EPA-600/2-75-038
October 1975
Environmental Protection Technology Series
LIME USE IN WASTEWATER TREATMENT:
DESIGN AND COST DATA
Municipal Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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EPA-600/2-75-038
October 1975
LIME USE IN WASTEWATER TREATMENT:
DESIGN AND COST DATA
by
Denny S. Parker, Emilio de la Fuente,
Louis O. Britt, Max L. Spealman,
Richard J. Stenquist, and Fred J. Zadick
Brown and Caldwell
Walnut Creek, California 94596
Contract No. 68-03-0334
Project Officer
James E. Smith, Jr.
Wastewater Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Municipal Environmental
Research Laboratory, U.S. Environmental Protection Agency, and
approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the U.S.
Environmental Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or recommendation
for use.
11
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FOREWORD
Man and his environment must be protected from the adverse
effects of pesticides, radiation, noise, and other forms of pollution,
and the unwise management of solid waste. Efforts to protect the
environment require a focus that recognizes the interplay between
the components of our physical environment—air, water, and land.
The Municipal Environmental Research Laboratory contributes to this
multi-disciplinary focus through programs engaged in
O studies on the effects of environmental contaminants
on the biosphere, and
O a search for ways to prevent contamination and to
recycle valuable resources.
The research reported here was performed for the Ultimate Disposal
Section of the Wastewater Research Division to provide design and cost
data on lime use, reuse, and recovery in wastewater sludge handling and
disposal operations. The information presented in this report is of
immediate use to the treatment plant designer and should make possible
improved operation as well as operation at a reduced cost.
111
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ABSTRACT
This report presents design and cost information on lime use in wastewater
treatment applications. It includes design and cost information on lime handling,
liquid processing, solids generation and dewatering, lime recovery and ultimate
ash disposal. The report takes a design manual approach so that the information
presented has maximum usefulness to environmental engineers engaged in both
the conceptual and detailed design of wastewater treatment plants.
Design data on alternate sludge thickening and dewatering processes are
presented with special emphasis on wet classification of calcium carbonate from
unwanted materials and on maximizing the dewatering of wasted solids.
Alternative recalcining techniques are assessed and problem areas identified. A
relatively new technique for beneficiation of the recalcined product is presented.
Approaches to heat recovery are presented that minimize the net energy require-
ments for recalcination and incineration.
A computer program for computation of solids balances is included as a design
aid and two case histories are presented which portray the cost of lime treatment,
sludge processing and lime reclamation.
This report was submitted in fulfillment of Project Number CI-73-0131, Contract
Number 68-03-0334, by Brown and Caldwell, Consulting Engineers, under the
sponsorship of the U.S. Environmental Protection Agency. Work on the first
draft was completed as of June, 1974.
IV
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CONTENTS
Page
Abstract iv
List of Figures viii
List of Tables xii
Acknowledgments xvi
Sections
I Conclusions 1
II Recommendations 3
III Introduction 4
Purpose and Scope 5
Background 5
References 6
IV Fundamentals of Lime 7
Definitions 7
Lime in Wastewater Treatment 8
Lime Slaking 8
Selection of Lime 13
V Handling of Lime 15
Lime Delivery 15
Lime Unloading and Storage . 16
Lime Feeders 19
Dissolving of Lime 25
In-Plant Transport Methods 28
Safety Considerations 31
References 32
VI Liquid Processing with Lime 33
General Considerations 33
Process Chemistry 33
Lime Addition 47
Control of Lime Dosage 48
Flocculation 52
Alternate Processes for Primary Application 53
Recarbonation 63
Tertiary Applications 66
Design Considerations for Primary Clarifiers 66
References 72
v
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CONTENTS (continued)
Sections Page
VII Lime Sludge Thickening and Dewatering 77
General Considerations 77
Sludge Thickening 77
Sludge Dewatering 85
Sludge Cake Conveying 125
References 128
VIII Slime Sludge Recalcination and Waste Sludge Incineration . . 131
General Considerations 131
Lime Sludge Recalcination 132
Handling of Reclaimed Lime 148
Related Processes 157
Summary of Lime Recovery Case Histories 164
Waste Sludge Incineration 171
Energy Considerations 171
References 184
IX Air Quality Considerations 188
References 192
X Mass Equilibrium Balances of Solids Processing
Systems by Digital Computation 193
Description of Program 197
Derivation of Equations and Program Mechanics 205
Material Balances for Several Cases 209
References 216
XI Ultimate Disposal of Ash 217
Ash Characteristics 217
Uses of Sludge Ash 217
Ash Handling Prior to Disposal 220
Final Disposal Sites 221
References 222
XII Development of Cost Estimates 223
General Considerations 223
The Lower Molonglo Water Quality Control Centre .... 224
The CCCSD Water Reclamation Plant 226
Cost Estimates for the CCCSD Water Reclamation Plant . . 228
References 244
XIII List of Inventions and Publications 245
XIV Glossary 246
XV Appendices 248
vx
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CONTENTS (continued)
Page
APPENDIX A. LISTING OF SOLIDS 1A 249
APPENDIX B . OUTPUT FOR CASES 257
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FIGURES
No. Page
5- 1 Positive/Negative Pneumatic Conveying System 20
5- 2 Typical Screw Type Volumetric Feeder 23
5- 3 Typical Belt Type Gravimetric Feeder 24
5- 4 Typical Detention Type Slaker 27
5- 5 Typical Paste Type Slaker 29
6- 1 Effect of Phosphate Form on Calcium Carbonate
Precipitation 35
6- 2 Effect of Solids Concentration on Calcium Removal 36
6- 3 Lime and Iron Dose vs . Supernatant Quality for
CCCSD Wastewater 41
6- 4 Phosphorus Removal for Low pH Operation lime and Iron
Treatment of CCCSD Wastewater 44
6- 5 Effect of Lime Treatment on Salt Lake City Wastewater 45
6- 6 Calcium Loss to Supernatant and Phosphorous Precipitation 46
6- 7 Location of Lime Slakers at the CCCSD Water Reclamation Plant 49
6- 8 Lime Dosage Control Diagrams 50
6- 9 Lime Dosage Control Diagram - Feed Forward
Control Mode 51
6-10 Air Supply - Shearing Relationship for Preaeration-Flocculation 54
6-11 Phosphorous Removal as a Function of Lime Dose 56
6-12 Lime Requirement for pH 11 as a Function of Wastewater
Alkalinity 61
6-13 Typical Solids-Contact Clarifier 67
6-14 Primary Treatment Units at CCCSD Water Treatment plant 69
7- 1 Relationship between Increase in Solids Concentration
and Moisture Removal 78
Vlll
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FIGURES (continued)
No. Page
7- 2 Settling Characteristics of High Lime Sludge
at the Blue Plains Pilot Plant 80
7- 3 Typical Gravity Thickener 81
7- 4 Gravity Sludge Thickener at CCCSD Water Reclamation Plant 82
7- 5 Schematic Diagram of the Dissolved Air Flotation Process 84
7- 6 Effect of Moisture Content on the Cost of Sludge Combustion 86
7- 7 Effect of Moisture Content on the Cost of Sludge Combustion 87
7- 8 Conventional Plural Purpose Furnace Flow Sheet 88
7- 9 ATTF Solids Processing System 89
7-10 Solid-Bowl Conveyor Centrifuges 91
7-11 Vertical Centrifuge Installation at the CCCSD
Water Reclamation Plant 93
7-12 Summary of Constituent Recoveries During Wet Classification
without Lime Recycle 97
7-13 Summary of Constituent Recoveries During Wet Classification
with Lime Recycle 100
7-14 Effect of Feed Rate on Solids Recovery 102
7-15 Effect of Pond Setting on Dewatering at pH 11 102
7-16 Effect of Conveyor Speed on Polymer Requirement 103
7-17 Effect of Centrifugal Force on Solids Recovery 104
7-18 Effect of Feed Rate on Solids Recovery 105
7-19 Effect of Polymer Dosage on Lime Recovery 107
7-20 Effect of Polymer Dosage on Solids Removal 110
7-21 Schematic Diagram of Belt Type Vacuum Filter 111
7-22 Dewatering of Lime Sludge by Vacuum Filtration 113
IX
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FIGURES (continued)
No. Page
7-23 Effect of Drum Speed on Cake Solids Concentration 115
7-24 Effect of Drum Speed on Filter Loading 116
7-25 Effect of Drum Speed on Solids Capture 117
7-26 Schematic Diagram of a Pressure Filtration System 119
7-27 Relationship between Solids Concentration and
Specific Weight 127
8- 1 Effect of Excess Air on the Cost of Sludge Incineration 133
8- 2 Decomposition of Calcium Carbonate to Calcium Oxide 134
8- 3 Typical Multiple Hearth Furnace 137
8- 4 Schematic Diagram of a Pellet Bed Calcining System 141
8- 5 Typical Fluidized Bed Calciner 144
8- 6 Schematic Diagram of a Sand Bed Calcining System 146
8- 7 Typical Rotary Kiln Calciner 149
8- 8 Particle Size Distribution of Recalcined Lime 151
8- 9 Two Types of Air Classifier 152
8-10 Dry Classification of Recalcined Lime 154
8-11 Auxiliary Equipment for MHF at the CCCSD Water
Reclamation Plant 159
8-12 Lime Recovery at the South Tahoe Water Reclamation Plant 166
8-13 Piscataway Tertiary Treatment Plant 168
10-1 Effect of Blow down on Recovered CaO 212
10-2 Effect of Blowdown on Primary Sludge Production for Cases 213
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FIGURES (continued)
No. Page
11-1 Particle Size Analysis of Wastewater Sludge Ash 219
12-1 Flow Diagram of the CCCSD Water Reclamation Plant 227
XI
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TABLES
No.
Page
4- 1 Characteristics of Lime Chemicals 9
4- 2 Characteristics of Main Grades of Quicklime 10
4- 3 Characteristics of Quicklime and Hydrated Lime 14
5- 1 Sizing Data for Screw Conveyors and Bucket Elevators 17
6- 1 Solubility Products of Heavy Metal Salts 39
6- 2 Effect of Primary Clarifier pH on Performance at Waterford,
New York 55
6- 3 Operating Parameters for Primary Treatment in "PEP" Plants 58
6- 4 High pH Treatment of CCCSD Wastewater 60
6- 5 Lime and Iron Treatment of CCCSD Wastewater 62
6- 6 Maximum Clarifier Design Parameters 70
6- 7 Recommended Clarifier Design Parameters 71
7- 1 Some Basic Materials of Construction Used in Sharpies
Centrifuges 90
7- 2 Classification Data for Water Treatment Plant Sludges 95
7- 3 Run Data for Wet Classification 98
7- 4 Centrifuge Performance Summary - Lime Sludge Recycle
Project 99
7- 5 Effect of Flocculation pH on Second Stage Cake Dryness 105
7- 6 Dewatering of High Lime "IPC" Solids after Centrifuge
Classification 106
7- 7 Dewatering of "IPC" Waste Solids (Whole Sludge) 108
7- 8 Pressure Filtration of Centrate at Blue Plains 121
7- 9 Pressure Filtration of Centrate at CCCSD 121
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TABLES (continued)
No. Page
7-10 Comparison of Machine and Floor Area Requirements for
Alternate Flow Sheets at 1.31 CU M/SEC 122
7-11 Comparison of Water Evaporated for Alternate Dewatering
Systems at 1.31 CU M/SEC 124
8- 1 Typical Temperature Profile in Six Hearth Furnace 138
8- 2 Temperature Profile in Lime Recalcination Furnace for CCCSD 138
8- 3 Standard Multiple Hearth Furnace Sizes 140
8- 4 Size Distribution Analysis of Recalcined Lime from a MHF 150
8- 5 Comparison of Accepts and Dust Composition during ATTF
Test Work 155
8- 6 Component Recoveries in Classification Tests during ATTF
Test Work 155
8- 7 Typical Size Distribution for Pellets from a Fluidized
Bed Calciner 156
8- 8 Typical Heat Values of Fuel Oils 161
8- 9 Typical Sound Levels 162
8-10 Permissible Noise Exposures 163
8-11 Sound Pressure Level of MHF Equipment 163
8-12 Comparison of Primary Sedimentation Performance with and
without Lime Recycle 170
8-13 Materials Balance for MHF in Recalcine Mode 173
8-14 Heat Balance for MHF in Recalcine Mode 174
8-15 Summary of Heat Balances for MHF in Recalcine Mode 177
8-16 Materials Balance for MHF at Three Moisture Levels
of Second Stage Cake 179
8-17 Summary Heat Balance for MHF at Three Moisture Levels
of Second Stage Cake 179
XI11
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TABLES (continued)
No.
8-18 Auxiliary Fuel Requirements of MHF after Heat Recovery 180
8-19 Overall Materials Balance for Fluidized Bed Calciner 182
8-20 Overall Heat Balance for Fluidized Bed Calciner 183
9- 1 Solids Composition of Lime Furnance Off-Gases, Percent 189
10- 1 Common Prefixes Used in Program "Solids 1A" 194
10- 2 Common Suffixes Used in Program "Solids 1A" 195
10- 3 Other Symbols Used in Program "Solids 1A" 196
10- 4 Format for Data File "Dat. 1" 201
10- 5 Format for Data File "Dat. 2" 202
10- 6 Format for Data File "Dat. 3" 202
10- 7 Materials Balance Description for Magnesium Oxide
in the Primary Sludge 207
10- 8 Solids Processing Sequence Options for Various Cases 210
10- 9 Materials Balance Comparisons for Various Solids
Processes Cases 211
10-10 Calculated Solids Balances for Cases 100, 117, 120, 121
and 122 215
11- 1 Physical Properties of Sludge Ash 218
11- 2 Classification of Ash Particles by "BAHCO" Micro Particle
Size Analyzer 218
11- 3 Particle Size of "FBR" Ash 218
12- 1 Design Data for Flocculation - Sedimentation Basins at the
Lower Molonglo WQCC 225
12-2 Cost Comparison Between Solids - Contact Clarifiers and
Rectangular Flocculation - Sedimentation Tanks 225
12- 3 Design Data for the CCCSD Water Reclamation Plant 229
xiv
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TABLES (continued)
No.
12- 4 Capital Cost for Lime Treatment and Recovery at the CCCSD
Water Reclamation Plant 233
12- 5 Capital Cost of Alternate Dewatering Process at the CCCSD
Plant - Vacuum Filters in a Plural Purpose Furnace Flow Sheet 235
12- 6 Capital Cost of Alternate Dewatering Process at the CCCSD
Plant - Filter Presses Substituted for Centrifugal Dewatering in
the Second Phase 236
12- 7 Operation and Maintenance Cost for Lime Treatment and
Recovery at the CCCSD Water Reclamation Plant 238
12-8 Operation and Maintenance Cost for Alternate Dewatering
Process at the CCCSD Plant - Vacuum Filters 239
12- 9 Operation and Maintenance Cost for Alternate Dewatering
Process at the CCCSD Plant - Filter Presses 240
12-10 Fuel Requirements for Alternative Cases 241
12-11 Comparison of Total Annual Costs for Lime Treatment and
Solids Processing 242
B-l Case Descriptions 258
xv
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ACKNOWLEDGEMENTS
The report was prepared by Brown and Caldwell, Consulting Engineers, of
Walnut Creek, California. Project Manager and Project Engineer for this work
were Dr. D.S. Parker and Mr. E. de la Fuente, respectively. Other contributors
were Messrs. L.O. Britt, M.L. Spealman, R.J. Stenquist, andF.J. Zadick. This
report reflects the design and research experience of both Brown and Caldwell
and Caldwell Connell Engineers, an Australian affiliate. Indirect contributors to
this report were the engineers of those two firms who have worked on lime
applications to wastewater treatment. In addition to those already named, these
engineers include Dr. D.H. Caldwell and Messrs. R.C. Aberley, J.A. Cotteral,
D.L. Eisenhauer, M.J. Flanagan, W.Henry, R.B. Sieger, K.E. Train, and
W.R. Uhte.
Mr. R.B. Thompson, of Industrial Pollution Control, Inc., Westport, Connecticut,
served as a special consultant on fluid bed recalcination.
The Central Contra Costa Sanitary District's interest in lime treatment led to the
operation of its Advanced Treatment Test Facility (ATTF) . The experience gained
in this operation of ATTF has broadened this effort considerably.
A number of manufacturers contributed valuable information, principal among
these are BIF, Dorr-Oliver, Inc., Envirotech Corp., Passavant Corp., Nichols,
Sharpies-Stokes and Wallace and Tiernan, Divisions of The Pennwalt Corp.,
Komline-Sanderson Engineering Corp., Walker Process Equipment and
Bird Machine Co.
Mr. Robert Boynton, Executive Director of the National Lime Association,
volunteered his time and reviewed the final draft of this report.
A number of individuals and agencies were kind enough to host site visits of
their facilities and/or offer their comments on lime treatment processes. These
included: Messrs. F. Krause and C.W. Bellows, Board of Water and Light,
Lansing, Michigan; Messrs. P. Hinkley, C.E. Kilpatrick and H. Munn, S.D.
Warren Co., Muskegon, Michigan; Mr. L. Martin, City of Holland, Michigan,
Mr. W. Ranson, City of Hastings, Michigan; Mr. J.L. Hall, Dade Water and
Sewer Authority, Hialeah, Florida; Messrs. T. Saygers and R.C. Stout of the
City of Dayton, Ohio; Messrs. D.F. Bishop, S.M. Bennett, T. Pressley, and
T.P. O'Farrell of the EPA-DC Blue Plains Pilot Plant, and Dr. C. Lewis,
Consultant to the U.S. Lime Division of the Flintkote Co.
Dr. James E. Smith Jr., of the U.S. Environmental Protection Agency's
Municipal Environmental Research Laboratory (MERL), Cincinnati, Ohio,
served as Project Officer for this study. Dr. Eobert B. Dean, also of
the MERL, provided early inspiration to this investigation.
xvi
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SECTION I
CONCLUSIONS
The purpose of this report is to present design and cost information on lime
handling, liquid processing, solids generation and dewatering, lime recovery and
ultimate ash disposal. Since the report takes a design manual approach rather
than a research investigation approach, the conclusions are of a different nature
than those which would normally be found in most Office of Research and
Development reports. The following conclusions were drawn:
1. Lime treatment of raw sewage is an attractive process with many
advantages, has wide applicability, is state-of-the-art technology and
should be evaluated in the selection procedure of treatment alternatives.
2. The choice of coagulants to be used in waste treatment processes should
be based on cost and performance comparisons. The selection process
should consider both chemical costs and the costs of sludge processing,
as considerable savings can be made by careful choice of operating pH
and supplemental metal salts for coagulation.
3. Combined sludges generated by lime coagulation in a chemical primary
sedimentation tank can be effectively wet classified into two components
with a solid bowl centrifuge. One component, the cake, contains the
bulk of the calcium carbonate and silica. The other component, the
centrate, contains the bulk of the organics and other chemical pre-
cipitates. Wet classification produces a cake ideal for recalcination,
as it is high in calcium carbonate and low in moisture content.
4. Sludge handling processes incorporating wet classification are more
effective in reducing the total water to be evaporated in furnaces than
processes not employing wet classification.
5. Sludge handling processes incorporating wet classification coupled with
pressure filtration of the centrate are less costly than processes where
whole sludge recovery is practiced.
6. Lime recovery through recalcination can produce a readily reusable
quicklime that can significantly reduce chemical costs in larger plants.
7. The multiple hearth furnace (MHF) is well established in the wastewater
sludge recalcination field as a result of operational experience with
tertiary lime sludges and large-scale recycling tests with raw wastewater
lime sludges. The fluidized bed reactor (FBR) has been used in similar
applications, but operating experience has not yet been obtained in the
wastewater field. Developmental work will have to be done to establish
the FBR as a working tool. The rotary kiln needs substantial research
and development work before it can be applied with confidence to waste-
water sludge applications.
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8. When applied with energy recovery features, both the MHF and the FBR
can be competitive, on an energy basis, with the industrial production of
lime from limestone.
9. Recalcined lime applied in the primary sedimentation process causes more
complete phosphorus removal and improves the softening reactions when
compared to the use of "new" lime alone.
10. Sludge handling processes incorporating wet classification recycle
substantially less unwanted solids than processes not employing wet
classification.
11. When centrifugation and pressure filtration are used, the use of recalcined
lime has been shown to improve the dewatering of waste sludges generated
in lime treatment.
12. When centrifuges are used for wet classification or whole sludge recovery,
dry classification of the recalcine furnace product is essential for control-
ling the level of silica in the system. High levels of silica recycle cannot
be tolerated due to centrifuge wear.
13. Relative effectiveness of the alternative dewatering processes for the
centrate from the wet classification step are as follows: pressure filtration,
vacuum filtration and centrifugation. However, vacuum filtration rates are
low and the cake does not separate easily from the septum.
14. As a rule, the pH of operation of the chemical primary tank must be con-
siderably in excess of pH 9.5 to generate enough calcium carbonate to
justify lime recovery.
15. Low lime treatment plants are considerably less efficient in phosphorus
and organic removal than either high lime treatment plants or plants
incorporating the use of lime with other metal salts.
16. Flocculation pH influences the dewatering processes significantly. A pH
greater than 11.0 adversely affects the dewatering of the wet classification
centrate. Higher filter yields on nonclassified whole sludges are obtained
with high pH sludges (pH >11.5) than with low pH sludges (pH < 11.5) .
17. Rectangular sedimentation tanks incorporating preaeration for grit
removal and flocculation are lower in capital cost than circular tanks
with separate grit removal.
18. The quantity of sludge produced where lime is used in a primary
sedimentation tank can be accurately estimated by high-speed digital
computation.
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SECTION II
RECOMMENDATIONS
1. The Energy Crisis has brought to the forefront the need for consideration
of the impact that the choice of a particular treatment process has on
energy demands. Rapid application and development of the use of heat
recovery in incineration systems is justified. The full economic and
environmental benefits of such applications should be investigated.
2 . Lime treatment is not a new-untried technology; the environmental
engineering profession should adopt it as one of its standard techniques.
3. As lime treatment techniques advance in their development, this develop-
ment should be documented to expand the data base, especially in the
areas of economics and long-term plant operating data.
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SECTION III
INTRODUCTION
Increasingly, waste treatment systems are being designed to produce effluents of
substantially higher quality than can be obtained by conventional primary or
secondary processes. These new, "advanced waste treatment" systems are
oriented toward the removal of sewage constituents which are not significantly
removed by conventional treatment processes. These advanced waste treatment
systems often incorporate the addition of coagulant chemicals for enhanced
phosphorus, solids, grease or heavy metals removal. Coagulant chemicals that
are commonly in use today include iron (ferrous or ferric) , aluminum (alum or
sodium aluminate) , and calcium (lime) .
Lime is an attractive chemical for utilization in advanced waste treatment systems,
and has been selected as the chemical of choice in a number of situations. In some
locales lime costs may be lower than either aluminum or iron compounds, and lime
sludges are generally easier to dewater than ferric and alum sludges . The use of
lime allows higher surface overflow rates on sedimentation tanks than does an iron
or aluminum salt, and this is an important factor for upgrading existing treatment
plants. In all cases, however, coagulant choice should be based on an engineering
economic evaluation of each alternative.
Lime was used in waste treatment long before the present era of "advanced waste
treatment" (AWT) . An example of this was the Laughlin Process, which was used
during the 1930's and employed lime in a first stage system followed by ferric
chloride in a second stage. Chemical treatment was considered a competitive
process to biological treatment in the 1920's and early 1930's but was supplanted
in later years by refinements of the activated sludge and trickling filter processes
which seemed to be more promising for strictly BOD removal.
Interest in lime treatment rekindled in the 1960's when environmental concern
began to be expressed about other sewage constituents such as phosphorus, heavy
metals and viruses. This concern spawned the present AWT era in the tech-
nology of sewage treatment. The use of lime in the treatment scheme enhances
removals of phosphorus, metals and viruses over that obtained by conventional
primary and biological treatment schemes.
Initial full-scale applications of lime treatment in the AWT era were so-called
"tertiary" applications and followed conventional biological treatment. An example
of such a practice is at South Lake Tahoe. Generally, these applications were
primarily intended for phosphorus removal, but heavy metals, suspended solids
and virus removals were also obtained . In the particular case of South Lake Tahoe,
pH elevation for ammonia stripping was also desired . Some of the later applications
of lime in AWT have integrated lime precipitation into an earlier stage, the primary
stage of the treatment system. In terms of historical perspective, this could be
considered a partial reversion to the chemical treatment systems of the 1920's and
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1930's. The main difference is that downstream processes normally polish the
chemical primary effluent. The advantage gained from moving lime forward from
the tertiary stage is that one or more treatment stages can be eliminated, making
the overall treatment system less complex.
PURPOSE AND SCOPE
This report is basically concerned with the design of treatment facilities where
lime is incorporated in the primary stage of treatment. Tertiary applications have
been well documented in the literature. Examples of primary stage applications
are:
1. Low level lime addition into the primary for phosphorus removal followed
by biological treatment for organic reduction.
2. Moderately high level lime addition into the primary for organic reduction
to permit nitrification in a biological treatment step.
3. Lime addition into the primary, followed by filtration and activated
carbon adsorption.
4. Lime addition into the primary for improved organics, grease, and heavy
metals removal, followed by ocean disposal of the lime clarified effluent.
This review presents design and cost information on lime handling, liquid proces-
sing, solids generation and dewatering, lime recovery and ultimate disposal.
BACKGROUND
Much of the information contained in this manual has been derived from the
experience of Brown and Caldwell, of Walnut Creek, California and Caldwell
Connell Engineers of Melbourne, Australia, gained in the design of four treatment
plants which will employ lime in the primary stage of treatment. Two of these
plants, the Central Contra Costa Sanitary District (CCCSD) plant and the City of
Livermore plant, are located in the State of California and are oriented towards
water reclamation. Two other plants, Canberra and Darwin, are located in
Australia and are oriented towards water pollution control. Practical operating
experience has been gained in full-scale operations in conjunction with the CCCSD
at the CCCSD Advanced Treatment Test Facility (ATTF) !'2 where chemical pri-
mary flows average up to 2.5 mgd. Full scale liquid and solids processing
studies have been conducted at the ATTF . Additional information was compiled
from the literature covering lime use in water and wastewater treatment,
manufacturers data and information data supplied by the Environmental
Protection Agency, and from site visits made during the project. These sources
are specifically referenced where used and summarized in the acknowledgments
section.
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REFERENCES
Horstkotte, G.A., D.G. Niles, D.S. Parker, and D.H. Caldwell. Full-
Scale Testing of a Water Reclamation System. Journal Water Pollution
Control Federation, 46, 181 (1974).
Parker, D.S., K.E. Train and F.J. Zadick. Sludge Processing for
Combined Physical-Chemical-Biological Sludges. Environmental
Protection Agency. Washington, D.C. Report No. EPA-R2-73-250.
July, 1973, 141 p.
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SECTION IV
FUNDAMENTALS OF LIME
DEFINITIONS
Lime is a general term applied to several chemical compounds that share the
common characteristic of being highly alkaline. In the water and wastewater
treatment fields, the term is usually applied to quicklime and hydrated lime.
Both types of lime are frequently used and are readily available throughout the
United States. The definitions given below are intended to clarify the confusing
terminology often found when dealing with different forms of lime. Standard
definitions used in the industry follow.
Limestone is the basic compound from which usable lime forms are derived.
There are two kinds of limestone: (1) high calcium limestone which is almost
entirely calcium; and (2) dolomitic limestone which is a double carbonate mineral
of calcium and magnesium containing 35 to 45 percent of the latter, expressed as
magnesium oxide.
Quicklime is derived from high calcium limestone by a high temperature calcina-
tion process . Quicklime contains about 90 percent calcium oxide, and for this
reason is also called calcium oxide. Two other terms sometimes applied to
quicklime are burned lime and unslaked lime. Quicklime does not react uniformly
when applied directly to water or wastewater but must first be converted to the
hydrate Ca (OH)2.
Hydrated lime or slaked lime is a dry powder obtained by a chemical reaction
that occurs when sufficient water is added to quicklime to satisfy its affinity for
water. This form of lime is also referred to as hydrate. The chemical composition
of hydrated lime depends on the calcium oxide content of the quicklime from which
it is derived. A high calcium quicklime will provide a high calcium hydrated
lime containing 72 to 74 percent calcium oxide and 23 to 24 percent water of
hydration.
Pebble or crushed lime is the most common form of quicklime, and the effective
diameter of the pebbles varies from about 1/4-inch to 2 inches. This lime is
produced mostly in rotary kilns.
Lump lime is the product whose pebbles or lumps range in effective diameter from
eight down to two or three inches. Lump lime is produced in stationary vertical
kilns and is crushed after burning.
Recalcined lime is the product recovered after burning lime sludge from a water
softening or wastewater plant. Calcination takes place in a rotary kiln or any of
several types of furnaces available in the industry. (See Section IX) .
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So far, no standard specifications have been issued for lime to be added to
wastewaters. American Water Works Association (AWWA) Standard B202-54, for
quicklime used in water works, can be followed when specifying lime for waste-
water treatment. Tables 4-1 and 4-2 summarize the main characteristics of lime
chemicals in general, and of quicklime in particular.
LIME IN WASTEWATER TREATMENT
Chemical treatment of municipal wastewaters has been practiced for almost a
century. It is usually employed as a simpler and more flexible alternative to
secondary biological processes, although it is not as effective in removing soluble
organic matter. While chemical treatment has never been widely practiced, it was
found particularly useful when colloidal solids and finely divided suspended
matter could not be removed by plain sedimentation, and coagulants had to be
added to the wastewater. Chemical treatment has found its widest application in
the treatment of industrial wastes, where its flexibility, lower cost and simplicity
of operation and maintenance were all attractive assets to industry. The fact that
some trade wastes are either not amenable to biological treatment or toxic to the
microorganism population has also contributed to the wide application of chemical
treatment in the industrial wastes field.
The advent of AWT processes has brought a new popularity to chemical treatment.
The inability of conventional biological treatment to effectively remove nutrients,
i.e., nitrogen and phosphorus, and other organic and inorganic pollutants, paved
the way for physical-chemical-biological treatment. These combined processes
have put the goal of wastewater reclamation and reuse well within the confines of
present day technology- The use of lime as a coagulant in AWT is due to its well
established efficacy in removing phosphorus from raw wastewaters. Additional
benefits derived from lime coagulation in the primary treatment stage include the
increased removal of organic matter, which decreases the organic load on
subsequent biological processes; the enhanced removal of heavy metals and
viruses; and, as the pH value is raised above 9.5, precipitation of magnesium
as magnesium hydroxide. The addition of lime to raw wastewater is treated in
detail in Section VI.
LIME SLAKING
Slaking is a chemical process which makes quicklime reactive in water and
wastewater. "Slaking" and hydration are synonymous terms from a chemical
standpoint. As used in the lime industry, however, slaked lime is hydrated
quicklime containing considerable excess water. In contrast commercial
hydrated lime is a dry, ultrafine white powder, more concentrated than aqueous
forms of slaked quicklimes; however, chemically both are the same, i.e. hydro-
xides .
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Table 4-1. CHARACTERISTICS OF LIME CHEMICALS
Chemical
Common name
Formula
Quicklime
CaO
Recovered lime
CaO
Dolomitic lime
CaO • MgO
(MgO content
varies)
Hydrated lime
Ca(OH)
Carbide lime
Ca(OH)2
Dolomitic hydrated
lime
Ca(OH), + Mg(OH)
z z
Limestone
(unbumed Itrne)
CaCO_
3
Dolomite
CaCO. • MgCO
Shipping data
Available
forma
Pebble
Crushed
Lump
Ground
Pulverized
Pellets
Pebble
Crushed
Lump
Ground
Pulverized
Powder
(Passes
200 mesh)
Powder
70 - 90%
(200 mesh)
Slurry
Monohydrated
powder
slaked at
atmos. press.
Dihydrate
powder
slaked at
high press .
and temp .
Powder
Granules
Ground
Lump or
crushed
Ground
Powder
Containers
and
requirements
Moisture proof
bags - 80-100
Ib . ; wood bbl . ;
bulk - CA .
Store dry max.
60 days; keep
container
closed.
Bulk delivery
direct from
kiln to
storage bin
Bags, 50-60
Ib.; bulk -
CA; bbl.
Bags - 50 Ib.;
Bbl. - 100 Ib.;
Bulk - C/L
(Store dry)
Bulk
Bags - 50 Ib . ;
Bbl.
Bulk - CA
(Store dry)
Bags - 50 Ib.;
80 Ib.
100 Ib. drums;
Bulk - CA
Bags - 50 Ib.;
Drums
Bulk - CA
Physical and chemical characteristics
Appearance
and
properties
White (light grey,
tan) lumps to
powder.
Unstable, caustic
irritant .
Slakes to hydrox-
ide slurry evolv-
ing heat .
Air slakes to
CaCO
Sat. Sol.
pH 12.4
Light grey, tan
Same properties
as quicklime
Same appearance
and properties as
quicklime,
except MgO
slakes slowly
White, 200-400
mesh; powder
free of lumps;
caustic, dusty
irritant;
absorbs H.O and
CO from air to
form Ca(HCO ) .
Sat. Sol.
pH 12.4
Coarse, grey
powder; grey
slurry (35%
solids)
Tan to white
powder free
of lumps
(-200 mesh);
caustic, dusty
irritant; Sat . Sol .
pH 12.4
White amorphous
powder; Sat. Sol.
pH 9 - 9 . 5
White, grey, tan;
Sat. Sol.
pH 9 - 9.5
Weight
Ib./cu. ft.2
(bulk density)
55 to 75
To calculate
hopper capacity -
use 60;
Sp.G., 3.2-3.4
Pebble, 60-65
Ground, 50-75
Lump, 50-65
Powder, 37-63,
Avg. 60
Sp.G., 3.2-3.4
35 to 50
To calculate
hopper capacity -
use 40; some 20
to 30 - use 23;
Sp. G., 2.3-2.4
35 to 55
Monohydrate
25 to 37;
Dihydrate
27 to 43;
To calculate
hopper capacity -
use 40;
Sp.G. , 2.65-2.75
Powder, 35-60;
Granules, 100 -
115;
Sp.G., 2.65-2.75
87 to 95;
Sp.G. , 2.8-2.9
Commercial
strength
70 to 96% CaO
(Below 88% can
be poor quality)
75 to 90% CaO
CaO -
55 to 57.5%;
MgO -
37.6 to 40.5%
Ca(OH)
82 to 98 %;
CaO -
62 to 74%
(Std. 70%)
95% Ca(OH)2
Monohydrate
Ca(OH) - 62%
MgO - 34%;
Dihydrate
Ca(OH) - 54%
Mg(OH) - 42%
(approx.)
96 to 99%
Varies
Solubility
in water
g/100 ml. @ 25°C
Reacts to form
Ca(OH)
Each Ibf of
quicklime will
form 1.16 to 1.32
Ib. of Ca(OH) ,
with 2 to 12%
grit, depending
on purity.
Same as
quicklime
Slakes to form
Ca(OH)2 slurry
plus MgO, which
slakes slowly
0.18 @ 0°C
0.16 @ 20°C
0.15 @ 30°C
0.077 @ 100°C
Same as Ca(OH)
Same as Ca(OH)
0.0013 @ 20°C
0.002 @ 100°C
Approx. same as
limestone
Reproduced by permission of BIF, a Unit of General Signal Corporation.
' 1 Ib/cu ft = 16 kg/cu m
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Table 4-2. CHARACTERISTICS OF MAIN GRADES OF QUICKLIME1
Grades
High calcium
Medium calcium
Low calcium
Dolomitic
Magnesium
Calcium content
> 88% CaO
75 - 88% CaO
<60 - 76% CaO
51 - 58% CaO
35 - 41% MgO
5 - 35% MgO
Dolomitic lime could also be
classed as a low calcium lime.
Form
Lump
Lump crushed
Pebble
Pellet
Ground
Pulverized
Particle size
3" - 8" and smaller
1/2" - 2 1/2" to dust
1/4" - 1 1/2" and smaller
to dust
20 to 100 mesh
-8 to -100 mesh
+100 to -200 mesh
Burned or
calcined
Calcination temperature degrees F
Slaking characteristics
Soft
Normal
Over
Hard
Calcined Just above the decomposition
temperature necessary—1,800 to 2,400°F
in a minimum time.
Calcined at about 2,400 to 2,600°F in a
minimum time.
Calcined at 2,500 to over 2,600°F. If
lower, then time would be longer.
Calcined above 2,600°F. If at a lower
temperature, time would be longer.
Very quick slaking and
temperature rise
Fast to medium slaking
and temperature rise
Medium to slow slaking
and temperature rise
Slow to very slow slaking
and temperature rise
Reproduction by permission of BIF, a Unit of General Signal Corporation.
Time of calcination, type of kiln, composition of limestone and the composition
of the surrounding atmosphere (CO2 content in kiln), are all factors in the type
of burned lime produced, as to reactivity, etc. At a lower ratio (say 2.5 - 1)
reaction could be quicker or at least similar. Air slaking will increase slaking
time and decrease the temperature rise.
Depending upon the proportions in which quicklime and excess water are com-
bined, the hydration process can yield a milk-of-lime, a lime slurry, or a viscous
lime paste of varying degrees of consistency. As will be seen later, the different
types of slaked lime lend their names to the mechanical equipment used to mix
quicklime and water. Predictably, this type of equipment is called a lime slaker
and it is described in Section V.
10
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Lime slaking provides two available hydroxyl ions that react readily. The
process is exothermic, i.e., appreciable heat is emitted during the chemical
reaction. The progression from limestone to slaked lime is shown below.
Limestone
Heat
Calcination
Carbon dioxide
CaCO,
+
At
I
CO.
Quicklime
Quicklime
+
Water
Slaked lime
Slaking (Hydration)
CaO
CaO
H20
Ca(OH)2
Heat
At
Several variables influence the required slaking time and quality of the resulting
hydrated lime. The National Lime Association lists the following:
1. Reactivity of the quicklime: whether the quicklime is hard, soft, or
medium burned will influence the speed of slaking and temperature
attainment.
2. Particle size and gradation of quicklime: whether the quicklime is lump,
pebble, ground, pulverized, or run-of-the-mill gradation is important.
The finer sizes of the same quality slake most rapidly.
3. Optimum amount of water: whether too much or too little water is used.
Limes vary in their optimum water: lime ratio.
11
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4. Temperature of water: whether slaking water is too cold or possibly
too hot (steam) for the particular slaking conditions can affect the
product.- Slow reacting limes need heated water; reactive limes do not.
5. Distribution of water: the manner in which water is introduced into the
slaking chamber is a factor, and an even flow is desired.
6. Agitation: too vigorous or insufficient agitation of quicklime and water
is undesirable. Some agitation is necessary.
The standard tests to determine the optimum slaking conditions for a given type of
quicklime are AWWA B-202-65 and ASTM specification C110 on Physical Tests of
lime. The reactivity of quicklime in water is expressed as the number of minutes
required for a temperature rise of 40 degrees Centrigrade (104 F) . Reactivity is
classified as follows:
High-reactivity lime will show a 40 C temperature rise in 3 minutes or less
and will complete the reaction within 10 minutes.
Medium-reactivity lime will show a 40 C temperature rise in 3 to 6 minutes
and will complete the reaction in 10 to 20 minutes.
Low-reactivity lime will require more than 6 minutes to show a 40 C
temperature rise and will require more than 20 minutes to complete the
reaction.
Under AWWA B-202 the particular quicklime will be rejected if the sample tested
fails to produce more than a 10 C (50 F) rise in temperature in 3 minutes or fails
to reach the maximum temperature in 20 minutes when slaked under test conditions
It should be pointed out that these rules are applicable to commercial grades of
quicklime and are not intended to cover recalcined limes. The standard test has
aroused considerable controversy. A leading manufacturer of paste-type slaking
equipment has the following comments:
"This test is intended to predict the slaking characteristics of quicklime. It
is obviously slanted toward the slurry slaker approach, as it uses a 4: 1
water: lime ratio. We question its value. As an example, an oyster-shell
lime barely qulified as a low-reactive lime. When the water was reduced to
a 2: 1 ratio, it qualified as a medium-reactive lime. When repeated at 120 F,
it reacted almost violently. This same lime is being successfully slaked in
a paste slaker."
The effect of water temperature and water-lime ratios on the slaking process will
be further discussed when describing lime slakers in (Section V) .
12
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SELECTION OF LIME
As mentioned earlier, quicklime and hydrated lime are frequently used in water
and wastewater treatment. Which type to use in a particular situation is influenced
by a number of factors, such as scale of operation, method cost, transportation
cost, and availability. Material cost depends on whether bagged or bulk lime,
hydrated or quicklime is used. The choice between purchasing lime in bags or
in bulk is a direct function of rate of use. Where chemical requirements are small,
bagged lime is preferred. Conversely, at the larger treatment plants it is more
efficient and economical to handle bulk lime. More details about lime delivery
and handling will be given in the next chapter.
The selection of quicklime or hydrated lime also depends on economics and avail-
ability. The cost of hydrated lime is about 30 percent greater than the cost of a
quicklime with the same calcium oxide content. The difference is due to the higher
production cost of the former and to higher transportation charges; on the other
hand, the capital cost of the slaking equipment required when quicklime is used,
will tend to offset the savings in material cost. The source of supply and its
relation to transportation costs also play an important role in determining whether
quicklime or hydrated lime should be selected. Other factors to consider are
storage space available at the treatment plant, plant process layout in relation to
storage location, material handling problems, and the storage requirements of the
two types of lime.
In analyzing the factors discussed above, the National Lime Association offers the
following comments:
1. Where lime consumption is small, such as 50 to 1,000 Ib/day, i.e., 1 to
20 50-lb bags, bagged hydrated lime is clearly indicated. Probably this
limit could be extended to 1,500 Ib/day, but at this point, if lime is being
consumed seven days a week, consumption will reach 22^ tons/month.
Then, the economy of truck load bulk shipments of 15 to 20 tons starts to
become attractive. But then bulk silo storage and unloading facilities
may have to be purchased and installed. If headroom is unavailable for
a silo and there is ample ground floor space for storing bags, then the
use of bagged hydrate may be justified up to 2,000 Ib/day or even more.
2. With respect to bulk lime, hydrate is generally indicated up to 3 to
4 tons/day (100-125 ton/month) over quicklime. At this point the
inherent economy of quicklime, in spite of slaking expense, should be
considered. Again, due to peculiar plant conditions the use of hydrate
up to 200 tons/month may be warranted; however, above this figure it
is quicklime's province. Many of those plants that use quicklime in the
lower ranges suggested for hydrate may be saving little or nothing due
to greater losses of lime through air slaking and recarbonation. This is
particularly true if the quicklime is highly reactive, of small particle
size, and is used under humid conditions. Hydrate is more stable and
stores better.
13
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'j5 u6 ^S! W^th m°St en9ineering decisions, selection of the type of lime to be
used should be based on a detailed economic analysis, taking into account all the
factors just mentioned. Table 4-3 summarizes the characteristics of quicklime
and hydrated lime.
Table 4-3. CHARACTERISTICS OF QUICKLIME AND HYDRATED LIME
Formula
Molecular Weight
Physical State
Particulate Size
Bulk Density, Ib/cu ft
Specific Gravity
Affinity for Water
Solubility
Stability in Bagged Storage
pH of Saturated Solution
Quicklime
CaO
56.1
White solid
Pulverized to lump
55 to 75
3.-2 to 3.4
Reacts quickly to form
Ca(OH)2 with heat of
formation, 490 Btu/lb.
Slightly, varies inversely
with temperature
In multiwalled bags, max.
60 days
12.4
Hydrated Lime
Ca(OH)2
74.1
White solid
Power, 200 to 400
mesh
35 to 50
2.3 to 2.4
Absorbs H2O and CO2
from air to form
CaCo3
Slightly, varies inversely
with temperature
Up to 6 months.in dry
tight bags
12.4
14
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SECTION V
HANDLING OF LIME
LIME DELIVERY
Lime can be delivered either in bags or in bulk. The choice between these two
forms depends mostly on the rate of chemical use at the treatment plant. Bagged
lime is delivered in truck or rail car. Once at the treatment plant, the bags are
transferred by hand truck, fork lift, or overhead crane to storage. When a large
number of bags are used, it is advantageous to purchase lime in palletized ship-
ments and use fork lift trucks to take the pallets to storage. In addition to saving
space and labor, this procedure also minimizes bag breakage. Other methods of
handling bagged lime will be reviewed when discussing in-plant transport
practices . When lime use justifies bulk shipments, delivery can be made by
using covered hopper railroad cars, container and box cars, and a variety of
specially designed trucks. Bulk delivery offers many advantages: lower initial
cost; faster unloading; reduced labor cost for handling; elimination of losses due
to torn bags and spillage; and improved safety, operating, and housekeeping
conditions.
The method of transport to the plant is based primarily on economics. When
railroad access is feasible and the rate of use justifies the cost of railroad siding
and unloading facilities, delivery by rail is usually cheaper since a railroad car
has three times the load carrying capacity of a bulk truck. The CCCSD water
reclamation plant-1- includes a complete in-plant railroad system connected to the
Atchison, Topeka and Santa Fe railway mainline. Three chemical unloading
platforms are being provided to unload lime, chlorine, ferric chloride, methanol,
and carbon dioxide.
Where a railroad siding is not practical or the distance from the shipping point is
relatively short, a.trailer truck is a fast and economical way to deliver bulk ship-
ments. Unlike rail cars, trucks can have access to nearly all areas within the
treatment plant; therefore, there is more flexibility in selecting the location for
storage. Also, the length of unloading lines can be kept at a minimum by parking
trucks close to the storage facilities. The pneumatic truck is available in two
basic designs. The more widely used is the self-unloading type, in which con-
veying air is supplied by a positive displacement blower mounted on the trailer.
Lime is blown from the truck directly to storage through a 4-inch pipeline. The
second type of pneumatic truck requires an external souce of compressed air, or
a separate mechanical conveyor system, to transfer lime to storage. Blower
trucks are available in capacities varying from 20 to 36 cu m (700 to 1,300 cu ft) .
The latter can deliver up to 20 tons of hydrated lime and 24 tons of quicklime. 2
The larger capacities are accommodated by dividing the trailer into compartments,
each provided with a sloping or hoppered bottom to facilitate material outflow.
Further details on truck design an available in the literature.
15
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LIME UNLOADING AND STORAGE
Unloading bagged lime is a simple operation and was previously described under
Lime Delivery. The following storage precautions are recommended by the
National Lime Association:
"Storage areas for bagged materials must be covered to prevent rain
from wetting the bags. Hydrated lime is normally packed in multiwall
paper bags which are not resistant to free water or humid air. Quicklime
is also packaged in multiwall paper bags, one or more of the plies moisture
proofed. This moisture proofing is effective in preventing the entrance of
humid air but is not usually designed to be effective against liquid water.
This is particularly true at the valve where humid air or liquid water may
enter more readily and start slaking the lime; and the heat and swelling
will cause the bags to burst. Hence, quicklime storage must be designed
to avoid any accidental contact with water. As an example, in one storage
warehouse, a good tight roof was provided, but the bags were stored close
to the door. This door was inadvertently left open a few inches during a
driving rain which wetted the bags at the bottom of the pile. These broke
open and the pile collapsed, resulting in an expensive clean-up operation
together with considerable loss of lime. Because of the heat generated in
accidental slaking of lime, bagged quicklime should never be stored
adjacent or too close to combustible materials."
"Hydrated lime may be stacked as much as twenty bags high without
injuring the bottom bags (higher when palletized) . In dry storage,
hydrate may be stored for periods up to one year without encountering
serious deterioration. When stored for extended periods, a slight
increment of carbon dioxide may be found at the corner of the bag near
the valve. This carbonation during storage is usually evident only after
storage for at least sbc months and then does not penetrate more than
about one-half inch into the bag near the valve."
"Quicklime will deteriorate in storage at a much more rapid rate than
hydrated lime. Under good storage conditions, with multiwall moisture
proofed bags, quicklime may be held as long as six months, but in
general should not be stored over three months. Care should be
exercised to use the material in the order it is received, rather than
maintain an inactive reserve stock which may not be consumed for
several months."
Bulk shipments of lime can be unloaded from rail cars or trailer trucks by
mechanical or pneumatic equipment. The latter method has gained wide accept-
ance because of its simplicity and high unloading speed. Either system can be
used to unload lime when effective particle diameters are smaller than 2^-inch
(6.4 cm) but H-inch (3.2 cm) or smaller is preferable for efficient pneumatic
conveying.2
16
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Mechanical handling usually involves several steps. Lime is first transferred
from delivery car or truck into a receiver hopper. From this hopper, some type
of conveyor (screw, belt, etc.) is used to feed the material to the elevating
equipment (bucket elevator, screw-lift, etc.) which finally discharges it into the
storage bin or silo. The basic equipment can be arranged in a variety of ways to
suit each particular situation, e.g., an inclined screw conveyor can be used to
transfer lime directly from receiving hopper to storage bin when headroom is
available and the silo is of limited height. Table 5-1 gives information published
by the National Lime Association for preliminary sizing of mechanical conveyors
and elevators. Mechanical handling of lime will be discussed in more detail under
In Plant Transport Methods .
Table 5-1 . SIZING DATA FOR SCREW CONVEYORS AND BUCKET ELEVATORS
Screw Conveyor Data
Screw size
(inches)
6
9
12
16
Normal rpm
50
50
50
50
Tons quicklime
(per hour)
2 - 2-1/2
7-8
15 - 20
45 - 50
Bucket Elevator Data
Bucket size
(inches)
6x4
8x5
10 x 6
12 x 7
14 x 7
Bucket spacing
cm
33
41
46
46
48
inches
13
16
18
18
19
Speed
m/min
69
70
82
93
110
ft/min
225
230
270
305
360
Tons quicklime
(per hour)
8-10
15 - 20
30 - 35
58 - 65
50 - 60
17
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Lime unloading which uses pneumatic conveying equipment usually results in a
simpler and more flexible arrangement than that obtained by mechanical con-
veyors. Dusting, a common occurrence around lime unloading operations, is
reduced to a minimum and can be completely eliminated where a negative pres-
sures system is used. These advantages have to be weighted against greater
power requirements for pneumatic than for mechanical conveying systems of
equal capacity. Safety considerations also favor the pneumatic approach, since
there are no moving parts and, therefore, no risk of injury to the operator. The
pneumatic conveyor transports material in suspension by means of a high velocity
air stream. For quicklime and hydrated lime, this velocity varies from 914 to
1520 meters per minute (3,000 to 5,000 fpm) . The higher values are required to
blow quicklime because of its higher bulk density (880-960 kg/cu m or 55-60 lb/
cu ft) than pebble quicklime bulk density (400-560 kg/cu m or 25-25 Ib/cu ft) for
hydrate.
Two types of in-plant pneumatic systems are commonly used to unload dry
chemicals: negative pressure (vacuum) and positive/negative pneumatic con-
veyors. The equipment is commonly provided as a package. The lighter units
can be mounted on skids, casters, or wagon type trailers when the application
calls for a portable unit. The higher capacity unloading systems are normally
stationary. The negative pressure unloading system consists of an intake nozzle,
a receiver-separator, a vacuum pump, accessories, and interconnecting piping.
To unload a rail car or truck, the intake nozzle is attached to the vehicle hoppers
through quick-opening couplings. The intake assembly is usually mounted on a
skid base to facilitate handling. Lime is drawn directly into the conveying line
by air flow under the suction created by the vacuum pump. The air stream then
conveys the fluidized material to the receiver-separator (usually a bag-type
filter) . In the filter receiver lime separates from the air by cyclonic action, drops
to the cone shaped bottom and is discharged to the storage silos through a rotary
valve feeder. Conveying air is cleaned as it flows through the filter bags and,
after passing through the vacuum pump, is exhausted to the atmosphere.
Vacuum systems are limited to operating pressures of 25 to 30 cm of (10 to 12 in.)
Hg below atmospheric pressure and by the number of storage bins which can be
filled from a single receiver-separator. When pressure losses exceed 30cm
(12 in.) Hg, or when lime is stored in a large number of silos, a positive/negative
pneumatic conveyor is required .
Positive pressure conveyors are normally used when material must be delivered to
several separated storage bins located at considerable distances from the delivery
station. In a positive pressure system, the conveying stream is created by the air
discharged from a blower, and this air "pushes" the solids through the conveying
line. Normally, a rotary positive displacement unit or, less frequently, a cen-
trifugal blower is used. Most positive pressure systems operate within the range
of the positive displacement blower or up to 1.05 kg/sq cm (15 psig)
18
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A positive/negative pressure pneumatic conveyor has certain features of the
vacuum system and the distribution flexibility of the positive pressure system.
A vacuum system can be converted to a combination system by connecting the
vacuum pump exhaust pipe to the rotary valve feeder of the receiver-separator.
Thus material collected in the separator is discharged into a positive conveying
line. The rotary valve acts as an air lock between the negative and positive sides
of the system. Material is then distributed to the storage bins through individual
feed lines or through a series of two-way diverter valves. A typical positive/
negative pneumatic conveyor is shown in Fig. 5-1.
Quicklime and hydrated lime can be stored in hopper-bottom concrete or steel
facilities since both are noncorrosive materials. The interior of storage vessels
should not be painted to avoid the possibility of product contamination. Storage
bins or silos must be airtight to prevent air slaking caused by the moisture con-
tent of atmospheric air. In this respect, hydrated lime is more stable than
quicklime when stored for extended periods. There are some differences between
quicklime and hydrated lime which must be considered in designing the storage
facilities. Quicklime lime is generally free-flowing and will discharge readily
from storage bins if the hopper bottoms have a minimum slope of 60 degrees from
the horizontal. This value is related to the angle,of repose of quicklime which, on
the average, can vary between 50 to 55 degrees. Nevertheless, it is considered
good practice to provide some type of flow-aiding device to regulate material dis-
charge under all conditions. Hydrated lime, on the other hand, has a tendency to
arch because of its physical characteristics and much smaller particle size.
Therefore, more elaborate mechanical or aeration activators are necessary to
insure a continuous discharge of material from storage. Detailed descriptions of
the various types of devices commonly used to facilitate free flow of material from
storage can be found in references 2 and 4.
Sizing of storage facilities should be based on daily lime demand, type and
reliability of delivery, future chemical requirements, and flexibility of expansion.
A minimum sufficient storage should be provided to supply a 7-day lime demand,
however, sufficient storage to supply lime for 2 to 3 weeks is desirable. In any
case, the total storage volume should be at least 50 percent greater than the
capacity of ±he delivery rail car or truck to insure adequate lime supply between
shipments. Average bulk density values used in structural design are 640 kg/
cu m (40 Ib/cu ft) for hydrated lime and 960 kg/cu m (60 Ib/cu ft) for quicklime.3
LIME FEEDERS
The term feeder, as used in this report, refers to the mechanical devices employed
to continuously deliver a measured amount of dry lime to the mixing equipment.
Solution feeders are mostly limited to the smallest treatment plants, where bagged
hydrated lime is handled and process lime is prepared in batch or intermittent
form.
There are two basic types of dry chemical feeders: volumetric and gravimetric.
Each type is in turn available in a variety of designs and models, according to
the preferences of equipment manufacturers. Regardless of type, all dry feeders
share two essential components:
19
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DUST COLLECTOR
FILTER -
RECEIVER
ROTARY
AIR LOCK
TYPICAL
DIVERTER
VALVE
INTAKE MANIFOLD
BLOWER AND MOTOR
MATERIAL
UNLOADING NOZZLE
Figure 5-1 Typical positive-negative pneumatic conveying system
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1. A day storage hopper, where material is transferred from the lime silos
to provide a uniform supply to the feeding element. This hopper has a
contracting bottom through which the chemical flows by gravity.
2. An adjustable feeding element to vary the rate of chemical feed. The
feed rate is controlled by volume (volumetric feeder) or by weight
(gravimetric feeder) .
When hydrated lime is used, a solution tank is frequently added to mix lime with
water and form a slurry, which is then fed to the process. If quicklime is used,
the solution tank is replaced by the slaking equipment.
Day Storage Hoppers
The capacity of the day hopper should be sufficient to store no less than eight
hours' supply at the maximum feed rate. In most cases, the hopper bottom slopes
at least 60 degrees. This angle would normally assure free flow of quicklime
independent of particle size. On the other hand, hydrated lime will tend to
arch or bridge, even if the bottom slope is steeper than 60 degrees. Closely
related to bridging is the phenomenon of flooding which occurs when an arch of
material suddenly collapses and inundates the feeder. Various types of agitating
devices are used to prevent arching. Several manufacturers of chemical feeders
(Bif, Infilco, Wallace & Tiernan, among others) incorporate paddle type (internal)
or pulsating diaphragm type (external) agitators as part of their feeding equip-
ment. When the storage hopper is not included with the feeder, three general
classes of agitators are available: electromagnetic or electromechanic vibrators
as manufactured, by Eriez, Jeffrey, Syntron and others; aerators (air pads and
air diffusers) , as manufactured by Airnetics, Bibco, National and others; and
the live-bottom bins originally developed by Vibra Screw. Regardless of their
operating principle, agitators aim at promoting the flow of bulk materials that
tend to pack in storage containers. It is critical to stop agitation when the feeder
is not in use, since continuous vibration could actually defeat its purpose by
deaerating the material and increasing its density (packing) .
The flood prevention device most commonly used is the rotary vane inlet valve
which allows only a fixed amount of material to discharge from the storage hopper
at any given time. The rotary valve is also utilized as a volumetric feeder.
Volumetric Feeders
Volumetric feeders deliver a constant, preset volume of chemical regardless of
changes in material density. The accuracy of the volumetric feeder is closely
related to the physical characteristics of the chemical and is greater for uniform,
cohesive materials which tend to flow readily. On the other hand, this type of
feeder is less reliable when the density of the material handled varies. Varia-
tions in density can be compensated by recalibrating the feeder whenever a
change occurs. Nevertheless, in the case of hydrate and quicklime, which
exhibit wide variations in bulk density, the error of a volumetric feeder is
normally in the 5 percent range by volume.
21
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Most volumetric feeders operate on the principle of displacing a predetermined
volume of chemical from the point where it leaves the storage hopper to the point
of material discharge. The method used to move the material can be a travelling
(Wallace & Tiernan) or vibrating (Vibra-Screw) belt; a screw-type feeder (BIF,
Vibra-Screw W&T); an oscillating throat at the base of a hopper (BIF); a roll-
type feeder (W&T); a rotary vane or paddle (BIF); or a vibrating feeder _
(Syntron) Although a few other types of volumetric feeders are still found in
treatment plants,2 the types listed above are the most frequently used._ The
screw or helical conveyor appears to have gained wide acceptance in lime feeding
applications and each of the leading manufacturers offer several modifications of
the basic configuration. A screw feeder is a positive displacement device that
delivers a constant stream of chemical from the storage hopper. Feeder capacity
can be varied by simply adjusting the speed of the screw shaft. Fig. 5-2
illustrates a typical screw type feeder. The capacity range of volumetric feeders
varies widely from as low as 6 to 1 for the roll-type, which is driven by a con-
stant speed motor, up to 200 to 1 for a screw feeder which is equipped with
variable speed drive. For best results, lime feeders should be selected to
operate in the 40 to 1 range. Volumetric feeders are considerably cheaper than
the gravimetric type, therefore their application can be justified when only
limited funds "are available or when greater chemical feeding accuracy is not
required.
Gravimetric Feeders
A gravimetric feeder is indicated when chemical dosage must be accurately and
reliably measured. In this type of feeder, the quantity of material discharged in
a unit of time is continuously weighed and the speed of operation automatically
adjusted to maintain a constant weight. Consequently, feeder accuracy is not
affected by changes in bulk density and variations in particle size. Despite its
higher first cost, a gravimetric lime feeder is often warranted, even for small
treatment plants. Apart from eliminating the need for recalibration, savings in
chemicals are frequently achieved due to greater feeding accuracy and reliability,
i.e., operation and maintenance costs are reduced.
Gravimetric feeders are available in three types: pivoted belt, rigid belt and
loss-in-weight hopper. The two belt types include an endless traveling belt
conveyor supported on weighting scales, a counter-weight assembly to balance
the load on the belt and controls to automatically adjust the rate of feeding. The
loss-in-weight type uses the loss of weight in a hopper, rather than the
instantaneous weight on a belt conveyor, to adjust the material feed rate. Belt
type gravimetric feeders are available from a number of manufacturers including
BIF, Jeffrey, Syntron, Vibra-Screw and W&T. Flow of material is normally
regulated by throttling an inlet gate located in the passage between storage
hopper and belt; by changing the speed of a rotary inlet valve, or by changing
the belt speed. Control action can be achieved by mechanical, pneumatic,
electric or electronic means. Fig . 5-3 shows a typical gravimetric feeder.
22
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Ul
MOTOR
GEAR REDUCER
FEED RATE REGISTER AND
FEED ADJUSTING KNOB
SOLUTION CHAMBER
HOPPER
ROTATING AND
RECIPROCATING
FEED SCREW
JET MIXER
DWG. NO. 1643
Figure 5-2 Typical screw type volumetric feeder (courtesy of Wallace & Tiernan,
division of Pennwalt Corporation)
-------
Figure 5-3 Typical belt type gravimetric feeder (courtesy of Wallace & Tiernan,
division of Pennwalt Corporation)
-------
The standard capacity range of a gravimetric feeder (10-100 to 1) can be greatly
increased by combination of control modes or the addition of equipment options.
For instance, Wallace & Tiernan inlet gate or rotary valve control (10 to 1 range)
can be combined with a variable belt speed control (20 to 1) for a combined range
of 200 to 1. This can be further increased by adding a 10 to 1 gear box for a
resultant capacity range of 2000 to 1. The loss-in-weight type, developed by
BIF, is electronically controlled and has a capacity range of 10 to 1. Most
manufacturers of gravimetric feeders will guarantee a minimum accuracy of
within + 1.0 percent, by weight, of the set rate. For uniform and free flowing
materials, the error can be reduced to + 0.25 percent.
DISSOLVING OF LIME
As indicated previously, before a measured amount of lime is fed to water or
wastewater, it is first mixed with water either in a dissolving tank (hydrated
lime) or in a slaker (quicklime) . In each case, mixing of lime and water is done
for different reasons. Hydrated lime is prewetted to facilitate transport to the
point of application and improve dispersion and efficency after it is added to the
process. In general quicklime does not react uniformly with water and therefore
should never be applied dry. The only exception would be a high calcium, soft
burned quicklime of small particle size and uniform grading. (The most common
form of commercial lime is the crushed or pebble type, which ranges in effective
partial diameter from about 2 to 1/4 inches) .
Lime Dissolvers
Both volumetric and gravimetric feeders handling hydrate can be readily fitted
with dissolving or solution tanks. Dissolvers are often supplied as part of a
packaged feeder-solution system. Dissolvers are usually sized to provide three
to five minutes of detention at the maximum rate of feed. Concentration of lime
solution is usually kept at or below 6 percent. Mixing and agitation is
accomplished by water or compressed air jets at a minimum pressure of 2.8 kg/
sq cm (40 psi) or by mechanical agitators. Depending on the solution tank
size, one or two impeller type agitators are provided to effect a more rapid and
thorough mixing of lime and water. Due to the noncorrosive properties of lime
solutions, dissolving tanks are usually made of steel.
Lime Slakers
A lime slaker is used to add water to quicklime and accomplish the slaking
reaction. Two basic types of slakers are available: detention type which pro-
duces a lime slurry, and pug mill or paste type which produces a viscous, paste-
like product. Both types are provided with dilution tanks to lower the concentra-
tion of slaked lime to that of a milk-of-lime (thin slurry) . They also include grit
removal equipment, vapor and dust separators, and thermostatic controls for
personnel safety.
25
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The major difference between the two types of slakers rests in the ratio, by
weight, in which water and lime are mixed. In detention slakers this ratio
averages 3i to 1 on a weight basis, while in paste slakers, the proportion of
water to lime is about 2 to 1. In mixing water and quicklime, two extreme con-
ditions should be avoided. When too much water is added, i.e., water-lime
ratios in excess of 6 to 1, the surface of the material hydrates rapidly forming
a coating which hinders water penetration to the center of the particle disintegra-
tion. This reaction is commonly called "downing" and results in delayed or
incomplete slaking and coarser hydrate particles. Downing is more likely to
occur when cold slaking water is used. On the other hand, if insufficient water
is added, "burning" will occur as a result of excessive reaction temperature
(120-260 C) . Some slaking water escapes as steam and this loss will leave a
considerable portion of particles unhydrated.
Dentention Slakers - The detention type slaker is manufactured in the
United States by BIF and Dorr-Oliver at the present time. The BIF unit is divided
in two, three, or four compartments, depending on slaker capacity and detention
time needed for complete hydration. Quicklime is fed continuously to the first
compartment where water is added and the mixture blended by a propeller-type
agitator. The lime slurry formed overflows into the second compartment where
the slaking process is completed. Mechanical agitation is provided to promote
hydration by continuously exposing lime particles to moisture. In case a third
and fourth slaking compartment is required, the principle of operation is the same
and each additional compartment will be equipped with a separate agitator. From
the last slaking compartment the hot slurry overflows into a separation chamber
where it is further diluted and agitated by water jets to promote settling of grit
particles. In the large capacity models, i.e., above 450 kg/hr (1000 Ib/hr) , a
helical screw, driven by an electric motor, is recommended for continuous
removal of grit. Below 1000 Ib/hr (450 kg/hr) grit removal is done manually.
Finally, the milk-of-lime slurry flows over a weir into the outlet. Fig. 5-4 shows
the BIF detention slaker .
Due to the higher water-to-lime ratio, a detention type slaker operates at a much
lower temperature than a paste slaker; consequently, the slaking process requires
a longer retention time to reach completion (about 20 to 30 minutes as compared to
5 to 10 minutes for paste slakers) . To accelerate the hydration reaction, the body
of a detention slaker is insulated to reduce heat losses. A coil type heat exchanger
is also offered as an option to preheat the slaking water by recovering some of the
heat of hydration from the mixing compartment. If hot water is available, it can
be blended with slaking water to obtain a desirable process temperature of 77-
88 C . It should be pointed out that the ideal slaking temperature is closely related
to the reactivity of quicklime. If the material handled is a quick reacting lime
("soft" burned) , water at ambient temperature would still produce quick slaking
and temperature rise. Conversely, "hard" burned quicklime would normally
slake very slowly and the addition of cold water will tend to further delay the
reaction.
26
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ro
LIME FEEDER
ACCESS COVER
GRIT
REMOVER
HEAT EXCHANGER
(OPTIONAL)
FEEDER
INLET
WATER
CONTROL
DISCHARGE
WEIR
MIXER
DUST AND
VAPOR
REMOVER
DILUTION WATER
Figure 5-4 Typical detention type slaker (courtesy of BIF, a unit of General Signal Co.)
-------
Several methods can be used to control the supply of slaking water. Manual
control is the simplest and can be used when the rate of lime feed is fairly constant.
As will be seen later however, feeder operation is often controlled by variables
such as wastewater flow and pH; then the amount of water of hydration has to be
adjusted accordingly to maintain the required water-to-lime ratio.
Paste Slakers - Paste type slakers are manufactured by Wallace & Tiernan and
Infilco. The design and operation principle of these units are very similar so the
description now given applies to both. The slaker body is divided into two com-
partments . Quicklime and water are fed continuously to the inlet end of the
slaking compartment in a ratio of approximately 2 to 1 (water to quicklime) by
weight. The lime-water mixture is thoroughly mixed and moved to the discharge
end of this compartment by two sets of counter-rotating (pug mill) paddles. The
mixing paddle shafts are driven by a gear reduction unit. The torque exerted on
the gear reduction unit controls the hydration water supply through a torque
actuated valve. An increase in torque, indicating an increase in viscosity of the
paste, opens the water valve and admits additional water to the inlet end of the
slaking compartment. High consistency of the paste is maintained to carry grit
and inert material through the slaking compartment. When it reaches the end of
the first compartment, slaked lime flows over a weir and drops into the grit
removal compartment. As it moves over the weir, the heavy paste is broken by
water jets and diluted to a lime slurry. Water-to-lime ratio of the slurry varies
with changes in slaker input, since the supply of dilution water is normally
constant. Once in the second compartment, rakes attached to the same shaft as
the mixing paddles agitate the slurry to keep the lime particles in suspension.
The slurry then flows under a dust shield and over a weir to the discharge port
in the slaker. An external grit conveyor is attached to the discharge compartment.
A classifier is provided in the bottom section of the grit conveyor for separation of
the grit from the slaked lime. Water is applied in the grit conveyor to continuously
wash lime from the grit particles. Fig. 5-5 shows the Wallace & Tiernan paste
slaker.
Because of the low water to quicklime ratio, more heat is generated during the
slaking reaction in a paste slaker than in a detention type unit. Therefore the
former operates at higher temperatures (190-210 F) and shorter detention times.
The high operating temperature also eliminates the need to insulate the slaker
body. The lower detention time required by the paste slaker results in a more
compact design of this unit as compared with a detention type slaker of the same
capacity.
IN-PLANT TRANSPORT METHODS
In the small treatment facility using bagged hydrated lime, in-plant handling is
commonly limited to taking bags from storage, either manually or with the aid of
a hand truck or fork lift, and emptying them into the storage hopper of the
chemical feeder. To facilitate bag dumping, day hoppers can be equipped with
a filling canopy which includes a bag splitter, a screen and a dust collector. As
both the treatment plant size and the chemical requirements increase, the methods
of transporting lime become more elaborate. In-plant transport systems can be
divided into two general groups: mechanical and pneumatic.
28
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QUICKLIME
\Q
TORQUE CONTROLLED WATER VALVE
DUST SHIELD
RIT DISCHARGE
PADDLES DILUTION CHAMBER
SLAKING COMPARTMENT SLURRY DISCHARGE SECTION
CLASSIFIER
GRIT ELEVATOR
WATER FOR GRIT WASHING
Figure 5-5 Typical paste type slaker
(courtesy of Wallace £ Tiernan, division of Pennwalt Corporation)
-------
As was mentioned before, mechanical conveyors require less power to operate
per ton of solids handled than pneumatic conveyors, and therefore the type of
transport system to use is a matter of careful evaluation. It is common to combine
pneumatic and mechanical units and retain the best features of each method to
achieve flexibility, reliability and economy of operation.
Mechanical Transport
In-plant mechanical transport systems include a variety of conveying devices
used to move material from one point to another which is at either the same or a
different elevation. Mechanical conveyors and elevators were briefly discussed
under lime unloading methods. They find further application where chemicals
have to be transferred from storage to the point of usage. Where lime recalcination
is practiced, mechanical conveyors can be used to return the reclaimed product to
storage and also to transport the inert ash to a loading area prior to final disposal.
Of the various types of conveying and elevating equipment found in industrial
plants, only a few have been used in water and wastewater treatment plants. Belt
and screw conveyors, bucket elevators, Screw-Lifts, and combination conveyor-
elevator (Bulk-Flo) are the types most commonly seen in municipal applications.
Belt conveyors are the most versatile and widely used type of mechanical conveyor
They can transport dry materials over paths beyond the capability of any other con-
veying device. However, belt conveyors are not recommended for the transport
of lime, particularly hydrate or reclaimed lime, because of dusting. The dust
problem can be solved by adding covers over the conveyor and an exhaust air
system to collect the dust. This configuration however, eliminates some of the
basic advantages of the belt conveyor concept and there are simpler ways to
approach a dusting situation .
Screw conveyors are one of the oldest and simplest methods of handling granular
materials which exhibit noncorrosive and low abrasion characteristics . The basic
screw conveyor is compact and can be mounted in horizontal and inclined positions.
This versatility is particularly advantageous in congested locations, when the
distance does not exceed about 60 meters (200 feet) , and the slopes are not greater
than about 35 degrees. Preliminary sizing information for screw conveyors has
been given in Table 5-1.
Bucket elevators are widely used to elevate bulk materials. Bucket elevators are
available in two types: chain-mounted and belt-mounted, and the latter is used
when handling abrasive materials . Data for preliminary sizing of bucket elevators
has also been given in Table 5-1.
The Screw-Lift is a vertical screw conveyor installed in a dust proof enclosure.
The unit is compact and it is used to elevate both granular and pulverized
materials. The Screw-Lift is normally fed by a horizontal screw conveyor, and
therefore it could also be considered as a combination conveyor-elevator.
Bulk-Flo is an enclosed elevator and conveyor which can carry bulk materials in
horizontal, vertical or inclined positions. This flexibility can then be used to
replace several straight line conveyors with a single unit.
30
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Mechanical material handling is a specialized field and the final design of a
mechanical system for in-plant conveying of lime should be done in consultation
with the equipment manufacturers. Rexnord (previously Rex Chainbelt) and
Link-Belt are two companies in the wastewater treatment field with extensive
experience in materials handling .
Pneumatic Transport
The basic types of pneumatic transport systems were described earlier under the
section entitled Transport Methods. Pneumatic conveying can also be used for
in-plant lime transport. This approach becomes more advantageous as the size of
the plant increases and chemical processes become more sophisticated. Pneumatic
conveying is probably the only streamlined means of moving chemicals in a large
treatment facility where the process areas are interconnected through piping
tunnels. As an example, in the CCCSD water reclamation plant, quicklime and
recalcined lime will be handled in pneumatic conveying systems. These systems
include quicklime unloading; transfer of a mixture of quicklime and recalcined
lime over a distance of about 120 meters or 400 feet from the storage silos to the
slakers day hopper; and return of reclaimed lime to storage (a distance of about
300 meters or 1,000 feet) . Also, inert ash is transported pneumatically from the
sludge burning furnaces to holding hoppers from where it is loaded into trucks
for final disposal.
Pneumatic conveying is still much as an art as it is a science. Design depends
largely on practical knowledge, and the judgment and experience of the equipment
manufacturers plays a key role. A number of companies specialize in the pneumatic
field (Butler, Fuller, Semco, Sprout-Waldron) . The more progressive manu-
facturers would normally size a conveying system only after the particular material
has been tested in a pilot plant. Close cooperation between the purchaser and the
manufacturer is required to arrive at a sound design. A satisfactory approach
could be for the purchaser to prepare a comprehensive performance specification,
preceded by a careful assessment of the knowledge and experience of the equipment
manufacturers.
SAFETY CONSIDERATIONS
Although lime is considered a nonhazardous chemical, certain precautions should
be observed regarding the caustic nature of the material. A comprehensive
review of safety practices can be found in reference 2 of this section.
31
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REFERENCES
1. Brown and Caldwell. Plans and Specifications for Water Reclamation
Plant, Stage 5A-Phase 1. Central Contra Costa Sanitary District,
California, April, 1973.
2. Lime Handling, Application, and Storage in Treatment Processes.
National Lime Association. Washington, D .C . Bulletin 213. May, 1971.
pG-18.
3. Lime for Water and Wastewater Treatment. BIF . Providence, R.I., Ref
No. 1.21-24. June, 1969. 19 p.
4. Kraus, M.N. Pneumatic Conveying-General Considerations, Equipment
and Controls. Reprinted from Chemical Engineering. New York, N.Y.
31 p. April, 1965.
32
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SECTION VI
LIQUID PROCESSING WITH LIME
GENERAL CONSIDERATIONS
Lime can be added to wastewater either ahead of primary treatment or following
biological treatment. In the latter case, lime addition is mostly practiced to
remove phosphorus, i.e. , as part of a typical tertiary treatment sequence. 1
On the other hand, when the use of lime in the primary treatment stage is coupled
with biological treatment, much of the organic carbon load is removed from sub-
sequent treatment processes. This reduction in the organic carbon load reduces
the needed size of subsequent biological units and allows stable oxidation of
ammonia to nitrate (nitrification) .2 Besides the removal of organic matter, lime
improves the removal of phosphorus, heavy metals , grease and viruses . Although
the use of lime for phosphorus removal is less efficient with raw wastewaters than
it is in tertiary treatment, the residual phosphorus concentration in the primary
effluent is sufficiently low for effective biological uptake in the activated sludge
process.3/4
The improved BOD and suspended solids removal associated with chemical addi-
tion greatly increases the mass of raw sludge settled in the primary tanks. When
excess sludge from biological treatment is returned to the primaries, the result-
ing physical-chemical-biological precipitation contains all of the sludge produced
in the liquid treatment phase. Precipitation of all sludges in a single basin can
simplify subsequent handling of solids. It has generally been found that primary
sludges more readily dewater than secondary sludges.^ Methods for computing
sludge quantities are presented in Section X.
PROCESS CHEMISTRY
Many chemical reactions occur when lime is added to raw wastewater. When
lime alone is added, the reactions producing most of the sludge involve calcium,
magnesium and phosphorus. Other chemical reactions take place coincidentally,
such as changes in alkalinity, and precipitation or adsorption of heavy metals.
However, calcium, magnesium and phosphorus precipitation are responsible
for the bulk of the inorganic chemical sludge production. At the same time,
chemical coagulation of the raw sewage solids takes place, resulting in the co-
precipitation of the organic sludge. The chemistry of the process is extra-
ordinarily complex, so only a process-oriented review is presented.
33
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Calcium Carbonate Precipitation
At moderate to high lime doses, the bulk of the calcium added to the process is
precipitated as calcium carbonate according to the reaction:
Ca(OH)2 + Ca(HC03)2 - >2CaCO3 + 2^0 (6-1)
Water chemistry equilibria would suggest much lower levels of soluble calcium
than do actually occur in chemical primary effluents where lime addition is
practiced. In other words, the reaction indicated in equation 6-1 usually does
not closely approach equilibrium conditions as might be defined by water
chemistry transposed from water softening theory. Considering the host of con-
stituents in raw wastewater not present in raw municipal water supplies, it is not
surprising to find that there may be competitive reactions that inhibit calcium
carbonate precipitation.
Schmidt and McKinney,3 in fact, demonstrated with jar tests that polyphosphate
could completely inhibit calcium carbonate precipitation up to a pH of 9.5 Ortho-
phosphate also caused inhibition of the reactions , as shown in Figure 6-1 . The
theory cited for this inhibition is that phosphorus is adsorbed on the growing
faces of the calcium carbonate crystal, preventing further calcium carbonate
growth. Schmid and McKinney concluded that lime recovery is not justified for
low pH operations, since there is very little, if any, calcium carbonate preci-
pitation below a pH of 9 . 5 .
Control of nucleation of the calcium carbonate crystal and crystalline growth are
important factors governing the extent of completion of the reaction indicated in
equation 6-1. Allowing the reaction to take place in the presence of calcium
carbonate crystals enhances both the reaction rate and the extent of its comple-
tion. In terms of the treatment process, crystals can be recycled from the sedi-
mentation tank underflow to encourage calcium carbonate precipitation. This
principle has long been recognized in water treatment practice and has led to the
development of solids contact-type clarifiers. For instance, Hartung7 found that
in a water softening operation soluble calcium decreased when the solids concen-
tration in the reaction chamber was increased from one and a half to two percent
total solids by weight. Stone^ found in both laboratory and full-scale water
softening tests that the soluble calcium level was decreased by solids recycle. It
was concluded that the lime dose could be reduced for the same effluent hardness
with solids recycle; or alternatively, at the same lime dose, effluent hardness
could be reduced by solids recycle .
In a raw wastewater application, Horstkotte, et al.9 found that with no solids
recycle, the hardness increase across the primary sedimentation tank was 32
mg/1 at pH 11.0 operation. With solids recycle and the maintaining of flocculator
solids in the 900 to 1500 mg/1 level, the hardness increase across the primary
was only 6 mg/1. Most of the change occurred in the calcium ion concentration.
34
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200
INITIAL
—X- 50 mg/l Poly- P04
mg/l Ortho "
25 mg/l Poly "
-0-50mg/l Orfho "
-O--NO po4
200 mg/l C03=
200mg/l CO**
8.5
Figure 6-1 Effect of phosphate form
on calcium carbonate precipitation
PressleyiO studied the effect of sludge recycle on coagulation in jar test experi-
ments of raw wastewater. At a pH of 11.65, the rate of removal of soluble
calcium was calculated as a function of time. Fig. 6-2 shows the effect of solids
content on the rate of calcium removal. As can be seen, little is gained in terms
of improving the calcium carbonate reaction rate by increasing the solids level
above 2500 mg/l.
35
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to
'o 4
_o ——e €>
o:
o
LJ
1 23456
TOTAL SOLIDS CONCENTRATION XI03mg/l
Figure 6-2 Effect of solids concentration on calcium removal
The importance of solids recycle is not limited to hardness considerations. If
the calcium carbonate reaction is not complete, the effluent from the clarifier
will remain unstable with respect to calcium carbonate precipitation, unless pH
adjustment is made. The result of this instability is that the calcium carbonate
will plate out on the clarifier itself and downstream structures. For instance,
at the South Tahoe Plant, where a tertiary lime application is made and only
minimal solids recycle is practiced, copious quantities of solids are deposited
on the weirs, piping, and distribution trays above the ammonia stripping tower.
Similar scaling has been observed in clarifier weirs prior to pH adjustment at
the CCCSD's ATTF. In comparison, far less scale formation has been reported
at Envirotech's Salt Lake City pilot plant where solids contact units have been
employed. In the latter case, between 0.2 to 1.2 percent TS has been employed
in the reaction zone, 12 a level which is much greater than the cited solids
recycle applications.
The stability of the effluent is exceptionally important in those treatment systems
employing ammonia stripping for nitrogen removal, as calcium carbonate scaling
on the tower media has been one of the major operating difficulties of the ammonia
36
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stripping process. It should be recognized that ammonia is stripped at high pH.
Even effluents which have been stabilized to calcium carbonate at pH 11 will
contain free Ca(OH)2 which can react with CC>2 from the air producing scale.
Calcium Phosphate Precipitation
Precipitation of calcium phosphate creates another lime coagulant demand and
leads to further sludge precipitation. The exact nature of the precipitate is the
subject of continuing controversy. Up until recently, the nearly universal
opinion has been that the form of calcium phosphate precipitated was crystalline
hydroxy apatite, which has the formula CasOH (PC^) 3. Recently, Menar and
JenkinsS evaluated calcium phosphate and calcium carbonate precipitation
phenomena in both "chemically defined" water systems and in actual wastewater
coagulation. Crystalline hydroxy apatite could not be detected either by x-ray
diffraction techniques or by solubility tests. Rather, the solubility data suggested
the formation of an amorphous tricalcium phosphate, Ca^ (POq) 2 • Further, in the
chemically defined systems, where raw sewage organics were absent, Menar and
Jenkins found that a phase change eventually took place, whereby crystalline
tricalcium phosphate (Ca3 (PC^) 2 • 41^0) was formed. The extent of completion
of the reaction was not evaluated, nor could the presence of the crystalline phase
be detected in the wastewater systems tested.
In explaining the absence of hydroxyapatite Menar and Jenkins^ make the follow-
ing statement:
"Magnesium appears to inhibit the nucleation of calcium phosphate, to slow
down the formation of apatite from amorphous calcium phosphate, and to
stabilize the formation of tricalcium phosphate."
For the purposes of this report, the simplifying assumption is made that all
phosphate precipated is present in the form of amorphous tricalcium phosphate
according to the reaction:
3Ca(OH)2 + 2POJ > Ca3 (PO4) 2 + 6 OH~ (6-2)
Obviously, this is not the only phosphorus removal mechanism operative, since
there are other forms of phosphorus than orthophosphate present in raw sewage.
As with calcium carbonate solids recycle, the presence of preformed calcium
phosphate solids has a catalytic effect on the formation of the calcium phosphate
solid phase. Albertson and Sherwood^ showed with jar tests run on waste-
water that .solids recycle significantly reduces residual phosphate concentration
at constant pH up to a pH of 11. Further, in one case, the effect of solids re-
cycle was to reduce by 50 percent the dose required to achieve the same residual
soluble phosphate. Menar and JenkinsS showed that the activity product or
solubility of tricalcium phosphate decreased with increased solids levels in
"chemically defined" systems in experiments conducted up to a pH of 8.
37
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Contrary to the results of previous investigators, Pressley^O found that soluble
phosphate residuals increased with the level of solids recycle in jar tests and
that the "organic phosphorus" fraction in the recycle solids accounted for the
increase in the systems studied. No increase in orthophosphorus residuals was
observed.
Magnesium Hydroxide Precipitation
For most wastewaters, magnesium is not precipitated until enough lime is added
to raise the pH above 10.0. The chemical reaction involved is:
Mg++ + Ca (OH) 2 > Mg (OH) 2 + Ca++ (6-3)
Soluble magnesium levels are a function of pH and typical values follow:
pH Soluble Mg as CaCO,,, mg/1
O
10.0 370
10.2 145
10.4 57
10.6 22
10.8 9
11.0 4
In raw sewage applications, the magnesium hydroxide reaction does not closely
approach the equilibrium predicted on the basis of Mg (OH) 2 solubility. For
instance, at the CCCSD's ATTF, the effluent magnesium averaged 33 mg/1 at pH
11.0, when a supplemental coagulant dose of 14 mg/1 of ferric chloride was
added. Apparently the magnesium hydroxide reaction is inhibited, although
the specific inhibition mechanism is as yet undefined.
Trace Metals Precipitation
Of the unit processes available for waste treatment today, lime precipitation is
one of the most effective methods for removing heavy metals and, as a rule, is
more effective than either iron or aluminum . 13,14,15 Trace metals are of
significance in water pollution control because many are toxic to the biota in the
receiving waters, either at their discharge concentration or through concen-
tration in living cell tissue. Other metals are micronutrients essential for
biological growth.
Lime removes trace metals from wastewater through adsorption, flocculation, or
by conversion of soluble metals to an insoluble precipitate. Most metals form
insoluble hydroxides, oxides, carbonates, sulfates, or chlorides. 14 Solubility
data were summarized by Argaman and Weddlel4 ancj are presented in Table 6-1
for the common trace metals and their precipitates. As can be seen, silver,
cadmium, cobalt, copper, iron, mercury, manganese, nickel, lead and zinc
ought to form relatively insoluble hydroxides or oxide precipitates when lime
treatment is practiced. Actual performance often does not match predicted
chemical equilibrium because of slow rates of reaction or the formation of
38
-------
Table 6-1 . SOLUBILITY PRODUCTS OF HEAVY METAL SALTS
Metal
Ag, Silver
Ba, Barium
Cd, Cadmium
Co, Cobalt
Cu, Copper
Fe, Iron
Hg, Mercury
Mn, Manganese
Ni, Nickel
Pb, Lead
Zn, Zinc
Oxide or Hydroxide
-8
AgO 1.9x10
_ _
-14
Cd(OH) 2. 0x10
Co(OH) 1.6xlO~15
-19
Cu(OH) 1.6x10
-39
Fe(OH) 2. 0x10
G
-26
HgO 4. 0x10
-13
Mn(OH) 1.6x10
-15
Ni(OH) 2. 0x10
Pb O(OH) 1.3xlO~15
£i 2
Zn(OH) 1.6x10" 6
Carbonate
-
-9
BaCO0 1. 6x10
3
-
-
-
-
-
-
-
PbCO0 1. 5xlO~13
o
-10
ZnCO 2. 0x10
Sulfate
-
-10
BaSO 1. 1x10
4
-
-
-
-
-
-
-
PbSO, l.Sxlo"8
4
-
Chloride
-10
AgCl 2.8x10
-_ _
-
-
-
-
-
- -
-
_ _
-
Sulfide
-51
Ag S 1.0x10
2
_ _
-28
CdS 1.4x10
-
-38
CuS 4. 0x10
FeS
-53
HgS 3. 0x10
-16
MnS 7. 0x10
-
PbS 7.0xlO~
ZmS 4. 5x!0"24
Chromate
-13
Ag CrO 7.1x10
-10
BaCrO 2. 1x10
4
-
-
-6
CuCrO 3. 6x10
4
-
-9
HgCrO 2. 0x10
-
-
PbCiO S.OxlO"13
4
-
Ar senate
-
_ _
-
-
-
-
-
-
-2fi
Ni(AsO ) 3.1x10
PbHAsO 4. OxlO~36
4
Zn(AsO ) 1. 3xlO~38
LO
-------
complexes (chelation) . In other instances, removals may exceed predicted levels
through adsorption or coprecipitation on other compounds.
Two metals, barium and chromium, may pose problems in lime precipitation
systems. Barium does not form a hydroxide precipitate, and it is often not
removed efficiently with lime. In fact, Maruyama, et al. found, in pilot testing,
that ferric sulfate removes barium more efficiently than lime, since barium forms
an insoluble precipitate as a sulfate.15 Chromium in the hexavalent form exists
as an oxide (chromate or dischromate anion) , which forms a soluble salt with
most cations found in wastewater.14 if reduced to the trivalent form, the metal
may precipitate as an insoluble hydroxide (solubility product of 1.0 x 10 du) .
Coagulation
Unlike the situation in water treatment, lime is not added to raw wastewater for
the exclusive purpose of precipitating calcium or magnesium. Rather, lime is
ordinarily used for precipitation of phosphorus or metals, and for coagulation
of raw sewage solids. Only when water reclamation is to be practiced do hard-
ness considerations influence process operation.9 Criteria for coagulation of
raw sewage solids and precipitation of phosphorus compounds may set quite
different operating criteria than that for treatment of water hardness alone.
When pH is controlled at 10 or below and lime is the only coagulant, effluents
tend to be very turbid and have high concentrations of finely divided or dis-
persed solids. In other words, the effluents do not appear to be well coagulated.
This solids loss results in lower phosphorus removal, since some precipitated
phosphorus is lost over the effluent weirs. For cases where a very high degree
of phosphorus removal is required in primary treatment, the encouragement of
magnesium precipitation is often recommended. The reason is that magnesium
hydroxide forms a gelatinous matrix that binds the precipitated calcium
phosphate and calcium carbonate together into readily settleable floes. This
normally requires a pH of 10.5 or greater, depending on the raw water
magnesium content.
Menar and Jenkins^ have suggested that additional coagulants be employed for
high phosphorus removal below pH 10. Since above pH 8 to 9.6, calcite
(calcium carbonate) carries a net negative charge, a cationic material was
suggested for coagulation. While they showed that a high calcium ion concen-
tration could fill this role, they suggested that cationic polymers or alum or
ferric salts could be more efficient coagulants.
Jar tests conducted at the ATTF have demonstrated that the addition of ferric
chloride and its precipitation as ferric hydroxide could be substituted for the
high pH conditions conducive to magnesium hydroxide precipitation, while
obtaining similar supernatant turbidity and phosphorus levels. The jar test
were conducted on CCCSD raw sewage utilizing both lime and iron at the doses
and pH levels indicated in Figure 6-3. As can be seen in Figure 6-3, the
turbidity at a pH of 9.6 is equal to that obtained at a pH of 11.4. The high
clarity obtained at a pH of 9.6 was due to the use of 25 mg/1 of FeCl3 as a
supplemental coagulant. To obtain effluent phosphorus levels less than 1 mg/1
40
-------
11.0
IO.O
pH
9.O
8.0
75c
3.0
? 2.0
H
Q
00
tr
H I.O
°(
9.6
0.8
0.7
^ O.6
o
a" 0.5
1 0.4
0.
I 0.3
0.2
°'C
25mg/l FeCI3 ,ja-V~"^ /
\ B^t \ HIGH LIME CONTROL
\ ,,—*•"' — \ ATOm9/l FeCI3
^^•*^^"^ I0mg/l FeCI3-^
CONTROL POINT
' (NO CHEMICAL ADDED)
i l 1 1 1 1 1
) 50 100 150 200 250 300 350 400
CONTROL POINT
' (NO CHEMICAL ADDED) H.L. CONTROL
AT Omg/l FeCI3 -,
25mg/l FeCI3— -7 I0mg/l Fe CI3— 7 1
"^^^ ®^,^__/^_ i
l i l 1 i l l
D 50 100 150 200 250 300 350 4OO
CONTROL POINT H.L.CONTOL
•• TOTAL P-P045 TOTAL P AT Omg/l
AT Omg/l Fe CI3 FeCI3^^^_^^
yA^ ^V*^ TOTAL PAT
TOTAL PAT /^ v \ ^fe>»^~'<-)rTI9''' Fe ^'3
25mg/IFeCI3 ' \ \ \ \
v ^ \ \
PO/ AT /^ \ « / / H.L.CONTROL-^
OK / c r, X \ f / P04= AT Omg/l
25mg/eFeCI3 — ^ \ ' / Fe Cl
X / // 3
\ / £_P04S AT 10
IS mg/l FeCI3
1 1 1 1 1 1 1
) 50 100 150 200 250 300 350 40O
LIME DOSE Ca(OH)2,mg/l
Figure 6-3 Lime and iron dose vs. supernatant quality for^CCCSD
wastewater
41
-------
32O
> 300
z\
^E 280
*£
<8 260
Ouj 240
220
2OO
(
200
8 ISO
Ul _
If 160
I ro
s8 140
2 a
yo
120
o <
100
80*
<
100
I 90,
*i, 80
5 ro 7n
30 ru
§ ° 60
50
40
C
25mg/l IOmg/1
Fe CI3— ^. Fe CI3 — i
>• N\ R>^ \ HIGH LIME CONTROL
^•x ^> * ATOmg/l FeCI3— i
r CONTROL POINT
(NO CHEMICAL ADDED)
1 1 1 1 1 1 1
3 50 100 150 200 250 300 35O 4OO
25mg/l
\> I0mg/l
* \ \ HIGH LIME CONTROL
\ \ ATOmg/l FeCI3
_ CONTROL POINT ^&^ ^^^. S
(NO CHEMICAL ADDED) ^^/
i 1 1 1 1 1 T 1
3 50 100 150 200 250 300 360 40O
s — 25mg/l FeCI3
\ ./
' CONTROL POINT V A
- (NO CHEMICAL ADDED) \ S *
\ S \ S*^. HIGH LIME CONTROL
^ \ ^^""13^ ATOmg/l Fe Cl 3 1
V' /*^\i 1
I0mg/l FeCI3 ' \ /
\ '
1 I 1 1 I ^ I
' 50 100 150 200 250 300 35O 4OO
LIME DOSE Ca(OH)2,mg/l
Figure 6-3 (continued) Lime and iron dose vs. supernatant quality
for CCCSD wastewater
42
-------
P, however, the pH had to be raised to at least 9.85 (lime dose = 150 mg/1) .
Lower pH levels resulted in higher supernatant phosphorus as shown in Figure
6-4 for another jar test series. Nonetheless, Figure 6-4 demonstrates that there
is a broad pH range where comparable phosphorus removals are obtainable as
long as appropriate iron doses are employed.
Other items of interest in Figure 6-3 are the alkalinity and hardness data. Note
that there is no clear minimum solubility point for calcium, rather there is a
broad range where the calcium concentration is roughly in the same range (pH
10.3 to 11.0) . This is contrary to what would be predicted from water softening
experience which usually indicates a minimum solubility point for calcium in the
pH 9.5 to 10 range. Note also that magnesium is not completely removed at pH
11.4, contrary to solubility predictions. Very little magnesium is precipitated
up to a lime dose of 250 mg/1 (pH = 10.1) , yet excellent clarity is obtained. This,
again, is evidence that iron has substituted for magnesium as the coagulation aid.
Quite similar hardness relationships were reported by Burns and Shell-^ for
Salt Lake City wastewater when lime was used without supplemental coagulants.
Effluent calcium was lowest in a pH range from 10 to 11, with a minimum at pH
of 10.4. Complete magnesium removal did not occur even at a pH of 11.5
(Figure 6-5) .
These hardness relationships led to the decision to select an operating pH of 11.0
at the ATTF. This was the point of minimum total hardness, which is a consid-
eration when the treatment product is to be reused. The data in Figure 6-3 on
CCCSD wastewater can be reworked to show another interesting relationship.
Knowing the lime requirement for phosphorus removal (Equation 6-2) , and the
measured supernatant calcium, the loss of calcium to tricalcium phosphate
formation and to soluble calcium in the supernatant can be calculated. Theoret-
ically, this loss when subtracted from the lime dose, gives the lime precipitated
as calcium carbonate. Obviously, if all the calcium added is lost to the super-
natant and phosphorus precipitation, there can be no lime recovery as no
calcium carbonate is precipitated. In Figure 6-6, the calcium loss is expressed
as a percent of the lime dose (as CaCO3) and plotted against the lime dose (as
Ca(OH) 2) . It can be seen that at pH 9.5 nearly all the calcium is lost. Other
investigators have also found that at pH 9.5 or less, there is essentially no
calcium carbonate formation .3,6,12 jt can aiso j-,e seen from Figure 6-6, that
the pH must be at least 10 for the loss to be less than 30 percent, leaving 70
percent for lime recovery. In practice, losses occur in other parts of the
treatment system, and obtainable recovery is even less.
Subsequent work done in connection with the design of a wastewater treatment
plant in Australia showed that either ferrous or ferric sulfate could be sub-
stituted for ferric chloride. Also, an investigation at the ATTF showed that
alum or aluminate could be substituted for ferric chloride as the supplemental
coagulant.
The choice of coagulants to be employed should be based on jar tests for
screening purposes, and if possible, final selection should be based on pilot
43
-------
4.0
3.0
r 2.5
a 2.0
o
I '•*
Q.
0.5
0
50mg/| FeCt3
IOmg/1 FeCI3
FeCI3
_L
50 100 150 2OO 250
LIME DOSE Ca(OH)2,mg/l
300
350
400
pH
12.0
11.0
10.0
9.0
8.0
7.0
6.0
LOW LIME W/
IOmg/1 FeCI3-
LOW LIME W/
25mg/l Fe CI3
LOW LIME W/
50mg/IFeCI3
_L
400mg/l Ca(OH)2
Omg/l Fe CI3
_L
50 100 I5O 200 250
LIME DOSE Ca(OH)2,mg/l
300
350
400
Figure 6-4 Phosphorus removal for low pH operation.
Lime and iron treatment of CCCSD wastewater
44
-------
900-
RAW WASTEWATER
ALK= 240mg/l
12
LIME TREATMENT pH, UNITS
Figure 6-5 Effect of lime treatment on Salt Lake City
wastewater
45
-------
LU
£
UJ
CL
C/T
(/)
O
o
100
80 -
60 -
40 -
20 -
0
50 100
150 200 250
LIME DOSE, Ca(OH)2
9.5
300 350 400
Figure 6-6 Calcium loss to supernatant and phosphorus precipitation
-------
or plant scale testing. Cost and performance comparisons should dictate
coagulant choice.
Hydrolysis
The discussion of lime treatment process chemistry would not be complete with-
out mention of the concept of "hydrolysis". Certainly, no aspect of this subject
is more controversial than the role of hydrolysis. Zuckerman and Molof16 have
theorized that, by managing the lime treatment stage, the downstream activated
carbon treatment or activated sludge treatment can be optimized. The procedure
suggested was that at high pH (11.5 in the wastewater studied) high molecular
weight organics (e.g.,MW > 1200) are hydrolyzed to low molecular weight
organics (MW «"•- 400) . Zuckerman and Molofl6 concluded that high molecular
weight organics are not efficiently adsorbed, whereas low molecular weight
organics are. It has also been suggested that the activated sludge process would
also benefit by hydrolysis in the chemical primary on the basis that low molecular
weight organics are more easily and completely degraded.
No other investigators have documented or supported the "hydrolysis"
concept as advanced by Zuckerman and Molof. In fact, reviewers and other
researchers have made contrary conclusions. Weber, ' in a discussion,
questioned the character of the high molecular weight organics determined by
the gel-permeation chromatography and wondered if they were in fact colloidal
material. If they were really colloidal material, they could have been removed
by coagulation rather than hydrolysis. Weber disputed the molecular weight
concept as a determing factor in carbon efficiency for a number of reasons (see
discussion) . He also provided high pH data which showed no significant
hydrolysis effect at a pH of 11.5. In a later discussion, Weber^ concluded that
hydrolysis-adsorption could not demonstrate any advantage in terms of effluent
quality when compared to other physical-chemical effluents. McDonald, et al_,
found very little high molecular weight material in raw wastewaters from various
locations. The proportion of this material was always less than 10 percent, which
is contrary to the findings of Molof and Zuckerman.20 if there are essentially no
high molecular weight materials present, there can be no benefit from their
hydrolysis. Westrick and Cohen^l found no benefit in high pH lime operation to
carbon adsorber efficiency as compared to low pH lime operation or ferric opera-
tion. These findings are again contrary to the findings of Zuckerman and Molof.
The weight of evidence appears to be against the concept of hydrolysis
significant effect in lime treatment of raw wastewater.
as a
LIME ADDITION
Lime is added in sufficient quantity to increase the wastewater pH to the level
required by the treatment process. The amount of lime needed is a function of
wastewater flow, total alkalinity and calcium hardness. When lime is fed ahead
of the primary clarifiers, the lime slurry should be added at a point of high
turbulence in the wastewater. This turbulence can be created by a sudden drop
in the hydraulic profile, as by passage of the liquid through a Parshall flume or
47
-------
over a weir or may be produced by a mechanical agitator or mixer. The degree
of agitation is more important than the mixing period. When using mechanical
rapid mixers, scaling of the shaft and impeller is likely to occur. Also, unless
removed, rags will tend to wrap around it. Therefore, to facilitate maintenance,
provisions should be made for duplicate units.22
Where preaeration is provided for the removal of grit, the addition of lime ahead
of the preaeration tanks could offer several advantages. When quicklime is used,
the lime slakers do not require grit removers, since grit particles will settle in
the preaeration tanks. This arrangement saves power, simplifies maintenance
and provides a more compact equipment layout. The savings in space can be
significant when paste type slakers are specified since, as was pointed out before,
they require considerably less floor space than detention slakers.
Also, if the slakers can be located nearby or directly above the point of chemical
application, the difficulties of slurry handling can be largely eliminated. Pro-
blems associated with the transport of lime slurries derive from the fact that the
water in which lime is suspended, because of its high pH, undergoes a softening
reaction with the precipitation of calcium carbonate. This forms a dense hard
scale which in time will plug the solution lines.23 At the wastewater treatment
plant in Holland, Michigan, the lime slurry line has to be cleaned with a special
polurethane tool ("Poly-Pig") every other day to keep it clear.2^ The scale also
forms at the point where lime is added to the treatment process.^
Fig. 6-7 shows the 3600 kg/hr (8000 Ib/hr) paste slakers in the CCCSD water
reclamation plant2^ located above a steep channel. A hydraulic jump occurs in
this channel when the rapidly moving flow encounters the horizontal water surface
of the preaeration and flocculation tank. The turbulence created by the jump will
be used to mix lime, ferric chloride and polymer with the raw wastewater.
CONTROL OF LIME DOSAGE
Lime dosage control is normally based on one or more of the following measure-
ments: plant flow, influent pH and effluent pH. Because there is no correlation
between wastewater flow and wastewater characteristics (e.g., BOD, suspended
solids, alkalinity, and the like) , it is generally recommended that one of the
following three methods be used to control lime dosage to maintain a fixed pH
level in the flocculation tank:
1. Influent flow and off-line measurement (i.e., periodic laboratory
analysis of wastewater samples) of flocculator pH.
2 . Influent flow and on-line measurement (i.e., continuous measurement
by a pH sensor) or flocculator pH.
3. Influent flow and on-line measurement of influent and flocculator pH.
Fig. 6-8 (top) is an example of open-loop feeder control whereby the lime dosage
ratio is automatically proportioned to the influent flow rate. The pH in the lime
flocculator is manually measured at preset time intervals, and changes in the
48
-------
PNEUMATIC
CONVEYING
LINE
DAY STORAGE
HOPPER
ROTARY
VALVE
FLEXIBLE
HOSE
WEIR
AIR EXHAUST
LINE
CYCLONIC
SEPARATOR
LIME FEEDER
LIME SLAKER
FLOCCULATION TANKS
DISTRIBUTION CHANNEL
Figure 6-7 Location of lime slakers at the CCCSD water reclamation plant
49
-------
INFLUENT FLOWS OFF-LINE FLOCCULATION pH
>—1±3
INFLUENT
V
PH
FLOCCULATOR
PRIMARY
CLARIFIER
INFLUENT FLOW 3 ON-LINE FLOCCULALTION pH
INFLUENT
Figure 6-8 Lime dosage control diagrams
50
-------
dosage rate can be made by changing the setting on the ratio relay FY via manual
loading station HIK. The control system shown in Fig. 6-8 (bottom) is an example
of compound loop control whereby the dosage rate is proportional to flow, and the
dosage controller AIC acts as a dosage trimming device, compensating for varia-
tions in lime demand as measured by the pH in the flocculator. Optimum dosage
control is attainable with a feedforward control system with feedback trim. The
feedforward portion of the control system is used to calculate the desired lime
dosage per unit of influent flow based on the measurement of influent flow and pH.
Although there is not a consistent relationship between influent pH and lime dose,
the feedforward control action results in a first approximation to the required
dosage.
The feedback controller is then used to compensate for changes in wastewater
characteristics that have not been taken into consideration in the feedforward
calculation. In addition, the feedback controller also compensates for inaccuracies
in the various transmitters and computing elements in the Control System. For the
Control System shown in Fig. 6-9, the feedback controller AIC adjusts the ratio
setting of ratio relay UY, if the feedforward prediction, executed through relay
FY1, proves inaccurate as determined by the flocculator pH measurement.
^J
I
•LI ME FEEDER!
INFLUENT
1
loH
i CA1T) -
1
™" ^™
"Vv /^\
(AIT)
FLOCCULATOR
PRIMARY
ri ARIFIFR
Figure 6-9 Lime dosage control diagram - feed forward control mode
51
-------
Symbols in Figs. 6-8 and 6-9 follow Instrument Society of American's (ISA)
Standard S5.1, Instrumentation Symbols and Identification. A comprehensive
review of the principles of instrumentation and control and their practice in the
wastewater treatment field is presented in reference 26.
FLOCCULATION
The unit process of flocculation is concerned with the aggregation of particles
which have been destabilized -in a preceding coagulation step . In a flocculation
basin, opportunities for particle collision are provided by inducing fluid motion
so that larger floes can be produced and separated in a subsequent sedimentation
step . Design considerations involve energy input (such as "G", the root mean
square (rms) velocity gradient) , detention time, degree of flocculator compart-
mentalization, and the type of shearing device (such as paddle design) .
Consideration must be given to floe breakup in addition to floe aggregation. In
general, the rate of floe breakup varies with the level of turbulence. At Mgh
levels of turbulence floe breakup can predominate over floe aggregation.
Flocculation design concepts have been investigated in detail for other waste and
water treatment applications, but comparitively little work has been done with
flocculation processes in wastewater treatment using lime as the coagulating agent.
Parker and Niles28 found that a preaeration-grit removal tank could be used for
flocculation when lime was used as a coagulant. The currents caused by the
release of diffused air in the grit removal tank encourage the formation of large
flocculant particles which settled readily. By using air instead of mechanical
means, the problems associated with rag fouling of mechanical flocculators were
avoided. The same has not been found true when ferric chloride was used as the
principal coagulant. Indications were that maximum particle aggregation was pre-
vented due to floe breakup in the preaeration tank.29
When preaeration is used for flocculation, the coarse bubble air diffusers should
be of the swing arm type to allow maintenance without having to take the tank out
of service. Maintenance is required because of scaling inside the diffuser orifices,
which is caused by carbon dioxide in the preaeration air. Monthly cleaning of
diffusers may be required, although the maintenance period can be extended to as
long as three months by providing a high pressure air or water connection for
blowing out scale deposits.
Critical design criteria for flocculation in the preaeration tank are detention time
and aeration rate. Detention time at average dry weather flow should be no less
than 10 minutes and preferably 20 minutes for optimum results. The air supply to
the preaeration headers should be separately regulated and provided with flow
metering. Standard preaeration air requirements of 0.75 cu m per cu m (0.1 cu ft/
gal) of sewage are adequate as a maximum delivery capability for low pressure air.
While actual air usage has not been determined for applications such as at the ATTF
air rates for flocculation are normally set lower than for standard preaeration.
Preliminary estimates indicate that air requirements may be lower than that
normally used in preaeration. Care must be used to ensure adequate distribution
of turbulence throughout the preaeration tank to prevent deposition of organics or
chemical precipitation with the grit. A typical theoretical relationship (developed
52
-------
for the ATTF) between air rate and "G", the rms velocity gradient, is shown in
Figure 6-10.
Mechanical means may also be employed for inducing the turbulent shearing
necessary for flocculation. When mechanical means are employed, extreme care
must be taken in the design and operation of devices used for rag removal. It has
been found that when rags are screened, comminuted and then returned to the
sewage, rag fouling problems develop. For instance at the Hatfield Township
Plant, comminuted rags were found to reweave themselves and foul paddle-type
flocculators .30 Frequent maintenance was necessary. Rags have also fouled
turbine-type flocculators and draft tubes in solids contact units, such as at the
pilot plant at Salt Lake City .31 To overcome this problem, it is recommended that
rags be removed from the sewage after screening and disposed of separately when
mechanical flocculation is to be employed.
Another aspect of flocculation concerns solids contact. In addition to aiding
coagulation, solids contact promotes floe aggregation. Argaman and Kaufman
showed that the rate of flocculation was proportional to the number of particles,
the level of turbulence, "G", and the nature of the floe, in addition to other
factors.32 By increasing the solids concentration, flocculation efficiency may
be enhanced.
Solids contact may be promoted by two means, solids recycle or integral recircula-
tion in a "solids contact clarifier". Solids recycle has been used at CCCSD's ATTF
to maintain the solids concentration between 900 and 3900 mg/1. Solids recycle
was accomplished by pumping a portion of the underflow solids back to the influent
to the preaeration tank. Integral recirculation is described under primary clarifier
design. Burns and Shell found that the solids level in the recirculation zone had to
be limited to 4000 to 6000 mg/1 to prevent prolonged contact and effluent deteriora-
tion due to septicity. Common detention times (based on influent flow) cited for the
recirculation zone in a solids contact clarifier were given as 15 to 30 minutes.-^
ALTERNATE PROCESSES FOR PRIMARY APPLICATION
Depending upon pH level, the addition of lime to raw wastewaters has resulted in
three distinct processes, each of which is intended to achieve different degrees of
basically the same objectives. These processes are: the Low Lime Process, the
High Lime Process, and a process employing lime and other metal salts.
The low lime process normally operates in a pH range of 9.5 to 10.5. Phosphorus
removals are lower than for the high lime process, since magnesium is not pre-
cipitated to coagulate the colloidal phosphorus. Solids and organics removal are
also somewhat lower for the same reason.
The high lime process must operate at a pH of at least 10.5, so that magnesium
precipitation can aid coagulation. While the lower limit of operating pH is given
as 10.5, operation for most applications has usually been at 11.0 or even higher
for a number of reasons that will be discussed in detail.
53
-------
1000
800
600
500
400
300
200
,_ 150
UJ
5
g 100
(= 80
3
£ 60
| 50
o" 40
30
20
15
10
1
FUNC
^
I T 1 1 — i — riii r
DESIRABLE OPERATING RANGE
;TION RATE.SCFM G, sec-'
PREAERATION (O.I CF/gol)
LIME REACTION,FLOCCULATION
^
^
S>
^
^
^
(
\
(
(
(
x"
3 =
i =
3 =
:FI»
:F
220
35-220
f
29
dil
CF
t/lo
rec
x*
.5
FfL
~H
P«
ict
^»r
y
/Q'h
ser dept
/CF rea
•r = 1.3 S
or= 539^
130 sec'1 .
30-130 _
^
h, 10'
ctor
>CFM
D
^
10 15 20 30 40 50 60 80 100
AIR RATE, SCFM
150 200 300
Figure 6-10 Air supply - shearing relationship
for preaeration - flocculation
54
-------
The third lime process is a relatively recent development. Lime is coupled with
another metal salt, such as iron, to enhance the removal of phosphorus, organics
and other solids. The metal salt permits production of a high quality effluent
without the need to precipitate magnesium. As a result, lower lime doses are
possible. Operating pH normally will be between 9.5 and 11.0.
Low Lime Process
The low lime process is a relatively economical method, from a chemical cost stand-
point, to remove a large percentage of phosphorus from wastewater. Inspection of
the data in Fig. 6-11 shows that beyond a given initial removal (eighty percent),
the incremental amount of lime required to precipitate incremental quantities of
phosphorus increases rapidly. If the desired level of phosphorus removal falls
within the steeper portion of the curve, a relatively low dosage of coagulant will
be sufficient. It can be observed that there is a minimum dose required before
normal primary treatment removals are exceeded. As an example, in jar tests
conducted by Tofflemire and Hetling33 it was observed that 85 percent removal
of phosphorus was obtained with a dosage of 125 mg/1 of Ca (OH) 2 at pH 10.
Albertson and Sherwood1* reported similar results.
Figure 6-11 is derived from a pilot treatment study at Kansas State University34
where the primary operation was at a low overflow rate of 12.2 cu m/day/sq m
(300 gpd/sq ft) . The allowable upper limits for overflow rate were not defined
in the study. Lower phosphorus removals have been reported by Burns and
Shell. In one run, the removal was only 41 percent at pH 9.8, at 270 mg/1
total alkalinity and a lime dosage of 270 mg/1 as Ca (OH) 2-
The amount of lime required to precipitate phosphorus will normally cause
coagulation also; therefore, suspended solids are removed along with phosphorus.
Table 6-2 gives the results reported by Tofflemire and Hetling for approximately a
month of clarifier operation at each pH value shown. Clarifier overflow rate was
16.3 cu m/day/sq m (400 gpd/sq ft) . Coagulation aids have been used to
increased the settling velocity and to flocculate insoluble phosphorus. The
former is achieved by adding small dosages (lower than 1.0 mg/1) of organic
polyelectrolites. ^°
Table 6-2. EFFECT OF PRIMARY CLARIFIER pH ON PERFORMANCE
AT WATERFORD, NEW YORK
pH
9.9
10.3
10.8
COD
mg/1
542
548
782
Influent
COD
% Sol.
40.9
25.5
23.1
S.S
mg/1
240
356
548
Removals
COD
%
60.7
69.5
75.6
S.S
%
76.3
88.5
91.0
Effluent
Turbidity
JTU
36
20
27
55
-------
100
90
80
70
60
50
40
30
°- 20
10
0
UJ
LU
CL
LU
IT
8O% REMOVAL
0
50
100
150 200 250
LIME DOSAGE, mg/l Ca(OH)2
300
300
400
450
Figure 6-11 Phosphorus removal as a function of lime dose
-------
Three full-scale plants (Holland, Mich.; Hastings, Mich, and Hatfield Township,
Pa.), using the low lime process were surveyed in connection with this project.
All of the plants were designed around the "PEP" process patented by Dorr-Oliver
and feature sludge recirculation to the flocculator zone. Operating data for these
plants are shown in Table 6-3. As can be seen, primary performance in two of the
plants is low. This may be due to insufficient lime dose (see Fig. 6-11) , or to
excessive overflow rate.
In general, design overflow rate for low lime applications is fairly low and runs
about 16-32 cu m/day/sq m (400-800 gpd/sq ft) at average dry weather flow.
Dorr-Oliver recommendation for overflow rates at peak wet weather flow is 33 to
40 cu m/day sq m (800 to 1000 gpd/sq ft) .
High Lime Process
When certain requirements on final effluent water quality demand raising the
wastewater pH to 11 or 11.5, i.e., to increase lime dosages, the resulting pro-
cess is called the High Lime Process. The figures given in Table 6-2 show the
improvement in BOD (COD) and suspended solids removal with increased pH
values. As was mentioned earlier, wastewater clarification in the high lime
process is directly related to the removal of magnesium in the form of magnesium
hydroxide. The reaction of magnesium with calcium hydroxide requires a pH
greater than 10.5. Clarification is further enhanced by the precipitation of
additionalcalcium carbonate which improves floe stability and settling charac-
teristics. The high lime process also aids in removing phosphorus, ammonia
nitrogen (via air stripping) and certain viruses. Phosphorus removal as a
function of lime dose approaches a logarithmic relationship. After the initial
fraction is removed, further unit precipitation of phosphorus occurs with
successively increasing lime dosage.
The efficiency of ammonia air stripping as a result of high lime treatment depends
on the pH of the wastewater. The process requires a high pH to achieve efficient
removal of ammonia, because this nitrogen compound is very soluble in water and
is highly ionized at pH 7.0. The following table illustrates equilibrium conditions
between ammonium hydroxide and disassociated ammonia at various pH levels:
pH NH4OH:
7.0 0.0055:1
8.0 0.055:1
9.0 0.55:1
10.0 5.5:1
11.0 55:1
Since only the undisassociated ammonium hydroxide can be removed by air
stripping, the process is practical only at pH levels of 10.5 and higher.
57
-------
Table 6-3. OPERATING PARAMETERS FOR PRIMARY TREATMENT IN "PEP" PLANTS
Plant
Hastings
Holland
Hatfield
Present ADWF ,
cu m/d (mgd)
3,030 (0.8)
15,140 (4.0)
8,320 (2.2)
Ca(OH)2
dose,
mg/1
297
166
394
PH
9.6
9.3
9.5
Present ADW
overflow rate,
cu m/day sq m
(gpd/sq f)
29 (700)
21 (520)
16 (390)
P
removal,
percent
68
34
58
SS
removal ,
percent
71
44
45
BOD
(COD)
removal ,
percent
58
(a)
77 (61)
Reference
No.
35
36
37
en
CO
(a) Not available
-------
The removal of virus through high lime treatment appears virtually complete.
Cooper, et al.^0 found that a pH of 11.0 resulted in no detection of inoculated
polio virus Type I. Lower operating pH values resulted in detectable levels of
virus. Other unit processes, such as activated sludge, sand filtration, and
carbon adsorption did not completely remove the virus.
Table 6-4 summarizes the results obtained in the Contra Costa ATTF when
operating in the high lime process. The table shows the high degree of organics
removal possible when the high lime process is used. For comparison, results
from a control primary are shown.
As increasing quantities of lime are added to the wastewater, recovery of the
spent chemical by recalcination becomes economically attractive. Basically,
calcination converts calcium in the lime sludge to calcium oxide. Calcium must
be in the carbonate form for lime recovery to be a feasible process. As was
mentioned earlier, it has been found that the pH has to be raised above 9.5
before calcium carbonate will begin to precipitate from the wastewater. Another
factor is the alkalinity of the wastewater. In highly alkaline wastewaters,
additional CaCO3 will be precipitated at high pH levels. Therefore, for the same
lime dosage, the flow at which lime recovery becomes feasible is smaller for plants
treating a highly alkaline wastewater. Figure 6-12 illustrates the relationship
between lime dosage and wastewater alkalinity in the high lime process .41
Lime and Other Metal Salts
The coupling of lime with other metal salts for wastewater coagulation is a fairly
recent development. It derives from the practice in water softening plants, where
metal salts are used in the recarbonation stage to improve the flocculation of the
finely divided calcium carbonate precipitate. The first application of lime coupled
with iron was reported by Wuhrman.42 irOn (Fe++ ) was used at a dose of 1 to 2
mg/1 as a flocculation aid to improve phosphorus precipitation in the pH range of
10.5 to 11.0. The lime was applied to secondary effluents. Wuhrman also noted
that excess biological sludge could effectively be coprecipitated with the lime
sludge. Lime has been coupled with alum in precipitation of oxidation pond
effluents .43 A pilot plant operated by the Napa County Sanitation District
obtained 83 percent SS removal when operating at a pH of 10.8 the lime dose (as
Ca (OH) 2) was 260 mg/1 and was coupled with an alum dose (as Al2 (804)3.
18H2O) of 50 mg/1. Bishop, et al_., 44 employed ferric chloride with lime at low-
pH operation but has not repoTted the details.
Considerable experience has been gained at the Advanced Treatment Test Facility
in the use of lime coupled with ferric chloride. ^ Results are summarized in
Table 6-5. Comparing these results to those obtained with the use of lime alone
(Table 6-4) , it can be seen that there is relatively little difference in the removals
obtained for the conventional parameters (BOD, SS, TOG) . Moreover, it can be
seen that the phosphorus removal obtained at pH 10.2 with iron, exceeds that
obtained at pH 11.5 without iron. Chemical dose, is of course, appreciably less
at the low pH. Further, there is approximately 28 percent less solids generation
at pH 10.2 than 11.5.45 Grease removal is also considerably better with lime and
iron operation compared to lime alone.
59
-------
Table 6-4 HIGH pH TREATMENT OF CCCSD WASTEWATER
C onstituent
(mean value)
BOD5
SS
vss
Turbidity
TOC
Soluble organic carbon
Total phosphorus as P
Settleable solids
Calcium hardness6
Magnesium hardness6
Hardness increase6
Grease
o
pH 11.5 operation
Ca (OH) • 500 mg/1
£
Raw
sewage
mg/1
190
199
-
-
107
16
9.4
8.2d
76
96
-
57
Control primary
mg/1
103
57
43
35C
59
16
-
0.3d
-
-
-
32
%
removed
46
71
-
-
45
0
-
95
-
-
-
44
Chemical primary
mg/1
50
41
20
16C
37
23.4
0.96
nil
168
40
46
12
%
removed
74
79
-
-
65
-46
90
100
-
-
-28
79
pH 11.0 operation'3
Ca (OH)2: 400 mg/1
Raw
sewage
mg/1
192
195
-
-
118
17
9.2
9.5d
76
103
-
53
Control primary
mg/1
121
57
46
40C
68
21
-
0.2d
-
-
-
42
%
removed
37
71
-
-
42
-24
-
98d
-
-
-
21
Chemical primary
mg/1
60
47
25
26C
48
28
2.3
<0.1d
156
59
36
19
%
removed
69
76
-
-
59
-65
75
>99
-
-
-20
64
CTl
O
December 22, 1971 to February 10, 1972, at average flow 1.30 mgd.
February 11 to February 28, 1972, at average flow 1.12 mgd.
°JTU
dml/l
as CaCC)
-------
500
O
<5
0>
I
O
I
Q.
o:
£
D
UJ
a
s
ir
UJ
o
a
UJ
400
300
200
100
_L
_L
0
100 200 300
WASTEWATER ALKALINITY mg/l-CaC03
400
500
Figure 6-12 Lime requirement for pH 11
as a function of wastewater alkalinity
61
-------
Table 6-5 LIME AND IRON TREATMENT OF CCCSD WASTEWATER
Constituent
(mean value)
BOD
O
ss
vss
Turbidity
TOC
Soluble organic carbon
Total phosphorus as P
Settleable solids
Calcium hardness as
CaCO
O
Magnesium hardness
as CaCO
O
Hardness increase as
CaC03
Grease
f\
pH 11.0 operation
Ca(OH) : 400; Fed : 14
Z 3
Raw
sewage
mg/1
210
305
130
23
9.5
13. 2d
75.5
90
-
146
Control primary
mg/1
109
69
49
45C
72
18
0.13d
-
-
-
-
%
removed
48
78
45
21
99
-
-
-
-
Chemical primary
mg/1
53
27
14
14C
37
24
0.85
nil
139
32.5
6
9.5
%
removed
75
91
72
-4
91
100
-
-
-4
94
pH 10.2 operation
Ca(OH) : 289; FeCl : 24
2i o
Raw
sewage
mg/1
178
235
117
20
9.4
12. ld
72
90
-
66
Control primary
mg/1
106
59
48
41C
68
17
.1
-
-
-
-
%
removed
40
75
42
15
99
-
-
-
-
Chemical primary
mg/1
59
31
19
15 c
43
25
0.68
<0.1d
148
70
56
8
%
removed
66
87
63
-25
93
>99
-
-
-34
88
to
March 23, 1972 to April 5, 1972 at average flow 1.19 mgd.
April 7, 1972 to April 30, 1972 at average flow 1.20 mgd.
°JTU
dml/l
-------
It is probable that future applications of lime to raw sewage coagulation will
increasingly employ supplementary dosages of other metal salts because of the
savings in chemical and solids handling costs.
RECARBONATION
Raising the pH of wastewater by lime will result in deposition of calcium scale on
surfaces with which the water comes in contract. To prevent this the pH is
adjusted downward to a value of about 7 by the addition of carbon dioxide (CO2)
after the wastewater leaves the lime treatment unit and before it undergoes other
treatment processes (an exception involves ammonia stripping which requires
high pH) . The hydroxides and carbonates which have been produced in raising
the pH are reconverted to bicarbonates according to the following reactions:
Ca (OH) 9 + CO9 > CaCOQ + H0O
Z Z o Z
CaCO3 + CO 2 + H2O >Ca (HCOg) 2
Recarbonation is a process which has been used for many years in water treatment
for downward adjustment of pH following lime-soda water softening. The recent
increase in the use of lime for treatment of wastewaters has resulted in recarbona-
tion being increasingly used in advanced waste treatment schemes.
Sources of Carbon Dioxide
There are three principal sources of carbon dioxide for recarbonation: (1) liquid
carbon dioxide; (2) combustion of a fuel such as propane or fuel oil, and (3) stack
gas from either a lime recalcining furnace or a sludge incineration furnace. In
most waste treatment applications, the latter source is usually used. Stack gas
from sludge incineration contains 8-14 percent carbon dioxide, and gas from a
lime recalcining furnace contains 14-20 percent carbon dioxide.
It is interesting to note that at the CCCSD's ATTF sufficient carbon dioxide is
normally supplied by the biological oxidation reactions in the nitrification units to
lower the pH to the desired value as the wastewater enters the aeration tanks.^
Liquid C02 is used on a standby basis when the pH in the aeration tanks becomes
too high for efficient biological oxidation. When external carbon dioxide is
required, it is added directly to the aeration tanks.
The quantities of carbon dioxide necessary for recarbonation can best be deter-
mined by laboratory tests. The best procedure is to bubble COo into a sample of
lime-treated wastewater under conditions likely to ensure nearly complete transfer
efficiency; required dosage generally range from 200 to 400 mg/1. It is possible to
compute directly the dose of carbon dioxide necessary to lower the pH to 8.3 (i.e.,
to change hydroxide and carbonate alkalinity to bicarbonate alkalinity) if the initial
types and quantities of alkalinities present are known. An example of such a
calculation is given by Gulp and Gulp.
63
-------
Recarbonation Equipment
Recarbonation equipment consists of a reaction basin for recarbonation to take
place, equipment required to produce and deliver the carbon dioxide to the basin,
and a diffusion system to add the carbon dioxide to the wastewater.
Regarding reaction basin design, it is important to note that the recarbonation
reaction is not instantaneous. Although the COo gas may enter the water as dis-
solved CO2 rapidly, the time required for recarbonation reactions to be completed
and the pH to be lowered to the desired value may be 10 to 15 minutes. Thus,
sufficient detention time must be allowed in the basin or scale will form on the
surfaces of downstream units and piping.
Design of the reactor also depends on whether the pH adjustment is made in one
or two stages. When lime is used in tertiary treatment in high lime application, it
is common practice to recarbonate in two steps. In the first step the pH of the
wastewater is usually reduced to a value near 9.3. This is the point of minimum
solubility of calcium carbonate in tertiary treatment applications. This calcium
carbonate is then settled in the reaction basin and can be reclaimed by recalcin-
ing. At South Tahoe11 about 17 percent of the lime which is recovered comes
from the recarbonation settling basin. In the second step of the recarbonation
process, the pH is brough down to about 7.0 to provide a stable effluent.
If two-stage recarbonation is used, sufficient detention time must be allowed to
provide both reaction and settling in the first stage. Gulp and Gulp recommend
at least 30 minutes with an overflow rate of not more than 98 cu m/sq m/day
(2,400 gal/sq ft/day) . Provisions should be made for sludge removal in the
settling basin. In single-stage recarbonation Gulp and Gulp recommend a
detention time of at least 15 minutes. However, no provisions for settling and
collection of sludge are required.
The equipment required to deliver the carbon dioxide to the reaction basin will
depend on the source of the carbon dioxide.46 If liquid CO2 is used, it can be
fed in either the gaseous or liquid form. In either case, pressure reduction cools
the carbon dioxide as it is withdrawn from its insulated, pressurized storage
container, and care must be taken to prevent dry ice formation. To prevent icing,
storage containers are provided with means to heat the unit. For gas feed, an
orifice plate in the feed line can be used to measure the flow. For liquid feed,
equipment similar (except for materials) to solution-feed chlorinators may be used.
If fuel is burned to produce carbon dioxide, either underwater burners utilizing
natural gas or pressure generators, which can burn a variety of fuels, are usually
used. Pressure or forced-draft generators operate by compressing air and fuel in
a chamber at sufficiently high pressure to allow discharge directly to the water
after combustion. With underwater burners, air and natural gas are compressed
and then burned at the point of application. When stack gas from a furnace is used
as a source of carbon dioxide, the gas is passed through a wet scrubber to remove
paniculate matter and for cooling. The gas is then fed through a compressor in
order to attain sufficient pressure to feed against approximately 2.4m (8 ft) of
water.
64
-------
The type of diffusion system utilized will depend in part on the source of carbon
dioxide. For example, underv/ater burners act both to produce carbon dioxide
and to diffuse it into the wastewater; for liquid carbon dioxide, cotton fabric hose
with controlled porosity may be used.
For dispersing gaseous carbon dioxide into the wastewater, commercial devices
such as those manufactured by Walker Process or Lightnin (Mixing Equipment Co.)
are available. These consist of a propeller mixer placed above a sparger through
which carbon dioxide is added to the wastewater. The bubbles formed by such
systems are quite small (on the order of 1 mm) , and gas transfer efficiencies can
range up to 90 percent. Gulp and Gulp described an absorption system consisting
of a grid of perforated PVC pipe that is submerged 2.4m (8 ft) in the wastewater.
Transfer efficiencies of 85 percent or greater can be obtained with 4.7 mm(3/16-in)
diameter holes that discharge 0.03 to 0.05 cu m/min (1.1 to 1.65 cfm) of gas. They
recommend that the holes be spaced along the pipe at least 7.6 cm (3-in) apart,
and that the pipes be spaced 0.46 m (1.5 ft) apart.
Since the recarbonation reaction takes considerable time and gas transfer can be
accomplished fairly rapidly, it is often convenient to add gas only in the first
portion of the reaction basin. However, this may result in incomplete transfer
unless pure COo is used. The concentration of CC>2 which can be dissolved in
water depends on the partial pressure of CC>2 in the gas. For example, if stack
gas is used, the equilibrium concentration of CC^ in the wastewater may be less
than the required dosage. In order to overcome this, it may be necessary to add
carbon dioxide over a large fraction of the detention time, so that as carbon dioxide
is removed from solution by the recarbonation reactions, more can be transferred
from the gaseous phase into solution.
Single-Stage vs Two-Stage Recarbonation
When lime is applied to raw wastewater, it is doubtful that the recarbonation
should be carried out in two steps, rather the pH be brought down to about 7 in
a single step . Horstkotte, et aj.. ,9 found little difference in hardness where two-
stage and single stage operations were compared during studies at the ATTF for
pH less than 11.0. From this observation, it can be deduced that very little cal-
cium carbonate precipitation will occur after first-stage recarbonation for most pH
levels in the chemical primary. Studies at the Cleveland Westerly Plant^7 tend to
confirm this conclusion. When the chemical primary clarifier was operated at
pH 10.5, it was found that very little sludge was precipitated in the second-stage
of 2-stage recarbonation. Calcium hardness across the clarifier was reduced only
6 mg/1. However, when the operating pH was raised to 11.5 to 12 .0, large
quantities of calcium carbonate were precipitated in the second of the two recar-
bonation stages. When single-stage recarbonation was practiced, no significant
precipitation following recarbonation was observed. In Studies at Blue Plains,
O'Farrell^S found that two-stage recarbonation in raw sewage coagulation at a
pH of 11.4 to 11.7 resulted in sludge production of 0.9 kg/cu m (7.5 lb/1000
gallons); when lime and iron were used at a pH of 10.5, only 0.4 to 0.5 kg/cu m
(3.5 to 4.0 lb/1000 gallons) of sludge was obtained.
65
-------
In summary, two-stage recarbonation appears to have a role to play only in
tertiary treatment applications and in those few primary treatment applications
where the pH is considerably above 11.0. Since effluents of the same quality can
be obtained where lime, at lower dosages, is used in combination with other salts,
two-stage operation at high pH is not economically justified. The latter process
also produces greater quantities of sludge than lime coupled with metal salts.
TERTIARY APPLICATIONS
Lime use in tertiary treatment applications has been covered in detail in References
1, 11 and 46, based mostly on the experiences gained at the South Tahoe Water
Reclamation Plant. The main advantages of the tertiary treatment approach are
listed as greater flexibility of the operation because the biological and chemical
processes are separated; and the separation of the organic, i.e., primary and
secondary, sludges from the chemical ones, which tends to facilitate subsequent
handling of the sludge and prevent the build up of inerts if lime recovery is
practiced. It was acknowledged that the principal drawback of tertiary treatment
was its high initial cost.
Although a comparison between the two lime processes is beyond the scope of this
manual, it should be pointed out that two years of operation at the CCCSD's ATTF
have demonstrated the stability of a biological system, i.e., nitrification-denitri-
fication, following the addition of lime to raw wastewaters. The test facility also
showed that combined sludges can be effectively classified with a solid bowl
centrifuge, thereby minimizing the problem of recycling inerts. (See also
Section VIII) .
DESIGN CONSIDERATIONS FOR PRIMARY CLARIFIERS
When lime (or any other chemical) is added to raw wastewaters to increase the
removal of suspended solids, phosphorus and toxic materials, the unit operations
required are similar to those found in water treatment plants, i.e., rapid mixing,
flocculation, sedimentation and sludge handling. These four processes have often
been integrated into a single unit resulting in the upflow solids contact clarifier or
sludge blanket clarifier. In connection with water treatment, it has been stated
that the main advantage of this design, when compared to the separate tank
approach, is its lower construction cost. Another important feature of the solids
contact tank is the ability to bring the raw wastewater in contact with high con-
centrations of suspended solids. Figure 6-13 shows a typical solids contact unit.
It has often been stated that solids contact units are lower in capital cost than
primary sedimentation tanks. However, detailed examination of this in Section XII
shows that there is no economic advantage to solids contact units. It has now been
common practice for many years to provide grit chambers ahead of the main treat-
ment units y to protect mechanical equipment and, when sludge digestion is
practiced, to prevent grit accumulation in the digestion tanks. Therefore, grit
removal facilities are usually required and, preferably, precede the primary
clarifiers. As mentioned earlier, a preaeration and grit removal tank can perform
well as a flocculation basin. This flocculation can be provided with conventional
66
-------
primary tanks at no extra cost if preaeration is used for grit removal. In com-
parison, the solids contact unit must have previous grit removal so that the
functions of flocculation and grit removal cannot be combined.
CHEMICAL FEED PIPING
INLET
PERIPHERAL
LAUNDER
OUTLET
SUPPORT
RODS
RECIRCULATION
DRUM
SLUDGE PIPE
TO SUMP
Figure 6-13 Typical solids contact clarifier
(courtesy of the Eimco Corporation)
In lieu of grit removal tanks and a pumped grit slurry system, effective grit
separation can be accomplished by degritting the primary sludge. With this system
relatively thin primary sludge is pumped to centrifugal cyclonic separators. The
grit separators would discharge the heavier , inorganic particles to a grit classifier
with both the classifier and centrifugal separator overflowing to a sludge sump.
Sludge would then be pumped from this sump to the thickening tanks. Although
lower in first cost than separate grit removal tanks, disadvantages of sludge
degritting include increased odor production because of an open classifier and
sludge sump, plus more difficult maintenance of grit separation equipment due to
67
-------
the higher concentrations of organic material which may cause fouling of the equip-
ment. The lower sludge concentration also requires larger thickening tanks, which
offsets some of the cost savings of sludge degritting.
Gulp and Culp46 have also pointed out that sludge blanket clarifiers are difficult to
control under varying flow rates or changing physical and chemical composition of
the wastewater. Another operational problem in certain upflow clarifiers, when
used in primary lime applications, is the tendency of rags and similar materials to
wrap around the flocculator paddles. Shuckrow and Bonner,46 based on pilot plant
studies at the Westerly WTP in Cleveland, have recommended against the use of
solids contact units for the full-scale plant. They found severe difficulties in
maintaining a sludge blanket in the clarifier and stated that this problem would
be further aggravated under variable hydraulic loadings.
Burns and Shell have reported stable operation of a solids contact clarifier.12 This
was a solids contact operation and not sludge blanket clarification operation; this
kept sludge out of the clarification zone. Sludge was kept at or below the bottom of
the reaction well (Fig. 6-13) .
Conventional primary sedimentation basins are commonly of circular or rectangular
cross section, although some equipment manufacturers offer a square tank design.
Fig. 6-14 shows a typical section of the chemical primary treatment units designed
for the CCCSD Water Reclamation Plant.2^ A compact layout has been provided by
the common wall construction of rectangular tanks and by the separation of the
flocculation and sedimentation tanks by the distribution channel over an equipment
gallery. The gallery houses the grit, sludge and scum pumps, the preaeration
blowers and the associated pipine and appurtenances. The primary sedimentation
tank in the ATTF has two basic functions: separation of the solids from the liquid
and thickening of the solids. While the water reclamation plant under construction
will incorporate separate thickening stages, considerable thickening takes place
in the primary sedimentation tank itself.
From the surface of the ATTF tank the sludge could be seen to settle out very
rapidly. Sludge profiles taken along the bottom confirmed that the bulk of the
sludge settled out in the first three-eighths of the primary tank. Expansion of the
sludge layer into the effluent end of the primary tank was taken as evidence of
sludge thickening failure, since no significant increase in underflow solids con-
centration occurred at the time of layer expansion. On this basis, it is estimated
that only 50 percent of the tank floor is effective in thickening.
Whenever sludge intruded under the effluent weirs or beyond, large floes immedi-
ately began appearing in the effluent. As long as the sludge layer was held in the
first half of the tank, no large floes appeared. This factor helps explain the
observed stability of these clarifiers as a function of overflow rate. Little deteri-
oration in effluent quality occurred up to a maximum hourly overflow rate of 90 cu
m/day/sq m (2200 gpd/sq ft) . During these tests, the average dry weather over-
flow rate was 59 cu m/day/sq m (1440 gpd/sq ft) . The detention time at the peak
rate of flow was only 0.9 hours. The good separation of thickening and clarification
functions in the conventional rectangular primary allows relatively high overflow
rates to be obtained.
-------
AGITATION AIR
HEADER
HELICAL SCUM SKIMMER
PIPE CHASE
PRIMARY
SEDIMENTATION
TANK
.Jb
PREAERATION ,
FLOCCULATION 8
GRIT REMOVAL
TANK
DISTRIBUTION
CHANNEL
LONG; TUDINAL
SLUDGE COLLECTOR
SCUM TO EJECTOR
EQUIPMENT
GALLERY
.^-AERATION
HEADER
SLUDGE RECIRCULATION
LINE
SLUDGE CROSS COLLECTOR
GRIT HOPPER
Figure 6-14 Primary treatment units at CCCSD water treatment plant
-------
The degree to which sludge could be thickened was affected by process pH. At
pH 11.0 and above when lime alone was added to the primary, the sludge could be
thickened to as much as 9 or 10 percent total solids (TS) . However, at about 7 per-
cent total solids and above, coning and bridging occurred in the sludge hoppers,
and septic sludge zones developed. This problem can be minimized by designing
steeper hoppers and providing positive feeding of sludge to the suction line of the
sludge pumps. When the pH was dropped to 10.2, "thinner" sludges were obtained
The sludge could not be thickened to greater than 4.2 percent TS . However, when
an anionic polymer coagulant aid was employed at a dose of 0.25 mg/1, 6.0 percent
TS was attained in the underflow. Burns and Shell12 have reported on the solids
content of sludges over a slightly different pH range. At pH values above 11.5,
the lime sludge thickening properties were significantly poorer than at pH 10.5 to
11.0.
Table 6-6 and 6-7 give maximum and recommended design parameters respectively
to size primary clarifiers of both solids contact and rectangular design. The
rectangular tank design for which these figures are applicable is that which is
depicted in Fig. 6-14. Other rectangular tank designs may have differing limiting
overflow rates and caution should be used in establishing design overflow rates
unless specific test data is available. While solids contact type units are designed
at approximately the same surface overflow rates as conventional rectangular pri-
mary tanks, considerably longer hydraulic retention times are employed. This
translates into the need for deeper tanks when solids-contact units are designed.
Even considering the separate preaeration and grit removal tank (at 20 minutes
retention) as an addition to conventional tank cost, solids-contact units require
greater structure size and therefore greater cost.
Table 6-6 MAXIMUM CLARIFIER DESIGN PARAMETERS
Flow
Average dry weather
(ADWF)
Peak dry weather
(PDWF)3
Rectangular tank
Overflow rate
cu m/d/sq m (gpd/sq f)
59 (1,440)
90 (2,200)
Detention
time, hours
1.3
0.9
Solids contact clarifier
Overflow rate
cu m/d/sq m (gpd/sq f)
44 (1,080)
73 (1,800)
Detention
time, hours
2.5 3.0
1.5 2.0
Peak flow during dry weather of 1 2 hour duration.
Based on Reference 38.
It should be noted that Tables 6-6 and 6-7 apply to an operating pH of equal to or
greater than 10.5. For both types of clarifiers, the design data are for highly
buffered wastewaters (alkalinity 200-300 as CaCO3) . Low alkalinity wastewater
would result in lower calcium carbonate precipitation and different, as yet
undefined, criteria would apply. Criteria for low lime applications are not as
well defined and were briefly discussed in a preceding section.
70
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Table 6-7 RECOMMENDED CLARIFIER DESIGN PARAMETERS
Flow
Average dry weather
(ADWF)
Peak dry weather
(PDWF) a
Peak wet weather
(PWWF)
Rectangular tank
Overflow rate
cu m/d/sq m (gpd/sq f)
49 (1,200)
73 (1,800)
147 (2,400)
Detention
time, hours
2.2
1.4
0.7
Solids contact clarifier
Overflow rate
cu m/d/sq m (gpd/sq f)
24 41 (580 - 1,010)
76 (1,870)
Detention
time, hours
1.4 2.8
-
1.4 1.9
Peak flow during dry weather of 1 - 2 hour duration.
Based on Reference 12.
Proportioned from Table 6-6.
71
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REFERENCES
1 Process Design Manual for Phosphorus Removal. Black & Veatch,
Consulting Engineers. Washington, D.C. Environmental Protection
Agency - Technology Transfer. October, 1971. pp. 10/23-10/27.
2. Parker, D.S., K.E. Train, andFJ. Zadick. Sludge Processing for
Combined Physical-Chemical-Biological Sludge. Washington, D.C.
Environmental Protection Agency, Report Number EPA-R2-73-250,
July, 1973. 141 p.
3. Schmid, L .A. and R .E . McKinney. Phosphate Removal by a Lime-
Biological Treatment Scheme. Journal of the Water Pollution Control
Federation. 41, 1259-1276, July, 1969.
4. Albertson, O.E. and R.J. Sherwood. Phosphate Extraction Process.
Journal of the Water Pollution Control Federation. 41_, 1467-1490,
August, 1969.
5. Adrian, D.D. and J.E. Smith, Jr. Dewatering Physical-Chemical Sludges.
Applications of New Concepts of Physical-Chemical Wastewater Treatment.
W.W. Eckenfelder, and L.K. Cecil. New York, Pergamon Press, Inc.
September, 1972. p. 273-289.
6. Menar, A. and D. Jenkins. Calcium Phosphate Precipitation in Wastewater
Treatment. Sanitary Engineering Research Laboratory, University of
California, Berkeley, California, SERL Report No. 72-6. June, 1972. 96 p.
7. Hartung, H.O. Treatment Plant Innovations in St. Louis County, Missouri.
Journal of the American Water Works Association. 50: 965-974, July, 1958.
8. Stone, R.W. The Effect of Lime Sludge Return on Hardness Removal and
Solids Carryover in the Lime Softening Process. Thesis submitted to the
University of Texas in Partial Fulfillment of the Requirements for the
Degree of Master of Science in Environmental Health Engineering.
January, 1968.
9. Horstkotte, G.A., D. G. Miles, D.S. Parker, andD.H. Caldwell. Full-
Scale Testing of Water Reclamation System. Central Contra Costa Sanitary
District and Brown and Caldwell. (Presented at the 45th Annual Conference
of the Water Pollution Control Federation. Atlanta. October 12, 1972). 22 p.
10. Pressley, T. Personal Communication to D .S . Parker. Environmental
Protection Agency - Blue Plains Pilot Plant. October 11, 1973.
72
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11. Advanced Wastewater Treatment as Practiced at South Tahoe, South Tahoe
Public Utility District. Washington, D.C. Project 17010 ELQ. Environ-
mental Protection Agency. August, 1971. 436 p .
12. Burns, D.E. and G.E. Shell. Physical-Chemical Treatment of a Municipal
Wastewater Using Powdered Carbon. Envirotech Corporation. Salt Lake
City. Report No. EPA-R2-73-264 for Environmental Protection Agency.
August, 1973. 230 p.
13. Nilsson, R. Removal of Metals by Chemical Treatment of Municipal Waste-
water. Water Research. 5:51-56, May, 1971.
14. Argaman, Y. and C.L. Weddle. The Fate of Heavy Metals in Physical-
Chemical Treatment Processes. AICHE Symposium Series "Water 1973".
15. Maruyama, T., S.A. Hannah, and J.M. Cohen. Removal of Heavy Metals
by Physical and Chemical Treatment Processes. (Presented at 45th Annual
Conference of the Water Pollution Control Federation. Atlanta. October 12,
1972) .
16. Zuckerman, M.M. and A.H. Molof. High Quality Reuse Water by Chemical-
Physical Wastewater Treatment. Journal of the Water Pollution Control
Federation. 42_: 437-456, March, 1970.
17. Weber, W. J. Discussion of Paper 1-21. In: Advances in Water Pollution
Research. Proceedings of the 5th International Conference held in
San Francisco and Hawaii, 1970, S.H. Jenkins (ed.) . Oxford, Pergamon
Press, 1971. p. 1-21/22.
18. Weber, W.J. Discussion. Journal of the Water Pollution Control Federation
42_: 456-463, March, 1970.
19. McDonald, G.C., W.J. Greene, F.W. Hardt, R.D. Spear, Washington,
D.W., andN. L. Clesceri. Discussion of Paper 1-21. In: Advances in
Water Pollution Research, Proceedings of the 5th International Conference
held in San Francisco and Hawaii, 1970 S .H. Jenkins (ed.) . Oxford,
Pergamon Press, 1971. p. 1-21/23.
20. Molof, A.H. and M.M. Zuckerman, High Quality Reuse Water from a Newly
Developed Chemical-Physical Treatment Process. In: Advances in Water
Pollution Research, Proceedings of the 5th International Conference held in
San Francisco and Hawaii, 1970. S.H. Jenkins (ed.) . Oxford, Pergamon
Press. 1971. p. 1-21/22.
21. Westrick, J . J . and J .M. Cohen. Comparative Effects of Chemical Pretreat-
ment on Carbon Adsorption. (Presented at 45th Annual Conference of the
Water Pollution Control Federation. Atlanta. October 11, 1972) .
73
-------
22. Gulp, G.L. Design of Facilities for Physical-Chemical Treatment of Raw
Waste Water. Gulp, Wesner, Gulp. Corona del Mar. Environmental
Protection Agency. Technology Transfer Seminar Publication. August,
1973. 29 p.
23. Lime. Wallace & Tiernan . Belleville, N.J. Sales Services Department
Bulletin Number T60. 350-1. April, 1970. 12 p.
24. Martin, Larry. Personal Communication to D.S . Parker. City of Holland,
Michigan. October 6, 1973.
25. Brown and Caldwell. Plans and Specifications for Water Reclamation Plant,
Stage 5A - Phase 1. Central Contra Costa Sanitary District. California.
April, 1973.
26. Babcock, R.H. Instrumentation and Control in Water Supply and Waste-
water Disposal. Reprinted from Water and Wastes Engineering. 1968.
89 p.
27. Parker, D .S ., W. J. Kaufman, and D. Jenkins. Floe Breakup in Turbulent
Flocculation Processes. Journal of the Sanitary Engineering Division.
Proceedings of the ASCE. 98_ (SA1): 79-99, February, 1972.
28. Parker, D.S. andD.G. Niles. Full-Scale Test Plant at Contra Costa Turns
Out Valuable Data and Advanced Treatment. Bulletin of the California
Water Pollution Control Association. 9 (1): 25-27, July, 1972.
29. Alternative Treatment Processes for Reductions of Turbidity, Color,
Floatables, Grease and Settleable Matter. Brown and Caldwell, Consulting
Engineers. Report for the City and County of San Francisco. September,
1971. p. 23-53.
30. Love, R. and F. Gaines. Personal Communication to D.S. Parker.
Hatfield Township Municipal Authority. August 23, 1973.
31. Burns, D .E . and D. J. Cook. Physical-Chemical Treatment of Municipal
Waste. Progress Report No. II. Envirotech Corporation, Salt Lake City.
PRF-11, March 15, 1973.
32. Argaman, Y. and WJ. Kaufman. Turbulence and Flocculation. Journal
of the Sanitary Engineering Division, Proc. of the ASCE. 96 (SA2): 223-
241. April, 1970. ~~
33. Tofflemire, T J. and L J ..Hetling . Treatment of a Combined Wastewater by
the Low Lime Process, Journal Water Pollution Control Federation, 45, 210
(1973). —
74
-------
34. Pilot Plant Demonstration of a Lime-Biological Treatment Phosphorus
Removal Method. Department of Civil Engineering, Kansas State
University. Manhattan. Project 17050 DCC . Environmental Protection
Agency. September, 1972. 43 p.
35. Ranson, William. Personal Communication to D .S . Parker. City of
Hastings, Michigan. October 6, 1973.
36. Martin, Larry. Personal Communication to E . de la Fuente. City of
Holland, Michigan. October 26, 1973.
37. Gaines, F.R. Personal Communication to E . de la Fuente. Hatfield-
Township Municipal Authority, Pennsylvania. October and December,
1973.
38. Shell, G.L. Personal Communication to D .S . Parker . Envirotech
Corporation. Salt Lake City. August 31, 1972.
39. Convery, J.J. The Use of Physical-Chemical Treatment Techniques for
the Removal of Phosphorus from Municipal Wastewaters. (Presented at
the Annual Meeting of the New York Water Pollution Control Association.
New York. January 29, 1970) . 39 p.
40. Cooper, R.C., R.C. Spear, andF.C. Schaffer. Virus Survival in the
Central Contra Costa County Water Renovation Plant. School of Public
Health, University of California. Berkeley. January, 1972. 38 p.
41. Mulbarger, M.C., E. Grossman, III, R.B. Dean, andO.L. Grant. Lime
Clarification, Recovery, Reuse and Sludge Dewatering Characteristics.
Journal of the Water Pollution Control Federation. 41_: 2070-2085,
December, 1969.
42. Wuhrman, K. Objectives, Technology, and Results of Nitrogen and
Phosphorus Removal Processes. In: Advances In Water Quality Improve-
ment, E.F. Gloyna and W.W. Eckerfelder (eds.) . Austin. University of
Texas Press, 1968. p 21-43.
43. Caldwell, D.H., D.S. Parker, and W.R. Uhte. Upgrading Lagoons.
Brown and Caldwell. San Francisco. Environmental Protection Agency.
Technology Transfer Seminar Publication. August, 1973. 43 p.
44. Bishop. D.F., T.P. O'Farrell, and J.B. Stamberg. Physical-Chemical
Treatment of Municipal Wastewater. Journal of the Water Pollution Control
Federation. 44: 361-371, March, 1972.
45. Parker, D.S., D.G. Niles, and F.J. Zadick. Processing of Combined
Physical-Chemical-Biological Sludge. Brown and Caldwell and the Central
Contra Costa Sanitary District. (Presented at 46th Annual Conference of
the Water Pollution Control Federation. Cleveland. October 1, 1973) . 23 p.
75
-------
46. Gulp, R.S. and G.L. Gulp. Advanced Wastewater Treatment. First
Edition. New York, Van Nostrand Reinhold Company, 1971. 310 p.
47. Shuckrow, A.J. and W.F. Bonner. Development and Evaluation of
Advanced Waste Treatment Systems for Removal of Suspended Solids,
Dissolved Organics, Phosphate and Ammonia for Application in the City
of Cleveland. Battelle-Northwest, Richland. Zurn Environmental
Engineers. June, 1971. 96 p.
48. O'Farrell, Thomas. Personal Communication to D.S . Parker. Environ-
mental Protection Agency, Blue Plains Pilot Plant. October 11, 1973.
49. Sewage Treatment Plant Design. Water Pollution Control Federation.
Washington, D.C. Manual of Practice No. 8. 1959. 375p.
76
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SECTION VII
LIME SLUDGE THICKENING AND DEWATERING
GENERAL CONSIDERATIONS
Sludge thickening and dewatering are preparation or pretreatment steps which
normally precede further sludge processing or final disposal. In wastewater
treatment, thickening and dewatering have often been considered as different
types of processes; in fact, thickening is a dewatering process. As currently
applied, however, sludge thickening implies solids concentration with the aim
of reducing the volume of sludge to be handled in subsequent treatment steps.
Dewatering implies further removal of water, generally by mechanical means,
to produce a relatively dry sludge cake for further treatment or disposal.
Land methods of sludge dewatering have not been included in this section, since
in the majority of applications, they constitute the ultimate method of sludge
disposal. For a discussion of ultimate disposal of ash, see Section XI.
SLUDGE THICKENING
Although sludge thickening is a preliminary process, it removes a major amount
of liquid from the sludge. The curves presented in Fig. 7-1 show the reduction
of water content under varying degrees of thickening. For example, when the
sludge concentration is increased from 1.5 to five percent, over 70 percent of
the original moisture is removed.
Two methods are commonly used to thicken sludge - gravity and air flotation. In
general, the gravity method is used to thicken primary sludges; i.e., sludges
that settle readily, while air flotation is employed when dealing with the lighter
biological sludges.
1 2
A third thickening method, using centrifugal equipment, ' is gaining accept-
ance, generally as an alternative to dissolved air flotation. When centrifuges
are applicable, their use results in considerable savings in floor space require-
ments. Power costs, however, are likely to be higher than with gravity or air
flotation thickeners.
Gravity Thickening
The results obtained at the CCCSD's ATTF in terms of thickening in the primary
clarifiers lead to the conclusion that gravity thickening has clear advantages
when dealing, with the heavy lime sludges generated from primary treatment
applications. This process is not only simple to operate but also more econom-
ical than dissolved air flotation or centrifugation.
77
-------
100
23456789 10 II
INCREASE IN SOLIDS CONCENTRATION, PERCENT BY WEIGHT
Figure 7-1 Relationship between increase in solids concentration and
moisture removal (after Katz (12))
Scant information is available on gravity thickening of primary lime sludge.
Black and Lewandowski conducted a three-month plant scale operation at
Richmond Hill, Ontario, where lime sludge concentrations of up to 12 percent
solids were achieved in gravity thickeners.^
Burns and Shell have reported the results of eight months of laboratory
thickening tests at pH values between 9.8 and 11.6. From these results they
conclude that "the moderate treatment pH (below 11.0) sludges tested were
generally more concentrated than the high treatment pH sludges (above 11.5) ."
Burns and Shell also stated that "it appears that the more concentrated the
chemical clarifier underflow (initial solids) the more the solids can be concen-
trated." During the same work, Burns and Shell also evaluated the effect of
polyelectrolytes as flocculation aids on thickener performance. They concluded
that, although the continuous use of polyelectrolytes solely to reduce the thick-
ener size was probably unjustified, the addition of chemicals would maintain a
high underflow concentration under decreasing feed solids concentration.
78
-------
At the time this report was being prepared, Burns and Shell were reevaluating
their projections for thickener performance. A compression zone analysis
indicated that to obtain ultimate sludge concentration (18-25 percent TS) ,
thickener solids loading would have to be reduced below 49 kg/sq m/day
(10 Ib/sq ft/day) , which is considerably lower than the 196 - 245 kg/sq m/day
(40 - 50 Ib/sq ft/day) previously recommended.5 This came to light when they
found that the results obtained in the laboratory tests could not be reproduced
in a 2.4m (8ft) diameter gravity thickener .6, / Thickener performance was
erratic, varying from no additional concentration to about 35 percent increase
in the feed solids concentration. The concentration of feed solids ranged from
8.1 to 12.0 percent TS. Average thickener loading was 78 kg/sq m/day (16 Ib/sq
ft/day) . The most recent recommendations on the design of gravity thickeners
based on the work at Salt Lake City are included in Reference 8.
Investigators at EPA's Blue Plains pilot plant have conducted tests on the thick-
ening properties at high lime sludge.9 Interfacial settling velocity as a function
of total solids concentration is shown in Fig. 7-2. Essentially, no differences in
settling rates were observed between cases where recalcined lime was used and
where only new lime was used. Using a batch flux method of analysis, it was
concluded that with a solids loading of 673 kg/sq m/day (138 Ib/sq ft/day) , 10
percent underflow solids could be obtained. Similarly, at a solids loading of
430 kg/sq m/day (88 Ib/sq ft/day) , it was calculated that 20 percent total solids
in the underflow could be obtained. The investigators cautioned, however, that
this data had not been verified in continuous thickening tests.
Gravity thickeners are commonly deep circular tanks provided with a rotating
arms mechanism for sludge agitation and collection. The feed sludge is intro-
duced into a circular influent well and the overflow is usually collected over
peripheral weirs. The thickened underflow forms a sludge blanket so the unit
performs not unlike a solids contact clarifier. Sludge is withdrawn, contin-
uously or intermittently, from a centrally located bottom hopper. A typical
section of a gravity thickener is shown in Fig . 7-3.
To prevent septic conditions in the thickener, the use of chlorine has been rec-
ommended. The dosage should produce a residual chlorine concentration of
0.5 to 1.0 mg/1.2 Low pressure air has also been used to prevent septicity.
The gentle agitation provided by the compressed air also aids in promoting
solids concentration by allowing entrapped water to escape through the sludge
blanket. 10 This approach is seen in Fig. 7-4, which shows a cross section of
the lime sludge thickener at the CCCSD water reclamation plant.11 A 20-ft
deep existing digester is being converted into a thickening tank. Design
loading is 390 kg/sq m/day (80 Ib/sq ft/day) and the lime sludge will be fed at
an approximate concentration of 6 percent TS . Compressed air can also be used
to fluidize the sludge blanket to control maximum solids concentration and to
allow low-torque starting of the rotating arms.
79
-------
1
o
3
UJ
>
o
Ul
to
O WITHOUT LIME REUSE
A WITH LIME REUSE
20 -
8
12
16
20
24
TOTAL SOLIDS, PERCENT
Figure 7-2 Settling characteristics of high lime sludge
at the Blue Plains pilot plant
80
-------
MANUAL ARM LIFT
VERTICAL
ADJUSTABLE^
DIFFUSER
ARM 8 CONCENTRATOR ASSEMBLY
THICKENED SLUDGE
Figure 7-3 Typical gravity thickener (courtesy of Walker Process)
Although the concentration of solids that takes place in the primary sedimentation
tank (see Section VI) could justify eliminating separate gravity thickeners, the
latter also perform as sludge flow equalization basins. This function is as
important as solids concentration to smooth out the flow of solids to downstream
treatment processes. Since sludge production varies during the day, removal
from the primary clarifiers is normally intermittent to insure that only well
compacted sludge is withdrawn. The presence of thickeners then allows a
fairly constant sludge feed to the centrifuges or furnaces which is essential for
steady state operation. It is under steady state conditions that the dewatering
and incineration equipment can achieve peak performance.
Surface skimming has not always been employed on gravity thickening tanks.
Surface skimming has been found to be mandatory on tanks receiving centrate
from a centrifuge classification step at the CCCSD's ATTF. (See a later
discussion of classification in this section) . The centrifuge operation caused
81
-------
00
Id EXHAUST
A/RUNE
•— A IK LINE. SPACING
TO as otreRM/NCD
BY MMUfjCTUKtR
/
-------
the incorporation of fine bubbles into the centrate, resulting in some foam flota-
tion. This phenomenon has been used at Blue Plains^ to accomplish flotation
thickening, as is discussed in this section under Flotation Thickening.
Thickening data obtained to date have resulted in wide variations in terms of
design recommendations. Therefore, development of firm design criteria will
have to await further investigation.
Flotation Thickening
Thickening of sludge by dissolved air flotation has seen wide acceptance in
recent years, particularly in waste activated sludge applications. To separate
solids from water by flotation, gas bubbles are formed by dissolving air into the
water at a pressure of approximately 2.8 kg/sq cm (40 psig) . The air charged
stream is then mixed with the sludge where the pressure is released forming
fine air bubbles which adhere to the solid particles. Once introduced into the
tank, the lowered specific gravity of the solid particles causes them to rise to
the surface. As the solids accumulate, a blanket of sludge is formed. An over-
head skimmer removes the top of the sludge blanket, where the high solids
concentration occurs, and discharges it to a sludge hopper. The relatively
clear underflow moves out of the separation zone under a submerged baffle and
flows over the effluent weir. Fig. 7-5 shows a schematic diagram of the air
flotation process.^ The pressurized flow source may be recycled thickener
underflow, plant effluent or some other process flow.
When centrifugal equipment is used for separation of calcium carbonate from
other waste solids (see Wet Classification in this section) , the high speed
centrifuge operation tends to aerate the sludge and to create fine bubbles in the
centrate. These bubbles behave as air bubbles would in a conventional air
flotation system when the centrate enters a quiescent tank. Bennett 9 has used
this effect to accomplish thickening of the centrate solids without a supplementary
air dissolution step. Centrate at 2-3 percent total solids, has been thickened by
this procedure to 4.7 to 7.3 percent total solids. Bennett cautioned, however,
that the transfer of the centrate to the thickening tank must be immediate to
prevent bubble release from the sludge. To insure consistent operation, it is
desirable to make provisions for standard air dissolution equipment.
The application of conventional air flotation equipment to thicken lime sludges
must be approached with caution. The introduction of carbon dioxide from the
pressurized air may cause scaling of equipment with the accompanying main-
tenance problems. Purified oxygen or nitrogen might prove a better gas source
than ambient air for dissolved air flotation in this application, since they con-
tain a negligible quantity of carbon dioxide.
Specific design criteria for flotation thickening of lime sludges have not been
published to date.
83
-------
SLUDGE
FLOW
TO BE
THICKENED
CO
*>,
PRESSURE
REDUCTION
VALVE
THICKENED
^SLUDGE
BASIN
.THICKENER
EFFLUENT
AIR
INJECTION
. t
AIR
SOLUTION
TANK
PRESSURIZED
FLOW SOURCE
PRESSURIZATION
PUMP
^-AIR-CHARGED
STREAM
Figure 7-5 Schematic diagram of the dissolved air flotation process
-------
SLUDGE DEWATERING
The main purpose of mechanical dewatering is to minimize the moisture content of
the sludge. When oriented towards incineration, a more specific purpose is to
increase the volatile content per pound of wet sludge. Approximately 450 kg-cal
(1800 Btu) are required to evaporate a pound of water (at an off-gas temperature
of 700 F); therefore, excessive moisture increases the thermal load on the incin-
eration process and the amount of auxiliary fuel required. The influence of
moisture content on the cost of sludge incineration is shown in Figs. 7-6 and 7-7
for primary sludge.2
Two methods are commonly used in the United States for sludge dewatering -
vacuum filtration and centrifugation. A third method, utilizing filter presses,
enjoyed limited use in the past, 10 although in recent years there has been
renewed interest in pressure filtration for dewatering the more difficult sludges.
Pressure filtration of sludge has been practiced in Europe for many years.
The methods employed for sludge dewatering have a marked impact on the solids
processing design, when the objective is recovery of lime from sludges. When
vacuum or pressure filtration is used to dewater the primary-generated sludge,
all of the sludge is captured in a single dewatering stage. Therefore, all of the
sludge must be recalcined in a Plural Purpose Furnace (Fig. 7-8) . Inerts (con-
stituents other than calcium carbonate or calcium oxide) must be controlled from
building up through recycling after several passes; therefore, blowdown of a
portion of the recalcined product is mandatory with consequential loss of a
portion of the reclaimed lime. 3 Dry classification, a process described in detail
in Section VIII, allows this ash blowdown to be somewhat more efficient in terms
of rejecting silica inerts .
When centrifugation is employed, it is possible to classify the calcium carbonate
from most of the magnesium, phosphorus, and iron compounds as well as from
the organics. A high calcium carbonate cake is produced which can be
recalcined (Fig. 7-9) to produce reclaimed lime. Dry classification can be
effectively employed in this flowsheet to blow down silica. The centrate from
the wet classification step containing the waste solids can be disposed of by a
number of procedures. One alternate, shown in Fig. 7-9, is to use another
centrifuge to separate the waste solids and use incineration to produce an ash
residue for final disposal. Another alternative would be to employ lime stabi-
lization of the solids prior to dewatering, followed by direct disposal of the cake
as land fill. Alternately, digestion of the centrifuge centrate could be used
before final disposal.3
Centrifugation
Centrifuges have long been used for sludge dewatering, although at a limited
scale, due mostly to their early design and construction deficiencies. 10 How-
ever, the development of the present efficient machines has led to the wide
acceptance of centrifuge equipment for mechanical dewatering applications. The
theory of centrifugal separation has been presented in References 10 and 13.
85
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0
WITH HEAT
RECOVERY AND
PREHEAT AIR TO
1000° F
WITHOUT HEAT
RECOVERY
% TOTAL SOLIDS IN SLUDGE
AT 75% VOL AND 5270KG-CAL/KG (9500 BTU/LB.) VOLATILE
Figure 7-6 Effect of moisture content on the cost of sludge combustion
86
-------
o
o
o
o:
ff
o
O
si-
CD
a:
a
I
o
2
o
— x
_j _i
uj - ~>c
% °
< o
< <£
0
% TOTAL SOLIDS VS. AUX FUEL
EXIT TEMP AT 1500° F EXCESS AIR 20%
(I) 1970 DOLLARS
(I)
$2.56/TON
(I)
$1.76/TON
(I)
$0.92/TON
25
275
30
% TOTAL SOLIDS IN SLUDGE
SLUDGE 75% VOL. AND 5500KG - CAL/KG (10,000 BTU/LB) VS.
Figure 7-7 Effect of moisture content on the cost of sludge combustion
87
-------
MAKEUP LIME
1
L IME
STORAGE
PRIMARY CLAR IFIER
LAKERi
u
RAW SEWAGE A
FILTRATE
TO
PRIMARY
CAKE
J-
PRIMARY
EFFLUENT
MULTIPLE
HEARTH
RECALCINE;
FURNACE
DRY
CLASSIFICATION
JRECYCLE LIME TO STORAGE
VACUUM
FILTER
OR
CENTRIFUGE
OR
FILTER PRESS
GAS
SCRUBBER
ASH
ASH
SLOWDOWN
ASH REJECTS
ACCEPTS
Figure 7-8 Conventional Plural Purpose Furnace flow sheet
88
-------
FROM
RECALCINING FURNACE
1
MAKEUP
LIME
WASTE
BIOLOGICAL
SOLIDS
LIME
STORAGE
S LAKER
W '
CENTRATE RETURN
RAW
SEWAGE
LIME
REACTOR
(PREAER-
ATION)
ATTF
PRIMARY CLARIFIER
. _--^
PRIMAR
EFFLUEf
FIRST
STAGE
THICKENER
WET
CLASSIFICATION
SECOND
STAGE
THICKENER
2nd STAGE CENTRIFUGE
OR
FILTER PRESS
OR
VACUUM FILTER
MULTIPLE
HEARTH
RECALCINE
FURNACE
'GAS
SCRUBBER
IRECALCINED
ASH
REJECTS
DRY
CLASSIFICATION
RECYCLE LIME TO STORAGE
CENTRATE TO
PRIMARY
MULTIPLE
HEARTH
FURNACE
HIGH LIME
ACCEPTS
ASH TO DISPOSAL
Figure 7-9 ATTF solids processing system
89
-------
Three general types of centrifuges are available today - basket, disc, and solid
bowl. However, only the last type is capable of producing both a dry sludge
cake and a well clarified centrate in a single step.
The main elements of a solid bowl, scroll type centrifuge are the rotating bowl
and the conveyor mechanism. The solids, under the effect of the separating
force ("G" force) settle in the cylindrical-conical bowl, and are then picked up
by the screw conveyor which carries the settled solids to the discharge ports.
Solid bowl centrifuges used in sludge dewatering are available in two basic flow
configurations - concurrent and counter-current. In the concurrent design, the
feed is introduced at one end and the liquid and solids travel together toward the
outlet ports. In the counter-current type, the feed is introduced near the conical
portion of the bowl (the dewatering beach) . The solids are moved in one direction
while the centrate is discharged in the opposite direction. Fig. 7-10 shows both
types of centrifuges.
Solid bowl centrifuges can be manufactured of various alloys to provide protection
under abrasive or corrosive operating conditions . Table 7-1 lists materials of con-
struction used by a major manufacturer of centrifuge equipment. Where an abrasion
problem is more likely to occur, such as in the feed zone and conveyor flights,
hard surfacing techniques are often used to provide abrasion-resistant materials.
Table 7-1. SOME BASIC MATERIALS OF CONSTRUCTION USED IN
SHARPLES CENTRIFUGES
METALS
ABRASION RESISTANT
MATERIALS
CORROSION RESISTANT
COATINGS
Steel, Carbon & Alloy
Stainless
304, 304L, 316, 316L
317L, 329, 17-4PH, 431
(Miso PH Grades)
Carpenter 20-Cb 3
Titanium, C. P. Grades
Ti (6 A1-4V,), Ti (0. 2% Pd)
Hastelloy B; C-276
Wiscalloy B, C (Low Carbon)
Monel 400, K-500
Inoaloy 800, 825
Nickel 200
Tungsten Carbide (Solid)
Tungsten Carbide (Plasma Fused)
Tungsten Carbide Composites
WC & Steel Matrix
WC & Hastelloy Matrix
WC & Ni, Dr, B, Matrix
WC & Co, Cr, W Matrix
Formaflex Coatings
Ceramics (Solid)
Ceramics (Plasma & Flame Sprayed)
Hard Chromium & Armaloy
Cobalt-Chrome-Tungsten
(Stellite-Stoody)
Nickel-Chrome-Boron
(Colmonoy-Coast)
Hard Rubber
Neoprene
Kynar
TFE
Penton
Tin, Cadmium, Zinc
Nickel (Electroless)
Chromium
Multiple Paint Systems
Epoxy-Phenolic
Urethane, Vinyl
Alkyd, Plastisol
Organic Zinc
90
-------
-f
FEED
SOLIDS
DISCHARGE
CENTRATE
Concurrent flow centrifuge (courtesy of Bird Machine Company)
LIQUIDS
DISCHARGE
-Counter-current flow centrifuge (courtesy of Sharpies-Stokes
Division of Pennwalt Corporation)
Figure 7-10 Solid-bowl conveyor centrifuges
91
-------
Centrifuges are normally designed for horizontal installation, although one
manufacturer, Sharpies, offers a line of vertical units. Among the advantages
attributed to the vertical centrifuge, when compared to the horizontal design,
are smaller floor space requirements and higher unit capacity. The latter
feature is particularly advantageous in large installations where the required
number of horizontal machines can be replaced by a smaller number of vertical
units. This reduction of equipment would often compensate for the higher initial
cost of the vertical centrifuges . At the CCCSD water reclamation plant, the
capital cost of providing four vertical machines to wet classify 110,000 kg of dry
solids (DS) per day (242,000 Ib/day DS) and to clarify 40,800 kg/day (90,000
Ib/day) DS (wet classification will be described later in this section) was 7.5
percent lower than the alternative to supply six horizontal machines to handle
the same sludge quantities. Each alternative included the cost of the auxiliary
equipment normally required for centrifuge operation. Fig. 7-11 shows the
vertical centrifuge layout at the CCCSD plant. H
Sludge dewatering by centrifugation is affected by both process and machine
variables. The Water Pollution Control Federation (WPCF) manual on sludge
dewatering practices lists the following:
"Process Variables:
(a) sludge feed rate,
(b) sludge solids characteristics,
(c) sludge consistency,
(d) sludge temperature, and
(e) chemical addition."
"Machine Variables:
(a) bowl design;
i L/D ratio,
ii bowl angle,
iii flow pattern
(b) bowl speed,
(c) pool volume,
(d) conveyor design, and
(e) relative conveyor speed ."
The effects of some of these variables will be covered in detail under Wet Classi-
fication . The best way to evaluate all of the variables listed above is through
pilot plant testing. Test centrifuges are available from several equipment
manufacturers, which use a scale-up factor, £ , to predict results at full scale
ope ration.14
92
-------
SHAFT COOLING\
AIR DUCT
MULTIPLE
HEARTH
FURNAC
CENTRIFUGE
DRIVE MOTOR
TYPICAL
SCREW CONVEYOR
DRIVE
CASING VENT
TYPICAL
WORKING PLATFORM
PLAN
CENTRIFUGE
FEED
BELT DRIVE
GUARD
GRATING
CENTRATE
DISCHARGE
-SHAFT COOLING
AIR DUCT
HEARTH 1
(AFTERBURNER)
HEARTH 2
HEAR
TH 3
TRANSFER SCREW
CONVEYOR
FEED SCREW
CONVEYOR
ELEVATION
Figure 7-11 Vertical centrifuge installation at the CCCSD water reclamation
plant
93
-------
Scaling Factors -
14
The equation for £ is as follows:
4R1 + 4ix2
v
where: L = bowl length, cm
R! = radius of the liquid surface, cm
R2 = radius of the inner wall of the bowl, cm
w = rate of rotation, rad/sec.
These terms have been represented in Fig. 7-10. The £ factor represents the
area, in sq cm, of a theoretical gravity sedimentation tank having equivalent
clarification characteristics to the centrifuge. Thus, £ can be used to relate
capacities of different centrifuges, such as the filtering surface area which is
used in sizing vacuum filters .
There is some controversy among centrifuge manufacturers concerning the
appropriate bowl length to be employed in the S equation. Some manufacturers
use the total bowl length, some include the portion of the dewatering beach
that is wetted, and still others include only that portion of the beach between
the liquid discharge and the mid-point of the feed ports. From a theoretical
standpoint, the effective clarification length is most closely approximated by
the latter definition for the counter-current design (see Fig. 7-10) . At any
rate, if machines of different manufacturers are to be compared, I> must be
calculated on the same basis for each. The calculation of the SL factor is one of
the essential steps in comparing equipment proposals of different manufacturers.
However, it must be remembered that the value of
-------
From the above calculation, it would be expected that it would take four of
Manufacturer A's machines to do the job that three of Manufacturer B's machines
would do.
Wet Classification
The problem in recovering lime from raw sewage sludge is that many constituents
are precipitated with the sludge besides calcium carbonate. As explained in
Section VI, organics, phosphorus, magnesium, iron, and other constituents are
coprecipitated with calcium carbonate. These constituents, if left with the
calcium carbonate during recalcining, are returned to the process. Eventually,
these "inerts" build up to such a magnitude that the solids processing facilities
are overwhelmed. This problem has been the major reason that recovery of lime
added in the primary sedimentation tanks has not been practiced. 15 The problem
of lime recovery has also been a deterrent to the use of lime in raw sewage
coagulation.
Sludge solids vary greatly both in size and density and as a result, they settle at
widely different rates. The process whereby the sludge constituents are
separated into various categories based on this spread in settling rates is called
wet classification. Centrifugal action magnifies the difference in settling of solids
particles; therefore, centrifuges are particularly suitable for wet separation.
The ability of centrifuges to classify particles on the basis of both size and
density has been used in industrial applications for many years. 16 Wet classi-
fication has been used for over three decades to control inerts buildup in water
softening plants practicing lime reclamation.I7/18,19 Classification data from
three studies where Bird centrifuges were employed are shown in Table 7-2.
Except for anamolous behavior with silica, good rejection of all components was
obtained, while retaining silica. The procedure for calculation of the recoveries
has been described previously.3
Table 7-2. CLASSIFICATION DATA FOR WATER TREATMENT
PLANT SLUDGES
Plant
Constituent
Total Solids
Calcium
Magnesium
Iron
Aluminum
Silica
Recovery of stated constituent, percent
Wright Aeronautical
Corp. , Cinncinati, Ohio
Run 1
74
84
51
43
17
Run 2
81
88
57
11
40
Run 3
96
100
36
53
<1
38
Columbia Steel
Corp. , Provo, Utah
Run 1
92
96
3
51
50
92
Run 2
85
90
3
47
58
Marshalltown,
Iowa"
Control
80
89
16
62
Cycle 1
75
98
20
58
Cycle 2
75
95
9
66
Cycle 3
77
92
20
70
Findlay
Ohioc
73
77
40
Reference 17
^Reference 18
cReference 19
95
-------
In the case of lime sludges, the purpose of wet classification is to maximize
recovery of calcium carbonate in the centrifuged cake while rejecting the other
components to as great an extent as possible. The calcium carbonate crystals
settle more rapidly than the other solids . Consequently, a partial recovery of
the total solids with a centrifuge concentrates the calcium carbonate along with
the heavy inert solids in the cake.
Classification Efficiency - Classification efficiency of a centrifuge is expressed
in terms of the percentage of the particular constituent in the feed that is
recovered in the cake. Good classification efficiency is achieved when calcium
carbonate recovery is high and when recovery of the other constituents is low.
In pilot plant studies at the CCCSD's ATTF,3'20 the recovery of each component
was compared with the total solids recovery, to get an indication of the efficiency
of component classification. The relationships derived from this analysis are
shown in Fig. 7-12. From the figure, it can be observed that there is a fairly
broad range in which fairly high calcium carbonate recovery is coupled with
reasonable classification. For instance, at 50 percent total solids recovery, 70
percent of the calcium carbonate is recovered with less than 30 percent of the
other major constituents, while at 70 percent total solids recovery, almost 90
percent of the calcium carbonate is recovered with less than 50 percent of the
other major constituents, except the acid insoluble inerts. The one constituent
without good classification characteristics is the acid insoluble inerts. Re-
coveries shown in Table 7-3 range from 41 to 100 percent recovery. Quite wide
variation in recovery of these inerts was obtained, perhaps because of variations
in composition of these inerts in the feed sludge. In subsequent work21 where
recalcined lime was recycled, the acid insoluble inerts were found to be com-
prised primarily of silica (80 to 90 percent) .
Data obtained at the CCCSD's ATTF on classification during a representative
period of lime reuse are shown in Table 7-4.21 During this work, specific tests
on the silica levels in the sludge allowed the determination of silica recovery at
85 percent. This means that there is essentially no rejection of silica; it is
recovered at nearly the same level as calcium carbonate. A plot of the classi-
fication relationships determined during the ATTF test work on lime recycling
is shown in Fig. 7-13. Classification for all constituents, except ferric
hydroxide and silica, was similar to that experienced without lime recycle
(Fig. 7-12) . With silica, it was found that recovery increased from less than
the calcium carbonate recovery prior to lime recycle to a level greater than
the calcium carbonate recovery after lime recycle.21 Apparently, the furnace
operation altered the classification characteristics of the silica recycled to the
process. Iron recoveries were consistently greater than experienced previously,
even during the period prior to the actual implementation of lime recycle. It is
felt that this was due to the addition of iron to the downstream nitrification
system, so that iron precipitates entered the primary incorporated into the waste
activated sludge, rather than as a supplemental coagulant as in previous work.
96
-------
too
20
RECOVERY
OF
40
TOTAL
6O 8O
SOLIDS, PERCENT
IOO
Figure 7-12 Summary of constituent recoveries during wet classification
without lime recycle
Besides demonstrating the feasibility of wet classification of lime sludges, the
data presented in Table 7-3 show the wide range in degree of classification
attained. These variations are due primarily to differences in centrifuge
operating conditions. The principal variables are feed rate, centrifugal force
and pond depth setting.
97
-------
Table 7-3. RUN DATA FOR VJE'- CLASSIFICATION
Process Parameters
Hun
'2-7
2-5
2-1
2--J
2-32
2-]2a
Machine
Sharpies
P-liOO
Sharpies
N~1 P-3000
.1-4
S-12
8-9
8 -is
n-5
8-41
8-40
4-3-72
4-134
4-106
4-105
4-123b
Sharpies
P-600
Centrifugal
fo rcc
per Ib
mass, R'.S
2100
1050
2100
2100
1500
1500
3050
2100
Conveyor
speed,
AliPW
an
35
IB
2(i
05
50
9
Conveyor
pitch,
in.
2
3
1
Pond
number
1
3
1
3
1
2
3
1
1
4
Feed
rate ,
gpmc
s
10
10
12
9
3
23
49
25
49
21
49
19
43
10
5
7
14
4
Floccula-
tion
Pll
11.5
11 .0
10.2
Recoveries in Cake, percent
Total
solids
-------
Table 7-4. CENTRIFUGE PERFORMANCE SUMMARY-LIME SLUDGE
RECYCLE PROJECT
Date
7-27
29
31
8-2
4
6
8
10
Mean
Total
Solids
Recovery
Percent
62. 9
61. S
60.4
57. 7
53.4
55.2
56,6
53.0
57.6
Recoveries in Centrifuge Cake, Percent
CaC03
87.4
82. 1
82.7
78.8
77.9
78.3
76.8
84.7
81.0
Volatile
Matter
42.8
38.5
40.4
35.7
32.0
33.2
35.9
29.0
35. 9
Ca3(P04)2
18.0
21.8
17. 8
21.5
19.7
23.4
21.4
19.5
20.4
Mg(OH)2
7.5
28.9
41.8
30.3
25.6
25.6
36.3
18.7
26.8
Fe(OH)3
62. 9
54.0
48.3
43.2
53.4
55.2
51.9
53.0
52.7
Si02
66.2
75.8
99.6
82. 3
94.0
84.1
90.0
84.6
Otherb
(100)
61.8
84.6
69.2
(100)
47.3
75.5
63.7
75.3
Operational pH in the primary was 11. 0; the machine was the Sharpies P3000
operating at 2100 G, a pond setting of 1, and an influent flow rate ranging
.from 2. 2 to 2. 5 I/sec (35. 2 to 40. 0 gpm)
Acid insoluble inerts other than silica
Effect of Feed Rate - One of the most important parameters in the design of
equipment is the feed rate and the effect of variations in feed rate. Fortunately,
wide variation in feed rate can be tolerated for the purpose of constituent
classification. Examination of the data in Table 7-3 reveals that for runs made
under the same conditions, except for feed rate, there was only a slight deteri-
oration in constituent classification with an increase in feed rate.
Effect of Centrifugal Force - Another important variable in centrifuge opera-
tion is the centrifugal force. Most of the runs were made at a centrifugal force
per unit mass of 2,100 times the acceleration of gravity (G) . However, a few
runs were made at different G levels. Over the range of about 1,000 to 3,000
G, recovery of calcium carbonate increased only slightly with an increase in
centrifugal force.
Effect of Pond Setting - The depth of the liquid layer in the centrifuge bowl
would be expected to be an important variable. Increasing the depth of the
liquid (increasing pond number) had an adverse effect on the separation of
constituents. The best constituent separation was always attained at the
lowest pond setting. For example, runs 8-4 and 8-5 (Table 7-3) held all
process parameters constant except pond setting. The pond setting of 1 as
compared to 3 gave a higher recovery of calcium carbonate and a greater
rejection of all other components .
Effect of Lime Dosage, or pH - There is some indication that calcium carbonate
is more easily classified from the other components at a high pH than at a low
pH. Further, calcium carbonate recovery was better at a high pH than at a
low pH. However, some of the other variables were also changed simultaneously
with pH, and the pH effect could therefore not be firmly established. For
example, runs made at pH of 10.2 and 11.5 were made with different machine
99
-------
conveyors, while runs made at pH 11.0 were made with the larger of the two
machines. Also, the concentration of the various constituents in the sludge
was substantially different at the various pH levels, and that also could account
for the differences in degree of classification.
100
LU
O
£T
UJ
CL
CO
I-
LLl
Z3
j-
h-
co
o
U.
O
a:
UJ
>
o
o
LU
o:
0
20 40 60 80 100
RECOVERY OF TOTAL SOLIDS, PERCENT
Figure 7-13 Summary of constituent recoveries during wet classification
with Iime recycle
100
-------
Dewatering During Wet Classification -
Besides classifying the individual constituents of the solids, the dewatering of
the recovered cake must also be considered. Factors which are important are
the centrifuge operating conditions and the lime dosage or pH level used in the
primary treatment from which the sludge is produced. As with the classifica-
tion of solid constituents, the extent of dewatering is affected by several
centrifuge operating variables. The effects of feed rate, centrifugal force and
pond setting have been studied to determine their relative importance.
Effect of Feed Rate - As was noted in the discussion of constituent classifica-
tion, feed rate can be varied over a wide range with only a minor effect on
classification. Feed rate was also found to have little effect on total solids
recovery at all pH levels. For instance at pH 11.0 (Fig. 7-14) total solids
recovery at a pond setting of 1, decreased only from 63 to 54 percent when
flows increased from 0.9 to 3.2 I/sec (15 to 50 gpm) , more than a threefold
range.
Effect of Centrifugal Force - For constituent classification, centrifugal force
seemed to have a slight influence. For dewatering and solids recovery, how-
ever, the tests showed that centrifugal force is an important variable. In-
creasing the centrifugal force improved dewatering (Fig. 7-14 and 7-15) . A
centrifugal force of 2100 appears to be adequate for dewatering.
Effect of Pond Setting - The liquid depth (pond setting) had a substantial
effect on cake dryness (Fig. 7-15) . For dewatering, as in classification, the
best results were obtained with as shallow a liquid depth as possible (pond
setting No. 1) .
Centrate Processing by Centrifugation -
One alternative for processing the centrate from the wet classification stage is
to dewater the centrate in a second stage centrifuge and incinerate the cake.
In addition to dewatering the rejected solids from wet classification, a high
recovery of solids in the second stage is necessary to prevent a large return
of solids to the primary treatment process. The solids to be captured in the
second centrifuge stage are the slow-settling solids which were rejected in
the first centrifuge stage. Different operating conditions must therefore be
used in the second stage than in the first stage. Efficient capture requires
the addition of a polymer and a high centrifugal force to improve the settling
characteristics. Since it was found that with high recoveries the extent of
classification among the constituents was small, the major concern is the de-
watering and capture of the solids .
Effect of Conveyor Speed - Since the solids separated by centrifugal force are
removed from the bowl with a conveyor, its speed relative to the bowl speed
(A rpm) is one of the important operating variables. An example of the effect
of conveyor speed is shown in Fig. 7-16. The polymer requirement to attain
an 80 percent recovery of solids was reduced to about half by increasing the
conveyor speed from 8 to 12 A rpm. However, the extent of dewatering was
101
-------
100
90 -
a
lu
o
-------
reduced by the increased conveyor speed. Apparently there is an optimum
conveyor speed that gives the best balance between polymer usage and extent
of dewatering for a given feed and set of operating conditions.
100
80
kl
-------
100
8O
a
UJ
o
cc
kl
Q.
60
Uj
i>
o
CO
Q
20
Conveyor pitch, In.: 3 for P-3000
1 for P-600
Polymer: ICI Atlasep 2A2
_L
SYM
BOL
©
A
H
A
PH
11.0
1 1.0
11.0
11.2
11.2
MACHINE
P-3000
P-3000
P-3000
P-600
P-600
FEED RATE,
gpm
30.7
29.0
30.7
3.5
3.5
POND
SETTING
4
4
4
3 '/2
CONVEYOR
ARPM
18
11
16
10
10
FORCE,
g
3200
2100
I5OO
3O50
2100
CAKE,
% SOLIDS
16.0- 17.1
15.5- 17.4
11.4- 11.8
12.8-13.8
II. 4-12. 8
23456
POLYMER DOSAGE, IB / TON DRY SOLIDS
Figure 7-17 Effect of centrifugal force on solids recovery
Effect of Feed Rate - In the centrifuge test runs shown in Fig. 7-18, the feed
rate was varied from 0.9 to 1.8 I/sec (14 to 29 gpm) with no significant change
in polymer requirement or percent of solids recovered. There was an apparent
slight increase in cake water content at the higher feed rate. At the low feed
rate of 0.7 I/sec (11 gpm), about a third of the maximum rate used, solids
recovery was slightly better, and the polymer requirement was reduced. Fig.
7-18 shows that a wide range of feed rates can be used without changing the
efficiency to any great extent, which will lend flexibility to prototype operation.
For the runs at different feed rates, the conveyor speed was also varied to
maintain a relatively constant ratio of feed rate to conveyor speed. Since the
concentration of solids in the feed was essentially constant, the amount of solids
removed per conveyor revolution was also maintained constant, thereby essen-
tially eliminating the effect of conveyor speed on cake dryness.
Effect of Flocculation pH - No relationship was found between flocculation pH
and the polymer dose required to attain a given recovery level. However,
significant differences occurred in the observed dewatering. A flocculation pH
greater than 11.0 had a detrimental effect on second stage water content as
shown in Table 7-5. This difference would have a significant impact on sludge
incineration costs and would be a drawback to lime recovery with a flocculation
pH greater than 11.0.
104
-------
Table 7-5, EFFECT OF FLOCCULATION pH ON SECOND STAGE
CAKE DRYNESS
pH
11.2 to 11.5
11.0
10.2
Total solids in cake, percent
Range
11.0 to 14.4
15.5 to 19.6
13.7 to 20.3
Median
11.8
17.2
18.4
100
80
Uj
60
ct
lu
40
to
Q
-j
O
20
Machine; Sharpies P 3000
Pond • 4
Conveyor pitch , in : 3
Centrifugal force, g: 2100
Polymer : Atlasep 2A2
SYMBOL
0
0
A
FEED RATE
gpm
29.0
14.0
1 1.0
CONVEYOR
RPM
11
6
4
FEED,
% SOL IDS
1.6
1.5
1.6
CAKE,
% SOLIDS
15.5-17.4
16.8-19.0
16.4-18.0
23456
POLYMER DOSAGE, LB/TON DRY SOLIDS
Figure 7-18 Effect of feed rate on solids recovery
105
-------
Sludge Recarbonation - Some lime sludge processing flow sheets include pH
adjustment of the sludge with carbon dioxide ("recarbonation") prior to sludge
processing. The purpose of recarbonation is to dissolve the magnesium hydroxide
fraction which may hinder dewatering if left in the sludge. 1 Parker, et al.3
investigated recarbonation of the sludge prior to second stage centrifugation. In
general, there appeared to be little, if any, benefit derived from recarbonation
of the first or second stage feed sludge. The lowest pH investigated by Parker
et al. was 9.0. At this level, there was essentially no magnesium hydroxide
disTolved from the sludge. Therefore the findings of no change in sludge de-
watering properties by these investigators is not surprising.
Thompson and Black22 investigated dissolution of magnesium hydroxide from
water treatment plant sludge. It was found that a pH of 7.3 was required for
complete dissolution. They reported that the partial pressure of carbon dioxide
determined the rate of magnesium dissolution. Considering the work of
Thompson and Black,22 it appears that future work on sludge recarbonation
should be done with pH levels lower than that used by Parker, et al.3 Special
attention should be given to whether other materials (such as phosphate, calcium
or organics) are released in the process. The effects of centrate return to the
plant should also be evaluated.
Effect of Lime Recycle - Bennett evaluated lime sludge recalcination and reuse
at the Blue Plains pilot plant on sludge generated from raw sewage coagulation.9
Limited centrifuge data indicate a marked reduction in polymer requirements
when reclaimed lime was reused. (See Fig. 7-19) . The favorable influence on
sludge dewatering of recycling the inerts with the reclaimed lime can be com-
pared to the planned use of fly ash in other dewatering applications. Additional
data from the Blue Plains pilot plant on centrate treatment is given in Table 7-6.
Table 7-6. DEWATERINC OF HIGH LIME "!PC" SOLIDS AFTER
CENTRIFUGE CLASSIFICATION
Dewatering Method
Vacuum Filter
Filter Press3"
Centrifuge
Vacuum Filter
Filter Pressa
Centrifuge
Lime
Reuse
No
No
No
Yes
Yes
Yes
Feed Solids
Cone. , % TS
7. 7
7.5
5.7
5.2
2.6
6.6
Loading
7. 3-9. 8 kg/sq m-hr
(1. 5-2. 0 Ib/sq ft-hr)
1,169 kg/cu m (73
Ib/cu ft) 197 min cycle
35-48 ton DS/day
4. 9 kg/sq m-hr
(1. 0 Ib/sq ft-hr
1,202 kg/cu m (75
Ib/cu ft) 155 min cycle
35-50 ton DS/day
Cake Solids
Cone. , % TS
24-25
29-34
14-16
25-26
34
14-16
Chemical
Cost, $/ton
None
None
4-5
None
None
1-4
Xichols 1 sq ft filter press
Sharpless P600 centrifuge operated in high recovery mode.
106
-------
100
LU
O
o:
UJ
CL
o:
UJ
O
o
uu
cc
POLYMER DOSAGE, LB/TON
Figure 7-19 Effect of polymer dosage on lime recovery
-------
Whole Sludge Recovery with Centrifuges -
In addition to its classification capability, a centrifuge can also be used for whole
sludge recovery. A typical flow sheet for this application has been shown in
Fig. 7-8. Typical data from the Blue Plains pilot plant on operation for whole
sludge recovery is given in Table 7-7.
Table 7-7. DEWATERING OF "IPC" WASTE SOLIDS (WHOLE SLUDGE)
Sludge Source
IPC High Lime
IPC Low Lime
Vacuum Filter
Cake
Solids,
% TS
35-36
28-29
Loading,
kg/sq m-hr
(Ib/sq ft-hr)
30-45 (6-9)
10-15 (2-3)
Centrifugea
Cake
Solids,
% TS
28-32
28-29
Recovery, %
98-99
91-99
Cake
Production,
ton/day
43-90
85-90
Filter Press
Cake
Solids,
% TS
44-45
45-4Y
Cycle,
hrs.
1.0-1.2
2.6-3.6
Bulk Density,
kg/cu m (Ib/cu ft)
1378-1794 (86-112)
1250-1314 (78-82)
'Sharpies P600 centrifuge in high recovery mode
[chols 1 sq ft filter press
, on;
bNi.
Shuckrow and Bonner^ have reported the results of dewatering tests on primary
lime sludges in a 5.7 I/sec (90 gpm) pilot plant located in Cleveland. The pH
of the centrifuge feed was 10.5. When the centrifuge was operated at 5,000 rpm
(2,120 G) , solids capture ranged from 50 to 80 percent solids and the solids
concentration in the cake varied from 20 to 45 percent. Centrifuge performance
at 3,500 rpm (1,020 G) produced only a one percent drop in cake solids concen-
tration. Shuckrow and Bonner found that to increase solids capture to 95 per-
cent, approximately 0.55 to 0.75 kg (1.2 to 1.7 pounds) of polymer per ton of
dry solids were required. It was found that at 5,000 rpm the required polymer
dose was 30 percent lower than at 3,500 rpm for equal centrate quality. De-
watered sludge solids content was dependent on solids capture; solids content
averaged 26 percent at 70 percent capture and 22 percent at 90 percent capture
when using polymer conditioning .
Brown and Caldwell24 tested whole sludge recovery on sludge generated at pH
10.2 at the ATTF. In order to obtain 90 percent recovery at 2,000 G, it was
necessary to use 0.7 to 0.9 kg of anionic polymer per ton of dry solids (1.5 to
2.0 Ib/ton) . Cake solids varied from 19.5 to 28.4 percent TS.
Sludges generated in a two-stage lime treatment system processing partially
clarified raw wastewater have been tested at a 0.6 to 1.2 I/sec (10 to 20 gpm)
pilot plant at the CCCSD treatment plant.25 it was found that sludge generated
at pH 10.2 dewatered more easily than sludges at pH 10.8. To obtain 90 percent
recovery required 0.14 to 0.45 kg of anionic polymer per ton DS (0.3 to 1.0 lb/
ton) . Inspection of the data at pH 10.8 indicates that increasing the "G" level
from 750 to 2,100 improved recoveries from 72 to 90 percent at a polymer dose
of 0.17 kg per ton DS (0.38 Ib/ton) . Cake dryness was strongly related to
recovery in the centrifuge. At 90 percent recovery, 24 percent TS in the cake
108
-------
was obtained; at 80 percent recovery, 28 percent TS was obtained; at 70 percent
recovery, 33 percent TS was obtained; and at 60 percent recovery, 37 percent
TS was obtained .
found that a pH of 10 was optimum for good centrifuge results on primary
lime sludge. He obtained average cake concentrations of 33 percent and solids
recoveries of 78 percent without the use of polymers . However, centrate quality
was poor (1.3 percent SS) . Addition of an anionic polyelectrolyte resulted in
reductions of centrate solids in proportion to the polymer dose. Fig. 7-20 shows
the effect of polymer addition on suspended solids removal.
Tofflemire and Hetling27 conducted centrifuge dewatering tests using primary
sludge from a 0.3 I/sec (5 gpm) low lime pilot plant. Solids recoveries were
excellent, ranging from 93 to 100 percent at a conveyor speed of 4,600 rpm and
86 to 100 percent at 5,000 rpm. The pH varied from 8.6 to 12.3. Contrary to
the results obtained at Cleveland, 23 Tofflemire and Hetling found that, as long
as fresh lime sludge was fed to the centrifuge, the addition of an anionic polymer
did not appear to affect the recovery of solids .
Vacuum Filtration
Historically, vacuum filtration has found wide acceptance for dewatering muni-
cipal and industrial sludges. In the municipal field, the leading role of vacuum
filters has only been recently challenged by the increasing use of centrifuges
in sludge dewatering applications . An excellent review of the theory of sludge
filtration is given in Reference 10 .
Basically, a vacuum filter consists of a rotating drum partially (20 to 40 percent)
submerged in a sludge tank or pan. The drum cylindrical surface is covered
with the filter medium and a vacuum of about 25 to 65 cm (10 to 26 inches) of Hg
is applied between the drum compartments and the filter medium . As the drum
passes through the pool of sludge, solids are attracted to the drum surface by
the vacuum effect forming a sludge mat (filter cake) . Moisture (filtrate) is
extracted and filtered through both sludge cake and filter medium . As the drum
rotates, the captured solids undergo further dewatering. Before the next pick-
up and dewatering cycle begins, filter cake is scraped off the drum surface and
falls into a mechanical conveyor . This conveyor then carries the dewatered
sludge to a loading area, to storage, or to further processing stages . The
filtering medium is usually a cloth or metal belt (belt-type filters) , or a double
layer of stainless steel coil springs (coil-type filters) . Several variations of
these basic designs are also available. Fig. 7-21 show a typical belt-type
filter .
The performance of a given vacuum filter installation depends both on the
sludge characteristics and on the filter operating variables. Sludge type, age,
solids concentration, and chemical composition are some of the sludge charac-
teristics that affect the vacuum filtration process . Operating variables include
applied vacuum, filter submergence, chemical conditioning, type of filter media,
and drum rotational speed. All these sludge and operating variables influence
109
-------
IOO<
90
3 Z e°
o LU
70
60
O.I 0,2 0.3 0.4 0.5
POLYMER DOSAGE, LBS/DRY TON SOLIDS
O.6
10,000
I
Q.
<0
Q
O
to
Q
Ul
Q
a
ki
0.
8,000 —
6,000 -
4,000 —
2,OOO —
CENTRIFUGE CONSTANTS
Feed Rate
Bowl RPM
RPM
Pond Depth
24 GPM
3250
- 27
3'/2
O.I 0.2
POLYMER DOSAGE,
0.3 0.4 O.5
LBS/DRY TON SOLIDS
0.6
10,000
- 8,000
6,000
4,000
-------
FILTER DRUM
EQUALIZATION BAR
DISCHARGE
ROLL DRIVE
DISCHARGE ROLL
^-FILTER CAKE
CLOTH SPRAY PIPES
PERFORATED WASH ROLL
WASH TROUGH
DISCHARGE BRACKET
FILTER VAT-
VFILTER AGITATOR
Figure 7-21 Schematic diagram of a belt type vacuum filter (courtesy of Komline-Sanderson
Engineering Corporation)
-------
the filtration process performance expressed in terms of sludge cake moisture
content, solids recovery, cake thickness, filter yield, and filtrate clarity.
Although lime has been intensively used in vacuum filtration of sludges, either
alone or, more commonly, coupled with ferric chloride, its role has been
primarily as a conditioning agent to improve the dewatering and handling charac-
teristics of the sludge. Dewatering of primary generated lime sludges by vacuum
filtration is a far less common practice. Burns and Shell6 conducted numerous
vacuum filter tests, using the test leaf method, 10 on both moderate « 11.0) and
high (> 11.5) pH treatment sludges. The results of these tests, adjusted by a
scale up factor, together with the operating conditions, are given in Fig. 7-22.
Conditioning the sludge with 0.09 to 0.27 kg (0.2 to 0.6 Ib) of anionic polymer
per ton of dry solids increased the vacuum filter yields from 30 to 70 percent
above the values obtained from Fig. 7-22.
Mulbarger et al. * used filter leaf tests following gravity thickening to determine
the dewatering characteristics of lime sludges during bench scale studies of
lime clarification, recovery, and reuse. The sludges had been produced by lime
treatment of secondary effluent. Two-stage treatment was selected for study at a
pH equal to or larger than 11. The investigators found that reclaimed limes pro-
duced sludges which were easier to filter than new lime sludges. They attributed
this to the presence of recycled inerts acting as a filter aid. Filter cake solids
varied between 28 and 45 percent for the range of lime dosage studied. Recovery
efficiencies of the gravity thickener-vacuum filter system for total solids, calcium,
phosphorus, and magnesium varied between 96 and 100 percent (without sludge
carbonation) .
Leaf tests on polymer conditioned centrate from a centrifugal classification step
were conducted at the CCCSD's ATTF . The centrate was difficult to dewater
and resulted in extremely low filter yields, ranging from 1.75 to 2.20 kg/sq
m/hr (0.36 to 0.45 Ib/sq ft/hr) . The feed solids concentration was only 2.4
percent. Other tests produced even lower filter yields, ranging from 0.98 to
1.46 kg/sq m/hr (0.2 to 0.3 Ib/sq ft/hr) . Also, the discharge characteristics
of the filter cake were poor.3
Best media in the ATTF tests on centrate was a synthetic fabric (Eimco Dynel
DY453) . The centrate solids did not contain enough fibrous material to allow
solids capture on the coil filter medium tested.
Whole high-lime sludge (pH 11) was somewhat easier to dewater, with filter
yields ranging from 8.8 to 13.2 kg/sq m/hr (1.8 to 2.7 Ib/sq ft/hr) without
polymer conditioning. These yields are consistent with the data of Burns and
Shell (Fig. 7-22) since the feed solids for the ATTF tests ranged from 3.0 to
3. 6 percent total solids .
Investigators at Blue Plains have extended considerable effort towards defining
vacuum filtration operating parameters for lime sludge generated by an indepen-
dent physical-chemical system (IPC) .9 The IPC System consisted of lime
coagulation, flocculation, sedimentation, filtration, and activated carbon
adsorption. Vacuum filtration data on whole primary sludge are shown in
112
-------
CT
(O
100.0
90.0
80.0
70.0
60.0
50.0
40.0
30.0
20.0
^
uT
2
O
I
Ld
O
CO
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
i.O
OPERATING CONDITION:
3/16 INCH CAKE
33% DRUM SUBMERGENCE
20 INCHES OF HG VACUUM
0.8 SCALE-UP FACTOR
NO CONDITIONING CHEMICALS
FILTER CAKE
MOISTURE CONTENT
68-72% BY WGT.
FILTER CAKE
MOISTURE CONTENT
65-68% BY WGT.
O = DATA AT pH > 11.5
A = DATA AT pH
-------
Table 7-7. Consistent with the experience of Burns and Shell,5 high lime sludge
filtered at a higher rate than low lime sludge. Similar experience was gained at
Blue Plains on centrate (Table 7-6) , as found at the ATTF . Filter yields were
higher, 4.9 to 9.8 kg/sq m-hr (1.0 to 2.0 Ib/sq ft/hr) compared to 0.98 to
2.2 kg/sq m/hr (0.20 to 0.45 Ib/sq ft-hr) at the ATTF, but feed solids were
greater at Blue Plains as a result of flotation thickening.
In summary, the leaf-test data of Burns and Shell (Fig. 7-22) stand up well
compared to the results of other investigators and can be used for design purposes
on vacuum filters treating lime sludge from primary applications. However, two
features on Fig. 7-22 should be highlighted. First, there is variation in filtration
rates above and below the trend lines shown, reflecting day-to-day variations in
sludge characteristics. Since sludge quality will be subjected to variations, some
conservatism in the application of Fig . 7-22 is justified. The other design factor
apparent in Fig. 7-22 is that the filtration rate is strongly affected by feed solids
concentration. To obtain an economic filter loading, for example 24 kg/sq m/hr
(5 Ib/sq ft/hr) , the feed solids concentration must be between 10 and 13 percent
total solids. This requires consistent performance out of the preceding thick-
ening step. If thickener performance should deteriorate, the allowable vacuum
filter loadings would be lower, and the sludge inventory will build up in the
thickener. This in turn might result in further thickening deterioration. Stand-
by vacuum filtration capacity should be provided to avoid overloading of filters.
While both Burns and Shell^ and the Blue Plains investigators^ found that
polymer conditioning was not required for vacuum filtration of whole sludge,
others have reported the need for polymer addition. Shuckrow and Bonner23
conducted pilot studies of lime sludge in a 3 ft diameter belt drum filter. Raw
sludges had been generated at a clarifier pH ranging from 10.0 to 12.2. They
found that vacuum filter performance was dependent on influent solids content,
polymer dose, and drum speed. The effect of these parameters is plotted in
Figs. 7-23, 7-24, and 7-25 for sludges generated at pH 10.5. Cake solids
ranged from 19 to 36 percent dry solids and filter loadings rates varied from
14.6 to 92.8 kg/sq m/hr (3 - 19 Ib/sq ft/hr) . Cake solids content was mainly
dependent on filter loading rate. The addition of less than 0.9 kg (2 Ibs) of
polymer per ton of dry solids allowed loading rates up to three times higher
than without polymer conditioning. Maximum loading rates were obtained at
the fastest drum speeds (50 rph) , but a wetter cake was produced causing it to
adhere to the filter medium. Solids capture was found to be strongly dependent
on solids content and only slightly dependent on drum speed.
It is recommended that facilities for polymer conditioning be provided to be used
in case actual operation demonstrates this need. Polymer conditioning is some-
times required periodically only, as is often found in treatment plants receiving
seasonal industrial wastes. In any event, facilities for polymer addition provide
flexibility of operation and a margin of safety in case that changes in sludge
characteristics might occur. An additional benefit of polymer conditioning is
that, by increasing the filter loading, it allows reduction of the filter area
required.
114
-------
38
36
34
32
2 30
d
en
LU
^
3 28
26
24
22
20
6.3 % DS
0.9 LB/TON
6.3 %DS 1.9 LB/TON
9.9 %DS
1.0-1.3 LB/TON
10 20 30 40 50
DRUM SPEED (REVOLUTION/HR)
60
Figure 7-23 Effect of drum speed on cake solids concentration
115
-------
16
14
12
o:
I
O '0
en
m
8
Q
3
cc
0
9.9% DS
1.0-1.3 LB/TON
I3.4%DS-0.7LB/TON
6.3%DS-0.9 LB/TON
0
10 20 30 40 50
DRUM SPEED (REVOLUTION /HR)
60
Figure 7-24 Effect of drum speed on filter loading
116
-------
100
96
92
88
84
ui
o:
80
3
en
Q
'3.4 % 1,4 LR/THIM
9.9% -I.O-I.3LB/TON
6.3% -I.9LB/TON-
13.4% -0.7LB/TOIM
76
72
0
10
20 30 40 50
DRUM SPEED (REVOLUTION/HR.)
60
Figure 7-25 Effect of drum speed on solids capture
117
-------
Although vacuum filtration seems to yield fairly dry cakes and achieve excellent
solids recovery, it does not permit classification of the sludge constituents prior
to lime calcination. Consequently, a large proportion of inerts and other unde-
sirable solids are recycled through the treatment processes. The amount of
recycled solids can be decreased either by wasting reclaimed lime ("blow down")
or by dry classification of the recalcination product. However, wet classification
is a more efficient process to separate calcium carbonate from the undesirable
components of the sludge cake.
Vacuum filtration of centrate from a classification step does not appear to be
economically attractive, since filter loading rates are so low. and the cake
discharge properties are poor.
Pressure Filtration
Filter presses are used extensively to dewater sludges from the chemical process
industry. As indicated before, they have been used mostly in Europe for de-
watering municipal sludges. In the U.S., pressure filtration has found limited
application in the water treatment field to dewater coagulant (i.e., alum) sludges^
and in the wastewater field to dewater a digested mixture of primary and trickling
filter sludges .29
Steward^O has listed two installations where filter presses are being used to
dewater lime sludges and one that treats a lime and ferric chloride sludge.
Although in two or these plants the sludge cake is incinerated, no attempt has
been made to recalcine and reuse the lime.
Pressure filtration is a batch process. Basically, the process utilizes a high
pressure differential up to 15.8 kg/sq cm (225 psig) to produce a sludge cake
ranging between 30 and 65 percent solids. Sludge is fed to a series of filter
plates lined with the filter medium which typically has been precoated with a
filter aid, commonly fly ash. The filter feed system is designed to satisfy
initial high volume-low pressure and final low volume-high pressure require-
ments. Normally, the average dewatering cycle takes less than two hours, after
which the hydraulic pressure is relieved and the filter opened. The cake
formed inside the chamber then drops, through cutting bars, directly to a
loading truck or, more commonly, onto a belt conveyor underneath the filter.
If the cake is to be incinerated, the conveyor discharges it into a storage bin.
Since stored cake will tend to bridge over the discharge opening and, in the
case of the wetter cakes, to adhere to the bin walls, the design of the storage
facilities deserves special attention. Fig. 7-26 shows a schematic diagram of
a pressure filtration system. Media conditioning by placing a protective layer
of porous material on the filter media before the dewatering step is often
practiced to prevent premature blinding of the filter. (Ash from a sludge
incinerator can be used as a pre-coat material, see Section XI) .
In lime recovery application, filter presses have the same limitation that vacuum
filters do, namely, their inability to classify the sludge solids prior to incinera-
tion. They present the added disadvantages of intermittent operation coupled,
in some systems, with the need to clean the filter media after every cycle and to
118
-------
ASH
INFLUENT^
SLUDGE
STORAGE
IFEEDER
V
MIX
TANK
CONTACT
TANK
FILTER
FEED PUMP
J_
MEDIA
CONDITIONING
} (IF REQUIRED)
t
l
6
L-.
PUMP
EQUALIZING
TANK
FILTER PRESS
V
I
1
I
I -*»
FILTER
CAKE
EFFLUENT FILTRATE
RECYCLE
FILTRATE
TANK
Figure 7-26 Schematic diagram of a pressure filtration system (courtesy of Passavant Corporation)
-------
pre-coat it before the next dewatering cycle can start. These drawbacks are
partially offset by the fact that the entire process can be automated.30 Data on
a whole sludge application are shown in Table 7-7.9
The greatest potential for pressure filtration in lime sludge applications seems
to lie in the dewatering of first stage centrate. Bennett31 has reported filtrate
solids concentrations greater than 30 percent obtained on a 1 sq ft pilot filter
press operated at 7 kg/sq cm (100 psi) . The pH of the lime sludge fed to the
classifying centrifuge was 11.5. Cake discharged from the filter press without
difficulty and no conditioning chemicals were required. Tables 7-6 and 7-8
present data obtained at the Blue Plains pilot plant on centrate filtration. One
of the principal advantages of pressure filtration is evident in Table 7-8, namely
high filtrate clarity. Lime recycle appears to reduce the cycle time required
for pressure filtration (Table 7-8) . Apparently, the recycling of lime to the
primary sedimentation tank is equivalent to the use of fly ash for sludge condi-
tioning in terms of its effect on filter performance. Comparable results have
been obtained at the CCCSD's ATTF on centrate (Table 7-9) . Both the cycle
time and the obtainable cake solids are lower than obtained at Blue Plains when
no lime was recycled; this difference is likely due to differences in quality of
the sludges.
Comparison of Dewatering Techniques
As introduced at the beginning of this section, there are several approaches to
sludge dewatering. The method of dewatering has a marked impact on the
recovery of lime. Of the alternatives considered, only the solid bowl centrifuge
allows control over the amount of inerts recycled in the process. If a vacuum
filter or filter press is utilized, furnace products must be blown down to con-
trol inerts which cause a loss of reclaimed lime.
Equipment Requirements -
To compare equipment requirements for the alternate flowsheets (Figs. 7-8 and
7-9) , Table 7-10 was prepared. To lend some reality to the comparison, actual
manufacturers' equipment models were used for illustration purposes. In all
cases, the model chosen was the largest unit made by the manufacturer. This
reduced the total number of machines required for each alternate. Machines of
other manufacturers having similar sludge processing capacity may be substi-
tuted for those listed in the table.
In the ATTF flowsheet, two types of solid bowl centrifuges are given for the
first dewatering function, vertical and horizontal. In the second stage dewater-
ing step, vacuum filtration and filter pressing are presented as alternates. In
the Plural Purpose Furnace flowsheet, centrifugation, vacuum filtration, and
filter pressing alternatives are illustrated. The centrifugation alternatives are
based on those included in the plans and specifications for the CCCSD Water
Reclamation Plant. H The filter pressing alternatives are based on CCCSD and
Blue Plains data (Tables 7-8 and 7-9) . Second stage vacuum filter loading is
based on ATTF and Blue Plains data.31 Vacuum filtration of whole sludge is
based on Cleveland Westerly data (Figs. 7-23, 7-24, and 7-25) .23
120
-------
Table 7-8. PRESSURE FILTRATION OF CENTRATE AT BLUE PLAINS
Bun No.
1. No lime recycle,
thickened by flotation
2. No lime recycle,
thickened by flotation
3. Lime recycle, no
thickening
4. Only one recycle of
lime, thickened by
centrifugation
5. Only one recycle of
lime , thickened by
centrifugation
6. With one recycle,
thickened by flotation (2)
Feed
solids,
%
7.3
7.7
2.6
3.7
9.8
4.7
Cake solids, %
Outside
33.1
34.6
30.3
31.2
31. 8
31.1
Middle
29.9
37.3
34.0
28.2
31.6
29.0
Inside
26.6
32.4
26.6
27.6
31.1
26.5
Filtrate solids, %
SS,
mg/1
60
47
106
644
228
TS,
mg/1
1212
1630
588
Cycle
hrs
3.32
3.30
2.58
3.75
1.34
2.5
Bulk density
kg/cu m (Ib/cu ft)
1195 (74.6)
1149 (71.7)
1202 (75.0)
1158 (72.3)
1173 (73.2)
1136 (70.9)
No. of
cells
3
3
1
2
2
2
Temp. 11-15 C, (52-50 F) operating pressure 7 kg/sq cm (100 psi) test performed on 0. 09 sq m ( 1 sq ft) Nichols
pilot filter press (2) thickened in the pilot 1 sq ft dissolved air flotation unit.
Table 7-9. PRESSURE FILTRATION OF CENTRATE AT CCCSD
Run no .
1
2b
3
4
5b
6
Filter3 cycle
time, hr
2.75
2.0
2.2
3.0
2.5
2.0
Feed solids,
percent
4.1
3.4
4.1
3.3
3.4
3.4
Cake solids ,
percent
26.5
24.1
24.6
23.0
26.6
24.8
Feed pHC
10.75
12.0
10.75
10.4
11.9
10.8
Cake thickness,
cm (inch)
2.54 ( 1.0)
2.54 ( 1.0)
2.54 ( 1.0)
3.18 (1.25)
3.18 (1.25)
2.54 ( 1.0)
Tests performed with a Nichols 0.09 sq m (1 sq ft) filter press at 7 kg/sq cm (100 psig) .
Tests performed with the addition of dry classification rejects on an 8 percent dry weight basis.
Primary sedimentation operated at pH 10.8.
121
-------
Table 7-10. COMPARISON OF MACHINE AND FLOOR AREA REQUIREMENTS FOR ALTERNATE FLOW
SHEETS AT 1.31 CD M/SEC (30 MGD)
Plow sheet
CCCSD's ATTF
at pH 11 ,0d
Plural purpose
furnace at
20% ash
blowdown
First stage
sludge
dewatered,
kg/day
(lb/day)/
percent TS
101,729
(224,312)/8
98,806
(217,875)/8
96,783
(213,414)78
101,725
(224,312)78
133,064
(293,415)78
132,843
(292,928)78
126,835
(279,680)78
Machine
Centrifuge:
Sharpies
P68006
Centrifuge:
Sharpies
P68006
Centrifuge:
Sharpies
P6800
Centrifuge:
Sharpies
P5400
Centrifuge:
Sharpies
P68008
Vacuum filter
Elmco belt
12 x 20
Filter press
Nichols
72" x 48"
Loading ,
metric
(English)
14.4 I/sec
(221 gpm)
13.6 I/sec
(215 gpm)
13.3 I/sec
(211 gpm)
14.4 I/sec
(221 gpm)
18.2 I/sec
(289 gpm)
39 kg/sq m-hr
(8 Ib/sq ft-hr)
45% TS,
1 . 2 hr cycle
No. units
required
1
1
1
1
1
2
3
Floor area ,
sq m (sq ft)
each/total
6.9 (74)7
6.9 (74)
6.9 (74)7
6.9 (74)
6.9 (74)7
6.9 (74)
17.7 (191)7
17.7 (191)
6.9 (74)7
6.9 (74)
28.5 (307)/
57.0 (614)
25.7 (276)7
77.1 (828)
Second stage
sludge
dewatered ,
kg/day
(lb/day)/
percent TS
38,258
(84,363)/4
36,219
(79,865)/4
35,132
(77,469)/4
38,259
(84,363)/4
-
-
Machine
Centrifuge:
Sharpies
P68006
Vacuum filter
Elmco belt
12 x 20
Filter press
Nichols
72" x 48"
Centrifuge:
Sharp Les
P5400
-
-
Loading ,
metric
(English)
10.9 I/sec
(172 gpm)
4.9 kg/sq m-hr
(1 Ib/sq ft-hr)
25% TS ,
2.25 hr cycle
5.4 1/360
(86 gpm)
-
~
"
No. units
required
1
5
3
2
-
~
"
Floor area ,
sq m (sq ft)
each/total
6.9 (74)/
6.9 (74)
28.5 (307)/
142.5 (1,535)
25.7 (276)/
77.1 (828)
17.7 (191)/
35.4 (382)
-
~
"
Total
floor area,
both stages
sq m (sq ft)
13.8 (148)
149.4 (1,609)
84 (902)
53.1 (573)
6.9 (74)
57.0 (614)
77.1 (828)
Total no. of
machines
(both stages)
2
6
4
3
1
2
3
tsj
See Section X for solids balances.
Machine only, not including ancillary equipment such as chemical feed equipment, cake conveying equipment, piping, etc.
Standby equipment is not included, normal practice requires standby capacity.
Two furnaces are required.
Vertical machine.
Horizontal machine.
Number of units per furnace.
-------
Comparing flowsheets, it can be seen from Table 7-10 that less dewatering equip-
ment is required for the Plural Purpose Furnace flowsheet than for the ATTF
flowsheet. Among the Plural Purpose Furnace flowsheet alternates, the least floor
area is required for the centrifuges. This reflects more compact equipment
arrangements possible with centrifuges. Among the ATTF flowsheet alternatives,
the centrifuges also require the least number of machines and the least total floor
area. The floor area requirements for ancillary equipment, e.g., sludge condi-
tioning equipment, feed pumps, etc., are considered similar for each alternative
and are not included in the comparison. As a general rule, floor requirements
for auxiliary systems usually exceed those for the dewatering machines themselves
Maintenance -
Maintenance requirements will differ among the machine alternates and are
difficult to quantify. High speed centrifugals, even with hard surfacing of the
conveyor, will require periodic resurfacing. The operating period between
overhauls will depend on the amount of sandy material contained in the feed
sludge. Efficient grit removal is of paramount importance when dewatering
with centrifuges. Vacuum filter belt and the filter medium in filter presses
require routine cleaning and may eventually have to be replaced. Their service
life, however, is usually not affected by grit. Pressure filtration, even with
the degree of automation provided in today's systems, requires more operator
attention than vacuum filtration or centrifugation. The presence of an operator
is recommended during the cake discharge cycle to make sure that all filter cakes
drop from the press plates.
Relative Dewatering -
The alternatives must also be evaluated in terms of the basic dewatering objec-
tive, water elimination. This objective receives special emphasis when incin-
eration follows dewatering, as approximately 450 kcal (1,800 Btu) are required
to evaporate a pound of water (at off-gas temperature of 700 F) . Table 7-11 has
been prepared which presents an analysis of the weight of water which must be
evaporated in the furnaces for each alternate presented in Table 7-10. Com-
paring the results for the ATTF flowsheet to the results for the Plural Purpose
Furnace flowsheet, it can be seen that there is no disadvantage in incorporating
the wet classification process into the ATTF flowsheet in terms of the energy
required to evaporate water. In fact, there is a considerable advantage to the
ATTF flowsheet.
Employing pressure filtration in the second dewatering stage of the ATTF flow-
sheet has a substantial advantage over vacuum filtration or centrifugation in
terms of the energy required for incineration. This factor will no doubt
encourage wider utilization of pressure filtration in this energy-conscious age.
Flexibility -
The centrifugation process has demonstrated greater stability to changes in
influent characteristics than either the vacuum filtration process or pressure
filtration. This is partially indicated by the effect of influent solids level on
123
-------
Table 7-11. COMPARISON OF WATER EVAPORATED FOR ALTERNATE DEWATERINC SYSTEMS
AT 1.31 CU M/SEC (30 MCD)
Flow Sheet
and Dewatering
ATTFa
1st: centrifuge
2nd: centrifuge
ATTFb
1st: centrifuge
2nd: vacuum filter
ATTF°
1st: centrifuge
2nd: filter press
Plural Purpose Furnace
centrifuge
Plural Purpose Furnace6
vacuum filter
Plural Purpose Furnace
filter press
Dry Solids
Burned in
First Stage,
kg/day (Ib/day)
62,977 (139,950)
62,104 (138,011)
61,653 (135,945)
126,204 (278,281)
126,204 (278,281)
126,204 (278, 28i)
Percent
Total
Solids
58
58
58
24
28
44
Water
Evaporated
First Stage,
kg/day (Ib/day)
46,961 (101,343)
45,323 ( 99,939)
44,645 ( 98,443)
399,648 (881,223)
324,526 (715,580)
160,624 (354,176)
Dry Solids
Burned in
Second Stage,
kg/day (Ib/day)
33,136 (73,614)
33,782 (75,073)
34,782 (76,694)
-
-
-
Percent
Total
Solids
17
20
25
-
-
-
Water
Evaporated
Second Stage,
kg/day (Ib/day)
162,998 (359,410)
136,187 (300,292)
104,346 (230,002)
-
-
-
Total Water
Evaporated
kg/day (Ib/day)
209,960 (460,753)
181,510 (400,231)
148,991 (306,776)
399,468 (881,223)
324,526 (715,580)
160,624 (354,174)
jTCase 100, Section X
Case 101, Section X
°Case 102, Section X
Case 106, Section X
?Case 114, Section X
Case 117, Section X
-------
filter yield for vacuum filters shown in Fig. 7-22 and the effect of influent con-
centration on cycle time for pressure filters in Table 7-8. This makes the vacuum
filters and pressure filters more dependent on the uniformity of operation of up-
stream thickening process than the centrifuge.
Choice -
Choice of the dewatering process must be based on evaluation of all the factors
listed in this section, past experience and preferences of the operating agency
and the consulting engineer, operator competence and training, economics and
local factors. The relative ranking of these factors may be different for many
situations and lead to quite different solutions. The multiplicity of dewatering
designs in evidence today is testimony to the variability in solutions.
SLUDGE CAKE CONVEYING
Sludge cake can be pumped or transported by mechanical or pneumatic methods.
First stage centrifuge cake is usually too dry to be handled by pumps. Attempts
to convey first stage cake from the ATTF with a progressive cavity, positive
displacement pump were unsuccessful. Second stage cake, however, having the
consistency of a slurry, can be pumped with positive displacement units. Cen-
trifugal, torque-flow pumps have also been used to handle lime sludge. Aldworth32
has reported the use of this type of unit to recirculate lime sludges of up to 28
percent solids concentration, in digestion tanks. He recommended abrasion-
resistant construction for this application.
Mechanical conveyors are similar to the ones used to move dry materials (see
Section V) . Belt and screw conveyors and bucket elevators are often employed
to transport the wet sludge cake to storage or to feed it to the incinerator.
Screw conveying gave satisfactory results at the ATTF. "Totally enclosed"
conveyor designs are also available. This type of mechanical conveyor features
a series of flights dragged by one or two hardened chains. The conveying flights
are enclosed in a rectangular casing. The return flights may be housed in the
same casing or in a separate one. Apart from the advantage of enclosed trans-
port of sludge cake, this conveyor is designed to change directions, a capability
not possessed by conventional belt or screw conveyors. The degree and extent
of directional changes varies among the various designs. As it was pointed out
in Section V, selection of mechanical conveyors should be done in consultation
with the equipment manufacturers .
The pneumatic conveying equipment used in wet sludge applications is of the
pressure vessel (i.e., pneumatic ejector) type. Pneumatic ejection of sludge
cake offers several advantages. The material is completely enclosed and can
be conveyed in any direction, above or below grade. The flexibility of trans-
port is particularly advantageous in multiple hearth furnace applications since
it permits locating the dewatering equipment at or near ground level instead of
above the top (feeding) hearth. The saving achieved by eliminating the elevated
structures required to support the dewatering equipment can be substantial.
The key to successful application of pneumatic conveying techniques to sludge
cakes lies in the characteristics of the sludge. Although cakes at solid concen-
125
-------
trations of 40 to 50 percent DS have been successfully handled in pneumatic
ejectors,33 some sludges are difficult to expel from the vessel. In these cases,
the compressed air usually blows holes through the sludge mass instead of
forcing it through the discharge opening. Some manufacturers of pneumatic
conveying equipment have pilot plant facilities33 where the suitability of the
sludge to pneumatic handling can be tested.
In sizing sludge conveyors, the specific weight of the material is often required.
Fig. 7-2?34 was developed for converting from mass loading rates to volumetric
loading rates. The data presented is for dense high calcium carbonate cake. In
those cases where the cake is crumbled prior to transport and air is entrapped,
a rule of thumb is to reduce the specific weight by half.
126
-------
18
16
-J
CQ
3;
CO
u]
u
o
Uj
CL
14
!O
8
SPECIFIC WT- VS - % SOLIDS
USING 2.4 g/ml FOR SPECIFIC
GRAVITY OF SOLIDS (HIGH IN CaCOs)
o
10
20
3O 4O SO
PERCENT SOLIDS
6O
70
80
9O
Figure 7-27 Relationship between solids concentration and specific weight
-------
REFERENCES - SECTION VII
1. Mulbarger, M.C., E. Grossman, III, R.B. Dean, and O.L. Grant. Lime
Clarification, Recovery, Reuse and Sludge Dewatering Characteristics.
Journal of the Water Pollution Control Federation. 41_: 2070-2085, December
1969.
2. Balakrishnan, S ., D .E . Williamson, and R.W . Okey. State of the Art Review
on Sludge Incineration Practice. Resource Engineering Associates.
Washington, D.C. Project 17070 DIV. Federal Water Quality Administration.
April 1970, 135 p.
3. Parker, D.S., K.E. Train, andF.J. Zadick. Sludge Processing for Com-
bined Physical-Chemical-Biological Sludges. U.S. Environmental Pro-
tection Agency, Washington, D.C. Report No. EPA-R2-73-250, July 1973.
141 p.
4. Process Design Manual for Phosphorus Removal. Black & Veatch, Consulting
Engineers. Washington, D .C. U.S. Environmental Protection Agency -
Technology Transfer. October 1971. pp. 10/23 - 10/27.
5. Burns, D.E., andG.L. Shell. Physical-Chemical Treatment of a Municipal
Wastewater Using Powdered Carbon. Envirotech Corporation. Salt Lake
City. Report for U .S . Environmental Protection Agency. Report No. EPA-
R2-73-264. 1973. 230 p.
6. Burns, D.E. Physical-Chemical Treatment of Municipal Waste, Progress
Report No. 10. Envirotech Corporation, Salt Lake City. PRF-10. March 8,
1973. 26 p.
7. Burns, D.E. Physical-Chemical Treatment of Municipal Waste, Progress
Report No. 11. Envirotech Corporation, Salt Lake City. PRF-11.
March 15, 1973. 32 p,
8. Burns, D.E., G.L. Shell, D.J. Cook, and R. Wallace. Physical-Chemical
Treatment of Municipal Waste. Envirotech Corporation. Salt Lake City.
Draft Report for the U .S . Environmental Protection Agency. Contract No.
68-01-0183, 1974.
9. Bennett, S.M. Personal Communication to D .S . Parker. U .S . Environmental
Protection Agency - Blue Plains Pilot Plant. October 11, 1973.
10. Sludge Dewatering. Water Pollution Control Federation . Washington, D .C .
Manual of Practice No . 20 . 1969. 115 p.
128
-------
11. Brown and Caldwell, Consulting Engineers. Plans and Specifications for
Water Reclamation Plant, Stage 5A - Phase 1. Central Contra Costa
Sanitary District. California. April 1973.
12. Katz, W.J., and A. Geinopolos. Sludge Thickening by Dissolved Air
Flotation. Journal of the Water Pollution Control Federation. 39_, 946-957,
June 1967.
13. Kirk-Othmer. Encyclopedia of Chemical Technology, 2nd Edition. New York
John Wiley & Sons, 1964. Volume 4, p. 710-722.
14. Perry, J.H. Chemical Engineers'Handbook. Fourth Edition, New York,
McGraw-Hill Book Co., 1963, p. 19-93.
15. Gulp, G.L. Design of Facilities for Physical-Chemical Treatment of Raw
Wastewater. Gulp, Wesner, Gulp. Corona Del Mar. U .S . Environmental
Protection Agency. Technology Transfer Seminar Publication. August 1973.
29 p.
16. Keith, F.W., Jr., andC.E. Trump. Centrifugal Classification of Waste
Sludge Components. Sharpies-Stokes Division, Pennwalt Corporation,
(Presented at the Annual Meeting of the New England Water Pollution
Control Association, Hyannis, October 24, 1973) 19 p.
17. Sheen, R.T. , and H.B. Lammers. Recovery of Calcium Carbonate or Lime
from Water Softening Sludges. Journal of the American Water Works Assoc.
36:1145-1169, November 1944.
18. Pederson, H .V . Calcination Sludge From Softening Plant. Journal of the
American Water Works Assoc. 36: 1170-1177, November 1944.
19. Nelson, F.G. Recalcination of Water Softening Sludge. Journal of the
American Water Assoc. 36_: 1178-1184, November, 1944.
20. Parker, D.S., D.G. Niles, andF.J. Zadick. Processing of Combined
Physical-Chemical-Biological Sludge. Brown and Caldwell and the Central
Contra Costa Sanitary District. (Presented at the 46th Annual Conference
of the Water Pollution Control Federation. Cleveland. October 1, 1973) .
23 p.
21. Brown and Caldwell, Consulting Engineers. Final Report, Lime Sludge
Recycling study. Prepared for the Central Contra Costa Sanitary District,
Walnut Creek, California. 1974.
22. Thompson, C.G., and A.P. Black. Demonstration of the Magnesium
Coagulation System at Montgomery, Alabama. In: Minimizing and
Recycling Water Plant Sludge, AWWA Seminar. Proceedings. New York.
American Water Works Association, 1973. p. VI-1 to VI-45.
129
-------
23. Shuckrow, A.J., and W.F. Bonner. Development and Evaluation of
Advanced Waste Treatment Systems for Removal of Suspended Solids,
Dissolved Organics, Phosphate and Ammonia for Application in the City
of Cleveland. Battelle-Northwest. Richland, Washington. Report to Zurn
Environmental Engineers . June 1971. 96 p..
24. Parker, D.S . Internal Memorandum, Low Lime Centrifuge Test Results.
Brown and Caldwell, San Francisco, California. May 1972. 7 p.
25. Gibbs, O.J. Field Test Report, Sewage Sludge at the CCCSD Sewage
Treatment Plant. Bird Machinery Co., Lafayette, California. Field Test
Report No. WCD-38. October 1971. 9 p.
26. Smith, A.G. Centrifuge Dewatering of Lime Treated Sewage Sludge.
Ministry of the Environment. Toronto. Paper No. 2030. May 1972. 22 p.
27. Tofflemire, T.J., andL.J. Hetling . Treatment of a Combined Wastewater
by the Low Lime Process. Journal Water Pollution Control Federation, 45,
210, 1973.
28. Disposal of Wastes from Water Treatment Plants. American Water Works
Association Research Foundation. Washington, D.C. Report Number 12120
ERC. Federal Water Pollution Control Administration. August 1969. 73 p.
29. Gerlich, J.W., andM.D. Rockwell, Pressure Filtration of Wastewater Sludge
with Ash Filter Aid. U.S . Environmental Protection Agency Report Number
EPA-R2-73-231, June 1973. 153 p.
30. Steward, C.R. Personal communication to D .S . Parker. Passavant
Corporation. Birmingham, Alabama. September 28, 1973.
31. Bennett, S.M. Personal communication to D .S . Parker. U .S . Environmental
Protection Agency - Blue Plains Pilot Plant. September 17, 1973.
32. Aldworth, G.A. Some Plant Design Considerations in Phosphorus Removal
Facilities. James F. MacLaren Limited, (Presented at the Phosphorus
Removal Design Seminar, Toronto, Ontario, May 28 - 29, 1973) 19 p.
33. Blanchard, C.T. Personal communication to E. de la Fuente. CPC
Engineering Corporation, Sturbridge, Massachusetts. January 8, 1974.
34. Foy,H.E. Personal communication to D .S . Parker. Envirotech Corporation,
SanMateo. 1972.
130
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SECTION VIII
LIME SLUDGE RECALCINATION AND WASTE SLUDGE INCINERATION
GENERAL CONSIDERATIONS
Lime recovery from chemical sludges has been practiced in the pulp and paper
industry and in the water softening field 1 for many years. In wastewater treat-
ment however, the practice is much more recent dating back to 1968 when the
South Tahoe water reclamation plant began to successfully reclaim lime from the
tertiary treatment sludge.2
The economics of lime recovery from wastewater sludges are quite different than
for water softening sludges. In the latter case, since the softening reactions
cause calcium hardness to precipitate as calcium carbonate, generally more lime
is produced than is added for treatment. As a result, lime recovery operations
in the water softening industry often show a profit.! On the other hand, due to
process inefficiencies and losses, which will be explained later, only 50-70
percent recoveries of the required lime dose are usually possible from waste-
water lime sludges. Consequently, new lime must be purchased to make up for
the losses. Once steady state conditions are reached, the quantity of make up
lime required can be expected to remain constant.
Lime recovery from wastewater sludge is attractive because recalcination, being
a combustion process, can also be regarded as a method of sludge disposal.
Therefore by recalcining the lime sludge, not only the spent chemical is re-
claimed to be used again, but also the expensive problem of process solids
disposal is greatly simplified at the same time.
In general, sludge incineration involves two steps, (a) drying and (b) com-
bustion. In turn, the drying and combustion processes consist of the following-
phases: (1) raising the temperature of the feed sludge to 100 C (212 F) ,
(2) evaporating water from the sludge, (3) increasing the water vapor and air
temperature of the gas, (4) increasing the temperature of the dried sludge
volatiles to the ignition point, and (5) combustion of the volatiles . The end
products of combustion are water vapor, carbon dioxide, sulfur dioxide,
nitrogen gas and inert ash.
Another important consideration in incineration processes is the required
amount of combustion air. When any material burns, it combines with the
oxygen in the air. The amount of air required can be theoretically calculated
from the sludge composition .3 This amount is called "theoretical air", In
practice, however, it is necessary to supply more air than is theoretically
required since it is not possible to distribute the air evenly over the burning
bed of material. The amount of air supplied in addition to the theoretical air
is called "excess air" and is usually given as a percentage of the theoretical
131
-------
air. So, burning with 100 percent excess air means supplying twice as much air
as is theoretically necessary. The fundamental requirement is that enough air
be admitted to the incinerator to ensure proper combustion of the sludge. If not
enough air is admitted, the sludge will burn with a smoky flame, produce pro-
ducts of incomplete combustion such as carbon monoxide, and emit offensive
odors. Insufficient air may also encourage formation of clinkers in certain types
of incinerators . On the other hand, after the theoretically required air is supplied
the more excess air is admitted, the cooler the incinerator will become and the
more auxiliary heat will be required to maintain combustion. Fig. 8-1 illustrates
the relationship between auxiliary fuel and excess air. 4 Gas costs are rising and
the fuel costs per ton can be proportionately increased over that shown in Fig.
8-1 to reflect local conditions .
LIME SLUDGE RECALCINATION
Recalcination of lime sludges is a process in which sludge is burned to decompose
calcium carbonate to calcium oxide (lime) for reuse in treating more wastewater.
The incinerator temperatures required to achieve this conversion are 871-982 C
(1600-1800 F) and the decomposition is expressed by the following equation:
CaC03 > CaO + CC>2 (gas)
Quantitatively this equation can be represented as a function of CC>2 concentra-
tion and temperature as shown in Fig. 8-2.5 Since any incinerator will contain
10-20 percent CC>2 by volume it can be seen that active and energetic decomposi-
tion can be expected when the solids reach temperatures above 760-816 C (1400-
1500 F) . Any hydrated materials such as magnesium and iron hydroxides will
decompose to their respective oxides well below these temperatures.
During the test work at the CCCSD's ATTF, it was found that the conversion
efficiency of calcium carbonate was related to temperatures in the recalcining
hearths of the multiple hearth furnace.6 To obtain 95 percent lime recovery
efficiency, a temperature of 932 C (1710 F) in the recalcining hearth was
required. The carbon dioxide content was 13-17 percent, and Fig. 8-2 shows
that the practical recalcining temperature is considerably greater than the
theoretical value, because (a) a temperature difference is needed to transfer
heat between the gas and the solids being recalcined and (b) the equilibrium
data (Fig. 8-2) were obtained at long contact times and do not apply exactly in
a practical circumstance where reaction time is net long.
Carbon dioxide liberated during combustion can be collected and used for pK
adjustment, i.e. , recarbonaticn, in the lime treatment system.
As indicated in Section VI, lime recovery is economically attractive in high lime
applications since the additional benefits derived from higher lime doses can be
justified when lime is to be recovered. At this range of pH (11-11.5) , the
precipitation of magnesium as magnesium hydroxide is practically complete and
the calcined magnesium (MgO) does not react in water. Consequently, unless-
the lime sludge is classified to remove magnesium prior to incineration, the
132
-------
LL
O
O
O
O
o:
ui
u
O
Q
_l Z
O <
O CD
tr o
^ E
d|
U- a
> £
< O
Zi O
a:
Z)
% EXCESS AIR VS AUXILIARY FUEL
SLUDGE AT 30% TS, 70% VOL 8 10,000 BTU/lb
EXIT TEMPERATURE AT8I6C( I500F)
.- 4
0
$3.70/TON
:D
1970 DOLLARS
$0.92/TON
I
(I)
I
20 40 60
% EXCESS AIR FOR SLUDGE
EXCESS AIR FOR NATURAL GAS AT 2O% (CONSTANT)
80
100
Figure 8-1 Effect of excess air on the cost of sludge incineration
133
-------
IOO
90
10
400 500
600 700 800 900 IOOO
TEMPERATURE.C
Figure 8-2 Decomposition of calcium carbonate to calcium oxide
134
-------
recalcining process will render a product with a high percentage of unreactive
magnesium oxide. By contrast, wet classification of the lime sludge is expected
to reduce the proportion of magnesium oxide in the recalcined product to 5
percent or less by weight.? However, even after wet classification, other inerts
will build up in the system because complete rejection of inerts is not achieved.
Inerts which build up are magnesium, phosphorus, iron, silica and other
compounds. As a result, the available lime in the recalcined product may be
only 60 to 77 percent.7,8
Inerts buildup can also be controlled by continuously purging ("blowing down")
a portion of the furnace product to equal the incremental increase in non-carbonate
solids added to the lime sludge during precipitation.9 Naturally, the blowdown
also wastes a portion of the reclaimed calcium oxide so make up lime is required.
Solid balances presented in Section X, Table 10-10, show that in a flow sheet
without wet classification, 28 percent of the furnace product must be purged to
approximate the amount of solids generated in a system that incorporates wet
classification (Fig. 7-9) . Also, at 28 percent ash blowdown, the makeup lime
requirements are 55 percent of the overall requirements; in the flow sheet with
wet classification, makeup lime accounts for only 38 percent of the total require-
ments. Thus, product purging is a wasteful means of controlling inerts as the
overall recovery of lime in the process is reduced.
Another means for increasing the effectiveness of purging is to use dry classifi-
cation. It may be used alone or in conjunction with wet classification. As
described later in this section, dry classification uses particle size selection to
preferentially reject silica from the system.
Three types of recalcining plants are used to recover lime from process sludges:
rotary kilns, fluidized bed reactors and multiple hearth furnaces. The first
two types have been used extensively in industrial and water softening appli-
cation. The multiple hearth furnace seems to have taken the lead in lime
recovery applications from wastewater sludges.
Multiple Hearth Furnaces
2
Multiple hearth furnaces (MHF) are used at South Tahoe, California, Colorado
Springs, Colorado and Piscataway, Maryland for full scale recovery of lime
from tertiary treatment wastewater sludge. Four additional installations are
under different stages of construction in the U.S. and several more are in the
planning and design phases. 10 The MHF was initially developed for use in
the mining industry for roasting ores. It has been widely used in municipal
applications for disposal of both primary and biological sludges for over 40
years. H Other solid products of wastewater treatment including grit, scum
and screenings have also been incinerated in the MHF . The popularity of
multiple hearth units can be attributed to their simple design and flexibility
of operation under varying feed rates. ^
The multiple hearth furnace is a circular structural steel shell lined with re-
fractory brick, and the interior is divided into separate compartments (i.e. ,
135
-------
hearths) by horizontal brick arches. An air cooled central shaft supports the
cantilevered rabble arms (two or four) provided on each hearth. Revolving
rabble arms move the sludge from hearth to hearth alternately inwards and
outwards so the sludge travels radially the full width of each hearth before
dropping to the next one. This travelling pattern has been used to name the two
hearth types. Those in which sludge enters near the periphery and exits through
openings around the center shaft are called "in-feed" hearths. Those in which
sludge is rabbled from the center towards the hearth periphery, where the drop
holes are located, are called "out-feed" hearths. Fig. 8-3 shows a typical MHF.
As the material passes down through the furnace, three distinct zones are estab-
lished. The upper hearths form a drying and gas cooling zone. Here, vaporiza-
tion of some free moisture occurs as well as cooling of exhaust gases by transfer
of heat from the hot gases to the sludge. Intermediate hearths form a high tem-
perature burning zone, or combustion zone, where all volatile gases and solids
are burned. Combustion of most of the total fixed carbon takes place on the
lowest hearth of the combustion zone. The bottom hearths of the furnace function
as a cooling and air-preheating zone where ash is cooled by giving up heat to the
returned shaft cooling air. The relative location of the zones will tend to shift
as the result of changes in the quality and quantity of the feed, i.e., the sludge
feed rate and the moisture content of the cake. If there is enough combustible
matter in the sludge cake, sufficient heat will be liberated by the burning solids
to drive off the moisture in the sludge cake on the upper hearths to the point
where this material itself will ignite as it reaches the combustion zone. Thus,
the incineration process may be self-sustaining (autogenous combustion) .
A comprehensive thermal analysis of combustion in the MHF is given in Reference
11. In general, sludge has to be 25-30 percent solids with a volatile solids
content of 70 percent (and no solids to be calcined) for autogenous combustion.
If afterburning is required to control air pollution (see Section IX) , auxiliary
fuel is necessary to reach afterburning temperatures, although autogenous
combustion could still occur in the burning hearths.
A temperature profile across a typical sludge furnace is given in Table 8-1. ^
For design purposes, excess air for combustion of volatiles in the sludge is
usually set at 50-75 percent. Normal operation conditions may show a lower
percentage of excess air. 12
For a given solids load to a MHF, lime recalcination requires additional hearths
over the number normally required for sludge combustion. In the CCCSD water
reclamation plant,13 the furnaces will have ten hearths (an eleventh hearth
will be used as an afterburner) . Approximately two hearths are required to
dry the feed, two hearths to preheat the feed to calcining temperature (899 C
(1650 F) solids temperature or about 1010 C (1850 F) gas temperature) , four
hearths to get complete calcination and two hearths to cool the product.14
Excess air for sludge recalcination is normally set at 100 percent. Table 8-2
gives the anticipated temperature profile for the CCCSD lime furnaces.
136
-------
EXHAUST GASES
OUTLET
TYPICAL
IN-FEED
HEARTH
TYPICAL
OUT-FEED
HEARTH
SHAFT
COOLING
AIR INLET
TYPICAL
RABBLE ARM
CENTRAL
SHAFT
ASH
DISCHARGE
PORT
CENTRAL
SHAFT DRIVE
Figure 8-3 Typical multiple hearth furnace (courtesy of BSP Division-
Envirotech Systems, Inc.)
137
-------
Table 8-1. TYPICAL TEMPERATURE PROFILE
IN SIX HEARTH FURNACE
Hearth No.
1 (Top)
2
3
4
5
6 (Bottom)
Temperature
C
427
649
899
788
649
149
F
800
1,200
1,650
1,450
1,200
300
Table 8-2. TEMPERATURE PROFILE IN LIME
RECALCINATION FURNACE FOR CCCSD
Hearth No.
1 (Top)
2b
3
4
5
6
7
8
9
10
11 (Bottom)
C
76 Oa
427
677
899
1,010
1,010
1,010
1,010
1,010
677
399
F
l,400a
800
1,250
1,650
l,850e
1,850C
1,850C
1,850°
1,850C
1,250
750
Temperature
, Top hearth used as afterburner
Feed hearth
Test work indicates that a temperature
as low as 932 C (1, 710 F) may be
adequate.
138
-------
The MHF is sized based on solids loading per unit of hearth surface area. Sizing
is influenced by the characteristics of the sludge cake, including moisture, volatile
solids, inerts content, and calorific value. 34 to 59 kg of wet sludge per hour per
square meter of hearth area (7-12 Ib/hr/sq ft) is the range of loading rates com-
monly used in determining the required hearth area. 12 Rates for recalcining
furnaces are generally in the low end of this range. The somewhat lengthy pro-
cedure used to size a MHF has been greatly simplified by the development of
digital computer routines .11/12
The modular construction of MHFs allows their use in a wide range of solids
loadings. Typically, additional capacity is obtained by increasing the furnace
diameter, increasing the number of hearths, or both. Table 8-3 shows the
standard furnace sizes offered by a large manufacturer of the MHF . 12 The same
manufacturer has developed a "Plural Purpose" furnace (a patented application) .^
This concept permits the use of a single unit for both lime recalcination and
organic sludge incineration (Fig. 7-8) . Scum, grit and screenings can also be
burned together with the lime and organic sludges. The reclaimed lime is
separated from the inerts by dry classification techniques. 12 Dry classification
will be covered in detail later in this section.
Fluidized Bed Reactors
Fluidized bed reactors (FBR) are the type of recalciners most commonly used to
recover lime from water softening sludges. 1 The FBR is also used in the pulp
and paper field and in other industrial applications such as ore roasting,
calcination of phosphate rock and limestone, etc. In wastewater treatment,
fluidized bed techniques were first applied in Lynnwood, Washington in 1963 to
burn both raw sludge and scum. 16 The first full-scale application of a FBR in
lime recalcination from wastewater sludge was started in Elkhart, Indiana in
1974.17
Basically, a FBR consists of a vertical steel shell internally divided into hori-
zontal compartments. In general, the number of compartments depends on the
type of material burned in the reactor and its mode of operation. A layer or
"bed" of the granular material (either lime pellets or sand) is placed at the
perforated bottom of a compartment. As preheated air flows into the burning
section, its upward velocity suspends the solid particles and the bed expands.
This mixture of solids and gas is said to be fluidized since it behaves not unlike
a true liquid. 18 The physical appearance of the fluidized bed has been described
as similar to boiling water due to the intense mixing between air and bed
material. Combustion of either fuel or sludge takes place within this bed and
is completely dependent upon this intense mixing action.
Two distinct types of fluid bed systems have been applied to lime recovery from
waste calcium carbonate sludges . The bed in one type of unit (Fig . 8-4) consists
of pellets of recalcined lime. In the other type of unit, sand is used to form the
fluid bed.
139
-------
Table 8-3. STANDARD MULTIPLE HEARTH FURNACE SIZES (COURTEST OF BSP DIVISION-
ENVIROTECH SYSTEMS, INC.)
I.D.
13"
20"
30"
39"
54"
5 1/2'
7'
8 1/2"
10 1/2'
12'
14 1/2'
16 1/2'
18'
20'
23 1/2'
26'
28'
O.D. for
wall thickness of
6"
18"
@ 2 1/2"
30"
@ 5"
3'
@ 3"
4'3"
5'6"
6'6"
8'0"
9'6"
11'6"
13'0"
15'6"
17'6"
19'0"
21'0"
24'6"
27'0"
29'0"
9"
44"
@ 7"
4.9.1
6'
71
8'6"
10'
12'
13'6"
16'
18'
19'6"
21'6"
25
27'6"
29'6"
13 1/2"
4'6"
6'9"
7'9"
9'3"
19'9"
12'9"
14'3"
16'9"
18'9"
20'3"
22'3"
25'9"
28'3"
30'3"
Col.
height3
1'
1'3"
1 1/2"
2 1/2"
4'
4'
51
6 1/2'
6 1/2"
6 1/2"
7'
7'
8'
8'
8'
8'
8'
Square feet of effective hearth area and "normal" shell height"
Hearths
1
1
2
4
7
15
24
32
47
80
97
143
181
215
269
382
463
610
2
2 1/4
1'8"
4
2'0"
8
2 '2"
14
3'6"
31
4'2"
47
4'8"
65
6'3"
94
6'3"
148
8'4"
195
6'9"
286
8'0"
363
8'4"
431
8'4"
538
9'6"
764
11'4"
926
12'7"
1,155
13'
3
2 1/4
6
12
19
42
63
96
138
227
287
422
534
634
790
1,145
1,389
1,690
4
3
3'4"
8
4'0"
16
4'4"
28
6'
63
7'4"
94
8'3"
130
lO'lO"
188
10' 8"
295
14'0"
390
11'8"
573
13'2"
727
14'3"
863
14'4"
1,077
16'1"
1,528
18'9"
1,852
20'9"
2,235
22'
5
10
20
32
74
110
161
235
374
487
716
908
1,078
1,346
1,909
2,315
2,770
6
12
6'0"
24
6'
37
8'6"
85
10'6"
125
ll'ld"
193
15'5"
276
IS'l"
442
19'8"
575
16'7"
845
18'7"
1,068
20'2"
1,268
20'2"
1,580
22'9"
2,292
26'2"
2,778
28'10"
3,315
31'
7
28
42
98
145
225
323
521
672
988
1,249
1,483
1,849
2,674
3,241
3,850
8
32
7 '8"
48
ll'O"
112
13'8"
166
15 '5"
256
20'0"
364
19'5"
589
24'4"
760
21'5"
1,117
24'1"
1,410
26'0"
1,660
26'1"
2,084
29'6"
3,056
33'7"
3,704
36'11"
4,395
40'
9
36
54
126
187
288
411
668
857
1 ,260
1,591
1,875
2,350
3,438
4,167
4,930
10
40
9'4"
61
13' 6"
140
16'10"
208
19 '0"
319
24'7"
452
23'10"
736
31'0"
944
26'4"
1,400
29'6"
1,752
31'11'
2,060
31'H1
2,600
36'2"
3,818
41'
4,630
45'
5,475
49'
11
351
510
815
1,041
1,540
1,933
2,275
2,860
4,200
5,093
6,010
12
383
560
883
36'8"
1,128
31' 2"
1,675
35'0"
2,090
37'9"
2,464
37'10"
3,120
42'11"
4,584
48'5"
5,556
53'1"
6,555
58'
Dimension H in Fig. 8-3 .
Dimension L in Fig. 8-3.
-------
,TO ATMOSPHERE
EXHAUST
FAN
TO
PRODUCT
STORAGE
BINS
FUEL OIL
V-A BLOWER
Figure 8-4 Schematic diagram of a pellet bed calcining system (courtesy of Dorr-Oliver Incorporated)
-------
17
A wide range of capacities can be accommodated with the FBR. Lamb has
reported 18 lime mud reburning installations as of March 1972, ranging in
capacity between four and 220 tons of lime per day. The maximum capacity of a
single fluidized bed calciner is estimated at 250 tons of lime per day. Sand bed
reactors have been built from four to 20 ft in internal diameter for the incineration
of wastewater sludges.
The FBR is sized on the basis of the gas velocity required to fluidize the bed
material. For pellet bed type units, velocities of approximately 1.8 m/sec
(6 ft/sec) are usual whereas for sand bed units, the superficial reactor velocity
is about 0.6-0.9 m/sec (2-3 ft/sec) . Any given bed material will fluidize only
over a limited range of gas velocities and this fact imposes a limitation on the
flexibility of the FBR to accommodate variations in capacity much beyond + 20
percent of design without serious losses in efficiency. In a practical sense the
capacity in terms of tons of sludge per square foot per hour is largely governed
by its moisture content and its calcium carbonate content—the two principal
contributors to heat requirements.
An attractive feature of the FBR is its ability to restart quickly on shut down. The
fluidized bed acts like a large heat reservoir. Normally a hot sand bed will lose
only 0.5 C per hour during down time. 19 The FBR can also build up temperature
rapidly due to the high heat transfer properties of the gas-bed mixture. Heat
transfer rates for an FBR bed are some 5 to 25 times that of gas alone. -^ As a
result of the heat properties of a FBR, shut down-start up cycles are much
shorter than for a MHF .
Pellet Bed Units -
In the fluidized bed system that has been used to recover lime from water soft-
ening and pulp and paper mill sludges, the pellet bed reactor is only the
calcination and cooling part of the lime recovery system. Essential to the
operation of the system are some related processes which will now be described.
After passing through a thickening-dewatering stage (see Fig . 8-4 and Section
VII) , sludge cake is mixed with predried calcium carbonate in a paddle type
mixer. Mixing with a dry product, required because dewatered cake is sticky
and difficult to transport, results in the formation of easily moveable lumps.
From the paddle mixer solids are discharged into a cage mill. Here, the lumps
are broken up and the solids are exposed to a stream of exhaust gases from the
reactor. The solid particles are rapidly dried by the hot gases and carried to
a cyclone where the dried carbonate is separated from the gas stream. A
portion of the material collected in the cyclone is returned to the paddle mixer
to condition dewatered cake and the remainder is transferred to a dried sludge
storage bin. From the storage bin, a pneumatic conveyor feeds the dried sludge
to the burning compartment of the FBR. Fuel, either gas or oil, is also injected
into this compartment. Once in the burning compartment, where temperatures
are maintained at 816-927 C (1500-1700 F) , the calcium carbonate particles are
rapidly converted to calcium oxide. The CaO particles agglomerate into larger
particles, aided by the violent mixing in the bed. To promote pellet formation
and to control its size, an agglomerating agent (soda ash) is normally introduced
142
-------
along with the feed sludge. Crushed lime pellets are added as seed particles.
Lime pellets are discharged from the calcining zone to the cooling section
through an internal transfer pipe. In the cooling compartment hot lime is
fluidized with incoming air which lowers the product temperature to 227 C (440 F)
and in turn, preheats the air to that same temperature before entering the calcin-
ing section. Cooled, dust free pellets are continuously transferred from the
cooling compartment to a storage bin through a bucket elevator. Fig. 8-5 shows
a cross section of a typical fluidized bed calciner.
One attractive feature of the pellet bed unit is the heat recovery that is integral to
the system. Hot off-gases from the reactor are used for flash drying of the cake
fed to the system. Discharge gas temperature from the system usually is only
135 to 149 C (275 to 300 F) ,20,21 compared to the usual 427 C (800 F) in a MHF
(without after burning) or 816 C (1500 F) in a sand bed FBR. As a consequence,
the pellet bed unit requires from one-half to one-third the fuel per ton of CaO of
a sand bed FBR.2^ The excess air required for the burning of either or both the
fuel and sludge is only 20-30 percent as opposed to 70-100 percent in the MHF.
Up to the present time, the pellet bed FBR has been applied strictly to paper pulp
mill and water softening applications. The process will be applied to a tertiary
treatment lime sludge in a plant currently under construction in Virginia.1'
The chief U.S . manufacturer of the unit, Dorr-Oliver Incorporated, is cautious
about the application of the pellet bed FBR to lime sludges generated in the
primary sedimentation tank. The main concerns expressed are related to whether
excessive dusting would occur in the reactor due to the increased level of inerts
in a cake generated by primary processes as compared to tertiary processes. In
one water softening application, granular silica in the raw influent increased
dust losses from the normal 15 percent loss up to 25 percent. It was concluded
that if the pellet bed FBR is going to be applied to lime recovery in raw waste-
water treatment, further research on the control of pelletization in the process
is required.22 The same note of caution is expressed by Krause.23 He noted
that even sludges from similar application, but different locations, differed in
their behavior in the pellet bed FBR. A considerable period must be allowed
after start up for fine tuning and modification of the system to allow its full
performance to be obtained.
When the pellet bed reactor is applied to wastewater sludges, attention must also
be given to odor control in the unit. During incineration of organic sludges, it
is often contended that the combustion zone must be held at 649-816 C (1200 to
1500 F) for effective destruction of odorous substances (see Section IX) . While
it is true that the pellet bed FBR operates at 816 C (1500 F) in the calcining zone,
the hot off-gases are used to dry the cake in a cage mill. As a result of the pre-
drying of the lime cake before it is fed to the reactor, the off gas temperature
ahead of the wet scrubber is in the range of 135 to 149 C (175 to 300 F) . Conse-
quently, odors may be created in the drying zone from volatilization of organics.
Afterburning of the off-gases may be required if the pellet bed FBR is applied to
lime recalcination of raw wastewater sludge. Afterburning will naturally reduce
its overall fuel efficiency -
143
-------
HOT GAS TO DRYER
PREHEAT BURNER
TRANSFER PIPE
RECYCLE CRUSHED PELLETS
GUNS
v^§?'ffl-_^FUEL GUNS
T. ~f- ^-'J -\ l^ •
PELLETIZED PRODUCT
AIR
Figure 8-5 Typical fluldlzed bed calclner
(courtesy of Dorr-Oliver Incorporated)
144
-------
Due to lower levels of organic solids in tertiary lime sludges, afterburning may
not be required for tertiary treatment applications.
Sand Bed Units -
Originally, the sand bed FBR was developed to incinerate sludges from both
primary and biological treatment. It has since been applied to lime sludges as
well. Differences from the basic pellet bed unit are the elimination of the sludge
drying step, the dewatered cake being fed directly to the burning zone of the FBR
by a positive displacement pump or a screw conveyor; and the replacement of the
bed of lime pellets used with water softening and paper pulp sludges with a bed
of graded silica sand. Fig. 8-6 shows the modified flow sheet for applications
involving lime treatment of raw wastewater.
In the modified FBR for lime recalcination, pellet formation is inhibited and all the
calcium oxide particles are carried by the exhaust gases to a hot cyclone where
CaO is separated from the gas stream. From the cyclonic collector, lime dis-
charges into a quenching tank, where it is slurried by the cooling water and then
discharged to a collection tank. Slaking of the lime to Ca(OH) 2 takes place in
this tank. In this tank, which also receives water discharged from the wet
scrubber and a conditioning ash slurry, the lime slurry is further diluted and
then pumped to an ash thickener. In the process of dilution, the lime is dis-
solved, resulting in a nearly saturated solution of calcium hydroxide and
leaving the other constituents in suspension. Albertson24 has reported that the
separation of the suspended matter from the calcium hydroxide solution in the
thickener is extremely rapid. Overflow rates of 100 to 120 cu m/day/sq m (2500
to 3000 gpd/sq ft) may be possible. Supernatant from the thickener, containing
the calcium hydroxide, is then returned to the primary clarifier to recycle the
lime. Thickener underflow is pumped to a dewatering step prior to final ash
disposal.
At the time this manual was being written, no full-scale operational data were
available on the modified FBR flow sheet shown in Fig. 8-6. Albertson and
Sherwood-^ have reported the results of lime recovery tests conducted both in
a 12-inch, laboratory scale reactor and in a 4-ft FBR used to incinerate organic
sludge. In these tests lime sludge, obtained during bench scale studies of lime
precipitation, was mixed with centrifuged organic cake and the mixture was
fed to the reactor. Bed temperature was maintained at 871 C (1600 F) . The
combustion gases then passed through a cyclone separator and a wet scrubber.
Laboratory analysis of the solids in the cyclone underflow showed that 79.6-90
percent available lime was captured in the unit.
Experience at Holland, Michigan - As mentioned before, there is no informa-
tion available on full-scale operation of a sand bed-type FBR on wastewater
sludges. The closest operation similar to lime recalcination is the FBR in
operation at Holland, Michigan. At Holland, the FBR is used for sludge
disposal for a low lime treatment plant rather than for lime recalcination. As
a result, it does not have the hot cyclone and recovery system shown in Fig.
8-6. Nonetheless, the furnace is operated at 816 C (1500 F) ,26 This operating
145
-------
-TO ATMOSPHERE
01
BOOSTER PUMP
e?
FLUIDIZED BED REACTOR
CENTRIFUGE
THICKENED
SLUDGE
lAAAAA/V
FEED SCREW
CONVEYOR
FUEL OIL
PUMP
ASH THICKENER OVERFLOW
RETURN TO PLANT INFLUENT
Figure 8-6 Schematic diagram of a sand bed calcining system
(courtesy of Dorr-Oliver Incorporated)
-------
temperature is sufficient for recalcination in a FBR. Certain operating experiences
with this unit are worthy of discussion.
The FBR at Holland is a 4 m (13 ft) ID unit with a 1.5 m (60-inch) expanded bed.
A total of 14 burners are provided. Normally, a screw conveyor is used to feed
centrifuge cake. In cases where the centrifuges are down, thickened slurry may
be fed through four feed ports using a Moyno pump. The unit has considerable
overload capacity. It has been fed at 725 kg/hr (1600 Ib/hr) without difficulty
while its design is for 408 kg/hr (900 Ib/hr) ,26
The current operating problem is that material is building up in the venturi
scrubber causing high head losses in the gas discharge from the unit.26 it is
likely that calcium oxide is slaking in the scrubber, causing a deposit to form,
much as occurs in a lime slaker. This condition requires at least semiannual
maintenance.
Some pelletization has occurred on the sand bed particles, and bed material must
be blown down to hold a constant bed volume in the system. Martin26 stated that
a volume equal to the bed volume has been blown down in approximately a seven-
month period. After this initial blowdown, the sand particles seemed to have
reached a maximum size and no further removal has been found necessary.27 n
has been found that 40 to 50 percent of the bed is calcium oxide. If pelletization
occurs in a sand bed FBR, it defeats the intended mode of operation of the unit
for recalcination, since product is removed from the effluent gases rather than
from the bed. Dorr-Oliver states that pelletization has not occurred in a recal-
cining application where the sludge contains calcium carbonate from a tannery
waste treatment plant. It is felt that the occurrence of unintentional pellet
formation is affected by the type of inerts in the waste sludge, which may be
unique in each application.22 Further research on pelletization is required to
define the conditions necessary for its control in the sand bed FBR before it can
be applied with certainty to wastewater lime sludges.
Rotary Kiln Calciners
Until 1963, when the first fluidized bed reactor was installed at S-.D. Warren Co.
in Muskegon, Michigan,20 the rotary kiln calciner (RKC) was the conventional
method to recover lime in the pulp and paper mill industry. Rotary kilns have
also been successfully used to reclaim lime from water softening sludges. 1 To
date, no attempts have been made to apply the RKC to the recovery of lime from
wastewater sludges.
A typical RKC consists of a long rotating steel shell lined with a refractory
material. The shell is slightly inclined to facilitate movement of sludge along the
kiln. Dewatered lime sludge is fed and off-gases exhausted at the upper end of
the shell. This section is provided with a heat recovery chain to facilitate the
exchange of heat between the sludge cake and the hot exhaust gases. Sludge is
dried in this end of the RKC. After a residence time of one and a half hours and
before being discharged at the lower, or firing end of the shell, sludge is
nodulized (i.e., agglomerated in round-shape lumps) and converted to calcium
oxide in the calcining zone. From the rotary shell, the product enters a peri-
pheral tube cooler from which it is mechanically transferred to storage.
147
-------
The temperature of the calcining zone is maintained at approximately 1093 C
(2000 F) , considerably higher than the theoretical temperatures required for
recalcination. Temperatures as high as 1371 C (2500 F) have been used in some
applications. Exhaust gases are emitted at 204 C (400 F) . In the integral tube
cooler, recalcined lime is cooled to approximately 316 C (600 F) . The RKC
requires higher temperatures than the MHF or FBR because the particle size of
calcium carbonate in the rotary kiln is so much larger than in the other recal-
cining units. A higher temperature is required to provide the necessary force so
that carbon dioxide can be driven out of the center of the larger clumps. Uneven-
ness of particle sizes requires higher temperatures than necessary for the bulk
of the particles .28,29 A schematic diagram of a typical RKC is shown in Fig. 8-7.
It seems unlikely that rotary kilns will find application in recovering lime from
wastewater sludges. The RKC requires appreciably more area than either
multiple hearth furnaces or fluidized bed reactors. Also, the RKC would be
limited only to large installations processing more than 50 tons of product per
day. Perhaps more important is the fact that rotary kiln technology is completely
foreign to the wastewater treatment field whereas the MHF and the FBR have been
successfully applied to the disposal of wastewater sludges for many years. 12,16
As a result, a wealth of experience has been gained in these installations and
important modifications have been made, and new designs incorporated, to the
original equipment. It could take the manufacturers of rotary kilns a comparable
investment, both in time and money, to develop the expertise required to
satisfactorily recover lime from wastewater sludges.
HANDLING OF RECLAIMED LIME
The type of process used to recalcine wastewater sludges has a direct influence
on the way the reclaimed lime is handled. In the case of the FBR, each type of
recalcine reactor produces a unique product; consequently, product handling
differs among reactor types .
Handling of Lime from the MHF
As mentioned earlier, recalcined lime from a multiple hearth furnace is dis-
charged at the bottom hearth. Unless operating difficulties cause the formation
of lumps (clinkers) , the lime discharged from the furnace is a fine, powder-like
product. Table 8-4 show the size analysis of a typical sample of recalcined lime
taken at Concord, California.6 As shown in Table 8-2, the discharge tempera-
ture of the recalcined product is approximately 399 C (750 F) . To protect
operating personnel from injury and to avoid the need to use heat resistant
material in process equipment, it is advisable to cool the lime to a temperature
of 38-93 C (100-200 F) . Several types of industrial coolers can be used for this
application. At the CCCSD water reclamation plant, water cooled, disc-type
coolers will be supplied. After cooling, the reclaimed lime is either transported
to storage by mechanical or pneumatic conveyors (see Section V) or it can be
classified, using dry techniques, to separate inert solids and other undesirable
constituents from the recalcined product.
148
-------
t
SECONDARY
SCRUBBER
STACK
-WATER
I.D.FAN
Y
WASTE
CENTRIFUGE
PRIMARY
SCRUBBER
SECONDARY AIR
FILTER CAKE
CONVEYOR
BUCKET_
ELEVATOR
NATURAL GAS
PRIMARY
AIR FAN
\f~~~~
LAAAAAAAAAAAAAAAA/\/g
PRODUCT SCREW
LIME
STORAGE
BIN
PRODUCT
Figure 8-7 Typical rotary kiln calciner
-------
Table 8-4. SIZE DISTRIBUTION ANALYSIS OF RECALCINED LIME FROM A MHh
Particle size
U.S. mesh3
100
140
200
270
325
b
Microns
44.00
34.48
31.22
24.77
15.57
11.12
7.55
3.34
1.36
< 1.36
Weight retained, grams
Sample 1
0.8100
1.3091
1.5756
3.1673
6.2182
Sample 2
3.3822
0.8490
2.5264
12.5030
22.8780
40.3914
51.0089
18.7903
e
Percent
retained
0.36
0.58
0.69
1.39
2.74
1.97
0.55
1.51
7.42
13.66
24.01
30.91
11.72
2.49
Cumulative
percent passing
99.64
99.06
98.37
96.98
94.24
92.27
91.72
90.21
82.79
69.13
45.12
14.21
2.49
Sieve analysis
Bahco analysis
C Weight of sample: 227.0706 grams
Weight of sample: 155 . 3664 grams
6 Weight smaller than 1. 36yw.: 3.0362 grams
Dry Classification of Reclaimed Lime -
Dry (i.e., air) separation of reclaimed lime can be used in lieu of the wet classi-
fication process described in Section VII or in addition to it. In the former case,
this method of solids separation can be used in conjunction with sludge dewater-
ing by vacuum filters or filter presses (Fig. 7-8) . In the latter, dry classifica-
tion aims at increasing the purity of the recalcined product beyond that obtained
by wet classification alone (Fig. 7-9) . Dry classification has been found most
effective for blowing down silica from the system shown in Fig. 7-9.6
Most air classifiers operate on the principle of centrifugal separation combined
with the effect of opposing drag forces created by a current of air. The settling
rates of particles are increased many times when centrifugal forces are used
in place of gravitational acceleration. Once the difference in settling rate
between particles of two given sizes has been magnified, the classifier separates
them into two groups when centrifugal and drag forces reach equilibrium. The
point of equilibrium, at which a particle of certain size is either accepted or
rejected by the classifier is called the "cut point". The Envirotech Corporation
has found that a cut point at the 45 micron (>*) particle size achieves a partial
classification of the acid insoluble inerts (mostly silica) from the other materials.
Fig. 8-8 shows the size distribution of a furnace product sample taken during an
extended test of lime sludge recycling at CCCSD.6 It can be seen for this single
sample that a fairly good rejection of silica can be obtained while recovering the
150
-------
bulk of the reclaimed lime at cut point points between 20 and 45 /* . The selection
of the cut point is best established in field trials. The accepts include fine dust
particles ( < 5yU ) which normally must be retained for reuse in the process.
This is accomplished by a second separation step that takes place in two stages.
First in a cyclonic separator where the solid particles are driven by centrifugal
force to the cyclone wall while the dust laden air escapes through the gas outlet.
Dust is subsequently removed, in the second stage, in a bag type filter. The
rejects (coarse) portion after discharge from the classifier is usually carried
directly to waste by mechanical or pneumatic conveyors.
100 \—
Date Collected 8-6-73
10
15
20 25 30 35 40
PARTICLE SIZE, MICRONS
45
Figure 8-8 Particle size distribution of recalcined lime
Several types of classifiers are available which can successfully accomplish size
classifiction of the furnace product. Both the Bauer "Centri-Sonic" classifier and
the BSP Air Classifier have successfully been applied to this application. The
Bauer machine (shown in Fig. 8-9) is typical of conventional classification design
and operates with a rotating classifier section. The feed, admitted at the top,
first passes through a dispersing rotor which ensures that each individual
particle is free to move in the classifier zone. The particles then move downward
between the louver curtain and the rotating classifier where they are intercepted
151
-------
to
DISPERSING
ROTOR
LOUVER
CURTAIN
-DECK
SELECTOR
• FINE ACCEPTS •.". '. ; :-*T
REJECT FAN
BAUER "CENTRI-SONIC"
BEND
CLASSIFYING
CHAMBER
BAFFLE
PLATE B
SECONDARY
AIR
FEED AND AIR
INTAKE
BAFFLE
PLATE A
EXHAUST
ORIFICE
(ACCEPTS)
COARSE
REJECTS
BSP AIR CLASSIFIER
Figure 8-9 Two types of air classifiers
-------
by a controlled flow of air. The air is forced through the classifier carrying with
it the fine particles and excluding the coarse particles which are held out by drag
forces. The "cut point" in the Bauer design is determined by the air rate; the
classifier speed; the number of deck openings, as fixed by the position of the
deck selector; and the rotating classifier design.
The BSP air classifier is unique in that it does not incorporate moving parts (Fig.
8-9) . The sharp bend after the introduction of the feed moves the bulk of the
solid particles sliding against the inside of baffle plate A leaving a nearly clean
gas stream passing on the outside of this baffle plate, next to the chamber wall.
At the bottom of baffle plate A, the gas stream crosses a curtain of particles sliding
off the inside of the baffle plate producing a separation between the particles,
allowing each to react separately to the drag and centrifugal forces induced on it
in the chamber. Large particles settle by gravity to the bottom of the chamber.
Intermediate size particles and fines flow with the gas in a controlled spiralling
stream. Each of these particles is subjected to a centrifugal force, tending to
move it to the chamber walls, and to a drag force, created by the gas stream,
tending to move the particle to the exhaust orifice. At the "cut point", the two
forces are equal. Particles larger than the cut point are affected predominately
by centrifugal forces and flow outwardly until they impinge on the chamber wall
and settle by gravity to the classifier bottom. Particles smaller than the "cut
point" are affected mostly by drag forces and are swept out with the gas stream.
The BSP classifier "cut point" is controlled by the chamber dimensions, rate of
air flow and secondary air flow.
Fig. 8-10 shows the adaptation of the basic air classification system to the separ-
ation of calcium carbonate from inerts in applications involving lime recovery
from wastewater sludges.
Using sludge generated at the ATTF, full-scale tests on air classification were
conducted at Concord, California^ in a BSP air classifier. During the course of
the Concord tests it was initially felt that the dust collected in the bag filter (see
Fig. 8-10) should be wasted from the process; this was done because initial
batch testing showed the dust to be high in phosphates. However, when tested
at the ATTF with wet classification blowing down phosphorus, the dust did not
contain excessive amounts of phosphorus. Table 8-5 compares the phosphorus
and other constituent levels in the accepts to those in the dust during a period
in the ATTF operation when the process was believed to be close to steady state.
Due to the small effect of phosphorus, dust was returned to the process along
with the other accepts .
Dry classification performance is expressed similarly to wet classification per-
formance; for good classification, high recovery of calcium oxide to the accepts
and dust is desired with low recovery of all other constituents. As shown in
Table 8-6, essentially no classification of calcium oxide from the other constit-
uents occurred, except for silica and iron. The period of July 27 to August 30
represented production operation of the classifier during the lime recycle project.
The runs on September 20 represented an attempt to operate the classifier closer
to design conditions. During the production runs, the classifier was not loaded
153
-------
INLET HOPPER
CLASSIFER UNIT
ACCEPTS
EXHAUST
DUCT THRO
ROOF
TYPICAL
BLOWER
REJECT BIN
FOR ASH
HAULING
ASH
DISCHARGE
FROM
FURNACE
TYPICAL
ROTARY FEEDER
ACCEPTS
TO LIME
STORAGE
Figure 8-10 Dry classification of recalcined lime (courtesy of Envirotech Systems, Inc.)
-------
Table 8-5. COMPARISON OF ACCEPTS AND DUST COMPOSITION
DURING ATTF TEST WORK
Date
August 6, 1973
August 10, 1973
August 12, 1973
Sample
Accepts
Dust
Accepts
Dust
Accepts
Dust
Calculated composition, percent dry weight
CaO
61.9
58.3
60.4
61.4
61.1
64.6
MgO
4.3
6.9
4.5
8.2
4.0
5.7
CaCO3
7.4
13.5
7.4
10.1
3.5
5.8
Ca3(P04)2
7.0
10.1
7.2
10.2
7.1
9.7
Fe203
1.6
1.4
1.5
1.4
1.7
1.6
Si02
11.1
1.2
10.7
0.6
15.5
3.0
Other
0.9
0.3
2.3
1.6
1.1
1.3
Table 8-6. COMPONENT RECOVERIES IN CLASSIFICATION TESTS
DURING ATTF TEST WORK
Date
(1973)
July 27
July 31
Aug. 6
Aug. 12
Aug. 14
Aug. 16
Aug. 18
Aug. 20
Aug. 22
Aug. 24
Aug. 26
Aug. 28
Aug. 30
Mass
average
Sept. 20-1
Sept. 20-2
Sept. 20-3
Mass
c
average
Classifier load
kg/hr Ib/hr
—
—
729 1,607
670 1,477
592 1,305
562 1,240
718 1,583
622 1,382
702 1,548
730 1,609
848 1,870
776 1,710
789 1,740
703b l,551b
227 500
227 500
454 1,000
303 667
Recovery to accepts and dust of stated constituent, percent
CaO
99.2
99.2
93.8
95.5
98.5
96.3
97.6
94.8
97.5
97.6
98.2
98.8
96.7
97.3
98.2
97.6
98.5
98.1
Si02
84.6
80.6
88.6
92.2
95.1
93.9
92.7
89.4
94.8
92.0
92.6
94.7
90.3
91.8
79.0
67.6
78.8
76.1
MgO
98.2
98.1
93.1
95.3
98.6
95.4
95.8
93.4
98.2
97.1
97.9
98.8
95.7
96.8
95.5
96.1
97.3
96.6
CaCOg
98.2
99.0
93.1
95.8
97. 8
95.5
96.1
96.5
96.3
97.5
97.1
93.8
98.4
97.7
97.9
98.5
98.6
98.4
Ca3(P04)2
98.0
97.8
93.1
95.0
98.2
96.0
97.1
94.0
97.2
97.0
97. 3
98.1
95.7
96.6
94.6
95.2
96.6
95.7
Fe203
91.4
92.2
92.0
94.3
97.1
94.7
94.9
92.3
96.1
95.4
95.8
96.7
93.6
94. 5
88. 0
84.1
84. 7
86.4
Other
96.8
96.3
85.7
94.8
97.4
94.9
94.3
98.3
81.0
75.9
100.0
100.0
99.1
95.4
84.2
93.3
97.3
92.9
Total
recovery,
percent
98.1
97.8
93.0
94.9
97.9
95.5
96.8
94.1
97.1
96.4
97.0
98.0
95.1
96.5
94.5
93.8
96.0
94.4
July 27 to Aug. 30
bExcluding July 27 and 31
cSept. 20 only
155
-------
on a steady set basis. Furnace product, that had been stored in the thermal disc
cooler (see Case History) and a water jacket conveyor, was loaded into the classi-
fier on an intermittent basis. This resulted in surges in operation which adversely
affected process efficiency. Constant rate operation on September 20, 1974 pro-
duced performance consistent with Envirotech's previous experience.
Even under the best conditions, the rejection of silica and iron is not high as
compared to the rejections obtained for most constituents in wet classification.
Nonetheless, silica is not classified well in the wet classification process; there-
fore, dry classification provides a means to blow down additional amounts of a
difficult to reject constituent. As will be shown in Section X, dry classification
is a more efficient means of blowing down silica than direct wasting of the furnace
product.
Handling of Lime from the FBR
As described earlier, lime recovered in a pellet bed reactor is discharged from
it in pelletized form. Recalcination of water softening sludges and pulp and
paper mill sludge shows that the product obtained in these applications is a
dense, dust free lime pellet which can be handled without difficulty in mechani-
cal or pneumatic conveyors (see Section V) . A typical size distribution for this
material is given in Table 8-7.30
Table 8-7. TYPICAL SIZE DISTRIBUTION FOR PELLETS FROM A
FLUIDIZED BED CALCINER
Accumulative weight
retained, percent
1.5
13.5
24.6
50.1
81.5
19. 5a
U.S. Sieve
series
6
8
10
14
20
< 20
Weight with particle size smaller than 20 mesh
A distinctive feature of the sand bed FBR used in wastewater sludge applications
(see Fig . 8-6) is the handling of reclaimed lime in slurry form. The problems
associated with lime slurry handling were described in Section VI under Lime
Addition. The National Lime Association lists several corrective measures to
minimize scaling problems.31 Engineers considering a sand bed FBR to recover
lime from wastewater sludges should give careful attention to these types of
problems and provisions to either correct or alleviate them should be incorporated
into the design.
156
-------
Handling of Lime from the RKC
As shown in Fig. 8-7, reclaimed lime discharged from a RKC (rotary kiln calciner)
is transported to storage via mechanical conveyors. Since the nodulized pro-
duct from a kiln occasionally includes large lumps, up to 15-20 cm (6-8 inch) in
size,32 the recalcined lime is normally screened so only 1.9-2.5 cm (3/4 - 1 inch)
particles are discharged to the screw conveyor. In the lime reclamation plant at
Miami, Florida, lumps retained in the screen are put through a crusher and then
fed to the same screw conveyor.32 Reclaimed lime, discharged at approximately
316 C (600 F) from the RKC, is not usually cooled prior to storage; mechanical
conveyors must therefore be designed to handle the hot product.
RELATED PROCESSES
Incineration is not the ultimate means to dispose of wastewater sludges. All com-
bustion processes yield two end products: a solid residue or ash and a gaseous
product, usually called exhaust or off-gases. Both have important effects on the
environment and must therefore be subjected to further treatment before final
disposal. Furthermore, off-gases are a source of heat that can be recovered.
Methods used to handle ash are covered in detail in Section XI. Handling of
exhaust gases is described in the following paragraphs. A third environmental
concern, noise, is often associated with incineration systems. Since noise and
its control in areas where operators are present is receiving increasing attention
by federal and state authorities, methods to reduce noise levels around incinera-
tion installations will also be briefly reviewed.
Off Gases Scrubbing
It has been stated^S that uncontrolled gases emitted from the MHF and the sand
bed FBR contain approximately 0.9 and 8.0 grains per dry standard cubic foot
(gr/dscf) of particulate matter respectively. Since the air quality standards
(see Section IX) limit particulate emissions to the atmosphere to 0.03 gr/dscf
maximum, high efficiency scrubbers are required to reduce incinerator emissions
to acceptable levels.
Particle collection equipment has been classified34 as follows:
"1. High-efficiency, high-cost collectors:
a. Electrostatic precipitators.
b. Sonic agglomerators.
2. High-efficiency, moderate-cost collectors:
a. Fabric or fibrous filters .
b. Wet collectors , packed towers , scrubbers, and centrifugals .
3. Low-cost, lower efficiency designs:
a. Cyclones and dry centrifugals.
b. Dry dynamic.
c. Inertial."
157
-------
To control the emission of participate matter, multiple hearth furnaces are
usually equipped with inertial wet scrubbers of the impingement baffle or
Venturi designs. In fluidized bed reactors, due to their operational features
which result in higher emission of particulates, the wet scrubber is often
preceeded by dry cyclones which reduce the dust load of the secondary (wet)
collector.
The MHF used to recalcine lime from wastewater sludge can be expected to have
higher particulate emissions than units burning organic sludges. This is due
not only to the characteristics of the feed material but also to the fact that classi-
fied lime sludge cakes, at 50-60 percent solids concentration, would tend to dry
in the top hearth (feed hearth) where the off-gases are removed from the
furnace. Dried particles could then be carried by the outgoing gases. In one
testing and two full-scale installations, the dust load from multiple hearth
furnaces recalcining lime has been found to average approximately 30 Ib per
1000 Ib of exhaust gases. The dust loading would sometimes justify the use of
a cyclonic precleaner ahead of the wet collector. Cyclones are highly efficient
in removing medium and coarse dust particles. Particulate matter collected in
the dry cyclone, containing an appreciable percentage of calcium carbonate, can
be returned to one of the furnace's burning hearths for recalcination. To
minimize carry over of small lime particles (passing a 200 mesh) , the gas
velocity inside a MHF should be maintained below 10 fps. 14
Fig. 8-11 shows the arrangement of the scrubbing equipment for the lime recal-
cination furnaces at the CCCSD water reclamation plant. The wet scrubber is a
three stage venturi-spray unit designed for low head loss operation. Besides
removing particulate matter, wet scrubbers also cool the off-gases to avoid the
formation of a steam plume. A temperature of approximately 43 C (110 F) is
required to suppress a stack plume. 12
A more detailed review of gas cleaning techniques is beyond the scope of this
report. The reader is referred to a series of reports published by the American
Petroleum Institute on the Removal of Particulate Matter from Gaseous Wastes for
a comprehensive coverage of this subject. (Reference 34 is part of this series) .
Selection of scrubbing equipment should be made in consultation with the manu-
facturers of incineration systems or even left entirely to them if a performance
specification, warranting compliance with the applicable air pollution standards,
is used to select the incineration equipment.
Waste Heat Recovery
Incineration of wastewater sludges requires that sufficient heat be generated:
1) to evaporate the remaining moisture from dewatered cakes, and 2) to ignite
and burn the dried sludge. Furthermore, when lime is to be recovered, addi-
tional heat is required to convert calcium carbonate in the sludge to calcium
oxide. Heat is derived from combustion of volatile matter in the sludge and
from auxiliary fuel supplied through the incinerator burners. Heat generated
by combustion leaves the incinerator in the exhaust gases, in the hot ash
product, and, in the case of the MHF, in the air used to cool the central shaft.
158
-------
/50 PS/6 STEAM
TO ATMOSPHERE
TO ATMOSPHERE
SCRUBBER
STACK
^
ffrr
1
SHAFT COOLING
k
:^- WASTE HE
RECOVERY Bl
BOILER FEED
AIR BYPASS
*~\
AFTER 1
BURNER-^ f
? \ ^
L CIIO*
Ji^
Kt
t A r* c
CYCLONIC
DRY I
SCRUBBER
WET
SCRUBBER
CENTRI-
FUGED
SLUDGE
FEED
+-SHAFT
COOL ING
AIR RETURN
INDUCED DRAFT
FAN
AUXILIARY
AIR SUPPLY
DUCT
DUST RETURN
SCREW
CONVEYOR
THICKENED SCUM FEED
I J-
. FUEL OIL TO BURNER
_ | -2-
N AT URAL GAS TO
BURNER
AUXILIARY SHAFT
COOLING AIR FAN
SLUDGE GAS TO
FURNACE
SHAFT
COOLING
AIR FAN
FLAME TRAP
ASH
TO GRINDER
COMBUSTION
AIR FAN
CENTER SHAFT DRIVE
Figure 8-11 Auxiliary equipment for a MHF at the CCCSD water reclamation
plant
159
-------
The heat loss in the hot ash product cannot be recovered economically but is
normally a small fraction of the total heat generated. Heat losses by radiation
to the surroundings are minimized by the use of thermal insulation. The other
two ways in which heat may leave the incinerator, and heat recovery methods
applicable to them, are discussed below.
In multiple hearth furnaces, the heat contained in the warmed shaft cooling air,
at a temperature of 149-260 C (300-500 F) , would normally be recovered by using
it as part of the combustion air, thus reducing fuel requirements. As mentioned
earlier, in the pellet bed calciner (see Fig. 8-4) , the reactor off-gases are used
to dry the lime sludge before it is fed to the FBR, thereby practically eliminating
the need for auxiliary fuel to evaporate water in the reactor. In the sand bed
units (see Fig. 8-6) , the drying step has been eliminated so no heat recovery
step is inherent.
Apart from the heat recovery features included in multiple hearth and fluidized
bed incineration systems, heat can be recovered from incinerator off-gases by
using them to generate steam in a waste heat boiler. A waste heat boiler is
essentially a heat exchanger in which heat is extracted from hot gases and
transferred to water to generate steam. A water-tube type (water inside the
boiler tubes, hot gases outside the tubes) is generally to be preferred over a
fire-tube type boiler (gas inside, the tubes, water outside) .36 A basic water-
tube boiler would consist of two steel boiler drums placed one above the other,
with a multiplicity of small diameter boiler tubes connecting the two drums.
Drums and tubes are enclosed in a refractory lined housing having an inlet and
an outlet for the gases from which heat is being reclaimed. The heat recovered
with a typical waste heat boiler is approximately 75 percent of that contained in
the hot gases at a reference temperature of 15.6 C (60 F) . This value is an
assumed average ambient temperature which is customarily used in combustion
calculations. Heat losses to the surroundings from the casing would be about
two percent of the heat transferred from hot gases to steam.
For the CCCSD water reclamation plant, each multiple hearth furnace has been
provided with a waste heat boiler. Each boiler is capable of generating 15,870
kg/hr (35,000 Ib/hr) of steam at a pressure of 10.5 kg/sq cm (150 psig) and a
temperature of 185 C (365 F) .37 Heat is obtained from 52,200 kg/hr (115,000
Ib/hr) of exhaust gases leaving the furnace at 760 C (1400 F) . In passing
through the boiler and generating steam, the gases are cooled to approximately
232 C (450 F) . The high pressure steam produced is used to power turbine-
driven aeration blowers and boiler feed water pumps and to supply heat to the
plant's air conditioning and heating systems.
In Fig. 8-11, a waste heat recovery boiler in a typical MHF at the CCCSD plant
has been shown. Worth noticing is the location of the dry cyclone precleaner
provided ahead of the wet scrubber, which also reduces the load of fly ash
going to the boiler. In the design of the boiler, particular attention should be
given to the dust load and the size of the particles entering the boiler.
160
-------
Heat recovery can be expressed as a percentage of the heat input to the incinerator
by making a complete heat balance for the incinerator and the waste heat boiler.
To make this balance the following parameters must be known: feed rate and com-
position of the sludge; heat of combustion of the sludge volatile solids; amount of
excess air and furnace temperature required for complete combustion; and physical
dimensions and thermal characteristics of the incinerator. In addition to the
parameters just listed, the properties and heating value of the fuel must also be
known. The heating value of fuels is expressed in two ways, (1) as the high
heat value (HHV) also known as "gross" heat value and (2) as the low heat value
(LHV) , also called the "net" heat value. The essential difference between the
HHV and the LHV is the heat of condensation of water equivalent to the hydrogen
contained in the fuel. Because the water formed in combustion always leaves the
furnace as water vapor (uncondensed) , the heat of condensation of the water is
unavailable for use. Therefore, in combustion calculations, the LHV is the one
normally used.
The heating value of gaseous fuels is usually expressed as the HHV of 0.028 cu m
(one cubic foot) of the gas measured at 15.6 C (60 F) and a pressure of 76 cm
(30 inches) of mercury. Thus, a stated heating value of 9,450 kcal/cu m
(1,050 Btu/cu ft) for natural gas normally means the HHV for the conditions
stated. The LHV for such a gas would be about 8,550 kcal/cu m (950 Btu/cu
ft) , the exact difference between the HHV and the LHV depending upon the gas
composition. For liquid and solid fuels, the heating values are normally
expressed in kcal/kg (Btu/lb) . Approximate heat values for common petroleum
fuel oils are given in Table 8-8.
Table 8-8. TYPICAL HEAT VALUES OF FUEL OILS
Type
No. 6 - Heavy
No. 6 - Light
No. 2 (Diesel)
Weight
kg/cu m
17.85
16.67
14.72
Ib/gal
8.34
7.79
6.88
Heat values, kcal/kg (Btu/lb)
HHV
10,290(19,540)
10,560(19,020)
10,960(19,750)
LHV
9,730(17,540)
9,950(17,930)
10,270(18,510)
Noise Control
Noise can be defined as undesired sound. The intensity of sound is usually
measured in decibels (dBA) , a term that expresses the relative magnitude of a
particular sound when compared to a reference sound pressure level. One
decibel is equal to a force of 0.002 dyne per square centimeter. It is important
to keep in mind that decibels are measured not on an arithmetic but on a loga-
161
-------
rithmic scale. Thus a reduction of 3 dBA is almost a 50 percent reduction of
noise energy. Typical sound levels are given in Table 8-9. ^
Table 8-9. TYPICAL SOUND LEVELS
Class
Very faint
(threshold of audibility)
Faint
Moderate
Loud
Very loud
Deafening
Threshold of feeling
Found in
Sound proof room
Whisper
Quiet conversation
Private office
Average conversation
Average office
Average factory
Average street noise
Noisy office
Noisy factory
Unmuffled truck
Loud street
Boiler factory
Nearby riveter
Sound level,
dBA
10
20
30
40
50
50
60
70
80
90
90
100
100
110
120
The Occupational Safety and Health Act of 1970 (OSHA) considers noise above
certain established levels as occupational hazards, i.e., possible loss of
hearing, and has established limits of exposure for workers subjected to noisy
environments. Table 8-10 shows permissible noise exposure set forth by OSHA
Federal and state industrial safety orders have also limited the degree of noise
exposure that employees may endure without ear protection devices.
Due to the auxiliary equipment normally associated with sludge incineration
systems, a large number of noise sources are located near incinerators. Gen-
erally speaking, the sound produced by a machine is directly related to the
horsepower input to it. Also, high speed machines are noisier than low speed
units. As an example, Table 8-11 gives estimated sound pressure levels for
one of the multiple hearth furnaces at the CCCSD water reclamation plant.38
The values given are for the equipment operated alone without background
noise. As seen in Table 8-11, the noise level is controlled by fan and blower
noise. Since several pieces of equipment operate simultaneously, the overall
sound pressure level will be higher than shown in the table. For example, if
the maximum noise level allowed in the incineration area is set at 95 dBA, the
noise produced by the shaft cooling fan has to be lowered to meet the combined
noise level.
162
-------
Table 8-10. PERMISSIBLE NOISE EXPOSURES
Sound Level,
dBA
Duration per
day, hours
90
92
95
97
100
102
105
110
115
6
4
3
2
1
1/2
1/4 or less
Table 8-11. SOUND PRESSURE LEVEL OF MHF EQUIPMENT
Furnace
Center shaft drive
Center shaft cooling air fan
Combustion air fan
Induced draft fan
Lump breaker (intermittent)
Lump breaker (continuous)
Ash cooler
Screw conveyor
Pneumatic conveyor air lock valve
Pneumatic conveyor air blower
Air classification system
Feed bin vibrator (full bin)
Feed bin vibrator (empty bin)
Rotary feeder
Air classifier
Air filter (intermittent)
Pneumatic conveyor air blower
Ash bin discharge screw conveyor
Motor
HP
15
20
40
50
1 1/2
10
2
1/2
10
1/2
25
15
3
dBA @ 3 ft
distance
70
95
85
85
90
80
65
60
50
90
30
70
50
86
90
90
60
163
-------
Several techniques can be applied to control noise. The level of sound generation
of the source can be reduced. Examples of this approach are the installation of
acoustic enclosures around the entire fan or blower assembly, the addition of
inlet and discharge silencers, and the use of low noise electric motors. Equipment
enclosures have resulted in average reductions of 4 dBA.39 intake silencers can
reduce inlet noise levels by 10-15 dBA,38,40 while discharge mufflers have
resulted in an additional reduction of 6 dBA.39 Reductions of 4 dBA in the sound
pressure level have been reported for blowers enclosed in acoustic shields. 39
When the incineration equipment is housed in a building, further reduction can
be obtained by adding absorbing material to the walls to reduce the reverberant
sound level. Dobbs40 has reported that a noise reduction of approximately 8-10
dBA could be accomplished with the use of 3-inch thick glass fiber boards for
acoustical absorption.
Vibration isolation is another method of noise control. Large fans and blowers
should be mounted on a heavy inertia base and attached to it with vibration isola-
tors of the combined spring and rubber type.40 Since piping can transmit the
sound generated by machinery, the junction between equipment and ducts should
be through a flexible connector. The flexible connectors should have sufficient
mass to be at least equal to that of the duct walls.40 Lead loaded vinyl or rubber
are thus better insulators than the canvas fabric found in standard connectors.
SUMMARY OF LIME RECOVERY CASE HISTORIES
Several wastewater treatment plants have practiced lime recovery either on an
experimental or full-scale basis. Information is available from two tertiary
treatment plants (South Tahoe and Piscataway) and two plants practicing
primary lime addition (Blue Plains and Central Contra Costa) . A brief descrip-
tion of the lime recovery operations in each of these four plants is given below.
South Tahoe Water Reclamation Plant
The water reclamation experiences at the South Tahoe plant have been extensively
documented and reported. Reference 2 of this section is a report covering three
years operation of the 7.5 mgd advanced wastewater treatment plant. The
summary that follows highlights the thickening, dewatering and recalcination
processes only .41
At South Tahoe, secondary effluent from the activated sludge process is treated
with lime, clarified, passed through an air scrubber to remove ammonia, recar-
bonated, and finally treated by filtration and carbon adsorption. Sludges from
the lime clarifier and recarbonation basin are first gravity thickened and then
dewatered in a solid bowl centrifuge. The sludge cake is calcined and recycled
for reuse along with makeup lime in the lime clarifier. A second centrifuge
dewaters the centrate from the first unit and its cake is conveyed to an organic
sludge MHF. The first centrifuge is a concurrent type one and is operated in a
wet classification mode (see Section VII) . The centrate is sent to the second
centrifuge of the same type where the remaining solids are removed. The
centrifuges can be operated at 2200, 1800, or 1600 rpm. Initial tests were
164
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2
carried out on the lime mud feed stream to determine optimum operating speed.
Data showed approximately the same percent solids in the cake and the same
recovery of solids at all three speeds. The lowest speed was selected to reduce
wear and maintenance.
At South Tahoe it has been found that the percent capture or recovery of lime
into the first stage cake decreases linearly with increasing feed rate of lime
sludge. At approximately 8 percent solids in the feed, 93 percent capture was
achieved at a feed rate of 10 gpm. When the feed rate was increased to 20 gpm,
solids capture dropped to 79 percent.41
The South Tahoe report^ states that at a flow of 7.5 mgd through the water recla-
mation plant, the total blowdown of waste solids from the lime clarification opera-
tion would be about 17 tons per day of lime mud (dry CaO basis) if there were
no lime recovery. With lime recovery, this quantity is reduced to about 1.5 tons
per day. The cost of recalcined lime at Tahoe ($31.61/ton CaO) is slightly
higher than that of make up lime. This figure however, does not take into
account the savings in sludge disposal realized through reduction of the solids
volume achieved by incineration and the on-site production of CC>2 for recar-
bonation.
The centrifuged cake is fed by a belt conveyor to a 4.1 m (14.3 ft) diameter, six
hearth MHF. The recalcined lime is discharged by gravity through a crusher
to a thermal disc cooler where lime temperatures are lowered from 371 C to
38-66 C (700 F to 100-150 F) . Cooled lime drops into a rotary air lock and is
pneumatically conveyed to a 35 ton capacity recalcined lime storage bin for
reuse. Stack gases are scrubbed in a multiple tray scrubber before being
exhausted to the atmosphere. A portion of the gases are recycled to the recar-
bonation system. Solids are continuously wasted to prevent a buildup of inerts
in the recycled product.
Since 1968 the South Tahoe plant has successfully recalcined lime sludge from the
lime chemical treatment process. Over this period makeup lime has accounted
for only 28 percent of the calcium oxide used. Monthly CaO values in the
recalcined lime have averaged 66.0 percent over the entire period.2 A reduc-
tion of approximately 40 percent in fuel requirements was achieved when
centrifugal classification was used rather than whole sludge recovery. 2
The influence on lime activity of recalcined temperature, rabble arm speed and
feed rate were investigated at South Tahoe. Of the three parameters, temperature
had the most effect on recalcined lime activity. The CaO content in the recalcined
lime was increased 15 percent by raising the temperatures from 871 to 1038 C
(1600 to 1900 F) . At nine tons of solids to the MHF per day, the optimum recal-
cining conditions were 1038 C (1900 F) on hearths numbers 4 and 5 with a 1.5-
2.0 rpm rabble arm speed.
Fig. 8-12 is a schematic diagram of the lime sludge handling facilities at South
Tahoe.2
165
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CENTRATE
TO PRIMARY
CLARIFIER
INFLUENT
CHANNEL
SPENT
LIME
PUMP-
CENTRIFUGE
FOR LIME
SLUDGE
MAIN
STACK
INDUCED
DRAFT
FAN
X
BYPASS-
DAMPER
WET -\ /
SCRUBBERy
Y
DRAIN
LIME
RECALCINING
FURNACE •
CENTRIFUGE
FOR LI ME OR
/SEWAGE
'SLUDGE
FURNACE
RABBLE
ARM DRIVE
REVERSIBLE
BELT CONVEYOR -
BYPASS \f /
DEWATERED/Y
LIME SLUDGE *
STORAGE BIN
SHAFT COOLING
AIR RETURN
TO
SEWAGE
SLUDGE
FURNACE
LOADING
#•
1
1 — 1
J
r
^
i
THERMAL
rDISC.
COOLER
^ /ROIARY
'Am LUOK .
* i
fa<
s
_l
Q
Ul
2
y
<
o
\ LU /
±
/BIN\
Q.
LL)
FROM
CHEMICAL
CLARIFIER
SLUDGE
PUMP
FROM LIME
DELIVERY
TRUCK
PNEUMATtC \
UNLOADING
AND
CONVEYING EQUIP
-TYP LIME FEEDER
-TYR LIME SLAKER
COMBUSTION
AIR BLOWER
SHAFT
COOLING
AIR BLOWER
RECALCINED
LIME BLOWER
RECALCINED
LIME TO
SPLITTER
BOX
FRESH
LIME TO
SPLITTER
BOX
Figure 8-12 Lime recovery at the South Tahoe water reclamation plant
166
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Piscataway Advanced Wastewater Treatment Plant
The EPA is supervising the operation of a 0.22 cu m/sec (5 mgd) tertiary facility
at Piscataway, Maryland. The system employs two-stage lime treatment, effluent
filtration and activated carbon adsorption (Fig. 8-13) . A single sludge dewater-
ing stage (centrifugation) is employed. Because the centrifuge is operated at
high recovery, the inerts are retained in the recalcined lime.42
The recalcined product has an available lime index of 60 percent. The calcium
oxide content might even be lower if it were not for the fact that the secondary
effluent is low in phosphorus concentration (3.1 mg/1 as P) . During a 36-day
operating period when 26 percent of the furnace produce was blown down, 68
percent of the total dose of 271 mg/1 CaO was recalcined lime. The resulting pH
for this operation was 11.45. Secondary effluent alkalinity is approximately
100 mg/1 as CaCO3.42
Blue Plains Advanced Wastewater Treatment Plant
A two and one-half month test of lime recovery from combined sludges has been
conducted at the EPA-DC Blue Plains Pilot Plant.43 The system consisted of an
Independent Physical Chemical treatment (IPC) pilot plant with two stage lime
precipitation, dual media filtration and granular carbon adsorbtion treating
District of Columbia raw wastewater at 189,000 Ipd (50,000 gpd) . The first stage
of clarification with lime addition was operated at approximately pH 11.5 while
the second stage with CC^ recarbonation was operated at pH 10.0-20.5 with an
Fe+++ dosage of 5 mg/1 as added flocculant. Solids from the clarification system
were gravity thickened to 9-13 percent solids and classified in a Sharpies model
P600, 6-in. diameter solid bowl centrifuge to separate carbonate and noncar-
bonate solids. The centrifuge cake at 51 percent solids was calcined in a multiple
hearth furnace, mixed with make-up lime and recycled to the clarification system.
The centrate was wasted from the lime recycle system and dewatered by alternate
centrifugation, vacuum filtration and pressure filtration systems.
The classification centrifuge operated at approximately 74 percent solids recovery.
At this solids recovery the constituent recovery of CaCO3 averaged 93.0 percent
while that of Ca3 (PO4) 2, Mg(OH)2 and volatile solids averaged 37.3, 46.0 and
41.3 percent, respectively. The classification centrifuge prevented a buildup of
inert materials in the recalcined product; during the test period, the fraction of
calcium oxide hovered between 70 and 80 percent. During the test period, the
fraction of reclaimed lime of the total dose was 72.5 percent.
Comparing the use of virgin lime or recalcined lime, effluent qualities of the
IPC system were equivalent during periods when the plant was run under
computer control. The comprehensive investigations of the Blue Plains investi-
gators in the area of dewatering second stage centrate has been summarized in
Section VII.
Central Contra Costa Sanitary District Water Reclamation Plant
In connection with the design of the CCCSD's Water Reclamation Plant, test work
has been conducted at its Advanced Treatment Test Facility on the reclamation
167
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SECONDARY EFFLUENT
FIRST STAGE
LIME TREATMENT
RECARBONATION
SECOND STAGE
LIME TREATMENT
THICKENING
I
FILTER INLET
WELL
CENTRIFUGATION
I
F ILTRATION
RECALCINAT ION
VIRGIN LIME
NEUTRAL IZATION
TO PROCESS
REGENERATION
MAKE-UP
CARBON
CARBON
ADSORPT ION
1
TO POND
RETURN
Figure 8-13 Piscataway tertiary treatment plant
168
-------
and reuse of lime from lime sludges. ^ The test involved the setup of the follow-
ing experimental components of the system: (1) centrifuge (Sharpies P3000) for,
wet classification, (2) a screw conveyor positioned for loading a truck bed,
(3) a truck unloading hopper at the site of a nearby municipal MHF, (4) a tem-
porary belt conveying system for loading the MHF, (5) a thermal disc cooler and
water jacketed screw conveyor for cooling and conveying the furnace product,
(6) an air classification system for the purpose of separating silica from the
furnace product, (7) a hopper for storage of recalcined lime and (8) a slaker for
reclaimed lime hydration.
The experimental procedure involved wet classification by centrifuge of all of the
sludge produced at the ATTF in the chemical primary. The centrifuge cake was
trucked twice daily to another treatment plant (the City of Concord's plant) where
an existing MHF was available. The cake was unloaded from the trucks into a
receiving hopper, and sludge was conveyed from the hopper to the furnace at a
uniform rate by a temporary belt conveyor. Centrifuge cake was recalcined in
the MHF, and then the furnace product was cooled and fed to a dry classification
system. In the classification system the furnace product was separated into
three fractions—an accepts fraction, a coarse rejects fraction and a fine dust
fraction. Each fraction was stored in 55 gallon drums, labeled and weighed.
The accepts and fine dust drums were then trucked back to the CCCSD's ATTF
where the drums were unloaded into an accepts hopper. From the accepts
hopper lime was fed via a rotary valve to the slaker, and the slaked lime was
then directed back to the chemical clarifier.
Actual recycling of lime was carried out from July 17, 1973 to August 30, 1973, a
period of 5 weeks. Only a portion of this period can be considered representative
of design conditions. The late July period was characterized by erratic furnace
production caused by filling the space between the rabble arms and the hearth
bottom ("bedding down") , and certain operational difficulties with the centri-
fuge and the furnace which affected furnace production adversely. After
August 10, 1973, the centrifuge performance deteriorated markedly due to
centrifuge wear. The rented centrifuge did not have hardened surfaces and
therefore the scroll suffered considerable wear. The end result was that after
August 10, calcium carbonate recovery decreased significantly. Therefore,
the period of August 1 to 10 best represents design conditions. During this
period, 7,110 kg (15,660 Ib) of new lime (Ca(OH)2) was used, while 10,199 kg
(22,465 Ib) of reclaimed lime was returned to the process. Thus, 17,309 kg
(38,125 Ib) of total lime was used, resulting in a dose of 332 mg/1 of calcium
hydroxide since the total flow for the 10-day period was 52,235 cu m (13.8 mil
gal) . This dose corresponded with an operational pH of 11.0.
One artifact was imposed on the experiment that will not be presented in the
CCCSD design. The Concord MHF had only wet scrubbing of the stack gasses,
whereas the CCCSD design incorporates a dry cyclone prior to the wet
scrubber. The solids captured in the cyclone are returned to the MHF for
recalcination and reuse in the process. During the tests at Concord, approxi-
mately 21 percent of the calcium carbonate fed to the furnace were exhausted
with the stack gases. Analysis of the particle size of this material indicates
169
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that 59 percent of this material will be captured in a cyclone of CCCSD design.
Assuming that a dry cyclone could have been installed during the Concord tests,
a total of 12,165 kg (26,823 Ib) of lime could have been returned to the process.
Under this condition, a total of 70.4 percent of the total dose would derive from
reclaimed lime. This value is in excellent agreement with the predicted recycle
level of 69 percent.7-44 Calcium oxide content of the reclaimed lime during the
10-day period averaged 64 percent; the predicted content was 63 percent.' The
lime slaked readily and the average temperature rise in the AWWA slaking rate
test was 36.2 C (range 33.7 to 39.5 C) . The temperature rise is lower than the
40 C minimum stipulated for new lime in the AWWA test; however, this merely
indicates that the reclaimed lime has a lower CaO content than new lime.
Chemical primary treatment performance during the lime recycling period was
superior to a period preceding the lime recycling (Table 8-12) . Organic re-
movals improved, as indicated by the BOD5, SS, TOC and soluble organic
carbon measurements. Phosphorus removal markedly improved, and this
eliminated the need for supplemental coagulant addition that had previously been
necessary for obtaining high phosphorus removals at pH 11.0 or less (see
Tables 6-4 and 6-5) . The data in Table 8-12 also indicates that the calcium
reaction was more complete during lime recycling than prior to it.
Table 8-12. COMPARISON OF PRIMARY SEDIMENTATION PERFORMANCE
WITH AND WITHOUT LIME RECYCLE
Constituent
(mean value)
BOD
SS
TOC
Soluble organic carbon (SOC)
Total phosphorus as P
Orthophosphate as P
Calcium hardness
d
Magnesium hardness
Hardness increase
With lime recycle
pH 11.0 operation
Ca(OH) -335 mg/1
Raw
sewage,
mg/1
177
230
145
27
10.9
10.4
101
106
Chemical
primary,
mg/1
50
25
34
23
0.60
0.40
127
23
45
Percent
removed
72
89
77
14
95
96
+28
Without lime recycle
pH 11.0 operation0
Ca(OH) -332 mg/1
z
Raw
sewage ,
mg/1
207
205
126
24
11.0
10.4
67
100
Chemical
primary,
mg/1
75
38
44
29
1.45
1.04
144
25
+2
Percent
removed
64
81
65
-19
87
90
_
-1
July 27 to August 30, 1973, at an average flow of 5,300 cu m/day (1 .40 mgd)
July 1 to July 25, 1973, at an average flow of 5 ,030 cu m/day (1.33 mgd)
No ferric chloride addition
As CaCCX
170
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WASTE SLUDGE INCINERATION
As stated in Section VII, when wet classification is employed to separate the
calcium carbonate portion from the other constituents of the lime sludge, one
method to dispose of the waste solids in the centrifuge centrate is to thicken and
dewater it prior to incineration (Fig. 7-9) . Incineration of first-stage centrate
cake is similar to incineration of municipal sludge (the purpose is obviously the
same, i.e., the destruction of volatile matter to produce an inert ash residue for
final disposal) . The calorific value of the dewatered centrate cake has been
estimated at 5,000 to 5,550 kg-cal per kg of volatile solids (9,000 to 10,000 Btu/lb
VS) ,37 which is close to that of biological sludges. ^ Wet classification does not
normally achieve. 100 percent capture of calcium carbonate (Section VII); there-
fore the centrate from the first stage centrifuge will contain some CaCOs as well
as other inorganic chemicals such as magnesium, phosphorus and iron com-
pounds. Since these compounds are inert, their presence tends to reduce the
thermal value of the centrate cake. Moreover, the endothermic decomposition of
CaCC>3 to CaO further increases the thermal load on the incinerator. A similar
situation occurs when conditioning chemicals are added to organic sludges to
improve their dewatering characteristics .
As it was shown in Figs. 7-6 and 7-7 and in Table 7-10, the moisture content of
the dewatered cake, i.e., the weight of water which must be evaporated prior to
combustion, has a decisive influence on both performance and economics of
waste sludge incineration. Centrifuge centrate, as biological sludges, is also
difficult to dewater. This is indicated in Table 7-11, which shows solids con-
centrations ranging from only 17 percent TS for centrifugal (second stage)
dewatering to 25 percent TS for a filter press operated at 100 psi.
Due to the similarities between centrate from centrifugal classification and bio-
logical sludges, it can be assumed that the same incineration systems can be
applied to burn both types of dewatered sludges. Sludge incineration practices
have been reviewed in Reference 4. Rotary kilns, which are not covered in
that report, cannot be used to incinerate municipal sludges due to the relatively
high moisture content of the sludge cake.
The presence of lime in the incinerator off-gases might prove troublesome,
particularly in fluidized bed reactors. Since the normal operating temperature
of the reactor is 760-816 C (1400-1500 F) , some of the CaCC>3 particles carried
with the exhaust gases will be converted to the oxide form. In the sand bed
FBR, which is normally used for sludge incineration, exhaust gases are
scrubbed in a wet scrubber before being discharged to the atmosphere. It is
possible for the CaO to slake in the scrubber thereby causing scaling deposits
in this unit (see Section V) .
ENERGY CONSIDERATIONS
The Energy Crisis has affected practically every field of activity in the U.S. and
in wastewater treatment, its impact has been acutely felt in plants where solids
disposal by incineration is practiced. In some instances, the scarcity of fuels
171
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has forced the shut down of sludge incinerators and alternate means of sludge
disposal had to be found and implemented within a short period of time. Where
possible, dewatered cake can be trucked to sanitary dumps. As both the size of
the plant and the distance to the dump increases, the amount of fuel consumed •
in trucking could become an energy consideration on its own and should be
compared with the fuel requirements for incineration.
In lime recovery from wastewater sludges, the energy considerations are
different than for direct sludge incineration. Since new lime is obtained by
calcining of limestone, its production is also a process of high energy consump-
tion. Thus, to evaluate properly the merits of recovering lime from wastewater
sludges from an energy standpoint, a comparison in terms of energy requirements
should be made between reclaiming spent lime at the wastewater treatment plant
and producing new lime from limestone. For a true comparison, the energy used
in transporting new lime to the treatment plant should be added to the energy of
production to arrive at the overall energy requirements of makeup lime.
Before introducing numerical calculations, it should be pointed out that what
follows is not a typical economic comparison. No capital, operating or annual
costs are presented in this section, since no attempt has been made to assign a
dollar value to the processes examined. Rather, the following paragraphs will
try to bring the practice of lime sludge recalcination into a balanced perspective.
Incineration processes are highly visible and therefore, an easy target for those
concerned with fuel consumption. Costs will be presented in Section XII. To
illustrate the energy comparison, materials and heat balances for both a MHF and
a FBR will be developed based on the design loadings for the CCCSD's water
reclamation plant.37 Since cake moisture plays a decisive role in the economics
of sludge incineration, heat balances have been made at different percentages of
solids in the second stage cake (see Fig. 7-9) .
Energy Requirements of the MHF
The following conditions have been assumed:
1. Sludge flow rate and composition, as shown in the materials balance,
Table 8-13.
2. Excess air for volatiles combustion to be 100 percent of theoretical
requirement.
3. Temperature of exhaust gases, 760 C (1400 F) , required for after-
burning.
4. Fraction of calcined solids passing through the dry cyclone and
entering the wet scrubber, 7 percent of the total calcined solids. The
remaining portion is discharged from the bottom hearth.
The materials balance, Table 8-13, requires an explanation of the chemical re-
actions assumed to take place in the furnace. The volatile solids were assumed
to be burned completely to carbon dioxide, water, and elemental nitrogen. The
172
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conversion of calcium carbonate to calcium oxide was taken as 90 percent com-
plete. Magnesium and ferric hydroxides were assumed to be converted completely
to the respective oxides. The combustion products of the auxiliary fuel (natural
gas) were assumed to be carbon dioxide and water.
Table 8-13. MATERIALS BALANCE FOR MHF IN RECALCINE MODE
Inputs
Water
Sludge solids:
Volatile s
CaCOs
Mg(OH)2
Fe(OH)2
SiO2, etc.
Natural gas ,
J3
Combustion air
Total of Inputs
Outputs
Q
Gases :
H2O
co2
°2
N2
Calcined solids
Q
From bottom hearth
CaO
CaCOa
Others
With off gasesfc
CaO
CaC03
Others
Total of Outputs
kg/hr
596
1,873
66
15
288
4,228
3,053
1,244
2,886
878
175
321
6&
13
24
2,838
2,838
406
16,806
22,888
21,411
1,374
103
22,888
Ib/hr
1,312
4,125
145
34
634
9,313
6,724
2,739
28,384
1,934
384
706
146
29
53
6,250
6,250
894
37,018
50,412
47,160
3,024
228
50,412
Notes:
a
All figures taken at 15.6 C (60 F).
Includes excess air.
Taken at 760 C (1400 F).
93 percent of the total.
7 percent of the total.
Calculation of the amount of auxiliary fuel required is described in the explana-
tion of Table 8-14, which shows the heat balance. Combustion air requirement
was calculated by stoichiometry, using specified excess air of 100 to 10 percent,
respectively, for the volatiles and the auxiliary fuel, together with analyses for
173
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the volatiles and the fuel. Atmospheric moisture in air was taken as 0.0055 Ib of
water per Ib of dry air. The heat balance shown in Table 8-14 is based on a
customary reference temperature of 15.6 C (60 F) and all materials entering the
furnace are assumed to enter at that temperature. The term "sensible heat",
which is used in Table 8-14, means the heat content above 15.6 C (60 F) in the
process stream named. The itimized explanations of Table 8-14, given below,
include essential basic data and assumptions used in making the heat and
materials balance calculations.
Table 8-14. HEAT BALANCE FOR MHF IN RECALCINE MODE
Item
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Heat Requirements:
To evaporate moisture in sludge
Heat loss in calcined solids
For heat loss by radiation
For net heat loss in shaft cooling air
Heats of reaction, CaCO3 & Mg(OH)2 decompositions
Sensible heat at 1 ,400 F in gases from incineration
and calcination
Total Heat Requirements
Heat Inputs:
From volatiles, using low heat value (LHV)
From auxiliary fuel (net available at 1,400 F)
Total Heat Inputs
Gross heat input from auxiliary fuel, based on LHV
Sensible heat in auxiliary fuel combustion gases
@ 1,400 F
Sensible heat at 1 ,400 F in evaporated water
Total sensible heat in furnace off -gases
Heat recoverable with waste heat boiler
kcal/hr
2,704,900
214,100
114,700
66,200
759,000
2,171 .100
6,030,000
3,050,500
2,979.500
6,030,000
4,634,400
1,654,900
1,035,600
4,861,600
3,548,900
Btu/hr
10,734,000
849,600
455,000
262,600
3,011,900
8,615.400
23,928,500
12,105,200
11 .823.300
23,928,500
18,390,400
6,567,100
4,109,400
19,291,900
14,083,000
Item 1, is the heat required to convert 2,838 kg (6,250 Ib) of liquid water at
15.6 C (60 F) into water vapor at 760 C (1,400 F) . From steam tables this heat
requirement per kg of water is 954.3 kcal (1,717.4 Btu/lb) .
Item 2, the heat loss in the calcined solids, is for 1,374 kg/hr (3,024 Ib/hr)
leaving the bottom hearth at 649 C (1,200 F) and 103 kg/hr (228 Ib/hr) leaving
the off-gases at 760 C (1,400 F) . The average specific heat used was 0 2264
Btu/lb/F.
Item 3 is an average of the figures supplied by two manufacturers of the MHF
who provided heat balances for a furnace of the size to be used based on their
experience.
Item 4 is also an average of the figures supplied by the same two MHF manu-
facturers . A large amount of air is required to cool the rotating central shaft
and rabble arms in a MHF, but 85-90 percent of the heat in this warmed air can
be recovered directly by returning it to the furnace as combustion air. Item 4
174
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is the 10-15 percent of the heat in this air stream which is lost by radiation and
air leakage.
Item 5 is the heat required for the endothermic chemical reactions:
CaC03 >CaO + CO2
Mg (OH) 2 >MgO + H2O (gas)
The heat of reaction for calcium carbonate decomposition is 436.7 kcal/kg (786.8
Btu/lb) of CaCC>3; for magnesium hydroxide conversion to the oxide, 347.9 kcal/
kg (626.8 Btu/lb) of Mg (OH) 2. The heat of conversion of ferric hydroxide to
the oxide is negligible because of the small amount present.
Item 6 is the difference in heat content between 15.6 and 760 C (60 and 1,400 F)
for the sum of: (1) the gaseous combustion products of the volatile solids,
including the 100 percent excess air which was specified to insure complete com-
bustion of the volatiles; (2) the carbon dioxide evolved in calcium carbonate
decomposition; and (3) the water vapor evolved in converting magnesium and
ferric hydroxides to the respective oxides.
Item 7 is the sum of Items 1 through 6.
Item 8 is the heat generated by combustion of the volatile solids based on a low
heat value (LHV) of 5119 kcal/kg (9,223 Btu/lb) . This was calculated from a
stated high heat value (HHV) for the volatiles of 5550 kcal/kg (10,000 Btu/lb)
and the hydrogen content of the volatiles. Composition of the volatiles was
taken as:
Carbon 55.8 percent, Hydrogen 8.2 percent, Oxygen 31.0 percent,
Nitrogen 5.0 percent.
Item 9 is the heat required for the sum of the heat inputs to equal the sum of the
heat requirements . Numerically, it is equal to Item 7 minus Item 8. The fuel
requirement shown in Table 8-13 is obtained by dividing Item 9 by 7,338 kcal/kg
(13,221 Btu/lb) which is the calculated net, or effective, heating value per
kilogram (pound) of auxiliary fuel at 1,400 F.
Item 10 shows that the sum of the heat inputs equals the total heat requirements.
Item 11, the gross heat input from the auxiliary fuel, is obtained by multiplying
the kilograms (pounds) per hour of auxiliary fuel required, as calculated from
Item 9, by the LHV for the fuel in kcal/kg (Btu/lb) . The definition of heating
value of a fuel is the heat evolved per unit weight when the fuel is burned and
the combustion products cooled to 15.6 C (60 F) . This is exactly equivalent to
assuming the fuel to be burned and the heat to be evolved at this temperature.
Therefore, in order to obtain the effective heating value of a fuel at a tempera-
ture above 15.6 C (60 F) , in this case 760 C (1,400 F) , the heat required to
raise the combustion products to the higher temperature must be subtracted
from the published heating value. Published heating values are given in two
175
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ways, as the high heat value (HHV) , and the low heat value (LHV) . The essential
difference between HHV and LHV is the heat of condensation at 15.6 C (60 F) of
the water formed by combustion of hydrogen in the fuel. The LHV has been used
in these combustion calculations because the heat of condensation of water formed
in combustion is unavailable in ordinary combustion processes and excluding it
allows a clearer presentation of the heat balance. In this case, the fuel was
assumed to be natural gas having a LHV of 11,413 kcal/kg (20,564 Btu/lb) and
the following analysis:
Carbon 73.48 percent, hydrogen 23.20 percent, Oxygen 1.10 percent,
Nitrogen 2.22 percent.
The calculated net or effective heating value of the gas at 760 C (1,400 F) , when
burned with a specified 10 percent excess combustion air, is 7338 kcal/kg (13,221
Btu/lb) of gas. Details of this calculation can be found in books dealing with
combustion stoichiometry.
Item 12 is the difference in heat content, between 760 C (1,400 F) and 15.6 C
(60 F) of the auxiliary fuel combustion products, including the 10 percent of
excess combustion air assumed to be used with the fuel. Item 12 is the arithmetic
difference between Item 11 and Item 9.
Item 13 is the difference in heat content between 760 and 15.6 C (1,400 F and
60 F) of the water vapor evaporated from the sludge. From steam tables the
difference in heat content of water vapor between these two temperatures is
364.9 kcal/kg (657.5 Btu/lb) .
Item 14 is the sum of Items 6, 12, and 13. It is the difference in heat content
between 760 and 15.6 C (1,400 F and 60 F) of all gases leaving the furnace.
Item 15, the heat potentially recoverable from the furnace off-gases by generating
steam in a waste heat boiler, is taken as 73 percent of Item 14. In addition to
generating steam, the waste heat boiler will have the useful function of cooling
the furnace gases to about 219 C (425 F) , thereby greatly reducing the cooling
load on the wet scrubber.
Table 8-15 is a summary presentation of the heat balance which may be more
readily understood by readers who are unfamiliar with heat balance calculations.
Discussion -
From the heat balance in Table 8-14, it can be seen that of the total heat gener-
ated in the furnace, approximately 40 percent is from combustion of sludge
volatiles and 60 percent from the auxiliary fuel. In other words, Item 8 is
approximately 40 percent of the sum of Items 8 and 11. To evaluate the thermal
energy requirement to reburn lime in this way, in comparison with the thermal
energy requirement to produce fresh calcium oxide from limestone in a conven-
tional plant, the heat recoverable in a waste heat boiler should be taken into
account where a use for steam exists, as in the case of the CCCSD's water
reclamation plant. To account for the energy requirement to transport calcium
176
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oxide from the producer to the user, the energy requirements of transportation
are as follows4°:
Rail transport - 98 kcal per ton-km (624 Btu per ton-mile)
Truck transport - 542 kcal per ton-km (3,462 Btu per ton-mile) .
Table 8-15 SUMMARY OF HEAT BALANCES FOR MHF IN RECALCINE MODE
Gross Heat Inputs
Combustion of volatile solids
From auxiliary fuel
Total of Inputs
Heat Accounted for
To evaporate water at 60 F
Loss by radiation
Loss in shaft cooling air
Chemical reaction heats , CaCC>3 & Mg(OH>2
Heat loss in calcined solids
Heat content above 60 F in off-gases
Total Accounted for
kc«i/V
3,050,500
4,634,400
7,684,900
1,669,300
114,700
66,200
759,000
214,100
4,861,600
7,685,900
Btu/hr
12,105,200
18,390,400
30,495,600
6,624,600
455,000
262,600
3,011,900
849,600
19,291,900
30,495,600
The materials balance (Table 8-13) shows 878 kg (1934 Ib) of CaO, equivalent
to 0.967 ton, to be recovered with a gross thermal energy input (Item 11, Table
8-14) of 4.6 x 106 kcal (18.4 x 106 Btu) . Heat recoverable with a waste heat
boiler from the furnace off-gases amounts to 3.5 x 10^ kcal (14.1 x 10^ Btu) .
The difference between these two heat quantities may be taken as the energy
requirement to reburn 0.967 ton of CaO, which is equivalent to 1.1 x 10^ kcal
per ton (4.5 x 106 Btu/ton) of reburned CaO.
The thermal energy requirement to produce CaO from limestone, in modern rotary
kilns equipped with efficient heat recovery devices, is approximately 1.5 x 106 kcal
(6 x 10° Btu) per ton of CaO. 4?-48 -phe rail line distance from a competitive
supplier's plant to Martinez, California, where the CCCSD plant is located, is
approximately 550 miles. Using .98 kcal per ton-km (624 Btu per ton-mile) for
rail transport, the energy requirement for transport is approximately 86,000
kcal (343,000 Btu) per ton of CaO. Thus, the total thermal energy requirement
for a ton of fresh CaO delivered to the CCCSD's water reclamation plant is 1.6 x
106 kcal (6.3 x 106 Btu) compared with 1.1 x 106 kcal (4.5 x 106 Btu) for in-
plant recalcination.
Incineration of Second Stage Cake -
To illustrate the thermal effect of cake moisture in the incineration of dewatered
sludges, materials and heat balances for three different levels of cake moisture
are developed in the following paragraphs. Source of sludge in these cases is
the thickened centrate from a classification centrifuge (see Fig. 7-9) . Since
the purpose of this calculation is to show the relationships between cake moisture
177
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and heat demand, the example only covers incineration in a MHF. Incineration
in a FBR would show similar increases in heat requirements with increased
percentages of moisture in the cake.
The heat and materials balances were calculated by the same methods used for
dewatered primary sludge, described earlier in this section, taking into account
the differences in sludge solids composition. Calculated results are presented
for sludge moisture levels of 88, 81 and 70 percent by weight. The two higher
values represent moisture contents obtainable in centrifuged cakes; while the
lowest value might represent moisture content of a cake produced by a filter press,
Compostion of sludge solids, in weight percent, was taken as:
Organics (volatiles) 44.6 percent
CaC03 15.3
Ca5(P04)3(OH) 17.7
Mg(OH)2 7.4
MgO 3.4
Fe(OH)3 2.1
Fe2O3 0.9
SiO2 and others 8.6
Total 100.0 percent
The fuel value (HHV) of the volatiles was taken as 5,550 kcal/kg (10,000 Btu/lb)
and the calculated low heat value (LHV) was taken as 5,119 kcal/kg (9,223 Btu/
Ib) , the same as for the volatiles in the primary sludge. The conservative
assumption was made that calcium carbonate, magnesium hydroxide and ferric
hydroxide were converted to the respective oxides. The specified gas exit
temperature from the furnace was 760 C (1,400 F) . The basis for calculating
the heat loss in the ash was 93 percent by weight leaving the bottom hearth at
649 C (1,200 F) and 7 percent leaving in the effluent gases at 760 C (1,400 F) .
This high exit temperature is required to destroy odorous organic compounds.
The auxiliary fuel was assumed to be natural gas with a low heating value (LHV)
of 11,413 kcal/kg (20,564 Btu/lb) . A customary reference temperature of 15.6 C
(60 F) , was used, with all inputs to the furnace assumed to be at that temperature
The effect of reducing the sludge moisture content on auxiliary fuel requirement
can be seen in the materials balance, Table 8-16. Reducing sludge moisture
from 88 to 70 percent reduces the auxiliary fuel requirement by 74.9 percent.
For a reduction in moisture from 88 to 81 percent, the reduction in auxiliary
fuel is 46 percent.
Heat recoverable in a waste heat boiler attached to the MHF is shown for each of
the three moisture levels as Item 10 in Table 8-17, the heat balance tabulation.
Item 10 is taken as 73 percent of Item 8.
For situations where by-product steam can be used, examining the net auxiliary
fuel requirement to incinerate the sludge may be of interest. If the heat recover-
able with the waste heat boiler (Item 10, Table 8-17) , is deducted from the gross
auxiliary fuel input, (Item 2, Table 8-17) , the difference may be taken as the net
178
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Table 8-16. MATERIALS BALANCE FOR MHF AT THREE MOISTURE LEVELS
OF SECOND STAGE CAKE
Materials
Inputs:
Water in sludge cake
Volatile solids in sludge cake
Inorganic solids in sludge cake
Natural gas
Combustion air, total weight
Total of Inputs
Outputs:
Gases3
H20
C02
02
N2
Total for gases
Ash
Total of Outputs
Cake moisture, % weight
88
kgAr
9,712
590
734
1,149
28,991
41,176
12,722
4,381
1,244
22,212
40,559
617
41,176
Ib/hr
21,391
1,300
1,617
2,531
63,856
90,695
28,022
9,649
2,740
48,926
89,337
1,358
90,695
81
kgAr
5,646
590
734
621
19,428
27,091
7,509
2,958
1,044
14,891
26,402
617
27,019
Ib/hr
12,436
1,300
1,617
1,367
42,793
59,513
16,539
6,515
2,299
32,802
58,155
1,358
59,513
70
kg/hr
3,090
590
734
289
13,423
18,126
4,232
2,064
918
10,295
17,509
617
18,126
Ib/hr
6,806
1,300
1,617
636
29,566
39,925
9,321
4,547
2,023
22,676
38,567
1,358
39,925
At 760 C (1400 F).
Table 8-17. SUMMARY HEAT BALANCE FOR MHF AT THREE MOISTURE
LEVELS OF SECOND STAGE CAKE
Item
No.
1
2
3
4
5
6
7
8
9
10
Gross Heat Inputs
Volatile solids combustion
Natural gas auxiliary fuel
Total of Inputs
Heat Accounted For:
To evaporate water at 15. 6 C
(60 F)
Loss by radiation
Net loss in shaft cooling air
Chemical reaction heats
Heat loss in calcined solids
Heat content above 15.6 C (60 F)
in furnace off gases
Total Heat Accounted For
Heat recoverable with waste heat
boiler:
Cake moisture, % weight
88
1000
kcal/hr
3,021
13,116
16,137
5,713
115
66
114
95
10,034
16,137
7,325
1000
Btu/hr
11 ,990
52,047
64,037
22,672
455
263
451
375
39,821
64,037
29,069
81
1000
kcal/hr
3,021
7,084
10,105
3,321
115
66
114
95
6,394
10,105
4,668
1000
Btu/hr
11,990
28,111
40,101
13,181
455
263
451
375
25,376
40,101
18,524
70
1000
kcal/hr
3 ,021
3,296
6,317
1,818
115
66
114
95
4,109
6,317
3,000
1000
Btu/hr
11,990
13,079
25,069
7,214
455
263
451
375
16,311
25,069
11,907
Based on LHV.
179
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fuel requirement to incinerate the sludge. The values for the three sludge
moisture levels are presented in Table 8-18. Table 8-18 shows in another way
the fuel saving benefit to be derived from reducing sludge moisture content to
the lowest feasible level; at 30 percent moisture, the net heat required to incin-
erate the sludge cake after heat recovery is negligible.
Table 8-18. AUXILIARY FUEL REQUIREMENTS OF MHF AFTER HEAT
RECOVERY
Item
Gross auxiliary fuel input
Recovery in waste heat boiler
Net heat required to incinerate
sludge cake
Cake moisture, % weight
88
1000
kcal/hr
13,116
7,325
5,790
1000
Btu/hr
52,047
29,069
22,978
81
1000
kcal/hr
7,084
4,668
2,416
1000
Btu/hr
28,111
18,524
9,587
70
1000
kcal/hr
3,296
3,001
295
1000
Btu/hr
13,079
11,907
1,172
In the design of CCCSD water reclamation plant, steam generated by the waste
heat boilers on the two multiple hearth furnaces is sufficient to supply 94 per-
cent of the average steam requirements of the aeration blowers. ^° Each of three
blowers, driven by a 2,750 hp steam turbine, is capable of supplying 1680 cu m/
min (60,000 scfm) to the oxidation-nitrification system. Package steam boilers
are provided to meet peak steam requirements.
Energy Requirements of the FBR
Materials and heat balances are presented below for the same composition and
hourly input rate of dewatered primary lime sludge as was used in calculating
the heat and materials balances for the MHF.
As stated earlier in this section, the pellet bed FBR is in use to recover lime
from water softening and pulp and paper mill lime sludges. A feature of this
flow sheet is the use of the hot gases from the calcining reactor to evaporate
water from the incoming sludge, whereby the feed to the calciner is moisture-
free. This use of the hot gases from the calciner, therefore, is an important
heat recovery feature which is of interest with respect to energy conservation.
Up to now, the pellet bed reactor has not been used on sewage plant sludges.
The drying of the sludge takes place at a relatively low temperature, with the
gases leaving the dryer at a temperature of 163 C (325 F) . Because of this low
temperature, there is the possibility that some volatile odorous compounds
might not be destroyed and might escape through the final scrubber to the
atmosphere.
180
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Calculation of the materials and heat balances for the pellet bed calciner is rela-
tively complex and requires the use of data which were supplied by Dorr-Oliver,
Inc.^0 The data supplied by Dorr-Oliver are:
1. 15 percent of dry solids feed to the dryer is lost by carry-over to the
scrubber.
2. 15 percent of the calcined product returns to the dryer by carry-over.
3. CaO and MgO in the calcined product carry-over to dryer recombine to
form CaCO3 and Mg (OH) 2.
4. Radiation heat losses from calciner and dryer are about 5 percent of the
heat input to each.
5. Air in-leakage to the dryer (which is under suction) is 60 mole percent
of the calciner stack gas flow.
6. Gas temperature leaving calciner 899 C (1650 F) .
7. Gas temperature leaving dryer 163 C (325 F) .
8. Water is injected into the hot gases leaving the calciner to reduce the
temperature to 760 C (1,400 F) , to protect the dryer system from too
high a temperature.
Other pertinent data are:
1. Heating value (LHV) of sludge volatiles was taken as 5119 kcal/kg
(9,223, Btu/lb).
2. Auxiliary fuel was assumed to be natural gas having a LHV of 11,413
kcal/kg (20,564 Btu/lb) .
3. Temperatures of streams entering the system was taken as 15.6 C
(60 F) except for the combustion and fluidizing air, supplied by
blower, which was taken as 54 C (130 F) .
4. Recalcination in a pellet bed FBR requires the addition of a small
amount, less than 0.3 percent, of soda ash (Na2 003) to cause
pellet formation. This small addition was considered negligible
in the materials balance.
The calculations for materials and heat balances are shown in Tables 8-19 and
8-20, respectively. It will be apparent that separate but interrelated materials
and heat balances must be made for the dryer, the calciner, and gas cooler
(water quench to reduce calciner gas temperature from 899 to 760 C (1,650 to
1,400 F)) , in order to obtain the overall balances .
181
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Table 8-19. OVERALL MATERIALS BALANCE FOR FLUIDIZED BED CALCINER
Item
Inputs
Volatile solids
CaCO3
Mg(OH)2
Fe(OH)3
Inerts
Water in sludge
Water to gas cooler
Natural gas
Theoretical combustion air
Excess combustion air
Air in-leakage to dryer
Subtotals
Total
Outputs
N2
H20
C02
°2
Volatile solids
CaCO3
Mg(OH)2
Fe(OH)3
Inerts
CaO
MgO
Fe203
Subtotals
Total
To dryer
kg/hr
596
1,873
66
15
288
2,838
-
122
6,021
4,914
7,348
24,081
Ib/hr
1,313
4,125
145
34
634
6,250
268
13,263
10,823
16,187
53,042
To gas cooler
kg/hr
555
555
Ib/hr
-
-
1,223
1,223
To calciner3
kg/hr
507
1,873
66
15
288
-
-
-
-
-
2,749
Ib/hr
1,117
4,125
145
34
634
-
6,055
24,636 kg/hr (54,265 Ib/hr)
To scrubber
kg/hr
14,003
4,136
2,063
2,823
89
281
10
2
43
23,450
Ib/hr
30,843
9,111
4,544
6,219
197
619
22
5
95
-
-
-
51,655
As product from calciner
kg/hr
-
-
-
_
-
-
245
892
39
10
1,186
Ib/hr
-
539
1,965
85
21
2,610
24,636 kg/hr (54,265 Ib/hr)
Input to calciner is not additive to dryer input but comes from dryer.
The heat input from auxiliary fuel (LHV) is shown in Table 8-20 as 1,389,000
kcal/hr (5,511,000 Btu/hr) . Table 8-19 shows the reburned lime (CaO) pro-
duced as 892 kcal/hr (1,965 Ib/hr) , equivalent to 0.982 ton/hr. The auxiliary
fuel requirement per ton of CaO therefore is 1,414,000 kcal/ton (5,612,000
Btu/ton) .
182
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Table 8-20. OVERALL HEAT BALANCE FOR FLUIDIZED BED CALCINER
Gross Heat Inputs:
Volatile Solids
Natural Gas
Combustion and excess air @ 54 C (130 F)
Heats of recarbonation and rehydration
Total of Inputs
Heat Accounted For:
Heat of evaporation of 2,838 kg (6,250 Ib) water in sludge
Heat of evaporation of 555 kg (1 ,223 Ib) water in gas cooler
Heat of reaction, CaCOs— vCaO + CO2
Heat of reaction, hydroxides — > oxides
Radiation loss from calciner
Radiation loss from dryer
Sensible heat loss in product
Sensible heat loss, solids to scrubber
Sensible heat loss, gases to scrubber
Total
Btu/hr
10,289,200
5,511,200
376,000
500,600
16,677,000
6,624,400
1,295,800
3,245,600
90,900
800,000
600,000
174,500
60,900
3,784,900
16,677,000
kcal/hr
2,592,800
1,388,800
94,800
126,200
4,202,600
1, 669,400
326,500
817,900
22,900
201,600
151,200
44,000
15,300
953,800
4,202,600
Comparison may be made with the thermal energy requirements given before for
one ton of CaO. These were:
1. Reburning in a MHF with credit taken for heat recovery by means of
waste heat boiler: 1,122,000 kcal/ton (4,454,000 Btu/ton) .
2. Fresh CaO produced in a modern limestone plant in Nevada and trans-
ported to Martinez, California: 1,598,000 kcal/ton (6,343,000 Btu/ton) .
If the emission of odors is a problem with the pellet bed calciner operating on
sewage sludge, reheating the off-gases to 760 C (1,400 F) in an afterburner
might be considered a possible solution to the problem. While this could be
done physically, the thermal energy requirement would be so large that this
approach seems impractical.
In the sand bed FBR installed in Elkhart, Indiana17, the wet sludge is fed directly
to the calciner and all of the recalcined product leaves the reactor in the gas
stream. About 85 percent of the calcined lime is separated from the gas stream
in a cyclone and the remainder is removed in a wet scrubber. If a waste heat
boiler could be successfully operated on gas with this high content of solids, or
if the solids content of the gas could be substantially reduced, the same waste
heat recovery process might be applied as in the case of the MHF. However, as
the Dorr-Oliver Fluo-Solids process now stands, major alterations to it would be
required to allow energy recovery by means of a waste heat boiler.
183
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\
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U.S. Environmental Protection Agency. Technical Report No. 13 - Sewage
Treatment Plants . Tune 1973. p. 57-61.
34. Removal of Particulate Matter from Gaseous Wastes - Filtration. Department
of Chemical Engineering, University of Cincinnati. New York. American
Petroleum Institute, 1961. 56 p .
35. Simonds , S.R. Personal Communication to W . Henry. Envirotech Corpora-
tion, SanMateo, California. May 30, 1972.
36. Baumeister-Marks. Standard Handbook for Mechanical Engineers , Seventh
Edition. New York, McGraw-Hill Book Company, 1969. Sections 7, 9, and
12.
37. Brown and Caldwell. Plans and Specifications for Water Reclamation Plant,
Stage 5A - Phase 1. Central Contra Costa Sanitary District. California.
April 1973.
38. Foy,H.E. Personal Communication to D .L . Eisenhauer. Envirotech Corp-
oration, Brisbane, California. May 19, 1972.
39. Testing for Determination of Blower Produced Sound Levels and Blower
Adaptation for Sound Control. Butler Manufacturing Company-Salina
Division. Salina, Kansas . October 1, 1972 . 5 p.
186
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40. Dobbs.B.D. Personal Communication to D.L. Eisenhauer. Fitzroy & Dobbs,
Acoustical Consultants, San Rafael, California. November 20, 1972.
41. Farrell,J.B. Sludge Information Summary No. 2. (Presented at the EPA
Technology Transfer Design Seminar on Sludge Handling and Disposal) .
Anaheim, California. November 13-23, 1972.
42. O'Farrell, T.P. Letter Communication to D.S . Parker. U.S . Environmental
Protection Agency - Blue Plains Pilot Plant, May 17, 1974.
43.- Bennett, S.M. Letter Communication to D.S . Parker. U.S . Environmental
Protection Agency - Blue Plains Pilot Plant. May 1974.
44. Parker, D.S., D.G. Niles, andF.J. Zadick. Processing of Combined
Physical-Chemical-Biological Sludge. Brown and Caldwell and the Central
Contra Costa Sanitary District. (Presented at 46th Annual Conference of the
Water Pollution Control Federation. Cleveland. October 1, 1973) . 23 p.
45. Schmid, L.A., andR.E. McKinney. Phosphate Removal by a Lime-
Biological Treatment Scheme. Journal of the Water Pollution Control
Federation. 41: 1259-1276, July 1969.
46. Commoner, Barry. The Environmental Cost of Economic Growth. Commission
on Population Growth and the American Future. Research Reports, Vol. III.
47. Huges , H.H. Personal Communication to M .L . Spealman . U.S. Lime
Division of the Flintkote Company, Oakland, California. March 1974.
48. Meier, Morris. Personal Communication to M .L. Spealman. Allis-Chalmers
Manufacturing Co., San Francisco, California. March 1974.
49. Brown and Caldwell, Consulting Engineers. Report on Energy Requirements
for Alternative Modes of Operation of Water Reclamation Plant. Prepared for
the Central Contra Costa Sanitary District, Walnut Creek, California. 1974.
50. Lamb, D.R. Personal Communication to M .L . Spealman. Dorr-Oliver
Incorporated, Oakland, California. March 1974.
187
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SECTION IX
AIR QUALITY CONSIDERATIONS
An important problem connected to the operation of sludge incinerators is air pol-
lution . The air pollutants emitted from incinerators that must in general be con-
trolled include:
Particulate matter
Nitrogen oxides (NO )
X
Sulfur oxides (SO )
yC
Odorous substances
Trace quantities of metals, pesticides, polychlorinated biphenyls (PCB) and
other organic compounds.
The particulate matter released by incinerators burning lime treated sludges
includes small amounts of calcium carbonate (CaCO3) , calcium oxide (CaO) ,
tricalcium phosphate (Cag (P04) 2) , magnesium oxide (MgO) and inert solids.
Representative proportions of these constituents which might be expected in the
furnace off-gases are given in Table 9-1, where predicted compositions^ are
compared to actual measurements during the CCCSD's Lime Sludge Recycling
Study.2
A modern sludge incinerator, provided with an adequate scrubbing system and
properly operated, is capable of producing acceptable stack emissions of parti-
culate matter, nitrogen oxides, sulfur oxides and odors.3 The Task Force on
sewage sludge incinerators found however, that while the gas emissions are
below pollutant levels, most installations did not efficiently control the discharge
of particulate matter.
Under the provisions of the Clean Air Act of 1970, the U .S . Environmental Pro-
tection Agency (EPA) has implemented standards of performance for municipal
sewage treatment plants which would limit the emission of particulate matter
from new incinerators burning process sludges.4 There are also state and
local codes covering sludge incinerator emissions and under the Clean Air Act
of 1970, state and local codes may not be more lenient but can be more stringent.
Typical of these is the regulations of the Bay Area Air Pollution Control District
(BAAPCD) . The BAAPCD has jurisdiction over nine counties in the San Francisco
Bay Area in California. Regulation 2 of the BAAPCD covers particulate emissions
in terms of capacity and maximum emission by weight per dry standard cubic
foot (DSCF) . The weight is corrected for auxiliary fuel consumed in the com-
bustion of sludge.^
188
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Table 9-1. SOLIDS COMPOSITION OF LIME FURNACE OFF - CASES,
PERCENT
Constituent
CaCOs
CaO
Ca3(PO4)2
MgO
Inerts
S1O2
Other
Total
Unaccounted for
Design
condition
62.5
20.5
5.5
3.5
8.0
0
Measurements during lime Sludge Recycling Study
August 16, 1972
Test 1
68.0
10.4
4.4
4.8
4.9
0.8
0.0
5.7
6.7
Test 2
59.3
20.6
4.5
4.6
4.4
0.7
0.0
5.1
5.9
September 11, 1972
Test 1
64.6
19.8
3.7
3.4
6.6
0.6
0.0
7.2
1.3
Test 2
67.7
16.5
3.1
3.2
6.6
0.5
0.0
7.1
2.4
Reference 1.
Reference 2.
In view of the state of flux in which air pollution control regulations seemed to be at
the time this report was written, it would appear to be in the best interest of each
project to design for the most rigid control regulations whether they be federal,
state, or local.
Under the present EPA standards, dated March 8, 1970, particulate emissions to
the atmosphere would be limited to: 4
11 1. No more than 70 miligrams per normal cubic meter (mg/Nm^) undiluted,
or 0.031 grains per dry standard cubic foot (gr/dscf) .
2. No more than 10 percent opacity."
These same standards do not mention gas pollutant control since the
exhaust concentrations of SOX, NO,,, and CO emitted by a sludge incinerator
are below serious pollutant levels .° However it is advisable to check state and
local regulations for compliance of the gaseous emissions.
In the proposed standards, particulate matter is defined as "any material, other
than uncombined water, which exists in a finely divided form as a liquid or solid
at standard conditions." Opacity is defined as "the degree to which emissions
reduce the transmission of light and obscure the view of an object in the back-
ground."
189
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4
The following paragraphs are included in the standards:
"Available data indicate that, on the average, uncontrolled multiple-hearth
incinerator gases contain about 0.9 gr/dscf of particulate matter. Uncontrolled
fluid bed reactor gases contain about 8.0 gr/dscf. For average municipal
sewage sludge, these values correspond to about 23 Ib/hr in a multiple-hearth
unit and about 205 Ib/hr in a fluid bed unit. Particulate collection efficiencies
of 96.6 to 99.6 percent will be required to meet the standard, based on the
above uncontrolled emission rate. Emissions will be on the order of 1.0
Ib/hr."
"Existing state or local regulations tend to regulate sludge incinerator emis-
sions through incinerator codes or process weight regulations. The most
stringent state or local limit, 0.03 gr/dscf, is based on a test method that is
different from the reference methods in that it includes impingers. Many
state and local standards are corrected to a reference base of 12 percent
carbon dioxide or 6 percent oxygen. Corrections to carbon dioxide or
oxygen baselines are not directly related to the sludge incinerator rate
because of the high percentage of auxiliary fuel required. In some regula-
tions, the carbon dioxide from fuel burning is subtracted from the total in
determinations of compliance."
"For a typical incinerator with a rated dry solids charging rate of 0.5 ton/hr
at a gas flow rate of 3,000 dscfm, the proposed standard would allow the
incinerator to emit 0..8 Ib/hr of particulate matter. The reference process
weight regulation would limit emissions to 6.3 Ib/hr, based on a charging
rate of wet sludge (80 percent water) of 5,000 Ib/hr. Dry solids charging
rates for new incinerators will range from 0.5 to 4.0 tons/hr, with gas flow
rates of 1,000 to 20,000 dscfm."
The production of odors and their control is also a consideration in the operation
of sludge incinerators. It has been indicated that the range of temperatures for
effective control is 649-816 C (1200-1500 F) .7 Since the MHF operates at 760-
982 C (1400-1800 F) in the burning hearths8 and the FBR operates at a minimum
of 760 C (1400 F) 7, both types of incinerators reach operating temperatures that
are considered effective in the destruction of odorous substances. Nevertheless,
due to certain features of these incineration systems, both may require an after-
burner to ensure off-gases deodorization, particularly in those cases where
odorous volatile organics are present in the sludge. In the case of a MHF, since
raw sludge is introduced to the upper hearth where, the drying of sludge occurs
before combustion, the temperature of the exit gas from the upper hearth varies
from 260 to 593 C (500 to 1100 F) 8 which is below the temperature range for
effective odor control. In the pellet bed FBR, the exhaust gases are normally
cooled and mixed with the sludge cake (see Section VIII) . The preheated
mixture then passes through a two-stage cyclonic separator before the off-gases
are discharged to atmosphere. Due to the intimate mixing of gas and cake solids,
some volatiles may be picked up from the latter and carried over with the
exhaust gas. These volatiles are a potential source of odors.
190
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Another important area of concern has been the destruction of pesticides and
polychlorinated biphenols (PCB) . Both multiple-hearth furnaces with after-
burners and fluidized bed reactors will reduce these pollutants to an acceptable
level. Research^ has shown that 99.9 percent of the PCB contained in sewage
sludges is destroyed in a multiple-hearth furnace operated at an exit gas tempera-
ture of 593 C (1100 F) .
The use of a high energy scrubber, such as venturi or impingement type, that is
required to achieve the maximum particulate removal from the exit gas stream,
will also further reduce the pollutant gases. The total energy required by either
of the above types of scrubbers is approximately the same (see Section VIII) .
191
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SECTION IX
REFERENCES
1. Simonds, S.R. Personal Communication to W. Henry. Envirotech Corpora-
tion. San Mateo, California. May 30, 1972.
2. Brown and Caldwell, Consulting Engineers. Final Report, Lime Sludge
Recycling Study. Prepared for the Central Contra Costa Sanitary District,
Walnut Creek, California. 1974.
3. EPA Task Force Report, "Sewage Sludge Incineration", U .S . Environmental
Protection Agency, Office of Research and Monitoring, EPA-R2-72-040,
August 1972 (NTIS PB211323) .
4. Environmental Protection Agency. Air Programs, Standards of Performance
for New Stationary Sources, Additions and Miscellaneous Amendments.
Federal Register, Vol. 39, No. 47, March 8, 1974.
5. Bay Area Air Pollution Control District Regulation 2. San Francisco.
Novembers, 1971. 54 p.
6. Goldberg, Morris. Personal Communication to L.O . Britt. U.S. Environ-
mental Protection Agency, 9th Regional Office. San Francisco, California.
November 19, 1973.
7. Millward, R.S ., and W.A. Darby. Fluidized Bed Combustion. (Presented
at the Thirteenth Annual Waste Engineering Conference, University of
Minnesota). Minneapolis. December 10, 1966. 17 p.
8. Sebastian, F .P . Advances in Incineration and Thermal Processes . Short
Course on the Theory and Design of Advanced Waste Treatment Processes.
California, Berkeley. September 30 - October 1, 1973.
9. Miller, W. News Release. Envirotech Corporation, Menlo Park. October 10,
1972.
192
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SECTION X
MASS EQUILIBRIUM BALANCES OF SOLIDS PROCESSING
SYSTEMS BY DIGITAL COMPUTATION
The design and operation of a chemical sludge solids processing system requires
the computation of theoretical mass equilibrium values for each component in all
process streams of importance. For the solids processing systems such as those
shown in Fig. 7-8 and 7-9, manual computation of mass equilibrium values for
each component in every process stream is a tedious and time consuming process.
Furthermore, new mass equilibrium values for each component need to be calcu-
lated each time a change in an operational parameter is made. The importance of
having a theoretical model capable of predicting accurate mass equilibrium values
for all components in such a complex process can not be overstressed. Rapid
calculation of component equilibrium values for various operational modes is
important in monitoring the operation of a solids processing system of this type.
Also, in the design of this type of system, many different modes of operation
must be evaluated before final design decisions are made. A computer program
is then needed that can model the system and calculate mass equilibrium values
for differing modes of operation.
A computer program, SOLIDS 1A, has been developed to solve (by direct nonit-
erative equations) for the equilibrium mass values of all components in the
solids processing sequence shown in Fig. 7-8 and 7-9. The solids processing
sequence employs wet classification of primary sludge with recalcination of the
recovered sludge solids; with options for second stage dewatering of the centrate
from the wet classification step, and incineration of the recovered solids from
the dewatering step. Also optional in the solids processing sequence are blow-
down of a portion of the recalcination furnace product, dry classification of the
recalcination furnace product to selectively purge inert materials from the
process, and the ability to recycle furnace wet scrubber water back to the
primary- By appropriate adjustment of input data, the program is readily
adapted to substitution of vacuum filters or filter presses for the second stage
dewatering step; or a Plural Purpose Furnace flow sheet (Fig. 7-8) can be run
by inputting high recoveries in the first stage dewatering step. In this event,
centrifuges, vacuum filters, or filter presses could be assumed.
In the program, a simplifying assumption is made that solids in the thickener
overflows are not returned to the primary stage. In terms of the first stage
thickener, such overflows have no impact on any process stream except the
primary sludge stream. In terms of the second stage thickener, it is assumed
that the "thickener" is more-or-less a holding tank with little or no thickening
action taking place so that no stream would return to the primary.
193
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This program was compared to the full-scale test data generated during test work
on lime recalcining and recycle at the CCCSD's ATTF. Agreement between pro-
totype and computer output was found to be reasonably good.l The program was
developed in Fortran IV language for use on the time sharing service of General
Electric Information Services, Business Division. It can be easily modified for
use on other time share or batch processing services. A listing of the program
is given in Section XV. A; symbols used in the program are given in Tables 10-1
through 10-3. If for some reason the design engineer does not have convenient
access to a computer, the equations presented in this section and in the program
listing in Section XV. B can be used for manual calculations.
Table 10-1. COMMON PREFIXES USED IN PROGRAM "SOLIDS 1A"
Prefix
Meaning
CA
CAC
CAP
CAO
CAH
FE
FEOH
FEO
FECL3
XMG
XMGH
XMGO
ORG
P
SI
All
XLB
RE
TOTLB
FR
Calcium as Ca
Ca CO_, Calcium carbonate
Ca« (POJ2/ Tri calcium phosphate
Ca O, calcium oxide
Ca (OH)2/ calcium hydroxide
Iron as Fe
Fe (OH) -, Ferric Hydroxide
Fe2 O3, Ferric oxide
Fe CL3, Ferric chloride
Magnesium as Mg
Mg (OH)?, Magnesium Hydroxide
Mg O, Magnesium oxide
Organics, Volatile Matter
Phosphorus as P
Si O2, Silicon dioxide
Acid insoluble inerts
(Other than silica)
Pounds of
Recovery of
Total pounds of
Fraction of
194
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Table 10-2. COMMON SUFFIXES USED IN PROGRAM "SOLIDS 1A"
Suffix
Meaning
-MGL
-IN,-INF
-OUT, -EFF, -EF
-SLG
-CAK1
-CNT1
-CAK2
-CNT 2
-1
-2
-WAS
-SSI, -SSIN
-SSO, -SSOUT
-FP
-FPI
-F
-FI
-CL
-CR
-RS
-BD
-SE1
-SE2
-IP
-IND
-EFD, EFFD
In units of mg/1
Into the primary flocculation basin
Out of the primary sedimentation basin
(primary effluent)
In the primary sludge
In the first stage centrifuge cake
In the first stage centrifuge centrate
In the second stage centrifuge cake
In the second stage centrifuge centrate
(Recovery) In the first stage centrifuge
(Recovery) In the second stage centrifuge
Waste activated (secondary) sludge added
to the primary
Suspended solids into the primary
Suspended solids out of the primary (in
the effluent)
In the recalcination furnace (product stream)
In the incineration furnace (product stream)
(Recovery) In the recalcination furnace
(Recovery) In the incineration furnace
(Recovery) In the classifier for recalcined
product
In the classifier reject stream
In the recycled solids accepts stream back
to the primary
In the blowdown stream from the
recalcination furnace
In recalcination furnace wet scrubber
effluent stream
In incineration furnace wet scrubber
effluent stream
In the first pass precipitation (sludge) in
the primary
Dissolved in the primary influent raw sewage
Dissolved in the primary effluent
195
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Table 10-3. OTHER SYMBOLS USED IN PROGRAM "SOLIDS 1A"
Symbol
Meaning
XMGD
FECL3MGL
CAHTODOS
FRBD
RECALEFF
XMGEFMGL
FRAIISSO
FRAIISSI
FRSIWAS
FRAIIWAS
FRVWASIN
FRVSSIN
FRVSSOUT
FRSISSI
FRSISSO
FRSINEW
FRAIINEW
FRMGONEW
FRCAONEW
CAOTOMGL
CAONEW
TOTLBNEW
CAONMGL
CAORMGL
CAORSFRA
Flow into the primary, mgd
Dose of Fe CL3 to the primary, mg/1
Total dose of calcium hydroxide to the
primary in units of mg/1
Fraction of recalcination furnace stream
to blowdown
Recalcining efficiency of converting
Ca CO3 to Ca O
Magnesium as Mg in primary effluent, mg/1
Wt. Fraction of acid insoluble inerts in
suspended solids out (effluent)
Wt. fraction of acid insoluble inerts in
suspended solids into the primary
Wt. fraction silicon dioxide in waste
activated sludge
Wt. fraction acid insoluble inerts in waste
activated sludge
Wt, fraction volatile solids in waste
activated sludge to the primary
Wt. fraction volatile solids in influent
suspended solids
Wt. fraction volatile solids in effluent
suspended solids
Wt. fraction silicon dioxide in influent
suspended solids
Wt. fraction silicon dioxide in effluent
suspended solids
Wt. fraction of stated component in the
new (makeup) dry lime solids added to
the primary
Total dose to primary of CAO, in mg/1
Makeup CAO (lime) added to primary
Total new makeup lime added,
including impurities, Ib
CAO makeup added to primary, as mg/1
CAO in recycled solids (RS) stream, as
mg/1
CAO in recycled solids stream, fraction
of total CAO dose
196
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Table 10-3. OTHER SYMBOLS USED IN PROGRAM "SOLIDS 1A"
(CONTINUED)
Symbol
Meaning
TOTRE 1
TOTRE2
TOTRECL
SEREC
CLASSIF
FURNACE
Total solids recovery in the first stage
centrifuge (wet classification)
Total solids recovery in the second stage
centrifuge (dewatering)
Total solids recovery in dry classification
of recalcined furnace product (recovery
in accepts stream)
Option code for return or nonreturn of furnace
scrubber water to the primary
Option code for including or excluding dry
classification of furnace product
Option code for including or excluding second
stage dewatering and incineration of cake in
the processing sequence
DESCRIPTION OF PROGRAM
For a given set of operating conditions and unit performances, the equilibrium
mass values for the following components are calculated for each process stream:
Organics
Calcium carbonate
Calcium phosphate
Magnesium hydroxide
Magnesium oxide
Ferric hydroxide
Ferric oxide
Silicon dioxide
Acid insoluble inerts
Calcium oxide
(volatile matter)
(CaCO3)
(Ca3(P04)2)
(Mg(OH)2)
(MgO)
(Fe(OH)3)
(Fe203)
(Si02)
(other than
(CaO)
The program also calculates the fraction of the total lime dose (as CaO) to the
primary contributed by the recycled CaO from the recalcining furnace.
Description of Input
Inputs are required to specify the type of operation desired as described under 1
and 2 below:
1. The type of processing sequence (either Plural Purpose Furnace or
ATTF system cases, i.e. , dewatering alone or wet classification
197
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followed by dewatering) to be specified is inputted by using the appro-
priate code for "FURNACE". For ATTF system cases, "FURNACE" = 2.0,
while for Plural Purpose Furnace cases, "FURNACE" = 1.0. Also, if a
dry classifier is included in the processing sequence, "CLASSIF" = 1.0,
while if no dry classifier is wanted, "CLASSIF" = 0.0. If a blowdown
stream from the recalcination furnace product is desired (with or without
the dry classifier) the appropriate fraction of the furnace product stream
to be the blowdown is inputted for "FRBD". If no blowdown is wanted,
set "FRBD" = 0.0. The blowdown stream is located ahead of dry classi-
fication in the processing sequence. If furnace scrubber effluent water
is to be returned to the primary, then set "SEREC" = 1.0. If not, then
set "SEREC" = 0.0.
2. The order of process and performance parameters to be inputted is:
a. Flow rate in MGD as "XMGD".
b. Waste activated sludge solids added to the primary, in Ib/day as
"XLBWAS".
c. Ferric chloride dose to the primary, mg/1 as "FECL3MGL".
d. Total lime dose as Ca (OH) 2, in mg/1 as "CAHTODOS" .
e. Fraction blowdown as "FRBD".
f. Recalcining efficiency of converting CaCC>3 to CaO, fraction, as
"RECALEFF" (as measured on the furnace product) .
g. "FURNACE" as 2.0 or 1.0, and "CLASSIF" as 1.0 or 0.0 as explained
previously.
h. Primary pH as "PH"
i. "SEREC" as 1.0 or 0.0, as explained previously-
j. Iron as Fe in the primary influent raw sewage, mg/1, as "FEINFMGL".
k. Silica dissolved in the primary influent raw sewage, in mg/1 of
SiOo, and silica dissolved in the primary effluent in mg/1 of SiOo,
as lfSIINDMGL", and "SIEFMGL", respectively.
1. Suspended solids in the primary influent in mg/1 as "SSINMGL",
and suspended solids in the primary effluent in mg/1 as "SSOUTMGL".
m. Magnesium as Mg in primary influent, mg/1, as "XMGINMGL", and
in the effluent (mg/1) as "XMGEFMGL".
n. Calcium (dissolved and suspended) as Ca in the primary influent,
mg/1, as CAINFMGL, and calcium (dissolved and suspended) as
Ca in the primary effluent as "CAEFFMGL".
198
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o. Total phosphorus as P, mg/1, in the primary influent as "PINFMGL",
and in the effluent as "PEFFMGL".
p. Iron as Fe in the primary effluent, mg/1 as "FEEFFMGL".
q. Weight fraction of acid insoluble inerts (inerts other than SiC^)
present in the suspended solids in the effluent as "FRAIISSO", and
in the primary influent as "FRAIISI".
r. Weight fraction SiO2 in waste activated sludge solids as "FRSIWAS",
and the weight fraction acid insoluble inerts in the waste activated
sludge solids as "FRAIIWAS".
s. The weight fraction of volatile matter in the waste activated sludge
solids as "FRVWASIN", in the suspended solids in the influent
"FRVSSIN" and in the suspended solids in the effluent as "FRVSSOUT".
t. The weight fraction SiOo in the suspended solids in influent as
"FRSISSI", and in the effluent as "FRSISSO".
u. The weight fraction of SiC>2, acid insoluble inerts, MgO and CaO in
the new makeup lime solids as "FRSINEW", "FRAIINEW", "FRMGONEW",
and "FRCAONEW", respectively.
v. Recoveries of all components in the first stage (wet classification)
centrifuge cake as fraction recovered:
RECAP1 is recovery of Ca3(PC>4) 2)
RECAC1 is recovery of CaCO3
RESI1 is recovery of SiC>2
REAII1 is recovery of acid insoluble inerts
REXMGH1 is recovery of Mg (OH) 2
REXMGO1 is recovery of MgO
REFEOH1 is recovery of Fe (OH) 3
REFEO1 is recovery of Fe2O3
REORG1 is recovery of organics (volatile matter)
w. Similarly, fractional recoveries for all components in the second
stage (dewatering) centrifuge cake are inputted as in "v" above,
with the suffix being "2" instead of "1":
RECAP2, RECAC2, RESI2, REAII2, REFEOH2, REFEO2,
REORG2, REXMGH2, REXMGO2 are inputted.
x. Fractional recoveries of all components in the recalcination furnace
are inputted (suffix is "F" for these components) . Furnace
recovery means what is recovered as furnace product. Whatever is
lost to the furnace dry cyclone is presumed to be recovered in a
wet scrubber and the scrubber water returned to the primary.
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Recalcination furnace recovery inputs are:
RECAPF, RECACF, RESIF, REAIIF, REFEOHF, REFEOF, REORGF,
REXMGHF, REXMGOF.
The recovery of organics and metal hydroxides in the furnaces are
intrinsically zero in the program, because all organics are assumed
to be combusted, and all metal hydroxides (Fe (OH) 3 and Mg (OH) 2)
are assumed to be converted to metal oxides (Fe2O3 and MgO) .
Hence, the recoveries of the metal oxides in the furnaces will be
used for the metal hydroxides because they will exit the furnaces as
metal oxides. Also, CaCO3 is converted to CaO in the furnace, and
the program uses the CaCO3 recovery and recalcine efficiency to
determine the CaO in the furnace product.
y. The fractional recoveries of all components in the incineration
furnace are inputted, similar to those for the recalcination furnace.
The inputs are given the suffix "FI" for the incineration furnace.
Recovery inputs are:
RECAPFI, RECACFI, RESIFI, REAIIFI, REFEOHFI, REFEOFI,
REORGFI, REXMGHFI, REXMGOFI.
Again, recoveries are defined as in the case discussed above for the
recalcination furnace, and inputs for recoveries of organics and
metal hydroxides will be zero.
z. The fractional recoveries of compounds in the dry classifier for
recalcined product are inputted last. The fractional recovery is
defined as the mass of material accepted and recycled back to the
primary divided by the total mass of material classified. Classifier
rejects are assumed to be discarded. Again, recoveries of organics,
and metal hydroxides are inputted as zero because none of these
appear in the recalcined product to be classified.
Inputs are given the suffix "CL", as:
RECAPCL, RECACCL, RESICL, REAIICL, REFEOHCL, RECAOCL,
REFEOCL, REORGCL, REXMGHCL, REXMGOCL.
The recovery of CaO is inputted here because it is present in the
recalcination furnace product, as a separate compound, along with
the remaining CaCO3 that was not recalcined. If no dry classifier is
to be used, input the recoveries of all components (except organics,
Mg(OH)2 and Fe(OH)3, which are zero) in the classifier as 1.0
(total recovery) .
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Input Data Format
The input data is arranged into three data files (e.g., three separate magnetic
cards, three sets of punch cards, etc.) . The first input file, which is called
"DAT1" simply lists a line number followed by the input terms. There are two
lines on the first (DAT1) file. Line numbers have been assigned arbitrarily.
The first input file is shown in Table 10-4.
Table 10-4. FORMAT FOR DATA FILE "DAT!"
Input parameters in computer code
Description
Sample file list
L,XMGD,XLBWASIN,FECL3MGL,CAHTODOS,
FRBD.RECALEFF
L , FURNACE , CLASSIF , PH , SEREC , FEINFM GL ,
SIINDMGL.SIEFDMGL
File list no. , primary flow, Ib/day waste
activated sludge added; FeCL dose,
total dose of lime as mg/1 of Ca(OH),
fraction blowdown,
recalcination efficiency
'2'
File list no. , furnace option code, classifier
option code, primary pH , furnace scrubber
water return option, Iron as rng/1 Fe
in raw sewage, dissolved silica as
mg/1 SiO in raw sewage and primary
effluent
110,30.0,9746.0,14.0,400.0,
0.0,0.95
115,2.0,0.0,11.0,1.0,0.0,
0.0,0.0
A sample of the numbers which might be used for a two stage centrifuge-furnace
case with dry classification of the recalcined product is shown (case 100,
Section XV. B) . The format is in the "variable specification", so that any
floating point format can be used for any of the input numbers. The first number
on each line is the line number required to construct a data file list by the time
share service.
The second group and third groups of input data, which the program recognizes
as files "DAT2" and "DATS" are shown in Tables 10-5 and 10-6.
It is important to input recovery values for all components, even those that are
intrinsically zero (as recovery of organics or metal hydroxides in the furnaces
or classifier - in these cases, the input values would be 0.0) . Also, in the
case that any component will not be present in the primary influent or in any
stream added to the primary (hence, this component will not be in any of the
process streams printed out) , it is important to input hypothetical recovery
values for that component in either the first stage or second stage centrifuge to
prevent division by zero in certain equations. In fact, if ever the recoveries in
both the first and second stage centrifuge are inputted as zero for a particular
component, division by zero results, causing the calculated amount of that com-
ponent present in the primary sludge to be infinite.
Outputs
The program prints out calculated equilibrium values as well as some specified
recoveries, performance parameters, and operational conditions. Output for the
cases evaluated for this report are shown in Section XV. B .
201
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Table 10-5. FORMAT FOR DATA FILE "DAT2"
Input parameters in computer code
Description
Sample file list
L,SSINM(.;L, SSOUTMGLrXMCINMGL,XMGEFMGL,CAINFMGL,CAEFrMGL
L, PINFM! ;L, PErrMGL,FCErFMGL,FARIISSO,FRAlISSI
L, FRSIVVAS , FRAIIWAS , FRVWASIN , FRVSSIN , FRVSSOUT
L, FRSISSI ,FRSISSO, FRSINEW , FRAIINEW , FRMGONEW, FRCAONEW
File list no. , influent primary suspended solids (mg/1);
effluent primary suspended solids (mg/1); magnesium as
Mg in the primary influent (mg/1); primary effluent total
Mg as Mg (mg/1); primary influent calcium as Ca (mg/1);
Primary effluent total calcium as Ca (mg/1)
Tile list no. , influent total P as P (mg/1), primary
effluent total P (mg/1); primary effluent total Fe as
Fe (mg/1); weight fractions of: acid insoluble inerts
in effluent suspended solids, acid insoluble inerts in
Influent suspended solids
File list no. , weight fractions of: SiO in waste
activated sludge, acid insoluble inerts in waste
activated sludge, volatile matter in waste activated
sludge, volatile matter in Influent suspended solids,
volatile matter in effluent suspended solids
File list no., weight fractions of: SiO- In influent
suspended solids, SiO. in effluent suspended solids,
makeup lime, MgO in makeup lime, CaO In makeup lime
131,240.0,26.0,22.3,8.74,30.0,60.0
132,10.0,0.66,0.0,0.0024,0.0024
141,0.035,0.0024,0.80,0.80,0.80
151,0.035,0.035,0.027,0.0096,0.07,0.89
Table 10-6. FORMAT FOR DATA FILE "DAT3"
to
o
L, RECAP! ,RECAC1 , RESI1 ,REAII1
L , REXMGH 1 , REXMGO1, REFEOH 1, REFEO1, REORG1
L, RECAP2, RECAC2 ,RESI2 ,REAII2, REFEOH2
L, REFEO2, REORG2, REXMGH 2 , REXMGO2
L , RECAPF . RECACF , RESIF , REAIIF , REFEOHF
I., REFEOF, REORGF, REXMGHF , REXMGOF
L, RECAPFI, RECACFI, RESIFI, REAIIFI, REFEOHFI
L , REFEOFI, REORGFI, REXM GHF1. REXMGOFI
L, RECAPCL , RECACCL , RESICL, REAIICL, REFEOH CL, RECAOCL
L, REFEOCL , REORGCL, REXMGHCL . REXM GOCL
Description
Recoveries in the first stage centrifuge of:
File list no., Ca (PO ) CaCO SiO
Acid Insol. Inerts
File list no., Mg(OH) MgO, Fe(OH) ,
FB203, Organics
Recoveries in the second stage centrifuge of:
File list no., Ca (PO ) , CaCO SIO ,
Acid Insol. Inerts, FefOH) 3
File list no., Fe O Organics, Mg(OH)
MgO 2 3 2
Recoveries in the recalcination furnace of:
File list no., Ca (PO ) CaCO SiO
Acid Insol. Inerts, FefOH)
File list no., Fe O Organics, Mg(OH)
MqO 2 3 2
Recoveries in the incineration furnace of:
File list no. , Ca (PO ) , CaCO , SiO ,
Acid Insol. Inerts, FefOH) 3
File list no., Fe,O Organios, Mg(OH)
MgO
Recoveries in the dry classifier of:
File list no., Ca (PO ) CaCO , SiO ,
Acid Insol. Inerts, FefOH) , CaO
File list no., Fe O Organics, Mg(OH)
MgO 2 J 2
Sample file list
161,0.20,0.825,0.90,0.77
171,0.27,0.27,0.30,0.30,0.40
181,0.90,0.99,0.97,0.81,0.90
182,0.90,0.78,0.90,0.90
191,0.94,0.93,0.98,0.87,0.0
192,0.95,0.0,0.0,0.92
201,0.94,0.93,0.98,0.87,0.0
202,0.95,0.0,0.0,0.92
211,0.957,0.984,0.761,0.929.0.0,0.981
212,0.864,0.0,0.0,0.966
-------
The first output line is for primary operating pH, primary flow (MGD) , and lime
use as calcium oxide. The total lime dose required for primary operation at pH
11.0 is printed (this was an input value) . Calculated values for the doses (mg/1)
of required makeup lime and recovered recalcined lime are printed also on the
first line , as well as the fraction of the total dose contributed by the recovered
lime (CaO) .
The second output line simply prints out the inputted values for the dose of
(mg/1) used in the primary and the amount of waste biological sludge added to
the primary.
The third output line prints out the specified fraction of recalcination furnace
product to be blown down and the specified efficiency of recalcination (fractional
conversion) of CaCC>3 to CaO, as measured in the furnace product.
The fourth output lists the weight fractions of SiC>2, acid insoluble inerts, MgO
and CaO specified in the new (makeup) lime solids added to the primary.
The fifth output line lists the primary influent compositon (mg/1) of suspended
solids, magnesium, calcium, phosphorus, SiOo, acid insoluble inerts, and iron.
The suspended solids composition in the raw sewage does not include the waste
activated sludge solids added to the primary. The SiO2 composition, however,
for program calculation reasons, does include the SiO2 present in the raw sewage
suspended solids, the waste activated sludge solids, and the makeup lime.
Similarly, the acid insoluble inerts includes what is present in the raw sewage
suspended solids , the added waste activated sludge solids , and the new added
makeup lime. The magnesium, calcium and phosphorus composition values are
based on total magnesium, calcium and phosphorus (as the elements) in the raw
sewage.
The sixth output line lists the primary effluent composition values (mg/1) speci-
fied for total calcium, magnesium, phosphorus and iron (Fe) as the elements, as
well as composition values for suspended solids, Si02 and acid insoluble inerts.
The SiO2 and acid insoluble inerts values are calculated from the inputted weight
fraction of each component present in the effluent suspended solids.
The next several outputs are for the amount of each component present in each
process stream. The "First Pass Precipitation" stream is the amount of each com-
ponent that would precipitate in the primary sludge if the primary was isolated
and received only raw sewage and chemical addition streams; that is, there are
no return streams to the primary sedimentation tank from solids processing
operations. For the purpose of this calculation, the fraction of lime that comes
from the recalcined product is assumed to be 100 percent CaO. Note that CaO
and Fe2O3 will always be zero in this stream , because CaO added reacts to form
CaCO3 and FeCl3 added precipitates as Fe(OH) 3 and not Fe2O3_
The "Primary Sludge" component output includes the materials in the first pass
precipitation stream plus all materials recycled to the primary from the
following streams: recycled (recalcined) solids, centrate recycle (second stage
203
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or first stage, depending on what mode of operation is desired) to the primary,
and furnace wet scrubber water returned to the primary. Note again it is
assumed that there will never be any CaO present in the primary sludge (it all
precipitates as
The "First Stage Cake" stream is calculated by using the recoveries inputted for
each component in the first stage centrifuge (wet classification) step . Note that
any separation process (centrifuge, filter press, vacuum filter, etc.) could be
used for the first stage dewatering step .
The "First Stage Centrate" stream is the portion of the primary sludge not
recovered in the first stage dewatering step .
The "Recalcination Furnace Product" stream is the mass of each component
recovered from the recalcination of the first stage cake stream . The recovered
furnace product is calculated by subtracting from the furnace feed the portion
of material not recovered in the furnace. This portion is calculated from the
inputted recoveries for each component.
The "Recalcination Furnace Wet Scrubber" stream is, as explained before, the
unrecovered portion of material in the recalcination furnace which is returned to
the primary via wet scrubber water.
The "Recycled Solids Accepts" stream is the portion of recalcination furnace pro-
duct, minus any blowdown (if specified) , which has been accepted by the dry
classification step. If no dry classification step is specified, the recycled solids
stream is the recalcination furnace product stream, less any blowdown.
The "Second Stage Cake" component stream is calculated from inputted component
recoveries for the second stage centrifuge (dewatering step) . The second stage
cake is that portion of the first stage centrate solids (from wet classification)
which is recovered by dewatering .
The "Second Stage Centrate" is the portion of the first stage centrate not
recovered in the dewatering step, and therefore recycled back to the primary.
The "Incineration Furnace Waste Ash" stream is the portion of the second stage
cake which is recovered (not lost to the incineration furnace wet scrubber) in
the incineration furnace product. This ash product is disposed to waste. Note
that the incineration furnace is run at a lower temperature than the recalcination
furnace, so it is assumed that no CaCOg is recalcined to CaO; however, metal
hydroxides are assumed to be converted to the oxides .
The "Incineration Furnace Wet Scrubber" stream is the portion of unrecovered
material in the incineration furnace, which is captured by a final wet scrubber
and returned to the primary.
The "Recalcination Furnace Blowdown" stream is the portion of the furnace pro-
duct that is to be wasted (or "blown down") to purge the system of inerts. This
stream is printed out only if there is a blowdown fraction specified.
204
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The "Classifier Rejects Stream" is the material rejected by the dry classifier and
disposed of as waste. This stream is shown only if there is a dry classifier for
recalcined furnace product.
The final output group lists the inputted recoveries for each component in the first
stage (wet classification) centrifuge, recalcination furnace, second stage (de-
watering) centrifuge, incineration furnace and dry classifier. The calculated
total recovery of solids in the wet classification, dewatering, and dry classification
steps is shown also.
DERIVATION OF EQUATIONS AND PROGRAM MECHANICS
The equations used to solve for the equilibrium mass values of each component
present in the primary sludge are the key equations. Once the total composition
of the primary sludge is known, the composition of every other process stream
can be easily obtained by using the component recovery values inputted for the
first and second stage centrifuges (wet classification and dewatering steps) , the
recalcination and incineration furnaces, and the dry classifier. The chemical
reactions producing sludge precipitates have been described in Section VI.
Metal Hydroxides and Organics
Basically, the amount of a component precipitated in the primary sludge is the
summation of the amounts of that component present in all the streams, or
chemicals returned or fed to the primary; less the amount of that component
leaving in the primary effluent. The ferric hydroxide (Fe(OH)3) precipitated in
the primary sludge from the chemical addition of ferric chloride, plus the ferric
hydroxide returned to the primary from the recycled centrate, plus the Fe in the
raw sewage (taken as Fe(OH) 3) , minus the ferric hydroxide leaving in the
effluent; equals the equilibrium amount of Fe(OH) 3 present in the primary sludge
for a given mode of operation. Recall, FEOHSLG is the symbol for the equilibrium
mass value of Fe(OH) 3 in the primary sludge. In terms of the program symbols
(Tables 10-1 to 10-3) and Fortran algebra the equation would be:
FEOHSLG = (FECL3) * (107./162.5) + FEOHCNT2
- (FEEFF) * (107./56.) + (FEINFMGL)
* (XMGD) * (8.33) * (107./56.) (1)
The conversion factors of FECL3 and FEEFF in equation (1) convert ferric chloride
and elemental iron (Fe) to equivalent Fe (OH) 3 .
There are two unknowns in equation (1); FEOHSLG and FEOHCNT2. Therefore,
in order to solve the equation, the number of unknowns must be reduced to one.
To accomplish this, the FEOHCNT2 (Fe(OH)3 in the recycled centrate) can be
related to FEOHSLG (the Fe(OH) 3 in the primary sludge at equilibrium) by apply-
ing the recovery factors for Fe(OH) 3 in the first and second stage centrifuge
operations. Thus:
FEOHCNT2 = (1.-REFEOH1) * (1.-REFEOH2) * (FEOHSLG) (2)
205
-------
3
Recall, REFEOH1 is the recovery of Fe(OH)3 in the first stage centrifuge, so
(1.-REFEOH1) is the fraction of the Fe(OH) 3 in the primary sludge that appears
in the first stage centrate. Likewise, (1 .-REFEOH2) is the fraction of the Fe(OH)
in the first stage centrate that is not recovered in the second stage centrifuge
(dewatering step) and appears in the second stage centrate. Hence, solving
the original equation for the equilibrium value of Fe (OH) 3 in the primary sludge
gives:
FEOHSLG - ((FECL3) * (107./162.5) + (FEINFMGL) * (107./56.)
* (XMGD) * (8.33) - (FEEFF) * (107./56))
/ (l.-(l.-REFEOH2) * (1.-REFEOH1)) (3)
All the terms on the right hand side of the equation are known, allowing a simple
algebraic solution for FEOHSLG.
Once the value of FEOHSLG is obtained, the amount of Fe (OH) 3 in the first stage
cake (FEOHCAK1) can be obtained by multiplying FEOHSLG by the recovery of
Fe(OH) 3 in the first stage centrifuge (REFEOH1) as follows:
FEOHCAK1 = (FEOHSLG) * (REFEOH1) (4)
Similarly the Fe(OH) 3 in the first stage centrate would be:
FEOHCNT1 = FEOHSLG * (1.-REFEOH1) (5)
The Fe(OH) ~ in the second stage cake is found from:
FEOHCAK2 - (FEOHCNT1) * (REFEOH2) (6)
As mentioned before, there is no Fe(OH)3 in either of the furnace products, or in
the furnace wet scrubber water streams which are returned to the primary.
A similar set of equations can be used to solve for Mg (OH) 2 and organics in the
various process streams (see Section XV. A) . Recall, there is no Mg (OH) 2 or
organics in either of the furnace products, or in the furnace scrubber water
streams. Magnesium hydroxide entering the primary is composed of that Mg (OH) 2
present in the recycle centrate stream plus that precipitated from reactions of
magnesium ions present in the raw sewage. The organics coming into the primary
are from the volatile portion of the influent suspended solids and added waste
activated sludge solids, plus the organics in the recycled centrate stream.
Metal Oxides
The solution for the equilibrium values of metal oxides (Fe2O3 or MgO) in the
primary sludge uses basically the same approach as that for the metal hydrox-
ides except that more streams are involved in the balance. For instance, the
MgO present in the primary sludge at equilibrium is composed of MgO from the
following sources: (1) Recycled recalcined solids stream; (2) Trace amount
(as impurity) in new makeup CaO added; (3) Wet scrubber water stream from
recalcining furnace; (4) Wet scrubber water stream from incineration furnace;
206
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and (5) Recycled centrate stream. The metal hydroxides that are converted to
metal oxides in each furnace must be included as part of the recycled metal oxide
streams. Hence, there is more metal oxide in the furnace product than in the
feed because of the metal hydroxide converted to oxide in the furnace. A mate-
rial balance for the MgO in the primary sludge (XMGOSLG) , is shown in Table
10-7. The sources contributing to the equilibrium value of MgO in the primary
sludge are listed, with the corresponding equations used in the program to
describe the MgO source.
Table 10-7. MATERIAL BALANCE DESCRIPTION FOR MAGNESIUM OXIDE
IN THE PRIMARY SLUDGE
Sources contributing to
primary sludge equilibrium MgO
Program equation for MgO source
MgO in recycled solids from conversion of
Mg(OH)7 to MgO in the recalcining furnace
MgO in recalcining furnace scrubber water due to
Mg(OH) conversion to MgO and captured by the
wet scrubber
MgO in incineration furnace scrubber water due to
Mg(OH) conversion to MgO in the furnace and
captured by the wet scrubber
MgO as impurities in new lime
MgO from second stage centrate recycle
MgO from recycled solids stream that was present
in the first stage cake as MgO
MgO from the recalcination furnace wet scrubber
(this is MgO that was present as MgO in the
first stage cake but not recovered in the
furnace)
MgO from the incineration furnace wet scrubber
(this is MgO that was present as MgO in the
second stage cake but not recovered in the
furnace)
XMGOSLG = the sum of the following terms:
(XMGHCAK1) * (REXMGOF) * (l.-FRBD)
* (REXMGOCL) * (40./58.3)
(1.-REXMGOF) * (XMGHCAK1) * (40./58.3)
(l.-REXMGOFI) * (XMGHCAK2) * (40./58.3)
XMGO NEW
XMGOSLG * (1.-REXMGO1) * (1.-REXMGO2)
XMGOSLG * (REXMGO1) * (REXMGOF)
* (REXMGOCL) * (l.-FRBD)
(XMGOSLG) * (1.-REXMGOF) * (REXMGO1)
(XMGOSLG) * (1.-REXMGO1) * (REXMGO2)
* (1 .-REXMGOFI)
The equations in the right hand side of Table 10-7 can be summed up, and
solved for XMGOSLG, the equilibrium value for MgO in the primary sludge.
This results in:
XMGOSLG = ((XMGHCAK1) * (REXMGOF) * (l.-FRBD)
* (REXMGOCL) * (40.758.3) + (1.-REXMGOF)
* (XMGHCAK1) * (40.758.3) + (XMGONEW)
+ (l.-REXMGOFI) * (XMGHCAK2) * (40.758.3))
/ (1.-REXMG01) * (1.-REXMGO2) * (l.-FRBD)
- (1.-REXMGOF) * (REXMGO1) - (1.-REXMGOF)
* (REXMGO1) - (1.-REXMGO1) * (REXMGO2)
* (l.-REXMGOFI)
(7)
207
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This is the approach used to solve for the equilibrium mass values for all quan-
tities in the primary sludge. The equations can be examined in the program
listing in Section XV. A. The equation for MgO was used as an example because
it illustrates most of the concepts employed in solving for the mass equilibrium
values of each component.
Inert Materials
The inert components represented in the program are silicon dioxide (SiC^) and
acid insoluble inerts (inerts other than SiO2) . The inerts come into the primary
as part of the suspended solids and waste activated sludge solids, as impurities
in new (makeup) lime added to the primary, and in the case of silica, as dis-
solved material in the raw sewage. The method of solving for the equilibrium
values of SiC>2 and acid insoluble inerts in the primary sludge is similar to that
for MgO. However, neither of the two inert components have hydroxide forms,
and it has been assumed that they behave as inerts in the furnace.
Tri Calcium Phosphate
Tri calcium phosphate (Ca3 (PO^) 2) is assumed to behave as an inert material
during recalcination or incineration, and its equilibrium value in the primary
sludge is calculated by a similar approach as for the inerts and metal oxides.
Calcium Carbonate and Calcium Oxide
The calcium carbonate that precipitates in the primary sludge is calculated by
adding the calcium (as calcium carbonate) in the raw influent sewage, the calcium
oxide (as calcium carbonate) in the total lime (makeup plus recycle) , the calcium
carbonate from the centrate recycle, the calcium carbonate from the recycled
solids from the recalcine-classification operation, and the calcium carbonate
returned to the primary in the wet scrubber water streams from both furnaces;
minus the amount of calcium precipitated by the phosphorus (as 033^04) 2)
which is removed in the primary, and minus the calcium (as calcium carbonate)
leaving in the primary effluent. In the recalcining furnace, if the recalcination
efficiency is less than one, then some CaCOg will appear in the furnace product.
The recovery of calcium oxide in the recalcining furnace is assumed to be equal
to the recovery of CaC03, since CaCO3 is converted to CaO in the recalcining
furnace. Recalcine efficiency as a fraction is defined in terms of the split
between CaO and CaCO3 in the furnace products as follows:
RECALEFF = CAOFP * (100./56.) / (CAOFP * (100./56.) + (CACFP))
The CaO picked up by the wet scrubber is assumed to react to form CaCO3.
Hence the CaC03 not recalcined in the furnace but lost out the stack, and the
CaO lost out the stack, are both treated as CaCO3 in computing the loss of non-
phosphorus calcium to the furnace wet scrubber water.
It is assumed that there is no recalcination of CaC03 to CaO in the incinerator
furnace since this furnace is operated at a temperature lower than the conver-
sion temperature (see Section VIII) .
208
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The total lime dose required for a certain mode of operation is inputted to the pro-
gram as Ca(OH) 2, mg/1. The program converts this dose to equivalent CaO for
computations.
The amount of each component that would precipitate in a once through primary
operation is calculated by the program. In the case of CaCO3, the total lime dose
(recycled plus makeup) would be considered as a chemical addition stream to the
primary in order to determine the amount of CaCC>3 that would precipitate in a
first pass situation. The amount of calcium (as calcium carbonate) in the raw
sewage plus the calcium carbonate precipitated from total lime additions, minus
the calcium (as CaCC^) lost to the effluent and to the precipitated Ca3(PC>4)2,
gives the calcium carbonate in the first pass precipitation.
MATERIAL BALANCES FOR SEVERAL CASES
Several cases were run on the computer, simulating various process modes of
operation. The cases were constructed using data on unit processes presented
in earlier sections of this report as well as other reports on the ATTF test work
(1, 2) . Table 10-8 summarizes the process description for each case. Most runs
were made simulating pH 11.0 operation, with a primary flow rate of 1.31 cu m/
sec (30 mgd) , 400 mg/1 of Ca (OH) 2 as a total lime dose, and 14 mg/1 of FeCls
added to the primary. The processing sequence was varied to simulate both
Plural Purpose Furnace and ATTF System cases, employing one stage (high
recovery) or two stage (wet classification and dewatering) processing of
primary sludge. Other process options included or excluded in the cases were
dry classification and/or blowdown of recalcined furnace product.
Table 10-9 lists some of the important solids balance comparisons for various
solids processing cases. At pH 11.0, with both wet classification and dewater-
ing of primary sludge solids, comparisons were made using a solid bowl centri-
fuge for wet classification and either a solid bowl centrifuge, vacuum filter, or
filter press for the second stage dewatering step. The solids processing
sequence employed for each case is described in Table 10-8 (100, 101 and 102) .
The use of pressure filtration for the second stage dewatering step has an advan-
tage over a solid bowl centrifuge or vacuum filter in that the amount of sludge
produced in the primary is slightly less, because less solids are recycled back
to the primary from the dewatering step. The amount of makeup lime required
for each case is not significantly different. Pressure filtration results in a
significantly drier second stage cake than either vacuum filtration or centrifu-
gation. This property results in less moisture to be evaporated (Table 7-11)
and less energy requirement for the second stage MHF (Table 8-18) .
In Plural Purpose Furnace cases 106, 114 and 116, dry classification as well as
a 20 percent blowdown of furnace product was included. The blowdown was
included to keep the amount of silica produced in the primary as low as possible
without wasting too much CaO. Fig. 10-1 shows the effect of blowdown for a
Plural Purpose Furnace case upon recovery of CaO. The optimum operating
blowdown will depend on the economics for each situation. Fig. 10-2 shows the
effect of furnace blowdown on primary sludge production. The amount of sludge
209
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Table 1Q-8. SOLIDS PROCESSING SEQUENCE OPTIONS FOR VARIOUS CASES
Case
a
no.
ioob
ioib
102b
106°
114°
116°
117b
120b
121b
122b
113°
112°
pH
11:0
11.0
11.0
11.0
11.0
11 .0
11.0
11.0
10.2
11.5
11.0
11.0
Ca(OH)2
dose,
mg/1
400
400
400
400
400
400
400
400
289
500
400
400
FeC13
dose,
mg/1
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
24.0
0.0
14.0
14.0
Processing options
Wet
classification
of
primary sludge
Solid bowl
centrifuge
Solid bowl
centrifuge
Solid bowl
centrifuge
Solid bowl
centrifuge
Vacuum filter
Filter press
Solid bowl
centrifuge
Solid bowl
centrifuge
Solid bowl
centrifuge
Solid bowl
centrifuge
Vacuum filter
Solid bowl
centrifuge
Recalcination
MHF
MHF
MHF
MHF
MHF
MHF
MHF
MHF
MHF
MHF
MHF
MHF
Dry
classification
of
recalcined ash
Yes
Yes
Yes
Yes
Yes
Yes
No
No
Yes
Yes
Yes
Yes
Slowdown ,
percent
0
0
0
20
20
20
0
28
0
0
0
100
Dewatering of
first stage
centrate
Solid bowl
centrifuge
Vacuum filter
Pressure filter
press
No
No
No
Solid bowl
centrifuge
Solid bowl
centrifuge
Solid bowl
centrifuge
Solid bowl
centrifuge
No
No
Incineration of
second stage
cake
MHF
MHF
MHF
None
None
None
MHF
MHF
MHF
MHF
None
None
NJ
M
O
All plant flows at 1.31 cu m/sec (30 mgd)
ATTF System Case - two-stage dewatering
Plural Purpose Furnace Case - single stage dewatering
-------
Table 10-9. MATERIAL BALANCE COMPARISONS FOR VARIOUS SOLIDS PROCESSES CASES
Case
no.
100
101
102
106
114
116
117
120
121
122
113
112
pH '
11.0
11.0
11.0
11.0
11.0
11 .0
11.0
11.0
10.2
11.5
11.0
11.0
Primary
sludge
production,
kg per day
(Ib per day)
100,940
(224,312)
98,043
(217,875)
96,036
(213,414)
132,036
(293,415)
131 ,817
(292,928)
125,856
(279,680)
111,327
(247,394)
99,788
(221,752)
82,539
(183,421)
111,780
(248,401)
338,620
(752,489)
93,482
(207,738)
First stage cake to
recalclning
kg per day
(Ib per day)
62,977
(139,950)
62,104
(138,011)
61 ,653
(135,945)
126,204
(278,281)
126,204
(278,281)
126,204
(278,281)
72,162
(160,360)
62,283
(138,407)
42,803
( 95,119)
76,079
(169,066)
321,689
(714,865)
89,610
(199,134)
Percent
TS
58
58
58
24
28
44
58
58
42
58
28
24
Recycled
solids from
recalcinlng,
kg per day
(Ib per day)
29,962
( 66,583)
29,986
( 66,636)
29,579
( 65,733)
56,290
(125,089)
56,290
(125,089)
56,290
(125,089)
40,527
( 90,062)
22,406
( 49,792)
19,705
( 43,789)
37,161
( 82,580)
245,329
(545,177)
0
(0)
Recycled
solids from
dewatering
step ,
kg per day
(Ib per day)
4,837
(10,749)
2,156
( 4,792)
348
( 775)
6,810
(15,134)
6,590
(14,646)
629
( 1,398)
4,892
(10,873)
4,795
(10,657)
7,088
(15,752)
4,517
(10,039)
16,930
(37,624)
3,871
( 8,604)
Recycled
solids from
furnace wet
scrubbers ,
kg per day
(Ib per day)
4,844
(10,766)
4,805
(10,679)
4,793
(10,650)
6,828
(15,174)
6,828
(15,174)
6,828
(15,174)
5,069
(11,265)
4,741
(10,537)
3,259
( 7,243)
5,703
(12,675)
20,301
(45,115)
4,491
( 9,981)
Second stage cake to
incineration
kg per day
(Ib per day)
33,126
(73,614)
33,782
(75,073)
34,782
(76,694)
Q
(0)
0
(0)
0
(0)
34,272
(76,161)
32,709
(72,688)
32,647
(72,550)
31,182
(69,295)
0
(0)
0
(0)
Percent
TS
17
20
25
-
-
-
17
17
18
13
28
-
Furnace
ash to
disposal
kg per day
(Ib per day)
19,433
(43,186)
19,071
(42,382)
19,486
(43,302)
0
(0)
0
(0)
0
(0)
20,546
(45,658)
19,043
(42,318)
17,264
(38,365)
18,220
(40,491)
0
(0)
0
(0)
Makeup CaO
b
CaO,
kg per day
(Ib per day)
12, .786
(28,413)
12,583
(27,963)
12,786
(28,413)
13,494
(29,988)
13,494
(29,988)
13,494
(29,988)
12,359
(27,464)
18,611
(41,358)
12,729
(28,288)
15,001
(33,336)
8,085
(17,967)
34,039
(75,644)
Percent
of total
CaO dose
38.0
37.0
38.0
40.0
40.0
40.0
36.0
55.0
52.0
35.0
24.0
100.0
Dry
classifier
rejects,
kg per day
(Ib per day)
1,602
( 3,560)
1,598
( 3,553)
1,575
( 3,500)
17,364
(38,587)
17,364
(38,587)
17,364
(38,587)
0
(0)
0
(0)
1,484
( 3,299)
1,760
( 3,913)
11,101
(24,669)
0
(0)
Recalcination
furnace
blowdown
stream ,
kg per day
(Ib per day)
0
(0)
0
(0)
0
(0)
14,730
(32,735)
14,730
(32,735)
14,730
(32,735)
0
(0)
8,713
(19,363)
0
(0)
0
(0)
0
(0)
41,184
(91,521)
I\J
Includes CaO.
Basis 89 percent CaO.
-------
generated in the primary increases sharply as percent blowdown is decreased
from about 20 percent to zero percent. Figs. 10-1 and 10-2 are based on cases
103-112, presented in Section XV. B.
1-0
UJ
t/>
o
Q
Q
o
O
0-8
fe 0-6
z
o
o
o: 0 .4
u_
o
o
O
Q
6
UJ
cr
0.2 0.4 0.6
BLOWDOWN FRACTION
0-8
1-0
Figure 10-1 Effect of blowdown on recovered CaO
For the Plural Purpose Furnace cases 106, 114, and 116 in which there is a high
recovery step for dewatering primary sludge, followed by furnaces for both
combined recalcination and incineration of cake solids, there is more sludge
production in the primary than for any of the three ATTF System cases (100,
101, and 102) when the makeup lime requirement is comparable. The mass of
212
-------
800,000
700,000
600,000
CD
400,000
200,000
100,000
360,000
315,000
270,000
225,000
180,000
135,000
90,000
45,000
0 0.2 0.4 0.6 0.8 10
SLOWDOWN FRACTION
Figure 10-2 Effect of blowdown on primary sludge production for
cases 103-112
213
-------
cake solids to be fed to the Plural Purpose Furnace is greater than the combined
amount of first and second stage cake fed to the two furnaces for the ATTF
System cases. Further, considering the dryness of the cakes produced, there is
more water to be eliminated for the Plural Purpose Furnace cases than the ATTF
System cases (Table 7-11) .
A basis for judging the effectiveness of wet classification is presented by the
computer output listed in Section XV. B . For case 117, the solids that would be
produced on a single pass through the primary are 82,527 kg/day (183,395
Ib/day) . Recycle streams increase primary sludge production to 111,327 kg/day
(247,394 Ib/day) . Thus, 28,799 kg (63,998 Ib) of unwanted solids are returned
to the primary sedimentation tank amounting to 26 percent of the solids appear-
ing in the underflow. Insertion of dry classification improves the picture consi-
derably (Case 100, Section XV. B) . Single pass precipitation for this case is
82,579 kg/day (183,509 Ib/day) with recycle streams increasing primary sludge
production to 100,940 kg/day (224,312 Ib/day) . In this case unwanted solids
appearing in the primary underflow is 18,361 kg/ day (40,803 Ib/day) , amount-
ing to 18 percent of the underflow solids. The improvement over case 117 is
primarily due to increased silica blowdown attributable to the dry classifier.
The beneficial effect of the dry classification step is portrayed in Table 10-10.
Case 100 is an ATTF System case with dry classification whereas, in case 117,
the dry classification step has been omitted. As can be deduced from the table,
silica builds up to quite high levels (31 percent as SiC^) in the recalcined pro-
duct without dry classification; when dry classification is employed the silica
is reduced to only 10 percent (as SiC^) of the recalcined product. Silica in the
recalcined product can also be reduced by blowing down directly from the
furnace product, instead of by dry classification (case 120, Table 10-10) . By
using 28 percent blowdown, the silica content can be reduced to 13 percent.
However, this is accomplished at the expense of lime consumption. The per-
centage recycled lime decreases from 62 to 45 percent.
Two other cases were included in Table 10-10, employing pH values of 10.2 and
11.5 in the primary. In Case 121, (pH 10.2) because of increased difficulty of
classifying and dewatering the sludge, the percentage of makeup lime is signi-
ficantly higher than for a similar processing sequence at pH 11.0 (Case 100) .
At pH 11.5 in the primary (case 122) , sludge wet classification and dewatering
are slightly improved over the pH 11.0 operation, and the percent of makeup
lime required is slightly lower than for the similar operation at pH 11.0 (case
100) . The actual mass of makeup lime at pH 11.5 is greater than that required
for pH 11.0 operation because of the higher total lime dose needed to reach pH
11.5.
Comparisons between operation at pH 10.2, 11.0 and 11.5 are interesting (Cases
121, 100 and 122 respectively in Table 10-10) . Twenty-two percent more solids
are generated in the primary at pH 11 than 10.2, while 35 percent more are
generated at pH 11.5 than 10.2. The effect of increased sludge production is
primarily felt in the recalcination furnace; increased doses of lime increase the
quantity of calcium carbonate to be recalcined. It is noticeable that the second
stage cake to be incinerated stays fairly constant, despite changes in pH levels
between cases.
214
-------
Table 10-10. CALCULATED SOLIDS BALANCES FOR CASES 100, 117,
120, 121 and 122
Parameter
pH
Ca(OH) dose, mg/1
FeOlj, mg/1
Recycled lime , percent
Recalcined product blowdown , percent
Ash classification
Primary sludge , kg/day
(Ib/day)
Organics
CaCO3
sio2
Ca3(P°4'2
OtherC
Total
First stage cake, kg/day
(Ib/day)
Organics
CaCO
sio2
Ca3(P04,2
OtherC
Total
Recycled solids , kg/day
(Ib/day)
CaO
CaCOj
S102
Ca3(P04)2
Other1"
Total
Second stage cake, kg/day
(Ib/day)
Organics
CaCO3
sio2
Ca3(P04>2
OtherC
Total
Solids processing case no.
iooa
11.0
400
14
62
0
Yes
26,222
( 58,272)
53,087
(117,972)
4,523
( 10,053)
7,651
( 17,003)
9,455
( 21,012)
100,938
(224,312)
10,489
( 23,309)
43,797
( 97,327)
4,071
( 9,047)
1,530
( 3,401)
3,089
( 6,866)
62,976
(139,950)
21,257
( 47,239)
2,003
( 4,453)
3,036
'( 6,747)
1,376
( 3,059)
2,288
( 5,085)
29,960
( 66,583)
12,271
( 27,271)
9,197
( 20,439)
438
( 975)
5,508
( 12,242)
5,709
( 12,687)
33,123
( 73,614)
117b
11.0
400
14
64
0
No
26,222
( 58,272)
53,124
(118,054)
14,418
( 32,042)
7,742
( 17,206)
9,819
( 21,821)
111,325
(247,394)
10,489
( 23,309)
43,827
( 97,394)
12,976
( 28,837)
1,548
( 3,441)
3,320
( 7,379)
72,160
(160,360)
21,684
( 48,187)
2,038
( 4,529)
12,717
( 28,261)
1,455
( 3,235)
2,632
( 5,851)
40,526
( 90,062)
12,271
( 27,271)
9,203
( 20,453)
1,398
( 3,108)
5,575
( 12,389)
5,823
( 12,941)
34,270
( 76,161)
120b
11.0
400
14
45
28
No
26,222
( 58,272)
52,490
(116,646)
4,562
( 10,139)
7,184
( 15,965)
9,337
( 20,750)
99,795
(221,752)
10,489
( 23,309)
43,304
( 96,233)
4,106
( 9,125)
1,436
( 3,193)
2,946
( 6,547)
62,281
(138,407)
15,426
( 34,281)
1,449
( 3,222)
2,897
( 6,439)
972
( 2,161)
1,660
( 3,689)
22,404
( 49,792)
12,271
( 27,271)
9,094
( 20,209)
442
( 983)
5,172
( 11,495)
5,728
( 12,730)
32,707
( 72,688)
121a
10.2
289
24
48
0
Yes
27,923
( 62,052)
33,948
( 75,441)
4,938
( 10,975)
7,971
( 17,714)
7,757
( 17,239)
82,537
(183,421)
9,773
( 21,718)
24,443
( 54,318)
4,445
( 9,878)
2,072
( 4,606)
2,069
( 4,599)
42,802
( 95,119)
11,863
( 26,364)
1,118
I 2,485)
3,315
( 7,367)
1,864
( 4,143)
1,543
( 3,430)
19,703
( 43,789)
14,157
( 31,461)
7,889
( 17,532)
400
( 889)
5,485
( 12,191)
4,715
( 10,478)
32,646
( 72,550)
122a
11.5
500
0
65
0
Yes
25,225
( 56,057)
65,996
(146,659)
4,738
( 10,531)
7,693
( 17,096)
8,126
( 18,058)
111,778
(248,401)
10,342
( 22,983)
56,757
(126,127)
4,312
( 9,583)
1,769
( 3,932)
2,898
( 6,440)
76,078
(169,066)
27,547
( 61,217)
2,596
( 5,771)
3,216
( 7,147)
1,591
( 3,537)
2,208
( 4,908)
37,158
( 82,580)
11,608
( 25,797)
9,147
( 20,327)
413
( 919)
5,331
( 11,847)
4,681
( 10,404)
31,180
( 69,295)
a Dry classifier in operation.
No dry classifier in operation.
215
-------
REFERENCES - SECTION X
1. Brown and Caldwell, Consulting Engineers. Lime Sludge Recycling Study.
Prepared for the Central Contra Costa Sanitary District, Walnut Creek,
California, June 1974.
2. Parker, D.S., K.E. Train and F.J. Zadick. Sludge Processing for Combined
Physical-Chemical-Biological Sludges. U.S. Environmental Protection Agency,
Washington, D.C. Report Number EPA-R2-73-250, July 1973. 141 p.
216
-------
SECTION XI
ULTIMATE DISPOSAL OF ASH
Although incineration of wastewater sludges greatly reduces the volume of waste
material, it produces an end product, ash, for which a final place must be found
before the solids disposal problem can be considered solved.
ASH CHARACTERISTICS
The term "ash" is somewhat loosely applied to various waste products of inciner-
ation and related processes. Apart from the most common use of the name (the
solid product of combustion discharged at the bottom of multiple hearth furnaces)
dust particles, carried with the off-gases and captured in dry cyclones or re-
moved in a wet scrubber, are sometimes referred to as ash. Finally, the rejects
from the dry classification process described in Section VIII, can also be consi-
dered as ash, although they contain reactive lime. Each of these ash-like pro-
ducts is handled in a different way but all would eventually converge in a
common waste stream to be carried to the point of ultimate disposal.
Gerlich and Rockwell^ have characterized the physical properties of wastewater
sludge ash discharged from a MHF . The data are shown in Table 11-1. The
physical and chemical properties of the ash are likely to vary from plant to
plant. These differences are due to sludge characteristics, use of chemical
conditioners, type of incinerator and combustion temperature. This variation
is illustrated in Table 11-2, which shows particle size distribution of ash from
three wastewater treatment plants.2 Gerlich and Rockwell^ have also reported
the results of particle size analyses of sludge ash. These results are shown in
Fig. 11-1.
As was mentioned before, combustion ash from a FBR is removed in a wet
scrubber. Ash is then separated from the scrubbing water in a hydrocyclone.
A particle size analysis of the dried cyclone underflow is given in Table 11-3.3
USES OF SLUDGE ASH
Since in wastewater treatment plants practicing sludge incineration there is a
continuous supply of the waste product of combustion, attempts have been made
from time to time to find a use for it. So far these efforts have been mostly
directed towards using ash as a sludge conditioner prior to mechanical dewater-
ing,l,2 although ash from the organic sludge furnace was experimentally used at
South Tahoe to condition flotation thickened mixtures of primary, waste activated
and lime sludges prior to incineration. 4 Sludge ash has also been tried as raw
material for the phosphate industry5 and as a construction material.6
217
-------
Table 11-1. PHYSICAL PROPERTIES OF SLUDGE ASH
Specific gravity
Bulk density, kg/cu m (Ib/cu ft)
Color
Mean particle size, mm
Range of particle size, mm
2.63-2.78
800 (50)
Yellow
29
22-40
Table 11-2. CLASSIFICATION OF ASH PARTICLES BY "BAHCO" MICRO
PARTICLE SIZE ANALYZER
Percent of given size
Effective particle
size (10~3 mm)
0.00 0.92
0.92 1.60
1.60 2.97
2.97 - 7. 71
7.71 - 12.19
12.19 - 20.75
20.75 24.72
24.72 27.30
>28.38
<420.
Kansas City
1.49
2.95
5.70
9.05
14.56
22.41
9.21
8. 83
25. 80
Lake Tahoe
1.38
2.71
7.53
9. 83
10.95
16.20
10.13
4.28
36.99
Millcreek
2.22
3.70
7.81
21.86
26.52
22.46
6.83
8.60
CO 0
Table 11-3. PARTICLE SIZE OF "FBR" ASH
Mesh
48
65
100
150
200
325
-325
Microns
295
208
147
104
74
43
-43
Retained
%
2.07
9.7
37.0
43.6
46.6
61.8
38.2
218
-------
100
LU
* 90h
£ eoh
I- <
x Q
o z 70h
o
w 60
50
40
30
z 20
LL)
CJ
S 10
Q.
4 5 6 7 8 10 20 30 40 50
MICRON DIAMETER (yu)
100
Figure 11-1 Particle size analysis of wastewater sludge ash
Although ash conditioning of wastewater sludges has experienced limited
success, the results so far are inconclusive and even conflicting . 1 /2 Moreover,
this application cannot be considered a method of disposal. The portion of ash
added to the sludge is recycled through the dewatering-incineration process
while the remaining still has to be disposed of. Also worth noting is the fact
that ash acts as an inert filler, thereby lowering the heat content of the sludge
cake. This will tend to offset some of the benefits of improved solids dewatering
on the cost of sludge incineration.
Obferkuch, et al.^ prepared an economic analysis of the commercial uses of ash
and sludges generated in wastewater treatment plants using lime treatment. In
the evaluation of sludge (or ash) for agricultural uses, it was concluded that
the product had no economic value in comparison to commercial products
(aglime, agrock, and fertilizers) , but that it could be given away to farmers.
In fact, uses of sludge for agricultural purposes is a common practice in the
U.S. and abroad and is, in many cases, an economically feasible method of
sludge disposal.
219
-------
In their evaluation of sludge (or ash) as a product for the phosphate industry,
Obferkuch, et aL concluded that the cost of processing the sludge far exceeded
the value of the product.
Since the physical and chemical composition of sludge ash is not greatly different
than the composition of coal fly ash, Gray and Penessis6 conducted a study to de-
termine if the former could be used as a construction material. Fly ash has long
been successfully used in road subbases, lightweight back-fills and load-
bearing fills. Other uses of fly ash include building block material, concrete
additive and soil stabilizer. Physical, chemical and engineering properties
determined by Gray and Penessis included "grain size distribution, chemical
and mineralogic composition, specific gravity, leachate composition, compaction-
strength characteristics, frost heave behavior, and response to Portland cement
stabilization". Ash samples were obtained from eight wastewater treatment plants.
The tests conducted on compacted ash samples showed the suitability of sludge
ash as a load-bearing fill, however, ash would have to be stabilized with Portland
cement before use in subbases and structural fills. Cement addition requirements
ranged from 3 to 7 percent.6 Significantly, it was concluded that ash from treat-
ment plants using lime for flocculation and sludge conditioning, would have
improved strength and durability after wetting and compaction.
Although the potential use of sludge ash appears encouraging, actual use of this
product has been limited. Local market conditions and acceptability of ash as a
suitable construction and building material are two of the factors more likely to
influence its useful application. In the great majority of installations, sludge
ash remains a waste product to be disposed of.
ASH HANDLING PRIOR TO DISPOSAL
Ash produced during sludge incineration can be handled in dry or in wet form.
Dry ash is discharged from a MHF, from dry cyclones and as rejects from the
air classification process (see Section VIII) . Wet ash is discharged from wet
scrubbers.
Dry Ash Handling
Ash from the MHF, often after grinding and cooling, can be handled in pneu-
matic or mechanical conveyors. The same devices can be used to convey ash
collected in dry cyclones and rejected by air classifiers. The conveyors
normally transport the waste product to storage bins, from which it is loaded
into trucks and carried to the disposal site. To avoid dusting, the dry ash is
normally wetted before being loaded. The screw conveyor transferring the
product from storage to truck is often used for the wetting operation, since
spray nozzles can be easily installed on the conveyor.
Wet Ash Handling
The handling of wet ash usually follows an elaborate path. In the fluidized bed
calciner shown in Fig. 8-6, the underflow of the ash thickener, which contains
most of the inert product, is pumped to a vacuum filter for dewatering. The
220
-------
ash cake is then ready for final disposal. In the FBR used for sludge incinera-
tion, ash removed in the wet scrubber is separated from the scrubbing water in
a hydrocyclone. The cyclone underflow is then dewatered in a rake type classi-
fier from which it is discharged to a storage hopper or to a truck parked under-
neath .
Dry ash discharged at the bottom of a MHF can also be handled in wet form. The
hot product discharges into a quench tank where cooling water is added. The ash
slurry thus formed is subsequently pumped to the disposal site. Abrasion-
resistant pumps, of the type used to handle grit slurries, are recommended for
this application.
When wet scrubbing is the last step in the dust collection train, the amount of ash
removed in the scrubber can be expected to be small and the scrubbing water can
be discharged to the drainage system and returned to the influent end of the
plant. This is often the case in a MHF installation (see Fig. 8-11) .
FINAL DISPOSAL SITES
When a beneficial use is not found, sludge ash is normally disposed of in land-
fills or in lagoons. The former is generally associated with dry transport while
the latter is used when ash is handled as a slurry. Dry ash deposited in a
landfill should be covered before the water added during loading evaporates and
the dried ash causes a serious dusting problem. Ash lagoons are similar to
conventional sludge lagoons, although the potential odor problem associated with
the latter does not exist in ash lagoons. As shown in Table 11-1, sludge ash has
a high specific gravity and will settle rapidly in the lagoon. As long as a layer
of water is kept over the settled ash, the possibility of drying and dusting is
eliminated.
221
-------
REFERENCES - SECTION XI
1. Gerlich, J.W., and M.D. Rockwell. Pressure Filtration of Wastewater Sludge
with Ash Filter Aid. U.S. Environmental Protection Agency, Washington, D.C.
Report No. EPA-R2-73-231. June 1973. 153 p.
2. Smith, I.E., S.W. Hathaway, J.B. Farrell and R.B. Dean. Sludge Condi-
tioning with Incinerator Ash. (Presented at the 27th Purdue Industrial
Waste Conference, May 2-4, 1972) .
3. Albertson, O.E. Low Cost Combustion of Sewage Sludges. (Presented at
the 35th Annual Conference of the Water Pollution Control Federation.
October 8, 1963) .
4. Gulp, R.S ., and G.L. Gulp. Advanced Wastewater Treatment. First
Edition. New York, Van Nostrand Reinhold Company, 1971. 310 p.
5. Obferkuch, R.E., T. Ctvrtnicek, and S.M. Mehta. Study of Utilization
and Disposal of Lime Sludges Containing Phosphates. U.S . Environmental
Protection Agency, Washington, D.C. Project #17070FBE. March 1972.
78 p.
6. Gray, D.H., and C. Penessis. Engineering Properties of Sludge Ash.
Journal of the Water Pollution Control Federation. 44: 847-858, May 1972.
222
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SECTION XII
DEVELOPMENT OF COST ESTIMATES
GENERAL CONSIDERATIONS
It has been customary practice to present cost data in the form of cost curves
relating a given design parameter, such as flow, organic loading, etc., to a
certain type of cost, such as construction, capital, annual, etc. The curves are
generally adjusted to a common base year through a cost index. Among these,
the Engineering News Record (ENR) Construction Cost Index is the most widely
used. Although useful for preliminary cost estimates to compare engineering
alternatives, there are practical limitations to the use of cost curves. The curves
normally reflect average conditions and therefore do not reflect the influence of
several important factors . These factors include soil conditions , architectural
and landscaping treatment, allowances for future expansion, local labor condi-
tions, degree of automation, process sophistication, etc. With regards to new
treatment processes, another important drawback of cost curves is the limited
availability of actual construction and operation and maintenance cost data from
which the curves may be constructed, since many of these plants are still in the
planning and design stages.
In view of the factors considered above, a Case Example format has been deter-
mined to be a more suitable approach for this report. Since the water reclama-
tion plant for the Central Contra Costa Sanitary District (CCCSD) , California,
was bid in June 1973, actual construction costs for many of the main processes
described in the preceeding sections are now available and can be readily
adjusted to reflect present economic conditions. Construction costs are broken
down in this section by unit operations, i.e., chemical addition, flocculation
and sedimentation; centrifugation; etc. To present variations in the basic flow
sheet, alternate units are substituted for the original ones; for example, centri-
fuges have been replaced by vacuum filters and filter presses.
Detailed engineering cost estimates were also available for another advanced
treatment plant, the Lower Molonglo Water Quality Control Centre in Australia.
Estimates from this facility have been used to illustrate the cost difference
between solids-contact lime reactors and rectangular flocculation and sedimen-
tation tanks.
Operating costs are based on chemical use, installed horsepower, and fuel con-
sumption where applicable. Fuel use has been based on materials and heat
balances similar to those developed in Section VIII and presented in an engineer-
ing report.1 With the exception of calcination and incineration processes, where
the continuous presence of an operator is normally required by codes, it is difficult
to assign a cost value to operator attendance since this is a direct function of the
degree of automation provided, which varies widely from plant to plant. As an
example, the CCCSD water reclamation plant is entirely controlled by a computer-
223
-------
o
based system and most processes are continuously monitored by the computer >
The presence of an operator for control purposes is therefore not required. This
is certainly not the case in smaller or less sophisticated facilities where conven-
tional analog instruments are used or manually controlled units have been
provided.
Wherever possible, maintenance costs have been based on the equipment manu-
facturer's recommendations for preventive maintenance frequency and procedures.
It should be pointed out that, with the possible exception of the largest treatment
plants, equipment maintenance is performed by the plant operators; consequently,
for smaller plants a portion of the manpower requirements for preventive main-
tenance is included under operation attendance.
THE LOWER MOLONGLO WATER QUALITY CONTROL CENTRE
The Lower Molonglo Water Quality Control Centre is an advanced treatment facility
for the Australian Capital territory. Initial dry weather flow capacity of the plant
is 109,000 cu m/day (28.8 mgd) , practically equal to the capacity of the CCCSD
water reclamation plant. The treatment processes include lime coagulation for
phosphorous and solids removal; nitrogen removal by a modified nitrification-
denitrification system; dual media filtration for removal of virus and residual
suspended solids; effluent disinfection; wet classification and solids dewatering
by centrifugation; lime reclamation; and solids disposal by incineration.
Originally, design of the plant included solids-contact clarifiers and ammonia
stripping towers for nitrogen removal.3 Subsequently, limitations of the
ammonia stripping process led to its replacement by a modified nitrification-
denitrification process.4 Also, the dry classification of recalcined lime initially
considered, was replaced by a combination of wet and dry classification, based
on the experimental worked conduct at the CCCSD's ATTF (see Sections VII and
VIII) . The solids-contact lime reactors were substituted with rectangular sedi-
mentation tanks. This change was also based on results obtained at the ATTF.5
Design parameters for both types of flocculation-sedimentation tanks are given
in Table 12-1.
The two design reports on the Lower Molonglo WQCC included detailed engineer's
estimates of construction costs of the proposed facilities. Costs were based on
bidding conditions prevailing in Australia in June 1970. Table 12-2 shows costs
in Australian dollars for both types of flocculation-settling basins. Since the
purpose is to compare these two alternatives, the figures given in Table 12-2
have not been converted to American dollars nor adjusted to reflect present
construction costs. However, it can be seen that rectangular tanks are consi-
derably less costly than solids-contact clarifiers. Although the original Lower
Molonglo WQCC design contemplated solids dewatering by vacuum filtration
following gravity thickening; and therefore, the proposed processes did not
include grit removal; grit removal chambers ahead of the primaries have been
added to the cost of the solids-contact clarifiers alternative in Table 12-2, to put
the comparison on an equal treatment basis .
224
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Table 12-1 . DESIGN DATA FOR FLOCCULATION
AT THE LOWER MOLONGLO WQCC
SEDIMENTATION BASINS
Parameter
Solids-contact
clarifier
Rectangular flocculatlon
sedimentation tanks
Lime dosage, mg/1 as CaO
Solids - contact clarifiers
Number
Diameter, m (ft)
Depth, m (ft)
Effective surface area each, sq m (sq ft)
Overflow rate at ADWF, cu m/day sq m (gpd/sq ft)
Detention time in flocculation zone at ADWF, min
Detention time at ADWF,b hr
Hydraulic capacity each, 1, 000 cu m/day (mgd)
Preaeration-grit removal tanks
Number
Width, m (ft)
Length, m (ft)
Average depth, m (ft)
Detention time at ADWF,b min
Primary sedimentation tanks
Number
Width, m (ft)
Length, m (ft)
Average depth, m (ft) ,
Overflow rate at ADWF, cu m/day sq m (gpd/sq ft)
Detention time at ADWF,b hr
Hydraulic capacity each, 1,000 cu m/day (mgd)
250
42.7 (140)
6.1 (20)
1,208 (13,000)
24. 9 (610)
20
5.8
125 (33)
250
9.1 (30)
24.1 (79)
4.0 (13)
24
11.9 (39)
67.1 (220)
2.9 (9.5)
28.8 (705)
2.1
151 (40)
, Preaeration and grit removal tanks used for flocculation.
Average dry weather flow.
Table 12-2. COST COMPARISON BETWEEN SOLIDS-CONTACT CLARIFIERS
AND RECTANGULAR FLOCCULATION-SEDIMENTATION TANKS
Cost item
Solids-contact
clarifiers
Rectangular
tanks
Solids separation
Preaeration -
grit removal
Total, A.$
1,035,000
602,000
1,637,000
753,000
602,000
1,355,000
225
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THE CCCSD WATER RECLAMATION PLANT
The water reclamation plant is a 114,000 cu m/day (30 mgd) facility scheduled
for completion in 1976. Once in operation, the plant will produce water for
industries located along the southern shore of Suisun Bay, in the Sacramento
River estuary. In 1972 the CCCSD completed contract negotiations with the
Contra Costa County Water District (CCCWD) for the purchase of an estimated
72,000 cu m/day (19 mgd) increasing by 1980 to an average of 91,000 cu m/day
(24 mgd) with a peak daily use of 121,000 cu m/day (32 mgd) . Industries will
use about 75 percent of the reclaimed water for cooling and the remainder for
process purposes. Reclaimed water that is produced in excess of industry's
needs will be discharged directly to Suisun Bay. A flow diagram of the CCCSD
water reclamation plant is shown in Fig. 12-1. As stated in Section VI, lime is
added ahead of the preaeration and grit removal tanks. A brief description of
the plant units associated with lime treatment, recovery and reuse is given below.
Liquid Processing
After bar screening and influent pumping, combined preaeration and grit removal
will be obtained in two reinforced concrete tanks designed to provide a detention
time of 20 minutes at average dry weather flow. Air at the rate of 0.08 to 0.16 cu
m/min (3 to 6 cfm) per foot of tank length will be introduced along the side of
each tank through header pipes fitted with air diffusion units. Grit will be
removed as a result of the currents set up by the rising column of air and
deposited in hoppers under the air piping. Material in the hoppers will be
pumped directly to cyclonic separators located in the solids conditioning
building. After dewatering, grit will be conveyed to the sludge incineration
furnace. Lime will be added to the wastewater flow in the distribution channel
feeding the preaeration and grit removal tanks. Lime coagulation of the waste-
water will be performed in the air-stirred preaeration tanks.
Primary sedimentation will take place in four rectangular reinforced concrete
tanks. Each tank is designed for a detention period of 2.2 hours and an over-
flow rate of 31.8 cu m/day/sq m (780 gpd/sq ft) at average dry weather flow
conditions. Each sedimentation tank will be equipped with two longitudinal
sludge collection mechanisms and a cross collector. After collection at the
influent end of the tanks, the lime sludge will be removed by positive displace-
ment pumps and pumped first to the sludge thickening tanks. From there, it
will be discharged at a constant rate to the solids dewatering and incineration
processes. Scum collected on the water surfaces in the sedimentation tanks will
be moved to the inlet ends by water jets and removed from the tanks by skimming
mechanisms which will drop the accumulated material to a receiving sump. From
here, primary scum will be pumped to a scum concentrator at the solids condi-
tioning building . Thickened scum will then be incinerated .
Solids Processing
The solids processing systems consist of processes for classification and dewa-
tering of the primary sedimentation tank underflow; scum and grit dewatering;
recalcining of the calcium carbonate-rich solids discharged from the centrifuge
226
-------
to
Figure 12-1 . Flow diagram of the CCCSD water reclamation plant.
-------
classification stage; and incineration of the solids discharged from the dewater-
ing stage, together with the dewatered scum and grit. Two of the existing sludge
digestion tanks will be used as storage and thickening tanks for the sludge under-
flow from the primary sedimentation tanks. The modified tanks consist of circular
reinforced concrete tanks 18.9 m (62 ft) in diameter and side water depths of 7.2
m (23.5 ft) and 9.9 m (32.5 ft) .
The solid-bowl centrifuges will operate in series. The first stage centrifuges
will classify or separate the phosphorus and organic solids from the calcium
solids, and the second stage centrifuges will dewater the centrate discharged
from the first stage centrifuge. The calcium solids discharged in the cake from
the first stage centrifuges will be recalcined in multiple hearth furnaces, and the
undesirable chemical precipitates and organic solids will be discharged in the
centrate. The second stage dewatering centrifuges will produce a centrate of
high clarity, and the cake will be discharged to the sludge, scum, and grit
incinerating furnace.
The multiple-hearth furnaces will be equipped with sufficient drying, combustion
and cooling hearths to provide odor-free operation and complete combustion of
all organic material. The temperature in the combustion zone will be automati-
cally controlled to ensure efficient combustion, and each incinerator will be
equipped with a full complement of safety controls. The furnaces are designed
for recalcining of lime sludge as well as for combustion of organic material. All
gases of combustion will be afterburned at 760 C (1400 F) and scrubbed in dry
scrubbers. Waste heat boilers will be used to recover heat in the form of steam.
The exit gas from the boilers will be cooled in wet scrubbers and, when
necessary, reheated prior to release to the atmosphere to prevent the formation
of a vapor plume on cold days .
Recalcined lime from the furnaces will be conveyed pneumatically to lime storage
bins located in the chemical storage area. Sufficient storage volume will be pro-
vided for a full week's supply of lime, and makeup lime may be added to the
storage bins through a pneumatic delivery system from bulk delivery trucks or
rail cars. Lime will also be conveyed pneumatically from storage to the lime
feeders and slakers. The slakers and the automatically controlled gravimetric-
type feeders will be located just above the distribution channel feeding the
preaeration and grit removal tanks.
Table 12-3 shows the design data for the processes described in the preceeding
paragraphs. Some differences will be noted in the solids loads as indicated in
Table 12-3 and the current solids balance for the system (Case 100, Section XV) .
These reflect the estimates prevailing at the time of design vs. the post design
estimates prevailing currently. Design values are shown in Table 12-3, since
they were the basis of design.
COST ESTIMATES FOR THE CCCSD WATER RECLAMATION PLANT
Detailed cost estimates will be presented for the following processes:
1. Lime addition, flocculation and sedimentation.
228
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Table 12-3. DESIGN DATA FOR;CCCSD WATER RECLAMATION PLANT
Design Loadings - Stage 5A
Population served, thousands 310
Flow contribution, 1 pcd (gpcd) (industrial flow not included) 303 (80)
Flow
Average dry weather cu in/day (mgd) 113,550 (30)
Maximum dry weather cu m/day (mgd) 181,680 (48)
Peak wet weather cu m/day (mgd) 529,900 (140)
Loadings
BOD, 1,000 kg/day (1,000 Ib/day) 24.5 (54)
BOD, including recycle 1,000 kg/day (1,000 Ib/day) 27.2 (60)
Suspended solids, 1,000 kg/day (1,000 Ib/day) 27.2 (60)
Suspended solids, including recylcle, 1, 000 kg/day (1, 000 Ib/day) 32.7 (72)
Total nitrogen as N, mg/1 30
Total phosphorus as P, mg/1 11
Preaeration, Flocculation, Grit Removal
Tanks
Number, one existing 2
Width, m (ft) 9.1 (30)
Length, m (ft) 18.8 (61.5)
Average water depth, m (ft) 4.6 (15)
Design capacity, cu m/day (mgd) 113,550 (30)
Detention time, ADWF, hr 0.33
Max hydraulic capacity, cum/day (mgd) 283,875 (75)
Air supplied, cu m/m (cu ft/gal) 0.74 (0.10)
Grit pumps
Number 6
Capacity, each unit, I/sec (gpm) 12.6 (200)
Primary Chemical Feed Equipment
Lime slaker hopper
Number 3
Capacity, each unit, cum (cu ft) 2.1 (75)
Lime feeder
Number 3
Type gravimetric
Capacity, each unit, kg (Ib) CaO per hour 3.630 (8,000)
Lime slaker
Number 3
Type paste
Capacity, each unit, kg (Ib) CaO per hour 3,630 (8,000)
Primary Sedimentation
Tanks
Number, two existing 4
Width, (ft) H-6 (38)
Length, (ft) 77.4 (254)
Average water depth, (ft) 2.9 (9.5)
Detention time, ADWF, hr 2.2
Overflow rate, ADWF, cu m/day/sq m (gpd/sq ft) 31.8 (780)
Mean forward velocity, m/min (ft/min) 0.58 (1.9)
Design capacity, each tank, cu m/day (mgd) 37,850 (10)
Max hydraulic capacity, each tank, cu m/day (mgd) 141,938 (37.5)
Effluent collection pipes
Number per tank 4
Diameter, cm (inch) 50-8 (2°)
Primary sludge pumps
Number 4
Capacity, each unit, l/sec(gpm) 12.6 (200)
Primary sludge recirculation pumps
Number 2
Capacity, each unit, I/sec (gpm) 3-8 (6°)
Primary scum pumps
Capacity, each unit. I/sec (gpm) 3. 8 (6.0J
(continued)
229
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Table 12-3. DESIGN DATA FOR THE CCCSD WATER RECLAMATION
PLANT (CONTINUED)
Primary Treatment Performance
BOD removal
Percent 70
1,000 kg/day (1,000 Ib/day) 19-1 (42)
Suspended solids removal
Percent 70
1,000 kg/day (1,000 Ib/day) 22.7 (50)
Primary Effluent
BOD, 1,000 kg'/day (1,000 Ib/day) 8.2 (18)
Suspended solids, 1,000 kg/day (1,000 Ib/day) 10 (22)
Sludge Thickening
Primary sludge thickener (existing digester)
Tanks
Number 1
Diameter, m (ft) 18.9 (62)
Side water depth, m (ft) 5.84 (19.17)
Surface area, sq m (sq ft) 280 (3,020)
Volume, each tank, 1,000 cu m(1,000 cu ft) 1.7 (62)
Detention time, hr 23
Sludge to thickener, 1,000 kg/day (1,000 Ib/day) 110.3 (243)
Surface loading, kg/day/sq m (Ib/day/sq ft) 390 (80)
Solids recovery, percent 90
Average sludge solids cone, percent 6
Average thickened sludge solids cone, percent 8
First stage centrifuge feed pumps
Number 3
Capacity, each unit, I/sec (gpm) 20.8 (330)
Air mixing blower
Number 2
Capacity, each unit, at discharge pressure, cu m/min (cfm) 35 (1,250)
Discharge pressure, kg/sq cm (psig) 1.3 .(18)
Centrate thickener, (existing digester)
Tanks
Number 1
Diameter, m (ft) 18.9 (62)
Side water depth, m (ft) 10.11 (33.17)
Surface area, sq m (sq ft) 280 (3,020)
Volume, 1,000 cum (l.OOOcuft) 2.7 (95)
Detention time, hr 22
Sludge to thickener, 1,000 kg/day (1,000 Ib/day) 58 (128)
Surface loading, kg/day/sq m (Ib/day/sq ft) DS 205 (42)
Solids recovery, percent 90
Average centrate solids cone, percent 1.5
Average thickened centrate solids cone, percent 3
Second stage centrifuge feed pumps
Number 3
Capacity, each pump, I/sec (gpm) 26.5 (420)
Centrifagation
First stage centrifuge
Number 2
Type solid bowl
Max feed rate, I/sec (gpm) 16.1 (255)
Feed solids cone, percent 8
Max G force, G 3,100
Cake solids cone, percent 55
Centrate solids cone, percent 2
Horsepower 250
Second stage centrifuge
Number 2
Type solid bowl
Max feed rate, I/sec (gpm) 16.4 (260)
Feed solids cone, percent 4
Max polymer dosage, kg/ton (Ib/ton) DS 0.9 (2)
Max G force, G 3,100
Cake solids cone, percent (minimum) 14
Centrate solids cone, percent 0,5
Horsepower 250
(continued)
230
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Table 12-3. DESIGN DATA FOR THE CCCSD WATER RECLAMATION
PLANT (CONTINUED) ___
Furnaces
Sludge incineration
Number 1
Type MHF
Outside diameter, m (ft) 6.78 (22.25)
Hearths 11
Off gas temperature C (F) 760 (1,400)
Ash, kg/hr (Ib/hr) 817 (1,800)
Loading, 1,000 kg/day (1,000 Ib/day) DS 31.8 (70)
Feed solids cone, percent 12-18
Volatile solids, percent 43
Lime recalcination
Number 1
Type MHF
Outside diameter, (ft) 6.78 (22.25)
Hearths 11
Off gas temperature C (F) 760 (1,400)
Ash, kg/hr (Ib/hr) 1,589 (3,500)
Loadings, 1,000 kg/day (1,000 Ib/day) DS 68 (150)
Feed solids cone percent 50-60
Volatile solids, percent 21
CaCOs feed, 1,000 kg/day (1,000 Ib/day) 44.5 (98)
Furnace Auxiliary Equipment
Lump breaker
Number 2
Capacity, each unit, kg (Ib) per hour 2,270 (5,000)
Ash cooler
Number 2
Outlet ash temperature, C (F) 93 (200)
Exhaust gas equipment
Dry scrubber
Number 2
Max entering gas temperature, C (F) 760 (1,400)
Efficiency, percent 70
Waste heat boiler
Number 2
Capacity, each unit, mil kg-cal/hr (mil Btu/hr) 8.8 (35)
Max entering gas temperature, C (F) 760 (1,400)
Exiting gas temperature, C (F) 232 (450)
Wet scrubber
Number 2
Max entering gas temperature, C (F) 288 (550)
Exiting gas temperature, C (F) 49 (120)
Scrubber water pumps
Number 12
Capacity, each pump, I/sec (gpm) 54.3 (860)
Ash hoppers
Number 4
Capacity, each hopper, cum (cu ft) 35 (I.250)
Sludge, Scum and Grit Reduction
Loadings
Scum, kg/day (Ib/day) DS 636 (1,400)
Grit, kg/day (Ib/day) DS 1,272 (2,800)
Sludge 1,000 kg/day (1,000 Ib/day) 31.8 (70)
Volatile solids, percent 43
Feed solids cone, percent 12-18
Scum dewatering equipment
Thickener
Number 1
Surface loading kg/day/sq m (Ib/day/sq ft) DS 68.3 (14)
Thickened scum pumps
Number 2
Capacity, each pump, I/sec (gpm) °-°9 (1-5)
Grit dewatering equipment
Separator
Number 4
Capacity, each unit, I/sec (gpm) 6.3 (100)
Dewaterer
Number 2
Capacity, each unit, i/sec (gpm) 7.9 (125)
231
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2. Gravity sludge thickening.
3. Sludge classification and dewatering.
4. Lime recalcination and sludge incineration.
5. Related processes, i.e., heat recovery and pneumatic conveying.
The basic cost will be developed for the type of units included in the CCCSD plant
As previously stated, these units will be replaced for illustration purposes by
other units capable of comparable performance. The alternates considered are:
1. Dewatering of first stage centrate by pressure filtration prior to sludge
incineration.
2. Primary sludge dewatering by vacuum filtration prior to lime recalcina-
tion in Plural Purpose furnaces .
Capital Costs
Capital costs of the units associated with the lime treatment and recovery at the
CCCSD's plant are presented in Table 12-4. Construction costs given in the
table are representative of bidding conditions in the San Francisco Bay Area
during June 1973, representing an ENR Construction Cost Index of 2000. These
costs are based on a combination of the engineer's estimate and bidding informa-
tion submitted by the general contractor. Engineering includes field surveying
and soil investigations, design, preparation of plans and specifications, office
engineering during construction, resident engineering, inspection, materials
testing and construction surveying. Engineering costs depend on factors such
as the size and complexity of the work, required construction period, owner
facilities, etc. Engineering charges are computed by several methods, or
combination of two or more of these methods .6 in the table a value of 12 percent
has been used for illustration purposes. Contingencies cover such factors as
removal of unknown structures and alterations and changes during construction.
Contingency charges for construction are usually set at 5 to 10 percent of the
total construction cost of the project. A contingency allowance of 5 percent has
been used in Table 12-4 to arrive at a total capital cost.
In Section VII, a comparison of dewatering techniques was made for a 1.31 cu
m/sec (30 mgd) plant. The results of this comparison are shown in Table 7-10.
The data presented in Table 7-10 have been used in the evaluation of the impact
of alternate dewatering equipment on lime treatment costs as if this equipment
had been applied to the CCCSD water reclamation plant. Table 12-5 presents
capital cost data for the substitution of vacuum filters for two-stage centrifugal
dewatering, converting the CCCSD design from an ATTF processing system
(Fig. 7-9) to a Plural Purpose Furnace flow sheet (Fig. 7-8) . Another estimate
is presented in Table 12-6 which involves the substitution of filter presses for
the second stage centrifugal dewatering of the CCCSD design. The two alterna-
tives evaluated produce differing quantities of wet sludge to be incinerated.
This has a significant impact on MHF sizing and cost. To account for this effect,
232
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Table 12-4. CAPITAL COST FOR LIME TREATMENT AND RECOVERY
AT THE CCCSD WATER RECLAMATION PLANT
Item
I
II
III
IV
V
VI
VII
Process
Flocculation, grit removal and primary sedimentation. Includes one
covered preaeration tank and two sedimentation tanks; distribution
and effluent channels; preaeration, sludge collection and scum re-
mova.1 equipment; lime feed building and equipment; equipment gal-
lery; grit, sludge and scum pumps; piping; electrical switchgear;
controls and instrumentation.
1. Lime feeders and slakers (three units).
2. Flocculation and grit removal tank.
3. Primary sedimentation tanks.
Subtotal
Gravity sludge thickening. Includes conversion of two existing
digesters to thickeners; sludge thickening equipment; piping; con-
trols and instrumentation.
Wet classification. Includes two vertical centrifuges; piping; con-
trols and instrumentation.
Sludge dewatering. Includes two vertical centrifuges; polymer feed
equipment; piping; controls and instrumentation.
Lime recalcination. Includes one complete multiple hearth furnace;
material conveyors; dry classification equipment; piping; switchgear;
controls and instrumentation.
Sludge incineration. Includes one complete multiple hearth furnace;
material conveyors; grit and scum handling equipment; piping;
switchgear; controls and instrumentation.
Belated process.
1. Heat recovery equipment. Includes two waste heat recovery
boilers and two package steam boilers; boiler feed water
system; piping; controls and instrumentation.
Struct.
& bldg. a
81,000
163,000
408,000
36,000
e
5,000f
463,000
467,000
e
Mechanical
equip, b
110,000
33,000
301,000
93,000
439,000
464,000
2,194,000
2,291,000
446, 000
Piping
2,000
66,000
31,000
9,000
209,000
217,000
26,000
55,000
213,000
Elect. &
ins trum entation0
17,000
61,000
174,000
12,000
85,000
91,000
396,000
418,000
88,000
Total cost,
dollars'3
210,000
323,000
914,000
1,447,000
150,000
733,000
777,000
3,079,000
3,231,000
747,000
U)
U)
-------
Table 12-4. CAPITAL COST FOR LIME TREATMENT AND RECOVERY AT
THE CCCSD WATER RECLAMATION PLANT (CONTINUED)
Item
VII
Process
2. Pneumatic conveying and storage. Includes penumatic con-
veying equipment to (a) unload make up lime, (b) transport
reclaimed lime from furnace to storage bins, (c) transfer
process lime from storage to slaker day hoppers, (d) trans-
port ash to storage; lime storage bins; blowers and auxiliary
equipment; screw conveyors; rotary air locks; air filters;
piping; controls and instrumentation.
3. Auxiliary facilities. Includes the percentage allpcated to
solids processing of administration and maintenance buildings;
piping tunnels; outside piping; fuel storage; electrical sub-
stations and general site development.
Struct.
& bldg. a
g
g
Mechanical
equip. "
g
g
Piping
g
g
Elect. &
instrumentation0
g
g
Total cost,
dollars^
593,000
3,091,000
IV)
OJ
Total construction cost
Engineering, 12 percent of construction cost
Contingencies, 5 percent of construction cost
Total capital cost
13,848,000
1,662,000
692,000
16,202,000
facilities are housed in multipurpose structures and buildings, cost were obtained in proportion to floor space occupied.
Includes installation cost.
.Does not include computer cost.
gBased on June 1973 prices (ENE Index: 2,000).
„ Equipment housed in the furnace building.
Cost of housing polymer feed equipment only.
-------
Table 12-5. CAPITAL COST OF ALTERNATE DEWATERINC PROCESS AT THE CCCSD
PLANT - VACUUM FILTERS IN A PLURAL PURPOSE FURNACE FLOW SHEET
Item
VIII
IX
X
Process
From total construction cost in Tabie 12-4, delete items III, IV, V
and VI.
Vacuum filters.6 Includes three belt-type vacuum filters complete
with base; vacuum, sludge and filtrate pumps; cake conveyor;
chemical conditioning equipment; piping; controls and instrumen-
tation.
Lime and sludge furnaces. £ Includes two complete multiple hearth
furnaces; material conveyors; dry classification equipment; grit and
scum handling equipment; piping; switchgear; controls and instrumen-
tation.
Add allowance on Items IX for larger furnaces. %
Struct.
& bldg. a
-
212,000
930,000
-
Mechancial
equip, b
-
430,000
4,485,000
-
Piping
-
321,000
81,000
-
Elect. &
instrumentation0
-
74,000
814,000
-
Total cost,
dollars^
6,028,000
1,037,000
6,310,000
701,000
NJ
UJ
Total construction cost
Engineering, 12 percent of construction costs
Contingencies, 5 percent of construction cost
Total capital cost
14,076,000
1,689,000
704,000
16,469,000
rwhen facilities are housed in multipurpose structures and buildings, cost were obtained in proportion to floor space occupied.
Includes installation cost.
.Does not include computer cost.
Based on June 1973 prices (ENR Index: 2,000).
.Vacuum filters to be housed in enlarged furnace building; see Table 7-11 for equipment sizing.
Furnaces operated in Plural Purpose mode (20% blowdown).
gMaximum solids load is 39 kg/sq m/hr (8 Ib/sq ft/hr) vs. 35.1 kg/sq m/hr (7.2 Ib/sq ft/hr) for the CCCSD plant design (See Table 12-10).
-------
Table 12-6. CAPITAL COST OF ALTERNATE DEWATERING PROCESS AT THE CCCSD PLANT -
FILTER PRESSES SUBSTITUTED FOR CENTRIFUGAL DEWATERING IN THE SECOND PHASE
Item
-
XI
XII
Process
From total construction cost in Table 12-4, delete Item IV.
Filter presses. e Includes four 7. 4 kg/sq cm (105 psi) filter presses
complete with drip flaps, safety curtains, cloths, feed pump, piping,
controls and instrumentation,
Less allowance on Items VI and VI for smaller furnaces.
Struct.
& bldg. a
-
254,000
-
Mechanical
equip
-
880,000
-
Piping
-
428,000
-
Elect. &
ins trumentationc
-
203,000
-
Total cost,
dollarsd
13,071,000
1,165,000
2,103,000
NJ
OJ
Total construction cost
Engineering, 12 percent of construction
Contingencies, 5 percent of construction cost
Total capital cost
12,733,000
1,528,000
637,000
14,898,000
facilities are housed in multipurpose structures and buildings, cost were obtained in proportion to flow space occupied.
Includes installation cost.
,Does not include computer cost.
eBased on June 1973 prices (ENB Index: 2, 000).
..Filter presses to be housed in enlarged furnace building, see Table 7-11 for equipment sizing.
Maximum solids load is 23.4 kg/sq m/hr (4. 8 Ib/sq ft/hr) vs. 35.1 kg/sq m/hr (7.2 Ib/sq ft/hr) for the CCCSD plant design (See Table 12-10).
-------
the cost of the multiple hearth furnaces in the two alternates were adjusted up-
wards or downwards proportionate to the wet sludge load on the MHF.
The capital cost of the Plural Purpose Furnace flow sheet is 2 percent more costly
than the CCCSD design, while the substitution of filter presses yields costs 14
percent less costly than the CCCSD design.
Operation and Maintenance Costs
Predicted operation and maintenance (O&M) costs of the lime treatment and
recovery processes at the CCCSD water reclamation plant are given in Table
12-7. The cost of operating labor shown in the table reflect the computer control
features of the CCCSD plant. Labor charges include a proportional share of the
cost of administration, supervisory and laboratory staff recommended for the
water reclamation plant. In computing operating outlays, the following unit costs
were used:
Power: 1.283 £/kw-hr
Natural gas: 6.148 £71000,000 Btu (1 Therm)
Lime (92% CaO) : $30.55/ton
Ferric Chloride (dry basis) $100/ton as FeCl3
Anionic polymer: $1.25/lb
Labor cost (including fringe benefits) $9.00/man-hr.
The O&M costs for the alternate dewatering processes described in Tables 12-5
and 12-6, are given in Tables 12-8 and 12-9, respectively. Fuel costs in Tables
12-7, 12-8 and 12-9 are based on material balances calculated using the computer
program described in Section X. A summary of fuel requirements of the cases
studied is given in Table 12-10. Comparing O&M costs, it can be seen that the
Plural Purpose flow sheet (Table 12-8) is 7 percent more costly than the CCCSD
design, while the filter press alternate is 9 percent less costly than the CCCSD
design.
Total Annual Costs
Total annual costs are compared in Table 12-11. The CCCSD design is 3.5 per-
cent less costly than the Plural Purpose flow sheet. Substitution of filter presses
for the centrifuges in the second stage dewatering step at the CCCSD design
would allow savings of nine percent of the annual cost of the CCCSD design. (It
should be noted that the filter press information became available after the design
of the CCCSD plant was completed. Solids processing using filter presses will
be considered as an alternative in future plant expansions) .
Cost of Reclaimed Lime Production vs. Purchased Lime
It is not an easy matter to separate the cost of lime recovery from the cost of
solids disposal in the ATTF solids processing system. It could be argued that
the thickening, dewatering and incineration steps are all required for sludge
disposal and that the incremental cost of lime recovery is only the capital and
O&M costs of the extra energy required to convert calcium carbonate to calcium
237
-------
Table 12-7. OPERATION AND MAINTENANCE COST FOR LIME TREATMENT AND
RECOVERY AT THE CCCSD WATER RECLAMATION PLANT
Item
I
II
III
IV
V
VI
VII
VIII
DC
Process
Chemical addition
Preaeration and grit removal
Primary sedimentation
Sludge thickening
Wet classification
Sludge dewateringb
Lime recalcination
Sludge incineration
Related processes
a. Heat recovery
b. Pneumatic conveying
Cost item, dollar/year
Energy
Power
500
8,500
2,600
200
23,400
25,700
38,300
36,500
11,500
11,000
Fuel
-
-
-
-
-
-
12,100
53,200
-
-
Chemicals
Lime
173,400
-
-
-
-
-
-
-
-
-
Polymer & other
-
-
-
-
-
38,300a
-
-
3,000
-
Operating
labor
3,900
6,000
16,700
2,800
23,600
23,800
25,500
26,200
19,600
10,900
Maintenance, repairs
& supplies
5,500
3,100
3,700
1,900
11,000
11,600
43,900
45,800
44,900
35,600
Total O&M cost
Total O&-AI
cost
183,300
17,600
23, 000
4,900
58,000
99,400
119,800
161,700
79,000
57,500
804,200
U)
00
,At 0. 9 kg (2 Ib) per ton DS
Case 100, Section X
-------
Table 12-8. OPERATION AND MAINTENANCE COST FOR ALTERNATE DEWATERINC
PROCESS AT THE CCCSD PLANT - VACUUM FILTERS
Item
I
II
III
IV
V
VI
VII
Process
Chemical addition
Preaeration and grit removal
Primary sedimentation
Sludge thickening
Sludge dewateringa
Lime recalcination
Related processes
a. Heat recovery
b. Pneumatic conveying
Cost item, dollar/ vear
Energy
Power
500
8,500
2,600
200
24,100
74,800
11,500
11,000
Fuel
-
-
-
-
-
122,700
-
-
Chemicals
Lime
183,100
-
-
-
-
-
-
-
Polymer & other
-
-
-
-
66,800b
-
3,000
-
Operating
labor
3,900
6,000
16,700
2,800
45,500
51,700
19,600
10, 900
Maintenance, repairs
& supplies
5,500
3,100
3,700
1,900
11,500
87,800
44, 900
35,600
Total O&M cost
Total O&M
cost
193,000
17,600
23,000
4, 900
147,900
337, 000
79,000
57,500
859, 900
NJ
CO
,Case 114, Section X, Plural Purpose flow sheet.
At 0. 45 kg (1 Ib) ton of DS.
CTwo furnaces operating on Plural Purpose mode - 20 percent blowdown.
-------
Table 12-9. OPERATION AND MAINTENANCE COST FOR ALTERNATE DEWATERING
PROCESS AT THE CCCSD PLANT - FILTER PRESSES
Item
I
II
III
IV
V
IV
VII
VIII
rx
Process
Chemical addition
Preaeration and grit removal
Primary sedimentation
Sludge thickening
Wet classificationa
Sludge dewateringa
Lime recalcination
Sludge incineration
Related processes
a. Heat recovery
b. Pneumatic conveying
Cost item, dollar/year
Energy
Power
500
8,500
2,600
200
23,400
5,100
38,300
36,500
11,500
11,000
Fuel
-
-
-
-
-
-
11,800
21,300
-
-
Chemicals
Lime
173,400
-
-
-
-
-
-
-
-
-
Polymer & other
-
-
-
-
-
-
-
-
3,000
-
Operating
labor
3,900
6,000
16,700
2,800
23,600
28,100
25,500
26,200
19,600
10,900
Maintenance, repairs
& supplies
5,500
3,100
3,700
1,900
11,000
26,400
43,900
45,800
44, 900
35,600
Total O&M cost
Total O&M
cost
183,300
17,600
23,000
4,900
58,000
59,600
119,500
129,800
79,000
57, 500
732,200
Case 102, Section X, ATTF Solids Processing System with pressure filtration in the second stage.
-------
Table 12-10. FUEL REQUIREMENTS FOR ALTERNATIVE CASES
Wet cake rate, kg/day
(Ib/day)
Furnace loading rate,
kg/sq m/hr(lb/sq ft/hi)
Gross heat inputs
Combustion of vola-
tiles
Net-auxiliary fuel
Total
Heat accounted for
Usesa
Total sensible heat in
stack gases
Heat recoverable in
waste heat boilerb
Gross heat-auxiliary
fuelc
Total gas required
Gas assigned to recal-
cination or incinera
tion
Total gas assigned
to recalcination and
incineration
ATTF system case with
(Case 1
Eecalcine
furnace
109,400 (241,000)
19 (3.9)
kg-cal/hr BTU/hr
2,453,918 9,737,770
2,105,992 8,357,113
4,559,910 18,094,883
1,275,546 5,061,691
3,284,364 13,033,192
4,559,910 18,094,883
2,397,609 9,514,320
3,275,669 12,998,688
kg/hr Ib/hr
287 632
77 169
kg/hr
416
2nd stage centrifuge
00)
Waste sludge
furnace
204,600 (450,700)
35.1 (7.2)
kg-cal/hr BTU/hr
2,857,172 11,337,984
5,839,287 23,171,773
8,696,459 34,509,757
1,559,117 6,186,973
7,137,342 28,322,784
8,696,459 34,509,757
5,210,259 20,675,632
9,082,451 36,041,473
kg/hr Ib/hr
795 1,752
339 746
Ib/hr
915
ATTF system case wit]
(Case 1(
Recalcine
furnace
106,400 (234,400)
18.3 (3.75)
kg-cal/hr BTU/hr
2,383,920 9,460,000
2,045,736 8,118,000
4,429,656 17,578,000
1,239,336 4,918,000
3,190,320 12,660,000
4,429,656 17,578,000
2,328,984 9,242,000
3,182,004 12,627,000
kg/hr Ib/hr
279 614
75 165
kg/hr
211
i 2nd stage filter press
12)
Waste sludge
furnace
137,100 (302,000)
23.4 (4.8)
kg-cal/hr BTU/hr
3,172,252 12,588,300
3,404,362 13,509,372
6,576,614 26,097,672
1,447,469 5,743,923
5,129,145 20,353,749
6,576,614 26,097,672
3,744,275 14,858,236
5,295,158 21,012,533
kg/hr Ib/hr
464 1,021
136 299
Ib/hr
464
Plural purpose with
vacuum filter
per furnace basis
(2 furnaces required)
451,200 (993,880)
39 (8)
kg-cal/hr BTU/hr
2,644,356 10,493,475
6,310,310 25,040,912
8,954,666 35,534,387
1,633,057 6,480,383
7,321,609 29,054,004
8,954,666 35,534,387
5,344,787 21,209,472
9,815,083 38,948,739
kg/hr Ib/hr
859 1,893
391 861
kg/hr Ib/hr
782 1,722
KJ
^Evaporation of water, radiation losses, shaft heating air, heat of reaction, heat loss in calcine product.
Taken as 73 percent of total sensible heat of furnace off gases.
°Batio to net heating value: 20, 564/13, 221 = 1. 555402 (cf Section VIII).
Calculated as the difference between the gross heat from auxiliary full less that recovered in the waste heat boiler, divided by the gross heat-input
times the total gas required; e.g., for the recalcine furnace in Case 100: 632 (12,998,688 - 9, 514, 320)/(12, 998,688) =169.
-------
oxide plus the cost of operation of the dry classification step. On this basis, the
cost of reclaimed lime would be low. Investigators at South Tahoe reasoned that
the reclaimed lime cost was the total cost of the recalcining step, since lime sludge
thickening and dewatering would be common to any lime coagulation process.7
Costs for the example in this report are calculated on the same basis as for South
Tahoe, and include only the recalcination step. The O&M and annual cost estimate
for recalcination totals $388,200/yr. Since it was found that recalcined lime
eliminated the need for the use of ferric chloride as a supplemental coagulant
(Table 8-12) , a savings of $63,800 can be credited to recalcination, leaving a
balance of $324,400/yr. For this case, 8620 tons/yr of CaO are returned to the
process . The unit cost of recalcination is $37.63 per ton of CaO. While it appears
that recalcined lime costs 13 percent more than new lime, several other factors
must be considered. First, the recent quotation of $33.20 per ton (100% CaO) has
been made by the manufacturer with the cautionary statement that a significant
increase in cost is expected in the near future. Second, a portion of the cost of
recalcination could be attributed to ultimate disposal of the large quantity of
calcium carbonate sludge generated by the process. On this basis, the cost of
reclaimed lime is considered competitive with the cost of new lime for this case.
Table 12-11 . COMPARISON OF TOTAL ANNUAL COSTS FOR
LIME TREATMENT AND SOLIDS PROCESSING
System
CCCSDdesigna
1st: centrifuge
2nd: centrifuge
Plural Purpose^3
(vacuum filters)
Modified design0
1st: centrifuge
2nd: filter press
Cost category, dollar/year
O&M
804,200
859,400
732,200
Annual cost
of capital
1,412,600
1,435,800
1,298,900
Total
annual cost
2,216,800
2,295,200
2,031,100
bCase 100, Section X
Case 114, Section X
dCase 102, Section X
CEF at 20 years and 6 percent = 0. 08718456
242
-------
Cost of Sludge Processing
The entire sequence of operations in the CCCSD Water Reclamation Plant, begin-
ning with thickening and ending with the production of ash for ultimate disposal
and reclaimed lime for reuse, can be considered the sludge processing system.
The unit cost of operation for the total system expressed per ton of DS processed
is of interest. The annual cost of capital for the system is $l,265,000/yr, exclu-
sive of Item I in Table 12-4. O&M cost totals $580,300, exclusive of Items I, II and
III in Table 12-7. Total annual cost is $l,845,300/yr. A total of 33,490 tons/yr of
new sludge is precipitated in the system, exclusive of recycled solids. Therefore
the unit cost of sludge processing is $55,10/ton of DS . This cost is competitive
with the cost of other sludge disposal systems. The cost can also be expressed
per unit of wastewater treated; on this basis the cost is $167/mil gal based on an
average dry weather flow of 30 mgd.
243
-------
SECTION XII
REFERENCES
1. Brown and Caldwell, Consulting Engineers. Report on Energy Requirements
for Alternative Modes of Operation of Water Reclamation Plant. Prepared for
the Central Contra Costa Sanitary District, Walnut Creek, California. 1974.
2. Flanagan, M.J . Direct Digital Control of Central Contra Costa Sanitary
District Water Reclamation Plant. (Presented at IAWPR Specialized Con-
ference, London). September, 1973. 12 p.
3. Caldwell Connell Engineers. Design Report - Lower Molonglo Water Quality
Control Centre. Prepared for the National Capital Development Commission,
Canberra, Australia. April, 1971.
4. Caldwell Connell Engineers. Revisions to Design Report - Lower Molonglo
Water Quality Control Centre. Prepared for the National Capital Development
Commission, Canberra, Australia. May, 1972.
5. Parker, D.S., K.E. Train, andF.J. Zadick. Sludge Processing for Com-
bined Physical-Chemical-Biological Sludges. U.S. Environmental Protection
Agency, Washington, D.C. Report No. EPAR2-73-250, July, 1973. 141 p.
6. Consulting Engineering - A Guide for the Engagement of Engineering
Services. American Society of Civil Engineers, New York. ASCE Manual
on Engineering Practice Number 45. July, 1972. 96 p.
7. Advanced Wastewater Treatment as practiced at South Tahoe. South Tahoe
Public Utility District. Washington, D.C. Project 17010 ELQ. U.S. Environ-
mental Protection Agency. August 1971. 436 p .
244
-------
SECTION XIII
LIST OF INVENTIONS AND PUBLICATIONS
No inventions have resulted from this work, nor have any patent applications
been made as a result of this work. All processes described in this work were
state-of-the-art prior to inception of this project. To date (May, 1974) no
publications have resulted from this work.
245
-------
SECTION XIV
GLOSSARY
This glossary explains the various abbreviations used throughout the report; see
Tables 10-1, 10-2, and 10-3 for symbols used in the computer program.
Btu British thermal units
C degrees Celsius
cfm cubic feet per minute
cfs cubic feet per second
cu ft cubic foot (feet)
cu m cubic meter
DS dry solids
F degree Farenheit
FBR fluidized bed reactor
ft foot (feet)
G gravitational force per pound mass,
feet per (second) 2
gal gallon (s)
gpd gallons per day
gpm gallons per minute
HHV high heat value
in. inch(es)
kg kilogram (s)
kcal kilocalories
L bowl length, cm
1 liter (s)
lb pound (s)
LHV Low heat value
I/sec liters per second
m meter
mgd million gallons per day
mg/1 milligram (s) per liter
MHF multiple hearth furnace
PPm part(s) per million
pound (s) per square inch
radius of the liquid surface, cm
radius of the inner wall of the bowl, cm
rotary kiln calciner
difference in revolutions per minute
for centrifuge, A RPM is bowl speed
E minus conveyor speed
" sigma" factor
s<3 ft square foot (feet)
sqin. square inch (es)
sc! m square meter
246
-------
SS suspended solids
TS total solids
VS Volatile solids (or volatile matter)
w rate of rotation, rad/sec
wt weight
247
-------
SECTION XV
APPENDICES
The attached appendix is in two parts. Appendix A contains a listing of the
solids balance computer program, SOLIDS IA, which has been described in detail
in Section X. Appendix B contains copies of the output from this program for
23 cases that were run for this project. Table B-l is an index for these cases.
248
-------
APPENDIX A
LISTING OF SOLIDS 1A
249
-------
SOLIDS1A 11:50PDT
100C THIS IS A PROGRAM TO CALCULATE THE EQUILIBRIUM MASS BALANCES FOR
HOC SEVERAL COMPONENTS IN A LIME SLIDGE PROCESSING SEQUENCE EMPLOYINB
I20C WET CLASSIFICATION,RECALCIUATION,DRY CLASSIFICATION OF RECALCIN-
150C ED PRODUCT,DEWATERING AND INCINERATION OF CENTRATE SOLIDS FROM WET
140C CLASSIFICAT!ON,WITH OPTIONS FOR SLOWDOWN OF RECALCINED PRODUCT,
150C OR SINGLE FURNACE CASE WITH NO DEWATER ING AND INCINERATION STEPS.
160C IF FURNACE STACK LOSSESCRECOVERED IN THE WET SCRUBBER) ARE TO BE
I70C RETURNED TO THE PRIMARY, THEN INPUT "SEREC" AS 1.0. IF THE WET
18DC SCRUBBER EFFLUENT IS NOT TO BE RETURNED TO THE PRIMARY, THEN
190C INPUT "SEREC" AS 0.0
200C IF NO SLOWDOWN IS WANTED, THEN "FRBD" =0.0.
210C IF NO CLASSIFIER FOR RECALCINED PRODUCT IS WANTED,"CLASSIF"=0.0.
220C IF CLASSIFIER IS EMPLOYED, LET "CLASSIF" =1.0.
230C IF NO SECOND STAGE CENTRIFUGE AND INCINERATION FURNACE ARE USED,
240C LET "FURNACE" EQUAL 1.0; IF THEY ARE INCLUDED, LET "FURNACE"=2.0.
250C IF NO CLASSIFIER EMPLOYED, INPUT ALL COMPONENT CLASSIFIER RECOVERY
260C FRACTIONS AS 1.0, CTOTAL RECOVERY), EXCEPT ORGANICS, FECOHJ3, AND MGOXJ2
270C WHICH ARE ALL ZERO.
280C INPUT THE RECOVERIES OF ORGANICS, FE(OH)3, MG(OH)2 IN FURNACES
290C AND CLASSIFIER AS 0.0 FOR ALL CASES.
300C IF NO SECOND STAGE CEt^TRIFUGE OR INCINERATION FURNACE USED, LET THE
310C RECOVERY OF ALL COMPOUNDS IN THESE EQUAL ZERO.
320C PROGRAMMER: F.J. ZADICK,BROWN 6 CALDWELL, SAN FRANCISCO, CALIF.,FEB., 197"t
330 FILELIST "DAT1","DAT2","DAT3"
3"tO 110 FORMATCV)
3<»5
350C STATEMENT 224 is USED TO SUPRESS DIAGNOSTICS DURING COMPILING
360 224 L=123+L
365
370C READ FROM FILES DAT1, DAT2, DAT3
380 225 READCl,110)L,XMGD,XLBWASIN,FECL3MGL,CAHTODOS,FRBD,RECALEFF
390 227 READC1,110)L,FURNACE,CLASSIF,PH,SEREC,FEINFMGL,SIINDMGL,SIEFDM6L
1)00 2.9 READ(2,110X,SSINlMGL,SSCnjTMGL,XMG^riGL,XMGEFMGL,CAINFMGL,CAEFFMGL
410 231 READC2, 110X,PINFMGL,PEFFMGL,FEEFFMGL,FRAIISSO,FRAIISSI
1(20 233 READC2, 110X,FRSIWAS,FRAIIWAS,FRVWASIN,FRVSSIN,FRVSSOUT
430 235 READC2,110)L,FRSISSI,FRSISSO,FRSINEW,FRAIINEW,FRMGONEW,FRCAONEW
440 237 READC3, 110X,RECAP1,RECAC1,RESI1,REAII1
450 239 READ(3,110X,REXMGH1,REXMG01,REFEOH1,REFE01,REORG1
460 241 READC3, 110X,RECAP2,RECAC2,RESI2,REAII2,REFEOH2
470 243 READC3, 110X,PEFEO2,REORG2,REXMGH2,REXMGO2
480 245 READ(3,110X,RECAPF,RECACF,RESIF,REAIIF,REFEOHF
490 247 READC3,110X,REFEOF,REORGF,REXMGHF,REXMGOF
500 249 READC3, 110)L,RECAPFI,RECACFI,RESIFI,REAIIFI,REFEOHFI
510 251 READ(3,110X,REFEOF],REORGFI,REXM6HFI,REXMGOFI
520 253 READC3,110)L,RECAPCL,RECACCL,RESICL,REAIICL,REFEOHCL,RECAOa.
530 255 READC3,110X,REFECCL,REORGCL,REXMGHCL,REXMGOCL
540 800 XLBSSII^XMGD-S.SS-SSir-MGL
550 803 XLBSSOUT=XMGO"8.33"SSOUTMGL
560 805 XMGINF=XMGD-"8.33::XMGnM;L
570 807 XMGEFF=XMGD"8.33::XMGEFMGL
580 810 CAINF=XMGD"8.33"-CAINFMGL
590 814 CAEFF:XMGD=:8.33::CAEFFM&L
600 816 PIN^XMGD-S^^INFMGL
610 818 PEFF=XMGD=:8.33::PEFFMG1.
620 822 AIIEFFiXLBSSOUT^CFRAIISSO)
630 828 FEEFF=XMGD::8.33"FEEFFMGL
640 SIlrO=SIINDMGL"8.33:rXMGD
650 SIEFFD^SIEFDMGL-S.SS^XMGD
660 826 SIEFF=XLBSSOUT::CFRSISSO)+SIEFFO
670 830 FECL3=XMGD:;8.33::FECL3MGL
680 834 CAHTOTLB^CAHTODOS-XMGD1^.33
690 836 CAOTOTLB=CAHTOTLB"C56./74.)
700 837 CAOTOMGL=CAHTODOS"56./74.
705
710C CALCULATE FECOH)3 IN PRIMARY SLUDGE
720 840 FEOHSLG=((FECL3)::C107./l62.5)+(FEINFMGL)"C107./56.)"CXMGD)»C
730 S8.33)-(FEEFF)KC107./56.))/(!.-O.-REFEOH2)«O.-REFEOH1)>
740C CALCULATE FE(OH)3 IN OTHER LIQUID STREAMS
750 842 FEOHlP=CFECL3)::C107./162.5)-(FEEFF)"C107./56.>i.CFEINFMGL)K<
760 6XMT,D):=C8.33D"C107./56.)
770 844 FEOHCAK1=CREFEOH1)"CFEOHSLG)
780 850 FEOHCNT1=CFEOHSLG)-CFEOHCAK1)
790 853 FEOHCAK2=(FEOHCNT1)"(REFEOH2)
800 856 FEOHCNT2=(FEOHCNT1)::(1.-REFEOH2)
805
250
-------
8IOC NO FE(OH)3 IN ASH STREAMS OR SCRUBBER WATER
820 859 FEOHFP=0.0
8JO 862 FEOHFPI=0.0
81)0 861* FEOHRS=0.0
850 867 FEOH8D=0.0
860 870 FEOHCR=0.0
865
870C FE(OH)3 MOT PRESCNT IK EITHER FURNACE 'PRODUCT OR CLASSIFIER ACCEPTS
880 873 REFEOHF=0.0
890 876 REFEOHCL=0.0
900 879 REFFOHFI=0.0
910 880 FEOHSE1=0.0
°20 881 FEOHSE2=0.0
U30 IFCSEREC.EQ.0.0) GO TO 885
935
94CC CALCULATE FE203 IN PRIMARY SLUDGE
950 883 FEOSLG=CCFEOHCAKn::CREFEOF)"C 160./21CFEOH
960 ECAKl)::Cl.-REFEOF)"C160./21't.>CFEOHCAK23::Cl.-REFEOFO"C160./21l*.)
970 S)/Cl.-Cl.-REFE01)"(l.-REFE023-fREFE01)"(PEFEOF)"Cl.-FRBD)"(REFEOCL
9£(J E3-CREFE01)"Cl.-REFEOF3-Cl.-REFEOn::CREFE02)"Cl.-REFEOFO)
990 IF(SEREC.EQ.l.O) GO TO 895
1000 885 FEOSLG=CCFEOHCAK13"CREFFCF)"C160./211».)"Cl.-FRBD)KCREFEOCL))/
1010 C(l.-Cl.-REFE01)::Cl.-REFt02)-(REFE01)"CREFEOF)::Cl.-FRBD):!(REF
1020 SEOCL))
1025
1030C CALCUALTE FE203 IN CTJ-ER STREAMS
1040 B95 FEOCAK1=FEOSLG:H'PEFE01)
1050 898 FEOCHT1=FEOSLG"C1.-PEFE01)
1060 901 FEOCAK2=FEOCNT1::(REFE02)
1070 905 FEOCNT2=FEOCNT1"(1.-REFE02)
1080 908 FEOFP=FEOCAKl-CP.EFEOF>|.FEOHCAKl"CREFEOF5«Cl60./21lt.)
1090 910 FEOBD=FEOFP:;(FRBD)
1100 911 FE01P=0.0
1110 912 FEORS=FEOFP::(1.-FRBD)"(REFEOCL)
1120 911* FEOCR=FEOFP;:C1.-FRBD):;C1.-REFEOCL)
1130 916 FEOFPI = FEOCAK2"CREFECFI>(FEOHCAK2)::CREFEOFO
1140 917 FEOSEl=FEOCAKl"Cl.-REFEOF>CFEOHCAKl)"(l.-REFEOF);5C160./21't.)
1150 IF(SEREC.EQ.O.O) GO TO 919
1155
1160C CALCULATE CA3CTO14)2 IN PRIMARY SLUDGE
1170 918 CAPSLG=CCPINF-PEFF)"(310./62.)VC1.-C1.-RECAP13"C1.-RECAP2)-CRECA
1180 GP1)::CRECAPF)::(1.-FRBD)::CRECAPCL)-CRECAP1)::C1.-RECAPF)-C1.-RECAP1)
1190 5::Cl-.-RECAPFI)::CRECAP2))
1200 IFCSEREC.EQ.1.0) GO TO 921
1210 919 CAPSLG=CCPn^F-PEFF)"C310./62.))/Cl.-Cl.-RECAPl)::(l.-RECAP2)-CRECA
1220 6P1)::CRECAPF)::C1.-FRBD)"CRECAPCL)5
1225
1230C CALCULATE CA3CP0452 IN OTHER STREAMS
1240 921 CAPlP:(PlNF-PEFF}"(31G./62.:>
1250 922 CAPCAK1=CAPSLG::CRECAP1)
1260 923 CAPFP=CAPCAK1;:CRECAPF)
1270 925 CAPCrm=CAPSLG::Cl.-RECAPl)
1280 927 CAPCAK2=CAPCNT1::CRECAP2)
1290 929 CAPCNT2=CAPCNT1::O.-RECAP2)
1300 931 CAPFPI=CAPCAK2::CRECAPFO
1310 933 CAPBD=CAPFP;:(FRBD)
1320 935 CAPRS=CAPFP::C1.-FP.BD)"(RECAPCL)
1330 937 CAPCR=CAPFP;:Cl.-FRBD)::Cl.-RECAPCO
13"tO 939 CAPSE1=CAPCAK1:!O.-RECAPF)
1350 940 CAPSE2=CAPCAK2::C1.-RECAPFO
1355
1360C CALCULATE MGCOH52 IN PRIMARY SLUDGE
137C 941 XMSHSLG=C(XMGINF-XMGEFF);:C58.3/2'*.3))/Cl.-Cl.-REXMGH13::(l.-REXMGH2
1380 £))
1385
1390C CALCULATE MGCOH)2 IN OTHER STREAMS
mOO 942 XNGHlP=C>T-lGINF-X/'GEFF)::C58.4/2'*.3!)
1410 943 XMGHCAK1=W1GHSLG::CREXMGH1)
1420 945 X)-1SHCNT1=XMGHSLG::C1.-REXM5H1)
1430 947 X)-T,HCAK2=CXMGHCNTiy:(REXMG-H2)
11)1*0 949 X/-1GHCNT2=CXt-1GHCNTl)::(l.-REXMGH2)
1445
1450C NO MG(OH)2 IN ASH STREAMS
1460 951 XMSHFP=0.0
1470 953 >MGHRS=0.0
1480 955 XMGHED=0.0
1490 957 XMGHFPI=0.0
1500 959 X)«HCR=0.0
1505
251
-------
-1510C NO MGCOH)2 PRESENT IN EITHER FURNACE PRODUCT OR CLASSIFIER ACCEPTS
1520 961 REXMGHF=0.0
1530 963 REXMGHFI=0.0
15W 965 REXMGHCL=0.0
IS'tS
1550C NO MG(OH)2 IN SCRUBBER WATER
1560 966 XMGHSE1=0.0
1570 967 XM6HSE2=0.0
1575
1580C CALCULATE ORGANICS IN PRIMARY SLUDGE
1590 969 OR6SLG=CCXLBSSIN)::(FRVSSIN>CXLBWASIN)"CFRVWASIN)-CXLBSSOUT>(FRVS
1600 £50UT))/C1.-C1.-REORGO"C1.-REORG2))
1605
1610C CALCULATE ORGANICS IN OTHER LIQUID STREAMS
1620 972 ORG1P=(XLBSSIN)"CFRVSSINMXLBWASIN)"CFRVWASIN)-XLBSSOUT"FRVSSOUT
1630 973 ORGCAK1=ORGSLG"(REORG1)
^O 975 ORGCNT1=ORGSLG"C1.-REORG1)
1650 977 ORGCAK2=ORGCNT1"(REORG2)
1660 979 ORGCNT2=ORGCNT1::(1.-REORG2)
1665
1670C NO ORGANICS IN ASH STREAMS
1680 981 ORGFP=0.0
1690 983 ORGFPI=0.0
1700 985 ORGCR=0.0
1710 987 ORGBD=0.0
1720 989 ORGRS=0.0
1725
1730C NO ORGANICS IN SCRUBBER WATER
17itO 990 ORGSE1=0.0
1750 991 ORGSE2=0.0
1760 992 REORGF=0.0
1765
1770C ORGANICS NOT PRESENT IN EITHER FURNACE PRODUCT OR SCRUBBER WATER
1780 993 RFORGFI=0.0
1790 995 REORGCL=0.0
1800 IFCSEREC.EQ.0.0) GO TO 998
1805
1810C CALCULATE CAC03 IN PRIMARY SLUDGE
1820 997 CACSLG=CCCAINF-CAEFF)"C100.AO.)+(CAOTOTLB)"(100./56.)-CPINF-PEFF)
1830 S'!C120./62.0)::(100./1tO.))/Cl.--CRECACl)"(RECACf->"Cl.-FRBD):;CREMCCL)
1840 6::Cl.-RECALEFF)-(l.-RECACl)"(;i.-RECAC2)-CRECACl)"(l.-RECACF)-Cl.-RE
1850 6CACO"CRECAC2)::C1.-RECACFI))
1860 IFCSEREC.EQ.1.0) GO TO 1000
1870 998 CACSLG=((CAINF-CAEFF)"C100./'tOO+CCAOTOTLB)::C100./56.)-CPIMF-PEFF)
1880 S::C120./62.0)"C 100./<*0. ))/(!.-CRECACn::CRECACF)"Cl.-FRBD)"CRECACCL)
1890 E::C1.-RECALEFF)-C1.-RECAC1)::C1.-RECAC2))
1895
1900C CALCULATE CAC03 IN OTHER STREAMS
1910 1000 CAClPiCCAINF-CAEFFJ-ClOO./^OO+CAOTOTLB-ClOO./se.J-CPIMF-PEFF^'Cl
1920 C20./62.)::(100./I)0.)
1930 1001 CACCAK1=CACSLG"CRECACO
ig'tO 1002 CACFP=CRECACF)::CCACCAK1)::C1.-RECALEFF)
1950 lOOll CACCNT1=CACSLG::C1.-RECAC1)
1960 1007 CACCAK.2=CACCNT1"CRECAC2)
1970 1009 CACCNT2=CACCNT1"(1.-RECAC2)
1980 1011 CACFPI=CACCAK2"CRECACFO
1990 1012 CACSE1 = (CACCAK1)"G.-RECACF)
2000 1013 CACSE2=CACCAK2"(1.-RECACFO
2010 1015 CACBD=CACFP"(FRBD)
2020 1017 CACRS=CACFP"C1.-FRBD)"CRECACCL)
2030 1018 CACCR=CACFP"C1.-FRBD)"C1.-RECACCL)
2035
20"*OC CALCULATE CAO IN RECALCIMATION FURNACE PRODUCT
2050 1019 CAOFP=CACCAK1::(R£CACF>:CRECALEFF)"C56./100.)
2055
2060C CALCULATE CAO IN THE SLOWDOWN AND CLASSIFIER STREAMS
2070 1021 CAOBD=(CAOFP3::(FRBD)
2080 1023 CAORS=CAOFP"a.-FRBD)"CRECAOCL)
2090 1025 CAOCR=CAOFP"C1.-FRBD)"C1.-RECAOCL)
2095
2100C CALCULATE NEW LIME REQUIRED
2110 1027 CAONEW=CAOTOTLB-CAORS
2115
2120C NO CAO IN RECALCINE FURNACE SCRUBBER WATER
2130 1028 CAOSE1=0.0
2135
21<*OC NO CAO IN INCINERATION FURNACE WASTE ASH
2150 1029 RECAOFI=0.0
2160 1031 TOTLBNEW=CAONEW/FRCAONEW
2165
2170C NO CAO IN SECOND STAGE DEWATERING STREAMS
2180 1033 RECA02=0.0
2190 1035 CAOM"GL=CCAOMEW)/C8.33KXMGD)
2195
252
-------
2200C NO CAO IN FIRST STAGE DEV/ATERING STREAMS
2210 1037 RECA01=0.0
2220 1039 CAORM6L=CCAORSVC8.33::XMGD)
2225
2230C NO CAO IN SECOND STAGE CENTRATE
221)0 1041 CAOCNT2=0.0
2250 1042 SLMDOS^CAONMGL+CAORMGL
2260 1044 CAORSFRA=CAORMGL/SUMDOS
2265
2270C NO CAO IN LIQUID STREAMS
2280 1047 CAOCAK2=0.0
2290 1048 CA01P=0.0
2300 1049 CAOSLG=0.0
2310 1051 CAOCAK1=0.0
2320 1055 CAOCNT1=0.0
2330 1056 CAOSE2=0.0
2335
2340C NO CAO IN INCINERATION FURNACE WASTE ASH
2350 1057 CAOFPI=0.0
2355
2360C SUM THE SOURCES OF ACID INSOL.INERTSCEXCEPT SILICA INTO THE PRIMARY ON FIRST PASS
2370 1061 AIIIN= (TOTLBNEW)"CFRAIINnO+CXLBSSIN)::CFRAIISSO+(XLBWASIN)«
2380 ECFRAIIWAS)
2385
2390C CALCULATE ACID INSOL.INERTS PRECIPITATED ON FIRST PASS
2400 AII1P=AIIIN-AIIEFF
2410 1062 AIIINMGL=AIIIN/C8.J3!!XMGD)
2420 IF(SEREC.EQ.O.O) GO TO 1064
2425
2430C CALCULATE ACID INSOL.INERTS IN PRIMARY SLUDGE
2440 1063 AI ISLG=C(AinN)-CAIIEFF5)/(l.-Cl.-REAIIl)::Cl.-REAII2>CREAIIl):!CRE
2450 £AIIF)"C1.-FRB03::(REAIICL)-(1.-REAII1)::(REAII2)::(1.-REAIIFO-(REAII
2460 C13-C1.-REAIIF))
2470 IF(SEREC.EQ.l.O) GO TO 1065
2480 1064 AIISLG=CCAlIIN-AIIEFF3)/Cl.-Cl.-REAin)"Cl.-REAII2>CREAII13«CRE
2490 CAII F)::(l. -FRBD)"(REAI ICD)
2495
2500C CALCULATE ACID INSOL.INERTS IN OTHER STREAMS
2510 1065 AnFP=CAIISLrO"(REAin)xCREA1IF)
2520 1067 AIICAKl=CAIISLC,):;CREAnl)
2530 1071 Al 1CNT1 = (A11SLG)::(1.-REAII1)
2540 1073 A1ICAK2=(AI1CNT1)"CREA112)
2550 1075 A1ICNT2=(AIICNT1)"(1.-REAI12)
2560 1077 AIIBn=(A!IFP)"(rRBD)
2570 1079 AIIRS=CAIirFO::(l.-FRBD)"CREA!ICL)
2580 1081 AI]FP1 = (AI ICAIO)"(RCA1IF1)
2590 1083 AIICR=(AIirr)::(].-FRBn):!Cl.-REAnCL)
2f,oo
2610 103
2615
2620C SUM THE SOURCES OF SI02 INTO THE PRIMARY ON THE FIRST PASS
2630 1085 SIIN= (XLBSSIN)::(FRSISSD+(XLBWASIN;)"(FRSIWAS>4-CTOTLBNEVO"(FRS
2640 SINEW>+CSIIND)
2645
2650C CALCULATE SI02 PRECIPITATED ON THE FIRST PASS
2660 S1021P=SIH1-SIEFF
2670 1086 SIIMMGL=SIIN/C8.33::XMGD:)
2680 IF(SEREC.EQ.O.O) GO TO 1088
2685
2690C CALCULATE SI02 IN THE PRIMARY SLUDGE
2700 1087 SISLG:CCSIIN5-CSIEFF))/C1.-C1.-RESI1)"C1.-RESI2)-CPESIO"CRESIF)::(
2710 Sl.-FRBO>:CRESICL>Cl.-RESIl)"CRESI2)"Cl.-RESIFO-CRESIir"Cl.-RESIF
2720 6)5
2730 IF(SEREC.EQ.l.O) GO TO 1089
2740 1038 SISLG=CCSIIN)-(SIEFF))/C1.-C1.-RESI1)::C1.-RESI2)-CRESI13"CRESIF)::(
2750 £1.-FRBD)::CRESICL))
2760 1089 SIEFFMGL=S[trF/(8.33"XMGD)
2765
2770C CALCULATE SI02 IN OTHER STREAMS
2780 1090 S!FD-CS!SLG}"CP.E5I1)::CP.ES!F)
2790 1091 SICAK1=CSISLG)"(RESI1)
2800 1093 SICNT1=(SISLG)"C1.-RESI1)
2810 1095 SICAK2=CSICNT1)::CRESI2)
2820 1097 SICNT2=(SICNT1)"O.-RESI2)
2830 1099 SIBD=CSIFP);:(FRED)
2840 1101 SIRS=CSIFP)"(1.-FRED)"CRESICL)
2850 1103 SIFPI = (SICAK2)"(PESIFD
2860 1105 SICR=CSIFP)"(1.-FRBD5"C1.-RESICL)
2870 1106 SISE1=SICAK1;:C1.-RESIF)
2875
5880C CALCULATE MGO INPUT FROM NEW LIME
2890 1107 XMGONEW=(FP>'GCt\EW):;(TOTLBNEVO
2900 1108 XMG01P=XMT,ONEW
253
-------
2910 IF(SEREC.EQ.O.O) GO TO 1110
2915
2920C CALCULATE MGO IN PRIMARY SLUDGE
2930 1109 XMGOSLG=CCXMGHCAKn::CREXWOF)"(l.-FRED)"CREXMGOCL)::C'tO./58.3>Cl.
29M S-REXMGOF)"CXMGHCAKl5:;CttO./58.3>CXMGONEV,0+Cl.-REXMGOFO"CXNGHCAX2
2950 £)"CitO./58.3))/(l.-Cl.-REXMGOO"Cl.-REXMG02)-CREXMGOn!!CREXMGOF)»CR
2960 £EXW»CL>Xl.-FRBD)-a.-REXMGOF):KREXMG01)-(l.-REXMG01)"(REXMG02)"(
2970 El.-REXMGOFI))
2980 IFCSEREC.EQ.1.0) GO TO 1111
2990 1110 XMGOSLG=((XN1GHCAia)"(REXMGOF)"a.-FRBD)"(REXMGOCL)"(40./58.3)
3000 6+CXMGONEW))/a.-Cl.^EXMG01)"a.-REXMG02)-(REXMG01)"(REXMGOF)"(R
3010 SEXMGOCL)"(1.-FRBD))
3015
3020C CALCULATE MGO IN OTHER STREAMS
3030 1111 XMGOCAK1=XMGOSLG::CREXMG01)
3040 1113 XMGOCNT1=XMGOSLG"C1.-REXMGO1)
3050 1115 XMGOCAK2=XMGOCNT1::CREXMG02)
3060 1117 XMGOCNT2=XMGOCNT1::O.-REXMG02)
3070 1119 XMGOFP=XMGOCAKl"CRE»COF)+XMGHCAKl::CREXMGOF)::C'tO./58.3)
3080 1121 XMGOBD=XMGOFP"(FRBD)
3090 1123 XMC-OP.S=XMGOFP"(1.-FRBD)::(REXMSOCL)
3100 1125 XMGOCR= XMGOFP"(1.-FR£D);:(1.-REXMGOCL)
3110 1127 XMGOFPI=XMGOMK2"CREXMGOFI)4.(XMGHCAK2)"(REXMGOFI)
3120 1129 XMWSEl = (XMTOCAKl)"(l.-REXMGOF)4XMC-HCAK2"Cl.-REXMGOFI)"C1*0./58.3)
311(0 1132 FEOSE2=FEOCAK2"a.-REFEOFI)+(FEOHCAK2)"a.-REFEOFl)::a60./210
3530 367 FOF^WT(8X,F5.2,1GX,F5.2)
3540 415 FORMO,T(1H-,35H "PRIhWRY SLUDGE COMPONENTS,LB/DAY")
3550 420 FGRKAT(lH-,/9H ORGANICS,16X,F9.0,1H ,/4H CAO,21X,F9.0,1M ,/6M CACO
3560 83,19X,F9.0,1H ,/4H MGO,21X,F9.0,1H ,/8H MG(OH)2,17X,F9.0,1H ,/6H F
3570 SE203,19X,F9.0,1H ,/8H FECOH)3, 17X..F9 . 0,1H ,/5H SI02, 20X, F9 .0,1H ,
3580 S/19H ACID If.,SOL. INERTS,6X, F9.0, 1H ,/10H CA3CP04)2,15X,F9. 0.//6H T
3590 EOTAL,17X,FU.O)
3600 400 FORMATO-H-, //f.4H : PRIMARY EFFLUENT COMPOSITION MG/L
3610 6 ")
3620 410 FORMATCeW "SUSP.SOLIDS"WGNESIUH"CALCIUM"PHOSPHORUS"SI02"A. I INE
3630 CRTS::IROM::)
3640 411' FORMAT(5X,F5.1,6X, FJ. l,"tX,F5. 1,4X,F6.2, 3X,F5 . 1, 2X,F5. 1, 2X,F6.2)
3650 430 FORMAT(lH-,//37H -FIRST STAGE CAKE COMPONENTS,LB/DAY")
3660 440 FORMAT(lH-,//50H "RECALCINATION FURNACE PRODUCT COMPONENTS,LB/DAY"
3670 E)
3680 450 FORMATClH-,//41H "FIRST STAGE CENTRATE COMPONENTS,LB/DAY")
3690 460 FORMATClH-,//38H "SECOND STAGE CAKE COMPONENTS,LB/DAY")
3700 470 FORMAT(lH-,//50H "SECOND STAGE CENTRATE RECYCLE COMPONENTS,LB/DAY"
3710 5)
254
-------
3720 "480 FORMAT(lH-,//51H "INCItERATION FURNACE WASTE ASH COMPONENTS,LB/DAY
3730 e:0
3740 490 FORMAT OH-,//51H ::RECALCINATION FURMACE SLOWDOWN COMPONENTS, LB/DAY
3750 6")
3760 495 FORMAT(lH-,//4J*H "RECYCLED SOLIDS ACCEPTS COMPONENTS, LB/DAY")
3770 500 FORMATClH-,//3SH -CLASSIFIER REJECTS COMPONENTS, LB/DAY")
3780 505 FORMAT(lH-,//55H -RECOVERIES OF COMPONENTS IN PROCESS STREAMS,FRAC
3790 ETION")
3800 508 FORMATC55H FIRST " RECALCINE "SECOND"INCINEFATION" DRY)
3810 510 FORMATC55H STAGE STAGE )
3820 515 FORMATC60H CAKE FURNACE CAKE FURNACE CLASS!
3830 EFIER)
3840 518 FORMAT(1H1,/9H ORGANICS, 3X.F4.2, 7X, F4.1, 5X, F4 . 2, 6X, F4 . 2, 7X, F4. 2)
3850 520 FO,VWT(im,/4H CAO, 8X,F4.2, 7X, F4. 2, 5X, F4 . 2, 6X, F4. 2, 7X,F4. 2)
3860 522 FORMAT(1H1,/6H CAC03,6X,F4.2,7X, F4. 2, 5X,F4.2,6X,F4.2,7X,F4.2)
3870 525 FORMAT(1H1,/4H MGO, 8X,F4. 2, 7X, F4. 2, 5X, F4. 2, 6X, F4 . 2, 7X, F4. 2)
3880 530 FOPMATC1H1,/8H MG(OH)2,4X, F4. 1, 7X, F4. 2, 5X,F4 . 2, 6X, F4 . 2, 7X,F4 . 2)
3890 535 FORMAT(1H1,/6H FE203,6X,F't.2/7X,Flt.2,5X,Fl|.2,6X,Fl(.2,7X,F'*.2)
3900 540 FOPMATCIHI^/SH FECOH^,1)/, F4. 2, 7X,F4 . 2, 5X, F4. 2, 6X, F4. 2, 7X,F<*.2)
3910 545 FOPJ^TC1H1,/5H SI02,7X,F4.2, 7X,F4.2, 5X, F4. 2, 6X,F4. 2, 7X,F4.2)
3920 550 FOPJ-'ATClHl,/?^! IKERTS, 5X, F4. 2, 7X, F4 . 2, 5X, F4. 2, 6X,F4.2, 7X, F4. 2)
3930 551 FORMATC1H1,/10H CA3(P04)2,2X, F4.2, 7X, F4.2,5X, F4.2,6X, F4.2, 7X,F4.2)
3940 553 FORMAT(1H1,/6H TOTAL,6X, F4. 2, 16X, F4. 2, 17X, F4. 2)
3950 560 FORMATClHl,44H::r.'BV MAKEUP LIME ADDED, FRACTION COMPOSITIONK)
3960 570 FORMATC1H1,44H;'- SI02 :; ACID INSOL. INERTS :: MGO "CAO ")
3970 573 FORMATC2X,F5.2,9X,F5.2,11X,F5.2, 2X,F5.2)
3980 620 FORMAT(lH-,//6'*H " PRIMARY INFLUENT COMPOSITION,MG/L
3990 S ")
4000 630 FORMATC64H "SUSP.SOLIDS"MAGNESIUM::CALCIUM"PHOSPHORUS"SI02"A. I . INE
4010 CRTS::IRON::)
4020 633 FORMATC5X,F5.1,6X,F5.1,4X,F5.1,4X,F6.2,3X,F5.1,2X,F5.1,2X,F6.2)
4030 1199 PRINT 301
4040 1200 PRINT 300
4050 1201 PRINT 301
4060 1205 PRINT 310
4070 1210 PRINT 315
4080 1215 PRINT 320
4090 1220 PRINT 321,PH,XMGD,CAOTOMGL/CAONMGL,CAORMGL,CAORSFRA
4100 1221 PRINT 301
4110 1225 PRINT 340
4120 1240 PRINT 350
4130 1250 PRINT 353,FECL3M;L,X1_BWASIN
4140 1251 PRINT 301
4150 1260 PRINT 360
4160 1270 PRINT 365
4170 1280 PRINT 367,FRBO,RECALEFF
4180 1281 PRINT 301
4190 1290 PRINT 560
4200 1300 PRINT 570
4210 1310 PRINT 573,FRSINEW,-FRAIINEW,FRMGONEW,FRCAONEW
4220 1311 PRINT 301
4230 1390 PRINT 620
4240 1400 PRINT 630
4250 1410 PRINT 633,SSINM£L,XMGINMGL,CAINFMGL,PINFMGL,SI INMGL,AI IINMGL, FE1NFMGL
4260 1420 PRINT 400
4270 1430 PRINT 410
4280 1432 PRINT 411, SSOUT>GL,XMGEFMGL,CAEFFMGL,PEFFMGL, SIEFFMGL.AI IEFMGL,
4290 EFEEFFMGL
4300 1433 PRINT 301
4310 1434 PRINT 354
4320 1435 PRINT 420,ORG1P,CA01P,CAC1P,XMG01P,XMGH1P/FE01P,FEOH1P,SI021P,
4330 £AII1P,CAP1P,TOT13
4340 1436 PRINT 301
4350 1440 PRINT 415
4360 1450 PRINT 420,ORGSLG,CAOSLG,CACSLG,XMGOSLG,XMGHSLG,FEOSLG,FEOHSLG,SISI_
4370 CG,AIISLG,CAPSLG,TOT1
4380 1453 PRINT 301
4390 1460 PRINT 430
4400 1470 PRINT 1)20,ORGCAK1,CAOCAK1,CACCAK1,XMSOCAK1,XM6HCAK1,FEOCAK1,FEOHCA
4410 SK1,SICAK1,AIICAIU,CAPCAK1,TOT2
4420 1473 PRINT 301
4430 1475 PRINT 450
4440 1476 PRINT 420,ORGOrTl,WOCrrrl,CACCOTl,XMSOChn-l,X>WHCNTl,FECOJT:,FEOHCN
4450 CTl,SICNTl,AnCNTl,CAPCMTl,TOT3
4460 1477 PRINT 301
4470 1480 PRINT 440
4480 1490 PRINT 4:0,ORGFP,CAOFP,CACFP,XMGOFP/XMGHFP, FEOFP, FEOHFP,SIFP-, AIIFF
4490 CCAPFP, TOT4
4500 1492 PRINT 301
4510 1493 PRINT 355
4520 1494 PRINT 420,ORGSEl,C/>OSEl,CACSEl,XMr.OSEl,XMf.HSEl,FEOSEl,FEOHSEl,SISE
255
-------
1(530 n,AIISrl,CAPSEl,TOT5
WO 1495 PRINT 501
WO 11(06 PRINT 1(95
1(560 1497 PRINT 1(20,ORGRS.CAORS^CRS.XMTORSjXWHRS^ORS^EOI-RS,SIRS,AI IRS,
1(570 try\fR5,TOT6
1(580 1418 PPIW 301
man lU'iu irmjt:i*\rr..f:o.j.o} co TO jn»-
1(600 1500 PRINT i(60
1(610 1510 PRINT M20,ORGCAK2,CWD«2/CACCAK2,X^^XAK2/»KHCAK2,FEOCAK2,FEaHCA
1(620 CK2,SICAK2,AIICAK2,CAPCAK2,TOT7
1(630 1511 CONTINUE
i(6i(0 1513 PRINT 301
1(650 1560 PRINT 1(70
1(660 1570 PRINT i(20,ORG<>rn/aMX^2,CACCNT2,XMGOChlT2,XMGHCNT2,FEOCNT2/FEOHCN
1(670 ET2,SICNT2,AIICNT2,CAPCNT2,TOT8
1(680 1575 PRINT 301
"(690 1580 PRINT 1(80
1(700 1590 PRINT lt20,ORGFPI,CAOFPI,CACFPI/XMGOFPI,XNGHFPI,FEOFPI,FEOHFPI,SIFP
1(710 SI,AIIFPI,CAPFPI,TOT9
1(720 1595 PRINT 301
1(730 1596 PRINT 356
1(71(0 1597 PRINT 420,ORGSE2,U\OSE2,CACSE2,XMGOSE2,XMGHSE2,FEOSE2,FEOHSE2,SISE
"(750 62,AIISE2,CAPSE2,TOT10
1(760 1598 PRINT 301
1(770 1599 CONTINUE
1(780 1600 IF(FRBD.EQ.O.O) GO TO 1617
1(790 1601 PRINT 1(90
1(800 1603 PRINT 420,ORGBD,CAOBD,CACBD,XMGOBD,XMGHBD,FEOBD,FEOHBD,SIBD,AIIBD,
"(810 &CAPBD,TOT11
1(820 1617 CONTINUE
"(830 1620 IFCCLASSIF.EQ.O.O) GO TO 1650
1(840 1630 PRINT 500
1(850 161(0 PRINT l+20,ORGCR,CAOCR,CACCR,XMGOCR,XMGHCR,FEOCR,FEOHCR,SICR,AIICR/
1(860 ECAPCR,TOT12
1*870 161(3 PRINT 301
1(880 1650 PRINT 505
1(890 1652 PRINT 301
1(900 1660 PRINT 508
1(910 1670 PRINT 510
1(920 1680 PRINT 515
1(930 1690 PRINT 518/REORG1,REORGF,REORG2,REORGFI,REORGCL
1(940 1695 PRINT 520,RECA01,RECACF,RECA02,RECAOFI,RECAOCL
4950 1700 PRINT 522,RECAC1,RECACF,RECAC2,RECACFI,RECACCL
4960 1710 PRINT 525,REXMGG1,REXMGOF,REXM»2,REXMSOFI,REXMGOCL
4970 1720 PRINT 530,REXMGH1,REXMGHF, REXMGH2,REXMGHFI ,REXMGHCL
4980 1730 PRINT 535,REFE01,REFEOF,REFE02,REFEOFI,REFEOCL
4990 1740 PRINT 540,REFEOH1,REFEOHF,REFEOH2,REFEOHFI,REFEOHCL
5000 1750 PRINT 545,RESI1,RESIF,RESI2,RESIFI,RESICL
5010 1760 PRINT 550,REAII1,REAIIF,REAII2,REAIIFI,REAIICL
5020 1761 PRINT 551,RECAP1,RECAPF,RECAP2,RECAPFI,RECAPCL
5030 1762 PRINT 553,TOTRE1,TOTRE2,TOTRECL
5040 1763 CONTINUE
5050 1800 STOP;END
256
-------
APPENDIX B
OUTPUT FOR CASES
257
-------
Table B-1 . CASE DESCRIPTIONS
a
Case no.
100b
lolh
102b
103°
104°
105°
106°
107 =
108
109°
iioc
111°
112°
113C
114C
115C
116°
117b
118b
119
!2°H,
b d
121K
h e
122 '
First stage wet
classification
Centrifuge
Centrifuge
Centrifuge
Centrifuge
Centrifuge
Centrifuge
Centrifuge
Centrifuge
Centrifuge
Centrifuge
Centrifuge
Centrifuge
Centrifuge
Vacuum filter
Vacuum filter
Pressure filter
Pressure filter
Centrifuge
Centrifuge
Centrifuge
Centrifuge
Centrifuge
Centrifuge
Second stage
dewatering
Centrifuge
Vacuum filter
Pressure filter
None
None
None
None
None
None
None
None
None
None
None
None
None
None
Centrifuge
Centrifuge
Centrifuge
Centrifuge
Centrifuge
Centrifuge
Incineration of
second stage cake
Yes
Yes
Yes
No
No
No
No
No
No
No
No
No
No
No
No
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Classifier for
recalcined
product
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
No
Yes
Yes
Slowdown of
recalcination
furnace product,
percent
0
0
0
0
10
15
20
24
28
31
35
45
100
0
20
0
20
0
20
24
28
0
0
All cases are for the following conditions (unless noted):
pH: 11.0
Primary flow: 1.31 cu m/sec
Fed, dose to primary: 14.0mg/l
Ca(OH)2dose: 400.0mg/l
ATTF System case
Plural Purpose Furnace case
pH 10.2, 289 mg/1 Ca(OH) 24.0 rng/1 Fed.
£ 3
pH 11.5, 500 mg/1 Ca(OH) 0.0 mg/1 Fed,
L, O
258
-------
CASE 100
"FIRST PASS PRECIPITATION COMPONENTS,LB/DAY:1
DAT1
110,30.0,97%.0, lit.0,400.0,0.0,0.95
115,2.0,1.0, 11.0,1.0,0.0,0.0,0.0
DAT2
131,2:PH - MGD-TOTAL DOSE-NEW LIf-€>! RECYCLED LIME"
MG/L MG/L MG/L FRACTION
11.0 30.00 302.7 113.7 189.0 0.62
"FECL3 DOSE:=WASTE BIOLOGICAL SLUDGE"
" MG/L " ADDED, LB/DAY K
14.0 9746.0
ORGAN ICS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
23309.
0.
97327.
1817.
2368.
255.
743.
9047.
1683.
3401.
139950.
"FIRST STAGE CENTRATE COMPONENTS, LB/DAYI!
^FURNACE BLOVOCH*JKRECALCINING EFFICIENCY"
* FRACTION » FRACTION x
0. 0.95
"NEW MAKEUP LIME ADDED,FRACTION OPPOSITION"
" SI02 " ACID INSOL. INERTS K MGO "CAO "
0.03 0.01 0.07 0.89
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
34963.
0.
20645.
4912.
6402.
596.
1734.
1005.
503.
13603.
84363.
>'• PRIMARY INFLUENT COMPOSITION,MG/L «
>:SUSP.SOLIDSItMAGNESIUM"-CALCIUM:IPHOSPHORUS::SI02'1A. I. INERTS11! RON"
240.0 22.3 30.0 10.00 13.2 1.9 0.
K PRIMARY EFFLUENT COMPOSITION,MG/L «
XSUSP.SOLIDS1!MAGNESIUM!;CALCIUM"PHOSPHORUSI!SI02':A. I . INERTS"IRON"
26.0 8.7 60.0 0.68 0.9 0.1 0.
"RECALCINATION FURNACE PRODUCT COMPONENTS, LB/DAY*
ORGAN ICS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
0.
48154.
4526.
3166.
0.
770.
0.
8866.
1464.
3197.
70143.
259
-------
"RECALCINATION FURNACE WET SCRUBBER WATER COMPONENTS,LB/DAY"
"INCINERATION FURNACE WET SCRUBBER WATER COMPONENTS,LB/DAY*
ORGAN I CS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL. INERTS
CA3CP04)2
TOTAL
0.
0.
6813!
275.
0.
41.
0.
181.
219.
201*.
7733.
ilNV, ll^lUVt 1 1 Win I i^ruinvt m^ I
ORGANICS
CAO
CAC03
MGC
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL. INERTS
CA3CPO"O2
1 J^f\ULJU[_l\
0.
0.
11(31.
670.
0.
85.
0.
20.
53.
735.
TOTAL
2993.
"RECYCLED SOLIDS ACCEPTS- COMPONENTS, LB/DAY«
TOTAL
66583.
''-CLASSIFIER REJECTS COMPONENTS, LB/DAY«
ORGANICS
CAO
CAC03
MOO
MG(OH)2
•FE203
FECOH03
SI02
ACID INSOL. INERTS
CA3CP04)2
0.
"47239.
4453.
3059.
0.
666.
0.
6747.
1360.
3059.
ORGANICS
CAO
CAC03
MSO
MGCOH)2
FE203
FECOH)3
SI02
ACID INSOL. INERTS
CA3CP04)2
0.
915.
72.
108.
0.
105.
0.
2119.
104,
137.
TOTAL
3560.
"SECOND STAGE CAKE COMPONENTS, LB/DAY«
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FE(OH)3
SI02
ACID INSOL. INERTS
CA3(P04)2
27271.
0.
20439.
4421.
5762.
536.
1561.
975.
407.
12242.
"RECOVERIES OF COMPONENTS IN PROCESS STREAMS,FRACTION"
TOTAL
7361"(.
FIRST " RECALCINE 1!SECOND«INCINERATION!! DRY
STAGE
CAKE FURNACE
"SECOND STAGE CENTRATE
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FECOH)3
SI02
ACID INSOL. INERTS
CA3(P04)2
TOTAL
-INCINERATION FURMACE
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL. INERTS
CA3CP04)2
RECYCLE COMPONENTS, LB/DAY"
7692.
0.
206.
1(91.
61(0.
60.
173.
30.
96.
1360.
1071(9.
WASTE ASH COMPONENTS, LB/DAYK
0.
0.
19008.
9369.
0.
1992.
0.
956.
354.
11508.
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH33
SI02
INERTS
CA3CPQ1O2
TOTAL
0.40
0.
0.83
0.27
0.27
0.30
0.30
0.90
0.77
0.20
0.62
0.
0.93
0.93
0.92
0.
0.95
0.
0.98
0.87
0.9"(
STAGE
CAKE FURNACE
0.78
0.
0.99
0.90
0.90
0.90
0.90
0.97
0.81
0.90
0.87
0.
0.
0.93
0.92
0.
0.95
0.
0.98
0.87
0.9"(
CLASSIFIER
0.
0.98
0.98
0.97
0.
0.86
0.
0.76
0.93
0.96
0.95
PROGRAM STOP AT 3250
USED
.91 UNITS
TOTAL
43186.
260
-------
CASE 101
DAT1
110,30. 0,9746.0,14. 0,1*00.0,0.0,0.95
115,2.0,1.0,11.0,1.0,0.0,0.0,0.0
DAT2
131,240. 0,26.0,22.3,8.7"*, 30.0,60.0
132,10.0,0.68,0.0,0.0024,0.002'*
141,0.035,0.0024,0.80,0.80,0.80
151,0.035,0.035,0.027,0.0096,0.07,0.89
DAT3
161,0.20,0.825,0.90,0.77
171,0.27,0.27,0.30,0.30,0.40
181,0.94,0.94,0.94,0.94,0.9"»
182,0.94,0.94,0.94,0.94
191,0.94,0.93,0.98,0.87,0.0
192,0.95,0.0,0.0,0.92
201,0.94,0.93,0.98,0.87,0.0
202,0.95,0.0,0.0,0.92
211,0.957,0.984,0.761,0.929,0.0,0.981
212,0.864,0.0,0.0,0.966
LIME SOLIDS PROCESSING MASS BALANCE
" "FLOW- LIME USE AS CAO «
::PH - MGD'H'OTAL C«SE"NEW LIME" RECYCLED LIME"
MG/L MS/L MG/L FRACTION
11.0 30.00 302.7 111.9 190.8 0.63
"FIRST PASS PRECIPITATION COMPONENTS,LB/DAY"
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
50580.
0.
105069.
2200.
8144.
0.
2304.
3061.
453.
1.1645.
183456.
"PRIMARY SLUDGE COMPONENTS,LB/DAY"
ORGANICS
CAO
CAC03
MGO
MGCOO2
FE203
FECOH53
SI02
ACID INSOL.
CA3CP04)2
TOTAL
INERTS
52469.
0.
119060,
6324.
8502.
797.
2405.
10106.
1924.
16288.
217875.
"FIRST STAGE CAKE COMPONENTS. LB/DAY"
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FECOH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
20987.
0.
98225.
1708.
2296.
239.
721.
9096.
1482.
3258.
138011.
"FECL3 DOSE^ASTE BIOLOGICAL SLUDGE-
•" MG/L " ADDED, LB/DAY *
14.0 9746.0
"FURNACE BLOWDOWN-RECALCINING EFFICIENCY*
" FRACTION " FRACTION K
0. 0.95
:=NEW MAKEUP LIME ADDED, FRACTION COMPOSITION"
" SI02 :: ACID INSOL. INERTS " MGO "-CAO "
0.03 0.01 0.07 0.89
«FIRST STAGE CENTRATE COMPONENTS,LB/DAY"
ORGAfUCS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH03
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
31481.
0.
20836.
4617.
6207.
558.
1683.
1011.
443.
13030.
79865.
"RECALCULATION FURNACE PRODUCT COMPONENTS,LB/DAY-
" PRIMARY INFLUENT COMPOS IT ION,MG/L "
"SUSP.SOLIDS"MAGNESIUM::CALCIUM::PHOSPHORUS"SI02"A. I . INERTS"IRONK
240.0 22.3 30.0 10.00 13.2 1.9 0.
K PRIMARY EFFLUENT COMPOSITIO^MG/L a
«SUSP.SOLIDS::MAGNESIUM::CALC!UM"PHOSPHORUS!;SI02!cA.I.INERTS!tIRON![
26.0 8.7 60.0 0.68 0.9 0.1 0.
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FECOH53
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
0.
48598.
4567.
3020.
0.
7J9.
0.
8914.
1289.
3062.
70190.
261
-------
"RECALCINATION FURNACE WET SCRUBBER WATER COMPONENTS,LB/CWY*
ORGAN ICS
CAO
CAC03
MGO
M6(OH)2
FE203
FECOt-03
SI02
ACID INSOL. INERTS
CA3(P04)2
TOTAL
0.
0.
6876.
263.
0.
39.
0.
182.
193.
195.
7747.
"RECYCLED SOLIDS ACCEPTS COMPONENTS,LB/DAY!1
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH33
SI02
ACID INSOL. INERTS
CA3(P04)2
TOTAL
0.
47674.
4494.
2917.
0.
639.
0.
6783.
1197.
2930.
66636.
"SECOND STAGE CAKE COMPONENTS,LB/DAY*
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
29592.
0.
19585.
4340.
5834.
524.
1582.
950.
416.
12249.
75073.
"INCINERATION FURNACE WET SCRUBBER WATER COMPONENTS, LB/DAY*
ORGAN I CS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
0.
0.
1371.
667.
0.
85.
0.
19.
54.
735.
2932.
"CLASSIFIER REJECTS COMPONENTS, LB/DAY"
ORGAN I CS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL. INERTS
CA3(P04)2
TOTAL
0.
923.
73.
103.
0.
101.
0.
2130.
92.
132.
3553.
RECOVERIES OF COMPONENTS IN PROCESS STREAMS,FRACTION"
"SECOND STAGE CENTRATE RECYCLE COMPONENTS,LB/DAY"
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH)3
SI02
ACID INSOL. INERTS
CA3(P04)2
TOTAL
"INCINERATION FURNACE WASTE
ORGAN I CS
CAO
CAC03
MGO
MGCOH52
FE203
FE(OK)3
SI02
ACID INSOL. INERTS
CA3CP01O2
TrvrAi
1889.
0.
1250.
277.
372.
33.
101.
61.
27.
782.
4792.
ASH COMPONENTS, LB/DAY!!
0.
0.
18214.
9360.
0.
2001.
0.
931.
362.
11514.
FIRST !1 RECALCINE
STAGE
CAKE FURNACE
ORGANICS
CAO
CAC03
MGO
MGCOH52
FE203
FECOH)3
SI02
INERTS
CA3CP04)2
TOTAL
0.40
0.
0.83
0.27
0.27
0.30
0.30
0.90
0.77
0.20
0.63
0.
0.93
0.93
0.92
0.
0.95
0.
0.98
0.87
0.94
!ISECOND!!INCINERATION1! DRY
STAGE
CAKE
0.94
0.
0.94
0.94
0.94
0.94
0.94
0.94
0.94
0.94
0.94
FURNACE
0.
0.
0.93
0.92
0.
0.95
0.
0.98
0.87
0.94
CLASSIFIER
0.
0.98
0.98
0.97
0.
0.86
0.
0.76
0.93
0.96
0.95
PROGRAM STOP AT 3250
USED
.90 UNITS
262
-------
CASE 102
DAT1
110,30.0,97%.0,14.0,400.0,0.0,0.95
115,2.0,1.0,11.0,1.0,0.0,0.0,0.0
DAT2
131,21(0.0,26.0,22.3,8.74,30.0,60.0
132,10.0,0.68,0.0,0.0024,0.002'*
141,0.035,0.0024,0.80,0.80,0.80
151,0.035,0.035,0.027,0.0096,0.07,0.89
DAT3
161,0.20,0.825,0.90,0.77
171,0.27,0.27,0.30, 0.30,0.40
181,0.99,0.99,0.99,0.99,0.99
182,0.99,0.99,0.99,0.99
191,0.94,0.93,0.98,0.87,0.0
192,0.95,0.0,0.0,0.92
201,0.94,0.93,0.98,0.87,0.0
202,0.95,0.0,0.0,0.92
211,0.957,0.984,0.761,0.929,0.0,0.981
212,0.864,0.0,0.0,0.966
LIME SOLIDS PROCESSING MASS BALANCE
•" "FLOW* LIME USE AS CAD «
"PH - MGD'TOTAL DOSE-NEW LIME" RECYCLED LIME*
MG/L MG/L MG/L FRACTION
II.0 30.00 302.7 113.7 189.0 0.62
"FIRST PASS PRECIPITATION COMPONENTS, LB/DAY"
ORGANICS
CfO
CAC03
MGO
MGCOH)2
FE203
FECOH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
50580.
0.
105069.
2234.
8144.
0.
2304.
3075.
458.
11645.
183509.
"PRIMARY SLUDGE COMPONENTS,LB/DAY"
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FECOH53
SI02
ACID INSOL.
CA3CP04)2
TOTAL
INERTS
50885.
0.
117972.
5983.
8190.
736.
2320.
9988.
1865.
15474.
213414.
-FIRST STAGE CAKE COMPONENTS,LB/DAY"
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FECOH)3
SI02
ACID INSOL.
CA3
-------
::RECALCINATION FURNACE WET SCRUBBER WATER COMPONENTS, LB/DAY*
ORGAN I CS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH33
SI02
ACID INSOL.
CA3CP04)2
TOTAL
0.
0.
6813.
251.
0.
37.
0.
180.
INERTS 187.
186.
7653.
x INCINERATION FURNACE WET
ORGANICS
CAO
CACO3
MGO
MGCOH)2
FE203
FECOH33
SI02
ACID INSOL. INERTS
CA3CPO
-------
CASE 103
KFIRST PASS PRECIPITATION COMPONENTS,LB/DAY«
DATl
110, 30.0,9746.0,14.0,400.0,0.0,0.95
115,1.0,1.0,11.0,1.0,0.0,0.0,0.0
DAT2
131,240.0,26.0,22.3,8.74,30.0,60.0
132,10.0,0.68,0.0,0.0024,0.0024
141,0.035,0.0021*, o.80,0.80,0.80
151,0.035,0.035,0.027,0.0096,0.07,0.89
ORGAN ICS
CAO
CAC03
MGO
MGCOH)2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3CP04)2
TOTAL
50580.
0.
105069.
mm.
8144.
0.
2304.
2758.
346.
11645.
182259.
DAT3
161,0.
171,0.
181,0.
182,0.
191,0.
192,0.
201,0.
202,0.
211,0.
212,0.
89,0.99,0.99,0.95
97,0.97,0.87,0.87,0.91
0,0.0,0.0,0.0,0.0
0,0.0,0.0,0.0
94,0.93,0.98,0.87,0.0
95,0.0,0.0,0.92
0,0.0,0.0,0.0,0.0
0,0.0,0.0,0.0
957,0.981*, 0.761,0.929,0.0,0.981
864,0.0,0.0,0.966
ORGAN i cs
CAO
CAC03
MSO
FE203
FE(OH)3
SI02
ACID INSOL.
CA3CPO'*)2
TOTAL
SLUDGE COMPONENTS, LB/DA Y1-'
55582.
0.
120024.
224681.
8381.
13343.
2648.
11895.
INERTS 5890.
323717.
766161.
LIME SOLIDS PROCESSING MASS BALANCE
* KFLOW* LINE USE AS CAO -
KPH " MGD;rTOTAL DOSE^EW LINE" RECYCLED LINE"
MG/L MG/L MG/L FRACTION
11.0 30.00 302.7 71.9 230.8 0.76
=FTRST STAGE CAKE COMPONENTS,LB/DAY^
KFECL3 DOSE::WASTE BIOLOGICAL SLUDGE*
" MG/L ~ ADDED, LB/DAY »
14.0 9746.0
"FURNACE BLOWDOWN-RECALCINING EFFICIENCY15
x FRACTION " FRACTION *
0. 0.95
::NEW MAKEUP LIME ADDED,FRACTION COMPOSITION"
" SI02 " ACID INSOL. INERTS :: MGO "CAO *
0.03 0.01 0.07 0.89
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH)3
SI02
ACID INSOL.
CA3CP04)2
TOTAL
INERTS
50580.
0.
118823.
217940.
8130.
11609.
2304.
11776.
5595.
288108.
714865.
TIRST STAGE CENTRATE COfPONENTS,LB/DAY::
* PRIMARY INFLUENT COMPOSITION,MG/L K
"SUSP SOLIDS::MAGNESIUM::CALC1UM:IPHOSPHORUS::SI02"A.I . INERTS^IRON"
240.0 22.3 30.0 10.00 " " ' '•
11.9 1.4
0.
X PRIMARY EFFLUENT COMPOSITION,MG/L *
"SUSP SOL!DS"MAGNESIUM::CALC:UM::PHOSPI-ORUS"SI02::A. I . INERTS^IRON*
26 0 8.7 60.0
0.68
0.9
0.1
0.
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3CPO4)2
TOTAL
UJERTS
5002.
0.
1200.
6740.
251.
1735.
344.
119.
294.
35609.
51296.
265
-------
„ „„„, „., , D,^v» "RECOVERIES OF COMPONENTS IN PROCESS STREAMS,FRACTION"
"RECALCINATION FURNACE PRODUCT COMPONENTS, LB/DAYK
FIRST « RECALCINE "SEGONDXINCINERATION* DRY
r irvs i n.L.>-^tv. J (^L.
ORGANICS 0. STAGE
CAO 58789. ru.F RRMArp
CAC03 5525. CAKE RJRNftCE
M60 205637. ORGANICS 0.91 0.
MGCOH)2 0.
FE203 12665. CAO 0 0 93
ACID INSOL. INERTS "*868.
CA3(PO
-------
CASE 104
"FIRST PASS PRECIPITATION COMPONENTS,LB/DAY"
DAT1
110,30.0,9746.0,14.0,400.0,0.1,0.95
115,1.0,1.0,11.0,1.0,0.0,0.0,0.0
DAT2
131,240.0,26.0,22.3,8.74, 30.0,60.0
13.2., 10.0,0.68,0.0,0.0024,0.0024
141,0.035,0.0024,0.80,0.80,0.80
151,0.035,0.035,0.027,0.0096,0.07,0.89
ORGANICS
CAO
CAC03
MGO
MGCC+O2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3CP04)2
TOTAL
INERTS
50580.
0.
105069.
1888.
8144.
0.
2304.
2941.
mi.
11645.
182982.
DAT3
161,0.89,0.99,0.99,0.95
171,0.97,0.97,0.87,0.87,0.91
181,0.0,0.0,0.0,0.0,0.0
182,0.0,0.0,0.0,0.0
191,0.94,0.93,0.98,0.87,0.0
192,0.95,0.0,0.0,0.92
201,0.0,0.0,0.0,0.0,0.0
202,0.0,0.0,0.0,0.0
211,0.957,0.984,0.761,0.929,0.0,0.981
212,0.864,0.0,0.0,0.966
LIME SOLIDS PROCESSING MASS BALANCE
KPRIMARY SLUDGE COMPONENTS,LB/DAYX
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
55582.
0.
119406.
58311.
8381.
7391.
2648.
9621.
3032.
100359.
364731.
K -FLOW5-" LIME USE AS CAO «
KPH K MOD-TOTAL DOSE1!NEW LIME11 RECYCLED LIME"
MG/L MG/L MG/L FRACTION
11.0 30.00 302.7 96.1 206.6 0.68
"FECL3 DOSE'WSTE BIOLOGICAL SLUDGE*
* MG/L » ADDED, LB/DAY :1
14.0 9746.0
"FURNACE BLOWDOWN-RECALCINING EFFICIENCY"
K FRACTIC*1 !t FRACTION "
0.1IJ 0.95
"NEW MAKEUP Ll^€ ADDED,FRACTION COMPOSITION11
!l SI02 K ACID INSOL. INERTS !! MGO !1CAO "
0.03 0.01 0.07 0.89
x PRIMARY INFLUENT COMPOS IT ION, MG/L »
!!SUSP. SOLIDS!1MAGNESIUMI:CALCIUM:tPHOSPHORUS!:S I02:!A. I . INERTS"IRON:1
240.0 22.3 30.0 10.00 12.7 1.7 0.
« PRIMARY EFFLUENT COMPOSITION,MG/L «
"SUSP SOLIDS::MAGNESIUM>:CALCIUM::PHOSPHORUS:;SI0211A.I.INERTSI1IRON«
26 0 8.7 60.0 0.68 0.9 0.1 0.
267
-------
CASE 105
KFIRST PASS PRECIPITATION COWONENTS,LB/OAY*
DAT1
110,30.0,9746.0,14.0,400.0,0.15,0.95
115,1.0,1.0,11.0,1.0,0.0,0.0,0.0
DAT2
131,21*0.0,26.0,22.3,8.74,30.0,60.0
132,10.0,0.68,0.0,0.002if, 0.0024
1"» 1,0.035,0.0024,0.80,0.80,0.80
151,0.035,0.035,0.027,0.0096,0.07,0.89
ORGANICS
CAO
CAC03
MGO
MGOO2
FE203
FECC+O3
SI02
ACID INSOL.
CA3CP04)2
TOTAL
INERTS
50580.
0.
105069.
212l».
8Wt.
0.
2301*.
3032.
W.
1161*5.
DAT 3
"PRIMARY SLUDGE COMPONENTS,LB/DAY*
161,0.89,0.99,0.99,0.95
171,0.97,0.97,0.87,0.87,0.91
181,0.0,0.0,0.0,0.0,0.0
182,0.0,0.0,0.0,0.0
191,0.94,0.93,0.98,0.87,0.0
192,0.95,0.0,0.0,0.92
201,0.0,0.0,0.0,0.0,0.0
202,0.0,0.0,0.0,0.0
211,0.957,0.984,0.761,0.929,0.0,0.981
212,0.864,0.0,0.0,0.966
LINE SOLIDS PROCESSING MUSS BALANCE
" "FLOW" LIME L-SE AS CAO x
"PH ••• MGO::TOTAL DOSE::NEW Ll'TE- RECYCLED LIME*
MG/L MG/L MG/L FRACTION
11.0 30.00 302.7 108.1 194.7 0.64
"FECL3 DOSE::WASTE BIOLOGICAL SLUDGE"
- MG/L - ADDED, LB/QAY K
14.0 9746.0
"FURM^CE BLOWDOWN-RECALCININ6 EFFICIENCY1'
'•'• FRACTION " FRACTION x
0.15 0.95
::NEW K4KEUP LIME ADDED,FRACTION COMPOSITION"
" 5102 :: ACID INSOL. INERTS -' MSO "CAO *
0.03 0.01 0.07 0.89
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH53
SI02
ACID INSOL.
CA3CP0452
TOTAL
55582.
0.
119099.
INERTS
8381.
5866.
2648.
8849.
2548.
74617.
320082.
" PRIMARY INFLUENT COMPOSITION,MG/L K
"SUSP. SOLIDS::MAWJESILW::CALCILW::PHOSPHORUS"SI02::A. I . INERTS"IRON"
240.0 22.3 30.0 10.00 13.0 1.8 0.
=• PRIMARY EFFLUENT COMPOSITION,MG/L !:
"SUSP. 5OLIDS::MAGNESHM::CALCIUM::PHOSPHORUS::SI02"A. I. INERTS"IRON"
26.0 8.7 60.0 0.68 0.9 0.1 0.
268
-------
CASE 106
"FIRST PASS PRECIPITATION COMPONENTS,IB/DAY"
DAT1
110,30.0,97%.0,14.0,1*00.0.0.20,0 95
"5,1.0,1.0,11.0,1.0,0.0,o'o,0.0
DAT2
131,21(0.0,26.0,22.3,8.74,30.0,60.0
132,10.0,0.68,0.0,0.0024,0.0021*
lit 1,0.035,0.0024,0.80,0.80,0.80
151,0.035,0.035,0.027,0.0096,0.07,0.89
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FEO>03
SI02
ACID INSOL.
CA3CP04)2
TOTAL
INERTS
50580.
0.
105069.
2358.
8144.
0.
2304.
3122.
475.
11645.
183697.
DAT3
"PRIMARY SLUDGE COMPONENTS,LB/DAY"
161,0.89,0.99,0.99,0.95
171,0.97,0.97,0.87,0.87,0.91
181,0.0,0.0,0.0,0.0,0.0
182,0.0,0.0,0.0,0.0
191,0.94,0.93,0.98,0.87,0.0
192,0.95,0.0,0.0,0.92
201-,0.0,0.0,0.0,0.0,0.0
202,0.0,0.0,0.0,0.0
211,0.957,0.984,0.761,0.929,0.0,0.981
212,0.864,0.0,0.0,0.966
LIME SOLIDS PROCESSING MASS BALANCE
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FECOH)3
SI02
ACID INSOL.
CA3CP04)2
TOTAL
INERTS
55582.
0.
118794.
33391.
8381.
4769.
2648.
8227.
2239.
59385.
293415.
K "FLOW* LIME USE AS CAO «
:W " MGO-TOTAL DOSE::NEW LIME" RECYCLED LIME"
MG/L MG/L MG/L FRACTION
11.0 30.00 302.7 120.0 182.7 0.60
"FIRST STAGE CAKE COMPONENTS, LB/DAY"
"FECL3 DOSE::WASTE BIOLOGICAL SLUDGED
K MG/L ••'• ADDED, LB/DAY x
14.0 974S.O
"FURNACE BLOWDOW:!RECALCINING EFFICIENCY*
" FRACTION « FRACTION *
0.20 0.95
KNEW MAKEUP LIME ADDED, FRACTION COMPOSITION"
" SI02 :: ACID INSOL. INERTS " MGO "CAO x
0.03 0.01 0.07 0.89
ORGANICS
CAO
CAC03
MGO
MGCOI-02
FE203
FECOH)3
SI02
ACID INSOL.
CA3CP0452
TOTAL
INERTS
50580.
0.
117606.
32389.
8130.
4149.
2304.
8144.
2127.
52853.
278281.
"FIRST STAGE CENTRATE COMPONENTS, LB/DAY"
K PRIMARY INFLUENT COMPOSITION,MG/L "
!!SUSP.SOL1DS"MAGNESIUM"CALCIUM::PHOSPHORUS"SI02::A. I . INERTS"IRON"
240.0 22.3 30.0 10.00 13.4 2.0 0.
» PRIMARY EFFLUENT COMPOSITION,MG/L «
«SUSP.SOLIDS"MAGNESIUM"CALCIUM"PHOSPHORUS"SI02"A. I . INERTS:IIRON:!
26.0 8.7 60.0 0.68 0.9 0.1 0.
ORGANICS
CAO
CAC03
MGO
MGCOt-02
FE203
FE(OH)3
SI02
ACID INSOL.
CA3CP04)2
TOTAL
5002.
0.
1188.
1002.
251.
620.
344.
82.
112.
6532.
15134.
269
-------
>:RECALCIUATION FURNACE PRODUCT COMPONENTS, LB/DAY"
"CLASSIFIER REJECTS COMPONENTS, LB/DAY"
ORGAN 1CS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH03
SI02
ACID INSOL. INERTS
CA3(P04)2
TOTAL
"RE CALCINATION FURNACE
ORGAN I CS
CAO
CAC03
MGO
MGCOH)2
FE203
FECOHJ3
SI02
ACID INSOL. INERTS
CA3(P04)2
TOTAL
0.
58187.
5469.
34930.
0.
5578.
0.
7982.
1850.
1*9681.
163676.
WET SCRUBBER WATER COMPONENTS, LB/DAY*
0.
0.
8232.
3037.
0.
291!.
0.
163.
276.
3171.
ism.
"RECYCLED SOLIDS ACCEPTS OPPONENTS, LB/DAY*
ORGAN I CS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH)3
SI02
ACID INSOL. INERTS
CA3(P04)2
TOTAL
"RECALCINATION FURNACE
ORGAN I CS
CAO
CAC03
MGO
MGCOH32
FE203
FECOH)3
SI02
ACID INSOL. INERTS
CA3(PO
-------
CASE 107
"FIRST PASS PRECIPITATION COfPONENTS,LB/DAY*
DAT1
110,30.0,9746.0, lit.0,1*00.0,0.24,0.95
115,1.0,1.0,11.0,1. 0, 0.0,0.0,0.0
DAT2
131,2'tO. 0,26.0,22.3,8. 71*, 30. 0,60.0
132,10. 0,0.68, 0.0,0.002i»,0.0021*
1"*1,0.035,0.002"*, 0.80,0.80,0.80
151,0.035,0.035,0.027,0.0096,0.07,0.89
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH)3
SI02
ACID INSOL.
CA3CPOIO2
TOTAL
INERTS
50580.
0.
105069.
251*5.
8m.
0.
2301*.
319i».
501.
1161*5.
183981.
DAT3
161,0.89,0.99,0.99,0.95
171,0.97,0.97,0.87,0.87,0.91
181,0.0,0.0,0.0,0.0,0.0
182,0.0,0.0,0.0,0.0
191,0.91*,0.93,0,98,0.87,0.0
192,0.95,0.0,0.0,0.92
201,0.0,0.0,0.0,0.0,0.0
202,0.0,0.0,0.0,0.0
211,0.957,0.98"*, 0.761,0.929,0.0,0.981
212,0.86i*,0.0,0.0,0.966
SOLIDS PROCESSING MASS BALANCE
"PRIMARY SLUDGE COMPONENTS, LB/MY*
ORGANICS
CAO
CAC03
MGO
MGCOH32
FE20J
FECC+03
SI02
ACID INSOL.
CA3CPCHO2
TOTAL
INERTS
55582.
0.
118551.
28^88.
8381.
1*090.
261*8.
7809.
2061.
5101*8.
278658.
1! "FLOW-1 Llf-E USE AS CAO «
«PH " MGO'TOTAL DOSE::NEW LIME= RECYCLED LIME*
MG/L MG/L MC-/L FRACTION
11.0 30.00 302.7 129.5 173.2 0.57
"FIRST STAGE CAKE COMPONENTS,L8/DAY"
"FECL3 DOSE::WASTE BIOLOGICAL SLUDGE"
K MG/L :: ADDED, LB/DAY K
1<*.0 971*6.0
ORGANICS
USED .60 UNITS
"FURNACE BLOWDOVM::RECALCINING EFFICIENCY*
•'• FRACTION '•'• FRACTION *
0.21* 0.95
:!NDV MAKEUP LIME .ADDED, FRACTION COMPOS ITION*
!! SI02 « ACID INSOL. INERTS :; MGO KCAO *
0.03 0.01 0.07 0.89
110, 30.0,97'+6.0,11*. o,i*00.0,0.28,0.95
115,1.0,1.0,11.0,1.0,0.0,0.0,0.0
NEW DAT1
READY
110,30.0,971*6.0,11*.0,400.0,0.28, 0.95
115,1.0,1.0,11.0,1.0,0.0,0.0,0.0
OLD CSOLIDS1
* PRIMARY INFLUENT COMPOSITION,MG/L *
«SUSP.SOLIDS:WGNESIUM-~KLALCIl*li:PHOSPHORUS"SI02"A. I. INERTS:tIRON=«
21*0.0 22.3 30.0 10.00 13.7 2.1 0.
- PRIMARY EFFLUENT COMPOSITION,MG/L a
"SUSP.SOLIDS::MAGNESIUM:'-CALCIUM----PHOSPHORUS"SI02::A.I.INERTS«IRCt«(«
26.0 8.7 60.0 0.68 0.9 0.1 0.
271
-------
CASE 108
KFIRST PASS PRECIPITATION COMPONENTS,LB/DAY"
OATl
110,30.0,9746.0,14.0,400.0,0.28,0.95
115,1.0,1.0,11.0,1.0,0.0,0.0,0.0
DAT2
131,240.0,26.0,22.3,8.74,30.0,60.0
132,10.0,0.68,0.0,0.0024,0.0024
141,0.035,0.0024,0.80,0.80,0.80
151,0.035,0.035,0,027,0.0096,0.07,0.89
ORGANICS
CAO
CACO3
MGO
MG(OH)2
FE203
FEC003
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
50580.
0.
105069.
2730.
8144.
0.
2304.
3266.
526.
11645.
184264.
OAT3
161,0.89,0.99,0.99,0.95
171,0.97,0.97,0.87,0.87,0.91
181,0.0,0.0,0.0,0.0,0.0
132,0.0,0.0,0.0,0.0
191,0.94,0.93,0.98,0.87,0.0
192,0.95,0.0,0.0,0.92
201,0.0,0.0,0.0,0.0,0.0
202,0.0,0.0,0.0,0.0
211,0.957,0.984,0.761,0.929,0.0,0.981
212,0.864,0.0,0.0,0.966
LIME SOLIDS PROCESSING MASS BALANCE
"PRIMARY SLUDGE COMPONENTS, LB/DAY*
ORGANICS
CAO
CAC03
MGO
MS(OH)2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
55582.
0.
118309.
24827.
8381.
3535.
2648.
7446.
1923.
44764.
267415.
" "FLOW* LIME USE AS CAO "
"PH " MGD-TOTAL DOSE::NEW LIME" RECYCLED LIMEK
MG/L MG/L MG/L FRACTION
11.0 30.00 302.7 138.9 163.8 0.54
"FECL3 DOSE::WASTE BIOLOGICAL SLUDGE*
" MG/L » ADDED, LB/DAY K
14.0 9746.0
"FURNACE BLOWDOW-RECALCINING EFFICIENCY*
'•'• FRACTION K FRACTION x
0.28 0.95
::NEW MAKEUP LIME ADDED, FRACTION COMPOSITION*
" SI02 :: ACID INSOL. INERTS '" MGO "-CPO K
0.03 0.01 0.07 0.89
* PRIMARY INFLUENT COMPOSITION,MG/L *
"SUSP.SOLIDS::MAGNESIUM::CALCIUM::PHOSPHORUS"SI02::A.I.INERTS*IRONS
240.0 22.3 30.0 10.00 14.0 2.2 0.
* PRIMARY EFFLUENT COMPOSITION,MG/L K
=SUSP.SOLIDS::MAGNESIUM"CALCIUM::PHOSPHORUS"SI02"A. I. INERTS::IRON*
26.0 8.7 60.0 0.68 0.9 0.1 0.
272
-------
CASE 109
"FIRST PASS PRECIPITATION COMPONENTS,LB/CAY*
DAT1
110,30.0,9746.0,1<». 0,
-------
CASE 110
KFIRST PASS PRECIPITATION COMPONENTS,UB/OW*
DAT1
110,30.0,9746.0,14.0,400.0,0.35,0.95
115,1.0,1.0,11.0,1.0,0.0,0.0,0.0
DAT2
131,240.0,26.0,22.3,8,7"*, 30.0,60.0
132,10.0,0.68,0.0,0.0024,0.0024
I1*!, 0.035,0.002"*, 0.80,0.80,0.80
151,0.035,0.035,0.027,0.0096,0.07,0.89
ORGANICS
CAO
CAC03
MGO
MGCOHD2
FE203
FECOH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
50580.
0.
105069.
JOS'*.
81V*.
0.
230
-------
CASE 111
"FIRST PASS PRECIPITATION COMPONENTS, LB/DAY"
DAT1
110, 30.0,9746. 0, l
-------
XRECALCINATION FURNACE PRODUCT COMPONENTS, LB/DAY;:
"CLASSIFIER REJECTS COMPONENTS,LB/DAY*
ORGAN! CS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH)3
SI02
AC 10 INSOL. INERTS
CA3CPCCO2
TOTAL
!:RECALCINATION FURNACE
0.
57
-------
CASE 112
"FIRST PASS PRECIPITATION COMPONENTS,LB/DAY"
DAT1
110,30.0,9746.0,14.0,400.0,1.0,0.95
115,1.0,1.0,11.0,1.0,0.0,0.0,0.0
DAT2
131,240.0,26.0,22.3,8.74, 30.0,60.0
132,10.0,0.68,0. .0,0.0024, 0.0024
Ml, 0.035,0.0024,0.80,0.80,0.80
151,0.035,0.035,0.027,0.0096,0.07,0.89
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH53
SI02
ACID INSOL.
CA3CPOJt)2
TOTAL
INERTS
50580.
0.
105069.
5950.
8144.
0.
230
-------
::RECALC1UATION FURNACE PRODUCT COMPONENTS,LB/DAY"
"CLASSIFIER REJECTS COMPONENTS,LB/DAY"
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH53
SI02
ACID INSOL.
CA3CPO'*)2
TOTAL
INERTS
0.
55897.
5253.
11528.
0.
1722.
0.
"*508.
968.
new.
91521.
ORGAN1CS
CAO
CAC03
MGO
MG(OH)2
FE203
FFC003
5102
ACID INSOL.
CA3CFXTO2
TOTAL
INERTS
"RECALCINATION FURNACE WET SCRUBBER WATER COMPONENTS,LB/DAY"
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3CP0432
TOTAL
0.
0.
7908.
1002.
0.
91.
0.
92.
1<*5.
7"*3.
9981.
"RECYCLED SOLIDS ACCEPTS COMPONENTS,LB/DAY*
ORGANICS
CAO
CAC03
MGO
MGCOH02
FE203
FECOH53
SI02
ACID INSOL.
CA3(PO
-------
CASE 113
DAT1
"FIRST PASS PRECIPITATION COMPONENTS,LB/DAY"
110,30.0,97^6.0,14.0,1(00.0,0.0,0.95
115,1.0,1.0,11.0,1.0,0.0,0.0,0.0
DAT2
131,240.0,26.0,22.3,8. 74, 30.0,60.0
132,10.0,0.68,0.0,0.0024,0.0024
mi, 0.035,0.002i», 0.80,0.80,0.80
151,0.035,0.035,0.027,0.0096,0.07,0.89
ORGAN ICS
CAO
CAC03
MGO
MGCOH)2
FE203
FECOH)3
SI02
ACID INSOL.
CA3CP04)2
TOTAL
INERTS
50580.
0.
105069.
I'm.
am1*.
o.
2304.
2758.
346.
1161*5.
182259.
DAT3
"PRIMARY SLUDGE COMPONENTS, LB/DAY"
161,0.95,0.95,0.95,0.95
171,0.95,0.95,0.95,0.95,0.95
181,0.0,0.0,0.0,0.0,0.0
182,0.0,0.0,0.0,0.0
191,0.94,0. 93,0.98,0.87,0.0
192,0.95,0.0,0.0,0.92
201,0.0,0.0,0.0,0.0,0.0
202,0.0,0.0,0.0,0.0
211,0.957,0.984,0.761,0.929,0.0,0.981
212,0.864,0.0,0.0,0.966
LIME SOLIDS PROCESSING MASS BALANCE
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3CP01O2
TOTAL
INERTS
53242.
0.
125077.
229411.
8558.
12220.
2425.
12396.
5890.
303272.
752489.
* "FLOW11 LIME USE AS CAO "
«PH :: MGD-TOTAL DOSE-NEW LIME" RECYCLED LIME"
MG/L MG/L MG/L FRACTION
11.0 30.00 302.7 71.9 230.8 0.76
"FIRST STAGE CAKE COMPONENTS,LB/DAY"
KFECL3 DOSE"WASTE BIOLOGICAL SLUDGE"
x MG/L J! ADDED, LB/DAY «
14.0 9746.0
"FURNACE BLOWDOWN"RECALCINING EFFICIENCY"
« FRACTION !! FRACTION "
0. 0.95
KNEW MAKEUP LIME ADDED,FRACTION COMPOSITION"
* SI02 « ACID INSOL. INERTS « MGO "CAO *
0.03 0.01 0.07 0.89
ORGANICS
CAO
CAC03
MGO
FE203
FECOH)3
SI02
ACID INSOL.
CA3CP0452
TOTAL
INERTS
50580.
0.
118823.
217940.
8130.
11609.
2304.
11776.
5595.
288108.
714865.
"FIRST STAGE CENTRATE COMPONENTS,LB/DAY"
K PRIMARY INFLUENT COMPOSITION,MG/L "
KSUSP.SOLIDS!=WGNESIUM"CALCIUMI;PHOSPHORUS"SI02!:A. I. INERTS:!IRON"
240.0 22.3 30.0 10.00 11.9 1.4 0.
K PRIMARY EFFLUENT COMPOSITION,MG/L "
KSUSP.SOLIDS!!MAGNESIUM!!CALCIUM!CPHOSPHORUSI!SI02"A. I. INERTS5CIRONM
26.0 8.7 60.0 0.68 0.9 0.1 0.
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
2662.
0.
6254.
11471.
428.
611.
121.
620.
294.
15164.
37624.
279
-------
"RECALCI NATION FURNACE PROPUCT COMPONENTS, LB/DAY"
''RECOVERIES OF COMPONENTS IN PROCESS STREAMS,FRACTION"
ORGANICS
CAO
CAC03
M30
MGCOH)2
FE203
FECOH53
SI02
ACID INSOL. INERTS
CA3CPCXO2
TOTAL
-'RECALCINWION FURNACE
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL. INERTS
CA3CPCJt)2
TOTAL
"RECYCLED SOLIDS ACCEPTS
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FE(OH)3
SI02
ACID INSOL. INERTS
CA3CPOW2
TOTAL
0.
58789.
5525.
205637.
0.
12665.
0.
115:SECOND"INCINERATION>; DRY
STAGE STAGE
CAKE FURNACE CAKE FURNACE CLASSIFIER
ORGANICS 0.95 0. 0. 0. 0.
CAO 0. 0.93 0. 0. 0.98
CAC03 0.95 0.93 0. 0. 0.98
MGO 0.95 0.92 0. 0. 0.97
MGCOH)2 0.95 0. 0. 0. 0.
FE203 0.95 0.95 0. 0. 0.86
FECOH53 0.95 0. 0. 0. 0.
SI02 0.95 0.98 0. 0. 0.76
INERTS 0.95 0.87 0. 0. 0.93
CA3CPO
-------
CASE
"FIRST PASS PRECIPITATION COMPONENTS,LB/DAY"
DAT1
110,30.0,9746,0,14.0,400.0,0.20,0.95
115,1.0,1.0,11.0,1.0,0.0,0.0,0.0
OAT2
131,240.0,26.0,22.J,8.74,30.0,60.0
132, 10.0,0.68,0.0,0.0021*, 0.0024
1<*1,0.035,0.0021*, 0.80,0.80,0.80
151,0.055,0.035,0.027,0.0096,0.07,0.89
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FECOt-03
SI02
ACID INSOL.
CA3CP04;>2
TOTAL
INERTS
50580.
0.
105069.
2358.
8144.
0.
2304.
3122.
475.
11645.
183697.
DAT3
161,0.95,0.95,0.95,0.95
171,0.95,0.95,0.95,0.95,0.95
181,0.0,0.0,0.0,0.0,0.0
182,0.0,0.0,0.0,0.0
191,0.94,0.93,0.98,0.87,0.0
192,0.95,0.0,0.0,0.92
201,0.0,0.0,0.0,0.0,0.0
202,0.0,0.0,0.0,0.0
211,0.957,0.984,0.761,0.929,0.0,0.981
212,0.864,0.0,0.0,0.966
LIME SOLIDS PROCESSING MUSS BALANCE
"PRIMARY SLUDGE COMPONENTS,LB/DAY"
ORGANICS
CAO
CAC03
MGO
MG(Ot-02
FE203
FECOH53
SI02
ACID INSOL.
CA3CP04)2
TOTAL
INERTS
53242.
0.
123796.
34094.
8558.
4367.
2425.
8573.
2239.
55634.
292928.
* "FLOW" LIME USE AS CAO «
«PH * MGD'TOTAL DOSEJCNEW LIMEI: RECYCLED LIME1!
MG/L MG/L MG/L FRACTION
11.0 30.00 302.7 120.0 182.7 0.60
"FIRST STAGE CAKE COMPONENTS,LB/DAY"
"FECL3 DOSE!:WASTE BIOLOGICAL SLUDGE"
J: MG/L :t ADDED, LB/DAY :t
14.0 9746.0
"FURNACE BLOWDOWN"RECALCINING EFFICIENCY"
- FRACTION " FRACTION K
0.20 0.95
:tNEW MAKEUP LIME ADDED, FRACTION COMPOSITION"
" SI02 » ACID INSOL. INERTS " MGO "CAO *
0.03 0.01 0.07 0.89
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FECOH)3
SI02
ACID INSOL.
CA3CP04)2
TOTAL
INERTS
50580.
0.
117606.
32389.
8130.
4149.
2304.
8144.
2127.
52853.
278281.
"FIRST STAGE CENTRATE COMPONENTS, LB/DAY"
* PRIMARY INFLUENT COMPOS IT ION,MG/L *
"SUSP.SOLIDS"MAGNESIUM!:CALCIUM"PHOSPHORUS"S I02«A. I. INERTS"IRON"
240.0 22.3 30.0 10.00 13.4 2.0 0.
« PRIMARY EFFLUENT COMPOS ITION,MG/L "
"SUSP. SOL 1 DS::MAGNES I UM"CALC IUM-PHOSPHORUS "S102"A. I. INERTS" I RON"
26.0 8.7 60.0 0.68 0.9 0.1 0.
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3(PO>O2
TOTAL
INERTS
2662.
0.
6190.
1705.
428.
218.
121.
429.
112.
2782.
14646.
281
-------
*RECALCINATION FURNACE PRODUCT COMPONENTS, LB/DAY*
CLASSIFIES REJECTS COMPONENTS, LS/DAY"
ORGAN IC5
CAO
CAC03
MGO
HG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL. INERTS
CA3CPO
-------
CASE 115
tWTl
"FIRST PASS PRECIPITATION COMPONENTS, LB/DAY"
110,JO.O,97't6.0,m.O/3
SI02
ACID INSOL.
CA3CP01*)2
TOTAL
INERTS
50580.
0.
105069.
mi*.
81V*.
0.
230
-------
::RECALC I NATION FURNACE PRODUCT COMPONENTS, LB/OAY«
"RECOVERIES OF OPPONENTS IN PROCESS STREWS,FRACTION"
FIRST « RECALCINE KSECOND«INCINERATION!t DRY
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH)3
SI02
ACID INSOL. INERTS
CA3CPQ102
0.
58789.
5525.
205637.
0.
12665.
0.
1151*0.
1*868.
270822.
ORGAN ICS
CAO
CAC03
MGO
TOTAL 56981*5. MG(OH)2
FE203
FECOH)3
SI02
"RECALCIN1ATION FURNACE WET SCRUBBER WATER COMPONENTS, LB/DAY" INERTS
CA3(PO'O2
TOTAL
PROGRAM STOP AT 3250
USED .80 UNITS
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FEC003
SI02
ACID INSOL. INERTS
CA3CPCC02
TOTAL
0.
0.
8318.
17881.
0.
667.
0.
236.
Til.
17287.
"(5115.
STAGE
CAKE
0.99
0.
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
FURNACE
0.
0.93
0.93
0.92
0.
0.95
0.
0.98
0.87
0.91*
STAGE.
CAKE
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
FURNACE
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
CLASSIFIER
0.
0.98
0.98
0.97
0.
0.86
0.
0.76
0.93
0.96
0.96
"RECYCLED SOLIDS ACCEPTS CCMPONENfTS, LB/DAY*
ORGANICS 0.
CAO 57672!
CAC03 51437.
MGO 19861*5.
MG(OH)2 0.
FE203 10942.
FE(OH)3 0.
SI02 8782.
ACID INSOL. INERTS
-------
CASE 116
"FIRST PASS PRECIPITATION COMPONENTS,LB/DAY*
DAT1
110,30.0,9746.0,14.0,400.0,0.20,0.95
115,1.0,1.0,11.0,1.0,0.0,0.0,0.0
BAT2
131,240.0,26.0,22.3,8.74,30.0,60.0
132,10.0,0.68,0.0,0.0024,0.0024
141,0.035,0.0024,0.80,0.80,0.80
151,0.035,0.035,0.027,0.0096,0.07,0.89
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FECOH)3
SI02
ACID INSOL.
CA3CP04)2
TOTAL
INERTS
50580.
0.
105069.
2358.
8144.
0.
2304.
3122.
475.
11645.
183697.
DAT3
161,0.
171,0.
181,0.
182,0.
191,0.
192,0.
201,0.
202,0.
211,0.
212,0.
995,0.995,0.995,0.995
995,0.995,0.995,0.995,0.995
0,0.0,0.0,0.0,0.0
0,0.0,0.0,0.0
94,0.93,0.98,0.87,0.0
95,0.0,0.0,0.92
0,0.0,0.0,0.0,0.0
0,0.0,0.0,0.0
957,0.984,0.761,0.929,0.0,0.981
864,0.0,0.0,0.966
"PRIMARY SLUDGE COMPONENTS, LB/DAY*
SOLIDS PROCESSING MASS BALANCE
ORGANICS
CAO
CAC03
MGO
MGCOt-02
FE203
FECOH)3
SI02
ACID INSOL.
CA3CP04)2
TOTAL
INERTS
50834.
0.
118197.
32552.
8171.
4170.
2315.
8185.
2137.
53118.
279680.
:t "FLOW* LIME USE AS CAO Jt
«PH :t MGO-TOTAL DOSE!:NEW LIMEK RECYCLED LIME"
MG/L MG/L MG/L FRACTION
11.0 30.00 302.7 120.0 182.7 0.60
"FIRST STAGE CAKE COMPONENTS, LB/DAY*
"FECL3 DOSE!!WASTE BIOLOGICAL SLUDGE"
x MG/L !! ADDED, LB/DAY !t
14.0 9746.0
"FURNACE BLOWDOWN-RECALCINING EFFICIENCY"
K FRACTION K FRACTION "
0.20 0.95
"NEW MAKEUP LIME ADDED,FRACTION COf-POSITION"
» SI02 » ACID INSOL. INERTS !t MGO J:CAO !t
0.03 0.01 0.07 0.89
ORGANICS
CAO
CAC03
MSO
MGCOH32
FE203
' FECOI-03
SI02
ACID INSOL.
CA3CP0452
TOTAL
INERTS
50580.
0.
117606.
32389.
8130.
4149.
2304.
8144.
2127.
52853.
278281.
!:FIRST STAGE CENTRATE COMPONENTS, LB/DAY*
Jt PRIMARY INFLUENT COMPOSITION,MG/L "
KSUSP.SOLIDSKMAGNESIUM:!CALCIUM!tPHOSPHORUS"SI02"A.I.INERTS:!lRON)l
240.0 22.3 30.0 10.00 13.4 2.0 0.
x PRIMARY EFFLUENT COMPOSITION,MG/L "
»SUSP SOLIDS)!MAGNESIUM1!CALCIUM!!PHOSPHORUS1:SI02!IA.I. INERTS" I RON"
26.0 8.7 60.0 0.68 0.9 ' 0.1 0.
ORGANICS
CAO
CAC03
MGO
MGCOt-02
FE203
FECOH53
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
254.
0.
591.
163.
41.
21.
12.
41.
11.
266.
1398.
285
-------
::RECALClrWTION FURNACE PRODUCT COMPONENTS, LB/DAY*
ORGANIC5 0.
CAO 58187.
CACOI S469.
MGO Jl.930.
M6(OH)2 0.
FE203 5578.
FECOH53 0.
SI02 7982.
ACID INSOL. INERTS 1850.
CA3CP01O2 1*9681.
TOTAL 163676.
'^CLASSIFIER REJECTS COMPONENTS,LB/DAY*
ORGAN ICS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3CPO
-------
OASE 117
•"FIRST PASS PRECIPITATION COMPONENTS,LB/DAY*
DAT1
110,30.0,9746.0,14.0,400.0,0.0,0.95
115,2.0,0.0,11.0,1.0, 0.0,0.0,0.0
DAT2
131,240.0,26.0,22.3,8.74, 30.0,60.0
132,10.0,0.68,0.0,0.0021*, 0.0024
141, 0.035,0.0024,0.80,0.80,0.80
151,0.035,0.035,0.027,0.0096,0.07,0.89
ORGAN ICS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOHJ3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
50580.
0.
105069.
2160.
8144.
0.
2304.
3046.
448.
11645.
183395.
DAT3
161,0.20,0.825,0.90,0.77
171,0.27,0.27,0.30,0.30,0.1*0
181,0.90,0.99,0.97,0.81,0.90
182,0.90,0.78,0.90,0.90
191,0.94,0.93,0.98,0.87,0.0
192,0.95,0.0,0.0,0.92
201,0.94,0.93,0.98,0.87,0.0
202,0.95,0.0,0.0,0.92
211,1.0,1.0,1.0,1.0,1.0,1.0
212,1.0,1.0,1.0,1.0
LIME SOLIDS PROCESSING MASS BALANCE
"PRIMARY SLUDGE COMPONENTS,LB/DAY*
ORGANICS
CAO
CAC03
MGO
MGCOH32
FE203
FE(OH)3
SI02
ACID INSOL.
CA3CP04)2
TOTAL
INERTS
58272.
0.
118054.
6784.
8770.
1026.
2477.
32042.
2764.
17206.
247394.
K "FLOW" LIME USE AS CAO x
"PH " MGD'TOTAL DOSE:=NEW LIMEJ: RECYCLED LIME"
MG/L MG/L MG/L FRACTION
11.0 30.00 302.7 109.9 192.8 0.64
"FIRST STAGE CAKE COMPONENTS,LB/DAY*
«FECL3 DOSE:VASTE BIOLOGICAL SLUDGE"
); MG/L J! ADDED, LB/DAY :t
14.0 9746.0
"FURNACE BLOWX)WN:(RECALCINING EFFICIENCY"
« FRACTION K FRACTION *
0. 0.95
>:NEW MAKEUP LIME ADDED, FRACTION COMPOSITION"
K SI02 '•'• ACID INSOL. INERTS " MGO "CAO "
0.03 0.01 0.07 0.89
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FECOH)3
SI02
ACID INSOL.
CA3CP0452
TOTAL
INERTS
23309.
0.
97394.
1832.
2368.
308.
743.
28837.
2128.
3441.
160360.
:!FIRST STAGE CENTRATE COMPONENTS,LB/DAYK
« PRIMARY INFLUENT COMPOSITION,MG/L «
KSUSP.SOLIDS!=MAGNESIUM!:CALCIUM:tPHOSPHORUS"SI02"A. I. INERTS111 RON"
240.0 22.3 30.0 10.00 13.1
1.9
0.
" PRIMARY EFFLUENT COMPOSITION,MG/L
"SUSP.SOLIDS!:MAGNESIUM"CALCIUM::PHOSPHORUS::SI02"A. I
26.0 8.7 60.0 0.68 0.9
. INERTS:!IRONX
0.1 0.
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
S102
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
34963.
0.
20659.
4952.
6402.
718.
1734.
3204.
636.
13765.
87034.
287
-------
"RECALCINATION FURNACE PRODUCT OPPONENTS, LB/DAY*
"INCINERATION FLRNACE WASTE ASH COMPONENTS, LB/DAY*
ORGANICS
CAO
CAC03
MGO
FE203
FECC+03
SI02
ACID INSOL. INERTS
CA3CPCJO2
TOTAL
0.
it8187.
1(529.
3180.
0.
820.
0.
28261.
1851.
3235.
90062.
ORGANICS
CAO
CAC03
MGO
MGCOH32
FE203
FE(OH)3
SI02
ACID INSOL.
CA3CP01O2
TOTAL
INERTS
0.
0.
19021.
91*02.
0.
2096.
0.
30
-------
CASE 118
DAT1
"FIRST PASS PRECIPITATION COMPONENTS,LB/DAY"
110,30.0,9746.0,14.0,400.0,0.20,0.95
115,2.0,0.0,11.0,1.0,0.0,0.0,0.0
DAT2
i3i,24o.o,2&.o,22.3,8.74,3o.o,6o.o
132, 10.0,0.68,0.0,0.0024,0.0024
I'd, 0.035,0.0024,0.80,0.80,0.80
151,0.035,0.035,0.027,0.0096,0.07,0,89
DAT 3
161,0.20,0.825,0.90,0.77
171,0.27,0.27,0.30,0.30,0.40
181,0.90,0.99,0.97,0.81,0.90
182,0.90,0.78,0.90,0.90
191,0.94,0.93,0.98,0.87,0.0
192,0.95,0.0,0.0,0.92
201,0.94,0.93,0.98,0.87,0.0
202,0.95,0.0,0.0,0.92
211,1.0,1.0,1.0,1.0,1.0,1.0
212,1.0,1.0,1.0,1.0
ORGANICS
CAO
CAC03
MGO
MGCOt-02
FE203
FECOH)3
SI02
ACID INSOL.
CA3CP04)2
TOTAL
INERTS
50580.
0.
105069.
2944.
8144.
0.
2304.
3348.
555.
11645.
184589.
"PRIMARY SLUDGE COMPONENTS, LB/DAY"
ORGAN ICS
CAO
CAC03
MGO
MGO>02
FE203
FE(OH)3
SI02
ACID INSOL.
CA3CP0432
TOTAL
INERTS
58272.
0.
117045.
7010.
8770.
776.
2477.
12334.
1876.
16301.
224860.
-FIRST STAGE CAKE COMPONENTS,LB/DAY"
LIME SOLIDS PROCESSING MASS BALANCE
" "FLOW51 LIME USE AS CAO »
"PH " MGO-TOTAL DOSE"NEW LIME" RECYCLED LINE"
MG/L MG/L MG/L FRACTION
11.0 30.00 302.7 149.8 152.9 0.51
"FECL3 DOSE::WASTE BIOLOGICAL SLUDGE"
:: MG/L '•'• ADDED, LB/DAY »
14.0 9746.0
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
23309.
0.
96562.
1893.
2368.
233.
743.
11101.
1445.
3260.
140912.
"FIRST STAGE CENTRATE COMPONENTS,LB/DAY"
"FURriACE BLOWDOWN-RF.CALCINING EFFICIENCY'1
•••• FRACTION '••• FRACTION «
0.20 0.95
"•NEW MAKEUP LIME ADDED, FRACTION COMPOSITION"
" 5102 " ACID INSOL. INERTS >: MGO :CCAO :I
0.03 0.01 0.07 0.89
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH)3
SI02
ACID INSOL.
CA3CP04)2
TOTAL
INERTS
34963.
0.
20483.
5118.
6402.
543.
1734.
1233.
431.
13041.
83948.
K PRIMARY INFLUENT COMPOSITION,MG/L
"SUSP. SOL IDS!=MAGNES I Uf^CALC I UM"PHOSPHORUS"S 102"A. I. INERTS" I RON"
240.0 22.3 30.0 10.00 14.3 2.3 0.
:: PRIMARY EFFLUENT COMPOSITION,MG/L !t
!.-SUSP.SOLIDSI«AGNESIUM;tCALCIUM"PHOSPHORUS!:SI02!:A. I. INERTS-IRON"
26.0 8.7 60.0 0.68 0.9 0.1 0.
"RECALCINATION FURNACE PRODUCT COMPONENTS,LB/DAY"
ORGANICS
CAO
CAC03
MGO
MT, (OH) 2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
0.
47775.
4490.
3236.
0.
749.
0.
10879.
1257.
3065.
71450.
289
-------
'^CALCINATION FURNACE WET SCRUBBER WATER COMPONENTS, LB/DAY"
ORGAN ICS
WO
CAC03
MGO
MS(OH)2
FE203
FE(OH)3
SI02
ACID INSOL. INERTS
CA3(P04)2
TOTAL
0.
0.
6759.
281.
0.
39.
0.
222.
188.
196.
7686.
"RECYCLED SOLIDS ACCEPTS COMPONENTS, LB/DAY1'
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
0.
38220.
3592.
2589.
0.
599.
0.
8703.
1005.
2452.
57160.
"SECOND STAGE CAKE COMPONENTS, LB/DAY*
ORGAN I CS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL. INERTS
CA3(P04)2
27271.
0.
20278.
4606.
5762.
489.
1561.
1196.
350.
11737.
:=INCINERATION FURNACE WET SCRUBBER WATER COMPONENTS,LB/MY"
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL. INERTS
CA3CP04)2
TOTAL
0.
0.
1419.
685.
0.
83.
0.
24.
45.
704.
2961.
"RECALCINATION FURNACE SLOWDOWN COMPONENTS,LB/DAY"
ORGAN I CS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL. INERTS
CA3CP04)2
0.
9555.
898.
61*7.
0.
150.
0.
2176.
251.
613.
TOTAL
14290.
TOTAL
732149.
"RECOVERIES OF COMPONENTS IN PROCESS STREAMS,FRACTION-
FIRST » RECALCINE "SECOND-ING INERATION5! DRY
"SECOND STAGE CENTRATE
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH)3
SI02
ACID INSOL. INERTS
CA3(P04)2
TOTAL
RECYCLE COMPONENTS, LB/DAY"
7692.
0.
205.
512.
6")0.
5"t.
173.
37.
82.
1301*.
10699.
"INCINERATION FURNACE WASTE ASH COMPONENTS, LB/OAY!!
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FE(OH)3
SI02
ACID INSOL. INERTS
CA3(P04)2
0.
0.
18859.
9538.
0.
m?.
0.
1172.
304.
11032.
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH53
SI02
INERTS
CA3CP01»)2
TOTAL
STAGE
CAKE
0.40
0.
0.83
0.27
0.27
0.30
0.30
0.90
0.77
0.20
0.63
PROGRAM STOP AT
USED
FURNACE
0.
0.93
0.93
0.92
0.
0.95
0.
0.98
0.87
0.94
3250
STAGE
CAKE
0.78
0.
0.99
0.90
0.90
0.90
0.90
0.97
0.81
0.90
0.87
FURNACE
0.
0.
0.93
0.92
0.
0.95
0.
0.98
0.87
0.94
CLASSIFIER
0.
1.00
1.00
1.00
0.
1.00
0.
1.00
1.00
1.00
0.80
.90 UNITS
TOTAL
42853.
290
-------
CASE 119
DAT1
"FIRST PASS PRECIPITATION COMPONENTS, L8/DAY"
110,30.0,974G.0, l; FRACTION " FRACTION )!
0.24 0.95
'•MEW MAKEUP LIME ADDED, FRACTION COMPOSITION"
- SI02 " ACID INSOL. INERTS :: MGO "CAO "
0.03 0.01 0.07 0.89
"FIRST STAGE CENTRATE' COMPONENTS,LB/DAY*
ORGANICS
CAO
CACO3
MGO
MGCOH)2
FE203
FECOH33
SI02
ACID INSOL.
CA3CP04)2
TOTAL
INERTS
34963.
0.
20448.
5146.
6402.
511.
1734.
1111.
411.
12905.
83631.
K PRIMARY INFLUENT COMPOSITION,MG/L
"'SUSP. SOLIDS-MAGNESIUM-CALCIUM-PHOSPHORUS-S102"A. I. INERTSKIRON" .
240.0 22.3 30.0 10.00 14.5 2.4 0.
RECALCULATION FURNACE PRODUCT COMPONENTS, LB/DAY::
ORGANICS
CAO
CAC03
MGO
PRIMARY EFFLUENT COMPOS IT ION, MG/L •" MG(OH)2
!:SUSP.SOLIDS"MAGNESIUM"CALCIUM"PHOSPHORUS"SI02"A.I.INERTS-IRON" FE203
26.0 "8.7 60.0 0.68 0.9 0.1 0. FE(OH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
0.
47693.
4482.
3246.
0.
736.
0.
9800.
1197.
3033.
70186.
291
-------
"PECALCINATION FURNACE WET SCRUBBER WATER COMPONENTS,UP/DAY"
ORGAN1CS
CAO
CACOJ
MGO
MT, (OH) 2
FE203
FECOH)3
5102
AC10 INSOL. INERTS
CA3(P04)2
TOTAL
0.
0.
6748.
282.
0.
39.
0.
200.
179.
194.
761*1.
"INCINERATION FURNACE WET SCRUBBER WATER COMPONENTS,IB/DAY"
"RECYCLED SOLIDS ACCEPTS COMPONENTS,LB/DAY"
ORGAN ICS
CAO
CAC03
MGO
MGCOH)2
FE203
FE(OH)3
SI02
ACID INSOL. INERTS
CA3CPO
-------
CASE 120
DAT1
"FIRST PASS PRECIPITATION COMPONENTS, LB/DAY"
110, 30.0,9746.0,11*. 0,1)00.0,0.28,0.95
115,2.0,0.0,11.0,1.0,0.0,0.0,0.0
DAT 2
131,21*0.0,26.0,22.3,8.74,30.0,60.0
132,10.0,0.68, 0.0,0.00211,0.0024
141,0.035,0.002'), 0.80,0.80,0.80
151,0.035,0.035,0.027,0.0096,0.07,0.89
DAT 3
161,0
171,0
181,0,
182,0
191,0.
192,0.
201,0.
202,0,
211,1.
212,1.
20,0.825,0.90,0.77
27,0.27,0.30,0.30,0.1*0
90,0.99,0.97,0.81,0.90
90,0.78,0.90,0.90
94,0.93,0.98,0.87,0.0
95,0.0,0.0,0.92
94,0.93,0.98,0.87,0.0
95,0.0,0.0,0.92
0,1.0,1.0,1.0,1.0,1.0
0,1.0,1.0,1.0
ORGANICS
CAO
CAC03
MSO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3CP0452
TOTAL
INERTS
50580.
0.
105069.
3253.
8144.
0.
2304.
3468.
598.
11645.
185061.
"PRIMA.RY SLUDGE COMPONENTS, LB/DAY51
ORGANICS
CAO
CAC03
MGO
MGCOI-02
FE203
FECOH03
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
58272.
0.
116646.
7086.
8770.
687.
2477.
10139.
1710.
15965.
221752.
LIME SOLIDS PROCESSING MASS BALANCE
" "FLOW71 LIME USE AS CAO *
"PH " MGD-TOTAL DOSE"NEW LIME-" RECYCLED LIMEI:
MG/L MG/L MG/L FRACTION
11.0 30.00 302.7 165.5 137.2 0.45
"FECL3 DOSE::WASTE BIOLOGICAL SLUDGE"
" MG/L " ADDED, LB/DAY "
14.0 9746.0
"FIRST STAGE CAKE COMPONENTS, LB/DAY"
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FECOH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
23309.
0.
96233.
1913.
2368.
206.
743.
9125.
1317.
3193.
138407.
"FURNACE BLOWDOWN"RECALCINING EFFICIENCY"
:: FRACTION " FRACTION J:
0.28 0.95
"NEW MAKEUP LIME ADDED,FRACTION COMPOSITION"
" SI02 :c ACID INSOL. INERTS " MGO "CAO !'
0.03 0.01 0.07 0.89
"FIRST STAGE CENTRATE COMPONENTS,LB/DAY"
ORGANICS
CAO
CAC03
MGO
MGCOH02
FE203
FECOH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
34963.
0.
20413.
5173.
6402.
481.
1734.
1014.
393.
12772.
83345.
" PRIMARY INFLUENT COMPOSITION,MG/L «
"SUSP.SOLIDS"MAGNESIUM"CALCIUM"PHOSPHORUS"SI02"A.I.INERTS"!RON"
240.0 22.3 30.0 10.00 14.8 2.5 0.
" PRIMARY EFFLUENT COMPOS IT ION,MG/L >'
"SUSP. SOL I DS::MAGNES IUM"CALC I UM"PHOSPK1RUS"S 102"A. I . INI[RTS" I RON"
26.0 8.7 60.0 0.68 0.9 0.1 0.
"RECALCINATION FURNACE PRODUCT COMPONENTS,LB/DAY"
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
0.
47612.
4475.
3255.
0.
724.
0.
89M.
111(6.
3001.
69155.
293
-------
!:RECALCINATION FURNACE WET SCRUBBER WATER COMPONENTS, LB/CAY"
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL. INERTS
CA3CPQ1O2
TOTAL
0.
0.
6736.
283.
0.
38.
0.
183.
171.
192.
7603.
"RECYCLED SOLIDS ACCEPTS COMPONENTS,LB/DAY-
ORGANICS
CAO
CAC03
MGO
MGCOH52
FE203
FE(OH)3
SI02
ACID INSOL. INERTS
CA3(PO
-------
CASE 121
DAT1-
110, 30.0,12995.0,21*.0,289.0,0.0,0.95
115,2.0,1.0,10.2,1.0,0.0,0.0,0.0
DAT2
131,2140.0,26.0,22.3,15.6,30.0,65.2
132,10.0,0.68,0.0,0.0024,0.0021*
141, 0.035,0.0024, 0.80,0.80,0.80
151,0.035,0.035,0.027,0.0096,0.07,0.89
"FIRST PASS PRECIPITATION COMPONENTS, LB/DAY*
ORGANICS
CAO
CAC03
MGO
MGCOH52
FE203
FE(OH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
531/9.
0.
61*335.
2225.
1*024.
0.
3949.
3185.
"*65.
116<*5.
143007.
DAT3
161,0.26,0.72,0.90,0.61*
171,0.25,0.25,0.18,0.18,0.35
181,0.93,0.83,0.81,0.68,0.75
182,0.75,0.78,0.90,0.90
191,0.94,0.93,0.93,0.87,0.0
192,0.95,0.0,0.0,0.92
201,0.94,0.93,0.98,0.87,0.0
202,0.95,0.0,0.0,0.92
211,0.957,0.984,0.761,0.929,0.0,0.981
212,0.8611,0.0,0.0,0.966
"PRIMARY SLUDGE COMPONENTS,LB/DAY"
ORGANICS
CAO
CAC03
MGO
MS(OH)2
FE203
FE(OH)3
S102
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
62052.
0.
75441.
4942.
4343.
1146.
4968.
10975.
1840.
17714.
183421.
LIME SOLIDS PROCESSING MASS BALANCE
» "FLOW" LIME USE AS CAO »
-PH - MGD-TOTAL DOSE::NEW LIME" RECYCLED LIMEJ;
MG/L MG/L MG/L FRACTION
10.2 30.00 218.7 113.2 105.5 0.48
"FECL3 DOSE"WASTE BIOLOGICAL SLUDGE"
" MG/L " ADDED, LB/DAY "
24.0 12995.0
"FIRST STAGE CAKE COMPONENTS, LB/DAY*
ORGANICS
CAO
CAC03
MGO
MGCOHJ2
FE203
FECOH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
21718.
0.
54318.
1235.
1086.
206.
894.
9878.
1178.
4606.
95119.
"FURNACE BLOWDOWN-RECALCINING EFFICIENCY"
« FRACTION » FRACTION *
0. 0.95
"NEW MAKEUP LIME ADDED, FRACTION COMPOS ITI ON"
» SI02 !! ACID INSOL. INERTS :c MGO I!CAO «
0.03 0.01 0.07 0.89
"FIRST STAGE CENTR-VT. rrir'PONENTS LB/DAY"
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FECOH)3
SI02
ACID INSOL.
CA3CP04)2
TOTAL
INERTS
40334.
0.
21123.
3706.
3257.
940.
4073.
1098.
663.
13108.
88303.
« PRIMARY INFLUENT COMPOS IT ION, MG/L *
»SUSP.SOLIDS!:MAGrESIUM"CALClUM"PHOSPHORUS"SI02!!A. I . INERTS" I RON"
240.0 22.3 30.0 10.00 13.7 1.9 0.
* PRIMARY EFFLUENT COMPOSITION,MG/L ;t
"SUSP.SOLIDS"MAGt,'ESlUM"CALCIUM"PHOSPHORUS"SI02"A. I . INERTS"IRON"
26.0 15.6 C5.2 0.68 0.9 0.1 0.
"RECALCULATION FURf-WCE PRODUCT COMPONENTS,LB/DAY"
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FECOH)3
SI02
ACID INSOL.
CA3(P04)2
TOTAL
INERTS
0.
26874.
2526.
1822.
0.
831.
0.
9680.
1025.
4329.
47087.
295
-------
"RECALCULATION FURNACE WET SCRUBBER WATER COMPONENTS, LB/DAY11
ORGANICS
CAO
CAC03
MGO
MGC002
FE203
FECOI-03
SI02
ACID 1NSOL. INERTS
TOTAL
0.
0.
3802.
158.
0.
W*.
0.
198.
153.
276.
1*631.
"RECYCLED SOLIDS ACCEPTS COMPONENTS,L8/DAY*
ORGANICS
CAO
CAC03
MGO
MSCOH)2
FE203
FEC003
SI02
ACID INSOL.
CA3(POl*)2
TOTAL
"SECOND STAGE
ORGANICS
CAO
CAC03
MGO
MGCOH52
FE2O3
FE(OH)3
SI02
ACID INSOL.
CA3(POl*)2
0.
26361*.
21*85.
1760.
0.
718.
0.
7367.
INERTS 952.
i)li*3.
1*3789.
CAKE COMPONENTS, LB/DAY"
311*61.
0.
17532.
3336.
2931.
705.
3055.
889.
INERTS 1*51.
1?191.
."INCINERATION FURNACE WET SCRUBBER WATER COMPONENTS,LB/DAY*
ORGANICS
CAO
CAC03
MGO
M6COH)2
FE203
FE(OK>3
SI02
ACID INSOL.
CA3CP0452
TOTAL
INERTS
0.
0.
1227.
1*28.
0.
H*9.
0.
18.
59.
731.
2612.
CLASSIFIER REJECTS COMPONENTS, LB/DAYK
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FE(OH)3
SI02
ACID INSOL. INERTS
CA3(PO"*)2
TOTAL
0.
511.
1*0.
62.
0.
113.
0.
231t.
73.
186.
3299.
TOTAL
72550.
^RECOVERIES OF COMPONENTS IN PROCESS STREAMS, FRACTION"
"SECOND STAGE CENTRATE RECYCLE COMPONENTS,LE/DAYX
FIRST :! RECALCINE «SECOND::INCINERATION" DRY
ORGANICS
CAO
CAC03
MGO
MG(OH)2
FE203
FECOH)3
SI02
ACID INSOL. INERTS
CA3CP01O2
TOTAL
"INCINERATION FURMACE
ORGANICS
CAO
CAC03
MGO
MGCOH)2.
FE203
FECOH)3
SI02
ACID INSOL. INERTS
CA3CP0102
8873.
0.
3591.
371.
326.
235.
1018.
209.
212.
918.
15752.
WASTE ASH COMPONENTS, LB/DAY"
0.
0.
16305.
5766.
0.
3572.
0.
871.
392.
m59.
STAGE
CAKE FURNACE
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FECOH)3
SI02
INERTS
CA3CPQ1O2
TOTAL
0.35
0.
0.72
0.25
0.25
0.18
0.18
0.90
0.61*
0.26
0.52
0.
0.93
0.93
0.92
0.
0.95
0.
0.98
0.87
0.91*
STAGE
CAKE
0.78
0.
0.83
0.90
0.90
0.75
0.75
0.81
0.68
0.93
0.82
FURNACE
0.
0.
0.93
0.92
0.
0.95
0.
0.98
0.87
0.91*
CLASSIFIER
0.
0.98
0.98
0.97
0.
0.86
0.
0.76
0.93
0.96
0.93
PROGRAM STOP AT 5050
USED
.90 UNITS
TOTAL
38365.
296
-------
CASE 122
DAT1
110,30.0,9746.0,0.0,500.0,0.0,0.95
115,2.0,1.0,11.5,1.0,0.0,0.0,0.0
DAT 2
131, 2<40.0,35.0,22.3, 9. 72,28.8, 72.8
132,10.0,0.96,0.0,0.0024,0.0024
141,0.035,0.0024,0.80,0.80,0.80
151,0.035,0.035,0.027,0.0096,0.07,0.89
-FIRST PASS PRECIPITATION COMPONENTS, LB/DAY*
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FECOHJ3
SI02
ACID INSOL.
CA3CP04)2
TOTAL
INERTS
1*8780.
0.
130431.
2622.
7555.
0.
0.
3146.
506.
11295.
20"*336.
DAT3
161,0.23,0.86,0.91,0.75
171,0.30,0.30,0.18,0.18,0.41
181,0.90,0.99,0.97,0.81,0.75
182,0.75,0.78,0.90,0.90
191,0.94,0.93,0.98,0.87,0.0
192,0.95,0.0,0.0,0.92
201,0.94,0.93,0.98,0.87,0.0
202,0.95,0.0,0.0,0.92
211,0.957,0.984,0.761,0.929,0.0,0.981
212,0.864,0.0,0.0,0.966
"PRIMARY SLUDGE COMPONENTS, LB/DAY*
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FE(OH)3
SI02
ACID INSOL.
CA3CP0452
TOTAL
INERTS
56057.
0.
146659.
7674.
8110.
0.
0.
10531.
2274.
17096.
248"t01.
LIME SOLIDS PROCESSING MASS BALANCE
"FLOW11 LIME USE AS CAO -
"-PH ~ MGD^TOTAL DOSE::NEW LIME" RECYCLED LIME*
MG/L MG/L MG/L FRACTION
11.5 30.00 378.4 133.4 2^5.0 0.65
"FECL3 DOSE::WASTE BIOLOGICAL SLUDGE*
" MG/L " ADDED, LB/DAY "
0. 9746.0
"FIRST STAGE CAK
ORGANICS
CAO
CAC03
MGO
MGCOI-02
FE203
FE(OH)3
5102
ACID INSOL.
CA3CP04)2
TOTAL
INERTS
22983.
0.
126127.
2302.
2433.
0.
0.
9583.
1705.
3932.
169066.
"FIRST STAGE CENTRATE COMPONENTS,LB/DAYX
"FURNACE BLOWDOWN:!RECALCINING EFFICIENCY*
-: FRACTION " FRACTION "
0. 0.95
"NEW MAKEUP LIME ADDED, FRACTION COMPOSITION*
:: SI02 - ACID INSOL. INERTS :: MGO ::CAO "
0.03 0.01 0.07 0.89
ORGANICS
CAO
CAC03
MGO
MGCOH)2
FE203
FE
-------
-RECALCULATION FURNACE WET SCRUBBER WATER COMPONENTS,LB/WY»
ORGANICS
CAO
CAC03
MOO
MG(OH)2
FE203
FECOI-03
SI02
ACID INSOL. INERTS
CA3(PO
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-75-038
3. RECIPIENT'S ACCESSI Ol* NO.
4. TITLE AND SUBTITLE
LIME USE IN WASTEWATER TREATMENT:
DESIGN AND COST DATA
5. REPORT DATE
October 1975 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
Dermy S. Parker, Emilio de la Fuente,
Louis 0. Britt, Max L. Spealman, Richard J. Stenquist,
and Fred J. Zadick
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Brown and Caldwell
Consulting Engineers
1501 N. Broadway
Walnut Creek, California 94596
10. PROGRAM ELEMENT NO.
1BB043; RQAP 21-ASD; Task 18
11. CONTRACT#55}QSSf NO.
68-03-0334
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF RE PORT AND PERIOD COVERED
Final, 6/29/73 - 5/30/74
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report presents design and cost information on lime use in wastewater treatment
applications. It includes design and cost information on lime handling, liquid
processing, solids generation and dewatering, lime recovery and ultimate ash disposal
The report takes a design manual approach so that the information presented has
maximum usefulness to environmental engineers engaged in both the conceptual and
detailed design of wastewater treatment plants.
Design data on alternate sludge thickening and dewatering processes are presented
with special emphasis on wet classification of calcium carbonate from unwanted
materials and on maximizing the dewatering of wasted solids.
Alternative recalcining techniques are assessed and problem areas identified. A
relatively new technique for beneficiation of the recalcined product is presented.
Approaches to heat recovery are presented that minimize the net energy requirements
for recalcination and incineration.
A computer program for computation of solids balances is included as a design aid and
two case histories are presented which portray the cost of lime treatment, sludge
processing and lime reclamation.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Sludge disposal, Dewatering, Centrifuging
b IDENTIFIERS/OPEN ENDED TERMS
Sludge treatment, Ulti-
mate disposal, Chemical
precipitation, Solid
wastes, Chemical sludge
processing, Centrifugal
classification, Centrifu-
gal Dewatering, Recalcina
tion. Chemical treatment
COSATl I;icld/Group
13B
13. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19 SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
315
20 SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
299
U S GOVfRNMFNI PRINTING (HHU 1975-657-695/5328 Region No. 5-11
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