PROCESS DESIGN  MANUAL
                  FOR
          CARBON ADSORPTION
U.S.  ENVIRONMENTAL PROTECTION  AGENCY
            Technology Transfer
              October 1973

-------
                              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.

-------
                                     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

-------
                            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

-------
                       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

-------
                              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

-------
                         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

-------
                         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

-------
                         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

-------
                                                      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.

-------
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

-------
                         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

-------
                                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

-------
                          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

-------
                                    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

-------
                                    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

-------
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

-------
                                    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

-------
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

-------
                                    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

-------
     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

-------
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)
                                                                                                     rts
                                                            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
                                3-60

-------
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
                                           3-61

-------
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.
                                            3-62

-------
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
                                           3-63

-------
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.
                                           3-64

-------
     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.
                                           3-65

-------
                      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
                                             3-66

-------
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.
                                           3-67

-------
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.
                                            3-68

-------
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).
                                         3-69

-------
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).
                                         3-70

-------
                                     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

-------
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

-------
      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

-------
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

-------
 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

-------