EPA-670/2-73-043
August 1973
Environmental Protection Technology Series
Summary Report: Pilot Plant Studies On
Dewatering Primary Digested Sludge
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C. 20460
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
degradation from point and non-point sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards.
EPA REVIEW NOTICE
This report has been reviewed by the Office of Research and
Development, EPA, and approved for publication. Approval
does not signify that the contents necessarily reflect the
views and policies of the Environmental Protection Agency, nor
does mention of trade names or commercial products constitute
endorsement or recommendation for use.
-------
EPA-670/2-73-043
August 1973
SUMMARY REPORT: PILOT PLANT STUDIES
ON DEWATERING PRIMARY DIGESTED SLUDGE
By
John D. Parkhurst
Raymond F. Rodrigue, Ph.D.
Robert P. Miele
Stephen T. Hayashi
Los Angeles County Sanitation District
Los Angeles, California 90057
Contract No. R801658
Program Element 1B2043
Project Officer
Dr. Robert B. Dean, Chief
Ultimate Disposal Research Program
National Environmental Research Center
Cincinnati, Ohio
Prepared for
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $2.10
-------
ABSTRACT
During the interim from April, 1970 thru January, 1972
an extensive sludge dewatering investigation was con-
ducted at the Joint Water Pollution Control Plant (JWPCP)
a 380-mgd (1.43 million-cu m/day) primary treatment facil-
ity owned and operated by the Los Angeles County Sanita-
tion Districts. Discharge requirements imposed on the
effluent from this facility necessitated that at least
95 percent of the suspended solids be removed from the
primary digested sludge.
The applicability of heat treatment as a means of condi
tioning digested sludge for dewatering was investigated.
Also considered were such conditioning aids as polymers,
chemicals and flyash. Sludge dewatering schemes utilizing
horizontal scroll centrifuges, imperforate basket centri-
fuges, vacuum filters and pressure filters were thoroughly
studied. Operational results were obtained from twenty
conditioning-dewatering test systems of which five suc-
cessfully produced the desired suspended solids removal.
Full scale cost estimates were produced for each of these
five systems.
Estimates were prepared for the requirements and costs
associated with ultimate disposal of dewatered sludges
generated from each successful dewatering scheme. Three
disposal alternatives were considered, namely, truck
hauling of dewatered sludge from the JWPCP to a landfill;
pipeline transport of digested sludge to a landfill with
dewatering and disposal thereat; and incineration at the
JWPCP with truck hauling of the ash residue to a landfill.
Combining the disposal costs with the dewatering costs
yielded estimates for fifteen total sludge handling systems
Remote area transportation and disposal costs were derived
for comparative purposes.
11
-------
It was concluded that a 2-stage centrifuge sludge dewater
ing scheme (polymer addition to the second stage) with
truck hauling of dewatered sludge solids to a landfill
was most suitable for the JWPCP.
This report was submitted in fulfillment of Contract
Number R801658 under the partial sponsorship of the
National Environmental Research Center, United States
Environmental Protection Agency by the Los Angeles County
Sanitation Districts, Los Angeles, California 90057.
111
-------
CONTENTS
Abstract
List of Figures
List of Tables
Acknowledgments
Sections
I SUMMARY $ CONCLUSIONS
II INTRODUCTION
III SANITATION DISTRICTS' WASTEWATER SYSTEM
A. Description of the JWPCP System
B. Characterization of Process Ef-
fluents at JWPCP
C. Background Information Summary
IV RESEARCH APPROACH AND EXPERIMENTAL SETUP
A. Research Site
B. Chemical Station
C. Porteous Process and Accessory
Dewatering Equipment
D. Horizontal Scroll Centrifuge
E. Basket Centrifuge
F. Rotary Drum Vacuum Filter
G. Pressure Filter
H. Incinerator
V CONDITIONING SYSTEMS
A. Porteous Heat Treatment
B. Polymer Conditioning
C. Chemical Conditioning
D. Flyash Conditioning
Page
ii
vi
X
xvi
1
9
13
14
18
24
26
28
31
32
37
41
44
47
50
54
54
63
64
65
IV
-------
CONTENTS-cont'd
Sections Pase
VI DEWATERING SYSTEMS 67
A. Picket Thickening of Cooked 68
Digested Sludge
B. Horizontal Scroll Centrifugation 73
C. Basket Centrifugation 103
D. Vacuum Filtration 118
1) Coil Filter 120
2) Rotary-Belt Vacuum Filter 131
3) Horizontal Belt Filter 136
(Extractor)
E. Pressure Filtration 138
VII SUMMARY DISCUSSION OF TEST WORK 151
VIII COST ESTIMATES 159
A. Dewatering Costs for Two-Stage 160
Centrifugation
B. Dewatering Costs for Coil 162
Filtration
C. Dewatering Costs for Rotary-Belt 164
Vacuum Filtration
D. Dewatering Costs for Pressure 168
Filtration
E. Dewatering Cost Summary 168
F. Ultimate Disposal Cost — Truck 171
Hauling to a Landfill
G. Ultimate Disposal Cost--Pipeline 174
Transport § Landfill Dewatering
H. Ultimate Disposal Cost--Inciner- 181
ation with Landfill Disposal of
Ash Residue
IX COST SUMMARY OF SLUDGE PROCESSING SYSTEMS 185
X COST SUMMARY FOR REMOTE DISPOSAL 192
XI BIBLIOGRAPHY 197
v
-------
FIGURES
No. Page
1 Schematic Flow Diagram--Joint Water Pollu- 15
tion Control Plant
2 Schematic Flow Diagram of Sludge Dewatering 17
Station
3 Joint Water Pollution Control Plant--Sludge 29
Dewatering Research Site
4 Schematic Diagram--Sludge Storage Tanks at 30
Dewatering Research Site
5 Schematic Flow Diagram--Chemical Station 33
6 Heat Conditioning Pilot Plant Assembly 34
7 Schematic Flow Diagram--Heat Conditioning 36
Pilot Plant
8 Cross-Section of a Countercurrent Flow 39
Horizontal Scroll Centrifuge
9 Schematic Diagram of a Basket Centrifuge 42
10 Rotary Drum Vacuum Filter Pilot Plant 45
Assembly
11 Pressure Filter Pilot Plant Assembly 48
12 Skid Mounted Pilot Plant Incinerator Assembly 51
13 Schematic Flow Diagram--Equipment used to 69
Evaluate the Picket Thickening Properties
of Heat Conditioned Digested Sludge
14 Suspended Solids in Decantate as a Function 72
of Overflow Rate in a Picket Thickening
Clarifier
15 The Effect of Decanter Pool Depth on the 79
Centrifugal Recovery of Suspended Solids
from Unconditioned Primary Digested Sludge
VI
-------
FIGURES-cont'd
No. Page
16 The Effect of Decanter Pool Depth on Cake 80
Dryness Obtained During Centrifugal Dewater-
ing of Unconditioned Primary Digested Sludge
17 Dewaterability of Unconditioned Primary Di 82
gested Sludge in a 36-in. x 96-in. Bird
Horizontal Scroll Centrifuge
18 Typical Dewatering Performance Curves for a 83
36-in. x 96-in. Bird Horizontal Scroll
Centrifuge Fed Unconditioned Primary Di-
gested Sludge
19 Horizontal Scroll Centrifuge--Sludge Dewater- 88
ing Performance as Effected by Various
Cationic Polymers
20 Horizontal Scroll Centrifuge--Erratic Sludge 91
Dewatering Performance Obtained with Poly-
mer Usage
21 Schematic Flow Diagram--Dewatering System 92
for Heat Conditioned Sludge
22 Schematic Flow Diagram--Dewatering Systems 93
for Thickened Heat-Conditioned Sludge
23 The Effect of Feed Rate on the Centrifugal 97
Capture of Suspended Solids from Unthick-
ened and Thickened Heat-Conditioned Di-
gested Sludge
24 Suspended Solids Removal by Heat Condition- 99
ing, Optional Thickening and Dewatering
by Horizontal Scroll Centrifugation
25 The Effect of Polymer Dosage on the Centri 102
fugal Capture of Suspended Solids from
Unthickened and Thickened Heat-Conditioned
Digested Sludge
vn
-------
FIGURES-cont'd
No. Page
26 Solids Recovery in a Basket Centrifuge at 106
Different Time Intervals During Feed Cy-
cles at Various Feed Rates
27 The Effect of Feed Rate to a Basket Cen- 108
trifuge on the Resulting Cake
28 Solids Recovery in a Basket Centrifuge at 111
Different Time Intervals During Feed Cy-
cles at Various Feed Rates
29 The Effect of Feed Rate to a Basket Centri- 112
fuge on the Resulting Cake
30 The Influence of Polymer Dosage on Suspend- 114
ed Solids Recovery in a Basket Centrifuge
31 The Effect of Polymer Dosage on Cake Solids 115
from a Basket Centrifuge
32 Profile of Cake Solids Buildup in a Basket 117
Centrifuge at Various Feed Rates
33 Schematic Flow Diagram--Dewatering of 119
Thickened and Unthickened Portrate by
Vacuum Filtration
34 Solids Recovery from Polymer Conditioned 123
Digested Sludge in a Coil Filter at
Various Loading Rates
35 Solids Recovery in a Coil Filter at Two 126
Different Lime Dosages for Various Load-
ing Rates
36 The Effect of Ferric Chloride Dosage on 127
Solids Recovery in a Coil Filter at Two
Different Loading Rates
Vlll
-------
FICURES-cont'd
No.
37 Suspended Solids Removal from Digested 130
Sludge Fed to a System Incorporating
Heat Conditioning, Intermediate Thick-
ening and Vacuum Filtration of the
Thickened Portrate Stream in a Coil Filter
38 The Effect of Feed Time on Cake Solids 143
During Pressure Filtration of Digested
Sludge
39 The Effect of Feed Time on Cake Solids 144
During Pressure Filtration of Digested
Sludge
40 Loading Rate as a Function of Feed Time 145
During Pressure Filtration of Chemically
Conditioned Digested Sludge
IX
-------
TABLES
No.
Average Solids Makeup of Various Process 20
Effluents at JWPCP
Average Chemical Composition and 'MPN' 21
Content in Various Process Effluents
at JWPCP
Effluent Qualities and Effluent Quality 23
Requirements at JWPCP
Data Summarizing the Solids Characteristics 56
of 'JWPCP1 Primary Digested Sludge Both
Before and After 30 Minutes of Cooking
at Various Reactor Temperatures
Data Summarizing the Solids Characteristics 57
of 'JWPCP1 Primary Digested Sludge Both
Before and After 40 Minutes of Cooking
at Various Reactor Temperatures:
Data Summarizing the "COD" Characteristics 58
of 'JWPCP' Primary Digested Sludge Both
Before and After 50 Minutes of Cooking
at Various Reactor Temperatures
Data Summarizing the "COD" Characteristics 59
of 'JWPCP' Primary Digested Sludge Both
Before and After 40 Minutes of Cooking
at Various Reactor Temperatures
Data Summarizing the Quiescent Settling 60
Characteristics of Suspended Solids in
30-Minute Heat-Conditioned Digested
Sludge
Data Summarizing the Quiescent Settling 61
Characteristics of Suspended Solids in
40-Minute Heat-Conditioned Digested
Sludge
x
-------
TABLES-cont'd
No. Page
10 Data Summarizing the Effect of Clarifier 71
Overflow Rate on the Picket Thickening
Properties of Cooked Digested Sludge
11 Data Summarizing the Effect of Varying 74
Pool Depths on the Dewatering Perfor-
mance of a Horizontal Scroll Centrifuge
When Fed Primary Digested Sludge in a
200-GPM Flowstream
12 Data Summarizing the Effect of Varying 75
Pool Depths on the Dewatering Perfor-
mance of a Horizontal Scroll Centrifuge
When Fed Primary Digested Sludge in a
250-GPM Flowstream
13 Data Summarizing the Effect of Varying 76
Pool Depths on the Dewatering Perfor-
mance of a Horizontal Scroll Centrifuge
When Fed Primary Digested Sludge in a
3QO-GPM Flowstream
14 Data Summarizing the Effect of Varying 77
Pool Depths on the Dewatering Perfor-
mance of a Horizontal Scroll Centrifuge
When Fed Primary Digested Sludge in a
550-GPM Flowstream
15 Data Summarizing the Effect of Varying 78
Pool Depths of the Dewatering Perfor-
mance of a Horizontal Scroll Centrifuge
When Fed Primary Digested Sludge in a
400-GPM Flowstream
16 Data Summarizing the Sludge Dewatering 85
Performance of a Horizontal Scroll Cen-
trifuge as Effected by Varying Dosages
of Nalco 610
XI
-------
TABLES-cont'd
No. Page
17 Data Summarizing the Sludge Dewatering 86
Performance of a Horizontal Scroll Centri-
fuge as Effected by Varying Dosages of
WT-2570
18 Data Summarizing the Sludge Dewatering Per- 87
formance of a Horizontal Scroll Centrifuge
as Effected by Varying Dosages of
Hereoflo.c 810--Run No. 1
19 Data Summarizing the Sludge Dewatering Per- 90
formance of a Horizontal Scroll Centrifuge
as Effected by Varying Dosages of
Hercofloc 810--Run No. 2
20 Data Summarizing the Dewaterability of 95
Unthickened Heat-Conditioned Digested
Sludge by Horizontal Scroll Centrifugation
21 Data Summarizing the Dewaterability of 96
Thickened Heat-Conditioned Digested
Sludge by Horizontal Scroll Centrifugation
22 Data Summarizing the Centrifugal Dewaterabil- 100
ity of Unthickened Heat-Conditioned Digest-
ed Sludge with Polymer Conditioning
23 Data Summarizing the Centrifugal Dewaterabil 101
ity of Thickened Heat-Conditioned Digested
Sludge with Polymer Conditioning
24 Data Summarizing the Dewatering Performance 105
of a Basket Centrifuge at Various Feedrates
25 Data Summarizing the Effect of Polymer Addi 109
tion on the Dewatering Performance of a
Basket Centrifuge at Various Feedrates
26 Data Summarizing the Effect of Varying Poly- 113
mer Dosages on the Dewatering Performance
of a Basket Centrifuge
XII
-------
TABLES-cont'd
No. Page
27 Data Summarizing the Build-Up of Cake 116
Solids Within a Basket Centrifuge for
Various Feedrates
28 Data Summarizing the Effect of Loading 122
Rate on the Filtration Characteristics of
Polymer Conditioned Digested Sludge in a
Vacuum Coil Filter
29 Data Summarizing the Dewatering Characteris- 125
tics of Chemically Conditioned Digested
Sludge in a Vacuum Coil Filter
30 Data Summarizing the Dewatering Characteris- 129
tics of Thickened Heat-Conditioned Digested
Sludge by Vacuum Coil Filtration
31 Data Summarizing the Dewatering Characteris- 132
tics of Polymer Conditioned Digested
Sludge in a Rotary-Belt Vacuum Filter
32 Data Summarizing the Dewatering Characteris- 133
tics of Chemically Conditioned Digested
Sludge in a Rotary-Belt Vacuum Filter
33 Data Summarizing the Dewatering Characteris- 134
tics of Thickened Heat-Conditioned Digested
Sludge by Rotary-Belt Vacuum Filtration
34 Data Summarizing the Dewatering Characteris- 137
tics of Thickened Heat-Conditioned Digested
Sludge by Vacuum Extraction
35 Data Summarizing the Dewatering Characteris- 142
tics of Chemically Conditioned Digested
Sludge in a Pressure Filter
36 Data Summarizing the Effects of Ash and Lime 147
Addition to Digested Sludge on Dewatering
Performance in a Pressure Filter
Xlll
-------
TABLES-cont'd
No.
37 Data Summarizing the Dewatering Characteris- 149
tics of Unthickened and Thickened Heat-
Conditioned Digested Sludge by Pressure
Filtration
38 Data Summarizing the Optimum Performance of 152
Various Investigated Sludge Conditioning
and Dewatering Systems at JWPCP
39 Performance Summary of Five Selected Dewater- 158
ing Schemes Having Full-Scale Potential for
Meeting the Imposed Discharge Standards
40 Cost Estimate Summary for Two-Stage Centrifu- 161
gation
41 Cost Estimate Summary for Vacuum Coil Filtra- 163
tion with Polymer Conditioning
42 Cost Estimate Summary for Rotary-Belt Vacuum 165
Filtration with Lime Conditioning
43 Cost Estimate Summary for Rotary-Belt Vacuum 166
Filtration with Heat Conditioning and Inter-
mediate Thickening
44 Cost Estimate Summary for Pressure Filtration 169
with Lime and Ferric Chloride Conditioning
45 Summary of Cost Estimate for Five Potential 170
Full-Scale Sludge Dewatering Schemes
46 Itemized Costs for Landfill Hauling and Dis- 175
posal of Dewatered Sludge from Various De-
watering Systems
47 Summary of Costs for Landfill Hauling and 176
Disposal of Dewatered Sludge from Various
Dewatering Systems
48 Itemized Pipeline-Disposal Costs for Various 179
Dewatering Systems
xiv
-------
TABLES-cont'd
No. Page
49 Summary of Pipeline-Disposal Costs for 180
Various Dewatering Systems
50 Itemized Costs for Dewatered Sludge Incinera- 182
tion with Ash Hauling to a Landfill
51 Summary of Costs for Dewatered Sludge Incin- 183
eration with Ash Hauling to a Landfill
52 Total Sludge Handling Cost Summary--Dewater- 186
ing at JWPCP with Truck Hauling for Land-
fill Disposal
53 Total Sludge Handling Cost Summary--Pipe- 187
line Transportation and Landfill Dewater-
ing and Disposal
54 Total Sludge Handling Cost Summary--Dewater- 189
ing and Subsequent Incineration at JWPCP
with Truck Hauling of Ash to Landfill
55 Summary Cost Comparison of Alternative Sludge 190
Handling Systems
56 Remote Area Transportation and Ultimate 195
Disposal Costs
57 Comparison of Remote Disposal System Costs 195
xv
-------
ACKNOWLEDGEMENTS
The research done during the course of this project and
reported on herein would not have been possible without
the cooperation and assistance of personnel of the various
companies whose equipment was represented in the sludge
dewatering program. These companies are mentioned through-
out the report. Also deserving recognition for his contri-
bution to the preparation of this report is Mr. David D.
Herold, Assistant Project Engineer. Grateful appreciation
is extended to Rochelle Armijo for her valuable assistance
in typing this manuscript and to Elliott Tsujiuchi,
Vladimir Novy and John Cussen for their valuable assistance
in providing the illustrations which accompanied the text.
Special thanks are given to the Districts' Maintenance
personnel for their assistance in installing, operating
and maintaining the various pilot plant units tested, to
the Districts' Laboratory personnel for the sample analyses
which provided the evaluative data presented herein and to
others in the Districts' engineering staff who provided
input for this investigation. Dr. Robert B. Dean, Chief,
Ultimate Disposal Research Program, EPA, National Environ-
mental Research Center, Cincinnati, Ohio, served as
Project Officer.
xvi
-------
SUMMARY § CONCLUSIONS
The Los Angeles County Sanitation Districts conducted a 14-
month pilot and plant scale sludge dewatering research pro-
gram aimed at selecting a system to remove approximately
95 percent of the suspended solids contained in high rate
anaerobically digested primary sludge. An existing dewater-
ing system at the site of the research consisted of six
36-in. x 96-in. (91.4-cm x 243.8-cm) horizontal scroll cen-
trifuges. During the course of the study both digested
sludge and centrate from the existing centrifuges were used
as feed to the various dewatering systems investigated.
Based on the results of the research, cost estimates for
dewatering and ultimate disposal of 300 dry tons (272 metric
tons) per day of wastewater solids were prepared.
The following conclusions have been drawn from the study:
Sludge Conditioning
1. High suspended solids recovery from digested sludge
was not attainable without some form of conditioning.
Acceptable results were obtained by the addition of
polymers, lime and ferric chloride in various combina-
tions .
2. Optimum dosage ranges per ton of solids were: cationic
polymer, 3-10 Ibs/ton (1.5-5.0 kg/metric ton); lime as
Ca(OH)2, 500-600 Ibs/ton (250-300 kg/metric ton);
ferric chloride, 80-120 Ibs/ton (40-60 kg/metric ton).
3. Heat conditioning also produced sludges which could be
dewatered on the experimental equipment. Optimal heat
conditioning of digested sludge occurred at a tempera-
ture of 350°F (175QC) and a detention time of 40 min-
utes .
4. Gravity sedimentation of heat conditioned sludge was
enhanced by picket thickening. The performance of a
picket thickening clarifier on optimally heat-condi-
tioned digested sludge was such that at an overflow of
225 gpd/sq ft (9.2 cu m/day/sq m), a decanted liquor
-------
containing 3700 mg/1 o£ suspended solids was obtained;
higher overflow rates yielded increased concentrations
of suspended solids in the decantate.
Dewatering: Horizontal Scroll Centrifugation
1. A 36-in. x 96-in. (91.4-cm x 243.8 cm) horizontal
scroll centrifuge was operated at a bowl speed of
1300 rpm (900 gravities) and a differential speed of
15 rpm. Tests on unconditioned digested sludge pro-
duced the following results:
a. At a constant feed rate, increasing the pool
depth increased both suspended solids recovery
and cake moisture content, while at a constant
pool depth, solids recovery decreased and cake
dryness increased with increasing feed rate.
b. The maximum solids recovery attainable was 55
percent at a feed rate of 200 gpm (12.6 I/sec)
and a maximum pool depth setting of 3.4 inches
(8.6 cm); dewatered sludge cake was 21% solids
by weight.
2. Under the same machine operating conditions as listed
above, cationic polymer conditioning at a constant
feed rate of 250 gpm (15.8 I/sec) in the 36-in. x
96-in. (91.4-cm x 243.8-cm) horizontal scroll centri
fuge produced the following results:
a. The highest solid recovery was achieved when
polymer was injected into the sludge stream
within the bowl of the centrifuge; polymer in-
jection into either the suction or discharge
lines of the feed pump yielded lower recovery.
b. Apparent changes in the characteristic of di-
gested sludge from day to day influenced the
ability of polymers to enhance suspended solids
capture in the centrifuge. Results obtained
under identical operating conditions were un-
predictable .
c. Under responsive sludge conditions the polymer
dosage necessary to achieve 95 percent solids
recovery was about 10 Ibs/ton (5.0 kg/metric ton);
dewatered sludge cake was 20% solids by weight.
3. Using a 6-inch (15.2-cm) diameter pilot scale horizon-
tal scroll centrifuge, a maximum suspended solids
-2-
-------
removal of 81 percent was obtained with a system
employing heat conditioning of digested sludge followed
by horizontal scroll centrifugation; the same system
obtained about 90 percent removal with the addition of
3.5 Ibs/ton (1.75 kg/metric ton) of polymer to the
bowl of the centrifuge. In both cases, generated cakes
were 31% solids by weight.
4. Dewatering of digested sludge--heat conditioned and
thickened--in a 6-inch (15.2 -cm) diameter horizontal
scroll centrifuge yielded a suspended solid removal
of 85 percent; about 91 percent removal was experienced
with the addition of 3.0 Ibs/ton (1.5 kg/metric ton)
of polymer to the centrifuge bowl; cake solids were
approximately 25% by weight.
Dewatering: Basket Centrifuges
1. Without sludge conditioning, tests conducted with a
basket centrifuge operated at 1300 gravities and fed
centrate from the existing horizontal scroll centri-
fuges revealed that:
a.
Average solids recovery varied inversely with
feed rate.
b. A maximum solids recovery of 80 percent was
attained; corresponding cakes were at 8% solids
by weight.
2. Tests conducted with cationic polymer conditioning of
centrate fed to a basket centrifuge revealed:
a. Solids recovery was highest when the polymer
solution was sprayed into the sludge stream
within the bowl; polymer injection into either
the suction or discharge lines of the feed pump
yielded lower recoveries.
b. With a polymer dosage above 1-2 Ibs/ton
(0.5-1.0 kg/metric ton), a solids recovery of
95 percent was obtained. Recovery was not
greatly affected by increased feed rates.
c. At a given feed rate, increased polymer dosages
served to increase the duration of the feed
cycle which resulted in increased cake dryness.
d. Optimum results indicated that the basket cen-
trifuge could capture 95 percent of the suspended
solids from the centrate of the horizontal scroll
-3-
-------
centrifuge, producing a cake of about 201 solids
by weight. A polymer dosage of 4 Ibs/ton
(2 kg/metric ton) was required to obtain this
performance.
e. A system of basket centrifuges in series with
horizontal scroll centrifuges yielded an effluent
containing 1500 mg/1 or less of suspended solids
and generated cakes (1st and 2nd stage blends)
of 25% solids by weight; a polymer dosage of
4 Ibs/ton (2 kg/metric ton) is added to the bas-
ket centrifuge.
Dewatering: Vacuum Filters
1. Vacuum coil filtration tests on digested sludge re-
vealed that:
a. With polymer conditioning, consistent suspended
solids recovery of 95 percent was only achieved
with dosages of 10 Ibs/ton (5 kg/metric ton) or
more; erratic recovery occurred at lesser
dosages.
b. At a polymer dosage of 10 Ibs/ton (5 kg/metric
ton), solids recovery and generated cake (18%
solids by weight) remained unaffected by varia-
tions in solid loading rates up to 18 Ibs/
hr/sq ft (87.8 kg/hr/sq m).
c. With lime and ferric chloride conditioning,
suspended solids capture varied inversely with
solids loading rate, although cake dryness
(about 25% solids by weight) was relatively
unaffected.
d. A maximum solids recovery of 92 percent was
experienced at a solids loading rate of
1.5 Ibs/hr/sq ft (7.3 kg/hr/sq m) and a lime,
as Ca(OH)2, and ferric chloride dosage of
600 Ibs/ton (300 kg/metric ton) and 80 Ibs/ton
(40 kg/metric ton), respectively; greater or
lesser amounts of ferric chloride or lesser
amounts of lime produced inferior re-
sults .
e. A maximum suspended solid recovery of 70 percent
was experienced from a system employing heat
conditioning, thickening and filtration of
-4-
-------
digested sludge at a solids loading rate of
3 Ibs/hr/sq ft (14.6 kg/hr/sq m); cake solids
were approximately 31% by weight.
2. Rotary-belt vacuum filtration tests on digested sludge
revealed that:
a. When polymer conditioning was attempted, rapid
blinding of the filter media occurred.
b. With lime conditioning, suspended solids re-
covery in excess of 99 percent was achievable
at a lime dosage of 600 Ibs/ton (300 kg/metric
ton) as Ca(OH)2 and a maximum solids loading of
1.5 Ibs/hr/sq ft (7.3 kg/hr/sq m); generated
cakes were 35% solids by weight. This perfor-
mance was not enhanced by the inclusion of ferric
chloride conditioning.
c. A system employing heat conditioning and thicken-
ing prior to filtration produced a maximum sus-
pended solids removal of 92 percent and, corres-
pondingly, discharged cake having a solids con-
tent of 37% by weight; the maximum solids loading
rate to the filter was 3.3 Ibs/hr/sq ft
(16.1 kg/hr/sq m).
Dewatering: Pressure Filter
1. Rapid blinding of the filter media occurred when
cationic polymers were used as the conditioning aid.
2. When chemical (lime and ferric chloride) or ash con-
ditioning was employed, the resulting filtrates
generally contained less than 100 mg/1 of suspended
solids; increasing the length of the feed cycle
effected an increase in cake dryness and a corres-
ponding decrease in the overall solids loading.
3. For a particular lime dosage and feed time, drier
cakes were generated as the ferric chloride dosage was
increased up to 120 Ibs/ton (60 kg/metric ton).
4. With chemical conditioning, optimum performance was
achieved with a 2-hour run time and a lime, as CafOH^,
and ferric chloride dosage of 500 Ibs/ton
(250 kg/metric ton) and 120 Ibs/ton (60 kg/metric ton),
respectively; generated cakes were 40% solids by weight
5. Ash conditioning was most successful when a small
amount of lime was included for raising the pH;
-5-
-------
optimum performance was acheived with an ash dosage
of 4000 Ibs/ton (2000 kg/metric ton).
6. Using a diatomaceous earth precoat, pressure filtra-
tion of heat conditioned sludge yielded filtrates
containing less than 100 mg/1 of suspended solids;
generated cakes were 30% solids by weight but dis-
charged poorly from the filter cloth media.
7. Although pressure filtration of thickened, heat
conditioned sludge produced cakes (38% solids by
weight) having excellent discharge properties, the
combined effluent (filtrate plus thickener overflow)
from such a system contained 3100 mg/1 of suspended
solids„
Disposal
1. Truck hauling of dewatered sludge to a landfill,
pipeline transport of digested sludge to a landfill
with subsequent dewatering at the landfill, and
incineration with ash hauling to a landfill were
considered for ultimate sludge disposal. Preliminary
investigations indicated thatultimate disposal of
sludge to the land via soil reclamation or lagooning
could also hold promise as a long term sludge dis-
posal scheme.
2. Although there may be some minor economic advantages
to be gained from incineration, the potential air
pollution problems associated with incineration were
such that the process was not considered to be a
feasible solution for ultimate sludge disposal in the
Los Angeles Basin.
3. The lack of sufficient technical knowledge concerning
soil reclamation or lagooning preclude these disposal
methods from immediate consideration.
Costs
Estimates for dewatering and disposal were based on
300 dry tons/day (272 metric tons/day). This number
was selected as representing existing sludge quantities
arid was used for comparative purposes. Actual quanti
ties used in the design of a full scale system are
higher than 300 tons/day (272 metric tons/day) . A
10-year life was assumed for all equipment for pur-
poses of capital amortization at 6%.
-6-
-------
2. Cost estimates for the five combinations of sludge
conditioning and dewatering which met the established
criteria indicated the unit cost ranged from $11.10/ton
($12.20/metric ton) for a two-stage centrifugation
system utilizing polymer conditioning in the second
stage to $28.30/ton ($31.20/metric ton) for a pressure
filtration system using lime and ferric chloride as
conditioning agents.
3. The cost of truck hauling of dewatered sludge to a
landfill varied directly with the quantity of sludge
to be hauled. Total cost varied from $10.90/ton
($12.00/metric ton) for heat conditioned, gravity
thickened, vacuum filtered sludge to $23.00/ton
($25.40/metric ton) for the polymer conditioned,
vacuum filtered sludge.
4. Combining dewatering and truck hauling estimates
yielded costs ranging from $29.10/ton ($32.10/metric
ton) for a two-stage centrifuge system to $44.00/ton
($48. 50/metric ton) for a pressure filtration system.
5. Cost estimates for pipeline transport to a landfill
varied from $15.25/ton to $22.10/ton ($16.80/metric ton
to $24.40/metric ton).
6. Combining dewatering estimates with the pipeline
transport scheme for disposal yielded costs ranging
from $29.50/ton ($32.50/metric ton) for heat condi
tioning, gravity thickening, vacuum filtration de-
watering to $44.80/ton ($49.40/metric ton) for pressure
filtration of lime and ferric chloride conditioned
sludge.
7. Incineration costs ranged from $8.30/ton to $24.50/ton
($9.20/metric ton to $27.00/metric ton). These esti-
mates were based on certain assumed air pollution
control equipment.
8. The most economical sludge processing system for
the JWPCP based on cost estimates for dewatering and
disposing of 300 dry tons/day (272 metric tons/day)
was a two-stage centrifuge system utilizing polymer
conditioning in the second stage with disposal by
truck hauling to a landfill.
System Selection
1. A two stage centrifuge system utilizing polymer con-
ditioning' was selected as the dewatering system for
the JWPCP because:
-7-
-------
a. The system produced very reliable results
throughout the study.
b. A two stage system will allow continued use of
the horizontal scroll system which offers the
advantage of familiarity of operation on the
part of the JWPCP staff.
c. It provides the lowest total cost system of
those meeting the quality criteria.
Truck hauling to a landfill was selected over pipe-
line transport to the landfill for the following
reasons:
a. The lower capital cost and greater flexibility
of a truck hauling system.
b. The pipeline system would have required too long
a time period to construct.
c. The dewaterability of the digested sludge when
it reached the landfill via pipeline was unknown,
-8-
-------
INTRODUCTION
One of the most difficult aspects of wastewater treatment
today is the processing and disposal of sewage sludges. A
large portion of the waste treatment methods in use through-
out the country only serve to concentrate the incoming
pollutional material into a reduced portion of the total
waste flow. Assuming that discharge standards are met, this
permits easy disposal of the bulk of this flow to a natural
water environment. It is the residual concentrate, i.e. the
sludge remaining, which must undergo additional and more re-
fined processing prior to being acceptable for discharge in-
to one of nature's reservoirs.
Numerous processes or combinations thereof are being used
throughout the country for treating and handling wastewater
sludges. Typical among these are such processes as sludge
thickening; aerobic digestion; conventional or high rate
anaerobic digestion; elutriation; sludge conditioning with
chemicals, polymers, flyash, heat, etc; lagooning; mechanical
dewatering; dehydration; and incineration. In any particular
treatment facility, the applicability of a sludge handling
step is primarily dependent on the sludge type, its physical
and chemical makeup, and the character of the wastewater from
which the sludge was derived. Of course, the overall success
of any sludge handling scheme depends on how well each pro-
cess is selected and combined with one another in order to
meet the disposal requirements of a particular situation.
The use of anaerobic digestion to stabilize and render
sludges innocuous for final disposal is practiced at many
wastewater treatment plants including the Joint Water Pollu-
tion Control Plant (JWPCP)--a coastal, primary treatment
facility owned and operated by the County Sanitation Districts
of Los Angeles County, hereinafter referred to as the
"Districts". Prior to 1959, the waste digested sludge from
this facility was processed on open drying beds located
adjacent to the plant. Increasing residential and commercial
growth coupled with the difficulty of maintianing a nuisance-
free operation led to the eventual abandonment of this
practice.
-9-
-------
Present treatment operations at the JWPCP provide for sludge
handling in the following manner. Raw primary sludge (6%
solids) is pumped into digesters wherein it is subjected to
high-rate anaerobic decomposition. Following an 11 to 12-day
digestion period, waste digested sludge (4% solids) undergoes
partial dewatering by means of solid bowl centrifugation.
The centrifuged effluent, hereinafter referred to as centrate,
is screened to remove large-sized floatable material. The
screened centrate is processed through a sludge washing tank
to remove any floatable material remaining. Approximately
30 percent of the suspended material is removed from the
digested sludge by centrifuging, screening and washing prior
to ocean discharge. The dewatered solids (centrifuged cake
and centrate screenings) are spread on adjacent acreage and
allowed to air dry; this material is then taken by a fertili-
zer company for incorporation into various fertilizer pro-
ducts .
Throughout the 1960's, the discharge of centrate to the
marine environment had been acceptably practiced at the
JWPCP. During that period, the ocean waters adjacent to the
outfall discharge point were monitored to insure that the
water quality standards placed on the receiving body were
being met.
In September of 1970 the Los Angeles Regional Water Quality
Control Board promulgated new standards on the effluent
being discharged to the ocean from the JWPCP. It was readily
apparent that compliance with the new edict would require a
major supplementation to the existing treatment facilities.
Additional primary clarifier capacity would be needed to
bring about greater suspended solids removal from the in-
coming wastewater stream. Moreover, the new standards man-
dated a criterion for a sludge dewatering system which
would be capable of recovering at least 95 percent of the
suspended material from the waste digested sludge stream,
i.e. the effluent from such a system would be expected to
contain no more than 1500 mg/1 of suspended solids. :
Consideration was then given to the sludge quantities in-
volved at the JWPCP, to the complexities and anticipated
high costs associated with solids capture to the extent
demanded, and to the alternatives available for dewatered
solids disposal. One of the first decisions that had to be
made was whether or not to retain anaerobic digestion as an
integral part of the sludge handling system. Despite the
fact that raw sludges were known to be more easily de-
watered, the Districts decided in favor of digestion in
view of the extensive commitment already made to that pro-
cess at the JWPCP.
-10-
-------
The Districts approach to the sludge problem was threefold.
First, methods of additional dewatering of the centrate
material from the existing horizontal scroll centrifuge sta-
tion would be sought out. This would provide the advantage
of utilizing dewatering equipment already installed and also
offer the potential to continue the supply of solids for
fertilizer production. The second approach was to investi
gate dewatering schemes which would not incorporate usage
of the existing centrifuge station. Finally, an analysis
of each of the successfully contrived dewatering schemes
would be made along with the alternatives for dewatered
solids disposal so as to arrive at the most practical and
economical means of solving the problem.
Beginning in November 1970, the manufacturers of various
sludge conditioning products and sludge dewatering equipment
were sought out regarding the applicability of their merchan-
dise to the sludge problem at the JWPCP. A study was con-
ducted to determine the dewatering capabilities of the
existing solid bowl centrifuge station as influenced by
variations in several parameters. Promising sludge con-
ditioners and other dewatering equipment were evaluated on
a pilot plant scale. Each dewatering unit was evaluated by
itself and in conjunction with one another as a total system.
A research site was constructed on the premises of the JWPCP
to accomodate the pilot plant units. A small chemical sta-
tion was built for batching polymers into solution. Also,
one of the existing solid bowl centrifuges was isolated and
rigged for test purposes. By January of 1971, the 2-year
research program was underway.
The following is a report on the results of the piloted
research work conducted at the JWPCP. Details are presented
on the performance of each of the conditioning-dewatering
systems investigated. Of the many schemes evaluated, five
were selected which, in addition to meeting the effluent
requirements, were judged to provide a practical and econo-
mical solution to the problem. In this regard, full scale
cost estimates were prepared for each and are presented
herein.
Consideration was then given to the manner in which dewatered
solids could be ultimately disposed of. For each of the
five chosen dewatering schemes, cost estimates were prepared
for the ultimate disposal of these solids by three methods,
namely
-11-
-------
(1) Landfilling, with pipeline transport of primary
digested sludge to a landfill for dewatering and
solids disposal;
(2) Landfilling, with truck transport of the dewatered
solids from the JWPCP to a landfill;
(3) Incineration at the JWPCP with truck transport of
the ash to a landfill.
These costs are also presented in this report. The alter-
native costs of the five dewatering schemes and three dis-
posal schemes were then combined to provide fifteen total
system cost alternatives. This, along with other intangible
criteria, enabled the Districts to select a sludge management
system most suitable for their situation.
In addition to the above, a brief study was made of the costs
for remote disposal of JWPCP's digested sludge. The esti-
mates were made to aid in the selection of a dewatering pro-
cess which might prove to be compatible with some future
sludge disposal scheme utilizing a remote area. These
estimates are presented and discussed in this report.
12-
-------
SANITATION DISTRICTS' WASTEWATER SYSTEM
The County Sanitation Districts of Los Angeles County is
comprised of 26 individual districts. As a combined group
they form one of the largest systems in existence today.
At present, the Districts provide service for 71 incorporated
cities and several large tracts of unincorporated land.
Together, they constitute a 730 sq mile (1891 sq km) area
from which 450-mgd (1.70 million cu m/day) of wastewater is
derived. The collective population being served in this area
is now approaching 4 million people. The Districts handle
70 percent of the total industrial wastewater load generated
within Los Angeles County which amounts to about 180 mgd
(0.68 million cu m/day). Thus, 40 percent of the municipal
wastewater managed by the Districts is of industrial origin.
Characteristically then, the overall wastestream is quite
atypical and, in many respects, is difficult to treat.
At present, the Sanitation Districts manages and operates
eleven wastewater treatment facilities, the largest of which
is the Joint Water Pollution Control Plant (JWPCP) -- a
380-mgd (1.43 million cu m/day) primary treatment facility
located in the City of Carson, California. The JWPCP is
situated in the southern part of Los Angeles County approxi-
mately 6 miles (9.7 km) from the Pacific Ocean. The other
10 treatment plants -- secondary treatment facilities which,
within their own respective capacity, process wastewater
flows ranging from 0.3 to 31 mgd (1100 to 117,300 cu m/day)--
collectively handle the remaining 70 mgd (0.27 million cu
m/day) and are situated more inland and further to the north.
Five small inland plants provide separate treatment and
disposal of their own generated sludges. The other five
plants, which collectively process 63 mgd (0.24 million cu
m/day) of wastewater, each discards its accumulated raw
primary and secondary sludges into the sewer system which
ultimately terminates at the JWPCP. The sludge solids load
imposed on the JWPCP treatment facility, therefore, repre-
sents that derived from 443 mgd (1.68 million cu m/day) of
wastewater flow, that being 98.4 percent of the Districts'
total wastewater responsibility.
-13-
-------
DESCRIPTION OF THE JWPCP SYSTEM
The Joint Water Pollution Control Plant has been in opera-
tion since about 1935. Since that time, Los Angeles County
has experienced considerable dynamic growth in both popu-
lation and industry. To cope with this, the JWPCP_has had
to be periodically expanded and augmented to provide suf-
ficient capacity and treatability for the increased waste-
water flow.
The sewerage system tributary to the JWPCP consists of a
vast network of interceptors and trunk lines which carries
domestic wastewater from the dwellings of nearly 4 million
people. An estimated 30,000 industries and commercial
establishments are serviced by the network. In certain
areas, the system is also utilized for the disposal of oil
brine wastes. Upon reaching the terminus, 380 mgd (1.43
million cu m/day) of a highly mineralized waste mixture
enters the JWPCP for treatment.
Figure 1 is a schematic of the existing treatment and dis-
posal system at the JWPCP. Wastewater flows into the plant
through several trunk sewers. From the inlet works, it is
introduced to a parallel system of fixed bar screens for
removal of coarse-sized suspended material. Automechanical
rakes remove the trapped screenings from within the flow-
stream. The rakings are conveyed to a parallel system of
grinders, ground to smaller fractions, and reintroduced
into the plant influent for precautionary rescreening.
The effluent passing through the screens is hydraulically
lifted when necessary, prechlorinated for odor control,
and then directed to a system of aerated grit chambers where
in the flow through velocity is sufficiently reduced to
facilitate the sedimentation of grit. Dispersed air bubbles
serve to scrub the descending grit free of lighter organic
material. Settled grit is continuously scraped from the
bottom of each chamber, conveyed into a drainage hopper, and
later hauled by truck to a landfill for disposal. The
effluent from the grit chambers is channeled into a network
of primary sedimentation tanks which have a detention time
of approximately one hour. Primary effluent is directed to
the effluent pump works to be transported to the ocean for
disposal.
The pumping of raw sludge from the primary sedimentation
tanks is controlled by radioactive density meters. The con-
trol is such that a raw sludge mixture of about 6% suspended
solids concentration (60,000 mg/1) is maintained during
14-
-------
FIGURE I
Schematic flow diagram
Joint Water Pollution Control Plant
PRECHLORINATION
POST CHLORINATION
6 MILES i
8' TUNNEL
12 TUNNEL
MANIFOLD
STRUCTURE
CENTRATE
WASH
TANK
WASTE BURNING
GAS TO
CONTRACTOR
GAS
P UMP
EF FLUENT PUMP
8 GENERATOR
GAS ENGINES
BOILERS
AUTOMATIC
SLUDGE FEED
CONTROLS
SLUDGE
DENSITY
MEASUREMENT
CENTRATE
GAS
RECYCLE.
SLUDGE
GAS
STEAM
SLUDGE
DICE STION
TANKS
DEWATERING STATION
DETAILED IN FIGURE 2)
DRIED SLUDGE TO
•»*
FERTILIZER CONTRACTOR
-------
removal. This material is then fed in an automatically
prearranged manner to a battery of high-rate anaerobic
digestion tanks. Gas is collected at the top of each tank
for drawoff. A portion of this gas is recycled through
several vertical draft tubes located in each tank. A gas
lifting effect results in each tube which, in turn, imparts
a slow continuous turnover or mixing of the tanks' contents.
Mixing, along with direct steam injection (controlled to
maintain the mixture at a temperature of 94°F) , produces
high rate digestion. The sludge gas is utilized for fuel
to operate both the digester steam boilers and the large
gas engines which drive the effluent pumps and electrical
generators at the JWPCP. Surplus gas is sold to an adjacent
oil company or burned off as waste. A standby propane supply
is also available to supplement the digester gas fuel. The
digester operation at JWPCP effectively reduces the volatile
matter content of the raw sludge by about 50 percent and
produces approximately 5.2 million cu ft/day (145,600 cu
m/day) of useable digester gas having an average heat
value of 600 BTU/std cu ft (5400 kg-cal/std cu m).
Following an 11- to 12-day residency time, the digested
sludge is collected in a holding tank (wet well) for control-
led pumping to a dewatering station consisting of centrifuges
and vibrating screens. A detailed schematic of this
station is shown in Figure 2. Six centrifuges (36-in. x
96-in. (91.4-cm x 243.8-cm) horizontal scroll decanter type
manufactured by Bird Machine Company) are arranged 3 in
a row on both sides of a common pipe gallery containing the
digested sludge feed line, the centrate drain line and a
wash water supply line. The configuration of the piping
network is such that the machines operate in parallel to
one another. Digested sludge, pumped from the sludge wet
well, is fed into branch lines leading to each centrifuge.
The centrate from each machine flows by gravity into a
common drain line leading to the centrate collection well,
A pump transfers centrate from the collection well to a paral
lei operating system of vibrating screens. Gravity flow o£
the screened centrate to a wash tank follows. The centri-
fuged cake solids and screenings are blended and conveyed
into a truck for spreading and open air drying on land ad-
jacent to the dewatering station. Daily mechanical turning
of the land spread solids accelerates the air drying process
and provides enhanced aerobic conditioning and reduced odor
levels. After one month, the dried solids are removed by
a contractor for incorporation into soil conditioning ferti
lizer products.
-16-
-------
FIGURE 2
Schematic flow diagram of sludge dewatering station
CENTRIFUGES
CAKE AND SCREENINGS
TO DRYING BEDS
VIBRATING SCREENS
CENTRIFUGES
DIGESTED
SLUDGE
CAKE AND SCREENINGS
TO DRYING BEDS
SCREENED
CENTRATE
TO SLUDGE
WASH TANK
-------
Upon entering the wash tank, screened centrate is elutriated
with 2 parts of water to wash the centrate solids free of
surplus floatables and grease. These are skimmed off and
recycled back to the digester. The washed centrate is then
directed for dilution with the primary effluent being
channeled to the effluent works. This final effluent blend
is chlorinated to meet with the ocean bacteriological stan-
dards and then pumped through 6-mile tunneled conduits to a
structure (located at Whites Point on the Palos Verdes Penin
sula) whereat it is discharged to the Pacific Ocean through
a system of submarine outfalls. The discharged effluent
enters the ocean at a depth of 150-200 feet (46-61 meters)
through multiple diffusers at the outfall termini, approxi
mately 2 miles (3.2 km) offshore.
CHARACTERIZATION OF PROCESS EFFLUENTS AT JWPCP
During the interim period from April 27, 1970 to August 18,
1970 daily grab samples of digested sludge, centrate and
primary effluent were collected at the JWPCP and analyzed
for their physical, chemical and bacteriological makeup.
The main purpose of this was to characterize centrate,
to evaluate the performance of the existing centrifuges
at the dewatering station, and to quantitatively and
qualitatively assess the proportional ingredient contri-
butions of primary effluent and centrate when blended and
discharged to the ocean as plant effluent. Because of the
large quantity of analytical work required to completely
characterize the individual samples collected, only a small
number of constituents were selected for determination.
These were chosen on the basis of their relative importance
as a polluting agent, ease of determination, degree of
fitness into the normal laboratory routine, and interrelate-
ability.
A quantitative assessment was made for total solids, in-
cluding volatile and fixed components; suspended solids;
floatable and nonfloatable suspended solids, including the
respective volatile and fixed fractions of each; settleable
solids; and dissolved solids, including volatile and fixed
components of the solubilized material. Most of these
factors were determined in accordance with the procedures
outlined in Standard Methods^-. Laboratory centrifugation
at 28,800 gravities for 15 minutes followed by filtration
through a 0.8 ju membrane filter served to fractionate the
samples for separate measurement of the suspended and dis-
solved fractions. Floatable solids in primary effluent
samples were determined using a method developed by
Engineering Science2. This method was modified somewhat
18-
-------
in order to measure this factor in the digested and centrate
sludge samples. Settleable solids in the sludge samples
were indirectly determined utilizing dilution techniques.
Chemical characterization included an analysis of each
sample for biochemical oxygen demand (BOD); chemical oxygen
demand (COD); organic, ammonium, nitrate and nitrite nitrogen;
total phosphorous; sulfide, sulfate and thiosulfate; phenols
and cyanide; alkalinity and hydrogen ion concentration (pH);
oxidation-reduction potential (ORP); and 30-minute chlorine
demand. In addition, samples were analyzed for their total
grease content, i.e. for the amount of material extractable
by hexane. For the most part, the above chemical analyses
were run on each sample both before and after suspended solids
removal. This enabled the chemical load of each effluent to
be separated into that contributed by either the suspended
or dissolved solids fraction.
Presented in Table 1 are tabulated averages of all compiled
solids data acquired from the analysis of daily grab samples
of primary effluent, digested sludge and centrate taken
during the 4 month surveillance study of the JWPCP process
effluents. A similar tabulation of the chemical and
bacteriological data averages for these samples is presented
in Table 2. In both tables, corresponding data are presented
to reflect the concentration of each constituent in the plant
effluent -- that effluent being a blend of 380 mgd (1.43
million cu m/day) of primary effluent with 1.8 mgd
(6,800 cu m/day) of centrate from the dewatering station.
These latter data are calculated values based on the re-
spective daily flows of the two component effluents.
A correlative comparison of the suspended and dissolved
solid averages of Table 1 with the chemical data averages
of Table 2 provided the Districts with the following ob-
served information.
(1) More than 90 percent of the total COD, BOD,
organic nitrogen, total phosphorous and
chlorine demand in centrate and digested sludge
were attributable to the suspended solids of each.
(2) The grease content in digested and centrate
sludge was found to comprise a sizeable por-
tion (approximately 20 to 25 percent) of the
total solid load of each.
-19-
-------
Table 1: AVERAGE SOLIDS MAKEUP OF VARIOUS PROCESS EFFLUENTS AT JWPCP*
-mg/1-
--^^^ SAMPLED
-^_ MATERIAL
FACTOR --^^
MEASURED ' • — ^__
TOTAL SOLIDS
A. Total Volatile Solids
B. Total Fixed Solids
C. Total Suspended Solids
1. Floatable Suspended
a. Volatile
b. Fixed
2. Nonfloatable Suspended
a. Volatile
b. Fixed
D. Total Dissolved Solids
1. Volatile Dissolved
2. Fixed Dissolved
E. Settleable Solids**
DIGESTED
SLUDGE
41,330
23,241
18,089
38,852
241
93
148
38,611
22,352
16,259
2,478
796
1,682
~1,000
CENTRATE
30,302
18,460
11,842
27,898
110
92
18
27,788
17,453
10,335
2,404
915
1,489
~1,000
PRIMARY
EFFLUENT
2,069
550
1,519
176
1
1
0
175
78
97
1,893
471
1,422
1.7
PLANT
EFFLUENT***
2,202
634
1,568
307
~1
-0
306
160
146
1,895
473
1,422
4.0
O
i
"JWPCP data based on daily averages (April-August, 1970)
**Units for settleable solids are ml/1
***The plant effluent from JWPCP is a combined blend of 380 mgd of primary etfluent
and 1.8 mgd of centrate from the sludge dewatering station. Tabulated values
are calculated on this basis.
Unit Conversions: (mgd) x 3,785 = (cu m/day)
-------
Table 2: AVERAGE CHEMICAL COMPOSITION AND 'MPN' CONTENT IN VARIOUS PROCESS EFFLUENTS AT JWPCP'
,t
^--^^ SAMPLED
^-^ MATERIAL
FACTOR ^-^-^
MEASURED ^\^
BOD (mg/1 0)
COD (mg/1 0)
Organic Nitrogen (mg/1 NJ
Ammonia Nitrogen (mg/1 N)
Nitrite Nitrogen (mg/1 N)
Nitrate Nitrogen (mg/1 N)
Total Phosphorous (mg/1 P)
Sulfide (mg/1 S)
Sulfate (mg/1 804)
Thiosulfate (mg/1 S203)
Phenols (mg/1 CfiH5OH)
Cyanide (mg/1 CN)
Alkalinity (mg/1 CaC03)
pH (pH units)
30-min Cl Demand (mg/1 Cl)
ORP (millivolts)
MPN (No. /ml)
Grease (mg/1 Hex. Ext.)
DIGESTED
SLUDGE
Average
Total
4,702
38,996
1,061
487
ft
*
238
100
*
2.8
0.09
5,246
7.1
2,556
-210
4.1x106
8,354
Average
Soluble
261
498
50
470
0.0
0.2
3.3
0.0
1.8
2,927
7.8
22
+40
--
CENTRATE
Average
Total
4,396
21,333
863
420
A
ft
204
92
A
8
2.5
0.05
5,024
7.5
2,208
-214
l.SxlO6
7,762
Average
Soluble
285
701
86
401
0.0
0.2
3.0
0.0
15
0
1.4
2,580
8.0
20
+50
--
PRIMARY
EFFLUENT
Average
Total
284
452
31
42
A
ft
7.2
0.0
*
131
6.5
0.2
359
8.2
69
-20
l.SxlO6
44
Average
Soluble
216
335
24
40
0.0
0.2
3.6
0.0
389
97
4.9
355
8.1
60
-3
--
EFFLUENT**
Average Average
Total Soluble
303 Z16
551 337
35 24
44 42
0.0
0.2
8.1 3,6
0.4 0.0
387
130 97
6.5 4.9
0.2
381 366
8.2 8.1
79 60
1.8x106
81
I
to
* Not feasible to evaluate by standard laboratory methods.
** Plant effluent from JWPCP is a combined blend of 380 mgd of primary effluent and 1.8 mgd of
centrate from the sludge dewatering station. Tabulated values are calculated on this basis.
t JWPCP data based on daily averages (April-August, 1970)
Unit Conversions: (mgd) x 3,785 = (cu m/day)
-------
(3) The relative contribution of the suspended
solids in centrate to the settleable solids
in the JWPCP plant effluent was approximately
3.0 ml/1; that from primary effluent was
1.0 ml/1.
(4) The total average grease load in the plant
effluent from the JWPCP was calculated to be
81 mg/1 of which 44 mg/1 was from the primary
effluent and the remaining 37 mg/1 was con-
tributed by the centrate.
(5) On the average, approximately 30-31% of the
suspended solids were removed or captured by the
centrifugal sludge dewatering process;
the remainder was being discharged to the ocean.
(6) The addition of centrate to the primary effluent
significantly increased the suspended solids,
total BOD, COD, and chlorine demand.
In addition to the above, two important observations were
made with regard to the data acquired from each individual
sample (individual sample data not presented herein).
First, the physical and chemical consistency of digested
sludge remained relatively constant throughout the 4-month
monitoring period whereas that of centrate did not.
Evidently, centrifuge performance at the dewatering station
was irregular. Second, total grease was a varying factor
in both centrate and digested sludge but remained relatively
constant in primary effluent.
The suspended solid, settleable solid and BOD data averages
from Tables 1 and 2 for centrate, primary effluent and
JWPCP plant effluent are retabulated in Table 3. Also
tabulated are the numerical limits placed on these three
parameters by the discharge standards issued in September
of 1970 by the Los Angeles Regional Water Quality Control
Board (WQCB). Quite clearly, these data revealed that the
primary effluent itself did not meet the requirements and
would therefore have to be upgraded. Moreover, it was
apparent that the centrate solids contributed substantially
toward the inferior quality of the plant effluent and that
compliance with the new standards would necessitate a size-
able removal of the material from the sludge effluent stream,
22-
-------
Table 5: EFFLUENT QUALITIES* AND EFFLUENT QUALITY REQUIREMENTS
AT JWPCP
^~--_^^ LOCATION
PARAMETER ^^^^-^_
Biochemical Oxygen
Demand (BOD) -mg/1-
Suspended Solids -mg/1-
Settleable Solids -ml/1-
CENTRATE
4,396
27,898
«1,000
PRIMARY
EFFLUENT
284
176
1.7
PLANT EFFLUENT
Existing**
303
307
4.0
WQCB Discharge
Requirements***
250
200
1.0
*JWPCP data based on daily averages (April - August, 1970)
**Plant effluent from JWPCP is a combined blend of primary effluent
(currently 380 mgd) and centrate (currently 1.8 mgdj from the sludge
dewatering station. Tabulated values are calculated on this basis.
***WQCB requirement for BOD and suspended solids based on monthly average
of daily samples; settleable solids requirement based on daily sample
Unit Conversions: (mgd) x 3,785 = (cu m/day)
-------
BACKGROUND INFORMATION SUMMARY
In retrospect, the overall problem at JWPCP seemed to be
one of solids removal. The Districts' decision to add
fourteen new sedimentation tanks to the existing capacity_
at the JWPCP was deemed sufficient for removing the additional
suspended material- necessary to reduce the overall BOD and
settleable solids to levels acceptable for discharge. In
conjunction with this, however, the digested sludge would
necessitate dewatering to the extent of removing 95 percent
of its suspended solid load. This appeared to be a reason-
able course to pursue but a difficult task to accomplish
in view of the following:
(1) The high quantity of sludge necessitating
dewatering (1.8 mgd) (6800 cu m/day).
(2) The atypical nature of this sludge as a
result of the high industrial component.
(3) The fineness of the sludge solids as a
result of attrition in the digesters and
in the vast sewerage system tributary to the
JWPCP.
The selection of any dewatering scheme to achieve these
desired end results would be dictated by the economics of
that process and the means by which the recovered solids
might be disposed of. Achieving high solid recoveries
would simply mean capturing more of the finely suspended
particulate matter from the digested sludge slurry.
Because of the high ratio of biologically bound water
associated with these fines, the additional capture would
certainly lead to a cake of considerably greater moisture
content than that presently obtained. Moreover, if some
form of sludge conditioning were required to attain the
desired degree of dewaterability, its use might render the
recovered solids useless for fertilizers. Hence, alterna-
tive means of solids disposal would have to be sought out.
If landfill disposal were selected, then the dewatered cake
solids would have to be sufficiently devoid of moisture
for truck hauling and landfill handling. The Districts'
refuse department had estimated that 75% moisture or less
would be suitable in this respect. However, the economics
of hauling versus moisture removal would dictate the de-
sired constituency of the final cake product. A dewatering
system capable of removing 95 percent of the suspended
-24-
-------
solids from the digested sludge stream would result in
approximately. 300 .tons/day (272 metric tons/day) of
dry solids requiring disposal. At '.25% solids concentration
by weight, this would necessitate hauling about 1200 tons
(1088 metric tons) of wet material per day. Despite these
large tonnages, landfill disposal would seemingly appear
attractive in view of the nearby location of the Districts'
operated Palos Verdes Landfill, approximately 4 miles
(6.4 km) from the JWPCP. Unfortunately, the projected
3- to 4-year useful life remaining at this facility would
render its use for sludge solids disposal short lived.
The closest alternate disposal facility would be either
the Mission Canyon Landfill or the Puente Hills Landfill,
each approximately 30 miles (48 km) from the JWPCP.
Certainly, the economics of hauling to either of these
facilities would take on a slightly different picture.
Incineration would surely qualify as an appropriate means
for reducing the overall tonnage requiring disposal. Con-
sidering the volatile content of the sludge solids and assum-
ing that the sludge could be dewatered to a suitable extent,
the combustion process would likely be autogenous, i.e.
self supporting. If so, then the heat value gained might
be conserved for usage elsewhere. The inert ash would
perhaps be useful for conditioning the centrate or di-
gested sludge prior to dewatering. Or if such chemicals
as lime are necessary for the dewatering process, their
recovery might be possible in a recalcining scheme. On
the surface, it would appear that sludge incineration had
an obvious place in the overall scheme of things at the JWPCP
In view of the air pollution problem existing in Los
Angeles County, however, public and regulatory acceptance
of such an operation would prove difficult and costly to
attain. Besides, the Districts had no desire to augment
the air pollution problem for the sake of solving its
sludge problem.
In view of the previous, it can readily be seen that
the Districts sludge problem was one of sizeable magnitude
and complexity and a considerable investment would be
required to effect its solution. Moreover, the success
of the operation would be dependent on the reliability
of the chosen sludge dewatering scheme.
-25-
-------
RESEARCH APPROACH AND EXPERIMENTAL SETUP
Preliminary cost assessments were made for several full
scale sludge dewatering and disposal schemes. The resulting
estimates indicated that, whatever the means, a sizeable
amount of money would be required to dewater to the extent
desired. This prompted the Districts to decide upon a
course of investigating each promising conditioning aid
and dewatering equipment on a piloted basis so as to
arrive at the most worthwhile economical scheme.
At the JWPCP, full-scale horizontal scroll centrifuges
already existed and thus became the logical starting point
for the research work. Preliminary observations had indi
cated that about 30 percent of the suspended material was
being removed from digested sludge fed to the dewatering
station. Generated cakes had a solids content ranging
between 30% and 35% by weight. It was generally felt that
this performance could be improved. However, a systematic
evaluation of various operational parameters would be
necessary in order to verify this and define the limita-
tions involved. Accordingly, preparations were made to
isolate one of the centrifuges for test purposes.
In addition to horizontal scroll centrifuges, other types
of dewatering equipment which seemed to have a potential
application for handling either digested sludge or centrate
included basket and disc centrifuges, coil and cloth belt
vacuum filters, and pressure filters. Representative equip-
ment was procured from available sources, and mention of
product names does not imply endorsement by the Districts
or the EPA. A basket and disc centrifuge were acquired
from Sharpies Centrifuge Company, a Division of Pennwalt
Corporation. A coil filter was obtained from Komline
Sanderson, Inc. Two cloth belt vacuum filters a rotary
drum type and a horizontal belt type, called an extractor --
were furnished from Eimco Corporation, a division of
Envirotech Corporation; a diaphragm press was also\provided
26-
-------
by this corporation. A pressure filter was acquired from
the Beloit-Passavant Company. A description of each of
these units will be provided later in this report.
In conjunction with the above dewatering equipment, four
methods of sludge conditioning would be evaluated. These
included polymer conditioning, chemical conditioning
(lime and/or ferric chloride), heat conditioning and
flyash conditioning. Contacts made with various polymer
manufacturers revealed that cationic polymers would be
most suitable for testing. Accordingly, arrangements were
made for purchasing their various recommended products as
the needs of the research work dictated. The procuration
of lime and ferric chloride for this investigation posed
no problem since these products were quite readily available
on the open market. Special equipment would be needed,
however, if heat and flyash conditioning were to be eval
uated.
Contacts were made with manufacturers of heat conditioning
equipment regarding an investigation of their respective
processes on a pilot plant scale. As a result, the Districts
rented a 200 gallon-per-hour (12.6 1/min) Porteous pilot
plant.
Two lines of approach were available to the Districts re-
garding the conditioning of sludge with flyash. Either
incinerated ash from an outside facility could be pro-
cured for use in this study, or suitable equipment could
be made available to the Districts for the generation of
its own flyash. The latter approach was chosen since it
would provide the Districts with the opportunity of assessing
the combustion properties of the various sludge cakes
generated from the different dewatering equipment to be
tested. Accordingly, incinerator manufacturers were sought
out in this regard. As a result, an arrangement was made
with BSP Envirotech to furnish a six-tier multiple hearth
incinerator for the study.
Considering the large number of products and manufacturing
equipment which were to be evaluated at the JWPCP, it was
evident that a suitable research facility would be required
at which to conduct the \\rork. An area was selected within
the confines of the treatment plant and a research site and
chemical station were constructed. A detailed description
of each of these are presented in the following subsections
along with a followup description of each of the pilot plant
units tested.
27-
-------
RESEARCH SITE
The area selected for the research work was located adjacent
to the existing dewatering station at the JWPCP (see
Figure 3). Following grading and placement of a 6-inch
(15.2 cm) compacted rock base, an 80-ft by 85-ft (24.4-m by
25.9-m) reinforced concrete slab was formed and poured in
place. A sloped, concrete drainage channel of 24-inch
(61-cm) width was constructed along one side of the slab.
Its purpose was to collect the drainage from the slab area
and to serve as an effluent disposal point for the various
pilot plant units tested. The drainage channel terminated
at a sump. An automatically controlled sump pump was instal
led to recycle the collected drainage and effluent wastes
back into the treatment plant system.
A centrally located electrical panel (Westinghouse model)
equipped with starters and breakers of various sizes was
installed on the research slab area. This served as the
distributing power source for all miscellaneous electrical
equipment (pumps, mixers, lights, etc.) as well as the
pilot plant units themsleves. The panel, in turn, was
supplied power from an existing breaker panel at the
JWPCP dewatering station. For nightwork purposes, a large
overhead 400-watt floodlight was installed atop a 30-ft
(9.2-m) high pole located on one corner of the research
site. The area was unroofed and exposed to the weather.
Two 10-ft (3.0-m) diameter, 8-ft (2.4-m) high cylindrical
fiberglass tanks (Figure 4), each of 4,700-gal. (17.8-cu m)
capacity, were installed adjacent to one another on the
research slab. These served as sludge holding reservoirs
and were the source of sludge feed material for the pilot
plant units tested. Each tank was equipped with tie-down
lugs and an externally wall mounted ladder. A 20-inch
(51-cm) diameter manway was located on top to provide tank
access. The tanks were each furnished with four vertical
wall mounted baffles, each located at 90° from one another
around the internal periphery. In addition, each tank was
equipped with an internally, top-located wash water spray
ring for washing of the tanks' walls.
A network of piping was constructed from the existing
centrifuge dewatering station to each tank. The arrangement
and tie-ins were such that either tank could be filled with
any of the following:
-28-
-------
FIGURE 3
Joint Water Pollution Control Plant
Sludge dewatering research site
EXISTING CENTRIFUGE
DEWATERING STATION
POLYMER STORAGE
TANKS (DETAILED IN
FIGURE 5)
MANHOLE
PUMP
SLUDGE DRAIN LINE
\ POLYMER
\ FEED
\ LINE —
rWATER LINE
AIR COMPRESSOR
SLUDGE SUPPLY LINE
•^SLUDGE
FEED LINE
PUMP
CONCRETE SLAB
TO PILOT
PLANT UNITS
PROPANE TANK
• SUMP
PUMP
-TANK AND
MIXER
ASSEMBLY
DRAINAGE
-CHANNEL
29-
-------
FIGURE 4
Schematic diagram
Sludge storage tanks at dewatering research site
O
I
WATER
TANK DRAIfgl h—I
MIXER
BAFFLE
(TYP.)
ACCESS WAY
ao
SLUDGE
FEED
MIXER
SUPPORT
STRUCTURE
-------
(1) digested sludge fed to the dewatering station,
(2) centrate effluent from the Bird centrifuges,
(5) screened centrate effluent from the vibrating
screens.
An overflow drain line was connected at the top of each tank
to prevent accidental overflow1 of the tanks contents during
filling. Other miscellaneous pipe connections were arranged
for either draining each tank or directing their respective
contents (by gravity feed or controlled pumping) to anv of
the pilot plant units tested. Controlled feeding was accom-
plished using a variable speed progressive cavity pump
(Moyno type, Model 1L4) with capacities ranging from 30 to
78 gpm (1.9 to 4.9 I/sec). The overflow and drainage from
each tank were conduited back into the treatment plant-
system .
In order to keep the contents of each tank in a somewhat
homogeneous state for distribution to each pilot plant,
each tank was provided with a slow speed (84 rpm), 2-hp
(1.5-kw) mixer (Lightnin Model 71-Q-2). Each mixer was
equipped with a 57-inch (94-cm) diameter turbine type
propeller mounted on the end of a 2-inch (5.1-cm) diameter,
114-inch (290-cm) long shaft. The mixer assembly was
supported over each tank by a spanned steel frame structure
fabricated by plant personnel.
A 500-gal. (1.1-cu m) propane tank was installed adjacent
to the slab area. This served as a reservoir for the
necessary fuel required for operating some of the pilot
plant units. A compressor and air storage tank was provided
to supply compressed air as the needs dictated. Also, two
portable buildings were furnished to house the operating
and maintenance research personnel and to provide storage
for tools, miscellaneous piping, valves and other appurte-
nances .
CHEMICAL STATION
A small area was selected between the research slab area
and the existing centrifuge dewatering facility for the
construction of a chemical mixing station (refer to Figure 3
for location). Here, polymer solutions could be batched in-
to desired solutions and control fed to any of the pilot
plant units on the slab area or to one of the 36-in. x 96-in
(91.4-cm x 245.S-cm) horizontal scroll centrifuges at the
-31
-------
dewatering station that was isolated for test purposes.
The station consisted of 2 cylindrical fiberglass tanks,
each of 1,400-gal. (5,300-1) capacity (Figure 5). Each
was equipped with an eductor for injecting dry polymers
into solution and with a mixer for effecting solution homo-
geneity. The mixers were 2-horsepower (1.5-kw) direct
drive units (Lightnin Model ND-4A) operable at a constant
speed of 1,750 rpm. Located at the middle and end of each
mixer shaft was a 12-inch (30.5-cm) diameter, tri-bladed
mixing propeller. Two progressive cavity Moyno pumps
(Model 1L3) were installed at the station for controlled
delivery of batch polymer solutions to the processing units,
One of the pumps was a fixed speed unit whereas the other
was of variable speed. Between the two, batched polymer
feedrates from 0.6 to 13.6 gpm (0.04 to 0.86 I/sec.) were
possible.
Located at the discharge end of each pump was another
eductor connected to a meterable water supply. This
enabled the pumped polymer solution passing within the
eductor to be further diluted to any desired degree.
Additional equipment, such as rotameters, water meters,
pressure reducing valves, and miscellaneous globe and
gate valves were incorporated into the piping network of
the station as was necessary for controlling and metering
specific quantities and flow rates of water.
PORTEOUS PROCESS AND ACCESSORY DEWATERING EQUIPMENT
The major components making up the 200-gal./hr (12.6-1/min)
pilot plant unit used in this investigation consisted of
the following individual pieces of equipment (see Figure 6)
(1) A Moyno mazorator (grinder),
(2) A high pressure progressive cavity pump (Moyno
type),
(3) Two heat exchangers -- one for preheating and one
for cooling,
(4) A 240-gal (908-1) reactor pressure vessel,
(5) A steam generating boiler unit equipped with a
boiler blowdown system,
(6) Miscellaneous pumps and expansion tanks for
-32-
-------
FIGURE 5
FIBERGLASS
TANK
Schematic flow diagram
Chemical station
EDUCTOR
WATER METER
DRY POLYMER
ROTAMETER
GATE VALVE
ROTAMETER
PUMP
BATCHED
POLYMER
SOLUTION
GLOBE VALVE—i
PRESSURE
REDUCING
VALVE
DILUTION
EDUCTOR
WATER SUPPLY
POLYMER STREAMS TO
DEWATERING EQUIPMENT
-------
FIGURE 6
Heat conditioning pilot plant assembly
COOKED
SLUDGE
.(PORTRATE)
BLOW
DOWN
SYSTEM
WASTE
SLUDGE
FEED
GRINDER-
SLUDGE
FEED
PUMP
EXPANSION TANK
CIRCULATING PUMP
BOILER PREHEAT TANK
BOILER FEED PUMP
CIRCUIT BREAKERS
-------
(a) the heat exchanger circulating water
system and
(b) boiler feed water system,
(7) An electrical control panel.
In addition, other miscellaneous equipment (ball valves,
check valves, regulating valves, relief valves, liquid
level controls, pressure gauges, temperature gauges, etc.)
were an integral part of the unit as was necessary for its
operation. All miscellaneous equipment and components
were mounted on a steel platform and prepiped into a
workable system. The skid mounted assembly was delivered
to the Districts' research site for evaluation.
A flow schematic of the Porteous heat treatment system is
presented in Figure 7. As noted, waste sludge, fed through
a grinder, is pumped through the inner tube of the pre-
heating heat exchanger and into the reactor pressure vessel.
While this is happening, hot circulating water crossing
over from the other heat exchanger, henceforth called the
"cooler", is passed through the annulus of the preheater
whereupon its thermal energy is transferred over to the
waste sludge phase. As the preheated waste sludge enters
the reactor, sufficient high pressure steam is injected
into the sludge flowstream as is necessary to bring the
reactor contents to some desired operating temperature.
Following a preset residence time (cooking time within
the reactor vessel), the cooked sludge is discharged under
pressure into the inner tube of the deheating heat exchanger.
Cooled circulating water crosses over from the cooler where-
in it becomes heated by thermal energy transferred from the
cooked sludge phase. Once heated, the exiting hot circu-
lating water is redirected to the preheater to give up its
energy to the newly introduced waste sludge. The final
cooled, cooked sludge exiting the deheater is the desired
heat conditioned product which is available for further
processing. This product will hereinafter be referred to
as "portrate".
Accessory equipment was furnished with the Porteous pilot
plant unit enabling further processing studies to be carried
out on the portrate. Included were a picket thickening
tank, a horizontal scroll centrifuge, an extractor (top
loading, horizontal cloth belt vacuum filter), and a dia-
phragm press. The following is a brief description of each
of these.
-35-
-------
FIGURE 7
Schematic flow diagram
Heat conditioning pilot plant
COOLED
REACTOR GASES
PREHEATING TANK
WASTE
SLUDGE
(GRINDER)
BOILER WATER
HOT REACTOR GASES
.BOILER
SOFTENED
WATER
PUMP
PREHEATED
SOFTENED WATER
PROPANE
FUEL
PROGRESSIVE
CAVITY PUMP
WATER
SUPPLY
NITROGEN-
EXPANSION
TANK
HEAT EXCHANGER
HIGH
PRESSURE
STEAM
INSULATED
.REACTOR
m
\
PREHEATED SLUDGE
CIRCULATING
WATER
HOT COOKED SLUDGE
COOLED
COOKED SLUDGE
(PORTRATE)
HEAT EXCHANGER
-------
(1) Picket Thickening Decant Tank - A 390-gallon
(1476-liter) cylindrical tank with a conical
shaped bottom. Unit was equipped with a rotary
driven bottom sweeper with attached vertical pickets
(2) Horizontal Scroll Centrifuge A Sharpies P-600
unit equipped with fixed speed bowl drive and
variable speed scroll drive motors. A storage
feed tank and a progressive cavity feed pump
accompanied the unit.
(5) Extractor -- A 12-foot (3.7-meter) long Eimco
horizontal top loading vacuum filter equipped
with variable speed driven cloth belts having
a one-foot (0.3-m) wide face.
(4) Diaphragm Press -- An Eimco experimental unit
consisting of a moveable cloth belt within a
hydraulically operated press plate. An air
operated high pressure feed pump accompanied
the unit.
Other pilot plant equipment were also assessed as to their
portrate dewatering capabilities. A description of these,
however, will be presented in more detail in subsequent
subsections.
Installation of feed, drain, water, compressed air and
reactor vent lines was made between the Porteous pilot plant,
the various accessory equipment, and the existing research
facilities. Installment of a high pressure gas line served
to connect the propane tank to the boiler of the pilot plant
unit. Minimization of boiler scaling was accomplished with
the hook-up of a Culligan soft water unit to the boiler feed-
water system. A radioactive source and detectors were in-
stalled on the reactor as an integral part of the automatic
level control system. A high pressure nitrogen source was
tied into the expansion tank of the circulating water system.
This enabled controlled pressurization of the circulating
water within the heat exchangers.
HORIZONTAL SCROLL CENTRIFUGE
Horizontal scroll centrifuges generally fall into three basic
shapes, namely conical, cylindrical and cylindrical-conical.
Both the Sharpies P-600 decanter and Bird centrifuge used
in this investigation were of the cylindrical-conical type.
Both were capable of dewatering on a continuous basis with
countercurrent discharge of the fractionated effluents.
37-
-------
A typical section of one of these centrifuges is presented
in Figure 8. Basically the unit consists of two horizontally
rotating elements. The outer rotating element is a solid.
cylindrical shell joined at one end to a section of a
truncated conical shell. The ends of this bowl assembly
are supported by a head plate with an integral trunnion.
The inner rotating element resides within the bowl and con-
sists of a smaller diametered cylindrical hub and hollow
shaft assembly with an attached blade formed axially around
the outer wall to produce a helical screw. During operation,
this screw assembly is driven by a planetary gear reduction
unit at a somewhat slower speed than the bowl. The net
effect is a screw conveyor inside of a revolving bowl.
The entire rotating assembly is mounted on a frame to which
is bolted a semi-cylindrical welded steel top cover.
The sludge slurry is fed into the machine through a hollow
stationary pipe extending part way into the hollow shaft of
the screw conveyor or scroll. This feed material is deposit-
ed within one of two compartmentalized chambers within the
scroll. Multiple ports situated around the outer wall of
this rotating chamber allow passage of the sludge into the
outer bowl region. Because of the difference in rotational
speeds, sludge entering the bowl region is distributed uni-
formly around the bowl wall. The other chamber within the
scroll is generally used for receiving a separately fed
chemical stream and independently distributing or injecting
it into that already present within the bowl region; when
not in use, the diffusion ports of this chamber are usually
sealed off to prevent backflow intrusion of unwanted material.
The distribution of sludge against the bowl wall results in
the formation of a rotating annular pool whose depth is
regulated by adjustable overflow weirs situated at the large
diameter end of the bowl. As the liquid moves towards
these weirs, the suspended solids centrifugally gravitate
or migrate through the pool towards the bowl wall. Thus, the
liquid overflowing the weir (centrate) has a reduced sus-
pended solids load. The solids which are deposited
against the bowl surface are scrolled back through the
moving liquid pool and up the conical beach whereupon they
eventually break through the pool's liquid surface and under-
go drainage prior to discharge through exit ports. The
dewatered sludge cake and centrate are discharged into
separate external hoppers mounted beneath the machine.
The Bird centrifuge selected for evaluation was one which
operated at a constant bowl speed of 1300 rpm and thereby
-38-
-------
FIGURE 8
Cross-section of a countercurrent flow horizontal scroll centrifuge
CENTRATE
UD
PLANETARY
GEAR BOX
CENTRATE
CHEMICAL FEED CHAMBER
SLUDGE FEED CHAMBER
SOLIDS
CHEMICAL
FEED
WASTE
SLUDGE
FEED
SOLIDS
-------
produced 900 gravities at the wall of the cylindrical
section. The planetary gear reduction was such that
the differential speed between the bowl and scroll re-
mained constant at about 15.3 rpm. The machine was first
removed from its pedestal, dismantled, reconditioned and
modified as was necessary for test purposes. This in-
cluded refacing the scroll blades to their original di-
mensions, providing reinforced support to the cover at the
cake discharge end, opening the chemical chamber injection
ports leading to the bowl of the machine, installing a multi-
tubed feed pipe for independent injection of both sludge
and polymer solution into respective chambers within the
scroll, and adapting a skimming device at the centrate dis-
charge end of the bowl which would enable the pool depth
within to be externally adjusted during machine operation.
The machine was then reassembled and put back on its
pedestal.
A variable speed driven progressive cavity pump (Moyno
type) was installed for controlled sludge feeding to the
centrifuge. The speed range was such that sludge feedrates
ranging from 100-450 gpm (6.3-28.4 I/sec) were possible.
The installation of the pump was such that its suction side
was tied into the main sludge line feeding all six centri-
fuges at the station. Thus, as long as sludge was being
delivered to the station, some would be available (under
pressure) for controlled pumping to the test centrifuge.
Plastic (PVC) pipe was installed from the chemical station
to the centrifuge installation. Tie-ins were such that
chemicals could be optionally injected into either the
suction or discharge side of the sludge feed pump or
separately into the bowl of the centrifuge itself. With
this work completed, the unit was ready for evaluation.
The experimental setup with the Sharpies P-600 decanter
was somewhat similar, though on a much smaller scale. The
centrifuge itself operated at a constant bowl speed of
5000 rpm. The unit was equipped with a variable speed
back drive which enabled the differential speed between the
bowl and the scroll to be varied from 7 to 44 rpm. Over-
lapping the bowl weir plate on the discharge end of the bowl
was a second circular plate with four sets of punched
holes located along spiral arms radiating outward from the
plate's center. Rotational adjustment of this overlapping
plate enabled any one of the four sets of holes to be
aligned with the larger weir holes of the inner fixed plate.
Thus, four optional pool depth settings were available;
-40-
-------
partial dismantlement of the machine, however, was necessary
to change from one pool depth setting to another. The feed
pipe was multitubed for independent feeding of sludge and
optional chemicals into the bowl. Variable speed driven
Moyno pumps were provided for metering both the sludge and
chemical feedrates. The respective pump sizes and speed
variations were such that sludge feedrates ranging from 1.0
to 5.8 gpm (3.8 to 21.9 1/min) and chemical feedrates
ranging from 0.02 to 0.18 gpm (0.08 to 0.68 1/min) were
possible. Preceding each pump was a small reservoir tank.
The sludge tank was equipped with feed, drain and overflow
lines; the chemical tank was furnished with an eductor,
a mixer, and a meterable water supply.
BASKET CENTRIFUGE
Basket centrifugation of waste slurries is basically a
batch type operation. Sludge is fed and dewatered simul
taneously along with continuous discharge of the clarified
effluent (centrate). The dewatered solids are retained
for later discharge at a time when the throughput of feed
material has been temporarily ceased.
A typical section of a basket centrifuge is shown in
Figure 9. Characteristically, the unit consists of an
imperforate cylindrical bowl which rotates about a vertical
axis. An annular baffle is attached to the upper end of
the bowl, thereby forming a weir whose crest is situated
some distance radially inward from the bowl wall. A similar
arrangement exists at the bottom of the bowl except that it
is much more a floor structure and does extend inwardly
to a greater extent than the weir. The overall configura-
tion of this assembly is such that it appears like a basket
with a lip on the top.
Feed material is introduced at or near the axis of rota
tion and is directed towards the bottom of the basket there-
at to be accelerated outward towards the bowl wall. A
separate though somewhat similar feed arrangement exists
for optional addition of chemical solutions. During the
initial stages of the feed cycle, the material introduced
to the bowl near the bottom flows upwards towards the top
lip or weir whereat its progression is temporarily halted
and a trapped, annular pool begins to form. As feeding
continues, the trapped pool deepens until its surface reaches
the crest of the upper weir. Liquid then begins to over-
flow the weir signifying the end of the fill cycle and the
-41
-------
FIGURE 9
Schematic diagram of a basket centrifuge
FEED
POLYMER
SKIMMINGS
-------
beginning of an equilibrium feed-discharge phase of opera-
tion.
In the equilibrium phase, the trapped annular pool region
between the bowl wall and the weir crest becomes a quiescent
zone for the gravitational movement of suspended solids.
Overlying this is a thin moving liquid layer travelling
upwards towards the discharge end. Suspended material,
while within this moving layer, migrates towards the
quiescent zone for continued settling. Hence, a discharged
overflow or centrate results having a reduced suspended
solids load. During the equilibrium phase, solids accumu-
lating within the quiescent zone build up and compact
against the bowl wall. This continues until the capacity
of that region for solids accumulation becomes exhausted.
At this point, the rejected solids are carried out with the
overflow causing centrate clarity to diminish. This signi-
fies the end of the feed cycle. Feed to the unit is then
halted until the dewatered solids are removed from the bowl.
The accumulative buildup of solids during the feed cycle
is such that those solids residing closest to the bowl
wall are more compact; thus, the solids cake in that
location contains less moisture per unit of occupied volume
and is therefore drier. Conversely, solids residing more
inward and away from the wall are progressively less com-
pact making the collected cake in that region correspondingly
wetter. The progression is such that at the crest of the
overflow weir lies a semidewatered paste and a thin layer
of unclarified liquid. This latter material is removed to
any desired depth by means of a skimmer. The skimmed con-
tents are discharged through a hose. This is accomplished
while the centrifuge is running at full speed. The skimmer
is then retracted and the bowl is decelerated to a very
slow speed whereupon the remaining drier cake is peeled
from the wall with a large bladed knife. The knifed con-
tents fall through open quadrants at the bottom of the
basket for conveyance to a discharge point. Upon retraction
of the knife, the solids discharge cycle is completed. The
bowl is reaccelerated to full speed and the feed cycle re-
initiated.
Two basket centrifuges were utilized in the Districts'
dewatering study. The first was a 30-inch (76-cm) diameter
machine driven by an electric motor at a constant speed of
1750 rpm. This provided 1300 gravities at the wall of the
bowl. The 4-inch (10.2 cm) weir lip in conjunction with
-43-
-------
the basket's length provided a 6-cu ft (0.17-cu m) annular
reservoir for solids accumulation. The basket of this unit
was not equipped with an open bottom for solids discharge.
Consequently, all accumulated cake solids were removed by
skimming. This latter aspect proved troublesome for this
work, and so a second machine was brought in to take its
place. This second unit was equipped with a 40-inch
(102-cm) diameter bowl and was hydraulically driven to
provide an upper speed of 1500 rpm (1300 gravities at the
bowl face) during feeding and skimming. Provisions were
such that the solids (or a portion thereof) could be
knifed out upon hydraulic deceleration to a lower bowl
speed (approximately 100 rpm). The 6-inch (15.2 cm) weir
lip in conjunction with the basket length provided a 9-cu ft
(0.25-cu m) annular reservoir for solids accumulation.
The unit was completely furnished with the necessary controls
which enabled full automation of the entire operation.
Both of the above discussed centrifuges were evaluated in
the second stage mode as to their capabilities for de-
watering centrate from the existing solid bowl centrifuge
station. A variable speed progressive cavity feed pump
(Moyno type) was used to meter the feeding of first stage
centrate to each unit tested. Speed ranges were such that
feedrates ranging from 10-70 gpm (0.60-4.41 I/sec) were
possible.
ROTARY DRUM VACUUM FILTER
Two types of rotary drum vacuum filters were evaluated
as part of the Districts research work, namely an Eimco
cloth belt filter and a Komline-Sanderson coil filter.
Both were pilot units of the same size and basic configura-
tion. Both were mounted on a steel platform along with other
miscellaneous components (electrical panel, drive motors,
vacuum and filtrate pumps, liquid-air separators, etc.)
necessary for functional operation and testing. Figure 10
shows the basic layout of the skid-mounted assembly of each.
Situated near one end of each filter unit is a variable
speed driven, 3-foot (0.9-m) diameter cylindrical drum
having a one-foot (0.3-m) wide face. Located at the opposite
end is a roller assembly, the rotation of which axially
parallels that of the drum. Looped peripherally around
the drum and roller assembly is the belted filter media.
In the case of the coil filter, this consisted of a two-
layered mat of stainless steel, 0.41-inch (10.4-mm) diameter
helically coiled springs layed in corduroy fashion. The
-44-
-------
tn
FIGURE 10
Rotary drum vacuum filter pilot plant assembly
WASTE SLUDGE
CAKE
DISCHARGE
LIQUID AIR
SEPARATERS
WATER
CHEMICAL
OR POLYMER
CONDITIONER
CONDITIONER
BATCHING
TANK
EXHAUSTED
AIR
FILTRATE
-------
media for the Eimco unit consisted of a one-foot (0.3-m)
wide woven cloth belt of synthetic material (nylon or
polypropylene).
During operation, a sludge slurry is control fed to a
reservoir for optional contact with a separately fed
conditioning aid prepared in a batch tank. Gentle agita-
tion is provided to flocculate the particulate matter
within the mixture. Following a brief contact period, the
conditioned sludge is control fed to the vacuum filter
reservoir. The reservoir is equipped with a bottom agitator
to further coagulate the sludge and prevent localized
settlin'g. The volumetric region of this reservoir is such
that a bottom portion of the supported filter drum lies
within its confines and, hence, is partially submerged in
the preconditioned mixture. During drum rotation, the
overlaying filter media belt is endlessly fed into and
out of the flocced slurry. The filter drum itself is
internally compartmentalized. Each compartment has inter-
nal piping which terminates at a trunnion on one side of
the drum. An automatic valve is located at this trunnion
which enables separate and controlled distribution of
applied vacuum to each compartment. As a compartment of
a drum becomes submerged in the slurry, vacuum is auto-
matically applied, thereby drawing sludge through the over-
lying filter media into the drum chamber. During the
initial stage of submergence, sludge particles larger than
the media pores are impeded from passage. They, therefore,
began to accumulate on the media surface into a formed
cake which, in turn, impedes the passage of finer solids
into the drum chamber. As submergence continues for each
compartment, solids accumulate on the filter media. Only
the liquid and very fine solids fraction actually pass
through the pores of this formed cake boundary; this
clarified material, called filtrate, is continually carried
out of the compartment with the exhausted air into air-
liquid separator tanks wherefrom it is pumped for further
processing or discharge. As the compartment emerges from
the filter reservoir, the resulting formed cake is further
dried by mass transfer of the retained liquid phase to air
drawn through the cake by the applied vacuum. This con-
tinues up until the filter media breaks contact with the
rotating drum surface. At this point, the applied vacuum
is ceased and the compartment is automatically brought to
atmospheric pressure. The dried cake product is conveyed
to the roller assembly end to be discharged from the media
belt.
-46-
-------
In the coil filter, the two layers of springs travel over
different rollers (one in front of the other) and, hence,
separate from each other. Dried cake is thus lifted from
the lower layer and discharged from the upper layer by means
of a tine bar. After passing over the discharge rollers,
the coil springs are flexed in two different directions
while being spray washed. This insures that a constantly
clean filter media is being applied to the drum surface
at the start of the cake formation cycle. In the cloth
belt unit, the filter media travels, first, over a flex
bar and then over a discharge roller having an opposingly
wound helical ridge along each half of its length. The
bar and roller serve to shear and, hence, break the sheet
of dried cake away from the cloth media enabling it to
discharge freely. The cloth media is then spray washed
prior to its return to the filter drum for resubmergence
into the conditioned sludge slurry within the filter re-
servoir.
PRESSURE FILTER
The components of the Beloit-Passavant pilot pressure
filter assembly were delivered to the JWPCP research site
on four steel platforms or skids. The assembly included
an electrical panel, a conditioning tank (equipped with
a paddle mixer and transfer pump), two pressure tanks, an
air compressor, and the filter press. An operational lay-
out of the system is shown in Figure 11.
The filter press assembly consisted of four 2-ft (61-cm)
diameter, moveable concave plates which, when butted
against one another, provided three 0.38-cu ft (0.01-cu m)
compartmentalized chambers linked together through a central
port. The periphery of each chamber was sealable from the
outside by means of annular rubberized gaskets. The face
of each plate served as the filter surface, each having an
area of approximately 3 sq ft (0.28 sq m). The interior
plates each provided two filter surfaces whereas the end
plates provided only one. Hence, a total of six filter
surfaces were available which, as a whole, furnished 18 sq ft
(1.68 sq m) of filter area. Wire mesh screens were fitted
onto the face of each plate to act as backing for an over-
layed filter media. The filter media was a woven cloth of
synthetic material, the edges of which were caulked into an
annular recessed notch around the face of each plate.
-47-
-------
oo
FIGURE II
Pressure filter pilot plant assembly
PRECOAT
MATERIAL
OMPRESSOR
SLUDGE
CONDITIONER
PRESSURE
FEED TANK
PROGRESSIVE
CAVITY PUMP
HIGH
PRESSURE
OIL
FILTRATE
-------
Pressure filtration is a batch type of operation. Sludge
is fed to the conditioning tank and is mixed with added
conditioning agents (lime, ferric chloride, polymer, ash,
etc.). Meanwhile, the filter press plates are closed by
means of a hydraulic ram actuated by compressed air. A
precoating mixture (diatomaceous earth or flyash, etc.
slurried with water) is batched in a small pressure vessel
called the precoat tank and then pressure fed at a very high
rate into the filter press. The net effect is that the
filter media within becomes coated with a very thin layer
of the precoat material. Therein, this material will serve
to obviate premature blinding of the filter media during
sludge feeding and provide readily parting planes between
the cloth and later discharged cakes from each chamber.
Upon completion of the precoat cycle, the conditioned sludge
is pumped from the conditioning tank to a second pressure
vessel called the pressure feed tank. The tank and contents
are then isolated and pressurized to about 30 psig (2.1 kg/sq
cm). Following this, the feed cycle to the filter press
is initiated.
Pressurized conditioned sludge enters the filter through
a center feed port and distributes itself uniformly through
all four chambers. Solid particles deposit against the
precoated filter media, while the bulk of the liquid phase
and a very small portion of the suspended fines pass through
and follow a septum to outlet ports in each plate. The
liquid exiting these ports is the filtrate product. As the
feed cycle progresses, the retained solids compress and
accumulate within each chamber and, in doing so, impart in-
creased resistance to the porous flowthrough movement of
the liquid phase. To overcome this, pressure to the feed
tank and, hence, to the pressure fed conditioned sludge is
increased gradually to a maximum of 220 psig (15.5 kg/sq
cm). With the passage of time solids buildup reaches a de-
sired maximum, thus signifying the end of the feed cycle.
Feed to the press unit is stopped and all systems undergo
depressurization. Oil flow reversal initiates retraction
of the pressure filter's hydraulic ram. One by one, the
butted filter plates are pulled apart. As each plate
separates from the stack, the accumulated filter cake
(from the opened chamber in between) shears from the filter
surfaces and gravity discharges. Upon removal of all com-
partmentalized cakes, the plates are washed while prepara-
tions are made for the next batch run.
-49-
-------
INCINERATOR
The major components making up the pilot incineration
plant used in this investigation consisted of the
following pieces of equipment (see Figure 12).
(1) A six-tier multiple hearth incinerator.
(2) Two screw conveyors--one for feeding dewatered
sludge into the furnace and one for discharging
ash residue.
(3) Rabble arm and drive mechanism.
(4) Combustion air blower.
(5) Stack gas scrubber.
(6) Draft induction fan.
(7) Oxygen sampling apparatus.
(8) Electrical control panel.
In addition, other miscellaneous equipment (pressure and
automatic regulating valves, flow meters, burners, temper-
ature and pressure sensing devices, chart recorders, etc.)
were an integral part of the assembly as was necessary for
its operation. All miscellaneous equipment and components
were mounted on a steel platform and properly connected into
a functional system. The skid mounted assembly was de-
livered to the JWPCP research site for trial combustion of
various dewatered sludge cakes and, hence, generation of
a flyash conditioning product.
The six-tier multiple hearth furnace was a 30-in. (76-cm)
diameter unit having 16 sq ft (1.5 sq m) of hearth area.
Hearths No. 1 thru No. 5 were equipped with individual
burners and thermocouple sensors. Hearth No. 6 was rigged
for pressure sensing. A combustion air blower furnished
the air to operate each propane fueled burner. Air de-
livery to each burner was automatically controlled by
throttling valves in accordance with the intensity of
burner operation required to maintain a desired hearth
temperature. Fuel flow to each burner was, in turn, auto-
matically regulated by the amount of air flow being ad-
ministered. The gases of combustion were drawn from the
furnace by means of an induction fan. The rate of with-
drawal of these gases was automatically controlled by a
draft throttling valve in accordance with maintaining both
a desired negative pressure on the lowest Hearth No. 6 and
-50-
-------
FIGURE 12
Skid mounted pilot plant incinerator assembly
DEWATERING
SLUDGE FEED
ASH SCREW
CONVEYOR
ASH
FURNACE
•BURNERS
ui
UJ
cc
UJ
H
<
&
(T
UJ
COMBUSTION
AIR
BLOWER
O
AIR
(T
UJ
m
m
o
oc
O
in
VI
DRAIN
WATER
-DRAFT
THROTTLING
VALVE
XYGEN
SAMPLE
PORT
CONTROL
PANEL
-------
a sufficient amount of excess air (oxygen) in the stack
gases. Excess air control was accomplished by the feed
back of monitoring equipment analyzing the oxygen content
of a continuously sampled stream of the discharge stack
gases.
A conveyor belt was installed to convey the dewatered
sludge material from ground level up to the inlet feed
hopper located at hearth No. 3. Because of the small
size of the furnace, sludge cakes were physically broken
up into small chunks prior to loading on the conveyor
feed belt. A multibladed chopping tool was devised for
this purpose. Upon entering the feed hopper, the cake
chunks are screw conveyed into the furnace to undergo in-
cineration. Therein, the solids are conveyed spirally
around the hearth floor towards a central exit port. The
solids fall through this port to the hearth below, i.e.
hearth No. 4; therein, they are conveyed spirally outward
toward the furnace wall where an annular exit port, i.e.
the entrance to hearth No. 5, is located. Following cen-
tral conveyance across the floor of hearth No. 5 and out-
ward conveyance across the floor of hearth No. 6, the
remaining solids, i.e. the ash residue, fall into a
hopper and are discharged from the furnace by screw con-
veyance through a water jacketed conduit. The discharged
ash clinkers are fed to a hammer mill to be pulverized to
flyash constituency for use as a sludge conditioning aid.
The conveyance of the solids across the individual hearths
is accomplished by plow teeth attached to horizontally sus-
pended arms. The arms are fixed to a shaft running ver-
tically through the center of the furnace to a variable
speed drive unit. During operation, the shaft is rotated
about its vertical axis at a preset speed. The attached
arms (four in each hearth situated crosswise) sweep above
and across the hearth floor dragging the plow teeth through
the residing solids. The configuration and arrangement of
the plow teeth along each arm is such that the solids are
plowed back and forth along the spiral path of movement.
The net effect is one of providing greater turnover of the
residing solids. This increases the frequency of exposure
to the overlying gases which, in turn, enhances the rapidity
of the incineration process.
A majority of the residual moisture in the dewatered sludge
fed to the furnace is removed by evaporation on hearth No. 3
Ignition and flame burning take place on hearth No. 4. On
hearth No. 5, the fixed hydrocarbons are burned in glowing
-52-
-------
charcoal fashion. Residual burning and preliminary cooling
of the ash residue occur in lowermost hearth No. 6. The
uppermost hearths (Nos. 1 and 2) are used for the after-
burning of generated combustion gases drawn upward by the
draft induction fan from the hearths below. Water is sprayed
into the hot afterburned gases exiting hearth No. 1. The
partially cooled gases are then directed into a water
scrubber for further cooling and, more importantly, for
removal of any fine particulate matter which may have been
carried out of the furnace in the gas stream. The cooled
clean gases were then discharged to the atmosphere.
53-
-------
CONDITIONING SYSTEMS
Four forms of sludge conditioning were evaluated as part
of the Districts' research work. These included heat
conditioning, conditioning with cationic polymers, chemical
conditioning with ferric chloride and/or lime, and flyash
conditioning. In this country, polymers and chemicals are
probably the most conventional and widely used means of con-
ditioning sewage sludges for dewatering purposes. Flyash,
as a sludge conditioning aid, is frequently utilized by
installations employing incineration for solids disposal.
The use of heat treatment as a means of conditioning sludges
prior to dewatering has been practiced quite extensively in
Europe since its introduction in 1932. During the last
decade, however, a few heat treatment installations have
been showing up across the United States. Although some
were not too successful at first, rapid engineering and
developmental changes have resulted in processes which are
gaining wide acceptance.
In the subsequent text, data results from Porteous heat con-
ditioning of JWPCP digested sludge are presented and dis-
cussed. Pertinent information on polymer, chemical and
flyash conditioning is also presented as it related to
this work.
PORTEOUS HEAT TREATMENT
Basically, the heat conditioning process is continuous
pressure cooking. Waste sludges are heated under pressure
to some temperature greater than 310°F (155°C). Under these
conditions, proteinaceous material surrounding a sludge
particle is hydrolized to a large extent. Thus, bound water,
i.e. that originally bound to the particle by this material,
is released thereby permitting each particle in the fluid
medium to behave as its specific gravity intended it to and
not as some sort of gelatinous colloid.
-54-
-------
Obviously, the overall effectiveness of this process is
dependent on the temperature necessary to carry out this
reaction. Also, sufficient reaction time is necessary to
insure the completeness of bound water release. At the
temperatures under consideration, however, other side
effects do take place which warrant some mention. These
include the thermal transfer of material from the sus-
pended to the dissolved phase and the thermal decomposi
tion of some organics to less complex forms and/or gaseous
by-products. Since the degree to which these side effects
occur is increased with increased reaction time and tem-
perature, it becomes apparent that the most optimum tem-
perature-time combination for sludge conditioning is that
employing the minimum temperature necessary to effective-
ly destroy the gel like structure.
Within the operational limits of the Porteous pilot plant
itself, the effect of two reactor cooking times (30
and 40 minutes) were investigated. At each detention
time, primary digested sludge was cooked at each of sev-
eral temperatures ranging from 330°F to 395°F
(165°C to 200°C) . During each run, samples of primary
digested sludge feed and the thermally treated product,
hereinafter referred to as "portrate", were taken and
later analyzed in the laboratory for their suspended and
dissolved solid contents. Corresponding fixed and
volatile fractions of each were also determined. In
addition, each sample was analyzed for total and soluble
COD. Data results from this work are presented in
Tables 4 thru 7.
At the end of each time-temperature run, a 2-liter grab
sample of portrate was collected in a graduated cylinder.
The quiescent settling characteristics of this material
were then observed over a one-hour period of time. At the
end of this period, 100-ml samples of both the top and
bottom suspension layers within the cylinder were each
pipetted off and analyzed for their suspended and dissolved
solid contents. Corresponding fixed and volatile fractions
of each were also determined. The results of these
analyses are presented in Tables 8 and 9.
Specifically, the data of Tables 4 thru 7 provide much
insight into some of the physical transformations that
had taken place within the sludge medium as a result of
thermal conditioning. Regardless of the cooking time or
cooking temperature investigated, the heat conditioning
process effected both an increase in dissolved solids
-55-
-------
Table 4 ; DATA SUMMARIZING THE SOLID CHARACTERISTICS OF JWPCP PRIMARY DIGESTED SLUDGE
BOTH BEFORE AND AFTER 30 MINUTES OF COOKING AT VARIOUS REACTOR TEMPERATURES.
REACTOR
TEMPERATURE
.OF.
330
340
350
360
370
380
390
395
REACTOR FEED SOLIDS DATA*
Suspended Form
Total
-*-
3.27
3.21
3.27
3.46
3.35
3.40
3.29
3.32
Volatile
-*-
1.99
1.99
1.99
2.12
2.14
2.16
2.06
1.84
Fixed
-*-
1.27
1.22
1.28
1.34
1.21
1.24
1.24
1.48
Dissolved Form
Total
-*-
0.17
0.18
0.19
0.18
0.21
0.19
0.19
0.16
Volatile
-*-
0.05
0.11
0.09
0.07
0.09
0.07
0.10
0.06
Fixed
-%-
0.12
0.07
0.10
0.11
0.12
0.12
0.09
0.10
PORTRATE SOLIDS DATA
Suspended Form
Total
-*-
3.06
2.41
2.74
2.65
2.51
2.76
2.54
2.79
Volatile
-%-
1.74
1.35
1.53
1.50
1.40
1.54
1.33
1.35
Fixed
-%-
1.32
1.06
1.21
1.15
1.11
1.21
1.21
1.44
Dissolved Form
Total
-%-
0.42
0.53
0.45
0.52
0.53
0.55
0.50
0.44
Volatile
-*-
0.33
0.49
0.40
0.44
0.46
0.46
0.45
0.36
Fixed
-%-
0.09
0.04
0.05
0.08
0.07
0.09
0.05
0.08
I
Ul
o\
* The solid values reported have been corrected for dilution with grinder seal water and
condensed steam.
Unit Conversions: 0.56 (°F-32) = (°C}
(% Solids) x 10,000 =(mg/I)
-------
Table 5: DATA SUMMARIZING THE SOLIDS CHARACTERISTICS OF 'JWPCP* PRIMARY DIGESTED SLUDGE
BOTH BEFORE AND AFTER 40 MINUTES OF COOKING AT VARIOUS REACTOR TEMPERATURES.
RfiACTOR
TEMPERATURE
-°F-
330
335
340
345
350
355
360
365
370
375
380
385
395
REACTOR FEED SOLIDS DATA*
Suspended Form
Total
-%-
3.03
3.06
4.75
3.53
3.11
3.08
3.27
3.14
3.23
3.04
2.96
3.47
3.24
Volatile
-%-
-
-
-
2.23
1.91
1.88
1.98
1.79
1.49
1.73
1.76
2.04
1.79
Fixed
-%-
-
-
-
1.30
1.20
1.20
1.29
1.35
1.74
1.31
1.20
1.43
1.45
Dissolved Form
Total
-!-
0.21
0.20
0.22
0.22
0.20
0.14
0.18
0.16
0.13
0.25
0.22
0.18
0.15
Volatile
-*-
-
-
-
0.10
0.08
0.02
0.04
0.03
0.07
0.11
0.08
0.02
0.06
Fixed
-%-
-
-
-
0.12
0.12
0.12
0.14
0.13
0.06
0.14
0.13
0.16
0.09
PORTRATE SOLIDS DATA
Suspended Form
Total
-%-
2.50
2.55
3.87
2.65
2.39
2.49
2.62
2.47
2.32
2.39
2.33
3.04
2.60
Volatile
-*-
-
-
-
1.58
1.32
1.38
-
1.21
-
1.24
1.19
1.57
1.28
Fixed
-\-
-
-
-
1.07
1.07
1.11
-
1.26
-
1.15
1.14
1.47
1.32
Dissolved Form
Total
-*-
0.39
0.42
0.56
0.40
0.40
0.42
0.38
0.41
0.46
0.49
0.51
0.45
0.44
Volatile
-%-
-
-
-
0.29
0.30
0.33
-
0.32
0.41
0.39
0.43
0.34
0.39
Fixed
-%-
-
-
-
0.11
0.10
0.09
-
0.09
0.05
0.10
0.08
0.11
0.05
I
en
* The solids values reported have been corrected for dilution with grinder seal water
and condensed steam.
Unit Conversions: 0.56 (°F-32) =
(% Solids) x 10,000 = (mg/1)
-------
Table 6; DATA SUMMARIZING THE "COD" CHARACTERISTICS OF 'jWPCP' PRIMARY DIGESTED SLUDGE
BOTH BEFORE AND AFTER 30 MINUTES OF COOKING AT VARIOUS REACTOR TEMPERATURES.
REACTOR
TEMPERATURE
_oF.
330
340
350
360
370
380
390
395
REACTOR FEED "COD" DATA*
Total
-mg/1-
32,300
34,840
35,460
35,785
33,074
34,842
35,450
34,290
Soluble
-mg/1-
290
290
289
286
268
270
275
243
PORTRATE "COD" DATA
Total
-mg/1-
30,700
32,350
-
31,650
-
-
31,900
29,300
Soluble
-mg/1-
4,450
5,550
5,800
6,280
6,070
6,200
6,300
6,400
en
oo
* The "COD" values reported have been corrected for dilution with grinder seal water
and condensed steam.
Unit Conversions: 0.56 (°F-32) = (DC)
-------
Table 7: DATA SUMMARIZING THE "COD" CHARACTERISTICS OF 'JWPCP* PRIMARY DIGESTED SLUDGE
BOTH BEFORE AND AFTER 40 MINUTES OF COOKING AT VARIOUS REACTOR TEMPERATURES.
REACTOR
TEMPERATURE
-°F-
355
360
365
370
375
380
385
395
REACTOR FEED "COD" DATA*
Total
-mg/1-
41,440
34,620
33,910
32,330
30,390
35,300
36,040
32,950
Soluble
-mg/1-
330
280
380
310
240
280
310
280
PORTRATE "COD" DATA
Total
-mg/1-
38,400
36,300
29,600
28,500
24,300
28,900
27,600
29,300
Soluble
-mg/1-
5,280
4,260
5,330
5,910
5,670
5,950
6,830
6,400
* The COD values reported have been corrected for dilution with grinder seal water
and condensed steam.
Unit Conversions: 0.56 (°F-32) = (°C)
-------
Table 8: DATA SUMMARIZING THE QUIESCENT SETTLING* CHARACTERISTICS OF SUSPENDED SOLIDS IN
30-MINUTE HEAT-CONDITIONED DIGESTED SLUDGE**
REACTOR
rEMPERATURI
-°F-
330
340
350
360
370
380
390
395
SOLID CONC. IN "UPPER" 100 ml after SETTLING
Total Form
Total
-1-
0.98
0.92
1.10
0.89
0.81
0.88
0.91
0.76
Volatile
-%-
0.66
0.66
0.75
0.65
0.61
0.66
0.67
0.57
Fixed
-%-
0.32
0.26
0.35
0.24
0.20
0.22
0.24
0.18
Suspended Form
Total
-%-
0.56
0.50
0.65
0.37
0.30
0.33
0.42
0.33
Volatile
-%-
0.33
0.32
0.36
0.20
0.18
0.20
0.23
0.15
Fixed
-%-
0.23
0.18
0.29
0.17
0.12
0.13
0.19
0.18
SOLID CONC. IN "LOWER" 100 ml after SETTLING
Total Form
Total
-%-
6.05
6.72
6.76
6.42
7.01
6.98
7.24
6.42
Volatile
-%-
3.72
3.98
3.88
3.96
4.18
4.10
4.11
3.23
Fixed
-%-
2.33
2.74
2.88
2.46
2.83
2.88
3.13
3.19
Suspended Form
Total
-!-
5.63
6.30
6.31
5.90
6.50
6.44
6.74
6.00
Volatile
-%-
3.38
3.64
3.48
3.52
3.76
3.65
3.66
2.81
Fixed
-%-
2.25
2.66
2.83
2.38
2.74
2.79
3.08
3.19
I
ON
O
* Data were acquired from samples taken after one-hour of settling in a 2-liter graduated cylinder.
** All tabulated data pertain to the thermal processing of JWPCP primary digested sludge.
Unit Conversions; 0.56 (°F-32) = (°C)
(I Solids) x 10,000 = (mg/1)
-------
Table 9: DATA SUMMARIZING THE QUIESCENT SETTLING CHARACTERISTICS OF SUSPENDED SOLIDS IN
40-MINUTE HEAT-CONDITIONED DIGESTED SLUDGE**
REACTOR
TEMPERATURE
_oF.
330
335
340
345
350
355
360
365
370
375
380
385
395
SOLID CONG. IN "UPPER"100 ml after SETTLING
Total Form
Total
-!-
0.75
0.84
0.79
0.66
0.58
0.69
0.80
0.79
0.81
0.78
0.78
0.74
0.82
Volatile
-*-
0.47
0.56
0.62
0.44
0.42
0.47
0.54
0.53
0.59
0.56
0.60
0.51
0.59
Fixed
-%-
0.28
0.28
0.18
0.22
0.16
0.22
0.26
0.26
0.22
0.22
0.18
0.23
0.23
Suspended Form
Total
-%-
0.36
0.42
0.23
0.26
0.18
0.27
0.42
0.39
0.36
0.29
0.26
0.29
0.39
Volatile
-%-
-
-
-
0.15
0.11
0.14
-
0.21
0.18
0.16
0.17
0.17
0.21
Fixed
-%-
-
-
-
0.11
0.07
0.13
-
0.18
0.18
0.13
0.09
0.12
0.18
SOLID CONG. IN "LOWER" 100 ml after SETTLING
Total Form
Total
-%-
5.76
6.36
5.25
5.34
5.38
5.83
5.97
5.95
6.41
5.66
6.07
6.59
6.61
Volatile
-%-
3.17
3.58
3.50
3.30
3.14
3.29
3.37
3.13
3.86
3.05
3.16
3.36
3.36
Fixed
-%-
2.59
2.78
1.75
2.04
2.24
2.54
2.60
2.82
2.55
2.61
2.91
3.23
3.25
Suspended Form
Total
-%-
5.37
5.94
4.69
4.94
4.98
5.40
5.58
5.54
5.96
5.17
5.56
6.14
6.18
Volatile
-%-
-
-
-
3.01
2.83
2.96
-
2.80
3.46
2.66
2.73
3.01
2.97
Fixed
-%-
-
-
-
1.93
2.15
2.44
-
2.74
2.50
2.51
2.83
3.13
3.21
* Data were acquired from samples taken after one-hour
** All tabulated data pertain to the thermal processing
Unit Conversions: 0.56 (°F-32) = (°C)
(% Solids) x 10,000 = (mg/1)
of settling in a 2-liter graduated cyclinder.
of JWPCP primary digested sludge.
-------
and a decrease in the suspended solids content. Most of
this change took place in the volatile fraction of each,
with the fixed fractions remaining relatively constant.
The effect was NOT a corresponding one since there were
some losses in total volatile matter.
Accordingly, two phenomena occurred while heat treating
the JWPCP's primary digested sludge. First the volatile
material injected into the reactor vessel underwent thermal
breakdown to some degree. This resulted in gaseous by-
products which were carried off with the vented reactor
gases. Second, some of the suspended volatile material
was driven into the soluble phase. No correlation
existed between the degree to which each of these phe-
nomena occurred and the time or temperature of the heat
conditioning reaction.
The thermal solubilization of organics which took place
during heat conditioning of digested sludge is evidenced
by the soluble COD data of Tables 6 and 7. Soluble COD
did appear to increase with increased cooking temperature
in the ranges investigated. No correlation, however was
observed with respect to cooking time.
The data of Tables 8 and 9 manifest the difference in the
degree of sludge conditioning which took place at the
various reaction temperatures investigated. At the lower,
30-minute reactor cooking time (Table 8) , increased
cooking temperatures from 330°F to 360°F (165°C to 180°C)
resulted in a decrease in the concentration of suspended
material remaining in the UPPER 100-ml layer after one
hour of quiescent settling. Further temperature increases
up to 395°F (200°C) did nothing to improve this condition.
A similar trend was observed at the 40-minute reactor
cooking time (Table 9). However, the breakpoint occurred
at 350°F (175°C) instead. Further temperature increases
from 350°F to 395°F (175°C to 200°C) provided no inducement
for additional settling of particulate matter from the
UPPER 100-ml suspension layer. In fact, there was some
indication that a minor reversal was taking place.
No relationship between suspended solid concentrations in
the LOWER 100-ml suspension layers and cooking temperature
was evident at either the 30- or 40-minute cooking time.
Observed concentrations in the lower layer appeared to be
a function of the initial solids content of the feed prior
to cooking.
-62-
-------
It was apparent from Tables 8 and 9 that, with respect
to the two breakpoint temperatures, the additional 10
minutes of cooking time, i.e. 40 minutes at 350°F (175°C),
did impart slightly better settling qualities to the
suspended material in portrate. It was therefore decided
this was the OPTIMUM time-temperature combination for heat
conditioning of the JWPCP's primary digested sludge. All
followup studies concerned with the dewatering of portrate
were conducted with digested sludge thermally conditioned
under these conditions.
POLYMER CONDITIONING
The addition of polyelectrolytes to sludge is carried out
to improve the coagulation and flocculation of fine solid
particles held in suspension in the liquid. Polyelec-
trolytes (commonly referred to as polymers) are water-
soluble organic molecules with molecular weights up to
10 million. These polymers contain chemical groups which
are capable of undergoing electrolytic dissociation in
solution, resulting in long-chained highly charged ions.
Polymers are classified into three different types
(anionic, cationic, nonionic) depending on their ionic
character.
Fine particles dispersed in water are held in suspension
primarily because of their extremely small size. A small
particle has a high surface area to mass ratio • Conse-
quently, surface phenomena, such as state of hydration
and electrostatic repulsion, tend to negate the effects
of gravitational forces, thus preventing aggregation and
sedimentation of solid particles. Addition of polymers
to a solution increases sedimentation in two ways. First,
the long-chained polymer molecule chemically and/or
physically bonds itself to the adsorbent surfaces of
sludge particles. The net effect is the formation of
bridges between these otherwise discrete particles, result
ing in flocculation. Also, the charge-carrying polymer
reduces the net electrical repulsive forces at particle
surfaces, thus decreasing the resistence of the particles
to form aggregates. The action of anionic polymers is
apparently mostly due to physical attachment, whereas
cationic polymers are effective primarily because of
their ability to reduce electrical repulsion. Once con-
tact between particles is achieved, the forces of attrac-
tion (Van der Waals forcesj become significant enough to
-63-
-------
resist breakup of the particles through the mild agitation
necessary to induce flocculation. Consequently, aggregates
accumulate with lower surface area to mass ratios, and
sedimentation by gravity occurs more readily.
The effects of using cationic polyelectrolytes as a sludge
conditioning agent in the various pilot plant units are
discussed in detail later in this report.
CHEMICAL CONDITIONING
Chemicals are added to sludges to coagulate and flocculate
the fine particles which, under normal conditions, remain
discreetly suspended in the liquid phase. In primary
digested sludges, this stability is attributable in part
to the particles' net negative charge. Hence, neutraliza-
tion of this charge is necessary before coagulation can
occur. Multivalence cations are generally used for this
purpose. Their addition to the sludge serves to depress
the electronegativity of the charged particles, thereby
reducing the zeta potential to a level below the
Van der Walls attractive forces. In general, the coagula-
tion and precipitating power of the added cations geo-
metrically increases with the valence. When necessary,
alkalinity is also added.
In this investigation, laboratory studies revealed that
chemical coagulation of the suspended material in the
JWPCP digested sludge was best under conditions of high pH.
Accordingly, lime was selected to accomplish this in the
pilot plant studies. In addition, ferric chloride (Fed?)
was selected as the charge neutralizing agent for coagula-
tion.
The addition of lime aids in the formation of floe particles
by increasing the (OH") radical in solution. Under these
conditions, the followup addition of the ferric salt re-
sults in the formation of an insoluble ferric hydroxide.
The basic reaction governing this formation is
Fe3+ + 3 OH > Fe(OH)3
where the solubility product (Fe3+)(OH')3 = 10-36.
-64-
-------
The lime used in the test program was purchased in dry
powdered form as calcium hydroxide, Ca(OH)2, with an
approximate purity of 95 percent. Lime conditioning
in conjunction with pressure filtration tests was
accomplished by directly adding a weighted amount of the
dry material (as received) to a known volumetric quantity
of sludge residing in the unit's conditioning tank. In
all other cases, liquid solutions of this material were
batched for controlled feeding to the unit or system
being evaluated. Throughout the report, lime dosages-
stated in terms of Ca(OH)7--actually denote the weight of
dry material (including impurities) added per unit weight
of dry sludge solids.
Buchner Funnel tests run by the Districts' laboratory
personnel indicated that chemical conditioning of the
JWPCP primary digested sludge for pilot plant dewatering
would be optimized in the ferric chloride and/or lime
dosage ranges of 40-120 Ibs/ton (20-60 kg/metric ton) and
400-800 Ibs/ton (200-400 kg/metric ton) as Ca(OH)<> respective
ly. Data results regarding dewatering studies con'ducted
with chemical dosages in these ranges are presented later
in this report.
FLYASH CONDITIONING
Flyash is a complex, heterogeneous inert material whose
physical and chemical properties are, for the most part,
dependent on its source. It is these properties which
affect its action as a sludge conditioner. When added to
a sludge mixture, sludge particles become bonded to the sur-
face of the flyash particles by means of chemical and/or
electrostatic interactions. Additional alkalinity is
sometimes necessary to enhance these reactions. The
overall effect is such that an intimately mixed three-
dimensional lattice is formed, the strength and rigidity
of which is dependent on the properties of both the sludge
and flyash particulate matter. Such a structure enables
the development of numerous passages or pores to occur
during dewatering and compaction of the cake solids, thus
allowing for unrestricted flowthrough movement of the
fluid medium. This results in a dewatered sludge cake
of lower residual moisture content.
-65-
-------
In this study, flyash conditioning was only evaluated
in conjunction with dewatering by pressure filtration.
Incineration of the various dewatered sludge cakes
produced an ash residue which, when pulverized, became
the resulting flyash conditioning material.
-66-
-------
DEWATERING SYSTEMS
The availability of the various pilot plant dewatering
equipment enabled a variety of conditioning-dewatering
schemes to be set up and evaluated. Some of the units
were assessed as to their capabilities for dewatering
centrate from the existing centrifuge station at the
JWPCP; for purposes of discussion, the term "Bird centrate"
will be used hereafter when referring to the feed material
of such schemes. Also, much of the equipment was eval-
uated using digested sludge as the feed material. Overall,
the evaluations incorporated the various conditioning
steps discussed in the previous section.
Regarding those schemes incorporating heat conditioning,
consideration was only given to the processing of
optimally prepared portrate sludge, i.e. digested
sludge cooked at 350°F (175°C) for 40 minutes. First,
the picket thickening characteristics of portrate were
investigated. Other dewatering equipment were then
evaluated as to their individual ability to dewater the
thickened portrate. Some studies were also conducted
to assess whether the cooked sludge could be directly
dewatered without any intermediate thickening step.
Regarding portrate centrifugation studies, the effect of
secondary conditioning with a cationic polymer was also
evaluated.
The following is a detailed presentation of the data
generated from the research work. In this regard, the
details and capabilities of each dewatering unit are
presented separately and discussed.
-67-
LioKM.KY U.S. EPA
-------
PICKET THICKENING OF COOKED DIGESTED SLUDGE
Presented in Figure 13 is a flow schematic of the experi-
mental setup used for evaluating the picket thickening
properties of optimally heat-conditioned digested sludge.
As noted, a small storage tank and a variable speed feed
pump were incorporated in series between the Porteous
unit and the thickening tank. Portrate, intermittently
discharged to and accumulated in the storage tank, would
serve as the reservoir from which it would be steadily
pumped at various feedrates to the clarifier. In
accordance with the output from the Porteous unit, a
maximum steady state feedrate of 3.4 gpm (0.21 I/sec)
would be possible. The storage tank was equipped with
an overflow drainage line, thus providing excess storage
relief during periods when clarifier feedrates below
maximum were being investigated.
Overall, the following two capabilities are seen to have
been built into this system. First, a continuously fed
clarifier would provide a continuous steady stream of
decant (overflow) from the overflow weir of the thicken-
ing tank. Second, cessation of the tank feed would
enable thickening of the tank's contents without over-
flow .
The manner in which the thickening tests were conducted
was as follows. At the beginning of each test run, cooked
sludge was fed directly from the Porteous unit into the
clarifier. The picket thickener remained de-energized
during filling. When the tank became full, the portrate
was then diverted into the storage tank and pump assembly
for controlled feeding at one of four test feed rates.
The picket thickener was simultaneously energized. Follow
ing one hour of picket thickening with continuous over-
flow, a one-liter sample of each of the overflow and
underflow was taken. Time permitting, a second set of
samples was taken following a second hour of picket
thickening with continuous overflow. The feeding of
portrate to the clarifier was then discontinued. The
material still remaining in the tank, however, was
allowed to picket thicken overnight. Following 16 hours
of picket thickening without continuous overflow, samples
of both the upper and lower suspension layers were taken.
-68-
-------
FIGURE 13
Schematic flow diagram
Equipment used to evaluate the picket thickening properties
of heat conditioned digested sludge
PRIMARY
DIGESTED
SLUDGE
PORTEOUS PROCESS
HEAT TREATMENT
STORAGE
TANK
STORAGE RELIEF
TO DRAIN
o
Q ^
r> uj
en <
UJ Q_
o
Q_
VARlABLE SPEED
PROGRESSIVE
CAVITY PUMP
PICKET
DRIVE
THICKENING TANK
^te
THICKENED
PORTRATE
UNDERFLOW
DECANTED
OVERFLOW
-------
All samples were analyzed for their total, dissolved and
respective fixed and solid fractions. Corresponding
suspended and volatile solid fractions were determined
by subtraction.
Data summarizing the picket thickening properties of
portrate sludge are presented in Table 10. The clarifier
feedrate was varied between 1.2 and 3.4 gpm
(0.08 and 0.21 I/sec) resulting in overflow rates between
225 and 635 gpd/sq ft (9.2 and 25.9 cu m/day/sq m). The
test runs at each of the indicated feedrates were carried
out in triplicate. Hence, the tabulated values shown
in Table 10 are averages of data acquired from individual
test runs.
During continuous feeding (a situation which provided
continuous overflow) an equilibrium state of operation
was achieved after one hour of picket thickening.
Continued operation for an additional one-hour period
served only to thicken the material in the bottom of the
tank. Overflow quality remained relatively unchanged as
seen by the 2-hr data taken when the overflow rate was
either 375 or 560 gpd/sq ft (15.3 or 22.8 cu m/day/sq m).
With respect to the one-hour thickening runs, the average
concentration of suspended solids in the decanted over-
flow decreased with decreasing feed rates. The effect is
graphically depicted in Figure 14 of this report. At an
overflow rate of 635 gpd/sq ft (25.9 cu m/day/sq m) a
decanted liquor resulted containing 0.53% (5300 mg/1)
of suspended material. At the lower 225 gpd/sq ft
(9.2 cu m/day/sq m) overflow rate, the suspended solids
content in the decantate was 0.371 (3700 mg/1). The
dashed portion of the curve at the bottom is a projection
based on the average of the suspended solids remaining
in the UPPER suspension layer following overnight
thickening. This value of 1900 mg/1 (0.19%) represents
the average absolute minimum to which suspended solids
in the overflow could be reduced by this type of gravity
thickening operation; it also indicates that an
absolute maximum of 95 percent of the suspended material
could be removed from the JWPCP's digested sludge by
the system as a whole.
In all cases, picket thickening increased the suspended
solid concentrations in the underflow suspension layer of
-70-
-------
Table 10 : DATA SUMMARIZING THE EFFECT OF CLARIFIER OVERFLOW RATE ON THE PICKET
THICKENING PROPERTIES OF COOKED DIGESTED SLUDGE*
CLARIFIER
OVERFLOW
RATE
•gpd/sq ft-
225
375
560
635
PICKET
THICKENING
TIME
-hr-
1.0
16.0
1.0
2.0
16.0
1.0
2.0
16.0
1.0
16.0
WITH or
WITHOUT
CONTINUOUS
OVERFLOW
With
Without
With
With
Without
With
With
Without
With
Without
AVERAGE SUSPENDED SOLIDS IN THICKENING TANKS
UPPER Suspension Layer
Total
-!-
0.37
0.19
0.42
0.39
0.19
0.48
0.48
0.17
0.53
0.20
Volatile
-%-
0.21
0.12
0.25
0.24
0.13
0.27
0.28
0.09
0.29
0.16
Fixed
-%-
0.16
0.07
0.17
0.15
0.06
0.21
0.20
0.08
0.24
0.04
LOWER Suspension Layer
Total
-\-
7.78
10.82
6.29
7.82
10.30
7.07
9.97
14.93
6.14
7.96
Volatile
-%-
4.33
6.00
3.62
4.49
5.81
4.10
5.67
8.51
3.59
4.51
Fixed
-%-
3.45
4.82
2.67
3.33
4.49
2.97
4.30
6.42
2.55
3.44
*A11 data pertain to JWPCP waste digested sludge cooked at 350°F (175°C) for 40 minutes.
Tabulated values are averages of individual data acquired from triplicate runs.
Unit Conversions: (gpd/sq ft) x 0.0408 = (cu m/day/sq m)
(% Solids) x 10,000 = (mg/1)
-------
FIGURE 14
r-o
Suspended solids in decantate as a function of
overflow rate in a picket thickening clarifier
CO
Q
0
CO
O
U)
Q
5"
SUSPEI
AVERAGE
\j. i
0.6
^ 0.5
§0.4
•
_J
or
^0.3
0.2-
O.I
n
1 1 1 1 1 i 1
—
.S
^^-^
1 1 1 1
—
—
„_
/
^— / FEED: —
/' JWPCP DIGESTED SLUDGE
/ COOKED AT 350°F (175° C)
/_ FOR 40 MINUTES _
UNIT CONVERSIONS;
(gpd/sqtt)
(% solids) x
1 1 1 1 1 1 1
x 0.04 = (cu m/day/sq m .)
10,000 = (mg/l) ~
1 1 1 1
0
100 200
300 400 500 600 700 800 900
OVERFLOW RATE , gpd / sq ft
1000 1100 120
-------
the clarifier. The average concentration values increased
with increased thickening time but varied randomly with
increasing overflow rates.
HORIZONTAL SCROLL CENTRIFUGATION
Horizontal scroll centrifugation studies were restricted
to the processing of the JWPCP digested sludge. Initial-
ly, the isolated Bird centrifuge was assessed as to its
capabilities for dewatering digested sludge without the
use of conditioning aids. This enabled the base
performance of the machine to be established and provided
much insight into followup work utilizing polymer condi-
tioning aids. Studies on the centrifugal dewatering
of heat-conditioned digested sludge were conducted with
the Sharpies P-600 decanter.
The evaluation of the base performance of the Bird decanter
was carried out in a manner which enabled the effect of
variations in sludge feed rate and bowl pool depth to,
be independently assessed. Considered in this respect
were primary digested sludge feedrates between
200 and 400 gpm (12.6 and 25.2 I/sec) and pool depths
between 1.0 and 3.4 inches (2.5 and 8.6 cm). The
rotational speed of the bowl was held constant at 1300 rpm.
The differential speed, i.e. the speed difference between
the bowl and scroll, remained fixed at 15.3 rpm. During
all test runs, the chemical chamber and injection tubes
were purged with 7 gpm (0.4 I/sec) of water to prevent
backflow intrusion of the sludge material. The data
obtained from this test evaluation are presented in
Tables 11 thru 15. Since the Bird centrifuge had been
completely reconditioned prior to testing, the tabulated
results demonstrated the base performance of the machine
under conditions of little or no wear. It is to be
noted that many of the runs were randomly duplicated,
thus adding support and surety to the data obtained.
Tabulated data averages are presented for the cake
qualities and suspended solids recoveries obtained in the
duplicate runs.
•\
The base performance results obtained from this work
are graphically depicted in Figures 15 and 16. Regard-
less of the sludge feedrate to the centrifuge, the
general trend was for suspended solids capture to increase
and cake dryness to decrease as pool depth was increased.
-73-
-------
Table 11: DATA* SUMMARIZING THE EFFECT OF VARYING POOL DEPTHS ON THE DEWATERING
PERFORMANCE OF A HORIZONTAL SCROLL CENTRIFUGE WHEN FED PRIMARY DIGESTED
SLUDGE IN A 200-GPM FLOWSTREAM.
POOL
DEPTH
- inches -
1.0
1.0
1.5
2.0
2.0
2.5
2.5
3.0
3.5
SUSPFJtf)ED SOLIDS CONCENTRATION
Digested
Sludge
Feed**
-%-
2.68
3.25
3.29
3.17
3.26
3.77
3.43
3.73
3.73
Centrate
-%-
1.87
2.52
2.29
2.08
2.16
1
2.11
1.99
2.09
1.86
Centrifuged
Cake
-%-
Individual"
29.4
40.2
31.5
23.9
26.2
30.0
30.3
24.6
20.6
Average
34.8
31.5
25.1
30.1
24.6
20.6
SUSPENDED
SOLIDS
RECOVERY
-%-
Individual
32.2
23.9
32.8
37.5
36.9
47.5
45.0
48.1
55.2
Average
28.1
32.8
37.2
46.3
48.1
55.2
*A11 data pertain to dewatering of JWPCP primary digested sludge in a 36-inch x 96-inch
horizontal scroll centrifuge.
**Reported values are corrected for dilution with 7 gpm of water purging through the chemical
chamber.
Unit Conversions:
(inches) x 2.54 = (cm)
Solids) x 10,000 = (mg/1)
(gpm) x 0.0631 -= (I/sec)
-------
Table 12: DATA* SUMMARIZING THE EFFECT OF VARYING POOL DEPTHS ON THE DEWATERING PERFORMANCE
OF A HORIZONTAL SCROLL CENTRIFUGE WHEN FED PRIMARY DIGESTED SLUDGE IN A 25Q-GPM
FLOWSTREAM
POOL
DEPTH
- inches -
1.0
1.5
2.0
2.5
3.0
3.0
3.4
SUSPENDED SOLIDS CONCENTRATION
Digested
Sludge
Feed**
-1-
Centrate
>
3.32
3.20
3.55
3.47
3.63
3.05
3.41
2.61
2.36
2.44
2.23
2.23
1.86
1.95
Centrifuged
Cake
Individual
37.0
36.5
31.8
29.8
23.0
24.8
22.6
Average
37.0
36.5
31.8
29.8
23.9
22.6
SUSPENDED
SOLIDS
RECOVERY
Individual
22.9
28.1
34.1
38.8
42.8
42.1
46.9
Average
22.9
28.1
34.1
38.8
42.5
46.9
-J
en
* All data pertain to dewatering of JWPCP primary digested sludge in a 36-inch x 96-inch
horizontal scroll centrifuge.
** Reported values are corrected for dilution with 7 gpm of water purging through the chemical
chamber.
Unit Conversions: (inches) x 2.54 = (on)
~~~ (% Solids) x 10,000 = (mg/1)
(gpm) x 0.0631 = (I/sec)
-------
Table 13; DATA* SUMMARIZING THE EFFECT OF VARYING POOL DEPTHS ON THE DEWATERING PERFORMANCE
OF A HORIZONTAL SCROLL CENTRIFUGE WHEN FED PRIMARY DIGESTED SLUDGE IN A 500-GPM
H,OWSTRliAM.
POOL
DEPTH
- inches -
1.0
1.0
1.5
1.5
2.0
2.0
2.5
2.5
3.0
3.0
3.4
SUSPENDED SOLIDS CONCENTRATION
Digested
Sludge
Feed**
3.30
3.01
3.48
3.01
3.41
3.14
3.29
3.39
3.30
3.44
3.59
Centrate
2.62
2.43
2.51
2.37
2.42
2.41
2.25
2.24
2.22
2.11
2.22
Centrifuged
Cake
Individual
41.7
41.3
40.7
36.2
33.9
36.6
30.1
33.7
26.2
27.1
25.0
Average
41.5
38.5
35.3
31.9
26.7
25.0
SUSPENDED
SOLIDS
RECOVERY
Individual
22.0
20.4
29.7
22.9
31.4
25.0
34.1
36.5
35.9
42.0
42.0
Average
21.2
26.3
28.2
35.3
39.0
42.0
er>
* All data pertain to dewatering of JWPCP primary digested sludge in a 36-inch x 96-inch
horizontal scroll centrifuge.
** Reported values are corrected for dilution with 7 gpm of water purging through the chemical
chamber.
Unit Conversions:
(inches) x 2.54 = (on)
(% Solids) x 10,000 = (mg/1)
(gpm) x 0.0631 = (I/sec)
-------
Table 14: DATA* SUMMARIZING THE EFFECT OF VARYING POOL DEPTHS ON THE DEWATERING PERFORMANCE
OF A HORIZONTAL SCROLL CENTRIFUGE WHEN FED PRIMARY DIGESTED SLUDGE IN A
350-GPM FLOWSTREAM.
'POOL
DEPTH
- inches -
1.0
1.5
2.0
2.5
2.5
3.0
3.0
3.4
3.4
SUSPENDED SOLIDS CONCENTRATION
Diges'ted
Sludge
Feed**
3.52
3.41
3.40
3.46
3.46
3.34
3.49
3.31
3.46
Centrate
2.90
2.71
2.56
2.42
2.37
2.32
2.28
2.14
2.19
Centrifuged
Cake
Individual
41.9
39.8
36.4
32.5
31.5
32.1
28.8
28.1
20.2
Average
41.9
39.8
36.4
32.0
30.5
24.2
SUSPENDED
SOLIDS
RECOVERY
Individual
19.1
22.0
26.4
32.5
34.1
33.1
37.7
38.3
41.2
Average
19.1
22.0
26.4
33.3
35.4
39.8
* All data pertain to dewatering of JWPCP primary digested sludge in a 36-inch x 96-inch
horizontal scroll centrifuge.
** Reported values are corrected for dilution with 7 gpm of water purging through the chemical
chamber.
Unit Conversions:
(inches) x 2.54 = (on)
(% Solids) x 10,000 = (mg/1)
(gpm) x 0.0631 = (I/sec)
-------
Table -15 : DATA* SUMMARIZING THE EFFECT OF VARYING POOL DEPTHS ON THE DEWATERING
PERFORMANCE OF A HORIZONTAL SCROLL CENTRIFUGE WHEN FED PRIMARY
DIGESTED SLUDGE IN A 400-GPM FLOWSTREAM.
POOL
DEPTH
- inches -
1.0
1.0
1.5
1.5
2.0
2.0
2.5
3.0
3.0
3.4
3.4
SUSPENDED SOLIDS CONCENTRATION
Digested
Sludge
Feed**
3.10
3.44
3.25
3.45
3.12
3.48
3.40
3.05
3.34
3.01
3.47
Centrate
2.43
2.76
2.49
2.73
2.23
2.65
2.43
2.07
2.41
1.91
2.31
Centrifuged
Cake
-*-
Individual
41.2
40.5
i
40.7
38.2
41.6
34.8
30.4
30.9
28.0
25.6
25.5
Average
40.8
39.5
38.2
30.4
29.4
25.6
SUSPENDED
SOLIDS
RECOVERY
Individual
22.8
21.2
24.9
22.7
30.4
25.9
31.2
34.5
30.5
39.2
36.9
Average
22.0
-
23.8
28.2
31.2
32.5
38.1
I
\1
oo
All data pertain to dewatering of JWPCP primary digested sludge in a 36-inch x 96-inch
horizontal scroll centrifuge.
** Reported values are corrected for dilution with 7 gpm of water purging through the chemical
chamber.
Unit Conversions: (inches) x 2.54 = (cm)
(% Solids) x 10,000 = (mg/1)
(gpm) x 0.0631 = (I/sec)
-------
FIGURE 15
60
The effect of decanter pool depth on the centrifugal
recovery of suspended solids from unconditioned
primary digested sludge
* 55
cr
50
o
O 45
LJ
o:
40
CO
o
_j
a
CO
o 30
UJ
Q
g
Q_
CO
Z> 20
CO
15
FEED' PRIMARY DIGESTED SLUDGE
CENTRIFUGE: 36" x 96" BIRD
HORIZONTAL SCROLL DECANTER
BOWL SPEED= 1300 rpm (900 g)
DIFFERENTIAL SPEED: I5.3rpm
UNIT CONVERSIONS:
(gpm) x 0.0631 =(l/sec)
(inches) x 2.54 = (cm)
THROUGHPUT RATE
~ 200 gpm
250 gpm
300 gpm
350 gpm
400 gpm
0
1.0
2.0 3.0 4.0 5.0
POOL DEPTH , inches
6.0
7.0
-------
FIGURE 16
00
o
I
The effect of decanter pool depth on cake dryness obtained during
centrifugal dewatering of unconditioned primary digested sludge
o
a
LJ
o
ID
LL
E
UJ
o
U_
o
50
45
40
35
30
£ 25
O
O 20
CO
Q
-I 15
O 0
CO
I
I
\
\
1
I
I
III!
FEED: PRIMARY DIGESTED SLUDGE
CENTRIFUGE: 36" x 96" BIRD ~
HORIZONTAL SCROLL DECANTER
BOWL SPEED: |300 rpm (900 g) _
DIFFERENTIAL SPEED: 15.3 r pm
UNIT CONVERSIONS:
(gpm) x O.063I = (I/sec)
(inches) x 2.54 = (cm)
THROUGHPUT RATE
200 gpm
250 gpm
300 gpm
350 gpm
-• 400 gpm
I I
1
1
1.0
2.0 3.0 4.0
POOL DEPTH , inches
5.0
6.0
-------
For any particular pool depth, decreasing solids recovery
and increasing cake dryness were generally experienced
as the sludge feedrate was increased within the range
investigated. The comparative reversed trends of
Figures 15 and 16 as well as the display of a somewhat
linear family of curves in each suggested that cake
quality was a function of suspended solids recovery.
This proved to be the case as is demonstrated by the
plot of these data shown in Figure 17. The dependency
is seen to be a linear one. Also, the phenomena is
understandable since the experienced incremental
increases in suspended solids captures consisted, for
the most part, of finely suspended material containing
a proportionally larger amount of surface bound water
per unit of particle mass.
In the absence of any conditioning of the JWPCP primary
digested sludge, the results depicted in Figure 17
define the absolute performance (under conditions of
little or no wear) of the Bird horizontal scroll
centrifuge. Mathematically, this performance is defined
by the corresponding linear equation
R = -(1.41)C + 78.4 , with (20< C >42)
where R = percent solids capture, %
C = dry weight percentage of cake solids, I
A typical base performance curve demonstrating the
capabilities of the test centrifuge under a fixed set of
operating conditions is presented in Figure 18. Such
performance curves for the other investigated sludge
feedrates, or for that matter, any feedrate would
take on a similar format as this one shown. From an
operational standpoint, use of such curves would enable
centrifuge operating conditions to be set up on the
basis of a desired result.
In an attempt to further increase the solids capture
in the Bird horizontal scroll centrifuge, polymer
addition to the primary digested sludge feed was investi-
gated. A number of commercially available cationic
polymers were tested. All tests were conducted with the
sludge feed, bowl speed, differential speed and pool
depth held constant at 250 gpm (15.8 I/sec), 1300 rpm,
15.3 rpm and 3.4 inches (8.6 cm), respectively. Only
chemical dosage was allowed to vary.
-81-
-------
FIGURE
o
OO ° •.
CO
Q
O
CO
LL)
O
40
30
20
10
Dewaterability of unconditioned primary digested sludge in a
36" x 96" Bird horizontal scroll centrifuge
THROUGHPUT RATE*
LINE EQUATION
R= (-1.41) C +78.4
(20
-------
FIGURE 18
Typical dewatering performance curves for a 36" x 96"
OO
O4
I
50
45
- 40
>
QL
LU
> 35
O
O
o:
CO
Q
o
CO
Bird horizontal
scroll centrifuge fed unconditioned primary digested sludge
30
25
20
0
RECOVERY
1.0
Till
O FEED RATE-- 250 gpm (15.8 I/sec)
BOWL SPEED: 1300 rpm (900 g) '
DIFFERENTIAL SPEED: 15.3 rpm
UNIT CONVERSIONS:
(inches) x 2.54 = (cm)
2.0 3.0 4.0
POOL DEPTH, inches
5.0
6.0
-------
Regarding all test runs reported on herein, polymer_
solutions were injected into the sludge stream within
the bowl of the centrifuge. Some test work was conducted
to determine if changing the polymer addition point would
enhance solids recovery. Two alternate injection points
were considered, namely the suction and the discharge
sides of the sludge feed pump; both, however, yielded
inferior results comparatively. Consequently, polymer
injection to the centrifuge bowl was deemed best for the
JWPCP installation.
Overall, the results of this part of the investigation
revealed the following two important findings.
(1) High suspended solid recoveries (approximately
95 percent) were sometimes obtainable with
each of the cationic polymers tested.
(2) For any particular polymer product used, de-
watering performance under a fixed set of
operating conditions was not always repro-
ducible.
It is important that these two findings be kept in mind
when interpreting the following presented data.
The first finding is evidenced by the performance data
of Tables 16 thru 18 which respectively summarize some
trial-run dewatering results on the Bird horizontal
scroll centrifuge as effected by varying dosages of
three different cationic polymers (Nalco 610, Calgon
WT-2570, and Hercofloc 810). For comparative purposes,
the experienced solid recoveries are plotted as a
function of polymer dosage in Figure 19: In all cases,
increased polymer dosages effected increased solids
recovery up to a point whereupon further dosage increases
yielded no additional recovery. Although the recovered
maximums were relatively the same for each polymer
tested, the minimum "break point" dosage necessary to
attain this result differed markedly. Approximately
5 Ibs/ton (2.5 kg/metric ton) of Hercofloc 810 were
needed to attain a 94 percent solids recovery maximum.
This is to be compared with the 8 Ibs/ton (4.0 kg/metric
ton) of Nalco 610 and 10 Ibs/ton (5.0 kg/metric ton)
of WT-2570 necessary to achieve solids recovery maximums
of 95 percent and 96 percent, respectively. During
polymer usage, the solids content of the discharging cakes
randomly ranged between 181 and 22% by weight.
-84-
-------
Table 16: DATA* SUMMARIZING THE SLUDGE DEWATERING PERFORMANCE OF A HORIZONTAL SCROLL
CENTRIFUGE AS EFFECTED BY VARYING DOSAGES OF NALCO 610.
PARAMETERS
T.Sludge Feed Rate 250 gpm (15.8 I/sec)
2. Bowl Speed 1300 rpm
3. Differential Speed 15.3 rpm
4. Pool Depth 3.4 inches (8.6 cm)
5. Flowrate from Chemical Station... 16 gpm (1.0 I/sec)
OO
Cn
I
SUSPENDED SOLIDS CONCENTRATION
Sludge
Feed**
-%-
3.92
3.68
3.70
3.72
3.57
3.89
2.96
2.71
2.39
Centrate
-\-
2.55
1.75
1.33
0.94
0.17
0.17
0.15
0.13
0.12
Cake
-%-
23.3
18.5
18.4
19.5
18.6
19.5
16.0
16.4
15.8
CHEMICAL
DOSAGE
-Ibs/ton-
0.0
1.1
2.2
3.2
9.0
9.3
13.5
17.7
18.4
PERCENT RECOVERY
OF
SUSPENDED SOLIDS
-%-
34.6
54.7
66.7
76.7
95.9
96.3
95.6
95.7
95.6
* All data pertain to dewatering tests conducted on JWPCP primary digested sludge
with a 36-inch x 96-inch horizontal scroll centrifuge.
** Reported values are corrected for dilution with 16 gpm (1.0 I/sec) of polymer
solution from the chemical station.
Unit Conversions: (% Solids) x 10,000 = (mg/1)
(Ibs/ton) x 0.5 = (kg/metric ton)
-------
Table 17: DATA* SUMMARIZING THE SLUDGE DEWATERING PERFORMANCE OF A HORIZONTAL SCROLL
CENTRIFUGE AS EFFECTED BY VARYING DOSAGES OF WT-2570.
PARAMETERS
I
CO
Sludge Feed Rate 250 gpm (15.8 I/sec)
Bowl Speed 1300 rpm
Differential Speed 15.3 rpm
Pool Depth 3.4 inches (8.6 cm)
SUSPENDED SOLIDS CONCENTRATION
Sludge
Feed**
-%-
3.96
3.71
3.61
3.76
3.68
4.19
3.65
3.57
3.80
3.87
3.85
Sludge
Centrate
-%-
2.49
2.11
1.51
1.40
0.91
0.60
0.33
0.17
0.16
0.15
0.17
Cake
-%-
27.6
20.4
18.7
18.9
18.4
22.2
23.6
19.5
20.8
20.2
20.2
CHEMICAL
DOSAGE
-Ibs/ton-
0.0
1.1
2.2
3.2
4.4
6.5
8.8
10.1
10.5
11.4
12.5
PERCENT RECOVERY
OF
SUSPENDED SOLIDS
-%-
36.5
44.1
60.3
65.2
77.6
87.1
91.7
95.7
96.3
96.5
96.2
* All data pertain to dewatering tests conducted on JWPCP primary digested sludge
with a 36-inch x 96-inch horizontal scroll centrifuge.
** Reported values are corrected for dilution with 16 gpm (1.0 I/sec) of polymer
solution from the chemical station.
Unit Conversions:
(% Solids) x 10,000 = (mg/1)
(Ibs/ton) x 0.5 = (kg/metric ton)
-------
Table 18:
I
OO
DATA* SUMMARIZING THE SLUDGE DEWATERING PERFORMANCE OF A HORIZONTAL SCROLL
CENTRIFUGE AS EFFECTED BY VARYING DOSAGES OF HERCOFLOC 810--Run No. 1
PARAMETERS
Sludge Feed Rate 250 gpm (15.8 I/sec)
1
2
3
4
5. Flowrate from Chemical Station... 16 gpm (1.0 I/sec)
Bowl Speed 1300 rpm
Differential Speed 15.3 TPn[
Pool Depth 3.4 inches (8.6 cm)
SUSPENDED SOLIDS CONCENTRATION
Sludge
Feed**
-%-
3.68
3.69
3.62
3.65
3.61
3.55
3.43
3.80
3.77
3.81
3.69
3.77
3.78
Centrate
-%-
2.16
1.43
0.93
0.49
0.28
0.25
0.25
0.25
0.22
0.28
0.27
0.26
0.23
Cake
-%-
23.9
19.0
18.8
19.4
19.0
20.4
20.1
21.4
19.9
21.0
20.2
20.6
22.5
CHEMICAL
DOSAGE
-Ibs/ton-
0.0
1.1
2.2
3.3
4.4
5.7
7.1
7.2
8.5
9.5
10.9
11.7
12.7
PERCENT RECOVERY
OF
SUSPENDED SOLIDS
-*-
41.2
63.5
76.4
86.1
93.1
93.8
93.3
94.0
94.7
93.6
93.6
93.8
94.5
* All data pertain to dewatering tests conducted on JWPCP primary digested sludge
with a 36-inch x 96-inch Bird horizontal scroll centrifuge.
** Reported values are corrected for dilution with 16 gpm (1.0 I/sec) of polymer
solution from the chemical station.
Unit Conversions: (I Solids) x 10,000 = (mg/1)
(Ibs/ton) x 0.5 = (kg/metric ton)
-------
FIGURE 19
oo
oo
100
Horizontal scroll centrifuge: sludge dewatering performance
as effected by various cationic polymers
T
T
CENTRIFUGE: 36" x 96" BIRD DECANTER
BOWL SPEED: 1300 rpm (900 g) ~~
DIFFERENTIAL SPEED= 15.3 rpm
POOL DEPTH: 3.4" (8-6 cm)
FEED: PRIMARY DIGESTED SLUDGE ~~
FEED RATE= 250 gpm (15.8 I/sec)
CHEMICAL FEED RATE:
1.6 gpm (1.0 I/sec) —
UNIT CONVERSIONS:
(Ibs/ton) x 0.5 = (kg/metric ton)
POLYMER
CAKE
SOLIDS
HERCOFLOC 810 19-22%-
NALCO 610 16- 19%
CALGON WT-2570 18-22%
I
8 10 12 14 16
POLYMER DOSAGE , Ibs/ton
18
20
22
24
-------
The second finding is evidenced by a comparison of the
data in Table 18 with that in Table 19 obtained from
a trial run conducted on a different day but under
identical test conditions with the same polymer
(Hercofloc 810) . The solids recovery data from these
two tables are plotted as a function of polymer dosage
in Figure 20. As noted, only 86 percent suspended
solids capture was possible in the latter run as com-
pared to 94 percent in the former. Both occurred,
however, at approximately the same "break point"
dosage of 5 Ibs/ton (2.5 kg/metric ton). Since similar
recovery differences were observed with several of
the polymer products tested and because a thorough check
revealed the absence of any problem with the chemical
distributing or centrifuge systems, it could only be
surmised that the anomaly was the result of some ever
changing quantitative or qualitative characteristic of
the sludge feed material which interfered with and
partially negated the polymer's activity.
Regarding other cationic polymer products tested
(Dow C-41, Calgon WT-2580, Hercofloc 814-X and
Magnifloc 560-C) , the "break point" dosages required
of each to achieve maximum solids capture ranged from
5 to 14 Ibs/ton (2.5 to 7.0 kg/metric ton). For the
most part, the solids content of discharging cakes
ranged between 181 and 22% by weight. Dilution of
batched polymer solutions to something less than
0.5% (5000 mg/1) prior to injection into the sludge
stream did nothing to enhance suspended solid recoveries.
The centrifugal dewaterability of optimally heat-condi-
tioned digested sludge was carried out in the following
manner. First, efforts were applied towards centrifuging
unthickened portrate both with and without cationic
polymer addition. Followup work was then similarly
conducted on thickened portrate underflow from the
picket thickening clarifier. A flowsheet schematic of
each of the two described systems is presented in Figures
21 and 22. As noted, each system was set up to provide
for optional polymer injection into the centrifuge bowl.
Only one cationic polymer was used for this work, namely
Hercofloc 810.
Held constant throughout this phase of the test program
were the heat conditioning variables. Digested sludge
was cooked for 40 minutes at 350°F (175°C) in the
Porteous pilot plant unit. Discharged portrate was
-89-
-------
Table 19: DATA* SUMMARIZING THE SLUDGE DEWATERING PERFORMANCE OF A HORIZONTAL SCROLL
CENTRIFUGE AS EFFECTED BY VARYING DOSAGES OF HERCOFLOC 810--Run No. 2
PARAMETERS
Sludge Feed Rate 250 gpm (15.8 I/sec)
Bowl Speed 1300 rpm
Differential Speed 15.3 rpm
Pool Depth 3.4 inches (8.6 cm)
Flowrate from Chemical Station... 16 gpm (1.0 I/sec)
SUSPENDED SOLIDS CONCENTRATION
Sludge
Feed**
-%-
3.42
3.40
3.38
3.52
3.56
3.45
3.39
3.35
Centrate
-%-
1.95
1.31
0.75
0.59
0.50
0.54
0.56
0.45
Cake
-\-
21.6
17.8
17.2
18.6
17.9
18.1
18.4
19.3
CHEMICAL
DOSAGE
-Ibs/ton-
0.0
1.2
3.5
6.9
7.7
10.5
11.8
13.2
PERCENT RECOVERY
OF
SUSPENDED SOLIDS
-%-
43.1
65.0
79.8
85.0
87.5
86.0
85.0
87.7
o
I
*A11 data pertain to dewatering tests conducted on JWPCP primary digested sludge
with a 36-inch x 96-inch horizontal scroll centrifuge.
**Reported values are corrected for dilution with 16 gpm (1.0 I/sec) of polymer
solution from the chemical station.
Unit Conversions:
(% Solids) x 10,000 = (mg/1)
(Ibs/ton) x 0.5 = (kg/metric ton)
-------
FIGURE 20
00
Horizontal scroll centrifuge; erratic sludge dewatering
performance obtained with polymer usage
O
-DATA FROM AUG. 10,1971
D
-DATA FROM MAY II ,1971
CAKE QUALITY^ 20*1% SOLIDS
CENTRIFUGE: 36" x 96" BIRD DECANTER
BOWL SPEED= 1300 rpm (900 g)
DIFFERENTIAL SPEED= I5.3rpm
POOL DEPTH: 3.4" (876cm)
FEED: PRIMARY DIGESTED SLUDGE
CHEMICAL FEED RATE: I6gpm (1.0 I/sec)
FEED RATE: 250 gpm (15.8 I/sec)
POLYMER: HERCOFLOC eio
UNIT CONVERSIONS:
(Ib/ton) x 0.5 =(kg/metric ton)
I
8 10 II 12 13
POLYMER DOSAGE , Ibs/ton
14
15
16
17
-------
FIGURE 21
Schematic flow diagram
Dewatering system for heat conditioned sludge
PRIMARY
DIGESTED
SLUDGE
PORTEOUS
PORTEOUS PROCESS
HEAT TREATMENT
OLUUOC. |
(PORTRATE)"
STORAGE
TANK
I
to
t-o
POLYMER
SOLUTION
PUMP
PUMP
OPTIONAL |
SHARPLES P-600
HORIZ. SCROLL
CENTRIFUGE
CENTRATE
CENTRIFUGED
CAKE
-------
FIGURE 22
Schematic flow diagram
Dewatering systems for thickened heat-conditioned sludge
£ PRIMARY
1 DIGESTED
SLUDGE
PORTEOUS
PROCESS
HEAT
TREATMENT
POLYMER
SOLUTION
PUMP
PICKET
DRIVE
PORTEOUS r
SLUDGE '
(PORTRATE)
STORAGE
TANK
MP(JP-
PUMP
OPTIONAL
STORAGE
k.TANKJ
Mp(Tp-
THICKENING TANK
THICKENED
PORTEOUS
SLUDG
PUMP
SHARPLES P-600
HORIZ. SCROLL
CENTRIFUGE
CENTRATE
LL
a:
UJ
a
LU
o
LU
a
CENTRIFUGED
CAKE
CLARIFIED
EFFLUENT
BLEND
-------
collected in a small storage tank for controlled steady-
state feeding into either the centrifuge or the picket
thickening clarifier. In the latter case, the administra-
tion of portrate was fixed to provide a continuous over-
flow rate of 225 gpd/sq ft (9.2 cu m/day/sq m). From
Figure 14, a decanted overflow having a 0.371 (3700 mg/1)
suspended solids concentration would be expected. Other
test variables held constant throughout this study were
the centrifuge bowl speed (5000 rpm) and the differen-
tial speed (12 rpm) between the bowl and scroll. Also,
the centrate weir was adjusted to that setting which
provided the deepest pool depth possible without over-
flowing the drainage beach area of the machine.
Regarding those tests conducted without polymer addition,
the unthickened and thickened portrate streams were fed
to the centrifuge at each of several feedrates ranging
from 1.2 to 3.4 gpm (0.08 to 0.21 I/sec). With polymer
conditioning, the investigated feedrates were 1.2 and
3.4 gpm (0.08 and 0.21 I/sec) for the unthickened por-
trate stream and 3.4 gpm (0.21 I/sec) for the thickened
portrate stream. At each of these, polymer dosage was
allowed to vary.
In the absence of polymer conditioning, data summarizing
the centrifugal dewaterability of both unthickened and
thickened portrate at various throughput rates are pre-
sented in Tables 20 and 21, respectively. In both tables,
the tabulated solids recovery effected by the centrifuge
are based on the initial suspended solids being fed to
the machine only and not to the system as a whole. Addi-
tional data are tabulated which show the quality of the
final effluent blend (decantate plus centrate) and the
overall suspended solids removal by the system, i.e. remov-
al by thermal volatization, elimination by thermal transfer
to the dissolved phase, and centrifugal capture in the
cake. These latter removal values were calculated on
the basis of 3.51 (35,000 mg/1) suspended solids in the
digested sludge fed to the system.
The centrifugal solids capture data in Tables 20 and 21
are plotted in Figure 23 as a function of centrifuge
feedrate. As noted, the effect was, for all practical
purposes, linear in the range of feedrates investigated.
Increased feedrates to the centrifuge effected a decrease
in solids capture. For any particular feedrate to the
centrifuge, capture was greatest percentagewise when
centrifuging thickened portrate. For this same material,
however, centrate quality was poorest. Nevertheless,
-94-
-------
Table 20: DATA* SUMMARIZING THE DEWATERABILITY OF UNTHICKENED HEAT-CONDITIONED DIGESTED
SLUDGE BY HORIZONTAL SCROLL CENTRIFUGATIOTJ
PARAMETERS
Y. Processed Material: JWPCP Primary Digested Sludge
2. Porteous Conditioning:... 40 min @ 350°F (175°C)
3. Centrifuge: Sharpies P-600 solid bowl decanter
4. Bowl Speed: 5000 rpm
5. Differential Speed: 12 rpm
6. Pool Depth: maximum possible
CENTRIFUGE
FEEDRATE
-gpm-
1.2
1.5
2.0
2.5
3.0
3.4
SUSPENDED SOLIDS CONCENTRATIONS
Un thickened
Portrate Feed
-*-
2.68
2.47
2.41
2.53
2.57
2.24
Centrate
-%-
0.74
0.73
0.86
1.01
1.11
1.01
Cake
-%-
32.3
31.5
33.1
32.6
35.7
31.3
SUSPENDED SOLIDS
CAPTURE IN
CENTRIFUGE
-%-
74.1
72.1
66.0
62.0
58.6
56.7
TOTAL SUSPENDED
SOLIDS REMOVAL
BY SYSTEM**
-%-
80.7
81.0
77.4
73.4
70.5
73.5
I
to
1/1
* All data pertain to tests conducted with JWPCP primary digested sludge.
** Removal by"System" includes centrifugal capture, thermal volatization, and thermal transfer
to the dissolved phase. Calculated values are based on a suspended solids concentration
of 3.5% in the digested sludge fed to the system.
Unit Conversions: (gpm) x 0.0631 = (I/sec)
(% Solids) x 10,000 = (mg/1)
-------
Table 21: DATA* SUMMARIZING THE DEWATERABILITY OF THTrKHMFD HEAT-CONDITIONED DIGESTED
SLUDGE BY HORIZONTAL SCROLL CENTRIFUGATION
PARAMETERS:
TT
2.
3.
4.
5.
6.
7.
Processed Material: JWPCP primary digested sludge
Porteous Conditioning: 40 min @ 350°F (175°C)
Thickener Overflow Rate:... 225 gpd/sq ft (9.2 cu m/day/sq m)
Centrifuge: Sharpies P-600 horizontal scroll centrifuge
Bowl Speed: 5000 rpm
Differential Speed: 12 rpm
Pool Depth: maximum possible
CENTRIFUGE
FEEDRATE
-gpm-
1.2
2.0
3.0
SUSPENDED SOLIDS CONCENTRATION
Unthickened
Portrate Feed
-!-
11.27
11.08
8.08
Centrate
-%-
3.32
4.13
3.55
Cake
-!-
24.9
25.8
28.5
SUSPENDED
SOLIDS CAPTURE
IN CENTRIFUGE
-!-
81.4
74.7
64.1
SUSPENDED SOLIDS
IN EFFLUENT BLEND
(Decantate+Centrate)
-\-
0.61
0.69
0.70
TOTAL SUSPENDED
SOLIDS REMOVAL
BY SYSTEM**
-!-
84.7
82.5
82.0
0\
I
* All data pertain to test conducted on JWPCP primary digested sludge.
** Removal by "System"' includes centrifugal capture, thermal volatization, and thermal transfer
to the dissolved phase. Calculated values are based on a suspended solids concentration of
3.5% in the digested sludge fed to the system.
Unit Conversions: (gpm) x 0.0631 = (I/sec)
(% Solids) x 10,000 = (mg/1)
-------
FIGURE 23
to
100
- 90
LU
DC
8°
O
CO
O
UJ
W
ID
CO
70
60
50
40
30
0
The effect of feed rate on the centrifugal capture of
suspended solids from unthickened and thickened
heat-conditioned digested sludge
i i r
THICKENED HEAT
T
T
CONDITIONED SLUDGE FEED
UNTHICKENED HEAT
CONDITIONED SLUDGE FEED
I I I f I
PROCESSED MATERIAL:
PRIMARY DIGESTED SLUDGE
HEAT CONDITIONING:
40 MINUTES AT 350°F (I75°C)
THICKENER OVERFLOW RATE -
225 gpd/sq ft (9.2 cu m/day/sq m)
CENTRIFUGE^ SHARPLES p-eoo —
HORIZ. SCROLL DECANTER
BOWL SPEED: 5OOO rpm _
DIFFERENTIAL SPEED: 12 rpm
POOL DEPTH: MAXIMUM POSSIBLE
UNIT CONVERSIONS:
(gpm) x 0.063! = (I/sec)
1.0 2.0 3.0 4.0
FEED RATE TO CENTRIFUGE , gpm
5.0
6.0
-------
a blend of this poor quality centrate with the decantate
from the picket thickener produced a final effluent of
superior quality to that of the unthickened portrate
system. Correspondingly, the overall suspended solids
removed by the system incorporating a thickening step
was greatest, regardless of the feedrate to the centri
fuge. This latter observation is depicted in the graphi
cal plot of Figure 24. All sludge cakes obtained from
the centrifugation of thickened portrate were wetter
than those generated from unthickened portrate. This was
especially true at the lower feedrates.
The addition of a cationic polymer (Hercofloc 810) to
the unthickened or thickened portrate sludge streams
within the bowl enhanced the recovery of suspended solids
by horizontal scroll centrifugation. Data summarizing
these results are presented in Tables 22 and 23, respec-
tively. Polymer dosages and corresponding centrifugal
solids capture are based on the suspended solids fed
to the centrifuge only and not to the system as a whole.
Additional data are presented in both tables which show
the overall suspended solids removal by each system.
Moreover, data values are presented in Table 23 showing
the resulting suspended solids content in the final
effluent blend (decantate plus centrate) .
The effect of polymer dosage on centrifugal solids cap-
ture from unthickened and thickened portrate sludge is
graphically depicted in Figure 25. Regarding the unthick-
ened material, greatest capture was experienced at the
lower feedrate regardless of the polymer dosage. At a
throughput rate of 1.2 gpm (0.08 I/sec), maximum solids
recovery (88-89 percent) occurred at a "break point"
polymer dosage of about 4 Ibs/ton (2.0 kg/metric ton).
Continued increases in polymer dosage beyond this yielded
no appreciable gains in solids capture. At the 3.4 gpm
(0.21 I/sec) throughput rate, polymer dosage had a some-
what linear effect on solids capture. Greatest solids
capture (83 percent) occurred at the highest polymer
dosage administered, namely 10.6 Ibs/ton (5.3 kg/metric ton)
The effect of increased polymer dosages beyond this were
not investigated.
In conjunction with polymer addition, centrifugal cap-
tures were enhanced with the incorporation of Porteous
sludge thickening prior to centrifuging. This is evi
denced by the vertical displacement of those two curves
-98-
-------
FIGURE 24
ID
10
-------
Table 22: DATA* SUMMARIZING THE CENTRIFUGAL DEWATERABILITY OF UNTHICKENED HEAT-CONDITIONED
~DIGESTED SLUDGE WITH POLYMER CONDITIONING.
PARAMETERS
1.
2.
3.
4.
5.
6.
Processed Material: JWPCP primary digested sludge
Porteous Conditioning:... 40 min @ 350°F (175°C)
Centrifuge: Sharpies P-600 horizontal scroll centrifuge
Bowl Speed: 5000 rpm
Differential Speed: 12 rpm
Pool Depth: maximum possible
CENTRIFUGE
FEEDRATE
-%-
1.2
3.4
SUSPENDED SOLIDS CONCENTRATION
Unthickened
Portrate
Feed
-*-
2.68
3.00
2.33
2.40
2.36
2.13
2.13
2.07
2.05
2.03
2.07
1.94
2.01
1.90
2.15
Centrate
-*-
0.74
0.38
0.32
0.29
0.34
1.05
0.84
O.S4
0.80
0.76
0.61
0.61
0.53
0.41
0.39
Cake
-*-
32.3
31.5
28.2
29.5
27.1
30.4
28.6
29.2
27.6
26.4
26.8
25.1
27.7
28.0
28.9
CHEMICAL
DOSAGE
-Ibs/ton-
0.0
3.4
6.5
7.5
9.2
0.0
1.7
2.6
3.2
3.9
4.6
6.0
7.0
9.3
j 10.6
SUSPENDED
SOLIDS
CAPTURE IN
CENTRIFUGE
-%-
74.1
88.3
87.3
88.8
86.8
52.6
62.2
61.3
62.5
64.6
72.0
70.3
75.1
79.4
83.2
TOTAL SUSPENDED
SOLIDS
REMOVAL BY
SYSTEM**
-%-
80.7
90.2
91.9
92.6
91.4
72.5
78.3
78.3
79.4
80.6
84.5
84.6
86.5
89.6
90.1
o
o
I
*A11 data pertain to
**Removal by "System"
the dissolved phase
digested sludge fed
Unit Conversions:
tests conducted with JWPCP primary digested sludge.
includes centrifugal capture, thermal1volatization, and thermal transfer t,o
Calculated values assume a suspended solids concentration of 3.51 in the
to the system.
(gpm) x 0.0631 = (I/sec)
(Ibs/ton) x 0.5 = (kg/metric ton)
(% Solids) x 10,000 = (mg/1)
-------
Table 23: DATA* SUMMARIZING THE CENTRIFUGAL DEWATERABILITY OF THICKENED HEAT-CONDITIONED
DIGESTED SLUDGE WITH POLYMER CONDITIONING.
PARAMETERS
1. Processed Material: JWPCP primary digested sludge
2. Porteous Conditioning: 40 min @ 35QOF (175°C)
3. Thickener Overflow Rate:... 225 gpd/sq ft (9.2 cu m/day/sq m)
4. Centrifuge: Sharpies P-600 horizontal scroll centrifuge
5. Bowl Speed: 5000 rpm
6. Differential Speed: 12 rpm
7. Pool Depth: maximum possible
CENTRIFUGE
FEEDRATE
-*-
1.2
SUSPENDED SOLIDS CONCENTRATION
Thickened
Portrate Feed
-%-
11.27
8.01
9.28
9.10
4.65
Centrate
-%-
3.32
0.29
0.23
0.15
0.12
Cake
-*-
24.9
24.5
24.9
24.6
26.8
CHEMICAL
DOSAGE
-Ibs/ton-
0.0
3.2
4.1
6.9
13.5
i
SUSPENDED
SOLIDS
CAPTURE
IN
CENTRIFUGE
-%-
81.4
97.5
98.4
99.0
97.8
SUSPENDED
SOLIDS IN
EFFLUENT BLEND
'Decantate+Centrate]
-%-
0.61
0.36
0.36
0.35
0.34
TOTAL SUSPENDED
SOLIDS
REMOVAL
BY
SYSTEM
-%-
84.7
91.0
91.0
91.3
91.4
* All data pertain to tests conducted with JWPCP primary digested sludge.
** Removal by "System" includes centrifugal capture, thermal volatization, and thermal transfer to
the dissolved phase. Calculated values assume a suspended solids concentration of 3.5% in the
digested sludge fed to the system.
Unit Conversions: (gpm) x 0.0631 = (I/sec)
(Ibs/ton) x 0.5 = (kg/metric ton)
(* Solids) x 10,000 = Crag/1)
-------
FIGURE 25
The effect of polymer dosage on the centrifugal capture of
suspended solids from unthickened and thickened
heat-conditioned digested sludge
CENTRIFUGE FEED RATE
THICKENED
UNTHICKENED
UNTHICKENED
1.2 gpm (0.08 I/sec)
I .2 gpm (0.08 I/sec)
3.4 gpm (0.21 I/sec)
PROCESSED MATERIAL:
PRIMARY DIGESTED SLUDGE _
HEAT CONDITIONING:
40MINUTES AT 350°F(I75°C)
THICKENER OVERFLOW RATE:
225 gpd/sq ft (9.2 cu m/day/sq m )
CENTRIFUGE: SHARPLES P-600 —
HORIZ. SCROLL DECANTER
BOWL SPEED-' 5000 rpm _
DIFFERENTIAL SPEED: 12 rpm
POOL DEPTH: MAXIMUM POSSIBLE^
UNIT CONVERSIONS: _
(gpm) x 0.0631 = (I/sec) ~
I
8 10 12 14 16
POLYMER DOSAGE , Ibs/ton
18
20 22
24
-------
in Figure 25 which reflect the performances obtained
at the_1.2-gpm (0.08-1/sec) throughput rate. Regarding
the thickened material, maximum solids capture
(98-99 percent) occurred at a "break point" polymer
dosage of about 4 Ibs/ton (2.0 kg/metric ton). Further
polymer dosage increases yielded no additional recovery
gains. The resulting centrates were superior to those
obtained from centrifuging unthickened portrate. But
considering a blend of this centrate with the decantate
from the thickener, the overall suspended solids load in
the effluents from both systems would be about the same,
i.e. approximately 0.36% (3600 mg/1). Based on 3.5%
(35,000 mg/1) suspended solids in digested sludge fed to
either system, an overall suspended solids removal of
about 91 percent would be experienced, at best, with
the incorporation of a secondary polymer conditioning
step and low centrifuge throughput rates.
Considering that a polymer solution was being injected
into each system, cake qualities were better than expect
ed. When thickening was employed, cake dryness remained
relatively constant at about 24-25% solids by weight.
Without the intermediate thickening step, generated cakes
were greater than 26% solids by weight. This is to be
compared with the 20% cakes obtained from previously
discussed experiments using polymers in the isolated
Bird test centrifuge at the JWPCP. Evidently, the heat
conditioning step enhances cake dryness in a centrifugal
dewatering operation incorporating polymers.
BASKET CENTRIFUGATION
Basket centrifuge test work was limited to an assess-
ment of its potential for dewatering 'Bird' centrate in
the second stage mode. The existing Bird centrifuge
station was operated in its normal manner, i.e. with
about 30 percent suspended solids removal from the in-
coming digested sludge stream. Followup centrifuge work
with the 30- and 40-inch (76- and 102-cm) basket units
was then conducted both with and without polymer condi
tioning of the Bird centrate feed stream. Throughout
the testing, the rotational speeds of each unit were such
that the generated radial acceleration was held constant
at 1300 gravities.
Data from both piloted centrifuges were acquired in ac-
cordance with the following general sampling procedure.
-103-
-------
During the course of a run, a grab sample of the feed
material (Bird centrate) was taken. At different time
intervals during the feed cycle grab samples of centrate
were also taken. The feed cycle was terminated upon the
acquisition of a centrate sample approximately one minute
after the occurrence of break-through, i.e. the point at
which centrate quality began to deteriorate. Centrate
quality deterioration was both rapid and visually observ-
able in runs incorporating polymer addition only. With-
out the use of polymers, the occurrence of breakthrough
was quite unclear and was more or less determined by the
experience of operation.
Cake samples were acquired in three different ways depend-
ing on which centrifuge was being evaluated and the type
of data requiring generation. In the 30-inch (76-cm)
unit, most of the accumulated solids were skimmed into a
55-gal. (208-liter) container and, after thorough mixing,
sampled compositely; if an unskimmable heel remained in
the basket, a composite of this material was also taken
and weighted with the skimming sample to determine average
cake dryness. Regarding most runs with the 40-inch
(102-cm) unit, a small amount of the liquid-paste layer
was skimmed off and discarded while the remaining solids
were knifed out and sampled at one-inch (2.5-cm) inter-
vals, thereby enabling an average cake dryness to be
determined; in a few of the runs, however, the generated
cakes were skimmed and sampled at one-inch (2.5-cm) inter-
vals followed by separate sampling of any unskimmable heel,
This latter procedure enabled solids build-up at inter-
vals within the bowl to be assessed.
Tests with the 30-inch (76-cm) unit revealed that, with-
out polymer usage, both solids recovery and cake quality
were a function of the feedrate to the centrifuge. Data
summarizing the base performance of the basket centrifuge
for four different feedrates of Bird centrate are present-
ed in Table 24. As noted, the total time of the feed
cycle was decreased as the feedrate was increased. For
each of these runs, the dependency of solids recovery
on the duration of the feed cycle is graphically depicted
in Figure 26 and is typical of a batch operation of this
type. For any particular feedrate, the instantaneous
solids recovery decreased with increased feed time. Also,
instantaneous capture and, therefore, instantaneous cen-
trate effluent quality decreased as throughput rate was
increased. Even at the lowest 15-gpm (0.95 I/sec) feed-
rate tested, solid recoveries of only 82-84 percent were
-104-
-------
Table 24; DATA* SUMMARIZING'THE DEWATERING PERFORMANCE
OF A BASKET CENTRIFUGE AT VARIOUS FEEDRATES.
PARAMETERS
IT Operation: 2nd stage mode
4.
Feed Material:... Bird centrate
(no conditioning)
Centrifuge: 30-inch (76-cm) Sharpies
basket centrifuge
Bowl Speed: 1750 rpm (1300 G's)
FEEDRATE
-gpm-
15
28
38
48
FEED
TIME
-min-
4
6
8
10
2
3
4
5
2
3
4
2
3
4
SUSPENDED SOLIDS
'Bird' Centrate
Feed
-%-
2.19
2.63
2.56
2.78
CONCENTRATION
Basket
Centrate
-%-
0.50
0.59
0.76
1.07
1.00
1.07
1.22
1.39
1.21
Cake
-I-
8.1
9.8
1.32 0.1. 8
1.46
1.84
1.94
2.02
13.2
SUSPENDED
SOLIDS
CAPTURE
L -%-
82.3
78.8
72.1
58.9
69.0
66.6
61.2
54.9
58.8
54.5
49.0
39.3
35.4
32.3
* All data pertain to the tests conducted on 'Bird centrate1,
i.e. the centrate effluent discharged from the existing
horizontal scroll centrifuge station operating in its
normal mode at JWPCP.
Unit Conversions:
, (gpm) x 0.0631 = (I/sec)
(% Solids) x 10,000 = (mg/1)
-105-
-------
FIGURE 26
o
ON
i
Ld
cc.
ID
H-
0.
<
o
CO
Q
Lu!
Q.
CO
ID
CO
Solids recovery in a basket centrifuge at different time intervals during
feed cycles at various feed rates
00
80
70
O 60
CO
50
40
30
OPERATION: 2ND STAGE MODE
FEED: BIRD CENTRATE
CENTRIFUGE: 30-INCH (76-cm)
IMPERFORATE BOWL BASKET CENTRIFUGE
BOWL SPEED: 1750 r p m (1300 g)
FEED RATE
15 gpm (0.95 I/sec)
28 gpm (1.77 I/sec)
38 gpm (2.40 I/sec)
48 gpm (3.0 3 I /sec)
0
8 10 12 14
FEED TIME , min
16
18
20
22
24
-------
obtainable during the first 4 minutes of the feed cycle.
The decrease in solids recovery with increasing feedrate
can be attributed partly to the corresponding decrease
in detention time and partly to the increased turbulence
and shear phenomena occuring within the moving liquid
layer during the equilibrium feed-discharge phase. The loss
in solids capture with feed time is indicative of their re-
jection from the quiescent settling zone due to solids
accumulation therein. Indeed, the rapidity of this loss
reflects the poor quality of the cakes discharged at the
end of each feed cycle (Table 24). The effect of centrifuge
feedrate on the average dryness of accumulated cake solids
is graphically depicted in Figure 27. Cake dryness increas-
ed linearly from 8 to 131 solids by weight as the applied
feedrates were increased from 15 to 48 gpm (0.94 to
3.03 I/sec). Wetter cakes can be attributed to the in-
creased capture of finely suspended material containing
more bound water per unit of particle mass. Evidently,
this more than offset any additional dryness effected as
a result of increased compaction time due to longer feed
cycles at lower feedrates.
In an attempt to increase the solids capture in the
30-inch (76-cm) unit, some preliminary work incorporating
polymer addition to the basket centrifuge was conducted.
The results were encouraging enough to warrant a more
detailed investigation of such in the larger 40-inch
(102-cm) diameter unit. To simplify the evaluation, only
one polymer (Dow C-41) was utilized for this phase of the
work. The possibility of other polymer products doing a
similar or perhaps better job was not discounted. With
respect to all test runs reported on in this regard,
polymer solutions were batched to a 0.1% (1000 mg/1)
concentration and spray injected into the Bird centrate
stream within the bowl of the centrifuge. Polymer injec-
tion at various points in the sludge feed line was looked
at briefly; results, however, were significantly inferior.
Consequently, polymer injection into the bowl of the
basket was deemed best for this type of second stage
centrifugation process at the JWPCP.
Overall, both suspended solids capture and generated cake
quality was greatly enhanced as a result of polymer addi
tion. The data in Table 25 summarize the effect of an
equivalent dry polymer dosage of 4 Ibs/ton
(2.0 kg/metric ton) on the dewatering performance of the
40-inch (102-cm) basket centrifuge fed Bird centrate
at each of several feedrates. As in the case of the
-107-
-------
FIGURE 27
CD
00
The effect of feed rate to a basket centrifuge on the resulting cake
t- ^o
2 ^
UJ *
H £
O <
o o
co Q
Q IJJ
- CD
o5
(o 2
$2
< Q
tr
UJ U_
§°
10
0.
OPERATION •• 2ND STAGE MODE
PROCESSED MATERIALS BIRD CENTRATE
CENTRIFUGE^ SO-INCH (?6-cm)
IMPERFORATE BOWL BASKET
CENTRIFUGE
BOWL SPEED: I750 rpm (1300g)
CONDITIONING^ NONE
UNIT CONVERSIONS:
(gpm) x 0.0631 = (I/sec)
0 10 20 30 40 50 60 70 80 90 100
CENTRIFUGE FEED RATE, gpm
no
120
-------
Table 25:
DATA* SUMMARIZING THE EFFECT OF POLYMER ADDITION
ON THE DEWATERING PERFORMANCE OF A BASKET CENTRI-
FUGE AT VARIOUS FEEDRATES.
PARAMETERS
1
2
3
4
5
6
Operation: 2nd stage mode
Feed Material:.... 'Bird' centrate
Centrifuge: 40-inch (102-cm) Sharpies
basket centrifuge
Bowl Speed: 1500 rpm (1300 G's)
Polymer: Dow C-41
Polymer Dosage:... 4 lbs/ton(2.0 kg/metric ton)
FEEDRATE
-gpm-
20
30
40
50
60
FEED
TIME
-min-
5.0
14.0
24.0
26.0
27.0
3.5
12.5
15.5
16.5
3.0
5.0
9.0
11.0
13.0
14.0
3.5
6.5
8.5
10.5
11.0
11.5
3.5
4.5
6.5
8.0
9.0
9.5
SUSPENDED SOLIDS CONCENTRATION
'Bird' Centrate
Feed
-%-
3.13
3.36
2.79
2.97
2.42
Basket
Centrate
-%-
0.13
0.14
0.15
0.32
1.02
0.14
0.15
0.34
1.00
0.14
0.14
0.14
0.14
0.86
1.40
0.15
0.15
0.15
0.18
0.41
0.89
0.17
0.17
0.17
0.19
0.34
1.01
Gake
-l-_j
22.1
19.6
19.0
18.2
16.3
SUSPENDED
SOLIDS
CAPTURE
-*-
96.4
96.1
95.9
91.0
70.1
96.5
96.3
91.5
74.0
95.7
95.7
95.7
95.7
72.5
53.8
95.4
95.4
95.4
94.9
88.2
73.6
94.0
94.0
94.0
93.2
87.8
62.1
* All data pertain to the tests conducted on 'Bird' cen-
trate , i.e. the centrate effluent discharged from the
existing horizontal scroll centrifuge station operating
in its normal mode at JWPCP.
Unit Conversions:
(gpm) x 0.0631 = (I/sec)
(% Solids) x 10,000 = (mg/1)
-109-
-------
base performance evaluation (refer to Table 24) , the
total time of the feed cycle decreased as the feedrate
was increased, respectively. Figure 28 graphically
depicts the instantaneous solids capture experienced as a
function of feed time for each of the feedrates investi
gated. The resulting break-through curves display the fact
that in the 20-60 gpm (1.26-3.78 I/sec) feedrate range,
suspended solid recovery maximums of 94-96 percent,
respectively, are obtainable up to some point in time
(depending on the feedrate.) At break-through, suspended
solids capture rapidly drops off, thereby indicating that
tha capacity of the quiescent zone for accumulating solids
has been exhausted. As noted, the time of this occurrence
decreased with increasing feedrate to the centrifuge and
had the corresponding effect of reducing the average
solids content in the resulting discharged cakes. This
latter effect is graphically depicted in the plot of
average cake dryness with feedrate in Figure 29.
Data are presented in Table 26 which summarize the effect
of adding various dosages of polymer to a 30-gpm
(1.89 I/sec) Bird centrate feedstream in the 40-inch
(102-cm) basket centrifuge. For each polymer dosage,
instantaneous suspended solid recoveries are plotted as
a function of feed cycle time (Figure 30). In addition
to promoting a very slight increase in maximum solids
capture, increased polymer dosing had the effect of pro-
longing the duration of a feed cycle before break-through
and recovery dropoff occurred. As noted in Table 26, the
extended run time enabled more compaction of the accumu-
lated solids to occur in the quiescent zone, thereby
providing for an increase in the average solids content
of the discharged cakes. The effect is graphically por-
trayed in the plot in Figure 31.
In conjunction with the effect of feed time and polymer
addition, some data were acquired showing the build-up
of accumulated solids within the bowl of the basket
centrifuge at each of several feedrates. A summary of
these data are presented in Table 27 for the situation
when the polymer dosage was held constant at 4 Ibs/ton
(2.0 kg/metric ton). A graphical profile of these data
is shown in Figure 32. Displayed is the fact that as
captured solids accumulated from the bowl wall to the
centrate overflow weir, the localized cake solids content
correspondingly decreased. Also, localized cake dryness
decreased as the feedrate to the machine was increased.
Regarding the profile, it is to be noted that the first
-110-
-------
FIGURE 28
00
Uj 90
o:
Solids recovery in a basket centrifuge at different time
intervals during feed cycles at various feed rates
o
CO
Q
a
UJ
Q
CO
80
70
O
co 60
50
UJ
Q_
CO 40
30
0
T
T
OPERATION' 2ND STAGE MODE
FEED: BIRD CENTRATE
CENTRIFUGE: 40-iNCH (i02-cm)
IMPERFORATE BOWL BASKET
CENTRIFUGE
BOWL SPEED: 1500 r pm (1300 g)
POLYMER: DOW c-4i
POLYMER DOSAGE: 4lbs/ton
(2.0 kg/metric ton)
FEED RATE
20 gpm (1.26 I/sec)
30 gpm (1.89 I/sec)
40 gpm (2.52 I/sec)
50 gpm (3. 16 I/sec)
60 gpm (3.78 I/sec)
I I
8 12 16 20 24 28 32
FEED TIME, min
36
40
44
48
-------
FIGURE 29
The effect of feed rate to a basket centrifuge on the resulting cake
23
h- 22
Z 55
£ "
5 LJ 2
O ^
u S
CO Q 20
Q Uj
o °c
CO < 19
O
UJ CO
§ 0 18
UJ U_
T
1
T
T
T
T
OPERATION: 2ND STAGE MODE
FEED: BIRD CENTRATE
CENTRIFUGE: 40-iNCH (io2-cm)
IMPERFORATE BOWL BASKET
CENTRIFUGE
BOWL SPEED: JSQO rpm (1300 g)
POLYMER: DOW C-41
POLYMER DOSAGE: 4 Ibs /ton
(2.0 kg/metric ton)
UNIT CONVERSIONS:
(gpm) x 0.0631 - (I/sec)
I
I
I
I
0 10 20 30 40 50 60 70 80
FEED RATE,gpm
90
100 110 120
-------
Table 26: DATA* SUMMARIZING THE EFFECT OF VARYING POLYMER
DOSAGES ON THE DEWATERING PERFORMANCE OF A
BASKET CENTRIFUGE.
PARAMETERS
T~. Operation: 2nd stage mode
2. Feed Material:... 'Bird* centrate
3. Feed Rate: 30 gpm (1.89 I/sec)
4. Centrifuge: 40-inch (102-cm) Sharpies
Basket Centrifuge
5. Bowl Speed: 1500 rpm (1300 G's)
6. Polymer: Dow C-41
FEED
TIME
-min-
3.5
6.5
9.5
10.5
3.5
12.5
15.5
16.5
3.5
12.5
17.5
19.5
20.5
SUSPENDED SOLIDS CONCENTRATION
'Bird' Centrate
Feed
2.79
3.36
2.84
Basket
Centrate
0.14
0.14
0.16
1.25
0.14
0.15
0.34
1.00
0.10
0.10
0.11
0.63
1.87
Cake
16.4
19.6
22.1
POLYMER
DOSAGE
~2
"4
~9
SUSPENDED
SOLIDS
CAPTURE
95.8
95.8
95.2
59.8
96.5
96.3
91.5
74.0
96.9
96.9
96.6
80.1
37.3
*A11 data pertain to the tests conducted on 'Bird' cen-
trate , i.e. the centrate effluent discharged from the
existing horizontal scroll centrifuge station operating
in its normal mode at JWPCP.
Unit Conversions:
(% Solids) x 10,000 = (mg/1)
(Ibs/ton) x 0.5 = (kg/metric ton)
-113-
-------
FIGURE 30
UJ
cc
ID
h-
Q_
<
O
CO
Q
100
90
80
70
_J
O 60
CO
Q
UJ
Q
50
LJ
Q_
CO 40
CO
30
The influence of polymer dosage on suspended solids
recovery in a basket centrifuge
POLYMER DOSAGE
2lbs / ton
4lbs/ton
9 IDS / ton
OPERATION: 2 ND STAGE MODE
FEED: BIRD CENTRATE
FEED RATE: 30 gpm (1.89 I/sec)
CENTRIFUGE^ 40-iNCH (io2-cm) IMPERFORATE"
BOWL BASKET CENTRIFUGE
BOWL SPEED= isoo rpm (1300 g)
POLYMER: DOW c-4i
UNIT CONVERSIONS:
(Ibs/ton) x 0.5 = (kg/metric ton)
8 12 16 20 24 28 32
FEED TIME.min
36
40
44
48
-------
Cn
i
FIGURE 31
The effect of polymer dosage on cake solids from a basket centrifuge
23
22
_i e>
0 5
co <
o 2
< Q
ce
UJ i,
a 20
19
8
16
OPERATION • 2ND STAGE MODE ~
FEED: BIRD CENTRATE
FEED RATE: 30gpm (1.89 I/sec) -
CENTRIFUGE' 40-INCH (102-c m) IMPERFORATE
BOWL BASKET CENTRIFUGE _
BOWL SPEED: I500rpm (1300 g)
POLYMER: DOW c-4i _
UNIT CONVERSION:
(Ibs/ton) x 0.5 = (kg/metric ton) —
I
0
6 8 10 12 14 16 18
POLYMER DOSAGE , Ibs/ton
20
22
24
-------
Table 27: DATA* SUMMARIZING THE BUILD-UP OF CAKE SOLIDS
WITHIN A BASKET CENTRIFUGE FOR VARIOUS
FEEDRATES.
PARAMETERS
TT. Operation: 2nd stage mode
2. Feed Material;.,.. 'Bird' centrate
3. Centrifuge: 40-inch (102-cm) Sharpies
basket centrifuge
4. Bowl Speed: 1500 rpm (1300 G's)
5. Polymer; Dow C-41
6. Polymer Dosage:... 4 Ibs/ton (2.0 kg/metric
ton)
FEEDRATE
-gpm-
20
30
40
j; DISTANCE
FROM
WEIR
CREST
- inches -
i . U
2.0
3.0
4.0
5.0
5.5
6.0
1.0
2.0
3.0
4.0
5.0
5.5
6.0
1.0
2.0
3.0
4.0
5.0
5.5
6.0
DISTANCE
FROM
BOWL WALL
-inches-
5 . 0
4.0
3.0
2.0
1.0
0.5
0.0
5.0
4.0
3.0
2.0
1.0
0.5
0.0
5.0
4.0
3.0
2.0
1.0
0.5
0.0
CAKE
SOLIDS
-%-
13
18
21
23
25
26
27
12
17
19
21
23
25
26
10
15
18
20
22
24
25
* All data pertain to the tests conudcted on 'Bird cen-
trate , i.e. the centrate effluent discharged from the
existing horizontal scroll centrifuge station operating
in its normal mode at JWPCP.
Unit Conversions:
(gpm) x 0.0631 =
(inches) x 2.54 = (an)
116-
-------
FIGURE 32
Profile of cake solids buildup in a basket centrifuge at various feed rates
20 gp m
30 g p m
40 g p m
OPERATIONS' 2ND STAGE MODE
FEED= BIRD CENTRATE
CENTRIFUGE: 40-INCH (102-cm)
IMPERFORATE BOWL BASKET CENTRIFUGE -
BOWL SPEED: 1500 rpm (1300 g)
POLYMER: DOW c-4i —
POLYMER DOSAGE: 4lbs/ton(2.0 kg/metric ton)
UNIT CONVERSIONS:
V (inches) x 2.54 = (cm)
\ (gpm) x 0.0631 = (I/sec)
23456789
DISTANCE FROM BOWL WALL , inches
10
12
-------
one-inch (2.5-cm) of accumulated material was skimmed off
and discarded. Thus, the material in the remaining
5-inch (12.7-cm) annular ring would have average solids
contents of 21.7%, 20.1% and 18.9% for the 20, 30 and
40 gpm (1.26, 1.89, and 2.52 I/sec) runs, respectively.
If instead, however, 2 inches (5.1 cm) of material were
skimmed off and discarded, then the remainder in the
4-inch (10.2-cm) annular ring would have corresponding
average solids contents of 23.0%, 21.4% and 20.2%, respec-
tively- -an overall increase of 1.3% for each run.
In summary, polymer addition to the basket centrifuge
operating in the second stage mode was found to be
necessary for producing a final effluent containing
1500 mg/1 or less of suspended material. The test data
indicated that several combinations of feedrate and polymer
dosage can be used to obtain the same average cake dryness.
In an actual operation, average cake dryness can also
be increased simply by skimming off more of the wetter
material close to the weir lip and recycling it. For the
operation at the JWPCP, it was determined that a 20% cake
would be required of a basket centrifuge operating in the
second stage mode. A blend of this with the 35% cakes
produced from the existing horizontal scroll centrifuge
station would result in a cake mixture of 25% solids by
weight. This could be accomplished with a polymer dosage
of approximately 4 Ibs/ton (2.0 kg/metric ton) based on
feed solids to the basket units. This corresponded to a
dosage requirement of about 3 Ibs/ton (1.5 kg/metric ton)
based on the digested sludge solids fed to the system
as a whole.
VACUUM FILTRATION
The vacuum filtration studies at the JWPCP encompassed an
evaluation of a coil filter (rotary drum type) and two
cloth belt filters (rotary drum type and horizontal belt
type) for dewatering either primary digested sludge or
Bird centrate. Attempts to dewater Bird centrate were,
in all cases, completely unsuccessful due to lack of
significant cake buildup on either the coil or cloth
belts. Also, it was not possible to dewater the JWPCP
primary digested sludge in any of the units without
incorporating some form of conditioning. In accordance
with the schematic in Figure 33, all vacuum filters were
assessed as to their capability to dewater heat-conditioned
digested sludge both with and without intermediate por-
trate thickening. Regarding both rotary drum filters,
118-
-------
FIGURE 33
Schematic flow diagram
Dewatering of thickened and unthickened portrate by vacuum filtration
PICKET
DRIVE
PORTEOUS
PROCESS
HEAT
CONDITIONING
SLUDGE '
(PORTRATE)
STORAGE
TANK
^S
PRIMARY
DIGESTED
SLUDGE
=f
PUMP
I
|
STORAGE
STANK >
IMP(TP-
"1 I .. I -^—THICKENING TANK
THICKENED
PORTEOUS
SLUDGE
PUMP
VACUUM
FILTER
FILTRATE
a:
LU
a
UJ
o
UJ
o
FILTERED
CAKE
CLARIFIED
EFFLUENT
BLEND
-------
two other conditioning aids were considered, namely chem-
ical conditioning with ferric chloride and/or lime, and
polymer conditioning with Nalco 610-
In general, the procedure for evaluating each filter
unit was similar. Digested sludge was first conditioned
and then fed to the respective vacuum filter being tested.
Under each conditioned state, several filtration runs
were conducted, each at different belt speeds. This en-
abled solids loading to be varied and its influence to be in
dependently assessed under a constant set of- conditions.
During each run, several minutes were allocated for an
equilibrium state of operation to be established.
Pursuant to this, one sample each of the feed, filtrate
and cake discharge were taken for followup solids analysis.
Coil Filter
Some preliminary test work was carried out to assess
the effect of various dosages of polymer (Nalco 610)
on the filtration properties of digested sludge. Con-
sidered in this respect were polymer doses ranging from
0-25 Ibs/ton (0.0-12.5 kg/metric ton). The test work
was conducted with the belt speed fixed to provide a
constant solids loading of approximately 5 Ibs/hr/sq ft
(24.4 kg/hr/sq m)--a loading considerably low for this type
of operation but purposely selected to insure adequate
cake formation. Based on several runs carried out at
each of several polymer doses within the investigated
range, the following was concluded:
(1) At polymer dosages between 0-4 Ibs/ton
(0.0-2.0 kg/metric ton), solids recovery
was negligible.
(2) At a polymer dosage of 5 Ibs/ton
(2.5 kg/metric ton), solids recovery was
sparsely achieved; when experienced, gen-
erated cakes were about 231 solids by
weight but were thin and discharged poorly.
(3) Solids recovery was regularly experienced
at a polymer dose of 6 Ibs/ton
(3.0 kg/metric ton) but erratically
ranged from 62-95 percent capture; filter
cakes ranged from 19-21% solids by weight.
(4) Solids recovery remained erratic in the
polymer dosage range of 7-9 Ibs/ton
(3.5-4.5 kg/metric ton) but decreasingly
-120-
-------
so as the upper dosage was approached;
generated cakes ranged between 16-20%
solids by weight at each dosage interval.
(5) At a polymer dosage of 10 Ibs/ton
(5.0 kg/metric ton), solids recovery
stabilized between 90-98 percent capture;
polymer dosages beyond this did nothing
to enhance this situation. Cake quality
remained within a constant range of 16-20%
solids by weight.
Based on the above, it was decided that a polymer dosage
of at least 10 Ibs/ton (5.0 kg/metric ton) would be
required to consistently produce a filtrate having an
average suspended solids concentration of 1500 mg/1.
It was also decided that the filter loading study would
be carried out under this fixed condition.
Presented in Table 28 are data summarizing the effect of
loading rate on the coil filter's capability of dewatering
the JWPCP digested sludge conditioned with 10 Ibs/ton
(5.0 kg/metric ton) of Nalco 610. As noted, the table
is comprised of data acquired from four individual runs,
each from a different day. The effect of loading rate
on suspended solids capture for each of these runs is
graphically depicted in Figure 34. A comparison of the
curves reveals that throughout the investigated range of
loading rates, the capture of suspended solids varied
between 87-99 percent. Regarding two of the runs, solid
recoveries of 97 percent or better were consistently
obtained. The observed differences might be attributed
to day-to-day variations in the particle size distribution
within the sludge material itself. This would likely
have an effect on the body of the formed cake doing the
filtering. Because of the large porosity factor in coil
filters, slight changes in cake body would significantly
affect filtration performance. Similar observations
were encountered in other runs not reported on herein.
Overall, though, an average suspended solids recovery of
95% was achieved. For the most part, discharged cakes
were at 18% (±2%) solids by weight. As in the horizontal
scroll centrifuge tests, this demonstrated the contribu-
tion of bound water associated with the capture of finely
suspended particles from the sludge feed material.
Regarding chemical conditioning, coil filtration tests
were conducted in conjunction with ferric chloride and
lime dosages ranging, respectively, from 40-120 Ibs/ton
-121-
-------
Table 28: DATA* SUMMARIZING THE EFFECT OF LOADING RATE ON THE FILTRATION
CHARACTERISTICS OF POLYMER CONDITIONED DIGESTED SLUDGE IN
A VACUUM COIL FILTER.
PARAMETERS
1. Filter: Komline Sanderson coil filter
2. Vacuum: form § dry pressure differential
@ 12-inches Hg (305-mm Hg)
3. Polymer: Nalco 610
4. Polymer Dosage:... ~10 Ibs/ton (5.0 kg/metric ton)
SUSPENDED SOLIDS CONCENTRATION
Uncon-
ditioned
-%-
4.05
4.06
4.08
3.52
3.48
3.50
3.47
3.69
3.88
3.89
3.90
4.43
4.27
4.51
4.47
Con-
ditioned**
-%-
3,47
3.48
3.50
3.02
2.98
3.00
2.98
3.16
3.33
3.34
3.34
3.80
3.66
3.87
3.83
Filtrate
a
~ o "
0.44
0.19
0.53
0.46
0.26
0.08
0.08
0.07
0.07
0.04
0.07
0.10
0.14
0.10
0.14
Filter
Cake
-%-
18.2
17.8
18.0
18.0
17.2
18.1
21.7
18.4
18.0
18.8
19.8
17.0
18.0
17.8
17.2
CALCULATED
SOLIDS
LOADING
-lbs/hr/
sq f ti-
ll.].
13.7
16.3
6.9
9.4
12.0
5.2
6.9
10.3
12.9
15.4
8.6
12.0
14.6
18.0
SUSPENDED
SOLIDS
CAPTURE***
-%-
89.5
95.6
87.4
87.0
92.7
97.8
97.7
98.2
98.3
99.0
98.3
97.9
96.9
98.0
97.1
*A11 data pertain to filtration studies on JWPCP primary digested
sludge.
**Data corrected for the addition of polymer solution batched at a
concentration of 1250 mg/1.
***Computed values are based on suspended solids in the conditioned
feed.
Unit Conversions:
(Ibs/hr/sq ft) x 4.88 = (kg/hr/sq m)
(% Solids) x 10,000 = (mg/1)
122-
-------
FIGURE 34
to
Solids recovery from polymer conditioned digested sludge
in a coil filter at various loading rates
LJJ
01
Z>
h-
0_
o
CO
Q
100
90
80
70
O 60
CO
a
UJ
a
LtJ
CO 40
ID
CO
30
AUG. 27,1971
0
AUG. 26,1971
SEPT. 2 , 1971
AUG. 25 ,1971
FEED: PRIMARY DIGESTED SLUDGE
FILTER: KOMLINE - SANDERSON COIL FILTER
VACUUM: FORM AND DRY PRESSURE
DIFFERENTIAL AT 12-INCHES Hg (305-mm Hg)
POLYMER: NALCO 610
POLYMER DOSAGE: 10 Ibs/ton (5.0 kg/metric ton)
UNIT CONVERSIONS:
(Ibs/hr/sq ft) x 4.88 = (kg/hr/sq m)
10 15 20 25
SOLIDS LOADING RATE , Ibs / hr / sq f t
30
-------
(20-60 kg/metric ton) and 500-600 Ibs/ton (250-
300 kg/metric ton) as Ca(OH)2. The work was conducted
in a manner which enabled variations in solids loading
rates to be included and their relative influence to be
independently assessed. The results of this work are
summarized in Table 29. As noted, the listed solids
loading and capture values were computed on the basis of
actual suspended solids concentrations in the conditioned
feed.
The effect of solids loading on suspended solids recov-
ery is graphically portrayed in Figure 35 for two lime
dosage situations, both incorporating a constant ferric
chloride dosage of 80 Ibs/ton (40 kg/metric ton). In
both cases, a rapid decrease in solids capture was ex-
perienced as the loading rate was increased from
1.6 to 3.2 Ibs/hr/sq ft (7.8 to 15.6 kg/hr/sq m). For
any particular loading rate in this range, increasing
the lime dosage from 500 to 600 Ibs/ton (250-
300 kg/metric ton) as Ca(OH)2 effected an increase in
recovery. The effect was only slight at the
1.6 Ibs/hr/sq ft (7.8 kg/hr/sq m) loading rate whereat
maximum solids capture occurred.
The effect of ferric chloride dosage on solids recovery
is graphically shown in Figure 36 for two different
loading rates with the lime dosage held constant at
550-600 Ibs/ton (275-300 kg/metric ton) as Ca(OH)2.
Though somewhat sketchy, the results indicate that op-
timum operation is attained with a ferric chloride dosage
of about 80 Ibs/ton (40 kg/metric ton). At dosages
beyond this, an overdosed situation apparently occurred
which negated coagulation and dewatering of the sludge
particles.
Throughout all of the test runs with chemical conditioning,
discharged filter cakes remained relatively constant
at about 25-26% solids by weight (Table 29). This is
to be compared with the 18% cakes attained in coil
filtration tests with polymers. The enhanced dryness is
to be expected, however, in view of the quantity of
insoluble solids added by chemical conditioning.
With regards to heat conditioning, efforts to dewater
unthickened portrate by coil filtration were entirely
unsuccessful. The porosity of the coils was such that
the bulk of the suspended solids in portrate fed to the
124-
-------
Table 29: DATA* SUMMARIZING THE DEWATERING CHARACTERISTICS OF CHEMICALLY CONDITIONED
DIGESTED SLUDGE IN A VACUUM COIL FILTER
PARAMETERS
1. Filter:
2. Vacuum:
Komline Sanderson coil filter
form § dry pressure differential @ 12-inches Hg (305-mm Hg)
CHEMICAL DOSAGE
Fe C13
-Ibs/ton-
40
80
120
Lime
as Ca(OH)2
-Ibs/ton-
560
500
600
600
SUSPENDED SOLIDS CONCENTRATION
Sludge Feed
Uncon-
ditioned
-%-
3.73
3.54
3.54
3.42
Con-
ditioned**
-%-
3,04
2.88
2.85
2.71
Filtrate
-%-
0.51
1.57
0.36
0.70
1.58
0.25
0.47
1.18
1.70
Filter
Cake
-%-
25.9
26.1
24.2
25.7
26.0
25.8
26.0
26.1
26.0
CALCULATED
SOLIDS
LOADING
-lbs/hr/
sq ft
1.6
2.4
1.6
2.4
3.3
1.6
2.4
3.2
1.6
SUSPENDED
SOLIDS
CAPTURE***
-%-
84.9
51.5
88.8
77.8
48.1
92.1
85.0
61.4
39.9
to
Cn
*A11 data pertain to filtration studies on JWPCP primary digested sludge.
**Data corrected for the addition of lime and Fe Cl3 solutions batched at 2% and
1% concentrations, respectively.
***Computated values are based on suspended solids in the conditioned feed.
Unit Conversions:
(Ibs/ton) x 0.5 = (kg/metric ton)
(lbs/hr/ sq ft) x 4.88 = (kg/hr/sq m)
(% Solids) x 10,000 = (mg/1)
-------
FIGURE 35
I
M
IX)
Solids recovery in a coil filter at two different
lime dosages for various loading rates
UJ
a:
0_
<
o
CO
O
CO
Q
UJ
O
UJ
Q.
CO
15
CO
100
90
80
70
60
50
40
1
600 Ibs/ton LIME AS Ca(OH)2
500 Ibs/ton LIME AS Ca(OH)2
CAKE SOLIDS: 25% ±1%
30
I I
0
FEED: PRIMARY DIGESTED SLUDGE -
FILTER: KOMLINE-SANDERSON
COIL FILTER
VACUUM^ FORM AND DRY PRESSURE
DIFFERENTIAL AT 12-INCHES Hg
(305-mm Hg)
FeCI3 DOSAGE: 80 Ibs/ton
UNIT CONVERSIONS:
(Ibs/ton) x 0.5 = (kg/metric ton)
(Ibs/hr/sq ft) * 4.88 = (kg/hr/sq m)
1234
SOLIDS LOADING RATE , Ibs/hr/sq ft
-------
FIGURE 36
100
LJ
C£
ID
I-
CL
<
O
CO
Q
Q
LJ
Q
2
LU
Q_
CO
ID
CO
90
80
70
60
50
40
30
The effect of ferric chloride dosage on solids recovery
in a coil filter at two different loading rates
FEED: PRIMARY DIGESTED SLUDGE
FILTER: KOMLINE-SANDERSON
COIL FILTER
VACUUM: FORM AND DRY PRESSURE —
DIFFERENTIAL AT 12-INCHES Hg
(305-mm Hg)
LIME DOSAGE: 550-600 Ibs/ton AS
Ca(OH)2
UNIT CONVERSIONS^
(Ibs/ton) x 0.5 = (kg/metric ton)
(Ibs/hr/sq ft) x 4.88 = (kg/hr/sq m)
LOADING RATE
6 Ibs/hr/sq ft
4 Ibs/hr/sq ft
0 20 40 60 80 100 120 140 160
FERRIC CHLORIDE , Ibs/ton
180 200 220 240
-------
filter passed through the coils, thereby remaining in
the filtrate. Cake development was nil. Hence the
application was declared totally ineffective.
Some degree of success was arrived at with attempts to
filter thickened portrate. Data summarizing results
obtained at three different loading rates are presented
in Table 30. The tabulated solids recovery effected
by the filter are based on the initial suspended solids
being fed to the machine only and not to the system as
a whole. Additional data are tabulated which show the
quality of the final effluent blend (decantate plus
filtrate) and the overall suspended solids removal by
the system, i.e. removal by thermal volatization,
elimination by thermal transfer to the dissolved phase,
and capture in the filter cake. These latter removal
values were calculated on the basis of 3.5% (35,000 mg/1)
suspended solids in the waste digested sludge fed to the
system.
For comparison, filter solids capture and suspended
solids removal by the system are plotted in Figure 37 as
a function of solids loading applied to the filter.
Increasing the solids loading from 3 to 7 Ibs/hr/sq ft
(14.6 to 34.2 kg/hr/sq m) resulted in a rapid decrease
in captured solids and a corresponding decrease in that
removed by the system. Even at the lowest loading only
about 70 percent solids removal was attained. The poor
filtrate qualities listed in Table 30 reflect the pro-
blem of coil porosity coupled with the effect of heat
conditioning on particle size distribution. Evidently,
the floe particles are small and pass through the filter
coils quite readily with the filtrate.
The data of Table 30 indicated that a slight decrease
in cake solids content (31% to 28% solids by weight)
occurred as the loading rate was increased. In compar-
ison to those cakes generated in either of the two
previously discussed chemical or polymer conditioning
systems, these were much drier and gave evidence of the
bound water release effected by heat conditioning.
Unfortunately, a blend of the poor quality filtrates
with decantate from the picket thickener resulted in
effluent mixtures containing greater than 10,000 mg/1
of suspended solids--a situation which would not be
tolerated at the JWPCP.
-128-
-------
Table 50: DATA* SUMMARIZING THE DEWATERING CHARACTERISTICS OF THICKENED HEAT-CONDITIONED
DIGESTED SLUDGE BY VACUUM COIL FILTRATION
PARAMETERS
1. Processed Material: JWPCP primary digested sludge
2. Porteous Conditioning: 40 min 8 35QOF (175°C)
3. Thickener Overflow Rate:... 225 gpd/sq ft (9.2 cu m/day/ sq m)
4. Filter: Komline-Sanderson coil filter
5. Vacuum: form § dry pressure differential
@ 12-inches Hg (305-nrn Hg)
SUSPENDED SOLIDS CONCENTRATION
Thickened
Portrate
Feed
-%-
5.93
5.64
Filtrate
-4-
2.30
3.14
5.00 4.54
Filter
Cake
-4-
31.2
29.0
28.1
CALCULATED
FILTER
SOLIDS
LOADING
-Ibs/hr/sq ft-
3
5
7
SUSPENDED
SOLIDS
CAPTURE
IN FILTER
-%-
66.1
49.7
11.0
SUSPENDED SOLIDS
IN EFFLUENT
BLEND
(Filtrate + Decantate)
-4-
1.08
1.48
2.37
\
TOTAL SUSPENDED
SOLIDS REMOVAL
BY SYSTEM**
-4-
71.6
60.8
35.3
IN)
to
*A11 data pertain to test conducted on JWPCP primary digested sludge.
**Removal by*Systern"includes filter capture, thermal volatization, and thermal transfer
to the dissolved phase. Calculated values are based on a suspended solids concentration
of 3.51 in the digested sludge fed to the system.
Unit Conversions:
(Ibs/hr/sq ft) x 4.88 = (kg/hr sq m)
(4 Solids) x 10,000 = (mg/1)
-------
CD
I
80
-70
FIGURE 37
Suspended solids removal from digested sludge fed to a system
incorporating heat conditioning, intermediate thickening and vacuum
filtration of the thickened portrate stream in a coil filter
60
UJ
or
CO
a
50
Q
LLJ
0 30
2
LLJ
Q.
CO 20
CO
0
0
REMOVAL BY
SYSTEM-
FILTER CAPTURE
FROM THICKENED
HEAT CONDITIONED
SLUDGE
UNIT CONVERSIONS :
(Ibs/hr/sq ft) x 4.88 = (kg/hr/sq m)
— NOTE-
REMOVAL BY "SYSTEM" INCLUDES FILTER
CAPTURE, THERMAL VOLATIZATION , AND
- THERMAL TRANSFER TO THE DISSOLVED
PHASE.
PROCESSED MATERIAL:
PRIMARY DIGESTED SLUDGE
HEAT CONDITIONING
40 MINUTES AT 350°F (I75°C)
THICKENER OVERFLOW RATE: —
225 gpd/sq. ft (9.2 cu m/day/sq m)
FILTER: COIL FILTER
VACUUM' 12 INCHES Hg (305mm Hg)
3456789
SOLIDS LOADING RATE , Ibs/hr/sq ft
10
-------
In review, coil filtration tests incorporating polymer
conditioning at 10 Ibs/ton (5.0 kg/metric ton) yielded
the highest solids loading rate -- approximately
18 Ibs/hr/sq ft (87.8 kg/hr/sq m) ; filter cakes, however,
were wettest (18% solids by weight). Solid captures of
92 percent and cake qualities of 25-26% solids by weight
were experienced with lime and ferric chloride dosages of
600 Ibs/ton (300 kg/metric ton) as Ca(OH)? and 80 Ibs/ton
(40 kg/metric ton) , respectively; these results could
only be accomplished, however, at a loading rate of
about 1.5 Ib/hr/sq ft (7.3 kg/hr/sq m) -- a rate deemed
economically impractical for a coil filter operation.
Finally, driest cakes (approximately 30% solids by weight)
were attained in the thermal-thickening-filtration system;
solids removal (maximum of 70 percent) was poorest not
to mention the impractical low loading rate of
3 Ibs/hr/sq ft (14.6 kg/hr/sq m) necessary to achieve this.
Rotary-Belt Vacuum Filter
Specific resistance (SR) determinations and filter leaf
tests were conducted in the laboratory prior to actual
belt filtration tests. The derived information proved
useful in eliminating much of the pilot plant work that
would have otherwise been necessary. For example, SR
tests revealed that under a differential vacuum pressure
of 20-25 inches Hg (505-630 mm Hg), cloth belt filtration
of heat-conditioned digested sludge would not be possible
without intermediate thickening. Similar tests also
revealed that digested sludge would not filter directly
unless preconditioned with at least 10 Ibs/ton
(5.0 kg/metric ton) of a cationic polymer (Nalco 610)
or 400 Ibs/ton (200 kg/metric ton) of lime as Ca(OH)2.
Filter leaf tests conducted with six different synthetic
cloth materials enabled three to be selected for pilot
testing. In the actual pilot plant work, best results
were achieved with one belt material (Polypropylene 854-F)
regardless of the type of conditioning. For purposes of
this report, only those results will be presented herein.
Data summarizing the dewatering characteristics of polymer
and lime conditioned digested sludge in an Eimco-belt
vacuum filter are presented in Tables 31 and 32, respec-
tively. Those of thickened heat-conditioned digested
sludge are presented in Table 33. As noted in Table 32,
data are presented for lime dosages of 400, 600 and 800
Ibs/ton (200,300 and 400 kg/metric ton) as Ca(OH)2 with
-131-
-------
Table 31: DATA* SUMMARIZING THE DEWATERING CHARACTERISTICS OF POLYMER CONDITIONED DIGESTED
SLUDGE IN A ROTARY-BELT VACUUM FILTER
PARAMETERS
Filter: Eimcobelt vacuum filter
1.
2.
3.
4.
5. Polymer Dosage:... 10 Ibs/ton (5 kg/metric ton)
Belt Material: Polypropylene 854-F
Vacuum: form § dry pressure differential @ 25-inches Hg (630-mm Hg)
Polymer: Nalco 610
SUSPENDED SOLIDS CONCENTRATION
Conditioned
Sludge Feed
3.78
3.91
3.79
Filtrate
-*-
0.06
0.04
0.05
Filter Cake
22.3
18.2
18,9
CALCULATED
SOLIDS
LOADING
-Ibs/hr/sq ft-
0.9
1.0
1.1
SUSPENDED
SOLIDS
CAPTURE
98.7
99.2
98.9
CAKE
DISCHARGE
PROPERTIES
Poor
Poor
Poor
to
i
*A11 data pertain to filtration studies on JWPCP primary digested sludge.
Unit Conversions: (Ibs/hr/sq ft) x 4.88 = (kg/hr/sq m)
(I Solids) x 10,000 = (mg/1)
-------
Table 32: DATA* SUMMARIZING THE DEWATERING CHARACTERISTICS OF CHEMICALLY CONDITIONED DIGESTED
SLUDGE IN A ROTARY-BELT VACUUM FILTER.
PARAMETERS
Y. Filter: Eimco belt vacuum filter
2. Belt Material:... Polypropylene 854-F
3. Vacuum: form § dry pressure differential @ 25-inches Hg (630-mm Hg)
4. Fe Cl3 Dosage:... None
LIME
DOSAGE
as Ca(OH)2
-Ibs/ton-
400
600
800
SUSPENDED SOLIDS CONCENTRATION
Conditioned
Sludge Feed
-%-
4.45
4.37
4.17
4.60
4.63
4.55
5.37
5.28
5.29
5.33
Filtrate
-%-
0.05
0.09
0.08
0.02
0.03
0.02
0.01
0.01
0.02
0.04
Filter Cake
-%-
28.4
36.6
31.6
32.8
35.2
36.8
33.1
34.5
35.0
34.3
CALCULATED
SOLIDS
LOADING
-Ibs/hr/sq ft-
0.8
0.9
1.1
1.3
1.5
1.7
1.5
1.7
2.0
2.2
SUSPENDED
SOLIDS
CAPTURE
-%-
99.1
98.2
98.3
99.6
99.4
99.6
99.8
99.8
99.7
99.4
CAKE
DISCHARGE
PROPERTIES
q,
~ o ~
Good
Good
Fair
Good
Good
Fair
Good
Good
Fair
Poor
o-l
*A11 data pertain to filtration studies on JWPCP primary digested sludge.
Unit Conversions:
(Ibs/ton) x 0.5 = (kg/metric ton)
(Ibs/hr/sq ft) x 4.88 = (kg/hr/sq m)
(% Solids) x 10,000 = (mg/1)
-------
Table 35: DATA* SUMMARIZING THE DEWATERING CHARACTERISTICS OF THICKENED HEAT-CONDITIONED
DIGESTED SLUDGE BY ROTARY-BELT VACUUM FILTRATION
PARAMETERS
T.
2.
3.
4.
5.
6.
Processed Material: JWPCP primary digested sludge
Porteous Conditioning: 40 min @ 350°F (175°C)
Thickener Overflow Rate:... 225 gpd/sq ft (9.2 cu m/day/ sq m)
Filter: Eimcobelt vacuum filter
Belt Material: Polypropylene 854-F
Vacuum: form § dry pressure differential @ 25-inches Hg
(630-mm Hg)
Thickened Portrate Feed:... 9.21% suspended solids
SUSPENDED SOLIDS
CONCENTRATION
Filtrate
-%-
0.09
0.14
0.11
0.13
0.16
0.49
Filter
Cake
-%-
37.4
36.5
36.4
35.7
35.8
34.9
CALCULATED
FILTER
SOLIDS
LOADING
-Ibs/hr/sq ft-
2.1
2.5
2.6
3.3
3.9
4.6
SUSPENDED
SOLIDS
CAPTURE IN
FILTER
-%-
99.3
98.9
99.1
98.9
98.7
96.0
CAKE
DISCHARGE
PROPERTIES
Good
Good
Good
Good
Fair
Poor
SUSPENDED SOLIDS
IN EFFLUENT
BLEND
(Filtrate + Decantate)
-%-
0.31
0.32
0.32
0.32
0.33
0.39
SUSPENDED
SOLIDS
REMOVAL BY
SYSTEM**
-*-
91.9
91.7
91.7
91.7
91.4
89.9
*A11 data pertain to test conducted on JWPCP primary digested sludge.
**Removal by"System" includes filter capture, thermal volatization, and thermal transfer
to the dissolved phase. Calculated values are based on a suspended solids concentration
of 3.5% in the digested sludge fed to the system.
Unit Conversions:
(Ibs/hr/sq ft) x 4.88 = fkg/hr/sq m)
(% Solids) x 10,000 = (ing/1)
-------
no accompanying ferric chloride dosage. Test work was
conducted at each of these in combination with 60 Ibs/ton
(30 kg/metric ton} of ferric chloride; data results
however, were similar to those of Table 32.
Although filtrates of excellent quality were attained
in the filtration tests on polymer conditioned sludge
(Table 31) , the discharge characteristics of the generated
filter cakes were, in all cases, poor. At loading rates
above 1.1 Ibs/hr/sq ft (5.4 kg/hr/sq m), the filter cakes
were very thin and wet and, as a consequence, would not
discharge at all. Even at the low loading rates shown,
the generated cakes were too wet to permit a clean
discharge without assistance from the operator. Typically,
these 18-20% cakes demonstrate the bound water effect
as a consequence of high solids capture (99 percent).
Filtrates of excellent quality were also attained in
filtration tests on lime conditioned sludge (Table 32).
As opposed to polymer conditioning, the addition of lime
served to enhance the dryness of the generated filter
cakes. Consequently, loading rates could be adjusted
to promote the build-up of thicker cakes which had good
discharge properties. When the lime dosage was 400 Ibs/ton
(200 kg/metric ton) as Ca(OH)2> it was necessary to reduce
the loading to 0.9 Ibs/hr/sq ft (4.4 kg/hr/sq m) to achieve
this result. By increasing this dosage to 600 Ibs/ton
(300 kg/metric ton) as Ca(OH)2, loadings up to
1.5 Ibs/hr/sq ft (7.3 kg/hr/sq m) were possible while
still retaining the good cake discharge property; also,
filtrate quality was slightly improved and filter cakes
were a little drier. Increasing the lime dosage up to
300 Ibs/ton (400 kg/metric ton) as Ca(OH)2 did little
to improve upon this situation.
In terms of solids loading, vacuum filtration of thickened
portrate was best. As shown in Table 33, good cake dis-
charge was possible up to a solids loading of
3.3 Ibs/hr/sq ft (16.1 kg/hr/sq m). Cake solids were at
35.7% by weight and the resulting filtrate contained
1300 mg/1 of suspended solids. The dry filter cakes lend
support to the release of bound water effected by heat
conditioning. Based on the suspended solids in the
thickened portrate feed, suspended solid captures of about
99 percent were possible with the filter unit. System
removals are somewhat lower, however, when consideration
is given to the quality of the decantate from the thickener
As noted, overall suspended solids removals of about
-135-
-------
92 percent would be experienced by the thermal-thickening-
filtration system. The resulting effluent (filtrate plus
decantate) would contain about 3200 mg/1 of suspended
material. On the premise that this effluent would re-
ceive some form of biological treatment (required because
of the high soluble BOD characteristic induced by thermal
conditioning), it was expected that this suspended solid
component could be reduced to the 1500 mg/1 deemed
acceptable for mixing with the JWPCP primary effluent
prior to discharge.
Horizontal Belt Filter (Extractor)
As previously mentioned, the extractor pilot plant was
only assessed as to its capabilities for dewatering
thickened heat-conditioned digested sludge. The cloth
belt furnished with the unit was one which was recommended
by Eimco representatives as being likely to do a satis-
factory job. This recommendation was based on filter
leaf tests conducted on the JWPCP's digested sludge after
thermal conditioning and thickening.
On the whole, efforts to dewater thickened portrate by
vacuum extraction were not too successful. Attempts to
load the extractor at a normally typical 20 to
40 Ibs/hr/sq ft (97.6 to 195.2 kg/hr/sq m) solids loading
resulted in no cake formation whatsoever. In fact, cake
formation was not possible until the loading was reduced
below 10 Ibs/hr/sq ft (48.8 kg/hr/sq m). Further reduc-
tion was even necessary before the cake would even half-
way discharge by itself.
For the effort involved, only two of the many attempted
runs yielded informative data. The results of these runs
are tabulated in Table 34. At a solids loading of
3.6 Ibs/hr/sq ft (17.6 kg/hr/sq m), a 92.3 percent solids
capture was effected by the filter. Generated cakes
were at 29.4% solids by weight and had poor discharge
properties. Further loading reduction to 2.7 Ibs/hr/sq ft
(13.2 kg/hr/sq m) served to increase s,olids capture only
slightly. A drier cake (34.6% solids by weight) ensued,
however, and the filtrate was of somewhat better quality
(8100 mg/1 suspended solids). Cake discharge improved
slightly but was not consistent. At the lower loading,
a resultant blend of the filtrate with the decantate from
the thickener would yield an effluent mixture containing
0.44% (4400 mg/1) suspended solids. Overall suspended
solids removal from the system would be about 89 percent.
-136-
-------
Table 34: DATA* SUMMARIZING THE DEWATERING CHARACTERISTICS OF THICKENED HEAT-CONDITIONED DIGESTED
SLUDGE BY VACUUM EXTRACTION
PARAMETERS
1.
2.
3.
4.
5.
6.
Processed Material: JWPCP primary digested sludge
Porteous Conditioning: 40 min @ 350°F (175°C)
Thickener Overflow Rate:... 225 gpd/sq ft (9.2 cu m/day/ sq m)
Filter: Eimco vacuum extractor
Cloth Belt: manufacturer's recommendation
Vacuum: 20-inches Hg (505-mm Hg)
SUSPENDED SOLIDS CONCENTRATION
Thickened
Portrate Feed
-%-
9.13
9.84
Filter
-%-
0.81
1.09
Filter
Cake
-%-
34.6
29.4
CALCULATED
FILTER
SOLIDS
LOADING
-Ibs/hr/sq ft-
2.7
3.6
SUSPENDED
SOLIDS
CAPTURE
IN FILTER
-%-
93.3
92.3
CAKE I
DISCHARGE
PROPERTIES
•
Fair
Poor
1 SUSPENDED SOLIDS
[ IN EFFLUENT
| BLEND
i (Filtrate + Decantate)
-*-
0.44
0.49
SUSPENDED
SOLIDS
REMOVAL. BY
SYSTEM**
-%-
88.6
87.5
*A11 data pertain to test conducted on JWPCP primary digested sludge.
**Removal by"System*includes filter capture, thermal volatization, and thermal transfer
to the dissolved phase. Calculated values are based on a suspended solids concentration
of 3.5% in the digested sludge fed to the system.
Unit Conversions: (Ibs/hr/sq ft) x 4.88 = (kg/hr/sq m)
(% Solids) x 10,000 = (mg/1)
-------
Even considering any additional removal with followup
biological treatment, such a system would be economical-
ly impractical due to the low filter loadings required
to achieve these results.
PRESSURE FILTRATION
Two types of filter presses were evaluated in this phase
of the work, namely a Beloit-Passavant pressure filter
and an Eimco diaphragm press. A majority of the research
was conducted with the former. Due to the unsuccessful
nature of the latter, only a limited amount of work was
carried out. The results of the research are presented
in the following.
The Beloit-Passavant pressure filter was assessed of its
capabilities for dewatering either primary digested sludge
or Bird centrate. It was quickly discovered that de-
watering of the latter was not a feasible operation due
to the extremely wet cakes generated. This was attributed
to both the fine nature and low concentration of the
suspended solids in the centrate feed material. Therefore,
the remaining research with the pressure filter was
carried out directly on digested sludge.
Pressure filtration of primary digested sludge could not
be accomplished without some form of conditioning. There-
fore, the performance of the pressure filter was assessed
on sludges conditioned by either chemicals (lime and
ferric chloride), polymers, flyash, or heat. All attempts
to dewater polymer conditioned sludge proved to be totally
unsuccessful due to rapid blinding of the filter media.
Consequently, further evaluation of this type of condition-
ing was discontinued. An attempt was also made to thicken
the digested sludge with polymers as a prelude to chemical
conditioning in the hope that lower chemical require- '
ments would result. However, such was not found to be
the case.
The independent variables which control the operation of
a pressure filter are the type of sludge conditioning,
type of precoat, feed cycle time and feed pressure. All
of these variables exert some influence on cake dryness,
filtrate suspended solids and filter loading rate. Precoat
of the filter is necessary to prevent blinding and insure
that the cake can discharge cleanly. Diatomaceous earth
and flyash are two materials which are suitable for this
-138-
-------
means. In this work, the type and amount of precoat
was kept constant for each form of sludge conditioning
studied. When the sludge was conditioned by chemicals 01
heat, diatomaceous earth was used for the precoat; with
ash conditioning, ash was used for the precoat. Based
on the manufacturer's recommendation, 4.5 Ibs (2.0 kg)
of precoat material was necessary for every 100 sq ft
(9.3 sq m) of filter area. Preliminary tests indicated
that a greater amount of precoat would not improve fil
tration rate or cake dryness, whereas an insufficient
amount resulted in blinding of the filter media. Hence,
the manufacturer's recommendation was closely adhered
to in the test work.
The nature of the pressure filter operation required that
feed pressure be increased with time to overcome the
resistance from build-up of solids within the filter
chamber. In this work, the pattern of pressure increase
and length of time to progress from the initial pressure
of 30 psig (2.1 kg/sq cm) to the final pressure of 220 psig
(15.5 kg/sq cm) was kept constant for runs with each form
of conditioning. With chemical and ash conditioning,
this final pressure was allowed to be reached in 60
minutes in accordance with an increasing pressure pat-
tern recommended by the manufacturer. Accordingly, pres
sure was increased in increments of 15 psi (1.1 kg/sq cm)
every 5 minutes until 220 psig (15.5 kg/sq cm) was
attained. This pressure was then maintained for the
remainder of the run. For runs of less duration, maximum
pressure was that obtained at the end of the feed cycle.
Although this varied from the above procedure, it was
done to simulate actual operating conditions. For heat
conditioned sludge the formed floe proved to be more
delicate than the chemically conditioned floe, resulting
in rapid blinding of the filter. To overcome this,
the length of time to reach maximum pressure was increased
from 60 minutes to 100 minutes by lowering the incremental
increase to 10 psi (0.7 kg/sq cm) every 5 minutes.
Operation of the pressure filter is such that, for all
practical purposes, filtrate quality can be considered to
be independent of conditioning and feed cycle time. The
filter either works and produces an excellent filtrate
or it blinds and produces no filtrate. With sufficient
conditioning the filtrate usually contained less than
100 mg/1 of suspended solids. Consequently, filtrate
quality was not a major concern in evaluating the
pressure filter nor in determining the operational criteria
for its operation.
139-
-------
Since type and amount of precoat and feed pressure were
essentially kept constant throughout the evaluation,
only the conditioning and feed time were operational
variables. Also, since filtrate quality was acceptable in
all successful runs, cake dryness and loading rate became
the only dependent variables. Of these, cake dryness
was determined to be the more important.
The following general test procedure was used to evaluate
the system. After the feed was pumped into the mix tank,
grab samples of the feed were taken. One was taken
without conditioning, and a second after conditioning.
During the feed cycle, grab samples of the filtrate
were collected every 15 minutes. From these samples
one composite sample was taken. Determination of cake
solids presented a problem. After inspecting the cakes
from three chambers, their nonuniform solids content
became apparent. All of the cakes were about the same
consistency; however, the dryness of each cake increased
with outward radial progression from the center core. To
capture this variation in dryness three samples were taken
as representative samples of each compartmentalized cake.
An arithmetic average was used to represent the average
cake solids.
A general analysis of the performance of the pressure
filter can be made, regardless of the type of conditioning
agents used. Based on this, the following was determined:
(1) From information obtained from published litera-
ture as well as from the manufacturer, it was
expected that sludge dewatering characteristics
would be better with higher concentrations of
suspended solids in the feed material. This was
generally found to be true when the sludge solids
concentration was increased by gravity thicken-
ing or by addition of chemicals or flyash as a
body feed material.
(2) Visual inspection of the feed sludge revealed
that a large portion of the solids consisted
of fine particles. For effective filtration
to occur, good coagulation of these fine parti-
cles was necessary. In the case of heat condi
tioned sludge this would be accomplished by
gravity thickening of the portrate; for chemi
cal or ash conditioned sludge, coagulation
would be induced by maintaining a high pH.
A pH of around 10 is usually necessary for
-140-
-------
good coagulation of colloidal particles. For
coagulation of the fines in the JWPCP's sludge,
a pH of 11.5 was found to be necessary. Conse-
quently, the amount of lime added to the feed
sludge was based on the requirement of raising
the pH to promote good coagulation.
(3) In spite of the pattern used for increasing the
operating pressure to overcome resistance from
solids accumulation within the filter, there
was a rapid decrease in the instantaneous
flowrate through the unit. Thus, the solids
loading rate became lower as the duration of the
feed cycle progressed.
(4) Increasing the feed cycle promoted compression
of the accumulated solids within the press and,
h^nce, increased cake dryness. Therefore,
there existed an inherent trade-off in the
operation of the pressure filter between cake
solids and loading rate, i.e. the drier the
cake, the lower the solids loading rate.
Data summarizing test results on the pilot plant pressure
filter under variable feed cycles with various lime and
ferric chloride dosages are presented in Table 35. For
a constant lime dosage of 400 Ibs/ton (200 kg/metric ton)
as Ca(OH)2, the effect of feed time on the solids content
of generated cakes at each of several ferric chloride
dosages is shown in Figure 38. The same effect is shown
in Figure 39 for a constant lime dosage of 500 Ibs/ton
(250 kg/metric ton) as Ca(OH)2. The plotted results in
both figures indicate that regardless of the feed time,
drier cakes are obtained with increased ferric chloride
dosage up to 120 Ibs/ton (60 kg/metric ton). Ferric
chloride dosages greater than this were not considered
due to its corrosive properties and its adverse tendency
to lower the pH of the system. A comparison of Figures
38 and 39 reveals that generated cakes were driest when the
higher lime dosage was used. The curves also reveal that,
beyond a feed cycle of 2 hours, cake dryness does not
increase significantly. A plot of loading rate versus
feed time is presented in Figure 40 for the situation
when the lime and ferric chloride dosage was held con-
stant at 500 Ibs/ton (250 kg/metric ton) as Ca(OH)2 and
120 Ibs/ton (60 kg/metric ton), respectively. From this
it is seen that the loading rate decreased rapidly as
141-
-------
Table 55: DATA* SUMMARIZING THE DEWTERING CHARACTERISTICS OF
CHEMICALLY CONDITIONED DIGESTED SLUDGE IN A PRESSURE
FILTER
PARAMETERS
1. Filter: Beloit-Passavant pressure filter
2. Pressure:... Initial @ 30 psig (2.1 kg/sq on);
maximum @ 220 psig (15.5 kg/sq on)
3. Precoat:.... Diatomaceous earth
CHEMICAL DOSAGE
FeCl3
-Ibs/ton-
80
100
120
Lime
as Ca(OH)2
-Ibs/ton-
400
600
400
500
400
500
CYCLE
TIME
-hr-
1.0
2.0
3.0
0.5
2.0
3.0
0.5
1.5
2.0
3.0
0.75
1.0
2.0
3.0
0.5
1.0
2.0
2.5
0.5
0.75
1.5
3.0
SUSPENDED SOLIDS CONCENTRATION
Sludge
Feed**
-%-
3.57
3.55
3.77
3.60
3.85
3.56
4.02
3.64
3.50
3.64
4.07
4.17
3.58
3.24
3.53
3.32
3.60
3.30
3.98
4.01
3.64
4.01
Filtrate"*"
-!-
.008
.001
.001
.005
.004
.005
.004
.003
.001
.003
.001
.001
.001
.009
.001
.003
.001
.002
.001
.001
.001
.004
Filter
Cake
-%-
23.3
29.0
30.1
25.7
36.0
39.2
21.1
29.9
31.1
33.0
28.5
30.4
36.8
38.2
21.1
29.0
35.1
35.7
27.9
32.2
38.8
41.0
FLOW
-gal.-
72
70
54
98
120
36
96
83
67
82
97
122
41
60
92
114
70
63
67
108
CALCULATED
SOLIDS
LOADING**
-Ibs/hr/sq ft-
0.59
0.41
1.80
0.87
0.62
1.42
1.08
0.45
1.68
1.60
0.80
0.61
1.33
0.98
0.78
0.70
2.58
1.57
0.75
0.66
*A11 data pertain to filtration studies on JWPCP primary digested sludge.
**Not corrected for the addition of FeClj and lime.
***Data are indicative of suspended solid captures in excess of 99 percent.
Unit Conversions: (gal.) x 3.785 = (liters)
(Ibs/ton) x 0.5 = (kg/metric ton)
(Ib/hr/sq ft) x 4.88 = (kg/hr/sq m)
(% Solids) x 10,000 = (mg/1)
142-
-------
FIGURE 38
The effect of feed time on cake solids
during pressure filtration of digested sludge
PROCESSED MATERIAL^
PRIMARY DIGESTED SLUDGE
FILTER- BELOIT-PASSANT PRESSURE
FILTER
PRECOAT' DIATOMACEOUS EARTH
LIME DOSAGE- 400 Ibs/ton AS Ca(OH)2 _
UNIT CONVERSIONS^
(Ibs/ton) x 0.5 = (kg/metric ton) —
FeCI3 DOSAGE
80 Ibs/ton
100 Ibs/ton
120 Ibs/ton
FEED TIME , hr
-------
FIGURE 39
The effect of feed time on cake solids
during pressure filtration of digested sludge
T
T
T
T
T
PROCESSED MATERIAL:
PRIMARY DIGESTED SLUDGE
FILTER: BELOIT-PASSAVANT
PRESSURE FILTER
PRECOAT: DIATOMACEOUS EARTH
LIME DOSAGE: 500 Ibs/ton AS Ca(OH)2
UNIT CONVERSIONS^
(Ibs/ton) x O.5 = (kg/metric ton)
FeCI3 DOSAGE
100 Ibs/ton
120 Ibs/ton
1
1
FEED TIME, hr
-------
FIGURE 40
Loading rate as a function of feed time during pressure
filtration of chemically conditioned digested sludge
T
r
\
l/l
cr
to
-C
\
CO
^Q
•»
UJ
I-
or
2
— |
O
PROCESSED MATERIAL:
PRIMARY DIGESTED SLUDGE
FILTER: BELOIT-PASSAVANT
PRESSURE FILTER
PRECOAT: DIATOMACEOUS EARTH
LIME DOSAGE: 500 Ibs/ton AS Ca(OH)2
FeCI3: 120 Ibs/ton
UNIT CONVERSIONS:
(Ibs/ton) x 0.5 = (kg/metric ton)
(Ibs/hr/sq ft) x 4.88 * (kg/hr/sqm)
0
4
FEED TIME , hr
-------
the duration of the feed cycle was increased to 1.5 hours.
Increased feed cycle time beyond this served to reduce
the overall loading rate only slightly.
Upon analyzing the above data, it was generally felt
that pressure filtration of chemically conditioned digest-
ed sludge was optimum when the lime and ferric chloride
dosage was 500 Ibs/ton (250 kg/metric ton) as Ca(OH)2
and 120 Ibs/ton (60 kg/metric ton), respectively. Optimum
cake dryness would be achieved with a 2-hr feed cycle and
would result in an overall solids loading of 0.7 Ibs/hr/sq ft
(3.4 kg/hr/sq m). Under these conditions, discharge cakes
of 401 solids by weight would be generated. Resulting
filtrates would have a suspended solids concentration of
100 mg/1 or less.
Flyash conditioning was investigated as an alternative
to chemical conditioning. The use of flyash is dependent
upon incineration of the produced cake to obtain the ash
conditioning material. Results from the testing of flyash
as a conditioning agent are summarized in Table 36.
Initially, studies were carried out using 2000 Ibs/ton
(1000 kg/metric ton) of flyash as a body feed material.
Without the use of lime, a 37% cake was generated in a
2-hour feed cycle; the solids loading rate, however,
was low. When 450 Ibs/ton (225 kg/metric ton) of lime
as Ca(OH)2 was added, generated cake dryness was increased
to 471 solids weight. More importantly, the solids
loading rate and total flow through the filter almost
tripled. This indicated the importance of lime addition
for raising the pH of the flyash conditioned sludge.
Tests were run to determine the effects of increasing the
ash dosage to 3000 and 4000 Ibs/ton (1500 and
2000 kg/metric ton). For runs under similar conditions,
conditioning with 4000 Ibs/ton (2000 kg/metric ton) of
flyash produced a drier cake than with the lower ash
dosage. At the higher ash dosage, an increase in the
feed cycle time effected an increase in cake dryness.
As noted, a small amount of lime was used to raise the
pH of the conditioned sludge and induce coagulation.
Following a one-hour feed cycle, a discharged cake of
43% solids by weight was generated. As noted, an actual
sludge solids loading of 0.5 Ibs/hr/sq ft
(2.4 kg/hr/sq m) was experienced. Increasing the
feed cycle to 3 hours served only to increase cake dryness
slightly. A corresponding reduction in solids loading
was also effected. While the resulting cake was about
-146-
-------
Table 36: DATA* SUMMARIZING THE EFFECTS OF ASH AND LIME ADDITION TO DIGESTED SLUDGE ON
DEWATERING PERFORMANCE IN A PRESSURE FILTER
PARAMETERS
1. Filter: Beloit-Passavant pressure filter
2. Pressure:... Initial @ 30 psig (2.1 kg/sq on) to maximum @ 220 psig
(15.5 kg/sq on)
3. Precoat: Diatomaceous earth
4. Flyash: Pulverized ash residue from BSP mutliple hearth pilot
plant furnace
ASH
DOSAGE
-Ibs/ton-
2000
3000
4000
LIME
DOSAGE
as Ca(OH)2
-Ibs/ton-
0
450
50
100 ,
150
FEED
CYCLE
TIME
-hr-
2.0
2.0
1.0
2.0
3.0
SUSPENDED SOLIDS CONCENTRATION
Sludge
Feed**
-%-
4.12
3.60
3.62
3.67
3.53
3.53
3.50
Filtrate***
-*-
0.004
0.003
0.003
0.005
0.012
0.008
0.008
Filter
Cake
-%-
36.6
47.2
45.1
43.0
43.2
47.1
49.6
TOTAL
FLOW
-gal-
23
54
51
37
31
43
50
CALCULATED
SOLIDS
LOADING**
-Ibs/hr/sq ft-
0.23
0.60
0.43
0.38
0.50
0.35
0.27
I
h-'
-pi
*A11 data pertain to filtration studies on JWPCP primary digested sludge,
**Not corrected for the addition of ash and lime.
***Data are indicative of suspended solid captures in excess of 99 percent.
Unit Conversions:
(gal) x 3.785
(Ibs/ton) x 0.5
(Ib/hr/sq ft) x 4.88
(% Solids) x 10,000
(liters)
(kg/metric ton)
(kg/hr/sq m)
fmg/1)
-------
50% solids by weight, consideration was also given to the
fact that two-thirds of the solids were recycled ash.
Further analysis revealed that the ratio of water to
sludge solids in that cake was the same as that optimally
obtained with chemical conditioning.
With regards to heat conditioning, the dewatering charac-
teristics of the pressure filter on both thickened and
unthickened portrate were looked at briefly. The results
of these tests are summarized in Table 37. Through heat
conditioning, the suspended solids in the feed are reduced
to 2.5% (25,000 mg/lj . Because of the low feed solids a
longer feed time is needed to dewater the unthickened
sludge and form a dry cake. Typical results showed that a
2-to 3-hour feed time was necessary to generate a cake of
30% solids by weight. Cake discharge from the opened
plates, however, was poor. Solids loadings to the filter
reached an optimum of 0.59 Ib/hr/sq ft (2.9 kg/hr/sq m).
Filtrate quality was again excellent, with essentially
100% suspended solids removal from the system. For com-
parison, a 2-hour filtration run was carried out using
thickened portrate for feed material. Cake solids were
at 38% by weight and the corresponding filtrate was of
excellent quality. The solids loading for the run was
calculated to be 1.05 Ibs/hr/sq ft (5.1 kg/hr/sq m).
It was obvious from the above that some benefits did
prevail by the inclusion of the intermediate thickening
step into the system. Drier cakes with superior discharge
properties were obtained in a shorter period of operating
time. Also, solid loadings to the filter were nearly
doubled. These benefits, however, were offset by sacri
fices in overall effluent quality. Though filtrate quality
remained unaffected, consideration was given to the decant-
ed overflow from the thickening clarifier. A combined
filtrate-decant effluent would contain about 0.32%
(3200 mg/1) suspended solids. Hence, an overall suspended
solids removal of 92 percent would be possible from such
a system.
Attempts to evaluate the dewatering capabilities of the
diaphragm press were, for the most part, unsuccessful.
The relatively small size of the feed system to the unit
made it impossible to inject most of the conditioned
digested sludges into the filtration chamber. Some success
was realized with unthickened portrate (probably because
of the low suspended solids content of that material).
However, attempted runs were of such short duration that
-148-
-------
Table 57: DATA* SUMMARIZING THE DEWATERING CHARACTERISTICS OF UNTHICKENED AND THICKENED
HEAT-CONDITIONED DIGESTED SLUDGE BY PRESSURE FILTRATION
PARAMETERS
IT
2.
3.
4.
5.
6.
Processed Material: JWPCP primary digested sludge
Porteous Conditioning: 40 min @ 350°F (175°C)
Thickener Overflow Rate:... 225 gpd/sq ft (9.2 cu m/day/sq m)
Filter: Beloit-Passavant pressure filter
Pressure: Initial @ 30 psig (2.1 kg/sq on);
Maximum @ 220 psig (15.5 kg/sq cm)
Precoat: Diatomaceous earth
WITH
AND
WITHOUT
THICKENING
Without
With
CYCLE
TIME
-hr-
2.0
2.5
3.0
2.0
SUSPENDED SOLIDS CONCENTRATION
Sludge
Feed
-%-
3.46
2.41
2.69
11.32
Filtrate
-*-
0.010
0.002
0.004
0.004
Filter
Cake
-*-
33.8
30.2
30.0
38.1
TOTAL
FLOW
-gal-
63
118
119
37
CALCULATED
SOLIDS
LOADING**
-Ibs/hr/sq ft
0.50
0.52
0.59
1.05
SUSPENDED
SOLIDS IN
EFFLUENT BLEND
(Decantate + Filtrate~
"\. /-^
^>
-------
numerical assessment of the unit's capabilities was not
possible. Visually, its performance looked promising
though. Filtrates were of excellent quality (less than
100 mg/1 of suspended solids). Resultant cakes were at
30% solids by weight but were extremely thin and, as a
consequence, would not discharge from the filter media.
It was generally felt, however, that minor changes in the
unit's design would greatly enhance its capabilities for
future application.
150-
-------
SUMMARY DISCUSSION OF TEST WORK
Thermal conditioning of the JWPCP's digested sludge was
dependent on sludge cooking time and the associated cook-
ing temperature. A temperature of 360°F (180°C) was re-
quired if sludge was to be cooked for only 30 minutes.
Allowing 40 minutes of cooking time enabled the required
cooking temperature to be reduced to 350°F (175°C). In
terms of solids settleability, optimum conditioning of
digested sludge occurred under the latter set of operating
conditions. This, therefore, became the manner in which
portrate was prepared for use in evaluating other pro-
cessing equipment.
Optimum performance of the picket thickening clarifier
occurred when the feedrate to the unit was lowest. Accord-
ingly, this corresponded to an overflow rate of
225 gpd/sq ft (9.2 cu m/day/sq m). Depending on the con-
centration of suspended solids in the fed portrate and the
allowed thickening time, sludge thickening in the range of
6-12% (60,000-120,000 mg/1) suspended solids was possible.
Decanted overflow from the thickener contained about
3700 mg/1 of suspended material.
Data, comparatively summarizing the OPTIMUM performance
of various sludge conditioning-dewatering systems investi
gated at the JWPCP, are presented in Table 38. Reference
is made to the previous text for a more detailed presenta
tion and discussion of the work with each system.
Test work conducted on a full scale 36-inch x 96-inch
(91.4-cm x 243.8-cm) Bird centrifuge revealed that, without
any form of sludge conditioning, the maximum solids re-
covery obtainable was about 55 percent. This was accom-
plished at a sludge feedrate of 200 gpm (12.6 I/sec)
while centrifuging at 900 G's with the pool depth set to
the 3.4-inch (8.6-cm) maximum. Generated cake solids
were 21% by weight. Cationic polymer conditioning enhanced
151
-------
Table 38: DATA SUMMARIZING THE OPTIMUM PERFORMANCE OF VARIOUS
INVESTIGATED SLUDGE CONDITIONING AND DEWATERING SYSTEMS
AT JWPCP
PARAMETERS
1. Heat Treatment: ,
2. Thickener overflow rate:.,
40 min @ 350°F (175°C)
225 gpd/sq ft
(9.2 cu m/day/sq m)
3. Polymer: Cationic
4. Chemicals: Ferric Chloride and/or Lime
DEWATER-
ING
SYSTEM
Horizontal
Scroll
Centrifuge
Basket
Centrifuge
(2nd Stage)
Vacuum
Coil
Filter
Rotary-Belt
Vacuum
Filter
Vacuum
Extractor
Pressure
Filter
Diaphragm
Press
CONDITIONING**
AND
PRELIMINARY
PROCESSING
1 .None
2. Polymer (10 Ibs/ton)
3. Heat
4. Heat + polymer (3. 5 Ibs/ton)
5. Heat + thickening
6. Heat + thickening + polymer (3 Ibs/ton)
1. Horizontal Scroll Centrifugation
2. Horizontal Scroll Centrifugation +
polymer f4 Ibs/ton) to 2nd stage
1. Polymer (10 Ibs/ton)
2.FeCl3 § Lime (80 5 600 Ibs/ton)
3. Heat + Thickening
1. Polymer (10 Ibs/ton)
2. Lime (600 Ibs/ton)
3. Heat + thickening
l.Heat + thickening
!.FeCl3 § Lime (120 § 500 Ibs/ton)
2. Heat
3. Heat + Thickening
4. Ash (4000 Ibs/ton) § Lime
l.Heat
SUSPENDED
SOLIDS CONTENT
Ef-
fluent
from
System
-%-
1.86
0.15(1)
0.73
0.38
0.61
0.34
0.50
0.15
0.15
0.25
1.08
0.04
0.02
0.32
0.44
0.01
0.01
0.31
0.01
0.01
De-
watered
Cake
Solids
-*-
21
20
31
31
25
25
12
25
18
26
31
18 W
35
36
35
40
30(2)
38
47
30UJ
SUS-
PENDED
SOLIDS
REMOVAL
FROM
SYSTEM
-*-
55
95
81
90
85
91
89
95
95
92(3)
70
99
99+
92
89
99+
99+
92
99+
99+
(1) Not consistently obtainable (2) Poor Cake Discharge (3) Low Loading
* All data pertain to tests conducted on JWPCP digested sludge.
** Lime dosages are expressed in terms of Ca(OH)2.
Unit Conversions: (Ibs/ton) x 0.5 = (kg/metric ton)
(% Solids) x 10,000 = (mg/1)
152-
-------
the centrifugal capture of suspended solids. Several
different polymer products were tested in this regard.
All tests were conducted under the same machine operating
conditions stated above. The sludge feedrate was held
constant at 250 gpm (15.8 I/sec). Polymer solutions
were added by bowl injection. While the performance of
each polymer was slightly different from one another,
it was generally concluded that to obtain a centrate of
1500 mg/1 or less (95 percent capture), a polymer dosage
of 10 Ibs/ton (5.0 kg/metric ton) was required. This
performance was also found to be unpredictable on a day-
to-day basis due to changing characteristics in the sludge
feed material. Resulting centrifuged cakes were about
20% solids by weight a value somewhat lower than desired
but copeable should the system be economically justified.
Heat conditioning, with or without intermediate portrate
thickening, provided some enhancement for sludge solids
dewatering in a horizontal scroll centrifuge. However,
the experienced recoveries (85 and 81 percent, respec-
tively) were deemed to be insufficient for meeting the
WQCB standards placed on the JWPCP. The addition of
3.0-3.5 Ibs/ton (1.50-1.75 kg/metric ton) of cationic
polymer to either the unthickened or thickened portrate
streams within the centrifuge bowl enabled overall suspend-
ed solids removals of 90-91 percent to be achieved. No
effect was seen on the discharge cakes . The fact that
wetter cakes were obtained when intermediate thickening
was employed is attributable to the increased solids load-
ing to the centrifuge; lower throughput rates of thickened
portrate would probably have effected drier cakes but
were not investigated. On a full scale basis, the effluent
from such a system would require some form of biological
treatment due to the high soluble BOD component (estimated
at 5000 mg/1). Although additional solids removal would
likely occur to meet the standards, the required condition-
ing (heat conditioning plus polymer addition) would
render the systems economically unattractive.
Without the usage of polymers, basket centrifugation of
Bird centrate would be inadequate for meeting the WQCB
standards. Also, the 12% cakes (resulting from a blend
of those derived from the first and second stage) would
require additional dewatering to render them handleable.
Polymer addition to Bird centrate within the bowl of the
basket centrifuge was found to enhance solids capture and
cake dryness. Cake solids of 20-22% by weight were ob-
tained from the second stage with a polymer dosage of
-153-
-------
4 Ibs/ton (2.0 kg/metric ton). Based on the suspended
solids contained in the JWPCP's digested sludge, this
corresponded to a system polymer dosage of less than
3 Ibs/ton (1.5 kg/metric ton). Overall solid captures
would be such that the resulting effluent would contain
about 1500 mg/1 of suspended material. A blend of first
and second stage generated cakes would result in one
having an average solids content of 25% by weight.
Noteworthy is the fact that the cakes derived from basket,
centrifugation were easily handled on a belt conveyor
inclined at 30° from the horizontal.
Coil filtration of the JWPCP primary digested sludge was
best when polymers were used as the conditioning aid.
A dosage of about 10 Ibs/ton (5.0 kg/metric ton) was
required to consistently produce a filtrate having an
average suspended solids concentration of 1500 mg/1.
This performance was obtainable with loading rates up
to 18 Ibs/hr/sq ft (87.8 kg/hr/sq m). Generated filter
cakes were about 18% solids by weight and remained unchang
ed with longer dry cycles at reduced belt speeds. As in
horizontal scroll centrifugation with polymer addition,
the wet cakes were attributable to the bound water
associated with the higher percentage of fines in the
captured solids. Though drier cakes would be more de-
sireable, it was generally felt that those from the
coil filter would be manageable. Drier cakes were ob-
tainable when lime and ferric chloride were used as the
conditioning aid. Suspended solids captures were maxi
mized at 92 percent recovery with a lime as Ca(OH)2
and ferric chloride dosage of 600 and 80 Ibs/ton
(300 and 40 kg/metric ton), respectively, in combina-
tion with a solids loading rate of 1.6 Ibs/hr/sq ft
(7.8 kg/hr/sq m). In comparison to the 18 Ibs/hr/sq ft
(87.8 kg/hr/sq m) attainable with polymer usage, this
low loading would render such a sludge handling system
economically undesirable in spite of the better quality
cakes (26% solids by weight) obtained. Coil filtration
of thickened heat-conditioned digested sludge produced
the driest coil-filter cakes (31% solids by weight).
Unfortunately, suspended solid removals (70 percent)
were the lowest compared to any of the other systems
listed in Table 38. A further drawback was the low
loading rate of 3 Ibs/hr/sq ft (14.6 kg/hr/sq m) neces-
sary to achieve these results. The poor performance ex-
perienced with this latter system was ascribed to the
porous nature of the coil spring media.
-154-
-------
Although solid, recoveries of 99 percent were obtained -by
rotary-belt vacuum filtration of polymer conditioned
digested sludge, generated filter cakes were thin and
wet (18% solids by weight) and discharged poorly from
the unit. Consequently, the system was eliminated for
further consideration. Similar captures were achieved
when lime was used as the conditioning agent. Optimum
results were achieved at a lime dosage of 600 Ibs/ton
(300 kg/metric ton) as Ca(OH)2 while operating at a
loading rate of 1.5 Ibs/hr/sq ft (7.3 kg/hr/sq m) to the
unit equipped with a Polypropylene 854-F cloth belt.
The inclusion of ferric chloride did not add or detract
from this situation. Yielded filtrates contained
approximately 200 mg/1 of suspended material. Filter
cakes (35% solids by weight) were excellent and discharged
freely and completely from the belt. Somewhat higher
loadings and drier cakes were attained when subjecting
thickened heat-conditioned digested sludge to rotary-
belt vacuum filtration. As with lime addition, best
performance was experienced with the Polypropylene 854-F
belt media. Generated cakes of 36% solids by weight dis-
charged freely and completely from the unit at a solids
loading up to 3.3 Ibs/hr/sq ft (16.1 kg/hr/sq m).
Filter capture was such that the resulting filtrate con-
tained about 1300 mg/1 of suspended solids. However,
a blend of this effluent with the decantate from the
thickener would result in a system effluent containing
3200 mg/1 of suspended material. Overall, this would
correspond to suspended solid removals of 92 percent
a value which includes filter capture, thermal volatiza-
tion and thermal transfer to the dissolved phase. Upon
subjection of this effluent to biological treatment
(required for soluble BOD reduction), additional removals
would likely be effected to render it acceptable for
primary effluent blending and ocean discharge.
As with rotary-belt vacuum filtration, vacuum extraction
(horizontal-belt filtration) of heat-conditioned digested
sludge was only possible with the incorporation of the
intermediate thickening step. Generated cakes were 35%
solids by weight but were thin and discharged somewhat
poorly. This result was attained at a loading rate of
2.7 Ibs/hr/sq ft (13.2 kg/hr/sq m) -- a rate drastically
below that normally encountered for such an operation.
From the standpoint of effluent quality, the best per-
forming system was that utilizing pressure filtration
in conjunction with either chemical, ash or thermal
-155-
-------
conditioning. With chemical conditioning, optimum
results obtained by analysis of all the data indicated
that a 40% cake would be produced in a 2-hour feed cycle
time utilizing lime and ferric chloride dosages of
500 Ibs/ton (250 kg/metric ton) as Ca(OH)9 and
120 Ibs/ton (60 kg/metric ton), respectively. Under these
conditions, solids loading (excluding the contribution
of the conditioning aids) over the feed period would
be about 0.7 Ibs/hr/sq ft (3.4 kg/hr/sq m); yielded
filtrates would contain less than 100 mg/1 of suspended
material. Similar filtrates were obtained when ash was
used as the conditioning aid. Best results were
achieved when 2 Ibs (0.90 kg) of ash were added per
one pound (0.45 kg) of sludge solids. In addition,
100-150 Ibs/ton (50-75 kg/metric ton) of lime as Ca(OH)2
was required to raise the pH of the sludge. A 2-hour
feed cycle under these conditions yielded cakes of 47%
solids by weight. But since two-thirds of the solids
were flyash, the actual sludge solids loading during the
cycle was only 0.35 Ibs/hr/sq ft (1.7 kg/hr/sq m)
i.e. exactly half that obtained with ferric chloride and
lime conditioning. Analysis also indicated that the
ratio of water to sludge solids in the cake would be
the same as that in the 30% cakes produced with chemical
conditioning. Pressure filtration of heat-conditioned
digested sludge (without thickening) also produced
filtrates containing less than 100 mg/1 of suspended
solids. Generated cakes (30% solids by weight) were
certainly acceptable, though a 2.5-hour feed cycle time
was required to produce them. Under this type of operation,
a sludge solids loading of about 0.52 Ibs/hr/sq ft
(2.5 kg/hr/sq m) would only be possible. The incorporation
of an intermediate portrate thickening step served to
eliminate the fines, thereby allowing solids loadings of
1.05 Ibs/hr/sq ft (5.1 kg/hr/sq m) to be experienced.
Filter cakes of 38% solids by weight were produced during
2-hour feed cycles. Produced filtrates contained less
than 100 mg/1 of suspended material but served only to
dilute the decantate to a resultant effluent having
3200 mg/1 of suspended material. Based on 3.5%
(35,000 mg/1) suspended solids in the JWPCP's digested
sludge, this corresponded to an overall suspended solids
removal of 92 percent. Considering the equipment in-
volved in the various pressure filtration alternatives just
discussed, the operation with chemical conditioning had the
appearance of being most economical. Usage of polymers
-156-
-------
was not a considered alternative since rapid blinding of
the pressure filter media resulted when polymer condi
tioning was attempted.
Attempts to dewater unthickened heat-conditioned digest-
ed sludge in a diaphragm press were somewhat discouraging.
Although yielded filtrates contained less than 100 mg/1
of suspended material, rapid blinding of the filter media
was encountered, thus resulting in feed cycles of short
duration and little cake buildup. Hence, the thin generated
cakes (30% solids by weight) discharged poorly. Because
of the experimental setup, it was not possible to pres-
sure feed thickened portrate into the unit. Dewatering
tests in conjunction with other forms of conditioning
were not conducted.
In summary, the pilot plant research on the dewatering
of the JWPCP primary digested sludge produced five schemes
capable of dewatering to the extent necessary to allow
the WQCB discharge standards to be met. These are sum-
arized in Table 39. With the exception of the thermal
thickening-vacuum filter scheme, all of these systems
produced an effluent suspended solids of 1500 mg/1 or
less; based on a limited number of BOD tests run on the
various filtrate and centrate effluents, the resulting
BOD of these four systems would be 1000 mg/1 or less.
By subjecting the effluent from the thermal-thickening-
filtration scheme to biological treatment, the tabu-
lated suspended solids and BOD would be reduced to 500 mg/1
and 1000 mg/1, respectively, thus falling within the
above discussed levels. On a full-scale basis, the
1.8 mgd (6800 cu m/day) of effluent from any system
would be diluted approximately 200-to-one when combined
with the 380 mgd (1.43 million cu m/day) of primary
effluent. Hence, the anticipated concentrations of sus-
pended solids and BOD from any dewatering system effluent
would, at most, add 7.5 mg/1 of suspended solids and
2.5 mg/1 of BOD to the combined plant discharge.
All of the five selected schemes which met the desired
end result required some form of sludge conditioning,
i.e. polymers, chemical or heat. Cakes resulting from
the five systems varied in solids content from 18% to 40%
by weight. Of the five systems, one would allow contin-
ued use of the existing horizontal scroll centrifuges.
157-
-------
Table 59: PERFORMANCE SUMMARY* OF FIVE SELECTED DEWATERING SCHEMES HAVING FULL-SCALE POTENTIAL
FOR MEETING THE IMPOSED DISCHARGE STANDARDS
DEWATERING
SYSTEM
Two-Stage
Centrifugation
(Horizontal Scroll
+ Basket)
Vacuum Coil
Filtration
Rotary-Belt
Vacuum
Filtration
Pressure
Filtration
TYPE OF
CONDITIONING
Cationic Polymer
to 2nd Stage
Basket Centrifuge
Cationic
Polymer
Lime as Ca(OH)2
Heat Treatment
and Picket
Thickening**
Lime as Ca(OH)2
Ferric Chloride
CHEMICAL
OR
POLYMER
DOSAGE
-Ibs/ton-
3
10
600
X
500
120
EFFLUENT
SUSPENDED
SOLIDS
-mg/1-
1500
1500
200
3200***
100
EFFLUENT
BOD
-mg/1-
1000
1000
500
5000***
200
CAKE
SOLIDS
-%-
25
18
35
36
40
*Tabulated data pertain to performance results obtained from pilot plant tests on JWPCP
digested sludge.
**Porteous conditioning for 40 minutes @ 350°F (175°C) with followup thickening; thickner
overflow rate @ 225 gpd/sq ft (9.2 cu m/day/sq m).
***Biological treatment of effluent will reduce suspended solids and BOD concentrations to
500 mg/1 and 1000 mg/1, respectively.
Unit Conversions; (Ibs/ton) x 0.5 = (kg/metric ton)
-------
COST ESTIMATES
Having determined the performance of all combinations
of conditioning and dewatering systems tested at the
JWPCP and concluding that five of these schemes would
enable the effluent discharge requirements to be met,
cost estimates were prepared to provide a rationale for
selecting a full scale process. These included:
(1) Capital and operating costs for the five
selected dewatering systems.
(2) Ultimate disposal costs by two methods, namely
(a) Landfilling, with transport of the sludge
either by truck (in a dewatered condition)
or by pipeline with dewatering at the
landfill.
(b) Incineration, with ash hauling to the
landfill.
The costs of dewatering and disposal were combined to
provide an estimate of the cost for a total system. In
addition, a brief study was made of the prospective costs
associated with remote disposal of digested sludge.
These latter estimates were made to aid in selecting a
dewatering process that would be compatible with some
future scheme of ultimate sludge disposal to a remote area
The data used in preparing the dewatering-disposal costs
were derived from several sources. Equipment manufactur-
ers provided estimates of their respective equipment
costs along with recommendations regarding power, labor,
maintenance and standby equipment. Hourly labor costs
were obtained from records associated with the operation
of the existing centrifuge station at the JWPCP. Site
preparation, building, conveyor and engineering costs,
etc. were estimated with the assistance of the Districts'
Design Division. Truck hauling and landfill disposal
costs were obtained with the aid of the District's
159-
-------
Refuse Department; truck hauling times were estimated
from records secured through previous experience in
hauling sludge from the JWPCP to a landfill.
Because the data for the estimates were obtained from
various sources, every effort was made to be consistent
with respect to the common factors used in each estimate.
The assumption was made that the hourly labor charge
would be the same for every system. Also, the same unit
cost was used for whatever power, polymers and chemicals
were required in each scheme. Moreover, it was assumed
that all dewatering systems, including truck loading
facilities for hauling, would be housed within a building,
Since the purpose of the cost estimates was to provide
a method of comparing various processes, the costs for
components which were common to all alternatives,
i.e. wet wells pumps, influent and effluent piping, etc.,
were not included. For similar reasons, the volumetric
quantity of digested sludge to be handled was placed at
2 mgd (7500 cu m/day) --an amount slightly in excess of
present day production. Based on 3.81 suspended solids
concentration and 95 percent solids capture, the quan-
tity of sludge to be dewatered would therefore be about
300 dry tons (272 metric tons) per day. No attempt was
made to provide estimates of future sludge quantities
and handling costs for the useful life of the dewatering
system.
DEWATERING COSTS FOR TWO-STAGE CENTRIFUGATION
The cost estimate for a two-stage centrifugation system
is shown in Table 40. It was assumed that the existing
horizontal scroll centrifuges would continue to operate
in their present manner; hence, no capital expenditures
were estimated for that part of the system. The para-
meters used in making up the capital cost estimate were
as follows:
(1) Polymer dosage 800 Ibs/day
(360 kg/day) to
the second stage
component
(2) Building area required.... 20,000 sq ft
(I860 sq m) for hous-
ing both stages.
-160-
-------
Table 40: COST ESTIMATE SUMMARY FOR TWO-STAGE CENTRIFUGATION
CONDITIONS
1. Sludge conditioning: polymer dosage of 4 Ib/ton
(2 kg/metric ton) to second stage
centrifuge
2. Centrate suspended solids:... 1500 mg/1
3. Cake solids: 25% solids by weight (blend of
cakes from each stage)
CAPITAL COST
1. Basket centrifuges - installed
2. Polymer storage and feed system - installed
3. Conveyor - 300 ft (90 m)
4. Building - 20,000 sq ft (1860 sq m), installed
5. Contractor - (10% of items 1 § 2)
6. Contingencies
7. Engineering - flat fee
Total Capital Cost
OPERATION 6 MAINTENANCE COST
1. Labor
2. Power
3. Water
4. Maintenance materials
5. Polymers
6. First stage operating cost
Total Operation §
Maintenance Cost
-161-
$1,450,000
70,000
35,000
300,000
150,000
340,000
500,000
$2,895,000
$ 44,000/yr
82,000/yr
6,000/yr
30,000/yr
290,000/yr
360.000/yr
$ 812,000/yr
-------
Results of the research work indicated that twenty-two
48-inch (122-cm) diameter imperforate basket centrifuges-
the largest size currently manufactured--would be re-
quired to treat the approximate 2 mgd (7500 cu m/day)
of centrate flow from the existing centrifuge station.
In the estimate, three standby units were provided. The
cost of the centrifuges was supplied by the Sharpies
Centrifuge Company. The cost of a polymer system
capable of providing a dosage of 4 Ibs/ton
(2.0 kg/metric ton) to the first stage centrate was esti-
mated by Districts personnel. The provision was made
for additional conveyor capacity for handling the second-
stage generated cakes. A building was to be provided
for housing both the horizontal scroll and basket centri
fuges along with their respective cake conveyance systems,
The building was assessed at $15.00/sq ft ($161.00/sq m).
Controls for the basket centrifuge system would be housed
in this building. The polymer station would be located
outside.
The operating labor and power requirements were supplied
by Sharpies' personnel and were based on prior experience
at other installations. Maintenance materials were esti
mated at 2 percent of equipment cost per year. Based on
intended competitive bidding, polymer cost was estimated
at $1.00 per pound ($2.20/kg). The operating cost of
the first stage system was taken from the JWPCP cost
records for the year 1971.
DEWATERING COSTS FOR COIL FILTRATION
A cost estimation for a coil filtration system using
polymers as the conditioning agent is shown in Table 41.
The parameters used in making the capital cost estimate
were as follows:
(1) Polymer dosage 3000 Ibs/day (1360 kg/day)
(2) Filter loading rate.. 12 Ibs/hr/sq ft
(58.6 kg/hr/sq m)
(3) Building area
required 10,000 sq ft (930 sq m)
The filter loading rate was selected by Komline-Sanderson
based on their analysis of the research data and falls
well within the range of experimental data obtained. At
-162-
-------
Table 41: COST ESTIMATE SUMMARY FOR VACUUM COIL FILTRATION WITH
POLYMER CONDITIONING
CONDITIONS
1. Sludge conditioning: polymer dosage of 10 Ib/ton
(5.0 kg/metric ton)
2. Filtrate suspended solids:... 1500 mg/1
3. Cake solids: 18% solids by weight
CAPITAL COST
1. Filters, pumps, etc. - installed
2. Polymer addition system - installed
3. Building - 10,000 sq ft (930 sq m),
installed
4. Contractor - (10% of items 1 § 2)
5. Contingencies
6. Engineering - flat fee
Total Capital Cost
OPERATION 5 MAINTENANCE COST
1. Labor
2. Power
3. Water
4. Maintenance materials
5. Polymers
Total Operation §
Maintenance Cost
$ 620,000
90,000
150,000
70,000
150,000
100,000
$1,180,000
$ 44,000/yr
26,000/yr
50,000/yr
10,000/yr
1,100,000/yr
$l,230,000/yr
163-
-------
design loading, four 11%-ft (3.5-m) diameter by 16-ft
(4.9-m) wide filters would be required. Cost estimates
for the filters was provided by Komline-Sanderson.
Labor and power requirements were provided by Komline-
Sanderson. Water estimates were based on that required
for polymer makeup, polymer dilution, and spray washing
of the filter coils. Maintenance material was estimated
at 2 percent of equipment costs. Polymer costs were
estimated at $1.00 per pound ($2.20/kg).
DEWATERING COSTS FOR ROTARY-BELT VACUUM FILTRATION
An outlined cost estimate for a rotary-belt vacuum fil
tration system using lime conditioning is presented in
Table 42. Capital costs were estimated on the basis of
the following parameters:
(1) Lime dosage 90 tons/day
(82 metric tons/day)
as Ca(OH)2
(2) Filter loading rate 1.5 Ibs/hr/sq ft
(7.3 kg/hr/sq m)
(3) Building area required.... 20,000 sq ft
(1860 sq m)
Based on the 2-mgd (7500-cu m/day) design flow, thirty
one filter units (including two standby units), each
12-ft (3.7-m) in diameter with a 20-ft (6.1-m) wide
face, would be required. The costs for these filters
was furnished by Envirotech Corporation; on the basis
of experience at other installations, associated costs
for labor, power, maintenance materials and water re-
quirements were also provided. A lime cost of $23.25/ton
($25.60/metric ton) was used. Costs for a lime facility
were obtained from Districts' records pertaining to the
recent construction of an existing facility of identical
capacity for the JWPCP chlorination station.
Presented in Table 43 is a cost estimate for a rotary-
belt vacuum filtration system incorporating heat condi
tioning and intermediate thickening. The following
parameters were used in making the capital cost estimates
-164-
-------
Table 42: COST ESTIMATE SUMMARY FOR ROTARY-BELT VACUUM FILTRATION
WITH LIME CONDITIONING
CONDITIONS
1. Sludge conditioning: lime dosage of 600 J.b/ton
(300 kg/metric ton) as Ca(OH)2
2. Filtrate suspended solids:... 200 mg/1
3. Cake solids: 35% solids by weight
CAPITAL COST
1. Filters - installed $3,200,000
2. Chemical handling system - installed 1,000,000
3. Building - 20,000 sq ft (1860 sq m), installed 300,000
4. Conveyors - 400 ft (120 m) 50,000
5. Contractor - (10% items 1 § 2) 325,000
6. Contingencies 500,000
7. Engineering - flat fee 500,000
Total Capital Cost $5,875,000
OPERATION § MAINTENANCE COST
1. Labor
2. Power
3. Maintenance materials
4. Chemicals
5. Water
Total Operation §
Maintenance Cost
$ 260,000/yr
290,000/yr
20,000/yr
765,000/yr
30,000/yr
$l,365,000/yr
165-
-------
Table 43: COST ESTIMATE SUMMARY FOR ROTARY-BELT VACUUM FILTRATION WITH
' HEAT CONDITIONING AND INTERMEDIATE THICKENING
CONDITIONS
1. Sludge conditioning: Heat conditioning followed by
gravity thickening
2. Filtrate suspended solids:... 3200 mg/1
3. Cake solids:..... 36% solids by weight
CAPITAL COST
1. Heat treatment - installed
2. Thickeners - installed
3. Filters - installed
4. Building - 15,000 sq ft (1400 sq m),
installed
5. Conveyor (200 ft.)
6. Contractor (101 of items 2, 3, § 5)
7. Contingencies
8, Engineering - flat fee
9. Biological treatment plant for effluent
Total Capital Cost
OPERATION £ MAINTENANCE COST
1. Labor
2. Power
3. Fuel
4. Water
5. Maintenance material
6. Biological treatment plant
Total Operation §
Maintenance Cost
-166-
$6,100,000
170,000
950,000
225,000
25,000
120,000
250,000
500,000
2,500,000
$10,840,000
$ 155,000/yr
120,000/yr
350,000/yr
25,000/yr
40,000/yr
250,000/yr
$ 940,000/yr
-------
(1) Heat conditioning 40 min @ 350°F
(175°C)
(2) Thickener overflow rate.... 225 gpd/sq ft
(9.2 cu m/day/sq m)
(3) Suspended solids reduction
by heat conditioning 20 percent
(4) Filter loading rate 4 Ibs/hr/sq ft
(19.5 kg/hr/sq m)
(5) Building area required..... 15,000 sq ft
(1400 sq m)
Based on the previous test work, cost estimates of the
heat conditioning system, picket thickeners and vacuum
filters along with the associated labor, power, main-
tenance materials and water requirements were furnished
by Envirotech Corporation. Nine 150-gpm (9.5-1/sec)
heat conditioning units, three 60-ft (18.3-m) diameter
gravity picket thickeners, and seven 12-ft (3.7-m) diameter
by 20-ft (6.1-m) wide vacuum filters (including one
standby filter) would be needed for a full scale installa-
tion. A building would be furnished to house the vacuum
filters and the controls for the thermal conditioning
units, thickeners and filter units. The thickeners would
be covered and located outside with the heat conditioning
units. Vented reactor gases and trapped thickener gases
would be discharged to an afterburner.
An estimate for biological treatment of the combined
filtrate and thickener decantate was prepared by Districts'
personnel. The estimate was based on the assumption
that this high strength effluent waste would be amenable
to biological treatment and that the sludge produced
would settle in conventional final clarifiers. The
biological facility would incorporate large turbine aera-
tors and a lengthy detention time (more than 24 hours).
Such a detention time would minimize sludge production
such that the quantities requiring disposal would be
insignificant. Power was determined to be the major
operating cost of the biological treatment facility and
was estimated to be in excess of $200,000 per year.
167-
-------
DEWATERING COSTS FOR PRESSURE FILTRATION
Capital and 0 § M costs for a pressure filtration sys-
tem using lime and ferric chloride as conditioning agents
are presented in Table 44. The parameters used in mak-
ing the capital cost estimates were as follows:
(1) Chemical Dosage
(a) Lime 75 tons/day
(68 metric tons/day)
as Ca(OH)2
(b) Ferric Chloride 18 tons/day
(16.3 metric tons/day)
(2) Precoat
(diatomaceous earth) 4.5 lbs/100 sq ft
(0.2 kg/sq m)
(3) Building area required 15,000 sq ft
(1400 sq m)
Based on test data, a total of four filter presses, each
containing 140 chambers of 80-inch (200-cm) square plates,
would be required. Filter press costs and the associated
labor and power requirements were furnished by Beloit-
Passavant. A cost estimate for the chemical handling
system was made by Districts personnel. Water would be
required for lime slaking. Maintenance and material
costs were estimated at one percent of equipment costs.
The entire system would be housed in a building costing
$15.00/sq ft ($161.00/sq m). Chemical and precoat costs
were assessed in accordance with the following:
(1) Lime $23.25/ton
($25.60/metric ton)
(2) Ferric Chloride $120.00/ton
($132.40/metric ton)
(3) Diatomaceous earth $68/ton
($68.00/metric ton)
DEWATERING COST SUMMARY
A summary of the cost estimates for the five dewatering
systems considered is shown in Table 45. To arrive at
a yearly cost and a cost per ton for each dewatering
scheme, an amortization period had to be selected. It was
-168-
-------
Table 44: COST ESTIMATE SUMMARY FOR PRESSURE FILTRATION WITH LIME
AND FERRIC CHLORIDE CONDITIONING
CONDITIONS
1. Sludge conditioning:
2. Filtrate suspended
solids:
3. Cake solids:
Lime-500 Ibs/ton (250 kg/metric ton)
as Ca(OH)2
FeCIs -120 Ibs/ton (60 kg/metric ton)
Precoat
(diatomaceous earth) - 4.5 lb/100 sq ft
(0.2 kg/sq m)
100 mg/1
40% solids by weight
CAPITAL COST
1. Filters, pumps, conveyors, controls
2. Chemical handling, storage, feeding system
- installed
3. Building - 15,000 sq ft (1400 sq m), installed
4. Installation (15% of item 1)
5. Contingencies
6. Engineering - flat fee
Total Capital Cost
OPERATION § MAINTENANCE COST
1. Labor
2. Power
3. Water
4. Maintenance material (1% pf equipment)
5. Chemicals
Total Operation §
Maintenance Cost
$5,000,000
1,300,000
225,000
750,000
500,000
300,000
$8,075,000
$ 175,000/yr
45,000/yr
30,000/yr
50,000/yr
1,700,000/yr
$2,000,000/yr
-169-
-------
Table 45: SUMMARY OF COST ESTIMATE FOR FIVE POTENTIAL FULL-SCALE
SLUDGE DEWATERING SCHEMES
PARAMETERS
1. Process Material: JWPCP primary digested sludge
2. Design Flow: 2 mgd (7500 cu m/day)
3. Effluent BOD: 1000 mg/1 or less
4. Effluent Suspended Solids:... 1500 mg/1 or less
5. Cake Solids: 18-40% solids by weight
CONDITIONING
AND
DEWATERING
SYSTEM
Two Stage Centrifugation
(polymer conditioning
in 2nd stage)
Vacuum Coil Filtration
(polymer conditioning)
Rotary- Belt Vacuum
Filtration
(lime conditioning)
Rotary-Belt Vacuum
Filtration
(heat conditioning §
intermediate thickening)
Pressure Filtration
(lime § ferric chloride
conditioning)
CAPITAL
COST
-103$-
2,900
1,200
5,900
10,840
8,100
0 § M
COST
-103$/yr
810
1,230
1,365
940
2,000
TOTAL COST*
Yearly
Basis
-103$/yr-
1,210
1,390
2,165
2,415
3,100
Tonnage
Basis**
-$/ton-
11.10
12.70
19.80
22.10
28.30
PRESENT
WORTH***
-103$-
8,900
10,200
15,900
17,800
22,800
*Includes capital cost amortized at 6% for 10 years.
**Based on 300 dry tons (272 metric tons) per day,
***Based on 61 for 10 years.
Unit Conversions: ($/ton) x 1.103 = ($/metric ton)
170-
-------
decided that a 10-year period would be used for all
estimates despite the fact that some of the dewatering
equipment and the auxiliary capital items -- buildings,
conveyors, etc. -- would probably have longer useful
lives than that. The rationale used in making this
decision was based on the uncertainty of future waste-
water treatment methods at the JWPCP coupled with the
possibility of future sludge disposal methods which
would not necessitate dewatering. Hence, the sludge
disposal system selected at this time would be consid-
ered an interim facility with a probable useful life
of not more than 10 years. An interest rate of 6% was
used in conjunction with the 10 year amortization period.
As can be seen from Table 45, there is a large variation
in costs for the five systems considered. Capital cost
varies from $1,200,000 for a vacuum coil filtration sys-
tem to almost $11,000,000 for a heat conditioning-vacuum
filtration scheme that would require a biological facil
ity for further effluent treatment. Operating and main-
tenance costs also vary by a factor of almost three,
with the two-stage centrifuge system exhibiting the low-
est 0§M cost of $810,000 per year.
The yearly costs of the dewatering schemes indicate
that costs range from $11.10/ton ($12.20/metric ton)
for a two-stage centrifuge system to $28.30/ton
(31.20/metric ton) for pressure filters. The other
system which utilizes polymer conditioning, i.e. coil
vacuum filters, shows a relatively low cost of $12.70/ton
($14.00/metric ton). The two systems utilizing lime
conditioning, i.e. belt vacuum filters and pressure filters,
are more costly due to the high capital cost of the lime
handling facility; also, the relatively low loading rate
on the filters necessitates high capital expenses for
dewatering equipment. The heat conditioning-vacuum
filter scheme is relatively inexpensive as a dewatering
system; however, the biological facility required for
effluent treatment increases both the capital and oper-
ating cost of that scheme rather substantially.
ULTIMATE DISPOSAL COST -- TRUCK HAULING TO A LANDFILL
Presented herein are cost estimates for the full scale
handling and disposal (truck hauling to a landfill) of
dewatered sludge solids (cakes) generated by each of
the previous five sludge dewatering schemes economically
-171-
-------
assessed. Some preliminary field studies were conducted
at the Districts' Palos Verdes Landfill. Several truck
loads of dewatered sludge were hauled to this facility
and trial blended with various amounts of refuse. As a
result it was determined that a dewatered sludge of 20%
solids by weight or more could be effectively handled
in the routine operation of a landfill.
Regarding the cost estimates, two District operated land-
fills -- the Mission Canyon Landfill and the Puente Hills
Landfill -- were considered as possible disposal points.
Both landfills are located about 30 miles (48.3 km)
from the JWPCP by freeway and surface streets and have
sufficient disposal capacity for the next 50 years. Despite
the 6-mile (9.7-km) proximity of the Palos Verdes Landfill,
the facility was not considered for ultimate disposal
since its useful capacity will have been exhausted 3
years hence.
In making the cost estimate, some basic assumptions
were made regarding the type of operation that would be
followed. These, along with basic criteria used in de-
riving the estimates, are listed in the following.
(1) Dewatered sludge would be hauled on an
8-hr/day basis, seven days a week.
(2) Hauling would be done by truck and trailer
rigs, each handling 23 tons/load
(20.9 metric tons/load) and making
3 trips/day to the landfill site.
(3) Truck and trailer rigs would cost $42,000
each and have a 10,000-hr useful operating
life which, on an 8-hr/day use basis, is
equivalent to 3.4 years. Operation and
maintenance (gas, tires, repairs, etc.)
costs were assessed at $7.50/hr/rig and
$8.00/hr/rig, respectively.
(4) Loading of the dewatered sludge onto hauling
vehicles would be accomplished with 4-cu yd
(3-cu m) bucket type skip loaders, each
handling 120 tons/hr (109 metric tons/hr).
Each loader would cost $67,000 and have a
useful operating life of 10,000 hours
(3.4 years on an 8-hr/day operating basis). Oper-
ation and maintenance costs were assessed at
$10.50/hr/unit and $8.00/hr/unit, respectively.
-172-
-------
(5) During periods of nonhauling (16 hr/day),
dewatered sludge would be stored at the JWPCP.
A total of 3-days storage capacity would be
provided for in case of rain or operational
difficulties at the landfill.
(6) Sludge storage and loading facilities at the
JWPCP would be completely enclosed within a
building. The building would house the sludge
product in a triangular pile 25-ft (7.6-m)
high by 75-ft (22.8-m) wide and of sufficient
length for the required stored volume. The
building would be 35-ft (10.7-m) high by
120-ft (36.6-m) wide and of necessary length
to accomodate 3-day's storage. The building
would be equipped with the necessary ventil
ation and air pollution equipment to prevent
odors. Capital cost of the building was assess-
ed at $15.00/sq ft ($161.00/sq m). Operating
costs (labor to uncover and cover hauling
rigs, tabulate payloads, wash trucks, etc.
on an 8-hr/day, 7-day/wk basis) were figured
on the basis of required manpower at a cost of
$14,000/yr/man. Maintenance costs were
assessed at 60£/yr/sq ft ($6.50/yr/sq m) of
building area.
(7) A second building would be necessary for the
repair and maintenance of skip loaders and
hauling rigs. The structure was sized on the
basis of providing 100 sq ft (9.3 sq m) of
floor area per vehicle for the total number
of vehicles required in the disposal system.
The capital cost of the building was assumed
at $20/sq ft ($215/sq m).
(8) During periods of nonhauling, a paved parking
area was assumed necessary for the truck and
trailer rigs. Each rig would measure 8-ft
(2.4-m) wide by 60-ft (18.3-m) long. To
facilitate vehicle movement and parking, the
area provided would be 2% times the total area
necessary to occupy all rigs. Pavement costs
were assessed at $1.00/sq ft ($10.80/sq m).
(9) Maintenance and operation costs for both the
vehicle maintenance building and the parking lot
(power, lighting, washing, upkeep, etc.) were
based on records of the Districts' past ex-
periences .
-173-
-------
Table 46 shows the individual components of capital and
operating cost for hauling dewatered sludge to a land-
fill for each of the five dewatering systems investigated.
The estimates were based on dewatering 300 dry tons/day
(272 metric tons/day) of solids. In dewatering schemes
where lime would be used as the conditioning agent, the
quantity of solids appearing as lime in the dewatered
cake was added to the 300 tons (272 metric tons) of sludge
solids per day. In the case of heat conditioning, the
quantity of solids to be hauled would be less than
300 tons/day (272 metric tons/day), reflecting the solubil
ization of solids during heat conditioning; for computa-
tional purposes, the generated cakes were assumed at 35%
solids (instead of the 36% solids previously cited) .
In addition, the assumption was made that the 181 cakes
generated by the coil-polymer filtration scheme could be
rapidly air dried to 20% solids -- a value deemed neces-
sary for hauling and landfill handling.
A summary of the dewatered sludge hauling costs is pre-
sented in Table 47. The capital cost of the truck rigs
and skip loaders was amortized over a 3.4-year period
(the approximate life of the vehicles based on 8-hr/day
usage). To be .consistent with the dewatering system
amortization period, the buildings and parking area
were amortized over a 10-year period. The estimated
costs are seen to range from $10.90/ton
($12.00/metric ton) for a thermal-thickening-vacuum
filtration scheme to $23.00/ton ($25.40/metric ton)
for a coil vacuum filtration scheme. The low cost with
the former was attributable to the reduced quantity and
dry condition of the cakes necessitating hauling.
ULTIMATE DISPOSAL COST--PIPELINE TRANSPORT § LANDFILL
DEWATERING
An alternative to truck hauling of dewatered sludge to
a landfill disposal point is pipeline transport of the
digested sludge to the landfill in its liquid form and
dewatering thereat. This scheme affords the advantage
of requiring fewer hauling rigs (some trucks would be
required for transporting dewatered sludge within the
landfill premises) which must be balanced against a high
pipeline capital cost and the uncertainty of long dis-
tance sludge pumping.
174-
-------
Table 46: ITEMIZED COSTS FOR LANDFILL HAULING AND DISPOSAL OF DEWATERED SLUDGE FROM
VARIOUS DEWATERING SYSTEMS
PARAMETERS
L!Material for disposal:... Dewatered primary digested sludge
2. Hauling mode: Truck and trailer rig
3. Hauling Period:. 8 hrs/day, 7 days/wk
4. Landfill Distance: 30 miles' (48 km) from JWPCP
^ ^^ DEWATERING
- — ^gYSTEM
ITEM ~--~^_
Cake Solids ($)
Quantity Hauled (tons /day) *
Capital Cost (103$)
1. Truck Rigs
2. Skip Loaders
3. Storage Bldg.
4. Maintenance Bldg.
5. Parking Area
TOTAL CAPITAL COST
0 $ M Cost (I03$/yr)
1. Truck Rigs
2. Skip Loaders
3. Storage Bldg.
4. Maintenance Bldg.**
5. Landfill fee
TOTAL 0 § M COST
TWO
STAGE
CENTRIFUGATION
(polymer)
25
1,200
760
135
290
40
25
1,250
765
110
80
15
660
1,630
VACUUM
COIL
FILTRATION
(polymer)
20
1,500
960
200
360
55
25
1,600
990
160
100
20
820
2,090
ROTARY- BELT VACUUM
FILTRATION
(Lime)
35
1,150
755
135
270
40
25
1,225
765
110
80
15
630
1,600
Heat §
Thickening)
35
660
460
135
150
30
15
790
450
110
50
10
360
980
PRESSURE
FILTRATION
(Lime §
FeC13)
40
1,000
670
135
235
40
30
1,100
680
110
70
10
550
1,420
*Based on 300 dry tons/day of solids.
**Includes parking area.
Unit Conversions: (tons/day) x 0.907 = (metric tons/day)
-------
Table 47: SUNMARY OF COSTS FOR LANDFILL HAULING AND DISPOSAL OF DEWATEREB SLUDGE FROM VARIOUS
DEWATERING SYSTEMS
PARAMETERS
Y. Material for disposal:... Dewatered primary digested sludge
2. Hauling mode: Truck § trailer rig
3. Hauling Period: 8 hrs/day, 7 days/wk
4. Landfill Distance:... 30 miles (48 km) from JWPCP
DEWATERING
SYSTEM
Two Stage Centrifugation
(polymers to 2nd Stage)
Vacuum Coil Filtration
(polymers)
Rotary-
Belt
Vacuum
Filtration
(lime)
(heat §
thickening)
Pressure Filtration
(lime $ FeCls)
QUANTITY
HAULED
-tons/day-
1,200
1,500
1,150
600
1,000
CAPITAL
COST
-1Q3$-
1,250
1,600
1,225
790
1,100
0 § M
COST
-103$/yr-
1,630
2,090
1,600
980
1,420
TOTAL COST*
Yearly
Basis
-103$/yr-
1,970
2,520
1,930
1,190
1,720
Tonnage
Basis**
-$/ton
18.00
23.00
17.60
10.90
15.70
PRESENT
WORTH
-103$-
13,900
17,900
13,700
8,400
12,200
*Includes capital costs amortized on the following basis:
(a) Truck § trailer rigs and skip loaders @ 6% for 3.4 years.
(b) Buildings and parking area @ 6% for 10 years.
**Based on 300 dry tons/day of solids.
Unit Conversions: (tons/day) x 0.907 = (metric tons/day)
f$/ton) x 1.103 = ($/metric ton)
-------
In making the cost estimate for a pipeline to convey
digested sludge to a landfill, the following assumptions
were made:
(1) In accordance with a selected route along the
Los Angeles River and Rio Hondo, the total
pipeline distance would be 27.6 miles
(44.4 km). On the basis of design flow and
keeping the flowthrough velocity between
4-7 ft/sec (1.2-2.1 m/sec), a 14-inch
(35.6-cm) diameter welded steel pipe would
be used. The cost of the pipe, fittings,
welding, excavation and backfilling, pipe
placement and street repaving was estimated
at $22/ft ($72/m).
(2) Sludge pumping to the landfill would be ac-
complished in a single hydraulic lift. The
pump station would be located at the JWPCP
and would consist of three positive displace-
ment pumps (one would act as a standby unit)
with 1100-hp (820-kw) ratings. The cost of
each pump (including installation) would be
about $55,000.
(3) A pump station would be located at the terminal
landfill site for distribution of the incoming
sludge slurry to the dewatering system. The
cost of the station (including wet well, con-
trols, instrumentation, etc.) was estimated
from District records.
(4) Maintenance of the pipeline would include
occasional pigging of the entire line -- a job
estimated to require one full day to accomplish.
A well equipped repair crew would be available
to effect prompt repair of pipeline leaks.
The costs associated with this was obtained
from an analysis of data from other pipeline and
high pressure slurry systems.
(5) The operation and maintenance costs for the
pump stations at both the JWPCP and the terminal
landfill site were determined from the Districts'
records of its own operating experiences.
(6) The effluent from the landfill dewatering
station would be disposed of in the Districts'
sewerage system.
-177
-------
(7) The dewatered sludge would be stored at the
landfill for a 15-hour period with landfilling
to take place only during the regular landfill
operating periods. The sludge storage and
handling facility would be identical to that
discussed in the previous section for the
truck hauling scheme.
(8) The costs for disposal of the dewatered sludge
cake were derived using the same assumptions
for truck costs in the previous sludge hauling
section.
Presented in Table 48 is an itemized cost breakdown for
a pipeline-landfill disposal system for each of the five
dewatering schemes previously selected. As noted, the
cost of the pipeline portion of the system would be
identical for each dewatering scheme since, in all cases,
the same volumetric quantity of sludge slurry would
require transportation to the landfill site. Included in
the operating cost is a sewer connection surcharge for
discharge of the effluent from the dewatering system
alternatives. This fee was calculated from a formula
contained in the Districts' Industrial Waste Ordinance.
A summary of the pipeline transportation and landfill
disposal costs for the five dewatering alternatives is
presented in Table 49. In amortizing the capital cost
of the pipeline, a pipeline life of 20 years was assumed.
Though inconsistent with the 10-year amortization period
used for the dewatering system alternatives, justification
for the 20-year period was based on the assumption that
the pipeline would play a vital role in an ultimate dis-
posal scheme for the future. On a dry tonnage basis, the
estimated pipeline transportation and landfill disposal
costs ranged from $15.25/ton ($16.80/metric ton) for the
thermal-thickening-filtration scheme to $22.10/ton
($24.40/metric ton) for a coil vacuum filtration scheme.
As with the truck hauling disposal costs (discussed in
the previous section), the low cost associated with the
thermal-thickening-filtration scheme was attributed to
the lesser quantity of solids requiring disposal
(a consequence of thermal destruction and solubilization).
However, because the pipeline itself would be a substan-
tial portion of the total cost and because its cost
would be independent of the method of sludge dewatering,
the difference between the lowest and highest pipeline-
-178-
-------
table 48: ITEMIZED PIPELINE-DISPOSAL COSTS FOR VARIOUS DEWATERING SYSTEMS
PARAMETERS
1. Material pipelined: JWPCP primary digested sludge
2. Pipeline Distance: 27.6 miles (44.4 Ion)
3. Dewatering § Disposal:... at landfill
UD
^-. DEWATERING
^-\SYSTEM
ITEM ^"~^\
Capital Cost (103$)
1. Pipeline
2. Pump station @ JWPCP
3. Pump station @ landfill
4. Effluent sewer
connection
5. Truck § skip loaders
6. Storage Bldg.
7. Maintenance bldg*
TOTAL CAPITAL COST
0 § M Cost (103$/yr)
1. Pipeline
2. Pump station @ JWPCP
3. Pump station @ landfill
4. Sewer connection
surcharge
5. Trucks 5 skip loaders
6. Storage bldg.
7. Maintenance bldg*
8. Landfill fee
TOTAL 0 § M Cost
TWO
STAGE
CENTRI-
FUGATION
^polymer)
3,220
330
110
50
300
540
60
4,610
10
180
30
100
260
100
10
660
1,350
VACUUM
COIL
FILTRATION
(polymer)
3,220
330
110
50
410
675
80
4,875
10
180
30
110
360
125
10
820
1,645
ROTARY- BELT VACUUM
FILTRATION
(Lime)
3,220
330
110
50
300
520
60
4,590
10
180
30
80
260
100
10
630
1,300
Heat §
Thickening)
3,220
330
110
50
260
300
40
4,310
10
180
30
250
215
60
10
360
1,115
PRESSURE
FILTRATION
(Lime $ FeCls)
3,220
330
110
50
300
450
55
4,515
10
180
30
60
260
80
10
550
1,180
""•Includes parking area.
NOTE: Refer to Table 46 for tonnages requiring disposal
-------
Table 49: SUMMARY OF PIPELINE-DISPOSAL COSTS FOR VARIOUS DEWATERING SYSTEMS
PARAMETERS
Y. Material Pipelined: JWPCP primary digested sludge
2. Pipeline Distance: 27.6 miles (44.4km)
3. Dewatering § Disposal:... at landfill
oo
o
DEWATERING
SYSTEM
Two Stage Centrifugation
(polymers to 2nd Stage)
Vacuum Coil Filtration
(polymers)
Rotary-
Belt 1 (Lime)
Vacuum l(Heat §
Filtration Thickening)
Pressure Filtration
(lime $ FeCls)
CAPITAL
COST
-1()3$-
4,610
4,875
4,590
4,310
4,515
0 § M
COST
-l()3$/yr-
1,350
1,645
1,300
1,115
1,180
TOTAL COST"
Yearly
Basis
-103$/yr-
2,020
2,420
1,940
1,670
1,810
Tonnage
Basis**
-$/ton-
18.50
22.10
17.75
15.25
16.50
PRESENT
WORTH***
-103$-
14,600
17,000
14,200
12,500
13,200
*Includes capital cost amortized on the following basis
(a) Pipeline @ 6% for 20 years
(b) Trucks and skip loaders @ 6% for 3.4 years
(c) Buildings and parking area @ 6% for 10 years.
**Based on 300 dry tons/day (272 metric tons/day) of solids.
***Based on 6% for 10 years.
Unit Conversions: ($/ton) x 1.103 = ($/metric ton)
-------
transportation, landfill-disposal cost is seen to be
less than that difference encountered for truck trans-
portation of dewatered sludge from the JWPCP.
ULTIMATE DISPOSAL COST -- INCINERATION WITH LANDFILL
DISPOSAL OF ASH RESIDUE
A third disposal alternative was that of dewatered
sludge incineration at the JWPCP with truck hauling of
the ash residue to a landfill. A pilot incinerator had
been under evaluation at the JWPCP sludge dewatering
research site for several months. All of the testing
done on the unit was conducted on a short-term batch
basis to assess the burning capabilities of the various
cakes generated from the piloted dewatering systems
investigated. Although the results of this work are
not contained herein, the derived data enabled optimum
loading rates to be determined as a function of cake
moisture and volatile solids content. Because the in-
cinerator unit was not operated in a long-term, .steady-
state manner, air pollution measurements were not attempt
ed.
Cost estimates for incinerators to burn the various de-
watered sludge cakes from the five alternative dewatering
schemes were furnished by Envirotech Corporation. The
estimates included the necessary air pollution control
equipment to meet or exceed the existing APCD standards.
The incinerators were sized from heat value data and
loading rates acquired from the Districts' research work.
The above estimates are presented in Table 50 along with
other itemized costs related to truck hauling of the
incinerated ash residue to a landfill. The basis for
deriving the ash handling and disposal costs were identi-
cal to those used for direct handling and hauling of
dewatered sludge cakes except that incinerator ash would
be stored on the JWPCP's acreage for 15 hours per day,
with the full day's production being hauled to the
landfill during the 8-hour daytime period. Operation
and maintenance costs for the incineration system were
provided by Envirotech Corporation.
A summary of the incineration and ash hauling estimates
for each of the five potential dewatering alternatives
is presented in Table 51. The thermal-thickening-
filtration system provided the lowest cost of $8.30/ton
181
-------
Table 50: ITEMIZED COSTS FOR DEWATERED SLUDGE INCINERATION WITH ASH HAULING TO A LANDFILL
PARAMETERS
T.Material for disposal:... Dewatered primary digested sludge
2. Ash hauling mode: Truck and trailer rig
3, Hauling period: = ., 8 hrs/day, 7 days/wk
4. Landfill Distance: 30 miles (48 km) from JWPCP
^--^_ DEWATERING
^^--^SYSTEM
ITEM ^^"^-__
Incinerators required
Ash to be hauled* (tons/day)
Capital Cost (103$)
1 . Incinerators
2. Site preparation
3. Trucks § skip loaders
4. Maintenance bldg.**
TOTAL CAPITAL COST
0 § M Cost (103$/yr)
1. Fuel
2. Power
3. Labor
4. Maintenance materials
5. Ash handling system***
TOTAL 0 § M COST
TWO
STATE
CENTPJFUGATION
(polymer)
,_2 .,
130
2,700
100
260
__2S_
3,085
750
30
20
10
305
1,115
nffiCUlM-"
COIL
FILTRATION
(polymer)
3
155
3,500
100
300
25
3,925
1,620
35
20
10
385
2,070
ROTARY-BELT VACUUM
FILTRATION
(Lime)
h"— 2 .
210
2,600
100
300
25
3,025
870
30
20
10
425
1,355
(Heat §
Thickening)
__ _r__—
110
1,750
100
260
25
2,135
225
15
20
10
285
555
PRESSURE' ' " '
FILTRATION
(Lime
§ FeClj)
. . .-T- .... . . .
210
2,500
100
300
25
2,925
665
25
20
10
425
1,145
OO
K)
I
*Based on 300 dry tons/day less 99.5 percent destruction of volatile component.
**Includes parking area.
***Includes truck § trailer rigs,skip loaders, maintenance building and parking area.
Unit Conversions; (tons/day) x 0.907 = (metric tons/day)
-------
Table 51: SUMMARY OF COSTS FOR DEWATERED SLUDGE INCINERATION WITH ASH HAULING TO A LANDFILL
PARAMETERS
Y.Material for disposal:... Dewatered primary digested sludge
2. Ash hauling mode: Truck § trailer rig
3. Hauling period: 8 hrs/day, 7 days/wk
4. Landfill Distance: 30 miles (48 km) from JWPCP
DEWATERING
SYSTEM
Two Stage Centrifugation
(polymers to 2nd Stage)
Vacuum Coil Filtration
(polymers)
Rotary-
Belt (Lime)
Vacuum (Heat §
Filtration Thickening)
Pressure Filtration
(lime § FeCljO
QUANTITY
OF ASH
HAULED
-tons/day-
130
155
210
110
210
CAPITAL
COST
-10'5$-
3,085
3,925
3,025
2,135
2,925
0 § M
COST
-103$/yr-
1,115
2,070
1,355
555
1,150
TOTAL COST*
Yearly
Basis
-103$/yr-
1,600
2,690
1,850
910
1,620
Tonnage
Basis**
-$/ton-
14.60
24.50
16.90
8.30
14.80
PRESENT
WORTH***
-103$-
11,300
19,200
13,000
6,300
11,400
OO
*Includes capital costs amortized on the following basis:
(a) Incinerators, building and parking area @ 6% for 10 years
(b) Truck § trailer rigs and skip loaders @ 6% for 3.4 years.
**Based on 300 dry tons/day of solid handled.
***Based on 10 years @ 6%.
Unit Conversions: (tons/day) x 0.907 = (metric tons/day)
($/ton) x 1.103 = ($/metric ton)
-------
($9.20/metric ton). This was attributed to the high
heat value and low moisture content of the dewatered
sludge and to the low tonnage of solids requiring pro-
cessing. The incinerator estimates are based on an oper
ation which would result in exit gas temperatures of
1600°F (870°C). Though this value greatly exceeds that
needed for proper incineration, a requirement for such
was anticipated in regards to a forthcoming EPA Task
Force report. If the future indicated that this would
not be required, then a substantial savings in fuel
utilization would result.
-184-
-------
COST SUMMARY OF SLUDGE PROCESSING SYSTEMS
Presented in Table 52 are summarized cost estimates for
digested sludge dewatering at the JWPCP with subsequent
hauling of dewatered sludge to a landfill for disposal.
These costs were derived by combining the disposal costs
in Table 47 with those in Table 45 for each of the five
potential full-scale dewatering schemes under considera-
tion. The combined costs indicated that a two-stage
centrifugation system would be the most economical dewater-
ing system when hauling was the disposal method. The
total sludge handling cost was estimated at $29.10/ton
($32.10/metric ton), with about 40 percent attributable
to dewatering and 60 percent attributable to disposal
of the dewatered sludge. It is to be recalled that this
estimate excluded the cost incurred for the existing
horizontal scroll centrifuge station. Replacement costs
for this facility would approximate $1,000,000; this
would increase the above estimate by an additional
$2.00/ton ($2.20/metric ton).
Contained in Table 53 are summarized cost estimates for
pipeline transportation of the JWPCP primary digested
sludge to a landfill with subsequent dewatering and
disposal thereat. These costs were obtained by combining
the estimates in Table 49 with those in Table 45 (with some
modifications) for each of the dewatering schemes con-
sidered. Dewatering cost modifications were required
in accordance with the following:
(1) With dewatering at the landfill, the existing
horizontal scroll centrifugation system at the
JWPCP would not be utilizable unless it was
moved to the landfill site and reinstalled.
Hence, the estimates for the two-stage centrifu-
gation scheme was increased to include the con-
struction and installation costs for such a
relocation.
-185-
-------
Table 52: TOTAL SLUDGE HANDLING COST SUMMARY--Dewatering at JWPCP with Truck Hauling for
Landfill Disposal
PARAMETERS
Y.Dewatered Material:... JWPCP primary digested sludge
2. Hauling Period: 8 hrs/day, 7 days/wk
3. Landfill Distance: 30 miles (48 km) from JWPCP
DEWATERING
SYSTEM
Two Stage Centrifugationf
(polymers to 2nd Stage)
Vacuum Coil Filtration
(polymers)
Rotary-
Belt fLime)
Vacuum (Heat §
Filtration Thickening)
Pressure Filtration
(lime § FeCls)
CAPITAL
COST
-1Q3$-
4,150
2,800
7,125
11,630
9,200
0 § M
COST
-103$/yr-
2,440
3,320
2,965
1,920
3,420
TOTAL COST*
Yearly
Basis
-103$/yr-
3,180
3,910
4,095
3,605
4,820
Tonnage
Basis**
-$/ton-
29.10
35.70
37.40
33.00
44.00
PRESENT
WORTH***
-103$-
22,800
28,100
29,600
26,200
35,000
*Includes capital costs amortized on the following basis:
(a) Truck § trailer rigs and skip loaders @ 6% for 3.4 years
(b) Dewatering station, buildings and parking area @ 6% for 10 years.
**Based on 300 dry tons/day (272 metric tons/day) of solids handled.
***Based on 6% for 10 years.
tDoes not include $1,000,000 capital value of existing first stage centrifuges
equivalent to an additional $2.00/ton total cost.
Unit Conversions: ($/ton) x 1.103 = ($/metric ton)
-------
Table 55: TOTAL SLUDGE HANDLING COST SUMMARY--Pipeline Transportation and Landfill
Dewatering and Disposal
PARAMETERS
Y.Transported and Dewatered Material:... JWPCP primary digested sludge
2. Pipeline Distance: 27.6 miles (44,4 km)
DEWATERING
SYSTEM
Two Stage Centrifugationf
(polymers to 2nd Stage)
Vacuum Coil Filtration
(polymers)
Rotary-
Belt (Lime)
Vacuum (Heat §
Filtration Thickening)
Pressure Filtration
(lime § FeCls)
CAPITAL
COST
-103$-
8,210
6,075
10,490
12,610
12,615
0 f, M
COST
-103$/yr-
2,160
2,875
2^665
1,805
3,180
TOTAL COST*
Yearly
Basis
-103$/yr-
3,320
3,810
4,125
3,235
4^910
Tonnage
Basis**
-$/ton-
30.40
34.80
37.75
29.50
44.80
PRESENT
WORTH***
-103$-
24,100
27,200
30^^00
25,900
36,000
^Includes capital cost amortized on the following basis:
(a) Pipeline @ 6% for 20 years
(b) Trucks and skip loaders @ b$ for 3.4 years
(c) Dewatering station, buildings and parking area @ 6% for 10 years.
**Based on 300 dry tons/day (272 metric tons/day) of solids handled.
***Based on 6% for 10 years.
tDoes not include $1,000,000 capital value of existing first stage
centrifuge equivalent to an additional $2.00/ton total cost.
Unit Conversions: ($/ton) x 1.103 = (I/metric ton)
-------
(2) Regarding the thermal-thickening-filtration
scheme, the associated pipeline cost was
derived to reflect the industrial waste sur-
charge pertinent to the high BOD and suspended
solids in the effluent from that dewatering
system. Hence, the estimate for the dewater-
ing scheme was adjusted to exclude the capital
and 0 § M costs for biological treatment.
The combined costs indicated that the most economical
system utilizing pipeline transporation was that incor-
porating the thermal-thickening-filtration scheme at
the landfill. In this regard, the total sludge handling
cost was estimated at $29.50/ton ($32.50/metric ton).
Of this total, about 48 percent was attributable to
dewatering, with the remaining 52 percent associated
with pipeline transportation and landfill disposal.
Presented in Table 54 are summarized cost estimates for
digested sludge dewatering at the JWPCP with subsequent
disposal of the dewatered sludge by incineration and ash
hauling to a landfill. These costs were acquired by
combining the disposal costs in Table 51 with those in
Table 45 (with one modification) for each of the dewater-
ing alternatives. The thermal-thickening-filtration
estimates were modified to reflect a savings in heat
conditioning fuel costs resulting from the use of recover-
ed heat from the incineration process. As is noted,
the most economical system employing incineration and
ash hauling was that incorporating sludge dewatering
by two-stage centrifugation. The total sludge handling
cost for this sytem was estimated at $25.70/ton
($28.30/metric ton). Sludge dewatering comprised about
43 percent of this total, with the remaining 57 percent
attributable to disposal.
A summary of the total costs of the five alternative
dewatering schemes for each of the three disposal alter-
natives is presented in Table 55. As is noted, the
estimates associated with each method of disposal are
ranked in order of increasing cost. Of the fifteen alter-
natives, two-stage centrifugation with incineration and
ash hauling provided the most economical means of sludge
handling and disposal. Accordingly, the total cost for
such a system would be $25.70/ton ($28.30/metric ton)
or about $2.8 million/yr based on handling 300 dry tons/day
(272 metric tons/day) of solids; this is about 12 percent
188-
-------
Table 54: TOTAL SLUDGE HANDLING COST SUMMARY--Dewater ing and Subsequent Incineration at JWPCP
with Truck Hauling of Ash to Landfill
PARAMETERS
TiDewatered Material:... JWPCP primary digested sludge
2. Hauling Period: 8 hrs/day, 7 days/wk
3. Landfill Distance: 30 miles (48 km) from JWPCP
DEWATERING
SYSTEM
Two Stage Centrifugationt
(polymers to 2nd Stage)
Vacuum Coil Filtration
(polymers)
Rotary-
Belt (Lime)
Vacuum (Heat §
Filtration Thickening)
Pressure Filtration
(lime § FeCls)
CAPITAL
COST
-103$-
5,985
5,125
8,925
12,975
11,025
0 § M
COST
-103$/yr-
1,925
3,300
2,720
1,320
3,150
TOTAL COST*
Yearly
Basis
-103$/yr-
2,810
4,080
4,015
3,150
4,720
lonnage
Basis**
-$/ton
25.70
37.20
36.70
28.75
43.10
PRESENT
WORTH***
-103$-
20,200
29,400
28,900
22,800
34,200
*Includes capital costs amortized on the following basis:
(a) Dewatering station, incinerators, building and parking area
@ 6% for 10 years
(b) Truck § trailer rigs and skip loaders @ 6% for 3.4 years.
**Based on 300 dry tons/day (272 metric tons/day) of solids handled.
***Based on 6% for 10 years.
tDoes not include $1,000,000 capital value of existing first stage
centrifuge equivalent to an additional $2.00/ton total cost.
Unit Conversions: ($/ton) x 1.103 = ($/metric ton)
-------
Table 55: SUMMARY COST COMPARISON OF ALTERNATIVE SLUDGE HANDLING SYSTEMS
DISPOSAL
ALTERNATIVE
Truck
Hauling
to a
Landfill
Pipeline
Transportation
with Landfill
Dewatering §
Disposal
Incineration
with
Ash Hauling
to a
Landfill
DEWATERING SYSTEM ALTERNATIVE
1. Two Stage Centrifugation (polymers to 2nd Stage) t
2. Rotary-Belt Vacuum Filtration (heat § thickening)
3. Vacuum Coil Filtration (polymers)
4. Rotary-Belt Vacuum Filtration (lime)
5. Pressure Filtration (lime $ FeCls)
1. Rotary-Belt Vacuum Filtration (heat § thickening)
2. Two Stage Centrifugation (polymers to 2nd stage) t
3. Vacuum Coil Filtration (polymers)
4. Rotary-Belt Vacuum Filtration (lime)
5. Pressure Filtration (lime $ FeCl^)
1. Two Stage Centrifugation (polymers to 2nd stage) t
2. Rotary-Belt Vacuum Filtration (heat § thickening)
3. Rotary-Belt Vacuum Filtration (lime)
4. Vacuum Coil Filtration (polymers)
5. Pressure Filtration (lime $ FeCl^)
TOTAL COST*
Yearly
Basis
-103$/vr-
3,180
3,605
3,910
4,095
4,820
3,235
3,320
3,810
4,125
4,910
2,810
3,150
4,015
4,080
4,720
Tonnage
Basis**
-$/ton-
29.10
33.00
35.70
37.40
44.00
29.50
30.40
34.80
37.75
44.80
25.70
28.75
36.70
37.20
43.10
*Cost pertain to the complete handling of JWPCP primary digested sludge.
**Based on 300 dry tons/day (272 metric tons/day) of solids handled.
tDoes not include $1,000,000 capital value of existing first stage
centrifuge equivalent to an additional $2.00/ton total cost.
Unit Conversions: ($/ton) x 1.103 = ($/metric ton)
-------
lower than the lowest cost estimated for the other two
disposal alternatives. The thermal-thickening-filtra-
tion scheme with incineration and ash hauling was the
next lowest cost alternative. Ranking third was two
stage centrifugation in combination with truck hauling
to a landfill. Falling close behind this was the
system incorporating pipeline transportation with land-
fill dewatering by the thermal-thickening-filtration
scheme. All other schemes were estimated to be in excess
of $30.00/ton ($33.00/metric ton).
Although incineration yielded the lowest total system
cost, it was felt that the social and technical problems
associated with the air pollution dilemma in Los Angeles
would place the Districts in a questionable position
should such a system be constructed. Also, the APCD
might impose more stringent standards if incineration
were proposed; this would necessitate additional capital
expenditures for more air pollution control equipment
which could conceivably render the system uneconomical.
Further, the possibility existed that the atmospheric
discharge of certain substances (pesticides, heavy metals,
etc.) would not be sufficiently controllable by any means.
In view of these unknowns, the low cost incinceration
system was eliminated for further consideration.
In addition to affording the next most economical system,
the two-stage centrifugation-truck hauling scheme afford-
ed the advantage of a relatively low capital cost --a
factor which was desirable in a system having a short
life. Also, the reliability and flexibility of the system
had been demonstrated quite clearly. On the other hand,
pipeline transportation of digested sludge to a landfill
disposal point had the advantages of eliminating the
placement of large trucks on an already congested freeway
system, eliminating the accompanying air pollutants dis-
charged by the trucks, and combining the dewatering and
disposal systems in the same physical location; in addi
tion, the effluent from the dewatering station would be
discharged to the sewer rather than directly to the ocean,
thus relaxing the strict effluent quality restrictions
on the dewatering system. Corresponding disadvantages
were the high capital cost of the pipeline itself, the
unknowns involved in pumping digested sludge over long
distances, and the effects of such on sludge dewater-
ability.
-191
-------
COST SUMMARY FOR REMOTE DISPOSAL
A future alternative for ultimate disposal of digested
sludge from the JWPCP is that of remote disposal. Multiple
possibilities exist for sludge disposal to a remote area.
Two such possibilities are considered herein, namely
rail or pipeline transport to the upper desert region
with disposal by either lagooning or soil reclamation.
Because many basic assumptions were necessary to derive
the comparative costs, it is to be realized that the
estimates presented herein do not possess the accuracy
of those pertaining to the dewatering-diposal alterna-
tives-- presented in prior sections. However, they do
enable an "order of magnitude" comparison to be made.
In making the cost estimate for a pipeline to convey
digested sludge from the JWPCP to a remote area, the
following criteria and assumptions were used:
(1) Without selecting a particular location for
the pipeline terminus, it was estimated that
a 14-inch (35.6-cm) diameter, 100-mile
(161-km) long, welded steel pipe would be
required. A maximum static head of 3500 ft
(1067 m) was assumed.
(2) Pipeline pumping would be accomplished with
three pump stations, each located at inter-
vals along the route.
(3) A control system for the entire route plus
storage tanks at the JWPCP and the terminus
would be provided.
(4) Capital and 0 § M costs would be derived in
a manner similar to those previously acquired
for the pipeline-landfill transportation scheme.
192-
-------
The criteria used for deriving the cost estimate for
rail transportation to a remote area were as follows:
(1) Digested sludge would be thickened (using
polymers) to a solids concentration of 6%
(60,000 mg/1) at the JWPCP and then hauled
daily to the remote disposal point in
20,000-gal. (75.7-cu m) railroad tank cars.
(2) Assuming a roundtrip time of 24 hours, 100
tank cars would be required (including 16 cars
for_emergency and standby purposes), each
having an approximate purchase price of
$25,000. Operation and maintenance costs were
assessed at 2<|:/car/mile (1. 24^/car/km) .
(3) In consultation with the Southern Pacific Rail
road Company, freight charges of $200/car/round
trip would be levied less $18/car/100 miles
($11.20/car/100 km) when fully loaded; on a
net basis, this would amount to about
$5.9 million/yr.
(4) Sludge loading into the tank cars would be
accomplished with a semi-automated system.
At the terminus, a trestle arrangement would
enable transported sludge to be gravity
drained into a lined sump from which it would
be pumped into enclosed storage tanks to await
disposal.
(5) Since a main railroad line presently passes
through the JWPCP acreage, only a spur would
be required to convey the tank cars in and
out of the premises. At the terminus, however,
five miles of trackage were assumed necessary
to get the loaded cars from a main line to
some remote disposal site.
The requirements and cost estimates for remote disposal
by lagooning were based on the following criteria:
(1) Sealed lagoons having a 6-ft (1.8-m) initial
depth would be provided such that the perme-
ability would be 0.002 ft (0.061 cm) of water
per year (a WQCB requirement). Assuming an
evaporation rate of 80 in/yr (203 cm/yr) and
a dried sludge density of 30 Ib/cu ft
-193-
-------
(480 kg/cu mj, the useful life of each lagoon
would be 10 years. Hence, 2000 acres (810 ha)
would be required to provide for a 30-year
capacity.
(2) For estimate purposes, the total 2000 acres
(810 ha) would be purchased but only 540 acres
(220 ha) of lagoons would be constructed. Land
costs were assessed at $2500/acre ($1012/ha)
and the cost for constructing the 540 acres
(220 ha) of lagoon capacity was estimated at
$7,000,000. Distribution piping, loading and
spreading equipment, and the necessary facili
ties for labor forces and equipment was esti
mated at $1,000,000.
(3) The operation and maintenance costs would include
property taxes of 10% of the assessed value. No
allowances would be made for the leasing of the
1460 acres (590 ha) not being used initially
for lagoons.
Soil reclamation costs were derived on the basis of the
following assumptions and criteria:
(1) A 10,000-acre (4050-ha) land capacity would
be purchased at $2500/acre ($1012/ha).
The assumption was made that adjacent acreage
would be available and, therefore, purchased
as was needed to maintain the reclamation
operation. Distribution piping and the equip-
ment necessary for sludge spreading and tilling
with the soil was assessed at $1,000,000.
(2) The operation and maintenance costs would in-
clude property taxes of 10% of the assessed
value. It was assumed that a 10,000-acre
(4050~ha) inventory would always be maintained.
No credit was assumed for the sale or leasing
of reclaimed acreage.
The individual capital and operation § maintenance costs
for each of the remote area transportation and disposal
alternatives are presented in Table 56. In terms of a
total system, these individual costs would combine into
the system costs shown in Table 57. The pipeline trans -
port-lagooning scheme would bear some consideration be-
cause of its low operating cost ($800,000/yr). If the
capital cost is amortized at 6% over a 30-year period,
the total yearly cost would approximate $3,000,000,
194-
-------
REMOTE AREA TRANSPORTATION AND ULTIMATE DISPOSAL COSTS
PARAMETERS
Y.Material for Disposal:... JWPCP primary digested
sludge
2. Remote Area Location: approximately 100 miles
(161 km) from JWPCP
FUNCTION
Transportation
Disposal
MODE
1. Pipeline
2. Rail
1. Lagooning
2. Soil Reclama-
tion
r4t5T"t*AT
\jf\i JL i fVi^
COST
-103$-
17,000
5,000
13,000
26,000
0 § M
COST
i -103$/yr-
600
7,000
200
900
TABLE 57: COMPARISON OF REMOTE DISPOSAL SYSTEM COSTS
PARAMETERS
TiMaterial for Disposal:... JWPCP primary digested
sludge
2. Remote Area Location:.... approximately 100 miles
(161 km) from JWPCP
REMOTE DISPOSAL
SYSTEM
1. Pipeline transport $ lagooning
2. Pipeline transport § soil
reclamation
3. Rail transport § lagooning
4. Rail transport § soil
reclamation
CAPITAL
COST
-in3$-
30,000
43,000
18,000
31,000
0 § M
COST
-103$/yr-
800
1,500
7,200
7,900
-195-
-------
or $27.50/ton ($30.30/metric ton) based on 300 dry tons/day
(272 metric tons/day) of solids handled. This estimate
is slightly below the $29.10/ton ($32.10/metric ton)
estimated for the two-stage centrifugation system with
truck hauling to a landfill. The pipeline transport-
soil reclamation scheme might also merit consideration
since the operation and maintenance costs conservatively
excluded any savings which would be attributable to the
yearly sale of reclaimed land. The high operation and
maintenance costs for the trail transport schemes are
attributed mostly to the levied freight charges. Since
these charges were relatively firm and fixed, economic
consideration for such an operation would be unjustifiable.
196-
-------
BIBLIOGRAPHY
1. Standard Methods for the Examination of Water and
Wastewater,Thirteenth Edition, American Public
Health Association, Inc., New York (1971).
2. "Determination and Removal of Floatable Material
from Waste Water," Summary Report, Engineering
Science, Inc. , Arcadia, California, 1965.
3. Games, B.A., and Eller, J.M., "Characterization
of Wastewater Solids," Journal WPCF, Vol. 44,
No.8, August 1972, pp. 1498-1517.
4. Hirst, G., Mulhall, K.G., and Hemming, M.L.,
"The Sludge Heat Treatment Plant at Pudsey--
Operating Experiences," presented to the North
Eastern Branch of the Institute of Water Pollution
Control, March 1971.
5. Brooks, R.B., "Heat Treatment of Sewage Sludges,"
Journal of the Institute of Water Pollution Control,
No. 2, 1970.
6. Everett, J.G., "Dewatering of Wastewater Sludge by
Heat Treatment," Journal WPCF, Vol. 44, No.1,
January 1972, pp. 92-100.
7. Hopkins, G.J., and Jackson, R.L., "Polymers in the
filtration of Raw Sludge," Journal WPCF, Vol. 43,
No. 4, April 1971, pp. 689-698.
8. Dahl, B.W., Zelinski, J.W., and Taylor, O.W.,
"Polymer Aids in Dewatering and Elutriation,"
Journal WPCF, Vol. 44, No. 2, February 1972,
pp. 201 211.
-197
-------
9. Tenney, M.W., Echelberger, W.F., Coffey, J.J., and
McAlobn, T.J., "Chemical Conditioning of Biological
Sludges for Vacuum Filtration," Journal WPCF,
Vol. 42, No. 2, Part 2, February 1970, pp. R1-R20-
10. Tenney, M.W., and Cole, T.G., "The Use of Flyash in
Conditioning Biological Sludges for Vacuum Filtra-
tion," Journal WPCF, Vol. 40, No. 8, Part 2,
August 1968, pp. R281-R302.
11. Edde, H.J., and Eckenfelder, W.W., Jr., "Theoretical
Concept of Gravity Sludge Thickening; Scaling~Up
Laboratory Units to Prototype Design," Journal WPCF,
Vol. 40, No. 8, Part 1, pp. 1486-1498.
12. Jordan, V.J., Jr., and Scherer, C.H., "Gravity
Thickening Techniques at a Water Reclamation Plant,"
Journal WPCF, Vol. 42, No. 2, Part 1, February 1970,
pp. 180-189.
13. Albertson, O.E., and Guidi, E.E., Jr., "Centrifugation
of Waste Sludges," Journal WPCF, Vol. 41, No. 4,
April 1969, pp. 607-628.
14. O'Donnell, C. and Keith, F,W., Jr., "Centrifugal
Dewatering of Aerobic Waste Sludges," Journal WPCF,
Vol. 44, No. 11, November 1972, pp. 2162-2171.
15. Hebb, M.H., and Smith, F.M., "Centrifugal Separation,"
Encyclopedia of Chemical Technology, Vol. 3, 1st Ed.,
pp. 501-521.
16. Vesilind, P.A., "Estimation of Sludge Centrifuge
Performance," Journal of the Sanitary Engineering
Division, Proceedings of tFe" ASCE, Vol. 96, NoT~SA~3,
June 1970, pp. 805-818.
17. Stevens, M.H., "Dewatering Sludges and Slurries by
Centrifugation," In-house report of Sharples-
Pennwalt Corporation.
18. Keith, F.W,, Jr., "The Use of Centrifuges in Disposal
of Solids from Wastes,," In-house report of Sharples-
Pennwalt Corporation.
198-
-------
j-9. Landis, D.M., "Centrifuges for Primary, Digested
and Activated Sludge Concentration--Waste Disposal,"
Technical Publication of the DeLaval Separator
Company presented at the American Institute of
Chemical Engineers, May 1969, Cleveland, Ohio.
20. Vaughn, D.R., and Reitwiesner, G.A., "Disk-nozzle
Centrifuges for Sludge Thickening," Journal WPCF,
Vol. 44, No. 9, September 1972, pp. 1789-1797.
21. "Evaluation of the Eimco Solid Bowl Centrifuge
Dewatering Porteous Sludge," In-house report of
Envirotech Corporation, November 1971.
22. Thomas, C.M., "The Use of Filter Presses for the
Dewatering of Sewage and Waste Treatment Sludges,"
presented at the Forty-Second Annual Conference of
the Water Pollution Control Federation, October 1969,
Dallas, Texas.
23. Graefen, H., and Donges, H.J., "Studies on Para
meters Affecting Sludge Dewatering in Pressure
Filters," presented at the International Water
Pollution Research Conference, July-August, 1970.
24. Swanwick, J.D., Lussignea, F.W., and Baskerville, R.C.,
"Recent Work on the Treatment and Dewatering of
Sewage Sludge," presented at the International
Conference on Water Pollution Research, Sec. 2,
Paper No. 30, September 1962, London, England.
25. Eckenfelder, W.W., Jr., Industrial Water Pollution
Control, McGraw-Hill Book Company, New York (^1966) ,
pp. 236-269.
26. "Bulk Transport of Waste Slurries to Inland and
Ocean Disposal Sites," Summary Report, Bechtel
Corporation, for the Federal Water Pollution Control
Administration, Department of the Interior, Contract
No. 14-12-156, December 1969.
27. Dean, R.B., "Ultimate Disposal of Waste Water
Concentrates to the Environment," Environmental
Science § Technology, Vol. 2, Number 12, December 1968,
pp. 1079-1086.
-199-
-------
28. Graham, R.E., and Dodson, R.E., "Digested Sludge
Disposal of San Diego's Aquatic Park," presented at
the 41st Annual Conference of the Water Pollution
Control Federation, September 1968, Chicago, Illinois.
29. Graham, R.E., and Dodson, R.E., "Alternatives for
Sludge Disposal Metropolitan Sewerage System," pre-
pared for the City of San Diego, Utilities Depart-
ment, November 1968, San Diego, California.
30. Guarino, C.F., and Cameron, M.S., "Sludge Processing
in Philadelphia," Journal WPCF, Vol. 43, No. 8,
August 1971, pp. 1609-1616.
31. Bennett, E.R., Rein, D.A., and Linstedt, K.D.,
"Economic Aspects of Sludge Dewatering and Disposal,"
Journal of the Environmental Engineering Division,
Proceedings of the ASCE, Vol. 99, No. EE1,
February 1973, pp. 55-72.
32. Mar, B.W., "Sludge Disposal Alternatives - Socio-
Economic Consideration," Journal WPCF, Vol. 41,
No. 4, April 1969, pp. 547-552.
33. Harrison, J.R., Black, Crow and Eidsness, Inc.,
Consulting Engineers, "Solids Handling in Activated
Sludge Plants," presented at the Annual Joint
Meeting of the Atlantic Canada Section of the
American Water Works Association and the Canadian
Institute of Pollution Control, September 1971,
Halifax, Nova Scotia.
34. Sparr, A.E., "Sludge Handling," Journal WPCF,
Vol. 40, No. 8, Part 1, August 1968, pp. 1434-1442.
35. Gloyna, E.F., and Eckenfelder, W.W., Jr., Water
Quality Improvement by Physical and Chemical Processes,
Published for the Center for Research in Water
Resources by the university of Texas Press, Austin,
Texas (1970), pp. 341-436.
36. Burd, R.S., A Study of Sludge Handling and Disposal,
U.S. Department of the Interior, Federal Water
Pollution Control Administration, Office of Research
and Development, Grant No. PH 86-66-32, May 1968.
-200-
-------
37. "Utilization of Municipal Wastewater Sludge,"
WPCF Manual of Practice No. 2, Prepared Under the
Direction of the Technical Practice Committee by the
Subcommittee on Utilization of Wastewater Sludge,
Water Pollution Control Federation, Washington, B.C.,
1971.
38. "Sludge Dewatering," WPCF Manual of Practice No. 20,
Prepared Under Direction of the Technical Practice
Committee by the Subcommittee on Sludge Dewatering,
Water Pollution Control Federation, Washington, D.C.,
1969.
39. "Disposal of Water-Treatment-Plant Wastes,"
Committee Report, Journal American Water Works
Association, Vol. 64, No. 12, December 1972,
pp. 814-820.
40. "Chicago Reclaiming Strip Mines with Sewage Sludge,"
Civil Engineering-ASCE, Vol. 42, No. 9, September
1972, pp. 98-102.
41. "Sludge Handling: the hardest phase of waste
treatment," Environmental Science § Technology,
Vol. 5, No. 8, August 1971, pp. 670-671
42. Swanwick, J.D., "Modern Methods of Disposal of
Sludge," Reprint: Journal of the Institute of
Municipal Engineers, Vol. 96, No. 3, 1969, pp. 1-4.
43. Braun, R., "Problems of Sludge Disposal," presented
at the Second International Conference on Water
Pollution Research, Sec. 2, Paper No. 11, August
1964, Tokyo, Japan.
44. Swanwick, J.D., "Recent Developments in Sludge
Technology in the U.S.A.," Reprint: Journal of
the Institute of Water Pollution Control, No. 4,
1968, pp. 1 19.
45. Cardinal, P.J., Jr., "Advances in Miltihearth Incin-
eration, Regeneration and Sludge Heat Treatment,"
paper presented through BSP, a Division of Enviro-
tech Corp., pp. 1-27.
201-
-------
46. Zingler, E., "Significance and Limits of the Buchner-
Funnel-Filtration-Test (BFFT)," presented at the
Fifth International Conference on Water Pollution
Research, Sec. 2, Paper No. 31, July-August 1970,
pp. 1-8.
47. Sontheimer, H., "Effects of Sludge Conditioning with
Lime on Dewatering," presented at the Third Inter-
national Conference on Water Pollution Research,
Sec. 2, Paper No. 9, 1966, Munich, Germany.
48. Russo, F., and Carr, R.L., Jr., "Polyelectrolyte
Coagulant Aids and Flocculents: Dry and Liquid,
Handling and Application," Water and Sewage Works,
Reference Volume Nov. 1970, Vol. 117, pp. R72-R76.
49. Raynes, B.C., "Economic Transport of Digested Sludge
Slurries," presented at the 41st Annual Conference
of the WPCF, Sept. 1970, Chicago, Illinois.
50. Erickson, A.H., and Knopp, P.V., "Biological Treat-
ment of Thermally Conditioned Sludge Liquors,"
presented at the 5th International Conference on
Water Pollution Research, Sec. 2, Paper No. 33,
July-August 1970, pp. 1 14.
51. Anderson, M.S., "Sewage Sludge for Soil Improvement,"
U.S. Department of Agriculture, Circular No. 972,
November 1955, pp. 1-27.
-202-
-------
SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
i. Report !fn.
w
SUMMARY REPORT: PILOT PLANT STUDIES
ON DEWATERING PRIMARY DIGESTED SLUDGE
Parkhurst, J.D., Rodrigue, R.F., Miele, R.P., Hayashi, S.T.
County Sanitation Districts of
Los Angeles County
2020 Beverly Boulevard
" "
Environmental Protection Agency report number,
EPA-670/2-73-043, August 1973.
,
t,
L $." Pfforaiif'-' 0 r jra:?-' -ttitn
Re;.?ft Nr.
, t*c>n:txC:i,"'ji=i»t <:•'•.•.
R801658- 1B2043
/,?, Type*.•''Repot \nd
•——•••— ..— •—. • wiiwih.iwii wiitaivi • f u< I I. y w >i I wi / M ^ W W HIM M f^l I 11IO I
and operated by the Los Angeles County Sanitation Districts. Oc
on the effluent from this facility necessitated that at least 9
solids be removed from the primary digested sludge for disposal
j,, .,,-.., c. A 14-month pi lot and plant scale sludge dewaterjng study was conducted at the
Joint Water Pollution Contro Plant (JWPCP) -- a 380 mgd primary treatment facility ownec
—j .--i u.. .u. , „ .__.,... . ..._«_. *,_..«, c£s> Ocean discharge requirements
least 95 percent or the suspended
disposal by alternative means.
The applicability of heat, polymers, chemicals and flyash was investigated as a means of
conditioning digested sludge for dewatering. Sludge dewatering schemes utilizing horizon-
tal scroll centrifuges, imperforate basket centrifuges, vacuum filters, and pressure fil-
ter were thoroughly studied. Operational results were obtained from twenty conditioning-
dewatering test systems of which five successfully produced the desired suspended solids
removal. Full scale cost estimates were prepared for each of the five systems.
Estimates were prepared for the requirements and costs associated with the ultimate dis-
posal of dewatered sludges generated from each successful dewatering scheme. Three dis-
posal alternatives were considered, namely, truck hauling of dewatered sludge from the
JWPCP to a landfill: pipeljne transport of digested s]udge to a landfill with dewatering
and disposal thereat; and incineration at the JWPCP with truck hauling of the ash residue
to a landfi11. Combining the disposal costs with the dewatering costs yielded estimates
for fifteen total sludge handling systems. Remote area transportation and disposal costs
were derived for comparative purposes.
It was concluded that a 2-stage centrifuge sludge dewatering scheme (polymer addition to
the second stage) with truck hauling of dewatered sludge solids to a landfill was most
suitable for the JWPCP. (Rodrigue-LACSD).
i7a. Descriptor* *Primary digested sludge, *Pollution abatement, *Sludge conditioning,
*Sludge dewatering, *Sludge disposal, Heat treatment, Polymer addition, Chemical addition
Flyash addition, Sludge thickening, Horizontal scroll centrifuge, Imperforate basket
centrifuge, Coil vacuum filter, Cloth belt vacuum filter, Pressure filter, Incineration,
Landfill disposal, Pipeline transportation, Rail transportation, Lagooning, Land
reclamation.
l"b. Idiittifirrs
*Los Angeles, *Sludge processing, Pilot study, Performance data, Cost estimates.
20. Security Class.
(Page)
Raymond F. Rodrigue, Ph.D. | /
21. If.;, of
Pages
22. Price
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C. ZO24O
Los Angeles County Sanitation Districts
•US. GOVERNMENT PRINTING OFFIC6:1973 546-310/73 1-3
------- |