EPA 625/1-76-OOla
                          PROCESS DESIGN MANUAL
                                    FOR
                           PHOSPHORUS REMOVAL
                  U.S. ENVIRONMENTAL PROTECTION AGENCY
                              Technology Transfer
                     U.S. Environmental Protection Agfc:v-y
                     Great Lakes National Program Offica
                               .GLHPO Library
                                 April 1976

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                              ACKNOWLEDGMENTS
The original edition of this Design Manual (October 1971) was prepared for Technology
Transfer by Black & Veatch, Consulting Engineers.  This first revision to the basic text was
prepared  for Technology Transfer by the firm of Shimek, Roming, Jacobs and Finklea.
Major EPA contributors were E. F. Earth, J. M. Smith, C. A. Brunner, and J. B. Farrell of
the U.S. EPA Office of Research and Development, Cincinnati, Ohio. Major reviewers were
D. J. Lussier, J. C. Dyer, and R. M. Madancy of Technology Transfer.

Revisions to Chapters 4, 5, 10 and 11 have been made by J. Laughlin of Shimek, Roming,
Jacobs and Finklea in order to update the information in these chapters. Appendix A  has
been added to describe an EPA computer model for evaluating phosphorus removal strate-
gies.
                                     NOTICE

The mention of trade names or commercial products in this publication is for illustration
purposes and  does  not  constitute  endorsement or recommendation for use by the U.S.
Environmental Protection Agency.

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                                    ABSTRACT
The discharge of  phosphorus-containing  wastewaters  into  the  surface waters  of the
United  States has contributed to their over-fertilization and  eutrophication. As a result,
efforts are now being made  to remove phosphorus from wastewater.

This manual discusses phosphorus removal methods that  have been found  effective and
practical  for  use  at treatment  plants.  All the  methods  included  involve  chemical
precipitation of  the  phosphorus  and removal of the resultant precipitate. Precipitants
include  salts  of aluminum  and  iron,  and  lime.  The practical points  of addition are
before the primary settler, in the aerator of an activated sludge  plant, before the final
settler, or in a tertiary process.

Included in the  discussion of each treatment method  is a  description of the method,
pilot  or full-scale performance data, equipment  requirements, design  parameters,  and
costs. This information  should be of value to  designers, municipal officials, regulatory
agencies, city  planners, and treatment plant operators.
                                          111

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                            TABLE OF CONTENTS
CHAPTER                                                              PAGE

               ACKNOWLEDGMENTS                                    ii
               ABSTRACT                                              iii
               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
    2          BASIC DESIGN CONSIDERATIONS
                 2.1    Sources of Phosphorus                             2-1
                 2.2   State Regulatory Agencies                           2-2
                 2.3   State Standards                                   2-2
                 2.4   Provision for Future Plant Expansion and More
                       Stringent Effluent Requirements                     2-3
                 2.5   Flow Equalization                                 2-3
                 2.6   References                                       2-5
    3          THEORY OF PHOSPHORUS REMOVAL BY CHEMICAL
               PRECIPITATION
                 3.1    Forms and Measurement of Phosphorus                3-1
                 3.2   Chemistry of Removal by Precipitation                3-2
                 3.3   References                                       3-6
    4          PHOSPHORUS REMOVAL BY MINERAL ADDITION
               BEFORE THE PRIMARY SETTLER
                 4.1    General Considerations                             4-1
                 4.2   Phosphorus Removal Data for Alum Addition           4-4
                 4.3   Phosphorus Removal Data for Iron Addition            4-5
                 4.4   Overall Performance of Treatment Plants with
                       Mineral Addition to the Primary Settler                4-8
                 4.5    Dosage Selection and Correlation                     4-10
                 4.6   Case Histories                                     4-13
                 4.7    Costs                                            4-21
                 4.8   References                                       4-22
    5          PHOSPHORUS REMOVAL BY LIME ADDITION BEFORE
               THE PRIMARY SETTLER
                 5.1    Introduction                                      5-1
                 5.2    System Layout and Operation                       5-2
                 5.3    Case Histories                                     5-5
                 5.4    Other Experience                                  5-15
                 5.5    Sludge                                           5-23
                 5.6    Costs                                            5-30

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                      TABLE OF CONTENTS - Continued
CHAPTER                                                             PAGE

    5         PHOSPHORUS REMOVAL BY LIME ADDITION BEFORE
              THE PRIMARY SETTLER - Cont'd.
                 5.7    References                                       5-31
    6         PHOSPHORUS REMOVAL IN TRICKLING FILTERS BY
              MINERAL ADDITION
                 6.1    Pre-Design Decisions                                6-1
                 6.2    Process Options                                    6-1
                 6.3    Performance Data Using Aluminum Salts               6-2
                 6.4    Performance Data Using Iron Salts                     6-8
                 6.5    Choice of Chemical Addition                         6-8
                 6.6    Nature and Role of Chemicals Involved                 6-9
                 6.7    Dosage Selection and  Control                        6-10
                 6.8    Iron Leakage                                      6-13
                 6.9    Sampling and Analysis                              6-13
                 6.10   References                                       6-16
    7         PHOSPHORUS REMOVAL IN ACTIVATED SLUDGE
              PLANTS BY MINERAL ADDITION
                 7.1    Description of Process                              7-1
                 7.2    Mineral Selection and Addition                       7-3
                 7.3    Performance and Optimization                        7-9
                 7.4    Process Design Examples                            7-18
                 7.5    References                                       7-26
    8         PHOSPHORUS REMOVAL BY LIME TREATMENT OF
              SECONDARY EFFLUENT
                 8.1    Description of Process                              8-1
                 8.2    Typical Performance Data                           8-2
                 8.3    Criteria for Selection of Process                       8-9
                 8.4    Description of and Criteria for Choice of Equipment      8-10
                 8.5    Capital and Operating Costs                          8-19
                 8.6    References                                       8-21
    9         PHOSPHORUS REMOVAL BY MINERAL ADDITION TO
              SECONDARY EFFLUENT
                 9.1    Description of Process                              9-1
                 9.2    Summary of Design Information                      9-1
                 9.3    Laboratory and Pilot  Studies                         9-2
                 9.4    References                                       9-7
    10        STORAGE AND FEEDING OF CHEMICALS
                 10.1   Aluminum Compounds                             10-1
                 10.2   Iron Compounds                                  10-18
                 10.3   Lime                                           10-27
                 10.4   Other Compounds for pH Adjustment                 10-33
                                     VI

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CHAPTER

    10
    11
                     TABLE OF CONTENTS - Continued
STORAGE AND FEEDING OF CHEMICALS - Cont'd.
  10.5   Carbon Dioxide
  10.6   Polymers
  10.7   Chemical Suppliers
  10.8   Chemical Feeders
  10.9   Additional Reading
  10.JO  References
SLUDGE HANDLING AND DISPOSAL
  11.1   Introduction
  11.2   Generalized Assessment of Filtration Rates
  11.3   Quantity of Phosphorus Removal Sludges
  11.4   Dewatering at Specific Locations
  11.5   References
                                                     PAGE
1040
1043
1047
10-66
10-75
10-77

11-1
11-2
11-6
11-29
11-38
Appendix

    A
    B
                           LIST OF APPENDIXES
EVALUATING PHOSPHORUS REMOVAL STRATEGIES
METRIC CONVERSION CHART
A-l
B-l
                                   Vll

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                                 LIST OF FIGURES

Figure No.                                                                     Page

   4-1          Lebanon, Ohio Primary Treatment and Chemical Feeding
                Schematic                                                     4-2

   4-2          Schematic of Pre-Treatment of Plant Flow at Benton Harbor-
                St. Joseph Wastewater Disposal Plant                             4-3

   4-3          Soluble Phosphorus Removal by Ferric Chloride Addition           4-11

   4-4          Diurnal Variation of Ortho Phosphorus                            4-12

   4-5          Treatment Facilities at Pontiac, Michigan                          4-15

   4-6          Treatment Facilities at Trenton, Michigan                         4-19

   5-1          Typical Facilities for Low-Lime Addition  in Primary Treatment      5-4

   5-2          Treatment Plant at Newmarket, Ontario                           5-6

   5-3          System Layout at Contra Costa County                           5-10

   5-4          Treatment System at Rochester, N.Y.                             5-17

   5-5          Typical Effect of pH on Phosphorus Removal                     5-20

   5-6          Phosphorus Removal Process at Seneca Falls, N.Y.                  5-24

   5-7          Proposed Sludge Facility at Contra Costa County                   5-27

   5-8          Plant Scale Solids Testing System at Contra Costa                  5-28

   5-9          Sludge Classification Curves at Contra Costa                       5-29

   6-1          Richardson, Texas Treatment Plant Facilities                      6-3

   6-2          Chapel Hill, N.C. Treatment Plant Facilities                        6-6

   6-3          Phosphorus Removal by Iron Addition (Richardson, Texas)         6-12

   6-4          Iron Leakage During Phosphorus  Removal                        6-14

   7-1          Phosphorus Removal Capabilities of Activated Sludge Systems
                Receiving Settled Domestic Wastewater                            7-2

   7-2          Total Soluble Phosphorus Residual versus  Metal Ion Dose           7-4

   7-3          Influence of Point of Addition on Phosphorus Removal with
                Aluminum                                                     7-5

   7-4          Effect of pH on Phosphorus Removal from a Final Effluent         7-7
                                        IX

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                          LIST OF FIGURES - Continued

Figure No.                                                                     Page

   7-5          Comparison of the Effectiveness of Alum and Sodium
                Aluminate on Phosphorus Removal                               7-11

   7-6          Chemical Phosphorus Removal Envelope: High Rate
                Activated Sludge System                                        7-15

   7-7          0.2 mgd Biological Nitrification-Denitrification of Pilot Plant        7-16

   7-8          Effect of Aluminum Addition with pH Adjustment on Total
                Soluble Phosphorus Residual                                     7-18

   7-9          Physical Characteristics of High Rate Activated Sludge with
                Mineral Addition (8, 16)                                        7-22

   8-1          Single Stage Lime Treatment System                             8-3

   8-2          Two Stage Lime Treatment System                               8-4

   8-3          Effect of pH on Phosphorus Concentration of Effluent from
                Filters Following Lime Clarifier                                  8-7

   8-4          Typical Upflow Clarifier                                        8-11

  10-1          Typical Dry Feed System                                      10-4

  10-2          Viscosity of Alum Solutions                                    10-8

  10-3          Alternative Liquid Feed Systems for Overhead Storage            10-10

  10-4          Alternative Liquid Feed Systems for Ground Storage              10-11

  10-5          Freezing Point Curve for Commercial Ferric Chloride Solutions     10-19

  10-6          Viscosity vs Composition of Ferric Chloride Solutions at
                Various  Temperatures                                         10-20

  10-7          Typical  Lime Feed System                                     10-29

  10-8          Viscosity of Soda Ash Solution                                 10-34

  10-9          Viscosity of Caustic  Soda Solution                              10-36

  10-10         Typical Caustic Soda Feed System                              10-38

  10-11         Manual Dry Polymer Feed System                              10-44

  10-12         Automatic Dry Polymer Feed System                            10-46

  10-13         Plunger  Type Metering Pump                                   10-68

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                          LIST OF FIGURES - Continued

Figure No.                                                                     Page

   10-14         Diaphragm Type Metering Pump                                 10-69

   10-15         Screw Feeder                                                 10-71

   10-16         Positive Displacement Solid Feeder-Rotary                       10-72

   11-1          Effect of pH on Total Residual Phosphorus                       11-21

   11-2          Ratio of Lime Dose to Alkalinity (Both MG/L) for a
                Prescribed Final pH                                            11-22

   11-3          Precipitation of Calcium by Lime Addition                       11-25

   11-4          Precipitation of Magnesium by Lime Addition                     11-26

   11-5          Effect of Ferric Chloride on Sludge Dewatering                   11-36
                                        XI

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                                 LIST OF TABLES

Table No.                                                                      Page

   4-1          Phosphorus Removal Operating Data for Mineral Addition Before
                Primary Clarifier                                                4-6

   4-2          Effectiveness of Primary and Secondary Treatment with and
                without Mineral Addition for Phosphorus Removal                  4-9

   4-3          Design Data for Pontiac, Michigan                                 4-14

   4-4          Operating Data for Pontiac, Michigan                              4-16

   4-5          Design Data for Trenton, Michigan                                4-18

   4-6          Operating Data for Trenton, Michigan                             4-20

   5-1          Design and Operating Data for Newmarket, Ontario                 5-5

   5-2          Operating Results from Newmarket, Ontario                       5-8

   5-3          Construction Costs at Newmarket, Ontario                         5-9

   54          Effluent Requirements for CCCSD Treatment Facility               5-9

   5-5          Basic Data for  CCCSD                                           5-11

   5-6          Lime Treatment Results at CCCSD (12)                            5-13

   5-7          Lime and Metal Treatment Results at CCCSD (12)                  5-13

   5-8          Design Data for Rochester, N.Y.                                  5-16

   5-9          Results of Phosphorus Trial at Seneca Fails, N.Y.                    5-25

   5-10         Typical Capital Costs for Lime Treatment in Primary Facilities       5-30

   5-11         Typical Total Costs for  Lime Treatment in Primary Facilities         5-31

   6-1          Operating Data for Richardson, Texas                             6-4

   6-2          Operating Data for Chapel Hill, North Carolina                     6-7

   6-3          Iron Addition for Phosphorus Removal at Wyoming, Michigan        6-9

   6-4          Desirable Laboratory Analyses                                    6-15

   7-1          Metal Salt Comparison                                           7-8

   7-2          Comparison of Use of Alum and Sodium Aluminate at
                Pennsylvania State University                                     7-12
                                        xin

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                           LIST OF TABLES - Continued

Table No.                                                                      Page

   7-3          Comparison of Alum Addition to the Aerator and Conven-
                tional Activated Sludge at Pennsylvania State University
                for Flows Not Exceeding the Design Capacity of the Plant           7-13

   7-4          Combined Chemical-High Rate Activated Sludge System
                Performance                                                    7-14

   7-5          Summary of Design Calculations                                  7-24

   8-1          Lime Requirements                                             8-8

   8-2          Capital Cost of Lime Treating Facilities                            8-19

   8-3          Total Cost for Lime Treatment of Wastewater                     8-19

   9-1          1966 Estimated Costs for Tertiary Phosphate Removal with
                Alum                                                          9-2

   9-2          Nassau County Performance Data                                 9-3

   9-3          Nassau County Cost Estimates                                   9-3

   9-4          Removal of Total Orthophosphate by Coagulation-Clarification
                in the Dallas Demonstration Plant                                9-4

   10-1          Available Grades of Dry Alum                                  10-1

   10-2          Solubility of Alum at Various Temperatures                      10-2

   10-3          Crystallization Temperatures of Liquid Alum                     10-7

   10-4          Suppliers of Aluminum Chloride                                 10-16

   10-5          Cost of Liquid Alum Feed Facilities                              10-17

   10-6          Properties of Ferric Sulfate                                     10-23

   10-7          Cost of Liquid Ferric Chloride Feed Facilities                    10-26

   10-8          Cost of Lime Feed Facilities                                     10-32

   10-9          Materials Suitable for Caustic Soda Service                       10-39

   10-10        Carbon Dioxide Yields of Common Fuels                         10-40

   10-11        Cost of Polymer Feed Facilities                                  10-47
                                         xiv

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                           LIST OF TABLES - Continued




Table No.                                                                     Page



  10-12         Geographical Summary of Suppliers of Metal Salts and Lime        10-4-8



  10-13         Suppliers of Metal Salts and Lime                                10-49




  10-14         Polymer Sources and Trade Names                               10-59




  10-15         Soda Ash Manufacturers                                         10-65




  10-16         Types of Chemical Feeders                                      10-74




  11-1          Hypothetical Compilation of Dewatering Rates                    11-2




  11-2          Design Factors for Filtration of Conventional Sludges              11-4




  11-3          Design Factors for Filtration of Conventional Plus Metal Sludges     11-5




  11-4          Calculation of Chemical Sludge Production                        11-7




  11-5          Removal of Dissolved Materials During Chemical Addition          11-11




  11-6          Calculation of Total Sludge Mass with Metal Addition              11-14




  11-7          Information Needed to Calculate Lime Sludge Mass                11-23




  11-8          Calculation of Lime Sludge Mass                                 11-27
                                       xv

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                                    FOREWORD

The formation of the United States Environmental Protection  Agency marked a new era
of environmental  awareness  in  America. This Agency's  goals  are national in scope and
encompass broad  responsibility  in  the area of  air and water  pollution, solid wastes,
pesticides,  and radiation.  A vital part  of EPA's national  water  pollution control effort is
the constant development and dissemination of new technology  for wastewater treatment.

It is now clear that only the most effective design and  operation of wastewater treatment
facilities, using the latest  available techniques, will be  adequate to meet the future water
quality  objectives  and to  ensure  continued protection of the nation's waters. It is
essential that  this new technology be incorporated into the contemporary design of waste
treatment facilities to achieve maximum benefit of our  pollution control expenditures.

The purpose  of this manual is to provide the engineering  community and related  industry
a new source  of information to be  used in the planning, design and operation of present
and  future wastewater treatment facilities.  It is  recognized  that there are a number of
design manuals, manuals of standard practice, and design guidelines currently available in
the field that  adequately  describe and interpret current engineering practices as related to
traditional  plant design. It is the intent of this manual to supplement this existing body
of knowledge  by describing  new treatment methods, and by discussing the application of
new techniques for more effectively  removing a broad  spectrum of contaminants from
wastewater.

Much of the  information presented is  based on the  evaluation  and operation of pilot,
demonstration and full-scale plants. The design criteria  thus generated represent typical
values.  These  values should be used  as  a guide and should  be tempered with sound
engineering judgment based on a complete analysis of the specific  application.

This manual is one of several available through the Technology  Transfer Office of EPA to
describe recent technological advances and new information. This particular manual was
initially issued in October of  1971 and this edition represents the first revision to  the
basic text. Future editions  will be  issued  as warranted  by advancing state-of-the-art to
include new   data as  it  becomes available,  and  to revise  design  criteria as additional
full-scale operational information is generated.
                                        xvn

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                                    Chapter  1
                                INTRODUCTION
1.1    Purpose
The  technology for removal of phosphorus from  wastewater has developed rapidly  in
the last few years. The need for practical phosphorus removal procedures is a  result  of
the over-fertilization  and eutrophication of the Country's surface waters. This further
resulted  in  the  establishment  of  state  water  quality  standards  that limit the
concentration of  phosphorus  in  receiving  waters. As  an  example,  states that have
streams tributary  to  the  Great Lakes have  established wastewater effluent phosphorus
limits or require a fixed  percentage  reduction  of phosphorus. Several other states have
also established phosphorus  standards.

The Environmental Protection  Agency has  sponsored  many research and demonstration
studies at several  cities in the past few years  to advance  the knowledge of phosphorus
removal.  Local  and state governments and  private industries have also contributed  to
this work.  This manual is  intended to summarize process design information for the
best  developed removal methods that have resulted from  this governmental and private
effort.

1.2    Scope
This manual discusses a number of phosphorus removal methods that involve  chemical
precipitation.  Phosphorus removal obtainable   by  biological activity  alone is not  in-
cluded. Treatment  methods in which phosphorus removal occurs, but is not a  principal
objective,  are also omitted.  The latter group of processes includes ion  exchange, reverse
osmosis  and  other demineralization  treatments which at  present  are more closely
associated with wastewater renovation and reuse than  with  pollution  control. These will
be included  in updated versions  of the  manual when appropriate. One application of a
precipitation  method  that  has  been  omitted  and  which  is  of  growing  interest  is
complete lime treatment  of raw  sewage.  This application  will  be  included when the
manual is updated.
The  information included on  chemical  methods of phosphorus removal was  obtained
from  the available  literature,  progress  reports of demonstration studies,  and private
communications with investigators  actively  working in the field. Design guidelines have
been developed from  these sources.
The  information  contained  in this  manual is oriented  toward design methods and
operating procedures  for removal  of phosphorus from wastewater to  comply with state
water quality standards.  It is recognized that present  state standards may eventually be
superseded  with more stringent requirements for phosphorus removal.  Such revisions  in
state standards must  be considered  in design of treatment facilities  to minimize future
modifications to treatment plant structures.
                                          1  -  1

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Engineers are  often  faced  with circumstances  that  require  the design of  treatment
facilities with a limited amount of data, testing, and time. Such circumstances require
a more conservative design to allow for contingencies.  Since most phosphorus removal
methods are  of recent development, they fall into this category. Conservative  values are
given, therefore, when stating design parameters.
                                           1  - 2

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                                   Chapter  2
                     BASIC  DESIGN  CONSIDERATIONS
2.1    Sources of Phosphorus
Domestic  wastewater normally has a substantial  concentration of phosphorus  with  the
primary sources being a result of man's activities in the home.  Human wastes such as
feces, urine,  and waste food  disposal  account  for about 30 to 50%  of the phosphorus
in domestic  wastewater (1).  Detergents containing phosphate builders and  used princi-
pally for  laundering of clothes account  for the  remainder  of phosphorus, or about 50
to 70%. Other sources of phosphorus may cause deviation  from these percentages. For
example,  where sodium hexametaphosphate or other phosphorus compounds  are used
as corrosion  and scale  control chemicals in water supplies, the phosphorus added will
be present in the same concentration, although not  necessarily in the same form, as in
the  water supply.  This  source  can account  for 2  to 20%  of the  total phosphorus
present in the wastewater.

Industrial  wastewater  discharges  to  the  sanitary sewer system may either dilute  or
increase the  concentration of phosphorus present  in the combined wastewater. For
example,  wastewaters  from  pulp and paper  mills  may be  phosphorus  deficient and
therefore  dilution will  occur. On the other hand,  wastewaters  discharged from some
industries, such  as potato processing plants, may contain high concentrations  of phos-
phorus and  consequently may increase the phosphorus  concentration of  the combined
wastewater.

The  quantity of phosphorus  resulting from human  excretions reportedly ranges from
0.5  to 2.3  Ib  per capita  per year (2). The mean annual excretion is estimated to be
about 1.2 Ib per capita.  The mean  annual contribution of phosphorus from synthetic
detergents  with phosphate builders  is estimated to  be about  2.3  Ib  per capita,  at
present. Thus,  exclusive  of industrial wastes  and other phosphorus sources,   such  as
water softening  or sequestering agents, the domestic  phosphorus contribution to waste-
water is about 3.5 Ib per capita per  year.
On  this   basis,  the wastewater  phosphorus  concentration  may be estimated for a
community  where there  are  no  phosphorus data available.  Assuming a  population  of
5,000,  the  total  phosphorus  discharged equals   5,000x3.5=  17,500 Ib/year,   or
48 Ib/day. If a  wastewater flow  of 100 gal. per capita per day is assumed, the total
flow  is 0.5  million  gal.  per day  (mgd)   and  the   phosphorus  concentration in  the
wastewater is as follows:
                             48
                         0.5 x 8.34
                                     =   11.5 mg/1 (asP)
The  average total phosphorus concentration in domestic raw wastewater is found to be
about 10 mg/1 expressed as elemental phosphorus (P).

The  above  information  is provided to serve as a rough guide to engineers and not  as a
basis  of  design.  Sampling  of  the  wastewater   and  analyses  for  phosphorus   are
                                         2 - 1

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recommended in all cases.  It may also be necessary to survey the industries that will
be discharging wastewater to the sanitary sewer system, to determine their influence on
the concentration of phosphorus in the combined wastewater.

Among industrial sources of phosphorus may be potato processing wastes (3), fertilizer
manufacturing wastes (4), animal feedlot wastes (5), certain metal  finishing wastes (1,6),
flour processing wastes (7), dairy  wastes (8, 9),   commerical laundry  wastes (10), and
slaughterhouse wastes (11).  The amount of phosphorus may be quite variable depending
on the specific industrial plant.

2.2    State Regulatory Agencies
Each state  has  at  least one  organization responsible  for  water pollution prevention,
control,  and abatement activities.  In about half of the 50  states this  responsibility is
divided between  two state agencies. Usually one of these is the state health department
and  the  other  an organization  charged specifically by  statute with the conduct of the
state's water pollution  control  program. Although there has  been an intensification of
Federal activities in water  pollution control over the past twenty  years, much  of the
responsibility  for program  operations  rests with  the states.  Invariably  the appropriate
state agencies should  be consulted  in connection with the planning and  conduct of
water  pollution  control programs  at cities and  other  communities. The Environmental
Protection Agency  regional office personnel work closely with  state agencies  and  can
give  advice regarding the proper state agency contacts.

2.3    State Standards
As of June 1971, sixteen states had adopted wastewater effluent phosphorus standards.
In general,  these standards  have taken the form  of an  effluent concentration limit or a
requirement  for a specified percentage reduction in  the  phosphorus concentration in
the  raw  wastewater. In most  cases, effluent  concentration  limits range from  0.1  to
2.0 mg/1  as P,  with many  established  at  1.0 mg/1. Percentage reduction  requirements
range from  80 to 95%.

It should be   noted  that   neither  an  effluent  nor  a  percentage-reduction  standard
actually  limits the  phosphorus load in terms of  pounds of phosphorus discharged per
day.  Load  (Ib/day) is a direct function of both effluent  P concentration and daily
effluent volume. Assuming  the  effluent concentration standard is  being met,  an  increase
in the daily  flow  of effluent will  produce a  proportionate increase  in  the  mass of
phosphorus  discharged  daily  to  the  receiving  waters. If the  phosphorus  load  then
becomes  intolerable, adjustment downward of the effluent concentration standard  will
be  necessary. Similarly, adjustment  upward of a percentage-reduction standard will be
required if  the  phosphorus load becomes  objectionable as a result of  increased waste-
water flow  or increased P concentration in the raw wastewater or both.
 Effluent  concentration  standards  can  be  derived  from  receiving water  standards as
 indicated in the following  example.
          Receiving Water
               Phosphorus  concentration upstream             0.01 mg/1
                                           2 - 2

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         Receiving Water - (continued)
              Maximum allowable  phosphorus concentration   0.05 mg/1
              Low flow                                      140 ft3/sec (90 mgd)
         Wastewater
              Average daily  flow                             4.8  mgd
              Effluent  concentration standard                    X

         Mass Balance
              (0.01)(8.34)(90) + (X)(8.34)(4.8) = (0.05)(8.34)(90+4.8)
                                            X = 0.8 mg/1 P

Implicit in the above calculation is the assumption that the effluent is mixed thorough-
ly with the waters of the receiving stream. The low  flow selected is not necessarily the
low  flow  of record.  It  is usually the low flow  averaged over a period of 10  days or
less and having a return period  of once  in 10 years.

2.4    Provision for Future Plant Expansion
       and More Stringent Effluent Requirements
The  plant  site is  an important consideration in the design of  treatment works.  It is
highly desirable that sufficient site area  be  obtained to permit  initial construction of
the  required  system without  crowding  and  to  provide  space  for  future  expansion.
Treatment  systems are  likely to become  larger and  more complex in the future rather
than less so, and  failure to  obtain  ample site area  initially is almost certain to create
costly problems later.

Reduction  of  the  allowable effluent phosphorus concentration may  be necessary in
some states  as increases in  wastewater flow or  phosphorus  concentration of  the  raw
wastewater occur.  In some instances, merely increasing the chemical dosage may be the
only necessary change.  On  the other hand, it may  be necessary to  add an  additional
treatment sequence  such as filtration  to  the existing  facilities.  In  nearly every  case,
planning for  plant  expansion  or  more  stringent effluent  requirements  will result in
economy. Such planning should include  selection of a  plant layout that allows space
for addition  of facilities without removing existing processes from service.
Other  provisions  that  should  be  considered are  space within  chemical buildings for
additional coagulant storage and feeding equipment, space for  polymer storage and feed
equipment,  and adequate space for handling the additional solids generated by phos-
phorus removal processes.

2.5    Flow Equalization
The  cyclic  nature of  wastewater  flows,  in terms  of  volume  and  strength,  is  well
established.  While  the concept of flow  equalization  has been employed in the  field of
water supply, and in the treatment of some industrial wastes, it has not been widely
                                          2 - 3

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accepted  in  the municipal  pollution  control  field.  Anticipated problems  with solids
settling, odor, and septicity can be cited as the major factors limiting its use.

The  advent of stricter  stream standards, which  sometimes  require removal  of contami-
nants during peak flows, the elimination of plant bypassing,  and the increased removal
efficiencies  that are  possible  when  biological  or  chemical treatment  processes  are
operated at near steady-state conditions, have all  favored  the increased use of  flow-
smoothing, and  flow equalization devices ahead  of or integral with the  design of major
treatment works.

There are two major objectives in the design of flow equalization basins. The  first of
these is  simply  to  dampen  the diurnal flow variation  that  normally exists in typical
municipal wastewater collection systems to achieve  a constant or nearly constant flow
rate  through  the  downstream  treatment  processes.  In  this  type  of  system,  little
consideration  is given to controlling the concentration  changes  that  take place during
storage. The major  design factors are  supplying  enough air to keep  the basin  aerobic
and  to provide adequate mixing to prevent solids deposition.

The  second  objective  of flow  equalization is   to  provide the capacity to  distribute
shock loads of  toxic or process inhibiting substances over  a reasonable period of time
so as  to prevent system  failure and  to minimize  the periodic discharge  of harmful
contaminants  to the receiving stream or surface impoundment. Time-dependent concen-
tration profiles  and  flow-through curves are normally used to analyze the flow charac-
teristics of these systems and to determine  the  effect of tank geometry, placement of
effluent  weirs and  mixing  regime on  changes in contaminant  concentrations through
the basin.

In all cases the  added costs  of flow  equalization must be measured against the possible
reduction in  downstream process costs  and the  increased   efficiencies that  can  be
achieved by operating these processes under constant loading  conditions.
                                           2 - 4

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2.6    References

 1. "Phosphates in Detergents and the Eutrophication of America's Waters", Hearings
    before a  Subcommittee  of the Committee on  Government  Operations, House  of
    Representatives, 91st Congress, December  15-16,  1969,  U.S. Government  Printing
    Office, Washington (1970).

 2. Task  Group  Report, "Sources of Nitrogen  and  Phosphorus in Water  Supplies",
    JAWWA, 59:3, p 344 (1967).

 3. Mackenthun,  K. M.,  "The Phosphorus Problem", JAWWA, 60:9,  p 1047 (1968).

 4. Nemerow,  N. L.,  Theories and Practices of Industrial  Waste  Treatment,  Addison -
    Wesley, Reading,  Mass. (1963).

 5. Relationship of Agriculture to Soil and Water Pollution,  Cornell University Confer-
    ence on Agricultural Waste Management, Rochester, N.Y., Jan. 19-21, 1970.

 6. Anderson,  J. S., and  lobst, E. H.,  Jr., "Case History of Wastewater Treatment in a
    General Electric Appliance Plant", JWPCF,  40:10, p 1786 (1968).

 7. Dickerson,  B.  W., and  Farrell, P. J.,  "Laboratory  and Pilot  Plant   Studies  on
    Phosphate  Removal from  Industrial Wastewater", JWPCF, 41:1, p 56 (1969).

 8. McKee,  F. J., "Dairy Waste Disposal  by  Spray Irrigation", Sew.  & Ind.  Wastes,
    29:2, p  157  (1957).

 9. Lawton, G. W., et al.,  "Spray  Irrigation of Dairy Wastes",  Sew.  &  Ind.  Wastes,
    31:8, p 923 (1959).

10. Flynn, J. M., and  Andres, B.,  "Launderette  Waste Treatment Processes",  JWPCF,
    35:6, p783 (1963).

11. Wymore, A. H., and White, J. E., "Treatment of  Slaughterhouse Waste Using Anaer-
    obic and Aerated Lagoons",  Wat.   & Sew.  Works,  115:10,  p 492 (1968).
                                         2 - 5

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                                   Chapter  3
                  THEORY  OF  PHOSPHORUS   REMOVAL
                      BY  CHEMICAL  PRECIPITATION
3.1    Forms and Measurement of Phosphorus
Phosphorus  is  found  in wastewater  in three principal  forms:  orthophosphate  ion,
polyphosphates or condensed phosphates,  and organic phosphorus compounds. Ortho-
phosphate was  in the past often considered to be  PO,^  and was  reported in this way.
Actually,  there  are  a number of  forms of  orthophosphate  in  equilibrium, with the
predominant form changing  as pH  changes. At the  usual pH of municipal wastewater,
the predominant form is  HPO^".  With the present practice of reporting phosphorus as
P, one  does  not usually have to  be  concerned with the  actual  form.  It  is well to
remember, however,  that  the predominant form does change with pH. The  removal of
phosphorus with lime results primarily  from pH increase. Polyphosphates can be looked
upon  as polymers of phosphoric acid from which water has been removed. Materials of
various  molecular weight  are in widespread use. Complete hydrolysis  results in forma-
tion of orthophosphate.  The chemistry of organic  phosphorus compounds is complica-
ted. Their decomposition  also leads to  orthophosphate.

In raw  sewage there are substantial amounts  of all  three principal phosphorus forms.
During  biological  treatment,  significant changes take place.  As  organic materials are
decomposed,  their phosphorus content is  converted to orthophosphate.  On the  other
hand, inorganic phosphates  are utilized in forming biological floe. The polyphosphates
are for  the most part  converted to orthophosphate.  The result is that in  a well treated
secondary  effluent,  a  large  fraction of the  phosphorus is present as orthophosphate.
From the standpoint of  removal by precipitation,  this is fortunate  since the  orthophos-
phate is the easiest form to  precipitate.

Because phosphorus  will be  present in a variety of forms, both organic and inorganic,
the only satisfactory measure of treatment plant  removal  efficiency  must be based on
total  phosphorus  entering  the plant  in  the raw  wastewater and   total  phosphorus
discharged  in  the plant  effluent.  Inasmuch  as  all  colorimetric  tests for phosphorus
depend  upon the formation  of an  orthophosphate color  complex, it is essential in the
determination  of total phosphorus, to convert any polyphosphates  (condensed  phos-
phates)  and organic phosphorus  compounds  present  in the sample  to the  orthophos-
phate form. This  conversion  is accomplished  by  acid digestion of the sample in the
presence  of a  strong oxidizing  agent. Standard  Methods,  13th  edition (1), describes
several  procedures for determining  total phosphorus  as  well  as  the various forms of
phosphorus in wastewater.  A suitable procedure  for measuring  total phosphorus, in-
cluding the  preliminary  digestion  stage,  may be  selected  from  this  reference.  An
automated method  is described in FWPCA  Methods for Chemical Analysis of  Water
and Wastes (2).
                                          3  - 1

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3.2    Chemistry of Removal by Precipitation
The  materials found practical  for phosphorus precipitation include the ionic forms  of
aluminum, iron, and calcium.  The calcium is added as lime and the hydroxyl ions also
have a  role in phosphorus  removal.  The  chemistry of  phosphorus  removal by inter-
action  with metallic ions is complex. In the interests of brevity and simplicity, it is
assumed  in  the  following discussion  that  phosphorus  reacts  as the orthophosphate
          1}
form, PO4  , and that the reaction  products are as indicated. The polyphosphates and
organic  phosphorus are also removed, probably  by a combination  of more  complex
reactions and sorption on floe  particles. The  reactions  presented and the associated
computations are principally for  illustrative purposes and do not  purport to represent
the  true  reactants,  products  and  reaction mechanisms. Calculated  requirements  for
phosphorus  precipitants must  be viewed  as  no more  than  crude estimates subject  to
large variations in actual practice because the forms of phosphorus and the precipitates
may be substantially different  from those assumed.

       3.2.1   Aluminum Compounds as Phosphorus Precipitants
Aluminum  ions can combine with  phosphate ions to  form aluminum phosphate  as
follows:
                           A13+ +  PO43'	 A1PO4

The  above  equation  indicates  that the mole  ratio for  A1:PO4  is 1:1.  Inasmuch as the
mole ratio  of P:PO4 is also 1:1, the mole ratio  for  A1:P is 1:1  or 4f= 1  when both
aluminum and phosphorus  are  expressed  in terms of gram-moles or Ib-moles.  On  a
weight,  rather than a mole  basis, this means that 27 Ib  of Al will react with 95 Ib of
PO4 to form  122  Ib  of A1PO4.  Since  each  95 Ib (1 Ib-mole)  of PO4 contains 31 Ib
(1 Ib-mole) of P,  the weight relationship between  Al and  P is 27 Ib of Al to 31 Ib of P
or 0.87 for  this reaction.

The  principal  source of  aluminum for use in phosphorus precipitation is  "alum",  a
hydrated aluminum sulfate,  having the approximate formula  A^CSC^)^  HI^O (mol-
ecular  weight  of 594).   The chemical,   which  is also  known  as  "filter alum"  or
"papermaker's  alum",  averages  about 17% soluble aluminum  expressed as A^O-^  or
about  9.1%  expressed  as  AL  Its reaction with  PO4   may  be written as follows:

            A12(S04)3   14H20  + 2P043-*2A1P04 +  3SO42' + 14H2O

The  sulfate  remains  in solution  as SO4  . The above reaction  indicates that 1  Ib-mole
of  alum  (594 Ib)  will   react with  2 Ib-moles  (1901b) of PO43"  containing  62  Ib
phosphorus  to form  2  Ib-moles (244 Ib) of  A1PO4- The  weight  ratio of  alum  to
phosphorus  is,  therefore,  9.6:1.  The  alum requirement per pound of  phosphorus may
also be derived from the  A1:P  mole ratio as follows:
            Mole  ratio  A1:P  =  1:1
            Therefore weight ratio A1:P = 27:31 = 0.87:1
            Alum contains 9.1% Al
                                                 0 87
            Therefore,  alum required per Ib of  P  =   '    = 9.6 Ib
                                           3 - 2

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Stumm  and Morgan (3), state that the solubility of A1PO4 is pH dependent  and varies
as follows:
                                          Approximate
                              pH       Solubility (mg/1)
                               5              0.03
                               6              0.01 (minimum solubility)
                               7              0.3

The  optimum pH  for removal  of phosphorus probably lies in  the range of 5.5  to 6.5,
although some removal occurs above pH  6.5.

Addition  of alum will  lower  the pH  of wastewater  because of neutralization  of
alkalinity  and  release  of carbon  dioxide.  The  extent  of pH reduction will  depend
principally  on  the  alkalinity of the wastewater. The higher the alkalinity,  the  less  is
the  reduction  in  pH  for  a given  alum dosage. Most wastewaters  contain  sufficient
alkalinity so that even large alum dosages will  not  lower the  pH below about 6.0 to
6.5.  In  exceptional cases of low  wastewater alkalinity, pH reduction may be so great
that  addition of an alkaline  substance,  such  as sodium hydroxide, soda ash, or lime  will
be required.

Adjustment of the pH downward can  be accomplished by the  addition of sulfuric acid
but  this complicates the treatment  process and  it may be preferable simply to use a
higher alum dosage.

Bench,  pilot, and  full-scale studies have shown that considerably  higher  than stoi-
chiometric   quantities  of alum usually   are  necessary to meet phosphorus removal
objectives.  A competing reaction, responsible for the  pH reduction mentioned  above,   at
least partially accounts for the excess alum requirement. It  occurs as follows:

       A12(SO4)3  14H2O + 6HCO3'2A1(OH)3  + 6CG>2 +  14H2O + 3SO42'

The  following  ratios  of alum  (9.1%A1)  to  phosphorus are  believed reasonably repre-
sentative for alum treatment of municipal wastewater (4).

        D  D .  ,.                      A1:P                      Alum:P
        P  Reduction        		      	
          Required         Mole Ratio       Weight Ratio      Weight  Ratio
            75%             1.38:1             1.2:1               13:1
            85%             1.72:1             1.5:1               16:1
            95%              2.3:1             2.0:1               22:1

To achieve 85% P removal from a wastewater containing 11 mg/1 of P the alum dosage
needed would be (16)(11)= 176 mg/1 or  1470 lb/106  gal.

Sodium  aluminate  will also serve  as  a source of aluminum  for  the precipitation of
phosphorus.  The  chemical  formula for sodium aluminate  is  Na2Al2O4 or  NaAlO2.
                                         3 - 3

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One commercial form is the granular trihydrate, which may be written Na2O  AUOo  3H2O
and which contains about 46% A12O3 or 24% Al.

The sodium aluminate - phosphate reaction may  be represented as follows:

           Na2O.Al2O3  + 2P043' +  4H2O	> 2A1PO4  + 2NaOH  + 6OH~

In contrast to  alum,  which reduces pH,  a  rise  in pH may be  expected upon addition
of sodium  aluminate to wastewater.

The above  reaction  indicates  an A1:P  mole ratio  of 1:1, an   A1:P weight ratio  of
0.87:1, and a sodium  aluminate to P weight ratio  of about 3.6:1.

As  with the use of alum, mole and weight ratios  somewhat in excess of the theoretical
must be anticipated in practice.

       3.2.2  Iron Compounds as Phosphorus Precipitants
Both  ferrous  (Fe2+)  and  ferric (Fe3+) ions  can  be used  in  the  precipitation  of
                    Q I
phosphorus. With  Fe   a reaction  can be  written similar to  that  shown earlier for
precipitation of aluminum phosphate.  A 1:1 mole ratio of Fe:PO4  results.  Since the
molecular  weight of iron is 55.85, the weight ratio of Fe:P is 1.8:1.  Just as in the  case
of  aluminum,  a  larger  amount  of iron  is  required  in actual situations  than  the
chemistry  of the  reaction predicts.  With Fe2+ the situation is  more  complicated and
not fully  understood.  Ferrous phosphate  can be  formed.  The  mole ratio of  Fe:PC>4
would be 3:2. Experimental results indicate, however, that when Fe2+  is used, the mole
ratio of Fe:P will  be essentially the same as  when Fe3+ is used.

A number of  iron salts  are available  for use in  phosphorus precipitation. These include
ferrous sulfate, ferric sulfate, ferric chloride, and pickle liquor. Additional discussion of
these  is given  later.  All  will lower the pH of wastewater  because of neutralization  of
alkalinity.  Pickle liquor  contains substantial amounts of  free sulfuric  acid  or  hydro-
chloric acid.

Iron salts   are most effective for phosphorus removal at certain pH values.  For Fe3+
the  optimum pH range is  4.5 to 5.0. This is an unrealistically low pH, not attained in
most wastewaters.  Significant removal of phosphorus can be attained  at higher pH. For
  0-4-
Fe^   the   optimum pH is about  8 and good phosphorus removal can  be obtained
between 7 and 8.  The  acidity of ferrous salts,  and especially pickle  liquor, necessitates
addition of lime or sodium hydroxide  for  good results.  Where the  water  is aerated
following Fe^+ addition, the use  of a base may not be necessary.

       3.2.3   Lime as a Phosphorus Precipitant
Calcium ion reacts  with phosphate  ion in  the presence of  hydroxyl ion  to form
hydroxyapatite. This material has a variable composition, but an  approximate   equation
for  its formation can be written as follows, assuming in this case that  the  phosphate
present is  HPO4  .
             3 HPO42' + 5Ca2+ + 4OH~ 	>  Ca5(OH)(PO4)3 + 3  H2O
                                         3 - 4

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The  reaction is pH dependent. The solubility of hydroxyapatite is so low, however,
that  even at a pH as  low as 9.0,  a large fraction of  the phosphorus can be removed.
In lime treatment of wastewater, the operating pH may be predicated  on the ability to
obtain good suspended solids removal rather than  on phosphorus removal.

Although  it is  possible to calculate an approximate  lime dose for phosphorus removal,
this is generally not necessary.  In  contrast to iron and  aluminum salts, the lime dose is
largely determined by other reactions that take  place when  the  pH  of wastewater is
raised.  Some  of  these  reactions  are discussed  later. Only in  waters of  very  low
bicarbonate alkalinity  would  the phosphate  precipitation  reaction  consume  a  large
fraction of the lime added.
                                         3  - 5

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3.3    References

 1. Standard Methods for the  Examination of  Water and Waste-water, 13th Edition,
    American Public Health Assoc., New York  (1971).

 2. FWPCA  Methods  for Chemical Analysis  of Water and Wastes,  Federal Water
    Pollution Control Administration, U.S. Department of the Interior (Nov,  1969).

 3. Stumm,  W.  and  Morgan,  J. J.,  Aquatic  Chemistry,  p  521  Wiley-Interscience,
    John Wiley & Sons, Inc.,  New  York (1970).

 4. Allied Chemical  Corporation,  Industrial Chemicals  Division, "Use of Aluminum
    Sulfate for Phosphorus Reduction in Wastewaters", Unpublished  paper.
                                         3 -6

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                                    Chapter   4

                  PHOSPHORUS   REMOVAL  BY  MINERAL
              ADDITION  BEFORE  THE  PRIMARY  SETTLER
4.1    General Considerations

Removal  of phosphorus  from  wastewater can  be  accomplished  by modifying the
conventional  primary  treatment  process  to   include  chemical   precipitation  with
aluminum  or  iron  salts (1,2). The advantages  of phosphorus removal during primary
treatment  include flexibility in  chemical  feeding, adequate reaction times and mixing
conditions,  flocculation and  removal, of more suspended solids and  suspended BOD in
the primary settler, and  reduced  loading of suspended solids and  BOD  to  secondary
treatment  processes.  Significant  increases  in removals of both  suspended  solids and
BOD   can   occur concurrently  with  phosphorus  removal.   Phosphorus  removal  by
chemical addition is  amenable to  automatic control using process  instrumentation to
measure waste flow and/or phosphorus concentration.

The disadvantage of  addition of metal salts during  primary  treatment alone is that a
significant  amount of  the  phosphorus may not be in  the  ortho  form and may not be
easily  precipitated.  Higher phosphorus removals  can be obtained with chemical addition
beyond primary  treatment and with chemical additions at several points.

The  available  precipitation-flocculation  processes (3,4,5,6,7,8)  include   addition  of
ferrous or  ferric chloride,  ferrous  or  ferric  sulfate, aluminum  sulfate,  or  sodium
aluminate,   followed  by  flocculation  using  an  anionic  polymer   to  enhance  solids
separation.  A  strong  base  is often  added between  additions  of ferrous  iron  and
polymer to counteract the depression of pH by  the ferrous compounds.

In order  to provide effective  chemical additions to primary treatment units, the following
sequence is recommended:

       1.   Salt addition to raw sewage with thorough mixing. If a  base is to  be  used,
           it should be added  at least 10  seconds later.
       2.   Reaction for at least  five minutes.
       3.   Addition  of anionic  organic polymer  followed  by  flash  mixing  for  20 to
           60  seconds.
       4.   Mechanical  or air flocculation for 1  to 5  minutes.
       5.   Gentle delivery  of flocculated wastewater  to sedimentation units.

Mixing may be carried out in  specially designed  basins or advantage may be taken of
existing high turbulence areas  such as in  a Parshall  flume. Flocculation may  similarly
be carried out in specially constructed equipment or may be allowed to take place within
some  part of an existing system. Schematic diagrams of 2 plants, which demonstrate how
existing equipment can be  used with  mineral addition, are shown in Figures 4-1  and 4-2.
                                       4-  1

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The points of chemical addition will vary depending  on the particular situation.  It  is
important, however, that addition  points be  downstream of  return  streams, such as
digester  supernatant, if a high  degree  of phosphorus  removal is  required.

Optimum conditions for phosphorus  removal processes are best determined in two steps:
a laboratory feasibility study followed preferably  by  full-scale  plant trials if the plant
exists, or by pilot trials. The feasibility study should be a short-term laboratory evaluation
of  various chemical systems  to obtain preliminary estimates of chemicals required to
meet established phosphorus  removal standards. During the  plant trials,  chemicals  and
equipment should  be supplied for full-scale operation over a period of 30 days or longer,
to  obtain  detailed  design data.

Chemical  removal  of  phosphorus  from  wastewaters during  primary treatment  is  a
practical and  controllable process which  can  result  in  low  discharges of phosphorus
from existing primary  treatment plants  and secondary  treatment plants  of either the
trickling filter or  activated sludge type. Additional costs  for chemicals  and attendant
mixing, dispersing, and  monitoring equipment are moderate.

Data and  correlations given in  this chapter will  provide  guidance and permit making
design estimates. However, it would  be risky  to eliminate on-site  experimental studies
because  of   variations  in  equipment  design  and  operation,  and  in  wastewater
characteristics.

4.2    Phosphorus  Removal Data for Alum Addition

Alum  has been used  as  a  source of  aluminum  for  phosphorus   removal  in  raw
wastewater. Sodium aluminate  can  also  be used  if  the  natural  alkalinity of  the  raw
wastewater is too  low to prevent excessive reduction of pH  by alum.  However,  no
investigations  using aluminate  have  been  reported.  Tests  have  been  conducted  on
laboratory, pilot, and  plant scales to determine the feasibility of alum addition to  raw
wastewater.

Bench-scale tests of alum addition  were  conducted at Springfield,  Ohio  (9) and  Two
Rivers, Wisconsin  (10). All  bench  testing was  conducted  in the following  manner.
Samples of wastewater were  stirred  on a six-place stirrer  for approximately 2  minutes
at  100 rpm, followed by 18 minutes of gentle  stirring  (40  to  50 rpm). Alum additions
were made during  the  rapid  mix period.  When polymers  were used,  they were added
approximately 2 minutes after the  alum  addition. Treated  samples  were  allowed to
settle  for 30 minutes before total phosphorus analyses were made.

The respective states have required phosphorus  removals of 80% at Springfield  and 85%
at  Two  Rivers. At Springfield, an  average A1:P weight ratio of 1.9:1 (molar  ratio of
2.2:1)  was required  to  reduce the average influent  total phosphorus of 5 mg/1 by 80%.
Raw wastewater at  Two  Rivers required an average A1:P weight ratio of 0.93:1 (molar
ratio of 1.07:1)  to  reduce  the average  influent  phosphorus of 20.1 mg/1 by 85%. These
test data indicate  that  as  phosphorus  concentration increases, the A1:P ratio necessary
                                        4-4

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to obtain a specific per cent removal decreases. Individual tests at Two Rivers,  for  a
broad  range  of influent  phosphorus concentrations, also showed  the same variation.
Influent  total phosphorus ranged from  7.6 to 28.5 mg/1, and the A1:P weight  ratios
necessary to remove 85%  ranged  from 2.0:1 to 0.58:1, respectively.

A study  of alum addition for phosphorus removal was conducted at Lebanon, Ohio on
both  pilot and  plant  scales  (11) to  determine  whether chemical  treatment of raw
wastewater  could   be  used  successfully  to precede  activated  carbon  adsorption  for
organic removal.

A 15 gpm   pilot plant  was utilized to determine the most effective dosages  of alum  to
be studied  in  the  full-scale tests.  Data from the pilot  plant indicated that liquid alum
dosages  of  150,  250, and  350 mg/1, as A^SO^-j- HF^O, and  anionic polymer
dosages  of 0.25   and  0.5   mg/1  should  be evaluated. Only  the  Parshall  flume,
preaeration basin,  and  primary  clarifiers of the 1.5 mgd Lebanon plant were used  in
this  study.  Alum   was  fed  to  the  raw wastewater  at  the  Parshall flume to assure
complete mixing. The  preaeration basin was used for flocculation, with polymer being
added  toward the  end  of the  basin. The primary basins served as  settlers for the
precipitated  phosphorus.   Figure  4-1  shows  the   chemical  addition  arrangement  at
Lebanon which  was used  for  both alum and iron  studies. The  iron experiments will be
covered later in  this chapter.

Each  dosage was evaluated for five  days. A polymer dose of 0.5  mg/1  was found  to
be satisfactory for  improving  floe formation and  settling. An  alum dose of 250  mg/1,
A1:P weight ratio of 3.4:1  (molar ratio of 3.9:1), removed 93% of the phosphorus  in
this  high  alkalinity   (400  mg/1  as  CaCOo)   wastewater.  Effluent  phosphorus
concentration did not  exceed 0.7 mg/1  and averaged 0.5 mg/1. The alum dose of 150
mg/1,  A1:P  weight  ratio  of  1.5:1 (molar ratio of  1.7:1), removed only  74% of the
phosphorus; while  the alum  dose of  350 mg/1, A1:P weight ratio of 3.9:1 (molar ratio
of 4.5:1), reduced  the  phosphorus by  94%. The alum dose needed  to  meet the State
removal  requirement of  80%  would  fall  between  the 150  and  250 mg/1  dosages
studied.

4.3    Phosphorus  Removal Data  for Iron Addition

Operating data from several plants utilizing mineral addition before the prynary clarifier for
phosphorus removal are shown in Table 4-1.

With  primary treatment alone, phosphorus removals varied from 60  to 91%. In secondary
plants, iron addition before the primary resulted in phosphorus removals from 75 to 93%
over the entire plant. Iron doses varied between 10 and 90 mg/1, as Fe. The Lebanon study
showed that doubling the  iron dose (from 45 to 90 mg/1) with the same polymer addition
raised  phosphorus removal from 68 to 91%. Polymer  doses in all of the iron studies ranged
from 0.26 to 0.7 mg/1.
                                       4-5

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Iron carry-over occurred at Mentor, where  FeC^ addition alone resulted in an effluent
Fe  concentration of 42.5 mg/1.  Lime addition reduced the iron  leakage to an effluent
Fe  concentration of 11.6 mg/1. Polymers were ineffective in reducing iron  leakage.

Increased  suspended solids and BOD removals were  also obtained with  iron additions.
At  Grayling, Michigan, suspended  solids  removal was increased  by 27% to an  average
of  78%. At Benton Harbor, Michigan, where waste  activated  sludge is returned to the
primary,  iron  addition gave a  3.0% increase in solids removal  over the entire treatment
plant. An example of increased BOD  removal is seen  in the Grayling, Michigan study.
Removal  of BOD  in  the  primary was  increased  by  45%  after  iron  addition. This
resulted in a total BOD  removal of 58% in  the primary.

Typical  values  for  primary  settler  detention times were 2.3 hours  at  Mentor and 2.25
                                                                  3
hours at Benton Harbor. At Mentor, air at a r.ate  of  42.5  to 85 ft /minute was used
for flocculation in  the mixing area of the primary tank.

Although  lab  test  procedures should be  adjusted to best approximate individual  plant
conditions,  outlines of procedures used at two  locations may be useful as guidelines.
Jar tests were  conducted at Mentor in the following manner. Iron, lime,  and  polymer
were  added one minute apart  to  1,000  ml of raw wastewater at a  stirrer speed of 100
rpm.  The chemicals and raw wastewater were then  mixed for five minutes at  20 rpm,
and finally  the mixture was allowed to settle quiescently for  1/2 hour before a  portion
of the supernatant was pipetted  off for analysis.

4.4 Overall Performance of Treatment Plants with Mineral
    Addition to the Primary Settler

    4.4.1     Primary Treatment Alone

The relative efficiencies  of  primary and secondary treatment with and without primary
phosphorus  removal are  summarized   in  Table 4-2.  Phosphorus  removal  without
chemical precipitation  in the  primary  clarifiers  ranges  from only 10 to  20% through a
conventional secondary  treatment plant.  At least one  half or more of this removal is
due to  sedimentation  of  the  insoluble  phosphorus fraction  in the raw wastewater
during primary clarification. The  addition  of the  precipitation-flocculation process  in
primary  clarification will  result  in 70  to 90% removal  of  total  phosphorus in the
primary.  These  removal  levels  can  be  expected  only in well  designed  primary  clarifiers
that are not hydraulically overloaded. Suspended solids removals in the primaries will
be  increased from  40 to 70% to 60 to 75%. This increase occurs despite the additional
solids  generated  by phosphorus  removal.  BOD removals in  the primaries  will  be
increased  from  25 to  40%  to  40  to 50%.  The  additional  removal  is  primarily due  to
the suspended  BOD fraction.

       4.4.2   Effect on Secondary Treatment

Additional  phosphorus  removal through either trickling filter  or activated  sludge units
following  chemical precipitation  in  the primaries  can  amount to  10 to 15%. This
                                        4-8

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removal  is  attributed to  biological  flocculation.  Split addition  of metal in  both the
primary  and secondary portions of the plant should  be considered  if exceptionally high
levels  (>90%)  of  total  phosphorus  removal  are  desired.  Addition points  for the
secondary  metal  feed  at  or  near  the  effluent  end of the  biological treatment unit
should be included  in the design.

Increased capture of suspended  solids  in the primaries results  in  reduced  loading to the
secondary  units.  Although  the  solids entering the  secondary are reduced,  the  liquid
volumes  remain  the  same  and, therefore,  normal  detention times  should  be  used.
Essentially the  same amount of soluble BOD  must  be insolubilized  and removed. The
additional  removal  of  suspended solids  and BOD across the  primaries will  reduce the
amount  of  waste activated  sludge to  be  handled. Savings  in plant operating costs may
result  from  reduced  air  requirements for aeration, decreased  chlorine demand,  and
improved sludge filterability (28).


4.5    Dosage Selection and Correlation

The material  presented  in Chapters 6 and  7 on choice  of  chemicals and  dosage  in
trickling  filter  plants and  activated  sludge plants  generally  applies also   to  mineral
addition  in  primary plants. Therefore,  the  reader  is  referred  to these chapters for
discussions  of  requirements for influent  phosphorus data,  procedures  for obtaining
dosage design data,  calculations  of daily  doses, and  scheduling of dose rate  changes to
match phosphorus  variation. The  reader  is  also referred to  Chapter  10   for general
information on  various  chemicals.  Material  presented here  will be limited to comments
and/or data on dosage selection, dosage  correlation,  and influent  phosphorus variations.

It is  generally  desirable  to plot or correlate  test results  on  a  simple basis to  make
them  more  useful. A reasonably good correlation can be  obtained by plotting the log
of  the fraction of soluble phosphorus remaining  as  a function of the weight ratio  of
metal  to soluble phosphorus.    Typical of  such plots  is Figure  4-3, where both the
fraction  of  soluble  phosphorus  remaining and  the percent  removed are plotted on the
log scale. The data in  Figure  4-3 are  from  several ferric  chloride  phosphorus removal
studies conducted in the Great Lakes region.

Since there is usually considerable scatter in the data, such correlations should be used
very  conservatively  as  a  guide  for  predicting doses. On-site  tests under actual plant
conditions  are always preferred as  the  basis  for such a  plot. The  required ratio  of
metal  ion  to influent  soluble phosphorus  for  a  specified  phosphorus removal can  be
obtained from such a plot. This ratio is multiplied  by the soluble influent  phosphorus
concentration in mg/1 to determine  the required chemical dose in mg/1.

As  will  be  discussed in  Chapter 6,  the  dose rate should  be varied during  the day  to
match more closely the  varying influent phosphorus concentration. The need for doing
this is illustrated by  Figure 4-4 where  some  typical data on the diurnal variation  of
ortho phosphorus in plant influent are presented.
                                       4-10

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                AVERAGES FOR 5-DAY WEEK INFLUENT TO PLANT
                     FLOW = 5.15 mgd
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                     SUSPENDED SOLIDS = 182 mg/1
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      FIGURE 4-U DIURNAL  VARIATION  OF  ORTHO  PHOSPHORUS
                                 4-12

-------
4.6    Case Histories

This section presents information on design and operation of three treatment plants which
remove  phosphorus by adding metals before primary settling and by adding polymers as
required to supplement these metals.

The plant at Pontiac, Michigan employs commercial grade ferric chloride as a metal source;
Trenton, Michigan uses waste pickle liquor; Waukegan, Illinois has successfully used three
liquid forms of metals: ferric chloride, alum, and waste pickle liquor. Operations have been
effective at all three plants, and details  are  presented  here  to  illustrate the  variety of
approaches to phosphorus removal which are presently being applied successfully.

       4.6.1  Pontiac, Michigan

The Auburn Plant in Pontiac, Michigan is a conventional activated sludge treatment plant
with an average design flow of 10 mgd. The facility was constructed in 1963 according to
design parameters presented in Table 4-3. Very simple chemical feed facilities were added to
permit addition of ferric chloride and polymers to the primary section of the plant as shown
in Figure 4-5.

A test program in  1969 (21) showed that feeding  ferric chloride and polymer ahead of the
primary clarifier was an effective procedure to remove 80  to 90 percent of total phosphorus
in the wastewater. Long-term analysis of concentrations and forms of phosphorus in plant
influent indicate soluble compounds represent 60 to 80 percent  of the  total phosphorus
present, and that orthophosphates represent 35  to 45 percent of total phosphate. There
appeared to be minimal iron leakage in the effluent, and overall plant performance, in terms
of BOD and SS removals was improved by this technique.


 The best point for addition of ferric chloride was just before the aerated grit chamber at the
 head of the plant. Theoretical displacement through the grit chamber was  approximately 10
 minutes, but  observations indicated  actual detention was  more on the order of 2  to 5
 minutes at average  flow rates.  This  was  sufficient time, however, for mixing and initial
 flocculation of the  metal salt.  Passage through the grit unit provided adequate lag  time
 before polymer addition.

 Since 1972, the plant has been operating approximately  as shown by the performance data
 in Table 4-4 (29).

 These  data, mostly  derived  from 1973 experience,  reflect a high-quality effluent and
 well-stabilized sludge. When feeding chemicals, the primary section of the plant removes 40
 to 60 percent of incoming BOD, 50 to 75 percent of incoming SS, and 50 to 75 percent of
 incoming total phosphorus.
                                       4-13

-------
                                     Table 4-3

                     DESIGN DATA FOR PONTIAC, MICHIGAN
Description

Design Flow, mgd
     Average Dry Weather                                                      10
     Peak Dry Weather                                                        20
     Maximum                                                                36

Primary Clarifiers
     Detention Time, 1 hr                                                        1.5
     Overflow Rate, 1 gpd/sq ft                                              1,000
     Sludge Solids Concentration, percent                                          6.5
     Sludge Volume, percent of total flow                                          0.08

Aeration Tanks
     Detention Time,^ hr                                                       6.5
     MLSS, mg/1                                                      2,000-3,000
     Return MLSS, percent                                                     40

Final Clarifiers
     Detention Time,^ hr                                                        1.9
     Overflow Rate,1 gpd/sq ft                                                790

Sludge Digesters
     Total Active Volume, cu ft                                            19 5,000

Vacuum Filters
     Total Area,  sq ft                                                         375
     Nominal Capacity, psf/hr                                                    4

' Based on Average Flow
There has been no evidence of serious problems related to escape of colloidal iron from the
treatment system. Some 2 to 3 mg/1 of soluble or colloidal iron is found both  in plant
influent and effluent.

Both ferric chloride and polymer are needed in this operation for good overall performance. If
iron  dosage is reduced below the indicated mole ratio of 1.7, or if polymer addition is
discontinued, effluent quality begins to degrade in a matter of a few hours.
                                      4-14

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                                    Table 4-4

                   OPERATING DATA FOR PONTIAC, MICHIGAN
Description

Flow, mgd                                                                    10

Influent Characteristics
     BOD,mg/l                                                              100
     SS,mg/l                                                                140
     Total P, mg/1                                                              5

Chemical Addition
     Iron Dose, mg/1                                                           15
     Iron Dose, Fe/P                                                            1.7
     Polymer Dose, mg/1                                                        0.3

Overall Plant Performance
     Effluent BOD, mg/1                                                       10
     Effluent SS, mg/1                                                         20
     Effluent Total P, mg/1                                                      1
     BOD Removal, percent                                                    90
     SS Removal, percent                                                      86
     Total P Removal, percent                                                  80

Digesters
     Temperature, deg F                                                       90
     Solids Loading, Ib VSS/cu ft/day                                            0.09
     Digested Sludge Concentration, percent                                       7.2
     Digested Sludge Volatile Fraction, percent                                   45

Vacuum Filters
     Loading, psf/hr                                                          3-4
     Cake Solids Concentration, percent                                       30-35
Volume of sludge produced by chemical addition is approximately the same as generated
during conventional treatment. The chemical sludge is more concentrated but there have
been  no problems with digestion  or  dewatering of sludges produced in this location.
Digested sludge is conditioned with ferric chloride and lime (at about the same dosage rates
as previously required for conventional sludge treatment) prior to vacuum  filtration. Cake
forms  readily on the filters but at modest yield rates. Both the vacuum filters and the
                                     4-16

-------
multiple hearth furnace which follows are operated continuously for periods of 60 to 75 hr
during midweek. The units are shut down, cleaned, and held on standby the rest of the time.
Cost of treatment chemicals in 1973 was 2<^/ 1,000 gal of wastewater treated. Of this cost,
85 percent was for ferric chloride. Exact cost records are not available on capital equipment
installed in  this system.  That modest equipment outlay consisted of fiberglass tanks and
chemical  metering  pumps.  Although  quite  workable,  this  temporary  chemical feed
arrangement is to be replaced by permanent improvements in a 1 974 plant expansion.

        4.6.2  Trenton, Michigan

Since December 1 970, Trenton, Michigan has operated a 5.5 mgd activated sludge treatment
plant with  addition  of pickle liquor and  polymer  for phosphorus removal and effluent
polishing (19,30).  Design data for the Trenton plant are listed in Table 4-5.

Pickle  liquor, the  only metal salt used on a long-term  basis at Trenton, is stored in two
rubber-lined steel  tanks having a capacity of 25,000 gal each. These tanks have hot water
heating coils to keep coagulant temperature high enough to prevent crystallization of solids
during cold  weather. The storage tanks are  filled by tank trucks bringing pickle liquor from
a nearby steel plant; the trucks discharge into the storage tanks by applying low pressure
compressed  air.  The  liquid metal salts are fed, by  gravity, in proportion  to the rate of
wastewater  flow  through  the plant  at   a  preselected  concentration of  metal. The
concentration can and is changed from time to time to meet changing needs.

Two polymer tanks,  each holding 500 gal, are outfitted  with variable flow metering pumps
which  can be manually  set  to predetermined  rates. These inject  polymer  between the
activated sludge aeration tankage and the  final clarifiers. Mechanical mixing equipment is
provided in a small  box between  these two operations, and medium  energy mixing is
provided there to blend polymers into the main flow.

Predesign pilot  scale testing and  plant scale  startup  operations  indicated  the system
performed best in  the mode illustrated by Figure 4-6. Pickle liquor was added just  ahead of
the aerated  grit  chamber, and the polymer was added to the activated  sludge effluent en
route to the final clarifier.

Both the polymer addition and tube settlers installed in the  final clarifier were intended to
improve collection and capture of fine floe observed in primary effluent during studies in
the late 1 960's.

Table 4-6 shows performance data typically observed at this treatment facility since it has
been in full scale service.

Subsequent  to these  operating data, an additional inflow of industrial waste amounting to 1
mgd has been added  to  the plant flow.  The treatment system is presently  accepting this
                                       4-17

-------
                                    Table 4-5

                    DESIGN DATA FOR TRENTON, MICHIGAN
Description

Design Flow, mgd
    Average Dry Weather                                                      5.5
    Peak Dry Weather                                                         6.5
    Maximum Rate                                                          16.5

Primary Clarifiers
    Detention Time, hr                                                       1.3
    Overflow Rate, ^ gpd/sq ft                                              1,440
    Weir Rate,l gpd/ft                                                    23,000

Aeration Tanks
    Detention Time, hr                                                       5.5
    Return Flow, percent of average                                           30

Final Clarifiers (Tube Module Type)
    Detention Time, hr                                                       3.5
    Tube Overflow Rate, gpd/sq ft                                          1,200
    Total Surface Overflow Rate, gpd/sq ft                                     500

Sludge Production
    Primary (dry), Ib/day                                                  4,000
    Secondary (dry), Ib/day                                               5,000
    Chemical (dry), Ib/day                                                 4,000
    Primary plus Chemical, percent                                             5
    Secondary, percent                                                     1.0-1.5

Gravity Thickening
    Solids Loading, psf/day                                                    6.2

Vacuum Filtration
    Area, sq ft                                                             360
    Nominal Capacity, psf/hr                                                  2-3

* Based on Average  Flow
 Including Return Flow
                                      4-18

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additional waste, plus other increased domestic loads, so that average daily flow is now 7.5
mgd. This additional waste includes an increase in BOD loading to the plant of about 4,000
Ib/day. Plant performance at this increased load  is reported as essentially the same as in
Table 4-6. Preliminary operating data from early 1974 indicate removal of 90 percent of the
BOD and SS, and  80  percent of total phosphorus. Sludge processing has continued on a
stable basis as indicated in Table 4-6.

Total cost of the 1974 facilities  was  $4.8 million. In this major construction project, it was
not possible to separate the relatively minor expenses related  to  the  chemical treatment
facilities themselves. Something on the order of $5,000 could be identified for expenditures

                                     Table 4-6

                  OPERATING DATA FOR TRENTON, MICHIGAN

Description

Flow, mgd                                                                      5.5

Influent Characteristics
     BOD, mg/1                                                                220
     SS, mg/1                                                                  300
     Total P, mg/1                                                                9.5
     OrthoP, mg/1                                                               5.1

Chemical Addition
     Iron Dose, mg/1                                                             20
     Iron Dose, Fe/P                                                              1.2
     Polymer Dose, mg/1                                                          0.4

Overall Plant Performance
     Effluent BOD, mg/1                                                         10
     Effluent SS, mg/1                                                           10
     Effluent Total P, mg/1                                                        1
     Effluent Ortho P, mg/1                                                       0.5
     BOD Removal, percent                                                      95
     SS Removal, percent                                                        97
     Total P Removal, percent                                                    89
     Ortho P Removal, percent                                                    90

Gravity Thickeners
     Thickened Sludge Concentration, percent                                      5.1
     Thickened Sludge Mass, Ib/day                                           16,500
     Cake Solids Concentration,  percent                                        15-20
                                      4-20

-------
for specific hardware, but concrete, electrical service, and other such features could not be
realistically identified as if they were an independent capital  improvement. At any rate,
facility costs would be very low when capitalized over a period of years.

In 1973, the total operating cost of this facility was approximately 2Q
-------
 4.8    References

 1. Duren,  J.  W.,  "Detergent  Builders  and  the  Environment",  Presented  to  the
   Chemical  Marketing Research Association,  Chicago, Illinois (February 24,  1971).

 2. Schuessler,  R.  G., "Phosphorus  Removal,  From  Domestic  Wastewater or  From
   Detergents?",  Presented at  the 57th Annual  Meeting  of the Chemical Specialties
   Manufacturers Association, New York, N.Y. (December 15, 1970).

 3. Leckie,  J.,  and   Stumm,   W.,   "Phosphate  Precipitation",  in  Water  Quality
   Improvement by Physical and Chemical Processes, Edited by  Gloyna,  E.  F., and
   Eckenfelder, W.  W., Jr., University of Texas Press,  Austin, Texas,  p 237 (1970).

 4. Daniels,  S.  L.,  "Phosphorus Removal  from Wastewater by Chemical Precipitation
   and Flocculation", Presented  at  the American Oil Chemists'  Society, 1971  Short
   Course, "Update on Detergents and Raw  Materials", Lake Placid,  New York  (June
   16, 1971).

 5. Johnson,  E. L., Beeghly, J. H.,  and Wukasch, R. F.,  "Phosphorus Removal with
   Iron and Polyelectrolytes", Public Works,  100:11, p 66  (1969).

 6. Schuessler,  R. G.,  "Phosphorus Removal  - A Controllable  Process", Chem.  Eng.
   Prog.  Symp. Series, 67:107, p 536 (1971).

 7. Wukasch, R. F., "The Dow  Process for  Phosphorus  Removal",  Presented at the
   FWPCA Phosphorus Removal Symposium,  Chicago, Illinois (June 19, 1968).

 8. Wukasch, R. F., "New Phosphate Removal  Process",  Wat.  and Wastes Eng., 5:9,  p
   58 (1968).

 9. Harriger,  R. D., and  Hoffman, F.  L., "Phosphorus Removal Tests  Springfield,
   Ohio  for Black  and Veatch Consulting Engineers", Technical Service Department,
   Allied Chemical Corporation, Industrial Chemicals Division, Syracuse,  New  York
   (1971).

10. Harriger,  R. D., and Hoffman, F.  L., "Phosphorus Removal Tests  Two Rivers,
   Wisconsin   for  Black  and  Veatch  Consulting   Engineers",  Technical  Service
   Department, Allied Chemical  Corporation, Industrial Chemicals Division, Syracuse,
   New  York (1970).

11. Feige, W.  A., "Full Scale  Mineral  Addition  at Lebanon, Ohio", Inhouse  Report,
   Environmental  Protection   Agency,  Water  Quality   Office,   Advanced   Waste
   Treatment Research Laboratory, Cincinnati,  Ohio (1971).

12. Hathaway,  S. W., and Smith, J.  E.,  Jr.,  "Fundamental Design  Concepts for the
   Lime  Stabilization of  Lebanon  Raw  Sludge", Environmental Protection  Agency,
   Water Quality Office,  Advanced Waste  Treatment  Research Laboratory, Cincinnati,
   Ohio, Unpublished paper (1971).
                                        4-2:

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13. Green, O., Eyer,  F.,  and Pierce,  D.,  "Studies  on  Removal  of Phosphates and
    Related  Removal  of  Suspended  Matter  and  Biochemical  Oxygen  Demand  at
    Grayling, Michigan, March   September 1967", Division of Engineering, Michigan
    Department  of  Health,  Lansing,  Michigan,  and  The  Dow  Chemical Company,
    Midland,  Michigan  (1967).

14. Leary, R. D. and  Ernest, L.  A.,  "Municipal  Utilization of an Industrial Waste for
    Phosphorus Removal":  Presented  at the 32nd Porcelain Enamel Institute Technical
    Forum at the University of Illinois (October 8, 1970).

15. 	, "Studies  on Removal of  Phosphates and  Related  Removal  of
    Suspended  Matter and  Biochemical Oxygen  Demand at Lake Odessa, Michigan,
    May-October, 1967," Wastewater Section, Division of Engineering, Michigan Depart-
    ment  of Public Health, Lansing,  Michigan, and The Dow Chemical Company, Midland,
    Michigan  (1967).

16. Johnson,  E.  L., Beeghly,  J. H.,  and Wukasch, R. F.,  "Phosphorus Removal with Iron
    and Polyelectrolytes," Public Works, 100:11, p 66 (1969).

17. Boggia, C.,  and  Herriman,  G. L., "Pilot  Plant  Operation at  Warren,  Michigan,"
    Proceedings  of the 43rd Annual Conference  of the Michigan Pollution  Control
    Association (1968).

18. Connell, C. H., "Phosphorus Removal and Disposal From Municipal  Wastewater," U.S.
    EPA Report No. 17010 DYE (February, 1971).

19. Hennessey, T. L., "Pilot Studies, Design and  Operation of a Modified Activated Sludge
    Plant  Using Pickle Liquor and Tube Settlers," Annual Meeting WPCF, Atlanta, Georgia
    (October, 1972).

20. Wilson, Thomas E., Greeley and Hansen Engineers, Chicago, Personal Communication
    (1973).

21. Hennessey, John,  Jelinski, Robert,  Beeghly,  Joel  H.,  and  Pawlak,  Timothy J.,
    "Phosphorus Removal  at  Pontiac,  Michigan," The Dow Chemical Company, Midland,
    Michigan.

22. Harriger,  R.  D.,  and Zuern, H. E., "Michigan City, Indiana, Wastewater Treatment
    Plant,  August  15-October 22,  1971, Chemical Precipitation of Phosphorus," Allied
    Chemical  Corporation.

23. Cole,  Don and Tveite, Paul, "Sodium Aluminate for Removal of Phosphate and BOD,"
    Public Works, p. 86 (October, 1972).

24. Robson, C. Michael, Nickerson, Gary L., and  Morrison, R., "Chemical Addition at Two
    Trickling  Filter Plants to Enhance  Treatment Efficiency," 45th Annual  Conference,
    WPCF, Atlanta, Georgia (October, 1972).

25. Berthume, Don, City of Essexville, Michigan, Personal Communication (1973).
                                       4-23

-------
26.  Gaughan, D. M. and Alvord, E. T., "Phosphorus Removal by Ferrous Iron and Lime,"
    Final Report by Rand Development Corp. for the County of Lake, Ohio and EPA's
    Water Quality Office on Federal Grant No. 172-01-68, Prepublication Copy (1971).

27.  Progress Reports, Mentor, Lake County, Ohio, FWPCA Grant  WRPD 172-01-68, May
    15, 1968 through May 31, 1969 and September 1, 1969 through July 31, 1970.

28.  Voshel, D., and Sak,  J. G., "Effect of Primary Effluent Suspended Solids and BOD on
    Activated Sludge Production," JWPCF, 40:5, Part  2, p R203 (1968).

29.  Hennessey, J., City of Pontiac, MI, direct communication.
30.  Hennessey, T. L., Consulting Engineer, Trenton, MI, direct communication.
                                      4-24

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                                    Chapter  5

            PHOSPHORUS REMOVAL  BY  LIME ADDITION
                    BEFORE  THE  PRIMARY SETTLER
5.1    Introduction

Use of lime to treat raw wastewater dates back to the mid-1800's. Observers recognized that
calcium formed a precipitate both with hardness and with phosphates. Under one patented
technique both phosphates and lime (CaO) were added  at the treatment plant to increase
the amount of precipitate formed and to aid removal of SS (1).

More recent  experimental  efforts involved lime treatment of raw wastewater to remove
phosphorus. These are typified by an investigation in New York, in which feeding 300 mg/1
of slaked lime to a typical domestic wastewater removed 94 percent of the phosphorus to an
effluent concentration of 0.6 mg/1, reduced SS by 95 percent to 4 mg/1, and reduced BOD
by 71 percent to an average of 101 mg/1 (2).

Other  studies have  suggested that lime  addition  to  primary treatment is  an efficient
technique (3, 4). These  studies were at bench-, pilot- and plant-scale and total phosphorus
removals obtained were  80 percent or more with concurrent reduction in BOD of 60 to 70
percent. In this work, sufficient lime was added to bring primary effluent to a pH of 9.5 or
10. This pH  level was tolerated without problems  in the activated sludge process which
followed;  carbon dioxide  generated  by biological  activity served to correct pH to near
neutral levels. Recirculation of lime  sludge was very beneficial. With sludge reseeding, as
much as 60 to 75 percent reduction in overall lime requirements were obtained compared to
tertiary lime treatment. Reaction time  required  to achieve settleable  lime-phosphorus
compounds was reduced from 1.0 hr without recirculation, to 0.25 hr with reseeding.

A number of other studies, from  bench tests  through plant-scale trials, helped to establish
lime addition to primary treatment as a viable alternate for phosphorus removal operations
(5,6,7).

The low-lime system described in  Section 5.2.1 can provide 80 percent phosphorus removal
on  a  consistent basis. By  adding tertiary  filtration and facilities for addition  of metal
coagulants and polymer, the  technique can reduce  total effluent  phosphorus to near  1.0
mg/1.

The high-lime system described in Section 5.2.2 offers an even higher level of efficiency.
With flocculant aids and filtration, it can consistently produce final phosphorus levels below
1.0 mg/1.
                                        5-1

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5.2    System Layout and Operation

Two basic systems are considered in this section. One involves relatively low lime dosages to
primary influent, with biological treatment serving both to recarboriate the wastewater and
remove additional phosphorus for metabolic needs.  The other approach entails high-lime
treatment in the primary  section,  followed by pH adjustment with supplemental carbon
dioxide and biological treatment. The two systems are discussed separately in this section,
after the comments below which  apply to both approaches.

Sludge disposal during lime addition will be more complex than in a conventional biological
plant.  Lime sludge may not  be  compatible with existing disposal processes. Total sludge
weight may be  doubled  or tripled  over conventional  operation. Recovery  of lime by
recalcining may  be less attractive in this process because treatment in primary units yields a
sludge which is  high  in concentration of organic and  extraneous inorganic  materials, and
relatively low in  recoverable lime compounds.

Lime treatment  appeals most where incoming hardness and  alkalinity are low because less
lime is needed  and  less sludge  is  produced. However,  turbid effluent may develop and
settling  aids may be  required  to supplement  bioflocculation  to  insure  a  clear final
effluent (8). Recirculation of lime sludge has proven beneficial to the basic reaction taking
place.  It promotes a more complete reaction, reduces scaling,  and lowers lime demand.

Removal of phosphorus by lime addition in primary treatment is accompanied by increased
BOD and SS removal at that point. This reduces organic load on secondary facilities and
could aid in establishing nitrification.

In evaluating lime treatment systems, the  effect of reduced  carbon loads on their activated
sludge unit should be considered. Since lower organic loadings to the secondary treatment
units  result in  less  cellular  synthesis, a reduction in sludge wasting  may be required.
However, if the  sludge is retained in the aeration system (in an  attempt to keep MLSS up to
some  prescribed level)  sludge age may extend to the point that settleability suffers and
phosphorus escapes by cell lysis.

Also, lime precipitation in the primary clarifier  will increase  the capture of silts or other
similar inorganic solids. These weighting agents will no longer  be carried into the activated
sludge unit for sorption onto mixed liquor solids, and this may result in a fluffier biological
floe.

        5.2.1  Low-Lime Treatment

The basic appeal of low lime addition  in primary treatment  stems from two fundamentals:
the chemical law of mass action and the need for phosphorus  in biological systems.

In the first of these, lime  precipitates more phosphorus during initial stages of their mutual
reaction than it  does when pH has been elevated and phosphorus concentrations are quite
                                        5-2

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low. This effective performance by lime usually continues through the first 75 percent of
phosphorus reduction, and that  occurs before pH  10 when  lime  demands for softening
reactions increase. Overall lime demands become much higher  when the process is operated
to reduce phosphorus to very low  levels.

Following initial phosphorus removal by lime, in the primary facilities, biological treatment
removes more phosphorus  as bacteria utilize it  to support  cell synthesis. Generally,
phosphorus is not a limiting nutrient in domestic biological treatment systems as long as
primary effluent contains at least 0.2 mg/1 of soluble phosphorus. Microorganisms demand
phosphorus to synthesize cells  in  direct response to the carbon concentration of the
incoming waste; in municipal wastewater,  carbon is the limiting element, not  phosphorus.
The result is lime precipitation can proceed at economical levels, then biological treatment
can further reduce phosphorus residuals to an acceptable effluent concentration.

The basic low-lime treatment system is shown schematically in Figure 5-1. One advantage of
this  process is the opportunity to use existing primary clarifiers for phosphorus removal.
Capital expenditure, therefore, could be relatively small. The process requires equipment for
feeding and flash mixing lime. Flocculation usually occurs in the inlet zone of the clarifier
but separate facilities may be preferred for this process. The elevated pH of primary effluent
is reduced by recarbonation due to carbon dioxide produced in biological metabolism. The
low-lime system may not be appropriate at trickling  filter plants unless high effluent pH is
tolerable, since recarbonation would be minimal in trickling filter units.

        5.2.2  High-Lime Treatment

For the purposes of this  manual, high-lime treatment is defined as the addition  of sufficient
lime in primary facilities to achieve pH 11. The basic system layout is generally as shown in
Figure  5-1,  for  low-lime treatment.  Recarbonation with stored carbon  dioxide may  be
necessary  and  facilities  for  this would  normally  be provided.   Recovery  of lime by
recalcination, an  alternate feature  discussed  later in this Chapter, would frequently  be
included in high-lime systems.

High-lime treatment  is  applicable  when  effluent  quality requirements  include  special
provisions  such  as softening (for  reuse), low levels of  soluble  compounds of  metals,
improved virus removal, or reliable and consistent reduction of phosphorus below 1.0 mg/1.
Some form of tertiary solids removal, such as filtration, would usually be employed in these
plants.

High-lime treatment  would  normally be  combined with  other  biological,  physical  or
chemical processes to provide an overall system of advanced waste  treatment.  If biological
treatment is included,  the  primary clarifier phosphorus residual should be high enough to
meet metabolic requirements.

High-lime treatment may result in a net increase in plant  effluent levels of total dissolved
solids and alkalinity. See Section 5.3.2.
                                        5-3

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                             FIGURE  5-1
   TYPICAL FACILITIES FOR LOW-LIME  ADDITION IN PRIMARY  TREATMENT

                           INFLUENT
    LIME-
                              MIX
                              1
                            PRIMARY
                           CLARIFIER
                          DE WATER
                            AND
                           DISPOSAL
                                         SLUDGE
                           ACTIVATED
                            SLUDGE
             RETURN
                              FINAL
                           CLARIFIER
         SLUDGE
CHLORINE-
EFFLUENT
                                     5-4

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5.3    Case Histories

Two case histories are included in this section. One involves low-lime addition in primary
treatment,  while  the  other  is a high-lime system. Both installations are further cited in
Section 5.5, and it is intended that information in this section will give better perspective to
those later comments on sludges involved.

       5.3.1   Newmarket, OntarioLow-Lime Process

Lime fed into the primary section  of an existing 2.4 mgd conventional activated  sludge
treatment plant in Newmarket was the first permanent installation for phosphorus removal
in  Ontario,  Canada (5,9).  Phosphorus removal  facilities  have been operational in
Newmarket since March, 1971.

The original treatment facility  (constructed  in 1963) included screening and grit removal in
an aerated tank with  5 to 10  minutes detention. The original design data and subsequent
operating data are shown in Table 5-1. A schematic of the Newmarket treatment facility is
shown in Figure 5-2.

                                     Table 5-1

         DESIGN AND OPERATING DATA FOR NEWMARKET, ONTARIO

       Operation                           Design Data       Operating Data

       Flow, mgd                               2.4                 1.9

       Primary Clarifiers
            Detention Time, hr                   1.6                 2.0
            Overflow Rate, gpd/sq ft          1,330               1,050

       Aeration Basins
            Detention Time, hr                   8                  10
            F/M, Ib BOD/day/lb MLSS            1.0                 0.81

       Final Clarifiers
            Detention Time, hr                   2.4                 3.0
            Overflow Rate, gpd/sq ft          1,000                800

       Chlorine Contact
            Detention Time, hr                   0.42                0.53

       ^When lime addition was established, efficient primary clarification reduced
         F/M to 0.2 Ib BOD/day/lb MLSS; concurrently, one aeration basin was shut
         down so  effective aeration time was reduced to 6.7 hr.
                                       5-5

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                                               UJ
       o
       t"-l
       C
in     LU
      UJ
                                                             kl
                                                             UJ
                                                             ac
                                                             u
                                                             to
                                                   5-6

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Sludge treatment  includes anaerobic digestion of combined primary and waste activated
sludges. The heated primary digester (40 ft. in diameter and 21.3 ft. deep) has a capacity of
2,000,000 gal and gas mixing is employed to distribute the daily solids loading of 0.1 Ib/cu
ft. A secondary digester, of similar size, completes the digestion process. Ultimate disposal is
by wet spreading on farmland.

Lime storage is in a 25 ft diameter by 17 ft deep tank (mostly underground) which holds 30
tons of hydrated lime made up to near a 30  percent slurry by weight. To put lime into
storage, bulk calcium hydroxide is discharged directly to the storage tank along with slurry
water. The new slurry, after thorough blending, is sampled and titrated to determine actual
lime concentration. This type of storage also allows use of waste carbide slurry from a local
acetylene plant. Continuous slurry agitation is provided by either of two centrifugal slurry
pumps mounted beside two positive  displacement lime feed pumps. Slurry pumps require
double mechanical seals for this severe service. Lime feed lines require flushing connections.

Lime feed is based on preselected dose rates with automatic interlock to rate of wastewater
inflow. Metered slurry is discharged into a new flash mix box, where inflow is mechanically
agitated for about 8 minutes.

Lime operating data reported in Table 5-2 is based on a 200 mg/1 slaked  lime dosage. Overall
phosphorus removal at this dosage was greater than 80 percent.

Performance was slightly less effective at a slaked lime dose of 175 mg/1. Also, waste carbide
lime, at rates equivalent to 150 mg/1  of slaked  lime, were reasonably effective in removing
phosphorus. However, the acetylene waste proved highly abrasive to pumps and also formed
heavy encrustations enroute to the biological unit. Carbonate scale problems  were fewer
using slaked  lime, but  occasional hosing down  of primary launders  was still necessary.
Encrustation did not occur in aeration basins.

Discharge of relatively alkaline  (average pH 9.6 with peaks to pH 11.5) primary effluent to
the activated sludge system does not appear to distress the biological process.

Waste activated sludge is returned to the primary clarifiers and the resulting sludge mixture
is  drawn to  anaerobic  digestion.  During conventional  operation   about  5 gal total
sludge/1,000 gal plant flow was produced. Primary underflow was about 4 percent solids, of
which 65 percent were volatile.

During lime addition, waste activated sludge production is reduced 50 percent due to  the
lower organic  loads on  secondary treatment. Additional sludge from lime reactions keep
primary underflow at 5  gal/1000 gal plant flow. In this mode, however, the solids content
averages 9 percent or more, of which  36 percent are volatile. The pH ranges from 8 to 10 in
this sludge. Concentrations up to 15 percent solids were obtained when operators thickened
in  situ by allowing sludge depth to  build to 2.5 ft on the clarifier bottom. No problems
developed with mechanical scrapers, and sludge lines remained unplugged.
                                      5-7

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                                      Table 5-2
               OPERATING RESULTS FROM NEWMARKET, ONTARIO
                       Conventional Treatment
Lime Treatment
                                           Percent                              Percent
                 Influent   Primary   Final   Removal   Influent    Primary   Final   Removal
BOD
ss
Total Phosphorus
Orthophosphate
Hardness
Alkalinity
PH
249
341
14.2
8.1
225
386
7.8
172
126
12.5
8.3
229
377
7.8
21
17
8.7
7.6
235
227
7.7
92
95
39
6
-
_
-
227
321
10.3
6.7
239
391
8.0
84
80
2.7
1.2
240
374
9.6
9
7
2.0
1.8
111
247
8.0
96
98
81
73
-
-
-
Note:  All data are mg/1 except pH;hardness and alkalinity are expressed as calcium carbonate.
Chemical-biological sludge is pumped to digestion, as in prior conventional operation. The
anaerobic system  has  adapted to this type sludge and complete  digestion is  obtained.
Operation over a period of months has indicated that digester stability was enhanced when
sludge was thickened by holding a sludge blanket nearly 2.0 ft deep in the primary clarifier.

This brought sludge pH down  to 9.5 or less on a consistent basis, and thickened the mass to
11 percent solids. Digested sludge has a pH near 7.2. Digestion produces normal amounts of
methane gas, but free carbon dioxide is reduced by consumption in recarbonation reactions.
Digester supernatant contains less than 5 mg/1 of soluble phosphorus.

Capital  costs, in 1971  dollars, for the lime treatment additions are shown in Table 5-3.
Operating costs are almost entirely limited to  the  200  mg/1  lime consumption. In this
instance, there is no increase in the cost of sludge handling because the volume of digested
sludge has remained unchanged.

       5.3.2  Central  Contra Costa Sanitary District (CCCSD), California-High-Lime
              Process

Recent  plant-scale  tests of lime addition before primary treatment  have  been conducted in
Contra  Costa  County,  California (10,11,12). A complete  advanced treatment test facility
has been in  operation since November 1971. Full-scale units provide tests of all elements of
a 30 mgd water reclamation system currently under construction and scheduled for start-up
in 1976. Since the  purpose of the CCCSD water reclamation system is to reclaim wastewater
for industrial reuse effluent requirements are quite strict and are listed in Table 5-4.
                                        5-8

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                                  Table 5-3

             CONSTRUCTION COSTS AT NEWMARKET, ONTARIO
Structures
Mechanical Work
Electrical Work
Equipment
Engineering
Miscellaneous

$23,000
20,000
8,000
5,000
9,000
4,000
Total $69,000
                                   Table 5-4

             EFFLUENT REQUIREMENTS FOR CCCSD TREATMENT
                                  FACILITY

                                                             Limit
           Constituent                                        (mg/1)
           Total Phosphorus                                      1-0
           BOD                                                10.0
           Total Nitrogen                                        5.0
           Hardness (as CaCO3)                                 300
           Alkalinity (as CaCO3)                                255
           TDS (maximum increment above water supply)          375
In order to demonstrate effectiveness of the planned 30 mgd treatment system, investigators
converted  existing  treatment facilities to various plant-scale  forms of advanced  waste
treatment. The final layout of the overall test facility is shown in Figure 5-3. Table 5-5 gives
pertinent data.

After  screening, raw sewage  passed a chemical addition  point where lime was added and
flash mixed with recycled primary sludge. Ferric chloride and polymer addition were also
possible at the same point. Wastewater then  flowed  to the preaeration  basin. Heavy grit
                                      5-9

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                   FIGURE 5-3
       SYSTEM LAYOUT AT CONTRA COSTA COUNTY

        RAW SEWAGE
                             FERRIC CHLORIDE
                             LIME
    FLOCCULATION AND
       PREAERATtON
             I
          PRIMARY
    SEDIMENTATION TANK
    CHEMICAL
    PRIMARY
    EFFLUENT i
CO;
       OX IDAT ION -
    NITRIFICATION TANK
         SECONDARY
    SEDIMENTATION TANK
N2
        SLUDGE RECYCLE

            SLUDGE TO
              SOLIDS
            PROCESSING
           AIR


           RETURN
           SLUDGE


             WASTE SLUDGE
           	+*  TO
              RAW SEWAGE
                    METHANOL
     DENITR IFICATION
            TANK
             I
                               MIXING
          AERATED
    STABILIZATION TANK
             I
            FINAL
    SEDIMENTATION TANK
          RETURN
          SLUDGE
             I
             WASTE SLUDGE
            +-   TO
              RAW  SEWAGE
     CHLORINE  CONTACT
             T
     ADDITIONAL TREATMENT
        FOR INDUSTRY
                      5-10

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                                   Table 5-5

                           BASIC DATA FOR CCCSD
          Operation

          Preaeration and Grit Removal
               Average Water Depth, ft                            11
               Detention Time, hr                                 0.53
               Design Flow/Tank, mgd                             2.5
               Air Supplied, cu ft/gal                              0.10
           Primary Clarification
                Average Water Depth, ft                            10
                Detention Time, hr                                 1.6
                Overflow Rate, gpd/sq ft                        1,200
                Design Flow/Tank, mgd                            2.5
particles such as sand and unreacted lime settled out there. The gentle air agitation following
lime addition promoted the growth of large  floe particles which were  readily settleable.
Long-term operation of this air mixing facility indicated it was effective, and this approach
eliminated problems associated with mechanical flocculators in raw wastewater.

Waste activated sludge was returned to the preaeration section; there it  mixed and settled
with the chemical and primary sludges. The system had no separate facilities for treatment
of waste activated sludge.

In the preaeration basin it appeared the  carbon dioxide content of agitation air might, by
the process of recarbonation, work against the lime reactions required  in the preaeration
unit. However, if all carbon dioxide in the air were transferred into  solution, less than 0.5
mg/1 dissolved carbon dioxide would be introduced. This was considered insignificant.
                                       5-11

-------
However,  carbon dioxide  in the preaeration air did cause scaling inside the orifices of the
coarse  bubble diffusers. Initially the tank had to  be drained every week or two to clean
plugged orifices. Installation of high-pressure air  blowoff facilities extended that period to
two months.  In the 30 mgd plant, swing diffusers will be provided so tanks will not have to
be taken out of service for diffuser maintenance.

The lime-treated effluent was then settled in the rectangular primary tanks under operating
parameters described previously in Table 5-5.

During the course of the studies lime dosage was varied, and supplemental coagulants were
utilized to modify effluent qualities. Data  for various modes  of operation are shown in
Tables 5-6 and 5-7.

Operation at pH 11 was  not as effective in phosphorus removal as operation at 11.5 (see
Table  5-5). The  phosphorus remaining in  the  primary effluent at pH 11 was 2.3 mg/1
compared with less than 1  mg/1 at the higher dose.

Ferric  chloride  was tested  as  a supplemental  coagulant to enhance capture of colloidal
phosphorus precipitates.  At pH 11, a ferric chloride  dose  of  14 mg/1 produced  primary
effluent phosphorus of less than 1 mg/1 (see Table 5-6).  Even  the relatively low lime  dose for
pH 10.2 was possible if compensated by ferric chloride dosage of 24 mg/1. In this operation
primary effluent total phosphorus averaged 0.68 mg/1.

Removals of BOD, SS, and  other parameters were comparable in each mode of operation.
However, increase in hardness across the primary varied considerably.  Operation at pH 11
with ferric chloride yielded the lowest effluent hardness.

The data in  Tables 5-6 and 5-7 represent results  when primary clarifier underflow solids
were recycled to the chemical addition  point. This  was done to improve precipitation
reactions involving calcium, magnesium, and phosphorus. Total solids in the lime reactor
were maintained in the range of 1,000 to 2,500 mg/1. Later with solids recycle discontinued,
the major performance change was in effluent  hardness. During operation at pH 11 with
ferric  chloride dose of 10 to 16 mg/1, hardness across the primary increased an average of 32
mg/1.  Under similar chemical  feed rates,  hardness increase  across the primary was 6 mg/1
when  flocculator solids were in the range of 900 to 1,500 mg/1 TSS. When flocculator solids
were  increased  to  1,700 to  3,900 mg/1,  hardness increase  across  the primary was 16
mg/1 (12).

Considerable  sludge thickening  occurred  in  the  primary clarifiers.  Concentration of
underflow sludge  varied with a  number  of factors, including the nature of  the raw
wastewater. When a  nearby cannery was in operation, underflow solids concentration did
not exceed 4.5  percent when operating at pH 11.  This seemed due to anaerobic action and
gasification of peach and tomato solids in the raw sludge. Otherwise, 5 percent total solids
in the underflow was maintained. Occasionally underflow at total solids levels of 9 percent
                                        5-12

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              Table 5-6
LIME TREATMENT RESULTS AT CCCSD (12)
Flow: 1.30 mgd
pH: 11.5
Ca(OH)2 500 mg/1

Total Phosphorus
BOD
SS
TOC
Turbidity (JTU)
Calcium Hardness
(as CaCO3)
Magnesium Hardness
(as CaC03)
Influent Control Primary Chemical Primary
mg/1 mg/1 % Removal mg/1 % Removal
9.4 - - 0.96 90
190 103 46 50 74
199 57 71 41 79
107 59 45 37 65
35 - 16
76 - - 168
96 - - 40
Flow: 1.12 mgd
pH. 11.0
Ca(OH)2 400 mg/1
Influent Control Primary Chemical Primary
mg/1 mg/1 % Removal mg/1 7< Removal
9.2 - - 2.3 75
192 121 37 60 69
195 57 71 47 76
118 68 42 48 59
- 40 - 26
76 156
103 - 59
Table 5-7
LIME AND METAL TREATMENT RESULTS AT CCCSD (12)
Flow: 1.19 mgd
pH: 11.0
Ca(OH)2: 400 mg/1
FeCl3: 14 mg/1

Influent Control Primary Chemical Primary
mg/1 mg/1 % Removal mg/1 % Removal
Total Phosphorus 9.5 - - 0.85 91
BOD 210 109 48 53 75
SS 305 69 78 27 91
'IOC 130 72 45 37 72
Turbidity (JTU) - 45 - 14
Calcium Hardness
(asCaCO3) 76 - 139
Magnesium Hardness
(asCaCO3) 90 - - 32
Flow 1.20 mgd
pH 10.2
Ca(OH),: 289 mg/1
FeCl3. 24 mg/1
Influent Control Primary Chemical Primary
mg/1 mg/1 % Removal mg/1 % Removal
9.4 - - 0.68 93
178 106 40 59 66
235 59 75 31 87
117 68 42 43 63
41 - 15
72 - - 148
90 - - 70
               5-13

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were obtained. At about 7 percent total solids, coning and bridging occurred in hoppers of
these particular tanks and septic sludge zones developed.

Contrary to experience with high-lime operation, underflow solids at pH 10.2 could not be
thickened to more than 4.5 percent.  Use  of an  anionic polymer at 0.25 mg/1 allowed
thickening  to 6 percent. An alternate anionic polymer did not significantly improve solids
underflow and neither polymer enhanced the effluent quality.

The pattern of deposition of solids in the primary  clarifier was studied. Most of the sludge
was found in the first three-eighths of tank length. The heavier solids settled out rapidly in
this zone and the rest of the tank served to settle  finally  divided solids. Continuously
operating scaper flights kept the bottom relatively  clean. The rectangular primary clarifier,
with preaerated grit removal, seemed suitable for the lime precipitation operation.

Primary  clarifier effluent  flowed to  the  activated sludge  nitrification-oxidation  tanks
directly with no  continuous intervening recarbonation stage. External CC>2 was added to
mixed  liquor only when needed by  vaporization form liquid storage. Normally, CC>2 was
only necessary when lime addition  operations were at pH 11.5 or higher. In-process CC>2
generation  was sufficient for  complete recarbonation  with  primary operation at pH  11.
Supplemental CCh was injected  to the first bay of the activated sludge tanks to avoid scaling
in the transfer channel. All CC2 sources contributed to lower pH to 7.5 in a short time.

CC>2 generated in the biological process from the oxidation of carbon provided most of the
recarbonation  requirements  in  all operating modes. The amount of CC2 generated  from
oxidation was calculated  from a total carbon balance around the oxidation-nitrification
stage and typically amounted to 55 mg/1 of CC>2 for recarbonation.

The amount of  CC2 generated from the hydrogen ions produced  during nitrification was
calculated from  alkalinity destruction, and  appeared to amount to some 115 mg/1 under
typical conditions. The denitrification operation, occurring  in a subsequent unit, was not
involved  in recarbonation of primary effluent.

Daily  supplemental  CC>2 requirements averaged  about 25  mg/1 after the process was
stabilized at pH 11.5. CC>2 demand  varied  diurnally according  to  the  strength of  the
wastewater.

The CCCSD treatment facility was equipped with a high-pH alarm to warn operators of the
need for exterior CO2- The  30  mgd water reclamation  plant will use a fully automated pH
control system.

It was recognized that, in this particular plug-flow activated  sludge system, the highest pH
levels  would  occur  in the first part of  the aeration  tankage.  With operation in  the
conventional mode, primary influent and return activated sludge  blended  at  the influent
end. Thus a large part of the  oxygen demand also occurred in  the  first part of the tank.
                                       5-14

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Enough oxygen to match the load in the head  end of this tank would maximize CC>2
generation there. In the 30 mgd reclamation plant, DO probes in each pass will allow varying
the diffused air input according to load.

An unusual feature of this plant was application of two-stage wet classification of raw sludge
by  centrifuges. The first-stage centrifuge received primary clarifier underflow (thickened in
situ) at a  high rate. It captured two-thirds of the solids present: the resulting cake was 50
percent solids by weight and contained 85  percent of the calcium carbonate in the feed
sludge. Feed sludge was not conditioned with chemicals. This first-stage separation provided
sludge for recalcination. The centrate  from the  first  centrifuge proceeded  to  a second
centrifuge designed for efficient capture of solids remaining in the feed. When treated with
polymer a drier cake was delivered. This cake which contained  most of the organics and
phosphorus precipitated  in the primary clarifier, was incinerated. Further information on
sludge handling is presented in Section 7.5.
5.4    Other Experience

This section  contains information on lime treatment plants under construction, on full-scale
studies, and  on related information which may be of benefit to  designers of phosphorus
removal facilities. This is not intended to be a complete listing, but should be representative.

       5.4.1    Rochester, N.Y.Low-Lime Process

Bench scale  treatability studies for phosphorus removal preceded design of a  100 mgd
treatment  plant  at  Rochester, New  York (13, 14). Activated  sludge  treatment  alone
removed about 20 percent of the influent phosphorus (8 mg/1 as P). This agreed reasonably
well with phosphorus required for biological metabolism.

Jar tests of chemical treatment were performed. These tests examined alternated chemical
procedures to achieve required 80  percent phosphorus removal. Lime, and ferric chloride
with anionic  polymers, were tried on raw wastewater. Either 100 mg/1 of lime as CaO (pH
9.5)  or  the  combination  of  40  mg/1 FeCl3  and  0.5  mg/1  anionic  polymer  reduced
phosphorus 70  percent. This removal plus biological removal raised overall reduction to 80
percent or more. BOD and SS reductions in jar tests were about 50 percent and 85 percent
respectively.  In this case, lime was selected due to: 1) overall economy, and 2) ease of sludge
handling in the  plant configuration to be described.

Existing  treatment plant  facilities  at Rochester include primary  clarifiers, Imhoff tanks,
sludge holding  tanks, coil filters, and sludge incinerators. Proposed improvements include
modification  primary clarifiers to add flocculation sections,  addition  of new  primary
clarifiers incorporating flocculation sections, conversion  of Imhoff tanks to complete-mix
activated sludge units, and addition of chlorination facilities. Plant startup is scheduled for
late 1975. Detention in flocculation sections  of existing clarifiers will be 20 minutes. In the
new primary clarifiers, flocculation time  will range up to 40 minutes. Existing  and new
                                       5-15

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primary clarifiers will have overflow rates of 1,000 gpd/sq ft and detention times of 2.3 and
2 hr, respectively,  at average design flow.  A schematic diagram of the expanded plant is
shown on Figure 5-4. Plant design is based on the criteria shown in Table 5-8.

Lime will be added just after flow passes the comminutors. The pH will be monitored ahead
of the flocculation basins and lime  addition will be automatically regulated to maintain pH
9.5.

Anionic polymer will be fed just ahead of the  flocculation basins when such addition is
necessary to improve settling. Provisions for returning solids from the  primary clarifiers to
the flocculation basins are included.

Although lime treatment and biological treatment should remove 80 percent of incoming
phosphorus, there  will  be  additional  facilities  for adding alum  to  aeration tanks.  This
subsystem may be used alone or may supplement lime treatment for greater phosphorus
removal.

Complete-mix  activated  sludge  is expected  to disperse  the  primary effluent rapidly,
permitting recarbonation by bacterial CO2- F/M  can be controlled over a broad range in the
configuration provided for aeration tanks.

Since 80 to 90 percent SS removal is expected in  the primary  clarifiers, the weight of
primary sludge (based only  on increased SS removal) will be 1.5 to 2.0 times conventional
primary sludge production. Sludge  produced by chemical precipitation must be added to
                                     Table 5-8

                      DESIGN DATA FOR ROCHESTER, N. Y.

            Average design flow, mgd                                100
            Maximum flow, mgd                                     200
            Minimum flow, mgd                                     50
            BOD loading, Ib/day                                250,000
            BOD concentration, mg/1                                300
            Suspended solids concentration, mg/1                     300
            Volatile suspended solids concentration, mg/1              240
            Total hardness, mg/1                                     200
            Phosphorus, mg/1 as P                                     8
                                      5-16

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this, raising the  total to about 3.0 times the normal amount. Primary sludge quantities at
design  flow with lime treatment are estimated at 175 tons/day. Since organic load on  the
activated sludge  section  will be reduced about 50 percent, activated sludge will be reduced
substantially. At design  loads with lime treatment, waste activated sludge is estimated at 30
tons/day, compared to about 75 tons/day if lime treatment were not used. Solids handling
facilities have been designed for a capacity of 270 tons/day.

Sludges will be combined and gravity thickened to a concentration of 5 percent. Thickeners
are designed for  a  solids  loading  of 13 Ib/day/sq ft. After thickening,  sludge  will be
dewatered on vacuum filters and incinerated in multiple hearth furnaces. Incinerator ash will
be  sluiced  and  pumped to two  0.5-acre lagoons,  each  having  a  water depth  of 11 ft,
operating in series. Effluent  from lagoons will be pumped back to the head of the plant.
Lagoons will probably have to be emptied every 9 to 12 months.

       5.4.2  Lower Allen Township, Pa.-Low-Lime Process

Recalcination  of sludge  generated by lime addition  in the primary  is one feature of a new
6.0 mgd plant at Lower Allen Township, Pennsylvania (15). This plant, where startup began
in February 1974, is a complete-mix activated sludge system with low-lime addition in the
primary section.

Rough screening, degritting, and comminution precede lime injection. Flash mixing blends
both recalcined  lime and recycled seed sludge form the  primary clarifier. Lime addition is
controlled  automatically within the range  of pH  9.4 to pH 9.8. Mixed flow is divided
between two flocculating clarifiers, each 85 ft in diameter and 12 ft in depth. These have a
design average overflow rate of 700 gpd/sq ft.

Primary effluent is treated  biologically in  four activated  sludge basins, each 45 ft, x 90 ft x
15  ft. Recarbonation reduces  pH  rapidly to between  7.5  and 8.5. Biological  uptake is
expected to complement lime precipitation in order that overall phosphorus reduction will
be  80 percent.  Phosphorus  concentration in influent wastewater  is 9.0 mg/1. Two  final
clarifiers are each 85 ft in diameter and 12 ft in depth.

Combined  primary and waste activated sludges are blended  and gravity thickened.  After
storage, sludge  is conditioned  before being fed to two parallel  solid-bowl centrifuges.
Dewatered cake from the centrifuges is fed  to a multi-hearth dual purpose furnace. In the
furnace, organic fractions  are  volatized while waste inert inorganic sludge is dried. The
furnace is also designed  to recalcine and recover quicklime for reuse at the head of the  plant.

        5.4.3  Manhattan, Kansas-Low-Lime Process

In  Manhattan, Kansas,  research  into phosphorus removal using  low lime and  biological
treatment  began  with  laboratory  scale investigations  (16). It   was found  that  both
orthophosphates and polyphosphates could be precipitated  readily. Complex phosphates
                                       5-18

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present in wastewater seemed to inhibit calcium carbonate precipitation, to the extent that
recalcination  for lime recovery seemed impracticable. In these studies, 150 mg/1 of slaked
lime raised pH to 9.5. Total phosphorus removal before biological treatment was 60 percent,
and  SS were reduced 90  percent. Lime-primary sludge production was about twice that
obtained in conventional operation and overall sludge production, including waste activated,
was about 1.5 times that found with conventional secondary treatment.

The low lime process was  operated  at a  constant pH. Performance of the downstream
complete-mix activated sludge system was not disturbed. Microbial CC>2 production in the
activated  sludge  unit  was  sufficient  to  maintain   pH  near  neutral.  A mixture  of
lime-precipitated  primary  sludge and waste activated  sludge was dewatered and  vacuum
filtered with small additions of anionic polymers.

A pilot scale demonstration of the technique  followed (17). The wastewater was typical
domestic wastewater generated at the rate of 80 gal/capita/day. Untreated wastewater had a
pH near 7, and other characteristics were BOD and SS near 200 mg/1, total phosphorus of 10
mg/1, alkalinity of 235 mg/1, hardness of 150 mg/1, calcium of 110 mg/1, and magnesium of
40 mg/1. The pilot facilities included a 15,000 gpd conventional treatment process, with
lime addition to the primary. Influent wastewater was supplied to the system on a diurnal
pattern  from a variable speed pump and lime slurry was injected into the discharge line of
that pump.  Flow then entered a mixing and  reaction tank where 'detention was near 2
minutes. Lime feed was made proportional  to flow initially, but was later converted to pH
control.

Primary clarification followed with a surface loading rate of 225 gpd/sq ft. Primary sludge
was extracted hourly. Primary effluent flowed into plug flow aeration tankage where it was
detained about 5  hr. The final clarifier had an overflow rate similar to the primary clarifier
but sludge withdrawal was  continuous.

Primary and  secondary  sludges were detained  separately in holding tanks large enough to
store  the sludge from an entire day's operation. This permitted more effective sampling than
could be obtained by compositing smaller portions. The two sludges were then blended into
a third tank for dewatering studies. The biological system operated to give sludge age of 12
to 15 days when MLSS was 2,000 mg/1.

During the pilot study, a number of the operational features were changed deliberately or
through  circumstance.  It  appeared  the  most  important operational  variable was pH
following addition of lime to the primary effluent. If that pH was held between 9.5 and 10,
phosphorus removals of 75 percent or more were generally obtained in the primary unit (see
Figure 5-5). Consistent phosphorus reduction was not obtained  unless the pH was kept at
9.8.  When pH was increased to  11.5, 90  percent phosphorus removal resulted, but a
considerably greater lime dosage was required.
                                       5-19

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It appeared that fine floe escaping the primary clarifier contained, in particulate form, most
of the 25 percent  total phosphorus residual which entered the biological section. Reduction
of the flow rate (which was already quite low in terms of surface loading of the primary
clarifier) did not materially improve  capture of precipitated phosphorus.  In this instance a
higher degree of performance was not obtained by the use of polymer.

Phosphorus removal in the biological section was 5 percent or less of the total phosphorus
coming into the treatment plant.

Lime treatment to pH 9.5 to  10  resulted in primary  BOD reductions near 60 percent, a
considerable improvement over the usual 30 or 40 percent obtained in plain clarification.  SS
concentrations were not materially reduced, as already mentioned in connection with lime
floe which was escaping the  primary  unit. CC>2 production by  bacteria in the activated
sludge unit neutralized final effluent to  levels near pH 8.

Addition of lime to the primary clarifier resulted in physical  and biological changes in the
activated sludge. Mixed  liquor turned  gold or  light brown instead of the usual chocolate
brown  characteristic  of this  operation. Bacteria in the culture tended  to shift  into
filamentous species. Among the scavenger organisms, population of free  swimming ciliates
declined, while rotifers increased to dominance.

The technique produced  two  to three times more total weight of sludge than generated
during conventional treatment. However,  with properly  administered polymer, the sludge
could  be concentrated.  The most attractive sludge treatment systems  involved  polymer
conditioning,  dewatering by  vacuum  filter or  centrifuge, and incineration or land fill.
Primary  sludge had a volatile fraction of 50 percent during lime addition, as opposed to 65
percent in conventional systems. Chemical sludge would compact to a 3 percent density in
0.5  hr.  This  concentration could be considerably improved  with an  anionic polymer.
Biological solids were produced at  the rate of about 50 mg/1 as the flow passed through the
aeration  tank. Biological sludge  represented  7  percent by weight  of the total  sludge
produced when using the lime technique.

Total sludge resulting from  lime treatment was estimated at  3,750 Ib/million  gal of flow.
This compared with 1,500 Ib/million gal, of which some one-third would be waste activated
sludge. Sludge conditioning with anionic polymer (2.5 Ib/ton dry solids) yielded a filtration
rate  of 5 Ib/sq  ft/hr.

Several problems developed during the  course of the study, and these should be considered
by designers of such plants. Milk of lime solution had a marked tendency to scale everything
it contacted prior to injection  into the wastewater. Following injection, lime depositing out
of treated  wastewater caused  scaling problems on the membrane of a pH probe, and on
wetted parts of an automatic phosphorus analyzer. These and other surfaces also tended to
collect a biological slime. Lime scale  on pH  probes  was removed every other day  by
submersing them into diluted acid.
                                       5-21

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This pilot plant used 60 deg. hoppers for sludge collection in the primary clarifier. They did
not work well with lime sludge which had a tendency to cling even to these sharply sloped
bottoms. In due time denitrification occurred within that trapped layer and floating solids
resulted. Observers noted that sludge also adhered to hopper walls in the final clarifier and
became anaerobic prior to withdrawal.  It appeared that this resulted in release of cellular
phosphorus into the effluent.

       5.4.4  Richmond Hill, OntarioLow-Lime Process

Following laboratory and pilot scale studies, a three-month plant scale investigation of lime
treatment for phosphorus  removal was conducted using a  0.2 mgd  section of a 2 mgd
conventional activated sludge plant in Richmond Hill, Ontario (18). Lime was added before
the primary clarifier on a continuous basis and no special mixing or flocculating equipment
was provided.

Raw wastewater had  alkalinity of 381 mg/1 and  total hardness  of 401 mg/1. Average total
influent phosphorus was 10.6 mg/1 (as P). Normal plant operation reduced total phosphorus
by 39 percent.  BOD and  SS removals in  the primary  clarifier were 21 and  37 percent,
respectively.

Lime dosage of 175 mg/1 produced a pH of 9.3. During lime addition, BOD and SS removals
in the primary clarifier averaged 72 and 78 percent, respectively. Total phosphorus removal
averaged 83  percent in  primary treatment, and  removal through the entire plant was 92
percent, resulting in a total phosphorus concentration in the secondary effluent of 0.9 mg/1.

Throughout  the study, soft  calcium carbonate  scale accumulated  on effluent weirs and
troughs of the primary clarifier but was easily sluiced away using a water hose. There was no
appreciable buildup on submerged surfaces within the primary clarifier.

Lime treatment did not upset the biological process in  the test section. The pH of 9.3 in
primary effluent was promptly reduced below 8 by CO2 generated in the aeration tank.
MLSS equilibrium  was  reached and maintained throughout  the study. Due  to improved
primary performance, organic loading to the conventional (activated sludge system) was
reduced and its behavior  shifted  to operation  as  an extended aeration process with no
secondary sludge wastage.

Sludge precipitated in the primary clarifier was a mixture of calcium phosphate, calcium
hydroxide, calcium carbonate, and coagulated organics and grit. This sludge was free flowing
and considerably different from the gelatinous matter previously produced in bench scale
studies. Sludge removed from the primary unit  had a solids content of 6 to 8 percent. It
gravity thickened readily  to  10 to 12 percent solids, but was difficult to dewater without
proper chemical conditioning. Biological activity in the  lime-sludge was inhibited by the
high lime content. The sludge proved free from noxious odors even after prolonged holding
under anaerobic conditions. Supernatant from the chemical sludge, after 5 weeks of storage,
                                        5-22

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contained no appreciable amount of phosphorus, either total or soluble. It was concluded
that lime treatment could be readily controlled either in response to flow or on the basis of
pH in a flash mixer or primary effluent.

       5.4.5  Seneca Falls, New York

A combined  biological-chemical precipitation process (proprietary  name "PhoStrip") for
phosphorus removal was applied in a short-term (30 day) study at the existing Seneca Falls,
N.Y.  treatment  plant  in  1973. This process involves modification of the conventional
activated sludge  process. A  schematic of the Seneca Falls treatment scheme is shown in
Figure 5-6.

The major  modification  to the activated  sludge process is  the  incorporation  of the
phosphate "stripping" tank in the return sludge line. This tank permits the return sludge to
become anaerobic which, apparently, induces the sludge organisms to secrete phosphate.
The phosphorus enriched supernatant  from  the stripper is then dosed with lime  and
returned to the primary clarifier for sedimentation of phosphorus. Data obtained during the
30-day trial are included in Table 5-9.

Reported chemical costs for the Seneca  Falls trial, based on a lime dosage of 24.1 mg/1 (as
CaO), were $2.01 per million gallons of raw wastewater. Additional costs would include the
phosphate stripper tank,  the lime  feeding, storage and mixing facilities, and associated
pumping facilities. At Seneca Falls, a spare clarifier was used as the phosphate stripper tank.
It is claimed  that total costs for the project due to chemical cost savings may result in sig-
nificant savings compared to conventional mineral addition.

       5.5    Sludge

Detailed information in Chapter 11  concerns amounts of sludge  generated  during  lime
addition,  and offers design  parameters required to select and size sludge treatment and
disposal  facilities. Additional information specifically related to sludge produced by  lime
addition in primary treatment operations is discussed in this section.

Plant scale centrifuge trials  on underflow from  lime treated  primary units at Newmarket,
Ontario, were considered successful (19). Centrifugation captured some 99 percent SS in the
feed,  and cake solids were  near 30  percent by  dry weight. The performance  of the solid
bowl  centrifuge was such that centrate contained  700 mg/1 SS and about  20 mg/1 total
phosphorus.  Centrate  was  returned  to the flash mixer preceding the primary  clarifier.
Polymer requirements were  less than  1 Ib/dry ton of solids. Overdosing of polymer caused
foaming in the centrate.

Sludge production during low lime addition at Manhattan,  Kansas (17) was 250 percent of
the weight of sludge produced by conventional treatment. However, being primarily a grainy
chemical sludge,  this mixture of primary and waste activated sludge was much easier to
handle, dewater, and dispose of than sludge produced during normal plant operation.
                                       5-23

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                               Table 5-9

  RESULTS OF PHOSPHORUS REMOVAL TRIAL AT SENECA FALLS, N. Y.

Plant Flow, mgd
    Design                                                        1.75
    Average                                                       0.9

Influent
    BOD, mg/1                                                   158
    P, mg/1                                                       6.3

Detention Times (based on average flow), hours
    Primary Clarifier                            t                    3.9
    Aerator                                                       5.5
    Secondary Clarifier                                             3.2
    Phosphate Stripper                                            18

Return Flows, percent of raw flow
    Sludge to Phosphate Stripper                                    24
    Sludge to Aeration Tank                                        10
    Supernatant to Primary Clarifier                                  14

Lime Dose, mg/1 as CaO                                             24.1

SS, mg/1
    Mixed Liquor                                              1,440
    Return Sludge to  Stripper                                    7,840
    Return Sludge to  Aerator                                   15,910

Effluent
    BOD, mg/1                                                     3.5
    P, mg/1                                                        0.55

Plant Performance
    BOD Removal, percent                                          98
    P Removal, percent                                            91
                                   5-25

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Canadian  studies (5), taken as a group, indicate total sludge production at a conventional
plant will increase from 1800 Ib/million gallons to 4600 Ib/million gallons with addition of
some 200 mg/1 lime to primary clarifiers.  Solids concentration increased  from 4.5 to 9
percent, so the volumetric increase was 25 percent.

In a  primary plant, sludge production increased  from 800 Ib/million gallons to 2400
Ib/million gallons with  solids concentration rising from 7 to 15 percent (a  net 50 percent
increase in sludge volume).

Plant-scale testing of two-stage centrifugation of combined lime-treated primary and waste
activated  sludge has been applied  at Central  Costa  County Sanitary District (CCCSD),
California (11). This permitted a degree of sludge classification vital to the integrated system
of lime recovery and sludge disposal to be utilized in  the  30 mgd  treatment plant under
construction at CCCSD. Figure 5-7  depicts the solids handling and disposal facilities which
will be incorporated in the 30 mgd plant; Figure 5-8 depicts the plant-scale sludge handling
system used at CCCSD to develop design data for the full-scale system.

The purpose of the first of the two centrifuges is to maximize recovery of calcium carbonate
while  rejecting  other  sludge components,  such  as  organic material, phosphorus  and
magnesium compounds, and other constituents coprecipitated with calcium carbonate. The
first-stage cake  represents phase, all of which have a  slower  settling rate than calcium
carbonate, are deliberately  carried out with  the process centrate and passed on to a
second-stage centrifuge operated  to obtain  high solids  recoveries. Second-stage solids are
incinerated (breaking down organic compounds in the process) and the total ash, including
fine  inert  materials, can  be disposed of  without recycling  back into  the  wastewater
treatment process.

Optimum first-stage performance in the  test  system  was  obtained after varying critical
centrifuge variables:  feed  rate,  centrifugal   force,  pool  depth,  and conveyor  speed.
Observations were made on individual sludge constituent recovery throughout a broad range
of these  process variables. Figure 5-9 shows the generalized  results. The definition of
performance allowed setting the centrifuge variables to capture a  high percentage of calcium
carbonate but a low percentage of all other sludge constituents.

Certain trends were noted in the  CCCSD  studies which may have  application in other
locations. In general, results followed past practice in centrifugation of calcium carbonate
and, almost with exception, followed basic centrifuge fundamentals.

When wastewater was lime treated to a pH of 11 or 11.5, the highest percentage of calcium
carbonate  was  recovered  in the first unit and  the greatest reject of extraneous solids
occurred. Sludge  produced  when  flocculating at  pH  10.2 was not as easily classified.
Separation was  most effective when pool depth in the  bowl was at very shallow  settings.
Dewatering of the  calcium carbonate cake  was materially improved by raising centrifugal
force to the range of 2,100 g's. Polymer preconditioning of sludge was not required.
                                        5-26

-------
     FIGURE 5-7 PROPOSED SLUDGE FACILITY AT CONTRA COSTA COUNTY
FROM
RECALCINING FURNACE
                 1 ' 1 '
                    MAKEUP
                    LIME
     WASTE
     B IOLOGICAL
     SOL IDS
                LIME
              STORAGE
                                        CENTRATE RETURN
                                                                    PRIMARY
                                                                   EFFLUENT
                                              PR IMARY C L AR IF IER
                                           FIRST
                                           STAGE
                                          T H ICKENER
   WET
   CL ASSIF ICAT ION
                                      SECOND
                                      STAGE
                                      THICKENER
                   MULTIPLE
                   HEARTH
                   RF. CALCINE
                   FURNACE
                                GAS
                            SCRUBBER
                     RECALCINED
                     ASH
                            REJECTS
                           2nd STAGE CENTRIFUGE
                                OR
                            FILTER PRESS
                                OR
                            VACUUM FILTER
                          CENTRATE  TO
                            PRIMARY
    QRY
    CLASS IFICATION
  RECYCLE  LIME  TO STORAGE
                                         MULTIPLE
                                          HEARTH
                                          FURNACE
HIGH LIMC
ACCEPTS
                                                 ASH  TO DISPOSAL
                                  5-27

-------
    FIGURE 5-8 PLANT SCALE SOLIDS TESTING SYSTEM AT CONTRA COSTA
 RAW
                                            PRIMARY
                                            -*
                                            EFFLUENT
                                                  Centrote Processing Alternatives
                   PRIMARY  CLARIFIER
Thickening
                                                        CENTRATE
                                                        T HICKENER
UNDERFLOW
   SOLIDS
Centrifugation  or
Classification
                                                                 SLUDGE
                                                                  TO
                                                              INCINERATOR
     HIGH
     CaC03
   ACCEPTS
     OR
    WHOLE
    SLUDGE
                                     SLUDGE TO
                                     INCINERATOR
                                   GAS
                                   SCRUBBER
                                                      2ND STAGE
                                                      CENTRATE TO
                                                      PRIMARY
                                                      CLARIFIER
          MULTIPLE
           HEARTH
          INCINERATOR
  Incineration or
  Recalcination
                      RECALCINED PRODUCT
                      OR  ASH
 First-stage centrate passed to the second centrifuge for further treatment. Several polymers
 were tried and some proved effective in increasing solids capture when fed at the rate of 2
 Ib/ton of solids. Solids recovery of 80 percent and  resulting cake dryness of 15 percent
 solids were typical operating levels obtained after experimentation. Setting the machine for
 maximum pool depth and operating near 2,100 g's gave satisfactory results in this particular
 installation.
                                      5-28

-------
        FIGURE 5-9 SLUDGE CLASSIFICATION CURVES AT CONTRA COSTA

    IOO
                     20
              RECOVERY
OF
4O
TOTAL
     60           8O
SOLIDS,  PERCENT
                                              too
The extensive investigations at this installation (11) have only been briefly summarized here.
The  conclusion is that,  in  this  instance, two-stage classification  by  centrifuges was
applicable.  Results of the operation were generally  predictable by centrifuge laws. Other
locations considering this type of operation should make comparable predesign studies.

It  is also worthwhile to note that sludge production  at the CCCSD  test installation was
predicted by theoretical procedures similar to those  described in Chapter 9. Actual sludge
production  was then  measured  under four different operating modes,  and  operating
experience agreed within about  10 percent with predicted values. These predictions and the
actual production rates both included biological sludge  from the nitrification-denitrification
system, as well  as settleable solids normally removed in primary treatment. In this case, the
organic  fraction of total  sludge  was  one-quarter to  one-third  of the combined weight
involved.
                                       5-29

-------
5.6    Costs

The  capital  cost of adding rapid mix and flocculation facilities to existing plants has been
estimated for  1,10, and 100 mgd plants. These should serve as a general guideline where
phosphorus is  to be removed by lime addition to the primary clarifier. Estimated costs for
rapid mix facilities include concrete basins (with detention of one minute at design flow),
and  mixers  with shafts and impellers of stainless steel. Flocculation facilities consist of
baffle walls and mixers to provide a flocculation chamber with 30 minute detention within
existing circular clarifiers. Estimated  costs of these  are given in Table 5-10 and  include
allowance for Contractor's installation, overhead, and profit, plus 20 percent for engineering
and contingencies. Figures given  relate to an EPA-STP Cost Index of 185.
                                    Table 5-10

         TYPICAL CAPITAL COSTS FOR LIME TREATMENT IN PRIMARY
                                   FACILITIES
                              1 mgd           10 mgd            100 mgd
        Rapid Mix
        Flocculation
$ 2,200
64,000
$ 13,000
264,000
$ 82,000
983,000
             Total            $66,200         $277,000         $1,065,000
 Investment figures for lime storage and feed facilities are given in Chapter 10.

 The cost/1000 gal for adding single-stage lime treatment to an existing plant was determined
 by amortizing capital cost at  6  percent over 25 years and adding the cost of chemicals.
 Operational expenses such as labor and power are not included.

 Lime costs/1000 gal are based on a chemical cost of $22/ton with 90 percent available CaO
 at a dosage  of 150 mg/1 as CaO. The equipment and chemical costs (^/lOOO gal) are given in
 Table 5-11.
                                       5-30

-------
                                  Table 5-11

         TYPICAL TOTAL COSTS FOR LIME TREATMENT IN PRIMARY
                                 FACILITIES

Equipment Amortization
Rapid mix and flocculator
Chemical storage and feed
system
Chemical Cost
Total Cost (Hi, 000 gal)
1 mgd

1.4

0.4
1.5
3.3
10 mgd

0.6

0.2
1.5
2.3
100 mgd

0.2

0.1
1.5
1.8
Costs  do not  include allowance  for  equipment for sludge  handling and  disposal and
corresponding  operating costs. Since  a  considerable  quantity  of  additional  sludge is
produced, this expense is likely to be substantial.
5.7    References

  1. Pearse, et ah, "Chemical Treatment of Sewage,"  Sewage Works Journal, 7:6, p. 997
    (1935).

  2. Karanik,  J. M., and Nemerow, N. L.. "Removal of Algal Nutrients," Water and Sewage
    Works

  3. Albertson,  O. W., and  Sherwood,  R. J., "Removing Phosphates  from  Wastewater,"
    Industrial Water Engineering, p. 30 (November, 1967).

  4. Albertson, O. E., and Sherwood, R. J., "Phosphate Extraction Process," JWPCF, 41:8,
    p. 1467 (1969).

  5. Boyko, B. I., and Rupke, J. W. G., "Technical Implementation of Ontario's Phosphorus
    Removal  Programme,"  Proc., 28th Purdue Industrial Waste Conference, Lafayette,
    Indiana (May, 1973).
                                    5-31

-------
 6. Spohr, Guenter, and  Talts,  Andres, "Phosphate Removal by pH Controlled  Lime
    Dosage," Public Works, p. 63 (July, 1970).

 7. Tofflemire, T. J., and Hetling, L.  J., "Treatment of a Combined Wastewater by the
    Low-Lime Process," Journal Water Poll. Control Fed., 45, p. 210 (1973).

 8. Bishop, Dolloff F., O'Farrell, Thomas P., and  Stamberg, John B., "Physical-Chemical
    Treatment of Municipal Wastewater," Journal WPCF, 44:3, p. 361 (March, 1972).

 9. Black, S.  A.,  "Lime  Treatment for Phosphorus Removal at the Newmarket/East
    Gwillimbury WPCP,"  Research  Paper No.  2032, Research Branch,  Ministry of the
    Environment, Ontario (May 1972).

 10. Parker, D., Brown & Caldwell Engineers, Private Communication (June, 1973).

 11. Parker,  D.  S.,  Zadick, F. J., and Train, K.  E., "Sludge Processing for Combined
    Physical-Chemical-Biological  Sludges," Grant  #R801445, Office  of Research and
    Monitoring, EPA (March, 1973).

 12. Horstkotte, G. A.,  et al., "Full-Scale Testing of a Water  Reclamation System," Jour
    WPCF, 46:1, p.  181-197 (January, 1974).

 13. Wahbeh, V.  N., "Design and Modification of the Rochester,  New York Wastewater
    Treatment  Plant for  Phosphorus  Removal,"  Presented  at the Technical Seminar/
    Workshop  on  Advanced Waste Treatment,  Chapel  Hill,  North Carolina  (February,
    1971).

 14. Weller, L., Black and Veatch, Kansas City, Mo., direct communication (1974).

 15. Paul,  P., Gannett, Fleming, Corddry and Carpenter, Inc.,  Harrisburg,  Pa., Direct
    Communication (1973).

 16. Schmid, L.  A., and McKinney, R.  E., "Phosphate Removal by a Lime-Biological
    Scheme," JWPCF, 41:7, p. 1259 (1969).

 17. Schmid, Lawrence L., "Pilot Plant Demonstration  of a Lime-Biological Treatment
    Phosphorus  Removal  Method," Water  Quality  Office,  Environmental  Protection
    Agency, Project 17050 DCC (September,  1972).

 18. 	 and Lewandowski, W., "Phosphorus Removal by Lime Addition
    to a Conventional Activated  Sludge Plant," Div. of Res. Publ.  No. 36, Ontario Water
    Resources Commission (November,  1969).

19. Smith, A. G., "Centrifuge Dewatering of Lime Treated Sewage Sludge," Research Paper
    No. W2030, Res. Br., Ministry of the Environment, Ontario (May, 1972).
                                      5-32

-------
                                    Chapter   6

           PHOSPHORUS  REMOVAL  IN   TRICKLING  FILTERS
                           BY  MINERAL  ADDITION
A logical approach to removal of phosphorus in  trickling filter plants would be the use
of  precipitating  chemicals  somewhere in  the system.  Iron  and aluminum  can both  be
used  for  this application. Because of their similar action,  iron and aluminum salts are
commonly  referred  to  collectively   as  minerals  in  wastewater  treatment  and  are
considered separately from  calcium (lime). Required physical facilities for adding iron
and aluminum are relatively dimple. They are covered,  along  with special considerations
for  specific  chemicals,  elsewhere  in  this  manual.  This  discussion will emphasize  the
merits of alternative addition points, review methods for  determining dosage, and report
studies where chemicals have been dosed  directly to  a trickling  filter  and to trickling
filter effluent.  Broader aspects of mineral addition for phosphorus  removal are covered
in other sections of this manual and  in several recent reports (1, 2, 3, 4).

6.1    Pre-Design Decisions

State  quality standards on phosphorus  usually  form  the  major basis for considering
mineral addition  for  a  given trickling filter plant.  However, phosphorus  concentration
in the effluent is only one factor involved;  effluent BOD and suspended solids will also
be  markedly reduced by  this form of chemical treatment.

Modification of  existing  trickling filter plants for phosphorus removal  is often a simple
operation, and inclusion of chemical treatment   facilities in  new  plants is a relatively
minor addition.  In  either  case,  capital  costs  for chemical  treatment equipment  are
relatively  low. Also, the  required degree  of phosphorus removal  has little  effect on
capital  cost.  Facilities for  80%  phosphorus removal  are  identical  to those  for  95%
removal.

On  the   other  hand,  operating  costs are  substantially  higher  to  obtain  successful
treatment  with  chemical addition.  More  constant surveillance  and  more  laboratory
support are needed than with a conventional plant. Added operating  costs  are on  the
order of 4^ to 5^ per 1,000 gal.  for reducing phosphorus (as  P) to 2 mg/1 with  an accom-
panying reduction of BOD  and  solids  to  15 mg/1.  For an additional 1^ to  2^ per 1,000
gal., phosphorus  can  be reduced to 1 mg/1  or less and BOD  and solids to 10 or  12 mg/1.
This  simultaneous reduction of phosphorus, suspended  solids and  BOD  may be  the
deciding factor for adopting chemical  treatment in a trickling filter plant.

6.2    Process Options

There  are three  locations  within  a  trickling filter plant  where chemical  precipitation
can be incorporated:  the primary  clarifier,  the  trickling filter, and the final clarifier.
The preferred approach  is to provide  facilities to serve both  the first  and  last of these
but not to add chemicals directly to the trickling filter.
                                        6 -  1

-------
Chemical  addition  to primary  clarifiers will  produce the  greatest sludge yield  of any
one  arrangement.  Since  treatment at this point will  reduce influent BOD about 50%, it
may be  an appealing approach in  an  existing plant which is organically overloaded.
Unfortunately, a  significant  amount of the phosphorus  present  may  not  be  in the
ortho  form at this stage and  may  not be effectively precipitated and  removed.  Even
after chemical treatment,  primary effluent  may remain  fairly turbid,  but will clear up
during passage through the rest of the plant.

Mineral addition  in the trickling filter does not seem to cause  any functional problems
although  the  filter may  blotch and slough more than  usual. A  modest  inorganic  film
often  forms  over  the  surface of  the rocks  but   does  not  seem  to  interfere  with
biological activity  or  cause  ponding. As data shown later will indicate,  however, high
degrees of phosphorus removal are  not  attained when chemicals  are added only to the
filter.  Poor removal may  result partly from short circuiting in  the filter.  This approach
is  not  recommended.

Treatment in  the  final clarifier alone is a risky approach. If the  operation is not  done
effectively,  poorly  treated effluent can  escape to the receiving water. In  spite of  these
reservations, experience  has  shown that precipitation in the finai  clarifier can be both
effective  and   controllable.  Orthophosphate  predominates  at  this   point  and  it
precipitates   readily.  Also,  bio-degradable  detergents  which  can   interfere  with
precipitation  are  largely  absent. If underflow  solids from  a  dosed  final clarifier  are
returned to the primary clarifier, it  will stimulate unusually effective clarification there.

In order  to allow  for incorporating the advantages  of  chemical  treatment in both the
primary  and secondary  clarifiers, it  is recommended that chemical addition and mixing
facilities  be  provided at  both  locations.  Facilities required  are  not  expensive  and
provision  for  mineral  addition  to   both  primary  and secondary   clarifier  gives
considerable flexibility of operation. Chemical treatment  in both clarifiers can then be
used if experience shows it to be the  most  effective technique  at the particular  plant
involved.

6.3    Performance Data Using Aluminum Salts

       6.3.1  Richardson, Texas

A  plant-scale  study was begun  at Richardson,  Texas,  in 1970 to evaluate the potential of
chemical  addition  to  remove phosphorus from  and  improve overall performance of the
City's  trickling filter plant (5). Major objectives were to reduce the effluent phosphorus
concentration  to 1.0 mg/1 (as P), or less, and to reduce effluent BOD and SS residuals to 15
mg/1 or less.

The existing  plant was  a  low-rate  trickling  filter  facility  with  combination primary
clarifier/digester units (clarigesters) as shown on Figure 6-1. Operating  data for a control
period before the addition of chemicals are shown in Table 6-1.
                                        6-2

-------
FINAL SLUDGE
    &
RECIRCULATION-
                               FINAL
                             EFFLUENT
                                      INAL CLARIFIER

                                     POLYMER
                                     JUNCTION BOX
[TRICKLING
 FILTERS
                                            PRIMARY
                                           CLARIFIERS
                                               &
                                           DIGESTERS
                                           (UNHEATED)
                                   SPLITTER BOX

                                       SUPERNATANT
                               RAW
                            WASTEWATER
                FIGURE 6-1   RICHARDSON,  TEXAS
                  TREATMENT PLANT  FACILITIES
                    DIGESTED
                     SLUDGE
                     .DRYING
                       BEDS
                                                         UPERNATANT
                                                         TREATMENT
                                6-3

-------
                              Table 6-1

               OPERATING DATA FOR RICHARDSON, TEXAS
1970
Description Control Period
Flow, mgd
Influent BOD, mg/1
Influent SS, mg/1
Influent P, mg/1
Primary Clarifier
Overflow Rate, gpd/sq ft
Primary Effluent BOD, mg/1
Primary Effluent SS, mg/1
Primary Effluent P, mg/1
BOD Removal, percent
SS Removal, percent
P Removal, percent
Trickling Filter
Depth, ft
Recirculation Ratio
Hydraulic Loading, mgd/acre
Organic Loading, Ib BOD/ 1 ,000 cu ft/day
Secondary Clarifier
Alum Dosage Rate, Average Al :P mole ratio
Overflow Rate, gpd/sq ft
Secondary BOD Removal, percent
Secondary SS Removal, percent
Secondary P Removal, percent
Overall Plant Performance
Effluent BOD, mg/1
Effluent SS, mg/1
Effluent P, mg/1
BOD Removal, percent
SS Removal, percent
P Removal, percent
1.5
166
155
11

400
*
*
*
*
*
*

6.5
0
3.9
*

-
390
*
*
*

20
15
8
88
90
27
1971-72
Extended Alum Run
(11 % Months)
1.6
170
155
11.4

425
115
110
8.6
32
29
25

6.5
0
4.1
14.0

1.6**
415
96
94
94

5
7
0.5
97
95
96
 *Not reported.
**Based on Influent P.
                                6-4

-------
Based  on operational trials, alum addition ahead  of the final clarifier was selected as the
most promising chemical additive system for an extended 1 P/z-month run. The flow diagram
for the upgraded system is shown on Figure 6-1.

It was found that a mole ratio (Al:  Influent P)  of 1.5 to 1.7 consistently yielded effluent
concentrations of 5 mg/1 of BOD, 7 mg/1 of SS and 0.5  mg/1 of total phosphorus (as P). The
corresponding effluent values for this plant prior  to chemical addition were  20,  15 and 8
mg/1, respectively. The improved plant performance obtained with this upgrading technique
was attributed in part to the low final clarifier overflow rate, careful management of final
clarifier sludge withdrawal to prevent disruption to and loss of the alum floe blanket and
frequent manual adjustment of the chemical feed pump rate to match alum dosage to mass
inflow of phosphorus. Alum treatment doubled the volume of anaerobically digested sludge
produced. However, the digested alum/biological  sludge  exhibited superior drying charac-
teristics on sand beds and could be removed in about one-half the normal time. Operating
data for the upgraded plant are shown in Table 6-1.

Chemical  costs were $0.05/1,000 gal of plant flow or $0.36/lb of phosphorus removed, with
phosphorus removal at  the 96 percent level. The  1970 capital costs associated with plant
modifications for chemical addition were $65,000, allocated as follows:

     New laboratory building                                             $21,000
     Laboratory equipment and furniture                                    6,000
     Chemical storage and feed equipment, plant  piping and
       metering modifications                                             38,000

          Total                                                          $65,000

       6.3.2   Chapel Hill, North Carolina

Promising results were obtained in removing phosphorus and in generally improving plant
performance  at Richardson, Texas, by the addition of alum to trickling filter effluent as
discussed  in Subsection 4.5.4.1. In view of these results, the University  of North  Carolina
Wastewater Research Center initiated  a follow-up study to further explore and confirm this
process at the Chapel Hill, North Carolina Wastewater Treatment Plant (6). Conducting a
similar chemical addition project at Chapel Hill  was considered worthwhile because it is a
typical high-rate trickling filter plant using recirculation, whereas the Richardson filters were
low-rate units. Furthermore, parallel  and identical  lines of treatment units were available at
Chapel  Hill,  allowing   direct comparison  of results  with  and  without  alum  addition.
Comparison of parallel results was not possible at  Richardson.

The wastewater treatment  plant at  Chapel Hill  is  a conventional  high-rate installation
treating predominately domestic wastewater. Incoming wastewater passes through  pretreat-
ment facilities for the removal of large solids and grit.  The flow is then divided into equal
portions  for  diversion  to two identical  lines of treatment, each consisting of a  primary
                                       6-5

-------
clarifier, trickling filter and final clarifier as shown on Figure 6-2. On one side of the plant,
a feed pump system was installed to add liquid alum to the trickling filter effluent just prior
to the final clarifier.

Operating  data for  the two  sides of the plant  are  shown  in Table  6-2. Significant
improvements in BOD, SS and phosphorus removals were achieved with an alum dosage rate
that ranged between an Al -.Influent P mole ratio of 1.5 and 2.2. Within this range and for
the loading rates shown, the final clarifier hydraulic loading appeared to be the significant
factor  affecting  process  efficiency.  Subsequent  phases  of  the study indicated  that
phosphorus removals of over 90 percent and BOD removals of about 95  percent could be
consistently  obtained  by lowering the final  clarifier  overflow  rate to 500  gpd/sq ft.
Recirculation of the final clarifier settled alum/humus  sludge  to  the primary clarifier for
thickening had a beneficial effect on primary treatment efficiency and decreased the organic
loading on the alum train trickling filter.

                                  FIGURE 6-2
              CHAPEL HILL, N.C. TREATMENT PLANT FACILITIES

                PRIMARY   TRICKLING      FINAL
               CLARIFIER      FILTER     CLARIFIER
INFLUENT
I





rO -
^^S
1 COMBINED
! SLUDGES
RECIRCU




LATION
1
> TFFLUENT

SETTLED FINAL
SLUDGE

                             SIDE 1(NO ALUM)
             PRIMARY  TRICKLING
            CLARIFIER    FILTER
  INFLUENT
   FINAL
CLARIFIER
                    COMBINED
                    SLUDGES
                                                               -  EFFLUENT
                                    RECIRCULATION
                                                       SETTLED FINAL
                                                           SLUDGE
                             SIDE 2(WITH ALUM)
                                       6-6

-------
                                 Table 6-2
           OPERATING DATA FOR CHAPEL HILL, NORTH CAROLINA
Description
Flow, mgd
Influent BOD, mg/1
Influent SS, mg/1
Influent P, mg/1
Primary Clarifier
Overflow Rate, gpd/sq ft
Primary Effluent BOD, mg/1
Primary Effluent SS, mg/1
Primary Effluent P, mg/1
BOD Removal, percent
SS Removal, percent
P Removal, percent
Trickling Filter
Depth, ft
Recirculation Ratio
Hydraulic Loading, mgd/acre^
Organic Loading, Ib BOD/ 1,000 cu ft/day
Secondary Clarifier
Alum Dosage Rate, Average Al :P mole ratio
Overflow Rate, gpd/sq ft
Secondary BOD Removal, percent
Secondary SS Removal, percent
Secondary P Removal, percent
Overall Plant Performance
Effluent BOD, mg/1
Effluent SS, mg/1
Effluent P, mg/1
BOD Removal, percent
SS Removal, percent
P Removal, percent
Side 1
(No Alum)
1.41
168
229
11.3

1,100
77
89
9.7
54
61
14

4.25
2.0
16.3
18.8


885
43
29
5

44
63
9.2
74
72
19
Side 2
(With Alum)
1.41
168
229
11.3

1,100
63
68
6.6
63
70
42

4.25
2.0
16.3
15.4

1.722
885
76
53
73

15
32
1.8
91
86
84
^Includes recirculation.
^Based on Influent P.
                                  6-7

-------
6.4    Performance Data  Using Iron Salts

Addition of iron to trickling filters has been studied at Detroit and Wyoming, Michigan.

The  Detroit Metro Water Department (7) compared the performance of pilot activated
sludge  and plastic-media trickling filter systems  in order to decide on the  design basis
for a  full-scale plant. Chemicals  were added  before the primary settler for both  the
trickling  filter and  activated   sludge  studies,  and  to  the  primary  effluent for  the
activated sludge study. The plastic-media trickling filter test  program  consisted of  a
series  of  16  experimental  runs.  Application   rates ranged  from  1.0 to  about  3.5
gpm/ft^  The  raw wastewater  inorganic phosphate averaged 7.9 mg/1  P with a range of
1.9 mg/1  to  26.6 mg/1. Without the addition  of chemicals,  total phosphate  removals
ranged from  18 to 57%.  With  the addition  of  15  mg/1 of  iron (pickle  liquor)  removals
were 34  to 77%. With  15 mg/1 iron and 0.3 mg/1 Dow  Purifloc A23  polymer,  removals
ranged from  47   to  80%. With 15  mg/1 iron,  0.3  mg/1  A23  polymer, and  30 mg/1
NaOH, removals  were  in the  range  of 67  to  78%. It was  concluded that control of
conditions  for  removal of phosphorus  using the plastic-media trickling filters would be
more  difficult than   in  the  activated  sludge   process. The  activated  sludge  process
achieved  more consistent and  higher phosphorus removals  with iron addition and  was
recommended  for  the full-scale  plant.

Dow  Chemical Company performed  plant scale iron  addition  tests at the Wyoming,
Michigan  trickling  filter  plant  (8,  9,  10).  The  1969  study was designed  for ferric
chloride  addition to  the  raw wastewater to take advantage of the additional BOD  and
suspended  solids  removal in the  primary.  However,  due  to  the recirculation  of  the
trickling  filter sludge with  its  high  phosphorus content, it was necessary  to  split  the
FeClo  addition  between the   raw  wastewater  and the trickling  filter  effluent.  The
chemical feed  and phosphorus  removal  data  are presented in Table 6-3.

To achieve the 80%  phosphorus  removal  required  by  the State, iron addition of 15
mg/1  to  the  raw  wastewater  and 3  to 4  mg/1  Fe    to the trickling filter effluent
along  with 0.3 mg/1  Purifloc  A23 were necessary.  Removal of  BOD during chemical
treatment  ranged  from 60% to 87% across  the plant.  Suspended solids removal in the
primary  averaged  75% with  an overall removal  of 87%. Iron addition to the Wyoming
trickling  filter plant  permitted greater than 80%  phosphorus  removal only  with  the
split chemical addition.

6.5    Choice  of Chemical  Addition

Since  in-plant chemical  precipitation  is  a  new technique,  pilot-scale data should be
obtained  prior  to design of  new facilities. However,  when the plant already exists,
full-scale trials may not be  any more expensive than  pilot-scale tests  and  they  will be
more reliable.
                                        6-8

-------
                                      Table 6-3
     IRON ADDITION FOR PHOSPHORUS REMOVAL AT WYOMING, MICHIGAN
                                                              Test No.
  Chemical Feed
      Fe   to raw wastewater, mg/1
         O i
      Fe   to trickling filter effluent, mg/1
      Purifloc A23, mg/1, before primary
           sedimentation
15
 5-7
 0.4
15
 3-4
 0.3
 15-20
  0
0.2-0.3
15
 7
 0
Total Phosphorus
Raw, mg/1


Primary effluent, mg/1
Removal, %
Final effluent,
Removal, %

mg/1


10.4
1.68
83.9
0.88
91.7

11.1
2.10
81.0
1.46
87.6

14.0
3.4
75.7
2.9
79.2

17.5
6.5
62.9
5.7
67.4
The jar test  is  a most important  tool  for both  designer  and operator when  using
chemical addition.  Information can be  obtained  inexpensively and in a short period of
time, however, certain  precautions should be taken.   An  auxiliary flash mix is  highly
desirable if the jar test  apparatus does not have capability for true high energy mixing.
After  intense  dispersion of trial chemicals,  flocculation can  be simulated by  careful
programming of  time and mixing  energy  levels so they approximate conditions  in the
plant.  The most  effective way to  match jar test  and plant  conditions is to adjust the
jar  test mechanism until it appears to  duplicate the hydraulic regime  observed directly
in  the  plant.  Duration of each mixing interval  should approximate  plant conditions,
assuming plug flow.  Finally, the machine should be left turning very slowly to approximate
settling conditions in the plant. A slight motion in the test jars is a better representation
of  clarifier conditions than if  stirring paddles are  turned off.  No matter how carefully
the rotation speed  and  timing  intervals are selected to approximate plant conditions, the
operator should  devote  considerable  practice to use of the  apparatus before his results
are accepted and used.

A wide variety  of  other bench scale and laboratory tests  (11, 12)   hold  considerable
promise in wastewater technology.  At this time, however, none of them have proved as
effective as the jar test.

6.6     Nature  and Role of Chemicals Involved

Compounds  mentioned  here   are  those  most   likely  to  be  selected  for  chemical
treatment  in a trickling filter plant. Of  the commercially  available metal salts  (13),
liquid  forms are  more  convenient  to  handle, especially at  small  plants. They may have
                                        6-9

-------
the  lowest  overall cost and  are generally  more  effective  than  dry forms. However, it
may  be  necessary  to  use  dry  salts because  transportation  of  pre-mixed solutions,
containing both water and salt, may be costly.

Metal  salt forms  include liquid  ferric chloride,  pickle liquor, liquid alum, and  sodium
aluminate. Information on properties  and handling these chemicals is given in Chapter 10.

Polymers are  available  in a variety  of forms, mostly dry powders.  Since the amount of
polymer required  is far less than the amount of metal salt, the problems  of using dry
polymer  compounds are not severe. Of  the three categories  of polymers (cationic,
anionic and nonionic) there is no universal choice regarding the most effective type.

Whenever  chemicals  are  chosen, they must perform  two main  functions: precipitate
phosphorus, and remove  all types of colloids in the water.  Phosphorus precipitation is
caused  solely  by metal  salts and  involves  conversion  of  soluble orthophosphate to
insoluble phosphate colloids. Following  that, both metal salts  and polymers serve to
coagulate (destabilize)  colloids.  Flocculation  of  destabilized  colloids  is  also  brought
about by both metal and polymers.

6.7    Dosage Selection and Control

Proper  dosage  selection and control  are major keys  to the  success  of  chemical
treatment  because  this  is  where  both  cost  and  performance  are  determined.  The
technique  selected must  be effective  but also should  be  simple and easily interpreted
by the operator.

In  the metal  salt  system, the key  parameters are the mole ratio  fed and the  effluent
phosphorus concentration.  As  a basis for dosage determination,  complete composite
hourly and daily  phosphorus analyses should be  performed initially.  These data will
provide a guide to both total daily  dose required and to daily  variations in dosing rate.

Once accomplished,  this task need not be repeated because subsequent  refinements can
be  based on  phosphorus concentration in the  final  effluent.  Phosphorus  observations
should be  made at both the primary  clarifier and the final sedimentation tank if direct
dosing of the  filter is discounted.

A  suggested  procedure  for setting  the  dose  is  as  follows.  First, express incoming
phosphorus in pounds per day, then  convert to Ib-mole/day by dividing by the  atomic
weight (Ib/lb-mole).  Atomic  weights are 31 for  phosphorus, 27  for aluminum  and 56
for iron.  Next set the  mole ratio  (metalrP)  at  the  proper value,  between 1.5:1  and
2:1, and  compute  the daily  coagulant  dose. An example calculation  is shown below:

              If incoming phosphorus (as P) is 310 Ib/day,
                       310/31 = 10 Ib-moles/day
              If desired mole ratio (M:P) is 2:1,
                        2
                       (-) (10)  = 20 Ib-moles metal  required
                                       6-10

-------
              Using liquid alum  having 4.37% Al,
                       (20) (27) = 540  Ib Al required
                       (540)/(11.1 Ib/gal.) (0.0437)
                       =  1,100  gal. liquid alum  required/day
Then take the total  volume to  be fed per day  and convert it into dosage  rates with
three to five  changes of rate per  day.  These different feed  rates should be selected to
match incoming phosphorus at  the point of injection. Dose  must be matched carefully
to phosphorus demand.  Feeding twice the amount  required  part of the time and  half
the  amount   the  remainder  of  the   time  will  waste  chemicals  and  lead  to  poor
performance.  In  fact, overfeeding chemicals can give as poor  results  as underfeeding;
this  stems from the  tendency of high  metal concentrations to drive  phosphorus colloids
into  a  highly stabilized state.  Dilution of  sewage  during rainy weather  makes little
difference in  the amount of metal salts required since total phosphorus, in terms of Ib/day,
remains about the same.

Changes in  feed  pump settings  can  be  made manually  according  to  a schedule
established and posted  beforetime. Several  types of  cam regulated feed  controls are
also  available  and  are effective (14).

After establishing the initial  feed program,  effluent  phosphorus should be  monitored
hourly  or continuously.  The plant should be kept on  a given feed schedule for at least
three to  five days, to  allow  the biological  reactions to  adjust  to  any  effects of
chemical dosing.  The effluent phosphorus data will  show  peak concentrations resulting
from dosing  improperly  for a period  of time. The  feed schedule can then be adjusted
to remove these  peaks.  Finally,  studies of different mole  ratios fed can be made and
the  results plotted as shown  on Figure  6-3.  These curves can  then be used to choose
the mole ratio required  to meet  effluent phosphorus standards.

Continuing  operation of  the  plant "should  be  monitored  carefully  and  adjustments
should  be  made  in the  chemical  feed schedule  when indicated by  consistently high
effluent phosphorus.  Chemical  feeding can be automated.

Polymer may be  needed  for  good   solids  removal.  Control  of  polymer  feeding  is
relatively  straightforward.   Polymer feed rates are usually kept  constant, but a reduced
feed rate  may be used  during periods of low flow.  Use of polymers may reduce metal
salt  demand  and make metal addition more attractive. Polymers  which  prove effective
in jar tests  should be carefully evaluated in plant  scale operation.  Typical dosage  is 1
mg/1 or  less. One  direct way  to judge  polymer effectiveness is  to  observe  effluent
turbidity.  Polymer feeding can also be automated.
                                       6-11

-------
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-------
6.8    Iron Leakage

Iron leakage may be a problem in  trickling filter  plants using iron precipitation.  Figure
6-4 shows some  typical data from  Richardson, Texas (5). The problem appeared worse
when iron was being fed in the final clarifier. It is evident that  polymer treatment will
reduce the escape of iron colloids.

6.9    Sampling  and Analysis

The use  of chemicals to remove phosphorus in trickling filter plants  will require greater
laboratory  space, facilities,  and  reagents  than  normal treatment.  Table 6-4  shows  a
typical  matrix of data  which  is desirable  at  a conventional plant,  as well as typical
analyses  required to support chemical treatment.

In  the  latter  matrix,  notice that the analyses  include both anion and  cation of the
chemical  being   fed.  Monitoring  of  alkalinity  is  optional  unless  the  effluent
concentration  drops below  50  mg/1 as CaCOo. Some  alkalinity is required  to provide
buffering and  prevent a lowering of pH which  would  have an  adverse effect  on both
chemical precipitation  and biological activity.

Observation of turbidity  in  the final effluent is a good test. There is strong  evidence
that phosphorus  and  turbidity  correlate  in  final  effluents  and  the turbidity  test
provides  a  simple and responsive on-site control tool.  Turbidity  may  be measured  in
the laboratory with  a  bench top meter or  in the plant  with a submersible disk lowered
in the final clarifier.  Observation of the height of the floe blanket in the  clarifier is
also a good means of  control.

Effluent  phosphorus concentration  should  be  determined  either on a semicontinuous
basis with an  automatic analyzer or  on an  hourly  basis  using automatic  or manual
sampling. In addition,  a daily  composite is also  advisable.  Sample portions  should be
flow-weighted  rather  than  time-weighted.  In  plants  enjoying   stable  effective
performance, the schedule may  be relaxed.

Signals from direct  reading  sensors and  automatic analyzers  can be  used  as  a basis for
automatic control of plant operation.
                                      6-13

-------
  10
LU
                 (a) IRON  LEAKAGE IN PLANT EFFLUENT
                            WHEN TREATING  IN
                            FINAL CLARIFIER
                                          . .WHEN TREATING
                                           /PLANT INFLOW
           I
             I       I      I	I
 I      I
   0.8    1.0    1.2    1.4    1.6    1.8   2.0    2.2    2.4

                         MOLE RATIO,  Fe3+/P

   0
   0.8
             (b) IRON LEAKAGE WHEN TREATING PLANT INFLOW
                                            IRON LOST  IN
                                            EFFLUENT
                                            W/0 POLYMER
                                    I
                                         RON LOST IN  EFFLUENT
                                        W/POLYMER IN  FINAL
                                        CLARIFIER
                                       I
1.0    1.2     1.4    1.6    1.8   2.0

               MOLE RATIO,  Fe3+/P
2.2    2.4
 FIGURE 6-4  IRON LEAKAGE DURING PHOSPHORUS REMOVAL
                              6-14

-------
TABLE 6-4  DESIRABLE LABORATORY ANALYSES
    ANALYSES  FOR  CONVENTIONAL TREATMENT








FLOW
TOT SOL
TOT VOL SOL
SUS SOL
SUS VOL SOL
SET SOL
BOD
DO
COD
pH
TEMP
R
A
W





X
X
X
X
X
X
X
X 	 |
X
X
X
p
R
1
M

E
F
F

X
X
X
X
X
X

X
X
X
F
1
L
T

E
F
F

X
X
X
X
X


X
X
X
F
1
N
A
L
F

F
F

X
X
X
X
X
X
X
X
X
X
R
E
C
1
R
C


X
X
X
X
X



X


S
L
U
D
G
E


X
X
X






X
X
S
U
p
E
R
N
A
T
X
X
X
X
X

X

X
X
X
 ADDITIONAL ANALYSES  FOR CHEMICAL TREATMENT









PHOS
ALK
FE
AL
so4
CL
TURB
R
A
W






X
X
X
X
X
X
X
P
R
1
M

E
F
F

X
X
X
X
X
X
X
F
1
L
T

E
F
F





X


F
1
N
A
L

E
F
F
X
X
X
X
X
X
X
R
E
C
1
R
C



X

X
X



S
L
U
D
G
E



X
X
X
X
X


S
U
P
E
R
N
A
T

X
X
X
X
X


                   6-15

-------
6.10   References

 1.  Nesbitt, J. B.,  "Phosphorus Removal -  The State-of-the-Art", JWPCF,  41:5, p
    701 (1969).

 2.  Hall, M.  W.,  and Engelbrecht, R. S., "Phosphorus  Removal - Past, Present, and
    Future", Wat.  and Wastes Eng., 6:8, p 50 (1969).

 3.  Scalf,  M. R.,  et  al,  "Phosphate Removal:  Summary  of Papers", Jour. SED, ASCE,
    95:SA5, p 817 (1969).

 4.  Stephan,  D.  G.,  and  Schaffer, R. B., "Wastewater Treatment  and  Renovation -
    Status of Process Development", JWPCF,  42:3, p 399  (1970).

 5. Derrington, R.  E.,  et al.,  "Enhancing  Trickling Filter Performance by  Chemical
    Precipitation," U.S. EPA Project No. 11010 EGL.

 6. Preliminary Report, Methods for Improvement of Trickling Filter Plant Performance.
    Part I, University of North Carolina, U.S. EPA Contract 14-12-505.

 7.  Detroit Metro Water Department, "Development  of  Phosphate Removal  Processes",
    Detroit,  Michigan  (July,  1970)  (Program  17010  FAH  Grant WPRD  51-01-67
    Advanced Waste Treatment  Laboratory, Cincinnati, Ohio),  Pre-publication  copy.

 8.  Condon,  W. R., "Design of the Wyoming, Michigan  Wastewater Treatment Plant
    Improvements", presented  at the Technical Seminar/Workshop on Advanced Waste
    Treatment, Chapel Hill, North Carolina (Feb.  9-10,  1971).

 9.  "Report on Wastewater Treatment Plant Improvements, Wyoming, Michigan", Black
    and Veatch of Michigan, Consulting Engineers, Kansas City, Missouri (1970).

10.  Stonebrook,  W. J., Dykhuizen, V., Beeghly, J. H., and Pawlak, T. J., "Phosphorus
    Removal  at a Trickling Filter Plant, Wyoming, Michigan", Unpublished (undated).

11.  TeKippe,  R.   J.  and  Ham,  R.  K., "Coagulation  Testing:   A Comparison  of
    Techniques - Part  1", JAWWA,  62:9, p  594  (1970).

12.  TeKippe,  R.   J.  and  Ham,  R.  K., "Coagulation  Testing:   A Comparison  of
    Techniques - Part 2", JAWWA,  62:10, p 620 (1970).

13.  "Coagulants  for  Waste Water Treatment", Chem. Eng. Prog.,  66:1,  p  36 (1970).

14.  McAchran, G.  E.  and  Hogue,  R.  D.,  "Phosphate  Removal  from  Municipal
    Sewage", Wat. &  Sew.  Works, 118:2, p 36 (1971).
                                     6-16

-------
                                    Chapter   7

     PHOSPHORUS  REMOVAL  IN  ACTIVATED  SLUDGE  PLANTS
                           BY  MINERAL ADDITION
7.1    Description of Process

The mechanism  of  phosphorus  removal  by  mineral  salt  addition, usually  iron or
aluminum compounds, in a biological  system  is through a combination of precipitation,
adsorption, exchange, and agglomeration as influenced by the pH  and ionic composition
of  the  water.  The  phosphorus  removal  technique is  operationally  simple  and  is
accomplished by direct mineral addition to  an aeration tank. Treatment  costs are largely
a function of the required effluent phosphate residual. Through optimization techniques,
any  degree  of phosphorus  removal  may  be  provided.  The  main  liability  is the
introduction of dissolved solids.

Phosphorus removal by  biological  systems alone, regardless of the internal mechanisms of
phosphorus  incorporation  into  the  sludge  solids,  is limited, and removal is primarily
controlled  by the magnitude of  solids wasting.  The net  amount of solids wasting  is
dictated  by the quantity and  type of  substrate received  and removed, system design and
operation, and solids capture in  the final effluent.  A high rate system, with its greater
solids production, would undoubtedly  have  the greatest  background phosphorus removal
potential by pure synthesis mechanisms. The magnitude  of this background removal can
be found by  plant measurement with existing facilities or estimated by knowledge of the
net solids production and phosphorus  concentration in the waste activated  sludge. Figure
7-1 shows the phosphorus  removal capability  for a variety of activated sludge systems at
typically reported values for domestic wastewater treatment.

Historically, the benefits derived from mineral additions to activated  sludge plants have
been  known  since  1938  (1).  Thomas  (2)  was  among the  first  to  point out the
increased  phosphorus removals.  Wirts  (3)   also  observed  the  increased  phosphorus
removals derived from a  metal bearing industrial waste at a municipal treatment  facility
in Cleveland, Ohio. Early investigators of mineral  addition for upgrading and modifying
activated sludge systems for phosphorus  removal  include Tenny  and  Stumm (4), Earth
and  Ettinger (5),  and Eberhardt  and Nesbitt (6). Earth, et al.,  conducted pilot  plant
investigations with a  three sludge system for  combined  chemical-biological nitrogen and
phosphorus  removal  (7).  Large  scale, long  term  investigations have  been recently
completed at Manassas, Virginia (8), Pennsylvania State University (9), and  Texas  City,
Texas  (10). Recent  publications  have examined  the use of  aluminum  (11) and  iron
(12) salts and investigated the  kinetics and  mechanisms  of phosphorus removal  using
these minerals (13).

In the treatment of  domestic wastewaters several  investigators,  most recently Rickert
and Hunter (14), have shown that in  a single sludge system a stable  organic residual  is
found  after aeration times of 30  to 60 minutes. Unfortunately, if treatment is stopped
                                       7  - 1

-------
      0.5
      O.U -
      0.3
      0.2 -
                                 I
                            TYPICAL
                        PERFORMANCE RANGE
                                  0.03 P/VSS
HIGH RATE
   A. 8.
                                               STD.  RATE
                                                 A.S.
                                               EXT. AER.
                                                 A.S.
                      Assume COD Removal  = 200 mg/1
                 (Prrmary Effluent - Soluble Final Effluent)
                                 I
         01234
                     PHOSPHORUS REMOVED, rag/I as P


FIGURE 7-1  PHOSPHORUS REMOVAL CAPABILITY OF ACTIVATED
SLUDGE SYSTEMS  RECEIVING SETTLED DOMESTIC  WASTEWATER
                             7 - 2

-------
 at  this point, bio-flocculation is  almost nonexistent and poor solids densities, settling
 characteristics and  effluent  quality  result.   However, when   incorporating  mineral
 addition,  these liabilities are overcome and there  exists an opportunity to derive capital
 savings from reduced  tankage requirements to compensate for the increased operating
 expenditures  associated  with mineral addition. Indeed, in many cases,  the use of  a
 short residence  time   activated  sludge  system  with  mineral  addition,  settling,  and
 filtration  may result in a higher quality effluent  for equal or lower costs  than a purely
 physical-chemical  approach of  coagulation,  settling,  filtration and  carbon  adsorption
 (15).  From  a liability  standpoint,  however, the  designer should be cognizant  of  the
 greater mass  of  generated  waste  activated  sludge  which must be successfully handled
 and treated for ultimate disposal.

 Mineral  addition   to   activated  sludge  for  phosphorus removal  offers  the following
 advantages:

       a. Ease of operation (direct  chemical  addition to existing unit processes).
       b. Relatively small  additional  solids  production (causing  increases  in  sludge
          density and  dewaterability).
       c. Flexibility to changing  conditions (treatment costs are  largely  a  function
          of the influent and required final effluent phosphorus concentrations).

 The  main   disadvantage   is  the   introduction  of dissolved  solids  which  in  some
 circumstances can be considered pollutants in their own right.

 7.2    Mineral Selection and Addition

 The selection  of  the  mineral to  use for  phosphorus removal involves a multitude of
 considerations. Any commercial  chemical,  or industrial waste   stream  (for example,
 pickle liquor  or  alum  sludge  from a water treatment plant) bearing available aluminum
 or  iron  has  potential application.  Ideally, the  best approach  requires comparative
 full-scale plant tests of several months duration.  This, of  course, is  usually  impossible,
 and  the  next best approach is to  run  comparative jar tests,  the  results of which may
 not  be directly applicable. However, they  are at  least indicative  of performance. As an
 illustrative example, the procedures and results from  the Manassas studies (8,  16)   are
 utilized in the subsequent paragraphs.

 Figure 7-2 shows the  total soluble phosphorus as a function of the metal ion dose  for
 the  Manassas  raw  wastewater,  for mixed  liquor  from a  high  rate  activated  sludge
 system, and  for  biologically  stabilized final  effluent. Since both the alum  and ferric
 chloride  can  cause  an  alkalinity depletion and potential pH  drop, pH values are  also
 recorded.  Superior  performance  for  alum  was  found  at  all  mass  dosages with  an
 apparent limiting  residual of  1.0 mg/1  as P  for  the raw wastewater and  final effluent,
 and  less  than 0.1  mg/1  as P for the  aerator mixed liquor. A  yellow  color in the
product water was noted with the higher iron dosages.

Replotting the aluminum  data from Figure  7-2  in Figure 7-3 shows the influence of
                                        7 - 3

-------
                                         FERRIC CHLORIDE

                                         AS Fe3
    20
PH
          Fe3+
          A13+
        6.9
        6.9
6.9
6.7
6.8
6,5
6.7
6.1
6.6
5.9
6.5
01
e
Q_
c/o
o
O
Cf>
                   Fe
                     3+
                                AERATOR

                                HIGH  RATE ACTIVATED SLUDGE

                                MLSS  = 1850 mg/l,%VOL= 80
                10
                   20         30         40

                      METAL ION DOSE, mg/1
                                                         50
    FIGURE 7-2  TOTAL SOLUBLE  PHOSPHORUS RESIDUAL VERSUS

                         METAL  ION  DOSE

      (Reprinted with  permission  from the  American Institute

           of Chemical  Engineers,  New  York,  N.Y.  10017)
                                7 - 4

-------
    1.2
    1.0
    0.8
CO

O
O
oo
t
I
O
O
    0.6
    O.U
    0.2
                     RAW WASTEWATER
                                           I
                  1.0          2.0          3-0          4.0


                         MOLES ALUMINUM ADDED

                   MOLE INITIAL TOTAL SOLUBLE PHOSPHORUS
5.0
          FIGURE 7-3 INFLUENCE OF  POINT  OF ADDITION

             ON  PHOSPHORUS  REMOVAL  WITH ALUMINUM

        (Reprinted with permission from the American  Institute

            of Chemical Engineers, New  York, N.Y.  10017)
                                7 - 5

-------
the point of addition  on the molar  effectiveness of the added  aluminum. Similar but
lower molar  curves are found with the iron versus phosphorus residual data. The lag in
phosphorus  removal effectiveness encountered  with  the  raw  wastewater and  aerator
mixed  liquor is thought  to be due  to  the presence  of unhydrolyzed phosphorus and
the occurrence of competing  side reactions for the metal ion. Aluminum and  iron are
known  to  form  insoluble  heavy   salts  with  certain hydrophilic  colloids   such  as
detergents and  soluble  proteins and their degradation products (17), all of which  would
be  present in  raw and  partially  stabilized wastewater. These  curves  indicate that at
molar ratios  of less than 1:1,  there is an obvious advantage in phosphorus  removal
derived  by  adding the chemical  to  a well  stabilized  liquid, whereas at molar ratios
above 1.5:1, enough metal  ion  has  been added  to satisfy the competing  side  reactions
and  all points  of addition are  equally effective.  The  data  indicate that very  low
phosphorus residuals are possible in a combined chemical-biological system and  that the
ideal point  of addition  would  be just  before  final solids-liquid separation  to  obtain
maximum biological stabilization of the soluble liquid phase.

Figure   7-4  shows the  influence  of wastewater and  process pH upon phosphorus
removal effectiveness with and without mineral additions. In  the upper graph of  Figure
7-4,  above pH 8,  phosphorus removal is occurring naturally  through the formation of
an  insoluble calcium-phosphate complex via  the natural  hardness  of the wastewater.
The  lower graph of Figure 7-4 shows that phosphorus removal at any molar dosage of
metal ion is  actually  controlled by  pH  dependent reactions,  optimally around  6 and 5
for aluminum and iron, respectively.  Since the optimum range  for aerobic oxidation of
carbonaceous  compounds  is  about  pH  6  to  8, it  can be seen  that  there  is  an
opportunity  for  the  simultaneous optimization   of  carbon  oxidation and  phosphorus
removal by aluminum  addition.  However, if nitrification is a treatment goal there exists
a conflict and, in turn, a compromise in pH  goals. Diminished nitrification performance
has been  reported when  alum additions have depleted the wastewater's  alkalinity to a
point where the pH was near optimum for phosphorus removal (9).

Table 7-1  provides a  further comparison  of representative sources of aluminum and
iron. It should be noted that dissolved  solids or  extraneous ions are introduced  and in
some circumstances  these ions may  be undesirable (18).  Alum and FeCl3  cause  an
alkalinity  loss,  and  without  buffering  capacity  in  the wastewater, a substantial pH
reduction may occur.  This can be  compensated  for by  adding a source of alkalinity,
such  as  lime,  or  by  using  aluminate.  Treatment  performance  can  deteriorate
dramatically  if the system pH  is  allowed to   fall  much  below  optimum  (5).  The
designer   should   be   aware  that  periods  of   heavy storm  water  infiltration  will
substantially  dilute the normal  alkalinity of the wastewater,  and if operation is carried
out  at  a  pH of 6, only  20 to  40  mg/1 of residual CaCO3 buffering  alkalinity may
remain  (8). The bottom  part of Table 7-1 shows a comparison of the metal salts on a
mole per  mole  basis,   assuming a  mole  of  metal ion  precipitates  one  mole  of
phosphorus. In practice this never occurs.  On this basis the possible  cost advantage and
alkalinity  advantage with iron is  lost and  the  aluminum salts show  a  potential for less
additional solids production.
                                       7 - 6

-------
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AEROBIC BIOLOGICAL
TREATMENT ZONE

ZONE FOR
PHOSPHORUS
REMOVAL
h *

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               I3+ ADDED AS ALUM
             Fe3+ ADDED  AS FERRIC CHLORIDE

                  I  Mole Metal  Ion
             CHEMICAL DOSE:
                             Mole Initial Total Soluble Phosphorus
                                      i         i          i
     0.20
                                                                  10
   FIGURE  7-U  EFFECT OF pH  ON PHOSPHORUS REMOVAL  FROM A

                           FINAL EFFLUENT

        (Reprinted  with  permission from the American  Institute

             of  Chemical  Engineers, New York, N.Y.  10017)
                                  7 - 7

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                                    Table 7-1
                           METAL SALT COMPARISON
                                                            Metal Salt
Liquid
Sodium
Aluminate

Liquid
Alum

Ferric
Chloride
(A13+) (A13+) (Fe3+)
                                                      (per Ib of Metal Ion)
Bulk Delivered Price at Manassas, $
Extraneous Ion
     Introduced, Ib
Maximum Alkalinity Loss as CaCOo, Ib
0.69
Na+
0.85
None
0.32
S042'
5.4
5.5
0.23
cr
1.9
2.7
                   (Per Ib of Phosphorus at a Mole Dosage of 1::
Bulk Delivered Price at Manassas, $
Extraneous Ion
     Introduced, Ib
Maximum Alkalinity Loss as CaCOo, Ib
Phosphorus Removal of Metal Ion, Ib
Additional Solids Production, Ib
0.60
Na+
0.74
None
0.87
0.28
S042"
4.7
4.8
0.87
0.41
cr
3.4
4.8
1.8
AlPO^
3.9
AlPO^
3.9
FePO^
 4.9
Several  other  points  should  be considered in mineral selection.  First, in the process
effluent the soluble Al, less  than  0.5  mg/1 (16), is apparently much lower than found
with  iron  additions,  6 mg/1  Fe  reported  at  Cleveland  (19).  Second,  alum adds  a
divalent  ion  (SO4  )  which  has a  proven  coagulation  benefit  (20).  Third,  both
Mulbarger (8)  and Long,  et  al.  (9), report improved product water clarity when using
alum in comparison to aluminate.
Chemicals can  be added  with confidence in the  activated  sludge  process just  before
solids-liquid separation,   assuming adequate  dispersal.  Studies  by  Allied  Chemical
Company  (21)  in a 25,000 gpd pilot  plant  indicated that the addition of alum at  the
seven-eights  point  in  the  aeration basin, along with  anionic polymer in the transfer
line, provided  the  optimum  phosphorus  removal,  coagulation and settling.  Polymer
dosages  were found  to be  optimum in  the  0.2 to 0.4 mg/1 range.  An  average A1:P
weight ratio of 2.1:1 was required to reduce the  average  influent total phosphorus of
3.6 mg/1 to 0.45 mg/1  in the effluent.
It  should be  noted  that utilization of  activated  sludge  aeration tanks  for  chemical
                                      7 - 8

-------
mixing and flocculation is a  compromise.  Typically, a  diffused  aeration  system will
have a  velocity  gradient  of  over  100  ft/second/ft  and  the  velocity  gradient  of  a
mechanical aeration system will be much higher. Water treatment experience has shown
that velocity  gradients greater  than 75 ft/second/ft will result in the  onset  of chemical
floe disintegration  (22). Undoubtedly,  some  chemical floe  as  well  as  biological floe
disintegration does  occur  in activated sludge tanks  and,  because of solids recycle, is
unavoidable.  Floe  disintegration  and mineral  overdose  both  lead  to  product  water
quality degradation. In new design situations it may be advantageous  to  provide a brief
period of gentle  solids agitation prior to solids separation to promote reflocculation  of
the  chemical-biological solids. This can be  done by gentle air  agitation, a  flocculation
tank,  or  a flocculator-clarifier.  The  designer  should  also  provide   the  capability  of
adding organic polymer,  if needed.  Nalco 676 and Atlas  2A2,  slightly anionic organic
polyelectrolytes,  have been successfully  used at dosages between 0.3 and 0.4 mg/1 (8).

7.3    Performance and Optimization

       7.3.1  Phosphorus Removal

At molar  dosages of  1  to 2, metal ion to phosphorus, soluble phosphorus  residuals  of
0.3  to  3.0 mg/1 as  P  are frequently encountered in the literature. Interpretation  of
some of  the  data is complicated  by failures to  establish biological  equilibrium  [90%
equilibrium values are reached  at approximately 2.2  times the  operating cell retention
time (16)]  prior  to  changing variables or initiating  an investigative run, and failure  to
consider and report pH.

Detailed   data from  iron  additions  to  activated  sludge  systems are  limited in the
literature  and consequently the more extensively  available data on aluminum addition
provide a  better source of definitive  design information.  However, a  few investigations
of iron additions to secondary treatment processes have  been  conducted on the pilot
and  full plant scale.

Pilot plant  studies by the  Detroit Metro Water Department,  in which several types  of
activated  sludge  systems  were  investigated, indicated that  the  most  effective  total
phosphate reduction was  provided by the  conventional   activated sludge process with
iron (FeC^ derived from pickle liquor)  fed to the primary effluent (23). The majority
of the  test runs  exhibited  removals  varying  from 75 to 85%  for inorganic phosphate
concentrations ranging from  1.9  to  26.6 mg/1  as  P in the raw wastewater. Phosphate
removals  by the activated sludge process  alone (no iron fed) fell principally  in the 55
to 70% range. It  was found that, in  general,  the  addition of iron to the conventional
activated  sludge  process  provided a  treatment system  capable of  consistently  high
phosphorus reduction. The step-feed, activated sludge  process, with the addition of iron
or iron, polymer  and caustic soda, also provided consistent total phosphorus reduction.
It  was concluded that the full-scale  plant  should  be  designed  for the activated sludge
process, arranged  for both  conventional and  step-feed configurations, and  that provision
be made for phosphorus removal, utilizing injection of steel pickle  liquor
                                       7 - 9

-------
A pilot plant (5,760 gpd) at Warren, Michigan (24) was designed to simulate the existing 36
mgd activated  sludge  plant,  with the addition  of one sand  filter and  one multimedia
filter  operated in  parallel after  the  final  clarifiers. Ferric  chloride was fed to the
effluent of the aeration basins to determine whether or not this method would meet
the State-required 80% phosphorus removal. Ferric chloride  addition at a ratio  of 1.5
mg/1  of  Fe  to  1.0  mg/1  of  soluble  PO^   reduced  the  average total phosphorus
concentration from 7.0  mg/1  to  1.2  mg/1  in  the effluent.  This amounted  to a
reduction  of  83%.

Leary, et al.,  of  the  Milwaukee  Sewerage  Commission (25), conducted a  one-year
plant-scale study of the use of waste  pickle liquor (FeSO^)  to enhance phosphorus
removal.   The  Milwaukee  Jones  Island  Plant  consists  of  a  single  primary  facility
followed  by  two  parallel  activated  sludge, plants. Pickle  liquor  was employed  for
phosphorus  removal at the  115 mgd  East  plant  during the test  period.  The 85  mgd
                                                                                 O-i_
West  plant served  as a control. Pickle liquor feed was equivalent  to an average Fe
dosage of 9.4 mg/1.   The  pickle  liquor  was added before  the aeration  tank  about
55  feet downstream  from the  point  of addition of return sludge. Based on a 1970
average total phosphorus concentration of 8.2 mg/1 P in the screened sewage, the  East
Side  plant,   with  iron addition,  accomplished  91.3% phosphorus  removal while  the
control West plant removed  83.1%. Effluent phosphorus  averaged 0.7 mg/1 at the  East
plant  and 1.4 mg/1 at the control plant. The return sludge phosphorous concentration
was  2.29%  P in the  control plant and 2.61%  P  in the  East (test) plant.  The  iron
content of the return sludge  was increased from  1.86 to  5.08%.
                                                               2_
The pickle liquor addition increased  the East plant effluent  804    concentration from
123  to  145  mg/1  and decreased the  alkalinity  from  213  to  169 mg/1 as CaCO3-
Yearly average pH  values were  7.0  and 7.1, respectively, for the East and West  plants.
The  free  acid in  the pickle  liquor  used  (two sources)  ranged   from  2.1  to 9.3%
H2S04.

Comparison of the BOD, COD, and suspended  solids removal  efficiencies of the West
and  East  plants indicated  that  the  addition of unneutralized pickle liquor did not
adversely  affect purification, and it  did not  cause problems  with the plant physical
facilities.  The results  of this one-year  study  indicated  that the use of  waste sulfuric
acid pickle  liquor  as  a source  of iron for phosphorus  precipitation and removal was
practical and effective in maintaining low plant effluent phosphorus  residuals.

In studies at  the University  of Missouri at  Rolla  (26), alum and aluminate at various
times were  fed to laboratory activated  sludge units and compared to a  control  unit.
The alum was more  effective, as shown on  Figure  7-5,  than  aluminate, based on the
A1:P  mole ratio. In  the activated sludge units which  were dosed  with aluminum, the
volatile mixed liquor suspended solids dropped to 50 to  60% of the total mixed liquor
suspended solids, compared  to a  value of 80% in  the control.  The aluminate units had
higher pH, but all pH values were in the range of 7.7 to 8.2.
                                       7 - 10

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Full-scale  studies  were conducted  at  Pennsylvania State  University  on the removal of
phosphorus by addition of aluminum to a 2.0 mgd activated sludge plant. These studies
began in 1969 and continued through 1970 (9). In the  first phase of the work, alum
and  sodium  aluminate were  compared  with respect  to  their ability to  precipitate
phosphorus.  To  prevent  biological upset due  to  mineral  solids displacing  biological
solids in the  mixed liquor, the volatile suspended solids  concentration was held  at the
same  level.  Since  the volatile fraction  of  the  total  mixed  liquor  suspended  solids
decreased  due to  mineral  solids  buildup, this  required  the  maintenance of a  higher
total suspended solids concentration in the mixed liquor.

The  data shown  by  Table  7-2  indicate that  alum  was  slightly superior  to  sodium
aluminate in  removing phosphorus from  the moderately  alkaline  wastewater. The  best
point of addition  for alum  was  found to be at the effluent channel of the aeration
basin  which carries mixed liquor  to  the  final settling basin. Addition of alum both at
the inlet  end of the  aerator and at  a  point about two-thirds of  the way  along the
basin  from the inlet  resulted in  lower  removal  efficiencies. Alum addition ahead of
aeration produced a cloudy effluent.

                                    Table 7-2

                      COMPARISON OF USE OF  ALUM AND
        SODIUM ALUMINATE AT PENNSYLVANIA STATE UNIVERSITY

                                                       Chemical*
Parameter                                    Alum             Sodium Aluminate
                                      Influent     Effluent    Influent    Effluent

Suspended Solids, mg/1                   134        19          94         25
BOD5, mg/1                              87         6          50          7
COD, mg/1                               244        31         160         36
Phosphorus as P, mg/1
     Filtered  Ortho                        6.4        0.28        5.4         0.51
     Filtered  Total                         7.6        0.27        6.9         0.57
     Unfiltered Ortho                     10.4        1.17        6.2         1.14
     Unfiltered Total                      12.4        1.48        8.6         1.53
Alkalinity as CaCO3, mg/1                                      156        103
pH                                       7.4        7.1          7.15        7.25
Alum Dosage as A12(SO4)3- 14H2O, mg/1          160
Na2Al2O4 dosage, mg/1                                                 44
A1:P Ratio  **, weight                         2.04:1                 2.04:1
S042-, mg/1                              24        131

  *Chemicals added at the effluent end of the aeration tank.
**A1:P ratio based on expression of phosphorus in the filtered ortho form.
                                      7 -  12

-------
Aluminate  addition was  found to be most  effective at a point  in the aeration basin
near the outlet. Aluminate  addition either before or after aeration produced a more
turbid  effluent.

Sludge  production  in  the  studies  comparing  alum  and aluminate showed  that  the
volume of  sludge  produced  per million gallons  of  wastewater treated  was about the
same  for both coagulants. However, the weight of  solids produced  was considerably
less for aluminate than alum.

Because alum  was  found to  be superior to aluminate in  removing phosphorus, further
study  of  alum  was performed for a period of one year. One-half  of the  activated
sludge  plant was used in the alum study  and the  other half was operated  without
chemical addition  for comparison.  Table  7-3  shows average  results  for  operation at
rates equal  to  or less than the plant design capacity.

                                   Table 7-3

  COMPARISON OF ALUM ADDITION TO THE AERATOR AND CONVENTIONAL
         ACTIVATED SLUDGE AT PENNSYLVANIA STATE UNIVERSITY
     FOR FLOWS  NOT EXCEEDING THE DESIGN CAPACITY OF THE  PLANT

                                            Effluent with        Effluent without
Parameter                      Influent     Alum Addition*        Alum Addition

Suspended Solids, mg/1           110              22                    26
BOD5,mg/l                       71               9                    13
COD, mg/1                       172              55                    68
Phosphorus as P, mg/1
     Filtered Ortho                6.7            0-28                   6.7
     Filtered Total                 6.3            0.36                   6.7
     Unfiltered Ortho              8.9            1.15                   7.2
     Unfiltered Total             10.0            1.41                   7.3
Alkalinity as CaCO3, mg/1        168              80                   120
pH                               7.6            6.75                  7.35
A1:P Ratio**, Weight                            2.97:1

 *Alum added  to  effluent  of aeration tank. Values  shown in this column are means
  for the  period of study.
**The  A1:P ratio is based  on expression of phosphorus  in the filtered ortho form.

Problems were  experienced  with loss of solids from  the  final basin during peak  flow
periods where  alum treatment was  being practiced.  It  was  believed,  however,  that
proper  allowance for peak flows in  design of such facilities would  eliminate  excessive
solids loss. The effluent insoluble phosphorus  concentration was found  to correlate well
with the effluent suspended  solids  concentration.

A 2,000 gpd pilot  operation  at the  main wastewater  treatment plant of  the District of
                                     7 -  13

-------
Columbia  was  operated  at a  constant  alum  dose  rate  (27).  The  pilot  plant is  a
four-stage  step aeration process  followed by secondary clarification. Alum was added to
the wastewater of moderate alkalinity (100 to 150 mg/1 as CaCO-j) at the fourth stage
of aeration using an A1:P weight ratio of 2:1 (molar ratio 2.3:1), based on an influent
phosphorus concentration of 8.15 mg/1  as P. Mixed liquor suspended  solids averaged
6,300 mg/1 with a volatile content  of 60% and a cell retention time  of about 5  days.
Total phosphorus  residuals  averaged  1.9 mg/1  as  P  (78% removal)  in the  clarifier
effluent.

Figure 7-6 shows  the  chemical phosphorus removal  found for the Manassas high rate
activated sludge plant  with  aluminate (16)  and  alum (8)  additions at slightly alkaline
pH values. Phosphorus concentrations for Figure  7-6 were  corrected  for biological
removal.  The  Manassas Pilot  Plant,  shown  in  Figure  7-7, is a  0.2  mgd three-stage
(nitrification-denitrification)  activated  sludge  system  operated  at  the  Greater Manassas
Sanitary  District of Prince William  County, Virginia. Table  7-4 shows  the  system
performance for 200 determinations  with alum addition. The  reader is referred to the
original  publication for more detailed information.

                                    Table 7-4

                      COMBINED CHEMICAL-HIGH RATE
                 ACTIVATED SLUDGE SYSTEM PERFORMANCE

                                                  Percent Less Than
Item                                Min.    _10     20    50    80     90     Max.

Primary Effluent
   COD, mg/1                          27    64     86    152    227   250     324
   P, mg/1                             2.2    3.8    5.0    8.4    11.4   12.8     18.5
   BOD5:COD*                      0.26                0.43                 0.56

High Rate Activated Sludge Effluent
   Soluble Phase
     COD, mg/1                        13    23     26     33     41     48     79
     P, mg/1                          0.2    0.8    1.0    2.0    3.0    3.6     6.8
     BOD5:COD*                    0.14                0.28                 0.36

   Solid Phase
     Suspended Solids,  mg/1              0   10     14     21     36     44     196
     BOD5:SS*                      0.10               0.23                 0.31
     COD:SS*                       0.43                0.58                 0.80
     P:SS*                         0.039               0.051               0.063

     Suspended Solids After
     Polymer Addition,** mg/1           00      1       2      8    1418

     Suspended Solids After
     Mixed Media Filtration**, mg/1      000       0      2     5    12
  *Ratio of minimum, median, and maximum monthly averages for each parameter
 **94 determinations
                                        7 - 14

-------
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-------
Optimization  of phosphorus  removals  with mineral additions  can be done  two ways:
by pH  adjustment to the  point of minimum solubility (pH 6 to 6.5, residual alkalinity
of 20 to 40  mg/1 as CaCOo) and by  splitting the chemical dose to  separate parts  of
the  treatment  system (8).  Optimization  maximizes  the  efficient  use  of chemical,
minimizes  additional solids production, and produces soluble phosphorus residuals  of
less than 0.5  mg/1.  Hais, et al. (27), indicated, using  step aeration with alum addition,
that above pH  6.6  a rapid increase  in the  effluent  phosphorus residual  occurred  with
increasing pH. However, operation with a mixed liquor  pH  of less than 6.2 caused  an
upset in the activated sludge  process. It was concluded that optimum  performance (0.6
mg/1  effluent  phosphorus  residual)  was  achieved  by  maintaining  a final stage  pH
between  6.3  and  6.6 at  an A1:P  weight ratio of  2:1. Mulbarger  (8) showed  the
capability  of  pH  adjustment with  a  denitrification system  and  demonstrated  the
advantages of  split  chemical  treatment in a multi-sludge  system.  Results from the pH
adjusted  system  are  shown  in  Figure  7-8.   Long,  et  al. (9),  found  a  natural  pH
adjustment  with  high doses of  alum  in   a  poorly buffered  wastewater  and  report
phosphorus residuals below 0.5 mg/1  at A1:P weight ratios of from 2:1 to 3:1.

Organism activity  and type  (9)  as  well as the  completeness of a  chemical reaction
affect  phosphorus removal and   are influenced  by the  temperature. No temperature
effect  has been  reported, however,  for the rate  of chemical reaction  (13) operating
between 10 and 20 C.

Mulbarger  (8,  16)  notes  that   the presence or  absence  of nonsettleable effluent
suspended  solids from a combined chemical-biological  system is more dependent upon
the ratio of  net volatile solids produced to aluminum added than upon pH, exceeding
an aluminum  to  phosphorus ratio, or exceeding  a  given aluminum  dosage.  It  is
recommended that this ratio  not  drop below  3 to 5. It is believed that the biological
volatile  solids provide exchange   and/or  sorption sites  of limited  capacity for  the
precipitated aluminum-hydroxy-phosphate complex, and that  these natural polymers aid
in clarification.  Thus, the  more biological solids  produced from the system  the greater
the aluminum dosage that  can be  used  without effluent suspended solids problems.

When  designing the  phosphorus  removal system,  the  designer should be  cognizant  of
the phosphorus levels in the  effluent suspended  solids. There  was a  nominal  1.0 mg/1
of phosphorus in  the effluent suspended solids from the high rate system at Manassas
(8).  After  pH  adjustment  and addition of  0.3 to 0.4  mg/1 of anionic polymer (Nalco
676),  effluent suspended  solids were reduced to 2  mg/1. Consequently, the effluent
total  phosphorus  was also reduced.  Polymer performance  was  also  reported  to be
influenced  by the pH (8).  If total phosphorus residuals  of less than  0.5 mg/1 as P are
required, a multimedia filtration system is  recommended. Dual  and  tri-media filtration
both provide  effective tertiary solids separation. Hais,  et  al. (27) showed that tri-media
filtration consistently removed between 5  and  10% more suspended  material than did
the dual-media filter. Filter runs  between  24  and 32 hours  were  regularly maintained.
Tri-media filtration performance was  reported  to  be superior  to  dual-media filtration
at Manassas (8).
                                       7  - 17

-------
                        1.0
2.0          3.0
ALUMINUM ADDED
4.0
5.0
                            	   Ib
                           CHEMICALLY REMOVABLE PHOSPHORUS'  Ib
             FIGURE  7-8   EFFECT OF ALUMINUM  ADDITION  WITH pH
             ADJUSTMENT ON  TOTAL  SOLUBLE PHOSPHORUS RESIDUAL
       7.3.2  Costs

Power  costs  for  combined  chemical-biological  treatment  are  negligible.  Maintenance
costs will  increase somewhat  due to the additional equipment. Capital expenditures for
storage  facilities,  instrumentation,  and equipment  will be  very low  at  larger  facilities
unless multi-media filtration is incorporated. Chemical costs will vary as a function of
the  incoming  phosphorus   concentration  and  the  required  phosphorus   residual.
Additional  expenditures  for pH  control  (alkalinity dependent)  and  solids  control
(polymer additions) may be necessary. See Chapter 10 for further information.
7.4    Process Design Examples

Four  design  example  problems  were  selected  for an  arbitrary  wastewater.  Each
illustrates  specific  points  in  combined  chemical-biological  wastewater  treatment  with
alum additions  for phosphorus  removal. Results  from the  Manassas  work  are used for
some of the calculations.

       Assumptions:

       a.  Net biological solids  production  =  0.28  Ib of volatile solids produced per Ib
          of COD  removed;  the  volatile solids contain  2% phosphorus; and  the  total
          solids average 80%  volatile.
       b.  The  biological system is  to  be  designed with a  minimum hydraulic contact
          time  of   1  hour  at the  maximum 4 hour hydraulic  peak. The  ratio  of
                                      7-18

-------
   maximum flow rate to average flow rate = 1.5. A  cell retention time (CRT)
   of two days is selected.
c.  Primary Effluent Characteristics:
                  COD  = 200 mg/1
                     P  =  10 mg/1
              Alkalinity  = 150 mg/1 as CaCO3
Find:
1.  Effluent COD, BOD5 and phosphorus
2.  Total solids production
3.  Alkalinity loss
4.  Dissolved solids addition
5.  Size of final clarifier, return  and waste sludge pumping systems.
6.  Chemical costs with the following delivered prices:
                  Alum    = $0.32/Ib A13+
                  Polymer = $1.50/lb polymer
                  Acid     = $0.02/lb H2SO4
                  Lime     = $0.01/lb Ca(OH)2
Example No.  1:  High rate system  for most efficient  chemical addition  with  pH
above 7 and no optimization by pH adjustment.
1.  Effluent COD, BOD5, and Phosphorus
   (See  Table  7-4. Note: Soluble  organics from a biological system vary as a
   function of the wastewater and dilution of the  refractory fraction. Manassas
   values are used for illustration  only.)
 Effluent soluble COD   =     ^227152    <41'33) + 33
                               5 + 33 = 38 mg/1

 Assume effluent suspended solids  = 20 mg/1
             Total effluent COD  = 20 (0.58) + 38
                                 = 12 + 38
                                 = 50 mg/1
                                7-19

-------
       Effluent BOD5  = 38 (0.28) + 20 (0.23)
                      =  10.6 + 4.6                              [Using BOD5 ratios
                                                                from Table
Background phosphorus removal per Ib COD removed
       = (biological solids production  ratio) (phosphorus content)
       = (0.28) (0.02)
       = 0.0056 Ib phosphorus removed
                Ib COD removed
[The  background phosphorus removal rate  at Manassas was found to be approximately
0.01 Ib P Removed
     Ib COD removed  ( } J
Background phosphorus removal expressed as concentration
       = (COD removal) (phosphorus removal per Ib COD removed)
       = (200-38)  (0.0056)
       = 0.9  mg/1
Chemically  removable phosphorus =  10.0 - 0.9 = 9.1 mg/1
Use Al   /chemically removable  phosphorus  dose  = 1.25 Ib/lb
From Figure  7-6 find 0.6 Ib of phosphorus removed per Ib of aluminum added at the
dosing ratio  of 1.25
Aluminum dose =  1.25 (9.1) =  11.3 mg/1 A13+
Chemical phosphorus removal = 0.6 (11.3) = 6.8  mg/1 P
Soluble phosphorus residual = 9.1 - 6.8 = 2.3 mg/1
Total effluent phosphorus  =  2.3 + 20 (0.05)                      [P/SS ratio from
                         =  3.3 mg/1 P                            Table 7-4]
 The preceding calculations are useful  from the standpoint that they show the pollutant
 fractions  in  both  the  soluble and  solid  phases.  Often a remarkable treatment im-
 provement can result  from effluent solids control and  minimization.
       2.  Alkalinity Loss
          Maximum possible alkalinity loss due to aluminum hydrolysis
                = 5.4 (5.5)  = 30 mg/1 as CaCO3

          which gives ~  =  2.7  Ib CaCO3 loss/lb A13+
                                      7-20

-------
At  an  aluminum added to  chemically removable  phosphorus ratio  of 1.16,  an  average
alkalinity  loss  of 2.3 Ib  CaCOg/lb AP+ was  measured  at  Manassas (8).  Like solids
production values, alkalinity losses are a function  of the proximity of aluminum  dose to
stoichiometric phosphorus requirements and the reaction pH.

       3.  Dissolved Solids Addition

                    9               ,         mg SO42"
                SO/' = (11.3 mg A1J+/1) (5.4	- ) =  61 mg/1
                   *                         mg A13+      	

Although  dissolved  solids  are  added to the system, the designer should remember that
other soluble wastewater components  (i.e.,  organics,  phosphorus,  alkalinity,  etc.) are
being removed. Prior  to the addition of sulfuric acid for pH  adjustment at Manassas, no
increase in dissolved solids was measured on a primary to final  effluent basis because of a
compensating loss of soluble wastewater components (8).

       4.  Final Clarifier and Pumping System
                Organic solids   =  57 mg/1
                Inorganic solids  =  43 mg/1
                     Total       = 100 mg/1
            Solids lost in effluent =  20 mg/1
             Solids accumulation =  80 mg/1

          CRT = 2 days, and aeration tank detention at average flow
                = 1.5 (1) = 1.5  hours
                             (24)(2)
          MLSS in aerator =    '    (80) = 2,560 mg/1

Since this is the final clarifier a conservative overflow rate  should be utilized. From
Figure 7-9 the minimum settling rate  of 1,150 gpd/ft2 was observed at a MLSS of 2,600
mg/1. To  provide for peak flow, the clarifier should be designed for an overflow rate of
          ^
770 gpd/ft , or less. It should have a 12 ft effective water  depth, and might be provided
with a surface skimmer.

       Maximum SVI at 2,600 mg/1 MLSS = 82 ml/gm  (Figure 7-9)
       Approximate return sludge concentration at worst condition
                   106    106
                               = 12,200 mg/1
                  SVI    82
       Solids balance equation where R is sludge return rate
                       + R) (MLSS) <_ (R) (return sludge cone.)
                                      7-21

-------
 E
 CT
 X
 uJ
 o
 UJ
 CD
 a
CM
 o
 Q.
 cn
      100
      75
       50
25
     1500
     1000
      500
                 MAXIMUM
                 MINIMUM
                 MAXIMUM
                 MINIMUM
            AVERAGE RANGE OF OPERATING

            SURFACE OVERFLOW RATE:  680-13W gpd/ft2
                 1000     2000     3000      4000      5000


                       MIXED LIQUOR SUSPENDED SOLIDS, mg/1
                                                      6000
        FIGURE 7-9  PHYSICAL CHARACTERISTICS OF HIGH RATE

          ACTIVATED SLUDGE WITH MINERAL ADDITION (8,16)
                                   7-22

-------
                       or considering just the case of equality,

                                  2,600
                      '  gave  12,200-2,600

                R = 0.4 Qaye

                (Actually,  effective   design  would  indicate  a 50%  capability;  i.e.,
                0.2  to  0.6 Qaye capability)

Solids to be wasted per day = 80 mg/1 at a minimum sludge solids concentration = 12,200
mg/1. Assume continuous wastage with separate pump.

                               80
                * T  	 X-*        *- V     _ f\ f\f\ /"C  f~\
                w  ~ ^ave   19 ?nn   ~ u-uuo:>  ^ave
                (Again, effective design  would indicate  a  50% capability;  i.e., 0.003
                to 0.01 Qave capability).
       5.  Alum Cost

                = (11.3)(0.32)(8.34)(10~3)  = 3.1 #1.000 gal.

       Additional  Comments

No mention has been made of the effect of sidestream  phosphorus contributions. With
conventional  solids  handling  and  treatment  processes,  gravity and flotation thickening,
filtration  and   centrifugation,  aerobic   and  anaerobic  digestion,   and  incineration,
phosphorus  recycle  should not  be  a  problem  and  any  that  occurs will largely  be
associated with the solids fraction of the minor process streams. However, processes that
cause biological  solids liquefaction and hydrolysis, such as heat treatment processes, will
result  in a substantial recycle  of soluble phosphorus  with a corresponding increase of
metal ion requirements.

       Example No. 2:  Same system as Example No. 1 but with sulfuric acid  addition
       for pH adjustment (residual alkalinity = 30 mg/1 as CaCOo) and polymer  addition
       for solids control.

Detailed  calculations are  not shown  for the problem since the  techniques are essentially
the same as in Example No. 1. Results are summarized, along with results from  the  other
examples, in Table 7-5. Highlights from this problem are as follows:

       1. COD, BODj, and  suspended phosphorus  concentrations in  the  effluent are
         substantially  reduced  by an  assumed polymer dose of 0.3  mg/1. The
         chemically removed phosphorus was calculated for this case by multiplying the
         0.6 Ib P removed/lb  A13+  added, from Figure  7-6,  by 1.33. The  1.33 was
         obtained from Figure 7-4, assuming an adjusted pH of about 6. The result was
         a phosphorus residual of 0.1 mg/1 with an  aluminum  dose  of 11.3 mg/1. But
                                      7-23

-------
        Figure  7-8  showed  from  experimental  data  a  nominal  0.5  mg/1  residual
        phosphorus at  this A1:P ratio and,  therefore, the conservative residual of 0.5
        mg/1 soluble phosphorus was chosen.
                                    Table 7-5

                     SUMMARY OF DESIGN CALCULATIONS

Item                         Example 1    Example 2    Example 3     Example 4

pH Adjustment                  No          Yes           Yes          Yes
Polymer Addition                No          Yes           Yes          Yes
Split Treatment*                 No          No           No           Yes
Mixed Media Filtration            No          No           Yes          Yes

Total Aluminum Dose, mg/1       11.3         11.3          27.3          18.2

Effluent Quality, mg/1
     Suspended Solids            20             2            0            0
     COD                       50           39           38
     BOD5                      15           11           11
     Total Phosphorus            3.3           0.6          0.2           0.2
     Total Soluble Phosphorus     2.3           0.5          0.2           0.2

Solids Production, mg/1
     Biological                   57           57           57           57+
     Chemical                    43           45           92           66

Alkalinity Loss
     Due to A13+ Addition        30           21           109           59
     mg/1 as CaCO3
    o
804  Increase  Due
to A13+ Addition, mg/1           61           61          147           98

Alum Cost, tl 1,000 gal.          3.1           3.1          7.4           4.9
Polymer Cost,  4 / 1,000 gal.        0           0.3          0.3           0.3
Acid Cost,  41 1,000 gal.           0           1.7            0           1.0

Total Cost, tf / 1,000 gal.          3.1           5.1          7.7           6.2

Clarifier Overflow Rate, gpd/ft2    770           670          360
Return Sludge Rate             0.4Q          0.6Q         0.9Q
Waste Sludge Rate             0.0065Q      0.008Q       0.012Q

*Split  treatment here incorporates mineral addition as in Example No.  1 without pH
  adjustment, followed by mineral addition with pH  adjustment at a later point.
                                   7-24

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2. The alkalinity loss due to hydrolysis was also reduced due to increased
   formation.  Using 96% strength sulfuric acid and  assuming a residual alkalinity
   of 30 mg/1 as CaCOo, a calculated  sulfuric acid requirement of 101 mg/1  was
   found. The sequence of chemical addition is  acid, alum,  and  polymer, with
   about 5 minutes of mixing at peak flows between each application.
                                               o
3. Dissolved solids additions totaled 156 mg/1 SO4  ; 61 mg/1 due to the alum and
   95 mg/1 due to the acid.

4. Because  of  improved  solids  capture,  the  operating  MLSS  in the  aerator
   increased  to 3,200  mg/1  necessitating  a lower surface  overflow rate in the
   clarifier, and greater return and waste sludge handling capability.

5. Chemical  costs  increased  to 5.1^/1,000  gal.  with  benefits  in phosphorus,
   suspended solids, BOD^ and COD removals.

Example 3: Assuming  mixed media filtration provides complete  solids control,
what  is the change in system calculations if a residual effluent phosphorus of 0.2
mg/1  as P is to be provided?

Highlights from this problem  are as follows:

1. Essentially  no differences  from  Example No. 2 are found in effluent COD and
   BOD. However,  the mixed media filter does provide positive  effluent solids
   control  in  the event of system  upset. An  A1:P weight ratio of 3 (Figure  7-8)
   was used.

2. The addition of alum caused  an alkalinity consumption of 109 mg/1, which
   would deplete the background alkalinity of the wastewater to 41 mg/1 as CaCOo.
   If a  substantially higher  alum  dosage  had  been required,   all  of   the
   alkalinity  might  have been  consumed,  and   addition  of lime might  have
   been necessary.
                                                     <-}
3. Dissolved  solids addition consisted of 147 mg/1 804   from the alum.
4. Additional solids productions resulted in an operating solids  level  of 4,800 mg/1
   in the aerator,  necessitating a lower  surface overflow rate and higher return
   and waste sludge capabilities than in earlier examples.

5. Total chemical treatment costs are raised to 7.7^/1,000 gal.

Example No. 4: Split  treatment  (chemical  addition at more than one  point) is
utilized for  a required effluent phosphorus concentration of 0.2 mg/1. Assume the
first point  of  addition is as in Example No. 1. Further  mineral addition will be
made to the effluent in Example  No.  1  either before filtration or during  a second
stage of biological treatment.
                                 7-25

-------
      1 .  Changes in effluent COD and BOD  are not calculated since this is dependent
         upon  whether  split  treatment  is practiced with just  filtration, or whether
         another biological  system  is added. In a real  situation it would be better to
         reduce the aluminum dose  below that  in  Example  No.  1  in the first stage
         system for more efficient chemical use. This  was not done here for design
         simplicity. Another possibility is addition of part of  the  chemical dose in the
         primary settler.

         The Al   dose of 6.9 mg/1 for the second addition was arrived at using Figure 7-8
         for a  pH adjusted  system.

      2. The alkalinity depletion due to aluminum addition was calculated as  59 mg/1
         as CaCOo. This would  leave a residual alkalinity of 91  mg/1. Sixty mg/1 as
         FUSO^ was  added  to  reduce  the  alkalinity  to 30 mg/1. Again, in a  real
         situation acid might not have to be added to this wastewater.
                                                                   ^
      3. Dissolved  solids additions were calculated as 98 mg/1  SO4   due to alum
                                9-
         addition and 59 mg/1 SO^   due to acid addition.

      4. Clarifiers were not sized in  this example. If two  biological processes were used
         in series,  the final  clarifier of  the first process could  be designed with an
         overflow rate from the middle' of the performance curve in  Figure 7-9.
       5. The cost of acid  is l.Oi / 1,000 gal.  Total chemical costs are 6.2tf / 1,000 gal.

       Comment: This final example, in comparison to example No. 3, shows the benefit
       derived from split chemical treatment for low phosphorus residuals.

7.5    References

 1. Guggenheim Process  Described  by:  Kiker, J. E., "Waste Disposal for Dairy Plants",
    Sanitarian (Los  Angeles)  16, p 11  to  17 (1953).  Florida Engng. Exp. Station 7,
    Leaflet  Series No.  51 (1953). Moore, R. B., "Biochemical Treatment  for Anderson,
    Ind.", Wat. Works and Sew., 85:11 (1938).

 2. Thomas, E.  A., "Phosphat-Elimination in der BelebtechlemannlagevonMannedorf und
    Phosphat-Fixation in See-und Klarschlamm", Vierteljahrsschrift der Naturforschenden
    Gesellschaft  in Zurich, 110, Schlussheft, S., p 419 (1965).

 3. Wirts, J. J.,  "Communications", Buckeye Bulletin (Summer, 1966).

 4. Tenny,  M.  W.,  and  Stumm, W. J., "Chemical Flocculation of Mirco-organisms in
    Biological Waste Treatment", JWPCF, 37:10, p 1370 (1965).

 5. Barth,  E.  F.,  and  Ettinger, M. B.,  "Mineral Controlled Phosphorus Removal in  the
    Activated  Sludge Process", JWPCF, 39:8, p 1361 (1967).

 6. Eberhardt, W. A., and Nesbitt, J. B., "Chemical Precipitation of Phosphorus  in a High
    Rate Activated Sludge System", JWPCF, 40:7, p 1239 (1968).
                                       7-26

-------
 7. Barth, E. F.,  Brenner,  R. C., and  Lewis,  R.  F., "Chemical-Biological Control of
    Nitrogen and Phosphorus in Wastewater Effluent", JWPCF, 40:12, p 2040 (1968).

 8. Mulbarger, M. C., "The Three Sludge  System  for Nitrogen and Phosphorus Removal",
    To be presented at the 44th Annual Conference of  the Water Pollution Control
    Federation, San Francisco, California  (October, 1971).

 9. Long, D. A., Nesbitt, J. B.,  and Kountz, R.  R., "Soluble Phosphate Removal in the
    Activated Sludge Process   A Two Year Plant  Scale  Study",  Presented at the  26th
    Annual  Purdue Industrial Waste Conference, Purdue  University,  LaFayette, Indiana
    (May, 1971).

10. Connell, C. H., and Frey, S. M., Private Communications (January, 1971).

11. Humenick, M. J.,and Kaufman, W. J., "An Integrated  Biological-Chemical Process for
    Municipal Wastewater Treatment", Presented  at the 5th  International Water Pollution
    Conference, San  Francisco, California (July, 1970).

12. Schmidt, F., and Ewing, L., "Phosphate Removal System for Small Activated Sludge
    Plants", Presented at the Pennsylvania Water Pollution  Control Association Meeting,
    State College, Pennsylvania (August, 1970).

13. Recht, H.  L., and  Ghassemi, M., "Kinetics and  Mechanism  of Precipitation  and
    Nature of the Precipitate Obtained  in Phosphate Removal from Wastewater Using
    Aluminum (III) and Iron (III) Salts", Water Pollution Control Research Series, 17010
    EKI, Contract  14-12-158, USDI, FWQA (April, 1970).

14. Rickert, D.  A., and  Hunter,  J. V., "Effects of Aeration Time on  Soluble Organics
    During Activated Sludge Treatment", JWPCF,  43:1, p  134 (1971).

15. Gulp, R.  L., and  Gulp, G.  L.,  Advanced  Wastewater Treatment, Van Nostrand
    Reinhold Company,  New York (1971).

16. Mulbarger,  M.  C.,   and Shifflett,  D.  G.,  "Combined  Biological and  Chemical
    Treatment for  Phosphorus Removal", Chem.  Eng. Prog.  Symp.  Series, 67:107, p  107
    (1970).

17. Sawyer, C. N., Chemistry for Sanitary Engineers, McGraw-Hill, New York (1960).

18. McKee,  J. E.,  and  Wolf,  H.  W., Water Quality Criteria,  Publication  No.  3-A,
    California Water Quality Board, Sacramento, California (1963).

19. Cherry, A. L., and  Schuessler,  R. G., "Private Company Improves Municipal Waste
    Facility", Wat. and Wastes Eng. 8:3, p 32 (1971).

20. Water Quality  and  Treatment,  2nd  Ed., American Water  Works  Association, New
    York  (1951).

21. Ockershausen, R. W., Harriger, R. D., and  Zuern, H. E., "Phosphorus Removal Tests
    with Alum" for Buffalo Sewer Authority, Buffalo, New York,  by Technical Service
                                      7-27

-------
    Department, Allied Chemical Corporation, Industrial Chemicals Division, Morristown,
    New Jersey (1971).

22. Fair, G. M., and  Geyer,  J. C.,  Water Supply and  Wastewater Disposal,  Wiley  and
    Sons, New York (1961).

23. Detroit Metro  Water Department, "Development  of Phosphate Removal Processes",
    Detroit, Michigan  (Program  17010  FAH Grant  WPRD  51-01-67  Advanced  Waste
    Treatment Laboratory, Cincinnati, Ohio), Prep ub lie at ion Copy (July,  1970).

24. Boggia,  C.,  and Herriman, G.  L.,  "Pilot Plant  Operation  at Warren, Michigan",
    Proceedings  of the 43rd  Annual  Conference of the Michigan Pollution  Control
    Association (1968).

25. Leary,  R.  D., Ernest, L. A., Powell, R. S., and Manthe, R. M., "Phosphorus Removal
    with Pickle Liquor in a 115 MGD Activated Sludge Plant", Sewerage Commission of
    the  City  of Milwaukee,  Wisconsin,  Grant No.  11010FLQ,  Water  Quality  Office,
    Environmental  Protection  Agency, Advanced Waste Treatment Research Laboratory,
    Cincinnati, Ohio, Prepublication Copy, (1971).

26. Grigoropoulos,  S. G., Vedder, R. C., and Max, D. W., "Fate of Aluminum-Precipitated
    Phosphorus  in  Activated  Sludge and Anaerobic  Digestion",  Presented at the 43rd
    Annual Conference of the Water Pollution Control Federation, Boston, Massachusetts
    (1970).

27. Hais, A. B., Stamberg, J.  B., and Bishop, D. F., "Alum Addition to Activated Sludge
    with Tertiary Solids Removal", Presented at the 68th National Meeting of the AIChE,
    Houston, Texas (March 1971).

28. Dean,  R.  B., "Sludge Handling", Presented at the  Advanced  Waste Treatment and
    Water  Reuse Symposium, 4th Session,  Sponsored by the Environmental Protection
    Agency, Dallas, Texas (Jan. 12-14, 1971).

29. Smith,  J.  E. Farrell, J. B., and  Dean, R. B., Unpublished Data from  the Advanced
    Waste   Treatment  Laboratory, Office of Research  and  Monitoring, Environmental
    Protection Agency, Cincinnati, Ohio (Jan., 1971)

30. Dotson, G. K., Unpublished Data from the Advanced Waste Treatment Laboratory,
    Office  of Research and Monitoring, Environmental Protection Agency, Cincinnati,
    Ohio (July, 1971).
                                      7-28

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                                   Chapter  8
            PHOSPHORUS  REMOVAL  BY  LIME  TREATMENT
                        OF  SECONDARY  EFFLUENT
8.1     Description of Process

       8.1.1   Theory

Lime  treatment of  wastewater is  essentially  the  same  process  as  the familiar lime
softening of drinking water  supplies. The  objectives, however, are quite different. While
softening may occur,  the primary objective is to remove phosphorus by precipitation as
hydroxyapatite. This reaction was described in Chapter 3.

During phosphorus  precipitation other important reactions occur.  The reaction of lime
with alkalinity, that results  in  calcium  removal when  carrying out softening, not only
takes  place  when  treating wastewater,  but may have a  very important  effect  on the
general efficiency of  the process. This  reaction can be considered  to take place  in the
two following ways:

                  Ca(HC03)2  + Ca(OH)2 * 2  CaCOg + 2 H2O

                  NaHCO3 + Ca(OH)2 > CaCO? + NaOH + H2O

The  first  equation  is that  for softening.  Some  wastewaters do  not  contain  enough
calcium,  however, for that  equation to  be satisfied. Calcium  carbonate  precipitation
may  still occur,  but by  the  second reaction.  The  reactions to  form  CaCO^ are
important for two  reasons:  the lime consumption  determines to a considerable  extent
the lime dose required  for operating the process,  and the  resulting CaCO^ acts as a
weighting agent to aid in settling of sludge.

Another reaction  that may be important is precipitation of Mg(OH)2  as follows:

                  Mg2+ +  2 OH" - Mg(QH)2

This reaction  does not approach completion until  the  pH is raised to  11.  Magnesium
hydroxide  is  a gelatinous precipitate which aids  colloid removal, but which  hinders
sludge thickening  and  dewatering.  Where  the pH must  be raised to  11 or above to
meet  a phosphorus  removal requirement  or some  other  treatment objective, Mg(OH>2
formation must be  considered.

In the two-stage  lime treatment process which will be described below, it is necessary
to  include recarbonation after  the  first  stage  to  reduce the pH  and  precipitate the
excess lime as CaCOo in the second stage. The following  reaction occurs:

                  Ca2+ + CO2 + 2 OH'  * CaCO3 + H2O

Carbon dioxide may also be used  to  lower pH  after lime treatment.  The important
                                                  ^
reaction in this case would be the conversion of Co^   to HCO3".
                                         - 1

-------
A final reaction that is  of major  concern,  where  lime  is to be  recovered  by sludge
recalculation, is  as follows:

                  CaCO3 A* CaO + CO2

The CaO produced would then be slaked to form Ca(OH>2 before use.

       8.1.2  Treatment Systems

Two lime treatment systems may be used with wastewater, single-stage and  two-stage.
Figure 8-1  shows a  single-stage  system. In single-stage  treatment  lime is mixed  with
feed water  to raise  the pH to a desired value. Although the  pH will depend upon the
required  phosphorus removal, it  is likely  to  be substantially  less than 11, and may be
less than  10. Precipitation of phosphate and other  materials, as indicated by  reactions
discussed  above,  takes  place.  Time is  allowed  in  the appropriate  equipment  for
precipitate particles to flocculate to sufficient size for good settling. The clarified water
from  the settler  may  be  discharged  directly  or  may   be  filtered  to improve  solids
removal.  Adjustment of  pH  with  CO2  may  be  necessary  before discharge  and  will
almost certainly  be  required  before filtration  to  prevent post-precipitation of CaCO3
from  the unstable water.  The settled lime sludge  may  be disposed  of as landfill or
may be  recalcined for recovery of lime.  In  the  latter  case, the  sludge  is thickened,
dewatered by centrifuge  or vacuum filter, and calcined.  The calcined product is then
slaked and  reused.  To  avoid  buildup  of inerts  in the  lime, some  of the  sludge or
recalcined lime  must be wasted  or the inerts must be  separated from the  sludge before
calcination.

Two-stage treatment is  somewhat  more  complicated than  single-stage treatment. In
typical two-stage treatment, shown in Figure  8-2, enough lime is added  to  the water in
the first  stage  to raise  the pH  above 11.  Precipitation of hydroxyapatite, CaCO3, and
Mg(OH>2  occurs.  Consideration   of   the  solubility  product  for  CaCOo   and  the
equilibrium  between  CO^   and HCO3~ shows that the  minimum  solubility  for Ca
occurs at   a pH  of about 10. At a  pH of  11   or above  there  is a  considerable
                   0-4-
concentration  of Ca    present in the water.  In two-stage treatment CO2 is added  after
the first-stage  settler to  bring  the  pH down to about  10 where  CaCO^  precipitation
results.  The CaCO-j  is  settled out  and  the clarified water  is either discharged or  sent
to filtration. As in  the  case of  single-stage treatment, pH reduction  may  be necessary
before discharge and probably would be  required before filtration.

8.2    Typical Performance Data

A number  of  full-scale  and pilot-scale  tertiary lime treatment  plants are  in operation
and more full-scale  plants are  beginning operation.  Only  one  plant, that at South  Lake
Tahoe, California, has operated  for a significant period with recalcination of sludge for
lime recovery.  Most aspects of  this 7.5  mgd  plant have been discussed in  detail by
Gulp  and  Gulp  (1).  Although the   data  on  handling of wastewater sludges for
recalcination and the  recalcination process itself  are  limited mainly to this  plant,
                                        8-2

-------
                                       CO

                                       CO

                                       I

                                       LU
                                       
-------
                                CO
                                >-
                                to
                                
-------
performance data on other parts  of  a  lime  treatment system are available from more
than  one  location.  Extensive  data have  been reported from pilot  plants  located  in
Washington, D.  C., (2) and Lebanon,  Ohio (3).

The  lime  treatment  system  at  Tahoe is a  two-stage  clarification  system  which  is
followed by pressure filters of the multimedia  type.  These contain  3 ft. of a mixture
of coal, sand, and garnet. The water passes through two filters in series.  The first stage
clarifier  is operated at a pH of 11. To  reach that pH requires about 300 mg/1 CaO.  A
small amount of polymer is used  to improve flocculation. The pH is reduced to  9.6 by
recarbonation  before the  second-stage  settler.  Before  filtration,  the  pH  is  further
reduced  to 7.5. A small amount  of alum (1  to  20  mg/1) or a combination  of alum
and polymer is used as filter aid.  Filter run length has varied  between 4 and 60  hours.

Phosphorus removal  at  this plant  always  has been good and has  improved as operating
experience  has  increased.  By returning  plant waste streams containing precipitated
phosphorus to  the first stage  flocculator,  it is now possible to obtain routinely an
effluent  with  less than  0.1  mg/1   P. Before the filters the  phosphorus concentration is
about 0.4  mg/1.

In  addition to  phosphorus removal,  there is  significant removal  of  organic materials.
During a period of intensive study of the first  stage of clarification (unpublished data)
77%  removal  of  BOD  and 61%  removal  of COD were  obtained. Although there was
not a large removal of suspended  solids, there was a significant change in the character
of the solids from organic to largely  inorganic.  Further removal of organic materials
and suspended  solids occurs over  the remainder of the system. Gulp  and Gulp  report
typical filter effluents with a  BOD of  3  mg/1, COD  of 25 mg/1, and turbidity  of 0.3
JTU.

Sludges from the  first stage settler and  the settler  following  recarbonation are sent  to a
gravity thickener. Solids concentration  increases  during  thickening from about  1% to
from  8 to 20%. Thickened sludge  is then centrifuged to form a  cake with from  30%
to  more than 40%  solids.  The cake is  next  calcined  in a  multiple hearth furnace and
the recovered lime slaked for  reuse. Initially it was  planned to operate  the centrifuge
for high solids  recovery in the cake. This necessitates discarding  a significant amount
of  the  recovered  lime to  prevent buildup of precipitated  phosphate  and other  inerts.
Since operation began, it has  been found  that much  of the phosphate and  some other
inert  materials  can  be  separated  from  the CaCOg  in the  sludge  by  operating with a
rather high solids concentration in  the  centrate. Approximately 90% of the  phosphorus
can be removed in  the  centrate,  for example, when 25% of the solids  entering the
centrifuge  are allowed to remain  in that stream. This classification procedure results in
a  loss  of about 15%  of the recoverable lime.  A  greater  degree  of  utilization of
recalcined  lime  compensates for   the  loss, however,  and  the load  on  the calcining
furnace is  reduced.  Over three years  of operation, mostly  without classification  in the
centrifuge,  the  average  concentration  of  CaO in  the recalcined  product  was  66%.
Recalcined  lime  made up 72%  of  the  total used at the plant.
                                          - 5

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Considerable  operating data  have  been  obtained by O'Farrell  and Bishop  (2) on  a
two-stage  system operated  at  the  EPAWQO-DC  Pilot Plant in  Washington, D. C.  This
50,000  gpd plant treated secondary  effluent from  a pilot  activated  sludge  system at
the municipal treatment plant. The first stage pH was maintained at about  11.7, using
a  lime  dose  of  about  400  mg/1   as  CaO,  and  the  pH after  recarbonation  was
maintained at about  10.3.  Ferric  iron was added at a  rate of  5 mg/1 in the  second
stage  to improve flocculation.  Water  from  the  second-stage settler was filtered  without
further  pH  adjustment through  gravity-flow  dual-media filters consisting of  anthracite
coal over  sand. The  average filter run  length was  more than 50 hours.

Phosphorus  removal  for the system was  similar to that  obtained at Tahoe; 0.09 mg/1
as  P  was  the  average  concentration  remaining.  Phosphorus  concentration  before
filtration averaged 0.13 mg/1.

In  addition there was significant  organic  and  suspended  solids removal. The  average
BOD  was reduced  from  15 mg/1  to 2.1  mg/1  before and 1.5 mg/1  after filtration.
Suspended solids were reduced  from 33 mg/1  to  17  mg/1 before filtration  and 3.8
mg/1  after filtration.

Sludge  from the second  stage  settler was returned  to  the first stage and  all sludge
removed from the system was from the  settler of the first stage. This  sludge contained
about 5% solids  and constituted about  1.5% of  the  feed volume. Although  there  was
sludge thickening and calcining equipment  available, only preliminary  study  was made
of  lime  reuse.  Limited results showed  improved  thickening  of  the sludge  when
recalcined lime was  recycled to the system.

A  75  gpm  single-stage  pilot  system  was  operated at  the  Lebanon, Ohio  Sewage
Treatment Plant. Feed water was activated sludge effluent. This  system, consisting of a
flocculator-clarifier   followed  by  dual-media filters  of anthracite  coal and  sand,  is
described  by  Berg,  et al.  (3). Sludge was gravity  thickened  and  discharged  to  sand
drying beds. The system  has been operated  over a pH range from about 9  to  11  with
most  data taken at  a pH  of  9.5.  Before  filtration  the  pH  was reduced to  about 8.8
with  sulfuric acid  to prevent  precipitation on the filter media.  Filter  run length
averaged about 90 hours.

Effluent phosphorus concentrations for the system are shown in Figure 8-3. The effect
of  pH   is  clearly  indicated.  Since   the  average  phosphorus  concentration   of  the
secondary effluent was about  10 mg/1  as  P, approximately 95% removal was obtained
at  a pH as  low as 9.5. Before filtration the average  phosphorus concentration was 0.75
mg/1  at a  pH  of 9.5.  Removal improved only slightly at higher  pH because of the
presence of precipitated phosphorus in the  effluent.

Average suspended solids concentration of the secondary effluent was 43.5 mg/1. This
was reduced to  16.5 mg/1 in the clarifier. Much of the  suspended matter in the clarifier
effluent consisted of inorganic precipitates.  After  filtration  the water  was  of high
clarity.  During a six month period when the biological  treatment plant operated  well,
turbidity  averaged 0.2 JTU.  Even when the suspended solids load from  the activated
                                        8-6

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  2.0
  1.5
en
E
  1.0
o
o
DC
O
3:
Q-


o
a:
a.
  0.5
    8.5
             9.0
                      9.5       10.0       10.5


                          CLARIF IER pH
                                                 11.0
11.5
                  FIGURE 8-3  EFFECT OF pH

                 ON PHOSPHORUS CONCENTRATION

                  OF  EFFLUENT FROM  FILTERS

                  FOLLOWING LIME  CLARIFIER
                              - 7

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sludge  plant was  high, the lime treatment  system produced water with a daily average
turbidity not exceeding 2.5 JTU.

During  a  two month  period  in  which extensive  measurement  of organic removal was
made,  total organic  carbon was reduced by  63% over  the  clarifier  and 68% over the
clarifier and  filters.  Organic carbon  measurements  taken  at  other times  indicated
removals of from 55  to  74%. Occasional BOD and COD samples indicated removals of
86% and 62%.

Sludge was  usually  removed  from  the settler  at  1.5 gpm giving a sludge concentration
of 2.8% solids. This was thickened to about  10% before being pumped to drying beds.
The  sludge  dewatered quickly  to  about 50% solids.  Equipment was not available for
recalcining the sludge.

The  lime  requirement is  an  important consideration  in  lime treatment.  This can vary
over a wide range depending on operating pH and water composition. From reactions
given earlier it  was  seen  that alkalinity  has an  important  effect  on the  lime dose.
Buzzell and Sawyer (4) have shown, for example,  that for several wastewaters the  lime
dose  required  to  reach  a  pH   of 11  correlated  approximately  with   alkalinity.
Examination of the earlier equations  would show also that calcium hardness can affect
lime dose. One  part  by  weight of CaO  can react with from  0.89 to 1.79 parts of
bicarbonate alkalinity  expressed as  CaCOo,  the lower value applying to very  soft waters
and  the higher value to  very  hard waters. In  addition  to  the  reaction of lime with
hardness,  other competing reactions occur  in lime treatment  of wastewater.  Also, there
may be incomplete reaction  of the lime. All of these  complications make  calculation
of lime dose  difficult. The  result is  that,  at present,  determination of lime  dose  is
largely empirical.  Approximate  values have already been given  for the plants at Tahoe
and  Washington,  D.C. Some approximate  values for the Lebanon work are  shown in
Table 8-1. It appears  from the data already available that the lime dose will usually be
in the  range  of  300  to  400 mg/1 as CaO for two-stage treatment, and from  150 to
200  mg/1  where single-stage treatment is  satisfactory.

                                     Table 8-1
            Feed Water
             Alkalinity
         (mg/1  as CaCO3)

                300
                300
                400

                400
LIME REQUIREMENTS


  Clarifier pH
Approximate Lime
      Dose
       9.5
      10.5
       9.5
      10.5
  (mg/1 of CaO)

       185
       270
       230
       380
                                       8 -8

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8.3    Criteria for Selection of Process

Lime treatment of secondary effluent  represents a significantly higher capital cost  and
somewhat  higher  operating  cost  for phosphorus  removal  than mineral  addition to  a
conventional treatment  plant.  Lime treatment  has,  however, several advantages  over
mineral  addition.  It  can  be  considered  more  dependable  since  it adds  additional
flocculation and  sedimentation steps to  the  system.  Upsets in the  conventional plant,
which  would  reduce  the efficiency  of  phosphorus removal by mineral addition, would
have less effect on tertiary  lime  treatment. Because  tertiary lime treatment is separate
from the conventional  treatment  plant, it  adds  flexibility  to operation of the system.
For  very high degrees  of phosphorus removal, lime treatment would be the method of
choice, not only  because of the inherent greater dependability  mentioned  above,  but
because  of the ability to  produce  an  effluent  slightly lower in phosphorus content.
Lime treatment decreases the total  dissolved  solids content of the water  by removal of
hardness and  alkalinity while mineral addition adds to the total dissolved solids. In the
case of  alum  addition, for  example, 5.3 parts by weight of sulfate are added for each
part of aluminum. Lime treatment has  the capability  of removing  turbidity to very  low
levels.  Where  there  are plans  for recreational reuse or certain industrial  reuses  of the
treated water,  low turbidity along with  low  phosphorus content of the lime treatment
effluent  is  very desirable.  Lime treatment offers  the opportunity for recovery  of the
treatment  chemical.  At  the  present time  there  are no acceptable  methods for recovery
of aluminum or iron  salts.

The choice of single-stage or two-stage lime  treatment depends partly upon the degree
of phosphorus removal required,  but more importantly, on the alkalinity of the water.
Unless a high treatment pH is used, waters with low alkalinity, in  the  range of  150
mg/1 as  CaCOo or  less,  form  a poorly  settleable floe because  of the low  fraction of
dense  CaCOo.  A pH above  10  is  needed even to obtain measurable CaCO^ production.
A pH  of  11  or above is then  needed  to precipitate  Mg(OH)2  which  aids in settling of
fine particles.  Since  neither  discharge  nor reuse  of  the high-pH  water is likely  to be
acceptable, addition of a second  treatment stage  after recarbonation  to  a pH of about
10  becomes generally necessary. It  would  be possible  to  recarbonate to a much lower
pH  and avoid the second  treatment stage,  but  this would  result in a high  calcium
effluent  and  would eliminate the chance to produce high CaCOo  sludge in situations
                                                               J
where  lime recovery  was  contemplated. Although  most   of the  phosphorus  removal
occurs   in  the high   pH  first  stage,   in  accordance  with the  pH dependence  of
phosphorus solubility  as  shown earlier by  Figure  8-3, some removal does also occur in
the  second stage.  Another  important reason  for including  the second stage is to assure
better  control of  clarification.  With  low alkalinity waters  there is sometimes difficulty
in settling the sludge  in  the first stage even at high pH. The second stage settler with
its  high  CaCOo sludge, prevents  solids  carryover  when the first stage settler  does  not
operate properly.

With high alkalinity waters, a well  settling floe is formed  at pH values as  low as  9.5.
There  is no need  for two-stage  treatment unless the required  degree  of  phosphorus
removal  necessitates a  high  pH. In  addition  to  obtaining a small  degree  of phosphorus
                                        8-9

-------
removal,  the  second stage would be used  in  these cases to lower calcium  content  in
the  effluent  and to obtain high CaCOg sludge  for  lime  recovery.  There is not yet
available  operating  experience  at enough  plants to  state positively the  alkalinity  at
which single-stage  treatment will perform  satisfactorily, from the standpoint  of floe
settleability. At  present,  experience  indicates  that  at  an alkalinity of  150  mg/1  as
CaCOg,  single-stage treatment probably  cannot  be  used. Between 150 mg/1  and 200
mg/1 settleability will probably  depend  on the amount  of organic floe present. Above
200 mg/1, settleability is likely to be satisfactory.

8.4    Description  of and Criteria for Choice  of Equipment

       8.4.1  Single-Stage System and First Stage
              of a Two-Stage System

Diagrams for  single and two-stage lime treatment  systems are shown in Figures 8-1 and
8-2. The  first part  of each system is made up of clarification equipment essentially the
same as that  found in  water treatment  plants.  It includes  a chemical feeding system
(see Chapter  10),  a rapid mix  tank,  a flocculator,  a settler, and a  means  for sludge
removal. Mixing, flocculation, and settling  may  be  carried out  in  separate vessels  or
tanks, or  they  may  be combined in  one integrated  unit. The  system  consisting  of
separate  tanks has  been used  for many  years in  water  treatment and was the system
adopted  for the  first stage of the Tahoe lime treatment plant. The integrated type  of
equipment is  sometimes referred  to  as  an upflow clarifier or a sludge blanket clarifier.
The latter  term  can be  misleading, however,  since not all  such  units operate with a
sludge blanket.  A  diagram of a  unit  that  does  not  operate  with a sludge  blanket  is
shown in  Figure  8-4.  Gulp  and  Gulp  (1)  recommend  the system of separate  tanks
because that system allows separate  control of each part of the process.  They  point
out  that such a system  has greater flexibility  in points of addition for chemicals.  They
also  point  out  that  in  the  integrated  units  with  a  sludge  blanket  there  may  be
difficulty in controlling the  blanket  height and  the  blanket  may become  anaerobic,
leading  to poor  phosphorus and  solids  removal.  Pilot  studies at  other locations have
shown that excellent  solids removal  can be  obtained  with  sludge blanket equipment,
but  that blanket instability could  be a problem.  On the other hand, pilot upflow  units
designed to operate without  a  sludge  blanket  have proved  to  be  very effective  at
Washington, D. C. (2). Results available at this time indicate that both the  system of
separate  tanks and  the  integrated units without  sludge blankets  should be considered
for design of new plants.

The  Tahoe  plant is an excellent  example of a system with the first stage consisting of
separate  tanks for  each unit process.  At the present time the  plant  must  be relied
upon heavily  as a guide to design of such  systems. Description of the equipment and
some design parameters are given by  Gulp and  Gulp.  The rapid mix tank  which  is
located  in  one  corner  of the flocculator  has about a 30 second residence  time  at
design flow. (The plant  usually runs with a daily average flow of about one  third of
design flow.)  Mixing is  accomplished  with a vertical shaft mixer.  The flocculator is a
                                        8 -  10

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           WASTEWATER
LIME
                          D
cu
Q
CO

Q
LLJ
_J
O

O
LLJ
                                            EFFLUENT
                              u
                        SLUDGE
          FIGURE 8-4  TYPICAL UPFLOW CLARIFIER
                      8 - 11

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square tank  with a depth  of 8 ft.  At design flow  the  residence time  is 4.5 minutes.
The  flocculator is provided  with air agitation, but operating experience  has  shown that
this  agitation is not  necessary. The  settler is circular with a center inlet. The depth is
                                                ^
10 ft and the design overflow rate  is 950 gpd/ft . There are two sludge pumps, one a
variable-speed centrifugal, and the other  a positive displacement Moyno.  Provision  has
been  made  to  return part  of  the  sludge  to  the  rapid  mix  tank. The  concept of
returning  sludge  to  the  section of  the clarification  equipment  where  precipitation is
taking place is called  solids contact.  The objective  is  to  hasten precipitation  and to
obtain larger precipitate particles which will settle well.

The  ease  with which  flocculation  occurs at Tahoe would suggest that a flocculator for
this  service presents no design problems.  Experience is,  however, limited. Pilot testing
would be very desirable to determine  the  flocculating  characteristics  of a  particular
wastewater.  Jar  tests  may  be of some  value.  Unfortunately, the effect  of solids
contact, which experience at Tahoe and  elsewhere indicates is beneficial, is  difficult to
duplicate  in a jar test.  If jar tests indicated good  flocculating  characteristics without
benefit of solids contact, however, flocculation should be as good or better with solids
contact.  When  pilot  studies are  carried out,  provision  should be  made  for solids
contact.

Comments concerning  the  effect  of solids contact  in jar  tests also apply  to  settling
rates  determined  from  these tests.  Rapid settling  without  benefit of solids  contact
would be  a strong indication that  settling  with solids contact  would also be  rapid.

Clarification  equipment  of  the integrated  type  for  use  in municipal water treatment is
manufactured by  a  large number  of companies. Units of  this type used for  treatment
of wastewater have been essentially of  the  same  design  as  used  for  municipal water
supplies.  The basins are usually circular  with the  rapid mix  and  flocculating sections
located at the  center  of the settler.  Agitation  for  mixing and  flocculating as  well as
power for sludge scrapers  is provided at the  center of the  settler. Solids contact is
usually provided,  and may be carried out with  best control  by external circulation of
sludge to  the mixing  section. In some designs,  however, internal recirculation is  used.
There  is  considerable  variation in  the  geometry  and complexity  of  the  mixing and
flocculating sections depending upon the  manufacturer.  The unit shown in Figure  8-4
is a  relatively  simply  type. Units from three  different manufacturers were used in pilot
work at  Lebanon, Ohio  and Washington, D. C. These and others at  additional locations
have performed effectively.  However, in some cases with operation of a sludge blanket,
difficulties  have  been encountered. A sludge blanket can be eliminated  by avoiding
designs  in  which the wall  separating the center  compartments from the  concentric
settler reaches close to the  bottom of the settler. The  design in Figure  8-4 prevents
sludge blanket formation.

There  has  been little effort to  modify this type of  equipment  from  use in water
treatment  to use with  wastewater.  Experience  at  Tahoe would suggest, for example,
that  less  flocculation time,  and probably  less  agitation, is required than  is generally
provided.   A  unit such  as  that shown  by  Figure  8-4 may have  about  40 minutes
flocculation  time at  design capacity  for water treatment, nearly  nine times  that  at
                                         8 - 12

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Tahoe.  Whether  modifications in such equipment would  be worthwhile remains  to  be
seen.

If  a designer  chooses to  use equipment  that  is on  the market, he  does not have
complete flexibility in specifying  the design.  Fortunately, equipment satisfactory for
water  supply treatment has  proved  satisfactory for wastewater, except that a  lower
settler overflow rate is necessary.  The single-stage treatment system at  Lebanon,  Ohio
                                                          ^y
was operated at a  constant  overflow rate  of  1,440 gpd/ft .  This proved satisfactory
even with a sludge  blanket. At Washington, D. C., tests were made  with settler rates as
high as  1,950 gpd/ft2 although the average  rate was 1,120 gpd/ft2.  For design, a peak,
                                                 ^
dry  weather overflow  rate of  1,200 to 1,400 gpd/ft  , with the  average somewhat lower,
appears reasonable.

       8.4.2  Recarbonation

In  a two-stage  system  recarbonation follows  the  first  stage  settler.  In a  single-stage
system  and following the  second  stage  of  a  two-stage system, pH  reduction  by
recarbonation may  be necessary  to  make the  effluent  suitable  for filtering  or for
discharge.  An excellent  discussion of all aspects of wastewater recarbonation is given
by  Gulp  and Gulp  (1). The  reader  is referred  to that publication, as well as one  by
Haney  and  Hamann  (5), especially  for  information  on sources   of  carbon dioxide.
Sources include stack  gas from sludge incinerators and lime recalciners, CC^ generators,
and commercial liquid
The equipment  used for contacting the CC^ and water may be simply a tank with the
gas  being  bubbled  through the  water.  This  is  the  system used  at  the Tahoe plant
where the height of  water over  the  CC>2 source is  8  ft. Pilot studies at  Washington,
D. C., with a tank  depth  of  1 1   ft  and a turbine mixer  to  reduce  bubble size  and
distribute bubbles, showed almost  100% absorption of CCK-

When  considering residence time,  the recarbonation tank following the first  stage of a
two-stage system  must  be  differentiated  from  the  recarbonation tank used just  to
reduce  effluent   pH. The  residence time  of the  recarbonator between the  first  and
second stages  is not  particularly  important. At Tahoe  the recarbonation tank is  only
large enough  to give a 5 minute residence  time at design flow.  In  the  Washington,
D.C.  studies, the  residence time was  15 minutes. A  problem that may arise  when
recarbonating  wastewater is foam formation. This  is most  pronounced  when  the  flow
of  bubbles  is concentrated  in parts  of the recarbonation  tank. The CC<2 distributing
system  should cover as well as possible the whole lateral area of the tank bottom.  This
would be especially  true if the residence time were as low as 5  minutes.

In  the  recarbonation  tank  used  just  for effluent  pH  adjustment,  sufficient  residence
time  must  be  allowed for  completion  of reactions   taking  place.  Gulp  and Gulp
recommend  15 minutes. In the Tahoe plant only 4 minutes is  provided at  design flow,
but  the  water flows to storage  ponds with a much longer residence  time before  the
water  is filtered. Just  as in the  case of recarbonation between stages of  a two-stage
system, good bubble distribution  is  important for prevention of excessive foaming.
                                         - 13

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Since  one  reason  for  using  a  two-stage  system  is  to  prevent  a high  calcium
concentration  in  the  effluent,  the pH  to  which  the water should  be recarbonated
between  stages is  that for maximum conversion of the calcium  to CaCOo. Where lime
recovery  is practiced, maximum  formation of CaCOo is also desirable because it results
in maximum CaO production.  The optimum  pH  is about  10. At Tahoe, for example,
10.3 was selected because tests showed that  pH  to  give maximum CaCCK production.

The  pH  to be selected when the objective of recarbonation is just pH reduction, will
depend on  a number  of factors. An  effluent  standard  may  determine this  pH. If
stabilizing the water to prevent post  precipitation  is the objective,  the pH may  be
determined by consideration  of the  Langelier  Index.  If, as in  the case of Tahoe, a
treatment step such  as  activated carbon adsorption is to follow lime treatment, this
will determine pH. In the latter case a  pH of about 7.5 has usually been selected.

The  CO 2 dose requirements  can be calculated from the chemical reactions taking  place
and  a  knowledge  of the concentrations of the various  forms  of alkalinity in  the water.
For  design of a new plant,  alkalinity data must be obtained  from samples of liquor
taken from jar tests run  at  the  same  pH values as planned for the plant. Results  must
be considered very  approximate, but   they do help  in sizing CC2 feeding  equipment.
Gulp and Gulp discuss the calculations  in detail. It  was found in  pilot plant work at
Washington,  D. C.  that  the  CO^ dose for recarbonation  between  the  stages  of a
two-stage treatment  system   can  be   calculated  reasonably  well  by   considering the
reduction in  calcium concentration  that  occurs.  This reduction  is   due   to CaCOo
                          7
formation  with  the  CO^    coming   from  the CC^-  The  calcium   content  before
recarbonation  can  be  determined  satisfactorily  from jar tests  run  at  the  desired
operating pH.  The  calcium  content   after  recarbonation  can  also  be  determined
approximately by jar test. Results from several pilot  plants indicate the soluble calcium
content at the pH of minimum solubility should be about 40 mg/1 as Ca. This figure
is probably just as good for calculations as a figure  obtained from a jar test. The CC>2
dose in mg/1 is then equal to:
                                   /44\
              (Ca reduction in mg/1)   .
                                   \40/
A safety  factor  of about 20% should  be added to the calculated  dose to compensate
for inefficiency in absorption.

       8.4.3   Second Stage Flocculation and Sedimentation

In two-stage  treatment, recarbonation  is followed  by the second stage  flocculation and
settling.  Experience  with  equipment for the second stage of  treatment  with  wastewater
is limited. Two  very different systems have been  tested. The simplest  is the system at
Tahoe. In the Tahoe plant  the equipment  used is just a longitudinal  settler with a 30
                                              O
minute  detention  time  and  a  2,400  gpd/ft   overflow rate  at  design  flow. No
flocculation equipment is provided. Gulp and Gulp (1) refer to the settler as a reaction
and  settling  basin.  It  has  been  found at  Tahoe  that  a significant part  of the
recarbonation reaction actually  occurs  in the settler. This is  shown by  the pH decrease
                                        8 - 14

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of  about 0.7 unit that occurs between the recarbonation tank and the settler outlet.
The clarification  that  results  at  Tahoe is  unusually  good  for the simplicity  of the
equipment.

Jar test and  pilot plant work  at  Washington, D. C. indicated that flocculation  after
addition of  a flocculating  aid  was required to obtain satisfactory clarification of that
water.  The  pilot tests  were run in upflow equipment of the integrated type discussed
earlier.  Without  a  flocculating  aid,  fine CaCOo  precipitate escaped  the settler,  even
                                                    ^)                        "\ I
at  a  settler  overflow  rate  as low as  1,100  gpd/ft . Using  5  mg/1  of Fe   ,  good
                                                                         ^
operation  was  observed  at  overflow  rates   as  high  as  1,950  gpd/ft .  Hydraulic
limitations  prevented  testing  at  higher rates.  Apparently,  the good contact between
solids  and water during flocculation  was beneficial in reducing CaCO^  supersaturation
in  the  effluent.  Precipitation  in the filters  following the  second stage  did not occur,
and no pH  reduction was required.

In  this work  the  sludge from the  second  stage was returned to  the mixing section of
the first  stage to serve as  a weighting agent.  In  waters of low alkalinity or expected
high loads of biological solids, this  procedure should be considered.

It  is difficult to recommend the  amount  of flocculation to provide and the overflow
rate to use  for second-stage treatment.  Jar tests would be of little value because of the
complication  of  first raising  the  pH  with lime  and then  lowering with  CO^-  Pilot
testing  may  be desirable.  Such a  pilot system would  have to include  the first  stage
equipment and  recarbonation  equipment, although  these could be of crude design. In
the absence  of pilot tests to indicate otherwise, flocculation should be provided in the
second-stage system.   If filtration is included,  a peak dry  weather overflow rate of up
to  2,000 gpd/ft^  in  the  settler may  be used.  If  filtration is not  provided, a somewhat
lower  overflow rate should be chosen to assure  reasonable effluent  quality during periods
when an upstream part of the system  is not operating properly.

        8.4.4  Filtration

The last step in a complete lime treatment system is filtration.  Although there are a
variety  of  filter types that  could  be  used, essentially all the recent  test work has been
done  with  downflow  filters  of  multimedia type. These  are  essentially the same in
design  as a  rapid sand filter, except that the media are graded  from coarse at the  filter
surface to fine at the filter outlet.  This is accomplished  by using media of different
densities with the largest  particles being  composed of  the  least dense material. The
result is a filter  bed which has far more  capacity  for removing  suspended  solids than
an  ordinary  sand filter, without impairing  effluent clarity.  Both gravity and pressure
filters  have  been used. Each has certain advantages. Generally,  however, pressure filters
are more appropriate at smaller plants.

Two media combinations  have  been  tested extensively. These are  dual-media of coal
and sand,  and  tri-media  of coal, sand,  and  garnet. Filters  used  at  Lebanon,  Ohio
following a  single-stage  system  (3)  and   filters  at  Washington,  D.C.  following  a
two-stage system (2) were  of  the dual-media type.  Both contained 18 in. of anthracite
                                        8 - 15

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coal over 6  in. of sand. Average particle  sizes  of the media at  Lebanon  were 0.75 mm
                                                                        ^
and 0.46 mm; at Washington, D.C., 0.9  mm and 0.45  mm. At 2 gpm/ft  the average
run length  at  Lebanon was  about 90 hours  using 8  ft of water  as the terminating
pressure loss. At  Washington, D. C., filter run length averaged  about 50 hours for an
average rate of 3.4  gpm/ft ^ and a terminating pressure loss  of 7 ft of water. High
clarity  waters were  obtained  in  each  case. Backwash in  both cases  was carried  out at
          "}
20  gpm/ft .  Backwash time was 5 minutes at  Lebanon  and 10 minutes  at Washington,
D. C.  In  the latter case, a surface wash was included.

These  run length figures give a rough idea of the results that may be expected at
other  locations. For maximum  run length at  a given  product quality, the depths of
media  and their particle sizes should be optimized. Although this was not done for  the
above-mentioned  filters, pressure  loss  distribution in the filters at Lebanon as reported
by  Berg, et al.  (3)  indicates  that good solids storage in the anthracite  was  being
obtained. Small pilot filters could  be used for optimization of the media.

A  reasonable design  rate  for  gravity-flow dual-media  filters  appears to be  about 3
gpm/ft .  Higher rates could result  in  inconveniently short runs during periods of high
solids  load.  Rates  much  lower  than  3  gpm/ft ^  result  in excessive  filter  costs,  not
justified by  the   longer filter runs. Very  long filter   runs  could  result  in  backwash
problems  from biological activity in the filters.  Recommendation of a 3 gpm/ft^ rate is
based  upon  having  good operation of the second-stage  settler. Frequent settler upsets
must be avoided.

Tri-media filters are  used at the Tahoe plant. These are pressure filters which at design
flow operate at  5  gpm/ft  .  Each  bed holds 3  ft of mixed coal, sand,  and garnet as
supplied by  Neptune Microfloc.  Two   filters  are  used in series, and  are  backwashed in
series,  usually when  the head loss  reaches 16  ft of water. Run length has varied from
4 hours during heavy solids load  to about 60  hours under good conditions. Backwash
is  carried out at  15 gpm/ft^.  The backwash  water  is  reprocessed through the lime
treatment system.  More details are given by Gulp and Gulp (1).

From  the available data,  it  is  difficult   to give precise criteria  for choosing between
dual-media or tri-media filters following lime treatment. The use  of  garnet allows for a
smaller particle size at the bottom of the filter than is possible with sand. In case of
floe weakness, the tri-media  filter offers, therefore, more protection  from turbidity
breakthrough. The cost, however, is slightly higher. Where the tri-media fill is not used,
filters  can still be backwashed  at the  onset of turbidity  breakthrough. Experience with
dual-media filters  on lime treated water  has not shown  sudden breakthrough to  be an
important problem. Where  water of the highest clarity is required, tri-media  filters may
be  of  most  value.

        8.4.5  Sludge Handling

The sludge  from a lime treatment system may  be handled in two general ways. It may
be  thickened,  dewatered,  and  disposed  of or  it  may  be  thickened,  dewatered,  and
                                        8 - 16

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recalcined to recover lime for reuse. For small plants, recalcination will not be economically
competitive  with  disposal and  should not  be considered unless there are restrictions
on disposal  which make  that  alternative difficult.   It can be  assumed generally that
for plants over  10 mgd,  recalcination of lime sludge will  be practical.  Recalcination
may  also be practical at plants somewhat smaller than  10 mgd, depending on  the cost
of purchased lime and other local  conditions.

Data  given  earlier indicate  that  the  volume  of  sludge from  lime  treatment  will vary
from  1.5%  to  several percent of  feed volume. Sludge concentration will probably be in
the  range  of  1% to 5%. The actual  weight of  sludge will vary with the  chemical
composition and  amount of  suspended  solids in  the  feed  water. Values have  been
observed in the range of 4 to  7 lb/1,000  gal.  Sludge production from the first stage of
a  two-stage  system or from a single-stage  system can be estimated approximately  by
weighing the dried sludge from jar tests  run  at  the planned operating pH. Additional
sludge produced  in the  second stage can be  assumed  to be the CaCC^ formed  from
calcium  concentration   reduction  during  recarbonation.   Calcium   content  before
recarbonation can be  obtained from the above-mentioned jar tests and after recarbonation
can be assumed  to be 40 mg/1  as Ca.

Design  information for  the  Tahoe  sludge  handling system  is  reported by  Gulp and
Gulp. (1) The  reader is referred to that publication  for further  information. The Tahoe
plant is  the only one which includes recalcination  of  sludge from the lime treatment
of wastewater,  and that  has  been operated for a long period of time. Paramenters  from
that  system can  be  used as  a rough guide  for  design. The gravity  thickener has  a
bottom scraper mechanism and is 8 ft  deep.  Overflow  from the thickener is returned
to either the primary clarifier or the first stage  of lime treatment.  The design solids
loading  is  200  Ib/day/ft^  and  the  design  overflow  rate  is  1,000  gpd/ft^.  Some
preliminary  data from pilot  work at Washington,  D. C.  suggest these loadings  are  high.
The   Tahoe  equipment was sized,  however,  to  handle a volume  of  sludge  equal  to
about 9% of the  plant design  flow. The actual volume of sludge should usually be less
than  one third of that volume.  At Washington,  D. C.,  recalcined lime was found  to
produce  a sludge which thickened significantly faster than sludge from virgin lime.

If lime is not  to be recovered  from the  sludge,  the underflow from the thickener can
be placed  directly on drying  beds for final  dewatering,  or it can be  dewatered by
centrifuge or vacuum filter.

If sludge  recalcination  is  planned, the  thickened  sludge  would be  dewatered, by
centrifuging  or filtering  and fed to  the  calcining  furnace.  The centrifuge may  have
advantages  over  filters for  this  purpose,  such as  the ability  to  separate phosphate
sludge from  CaCO^. Lime from the furnace is stored for reuse. It, along with  any new
lime,  must  be  slaked before use. Sludge can  be  pumped  from the thickener to the
centrifuge.  Cake  from the centrifuge must be transported by conveyor. At Tahoe the
centrate  is  sent  to  the  primary  clarifiers.  It  has been  found  at Tahoe  that, by
operating the  centrifuge  with   less  than  maximum   solids  capture,  much  of the
precipitated   phosphorus  can  be retained in  the centrate.  This  results  in  a higher
                                         - 17

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quality  lime.  This mode  of operation  requires a  second  centrifuge to  remove the
phosphorus  rich  solids  from the  centrate.  These  solids  may have  value  for  use in
fertilizer.

The  Tahoe  dewatering  and recalcining  system  is  described by  Gulp and Gulp.  The
centrifuge is a 24 by 60 in. concurrent flow type. The calciner is a 14 ft-3 in. diameter,
6  hearth  furnace operated  at  a  top  temperature  of  1,850 F.  Other  types of
furnaces have  been used in water  treatment plants and these should also be applicable
to  the  sludge   from  wastewater  treatment.  The  reader is referred   to  equipment
manufacturers for further information about centrifuges and furnaces.

       8.4.6   Control of Lime  and  Carbon Dioxide  Feed

The  feeding of lime to a  lime softening system can  be controlled in a  number of
ways. For the wastewater  application, the  most appropriate appears to  be control of
pH,  with the  pH value  being selected for good  suspended solids  removal or to  meet a
phosphorus  removal  requirement.   Where flow  equalization  is employed,  pH  sensing
alone should be  sufficient.  Where  there  is substantial diurnal  variation  in  flow,  better
control  can be  maintained  by  flow proportional-pH control.  Systems are available
for this  type of  control.

Carbon  dioxide  dose is also  controlled  by  pH. As in  the  case of lime feed, flow
proportional-pH control would be preferred  where there is diurnal variation in flow.

There  is  a tendency for pH electrodes  to become  coated  with precipitates and lose
sensitivity. The  precipitate  can be dissolved with acid. In some instances,  however, it
has been found  satisfactory  to  use manual control because  of difficulties with  the pH
control  system.

       8.4.7   Scale Formation  on Equipment

Because  the  water in a lime treatment  system  is supersaturated  to some degree with
CaCOo  and other precipitating  substances, there is  a tendency  for scale to form on
equipment and pipe  surfaces. The  problem is  particularly serious with  the lime slurry
from the slaker..  This  can  quickly  plug  the slurry  line to  the rapid mix tank. There
should  be easy  access  to  all  parts of  this  line for cleaning. At  one  small plant a
flexible  hose  was  used  to  feed lime slurry.   By periodically  flattening  or flexing  the
hose, the scale was  removed.   The  mechanical mixer in the  rapid mix  tank will also
become scaled  and must be cleaned.

Scale can also form  in  sludge lines  and  the effluent line from the  first-stage clarifier.
It is recommended that open  troughs be used wherever possible. Provision should be
made for cleaning lines when open conduits are not possible.

Possible  scaling of filters has already been  mentioned. Recarbonation before the filters
will  minimize  scale formation.
                                        8 - 18

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8.5    Capital and Operating Costs

Because  of  the  short  history of  lime  treatment of  wastewater, there is a scarcity of
capital and  operating cost information. Costs are available for the Tahoe plant  and are
reported by Gulp  and Gulp (1). Capital cost for the  7.5  mgd lime treating facility was
$1,115,000  and  cost of the filters was an additional $705,000. For  1969 the  estimated
operating costs  exclusive  of  equipment  amortization  were  7.3^/1,000  gal.  for  lime
treatment  without  filtration  and  2.8^/1,000  gal.  for  filtration.  Amortization of
equipment, based on costs adjusted to the 1969 national  average, interest of 5% for 25
years,  and  the  assumption  of  the  plant  operating  at full  capacity,  would  add
2.7^/1,000 gal. for treatment  without filtration and  1.8 #1,000 gal.  for  filtration. For
the  plant  operating  at  full  capacity  the  total  cost  of operation  would  then be
10.0#1,000  gal.  without  filtration and  14.6#1,000  gal.  including  filtration.  The
fraction  of  the  cost  resulting  from  amortization is  a substantial  31% even with the
assumption  of full capacity. There  is  an obvious need  to  keep equipment  size  to a
minimum.  Flow  equalization deserves strong consideration  when  planning  for  lime
treatment of secondary effluent to minimize the initial cost of new  equipment.

Additional  costs  for  lime treatment based  on information  from  Tahoe  and  other
sources  have been  reported  by Smith  and McMichael (6).  Tables  8-2 and  8-3 show

                                     Table 8-2

                 CAPITAL COST OF LIME TREATING FACILITIES

                                                         Cost ($)
          Treatment                                  Plant Size (mgd)
                                          U)               K)                100

Single-Stage  without Filtration           100,000         1,200,000          5,500,000
Two-Stage without Filtration             160,000         1,500,000          7,900,000
Dual-Media Filtration                    110,000          510,000          2,300,000

                                     Table 8-3

             TOTAL COST FOR LIME TREATMENT OF WASTEWATER

                                                    Cost (#1,000 gal.)
          Treatment                                  Plant  Size (mgd)
                                          LP               1P_                100
Single-Stage  without Filtration              13                 7                  4
Two-Stage without Filtration                16                 9                  6
Dual-Media Filtration                       8                 3                 1.4

costs  based  largely on  their  results. Capital costs  have been  updated to December,
1970. Amortization is at 6% for 25  years. For  1 mgd plants, recalcination equipment is
                                         - 19

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not  included.  All  lime would  be purchased. The  applicability of  recalcination  was
discussed  earlier.  Component  costs  making  up  the total cost figures  represent  an
average  for the whole  country.  Local conditions may cause  significant deviation  from
these values.
                                        8 - 20

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8.6    References

1. Gulp,  R.  L.,  and  Gulp,  G. L., Advanced Wastewater  Treatment, Van Nostrand
   Reinhold Company, New York (1971).

2. O'Farrell,  T.  P., and  Bishop,  D. F., "Lime Precipitation  in  Raw, Primary, and
   Secondary  Wastewater",  Presented  at  the  68th  National  Meeting  of  AIChE,
   Houston, Texas (March  1971).

3. Berg, E. L., Brunner, C. A., and Williams, R. T., "Single-Stage Lime Clarification of
   Secondary Effluent", Wat. and Wastes Eng.,  7:3, p 42 (1970).

4. Buzzell,  J.  C.,  and  Sawyer,  C.  N., "Removal  of Algal Nutrients  from  Raw
   Wastewater with Lime", JWPCF, 39:10, Part 2,  p R16 (1967).

5. Haney, P.  D., and  Hamann, C. L.,  "Recarbonation and Liquid Carbon  Dioxide",
   JAWWA,  61:10,  p 512 (1969).

6. Smith, R., and  McMichael, W.  F., "Cost  and  Performance Estimates  for Tertiary
   Wastewater Treating Processes",  Robert A.  Taft Water Research Center, Report No.
   TWRC-9 (June, 1969).
                                     8 -21

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                                    Chapter  9

                  PHOSPHORUS  REMOVAL   BY  MINERAL
                 ADDITION  TO  SECONDARY  EFFLUENT
9.1    Description of Process

Alum and  to a lesser extent iron salts have been evaluated as precipitants for phosphorus
in effluents from  conventional treatment plants. Both batch studies and continuous-flow
systems up to  2.5 mgd have successfully reduced phosphorus to very low levels.

Equipment  typically  consists of mixers,  flocculators, settlers, and  filters. Some work
has been  done, however, with  the  chemicals  added directly to  filters. Specific studies
are discussed  later and provide additional information on  equipment commonly used.

9.2    Summary of Design Information

An alum dosage  of about  200 mg/1  is  required for phosphate removal from typical
municipal  wastewater  while  dosages  of  50  to  100  mg/1  are  sufficient  for  effluent
clarification. Iron salts, while successful  in precipitating phosphate,  have found  little
application  because  of  residual  iron  remaining in the treated water. An A1:P molar
ratio  of  1:1  to  2:1  is required.  The optimum  pH  for alum  treatment is  near 6.0
while  for   iron  the  optimum  pH  is   near  5.0  (1).  The  pH  of  high alkalinity
waters  may be  reduced  either  by  using  high  dosages of   alum  or  by  adding
supplementary  dosages  of  sulfuric  acid.  Anionic  polyelectrolytes  are  useful  with
alum  in  improving settleability  of  floe.  Settling  alone  will  reduce  residual P  to
about  1 mg/1.

If higher  removals are  required,  filtration must be employed. With proper operation,
residual P  may  be reduced to less than  0.1 mg/1. Multimedia filters are preferred over
sand  filters  because  of the extended length of  run.  Microstrainers have  not  been
successful in removing alum  floe.
                                                                          /^
Surface overflow  rates  for clarifiers have ranged  from 580 to 1,440 gpd/ft ,  but for
consistent  removal of phosphate, the  lower  end  of the range  is preferred. Filtration
rates of 2  to 5 gpm/ft   are  used.

No process has yet been developed  for successfully  recovering alum  from sludge for
reuse  although  both alkaline  and acid  regeneration were investigated (2, 3). The sludge
can  be dewatered by  conventional  methods.  Because  dewatering  may  be  difficult,
design  of such  facilities should be conservative.

Costs for  tertiary treatment for  phosphate removal range  from 6  to  15^/1,000  gal.
depending on plant size  and degree of  treatment required.
                                        9 - 1

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9.3    Laboratory and Pilot Studies

       9.3.1   South Lake Tahoe (3, 4, 5, 6)

Liquid alum  was  used  to  precipitate phosphate  in  a  2.5  mgd  tertiary  plant at South
Lake  Tahoe,  California.  The  treated wastewater was  applied to multimedia filters for
solids removal without prior sedimentation.

Chemical feed was proportioned  automatically to flow, and  flash mixing was provided
by an in-line mixer in the filter influent line. The  filter media consisted of layers  of
anthracite coal, graphite, fine garnet  and coarse  garnet overlaying  a supporting bed  of
gravel. Two  filters  were  operated in series at  5  gpm/ft .  Backwash with secondary
plant  effluent was  initiated either by headless or by a rise in turbidity of the effluent.
Polyelectrolyte was used as a filter aid to control the  depth  of penetration of floe into
the filter beds.  With an alum dosage of 200 mg/1, 8 to 9 mg/1  P  in  the secondary
plant  effluent was reduced to 0.03  to 0.3 mg/1  P  in the filter  effluent.  Turbidities
were correspondingly reduced from 30 to 70 JTU to 0.2 to  3.0 JTU.

Efforts to regenerate alum from the sludge by both acid and alkaline  treatment proved
to be uneconomical and a lime treatment process was  developed as a substitute for the
alum  process. Lime could  be economically  recovered  for  reuse  and had  the added
advantage of producing a high pH which facilitated removal of nitrogen by ammonia
stripping.

Total  costs for phosphate removal only, as estimated  in 1966, are  shown in Table 9-1.

                                     Table 9-1

                    1966 ESTIMATED COSTS FOR  TERTIARY
                      PHOSPHATE REMOVAL WITH ALUM

         Plant Capacity (mgd)                     Total Cost (jj 1,000 gal.)
                    2.5                                      11.7
                   10                                         8.5
                  50                                         7.1
                 100                                         6.6
                 200                                         6.3

       9.3.2  Nassau County (7, 8)
Nassau County,  New  York,   is evaluating  treatment  methods  for its  wastewater  to
provide a product water  which  is suitable for  ground injection as  a  barrier  to salt
water intrusion.  A  pilot  plant has been operated at 400 gpm producing  a water which
in most  respects  exceeds  USPHS drinking water  standards. Effluent from high rate
activated sludge  is pumped into  a  40 ft diameter by 14 ft deep clarifier where alum
and poly electrolyte  are  added. Sludge  is  recirculated  into the coagulation  zone  to
improve  efficiency  of  floe formation.  The treated  wastewater then  passes downward
through a flocculation zone  and  upward  through a  clarification zone  to orifice  type
                                       9 -  2

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collectors. The  clarified wastewater passes to 2 dual-media  filters in parallel  operated at
3.0 gpm/ft2. Each filter consists of a 36 in. bed of No. 1-1/2 anthracite  (effective size
of 0.90 mm) above  a  12 in. layer of sand (effective size of 0.40 mm).  Filter backwash
includes air  scour, surface  wash and  high  and  low-rate backwashing. The  filter effluent
passes through 4 granular carbon contactors operating in series to remove  organics.

Typical  operating results with about 200 mg/1  alum are  shown in Table 9-2.

                                     Table 9-2
                    NASSAU COUNTY PERFORMANCE DATA
         Turbidity, JTU
         Color, Pt-Co  Units
         COD, mg/1
         P, mg/1
    Influent
    20 - 25
    20 - 40
        78
      Effluent
      0.2 -  1.5
         none
          13
      0.1 -  1.0
Costs have been estimated, for separate tertiary treatment only, at plant sizes of ],  10,
and  100 mgd as shown in Table 9-3.

                                     Table  9-3

                       NASSAU COUNTY COST ESTIMATES
         Process
              Coagulation
              Filtration
              Carbon adsorption

         Operating labor
         Total Cost

       9.3.3   Chicago, Hanover Park (9)
                                            (1)
 4.9
 1.8
 6.3
13.0
28.0
41.0
       Plant Capacity (mgd)
              (10)         (100)
         (Costs, H 1,000 gal)
 3.5
 1.1
 4.5
 9.1
 5.6
14.7
 3.2
 1.0
 4.0
 8.2
 1.8
10.0
Alum was  used  to  coagulate solids and  precipitate phosphate  from secondary effluent
at  Chicago's  Hanover  Park  tertiary  treatment  plant.  Treatment consisted of
coagulation-sedimentation  in  circular  clarifiers  followed by either rapid sand filtration
or microstraining for polishing.  Average annual  flow was 1.5 mgd.

Combined  coagulation plus sand filtration removed 34, 58, and 82% P  at  dosages of
38, 60, and  140 mg/1  of alum, respectively. Combined coagulation plus  microstraining
effected a  lower phosphate removal of 23%  at an alum dosage of 38 mg/1.  In general,
                                       9 - 3

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alum  coagulation under the test conditions  gave little or no improvement in suspended
solids removal over that obtained by sand filtration of uncoagulated  secondary effluent.
The microstrainer did not significantly remove alum-coagulated solids.

       9.3.4   Dallas (10)

Dallas, Texas, is operating a demonstration project designed to  provide necessary  design
data for upgrading of  the Dallas-White  Rock  trickling filter plant. Phosphorus removal
facilities include a solids contact upflow  clarifier unit and two multimedia filters. The
clarifier has a rise rate of 0.5 gpm/ft2  at the design flow of 100 gpm and  a detention
time  of 4 hours.  Both filters  contain^ anthracite over sand media. One is  a standard
gravity  filter. The  other is a biflow type,  with feed water entering at both the top and
bottom of the bed. Filtered water is removed by a manifold-lateral collector located  at
the mid-depth of the bed. The gravity filter  is designed for 50 gpm at a filtration rate  of
        0                                                                     *")
4 gpm/ft  . The biflow  filter is designed for  100 gpm at a filtration rate of 8  gpm/ft ,  or
        ^
4 gpm/ft^ for both the bottom and top of the bed.

The pilot plant  process has not yet been optimized  for phosphorus removal, however,
limited  data from  two  short test periods on trickling filter and activated sludge effluents
are shown in  Table 9-4.

                                    Table 9-4

  REMOVAL OF TOTAL ORTHOPHOSPHATE BY COAGULATION-CLARIFICATION
                   IN THE DALLAS DEMONSTRATION PLANT

                                       Trickling Filter            Activated Sludge
                                          Effluent                   Effluent
Lime  Dose, mg/1 CaO                        128                        133
FeCl3 Dose, mg/1  Fe3+                      25                         56
Soluble Phosphate  In, mg/1 P                  6.5                         7.0
Soluble Phosphate  Out, mg/1 P                 0.43                        0.21
% Soluble P Removed                         93.5                        97.0
Test Period, days                            12                          2

       9.3.5   Dayton (11)
Dayton, Ohio, used alum in a 310 gpm pilot plant to remove phosphate and suspended
solids from trickling filter effluent. The rectangular sedimentation basin was designed for
105 minutes  detention  and an overflow rate of  1,014 gpd/ft .  Two filters designed for
                       ^
loadings up to 8 gpm/ftz were used  for polishing effluent. One contained 30 in.  of sand
while  the other used  20 in.  of  anthracite overlaying 10 in. of sand. The sand had  an
effective size of 0.40 to 0.45 mm with a  uniformity coefficient of 1.35 to 1.70. The
anthracite had an effective size of 0.85 to  1.20 mm with a uniformity coefficient  of 1.35
to 1.80. Both air and water were used in backwashing.
Alum  with  activated   silica or anionic polyelectrolyte  as  coagulant  aids achieved
                                                         3
phosphate removals at  a  dosage rate of 5  Ib alum/lb PO^   down to residuals  of 4
                                       9-4

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mg/1 PC>4   in  filter effluents (89% removal of phosphate). Further removals down to
1  to 2  mg/1 PC>4   required in excess of 200 mg/1 alum. The clarifier was operated at
overflow rates of 655  to  1,035 gpd/ft2.

The filters  removed 30 to 70% of the applied phosphate load. The  dual  media filter
produced an effluent  comparable to that  from the sand filter  with  filter runs 2  to 3
times the length of the sand filter runs.

Costs to provide 90% phosphate  removal  with alum  for the  present 50 mgd flow in a
75 mgd plant were estimated at 6.5 to 8.2^/1,000  gal.

       9.3.6  Oxidation Pond  Effluents

At Lancaster, California, a research project  was initiated  to renovate wastewater for use
in   recreational  lakes (12). Existing  treatment  consisted  of  primary sedimentation
followed by 45 to  60 days detention in oxidation ponds. For coagulation, laboratory
jar tests showed alum to  be more effective on a  cost basis  than either  lime or ferric
sulfate.  Phosphate  residuals were  reduced to  1.1, 0.2, and  0.01  mg/1  P  with alum
dosages of  150, 200, and 300 mg/1,  respectively, at an optimum  pH near  6.0. Pilot
studies  showed  that  both  sedimentation and air  flotation would  provide satisfactory
separation of most of the  precipitated phosphates, however, filtration was necessary to
obtain the required low residuals of less than 0.15 mg/1  P.

Final specifications for a full  scale process  included  coagulation with  about  300 mg/1
alum  and  20 minutes  of  flocculation  with  a  conventional  paddle  flocculator,
sedimentation in  a horizontal clarifier with  an  overflow rate of  400  gpd/ft ,  and
filtration through  a dual  media gravity  filter consisting  of 18 in. of 0.5 mm  anthracite
over 8 in. of No.  20 sand.

Capital  costs of a  0.5 mgd facility were estimated' at $150,000 with operating costs of
$184/10"gal.   The total  cost of  capital,  operation,  and maintenance   for  a  3 mgd
facility  was  estimated  at S150/106 gal.

Alum was recently evaluated  by Shindala and Stewart (13) for phosphorus removal  and
polishing of waste  stabilization pond effluents in Mississippi. Jar tests were used in the
evaluation. Using a minimum  of 90% removal of phosphorus and 70% removal of COD
as criteria, the  optimum alum  dosage was 85 mg/1 at pH 5.5. With higher doses, up to
97%  phosphorus removal  and  85% COD removal  were observed.  Ferric  chloride  and
ferric sulfate were also tried but left a residual  iron color in the supernatant.

       9.3.7  Moving  Bed Filter (14)

Alum and  polyelectrolyte were  used  to treat  trickling  filter  effluent  in a proprietary
moving  bed  filter  at   Liberty  Corner,  New Jersey.  The  device, a   product  of
Johns-Manville Products Corp., used a bed of sand which is periodically moved upward
in an inclined  filter  vessel. Clean sand  is  fed  in  at  the bottom  of the  filter  and
floe-laden sand  is  removed mechanically at  the  top  as required  by pressure  drop,
                                       9  - 5

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leaving  a  fresh  filtration surface. The wastewater  being  filtered passes down through
the bed and flows through screens at the sides of the filter body.

A  major factor  controlling phosphate removal is the molar ratio of A1:P.  At an alum
dosage of 200 mg/1  and influent total  phosphorus  concentrations  on the  order of 25
to 28  mg/1  as  P (A1:P  ratio =  0.6  to  0.7), the total phosphorus removal  efficiency
averaged 90%. With  lower total phosphorus  concentrations (A1:P ratios =  1.2  to  2.6)
removal efficiencies  averaged  95% and  reached  as high  as 99%. The alum  treatment
also  removed  about  70% of  suspended  solids  leaving an average  of 15  mg/1  in the
effluent.

Capital  costs for a 1 mgd moving bed filter are  estimated at $264,000. Total operating
costs  for  such  an installation using 200 mg/1  alum are estimated at 12^/1,000 gal.
treated.
                                        9 - 6

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9.4    References
 1. Recht,  H.  L.,  and Ghassemi, M., "Kinetics  and Mechanism of Precipitation  and
    Nature of the Precipitate  Obtained  in  Phosphate  Removal  from Wastewater Using
    Aluminum  (III)  and  Iron (III)  Salts", Water  Pollution Control  Research  Series
    17010EKI, Contract 14-12-158, USDI, FWQA (April,  1970).

 2. Farrell,  J.  B.,  Salotto, B. V.,  Dean,  R.  B.,  and  Tolliver, W. E.,  "Removal of
    Phosphate  from  Wastewater  by  Aluminum  Salts  with  Subsequent Aluminum
    Recovery",  Chem. Eng. Prog. Symp. Series,  64:90, p 232 (1968).

 3. Slechta, A.  F.,  and Culp,  G. L., "Water Reclamation Studies at the South  Tahoe
    Public Utility District," JWPCF, 39:5, p  787 (1967).

 4. Culp,  R. L., "Wastewater Reclamation by Tertiary Treatment", JWPCF, 35:6, p  799
    (1963).

 5. Culp,  R. L., and  Roderick,  R.  E.,  "The  Lake Tahoe Water Reclamation Plant",
    JWPCF, 38:2, p 147 (1966).

 6. Culp,  R. L., "Wastewater  Reclamation at  South Tahoe Public Utilities  District",
    JAWWA, 60:1, p 84(1968).

 7. Rose,  J. L., "Injection of  Treated Waste Water into  Aquifers", Wat. & Wastes Eng.,
    5:10, p 40(1968).

 8. Rose,  J.  L., "Advanced Waste Treatment in Nassau  County, N. Y.", Wat.  &  Wastes
    Eng., 7:2, p 38 (1970).

 9. Lynam, B.,  Ettelt, G., and McAloon, T., "Tertiary Treatment at Metro Chicago by
    Means  of Rapid Sand  Filtration  and Microstrainers", JWPCF,  41:2 (Part  1),  p  247
    (1969).

10. Graeser,  H. J.,  and  Haney,  P.  D., "Dallas  Builds Center to  Study Wastewater
    Reclamation", Wat. &  Wastes Eng., 5:12, p  34 (1968).

11. Tossey, D.  F., Fleming, P.  J., and Scott, R. F., "Tertiary Treatment by Flocculation
    and Filtration", Jour. SED, ASCE, 96:SAI,  p 75  (1970).

12. Dryden, F.  D.,  and Stern,  G., "Renovated  Waste Water Creates Recreational Lake",
    Environmental Science & Tech., 2:4, p 268  (1968).

13. Shindala, A., and Stewart, J. W., "Chemical Coagulation of Effluents from  Municipal
    Waste Stabilization Ponds", Wat. & Sew. Works, 118:4, p  100 (1971).

14. "Phosphorus Removal Using Chemical Coagulation and a Continuous Countercurrent
    Filtration Process", Water Pollution Control  Research Series  17010EDO  USDI,
    FWQA (June 1970).
                                      9 -7

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                                 CHAPTER 10

                   STORAGE AND FEEDING OF CHEMICALS
10.1     Aluminum Compounds

The  principal aluminum compounds  that are commercially available  and suitable for
phosphorus precipitation are alum and sodium aluminate (1).  Both are available in either
liquid or dry forms.  Alum is acidic in nature  while sodium aluminate is alkaline and
this may be an  important factor in choosing between them.  Aluminum chloride should
be considered, and  is discussed  herein.

         10.1.1        Dry Alum

         10.1.1.1      Properties and Availability

The  commercial dry alum most used in wastewater treatment is known as  "filter alum"
and has the approximate chemical formula A^CSO^   14^0 and a molecular weight
of 594. Alum is white to cream in color.  The pH varies between 3.0 and 3.5 in aqueous
alum solutions having concentrations between  1% and  10%. Commercially available grades
and  their corresponding bulk densities and  angles of repose  are given in  Table  10-1:
                                  TABLE 10-1

                     AVAILABLE GRADES  OF DRY ALUM



         Grade                Bulk Density          Angle  of  Repose
                               Ib/cu ft

         Lump                 62 to  68                 varies

         Ground               60 to  71                   43

         Rice                  57 to  61                   38

         Powdered             38 to  45                   65
 Each grade has  a  minimum  aluminum  content of  17%, expressed  as  A^Oj.  This
 corresponds to a 9%  concentration  as aluminum.  Viscosity and solution crystallization
                                   10-1

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temperatures  are included in the subsequent section  on liquid alum.

Since dry alum is only partially hydrated, it is slightly hygroscopic. However, it is relatively
stable when stored under the extremes of temperature and humidity encountered in the
contiguous  United States.
The  solubility of commercial  dry  alum at various temperatures is listed in Table  10-2:


                                   TABLE 10-2

             SOLUBILITY  OF  ALUM AT VARIOUS TEMPERATURES
          Temperature                                Solubility
                F                                      Ib/gal

                32                                        6.03
                50                                        6.56
                68                                        7.28
                86                                        8.45
               104                                       10.16
Dry alum is not corrosive unless it absorbs moisture from the air, such as during prolonged
exposure to humid atmospheres.  Therefore, precautions  should be taken to ensure storage
space is  free of moisture.

Alum is  shipped in  100 Ib bags, drums, or in  bulk (minimum of 40,000 Ib) by truck
or  rail.   Bag shipments may be  ordered on wood pallets.  In 1973, the price range for
dry alum in bulk quantities is $60 to $65  per ton, F.O.B. the point of manufacture.
Freight  costs must be added  to  this.   Bagging  adds about $5  per ton to  the base cost
for bulk alum.  Names and locations of major producers are in a subsequent section.

          10.1.1.2      General Design Considerations

Water  utilities  usually use  ground  and  rice  alum   because  of their  superior  flow
characteristics.   These  grades have less tendency to lump or arch in storage  and therefore
provide more consistent feeding qualities.  Hopper agitation is seldom required with these
grades, and in  fact  may be  determined to  feeding due to  packing the contents of the
bin.
                                    10-2

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Alum dust is present  in  the  ground grade and  will cause minor irritation of eyes and
respiratory tract.   A  respirator will protect  against alum  dust.   Alum dust should be
thoroughly flushed from  the  eyes immediately  and washed  from the  skin  with  water.
Gloves should  be  worn to  protect  the  hands.   Because of minor irritation in handling
and  the  possibility  of alum  dust  causing rusting  of adjacent  machinery, dust removal
equipment is desirable.

          10.1.1.3      Storage

A typical storage  and feeding system for  dry alum is shown in Figure 10-1. Bulk alum
can be stored in mild steel or concrete  bins  with dust collector vents located in, above,
or adjacent to the equipment room.  Recommended storage capacity is about 30 days.
Dry alum in  bulk can be transferred with screw conveyors, pneumatic conveyors, or bucket
elevators made of mild steel.  Pneumatic conveyor elbows should have a reinforced backing
to withstand  abrasion.

Bags and  drums of alum should be stored in a dry location.  Bag or drum  loaded hoppers
should have storage capacity for eight hours at the nominal maximum feed rate so personnel
are not required to charge the  hopper more than once per shift. Converging hopper sections
should have  a minimum  wall slope  of  60  to  prevent arching.

Bulk Storage hoppers should have a discharge bin gate so feeding equipment may be isolated
for servicing.  The bin gate should  be followed  by a flexible connection,  and transition
hopper chute or hopper  which acts as a conditioning chamber  over the feeder.

          10.1.1.4      Feeding Equipment

The  feed  system includes  all components required for preparation of the chemical solution.
Capacities and assemblies should be selected to fulfill individual system requirements. Three
basic types  of chemical  feed equipment  are used:   volumetric, belt gravimetric, and
loss-in-weight gravimetric. Volumetric feeders are usually used  where  low initial cost and
lower  delivery capacities  are  the  basis  of  selection.  Volumetric  feeder mechanisms are
usually exposed to corrosive  vapors from  the dissolving chamber.  Manufacturers  usually
control this  problem by  use  of an electric heater  to keep  the  feeder housing dry or by
using plastic  components in  the  exposed areas.

Volumetric dry feeders  are  generally of the screw type.   Two  designs  of screw  feed
mechanism  are  available.   Both allow even withdrawal across  the bottom of the feeder
hopper to prevent dead zones.  One screw design is the variable pitch  type with the pitch
expanding evenly to  the discharge  point.   The  second screw  design is  the  constant
pitch-reciprocating type.  This type has each half of the screw  turned in opposite directions
so the turning and reciprocating motion alternately fills one  half  of the screw while the
other half is discharging.   The variable  pitch screw has one point of discharge, while the
constant  pitch-reciprocating screw has two  points  of discharge, one  at each end of the
                                     10-3

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                          FIGURE 10-1

                   TYPICAL DRY FEED SYSTEM
    ,-DUST COLLECTOR
       />
      XX-FILL PIPE (PNEUMATIC)
    K_	
BULK STORAGE
    BIN
                                   DAY HOPPER
                                   FOR DRY  CHEMICAL
                                   FROM BAGS OR  DRUMS,
                                         *-< ';.-
             BIN GATE
             FLEXIBLE
             CONNECTION
                ALTERNATE SUPPLIES  DEPENDING
                         ON STORAGE
                                                     DUST  COLLECTOR
                                                          XBAG  FILL
                                                            -SCREEN
                                                             WITH  BREAKER
                                                 SCALE OR  SAMPLE CHUTE
DUST AND VAPOR REMOVER
WATER
SUPPLY
             DRAIN
        SOLENOID VALVE
      CONTROL
       VALVE -^ROTAMETER


     PRESSURE  REDUCING
           VALVE
                        I
                  WATER SUPPLY
                                                            __ GRAVITY TO
                                                                APPLICATION
                                                                  PUMP
                                                                APPLICATION
                          10-4

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screw.  The  accuracy of volumetric feeders is influenced by  the character  of material
being fed and ranges between  1% for free-flowing materials to  7% for cohesive materials.
This accuracy is volumetric and is not related  to accuracy by  weight (gravimetric).

Where the  greatest  accuracy  and  more  economical use  of chemical  is  desired, the
loss-in-weight  type feeder should be selected.  This feeder is suited to low and medium
feed rates with a maximum of approximately 4,000  Ib/hour. The unit consists of a material
hopper and feeding mechanism mounted  on  enclosed scales.  The  feed  rate controller
retracts scale  poise  weight  to  deliver the  dry  chemical at the  desired rate.  The  feeding
mechanism must feed at this rate to  maintain the balance of  the scale.  Any unbalance
of the scale beam causes a  corrective change in output.  Continuous comparison of actual
hopper weight  with set hopper  weight  prevents cumulative  errors.  Accuracy of the
loss-in-weight  feeder is near 1% by weight of the set rate.

Belt-type gravimetric feeders span  the  capacity ranges of volumetric  and loss-in-weight
feeders and can be  sized for most applications in wastewater  treatment.   Initial expense
falls  between that  for  the volumetric feeder and the  loss-in-weight  feeder.  Belt-type
gravimetric  feeders  consist  of a basic belt  feeder incorporating a weighing  and  control
system.   Feed rates can be varied by  changing either the  weight per foot of belt, belt
speed,  or both.   Controllers in  general use are mechanical,  pneumatic, electric and
mechanical-vibrating. Accuracy specified for belt-type gravimetric feeders should be within
 1%  of set  rate.   This  equipment normally  includes mild steel hoppers, stainless steel
mechanism  components, and  rubber surfaced feed belts.

Because alum solution is corrosive, dissolving  or solution chambers should be constructed
of type 316  stainless steel, fiberglass reinforced  plastic (FRP), and plastics.  Dissolvers
should be sized for  preparation of the desired  solution strength.  The most dilute solution
strength usually recommended is  0.5 Ib of alum to  1 gallon of water, or a 6% solution.
The  dissolving chamber is  designed for a minimum  detention time  of 5  minutes at  the
maximum feed rate.   Because  excessive dilution may be detrimental to  coagulation,
eductors, or  float valves that would ordinarily  be used ahead of centrifugal pumps, are
not recommended.  Dissolvers  should be equipped with water meters and mechanical mixers
so the water to  alum ratio may  be properly established and controlled.

          10.1.1.5      Piping and Accessories

Pipe made  from  FRP or plastics  (polyvinyl  chloride, polyethylene, polypropylene, and
similar materials) is recommended for  alum  solution.   Care  must be taken to  provide
 adequate support for these piping systems, with  close attention given to spans between
supports so objectionable deflection will  not  occur.  Lined steel pipe is generally tougher
 and  more rigid,  but the  cost of providing a near perfect  lining may detract from  its
 suitability.
                                      10-5

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Solution flow by  gravity to the point of  discharge is  desirable.  When gravity flow is
not possible, transfer  components  should require  little or no  dilution.  When metering
pumps or proportioning weir tanks are used, return of excess flow to a holding tank
should be considered.  Metering pumps  are  discussed in the section  on liquid  alum.

Valves used in solution lines should be  plastic, type 316 stainless steel or rubber-lined
iron or steel.

          10.1.1.6      Pacing  and Control

Volumetric and gravimetric feeders are usually adaptable to operation from any standard
instrument control and pacing  signals.

When  solution must  be pumped, consideration should be given to use of holding tanks
between the dry feed  system and feed pumps; solution water supply should be controlled
to  prevent excessive  dilution.   The dry  feeders may be started and stopped from tank
level  probes.  Variable control metering pumps can transfer alum stock solution to  the
point  of application  without further  dilution.

Means should be  provided for  calibration of chemical feeders.  Volumetric feeders may
be  mounted  on platform  scales.   Belt feeders should include a sample chute and box
to  check actual delivery  with set  delivery.

Gravimetric feeders are usually furnished with  totalizers only.  Remote instrumentation
is frequently used with gravimetric equipment, but seldom used with volumetric equipment.

          10.1.2        Liquid Alum

          10.1.2.1       Properties and Availability

Liquid alum is  shipped in insulated tank cars or trucks.  During the winter it is heated
prior to shipment so  crystallization will not occur during transit. Liquid alum is shipped
at  a  solution  strength of about 4.37% as aluminum or about 8.3%  as A^O^ or 49% as
Al2(SO4)3    14H2O.   This solution  has a density of 11.1  Ib/gal at 60F and  contains
about 5.4 Ib  dry alum (17%  A^Oj) per gallon  of liquid. This solution will  begin to
crystallize at  30F and crystallizes at  18F.
                                      10-6

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Crystallization temperatures of other solution strengths are as follows (1) in Table  10-3:


                                   TABLE 10-3

             CRYSTALLIZATION TEMPERATURES OF LIQUID  ALUM
                                            Temperature  of
                                             Crystallization
                                                  op

                  5.19                            26
                  6.42                            21
                  6.67                            19
                  6.91                            17
                  7.16                            15
                  7.40                            13
                  7.66                            12
                  7.92                            14
                  8.19                            17
                  8.46                            20
                  8.74                            28


The viscosity  of various alum solutions  is given in  Figure  10-2.

Tank truck lots  of 3,000 to 5,000 gallons are available.  Tank car lots are available in
quantities of 7,000 to 18,000 gallons. The 1974 price of liquid alum on an equivalent
dry  alum (17%  A^O^)  basis is about $60 per ton, F.O.B. the point of manufacture.
Since liquid alum is  an  intermediate compound in  production  of dry alum, the liquid
form costs less.  However,  liquid alum  costs more  to transport since it is nearly half
water, by weight. Therefore, a cost tradeoff point can be established when exact chemical
costs and local freight rates are determined. Liquid alum will generally be more economical
than  dry alum if the point  of use is  within 100 miles  of the manufacturing plant; ease
of handling, storing and feeding liquid alum extend its practical transport limit to 200 miles
or  more.
                                     10-7

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CO
LLl
V)
UJ
o
CO
o
o
V)
                              FIGURE  10-2


                     VISCOSITY OF ALUM SOLUTIONS


                  (COURTESY OF ALLIED CHEMICAL  CO.)
           I   I   I   I    I   I    I   I    I   I   1    I   I       I   I    I   I
       30  40  50  60  70  80  90  100 110 120 130 140  150 160170 180 190 200 210 220

                              TEMPERATURE,F
                              10-8

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          10.1.2.2      General  Design Considerations

Bulk unloading facilities usually must be provided at the treatment plant.  Rail cars are
constructed for top unloading and therefore require an  air supply system and flexible
connectors  to  pneumatically  displace  the  alum  from  the car.   U.S. Department  of
Transportation  regulations concerning  chemical tank car unloading should be observed.
Tank truck unloading is usually  accomplished by gravity or by a  truck mounted pump.

Established  practice  in the treatment field has  been  to  dilute   liquid alum  prior  to
application. However, recent studies have shown that feeding undiluted liquid alum results
in better  coagulation  and settling.  This is reportedly due to  prevention of hydrolysis
of the alum.

No particular  industrial hazards  are  encountered in handling liquid  alum.  However, a
face  shield and gloves should be worn around leaking equipment. The eyes or skin should
be flushed and washed upon contact with liquid  alum.  Liquid alum becomes very slick
upon evaporation and  therefore  spillage should be  avoided.

          10.1.2.3       Storage

Liquid alum is stored  without  dilution at the shipping concentration. Storage tanks may
be open if indoors  but must  be closed and vented if outdoors.  Outdoor tanks should
also be heated, if necessary, to  keep the temperature above 25F to prevent crystallization.
Storage tanks should  be  constructed  of type 316 stainless steel;  FRP, steel lined with
rubber, polyvinyl chloride, or  lead; see subsequent section for further details.   Liquid
alum can be stored indefinitely  without deterioration.

Storage tanks should  be sized  according to  maximum feed rate, shipping time  required,
and quantity of shipment.  Tanks should generally be sized for 1-1/2 times the quantity
of shipments.  A 10-day  to 2-week supply should be provided to allow for unforeseen
shipping delays.

          10.1.2.4      Feeding  Equipment

Various types of gravity or pressure feeding and metering units are available.  Figures 10-3
and  10-4 illustrate commonly used feed systems.  The rotodip-type feeder or rotameter
is often  used  for gravity feed and the metering pump  for pressure feed systems.

The pressure or head available at the point of application frequently determines the feeding
system to be used.  The rotodip feeder can  be supplied from overhead storage by gravity
with the use of  an internal level  control valve, as shown by  Figure 10-3.  It may also
                                     10-9

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         FIGURE 10-3
ALTERNATIVE LIQUID FEED  SYSTEMS
     FOR OVERHEAD STORAGE
r-


FLOAT
VALVE-v
-rf
7^



ROTOD IP-TYPE FEEDER
OVERHEAD
STORAGE
TANK


CONTROL
VALVE
*




ROTAMETER
UJ
Ul
ce
1
O
F VALVE
K PRESSURE VALVE

r
METERING PUMP
                                          GRAVITY FEED
          10-10

-------
          FIGURE 10-4




ALTERNATIVE LIQUID FEED SYSTEMS




      FOR GROUND STORAGE






    PRESSURE FEED

/
(








GRAVITY


,-ROTOD IP-TYPE
/CTx r
\SJ\7 *

.

7



FEED
TRANSFER PUMF


FEEDER

i


'



\


^CONTROL VALVE
y ^ROTAMETER
n Jf 1. 1
^ 1 -





s n tv

^




IRCULATION

GROUND
STORAGE
TANK
1


> j
.j Q- iij
< a. Z oe
 i E i ^
u. a. oe co
_ CD LU
oe ci z ae
Z UJ OS ' ' "
0 uj " S
"s !s AS
Q T f f
1 0






PRESSURE
FEED
1 .

>,

         10-11

-------
be supplied by a centrifugal pump.  The latter arrangement requires an excess flow return
line  to the  storage  tank,  as shown by Figure 10-4.  Centrifugal  pumps should  be
direct-connected but  not close-coupled because of possible leakage into the motor, and
should be  constructed of type  316 stainless steel,  FRP, and plastics.

Metering pumps, currently available, allow a wide range of capacity to compare with the
rotodip and rotameter systems.  Hydraulic diaphragm type pumps are  preferable to other
type pumps  and  should be protected with an internal or external relief valve.  A  back
pressure valve is usually  required in the pump discharge to provide efficient check  valve
action.  Materials  of construction for feeding equipment should be as recommended  by
the manufacturer  for the service, but depending on the type of system,  will generally
include type 316  stainless steel, FRP, plastics, and rubber.

          10.2.1.5        Piping and  Accessories

Piping systems for alum should be FRP, plastics (subject to temperature limits), type 316
stainless  steel,  or  lead.  Piping and valves used  for alum solutions are also discussed in
the preceding section on dry alum.

          10.1.2.6       Pacing  and Control

The feeding  systems described  above are volumetric, and the feeders generally available
can be adapted to receive  standard  instrument pacing signals. The signals can be used
to vary motor speed, variable speed transmission setting, stroke speed and stroke length
where applicable.  A totalizer is usually furnished with  a rotodip-type feeder, and remote
instruments are available.   Instrumentation  is rarely used with rotameters and metering
pumps.

          10.1.3         Dry Sodium Aluminate

          10.1.3.1       Properties and Availability

Dry sodium  aluminate, Na2Al2C>4, is available from manufacturers listed in a subsequent
section.  Dry sodium aluminate is  shipped in 50  Ib bags and has  a bulk density ranging
from 40 to 50 Ib/ft . The A^Og content ranges from  41 to 46%. Dry sodium aluminate
is noncorrosive and the pH of a  1% solution is about 11.9.  Manufacturers should be
consulted  for more precise specifications of their  product.

The 1974 price of dry  sodium aluminate in 40,000 Ib shipments  ranges from $0.13 to
$0.15 per Ib, F.O.B. the point  of manufacture.  Prices increase substantially for smaller
shipments.
                                     10-12

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          10.1.3.2      General Design  Considerations

Requirements for  dry sodium  aluminate feed systems are generally  similar to  those for
dry aluminum sulfate.  Dry sodium aluminate is not available in bulk quantities. Therefore,
the small,  day-type  hoppers with manual filling arrangements as shown by Figure 10-1
are used.  Precautionary measures for handling sodium aluminate are similar to those for
strong alkalies, such  as caustic soda.   Contact with  skin, eyes, and clothing should be
avoided.  Aluminate  dust  or solution spray  should  not be breathed.

          10.1.3.3      Storage

Dry sodium  aluminate  is stored as received, in bags, and at optimum  conditions of 60
to  90F;  the recommended storage limit is  6 months.   Hopper  material of mild steel
is  completely adequate.  This chemical may or may not be free flowing, depending on
the manufacturer and grade  used.  Therefore, hopper agitation may be required. Sodium
aluminate deteriorates on exposure to the atmosphere and care should be taken to avoid
tearing  of bags.

          10.1.3.4      Feeding Equipment

Materials of construction for dissolving chambers may be mild steel or stainless steel and
selection may be influenced by conformity with adjacent equipment. Equipment  similar
to that shown by Figure  10-1  is applicable.  Standard practice for the free-flowing grade
of sodium aluminate calls for dissolvers sized for 0.5  Ib per gallon or  6% solution strength
with  a  dissolver  detention  time  of 5 minutes at the  maximum feed rate.

After dissolving dry  sodium aluminate in the  preparation of batch solutions, agitation
should be minimized or eliminated to  prevent deterioration of the solution.  Air agitation
is  not recommended, and  solution  tanks should be covered to prevent  carbonation of
the solution.

          10.1.3.5      Piping and Accessories

Materials  for  piping and transporting  dry sodium aluminate solution may be mild steel,
iron,  type 304 stainless steel,  concrete,  or  plastics.  The use of  copper,  copper  alloys,
and rubber should be  avoided.
                                     10-13

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          10.1.3.6      Pacing and Control

Pacing and control fundamentals are similar to those described for dry alum.  The amount
of dilution  is not a  consideration in the use  of sodium aluminate.  Therefore, the use
of float valves to satisfy centrifugal pump suction, and the use of eductors, is permissible.

          10.1.4        Liquid Sodium  Aluminate

          10.1.4.1      Properties and Availability

Liquid sodium aluminate is available from the manufacturers listed in a subsequent section.
There  is considerable variety in  the composition of liquid  sodium  aluminate  from the
manufacturers listed.  The A^Og content varies from 4.9 to 26.7%.  The lower solution
strengths are usually more expensive because of the cost of freighting the solution water.
Because  of  the  variety  of solution  strengths available,  the manufacturers should  be
contacted for more  specific information on density,  viscosity, and cost.

Liquid sodium aluminate is  available in  30-gallon drums  (380 Ib), tank truck,  and tank
car quantities.   The  approximate  1974  price  of liquid sodium aluminate in 40,000 Ib
quantities is about  $0.05 per Ib  (A12O3  content, 26.4% or  19.9%) P.O.  B.  point of
manufacture.

         10.1.4.2      General Design  Considerations

Because of  the alkaline nature of sodium  aluminate, it  should not be used in contact
with brass, copper, aluminum or  rubber.  Liquid sodium  aluminate is a strong alkali and
the same  precautions should  be  exercised in handling it as in handling  caustic  soda.

         10.1.4.3      Storage

Liquid sodium  aluminate  is  usually stored at  the shipping  concentration, either in the
shipping drums or in mild steel tanks.  Storage tanks may be located indoors  or outdoors;
however, outdoor tanks  should  be provided  with facilities  for  indirect  heating.  The
maximum recommended length of storage is two to three months.   Bulk  shipments can
be unloaded by gravity, pumping, or air pressure.  However, if air is used, it should first
be passed through lime-caustic soda breathers to remove carbon dioxide. Steam injection
facilities  are required at  the  unloading  site.

          10.1.4.4      Feeding  Equipment

Feeding equipment and systems  as described  for liquid  alum  generally  apply  to liquid
sodium aluminate except  with changes of requirements regarding dilution and  materials
of construction  as described  above.
                                     10-14

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Liquid sodium aluminate may be fed at shipping strength or  diluted to a stable  5 to
10% solution.  Stable solutions are prepared by direct addition of low hardness water
and  mild  agitation.   Air agitation  is not recommended.

          10.1.4.5       Piping and Accessories

Piping requirements are  the same as previously indicated for solutions of dry aluminate.

          10.1.4.6       Pacing and  Control

System pacing and control requirements are  the same  as described for liquid alum.

          10.1.5         Aluminum Chloride

Aluminum chloride is not as readily available as other compounds  previously discussed,
and  in some cases it  does not enjoy a competitive price structure; nevertheless, it should
be considered as  a source of aluminum by designers undertaking phosphorus precipitation
by metal  addition.

The  majority  of  the  aluminum chloride  production facilities in this country are located
near petroleum refining  centers  and petrochemical  complexes.  This is  because those
industries  consume three-fourths of the total production. Miscellaneous users of the balance
of the overall production include makers  of antiperspirants and a variety of other unrelated
manufacturing  operations.   Therefore,  a reliable  and economical  source of  aluminum
chloride may, in fact, be near the  proposed wastewater treatment project.

Much  of  the  aluminum  chloride  produced  is the  form of semi-pure anhydrous crystals
with  an  off-white  color.   This  product is derived  from  direct chlorination  of scrap
aluminum, and has a molecular weight of  133.3  and purities near 99 percent.  In some
instances purities may drop to 96 percent which is satisfactory  for wastewater treatment
if analysis shows other  compounds present are  acceptable.

Another solid form  is produced  by crystallization from hydrochloric  acid in  the form
of a hexahydrate, in  which six molecules of water attach to each molecule of aluminum
chloride.

The  most  usual  commercial form of liquid aluminum chloride  is in a 32-degree  Baume
solution; it contains 28  percent aluminum  chloride by weight.  This particular liquor is
not  universally produced, however, so designers should  be  prepared to consider other
concentrations  with  a fairly wide variety of  other chemical  compounds present.
                                     10-15

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Containers for shipping and storing should be  similar to those used for dry and  liquid
alum.  Handling  and feeding requirements  are also similar  to  those  used with  alum.
Designers should  check  with local producers for further details.

Designers may contact manufacturers operating  in at least seventeen plants in the U.S.
shown in Table  10-4:
                                   TABLE 10-4
                     SUPPLIERS OF ALUMINUM CHLORIDE
     Allied Chemical Corp.:
     Clinton Chemical  Co.:

     Dow Chemical Co.:

     E.  I. du  Pont de Nemours
         & Co.,  Inc.:
     FMC Corporation:

     Hercules Alchlor
         Chemical  Co., Inc.

     Monsanto  Co.:
     Pearsall  Chemical Corp.


     Reheis Co.,  Inc.:

     Stauffer Chemical  Co.:
El Segundo, Calif.;
Hegewisch, 111.;
Elberta, N.Y.

Houston, Texas

Freeport, Texas
Grasselli, N.J.;
East Chicago, Ind.

Nitro, W. Va.
Ravenna, Ohio

Everett, Mass.;
Texas  City, Texas

Phillipsburg, N.J.;
La Porte, Texas

Berkeley Heights, N.J.

Dominguez, Calif.;
Baton  Rouge, La.;
Elkton, Md.
                                     10-16

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          10.1.6        Estimated Initial  Costs  of  Adding Liquid Alum Feed  Facilities
                       to Existing Wastewater  Treatment Plants

Cost estimates of chemical storage and feeding equipment for 1, 10, and 100  mgd plants
have  been prepared based on the use of  liquid alum (8.3%  A^O^) for phosphorus
precipitation.  A mole ratio of A1:P of 2:1  was assumed to treat an influent phosphorus
concentration of 10 mg/1 as P.  This corresponds to  an alum dose of 191 mg/1 (17.4  mg/1
as aluminum).

Chemical  feed equipment was  sized for a peak feed rate of twice that calculated from
the mole  ratio.  Storage was  provided for at least 15 days at the average feed rate.  Th'*-
storage  time is arbitrary and  will vary at each installation depending on the distance to
and the reliability  of  the source of chemical supply.  Piping  and buildings to house the
feeding  equipment  are not included in the estimates.  At many locations the  chemical
feeding  equipment can be installed in existing buildings.  In all estimates, the costs include
an allowance for the  contractor's installation, overhead, and profit, and an allowance of
20% of the  construction cost for engineering and contingencies. The estimated costs for
each size plant are shown in Table 10-5. These figures correspond to an EPA Construction
Cost Index  of  185:
                                   TABLE  10-5

                   COST OF LIQUID ALUM FEED FACILITIES


            Plant Size                      Estimated 1973  Cost
             (mgd)                                 ($)

                1                                 15,000

               10                                 50,000

              100                                600,000
For the 1.0 mgd plant, feeding equipment for liquid alum includes two 25 gph hydraulic
diaphragm  pumps  (one  operating and  one standby) with the necessary accessories and
equipment  to  pace the  feed rate with plant flow.  Two 3,000-gallon  FRP tanks with
accessories  are provided  for  storage  of liquid alum. The total capacity  of 6,000 gallons
allows  some flexibility in ordering  and receiving 4,000-gallon tank  truck shipments.
                                    10-17

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For the  10 mgd plant,  liquid alum  is fed by three 125  gph rotodip-type feeders (two
operating and  one  standby)  with  the necessary  accessories  and  control panel  for
proportioning chemical feed to flow.  Alum is stored  in  four 11,500-gallon FRP tanks.

For the  100 mgd plant, liquid alum  is fed with seven 415 gph  rotodip-type feeders (six
operating and one standby) with the necessary control equipment.  Storage costs are based
on ten 50,000-gallon underground concrete  tanks for the rotodip feeders but eliminates
the need for heating the tanks.   Three  500-gallon FRP  day tanks are included in  the
estimate; one for each pair of feeders.  Four alum transfer pumps (three  operating and
one standby), with  a  capacity of 50 gpm at 50  ft of head are provided.

The cost of feeding  and storage facilities for the 100 mgd plant is greater than  10 times
the cost  of facilities for the  10 mgd  plant.  This is because underground storage facilities
were the basis of design for the  100 mgd plant in contrast to FRP tanks located in  an
existing  building  for the 10 mgd plant.  The cost of a building for the 1.0 and 10.0  mgd
plants would raise the cost substantially.  FRP tanks could be used for the larger plant;
however, structural  design  may necessitate   special  construction  requirements   for
underground FRP tanks.  FRP tanks located above ground and  on concrete foundations
would  require special  insulation  and heating.

10.2     Iron Compounds

          10.2.1         Liquid Ferric  Chloride

          10.2.1.1       Properties and Availability

Liquid ferric chloride (2) is a corrosive, dark brown oily-appearing solution having a typical
unit weight between 11.2 and 12.4 Ib/gal (35 to 45% FeCl3).  The ferric chloride content
of these  solutions is 3.95 to  5.58 Ib/gal.  Shipping concentrations vary from summer to
winter due  to  the relatively  high crystallization temperature of the more concentrated
solutions as shown  by Figure 10-5.   The  pH  of a 1% solution is 2.0.

The molecular  weight of ferric chloride is 162.22.  Viscosities of ferric chloride  solutions
at various temperatures are  presented  in Figure 10-6.

Liquid ferric chloride is shipped  in 3,000 to 4,000 gallon bulk  truckload lots,  in 4,000
to 10,000 gallon  bulk  carload lots, and in 5 and 13 gallon carboys.  Liquid ferric chloride
is produced at  the  locations listed in a subsequent  section. The  1974 price  of liquid
ferric chloride  in bulk quantities is  $0.045  per Ib (as ferric chloride), F.O.B. point of
manufacture.
                                      10-18

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                            FIGURE 10-5


                 FREEZING POINT CURVE FOR  COMMERCIAL


                     FERRIC CHLORIDE SOLUTIONS


                   (ADAPTED FROF1 DOW CHEMICAL CO.)
UJ
tr
UJ
a.

UJ
                            i	1	1	1

                               WATER UTILITY GRADE
    -20
                           3O                 40


                    PERCENT BY WEIGHT  IN WATER
                              10-19

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8
100
 80

 60
 50

 40

 30


 20

 15


 10

  8

  6
  5

  4
                          FIGURE  10-6

         VISCOSITY  VS  COMPOSITION  OF FERRIC  CHLORIDE

              SOLUTIONS AT VARIOUS TEMPERATURES

               (COURTESY OF DOW  CHEMICAL CO.)
           I    I     I     I    I     I     I    I     I     I
          (Absolute Viscositjr)=(Kinematic Viscosity)(Density)
           Cent!poises = Cent!stokes x Gin
                                     cc
                    10
                          20
50
                         10-20

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Tank trucks and cars are normally unloaded pneumatically, and operating procedures must
be closely followed to avoid spills and accidents. The safety vent cap and assembly (painted
red) should be removed  prior to opening the unloading  connection to  depressurize the
tank  car or truck, prior  to unloading.

          10.2.1.2      General  Design Considerations

Ferric chloride solutions are corrosive to many common materials and cause stains which
are difficult to remove.  Areas  which are subject  to  staining should be protected with
resistant paint or rubber mats.

Normal precautions should be employed when  cleaning  ferric chloride handling equipment.
Workmen should wear rubber gloves, rubber apron,  and goggles or a  face shield. If ferric
chloride comes in contact with the  eyes or skin, flush  with copious quantities of running
water  and call a physician.  If ferric chloride is ingested, induce  vomiting  and  call  a
physician.

          10.2.1.3      Storage

Ferric chloride solution can be stored as shipped.   Storage tanks should have  a free vent
or vacuum relief  valve.  Tanks may be constructed of FRP, rubber lined steel, or plastic
lined  steel.  Resin impregnated carbon or graphite are  also suitable  materials  for storage
containers.

It may be necessary in most instances to house liquid ferric chloride  tanks in heated
areas  or provide  tank heaters or  insulation to  prevent crystallization.  Ferric chloride can
be stored for long periods of time without deterioration. The total storage capacity should
be  1-1/2 times the largest anticipated shipment, and should provide at least a 10-day to
2-week supply of the chemical at  the design  average  dose.

          10.2.1.4      Feeding  Equipment

Feeding equipment and systems described for liquid  alum generally apply to ferric chloride
except  for materials of construction, and  the use  of  glass tube rotameters.

It may not be desirable to dilute the  ferric chloride solution from its shipping concentration
to a weaker feed solution because of possible  hydrolysis.   Ferric chloride solutions may
be transferred from underground storage to day tanks with impervious graphite or rubber
lined  self-priming centrifugal pumps having teflon  rotary and stationary seals.  Because
                                     10-21

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of the tendency for liquid ferric chloride to stain or deposit, glass-tube rotameters should
not be used for metering this  solution.   Rotodip feeders and diaphragm metering pumps
are often used for ferric chloride,  and should be constructed of materials such as rubber
lined  steel and plastics.

          10.2.1.5      Piping and Accessories

Materials for piping and transporting ferric chloride should be rubber or Saran lined steel,
hard rubber, FRP, or plastics.   Varying  should consist of rubber or resin lined diaphragm
valves, Saran  lined valves  with teflon diaphragms, rubber sleeved pinch  type  valves, or
plastic ball valves.  Gasket material for  large openings such as manholes in storage tanks
should be soft rubber; all other  gaskets should be graphite-impregnated blue asbestos, teflon,
or vinyl.

          10.2.1.6      Pacing and  Control

System pacing and control requirements are similar to those discussed previously for liquid
alum.

          10.2.2        Ferrous Chloride  (Waste Pickle  Liquor)

          10.2.2.1      Properties and  Availability

Ferrous  chloride,  FeC^, as a  liquid  is available in the form of waste pickle liquor from
steel processing.   The liquor weighs  between 9.9 and 10.4 Ib/gal and contains 20 to 25%
ferrous chloride  or about 10% available  iron.  A 22%  solution of  ferrous chloride will
crystallize at  a temperature of -4F.  The  molecular weight of ferrous chloride  is 126.76.
Free acid in waste pickle  liquor can vary  from 1  to 10% and usually averages about 1.5
to  1.0%.  Ferrous  chloride  is slightly  less corrosive than  ferric  chloride.

Waste  pickle  liquor  is available in 4,000-gallon truckload  lots and  a variety of carload
lots.  In  most instances the availability of waste pickle liquor will depend on the proximity
to steel processing plants.  Dow Chemical Company produces a waste pickle liquor, having
a  ferrous chloride content of about 22% at a 1974 price of $0.045 per  Ib  of ferrous
chloride  in  bulk  car  or truckload quantities,  F.O.B.  Midland, Michigan.

          10.2.2.2      General Design Considerations

Since ferrous chloride or  waste pickle liquor may not be available on a continuous basis,
storage and feeding equipment should be suitable for handling ferric chloride.  Therefore,
the ferric chloride  section should be referred to for storage and  handling details.
                                      10-22

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         10.2.3         Ferric Sulfate

         10.2.3.1       Properties and Availability
Ferric sulfate, Fe2(SO4)3   X  H2O, is marketed as a dry, partially hydrated product with
seven water molecules.  Typical properties are presented in  Table  10-6 below (3):
                                   TABLE 10-6

                       PROPERTIES OF FERRIC  SULFATE


         Molecular Weight                                 526

         Bulk  Density, Ib/cu ft                           56-60

         Water Soluble Iron
         Expressed as Fe                                 21.5%

         Water Soluble Fe+3                             19.5%

         Insolubles Total                                  2.0%

         Free  Acid                                       2.5%

         Moisture @ 105C                               2.0%
Ferric sulfate is shipped in car and truckload lots of 50  Ib and  100 Ib moistureproof
paper bags and 200 Ib and 400 Ib fiber drums. Bulk carload shipments in box and closed
hopper cars  are available.  The major producer is Cities Service Company, with a plant
located at Copper Hill, Tennessee.

The 1973 price of bulk ferric sulfate (21.8% Fe) is about $39 per ton, F.O.B. Copper
Hill, Tennessee.  Bagging adds some $6 to  $11  per ton over the bulk rate.

General precautions should be observed when handling ferric sulfate, such as wearing goggles
and dust masks, and areas of the body that come in contact with the dust  or vapor
should be washed promptly.
                                    10-23

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          10.2.3.2       General Design Considerations

Aeration of ferric sulfate should be held to a minimum because of the hygroscopic nature
of the material, particularly in damp atmospheres.  Mixing of ferric sulfate and quicklime
in conveying and dust vent systems  should be avoided as caking and excessive heating
can result.  The presence of ferric sulfate and  lime in combination has been known to
destroy cloth bags in pneumatic unloading devices (4). Because ferric sulfate in the presence
of moisture will stain, precautions similar  to those discussed for ferric chloride  should
be observed.

          10.2.3.3       Storage

Ferric sulfate is usually stored in the dry state either in the shipping bags or in  bulk
in concrete or steel bins.  Bulk storage bins should be as tight as possible to avoid moisture
absorption,  but dust collector vents are  permissible and desirable.  Hopper walls  should
slope 36% or more.

Bins  may be  located  inside or outside and the material transferred by  bucket elevator,
screw or air conveyors.  Ferric sulfate stored in bins usually absorbs some moisture and
forms a thin protective  crust which retards further absorption until the  crust is broken.

          10.2.3.4       Feeding Equipment

Feed solutions  are  usually made up  at  a water to chemical ratio of 2:1 to 8:1 (on a
weight  basis) with the usual ratio being 4:1 with a 20-minute detention time. Care  must
be taken not  to dilute ferric sulfate solutions to less than 1% to  prevent hydrolysis and
deposition of ferric hydroxide. Ferric  sulfate is actively corrosive in solution, and dissolving
and transporting equipment should be fabricated of type 316 stainless steel, rubber, plastics,
ceramics or lead.

Dry feeding requirements  are similar  to  those for dry alum except that belt  type  feeders
are rarely used because of their open type of construction.  Closed construction, as found
in the volumetric and loss-in-weight type feeders, generally exposes a minimum of operating
components to the vapor,  and thereby minimizes maintenance. A water jet vapor remover
should  be provided at the dissolver  to  protect both the machinery and operator.

          10.2.3.5       Piping and Accessories

Piping  systems for ferric sulfate should be  FRP, plastics,  type  316 stainless  steel, rubber
or glass.

          10.2.3.6       Pacing and Control

System pacing  and control are the same as discussed for dry  alum.
                                     10-24

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          10.2.4         Ferrous Sulfate

          10.2.4.1       Properties and Availability

Ferrous sulfate or copperas is a byproduct of pickling  steel and is produced as granules,
crystals,  powder, and lumps.  The  most common commercial form of ferrous sulfate is
FeSO4    7H2O, with a molecular weight of 278, and containing 55 to 58% FeSO4 and
20  to 21% Fe.  The product  has  a bulk density of 62 to 66  lb/ft3.  When dissolved,
ferrous  sulfate is acidic.  The composition of ferrous sulfate may be quite variable and
should be established by  consulting the nearest manufacturers.

Bulk, drum (400-lb) and  bag (50 and  100  Ib) shipments  are  available  from producers
at locations listed in a subsequent section.  The 1974 bulk price of ferrous sulfate  in
bulk  carload and truckload quantities is  about  $28 per ton (21% Fe), with an additional
$8  per  ton for bagging.

Ferrous sulfate is also available in a wet  state in bulk form  from some plants.  This form
is likely  to be difficult  to handle and the manufacturer should be consulted for specific
information and instructions.

Dry ferrous sulfate cakes at storage  temperatures  above 68F, is efflorescent in dry air,
and  oxidizes  and hydrates further  in moist  air.

General precautions  similar to those for  ferric sulfate with  respect to dust and handling
acidic solutions, should be observed  when working with  ferrous sulfate.  Mixing quicklime
and  ferrous sulfate  produces high temperatures and  the possibility  of fire.

          10.2.4.2       General Design  Considerations

The granular  form of ferrous sulfate has the best feeding characteristics  and gravimetric
or volumetric feeding equipment may be used.

The optimum chemical  to water ratio for continuous dissolving  is 0.5  Ib/gal or 6% with
a detention time of 5 minutes in the dissolvers.  Mechanical agitation should be provided
in the dissolver to assure  complete  solution.  Lead,  rubber, iron, plastics, and  type 304
stainless steel  can be used as construction  materials for handling solutions of ferrous sulfate.

Storage,  feeding and  transporting systems probably should be suitable for handling ferric
sulfate as  an  alternative to  ferrous sulfate.

          10.2.5         Estimated Initial Costs  of Adding  Liquid Ferric Chloride Feed
                        Systems to  Existing Wastewater Treatment  Plants
                                     10-25

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Costs of chemical storage and feeding equipment for 1, 10, and  100 mgd plants have
been estimated based on  the  use  of liquid ferric chloride  (basis:  35% ferric chloride)
for phosphorus precipitation.   A mole  ratio of Fe:P of 2.0:1 was assumed  to treat an
influent phosphorus concentration  of 10  mg/1 as P. This corresponds to a ferric chloride
dose of  104 mg/1 (36 mg/1 as Fe3+).

Chemical feed equipment was  sized for  a peak feed rate of twice that calculated from
the mole ratio.  Storage was provided for at least 15 days at the average feed rate. This
storage  time is arbitrary and will vary at each installation depending on the  distance to
and  the  reliability of the souce of chemical supply.  Piping and buildings to house the
feeding  equipment are not included.  At many locations the chemical feeding  equipment
can  be  installed in existing  buildings. All estimated costs include  an allowance for the
contractor's installation, overhead, and profit plus an allowance of 20% of the construction
cost for engineering and contingencies. The estimated costs for each size plant are shown
in Table 10-7.  These figures  correspond to  an EPA Construction Cost Index of 185:
                                    TABLE  10-7

            COSTS OF LIQUID FERRIC CHLORIDE FEED FACILITIES


            Plant  Size                        Estimated  1973 Cost
              (mgd)                                   ($)

                  1                                    15,000
                 10                                    50,000
                100                                   500,000
For the 1 mgd plant, the feeding equipment for liquid ferric chloride includes two 18 gph,
hydraulic diaphragm pumps (one operating and one standby) with the necessary accessories
and equipment to pace the feed  rate to the plant flow.  Liquid ferric chloride is stored
in  two 3,000-gallon FRP tanks with  accessories.  The 6,000-gallon total capacity allows
use of liquid ferric chloride in 4,000-gallon  tank truck  quantities.

For the 10 mgd plant, liquid ferric chloride is fed by three  90 gph rotodip-type feeders
(two  operating  and one  standby) with  the necessary accessories and  control panel for
proportioning chemical feed  to flow.

For the 100 mgd plant, seven 305 gph rotodip-type feeders (six operating and one standby)
are provided along  with  the necessary control equipment.  Storage is provided in eight
50,000-gallon rubber-lined concrete tanks located underground.  The underground storage
necessitates transfer pumps and day tanks for  the rotodip  feeders, but eliminates the need
                                     10-26

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for heating  the  tanks.  Three 500-gallon  FRP day tanks are included along with four
ferric chloride transfer pumps sized  for 35 gpm each at 50 ft  of head.

With regard  to the cost of the feed system  for the 100 mgd plant being out of proportion
to that for  a  10 mgd plant, the reader is  referred to Section 10.1.5  of this chapter  for
the discussion of underground  concrete storage vessels as opposed to FRP tanks.

10.3      Lime

          10.3.1        Quicklime

          10.3.1.1      Properties and Availability

Quicklime, CaO, has a density range of approximately 55 to 75  lb/ft3, and a molecular
weight  of 56.08.  A  slurry for feeding,  called  milk of lime,  can be prepared with up
to 45% solids.   Lime  is only slightly soluble, and both lime dust and slurries are caustic
in nature.  A saturated solution of lime  has a  pH of about  12.4.

Lime can be  purchased in bulk in both  car  and truckload lots.  It is also shipped in
80 and 100 Ib  multiwall  "moistureproof" paper  bags.  Lime is produced at the locations
listed in  a  subsequent section  (5).

 1974 prices for bulk pebble quicklime range from $18 per  ton to $22 per ton with the
higher prices generally in  the far west, and higher  than  average  in the north.  Bagging
adds  approximately $5 per ton to the cost.

The CaO content of  commercially  available  quicklime can vary  quite widely over  an
approximately  range of 70 to  96%.  Content below 88% is generally considered below
standard in the  municipal  use field (6).  Purchase contracts are often based on 90% CaO
 content with provisions for payment of a bonus for each  1% over and a penalty for each
 1% under the standard. A CaO content less than  75% probably should be rejected because
 of excessive grit  and difficulties in  slaking.

Workmen should wear protective  clothing and goggles to protect the skin and eyes, as
 lime  dust and  hot  slurry  can  cause severe burns.   Areas contacted by  lime should be
 washed immediately.   Lime  should  not  be mixed with chemicals which have  water of
 hydration.  The lime will be slaked by the water of hydration causing excessive temperature
rise and possibly explosive  conditions. Conveyors and bins used for more than one chemical
 should  be thoroughly  cleaned  before switching  chemicals.

          10.3.1.2      General Design Considerations

Pebble  quicklime, all passing a 3/4-in screen  and not more than 5% passing a No.  100
 screen, is normally  specified because of easier handling and less  dust.  Hopper agitation
                                     10-27

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is generally not required with the pebble form.  Published slaker capacity ratings require
"soft or normally burned" limes which provide fast slaking and temperature rise, but poorer
grades  of limes may  also be  satisfactorily  slaked by selection of the appropriate  slaker
retention  time  and capacity.

          10.3.1.3      Storage

Storage of bagged  lime should be in a dry place, and preferably elevated on pallets to
avoid absorption  of moisture.  System capacities often make the use of bagged quicklime
impractical.   Maximum storage period is about 60 days.

Bulk lime is stored  in air-tight concrete or steel bins having a 60 slope on the bin outlet.
Bulk lime can be  conveyed  by conventional bucket elevators and screw, belt, apron,
drag-chain, and bulk conveyors of mild steel  construction.  Pneumatic conveyors subject
the  lime  to air-slaking and  particle sizes may be reduced  by attrition.  Dust collectors
should be provided on manually  and pneumatically filled  bins.

          10.3.1.4      Feeding  Equipment

A typical lime storage and feed system  is illustrated in  Figure  10-7.  Quicklime feeders
are usually limited to the belt or loss-in-weight gravimetric types  because of the wide
variation of the bulk density.  Feed  equipment should have an adjustable feed range of
at least 20:1 to match the operating range of the associated slaker.  The feeders should
have an  over-under feed rate  alarm to immediately  warn of operation  beyond set limits
of control.   The feeder drive should be instrumented to be interrupted in the event of
excessive  temperature in  the  slaker compartment.

Lime slakers for  wastewater treatment should be  of the continuous type, and the major
components should include  one or more slaking compartments, a dilution compartment,
a grit separation  compartment and a continuous grit remover.  Commercial designs vary
in regard to the  combination of water to lime,  slaking temperature, and  slaking time,
in obtaining  the  "milk of lime"  suspensions.

The  "paste"  type slaker admits water as required to maintain a desired mixing viscosity.
This viscosity therefore sets the operating retention time of the slaker.  The paste slaker
usually operates with a low water to lime ratio (approximately 2:1 by weight), elevated
temperature, and five minute slaking time at maximum capacity.

The  "detention"  type slaker admits water to maintain a desired ratio with the lime, and
therefore the lime  feed rate  sets the  retention time of the slaker.  The detention slaker
operates with a wide range of water to lime ratios (2.5:1 and 6:1), moderate temperature,
and  a  10-minute  slaking time at maximum capacity.  A water to lime ratio of from 3.5:1
to 4:1  is most often used.   The operating temperature in  lime slakers is a function of
the  water to lime  ratio, lime quality, heat transfer,  and  water temperature.  Lime slaking
                                     10-28

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                                   FIGURE 10-7

                          TYPICAL LIME  FEED  SYSTEM
NOTE:  VAPOR REMOVER
NOT SHOWN FOR CLARITY
                                        -DUST C01LECTOR

                                                FILL PIPE (PNEUMATIC)
                    BULK STORAGE
                        BIN
                                                BIN GATE
                                                FLEX IBLE
                                                CONNECTION
                         SCALE
                                        FEEDER
   SOLENOID
    VALVE,
         OR SAMPLE CHUTE

ROTAMETERS
FLOW RECORDER
WITH PACING
TRANSMITTER,
       RO TOD IP-TYPE
          FEEDER
                                                         pH RECORDER
                                                         CONTROLLER
     GRAVITY  FEED

      RECIRCULATION
                                                                           BACK
                                                                        PRESSURE
                                                                          VALVE
                                 10-29

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evolves heat in hydrating the CaO to Ca(OH)2 and, therefore, vapor removers are required
for feeder  protection.

         10.3.1.5      Piping and  Accessories

Lime slurry should be transported by gravity in open channels wherever possible. Piping
channels and accessories may  be  rubber, iron, steel, concrete, and plastics.  Glass tubing,
such  as that in rotameters, will  cloud rapidly and therefore should not be used.  Any
abrupt  directional  changes  in piping should  include plugged  tees or crosses to allow
rodding-out of deposits.  Long sweep elbows should be provided to allow  the  piping to
be  cleaned  by the use of a  cleaning "pig".   Daily cleaning is desirable.

Milk  of lime  transfer pumps  should be of  the open impeller  centrifugal  type.  Pumps
having an iron body  and impeller with bronze trim are suitable  for this purpose. Rubber
lined pumps with rubber covered impellers are also frequently  used.  Make-up tanks are
usually  provided ahead of  centrifugal  pumps to  ensure  a flooded  suction at  all times.
"Plating-out" of lime is minimized by the use of soft water in the make-up  tank. Turbine
pumps  and eductors should be avoided in  transferring milk of lime  because  of scaling
problems.

          10.3.1.6       Pacing and Control

Lime slaker water proportioning  is integrally  controlled  or paced  from  the feeder.
Therefore, the feeder-slaker system will follow pacing controls applied to the feeder only.
As discussed previously, gravimetric  feeders are  adaptable  to receive most  standard
instrumentation pacing signals. Systems can  be instrumented to allow remote pacing with
telemetering of temperature  and feed rate  to a  central panel for  control purposes.

The lime feeding system may  be controlled by an  instrumentation system integrating both
plant flow and pH of the wastewater after lime addition. However, it should be recognized
that pH probes require daily maintenance in  this application to monitor the  pH accurately.
Deposits tend to build up on the probe and necessitate  frequent maintenance.  The low
pH lime treatment systems (pH  9.5 to 10.0) can  be more readily adapted to this method
of control than  high  lime treatment systems (pH 11.0 or greater) because less maintenance
of the  pH equipment is required.  In a closed loop pH-flow control system, milk of lime
is prepared on a batch  basis and transferred to a holding tank with variable  output feeders
set by  the  flow  and pH  meters to proportion the feed rate.  Figure 10-7 illustrates such
a control  system.

          10.3.2        Hydrated  Lime
                                      10-30

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          10.3.2.1       Properties  and Availability

Hydrated  lime, Ca(OH)2, has a working  density of 20 to 50  Ib/ft3,  tends to flood the
feeder, and will arch in storage bins if  packed.  The molecular weight is 74.08.  The
dust and slurry of hydrated lime are caustic in nature.  The 1973 cost of bulk hydrated
lime varies from  $20 to  $22 per  ton.   Bagged lime is  available but increases  the  cost
about $5  per  ton.  The availability of hydrated lime may be  determined  by contracting
manufacturers listed in a subsequent section. The pH of a saturated hydrated lime solution
is  the  same as that given for quicklime.

          10.3.2.2      General Design  Considerations

Hydrated  lime is slaked lime  and needs  only enough water added to  form milk of lime.
Wetting or dissolving chambers  are usually  designed to provide 5 minutes detention with
a ratio of 0.5 Ib per gallon of  water or  6% slurry at the maximum feed rate.  Hydrated
lime is  usually used where maximum feed rates do not  exceed 250  Ib/hour.  Hydrated
lime and  milk of lime will irritate the   eyes, nose, and  respiratory system and will dry
the skin.   Affected areas should be washed with water.

          10.3.2.3      Storage

Information given  for quicklime also applies to hydrated lime except that bin  agitation
must be provided.  Bulk  bin  outlets should be provided with non-flooding rotary feeders
and with hopper  slopes of 65%.

          10.3.2.4      Feeding Equipment

Volumetric or gravimetric feeders may be used, but volumetric feeders are usually selected
only for installations where comparatively low feed rates are required. Dilution  does not
appear  to be  important;  therefore, control of the amount of water used in the feeding
operation is not considered necessary. Inexpensive hydraulic jet agitation may be furnished
in the wetting chamber of the  feeder as an alternative to mechanical agitation.  The jets
should  be sized for the  available  water  supply pressure to obtain proper mixing.

          10.3.2.5       Piping  and Accessories

Piping and accessories as described for quicklime are  also appropriate for hydrated lime.

          10.3.2.6       Pacing  and  Control

Controls  as listed  for dry alum apply to hydrated lime. Hydraulic  jets should operate
continuously  and  only shut off when the feeder is taken out of service.  Control of the
feed rate  with pH  as well as  pacing with the plant  flow  may be used with hydrated lime
as  well as quicklime.
                                     10-31

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         10.3.3        Estimated Initial Costs of Adding Lime Feed Facilities to Existing
                       Wastewater Treatment Plants

Cost estimates of chemical storage and feeding equipment  have been prepared based on
the use of  hydrated lime for a 1 mgd plant, and pebble quicklime for 10 and 100 mgd
plants.  Lime feed rates are based on a dosage of 150 mg/1 and allow for peak rates
of twice this capacity.   Storage  was provided for at  least 15  days at the average rate
although it may be desirable  to provide 30 days for  dry  chemicals.  This storage time
is arbitrary and will vary at each installation depending on the distance to and the reliability
of the source of chemical supply. Piping and  buildings  to house  the feeding equipment
are not included in the estimates. The estimated costs of steel bins with dust collector
vents and  filling accessories are included for all  three plants.  The  chemical  feeding
equipment  can  be  installed in  existing buildings at  many locations.  In all estimates, the
costs include an allowance  for the contractor's installation, overhead, and profit, and an
allowance of 20% of the construction  cost of engineering and contingencies. The estimated
costs for each size  plant are shown in Table 10-8.  These  figures  correspond to an EPA
Construction  Cost Index of 185.
                                    TABLE  10-8

                        COST OF LIME FEED  FACILITIES
                                        Additional Cost  of
                       Estimated          Flow and pH
       Plant Size        Base Bid             Controls
         (mgd)            ($)                  ($)

             1            19,000                5,000            24,000
            10            95,000               15,000           110,000
           100           365,000              100,000           475,000
Equipment for the 1.0 mgd plant includes two volumetric feeder systems with manually
loaded  bins, dissolving  chambers  and accessories.  Equipment for the  10.0  mgd  plant
includes two gravimetric feeder-slaker systems.   Steel bins are  estimated  to  hold  1-1/2
truckloads of quicklime  each,  and it is assumed that the truck will be equipped with
a  pneumatic blower.  Equipment for  the  100.00 mgd  plant includes four  gravimetric
feeder-slaker systems. The  base estimate includes  the bin gate and feeder-slaker accessories
and  controls.
                                     10-32

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Costs for the flow  and pH  controls include holding tanks with mixers, and slurry feeders
with controls.   Flow  and pH metering instruments are not included.
10.4     Compounds  for pH Adjustment

          10.4.1         Soda Ash

          10.4.1.1       Properties and Availability
Soda ash, Na2CO^, is  available in two  forms.  Light soda ash has a bulk density range
of 35 to 50  lb/ft^ and  a  working density of 41 lb/ft3.  Dense soda ash has a density
range of 60 to 76 lb/ft3 and a working density of 63 lb/ft3.  The pH of a 1% solution
of soda  ash  is 1 1.2.

The  molecular weight  of soda  ash is 106.  Commercial purity ranges from 98 to 99%.
The  viscosities of sodium carbonate solutions are given in Figure 10-8.  Soda ash by itself
is not particularly corrosive, but in the presence of lime and water, caustic soda is formed
which is quite corrosive.

Soda ash is available in bulk  by truck,  box car and hopper car, and in 100 Ib bags from
locations listed in a subsequent section.  The  1974 price  for soda ash ranges from  $50
to $60 per ton, F.O.B. the point of manufacture; however, prices vary substantially between
manufacturers and should be obtained from  the closest manufacturers or local distributors.

          10.4.1.2      General Design  Considerations

Dense soda ash  is generally used in municipal applications because of superior handling
characteristics.  It has  little dust, good  flow characteristics, and will not arch in the bin
or flood the  feeder.  It is relatively hard to dissolve and  ample dissolver capacity must
be  provided.  Normal  practice calls for 0.5 Ib of dense  soda ash  per gallon of water or
a 6% solution retained for 20 minutes in  the dissolver.

The dust and solution are irritating to the eyes, nose, lungs and skin and  therefore general
precautions should be  observed and the affected areas should  be  washed promptly with
water.

          10.4.1.3      Storage

Soda ash is  usually stored in steel bins and where pneumatic filling equipment is used,
bins  should be provided  with dust collectors.  Bulk and bagged soda  ash tend to absorb
atmospheric   carbon dioxide  and  water forming  the  less  active  sodium bicarbonate
(NaHCOj).   Material recommended for unloading facilities  is steel.
                                     10-33

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eo
UJ
CO
CO
o
o
en
                         FIGURE  10-8


               VISCOSITY OF SODA ASH  SOLUTIONS


        (COURTESY PPG INDUSTRIES INC.,  CHEMICAL DIV.)
   6.0 
    5.0 -
                         10-34

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          10.4.1.4      Feeding  Equipment

Feed  equipment  as  described for dry alum is suitable for  soda ash.  Dissolving of soda
ash may be hastened by the use of warm dissolving water.  Mechanical or hydraulic jet
mixing  should  be provided in the dissolver.

          10.4.1.5      Piping and  Accessories

Materials  of  construction for piping and accessories should be iron, steel, rubber, and
plastics.

          10.4.1.6      Pacing and  Control

Controls as discussed for dry alum apply also to soda  ash equipment.

          10.4.2        Liquid Caustic Soda

Anhydrous caustic soda (NaOH) is available but its use is generally not considered practical
in water and wastewater treatment applications.  Consequently, only  liquid caustic soda
is discussed below.

          10.4.2.1      Properties and Availability

Liquid caustic soda  is shipped at two concentrations, 50% and  73% NaOH.  The densities
of the solutions  as  shipped are 12.76 Ib/gal  for the 50% solution and  14.18 Ib/ga  for
the 73%  solution.   These solutions contain  6.38  Ib/gal  NaOH  and  10.34 Ib/gal NaOH,
respectively.   The crystallization  temperature is 53F for  the 50% solution and  165F
for the  73% solution. The molecular weight of NaOH is 40. Viscosities of various caustic
soda  solutions  are presented  in Figure 10-9.  The pH of a 1% solution of caustic soda
is 12.9.

Truckload lots of 1,000  to  4,000 gallons are available  in the  50% concentration only.
Both  shipping concentrations can be obtained  in 8,000, 10,000, and 16,000 gallon carload
lots.  Tank cars  can be unloaded through the dome eduction pipe using air pressure or
through the  bottom valve by gravity or by  using  air pressure or a  pump.  Trucks are
usually  unloaded by gravity or with air pressure  or a truck  mounted pump.

Major producers of caustic soda and their  respective  plant   locations  are  listed in a
subsequent section.  The  current price for liquid caustic  soda  ranges  from about $75 to
$80 per ton (NaOH), F.O.B. the point of manufacture.
                                     10-35

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co
o
o
   200
   100

    80

    60


    40
    20





    10

     8

     6


     4
     1

   0.8

   0.6


   0-4
   0.2
                          FIGURE 10-9


             VISCOSITY OF CAUSTIC SODA  SOLUTIONS


              (COURTESY OF HOOKER CHEMICAL CO.)
                                              I    I
          I	I
I
I
I
I
I
I
I
I
     60   70   80  90  100  110 120  130 140 150  160 170  180 190 200


                          TEMPERATURE,  F
                        10-36

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          10.4.2.2      General Design Considerations

Liquid caustic soda is  received in bulk shipments, transferred to storage  and diluted as
necessary for feeding to  the  points  of application.   Caustic soda is  poisonous and  is
dangerous to handle.  U.S. Department of Transportation Regulations for "White Label"
materials must be observed.  However, if handled properly caustic soda poses no particular
industrial hazard.  To avoid accidental spills, all pumps, valves, and lines should be checked
regularly for leaks.  Workmen should be thoroughly instructed in the precautions related
to the handling of caustic soda.  The  eyes should be protected by goggles at all times
when exposure to mist or splashing is possible. Other parts of the body should be protected
as necessary to prevent alkali  burns.   Areas exposed to caustic soda should  be  washed
with copious  amounts of water for  15 minutes to 2  hours.  A physician should be called
when exposure is severe.   Caustic soda  taken internally should be  diluted with water or
milk  and  then neutralized with  dilute vinegar or  fruit  juice.   Vomiting  may occur
spontaneously but should not  be induced except on  the  advice of a  physician.

          10.4.2.3       Storage

Liquid caustic soda may  be stored  at the 50% concentration.  However, at this solution
strength, it crystallizes at  53F.  Therefore,  storage tanks must  be  located  indoors or
provided with heating and suitable  insulation if outdoors.   Because of its relatively high
crystallization temperature, liquid caustic soda is often diluted to a concentration of about
20% NaOH for storage.   A 20% solution of NaOH  has a  crystallization temperature of
about -20F.  Recommendations for  dilution  of both  73% and 50% solutions should be
obtained from the  manufacturer, because special considerations are necessary.

Storage  tanks for liquid caustic soda should be  provided with  an air vent for gravity flow.
The storage capacity should be equal to  1-1/2 times the largest expected  delivery, with
an allowance for dilution water, if used, or 2  weeks supply  at the anticipated feed rate,
whichever is  greater.   Tanks for storing  50%  solution at  a  temperature between 75F
and 140F may be constructed of  mild steel.   Storage  temperatures above  140F require
more elaborate  materials selection and  are not recommended.  Caustic soda will tend  to
pick  up iron when stored in steel vessels for extended  periods. Subject to temperature
and solution strength limitations, rubber, 316 stainless steel, nickel, nickel alloys, or plastics
may  be  used when iron  contamination must  be avoided.

          10.4.2.4       Feeding  Equipment

Further  dilution of liquid caustic soda below  the storage  strength may be desirable for
feeding  by volumetric feeders.   Feeding  systems as described for liquid alum generally
apply to caustic soda with appropriate  selection  of  materials of construction.  A typical
system schematic is shown in Figure  10-10.  Feeders will  usually  include  materials such
as  ductile iron, stainless steels, rubber, and plastics.
                                      10-37

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                      FIGURE  10-10

           TYPICAL  CAUSTIC SODA FEED  SYSTEM
                                -TRUCK  FILL LINE
DILUTION
 WATER
                     SODIUM HYDROXIDE
                       STORAGE TANK
                                              VENT,  OVERFLOW
                                              AND DRAIN
VENT,  OVERFLOW
AND DRAIN

MIXER
                                         SAMPLE TAP
                                     ODIUM HYDROXIDE
                                         FEEDER
                         POINT OF
                        APPLICATION
                      10-38

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         10.4.2.5
Piping  and Accessories
Transfer  lines from  the  shipping unit to the storage tank  should  be spiral-wire-bound
neoprene or rubber hose, solid steel pipe with swivel joints, or steel hose.  Because caustic
soda attacks glass, use of glass materials should be avoided. Other miscellaneous materials
for use with liquid  caustic soda feeding and handling equipment are listed below (7) in
Table  10-9:
                                   TABLE  10-9
             MATERIALS  SUITABLE FOR  CAUSTIC  SODA  SERVICE
     Components

     Rigid  Pipe
     Flexible Connections
     Diluting Tees
     Fittings
     Permanent  Joints
     Unions
     Valves  - Non-leaking (Plug)
         Body
         Plug
     Pumps  (Centrifugal)
         Body
         Impeller
         Packing
     Storage Tanks
                       Recommended Materials
                       for Use With  50% NaOH
                            Up to  140F

                       Standard Weight  Black  Iron
                       Rigid Pipe with Ells or Swing
                       Joints, Stainless  Steel or
                       Rubber Hose
                       Type 304 Stainless Steel
                       Steel
                       Welded or Screwed Fittings
                       Screwed Steel

                       Steel
                       Type 304 Stainless Steel

                       Steel
                       Ni-Resist
                       Blue Asbestos
                       Steel
          10.4.2.6      Pacing and Control

Controls as listed for  liquid alum also apply to liquid  caustic  soda equipment.
                                     10-39

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10.5     Carbon  Dioxide

         10.5.1         Properties and Availability

Carbon dioxide, CC^, is available for use in wastewater treatment plants in gas and liquid
form. The molecular weight of carbon dioxide is 44. Dry carbon dioxide is not chemically
active at normal temperatures and is a non-toxic safe chemical; however, the gas displaces
oxygen  and  adequate ventilation of closed areas should be  provided.   Solutions  of
carbon dioxide in water  are very reactive  chemically and form carbonic acid. Saturated
solutions of carbon dioxide have a pH of 4.0 at 68F.

The  gas form may be  produced on the treatment plant site by scrubbing and compressing
the combustion product  of lime recalcining furnaces,  sludge furnaces, or generators used
principally  for the production of carbon  dioxide gas only.  These  generators are  usually
fired with  combustible gases, fuel oil, or coke and have  carbon dioxide yields as shown
in Table 10-10 (8).
                                   TABLE 10-10

                CARBON DIOXIDE YIELDS OF COMMON FUELS
     Fuel                       Quantity                          Yield
                                                                     Ib

     Natural  Gas                1,000  ft3                          115
     Coke                       1  Ib                                 3
     Kerosene                   1  gal                               20
     Fuel Oil (No. 2)           1  gal                               23
     Propane                    1,000  ft3                          352
     Butane                     1,000  ft3                          454
The gas forms, as generated at the plant site, usually have  a  carbon  dioxide content of
between 6% and 18% depending on the source  and efficiency of the producing system.

The liquid form  is available from commercial suppliers in 20 to  50  Ib cylinders, 10 to
20 ton trucks and  30 to 50 ton rail cars.  The commercial liquid form has a minimum
carbon dioxide content  of  99.5%.
                                     10-40

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1974 prices range  from S33-S36 per ton for  3,000 tons per year  and over, to $71-$74
per ton for a quantity of 150 tons per year. These  prices include an allowance for freight
within a 100  mile  radius of the point of manufacture.  Another $6 or $7 per ton may
be  added for each additional 100 miles to the  point of destination.  Major producers
of  commercial carbon  dioxide  are listed in a subsequent section.

          10.5.2         General Design Considerations

Recovery of carbon dioxide from recalcining furnaces or incinerators is the least expensive
source, but maintenance of stack gas systems is likely to be extensive because of the
corrosive nature of the wet gas and the presence  of particulate matter.  Scrubber systems
are required to clean the stack gas and especially designed gas compressors are necessary
to  provide the process injection  pressure.

Pressure  generators and submerged  burners require  less maintenance because  the  system
pressure is established by compressors or blowers handling dry air or gas.  On-site generating
units have a limited range of carbon dioxide production  as compared  with the liquid storage
and feed  system,  and  therefore may require  multiple units.

The liquid carbon dioxide storage and feed system  generally includes  a temperature-pressure
controlled, bulk storage tank, an evaporation  unit, and  a gas feeder  to meter the gas.
Solution feeders, similar in construction to chlorinators, may also be used to feed carbon
dioxide.

          10.5.3         Storage

This section  applies  only  to  use of commercial  liquid carbon dioxide.   Liquid  system
capacities encountered in wastewater treatment usually  usually require on-site bulk storage
units.  Standard pre-packaged units are available,  ranging in  size  from  3/8  to 50 tons
capacity, and  are furnished with temperature-pressure controls to maintain approximately
300 lb/in2 at 0F  conditions.  The typical package unit  con tains refrigeration, vaporization,
safety  and control equipment.   The units are well insulated and protected for outdoor
location. The gas  from the evaporation  unit usually passes through  two stages of pressure
reduction before entering  the gas feeder to  prevent the formation of dry ice.

          10.5.4         Feeding Equipment

Feeding  systems for the  stack gas  source of carbon  dioxide consist  of simple  valving
arrangements,  for  admitting varying quantities of make-up air  to the suction  side of the
constant volume compressors, or for venting excess gas on the compressor discharge. A
typical system is  described by Gulp  and Gulp (9).
                                     10-41

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Pressure generators and submerged burners are regulated by valving arrangements on the
fuel and air  supply.   Generation of carbon  dioxide  by combustion is usually  difficult
to control, requires frequent operator attention  and  demands considerable maintenance
over the life of  the  equipment, when compared  to  liquid CC>2 systems.

Commercial liquid carbon dioxide is  becoming more generally used because of its high
purity, the simplicity and range  of feeding equipment, ease of control, and smaller, less
expensive piping  systems.  After vaporization, carbon dioxide with suitable metering and
pressure  reduction may  be fed  directly  to the point of application as a gas.  Metering
of direct  fed pressurized gas is  difficult due to  high  adiabatic expansion characteristics
of the gas.  Also, direct feed requires extremely  fine bubbles to insure the gas goes into
solution; this, in  turn, can lead to scaling problems. However, vacuum operated,  solution
type gas feeders are preferred.  Such feeders generally include safety devices and operating
controls in a compact panel housing, with materials of construction suitable for carbon
dioxide service.   Absorption  of carbon dioxide in the injector water supply approaches
100% when  a  ratio of  1.0 Ib of gas to  60 gal  of water is  maintained.

          10.5.5         Piping and Accessories

Mild steel piping and accessories  are suitable for use with cool, dry, carbon dioxide.  Hot,
moist gases, however, require the use of type 316 stainless steel or plastic materials. Plastics
or FRP  pipe are generally used for solution piping  and diffusers.  Diffusers should be
submerged at least 8 ft,  and  preferably deeper, to assure complete absorption  of the gas.

          10.5.6         Pacing and Control

Standard instrument signals and control components can be used to pace or control carbon
dioxide feed systems.

Using stack gas as the source of carbon dioxide, the feed rate can be controlled by proper
selection and operation  of compressors, by  manual  control of vent or  bleed valves, or
by automatic  control of such valves by  a pH meter-controller system.

In commercial carbon dioxide feed systems,  solution feeders may  function as controllers
and can be  paced by instrument  signals from pH monitors  and  plant  flow  meters.

In  feeding commercial carbon dioxide  directly to the point of application as  a gas, a
differential pressure transmitter and a control valve may function as the primary  elements
of a control system. Standard instrument  signals may be used  to pace or control the
rate of carbon dioxide  feed.

Carbon  dioxide  generators are  difficult  to  pace  or  control  other than by  manual or
automatic  operation  of  vent or bleed valves that waste a portion of the produced gas
according to the plant  requirements.
                                      10-42

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 10.6      Polymers

          10.6.1         Dry Polymers

          10.6.1.1       Properties and  Availability

Types of polymers vary widely in characteristics.  Manufacturers should be consulted for
properties, availability, and cost of the polymer being considered. References are available
that indicate the types and characteristics of polymers available (10, 11).  Bulk shipments
are generally  not desirable.  Polymers are  available in a variety of container or package
sizes.

          10.6.1.2       General Design Considerations

Dry polymer  and water must  be  blended and mixed to obtain a  recommended solution
for efficient  action.   Solution  concentrations vary from  fractions of  a percent up.
Preparation of the stock solution involves wetting of the dry material and usually an aging
period prior to application.    Solutions can be  very viscous, and  close  attention should
be paid to piping size and length and pump selections. Metered solution  is usually diluted
just prior to injection to the  process to obtain better dispersion at the point of application.

          10.6.1.3       Storage

General practice for storage of bagged dry chemicals should be observed.  The bags should
be  stored  in  a  dry, cool, low humidity area and  used in proper rotation, i.e., first in,
first out.

Solutions are  generally stored in type  316 stainless steel, FRP,  or plastic lined tanks.

          10.6.1.4       Feeding Equipment

Two types of  systems are frequently combined to feed polymers. The solution preparation
system  includes a manual or automatic blending system with  the  polymer dispensed by
hand or by a  dry feeder to  a  wetting jet and then to a mixing-aging tank at a controlled
ratio.  The aged polymer is transported to a holding tank where metering pumps or rotodip
feeders dispense  the polymer  to  the  process.   A schematic  of such a  system is shown
by Figure  10-11.  It is generally advisable to keep the holding or storage  time of polymer
solutions  to a minimum, 1  to 3 days  or  less,  to prevent deterioration of the product.

          10.6.1.5       Piping and Accessories

Selection  must be made after  determination of the polymer; however, type 316 stainless
steel or plastics are generally  used.
                                      10-43

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                      FIGURE 10-11

            MANUAL DRY POLYMER FEED SYSTEM
WATER SUPPLY
                                            DRY
                                            FEEDER
                                           DISPERSER
                                           MIXER
                                           DISSOLVING-AGING
                                                 TANK
                                           HOLDING TANK
                                           SOLUTION FEEDER
                               POINT OF
                              APPLICATION
                       10-44

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          10.6.1.6      Pacing and Control

Controls as listed for liquid alum apply to the control of liquid  dispersing feeders.

The solution preparation system  may  be  an automatic batching system, as shown by the
schematic on Figure  10-12, that  fills the holding tank with aged  polymer as required by
level probes.  Such a system is usually provided only at large plants.  Unitized solution
preparation units  are available, but have a  limited capacity.

          10.6.2        Liquid Polymers

          10.6.2.1      Properties and Availability

As  with  dry polymers,  there is a wide variety of products, and manufacturers should be
consulted for specific information.

          10.6.2.2      General  Design Considerations

Liquid systems differ from the dry systems only hi the equipment to blend the polymer
with water to prepare the solution.  Liquid solution preparation is usually a hand-batching
operation with manual filling  of a mixing-aging tank with water and  polymer.

          10.6.2.3      Feeding  Equipment

Liquid polymers need no aging and simple  dilution is the only requirement  for feeding.
The dosage of liquid polymers may be accurately controlled by metering pumps or rotodip
feeders.

The balance of the process is generally  the same as described for dry polymers.

          10.6.3        Estimated Initial Costs of Adding Polymer Feed  Facilities to
                       Existing  Wastewater Treatment Plants

Cost estimates of solution preparation and  feeder  equipment have been prepared, based
on  the  use of dry polymer, for  1, 10, and 100 mgd plants.  Chemical feed equipment
was sized to have a  capacity  sufficient to  prepare and feed  a 0.25% stock solution at
a dosage of 1 mg/1.  Piping and  buildings to house the feeding equipment and store the
bags are not included.  At many locations, the chemical feeding equipment can be installed
in existing  buildings.   All estimated  costs include  an  allowance  for  the  contractor's
installation, overhead, and  profit  plus an  allowance of 20%  of the construction cost for
engineering  and contingencies.   The estimated  costs for each size  plant are shown in
Table 10-11.  These  figures correspond to  an  EPA Construction Cost  Index of 185:
                                     10-45

-------
                                  FIGURE  10-12

                      AUTOMATIC DRY  POLYMER FEED  SYSTEM
       HOT
       MATER
             SOLENOID  /SCALE
            / VALVE
DISPERSES
NOTE:  CONTROL t INSTRUMENTATION
      WIRIN8 IS NOT SHOW
  POINT OF APPLICATION
SOLUTI ON
FEEDERS.^
^"~-



\
^i^
n

HOLDING TANK
1


                                                    TRANSFER PUMP
                                                         LEVEL PROBE
                                  10-46

-------
                                   TABLE  10-11

                     COST OF POLYMER  FEED FACILITIES


              Plant Size                       Estimated Cost
                 (mgd)                           ($)

                     1                                7,000
                   10                                31,000
                  100                             225,000


The  system for  the  1 mgd plant was based  on the polymer being manually fed to the
mixing tank, with mixing and solution feed equipment arranged for manual control.  Two
independent systems of tanks and feeders are included.  The system for the 10  mgd plant
includes two volumetric dry feeders  discharging  to two mixing  tanks, arranged for batch
control.  The  mixing tanks discharge to a single holding  tank from which two  solution
feeders take their  supply for  application to  the  process.  The  system for the 100 mgd
plant includes  four volumetric dry feeders complete with steel day hoppers, dust collectors,
bin gates and  flexible connectors.  The system operation is automatic for the preparation
and  transfer of aged polymer solution from four mixing tanks to two holding tanks. Ten
solution feeders meter the polymer  to the  treatment  process.

10.7     Chemical Suppliers

         10.7.1        Metal Salts  and Lime

The  first   and largest list of suppliers  concerns metal salts and  lime.  It  is divided
geographically  into  states,  which are tabulated  alphabetically.   Then, under each state,
production locations  are listed for the following alphabetized  chemicals:

                  alum (dry and/or liquid)

                  ferric  chloride

                  ferric  sulfate

                  ferrous sulfate

                  lime  (high calcium and/or dolomitic)

                  sodium aluminate (dry and/or liquid)
                                    10-47

-------
Table 10-12 summarizes extent and location of presently available  sources of metal salts
and lime:
                                  TABLE  10-12

   GEOGRAPHICAL SUMMARY OF  SUPPLIERS OF METAL SALTS AND LIME


     Location                                      Chemical

     25 States                                     Alum

     Michigan                                      Ferric chloride

     Tennessee                                     Ferric sulfate

     Ga., Md., Mo., NJ.                           Ferrous  sulfate

     32 states                                     Lime

     Ark., 111., La., Ga., Mo.                       Sodium  aluminate
Table  10-13 offers a detailed listing of metal salt and lime suppliers.  Persons interested
in contacting  chemical suppliers may direct inquiries to either the point of production
or to a nearby sales office for the chemical company involved.  This list does not include
potential or established suppliers of waste pickle liquor. Nor are pH adjusting chemicals
included here; these are  normally available  through most major chemical supply  firms.
                                    10-48

-------
                                TABLE 10-13
                   SUPPLIERS OF METAL  SALTS AND LIME
Location
Manufacturer
Chemical
ALABAMA
    Coosa Pines
    Demopolis
    Mobile
    Naheola

    Allgood
    Keystone

    Landmark
    Monte vallo
    Roberta
    Saginaw
    Siluria
American Cyanamid
American Cyanamid
American Cyanamid
Stauffer

Cheney Lime & Cement Co.
Martin Marietta Cement,
    Southern Division
Cheney Lime & Cement Co.
U.S.  Gypsum Co.
Southern  Cement Co.,
    Div.  Martin Marietta
    Corp.
Longview Lime Co., Div.
    Woodward Co., Div.
    Mead Corp.
Alabaster Lime Co.
Alum, Liquid
Alum, Liquid
Alum, Liquid and Dry
Alum, Liquid

Lime, High Calcium
Lime, High Calcium

Lime, High Calcium
Lime, High Calcium
Lime, High Calcium
Lime, High Calcium
Lime, High Calcium
ARIZONA
    Douglas
    Globe
    Nelson
Paul Lime Plant, Inc.
Hoopes  & Co.
U.S. Lime Div., The
     Flintkote Co.
Lime, High Calcium
Lime, High Calcium
Lime, High Calcium
ARKANSAS
    Pine Bluff

    Batesville
    Bauxite
Allied

Batesville White Lime
     Co., Div.  Rangaire
     Corp.

Reynolds Chemicals
Alum, Liquid

Lime, High Calcium
Sodium Aluminate,
     Dry
                                  10-49

-------
                  SUPPLIERS OF  METAL SALTS  AND LIME
Location
Manufacturer
Chemical
CALIFORNIA
    Bay Point
    Antioch
    El Segundo
    Richmond
    Vernon

    City of Industry

    Diamond Springs
    Lucerne Valley
    Richmond

    Salinas

    Westend
Allied
Imperial West Chemicals
Allied
Stauffer
Stauffer

U.S. Lime Div., The
     Flintkote Co.
Diamond Springs Lime  Co.
Pfizer,  Inc.,  Minerals,
     Pigments & Metals
     Div.
U.S. Lime Div., The
     Flintkote Co.
Kaiser  Aluminum &
     Chemical Corp.
Stauffer Chemical  Co.
Alum, Liquid and Dry
Ferric Chloride
Alum, Liquid
Alum, Liquid
Alum, Liquid

Lime, High Calcium

Lime, High Calcium
Lime, High Calcium
Lime, High Calcium
Lime, Dolomitic
Lime, High Calcium
COLORDAO
    Denver

    Ft. Morgan
Allied
Great Western Sugar Co.
Alum,  Liquid and Dry

Lime, High Calcium
CONNECTICUT
    Canaan
Pfizer, Inc., Minerals
     Pigments & Metals
     Div.
Lime, Dolomitic
FLORIDA
    Fernandina Beach
    Jacksonville
    Port St.  Joe
Tennessee Corp.
Allied
Allied
Alum, Liquid
Alum, Liquid
Alum, Liquid
                                  10-50

-------
                  SUPPLIERS OF METAL SALTS AND LIME
Location

FLORIDA (cont.)
    Brooksville
    Sumterville
Manufacturer
Chemical Lime Co.
Dixie  Lime and Stone Co.
                                                        Chemical
Lime, High Calcium
Lime, High Calcium
GEORGIA
    Atlanta (2)
    Augusta
    Cedar  Springs
    Macon
    Savannah

    Savannah

    Vinings
Burris; Allied
Tennessee  Corp.
Tennessee  Corp.
Allied
Allied

American  Cyanamid Co.

Vinings Chemical Co.
Alum, Liquid and Dry
Alum, Liquid and Dry
Alum, Liquid
Alum, Liquid
Alum, Liquid

Ferrous  Sulfate

Sodium  Aluminate,
     Liquid
ILLINOIS
     E. St. Louis
     Joliet

     Marblehead
     McCook
     Quincy
     So.  Chicago
     Thornton

     Chicago
Allied
American  Cyanamid

Marblehead Lime  Co.
Vulcan Materials Co.
Marblehead Lime  Co.
Marblehead Lime  Co.
Marblehead Lime  Co.

Nalco Chemical Company
Alum,  Liquid and Dry
Alum,  Liquid and Dry

Lime, High Calcium
Lime, Dolomitic
Lime, High Calcium
Lime, High Calcium
Lime, Dolomitic

Sodium Aluminum,
     Liquid and Dry
INDIANA
     Buffington
Marblehead Lime  Co.
 Lime, High Calcium
                                   10-51

-------
                  SUPPLIERS OF METAL SALTS AND LIME
Location

IOWA
    Davenport
Manufacturer
Linwood Stone Products
    Co., Inc.
Chemical
Lime, High Calcium
KENTUCKY
    Carntown
Black River Mining Co.
Lime, High Calcium
LOUISIANA
    Bastrop
    Baton  Rouge
    Monroe
    New Orleans
    Springhill

    Morgan City
    New Orleans
Stauffer
Stauffer
Allied
Allied
Stauffer

Pelican State Lime Corp.
U.S. Gypsum Co.
Alum, Liquid
Alum, Liquid
Alum, Liquid
Alum, Liquid and Dry
Alum, Liquid

Lime, High Calcium
Lime, High Calcium
MAINE
     Searsport
Northern
Alum, Liquid and Dry
MARYLAND
     Baltimore

     Baltimore (3)
     Woodsboro
Olin

Byproducts Processing
     Co., Inc.;
Glidden Co.;
Cosmin Corp.;

S.W. Barrick & Sons, Inc.
Alum, Dry

Ferrous Sulfate

Ferrous Sulfate
Ferrous Sulfate

Lime, High  Calcium
                                   10-52

-------
                  SUPPLIERS OF METAL SALTS AND LIME
Location

MASSACHUSETTS
    Adams
    Salem

    Adams
    Lee
Manufacturer
Holland
Hamblet & Hayes

Pfizer,  Inc., Minerals
    Pigments &  Metals
    Div.
Lee Lime  Corp.
Chemical
Alum, Liquid
Alum, Liquid and Dry

Lime, High Calcium
Lime, Dolomitic
MICHIGAN
    Detroit
    Escanaba
    Kalamazoo  (2)

    Midland
    Wyandotte

    Detroit
    Ludington
    River Rouge

    Cloquet

    Pine Bend

    Duluth
Allied
American Cyanamid
Allied; American Cyanamid

Dow Chemical Co.
Pennwalt Corp.

Detroit Lime  Co.
Dow Chemical Co.
Marblehead Lime Co.

American Cyanamid

North Star

Cutler Magner Co.
Alum, Liquid
Alum, Liquid
Alum, Liquid

Ferric Chloride
Ferric Chloride

Lime, High Calcium
Lime, High Calcium
Lime, High Calcium

Alum, Liquid

Alum, Liquid and Dry

Lime, High Calcium
MISSISSIPPI
    Monticello
    Vicksburg
American Cyanamid
Allied
Alum, Liquid
Alum, Liquid
                                  10-53

-------
                  SUPPLIERS OF METAL SALTS AND LIME
Location
Manufacturer
Chemical
MISSOURI
    St.  Louis

    Bonne  Terre

    Hannibal
    Ste. Genevieve
    Springfield

    Kansas City
National Lead

Valley  Mineral Products
    Co.
Marblehead Lime Co.
Mississippi Lime Co.
Ash Grove  Cement Co.

Conservation Chemical Co.
Ferrous Sulfate

Lime, Dolomitic

Lime, High Calcium
Lime, High Calcium
Lime, High Calcium

Sodium Aluminate,
     Liquid
NEVADA
    Apex
     Henderson

     McGill
     Sloan
U.S. Lime Div., The
     Flintkote  Co.
U.S. Lime Div., The
     Flintkote  Co.
Morrison-Weatherly Corp.
U.S. Lime Div., The
     Flintkote  Co.
Lime, High Calcium

Lime, Dolomitic and
     High  Calcium
Lime, High Calcium
Lime, Dolomitic and
     High  Calcium
NEW JERSEY
     Newark
     Warners

     Sayreville

     Newton
Essex
American  Cyanamid

National Lead

Limestone Products
     Corp. of America
Alum, Liquid and  Dry
Alum, Liquid and  Dry

Ferrous Sulfate

Lime,  High Calcium,
     Hydrate  Only
                                   10-54

-------
                  SUPPLIERS OF METAL SALTS  AND LIME
Location

NORTH CAROLINA
    Acme
    Plymouth
Manufacturer
Wright
American Cyanamid
                                                        Chemical
Alum, Liquid
Alum, Liquid
OHIO
    Chillicothe
    Cleveland
    Hamilton
    Middletown

    Ashtabula
    Carey
    Cleveland
    Delaware
    Genoa
    Gibson burg (2)
     Huron
     Marble  Cliff
     Millersville
     Woodville (2)
Allied
Allied
American Cyanamid
Allied

Union  Carbide Olefins Co.
National Lime &  Stone Co.
Cuyahoga Lime Co.
MCQ Co.
U.S. Gypsum Co.
Pfizer, Inc., Minerals,
     Pigments & Metal
     Div.; National
     Gypsum Co.
Huron Lime Co.
MCQ Co.
I.E. Baker Co.
Ohio Lime Co.; Standard
     Lime  & Refractories
     Div., Martin
     Marietta Corp.
Alum,  Liquid
Alum,  Liquid and Dry
Alum,  Liquid and Dry
Alum,  Liquid

Lime, High Calcium
Lime, Dolomitic
Lime, High Calcium
Lime, High Calcium
Lime, Dolomitic
Lime, Dolomitic
 Lime, High  Calcium
 Lime, High  Calcium
 Lime, Dolomitic
 Lime, Dolomitic
 OKLAHOMA
     Marble  City
     Sallisaw
 St. Clair Lime  Co.
 St. Clair Lime  Co.
 Lime,  High Calcium
 Lime,  High Calcium
                                   10-55

-------
                  SUPPLIERS OF METAL SALTS AND LIME
Location

OREGON
    North Portland

    Baker

    Portland
Manufacturer
Stauffer

Chemical Lime Co. of
    Oregon
Ash Grove Cement Co.
Chemical
Alum, Liquid and Dry
Lime, High Calcium
Lime, High Calcium
PENNSYLVANIA
    Johnsonburg
    Marcus Hook
    Newell

    Annville
    Bellefonte (2)

    Branchton
    Devault
    Pleasant Gap
    Plymouth Meeting
Allied
Allied
Allied

Bethlehem Mines Corp.
National Gypsum Co.;
    Warner Co.
Mercer Lime & Stone Co.
Warner Co.
Chemical Lime Inc.
G.&W.H. Corson, Inc.
Alum, Liquid
Alum, Liquid and Dry
Alum, Liquid

Lime, High Calcium
Lime, High Calcium

Lime, High Calcium
Lime, Dolomitic
Lime, High Calcium
Lime, Dolomitic
SOUTH CAROLINA
    Catawba
    Georgetown
Burris
American Cyanamid
Alum, Liquid
Alum, Liquid and Dry
SOUTH DAKOTA
    Rapid City
Pete Lien  & Sons, Inc.
Lime, High Calcium
                                  10-56

-------
                  SUPPLIERS OF METAL SALTS AND LIME
Location
Manufacturer
Chemical
TENNESSEE
    Chattanooga
    Counce
    Springfield

    Copper Hill

    Knoxville (2)
American Cyanamid
Stauffer
Burris

Cities Service Co.

Foote Mineral Co.;
     Williams Lime
     Mfg. Co.
Alum, Liquid and Dry
Alum, Liquid
Alum, Liquid

Ferric Sulfate

Lime, High Calcium
TEXAS
    Houston (2)

    Texas City
     Blum

     Cleburne

     Clifton
     Houston
     McNeil
     New  Braunfels
     Round  Rock

     San Antonio
Stauffer; Ethyl

Gulf Chemical &
     Metallurgical

Round Rock Lime
     Companies
Texas Lime Co., Div.
     Rangaire Corp.
Chemical Lime  Inc.
U.S. Gypsum Co.
Austin White Lime Co.
U.S. Gypsum Co.
Round Rock Lime
     Companies
McDonough Bros., Inc.
Alum,  Liquid and Dry

Ferrous Sulfate,
Ferric  Sulfate

Lime,  High Calcium

Lime,  High Calcium
Lime, High
Lime, High
Lime, High
Lime, High
Lime, High
Calcium
Calcium
Calcium
Calcium
Calcium
Lime, High Calcium
UTAH
     Grantsville

     Lehi
U.S. Lime  Div.,  The
     Flintkote Co.
Rollins  Mining Supplies
     Co.
Lime, Dolomitic and
     High Calcium
Lime, High Calcium
                                  10-57

-------
                  SUPPLIERS OF METAL SALTS AND LIME
Location
Manufacturer
Chemical
VERMONT
    Winooski
Vermont Assoc. Lime
    Industries, Inc.
Lime, High Calcium
VIRGINIA
    Covington
    Hope well
    Norfolk

    Clearbrook
    Kimballton (2)

    Stephens City
    Strasburg
Allied
Allied
Howerton  Gowen

W.S. Frey Co., Inc.
Foote Mineral Co.;
    National Gypsum Co.
M.J. Grove Lime Co.,
    Div. The Flintkote
    Co.
Chemstone Corp.
Alum, Liquid
Alum, Liquid
Alum, Liquid

Lime, High Calcium
Lime, High Calcium

Lime, High Calcium
Lime, High Calcium
WASHINGTON
    Kennewick
    Tacoma (2)
    Vancouver

    Tacoma
Allied
Allied; Stauffer
Allied

Domtar Chemicals Inc.
Alum, Liquid
Alum, Liquid
Alum, Liquid and Dry

Lime, High Calcium
WEST VIRGINIA
     Riverton
Germany Valley Limestone
     Div.,  Greer Steel Co.
Lime, High Calcium
                                  10-58

-------
                  SUPPLIERS OF  METAL  SALTS  AND LIME
Location                   Manufacturer                   Chemical

WISCONSIN
    Manasha               Allied                         Alum, Liquid
    Wisconsin  Rapids       Allied                         Alum, Liquid

    Eden                  Western Lime & Cement Co.    Lime, Dolomitic
    Green  Bay            Western Lime & Cement Co.    Lime, High Calcium
    Knowles               Western Lime & Cement Co.    Lime, Dolomitic
    Manitowoc            Rockwell  Lime Co.             Lime, Dolomitic
    Superior               Cutler-LaLiberte-                Lime, High Calcium
                              McDougall Corp.
         10.7.2       Polymer  Suppliers

Table 10-14 lists names and addresses of firms offering polymer which may prove effective
in treatment approaches described herein.
                                TABLE 10-14

                  POLYMER SOURCES AND TRADE NAMES



Source                                                  Trade  Name(s)

Allied Colloids, Inc.                                      Percol
One  Robinson Lane
Ridgewood, NJ   07450

Allstate Chemical Co.                                     Allstate
Post  Office Box  3040
Euclid, OH  44117
                                 10-59

-------
                  POLYMER SOURCES AND TRADE NAMES
Sources

Allyn Chemical Co.
2224 Fairhill Road
Cleveland, OH 44106

American Cyanimid Co.
Berdan Avenue
Wayne, NJ   07470

Atlad Chemical Ind.,  Inc.
Wilmington,  DE  19899

Berdell Industries
28-01 Thomson Avenue
Long Island  City,  NY  11101

Betz Laboratories, Inc.
Somerton Road
Trevose,  PA   19047

Bond Chemicals, Inc.
1500 Brookpark Road
Cleveland, OH  44109

Brennan  Chemical Co.
704 N. First Street
St.  Louis, MO  63102

The Burtonite Company
Nutley, NJ  07110

Calgon Corporation
Post Office  Box  1346
Pittsburgh, PA  15222
Trade Name(s)

Claron
Superfloc
Magnifloc
Sarbo
Atlasep

Berdell
Betz
Polyfloc
Bondfloc
Brenco
Burtonite
Cat-Floe
                                  10-60

-------
                  POLYMER SOURCES AND  TRADE NAMES
Source

Commercial Chemical
11 Patterson Avenue
Midland Park, NJ   07432

Dearborn Chemical  Div.
W. R. Grace &  Co.
Merchandise Mart Plaza
Chicago, IL  60654

Dow Chemical USA
Barstow Building
2020  Dow Center
Midland, MI   48640

Drew  Chemical Corp.
701 Jefferson Road
Parsippany, NJ  07054

DuBois Chemicals Div.
W. R. Grace &  Co.
3630  E. Kemper Road
Sharonville,  OH   45241

E. I.  DuPont  de Nemours & Co.
Eastern Laboratory
Gibbstown, NJ  08027

Environmental Pollution Investigation
    & Control,  Inc.
9221  Bond Street
Overland  Park, KS   66214
Trade Name(s)

Speedifloc



Aquafloc
Dowell
PEI
Purifloc
Separan XD

Drewfloc
Amerfloc
Flocculite
DuPont
Dynafloc
                                  10-61

-------
                  POLYMER SOURCES AND  TRADE NAMES
Source                                                  Trade Name(s)

Fabcon International                                      Zulcar
1275  Columbus Avenue                                   Fabcon
San Francisco, CA   94133

Henry W.  Fink & Co.                                    Kleer-Floc
6900  Silverton Avenue
Cincinnati, OH  45236

Gamlen Sybron Corp.                                     Gamafloc
321 Victory Avenue                                      Gamlose
S. San Francisco, CA   94080                             Gamlen

Garrett-Callahan                                          Garrett-Callahan
111 Rollins Road
Millbrae, CA

General Mills  Chemicals                                   Supercol
4620  N. 77th Street                                     Guartec
Minneapolis, MN  55435

Hercules,  Inc.                                            Hercofloc
910 Market Street
Wilmington, DE  19899

Frank Herzl Corp.                                        Perfectamyl
299 Madison  Avenue
New York, NY  10017

ICI America,  Inc.                                        Atlasep
Wilmington, DE  19899

Illinois Water Treatment Co.                              Illco
840 Cedar Street
Rockford,  IL  61102
                                   10-62

-------
                  POLYMER SOURCES AND  TRADE  NAMES


Source                                                  Trade Name(s)

Kelco Company                                          Kelgin
8225  Aero Drive                                         Kelcosol
San Diego, CA   92123

Key  Chemicals                                           Key-Floe
4346  Tacony
Philadelphia, PA   19124

Metalene Chemical  Co.                                    Metalene
Bedford, OH   44014

The Mogul Corporation                                   Mogul
20600 Chagrin Boulevard
Cleveland, OH  44122

Nalco Chemical Co.                                      Nalcolyte
6216  W. 66th PI.
Chicago, IL   60638

Narvon  Mining & Chemical  Co.                            Sink-Floe
Keller Avenue & Fruitville Pike                            Zeta-Floc
Lancaster, PA  17604

National Starch &  Chemical Corp.                         Floe-Aid
1700  W. Front Street                                    Natron
Plainfield, NJ  07063

O'Brein Industries,  Inc.                                   O'B Floe
95 Dorsa Avenue
Livingston,  NJ  07039

Oxford  Chemical Div.                                    Oxford-Hydro-Floc
Consolidated  Foods Corp.
Post  Office Box  80202
Atlanta, GA  30341
                                   10-63

-------
                   POLYMER SOURCES AND  TRADE NAMES
Source                                                    Trade Name(s)

Reichhold Chemicals, Inc.                                   Aquarid
RCI  Building
White Plains, NY  10602

Standard Brands Chem. Ind., Inc.                           Tychem
Post  Office Drawer K
Dover, DE  19901

A. E. Staley  Mfg.  Co.                                      Hamaco
Post  Office Box 151
Decatur,  IL   62525

Stein, Hall & Co., Inc.                                     Hallmark
605  Third Avenue                                         Jaguar
New York, NY   10016                                    Polyhall

Swift &  Company                                         Swift
Oakbrook, IL   60521

James Varley & Sons, Inc.                                 Varco-Floc
1200 Switzen Avenue
St. Louis, MO   63147

W. E. Zimmie,  Inc.                                        Zimmite
810  Sharon  Drive
Westlake, OH   44145
         10.7.3        Other Chemicals

A large number of manufacturers generate sodium hydroxide; it is produced concurrently
with chlorine, and sometimes elemental  sodium.  The compound is produced at nearly
100 plant sites in this country, and bulk storage is available in most major cities. Designers
are referred to chemical suppliers in their geographical area  for this  commodity.
                                   10-64

-------
Carbon  dioxide is generated  at some 75 locations around the  country, and in addition
the liquefied gas is stored in  bulk in nearly all major cities.  Some twenty manufacturers
are involved  in these operations,  and designers  are referred  to local chemical suppliers
for further information on carbon  dioxide.

About ten manufacturers produce soda ash in the United States. The 15 plant sites involved
are widely scattered  geographically, as follows in  Table 10-15:
                                   TABLE  10-15

                          SODA ASH MANUFACTURERS


         Ammonia-Soda Plants

         Allied Chemical Corp., Syracuse, N.Y.; Detroit, Mich.; Baton Rouge,
         La.

         Diamond Alkali Co.,  Painesville, Ohio

         Olin Mathieson Chemical  Corp., Saltville, Va.; Lake  Charles,  La.

         Pittsburgh Plate Glass  Co., Barberton, Ohio; Corpus  Christi, Texas

         Wyandotte Chemicals,  Corp., Wyandotte, Mich.


         Natural  Soda  Plants

         American  Potash  and Chemical Corp., Trona,  Calif.

         FMC Corp., Green  River, Wyoming

         Pittsburgh Plate Glass  Co., Bartlett, Calif.

         Stauffer Chemical Co., Westend, Calif.; Green  River, Wyoming


         Carbonation of Caustic Liquors

         Dow Chemical Co., Freeport, Texas
                                    10-65

-------
The  preceding list is from a reference written to supply such information on these and
many other related compounds:

                           Faith, W. L.; Keyes, D. B.;
                           & Clark, R.  L., Industrial
                           Chemicals, 3rd Ed., John
                           Wiley & Son, New York (1965).

10.8     Chemical Feeders

Chemical feed systems must be  flexibly designed to provide for a high degree of reliability
in light of the many contingencies which may affect their operation.  Thorough waste
characterization in terms of flow extremes and chemical requirements should precede the
design of the chemical feed system.  The design of  the chemical feed system must take
into  account the form of each chemical desired for feeding, the particular physical and
chemical characteristics of the  chemical, maximum waste  flows and the reliability of the
feeding devices.

In suspended and  colloidal solids removal from  wastewaters the chemicals employed are
generally in liquid or solid form.  Those in solid form are generally converted to solution
or slurry form prior to  introduction to the wastewater stream; however, some chemicals
are fed in a dry form.  In any case, some type of solids feeder is usually required. This
type of feeder has numerous different forms due to wide ranges in chemical characteristics,
feed rates and degree of accuracy required. Liquid feeding is somewhat more restrictive,
depending  mainly on liquid volume  and  viscosity.

The  capacity of  a chemical feed system is an  important consideration in both storage
and  feeding. Storage capacity  design must take into account the advantage of quantity
purchase versus the disadvantage of construction cost and chemical deterioration with time.
Potential delivery  delays and chemical use rates are necessary factors in the total picture.
Storage tanks or  bins for solid chemicals must be designed with proper consideration  of
the  angle of repose of the chemical and its necessary environmental requirements, such
as temperature and humidity.  Size and slope of feeding lines are important along with
their materials of construction with respect to the  corrosiveness of the  chemicals.

Chemical feeders must accommodate the  minimum and maximum feeding  rates required.
Baker (12) indicates that manually controlled feeders have a common range  of 20:1, but
this  range can be  increased to  about 100:1 with dual control systems.  Chemical feeder
control can be manual, automatically proportioned to flow, dependent on some  form  of
process feedback, or a combination of any two of these. More sophisticated control systems
are feasible if proper sensors are available.  If manual control  systems are specified with
the  possibility of  future automation, the feeders selected should  be amenable to this
conversion with a minimum of expense.  An example would be a feeder with an external
motor which could easily be replaced with a variable speed motor or drive when automation
                                     10-66

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is  installed (12).  Standby or backup units should be included for each type of feeder
used.  Reliability calculations will be necessary in larger plants with a greater multiplicity
of these units.  Points of chemical addition  and piping to them should be capable of
handling all  possible changes in dosing patterns in  order to have proper  flexibility of
operation.   Designed flexibility in hoppers, tanks, chemical feeders and solution lines is
the key to  maximum benefits  at  least cost (12).

Liquid  feeders are  generally in the form of metering pumps or orifices.   Usually these
metering pumps are of the positive-displacement variety, plunger or diaphragm type.  The
choice of liquid feeder is highly dependent on the viscosity, corrosivity, solubility, suction
and  discharge heads, and  internal  pressure-relief requirements (13).  Some  examples are
shown in Figure 10-13 and Figure 10-14.  In some  cases control valves and rotameters
may be all that is required.  In other cases, such as lime slurry feeding, centrifugal pumps
with open impellers are  used with appropriate  controls (14). More complete descriptions
of liquid feeder requirements  can be  found in the literature and elsewhere (13).

Solids characteristics vary  to a great degree and the choice of feeder must  be considered
carefully, particularly in the smaller-sized  facility where  a single  feeder may be used for
more than one  chemical.   Generally,  provisions should be made  to  keep all chemicals
cool and dry. Dryness is very important, as hygroscopic (water absorbing) chemicals  may
become  lumpy, viscous  or even rock  hard; other chemicals with less affinity for water
may become sticky from  moisture  on the  particulate surfaces, causing increased arching
in hoppers.   In either case, moisture  will affect the density  of the chemical and  may
result in under-feed.  Dust removal equipment should be used at shoveling locations, bucket
elevators, hoppers  and feeders for neatness,  corrosion  prevention and safety  reasons.
Collected chemical  dust may often be used.

The  simplest method for feeding solid chemicals is by hand. Chemicals may be preweighed
or simply shoveled  or poured by the bagful  into a dissolving tank.   This  method is of
economic necessity  limited to very small  operations, or to  chemicals  used  in very weak
solutions.

Because of the many factors, such as moisture content, different grades and compressibility,
which can  affect chemical density (weight to  volume ratio), volumetric feeding of solids
is  normally restricted to  smaller  plants, specific types of  chemicals  which are reliably
constant in composition and low rates of feed.  Within these restrictions, several volumetric
types are available.  Accuracy of  feed is usually limited to plus  or minus  2% by weight
but  may be  as high as plus or minus 5%.
                                      10-67

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                      FIGURE 10-13



               PLUNGER TYPE METERING PUMP



             (COURTESY OF WALLACE & TIERNAN)
/
                                           DISCHARGE VALVE
                         PLUNGER
SUCTION VALVE
                     10-68

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         FIGURE 10-14



   DIAPHRAGM TYPE METERING  PUMP



 (COURTESY OF WALLACE &  TIERNAN)
DISCHARGE VALVE
         10-69

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One type of volumetric dry feeder uses a continuous belt of specific width moving from
under the hopper to the dissolving tank.  A mechanical gate mechanism regulates the
depth of material on the  belt, and the rate of feed is governed by the speed of the belt
and/or the height of the gate opening.  The hopper normally is equipped with a vibratory
mechanism to reduce arching. This type of feeder is not suited for easily fluidized materials.

Another type employs a screw or helix from the bottom of the hopper through a tube
opening slightly larger than the diameter of the screw or helix. Rate of feed is governed
by  the speed of  screw or helix rotation.  Some screw-type designs are self-cleaning, while
others are subject to clogging.   Figure 10-15 shows a typical screw-feeder.

Most remaining types of volumetric feeders generally fall into the positive-displacement
category.  All  designs incorporate some form of moving cavity of a specific or variable
size.  In operation, the chemical falls  by gravity into the cavity and is more or less fully
enclosed and separated from  the hopper's feed.   The  size of the cavity, and the rate
at which the cavity moves and is discharged, governs the amount of material fed.  The
positive  control  of the chemical  may  place a low limit on rates of feed.  One unique
design   is   the   progressive   cavity   metering  pump,   a  non-reciprocating   type.
Positive-displacement feeders  often utilize air injection to  enhance  flowability of the
material.  Some  examples of positive-displacement units are illustrated in Figure  10-16.

The basic drawback of volumetric feeder design, i.e., its inability to compensate for changes
in the density  of materials, is overcome by modifying  the  volumetric design to include
a gravimetric or  loss-in-weight controller. This  modification allows for  weighing  of the
material as  it is fed.  The beam balance types measure the actual mass of material. This
is considerably  more accurate, particularly over a long period of time, than the less common
spring-loaded gravimetric  designs.  Gravimetric feeders  are used where feed accuracy  of
about plus  or  minus 1% is required  for  economy,  as  in large-scale  operations and for
materials which are  used  in small, precise quantities.  It should be noted, however, that
even gravimetric  feeders cannot compensate  for  weight  added to  the  chemical by excess
moisture. Many  volumetric feeders may be converted to loss-in-weight function by placing
the entire feeder on a platform scale which is tared to neutralize the weight of the feeder.

Good housekeeping and need for accurate feed  rates dictate that the gravimetric feeder
be  shut down and thoroughly cleaned  on a regular  basis.  Although many of these feeders
have automatic  or  semi-automatic  devices  which  compensate  to  some  degree  for
accumulated solids on the weighing mechanism, accuracy is affected, particularly on humid
days when  hygroscopic materials  are fed. In some cases, built-up chemicals can actually
jam the equipment.
                                      10-70

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                            FIGURE  10-15

                            SCREW FEEDER
 MOTOR AND
 GEAR REDUCER
 SOLUTION
CHAMBER
                                                           HOPPER
                                                           ROTATING &
                                                           RECIPROCATING
                                                           PEED  SCREW
                                                          SOLUTION
                                                           LEVEL
                                                            JET MIXER
                            10-71

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              FIGURE 10-16



POSITIVE DISPLACEMENT SOLID FEEDER-ROTARY
              10-72

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No discussion  of feeders is complete without at  least passing reference to dissolvers, as
any metered material must  be mixed with water to provide a chemical solution of desired
strength.  Most feeders, regardless of type, discharge  their material to a small dissolving
tank which is  equipped with a nozzle system and/or mechanical agitator depending on
the solubility of the chemical being fed.  Solid materials, such  as polyelectrolytes, may
be carefully spread into  a  vortex spray or  washdown jet of water immediately before
entering the dissolver.  It is essential that the surface  of each particle become thoroughly
wetted  before entering the  feed tank to ensure accurate dispersal and to avoid clumping,
settling or floating.

A dissolver  for a dry  chemical  feeder is unlike a  chemical feeding mechanism, which by
simple adjustment  and change of speed can  vary its output tenfold.  The dissolver must
be designed  for  the job  to be  done.   A  dissolver suitable for a rate of 10 Ib/hr may
not be  suitable for dissolving at a rate of 100 Ib/hr.  As a general rule, dissolvers may
b  oversized, but dissolvers for commercial ferric  sulfate or lime slakers do not  perform
well if  greatly oversized.

It is essential that specifications for dry chemical feeders include specifications on dissolver
capacity.   A number  of factors need  to be  considered in designing dissolvers of proper
capacity.  These  include detention  times and water requirements, as well as other factors
specific to individual  chemicals.

The  capacity of a dissolver is based on detention time, which is directly related to the
wettability  of  rate of  solution of  the  chemical.  Therefore, the dissolver must  be large
enough to provide the necessary  detention  for both the  chemical  and the water at the
maximum rate of  feed.  At lower rates of  feed,  the strength of solution or suspension
leaving  the  dissolver will be less, but the detention time will be approximately the same
unless the water supply to the dissolver is reduced.  When the water supply to any dissolver
is controlled for the purpose of forming a constant strength solution, mixing within the
dissolver must be  accomplished by mechanical means, because sufficient  power  will not
be available  from  the  mixing jets  at low  rates of flow.   Hot  water dissolvers  are  also
available in order  to  minimize the required  tankage.

The  foregoing  descriptions  give some  indication of the wide  variety of materials which
may be handled.  Because of  this variety,  a modern facility may contain any  number
of a variety of feeders with  combined or multiple materials capability.  Ancillary equipment
to the feeder also varied according to the material to be handled. Liquid feeders encompass
a limited number of design principles which account for density and viscosity ranges.  Solids
feeders,  relatively  speaking,  vary  considerably  due to the wide range  of physical  and
chemical characteristics, feed rates and  the degree of precision and repeatability required.
                                      10-73

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                                              TABLE 10-16

                                  TYPES OF CHEMICAL FEEDERS
                                                                                      Limitations
       Type of feeder



Dry feeder:
 Volumetric:
  Oscillating plate

  Oscillating throat (universal)

  Rotating disc

  Rotating cylinder (star)


  Screw

  Ribbon

  Belt
 Gravimetric:
  Continuous-belt and scale
  Loss in weight

Solution feeder:
 Nonpositive displacement:
  Decanter (lowering pipe)

  Orifice
  Rotameter (calibrated valve)
  Loss in weight (tank with
    control valve).
 Positive displacement:
  Rotating dipper
 Proportioning pump:
  Diaphragm

  Piston
Gas feeders:
 Solution feed
 Direct feed
            Use
Any material, granules or
   powder.
Any material, any particle
   size.
Most materials including
   NaF, granules or powder.
Any material, granules or
   powder.

Dry, free flowing material,
   powder or granular.
Dry, free flowing material,
   powder, granular, or lumps.
Dry, free flowing material up
   to IVi-inch size, powder or
   granular.

Dry, free flowing, granular
   material, or floodable
   material.
Most materials, powder
   granular or lumps.
Most solutions or light
   slurries.
Most solutions
Clear solutions
Most solutions
Most solutions or slurries

Most solutions. Special unit
   for 5% slurries. 1
Most solutions, light
   slurries.
Chlorine
Carbon dioxide
Chlorine
                                         Capacity
                                     (cubic feet per hr)
0.01 to 35

0.002 to 100

0.01 to 1.0

8 to 2,000
    or
7.2 to 300
0.05 to 18

0.002 to 0.16

0.1 to 3,000
0.02 to 2
0.02 to 80
0.01 to 10

0.16 to 5
0.005 to 0.16
    or
0.01 to 20
0.002 to 0.20
0.1 to 30

0.004 to 0.15

0.01 to 170
8,000 Ib/day max
6,000 Ib/day max
300 Ib/day max
 Range




 40 to 1

 40 to 1

 20tol

 lOtol
   or
100 to 1
 20tol

 lOtol

 lOtol
   to
100 to 1

100 to 1


100 to 1



100 to 1

 10 to 1
 lOtol


 30tol


100 to 1

100 to 1

 20tol
 20tol
 20tol
 lOtol
 Use special heads and valves for slurries.
                                                     10-74

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Table 10-16 describes several types  of  chemical feeders  commonly used in  wastewater
treatment.

10.9     Additional Reading

         10.9.1    General

    1.    Water Quality and Treatment, Third Edition, American Water Works Association,
         Inc., McGraw-Hill,  NY  (1971).

    2.    Water Treatment Plant Design, American Society of Civil Engineers, American
         Water Works Association,  and Conference  of  State Sanitary Engineers, NY
         (1969).

    3.    Ockershausen, R. W., "Safe Handling of Water Works Chemicals," JAWWA, 63:6,
         p.  336 (1971).

    4.    "Chemicals Used in Treatment of Water  and Wastewater," BIF Reference No.
         1.21-15, BIF Industries, Providence, RI  (1970).

         10.9.2    Aluminum Compounds

    5.    Truitt, V.,  "We Converted to Liquid Alum Treatment," Public Works,  99:11,
         p.  88 (1968).

    6.    "Aluminum  Sulfate," Allied Chemical Corporation, Morristown,  NJ (1968).

    7.    "Alum,"  American Cyanamid  Company,  Wayne, NJ (1964).

    8.    "Aluminum  Sulfate," Stauffer Chemical  Company, NY  (1967).

         10.9.3    Iron Compounds

    9.    "Handling Ferric Chloride," Dow Chemical Company, Midland,  MI (1965).

   10.    "Pennsalt Ferric Chloride," Pennsalt Chemicals Corporation, Philadelphia, PA
         (1965).
                                   10-75

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      10.9.4    Lime

11.    "Chemical Lime Facts," National Lime Association, Washington, D.C. (1964).

12.    Carr, R.  L., "Limestone to Lime to Slaked Lime," Water and Sewage Works,
      Reference No. 113:R.N., p.  R-61  (1966).

13.    "Chemicals Used  in  Water and Wastewater Treatment -  Calcium  Hydroxide
      (Hydrated Lime)," Water and Wastes Engineering,  7:1, p. 53 (1970).

14.    "Chemicals Used in Water  and Wastewater Treatment - Quicklime," Water and
      Wastes  Engineering,  7:5, p. 52 (1970).

15.    "Lime  Handling, Application  & Storage in Treatment Processes," National Lime
      Association, Washington, D.  C. (1971).

16.    "Chemistry and Technology  of Lime and  Limestone," Boynton, R. S., John
      Wiley &  Sons, New York, NY (1966).

      10.9.5    Soda Ash

17.    "Soda  Ash,"  Allied  Chemical Corporation, NY (1966).

18.    "What's Different  About FMC Soda Ash?", FMC  Corporation, NY (1964).

19.    "Stauffer  'Natural' Soda Ash," Stauffer Chemical  Company, NY (1964).

20.    "Wyandotte Soda Ash," Wyandotte Chemicals Corporation, Wyandotte, Michigan
      (1955).

      10.9.6    Caustic  Soda

21.    "Caustic  Soda," PPG Industries, Inc., Chemical Division, Pittsburgh, PA (1969).

22.    "Unloading   Liquid  Caustic from  Tank Cars,"  Manufacturing Chemists
      Association, Washington, D.C. (1968).

23.    "Properties and Essential  Information for Safe Handling  and Use of Caustic
      Soda," Manufacturing Chemists Association, Washington, D.C. (1968).
                                 10-76

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  24.    "Caustic Soda," Allied Chemical Corporation, NY  (1963).

  25.    "Caustic Soda Handbook," Diamond Alkali  Company, Cleveland, OH (1967).

  26.    "Dow  Caustic  Soda  Handbook,"  Dow  Chemical Company,  Midland,  MI
         (Undated).

  27.    "Hooker Caustic Soda," Hooker Chemical Corporation, Niagara Falls, NY (1966).

  28.    "Olin Caustic Soda," Olin Mathieson  Chemical  Corporation, NY (1961).

  29.    "Pennsalt Caustic Soda,"  Pennsalt Chemicals Corporation, Philadelphia,  PA
         (1964).

  30.    "Caustic Soda," Stauffer Chemical Company, NY  (1965).

  31.    "Caustic Soda  by Wyandotte," Wyandotte Chemicals Corporation, Wyandotte,
         MI (1961).

10.10    References

    1.    "Chemicals Used in Water and Wastewater Treatment-Aluminum Sulfate," Water
         and Wastes  Engineering,  Dec.  6:12, p. 46 (1969).

    2.    "Chemicals  Used in  Water and Wastewater Treatment-Ferric Chloride,"  Water
         and Wastes  Engineering,  7:3, p.  65 (1970).

    3.    "Ferri-Floc  for Water and Wastewater Treatment,"  Cities Service Co., Atlanta,
         GA (1972).

    4.    Schworm, W. B., "Iron Salts  for Water and Waste  Treatment," Public  Works,
         94:10,  p. 118  (1963).

    5.    "Lime for Water and Wastewater Treatment," BIF Reference No.  1.21-24, BIF
         Industries, Providence, RI (June,  1969).

    6.    National Lime  Association, direct  communication (May,  1971).

    7.    "Caustic Soda," PPG Industries, Inc., Chemical Division, Pittsburgh, PA (1969).
                                   10-77

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 8.    Haney, P. D. and Hamann, C. L., "Recarbonatkm and Liquid Carbon Dioxide,"
      JAWWA,  61:10, p. 512  (1969).

 9.    Gulp,   R.   L.  and  Gulp,  G.  L.,  Advanced  Wastewater  Treatment,  Van
      Nostrand-Reinhold Company, NY (1971).

10.    Carr, R. L., "Polyelectrolyte Coagulant Aids -  Dry and Liquid Handling and
      Application," Water and Sewage Works, Reference No. 114:R.N., p. 4-64 (1967).

11.    Russo,  F.   and   Carr,   R.   L.,   "Polyelectrolyte  Coagulant  Aids   and
      Flocculants:  Dry and Liquid,  Handling and Application," Water and Sewage
      Works, Reference  No. 117:R.N., p.  R-72 (1970).

12.    Baker,  R.  J.,  "Chemical  Feed  Systems Determine  Plant  Efficiency  and
      Reliability," Water and  Sewage Works, Reference No. 116:R-21  (November,
      1969).

13.    Russo, F.,   and  Carr,  R.  L.,  Jr.,  "Polyelectrolyte  Coagulant  Aids  and
      Flocculants:  Dry and Liquid,  Handling and Application," Water and Sewage
      Works, Reference  No. 117:R-72 (November,  1970).

14.    Gulp, R. L., and Gulp, G.  L., Advanced Wastewatewater Treatment, Van Nostrand
      Reinhold Company, NY (1971).

15.    R. P.  Lowe, "Chemical Feed Systems,"  10th  Annual Water Conf. of Eng. Soc.
      of W.  PA (October 17-19, 1949).
                                 10-78

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                                   CHAPTER 11

                      SLUDGE HANDLING  AND DISPOSAL
11.1     Introduction

A  high proportion  of wastewater treatment capital and operating cost is due  to sludge
handling and disposal.  Consequently, it is important that design engineers have reliable
information on quantities and  dewatering properties of sludges so  that solids handling
facilities can be properly designed.

Information on sludges produced in conventional wastewater treatment is widely  scattered,
and results  from  different locations are not related  well  to each other.  There is even
less information available on sludges produced  by the newer  processes for  phosphorus
removal.

There  has recently  been a concerted effort to provide  this necessary information.  One
group involved is  the staff of the  Ultimate Disposal Research Program operating as part
of the Advanced  Waste  Treatment Research Laboratory  of the National Environmental
Research Center in Cincinnati.

Material in this chapter comes from information compiled and organized  by  that group.
Their basic  data were obtained in several ways:

         a.   Grants and contracts aimed at obtaining comparative information
              on phosphorus-removal sludges have been  funded.

         b.   Reports  have been  prepared  which  summarize  information
              obtained on sludges in EPA Research and Development Grants
              where  useful sludge data  have  been collected.

         c.   Field  crews have visited certain plants where promising processes
              are being  implemented and have obtained comparative  data on
              sludges involved.

         d.   Visits have been made to municipalities and sludge data have been
              obtained from plant staffs.

         e.   Published  literature  has been surveyed  and information  of value
              on  sludges has been extracted.

         f.    Memoranda  have been  prepared  to organize  the  information
              available  and to  respond  to specific needs.
                                     11-1

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         g.   Experimental  investigations  of  sludge  dewatering  are  being
              conducted  at  several  locations by Advanced Waste  Treatment
              Laboratory staff.

All of these routes are still being actively pursued, although the collection of information
is  far from  complete.   However,  there  was  such  urgent need  for  this information
(e.g.,  inclusion in  this manual) that  an interim report was prepared, and this chapter was
developed from it.

Progress  on sludge handling and disposal  technology  will be dealt with in detail in a
forthcoming design manual on the  subject (1).

11.2     Generalized Assessment of Filtration Rates

At least  two groups (2) (3) have developed cost information computer  programs which
can be used to  predict the cost of alternative processing schemes for wastewater treatment
and for  phosphorus removal processes.  These programs have included in their  inherent
logic  (not  as input data) typical values for dewatering  rates, normal sludge  mass, and
additional sludge produced  by phosphorus removal processes.

Aside  from the output from these  cost estimated computer programs, reliable estimates
of the dewaterability  of various sludges can be of substantial value to those concerned
with  process design.   That type of information is presented in this  chapter.

When  attempting  to decide on proper  values for sludge dewatering properties,  there is
a  statistical  problem  of  within-plant  variations  and between-plant  variations.   The
between-plant  variations are sometimes extreme.  This  is  illustrated  in the following
hypothetical  compilation:
                                    TABLE 11-1

            HYPOTHETICAL COMPILATION OF DEWATERING  RATES
                                        Vacuum Filter Yield (Ib/hr-sq ft)
                                    Avg.  (40 Plants)        Std. Deviation

     Digested Mixed Sludge                4.0                    2.0
     Raw Mixed Sludge                   5.0                    3.0
                                     11-2

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The designer wishing to use data of this type to predict within-plant differences between
raw and digested sludges  will find tabulated values are  of little value because standard
deviations are so great.  Within-plant variations between  raw and digested sludge are less
than  indicated  in the  table.   Unfortunately,  within-plant  comparisons  are  virtually
unavailable  because usually  only one  type of sludge at a given plant is dewatered.

Information  relating various within-plant  sludges  to each other should eventually  be
collected.  In this  chapter there has been an attempt to estimate such relationships based
on experience  and information  from  the  sources  previously cited.   Relative values are
suggested here.   These  generalized figures should  be used only when  there is no other
information available.

The information in this section relates  only to vacuum filtration.  The important area
of centrifugation has been introduced  in  other  chapters, when  such information  was
available.  Section 11.4 also describes some case studies in  which centrifugation was used
as  a  dewatering  means, but data  are  insufficient  for development of generalized design
parameters.

There has been no consideration given  to lime sludges in this introductory section.  Sludges
produced by  lime addition, even  when added to  the  primary  clarifier,  contain  large
quantities of calcium carbonate and filter better than conventional or alum and iron sludges.
In addition, a different  approach is needed than for alum, iron, and conventional sludges.
Section  11.4 describes ease studies where lime sludge is dewatered by various means, and
Section  11.3.2 presents fundamentals involved.

          11.2.1         Conventional  Sludges

The  digested  total sludge from a  conventional primary plus activated sludge  plant  is
probably the commonest sludge encountered in wastewater treatment.   Consequently, it
has been selected  as  the  standard  against which other  sludges are  compared.

Table 11-2 shows estimated relative filtration  yields and  conditioning costs of  various
wastewater sludges compared to a standard digested primary plus waste activated sludge.
These values are for belt-type vacuum filters operated at optimum conditions, preceded
by a reasonable processing sequence including thickening if  clarifier sludge is dilute. Filter
cloth selection was appropriate for the  situation  to get satisfactory  solids capture.
                                      11-3

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                                   TABLE  11-2

      DESIGN  FACTORS FOR FILTRATION OF CONVENTIONAL SLUDGES


                         Relative*        Relative Cost            Cake Solids
   Sludge Type            Yield        of Conditioning**           Content

Raw Primary
 Plus WAS                 1.4                0.7                    28
Digested  Primary
 Plus WAS                 1.0                1.0                    26
Raw Primary
 Plus TF                  1.8                0.6                    32
Digested  Primary
 Plus TF                  1.3                0.9                    30
Digested  Primary           2.3                0.7                    33
Raw Primary               3.2                0.5                    35

*Avg. yield  for digested primary plus WAS is estimated at  4.0 Ib/hr-sq ft

**Average cost  of  conditioning is  $10/dry  ton,  1974 costs
An average value of 4.0 Ib/hr-sq ft is suggested for the yield when filtering digested primary
plus waste activated sludge.  If a good estimate of the yield for this or any other sludge
is available, it should be utilized and estimates of the yields for the other sludges obtained
by  means of the  factors  in  Table  11-2.

Mass of  sludge  produced in  wastewater treatment  can be  estimated  by  means  of
well-established procedures discussed  in Section 11.3.  Reduction in mass by digestion
can be estimated by volatile solids reduction.  Since digestion reduces mass approximately
50  percent, required filter area will be less for digested sludge than for raw sludge despite
slightly higher  yields for  raw sludges.

Some shortcomings of the tabulated numbers are evident.  No influence of solids content
is  indicated, although it  is  well known that, up  to  about  8% solids, filter  yield  is
proportional to solids content.  It must be presumed that appropriately designed thickeners
are used.  It becomes clear that when  a filter yield is chosen, there are implicit assumptions
about  the operations upstream.

Effect of elutriation is not included in Table  11-2.  Elutriation would reduce lime demand
substantially.   Polymer required  for  conditioning would  be reduced as well; elutriation
                                     11-4

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is  virtually a necessity for some digested  sludges (4).

No indication of range in solids content of filtered sludge cake is given.  This is  of
importance when the sludge is to be incinerated.  Some data (5) indicate that digested
primary and waste activated sludge would  have a solids content of about 28%. For raw
primary and  waste  activated sludge,  it would  be about 30%.  Slightly lower values are
suggested  in Table  11-2.
         11.2.2
Iron and Alum Sludges
Sludges produced  when  adding  ferric or aluminum salts have a substantially  different
character than conventional sludges.  Quantities are greater and handling and dewatering
properties are different. Changing the addition point in the processing scheme also produces
changes in  the  character of the  sludge.

Table  11-3 compares estimated vacuum filtration yields  and conditioning costs  of the
various metal-effected sludges relative to conventional digested  primary plus waste activated
sludge.
                                   TABLE  11-3

                      DESIGN  FACTORS FOR FILTRATION
                  OF CONVENTIONAL  PLUS METAL SLUDGES
Sludge Type

Aluminum  to  Primary

     Raw Primary Plus WAS
     Digested Primary Plus WAS
     Raw Primary Plus TF
     Digested Primary Plus TF
     Digested Primary
     Raw Primary

Aluminum  to  Aerator
                      Relative
                       Yield*
                         1.2
                         0.85
                         1.35
                         1.0
                         1.05
                         1.5
  Relative Cost
of Conditioning*
      1.3
      1.4
      1.2
      1.3
      1.0
      0.9
     Raw  Primary  Plus WAS
     Digested Primary Plus WAS
                         1.2
                         0.85
      1.3
      1.4
                                    11-5

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Iron to Primary

     Raw Primary Plus WAS                     1.3                   1.1
     Digested  Primary  Plus WAS                 0.95                  1.2
     Raw Primary Plus TF                       1.5                   1.0
     Digested  Primary  Plus TF                   1.1                   1.1
     Digested  Primary                            1.2                   0.8
     Raw Primary                               1.6                   0.7

Iron to Aerator

     Raw Primary Plus WAS                     1.3                   1.1
     Digested  Primary  Plus WAS                 0.95                  1.2

*Yields and costs are related to yield  and cost obtained with digested primary plus WAS
when no  chemicals are added  to the  wastewater.   See Table  11-2.

Estimates will  be more accurate if absolute yields for one or more sludges can be determined
for a particular situation.  The factors in the  table  can then  be used  to predict other
yields.  If no  information is  available, filter yield for digested conventional primary plus
waste activated sludge may be  estimated  to  be 4.0 Ib/hr-sq ft.

11.3      Quantity of  Phosphorus Removal Sludges

          11.3.1        Iron and Alum Sludges

When ferric iron or trivalent aluminum  are added to  wastewater containing phosphorus,
a  metal phosphate  precipitates and excess metal forms an insoluble hydroxide.  The
hydroxide acts as a flocculant  precipitate  which carries with it other  suspended solids
when it  settles.   In addition,  soluble  organic material apparently  is adsorbed  on the
precipitate and removed, as  discussed  later.

The amount and nature  of additional  sludge formed is a function of  the process addition
point.   For example, addition to  the  primary clarifier causes removal of much more
suspended solids  than occurs in conventional sedimentation.  Also, soluble organic material
is removed there.  However, the biological stage which follows  receives a lower BOD
wastewater; consequently,  the  amount of  biological sludge  is  reduced  correspondingly.

There are available  tabulations  which present average observed values of the amount of
sludge typically produced when iron and aluminum are added to wastewater (6). However,
there is still need for  a more precise method  of predicting sludge production so designers
can more accurately size sludge processing equipment.
                                     11-6

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A detailed procedure is  presented here for the case where these metals are added to the
conventional  processing  sequence of primary treatment plus either activated sludge or
trickling  filter.  In this  procedure the chemicals  may be added in primary or secondary
treatment, or as a tertiary process.  The  method requires that the following information
be available:   complete  processing sequence, wastewater characteristics (e.g., SS, BOD,
soluble TOC), and efficiency of solids removal  in  clarifiers.  Methods  are outlined for
predicting the following:  chemical sludge produced, extra sludge from improved clarifier
efficiency, extra sludge  from removal  of  soluble  materials by the chemicals, and reduced
amount of biological sludge when biological plant load is reduced.  In this manner, total
sludge  production,  related to  processing  conditions  and  wastewater  quality,  can  be
determined.   The method is  given in  Sections 11.3.1.1 through  11.3.1.5.
         11.3.1.1
Theoretical Production of Chemical  Sludge
Chemical sludge production may be  calculated by  assuming the metal added reacts first
with phosphorus compounds which are thereby removed, and that any excess metal forms
hydroxide.   The  calculation is illustrated in Table 11-4.
                                   TABLE 11-4
              CALCULATION  OF  CHEMICAL  SLUDGE PRODUCTION
Given:   Pin  =10 mg/1
          out
               =  1 mg/1
         Al Case:
         Fe  Case:
dose of  19  mg/1 Al
(Al/P atomic ratio  = 2.18)

dose of  40  mg/1 Fe
(Fe/P atomic ratio  = 2.22)
Aluminum
     Stoichiometry:

         Al + PO4  = Al PO4

         Al + 3 OH = Al (OH)3
                                    11-7

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        (9 mg/1 P)/(31)  = 0.29  millimoles/1 Al PO4
                                   (M.W. = 122)

        (19  mg/1 Al)/27 = 0.70 mmol/1 Al

        0.70 - 0.29 = 0.41 mmol/1 Al excess, goes to Al  (OH)3
                                   (MW = 78)

        (0.29 mmol/1 Al PO4)(122) =  35.4 mg/1 Al PO4

        (0.41 mmol/1 Al (OH)3)(78) = 32.0 mg/1 Al (OH)3

        Total = 35.4 +  32.0 =  67.4 mg/1

    Sludge Produced:

        67.4 mg chemical sludge per liter  of wastewater treated
        or 67.4/19 =  3.55 mg chemical sludge per mg Al
        or 67.4/9  =  7.48 mg chemical sludge per mg P removed

Iron

    Stoichiometry:

        Fe + PO4  = Fe PO4

        Fe + 3 OH = Fe (OH)3

        (9 mg/1 P)/(31)  = 0.29 mmol/1 Fe PO4
                               (M.W.  = 150.8)

        (40  mg/1  Fe)/(55.84)  = 0.72 mmol/1  Fe

        0.72 - 0.29 = 0.43 mmol/1 Fe excess, goes to Fe(OH)3
                               (M.W.  = 106.8)

        (0.29 mmol/1 Fe PO4)( 150.8)  =  43.7 mg/1 Fe  PO4

        (0.43 mmol/1 Fe (OH)3)( 106.8) = 45.9 mg/1 Fe (OH)2

        Total = 43.7  +  45.9  = 89.6 mg/1
                                   11-8

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     Sludge  Produced:

         89.6 mg of chemical sludge per liter of wastewater treated
         or 89.6/40 =  2.13 mg  chemical sludge  per mg  Fe
         or 89.6/9  =  9.96 mg  chemical sludge  per mg  P removed
The illustration in Table  11-4 shows that at approximately the same atomic ratio of metal
to phosphorus, 48 percent more  chemical  sludge is predicted for iron addition  than  for
aluminum addition.

Sludge production is related in Table  11-4 to mass of phosphorus removed per liter of
sewage  treated.   This is the most rational  procedure when sludge  mass is  calculated.
However,  it is frequently convenient  to relate sludge mass  to the mass of metal  added.
The following are estimated values for the ratio of sludge mass to metal dose as the metal/P
atomic ratio increases from zero  to infinity:

                  Al:       4.52 to  2.89 mg sludge/mg Al
                  Fe:       2.70 to  1.92 mg sludge/mg Fe

Information to verify these  calculated values is scarce.  Swedish experience (7)  indicates
the additional weight of sludge may be calculated from the following relationships:

          sludge (mg/1 of wastewater) = (4) (Al dose, mg/1)

          sludge (mg/1 of wastewater) = (2.5) (Fe dose, mg/1)

That  reference does not elaborate on the source of information although it  was drawn
from  Swedish practice at the time.  It is not stated whether additional mass from improved
suspended and dissolved  solids removal is included. The great majority of plants in Sweden
were  adding chemicals as a post-treatment after biological treatment.  Consequently, it
may  be presumed that  these  figures  indicate  total increase in  sludge  mass from Al or
Fe added to  the final effluent from a  biological  treatment plant.

Other studies (8) estimated additional sludge produced by alum addition to the  activated
sludge process. They report 4  to  3 mg addition solids per mg of Al as dose level increased
from  10  to  20 mg  Al/1.

Another report  (9)  has  estimated  chemical sludge  production when  alum was added to
secondary effluents.  The following relationship was observed:

     chemical sludge (mg/1  of wastewater) = (5.2)(A1 dose, mg/1)
                                    11-9

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                   Al/P atomic ratio  range:    2.0 to 2.8

This is  about 20 percent higher than the  Swedish figure  and about 45  percent higher
than indicated  in Table 11-4 for the stoichiometric relationship.

Data available,  then, indicate chemical sludge mass higher than the values  represented by
the simple stoichiometry indicated in Table  11-4.   There is reason to  conclude that
chemical sludge production could be higher than stoichiometric values because other cations
(such as heavy  metals) and anions can be incorporated into the complex ligand structures
of aluminum and ferric hydroxides.   Consequently, it is recommended that with either
Al or Fe, sludge mass be estimated to be 35  percent higher than the simple stoichiometric
values.

          11.3.1.2      Theoretical Production of Biological  Sludge

Biological sludge is produced and  wasted in both the  activated sludge process and the
trickling filter  process.

One source (10) reports the following  equation  for  excess  sludge  production in the
conventional activated  sludge process:

                   Wy/M    =    (0.79  F/M)  - (0.0714)

              where Wy    =    Ib  volatile suspended solids  produced per day

                     M     =    Ib  mixed liquor volatile suspended solids in the aerator

                     F     =    Ib  5-day BOD removed per day

Rearranging this equation,

                   Wy/F  =   (0.79)  - (0.0714/F/M)

The equation now  gives the mass of volatile solids produced per unit mass of BOD removed
(WV/F) as a function of the food to mass ratio.

A recent report (11) states that 50 percent of the sum of the BOD and suspended solids
fed  to  a trickling  filter is  converted to waste sludge.

If suspended solids and BOD concentrations in the wastewater as it enters the biological
treatment  step  are known, sludge production can be estimated by means  of  the above
relationships.
                                     11-10

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         11.3.1.3       Increase in  Production  of Sludge  From Sewage Solids

Suspended solids and dissolved solids in wastewater are removed by chemical treatment.
Sludge mass is increased by the direct  contribution  of the mass of these removed solids.

One  report (12) has summarized data on suspended solids removal from  well designed
physical-chemical pilot  plants.  For  an  average sewage and effective clarifiers, suspended
solids removal of 85 percent  can be achieved.  If the sewage is  high in suspended solids,
removals will be better.  This figure is substantially higher than the 50-75% removal range
suggested previously (13). However, those earlier figures included plants where chemicals
were added to an existing facility which might have been overloaded or were functioning
poorly for  other reasons.

The  mass of sludge produced from  suspended  solids removed  is calculated directly by
multiplying the change  in suspended solids  concentration by the  volume  of sewage.

There is also evidence  (12)  which indicates an appreciable mass of dissolved  materials
(i.e., filtrable through a 0.45  micron membrane filter) is removed by chemical treatment.
The following table presents this information along with data collected from other sources.
                                   TABLE 11-5

    REMOVAL  OF  DISSOLVED MATERIALS  DURING CHEMICAL ADDITION


    Source                                 Percent  Removals

                                    _Fe_                      Al_
                              SCOD   STOC         SCOD        STOC
    Eimco
      pilot plant  (14)                                  40            30
      laboratory (14)                                           ca.  30

    Friedman
      et al (15)                          30

    Farrell (16)                                                     27

    Westrick and
      Cohen (17)                45       42
                                   11-11

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    Note:    SCOD is  soluble  COD
             STOC is  soluble  TOC
Some of that date (16) represent the average removal obtained in seven batch experiments
in which raw sewage was treated with alum in a small clarifier (150  liter batches). Al/P
atomic* ratio  ranged from 1.6 to  2.8  and removals from 20  to 32 percent.

Based on the above data, it is concluded that soluble TOC removals will average 30 percent.
Data  are scant for COD and none  appear available for BOD.  It is assumed, however,
that removals will be the same for STOC.

The  mass of sludge associated with the soluble TOC removed is more than the  carbon
content involved.  It is estimated that, on the average,  the soluble compounds removed
by  Al and Fe treatment will average 40 percent carbon on a volatile solids basis. This
figure is in accord with the  carbon content of compounds tested in developing the TOC
test  for wastewaters (18).   Thus, to  obtain an estimate of the mass of sludge (volatile
basis) produced, TOC  removed should be multiplied by  1/0.40 or 2.5.

If only soluble COD  removed or soluble BOD removed is known, the problem is more
difficult, primarily because the relationship between mass and COD or BOD changes as
the degree of oxidation of the sewage changes.  For a secondary effluent, volatile mass/COD
is generally considered to be about  1.5 (19).  Assuming the BOD is  about 70 percent
of the COD, volatile  mass/BOD is 2.15.  For  raw sewage, which has a low degree of
oxidation,  the COD  is expected to be higher for a given mass.  Volatile mass/COD for
a raw sewage is estimated to be 1.1, approximately 10  percent lower than lowest values
previously  found  (19) for secondary effluent.  Volatile mass/BOD would be about  1.6.

In the above  discussion, mass relates to mass of volatile solids.  To obtain  total mass,
non-volatile solids must be included.  It is estimated that the ash content of these  soluble
solids is about 15  percent.  Mass of volatile solids should be multiplied by 100/(100-15)
or  1.18 to get total  solids.

Calculation  of sludge mass  resulting  from  removal  of soluble material  will  require
information on the absolute value of soluble TOC, COD or BOD. These values are rarely
measured.  An examination of previous data (14), where both SCOD and STOC were
measured,  showed that ratios of  soluble to total COD and TOC in the influent  sewage
were 0.30  and 0.38 respectively.  Other data (16) showed an STOC/TOC ratio of 0.64.
If data on soluble values of TOC or COD are  not available,  soluble TOC or COD may
be  estimated to be 50 percent of the  total TOC or COD.

The  correlations  for  predicting sludge  production require information on  total BOD
removal.   Some data (12) indicate  total BOD,  COD and TOC reductions are  about the
same and range from  50 to 85 percent depending on clarifier efficiency.  Removal of
                                    11-12

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65 percent is thereby chosen  as  a representative  figure and will  be used in example
calculations.

         11.3.1.4       Summary  of Calculation Procedures

The calculation procedure is described for various chemical addition points and is illustrated
with  a  specific example  in  Section 11.3.1.5.   Factors involved in that example  are
summarized here.

                            Chemicals Added to Primary

Chemical sludge is calculated on the basis of the phosphorus level and the chemical dose
in the manner illustrated in  Table 4.  Estimated mass should  be increased by  about
35 percent (see Section  11.3.1.1).

Additional suspended solids  removals in primary treatment are estimated using quantities
derived  per Section  11.3.1.3.   The additional suspended solids mass removed should be
added directly to  total sludge mass.

Mass  resulting from  dissolved  solids  removal has to be estimated  indirectly from soluble
TOC, COD or  BOD  removal.  Factors to  be  used in predicting mass have been discussed
in Section  11.3.1.3.   Equations relating soluble TOC, COD and BOD input levels to mass
of soluble  solids removed are summarized below:

     (soluble solids  mg/1)        =   STOCm(mg/l)x0.30x2.5xl.l8

                                 =   SCODin(mg/l)x0.30x l.lxl. 18
 The last two equations  apply  only to influents before oxidative processes  such as the
 activated  sludge process.

 Estimates of total  TOC,  COD or BOD removals are needed to estimate  the loading on
 the  biological processes  which follow  chemical treatment.  However, this information is
 not needed for estimating sludge formation in the chemical treatment step.

                        Chemicals Added to Activated Sludge

 The chemical sludge is  calculated  in  the manner described in  Section  11.3.1.1.
                                     11-13

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Addition of chemicals to the activated sludge process may produce a significant increase
in BOD and suspended solids removals.  This is particularly  true of a high rate activated
sludge plant or an overloaded  plant.   However, for a well-designed standard rate plant
addition  of chemicals will produce little additional sludge other than the chemical sludge
itself.  It is recommended that for a standard rate plant no  increase in mass be included
for additional suspended solids.   For special cases such as  an existing high rate plant,
judgment will have  to  be made  based on  available  information.

                     Chemicals Added After Biological Treatment

The chemical sludge is calculated  as in Section 11.3.1.1. If the tertiary  treatment follows
a standard rate activated sludge plant, additional sludge from improved suspended solids
and dissolved BOD removal can be  neglected.    For a trickling  filter plant, however,
additional  mass  removed  could be  important.    For one  plant (20)  a  substantial
improvement in BOD and solids  removal in a high  rate trickling filter plant resulted from
alum addition  before the final clarifier.   In one  series of  runs,  overall BOD removals
increased from 73%  to  91% and suspended solids removal increased from  70% to 84%.

At another plant (21),  under  conditions where  the final clarifier  was not hydraulically
overloaded, alum added after a standard rate trickling filter  brought BOD and suspended
solids from the  15-20  mg/1 levels to below  10  mg/1.

These results can be  used to calculate additional sludge brought down  with the chemical
sludge.

          11.3.1.5       Illustrative Calculation

Sludge  mass is calculated here  for a plant utilizing  primary  treatment with aluminum
introduced before  clarification, followed by  standard rate  activated sludge.   Details of
the calculation are presented in Table 11-6.  The existing  plant  is a  properly designed
plant operating within its design limits, which is changed only by introduction of a means
to  inject the  chemical and flocculate it  before  primary clarification.
                                    TABLE  11-6

       CALCULATION OF TOTAL SLUDGE MASS WITH METAL ADDITION

 Given:    Plant utilizes primary  clarification followed by standard rate activated sludge.
          Alum is to be added in a flocculation tank prior to the primary clarifier. Estimate
          the additional sludge produced  by alum  addition.
                                      11-14

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Primary clarifier of the existing plant is designed for 50%  suspended solids
removal (without chemical).  Activated sludge plant is designed for an F/MLVSS
ratio of 0.4.

Overall phosphorus removal is to be 90%. Estimate that this can be achieved
at an Al/P atomic ratio of 2.0.

     Influent  to Primary:                         P          10 rng/1

                                       Total BOD    =     172 mg/1

                                  Suspended Solids    =     240 mg/1

                                      Soluble TOC    =     40 mg/1

Sludge from Primary Treatment -  No Chemicals

Estimate 50% SS  removal, 30% total BOD removal and 0% STOC removal.

                      240  x 0.50 -  120 mg/1

Sludge from Primary Treatment -  Alum  Added

Estimate 90% P removal, 85% SS removal, 65% total BOD removal and  30%
STOC removal.

Al Dose:         (10/3I)(2)(27) =   17.4 mg/1

                     10 x  0.90 =    9.0 mg/1 P removal

                          9/31 =   0.29 meg (milliequivalent)/1  Al PO4

                       17.4/27 =   0.64 meg/1  Al

                   0.64 - 0.29 =   0.35 meg/1  Al  excess

                   0.29 x  122 =   35.4 mg/1 Al PO4

                     0.35 x 78 =   27.3 mg/1 Al (OH)3

                   35.4 +  27.3 =   62.7 mg/1 sludge produced

Chemical Solids:  Increase by  35%, per  Section 11.3.1.1
                   62.7 x  1.35 =   84.5 mg/1


                          11-15

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Suspended Solids:    240  x 0.85                  =    204 mg/1

Dissolved Solids:     40xO.30x2.5xl.18             =    35.4 mg/1

                           Total Sludge:              323.9 mg/1

Sludge from Activated  Sludge  -  No Chemicals

Equation from  Section 11.3.1.2

                    Wy/F  =    (0.79) -  (0.0714/F/M)

F/M is given as 0.4

     Wy/F = 0.79  - 0.18 = 0.61  Ib VSS/day/lb  BOD removed per day

                           or 0.61  mg VSS/mg BOD removed

BOD  in primary effluent is:

         172 x 0.70       =    120 mg/1

BOD  in final effluent is  estimated to be  almost  12 mg/1. See reference  (6).

           BOD removed   =    120 - 12 = 108 mg/1

  Therefore,  108 x 0.61    =    66  mg/1  VSS  produced

Assuming  the sludge is 70% volatile,

             66/0.70       =    94  mg/1  waste sludge

Sludge from Activated  Sludge  -  Al to Primary

BOD  in primary effluent is:

         172 x 0.35       =    60.2 mg/1

This is a very dilute  waste.  The existing activated sludge plant will be greatly
oversized.   Air  requirements and the  contact time  may be reduced.

Keeping F/M the same (0.4),

                  WV/F     =    0.61  (see above)


                           11-16

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         Estimate  BOD in final effluent to be 12  mg/1 (see  above).

                  BOD removed      =   60.2 - 12   =  38.2 mg/1

           Therefore,  38.2 x 0.61    =   23.3 mg/1  VSS  produced

         Assuming sludge  is 70%  volatile,

                    23.3/0.70        =    33.3 mg/1  waste sludge

         Summary of  Sludge Quantities  Calculated


                                          Sludge Quantities  (mg/1)
                                         No Chemical    Al Added

         Primary  Clarifier

         Sludge from  SS                    120           204

         Sludge from  Dissolved Solids         0            35.4

         Chemical Sludge                     0            84.5

         Total Clarifier Sludge               120           323.9

         Secondary Clarifier

         Waste Activated  Sludge              94            33.3

         Total Sludge                       214           357.2

         Total Sludge Excepting
            Chemical Sludge                 214           272.7
It is clear that chemical addition produces a substantial increase in the total sludge mass.
The increase is greater than just the amount of chemical sludge because, in the no-chemical
case, there is substantially more conversion of organic substances to  carbon dioxide and
water.

For a plant in which the chemical is added  to the activated sludge process, the increase
in mass will be virtually all due to the chemical sludge, since essentially the same amount
of biological degradation is occurring as in the  no-chemical case.
                                     11-17

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In the illustration, total sludge production (mass) was increased 67 percent when adding
aluminum.    The  chemical  sludge  increased sludge mass  40 percent.  The additional
27 percent sludge came  from  organic material  which would have been oxidized had it
reached the activated sludge aerator.  If the chemical had  been added  to the aerator,
sludge mass would have only increased 40 percent.  The greater sludge  mass which results
when the chemical is added to the primary must be balanced against the reduced dimensions
of the activated sludge aerator, the reduction in quantity of air needed, any differences
in the dewatering  properties of the different sludges, and differences in chemical demand
which may be dependent on  point of addition.

         11.3.2        Lime  Sludges

Lime is utilized for  phosphorus removal in  wastewater treatment by adding it just prior
to primary clarification or  after secondary clarification as a tertiary  treatment process.
As in  the case of metal addition to wastewater, average values  for the amount of sludge
produced have been tabulated  (6).  However, there is need for  more precise information
applied to  specific situations.

In response to this need, a procedure has been developed for predicting the mass of sludge
produced  when wastewater is treated with  lime  in a  tertiary  process.  Details of  this
procedure  are presented in  this  section.   The method  may  be  applied with minor
modification  when lime  is  added just prior to the primary  clarifier.

Unlike metal addition, the amount of sludge  produced by lime addition depends not only
on the degree of phosphate  removal desired, but also on alkalinity and other characteristics
of the wastewater.  In fact,  both   the amount  of sludge produced  and the degree of
phosphorus removal achieved by raising the pH to a given level both depend on the nature
of the water.

The  procedure in predicting sludge  quantity requires first  that  pH level be estimated for
the  desired phosphorus removal, then lime  dose is estimated, and finally sludge mass can
be calculated.  The individual steps are listed  below:

         a.   From desired P-residual and knowledge of the water type, estimate
              pH level.

         b.   From pH  level and alkalinity, estimate lime dose.

          c.   From amount  of P removed, calculate the hydroxyapatite sludge
              produced.

          d.   From magnesium removal, calculate magnesium hydroxide sludge
              produced.
                                      11-18

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         e.   From  calcium  balance,   calculate   calcium  carbonate  sludge
              produced.

         f.   From pH and alkalinity, verify that sufficient carbonate is present
              to supply  carbonate  in sludge.  If not, correct  outlet  calcium
              estimate.

         g.   Include in  total sludge production the inerts introduced with the
              lime.

If lime is added prior to the primary settler, the procedure for estimating sludge for tertiary
lime addition may be  used  with some modification.  However, the  correlation  between
pH  and the ratio of lime dose to alkalinity was developed from data obtained by adding
lime to  secondary effluents.  There is no assurance  it would fully apply to raw wastewater.
It would thus be  desirable  to establish  lime dose needed by actual tests.

When lime is added  prior to  the  primary settler, efficiency of the clarifier is increased
substantially.  From a previous review (12), it  is estimated that for well designed plants,
suspended  solids removal efficiencies  are in the  order of 85 percent.  This figure may
be  used to estimate additional  sludge solids removed in  the  primary  clarifier  by lime
addition.

The removal of dissolved organic solids  by  addition of lime prior to  the primary appears
to  be less  than obtained with metals.  One study (14) reported very small or  negative
removals.   Others  (17) reported substantially lower removals with lime than with metal.
Considering the relatively large  mass  of sludge from  lime treatment,  the  small amount
of  dissolved  organic  solids  brought down  in primary treatment  can  be neglected.

Some prior data (14) have been utilized to estimate whether material balance  calculations
similar  to  those described above correlate  with measured sludge  production. This case
is discussed in Section  11.4.2.2.  Measured values  were about 20 percent higher  than the
material balance figures.   It is probably advisable to utilize a factor of safety of this
magnitude  in estimating  chemical sludge production.

          11.3.2.1      Estimation of  Lime Dose  and Sludge  Production  in  Tertiary
                       Treatment

A quantitative calculation procedure for  estimating the required lime dose and the  quantity
of  sludge produced in  tertiary treatment of wastewater with lime is presented.  On-site
testing  for obtaining this information is recommended in specific  plant  designs.
                                     11-19

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          11.3.2.2      Lime Dose

The extent of phosphate removal is a function of a number of variables including chemical
composition  of the  waste water and  the nature of the phosphate  compounds contained.
The most important variable controlling phosphate removal and quality of effluent is pH
rather  than quantity of lime added.  Figure 11-1, reference  (22), shows a correlation of
P-removal as a function of pH, utilizing  data  from several  sources.

Another factor of importance is the hardness level of the wastewater.  In some cases (23)
it was necessary to go to pH in excess of 11 to get good clarification with the low hardness
water.  Others  (24) obtained satisfactory clarification at pH of about 10  in the hard water.

The chemistry  of lime-softening of natural waters is sufficiently well developed that the
charge  of lime required to achieve a given removal of calcium and magnesium can be
predicted  and  the final pH can be closely estimated.  With  wastewaters, suspended  and
dissolved  organic materials as  well as ortho  and polyphosphates  apparently affect lime
dosage required and can  cause  super-saturation of precipitating species.  Typically, lime
dose required  to reach a given pH  is higher than predicted from softening equations.
Likewise,  calcium and magnesium content of the product  water is higher than would be
predicted  for lime  treated natural waters.

A  correlation for estimating lime  dose  needed to bring a secondary effluent to a given
pH is presented in Figure 11-2.  It is based on data from several sources (23-27).  The
pH is reasonably well  correlated with the ratio of lime dose to initial  alkalinity.   Other
factors which  affect the  result are ratio  of  magnesium to calcium, ionic strength,  and
the phosphate level.  The effects caused  by these variables can be estimated, and computer
programs  have been developed  to make the  necessary  calculation  (22) (28).  However,
the accuracy of these calculations  is provisional because of the  uncertain effects of
contaminants in  wastewater.

Figure  11-2  can be utilized to predict  lime dose if an estimate of the desired pH level
can be made.   The curve is entered at  the ordinate, and  the abscissa,  the ratio of CaO
dose to alkalinity,  is  read from the graph.  If alkalinity  of the water is known,  active
CaO dose  can be calculated.  Total quicklime  dose can be calculated from active CaO
dose and  the active CaO content of the quicklime.

          11.3.2.3       Sludge Production

The principal reactions for estimating lime sludge  production axe:
                                     11-20

-------
                         FIGURE 11-1

          EFFECT OF pH ON TOTAL RESIDUAL PHOSPHORUS
   1.0
0)
E
   o.i
                                             '        I
                                         A POMONA
                                      ODX BISHOP (BLUE PLAINS)
                                         V BERG (LEBANON)
                                          NEVADA POWER CO.
                                         <  SOUTH TAHOE
      	 D
                       LOG P=3.51 - 0.392(pH)
     9.0
                                                      O
10.0
11.0
12.0
                             PH
                        11-21

-------
                               FIGURE 11-2

             RATIO OF LIME DOSE TO ALKALINITY (BOTH MG/L)
                       FOR A PRESCRIBED FINAL pH
                         1  1   1
   12
a:
LU
    10
I  9
 a
I  3
                                            ALKALINITY
SYMBOL  ALKALINITY REF  LOCATION
        (mg/l)
        100-125

         226

        440-460

         277

         450

         300
2  WASH., D.C.

4  S. TAHOE, CA

5  NINE SPRINGS, Wl

3  LEBANON, OH

6  LEBANON, OH

6  BATAVIA,  OH
            0.3       0.5    0.7    1.0          2.0
                             CaO/Alkalinity
              3.0
                      5.0
                              11-22

-------
         5Ca(OH)2 +  3HP04~-  -   Ca5OH(PO4)3 + 6OH~ +  3H20  (1)

         Mg++ +  2OH~  >   Mg(OH)2                             (2)

         Ca(OH)2 + HCO3"  "  CaCO3 + H2O + OH"            (3)

The information required and the steps to take in estimating the sludge production are
listed  below.  Informational input needs  are marked  with an asterik.


                                 TABLE 11-7

         INFORMATION NEEDED TO  CALCULATE LIME SLUDGE MASS
Information Needed

A.  P*in> desired P removal*
    (sometimes,  BOD^, desired BOD
    removal).  Results of jar  test
    or experience*

B.  Alkalinity of wastewater*, pH
    level, Figure  11-2
C.
D.
       ,  P removal, Equation 1
         , from analysis or estimate*,
         j, from  analysis or
    Figure 11-4, Equation 2
E.  Ca^, from analysis  or estimate*,
    CaQUf, from analysis or
        Figure 11-3,
    Ca from lime  dose  (see  item  B),
    Ca removal in HAP (see item C),
       Equation 3

F.  pH (see item A)
                                               Determination
                                               pH level
                                               CaO dose
Ca5OH (PO4)3(abbrev.:HAP)
             precipitated

Mg(OH)2 precipitated
                                               CaCO3  precipitated
                                               Verify that sufficient CO3
                                               is present.  If not,
                                               estimates of Caou^ were in
                                               error.
                                  11-23

-------
G.   Active  CaO  in  lime*                          Inerts brought in with
                                                   quicklime.
The  procedures for steps A and B have already  been presented.   Step C  requires no
explanation.   If estimates of Mgou^ and Caouf. are needed for steps D and  E, available
data (24) can be used as shown in Figure  11-3 and Figure  11-4.  They show the calcium
and  magnesium levels obtained at the clarifier outlet in long-term evaluation of tertiary
lime treatment of secondary effluent.  Magnesium (Figure  11-4) precipitation commences
at pH  10 and is essentially complete at pH  11. The percent in solution could be estimated
as declining from 100% at pH 10  to 0 at pH  11.

The  calcium  concentration (Figure 11-3)  is seen to  decline precipitously when pH is
increased  to 9.5.  Concentration then increases as pH is increased further.  This behavior
is rational in light of knowledge of bicarbonate-carbonate equilibria. When pH is increased,
bicarbonate ion is converted  to carbonate ion.  When the solubility product of CaCOg
is exceeded, precipitation occurs and Ca concentration falls.  As pH is increased further
by  more  Ca(OH)2 addition, eventually  all of COj is removed by CaCO^ precipitation.
Calcium  concentration  then increases as calcium hydroxide  dissolves to the limit  of its
solubility.

Step E outlines the calculation of calcium carbonate precipitation.  The calcium carbonate
deposited is calculated  from a calcium balance. After  considering the amount of calcium
removed in the hydroxyapatite (Ca5OH (PC^^),  the  CaCC^ is calculated from the net
loss  of calcium.

A verification  step is advisable to  determine  whether there is sufficient becarbonate to
account  for the  CaCOg produced.  Bicarbonate can be determined  from alkalinity. At
pH below about 8.3, all  of alkalinity measured is due to bicarbonate.  At pH below 7,
there is more  potential  carbonate available due to the presence of dissolved carbon dioxide,
which  is  not  measured in  the alkalinity test.  Estimates of dissolved CC>2 can be made
by  following  procedures outlined in "Standard Methods"  (29).  If the  bicarbonate is
insufficient to balance with lost  calcium calculated from  the material balance, calcium
in the  final effluent was estimated at too low a value. There is little likelihood of this
problem at pH levels below  about 10.8.

The entire procedure described, including the  verification step  and the totaling of all of
the  components  of the sludge, is shown in the illustration in Table 11-8.  It is evident
from the total quantities listed  at  the  end of the  table that calcium carbonate makes
up about three-quarters of the mass  of the sludge.   For this reason, substantial errors
could  occur in estimates of the other sludge quantities without  introducing much  error
into the final result.

-------
                   FIGURE 11-3


      PRECIPITATION OF CALCIUM BY LIME ADDITION
      100
 O)
 E
Zc*
w <

-------
                     FIGURE 11-4


       PRECIPITATION OF MAGNESIUM BY LIME ADDITION
       40
 O)

 E
O 
       30
< u
   U.
   LU  20
       10

                              I    I
  AVG INFLUENT .*v^

CONCENTRATION.^r-'-.
                  8
                        10
11
                    11-26

-------
                                 TABLE 11-8

                   CALCULATION  OF  LIME  SLUDGE  MASS


              Illustration of Procedure  for Estimating Sludge Quantity


Secondary Effluent Characteristics

         Phosphate Content                             10  mg/1  as P
         Alkalinity                                   300  mg/1  as CaCO3
         Calcium                                     100  mg/1
         Magnesium                                    20  mg/1

Treatment Conditions

         Remove  85% of phosphate by raising pH  to 10.5
         Final Phosphorus
          Content                                   1.5 mg/1 as P
         Estimate of Ca
          (Figure 11-3)                                50 mg/1
         Estimate of Mg
          (Figure 11-4)                                10 mg/1

Lime Dose

         From Figure 11-1, 0.92 mg CaO/mg alkalinity  at pH  10.5.
             Dose = 0.92 x  300 = 276  mg/1 CaO

         Assume quicklime is 90%  active  CaO

             Total quicklime - 176/0.90  = 307 mg/1

             Inerts with quicklime = (0.10)(307) = 30.7  mg/1

Sludge  from Phosphate

         (10 - 1.5)(502/93) = 45.8 mg/1  Ca5(OH)(PO4)3

Mg(OH)2 in Sludge

         (20 - 10)(58.3/24.3) = 24.0 mg/1 Mg(OH)2



                                  11-27

-------
Sludge from CaCOj Precipitation

         Input Ca = 100  from sec. effluent + (276)(40/56) from lime dose

         Output Ca =  45.8 x (5)(40)/(502) + 50                + Y

              (removed with              (remaining             (precipitated
              hydroxyapatite)             in solution)            as  CaCO3)

         Y =  100 + 197  -  18.3 - 50 =  129 mg/1

              129  x (100/40) = 323 mg/1  CaCO3  precipitated

         Total Sludge

         Inerts in  quicklime                                   30.7
         Ca5OH(PO4)3                                        45.8
         Mg(OH)2                                            24.0
         CaCO3                                             323.0

                                        Total         =      433.5  mg/1

Verification that Sufficient CO3 is Present

         300  mg/1 alkalinity (as CaCO3)

         300  x (1/50) =  6.0 g-equivalents  (or g-mols) HCO3

              HCO3 + Ca"1"1" + OH"   -  CaCO3 + H2O

         6.0 g-mols HCO3 can produce  6.0 g-mols CaCO3

              6.0 x  100 =  600 mg/1 CaCO3

         The  CO3 available could produce as much as 600  mg/1 CaCO3. This
         is substantially greater than the  amount calculated above (323 mg/1)
         from the calcium balance.  Thus, there is ample CO3 present. If there
         were insufficient CO3 (which can happen at ph of 11 and greater),
         it would indicate  that the  estimate of Ca++ after treatment was too
         low.  The amount  of CaCO3 indicated by  the calculation from the
         alkalinity would be  correct.
                                    11-28

-------
Additional Sludge from  Recarbonation

          Recarbonation  to  pH  9.5  will  reduce Ca concentration  to about
          30 mg/1 (see Figure  11-3).   For this example, the additional calcium
          carbonate sludge produced  is  calculated  as follows:

                        (50  -  30)(100/40) = 50 mg/1 CaCG>3

 11.4      Dewatering  at  Specific Locations

          11.4.1         Tertiary  Treatment  with Lime

          11.4.1.1       South Tahoe

At  South Tahoe, California, wastewater is treated  in conventional primary, followed by
a waste activated sludge  plant.  Phosphate is removed by tertiary lime treatment to pH 11
with  recarbonation.  A  comprehensive report describing the performance of the Tahoe
plant and sludge  dewatering aspects  has been published (25).

The tertiary lime sludge is dewatered and classified at Lake Tahoe by  means of solid
 bowl centrifuges.  Sludge is thickened to 8 percent solids.  It then flows at about 20  gpm
 to  a  75 HP Bird 24"  x 60"  solid-bowl  concurrent-flow  centrifuge.  The  centrifuge is
 deliberately  operated  with high losses  to the centrate in order to  reject magnesium
 hydroxide,  hydroxyapatite and  organic  solids,  leaving behind a high  concentration of
 calcium  carbonate in  the  cake.  The cake is calcined and  is recovered.  The centrate is
 sent  to  a second centrifuge, polymer is added, and solids  are removed as  a 30% solids
 cake.

 The fact that a  centrifuge tends to reject fine low-density solids may lead  to fears  that
 fine solids will build up in the system.  This has apparently not occured at South Tahoe.

          11.4.1.2      Blue Plains  Pilot Plant

 At the Blue Plains pilot plant, a substantial amount of information  was obtained on the
 sludges  produced  by  treating secondary  effluent  with lime.  This  information  will be
 published soon  as a report  in the EPA series (30).

 Secondary effluent from the District  of Columbia's Blue Plains Treatment Plant was treated
 with lime to a pH range of  11 to 12 for phosphate removal. Instead of utilizing second-stage
 recarbonation to remove excess Ca ions and recover additional calcium carbonate, sodium
 carbonate was added  to the single clarifier for  this purpose.  The sludge produced was
 continuously thickened, vacuum filtered, calcined,  slaked  and  recycled  to the  tertiary
 clarifier to supply the bulk  of the lime demand.  Information on sludge thickening and
 dewatering was  obtained  with and without recycle of reclaimed lime.
                                      11-29

-------
Most  of the data during recycle  operations were obtained at 56  percent  recovery; that
is,  56 percent  of  the  active  lime  dose  consisted  of  recycled  lime.    Recycle was
approximately  3 pounds of recycled solids to  one  pound  of fresh lime.   Lime  dose
consisted  of 300 mg/1 of active  lime plus 240 mg/1 of  inerts.

Buildup of inerts did not affect phosphorus removal but increased solids loading through
the sludge handling system.  Solids content of sludge removed from the clarifier was 20  g/1
for no-recycle  operation  and 32  g/1 for 56 percent  recycle.

The sludge  was  thickened  in a 6-foot  diameter vessel equipped with pickets.   Sludge
thickened to 15-20% solids for recycle as well as no-cycle operations, despite solids loading
rates  over 70 percent higher for the recycle  case.

Information  on filtration was obtained from  filter leaf tests.  Equations for form rate
for the recycle and  no-recycle cases were developed.  These equations, rearranged slightly
to  give results in terms of yield and cycle time, are:

          No Recycle:   Y =  (2.18) (f)-5(Q '84 (p) '21/ (0) '5

          Recycle:       Y =  (3.28) (f) -5 (C) -80 (p) -26 / (0) -5

          Where         Y =  yield, Ib/hr-sq ft

                        0 =  cycle time (min), or  reciprocal of rpm

                        C =  Solids concentration,  wt %

                        p =  operating  vacuum, in. Hg

                        f =  fraction submergence

Calculating  filter yield at the following conditions,

                        f =  0.25

                        C =  15% solids

                        p =  15"  Hg vacuum

                        0=1 min.  (i.e.,  1  rpm)
                                      11-30

-------
gives  the  following result:

          No Recycle:   Y =  18.7  Ib/hr-sq ft

          Recycle:       Y =  29.0  Ib/hr-sq ft

This  study  reports  substantial  cake cracking which reduced  vacuum across  the filter.
Nevertheless, solids  contents  from 30-40% were  generally obtained.  It was also noted
that,  after a process upset which caused biological solids to carry over into the tertiary
treatment system, filter yield deteriorated drastically.   However, filtration was possible
without chemical  conditioning.

          11.4.1.3       Butler, Indiana

At  Butler, wastewater is treated in a 0.4 mgd conventional primary plus trickling filter
plant.  Primary settling precedes two-stage biological filters. Conventional sludge is digested
and dried  on beds.  Phosphorus  is removed by  tertiary lime in a reactor-clarifier at pH  10.
Chemical  dose  is  150 mg/1 quicklime  plus  ferric chloride and polymer to aid settling.
Total phosphorus removal is about 80  percent.   Sludge  is not dewatered and is pumped
to  a  lagoon.

The Butler  plant is somewhat  unique  in that the wastewater is quite hard (300 mg/1)
and its magnesium content is high (30  mg/I).  Ordinarily, good phosphorus removal is
achieved in water of this type at a  lower pH than  in soft  low-magnesium water.  Required
phosphorus  removal  was only  80%  and a pH of  10 was sufficient to get satisfactory
performance.

Sludges leaving  the reactor-clarifier  were about  8.4 percent solids.  Overnight settling
increased  this to 9.0 or  9.5  percent.  Lagoon sludge, even after only a few days settling,
was about 17%  suspended solids.  Fresh sludge from the  reactor-clarifier  could be filtered
at 5.6 Ib/hr-sq  ft at a cycle time of 2.9 min and 33% immersion.  Higher yield could
be  achieved at lower cycle times  but this produced cakes less than one-eighth inch thick,
which caused problems  with  cake release.

Sludge was mostly  mineral in nature. Percent volatile solids  was under 10%. Magnesium
content of  the sludge was  low.   At higher pH, more magnesium would  have been
precipitated,  which  could have  produced a poorer filtering  sludge.

          11.4.2         Lime to  Primary Settler

          11.4.2.1       Contra Costa

The Contra Costa Sanitary District, Walnut Creek, California, has carried out pilot  and
plant  scale evaluations of an integrated process for handling sludges produced by adding
                                     11-31

-------
lime to primary wastewater treatment. This work has been reported (31) and is discussed
in Chapter 5.

The treatment process comprises lime flocculation with polymer or ferric chloride followed
by  primary sedimentation,  activated  sludge under conditions such that nitrification is
achieved, denitrification with  methane addition, and chlorination.  Waste activated sludge
is recycled to the raw sewage to be removed from the primary  clarifier along with  the
chemical-primary sludge. Denitrification sludge is also returned to the incoming raw sewage,
but its amount  is negligible.

In  addition  to  investigations  of  process  performance,   studies  were  made   to
evaluate  (a) predictive  methods for  estimating sludge  production,  (b) the  degree  of
thickening achieved in primary clarification, (c) the utility of two-step procedure in which
sludge is  centrifugally classified to recover calcium carbonate and the centrate is centrifuged
again to  remove solids,  and (d) anaerobic digestion of  the  first-stage  centrate.

Sludge mass predicted from  analysis  of influent and effluent analyses checked satisfactorily
with measured sludge mass.  Operation at pH 10.2 produced a clarifier sludge of about
4.0 percent solids.   At  pH  11, higher sludge  solids could be  attained.   Centrifugal
classification achieved an 80% recovery  of  calcium carbonate in  relatively  dry  cakes of
42-57% solids.  Solids  remaining in the centrate could be removed by  polymer-assisted
second-stage centrifugation  at recoveries as  high as  90%.   Results were not as  good at
pH greater than 11. The centrates from the first centrifugation  could  be  anaerobically
digested,  although  volatile  solids   reduction  was lower than  for conventional sludge
processing. In addition, precipitated  magnesium redissolved in digester supernatant. Return
of  supernatant  to  process  would  increase lime  demand  and  magnesium would  be
precipitated again.  It is  believed that handling of supernatant by separate  treatment or
return to the secondary  process would  avoid that problem.

          11.4.2.2       Eimco  at Salt Lake City

Eimco Division  of Envirotech has  conducted a 100  gpm pilot  plant investigation of a
wastewater treatment system in which chemicals are added in the primary step and soluble
organic material is removed by  powdered activated carbon.  A progress report on  this
investigation has recently been published (14).

Comparisons of sludge  mass  calculated  from  clarifier input and output analyses  with
measured mass  showed reasonable  agreement.  When iron  was added  to  the  primary,
measured mass was  20%  higher than the calculated value.  However,  this additional mass
appeared  to include removal of soluble  organics.  When adding alum, calculated value
(including  soluble organic material) was virtually  the same as the measured value.   For
lime, measured  values  averaged  20%  higher than  calculated values.
                                      11-32

-------
Thickening and filtration  data were incomplete for iron and alum.  However, data with
lime were developed.  After 24 hours thickening, sludges  with pH values greater than
11.5 thickened to 2.0 to  9.8% solids, with median  near 7%.  For pH values less than
11.0, sludge  thickened to 9.0  to 18.0%  solids, with  median near  14%.

Filtration yields were obtained for high and low pH operation.  No polymer was needed.
For  low pH sludge at the  14% thickened solids content, maximum  filter yield was
6.0 Ib/hr-sq  ft.  For high pH sludge  at the 7% thickened solids content, maximum filter
yield was 3.0 Ib/hr-sq ft.

It should be noted that Salt Lake City wastewater is high in magnesium.  Operation  at
pH greater than 11.5 precipitates much more magnesium than precipitated at pH less than
11.0.  Since  magnesium hydroxide is a flocculant precipitate, this could account for the
low  solids  content of thickened sludge  from high pH operation.

          11.4.2.3      Cleveland Westerly

Extensive pilot plant work was  conducted at Cleveland's Westerly  plant preliminary  to
preparing a  design for a physical-chemical treatment plant. A report describing this work
is in progress (32).

Most of the  work was done  with lime added prior to the primary to reach a pH of 10.5.
Sludge  was  dewatered using a Bird pilot  plant centrifuge and  an Eimco belt-type pilot
plant vacuum filter.

Sludge solids content leaving  the clarifier was in the range of 6% to 14% solids. Thickening
prior to centrifugation was not needed. Solids recovery in the centrifuge was poor without
polymer. However, polymer doses of less than 2 Ib/ton gave recoveries of 95%.  Solids
content of  the sludge cake  ranged from  20  to  28 percent.

The lime-primary sludge could be filtered without polymers but performance  was improved
greatly   by  addition  of  small  quantities  of polymer.  Filtration  yields  in  excess  of
10 Ib/hr-sq  ft were recorded. Recoveries of solids were in the order of 95%. Cake solids
ranged  from 20  to  35%  with 28%  a typical value.

          11.4.2.4      Canadian Experience

The Province of  Ontario's Ministry  of the Environment has  carried out  a number  of
plant-scale testing programs at sewage treatment  plants. This work has been summarized
in several reports (33-35).   Some of that information (34) is summarized here.

The use of  lime in activated sludge  plants increased sludge production from a normal
level of about 180  mg/1  to  460 mg/1 during addition  of 200  mg/1  slaked  lime.  Sludge
solids content increased from 4.5% to 9%.  In  primary plants, sludge  production increased
                                     11-33

-------
from  80 mg/1 to  240 mg/1.   Sludge solids content  increased from  7%  to  15%.

Some difficulty was encountered with anaerobic digestion because of erratic dosage with
high pH sludge.   Subsequent studies have  shown  that holding the sludge longer in the
clarifier results in  a  fall in sludge  pH.  Digester operation is then normal except for high
solids content of  the  sludge.

Raw lime sludge was  dewatered successfully  in  a  continuous solids  bowl conveyor-type
centrifuge at the Newmarket/East Gwillimbury plant (36). A detailed investigation showed
high recoveries  could  be achieved  with polymer  addition.   At  these  high recoveries,
phosphorus  removal from the  centrate was also high (37).

With lime added to  the primary of  a conventional plant  (primary plus activated sludge),
filter yield increased from 5.2 to 7.2 Ib/hr-sq  ft, and  conditioning costs (lime plusFeClj)
fell from $16/ton down to  $1 I/ton.   Cake  solids content was  29%.

          11.4.3        Alum  and Iron Salts

          11.4.3.1       Blue Plains

Alum was added to the  300 mgd wastewater treatment plant at Blue Plains, Washington,
D.  C., for several months.   At this plant, primary  treatment  is  followed by  high rate
activated sludge.   Waste activated sludge is combined with sludge withdrawn  from the
clarifier, and the mixed sludge is thickened and digested. The digested sludge was elutriated
in two stages using polymer  to retain solids.  The sludge was filtered using polymer and
ferric chloride for  conditioning. The following information  on alum addition tests is based
on  discussions with plant operating personnel.

Alum was added  to the aerator in  gradually increasing dose until the average  dose was
40  mg/1 of alum  (9.1% Al).  This developed a relatively high  level  of aluminum in the
sludge because the Blue Plains wastewater is weak.

Alum addition did not affect thickening. Sludge leaving  the thickeners remained at 7.5%
solids. Digestion was likewise unaffected. Suspended solids leaving the digesters remained
at 3.5%.  Elutriation could be  carried out but a high polymer dose was required  to retain
suspended solids. Chemical costs for elutriation increased from $3/ton before alum addition
to  $7/ton  during  the  test.   Filter yields were  about the  same as with  prior operation,
but solids  content of  the cake dropped from 23% to 20%. Polymer condition cost for
filtration, which had  been $6/ton,  rose to $7/ton.

          11.4.3.2       Pomona

At  Pomona, California, a physical-chemical  plant has been in operation to produce a feed
stream  for  a long-term  test  of carbon  columns.  The wastewater has been treated in  a
                                     11-34

-------
primary clarifier with 22 mg aluminum per liter.  A field test was conducted to determine
the dewatering characteristics of this sludge.  That unpublished  report (38) is summarized
here.

Gravity thickening tests showed that, without polymer, sludge settled slowly. Thickening
rate  to produce a 4% solids  sludge was quite  low at 6.6  Ib/day-sq ft.  With polymer
addition, that  rate  increased  to  20 Ib/day-sq ft with  2  Ib/ton  of anionic  polymer and
to 70  Ib/day-sq ft with  6 Ib/ton.  Filtration rates with 12% lime  and polymer were less
than 2  Ib/hr-sq ft at the  low cycle  time of  2  min.  However, the  sludge employed was
only 2% solids.  Rate would  be expected to increase proportionately if thicker sludge
were available.

One  of the  reasons this field  test was conducted was to verify other data indicating that
sludges  produced when metals are  added to the primary  settle poorly and have lower
filter yields  than conventional sludge.  The Pomona field test corroborated these findings.

          11.4.3.3      Grand Rapids

The addition of ferric chloride at various points in the process was studied at Grand Rapids,
Michigan. The Grand Rapids plant has a conventional primary followed by activated sludge.
The  ferric  chloride  was  added in three different modes:   to the primary alone,  split
between the primary and the aerator, and to  the aerator alone.  An investigation of sludge
dewatering  was not  part  of this  project.  However, it was hoped that the filter yield
data routinely collected  at  this  plant  could  be  related  back  to the chemical  dosing
conditions.

Monthly average filter yields, cake solids, and chemical costs were supplied by Grand Rapids
staff and are presented in  Figure  11-5.  Large fluctuations in all three  filtration variables
are evident; however,  they are not correlated with ferric chloride dosing.  This finding
was predicted  by  Grand  Rapids staff who observed that  the  basic nature of the sludge
can change  from month to month and that necessary maintenance can cause step changes
in performance.  Some of the interferences noted at Grand  Rapids were:

         a.   Periodic  dumping of lime sludge from  a  water plant into the
              wastewater  collection system.

         b.   Performance changes in digestion.

         c.   Acid  cleaning of filter  cloths.

         d.   Cleaning of interior piping of vacuum filters.

         e.   Replacement of vacuum  system.
                                     11-35

-------
                                                                                 in
                                                                                 cc
                                                                                 D
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                                  11-36

-------
         f.   Periodic switch-over  from the incinerators, which  had a lower
              capacity than the vacuum filters and needed a dry cake, to landfill,
              where maximum output was desired and a dry  cake was not so
              important.

          11.4.3.4       Canadian Experience

Reference has been  made in Section 11.4.2.4 to the work reported by Ontario's Ministry
of the Environment.  Additional information from a summary paper (34) is included here.

When metal salts were utilized in activated sludge secondary plants, the dry solids sludge
production increased 5% to 25%.  Sludge concentration dropped slightly to 3.5 to 5.0%
from  the  normal 4.0 to 5.5%.

In primary  plants,  sludge  production increases substantially because  of increased solids
capture.  An increase of  100% was typical and 20% reduction in sludge solids  concentration
was reported.

In all cases where metal salts were  used  to precipitate phosphorus, normal digestion  was
observed.   Problems which developed were the result of increased hydraulic and volatile
solids loading.

Filtering rates were approximately halved for a primary plant when alum was added. Lime
and ferric chloride  conditioning  costs increased  from $3.10/ton to  $9.50/ton.  Solids
content of  cake  dropped  from 31% down to  19%.  For a secondary plant with alum
added to  the  primary, filtering rate fell from 5.2 to 4.8 Ib/hr-sq  ft, and conditioning
chemical cost increased  slightly.  Cake solids was typically 15.9% with alum addition.

          11..4.3.5       Chapel Hill

Chapel Hill has a 5  MGD trickling filter plant which is conveniently split into two parallel
treatment plants, each with its own primary  clarifier, high rate trickling filter, and final
clarifier.  During an  experimental program, the wastewater from one train was dosed with
alum  for phosphorus removal, just before it entered the  final clarifier. A  field trip  was
arranged to this unique facility to determine the impact of alum addition on the wastewater
sludge.  Unpublished  results (39) are  summarized  here.

Data obtained indicated sludge  from the secondary clarifier following the alum-dosed train
was essentially  unfilterable, even with polymer addition.   Since this was a high-rate filter
with substantial recirculation before  the clarifier, the sludge was very low in organic matter.
The control secondary clarifier sludge showed reasonable filter  yields.  Secondary sludges
from  both trains were recirculated  to  their respective primary clarifiers and removed as
mixed primary-secondary sludges.  Filter leaf tests showed that there  was no substantial
difference in the filter yields  from the two  trains.
                                     11-37

-------
Data supplied by University of North Carolina staff who operate the plant indicated that
4.75 Ib extra sludge was generated per Ib of Al added. They also indicated that difficulty
was encountered during  alum  trials in their two-stage digester:   the solids content of the
supernatant leaving  the  second digester was  unusually high.

11.5     References

   1.     "Process Design Manual for Sludge Handling and Disposal," Technology Transfer,
         U. S. Environmental Protection Agency (1974).

   2.     Smith, R., Eilers, R., "Wastewater Treatment Plant Cost Estimating Program,"
         NTIS  PB  219472 (April, 1971).

   3.     Yeaple, D. S., Barnes,  D. A., and  DiGiano, F.  A., JBF Corp., "A Computer
         Model for Evaluating Local Phosphorus  Removal  Strategies,"  Environmental
         Protection Agency  Contract 68-01-0758,  Draft Report (January 3,  1973).

   4.     Mogelnicki, S., Los  Angeles Technology Transfer  Session (November,  1972).

   5.     Teletzke, G. H., "Sludge  Dewatering by Vacuum Filtration," Rocky Mountain
         Sew.  &   Ind.  Wastes  Assoc.   Annual  Meeting, Colorado   Springs, CO
         (October  24-26, 1960).

   6.     Adrian,  D.  D., Smith, J.  E.,  Jr., "Dewatering  Physical-Chemical Sludges,"
         Vanderbilt Symp.,   "Applications  of  New  Concepts  of Physical-Chemical
         Wastewater Treatment," in  press (September  18-22,  1972).

   7.     Isgard, E., "Chemical Methods in Present  Sewage Purification Techniques," 7th
         Effluent  and Water Treatment Exhib. and  Conv.,  London  (June 25,  1971).

   8.     Mulbarger, M.  C., Shifflett, D. G., "Combined Biological and Chemical Treatment
         for Phosphorus Removal," Chem. Engr. Prog. Symp. Ser. 67, No. 107, 107-116
         (1970).

   9.     Farrell,  J.  B.,  "Alum-Phosphate  Sludges:  Dewaterability  and  Aluminum
         Recovery  by Lime Treatment," In-House Report, Adv. Waste Treatment Research
         Lab.,  NERC,  Cincinnati, OH, U. S. Environmental Protection Agency (June,
         1973).

  10.     Smith, R., "Estimating the  Rate of Sludge Production in the Activated Sludge
         Process,"  Memo (October 10, 1972).
                                    11-38

-------
11.     City of Austin and University of Texas, "Design Guides for Biological Wastewater
       Treatment Processes,"  U.  S. Environmental Protection Agency Water Pollution
       Control  Research Series 11010 ESQ  (August, 1971).

12.     Kreissl, J. F., Westrick, J. J., "Municipal Waste Treatment by Physical-Chemical
       Methods,"   Vanderbilt   Symp.,   "Applications   of  New   Concepts   of
       Physical-Chemical Wastewater Treatment,"  (September 18-22,  1972).

13.     "Process  Design Manual  for  Phosphorus  Removal,"  U.  S.  Environmental
       Protection Agency  (October,  1971).

14.     Burns, D. E., Shell, G. L.,  "Physical-Chemical Treatment of Municipal Wastewater
       Using Powdered Carbon,"  Final Report, U.  S. Environmental Protection Agency
       Project No.  17020 EFB  (1972).

15.     Friedman, L. D., Weber, W.  J.,  Bloom, R., and Hopkins, C. B.,  "Improving
       Granular Carbon Treatment," Water  Pollution Control Research Series 17020
       GDN (1971).

16.     Farrell,  J. B., unpublished  data.

17.     Westrick, J.  J.,  Cohen, J. M., "Comparative Effects of Chemical Pretreatment
       on Carbon Adsorption," 47th Annual Conf., Water Pollution Control Federation,
       Atlanta,  GA  (October, 1972).

18.     Schaffer, R. B., Van Hall, C. E.,  McDermott, G.  N., Barth, D., Stenger, V. A.,
       Sevesta,  S. J., and Griggs, S. H., "Application of a Carbon Analyzer in Waste
       Treatment,"  JWPCF, 37:11, p. 1545-56.

19.     Bunch, R. L., Barth, E. F., and Ettinger, M. B., "Organic Materials in Secondary
       Effluents," JWPCF,  33:2, p.  122-26 (February,  1961).

20.     Brown, J. C., "Alum Treatment of High-Rate Trickling Filter Effluent at Chapel
       Hill, North  Carolina,"  Durham, NC  (April,  1973).

21.     Derrington,  R.  E., Stevens, D. H., and Laughlin, J.  E., "Enhancing Trickling
       Filter Plant  Performance by  Chemical Precipitation," U. S.  Environmental
       Protection Agency,  Grant #11010 EGL,  (July, 1973).

22.     Seiden,  L.,  Patel, K.,  "Mathematical Model  of Tertiary  Treatment by Lime
       Addition," Report No. TWRC-14, FWPCA (September, 1969).

23.     O'Farrell, T. P., Bishop, D. F., and Bennett, S. M., "Advanced Waste Treatment
       at Washington, D.  C.," "Water-1969," Chem. Engr. Prog. Symp. Ser.  65, No. 97,
                                 11-39

-------
       p. 251-58.

24.    Berg, E. L., Brunner, C. A., and Williams, R. T., "Single-Stage Lime Clarification
       of Secondary Effluent,"  Water & Wastes Engr.,  (March,  1960).

25.    South Tahoe  Public  Utility  District, "Advanced Waste  Water Treatment  as
       Practiced at South Tahoe," Water Pollution Control Research Series 17010 ELQ,
       p. 89 (August, 1971).

26.    Malhotra,  S.  K.,  Lee, G. F., and  Rohlich, G. A.,  "Nutrient Removal from
       Secondary Effluent by Alum Flocculation  and  Lime Precipitation," Internatl,
       Jour. Air-Water Poll,  8,  p. 487-500 (1964).

27.    Mulbarger, M. C., Grossman,  E.  Ill, Dean, R. B., and Grant, O.  L.,  "Lime
       Clarification,   Recovery,   Reuse,  and  Sludge   Dewatering  Characteristics,"
       Jour  WPCF, 41:12, p. 2070-85 (1969).

28.    Smith, R., "Calculation of Ionic Equilibria by Means of the Digital Computer,"
       Advanced  Waste Treatment Research Lab., Cincinnati, OH (November,  1966).

29.    "Standard  Methods  for  the  Examination  of  Water   and  Wastewater,"
       13th Edition,  APHA, AWWA, WPCF, Washington, D. C. (1971).

30.    Bennett, S. M., Bishop, D. F., "Solids Handling and Reuse of Lime Sludge,"
       Environmental Protection Agency Contract #14-12-818,  11010 FYM.

31.    Parker,  D. S.,  Zadick, F. J., and Train, K. E., "Sludge Processing for Combined
       Physical-Biological Sludges," Environmental Protection Agency, R2-73-250 (July,
       1973).

32.    Zurn  Engineers  and  Battelle/NW,  "Westerly   Advanced  Waste  Treatment
       Facility:  Process  Development  and  Engineering  Design,"  Draft Version
       (September  16,  1971).

33.    Van Fleet, G. L., Barr, J. R., and Harris, A. J., "Treatment and Disposal  of
       Chemical  Phosphate Sludges in Ontario,"  Water Pollution Control  Federation
       Meeting, Atlanta, GA (October, 1972).

34.    Boyko, B. I.,  Rupke, J. W. G., "Design Considerations in the Implementation
       of  Ontario's  Phosphorus  Removal  Program,"   Phosphorus Removal  Design
       Seminar, Toronto, Ontario, Ministry of the Environment (May 28-29,  1973).
                                 11-40

-------
35.     Knight, C. H., Mondoux, R. G., and Hambley, B., "Thickening and Dewatering
       Sludges Produced in Phosphorus Removal," Phosphorus Removal Design Seminar,
       Toronto,  Ontario,  Ministry  of  the Environment  (May  28-29,  1973).

36.     Black, S.  A., "Lime Treatment for Phosphorus Removal at the Newmarket/East
       Gwillimbury WPCF, an Interim Report," Ontario Ministry of the Environment,
       R.P.W.  2032 (May, 1972).

37.     Smith, A. G., "Centrifuge Dewatering of Lime Treated Sewage  Sludge," Ontario
       Ministry of the  Environment, R.P.W. 2030  (May,  1972).

38.     Hathaway, S. W.,  Unpublished Report for EPA/NERC  (August 27,  1973).

39.     Hathaway, S. W.,  Unpublished Report for EPA/NERC  (September,  1972).
                                11-41

-------
                                  APPENDIX  A

       EVALUATING  PHOSPHORUS  REMOVAL  STRATEGIES
A computer model for evaluating a number  of strategies for removing phosphorus in
wastewater has been developed for EPA.1  This  model reports to the user the total cost of
a selected  strategy for  removing phosphorus. 22 treatment schemes  can  be selected and
evaluated depending on local conditions. These schemes are:

     1. Alum & Polymer Addition to Primary Settler
     2. Ferric Chloride & Polymer Addition to Primary Settler
     3. Ferrous Chloride & Lime Addition to Primary Settler
     4. Lime Addition to Primary Settler
     5. Alum & Polymer Addition to Flocculation Basin
     6. Ferric Chloride & Polymer Addition to Flocculation Basin
     7. Ferrous Chloride & Lime Addition to Flocculation Basin
     8. Lime Addition to Flocculation Basin
     9. Alum Addition to Aeration Basin
    10. Ferric Chloride Addition to Aeration Basin
    11. Sodium Aluminate Addition  to Aeration Basin
    12. Alum Addition to Aeration Basin & Multi-Media Filtration
    13. Ferric Chloride Addition to Aeration Basin & Multi-Media Filtration
    14. Sodium Aluminate Addition  to Aeration Basin & Multi-Media Filtration
    15. Alum Addition After Trickling Filter
    16. Ferric Chloride Addition After Trickling Filter
    1 7. Alum Addition After Trickling Filter & Multi-Media Filtration
    18. Ferric Chloride Addition After Trickling Filter & Multi-Media Filtration
    19. Alum Addition to Flocculation Basin After Conventional Secondary Treatment
    20. Ferric Chloride Addition to  Flocculation After Conventional Secondary Treatment
    21. Lime (1-Stage) Addition to  Flocculation After Conventional Secondary Treatment
    22. Lime (2-Stage) ^ Addition to  Flocculation  Basin  After Conventional  Secondary
       Treatment

Four  levels  of  effluent phosphorus concentration  (total  unfiltered phosphorus)  were
assumed to be achievable depending upon the type of treatment provided. These are:

       2.0 mg/1   (Option  1)  Chemical addition to  the primary clarifier.  (Treatment
                 schemes 1-4)
                 (Option 2) Chemical addition to a flocculation basin prior to the primary
                 clarifier. (Treatment schemes 5-8)
                 (Option 3) Chemical addition to the aeration basin. (Treatment schemes
                 9-11)
 1 "A computer Model for Evaluating Community Phosphorous Removal Strategies," prepared for U.S. EPA
 by JBF Scientific Corp., Burlington, Mass., Report No. 400/9-73/001 (Oct. 1973).
                                      A-l

-------
                 (Option  4)  Chemical  addition  after  the trickling filter.  (Treatment
                 schemes 15-16)

       0.5 mg/1   (Option 5) Chemical  addition to  the  aeration basin plus multi-media
                 filtration. (Treatment schemes 12-14)
                                                 or

                 Chemical addition after  the  trickling filter plus multi-media filtration.
                 (Treatment schemes 17-18)
                 (Option 6) Addition of lime to  a flocculation basin following conven-
                 tional secondary treatment. (Treatment scheme 21)
       0.3 mg/1   (Option 7) Addition of alum or ferric chloride to a flocculation basin
                 following  conventional  secondary treatmentone  stage.  (Treatment
                 schemes 19-20)
       0.1 mg/1   (Option 6) Addition of lime to  a flocculation basin following conven-
                 tional secondary treatmenttwo stages. (Treatment scheme 22)

The  model  has  been  designed  specifically for planning purposes and  can be used  by
municipalities, planning agencies and government policy organizations. In order to insure its
usefulness, EPA  plans to periodically update the model as additional performance data on
phosphorus removal processes becomes available.

The phosphorus  removal model (REMOVE) is designed to provide an estimate of the cost to
a particular community of achieving a designated level of phosphorus removal. The program
begins with the entry of data describing the community in terms of population and future
trends, the treatment plant in terms of present size and  excess capacity, and the influent
wastewater characteristics. The  data can be entered interactively through a subroutine
(SYSTEM).

After input  data have been entered, the user has the opportunity to investigate  various
control strategies for achieving a low phosphorus concentration  in the  wastewater effluent.
Typically, the effects on cost of reducing phosphorus in detergent products, of increasing or
decreasing the amount of government  financing available, or of using various treatment
options can be investigated.

It is important to note that the model has been developed as a simulation only and as such
does not achieve a mathematical optimization.

From the description of the  community, treatment plant, wastewater characteristics, and
desired strategy  the model will design a  treatment plant incorporating the present plant as
described  by the user  and will add those processes  or additional equipment necessary to
achieve  the  desired effluent level.  The  program  converts the  sizing information into
construction  costs, operating man-hours, maintenance man-hours, and total material and
supply costs for each process.
                                       A-2

-------
The following pages illustrate the type of print-out obtained when using the computer
model. The particular cases illustrated here are a 5 mgd trickling filter plant and a 20 mgd
activated sludge treatment plant.
                     5  MGD TRICKLING  FILTER  PLANT
                 TREATMENT COSTS  IN  CENTS/1000  GAL
P
GOVFF
RESTRICT

SCHNO
1
2
3
k
5
6
7
8
9
10
11
12
13
16
17
18
21
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 2
.8
6.7
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                             2
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13
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18
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10
15
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8
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                       10.5
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                                                      yes
                                                     10.2
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                                                     11.5
                                                      7.7
                                                     11.2
   NOTES:
   1.  P  =  Phosphorus  effluent  level  in ms/1,
   2.  GOVFF = Fraction  of construction cost  financed
               by  federal and state governments.
   3.  RESTRICT =  Restrictions  on  phosphate  decereents
   k.  SCHNO = Treatment scheme  number.
   5.  	  = Lowest  treatrrent cost.
                               A-3

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                             PERIODIC OPERATING COSTS
PROCESS NAME
RAW WSTE PNiP
PRE TRETMENT
PRIM SETTLER
PRMYSLGE PMP
TRKLNG FILTR
SECY SETTLER
RECIRC PMPNG
CHLORNE FEED
CHLORNE BASN
GRAV THICKNR
SLGE HLD TNK
VACUUM FILTR
ALUM FEEDING
FECL FEEDING
LIME FEEDING

TOTALS =
 OPERATING MAN-HOURS
  (MAN-HOURS/TP)
AVE.    MAX.    MIN.
               MAIMTAiriAHCE MAN-HOURS
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                              u,:v!T  COST  DATA
                           (CENTS/ijiC  GALLONS)
PROCESS NAME   AMORTIZATION
LAF'IR
MATERIAL  SUPPLY    TOTAL
RAW WSTE PKP
PRE TRETMENT
PRIM SETTLER
PRMYSLGE PMP
TRKLNG FILTR
SECY SETTLER
RECIRC PMPNG
CHLORNE FEED
CHLORNE BASN
GRAV THICKNR
SLGE HLD TNK
VACUUM FILTR
ALUM FEEDING
FcCL FEEuING
LIME FEEDING
TOTALS =
TIME SINK Af
PERIOD USEO
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2
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U
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9
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50
50
' r
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12
UNIT COGTo Fj:< SOLID WASTE  DISPOSAL  (CENTS/ 10
TOTAL ON'IT COST  (CENTS/lu OG  GAL)  =  7.66
                                                             7. G i
                    GAL. )  =  u.50
                               A-7

-------
p
GOVFF
RESTRICT

SCMNO
1
2
5
i
5
6
7
8
9
10
11
12
15
U
15
10
17
18
21
               20 MdD ACTIVATED
             TRtATMLNT COSTS IN
               .8
              yes
                     SLUOf.E PLANT
                     CENTS/1000 GAL.
7.9
L.k
11
7
16
9
11
8
17
10
3
6
11
. 1
.6
.5
.P
.7
.1
. 1
.1+
. 5
. 2
.2
9
6
13
8
10
6
Ik
8
3
5
11
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9.
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7.U
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      16.3
      12.3
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                     0.5
                      .8
                           lO.b
                            8. 8
                           13.8
                            8.9
                           10.0
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                      .R
                     yes
                            6.
                            6.3
                            6.8
                            7.1
NOTES:
1. P = Phosphorus effluent level  in mr;/1 .
2. GOVFF = Fraction of construction cost financed
           by federal and state governments.
3. RESTRICT = Restrictions on phosphate  duter ;ents
k. SCHNO = Treatment scherre number.
D. 	 = Lowest treatment cost.
                        A-8

-------

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-------
                             PERIODIC OPERATING  COSTS

PROCESS NAME     OPERATING MAN-HOURS   MAINTAINANCE  MAN-HOURS
                  (KAN-HOURS/TP)           (VAN-HOURS/TP)
                AVE.    MAX.    MIN.    AVE.     MAX.     MIN.

RAW WbTE PMP      0.      0.       0.       0.       C.       0.
PRE TRETMENT      0.      0.       0.       0.       C.       0.
PRIM SETTLER      0.      0.       0.       0.       0.       0.
PRMYSLGE PMP      0.      0.       0.       0.       G.       0.
AERTN BASIN       0.      0.       0.       0.       0.       0.
MECH AERATN       0.      0.       0.       0.       0.       0.
SECY SETTLER      0.      0.       0.       0.       0.       0.
RECIRC PKPNG      0.      0.       0.       0.       0.       0.
CHLORNE FEED      0.      0.       0.       0.       0.       0.
CHLORNE BASN      0.      0.       0.       0.       0.       0.
GRAV THICKNR     kl.     ll.     1*1.      23.      23.      25.
SLGE HLD INK      0.      0.       0.       T.       0.       0.
VACUUM FILTR   3013.   3013.   3013.    3f9.     3f,9.     359.
FECL FEEDING      0.      0.       0.   285U.    2S8U.    2i*.
LIME FEEDING      0.      0.       0.   2003.    2003.    2009.

TOTALS =       3055.   3055.   3055.   52.U.    5 2 P I*.    521*.
                             A-10

-------
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-------
                                                            0..'.
                             UNIT COST DAT-\
                          (CEMS/100G GALLONS)

PROCESS NAME   AMORTIZATION   LAP.OP,   MATERIAL  i  SUPPLY    TOTAL
                                             C.I
                                             0.0
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PRE TRETMENT
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PR.'-'.YSLGE PMP
AERTN BASIN
KECH AERATN
SECY SETTLER
RECI3C PM.PNG
CHLORNE FEED
CHLORNE 8ASN
GRAV THICKNR











SLGE HLD TNK
VACUUM. FILTR
FECL FEEDING
LIME FEEDING
TOTALS 






TIME SINK
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2
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7

9
10
11
12
13
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15
16
17
18
19
20
TOTALS 
1
1
1
1
1
1
1
1
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1
1
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1
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5
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2553
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COST
?/TP)
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638
638
638
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638
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36
36
36
36
36
36
36
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56
36
36
36
36
36
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36
36
36
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                                                            0. .1
                                                            0.05
                                                            0 . C!
                                                            -1.5C
                                                            U . Ul
                                                            5.31
UNIT COSTS FOR SOLID WASTE DISPOSAL  (CENTS/1000   GAL.)
TOTAL UNIT COST (CENTS/1000 GAL) = 6.18
                                                        =  D.R7
                            A-12

-------
   Multiply

Inches
Feet
Square Feet
Cubic Feet
Pounds
Gallons
Gallons/Minute
Feet/Second
        APPENDIX B

METRIC CONVERSION CHART

            By                      To Get
          2.54
          0.3048
          0.0929
          0.0283
          0.454
          3.79
          5.458
          0.305
Centimeters
Meters
Square Meters
Cubic Meters
Kilograms
Liters
Cubic Meters/Day
Meters/Second
                                                  Environmental
                                                    Lakes National fi
                                                         GLHPO
                             B-l

-------