during sampling of the pri-
mary effluent on October 2k , 1975 falls below the average SS concentration
for raw CSO but does fall within many of the ranges reported. Therefore,
the primary effluent could be considered as a raw CSO with a slightly below
average pollutional concentration.
On November 3§ 1975, another CSO event occurred in Kenosha and a primary
effluent sample was again taken with one of the primary sedimentation tanks
out of service. The sample was taken 7.5 hours after the overflow began
and the SS concentration was Jl^f mg/I, 5^ percent greater than the average.
This result provided another Indication that the conditions being used did
result In an Increased carryover of sot ids to the activated sludge process.
It was finally decided that one primary sedimentation tank would be taken
out of service during a major CSO event, one that produced maximum flow
through the primary treatment plant, so that the sludge produced by the
activated sludge process could be used as the CSO sludge from Kenosha.
The mobile centrifuge sludge dewaterlng van arrived In Kenosha on November
10, 1975 and a major CSO event occurred on November 9-10. It was assumed
-------
TABLE 6. COMPARISON OF QUALITY OF COMBINED
SEWAGE FOR VARIOUS CITIES3
Type of wastewater
location, year,
ref. no. 5
Typical Treated Municipal
Primary effluent
Secondary effluent
Selected Combined h
Berkeley, CA, 1968-69
Brooklyn, NY, 1972
Bucyrus, OH, 1968-69
Cincinnati, OH, 1970
Des Moines, IA, 1968-69
Detroit, MI, 1965
Kenosha, Wl , 1970
Milwaukee, WI» 1969
Northampton, U.K., 1960-62
RacJne, Wl f 1971
Roanoke, VA, 19&9
Sacramento, CA, 1968-69
San Francisco, CA, 1969-70
Washington, O.C., 1969
avg.
80
15
100
1,051
470
1,100
295
274
458
244
400
439
78
125
68
622
SS, rag/1
range
40-120
10-30
40-150
132-8,759
20-2,440
500-1,800
155-1,166
120-804
—
113-848
200-800
—
—
56-502
4-426
55-2,000
Data presented here are for general comparisons only. Since
different sampling methods, number of samples, and other pro-
cedures were used, the reader should consult the references
before using the data for specific planning purposes.
Infiltrated sanitary sewer overflow.
55
-------
that CSO sludge conditions existed (one primary sedimentation tank was out
of service and the primary treatment plant was receiving maximum flow).
Ten hours after the start of the CSO event, an 18,9 liter (5 gal.) sample
of the waste activated sludge (WAS) was obtained.- This sample was used for
the bench scale flotation thickening tests. The 10 hour waiting period was
based on the time from the arrival of CSO at the plant to the time the CSO
sludge would be withdrawn from the final"clarifiers. Thirteen hours after
the start of the CSO event U»355 liters (3,000 gal.) of thickened sludge
was pumped into a tank truck. The sludge was used for the centrifuge CSO
sludge dewatering tests using the 121.9 cm (48 to.) basket centrifuge on
the centrifuge van. The results of these tests will be described later,
V/hlle the CSO sludge was being obtained, the treatment plant operator men-
tioned that the volume of grit being generated that day was significantly
greater than usual. This was another indication that the CSO event did
increase the solids loading on the plant and that many of these solids
would be present in the WAS being used as CSO sludge.
FLOTATION THICKENING TESTS
The sludges used for the flotation thickening tests were obtained from the
holding tank from which the WAS was fed to the full-scale flotation thicken-
ing facility. No chemical addition was studied because the Kenosha Water
Pollution Control Plant does not use chemical addition fn Its flotation
thickening process. From preliminary tests using dry-weather WAS, an optimum
recycle rate (ratio of pressurized flow to WAS flow) of 242 percent was
selected. This recycle rate was held constant for all the tests so that the
results of the tests could be directly compared among the following three
sludges tested: dry-weather plant WAS, CSO sludge, and a combination of
dry-weather WAS and CSO sludge.
The following calculations were used In determining the appropriate combina-
tion of dry-weather and CSO sludges to be used.
I. Kenosha CSO area 539 hectares (1331 acres).
2. Assume 50 percent of rainfall results in CSO.
3. Assume 1.2? cm (0.5 in.) rainfall = 34,197,323 liters (9,034,360 gal.)
of CSO.
4. Contact stabilization treatment will produce a sludge volume equal
to 3.5 percent of volume treated (I).
5. CSO sludge produced = I,196,908 liters (316,224 gal.)
6. Assuming a two day bleedback: flow of CSO sludge to thickener =
598 mVday (158,112 gpd).
7. Average flow of dry-weather plant's WAS = 594 m /day (157,000 gpd),
0. Ratio of CSO sludge/dry-weather WAS « 1.
Therefore, for the CSO sludge/dry-weather WAS combination flotation thicken-
ing tests, equal volumes of the two sludges were used.
56
-------
The results of the flotation thickening tests performed are summarized in
Figures 13, 14, 15, and 16 for the flotation thickening of the dry-weather
WAS (2 tests), the CSO sludge, and the combination, respectively. It should
be noted that the full-scale thickeners at Kenosha produce a thickened
floated sludge of about 41 solids at a mass loading of approximately 49 kg/
rn /day (10 1b/ft2/day).
For the dry-weather sludge (Figures 13 and 14), a sludge concentration of k
percent can be obtained at a mass loading of 48,9-73.4 kg/m^/day (10-15 Ibs/
ft^/day). For the CSO sludge (Figure 15), a sludge concentration of 4
percent can be obtained at a mass loading of about 53.8 kg/m2/day {II Ibs/
ftz/day), and for the combination of dry-weather and CSO sludge (Figure 16)t
a 4 percent sludge concentration can be obtained at a mass loading of about
44.0 kg/m2/day (9 1bs/ft2/day).
The results indicate that the flotability of the three sludges is fairly
similar with the CSO sludge and the CSO sludge/dry-weather sludge combina-
tion possibly being slightly more difficult to float than the dry-weather
WAS alone. One possible reason for the slight decrease in allowable mass
loadings to achieve a 4 percent thickened sludge concentration could be the
presence of more non-volatile solids, which are more difficult to float,
In the CSO sludge.
CENTRIFUGE DEWATERING TESTS
30.5 cm (12 tn.) Basket Centrifuge - Dry-Weather Sludges
Preliminary centrifuge sludge dewatering tests were conducted at the Kenosha
Water Pollution Control Plant from August 7 through August 13, 1975. Tests
were conducted using dry-weather thickened WAS; and a combination of dry-
weather thickened WAS and dry-weather primary sludge. The combination of
the two sludges was based on the average dally flows of each sludge to the
anaerobic digesters. These values were obtained from the plant operating
records. The two sludges were both tested at this point in order to develop
data on their dewatering characteristics which could be compared between
the two and compared to the dewatering characteristics of the Kenosha CSO
sludge which were expected to be similar. Both sludges were tested with
and without polymer addition. The polymer used was Percol 728, a high molec-
ular weight catlonlc polymer, which was selected on the basis of experience
and on preliminary screening tests.
The samples of thickened WAS and primary sludge were obtained from the sam-
pling points used by the treatment plant personnel to obtain their required
samples, A volume of sludge was obtained each day sufficient to conduct all
of the tests scheduled for that day. The sludge was then poured into a
113.5 liter (30 gal.) container and the feed pump intake was placed in It.
When primary sludge was used, it was screened with a 0.64 cm (0.25 in.) mesh
screen as it was poured Into the container. This was necessary to prevent
plugging of the sludge feed pump during operation. During the testing, the
contents of the container were periodically1 mixed to insure that solids
57
-------
oo
(U
TJ
539
490
441
392
-I 294
cn
245
196
1 147
98
-(110)
.(100)
.(90)
.(80)
•(70)
-(60)
•(40)
-(30)
-(20)
-(10)
INITIAL SLUDGE CONCENTRATION - 9700 mg/1
12345
ESTIMATED FLOATED SLUDGE SOLIDS CONCENTRATION, %
Figure 13. Flotation thickening tests run I - Kenosha dry-weather WAS.
-------
539 p(110)
.(100)
-(90)
.(80)
.(70)
.(60)
.(50)
-(40)
-(30)
-(20)
(to)
^ 441
•o
*£ 392
it-
's,
C 343
,
294
245
o
I/I
147
98
INITIAL SLUDGE CONCENTRATION - 10,200 mg/1
1 2345
ESTIMATED FLOATED SLUDGE SOLIDS CONCENTRATION, I
Figure 14. Flotation thickening tests run 2 - Kenosha dry-weather WAS.
-------
53%
490
m
•o
392
*->
>4~
1 343
X
5 294
CM
245
E 196
3
to
w *
S 98
(no)
r 000)
(90)
(30)
(70)
(60)
• (50)
- (40)
(30)
(20)
I- (10)
INITIAL SLUDGE CONCEHTRATIOH - 13,800 mg/I
12345
ESTIMATED FLOATED SLUDGE SOLIDS CONCENTRATION, %
Figure 15. Flotation thickening tests run 3 • Kenosha
wet~weather WAS.
-------
cl
4-1
H-
jQ
7
-o
CM
1
LOAD IMG,
«/j
<
539
i
4,41
332
343
i
2,94
245
147
98
*
-(no)
-(100)
-(90)
-(80)
-(70)
.(60)
•(50)
-(30)
•(20)
-do)
i
INITIAL SLUDGE CONCENTRATION - 1V,200 rag/1
12345
E? IMATED FLOATED SLUDGE SOLIDS CONCENTRATION, %
Figure 16. Flotation thickening tests run 4 - Kenosha wet- and dry
weather WAS combination.
-------
separation did not occur,
Thirteen tests were conducted and the tabulated results are presented In
Tables Al to A13 In Appendix A. Tables Al to A3 present the results for the
tests using dry-weather thickened WAS; Tables A4 to A6 for tests using the
combination of dry-weather primary sludge and thickened WAS; Tables A7 to
A10 for tests using dry-weather thickened WAS with polymer addition; and
Tables AH to A13 for tests using the sludge combination with polymer
addition.
Figure 17 presents the cake concentrations (% soltds) achieved for the two
dry-weather sludges at varying rates without polymer addition. It can be
seen that the mixture of primary sludge and thickened WAS consistently
dewatered to a greater cake concentration than did thickened WAS alone.
Figure 18 shows the corresponding percentage SS recoveries achieved for the
two types of sludges tested. In this case, the percentage SS recovery Is
higher for the thickened WAS alone, without the primary sludge included.
From Figures I? and 18 and other data In Appendix Tables Al through A6, the
following operating parameters and corresponding performance appear to be
optimum In centrifuge dewatering the Kenosha dry-weather sludges without
chemicals.
Cake solids Solids
Sludge Feed rate concentration recovery
tested (kg/hr) % %_ _
Thickened WAS 2.6 11.5 96
Primary sludge
plus thickened
WAS *i.O \k.Q 3k
Chemicals, as an adjunct to centrifuge dewatering, were also investigated for
the Kenosha dry-weather sludges using the organic polymer, Percol 728. The
effect of polymer on centrifuge performance was Investigated at the developed
optimum feed rates (see above) obtained when no chemicals were used. Figure
19 presents the resultant cake concentrations and percentage SS recoveries
when polymer addition was employed to the centrifuge dewatering of thickened
WAS alone at a constant feed rate of 3*0 kg dry solids/hr (6.6 Ib/hr), and
Figure 20 presents the results for the sludge combination when polymer was
added where the feed rate was constant at *u6 kg/hr (10.0 Ib/hr). Again,
the sludge combination of primary and thickened WAS achieved higher cake
concentrations and lower solids recoveries than for the thickened WAS alone.
For example, from the polymer (Percol 728) testing, It was found that for
a constant feed rate of 3.0 kg/hr (6.6 Ib/hr) of thickened WAS, the addition
of 2.3 g of polymer/kg of dry solids (2.3 lb/IOOO Ib/soltds) Increased the
solids recovery rate from 96-5 to 99.3 percent whereas the cake concentra-
tion decreased from 11.4 to 10.2 percent. This decrease in the cake con-
centration is attributed to the fact that as polymer Is added, higher
62
-------
in
Tl
g'12
o
o
o
n
O Thickened WAS
X Thickened WAS
plus primary
(2.2) (k.k) (6.6) (8.8)
t i i i
(11.0) (13^2)
123^5
FEED RATE, kg solids/hour (lb solids/hour)
Figure 17. 30.5 cm (12 In.) Basket centrifuge tests on Kenosha
dry-weather sludges (without chemicals).
-------
97
O Thickened WAS
X Thickened WAS
plus primary
Of
UJ
o
UJ
t£.
§ 95
UJ
UJ
UJ
a.
(2f2)
(6.6)
(8.8)
(11.0)
(lj.2)
123^5
FEED RATE, kg solids/hour (ib solids/hour)
Figure 18. 30.5 cm (12 In.) Basket centrifuge tests on Kenosha dry-weather
sludges (without chemicals).
-------
TOO
GC
UJ
o
(_>
UJ
DC
o
(A
Ul
o
I/)
10
123*5
POLYMER FEED RATE, g polymer/kg solids (lb polymer/tOOO lt» solids)
Figure 19. 30.5 cm (12 In.) Basket centrifuge tests on Kenosha dry-weather
thickened WAS alone (with polymer and feed rate * 3.0 kg/hr).
-------
-99
LJ
o
o
CC
to
o
t/i
o
_1
o
UJ
<£
x
/
1 2 3 *
POLYMER FEED RATE, g polymer/kg solids (Ib polymer/1000 Ib solids)
Figure 20. 30.5 cm (12 in.) Basket centrifuge tests on Kenosha combined
dry-weather sludges (with polymer and feed rate = 4.6 kg/hr*)«
-------
recoveries are achieved but the cake concentration can decrease because more
and more smaller and lighter participates are retained In the cake. For a
Constant feed rate of 4,6 kg/hr (10.1 Ib/hr) of the combination of primary
sludge and thickened WAS, a polymer addition rate of 0.3 g/kg (0,8 lb/1000
Ib solids) increased the SS recovery from about 94.4 to 98.1 percent, but
again the resultant cake concentration decreased from 13.8 percent to 13.5
percent solids. The polymer rates selected as optimum are based on the con-
siderations of acceptable results at a minimum use of the polymer.
From these preliminary tests, the following conclusions were drawn and later
applied as a guide to the centrifuge dewaterfng tests using the full-scale
121.9 cm (48 in.) basket centrifuge,
1, Because of the minimal benefits achieved by the polymer during
testing and the additional costs and handling problems associated
with a polymer addition system, polymer addition was eliminated as
a parameter to be considered during full-scale testing.
2. As expected, significantly higher loadings may be used when centrl-
fuging combined sludges than when centrlfugfng WAS alone.
121.9 cm (48 In.) Basket Centrifuge (CSO and Combined Dry-Weather Sludge)
The full-scale sludge dewatering tests for CSO sludge and dry-weather sludges
using the 121-9 cm (48 in.) basket centrifuge on the mobile centrifuge van
were conducted at the Kenosha Water Pollution Control Plant from November 11
through November 19, 1975- A major CSO event occurred In Kenosha on November
9-10 and the mobile centrifuge van arrived at the treatment plant on the
morning of November 10. Therefore, CSO sludge was immediately available
for testing.
For purposes of this discussion, CSO sludge refers to thickened WAS sludge
derived from the treatment of CSO. Moreover, dry-weather sludge hereinafter
refers to the combined sludges comprised of thickened VJAS and primary sludge
produced from the treatment of dry-weather sewage.
The CSO sludge was obtained as It carae off the full-scale flotation
thickening units. The thickened sludge was pumped into a 11,355 liter
(3,000 gal.) tank truck and this sludge supply was then used for six 121.9
cm (48 in.) basket centrifuge tests over the next two days. The data
obtained from these six thickened WAS CSO sludge tests are given in Tables
A14 to A19 In Appendix A. They are summarized in Table 7«
After completion of the CSO sludge tests, 121.9 on (43 in.) basket centri-
fuge tests were conducted using the dry-weather sludges from the Kenosha
treatment plant. Dry-weather sludge was obtained by pumping 5i6?8 liters
(J500 gal.) of dry-weather thickened WAS into a tank truck and adding to
that 5,6?S liters (1500 gal.) of primary sludge. Six tests were again
performed and the results are presented In Tables A20 to A25 in Appendix A.
The results of these dry-weather tests are summarized In Table 8.
67
-------
ON
co
TABLE 7. RESULTS OF 121.9 CM (k8 IH) BASKET CENTRIFUGE TESTS
USING WET-WEATHER, THICKENED WAS SLUDGE FROM
KENOSHA, WISCONSIN
Feecf rate
Run
no.
I
2
3
k
5
6
].
A/
min
95
54
111
60
69
40
Mass ba
(gpm)
(25.1)
(14.3)
(29.4)
(15.8)
(18.1)
(10.6)
lances
kg/
win
3.14
0.82
4.00
1.94
2.35
1.05
computed
(Ib/mln)
(6.92)
(1.80)
(8.80)
(4.27)
(5.18)
(2.32)
using the
Cake
concentration .
by balance!
12.
6.
n.
7.
14.
3.
following
1
5
1
4
I
9
samples^
15.5
17-5
13.0
17.4
15.0
9.0
formula: ,»
r ex
J* t ,
maxlmumj
47.4
31.0
27.1
37.9
32.3
33.7
FR x FC x
Percent
recovery
82
93
74
92
95
96
FCT -
.1
.1
.2
.5
.2
.5
CE -
Cyc 1 e
tfme,
mln
12
32
10
15
14
16 1/2
S
K
Where-. C <* cake concentration (I T.S.)
FR ** sludge feed rate 1pm (gpin)
FC « sludge feed concentration (% T.S.)
FCT « sludge feed cycle time (mfn.)
CE = Hters (gallons) of cent rate generated x % T.S. of cent rate
S **, liters (gallons) of skimmings generated x % T.S. of skimmings
K » Hters (gallons) of cake generated
2. The values reported In this column represent the average analytical values obtained from the
actual cake samples that were taken.
3. The values reported In this column represent the maximum value obtained for the cake sample
for each respective run.
-------
TABLE 8. RESULTS OF 121.9 CM (48 INCH) BASKET CENTRIFUGE
TESTS USING DRY-WEATHER, THICKENED WAS AND PRIMARY
SLUDGES FROH KENOSHA, WISCONSIN
Feed rate
Run
no.
7
8
9
10
11
12
1.
If
min
88
54
39
35
38
58
(.spin)...
(23.2)
(14.2)
(10.2)
(9.3)
(10.1)
(15.4)
kg/
mm
3.59
2.18
1.56
0,54
1.25
3.31
Mass balances computed
(.1 fa/ml i
(7.90)
(4.18)
(3.43)
(1.19)
(2.75)
(7.28)
using the
_CaJ
-------
From Tables 7 and 8, It can be seen that three different values are given
for the centrifuge cake concentrations. The first value by balance, was de-
termined by a mass balance using the feed, centrate, and skimmings data and,
then calculating the average centrifuge cake concentration. The second
value by sampling, is the average value obtained from the actual cake
samples that were taken. The third value, maximum, Is the maximum value
found for the cake samples taken. It represents the concentration of the
last portion of cake to be removed from the basket centrifuge.
The cake concentrations determined by the mass balance were the ones used
for the evaluation of the data because of the difficulty encountered in
obtaining representative samples. Examination of Tables 7 and 8 indicates
that the mass balance usually predicts a lower cake concentration than Is
obtained by sampling. The discharge of the cake from the 121.9 cm (48 in.)
centrifuge progresses from the very wet cake to the very dry as the auto-
matic plow scrapes the cake away from the wall of the centrifuge. While
the dryer portions of the cake are easier to sample, the very wet cake that
discharges Initially flows freely and it Is difficult to sample. Failure
to obtain a representative sample of this very dilute cake would result In
the average of the cake samples indicating a dryer cake than would actually
be produced. Therefore, the cake concentration predicted by the mass
balance was used as the most indicative of the 132 liters (35 gal«) to
348 liters (92 gal.) of cake remaining in the basket after skimming has been
completed.
Figure 21 presents the cake concentrations achieved for varying feed rates
of both CSO sludge and the dry-weather sludges. It appears that a drier
cake is obtained when centrlfuging the dry-weather sludges than when centrl-
fuging CSO sludge. The CSO sludge achieves a maximum cake concentration of
14 percent at a solids feed rate of 2.35 kg/mln (5.2 1b/mln.). As the feed
rate increases above 2.35 kg/mln (5-2 lb/mln.), the resultant cake concentra-
tion decreases. On the other hand, the cake concentration for the dry-wea-
ther sludges continued to increase over the range of solids feed rates In-
vestigated. The driest cake, 17«5 percent solids, was achieved at the high-
est feed rate tested, 3.6 kg/mln (8.0 lb/mln). The plot In Figure 21 Indi-
cates that the cake concentration may Increase further as the feed rate is
Increased up to some maximum point as was found for the CSO sludge.
Figure 22 shows the percentage SS recoveries achieved at varying feed rates
for the CSO sludge and the dry-weather sludges. The recoveries were similar
for the two types of sludges up to a feed rate of 2,35 kg/mln (5.2 Ib/mln).
Above 2.35 kg/mln (5.2 Ib/mln), the solids recovery for the CSO sludge de-
creased rapidly, dropping from 95«5 percent at 2.35 kg/min (5-2 Ib/mln) to
74 percent at 4.0 kg/min (8.8 Ib/roln). The recovery rate for the dry-weather
sludges also decreased, but only slightly; from 95 percent at 2.35 kg/min
(5-2 ib/mln) to 93-5 percent at 3.6 kg/mln (8.0 Jb/raln).
The reason for the centrifuge dewaterlng differences observed between the
two sludges could be that the dry-weather sludge, while containing thickened
WAS, contains a relatively large amount of raw primary sludge solids. The
CSO sludge, on the other hand, Is mainly a biological sludge. The raw pri-
70
-------
--4
ut
O
to
CJJ
O
Z"
a:
E
>-
<
cc
25
20
10
2 5
LU
O
O
DRY-WEATHER
X- SLUDGE
2 3
FEED RATE, kg/mln (Ib/min)
o C50
SLUDGE
(8.8)
I
Figure 21. Relationship between cake concentration and solids feed rate
[121.9 cm ('18 In.) basket centrifuge tests - Kenosha sludges].
-------
-•4
NJ
LU
>
o
o
UJ
o
100
90
30
LU
£ 70
60
DRY-WEATHER
SLUDGE
(2,2)
(6.6)
2 3
FEED RATE, kg/mln (Jb/mln)
CSO
SLUDGE
(8.8)
i
Figure 22. Relationship between so]Ids recovery and solids feed rate
[121.9 cm (48 In.) basket centrifuge tests - Kenosha sludges].
-------
mary solids will dewater quite readily at low centrifuge detention times,
(high loadings) whereas the biological sludge Is more difficult to dewater
with high loadings resulting tn less solids capture and a wetter cake due
to a reduction in the time the captured soltds are exposed to the centrifugal
force.
121.9 cm (48 In.) Basket Centrifuge Tests -Wet-Weather andPry-Weather
Combined S1udges
The full-scale centrifuge dewaterlng tests using the Kenosha wet-weather/
dry-weather sludge combination were conducted on September 10-15, 1976, A
CSO event occurred In Kenosha on September 8, 1976. At the beginning of the
event, one primary sedimentation basin was removed from service. This In-
creased suspended solids In the primary effluent, thus simulating a CSO
generated wastewater. Next, a 22,710 liter (6,000 gal.) tank truck was
filled with 7,950 liters (2,100 gal.) of dry-weather primary sludge from the
primary tank that had been removed from service. To this, 6,050 liters
(1,600 gal.) of dry-weather flotation-thickened waste activated sludge was
added to the tanker. Twelve hours after the CSO event, the tanker was filled
with 8,700 liters (2,300 gal.) of flotation- thickened WAS consisting of 1,900
liters (500 gal.) of dry-weather sludge and 6,800 liters (1,800 gal.) of wet-
weather sludge. The twelve hour waiting period was required because of de-
tention times through the Kenosha Water Pollution Control Plant. The sludge
ratios used were based on average dally sludge production at the dry-
weather plant and on the CSO sludge generated from a 1.27 cm (0.5 in.) rain-
fall using a two day bleedback.
The thickened sludge supply was continuously mixed by means of a recircula-
tion pump and fed to the 121,9 cm (48 in.) basket centrifuge. A total of
nine test runs were conducted. Five of the runs were conducted without
polymer. The data obtained from these nine tests using the wet-weather/dry-
weather combination sludge are presented In Tables A-26 to A-J4 in Appendix
A. The results are summarized In Table 9. As in the previous sections,
cake concentrations were reported by mass balance, average sample concen-
tration, and maximum sample concentration. All of the percent recoveries
were calculated from mass balance cake concentraI ton.
Figure 23 presents a plot of feed rate versus cake concentration for the
nine test runs. Cake concentrations for the runs conducted without polymer
varied from a low of 6.4 percent to a high of 14.3 percent. For the runs
with polymer, the cake concentration range was 5.2 to 14.8 percent. Optimum
cakes for both sludges were obtained at feed rates of 2.0-3-0 kg/mln (4.4-
6.6 Ib/mln), The graph demonstrates that the cake concentration of the two
sludges reacted in a similar manner ^or variations In feed rate.
A plot of feed rate versus solids recovery is shown In Figure 24 for the test
runs conducted both with and without polymer. Percentage suspended solids
recovery for the tests without polymer varied from 64.2 percent to 94.6 per-
cent. All of the runs conducted with polymer had solids capture values tn
excess of 90 percent. From the graph, It can be seen that solids recoveries
decrease rapidly for runs without polymer at centrifuge loadings tn excess
of 2.0 kg/min (4.4 Ib/min). The recoveries for the tests in which polymer was
73
-------
--si
-t-
TABLE 9. RESULTS OF 121.9 CM (48 IN.) BASKET CENTRIFUGE
TESTS USING A MIXTURE OF WET-WEATHER/DRY-WEATHER
THICKENED SLUDSE FROM KENOSHA, WISCONSIN
Run
No.
13
14
15
16
17
18
19
20
21
1/mlft
54
95
38
70
109
44
44
61
81
Feed
2E2.
14.3
25.0
10.0
18.5
28.8
11.7
11.7
16.0
2K5
rate
kfl/mln
1.97
1.76
1.90
1.30
3.99
1.07
1.09
2.58
4.51
Ib/mln
4.34
3.88
4.18
2.87
8.78
2.36
2.41
5.69
9.93
Cake
By balance
14.3
6.4
12.7
8.1
12,7
5.7
5.2
14.8
12.9
concentration
' Samples^
13.2
45.1
31.6
28.4
22.6
24.1
25.9
20.2
18.2
, 1
Maximum 3
14.6
46.5
38,2
35.7
28.7
24.6
31.5
21.0
20.1
Percent
recovery
94.6
77.8
87.7
87.0
64.2
94.2
97.2
97.8
93.1
Cycle
time
(mtn)
25
17
23
24
15
20
25
22
11
Note; Runs 13-17 No polymer addition
Runs 18-21 Polymer addition
continued
-------
TABLE 9. (continued)
1. Mass balances computed using the following formula: r FR xFC x FCT - CE-S
u K
Where: C = cake concentration (% T.S.)
FR « sludge feed rate 1pm (gpm)
FC «* sludge feed concentration (% T.S,)
FCT = sludge feed cycle time (nun.)
CE = liters (gallons) of centrate generated x % T.S. of centrate
S « liters (gallons) of skimmings generated x % T.S, of skimmings
K* liters (gallons) of cake generated
2. The values reported In this column represent the average analytical values obtained from
the actual cake samples that were taken.
3. The values reported in this column represent the maximum value obtained for the cake
sample for each respective run.
-------
o
ts>
^: 20
Ul
o
i
OS
UJ
I-
10
UJ
o
x
o
o
I
u
0NO POLYMER ADDITION
APOLYHER ADDITION 0.76-2.76 kgAwtrie ton
(1.6-5.5 Ib/ton)
1.0
(2.2)
2.0 3.0
(4.*) (6.6)
FEED RATE, kg/min (Ib/mln)
(8.8)
5-0
(11.0)
FJgure 23. Relatfonshlp between cake concentration and solids feed rate 121.9 cm (W In.)
basket centrifuge tests-Kenosha wet-weather/dry-weather sludge combination.
-------
loo r
e
90 -
©
80
V)
UI
I
LU
O
a:
ui
Q-
POLYMER ADDITION
ADD1TIOM
0".76-2.76 kg/metric ton
(1.6-5-5 Ib/ton)
J
1.0
(2.2)
2.0 3.0
(4.4) (6.6)
FEED RATE, kg/mln (Ib/mfn)
(8.8)
5.0
(11.0)
Figure 2^». Relationship between solids recovery and solids feed rate 121.9 cm (48 In.)
basket centrifuge tests - Kenosha wet-weather/dry-weather sludge combination.
-------
used remained uniform oyer the entire feed range of 1,0 to 4,5 kg/mln (2.2-
10,0
Figure 25 Is a plot of cake concentration and solids recovery versus polymer
dosage. The graph demonstrates decreasing cake concentration with Increasing
polymer addition. Solids recovery remained uniform over the polymer dosage
range. The test runs determined that the optimum polymer dosage was 1.40
kg/metric ton (2.8 Ib/ton), which yielded a cake concentration of 14.8 per-
cent with a corresponding 97.8 percent suspended solids recovery.
EFFECT OF CENTRIFUQATIQN ON HEAVY METALS DISTRIBUTION
Heavy metal determinations for the feed to the centrifuge, the skimmings and
cake retained fay the centrifuge and the centrate discharged from the centri-
fuge were made during centrifugalIon of the Kenosha dry-weather and CSO
sludges. The determinations were made on composite samples which were pre-
pared from the grab samples taken from expected optimum testing runs. The,
samples for the dry-weather determinations were taken during the 30.5 cm
(12 in.) basket centrlfugation tests using Kenosha dry-weather thickened WAS
on August 7, I975« The results are presented in Table 10. The samples for
the CSO sludge determinations were taken during the 121.9 cm (48 In.) basket
centrffugatfon tests using Kenosha thickened CSO waste activated sludge on
November 12, 1975- These results are given In Table 11.
Examination of Tables 10 and 11 shows that the two sludges investigated have
the following common characteristics:
I. The heavy metals appear to be solids related, that Is, they are a
part of or are attached to the solids. For example, for a given
heavy metal, the concentration Is consistently of the same magni-
tude, irrespective of the sample (feed, centrate, skimmings and
cake).
2. The highest metal concentrations observed were those associated
with zinc and copper.
3. The lowest metal concentration noted was that for mercury.
4. In general, for a given heavy metal or sample taken (feed, centrate,
skimmings or cake), the CSO and dry-weather sludge metal concen-
trations are similar and of the same magnitude.
The above similarities are noteworthy in view of the fact that the results
obtained were derived from samples taken about three months apart.
Comparisons of the data In Tables 10 and II also show that for the heavy
metals investigated, the dry-weather cake concentrations were consistently
higher than those for the CSO centrifuge cake.
78
-------
ioo r
in
£
o
i
«/]
o
o
I/I
90
80
15
o
u
u
o
o
10
FEED RATES:
-^-SIt kg/mln (2.36-9-93 lb/m!n)
1.0 1.0 3.0
(2.0) (4.0) (6.0)
POLYMER DOSAGE, kg/metric ton (Ib/ton)
0
Figure 25. Cake concantratJon and sol Ids recovery vs. polymer dosage
121.9 cm (48 in) basket centrifuge tests - Kenosha
wet-weather/dry-weather sludge combination.
79
-------
TABLE 10. HEAVY METAL CONCENTRATIONS FOR CENTRIFUGE TESTS
USING KENOSHA DRY-WEATHER SLUDGE (THICKENED WAS)
Concentrations I
n mg metal /kg
Feed Centrate Skimmings
Zinc
Lead
Nickel
Copper
Chromium
Mercury
(No Polymer
3681 3418
522 633
145-290 <380
1565 1266
783 759
1.62 2.03
Addition)
3832
571
109-217
1413
842
1.71
TABLE 11. HEAVY METAL CONCENTRATIONS FOR CENTRI
USING KENOSHA CSO SLUDGE
Zinc
Lead
Nickel
Copper
Chromium
Mercury
Concentrations !n
Feed Centrate
2690 2905
410 405
333 405
2110 1280
877 842
1.30 1.24
solids
Cake
3900
587
470
1650
709
3.57
FUGE TESTS
m§ metal7kg solids
Sk|mmings
3770
435
330
1945
1170
1.12
Cake
1980
254
234
1375
424
0.47
(No Polymer Addition)
80
-------
Comparison of the CSO feed data in Table 11 with that of a similar previous
Kenosha CSO sludge sample recorded in the literature (l) shows that the
heavy metal concentrations are similar for the two samples with the excep-
tion of zinc which was 7»15^ mg/kg as opposed to 2,690 mg/kg In Table II.
Presented in Table 12 are data obtained from mass balances performed to show
the effect of centrifugal Ion on the mass distribution of the heavy metals.
As expected, since the metals are solids related and centrlfugatIon is a
solids removal process, the major portltSn of the heavy metals are retained
In the cake and skimmings. This effect was slightly more pronounced In the
centrifugatfon of CSO sludge than for dry-weather sludge.
The results of the heavy metals analysis on the Kenosha wet-weather/dry-
weather sludge combination are presented In Table 13. The samples were taken
from the optimum runs of September 14-15. 1976. The metal analyses were
performed on the sludge feed, centrate, skimmings, and cake for samples both
with and without polymer. Cadmium analyses were Included due to increased
environmental concern with regard to this element.
Zinc and copper were found to be the two most concentrated metals with cake
concentrations of 8,4.75 mg/kg and A,155 mg/kg reported respectively, for sam-
ples without polymer. Mercury was the least concentrated of the metals
analyzed. The cadmium value of the cake was 45 mg/kg while the centrate con-
centration was reported at 32 mg/kg for samples without polymer addition.
A comparison between the samples In which polymer was added and those in
which it was not shows a definite pattern In metal distribution. With re-
gard to centrate quality, heavy metal concentrations were significantly re-
duced for zinc, lead, copper, and chromium for samples dosed with polymer.
Concentrations of nickel, mercury, and cadmium showed no significant change
between samples In which polymer was added and those In which it was not.
A mass heavy metals balance has been prepared for the Kenosha wet-weather/
dry-weather sludge combination for samples with polymer addition and those
without. This information Is shown in Table 14. The majority of the metals
had a lower concentration value by mass balance when compared to the actual
sample value. This is due In part to the difficulty in obtaining representa-
tive cake samples from the basket centrifuge. Metals recovery are also
listed In the Table. The samples to which polymer was added show consistent-
ly higher removals with all values in excess of 95 percent. This compares
to a recovery range of 77«4 - 85.8 percent for the metal samples with no
polymer addition.
All of the data presented here contributed to our storehouse of knowledge as
it relates to the presence and magnitude of heavy metals in sewage plant
sludges derived from dry- and wet-weather operations. As importantly, the
data provide an Insight into the effect of the distribution of the heavy
metals from centrifuge debater ing and thereby permit other necessary engi-
neering evaluations related to the ultimate disposal of the two streams
arising from centrifugation. For example, the residual centrate is usually
81
-------
TABLE 12. EFFECT OF CENTRIFUGAT1QN ON THE DISTRIBUTION OF
HEAVY METALS (BASED ON ONE LITER OF FEED SLUDGE)
(ALL VALUES IN mg)
ury-weather sludge
Zinc
Lead
Nickel
Copper
Chromium
Mercury
Feed
140.2
19.9
8.29
•59.6
29*8
.061?
Retained
(cake 6 skimmings)
122.8
17.0
7.32
53.0
25.4
.0564
Percent
retained
87.6
85.3
88.3
88.9
85.3
91.4
Centrate
17.4
2.91
0.97
'6.58
4.38
.0052
Percent
discharged
12.4
14.7
11.7
11.!
14.7
8.6
Zinc
Lead
Nickel
Copper
Chromium
Mercury
Feed
82.9
12.6
10.3
65.0
27.0
.0400
Retained
(cake & skimmings)
75.9
11.4
9.16
60.9
24.4
.0347
CSO sludge
Percent
retained
91.6
90.4
88.9
93.7
90.4
86.8
Centrate
7.04
1.20
1. 14
4.06
2.55
.0052
Percent
discharged
8.4
9.6
11.1
6.3
9.6
13.2
82
-------
TABLE 13. HEAVY METAL CONCENTRATIONS FOR
CENTRIFUGE TESTS USING KENOSHA
CSQ/DRY-WEATHER SLUDGE COMBINATION
Concentrations In nvg metal/kg solids
OS
feed
Zinc
Lead
Nickel
Copper
Chromium
Mercury
Cadmium
Without
polymer
7520
632
305
4050
1520
0.90
44
With
polymer
7530
621
3*5
3800
1475
0.33
39
Cent rate
Without
polymer
5200
640
280
2515
1265
0.85
32
With
polymer
1085
445
310
1240
668
0.70
36
Skimmings
Without
polymer
9980
775
370
3720
1995
1.30
55
With
joolymer
8920
662
330
4235
1785
1.00
47
Cake
Without
jjolyroer
8475
648
340
4155
1610
0.63
45
With
polymejl
7510
620
315
3740
1325
1.20
36
Polymer Addition; 1.1 kg/metric ton (2.2 Ib/ton)
-------
00
TABLE 14. HEAVY METAL MASS BALANCES FOR THE 121.9 CM
(48 IN.) BASKET CENTRIFUGE TESTS
KENOSHA CSO/DRY-WEATHER SLUDGE COMBINATION
Cake concentration mg metal/kg wetsample
Zinc
Lead
Nickel
Copper
Chrom j urn
Mercury
Cadmium
By mass
No
polymer
532.5
40.8
20.2
307-7
104.1
.057
3.1
balance
With
jjolyraer
523.3
45.4
26.5
273.!
101.1
.001
2.6
Sample
No
polymer
1064
81
44
521
203
.08
5.56
With
polymer
1438
118
61
7t6
253
.11*5
6,84
Maximum
No
polymer
1065
81
46
532
204
.08
5.63
With
_j»o1ymer
1450
118
64
726
258
.145
6.85
Percent
Ceeovery
No
polymer
84.0
76.8
78.6
85.8
81.2
77.4
83.4
With
polymer
98.2
96.4
99.5
98.3
97.7
-
95.5
-------
returned to the treatment plant and its heavy metal contribution and effect
on treatment and effluent quality has not heretofore been taken into account
in the treatment plant design. Moreover, the heavy metal concentration in
the centrifuge cake will have a bearing on the extent to which It can be
disposed of on land (by spreading or landfill).
85
-------
SECTION VIM
RESULTS OF SLUDGE THICKENING - CENTRIFUGATION
STUDIES CONDUCTED IN MILWAUKEE, WISCONSIN
Milwaukee was the second of three test locations visited during the course of
this project. The experimental tests were conducted between April and June,
1976. The Milwaukee Humboldt Avenue CSO site was chosen as the study
location to evaluate the thlckenlng-centrlfugatton process from a physically
generated wet-weather sludge. The corresponding dry-weather test facility
selected was the Milwaukee South Shore Water Pollution Control Plant.
As with the Kenosha CSO sludge, problems were encountered In obtaining a
representative thickened sludge from the Humboldt Avenue site. This site
consists of a storage facility as discussed previously in Section V. The
procedure used to obtain the CSO sludge was as follows: During a CSO event,
the detention tank mixers were removed from service. The facility thus acts
as a sedimentation basin. Following the CSO event, supernatant was
continuously drawn off over a period of days until only 30.5 cm (12 In.) of
sludge remained in the detention tank. This sludge was then pumped to above-
ground thickening facilities which consisted of a series of 1892.5 liter
(500 gal.) circular tanks. The sludge was allowed to thicken for 12 hours
with the decant being returned to the detention tank.
Following the final decant, a visual Inspection of the thickened sludge was
made. Its appearance indicated that the sludge was very stratified by
particle size, consisting of a very dilute supernatant and a coarse, gritty
subnatant. Prior to conducting dewaterlng tests, samples of the two
stratified sludges were obtained for laboratory analysis. The solids analy-
ses are presented below in Table 15. The total solids of the thickened
supernatant was O.I'* percent with a suspended solids value of 900 mg/1.
The corresponding total solids of the thickened subnatant was &J.37 percent,
consisting primarily of gritty material. To substantiate the particle
size of the gritty subnatant, a sieve analysis was conducted and is
presented In Table 16. The data obtained Indicated that 40.7 percent of the
gritty sludge would be retained on a No, 20 sieve (Q.8M mm). Since the
Humboldt Avenue Detention Tank utilizes settling and resuspenslon of solids,
it appears that the tank mixers are not capable of resuspendlng all of the
higher density particles from the tank bottom. This has resulted In a
gradual build-up of grit and gravel over a period of time, and is not
truly representative of typical CSO sludge.
In an effort to obtain a more realistic wet-weather sludge, a different
approach was used during the next CSO event. The detention tank was allowed
86
-------
TABLE \$. RESULTS OF THE THICKENED
SLUDGE SOLIDS ANALYSIS
Humboldt Avenue Detention Tank
Milwaukee, Wisconsin
Parameter _ Spernatant Subnatant
Total solids 0.14% 67.
Total volatile solids " 0.042 7.9*
Suspended soUds 0,09%
Volatile suspended solids 0.04%
TABLE 16. RESULTS OF THE THICKENED SLUDfiE
SUBNATANT SIEVE ANALYSIS
Humboldt Avenue Detention Tank
Milwaukee, Wisconsin
Percent of Cumulative Mesh opening
number total retained percent retained (millfmeters)
14
20
30
40
60
80
Pan
23.5
17.2
12.6
17.4
19.3
5.7
4.3
23.5
40.7
53.3
70.7
90.0
95.7
100. 0
1.4!
0.841
0.595
0.420
0.250
0.177
""
Dry bulk density = 1,4?8 gm/cc
to fill, and was gradually decanted off in a manner similar to the one
discussed previously. When the drawdown reached the 1.22 m (4.0 ft) depth,
all of the tank mixers were turned on. This depth was selected because it
is the minimum depth obtainable in which the mixers are sufficiently
submerged to allow adequate solids agitation. A grab sample of this sludge
was taken after 15 minutes of mixing and allowed to gravity thicken. Follow-
ing decantation, the sample was analyzed for soltds concentration. The
results are shown below:
Volatile
Total Total volatile Suspended suspended
solids solids solids solids
mo/1 mg/l jng/j ing/1
Sample No. I 197 68 94 35
87
-------
The total solids concentration value of 197 mg/1 was actually less than the
1400 mg/I total solids value obtained from the thickened sludge supernatant
discussed previously. Because of these results, it was decided to conduct
all testing using the initial procedure developed.
The test Intentions at the Milwaukee South Shore Water Pollution Control
Plant were to obtain dry-weather primary sludge, assumed to be the primary
sludge available after 5 days of dry-weather flow, and dewater It by the
centrifugation process. The gravity settled primary sludge was selected
because it most closely resembled the sludge generated by the Humboldt Avenue
CSO Detention Tank. Sufficient sludge to complete each day's testing was
drawn from the primary settling basins and stored In a sludge pumping pft.
At'the completion of each day's runs, the remaining sludge was pumped from
the pit. Prior to filling with fresh sludge, the pit was thoroughly washed
down and pumped dry.
BENCH SCALE CLARIFICATION TESTS
Bench scale clarification tests using Milwaukee wet-weather thickened sludge
supernatant, Milwaukee dry-weather influent wastewater, and a mixture of the
two in the proportion in which they are produced were conducted on June 29,
1976. Because of the relatively dilute residuals present in the wet-
weather sludge, bench scale clarification tests were conducted In lieu of
thickening tests. For purposes of comparison, the wet-weather sludge
settling characteristics were compared to Milwaukee South Shore incoming
wastewater. Six bench tests were conducted. Two each on the wet-weather
sludge, the dry-weather wastewater, and the combination of wet-weather
sludge and dry-weather wastewater. From Phase I (1), solids clarification
was obtained by addition of ferric chloride followed by two minutes of
flocculatIon. The bench scale clarification tests followed this procedure,
facilitated by polymer addition to strengthen the floe and a 15 second rapid
mix prior to the 2 minute flocculatton.
The proportioned mixture of the wet-weather sludge and the dry-weather
wastewater was based on the following calculations:
1. Milwaukee CSO area » 6804 hectares (16,800 acres).
2. Assume 50 percent of rainfall results In CSO,
3. Assume 1.27 cm (0.5 In.) rainfall = 431,641,400 liters (114,040,000
gal.) of CSO.
k. Physical treatment of the CSO will produce a sludge volume equal
to 0.9 percent of volume treated (1).
5. CSO sludge produced » 3,884,772 IIters . (1,026,360 gal.).
6. Assuming a two day bleedback: amount of CSO sludge produced =
1,942 nP/day (0.513 mgd).
7. Average dry-weather wastewater flow - 258,894 m /day (68.5 mgd).
-------
B. Ratio of CSO sludge/dry-weather wastewater = 0.01,
Thus, for every liter (0.26% gal.) of CSO sludge produced, 100 liters
(26.4 gal.) of dry-weather wastewater are produced. The results of the
gravity clarification tests for the wet-weather sludge, the dry-weather
wastewater, and the combination are presented fn Table 17. For the wet-
weather sludge, a settling rate of 27.4 cm/min (0.9 fpm) was obtained. The
detention time was 30 minutes. The sludge volume obtained was equivalent
to 17.5 ml/1 (17.5 gal./lOQQ gal.). The dry-weather wastewater had a
gravity settling rate of 2k.4 cm/mln (0.8 fpm) with a sludge volume of 45
ml/1 (45 gal./lOOO gal.) after 30 minutes of settling. The results of the
combination mixture were identical to that of the dry-weather wastewater.
Effluent suspended solids were quite uniform varying from a high of 16 mg/I
for the wet-weather sludge to a low of 12 mg/l for the combination sludge.
The results of the settling tests show that the wet-weather sludge has a
slightly higher settling rate than either the dry-weather wastewater or the
combination sludge. The results also indicate that the addition of wet-
weather sludge to dry-weather wastewater did not hinder the settling rate
or effluent quality,
CENTRIFUGE DEWATERING TESTS
121.9 cm (48 in.) Basket Centrifuge - Wet-Weather Sludge
The full scale CSO sludge dewatering tests using the mobile van's 121.9 cm
(48 in.) basket centrifuge were conducted at the Humboldt Avenue detention
tank on May 10-12, 1976.
In the Initial full-scale test runs, the thickened feed sludge supernatant
and subnatant were mixed and screened through 0.64 an (0.25 In.) mesh prior
to being fed to the 121.9 cm (48 in.) basket centrifuge. The screening was
required since the centrifuge Intake Is restricted to particles less than
0.64 cm (0.25 In.) diameter. Three runs were attempted, all of which had
to be terminated due to excessive basket vibration and plugging of the feed
line. The plugging developed as a result of stratification In the feed line
resulting from the high specific gravity of the grit particles.
To prevent damage to the feed pump and the 121.9 cm (48 in.) basket
centrifuge, It was decided to feed only the thickened sludge supernatant to
the centrifuge. The decision to use only the supernatant was also based on
the assumption that the gritty subnatant would be settled out In a CSO
treatment plant designed for the u$e of centrifuges.
One full scale run was conducted using the 121.9 cm (48 In.) basket to
centrifuge the thickened sludge supernatant. The length of run was 73
minutes at a feed rate of 223 llters/mln (59 gpm). The individual test data
obtained from this run are presented in Appendix B, Table Bl, and are
summarized below in Table 18.
89
-------
TABLE 17. RESULTS OF BENCH SCALE CLARfFICATION TESTS
MILWAUKEE, WISCONSIN
Run No.
Raw waste pH
Raw waste suspended
sol ids, mg/1
Chemical Treatment
FeClj, mg/1
Percol 728, mg/1
Rapid mix, sec.
Flocculatlon time, mfn.
Humboldt
wet- weather
1
8.2
198*
10
2
15
2
Avenue
sludge
2
8.2
198*
20
2
15
2
South
dry- weather
3
7.85
475
10
3
15
2
Shore
wastewater
4
7.85
475
20
3
15
2
Mixture of wet-
sludge and
•weather
dry-
weather wastewater
5
7.9
469
10
3
15
2
6
7.9
469
20
3
15
2
Settling Data
Settling rate, cm/ml n
(fpm)
Detention time, mtn.
Sludge volume, ml/ 1 (gal./
1000 gal.)
Scum volume, ml/I (gal./
1000 gal.)
27.4 (0.9) 27-4 (0.9) 24.4 (0.8) 24.4 (0.8) 24.4 (0.8) 24.4 (0.8)
30
15 (15)
0
30
20 (20)
0
30
45 (45)
30
45 (45)
30
45 (45)
30
45 (45)
Effluent pH
Effluent suspended
solids, mg/1
7.35
16
7.1
14
7.5
15
7.4
14
7.5
13
7.4
12
During the testing program, wet-weather sludge solids concentrations varied between 198-1400 mg/1.
This value represents the actual gravity thickened sludge concentration at the time of sampling and
should not be confused with a similar value (197 rag/1) reported previously for a sample taken with
the settling tank mixers running.
-------
TABLE 18. RESULTS OF 121.9 CM (48 IN.) BASKET CENTRIFUGE
TEST USING WET-WEATHER, THICKENED SLUDGE SUPERNATANT
FROM THE MILWAUKEE HUMBOLDT AVENUE SITE
Run
No . Tpm
I 223.3
Feed rate
gpm
59
kg/ml n_
.205
Ib/min
.452
Cake concentration, 1
by balance
1.77
samples
0.135
maximum
0.140
Percent recovery <= 92.5
Cycle time •» 73 rain.
The cake concentration obtained by mass balance was 1.77 percent compared to
a sample value of 0.135 percent. It should be noted that the cake concen-
trations are an actual composite of cake plus skim. No independent skim
samples were taken due to the dlluteness of the sludge.
Since the thickened sludge supernatant feed concentration was very dilute
(920 mg/1), the maximum solids loading was 0.205 kg/mln (0.452 Ib/min).
Theoretically, at this loading, It would take a run time of 65 hours to
completely fill the 454.2 liters (120 gal.) basket centrifuge. This Is
equivalent to centrifuging 870,550 liters (230,000 gal.) of thickened sludge
supernatant. Because of the dI lute concentration of the sludge and the
Impractical theoretical length of run time to fill the 121.9 cm (48 In.)
basket centrifuge, it was decided to terminate full scale testing, However,
supplementary test data were obtained from the Humboldt Avenue wet-weather
site using the 30.5 (12 In.) basket centrifuge. This information is
presented in the following section.
30.5 cm 0.2 In.) Basket Centrifuge - Wet-Weather Sludge
Supplementary centrifuge sludge dewaterfng tests were conducted at the
Milwaukee Humboldt Avenue Detention Tank on June 8-9, 1976. As with the
full scale testing, runs were conducted using the thickened sludge^super-
natant obtained from the CSO event of May 28, 1976. The data obtained from
the two test runs are detailed in Appendix Tables 82 and 83, with a summary
of the results shown in Table 19.
Excessively long cycle times were required (240 min) because of the low feed
solids concentration (0.066 percent). Run No. I was conducted without
polymer. Cake concentration for Run No. 1 was 18.3 percent with a 76.6
percent recovery. Run No. 2 was conducted with a catlonic polymer, Percol
728. This polymer was selected from laboratory screening tests. A cake
concentration of 28.4 percent was obtained with a corresponding recovery of
82 percent at a polymer dosage of 1.05 kg/metric ton (2.1 Ib/ton). The
cake concentrations reported were obtained from sample analysis. No
further testing was conducted due to the low feed solids concentrations.
-------
TABLE 19. RESULTS OF 30.5 CM (12 In.) BASKET CENTRI-
FUGE TEST USING WET-WEATHER THICKENED SLUDGE FROM
HILWAUKEE - HUMBOLDT AVENUE SITE
Case Cycle
Run Feed rate concentration Percent time,
No,
1
2
Ipm
10.
10.
2
2
gpm
2.7
2.7
kg/min
0.0006
0.001
Ib/mJn
0.
0.
0014
0023
1 TS
18
28
.3
.k
recovery
76
82
.6
.0
in In
2*fO
240
Run No. 1 - no polymer
Run No. 2 - Percol 7ZB polymer added.
Decanter CentrI[fupe Jests - Dr y-Vlea ther SIudge
The solids dewatering van was relocated at the Milwaukee South Shore Water
Pollution Control Plant on May 18, 1976.. Full scale field testing of the
Milwaukee South Shore dry-weather primary sludge using the decanter centri-
fuge began on May 25, 1976. The dewatering tests continued until June 3,
1976. The decanter centrifuge was selected In preference to the basket
because the primary sludge had a solids concentration of about 5 percent.
The results of the test data from the 21 runs conducted are presented In
Appendix Tables Bk to B24, A composite of these data are summarized In
Table 20. Runs No. 1-7 were conducted without polymer. Solids feed rates
were varied between 98.5 kg/hr (217 lfa/hr) and 337.8 kg/hr (744 Ib/hr)
during the testing. For the twenty-one runs, cake concentrations ranged
from 13.2 percent to 26.2 percent. The lowest recovery obtained during the
testing was k\ percent, while the maximum was 98 percent. For the seven
tests conducted without polymer, cake solids remained generally higher
than when polymer was added. However, solids capture was poor. This Is
Illustrated In the bar graph of cake solids and recovery versus the de-
watering run no. presented In Figure 26. For Runs Ho. 8-21, the bar graph
demonstrates the overall Improvement In centrate quality that results from
polymer addition to the feed sludge. Polymer dosages of the cat Ionic
polymer, Percol 728 ranged from 0,95-5-0 kg/metric ton (1.9-10.0 Ib/ton).
Figure 27 Is a plot of feed rate versus cake concentration and solids re-
covery for Runs No. 1-7 In which no polymer was added. Differential speeds
of 15 and 23 were used with pool radii settings of 101 mm and 103 mm. The
dry-weather primary sludge dewatered to a 16.7 to 26.2 percent cake. Corre-
sponding recoveries ranged from 4l to 53 percent. The poor solids capture
results Indicated that polymer addition would be required to effectively
dewater the South Shore Water Pollution Control Plant dry-weather primary
sludge.
92
-------
TABLE 20. RESULTS OF THE DECANTER CENTRIFUGE TESTS USING
DRY-WEATHER SLUDGE - MILWAUKEE SOUTH SHORE
WATER POLLUTION CONTROL PLANT
Run
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
gal ./min.
27,9
27.9
9.6
9.6
17.9
9.9
9.9
9.9
9-9
17.6
17.6
14,4
15.9
15.4
15.4
15.3
15.3
17.6
17.6
17.6
17.6
Feed
1/raln.
105.6
105.6
36.3
36.3
67.8
37.5
37.5
37.5
37.5
66.6
66.6
54.5
58.3
58.3
58.3
57.9
57.9
66.6
66.6
66.6
66.6
rate
Ib/hr.
744
726
249
245
465
260
255
260
260
436
444
352
304
367
341
339
338
217
498
403
449
kg/hr.
337.8
329.6
113. 0
111,2
211.1
118.0
115.8
118.0
118.0
197.9
201.6
159.8
138.0
166.6
154.8
153.9
153,4
98.5
226.1
183.0
203.8
Cake
concentration
(* TS)
26.2
19.9
17.3
16.9
21.7
20.1
16.7
14.5
15.4
16.0
14.9
16.1
13.2
17.4
17.4
17.0
16.2
17.8
16.3
20.1
16.4
Recovery
(* ss)
41
47
50
52
41
47
53
90
95
66
71
61
98
95
90
82
81
87
96
81
80
93
-------
30
25
H
a* 20
Vt
o
i is
2 10
5
Mft
^
s
s
s
s
s
s
s
s
s
s
s
s
.
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
*l
%
^
•
s
s
s
s
s
s
s
V
1 2 3 ft 5 6 78 9 10 11 12 13 H 15 16 17 18 19 20 21
RUN NO,*
IUU
90
80
V)
V*
69
£ 7°
UJ
>
1 60
ec
50
fto
-
•*
-
-
n
in
s
N
1
s
>
s
s
s
'
s
s
s
s
s
s
s
s
s
s
s
»
s
s
s
s
s
^
s
s
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^
s
s
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s
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s
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•Kh.
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N
I 2 3 4 56 7 8 9 10 II 12 13 1ft 15 16 17 18 19 20 21
RUN NO.*
RUN HO. 1-7, MO POLYMER ADDITION
Figure 26. Bar graph of cake solids and recovery vs. test runs
dry-weather sludge, Milwaukee, Wl.
-------
INOEPEKOENT VARIABLES
_ BOWL SPEED: 2?QO~RPM
POLYMER ADDITION: NOME
60
V)
tn
DC
UJ
e
o
40
20
*• 20
in » 23
R - 101 mm
23 RPM
103 mm
15 RPH
103 mm
FEED RATE, kg/hr (Ib/hr)
100
(220)
+
+
200
300
(660)
400
(880)
15
103 mm
23
103 mm
An - 23
R » 101 mm
Figure 2j. Cake solids and recovery vs. feed rate (kg/hr)
dry-weather sludge, Milwaukee, Wl
95
-------
The graph also shows that at a constant solids loading, as differential
speed Is Increased, solids recovery Increases while cake solids decrease.
At a constant feed rate and differential speed, recovery will increase while
cake concentration decreases If the pool radius Is decreased. This occurs
because liquid level In the centrifuge Is directly related to the poo! radius
setting and cake dryness directly corresponds with the pool depth.
Shown In Figures 28 and 29 are plots of feed rate versus cake solids and
solids recovery for typical runs conducted with polymer. As can be seen In
Figure 28, cake solids concentration ranged from a low of 13.2 percent total
solids to a high of 17.0 percent. Feed rates varied between I18-204' k§/hr
{260-450 lb/hr). The graph also demonstrates a decreasing cake concentration
with Increasing differential speed (An) for the South Shore Water Pollution
Control Plant primary sludge. This Is verified by Isolating on the four
highest solids loading points on the graph. For the differential speeds of
\S, 20 and 25 RPM, polymer dosage for these points are almost Identical at
rates of approximately 2.0 kg/metric ton (4.0 Ib/ton), At a uniform solids
feed rate of 200 kg/hr (440 lb/hr)f cake concentration Increases with
decreasing differential speed. The fourth point at this feed rate Is for
a run of An » 23 rpm. Although this cake Is slightly higher than the
point for An = 20 rpm, It Is reasonable to assume that if additional
testing were conducted, the runs for a differential speed of 23 rpm would
follow the general pattern established. The data also Indicate that cake
solids will be slightly reduced at a lower pool radius setting. Variations
In polymer dosage do not seem to significantly affect the cake concentra-
tions within the range of dosages examined In this plot.
Figure 29 shows the variations In solids recovery obtained at selected feed
rates, differential speeds, and pool radius settings for runs conducted
with polymer addition. Solids recovery varied from a low of 6l percent to
a high of 98 percent. Optimum captures were obtained at differential
speeds of 15 and 23 rpm. For a differential speed of 15 rpm, a pool radius
setting of 101 mm provided slightly better recoveries when compared to the
103 mm pool radius data.
The excellent results obtained at a differential speed of 23 rpm and a 103
mm pool radius setting are due In part to the slightly higher polymerr
dosages that were used when compared to the other differential speed
settings. Polymer addition for a fin - 23 was In the 2.4-3.2 kg/metric ton
(4.8-6.4 Ib/ton) range.
A graph of differential speed (An) versus cake solids and recovery was also
plotted and Is presented in Figure 30. The runs were conducted at a feed
rate of IM-I83 kg/hr (245-403 lb/hr) and a pool radius of 103 mm. The plot
Indicates that variations in differential speed (in) between 10 and 23 rpm
without polymer addition do not significantly affect cake concentrations or
centrate quality. For the runs with polymer, decreases In cake concentra-
tiotrand Increases In solids recovery are observed with increasing
differential speed.
-------
INDEPENDENT VARIABLES
BOWL SPEED: 2700 RPM
25
** 20
o
wo
O
o
,5
l5
10
100
(220)
O An - 25 WITH POLYMER: 1.6 kg/metric ton (3.2 Ib/ton)
X An * 20 WITH POLYMER: 1.6-2/0 kg/metric ton (3.2-4.0 Ib/ton)
A An - 23 WITH POLYMER: 2.4-3.2 kg/metric ton (4.8-6.4 Ib/ton)
• An - 15 WITH POLYMER: 1.7-2.4 kg/metric ton (3.3-4.8 Ib/ton)
ED An - 15 WITH POLYMER: 0.9-K4 kg/metric ton (1.9-2.8 Ib/ton)
125
(275)
150
(330)
175
(385)
200
(440)
225
(495)
FEED RATE, kg/hr
Figure 28- Cake solids vs. feed rate (kg/hr) dry-weather sludge, Milwaukee, WI
-------
INDEPENDENT VARIABLES
BOWL SPEED: 2700 RPM
100
90
SO
w?
w>
*e
RECOVERY,
»-j
o
60
50
40
{
mm
y*V^^_ __ R = 103 mm
Q *~~
"^•^ An - 23 WITH POLYMER: 2.4.-
_\ 3.2 kg/metric ton (4.8-
0 ~\ 6,4 Ib/ton)
"*"-, #
^-X/P^nwj fin „ 15 yjtH POLYMER: 0.9-
N^^^ " •*-. — j^ kg/metric ton
^^^^^ (1.9-2.8 1b/t«i)
^
""'x,
^ ->4* m, ^ " '5 WITH POLYMER: i.
*^ i** kg/metric ton (3.3-^.8
^** -^ ton^
~" ^--0
mmr
^^ An - 25 WITH POLYMER: 1.
^"^-^^ « JQ metric ton (3.2 Ib/ton)
^^^*^-i~f2L %
7-2.4
lb/
6 kg/
x -— . _
An - 20 WITH POLYMER: 1,6-2.0
kg/metric ton (3.2-4.0 lb/
ton)
-
i i I I i
100 125 150 175 200 225
220) (275) (330) (385) (W (495)
FEED RATE, kg/hr (Ib/hr)
Figure 29. Recovery vs. feed rate (kg/hr)
dry-weather sludge, Milwaukee, Wl
98
-------
100
80
cc
LU
LU
CC
o
VI
70
60
50
20
15 -
to
o
o
UJ
/
-C3
INDEPENDENT VARIABLES
cf
BOWL SPEED;
FEED RATE'.
POOL RADIUS:
2700 RPH
111-183 kg/hr (2^5-4031b/hr)
103 mm
©: NO POLYMER ADDITION
0; POLYMER ADDITION 2-3.2 kg/metric ton
Ci-6.4 Ib/ton)
10 15 20 25
DIFFERENTIAL SPEED (An), RPM
10 .
Figure 30,
Cake solids and recovery vs. differential speed (Un)
dry-weather sludge, Milwaukee, Wl.
99
-------
Figure 31 plots polymer dosage against cake solids and so)Ids recovery for
differential speeds of 15 and 23 rpm. Feed rates for these runs were
varied between Ml-226 kg/hr (245-498 Ib/hr). At a An - 15 rpm, cake solids
remained relatively uniform with Increasing polymer dosage. Solids re-
covery increased up to 1.4 kg/metric ton (2.8 Ib/ton)t then decreased
rapidly. At a differential speed of 23 rpm, cake solids decreased with
Increasing polymer dosage, while solids capture Increased.
EFFECT OF CENTRIFUGATION ON HEAVY METALS DISTRIBUTION
Heavy metals samples were obtained from centrifuge feed sludge, the centrate
and skimmings discharge, and the cake solids from the Milwaukee Humboldt
Avenue wet-weather sludge. The samples were obtained from the 30.5 cm (12
In.) basket centrifuge runs of June 8-9, 1976. The results of these heavy
metal determinations are presented In Table 21.
TABLE 21. HEAVY METAL CONCENTRATIONS FOR CENTRIFUGE
TESTS USING MILWAUKEE WET-WEATHER SLUDGE
Concentrations In mg metal/kg solids
Feed
without
polymer
Zinc 3125
Lead
Nickel
Copper
Chromium
Mercury
1563
1563
1719
3281
15.63
with
polymer
1415
943
943
2170
1887
11.32
Centrate
without
polymer
2667
"666?
6667
2000
6667
46.67
with
2632
5263
5263
1579
5263
36.84
Skimmings
without with
polymer polymer
7500
12500
12500
2500
8750
*
4545
4545
4545
2273
7273
31.82
Cake
without
polymer
2186
1694
770
765
3104
1.17
with
polymer
2200
2025
1060
1761
1514
-2.20
* Insufficient sample to conduct analysis (Polymer Dosage: 1.0 kg/metric
ton, 2.0 Ib/ton)
The data are compared for runs conducted with and without polymer. The
table shows that for the most part, slightly higher metal concentrations
were obtained In the cake from the runs In which polymer was used. The
highest metal concentrations In the cake were obtained for zinc, lead, and
chromium.
In addition, for all of the metals tested, centrate metal concentrations
were higher for the samples without polymer. The data appear to Indicate
that polymer is responsible for Increasing metal retention In the cake
while reducing metal concentrations In the centrate,
It should be noted that the dry weight metal concentrations are based on
samples containing very low amounts of solids. Therefore, some variation
100
-------
INDEPENDENT VARIABLES
BOWt SPEED:27700 RPM
POOL RADIUS: 101 and J03 rim
FEED RATE: 111-226 kg/hr (2*5-498 Ib/hr)
100 i-
o
u
UJ
Qt
to
O
0 An = 15 RPM
n => 23 RPM
60
a*
o
_j
o
UJ
20
10
1.0
(2.0)
2.0
(4.0)
3.0
(6.0)
4.0
(8.0)
5.0
(10.0)
POLYHER DOSAGE, kg/metrfc ton Ob/ton}
Figure 31. Cake solids and recovery vs. polymer dosage
dry-weather sludge, Milwaukee, Wl.
101
-------
In metal consistency exists from parameter to parameter tn Table 21. The
trend established by the data, however. Indicates that the heavy metals are
mostly of the same magnitude for the feed, centrate, skimmings, and cake,
and thus appear to be solids related.
The Milwaukee wefweather sludge heavy metal concentrations are quite varia-
ble when compared to a previous sludge sample (I). For comparable samples
with chemical addition, zinc Increased from 799 mg/kg to IMS mg/kg while
lead decreased from 2063 mg/kg to 9^3 mg/kg. Nickel Increased from 159 tng/
kg to 9J»3 rag/kg. Copper and chromium were up from previous values of 201
mg/kg and 2k3 mg/kg to present values of 2170 mg/kg and 1887 mg/kg. Mercury
concentration also Increased, These data Indicate that heavy metal concen-
trations of the Humboldt Avenue CSO sludge are quite variable and cannot be
adequately characterized by analyzing only a small number of samples.
The distribution of these wet-weather sludge heavy metals will play an Im-
portant role In any future CSO pollution abatement studies.
The Milwaukee South Shore dry-weather heavy metal composites were obtained
from the optimum full-scale decanter centrifuge runs of June 3, 1976. The
results of these heavy metal analyses for the primary sludge feed, and the
centrifuge centrate and cake are shown In Table 22. The heavy metal
samples were taken from test runs In which polymer was utilized.
Zinc and chromium had the highest metallic concentration In the cake samples
with values of 3300 mg/kg and 8550 mg/kg being obtained. Suprislngly, the
distribution of lead In the samples Indicated a low cake concentration (528
mg/kg)» with an unexpected high centrate value (1430 mg/kg). These data
would indicate metallic lead did not concentrate In the cake, which was
typically found for the other metals.
The data generated at the two Milwaukee test sites are comparable to the
Kenosha heavy metal data (Tables 10 and II). That Is, the heavy metals
appear to be concentrated In the solids through centrlfugatlon. Also, the
highest metal concentrations observed at both Milwaukee and Kenosha were
for zinc, copper, and chromium, while the lowest metal concentration was for
mercury.
102
-------
TABLE 22. HEAVY METAL CONCENTRATIONS FOR CENTRIFUGE TESTS
USING MILWAUKEE DRY-WEATHER SLUDGE (PRIMARY)
Concentrations In mg metal/kg solids
Zinc
Lead
Nickel
Copper
Chromium
Mercury
Feed
2700
750
kkS
705
7600
0.975
Cent rate
1735
1^30
240
380
1*800
0.365
Cake
3300
528
525
8*»0
8550
1.50
Polymer Dosage: 2.89 kg/metric ton (5.78 Ib/ton)
103
-------
SECT I DM IX
RESULTS OF SLUDGE THICKENING - CENTR1FUGAT1QH
STUDIES CONDUCTED IN RACINE, WISCONSIN
Racine, Wisconsin was the final thickening-dewatering test site utilized
during this study. The test procedure for this third phase of the project
was to conduct thickening-dewatering tests independently on both the dry-
weather sludge and on the CSO generated wet-weather sludge. The dry-weather
sludge was obtained from the Racine Water Pollution Control Plant and con-
sisted of a proportional mixture of primary sludge, thickened digester
supernatant, and thickened waste activated sludge. Dry-weather conditions
were assumed to exist after five days without a CSO event. The primary
plus thickened WAS sludge was used since it most closely resembled the
gravity thickened CSO sludge. Also, if CSO sludge were returned to the
Water Pollution Control Plant, it would be thickened in the primary settling
basins. The wet-weather sludge consisted of a mixture of screening backwash
water and floated sludge from the Olssolved-Air Flotation units which had
been allowed to gravity thicken in a sludge holding tank,
BENCH SCALE GRAVITY THICKENING TESTS
The Racine bench scale gravity thickening tests were performed during the
latter part of August, 1976- Tests were conducted on the dry-weather sludge,
wet-weather sludge, and on an appropriate mixture of the wet-weather/dry-
weather sludges. Dry-weather sludge consisted of a proportional mixture of
waste activated sludge, digester supernatant, and primary wastewater. This
mixture was used since WAS and digester supernatant are returned to the pri-
mary settling tanks for thickening. The wet-weather sludge consisted of
screening backwash water and floated sludge combined proportionally by flow.
Chemical addition was not studied since neither the Water Pollution Control
Plant or the Screening/Dissolved Air Flotation CSO site utilizes chemical in
their gravity thickening processes.
The method used to determine the correct amount of dry-weather and wet-
weather sludge to be used in deriving the wet-weather/dry-weather sludge
combination ratio ?s presented below:
I. Racine CSO area = 284 hectares (702 acres) (I).
2. Assume 50 percent of rainfall results in CSO.
3, Assume 1.27 cm (0.5 in.) of rainfall = 13,036,430 liters
(4,765,250 gal.) of CSO.
4, Screening/dissolved air flotation will produce a sludge volume equal
to 4.8 percent (I).
-------
5- CSO sludge produced « 865,750 liters (228,712 0al.).
6. Assuming a two day bleedback; flow of CSO sludge to the holding
tank » 433 n»3/day (114,366 gpd).
7. Average flow of dry-weather plant = 72,^0? m3/day (19,130,000 gpd).
8. Ratio of CSO sludge/dry-weather flow =» .01/1.
Therefore, for each liter (.26 gal.) of CSO sludge produced, 100 liters
(26.4 gal.) of dry-weather wastewater are generated. The results of the
gravity thickening tests performed on the dry-weather sludge, the wet-weather
sludge, and the wet-weather/dry-weather sludge combination are presented in
Figures 32, 33» and 3^« All of the thickening tests were conducted using
the Coe and Clevenger method of gravity thickening analysis.
The flux concentration curve for the dry-weather slydge (Figure 32) deter-
mined that a thickened sludge concentration of 3-0 percent could be obtained
at a mass loading of 1650 kg/ra2/day (338 Ib/ft2/day). If the solids loadinq
to the thickener were reduced to f!5Q kg/m2/day (236 Ib/ft2/day), the re-
sultant underflow sludge concentration could be Increased to 3.5 percent.
The wet-weather sludge settled very well and showed an excellent amenability
to gravity thickening. The wet-weather flux concentration curve is pre-
sented in Figure 33. Good settling characteristics were also observed for
this CSO sludge in the Phase I Report (I). In the Phase I gravity thickening
tests, an underflow solids concentration of 15 percent was expected at an
extremely high solids rate in excess of 2000 kg/m2/day (^00 Ib/ft2/day). In
this report, underflow sludge concentrations of 14.0 percent were achieved
at mass loadings of 1475 kg/m2/day (302 Ib/ft2/day). The results of the
wet-weather/dry-weather sludge combination thickening tests demonstrated
that a k.O percent thickened sludge would be obtained at a 885 kg/m^/day
(l8l Ib/ft2/day) mass loading. The flux concentration curve Is shown In
Figure 3*». Although the resultant sludge concentration Is slightly higher
than those expected for the dry-weather sludge, the loading is lower.
It was recognized that all of the above mass loadings are appreciably higher
than the typical design loadings suggested for gravity thickeners (14). Be-
cause of this, it is recommended that the above data be used only for compa-
rative purposes and not as actual design criteria.
CENTRIFUGE DEWATERING TESTS
Decanter Centrifuge Results-Ory-Weather Sludge
The Racine dry-weather sludge centrifugal ion tests were conducted between
August 2-9, I97& using a horizontal decanter centrifuge. The sludge used
for the dewaterlng tests consisted of a combination of primary sludge,
thickened digester supernatant, and thickened waste activated sludge. This
sludge mixture was pumped from the bottom of the Racine Water Pollution
Control Plant's primary settling basins Into a tank truck and transported
105
-------
2000 r
*B
T3
CM
*
"D
CM
O
o
1750
(359)
1500
(308)
1250
(250)
• 000
(205)
750
05^)
500
(103)
250
(51)
0
INITIAL SLUDGE CONCENTRATION »
700 mg/1
TANGENTS TO THE FLUX CONCENTRATION
CURVE AT THE SELECTED SLUDGE CONCEN-
TRATION SHOWS THE ALLOWABLE MASS
LOADING RATE FOR GRAVITY THICKENING
10,000 20,000 30,000 40,000 50,000
SLUDGE CONCENTRATION, mg/1
Figure 32. Flux concentration curve for dry-weather sludge, Racine, Wl
106
-------
ra
•a
E
•v.
cn
z
o
_J
(/I
1500
(308)
1250
(250)
INITIAL SLUDGE
CONCENTRATION - 480 ntg/1
150
(51)
TANGENTS TO THE FLUX CONCEN-
TRATION CURVE AT THE
SELECTED SLUDGE CONCENTRA-
TION SHOWS THE ALLOWABLE
IASS LOADING RATE FOR GRAVITY
THICKENfNG
W.OOO 80,000 120,000
SLUDGE CONCENTRATION, mg/1
~T5o
160,000
Figure 33. Flux concentration curve for wet-weather sludge
Racfne, Wi.
107
-------
1000
(205)
750
(154)
INITIAL SLUDGE CONCENTRATION - 690 mg/f
CM
4J
«*.
£ 500
(ro3)
I
CM
CJ
2:
5
s
t/i
CO
s
250
(50
TANGENTS TO THE FLUX CONCENTRA-
TION CURVE AT THE SELECTED
SLUDGE CONCENTRATION SHOWS THE
LLOWABLE MASS LOADING RATE FOR
GRAVITY THICKENING
10,000 10,000 30,000
SLUDGE CONCENTRATION, mg/1
40,000
50,000
Figure 34. Flux concentratfon curve for wBt-w«ath«r/dry"w«ather
sludge comb?nation Racine, WJ.
108
-------
to the mobile centrifuge van, which was located at the Racine wet-weather
site. It became necessary to truck the dry-weather sludge because of the
extensive construction being conducted at the Racine Water Pollution Control
Plant.
In all, a total of 27 decanter centrifuge dewatertng tests were conducted.
Sludge Sn th'e tank truck was continuously recfrculated by means of a high
rate centrifugal pump and fed to the decanter centrifuge. The duration of
each test run was 20-10 minutes, which is more than a sufficient amount of
time required for the centrifuge to reach and maintain equilibrium. Uhen
equilibrium was reached, grab samples were taken of the feed, centrate,
and cake. The samples from each day's test runs were returned to the lab
and analyzed for total and total volatile solids, suspended and volatile
suspended solids (when possible), or dissolved and volatile dissolved solids,
The majority of the tests were conducted with polymer, which was added to
aid the dewatering process. Preliminary lab screening tests indicated that
a cationic polymer, Percol 728, was the most effective. The polymer solu-
tion was prepared in concentrations of 0.1-0.2 percent.
Presented in Table 23 are the dewatering results of the 27 runs. Runs I
and 2 were conducted without polymer addition. Althougn cake concentra-
tions were high for these two runs (3^.8 and 38.1 percent), solids capture
was poor (67.1 and 71-5 percent), indicating the use of polymer would be
required. Thus, runs 3~27 were conducted with polymer. The bar graph In
Figure 35 demonstrates the increased recoveries obtained by adding polymer
to the sludge at dosages ranging from 0.7-3-9 kg/metric ton (1.^-7.9 Ib/ton),
{n several of the runs with polymer, capture rates in excess of 98 percent
were achieved.
Figures 36 and 37 are typical plots of cake solids and recovery versus
sludge feed rate for polymer dosages of 1.0-3.95 kg/metric ton (2.0-7.9
Ib/ton), Differential speeds of 5, 15, 21 and 26 RPH are plotted. As
shown in Figure 36, the sludge dewatered to a 20.0 to 30.8 percent cake.
The highest cake solids with polymer addition were obtained at low feed
rates and low differential speeds. However, the higher differentia? speeds
provided more uniform cakes in an optimum feed range from 200-350 kg
solids/hr (440-J70 Ib solids/hr). The plot also illustrates the effects
of polymer on cake concentration. For example, for the plot of differential
speed equal to 23 RPM, and reading right to left on the graph, cake solids
decrease as polymer dosage increases from 1.6 kg/metric ton (3-2 Ib/ton)
to 1.3 kg/metric ton (3.5 Ib/ton) and finally to 4.0 kg/metric ton (7-9 Ib/
ton). This pattern of decreasing cake concentration with Increasing polymer
dosage is also illustrated for An » 15 RPH, For a differential speed of
5 RPM, cake concentrations remain high at polymer dosages of 1.3 kg/metric
ton (2.6 Ib/ton) and 2.0 kg/metric ton (*j.O Ib/ton), but decreases rapidly
when polymer dosage Is decreased to 1,0 kg/metric ton (2.0 Ib/ton). All
of the above information indicates that independent of feed rate, an
optimum polymer dosage appears to occur between i.3"2.5 kg/metric ton
(2.5-5.0 Ib/ton).
109
-------
TABLE 23. RESULTS OF THE DECAMTER CENTRIFUGE TESTS USING
DRY-WEATHER SLUDGE - RACINE WATER POLLUTfON CONTROL PLANT
Run
No.
1
2
3
4
5
6
7
8
9
10
1!
12
13
14
15
16
17
18
19
20
21
22
23
2k
25
26
27
gal ./ml n
10.1
6.7
20.3
20.8
20.8
20.8
20.8
20.8
19.1
15.2
15.2
15.2
20.3
15.3
12.0
12.5
12.5
6.7
6.7
6.7
6.7
6.7
6.7
6.7
6.7
20.3
19.1
Feed
1/rnin
38.2
25.4
76.8
78.7
78.7
78.7
78.7
78.7
72.3
57.5
57-5
57.5
76.8
57.9
45.4
47.3
47-3
25.4
25.4
25.4
25.4
25.4
25.4
25.4
25.4
76.8
72.3
Rate
Ib/hr
455
466
394
60
46
96
276
536
275
425
455
740
98
988
767
775
866
459
452
459
459
452
459
459
466
183
73
kg/hr
207
212
179
27
21
44
125
243
125
193
207
336
45
449
348
352
393
208
205
208
208
205
208
208
212
83
33
Cake
Concentration
(1 TS)
34.8
38.1
24.1
23.0
20.0
30.0
24.3
26.3
30.8
28.8
27.0
30.8
20.6
29.4
28.5
28.0
28.6
29.0
29.2
25.6
31.6
35.5
35.1
26.2
30.1
20.9
23.3
Recovery
(I SS)
67.1
71.5
72.0
87.4
82.3
89.4
87.1
97.4
86.2
96,3
98.1
99.0
96.1
84.9
92.0
99.5
93-3
99.4
98.7
98.7
83.9
80.6
90.7
99.1
98.3
96.6
92.7
110
-------
20
I
2 3 «i 5 6 7 8 9 10 11 12 13 Ht 15 16 17 18 19 20 21 22 23 24 25 26 27
RUN 1(0.*
JOO
>
o
70
I 2 3 k 5 6 78 9 10 H 12 13 14 15 16 17 18 H 20 21 22 23 2*t 25 26 27
RUN HO.*
* Run No. 1-2, No Polymer Addition
Figure 35. Bar graph of cake solids and recovery vs,
test runs, dry-weather sludge, Racine, WI.
Ill
-------
Irt
to
Q
O
in
UJ
ko r
35
30
25
20
50
(110)
0 in =• 5
An = 15
An » 26
j7]
INDEPENDENTVARIABLES
BOWL SPEED: 2700 RPM
POLYMER DOSAGE; J.0-3.95 kg/metric ton (2.0-7.9 Ib/ton)
POOL RADIUS: 103 mm
too
(220)
150
(330)
200
250
(550)
300
(660)
350
(770)
(880)
450
(990)
FEED RATE, kg/hr (f/hr)
Figure 36. Cake solids vs. feed rate dry-weather sludge, Racine, Wl.
-------
too r
95 _
90
IS)
1 85
§
o
UJ
cc
80
75
A An
Q An
5
15
23
26
\
\
\
1
INDEPENDENT VARIABLES
BOWL SPEED: 2700 RPM
POLYMER DOSAGE: 1-3.95 kg/metric ton
(2-7.9 Ib/ton)
POOL RADIUS: 103 mm
JL
Ju
_L
J_
J.
50
(110)
100
(220)
150
(330)
200
250
(550)
300
(660)
350
(770)
400
(880)
450
(990)
FEED RATE, kg/hr (#/hr)
Figure 37« Recovery vs. feed rate (kg/hr) dry-weather sludge, Racine, V/l.
-------
The plot in Figure 37 shows the effects of varying feed rate, differential
speed, and polymer dosage on solids capture. Recoveries ranged from 32 to
99 percent. The best solids captures were obtained at conditions similar to
those observed for optimum cakes , that is, at high differential speeds of
15, 23 and 26 RPH, and at polymer dosages in the 1.3-2,5 kg/metric ton (2.5-
5.0 Ib/ton) range. Also, the optimum sludge feed rate for maximum solids
recovery was again in the solids range of 200-350 kg/hr (440-770 Ib/hr),
Polymer dosage versus cake concentration and solids recovery is plotted in
Figure 38 for selected runs. Typically, as shown in the plot, the addition
of polymer increases solids capture, while lowering the cake concentration.
Optimum solids recoveries occurred In the 1.3-2.5 kg/metric ton (2.5-5.0
Ib/ton) dosage range at differential speeds of 15 and 26 RPH. Figure 39
plots cake concentration and solids recovery against selected differential
speeds (An) for polymer dosages of I.75 and 2.55 kg/metric ton (3.5 and 5.1
Ib/ton). As can be seen by the graph, optimum cake yields and solids
captures were obtained at the higher differential speeds. Also, the higher
polymer dosage of 2.55 kg/metric ton (5.1 Ib/ton) provided more concentrated
cakes with higher recoveries than the lower polymer dosage.
jtecantej;.CentrI f uge^ Resu 1t s ~ Wet-Weather S1 udge
Wet-weather sludge dewatering was conducted at the Racine screening/dissolved
air flotation site between August 11-18, 1976. A CSO event occurred in
Racme on August 10, 1976. The CSO screening backwash and floated sludge
for the Racine wet-weather site are conveyed to a common holding tank. The
sludge obtained from the CSO event was allowed to gravity thicken overnight
in the sludqe holding tank. On the following day, August II, the supernatant
in the holding tank was decanted off and the thickened sludge was dewatered
using the decanter centrifuge. Although the thickened sludge was very dilute
in nature, the decanter centrifuge was used to provide a comparison of data
with the Racine dry-weather sludge. In all, a total of 12 dewatering runs
was conducted. The individual test run data are detailed In Appendix
Tables C-28 to C-39 with the tabulated results summarized In Table 2k. The
low solids feed rates are due to the diluteness of the thickened sludge.
During the dewatering tests, thickened feed solids varied between a low of
0.05 percent to a maximum of 0.58 percent. Runs No. 1-4 were conducted with-
out polymer. The effect of polymer addition on cake solids and recovery is
illustrated in the bar graph of Figure 40, Concentration of Percol 728
polymer varied from 0,96-3.16 kg/metric ton (I.92-6.31 Ib/ton). Solids
capture generally Improved with the addition of polymer. No significant
decrease In cake solids concentration was observed when polymer was added
to the feed sludge. All sludge was screened through a (.64 cm) (.25 in.)
mesh screen to prevent machine damage.
The plot of cake solids and recovery versus feed rate for the dewatering
runs In which polymer was not used is presented in Figure 41. The cake
solids curve shows relatively uniform concentrations can be maintained at
low loadings to the centrifuge. As expected at this low feed rate,
recovery increases with Increased loading to the machine. Recoveries
-------
INDEPENDENT VARIABLES
BOWL SPEED: 2700 RPM
POOL RADIUS: 103 mm
FEED RATE: 2?~393 kg/hr (60-866 tb/hr)
100
en
in
cc
>
o
l/J
o
o
tfl
9°
80
5
15
23
26
3:
o
o
30
20 L
1.0
(2.0)
2.0
3.0
(6.0)
k.Q
(8.0)
5.0
(10.0)
POLYHER DOSAGE, kg/metrfc ton (Ib/ton)
Figure 38* Cake solids and recovery vs. polymer dosage
(kg/metric ton) dry-weather sludge, Racine, Wl.
115
-------
INDEPENDENT VARIABLES
BOWL SPEED: 2700 RPM
POOL RADIUS: 103 mm
FEED RATE; 205-352 kg/hr (^52-775 lb/hr)
100
90
oe
UJ
o
o
80
10
30
An (RPM)
Q
UJ
O
UJ
30
• 2.55 kg/metric ton (5.1 1b/ton>
0 1.75 kg/metric ton (3-5 Ib/ton)
20
Figure 39« Cake solids and recovery vs. differential speed (in),
rpm dry-weather sludge, Racine, Ul.
116
-------
TABLE 24. RESULTS OF THE DECANTER CENTRIFUGE TESTS USING
WET-WEATHER SLUDGE - RACINE WET-WEATHER SITE NO. 1
Run
No.
1
2
3
4
5
6
7
8
9
10
H
12
gaK/m1n
13.5
12.8
18.0
33.3
12.8
17.2
17.2
17.2
33.3
33-3
12.8
12.8
Feed
_l/jLm
51.1
48.5
68.1
126.0
48.5
65.1
65-1
65.1
126.0
126.0
48.5
48.5
Rate
Ib/hr
16.2
37.1
4.3
15.0
14.7
39.6
16.3
12.0
28.3
12.1
25.0
22.4
kg/hr
7.4
16.3
2.2
6.8
6.7
18.0
7.4
5.5
12.8
5.5
11.4
10.2
Cake
•Concentration
% TS
18.6
25.9
30.8
33-7
30.1
32.1
30.8
23.4
25.5
30.5
26.2
26.4
Recovery
(% SS) *
69.0
63.4
52.4
60.9
91-3
92.4
89.9
89.9
89.8
71.4
92.5
63,0
117
-------
1 2 3 '* 5 6 7 3 9 10 It 12
RUN NO.*
RUN NO. 1-4, NO POLYHER ADDITION
«""•*»
in
K
£5
Q
_l
O
UJ
o
35
30
25
20
15
J 2 3
* RUN NO, 1-lf, MO PQLYHER ADDITION
5 6 7 89 10 11 12
RUN NO.*
Figure 40 * Bar graph of cake sol Ids and recovery vs. test runs
wet-weather sludge, Racine, WI.
118
-------
100
in
80
INDEPENDENT VAR I ABIES
BOWL SPEED: 2,700 RPH
POLYHER DOSAGE: NONE
POOL RADIUS: 103 mm
DIFFERENTIAL SPEED: 15
o
o
tli
oc
60
5.0
10.0
• 5.0
20,0
(I 1.0) (22.0) (33.0)
FEED RATE, kg/hr (Ib/hr)
30
-20 -
10 L
Figure ^1. Cake solids and recovery vs. feed rate
wet-weather sludge, Racine, Wl.
1)9
-------
without polymer varied between 52-69 percent. A similar graph for the eight
runs In which polymer was used fs shown In Figure 42. Three independent
plots for differential speeds of 6, 10 and 15 RPM are shown. As fn the
previous graph, cakes remained uniform with concentrations ranging from
23,4 to 32.1 percent. The highest cakes were obtained at the higher feed
rates and lower differential speeds. Solids recoveries varied from a low
of 63 percent to a high of 92.4 percent. The bulk of the test runs were in
the 90 percent capture range. Increasing feed rate had little or no
effect on recovery. Variations in pofymer dosage between 1.0-3.2 kg/metric
ton (2.0-6.4 Jb/ton) had only minimal effects on cake solids and recovery.
Differential speed versus cake solids and recovery for the runs with polymer
addition has been plotted in Figure 4$. The graph shows a uniform decrease
in cake concentration with increasing differential speed. Optimum cakes
were obtained at a differential speed of 6 RPM. Solids recoveries were good
at An's of 6 and 15 RPM. However, a sharp decrease in centrate quality was
observed at a differential speed of 10 RPM. If additional testing were
conducted, it can be assumed that the recovery at An a 10 RPM would approach
90 percent. Presented in Figure 44 Is the plot of polymer dosage versus
cake solids and solids capture for differential speeds of 6, 10 and 15 RPM.
The graph illustrates the increasing recoveries obtained by the addition of
polymer. Cake concentrations only decreased slightly. Optimum polymer
dosages were in the range of 1.0-3.2 kg/metric ton (2.0-6.4 Ib/ton).
EFFECT OF CENTRIFUGATIQH ON HEAVY METALS DISTRIBUTION
Heavy metal composite samples were obtained from the Racine dry-weather
sludge for the optimum runs of August 9, 1976. The wet-weather metal samples
were composited from the best runs of August II, I9J6. For the Racine
dry- and wet-weather sites, it was decided to analyze for both the total
and soluble metal portions. Cadmfum was also added to the list of analyses
at both sites because of recent discussions with regard to plant uptake of
this metal resulting from land application of municipal sludges. The
results of the Racine dry-weather and wet-weather heavy metal determina-
tions for the decanter centrifuge feed, centrate, and cake samples are
presented in Tables 25 and 26. The metal analyses are reported on a dry
basts of sludge with results shown as milligrams of metal per kilogram of
dry sludge. Soluble metal data are reported in milligrams metal per liter
of wet sludge. For the dry-weather sludge, the highest concentrations of
metal observed were for lead and zinc with cake values of 7350 mg/kg and
2100 mg/kg, respectively, being reported. The lowest metal concentration
observed was for mercury, which had a cake value of 1.507 mg/kg. The
dry-weather sludge data also show that the soluble concentrations of the
heavy metals are very low, with a centrate sample range from 0.02 mg/1
for cadmium and chromium to 0.22 mg/1 for zinc. Polymer was added to the
sludge at a rate of 1.8 kg/metric ton (3-5 Ib/ton),
The wet-weather heavy metal concentrations were typically less than the
dry-weather concentrations for the metals analyzed. However, metal
concentrations of the two sludges were often of the same magnitude. For
the CSO sludge cake, lead and zfnc were the most prevalent trace metals
120
-------
100
INDEPENDENT VARIABLES
BOWL SPEED:2,700 RPM
POLYMER DOSE: 0.96-3.16 kg/metric ton,
(1.92-6.31 Ib/ton)
POOL RADIUS: 103 mm
80
OC
UJ
O
o
yj
oe
er"
An
An
6 RPM
10 RPM
15 RPH
5.0
(II. 0)
10.0
(22.0)
15.0
(33.0)
20.0
FEED RATE, kg/hr (Ib/hr)
30
o
M
UJ
S£
'<
O
20
Hgure *»2. Cake solids and recovery vs. feed rate
wet-weather sludge, Racine, Wl.
121
-------
100
80
a*
u
o
u
70
VJ
- 3C-
o
VJ
2C-
10-
INDEPENPENT VARtABIES
BOWL SPIEDi 2,700 RPH
POLYHER OOSI: 0.96-J.I6 kg/metric ton,
(1.92-6,31 1b/ton)
* FEED RATE: 5.^-18.0 kg/hr
POOL RADIUS; 103 mm
5 10 15 20
DIFFERENTIAL SPEED, (An) RPH
Figure ^3. Cake solids and recovery vs. differential speed
wet-weather sludge, Racine, WI.
122
-------
w>
I/)
LU
ac
=>
Q-
O
to
o
*»
INDEPENDENT VARIABLES
BOWL SPEED: 2,700 RPM
POOL RADIUS: 103 nun
FEED RATE: 5-5-18.0 kg/hr (12. 1-39.6 lb/hr)
100 i-
90
80
70
(-/
/
trt
v%
£ 30
o
IU
25
20 L
•o
/
/
/*
0An
6 RPM
10 RPM
15 RPH
A
1.0
(2.0)
1.5
(3.0)
2.0
(4.0)
2.5
(5-0)
3.0
(6.0)
POLYMER DOSAGE, kg/metric ton (Ib/ton)
A
^J
A
-—. .-a
Figure kk.
Cake solids and recovery vs. polymer dosage
wet-weather sludge, Racine, Wl.
123
-------
TABLE 25. HEAVY METAL CONCENTRATIONS FOR CENTRIFUGE TESTS
USING RACIME DRY-WEATHER SLUDGE
Zinc
Lead
Nickel
Copper
Chromium
Mercury
Cadmium
Polymer
Feed
mg metal/ mg/1
kg sol Ids soluble
1450 0.28
6900 0.34
140 0.1
600 0.07
755 O.J3
4.81*2
47 0.02
dosage: 1.8 kg/metric ton
Centrate
mg metal/ mg/1
kg sol Ids soluble
302 0,22
313 0.1
134 0.1
96 0.03
154 0.02
0,738
9 0.02
(3.5 Ib/ton)
TABLE 26. HEAVY METAL CONCENTRATIONS FOR CENTRIFUGE
USING RACINE WET-WEATHER SLUDGE
Zinc
Lead
Nickel
Copper
Feed
mg metal/ mg/1
kg solids soluble
710 0.08
420 <0.05
490 <0.1
250 0.03
Chromium 110 0.02
Mercury
Cadmium
1.633
50 0.21
Centrate
mg metal/ mg/1
kg sol Ns soluble
247 0.02
205
-------
with reported values of 1850 mg/kg and 6AO rag/kg respectively. Mercury was
the least prevalent with a cake concentration of 0,485 nig/kg. As with the
dry-weather sludge, soluble CSO metal concentrations were low. The span for
centrate was from
-------
SECTION X
RESULTS OF ANAEROBIC DIGESTION STUDIES
Laboratory anaerobic digestion studies were performed to evaluate the short
and long term effects of feeding sludge containing storm-generated solids to
bench scale anaerobic digesters on an intermittent basis under controlled
conditions. The testing, sampling and evaluation procedures used as well as
a description of the laboratory anaerobic digesters employed In the study
have previously been described In Section VI.
The following provides the details of the investigations conducted using
Kenosha and Racine, Wisconsin dry-weather and storm-generated sludges.
RESULTS OBTAINED USING KENOSHA, WISCONSIN ORY-AND WET-WEATHER SLUDGES
Start*Up Debugging gr>(j |n-^ja] Testwork with Dry-Weather Sludges
Kenosha operates their full-scale digesters in the raesophlllc temperature
range using a mixture of primary and thickened waste activated sludge with
a hydraulic detention time of 20 days and an organic loading of 1.1 to \.k
kg volatile solIds/m3/day (0.069 to 0.086 Ib/ft3/day).
Initially, the two laboratory digesters were started up by feeding both di-
gesters with dry-weather primary and waste activated sludges. This start-
up period was preliminary to the actual investigation and was used to debug
and shakedown the laboratory digester equipment, refine operating, sampling
and analytical procedures, ensure that both systems were operating alike (to
establish the normal variations In operating parameters that might result
when feeding the two laboratory digesters alike), and to minimize any effect
of previous storms to the digesting sludge initially obtained from Kenosha.
During the preliminary start-up period which extended for about 60 days,
minimal data were obtained which are presented in Appendix D, Table D-1.
DJgester Operat ion and Loadings wl th Wet-Vfeather j>Judge
When a storm event occurs and the resulting CSO is treated to produce a
waste sludge, the wet-weather sludge is proportioned to the digesters In
addition to the dry-weather sludges. The additional full-scale digester
loadings for various storm simulated CSO solids accumulations were de-
veloped and are presented in Table D-2 in Appendix D for various total
rainfall amounts and for given full-scale digester feed addition times.
This Information was used in determining for a given storm event how the
wet-weather sludge could be proportioned to the full scale digesters In
126
-------
relation to the addition of the dry-weather sludges. Having this Informa-
tion for the full-scale digesters permitted a sound basis for loading the
laboratory digesters.
For example, for this study, the first storm event that occurred simulated
a 1.27 era (0.5 in.) rain event. The quantity of wet~weather sludge produced
by this event was determined from Table D-2, Appendix D, allowing a forty-
eight hour period (two feedings) to proportion the wet-weather sludge into
the digester. The calculations for loading for full-scale digesters under
this condition are presented in Table D-3, Appendix D, and the results
indicated that the total hydraulic loading to the digesters would be in-
creased by WS for the two day period over the normal dry-weather loading.
Therefore, for the laboratory digesters, the amount of sludge fed to the
two digesters for the two day period was Increased by 20% per day over the
normal dry-weather feed, that is, the control laboratory digester received
the Increase In dry-weather sludge whereas the test (or variant) digester
received the Increase In actual CSO sludge.
The laboratory digesters, both control and test (variant), also had a 20
day hydraulic retention time and an organic loading rate within the range
of that for the Kenosha full-scale digesters (see Table 27).
From Table 27f this study was comprised of four periods of investigation
which are described below. The raw data obtained for each period of study
are tabulated In Table 0-^, Appendix R.
In Table 27, the control period (day I to 14) represented that period
during which both digesters were fed only dry-weather primary and waste
activated sludges In the same manner as during the preliminary start-up
period except that more complete analyses and data were obtained during
the control period. Again, the purpose of the control period was to
show that both digesters were operating In a similar manner and to
establish the normal variations In operating parameters that might result
when feeding the two laboratory digesters alike.
The first simulated storm event occurred on day 15 (period $1, Table 27)
and simulated a 1.27 era (0.5 in.) rain event. The effect of this event
upon the feeding of the two laboratory digesters was previously described.
The second simulated/ralnfalI (day 25, period #2, in Table 27) imposed a
potentially more severe shock load to the digesters In that it simulated
a 2.5lt cm (I In.) rain and the entire sludge accumulated was added with
the normal daily loading amounting to an increased loading of 62 percent
over normal, (again both digesters were subjected to the loading shock under
similar conditions as outlined for simulated storm /'I).
During Period //3f an attempt was made to determine if the wet-weather waste
activated sludge used was measurably different from dry-weather waste acti-
vated sludge. During period $3, only waste activated sludge (no primary)
was fed to both digesters.
The volatile solids were monitored in the feed and withdrawn sludge on a
127
-------
TABLE 27, MONITORING PARAMETERS FOR CONTROL AND VARIANT LABORATORY
DIGESTERS (KENOSHA SLUDGES)
ISJ
oo
Period
Day from test start
Digester*
Volatile solids loading
(kg/day/mj)
Gas production (£/day)
standard deviation
Methane production (£/day)
standard deviation
Ratio, CO-: CH,
standard deviation
m gas/kg vol. sol destroyed
Volatile solids
feed sludge, %
digested sludge, %
% reduction **
Average temperature, °C
standard deviation
Storm simulation
rainfall - cm{In.)
Control #1
1 to
C_
1.14
6.3
±0.5
4.2
to. 4
47
±3.1
0.81
60
48
38
33
±1
None
13
W
1.14
6,2
±0.5
4.2
±0.3
47
±4.1
0.81
60
49
36
38
±1
14 to
C
1.14
7.6
±1.1
5.2
±0.7
46
±2.4
1.03
60
49
36
29
±1
1.27
24
W
1.14
7.4
±1.1
5.1
±0.8
45
±1.6
1.00
•60
49
36
37
±1
(0.5)
$2
25 to
C
1.11
8.6
±1.1
5.8
±0.6
49
±3-8
1.05
61
48
41
32
±1
2.54
32
W
1.09
9.1
±0.9
6.2
±0.5
46
±2.9
1.23
60
48
38
37
±1
CD
-
33
C_
0.98
5.8
±0.8
4.0
±0.5
41
±2.8
0.72
63
48
46
32
±1
13
to 43
W
0.97
5.2
±0.8
3.6
±0.5
40
±3.6
0.83
,
60
49 ,
36
37 :
±2
<••_
Note: In all tests performed, volumetric retention time *» 20 days.
* C *= control or dry-weather digester; W * test (variant) or wefweather digester.
** Calculate4 as per Reference (8).
-------
daily basis and were used as a measure of organic loading. The volatile
solids data in Table 27 indicate very little change was detected in the
organic content of the feed or in the subsequent reduction of volatile
solids until the third period (waste activated sludge feed only) during
which time the control showed a lOt increase in the reduction of volatile
solids compared to the digester being fed the storm generated waste acti-
vated sludge. This apparent improvement in digester performance may be
attributed to the fact that the volatile solids fraction of the dry-
weather waste activated sludqe was 3% higher than the wet-weather digester
feed (8). The total solids were about 0.71 lower for period #3 than for
the entire preceding time (3.1 vs. 3.8%), The actual loading in kg vola-
tile solIds/m3/day dropped from I.I to 0.98 for the control digester from
period #2 to period 13- A similar decline in organic loading was ob-
served In the digester receiving wet-weather waste activated sludge.
pHt Volatile Acjjds and Alkannjty of DtgesjEer^ Sludge
A plot of the difference in digester sludge pH (control digester minus test
digester) is presented in Figure 45a. The line xc represents the average
Difference for the control period. The two horizontal lines above and below
xc represent the limits of the range fn which 95S of the individual differ-
ence values may be expected to occur. These upper and lower range lines are
based on the standard deviation (±1.96 times standard deviation) of the
differences measured during the control period. During the 43 days of
operation the pH exceeded the confidence interval of the control period
seven times. The actual pH for both digesters was in the range of 7«3 to
7.7. The pH tended to be slightly more basic fn the control digester as
Indicated by the fact that the plot crossed the upper confidence interval
5 times. The pH exceeded the Imposed confidence interval 3 times during the
actual feeding of wet-weather/dry-weather sludges; once on day 25 (after the
simulated 1 inch rain with 2k hr. bleed-In) and twice during the feeding of
wasted activated sludge only In period 13» The other four times the pH
difference fell outside the interval both digesters were receiving the same
feed. The paired t-statlstic for each period (used to interpret long term
effects) indicated the pH was statistically equal during the entire kj day
run (952 confidence level, see Table 28).
The raw data In Table D-4, Appendix 0 show very little change in digester
alkalinity for the periods investigated, which averaged 4,000 mg/1 as CaC03.
The same observation can be made for volatile acids which were typically
between NO and 210 mg/l as acetic acfd. This range occurs on the lower end
of the useful range of the analytical procedure and must be considered as
much method induced as digester Induced.
SasM Production
Table 27 summarized the gas production parameters typically monitored or
suggested as sensitive indicators of digester performance for each of the
four periods. These Include total gas production (dry gas at standard
temperature and pressure) in I/day, rate of methane production In t/day,
129
-------
K
Control
«- #1
12
•H-1— #3
-H
Control'
12
Figure 45a and 45b. Effect of wet-weather sludge on anaerobic
digestion - Kenosha study (control digester minus test
digester pH and total gas production values).
130
-------
ratio of methane to cafbon dioxide, and an efficiency parameter of volume
of gas produced per unit weight of volatile solids destroyed (m3/kg).
Both the average total gas production and the efficiency of conversion
of volatile solids to gas tended to increase through day 32. The
plot of differences tn Figure k$b for total gas production shows the
increase was consistent for both digesters and could not be related to
wet-weather sludge effects as measured by the paired t-test (see Table 28}
except for period #3« There were no apparent short terra effects of storm
generated sludge on total gas production during this phase of the study.
The total gas production exceeded the 95X confidence interval only twice
and both times were during Identical loadings.
During period #3» when the digesters were fed waste activated sludge only,
all the monitored gas production parameters were at a lower level. The
control digester, however, produced significantly more total gas and me-
thane than the test digester (see Table 28 and Figures *»5b and ^6b). The
greater gas production observed for the control digester is probably due to
the higher reduction in volatile solids during this period (8).
There was no apparent significant difference in the carbon dioxide to
methane ratio between the two digesters for the periods investigated
that could be related to the addition of wet-weather sludge (see Figure
and Table 28).
TABLE 28. T-STAT1STIC TEST RESULTS (KENOSHA STUDY)
(51 SIGNIFICANCE LEVEL)
Gas
Parameter
production (I/day)
Methane production (I/day)
Rat
PH
lo: CO-/CH^
Control
period
C " W(ll)*
C - W(ll)
C • W(M)
C - W(ll)
Period
1!
C •
C •
C •
C «
> W{10)
>w{9)
- W(9)
• W<8)
Period
#2
C «
C •
C «
C •
» W(73
» W(7)
• W(7)
• W<3)
Period
#3
C
C
C
C
* w(9)
* W(8)
- W(7)
» w(5)
Notes
* Numbers In parentheses are degrees of freedom
C = Control or dry-weather digester
W - Test (variant) or wet-weather digester
Heavy Metals
Total heavy metal (mercury, lead, zinc, nickel, copper, chromium, iron
131
-------
DAY
CONTROL
II
-H-*
#3
CONTROL
**
#3.
Figure 46a and k6b. Effect of wet-weather sludge on anaerobic
digestion - Kenosha study (control digester minus test
digester CH^ and C02/CH^ values).
132
-------
and cadmium) analyses were performed six times during this investigation
on wet-and dry-weather digester feed sludges and on digester sludges from
both control and test digesters. The raw metals data obtained are pre-
sented in Table 0-5, Appendix 0 and are reported on both a wet weight and
dry weight basis. The metal analyses of the digester feed samples are in
agreement with those previously obtained from Kenosha dry-weather WAS and
CSO waste sludges and reported in Tables 10 and II.
Soluble heavy metal (lead, zinc, nickel, copper, iron and cadmium) analy-
ses were also performed, near the beginning and end of the investigation,
for both digester feed and digester sludge samples for the two laboratory
digesters. The raw data obtained are presented In Table D-6, Appendix 0.
The data show that the soluble concentrations of the heavy metals are
very low, ranging from
-------
v»
o
CONTROL
,--&—A- VARIANT
1 I
i 1
BACKGROUND
PERIOD
1 1
1 1
PERIOD
11
1 1 1 I
PERIOD
12
— 1 ' '
i 1
PERIOD
#3
} \
0 5 tO 15 20 25 30 35 *0 4!
Figure kj* Total gas production of control and variant digesters.
-------
quantitatively by a comparison of the standard deviations of these periods,
excluding the days of actual increased loading (\bt 15, 25) (the standard
deviations listed in Table 27 include values from the days of increased
loading). During the background period the standard deviation of total gas
production for both digesters was ±0.5 I/day, from day 16 to day 2*»
(period #1), the standard deviation was ±0.68 for the control and ±0.25 for
the test digester. The total gas production during the days following the
second and most severe simulated stom event (days 26-32, period ff2) had
standard deviations of ±0.82 for the control -and +0.8B for the test digester.
This high variance was apparently induced by the overloading shock alone and
could not be attributed to storm generated solids; the t-test for period #2
indicated gas production to be statistically equivalent (see Table
This is not to suggest that the storm generated waste activated sludge was
In all ways identical to the dry-weather waste activated sludge from the
Kenosha waste treatment plant. The result of the t-test on both total gas
produced and rate of methane produced during the period of waste activated
sludge loading (period #3) indicated the dry-weather sludge produced
statistically higher quantities of gas (averaging 0.6 I/day total gas, Q,*f
I/day methane), yielded a k&r4 reduction of volatile solids versus 36? for
the storm generated sludge, and contained 3% higher total volatile sol Ids
(Table 27). These data are consistent with previous combined sewage sludges
studied in the laboratory (l) which were generally lower In total volatile
solids than their dry-weather counterparts.
The role of metals Jn digester stability and their distribution in 33 U.S.
waste treatment plants was studied by Salotto e t. aj . , (13) » where the metals
were found to have a log normal distribution. The results of their study
are compared with the geometric means of the total metals concentration of
the raw and digested sludge in this study and Is summarized in Table 29-
The raw Kenosha sludge (digester feed) was higher than the data cited (13)
in zinc, copper, chromium and cadmium (whether dry-weather or storm) how-
ever, it was r.iuch lower In lead and mercury. In terms of percent! le grouping
for digester sludge, the control and the test digester sludges were equal
for all metals except copper where the control was in the 75th percent! le
and the test digester was in the 90th percent! le (2,100 mg/kg vs. 2,500
m9/kg) and chromium (control = 1090 mg/kg, test =• 1,200). The digester
sludge contained lower concentrations of mercury and lead than the geometric
mean of the 33 plants studied (13). These data indicate that the accumu-
lation of heavy metals as potentially toxic substances did not occur
either in the control or the storm feed digester.
RESULTS OBTAINED USING RACIHE, WISCONSIN - WET-UEATHER SLUDGE
An additional digestion study was performed using storm generated sludge
from the Racine, Wisconsin CSO treatment facility. It was felt that this
sludge, produced by physical /chemical treatment of combined sewer overflow,
might have a greater effect on digestion than the Kenosha CSO sludge.
Because of limited resources available for this extra digestion study, the
monitoring parameters were limited to total gas production, pH, volatile
35
-------
UJ
ON
TABLE 29. DISTRIBUTION OF HEAVY METALS IN KENOSHA SLUDGE
Geometric Means (mg metal/kg dry solids)
Digester feed sludqe
Metal
Mercury
Lead
Zinc
Nickel
Copper
Chromium
Iron
Cadm i urn
Cd/Zn Rat
Mercury
Lead
Zinc
Nickel
Copper
Chromium
Iron
Cadmium
Control Wet-weather EPA data(l4)
1.5
501
3,260
340
1,700
830
73,300
34
fo 1.04%
(Percent of plants
2.8
429
3,330
290
I »830
960
79,000
43
1.29%
Per cent I
studied by
8.2
1,150
1,740
420
740
940
—
27
1.55%
le Grouping Based on
EPA having similar
Digested sludge
Control Wet-weather EPA data(tj)
2.3
557
4,100
450
2,100
1,090
82,100
43
1.05%
EPA Data*
or lower metal
25%
50%
75*
75*
751
501
_
751
2.8
569
4,240
460
2,500
1,200
83,800
46
1,08%
concentrations)
251
50%
75%
75%
901
75%
-
75%
6.5
2,210
2,900
530
1,270
1,050
—
43
1,48%
50%
90%
751
751
75%
501
-
751
Reference 13
-------
solids, volatile acids, and some heavy metals concentrations and a few
alkalinity measurements.
Start-Upt jebugging and In itiaj Test Work wjthDry-Weather S1 udges
Because of construction work at the Racine sewage plant, the digesters were
overloaded and performing poorly during the period of the laboratory digester
work. Nevertheless, an attempt was made to start the laboratory digesters
using digested sludge and maintain the digesters with Racine dry-weather
sludge. After a 10 day period of operation, the gas volume produced remained
at a very 1
-------
TABLE 30. MONITORING PARAMETERS FOR CONTROL AND
VARIANT LABORATORY DIGESTERS (RACINE WET-WEATHER SLUDGE)
CO
Wet- weather
Control period feed
Day from test start
Digester*
Volatile solids loading
(kg/day/nr)
Gas production (I/day)
average
Std deviation
m gas/kg vol. sol. destroyed
Volatile solids
feed sludge, %
digested sludge, %
average
Std deviation
Average temperature, C
Std deviation
Storm simulation
rainfall - cm (In.)
Hydraulic retention tlme(days)
Volumetric loading, I/m /day
1
C_
1.39
8.7
0.6
0.88
64.6
57.2
0.79
32
0.7
20
50
to 21 22
w_ _c _w
1.39 1.77 K73
8.6 9-6 9.8
0.5
0.91
64.6 64.6 57-6
59.0 56.7 57.6
0.87
35 34 36
0.7
None 2.54(1)
20 17.4 17.5
50 63.7 57.3
Period
following
wet- weather feed
23
C
^fttmmmmmm
1.39
9.0
1.1
1.02
64.6
56.1
1.66
32
'0.8
20
50
to 28 -
_W
1.39
8.3
1.0
1.05
64.6
57.3
0.35
35
0.2
None
20
50
* C = control or dry-weather digester; W - variant or wet-weather digester
-------
duction varied from 7«7 I/day to 9,5 I/day. The difference tn dally gas
production for- the-two-digesters averaged -0*-!- I /day with* the control digester
producing the most gas on 12 of the 20 days measured. The paired comparison
t-test (15) showed that the difference fn daily gas production between the
two digesters could not be considered significant at the 35% confidence level.
The ratio of the volume of gas produced to the weight of volatile solids
destroyed for this period was similar for both digesters.
On the day of the simulated wet-weather feeding to the variant digester, the
gas production increased for both digesters and remained high for four days.
On the fifth day, however, the gas production from both digesters was marked-
ly lower. The average difference in daily gas production between the two
digesters after the simulated wet-weather feeding (including the data from
the day of the wet-weather feeding) was 0.5 I/day, The control digester
produced less gas on the day of the feeding but produced an average of 0.6
I/day more gas each of the days following the feeding. The paired compari-
son t-test showed that this difference in gas production was significant at
the 95% confidence level but could not be considered significant at the 99?
confidence level. The ratio of gas produced to volatile solids destroyed
was similar for both digesters and slrghtly higher than for the control
period.
pH, Vo 1 at_l 1 e So 1 ids , Volati I eAc ids and A1ka1i n it y of the D?gester S1 udgja
The pH value for both digesters remained stable through the entire test
period. The pH of the sludges removed from the two digesters were within
0.1 unit each day. The pfl values for both digesters were generally between
7.2 and 7.3»
The digesting sludge in the control digester consistently had a lower vola-
tile solids concentration during the control period. The difference between
the sludges was significant at the 95% confidence level using the paired
t-test. After the simulated wet-weather feeding, the control digester
sludge continued to have a lower volatile solids concentration on 5 of the 6
days measured. Although the reason for the difference In volatile solids
concentrations in the two digesting sludges is not known, it may be related
to the difference in temperature between the two digesters.
The volatile acid concentrations measured during these tests did not exceed
5^0 nig/1 during the control period. After the simulated wet-weather feeding,
the maximum volatile acid concentration measured was kkO mg/1 and the
volatile acid/alkalinity ratio was O.I?, well below the 0.3 to Q.*i ratio
where the digester might be considered to be under stress (3).
Heavy Hetals
Sludge removed from the digesters the week before the simulated wet-weather
feeding was used to form composite samples for each digester. Heavy metals
analyses (lead, zinc, nickel, copper, chromium, iron and cadmium) were per*
formed on these composite samples, on the sludcje added to each digester
during the simulated wet-weather feeding, and digester sludge six days after
139
-------
the wet-weather feeding. The results of these analyses are listed fn Table
31 in terms of weight of metal per weight of dry solids along with the geo-
metric mean value for metals found by the EPA in 33 digested sludges (13).
(Hetal concentrations In terms of both wet and dry weights are listed In
Appendix D-3, Table D-9). With the exception of lead, the simulated wet-
weather feed sludge contained lower concentrations of metals than the dry-
weather feed sludge (dry weight basis). The digested sludges (except lead)
from both digesters before and after the simulated wet-weather feeding all
contained similar concentrations of all heavy metals. In both digesters,
the lead concentration decreased after the simulated wet-weather feeding.
The digester sludge lead concentrations were well below the geometric mean
value reported by the EPA (13). Z5ncf nickel, and cadmium concentrations,'
however, were at least 150S greater than EPA raean values. The concentration
of chromium was about 10 times higher than the EPA mean value, A review of
the South Shore digester records from April to September \9J6 show that the
concentrations of metals in the laboratory digesting sludge were not unusual
for this sludge. In spite of the hlgh« chrorhtum concentration, the South
Shore digesters were operating satisfactorily during this period.
140
-------
TABLE 31. CONCENTRATION OF HEAVY METALS IN FEED, AND DIGESTER SLUDGES USING RACINE CSO
SLUDGE FOR SIMULATED WET-WEATHER FEED. (CONCENTRATIONS IN MG METAL/KG DRY SOLIDS)
Sludge
Feed s 1 udges :
Dry- weather
Simulated wet- weather
Digester sludges:
Control digester, before
wet-weather feeding
Control digester after wet"
weather feeding
Wet-weather digester before
wet-weather feeding
Wet-weather digester after
wet-weather feeding
Geometric mean of EPA data*
Percent of plants studied
by EPA having similar or
lower values*
Lead
411
488
521
456
544
437
2210
25
Zinc
4560
3090
—
4360
4740
4830
2900
75
Nickel
690
508
903
980
912
909
530
90
Copper
1090
894
1320
1380
1440
1364
1270
75
Chromium
9840
6970
12400
12000
12600
12300
1050
>95
1 ron
30500
23400
36100
35100
34000
33800
-
Cadmium
64
32
52
51
60
70
43
75
See Reference 13
-------
SECTION XI
DESIGN CRITERIA AND ECONOMIC CONSIDERATIONS
It is Important to note that It Is difficult to make generalizations regard-
ing the design criteria and economics associated with the thickening and
centrifuge dewatering of CSO treatment residues. This section presents de-
tailed criteria and economic evaluations for the specific individual sites in-
vestigated. The Information presented may be used as guidelines and as
first approximation of costs for applications which are similar to those
investigated. However, If closer approximations are desired, then the
specific site in question should be separately evaluated with respect to lo-
cale, rainfall patterns, type and location of CSO treatment systems, sludge
volumes generated and their characteristics, etc.
#
Design criteria for the individual sites investigated were obtained from the
discussions }n Section IV of this report and from the associated Appendix
data.
In providing cost estimates, equipment costs were obtained from manufacturer's
estimates. Other costs, such as operation, maintenance, power and amortiza-
tion were determined on a similar basis for all of the sites Investigated.
As much as possible, published cost data were utilized (16) after adjusting
them to reflect June 1976 prices (17)• Wherever similar unit processes
were applied at different test sites, the same cost estimating structure
was used. The discussion which follows, therefore, deals specifically, and
in relatively great detail, with the design criteria used, design calcula-
tions, capital, operating, maintenance, power and amortization costs and the
land requirements for the CSO sites investigated.
KENOSHA, Wl
Dry-Weather SJu_dge_
Kenosha dry-weather sludge consists of primary sludge and flotation thick-
ened WAS. Currently, this sludge is anaerobically digested. If the sludge
were to be dewatered as an alternative to digestion, the process schematic
shown on the next page is suggested.
As shown in the schematic, the two sludges would be blended tn a holding
tank and pumped to the basket centrifuges for dewatering. The cake could be
stabilized and landfilled, while the centrate would be returned to treat-
ment.
\k2
-------
PR f MARY SLUDGE
15MOO a/day (40,000 gpd)
«*-n SOLIDS
FLOAT-THICKENED WAS
227,100 it/day (60,000 gpd)
@ 3-4£ SOLIDS
HOLDING TANK
W/BLENDJNG
BASKET
CENTRIFUGATJQH
TO
17.5*
SOLIDS
CENTRATE
RETURN
Presented below are the basic dewatering design criteria:
1. Total daily sludge flow - 378,500 a/day (100,000 gpd) at =
5.0$ solids
378.500 Jl/day x 50,000 mg/1 x kg/106 mg - 18,925 kg/day (41,635 lb/
day) of sludge to process.
2. From Section IV, Table 3, 144 kg/hr (317 Ib/hr) of dry-weather
solids can be processed.
3, Determine number of centrifuges required with 25% standby:
Check hydraulic flow:
For a 5»0 percent feed, 113.6 i/min (30 gpm) per machine should not
be exceeded.
378,500 a/day
6 mach\nes x 1,440
43.8 fc/mln
Therefore six 121.9 x 76.2 cm (48" x 30") basket centrifuges would be re-
quired to process the dry-weather sludge. Two standby units are also recom-
mended. The total annual cost for this system would be $2f9,Q00/year as
summarized in Table 32. All of the data generated in Table 32 are based
on the assumptions listed in Table 33-
Wet-Weather Sludge
The Kenosha wet-weather sludge generated from a 1.27 cm (0.5 in.) rainfall
Is 598 m /day (158,112 gpd) at 0.83 percent solids, assuming a sludge bleed/
pump-back of 2 days. The thJckening-dewaterlng schematic ?s shown In
Figure 48. The biologically treated CSO sludge would be pumped to a flota-
143
-------
TABLE 32. KENOSHA, Wl - SUMMARY OF
COST AND SPACE REQUIREMENTS
DRY-WEATHER SLUO 5E
Equipment
cost requirements
Capital costs
!. Sludge pumping to thickener
2. Flotation thicNener
3, Sludge pumping to centrifuge
it. Centrifuge
Total capital cost
Annual Q&M Costs
1. Operation
pump to thickener
flotation thickener
pump to centrifuge
centrifuge
Subtotal
2. Maintenance
pump to thickener
flotation thickener
pump to cent r 1 f uge
centrl Fuge
Subtotal
3. Electricity
pump to thickener
flotation thickener
pump to centrifuge
centri f uge
Subtotal
Total annual 0£# cost
Total annual cost3'
(: 6S, 20 yr., zero salvage
and 15* contingency)
Land requirements
Cost/unlt(3)
13,925 kg/day
based on landl mg
(41,635 Ib/day)
of dry solids
S
4i.
5
S
S
~
S
"$"
S
$
153 r?
-
-
340,000
730,000
120,000
-
-
9,100
Si MO
ST,6W
-
-
4,000
8,600
"T2,£00
-
-
500
12, .400
"T7.40Q
33,600
219,900/yr
(1700 ft2)
WET- WEATHER SLUDGE
Cost/unit(S) based on handling
4967 kg/day (10,937 ibAlay)
of dry solids
$180,000
170,000
180,000
W0,000
$950,000
S 1,600
2,000
1,600
—iilfifi.
$ w, loo
S 700
500
700
goo
J" 2,900
5 130
1,500 -
100
900
I" 2,~5b~o
$ 16,300
Sllft.OOO/yr
20*.* m2 (2200 ft2)
WET- WEATHER/DRV- WFATHER SLOOSE
Cost/unlt($) based on handling
23,392 kg/day
(52,562 Ib/day)
of dry sol ids
$
S2,
S
S
S
5
S
$
$
S
390 m2
400,000
470,000
liOO.OOO
920,000
190,000
1,600
2,000
10,000
63,600
77,720
700
600
4,300
10,000
15, £00"
100
1,500
600
14,500
16,700
109,500
345,500/yr
(4200 ft2)
Total annual cost •" [total capfta! cost +0,15 total cap, cost] x amor, factor (,08718) {61, 20 yr)
+ [total annual 06H cost +0.15 total ann. OtM cost]
The 15& contingency was added to Include land cost and national cost variations
-------
TABLE 33. ECONOMIC EVALUATION ASSUMPTIONS
GENERAL ASSUMPTIONS
1. All costs are based on 1976 prices.
2. The derived costs are a function of dry solids handling. Thus, Individual
costs per piece of equipment may vary from site to site.
3. The costs generated are for equipment only and are exclusive of required
valvlng, holding tanks, flow distribution equipment, etc.
k. Costing Information was obtained from Reference No. 16 snd updated
to 1976 dollars using a multiplier of 1.42 as listed In Reference fk>. 17
5. Land requirements have been estimated for tne placement of equipment
only. Land allocations include 9.29 sq m (100 sq ft) per pump, 9.29
sq m (100 sq ft) per chemical feed system, 18.59 sq m (200 sq ft) per
centrifuge and a thickener and degrStting surface area based on twice
the required treatment area.
6. Assume polymer costs of $3.96/kg ($1.80/1b).
ASSUMPTIONS RELATED TO CSO GENERATED
1. Assume a 2-day bleed/pump-back of CSO sludge to the system.
2. Assume the waste volumes generated to be from a 1.27 cm (0.5 in.) rain-
fall over the entire CSO area.
3. Assume 50 CSO events/year. Assuming this and a 2-day bleed/pump-faack
of CSO sludge, equipment operation is estimated at TOO days/year.
4. The costs generated are Independent of any costs required to expand
the existing liquid handling facilities to treat the entire CSO area.
145
-------
a*
590 m3/day
(158,112 gpd} 9 0.33?
SOLIDS
FLOTATION THICKEN
SOLIDS
124,037 Jl/day
32,734 gpd
f
RETURN
BASKET
GENTR1FUGATIQN
TO 14.
SOLIDS
Assuming a 2-day bieed/pump-back of CSO to the treatment site)
Figure 48. TMckenlng-dewaterfng schematic Kenosha CSO sludge.
-------
tlon thickener where the solids would be concentrated to 4.0 percent, re-
sulting In a sludge reduction to 124,037 i/day (32,784 gpd). The thickened
sludge would then be dewatered to approximately 14,0 percent solids using
basket centrifuges.
The design criteria are shown below.
1. Total daily sludge flow » 598 m3/day (158,112 gpd) § 0.83% solids
598,454 i/day x 8,300 mg/I x kg/10fa rag = 4,967 kg/day (10,937 lb/
day) of sludge to process,
2. Determine area of thickening required:
From Section VII, a CSO sludge concentration of 4.0 percent can be
obtained at a mass loading of 53.8 kg/m2/day (11 Ib/ft2/day). There-
fore, required area for thickening would be:
rOCe" • 9" "2 093-5 ft2)
3. Check thickener hydraulic flow:
Underflow rate = 598,454 &/day - 6,484 £/m*/day (159 gal./ft2/day)
92.3 m*
4. From Section IV, Table 3, the processing rate to the basket centri-
fuges would be 103 kg/hr (227 lb/hr).
5. Determine number of centrifuges required with 251 standby:
4,967 kg/day ofsludge to process „ . . standbv
103 kg/hr x 24 l unlts ' standbV
6. Check hydraulic flow:
For a 4.0 percent feed, 113.6 Jl/rain. (30 gpra) per machine should not
be exceeded.
124,08? it/day /,,./•
•z -TT~i y-'-i-i vy = 43-1 £/mm.
2 machines x 1,440
Therefore, 3 - 121.9 x 76.2 cm (48" x 30") basket centrifuges are required.
Two machines would be on-line during wet-weather with one additional unit
acting as a standby.
be
The wet-weather system annual costs as summarized in Table 32 would
$1l4,000/year.
Wet-Weather/Dry-tfea ther Sludge CombI nation
In this process train, CSO sludge generated from a 1.27 cm (0»5 '"•) rainfall
and flotation thickened to 4.0 percent solids would be blended In a holding
tank with dry-weather primary and thickened WAS. The expected flow to the
147
-------
dewatering equipment would be 502,600 £/day (132,800 gpd) assuming a two-day
bleedback of CSO sludge. The expected sludge concentration would be 4.0 per-
cent. The schematic flow diagram is presented In Figure 49,
Shown below are dewaterlng design criteria:
1. Total dally sludge flow » 502,600 A/day (132,300 gpd) § * 4.7% solids
502,600 A/day x 47,500 mg/1 x kg/106 rag = 23,892 kg/day (52,562 lb/
day) of sludge to process,
2. From Section IV, Table 3, 99 kg/hr (218 Ib/hr) of wet-weather/dry-
weather sludge can be processed assuming no polymer addition.
3- The required area for thickening as discussed In the wet-weather
sludge design criteria would be 92.3 m (993«5 ft }.
4. Determine number of centrifuges required with 251 standby:
23,892 kg/day to process ,rt .„ . , , ..
' 99 kg/hr x A " 10 unlts * 3 standby
5. Check hydraulic flow:
For a 4.7 percent feed, 113.6 £/m!n. (30 gpm) per machine should
not be exceeded.
502,600 a/day w .. g . .
10 machines x 1,440 **'9 i/mrif
Thus, to process the wet-weather/dry-weather sludge, 13 basket centrifuges
121.9 K 76.2 cm (48" x 30") would be required. Three of the units would
act as standby machines. The total annual cost for this system is $345,500
as presented in Table 32.
MILWAUKEE, Wl
Dry-Weather Sludge
Milwaukee South Shore dry-weather primary sludge is currently generated at
an average rate of 868,658 £/day (229,500 gpd) at 5.7 percent solids. This
sludge Is presently fed directly to the anaerobic digesters for stabiliza-
tion. One alternative to this would be direct dewatering of the primary
sludge by centrifugatlon using a decanter-type centrifuge. The schematic
diagram illustrating this process is shown on the following page.
Based on the dewatering data presented in Section VIII, 15-20 percent haula-
ble cakes can consistently be produced. The dewatering design criteria
would be as follows:
1. Total dally sludge flow « 868,658 £/day (229,500 gpd) @ 5.7% solids
148
-------
CSO SLUDGE
593 m3/day
(153,112 §pd)
FLOTATION
THICKENED
TO k.0%
SOLIDS
RETURN J
12M87
(32,704 gpd)
*l.0% SOLIDS
HOLDING TANK
W/BLENDING
DRY-WEATHER PRIMARY SLU )GE
151,400 A/day (40,000 gpd}
b.Q - 7.0* SOLIDS
DRY-WEATHER THICKENED WAS
BASKET
502.600 £/day,feEHTR|FU6ATION
(132,800 gpd)
* k.7% SOLIDS
RETURN
CENTRATE
227,100 £/day (60,000 gpd)
3-k% SOLIDS
Figure k$. Solids dewaterlng schematic
Kenosha wet-weather/dry-weather sludge combination.
-------
POLYMER
PRIMARY SLUDGE •/7\JL DECANTER
868,658 */day (229,500 gpd) @ 5-71 V-/ | CENTRIFUGATION
SOLIDS
1
CAKE
863,658 £/day x 57,000 rag/1 x kg/106 rag - 49,51 * kg/day (108,930
Ib/day) of sludge to process.
2. From Section IV, optimal conditions were obtained at feed rates of
118-203 kg/hr (260-450 Ib/hr) for a 35.56 cm diameter x 86.36 cm
long rotor (14" x 34") decanter centrifuge. This is equivalent to
a throughput of 394-682 kg/hr (867-t500 Ib/hr) for a 50.8 cm diameter
x 199.4 cm long rotor (20" x 73.5") decanter centrifuge.
3. Determine number of centrifuges required with 25% standby:
' ' un,ts + 2 standby
4. Check hydraulic flow rate:
At optimal feed rates, flows of 37.9-68 i/mln (10-18 gpm) were
maintained. This is equivalent to a not-to-exceed flow rate of
190-340 fc/mln (50-90 gpm) for the 50.8 x 199-4 cm (20" x 78.5")
decanter centrifuge.
868,658 a/day . (2fi }
6 machines x I, 440
5. Estimate polymer requirements:
For the optimal conditions discussed in Section IV, polymer dosages
of 0.88-1.24 kg/metric ton (1.76-2.48 Jfa/ton) would be required.
x 0.88 kg polymer/metric ton -
a K /
n>
1000 kg/metric ton
43.57 kg (95.85 1b) polymer/day required.
Therefore, six 50.8 x 199,4 cm (20" x 78,5") decanter centrifuges would be
required. Two additional units would be available for standby. Polymer
requirements for this system would be 43-57 kg/day (95.85 Ib/day). It
should be noted that this design is based on sizing the units at the lower
optimal dry solids dewatering rate, and therefore stresses optimum solids
recovery. If optimum cake solids are limiting, the design should be based
150
-------
on the higher optimum feed rate values shown.
The total annual cost as shown in Table 3*» Is estimated at $483,*tOO/year.
AH of the data generated In Table 3** are subject to the assumptions Us ted
previously In Table 33«
Wet-Weather _S_1 udge
The Milwaukee wet-weather sludge gravity settles to 0.015-0.1*1 percent
solids without chemical addition as discussed in Section VIII. Since this
sludge concentration Is too dilute for economical full-scale dewatering,
the addition of chemical would be required. This step combined with gravity
settling would Increase solids to approximately 1.74 percent as reported
In Phase I (l). Based on the results discussed in Section IV, it Is antici-
pated that this sludge could then be dewatered to a 10 percent cake. An
allowance for grit removal would also have to be included. One possible
method of degrltting would be the application of a swirl concentrator in
lieu of conventional equipment. The concentrator would precede the dewater-
ing step to degrlt the settled sludge. Since this process has had only
limited exposure, its actual application would require an fn-depth prelimi-
nary study. The proposed wet-weather sludge process schematic is presented
in Figure 50.
The Milwaukee wet-weather criteria for design are discussed below:
1. Determine size of grit chamber required (assume conventional design)
Des I gn Pa rameters
Grft removal size = 65 mesh (.24 mm) (.01 in.)
V = settling velocity to remove grit on a No. 65 mesh =» 112.8 cm/
min (3-7 fpm) (13)
Depth/width ° 0/W = I
Vj. * flow through velocity = 30.5 era/sec (1.0 fps)
Q - 1,860,523 Vday * 1,362 m3/day (0.492 mgd)
2 , _. ,,.
'76 ft
Q » Avf «
2
D = Q/V,;
f
DWf
= 1,862
30.5 <
ro /day
:m/sec )
x 1
c 86
00 on/m
,400
D - .2? m (.89 ft)
Assume a Safety Factor = 2, then
D = 0.5^ m (1.78 ft); Say 0.61 m (2.0 ft)
W - .27 m (.89 ft); Say 0.31 m (1.0 ft)
151
-------
TABLE 34. MILWAUKEE, Wl - SUMMARY OF
COST AND SPACE REQUIREHENTS
DRY-WEATHER SLUDGE
Equipment cost
requirements
cost/unit(S) basod on handling
49,514 kg/day W.5 ton/day)
of dry sol Ids
Capital costs
1 . Sludge pumping
2, Sedimentation
3. Chemical feed
4, Centrifuge
5. Degrfttfng
Total capital cost
Annual OEM costs
T. Operation
pumping
sedimentation
chemical feed
centrifuge
degrlttlng
Subtotal
2. Maintenance
pumping
sad I men tat I on
chemical feed
centrifuge
degrlttlng
Subtotal
3, Electricity
pumping
sedimentation
chemJcal feed
centrifuge
degrlttlng
Subtotal
4, Chemical
Total annual 0$H cost
S
1
SI
5
S
$
r
S
T
$
$
540,000
60,000
.349,000
,903,000
13,200
6,000C
118,100
137,300
5,700
c
19,500
25,200
1.300
c
32,000
33,300
63,000
258,000
WET-WEATHER SLUDGE
cost/unit (5) based on handling
33,373 kg/day (35-6 ton/day)
of dry sol Ids
$
I
SI
S
T
$
r
S
5~
1
S
426,000,
732,700"
573,000
,051,000
33,000
,915,700
3,100
6,600
67,300C
22,400
700
no, *w
1,400
3,700
c
3,700
500
9,300
200
300
c
5,700
100
u,5oo
203,400
319,100
Total annual cost '
(3 68, 20yr, zero salvage
and 15% contingency)
Land requirements
$ 488,400/yr
283 sq m (3100 ft2}
S 659,300/yr
573 s
-------
CHEMICAL
RAW CSO
43l,64r,000 Si
OH,039,000 gal.)
0 0.015% SOLIDS
i
v/i
EXISTING
SEDIMENTATION
FACILITY
EFFLUENT TO RECEIVING STREAM
1,360,523 a/day (491,552 gpd) @ 1./4* SOLIDS
GRIT
REMOVAL
T
HO-
T
GRIT TO
LANDFILL, ETC,
POLYMER
BASKET
CENTRIFUGE
TO 10*
SOLIDS
CENTRATE RETURN
CAKE TO LANDFILL,
LAND APPLICATION,
ETC.
Figure 50. Dewataring schematic Milwaukee CSO sludge.
-------
Determine L;
D/V - 0.61 m x 100 cm/m g, .
112.8 cm/ratn
0.54 mln x 30.5 cm/sec x 0.6 «= 9.9 m (32.5 ft)
Assume a 0.3lm (1 ft) free board, then:
Use 1 chamber: D = 0.92 m (3.0 ft)
W » 0.31 m (1.0 ft)
L - 9.9 m (32.5 ft)
2. Total daily sludge flow- 1.860,523 A/day (491,552 gpd) § 1.
solids.
1,860,523 Vday x 17,400 mg/1 x kg/106 mg = 32,373 kg/day (71,221
Ib/day) of sludge to process.
3. For sizing purposes, assume an average dewaterlng feed rate of 94.6
liters/rain (25 gpm).
94.6 £/min x 60 mln x 17»400 mg/1 x kg/10 mg = 98.8 kg/hr
hr
(217 Ib/hr) of process sludge.
4. Determine number of centrifuges required with 25% standby:
5. Verify hydraulic flow:
For a 1.8% sludge, 151.4 £/min (40 gpm) should be exceeded
1.860 523 1/dav . „
machines x 1,440
6. Estimate polymer requirements:
From Section VIII, a polymer dosage of 1.05 kg/metric ton (2,1 1b/
ton) was required.
32,373 kg sludge/day 1.05 kgpolymer ., . m « ,,}
1,000 kg/metric ton metric ton ** m UHf° ID'
polymer/day required.
The design criteria indicate that eighteen 121.9 x 76.2 (48" x 30") basket
centrifuges are required to dewater the wet-weather sludge generated by a
1,27 cm (0.5 in.) rainfall over the entire Milwaukee CSO area. Four of
154
-------
these centrifuges would act as standby units. Polymer requirements are
estimated at 3k kg/day (74.8 Ib/day).
The expected cost to operate this wet-weather facility is $659,300/yr as
Identified in Table 3k and derived according to the assumptions of Table 33-
RACINE, VI
Sludge
The dry-weather sludge produced at the Racine Water Pollution Control Plant
consists of primary plus waste activated sludge. The WAS is returned to the
primary settling basins for thickening. The combined sludges are then
anaerobical ly digested. As discussed in Section IX, the undigested sludge
mixture was dewatered using a decanter centrifuge. During 1976, the Racine
Water Pollution Control Plant pumped an average of 405,000 £/day (107,000
gpd) of sludge at a concentration of 8.9 percent solids.
The alternative process flow diagram utilizing centrifuge dewatering is
shown below:
POLYMER
PRIMARY S THICKENED WAS
405,000 A/day (107,000 gpd) I 5.7?
(~^\ f fc, DECANTER j.
V-X CENTRIFUGATION^./
CENTRATE
SOLIDS
I
CAKE
-Design criteria-for the centrifuge dewatering of Racine dry-weather sludge
are shown below;
I. Total sludge flow - 405,000 A/day (107,000 gpd) @ 8.91 solids.
405,000 A/day x 39,000 mg/l x kg/106 mg » 36,045 kg/day (79,300 lb/
day) of sludge to process.
2. From Section IV, optimal dewatering conditions were maintained at a
feed rate of 336 kg/hr (740 Ib/hr). These results were obtained
using the 35.56 x 86.36 cm (14" x 34") decanter centrifuge. If the
155
-------
larger 50.3 x 199.4 cm (20" x 78.5") decanter centrifuges were
utilized, the equivalent throughput would be 1,120 kg/hr (2,424
Ib/hr) of dry solids.
3. Determine number of centrifuges required assuming 251 standby:
36,045 kg/day
1,120 kg/hr x 24
2 units + 1 standby.
4. Check hydraulic flow rate:
For optimal dewaterlng, a flow rate of 57.5 H/mln (15-2 gpm) was
maintained. An equivalent flow rate for the 50«8 * 199-4 cm
(20" x 78.5") decanter centrifuge Is 287.5 £/min (76 gpm).
5. Estimate polymer requirements:
As discussed In Section IV, polymer dosages of 1.2 kg/metric ton
(2.4 Ib/ton) would be required for optimal conditions.
(95-2 Ib) polymer/day required.
Thus, to dewater the Racine dry-weather primary plus thickened WAS, three
decanter centrifuges - 50. 8 x 199.4 cm (20" x 78.5") are required. One of
these units would be standby. The polymer requirements for the system
would be 43.25 kg (95.2 Ib) per day. The costs generated in Table 35 for
this system are estimated at an annual cost of $4o8,900/yr assuming the
criteria developed in Table 33 apply.
Wet-Weather^ S 1 [udge
The Racine wet-weather sludge produced from a 1.27 cm (0.5 in.) rain over
the CSO area is 433,000 Vday (114,400 gpd) for a two day bleedback. The
average solids concentration is 0.84 percent. A proposed thicken Ing/de-
water ing process train is shown In Figure 51. The treatment scheme includes
grit removal of the screening backwash water prior to its Introduction into
the sludge holding tank. The physical -chemical sludge resulting from
treatment can be gravity thickened to an estimated 14.0 percent solids as
shown in the bench scale thickening results of Section IX. This would result
in a thickened sludge volume of 51,945 liters 03,724 gal.) to be dewatered
over two days. It is expected that the dewatered cake would be approximately
32 percent dry solids, which makes it very acceptable for hauling.
The design criteria are discussed below.
156
-------
TABLE 35. RACINE, Wl - SUMMARY OF
COST AND SPACE REQUIREMENTS
Equipment cost
rcqul rements
Capital costs
! . Sludge pump trig
2. Thickening
3, Chemical feed
k. Centrifuge
5. Degrltttng
Total capital cost
Annual Q&ll costs
1. Operation
pumping
thickening
chemical feed
centrifuge
degrlttlng
Subtotal
2. Maintenance
pumping
thickening
chemical feed
centrifuge
degrletfng
Subtotal
3. Electricity
pump 1 ng
thickening
chemical feed
centrifuge
degrl ttlng
Subtotal
4. Chemical
Total annual 0SH cost
DRY-WEATHER SLUDGE
cost/un1t($) based on handling
36,045 kg/day (39-7 ton/day)
of dry solids
$ 469,000
-
30,000
1,136,000
-
$j, '635,000
$ 11,800
-
3,000a
30,300
-
5 105,700
$ 5,200
-
a
15,000
-
$ 20,200
$ 1,000
-
a
25,600
-
t 26,600
$ 60,600
$ 213,100
WET-WEATHER SLUDGE
cost/unlt($) based on handling
3,637 kg/day (4.0 ton/day)
of dry sol Ids
$ 40,000
60,000
10,000
125.000
71_,_QQQ.
S 306, 000
$ 1,400
600
1 ,000a
4,700
joo
$"~8',7oD'
$ 600
500
a
800
300
$ 2,200
? 50
SO
s
800
100
5 JToob
S 5,100
S 16,400
Total annual cost * c
(@ &%, 20 yr, zero salvage and
contingency)
Land requlremonts
15*
$408,gOO/yr
93 sq m (1000 ftZ3
S 49,SOO/yr
135 sq m (1,450 ft2)
Annual cost assumed to be 10% of capital expenditure
Tbta! annual cost « [tot. cap, cost +0.15 tot. cap. cost] x amor, factor (0.08718)
{6*. 20 yr} + [tot, ann. OSH cost + 0,15 tot. ann. OSM cost]
The 15t-contingency was added to Include land cost and national cost variations
157
-------
CO
RAW CSO
18,036,430 £ I
(4,765,239 gpd)
@ 0.034% SOLIDS
*
EXISTING CSO
TREATMENT
13
^ UJ 0 UJ z
L ^ uj _ i ce, h- e> Q
Ik y o — < s> j
o S
-------
1. Total dally sludge flow » 433,000 A/day (114,40"Q gpd) at 0.84%
solids. 433,000 £/day x 3,400 mg/1 x kg/106 mg - 3,637 kg/day
(8,002 Ib/day) of sludge to process
2. Determine area of thickening required;
The mass loadings obtained In Section IX appear excessive and will
not be used. For typical gravity thickener design, a mass loading
of 122 kg/m2/day (25 1b/ft2/day) is suggested (18). Then, the re-
required area for thickening would be:
3.637 kg/day of sludge to process „ 8 ffl2 ( 2)
122 kg/mvday
3- Check thickener hydraulic flow: 2 2
Overflow rate = 433,000 £/day » 14,530 A/m /day (356 gal./ft /day)
29.8 m2
4. Determine size of grit chamber required (Assume conventional design)
Design Parameters
Grit removal size =» 65 mesh (.24 mm) (.01 tn.)
V » settling velocity to remove grit on a No. 65
5 mesh - 112.8 cm/min (3-7 gpm) (18)
Depth/width = D/W = 0.25
V- = flow through velocity = 30.5 cm/sec (1.0 fps)
0, « 180,400 A/day = 130 m3/day (0.48 mgd)
0. -= AVf = DWVf - D'4D-Vf
4D2 - Q/V. - 180 m3/day x 100 cm/m = 0.007 m2 (0.076 ft2)
T 30.5 cm/sec x 86,400
D - 0.04 m (0.14 ft)
Assume Safety Factor = 2» then
0-0.1 m (0.3 ft)
W « 0.2 m (0.7 ft)
Determine L:
W/V » 0.2 m x 100 cm/m - „ , ,. -.
s — =* 0.2 mtn Flow Time
112.3 cm/min
159
-------
0.2 rain x 30.5 cm/sec x 0.6 = 3-7 m (12 ft)
Assume a 0.31 m (1 ft) free board, then:
Use 1 chamber: L =* 3.7 m (12 ft)
D » 0.41 m (\.k ft)
W « 0.2 m (0.7 ft)
5. From Section IV, Table 4, the processing rate to the decanter centri-
fuge was 18.0 kg/hr (39«6 Ib/hr). The reason for the low loading
rate was due to the dlluteness of the sludge. With proper gravity
thickening, the expected sludge feed rate Is estimated at 250 kg/hr/
machine (550 Ih/hr/machine) using the 35.56 x 86.36 cm (Ik1* x 3V1)
decanter centrifuge.
6. Determine number of centrifuges required:
3.637 kg/day of sludge to process = , . ,
250 kg/hr x 2k ' umt '
7. Check hydraulic flow:
For a 35.56 x 86.36 cm (14" x 34") decanter centrifuge, flows of
90.8 £-/min (24 gpm) should not be exceeded,
25,980 fc/day -184/1 (47 )
ne^x' | -£2i'n - / n ^ . / gpm;
8. Estimate polymer requirements:
From Section IV, Table 4, an estimated polymer dosage of 0.96 kg/
metric ton (1.92 Ib/ton) wfll be required.
3»637 kg sludge/day n n/. , , , . . .
1000 kg/met"iI ton7 x °'96 ks l»ly«r/i«tnc ton
3 3-5 kg (7.7 lb) polymer/day required.
In conclusion, the Racine wet-weather sludge can be dewatered using one
35.56 x 86.36 cm (IV1 x 34") decanter centrifuge. One additional centri-
fuge Is recommended as a backup unit. Polymer requirements to aid the de-
waterrng process are estimated at 3-5 kg (7.7 ?b) per day of operation. As
shown In Table 35i the total annual cost for this system would be $49,500/
year using the assumptions developed in Table 33.
160
-------
SECTION XM
REFERENCES
1. Gupta, M, K., et.a 1., "Handling and Disposal of Sludges Arising From
Combined Sewer Overflow Treatment - Phase 1", EPA Contract No. 68-03-
0242, Program Element IBB034, U.S. EPA Report No. EPA-600/2~77-G53a,
NTIS-PB 270 212
2. "Standard Methods for the Examination of Water and Wastewater", Hth
Edition, APHA-AWWA-WPCF, Washington, D.C., (1975).
3. Burd, R. S., "A Study of Sludge Handling and Disposal", USEPA Report No.
EPA-17070-05/68, NTIS-PB 179 5H, (May, 1968).
k. Personal communication with Gerald Jordan, Rexnord Research arid
Development, Milwaukee, Wl, (June, 1976).
5. Lager, J. A,, and Smith, W. G., "Urban Stormwater Management and Tech-
nology: An Assessment", USEPA Report No. EPA-670/2-74-040, NTIS-PB 2kO
687, (September, 1974).
6. "Methods for Chemical Analysts of Water and Wastes", U.S. EPA Report No.
EPA-625/6-74-003, Environmental Protection Agency, Cincinnati, Ohio
(1974).
7. "Analytical Methods for Atomic Absorption Spectrophotometry", Parkin-
Elmer Corporation, Norwalk, Connecticut, (1971).
3. "Anaerobic Sludge Digestion - MOP16", WPCF, Washington, D.C., (1968).
9. "Recommended Standards for Sewage Works", Health Education Seminars,
Albany, N.Y., (1971).
10. McNair, H. M. and Bonelll, E. S., "Basic Gas Chromatography", Consoli-
dated Printers, Berkeley, California, (1968).
11. Li, J. C. R., "Statistical Inference, Vol. 1", Edward Bros., Inc., Ann
Arbor, Michigan, (1969).
12. Graef, S. and Andrews, J. F., "Stability and Control of Anaerobic Di-
gestion", Journal ofthe Water Pollution ControlFederation, Vol. 46,
(April, 1974T' '
161
-------
13. Salotto, B.V., et. al., "Elemental Analysis of Wastewater Sludges from
33 Wastewater Plants11, Paper presented at EPA Research Symposium on
Pretreatment and Ultimate Disposal of Wastewater Solids, New Brunswick,
N.J., (May 21-23, 1974).
14. HcCarty, P.L., "Sludge Concentration - Needs, Accomplishments, and
Future Goals", JWPCF, 38:4, p. 503 (April, 1966).
15- Bowker, Albert H. and Lieberman, Gerald J., Engineering Stati s t ics,
Prentice-Hall, Inc., Englewood Cliffs, NJ, 1960, p. 175-178.
16. Metcalf S Eddy, "An Analysis of Construction Cost Experience for
Wastewater Treatment Plants", U.S. EPA Report No. 430/9-76-002,
NTtS-RB-257-455, (February, 19?6).
1?. U.S. Environmental Protection Agency, Office of Water Program
Operations, Municipal Construction Division, Sewage Management,
Disposal and Utilization, Miami, FL (December 14-16, 1976).
!8. Metcalf & Eddy, inc., "Wastewater Engineer", McGraw-Hfll, Inc.,
New York, NY, page 436 (1972).
162
-------
SECTION XIII
APPENDICES
APPENDIX A - KENOSHA, WISCONSIN CENTRIFUGE TEST DATA
TABLE A-l. 30.5 CM (t2 IN.) CENTRIFUGE BASKET TESTS - RUN NO. 1
Centrifuge Basket Used - 30.5 cm (12 in.)
Run No. 1
Date: August 7, 1975
Sludge Tested: Flotation-Thickened Dry-Weather WAS
PROCEDURE
Sludge was fed to the 30.5 on (12 In.) basket centrifuge (producing 1300 G's
at the basket wall) at a constant rate of 2.43 l/mln. (0.64 gpm) until an
abrupt decrease In the centrate quality was observed. A feed sample was
taken for analyses prior to centrtfugatlon and subsequent centrate samples
were taken during centrlfugatlon. A skimmings sample and two cake samples
were taken at the end of the run for total solids analysis. The reported
cake value is the average of the two samples. No polymer was utilized.
RESULTS
Time
Feed
Centrate
Centrate
Skimmings
Cakes
for 7.
8 5 ml
§ 6.5
--
5 min.
n.
min.
Vol
liters
18
-
-
0.
5.
.2
-
-
50
18
ume
gal.
4.8
—
—
0.
1.
13
37
mg/1
or 1
3
1,540
2
2
10
(11.98
SS
TS
.861
mg/1
.501
.651
.601
S 9.22)
Solids
Recovery
96
35
-
.0
• 7
-
ill
NOTES
1. Dissolved solids were approximately 475 rag/I-
2. Cake collapsed from the wall of the basket.
3. Volume reduction was 3-51 ^feed volume/cake volume)
163
-------
TABLE A-2. 30.5 CM (12 IN.) CENTRIFUGE BASKET, TESTS - .RUN No. 2
Centrifuge Basket Used - 30.5 cm (12 In.)
Run Ho, 2
Date: August 7, 1975
Sludge Tested: Flota11 on-ThIckened Dry-Meather WAS
PROCEDURE
Same as for Run No. 1, except sludge was fed at a constant rate of 1.14 1/mln
(0.30 gpm). No polymer was utilized.
RESULTS
Feed
Centrate
Centrate
Centrate
Skimmings
Cake
Time
for 11.5 min.
§ 7 min.
@ 10 min.
P 10,5 mtn.
—
Vo 1 ume
1 iters qal .
13.1 3-5
—
—
—
0.16 0.04
5.52 1.46
mg/1 SS
or % TS
3.84%
1 ,245 mg/1
1 ,385 mg/1
2.321
4.13*
11,461
(12. 97*9.96)
Solids
Recovery (%)
__
96.7
96.3
40.2
—
NOTES
1. Dissolved so)Ids were approximately 570 mg/1.
2. Cake fell from upper half of basket.
3. Volume reduction was 2.37.
164
-------
TABLE A-3. 30.5 CK (12 IN.) CENTRIFUGE BASKET TESTS - RUN NO. 3
Centrifuge Basket Used - 30.5 cm (12 In.)
Run No. 3
Date: August 7, 1975
Sludge Tested: FJotation-Thickened Dry-Weather WAS
PROCEDURE
Same as for Run No, I, except sludge was fed at a constant rate of 0.73 1/mIn
(0.19 gpm). No polymer was utilized.
RESULTS
Feed
Centrate
Centrate
Centrate
Centrate
Skimmings
Cake
TJme
for 20.2 mln.
I 10 mln.
1 13 mln.
@ 16 mln.
@ 19.5 mln.
—
Vo I ume
liters gal.
14.7 3.9
-_
—
—
—
0.23 0.06
5.45 1.44
mg/1 SS
or 1 TS
3.721
I ,393 mg/I
1,384 mg/1
1,363 mg/1
1.61%
4.741
11.361
(12.79 £ 9.93)
Solids
Recovery (1)
..
96.2
96.2
96.3
57.5
—
NOTES
1. Dissolved solids were approximately 505 mg/l
2. Cake fell from upper third of basket
3. Volume reduction was 2.70
165
-------
TABLE A-4, 30.5 CM (t2 IN.) CENTRIFUGE BASKET TESTS - RUN NO. 4
Centrifuge Basket Used - 30.5 cm (12 fn.)
Run No. 4
Date: August 8, 1975
Sludge Tested: Mixture.of Dry-Weather Flotation-Thickened WASand Dry-
Weather Primary SIudge
PROCEDURE
Mixture was 37.85 1 (10 gal.) of primary sludge mixed with 52.99 1 (14 gal.)
of thickened WAS. Procedure was then the same as for Run No. 1, except sludge
was fed at a constant rate of 1.70 1/min, (0.45 gpnt). No polymer was
utilized.
RESULTS
Vo ! ume
Feed
Cent rate
Cent rate
Skimmings
Cake
Time
for 8.0 mln.
@ 5 min.
8 7 rain.
—
liters
13.6
M> •»
_-
0.70
4.98
gal.
3.6
—
--
0.18
1.32
nig/1 SS
or * TS
4. 17%
2,250 mg/1
6,425 mg/1
2.861
14.091
(17.08 S 12
Solids
Recovery (%)
94,4
84.1
—
.81)
NOTES
1. Dissolved solids were approximately 1,194 mg/1
2. Cake fell from uppei* two-thirds of basket
3. Volume reduction was 2,73
166
-------
TABLE A-5. 30.5 CM (12 IN.) CENTRIFUGE BASKET TESTS - RUN NO. 5
Centrifuge Basket Used - 30.5 cm (12 In.)
Run No. 5
Date: August 8» 1976
Sludge Tested: Mixture of Dry-Weather, F1ota_t_io_n.-Thlckened WAS and
0 ry-Weather PrIroary Sludge
PROCEDURE
Mixture was 37-85 I (10 gal.) of primary sludge mixed with 52.99 (14 gal.)
of thickened WAS. Procedure and then the same as for Run No. 1, except
sludge was fed at a constant rate of 0.95 1/mln. (0.25 9pm)• No polymer
was ut!11 zed.
RESULTS
Feed
Cent rate
Cent rate
Cent rate
Cent rate
Skimmings
Cake
Time
for 18.0 m\n.
§ 8 mln.
§ 11 rain.
§ 14 rain.
@ !7 win.
—
Volume
liters gal.
17.1 4.5
—
—
—
—
0.30 0.08
5.38 1.42
mg/1 SS
or % TS
k.23%
2,210 mg/1
2,325 mg/1
3,000 rng/1
11,275 rag/I
k.2d%
13.441
(14.07 6 12.81)
Solids
Recovery (%)
94.6
94.3
92.7
72.6
—
NOTES
1. Dissolved solids were approximately I,166 mg/1
2. Cake fell from upper half of basket
3. Volume reduction was 3-18
167
-------
TABLE A-6. 30,5 CM (12 IN.) CENTRIFUGE BASKET TESTS - RUN NO. 6
Centrifuge Basket Used - 30.5 on (12 In.)
Run No. 6
Date: August 8, 19?5
Sludge Tested; MIxture of Dry-Weather, F1ota11on-Th\ckened WAS
and Dry-Weathei* Primary Sludge
PROCEDURE
Mixture was 37.85 I (10 gal.) of primary sludge mixed with 52.99 1 (14 gal.)
of thickened WAS. Procedure was then the same as for Run No. 1, except
sludge was fed at a constant rate of 0.55 1/ratn. (0.15 gpm). No polymer was
utilized.
RESULTS
Feed
Centrate
Cent rate
Centrate
Centrate
Centrate
Skimmings
Cake
Time
for 33.0 min.
§ 14 min.
§ 18 mln.
@ 22 mln.
@ 26 mtn.
§ 30 mfn.
m<**
Vol
liters
18.2
--
-_
—
--
—
0.20
5-46
ume
gal.
4.8
—
—
—
—
—
0.06
1.44
mg/1 SS
or % TS
4.051
1 ,425 mg/1
1,294 mg/1
1,435 mg/1
1,850 mg/1
2,475 mg/1
6.28*
14.461
(15.48 & 13.
Solids
Recovery (1)
96.3
96.7
96.3
95.2
93.6
—
45)
NOTES
1. Dissolved solids were approximately 1,562 mg/1
2. Cake fell from upper third of basket
3. Volume reduction was 3-33
168
-------
TABLE A-7. 30.5 CM (12 IN.) CENTRIFUGE BASKET TESTS - RUN NO. J
Centrifuge Basket Used - 30.5 cm (12 In.)
Run No. 7
Date: August 12, 1975
Sludge Tested; Flotation-Thickened, Dry^Weather WAS with. Polymer
PROCEDURE
Same as for Run No. I, except sludge was fed at a constant rate of 1.27 1/mtn,
(0.3^ gpm). A 0.051 solution of Percol 728 (a high molecular weight catlonlc
polymer) was fed at 1.15 g/kg (2.31 Ib/ton) (116.1 ml/mJn.) (.03 gpm).
RESULTS
Volume
Feed
Cent rate
Centrate
Skimmings
Cake
Time
for 10.0 mln.
§ 6 mln.
§ 9 mln.
—
~
Hters
12.7
—
._
0.06
5.62
gaK.
3.4
—
~
0.02
1.48
rag/I SS
or % TS
3.35%
436 mg/1
1.16*
3.871
9.70*
(9-74 s 9.67)
Sol ids
Recovery (%)
_-
98.9
71.7
—
„
NOTES
I. Dissolved solids were approximately 604 mg/1
2. Cake only slumped slightly at the top
3. Volume reduction was 2.26
169
-------
TABLE A-8. 30.5 CM (12 IN.) CENTRIFUGE BASKET TESTS - RUN NO. 8
Centrifuge Basket Unit - 30.5 cm (12 In.)
Run No. 8
Date: August 12, 1975
Sludge Tested: Flotation-Thickened,Dry-WeatherWAS withPolymer
PROCEDURE
Same as for Run No. 1, except sludge was fed at a constant rate of 1.26 1/min,
(0.33 gpm) • A 0.11 solution of Percol 728 (a high molecular weight catlonlc
polymer) was fed at 2.29 g/kg (4,57 Ib/ton) (116,1 ml mfn.)(.03 gpm).
RESULTS
Feed
Centrate
Cent rate
Centrate
Skimmings
Cake
Time
for 10.5 mln.
@ 6 mln.
@ 8 mln.
@ 10 m!n.
—
Volume
liters gal.
13.2 3.5
—
—
—
0.06 0.02
5.62 1,48
mg/1 SS
or 1 TS
4.031
303 mg/1
233 mg/1
2.101
2.78%
10.221
(10.61 & 9.82)
Solids
Recovery (1)
99.2
99.4
48.7
—
NOTES
1. Dissolved solids were approximately 682 mg/1
2. Cake slumped only slightly at the top
3. Volume reduction was 2.35
170
-------
TABLE A-9. 30.5 CM (12 IN.) CENTRIFUGE BASKET TESTS - RUN NO. 9
Centrifuge Basket Used - 30.5 cm (12 In.)
Run No. 9
Date: August 12, 1975
Sludge Tested: Flotation-Thickened, Dry-Weather MAS with Polymer
PROCEDURE
Same as for Run No. 1, except sludge was fed at a constant rate of 1.20 1/min.
(0.32 gpm). A Q.\% solution of Percol 728 (a high molecular weight cationic
polymer) was fed at 3.83 g/kg (7.66 lb/ton} (191.1 ml/mln.) (0,5 gpm).
RESULTS
Feed
Centrate
Cent rate
Centrate
Skimmings
Cake
Time
for 1 1 .5 mln.
@ 6 mln.
§ 8 mln.
@ 11 mln.
__
Volume mg/1 SS
liters gal. or 1 TS
13.8 3.6 k.16%
184 mg/1
172 mg/1
19,950 mg/1
00
5.68 J.50 $.3k%
(10.37 & 9.
Solids
Recovery (I)
—
99.6
99.6
51.3
—
52)
NOTES
1. Dissolved solids were approximately 593 mg/1
2. Cake stood firmly
3. Volume reduction was 2.43
171
-------
TABLE A-10. 30.5 CM (12 IN.) CENTRIFUGE BASKET TESTS - RUN NO, 10
Centrifuge Basket Used - 30.5 cm (12 In.)
Run No. 10
Date: August 12» 1975
Sludge Tested; F!QtatIon"ThIckenedt Dry-Weather WAS with Polymer
PROCEDURE
Same as for Run No. I, except sludge was fed at a constant rate of 0.72 l/mln.
(0.19 gpm). A 0.051 solution of Percol 728 (a high molecular weight cationlc
polymer) was fed at 0.93 S/kg 0-87 Ib/ton) (55.4 ml/mln.) (.015 gpm).
RESULTS
Feed
Centrate
Centrate
Centrate
Centrate
Skimmings
Cake
Time
for 19.0 mln.
§ 9 win.
@ 12 mln.
@ 15 mln.
§ 18 mtn.
—
Volume
1 1 ters gal.
13.7 3.6
—
—
«k **
-------
TABLE A-11. 30.5 CM (12 IN.) CENTRIFUGE BASKET TESTS - RUN NO. U
Centrifuge Basket Used - 30-5 cm (12 In.)
Run No. 11
Date: August 13, 1975
Sludge Tested: Hjxture of Dry-Weather,__Flotatlon^T_h_icke_ned__WA_S_an_d
Dry-Weather Primary SJ_udge With Polymer
PROCEDURE
Mixture was 37.85 1 (10 gal.) of primary sludge mixed with 52.99 1 (Ik gal.)
of thickened WAS. Procedure was then the same as for Run No. 1, except
sludge was fed at a constant rate of 1.62 1/min, (0.43 gpm). A 0.051 solu-
tion of Percol 728 (a high molecular weight catlonic polymer) was fed at
0.84 g/kg (1.67 Ib/ton) (130.0 ml/mln)(.034 gpm).
RESULTS
Feed
Centrate
Cent rate
Skimmings
Cake
NOTES
Time
for 10.0 mln
@ 5 min.
@ 8 min.
—
1. Dissolved solids were
2. Cake stood firmly
3. Volume reduction was 2
Volume
liters gal.
16.2 4.3
—
--
0 0
5.68 1.50
approximately 844
.35
mg/I SS Solids
or % TS Recovery (1)
4.793!
955 mg/1 98.0
856 mg/l 98.2
—
13.481
(14.69 £ 12.28)
mg/1
173
-------
TABLE A-12. 30.5 CM (12 IN.) CENTRIFUGE BASKET TESTS - RUN NO. 12
Centrifuge Basket Unit - 30.5 cm (12 In.)
Run No. 12
Date: August 13, 1975
Sludge Tested: jj|xt_ur_e_ of Dry-Weather, Tlota^lon-Thlckened WAS and
Dry-Weather Primary Sludge with Polymer
PROCEDURE
Mixture was 37.85 I (10 gal.) of primary sludge mixed with 52,99 1 (Ik gal.)
of thickened WAS. Procedure was then the same as for Run Ho. 1, except
sludge was fed at a constant rate of 1.62 1/mln. (0.43 gpm) • A 0.1? solu-
tion of Percol 728 (a high molecular weight catlonlc polymer) was fed at 1.73
g/kg (3.45 Ib/ton) (130 ml/mln.) (.Q34gPm).
RESULTS
Feed
Centrate
.Cent rate
Skimmings
Cake
NOTES
Time
for 9.0 mln
§ 5 rnln.
§ 8 mln.
I. Dissolved solids were
2. Cake stood firmly
3. Volume reduction was
Volume
liters g
14.6
0.10 0
5.58 1
approximately
2.62
ay.
3.9
.03
.47
704
mg/1 SS Solids
or % TS Recovery (%}
4.641
749 mg/1 98.4
1, MO mg/1 97.5
1.811
13.411
(15.26 & 11.56)
mg/l
174
-------
TABLE A~13. 30.5 CM (12 IN.) CENTRIFUGE BASKET TESTS - RUN NO. 13
Centrifuge Basket Used - 30.5 cm (12 in.)
Run No. 13
Date: August 13, 1975
Sludge Tested: Mfxtureof Dry.Weather, Flotatton-Thickened WAS and
Dry-Weather Primary Sludge with Polymer
PROCEDURE
Mixture was 37.85 I (10 gal.) of primary sludge mixed with 52.99 1 ("Ik gal.)
of thickened WAS. Procedure was then the same as for Run No. 1, except
sludge was fed at a constant rate of 1.66 1/min. (0.44 gprn). A 0.1? solu-
tion of Percol J28 (a high molecular weight catlonic polymer) was fed at
2.37 9/fcg (*•74 Ib/ton) (183.5 ml/mln) (.05 gpm).
RESULTS
Feed
Cent rate
Cent rate
Skimmings
Cake
Time
for 10.0 mln.
@ 5 min.
@ 8 mtn.
—
Vot
Ifters
16.6
—
—
0.11
5.57
ume
gal .
4.4
—
—
0.03
1.47
mg/1 SS
or % TS
4.66
593 rng/1
1,900 mg/1
0.731
14.141
(16.02 6 12.25)
Solids
Recovery
98.7
95.9
--
ID
NOTES
1. Dissolved solids were approximately 543 ng/l
2. Cake stood firmly
3. Volume reduction was 2.98
175
-------
TABLE A-14. 122 cm BASKET CENTRIFUGE TEST, KENOSHA - RUN NO. I
Location; Kenosha WPCP
Date: November 11, 1975
Run No.: 1
Sludge Type: Thickened WAS CSO Sludge
Basket Size: 122 cm (48 In.)
Basket Speed: 1375 rpm
Time of
Sample sample, mir.
Feed 1 0
Feed 2 6
Centra te 1 5
Centrate 2 7-5
Centrate 3 . 11
Centrate 4 12.5
Skimmings 1
Skimmings 2
Cake I
Cake 2
Cake 3
Cake 4
G Force: 1300
Feed Rate: 95 l/m!n
Centrate Breakover:
Length of Runt 12 ml
Volume of Skimmings:
Percent
total solids
3.03
3.58
0.264
0.937
2.04
2.10
4.00
4.78
6.58
8.20
3J.82
47.40
(25.1 gpm)
4.8 mln
n
276 i (73 gal.)
SS, mg/1
29,600
35,100
1,910
8,640
19,700
20,300
39,200
47,100
176
-------
TABLE A-15. \22 cm BASKET CEHTfUFUSE TEST, KENOSHA - RUN NO. 2
Location: Kenosha WPCP
Date: November 11, 1975
Run No. : 2
Sludge Type; Thickened WAS
Basket Size: 122 cm (48 in,
Basket Speed: 1375 rpm
CSO Sludge
,)
Time of
Sample sample, m!n
Feed 1
Feed 2
Feed 3 25
Centrate 1
Centrate 2
Centrate 3
Centrate 4 22
Centrate 5 27
Centrate 6 32
Centrate 7 35
Skimmings
Cake 1
Cake 2
Cake 3
Cake 4
10
13
.5
10
13
18
.5
.5
.5
.5
G Force: 1300
Feed Rate: 54 I/min
Centrate Breakover:
Length of Run: 35 ml
Volume of Skimmings:
Percent
total solids
0.83
1.51
3.37
0.155
0.151
0.163
0.178
0.195
0.899
1.03
4.50
7.02
19.07
31.00
26.54
(14.3 gpm)
8.4 mln
n
189 1 (50 ga
SS, mg/1
7,600
1MQO
33,000
823
790
900
1,060
1,230
8,260
9,590
44,300
177
-------
TABLE A-16. 122 cm BASKET CENTRIFUGE TEST, KENOSHA - RUN NO. 3
Location: Kenosha WPCP
Date: November 11, 1975
Run No.; 3
Sludge Type: Thickened WAS CSO Sludge
Basket Size: 122 era (48 In.)
Basket Speed: 1375 rpm
Time of
Sample sample, mln
Feed 1 5
Feed 2 10
Generate 1 5
Centrate 2 7
Cent rate 3 9
Centrate 4 10
Skimmings 1
Skimmings 2
Cake 1
Cake 2
Cake 3
G Force: 1300
Feed Rate: 111 1/m!n
Centrate Breakover:
Length of Run; 9 mln
Volume of Skimmings:
Percent
total solids
3.58
3.60
1.26
1.56
1.86
2.10
3.41
3.73
8.51
17.50
27.10
(29.4 gpm)
4.1 mln
276 1 (73 gal.)
SS» mg/1
35,000
35,300
1 1 ,800
14,900
17,900
15,900
33,400
36,600
178
-------
TABLE A-17. 122 cm BASKET CENTRIFUGE TEST, KENOSHA - RUN NO.
Location: Kenosha WPCP
Date: November It, 1975
Run No. : k
Sludge Type: Thickened WAS GSO Sludge
Basket Size: 122 on (48 in.)
Basket Speed: 1375 rpm
Time of
Sample sample, mtn
Feed 1 10
Feed 2 17
Cent rate 1 10
Centrate 2 15
Centrate 3 17
Skimmings
Cake 1
Cake 2
Cake 3
Cake 4
G Force: 1300
Feed Rate: 60 1/mfn (15.8 gpm)
Centrate Breakover: 7.6 mln
Length of Run: 15 mln
Volume of Skimmings: 189 1 (50 gal.)
Percent
total solids SS, mg/l
3.38 33,000
3.10 30,300
0.328 2,560
1.63 15,600
1.59 15,200
3.67 36,000
7.18
16.3
28.7
37.9
179
-------
TABLE A-18. 122 cm BASKET CENTRIFUGE TEST, KENOSHA - RUN NO, 5
Location; Kenosna WPCP
Date; November 12, 1975
Run No.: 5
Sludge Type; Thickened WAS CSO Sludge
Basket Size: 122 cm (48 In.)
Basket Speed: 1375 rpm
Time of
Sample sample, m!n
Feed f 5
Feed 2 12
Centrate 1 8
Centrate 2 10
Centrate 3 12
Centrate 4 14
Centrate 5 15
Skimmings 1
Skimmings 2
Cake 1
Cake 2
Cake 3
G Force: 1300
Feed Rate: 69 I/mfn (18,
Centrate Breakover: 6.6
Length of Run: 14 mfn
Volume of Skimmings: 276
Percent
total solids
2.90
4.14
0.339
0.307
0.316
0.436
0.821
2.74
3.48
6.75
23.2
32.3
I gpm)
mln
1 (73 gal.)
SS, mg/l
28,300
40,700
2,670
2,340
2,430
3,630
7,480
26,600
34,000
180
-------
TABLE A-I9. 122 cm BASKET CENTRIFUGE TIST, KENOSHA - RUN NO. 6
Location: Kenosha WPCP
Date: November 12, 1975
Run No.: 6
G Force: 1300
Feed Rate: kQ 1/mfn (10.6 gpm)
Centrate Breakover: H.3 rain
Sludge Type: Thickened WAS CSO Sludge Length of Run: 16 mln
Basket Size: 122 cm (kB in.) Volume of Skimmings: 170 1
Basket Speed: 1375 rpm
gal.)
Sample
Feed 1
Feed 2
Centrate 1
Centrate 2
Centrate 3
Skimmings
Cake 1
Cake 2
Cake 3
Time of
sample, min
1
17
13
16
17
Percent
total sol Ids
2.36
2.93
0.332
0.326
1.47
3.25
5.85
12.1
33.7
SS, mg/1
22,800
28,600
2,590
2,5*»0
13,900
31,700
181
-------
TABLE A-20. 122 cm BASKET CENTRIFUGE TEST, KENQSHA, RUN NO. 7
Location: Kenosha WPCP
Date: November 17, 1975
Run No.: 7
G Forces 1300
Feed Rate: 88 1/min (23.2 gpm)
Centrate Breakover: 5.2 mln
Sludge Type: Combined Dry-Weather* Length of Run: 10 mln
Basket Size: 122 on (48 fn.) Volume of Skimmings: 322 1 (85 gal.)
Basket Speed: 1375 rpm
Sample
Feed 1
Feed 2
Centrate 1
Centrate 2
Centrate 3
Skimmings 1
Skimmings 2
Cake 1
Cake 2
Cake 3
Time of Percent
sample, mln total solids
3 4.06
10 4.14
6 0.919
8 0.463
10 0.586
2.09
4.56
12.4
18.0
18.0
SS, mg/1
35,210
40,060
7,840
3,280
4,513
19,590
44,240
* Combined dry-weather sludge consisted of a 1:1 volumetric mixture of
thickened WAS and primary sludge.
182
-------
TABLE A-21. 122 cm BASKET CENTRIFUGE TEST, KENOSHA, RUN NO. 8
Location: Kenosha WPCP
Dates November 17, 1975
Run No.: 8
Sludge Type: Combined Dry-Weather*
Basket Size: 122 on (48 In.)
Basket Speed: 1375 rpm
Time of
Sample sample, mtn
Feed 1 3
Feed 2 14
Centrate 1 10
Centrate 2 13
Centrate 3 14
Centrate 4 15
Skimmings 1
Skimmings 2
Cake 1
Cake 2
Cake 3
G Force: 1300
Feed Rate: 5k l/mln
Centrate Breakover:
Length of Run: 14 m
Volume of Skimmings:
Percent
total solids
4.03
4.09
0.713
0.461
1.21
0.835
1.76
4.52
9.74
17.2
23.0
04.2 gpm)
8.5 mtn
in
276 1 (73 gal.)
SS, mg/1
38,990
39,560
5,781
3,261
10,710
6,992
16,270
43,850
* Combined dry-weather sludge consisted of a 1:1 volumetric mixture of
thickened WAS and primary sludge,
183
-------
TABLE A-22. 122 cm BASKET CENTRIFUGE TEST, KENQSHA - RUN NO. 9
Location; Kenosha WPCP
Date: November 17, 1975
Run No.: 9
Sludge Type: Combined Dry-Weather*
Basket Size: 122 cm (48 In.)
Basket Speed: 1375 rpm
G Force: 1300
Feed Rate: 39 1/mtn (10.2 gpm)
Centrate Breakover: 11,8 mln
Length of Run: **
Volume of Skimmings: 265 1 (70 gal.)
Sample
Feed 1
Feed 2
Centrate I
Centrate 2
Skimmings 1
Skimmings 2
Cake 1
Cake 2
Cake 3
Time of Percent
sample, mln total solids
3 4.11
14 3.84
12 1.49
14 0.804
3.71
3.44
19.5
23.8
23.5
SS, mj/1
39,790
37,090
13,550
6,688
35,730
33,000
* Combined dry-weather sludge consisted of a 1:1 volumetric mixture of
thickened WAS and primary sludge.
** Automatic shutoff due to excessive vibration.
184
-------
TABLE A-23. 122 cm BASKET CENTRIFUGE TEST, KENOSHA - RUN NO. 10
Location; Kenosha WPCP
Date: November 18, 1975
Run No . : 10
Sludge Type:
Basket Size:
Basket Speed:
Sample
Feed I
Feed 2
Feed 3
Feed 4
Feed 5
Feed 6
Cent rate 1
Cent rate 2
Centrate 3
Cent rate 4
Centrate 5
Centrate 6
Centrate 7
Skimmings
Cake 1
Cake 2
Combined Dry-Weather*
122 cm (48 in.)
1375 rpm
Tfme of
sample, min
2
15
23
29
43
72
16
24
40
50
60
70
76
G Force; 1300
Feed Rate: 35 1/min (9.32
Centrate Breakover: 12.9
Length of Run: 76 min
Volume of Skimmings: 151
Percent
total solids
1.57
2.09
0.75
0.37
1.03
2.95
0.280
0.223
0.203
0.232
0.241
0.267
1.23
3.82
12.2
27.9
gpm)
min
1 (40 gal.)
SS, mg/1
14,320
19,540
6,150
2,380
8,130
28,130
1,453
879
677
968
U063
1,322
10,970
36,890
* Combined dry-weather sludge consisted of a 1:1 volumetric mixture of
thickened WAS and primary sludge.
185
-------
TABLE A-24. 122 cm BASKET CENTRIFUGE TEST, KENQSHA - RUN NO. II
Location: Kenosha WPCP
Date: November 18, 1975
Run No.: 11
Sludge Type: Combined Dry-Weather*
Basket Size: 122 cm (48 In.)
Basket Speed: 1375
G Force: 1300
Feed Rate: 38 1/mln (10.1 gpm)
Centrate Breakover: 11.8 mln
Length of Run: 26 mln
Volume of Skimmings: 106 1 (28 gal.)
Sample
Feed 1
Feed 2
Centrate 1
Centrate 2
Centrate 3
Centrate 4
Centrate 5
Skimmings
Cake 1
Cake 2
Time of
sample, min
3
15
13
17
21
25
27
Percent
total solids
3.18
3.31
0.334
0.286
0.298
0.358
1.22 ,
0,247
9.03
23.5
SS, mg/1
30,450
31 ,750
1,987
1,513
1,632
2,224
10,800
1,117
* Combined dry-weather sludge consisted of a 1:1 volumetric mixture of
thickened WAS and primary sludge.
186
-------
TABLE A-25. 122 cm BASKET CENTRIFUGE TEST, KENOSHA - RUM NO, 12
Location: Kenosha WPCP
Date: November 19, 1975
Run No.: 12
Sludge Type: Combined Dry-Weather*
Basket Size: 122 on (48 En.)
Basket Speed; 1375 rpm
G Force: 1300
Feed Rate: 58 1/mln (15,4 gpm)
Centrate Breakover: 7.8 mln
Length of Run: 11 mln
Volume of Skimmings; 140 1 (37 gal.)
Sample
Feed 1
Feed 2
Centrate 1
Centrate 2
Centrate 3
Skimmings
Cake 1
Cake 2
Cake 3
Time of Percent
sample, mln total solids
3 5.
11 6.
9 2.
11 3.
12 3.
3.
5.
3.
37.
34
56
18
09
06
45
23
76
5
SS , mg/1
52,060
64,220
20,470
29,570
29,290
* Combined dry-weather sludge consisted of a 1:1 volunetrlc mixture of
thickened WAS and primary sludge.
187
-------
TABLE A-26. 122 era BASKET CENTRIFUGE TEST, KENOSHA - RUN NO. 13
Location: Kenosha WPCP
Date: September 10, 1976
Run No.: 13
Sludge Type: Wet-weather/dry-weather
ratio*
Basket Size: 122 cm (48 In.)
Basket Speed: 1375
5 Force: 1300
Feed Rate: 54.1 1/mln (14.3 gpm)
Centrate Breakover: 8.4 mfn
Length of Run: 25 rain
Volume of Skimmings: 155 £ (41
gal.)
Polymer Addition; None
Time of
Sample sample, mJn
Feed 1
Feed 2
Centrate 1
Centrate 2
Skimmings
Cake 1
Cake 2
15
25
15
25
Percent
TS
3.63
3.64
0,26
1,20
2.72
14.55
11.90
Percent
TVS
2.24
2.26
0.19
0.90
1.74
7-95
7.00
SS, mg/J
34,840
34,940
1,170
11,080
25,200
VSS, mg/1
21 ,630
21 ,880
1,000
8,540
16,210
S'J Wet-weather/dry-weather sludge consisted of a 1.2:1.2:1.0 volumetric
mixture of dry-weather primary, dry-weather thickened WAS and wet-weather
thickened WAS.
-------
TABLE A-27. 122 cm BASKET CENTRIFUGE TEST, KENOSHA - RUN NO. 14
Location: Kenosha WPCP
Date: September 14, 1976
Run No.; 14
Sludge Type: Wet-weather/dry-weather
ratio*
Basket Size: 122 cm (48 In.)
Basket Speed: 1375 RPM
G Force: 1300
Feed Rate: 94.6 1/mtn (25.0 gpm)
Centrate Breakover;4,8 min
Length of Run: 17 mln
Volume of Skimmings: 208 £ (55
gal.)
Polymer Addition: None
Sample
Feed 1
Feed 2
Centrate 1
Centrate 2
Skimmings
Cake 1
Cake 2
Time of
sample, min
10
17
10
17
Percent
TS
1.46
2.25
0.56
0.59
3.60
46.5
43.6
Percent
TVS
0.85
1.34
0.40
0.40
2.17
27.8
27.0
SS, rag/1
12,570
20,470
3,790
4,140
34,400
-
VSS, mg/1
7,410
12,310
2,960
3,000
20,660
* Wet-weather/dry-weather sludge consisted of a 1.2:1.2:1.0 volumetric
mixture of dry-weather primary, dry-weather thickened WAS and wet-weather
thickened WAS.
189
-------
TABLE A-28; 122 era BASKET CENTRIFUGE TESTS, KENOSHA - RUM NO. 15
Location: Kanosha WPCP
Date : September 14, 1976
Run No.: 15
Sludge Type; Wet-weather/dry-weather
ratio*
Basket Size: 122 cm (48 In.)
Basket Speed; 1375
G Force: 1300
Feed Rate: 37-9 1/rnln (10.0 gpm)
Centrate Breakover: 5-1 rain
Length of Run: 23 mln
Volume of Skimmings: 189 & (50
gal.)
Polymer Addition: None
Time of
Sample sample, mln
Feed 1
Feed 2
Feed 3
Centrate 1
Centrate 2
Centrate 3
Skimmings
Cake 1
Cake 2
13
J8
23
13
18
23
Percent
TS
4.17
5.19
5.70
0.69
0.96
?.Q4
3.34
38.7
24.4
Percent
TVS
2.38
2.88
3.27
0.52
0.70
0.79
2.38
11.8
U.3
SS, mg/1
39,470
49,670
54,770
4,970
7,590
8,280
31,600
VSS, mg/1
22,530
27,530
31,430
4,080
5,830
6,600
22,630
* Wet-weather/dry-weather sludge consisted of a 1.2:1.2:1.0 volumetric
mixture of dry-weather primary, dry-weather thickened WAS and wet-
weather thickened WAS.
190
-------
TABLE A-29. 122 cm BASKET CENTRIFUGE TEST, KENOSHA - RUN NO. 16
Location; Kenosha WPCP
Date: September 14, 1976
Run No.: 16
Sludge Type: Wet-weather/dry-weather
ratio*
Basket Size; 122 cm {48 In.)
Basket Speed: 1375 RPM
G Force: 1300
Feed Rate: 70.0 1/mfn (18.5 gpm)
Centrate Breakover: 6.5
Length of Run: 19
Volume of Skimmings: 189 1 (50
gal.)
Polymer Addition: None
Time of
Sample sample, min
Feed 1 9
Feed 2 14
Feed 3 19
Feed 4 24
Centrate 1 9
Centrate 2 14
Centrate 3 , 19
Centrate 4 24
Skimmings
Cake 1
Cake 2
Percent
TS
1.87
1.78
1.90
1.88
0.59
0.61
0.59
0.56
1.35
35.7
21.0
Percent
TVS
1.15
1.08
1.16
1.13
0.42
0.44
0.42
0.41
0.92
9-50
9-43
SS, mg/1
14,790
13,890
15,090
14,890
3,950
4,110
3,900
4,330
11,470
VSS, mg/1
8,530
7,830
8,630
8,330
3,160
3,070
3,120
3,010
8,070
* Wet-weather/dry-weather sludge consisted of a 1.2:1.2:1.0 volumetric
mixture of dry-weather primary, dry-weather thickened WAS and wet~
weather thickened WAS.
191
-------
TABLE A-30. 122 cm BASKET CENTRIFUGE TEST, KENOS.HA - RUN NO. '17''
Location: Kenosha WPCP
Date: September 14, 1976
Run No,: 17
Sludge Type: Wet-weather/dry-weather
ratio*
Basket Size: 122 era (48 In.)
Basket Speed; 1375
G Force: 1300
Feed Rate: 109.0 l/mln (28.8 gpm)
Centrate Breakover: 4.2 mln
Length of Run: 15 min
Volume of Skimmings: 189 £ (50
gal,)
Polymer Addition: None
Sample
Feed I
Feed 2
Feed 3
Centrate I
Centrate 2
Centrate 3
Skimmings
Cake I
Cake 2
Time of
sample, rain
9
12
15
9
12
15
Percent
TS
3-30
3.81
3.88
1.01
1.81
1.92
4.00
28.7
16.5
Percent
TVS
1.88
2.22
2,23
0.74
1.31
1.40
2.61
10.0
7.77
SS, ing/1
30,870
35,970
36,670
8,090
16,090
17,350
37,680
VSS, mg/I
17,610
21,010
21,110
6,340
12,000
12,900
24,880
Wet-weather/dry-weather sludge consisted of a 1.2:1.2:1.0 volumetric
mixture of dry-weather primary, dry-weather thickened WAS and wet-weather
thickened WAS.
192
-------
TABLE A-31. 122 cm BASKET CENTRIFUGE TEST, KENOSHA - RUN NO. 18
Location: Kenosha WPCP
Date: September 13, 1976
Run No.: 18
Sludge Type: Wat-weather/dry-weather
ratio*
Basket Size: 122 cm (48 in.)
Basket Speed: 1375 RPM
G Force: 1300
Feed Rate: 44.3 l/mln (11.7
Centrate Breakover: 10.3 min
Length of Run: 20 min
Volume of Skimmings: 189 i (50
gal.)
Polymer Addition: 2-76 kg/metric
ton (5.51 lb/ton)
Sample
Feed I
Feed 2
Feed 3
Centrate 1
Centrate 2
Centrate 3
Skimmings
Cake 1
Cake 2
Time of
sample, min
10,5
15
20
10.5
15
20
Percent
TS
2.38
2.42
2.45
0.33
0.38
0.37
2.50
23.5
24.6
Percent
TVS
1.45
1.46
1.48 "
0.21
0.26
0.26
1. 40
11.5
14.3
SS, mg/1
21,580
21,980
22,280
1,350
1,850
1,690
23,020
VSS, mg/1
13,280
13,380
13,580
1,060
1,460
1,380
12,920
* Wet-weather/dry-weather sludge consisted of a 1.2:1.2:1.0 volumetric
mixture of dry-weather primary, dry-weather thickened WAS and wet-
weather thickened WAS.
193
-------
TABLE A-32. 122 cm BASKET CENTRIFUGE TEST, KENOSHA - RUN NO. 19
Location: Kenosha WPCP
Date: September 13, 1976
Run No.: 19
Sludge Type: Wet-weather/dry-weather
ratio*
Basket Size: 122 cm (48 In.)
Basket Speed: 1375 RPM
G Force: 1300
Feed Rate: 44.3 l/mln (11.7 gpra)
Centrate Breakover: 10.3 min
Length of Run: 25 rain
Volume of Skimmings: 189 I (50
gal.)
Polymer Addition: 1.92 kg/metric
ton (3.84 Ib/ton)
Sample
Feed 1
Feed 2
Feed 3
Centrate 1
Centrate 2
Centrate 3
Skimmings
Cake 1
Cake 2
Time of
sample, mtn
11
20
25
11
20
25
Percent
TS
2,42
2.50
2.48
0.23
0.30
0.29
6.14
20.3
31.5
Percent
TVS
1.46
1.52
1.48
0.18
0.20
0.19
3.45
10.8
11.5
SS, mg/1
21,980
22,780
22,580
1,270
1,530
1,440
59,020
VSS, mg/1
13,440
14,040
13,640
1,010
1,240
1,160
33,130
Wet-weather/dry-weather sludge consisted of a 1.2." 1.2:1.0 volumetric
mixture of dry-weather primary, dry-weather thickened WAS and wet-
weather thickened WAS.
194
-------
TABLE A-33. 122 cm .BASKET CENTRIFUGE TEST, KENOSHA - RUN NO. 20
Location: Kenosha WPCP
Date: September 15, 1976
Run No.: 20
Sludge Type: Wet~weather/dry-weather
ratio*
Basket Size: 122 cm (48 In.)
Basket Speed: 1000 RPM
G Force: 700
Feed Rate: 60.6 l/mln (16.0 gpm)
Centrate Breakover: 7-5 m'n
Length of Run: 22 mln
Volume of Skimmings: 132 I (35
gal.)
Polymer Addition: 1.40 kg/metric
ton (2.81 Ib/ton)
Time of
Sample sample, mln
Feed 1
Feed 2
Feed 3
Feed 4
Cent rate 1
Cent rate 2
Cent rate 3
Cent rate 4
Skimmings
Cake 1
Cake 2
10
15
20
22
10
15
20
22
Percent
TS
4.92
4.31
3,82
4.04
0.35
0.32
0.30
0.45
4.57
19,3
21.0
Percent
TVS
2.49
2.48
2.28
2.32
0.24
0.22
0.21
0.32
2.94
9.14
10.1
SS, rtg/1
46,710
40,610
35,710
37,910
1,250
950
780
2,290
43,460
VSS, mg/1
23,460
23,360
21,360
21,760
1,070
830
730
1,870
28,080
•
* Wet-weather/dry-weather sludge consisted of a 1.2:1.2:1.0 volumetric
mixture of dry-weather primary, dry-weather thickened WAS and wet-
weather thickened WAS.
195
-------
TABLE A-34. 122 cm BASKET CENTRIFUGE TEST, KENOSHA - RUN NO. 21
Location: Kenosha WPCP
Date: September 15, 1976
Run No.: 21
Sludge Type: Wet-weather/dry-weather
ratio*
Basket Size: 122 cm (48 in.)
Basket Speed: 1000 RPM
G Force: 700
Feed Rate: 81.4 1/min (21.5 gpm)
Centrate Breakover; 5.6 m5n
Length of Run: 11 rain
Volume of Skimmings: 140 I (37
gal.)
Polymer Addition: 0.78 kg/metric
ton (1,56 Ib/ton)
Time of
Sample sample, mln
Feed 1 8
Feed 2 II
Centrate 1 8
Centrate 2 1 1
Skimmings
Cake I
Cake 2
Percent
TS
5.42
5.65
0.75
3.67
4.18
20.1
16.2
Percent
TVS
3.16
3.24
0.57
2.76
2.73
9.53
8.59
SS, mg/1
51,720
54,020
5,600
34,800
39,550
VSS, mg/1
30,190
30,990
4,470
26,350
25,950
Wet-weather/dry-weather sludge consisted of a 1.2:1.2:1.0 volumetric
mixture of dry-weather primary, dry-weather thickened WAS and wet-weather
thickened WAS.
196
-------
APPENDIX B - MILWAUKEE, WISCONSIN CENTRIFUGE TEST DATA
TABLE B-l. 122 cm BASKET CENTRIFUGE TEST - RUN NO. 1
Location: Humboldt
Date: May 10, 19J6
Run No.: 1
Avenue Detention
Tank
G Force: 1300
Feed Rate: 223 llter/mln (59 gpi
Sludge Type: Gravity Thickened CSO
Sludge
Basket Size: 122 cm (48 In.)
Basket Speed: 1375 RPM
Samp I e
Feed 1
Feed 2
Feed 3
Feed 4
Feed 5
Centrate 1
Cent rate 2
Centrate 3
Cent rale 4
Centrate 3
Cake
Cake
Time of
sample, min
3
7
17
50
65
3
7
17
50
65
Centrate Breakover: 2.
03 min
Length of Run: 73 m'n
Volume of Skimmings: -
Polymer Addition: None
Percent Percent
TS TVS SS
0.07
0.07
0.05
0.13
0.14
0.05
0.0ft
0.04
0.04
0.05
0.13
0.14
0.02
0.03
0.02
0.05
0.05
0.02
0.02
0.02
0.02
0.02
0.05
0.05
, mg/1
237
270
131
933
964
81
14
34
18
66
197
-------
TABLE B-2. 30.5 cm (J2 In.) CENTRfFUGE BASKET TESTS - RUN NO. J
Centrifuge Basket Used - 30.5 cm (12 In.)
Run No. 1
Date; June 8, 1976
Sludge Tested: Gravity Thickened CSO Sludge
PROCEDURE
Sludge was fed to the 30.5 cm (12 In.) basket centrifuge (producing 1300 G's
at the basket wall) at a constant rate of 10.22 1/mln (2.7 gpm) for 240
minutes. A feed sample was taken for analyses prfor to centrffugatfon and
subsequent centrate samples were taken during centrlfugatlon. A skimmings
sample and one cake sample was taken at the end of the run for total solids
analysis. No polymer was utilized.
RESULTS
Feed
Centrate
Centrate
Centrate
Centrate
Centrate
Centrate
Centrate
Centrate
Skimmings
Cake
Time
for 240 min
§ 30 min
@ 60 rain
§ 90 min
§ 120 min
§ 150 min
@ 180 min
@ 210 min
@ 240 min
-
-
Volume mg/1 SS Solids
liters gal. or % TS recovery, 1
2453 648 .0621
19 76.6
20
18
17
17
11
7
7
.00081
18.31
198
-------
TABLE B-3. 30.5 cm (12 In.) CENTRIFUGE BASKET TESTS - RUN NO. 2
Centrifuge Basket Used - 30.5 cm (12 In.)
Run No. 2
Date: June 9, 1976
Sludge Tested: Gravity Thickened CSO Sludge
PROCEDURE
Same as for Run No. 1, except a 0.11 polymer (Percol 728) solution was fed
at a constant rate of 0.014 2,/mln (0.0037 gpm).
RESULTS
Feed
Cent rate
Cent rate
Cent rate
Cent rate
Cent rate
Centrate
Cent rate
Centrate
Skimmings
Cake
Time
for 240 min
@ 30 mln
§ 60 mln
§ 90 mfn
8 120 m!h
@ 150 mln
§ 180 mln
@ 210 mln
@ 240 mjn
-
-
Volume mg/1 SS Solids
liters gal. or % TS recovery, 1
2*153 648 .0692
22 82.1?
10
8
28
22
22
22
17
.0655^
28.41
199
-------
TABLE B-4. AVNX 314 'DECANTER CENTRIFUGE TESTS
Location: Milwaukee South Shore WPCP Bowl Speed: 2700 RPM
Date: May 25, 1976 Pool Radius: 103 mm
Run No.: 1 Differential Speed: An =• 15 RPM
Sludge Type: Dry-Weather Primary Polymer Addition: None
Feed Rate: 105.6 llters/mln (27.9 gpm) Recovery:
Sample
Feed 1
Feed 2
Cent rate 1
Cent rate 2
Cake 1
Cake 2
Percent
total solids
5.92
5.65
3.83
3.88
27.0
25.3 -
Percent total
volati le sol ids
3.23
3.48
2.63
2.63
12.3
12.0
SS, rag/1
54,600
51,970
34,370
34,210
VSS, mg/1
29,840
32,420
23,900
23,890
TABLE B-5. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Milwaukee South Shore WPCP Bowl Speed: 2700 RPM
Date: May 25, 1976 Pool Radius: 103 mm
Run No.: 2 Differential Speed: An = 23
Sludge Type: Dry-Weather Primary Polymer Addition: None
Feed Rate: 105.6 llters/min (27.9 gpm) Recovery: 47%
Percent Percent total
Sample totaI sol Ids volatile sol kjs^ SS, mg/1 VSS, mg/1
Feed 1 5.61 3-42 51,570 31,790
Feed 2 5.71 3-5! • 52,550 32,680
Feed 3 5.6? 3-36 51,710 31,130
Centrate 1 3-6! 2.46 31,560 22,160
Centrate 2 3.84 2.56 33,790 23,180
Centrate 3 3-36 2.30 29,030 20,540
Cake 1 19.95 9-80
Cake 2 21.28 10.42
Cake 3 18.38 9-22
200
-------
TABLE 8-6. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Milwaukee South Shore WPCP
Date: May 25, 1976
Run No.: 3
Sludge Type: Dry-Weather Primary
Feed Rate: 36.3 Hters/min (9.6 gpm}
Bow] Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: An
Polymer Addition: None
Recovery: 501
23 RPM
Sample
Feed 1
Feed 2
Cent rate 1
Cent rate 2
Cake 1
Cake 2
Percent
total solids
5-76
5.51
3-53
3.49
17.5
17.1
Percent total
volatl 1e sol ids
3-59
3.35
2.35
2.43
8.8
8.7
SS, mg/1
53,030
50,530
30,730
30,310
VSS, mg/1
33,460
31,040
21,060
21,870
TABLE B-7. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Milwaukee South Shore WPCP
Date: May 25, 1976
Run No.: 4
Sludge Type: Dry-Weather Primary
Feed Rate: 36.3 llters/min (9.6 gpm}
Bowl Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: in
Polymer Addition: None
Recovery: 521
15 RPM
Sample
Feed 1
Feed 2
Feed 3
Centrate I
Centrate 2
Centrate 3
Cake 1
Cake 2
Cake 3
Percent
tpjal so 11 ds
5.58
5.47
5.59
3.43
3-33
3.28
16.8
17.4
16.6
Percent total
volatile sol Ids
3.38
3-19
3.43
2.36
2.29
2.28
8.9
9.1
8.7
SS, mg/1
51,260
50,130
51,330
29,660
28,700
28,190
VSS,mg/1
31,420
29,500
31,890
21,170
20,460
20,350
201
-------
TABLE B-8. 'AV'dx-'SlVDECANTER CENTRIFUGE TESTS*
Location: Milwaukee South Shore WPCP Bowl Speed: 2700 RPM
Date: May 25, 1976 Pool Radius: 103 mm
Run No.: 5 Differential Speed: An * 15
Sludge Type: Dry-Weather Primary Polymer Addition: None
Feed Rate: 67.8 l!ters/mln (17.9 gpm) Recovery:
Percent Percent total
Sample total solids volatile solids SS, mg/1 VSS, mg/1
Feed 1 5.74 3.49 52,810 32,430
Feed 2 5.63 3.78 51,730 35,370
Feed 3 5.84 3.24 51,260 29,970
Centrate 1 3.86 2.62 34,010 23,820
Centrate 2 3.85 2.53 33,890 22,920
Centrate 3 3.89
Cake 1 21.8
Cake 2 20.9
Cake 3 22.5
202
-------
TABLE B-9. AVNX 314 DECANTER CENTRIFUGE TESTS
Location:'Milwaukee South Shore WPCP
Date: May 26, 1976
Run No.: 6
Sludge Type: Dry-Weather Primary
Feed Rate: 37.5 liters/mln (9.9 gpm)
Bowl Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: £n = 10 RPM
Polymer Addition: None
Recovery:
Sample
Feed I
Feed 2
Feed 3
Centrate 1
Centrate 2
Centrate 3
Cake I
Cake 2
Cake 3
Percent
sol \ds
5.62
5,6k
5.63
3.55
3-54
3.55
20.6
19.8
19.0
Percent total
voIatlie sol Ids
3-52
3-29
3.36
2.47
2.46
2.37
10.9
10.3
10.4
SS^jng/l
52,440
52,610
52,470
31,740
31,630
31,700
VSS, rag/1
33,300
31,050
31,720
22,860
22,690
21 ,"860
203
-------
TABLE 8-10. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Milwaukee South Shore WPCP
Date: May 26, 1976
Run No.: 7
Sludge Type: Dry-Weather Primary
Feed Rate: 37.5 llters/mln (9.9 gpm)
Bowl Speed: 2700 RPM
Pool Radius: 101 mm
Differential Speed: An
Polymer Addition: None
Recovery: 53%
23 RPM
Sample
Feed 1
Feed 2
Feed 3
Centrate 1
Centrate 2
Centrate 3
Cake 1
Cake 2
Cake 3
Percent
total solids
5.64
5.59
5.37
3.33
3.24
3.25
16.7
16.8
16.7
Percent total
yolatllesolIds
3.37
3.37
3.23
2.33
2.25
2.23
8.3
8.9
8.6
SS, mg/1
52,610
52,080
49,920
29,450
28,550
28,680
VSS. mg/1
31,870
31,850
30,520
21,450
20,570
20,460
204
-------
TABLE B-1J. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Milwaukee South Shore WPCP
Date; May 27, 1976
Run No.: 8
Sludge Type: Dry-Weather Primary
Feed Rate; 37-5 l!ters/min (9.9 gpm)
Bowl Speed: 2700 RPM
Pool Radius: 101 mm
Differential Speed: fin = 15 RPM
Polymer Addition: 0.38 kg/metric
ton (1.76 Ib/ton)
Recovery:
Cample
Feed 1
Feed 2
Feed 3
Centrate I
Centrate 2
Centrate 3
Cake 1
Cake 2
Cake 3
Percent
total sol ids
5-63
5.70
5.53
1.65
0.91
0.81
14.7
14.4
Percent total
vo 1 at Me solids
3.50
3.46
3.37
1.14
0.61
0.54
9.0
9-1
8.8
SS, mg/1
52,480
53,250
51,540
12,660
5,260
4,320
VSS., mg/1
33,130
32,690
31,810
9,540
4,260
3,500
205
-------
TABLE B-12. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Milwaukee South Shore WPCP
Date: May 27, 1976
Run No.: 9
> I
Sludge Type: Dry-Weather Primary
Feed Rate: 37.5 Uters/mfn (9.9 gpm)
Bowl Speed: 2700 RPM
Pool Radius: 101 mm
Differential Speed: An
15 RPM
Polymer Addition: 1.33 kg/metric
ton (2.68 Ib/mon)
Recovery: 35%
Sample
Feed I
Feed 2
Feed 3
Centrate 1
Centrate 2
Centrate 3
Cake 1
Cake 2
Cake 3
Percent
total sol Ids
5.63
5.36
5.55
0.75
0.83
0.64
15.5
15.4
15-3
Percent total
volatile i jsol Ids
3.37
3.34
3.47
0.48
0.55
0.40
9-5
9.5
9-1
SSt mg/1
52,460
49,840
51,740
3,650
4,630
2,600
VSS, tag/}
31,750
31,520
32,820
2,930
3,650
2,130
206
-------
TABLE B-13. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Milwaukee South Shore WPCP
Date: May 2?, 1976
Run No.: 10
Sludge Type: Dry-Weather Primary
Feed Rate: 66.6 Uters/mln (17.6 gpm)
Bowl Speed: 2700-RPM
Pool Radius: 103 mm
Differential Speed: An
20 RPM
Polymer Addition: 1.5 kg/metric
ton (3.0 Ib/ton)
Recovery: 661
Sample
Feed 1
Feed 2
Centrate 1
Centrate 2
Cake 1
Cake 2
Percent
total solids
5.28
5.37
2,50
2.51
15.9
16.1
Percent total
volatile sol Ids
3.24
3.26
1.66
t.67
9.2
9.6
SS, rag/1
49,000
49,890
21,980
21,380
VSS, mg/1
30,520
30,720
14,710
14,870
207
-------
TABLE B-14. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Milwaukee South Shore WPCP
Date: May 27, 1976
Run No.: 11
Sludge Type: Dry-Weather Primary
Feed Rate: 66.6 liters/mln (17.6 gpra)
Bowl Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: An » 25 RPM
Polymer Addition: 1.48 kg/metric
ton (2.96 ]b/ton)
Recovery:
Percent
Sample
Feed 1
Feed 2
Feed 3
Cent rate 1
Centrate 2
Cent rate 3
Cake I
Cake 2
5.38
5.^5
5.44
2.49
2.45
2.03
14.8
14.9
Percent total
volati1e solids
3-30
3.40
3.29
1,66
1.63
1.36
8.5
9.1
S_S; mg/1
50,030
50,710
50,600
21,100
20,730
16,490
VSS,mg/1
31,140
32,200
31,050
14,760
14,410
11,710
208
-------
TABLE B-15. AVNX 314 DECANTER CENTRIFUGE TESTS
Location*. HUwaukee South Shore WPCP
Date: May 27, 1976
Run No.; 12
Sludge Type: Dry-Weather Primary
Feed Rate: 54.5 liters/mfn (14.4 gpm)
Bowl Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: An
20 RPM
Polymer Addition: 1.85 kg/metric
ton (3.69 Ib/ton)
Recovery:
Sample
Feed 1
Feed 2
Feed 3
Centrate 1
Cent rate 2
Centrate 3
Cake ]
Cake 2
Cake 3
Percent
total solIds
5,02
5.45
5-35
2.27
2.4?
3.37
16.1
15.6
16.6
Percent total
yolatile sol Ids
3.10
3.25
3.23
1.53
1.68
2.32
9.7
8.7
8.8
SS, nig/1
46,380
50,700
49,700
18,940
20,890
29,910
VSS, ing/1
29,130
30,640
30,490
13,420
14,990
21,360
209
-------
TABLE B-16-, AVNX 31k DECANTER CENTRIFUGE TESTS
Location: Milwaukee South Shore WPCP
Date: June 1, 1976
Run No.: 13
Sludge Type: Dry-Weather Primary
Feed Rate: 58,3 llters/mtn (15.9 gpm)
Bowl Speed: 2JOO RPM
Pool Radius: 103 mm
Differential Speed: An » 23 RPM
Polymer Addition: 3-22 kg/metric
ton (6,43 Jb/ton)
Recovery: $B%
SampJ^e
Feed 1
Feed 2
Feed 3
Cent rate 1
Centrate 2
Centrate 3
Cake 1
Cake 2
Cake 3
Percent
totaj^spl ids
5.35
4.93
2.45
0.48
0.41
0.40
11.6
15.3
12.7
Percent total
e sol ids
3.64
3.16
1.62
0.28
0.22
0.21
8.9
10.0
8.6
SS, mg/l
50,530
^,330
21,440
1,780
1,080
880
VSS, mg/1
3*» i 930
I4,8t0
1,450
840
680
210
-------
TABLE B-17. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Milwaukee South Shore WPCP
Date: June 1, 1976
Run No.: 14
Sludge Type: Dry-Weather Primary
Feed Rate: 58.3 llters/mln (15.4 gpm)
Bowl Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: An
18 RPM
Polymer Addition: 2.7 kg/metric
ton (5.39 Ib/ton)
Recovery: 95$
Samp1e
Feed 1
Feed 2
Feed 3
Centrate 1
Centrate 2
Centrate 3
Cake 1
Cake 2
Cake 3
Percent
total solids
5.07
4.98
5.14
0.59
0,73
0.47
17-1
17.4
17.6
Percent total
volatile solids
3.30
3.31
3.50
0.38
0.48
0.27
11.7
11.3
11.0
SS, mg/l
47,730
48,380
2,930
4,340
1,660
VSS, mg/1
31,590
31,710
33,570
2,370
3,350
1,320
211
-------
TABLE B-18. AVNX 31*1 PLANTER CENTRIFUGE TESTS
Location: Milwaukee South Shots, WPCP
Date: June I,
Run No.: 15
Sludge Type: Dry-Weather Primary
Feed Rate: 58 .,J Hters/raln 05.4 gpra)
Bowl Speed: 2700 RPH
Pool Radfus: 103 mm
Differential Speed:
13 RPM
Polymer Addition: 2.1? kg/metric
ton (4.33 lb/ton)
Recovery: 90?
Percent
Percent total
Sample
Feed 1
Feed 2
Feed 3
Cent rate 1
Centrate 2
Cent rate 3
Cake 1
Cake 2
Cake 3
total solids
4.76
4.76
4.65
0.95
0.98
0.75
15-7
18.4
18.1
volatile solids
3.05
3.03
2.94
0,68
O.S7
0.50
10.6
12.0
It. 5
SS, mg/1
44,570
44,570
43,480
6,520
6,780
4,5tO
VSS, mg/1
29,130
28,920
27,970
5,430
5,3tQ
3,570
212
-------
TABLE 8-19. AVNX 31*1 DECANTER CENTRIFUGE TESTS
Location: Milwaukee South Shore WPCP
Date: June 2, 1976
Run No.: 16
Sludge Type: Dry-Weather Primary
Feed Rate: 57-9 Hters/mfn (15-3 gpra)
Bowl Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: An - 15 RPM
Polymer Addition: 2.03 kg/metric
ton (4.07 Ib/ton)
Recovery: 82%
Sample
Feed 1
Feed 2
Feed 3
Centrate 1
Cent rate 2
Cent rate 3
Cake 1
Cake 2
Cake 3
Percent
total soHcte
5.13
4.73
4.20
1.63
1.77
0.96
16.8
17.2
17-0
Percent total
vo1_a_t_n_e _spj_ld_s_
3.36
3.18
2.67
1.30
0.94
0.75
10.5
II.0
10.1
SS, tag/1
48,740
44,810
39,410
13,760
9,690
7,030
VSS, mg/1
32,390
30,640
25,500
11,820
8,210
6,310
213
-------
TABLE B-20. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Milwaukee South Shore WPCP
Date: June 2, 1976
Run No.: 17
Sludge Type: Dry-Weather Primary
Feed Rate: 57-9 Hters/mtn (15-3 gpm)
Bowl Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: An
15 RPM
Polymer Addition: 1.54 kg/metric
ton (3.08 }b/ton)
Recovery: 81 %
Sample
Feed 1
Feed 2
Feed 3
Centrate 1
Centrate 2
Centrate 3
Cake 1
Cake 2
Cake 3
Percent
total sol Ids
4.65
5.00
4.36
0.76
1.19
i.go
15.6
16.4
16.6
Percent total
3.05
3.39
2.89
0.51
0.96
1.58
9.5
10.1
10.7
SS, mg/1
43,970
47,440
41,090
4,470
9,380
12,270
VSS, mg/1
29,340
32,690
27,730
3,930
8,460
14,640
21k
-------
TABLE B-21. AVNX 31*1 DECANTER CENTRIFUGE TESTS
Location: Milwaukee South Shore WPCP Bowl Speed: 2700 RPM
Date: June 3, 1976 Pool Radius: 103 mm
Run No.: 18 Differential Speed: An « 15 RPH
Sludge Type: Dry-Weather Primary Polymer Addition: k.kb kg/metric
Feed Rate: 66.6 llters/min (17.6 gpm) ton (8'93 lb/ton)
Recovery:
Percent Percent total
Sample. total solids volatile solids SS. rag/1 VSS, rng/1
Feed 1 2.75 1-75 2*1,670 16, 180
Centrate 1 0.63 Q.M» 3,530 3,0^0
Cake 1 17.8 J1.3
215
-------
TABLE B-22. AVNX 314' DECANTER' CENTRIFUGE TESTS
Location: Milwaukee South Shore WPCP
Date: June 3, 1976
Run No.: 19
Sludge Type; Dry-Weather Primary
Feed Rate: 66.6 liters/min (17.6 gpra)
Bow! Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: An
23 RPM
Polymer Addition: 2.29 kg/metric
ton (4.58 Ib/ton)
Recovery: 36%
Sample
Feed 1
Feed 2
Feed 3
Centrate 1
Centrate 2
Centrate 3
Cake I
Cake 2
Cake 3
Percent
total so1_t_d_s.
5.40
5.27
5-40
0.81
0.43
0.46
16.2
16.3
16.5
Percent total
yplatJIe _so_l_f_d_s_
3.53
3.21
3.25
0.58
0.26
0,28
9.9
9.8
10.5
SS, mg/l
51,190
49,860
51,200
5,330
1,540
1,830
VSS, mg/l
33,970
30,750
31,150
4,470
1,240
1,510
216
-------
TABLE B-23. AVNX 3t4 DECANTER CENTRIFUGE TESTS
Location: Milwaukee South Shore WPCP
Date: June 3, 1976
Run No.: 20
Sludge Type: Dry-Weather Primary
Feed Rate: 66.6 Uters/mln (17.6 gpm)
Bowl Speed; 2?00 RPM
Pool Radius: 103 mm
Differential Speed; An
11 RPM
Polymer Addition: 2.53 kg/metric
ton (5.05 Ib/ton)
Recovery: 811
Sample
Feed 1
Feed 2
Feed 3
Centrate 1
Centrate 2
Centrate 3
Cake 1
Cake 2
Cake 3
Percent
total sol
5.45
5.31
3.83
1-97
1.61
0.4?
20.6
20.7
19.0
Percent total
yoJ a 111e so 11ds
3.33
3.34
2.35
1.43
1.15
0.29
12.0
11.9
11.4
SS, mg/1
51,660
50,300
35,490
16,930
13,280
1,940
VSS, mg/1
32,000
31,100
22,220
12,990
10,210
1,620
217
-------
TABLE B-24. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Milwaukee South Shore WPCP
Date: June 3, 1976
Run No.: 21
Sludge Type: Dry-Weather Primary
Feed Rate: 66.6 llters/mln (17.6 gpm)
Bowl Speed: 2700 RPM
Pool Radius: 103 «n>
Differential Speed: An
15 RPM
Polymer Addition: 2.28 kg/metric
ton (4.56 Ib/ton)
Recovery: 801
Sample
Feed 1
Feed 2
Feed 3
Centrate 1
Centrate 2
Centrate 3
Cake 1
Cake 2
Cake 3
Percent
total sol Ids
5.25
5.30
' 5.58
2.37
1.35
1.19
17.8
15.4
16.1
Percent total
volatile solids
3.45
3.29
3.54
1.73
0.99
0.84
10.8
9.5
9.7
SS, mg/1
49t680
50,230
53,020
20,740
10,610
9,040
VSS, mg/1
33,090
31,550
34,100
15,970
8,660
'218
-------
APPENDIX C - RACINE, WISCONSIN CENTRIFUGE TEST DATA
TABLE C-l. AVNX 314 DECANTER CENTRIFUGE TESTS
Location; Racine WPCP
Date: August 2, 1976
Run No.: 1
Sludge Type: Dry-Weather Primary + WAS
Feed Rate: 38.2 1/mln (10.1 gpm)
BOMI Speed: 2700 RPH
Pool Radius: 103 mm
Differential Speed: An
Polymer Addition: None
Recovery: 67.IS
28 RPM
Percent
Percent total
Sample
Feed 1
Cent rate I
Cake I
total solids
9.00
4.09
34.8
volatile sol Ids
3.87
2.69
U.2
SS, mg/1
87,390
34,600
VSS, mg/1
37,290
22,760
TABLE C-2. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine WPCP
Date: August 2, 1976
Run No.: 2
Sludge Type: Dry-Weather Primary + WAS
Feed Rate: 25,4 1/mfn (6.7 gpm)
Bowl Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: An
Polymer Addition: None
RecoveryJ 71.51
26 RPH
Sample
Feed 1
Centrate I
Cake 1
Percent
total- solids
13.90
5.42
38.1
Percent total
volatile solids
6.0
3.54
10.7
SS, mg/1 VSS, mg/1
135,300 57,810
51,700 33,900
219
-------
TABLE C-3. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine WPCP
Date; August 2, 1976
Run No , : 3
Sludge Type: Dry-Weather Primary
Feed Rate: 76.8 1/mln (20.3 gpm)
WAS
Bowl Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: An
5 RPH
Polymer Addition: 1 kg/metric
ton (2 Ib/ton)
Recovery: 72.0?
Sample
Feed 1
Cent rate I
Cake 1
Percent Percent total
total solids volatile solids
3.88
1.30
24.05
2.31
0.76
.4.45
SS, mg/1
37,700
11,900
VSS, mg/1
22,500
7,340
TABLE C-4. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine WPCP
Date: August 2, 1976
Run No.: 4
Sludge Type: Dry-Weather Primary + WAS
Feed Rate: 78.7 t/min (20.8 gpm)
Bowl Speed: 2700 RPH
Pool Radius: 103 mm
Differential Speed: an * 15 RPH
Polymer Addition: 3*55 kg/metric
ton (7.1 Ib/ton)
Recovery: 87.41
Sample
Feed 1
Feed 2
Centrate I
Centrate 2
Cake 1
Cake 2
Percent
total solids
0.64
0.51
0.14
0.13
16.80
29.24
Percent total
volatile solids
0.41
0.34
0.07
0.07
10.46
19.51
SS. mg/1
5,330
4,080
640
570
VSS. mg/1
3,680
2,920
530
440
220
-------
TABLE C-7. AVNX 31* DECANTER CENTRIFUGE TESTS
Location: Racine WPCP
Date: August 2, 1976
Run No.: 7
Sludge Type: Dry-Weather Primary + WAS
Feed 'Rate: 78.7 1/mtn (20.8 gpm)
Bowl Speed: 2700 RPH
Pool Radius: 10$ mm
Differential Speed:
10 RPM
Polymer Addition: 0.7 kg/metrfe
ton (1.4 Ib/ton)
Recovery: 87.11
Sample
Feed 1
Feed 2
Centrate 1
Centrate 2
Cake 1
Cake 2
Percent
total solids
2.10
3.21
0.28
Q.6*t
24.36
24.17
Percent total
volatl 1e sol Ids
1.34
2.00
0.17
0.41
15.98
14.60
SS, rag/1
19,920
31,020
1,860
5,380
VSS, mg/1
12,980
19,580
1,480
3,600
TABLE C-8. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine WPCP
Date: August 2, 1976
Run No.: 8
Sludge Type: Dry-Weather Primary + WAS
Feed Rate: 78.7 1/mln (20.8 gpm)
Bowl Speed: 2700 RPM
Pool Radius: 103 m
Differential Speed: An = 10 RPM
Polymer Addition: 0.9 kg/metric
ton (1.8 Ib/ton)
Recovery: 97.41
Sample
Feed 1
Centrate 1
Cake 1
Percent
total solids
5.15
0.29
26.28
Percent total
vo1la.t H e so I Ids
2.30
0.21
15.59
SS. mg/1
50,500
1,620
VSS. mg/1
28,500
1,400
222
-------
TABLE C-9. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine WPCP
Date: August 5, 1976
Run No.: 9
Sludge Type: Dry-Weather Primary + WAS
Feed Rate: 72.3 1/mln (19.1 gpm)
Bowl Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: An
5 RPH
Polymer Addition: 1.3 kg/metric
ton (2.6 Ib/ton)
Recovery: 86.2%
Sample
Feed 1
Feed 2
Centrate 1
Cent rate 2
Cake I
Cake 2
Percent
total solids
1.78
3.97
0.25
0.93
29.4
32.1
Percent total
volatile solids
0.88
1,83
0.14
0.57
13-2
13.9
SS, mg/J
16,230
38,130
1,380
6,7*0
VSS, mg/l
8,070
17,570
830
4,240
TABLE C-10. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine WPCP
Date: August 5, 1976
Run No.: 10
Sludge Type: Dry-Weather Primary + WAS
Feed Rate: 57.5 1/min (15*2 gpm)
Bowl Speed: 2700 RPM
Pool Radius: 103 ram
Differential Speed: An - 15
Polymer Addition: 1.3 kg/metric
ton (2.5 lb/ton)
Recovery: 96.3%
Samp_l_e
feed I
Feed 2
Centrate 1
Centrate 2
Cake 1
Cake 2
Percent
total solids
5.17
6.01
0.33
0.55
26.0
28.8
Percent total
volatilesolids
2.33
2.72
0.21
0.36
11.6
10.8
SS, mg/l
50,130
58,530
1,380
3,520
VSS, mg/l
22,570
26,470
1,120
2,480
223
-------
TABLE C-13. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine WPCP
Date; August 5, 1976
Run No.: 13
Sludge Type: Dry-Weather Primary + WAS
Feed Rate: 76.8 1/mln (20.3 gpm)
Bowl Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: An
23 RPM
Polymer Addition: 3.9 kg/roe rfc
ton (7.9 lb/ton)
Recovery: 96.11
Sample
Feed 1
Feed 2
Cent rate 1
Cent rate 2
Cake 1
Cake 2
Percent
total solids
0.73
1.20
0.11
0.12 .
21.61
19-57
Percent total
volatile solfcjs
0.44
0.77
0.05
0.07
13.26
12.03
ss,
6,
11,
mg/1
500
160
430
290
VSS, mg/1
4,140 -,
7,380
320
190
TABLE C-14. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine WPCP
Date: August 6, 1976
Run No.: 14
Sludge Type: Dry-Weather Primary •*• WAS
Feed Rate: 57.9 1/mln (15-3 gpm)
Bowl Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: An * 15 RPM
Polymer Addition: 1.4 kg/metric
ton (2.8 lb/ton)
Recovery: 84.3%
Sample
Feed 1
Feed 2
Centrate 1
Centrate 2
Cake I
Cake 2
Percent
tota 1 ^sol ids
12.24
13.57
3.81
2.88
29.4
29.4
Percent total
vpJajtMje soilds
5.24
5.80
2.21
1.73
12.2
11.8
SS,mg/1
119,380
132,680
34,270
25,520
VSS, mg/1
50,990
56,590
20,570
15,500
225
-------
TABLE 015. AVNX 31* DECANTER CENTRIFUGE TESTS
Location: Racine WPCP
Date.* August 6, J976
Run No.; 15
Sludge Type; Dry-Weather Primary + WAS
Feed Rate: kS,k 1/ratn {12.0 gpm)
Bowl Speed; 2700 RPM
Pool Radius: 103 nwn
Differential Speed: An
15 RPM
Polymer Addition: 1.8 kg/metric
ton (3.6 ?b/ton)
Recovery; 92.0*
Simple
Feed 1
Feed 2
Cent rate I
Cent rate 2
Cake 1
Cake 2
Percent
total solids
12.56
12.99
0.96
3.0*1
28.6
28.4
Percent total
volatile solids
5.34
5-70
0.64
1.84
12.2
12.4
SSf rag/1
122,670
126,970
6,730
26,630
VSS, mg/1
51,950
55,550
4,630
16,230
TABLE C-16. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine WPCP
Date: August 6, 1976
Run No,: 16
Sludge Type: Dry-Weather Primary + WAS
Feed Rate: 47.3 l/mln (12.5 gpm)
Bowl Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: An
26 RPM
Polymer Addition: 1.8 kg/metric
ton (3.6 Ib/ton)
Recovery: 99.5%
Sample
Feed 1
Centrate 1
Cake 1
Percent
tota1 sol I ds
12.40
0.32
28.0
Percent total
vo 1 at lie soHds
5.33
0.19
12.3
SS, mg/1
121,HO
1,070
VSS, mg/j_
51,920
830
226
-------
TABLE C-17. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine WPCP
Date: August 6, 1976
Run No.: 17
Sludge Type: Dry-Weather Primary + WAS
Feed Rate: 47.3 I/mln (12.5 gpm)
Bowl Speed: 2700 RPn
Pool Radius: 103 nm
Differential Speed: in
22 RPM
Polymer Addition: 1.6 kg/metric
ton (3.2 Ib/ton)
Recovery: 93.3%
Sample
Feed 1
Centrate I
Cake 1
Percent
total solids
13-85
1.87
28.6
Percent total
volatile sol ids
5-93
1.15
11.4
SS, mg/1
135,610
16,270
VSS, mg/l
57,920
10,530
TABLE C-18. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine WPCP
Date: August 9, 1976
Run No.: 18
Sludge Type; Dry-Weather Primary + WAS
Feed Rate: 25.4 l/mln (6.7 gpm}
Bowl Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: in
15 RPM
Polymer Addition: 2.5 kg/metric
ton (5.9 Ib/ton)
Recovery: 99.41
Samp 1e
Feed 1
Centrate I
Cake 1
Percent
total sol Ids
13.7
0.37
29.0
Percent total
volat11e soIt ds
6.0
0.20
13.2
SS. mg/1
133,270
1,360
VSS, rag/1
57,810
640
22?
-------
. TABLE C-19. AVNX 3\k DECANTER CENTRIFUGE TESTS
Location: Racine WPCP
Date: August 9, 1976
Run No.: 19
Sludge Type: Dry-Weather Primary +• WAS
Feed Rate: 25.*» l/mln (6.7
Bowl Speed: 2700 RPM
Pool Radius: 103 nm
Differential Speed: in
15 RPM
Polymer Addition: 0.9 kg/metric
ton (1.7 Ib/ton)
Recovery: 98.7%
SampJ_e
Feed I
Cent rate 1
Cake 1
Percent
total solids
13.5
0.51*
29.2
Percent total
volatile solids
5.9
0.35
11.7
SS, mg/1
131,320
3,040
VSS, rag/1
56,810
2,060
TABLE C-20. AVNX 31* DECANTER CENTRIFUGE TESTS
Location: Racine WPCP
Date: August 9, 1976
Run No.: 20
Sludge Type: Dry-Weather Primary + WAS
Feed Rate: 25.4 1/mtn (6.7
Bowl Speed: 2?00 RPM
Pool Radius: 103 mm
Differential Speed: An «=• 23 RPM
Polymer Addition: 1.8 kg/metric
ton (3.5 Ib/ton)
Recovery: 98.7%
Sample
Feed 1
Centrate 1
Cake 1
Percent
total sol Ids
13.7
0.61
25.6
Percent total
_yo 1 1 a t He sol I d s
5.9
10.6
SS, mg/1
133,320
3,500
VSS, mg/1
56,810
2,500
228
-------
TABLE C-2J. AVNX
DECANTER CENTRIFUGE TESTS
Location: Racine WPCP
Date: August 9, 1976
Run No.; 23
Sludge Type: Dry-Weather Primary + WAS
Feed Rate: 25.4 1/mfn (6,7
Bowl Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: An « "J RPM
Polymer Addition: 2,6 kg/metric
ton (5.1 Ib/ton)
Recovery; 90.71
Sample
Feed 1
Cent rate 1
Cake 1
Percent
total solids
13-7
2.13
35.1
Percent total
volati le sol Ids
6.0
1.33
13.6
SS, jng/J
133,320
18,900
•
VSS, rag/1
57,740
11,800
TABLE C-24. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine WPCP
Date: August 9» 1976
Run No.: 24
Sludge Type: Dry-Weather Primary + WAS
Feed Rate: 25.4 1/mfn (6.7 gpm)
Bowl Speed; 2700 RPM
Pool Radius: 103 mm
Differential Speed: An
26 RPM
Polymer Addition: 2.6 kg/metric
ton (5.1 Ib/ton)
Recovery: 99.11
Sample
Feed 1
Centrate 1
Cake 1
Percent
total so11ds
13-7
0.45
26.2
Percent total
ygat||e
6.0
0.26
11,5
SS, mg/1
133,320
2,350
VSS, mg/1
57,740
1,000
230
-------
TABLE C-25. AVNX 314 DECANTER CENTRIFUGE TESTS
Location; Racine WPCP
Date: August 9, 1976
Run No.: 25
Sludge Type; Dry-Weather Primary
Feed Rate: 25.4 1/mtn (6.7 gpm)
WAS
Bowl Speed: 2700 RPM
Pool Radius; 103 mm
Differential Speed: An
15 RPM
Polymer Addition: 2.5 kg/metric
ton (5.0 !b/ton)
Recovery: 98.31
Samp 1 e
Feed 1
Centrate 1
Cake 1
Percent
total solids
13-9
0.67
30.1
Percent total
volatile solids
6.1
0.43
12.5
SS, mg/1
135,330
4,200
VSS, mg/1
58,810
2,830
TABLE C-26. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine WPCP
Date: August 9, 1976
Run No.: 26
Sludge Type: Dry-Weather Primary + WAS
Feed Rate: 76.8 1/min (20.3
Bowl Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: An
10 RPM
Polymer Addition: 2.1 kg/metric
ton (4.2 Ib/ton)
Recovery: 96.6%
Sample
Feed 1
Feed 2
Centrate 1
Centrate 2
Cake 1
Cake 2
Percent
total solids
1.22
2.38
0.14
1.77
19.84
22.14
Percent total
volatile solids
0.76
1.46
0.07
1.04
12.16
13.36
SS,mg/1
11,400
22,800
340
1,040
VSS. mg/1
7,440
14,160
280
810
231
-------
TABLE C-2J. AVNX 314 DECANTER CENTRIFUGE TESTS
Location; Racine WPCP
Date: August 9, 19/6
Run No.: 27
Sludge Type: Dry-Weather Primary + WAS
Feed Rate: 72.3 l/mfn (19.1 gpm)
Bowl Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: An « 10 RPM
Polymer Addition: 3.8 kg/metric
ton (7.6 Ib/ton)
Recovery: 67,41
Sample
Feed 1
Feed 2
Cent rate 1
Cent rate 2
Cake 1
Cake 2
Percent
total solids
0,74
0.79
0.20
0.20
23.1
23.5
Percent total
volatile solids
0.37
0.39
0.11
0.11
11.6
12.0
SS, mg/I
6,090
6,590
450
500
VSS, mg/1
2,970
3,170
250
300
TABLE C-28. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine Wet-Weather Site No. 1
Date: August 11, 1976
Run No.: I
Sludge Type: Thickened S/DAF CSO Sludge
Feed Rate: 51.1 1/mfn (13-5 9pm)
Bowl Speed: 2700 RPM
Pool Radius: 103 mra
Differential Speed: fin - 15 RPM
Polymer Addition: None
Recovery: 69.OS
jample
Feed 1
Centrate
Cake 1
Percent
totajLSO! Ids
0.24
0.13
18.6
Percent total
yoI[ait_11 e so lids
0.11
0.07
11.1
SS, mg/1
1,840
570
VSS, mg/1
780
260
232
-------
TABLE C-29. AVMX 3l*» DECANTER CENTRIFUGE TESTS
Location: Racine Wet-Weather Site No. 1 Bowl Speed: 2700 RPM
Date: August 18, 1976 Pool Radius: 103 mm
Run No.: 2 Differential Speed: fin = 15 RPM
Sludge Type: Thickened S/DAF CSO Sludge Polymer Addition: None
Feed Rate; kB.S 1/min (12.8 gpm) Recovery: 63.k%
Samp 1 e
Feed 1
Centrate I
Cake I
Percent
total solids
0.58
0.22
25.9
Percent total
volatile sol Ids
0.30
0.13
9.4
SS, mg/1
5,230
1,230
VSS, mg/1
2,720
820
TABLE C-30. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine Wet-Weather Site No. 1 Bowl Speed: 2700 RPH
Date: August 11, 1976 Pool Radius: 103 mm
Run No.: 3 Differential Speed: An ° 15
Sludge Type: Thickened S/DAF CSO Sludge Polymer Addition: None
Feed Rate: 68.1 1/mln (18 gpm) Recovery: $2.k%
Percent Percent total
Sample tota\ soIIds volatile solids SS, mg/1 VSS,mg/1
Feed 1 .0528 .0213 110 100
Centrate 1 .0503 .0205 50 35
Cake 1 ' 30.8 17.4
233
-------
TABLE C-31. AVNJ5 314 DECANTER CENTRIFUGE TESTS
Location: Racine Wet-Weather Site No. 1
Date: August 18, 1976
Run No.: 4
Sludge Type; Thickened S/DAF CSO Sludge
Feed Rate: 126 1/mfn (33-3 gpm)
Bowl Speed: 2700 RPM
Pool Radius; 103 w»
Differential Speed: An
Polymer Addition: None
Recovery: 99.4%
= 15
Sample
Feed 1
Centrate 1
Cake 1
Percent
total solids
0.090
0.062
33.7
Percent total
volatl le sol Ids
0.038
0.025
17.0
SSf mg/l
490
190
VSS, mg/l
300
110
TABLE C-32. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine Wet-Weather Site No. 1
Date: August 11, 1976
Run No.: 5
Sludge Type: Thickened S/DAF CSO Sludge
Feed Rate: 48.5 I/mln (12.8 gpm)
Bowl Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: An = 6 RPM
Polymer Addition: 2.58 kg/metric
ton (5.16 Ib/ton)
Recovery: 91.31
Sample
Feed I
Centrate 1
Cake 1
Percent
total solids
0,23
0.07
30.1
Percent total
volat?le sol Ids
0.13
0.04
14.2
SS, mg/l
1,740
150
VSS, mg/1
980
130
234
-------
TABLE C-33. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine Wet-Weather Site No. 1 Bowl Speed; 2700 RPM
Date; August 11, 1976 Pool Radius: 103 ran
Run No.: 6 Differential Speed; An - 6 RPM
Sludge Type: Thickened S/DAF CSO Sludge Polymer Addition: 0.96 kg/metric
Feed Rate: 65-1 1/mJn (17.2 gpm) ton {l'92 lb/ton)
Recovery: 32. k%
SampJ e
Feed I
Cent rate 1
Cake 1
Percent
total solids
0.46
0.09
32.1
Percent total
volat? le sol Ids
0.24
0.05
H.9
SS» mg/1
4,040
310
VSS, mg/1
2, 080
240
TABLE C-34. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine Wet-Weather Site No. 1 Bowl Speed: 2700 RPM
Date: August 11, 1976 Pool Radius: 103 mm
Run No.: 7 Differential Speed: in - 10 RPM
Sludge Type: Thickened S/DAF CSO Sludge Polymer Addition: 2.33 kg/metric
Feed Rate: 65.1 l/mln (17.2 gpm) ton (4'65 1b/ton)
Recovery; 89-9%
Percent Percent total
Sampjhe total^soJJ^ds vo I a 111 e _soj \ ds SS, ing/I VSS, mg/1
Feed I 0.19 0.09 ',480 800
Centrate 1 0.07 0.03 150 80
Cake 1 30.8 14.2
235
-------
TABLE C-35. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine Wet-Weather Site No. 1 Bowl Speed: 2700 RPM
Date: August 11, 1976" Pool Radius: 103 mm
Run"No.: 8 Differential Speed: An = 15 RPM
Sludge Type: Thickened S/DAF CSO Sludge Polymer Addition: 3.16 kg/metric
Feed Rate: 60.1 l/mln (17.2 gpm) ton (6'31 lb/ton)
Recovery: 89.91
Sample
Feed I
Cent rate I
Cake I
Percent
total solids
0.14
0.07
23.4
Percent total
volatile solids
0.07
0.32
11.2
SS, mg/1
980
100
VSS, mg/1
600
90
TABLE C-36. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine Wet-Weather Site No. I Bowl Speed: 2700 RPM
Date: August 11, 1976 Pool Radius: *103 mm
Run No.: 9 Differential Speed: An = 15 RPM
Sludge Type: Thickened S/DAF CSO Sludge Polymer Addition: 1.35 kg/metric
Feed Rate: 126 1/mln (33-3 gpm) ton (2'69 1b/ton)
Recovery: 89.81
Percent Percent total
Sabpjj^ tgta_1^jspl 1^ volatile solids SSA rog/.1_ VSS, mg/1
Feed 1 0.17 0.09 1,280 7&Q
Centrate 1 0.07 0.03 130 120
Cake 1 25.5 13.7
236
-------
TABLE C-3J. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine Wet-Weather Site No. 1
Date: August II, 1976
Run No.: 10
Sludge Type: Thickened S/DAF CSO Sludge
Feed Rate: 126 1/mln (33.3 gpm)
Bowl Speed: 2700 RPH
Pool Radius: 103 mm
Differential Speed: An = 10 RPM
Polymer Addition; 3.17 kg/metric
ton (6-34 Ib/ton)
Recovery: 71.41
Sample
Feed 1
Centrate 1
Cake 1
Percent
total solids
0.07
0.05
30.5
Percent total
volatl le sol ids
0.27
0.15
14.8
SS, mg/1
310
90
VSS, rag/1
200
70
TABLE C-38. AVNX 314 DECANTER CENTRIFUGE TESTS
Location: Racine Wet-Weather Site No, 1
Date: August 18, 1976
Run No.: 11
Sludge Type: Thickened S/DAF CSO Sludge
Feed Rate: 48.5 l/«!n (12.8 gpm}
Bowl Speed: 2700 RPM
Pool Radius: 103 mm
Differential Speed: An
15 RPM
Polymer Addition: 1.52 kg/metric
ton (3.04 Ib/ton)
Recovery: 92.5%
Sample
Feed 1
Centrate
Cake 1
Percent
total solIds
0.39
0.09
26.2
Percent total
volatile solids
0.20
0.05
11.9
SS, mg/1.
3,3*0
260
VSS, mg/1
1,680
210
237
-------
TABLE C-39. AVNX 3lk DECANTER CENTRIFUGE TESTS
Location: Racfne Wet-Weather Site No. ! Bowl Speed: 2700 RPM
Date: August 11, 1976 Pool Radius: 103 nun
Run No.; 12 Differential Speed: An = 10 RPM
Sludge Type: Thickened S/DAF CSO Sludge Polymer Addition: I.70 kg/metric
Feed Rate: *»8.5 l/mfn (12.8 gpm) ton (3'39 lb/ton)
Recovery: 63.01
Percent Percent total
Sampje total solIds volatile solIds SS, mg/_l. VSS, mg/1
Feed 1 0.35 0.19 2,9*iO 1,580
Centrate 1 O.I? 0.08 I,100 560
Cake 1 26.k 11.8
238
-------
APPENDIX D - BENCH SCALE ANAEROBIC DIGESTION TEST DATA AND CALCULATIONS
TABLE D-1. RAW DATA DURING START-UP PERIOD, KENOSHA ANAEROBIC DIGESTION STUDY
Date
9/2/75
9/5/75
9/8/75
9/9/75
9/10/75
9/11/75
9/12/75
9/13/75
9/14/75
9/15/75
9/16/75
9/17/75
9/18/75
9/19/75
9/20/75c
Diges-
ter
C
W
C
W
C
W
C
W
C
W
C
W
C
W
C
W
C
W
C
W
C
W
C
W
C
W
C
W
C
W
Temper-
ature.
°C
«•••
-_
--
—
32
37
28
30
29
31
29
32
33
35
34
35
35
38
35
30
36
38
33
36
-.-
._
33
38
34
37
Total gas
production
1/daya
7.5
6.0
__
--
8.0
7.3
8.4
8.9
7.3
8.1
8.0
8.0
—
--
__
*• tm,
_-.
--
—
._
__
__
8.5
8.1
—
»
8.1
8.6
__
— —
pH
7.10
7.15
7.13
7.15
7.20
7.20
7.30
7.35
7.30
7.30
7.55
7.55
7.30
7-25
7.15
7.20
7.20
7.21
7.25
7.50
7.30
7.35
7.20
7.25
7.30
7.20
7.30
7.30
7.30
7.40
vola-
tile
acids,
ftig/j
130
130
130
120
—
--
__
—
130
130
—
»_
—
—
«
—
--
--
—
__
_-
—
__
..
--
__
130
130
__
--
Comments
Leak In mixer shaft
guides
Adjusted sludge vol.
Adjusted temperature
control ler
Adjusted water bath
level
Daily adjustments
started to balance
digester temps.
Power off-used 1/2
* normal feed vol .
Return to normal
feed volume
Volatile sol ids re-
duction - 27.5*
a. I/day at 760 mln Hg and 20°C
b. Measured as acetic acid.
c. From Sept. 21 to Nov. 7 bath digesters were
the cultures. Monitoring resumed on Nov.
239
fed regularly to maintain
7, 1975.
-------
TABLE D-2. DETERHI NATION OF VOLUMES OF WET-WEATHER
SLUDGE GENERATED FROM KENOSHA STORK EVENTS
1, Combined sewer area (Kenosha, Wisconsin ) » 539 hectares (1331 acres).
2. CSO sludge volume produced (II solids) per volume of CSO treated = 0,035.
3, Example; For 2.54 cm (1 Inch) of total rainfall and a runoff coefficient
of 0.5,
a. CSO volume treated - 68.5.x 10 liters (18.1 x 10 gal.)
b. CSO sludge volume produced at II solids = 2.4 x 10 liters
(632,477 gal.)
c. Thickened CSO sludge volume at 41 solids «* 598,454 liters
(158,112 gal.)
d. Digester hydraulic loadings at various feed addition times.
Addition to
full-scale 2.54 cm (1") rain 1.27 cm (0.5") rain 0.63 cm (0.25") rain
digesters
for perjods^pf
12 hours
24 hours
48 hours
74 hours
96 hours
liters/
day
1.2xl06
Q.fixtO6
Q.SxIO6
Q.2x1Q6
O.lSxlO6
gpd
316,224
158,112
79,056
52,704
39,528
1 iters/
day
0.6xl06
0.3x10
O.lSxlO6
O.lxlO6
0.07x106
gpd
158,112
79,056
39,528
26,352
19,764
liters/
day
O.JxIO6
Q.lSxIQ6
0.07xl06
0.05xl06
O.OSxlO6
gpd
79,056
39,528
19,764
13,176
9,882
240
-------
TABLE D-3. CALCULATION OF DIGESTER SLUDGE LOADINGS FOR A
SIMULATED STORM EVENT [1.27 cm (0.5") rain] - KENOSHA, WISCONSIN
!. Given: a. 0.5" total rainfall storm event
b. Two day CSO sludge bleed Into digester
2. CSO slydge generated - 0.15 x 10 liters/day » 39,528 gpd (from Table D-l)
3. Dry-weather sludge feed to digesters
a. Primary sludge » 0.16 x 10 liters/day (41,100 gpd)
b. Thickened WAS - 0.22 x 10 liters/day (57,700 gpd)
c. Total dry-weather feed - 0.37 x 10 liters/day (98,800 gpd)
4. Total feed to digesters (CSO + dry-weather sludges)
0.53 x 10 liters/day (138,328 gpd) for two days
5. Hydraulic loading Increase
(138,328 - 98,800) / 98,800
241
-------
TABLE D-k. RAW DATA FROM KENOSHA BENCH SCALE DIGESTION STUDY
(C = Control digester; W =» Wet-weather digester)
IS3
4-.
Feed
TS, TVS,
Bay 1 1 pH
3,6 58 6.78
1 C
W
2 c 3.7 58 6.81
3 C
V
4 C 3.6 59 6.76
W
5 C
W
6 C
W
7 C 3-8 61 6.94
W
8 C
W
9 C
W
IOC
W
11C
y
12C 4,2 60 6.82
J3C
W
14C 3.9 60 6.67
W 3.7 60 6.73
Sludge Gas Production
Alka- rot,a}
, , . f produc-
' '", L WAS/ tlon CO,/
"f'L** primary 1/24 hr CO, CH, *
CaC03 % (STP) r r CH4
1,050 58.3/41.7 6.9
3.8
6.8
4.4
5.9
5.2
1,100 6.3 31 64 48
6.9 30 67 45
6.2 29 62 47
6.7 28 63 44
1,000 6.6 31 65 48
5.5 30 66 45
6.4 30 66 45
6.2 30 67 45
6.5 30 67 45
5.7 31 67 46
1,100 6.9 30 69 43
6.1 33 66 50
6.9 34 64 53
6,4 35 62 56
6.2 29 70 43
6.4 30 70 41
6.0 33 67 49
6.3 33 67 49
5.7 32 67 48
6,2 30 69 43
1,100 58,3/41.7 5.1 32 6? 48
6.9 32 67 48
6.6 34 65 52
6.6 33 66 50
1,400 71/29 a. 6 31 68 46
1.350 29/23 10,0 11 68 46
Digesting Sludge
Total
solids
3.0
2.9
2,9
2.9
3.0
3.0
2,9
2.9-
3.0
2.9
2.9
3,0
2.9
3.0
2.9
3.0
2.9
3.1
2.9
3.1
3.0
3.0
3.0
2.9
3.0
3.0
3.0
3.0
2.9
3.0
2.9
TVS,
*
49
49
49
50
49
51
48
49
47
48
48
50
48
50
49
51
48
50
49
49
48
49
49
48
49
49
48
49
49
49
48
50
7-49
7.57
7-51
7.60
7-51
7.58
7.56
7.62
7,65
7.68
7.63
7-72
7.6!
7.65
7.68
7-69
7,45
7.48
7.46
7.50
7.4<5
7-52
7.46
7«'»9
7.69
7-63
7.64
7.61
7-58
7.53
7.50
7.52
Alka-
linity
mg/1
as
CaCO,
3,900
3,900
4,000
4,000
3,900
4,000
4,000
4,000
4,000
4,000
4,000
4,100
4,000
3,900
4,000
4,000
4,000
3,900
4.000
3,900
4,000
4,000
4,000
4,000
4,000
4,000
4,000
4,000
4,000
4.000
4,000
3,900
Vol-
atile
acids
mg/1
as
acetic
186
186
136
232
210
200
140
140
140
140
115
115
140
140
186
140
115
115
315
IIS
162
139
115
US
Volatile
acids/
alka-
Hnity
0.05
0.05
0.05
0.06
0.05
Q.05
0.04
0.04
0.04
0.04
0.03
0.03
0.04
0.04
0.05
0.04
0.03
0.03
0.03
0.03
0.04
0.03
0.03
0.03
continued
-------
TABLE D-k. (continued)
B2i
IS C
w
16 C
W
17 C
tf
13CC
U
19 C
W
20 C
w
21 C
W
22 C
W
23 C
W
24 C
W
25 C
W
26 C
W
27 C
W
z3 c
W
29 c
U
30 C
W
Feed Sludge
Alka-
linity WAS/
TS, TVS, mc*La* Pr^Y
% * pH Caco3 *
3.8 60 6.64 !,400 71/29
3.7 59 6.72 1,400 42/29
58.3/41.7
58.3/41.7
58.3/41.7
3.8 60 6.65 1,500 58.3/41.7
58.3/41.7
58.3/41.7
58.3/41.7
58.3/41.7
58.3/41.7
58.3/41.7
58.3/41.7
3.98 60 58.3/41.7
58.3/41.7
3.61 61.0 7.2 500
3.47 59.4 7.12 1,300
3.82 60.1 7.20 1,100
Gas Production
Total
produc-
tion
1/24 hr
(STP)
8.9
9.2
6.2
7-4
7.8
6.6
7.8
7.0
7.4
6.7
7.1
7.0
8.2
7.1
6.8
6.7
6.9
6.8
6.4
7.1
10.4
J0.5
8.5
8.2
7.5
8.0
9.9
10.3
8.2
9.6
7.6
9.3
C|2
33
32
31
31
31
32
32
31
30
29
31
31
28
31
30
30
31
29
34
34/31
31
30
30
29
33
32
35
33
3!
32
I
66
67
68
69
67
63
67
67
69
68
68
68
67
68
69
68
68
65
64
64/68
68
69
70
71
66
67
67
66
68
68
CO,/
2
50
48
45
44
46
47
48
46
43
43
46
46
42
45
43
44
46
44
53
53/46
45
43
43
41
50
48
52
50
45
47
Digesting Sludge
Total
solids
2.9
3.1
2.7
2.9
2.8
2.9
2.85
3.00
2.90
2.92
2.8
2.9
2.8
2.9
2.8
2.9
2.7
2.7
2.90
2.84
3.02
2.98
3.06
3.03
3.01
3.20
2.99
2.80
TVS,
48
50
51.8
48
50
49
48
50
47
49
49
50
49
50
50
49
47
49
47.1
48.0
49
48.9
47.9
49.3
47.9
48.2
47.4
48.2
pH
7.50
7.52
7.85
7.88
7.54
7.69
7.45
7.40
7.45
7.42
7.75
7.69
7.74
7.77
7.91
7.76
7.83
7.94
7.72
7.65
7-73
7.63
7.72
7.63
7.67
7.67
... Vol-
*}**- atlle
'^f acids
C*«3 as^t.c
4,000 115
3,900 115
4,050
4,000
5.500 95
5,950 118
4,300
4,200
4,250 16Q-*
4,150 141
4,300
4,100
4,350
4,160
4,150 233
4,050 210
4,000
4,100
4,000
4,100
4,300
4,150
Volatile
acids/
alka-
linity
0.03
"-03
continued
-------
TABLE D-4. (continued)
K>
-e-
JS-
-
Day
31 C
W
32 C
\l
33 C
w
34 C
w
35 C
W
36 c
w
37 C
w
38 C
tf
39 C
u
40CC
W
41 C
w
42 C
W
43 C
V
TS,
t
t
3.12
3.22
3.22
3.22
1
3.22
3.22
3.22
3.22
3.22
3.22
3.22
3.22
3.22
3.22
. 3-22
3.22
3.22
3.22
3.22
3.22
3,14
3.23
Fesd
% nH
6.65
63 7-2
60.2 7. IS
60.2 ?.!5
60.2 7.15
60.2 7.15
60.2 7.15
60.2 7.15
60.2 7-15
60.2 7.15
60.2 7,15
60.2 7.15
60.2 7.15
60.2 7.15
60.2 7.15
60.2 7.15
60.2 7.15
60.2 7.15
60.2 7.15
60.2 7.15
60.2 7.15
63.1 7.19
59-8 7.09
Sludge
Alka-
linity WAS/
ntg/l as primary
r»rn £
vauU^ *
1,000
326
1,848
1,848
1,848
1,848
1,848
1,848
1,848
1,848
1,848
1,148
1,848
1,848
1,848
1,848
1,848
1,848
1,848
1,848
1,848
500
2,000
Gas Production
Total
produe-
tlon CO
1/24 hr "*2
(5TP) %
8,9 33
8.1 32
8.0 32
9.3 3!
7.8 30
7.0 30
6,0 29
5.6 28
6.0 29
5.5 30
5.9 27
5.5 26
5.6 28
4.7 27
5,2 27
4.4 25
6.1 29
5.3 26
5.5 26
4.6 25
5.3
4.5
5.1
4.3
5.4 25
4.9 25
CM
%
64
68
66
65
66
66
69
68
68
66
68
69
69
70
69
66
68
65
63
68
69
70
co2/
CHj,
52
47
48
48
45
45
42
41
43
45
40
38
41
39
39
36
43
40
41
4|
36
36
Digesting Sludge
Total
solids
2.92
2.94
2.90
2.99
2.89
2.95
2.8
2,86
2.78
2.95
2.86
2.97
2.84
2.96
2.9
2.81
2.90
2,76
2.82
2.72
2,78
TVS
%
46
47.6
46.7
47.9
47
45
47.8
49.3
47.1
48.4
47.9
49.1
48.9
50.3
54
47.2
49.3
47.3
48,5
47.7
48,8
. jiH
7.63
7.68
7.81
7.8
7.69
7.87
7.67
7.66
7.77
7.75
7.69
7.72
7.63
-7.69
7. S3
7.75
Alka-
linity
mg/1
as
«COj
4,000
3,900
4,400
4,200
4,350
4,300
4,300
4,200
4,450
4,300
4,200
4,200
4,200
4,300
4,000
4,200
Vol-
atile
acids
mg/1
as
ascetic
162.9
116.0
163.2
140
140
140
163
163
Volatile
acids/
Alka-
ttnlty
-------
TABLE 0-5. TOTAL HEAVY METAL ANALYSES FOR THE BENCH SCALE DIGESTION TESTS -
KENOSHA, WISCONSIN
(All analyses (n mg metal/kg)
Test
day
13
16
28
3$
43
Test Sludge
period sampled
Ford
Control Dig. SI, (C)
Dig, SI. (W)
Fsed (C)
/I Feed (V)
Dig. SI. (C)
Dig. 51. ft/)
Feed (C)
,, Feet! M
* Dig. SI EC)
Dig. SI. (W)
Fsed
« Dig. SI (C)
Dig. 51. (W)
Feed (C)
,. Feed (W)
" Dig. SI. (C)
Dig. SI, (U)
« Dig. SI. (C)
Dig. St. (U)
Ktrcury,
wet
0.052
0.052
0.06?
0*059
0.036
0.046
0,0?S
0.067
0,036
0.061
0.063
0.079
0.0?8
0.063
dry
1.43
1.77
2.30
2,30
3.05
1.70
2.70
1.80
1.20
1.90
2.30
2.30
2.90
2.50
lead,
wet
15
17
16
14
10
16
17
16
13
15
15
22
IS
17
I?
14
16
1C
17
17
-~dry
420
560
550
400
400
560
620
590
460
530
510
590
510
550
540
430
570
570
620
600
Zinc,
Mt
140
160
160
100
SO
97
130
86
SI
100
100
130
HO
120
94
110
110
120
134
130
dry
3,800
5,600
5.500
2,500
3,300
3,500
4,700
3,100
3,200
3,600
3,700
3,620
3,500
3,300
3,000
3,500
3,900
4,300
4,900
4,700
Nickel,
wet
10
to
10
10
in
20
20
10
Q
10
10
to
10
10
a
7
10
10
14
IS
dry
300
400
500
400
400
600
6OT
400
300
400
4(10
300
400
400
300
200
40
400
530
550
Copper,
wet
66
S3
36
81
50
5*
as
42
54
57
84
63
$8
70
55
55
54
71
50
60
dry
2,400
3,000
2,901)
2,300
1,000
2, Otto
3,000
1 ,500
i,°on
2,000
2,900
1,700
1,900
2,300
1 ,100
1,700
1,100
2, son
1 ,900
2,100
Chraralura,
wet
31
34
32
24
16
34
23
28
25
32
28
26
30
25
31
25
31
50
48
dry
900
1,100
1,200
900
920
1 ,"V>
1,200
820
390
890
1,100
7SO
338
1,000
800
°60
8SO
1,101
1,800
1,700
1 ran.
wet
3,100
2,800
2,700
2,700
2,200
2.400
2,400
2,100
2,300
2,200
2,300
2,300
2,200
2,400
2,100
2,400
2,200
2.300
2,300
2,400
dry
84,500
[00,000
92.5W
77,000
83,000
85,000
34 , 000
77,000
79,200
76,000
78,000
63,000
71,000
80,000
67,000
75,000
75,400
82,000
85,000
87 , 000
Cadmium,
wet
t.l
1.8
1.9
0.9
l.o
1.8
1.8
1.0
I.S
1 .2
1.2
1.2
1.2
1.3
1.1
1.4
1.:
1.2
1.0
1.0
dry
40
51
51
10
40
60
60
37
51
42
42
11
40
42
30
40
42
43
40
40
Mote: C » Control d(getter
W • Mat-weather digester
-------
NJ
45-
TABLE D-6. SOLUBLE HEAVY METAL ANALYSES FOR THE BENCH SCALE DIGESTION TESTS - KENOSHA, WISCONSIN
(All concentrations !nmg/1)
Test Test
day period Sludge sampled
Dig.
11-13 Control
Dig.
Feed
Feed
35 13
Dig.
Dig.
S 2 udge
S 1 udge
(W)
(0
Sludge
Sludge
CO
CM)
CO
Cw)
Lead
<0.05
0.08
0.08
0.07
0.06
-------
TABLE D-7. CALCULATION OF DIGESTER SLUDGE LOADINGS FOR A SIMULATED
STORM EVENT OF 2.54 cm (1 Inch) RAIN USING RACINE CSO SLUDGE
I. Average dry weather sludge feed Co Racine digesters Is 404995 I/day
(107,000 gpd) at 8.9% total solids, 36044 kg (79422 Ib) solids are
added dally.
2. For a 2.54 cm (1 Inch) rain event, the following amounts of CSO sludge
are expected:
1,731,500 £ (457,464 gal.) sludge at 0.841 total solids.
After thickening, this would be equivalent to:
121,407 *• (32,076 gal.) at 11.981 total solids or
14,567 kg (32,0*8 Ib) dry solids.
3. If the sludge from a 2.54 cm (1 Inch) ratn were added to the digesters
in one day, the ratio of CSO solids to dry-weather solids added to
the Racine digesters would be 14,567 kg/36,044 kg - 0.404.
4. To feed our laboratory digesters at a ratio of 0.404 parts CSO solids
per part of dry-weather solids, we need 0.404 x 4.30/11.98 - 0.145
volume of CSO sludge per volume of dry-weather sludge. Amounts added
to the wet-weather digester are:
Normal Dry-
Weather Sludge
Volume, ml
Volumetric loading, £/m /day
Hydraulic retention time, days
Total solids, conce., %
Total solids loading, kg/m /day
Volatile solids cone., 1
Volatile solids loading, kg/nr/day
900 ml
50
-
4.30
2.15
2.77
1.39
CSO Sludge
131 ml
7.3
_
11.98
0.87
5.24
0.38
Total Wet-
Weather Feed*
1031 ml
57.3
17.5
5.28
3.02
3.08
1.77
* Calculated values.
To feed the control digester at the same volatile solids loading (1.77
kg/m /day) using dry-weather sludge only, 900 ml x 1.77/1-39 • '147 ml
sludge Is needed. This would result in a total solids loading of 2.74
kg/nr/day and a volumetric loading of 63.7 £/nr/day or an equivalent
hydraulic retention time of 17.4 days for the wet-weather feed day.
247
-------
TABLE D-8. RAW DATA FROM BENCH SCALE DIGESTION STUDY USING RACINE CSO
SLUDGE FOR WET-WEATHER SIMULATION
Day
I
2
3
*
*•
oo 5
6
7
8
9
10
Date
8/23
8/24
8/25
8/26
8/27
8/28
8/29
8/30
8/31
9/1
Digester
C
W
C
W
C
W
C
W
C
W
C
W
C
W
C
W
C
W
C
W
Gas Production
£/day(STP)
9.5
9.3
9.4
8.3
9.0
8.8
9.0
8.8
8.4
7.8
8,1
8.3
8.2
8.6
7.8
8.2
7.7
8.2
8.9
8.2
Total
Sol Ids
2.76
2.86
2.86
2.91
2.82
2.86
2.88
2.90
2.87
2.79
2.83
2.84
2.85
2.83
2.83
2.80
2.86
2.86
2.97
2.97
Volatile
Solids
57.6
59.8
58.4
60.1
58.2
60.1
58.0
59.6
57.8
58.8
58.3
59.5
58.2
59.4
57.2
59.6
56.6
57.9
60.6
Alkalinity
mg/1 as
pH CaCOj
_
7.4
7.5
7-3
7.2
7.2
7.3
_
7.2
7.2
7-2
7.2
7.2
7.2
7.2
7.3
7.2
7.2
Volatile Acids
mg/I as
Acetic
-
140
540
40
50
.
-
95
85
«•*
210
470
-
260
390
continued
-------
TABLE 0-8. (continued)
Day
11
12
13
it
15
16
17
18
19
20
Date
9/2
9/3
9/4
9/5
9/6
9/7
9/8
9/9
9/10
9/11
Digester
C
W
C
W
C
W
C
W
C
W
C
W
C
W
C
W
C
W
C
W
Gas Production
*/day(STP)
9.2
9.0
9^2
8.4
8.4
8.2
8.4
8.4
8.5
9.5
9.5
9.3
9.1
8.3
8.0
8.6
8.6
8.6
8.0
Total
Sol Ids
1
2.90
2.86
2.89
2.82
2.86
2.80
2.93
2.86
3.01
2.89
2.96
2.92
2.90
2.86
2.92
2.87
2.87
2.89
2.88
2.88
Volatile
Solids
i
56.5
58.7
56.7
58.9
56.6
58.9
56.3
59.1
57.5
58.8
56.7
58.9
56.6
58.4
56.2
58.2
56.4
58.8
56.2
58.0
Alkalinity
mg/I as
pH CaC03
7.2
7.2
7.2
7-2
7.2
7.2
7.2
7.2
7.2
7.2
7.2
7-2
7.2
7.2
7.1
7.2
7.2
7.2
7.2
7.2
Volatile Acids
mg/1 as
Acetic
-
10
10
-
50
80
-
90
15
:!°o
30
270
I/O
340
continued
-------
TABLE D-8. (continued)
Day
21
22*
23
NJ
U1
0 2k
25
26
27
28
Date
9/12
9/13
9/U
9/15
9/16
9/17
9/18
9/19
Digester
C
W
C
W
C
W
C
W
C
W
C
W
C
W
C
W
Gas Production
A/day (STP)
-
-
"9."6
9.8
9.9
9.1
9.2
8.3
10.0
9.4
7-3
6.7
—
-
8.5
8.2
Total
Solids
1
2.95
2.92
2.98
2.95
2.95
3.00
3.00
2.93
-
—
3.26
2-93
2.91
2.8?
2.91*
2.88
Volatile
Solids
I
56.6
58.2
56.7
57-6
58.6
57-0
5^.0
57.3
_
—
55.8
57.3
55.7
57.8
56.5
56.9
Alkalinity
mg/1 as
pH CaCO.
7.2
7.2
7,3
7.3
7.3 2800
7.2 2400
7.3
7.3
7.2
7.3
7.2 3350
7.2 3350
_
- _
7.2
7.2
Volatile Acids
mg/1 as
Acetic
HO
300
20
20
50
<10
30
30
220
70
210
440
-
•wt
-
Note; C = control digester; W » wet-weather digester
continued
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TABLE D-8. (continued)
Feed Sludge ConcentratIonsj
Day I and 2 - 4.36? total solids, 65-1% volatile solids, 6.6 pH
Day 3 to day 11 - 4.29$ total solids, 64.61 voaltlle solids, 6.65 pH
Day 12 to day 12 - 4.31% total solids, 6k.6% volatile solids, 6.75 pH
Day 23 to day 28 - 4.421 total solids, 63.5? volatile solids
Day 22 - Control digester - 4.421 total solids, 63.5% volatile solids
Day 22 - Wet-weather digester - 5-23& total solids, 57.61 volatile solids
* Simulated wet-weather sludge feed day. Mixture of Racine CSO sludge ind dry-weather sludge
added to wet-weather digester at loading of 1,73 kg volatile solIds/nt-Vday. Dry~weather
sludge added to control digester at loading of 1.77 kg/nr/day.
-------
TABLE D-9. TOTAL HEAVY METAL ANALYSIS FOR THE BENCH SCALE
DIGESTION TESTS - RACINE, WISCONSIN
(All analyses in mg metal/kg)
NJ
Ul
Test
fiax.
IS/21
Lead
Sample description
ComposIte samples of
dig, sludge during
control period
Zinc
Nickel
Digester wet. dryr wet dry_
C 15 521
W 15.5 544 135 WO
Copper
Chromium
Iron
Cadmfun Manganese
wet jjrjr wet dry
xtt dry wet_ dry wet_ dry wet, d r;
26 903 38 1320 358 12400 1040 36100 1.5 52 8,9 309
26 912 1)1 1440 360 12600 970 34000 1.7 60 8,4 295
22
28
Feed to digesters
during wet-weather
simulation
Dig. sludge after
wet-weather
simulation
C
w
C
y
15-5
24
13-5
12.5
411
483
456
437
172
152
129
138
4560
3090
4360
4830
26
25
29
26
690
508
980
909
44
44
41
39
1090
894
1380
1364
371
343
355
352
9840
6970
12000
12300
1150
1150
1040
968
30500
23400
35100
33800
2.4
1.6
1.5
2.0
64
32
51
70
10.4
11.5
8.9
8.3
276
234
300
290
Note: C - Control digester
y • Wee-weather digester
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TABLE E-l. GLOSSARY
Anaerobic Digestion -
The process by which organic matter in sludge
is decomposed by bacteria In the absence of
free oxygen. This process usually takes
place under elevated temperatures in an en-
closed tank. A major by-product Is methane
gas.
Basket Centrifuge -
A centrifuge equipped with either an tmper-
forate or perforated cylindrical bowl,
mounted vertically and driven fay means of a
vertical spindle. These types of machines
operate in a batch type mode and are normally
equipped for complete automatic operation.
Bowl Speed -
Rotational speed of the centrifuge bowl
normally expressed in rpm's.
Cake -
The solid phase achieved after centrifuga-
tion of the solid-liquid slurry.
Centrate -
The liquid phase achieved after centrifuga-
tion of the solid-liquid slurry.
Centrifugatton -
The act of separating a mixture of solids
and liquids into a solid phase and a liquid
phase through centrifugal force.
Centrifuge -
A mechanical device utilizing centrifugal
force to achieve solids - liquid separation
of a solid-liquid mixture.
Combined Sewer -
A sewer which carries both sanitary sewage
and storm water run-off,
Combined Sewer Overflow (CSO) -
The flow In a combined sewer which is in
excess of the sewage system capacity. This
excess flow Is commonly diverted to a water
body without treatment.
continued
253
-------
TABLE E-l. (continued)
CSO Sludge -
The precipitated solid matter resulting from
the treatment of combined sewer overflows.
Decanter Centrifuge -
A centrifuge equipped with a horizontal
rotating conveyor mounted within an Inde-
pently rotating bowl. These machines operate
in a continuous mode and are normally equipped
for complete automatic operation.
Dewaterlng -
Any unit operation used to reduce the mo is- '*
ture content of sludge so that It can be
handled and processed as a semi sol id material
instead of a If quid. ' As It refers to this
report - the separation of a mixture of
solids and liquids Into a solids phase
(normally called cake) and a liquid phase
(normally called centrate or clarified
1 iquor).
Differential Speed -
Relative speed between centrifuge bowl and
solids conveyor. (Applies to decanter
centrifuge only).
Dry-Weather Sludge -
The precipitated solid matter resulting from
the treatment of sewage which has not had
its characteristics altered by rainfall,
snow me!ts etc.
Feed -
Solids-liquid slurry pumped Into the centrl'
fuge.
Feed Rate -
Rate of slurry flow pumped into the centri-
fuge, expressed either as 1pm (gpm) or kg
(Ibs) of dry solids per hour.
Polymer -
Organic chemical conditioner or coagulant
used for conditioning sludge prior to cen-
trlfugation.
continued
254
-------
TABLE E-l. (continued)
Pool Radius -
The distance between the center of the ro-
tating bowl and the surface of the liquid
retained within the rotating bowl). (Ap-
plies to decanter centrifuge only).
Scrollabillty -
A characteristic measure of the cake solids
deposited on the centrifuge bowl, (Applies
to decanter centrifuge only).
Skimmings -
Seml-dewatered solids removed from the
accumulated cake in a basket type centrifuge.
Sludge -
The accumulated solids removed from any
liquid processing stream.
Sludge Treatment -
Any unit operation which dewaters or
thickens the precipitated solids resulting
from the treatment of sewage.
Sludge Disposal -
The ultimate placement, distribution or
partial destruction of sludge. Common
methods of sludge disposal include land-
filling, land application, ocean dumping
and incineration.
So!ids Recovery -
A measure of centrifuge performance expressed
In percent suspended solids.
N * weight of sol Ids in solid j)hase (cake)
weight of solids in feed slurry
x 100
Suspended Solids (SS) -
Solids physically suspended in sewage which
can be removed by proper laboratory filtering.
continued
255
-------
TABLE E-1. (continued)
Thickening - Any physical and/or chemical process which
results In the concentration or compaction
of the solid phase of sewage sludges.
Generally, a liquid layer containing rela-
tively low solids 5s removed during the
thickening process.
Total Solids (TS) - The total amount of solids in solution and
suspension.
Waste Activated Sludge (WAS) - That portion of sludge from the secondary
clarlfier in the activated sludge process
that is wasted to avoid a buildup of solids
In the system.
Wet-Weather Sludge - See CSO sludge.
256
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1 REPORT NO,
EPA-600/2-77-053c
2,
3 RECIPIENT'S ACCESSION-NO,
4, TITLE ANOSUBTITLE
HANDLING AND DISPOSAL OF SLUDGES FROM
COMBINED SEWER OVERFLOW TREATMENT
Phase III - Treatability Studies
5 REPORT DATE
December 1977
6, PERFORMING ORGANIZATION CODE
7 AUTHOH(S)
R. Osantowski, A. Geinopolos, R.E. Wullschleger and
M.J. Clark
S, PERFORMING ORGANIZATION REPORT NO
9 PERFORMING ORGANIZATION NAME AND ADDRESS
Environmental Sciences Division
Envirex Inc. (a Rexnord Company)
5103 West Beloit Road
Milwaukee, WI 53214
10. PROGRAM ELEMENT NO.
1BC611
11. CONTRACT/GRANT NO
68-03-0242
12 SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory—Gin, ,OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 45268
13. TYPE OF REPORT AND PERIOD COVERED
Phase Ill-Final 7/75 - 5/77
14 SPONSORING AGENCY CODE
EPA/600/14
is.SUPPLEMENTARY NOTES Project Officer: Anthony N. Tafuri, 201-321-6679, 8-340-6679
Accompanying documents are "Handling atid Disposal of Sludges from Combined Sewer Over-
flow Treatment" Phase I - Characterization (EPA-6QO/2-77-Q53a) and Phase II - Impact
Assessment (rEPA-6QD/2-77-053b'L
18. ABSTRACT " " " "
This report documents the results of a project initiated to evaluate the handling and
disposal of combined sewer overflow (CSO) treatment residuals. Bench scale thickening
and pilot and full-scale centrifugation dewatering tests were performed at dry-weather
and CSO treatment sites in Kenosha, Racine and Milwaukee, WI. In addition, bench
scale anaerobic digestion studies were conducted to determine the effect of CSO
sludges on the anaerobic digestion stabilization process.
The results Indicated that the dewatering of CSO sludges appears feasible when the
sludges are first degritted, where required, and thickened prior to centrifugation.
Under optimum centrifuge operating conditions, thickened sludges were dewatered to
cake concentrations varying from 14.0% to 32% with solids recoveries ranging from 80%
to 99%. Similarly, the dry-weather sludges for the test sites dewatered to haulable
cakes. The bench scale anaerobic digestion studies showed that no significant adverse
effect was realized by adding CSO generated sludges to,dry-weather digesters.
Preliminary economic estimates indicate that first investment capital costs for
thickening-centrlfiguation of CSO sludges ranged from 0.31 to 2.92 million dollars
with annual costs of $49,500 to $659,300 per year when handling 4.0 to 36.5 tons
dry sludge per day, respectively.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DiSCRIPTORS
b.lDENTIFIiRS/OPEN ENDiD TERMS C, COSATI Field/Group
Combined sewers, Sludge, Sludge disposal.
Thickening, Dewatering
Sludge treatment,
Anaerobic digestion,
Centrifugation
13B
18 DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19 SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
271
20 SECURITY CLASS {Thispage)
UNCLASSIFIED
22. PRICE
EPA Farm 2320-1 (3.73)
257
ft U 8. (BVBMffllTf'WItllB Offltt 1OT-S&0-833/47
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