PROCESS DESIGN MANUAL
FOR
CARBON ADSORPTION
U.S. ENVIRONMENTAL PROTECTION AGENCY
Technology Transfer
October 1973
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ACKNOWLEDGMENTS
The original edition of this Design Manual (October 1971) was prepared for Technology
Transfer by the Swindell-Dressier Company, a Division of Pullman Incorporated. This first
revision to the basic text was also prepared for the Technology Transfer Office of the
U. S. Environmental Protection Agency by the firm of Cornell, Howland, Hayes and
Merryfield, Clair A. Hill and Associates (CH2M/HILL), and special consultants Russell L.
Gulp of the South Lake Tahoe Public Utility District and Dr. G. M. Wesner of the Orange
County (California) Water District. Major EPA contributors were J. M. Cohen, I. J.
Kugelman, J. M. Smith and J. J. Westrick of the U. S. EPA National Environmental
Research Center, Cincinnati, Ohio.
NOTICE
The mention of trade names or commercial products in this publication is for illustration
purposes and does constitute endorsement or recommendation for use by the U. S.
Environmental Protection Agency.
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ABSTRACT
The use of activated carbon for removal of dissolved organics from water and wastewater
has long since been demonstrated to be feasible. In fact, it is one of the most efficient
organic removal processes available to the engineer. The increasing need for highly
polished effluents from wastewater treatment plants, necessary to accommodate the
stringent requirements for both surface water quality and water reuse, has stimulated
great interest in carbon treatment systems. Both the great capability for organic removal
and the overall flexibility of the carbon adsorption process have encouraged its
application in a variety of situations. It readily lends itself to integration into larger, more
comprehensive waste treatment systems.
Activated carbon adsorbs a great variety of dissolved organic materials including many
which are nonbiodegradable. Adsorption is facilitated by the large surface areas on the
carbon granules which are attributable to its highly porous structure. Biological
degradation occurring on the granules complements the adsorption process in removing
dissolved organic material. Carbon in certain configurations also functions as a filter. The
greatest cost within the carbon treatment process is the cost of the carbon itself. Thermal
regeneration of the spent carbon makes the process economically feasible; the cost of the
regenerating equipment, however, represents only a small fraction of the total capital
equipment cost.
The most important design parameter is contact time. Hydraulic loading, within the
ranges normally used, has little effect on adsorption. The basic process configurations of
the physical plant include upflow or downflow, either under force of gravity or pump
pressure, with fixed or moving beds, and single (parallel) or multi-stage (series)
arrangement.
Data from both pilot and laboratory tests, as well as experience from existing full-scale
plants, must be carefully interpreted prior to the design of a new plant. Procedures for
preliminary tests are discussed here, and the characteristics of some full-scale plants,
planned or operating, are presented as well for illustrative purposes.
in
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TABLE OF CONTENTS
CHAPTER PAGE
ACKNOWLEDGMENTS //
ABSTRACT ///
TABLE OF CONTENTS v
LIST OF FIGURES vii
LIST OF TABLES xiii
FOREWORD xv
1 INTRODUCTION
1.1 Purpose 1-1
1.2 Scope 1-1
1.3 History 1-2
1.4 System Performance and Effluent Qualities 1-2
1.5 Additional Reading 1-4
1.6 Reference 1-4
2 ACTIVATED CARBON MANUFACTURE AND
CHARACTERISTICS
2.1 Activated Carbon — Introduction
2.2 The Activation Process 2-2
2.3 The Nature of Adsorption 2-3
2.4 Carbon Properties Relating to Adsorption 2-3
2.5 Carbon Particle Size 2-4
2.6 Adsorption Characteristics 2-4
2.7 References 2-6
3 GENERAL PROCESS DESIGN CONSIDERATIONS
3.1 Introduction 3-1
3.2 Design Flow 3-4
3.3 Wastewater Quality Considerations 3-6
3.4 Carbon Contacting Systems 3-7
3.5 Biological Activity in Carbon Contactors 3-17
3.6 Design Examples 3-21
3.7 Carbon Inventory 3-36
3.8 Carbon Transport 3-40
3.9 Carbon Regeneration Systems 3-52
3.10 Recycle Flows 3-61
3.11 Monitoring and Controls 3-61
3.12 Corrosion and Abrasion Control 3-68
3.13 Additional Reading 3-69
3.14 References 3-70
4 CARBON AND EVALUATION AND SELECTION
4.1 Introduction 4-1
4.2 Wastewater Characterization 4-1
4.3 Carbon Evaluation Procedures 4-2
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TABLE OF CONTENTS - Continued
CHAPTER
4
CARBON AND EVALUATION AND SELECTION - Cont'd.
4.4 Adsorption Isotherms
4.5 Pilot Carbon Column Tests
4.6 Biological Activity and Carbon Adsorption
4.7 References
CARBON ADSORPTION TREATMENT SYSTEM COSTS
5.1 Introduction
5.2 Capital Costs
5.3 Operation and Maintenance Costs, Tahoe Data
5.4 Personnel Requirements
5.5 Operation and Maintenance Costs
5.6 Effects of Recycle Flows on Costs
5.7 Cost Estimating Guides
5.8 Summary of Carbon Treatment Costs
5.9 Reference
TYPICAL TREATMENT FACILITIES
6.1 Introduction
6.2 Current Plant Design, Construction, and Operation
6.3 References
PAGE
4-4
4-5
4-17
4-20
5-1
5-1
5-10
5-17
5-17
5-22
5-23
5-23
5-31
6-1
6-1
6-25
Appendix
A
B
LIST OF APPENDIXES
Glossary of Terms Used with Granular Carbon
Control Tests — Carbon Adsorption and Regeneration
B.I Iodine Number
B.2 Molasses Number
B.3 Decolorizing Index
B.4 Methylene Blue Number
B.5 Hardness Number
B.6 Abrasion Number (Ro-Tap)
B.7 Abrasion Number (NBS)
B.8 Apparent Density
B.9 Sieve Analysis (Dry)
B.10 Effective Size and Uniformity Coefficient
B.ll Moisture
B.I2 Total Ash
Metric Conversion Chart
A-l
B-l
B-2
B-6
B-7
B-l 2
B-17
B-20
B-22
B-23
B-26
B-27
B-28
B-30
C-l
VI
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LIST OF FIGURES
Figure No. Page
3-1 Typical Treatment Schemes Utilizing Carbon Adsorption
as a Tertiary Step 3-2
3-2 Typical Physical-Chemical Treatment Schemes 3-3
3-3 Two Downflow Carbon Beds in Series 3-9
3-4 Pressure Drop Vs. Hydraulic Loading 3-13
3-5 Headloss on Bed Expansion 3-15
3-6 Expansion of Carbon Bed at Various Flow Rates 3-16
3-7 Air-Vacuum Release Valve Detail 3-18
3-8 Upflow Countercurrent Carbon Column, Orange County,
California 3-22
3-9 Top and Bottom Underdrains, Orange County, California 3-23
3-10 Section Through Top Underdrain, Orange County,
California 3-24
3-11 Carbon Filling Chamber, Orange County, California 3-25
3-12 Upflow Carbon Column Schematic - Normal Operation,
Orange County, California 3-27
3-13 Upflow Carbon Column Schematic - Upflow to Waste,
Orange County, California 3-28
3-14 Upflow Carbon Column Schematic- Reverse Flow,
Orange County, California 3-29
3-15 Upflow Carbon Column Schematic- Bypassing Carbon
Column, Orange County, California 3-30
3-16 Upflow Open Packed Bed Contactor 3-32
3-17 Upflow Open Expanded Bed Contactor 3-33
3-18 Pressurized Downflow Contactor, Pomona, California 3-35
3-19 Pressurized Downflow Contactor, Colorado Springs,
Colorado 3-37
VII
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LIST OF FIGURES - Continued
Figure No. Page
3-20 Pressurized Downflow Contactor, Rocky River, Ohio 3-38
3-21 Typical Downflow Gravity Contactor 3-39
3-22 Carbon Transfer with Upflow Column in Service 3-41
3-23 Carbon Delivery Rate (2-inch pipe) 3-43
3-24 Carbon Delivery Rate (1-inch pipe) 3-44
3-25 Pressure Drop of Carbon-Water Slurries (2-inch pipe) 3-45
3-26 Blowcase Transport System 3-46
3-27 Regenerated Carbon Wash Tank 3-49
3-28 Makeup Carbon Wash Tank 3-50
3-29 Carbon Regeneration System Schematic 3-54
3-30 Cross-Sectional View of Multiple Hearth Furnace 3-57
3-31 Typical Carbon Furnace Discharge Chute 3-58
3-32 Typical Carbon Furnace Quench Tank 3-59
3-33 Spent Carbon Drain Bin and Furnace Feed Arrangement 3-60
3-34 Carbon Contacting and Regeneration—Process Flow
Diagram with Upflow Contactors 3-66
4-1 Typical Breakthrough Curves 4-6
4-2 Adsorption Isotherm — Carbon A and B 4-7
4-3 Adsorption Isotherm — Carbon C and D 4-7
4-4 Upflow Pilot Carbon Column 4-10
4-5 Downflow Pilot Carbon Columns 4-11
4-6 COD Breakthrough Curves (Ideal) 4-12
4-7 COD Concentration at Various Bed Depths for Upflow
Pilot Column Charged with Brand A Carbon 4-14
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LIST OF FIGURES - Continued
Figure No. Page
4-8 Comparison of Adsorptive Capacities of Test Carbons
4.25 Feet Carbon Bed Depth, 4.6 Minute Contact Time 4-15
4-9 Comparison of Adsorptive Capacities of Test Carbons
14.25 Feet Bed Depth, 17.5 Minute Residence Time 4-16
4-10 Comparison of COD Removal Ability of Test Carbons
Small Depth, 14.25 Feet 4-18
4-11 Effect of Contact Time on COD Removal 4-19
5-1 Contactor System Costs Based on Contactor Size 5-4
5-2 Contactor System Costs Based on Design Flow and
30 Minutes Contact 5-5
5-3 Carbon Regeneration System Construction Cost 5-7
5-4 Carbon Regeneration Cost Vs. Throughput 5-9
5-5 Carbon Adsorption Pump Station Cost 5-11
5-6 Total Capital Cost Development 5-12
5-7 Carbon Adsorption Labor Requirements 5-18
5-8 Carbon Regeneration Labor Requirements 5-19
5-9 Carbon Adsorption Operation and Maintenance Costs 5-20
5-10 Carbon Regeneration Operation and Maintenance Costs 5-21
5-11 Total Annual and Unit Costs for Carbon Treatment 5-28
5-12 Total Capital Costs for Carbon Treatment 5-29
6-1 Tertiary Treatment Schematic — Arlington County, Virginia 6-3
6-2 Tertiary Treatment Schematic — Colorado Springs, Colorado 6-3
6-3 Tertiary Treatment Schematic — Dallas, Texas
(Trinity River Authority) 6-4
IX
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LIST OF FIGURES - Continued
Figure No. Page
6-4 Tertiary Treatment Schematic — Fairfax County, Virginia
(Lower Potomac Plant) 6-4
6-5 Tertiary Treatment Schematic — Montgomery County,
Maryland 6-5
6-6 Tertiary Treatment Schematic — Upper Occoquan
Sewerage Authority, Virgina 6-5
6-7 Tertiary Treatment Schematic - Orange County, California 6-6
6-8 Tertiary Treatment Schematic — Los Angeles, California 6-6
6-9 Tertiary Treatment Schematic - Piscataway, Maryland 6-7
6-10 Tertiary Treatment Schematic — St. Charles, Missouri 6-7
6-11 Tertiary Treatment Schematic — South Lake Tahoe,
California 6-8
6-12 Tertiary Treatment Schematic — Windhoek, South Africa 6-8
6-13 Physical-Chemical Treatment Schematic — Cortland,
New York 6-10
6-14 Physical-Chemical Treatment Schematic — Cleveland
Westerly, Ohio 6-10
6-15 Physical-Chemical Treatment Schematic — Fitchburg,
Massachusetts 6-11
6-16 Physical-Chemical Treatment Schematic — Garland, Texas 6-11
6-17 Physical-Chemical Treatment Schematic — LeRoy,
New York 6-12
6-18 Physical-Chemical Treatment Schematic — Niagara Falls,
New York 6-12
6-19 Physical-Chemical Treatment Schematic — Owosso, Michigan 6-13
6-20 Physical-Chemical Treatment Schematic — Rosemount,
Minnesota 6-13
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TABLE 1-1
ANTICIPATED PERFORMANCE OF VARIOUS UNIT PROCESS COMBINATIONS
(FROM REFERENCE 1)
SOURCE OF
WASTEWATER
FLOW
Preliminary'^)
Primary
Settling
Effluent
High Rate
Trickling
Filter
System
Effluent
Conventional
Activated
Sludge System
Effluent
ADDITIONAL
UNIT PROCESS
COMBINATIONS^)
c,s
C,S, F
C,S, F, AC
C,S, NS, F, AC
c,s
C,S, F
C,S, F, AC
C,S, NS, F, AC
F
c,s
C,S, F
C,S, F, AC
C,S, NS, F, AC
F
c,s
C,S, F
C,S, F, AC
C,S, NS, F, AC
ESTIMATED PROCESS EFFLUENT QUALITY
BOD
(mg/l)
50-100
30-70
5-10
5-10
50-100
30-70
5-10
5-10
10-20
10-15
7-12
1-2
1-2
3-7
3-7
1-2
0-1
0-1
COD
(mg/l)
80-180
50-150
25-45
25-45
80-180
50-150
25-45
25-45
35-60
35-55
30-50
10-25
10-25
30-50
30-50
25-45
5-15
5-15
TURB.
(JTU)
5-20
1-2
1-2
1-2
5-15
1-2
1-2
1-2
6-15
2-9
0.1-1
0.1-1
0.1-1
2-8
2-7
0.1-1
0.1-1
0.1-1
P04
(mg/l)
2-4
0.5-2
0.5-2
0.5-2
2-4
0.5-2
0.5-2
0.5-2
20-30
1-3
0.1-1
0.1-1
0.1-1
20-30
1-3
0.1-1
0.1-1
0.1-1
s.s.
(mg/l)
10-30
2-4
2-4
2-4
10-25
2-4
2-4
2-4
10-20
4-12
0-1
0-1
0-1
3-12
3-10
0-1
0-1
0-1
COLOR
(UNITS)
30-60
30-60
5-20
5-20
30-60
30-60
5-20
5-20
30-45
25-40
25-40
0-15
0-15
25-50
20-40
20-40
0-15
0-15
NH3 -N
(mg/l)
20-30
20-30
20-30
1-10
20-30
20-30
20-30
1-10
20-30
20-30
20-30
20-30
1-10
20-30
20-30
20-30
20-30
1-10
(1) C,S = coagulation and sedimentation; F = mixed-media filtration;
AC = activated carbon adsorption; NS = ammonia stripping.
Lower effluent NHg value at 18°C; upper value at 13°C.
(2) Preliminary treatment — grit removal, screen chamber.
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effluent quality of various unit process combinations which would be universally
applicable. However, a general indication of expected trends and relative performances is
presented in Table 1-1.
1.5 Additional Reading
1. Mattson, J. S. and Mark, H. B. Jr., Activated Carbon. Marcel Dekker, New York,
1971.
2. Smisek, M., and Cerny, S., Active Carbon. Elsevier Publishing Co., New York, 1970.
3. Adsorption from Aqueous Solutions. Symposium Proceedings, Advances in
Chemistry Series, 79, American Chemical Society, Washington, D. C., 1968.
1.6 Reference
1. Gulp, R. L., and Gulp, G. L., Advanced Wastewater Treatment. Van Nostrand
Reinhold, New York, 1971.
1-4
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LIST OF FIGURES - Continued
Figure No. Page
6-21 Physical-Chemical Treatment Schematic — Rocky River,
Ohio 6-14
6-22 Physical-Chemical Treatment Schematic — Vallejo,
California 6-14
B-l Example of Standard Curve for Decolorizing Index B-l 1
B-2 Testing Pan for Determining Hardness and Abrasion B-l8
B-3 Arrangement of Rotap Pans for Hardness and Abrasion Test B-l9
B-4 Apparent Density Test Apparatus B-24
B-5 Cumulative Particle Size Distribution Curve B-29
NOTE:
The following illustrations are from Advanced Wastewater
Treatment by Russell L. Gulp and Gordon L. Gulp,
copyright 1971 by Litton Educational Publishing, Inc., and
are reprinted herein with the permission of Van Nostrand
Reinhold Company: (Figures) 3-3, 3-29, 3-30, 3-33, 4-1,
4-2, 4-3, 4-4, 4-5.
XI
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LIST OF TABLES
Table No. Page
1-1 Anticipated Performance of Various Unit Process
Combinations 1-3
2-1 Properties of Several Commercially Available Carbons 2-5
5-1 Relative Costs of Various Contactor Systems 5-3
5-2 Unit Costs at South Lake Tahoe 5-13
5-3 Carbon Adsorption Operating and Capital Costs at
South Lake Tahoe 5-14
5-4 Carbon Regeneration Operating and Capital Costs
at South Lake Tahoe 5-15
5-5 Carbon Regeneration Operating and Capital Cost
Per Ton of Carbon Regenerated at South Lake Tahoe 5-16
5-6 Selected Unit Costs for Estimating Operation and
Maintenance Costs 5-22
5-7 Estimated Granular Activated Carbon Treatment Cost 5-24
5-7A Estimated Granular Activated Carbon Treatment Cost 5-26
5-8 Cost Distribution for Example Carbon Treatment
System 5-30
6-1 General Design Parameters 6-1
6-2 Tertiary Treatment Plants 6-2
6-3 Physical-Chemical Treatment Plants 6-9
6-4 Water Quality Requirements and Performance Data
at South Lake Tahoe 6-16
6-5 Water Quality at Various Stages of Treatment at
South Lake Tahoe 6-17
6-6 Carbon Efficiency per Regeneration Period at South
Lake Tahoe 6-18
xm
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LIST OF TABLES - Continued
Table No. Page
6-7 Carbon Furnace Parameters per Regeneration Period
at South Lake Tahoe 6-19
6-8 Furnace Operating Conditions for Four Batch
Regeneration Cycles at South Lake Tahoe 6-20
6-9 Carbon Losses During Batch Regeneration Periods
at South Lake Tahoe 6-21
6-10 Water Quality at Various Stages of Treatment at
Windhoek, South Africa 6-22
6-11 Water Quality at Pilot Plant at Orange County,
California 6-23
6-12 Effluent Requirements for Tertiary Treatment Plant
at Orange County, California 6-24
B-l Iodine Correction Factor B-5
B-2 Dilution Chart for Methylene Blue Determination B-l4
B-3 Methylene Blue Correction Chart B-l5
B-4 Suggested Sieves to be Used for Screen Analysis B-21
B-5 Factors for Calculating Mean Particle Diameter B-21
B-6 Example Effective Size and Uniformity Coefficient
Determination B-2 8
xiv
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FOREWORD
The formation of the United States Environmental Protection Agency marked a new era
of environmental awareness in America. This Agency's goals are national in scope and
encompass broad responsibility in the area of air and water pollution, solid wastes,
pesticides, and radiation. A vital part of EPA's national water pollution control effort is
the constant development and dissemination of new technology for wastewater treatment.
It is now clear that only the most effective design and operation of wastewater treatment
facilities, using the latest available techniques, will be adequate to meet the future water
quality objectives and to ensure continued protection of the nation's waters. It is
essential that this new technology be incorporated into the contemporary design of waste
treatment facilities to achieve maximum benefit of our pollution control expenditures.
The purpose of this manual is to provide the engineering community and related industry
a new source of information to be used in the planning, design and operation of present
and future wastewater treatment facilities. It is recognized that there are a number of
design manuals, manuals of standard practice, and design guidelines currently available in
the field that adequately describe and interpret current engineering practices as related to
traditional plant design. It is the intent of this manual to supplement this existing body
of knowledge by describing new treatment methods, and by discussing the application of
new techniques for more effectively removing a broad spectrum of contaminants from
wastewater.
Much of the information presented is based on the evaluation and operation of pilot,
demonstration and full-scale plants. The design criteria thus generated represent typical
values. These values should be used as a guide and should be tempered with sound
engineering judgment based on a complete analysis of the specific application.
This manual is one of several available through the Technology Transfer Office of EPA to
describe recent technological advances and new information. This particular manual was
initially issued in October of 1971 and this edition represents the first revision to the
basic text. Future editions will be issued as warranted by advancing state-of-the-art to
include new data as it becomes available, and to revise design criteria as additional
full-scale operational information is generated.
xv
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CHAPTER 1
INTRODUCTION
1.1 Purpose
In the thrust to cleanup and improve the nation's waters, much effort, time, and money
has been expended in the research and development of improved wastewater treatment
methods and processes. This work has been aimed at producing processes and systems
that will increase reliability and effectiveness of both existing wastewater treatment
facilities and developing totally new systems to be planned and constructed in the future.
One system which has been demonstrated to be capable of providing dependable and
efficient treatment and high quality effluents is granular activated carbon adsorption.
The purpose of this manual is to present information on design considerations and
descriptions of existing and planned applications of granular activated carbon adsorption
in the treatment of wastewaters.
1.2 Scope
This manual discusses and reviews activated carbon adsorption principles, pilot plant
techniques, general and detailed process design considerations, costs, operational
requirements, and describes existing or planned facilities.
This manual does not cover in detail wastewater treatment processes which normally
precede or follow carbon adsorption, except to note the extent to which these processes
affect the carbon adsorption system. Information in this manual pertains to the
application of granular activated carbon systems to municipal wastewater treatment, as
opposed to powdered carbon systems, because the experience with granular carbon
adsorption and regeneration systems is greater than with the emerging powdered carbon
technology.
Cost information has been compiled and estimates nave been prepared for major
individual unit processes and for various overall treatment systems. Where available, cost
information has also been included for facilities in actual operation. Transferring overall
system cost information to new locations must be done cautiously, since individual
differences can strongly influence costs for a particular project.
This manual discusses the application of granular activated carbon adsorption both as a
tertiary treatment process following conventional biological treatment systems, and as a
unit process which may be applied to raw or primary treated wastewaters in
physical-chemical treatment systems.
1-1
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In its initial applications, granular carbon adsorption was used in "tertiary" stages for
removal of additional organics from the effluent streams of conventional biological
treatment systems. Granular carbon adsorption is now also being used as a second stage
process in independent physical-chemical treatment (PCT) plants, since activated carbon
can remove biodegradable as well as refractory organics. In the present context,
physical-chemical treatment (PCT) refers to chemical coagulation and precipitation of raw
municipal and/or industrial wastewater, followed by adsorption on activated carbon for
removal of soluble and insoluble impurities.
At present, available data suggest that the effluent quality, cost, and reliability of PCT
for soluble organic removal falls in between the results obtainable with conventional
biological secondary treatment and "tertiary" carbon adsorption of biological secondary
effluent.
The efficiency of PCT for removal of phosphorus, heavy metals, and suspended solids is
substantially better than that of biological treatment systems and may approach that
achievable with tertiary systems.
1.3 History
The use of carbon for purposes other than fuel has been reported as early as 1550 B. C.
when it was used for medicinal purposes. The discovery of the phenomenon of
adsorption, as now understood, is generally attributed to Scheele, who in 1773 described
experiments on gases exposed to carbon. The earliest documented use of carbon for
removal of impurities from solutions is 1785 when Lowitz observed that charcoal would
decolorize many liquids. The first industrial application came a few years later when
wood char was used in a refinery to clarify cane sugar. In the 1860's charcoal was used
to remove tastes and odors from several municipal water supplies in England. However, it
has only been in the last 50 years that the techniques of enhancing the adsorptive powers
of charcoal through "activation" have been developed to a high degree on a scientific
basis.
During World War I, the purification capabilities of activated carbon were demonstrated.
A notable advance in the art was made during World War II with the development of the
catalytically active carbons used for military gas masks. Since that time, activated carbon
has been widely used as a process for separation and purification. Activated carbon is
routinely used in the food, pharmaceutical, petroleum, chemical and water processing
industries.
1.4 System Performance and Effluent Qualities
The performance and effluent quality obtainable from granular carbon treatment depends
on the character of the wastewater being treated and the proficiency with which the
facilities are operated. Due to these variations, it is impossible to present predictions of
1-2
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CHAPTER 2
ACTIVATED CARBON MANUFACTURE AND CHARACTERISTICS
2.1 Activated Carbon—Introduction
Activated carbon removes organic contaminants from water by the process of adsorption
or the attraction and accumulation of one substance on the surface of another. In
general, high surface area and pore structure are the prime considerations in adsorption or
organics from water; whereas, the chemical nature of the carbon surface is of relatively
minor significance. Granular activated carbons typically have surface areas of 500-1,400
square meters per gram. Activated carbon has a preference for organic compounds and,
because of this selectivity, is particularly effective in removing organic compounds from
aqueous solution.
Much of the surface area available for adsorption in granular carbon particles is found in
the pores within the granular carbon particles created during the activation process. The
major contribution to surface area is located in pores of molecular dimensions. A
molecule will not readily penetrate into a pore smaller than a certain critical diameter
and will be excluded from pores smaller than this diameter.
The most tenacious adsorption takes place when the pores are barely large enough to
admit the adsorbing molecules. The smaller the pores with respect to the molecules, the
greater the forces of attraction.
Activated carbons can be made from a variety of carbonaceous materials including wood,
coal, peat, lignin, nut shells, bagasse (sugar cane pulp), sawdust, lignite, bone, and
petroleum residues. In the past, carbons used in industrial applications have been
produced most frequently from wood, peat, and wastes of vegetable origin such as fruit
stones, nut shells and sawdust. The present tendency in wastewater treatment
applications, however, is toward use of various kinds of natural coal and coke which are
relatively inexpensive and readily available. Of interest is the potential utilization of
different wastes as raw materials; for example: waste lignin, sulfite liquors, processing
wastes from petroleum and lubricating oils, and carbonaceous solid waste.
The quality of the resulting activated carbon is influenced by the starting material. The
starting material is particularly important where selective adsorptive properties are
required, as, for example, in the treatment of wine, or in the separation of components
in preparative chemistry. For most activated carbons, however, some properties arising
from the nature of the starting material are masked by choice of production technique.
These production techniques can form granular activated carbons by crushing or pressing.
Crushed activated carbon is prepared by activating a lump material, which is then crushed
and classified to desired particle size. Pressed activated carbon is formed prior to
activ?tion. The appropriate starting material is prepared in a plastic mass, then extruded
2-1
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from a die and cut into pieces of uniform length. These uniform cylindrical shapes are
then activated. The necessary hardness is acquired in the activation process.
The ^hysical characteristics of hardness, a very important factor, are directly related to
the nature of the starting material for crushed activated carbons. For activated carbons
formed from pulverized materials, which are then bound together, the nature of the
binding agent is a major factor in determining the hardness of the finished product.
2.2 The Activation Process
Activated carbon is manufactured by a process consisting of raw material dehydration
and carbonization followed by activation. The starting material is dehydrated and
carbonized by slowly heating in the absence of air, sometimes using a dehydrating agent
such as zinc chloride or phosphoric acid. Excess water, including structural water, must
be driven from the organic material. Carbonization converts this organic material to
primary carbon, which is a mixture of ash (inert inorganics), tars, amorphous carbon, and
crystalline carbon (elementary graphitic crystallites). Non-carbon elements (f^ and C^)
are removed in gaseous form and the freed elementary carbon atoms are grouped into
oxidized crystallographic formations. [ 1 ] During carbonization, some decomposition
products or tars will be deposited in the pores, but will be removed in the activation
step.
Activation is essentially a two-phase process requiring burn-off of amorphous
decomposition products (tars), plus enlargement of pores in the carbonized material.
Burn-off frees the pore openings, increasing the number of pores, and activation enlarges
these pore openings. Activated carbon can be manufactured by two different
procedures: physical activation and chemical activation. Although both processes are
widely used, physically activated carbons are utilized in wastewater treatment while
chemically activated carbons are utilized elsewhere-such as the recovery of solvents. The
discussion of carbon activation herein is therefore limited to physical activation.
Carbonization and activation are two separate processes. The methods of carbonization
differ, and the method used will affect activation and the final quality of the carbon. The
essential steps in carbonization are as follows:
1. Dry the raw material at temperatures up to 170 degrees C.
2. Heat the dried material above 170 degrees C causing degradation with evolution
of CO, CO2 and acetic acid.
3. Exothermal decomposition of the material at temperatures of 270-280 degrees
C with formation of considerable amounts of tar, methanol and other
by-products.
2-2
-------
4. Complete the carbonization process at a temperature of 400-600 degrees C,
with a yield of approximately 80 percent primary carbon.
The carbonized intermediate product is then treated with an activating agent such as
steam or carbon dioxide (steam is most widely used). Steam, at temperatures of 750-950
degrees C, burns off the decomposition products exposing pore openings for subsequent
enlargement. All pores are not plugged with amorphous carbon, therefore some pores are
exposed to the activating agent for longer periods of time. Exposure to the activating
agent results in the widening of existing pores, and development of the macroporous
structure.
2.3 The Nature of Adsorption
Adsorption by activated carbon involves the accumulation or concentration of substances
at a surface or interface. Adsorption is a process in which matter is extracted from one
phase and concentrated at the surface of another, and is therefore termed a surface
phenomenon. Adsorption from wastewater onto activated carbon can occur as a result of
two separate properties of the wastewater-activated carbon system, or some combination
of the two: (1) the low solubility of a particular solute in the wastewater; and (2) a high
affinity of a particular solute in the wastewater for the activated carbon. According to
the most generally accepted concepts of adsorption, this latter surface phenomenon may
be predominantly one of electrical attraction of the solute to the carbon, of van der
Wads attraction, or of a chemical nature.
There are essentially three consecutive steps in the adsorption of dissolved materials in
wastewater by granular activated carbon. The first step is the transport of the solute
through a surface film to the exterior of the carbon. The second step is the diffusion of
the solute within the pores of the activated carbon. The third and final step is adsorption
of the solute on the interior surfaces bounding the pore and capillary spaces of the
activated carbon.
There are several factors which can influence adsorption by activated carbon,
including: (1) the nature of the carbon itself; (2) the nature of the material to be
adsorbed, including its molecular size and polarity; (3) the nature of the solution,
including its pH; and (4) the contacting system and its mode of operation.
This topic is considered in more detail elsewhere [1, 2, 3, 4].
2.4 Carbon Properties Relating to Adsorption
Because adsorption is a surface phenomenon, the ability of activated carbon to adsorb
large quantities of organic molecules from solution stems from its highly porous
structure, which provides a large surface area. Carbon has been activated with a surface
area yield of some 2,500 m2/gram, but 1,000 m2/gram is more typical.
2-3
-------
Total surface area is normally measured by the adsorption of nitrogen gas by the
Brunauer-Emmett-Teller (BET) method [5]. The distribution of this area into pores of
different diameters is measured by determining the amount of nitrogen desorbed at
intermediate pressures.
Another method for determining the area of pores above a lower size limit for a given
carbon is by measuring the amount of adsorbate of a given molecular size that is removed
from solution. For example, the amount of iodine adsorbed from solution has been
found to be proportional to the surface area contributed by pores having diameters
greater than 10 angstroms. Similarly, the adsorption of methylene blue and molasses can
be correlated with surface area in pores with diameters greater than 15 and 28 angstroms,
respectively.
Particle size is generally considered to affect adsorption rate, but not adsorptive capacity.
The external surface constitutes a small percent of the total surface area of an activated
carbon particle. Since adsorption capacity is related to surface area, a given weight of
carbon gains little adsorptive capacity upon being crushed to smaller size.
2.5 Carbon Particle Size
Activated carbons are classified according to their form: for example, powdered or
granular; and according to their use: for example, water or wastewater purification, sugar
decolorizing, and liquid or gas phase solvent extraction. Granular carbons are those which
are larger than approximately U. S Sieve Series No. 50, while powdered carbons are those
which are smaller. Properties of several commercially available granular carbons are
presented in Table 2-1.
Headloss in the carbon contactor is an important design consideration and is affected by
tne carbon particle size. The suspended solids concentration in the wastewater to be
treated by the carbon will also affect the headloss and will thereby be a factor in
selection of carbon particle size. The particle size headloss design considerations are
discussed in detail in Chapter 3.
2.6 Adsorption Characteristics
The adsorptive capacity of a carbon can be measured by determining the adsorption
isotherm with the wastewater under consideration. Simpler adsorption capacity tests such
as the Iodine Number or the Molasses Number may also be appropriate. Pilot tests are
also considered important. These tests are described in detail in the chapter on laboratory
and pilot tests (Chapter 4).
2-4
-------
TABLE 2-1
PROPERTIES OF SEVERAL COMMERCIALLY AVAILABLE CARBONS*
PHYSICAL PROPERTIES
Surface area, m^/gm (BET)
Apparent density, gm/cc
Density, backwashed and drained,
Ib/cu.ft.
Real density, gm/cc
Particle density, gm/cc
Effective size, mm
Uniformity coefficient
Pore volume, cc/gm
Mean particle diameter, mm
SPECIFICATIONS
Sieve size (U.S. std. series)
Larger than No. 8 (max. %)
Larger than No. 12 (max. %)
Smaller than No. 30 (max. %)
Smaller than No. 40 (max. %)
Iodine No.
Abrasion No., minimum
Ash (%)
Moisture as packed (max. %)
ICI
AMERICA
HYDRODARCO
3000
600-650
0.43
22
2.0
1.4-1.5
0.8-0.9
1.7
0.95
1.6
8
—
5
—
650
**
**
**
CALGON
FILTRASORB
300
(8x30)
950-1050
0.48
26
2.1
1.3-1.4
0.8-0.9
1.9 or less
0.85
1.5-1.7
8
—
5
—
900
70
8
2
WESTVACO
NUCHAR
WV-L
(8x30)
1000
0.48
26
2.1
1.4
0.85-1.05
1.8 or less
0.85
1.5-1.7
8
—
5
—
950
70
7.5
2
WITCO
517
(12x30)
1050
0.48
30
2.1
0.92
0.89
1.44
0.60
1.2
—
5
5
—
1000
85
0.5
1
* Other sizes of carbon are available on request from the manufacturers.
** No available data from the manufacturer.
— Not applicable to this size carbon.
-------
2.7 References
1. Weber, W. J., Jr., Physico chemical Processes for Water Quality Control. John Wiley
and Sons, Inc., New York, 1972.
2. Hassler, J. W., Activated Carbon. Chemical Publishing Co., 1963.
3. DeBoer, J. H. The Dynamic Character of Adsorption. Oxford University Press,
1968.
4. Mantell, C. L., Adsorption. McGraw-Hill Book Co., 1945.
5. Smisek, M., and Cerny, S., Active Carbon. Elsevier Publishing Co., New York, 1970.
2-6
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CHAPTER 3
GENERAL PROCESS DESIGN CONSIDERATIONS
3.1 Introduction
Activated carbon has been utilized in numerous industrial products and processes for
many years, and much of the present application technology has developed therefrom. In
the last ten years, granular activated carbon treatment of wastewater has been
demonstrated for both municipal and industrial applications. The process has become
much more attractive for widespread use due to the development of economical
regeneration methods and equipment.
There are currently two approaches for the use of granular activated carbon in
wastewater treatment. One approach is to use activated carbon in a "tertiary" treatment
sequence following conventional primary and biological secondary treatment. Tertiary
treatment processes involving carbon range from treatment of the secondary effluent with
only activated carbon to systems with chemical clarification , nutrient removal, filtration,
carbon adsorption and disinfection. Another approach utilizes activated carbon in a
"physical-chemical" treatment (PCT) process in which raw wastewater is treated in a
primary clarifer with chemicals prior to carbon adsorption. Filtration and disinfection
may also be included in PCT, but biological processes are not used. Flow diagrams for
some alternate treatment schemes for tertiary and PCT systems are shown in Figures 3-1
and 3-2. A detailed description of tertiary and PCT systems currently under design,
construction, or in operation is included in Chapter 6.
If biological treatment and efficient filtration precede carbon treatment, there are several
benefits: (1) the applied loads of BOD, COD, and other organics are reduced allowing
either the production of a higher quality carbon column effluent at a given contact time,
or the production of equal water quality at a shorter contact period, (2) the applied
loads of suspended and colloidal solids are less, thus reducing headless through the bed of
carbon, which may aid in solving problems of physical plugging, ash buildup, and
progressive loss of adsorptive capacity in the carbon particles after several cycles of
regeneration, and (3) the problems of biological growth, septicity, and hydrogen sulfide
production may be decreased by reducing the supply of bacterial food and oxygen
demanding substances applied to the carbon.
The PCT approach seeks to make maximum use of granular activated carbon by
extending its function of removing refractory dissolved organics to adsorption of
biodegradable organics as well, and, in some cases, by using the granular bed of carbon as
a filter to remove suspended and colloidal materials. With this approach the carbon is
loaded as heavily as possible within the limits of effluent water quality criteria. PCT will
result in capital cost savings when compared with biological treatment followed by
3-1
-------
CHEMICAL
COAGULATION AND
SEDIMENTATION
(OPTIONAL)
FILTRATION
MAKEUP ^____— -
CARBON "
CARBON
ADSORPTION
^T 1
CARBON
REGENERATION
FIGURE 3-1
TYPICAL TREATMENT SCHEMES UTILIZING CARBON
ADSORPTION AS A TERTIARY STEP
3-2
-------
COAGULANT
PRELIMINARY
TREATMENT
.L.
CHEMICAL
CLARIFICATION
-
FILTRATION
— ^
CARBON
ADSORPTION
^
DISINFECTION
MAKEUP ~^*\ W
CARBON
CARBON
REGENERATION
COAGULANT
PRELIMINARY
TREATMENT
u
CHEMICAL
CLARIFICATION
MAKEU
CARBO
—*
^
EXPANDED
UPFLOW
CARBON
ADSORPTION
A I
CARBON
REGENERATION
—•
FILTRATION
DISINFECTION
(b)
.COAGULANT
PRELIMINARY
TREATMENT
L
CHEMICAL
CLARIFICATION
MAKEU
CARBO
—*
^
CARBON
ADSORPTION
A I
CARBON
REGENERATION
—4
DISINFECTION
(c)
FIGURE 3-2
TYPICAL PHYSICAL-CHEMICAL TREATMENT SCHEMES
3-3
-------
tertiary treatment. However, it has been shown in several cases that only when biological
oxidation, chemical coagulation, filtration, and adsorption are operated in series as
separate processes can the effluent quality be optimized. The capabilities of PCX must be
evaluated in light of specific effluent quality requirements to determine its applicability
to a given problem.
Carbon adsorption and carbon regeneration are basically simple processes, and are
therefore quite reliable. Carbon is versatile and may be used in a variety of locations in
wastewater treatment plants. There is no single method of contacting or contactor design
which is best for all conditions because of the placement of carbon adsorption at
different points in the wastewater treatment unit operation sequence, and the varying
qualities of wastewater which may be applied to the carbon. Design, equipment, and
material selection may also be influenced by the total capacity of the plant under
consideration. There are fewer design variables in carbon regeneration systems, and
facilities are therefore more uniform in their concept and design. Also, somewhat more
standardized are carbon transport, monitoring, and control systems.
With the requirement for more complete wastewater treatment there also is a need for
greater reliability of unit processes and overall treatment systems. The ability of carbon
to continue functioning satisfactorily under certain shock hydraulic and organic loads
contributes to its reliability. The need for standby facilities to assure continuous plant
operation at full capacity under various service and emergency conditions should not be
overlooked.
This chapter presents information intended to assist engineers in the detailed design of
granular carbon contacting and regeneration systems and auxiliaries. This information is
drawn from theory and the experience gained from the design and operation of
laboratory, pilot, and full-scale carbon treatment systems.
3.2 Design Flow
Selection of the proper design flow also requires an analysis of the following factors:
1. Useful operating life of the plant
a. as influenced by normal wear-and-tear.
b. as influenced by technology.
2. Interest rates and the rate of inflation during the life of the plant.
3. Expected population changes in the plant service area.
3-4
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4. Changes in domestic living habits and consumer patterns (i.e., standard of
living).
5. Changes in levels and types of industrial activity in the plant's service area.
6. Recycle flows within the plant (which may amount to 5 to 25 percent of the
plant raw flow).
7. Changes in requirements for treated water quality.
One approach is to design the facility for a relatively short term, taking into account
only those future events and trends which can be foreseen with some certainty. At the
same time, the plant should be constructed so that its capacity can be increased as
needed without abandoning or greatly changing the original equipment. A good way to
accomplish this is by using the modular approach to plant design which provides for
plant expansion by building new plant units (or modules). Physical-chemical treatment
plants, and the carbon facilities in particular, are well-suited to the modular design
approach.
Additional capacity for removal of organics can be provided by adding extra spent carbon
storage capacity and by oversizing the regeneration facilities. In the original design, it is
often relatively inexpensive to oversize the regeneration equipment and to operate it
initially on a part-time schedule. Application of more organics to the carbon will increase
the quantity of carbon to be regenerated; however, there are some savings resulting from
continuous rather than intermittent operation of the furnace. Thus, nonproductive
operating costs, such as that associated with startup and shutdown, will be reduced but
will be offset by productive operating costs.
Since carbon adsorbers readily conform to modular design concepts, treatment plant
capacity may be increased by merely adding additional contactor vessels, as required. The
initial facility layout should anticipate future installation of additional contactors and
associated apparatus in order to minimize construction costs and disruption of plant
operations.
Streams of wastewater vary in their volume and chemical composition because of changes
in the processes or in the events which generate these streams. These variations frequently
exhibit clearly defined cycles. Municipal wastewater exhibits diurnal cycles corresponding
to the life patterns of the population, length of sewer, and size of the town. Infiltration
of ground water or storm water connections may have a marked effect on these cycles.
Industrial wastes may be influenced by the working hours of the plants, shift changes,
weekend shutdowns, summer holidays, or fluctuations in production rates caused by
seasonal marketing patterns. It is important to recognize that fluctuations occur in the
chemical character of the wastewater as well as in its volume.
3-5
-------
Provisions must be included in treatment plant design to handle these variations. In the
past, the major elements in a conventional plant usually have been designed on the basis
of the average dry weather flow expected at the end of the design period, although plant
hydraulics may have been designed on the basis of peak hourly flows. In cases of
greater-than-average flow, wastewater has often been permitted to pass through the
treatment plant as usual. The increased flow often results in poorer treatment, and an
effluent of poor quality may be discharged for a time during the high flow period.
One method of avoiding inferior effluent quality is to construct a flow equalization basin
preceding the plant. Excess flows or highly concentrated wastes can then be accumulated
during surges and later be allowed to enter the plant gradually without impairing
treatment efficiency. Some form of flow equalization may be advisable in any situation
where the processes themselves cannot readily accommodate the flow variations, or where
it is not economical to provide larger or standby units for the greater capacity
requirement. A detailed discussion of flow equalization facilities is presented in the
U. S. EPA Technology Transfer Process Design Manual for Upgrading Existing Wastewater
Treatment Plants.
Equalization of the wastewater flow has the following advantages:
1. The head and flow capacity of pump systems can be reduced with savings in
capital investment and the cost of electric power for operation.
2. The total head for operation of gravity flow units can be reduced for the lower
flow rate, thus decreasing construction costs.
3. Lower flow rates will allow the use of smaller pipelines, valves, and meters; and
the reduced span of instrument operating ranges may increase their sensitivity
and control capability.
4. Carbon contactors may be smaller or fewer in number without exceeding safe
design criteria.
3.3 Wastewater Quality Considerations
Wastewater quality parameters of concern in activated carbon treatment systems include
suspended solids, oxygen demand as measured by BOD, COD or TOC, other organics
such as MBAS, or phenol,and dissolved oxygen. If there are effluent requirements for any
or all of these parameters, then much of the design criteria must be established by
laboratory and bench scale tests as described in Chapter 4.
3-6
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3.4 Carbon Contacting Systems
The alternatives for carbon contacting systems include:
1. Downflow or upflow of the wastewater through the carbon bed.
2. Series or parallel operation (single or multi-stage).
3. Pressure or gravity operation in downflow contactors.
4. Packed or expanded bed operation in upflow contactors.
5. Materials of construction and configuration of carbon vessel.
a. Steel or concrete.
b. Circular or rectangular cross-section.
3.4.1 Upflow versus Downflow Contacting Systems
Upflow beds have an advantage over downflow beds in the efficiency of carbon use
because they can more closely approach continuous countercurrent contact operation.
Countercurrent operation results in the minimum use of carbon, or the lowest carbon
dosage rate. Upflow beds may be designed to allow addition of fresh carbon and
withdrawal of spent carbon while the column remains in operation. When these
operations are conducted almost continuously, the bed may be referred to as a pulsed
bed. A pulsed bed may be either an upflow packed bed or an upflow expanded bed.
Upflow packed beds require a high clarity influent (usually a turbidity less than about
2.5 JTU) which may be considered a disadvantage to their use. Upflow expanded beds
have the advantages of being able to treat wastewater relatively high in suspended solids,
and of being able to use finer carbon (which reduces the required contact time) without
excessive headlosses. Where upflow packed beds typically use 8 x 30 mesh carbon,
upflow expanded beds typically use 12 x 40 mesh.
The principal reason for using a downflow contactor is to use the carbon for two
purposes: (1) adsorption of organics and (2) filtration of suspended materials. The
principle advantage to the dual use of granular carbon is some reduction in capital cost.
This economic gain is offset, to an extent not now fully predictable, by loss of efficiency
in both filtration and adsorption, and perhaps also by higher operating costs. The
sacrifice in finished water quality which results from combined adsorption-filtration by
carbon may or may not be a factor depending upon the effluent quality required.
3-7
-------
Downflow beds may be operated in parallel or in series (multi-stage). Valves and piping
are provided in series installations to permit each bed to be operated in any position in
the series sequence, thus giving a pseudo-countercurrent operation. More than two beds in
series are seldom used because of the cost of required valves and piping.
Provision must be made to periodically and thoroughly backwash downflow beds to
relieve the pressure drop associated with the accumulation of suspended solids. Continued
operation of a downflow bed for several days without backwashing may compact or foul
the bed sufficiently to make it more difficult to expand the bed during backwash
without the use of an excessive quantity of backwash water, i.e., more than 5 percent of
the product water. Upflow beds may be flushed through a simple well screen inlet-outlet
system. Downflow beds require a false bottom support system, backwash facilities, and
controls similar to those used in waterworks practice for sand filters.
Equipment available for automatic operation of filters is highly developed, reliable, and
offers a satisfactory method of process control. Operation and control of upflow
countercurrent carbon columns, following efficient filters, are best accomplished by
simple, manual controls. Except for occasional flow reversal, valves serving separate
carbon columns are usually operated only during withdrawal and replacement of carbon
for regeneration, perhaps once every 4-6 weeks. Valve operation for this purpose is best
done manually with operator attendance and observation, and is not amenable to reliable
automatic control.
The use of downflow carbon contactors for the dual purposes of adsorption and filtration
provides capital cost savings. However, the carbon filter-contactor is basically a
surface-type filter, and, as such, is subject to the shortcomings of surface filters in
processing sewage. Upsets in pretreatment which produce sudden increases in suspended
solids or turbidity can completely blind the surface of a single media bed which requires
backwashing before it can be restored to service. If the upset in applied water quality
continues for an hour or two, then the supply of high-quality water necessary for
backwashing carbon filter-contactors may be exhausted. Separate filters can be
backwashed and placed back on line in 20 minutes or less. Backwashing a carbon
filter-contactor may require longer and a proportionally larger volume of water of higher
quality to avoid plugging the bottom of a deep bed and saturating it with adsorbed
organics. Whether using upflow or downflow contactors, filters protect carbon columns
from pretreatment upsets and increase the overall plant reliability.
The underdrain system used for downflow carbon beds is similar to that used for
conventional water filters and will not be discussed in detail here. Figure 3-3 illustrates a
two-bed series downflow system for carbon contact. As indicated, water is first passed
down through Column A and then down through Column B. When the carbon in Column
A is exhausted, the carbon in Column B is only partially spent. At this time, all carbon
in Column A is removed for regeneration, and is replaced with fresh carbon. Column B
3-8
-------
TO CARBON
REGENERATION
WASH WATER
SUPPLY
-ft
PIPING DIAGRAM
EFFLUENT
FILTER TO
WASTE
COL.
A
COL.
B
FIRST
FLOW A TO B,
RENEW CARBON
IN A
THEN,
FLOW B TO A,
RENEW CARBON IN
B
THEN,
FLOW A TO B, AND
CYCLE IS COMPLETE
COL.
A
COL.
B
FIGURE 3-3
TWO DOWNFLOW CARBON BEDS IN SERIES
3-9
-------
then becomes the lead column in the series. When the carbon in Column B is exhausted,
the carbon is removed for regeneration and is replaced with fresh carbon. With up flow
columns, no spare contactors are needed, because carbon can be withdrawn for
regeneration while the column remains in service.
3.4.2. Gravity versus Pressure Contacting Systems
The use of pressure vessels for carbon contactors will increase the flexibility of operation
since it will allow the system to be operated at higher pressure losses. This may allow the
carbon contact system to operate during upsets or variations in the wastewater flow.
Gravity contactors may be more economical since concrete and common wall
construction may be utilized. Examples for the design of both types of systems are given
later in this chapter.
3.4.3 Aspect Ratios
The aspect ratio of a carbon column is the bed depth to diameter ratio. With good design
of the flow distribution and collection systems, the aspect ratio is not a crucial factor,
and ratios of even less than 1:1 are satisfactory. However, if the granular bed itself is to
be used as a means of flow distribution, then high aspect ratios (greater than 4:1) are
desirable to minimize short-circuiting and dead spots in the bed. The current trend in
design is to provide inlet and outlet arrangements which distribute and collect the
influent and effluent water very uniformly across the entire cross-section of the bed, in
which case the aspect ratio is not important.
3.4.4 Number of Contactors
From a process reliability standpoint, there should be an adequate number of contactors
(or pairs of contactors if series units are used) to provide adequate treatment even with
one contactor (or pair of contactors) out of service for repairs. In large plants, this is not
a constraint since the physical limitations on individual contactor's size dictate a large
number of columns. Shop-assembled pressure vessels cannot be greater than 12 feet in
diameter and 60 feet overall length and still be transportable. At 30 minutes contact, the
maximum capacity per shop fabricated vessel is about 2 mgd with more typical designs
(see Figure 3-8) corresponding to about 1 mgd per column.
Most open concrete contactors will have a maximum capacity of 2-4 mgd per contactor
at 30 minutes contact, as the maximum area consistent with good flow distribution is
about 1,000 square feet. Thus, for plants of 5 mgd and above, provision of enough
contactors to insure plant reliability does not cause any added costs.
For small plants, it may be necessary to use two or more columns to provide flexibility
of operation even though one larger column capable of handling the entire flow may be
technically feasible. Some added carbon usage may be achieved by blending of the
3-10
-------
effluent from two columns. For example, with two columns in parallel and an effluent
COD standard of 20 mg/1, the effluent COD from one column may be allowed to reach
25 mg/1 if that from the other has reached only 15 mg/1, since the blended effluents still
meet the requirement. Some operating cost savings may result from the slight additional
carbon loading permitted by blending effluents from parallel columns if it is elected to
operate the columns in the manner suggested above.
The relative economics for various number of contactors for a given situation is discussed
in the literature [ 1 ] and this lengthy discussion will not be repeated here.
3.4.5 Flow Distribution and Collection Requirements and Other
Contactor Functions
The functions to be carried out for efficient operation of carbon contactors are rather
simple, but they are worthy of enumeration. The first is to provide contact between the
water and the carbon grains for the proper length of time. This requires good distribution
and collection of the water at the inlet and outlet of the carbon column, which is not
too difficult, as any granular bed is, in itself, a good flow equalizer. The shape of the
contacting portion of the vessel is not crucial if the water is properly distributed and
collected. Of importance in pulsed upflow beds is the function of uniform withdrawal of
spent carbon without mixing of partially spent carbon and without "rat-holing" the
center portion of the carbon in the column. A 45 degree cone bottom with strategically
located water jets is ideal for this function. In small tanks, a 60 degree cone bottom is
preferable. Another function is placement of the makeup and regenerated carbon on the
carbon in the column in a layer of uniform depth. In closed contactors, an inverted 45
degree cone serves the purpose very well. A dished top is cheaper, but the fresh carbon is
deposited only in the center of the bed, and thus some carbon efficiency is lost. Another
function is the separation of water and carbon at the inlet and outlet of the column. A
stainless steel well screen serves this purpose very well in a closed contactor. For 8 x 30
mesh carbon, a screen opening of 0.020 inch has proved satisfactory.
In open contactors of a design similar to gravity filters, the backwash collection troughs
should be covered with a screen to prevent loss of carbon during backwash.
3.4.6 Hydraulic Loading and Headless Characteristics of Carbon Beds
The flow rate and bed depth necessary for optimum performance will depend upon the
rate of adsorption of impurities from wastewater by the carbon. The general range of
jfJoJK~iates_XPx hydraulic loading) is 2-10 gpm/sq ft of cross-sectional area. Bed depths are
usually 10-30 feet' ——
Both theoretical analysis and experimental data support the contention that there are
critical velocities for liquids passing through porous beds which change the nature of the
resistance to diffusion. At low velocities, the solute content of the stagnant film
3-11
-------
surrounding the adsorbent particles may become depleted more rapidly than the solute
can be replaced by diffusion from the main body of the liquid. Thus, the diffusional
resistance across the film is controlling. As the velocity is increased, the point will be
reached where the controlling effect will be the inability of the adsorbent material to
remove the solute from solution as rapidly as it is transported to the surface from the
main body of the stream. Within the range of loadings of 2-10 gpm/sq ft, several studies
have found that velocity is not a limiting factor.
Hydraulic loading has an additional effect on carbon column operation. Increasing flow
rates through the carbon will cause increasing headlosses (AP). Headless is dependent on
the flow rate and carbon particle size. This relationship for clean water passing through a
bed of clean carbon is expressed in the formula:
AP =
Dc
where: AP = Pressure drop, inches
K = Constant
" = Viscosity, centipoise
V = Flow rate, gpm
Lc = Bed depth, feet
D = Mean particle diameter, mm
Dr = Column diameter, inches
Hydraulic headloss is then related directly to flow rate and inversely related to particle
size. Figure 3-4 illustrates the increasing pressure drop with increasing hydraulic loading
for different sized carbons from different manufacturers, operated in a downflow mode.
Because of the more favorable headloss characteristics, 8 x 30 mesh carbon is often
preferred for downflow beds while 12 x 40 mesh carbon may be preferable for upflow
beds because a lower upflow velocity is required for expansion.
The headloss for a given hydraulic loading with wastewater feed must be determined by
pilot testing. Since headloss development is such an important consideration in the design
of a carbon bed, hydraulic loading cannot be discussed in isolation from several other
design factors. If an excessive rate of headloss development (due to a high hydraulic
loading) is anticipated, an upflow bed should be given consideration. The choice of
3-12
-------
INCHES H2O
PRESSURE DROP [FT. OF BED DEPTH
U)
U)
•o
3D
m
C
3D
m
O
3D
O
•° -n
<^
u)
V c
< m
a w
3J I
O
D
Z
o> oo
O
3)
>
C w
n
o
i—
O
>
g
z
o
5 *
-o
CO
p
"Tl O)
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o
-------
gravity versus pressurized flow may also be influenced by the anticipated rate of headloss
development. Very high hydraulic loadings are practical only in pressurized systems.
Gravity flow in downflow beds is considered practical only at hydraulic loadings less than
about 4 gpm/sq ft.
Upflow expanded beds should be considered when high headloss is expected. At low flow
rates, the particles are undisturbed and the bed remains fixed. As the flow rate is
increased, however, a point is reached where all particles no longer remain in contact
with one another, and the carbon bed is expanded in depth. The flow rate required for
initial expansion of the bed is accompanied by a sizable increase in headloss. As the flow
rate is increased, there is further expansion of the bed. Flow rates required for further
expansion of the bed are accompanied by lesser increases in headlosses. Figure 3-5
illustrates the sharp increase in AP for initial bed expansion and the lower rate of
increase for further expansion. Figure 3-6 shows expansion of 8 x 30 and 12 x 40 mesh
carbon beds at various flow rates.
It has been found that at about a 10 percent expansion of an upflow bed, suspended
solids will pass through the bed. In Figure 3-6, a 10 percent expansion occurs at
approximately 6 gpm/sq ft for 12 x 40 mesh carbon and about 10 gpm/sq ft for 8 x 30
mesh carbon.
3.4.7 Backwash Requirements
The purpose of backwashing is to reduce the resistance to flow caused by solids that have
accumulated in the bed. The rate and frequency of backwash is dependent upon the
hydraulic loading, the nature and concentration of the suspended solids in the
wastewater, the carbon particle size, and the method of contacting (upflow, downflow).
A contactor operating at a hydraulic loading of 7 gpm/sq ft may be backwashed daily to
counteract excessive pressure drop. The same contactor operated at 3.5 gpm/sq ft, with
the same suspended solids loading,may require backwashing only every 2-1/2 days.
Backwash frequency may be determined by any of several criteria: buildup of headloss,
deterioration of effluent turbidity, or at regular predetermined intervals of time. It may
be convenient for operational reasons to arbitrarily backwash beds at one-day intervals,
for example, without regard for headloss or turbidity. The other criteria may only be of
interest during periods of shock solids loading when backwash frequency exceeds once
per day.
The removal of solids trapped in a packed upflow bed may require two steps: first, the
bottom surface plugging may have to be relieved by temporarily operating the bed in a
downflow mode, and second, the suspended solids entrapped in the middle of the bed
may have to be flushed out by bed expansion.
3-14
-------
FIXED BED
EXPANDED BED
8
o
111
FLOW RATE
FIGURE 3-5
HEADLOSS ON BED EXPANSION
3-15
-------
EXPANSION, % OF BED
O
m
X
•o
I*
|1
co O
r- o
0>
m o
33 "oo
> *
ro
Mo
O
CO
m
m CD
w m
O
-------
Often backwashing of packed upflow carbon contactors, which are preceded by filtration,
merely consists of increasing upflow from the normal rate of 5 to 6 gpm/sq ft (for 8 x
30 mesh carbon) to 10 to 12 gpm/sq ft for 10 to 15 minutes.
Backwashing a downflow contactor normally requires a bed expansion of 10-50 percent.
It is recommended that provisions for backwash flow rates of 12-20 gpm/sq ft be made
with the granular carbons of either 8 x 30 mesh or 12 x 40 mesh. Effective removal of
the solids accumulated on the carbon surface in downflow contactors requires: (a)
surface wash equipment utilizing rotating or stationary nozzles for directing high pressure
streams of water at the surface of the bed, (b) an air wash, or (c) a combination air-water
wash. A surface wash or air wash system is normally operated only during the first few
minutes of a backwash of 10-15 minutes. When backwashing is supplemented by this
scouring type of wash, the total amount of water to achieve a given degree of bed
cleaning may be reduced. Also, surface wash or air wash overcomes bed plugging that
may not be alleviated by normal backwash velocities. As a general rule, the total amount
of backwash water required should not exceed 5 percent of the average plant flow.
Backwash water may be effectively disposed of by recirculating it into the primary
sedimentation basin or elsewhere near the inlet of the wastewater treatment plant. A
return flow equalization tank may be advisable in order to reduce shock hydraulic loads
on the plant from waste washwater. This is particularly true for small plants.
Air scouring has been used successfully in test programs and appears to be suitable for
large-scale use. It is being used at Colorado Springs [ 2] and it is an accepted technique in
water filter operation.
Basically, the technique involves draining the water level to within about one foot of the
top of the carbon bed followed by introducing air at a rate of about 3 to 10 CFM/sq ft
to the bottom of the column at a velocity that will thoroughly agitate the entire carbon
bed. For breaking biological slimes from the carbon particles, 5 minutes of air scour
should be sufficient.
3.4.8 Air and Vacuum Release Requirements
Pressure carbon columns must be provided with an air and vacuum release valve,
protected by a screen to avoid plugging by carbon particles. Air must be released when
filling the column and the vacuum must be broken when draining a column to avoid
structural damage to the vessel. A detail of a typical air-vacuum release valve installation
is shown in Figure 3-7.
3.5 Biological Activity in Carbon Contactors
Under certain conditions, granular carbon beds provide favorable conditions for the
production of hydrogen sulfide (t^S) gas which has an unpleasant odor, and which may
3-17
-------
GALVANIZED
IRON DRAIN
GLOBE VALVE
PIPE FLANGE
THREAD WELL POINT
INTO COMPANION
FLANGE
FLANGED PIPE,
WELD TO TANK
COMBINATION PRESSURE
AIR AND AIR-VACUUM
RELIEF VALVE
CARBON
COLUMN
TANK
WELL POINT SCREEN, STAINLESS
STEEL, NO. 20 (0.020")
SLOT OPENING, REMOVABLE.
(FOR 8x30 MESH CARBON)
FIGURE 3-7
AIR-VACUUM RELEASE VALVE DETAIL
3-18
-------
contribute to corrosion of metals and damage concrete. The hydrogen sulfide is produced
by sulfate-reducing bacteria under anaerobic conditions. Conditions promoting or
accelerating the production of hydrogen sulfide in carbon contactors include:
1. Low concentrations or absence of dissolved oxygen and nitrate in the carbon
contactor influent.
2. High concentrations of BOD and sulfates.
3. Long detention times.
4. Low flow-through velocities.
It may be possible to prevent or correct problems of hydrogen sulfide generation by
eliminating one or more of the conditions necessary to sustain growth of the
sulfate-reducing bacteria. Most of the preventive measures must be provided in the design
of the carbon contacting system, but there are also some corrective measures which can
be taken in plant operation. The amount of actual plant operation experience in this
regard is limited. In plant design, the following measures may be taken to provide
flexibility for dealing with problems of hydrogen sulfide production:
1. Satisfy as much of the oxygen demand of the wastewater as possible by
providing biological treatment prior to carbon treatment.
2. Provide biological treatment and efficient filtration to reduce the load of
suspended and dissolved organics thus permitting the use of higher flow-through
velocities and reduced detention times in the carbon columns.
3. In packed beds of carbon, provide facilities for application of chlorine to the
influent. In addition, in upflow expanded beds it may be desirable to provide
for introduction of air, oxygen, or sodium nitrate (as a source of oxygen).
Because of the mass of cell growth produced, it may be less desirable to
introduce air or oxygen ahead of packed beds because of potential physical
plugging of the beds. These growths are flushed through expanded upflow beds,
but may be removed in sections of the plant which follow such as filters or
clarifiers.
Some remedial measures available in the operation of carbon facilities are:
1. Columns may be backwashed at more frequent intervals or backwashed more
violently by use of air scour or surface wash.
3-19
-------
2. Detention time may be reduced by taking some carbon contactor units off the
line, provided that the reduced carbon contact time is still sufficient to obtain
the desired removal of organics and that headlosses in the carbon columns
remaining on the line do not become excessive.
3. Chlorination or oxygen addition may be initiated.
As an example of correction in actual plant scale operation in a tertiary process sequence,
an incident at the South Tahoe plant is reviewed. The carbon facilities at this location are
provided with all of the design features recommended above. In eight years (1965-1973)
of carbon column operation, there has been only one occasion (in 1970) of about three
days duration of hydrogen sulfide production. When the odor was detected in the carbon
column effluent, it was observed that plant flow was less than half the design flow, and 7
of the 8 carbon columns were in service. This meant that the contact time was more than
40 minutes rather than the normal 17 minutes. Three of the columns were backwashed
with water containing DO and taken off the line. The remaining four columns were
similarly backwashed and operated at near the full design throughput rate, but with the
addition of 2 to 3 mg/1 of chlorine to the influent. After two days of operation on this
basis, hydrogen sulfide odors were no longer detected in the carbon column effluent.
In operations at the PCT pilot research facility at Pomona, California [3], it was found
that:
1. Measures which were used successfully at Tahoe to end F^S production in
carbon columns were not adequate when the influent consists of raw
wastewater that has received only chemical clarification.
2. Continuous chlorination of the carbon column influent at dosages up to 50
mg/1 reduced significantly, but did not stop F^S production.
3. Intermittent backwash, surface wash, and oxygen addition reduced, but did not
completely eliminate t^S.
4. Intermittent backwash, surface wash, and continuous oxygen addition to
DO = 4 mg/1 reduced sulfide formation, but stimulated biological growth and
headless in the carbon bed.
5. The addition of air wash to normal backwash and surface wash was not
effective against f^S, and 7 inches of carbon was lost from the bed.
6. The continuous addition of sodium nitrate to the carbon column influent at
the rate of 4 to 5 mg/1 as NO3 - N completely inhibited IH^S generation in the
column.
3-20
-------
At the Cleveland Westerly pilot plant [4], all efforts to eliminate sulfide odors in carbon
columns following PCT were found to be impractical. However, the BOD of the carbon
column influent at this plant ranged from 80 to 100 mg/1 as opposed to around 40 mg/1
at Pomona. The control methods used were: (1) daily backwashing at 10 gpm/sq ft plus
surface wash at 2 gpm/sq ft for 28 minutes, (2) continuous addition of NaNO-^ to the
influent, and (3) backwashing with water containing 27 mg/1 of chlorine (from NaOCl).
At dosages of 100 mg/1 of NaNO^ (expressed as NO^ ) sulfide production was eliminated,
but this high dosage was not considered economically practical.
Sulfides in the carbon column effluent can be removed by precipitation with iron or by
the addition of chlorine. However, at this time the most effective means of coping with
the H2$ problem appears to be to maintain aerobic conditions in the carbon contactors
rather than trying to remove ^S after it is formed. If the BOD applied to the carbon is
less than 5 mg/1, as is the case in most tertiary treatment schemes, the ^S problem is
easily controlled. For applied BOD values substantially higher than this, it appears that
use of upflow, aerobic expanded contactors followed by sedimentation or filtration is
preferable.
3.6 Design Examples
3.6.1 Upflow, Packed Bed, Pressurized
Figure 3-8 shows the upflow countercurrent packed bed carbon columns being installed
(1973) at the Orange County, California Water District (OCWD) tertiary treatment plant.
These are the last treatment units (except those for breakpoint chlorination) in a 15 mgd
plant employing chemical clarification, nitrogen removal and multi-media filtration.
Reclaimed water from this plant will be blended with desalted seawater for ground water
recharge. Similar carbon columns are being designed for the 22.5 mgd Upper Occoquan
Sewage Authority plant in Virginia. Similar type contactors have been in service for eight
years at the 7.5 mgd South Tahoe, California plant (except that the Tahoe columns have
12 feet long straight sidewalls rather than 24 feet, and provide 17 minutes contact rather
than 30 minutes as at OCWD and Occoquan). In each of these three plants, biologically
treated wastewater is subjected to high lime clarification (pH > 10.5), ammonia removal,
recarbonation, and mixed-media filtration prior to application to the carbon. Applied
turbidities will range from 0.1 to 1.0 JTU.
At the OCWD plant, there are 17 carbon columns each 12 feet in diameter with a 24 feet
long straight sidewall. At a plant flow of 15 mgd, 16 of these columns will provide 30
minutes nominal contact with the carbon. The 17th column is a spare, also to be used
for carbon storage. Each of the columns contains 2,700 cubic feet of 8 x 30 mesh carbon
and the hydraulic loading at design flow is 5.8 gpm/sq ft. Exterior views of these
columns are shown in Figure 3-8; details of the inlet and outlet screens are shown in
Figure 3-9; Figures 3-10 and 3-11 show the top screen system and the carbon filling
chamber.
3-21
-------
CARBON
FILLING
CHAMBER.
HYDRAULIC
GRADIENT
EFFLUENT
MANIFOLD
8" W.S.
EFFLUENT
8" FLOW
REVERSAL
LINE
24" W.S.
EFFLUENT
HEADER.
TRANSFER
JET HEADER
INFLUENT
MANIFOLD
10" W.S.
EFFLUENT
HEADER
8" W.S.
DRAIN
EFFLUENT
MANIFOLD
8" FLOW
REVERSAL
LINE
»8" W.S.
EFFLUENT
CARBON
COLUMN
DALL
FLOW
TUBE
DALL
FLOW
TUBE
24" W.S.
EFFLUENT
HEADER
INFLUENT
MANIFOLD
2" G.S. SPENT
ARSON LINE
6" WAFER /
STOCK VALVE
8" W.S. DRAIN
FRONT VIEW
SIDE VIEW
FIGURE 3-8
UPFLOW COUNTERCURRENT
CARBON COLUMN
ORANGE COUNTY, CALIFORNIA
3-22
-------
PIPE FLANGE ON
PIPE SECTION
FLANGED W.S.
PIPE WELD TO
TANK
CARBON
COLUMN
TANK
REMOVABLE WELL
SCREEN. 304 SS,
W 0.020" OPENINGS.
CLOSED BAIL
BOTTOM, 304 SS
FIGURE 3-9
TOP AND BOTTOM
UNOERDRAINS
ORANGE COUNTY, CALIFORNIA
3-23
-------
CARBON
FILLING
CHAMBER
UPPER
(OUTLET)
MANIFOLD
REMOVABLE
UNDERDRAIN
SCREENS
CARBON
LEVEL
(BOTTOM
SIMILAR)
FIGURE 3-10
SECTION THROUGH TOP UNDERDRAIN
ORANGE COUNTY, CALIFORNIA
3-24
-------
CARBON IN
EPOXY COATED
INSIDE
304 SS WELL SCREEN
0.020" OPENINGS
(OVERFLOW)
G.S.
DRAIN
FIGURE 3-11
CARBON FILLING CHAMBER
ORANGE COUNTY, CALIFORNIA
3-25
-------
Figure 3-12 shows the valve positions and flow pattern during the normal upflow
adsorption or service cycle of the columns at the OCWD plant. Filtered water enters the
bottom of the column through the screen manifold, flows upward through the carbon,
and leaves through the upper screen manifold. The hydraulic gradient lies at a level
between the top of the column and the carbon filling bucket. This makes it possible to
add fresh carbon (regenerated and makeup) at the top and to withdraw spent carbon
from the bottom while the column is in service. Therefore, carbon can be withdrawn
slowly and more or less continuously and replaced with fresh carbon. If carbon
withdrawal is intermittent, the usual practice is to withdraw and replace 5 to 10 percent
of the total contents of one column at a time.
Figure 3-13 shows the upflow-to-waste cycle of operation which is used after a major
transfer of carbon it if is necessary to clear the effluent of excessive carbon fines. Figure
3-14 shows the method of reversing flow downward through the column in order to clear
the top screens of carbon particles lodged in screen openings. Reverse flow also removes
any accumulated trapped particles in the bottom of the bed. Figure 3-15 merely shows
the valve positions for bypassing a column for inspection, maintenance, or repair.
As shown on Figure 3-10, a void space of about 10 percent of the total carbon column
volume is provided at the top of the columns. Occasionally, the flow to the column can
be increased from the normal rate of 6.3 gpm/sq ft to a flow in excess of 10 gpm/sq ft
to expand the carbon bed and to flush out particulate matter so as to reduce headless.
By placing the elevation of the point of spent carbon discharge below the top of the
carbon filling chamber on the column, it is possible to withdraw spent carbon by gravity
flow from the column while it is in normal service. If more rapid transfer is desired, the
wafer valve at the top of the column below the filling chamber may be closed and the
entire column pressurized (with high pressure water supply) for carbon removal. Note
that a pressure supply of dilution water is provided through a pipe cross at the bottom of
the column. This allows water to be added as necessary to obtain the desired carbon
slurry consistency for hydraulic transfer. The contactor is also equipped with a transfer
jet header which furnishes pressure water through eight tangential nozzles at the top of
the bottom cone. This water lubricates the cone surface and agitates the carbon to
facilitate uniform withdrawal of carbon across the entire cross-sectional area of the
column. This avoids dead spots and assists in obtaining maximum carbon efficiency.
3.6.2 Pulsed Bed, Pressurized
The contactor design already described for use as an upflow packed bed is suitable for
operation as a pulsed bed. The pulsed bed differs from the upflow packed bed only in its
method of operation which seeks to make the maximum possible use of the
countercurrent principle by continuously withdrawing and replacing small quantities of
carbon rather than in larger batches at intervals. Properly executed, this means that no
3-26
-------
EFFLUENT
MANIFOLD
FLOW
METER-
EFFLUENT
RATE-OF-FLOW
CONTROL VALVE
OPEN
CARBON COLUMN
(TYPICAL)
INFLUENT
MANIFOLD
3-WAY
VALVE
CLOSED
CARBON
/COLUMN
BYPASS
VALVE
CLOSED
INFLUENT
CARBON
COLUMN
INFLUENT
HEADER
VALVE
J- OPEN
-WASTE AND
DRAIN LINE
FIGURE 3-12
UPFLOW CARBON COLUMN SCHEMATIC
NORMAL OPERATION
ORANGE COUNTY, CALIFORNIA
3-27
-------
EFFLUENT
MANIFOLD
EFFLUENT
RATE-OF-FLOW
CONTROL VALVE
CLOSED
CARBON COLUMN
(TYPICAL)
INFLUENT
MANIFOLD
-WASTE AND
DRAIN LINE
FIGURE 3-13
UPFLOW CARBON COLUMN SCHEMATIC
UPFLOW TO WASTE
(USED AFTER ADDING CARBON TO COLUMNS TO FLUSH OUT FINES)
ORANGE COUNTY, CALIFORNIA
CARBON
/COLUMN
BYPASS
VALVE
CLOSED
INFLUENT
CARBON
COLUMN
INFLUENT
HEADER
VALVE
OPEN
3-28
-------
EFFLUENT
MANIFOLD,
TINAL
EFFLUENT
EFFLUENT
RATE-OF-FLOW
CONTROL VALVE
CLOSED
CARBON COLUMN
(TYPICAL)
INFLUENT
MANIFOLD
CARBON
'COLUMN
BYPASS
VALVE
CLOSED
INFLUENT
CARBON
/COLUMN
/INFLUENT
V^ h
HEADER
VALVE
OPEN
WASTE AND
DRAIN LINE
FIGURE 3-14
UPFLOW CARBON COLUMN SCHEMATIC
REVERSE FLOW
(USED TO FLUSH TOP SCREENS)
ORANGE COUNTY. CALIFORNIA
3-29
-------
EFFLUENT
MANIFOLD
-FINAL
EFFLUENT
EFFLUENT
RATE-OF-FLOW
CONTROL VALVE
CLOSED —
CARBON COLUMN
(TYPICAL)
INFLUENT
MANIFOLD
CARBON
'COLUMN
BYPASS
VALVE
OPEN
INFLUENT
HEADER
-WASTE AND
DRAIN LINE
3-WAY VALVE
CLOSED
3-WAY
VALVE
CLOSED
INFLUENT
f
CARBON
/COLUMN
INFLUENT
HEADER
VALVE
CLOSED
FIGURE 3-15
UPFLOW CARBON COLUMN SCHEMATIC
BY-PASSING CARBON COLUMN
ORANGE COUNTY, CALIFORNIA
3-30
-------
particle of carbon is withdrawn from use until it is completely exhausted in its capability
to adsorb organics even from the most concentrated wastewater which it contacts at the
bottom flow inlet (exhausted carbon outlet).
In contrast, any batch method of withdrawal involves removal of a mixture of partially
exhausted and completely exhausted carbon, compromising the countercurrent principle.
The larger the batch withdrawn, the greater the compromise and loss of carbon
efficiency. The single downflow reactor is the least efficient of all in this respect of
withdrawing carbon which is not fully saturated. With pulsed bed operation, the carbon
filling chamber would be kept full, or nearly so, in order that fresh carbon would
automatically keep the column full while exhausted carbon is being removed from the
bottom outlet.
3.6.3 Upflow Packed Bed, Open
The maximum diameter for factory fabricated steel tanks for carbon column vessels is
about 12 feet (to permit highway transport). In large wastewater treatment plants a 12
feet limit on diameter requires an excessive number of units to handle the total flow.
This means that steel vessels on-site fabricated or poured in place reinforced concrete
vessels should be used for large carbon contactors.
The cost of constructing large pressurized vessels on site is often so high that open vessels
are used. For upflow packed columns this introduces at least two new factors. First of
all, the freeboard from the surface of the carbon to the top of sidewall should allow for
10 percent expansion of the carbon plus freeboard. Also, the method of introducing
carbon is changed from a single point to a multiple point arrangement. Even with several
points of carbon introduction, it is necessary to operate large diameter open contactors at
upflow backwash rates after carbon addition in order to distribute the fresh carbon across
the entire top surface of the bed. This approaches, but does not equal, the uniformity of
distribution obtained from a central point at the top of the 45 degree conical top used in
smaller diameter beds.
Figure 3-16 is a sketch of a potential design for a 30-feet diameter by 26-feet carbon
depth reinforced concrete column. These columns would provide a 30 minute contact
time at a hydraulic loading of 6.5 gpm/sq ft. Not shown in the drawing are the beams
necessary to support the inlet and outlet screens.
3.6.4 Upflow Expanded Bed, Open
This type of carbon contactor is proposed for a 13 mgd (peak flow = 28 mgd) PCT plant
at Vallejo, California. The treatment process will consist of high lime (pH=ll) treatment
of raw wastewater, single stage recarbonation, carbon adsorption, and dual-media
filtration. Figure 3-17 illustrates the open upflow expanded bed carbon contactor to be
3-31
-------
NOTE: INFLUENT AND EFFLUENT SCREEN
SUPPORT BEAMS ARE NOT SHOWN.
30'-0" DIAM.
,EFFLUENT - 4 - 10"
WELL SCREENS
CLEAN-OUT
io
INFL. 4 - 10"
WELL
SCREENS.
3-—CARBON- IN
10" DIAM.
WELL SCREENS
14"
I
20"
20" EFFLUENT
TOP PLAN BOTTOM PLAN
FIGURE 3-16
UPFLOW OPEN PACKED BED CONTACTOR
20"
20" INFLUENT
3-32
-------
3CARBON-IN
INFLUENT
\
\
(}
\
—
••
0
"to
""
1
1
A
18' SQUARE
EFFLUENT REMOVABLE
TROUGH. /SCREEN
X
^
^
ii
o
CO
o
CO
--
p
CO
z
o
z9
^ i
I
0-
o :
O
CD
DC
O
FALSE
; BOTTOM
t ^-f - \^L • : - •••
EFFLUENT
} —
ft
FROM: PLAN^
PHYSICAL - C
PLANT AT VAL
CALIFORNIA
.CARBON-
[OUT
— —
\
FIGURE 3-17
UPFLOW OPEN EXPANDED BED CONTACTOR
3-33
-------
installed at Vallejo. There will be six contactors, each 18 feet square in plan by 36 feet
deep. The beds will operate at an average hydraulic loading of 4.6 gpm/sq ft with a
maximum rate of 10 gpm/sq ft. They will be equipped with air scour and hydraulic
backwash at 15 gpm/sq ft. The 12 x 40 mesh carbon bed will be 16 feet deep and
contact time varies from an average of 26 minutes to a minimum of 12 minutes. During
normal operation, the carbon bed will be expanded by 10 percent and during backwash
by 50 percent. The total headloss through the carbon is expected to be 4 to 5 feet. The
beds will have a false bottom fitted with filter underdrain nozzles. Each bed will contain
about 160,000 Ibs of carbon for a total of 800,000 Ibs. An additional 160,000 Ibs of
carbon will be held in reserve.
3.6.5 Upflow Expanded Bed, Pressurized
With carbon beds smaller than those schematically illustrated for Vallejo, it may be
advantageous to use closed, pressurized, factory fabricated steel tanks. Some freeboard
reduction might be made below that required for open top vessels, but space should be
provided for 50 percent expansion. In operation of expanded carbon beds, there is some
advantage to visual observation and control particularly in regulation of bed expansion
under variable flow rates.
3.6.6 Downflow Packed Bed, Pressurized
Figure 3-18 illustrates the contactor of this type used in the original pilot plant at
Pomona, California. It is equipped with surface wash and a double perforated metal plate
false bottom which distributes washwater across the bottom of the bed.
This perforated plate, or any other flat bottom support system, must be designed to
distribute the backwash water at the maximum anticipated rate and to withstand the
associated uplift force. The maximum backwash velocity at Pomona, 12 gpm/sq ft,
although adequate for expanding 16 x 40 mesh carbon, is not sufficient to provide 50
percent expansion of 8 x 30 mesh carbon. Even if backwash pumps were sized to force
an upward How of 20 gpm/sq ft through the carbon beds, the excessive pressure drop
across the plates might force them to warp or to be dislodged. Special consideration is
required to assure that these types of bottom support systems can hydraulically handle
maximum flows in both directions and remain in place.
Removal of the major part of the carbon from the carbon bed is facilitated by keeping
the bed flooded during withdrawal operations. The removal of the last stump or heel of
carbon in the farthest corner of the bed from the withdrawal port may be difficult. A
supplementary backwash (upflow) on the order of 3 to 6 gpm/sq ft, or nozzles in the
side of the column just above the underdrain system, will aid in flushing this last
quantity of carbon from the beds.
3-34
-------
6 FT.
20 1"
HOLES
WASH
WATER
is
I I I II I l
LL
(O
gllllS.B^BOLT RING
-,-^-INFLUENT
•"-"-BACKWASH
I I
Cb:
CARBON CHARGE
'SURFACE WASH
-CARBON BED
SURFACE
-*-CARBON DISCHARGE
METAL SCREEN
EFFLUENT
BACKWASH
FIGURE 3-18
PRESSURIZED DOWNFLOW CONTACTOR
POMONA, CALIFORNIA
3-35
-------
The Colorado Springs contactor (Figure 3-19) and the Rocky River contactor (Figure
3-20) both offer a flat bottom support for the carbon. Funnel shaped ports through the
support are provided for carbon removal.
The actual bottom support system utilized is different for the two contactors. The
Colorado Springs contactor (Figure 3-19) employs a perforated stainless steel plate into
which filter underdrain nozzles are inserted for backwash control and distribution. In
contrast, the Rocky River contactor (Figure 3-20) employs a porous tile filter bottom
covered with several inches of graded gravel.
Flat bottoms commonly used in downflow beds have been used successfully for many
years in water treatment plant filter design. They can be structurally sound and can
provide adequate distribution of backwash flow, although there have been both structural
and backwash system plant scale failures.
3.6.7 Downflow Packed Beds, Gravity, Open
Gravity downflow contactors may be designed similar to concrete rapid sand filters. A
typical design is shown in Figure 3-21. The requirements to be satisfied in downflow
carbon contacting are an adequate sidewall depth to provide for 50 percent bed
expansion during backwash and a means for drawing off the spent carbon to be
regenerated. Carbon can be removed from the contactor through a trough on top of the
underdrain system or the installation of funnels similar to those employed at Colorado
Springs or Rocky River.
A granular bed is an excellent flow distribution device not subject to flow channeling
unless the hydraulic design for entering and leaving flow is poor or unless foreign solids
are not regularly and completely washed from the bed so as not to accumulate and form
mud balls. Surface wash or air scour is essential.
Gravity downflow contactors can be designed using existing sand filter technology, with
the additional requirement for carbon withdrawal and addition noted above. The EPA
Process Design Manual for Suspended Solids Removal may be consulted regarding
filtration technology.
3.7 Carbon Inventory
While the size of carbon inventory required varies with the type of carbon contacting
system used, this is a relatively minor item to be considered in selection of the contactors
to be incorporated in the plant design.
With the use of upflow countercurrent beds operated in parallel, it is possible to operate
without any storage of carbon within the plant. Needs for makeup carbon at the time of
regeneration can be accurately anticipated both as to time when needed and quantity
3-36
-------
MANIFOLD
5'-4 CARBON
WITHDRAWAL LINES
FILTER
UNDERDRAIN
NOZZLE
INFLUENT
BACKWASH
INSERT
CARBON
BED
SURFACE
CARBON
INLET
STAINLESS
STEEL PLATE
"f'tt f"t"
CARBON OUTLETS
20'
-SEE
INSERT
FIGURE 3-19
PRESSURIZED DOWNFLOW CONTACTOR
COLORADO SPRINGS, COLORADO
3-37
-------
in
CM
WASH
CM
CARBON
INLET &
OUTLET
16'
n
n
.SURFACE
WASH
-CARBON
BED SURFACE
-SAND
-GRAVEL
-FILTER BLOCK
WATER OUTLET
FIGURE 3-20
PRESSURIZED DOWNFLOW CONTACTOR
ROCKY RIVER, OHIO
3-38
-------
SURFACE
WASH
EFFLUENT
SAND
GRAVEL
FILTER BLOCKS
'DRAIN
FIGURE 3-21
TYPICAL DOWNFLOW GRAVITY CONTACTOR
3-39
-------
required, and the makeup carbon can be delivered at the proper time for direct addition
to the contactors when space is available. Alternately, a carbon inventory equal to the
makeup for one regeneration cycle (about 8 percent of the carbon to be regenerated)
could be stored in the plant. Figure 3-22 illustrates how exhausted carbon can be
withdrawn and makeup carbon can be added to an upflow column while the column is
on stream and in service. In plants large enough to require several upflow columns to be
operated in parallel, it may be desirable to provide one extra carbon column which can
serve both as a redundant column and as a storage vessel for inventory carbon. The
capital cost for a column is more than for an equal amount of storage in a tank equipped
only for that purpose. However, the benefits of the dual use of the extra carbon
contactor-storage vessel more than offset the additional cost, and the dual purpose unit is
a good design feature which has been incorporated in several plants with upflow columns.
With the use of downflow columns, when carbon regeneration is required, the entire
contents of a single downflow unit or the first of two downflow units in series must be
withdrawn. This requires that one of the contacting units be taken out of service. A
carbon inventory equal to the contents of one contactor must be maintained for filling
the column which has been evacuated of carbon to be regenerated. With downflow
contactors, it is good practice to provide two storage vessels each with a capacity for the
contents of one contactor, one for exhausted carbon and one for makeup carbon. This
may eliminate the need for the spare contactor if provision is made for rapid transfer of
carbon in and out of the contactor from the two storage bins so as to limit the
downtime for the out-of-service contactors to an acceptable period.
In any event, the costs for carbon inventory with the use of downflow contactors is
greater than for upflow contactors. However, the cost difference is not large and may not
have any great effect on the choice between upflow and downflow contactors.
3.8 Carbon Transport
3.8.1 General
The primary use of air or pneumatic transport of carbon is in bulk-handling of makeup
carbon. Once carbon is introduced into the adsorption-regeneration system, it is usually
transported hydraulically in slurry form.
When spent carbon is to be removed from a contactor, the bed is normally fluidized to
allow the carbon to flow out of the contactor. Fluidizing of the bed assists in uniform
withdrawal of the spent carbon and prevents "rat-holing". Spent carbon is moved
hydraulically from the contactors to storage or dewatering facilities.
Handling characteristics have been experimentally studied by using water slurries of
Pittsburgh type CAL 12 x 40 mesh granular carbon in a 2-inch pipeline. The data
indicated that a maximum of 3 Ibs of carbon per gallon of water could be transported
3-40
-------
MAKUP
CARBON
SCREENED
OVERFLOW
PLACE TOP OF
DRAIN BIN BELOW
HYDRAULIC GRADIENT
IN COLUMNS
SPENT
CARBON
DRAIN
BIN
HYDRAULIC
GRADIENT
WATER
FLOW
CARBON
COLUMN-
CARBON
MOVEMENT
WATER IN
WATER
OUT —\
.SPENT
^CARBON
OUT
FIGURE 3-22
CARBON TRANSFER WITH
UPFLOW COLUMN IN SERVICE
3-41
-------
hydraulically, but that it is better to use one gallon of water for moving each pound of
carbon. The velocity necessary to prevent settling of carbon is a function of pipe
diameter, granule size, and liquid and particle density. The minimum linear velocity to
prevent carbon settling was found to be 3.0 fps. It is recommended that a linear velocity
between 3.5 to 5.0 fps be used. Velocities of over 10 fps are objectionable due to carbon
abrasion and pipe erosion. Carbon delivery rates are a function of pipe diameter, slurry
concentration, and linear velocity. Data from Calgon's studies are shown in Figures 3-23
and 3-24. Pressure drop data for various slurry concentrations and velocities in 2-inch
pipe are shown in Figure 3-25.
Pilot plant tests indicate that after an initial higher rate, the rate of attrition for activated
carbon in moving water slurries is approximately constant for any given velocity reaching
an approximate value of 0.12 percent fines generated per exhaustion-regeneration cycle.
This deterioration of the carbon with cyclic operation has been reported to be
independent of the velocity of the slurry (within the range recommended previously—3.5
to 5 fps). Loss of carbon by attrition in hydraulic handling apparently is not related to
the type of pump (diaphragm or centrifugal) used.
Carbon slurries can be transported by using water or air pressure (blowcase), centrifugal
pumps, eductors, or diaphragm pumps. The choice of motive power is a combination of
owner preference, turndown capabilities, economics, and differential head requirements.
The blowcase uses air or water pressure applied in a specially designed pressure vessel to
move the carbon slurry (see Figure 3-26). Carbon and water are slurried in a feed tank
located above the pressure vessel. The slurry falls into the pressure vessel and the valve is
closed. Air or water pressure is applied and moves the slurry out through the discharge
pipe. This method has found considerable success in commercial installations. If water is
used as the transporting medium, a suitable lining for mild steel or stainless steel should
be used to eliminate corrosion (see section 3.12).
Centrifugal pumps of either the open or closed impeller type are suitable if minimum
clearance for granule passage is maintained. Speed of the pump should be not more than
800-900 rpm to minimize degradation of the granules. A rubber or ceramic lined impeller
is recommended for resistance to abrasion. Throttling of the discharge or suction should
be avoided. Water jet eductors have been used successfully in specialized situations where
the other type mechanisms are not practical or available. They are easy to operate and
require little maintenance. Eductors have the disadvantage of being basically a single flow
rate device with little turndown capability so that they must be designed for the
maximum carbon flow and excess water is used at lesser carbon transfer rates.
For lower ranges of slurry concentrations any of the above mentioned pumps can be
used. However, at higher slurry concentrations, diaphragm slurry pumps or blow tanks are
preferred. For the pumping of a 25 percent granular carbon slurry, centrifugal pumps
3-42
-------
O
C
47
O
it
g
to
-------
70
60
ffi
OC 40
HI
>
2
oc
30
20
10
APPROXIMATE SLURRY FLOW (GPM)
5 10 15 20
25
MAXIMUM CARBON-
WATER RATIO
(3 LB CARBON/GAL
WATER)
RECOMMENDED
CARBON-WATER RATIO
(1 LB CARBON/GAL WATER)
MAXIMUM
RECOMMENDED^
VELOCITY-
4 6
LINEAR VELOCITY (FT/SEC)
10
SOURCE: PITTSBURGH ACTIVATED
CARBON COMPANY
FIGURE 3-24
CARBON DELIVERY RATE
(1 INCH PIPE)
3-44
-------
40
u.
O
§
oc
UJ
Q.
OC
UJ
ft
oc
O
oc
O.
30
10
3.0 LBS CARBON/GAL WATER.
2.0 LBS CARBON/GAL WATER,
1.0 LB CARBON/GAL WATER,
WATER ONLY
56789
LINEAR VELOCITY (FT/SEC)
10
11
12
SOURCE:
PITTSBURGH ACTIVATED
CARBON COMPANY
FIGURE 3-25
PRESSURE DROP OF CARBON-WATER SLURRIES
(2 INCH PIPE)
3-45
-------
SLURRY ^\\
DISCHARGE >A
VIRGIN OR
REGENERATED
CARBON
TREATED LIQUOR
OR WATER
LEVEL
INDICATOR
WATER OR
COMPRESSED
AIR
DRAIN
TO SEWER
SOURCE:
PITTSBURGH ACTIVATED
CARBON COMPANY
FIGURE 3-26
BLOWCASE TRANSPORT SYSTEM
3-46
-------
should have extra large suction inlets, a recessed non-clogging type of impeller, and an
extra large packing box with seal to protect the shaft from wear. Preferred materials of
construction include 316 stainless steel, silicon iron or rubber lining. This is true
especially for those components in contact with the abrasive slurry.
The eductor serves the two-fold purpose of mixing carbon and water and of accelerating
the transport fluid. It must, of course, have a pumped water supply associated with it to
assure pressure and flow. In such an application, the pump may be selected for its use in
pumping clean water. In most installations, the spent carbon is transported in excess
water, and as much of this water as possible must be removed prior to feeding this
material to the regeneration equipment.
Tests have indicated that dewatering of the spent carbon slurry can be successfully
accomplished mechanically by use of screens, classifiers, or forced air, or by gravity
separation with decanting of the water. Slurries containing 3 to 4 pounds of water per
pound of 12 x 40 mesh carbon have been dewatered to 50-60 percent moisture (wet
basis) by use of vibrating screens. In existing wastewater installations, slurries have been
dewatered to 40-55 percent moisture content by gravity drainage in a tank if sufficient
screen area is provided. Normally 10 minutes is sufficient to provide adequate reduction
of the moisture content.
The drainage bins should be large enough to provide an adequate source for the
controlled feed of the regeneration furnaces. The use of two drain bins will allow for a
continuous furnace feed by eliminating a waiting period for drainage to take place.
Dewatering screws have also proven to be satisfactory for dewatering. The use of a
dewatering screw will eliminate the need for a drain bin, but a spent carbon storage bin is
still needed to provide a constant feed to the dewatering screw. The size of the storage
and/or drain bin is dependent on the adsorption-regeneration system configuration. With
an upflow pulsed or countercurrent system, the storage bin must be large enough to
receive the entire slug that is withdrawn at one time. When the contents of a contactor
are regenerated as a batch, its contents can be withdrawn as it is regenerated allowing for
drainage, or its contents can be transferred to a storage bin making the contactor
available to receive regenerated carbon and be placed back on line.
Makeup carbon can either be delivered in bulk or in bags. With the development of
modern, economical and efficient methods of handling bulk activated carbon, it is
normally less expensive than bagged carbon, particularly if there is a railroad siding at the
plant site. If the quantity of makeup carbon is small, the savings of bulk delivery costs
over bag delivery must be weighed against the cost of storage facilities and receiving
systems required for bulk shipments.
For makeup systems using bagged carbon, the carbon can be introduced into the system
by dumping bags of virgin carbon into slurry bins or wash tanks from which it can be
transported hydraulically. Bulk carbon can be delivered by rail or truck. With specialized
3-47
-------
cars or trailers, the carbon is fluidized with air in the carriers and transported
pneumatically to storage tanks. If the makeup carbon is stored dry, it can be introduced
into the adsorption-regeneration system pneumatically. The air velocity should be
between 50 and 100 fps. The solids should occupy 3 to 12 percent of the volume or the
solids-to-air mass ratio should be between 30 and 100. If the makeup carbon is stored in
a slurry, it can be introduced into the system hydraulically.
Except for upflow expanded beds, both makeup carbon and regenerated carbon must be
washed before it is placed in carbon columns in order to remove fine carbon dust, and
thus avoid plugging and excessive headlosses in the carbon beds. The wash tank is first
filled with water, and then the carbon is introduced and washed with the fines passing
out through the screens along with the washwater to plant recycle. Then the wash tank
can be pressurized to convey the carbon to the carbon column or other desired point of
delivery.
De-fining may require approximately a one-hour carbon wash with backwashing of the
wash tank effluent screens about every 15 minutes. Typical makeup carbon and
regenerated carbon wash tanks are shown in Figures 3-27 and 3-28.
Once the regenerated carbon is washed, it may be held in the wash tank until it is
conveyed directly to the carbon contactors or it may be transported to a regenerated
carbon storage bin. The need for regenerated carbon storage bins is dependent on the
adsorption-regeneration system configuration.
For a system in which contents of a contactor are withdrawn in a batch with only one
"spare" contactor, there must be provisions for storing a volume of carbon to fill one
contactor. This storage can be prior to or following regeneration. For a system with two
"spare" contactors there is no need for storage in as much as the spent carbon can be
withdrawn from one contactor , and as it is regenerated, can be transferred directly to
the second "spare". "Spare" contactors refers to contactors not required onstream in the
adsorption process. Some upflow contactors are designed so that spent carbon can be
withdrawn and makeup carbon added without interrupting normal use of the contactor.
The recommended methods for hydraulic loading of granular carbon columns is to
employ a blowcase, eductor or centrifugal slurry pump. When these methods are not
practical, carbon can be loaded into the column in the dry state provided recommended
procedures are followed for column loading.
3.8.2 Hydraulic Loading Procedures
One of the advantages of filling columns hydraulically is that the carbon can be wetted
and partially deaerated before it enters the column. This minimizes the possibility of air
pockets in the column which lead to channeling. In moving bed systems, the regenerated
carbon is sometimes transported to the column in treated effluent. In fixed bed systems
3-48
-------
CARBON SLURRY
INLET FUNNEL
WAFER
'STOCK
VALVE
FLEXIBLE
COUPLING
SCREEN DRAIN
AND BACKFLUSH
CONNECTION
DRAIN FOR
SCREEN BACK-
FLUSH •
PRESSURE
WATER INLET.
WELL SCREEN,
SLOTS, 316 SS, 0.020"
CLOSED END
BAFFLE CONE, HOLE
IN BOTTOM, SUPPORT
WITH BARS WELDED
TO TANK '
100 PSI STEEL
'TANK EPOXY
COATED INSIDE
WELD TO TANK
WALL FOR SUPPORT
— STANDARD 12"
•If- BY 16" MANHOLE
WASHED CARBON
OUTLET AND WASH
WATER INLET
WAFER
STOCK
VALVE
FIGURE 3-27
REGENERATED CARBON WASH TANK
(FOR 8x30 MESH CARBON)
3-49
-------
MAKEUP CARBON
WASH TANK
BAG TYPE DUST
COLLECTOR WITH
POWERED SHAKER,
EXHAUST THRU ROOF
SLOPE DUMP HOPPER BOTTOM
FOUR WAYS TO DISCHARGE
PIPE OPENING AT BOTTOM
PROVIDE 3/8
MESH REMOVABLE
SCREEN
MAKEUP CARBON WASH TANK
SIMILAR TO REGENERATED WASH
TANK EXCEPT AS SHOWN, INCLUD^
ING PIPE CONNECTIONS
FIGURE 3-28
MAKEUP CARBON WASH TANK
3-50
-------
the use of a carbon-water slurry is usually the simplest and most economical means of
moving carbon. Provisions should be made to maintain an adequate carbon-liquid ratio in
the transport lines (1 Ib carbon per gal liquid).
When the column has been filled with slurry, there will be an excess of water. Therefore,
the product discharge valve must be opened or a screened overflow arrangement made in
order to discharge the excess liquid during the loading operation.
3.8.3 Piping and Valves
Carbon is an abrasive material and when hydraulically transported will tend to wear the
inside of pipes, particularly in elbows, tees, or other changes in direction or in locations
where high headloss and excessively turbulent flow are encountered. Long radius elbows
should be used for all bends to reduce wear at these points. Experience with unlined
straight pipes, however, has indicated very little wear of the inside surfaces of pipes on
the straight run after being in service for several years. The piping system should be
designed for easy disassembly and for flushing after each slurry transport operation. This
requires the use of sufficient cleanouts, flushing connections and drains.
Steel pipes have been used satisfactorily in applications where the slurry transport is not
continuous. Steel may also be used when the piping is readily accessible for repair or
replacement. More expensive materials or linings such as rubber, saran, glass, polyvinyl
chloride and stainless steel may be justified only under special conditions, or in industrial
installations where corrosive liquids are encountered.
Valves used in wastewater disposal systems may be classified in several categories, each of
which may be further subdivided according to various design options.
Diaphragm (straight way)
Globe
Rotary (ball, butterfly, cone, plug)
Slide (gate valve, shear gate, wafer stock)
Ball check
Swing check
In selecting a valve for installation in a slurry transport line, there are four major
considerations: the purpose of the valve, its effectiveness in accomplishing functional
requirements, the resistance of the valve to the abrasive effects of slurry transport and
3-51
-------
the costs. Because of the abrasive nature of carbon slurry, valves in slurry lines must not
be used for throttling service or flow control, this must be done on the water supply line.
Valves in carbon slurry lines are for shut off or check service only. Globe valve and gate
valves normally used in pipelines are not applicable because they will not positively seat
due to obstructions by carbon particles on the seat or wear of the seat by the abrasive
slurry. Preferred valves to assure positive off and on operations are rotary type such as
ball and plug valves. These valves should offer no restriction to slurry transport when in
the open position. The diaphragm valve, certain variations of which offer limited
restriction of the open passage, has a movable element of flexible rubber, leather or some
special composition, which will be worn over a period of use and will require
replacement. One valve which has given excellent service is the wafer stock or knife gate
valve.
Both swing type and ball check valves are suitable for backflow prevention in slurry
pumping. Although the seating face against which the closing device rests is susceptible to
abrasive wear and the flow is restricted by the configuration of the valve, there is no
acceptable substitute that can achieve the same purpose. If swing checks are used, they
may be of a type designed for use in a vertical line to minimize the deposit of carbon
particles in the valve seat. They are usually installed in pairs for greater reliability.
Regulation of slurry flow can best be accomplished by throttling the water supply line, as
there is no satisfactory valve for throttling flow of the abrasive carbon slurry.
If the carbon slurry piping system is 2 to 3 inches in size, the cost of periodically
replacing carbon lines of black steel pipe may be far less than installing a high priced
system of glass lined, rubber lined, fiberglass, or other abrasion resistant special pipe.
Automatic operation of carbon-contacting systems might be accomplished using standard
equipment. However, it is not required because of the extended lengths of time between
operations of the equipment; valves serving separate carbon vessels are usually operated
only during withdrawal and replacement of carbon for regeneration, except for occasional
flow reversals. Since this occurs only about once every one to two months, it may be
best to operate the valves manually, with operator observation and attendance. In
downflow arrangements in which the carbon beds act as filters in addition to providing
adsorption sites, operation can become more frequent and somewhat complex and
automatic valve operation may be desirable.
3.9 Carbon Regeneration Systems
To make granular activated carbon economically feasible for wastewater treatment in
most applications, the exhausted carbon must be regenerated and reused. When the plant
effluent quality reaches the minimum effluent quality standards or when a predetermined
carbon dosage is achieved, spent carbon is removed from the columns to be regenerated.
3-52
-------
Closely controlled heating in a multiple hearth furnace is presently the best procedure for
removing adsorbed organics from activated carbon. Thus, maximum effort has been
concentrated on optimization of thermal regeneration techniques in an atmosphere of
limited oxygen and steam.
A typical basic sequence for the thermal regeneration of carbon is as follows:
a. The granular carbon is hydraulically transported (pumped) in a water slurry to
the regeneration station for dewatering.
b. After dewatering, the carbon is fed to a furnace (usually of the multi-hearth
type) and is heated to 1500 degrees F - 1700 degrees F in a controlled
atmosphere which volatilizes and oxidizes the adsorbed impurities.
c. The hot regenerated carbon is quenched in water.
d. The cooled regenerated carbon is washed to remove carbon fines and
hydraulically transported to the adsorption equipment or to storage.
e. The furnace off-gases are scrubbed, (the scrubber water is returned to the plant
for processing) and may also pass through an afterburner.
A typical carbon regeneration system is shown in Figure 3-29.
The thermal regeneration process itself involves three steps:
a. Drying
b. Baking (pyrolysis of adsorbates), and
c. Activating (oxidation of the residue from the adsorbate).
The total regeneration process requires about 30 minutes: the first 15 minutes is a drying
period during which the water retained in the carbon pores is evaporated, a 5 minute
period during which the adsorbed material is pyrolyzed and the volatile portions thereof
are driven off, and a 10 minute period during which the adsorbed material is oxidized
and the granular carbon reactivated.
The theoretical required furnace capacity can be determined simply by multiplying the
carbon dosage (in Ibs of carbon per million gallons) by the daily flow rate in million
gallons per day. This will determine the Ibs of carbon per day that must be regenerated.
This computation does not allow for furnace downtime or other contingencies that must
be considered when actually specifying the furnace size to be installed.
3-53
-------
MAKEUP
CARBON
•OO
WATER BACK
TO PROCESS
>SPENT CARBON
DRAIN AND
FEED TANKS
.SCREW
CONVEYORS
CARBON
SLURRY
BIN
tf—00
CARBON
SLURRY
PUMPS
CARBON FINES
BACK TO
PROCESS-
CARBON
SLURRY
PUMP
.SPENT CARBON
FROM CARBON'
COLUMNS
SCRUBBER
AND AIR
POLLUTION
-CONTROL
EQUIPMENT
CARBON
REGENERATION
FURNACE
.STEAM
SUPPLY
-QUENCH
TANK
REGENERATED CARBON
DEFINING AND STORAGE
TANKS
REGENERATED
•CARBON TO CARBON
COLUMNS
FIGURE 3-29
CARBON REGENERATION SYSTEM SCHEMATIC
3-54
-------
An allowance of 40 percent downtime in selecting the furnace size provides a
conservative basis for furnace selection.
Multiple hearth furnaces used for regenerating carbon should provide a hearth area of
about one square foot per 40 Ibs of carbon to be regenerated per day.
The regeneration furnace should be designed so that the hearth temperatures, furnace
feed rate, rabble arm speed, and steam addition can be controlled.
The hot gases on the top hearth of the regeneration furnace contain both fine carbon
particulates and odorous materials visible as smoke. Since the wet spent carbon enters the
top of the furnace near the exit point for the exhaust gases, some of the more volatile
adsorbate is removed from the carbon and carried into the atmosphere without being
completely oxidized. Both this smoke and the carbon particulates might present air
pollution problems if left uncontrolled. Therefore, it is imperative that air pollution
control equipment be included in the design of the carbon regeneration furnace. Systems
are available and in use which include an afterburner, for removal of smoke and odors,
and a wet scrubber or bag filter for removal of particulates. These are designed as integral
parts of the furnace installation. Stringent air emission standards have been met by use of
a variable-throat Venturi-type scrubber with 20 inch pressure drop. [5]
As carbon is removed from service for regeneration, the spent carbon is usually
hydraulically transported to a drain bin. The drained carbon is dried during the first step
in a furnace which heats the carbon to less than 212 degrees F. During baking, the
temperature increases from 212 degrees F to 1,500 degrees F, by which time adsorbed
organics are thoroughly carbonized. This is accompanied by evolution of gases and by the
formation of a carbon residue in the micropores of the activated carbon. The objective of
this activating step is to oxidize the carbon residue with minimum resultant damage to
the basic pore structure, thereby effecting maximum restoration of the original properties
of the carbon. The activating gas temperature during this step is about 1,700 degrees F,
while the carbon temperatures range from 1,500 degrees F to 1,650 degrees F. Flue gas
supplemented by varying amounts of additional steam and limitation of oxygen produces
the desired atmosphere. The most important phase of the regeneration process is that of
activation, with the critical parameters being carbon temperature, duration of activation,
and steam or carbon dioxide concentration in the activating gas mixture. Since most
installations use direct-fired multiple hearth furnaces for regeneration, the combustion of
natural gas with air provides the required heat, while carbon dioxide, oxygen, and steam,
as part of the products of combustion, are the activating agents. Extra steam at
approximately one pound per pound of carbon regenerated is supplied. This requires
auxiliary steam generating equipment.
With the 6 hearth furnace at South Tahoe, the burners are located on hearths 4 and 6.
To maintain the desired carbon temperature, the temperatures on the various hearths are
approximately as follows: No. 1, 800 degrees; No. 2, 1,000 degrees; No. 3, 1,300 degrees;
3-55
-------
No, 4, 1,680 degrees; No. 5, 1,600 degrees; and No. 6, 1,680 degrees F. It was found
that the addition of steam on hearths 4 and 6 gave a more uniform distribution of
temperatures throughout the furnace. The effect of steam is to reduce the apparent
density and increase the Iodine Number of the regenerated carbon. About 1 Ib of steam
per Ib of dry carbon was used. Figure 3-30 is a drawing of a regeneration furnace
showing the main components.
The regenerated carbon is discharged from the bottom of the furnace into a quench tank.
Figure 3-31 shows a typical carbon furnace discharge chute. The outlet of the discharge
chute is below the water level in the quench tank. The water jets fed by the pressure
water supply must be placed to keep the carbon moving in the quench tank to prevent
carbon buildup and plugging of the tank's discharge lines. Figure 3-32 is a sketch of a
typical carbon furnace quench tank.
Partially dewatered carbon from drain bins can be fed into the furnace by a screw
conveyor. The conveyor should be equipped with a variable speed drive so the rate of
carbon feed to the furnace can be controlled accurately. The conveyor should be
constructed out of a corrosion resistant material. At South Tahoe, a 9-inch screw is used
with a 3-inch pitch at the lower end and a 9-inch pitch at the upper (furnace) end
(Figure 3-33). The low-pitch, metering section of the screw under the bin runs full of
carbon for accurate feed control, and the higher pitch, conveying section runs only
partially full to reduce the total driving torque required. If a dewatering bin is not used
in the regeneration sequence, a continuous dewatering screw can be used to feed the
regeneration furnace. Continuous dewatering screws have proven to be satisfactory for
dewatering the carbon to 50 percent moisture. The screw is fairly insensitive to
fluctuations in feed conditions up to a maximum capacity.
Regeneration Fuel—The total fuel requirement for the regeneration system is estimated to
be 4,250 Btu per Ib of carbon regenerated, exclusive of fuel used in the afterburner. This
figure is based on the following:
1. 3,000 Btu/lb carbon is required for furnace heat as determined from operating
data at South Tahoe and Pomona.
2. 1,250 Btu will generate one pound of steam which is sufficient for one pound
of carbon under regeneration, according to South Tahoe data.
The regeneration furnaces in use at South Tahoe and Pomona are both gas fired, and the
one at South Tahoe is equipped with propane standby. The heat requirements will not
vary substantially if the furnace size is larger than the 54-inch furnace used at South
Tahoe. Very little heat is lost in radiation, thus increasing the furnace hearth area to
perimeter ratio provides little savings in fuel.
3-56
-------
HEARTH
CARBON
IN
UUU . .LJUULJ
RABBLE ARM
RABBLE TEETH
"CARBON OUT
FIGURE 3-30
CROSS-SECTIONAL VIEW OF MULTIPLE HEARTH FURNACE
3-57
-------
BOTTOM OF
CARBON
FURNACE
316 SS
REGENERATED
CARBON DISCHARGE
PRESSURE
WATER SUPPLY
FOR PRECOOLING
CARBON
316 SS
SLIDE
GATE
E^
v /
^^
,
2" G.S. DRY
REGENERATED
CARBON SAMPLE
TRAP
•QUENCH TANK
FIGURE 3-31
TYPICAL CARBON FURNACE DISCHARGE CHUTE
3-58
-------
HOT CARBON
DISCHARGE
CHUTE
PRESSURE
WATER SUPPLY
PLAN
OVERFLOW
WEIR
W.S.P. OVER
FLOW WELL
WELL SCREEN, 316 SS
0.020" SLOTS, CLOSED
TOP
DRAIN
G.S. CARBON --
SLURRY PUMP
SUCTION LINES
HOT CARBON
DISCHARGE CHUTE,
316 SS
r \
PRESSURE
WATER SUPPLY
SECTION
FIGURE 3-32
TYPICAL CARBON FURNACE QUENCH TANK
3-59
-------
SPENT
CARBON IN
-STEEL DRAIN BIN
COAL TAR EPOXY
LINED
SCREENED
DRAIN
SCREENED
DRAIN
SECTION
DRAIN
LINE
.VARIABLE SPEED
SCREW CONVEYOR
DRIVE
LOW PITCH
METERING
SCREW
HIGH PITCH
CONVEYING
SCREW
TOP OF
CARBON FURNACE
SCREW CONVEYOR AND HOUSING
ARE FABRICATED FROM 316
STAINLESS STEEL
FIGURE 3-33
SPENT CARBON DRAIN BIN AND
FURNACE FEED ARRANGEMENT
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3.10 Recycle Flows
Because tertiary and PCT plants and other plants incorporating carbon treatment are
generally aiming at production of water quality better than that of secondary effluent,
the handling of internal plant process streams assumes importance. Many, if not all, of
these streams must be recycled through part or all of the plant rather than to be directly
discharged with the final effluent which would degrade its quality. Since carbon
treatment is at or near the downstream end of most flow charts, all of the recycle flows
must be added to the anticipated wastewater flows expected on the maximum day. These
recycle flows are significant in amount. They may range from 20 to 35 percent of the
maximum daily flow, or even higher in small plants. Flow from the scrubber on the
carbon regeneration furnace alone may be 400-600 gpm. If ignored, recycle flows can
seriously overload processes and equipment.
Some recycle flows such as scrubber water are constant in volume. Others such as carbon
column backflush water may be high volume, short duration flows, and storage for flow
equalization may be necessary. In some cases, if storage is provided, it may be possible to
release the recycle flows during off-peak flow periods.
The point at which recycle flows are reintroduced to the process should be considered.
Many will go to the head of the plant, others may only require filtration and carbon
treatment, and so on. Usually it is advantageous to return the recycled water to the
furthest downstream point in the process which will provide the necessary treatment.
Certain recycle flows originate within the carbon adsorption and carbon regeneration
portions of the plant. These include: column and surface backwash water; carbon column
to waste; transport water from dewatering tanks or screws; overflow from quench tanks;
water from de-fining or wash tanks; and exhaust gas scrubber water. Normally the
backwash water would be returned either ahead of the filters if they precede the carbon
columns or ahead of the chemical clarification step if there are no filters. Scrubber water
may be returned to the filter or chemical clarifier influent, along with transport water,
overflow from quench tanks, and water from carbon de-fining.
3.11 Monitoring and Controls
3.11.1 Expected Plant Performance
Because tertiary and PCT treatment processes are new to many operators, it is very
helpful for the design engineer to report, preferably both in person and by written
summary, what performance is expected from the carbon treatment and in carbon
regeneration. During plant startup, the designer should conduct appropriate testing
programs under actual operating conditions to substantiate predicted process performance
and to establish baselines for future plant operations. The report prepared by the design
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engineer for the plant operator should include the following: various unit design flows,
the design influent and effluent qualities, the characteristics of fresh and regenerated
carbon, the average time between carbon regenerations, the range of carbon usage rates,
and the results anticipated when the plant is operated above or below its rated design
capacity.
It is also the design engineer's responsibility to insure that the plant operator understands
the functions and utility of the meters, controls, analytical devices, and other instruments
installed to monitor and control the plant and the quality of water produced.
3.11.2 Control of Contactor Operation
The operation of any of the types of contactors previously discussed is a simple task,
although the series downflow beds introduce some complexities because of the greater
number of valves to be operated.
Basically, contactor operation consists of bringing the wastewater to be treated into
contact with the carbon at the proper throughput rate until as much of the adsorptive
capacity of the carbon is utilized as the capabilities of the installed system will allow.
Then, when the plant effluent no longer meets the desired quality standard, some
quantity of spent carbon must be removed for regeneration and replaced with an equal
quantity of regenerated and makeup carbon.
The plant operator has some control over flow rates and contact times between the
wastewater and the carbon by selecting the total number of contactor units which are
placed into service at a given plant influent flow. In operation of many plant processes, it
is good practice to keep as many units on the line as possible. This reduces unit loadings
on the processes and generally improves performance. This is also true to a certain extent
in the operation of carbon contacting systems, but there are some exceptions worthy of
note. Hydrogen sulfide generation has been a problem in some carbon adsorption
installations, particularly those which apply a heavy load of BOD, COD, and SS to the
carbon. Time is one important factor in the amount of sulfide produced, so that at low
flow periods in plant operation it may be advisable to remove enough contactor units
from service to limit the contact period to the design period. In any event, the total flow
should be divided about equally among all the contactors which are in service at any one
time. This can be done quite easily by measuring the flow by means of a Dall tube and
rate-of-flow indicator and adjusting the flows by means of a manually operated butterfly
valve. If the control valve is properly sized, valve settings ordinarily do not change with
hourly flow variations within a day, and the valves may only require readjustment when
flows increase or decrease sufficiently to require a change in the total number of units in
service.
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Flow adjustment for upflow expanded beds in the service or adsorption cycle requires
more attention than that just described. Sufficient minimum flow must be maintained in
each column to expand the carbon at least 10 percent. This is not a precisely fixed
quantity due to changes in water viscosity due to water temperature changes, change in
density of the carbon as it becomes saturated with organics, and changes in density and
particle size due to slime growths on the carbon. If the upflow contactor is operated at
less than 10 percent bed expansion, solids may accumulate within the bed and cause
development of excessive headlosses. If this occurs, it may be necessary to increase the
flow to produce an expansion of 10 to 50 percent in the affected unit for a long enough
period to flush out the particulate matter. For minor amounts of material, the unit may
be kept in service, but if the amount is enough to interfere with maintenance of the
desired effluent quality then it may be necessary to go from column to waste for a short
time.
Excessive headloss in packed beds may be either in the bed itself or in the top screens of
upflow units. If the loss is only in the screens, momentary flow reversal may be effective
in clearing the screens of lodged carbon particles and in reducing the headloss. If the
headloss is in the bed itself, then full backwashing (50 percent expansion) of downflow
beds is necessary. For upflow beds, a temporary increase in the flow rate with the unit
on the line in upflow may be sufficient, but periodically flow reversal followed by 10
percent bed expansion in upflow with the unit out of service is required. The frequency
of these operations is low, and it is doubtful that automation is warranted, although it
might be worthwhile for backwashing of downflow beds used as filters.
Another factor which requires control is the pH of the carbon column influent. Carbon
will function satisfactorily at any pH from 6.5 to 9.0, or perhaps even outside this range,
and a decrease in pH during a run between carbon replenishments is no problem, but
substantial increase in pH can cause desorption, particularly if the bed is nearing
exhaustion. In other words, if a bed of carbon has been operating at a pH of 7.0 for
several days or weeks and then the pH is raised to 8.5 for several hours, desorption may
occur, that is, previously adsorbed materials such as color, odor, COD, BOD, etc. may be
released to the column effluent. This is not a common problem or one that is difficult to
control, but it is a problem of which the operator must be aware.
The remaining principal item in the control of contactors is the determination of the
time to withdraw carbon for regeneration and replace it with regenerated and makeup
carbon. There are a number of ways to do this. In starting up a new plant, it may be
done initially by observation of effluent COD concentrations. If the value approaches the
predetermined maximum (say 10 to 20 mg/1 of COD) desired or mandatory value for an
appreciable time period of one or two days, then it probably is time to start a
regeneration campaign. In upflow contactors, it is usual to withdraw 5 to 10 percent of
the carbon from the bottom of each contactor during each regeneration cycle. In
downflow contactors, the entire contents of the lead contactor are removed for
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regeneration and, if there are two beds in series, the second bed is placed in the lead
position by changing valve positions accordingly. Once sufficient data is obtained from
operation of a particular plant on a given wastewater with the specific treatment provided
ahead of the carbon adsorption process, then there are other ways to determine the need
to initiate a regeneration cycle. If adequate records of plant operations and laboratory
tests are maintained, then experience will show: (1) the required carbon dosage in
pounds of carbon per million gallons of column throughput, and (2) the maximum or
optimum loading of the carbon particles by the crucial organic being removed (probably
COD in the case of domestic wastewaters) in terms of pounds adsorbed per pound of
carbon. Some examples may be useful in this regard. The carbon dosage required depends
on the strength of the wastewater feed to the carbon columns and the effluent quality
required. Some typical carbon dosages which might be expected are:
Pretreatment Typical Carbon Dosage,
Pounds Per Million Gals.
1. Tertiary, activated sludge,
high-lime (pH =11) clarification,
recarbonation, and mixed-media 200 - 400
filtration (average dosage in 5
years of operation at Tahoe =
210).
2. Secondary plus plain filtration 400 - 600
3. Physical-chemical (high lime,
pH = 11, treatment of raw waste 1,500 - 1,800
and primary clarification).
If dosage is to be used as the basis for initiating regeneration, then it should be
determined rather precisely for the particular plant in question. This may require at least
one year's operation. The above figures are a rough guide only, and may vary widely
from place to place even with the same process because of differences in the waters, in
plant operation, and in accordance with other variables including climate. Once the
dosage is known, then a combination of average COD concentration in the applied water
and total flow through the bed will establish the need for transfer of carbon. To use this
method, the plant design must include: flow measurement (and possibly flow totalizing
and recording) for each carbon column; laboratory equipment for running COD, BOD,
color, MB AS, turbidity, and other control tests; means for measuring the level and
calculating the volume of carbon in contactors, drain bins, and storage bins; access for
inventory of idle or makeup carbon in bags or other storage; and development of forms
for recording the movements and quantities of spent, regenerated, and makeup carbon, as
well as associated laboratory test results.
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3.11.3 Control of Carbon Regeneration
Figure 3-34 shows a typical carbon contacting and regeneration process flow diagram
with upflow contactors (packed bed), With the use of expanded upflow contactors, the
washing of makeup and regenerated carbon shown in Figure 3-32 may be omitted. For
downflow contactors, the regeneration portion of Figure 3-32 still applies; only the
contactor and the method of removing carbon from it would change.
Control of the quality of regenerated carbon is performed at the plant by the operator
by measuring the apparent density of the regenerated carbon, and later checked by
laboratory tests to measure the capacity of the regenerated carbon to adsorb a standard
iodine solution which determined the Iodine Number of the carbon. The A.D. (apparent
density) of virgin carbon is about 0.48 gm/cc. As carbon becomes saturated with
adsorbed organics, the A.D. may increase to 0.50 or 0.52, or more. As the carbon is
regenerated, organics are removed, and the carbon loses weight. If properly regenerated,
the A.D. will return to 0.48. The A.D. is easily and rapidly determined by weighing a
known volumn of carbon. The detailed procedure for performing the A.D. test is given in
Appendix B.
In carbon regeneration if the apparent density is greater than 0.49, the carbon is not
obtaining enough heat to volatilize a sufficient quantity of organic material. On the other
hand, if the apparent density is less than 0.48, the carbon is obtaining too much heat,
and carbon is being burned in the furnace.
The A.D. of the regenerated carbon can be varied by changing the following process
variables:
1. Temperature is the most critical factor in carbon regeneration; a higher
temperature will give a lower A.D. and a lower temperature will give a higher
A.D.
2. Carbon feed rate is the next critical factor in carbon regeneration. Increasing
the carbon feed rate will increase the carbon depth on the furnace hearths and
will reduce the amount of heat supplied to the carbon. This change will give
the carbon a higher A.D. Lowering the carbon feed rate will decrease the depth
of carbon and increase the amount of heat supplied to the carbon. In turn, the
carbon will have a lower A.D.
3. Increasing the steam feed rate will decrease the A.D. Decreasing the steam feed
rate will increase the A.D.
4. Furnace drive speed regulates the contact time in the furnace. Increasing the
drive speed will reduce the contact time. In practice, this is not as critical as
temperature and carbon feed rate.
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MAKEUP CARBON
REGENERATED CARBON
PRESSURIZE TANK
TO TRANSFER
CARBON TO COLUMNS
MAKEUP CARBON U
BAG DUMP ' *
^MAKEUP
CARBON
WASH TANK
WASTE
WASH
WATER
CARBON FILL
CHAMBER
PRESSURIZE
COLUMN TO
TRANSFER
SPENT CARBON
TO DEWATERING
TANK
REGENERATED
CARBON
WASH TANK
PRESSURIZE TO
TRANSFER
CARBON TO
COLUMNS
REGENERATED
CARBON SLURRY
PUMPS
INFLUENT
FIGURE 3-34
CARBON CONTACTING AND REGENERATION -
PROCESS FLOW DIAGRAM WITH UPFLOW CONTACTORS
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Do not change more than one process variable per half-hour interval. Typically, there will
be about a 5 to 10 percent loss of carbon during each regeneration cycle. The Iodine
Number of virgin carbon is about 935, of spent carbon about 580, and of regenerated
carbon from 800 to 900. The laboratory test procedure for determining the Iodine
Number of carbon is given in Appendix B.
The ash content of carbon may be used to detect any buildup of calcium or other
undesirable foreign material. The ash content of virgin carbon is about 5.2 percent. Just
prior to the first regeneration, the ash content may increase to about 5.7 percent, and
after the first regeneration, when used as a tertiary treatment process, to about 6.4
percent. In subsequent regenerations, there should be little or no change in the 5.7
percent and 6.4 percent values for spent and regenerated carbon. The procedure for
determining the ash content of carbon is given in a following section. Somewhat greater
ash buildups can be expected if lesser degrees of pretreatment are provided than assumed
above.
Carbon may lose some adsorptive capacity upon regeneration, particularly in the first
regeneration. Combustion of the adsorbed organics is never really complete. Some ash
accumulates in the carbon pores to obscure them and some carbon is burned with the
adsorbate, thereby decreasing carbon surface area. The net losses have been measured for
the Pomona pilot plant. In a four-stage series downflow carbon contactor, removal of
dissolved COD in the lead contactor declined from 89 to 71 percent in two regeneration
cycles, but thereafter remained virtually constant at 70 percent. This included the effect
of makeup carbon. At Pomona, secondary effluent with no pretreatment was applied
directly to the carbon, resulting in application of particulate matter to the carbon which
may have contributed to this loss in capacity. At South Lake Tahoe, where the
wastewater receives a high degree of pretreatment prior to application to the carbon,
removal of COD has not shown a decreasing trend. The removals of about 50 percent
COD achieved initially with virgin carbon were also achieved with carbon subjected to
four regeneration cycles.
Several controls must be provided for operation of the furnace and its auxiliaries. The
rate of spent carbon feed into the furnace determines the residence time of carbon in the
furnace which affects the degree of regeneration accomplished. The temperatures on each
hearth must be set at the desired value. Once set they should be automatically controlled.
The furnace atmosphere is controlled by the draft regulator, burner settings, and steam
addition. Draft controls should be automated, and the temperatures on each hearth
continuously recorded. Temperatures on the various hearths of a six hearth furnace
should be about as follows: No. 1, 800 degrees; No. 2, 1,000 degrees; No. 3, 1,300
degrees; No. 4, 1,680 degrees; No. 5, 1,600 degrees; and No, 6, 1,680 degrees F.
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A proportional flowmeter should be provided in each of the air-gas mixture lines to the
burners to insure a constant percentage of excess oxygen. In addition, provision should
be made so that steam can be added as required.
An ultraviolet scanner should be provided on each of the burners. Then in case of a
flame-out, the furnace is automatically shut down. Other safety features which should
automatically shut down the furnace are: high or low gas pressure, high combustion air
pressure, low scrubber water pressure, high stack gas temperature, and draft fan and shaft
cooling air fan, which should be on a standby power circuit to avoid possible damage to
the furnace rabble arms in the event of an electrical outage.
3.12 Corrosion and Abrasion Control
Dry carbon and carbon in water slurry is not corrosive. Carbon slurries will drain by
gravity to about 40 percent moisture in about 10 to 15 minutes time. It retains this
moisture for several weeks under normal storage conditions not subject to forced draft or
heating. Partially dewatered carbon is extremely corrosive and under conditions of
continuous exposure may produce pits in unprotected mild steel plant by electrolytic
corrosion at a rate as high as 1 /4-inch of depth per year. Steel can be protected by use of
a good coal-tar epoxy paint. A minimum of 3 coats to a total thickness of 10 to 24 mils
is recommended. The coating process must be rigidly supervised, inspected, and tested to
assure that a continuous coating of the epoxy is obtained. Steel tanks also can be
protected by installation of a properly designed cathodic protection system. However, a
very liberal extra thickness of steel (about 3/16-inch) should be allowed for corrosion
above pressure or other structural requirements. Stainless steel (304 or 316) is a good but
expensive material to use in contact with moist carbon. Fiberglass tankage is also a
satisfactory approach.
Present engineering practice appears to favor the use of mild steel protected with coal-tar
epoxy for carbon contactors, dewatering bins, wash tanks, and quench tanks; the use of
stainless steel for conveyors moving spent carbon to the regeneration furnace and for
screens in the carbon system; and the use of black steel pipe for carbon slurry lines.
Abrasion of pipelines by carbon slurry is a factor to be considered. However, experience
to date indicates that black steel will have a service life in excess of 10 years, so that it
may be less expensive to replace steel lines as required rather than to install pipelines of
stainless steel or with linings of glass or rubber. Abrasion is maximum at bends so that it
is helpful to use long radius fittings at changes in direction of flow and to use extra
heavy elbows and tees. Rubber or ceramic lined impellers are recommended for carbon
slurry pumps.
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3.13 Additional Reading
1. Process Design Manual for Upgrading Existing Wastewater Treatment Plants, U. S.
Environmental Protection Agency, 1973.
2. O'Farrell, Thomas P., et al., Advanced Waste Treatment at Washington, D. C.,
presented at the 65th Annual AICHE Meeting, Cleveland, Ohio, May, 1969.
3. Process Design Manual for Suspended Solids Removal, U. S. Environmental
Protection Agency, 1973.
4. Gulp, G. L., and Shuckrow, A. J., Physical-Chemical Techniques for Treatment of
Raw Waste-waters, Public Works (July, 1972).
5. Juhula, A. J., and Tupper, F., Laboratory Investigation of the Regeneration of Spent
Granular Carbon. FWPCA Report No. TWRC-7 (Feb., 1969).
6. Cover, A. E., and Wood, C. D., Appraisal of Granular Carbon Contactors, Phase HI.
FWPCA Report No. TWRC-12 (May, 1969).
7. Cover, A. E., and Pieroni, L. J., Appraisal of Granular Carbon Contactors, Phases I &
II. FWPCA Report No. TWRC-11 (May, 1969).
8. Rizzo, J. L., and Schade, R. E., Secondary Treatment With Granular Activated
Carbon. Water and Sewage Works, p. 307, August (1969).
9. Slechta, A. F., and Gulp, G. L., Water Reclamation Studies at The South Tahoe
Public Utility District. Journal Water Pollution Control Federation, p.787 (1967).
10. Gulp, Russell L, and Gulp, Gordon L. Advanced Wastewater Treatment. Van
Nostrand Reinhold, New York, 1971.
11. Chemical-Physical Wastewater Treatment. Phase 2: Activated Carbon Adsorption and
Polishing. Technical Paper No. 17, New York State Department of Environmental
Conservation, Jan., 1972.
12. Optimization of the Regeneration Procedure for Granular Activated Carbon. EPA
Report No. 17020 DAO, July, 1970.
13. Weber, W. J., Hopkins, C. B., and Bloom, R. Physicochemical Treatment of
Wastewater. Journal WPCF, p. 83, (Jan., 1970).
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3.14 References
1. Berthouex, P.M. Evaluating Economy of Scale. Journal WPCF, p. 2111, (November,
1972).
2. Progress Reports, Tertiary Treatment Plant, City of Colorado Springs. Department of
Public Utilities, EPA Project 17080 DIE.
3. Directo, L. S., Monthly Reports on the Pomona Pilot Plant.
4. Shuckrow, A. J. and Bonner, W. F., 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. A report by Battelle
Northwest to Zurn Environmental Engineers, 1971.
5. Advanced Waste Water Treatment as Practiced at South Tahoe. A report by the
South Tahoe Public Utility District for EPA (Project WPRD 52-01-67, 1971).
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CHAPTER 4
CARBON EVALUATION AND SELECTION
4.1 Introduction
The proper use of activated carbon as a unit process in the treatment of wastewater
requires the selection of an appropriate carbon and mode of operation. The selection of
an appropriate carbon for wastewater treatment requires a general understanding of the
physical properties together with the performance of certain analytical, comparative
procedures.
Before selecting a particular carbon for evaluation, both the characteristics of the
wastewater to be treated and the effluent requirements must be known.
The most important determinations in laboratory and pilot tests are: (1) the treatability
of the waste by carbon, and (2) development of design criteria. The performance of
various types of commercial carbons is the subject of some debate; however, the
performance of alternate carbons can be estimated from tests with pilot scale contactors.
The physical properties of activated carbon are also important, particularly those
properties related to its resistance to attrition losses from handling and regeneration.
4.2 Wastewater Characterization
To best utilize the adsorptive properties of a particular activated carbon, it is necessary to
know the specific wastewater characteristics. In general, activated carbon is exceptionally
suited for the adsorption of dissolved organics. Dissolved organics have been operationally
defined as those which pass through a 0.45 micron membrane filter. There are two types
of dissolved organics: biodegradable and refractory. Biodegradable dissolved organics are
defined as those that are broken down by biological action such as in an activated sludge
system. Refractory dissolved organics are defined as those which are not amenable to
biological action and remain in solution in the effluent from a biological treatment
system.
Biodegradable organics can be measured by the BOD test, but this test is of no value in
determining the quantity of refractory organics. A test that measures the total oxidizable
organic matter must be used, such as the TOC (total organic carbon) or the COD test. It
then follows, that the BOD test is of little value in analyzing the adsorptive properties of
activated carbon. The total organic carbon test is perhaps the quickest and most reliable
test to be used in evaluation of activated carbon. There are several organic carbon
analyzers on the market and all are relatively expensive. The COD test, however, can also
be used for an adequate evaluation of the adsorptive properties of activated carbon.
4-1
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Specific organic waste constituents such as those from industrial processes can be
identified using various analytical techniques, such as spectroscopic, spectrophotometric,
or chromatographic methods.
There are several inorganic and environmental parameters which may affect the evaluation
of activated carbon, namely: pH, temperature, and suspended solids. Decreasing pH and
increasing temperature increases the adsorptive characteristics of activated carbon,
therefore these two parameters should be held constant during the evaluation procedures.
Also, desorption may occur at pH values above 9.0 and adsorption is adversely affected
at this high pH.
Suspended solids may affect adsorption and interfere with analytical procedures,
therefore samples should be filtered prior to conducting tests. The effects of suspended
solids on carbon column operation were discussed in Chapter 2.
4.3 Carbon Evaluation Procedures
With the development of a basic understanding of how and what activated carbon will
adsorb, together with a general knowledge of waste characteristics, the next step is to
evaluate and select a carbon best suited for a particular purpose.
The suppliers of activated carbon generally provide a table of quality control parameters
for their products as shown in Table 2-1. Only a few of the parameters listed by the
carbon suppliers are of value in terms of comparing competing activated carbons. Some
of the appropriate physical properties that may be used to select one or several carbons
for further evaluation are as follows:
1. Surface area—Adsorption is a surface phenomenon, so surface area is a general
criteria for the capability of a particular carbon for adsorption.
2. Apparent density—This property is of little value in initial evaluation and
selection of an activated carbon, but is very useful as one of the measures of
successful regeneration. Apparent density measurement is a simple test, and the
density of saturated carbon relative to the density of regenerated carbon
indicates the degree of regeneration accomplished.
3. Bulk density-Useful in determining the volume requirements of a carbon
column after the contact time requirements have been established.
4. Effective size, mean particle diameter and uniformity coefficient—Measures of
the gradation of carbon particle size which are important in evaluating headless
in flow through granular beds.
4-2
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5. Pore volume—A measure of the total macropore and micropore volume of the
carbon which can be of some value in the selection and application of an
activated carbon for a specific waste constituent relative to molecular weight.
However, there are other more direct measures of the ability of an activated
carbon to adsorb different molecular weight substances which will be discussed
shortly.
6. Sieve analysis—Very useful in checking carbon production, in checking
conformance of purchased carbon to specifications, and in evaluating the
effects of plant carbon handling procedures on carbon attrition.
7. Abrasion number—Of limited usefulness at present because the equipment used
for testing is unreliable and tests are not reproducible. If the testing procedure
is made more reliable, this number may become helpful in evaluating the ability
of a carbon to withstand attrition.
8. Ash percent—Indicative of the raw material and manufacturing process used in
the manufacture of a particular activated carbon.
9. Moisture as packed, maximum percent—Useful only for shipping and
manufacturing purposes.
10. Iodine number—Can be correlated with the ability of an activated carbon to
adsorb low molecular weight substances. This value is determined by a
relatively easy test and is used widely to determine the restoration of
adsorptive capacity upon regeneration.
11. Molasses number, molasses value and molasses decolorizing index—Can be
correlated with the ability of an activated carbon to adsorb high molecular
weight substances from some liquids, but has not been particularly useful to
date for wastewater.
12. Pore size distribution (not usually listed by suppliers in their table of quality
parameters)—Characterizes the pore structure which has a great influence on
both equilibrium and rate of adsorption. Pore size distributions in the size
range of 20-2,000 Angstroms are calculated from nitrogen adsorption isotherms.
Pore size distributions are useful for selecting carbons which have high
adsorptive capacities for particular types of molecules.
The technical evaluation of activated carbons is best served by providing procedures for
the determination of adsorption rate and capacity together with a determination of the
ability of each carbon to withstand a specified level of mechanical attrition.
Unfortunately, at present, it appears that plant scale experience over a considerable
4-3
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period of time is the only reliable means of predicting the durability of a carbon with
respect to mechanical attrition losses, although some very fragile carbons can be
identified as unsuitable in the laboratory or brief pilot tests. The ability of granular
carbon to withstand handling and slurry transfer is of paramount importance in
wastewater treatment. Excessive attrition losses create carbon fines to an extent that
intolerable headlosses occur in flow through the beds with catastrophic results in plant
operation. Some good way to determine the ability of a carbon to withstand handling
must be developed for laboratory use, so that new products can be fairly evaluated
without waiting for long term plant trials, but at the moment reliance on the experience
in operating plants is the only safe way to proceed.
4.4 Adsorption Isotherms
The adsorption isotherm is the relationship, at a given temperature and other conditions,
between the amount of a substance adsorbed and its concentration in the surrounding
solution. If a color adsorption isotherm is taken as an example, the adsorption isotherm
would consist of a curve plotted with residual color in the water as the abscissa, and the
color adsorbed per gram of carbon as the ordinate. A reading taken at any point on the
isotherm gives the amount of color adsorbed per unit weight of carbon, which is the
carbon adsorptive capacity at a particular color concentration and water temperature. In
very dilute solutions, such as wastewater, a logarithmic isotherm plotting usually yields a
straight line. In this connection, a useful formula is the Freundlich equation which relates
the amount of impurity in the solution to that adsorbed as follows:
where:
/ i /-i l/n
x/m = kC
x = amount of color adsorbed
m = weight of carbon
k and n are constants
C = unadsorbed concentration of color left in solution
in logarithmic form:
log x/m = log k + l/n log C
in which l/n represents the slope of the straight line isotherm.
From an isotherm test, it can be determined whether or not a particular degree of
organic removal can be effected by adsorption alone. It will also show the approximate
adsorptive capacity of the carbon for the application. Isotherm tests also afford a
convenient means of studying the effects of pH and temperature on adsorption.
Isotherms put a large amount of data into concise form for ready evaluation and
4-4
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interpretation. Isotherms obtained under identical conditions using the same test solutions
for two test carbons can be quickly and conveniently compared to reveal the relative
merits of the carbons.
As mentioned previously, the Iodine Number and the Molasses Number also give an
indication of the adsorptive capacity of a carbon. The Iodine Number is the milligrams of
iodine adsorbed from a 0.02 N solution at equilibrium under specified conditions. The
Molasses Number is an index of the adsorptive capacity of the carbon for color bodies in
a standard molasses solution as compared to a standard carbon. The procedures for
determining the Iodine and Molasses Numbers are found in the appendix. These tests are
generally used for screening purposes.
As discussed earlier in Chapter 2, since granular carbon columns are dynamic systems, not
only are the equilibrium adsorption properties of the carbon important, but also the rates
of adsorption illustrated by Figure 4-1. Figure 4-1 shows breakthrough curves of a carbon
as obtained by passing a fluid containing an adsorbable substance through a packed bed
or carbon. The concentration of the adsorbable substance in the effluent stream from the
bed is plotted against the volume of fluid passed through. In Figure 4-1 the breakthrough
curve for Carbon E is much steeper than that for Carbon F. This will occur when the
rate of adsorption for Carbon E is much greater than that for Carbon F. Generally
speaking, greater rates for adsorption are desired for maximum efficiency of the carbon.
In actual use, operation is discontinued when the effluent concentration reaches an
unacceptable value. The carbon with the steepest breakthrough curve will, therefore, have
the longest service life even though the capacity of the carbons at equilibrium may be the
same or even higher. Thus, for selecting carbons and designing adsorption systems, the
rate of adsorption as reflected in the breakthrough curves, is an important consideration.
Figures 4-2 and 4-3 are presented to illustrate the interpretation of adsorption isotherms.
In Figure 4-2, the isotherm for Carbon A is at a high level and has only a slight slope.
This means that adsorption is large over the entire range of concentrations studied. The
fact that the isotherm for Carbon B in Figure 4-2 is at a lower level indicates
proportionally less adsorption, although adsorption improves at higher concentrations
over that at low concentrations. An isotherm having a steep slope indicates that
adsorption is good at high concentrations, but much less at low concentration. In general,
JLhe_sieepex-the~slope _x>f its isatherrriiJJie greater the efficiency .of, a^ carbon in^coiumn
gp_er_ation. In Figure 4-3, Carbon D is better suited to countercurrent column operation
than Carbon C. It has a higher capacity at the influent concentration, or more reserve
capacity. Carbon C in Figure 4-3 would be better than Carbon D for batch treatment.
The procedures for performing an adsorption isotherm are found in the appendix.
4.5 Pilot Carbon Column Tests
Although the treatability of a particular wastewater by carbon and the relative capacity
of different types of carbon for treatment may be estimated from adsorption isotherms,
4-5
-------
CONCENTRATION
TJ
o
CD
H 3J
x m
3J ^
8 i
O
c
30
<
m
O
3D
O
O
o
I-
c
2
-------
CARBON A.
X
CARBON B
FIGURE 4-2
ADSORPTION ISOTHERM, CARBON A AND B
CARBON C
CARBON D
FIGURE 4-3
ADSORPTION ISOTHERM, CARBON C AND D
4-7
-------
carbon performance and design criteria are best determined by pilot tests. Adsorption
isotherms are determined in a batch test and the treatment of wastewater by granular
activated carbon most often is effected in a continuous system involving packed beds
similar to filtering operations in waste treatment. Also, batch tests such as isotherms do
not measure the potential effects of biological activity which may occur in a column.
Pilot tests provide much more accurate estimates of the performance that can be
expected in a full-scale unit. Information which can be obtained from pilot tests includes:
1. Type of carbon.
2. Contact time.
3. Bed depth.
4. Pretreatment requirements.
5. Carbon dosage in terms of pounds carbon per million gallons of wastewater or
pounds organic material removed per pound of carbon.
6. Breakthrough characteristics.
7. Affect of biological activity including possible extension of the carbon capacity
as well as potential deleterious effects such as generation of hydrogen sulfide.
8. Headloss characteristics.
Pilot carbon column tests are performed for the purpose of obtaining design data for
full-scale plant construction. What information from pilot plant studies is needed for
plant design? It is assumed that one or two carbons have been selected which are
effective in treating the particular wastewater, since this can be done by laboratory
evaluation as already discussed. It is not necessary to run pilot column tests to reach this
point. Pilot column tests make it possible to do the following things:
1. Compare the performance of two or more carbons under the same dynamic
flow conditions.
2. Determine the minimum contact time required to produce the desired quality
of carbon column effluent, which is the most important of all design factors.
3. Check the manufacturer's data for headless at various flow rates through
different bed depths.
4. Check the backwash flow rate necessary to expand the carbon bed for cleaning
purposes.
4-8
-------
5. Establish the carbon dosage required, which will determine the necessary
capacity of the carbon regeneration furnaces and auxiliaries.
6. If the overall process or plant flow sheet has not been firmly established, check
the effect of various methods of pretreatment (influent water quality) upon
carbon column performance, carbon dosage and overall plant costs.
7. Evaluate the practical advantages and disadvantages that cannot be evaluated by
reading the experiences of others, for alternates such as use of upflow or
downflow carbon columns or the particle size of carbon to be used.
Figures 4-4 and 4-5 are schematic flow diagrams of upflow and downflow pilot carbon
columns. Details of construction of carbon column pilot plants are described in several
publications and are more or less apparent in Figures 4-4 and 4-5.
In all of the pilot plant tests, the pH and temperature should be observed to be certain
that they correspond to the values for the full-scale plant operation, since pH and
temperature can influence carbon treatment.
The first item among the things to be learned from pilot tests is a comparison of the
different carbons tested. This item overlaps to some extent all of the others listed above,
for they all may affect the selection of the carbon. However, the first item is aimed
principally at gathering data for the plotting of breakthrough curves. These curves are
obtained by passing the water containing the substances to be adsorbed through a column
of carbon. The concentration of the adsorbable substance in the column effluent is
plotted as the ordinate against the volume of water treated as the abscissa. As was
mentioned previously, breakthrough curves will determine the service life of a particular
carbon as applied to specified conditions.
The pilot test results will also allow a determination of the carbon dosage in terms of
pounds of carbon per million gallons of wastewater. Obviously, the dosage will vary with
the kind and concentrations of impurities contained in the wastewater. More importantly,
the dosage may vary from 200-1,800 Ib/million gallons depending upon the degree of
pretreatment provided for the wastewater before its application to the carbon and the
final effluent quality required.
In evaluating pilot column results, an understanding of the "wave front" concept is useful
(see Figure 4-6). As carbon becomes saturated, the zone of adsorption moves downward
(in the case of the downflow contactors) with only a gradual increase in the
concentration of organics in the carbon effluent, until this zone reaches the discharge
point in the column. At this time the organic concentration increases rapidly until it is
equal to the influent concentration.
4-9
-------
2 IN. CARBON
INLET
30-MESH SS
SCREEN
CO
(D
Z
_J
a.
0
O
a
z
UJ
a.
O.
UJ
Q
ID
_i
O
Z
—
V
RATE-SETTING
ROTAMETER \^
a>
ts
•
CM
•
:<9
CM
•
(O
N
•
CN
b>
0
TAP 6
^-*XH
TAP 5
— HXH
TAP 4
— KX>*
TAP 3
— HX1-*
TAP 2
^-^ -
^^^^s*J+
TAP 1
_B^X)W
^^^^^^^^^^
T-^T^Xlrt"
X
^ PILOT
CARBON
COLUMN
c. c:c t i i f hi
EFFLUEN
6 IN. DIAM.
PVC PIPE
30-MESH SS
^-SCREEN
PUMP
INFLUENT
HEADER
u
WATER
METER
DRAIN
TO OTHER IDENTICAL PILOT
CARBON COLUMNS
1 IN. CARBON
OUTLET
FIGURE 4-4
UPFLOW PILOT CARBON COLUMN
4-10
-------
INFLUENT-^-
6 IN. DIAM.
PLEXIGLASS-
CARBON BED-
RATE-SETTING
ROTAMETER
TO DRAIN
30-MESH
STAINLESS
STEEL SCREEN
WATER METER
SAMPLING TAP
FIGURE 4-5
DOWNFLOW PILOT CARBON COLUMNS
4-11
-------
TREATMENT
OBJECTIVE
FIGURE 4-6
COD BREAKTHROUGH CURVES (IDEAL)
4-12
-------
A broad wave front requires more carbon than a narrow wave front. However, the design
safety factor required with a broad front is less than that with a narrow front. That is,
when a breakthrough does occur, that amount of contaminant in the material coming
through will be relatively stable in the broad front system, whereas with a narrow front
after the breakthrough the concentration in contaminant will rise rapidly to equal that of
the concentration in the influent.
In a narrow front system, it is important that provision be made for sampling at a point
approximately 75 percent through the carbon train in order to monitor incipient
breakthrough. This is in addition to the monitoring point that would exist at the end of
the train.
This wave front factor will also affect the choice of systems in terms of using a fixed bed
versus a moving bed. In the classic fixed bed system, the liquid is pumped down through
the stationary bed until breakthrough occurs. This is satisfactory for broad front systems.
On the other hand, for a narrow front it could be preferable to utilize a moving bed
wherein the liquid is pumped upwards through the bed and periodically spent carbon is
removed from the bottom for regeneration while fresh carbon is added at the top. This
provides a large safety factor as there is always fresh carbon available in the system.
To illustrate the utility of pilot carbon column data, an example of pilot data and
analysis follows. These data were collected from pilot columns of the type shown on
Figure 4-4 at the South Tahoe Plant [ 1 ]. In this example, the purpose of the test was to
compare four commercially available carbons. Four upflow pilot columns were charged
with various types of carbon. Coagulated and filtered secondary effluent was pumped
through the four columns in parallel. Samples were collected from each of the sample
taps and analysed for COD at regular intervals. The resulting raw data are plotted on
Figure 4-7 for one illustrative column. These raw data contain much useful information,
but a mere plotting of COD vs. volume of water treated at various carbon depths yields a
somewhat difficult-to-grasp picture unless further data analysis is made. One observation
requiring no further analysis in this particular case was that one carbon (Brand C) was so
friable that it was disintegrating and the column had to be shut down due to excessive
headloss. Such an observation is of obvious utility if this brand of carbon were under
active consideration for plant scale use.
The amount of COD removal per pound of carbon was calculated for each of the brands
of carbon at various depths of carbon (as measured at the sample taps). The resulting
curves are shown on Figures4-8 and 4-9 for two illustrative carbon depths.
In the lower bed depths, the Brand C carbon appears to have reached a saturation value
of about 0.12 pound COD per pound of carbon. The other carbons did not appear to
have reached a saturation value at the end of the run. At greater depths, the differences
became more pronounced. After 0.25 pound COD per pound of carbon were applied,
Brand D carbon had removed twice as much as the Brand B carbon and a third again as
much as the Brand A carbon.
4-13
-------
15 20 25
GALLONS PASSED x 1,000
FIGURE 4-7
COD CONCENTRATION AT VARIOUS BED DEPTHS FOR
UPFLOW PILOT COLUMN CHARGED WITH BRAND A CARBON
4-14
-------
3
0.1
0.2
0.3
0.4 0.5 0.6
LB. COD APPLIED/LB. CARBON
0.7
O.S
0.9
1.0
FIGURE 4-8
COMPARISON OF ADSORPTIVE CAPACITIES OF TEST CARBONS
4.25 FEET CARBON BED DEPTH - 4.6 MINUTE CONTACT TIME
4-15
-------
.00
.00
.06
.10 .15 .20
LB. COD APPLIED/LB. CARBON
.25
FIGURE 4-9
COMPARISON OF ADSORPTIVE CAPACITIES OF TEST CARBONS
14.25 FEET BED DEPTH - 17.5 MINUTE RESIDENCE TIME
4-16
-------
Figure 4-10 shows the ratio of effluent COD concentration (C) to influent COD
concentration (CQ) at three bed depths. From this graph, Brand D carbon can also be
seen to be superior. By using the same data, the effects of contact time for the various
brands of carbon were also compared as shown on Figure 4-11.The Brand D carbon, at a
contact depth of only 9.25 feet, produced an effluent of the same quality as did the
Brand A carbon after a 14.25 foot contact depth. At the end of the run, the Brand D
carbon removed 56 percent of the influent COD at the 9.25-foot bed depth. During this
period, 14.25 feet of the Brand A carbon averaged 57 percent COD removal.
The conclusions drawn from this pilot column comparison of the four carbons include:
1. The sample of Brand C, 12 x 40 mesh activated carbon, was shown to have the
lowest saturation value (0.12 Ibs removed/lb carbon) of the carbons tested.
2. The Brand C carbon also demonstrated a tendency for excessive headloss
development. This problem may be related to the size and softness of the
carbon.
3. The Brand B carbon sample tested was shown to exhibit a comparatively low
rate of COD adsorption. Its saturation value was also below that of the Brand
D and Brand A carbons.
4. The Brand D carbon proved superior to Brand A carbon, both in adsorptive
rate and capacity. No saturation values were reached for these carbons during
the study period, however.
This illustrative example shows the utility of pilot tests for comparing alternative carbons.
They may also compare variables such as contactor configuration, varying degrees of
pretreatment, etc., as discussed earlier.
4.6 Biological Activity and Carbon Adsorption
The extension of carbon capacity by biological action may be very significant under
certain conditions. Weber [2] and several others have found that as activated carbon
adsorbs organics from raw sewage it creates a highly enriched substrate for biological
growth. This has two apparent treatment advantages: (1) extension of the carbon
adsorption service life and (2) removal of non-adsorbable materials due to the biological
activity. Weber [2] believes that the micro-organisms utilize the adsorbed organic matter
(providing the organics are biodegradable) from the activated carbon surface, thus making
the carbon available for continued use as an adsorbent. According to this concept, the
carbon will trap organics for subsequent utilization by the micro-organisms. The
limitation to biological regeneration is its inability to oxidize refractory
(non-biodegradable) organics. Treatment advantages due to biological growth on the
carbon may be offset by operational problems, as pointed out in Chapter 3.
4-17
-------
LBS. COD APPLIED
FIGURE 4-10
A COMPARISON OF THE COD REMOVAL ABILITY OF THE TEST CARBONS
SAMPLE DEPTH - 14.25 FEET
4-18
-------
1.0
0.9
0.8
O
u
. 0.7
K£
3 OC 0.6
iz
to
111 P 0.5
'O
O 0.3
O
80.,
0.1
BRAND B
.BRAND A
BRAND D
5 10
DEPTH OF CARBON, FEET
IS
FIGURE 4-11
EFFECT OF CONTACT TIME ON COD REMOVAL
(APPROXIMATELY 0.2 LB. COD APPLIED PER LB. CARBON)
4-19
-------
4.7 References
1. Smith, C. E., and Chapman, R. L., Recovery of Coagulant, Nitrogen Removal, and
Carbon Regeneration in Waste Water Reclamation, EPA Report, Project WPD-85,
June, 1967.
2. Weber, W. J., Jr., Friedman, L. D., and Bloom, R., Biologically Extended
Physicochemical Treatment, A paper submitted for the Sixth Conference of the
International Association on Water Pollution Research, Jerusalem, 18-24 June, 1972.
4-20
-------
CHAPTER 5
CARBON ADSORPTION TREATMENT SYSTEM COSTS
5.1 Introduction
Presented in this chapter are data to allow estimation of capital, operation, and
maintenance costs for the various components of activated carbon treatment systems.
Construction cost data are based insofar as possible on actual costs for plants existing or
under construction, and detailed cost estimates for plants currently under design. In order
to make the cost data current and comparable, the data has been adjusted by the use of
the EPA Sewage Treatment Plant Cost Construction Index. The costs presented herein are
based on a U. S. average cost index of 175.0 (valid approximately January, 1973).
Actual operation and maintenance costs experienced at the South Tahoe P. U. D. water
reclamation plant are presented in detail as an example, and as a basis for cost estimates.
All operation and maintenance costs are based on the condition of the plant operating at
design levels; the cost per gallon of water treated (as opposed to annual costs) will
increase under reduced plant operating load conditions.
The cost data are presented by a series of figures which are essentially based on either
flow or carbon dosage. Approximate total costs for carbon treatment are presented on
Figure 5-11 for various carbon dosages. More accurate, or adjusted carbon treatment costs
can be developed through use of Table 5-7, a detailed cost estimating guideline.
The potential limitations of these cost estimates must be recognized. The cost curves are
mainly graphical averages of numerous actual or estimated costs adjusted to a common
time reference. Individual costs may vary significantly due to location, site conditions,
associated treatment processes, economy of design, architectural features, union
requirements, utility costs, the degree of competitive bidding, and numerous other
factors. Also, actual cost data for construction, operation and maintenance are still quite
limited, particularly in the case of large plants. Therefore, use of the cost data presented
herein should be limited to initial process comparisons and selections, and preliminary
cost estimates.
5.2 Capital Costs
5.2.1 Contactor Systems
Types of Contactors—numerous types of carbon contactor systems have and will be
developed, including:
1. Upflow packed beds.
5-1
-------
2. Upflow expanded beds
3. Downflow packed beds in gravity and pressure units.
a. series
b. parallel
4. Various combinations of the above.
The operating characteristics and design examples of these systems have been discussed in
detail in Chapter 3. There is little cost difference between upflow packed and expanded
beds; the "packed" bed contactor is, in fact, usually sized so as to allow periodic
expansion of the bed for washing purposes.
Downflow series operated packed beds can be expected to be more expensive than
upflow parallel columns, while downflow parallel packed beds will be about the same
cost as upflow contactors. Both the upflow and downflow contactors would have an
equal contact time and volume; upflow contactors require a screening system at the top
while a downflow contactor, with additional free board, may allow the use of a less
expensive perforated header system. The downflow type contactor, however, will require
a more elaborate underdrain and will also require surface wash equipment. Therefore,
downflow and upflow contactors should be nearly equal in cost.
Next, consider the series downflow mode of operation, and evaluate the use of a single
upflow contactor of volume (V) compared to a two-stage series downflow contactor
system, each contactor having a volume of J-. Again, each system offers an equal contact
time. An economy of scale analysis can be utilized to estimate relative costs. The cost
exponent (M) for similar pressure vessels has proven to be about 0.65 [ 1 ] .
The relative costs can be computed as follows [ 1 ] :
0.65
2-stage " l -stage —
y
C- " C - — x
If Cj_stage and V are set at unity:
C2-stage = d/2) °'65 x (2)
C2-stage = L28
5-2
-------
where:
^1 -stage ~ ^ost °f sm§le contactor of volume V
^2-staee = Cost of 2 series contactors, each of volume -y
By this analysis, the 2-stage series downflow units would cost approximately 28 percent
more than single stage contactors. Table 5-1 presents a summary of relative costs of
various contactor systems available.
TABLE 5-1
RELATIVE COSTS OF VARIOUS CONTACTOR SYSTEMS
Cost Adjustment
System Factor
Upflow countercurrent packed bed 1.0
Upflow countercurrent expanded bed 1.0
Downflow-parallel 1 .0
Downflow-series 1.28
Materials of Construction— materials of construction will also influence contactor system
costs to some extent. For small contactors up to 12-foot diameter, shop-fabricated steel
vessels with coal tar epoxy internal coating prove most economical. Beyond 12-foot
diameter, field fabrication is usually necessary. Under this condition, concrete
construction is competitive, and offers reduced maintenance costs.
Actually, basic contactor costs represent only on the order of 25 percent of the cost of
the total contactor system including screens, piping, valves, instrumentation, building, and
so forth. Therefore, for large contactors, the choice of steel versus concrete should be
based on such factors as type of contactor, exposure, foundation conditions, local
contractor capabilities, salvage value, corrosion potential, etc. As will be illustrated
hereinafter, the materials of construction appear to have minimal impact on the total
construction cost of the contactor system.
Cost Estimates- cost estimating curves for carbon contactors are presented on Figures 5-1
and 5-2. On Figure 5-1, the costs are indicated relative to the effective volume per
contactor. As noted, these costs are not for the contractor only, but include total system
5-3
-------
10,000
9
8
7
6
1,000
9
8
8
u
o
oc
V)
100
9
8
7
6
5
4
COWTACTOft SY&Tf M
EPA STP INDiX - 175
PIPING., VALVES, STORAGE
:COSTS:
,. ,t -, f
2 3 45678 910 2 3 45678 9100
EFFECTIVE CONTACTOR VOLUME. 1.000 FT.3
FIGURE 5-1
CONTACTOR SYSTEM COSTS BASED ON CONTACTOR SIZE
5-4
-------
CONSTRUCTION COST, $1,000
O
O
I
O
CO
O
I
is
O
m
to
O
O
-------
costs, including a 10 percent allowance for makeup carbon storage. On Figure 5-2, the
costs are presented relative to plant flow with a contact time of 30 minutes.
The data points used in developing Figure 5-2 include a variety of contactor systems,
including both upflow and downflow of both steel and concrete construction. Again,
I type of contactor and materials of construction do not dramatically affect total system
1 cost.
\
5.2.2 Regeneration Systems
Carbon regeneration cost estimates have been divided into basic furnace system costs, and
complete regeneration system costs, as presented on Figure 5-3. The costs are referenced
to furnace hearth area. Required hearth area can be easily calculated from the required
pounds per day regeneration rate, and the design hearth loading, which is usually 40
Ibs/sq ft/day (see Chapter 3). As indicated, complete regeneration system costs add about
50 percent to the basic installed furnace costs.
5.2.3 Wastewater Treatment Plant Size for Economic Regeneration
of Granular Carbon
The purpose of this discussion is to determine the approximate plant capacity for various
types of AWT plants for which it is economical to provide on-site facilities for granular
carbon regeneration. At best, the figures derived will be for rough rule-of-thumb use.
Obviously, there will be enough differences in prevailing local conditions and available
alternates to require individual project consideration and analysis. For example, in some
metropolitan areas carbon regeneration facilities may be available on a commercial basis,
at a jointly owned and operated central regeneration plant, or by contract with a larger
sewer authority. The cost of loading and hauling spent and regenerated carbon would
have a great influence on the desirability of these alternates as compared to on-site
facilities. In addition, the use of powdered carbon on a throwaway basis may present a
good alternate for small plants in a few cases. The present discussion includes a
comparison of the costs of granular carbon regeneration at small plant scale versus the
costs of using granular activated carbon on a throwaway basis. The cost of disposal of the
spent granular carbon is so small compared to the cost of the carbon that it can be
ignored for this purpose.
The cost of granular activated carbon delivered to the plant site is taken at $0.33 per
pound which is probably typical for the continental United States at the present time. In
other locations (in Alaska, for example) the cost of granular carbon may be $0.40 per
pound or more.
Estimates of costs for regeneration of granular carbon can be made rather accurately for
small scale plants due to the fact that the regeneration must be done using the smallest
5-6
-------
INSTALLED CONSTRUCTION COST. $1.000
O
>
31
0
"
^30 m
i5 r
CO
C/)
m
-------
commercially available fully automated furnace (54-inch I. D.). (A 30-inch I. D. furnace is
available as a commercial, skid mounted unit, but is not automated to the degree that the
54-inch I. D. furnace is.) The 54-inch furnace has been in use for seven years at the
South Tahoe water reclamation plant and complete detailed cost records are available for
installation and operation of this system.
The rated capacity of this furnace when it was first installed was 6,000 Ibs/day, or about
63 Ibs/sq ft/day. However, EPA demonstration grant studies completed in 1971 showed
that the actual furnace capacity was very close to 3,800 Ibs/day or 40/lbs/sq ft/day.
Table 6-8 illustrates the actual data collected at Tahoe.
Using the current data, the 54-inch I. D. carbon regeneration furnace at Tahoe has a
maximum rated capacity of 3,800 Ibs/day. Granular carbon dosages for different plants
may range from 200 to 1,800 pounds per million gallons depending upon the character
of the wastewater, effluent requirements, the AWT processes used and the pretreatment
provided. Allowing 20 percent downtime, a 3,800 Ibs/day maximum capacity furnace
would have a firm capacity of 3,000 Ibs/day and might serve plants having rated
capacities up to 15 mgd depending upon their carbon dosage requirements.
Figure 5-4 gives the cost in cents per pound to regenerate carbon in a 54-inch gas-fired
multiple hearth unit at various furnace throughput rates up to 3,000 Ibs/day as derived
from the Tahoe data. From this curve, it is seen that when plant carbon regeneration
requirements are less than 190 Ibs/day, the cost of regenerated carbon equals the cost for
granular carbon used on a throwaway basis. Further, the curve shows that carbon
regeneration costs increase quite sharply for furnace throughputs less than 1,500 Ibs/day.
For intermediate needs ranging from 3,000 down to 1,500 Ibs/day of carbon, the carbon
regeneration costs only rise from $0.09 to $0.11 per pound, but from 1,500 down to
190 Ibs/day they increase from $0.11 to $0.30 per pound of carbon.
So far as provision for on-site carbon regeneration is concerned, small plants can be
placed into three categories according to their carbon usage:
1. For plants with carbon usage less than 200 Ibs/day, carbon regeneration
facilities should not be provided. If granular carbon is to be used, it would be
on a once-through throwaway basis, or the spent carbon would be transported
to and from a central regeneration station if one is available. This category
would include AWT plants using the tertiary sequence of treatment having a
carbon usage of about 250 pounds per million gallons (Ibs/mg) and smaller than
800,000 gpd capacity, and PCT plants having a carbon usage of about 1,200
Ibs/mg and smaller than 170,000 gpd capacity.
2. When average carbon regeneration requirements exceed 1,500 Ibs/day, there is
no question but that on-site carbon regeneration facilities should be built. This
5-8
-------
40
CO
£ 30
ILI
O
8
o
g »
cc
Ul
z
HI
OQ 10
cc
o
,COST PER POUND OF USING GRANULAR
CARBON ON A THROWAWAY BASIS
(54 I.D. MULTIPLE
HEARTH GAS-FIRED
FURNACE)
1000 2000 3000 4000
FURNACE THROUGHPUT, LBS. CARBON/DAY
5000
FIGURE 5-4
CARBON REGENERATION COST VS. THROUGHPUT
5-9
-------
category would include tertiary plants having capacities greater than 6 mgd and
physical-chemical plants rated at 800,000 gpd or more.
3. For carbon usages between 200 and 1,500 Ibs/day, which would include
tertiary plants with capacities between 0.80 and 6.0 mgd and PCX plants with
capacities between 170,000 and 800,000 gpd, the cost of on-site regeneration
must be compared to the costs of central regeneration and to the costs of
alternate treatment methods for removing refractory organics.
5.2.4 Influent Pump Stations
In most installations, a pump station will be required to force effluent through the
contactor system. Figure 5-5 can be used to obtain approximate costs for this type of
intermediate pump station. The costs are, of course, only approximate since the actual
costs will vary with location and total dynamic head requirements. Note also that a
common pump station is frequently used for series operation of filters ahead of, or after,
the carbon contactors.
5.2.5 Total Capital Cost Adjustment
To obtain total capital costs, the construction costs must be adjusted to account for
engineering, legal, administrative, land, and interest expenses. Figure 5-6 is provided for
this purpose. As shown, these items can add 20 to 25 percent to the construction cost of
a carbon treatment system.
5.3 Operation and Maintenance Costs—Tahoe Data
Extensive operation and maintenance cost analyses were developed at the South Tahoe
P. U. D. water reclamation plant based on actual expenses during 1969 and 1970. The
results are presented herein to illustrate relative costs and to serve as a basis for extension
of these data to current conditions and alternate capacity plants. The unit costs in effect
at Tahoe during the analysis period are summarized in Table 5-2. Resultant operation and
maintenance costs, and relative capital costs, for activated carbon treatment are shown in
Tables 5-3, 5-4, and 5-5. At Tahoe, activated carbon adsorption follows primary and
secondary treatment, chemical treatment and mixed-media filtration. The activated
carbon system includes eight steel columns, each containing 22-25 tons of 8 x 30 mesh
granular activated carbon. The filter effluent flows upward under pressure through the
columns.
Operational labor includes flow monitoring, sampling, and backwashing of columns.
Maintenance includes instrument calibration, corrosion inspection of the interior of the
columns, and repair of appurtenances. Fifty percent of the pumping costs, including
maintenance for pumping through filters and carbon columns was assigned to the carbon
adsorption system. The initial carbon charge for the carbon column was included in the
capital cost.
5-10
-------
CONSTRUCTION COST, $1,000
10 U A olO»^lOO^ioo(O<
M CO
en 01 -j oo
-------
100
9
8
7
6
H 3
OT
O
O
_l 2
<
t
O
< 1
° 8
7
6
5
USE THIS CURV^ TQ
t TOTAL CAPITAL CC^TSi
0.1
0.1
3 4567891 2 3 456789 10
ESTIMATED CONSTRUCTION COST, MILLION DOLLARS
20 30
FIGURE 5-6
TOTAL CAPITAL COST DEVELOPMENT
5-12
-------
Spent carbon is regenerated at 1,650 degrees to 1,750 degrees F in a multiple hearth
furnace. The furnace can be operated at feed rates of 100 to 6,000 Ibs/day. After
regeneration, the activated carbon is returned to the columns. Carbon losses used for the
cost analysis averaged 8.9 percent.
TABLE 5-2
UNIT COSTS AT SOUTH LAKE TAHOE (1)
Labor ^
Operations $ 6.11/hour
Maintenance $ 5.05/hour
Electricity(3) $12.10/1,000 kwh
Fuel (4) $ 0.0543/therm
Activated Carbon Makeup $ 0.305/pound
(1) All appropriate unit costs are for years 1969 and 1970 and are fob South Lake
Tahoe and include a 5 percent California sales tax.
(2) Labor costs include all direct and indirect monies paid upon the employees behalf.
The rates are averages for 1969 and 1970.
(3) Includes energy and demand charges.
(4) Natural gas at about 860 BTU/cu ft at 6,200 feet elevation and billed on the basis
of interruptible service.
5-13
-------
TABLE 5-3
CARBON ADSORPTION OPERATING AND CAPITAL COSTS
AT SOUTH LAKE TAHOE
1969-1970
Operating Costs $/Day
Electricity 47.34
Operating Labor 24.53
Maintenance Labor 3.27
Repair Material 1.15
Instrument Maintenance 4.24
Total Operating Cost 80.53
Total Cost $/Million Gallons
Operating ^) 10.74
Capital (2) 16.30
Total 27.04
(1) Total operating cost shown is based on a flow of 7.5 mgd. Total operating cost per
MG of water treated, including the 7.5 mgd plant influent plus recycle streams,
would be S8.77/MG.
(2) Includes initial carbon charge. All capital costs were adjusted to EPA, STP Index
127.0, amortized at 5 percent for 25 years.
5-14
-------
TABLE 5-4
CARBON REGENERATION OPERATING AND CAPITAL COSTS
AT SOUTH LAKE TAHOE
1969-1970
Operating Cost $/Day
Electricity 2.23
Natural Gas 6.15
Makeup Carbon 70.39
Operating Labor 91.90
Maintenance Labor 16.21
Repair Material 1.17
Instrument Maintenance 1.90
Total Operating Cost 189.95
Total Cost $/Million Gallons
Operating ^ 25.33
Capital (2) 5.20
Total 30.53
(1) Total operating cost shown is based on a flow of 7.5 mgd. Total operating cost per
MG of water treated would be $ 19.28/MG including 7.5 mgd plant influent, plus
recycle flows. Contactors are designed for 8.2 mgd.
(2) Capital costs were adjusted to EPA, STP Index 127.0 and amortized at 5 percent
for 25 years.
5-15
-------
TABLE 5-5
CARBON REGENERATION OPERATING AND CAPITAL COST
PER TON OF CARBON REGENERATED AT SOUTH LAKE TAHOE
1969-1970
Operating Cost $/Ton
Electricity 1.73
Natural Gas 4.72
Makeup Carbon 53.98
Operating Labor 68.74
Maintenance Labor 39.52
Repair Material 2.36
Instrument Maintenance 1.43
Total Operating Cost 172.48
Total Cost $/Ton
Operating 172.48
Capital 29.76
Total 202.24
5-16
-------
Electricity included power used for instrumentation, driving rabble arms, and fans for
shaft cooling, induced draft, and combustion air. Natural gas and makeup carbon are
self-explanatory. Operational labor included furnace operation, de-fining, transferring
spent and regenerated carbon, and regeneration efficiency analysis. Maintenance labor and
repair material were for the furnace, instrumentation, and carbon transfer appurtenances.
Maintenance costs for 1969 and 1970 included furnace startup and shutdown every 4 to
8 weeks, cleaning carbon dewatering and de-fining screens, carbon slurry pumps and
stack-gas scrubber. The extensive maintenance of furnace startup and shutdown would be
eliminated if regeneration were continuous.
5.4 Personnel Requirements
Personnel or labor requirements for varying-sized carbon treatment systems have been
separated in terms of operation, maintenance, and laboratory efforts. Estimated annual
man-hour requirements for each category are presented on Figures 5-7 and 5-8.
Operational labor for carbon adsorption includes flow monitoring and control, sampling,
and contactor backflushing. Maintenance in this area includes instrument calibration,
pump station upkeep and repairs, inspection, and repair of appurtenances.
Operational labor for carbon regeneration includes carbon transfer, furnace operation
including simple control analyses, and carbon defining. Maintenance labor includes
instrument calibration, furnace upkeep and repairs, transfer and de-fining equipment
repair, and cleanup.
Laboratory labor costs allow for performance of routine control analyses on carbon
contactor influent and effluent (COD or TOC, color, MBAS), plus analyses of composite
samples of spent and regenerated carbon quality (apparent density, Iodine Number,
occasional sieve analyses, etc.). No allowance is made for additional analyses as might be
performed for final effluent quality reporting, or for research purposes.
All personnel estimates include a 5 percent allowance for supervision and administrative
costs. The man-hour requirements were developed from actual experience at Tahoe, and
include the effect of labor efficiency. No adjustment is necessary to include an allowance
for "productive" man-hours.
5.5 Operation and Maintenance Costs
Annual operation and maintenance cost estimates are presented graphically on Figures 5-9
and 5-10. All costs are based on the assumption that the plant is operating at the design
rate. The various components of total annual costs were included so that they may be
individually adjusted to suit local conditions. The assumed unit costs are summarized in
Table 5-6.
5-17
-------
. ! ,. I. , i ^
4 5 6 7 8 9 10
FLOW, MGD
4 5678 9100
FIGURE 5-7
CARBON ADSORPTION LABOR REQUIREMENTS
5-18
-------
100.000
q
OC
O
X
D
Z
10,000
9
8
7
6
1,000
9
8
7
6
5
4
100
3 456789 10 2 3 456789 100
CARBON REGENERATION RATE, 1,000 LBS/DAY
FIGURE 5-8
CARBON REGENERATION LABOR REQUIREMENTS
5-19
-------
ANNUAL COST, $1,000
to co
-J
00 (O O
10 to
en o> ~j co ID
to
O
O
•o
00
§1 i
oz
m
o
O
(A
V)
Doo
O
O
o
-------
2,000
I
o
Z
8%
$.33/LB
$S/HR
$.06S/THERM
2 3 456789 10 2 3 456789 100
CARBON REGENERATION FURNACE CAPACITY, 1,000 LBS/DAY
FIGURE 5-10
CARBON REGENERATION
OPERATION AND MAINTENANCE COSTS
5-21
-------
TABLE 5-6
SELECTED UNIT COSTS FOR ESTIMATING
OPERATION AND MAINTENANCE COSTS
Item
Labor
Value
$5/hr
Basis for Selection
U. S. Department of Labor, Bureau of Labor
Statistics SIC Code 494-7 "Water, Steam and
Sanitary System" classification, Sept. 1972. Listed
value—$4.00/hr. Increased by 25 percent to adjust
to actual payroll costs.
Power $0.02/kwh Estimated national average power cost including
demand and energy charges w/o consideration of
other plant power demands.
Fuel $0.065/therm Northwest Natural Gas Company Firm Service-High
Load Factor rate schedule. Used average of $0.06 to
$0.07/therm depending on demand. Rates are about
average for the nation.
Again, the operation and maintenance cost are estimates primarily referenced to actual
experience at Tahoe. The estimates should be quite close for similar plants through
approximately 20 mgd. The accuracy may diminish for substantially larger plants, or
plants using considerably different contactor systems. This variance would be particularly
true in the case of adsorption system power requirements; shallow, non-pressurized
contactors would require substantially less power.
5.6 Effects of Recycle Flows on Costs
Potential recycle flows should be evaluated for each plant. Often times, final effluent is
used for internal plant non-potable water uses. Depending upon the pre- and
post-treatment sequence, recycle flows of up to 20 to 35 percent of plant influent flow
can occur. Typical uses include backwash water, scrubber water, chemical dilution water,
cooling water, and so forth. This recycle must of course be provided for, and thus will
increase the capital cost of the adsorption system. Pumping power will be the only
significant resultant increase in operation and maintenance cost.
5-22
-------
5.7 Cost Estimating Guides
Table 5-7 has been included for use as a guideline in using the cost curves presented
herein to develop preliminary cost estimates. Thus, the capital, operation and
maintenance and total annual costs can be estimated for any combination of flow and
estimated carbon dosage. Table 5-7A contains a completed example. Note that
adjustments can be made for alternate unit costs.
Figures 5-11 and 5-12 are included for carbon treatment estimating. These figures can be
utilized if the assumptions and unit cost bases of the various components are acceptable.
5.8 Summary of Carbon Treatment Costs
Table 5-8 contains a distribution of estimated costs for the examples developed in Table
5-7A. The total annual cost comparison shows that carbon treatment is a heavily
capitalized process, as indicated by the relatively large allocation for amortization. Note
that in this instance, the carbon contactor system represents 65 percent of the total
system capital cost. Design efforts should be directed at cost-saving approaches for
contactor systems if significant overall capital cost savings are to be realized. Conversely,
total costs are not very sensitive to changes in the cost of regeneration equipment.
Labor constitutes nearly one-half of the total system operation and maintenance costs for
this example. Makeup carbon and power constitute the major additional costs.
Inspection of Figures 5-10 and 5-11 will confirm that required carbon dosage has little
impact on total system capital cost, but of course directly affects operating costs and
hence total annual cost.
5-23
-------
SHEET 1 OF 2
TABLE 5-7
ESTIMATED GRANULAR ACTIVATED CARBON TREATMENT COST
PLANT_
OWNER.
PREPARED BY_
DATE
.PROJECT NUMBER.
DESIGN DATA SUMMARY
DESIGN FLOWS: AVG._
_MGO; PEAK
DESIGN CARBON DOSAGE:.
MGD
LBS/MG LBS/OAY
DESIGN REGENERATION RATE.
FURNACE HEARTH AREA
_LBS/DAY_
. SO. FT.
.LBS/SQ. FT./DAY
TYPE AND NUMBER OF CONTACTORS
CAPACITY EACH CONTACTOR MGD AT AVG. DESIGN FLOW,.
PSEUDO CONTACT TIME MINUTES (EMPTY CONTACTOR)
PRETREATMENT
_CU. FT. EFFECTIVE VOLUME
ESTIMATED BID DATE:.
ESTIMATED EPA STP COST INDEX
UNIT COSTS: POWER $ /kWh; LABOR $.
.(NATIONAL).
./HR.; FUEL $.
ESTIMATED CARBON MAKEUP.
COMMENTS
.PERCENT
.(LOCAL)
./THERM; CARBON $.
./LB.
CAPITAL COST ESTIMATE
ITEM
REFERENCE
INFLUENT PUMP STATION
CARBON CONTACTORS
CARBON REGENERATION SYSTEM
INITIAL CARBON CHARGE
ADJUSTMENTS
FIGURE
FIGURE
FIGURE
FIGURE
CALCULATION ESTIMATED
NOTES COST
USE PEAK DESIGN FLOW $
USE AVG. DESIGN FLOW
MULT. BY NO. OF
CONTACTORS
ADJUST FOR CARBON COSTS
DIFFERENT FROM S.33/LB.
5-24
-------
SHEET 2 OF 2
TABLE 5-7 (Continued)
CAPITAL COST ESTIMATE (Continued)
ITEM
REFERENCE
CALCULATION
NOTES
ESTIMATED
COST
TOTAL CONSTRUCTION COST AT EPA STP INDEX
COST INDEX CORRECTIONS
NATIONAL MULTIPLIER
LOCAL MULTIPLIER. .
175
ADJUSTED CONSTRUCTION COST
TOTAL CAPITAL COST
FIGURE.
$_
$_
(UNIT COST • $_
JMG)
OPERATION AND MAINTENANCE COST ESTIMATE
CARBON ADSORPTION
LABOR
POWER
MAINT. MATERIAL
TOTAL
REFERENCE ADJUSTMENT
REFERENCE VALUE FACTOR
FIGURE
_/YR
_/YR
(5.00)
ESTIMATED
ANNUAL
COST
JYR
./YR
CARBON REGENERATION FIGURE.
LABOR
MAKEUP CARBON
FUEL
POWER
MAINT. MATERIALS
TOTAL AT FURNACE CAPACITY:
ADJUSTMENT TO DESIGN DOSAGE:
LBS/DAY DOSAGE
TOTAL
LBS/DAY CAPACITY
_/YR
-/YR
(5.00) *-
-r) (^3 ) -
(.065")
./YR AT CAPACITY)
_/YR
-/YR
/YR
TOTAL OPERATION AND MAINTENANCE COST
TOTAL ANNUAL COST
CAPITAL AMORTIZATION:.
.PERCENT FOR
(UNIT COST
CAPITAL RECOVERY FACTOR
TOTAL ANNUAL COST -
(UNIT COST - $
5-25
-------
SHEET 1 OF 2
PLANT
TABLE 5-7A
ESTIMATED GRANULAR ACTIVATED CARBON TREATMENT COST
Clear Creek Water Reclamation Plant
OWNER
PREPARED BY__RLC
DATE
Unified Sanitary Authority, Clear Creek, California
12 February 1973
.PROJECT NUMBER W7618.6
DESIGN DATA SUMMARY
DESIGN FLOWS: AVG. 20 MGD: PEAK 40 MOD
DESIGN CARBON DOSAGE: 300 LBS/MG, 6,000 LBS/DAY
45 LBS/SQ. FT./DAY
DESIGN REGENERATION RATE 12,000 LBS/DAY
FURNACE HEARTH AREA 265 SQ. FT.
TYPE AND NUMBER OF CONTACTORS Upflow Countercurrent Packed. 15 (2 for storage of standby)
CAPACITY EACH CONTACTOR_L5_MGD AT AVG. DESIGN FLOVI.^Q^CU. FT. EFFECTIVE VOLUME
PSEUDO CONTACT TIME 30_MINUTES (EMPTY CONTACTOR)
PRETREATMEIMT Activated Sludge, Lime Clarification, Filtration
ESTIMATED BID DATE- January 1974
ESTIMATED EPA STP COST INDEX 185
.(NATIONAL).
190 (LOCAL)
UNIT COSTS: POWER $ .017 /kwh: LABOR $ 5-50/HR.; FUEL $ -060 /THERM; CARBON & -34 /LB.
ESTIMATED CARBON MAKEUP §L PERCENT
COMMENTS
CAPITAL COST ESTIMATE
ITEM
INFLUENT PUMP STATION
CARBON CONTACTORS
CARBON REGENERATION SYSTEM
INITIAL CARBON CHARGE
ADJUSTMENTS
Influent Pump Station
REFERENCE
CALCULATION
NOTES
FIGURE ±L USE PEAK DESIGN FLOW
FIGURE
FIGURE
5-2
5-3
USE AVG. DESIGN FLOW
MULT. BY NO. OF
CONTACTORS
FIGURE JLL ADJUST FOR CARBON COSTS
DIFFERENT FROM $.33/LB.
Split pump station costs
between filters and carbon
since they will operate in
series
ESTIMATED
COST
y 380,000
2,000,000
485,000
405,000
-190,000
5-26
-------
TABLE 5-7 A (Continued)
SHEET 2 OF 2
CAPITAL COST ESTIMATE (Continued)
ITEM
REFERENCE
CALCULATION
NOTES
TOTAL CONSTRUCTION COST AT EPA STP INDEX = 175
COST INDEX CORRECTIONS
NATIONAL MULTIPLIER 1-06
LOCAL MULTIPLIER
ADJUSTED CONSTRUCTION COST
TOTAL CAPITAL COST
1.025
FIGUREjh
-------
ANNUAL COST, $1,000
to u
in o> -vi oo to
§
NJ U
en o> -j oo -
CO
30(0
Q
O
I f
u
o
« ui o> vi go i
o o o o o o o i
TOTAL COST, $/MG
K)
8
-------
CAPITAL COST, MILLION DOLLARS
~j ooioo KJ u A a\ o> vi oo
-------
TABLE 5-8
COST DISTRIBUTION
FOR EXAMPLE CARBON TREATMENT SYSTEM
CAPITAL COSTS
Item Percent of Total
Influent Pump Station 6
Carbon Contactor System 65
Carbon Inventory 13
Carbon Regeneration System 16
TOTAL 100
OPERATION AND MAINTENANCE COSTS
Item
Adsorption System
Labor 32
Power 63
Maintenance Materials 5
TOTAL 100
Regeneration System
Labor 56
Makeup Carbon 37
Fuel 3
Power 2
Maintenance Materials 2
TOTAL 100
Combined System
Labor 48
Makeup Carbon 25
Fuel 2
Power 22
Maintenance Material 3
TOTAL 100
TOTAL ANNUAL COST
Capital Amortization 61
Operation and Maintenance • 39
TOTAL 100
5-30
-------
5.9 Reference
1. Berthouex, P. M., Evaluating Economy of Scale. Journal WPCF, p. 211 (November,
1972).
5-31
-------
CHAPTER 6
TYPICAL TREATMENT FACILITIES
6.1 Introduction
Methods for determining design criteria for equipment and carbon are outlined in
Chapters 3 and 4. Also, several example designs utilizing either existing facilities or
facilities under design were discussed in some detail in Chapter 3. Laboratory and pilot
scale studies are described in some detail in Chapter 4. It is worth noting again that a
well-planned and executed test program utilizing the wastewater to be treated is very
important to the successful design and operation of a full-scale system.
The general range of design criteria currently being used in both tertiary and
physical-chemical carbon treatment systems is shown in Table 6-1.
TABLE 6-1
GENERAL DESIGN PARAMETERS
Carbon Requirement
Tertiary plant 200-400 Ibs carbon per million gallons
PCT plant 500-1,800 Ibs carbon per million gallons
Hydraulic Loading 2-10 gpm/sq ft
Contact Time (empty bed basis) 10-50 minutes
Backwash Rate 15-20 gpm/sq ft
Contactor Configuration gravity or pressure vessels
steel or concrete construction
Flow Configuration upflow or downflpw
one stage or multi-stage
6.2 Current Plant Design, Construction, and Operation
Facilities for the treatment of municipal wastewaters have been divided into two
categories: tertiary treatment plants and physical-chemical treatment plants. Information
on tertiary treatment plants currently under design or construction or in operation is
summarized in Table 6-2. Flow diagrams for the tertiary plants are shown on Figures 6-1
through 6-12. Similar information for physical-chemical treatment plants is summarized in
Table 6-3 and Figures 6-13 through 6-22.
-------
TABLE 6-2
TERTIARY TREATMENT PLANTS
SITE
1. Arlington, Virginia
2. Colorado Springs, Colo.
3. Dallas, Texas
4. Fairfax County, Va.
5. Los Angeles, Calif.
6. Montgomery County,
Md.
7. Occoquan, Va.
8. Orange County, Calif.
9. Piscataway, Md.
10. St. Charles, Missouri
11. South Lake Tahoe,
Calif.
12. Windhoek, South
Africa
STATUS
1973
Design
Operating
Dec. '70 to Present
Design
Design
Design
Design
Design
Construction
Operating
Mar. '73 to Present
Construction
Operating
Mar. '68 to Present
Operating
Oct. '68 to Present
DESIGN
ENGINEER
Alexander Potter
Assoc.
Arthur B. Chafet
& Assoc.
URS Forest
& Cotton
Alexander Potter
Assoc.
City of Los Angeles
CH2M/Hill
CH2M/HMI
Orange County
Water District
Roy F. Weston
Moran and Cooke
CH2M/HMI
National Institute
for Water Research
Pretoria, So. Africa
AVERAGE
PLANT
CAPACITY
(MGD)
30
3
100
36
B<3)
60
18
15
5
5.5
75
1.3
CONTACTOR
TYPE
Downflow
Gravity
Downflow
Upflow
Packed
Downflow
Gravity
Downflow
Gravity
Upflow
Packed
Upflow
Packed
Upflow
Packed
Downflow
Pressure
Downflow
Gravity
Upflow
Packed
Downflow
Pressure
NO. OF
CONTACTORS
IN SERIES
1
2
1
1
2
1
1
1
2
1
1
2
CONTACT
TIME<1'
(MIN.)
38
30
10
36
50
30
30
30
37
30
17
30
HYDRAULIC
LOADING
(GPM/SQ.FT. )
2.9
5
8
3
4
65
5.8
5.8
6.5
3.7
6.2
3.8
TOTAL
CARBON
DEPTH
(FT.)
15
20
10
15
26
26
24
24
32
15
14
15
CARBON
SIZE
8x30
8x30
8x30
8x30
8x30
8x30
8x30
8x30
8x30
8x30
8x30
12x40
EFFLUENT
REQUIREMENTS12'
(OXYGEN DEMAND)
BOD < 3 mg/l
BOD < 2 mg/l
BOD
(1) Empty bed (superficial) contact time
for average plant flow.
(2) BOD: Biochemical oxygen demand
COD: Chemical oxygen demand
(3) 50 mgd ultimate capacity
-------
30 MGD
ACTIVATED
SLUDGE
FFFI UFNT
CHEMICAL
CLARIFICATION
RECARBONATON
ft SETTLING
MIXED MEDIA
FILTRATION
CHLORINATION
REAERATION
CARBON
ADSORPTION
TO FOUR
MILE RUN
BREAKPOINT
CHLORINATION
CARBON
REGENERATION
FIGURE 6-1
TERTIARY TREATMENT SCHEMATIC
ARLINGTON COUNTY, VIRGINIA
3 MOD
TRICKLING
FILTER
EFFLUENT
CHEMICAL
CLARIFICATION
DUAL MEDIA
FILTRATION
CARBON
ADSORPTION
CARBON
REGENERATION
TO IRRIGATION
SYSTEM AND
POWER PLANT
COOLING
CHLORINATION
FIGURE 6-2
TERTIARY TREATMENT SCHEMATIC -
COLORADO SPRINGS, COLORADO
6-3
-------
100 MGD
ACTIVATED
SLUDGE
EFFLUENT
FILTRATION
CARBON
ADSORPTION
CHLORINATION
CARBON
REGENERATION
REAERATION
TO WEST FORK
TRINITY RIVER
FIGURE 6-3
TERTIARY TREATMENT SCHEMATIC -
DALLAS, TEXAS (TRINITY RIVER AUTHORITY)
36 MGO
ACTIVATED
SLUDGE
EFFLUENT
CHEMICAL
CLARIFICATION
RECARBONATION
& SETTLING
MIXED MEDIA
FILTRATION
CHLORINATION
CARBON
ADSORPTION
TO POHICK
CREEK
BREAKPOINT
CHLORINATION
CARBON
REGENERATION
FIGURE 6-4
TERTIARY TREATMENT SCHEMATIC -
FAIRFAX COUNTY, VIRGINIA (LOWER POTOMAC PLANT)
6-4
-------
60 MOD
ACTIVATED
SLUDGE
EFFLUENT
CHEMICAL
CLARIFICATION
RECARBONATION
& SETTLING
MIXED MEDIA
FILTRATION
CHLORINATION
CARBON
ADSORPTION
TO POTOMAC
RIVER
BREAKPOINT
CHLORINATION
CARBON
REGENERATION
FIGURE 6-5
TERTIARY TREATMENT SCHEMATIC -
MONTGOMERY COUNTY, MARYLAND
18 MGD
ACTIVATED
SLUDGE
CHEMICAL
CLARIFICATION
RECARBONATION
& SETTLING
MIXED MEDIA
FILTRATION
BREAKPOINT
CHLORINATION
SELECTIVE ION
EXCHANGE
CARBON
ADSORPTION
TO BULL RUN
I
CARBON
REGENERATION
FIGURE 6-6
TERTIARY TREATMENT SCHEMATIC -
UPPER OCCOQUAN SEWERAGE AUTHORITY, VIRGINIA
6-5
-------
15 MOD
TRICKLING
FILTER
EFFLUENT
CHEMICAL
CLARIFICATION
AMMONIA
STRIPPING
RECARBONATION
& SETTLING
BLENDING
& STORAGE
BREAKPOINT
CHLORINATION
CARBON
ADSORPTION
TO INJECTION
WELLS
MIXED MEDIA
FILTRATION
CARBON
REGENERATION
FIGURE 6-7
TERTIARY TREATMENT SCHEMATIC -
ORANGE COUNTY, CALIFORNIA
MOD
ACTIVATED
SLUDGE
EFFLUENT
CARBON
ADSORPTION
CHLORINATION
CARBON
REGENERATION
TO INJECTION
WELLS
FIGURE 6-8
TERTIARY TREATMENT SCHEMATIC
LOS ANGELES, CALIFORNIA
6-6
-------
5 MOD t
ACTIVATED
SLUDGE
FFFI IIP NT
CHEMICAL
CLARIFICATION
RECARBONATION
& SETTLING
DUAL MEDIA
FILTRATION
CHLORINATION
CARBON
ADSORPTION
TO PISCATAWAY BAY
STABILIZATION
CARBON
REGENERATION
FIGURE 6-9
TERTIARY TREATMENT SCHEMATIC -
PISCATAWAY, MARYLAND
5.5 MGD
ACTIVATED
SLUDGE
EFFLUENT
CARBON
ADSORPTION
CHLORINATION
•+TO DARDEEN SLOUGH
CARBON
REGENERATION
FIGURE 6-10
TERTIARY TREATMENT SCHEMATIC
ST. CHARLES, MISSOURI
6-7
-------
7.5 MOD
ACTIVATED
SLUDGE
EFFLUENT
CHEMICAL
CLARIFICATION
AMMONIA
STRIPPING
RECARBONATION
It SETTLING
CHLORINATION
CARBON
ADSORPTION
TO INDIAN CREEK
RESERVOIR
MIXED MEDIA
FILTRATION
CARBON
REGENERATION
FIGURE 6-11
TERTIARY TREATMENT SCHEMATIC
SOUTH LAKE TAHOE, CALIFORNIA
RECARBONATION
ALGAE
FLOTATION
FOAM
FRACTIONATION
CHEMICAL
CLARIFICATION
BLENDING
ft STORAGE
CARBON
ADSORPTION
BREAKPOINT
CHLORINATION
TO MUNICIPAL
DISTRIBUTION
SYSTEM
FIGURE 6-12
TERTIARY TREATMENT SCHEMATIC
WINDHOEK, SOUTH AFRICA
6-8
-------
TABLE 6-3
PHYSICAL-CHEMICAL TREATMENT PLANTS
SITE
1- Cortland, N.Y.
2. Cleveland Westerly,
Ohio
3. Fitchburg, Mass.
4. Garland, Texas
5. LeRoy, New York
6. Niagara Falls, N.Y.
7. Owosso, Michigan
8. Rosemount, Minn.
9. Rocky River, Ohio
10. Vallejo, Calif.
STATUS
1973
Design
Design
Construction
Design
Design
Design
Design
Construction
Construction
Design
DESIGN
ENGINEER
Stearns & Wheler
Engineering-Science
Camp Dresser
& McKee
URS Forest &
Cotton
Lozier Engineers
Camp Dresser &
McKee
Ayres, Lewis,
Norris & May
Banister, Short,
Elliot, Hendncksc
and Associates
Willard Schade
& Assoc.
Kaiser Engineers
AVERAGE
PLANT
CAPACITY
(MGD)
10
50
15
30'3>
1
48
6
0.6
n.
10
13
CONTACTOR
TYPE
Downflow
Pressure
Downflow
Pressure
Downflow
Pressure
Upflow
Downflow
Downflow
Pressure
Downflow
Gravity
Upflow
Packed
Upflow
Downflow
Pressure
Downflow
Pressure
Upflow
Expanded
NO. OF
CONTACTORS
IN SERIES
1 or 2
1
1
2
2
1
2
3
(max.)
1
1
CONTACT
TIME'1'
(MIN.)
30
35
35
30
27
20
36
66
(max.)
26
26
HYDRAULIC
LOADING
(GPM/SQ.FT.)
4.3
3.7
3.3
2.5
7.3
3.3
6.2
4.2
4.3
4.6
TOTAL
CARBON
DEPTH
(FT.)
17
17
15.5
10
26.8
9
30
36
(max.)
15
16
CARBON
SIZE
8 x 30
8 x 30
8 x 30
8 x 30
12 x 40
8 x 30
12 x 40
12 x 40
8 x 30
12 x 40
EFFLUENT
REQUIREMENTS12'
(OXYGEN DEMAND)
TOD < 35mg/l
BOD < 15mg/l
BOD < 10mg/l
BOD < 10mg/l
BOD < IOmg/1
COD <112mg/l
BOD < 7 mg/l
BOD < 10 mg/l
BOD < 15 mg/l
BOD < 45 mg/l
(90% of time)
(1) Empty bed (superficial) contact time for average plant flow
(2) BOD: Biochemical oxygen demand
COD: Chemical oxygen demand
TOD: Total oxygen demand
(3) 90 mgd ultimate capacity
-------
10 MGD g
RAW SEWAGE
BAR
SCREEN
CHEMICAL
CLARIFICATION
r i
i
%
<
TO TIOU
BREAKPOINT
CHLORINATION*
g !
3HMIOGA
RIVER
i
CARBON
ADSORPTION
1
CARBON
REGENERATION
I
PRESSURE
STRAINERS
•USED ON PART OF FLOW WHEN
NECESSARY TO MEET TOTAL
OXYGEN DEMAND REQUIREMENTS
FIGURE 6-13
PHYSICAL CHEMICAL TREATMENT SCHEMATIC
CORTLAND, NEW YORK
50 MGD
RAW SEWAGE
BAR
SCREEN
COMMINUTION
AERATED
GRIT CHAMBER
FILTRATION
CHEMICAL
CLARIFICATION
CARBON
ADSORPTION
CHLORINATION
CARBON
REGENERATION
TO LAKE ERIE
FIGURE 6-14
PHYSICAL CHEMICAL TREATMENT SCHEMATIC
CLEVELAND WESTERLY, OHIO
6-10
-------
1.2 MGD
RAW
DOMESTIC
CCUIARC
COMMINUTION
SfTtLING
15 MGD TO
NASHUA RIVER
CARBON
ADSORPTION
1
CHEMICAL
CLARIFICATION
CARBON
REGENERATION
13.8 MGD
PAPER MILL
WASTEWATER
FIGURE 6-15
PHYSICAL CHEMICAL TREATMENT SCHEMATIC -
FITCHBURG, MASSACHUSETTS
PRIMARY
CLARIFICATION
TRICKLING
FILTERS
SECONDARY
CLARIFICATION
7.5 MGD
30 MGD
RA'
SEWAGE
EQUALIZATION
& AERATION
SCREENING
& DEGRITTING
22.5 MGO
CHEMICAL
CLARIFICATION
30 MGD
CARBON
ADSORPTION
CHLORINATION
TO
DUCK
CREEK
CARBON
REGENERATION
RECARBONATION
& SETTLING
FILTRATION
FIGURE 6-16
PHYSICAL CHEMICAL TREATMENT SCHEMATIC -
GARLAND,TEXAS
6-11
-------
1 MGO
RAW
SEWAGE
COMMINUTION
ft QRIT REMOVAL
CHEMICAL
CLARIFICATION
RECARBONATION
& SETTLING
BREAKPOINT
CHLORINATION
CARBON
ADSORPTION
MIXED MEDIA
FILTRATION
CARBON
REGENERATION
1
TO OATKA CREEK
FIGURE 6-17
PHYSICAL CHEMICAL TREATMENT SCHEMATIC -
LeROY, NEW YORK
48 MOD
RAW ™"
SEWAGE
MR
SCREEN
CHEMICAL
CLARIFICATION
CARBON
ADSORPTION
I i
CARBON
REGENERATION
CHLORINATION
TO NIAGAR
RIVER
FIGURE 6-18
PHYSICAL CHEMICAL TREATMENT SCHEMATIC
NIAGARA FALLS, NEW YORK
6-12
-------
6 MGD
RAW
SEWAGE
BAR SCREEN
CHEMICAL
CLARIFICATION
FILTRATION
CARBON
ADSORPTION
(DECHLORINATION)
BREAKPOINT
CHLOR (NATION
CARBON
ADSORPTION
TO SHIAWASSEE RIVER
CARBON
REGENERATION
FIGURE 6-19
PHYSICAL CHEMICAL TREATMENT SCHEMATIC -
OWOSSO, MICHIGAN
0.6 MGD |
RAW SEWAGE
SCREENING
CHEMICAL
CLARIFICATION
UPPER
'MISSISSIPPI
RIVER
SELECTIVE
EXCHANGE
CARBON
ADSORPTION
FIGURE 6-20
PHYSICAL CHEMICAL TREATMENT SCHEMATIC
ROSEMOUNT, MINNESOTA
6-13
-------
10 MOD
RAW —
SEWAGE
BAR
SCREEN
CHEMICAL
CLARIFICATION
CARBON
ADSORPTION
' 1
CARBON
REGENERATION
CHLORINATION
1 '
TO LAK
ERIE
FIGURE 6-21
PHYSICAL CHEMICAL TREATMENT SCHEMATIC -
ROCKY RIVER, OHIO
13 MGD
RAW
SEWAGE
GRIT
REMOVAL
CHEMICAL
CLARIFICATION
CHLORINATION
DUAL MEDIA
FILTRATION
CARBON
ADSORPTION
TO
SAN FRANCISCO BAY
CARBON
REGENERATION
FIGURE 6-22
PHYSICAL CHEMICAL TREATMENT SCHEMATIC
VALLEJO, CALIFORNIA
6-14
-------
6.2.1 Tertiary Treatment Plants
There were four full-scale tertiary treatment plants in operation in early 1973 which
utilize granular activated carbon in the treatment process:
1. South Lake Tahoe, California—This 7.5 mgd facility treats activated sludge
effluent and has been operating continuously and successfully since March
1968. The design criteria and operating results from this plant have been
reported in several other publications [1, 2, 3]. The plant effluent requirements
and the water quality at various points in the treatment process are shown in
Tables 6-4 and 6-5. Data pertaining to the activated carbon systems are shown
in Tables 6-6 through 6-9.
2. Windhoek, South Africa—This 1.3 mgd plant receives highly treated secondary
effluent and processes this wastewater for subsequent use in the city's
municipal water system. It has been operating successfully since October 1968.
The pilot studies and results of the full-scale plant operation have been
reported [4, 5, 6]. The quality of water at various points in the treatment
plant is shown in Table 6-10.
3. Colorado Springs, Colorado—This 3 mgd tertiary treatment plant has been
operating since December 1970. The secondary effluent supplied to this tertiary
treatment plant is from an overloaded filter system; however, facilities are
under construction to enlarge and upgrade secondary treatment. Some
difficulty was experienced in start-up of the chemical clarification and solids
handling system and it was several months before the tertiary facilities were
operating normally. Some of the test work preliminary to the design of this
plant has been reported [ 7 ].
4. Piscataway, Maryland—This 5 mgd plant began start-up operations in early
1973.
Two other tertiary treatment plants are currently under construction: one in St. Charles,
Missouri, and another in Orange County, California. The plant in Orange County is
scheduled for operation in June, 1974 and the design criteria have been reported [8,9].
Typical wastewater quality during the pilot study is shown in Table 6-11. The regulatory
agency effluent requirements are shown in Table 6-12. The detailed design specifications
have been completed for tertiary treatment plants in Arlington, Virginia, and Fairfax
County, Virginia; and detailed design is in progress on tertiary plants in Occoquan,
Virginia, and Montgomery County, Maryland. The preliminary design and project report
has been completed for tertiary plants in Dallas, Texas, and Los Angeles, California.
6-15
-------
TABLE 6-4
ON
WATER QUALITY REQUIREMENTS AND PERFORMANCE DATA
AT SOUTH LAKE TAHOE
DESCRIPTION
MBAS (mg/l), less than
BOD (mg/l), less than
COD (mg/l), less than
S.S. (mg/l), less than
Turbidity (JTU), less than
Phosphorus, (mg/l), less than
pH (units)
Coliform, MPN/1 00ml (3)
REQUIREMENTS
ALPINE(1)
CO.
0.5
5
30
2
5
LAHONTAN R.W.Q.C.B.^'
(% OF TIME)
50 80 100
0.3 0.5 1.0
3 5 10
20 25 50
1 2 4
3 5 10
No Requirements
6.5-8.5
Adequately
Disinfected
6.5-9.0
Median 2.0
Maximum Number
Consecutive Sample >23, 2
PLANT PERFORMANCE
(% OF TIME)
50 80 100
0.19 0.35 0.35
1.0 2.5 3.9
9 10 22
00 0
0.4 0.5 1.3
0.06 0.12 0.27
6.6-8.7
Median 2.0
Number of Consecutive
Samples >23, 0 (none)
(1) Alpine Co. is location of Indian Creek Reservoir.
(2) Lahontan Regional Water Quality Control Board.
(3) All 30 samples collected during November, 1969,
were found to be free of coliform organisms.
-------
TABLE 6-5
WATER QUALITY AT VARIOUS STAGES OF TREATMENT
AT SOUTH LAKE TAHOE
QUALITY
PARAMETER
BOD (mg/l)
COD (mg/l)
SS (mg/l)
Turbidity (JTU)
MBAS (mg/l)
Phosphorus (mg/l)
Coliform
(MPN/100 ml)
RAW
WASTEWATER
140
280
230
250
7
12
50
million
EFFLUENT
PRIMARY
100
220
100
150
6
9
15
million
SECONDARY
30
70
26
15
2.0
6
2.5
million
CHEMICAL
CLARIFIER
10
10
0.7
FILTER
3
25
0
0.3
0.5
0.10
50
CARBON
1
10
0
0.3
0.10
0.10
50
CHLORINATED
FINAL
0.7
10
0
0.3
0.10
0.10
< 2.0
s
-------
TABLE 6-6
CARBON EFFICIENCY PER REGENERATION PERIOD
AT SOUTH LAKE TAHOE
NOVEMBER 1968 THROUGH JANUARY 1971
PARAMETER
Carbon Dosage .,.
Obs. regenerated/million gallons treated)1"
Iodine Number'2'
Spent Carbon
Regenerated Carbon
Apparent Density (gm/mlr2'
Spent Carbon
Regenerated Carbon
Percent Ash'2'
Spent Carbon
Regenerated Carbon
Chemical Oxygen Demand
Percent Removal
Lbs. COD Applied
Lbs. COD Applied per MG
Lbs. COD Removed per MG
Lbs. COD Applied per Ib.
Carbon Regenerated (D
Lbs. COD Removed per Ib.
Carbon Regenerated H)
Methylene Blue Active Substances (MBAS)
Percent Removal
Lbs. MBAS Applied
Lbs. MBAS Applied per MG
Lbs. MBAS Removed per MG
Lbs. MBAS Applied per Ib.
Carbon Regenerated^)
Lbs. MBAS Removed per Ib.
Carbon Regenerated*! )
AVERAGE
207
583
802
0.571
0.487
6.4
6.8
49.9
28,250
162
81
0.78
0.39
77.0
995
5.7
4.4
0.027
0.021
MAXIMUM
418
633
852
0.618
0.491
7.0
7.2
63.3
54,970
254
149
1.56
0.71
93.0
1,675
10.7
8.2
0.045
0.039
MINIMUM
111
497
743
0.544
0.478
5.8
5.8
30.1
15,680
105
32
0.52
0.16
58.0
457
2.6
1.6
0.012
0.007
(1) Based on cu.ft. of carbon fed to furnace
at 30 Ibs/cu.ft.
(2) November 1968 through November 1970.
6-18
-------
TABLE 6-7
CARBON FURNACE PARAMETERS
PER REGENERATION PERIOD AT SOUTH LAKE TAHOE
NOVEMBER 1968 THROUGH NOVEMBER 1970
Parameter
Furnace Feed Rate' '
(Ibs/hr)
Fuel Requirements' '
(BTU/lb carbon)
Hearth Temperatures (degrees F)
No. 4 Hearth
No. 6 Hearth
Average
176
2900
1650
1670
Maximum
266
4510
1460
1560
Minimum
139
1820
1720
1740
(1) Amount fed to furnace per hr at 30 Ibs/cu ft
(2) Natural gas requirements per Ib of carbon fed to furnace at 860 BTU/cu ft and
18-20 psia
6-19
-------
TABLE 6-8
FURNACE OPERATING CONDITIONS FOR
FOUR BATCH REGENERATION CYCLES
AT SOUTH LAKE TAHOE
COLUMN CC-5 CC-5 CC-5 CC-8
CYCLE First Second Third Fourth
BATCH REGENERATION DATE 12/68 1/70 11/70 7/70
FURNACE FEED (Ibs/hr) 286 164 146 142
GAS CONSUMPTION (BTU/lb) 1980 2710 3330 3470
HEARTH TEMPERATURE (degrees F)
No. 4 Hearth 1660 1660 1700 1640
No. 6 Hearth 1650 1660 1700 1730
6-20
-------
TABLE 6-9
CARBON LOSSES DURING BATCH REGENERATION PERIODS
AT SOUTH LAKE TAHOEO)
Regeneration Period ^' Carbon Loss
May 1969 2.5%
Feb. 1970 6.2%
June 1970 5.9%
July 1970 8.6%
(1) Included regeneration of first cycle makeup carbon.
(2) About 1 ,200 cu ft of carbon is included in a regeneration period.
6-21
-------
TABLE 6-10
WATER QUALITY AT VARIOUS STAGES OF
TREATMENT AT WINDHOEK
ON
to
DETERMINATION
Total N (mg/l)
Organic N (mg/l)
Ammonia N (mg/l)
Oxides of N (mg/l)
Phosphates, as P04(mg/l)
ABS (mg/l)
BOD5 (mg/l)
Sulfate, as S04 (mg/l)
PH
RAW
WATER
35
3.2
14.9
17
10
8
30
108
8.5
PRIMARY
FLOTATION
32
1.3
14.0
17
Nil
7
4
228
7.1
LIME,
CHLORINE, AND
SEDIMENTATION
15
0.9
0.2
14
Nil
4
1
220
8.0
SAND
FILTRATION
14
0.7
0.3
13
Nil
4
1
220
8.0
ACTIVATED
CARBON
FILTRATION
13
Nil
0.1
13
Nil
0.7
0.3
220
8.0
-------
TABLE 6-11
WATER QUALITY AT PILOT PLANT AT
ORANGE COUNTY, CALIFORNIA
CONSTITUENT
Calcium
Magnesium
Sodium
Potassium
Bicarbonate
Sulfate
Chloride
Phosphate
Nitrogen
Organic
Ammonia
Nitrite
Nitrate
Total Dissolved Solids
Suspended Solids
BOD
COD
Methylene Blue
Active Substance
CONCENTRATION (mg/l)
INFLUENT
70-110
20-45
240-260
20-35
200-450
270-350
300-350
20-25
5-15
15-30
1
1
1,200-1,400
30-80
30-80
100-200
3-4
EFFLUENT
80
2
240-260
20-35
250
270-350
300-350
1
1
2
1
1
1,000-1,100
1
2
10-30
0.1
6-23
-------
TABLE 6-12
EFFLUENT REQUIREMENTS FOR TERTIARY TREATMENT PLANT AT
ORANGE COUNTY, CALIFORNIA
Constituent
Ammonium
Sodium
Total Hardness (CaCO3)
Sulfate
Chloride
Total Nitrogen (N)
Fluoride
Boron
MBAS
Hexavalent Chromium
Cadmium
Selenium
Phenol
Copper
Lead
Mercury
Arsenic
Iron
Manganese
Barium
Silver
Cyanide
PH
Electrical Conductivity
Taste
Odor
Foam
Color
Filter Effluent Turbidity
Carbon Adsorption Column
Effluent COD
Chlorine Contact Basin
Effluent
Maximum Concentration
(mg/1)
1.0
110.0
220.0
125.0
120.0
10.0
0.8
0.5
0.5
0.05
0.01
0.01
0.001
1.0
0.05
0.005
0.05
0.3
0.05
1.0
0.05
0.2
6.5-8.0
900 mhos/cm
None
None
None
None
1.0 JTU
30 mg/1
Free Chlorine
residual.
6-24
-------
6.2.2 Physical-Chemical Treatment Plants
There are no full-scale physical-chemical treatment plants currently in operation. Three
full-scale physical-chemical treatment plants are currently under construction. One in
Fitchburg, Massachusetts, will treat a combined domestic sewage and paper mill
processing waste. Others, in Rocky River, Ohio, and Rosemount, Minnesota, will treat
domestic sewage. Other physical-chemical treatment plants in the detail design stage are
Cortland, N. Y.; Cleveland Westerly, Ohio; LeRoy, N. Y.; Garland, Texas; Niagara Falls,
N. Y.; Owosso, Michigan; and Vallejo, California.
6.3 References
1. Slechta, A. F., and Gulp, G. L., Water Reclamation Studies at the South Tahoe
Public Utility District. JWPCF, pp. 787-814, (May, 1967).
2. Gulp, R. L., South Tahoe Still a Model. Water and Wastes Engineering, pp. 64-66,
(November , 1972).
3. Advanced Waste-water Treatment as Practiced at South Taho&.by STPUD for Water
Quality Office Environmental Protection Agency, Project 17010 ELQ (WRPD
52-01-67), (August, 1971).
4. Stander, G. J., and Van Vuuren, L. R. J., The Reclamation of Potable Water from
Wastewater. JWPCF, pp. 355-367, (March, 1969).
5. Stander, G. J., and Funke, J. W., Direct Cycle Water Reuse Provides Drinking Water
Supply in South Africa. Water and Wastes Engineering, pp. 66-67, (May, 1969).
6. Van Vuuren, L. R. J., et al., The Full-Scale Reclamation of Purified Sewage Effluent
for the Augmentation of the Domestic Supplies of the City of Windhoek presented
at the 5th International Water Pollution Research Conference, July-August, 1970.
7. Phillips, J. D., and Shell, G. L., Pilot Plant Studies of Effluent Reclamation. Water
and Wastes Engineering, pp. 38-41, (November, 1969).
8. Wesner, G. M., and Gulp, R. L., Wastewater Reclamation and Seawater Desalination
JWPCF, pp. 1932-1939, (October, 1972).
9. Wesner, G. M., Reuse is on Tap. Water and Wastes Engineering, pp. 46-47,
(November, 1972).
6-25
-------
APPENDIX A
GLOSSARY OF TERMS USED WITH GRANULAR CARBON
ABRASION NUMBER—The abrasion number of granular carbon is a measure of the
resistance of the particles to degrading on being mechanically abraded. It is measured by
contacting a carbon sample with steel balls in a pan on a Ro-Tap machine. The abrasion
number is the ratio of the final average (mean) particle diameter to the original average
(mean) particle diameter (determined by screen analysis) times 100.
ACTIVATED CARBON-Carbon which is "activated" by high-temperature heating with
steam or carbon dioxide producing an internal porous particle structure. The total surface
area of granular activated carbon is estimated to be about 1,000 m^/gm.
ADSORBATE—The material, e.g., color bodies, taste and odor compounds, which is
adsorbed on an activated carbon or other adsorbent.
ADSORBENT—A material, such as activated carbon, upon which adsorption takes place.
ADSORPTION—The adhesion of an extremely thin layer of molecules (of gas, liquid) to
the surfaces of solids (granular activated carbons, for instance) or liquids with which they
are in contact.
ADSORPTION ISOTHERMS-A measurement of the adsorptive capacity of an adsorbent
as a function of the concentration, or pressure, of the adsorbing material at a given
temperature. It is defined as the constant temperature relationship between amount
adsorbed per unit weight of adsorbent and the equilibrium concentration, or partial
pressure.
APPARENT DENSITY—The weight per unit volume of a homogeneous activated carbon.
To assure uniform packing of a granular carbon during measurement, a vibrating trough is
used to fill the measuring device.
ASH—The mineral constituent of activated carbon. It is normally defined as a weight
percent basis after a given amount of sample is reduced to ash.
AVERAGE (MEAN) PARTICLE DIAMETER-This is a weighed average diameter of a
granular carbon. A screen analysis is run and the average particle diameter calculated by
multiplying the weight of each fraction by its average diameter, adding the products, and
dividing by the total weight of the sample. The average diameter of each fraction is taken
as the size midway between the sieve opening through which the fraction has passed and
the sieve opening on which the fraction has passed and the sieve opening on which the
fraction was retained.
A-l
-------
BACKWASH—The process by which water is forced through a filtration bed in the
direction opposite to the normal flow, usually upward. During backwashing, the bed
expands allowing the material which has been previously filtered out to be washed away.
BACKWASH BED EXPANSION-The expansion that occurs when a filter bed is being
backwashed, usually expressed as a percentage of the backwashed and settled bed.
BED DENSITY, BACKWASHED AND DRAINED-The weight per unit volume on a dry
basis of a bed of activated carbon that has been backwashed and drained. This value is
usually lower than the corresponding apparent density due to the classification according
to size of the carbon granules during backwashing.
BED DEPTH(HEIGHT)-The depth of carbon, expressed in length units, which is parallel
to the flow of the stream and through which the stream must pass.
BED DIAMETER—The diameter of a cylindrical carbon column, measured perpendicular
to the stream flow.
BIOCHEMICAL OXYGEN DEMAND (BOD)-This is a measure of the concentration of
organic impurities, usually applied to wastewaters. It is the amount of oxygen required
by bacteria while stabilizing, usually for five days, organic matter under aerobic
conditions, expressed in mg/1.
BREAKTHROUGH CURVE-The relationship between the volume of liquid or gas
treated in a carbon column and the concentration or partial pressure of the component
being removed. This can be applied to color, taste and odor numbers, or other criteria of
purity.
CARBON COLUMN—A column filled with granular activated carbon whose primary
function is the preferential adsorption of a particular type or types of molecules.
CHEMICAL OXYGEN DEMAND (COD)-This is a measure of the amount of organic
material in a sample expressed in mg/1 of oxygen and is based on the ability of a strong
oxidizing agent under acid conditions to oxidize organic material to carbon dioxide and
water.
COLOR BODIES-Those complex molecules which impart color (usually undesirable) to a
solution.
CONTACT TIME-The time required for the liquid to pass through a carbon column
assuming that all the liquid passes through at the same velocity. It is equal to the volume
of the empty bed divided by the flow rate.
A-2
-------
COUNTERCURRENT OPERATION-Any contacting process, e.g., adsorption, where the
flows of influent wastewater and solid absorbent proceed in opposite directions. The
highest concentration of dissolved organics contacts the most nearly exhausted portion of
the adsorbent, while the virgin adsorbent contacts only the lowest concentration of
organics. The purpose of such a system is to take fullest advantage of the adsorptive
capacity of the nearly exhausted adsorbent. See under Moving Bed.
CROSS-SECTIONAL BED AREA-The area of activated carbon through which the
stream flow is perpendicular.
DESORPTION—The opposite of adsorption. A phenomenon where an adsorbed molecule
leaves the surface of the adsorbent.
EDUCTOR—A device with no moving parts used to force an activated carbon water
slurry through pipes to the desired location.
EFFECTIVE SIZE—The size of the particle that is coarser than 10 percent, by weight, of
the material. That is, it is the size sieve which will permit 10 percent of the carbon
sample to pass but will retain the remaining 90 percent. It is usually determined by the
interpolation of a cumulative particle size distribution.
FIXED BED—An adsorption process in which liquid being treated is allowed to pass
through a carbon column till the carbon becomes exhausted and the unit is removed
from service and completely recharged with fresh carbon. The carbon remains fixed in
position during the adsorption process.
FREEBOARD—The height to the top of the adsorption column, or wash through in the
case of sand filters, above the surface of the carbon.
HARDNESS NUMBER-This is the Chemical Warfare Service (CWS) test. The hardness
number is a measure of the resistance of a granular carbon to the degradation action of
steel balls in a pan in a Ro-Top machine. It is calculated by using the weight of granular
carbon retained on a particular sieve after the carbon has been in contact with steel balls.
HYDRAULIC LOADING—The quantity of flow passing through a column or packed bed
expressed in the units of volume per unit time per unit area; e.g., gpm/sq ft (superficial
velocity).
IODINE NUMBER—The iodine number is the milligrams of iodine adsorbed by one gram
of carbon at an equilibrium filtrate concentration of 0.02N iodine. It is measured by
contacting a single sample of carbon with an iodine solution and extrapolating to 0.02N
A-3
-------
by an assumed isotherm slope. Iodine number can be correlated with ability to adsorb
low molecular weight substances.
LOSSES ON REGENERATION-The loss of original carbon during regeneration due to
the burning off or mechanical breaking of the carbon. Losses are usually 5-10 percent for
coal-based carbons.
o
MACROPORE—The pores in activated carbon which are larger in diameter than 1,000 A.
MAKEUP CARBON—Fresh granular activated carbon which must be added to an
adsorption system after a regeneration cycle or when deemed necessary to keep the total
amount of carbon adequate. This is to replace carbon lost during regeneration.
MESH SIZE—The particle size of granular activated carbon as determined by the U. S.
Sieve Series. Particle size distribution within a mesh series is given in the specifications of
the particular carbon.
METHYLENE BLUE NUMBER-The methylene blue number is the milligrams of
methylene blue adsorbed by one gram of carbon in equilibrium with a solution of
methylene blue having a concentration of 1.0 mg/1.
o
MICROPORE—The pores in activated carbon which are smaller in diameter than 1,000 A.
MOISTURE-The percent by weight of water adsorbed on activated carbon.
MOLASSES DECOLORIZING INDEX (MDI) (DI)-This Westvaco method requires the
same technique as for molasses value but differs in the method of calculation. A
Spex-Mixer Mill is used for grinding. Approximately, it is the ratio of molasses color
capacity of a carbon to that of a standard carbon times 10. The MDI can be correlated
with the canacity to adsorb many high molecular weight substances.
MOLASSES NUMBER-The molasses number is calculated from the ratio of the optical
densities of the filtrate of a molasses solution treated with a standard activated carbon
and the activated carbon in question. This is a test method of Pittsburgh Activated
Carbon Company.
MOLASSES VALUE (MV)-This is the usual Westvaco method wherein the molasses
value is determined by optical density of a molasses residual filtrate after carbon
treatment. A standard carbon and molasses is used as a base for comparison of
adsorbabilities. A Spex-Mixer Mill is used for grinding.
MOVING (PULSED) BED-A moving bed incorporates an effective countercurrent
operation within a single column. This is accomplished by the removal of spent carbon
A-4
-------
from one end of the carbon bed and the addition of carbon at the other end. The flow
of liquid and carbon are in opposite directions, usually the carbon moves downward and
the liquid upward.
OVERBURNING—Excessive burn-off during reactivation resulting in high losses of
carbon.
PARALLEL COLUMNS—A treatment process in which the liquid being treated is split
into several separate streams and each small stream is treated in one single carbon
column.
PARTICLE DENSITY, WETTED IN WATER-The density of carbon in water assuming
all pores to be filled with water. The value can be calculated by use of the real density of
the activated carbon and the pore volume.
PARTICLE SIZE—Usually, this term refers to the sizes of the two screens, either in the
U. S. Sieve Series or the Tyler Series between which the bulk of a carbon sample falls.
For example, 8 x 30 means most of the carbon passes a No. 8 screen but is retained on a
No. 30 screen.
PARTICLE SIZE DISTRIBUTION-The particle size distribution in a given sample is
obtained by mechanically shaking a weighed amount of material through a series of test
sieves. It is the series of weights retained between the series of sieves.
PHYSICAL-CHEMICAL TREATMENT (PCT) PLANT-A treatment sequence in which
physical and chemical processes are used to the exclusion of explicit biological processes.
This does not exclude incidental biological treatment obtained on filter media or
adsorptive surfaces. In this sense, a PCT scheme is a substitute for conventional biological
treatment. A PCT scheme following an existing biological plant may by contrast be called
simply a tertiary plant, although it is also PCT in a general sense.
PORE SIZE DISTRIBUTION-A measure of the pore structure, which gives activated
carbons their unique adsorptive properties. Cumulative distributions give the relationship
between pore size, say diameter or radius, and volume in pores smaller, or larger, than
that size. Derivative, or interval, distributions indicate the amount of volume in pores
between certain close sizes. Pore size distributions in the micropores, or small pores, are
calculated from nitrogen adsorption isotherms while distributions in the macropores are
measured with the mercury penetrometer. Micropore distributions can be used to predict
adsorptive capacities for different molecular weight substances. The macropore
distributions can be correlated with rates of adsorption, important for many applications.
PORE VOLUME—The sum of the macro and micro pores in a carbon, or, in other words,
the total pore volume. This is expressed as volume per unit weight.
A-5
-------
PRESSURE DROP (HEADLOSS)—The drop of pressure across an adsorption column due
to the resistance of the carbon particles to the flow of liquids or gases through the
system.
REAL DENSITY—The density of the skeleton of a carbon particle. This is determined by
helium or mercury displacement. It usually comes close to that for graphite.
REGENERATION—Restoration of sorptive capacity to a used adsorbent by chemical or
thermal treatment.
RESIDENT (RETENTION) TIME-The theoretical length of time for a liquid to pass
through a carbon column assuming all the liquid moves through with the same uniform
velocity. It is equal to the volume of liquid in the column divided by the rate of flow.
The volume of liquid in a carbon column is simply the total volume of the column times
the void fraction.
SERIES COLUMNS—An adsorption process in which the effluent from a first column
becomes the influent for a second column, the effluent from the second column becomes
the influent for a third column, and so on.
SUPERFICIAL VELOCITY-The velocity of a liquid passing through a column or packed
bed expressed in the units of volume per unit time per unit area; e.g., gpm/sq ft.
SURFACE AREA—This is the amount of surface area per unit weight of carbon. The
surface area of activated carbon is usually determined from the nitrogen adsorption
isotherm by the Brunauer, Emmett and Teller Method (BET Method). Surface area is
usually expressed in square meters per gram of carbon.
THRESHOLD ODOR NUMBER-This test is based on a comparison with an odor-free
water obtained by passing tap water through a column of activated carbon. The water
under test is diluted with odor-free water until the odor is no longer detectable. The last
dilution at which an odor is observed is the threshold odor number.
TOTAL ORGANIC CARBON (TOC)-The TOC is a measure of the amount of organic
material in a water sample expressed in mg/1 of carbon. It is measured with a Beckman
Carbonaceous Analyzer or other instrument wherein the organic compounds are
catalytically oxidized to CO2 and measured by an infrared detector. This method is
frequently being applied to wastewaters.
TURBIDITY-A cloudiness of a liquid due to finely divided material in suspension which
may not be of sufficient size to be seen as individual particles by the naked eye, but
which scatters the light in passage through the liquid. It is frequently measured in
Jackson Turbidity Units (JTU).
A-6
-------
UNIFORMITY COEFFICIENT-This is obtained by dividing the sieve opening in
millimeters which will pass 60 percent of a sample by the sieve opening in millimeters
which will pass 10 percent of the sample. These values are usually obtained by
interpolation on a cumulative particle size distribution.
VOIDS IN PACKED BEDS—The volume between the carbon particles in a packed bed or
column expressed as a percentage of the total bed (carbon) volume. For Westvaco
granular carbons, the voids amount to about 40 percent.
WAVE FRONT—The wave front is the capacity gradient that exists in the critical bed
depth. It outlines the gradual transition of the carbon from "Fresh" to "Spent."
A-7
-------
-------
APPENDIX B
CONTROL TESTS - CARBON ADSORPTION AND REGENERATION
This appendix contains test procedures that are of importance in examination of both
spent and virgin granular activated carbon.
The tests on the following pages are listed in the order given below:
B. 1 Iodine Number
B. 2 Molasses Number
B. 3 Decolorizing Index
B. 4 Methylene Blue Number
B. 5 Hardness Number
B. 6 Abrasion Number (Ro-Tap)
B. 7 Abrasion Number (NBS)
B. 8 Apparent Density
B. 9 Sieve Analysis (Dry)
B.10 Effective Size and Uniformity Coefficient
B.ll Moisture
B.I2 Total Ash
B-l
-------
B. 1 Iodine Number
The Iodine Number is defined as the milligrams of iodine adsorbed by one gram of
carbon when the iodine concentration of the residual filtrate is 0.02 normal.
B.I.I Reagents and Equipment
Hydrochloric Acid, 5 percent weight-To 550 ml of distilled water add 70 ml of
reagent-grade concentrated hydrochloric acid (HC1).
Sodium Thiosulfate, 0.1 normal -Dissolve 25 grams of reagent-grade sodium thiosulfate
(^2820-3 SF^O) in one (1) liter of freshly boiled distilled water. Add a few drops of
chloroform to minimize bacterial decomposition of the thiosulfate solution. Standarize
the thiosulfate solution against 0.100 normal potassium biniodate (KH (103) 2)- Prepare
the 0.1000 normal KH (lO^) 2 using primary standard quality KH (10^) 2 which has
been dried overnight at 105 degrees C and cooled in a desiccator. Weigh 3.249 grams KH
(lOo) 2 and make-up to exactly one liter in a volumetric flask with distilled water. Store
in a glass-stoppered bottle.
To 80 ml of distilled water add, with constant stirring, one ml of concentrated sulfuric
acid (^2804), 10 ml of 0.1000 KH (lOj) 2 solution and approximately one gram of
potassium iodide (KI). Titrate the mixture immediately with the thiosulfate solution
adding 2-3 drops of starch solution when the iodine fades to a light yellow color.
Continue the titration by adding the thiosulfate dropwise until a drop produces a
colorless solution. Record the volume of titrate used.
1.000
Normality of sodium thiosulfate = — ; — rrr — — — - •
ml ot NanSoOo consumed
Z, £ J
Iodine Solution— Dissolve 12.7 grams of reagent-grade iodine C^) and 19.1 grams of
potassium iodide in a small quantity, approximately 20 ml, of distilled water. (If excess
water is used, materials will not go into solution.) Dilute to one (1) liter in a volumetric
flask with distilled water. Store in a glass-stoppered bottle in a dark place or use in a
dark bottle. To standarize the iodine solution, pipette 25.0 ml into a 250 ml Erlenmeyer
flask and immediately titrate with the 0.1 normal thiosulfate solution. Add 2-3 drops of
starch solution near the endpoint and continue titrating until solution is colorless. Record
the volume of titrant used.
ml of NaoS^Oo used x normality ^9890?
Normality of iodine solution = - f- L ->
,
Starch Solution-To 2.5 grams of starch (potato, arrowroot, or soluble), add a little cold
water and grind in a mortar to a thin paste. Pour into one (1) liter of boiled distilled
water, stir, and allow to settle. Use the clear supernatant. Preserve with 1.25 grams of
salicylic acid per one (1) liter of starch solution.
B-2
-------
Filter Paper-Whatman Folded No. 2V, 10.5 cm.
Spex-Mixer Mill-No. 8000 Spex-Mixer Mill and No. 8001 Grinding Vials, Spex Industries,
Inc., 3800 Park Avenue, Metuchen, New Jersey.
B.I.2 Procedure
Grind a representative sample of carbon in a Spex-Mixer Mill (usually 70 seconds) until
90+ 5 percent will pass a 325 mesh sieve (by wet sieve analysis). Load the Spex-Mixer
Mill with a 5.5 ± 0.5 gram sample and use 64 one-fourth inch diameter smooth steel
balls. An adequate sample of the pulverized carbon should then be dried at 140 degrees C
for one (1) hour, or 110 degrees C for three (3) hours. A moisture balance can also be
used.
Weigh 1.000 gram of the dried pulverized carbon (see Note 1) and transfer the weighed
sample into a dry, glass-stoppered, 250 ml Erlenmeyer flask. To the flask add 10 ml of 5
percent wt. HC1 acid and swirl until the carbon is wetted. Place the flask on hot plate,
bring contents to boil and allow to boil for only 30 seconds.
After allowing the flask and contents to cool to room temperature, add 100 ml of
standarized 0.1 normal iodine solution to the flask. Immediately stopper flask and shake
contents vigorously for 30 seconds. Filter by gravity immediately after the 30-second
shaking period through Whatman No. 2V filter paper. Discard the first 20 or 30 ml of
filtrate and collect the remainder in a clean beaker. Do not wash the residue on the filter
paper.
Mix the filtrate in the beaker with a stirring rod and pipette, 50 ml of the filtrate into a
250 ml Erlenmeyer flask. Titrate the 50 ml sample with standarized 0.1 normal sodium
thiosulfate until the yellow color has almost disappeared. Add about 1 ml of starch
solution and continue titration until the blue indicator color just disappears. Record the
volume of sodium thiosulfate solution used.
Notes on Procedure
1. The capacity of a carbon for any adsorbate is dependent on the concentration
of the adsorbate in the medium contacting the carbon. Thus, the concentration
of the residual filtrate must be specified, or known, so that appropriate factors
may be applied to correct the concentration to agree with the definition. The
amount of sample to be used in the determination is governed by the activity
of the carbon. If the residual filtrate normality (C) is not within the range
0.008N to 0.035N given in the Iodine Correction Table, the procedure should
be repeated using a different weight of sample.
B-3
-------
2. It is important to the test that the potassium iodide to iodine weight ratio is
1.5 to 1 in the standard iodine solution.
Calculation
Iodine Number = —
A — (2.2B x ml of thiosulfate solution used)
Weight of sample (grams)
_ N2 x ml of thiosulfate solution used
V_* """" — — - - -
50
X/m = mg iodine adsorbed per gram of carbon
Nj = Normality of iodine solution
N2 = Normality of sodium thiosulfate solution
A = Nj x 12693.0
B = N9 x 126.93
£j
C = Residual filtrate normality
D = Correction factor (obtained from Table B-l)
B-4
-------
TABLE B-l
IODINE CORRECTION FACTOR (D)
Residual
Filtrate
Normality
(C)
.0080
.0090
.0100
.0110
.0120
.0130
.0140
.0150
.0160
.0170
.0180
.0190
.0200
.0210
.0220
.0230
.0240
.0250
.0260
.0270
.0280
.0290
.0300
.0310
.0320
.0330
.0000
1.1625
1.1438
1.1250
1.1100
1.0950
1.0800
1.0675
1.0538
1.0413
1.0300
1.0200
1.0100
1.0013
0.9938
0.9863
0.9788
0.9725
0.9650
0.9600
0.9538
0.9488
0.9425
0.9375
0.9333
0.9300
0.9263
.0001
1.1613
1.1425
1.1238
1.1088
1.0938
1.0788
1.0663
1.0525
1.0400
1.0288
1.0188
1.0088
1.0000
0.9925
0.9850
0.9775
0.9708
0.9650
0.9588
0.9525
0.9475
0.9425
0.9375
0.9333
0.9294
0.9263
.0002
1.1600
1.1400
1.1225
1.1075
1.0925
1.0775
1.0650
1.0513
1.0388
1.0275
1.0175
1.0075
1.0000
0.9925
0.9850
0.9775
0.9700
0.9638
0.9588
0.9525
0.9475
0.9425
0.9375
0.9325
0.9288
0.9257
.0003
1.1575
1.1375
1.1213
1.1063
1.0900
1.0763
1.0625
1.0500
1.0375
1.0263
1.0163
1.0075
0.9988
0.9913
0.9838
0.9763
0.9700
0.9638
0.9575
0.9519
0.9463
0.9413
0.9363
0.9325
0.9288
0.9250
.0004
1.1550
1.1363
1.1200
1.1038
1.0888
1.0750
1.0613
1.0488
1.0375
1.0250
1.0150
1.0063
0.9975
0.9900
0.9825
0.9763
0.9688
0.9625
0.9575
0.9513
0.9463
0.9413
0.9363
0.9325
0.9280
0.9250
.0005
1.1538
1.1350
1.1175
1.1025
1.0875
1.0738
1.0600
1.0475
1.0363
1.0245
1.0144
1.0050
0.9975
0.9900
0.9825
0.9750
0.9688
0.9625
0.9563
0.9513
0.9463
0.9400
0.9363
0.9319
0.9275
1
0006
1513
1.1325
1
1163
1.1000
1.0863
1.0725
1.0588
1.0463
1.0350
1.0238
1.0138
1.0050
0.9963
0.9888
0.9813
0.9750
0.9675
0.9613
0.9563
0.9506
0.9450
0
9400
0.9363
0
9313
0.9275
.0007
1.1500
1.1300
1.1150
1.0988
1.0850
1.0713
1.0575
1.0450
1.0333
1.0225
1.0125
1.0038
0.9950
0.9875
0.9813
0.9738
0.9675
0.9613
0.9550
0.9500
0.9450
0.9394
0.9350
0.9313
0.9275
.0008
1.1475
1.1288
1.1138
1.0975
1.0838
1.0700
1.0563
1.0438
1.0325
1.0208
1.0125
1.0025
0.9950
0.9875
0.9800
0.9738
0.9663
0.9606
0.9550
0.9500
0.9438
0.9388
0.9350
0.9300
0.9270
.0009
1.1463
1.1275
1.1113
1.0963
1.0825
1.0688
1.0550
1.0425
1.0313
1.0200
1.0113
1.0025
0.9938
0.9863
0.9788
0.9725
0.9663
0.9600
0.9538
0.9488
0.9438
0.9388
0.9346
0.9300
0.9270
B-5
-------
B.2 Molasses Number
Molasses solutions are treated with pulverized activated carbon of unknown decolorizing
capacity and with a standard carbon of known Molasses Number. The optical densities of
the filtrates are measured and the Molasses Number of the unknown is calculated from
the ratio of the optical densities and the standard value.
B.2.1 Reagents and Equipment
Standard Carbon—Small quantities of standard carbon are available from the Chemical
Division, Westvaco Corporation.
Molasses Solution-Prepare by diluting 146 grams of blackstrap molasses with one (1)
liter of distilled water. The weight of molasses to be used varies with the particular lot of
molasses and is adjusted, if necessary, so that the standard carbon produces a filtrate with
an optical density (percent transmission) of 0.38 to 0.42.
Any grade of commercial molasses which may be purchased will vary considerably in
depth of color. The dilution of the initial solution to give the same final filtrate color
with the standard carbon compensates for such variations. Once such an adjustment has
been made on a given lot of molasses, the proper dilution may be made routinely. The
molasses solution is stored in a refrigerator and any unused portion discarded after 24
hours.
A suitable grade of blackstrap molasses can be purchased from Refined Syrups, Yonkers,
New York.
Spex-Mixer Mill - No. 8000 Spex-Mixer Mill and No. 8001 Grinding Vials,
Spex-Industries, Inc., 3880 Park Avenue, Metchun, New Jersey.
Filter Paper Suspension—Prepare by mascerating 16 circles of Whatman No. 3, 7-cm filter
paper in one (1) liter of distilled water.
Absorption Cell - Klett-Summerson, No. 902, 10-mm.
Immersion Plate - Klett-Summerson, No. 903, 7.5 mm.
B.2.2 Procedure
Grind a representative sample to carbon in a Spex-Mixer Mill until 90—5 percent will
pass a 325-mesh sieve (by wet sieve analysis). Load the Spex-Mixer Mill with a 5.5 - 0.5
gram sample and use 64 one-fourth inch diameter smooth steel-balls. An adequate supply
of the carbon should then be dried at 140 degrees C for one (1) hour or 110 degrees C
B-6
-------
for three (3) hours. Weigh 0.46 gram portions of pulverized standard carbon of known
decolorizing capacity and unknown carbon and transfer to separate 400 ml beakers. Add
50.0 ml of molasses solution to each beaker and stir until the carbon is thoroughly
wetted.
Place the beakers on hotplate and allow to boil for 30 seconds from time boiling
commences.
Immediately after boiling, filter the samples by vacuum through a Buchner funnel, using
Whatman No. 3 filter paper which has been previously coated by filtering 50 ml of the
filter paper suspension (see Note 1). Discard the first 10 to 15 ml of the sample filtrate
and collect the remainder.
Using a 2.5 mm effective light path and a 425 mju (blue) filter, compare the optical
densities of the samples against distilled water in a Fisher Electrophotometer or other
suitable instrument (See Note 2).
Notes on Procedure
1. The Buchner funnels and precoated filter paper should be prepared beforehand
so that no delay is encountered in filtering the samples. Discard the filtrate
from the filter paper suspension before filtering the samples.
2. Since the Fisher Electrophotometer is not equipped with 2.5 mm cells, the cell
holder was modified to accommodate the 10-mm, Klett-Summerson cell. A 2.5
mm effective light path is obtained by placing the cell with a 7.5 mm glass
immersion plate.
Calculations
KxB
Molasses Number = —-—
A
K = Molasses Value of Standard Carbon
A = Optical Density of Filtrate from Test Carbon
B = Optical Density of Filtrate from Standard Carbon
B.3 Decolorizing Index
Molasses solution is treated with different weights of a standard carbon of known
Decolorizing Index. The optical densitites of the filtrate are measured and plotted with
the known Decolorizing Index values to obtain a standard curve. A molasses solution is
then treated with pulverized activated carbon of unknown decolorizing capacity. The
optical density of the filtrate is measured and the Decolorizing Index is determined from
the standard curve.
B-7
-------
B.3.1 Reagents and Equipment
Blackstrap Molasses— This molasses is available only through the Chemical Division,
Westvaco Corporation, as selection is required to obtain molasses which provides
reproducible data from year to year.
Anhydrous Disodium Phosphate
Phosphoric Acid
Supercel Filter Aid
Standard D. I. Carbon-Small quantities of primary standard carbon are available from the
Chemical Division, Westvaco Corporation.
Filter Cloth— A chain cloth, 32-inches wide, made by T. Shriver and Company, Harrison,
New Jersey.
Electric Hot Plate— The hot plate is a Type H, 120 volts, 550 watts, made by Precision
Scientific Company. This hot plate is used without the refractory top.
Klett-Summerson Colorimeter— A No. 54 green filter and a 10 ml Klett-Summerson
absorption tube (12.5 mm light path) are used for reading the samples. The instrument is
zeroed using distilled water.
The instrument should give approximately the following reading when using a 0.5 normal
potassium dichromate (KCO-y) solution:
0.5 Normal Klett-Summerson
Potassium Dichromate Reading
20 Percent Dilution 155
60 Percent Dilution 280
100 Percent Dilution 350
Return instrument pointer to near zero after each reading.
Analytical Balance - Sensitivity to 0.5 milligram.
Spex-Mixer Mill - No. 8000 Spex-Mixer Mill and No. 8001 Grinding Vials, Spex
Industries, Inc., 3880 Park Avenue, Metuchen, New Jersey.
Filter Paper - Whatman No. 5, 15 cm.
-------
B.3.2 Preparation of Solutions
Buffer Solution-(8X)-104 grams anhydrous disodium phosphate (Na2HPO4> or
equivalent weight of crystalline phosphate, are dissolved in about 500 millimeters of
warm distilled water. When the phosphate is completely dissolved, make up to one liter
with distilled water. Acidify with concentrated reagent-grade phosphoric acid to pH 6.5 ±
0.1. For preparation of larger quantities, multiples of these weights and volumes may be
used.
Molasses Solution-Dilute 40 grams of the blackstrap molasses in about 50 ml (or amount
necessary) of distilled water (approximately 25 degrees C). Add 125 ml of buffer
solution, dilute to one liter with chilled distilled water (approximately 4 degrees C) and
mix thoroughly. (Solution will be about 13 degrees C). However, if the molasses solution
is to be used immediately the distilled water does not need to be chilled before using.
For preparation of larger quantities, multiples of these weights and volumes can be used.
A Buchner funnel fitted with a filter cloth, is precoated by slurrying Supercel filter aid
with a portion of the blackstrap molasses solution and filtering. Use sufficient Supercel
filter aid to provide a cake approximately one-half inch thick. After precoating, change
funnel to a clean filter flask. Pour the solution, to which a small amount of Supercel has
been added. The entire solution, is then filtered through the filter aid cake. (If necessary,
this solution should be refiltered until it is clear.) If this solution is not to be used
immediately, it must be refrigerated (at about 4 degrees C).
B.3.3 Preparation of Standard Curve
1. Weigh accurately (± 0.001 gram) the following weights of the groundf Standard
D. I. carbon (dried at 140 degrees C for one (1) hour or 110 degrees C for
three (3) hours) into 150 ml beakers: 0.200, 0.300, 0.400, 0.500, 0.600, 0.700,
0.900, and 1.00 gram.
2. Measure 50 ml of the molasses solution, using a graduated cylinder, and reading
the bottom of the menicus.
3. Add 10 to 20 ml of the molasses solution to the weighed carbon. Swirl the
contents of the beaker gently until the carbon is completely wetted. Use the
remaining portion of the molasses solution to wash down the sides of the
beaker.
t A ground sample is obtained by placing a 5.5 + 0.5 gram sample of dried carbon in a Spex-Mixer Mill Con-
taining 64 one-fourth inch diameter smooth steel balls until 90 + 5 percent will pass a 325 mesh screen (by
wet screen analysis).
B-9
-------
4. Place the beaker on the hot plate and bring the sample to a boil (the solution
should be brought to boiling in less than 200 seconds). Boil for 30 seconds and
then remove sample from hot plate.
5. Filter immediately by gravity using a Whatman No. 5, 15 cm. filter paper (or
equivalent). Allow all of the samples to filter.
6. Allow filtrate to cool to room temperature (approximately 25 degrees C).
7. Read the color of the samples, using the Klett-Summerson Colorimeter.
8. To prepare the Standard Curve, plot the Klett-Summerson readings of the
samples (from Step 1) versus the assigned Decolorizing Index Numbers (listed
in the following table) on semilogarithmic, 1 cycle x 70 divisions graph paper.
Weight of Standard Assigned Decolorizing
D. I. Carbon Index Number
0.200 6.5
0.300 8.6
0.400 11.2
0.500 14.0
0.600 16.9
0.700 19.9
0.800 23.0
0.900 27.0
1.00 30.8
Draw a straight curve line through these points. (See Figure B-l). A new standard curve
will need to be prepared for molasses solution which has been stored at 4 degrees C for
longer than 16 hours.
B.3.4 Preparation of Samples to be Tested
1. Weigh 0.460 + 0.001 gram of the dried ground carbon sample to be tested, and
transfer to a 150 ml beaker.
B-10
-------
600
500
400
300
z
00
c
I5
200
100
6.0
8.0
10.0 12.0 14.0
DECOLORIZING INDEX
16.0
18.0
20.0
FIGURE B-1
EXAMPLE OF STANDARD CURVE
B-ll
-------
2. Follow Steps 2 through 7 under Preparation of Standard Curve.
3. The D. I. of the carbon is determined from the Standard Curve.
B.4 Methylene Blue Number
The Methylene Blue Number is defined as the milligrams of methylene blue adsorbed by
one gram of carbon in equilibrium with a solution of methylene blue having a
concentration of 1.0 mg per liter.
B.4.1 Reagents and Equipment
Methylene Blue - Zinc-free, American Cyanamid Company. Dry the methylene blue to
constant weight. Prepare solutions of 20.00 and 1.00 g/1 concentration.
Colorimeter - An instrument such as the Klett-Summerson Industrial Model (for
colorimetric analysis).
Variable Speed Shaker - Will Scientific Catalog No. 23690 with Box Carrier Catalog No.
23696.
Filter Paper - Whatman No. 3, Qualitative.
Spex-Mixer Mill - No. 8000 Spex-Mixer Mill and No. 8001 Grinding Vials, Spex
Industries, Inc., 3880 Park Avenue, Metuchen, New Jersey.
B.4.2 Procedure
Grind a representative sample of carbon in a Spex-Miller Mill until 90 ± 5 percent will
pass a 325 mesh screen (by wet screen analysis). Load the Spex-Mixer Mill with a 5.5 ±
0.5 gram sample and use 64 one-fourth inch diameter steel balls. An adequate sample of
the carbon should then be dried at 140 degrees C for one (1) hour or 100 degrees C for
three (3) hours.
Add 5.00 grams of pulverized carbon to a 250 ml Erlenmeyer flask (see Note 1). Add 80
ml of methylene blue solution (20 grams per liter) to the beaker. Shake at about 150
oscillations per minute for 20 minutes using a mechanical stirrer. Immediately after the
stirring period, filter, through a Buchner funnel under vacuum, using Whatman No. 3
filter paper (see Note 2). Discard the first 10 to 15 ml of the sample filtrate and collect
the remainder.
B-12
-------
B.4.3 Colorimetric Analysis
Transfer the filtrate to a solution cell having a 40 mm effective depth and record the
reading using a colorimeter with a green (540 mju) color filter (see Note 4). Prepare a
standard curve using methylene blue concentrations of 0.4, 1.0, 3.0, and 5.0 mg/1 (see
Note 3). Determine the concentration of methylene blue by reference to the standard
curve (Table B-2). The methylene blue number is found by referring to Table B-3.
B.4.4 Notes on Procedure
1. The weight of sample taken is determined by the activity of the carbon. The
5.00 gram sample size is correct for carbons having methylene blue numbers
ranging from 264 to 330. For carbons of higher activity, it will be necessary to
use only a 4 gram sample while other carbons of lower activity will require
from 6 to 8 grams to reduce the concentration of methylene blue in the filtrate
reasonably close to that of the standards.
2. Prepare the filter beforehand by placing the filter paper in the funnel, wetting
it thoroughly and removing excess water with the vacuum. Discard the water
from the flask to prevent dilution of the test filtrate.
3. To prepare standards having methylene blue concentrations of 0.4, 0.6, 0.8,
1.0, 1.5, 2.0, 3.0 and 5.0 mg per liter, dilute 5.0 ml of the 1.0 gram per liter
methylene blue solution to one liter with distilled water. Then transfer 4, 6, 8,
19, 15, 20, 30, and 50 ml of the resulting solution to separate 50 ml
volumetric flasks and dilute to 50 ml with distilled water.
4. If the filtrate color is deeper than a reading corresponding to 5 mg/1 on the
standard curve, pipette 0.5, 1, 5, or 10 ml into a 50 ml volumetric flask and
dilute to the 50 ml mark with distilled water. Determine the methylene blue
concentration for the diluted sample and use the following formula to
determine filtrate concentrations:
., Diluted concentration x 50
Filtrate concentration, mg/1 - ml sample pipetted into volumetric
flask
B-13
-------
TABLE B-2
DILUTION CHART FOR METHYLENE BLUE DETERMINATION
Methylene Blue Concentration, mg/1
Color Standard
3
3-1/2
4
4-1/2
5
5-1/2
6
6-1/2
7
7-1/2
8
8-1/2
9
9-1/2
10
50 ml
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.25
1.50
1.75
2.00
2.50
3.00
4.00
5.00
No. of ml
10 ml
2.0
2.5
3.0
3.5
4.0
4.5
5.0
6.25
7.5
8.75
10.0
12.5
15.0
20.0
25.0
of Filtrate Taken
5 ml 1 ml
4.0
5.0
6.0
7.0
8.0
9.0
10.0
12.5
15.0
17.5
20.0
25.0
30.0
40.0
50.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
62.5
75.0
87.5
100.0
125.0
150.0
200.0
250.0
0.5 ml
40.0
50.0
60.0
70.0
80.0
90.0
100.0
125.0
150.0
175.0
200.0
250.0
300.0
400.0
500.0
B-14
-------
TABLE B-3
METHYLENE BLUE CORRECTION CHART
(mg Methylene Blue adsorbed per gram of carbon at a filtrate concentration of 1.0 mg/1)
Methylene Blue Number
Filtrate Concentration
mg Methylene Blue/1
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.2
1.5
1.75
2.0
2.5
3.0
3.5
4.0
4.5
5.0
6.0
6.25
7.0
7.5
8.0
8.75
9.0
10.0
*..
4 gm
416
414
410
408
407
406
405
402
399
398
396
394
391
388
387
386
385
384
382
381
380
380
378
377
376
5 gm
333
331
328
327
326
325
324
322
319
318
317
311
313
311
310
309
308
307
306
305
304
304
303
302
301
Sample Size
6 gm
277
276
273
272
271
270
270
268
266
265
264
262
261
259
258
257
256
256
255
254
253
253
252
251
250
7 gm
238
236
235
234
233
232
232
230
228
227
226
225
224
223
222
221
220
220
219
218
217
217
216
216
215
8 gm
208
207
205
204
203
203
202
201
200
199
198
197
195
194
193
193
192
192
191
191
190
190
189
189
188
B-15
-------
Methylene Blue Number
Filtration Concentration
mg Methylene Blue/1
12.5
15.0
17.5
20.0
25.0
30.0
35.0
40.0
45.0
50.0
60.0
62.0
70.0
75.0
80.0
87.5
90.0
100.0
125.0
150.0
175.0
200.0
250.0
300.0
400.0
500.0
4 gm
374
371
370
368
365
363
361
360
358
357
355
353
352
351
351
350
350
348
346
344
342
341
338
336
332
330
5 gm
299
297
296
295
292
291
289
288
287
286
284
283
282
281
281
280
280
279
277
275
274
273
271
269
266
264
Sample Size
6 gm
250
248
247
246
243
242
241
240
239
238
237
236
235
234
234
233
233
232
231
229
228
227
226
224
222
220
7 gm
213
212
212
211
209
208
207
206
205
204
204
203
202
201
201
200
200
199
198
197
196
195
194
192
190
188
8 gm
187
185
185
184
184
182
181
180
179
179
178
111
176
175
175
175
175
174
173
172
171
170
169
168
166
165
B-16
-------
B.5 Hardness Number (CWS)
A sample of carbon of a pre-selected mesh size is subjected to the action of steel balls on
a Ro-Tap machine. The resistance of the carbon to degradation by this action is termed
the Hardness Number.
B.5.1 Equipment
Ro-Tap - Sieve Shaker, Fisher Scientific Catalog No. 4-906.
Sieves - U. S. Standard Sieve Series, 8-inch diameter, full height sieves.
Hardness Testing Pan Assembly - See Figures B-2 and B-3.
B.5.2 Procedure
1. Weigh 50.0 grams of prepared size material (see Note 1) and place in a special
hardness testing pan (see attached figure).
2. Place 15 one-half-inch diameter and 15 three-eighth-inch diameter smooth steel
balls in the hardness testing pan.
3. Nest the hardness testing pan with a bottom receiving pan below, a half-height
blank pan and iron sieve cover above, and place assembly on the Ro-Tap
machine for 30 minutes with the tapper in operation.
4. At the end of the 30-minute period, remove the steel balls on a No. 4 sieve and
transfer the sample to a sieve nested on a bottom receiving pan (see Note 1).
5. Place the sieve assembly on the Ro-Tap machine for 3 minutes with the tapper
in operation.
6. Weigh the material remaining on the sieve and calculate the Hardness Number
as follows:
Hardness No. = weight of material retained on sieve x 2
B.5.3 Notes on Method
1. Selection of Special Sieve Sizes for Various Grades of Carbon
a. For 4x8, 4 x 10, 6x8, 6x12 and 6x16 mesh carbons, prepare 50.0
grams of 6 x 8 mesh material by shaking approximately 100 grams of
original sample for 3 minutes on a Ro-Tap machine, using the Nos. 6 and
8 sieves. Repeat, if necessary, until 50.0 grams are obtained. Use a No. 12
sieve for the final screening step.
B-17
-------
14 GA.SHEET
BRASS BROWN
& SHARP STD.
-------
•T* CORK
! U- LID
U
L.
HALF HEIGHT BLANK PAN
c
c
SPECIAL HARDNESS PAN
RECEIVING PAN
ELEVATION
NO SCALE
FIGURE B-3
ARRANGEMENT OF ROTAP PANS
FOR HARDNESS AND ABRASION TEST
B-19
-------
b. For 8 x 20, 8 x 30, 10 x 30, 12 x 30 and 12 x 40 mesh carbons, prepare
50.0 grams of 12 x 16 mesh material and use a No. 20 sieve for the final
screening step.
c. For 4x6 mesh carbon, prepare 50.0 grams of 4 x 6 mesh material and
use a No. 8 sieve for the final screening step.
d. For 8x14 mesh carbon, prepare 50.0 grams of 8 x 12 material and use a
No. 16 sieve for the final screening step.
B.6 Abrasion Number (Ro-Tap)
The Abrasion Number of carbon defines the resistance of the particles to degradation by
the action of steel balls in a Ro-Tap machine, and is calculated as the percentage change
in mean particle diameter.
B.6.1 Equipment
Ro-Tap - Sieve Shaker, Fisher Scientific Catalog No. 4-906.
Sieves - U. S. Standard A. S. T. M. Sieves, 8-inch diameter, full height.
Hardness Testing Pan Assembly - See attached drawing.
Steel Balls - Ten (10) one-half-inch diameter and ten (10) three-quarter-inch diameter
smooth steel balls.
B.6.2 Procedure
Make a dry sieve analysis of 100 grams of the material to be tested and save the screen
fractions. The sieve analysis is to be done exactly as specified in the Westvaco Dry Sieve
Analysis procedure except that the shaking time in the Ro-Tap is increased to ten (10)
minutes. Sieves should be selected according to the nominal particle size of the carbon as
set forth in attached Table B-4. Calculate the mean particle diameter of the sample from
the sieve analysis (see Table B-5).
Recombine the fractions from the sieve analysis and place in the special hardness pan
with 20 steel balls (see attached diagram of hardness pan and equipment list). Shake the
pan assembly on the Ro-Tap machine for 20 minutes with the tapper in operation.
At the end of the 20 minutes, remove the steel balls, make another sieve analysis and
calculate the mean particle diameter.
B-20
-------
TABLE B-4
SUGGESTED SIEVES TO BE USED FOR SCREEN ANALYSIS
NOMINAL SIEVE SIZE
12 x 40
14 x 40
8 x 30
10 x 30
12 x 30
U.S.S. (N.B.S.) SIEVE NUMBERS
12, 16, 20, 30, 40, Pan
14, 16, 20, 30, 40, Pan
8, 12, 16, 20, 30 Pan
10, 12, 16, 20, 30 Pan
12, 16, 20, 30 Pan
TABLE B-5
FACTORS FOR CALCULATING MEAN PARTICLE DIAMETER*
U.S.S. SIEVE
NUMBER
+4
4x6
6x8
8 x 10
10 x 12
12 x 14
14 x 16
16 x 18
18 x 20
20 x 25
25 x 30
30 x 35
35 x 40
40 x 45
45 x 50
50 x 70
70 x 80
80 x 100
MEAN OPENING
mm
5.74
4.06
2.87
2.19
1.84
1.55
1.30
1.10
0.92
0.78
0.65
0.55
0.46
0.39
0.33
0.25
0.19
0.16
U.S.S. SIEVE
NUMBER
4x8
8 x 12
12 x 16
16 x 20
20 x 30
30 x 40
40 x 50
50 x 60
60 x 70
70 x 100
MEAN OPENING
mm
3.57
2.03
1.44
1.02
0.72
0.51
0.36
0.27
0.23
0.18
*The mean particle diameter of each fraction is assumed to be midway between
the sieve opening in millimeters through which the material has passed and
the sieve opening in millimeters on which the material was retained.
B-21
-------
B.6.3 Calculations
AU XT u Final mean particle diameter ,„„
Abrasion Number = — \ 100
Original mean particle diameter
The mean particle diameter of the whole sample is computed by multiplying the weight
of the fraction by the respective mean sieve openings, summing these weighted values and
dividing by total weight of material caught on the sieves and pan. The following example
for a 12 x 30 mesh sample illustrates the method of calculation.
Weight Mean
Retained Opening Weighted
Sieve No. On Sieve, g mm Average
On 12 1.5 2.03a 3.0
16 25.1 1.44 36.1
20 50.2 1.02 . 51.2
30 22.5 0.72 16.2
Pan 1.1 0.00b 0
100.4 106.5
Mean Particle Diameter = 1QQ'4 = 1.061 mm
a. Assuming this material would pass the No. 8 sieve (or generally the next larger
sieve in the square root of two series).
b. Material caught on the pan is not considered in calculating the Mean Particle
Diameter.
B.7 Abrasion Number (NBS)
The apparatus consists essentially of an inverted T-shaped stirrer turning rapidly in a
cylindrical vessel containing the activated carbon. The clearance at the ends of the stirrer
and bottom are the only critical dimensions. The speed of the shaft is 855 + 15 rpm.
(Obtained with a 2:1 reduction by V belt from a 1,750 rpm motor 1/10 horsepower or
larger). A simple frame for holding the drive motor and bearing container assembly is also
required.
B-22
-------
Procedure
1. Prepare a sample of activated carbon by the recommended sampling procedures
having a volume of 250 to 300 ml.
2. Obtain a sieve analysis by the recommended sieving procedure. Discard the
fractions through No. 70 sieve and recombine all sieve fractions coarser than
No. 70 and place in hardness tester.
3. Operate the tester for 1 hour + 1 minute.
4. Repeat the sieve analysis for the stirred mixture.
5. Calculate the percentage through No. 70 and record as the percent dust
formation.
6. Calculate the average particle size, D, before and after stirring from the sieve
analysis by means of the following relationship:
n _ 2WiDi
u swT
where W is the weight of a sieve fraction, and the particle diameter, D, is
obtained as the arithmetic average of opening of sieves above and below the
fraction.
7. The percentage reduction in particle size is the decrease in average particle size
calculated as a percentage of the original average particle size.
8. Since this test abrades particles in proportion to their size, divide both
percentage reduction in particle size and percentage dust formation by particle
size (in mm) before stirring in order to reduce both results to a standard 1 mm
particle size.
B.8 Apparent Density
The apparent density is defined as the weight of carbon per unit volume expressed in
grams per cubic centimeter or pounds per cubic foot.
B.8.1 Equipment
Vibrator Feeder - See Figure B-4.
Cylinder - 100 ml A. S. T. M Graduated Cylinder
B-23
-------
RESERVOIR FUNNEL
CLAMPED TO RING
STAND
METAL VIBRATOR
DOOR BELL BUZZER
-FEED
FUNNEL
CLAMPED
TO RING
STAND
-100 ml ASTM
GRADUATED
CYLINDER
.SWITCH
TRANSFORMER
NO SCALE
FIGURE B-4
APPARENT DENSITY TEST
APPARATUS
B-24
-------
B.8.2 Procedure
Dry an adequate sample of the carbon to be tested at 140 degrees C for one (1) hour or
110 degrees C for three (3) hours. Place a representative sample of the dried carbon into
the reservoir funnel of the apparent density apparatus. Material which flows prematurely
into the graduated cylinder is returned to the reservoir funnel.
Fill the tared graduated cylinder to the 100 ml mark at a uniform rate so that filling
time is not less than 100 seconds nor more than 133 seconds. The rate can be adjusted
by changing the slope of the metal vibrator and/or raising or lowering the reservoir
funnel. A powerstat can be used to regulate the speed of the vibrator, thus regulating the
rate of filling of the cylinder. Determine the weight of the carbon in the graduated
cylinder to the nearest tenth of a gram (0.1 gm).
B.8.3 Calculations
Weight of Activated Carbon
Apparent Density, gm/cc =
100
B.8.4 Dimensions of Funnels and Vibrator
Metal Vibrator 1-3/4-inches wide
3-1/2-inches long
3/4-inch deep
Reservoir Funnel Top diameter 3-inches
Bottom Diameter 1-5/8-inches
Overall height 4-inches
Height to flared top 3-1/4-inches
Feed Funnel Top Diameter 3-1/2-inches
Bottom Diameter 15/16-inch
Overall Height 4-inches
Height to flared top 1-1/2-inches
B-25
-------
B.9 Sieve Analysis (Dry)
The distribution of particle sizes in a given sample is obtained by mechanically shaking a
weighed amount of material through a series of test sieves, and determining the quantity
retained by or passing given sieves.
B.9.1 Equipment
Riffle, Jones Sample - Will Scientific Catalog No. L-23621
Ro-Tap - Sieve Shaker, Fisher Scientific Catalog, No. 4-906
Brush - For metal surfaces, brass wire bristle, Will Scientific Catalog No. 6916
Sieves - U. S. Standard A. S. T. M. Sieves, 8-inch diameter, full height.
Balance having a sensitivity of 0.1 gram.
B.9.2 Procedure
Reduce the sample to be tested to 100 grams by means of a riffle (see Note 1). Assemble
the nest of desired sieves in order of decreasing size of opening, the sieve having the
largest openings mounted on top. Place the 100.0 gram sample in the top sieve, install
iron cover on top of the assembly and shake on the Ro-Tap machine for three (3)
minutes with the tapper in operation (see Note 2). Weigh and report the percent of
material retained on each sieve (see Notes 3 and 4).
Notes on Procedure
1. The sample is carefully reduced by repeated passes through the riffle until the
amount collected on one of the riffle pans is close to 100 grams. The entire
contents of that pan are then emptied onto a balance accurate to 0.1 gram and
weighed. No more than 5 grams should be added to, or taken from, the balance
without additional riffling. For example, if the entire contents from the riffle
pan weighed only 90 grams, the additional 10 grams should be obtained by
riffling another sample down to an approximate 10 gram portion, after which
the entire contents of that riffle pan are emptied onto the balance. Removing
large quantities from the balance or adding large quantities from the sample
stock without riffling will lead to erroneous results.
2. When sieving samples which are finer than 100 mesh, the shaking time must be
increased. Use 10 minute intervals until less than 2 grams are collected in the
receiving pan in a 10 minute interval.
3. The sieve should be lightly brushed with a brass wire bristle brush to free
particles held in the screen.
B-26
-------
4. The analysis should be rejected if the sum of the individual fractions is less
than 98.0 grams or more than 102.0 grams.
B.9.3 Sample Calculations
Wt. Retained on
Sieve No. Sieve, gms % Retained
8 6.4 6.4
12 17.5 17.6
16 23.5 23.7
20 48.0 48.3
Pan 3.9 3.9
Total 99.3
Weight Retained on Each Sieve
% Retained = x 100
Total Wt. Retained on all Sieves
B.10 Effective Size and Uniformity Coefficient
The Effective Size is defined as the size of the particle that is coarser than 10 percent, by
weight, of the material. It is usually determined by the interpolation of a cumulative
particle size distribution.
The Uniformity Coefficient is obtained by dividing the sieve opening in millimeters which
will pass 60 percent of a sample by the sieve opening in millimeters which will pass 10
percent of the sample. These values are usually obtained by interpolation on a cumulative
particle size distribution.
Procedure
1. Run a standard sieve analysis as outlined in the sieve analysis (dry) test
procedure.
2. From the percentage retained on each sieve, the cumulative percent passing
each sieve can be obtained (see Table B-6).
3. On probability x logarithmic paper, plot the sieve opening in millimeters on the
ordinate, or vertical scale, versus the cumulative percent passing each sieve on
the abscissa, or horizontal scale (see Figure B-5).
4. The Effective Size is determined as the millimeter opening at which 10 percent
passes on the cumulative percent passing scale.
B-27
-------
5. The Uniformity Coefficient is determined by dividing the millimeter opening at
which 60 percent passes by the millimeter opening at which 10 percent passes.
TABLE B-6
EXAMPLE EFFECTIVE SIZE AND
UNIFORMITY COEFFICIENT DETERMINATION
Sieve Sieve Opening Wt. Retained on Cumulative
No. Millimeters Sieve, grams % Retained % Passing
12 1.680 0.3 0.3 99.7
16 1.190 20.7 20.9 78.8
20 0.840 49.4 49.8 29.0
30 0.590 22.0 22.2 6.8
40 0.420 6.5 6.6 0.2
Pan 0.2 0.2
99.1 100.0
Effective Size: 0.66
1.04
Uniformity Coefficient: —•— ~ 1-575
0.66
B.ll Moisture
Moisture is the percent, by weight, of water adsorbed on activated carbon.
B.I 1.1 Procedure
1. Dry an aluminum moisture dish (2-inches in diameter by 7/8-inch deep) and lid
in an electric oven for thirty (30) minutes at 110 degrees C. Cool in a
desiccator and weigh.
2. Weigh approximately 2 grams of carbon into the tared dish, recording the exact
weight.
3. Place the dish containing the carbon (lid opened to allow the moisture to
escape) in the oven and allow to dry either three (3) hours at 110 degrees C, or
two (2) hours at 140 degrees C. Close lid tightly, remove from the oven, cool
the dish in a desiccator and weigh.
An alternate method is to use a moisture balance.
B-28
-------
II 0
5 6
(3
Z 5
0 05 0 1 02
99 99.5 998 999
CUMULATIVE % PASSING
FIGURE B-5
CUMULATIVE PARTICLE SIZE DISTRIBUTION CURVE
(FOR DETERMINATION OF EFFECTIVE SIZE & UNIFORMITY COEFFICIENT)
B-29
-------
B.I 1.2 Calculation
Loss in weight during drying
Percent moisture = x 100
Initial weight of sample
For example:
Weight of dish plus sample = 15.5543
Weight of dish = 13.5478
Weight of sample = 2.0065
Weight of dish plus dried
sample = 15.4635
Loss of weight nQf)8 = -0908
Percent Moisture = 2 0065 X ^^ = 4.53%
Values reported to the nearest 0.1 percent are satisfactory, i.e., in the above case, 4.5
percent.
B.I2 Total Ash
The total ash of a carbon is a measure of the amount of the inorganic matter present.
This test is accomplished by a combustion process in which organic matter is converted
to carbon dioxide and water at a controlled temperature to prevent decomposition and
volatilization of inorganic substances as much as is consistent with complete oxidation of
organic matter.
B.I 2.1 Apparatus
Electric Furnace - Any type which can be controlled at 600 + 25 degrees C.
Evaporating Dish - Shallow form, 80 mm diameter, 20 mm height.
Analytical Balance having a sensitivity of 0.1 mg.
Desiccator.
Oven, forced air circulation capable of temperature regulation between 100 and 150
degrees C.
B.I2.2 Procedure
Heat an evaporating dish in an electrically heated furnace for thirty (30) minutes at 600
+ 25 degrees C, cool in a desiccator, and weigh. Weigh five (5) grams of the sample (dry
weight basis) - dry at 110 degrees C for three (3) hours or 140 degrees C for one (1)
hour into the tared dish, recording the exact weight of the dish and sample.
B-30
-------
Ash the sample in the furnace at 600+. 25 degrees C. The time required for complete
ashing varies with the material being tested. Heating to constant weight assures complete
ashing (leaving the sample in the furnace overnight will assure complete ashing). During
ashing, the furnace door should be left slightly open to obtain an exchange of oxygen
and gases. After ashing, cool the dish and sample in a desiccator and weigh.
B.I3.3 Calculations
(Wt. dish and ash) - (Wt. dish)
% Total Ash = - r: . . , , . x 100
Dry weight of sample
B-31
-------
APPENDIX C
METRIC CONVERSION CHART
Multiply _By To Get
Inches 2,54 Centimeters
Feet 0.3048 Meters
Square Feet 0.0929 Square Meters
Cubic Feet 0.0283 Cubic Meters
Pounds 0.454 Kilograms
Gallons 3,79 Liters
Gallons/Minute 5.458 Cubic Meters/Day
Feet/Second 0,305 Meters/Second
-------
APPENDIX C
METRIC CONVERSION CHART
Multiply By_ To Get
Inches 2.54 Centimeters
Feet 0.3048 Meters
Square Feet 0.0929 Square Meters
Cubic Feet 0.0283 Cubic Meters
Pounds 0.454 Kilograms
Gallons 3.79 Liters
Gallons/Minute 5.458 Cubic Meters/Day
Feet/Second 0.305 Meters/Second
-------
APPENDIX C
METRIC CONVERSION CHART
Multiply _By To Get
Inches 2.54 Centimeters
Feet 0.3048 Meters
Square Feet 0.0929 Square Meters
Cubic Feet 0.0283 Cubic Meters
Pounds 0.454 Kilograms
Gallons 3.79 Liters
Gallons/Minute 5.458 Cubic Meters/Day
Feet/Second 0.305 Meters/Second
C-l
------- |