United States
           Environmental Protection
           Agency
           Municipal Environmental Research
           Laboratory
           Cincinnati OH 45268
EPA-600'2-79-083
August 1979
           Research and Development
&EPA
Review of
Techniques for
Treatment and
Disposal  of
Phosphorus-Laden
Chemical Sludges

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                RESEARCH REPORTING SERIES

Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology.  Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:

      1    Environmental Health Effects Research
      2.   Environmental Protection Technology
      3.   Ecological Research
      4.   Environmental Monitoring
      5.   Socioeconomic Environmental Studies
      6.   Scientific and Technical Assessment Reports (STAR)
      7    Interagency Energy-Environment Research and Development
      8.   "Special" Reports
      9.   Miscellaneous Reports

This report has been assigned to the  ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia  22161.

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                                   EPA-600/2-79-083
                                   August 1979
    REVIEW OF TECHNIQUES FOR TREATMENT
     AND DISPOSAL OF PHOSPHORUS-LADEN
             CHEMICAL SLUDGES
                    by

             Curtis J. Schmidt
             LeAnne E. Hammer
             Michael D. Swayne
               SCS ENGINEERS
       Long Beach, California  90807
          Contract No. 68-03-2432
              Project Officer

               R. V. Villers
       Wastewater Research Division
Municipal Environmental Research Laboratory
          Cincinnati, Ohio  45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
    OFFICE OF RESEARCH AND DEVELOPMENT
   U.S. .ENVIRONMENTAL PROTECTION AGENCY
          CINCINNATI, OHIO  45268

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                           DISCLAIMER


     This report has been reviewed by the Municipal  Environmental
Research Laboratory, U.S. Environmental  Protection Agency, and
approved for publication.  Approval  does not signify that the
contents necessarily reflect the views and policies  of the U.S.
Environmental Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or recommendation
for use.
                                11

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                            FOREWORD


     The Environmental  Protection Agency was  created because of
increasing public and governmental  concern about the dangers of
pollution to the health and welfare of the American people.   Nox-
ious air, foul water, and spoiled land are tragic testimony  to
the deterioration of our natural  environment.   The complexity of
that environment and the interplay between its components require
a concentrated and integrated attack on the problem.

     Research and development constitute that  necessary first
step in a solution of the problem, and involve a definition  of
the problem, the measurement of its impact, and a search for
solutions.  The Municipal Environmental Research Laboratory
develops new and improved technology and systems for the preven-
tion, treatment, and management of wastewater  and solid and  haz-
ardous waste pollutant discharges from municipal and community
sources; for the preservation and treatment of public drinking
water supplies; and to minimize the adverse economic, social,
health, and aesthetic effects of pollution.  This publication is
one of the products of that research; a most vital communications
link between the researcher and the user community.

     This report relates the actual operating  experiences of
treatment plants which practice phosphorus removal by chemical
addition, indicating that all of the various sludge treatment
unit processes for thickening, stabilization,  conditioning,  dewa-
tering, and reduction are adversely affected by phosphorus
removal.  The more promising methods for handling phosphorus-
laden chemical sludges were identified as pressure filtration of
iro'n sludges, flotation thickening of iron and aluminum sludges,
thermal conditioning of iron sludges, and land disposal of lime
sludges.
                               Francis T. Mayo
                               Director
                               Municipal Environmental Research
                               Laboratory - Cincinnati
                               111

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                            ABSTRACT
     Removal of phosphorus from wastewater normally  entails  pre-
cipitation of phosphates by the addition of a  chemical,  generally
either lime or a salt of iron or aluminum.  A  consequence  of phos-
phorus removal, therefore, is the production of sludge  which is
laden with chemical precipitates.  A survey of 174 municipal
plants using chemicals to remove phosphorus from wastewater  was
conducted in order to quantify the effects of  chemical  addition
on the sludge handling and disposal  operations at full-scale
plants.

     Because of the generation of chemical sludge,  phosphorus
removal adversely affects a treatment plant in two ways.   First,
the volume or mass of sludge that must be handled and disposed of
is significantly increased.  Second, the resulting  combined  chem-
ical-organic sludges thicken, dewater, and incinerate differently,
and often with more difficulty than do organic sludges  alone.
Both these factors combine to compound the problem  of processing
and disposing of sludge, and to increase the cost of its handling.

     Of the three types of chemicals normally  considered for phos-
phorus removal, iron salts generally appear to have  the least
overall adverse effect upon subsequent sludge  handling.   Primary
addition of the phosphorus removal chemical often has advantages
over secondary addition in terms of the volume and  solids  concen-
tration of the combined primary/secondary sludge.  At existing
plants which have gone to phosphorus removal,  it has generally
not been cost-effective to add a tertiary chemical  flocculation
and clarification step, unless exceptionally high effluent quality
was a goal in addition to phosphorus removal.   Neither has  it been
found economical at existing plants to separate chemical-1aden
sludges from other sludges for handling if the previous practice
has been to combine all the sludges (e.g., primary and secondary,
or primary, secondary, and tertiary).  Several older plants which
have inadequate volume capacity for sludge handling have found
that pumping chemical-laden waste activated sludge to the primary
clarifier influent for settling with the primary sludge reduces
the volume of combined sludge to be treated.  At these plants,
sludge handling considerations have either been judged to outweigh
the problem of deterioration of primary effluent quality,  or an
increase in secondary clarifier efficiency has counteracted  the
problem.   These conclusions about existing plants should not be

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applied to the design of new plants because of the different con-
straints on costs and options.

     Plant operating experiences have shown that all  of the vari-
ous sludge treatment unit processes for thickening, stabilization,
conditioning, dewatering, and reduction are adversely affected by
phosphorus removal.  The adverse impact is reduced when adequate
capacity is available to handle the increased sludge  quantity.
Compared to other alternatives, relatively few problems have been
encountered with pressure filtration of iron sludges, flotation
thickening of iron and aluminum sludges, thermal conditioning of
iron sludges, and land disposal of lime sludges.

     This report was submitted  in fulfillment of Contract No. 68-
03-0268 by SCS Engineers under  the sponsorship of the U.S.  Envi-
ronmental Protection Agency.  This report covers the  period from
July 15, 1976, to September 14, 1977.  Work was completed as of
October 1978.

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                             CONTENTS

Foreword	ill
Abstract	iv
Figures	ix
Tables	xii
Acknowledgments	xvi11

  1.  Introduction	1

  2.  Project Scope and Methods	3

  3.  Phosphorus Removal Impacts on Sludge	6

            Types of chemical sludges	6
            Quantities of chemical sludges generated	12
            Solids concentration and percent volatile solids
               of chemical sludges generated	26

  4.  Prevalence of Various Treatment and Disposal
         Methods for Chemical Sludges	29

            Introduction	29
            Sludge thickening	29
            Sludge stabil ization/reduction	29
            Sludge conditioning/stabilization	33
            SI udge dewatering	33
            Sludge heat drying	33
            SI udge reduction	33
            Sludge final disposal	33

  5.  Thickening of Chemical Sludges	34

            Gravity thickening	34
            Flotation thickening	40

  6.  Stabilization of Chemical  Sludges	46

            Anaerobic digestion	46
            Aerobic digestion	60
            Composting	67

  7.  Condition of Chemical Sludges	71

            Chemical conditioning	71
            Thermal conditioning	72

                               vi i

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CONTENTS (continued)


   8.  Dewatering of Chemical Sludges	82

             Drying beds	82
             Vacuum f il t rat ion	88
             Dry i ng lagoons	93
             Pressure filtration	98
             Centrifugation	105

   9.  Reduction of Chemical  Sludges - Incineration	112

             Introduction	112
             Questionnaire survey	112
             Case studies	115
             Literature	116
             Conclusions	117

  10.  Disposal of Chemical Sludges - Transport and Land
         Disposal	119

             Introduction	119
             Questionnai re Survey	119
             Literature	121
             Conclusions	123

  11.  State-of-the-Art Appraisal	124

Bibliography	133
Appendices

  A.   Phosphorus-Laden Sludge Management
          Questionnaire Form	141

  B.   Outline for Collection of Field Data	149

  C.   Case Studies	161

       Introduction to Case Studies	161
       Case Study C:   South Bend, Indiana	161
       Case Study D:   Sheboygan, Wisconsin	181
       Case Study E:   Coldwater, Michigan	195
       Case Study F:   Lakewood, Ohio	215
       Case Study G:   Mentor, Ohio	242
       Case Study H:   Brookfield, Wisconsin (Fox River)	256
       Case Study I:   Midland, Michigan	278
       Case Study J:   Port Huron, Michigan	293
       Case Study K:   Pontiac, Michigan	308


                               v i i i

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                              FIGURES
Number                                                        Page

   1    Points of chemical  addition for phosphorus
           removal	7

   2    Cubic meter (m )  sludge per kg  phosphorus
           removed  (gal  sludge per Ib removed)	22

                      3                   3
   3    Cubic meter (m )  sludge per mil m  plant
           influent	23

   4    Kilogram (kg)  sludge per kg phosphorus
           removed	24

   5    Kilogram (kg)  sludge per m  plant influent
           (Ib/MG plant  influent)	25

 C-l    South Bend, Indiana, wastewater treatment
           plant flow  diagram	166

 C-2    Tertiary upflow  clarifier configuration,
           South Bend, Indiana	169

 C-3    Flow pattern for  South Bend anaerobic  digester	173

 C-4    Sheboygan,  Wisconsin, wastewater treatment
           plant flow  diagram	185

 C-5    Sheboygan,  Wisconsin, gravity thickener
           hydraulic and  mass balance	186

 C-6    Coldwater,  Michigan, wastewater treatment
           plant flow  diagram	199

 C-7    Hydraulic and  solids mass balances  for wastewater
           and sludge  treatment operations, Coldwater,
           Michigan	202

 C-8    Flocculation channel, Coldwater, Michigan	206

 C-9    Lakewood, Ohio,  wastewater treatment plant
           flow diagram	218
                                IX

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FIGURES (continued)


Number                                                        Page
C-10    Lakewood, Ohio, anaerobic digester
           configuration
                                                              .222
C-ll    Lakewood, Ohio, hydraulic and solids mass balance
           during 63 mg/£ alum addition (Jan thru Dec 74)	227

C-12    Lakewood, Ohio, hydraulic and solids mass balance
           before alum addition (Nov 72 thru Oct 73)	228

C-13    1976 anaerobic digestion mass balance during
           double shift vacuum filter and flash dryer
           operation, Lakewood, Ohio	....234

C-14    Anaerobic digestion mass balance during liquid
           sludge hauling, Lakewood, Ohio	235

C-15    Greater Mentor wastewater treatment plant
           wastewater flow diagram	245

C-16    Dual  cell gravity thickeners and appurtenances,
           Mentor, Ohio	252

C-17    Brookfield, Wisconsin, wastewater treatment
           plant flow diagram	259

C-18    Materials balance for primary wastewater
           treatment operations at Brookfield, Wisconsin	262

C-19    Materials balance for secondary wastewater
           treatment operations at Brookfield	263

C-20    Brookfield, Wisconsin pressure filtration and
           incineration facilities	267

C-21    Pressure filter performance, Brookfield,
           Wisconsin	268

C-22    Mul tiple -hearth incinerator performance,
           Brookfield,  Wisconsin	•.	270

C-23    Midland, Michigan, wastewater treatment plant
           flow diagram	281

C-24    Midland, Michigan, sludge treatment flow diagram	286

C-25    Chemical feed  points  to aeration tanks, Port Huron,
           Michigan	295

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FIGURES (continued)


Number                                                        PA16

c-26     Port  Huron,  Michigan,  wastewater  treatment
            plant  flow  diagram	297

C-27     Port  Huron,  Michigan,  gravity thickener
            hydraulic and mass  balance	300

C-28     Wastewater treatment unit process flow
            diagram,  Pontiac, Michigan	315

C-29     Sludge  handling unit process  flow diagram,
            Pontiac,  Michigan	31 6

C-30     Pontiac,  Michigan,  hydraulic  and materials
            balance	318

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                              TABLES


Number                                                        Page

   1     Results of Plant Survey	4

   2     Prevalence of Phosphorus  Removal  Methods
           (Chemicals and Points  of Addition)  among
           Plants Responding to Questionnaire  Survey	  9

   3     Combination of Chemical-Laden  and Other Sludges  for
           Processing as Practiced by  Plants  in Questionnaire
           Survey	11

   4     Influence of Plant Size on Type(s)  of  Chemical(s)
           Used for Phosphorus Removal  among  Plants  in
           Questionnaire Survey	13

   5     SS and BOD Removal Efficiencies and Dry Weights
           of Suspended Solids Removed  at a Hypothetical
           Activated Sludge Plant	15

   6     Total Dry Weight of Suspended  Solids  and  Chemical
           Solids Removed during  Treatment Processes  at
           a Hypothetical Activated Sludge Plant	18

   7     Theoretical Kilograms of  Solids Generated per
           Kilogram of Phosphorus Removed at  a Hypothetical
           Activated Sludge Plant	19

   8     Comparison of Theoretical  Solids  Generation  Rates
           with Results of Questionnaire  Survey	26

   9     Solids Characteristics of Chemical  Sludges
           with and without Combination with  Other
           Plant Sludges	28

 10     Prevalence of Treatment and Disposal  Processes  for
           Chemical Sludges among Plants  Responding  to
           Questionnaire Survey.	30

 11     Impacts of Chemical Sludge upon Gravity Thickening
           Performance as Reported in  Questionnaire  Response. .. .35
                               XI 1

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TABLES (continued)


Number                                                        Pa

 12     Impacts  of Chemical  Sludges  upon  Flotation
           Thickener  Performance  as  Reported  in
           Questionnaire  Response ............................... 4
  13     Impacts  of  Chemical  Sludges  upon  Anaerobic
           Digester Performance  as  Reported  in
           Questionnaire  Response ............................... 47

  14     Impacts  of  Chemical  Sludges  upon  Aerobic
           Digester Performance  as  Reported  in
           Questionnaire  Response ............................... 61

  15     Projected  Costs  of  Various  Sludge Handling
           Alternatives  Following Aerobic Digestion
           at  Portage  Lake,  Michigan ($) ........................ 65

  16     Average  Sidestream  Characteristics at Grand
           Haven,  Michigan ...................................... 74

  17     Characteristics  of  Plants in Study of Thermal
           Conditioning  of  Chemical  Sludges ..................... 76

  18     Characteristics  of  Streams  and  Sidestreams
           Associated  with  Sludge Treatment  Operations .......... 78

  19     Results  of  Pilot  Scale Centrifugation of  Midland
           Thermally Conditioned Iron Sludge ..... . .............. 80

 20     Comparison  of  Sidestreams from  Plant and  Pilot
           Dewatering  Operations ............................... : 81

 21     Impacts  of  Chemical  Sludges  upon  Drying Bed
           Performance as  Reported  in Questionnaire
           Response ............................................. 83

 22     Polymer  Application  to Drying Beds ....... . .............. 87

 23     Changes  in  Vacuum  Filter Performance Reported
           as  a  Result of  Phosphorus Removal Chemical
           SI udge Addition ...................................... 89

 24     Impacts  of  Chemical  Sludges  upon  Drying
           Lagoon  Performance as Reported in
           Questionnaire  Response ............................... 95

 25     Sludge Treatment/Disposal Methods Used  by
           Plants Practicing Pressure Filtration ............... 100


                                * • •
                              xi 11

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 TABLES  (continued)


 Number                                                        Page

 26     Impacts  of  Chemical  Sludges  upon  Pressure
           Filter  Performance  as  Reported  in
           Questionnaire  Response	'°'

 27     Pilot Filter Press  Test  at  Holland, Michigan	104

 28     Centrate Characteristics  from  Various  Scroll
           Centrifugation Runs	1 08

 29     Impacts  of  Chemical  Sludges  on Centrifuge
           Performance as Reported  in  Questionnaire
           Response	-	.....110

 30     Impacts  of Phosphorus-Laden Chemical  Sludges  on
           Incinerator Performance  as  Reported in
           Questionnaire  Response	113

 31     Bibliography Information Index	127

 32     Key to Bibliography Information Index	131

 C-l     Description of Case Study Sites According  to  Plant
           Sel ection Factors	162

 C-2     Wastewater Treatment Process Design Parameters,
           South Bend, Indiana	167

 C-3     Summary  of 1976 Wastewater  Characteristics and
           Treatment Performance, South Bend, Indiana	168

 C-4     Sludge Treatment  Process Design Parameters
           South Bend, Indiana	171

 C-5     Chemical Sludge Production  and Gravity
           Thickening, South Bend,  Indiana	.....174

 C-6     Anaerobic  Digester Gas Production, South
           Bend, Indiana	176

 C-7     A  sample of Historical Data Indicating Average
           Plant Influent Characteristics, Suspended
           Solids,  and BOD Removal, Sheboygan, Wisconsin	182

C-8     Vacuum Filtration and  Incineration Performance
           before  and  after Phosphorus Removal ,
           Sheboygan ,  Wisconsin	189
                                xi v

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TABLES (continued)
Number
                                                             Pai
  C-9     Influent  and  Effluent  Wastewater  Characteristics
            and  Removal  Efficiencies,  Coldwater, Michigan	196

 C-10     General Plant Description  Summary,  Coldwater,
            Michigan	200

 C-ll     Sludge  Pumped from  Primary Clarifiers  to
            Primary  Digester, Coldwater, Michigan	208

 C-12     Sludge  Transferred  from Digesters to Drying
            Beds (or  Lagoon), Coldwater, Michigan	211

 C-13     Plant  Influent  Wastewater  Flow  Rates,
            Lakewood,  Ohio	216

 C-14     Plant   SS,  BOD,  and  Phosphorus  Concentrations
            before and during Alum  Addition  for Phosphorus
            Removal,  Lakewood,  Ohio	•	226

 C-15     Plant  SS, BOD,  and  Phosphorus Removals before
            and  during Alum  Addition for Phosphorus
            Removal,  Lakewood,  Ohio	229

 C-16     1976 Sludge  Treatment  Data during Do'uble Shift
            Vacuum Filter and Flash Dryer  Operation
            at  Lakewood,  Ohio	234

 C-17     Costs  of  Treating Alum Sludge during Single and
            Double Shift  Vacuum Filter and Flash Dryer
            Operation,  Lakewood, Ohio	238

 C-18     Costs  of  Alum Sludge Treatment  during  Single
            and  Double Shift Vacuum Filter and  Flash
            Dryer  Operation, Lakewood, Ohio	240

C-19     Influent  and  Effluent Wastewater  Characteristics
            and  Removal  Efficiencies, Mentor, Ohio	243

C-20     General Plant  Description  Summary,  Mentor, Ohio	246

C-21     Aerobic Digester Sludge Characteristics,
            Mentor, Ohio	250

C-22     Performance of  Dual Cell Gravity  Concentrators,
            Mentor, Ohio	254
                               xv

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TABLES  (continued)


Number                                                       £lfl£

C-23    Influent  and  Effluent  Wastewater  Characteristics
           and  Removal  Efficiencies,  Brookfield,  Wisconsin.... 257

C-24    General  Plant  Description  Summary,  Brookfield,
           Wisconsin	260

C-25    Changes  in  Primary  Clarifier  Performance  as  the
           Result of  Chemical  Addition  for  Phosphorus
           Removal,  Brookfield,  Wisconsin	264

C-26    Impacts of  Chemical  Addition  for  Phosphorus
           Removal  on  Final  Clarifiers, Brookfield,
           Wisconsin	266


 C-27    Pressure  Filter Performance,  Brookfield,
           Wi scons in	273

 C-28    Pressure  Filter and Incinerator Operational
           Cost per t (ton) Dry  Solids, Brookfield,
           Wisconsin	277

 C-29    Phosphorus  Removal  Impacts  on  Plant BOD and
           SS  Removals,  Midland, Michigan	282

 C-30    Impacts  of  Phosphorus  Removal:  Sludge
           Conditioning,  Thickening,  and Dewatering
           Characteristics  --  Variability with
           Conditioning  Method,  Thermal Conditioner
           Temperature,  and the  Recycling of Tertiary
           Filter Backwash  Water,  Midland,  Michigan	287

C-31    A  Comparison  of  the Characteristics of  the
           Sludges  Produced with Alum and Ferris
           Chloride,  Midland,  Michigan	290

C-32    Additional  Cost  for High Temperature Thermal
           Conditioning,  Midland,  Michigan	292

C-33    Direct  Effects  of Conditioning  Method on
           Performance  and  Operational  Costs of Solids
           Handling,  Port Huron, Michigan	304

C-34    Wastewater  Characteristics and  Removal
           Efficiencies,  Pontiac,  Michigan	310
                               xvi

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TABLES (continued)

Number                                                       Page
C-35    General  Plant Description Summary,  Pontiac,
           Michigan	312
C-36    Primary Clarifier Waste Stream Characteristics
           Pontiac, Michigan	317
C-37    Raw and Digested Sludge and Supernatant
           Characteristics, Pontiac, Michigan	320
C-38    Vacuum Filter Performance, Pontiac,  Michigan......... 322
C-39    Incinerator Performance, Pontiac,  Michigan	323
                               xvi i

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                         ACKNOWLEDGMENTS
     The project officer for this contract was R. V. Villiers,
Ultimate Disposal Section, Wastewater Research Division, Municipal
Environmental Research Laboratory, EPA, Cincinnati, OH.  SCS
Engineers personnel were Lee Hammer, Curt Schmidt, Don Sherman,
Mike Swayne, and Mark Montgomery.
     We wish to
and assistance:
thank the following people for their cooperation
Dr. J. B. Farrell
Municipal Environmental Research
   Laboratory, EPA
Cincinnati, OH

Mr. G. L. Van Fleet and
   Mr. P. Seto
Sanitary Engineering Branch,
Ontario Ministry of the
   Environment
Toronto, Ontario

Mr. Charles J. Sluskonis
Greater Mentor Wastewater
   Treatment Plant
Mentor, OH

Mr. John F. Budde
Fox River Water Pollution
   Control Center
Brookfield, WI

Mr. J. Michael Jeter
Bureau of Wastewater
South Bend, IN

Mr. John Hennessey and
   Mr. Jim Spangler
Pontiac Wastewater Treatment
   Plant
Pontiac, MI
                  Mr.  Larry Marshall
                  Lakewood Wastewater Treatment
                     Plant
                  Lakewood, OH

                  Mr.  Willis W.  Stubbe
                  Sheboygan Wastewater Treatment
                     Plant
                  Sheboygan, WI
                  Mr.  David
                  Coldwater
                     Plant
                  Coldwater,
H.  McKay
Wastewater

 MI
Treatment
                  Mr.  Paul  S.  Hendricks
                  Port Huron Wastewater
                     Treatment Plant
                  Port Huron,  MI

                  Mr.  Larry Dull and
                     Mr. Arthur Mass
                  Midland Wastewater Treatment
                     Plant
                  Midland, MI
                              xv m

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                            SECTION 1

                          INTRODUCTION


     Starting in the late sixties, regulatory agencies began
placing limits upon the phosphorus content of treated wastewater
effluents discharged to many surface receiving waters.  As a
result, over 400 municipal sewage treatment plants in the United
States and Canada are now required to implement additional chemi-
cal treatment steps to remove 80 percent or more of the phos-
phorus contained in the raw sewage.  There are several chemicals
which can be added to precipitate phosphorus in the form of phos-
phates from:  iron salts, aluminum salts, or lime.  All such pro-
cesses generate sludge which is laden with chemical precipitates.
This report focuses upon the problems being experienced in muni-
cipal sewage sludge management as a result of the addition of
these chemical-laden sludges to the sludge treatment processes.

     The municipal plants which were studied were operated to
achieve at least 80 percent removal of the phosphorus contained
in the raw sewage.  At higher or lower removal rates, the impacts
on sludge which are described in the report would be correspond-
ingly greater or lesser.  A few plants which were investigated
were not reaching 80 percent removal at the time of the study
because of problems in plant design, unusual waste characteris-
tics, plant hydraulic overload, or, in a few cases, inadequate
sludge handling capacity.

     Included early in this report are sections which describe
the changes in sludge volume and characteristics experienced by
treatment plants as a result of adding chemicals to remove phos-
phorus.  Emphasis is upon the differences in volume and charac-
teristics experienced by treatment plants as a result of adding
chemicals to remove phosphorus.  Emphasis is upon the differen-
ces in volume and characteristics resulting from use of each of
the common phosphorus removal  chemicals and the effects of utili-
zing alternate points of chemical addition in the sewage treat-
ment chain.

     Subsequently, the report discusses the effect of the chemical
laden sludges upon typical sludge treatment unit processes (e.g.,
thickening,  digestion, dewatering, incineration, etc.).  Problems
experienced  by various treatment plants are cited, and solutions
that were developed are described.  The information presented  is

                                1

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derived from a questionnaire survey (174 responses)  of treatment
plants practicing phosphorus removal,  field investigation case
studies of nine selected plants, and a review of pertinent liter-
ature.  Whenever possible, treatment plant names and locations
are referenced so that readers may obtain additional information
di rectly.

     Case  study reports of field investigations at selected treat-
ment plants are provided in the appendices.  These case studies
provide detailed information pertinent to sludge handling at a
variety of plants which are generally  representative of typical
phosphorus removal  technology.

     It is necessary to warn the reader that sludge  generation
and management are complex subjects.  Every sewage treatment
plant is a unique combination of variables in raw sewage charac-
teristics, treatment unit design, operational procedures, etc.
For these  reasons, it is often difficult to successfully trans-
fer technology or information on sludge volume and mass from one
plant to another.  However, the experience of others can serve
as a background basis for possible solutions to, or  avoidance of,
similar sludge management problems.  It is our hope  that this
report will be helpful in guiding sewage treatment plant design-
ers and operators toward a realization of potential  sludge manage'
ment problems and solutions when phosphorus removal  operations
are necessary.

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                            SECTION 2

                    PROJECT SCOPE AND  METHODS


     Removal of phosphorus from wastewater normally entails pre-
cipitation of phosphates by the addition of a  chemical, generally
either calcium hydroxide or a salt of iron or  aluminum.  A con-
sequence of phosphorus removal, therefore, is  the production of
a sludge which is laden with chemical  precipitates.  Because of
the generation of chemical precipitates, phosphorus removal
impacts adversely on a treatment plant in two  ways.  First, the
volume or mass of sludge that must be handled  and disposed of is
significantly increased. Second, the resulting combined chemical-
organic sludges thicken and dewater differently, and often with
more difficulty than do organic sludges alone.  Both these factors
combine to compound the problem of processing  and disposing of
sludge, and to increase the cost of its handling.

     Although increasingly more treatment plants are being required
by regulatory agencies to remove phosphorus, the information neces-
sary to competently design or modify engineering works to ade-
quately handle the phosphorus-laden chemical sludges is still
largely not available.  EPA's Office of Research and Development
perceived the need for a project to assemble and evaluate the
information needed to detail the most viable methods for handling
and disposing of chemical-1aden sludges produced by phosphorus
removal, and to identify those techniques which are most cost-
effective for dealing with them.  This no small  task because of
the variety of types of chemical-laden sludges and the number of
methods available for treatment and disposal of  them.

     It was the objective of this project to conduct extensive
data gathering and in-depth evaluation of available hard engineer-
ing data, including operating experience of plants practicing
phosphorus removal.  It is hoped that the information in this
report, when combined with other EPA research  on the subject
will enable the future preparation of satisfactory definitive
guidelines for use by federal and state agencies and consulting
engineers for treatment and disposal of chemical sludges.


     A literature search was conducted to gather all published
and unpublished literature pertinent to the management of  chemi-
cal  sludges.  Approximately 80  documents were reviewed and  found

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 to  contain  helpful  information.  These are listed in the biblio-
 graphy  to this  report;  To make the bibliography more useful, it
 is  preceded  by  a matrix index which enables the user to determine
 the  subjects  covered  in each document, and conversely to identify
 all  the  documents which include information about a subject of
 interest.

      An  extensive questionnaire survey was made in early 1977 of
 treatment plants practicing phosphorus removal, as identified by
 state regulatory agencies, EPA regional offices, and the Canadian
 Ministry of  the Environment of Ontario.  A copy of the question-
 naire mailed  out is shown in Appendix A to this report.  Question-
 naires  were  mailed  to over 400 plants.  A number of plants replied
 that they will  have phosphorus removal at some time in the future.
 A  total  of  361  plants were identified as currently practicing
 phosphorus  removal.   Table 1 shows the number of plants identi-
 fied as  removing phosphorus (361); those that responded to the
 survey  (174)  are broken down by state, plus Canada.


                  TABLE 1.  RESULTS OF PLANT SURVEY
State
(Name)
Cal if ornia
Colorado
Illinois
Indiana
Michigan
Minnesota
New York
Ohio
Pennsylvania
Wisconsin
Texas
Canada
Identified Plants
in State (No.)
2
1
22
26
91
12
8
34
13
59
1
92
Plants Responding
to Survey (No.)
1
1
5
7
59
4
4
16
9
26
1
41
           TOTAL                 361
     Considering the length of the questionnaire, the  response  of
almost 50 percent is excellent.  Phone call follow-ups were
required to obtain the response received, and to clarify  those
questionnaire responses that contained confusing information.
The questionnaire asked for a great deal of detailed  information,
and respondents supplied whatever data they had.  Unfortunately,
hard engineering and cost data were usually not available to  them.
Questionnaire responses are tabulated and/or summarized throughout
the report where appropriate to the subject being discussed.

     Based upon the questionnaire survey, literature  information,
and recommendations from knowledgeable persons, a total of nine
operating treatment plants were selected for field  investigations.
An average of one person week was spent gathering all  available
historical and current operating and design data at each  selected

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plant.  Emphasis was placed upon determining the effects of the
chemical sludge addition on sludge treatment processes, and upon
solving the problems encountered.  Appendix B shows the field
investigation outline form used.  Appendices C through K comprise
the case studies themselves.  Information gathered during the case
studies is utilized throughout the report to enhance discussions
of various unit treatment processes.

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                            SECTION 3

              PHOSPHORUS REMOVAL IMPACTS ON SLUDGE


TYPES OF CHEMICAL SLUDGES

      In this report a chemical sludge is any sludge containing
chemical precipitates derived from phosphorus removal.  The vari-
ous types of chemical sludges can be defined by the type(s) of
chemical(s) used, the type of plant, the point(s) of chemical
addition, and whether or not and how the primary, secondary, and
tertiary sludges are combined for processing.

      It appears that the only chemicals used by full-scale plants
for phosphorus removal are lime or salts of iron or aluminum.
Some  plants use more than one chemical.  Lime usually comes to
the plant as quicklime (CaO).  It is usually slaked to calcium
hydroxide lime (Ca(OH)2) before it is added to wastewater.  The
slaking process requires a great deal of equipment and some addi-
tional operator attention and is partly responsible for the rela-
tively infrequent use of lime for phosphorus removal.  The iron
salts that are used are ferrous sulfate (FeS04), ferrous chloride
(FeCl2)> and ferric chloride (FeCls).  Both ferrous sulfate and
ferrous chloride are waste products of the pickling process in
steel industries.  Waste pickle liquor containing ferrous iron
is the cheapest source of iron which can be used for phosphorus
removal in some areas of the country.  Ferric iron can also
occasionally be obtained as a by-product from certain industries
although this is rare.  The aluminum salts that are used for phos-
phorus removal  are aluminum chloride (AlClo), aluminum sulfate or
alum  ^12(504)3), and sodium aluminate (NaA102).  Polymers are
often used as coagulant aids with any of the phosphorus removal
chemicals.

      In most modern wastewater treatment plants, several points
are available for chemical  addition to precipitate phosphorus
(see Figure 1).  However, differences exist in the points of
addition which are available depending on  the type of plant and
the type of chemical  in use.

     Primary addition of any of the phosphorus removal chemicals
can be practiced.  Primary addition of ferrous iron salts is a
special  case because  the phosphates are not always precipitated
in the primary  clarifier, as is the case with other chemicals.

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 INFLUENT
WASTEWATER
           r
               PRIMARY ADDITION
i
                  PRIMARY
               CLARIFICATION
                CHEMICAL-LADEN
                PRIMARY SLUDGE
                                    CHEMICAL PRECIPITANT
                                    SECONDARY  ADDITION
                                     i        !        i
                                     i        i        i
                                            _i
                                                              TERTIARY ADDITION
BIOLOGICAL
TREATMENT
1
t .,

SECONDARY
CLARIFICATION
1
t

CHEMICAL
FLOCCULATION/
CLARIFICATION
EFFLUENT
WASTEWATER
                                                    CHEMICAL-LADEN
                                                   SECONDARY SLUDGE
CHEMICAL-LADEN
TERTIARY SLUDGE
            Figure 1.   Points of  chemical  addition  for  phosphorus  removal.

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 In order for ferrous iron to affect precipitation of phosphates
 to a significant extent, the sewage must either be aerated or the
 pH raised by adding lime or sodium hydroxide.  If ferrous iron is
 added to the primary stage without also adding a base to raise
 the pH, almost all of the phosphorus passes through the primary
 treatment without being removed.  If the plant has activated
 sludge treatment, the ferrous ions will be oxidized to ferric
 ions in the aeration basins, and phosphates will be precipitated
 and removed in the secondary clarifier.

     Secondary addition of any  chemical except lime can be prac-
 ticed.  Lime addition to the secondary treatment stage is not
 practiced because the high pH accompanying lime addition would be
 detrimental to the biological population of the system.  Secondary
 addition  includes addition before, directly into, or just after
 the activated  sludge aeration basins or trickling filters.

     Tertiary  addition  of chemicals in a third stage clarifier
 is occasionally  practiced. Either lime, aluminum salts, or ferrous
 iron salts  are used.  Some plants are designed with third-stage
 treatment primarily because it  is effective in removing BOD, SS,
 and metals  in  addition  to phosphorus.  Since  it is expensive
 to build  a  tertiary clarifier,  this practice  is uncommon when
 phosphorus  removal alone is the effluent quality objective.

     In trickling filter plants, chemicals are seldom added just
 ahead of, or directly dosed to, the filters themselves, but in
 activated sludge  plants, chemicals are frequently added just prior
 to or directly into the aeration basins.   In  trickling filter
 plants, the chemical would be added before the final clarifiers
 to avoid  staining and clogging  of the filters, while in an acti-
 vated sludge plant it can be advantageous  to  add the chemicals
 to the aeration  basins  to allow utilization of the mixing action
 which provides dispersion of the chemical  in  the wastewater.   It
 is sometimes found more effective to add the  chemical 2/3 or 3/4
 of the way  through the  aeration basin to minimize floe disruption.

     Table 2 presents the results of the questionnaire survey
 on the prevalence of the various phosphorus removal methods
 (chemicals and points of addition) among the  plants which res-
 ponded.  It also indicates the  number of these plants which use
 a polymer as a flocculation aid.  The table shows that chemical
 addition to the  secondary treatment stage  is  more prevalent than
 primary or tertiary addition.   Sixty-two percent of the  plants
 in the survey practiced secondary chemical addition whereas 26
 percent practiced primary addition and six percent added  the
 chemical  in a tertiary  step involving chemical flocculation and
 clarification.   The remaining six percent  used a combination of
 points  of addition.  The percentages are basically the same when
 the plants which did not have either a primary or secondary treat-
ment  step are excluded  from consideration.


                                8

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vo
                            TABLE  2.   PREVALENCE  OF  PHOSPHORUS REMOVAL  METHODS  (CHEMICALS  AND POINTS
                                         OF ADDITION) AMONG PLANTS  IN  QUESTIONNAIRE SURVEY
Point(s) of
Chemical Addition
Primary
Secondary
Tertiary
Primary and Secondary
Primary and Tertiary
Secondary and Tertiary
Total Number

Primary
Without
Secondary
10F3, 3A
NA
NA
NA
NA
NA
10F3, 3A

Aerated Lagoon or
Activated Sludge
Without Primary *
NA!
12F3, 2F2, 14A
1L+A
NA
NA
1F3
13F3, 2F2, 14A,
1L+A
Number of Plants
Primary Plus **
Activated Sludge
6L, 4FV3F,,, 5A,
1L+A J i
26F3, 9F2, 36A,
4L, 2F3, 1A
1F2, !L-i-F3, 1F,+A
2F3, 1A z
1L+A
NA
10L, 34F3, 13F2, 43A,
1L+F3, 2L+A, 1F2+F,,
1F2+A *
*
by Plant Type
Primary Plus
Trickling Filter
12F,, IF,, 1A
^ €~
3F3, 5A
1F3, 1A
1F3, 1L+A
NA
NA
17F3, 1F2, 7A, 1L+A

Total
6L, 26F3,4F2,9A
41F3, 11F,, 55A,
1F2+F3 i
4L, 3F3, 2A, 1L+A
3F3, 1F2, 1A.1L+F,,
1L+A, 1F2+A J
1L+A
1F3
10L, 74F3, 16FZ,
67A, 1L+F3, 4L+A

Total
Using Polymer
16F.,, 4A, 1L+A
J
20F3, 3F2, 12A
3L, 2F3
2F3, 1A, 1L+A
1L+A
1F3
3L, 41F-, 3F,, 17A,
3L+A 6 i
          L = Lime;
         F3 = Ferric iron salt;
A = Aluminum salt;
F- = Ferrous iron salt.
         fTwo plants  in this category have aerated lagoons but do not produce secondary sludge.
         *Three plants in this category have aerated lagoons with sludge removal from final clarifiers; seven plants  have the extended
          aeration modification of the activated  sludge process.
         * Three plants in this category have the extended aeration modification of the activated sludge process

         f NA = Not applicable.

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      Iron salts, either ferric chloride (FeCls), ferrous chloride
      2)> or ferrous sulfate (FeS04), were the most common chemi-
 cals  used among the plants in the survey.  Fifty-two percent of
 the plants were using iron.  Seventy-five plants used ferric
 chloride.  Both primary and secondary addition of ferric chloride
 were  common, with secondary addition being more prevalent.  Ter-
 tiary  ferric chloride addition was occasionally practiced.  One
 important factor influencing the frequency of iron usage was the
 availability of waste pickle liquor from steel mills in the Great
 Lakes  Region.  All of the 18 plants in the survey which used fer-
 rous  iron were obtaining it as an industrial by-product.  Most of
 these  plants added the chemical to the secondary stage.  The
 plants which added it to the primary did not accompany it with
 a  base,  and therefore the actual phosphate removal occurred mainly
 in  the secondary stage.

      Thirty-eight percent of the plants in the survey used alumi-
 num.   Secondary addition was much more common than primary, pos-
 sibly  due to difficulty in getting adequate mixing of the alumi-
 num with primary addition.  Two plants practiced tertiary addition
 of  aluminum.  Fifteen plants reported using lime -- four of them
 in  combination with another chemical.  Ten plants added it to the
 primary  stage, while five added it in a tertiary step.  With
 respect  to polymer usage, 43 percent of the plants using lime, and
 19  percent of the plants using ferrous iron, employed a polymer.
 Considering the two most commonly used chemicals -- ferric iron
 and aluminum -- polymer was used in combination with the former
 55  percent of the time, but it was used with the latter only 25
 percent  of the time.

      The chemical-1aden primary, secondary, or tertiary sludge
 resulting from lime, aluminum, or iron addition to remove phos-
 phorus can be processed separately from the other sludges pro-
 duced  in the plant, or all of the sludges can be combined for
 processing (e.g., primary and secondary, or primary, secondary,
 and tertiary).  Sludges can be combined in a sludge-processing
 unit  such as a thickener, digester, holding tank, or mixing tank.
 Alternatively, primary and secondary sludges are often combined
 by pumping the waste secondary sludge to the primary clarifier
 influent where it is mixed with raw sewage.  Solids derived from
 both the secondary sludge and the raw sewage are thus removed
 together in the primary clarifiers.  Table 3 shows that, except
 in the case of chemical-1aden tertiary sludges, it is more com-
 mon to combine chemical-laden and other sludges than to treat
 them separately.   Tertiary sludges were treated separately at six
 of the ten plants in the questionnaire survey practicing tertiary
 chemical  addition.  At the other four plants, the sludges were
 combined in or before a digester or a gravity thickener.  Among
 33 plants practicing primary chemical addition and having both
 primary and secondary sludges, the chemical-1aden primary sludge
was combined with the secondary sludge at 31 plants.  Thirty-nine
 percent of these combined by pumping the waste secondary sludge

                                10

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                 TABLE 3.    COMBINATION  OF CHEMICAL-LADEN AND  OTHER SLUDGES  FOR
                     PROCESSING AS  PRACTICED BY PLANTS IN  QUESTIONNAIRE SURVEY
Point at Which Chemical -Laden
and Other Sludges Were Combined




Plants Without Primary or
Secondary Clarification
• No primary sludge
• No secondary sludge
Plants With Both Primary and
Secondary Clarification
• Sludges not combined
* Combined in or before
primary clarifier
• Combined in or before
thickener
• Combined in or before digester
• Combined in or before dewatering
device
Total
Number of Plants by Point(s) of Chemical

Primary
Addition
Only

*
NA
13


2
12

13

6

0
46

Secondary
Addition
Only


28
NA


10
26

14

24

6
108

Tertiary
Addition
Only


1
NA


6
0

2

2

0
11
Primary
and
Secondary
Addition


NA
NA


1
3

1

3

0
8
Addition
Primary
and
Terti ary
Addition


NA
NA


0
0

1

0

0
1

Secondary
and
Tertiary
Addition


1
NA


0
0

0

0

0
1




Total


30
13


19
41

31

35

6
175+
NA - Not applicable.
One plant with tertiary addition is counted twice because it has no primary sludge, and
it has  secondary and tertiary sludges which are not combined.

-------
 to  the  primary  clarifier  influent; 42 percent combined sludges in
 or  before  a  gravity  thickener; and 19 percent in or before a
 digester.  Among  80  plants with  secondary chemical addition and
 both  primary and  secondary sludges, the  sludges were combined
 at  70 plants.   Thirty-seven  percent of these plants combined the
 sludges  by pumping to  the primary clarifier influent; 20 percent
 combined sludges  in  or before a  gravity  thickener; 34 percent  in
 or  before  a  digester;  and 9  percent in or before a dewatering
 device.

      Table 4 examines  the influence of plant size on the type(s)
 of  chemical(s)  used  for phosphorus removal among plants in the
 questionnaire survey.   The table indicates that the majority of
 plants  (74 percent)  treats no more than  5 mgd of wastewater.
 There is no  apparent correlation between plant size and chemical
 used.

 QUANTITIES OF CHEMICAL SLUDGES GENERATED

 Introduction

      The additional  sludge generated may be a major concern when
 implementing chemical  addition for phosphorus removal.  This sec-
 tion  will  first present a discussion of  stoichiometric relation-
 ships to determine the theoretical quantities of chemical pre-
 cipitates  by addition  of  lime, iron, and aluminum chemicals for
 phosphorus removal.   Second,  information taken from literature
 sources  on sludge generation  quantities  will be presented; and
 finally, the sludge  generation information developed from the
 treatment  plant survey will  be presented.  Literature and survey
 information  is  derived from  actual plant experience and will
 enable  comparison of theoretical and actual sludge generation
 rates.   Actual  generation is  expected to be greater than theore-
 tical  rates  because  of additional solids and BOD capture during
 chemical  treatment.

      There are  several  methods for estimating the mass of sludge
 which will be generated in a  particular  plant by phosphorus
 removal.   The best method to  use at an existing installation is
 a plant-scale test.  When a  full-scale test is infeasible at
 an  existing  plant or when an  engineer is designing a new plant,
 a pilot  plant test is  the next best method.  If this is impossi-
 ble but  the  actual wastewater to be treated is available, sludge
 mass  should  be  estimated from jar tests  with the wastewater. The
 jar test results  can be corroborated with estimates derived
 using a  calculation  method (see  Reference 27 for a procedure).
 The calculation method  is most effective when the parameter of
 chemical dosage can  be  determined using  jar tests.  The jar test
 relates  chemical  dosage to other parameters; iron or aluminum
 dosage is  related to phosphorus  removal; lime dosage is related
 to alkalinity of  the water and the pH level required.  If jar
 tests cannot  be carried out,  then judgements of these parameters
must be made  on the  basis of  past experience.

                               12

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                      TABLE 4.  INFLUENCE OF PLANT SIZE ON TYPE(S) OF CHEMICAL(S) USED FOR
                                PHOSPHORUS REMOVAL AMONG PLANTS IN QUESTIONNAIRE SURVEY
CO
Chemical (s)
Used

Lime
Ferric iron
salt
Ferrous iron
salt
Aluminum salt
Lime and Ferric
Lime and Aluminum
Ferrous and Ferric
Ferrous and Aluminum
Total






Number of Plants by Size
0.05-1 .0 mgd
3

31

3
28
0
0
0
0
65
1 .0-5.0 mgd
6

24

7
21
1
4
1
0
64
5.0-10.0 mgd
0

7

1
9
0
0
0
1
18
10.0-20.0 mgd
0

7

3
7
0
0
0
0
17
over 20.0 mgd
1

5

2
2
0
0
0
0
10
Total
10

74

16
67
1
4
1
1
174

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      Estimates  of  sludge  production have been made on a purely
 empirical  basis  by  noting  increases in production at plants which
 have  instituted  phosphorus  removal.  This method is useful only
 for generalizations  because of differences  in sewage characteris-
 tics  and  plant  design  and  performance.  Lime, iron, or alum addi-
 tion  to an  existing  plant  greatly affects the solids and BOD
 removal efficiency  of  the  plant; therefore, the increase in sludge
 production  caused  by chemical addition depends greatly on what
 the original  removal efficiency was.

 Theoretical  Sludge  Generation Quantities

      Knight,  Mondoux,  and  Hambley(40)  have  calculated sludge
 generation rates at a  hypothetical  sewage treatment plant.  The
 hypothetical  plant  has the following values:

      Flow  -  3,785  m3/day  (1.0 mgd)

      BOD    -  200 mg/£

      SS     -  250 mg/£

      Total  Dry  Weight  SS  per  Day -  947 kg (2086 Ib)

      P      -  10 mg/£

      P effluent limitation -  2 mg/£

      Table  5  presents, on  both dry  weight and percentage bases,
 the wastewater  solids  removal assumed  for this discussion for
 activated sludge systems:   1) with  no  chemical addition, 2) with
 chemical  addition  for  phosphorus removal prior to the primary
 clarifier,  and  3)  with tertiary chemical addition for phosphorus
 removal.   The daily  weights of dry  solids are derived simply by
 multiplying percentage removals by  total suspended solids weights
 in the influent.   Thus, the weights of chemical solids are not
 included.   These calculated weights do not  allow for the organics
 consumed  by endogenous respiration  or  for the soluble BOD con-
 verted during aeration into secondary  sludge solids.  For typical
 municipal wastewater of the composition shown, respiration and  BOD
 conversion  have  a negligible  effect on the  weight values.  How-
 ever, with  a high BOD,  low  suspended solids wastewater, a more
 detailed  calculation would  be advisable (see Reference 26 for  a
 procedure).

 Lime--
     Phosphorus  is precipitated by  lime as  hydroxyapati te, Ca,-  OH
      .   Assuming 89 percent  phosphorus removal and 10 mg/£  in
the influent, the dry  weight  of this precipitate from a 3,785
m3/day (1.0 mgd) plant  is  163 kg/day (359 Ib/day).
                                14

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            TABLE  5.   SS AND  BOD REMOVAL EFFICIENCIES AND DRY WEIGHTS OF SUSPENDED
                     SOLIDS  REMOVED AT  A HYPOTHETICAL ACTIVATED SLUDGE PLANT*
Primary Treatment



No Chemical Addition

Primary Chemical
Addition

Tertiary Chemical
Addition

Percent

SS
50


75


50

Removal

BOD
35


50


35

kg/day
(Ib/day)
SS Removed
473
(1041)

709
(1562)

473
(1041)
Secondary Treatment Tertiary Treatment
Percent
_^
SS
90


90


90

Removal

BOD
90


90


90

kg/day Percent Removal
(Ib/day)
SS Removed SS BOD
378
(833)

142
(312)

378 95 95
(833)
kg/day
(Ib/day)
SS Removed



—


47
(104)
Total
kg/day
(Ib/day)
SS Removed
851
(1874)

851
(1874)

898
(1978)
*We1ght of chemical solids and additional SS removed during chemical
 treatment not Included.

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      The  percentage  of  phosphorus  removed  is essentially  a  func-
 tion  of  pH,  with  substantial  removal  occurring  as  low  as  pH  9.0.
 Better  than  90  percent  removal  can  be  obtained  at  pH 11.0.   The
 pH  required  to  obtain 80  percent  removal of phosphorus  is below
 that  at  which  substantial  precipitation  of Mg(OH)2 occurs.   This
 affects  the  thickening  and  dewatering  characteristics  of  the
 sludge,  since  magnesium hydroxide  is  bulky and  dewaters slowly
 to  a  very low  consistency.

      The  lime.dosage needed to  attain  any  desired  pH level  depends
 on  wastewater  alkalinity,  hardness, and  the relative quantities
 of  calcium and  magnesium  ions.   In  practice, the bulk  of  the  lime
 added is  precipitated in  the  chemical  sludge as calcium carbonate.
 If  all  the lime added was  precipitated as  CaCOs, 1 kg  of  Ca(OH)2
 would yield  1.35  kg  of  CaCOs.   If  tne  lime was  used UP  in ma9~
 nesium  precipitation, 1  kg  of Ca(OH)2  would produce 1.35  kg  of
 CaCOs Plus °-39 kg-of Mg(OH)2 for  a total  of 1.74  kg.   One  kg of
 Ca(OH)2  precipitates 1.36  kg  of hydroxyapatite.

      Although  it  is  not possible,  according to  Knight,  Mondoux,
 and Hamble (40),  to  accurately  calculate the total amount of
 solids  that  will  precipitate  per  pound of  lime  added,  Parrel!
 (26)  has  presented  a procedure  for  estimating  the  required  lime
 dose  and  the quantity of  sludge produced for tertiary  treat-
 ment  of  a wastewater with  lime.  All  of  these  authors  agree  that
 if  the  wastewater which will  actually  be treated is available,
 the best  way to determine  lime  dose and  sludge  quantity is  by
 performing jar  tests.
                                    o
      For  the example of the 3,785  m /day (1 mgd) hypothetical
 plant of  Knight,  Mondoux,  and Hambley  (40), assuming that 125 mg/£
 of  Ca(OH)2 is  required  to  increase  the pH  to 9.5,  and  that  chemi-
 cal  precipitates  are produced at  the  rate  of 2.0 kg/kg  of Ca(OH)2
 added,  then  the total weight  of chemical precipitates  for the
 plant would  be  945  kg/day  (2082 Ib/day).   This  is  roughly equal
 to  the amount-of  sludge  solids  produced  without chemical  addition.

 Aluminum  Salts--
      Phosphorus  is precipitated by  aluminum ions to form  alumi-
 num - Al2(S04)s .  H20. A 60 percent excess  over the stoichio-
 metric ratio of aluminum  to phosphorus is  necessary because  alum
 neutralizes  alkalinity  to  lower pH.   The excess aluminum  is  pre-
cipitated  essentially as aluminum  hydroxide (Al (OH)3).

      In removing  80  percent of  the  phosphorus  from a 3,785  m3/day
 (1 mgd) plant,  the alum added will  produce 119  kg  (262  Ib)  of
A1P04 and  45 kg (100 Ib) of A1(OH)3 for  a  total weight  of chemi-
cal  solids of 164 kg/day  (363 Ib/day).

Iron Salts--
     Phosphorus is precipitated by  ferric  ions  to  form  FeP04- The
reaction  is very  similar to aluminum  precipitation, with  a  simi-
lar excess .of ferric ions needed over  the  stoichiometric  Fe/P

                                16

-------
ratio.  The excess ferric is precipitated as ferric hydroxide,
Fe(OH)3.  Ferrous iron may also be used.  If primary removal is
practiced, using ferrous iron and a base to raise the pH, phos-
phorus precipitates as Feo(P04)?.  However, the stoichiometric
ratio is 1.5 for ferrous insteaa of 1.0 with ferric.  If secon-
dary removal is practiced, using ferrous iron in the absence of
a base, the plant must have some modification of the activated
sludge process.  In this situation, the ferrous ion, Fe(II), is
converted to the ferric state, Fe(III).  Phosphorus precipitates
as FeP04 and excess iron precipitates as ferric hydroxide.  In
removing 80 percent of the phosphorus from a 3,785 m3/day plant,
ferric chloride added in 60 percent excess will produce 147 kg
(324 Ib) of ferric phosphate and 63 kg (138 Ib) of ferric hydrox-
ide for a total weight of chemical solids of 210 kg (462 Ib).

Summary--
     'Adding together the weights calculated for sewage and chemi-
cal solids gives the comparison shown in Table 6.  The weight
of additional SS removed by chemical  addition is not included.
The table shows the percentage of total plant solids produced  at
each treatment stage (primary, secondary, and tertiary).  For
instance, it indicates that the chemical solids produced during
lime addition make up over 50 percent of the total plant solids.
The dry weight of the total plant solids produced with lime addi-
tion is approximately twice that produced with either aluminum
or iron.  This is true whether the chemical is added at the pri-
mary or tertiary stage.  The weight of total plant solids produced
with either aluminum or iron is approximately equal.

     The data presented in Table 6 were used to calculate the
theoretical weights of solids generated per kg of phosphorus
removed, shown in Table 7.  These theoretical quantities will
be compared later in this section with values for the weights
of sludge per kg of phosphorus removed obtained from the litera-
ture and the treatment plant survey.   The literature and survey
data are based on actual plant operation and include the addi-
tional weight of SS removed during chemical treatment.

Sludge Generation Quantities as Reported in the Literature

     Recently there have been many studies reported in the liter-
ature dealing with the effectiveness of chemical addition for
phosphorus removal.  Unfortunately, since wastewater effluent
quality was the major concern of many of these studies, quantita-
tive determinations of sludge genreation rates were lacking. There-
fore the sludge generation values presented here, because they
represent only one or two information sources, should not be con-
strued as average sludge generation values.  These data should
merely be used to augment the sludge generation data from the
treatment plant survey found later in this section.
                                17

-------
CO
        TABLE 6.  TOTAL DRY WEIGHT OF SUSPENDED SOLIDS AND CHEMICAL SOLIDS REMOVED
           DURING TREATMENT PROCESSES AT A HYPOTHETICAL ACTIVATED SLUDGE PLANT*


SS Removed
Duri ng
Primary
Treatment
SS Removed
During
Secondary
Treatment
SS Removed
During
Tertiary
Treatment
Chemi cal
Solids
Produced

Total
Plant
Sludge
Solids


kg/day
(lb/day)

+
r
kg/day
(lb/day)


%
kg/day
(lb/day)


%
kg/day
(lb/day)


'%
kg/day
(Ib/day)


%
No Chemical
Addition

473
(1041)


55.5
378
(833)


44.5




—




—
851
(1874)


100
Primary Chemical
Addition
Lime
709
(1562)


39.5
142
(312)


7.9




—
9~45
(2082)


52.6
1796
(3956)


100
Al urn
709
(1562)


69.8
142
(312)


14.0




—
164
(362)


16.2
1015
(2236)


100
Iron
709
(1562)


66.8
142
(312)


13.4




—
210
(462)


19.8
1015
(2336)


100
Tertiary Chemical
Addition
Lime
473
(1041)


25.6
378
(833)


20.5
47
(104)


2.6
945
(2082)


51.3
1843
(4060)


100
Alum
473
(1041)


44.5
378
(833)


35.6
47
(104)


4.4
164
(362)


15.5
1062
(2340)


100
Iron
473
(1041)


42.7
378
(833)


34.1
47
(104)


4.2
210
(462)


19.0
1108
(2440)


100
     *Weight of  additional SS removed during chemical treatment not included.
     tPercent of total sludge produced in plant.

-------
      TABLE  7.   THEORETICAL  KILOGRAMS  OF SOLIDS GENERATED
             PER  KILOGRAM OF  PHOSPHORUS REMOVED AT A
              HYPOTHETICAL ACTIVATED SLUDGE PLANT*1"
Primary Chemical Addition
kg sludge SS/kg P removed
     Lime
     Aluminum
     Iron
             59
             33
             35
Tertiary Chemical Addition
     Lime
     Aluminum
     Iron
             61
             35
             37
*  Derived  from Table 6
t  Weight of additional SS removed during chemical treatment
   not included.
                               19

-------
 Lime--
      Primary  addition of 200 mg/£ of Ca(OH)2 in Ontario, Canada,
 to  achieve an 80 percent reduction in total phosphorus (10.3 to
 2.0 mg/l) resulted  in an increase in sludge generation from 0.17
 kg/m3  (141 Ib/MG) to 0.49 kg/m3 (4082 Ib/MG) (73).  The latter
 generation rate equals  59 kg of sludge per kg of phosphorus
 removed.  Another primary plant mentioned  in the same report
 showed  a  sludge increase from 0.16 kg/m3  (1316 Ib/MG) to only
 0.23 kg/m3 (1933 Ib/Mg) when adding 125 mg/a hydrated lime to
 achieve 80 percent  phosphorus removal.  A  theoretical discussion
 of  phosphorus removal reports 400 mg/a Ca(OH)o added to reduce
 effluent  phosphorus from 11.5 to 0.3 mg/a  will produce 0.75 kg/m3
 (6290  Ib/MG)  or approximately 68 kg of sludge per kg of phosphorus
 removed (19).

 Aluminum  Salts--
      Primary  addition of 150 mg/a aluminum sulfate  (alum) at the
 Barrie, Ontario, wastewater treatment plant to achieve 88 percent
 phosphorus removal  resulted in sludge generation of 0.3 kg/m3
 (2428  Ib/MG)  or 14  kg of sludge generated  per kg of phosphorus
 removed.  Secondary alum addition at the  Barrie plant of 75 and
 100 mg/a  generated  sludge at 0.39 and 0.31 kg/m3 (3275 and 2591
 Ib/MG)  respectively.  At one Canadian treatment plant, the pri-
 mary addition of 150 mg/a alum caused a negligible  sludge increase
 from 0.24 to  0.25 kg/m3 (2033 to 2049 Ib/MG); at a  second Canadian
 plant,  primary addition of 150 mg/a alum  caused a sludge quantity
 increase  of 55 percent  from 0.16 to 0.24  kg/m3 (1316 to 2033 Ib/MG)
 (73).

 Iron Salts--
      A  Canadian activated sludge plant adding 37.5  mg/a ferric
 chloride  to achieve over 95 percent phosphorus removal, experi-
 enced an  increase in sludge production from 6,200 m3/mil m3 to
 7,600'm3/mil  m3 with primary addition of  FeCls and  7,682 m3/mil m3
 with secondary addition of FeCls (2).  Primary addition of 20 mg/£
 FeCls at  Sarnia, Ontario, wastewater treatment plant to reduce
 the  effluent  phosphorus concentration by  80 percent  (5.71 to
 1.16 mg/a) ,   resulted in a sludge production of 0.2  kg/m3 (1,643
 Ib/MG), or 43 kg of sludge per kg of phosphorus removed (30). The
 previously mentioned EPA Technology Transfer Publication predicts
 that an 80 mg/£ FeCls dosage used to reduce a phosphorus concen-
 tration from  11.5 to 0.3 mg/a will produce 0.32 kg/m3 (2,662 1b/
 MG)   or 28.5 kg of sludge per kg of phosphorus removed (19).

 Sludge Generation Quantities as Reported  by the Treatment
 Plant Survey

     Approximately 100  plants responding  to the questionnaire  sur-
vey   provided  information pertinent to sludge volumes and/or weight.
Often only fragmentary data or crude estimates were  provided.   In
addition,  it is difficult to compare sludge generation by dif-
ferent treatment plants because such individual factors as raw

                                20

-------
sewage characteristics, plant design, etc., may have a profound
effect and distort the results.  Nevertheless, the responses were
analyzed to look for confirmation of the theoretical and litera-
ture information presented in the previous subsections.  The ques-
tionnaire data are displayed in the form of bar graphs in Figures
2 through 5.  The bars indicate average values based on the
responses of several treatment plants.  Each bar displays a dif-
ferent type of information.  Therefore, the value for each bar is
generally the average of data from a different set of plants than
was the basis for any other bar.  This explains some of the incon-
sistencies in the results.

     Figure 2 summarizes the reported sludge volume generated per
unit mass of phosphorus removed.  The numbers refer to sludge
volume before thickening.  The following trends are apparent:

     •  Lime addition generates roughly twice the volume of sludge
        as does alum or iron addition

     t  Chemical additions to the secondary treatment process
        generate substantially more sludge volume than chemical
        additions to the primary treatment process.  However, if
        the secondary sludge is recycled back to the primary tank,
        the overall plant  sludge volume is not appreciably more
        than if the chemicals were initially added to the primary
        treatment process.  In other words, there appears to be
        a definite disadvantage, in terms of total raw sludge
        volume generated,  to handling the secondary sludge sepa-
        rately.  Presumably, the secondary sludge thickens in
        the primary tank.

     Figure 3 summarizes the reported volume of sludge generated
per unit volume of plant influent.  As in Figure 2, the numbers
refer to sludge volume before thickening.  The trends found in
Figure 3 are similar to the Figure 2 results.  In addition, suf-
ficient questionnaire data was available to compare increases in
sludge volume resulting from the chemical addition with sludge
volumes generated prior to the chemical addition.  Increases in
sludge volume resulting from the addition of iron, aluminum, or
lime to the primary clarifiers were:

     •  25  percent  for  iron salt  additions
     «  58  percent  for  aluminum  salt  addition
     •  huge  for  lime  addition.

     As previously  stated, the  results  shown  are  averages  of  the
values reported by many  plants  and  should  not  be  used  for  pre-
dicting actual sludge volume at  a  specific  plant  since  many  other
plant-specific variables affect  sludge  volume.   It  should  also
be  noted that the huge   lime sludge  volumes  reported  are  greatly
decreased by sludge thickening.


                                21

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      Figure 4 summarizes the reported mass of sludge generated
 per  unit mass of phosphorus removed.  The results were inconclu-
 sive  in defining differences in sludge weight generated by the
 three common types of chemicals, i.e., lime, aluminum salts, and
 iron  salts.

      Table 7 shows the calculated weights of solids generated at
 a  hypothetical activated sludge plant with addition of various
 chemicals.  The effect of additional sludge generation due to
 improved plant efficiency is not included.  These sludge weights
 are  compared in Table 8 with the averages from Figure 4.  It can
 be seen that the average rates of sludge mass generation based on
 the  questionnaire  survey are higher than the theoretical quanti-
 ties  calculated.   This is a reasonable finding because the survey
 data  reflect the total increase in sludge mass due to phosphorus
 removal, including the effect of improved plant efficiency.


   TABLE 8.  COMPARISON OF THEORETICAL SOLIDS GENERATION RATES
               WITH RESULTS OF QUESTIONNAIRE SURVEY

Chemical Added
kg of dry soli
Theoretical *
Lime 60
Aluminum 34
Iron 36
ds/kg of P removed
Questionnaire"1"
70
35 - 75
40
  *  Derived from Table 7.
  t  Taken from Figure 4.


     Figure 5 summarizes the reported weight of sludge generated
per m3 of sewage treated.  Of particular interest on this figure
are the increases in sludge weight reported after chemical addi-
tion was implemented.  The average weight of the total plant
sludge increased 54 percent with iron addition, 18 percent with
alum addition.  Overall, the reported sludge weights were on  the
high side of the ranges expected from the theoretical calculations
presented earlier in this section.

SOLIDS CONCENTRATION AND PERCENT VOLATILE SOLIDS OF CHEMICAL
SLUDGES GENERATED

     In addition to changes in the amounts of sludges generated,
chemical  addition for phosphorus removal also has.an effect on
sludge physical  characteristics.  The major impacts on sludge

                                26

-------
characteristics, no matter which chemical is added for phosphorus
removal, are on the sludge total and volatile solids concentra-
tions.  Table 9, which is based on the questionnaire survey of
plants practicing phosphorus removal , shows the solids charac-
teristics of the sludges before thickening or other processing.
The sludges produced  by  iron primary addition can be seen to have
had the greatest average TS concentrations.  Somewhat less,con-
centrated were  the sludges produced  by iron tertiary and alum
primary addition.  The average TS concentrations of the iron ter-
tiary addition  and alum  primary addition sludges were similar.
The least concentrated sludges were  those produced by iron and
alum  addition to the  secondary step.  The average TS concentra-
tions of the iron secondary addition and alum secondary addition
sludges were similar.  The table indicates that for all of the
iron  and alum sludges, the average sludge TS concentration tended
to  be greater  when the  chemical sludge was combined with the other
sludges produced in the  plant.

      The sludge VS fraction (as a percentage of the TS concentra-
tion) appears to have  been highest when alum was added to the
secondary step. Alum sludges  had higher VS fractions than iron
sludges; and sludges  produced  by secondary  iron or alum addition
had higher  VS fractions  than those produced by primary or tertiary
addition.   The  table  shows that iron-tertiary sludge had a very
low VS  fraction; but  that, when it was combined with the other
sludges produced in the  plant,  the total plant sludge had a normal
VS fraction.

      The information  in  the table shows  that the  sludges produced
with  lime had low TS  concentrations.  This  information could be
misleading,  however,  unless it  is remembered that the sludges
were  sampled before thickening.  Lime sludges are readily thick-
ened  to around  10 percent  TS.   The VS fraction of the lime-tertiary
sludge  was  low, even  when  combined with  other plant sludges.
Unfortunately,  no information  on the volatile contents of sludges
produced by  primary addition of lime was contained  in the
questionnaire.
                                27

-------
                           TABLE 9.  SOLIDS CHARACTERISTICS OF CHEMICAL SLUDGES
                           WITH AND WITHOUT COMBINATION WITH OTHER PLANT SLUDGES
Type of chemical sludge
and whether combined with
other plant sludge(s)
Iron addition to primary step -
Primary sludge
Total plant sludge
Iron addition to secondary step -
Secondary sludge
Total plant sludge
Iron addition to tertiary step -
ro Tertiary sludge
00 Total plant sludge
Alum addition to primary step -
Primary sludge
Total plant sludge
Alum addition to secondary step -
Secondary sludge
Total plant sludge
Lime addition to primary step -
Primary sludge
Total plant sludge
Lime addition to tertiary step -
Tertiary sludge
Total plant sludge
Sludge characteristics (before thickening, digestion, etc.)
Total solids (%)
Volatile solids (% of TS)
Range Average

3.4 - 8.0 5.
2.31-10.0 5.

0.2 - 4.0 0.
0.5 - 7.75 4.

4.0 4.
4.64- 5.0 4.

3.3 - 4.35 3.
3.96- 5.0 4.

0.4 - 4.4 1.
1.0 - 7.0 3.

0.7 - 1.5 1.
0.64- 0.82 0.

2.5 - 4.0 3.
1.95 1.

26
73

93
13

0
82

95
49

41
82

1
73

3
95
Range

45-69
40-70

50-70
42-72

35
62

61-67
46-70

60-78
52-70

N/A
N/A

11-30
39
Average

57
57

62
62

35
62

65
59

67
59

N/A
N/A

21
39
Note:  N/A = not available.

-------
                            SECTION 4

               PREVALENCE OF VARIOUS TREATMENT AND
              DISPOSAL METHODS FOR CHEMICAL SLUDGES
INTRODUCTION
     The sludges resulting from chemical addition for phosphorus
removal at municipal wastewater treatment facilities generally
require treatment before final disposal.  The many unit processes
used for handling and disposal of these chemical sludges can be
segregated into the following categories: sludge thickening; sta-
bilization/reduction; conditioning/stabilization; dewatering;
heat drying; reduction; and final disposal.

     The prevalence of certain unit processes within the above-
mentioned categories, as determined from the treatment plant
questionnaire survey will be discussed on the following pages.
This narrative should be reviewed in conjunction with the infor-
mation on Table 10.

SLUDGE THICKENING

     Gravity thickening was the most prevalent thickening tech-
nique for all types of chemical sludges, and was practiced by 85
percent of the plants with a thickening step.  Flotation thicken-.
ing was used for thickening of waste activated sludges or occa-
sionally for combined primary sludge and waste activated sludge.
This was in accordance with the common application of air flota-
tion to the separate thickening of waste-activated sludges.   The
sludges that were flotation thickened were produced with secon-
dary addition of iron or aluminum, except in one case of primary
addition of iron.  Interestingly, centrifuge thickening was  prac-
ticed at six plants using lime, but was not applied to the thick-
ening of iron or aluminum sludges.

SLUDGE STABILIZATION/REDUCTION

     Anaerobic and aerobic digestion were the most prevalent
sludge stabilization/reduction processes.  Among plants using
iron salts,  anaerobic digestion was used considerably more fre-
quently than was aerobic digestion.  In contrast, aerobic diges-
tion was used almost as often as was anaerobic digestion among
plants using aluminum salts.  Anaerobic digestion of a lime sludge

                                29

-------
             TABLE 10. PREVALENCE OF TREATMENT AND DISPOSAL PROCESSES FOR CHEMICAL SLUDGES
                              AMONG PLANTS RESPONDING TO QUESTIONNAIRE SURVEY *
SI udge
Treatment and
Disposal Unit
Processes
Major Chemical Used and Point of Addition


Prim-
ary

Iron Salt
Second-
ary


Terti-
ary

Aluminum Salt
Prim- Second- Terti-
ary ary ary


Prim-
ary

Lime
Second-
ary


Terti-
ary



Total
CO
o
     Thickening
Gravity
Flotation
Centrifuge
Stabilization/
Reduction
Composting
Aerobic Dig.
Anaerobic Dig.
18
1
0


1
4
27
25
4
0


0
11
37
2
0
0


0
1
1
4
0
0


1
1
5
18
5
0


0
24
25
1
0
0


0
0
1
8
0
5


0
0
1
0
0
0


0
0
0
0
0
0


0
0
0
76
1Q
5


2
41
97
     Lime
     Stabilization

     Conditioning/
     Stabilization
Chemical
Conditioning
Elutriation

11 12 1 2 12 0 20 0 40
1200000003
     Thermal
     Conditioning
0       11

    (continued)

-------
    TABLE 10 (continued)
SI udae
Treatment and
Disposal Unit
Processes



Prim-
ary
Major

Iron Salt
Second-
ary
Chemical Used and Point of Addition


Terti-
ary

Aluminum Salt
Prim- Second- Terti-
ary ary ary


Prim-
ary


Lime
Second-
ary



Terti-
ary



Total
co
Dewatering
Pressure Filter
Air Drying Beds
Centrifuge
Vacuum Filter
Horizontal Moving
Screen Concen-
trator
Cylindrical
Rotating Gravity
Filter
Lagoon
Heat  Drying
Flash Dryer
Multiple Hearth
Dryer
1
17
0
12
0
3
20
0
13
0
0
0
0
1
0
1
2
1
1
0
1
18
4
10
2
0
0
0
0
0
2
1
0
0
0
0
0
0
0
0
1
0
1
0
1
8
58
6
37
3
                          0
                          0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
                                                                                                       16
1
2
                                                                                                (continued)

-------
     TABLE 10 (Continued)
on j
Sludge
Treatment and
Disposal Unit
Processes
^^W-A^^BVW^M^^^W

Prim-
ary

Iron Salt
Second-
ary
^^^^^^^^^^^^^^^^^^^^^^ta^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^«*^WMV-WII^^^^^^WW^^^^^^^^^^^^^^»«
Major Chemical Used and Point of Addi

Terti -
ary
Aluminum Salt
Prim- Second- Terti-
ary ary ary

Prim-
ary
tion
Lime
Second-
ary
^B^^^^_^^^HBVM^i^HHH_Hlk

Terti-
ary
^^^^^^^^•W^V^MM^^BB


Total
CO
     Reduction
Incineration 7
Final Disposal
Agricultural 18
Fields, Lawns,
Gardens
Land Reclamation
Sanitary Landfill 16
Private- or 8
Authori ty-owned
Dump- site
5

39


1
18
10


0

1


0
1
0


0

7


1
1
2


5

30


6
13
8


Q

1


0
0
0


5

5


1
4
2


Q

Q


0
0
0


0

1


0
0
1


22

102


9
53
31


       One plant  may use more  than  one method of thickening,  dewatering, etc.

-------
was occurring at one plant.  Three plants reported having compost-
ing operations involving iron or aluminum sludges.  Chemical  sta-
bilization by lime was practiced infrequently.

SLUDGE CONDITIONING/STABILIZATION

     Chemical conditioning was the most prevalent conditioning
method and was used for conditioning all types  of chemical  sludges
prior to dewatering.  Thermal conditioning was  in use at eleven
plants which had iron or aluminum sludges.  Elutriation was also
practiced by three plants with iron sludges.

SLUDGE DEWATERING

     Dewatering of chemical  sludges on air drying beds was  more
common than other dewatering methods, including vacuum filtration,
which followed it in frequency.  Both pressure  filters and  cen-
trifuges were also receiving application at a number of plants,
pressure filters being used  for iron, aluminum  and lime sludges,
and centrifuges for aluminum and lime sludges only.   Horizontal
and cylindrical screens were infrequently- used.  Sludge lagoons
were common, but often they  were not the sole dewatering method
used at a plant.

SLUDGE HEAT DRYING

     Heat drying by either flash or multiple hearth  dryers  was
practiced in only three plants.

SLUDGE REDUCTION

     Incineration with multiple hearth or fluidized  bed inciner-
ators was practiced at 22 plants.  Most of these plants handled
iron sludges, but both aluminum and lime sludges were also  incin-
erated.

SLUDGE FINAL DISPOSAL

     The two major final disposal sites for chemical sludges were
agriculture fields, lawns, or gardens; and sanitary  landfills or
dumps.  A sanitary landfill  is an engineered operation involving
the spreading of refuse on land in thin layers  which are com-
pacted and covered with earth each day.  In contrast, a dump is
a state-approved site where  sludge is spread or buried on land
(not to be later removed) and is not as closely controlled  as a
sanitary landfill; neither does it receive refuse.
                               33

-------
                            SECTION  5

                 THICKENING OF CHEMICAL  SLUDGES


GRAVITY THICKENING

Introduction

     As previously shown in Table 10,  a total of 76 (44 percent)
of the plants responding to the questionnaire survey maintained
gravity thickeners.  Among the plants  which reported having a
thickening  step, 85 percent utilized gravity thickening.   Gravity
thickening  is simple and is the least  expensive  of the available
thickening  processes used for sludge concentration prior  to
digestion and/or dewatering.  The process allows blending of
sludges and sludge flow rate equalization, thereby improving the
uniformity  of feed to the subsequent processes.

Questionnaire Survey

     Nine plants which were surveyed indicated that chemical addi-
tion was having a significant impact on their gravity thickening
process.  The impacts were attributed  to both increased sludge
quantities  and changed sludge characteristics and ranged  from
improvements in thickening to adverse  impacts.  The experiences
of five of  these plants are summarized in Table 11.  Four other
plants were case study sites and will  be discussed further on.

     Sludge settleabi1ity was a problem at two of the three
plants using iron; the third plant experienced improved settle-
ability during iron addition.  The two plants using lime found
that the sludge thickened readily to 7 to 10 percent TS.    Insuf-
ficient thickener capacity for the additional sludge was  a con-
cern at one of these plants, however.

Case Studies

     The case studies in the appendices contain detailed infor-
mation on the effects of chemical addition on gravity thickening.
The particular case studies which deal with this subject are
Sheboygan,  Wisconsin; Port Huron, Michigan; Lakewood, Ohio;  and
South Bend,  Indiana.  The experiences  at these plants are  similar
to the experiences of plants responding to the questionnaire  sur-
vey.   However, some unusual highlights of the case studies  can
be mentioned.
                               34

-------
                   TABLE 11.    IMPACTS  OF  CHEMICAL  SLUDGE  UPON  GRAVITY THICKENING PERFORMANCE
                                     AS REPORTED  IN QUESTIONNAIRE  RESPONSE
      Location
                 Size
                m3/day
                (mgd)
              Type of Raw
             Sludge Treated
         Impacts of Chemical Sludge
CO
     Mil ford,
     Michigan
     Wayne Co.-
     Wyandotte,
     Michigan
Ford Lake
WWTP,
Ypsilanti,
Michigan

Virginia,
Minnesota
     Hatfield Twp.-
     Colmar,
     Pennsylvania
  3,000    Iron-secondary and
  (0.8) •    primary from a con-
           ventional activated
           sludge plant

291,400    Iron-primary and
  (77)     secondary from a
           pure oxygen activat-
           ed sludge plant

 22,700    Iron-secondary and
  (6)      primary from a step
           aeration activated
           sludge plant

  8,700    Lime-primary and
  (2.3)    secondary from a con-
           ventional waste acti-
           vated sludge plant
                  8,700    Lime-primary,
                  (2.3)    aluminum-tertiary and
                           secondary from a
                           complete mix acti-
                           vated sludge plant
                                                    The sludge thickens better and is forming more
                                                    supernatant.  There is more room for sludge in the
                                                    thickeners, which are operated as holding tanks.
                                                    The sludge is harder to thicken.
                                                    (fluffier).
                                  It is lighter
It has been very difficult to handle the extra
sludge generated by phosphorus removal because the
thickener bulks back to the aeration tanks before
wasting is finished.

The plant converted from anaerobic digestion and
drying beds to gravity thickening, lime stabiliza-
tion and lagoons in anticipation of phosphorus re-
moval with lime.  The thickener produces an 8 to
10 percent TS sludge.

The sludge thickens to 7.0 percent TS.  Although
sludge settleability is fine, the additional  sludge
is overloading the thickener.  The thickener over-
flow contains 8,400 mg/jn, SS and 3,500 mg/Jl BOD.   The
superintendent feels that the high solids content of
the overflow is not hurting the plant because the
associated aluminum mixes with the raw sewage and
lime and may improve primary clarification.

-------
     At the Sheboygan, Wisconsin, case study site, primary and
secondary sludges were fed to a single thickening unit and gravity
thickened to an average TS'cOncentration of 8.6 percent before
chemical addition for phosphorus removal began.  After secondary
addition of ferric chloride was incorporated into the treatment
system, the sludge was gravity thickened to 7.76 percent TS on
the average.  The thickened sludge solids concentration was lower
after phosphorus removal was started despite an increase in the
average concentration of the primary sludge fed to the thickener.
Problems with floating of the sludge blanket and resulting high
solids overflow were experienced in thickener operation both
before and after phosphorus removal, but were more frequent after
phosphorus removal.  The problems with high floating sludge tended
to coincide with industrial waste discharges.  A means of reducing
thickener solids overflow was found which involved adding polymer
separately to the primary and secondary sludge feed lines to
achieve the same concentration of polymer in the sludge in each
line.  In other words, the amount of polymer added to each line
was proportional to the sludge flow.  The polymer was added
through a plastic hose to a point immediately before the discharge
end of the feed lines into the thickener center well.  The usual
dosage was 3 ppm.  During the first 4 months after proportional
polymer addition was started, the thickener overflow TS concen-
tration averaged only 154 mg/a, compared to previous concentra-
tions as high as 2,000 mg/a TS.

     At Port Huron, Michigan, aluminum sulfate was added to the
activated sludge basins for phosphorus removal.  The plant used
a Dorr-Oliver "Densludge" type SD gravity thickener.  Waste acti-
vated sludge was pumped to a box ahead of the thickener where it
was combined with primary sludge and polymer.  On the average,
the raw sludge thickened from 0.56 to 4.68 percent total solids,
and the overflow contained approximately 2,480 mg/£ SS.  However,
due to variations in the activated sludge wasting rate and inter-
mittent incinerator operation, performance of the gravity thickener
was very inconsistent.

     The thickened sludge concentration reached almost 6 percent
on a few good days; only about 4 percent on poor days.  The over-
flow solids concentration varied greatly from day to day between
about 100 mg/£ and 10,000 mg/£.  These variations were related  to
the addition of alum to the aeration basins.  Alum addition
increased the mass of activated sludge which was generated and
wasted.   This waste activated sludge had poorer  thickening  charac-
teristics than the primary sludge, so that when activated sludge
wasting rates were high, thickening was poorer.  Low thickened
sludge solids concentrations led to higher polymer requirements
for chemical conditioning.

     Recently at Port Huron, modifications in  thickener opera-
tion have been made with significant results.  Two identical  grav-
ity thickeners are used rather than just one.  In the past, the
sludge blanket depth approached 2.1 m (7 ft) in the  single  3.4

                               36

-------
m- (10 ft-) deep thickener.  Polymer addition was necessary to
aid solids capture and thickening.  With two thickeners, the
sludge blanket depth is maintained between 1.2 and 1.5 m (4 and
5 ft), and no polymer is used.

     The savings in polymer cost amounts to $2.75/t ($2.50/ton)
of dry solids.  It is also reported that a reduction in the
amount of phosphorus recycled to the head of the aeration basins
in the thickener overflow  has occurred.  This may mean a slight
decrease in the cost of phosphorus removal chemicals.

     The Lakewood, Ohio, plant treats aluminum waste activated
and primary sludges which  are combined in gravity thickeners.
The thickener overflow is  returned to the head of the plant.
Lakewood is an older facility whose effluent quality is impaired
due to hydraulic overloading and inadequate solids handling capa-
city.  Alum addition adversely affected gravity thickener opera-
tion as the result of the  generation of additional sludge solids.
The mass of waste activated sludge pumped to the thickeners
increased by  4.3 t/mil rrr  of  (360 Ib/MG) of wastewater treated.
These additional solids increased the overloading of the thick-
eners, and problems with bulking and poor overflow quality became
more severe.  The thickener overflow quality deteriorated to the
extent that the overflow contributed a higher loading of SS to
the primary clarifiers than did the plant influent.  The plant
alleviated the problem by  removing sludge from the thickeners at
a faster rate by increasing the capacity for digestion, dewater-
ing, and final disposal.   Inadequate capacity in these areas had
been causing  a bottleneck  in the solids-handling system.

     At South Bend, Indiana, lime was added to two tertiary up-
flow clarifiers for phosphorus removal.  The volume of lime
sludge generated was 1,158 m3/day (306,000 gal/day).  The average
sludge TS concentration was 4.0 percent.  Gravity thickening
reduced the sludge volume  to 454 nr/day (120,000 gal/day) and con-
centrated the sludge to 10.2 percent TS.

Literature

     Accounts of gravity thickening of chemical sludges presented
in the literature are summarized in the following paragraphs.

     An EPA pilot plant using lime for phosphorus removal and
lime recovery by recalcination found that the recycling of the
lime markedly improved the thickening properties of the sludge
(5).  With lime recycling, the solids were reduced to 26 percent
of their original volume after one hour of settling.  Without
lime recycling the same volume reduction required approximately
5 hours.  Typically the gravity thickener produced sludges of  15
to 20 percent solids for either sludge type.

     For a 15 percent solids thickener underflow concentration,
the improved  settling characteristics increased the thickener

                                37

-------
                                       2
capacity from a loading rate of 92 kg/m /day without lime recy-
cling to 1,470 mg/m^/day with recycling.  Since the increase in
thickener capacity was much greater than the actual increase in
solids loading, less thickener area was required during lime
recycling.

     The Holland, Michigan, wastewater treatment plant adds lime
to the primary clarifiers for phosphorus removal (43).  Excess
activated sludge from the final clarifiers is pumped to the thick-
ener and combined with the primary sludge.  An adequate supply of
dilution water is mixed with the activated sludge fed to the
thickener.  The dilution water, clarified secondary effluent,
serves two purposes.  It contains dissolved oxygen which helps
keep the thickener sludge from becoming septic.  It also lowers
the solids concentration in the feed to a level where the parti-
cles are not hindered in settling.  The thickener has produced
an underflow solids concentration of 7.4 to 17 percent TS.

     To improve thickener operation at Holland, the following
modifications were made:  The thickener was provided with vertical
pickets to help release supernatant from the sludge in compres-
sion; additional vertical mixing bars were attached to aid this
process; and there was a modification to the rakes to prevent
furrowina the sludge blanket.

     The centrate from the sludge centrifuges was  originally
returned to the sludge blanket in the thickener.   The return of
centrate to this blanket disrupted both the thickening and clari-
fication process.  The centrate lines were re-routed  to the ash
thickener.  The overflow from the ash thickener was returned to
the plant influent.

     An EPA study by the Wastewater Research  Division  of the
Municipal Environmental  Research  Laboratory  (76) examined  the
thickening characteristics of an  aerobically  digested  aluminum
sludge with and without  polymer conditioning.   Aerobically
digested waste activated sludge grom a  2  to  3  mgd  plant was
thickened in a 2-a graduated cylinder.  The  results were poor:
At initial sludge TS concentrations of  greater  than  1  percent,
virtually no thickening occurred.  With an  initial  sludge  TS
concentration of 0.86 percent, thickening  to  1.62  percent  was
possible.  Polymer conditioning improved  thickening  somewhat,
but the final sludge TS concentration was  still  below 3  percent.
Significant thickening occurred only at an  initial  TS  concentra-
tion of less than 1 percent both with and  without  polymer  con-
ditioning.


   - At Portage Lake,  Michigan, gravity thickening  of an aerobi-
cally  digested alum sludge was measured in laboratory cylinders  (2)
                               38

-------
(See page 64 for a description of the Portage Lake plant.)   Waste
activated sludge produced alternatively with and without alum
addition to the plant's aeration basins was digested in full-scale
aerobic digesters.  The laboratory tests showed that the sludge
produced with alum addition thickened more rapidly and to a higher
solids concentration than the sludge produced without alum  addi-
tion.

Conclusions

     The impacts of chemical addition for phosphorus removal  on
sludge gravity thickening are attributable to both increased
sludge quantities and changed sludge characteristics.

     Lime addition for phosphorus generally improved the thicken-
ing characteristics of the sludge.  Gravity thickened lime
sludges typically have an average TS concentration of 10 percent,
but the approximate range is 7 to 20 percent.  In contrast, sludge
thickening characteristics may be either favorably or adversely
affected by the addition of iron or aluminum salts.   At each
plant, the impact will depend on the influent wastewater charac-
teristics, the type of wastewater treatment, the relative propor-
tions of primary and secondary sludges, and the sludge pumping
procedures.

     Thickener overloading is a frequent result of the increased
amounts of sludge generated with any of the phosphorus removal
chemicals.  Even slight overloading causes serious problems
because of the sensitivity of gravity thickeners to  the critical
control variables of loading rate and sludge blanket depth.  In
most plants where problems have occurred, however, thickener
capacity was already insufficient before phosphorus  removal
began.

     The information which has been presented suggests several
ways of modifying plant operation to overcome some of the adverse
impacts of chemical sludges on thickening.  For instance, adding
lime or a polymer to the sludge as it enters the thickener can
be helpful.  At Sheboygan, Wisconsin, it was found that the suc-
cess of polymer addition depended upon finding the right point
of addition and dosage rate through a considerable amount of
experimentation.

     At several of the case study sites, return sidestreams were
suspected of disrupting thickener operation.  Recycle streams
such as digester supernatant and centrifuge centrate can carry
heavy loads of difficult-to-settle solids which have a negative
impact on sludge settleability.  Treating these sidestreams or
rerouting them to a different point in the plant may indirectly
cause an improvement in thickener operation.
                               39

-------
FLOTATION THICKENING

Introduction

      Flotation thickening is becoming an increasingly popular
method of sludge thickening prior to further handling.   Among the
variables that affect flotation thickening performance  are:

        Sludge feed solids concentration
        Sludge detention period
        Type and quality of sludge
        Solids and hydraulic loading rates
        Use of chemical aids.

      As a general rule, the higher the solids loading rate,  the
lower the solids concentration of the thickened sludge.   When
thickening a mixture of primary and waste activated sludge,  a
higher solids loading rate is allowed and a thicker sludge is
produced than when thickening waste activated sludge alone.  Higher
loading rates and thicker sludges also result from chemical  aids
(usually cationic polyelectrolytes), which increase the capture
of solids, improving the quality of the subnatant.

      Chemical addition for phosphorus removal can affect process
performance by changing the relative amounts of primary and  waste
activated sludge generated in a plant, by altering feed sludge
solids concentrations, or by modifying feed sludge quality.   Chem-
ical  addition can also affect process economics by changing  the
relative amounts of primary and waste activated sludges generated.
On an economic basis, flotation thickening is considered to  be
most  applicable to waste activated sludges, and is generally used
when  a plant has no primary sludge or when separate gravity  thick-
ening of primary sludge is provided.

Questionnaire Survey

      Used by 6 percent of the plants responding to the question-
naire survey, flotation was shown to be the second most common
method of chemical sludge thickening.  Unlike the more common
gravity thickening, which is applied to both trickling filter and
waste activated sludges, flotation is applied only to waste acti-
vated sludge.  Nine plants which responded to the questionnaire
survey commented upon the performance of their flotation units
and the impacts of the chemical sludges.  Table 12 summarizes
these comments, indicating the type of sludge treated at each
plant and the type of sludge treatment system.

     All  but one of the plants treated iron or aluminum waste
activated sludges.  These sludges were produced by secondary
addition  of the chemical and were not mixed with  primary sludge
before thickening.  The other plant was an exception because  it
practiced primary chemical addition and it thickened a mixture

                               40

-------
             TABLE  12.    IMPACTS OF CHEMICAL  SLUDGES UPON  FLOTATION  THICKENER  PERFORMANCE
                                      AS REPORTED  .IN  QUESTIONNAIRE  RESPONSE
Plant Location
Type of Sludge
  Treated
     Impacts of  Chemical
          Sludge
Performance with Chemical
         Sludge
     Further Treatment
Warren,
Michigan
Zilwaukee,
Michigan
MeHenry,
Illinois
Alum-secondary
(aeroblcally
digested)
Iron-secondary
(aerobically
digested) from
a plant with
no primary
treatment
Iron-primary
and secondary
(aerobically
digested)
Although the feed  sludge solids
concentration remained the same,
It was necessary to reduce the
hydraulic loading  rate by 10
or 20 percent.  No change in
polymer dosage was necessary.

The plant has always treated
iron sludge and, therefore,
comparisons cannot be made.
The SVI of the  chemical sludge
is only 60 to 70 compared to a
high SVI before iron addition
The proportion  of waste acti-
vated sludge 1n the thichener
feed has increased.  Before Iron
addition, cationic polymer was
used as a thickening aid and
the sludge was  easily concen-
trated to 7 to  8 percent TS.
With the iron sludge it has
been necessary  to use both
anionic and cationic polymers
and the thickened sludge only
reaches 5 to 6  percent TS.
Sludge at 1  percent TS is
thickened to 5 percent.
The sludge from  the aerobic
digester averages only 1.5
percent TS.   It  was thick-
ened by flotation to only
2.5 percent TS.  Flotation
was discontinued because it
could not deliver sludge
fast enough for  the vacuum
filters.   Polymer as a
thickening aid was tried
and it  lowered  the SS con-
centration of the subnatant
from 50 to 12 mg/fc, but had
no other effect.
Blending with primary  sludge;
Polymer conditioning;
Vacuum filtration;
Incineration
Polymer conditioning;
Vacuum filtration;
Sanitary landfill
                            Polymer conditioning;
                            Vacuum filtration;
                            Croplands
                                                                                                                (continued)

-------
            TABLE  12  (continued)
            Plant  Location
Type of Sludge
  Treated
     Impacts of Chemical
          Sludge
 Performance with Chemical
          SIudge
      Further Treatment
            Gurnee,
            Illionis
Iron-secondary    No impacts were noticed.
            Oak Creek,
            Wisconsin
Iron-secondary    No impacts were noticed.
ro
            Willoughby-
            Eastlake,
            Ohio
Alum-secondary    No impact;were noticed.
            Middleburg
            Hts., Ohio
Alum-secondary
(aerobically
digested) from
plant with no
primary treat-
ment
The average thickened sludge
TS concentration was 2.5
percent before alum addition
and since has been 3.3 per-
cent TS.
The feed sludge at 8500
ppm SS is thickened to 4.8
to 5.1 percent TS.  The
subnatant contains 70 to
80 mg/Ji SS,   Polymer is
used to aid solids capture.

Sludge at 1.0 to 1.5 per-
cent TS is thickened to
3.5 to 4.0 percent.  The
subnatant SS concentration
ranges under 500 ppm.
Polymer is used when a
high loading rate is needed
to keep up with a high
activated sludge wasting
rate.

The sludge can be concen-
trated to 4 percent, or as
high as 7 percent.  At the
higher concentration, the
sludge loading rate is
slower and the subnatant
contains more solids.  The
subnatant SS concentration
varies from 52 to 3000
mg/n. Polymer to aid thick-
ening is not used.

The subnatant SS concen-
tration is averaging 300
mg/4 SS.
                                                                                 Combined with primary  sludge;
                                                                                 Lime and FeClj conditioning;
                                                                                 Vacuum filtration;  Sanitary
                                                                                 landfill
                                                               Combined with primary sludge;
                                                               Anaerobic digestion; Drying
                                                               lagoons; Croplands or sanitary
                                                               landfill
                                                               Combined with primary  sludge;
                                                               Lime and Fed? conditioning;
                                                               Vacuum filtration;  Incinera-
                                                               tion or dumpsite
Lime and FeClg conditioning;
Vacuum filtration;  Incinera-
tion
                                                                                                                              (continued)

-------
      TABLE  12 (continued)
                         Type of Sludge
       Plant Location      Treated
                        Impacts of Chemical
                             Sludae
                                    Performance with Chemical
                                             Sludge
                                    Further  Treatment
       Kenosha,
       Wisconsin
       Frankenmuth,
       Michigan
Iron-secondary    No impacts were noticed
CO
Primary sludge
is anaerobically
digested then
sent to acti-
vated sludge
aeration basins.
The aluminum-
secondary sludge
is flotation
thickened
The plant has tried iron for
phosphorus removal  but feels
that the sludge is  easier to
thicken and.dewater when
sodium aluminate is used.
Sludge feed at 1 percent TS
is thickened to 4 percent
TS.  No polymer is used to
aid thickening because it
seems to provide no signi-
ficant improvement.

Feed sludge at 0.6 percent
SS can be concentrated to
3.5 percent TS, or as high
as 4.0 percent.  At the
higher concentration the
loading rate is slower,
however.  Thickening is
easiest when the sludge
density index of waste
activated sludge is kept
above one.  A small concen-
tration of polymer is used
(.011 kg/kg of solids)  to
help the sludge fall  off the
skimmers neatly, but it does
not increase the sludge
solids concentration.   The
subnatant averages 209 mg/j.
SS and 100 mg/fc BOD.
                                                               Combined with primary sludge;
                                                               Anaerobic digestion; Lime
                                                               and FeCl3 conditioning;
                                                               Pressure filtration; Crop-
                                                               lands
Lime and FeClq conditioning;
Vacuum filtration;  Sanitary
landfill

-------
of primary and secondary sludges.  Aerobic digestion of the sludge
before thickening was practiced by half of the plants listed in
the table, while fewer anaerobically digested after thickening.
All nine plants had a dewatering step, most using vacuum filters,
but one using a pressure filter and another using drying lagoons.

      Four of the plants reported a significant change in flota-
tion  unit performance related to the chemical sludges, while four
reported no change at all.  A ninth plant could not comment on
the impact of chemical addition, but described the performance of
their flotation unit with a chemical sludge.  Among the four
plants that noted significant changes, one reported a positive
impact: an increase in the thickened sludge TS concentration.
The other three plants reported negative impacts: the need to
reduce the sludge hydraulic loading rate, the need to use both
anionic and cationic polymers as thickening aids, and a decrease
in the thickened sludge TS concentration.

      Some of the plants reported that the addition of a polymer
to aid thickening was not necessary; others found that polymer
addition increased the allowable sludge loading rate or improved
the subnatant quality.  One plant noted that thickener perform-
ance  was aided by running the bottom flights of the unit contin-
ually instead of just when the bottom pumps were on.  Two plants
related good performance to either a high sludge volume or sludge
density index.

Li terature

      A theoretical discussion of sludge generation rates by
Knight, et al. (40), indicated that the waste activated sludge
portion of the total sludge produced in a plant is changed when
a phosphorus removal chemical is added ahead of the primary clar-
ifiers.  Theoretically, in a conventional activated sludge plant,
44.5  percent of the total sludge mass is waste activated; in the
same  plant with primary chemical addition, only 8 to 14 percent
of the total sludge mass is waste activated.  This is because of
the increased SS and BOD removals that occur during primary
treatment when chemicals are added.  According to the authors,
because only 18 to 14 percent of the sludge is waste activated,
separate flotation thickening of waste activated sludge is less
likely to be economical in a plant with primary chemical addition
than  in a conventional plant or one with secondary or tertiary
addition.   The advantages of flotation thickening would be dimin-
ished with such a small percentage of waste activated sludge.
                                        j

     At Portage Lake, Michigan, the flotation thickening capacity
of a,n aerobically digested alum sludge was measured  in  batch
laboratory-scale tests (2).  (See page  64  for a discussion of
the Portage Lake plant.)  Waste activated sludge produced alter-
natively with and without alum addition to the plantl:s aeration
                              44

-------
basins was digested in full-scale aerobic digesters.   The labora-
tory-scale tests indicated no difference between the  thickening
properties of the sludges produced.

Cone!us ions

     In some .cases, chemical sludges may flotation thicken  just
as well as, or better than, regular sludges.   However,  in other
cases, chemical sludges require a lower sludge loading  rate or
different polymers, and lower concentrations  of thickened sludge
solids are achieved.  Little information is available for drawing
further conclusions about the flotation thickening properties  of
various chemical sludges.  It is necessary that further informa-
tion be collected, however, in order to make  judgements about  the
cost effectiveness of flotation thickening of chemical  sludges.
In particular, information on allowable solids loading  rates with
chemical sludges is needed.  When the cost effectiveness of flo-
tation thickening is compared to that of gravity thickening, a
higher sludge loading rate is frequently one  of the most impor-
tant factors in favor of flotation.

     It is also necessary to determine allowable loading rates
for chemical sludges so that design engineers can size  equipment
properly.  It seems that presently, equipment is often  undersized.
At some of the plants listed in Table 12, a low sludge  through-
put rate was a problem.  The plants were having trouble achieving
a high rate that would avoid backlogs of sludge in the  clarifiers,
and that would provide thickened sludge fast  enough for subsequent
dewatering operations.  The plants also preferred a high rate  so
that they could run their sludge handling equipment for only one
shift per day.
                               45

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                            SECTION  6

                STABILIZATION  OF  CHEMICAL  SLUDGES
ANAEROBIC DIGESTION

Introduction

     As previously shown in Table 10,  97  (56  percent)  of  the
plants responding to the questionnaire survey reported that  they
have anaerobic digestion.  As with other  unit processes,  it  is
necessary to evaluate the anaerobic digestion process  as  a  com-
ponent of the entire sludge treatment/disposal  system.  For  exam-
ple: In order to properly compare the costs of anaerobic  diges-
tion of regular vs. chemical sludges,  differences  in  dewatering,
disposal, and supernatant treatment costs must be  analyzed  for
the total sludge management system.

Questionnaire Survey

     Twenty-one plants which were surveyed indicated  that chemical
addition was having a significant impact  on their  anaerobic  diges-
tion process.  Table 13 summarizes the experiences  of  those
plants.  All but one of the plants were treating iron and alum
sludges produced by primary or secondary  addition  of the chemical.
A single plant treated a lime sludge.   At this plant there  were
reportedly no adverse impacts of this type of sludge on anaerobic
digestion, but a slight increase in digester pH was noted.

     As the table shows, the most common  impact of chemical  addi-
tion at the plants was a sudden increase  in raw sludge volume and
mass.   A number of plants also noted changes in the settling
characteristics of the sludge.  The common results of these
impacts were:

     t  Increased energy requirements for sludge mixing, pumping
        and heating

     •  Difficulty in achieving adequate  digester mixing and
        heating

     •  Increased labor requirements for sludge pumping

     •  Increased digester gas production

                                46

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               TABLE 13.   IMPACTS OF CHEMICAL SLUDGES UPON ANAEROBIC DIGESTER PERFORMANCE
                                  AS REPORTED IN QUESTIONNAIRE RESPONSE
  Location
Richardson, TX
  Size-
 m3/day
  (mgd)

  6,720
(1.8)
    Type of
 Sludge Treated
•*V^VMV^M^H^^^^^^VM*-MW»4laiM4W«M*M

Alum-secondary and
primary from a
trickling filter
plant
Ashland, WI
  4,542
(1.2)
Alum-secondary and
primary from a
step-aeration ac-
tivated sludge
plant
 Impacts of Chemical Sludge

The raw sludge mass increased
by about .033 kg/m3 (275 lb/
MG).  The volume of digested
sludge increased by about 50
percent.  In the past, when
alum was added before the pri-
mary clarifiers, the solids in
the digester units stratified
and upset the digestion pro-
cess.  When the point of addi-
tion was moved to the second-
ary stage, no digestion
problems were observed.

The plant began secondary
treatment and vacuum fi.ltra-
tion at the same time that
phosphorus removal was begun.
At the time, of only primary
treatment, digester super-
natant characteristics were
good.  With secondary treat-
ment and phosphorus removal,
however, solids-liquid sepa-
ration in the secondary di-
gesters no longer occurred.
Adding polymer to the
digester did not solve the
problem.
 Performance with
 Chemical  Sludge
m*f^^f-^—~~~~t*—f, mmmmmm m !•

The digested
sludge averages
5 percent TS dis-
posal by vacuum
filtration and
incineration.
Digested sludge
vacuum filtered
and disposed of
in a landfill.
                                                                                              (continued)

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    TABLE 13 (continued)
Location
Parry Sound,
Ontario
Size-
m3/day
(mgd)
3,220
(0.85)
Type of
Sludge Treated
Iron-primary from
a plant with no
secondary treat-
ment; gravity
thickening before
digestion
Impacts of Chemical Sludge
The sludge is more difficult
to digest. It is necessary
to add 113 kg/mo (250 Ib/mo)
of lime to increase the
alkalinity in the digester.
Performance with
Chemical Sludge
Digested sludge
averages 8 per-
cent TS. Sludge
dried on drying
beds and dis-
posed of in a
landfill.
    Cedarburg, WI
00
    Fergus,
     Ontario
    Three Rivers, MI
  4,542       Alum-secondary
(1.2)         and primary from
              a conventional
              activated sludge
              plant;  gravity
              thickening be-
              fore digestion

  2,270       Iron-secondary
(0.6)         and primary from
              a conventional
              activated sludge
              plant

  4,730       Alum-primary or
(1.25)        lime primary and
              secondary from a
              conventional acti-
              vated sludge plant
The raw sludge volume in-
creased.  The pH in the
digester was raised to 8.2.
The volume of digested
sludge increased, raising
disposal costs.
Foaming in the digesters
occurred.  The volume of
digested sludge was in-
creased, raising disposal
costs.

With alum, increased raw sludge
volume and mass.  Poorer solids-
liquid separation in secondary
digester; therefore, less super-
natant can be removed.  With
lime, the huge volume of sludge
generated plugged all the lines
and filled the digesters, so it
was discontinued.
Digested sludge
is applied to
drying beds or
lagoons, or
hauled directly
to croplands.
Digested sludge
at 5 percent TS
is applied to
croplands.
Supernatant
contains 2.5
percent TS and
1,920 mg/X, BOD.
Digested sludge
TS concentration
is 5.3 percent.

    (continued)

-------
   TABLE  13  (continued)
Location
Size-
m3/day
(mgd)
Type of
Sludge Treated
Impacts of Chemical Sludge
Performance with
Chemical Sludge
   Watt's Creek
    STP, Shirley's
    Bay, Ontario
 18,620      Alum-secondary and
(4.92)       primary from a con-
             ventional activated
             sludge plant
vo
The raw sludge volume in-
creased 65 percent or more
as the percent solids de-
creased from 3.8 to 3.0
percent TS.  The sludge mass
increased by about 1,770
kg/day (3,900 lb/day).  The
retention time in the di-
gesters was reduced, re-
sulting in digester failure.
Supernatant TS concentration
increased.  Raw sludge vola-
tile content decreased from
about 70 to 64 percent.
Digested sludge TS decreased
from 5 or 6 percent to. 3
percent with an increase in
volatile matter from 50 to
55 percent.  The digester
temperature is hard to main-
tain due to insufficient
heat exchanger capacity with
the increase in sludge
volume.  Additional labor
costs for raw and digested
sludge pumping are estimated
at $32,500/yr.  Several experi-
mental changes in operating
procedures are planned: use of
iron for phosphorus removal
with primary addition to
Supernatant con-
tains 2.5 percent
TS.
                                                                                                  (continued)

-------
    TABLE 13 (continued)

Location
Size-
nrVday
(mgd)

Type of
Sludge Treated

Performance with
Impacts of Chemical Sludge Chemical Sludge
    Watt's Creek
     STP,  Shirley's
     Bay,  Ontario
      (cont'd)
    Gladstone,  MI
  2,839
(0.75)
en
O
   Silver Bay,  MN
  2,190
(0.58)
Alum-secondary
and primary from
a bio-surf
treatment plant
Alum-secondary
and primary
(gravity thickened
from a trickling
filter plant)
hopefully produce a more
compact sludge; settling of
supernatant in a holding
tank; liming of primary
sludge to improve settle-
ability; operation as a con-
tact stabilization plant.

Increased volume and mass of
sludge requires additional
labor and electricity for
pumping.  Additional elec-
tricity is also required for
mixing and natural gas for
heating.  Labor costs in-
creased by $ll,400/yr (2080
labor hours).  Cost of'elec-
tricity for mixing sludge in
digester increased by
$14.60/day (400 kwh/day).
The sludge does not settle as
well in the secondary di-
gester.  A heavier sludge
was obtained by returning the
secondary sludge to the pri-
mary clarifiers.

Solids-liquid separation in
the single-stage digester did
not occur after alum addition.
Both the raw and
digested sludge
average 4.0 per-
cent solids. The
raw sludge is
65 percent
volatile.
                                                                                                  (continued)

-------
TABLE  13  (continued)
Location
Size-
m3/day
(mgd)
Type of
Sludge Treated
Impacts of Chemical Sludge
Performance with
Chemical Sludge
Ford Lake WWTP,
 Ypsilanti, MI
Duffin Creek WPCP,
 Whitby, Ontario
Wei land, Ontario
 22,700      Iron-secondary and
(6.0)         primary from a step-
             aeration activated
             sludge plant;
             gravity thickening
             before digestion

 11,350      Lime-primary and
(3.0)         iron-secondary from
             a step-aeration
             activated sludge
             plant

 34,800      Alum-secondary and
(9.2)         primary from a step-
             aeration activated
             sludge plant
Increased sludge volume is
crowding the digester.
Digestion seems to be poorer
because of decreased volatile
fraction.
No adverse impacts on an-
aerobic digestion.  Digester
pH has increased a small
amount.  No additional costs
were incurred.

Both raw sludge volume and
mass increased.  The TS con-
centration of the raw sludge
decreased from 5.89 to 4.89
percent.   More energy was
required for digester heating
and sludge pumping.   Sludge
settling in the secondary
digester appeared slower.
Pumping costs increased by
$6,000/yr for labor and
$12,000/yr for electricity in
1976.   The cost of additional
natural gas for digester
heating was $2,000 in 1976.
The volume and mass  of di-
gested sludge increased,
raising disposal costs.
Raw sludge before
thickening is  2.5
percent TS and 70
percent volatile.
Digested sludge
is 10 percent  TS.

Digested sludge
TS concentration
is 5.7 percent.
The combined raw
sludge averages
4.89 percent TS
and the digested
sludge averages
10 percent TS.
Sludge disposal
is by trucking
liquid to crop-
lands.
                                                                                               (continued)

-------
    TABLE 13 (continued)
Location
Size-
m3/day
(mgd)
Type of
Sludge Treated
Impacts of Chemical Sludge
Performance with
Chemical Sludge
   Niagara  Falls,
    Ontario
 31i600
(8.3)
tn
   Weyauwega,  WI
    961
(0.25)
Iron-primary from
a plant with no
secondary treatment
Iron-secondary
from a conven-
tional activated
sludge plant with
no primary treat-
ment.  Gravity
thickening before
digestion
Raw sludge volume increased
from 53 to 76 m3/day (14,000
to 20,000 gpd) as TS concen-
tration dropped from 9 to 7
percent.  Sludge mass increased
by about 454 kg (1,000 lb)/day.
Digester gas production in-
creased.  The digester gas is
utilized for digester and
building heating, so natural
gas consumption was reduced.
Additional energy was required
to pump sludge to and from the
digesters and through the heat
exchanges.

The plant operators estimate
by visual observation that the
volume of raw sludge has
doubled.  Digestion is now
more difficult.  There is lit-
tle or no gas production.
Dewatering of the sludge by
vacuum filter is more difficult.
More ferric chloride and lime
are used for conditioning.
Digested sludge
TS concentra-
tion averages
12 percent.
Digested sludge
pumped to lagoons
and later trucked
to croplands.
The digested
sludge is 5 to
6 percent TS.
It is chemically
conditioned,
vacuum filtered
to 18 to 20
percent TS and
trucked to
croplands.
                                                                                                   (continued)

-------
   TABLE 13 (continued)
     Location
 Size-
nr/day
 (mgd)
    Type of
 Sludge Treated
Impacts of Chemical Sludge
Performance with
Chemical Sludge
   Ottawa, Ontario
276,000
(73)
Ul
   Belleville,
    Ontario
 29,900
(7-9)
   Port Dal nousie
    PCP, St.
    Catherines,
    Ontario
 28,600
(7.55)
Alum-primary from
a plant with no
secondary treat-
ment
Iron-secondary or
alum-secondary and
primary from a
conventional acti-
vated sludge plant
Iron-secondary and
primary from a con-
ventional activated
sludge plant
Raw sludge mass increased
from 4,100 to 17,700 kg/day
(9,000 to 39,000 Ib/day) as
TS decreased from 4.8 to
4.35 percent.  Raw sludge
volume increased by about
90 percent.  Liquid-solids
separation in digester is
more difficult.  Increased
digester gas production
experienced.

When iron was tried for
3 months, the digester
became upset; the pH dropped
to 4; volatile acids pro-,
duction increased; gas pro-
duction fell.  Presently,
with alum there are no
problems.  There was a
slight increase in sludge
production.
A 30 percent increase in
sludge volume resulted in
an increased cost for
natural gas to heat
digesters.
Digester super-
natant is 1.92
percent TS.  Raw
sludge feed is
67.2 percent
volatile.
Digested sludge
is 3.5 percent
TS.
Raw alum sludge
is 3.9 percent
TS, 70 percent
volatile.
Digested alum
sludge is 4.3
percent TS, 59
percent volatile.
Supernatant
contains 1 to 2
percent TS.

Raw sludge is
4.1 percent TS,
62.6 percent
volatile.
Digested sludge
is 4.3 percent
TS.

    (continued)

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     TABLE 13 (continued)
      Location
 Size-
m3/day
 (mgd)
    Type of
 Sludge Treated
Impacts of Chemical Sludge
Performance with
Chemical Sludge
    Port Weller PCP,
     St. Catherines,
     Ontario
    Sarnia, Ontario
en
    South Lyon, MI
    Lakeview WPCP,
     Mississauga,
     Ontario
 33,700
(8.91)
 30,300
(8.0)
  2,157
(.57)
159,000
(42)
Alum-secondary and
primary from a con-
ventional activated
sludge plant

Iron-primary from
a plant with no
secondary treat-
ment
Iron-secondary and
primary from a con-
ventional activated
sludge plant
Iron-secondary and
primary from a
step aeration acti-
vated sludge plant
A 26 percent increase in
sludge volume resulted in
an increased cost for
natural gas to heat digesters.

Raw sludge volume increased
from 83 to 113 m3/day (22,000
to 30,000 gpd).  Sludge TS
concentration decreased from
5.5 percent to 4.0 percent TS.
Sludge mass increased by 36
kg/day (80 Ib/day).  Digester
gas production increased from
1,820 to 2,240 m3/day (65,000
to 80,000 ft3/day).  No ad-
verse effects on anaerobic
digestion were observed.

It is necessary to add polymer
to the digester to aid
settling.
Digester pH and alkalinity
were lowered.  It is some-
times necessary to add lime
to the digester.
 Raw  sludge  is
 59.6 percent
 volatile.
 Raw sludge  is
 7  percent TS, 62
 percent  volatile.
 Digested sludge
 is 6 percent TS.

 The supernatant
 TS concentration
 is 1.8 percent
 and the  BOD con-
 centration  is
 6,000 to 10,000

-------
     t   Poor solids-liquid separation  and  high  supernatant  solids
        concentrations.

     Less  common results were:

     •   Poor digestion,  accompanied by moderate decreases  in
        digester pH, decreases  in volatile matter  destruction,  or
        decreases in gas production

     •   Digester upsets, with symptoms such as  the absence  of  gas
        production, low  pH, low volatile destruction,  and  increased
        production of volatile  acids

     t   Primary digester stratification

     t   Foaming in digesters.

     Adverse impacts on  anaerobic digestion were reported  both by
plants  using iron and plants using alum and with both  primary  and
secondary addition of the chemical.  There was one case in which
a plant experienced problems when using iron, but  observed no
significant adverse impacts after switching to alum.   Another
plant found that problems disappeared when the point  of addition
of alum was switched from the primary stage to the secondary stage.
Some plants achieved good thickening of sludge in  digesters while
others  achieved none at  all.

     Several plants reported average TS concentrations of  their
digested sludge.  These  ranged from 3.5 to 12 percent, with the
average value being 6.7  percent.

     The reduced volatile solids fraction of the raw  sludge was
felt to be significantly affecting digestion at two plants.  Other
plants  did not report any problems resulting from  the  reduced  VS
fraction.   The values for average VS fraction which were reported
ranged  from 59.6 to 70 percent of TS with the average  value being
65 percent of TS.  In many cases the VS loading was increased
when the plant treated chemical sludge, and thus resulted  in
increased gas production per cubic meter of digester  space.

Case Studies

     The case studies in the appendices contain detailed informa-
tion on the effects of chemical addition on anaerobic  digestion.
The particular case studies which deal with this subject are
Lakewood,  Ohio; Coldwater, Michigan; South Bend, Indiana;  and
Pontiac, Michigan.  The  experiences at those plants are similar
to the  experiences of plants responding to the questionnaire sur-
vey.  However, some unusual highlights of the case studies can be
mentioned.
                                55

-------
     At Lakewood, Ohio, anaerobic digester supernatant quantity
was  increased greatly when the digesters were overloaded with
alum sludge.  The excess supernatant was generated, not because a
greater sludge volume was being fed to the digesters, but because
sludge was  removed from the digesters at a slower rate due to
reduced vacuum filter and flash dryer capacity.  The supernatant
became very high in total solids.  Because of the recirculation
of this sidestream to the head of the plant, there were adverse
impacts on  the performance of both primary and secondary treat-
ment and gravity thickener operation.  By finding ways to pump
more sludge out of the digester, the volume and solids concentra-
tion of the supernatant was decreased.  Longer operation of the
vacuum filter and flash dryer was one method used.  Hauling liquid
sludge was  found to be a more successful method.  Eventually, how-
ever, it was concluded that it would be necessary to hire a con-
tractor to  clean out the secondary digesters, removing the grit
and other heavy materials which were reducing the effective volume
of the digesters.

     At Pontiac, Michigan, an increased volume of raw sludge was
pumped to the digesters at a lower average solids concentration
during phosphorus removal with ferric chloride and polymer.  The
net effect was an increase in the mass of primary sludge pumped
to the digesters per pound of SS in the plant influent.  There
was an increased volume of supernatant, but at a considerably
lower average solids concentration, indicative of better sludge
sett!eabi1ity within the digesters.  The chemical sludge had no
negative effects on digestion.  The plant manager felt that pri-
mary addition of the chemical had several benefits for plant oper-
ation which would not be realized with secondary addition:  The
primary sludge settled well and was easily pumped.  The removal
of additional solids during primary clarification because of
increased clarifier efficiency with ferric and polymer use actually
reduced the load on the aeration system.  At times the additional
primary sludge seemed to be balanced by reduced volume of waste
activated sludge generated because of reduced sludge growth in
the aeration basins.  The increased efficiency of the primary
clarifiers was very helpful in containing (and recycling) solids
from the digester supernatant.  If these solids were not contained
they would result in the degradation of secondary treatment.  The
supernatant volume was always large because of inadequate sludge
disposal resulting from down time on the vacuum filters.  The two
vacuum filters were inadequate from the start because of frequent
shut-downs due to lime-scale problems.  The filter media is acid
cleaned once per week, but the internal piping must still be taken
apart and cleaned on an annual basis.  Polymer conditioning of  the
sludge was tried but hasn't been as effective as conditioning with
1 ime.

     At Coldwater, Michigan, the TS concentration of the sludge
entering the digesters has increased since the start-up of  iron


                                56

-------
and polymer addition for phosphorus removal.  Most of the addi-
tional  solids produced and fed to the digesters were non-volatile.
The volatile fraction of the sludge decreased.  But the mass of VS
fed to  the primary digester has increased from 590 kg VS/day
(1,300  Ib VS/day) before phosphorus removal  to 720 kg VS/day
(1,590  Ib VS/day) during phosphorus removal.  The amount of diges-
ter gas produced increased from roughly 5,040 m3/mo (180,000 ft3/mo)
to 11,200 m3/mo (400,000 ft3/mo).

     At South Bend,  Indiana, combined primary and waste activated
sludge was gravity  thickened and then digested in two-stage anaer-
obic digesters.  Before being  fed  to the primary digesters, the
sludge was preheated.  The  plant accomplished phosphorus removal
by mixing  ferric chloride and  polymer with  the wastewater in ter-
tiary  upflow clarifiers.  The  resulting  iron  sludge was pumped
from the  clarifiers  to a  chemical  sludge gravity thickener.
Because of plant ,design,  the thickened  iron  sludge could not be
preheated  before it  was fed to the digesters.  It therefore was
capable of suppressing the  temperature  in the digester  into which
it was fed.  This  resulted  in  a  loss of  digester gas production.
Since  most of the  gas production took place  in the primary diges-
ters,  the  chemical  sludge was  fed  into  one  of the secondary diges-
ters.  The result  was a 4 to 5°C loss in temperature in this
digester,  but a  decrease  in total  digester  gas production was
avoided.

Literature

     Accounts of anaerobic  digestion of  iron  and aluminum sludges
available  in the literature can  be summarized as follows:

     • The presence  of iron and  aluminum precipitates  in digesting
       sludge does  not inhibit the action of  the anaerobic bacteria
       (22,  32,  44,  51, 63) .

     0 The volume  of gas  produced  per pound  of VS introduced to
       the digester  is similar for conventional  sludges and iron
       or  aluminum  sludges.  Gas composition  is  also similar (42,
       51).

     t During anaerobic digestion  of ferric  iron and aluminum
       sludges,  solubilization and release  of precipitated phos-
       phorus into  the supernatant does not  occur  (22,  32, 44,  51,
       63).

     • A difference  in the  behavior of  primary and waste activated
       sludges containing phosphates removed  by  the addition of
       ferrous iron  occurs when  they are digested.  A  significant
       release of  phosphorus can take place  upon anaerobic diges-
       tion of the waste  activated sludges.   In  contrast, there
       is an uptake  of phosphorus  when  the  primary sludges are
       digested.   This difference  in behavior is not hard to

                                57

-------
       explain.  The ferrous iron added during primary treatment
       remains in the ferrous form before and after the digestion
       of primary sludge.  However, the ferrous iron added to the
       aeration tank is mostly oxidized to the ferric form, which
       is then reduced back to ferrous upon anaerobic digestion,
       causing a release of phosphorus.

     • When digesting ferric iron or aluminum sludges, high con-
       centrations of iron or aluminum ions do not occur in the
       digester sludge or supernatant (44, 51).

     Successful anaerobic digestion of a lime sludge was demon-
 strated at the 9,092 m3/day  (24 mgd) Newmarket, Ontario, activated
 sludge plant  (6, 72).  The plant achieved 80 percent phosphorus
 removal by adding 200 mg/a lime (as Ca(OH);?} to the raw wastewater
 The addition  of lime caused  the mass of primary sludge TS to
 increase by 0.32 kg/m3 (2,670 Ib/MG).  The primary sludge contain-
 ing relatively small quantities of waste activated sludge, was
 treated by two-stage anaerobic digestion with ultimate disposal
 on croplands.  During lime addition, failure of the digestion pro-
 cess was caused by the high  pH (10.0 to 10.5) of the raw sludge.
 Intermittent  and frequent overdosing of lime was also responsible.

     It was found that by letting the sludge sit in the primary
 clarifiers longer the pH was lowered to 9.4 and the digesters
 could operate  satisfactorily.  Modifications were made so that a
 sludge blanket 1.5 to 2  ft (0.46 to 0.6 m) was maintained in the
 clarifiers.   After this  modification, the digesters continued to
 operate satisfactorily with  the primary sludge being fed at 8 to
 12 percent TS  compared to 3  to 4 percent TS before chemical addi-
 tion.  The digester operated at a pH between 7.2 and 7.4, with
 supernatant soluble phosphorus concentrations of 6 to 8 mg/i.
 Digested sludge was hauled at 10 to 11 percent solids, compared
 to 3 to 4 percent before lime addition, and volumes were somewhat
 1 ess.

     The experience at Barrie, Ontario, illustrated that decreas-
 ing the dosage of the phosphorus removal chemical by 25 percent
 could improve  sludge characteristics for digestion  (72).   Dosing
 at 200 mg/£ alum to the  raw  sewage to produce  a 0.5 mg/jj, total
 phosphorus concentration in  the plant effluent resulted in  a pri-
 mary sludge concentration of 2.76 percent TS.  This resulted in  an
 increased volume of sludge being transferred  to the digester,  a
 decrease in digester temperature and gas production,  and an
 increase in volatile acids.  At an alum dosage of 150  mg/£  an
 effluent phosphorus concentration of 1.2 mg/£  was achieved,  and
 the TS concentration of  the  primary sludge  rose to  4.25 percent.
 This returned digester operation to normal.

Conclusions

     Hydraulic or solids overloading of anaerobic digesters  is
the main  problem to result from chemical addition for  phosphorus

                                58

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removal.  This results in inadequate liquid retention time, poor
mixing, poor heating, and inadequate room for solids-liquid sep-
aration.  Volatile destruction is then poor; gas production is
lowered; and supernatant quality deteriorates.

     The easiest remedies for these situations lie in the design
stage.  For instance, poor mixing is currently a major defect in
the design of anaerobic digesters treating both conventional  and
chemical sludges.  With chemical sludges, and especially lime
sludges, present mixing is even more likely to be inadequate.
In cases where present mixing is suspected to be inadequate,  mix-
ing equipment should be operated full  time, with every advantage
taken to any pipeworks and pumps which can be utilized to provide
additional circulation.

     The situation is similar with regard to sludge heating in
digesters.  Chemical sludges can aggravate existing heating prob-
lems.  When there is a separate chemical sludge, it may be possi-
ble to avoid loss of digester temperature in the primary digester
by introducing the chemical sludge into the secondary digester.
This would prevent a suppression of digester gas production in the
primary digester where most of the gas is usually produced.

     Another major problem resulting from chemical addition is
poor solids-liquid separation in the digester.  Both iron and alu-
minum sludges can contain floes which do not settle readily.
Methods of improving the settling of these sludges include adding
polymer to the digester and sludge liming before digestion.  In
some situations  it may be possible to produce a sludge with better
settling characteristics by changing the type of phosphorus remo-
val chemical used, the chemical dosage, or the point of addition.
Also, in some cases, using a polymer in conjunction with the iron
or aluminum for  phosphorus removal could improve solids-liquid
separation in the digester.

     When poor supernatant is a problem as the result of digester
crowding, several steps can be taken to reduce the crowding.   Raw
sludge prethickening, when possible, can reduce sludge volume,
saving digester  space.  Sometimes thickening can be achieved in
existing holding tanks or by allowing sludge to remain on clari-
fier bottoms longer.  Also, in some cases, recirculating waste
biological sludge to the primary clarifiers will produce a thicker
combined sludge.

     Faster removal of sludge from digesters is another way of
reducing digester crowding.  Many plants may not be removing sludge
at a fast enough rate because of lack of disposal ability.  A pop-
ular way to meet this need is with liquid sludge hauling.

     When faced  with a poor supernatant, a plant may choose to
avoid drawing off supernatant except at times when it is clear.
However, there is then less reduction occurring in the volume of

                                59

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sludge for disposal.  In other situations, a plant which has
started phosphorus removal may be forced to remove more superna-
tant because of inadequate means of disposing of the additional
sludge which is fed to the digesters.  Settling of supernatant
solids in a holding tank may then be possible to avoid the deter-
ioration of wastewater treatment performance.

     Cleaning of digesters to remove grit is expensive, but it
is ultimately found to be necessary in many cases where greater
space and longer retention time in digesters are needed.  It is
not uncommon to find that effective digester volume has been
reduced drastically by accumulated grit.

AEROBIC DIGESTION

Introduction

     As previously shown in Table 10, 41 (24 percent) of the
plants responding to the questionnaire survey reported that they
had aerobic digestion.  Aerobic digestion is mostly used by smal-
ler treatment plants and/or for treatment of waste secondary
sludges.  Principal advantages cited for aerobic digestion over
anaerobic digestion are simpler operations, lower initial capital
cost, and better supernatant quality.  The major disadvantage is
the much higher operating cost due to high energy consumption.

     Two basic types of aerobic digestion systems exist.  Single-
stage digestion is a batch-type operation where the sludge is sup-
plied with air and completely mixed for a period of time, followed
by quiescent sett!ing and decanting of supernatant, all in one tank.
Two-stage digestion incorporates a separate tank for settling and
supernatant decanting.  Two-stage digestion is a continuous-feed
rather than a batch operation.

     As with other unit processes, it is necessary to evaluate the
aerobic digestion  process as a component of the entire sludge
treatment/disposal system.  For example:  In order to properly
compare the costs  of the aerobic and anaerobic digestion systems,
differences in dewatering, disposal, and supernatant treatment
costs must be analyzed for the total sludge management system.

Questionnaire Survey

     Four plants which were surveyed reported problems with aero-
bic digestion of chemical sludges.  Table 14 summarizes  the
experiences of those plants.

     The most common impact of chemical addition was  a  sudden
increase in raw sludge volume and mass.  This resulted  in  the
need for more secondary digester capacity, the  need  for  an
increased air supply rate to achieve adequate mixing,  and  higher
disposal costs.   Hauling the liquid digested sludge  to  croplands

                               60

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                   TABLE  14.    IMPACTS OF CHEMICAL SLUDGES UPON AEROBIC DIGESTER PERFORMANCE
                   	             AS REPORTED IN QUESTIONNAIRE RESPONSE
      Location
 Size-
m3/day
 (mgd)
   Type of
Sludge Treated
Impacts of Chemical Sludge
Performance with
Chemical Sludge
   Portland,  MI
CTl
1,135
(0.3)
    Merrickville,  OH
3,030
(0.8)
Iron-primary and
iron-secondary
from an activated
sludge plant
Iron-secondary
from an extended
aeration acti-
vated sludge
plant without
primary treat-
ment
Total raw sludge volume in-
creased from 8 to 19 m3/day
(2,000 to 5,000 gal/day).
Sludge TS decreased from
5.0 percent to 2.4 percent.
Sludge ma-ss increased by
about 91 kg (200 lb)/day.
A new secondary digester was
constructed to handle the
additional volume.  The
volume and mass of digested
sludge increased, raising
disposal costs.

The plant began operation with
phosphorus removal on-^stream.
Therefore, there is no com-
parison between digester
operation with and without
the iron sludge.  However,
the following operational
problems resulted from design
errors: (1) the air lift
pumps could not remove the
heavy sludge from the digester
fast enough; (2) the mass of
sludge was greater than anti-
cipated, so the air supply
rate was greater than pre-
dicted.
Digested sludge
TS is 5.0 percent.
Supernatant con-
tains 0.2 percent
TS.
                                                                                                  (continued)

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   TABLE 14 (continued)
     Location
 Size-
nr/day
 (mgd)
    Type of
 Sludge Treated
Impacts of Chemical Sludge
Performance with
Chemical  Sludge
  Addison,  MI
1,510
(0.4)
en
ro
  Columbia  Boro,
   PN
4,920
(1.3)
Alum-primary from
an aerated lagoon
plant
Alum-secondary
from a contact
stabilization
activated sludge
plant without
primary treat-
ment
The sludge volume fed to the
digester increased and the
sludge was heavier and more
difficult to pump.  Mixing
the sludge in the digesters
was also more difficult so
the air supply rate had to
be raised to accomplish this.
Sludge volume decreased from
113 to 90 m3/day (30,000 to
24,000 gal/day)as TS in-
creased from 0.5 percent
to 1.25 percent.  An addi-
tional 230 kg/day (500 lb/
day) dry TS is fed to di-
gester.  Digester superna-
tant volume has decreased.
The volume and mass of di-
gested sludge has increased,
raising disposal costs.
The digester
feed is 5.7 rrr/day
(1,500 gal/day)
primary sludge at
3.3 percent TS.
The digested
sludge is 6 per-
cent TS.   Super-
natant concen-
trations  are
320 mg/&  SS and
117 mg/&  8005.

The digested
sludge is 3 per-
cent to 4 per-
cent TS.   Super-
natant return is
68 m3/day
(18,000 gal/day)
at less than
0.5 percent TS
containing 500
to 1,000
BOD5.

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was the most common disposal method used.  The digested sludge
TS concentrations varied from 3 to 6 percent.

     No problems with deterioration of supernatant quality were
reported as the result of either the additional  sludge feed quan-
tities or the changed sludge characteristics.  This is significant
because poor supernatant quality is often an indicator of diges-
ter overloading.  Apparently, the capacity of the existing aerobic
digesters was usually adequate to handle the additional quantities
of«chemical sludges.  One plant reported the need for additional
secondary digester capacity to handle the chemical sludge, but
did not require additional primary digester capacity.

Literature


     Accounts of aerobic digestion of chemical  sludges available
in the literature can be broken down into laboratory-scale studies
on the one hand and pilot- or full-scale studies on the other hand.
The results of laboratory scale studies can be summarized as  fol-
1 ows:

     t Aerobic digestion of waste activated sludge is not affected
       to an appreciable degree, nor is it inhibited by the pre-
       sence, of iron or aluminum precipitates (28).

     t The release of soluble organic carbon and nutrients into
       the liquid phase is not enhanced by the presence of iron
       and aluminum precipitates (28).

     t An aeration period of 10 to 15 days provides satisfactory
       stabilization of iron- and alum- waste-activated sludges
       at a temperature of 20°C (28).

     • Dewatering characteristics of digested iron- and alum-waste
       activated sludges are poor, especially when long aeration
       periods are employed in batch treatment (28).

     t With iron- and alum-waste-activated sludges, batch digester
       operation results in a greater destruction of sludge vola-
       tile solids and a lower sludge oxygen uptake rate than
       semi-continuous operation.  However, the latter method pro-
       vides better sludge dewaterabi1ity and better supernatant
       quality (28).

     • Aerobic digestion can be successfully applied to lime-pri-
       mary sTudges, and the kinetics of the digestion process
       are not appreciably affected except at high lime dosages
       (33).

     • When treating lime-primary sludges, the digestion  system
       shows good buffering capacity, and the pH  of the system


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       is always maintained at 8.5 or above.   The latter is  con-
       trary to the process characteristics with  primary or  waste-
       activated sludge alone, which are a low buffering capacity
       and a pH reaching as low as 4.0 (33).

     t Aerobically digested lime-primary sludges  have good  set-
       tling and dewatering characteristics (33).

     It should be kept in mind that the above conclusions were
based on laboratory research.   An experimental study of full-scale
plant operation was conducted  at the Portage  Lake,  Michigan,
wastewater treatment plant (2).  The plant influent flow of  6,400
m3/day (1.7 mgd) was split after passing through  the aerated grit
chamber.  The rest of the plant was divided into  two identical
halves, each side consisting of a contract stabilization activated
sludge system and an aerobic sludge digester.  The  two 765-m3
(201,990-gal) digesters were single-stage, batch-type operation
units.  During the study, one  half of the plant was fed an  alum
dosage of 84 mg/£ just ahead of the contact basin,  while the
other half did not receive chemical feed.

     Alum addition increased the aerobic digester sludge feed vol-
ume by 16 percent and the dry  weight by 50 percent.  It increased
the digested sludge volume by  37 percent and the dry weight  by 92
percent.  However, the test was carried out in the  summer,  and it
was projected that under average annual conditions  there would be
only a 20 percent increase in  digested sludge volume and a  66 per-
cent increase in dry weight.  The alum-biological sludge was le'ss
amenable to aerobic digestion  than the biological sludge.  The
alum-biological sludge TSS reduction observed through aerobic
digestion under the summer conditions of the study was relatively
low, on the order of 12 percent.   It was predicted that the aver-
age annual rate would be even  less (2).

     The aerobically digested  sludge gravity thickening capacity,
as measured in laboratory cylinders, was higher for the alum-bio-
logical sludge than for the biological sludge.  Batch laboratory-
scale flotation thickening tests indicated no difference between
the thickening properties of the two digested sludges.  The alum
sludge was concentrated by flotation thickening from 0.75 to 3.5
percent SS without polymer addition at an air to solids ratio of
0.03.   Under these apparently  optimal conditions, the underflow
SS concentration was 88 mg/& SS.   It is  likely that addition of
cationic polymer could have improved the  performance  (2).

     Laboratory vacuum filtration  tests  conducted  by the Buchner
funnel method indicated that the alum-biological sludge filtered
slightly better than the biological sludge.   Both  sludges were
conditioned with ferric chloride.  Vacuum filter leaf tests  indi-
cated that the conditioned alum-biological sludge  could  be  dewa-
tered from 1.6 percent SS to a cake concentration  of  16  percent
SS at a filtration rate of 14.6 kg/m2/hr  (3.0  Ib SS/hr/sq ft)
(2).
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     An evaluation of the feasibility of sludge dewatering by
centrifugation was conducted using a 305-mm (12-in) diameter pilot-
scale basket centrifuge.  Several runs were performed at various
feed rates and feed solids concentrations.  After application of
the manufacturer's scale-up procedure, the results indicated that
a full  size 1.22-m (48-in) diameter basket centrifuge could dewa-
ter the digested alum-biological sludge at 1.6 percent feed SS
to a solid cake containing 16 percent TS at a rate of 158.9 kg
dry solids/hr (350 Ib/hr) with no chemical addition.   The SS con-
centration ranged from 300 mg/£ to 600 mg/£, and the  solids
recovery was 96 percent (2).

     Because of the good thickening characteristics of the alum-
biological sludge, it was predicted that a more concentrated sludge
could be removed from the digester by converting it to a two-stage
unit.  Plans were made to implement this by installing a concrete
partition in the existing digester and an air lift pump for trans-
ferring sludge from the bottom of the first stage to  the second
stage.   In year-round operation, it was estimated that digested
alum-biological sludge of 1.25 percent SS would be obtained with
the one-stage and 1.7 percent SS with the two-stage process (2).

     Based on the study results, the costs of various alternatives
for further sludge processing and disposal were considered.  All
of the alternatives assumed ultimate disposal on land at a loca-
tion about 11 km (7 mi) from the plant.  The alternatives were:
direct trucking by tanker at 1.7 percent SS; centrifugation or
vacuum filtration and hauling cake at 16 percent TS;  and flotation
thickening and tanker hauling at 4 percent SS.  Table 15 summa-
rizes the estimated costs of each alternative (2).
      TABLE 15     PROJECTED COSTS OF VARIOUS SLUDGE HANDLING
     ALTERNATIVES  FOLLOWING AEROBIC  DIGESTION  AT  PORTAGE  LAKE,
                       MICHIGAN, $  (2)
                      Direct     Basket    Vacuum
                     Trucking  Centrifuge  Filter  Flotation
Capital investment    79,000    143,000   137,000   202,000

Annual debt service    8,951     16,203    15,523    22,888

Annual operation      16,109     12,046    14,795    18,209
and maintenance

Total annual cost     25,060     28,249    30,318    41,097
                               65

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     The estimated capital  costs included all  mechanical  equip-
ment, building space, and vehicles required.   Operation and main-
tenance costs included labor,  power,  fuel,  chemicals,  snow removal,
and disposal site maintenance.   Aerobic digestion  costs were not
included.  Annual debt service  was based on 7.5 percent interest
over a useful life of 15 years.   All  costs  were intended  to reflect
January 1975 levels.  The projected costs showed direct trucking
to be the most economical alternative primarily because of the
relatively short haul distance.   However, if the one-way  haul  dis-
tance were increased from 11  km to 16 km (10 mi),  the  centrifuga-
tion system would yield the minimum annual  cost (2).

Conclusions

     Aerobic digesters can be a cost-effective means  of stabiliz-
ing chemical sludges when attempts are made by plant  management
to find procedures yielding maximum efficiency.  Often, however,
plant personnel  prefer to operate them merely as aerated sludge
holding tanks.   The  research conducted at Portage Lake, Michigan,
(2) showed that  the  TSS reduction observed through aerobic diges-
tion of alum-waste activated sludge was relatively low compared
to that observed for waste activated sludge, but that the alum
sludge thickened to  a higher solids concentration.  The investi-
gators concluded that the chief utility of aerobic,digestion of
chemical-biological  sludge may be sludge storage and  thickening.
No other reports of  poor digestibility of chemical sludges were
found in the literature.

     The information which has been presented  suggests the follow-
ing ways of modifying aerobic digester operation to achieve bet-
ter performance  when treating chemical sludges:

     • Converting a  one-stage to a two-stage system.   This is
       reported  to increase the digested sludge solids concentra-
       tion and  sludge dewaterabi1ity, while not adversely affect-
       ing supernatant characteristics.  This method may,  however,
       yield less volatile solids destruction  and require  a higher
       oxygen supply rate.

     • Installing a  new secondary digester (or  converting  an
       unused existing basin) to handle  the additional chemical
       sludge.   It may not be necessary  to install a new  primary
       digester  for  moderate increases in  sTudge volume.

     Although no reports of poor solids-liquid  separation  in aero-
bic digesters treating chemical sludges  were found in  the  present
study, there are situations in which this  problem will occur.   In
this case, the addition of polymer may aid settling of the sludge
in the digester  and  reduce the volume for  disposal.  This  method
could result in  significant savings by reducing trucking  costs
for hauling liquid sludge.  At Escanaba, Michigan (35),  solids-
liquid separation could not be achieved  in aerobic digesters

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treating waste activated sludge.  Addition of 25 to 30 mg/£ of
a cationic polymer resulted in sludge concentration of 1.8 to
2.2 percent TS.

COMPOSTING

     Composting is being viewed with increasing interest as a
sludge management alternative.  It is appealing because it con-
verts sludge into a product that is aesthetically acceptable,
essentially free of pathogens, and easy to handle.   The compost
produced can be used to improve soil structure, increase its
retention of water, and provide nutrients for plant growth.  How-
ever, the fact that the process may be relatively expensive (com-
pared to land application of liquid digested sludge, for example)
has prevented its widespread use in the past.  Several investiga-
tions in the United States and Canada are presently underway to
determine if composting can be made economical for widespread use.

      Since  sludge  characteristics  are an  important factor  in
 treatment costs,  the economics  of  composting are likely to differ
 for  chemical  sludges and  regular sludges.   In  the  preceding sec-
 tions of  this  report,  the characteristics of regular  sludges and
 chemical  sludges  resulting from phosphorus  removal were compared.
 In this section,  information  related to the  effects of phosphorus
 removal on  sludge  composting  is presented.   It is  intended to help
 answer  questions  about  the ability  of chemical sludges to  dry as
 expected  to  remain aerobic, and to  support  biological growth.  It
 will  also look at  the  value of  the  chemical  sludge compost as a
 fertilizer  and soil conditioner.

 Questionnaire  Results  and Case  Studies

      As previously shown  in Table  10, only  two  (1  percent) of the
 plants  responding  to the  questionnaire survey  were composting
 their chemical sludges.   Both of these plants  were case study
 sites.  At  the Midland, Michigan,  site, an  informal sludge com-
 posting operation  was  underway.  The operation utilized vacuum
 filtered  sludge cake containing iron precipitates  from the plant's
 primary addition  of iron  for  phosphorus removal.   The sludge cake
 may  have  been  particularly suitable  for composting because of the
 plant's thermal conditioning  step.   Thermal  conditioning  enabled
 production  of  a filter  cake which  was very  dry (about 50  percent
 dry  TS);  it  pasteurized the sludge;  and  it  eliminated the  need
 for  using chemical conditioners such as  iron  or  lime  which would
 further increase  the chemical content of  the  sludge cake.

     All  of  the plant's 4.6 m3/day  (10.8  yd3/day)  of  filter  cake
was  transported approximately 6.5  mi to the  city of Midland's
 sanitary  landfill  site, but not all  of it was  composted.   Some  of
 the  sludge was used for land  reclamation  at  the  landfill  site.
The  remainder  was  informally  made  into compost by  the city's


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Department of Forestry and used as soil conditioner in their on-
site ornamental tree nursery.  Both sludge-leaf compost and sludge-
sawdust compost were made in piles, with a minimum of attention
and labor from the City Forester and a few employees.  The compost
piles were simply turned over once every three days.

     The compost greatly enriched and conditioned the native hard
clay soil at the site.  The texture of the soil was greatly
improved by mixing in compost.  Over part of the tree nursery, 15
to 24 cm (6 to 8 in) of sludge cake was disced directly into the
soil, while on other plots, up to 0.6 cm (2 ft) of sludge-leaf
compost was used.  The sludge-leaf compost was not as rich a fer-
tilizer as the sludge disced in alone, but it may have improved
the texture of the soil more.  Whether sludge-leaf compost or
sludge alone was disced in,placing a sludge-sawdust mixture (T/2
sludge - 1/2 sawdust) on top of the soil produced even richer
growth.  Iron sludge composting at Midland, therefore, was both
successful and valuable to the city.

     It has not been possible to assess the costs invol ved because
the operation was very informal and the quantity of sludge used
was small.  It can be reasoned, however, that the costs would
have been raised as the result of iron addition for phosphorus
removal had not the initial impact of iron addition on filter
cake moisture content been overcome.  The initial impact was an
increase in filter cake moisture content, meaning higher costs
for sludge cake hauling and perhaps a slower rate of composting.
Filter cake dryness was restored, however, by raising the temper-
ature of the thermal conditioning unit, thus avoiding these prob-
lems at Midland.

     At Windsor, Ontario, a sludge disposal arrangement existed
between the Little River Pollution Control Plant and a commercial
composting operation.  After the plant hauled the sludge 11 mi to
the composting site, it payed $2.20/t ($2.00/ton) to the commer-
cial operation to handle the sludge from there.  The commercial
firm mixed the sludge with sawdust where it is dumped from the
truck in the field.  The sludge then dried in the field without
being turned over.  When dry, it was taken into a barn where  it
was worked considerably and piled.  The temperature  inside the
piles reached 66° to 71°C (150° to 160°F).  The operation was
monitored by the Ontario Ministry of the Environment to see that
it met health standards.  The product was shredded and then
bagged.  Further details of the private operation were proprie-
tary.  The sludge-sawdust compost material was sold  in bags for
$198/t ($180/ton) retail and $88/t  ($80/ton) wholesale.  Unbagged
compost was sold in bulk for $16/m3 ($12/yd3).  The  product was
marketed'as a soil additive and organic fertilizer primarily  for
home gardening and commercial greenhouse applications.

     At Little River, alum was added to the raw sewage for  phos-
phorus  removal.  The undigested sludge was centrifuged before


                               68

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being trucked to the composting site.  Alum addition resulted in
an increase in the average moisture content of the centrifuge
cake from 80 percent to 84 percent.  This increase in moisture
content raised the costs of hauling the sludge cake, and probably
also slowed the rate of drying of the sludge in the compost piles.
The owner of the composting operation reported having no problems
as the result of the presence of aluminum precipitates in the
sludge.  However, he felt that a lime sludge would make a better
product, which would cost perhaps $2.20/t ($2.00/ton) less to
make.

     Presently, the cost to the plant to dispose of 9,604 t/yr
(10,589 tons/yr) of dry sludge TS from the centrifuges is esti-
mated at $3.73/t ($3.38/ton).  This includes the cost of sludg-e
hauling and the fee paid to the composting operation to take the
sludge.

     The City of Windsor was planning to start a composting oper-
ation at its other plant, the West Windsor Pollution Control
Plant.  Sludge was to be composted in static piles with forced
ventilation.  Wood chips were to be used as the bulking agent.
Preliminary tests indicated that there was no difficulty in com-
posting the plant's undigested iron-primary sludge.  The cost of
composting 31,750 t/yr  (35,000 tons/yr) of dry sludge TS was
estimated at $7.50/t ($6.80/ton) of dry solids, a very low esti-
mate compared to many others fqund in the literature for sewage
sludges.  The estimate  included no land capital cost because the
land was already owned  by the city.  Similarly, there were to be
no sludge hauling fees  since the land was adjacent to the plant.
A total site preparation cost of $85,000 was estimated, with an
equipment cost of $114,000.  Assuming a ten-year life span for
the equipment and site  preparation, the total capital cost was
$20,000/yr, or $0.66/t  ($0.60/ton).

     The operating costs were estimated at $217,000/yr or $6.84/t
($6.20/ton) dry sludge.  The value of the compost produced was
expected to be about $8.82/t ($8.00/ton) in bulk sales, making
the project very economical.

Conclusions

     At at least two sites in the United States and Canada, a
valuable compost was produced from all or part of the chemical
sludge from a municipal wastewater plant with phosphorus removal.
Based on the experiences of these plants, it appears that the
presence of iron and aluminum precipitates in the sludge does not
inhibit the growth of the microorganisms which are necessary  for
composting.  The quality and value of the compst as a soil  condi-
tioner and fertilizer can be very high for iron and aluminum
sludges.  It is likely  that the value of a lime sludge compost
would be even higher because of the beneficial effects of the


                                69

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lime on soil  pH;  and one compost manufacturer thought that  lime
sludge compost would be cheaper to  produce  by the ton.

     There may be some problems with composting of iron and alu-
minum sludges, however.  The chemical  sludges often cannot  be
dewatered by vacuum filter or centrifuge to a moisture content
as low as that to which regular sludges can be dewatered.   When
this is the case, the cost of hauling  the sludge cake to the com-
posting site increases.  In addition,  a wetter sludge could be
expected to require more time for drying and composting to  occur,
increasing land requirements and operating  costs.  More bulking
agent and/or more ventilation of the compost piles could also
be necessary to keep the wetter sludge aerobic.
                               70

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                             SECTION 7

                 CONDITIONING OF CHEMICAL SLUDGES

CHEMICAL CONDITIONING

     Among the plants participating in this  study, 40 (23 percent)
out of 174 practiced sludge conditioning with chemicals such as
lime, ferric chloride, and polyelectrolytes.  The survey showed
chemical conditioning to be much more than other conditioning
methods for chemical sludges.

     The purpose of chemical conditioning is to improve the per-
formance of subsequent dewatering processes.  Maximum dewatering
performance requires the optimization of many more operating vari-
ables for chemical  conditioning than for thermal conditioning.
The type(s) of chemical  conditioner(s), the  dosage(s), and the
method(s) of application must be chosen, with a wide range of
choices and combinations possible.   The success of the condition-
ing process can only be measured by its effects on subsequent
dewatering, incineration, and disposal processes.  Therefore,
chemical conditioning has been discussed in  each of the sections
of this report dealing with dewatering and also in the section  on
incineration.   The reader is referred to those sections for
detailed information from the literature and from the field inves-
tigations and  questionnaire survey which were part of this study.

     In general, the most common impact of phosphorus removal on
chemical conditioning requirements for sludges  has been the rais-
ing of the dosages required for successful dewatering.  Increased
chemical dosages are undesirable not only because of the effect
on incinerator auxiliary fuel requirements:   with inorganic and
inert chemical conditioners, increased chemical dosages provide  a
drier cake on  a total solids basis, but the cake  is wetter on a
sludge (as opposed to total) solids basis.  That  is, the kg
water/kg dry sludge solids fed to the incinerator is higher.
Thus, more fuel is required for incineration.

     As far as auxiliary fuel requirements, the polyelectrolyte
conditioners have an inherent advantage, and the  inert materials
such as fly ash and sludge  ash have inherent disadvantages.  For
the same cake TS content, the polyelectrolyte-conditioned  sludge
cake will require significantly less  auxiliary  fuel  while  the
ash-conditioned sludge  cake  significantly more  auxiliary  fuel
than the lime and ferric chloride-conditioned  cake.
                                71

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     With regard to chemical sludges, then, particular attention
should be paid to cases where polyelectrolyte conditioners have
been successful in producing dry sludge cakes and have kept down
incinerator fuel requirements.  Also promising are cases where,
because of the presence of phosphorus removal chemicals in sludge,
fewer chemicals were required for conditioning.  In scanning the
sections of this report on dewatering, the reader will note that
in few instances have these ideal situations occurred, but in
some cases such as pressure filtration of an iron sludge and cen-
trifugation of lime sludge, there were promising results.

THERMAL CONDITIONING

Introduction

     Thermal conditioning is a technique which has been increas-
ingly used by consulting engineers in recent years.  Two types of
thermal conditioning exist.  The Zimpro process, often termed
low-pressure oxidation, differs from the Porteous or Farrer pro-
cesses in that air is injected into, rather than excluded from,
the process reactor.  Thermal sludge conditioning has several
benefits.  It stabilizes the sludge, enabling further handling
without pathogens, odors, or putrefaction.  It changes the cellu-
lar structure of the sludge, enabling thickening to a relatively
high solids concentration and thus reducing the volume to be
vacuum filtered; and it improves the dewatering characteristics
of the sludge, increasing filter yield and cake solids concen-
tration.  Its disadvantages are the capital and operating costs
of the process and production of a high COD decantate.

Questionnaire Survey

     As previously shown in Table 10. 11 (6 percent) of the
plants responding to the questionnaire survey reported that they
have thermal conditioning.  Of these 11 plants, 7 practiced anaer-
obic digestion before the thermal conditioning step.  The
digested and thermally conditioned sludge from these plants was
either applied to drying beds, applied directly to croplands, or
vacuum filtered.  At the other four plants which did not anaer-
obically digest, a gravity thickening step preceded thermal con-
ditioning.  At these plants the thermally conditioned sludge was
either vacuum filtered or centrifuged.

     Only three of the questionnaire respondents commented on the
performance of thermal conditioning at their plant or the impact
of the chemical sludge.  At the Maumee River plant in Waterville,
Ohio, a contact stabilization activated sludge plant, a combined
alum-secondary and primary sludge was treated.  The sludge was
gravity thickened, underwent Zimpro, Inc. low-pressure oxidation,
and was dewatered on a belt vacuum filter.  The plant used polymer
for further conditioning of the sludge before dewatering.  A  filter
cake of 35 percent TS was achieved.

                                72

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     At the Grand Haven, Michigan, plant, a 14,000 m3/day (3.7 mgd)
modified activated sludge plant, a combined iron-primary and waste
activated sludge was treated.  The raw sludge had an average TS
concentration of 4.38 percent.  The VS fraction was 65 percent of
TS.  The sludge was gravity thickened, underwent Zimpro, Inc.
low-pressure oxidation, and was vacuum filtered and incinerated.
The thermally conditioned sludge had a TS concentration of 11.8
percent.  Although the sludge was very difficult to dewater
because of a tannery waste received by the plant, thermal con-
ditioning was enabling a filter cake TS concentration of over 30
percent.  The high TS concentration of the filter cake enabled
economical operation of the incinerator.  A comparison of the
characteristics of Grand Haven's filtrate, thickener supernatant,
and thermal conditioning decantate is shown in Table 16.

     The plant was looking for an alternative to thermal condition-
ing for use when the unit was down for repair.  Chemical condition-
ing had been tried with more than 50 different polymers, but none
of them produced a filter cake of greater than 19 percent TS.

     The North Olmsted, Ohio, plant, a contact stabilization acti-
vated sludge plant, treated combined aluminum-secondary and pri-
mary sludge.  The sludge was gravity thickened, underwent Zimpro,
Inc. low-pressure oxidation, and was vacuum filtered.  The plant
achieved a filter cake of 46 percent TS and reported that the
performance was not affected by the addition of sodium aluminate
for phosphorus removal.  The thermal conditioner decantate con-
tained 3,000 mg/l SS and 2,631 mg/l BOD.

Case Studies

     The case studies in the appendices contain detailed infor-
mation on the effects of chemical sludges on thermal condition-
ing.  The particular case studies which deal with this subject
are similar to the experiences of other plants responding to the
questionnaire survey.  However, unusual highlights of the case
studies can be mentioned.

     At Port Huron, Michigan, the costs of thermal conditioning
using the Farrer system were compared with the costs of chemical
conditioning with polymer.  The plant practiced centrifugation
and incineration of the conditioned sludge.  When thermal condi-
tioning, the plant reduced its costs for conditioning polymer and
fuel oil (for incineration) by $12.63/t ($11.46/ton) and $37.71 t
($34.20/ton), respectively.  The operational and maintenance
expenses involved in thermal conditioning included $20.94/t
($19.00/ton) for natural gas, $1.08/t ($0.98/ton) for electricity,
$1.76/t ($1.60/ton) for boiler water conditioning and cleaning
chemicals, $1.68/t ($1.52/ton) odor control, and $9.52/t
($8.64/ton) for sidestream treatment.  The major operational and
maintenance concern, however, was the cost of supplies and labor
                                73

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                          TABLE  16.   AVERAGE SIDESTREAM CHARACTERISTICS  AT
                                       GRAND HAVEN, MICHIGAN
Type of Sidestream                 Thickener           Thermal  Conditioner
                                  Supernatant               Decantate                Filtrate
Volume (m3/day (gal/day))        889  (235,000)              140(37,000)                 31(8,230)
SS (mg/A)                        425                       2,295                      2,358
VSS (% of SS)                     70.3                        60.8                       62.6
COD (mg/A)                       N/A                      20,900                     18,267
BOD (mg/A)                       173                       7,737                      6,755

-------
for equipment maintenance and repair.  This cost was unknown,
because the unit was in use for a limited time only.  The equip-
ment suffered from extreme corrosion and erosion of heat exchanger
and connecting piping, and its operation was eventually discontin-
ued to alleviate the need to replace all the parts with stainless
steel.  Polymer conditioning was then relied upon.  The case con-
cluded that if the unit could have been operated at an equipment
maintenance and repair cost of less than $15.35/t ($13.92/ton) ,
it would have been more cost-effective than polymer conditioning.

     Without thermal conditioning, the sludge fed to the centri-
fuges was of a lower solids concentration, and more time was needed
to dewater it.  The filter cake solids concentration was also
reduced, and the capacity of the incinerator was reduced by about
454 kg/hr (1,000 Ib/hr).  Because of the high costs of operating
under these conditions, the plant was evaluating several alterna-
tive treatment systems.

     At Midland, Michigan, ferric chloride addition was found to
have adversely affected the performance of the Zimpro, Inc. ther-
mal conditioner.  The  impaired performance was evidenced mainly
by the poorer vacuum filter yield and lower filter cake TS concen-
tration.  It was found that excellent performance could be restored
by raising the temperature of the thermal conditioner from 185°C
(365°F) to 202°C (395°F).
 i
     The effect of ferric chloride addition on the thermal condi-
tioner decantate SS and BOD concentrations was unknown.  During
ferric addition, the decantate was low in SS (478 mg/£) but high
in BOD (6,000 mg/£).   The vacuum filter filtrate SS concentration
was high before, and even higher after, ferric addition began.
The BOD concentration  of the filtrate was also high before ferric
addition began but was not further increased by ferric addition.

     When alum addition for phosphorus removal was tried at Mid-
land there were poor conditioning and dewatering results even at
the higher thermal conditioner temperature.

Literature

     A single  literature  account of  thermal  conditioning  of  chem-
ical sludges was found (26).  Dewatering  of  the  thermally  condi-
tioned sludges by vacuum  filtration,  centrifugation,  or on  drying
beds was studied.  Three  plants  using the  Zimpro,  Inc.  low-pres-
sure oxidation system  were  involved.  The  characteristics  of
these plants are described  in Table  17.   At  the  Midland and  Lucas
County plants, the thermally conditioned  sludges  were  vacuum  fil-
tered, while at Defiance  sludge  was  applied  to drying  beds.   Some
of the Defiance sludge was  anaerobically  digested  rather  than
thermally conditioned  before being applied  to the  drying  beds.
Data from the plants were gathered which  characterized  the


                                75

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                             TABLE 17.   CHARACTERISTICS OF PLANTS  IN  STUDY OF THERMAL
                                      CONDITIONING OF CHEMICAL  SLUDGES (26)
Plant Location
Type of Raw
Sludge Treated
(m3/day (mgd))
Reactor
Temperature
(°C (OF))
Reactor
Pressure
(kg/ cm2 (psi))
Further Treatment/
Disposal
        Defiance,  Ohio
0>
       Midland,  Michigan
        Lucas  County,
          Ohio
Iron-primary and
secondary from an
activated sludge
plant
Iron-primary and
secondary from a
trickling filter
plant

Aluminum-primary
from a contact
stabilization
activated sludge
plant with no
primary treatment
171  (340)
16.52  (235)
193 (380)
182 (360)
31.63  (450)
21.09 (300)
Sludge drying beds;
dried sludge stock-
piling on land
adjacent to plant
Vacuum filters;
land disposal of
filter cake
Vacuum filters; land
disposal of filter
cake

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sidestreams associated with thermal conditioning, vacuum filtra-
tion, and anaerobic digestion, and are presented in Table 18.   In
the case of the decantate from the three thermal conditioning
units, the TS concentrations averaged 1 percent, with a VS fraction
of 74 to 87 percent of TS.  The decantates contained 0.3 to 0.6
percent organic carbon, almost all of which was soluble in each
case.  These observations indicate that the decantate exerted  a
high oxygen demand on the plant biological oxidation processes
when it was returned to the plant.  Sidestreams from subsequent
dewatering processes would be expected also to have been high  in
soluble organic carbon.  The amount of phosphorus, and either  iron
or aluminum, in the thermal conditioner decantate varied widely
between the plants.

     The Midland thermally conditioned iron sludge was dewatered
in a pilot-scale, solid-bowl scroll centrifuge at two different
bowl speeds and loading rates.  The results of this test are given
in Table 19.  At the higher of the two bowl speeds and loading
rates tested, both the centrate TS concentration and the percen-
tage of feed solids recovered in  the cake were greater than at
their lower rates.

     Table 20 contains a comparison of the sidestream characteris-
tics from  plant vacuum filter operations and pilot-scale centri-
fugation of the plant  sludges.  In the two comparisons made, the
vacuum  filter filtrate was  lower  in organic carbon, phosphorus,
and  iron or aluminum than the Scroll or basket centrifuge centrate.


Conclusions

     Few problems  have been experienced in thermal conditioner
operation  as the result of  chemical addition for phosphorus
removal.   Methods  of improving thermal conditioner operation when
treating chemical  sludges may include:

     t  Providing sludge storage facilities or alternate disposal
        methods such as liquid sludge hauling for periods when the
        thermal conditioner  is down for repair.  This is particu-
        larly important at plants  practicing incineration because
        chemical conditioning as a  substitute may not provide a
        filter cake of  adequate dryness.  Repair requirements for
        thermal conditioners seem  to be moderate to substantial.

     •  Raising the temperature of  the  unit.  This may reduce
        decantate SS concentrations and improve sludge dewaterabil-
        ity.

     There is some indication that vacuum filters may be more suit-
able for  the dewatering  of  thermally  conditioned chemical  sludges
than centrifuges.   However,  this  should  be  investigated further,
and  filter presses  should  also  be evaluated.


                                77

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TABLE 18.   CHARACTERISTICS  OF  STREAMS AND SIDESTREAMS
      ASSOCIATED WITH SLUDGE TREATMENT OPERATIONS  (26)
Stream or Fe or
Sidestream Al
Lucas County
Raw sludge 2,200
Midland
Raw sludge 7,250
Lucas County
Conditioned
sludge 3,045
Midland
Conditioned
sludge 12,233
Defiance
Conditioned
sludge 5,570
Lucas County
Decantate 5
Midland
Decantate 70
Defiance
Decantate 122
Defiance
Digested
sludge 2,545
Defiance
Supernatant 635
Midland
Filter cake 73,000
Midland
Filtrate 5,200
P
mg/a

1,157

1,867


1,955


4,317


1,483

20

723

66


656

26

17,000

2,300
Fe or Al
to P ratio

2.0

3.9


1.5


2.8


3.3

0.2

0.1

1.8


3.9

2.4

4.2

2.3
TOC
mg/£

4,800

41,830


10,650


—


52,400

2,937

6,000

5,090


10,600

6,400

500,000

4,000
SOC TS

2,441 29,450

5,467 86,333


4,950 47,412


— 200,000


5,019 110,000

2,887 9,183

5,800 10,667

3,902 10,340


2,050 35,000

2,180 17,500

7,400 598,000

3,200 7,200
% vs

57

54


53


41


48

87

76

74


47

53

42

62
                                                       (continued)
                         78

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TABLE 18 (continued)
Stream or
Sidestream
Fe or
  Al
 P
mg/fc
                                  Fe or AT
                                 to P ratio
TOC
SOC
mg/t,
TS
                                                          VS
Lucas County
 Filter cake   30,336   15,218       2.0

Lucas County
 Filtrate          95       69       1.4

Lucas County
 Filter cloth
 wash             100       64       1.6

Lucas County
 Digested
 sludge         1,680      950       1.8
                                      338,000    45
                       3,811    3,489    7,878     82
                       4,700   4,500    8,500     85
                       2,100     270   18,300     43
                                     79

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TABLE  19.   RESULTS OF PILOT SCALE CENTRIFUGATION OF
     MIDLAND THERMALLY CONDITIONED IRON SLUDGE  (26)

«o
O'



Bowl Speed, rpm

4,000
4,500
Loading Rate
.kg/hr (Ib/hr)

19.2 (42.3)
24.7 (54.4)
Cake Solids
% TS

33.3
49.0
Centrate Sol ids
% TS Polymer

4.5 no
9.6 no
Solids
Recovery, %

82.9
97.1

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eo
                               TABLE 20.   COMPARISON OF  SIDESTREAMS  FROM  PLANT AND
                                          PILOT DEWATERING  OPERATIONS (26)
Operation
Midland:
Vacuum filtration
filtrate
Scroll centrifugation
centrate
Lucas County:
Vacuum filtration
filtrate
Scroll centrifugation
centrate
Basket centrifugation
centrate
Fe or Al
to P ratio
520
640
95
458
260
P TOC SOC TS
mg/x, mg/& mg/& mg/&
230 4,000 3,200 7,200
170 5,600 4,400 9,600
69 3,811 3,489 7,878
354 6,560 4,180 14,500
200 9,800 2,000 8,000
% MS
62
64
82
68
84

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                            SECTION  8

                 DEWATERING OF  CHEMICAL  SLUDGES


DRYING BEDS

Introduction

     A total of 58 (33 percent) of the plants responding to the
questionnaire survey utilized drying beds for sludge dewatering.
Historically, sludge drying beds have  been mainly used by smaller
communities.  Principal advantages of  drying beds are their sim-
plicity and low maintenance costs.  The  chemical  cost and operat-
ing complexity of mechanical dewatering  equipment are additional
factors which favor drying beds.  Disadvantages  include their
large land requirements, inability to  dewater effectively year-
round in certain areas, and potential  odor problems.

Questionnaire Survey

     Nine of the questionnaire respondents which  have drying beds
reported problems with the handling of chemical  sludges.  All of
those plants used iron or aluminum salts for phosphorus removal.
Table 21 summarizes the experiences of-those plants.  Plants
using lime did not report any impacts, either positive or nega-
tive, on drying bed operation other than the need for additional
bed space to handle the extra sludge generated.

     The most common problems experienced in drying bed operation
were increases in sludge volume and mass, and poor sludge dewater-
ability.  These problems resulted in:  construction of additional
drying beds, addition of chemicals to  improve dewatering; modifi-
cations in sludge application procedures, lengthened sludge drying
times, or the abandonment of sludge drying beds in favor of ano-
ther dewatering process.  The point of chemical  addition did not
seem to influence the performance of iron or aluminum sludges  on
drying beds.  Plants with chemical addition  to primary or  secon-
dary stages reported the same general  problems.

     Parry Sound, Ontario, a primary plant adding ferric chloride
for phosphorus remova-1 , reported  rapid clogging of  their sand
drying beds with solids.  This problem was alleviated by replacing
the original bed sand with a coarser sand and by replacing  the
bed sand more frequently.


                               83

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                       TABLE 21.  IMPACTS OF CHEMICAL SLUDGES UPON DRYING BED PERFORMANCE
                                    AS REPORTED IN QUESTIONNAIRE RESPONSE
Location
Size-
nr/day
(mgd)
Type of
Sludge Treated
Impacts of
Chemical Sludge
Performance with
Chemical Sludge
    Addison, Michigan
    Escanaba, Michigan
00
to
    Rogers  City, Michigan
1,480    Alum-primary (aerobi-
(0.39)   cally digested)  from
         an  aerated  lagoon
         plant.

7,040    Iron-primary (anaero-
(1.86)   bically digested)
         from an activated
         sludge plant.
2,650    Iron-secondary (an-
(0.7)    aerobically digested)
         from a  conventional
         activated  sludge
         plant with no  pri-
         mary treatment.
The chemical sludge takes
longer to dewater on the
beds.
The sludge is not more
difficult to dewater, but
there is a larger volume.
A method was devised to
add polymer to the sludge
as it enters the drying
beds to increase the bed
turnover rate.  Also,
additional cement strips
were added in the drying
beds to allow mechanical
sludge removal.  This also
increases the bed turnover
rate.
                                                                           (continued)
                             The sludge at
                             3.2 percent TS
                             is applied to
                             sand drying beds.
                             When applied 8
                             to 12 in deep,
                             the sludge is
                             ready for re-
                             moval  by hand in
                             30 to 45 days.
                             It is best to fill
                             the beds to only

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    TABLE 21 (continued)


Location
Size-
m3/day
(mgd)

Type of
Sludge Treated

Impacts of
Chemical Sludge

Performance with
Chemical Sludge
     Rogers City, Michigan
      (cont'd)
     Flushing, Michigan
00
     Charlevoix, Michigan
     Coldwater, Michigan
4,580   Iron-secondary  and
(1.21)  primary (anaerobically
        digested)  from  a  con-
        ventional  activated
        sludge  plant.
1,100   Iron-secondary and
(0.29)  primary (anaerobi-
        cally digested) from
        a  complete mix acti-
        vated sludge plant.
6,780   Iron-primary and
(1.79)  secondary (anaero-
        bically digested)
        from a trickling
        filter plant.
                             8  in  for  fastest
                             drying  and  easiest
                             removal.

                             The estimated
                             operation and
                             maintenance costs
                             for the drying
                             beds  were about
                             $700  in 1976.
Before phosphorus
removal was begun, the
plant had only primary
sludge.  The sludge
at that time took one
half as long to dewater
and was slightly less
odorous.

The sludge volume was three
times greater after phos-
phorus removal, causing the
plant to construct 7 new
drying beds.  Cement bottoms
were put in both the old and
new beds.  The sludge takes
30 to 50 percent longer to
dry.
                                                                                                 (continued)

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    TABLE 21  (continued)
         Location
 Size-
 m3/day
 (mgd)
   Type of
Sludge Treated
   Impacts of
Chemical Sludge
Performance with
 Chemical Sludge
    Parry Sound, Ontario
    Ashland,  Wisconsin
00
     Three Rivers,  Michigan
3,200     Iron-primary (anaero-
(0.85)    bically digested)
          from a plant with  no
          secondary treatment.
4,540     Alum-secondary and
(1.2)     primary (anaerobically
          digested)  from a con-
          ventional  activated
          sludge plant.
 4,730     Alum-primary and
 (1.25)    secondary (anaero-
          bically digested)
          from a conventional
          activated sludge
          plant.
                    The sludge is finer and
                    more difficult to dewater.
                    To improve dewatering, a
                    more coarsely screened
                    sand was put in and the
                    sand is changed more often.

                    Sludge drying beds were
                    abandoned because the
                    gelatinous alum sludge
                    would not dewater.  The
                    plant began using a vacuum
                    filter instead.

                    The sludge takes longer
                    to dry on the beds.

-------
     The drying beds at Ashland, Wisconsin,  an activated sludge
plant with secondary addition of aluminum sulfate,  were abandoned
because of difficulties in dewatering the gelatinous alum sludge.
This plant switched to ferric chloride sludge conditioning and
vacuum filter dewatering.

Literature

     Literature accounts of drying bed dewatering of chemical
sludges are few, although the recent rise of chemical  addition
for phosphorus removal should change this pattern.

     An excellent discussion of chemical  sludge dewatering on
sand beds (48) relates sludge characteristics to sand  bed design.
It concludes:

     •  The most critical  sludge characteristic with regard to
        the use of sand beds is sufficient sludge compressibility
        to prevent sand bed penetration.   Compressibility is the
        variation of specific resistance  with pressure.  It influ-
        enced the rate of water loss of sludges applied to sand
        beds.

     •  Chemical sludge drainage rates depend upon the specific
        resistance and applied solids concentration.

     •  Air drying of chemical sludges occurs in two distinct
        phases.  Initially, a slow drying rate occurs, followed
        by a more rapid drying.

     •  The slow drying rate appears to be governed by the applied
        depth and drained solids concentration.  Rapid drying  is
        approximately equal to the rate of free surface water
        evaporation.

     The addition of a high molecular weight anionic polymer to
the drying beds at the Escanaba, Michigan, plant had a dramatic
effect on the sludge disposal operation (35).  The plant's aero-
bically digested sludge failed to dewater and dry out  in a rea-
sonable length of time.  The sludge had a tendency to  penetrate
and plug the sand bed.  Polymer addition  to the sludge as it
entered the beds resulted in faster drying time.  Before this
operation, extensive hauling of liquid sludge for land disposal
was necessary.  The sludge was flocculated by placing  a simple
plywood mixing box (4 ft by 4 ft by 1.5 ft) under the  bed dis-
charge valve.  The box contained a baffle to provide mixing and
a  notched overflow weir.  Polymer was added to the sludge as  it
entered the box by means of a portable tank and a small electric
pump mounted on a trailer.  A used fuel tank  (1.04 m3  or  275  gal)
with the top cut out made an excellent low cost tank.  As the
polymer was added to the mixing box, the sludge rate was  adjusted
until  a large floe formed.  The final concentration of polymer

                               86

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was dependent on the sludge TS concentration (Table 22).  Several
polymers were tried, with a high molecular weight anionic proving
to be the most effective.
          TABLE 22.  POLYMER APPLICATION TO DRYING BEDS
Sludge
% Solids
1.8
2.0
2.2
Cat ionic
mq/ a
83
92
104
Anioni
mg/£
23
26
29
c




      Drying  time was  evaluated  by  filling each of two beds with
 56.8  m3  (15,000 gal)  of  the  same sludge.  One bed had polymer
 added while  the other did  not.  During  the test period there was
 almost constant daily sunshine  and minimal rainfall.  At the end
 of  12 days,  the bed with the  polymer was dry enough to clean,
 while the  one without polymer required  34 days to dry.  During
 the summer,  drying time  varied  depending on climatic conditions
 and the  mass of dry sludge applied to the bed.  Average drying
 time  in  ideal weather was  10  to 14 days with the polymer added.

      Another benefit  derived  from  the polymer addition was a
 reduction  in odor  from the drying  beds.  The relatively high
 volatile content of the  digested sludge generated an offensive
 odor  when  it remained in the  liquid state for long  periods.

 Concl usions

      Improved drying  bed performance can be achieved if the fol-
 lowing modifications  are made:

      t   Improving  the performance  of upstream facilities,  e.g.,
         thickeners, digesters

      •   Adding chemicals to  improve sludge dewatering character-
         istics

      t   Optimizing sludge  loading  rates and bed turnover rates

      •   Changing the  drying  bed filter  material

      •   Covering open beds where climatic conditions adversely
         affect performance.
                                87

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 VACUUM  FILTRATION

 Introduction

     As shown  in Table 10, vacuum filtration is utilized by
 approximately  21 percent of the sewage treatment plants responding
 to  the  project questionnaire.  Vacuum filtration is an important
 sludge  treatment unit process for many plants generating phospho-
 rus-laden chemical sludges.  It has received substantial attention
 in  both the technical literature reviewed and the case studies
 conducted.  It was reported that vacuum filtration operational
 characteristics and performance results were definitely affected
 by  the  inclusion of chemical sludges with primary and/or secondary
 sludges normally produced.  The resulting changes were not in all
 cases detrimental, however, and solutions to the problems encoun-
 tered were often achieved by treatment plant personnel.

     In the following discussion it is assumed that the reader is
 familiar with  the theory and mechanical operation of vacuum fil-
 ters.   The operator of a vacuum filter strives for maximum solids
 capture, filter cake yield, and filter cake solids content, as
 well as to minimize costs.  Solids capture is usually expressed
 as  the  percent of the dry weight of sludge TS retained on the
 filter, i.e.,  that portion not returning to the treatment plant
 in  the  filtrate.  A solids capture of at least 90 percent is
 desired.

     Filter cake yield is expressed in terms of pounds of dry
 total sludge TS discharged from the filter media per hour per
 square  foot of filter media.  When chemicals are used for phos-
 phate removal, they increase the percentage of non-volatile solids
 in  the  sludge.  When comparing filter cake yields, correction
 should  be made to account for this difference.

     Cake solids content is expressed in terms of percent weight
 of  dry TS in the sludge cake.  The cake solids content normally
 increases with an increase in the TS concentration of the sludge
 being fed to the filter.

 Questionnaire Survey

     Table 23 summarizes the comments of 11 plants utilizing
 vacuum filtration which responded to the questionnaire survey.
Many plants reported that vacuum filtration problems resulted
 from the inclusion of phosphorus-laden chemical sludges with  the
biological  sludges previously processed.  Typically, the increased
sludge volume and solids mass stressed the capacity of the vacuum
filter.   In one extreme case, a plant reported increasing their
vacuum filtration operation from 40 hr/wk up to 168 hr/wk.  Doub-
ling of operational  time, e.g., from one to two shifts, was fairly
common.
                               88

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                   TABLE 23.  CHANGES  IN VACUUM FILTER PERFORMANCE REPORTED AS A RESULT OF
                                 PHOSPHORUS REMOVAL CHEMICAL SLUDGE ADDITION
    Location
     Type of Sludge
Changes in Vacuum Filter Performance Resulting from
   Phosphorus Removal Chemical Sludge Addition
    London,
    Ontario
Lime-primary and secondary
(conditioned with Fed3)
from an activated sludge
plant
Filter cake solids increased from 16.8 percent to
19.3 percent TS. Filter yield increased by 30 percent.
Cost of chemical conditioning increased from $15 to
$16 per ton of dry solids.
00
    Sheboygan,
    Wisconsin
Iron-secondary and primary
from a trickling filter
plant
Filter yield decreased by 25 percent,
    Hatfield
    Township,
    Pennsylvania
Lime-primary and alum-
secondary
Tremendous increase in sludge volume, required going
to a 24 hr/day, 7 day/wk operation on vacuum filter
as opposed to the former 40 hr/wk operation.
    Willoughby-
    Eastlake,
    Ohio
Alum-secondary and primary
from an activated sludge
plant
The sludge filter cake averages about 20 percent
higher moisture content than formerly because of
the alum addition. Filter discharge characteristics
(solids capture) deteriorated.  Experiments  with
various filter cloths showed that a sateen  weave
provided the best results.  Lime and ferric  chloride
sludge conditioners also impared filter operation.
                                                                                               (continued)

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 TABLE 23  (continued)
Location
     Type of Sludge
                                                   Changes in Vacuum Filter Performance  Resulting from
                                                      Phosphorus  Removal  Chemical  Sludge Addition
Warren,
Michigan
Alum-secondary and primary
from an activated sludge
plant.
                                                   Many other plant changes  were  incorporated con-
                                                   currently with the implementation  of  phosphorus  re-
                                                   moval,  making it impossible  to identify specific
                                                   changes caused by the  alum addition.  However,  it
                                                   appeared that the alum addition caused the sludge cake
                                                   solids  content to drop from  20 percent down to 16
                                                   percent. In addition,  the sludge conditioning
                                                   chemical was changed to polymer instead of lime  and
                                                   ferric  chloride. As the result of  more moisture  in
                                                   the sludge cake, subsequent  incineration energy
                                                   (natural gas) costs increased.
Ypsilanti,
Michigan
                       Iron-secondary and primary
                       from an activated sludge
                       plant
                            The plant found it very difficult to handle the 50
                            percent increase in sludge generated by implementation
                            of phosphorus removal.  The vacuum filter operation
                            time was increased by 50 percent, and solids increased
                            in the filtrate and throughout the plant.
Lakeville,
New York
Iron-tertiary and primary
and secondary from a
trickling filter plant
                                                   Changed from vacuum filtration  of raw sludge  to
                                                   vacuum filtration of anaerobically digested sludge.
                                                   More polymer was  needed to treat the  sludge.
Hilton,
New York
Alum-secondary and primary
from an activated sludge
plant
                                                   This plant operates both vacuum filters  and  centri-
                                                   fuges.  They found ng changes  due to alum addition  for
                                                   phosphorus removal. The vacuum filter yielded  a  20 per-
                                                   cent solids cake (sludge conditioned with lime and
                                                   ferric  chloride). The centrifuge yielded a 19  percent
                                                   solids  cake (polymer added).
                                                                                             (continued)

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 TABLE 23  (continued)
Location
     Type of Sludge
Changes in Vacuum Filter Performance Resulting from
   Phosphorus Removal Chemical Sludge Addition
Lakewood,
Ohio
Alum-secondary and primary
from an activated sludge
plant
Frankenmuth,
Michigan
Alum-secondary and primary
sludge (anaerobically
digested) from an activated
sludge plant
The mixed T:liquor  suspended solids concentration in-
creased from 2000 to 5000 mg/£, and the return sludge
solids concentration increased from 1.2 percent to
2 percent. The vacuum filter operating time has in-
creased to two shifts instead of one. The filter cake
solids concentration has decreased to 20 percent from
the former 25 percent because the alum sludge is more
difficult to dewater. Overall the cost of plant opera-
tion has increased about 40 percent due to the addi-
tion of alum for phosphorus removal.  The increased
cost includes labor (3 men at $32,000/yr), lime and
ferric chloride sludge conditioning at about
$21,000/yr, furnace fuel at $83,000/yr, and in-
creased hauling costs to the landfill.

The luxury uptake of phosphorus  in the activated
sludge unit due to high BOD in the influent (brewery
waste) has made the required phosphorus removal
obtainable with a minimum amount of chemical addition.
No problems have been experienced with vacuum
filtration.
Mil ford,
Michigan
 Iron-secondary and primary
 from an activated sludge
 plant
The plant experienced greatly improved vacuum filter
operation after the implementation of phosphorus
removal. The vacuum filter yield increased from
24 kg/m2/hr  (5 Ib/ft/hr) to 68 kg/m2/hr
(14 Ib/ft/hr) and cake solids increased from 16 per-
cent to 19 percent. In addition, there was a decrease
in the quantity of lime and ferric chloride needed
for sludge conditioning.

-------
     Also commonly reported was the requirement to change dosages
 or  types of conditioning chemicals used (polymers, ferric chlo-
 ride,  etc.). as a result of different sludge characteristics
 caused  by the  introduction of chemical sludges.

 Literature

     Most literature sources indicated that increased filter cake
 yield  can be expected from phosphorus-laden chemical sludges.
 Typical comments include the following:

     •  Laboratory vacuum filtration tests conducted by the Bli'ch-
        ner funnel method indicated that the alum digester sludge
        filtered slightly better than the control sludge.  Both
        sludges were effectively conditioned by ferric chloride
        at 4 percent by weight of TSS.  Specific resistances were
        10.9 x 105 sec^/g and 7.6 x 10)5 sec2/g for the control
        and alum digester sludges, respectively, after condition-
        ing.   Vacuum filter leaf tests indicated that the condi-
        tioned alum-biological sludge could be dewatered from 1.6
        percent TSS at a filtration rate of 14.6 kg TSS/m2/hr
        (3.0 Ib/ft2/hr) (2).

     •  A dual polyelectrolyte sludge conditioning sequence made
        it possible to attain vacuum filter yields of up to 49
        kg/mz/hr (10 Ibs/ft2/hr) on the phosphorus removal sludge
        solids (22).

     •  Alum addition to wastewater for the removal of phosphorus
        also produced a waste activated sludge which is easier to
        dewater.  Also, when this sludge is combined with raw pri-
        mary sludge, the resulting mixture again shows an
        increased ability to be dewatered (51).

     •  Vacuum filtration of iron sludge at the North Toronto
        plant  showed the filter yield to increase from 11.08 to
        23.14  kg/m2/hr (2.27 to 4.74 Ib/ft2/hr).  However, these
        data are not considered typical in view of the fact that
        an extremely low capture of solids was obtained.  No data
        are available on sludge conditioning chemical requirements
        at this plant (72).

Conclusions

     Some plants have experienced adverse effects on vacuum fil-
ter operation as the result of the addition of phosphorus-laden
chemical sludges, while other plants have not.  Unfortunately,
there are no clear patterns apparent on which to base recommenda-
tions for "best" treatment.  Treatment plants which are  imple-
menting phosphorus removal should conduct bench-top  (or  prefer-
ably pilot)  tests, to determine the combination of  phosphorus
removal chemicals and sludge conditioning chemicals to obtain

                               92

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optimum vacuum filter performance.  Experiments with various fil-
ter media are also suggested.

     Some generalizations may be made as follows:

     •  Many plants reported operating their vacuum filters addi-
        tional shifts to handle the additional  chemical  sludges
        generated.

     •  It is advantageous to thicken and condition the  sludge
        prior to vacuum filtration in order to  increase  filter
        yield and filter cake solids concentration.

     •  Ferric chloride and lime are reported successful  in con-
        ditioning alum sludges.  Even with conditioning,  however,
        it is common for alum sludges to have a lower percentage
        of filter cake solids; al urn siudges are  more difficult to
        dewater.

     •  Polymers have been reported successful  in  conditioning
        iron sludges.

     •  Filtration of combined primary-secondary sludges  is pre-
        ferable to filtration of secondary sludges alone.

     •  Iron sludges are more corrosive, so system component
        materials should be selected for corrosion resistance.

     •  Lime addition for phosphorus removal greatly increases
        the amount of sludge generated, and system components
        should be sized to accommodate the anticipated increase.
        Lime scaling may be a problem on wetted surfaces,  so
        maintenance access for cleaning should  be  provided.

     •  Many dramatic improvements in sludge filterabi1ity have
        been reported as resulting from the proper use of polymers
        during sludge treatment steps prior to  filtration.

     Reported changes in filter yield and filter cake solids
showed a confused pattern, with some plants experiencing increased
yields and solids, and others showing poorer results than were
experienced with non-chemical sludges.  Alum sludge particularly
was singled out as often difficult to dewater.

DRYING LAGOONS

Introduction

     Drying lagoons form a simple, low-cost sludge dewatering
system which is limited in application to areas where large quan-
tities of cheap land are available.  Of plants  which responded
to the questionnaire survey and/or were field investigated during


                               93

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this study, drying lagoons were used by 15 out of 174 (9 percent).
Lagoons were the third most common dewatering method for chemical
sludges, following drying beds and vacuum filtration.

     In evaluating the impact of phosphorus removal  by chemical
addition on drying bed operation, we must consider how sludge
drying rates will be affected and how plants may respond to the
need for additional drying bed capacity for increased sludge
volume.  Sludge drying rate is important because sludges that
take longer to dry have lower solids loading rates,  and they
require more space/ton of dry solids.  Sludges that  dewater slowly
also tend to be the cause of odor problems.  The need for addi-
tional drying lagoon capacity is often problematical for plants
because of the expenses involved in making more space available.

Questionnaire Survey and Case Studies

      As shown in Table 24, relatively little information on
lagoon operation was obtained from the surveyed plants.  Evi-
dently, little monitoring of sludge drying rates, dried sludge
TS concentrations, etc., is performed.  The comments in Table 24
indicate that often lagoons were used as stand-by or supplemen-
tary operations in addition to other dewatering methods, and
since they were not relied on closely, they were not monitored.
Furthermore, at some of the plants, lagoons were treated as stor-
age areas rather than as a dewatering method.  In some cases,
the plants did not expect to completely fill their lagoons for
several years, so they had not been particularly concerned over
control of dewatering rates or over sludge removal.

     On the other hand, Table 24 also contains comments from
plants which had run out of lagoon space and had been forced
either to clean out the filled lagoons to make space available,
or to purchase land and construct new ones.  Both of these alter-
natives were considered expensive by the plants.

     Some of the plants mentioned that their need for additional
lagoon space was created by the additional sludge generated by
phosphorus removal.  Other adverse impacts of phosphorus removal
which were mentioned included slower sludge drying rates, failure
of the sludge to dewater, and odor problems.  In contrast, there
were other reports of chemical sludges which settled readily in
the lagoons, formed clear supernatants, and posed no odor prob-
1 ems.

Conclus ions

     Drying lagoon operation is often made more expensive and
difficult by the need to handle chemical sludges because of
greater sludge volumes and slower drying rates.  Plants must  be
prepared to provide more space for the extra sludge  volume  by
constructing new lagoons or by cleaning out existing ones which

                               94

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              TABLE  24.   IMPACTS OF CHEMICAL SLUDGES UPON DRYING LAGOON PERFORMANCE AS
                                   REPORTED IN QUESTIONNAIRE RESPONSE
     Plant
    Location
  Type of Sludge Treated
 Impacts of Chemical Sludge     Performance with Chemical Sludge
    Virginia,
    Minnesota
VD
vn
     Ottawa,
     Ontario
     (Green
     Creek)
     Berrien
     Springs,
     Michigan
Lime-primary and secondary
(gravity thickened) from
an activated sludge plant
Alum-primary (anaero-
bically digested) from a
plant with no secondary
treatment
 Iron-tertiary from an
 activated sludge plant
When phosphorus removal was
begun with lime, the plant's
digester and drying beds were
abandoned. It was believed
that the lime sludge could
not be fed to the digester
without causing problems. A
gravity thickener and drying
lagoons were chosen instead.
The sludge was limed at the
thickener to reduce odors,
using 200 Ib/day lime at
$0.15/lb.

Alum addition created about a
90 percent increase in sludge
volume, or approx. an addi-
tional 378 m^/day (100,000
gpd). This necessitated the
construction of 28.5 acres
extra lagoon space (for a
total of 56 acres) at a cost
of $690,000.

The chemical sludge is pumped
directly to a holding lagoon
which has a 20-yr design capa-
city.  Organic sludge is
treated separately.
An 8 to 10 percent TS sludge was
generated by the thickener. But
the sludge would not dry in the
lagoons. The sludge also emitted
a very offensive odor after a
period of time even when heavily
limed.  The lagoons were aban-
doned and the sludge is hauled
at 8 to 10 percent TS to a dis-
posal site.
There have been no odor
problems.
                                                                                                 (continued)

-------
    TABLE 24 (continued)
     Plant
    Location
               Type of Sludge Treated
                               Impacts of Chemical Sludge     Performance with Chemical Sludge
    Coldwater,  Iron-primary and secondary
    Michigan    (anaerobically digested)
                from a trickling filter
                plant
vo
en
North
Madison,
Ohio
Lime-tertiary from an
activated sludge plant
    Sturgis,    Alum-tertiary from a
    Michigan    trickling filter plant
The sludge drying lagoon was
cleaned out shortly after
chemical addition for phos-
phorus removal was initiated
to provide.additional sludge
drying space. This was
necessitated by a slower
sludge drying rate as well as
greater quantities of digest-
ed sludge.

The plant has had phosphorus
removal since it started
operation in November of 1974.
Therefore, it is not possible
to compare operation with and
without chemical sludge.
                                                                          Sludge is  sent  to  the  lagoons
                                                                          on  a  sporadic basis  at times
                                                                          when  the drying beds are  full
                                                                          and there  is a  need  to make
                                                                          room  in the digesters.  No formal
                                                                          records have been  kept as to the
                                                                          characteristics of the sludge  in
                                                                          the lagoon.
 The lime sludge is pumped to 2
 lagoons which are 61  m by 30.5 m
 (200 ft by 100 ft).  The sludge
 settles and a clear supernatant
 is decanted by a pipe at the
 1.5-m (5-ft) water height.
 Cleaning the lagoons  is an
 expensive problem. Both are full.
 $7,000 was paid in 1976 to  a
 private contractor to clean 1/4
 of a lagoon.

The chemical sludge is not com-
bined with primary and secondary
sludges.  It is pumped separately
to so-called "dry lagoons."
When a lagoon is filled it is
allowed to dry and then scari-
fied. This has not been done yet
as a laqoon has not been filled.
                                                             (continued)

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TABLE  24  (continued)
 Plant
Location
 Type of SLudge  Treated       Impacts of Chemical Sludge      Performance with  Chemical  Sludge
Ludington,   Lime-tertiary from an
Michigan     activated sludge plant
 Watt's
 Creek
 STP,
 Shirley's
 Bay,
 Ontario
 Niagara
 Falls,
 Ontario
Alum-secondary and primary
(anaerobically digested)
from an activated sludge
plant
Iron-primary (anaero-
bically digested) from a
plant with no secondary
treatment
                                                            The chemical  sludge  is  not  com-
                                                            bined with primary and  secondary
                                                            sludge. It is Dumped to lagpons
                                                            which are not expected  to be
                                                            filled for 20 yrs.
With alum addition the raw
sludge volume has increased
65 percent or more.  The
digested sludge solids concen-
tration decreased from 5.5
percent to 3 percent, meaning
an even greater increase in
digested sludge volume.  In-
creased holding lagoon space
is planned to accommodate the
extra sludge. An additional
sludge hauling cost  of $25,000
is anticipated for 1976.

The sludge from the  digesters
has a lower TS concentration
and the volume is greater.
The lagoons must be  filled to
deeper depths to accommodate
the extra volume. The sludge
takes longer to dry  in the
lagoons and does not reach the
same solids concentration as
before.

-------
have been used simply as storage areas.   They must also antici-
pate the possibility of slower sludge drying rates,  causing an
even further demand for greater capacity.   Where capacity is
unavailable, alternative means of sludge handling such  as liquid
sludge hauling or mechanical dewatering  will have to be consid-
ered.

PRESSURE FILTRATION

Introduction

     Pressure filters have long been used in Europe  to  process
difficult-to-dewater sludges.   During the last five  years, there
has  been a substantial  increase in the use of pressure  filters in
the  U.S.  Improvements  in equipment and  greater quantities of
difficult-to-dewater sludges,  such as iron and alum  sludges,
account for the increase.

     For conventional (non-chemical) sludges, the process pro-
duces a drier filter cake than either vacuum filtration or cen-
trifugation.  Total solids concentrations of 40 to 60 percent
are  generally achieved  with undigested primary and secondary
sludges, and concentrations of 40 to 45 percent TS are typical
for  digested primary and secondary sludges.  Sludge  thickening
is usually required prior to filtration  for all but  primary
sludges.  Proper sludge conditioning is  necessary in order to
achieve the best filter results.

     Evidently, the only conditioning method utilized at present
is chemical conditioning.  Polymer, lime, ferric chloride, fly
ash, lime kiln flue dust, and sludge incinerator ash are the con-
ditioners used.  Frequently, a combination of approximately 5
percent (of the dry weight of the sludge) FeCl3 and  10  percent
lime is employed.  The  use of an additional 100 to 250  percent
ash  can usual ly increase filter cake dryness by about 5  percent.

     For conventional sludges, the cost  of dewatering by pressure
filtration is higher than the cost of vacuum filtration or cen-
trifugation.  However,  the drier cake produced may result  in cost
savings in the downstream disposal processes which offset  or
exceed the higher cost.  The highest operation and maintenance
expenses for pressure filtration are typically the cost of labor
and  the cost of chemical conditioners.

     When dewatering chemical  sludges, both the performance char-
acteristics of the process and the energy,  labor, and chemical
requirements are altered.  Consequently, the costs associated
with pressure filtration, and also with  the downstream disposal
processes,  are changed.  It is desirable to determine whether
chemical  sludges enhance or decrease the cost-effectiveness  of
pressure filtration in  relation to other dewatering methods.
                               98

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Questionnaire Survey

     A total of eight (46 percent) of the plants responding  to
the questionnaire survey reported that they have pressure filters.
Only six questionnaire respondents commented upon the performance
of pressure filtration at their plant or the impacts of the  chem-
ical sludge.  Table 25 indicates the sizes of the six plants  and
the sludge treatment/disposal methods which were used.   Thicken-
ing and digestion of the raw sludge were common.  Two plants
practiced incineration of the dewatered filter cake.  A variety
of sludge conditioners were used prior to dewatering.  A single
plant used an organic polymer.  The others, including the two
plants with incineration, used inorganic conditioners.

     Table 26 presents data and comments from the questionnaires
pertaining to pressure filter performance with conventional  and
chemical sludges.  Four of the plants used plate and frame-type
pressure filters and two used unusual types of filter processes.
The plants, which had iron and lime sludges, reported that,  when
handling the chemical sludges, they needed smaller dosages of
chemicals to condition the sludges before dewatering.  These
plants had filter cake solids concentrations of 40 to 50 percent
TS.

Case Studies

     The case study of Brookfield, Wisconsin, in Appendix H,  stu-
dies the impacts of an iron sludge on the plant's plate and  frame
pressure filter.  Phosphorus removal with ferrous sulfate resulted
in an increase  in the mass of sludge generated which was offset
by a decrease in the weight of chemicals needed for conditioning.
Although roughly 30 percent more sludge TS was generated during
phosphorus removal, the dry weight of the filter feed, consisting
of both sludge  and conditioning chemicals, was greater by only
15 percent.  The dosage of incinerator ash for conditioning was
lowered from 85 percent to 60 percent.  The FeCl3 dosage also
decreased somewhat, to a dosage of 6 to 8 percent.  The lime
dosage remained constant at 17 percent.

     The chemical sludge did not alter the TS concentration of
filter cake, which remained at 43 percent.  The VS  fraction of
cake TS decreased only slightly, from 33.6 to 32.6  percent.   Two
positive impacts of the chemical sludge were a decrease in the
average length  of a filter run from 2.83 to 1.73 hr/run and an
increase from 75 to 90 percent in the filter cake solids recovery.

     The costs  of sludge treatment and disposal at  Brookfield
were lower for  the iron sludge.  A decrease of about $1.47/t
($1.33/ton) occurred because of decreases in the amounts of chem-
ical conditioners and electricity used by the pressure filter.
                               99

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        TABLE 25.  SLUDGE TREATMENT/DISPOSAL METHODS USED BY PLANTS PRACTICING PRESSURE FILTRATION
Plant Location
Saline, MI
Westfield, NY
Kenosha, HI
Coloma, MI
o Brookfield, WI
Hatfield
Township
Col mar, PA
Size
(m3/day
(mgd))
4,807
(1.27)
5,678
(1-5)
75,700
(20)
4,542
(1.2)
9,084
(2.4)
8,706
(2.3)
Thickening
None
Gravity
thickening
Flotation
thickening
of WAS
Gravity
thickening
Gravity
thickening
Gravity
thickening
Digestion
Anaerobic
digestion
Aerobic
digestion
Anaerobic
digestion
None
Aerobic
digestion
of WAS
None
Chemical Conditioning
FeCls, Lime, Fly Ash
conditioning
Polymer conditioning
Fed 3, Lime
conditioning
Lime Kiln Flue Dust
conditioning
Fed 3, Lime,
Incinerator Ash
conditioning
Lime conditioning
Incineration
None
None
None
None*
Multiple
hearth
incineration
Multiple
hearth
incineration
Disposal
Sanitary
landfill
Sanitary
landfill
Cropland
Cropland
Sani tary
landfill
Sanitary
landfill
* When the plant began operation  in  1973, multiple  hearth  incineration was used and chemical conditioning
  was performed with  lime and  incinerator ash.
t In the past, FeCls  was also  used for  chemical  conditioning.

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               TABLE 26.   IMPACTS OF CHEMICAL SLUDGES UPON PRESSURE FILTER PERFORMANCE
                                AS REPORTED IN QUESTIONNAIRE RESPONSE
 Plant
Location
 Type of Sludge Treated
 Impacts of Chemical Sludge     Performance with Chemical Sludge
Saline,
Michigan
Westfield,
New York
Kenosha,
Wisconsin
Iron-primary and secondary
from a trickling filter
plant
Aluminum-secondary from
a two-stage long-term
activated sludge plant
with no primary treat-
ment
Iron-secondary and pri-
mary from a conventional
waste activated sludge
plant
The entire plant was expanded
and the pressure filter was
installed when phosphorus re-
moval was begun. Therefore
there is no comparison between
pressure filter operation with
and without the iron sludge

The plant incorporated phos-
phorus removal since it went
into operation. Therefore,
there is no data on the im-
pacts of the aluminum sludge.
The amount of FeCl3 required
for chemical sludge condition-
ing was reduced from 5 percent
to 3% percent.  (The lime
dosage is 18 to 22 percent.)
The digested sludge at 9 percent
TS produces a filter.cake which
averages 41 percent TS.  The
cake vs fraction averages 62
percent of TS.
The plant is using an unusual
type of belt filter press which
is similar to a vacuum filter
with a belt squeezing the sludge
to the cloth. The sludge is
difficult to dewater because it
is all waste activated. The
filter cake TS concentration
averages 11.5 percent. Polymer
conditioning of the aluminum
sludge was found to be more
successful than conditioning
with FeClo and lime.

The digested sludge at 4.8 per-
cent TS produces a filter cake
which averages 40 percent TS.
                                                                                             (continued)

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    TABLE  26 (continued)
      Plant
     Location
 Type of Sludge Treated
             Impacts of Chemical  SLudge     Performance  with  Chemical Sludge
     Coloma,
     Michigan
o
ro
     Brookfield
     Wisconsin
     Hatfield
     Twp,
     Col mar,
     Penn-
     sylvania
Lime-primary and
secondary from a
filter plant
alum-
trickling
Iron-secondary and pri-
mary from a contact
stabilization activated
sludge plant

Lime-primary secondary
and alum-tertiary from
a complete-mix acti-
vated sludge plant
The use of lime increases the
TS concentration of the thick-
ened sludge. It also decreases
the requirement for Time kiln
flue dust for chemical  condi-
tioning.
            See the following case study
            discussion of Brookfield.
            The amount of sludge generat-
            ed when a plant expansion in-
            cluding phosphorus removal
            took place was much greater
            than expected. At that time
            the plant was practicing
            vacuum filtration and incin-
            erating a 22 percent TS filter
            cake. The incinerator loading
            rate was too low to keep up
            with the amount of sludge gen-
            erated. In response to this
            problem, the vacuum filter was
The estimated average filter
cake TS concentration is 40 per-
cent. The plant used incinera-
tion when it began operation but
it was very expensive because
of the low VS content of the
sludge. Due to the large amounts
of lime, lime flue dust and in-
cineration ash used for phos-
phorus removal and sludge
conditioning the VS fraction of
filter cake TS was only 20 to
30 percent.
                                The plant has an unusual  type  of
                                filter press which has been
                                adapted from the old belt vacuum
                                filter. Sludge is actually
                                vacuum filtered and then  carried
                                by the long vacuum filter belt
                                to a diaphragm-type filter press.
                                The system produces a 45  to 50
                                percent TS filter cake which has
                                a VS fraction ranging from 27
                                to 40 percent of TS. The  filter
                                contains 299 rag/* SS, 16  mg/'A
                                VSS, 917 mg/fc COD, and
        (continued)

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    TABLE 26 (continued)
     Plant
    Location     Type of Sludge Treated	Impacts of  Chemical Sludge      Performance with  Chemical  Sludge


                                             adapted to a diaphragm-type      872 mg/£ BOD.
                                             filter press. They  produced a
                                             45 to 50 percent  filter cake.
                                             This allowed a higher  incin-
                                             erator loading rate. The addi-
                                             tion of lime for  phosphorus
                                             removal is believed to be re-
                                             ducing the lime requirement
                                             for chemical conditioning.
**>

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 Literature

     An evaluation of lime sludge dewatering by centrifugation
 and pressure filtration was made at the Holland, Michigan, waste-
 water treatment plant (43).  The design of the plant included
 addition of lime to the primary step for phosphorus removal and
 aluminum addition to the activated sludge treatment step for
 effluent polishing.  Sludge treatment was provided by primary
 sludge degritting, primary and waste activated sludge gravity
 thickening, centrifugation and fluidized bed incineration.

     With this system, a 30 to 32 percent TS centrifuge cake was
 incinerated, and the cost of fuel (natural gas) for incinerator was
 found to be a major operational expense at $26.92/t of dry cake
 solids (24.42/ton) in 1974.  Pressure filtration was then con-
 sidered as a means of reducing the fuel requirement by increasing
 the sludge cake TS concentration.  The resvilts of a pilot test
 are shown in Table 27.  A 0.093 m2 (1 ft2) pilot press with
 three plates and two chambers was operated at 125 psig pressure
 for this test.
 TABLE 27.   PILOT FILTER PRESS TEST AT HOLLAND, MICHIGAN (43)
Total
Sol ids
in Feed
% TS
11.2


Fil tration
Rate ?
(gal/hr/fl; )
(l/hr/m2)
178
(4.33)


Cake
Cone .
%
41.54
with thick-
ness 1.25"

Pressure
kg/m^
(psig)
8.8
(125)


Polymer
, kg/t ,
(Ib/ton)
1.5
(3 Ib/ton)
Hercules 859-C
     Based on the pilot test data, estimates of the performance
and cost of full-scale pressure filtration were made.  It was
assumed that polymer conditioning of the sludge would be used.
It was estimated that a pressure filter operating at 225 psig
would produce a cake of 45 percent TS.  The filtration cycle
would be 1 hr based on a feed sludge TS concentration of 8 per-
cent.  With the incinerator operating at a freeboard temperature
of 827°C (1,520°F), and with a 28 percent volatile filter cake,
the fuel cost would be $12.03/t ($11.15/ton).

     Pressure filtration was compared to dewatering with a cen-
trifuge or with the existing vacuum filters at the Hatfield
Township, Pennsylvania, plant (31).  This plant was described  in
Tables 25 and 26.  A mixture of lime-primary, waste activated
and alum-tertiary sludges was dewatered by the three different
methods under similar operating conditions.  The pressure filter

                              104

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produced a drier cake with greater recovery of solids than either
the vacuum filter or tlie solid bowl centrifuge.   A 41 percent TS
filter cake was achieved with sludge conditioning with 15 percent
1 ime.

Conclusions

     There is insufficient data to make conclusions about the
dewatering of alum and waste activated sludges with pressure fil-
ters.   But there are indications that the results are not as good
for these sludges as they are for iron or lime sludges and for
primary or combined primary and secondary sludges.

     The results of the questionnaire survey, case studies,  and
literature search have not included any mention  of adverse
impacts of iron or lime sludges on pressure filtration.   These
sludges dewater well on pressure filters, with.filter cake TS
concentrations of 40 to 50 percent and often with reduced chemi-
cal requirements for sludge conditioning.  Because of the reduc-
tion in chemical costs, the cost-effectiveness of this dewatering
method alternative can be favorably affected.

CENTRIFUGATION

Introduction

     Sewage sludge dewatering ~by centrifuges began to evolve in
the 1950's.  Their use has been gradually increasing due to  bet-
ter engineering and materials of construction.  Of plants which
responded to the questionnaire survey and/or were field investi-
 ?ated during this study, centrifuges are used by 6 out of 174
 3 percent).  Several additional plants have conducted promising
pilot tests with centrifuges and are considering their future
full-scale use to help solve sludge management problems.

     Proper centrifuge design is complex, and it is assumed  that
the reader has a basic knowledge of centrifuge design and opera-
tional factors.  Essentially, centrifuges have the same objec-
tives as vacuum filters, e.g., maximum solids capture, maximum
yield per unit of energy consumed, high solids concentration in
the sludge cake, and low total cost.  In addition, since centri-
fuges are high maintenance units, it is desirable to have good
resistance to abrasion and long-living moving parts.

     Most centrifuges dewatering municipal sewage sludge are of
the continuous, solid bowl, conveyor type.  A relatively new,
low-speed, solid bowl centrifuge which was developed in Europe
is now available in the United States and is reported to have
some significant advantages.  Basket centrifuges are also avail-
able.

     Because each sludge and treatment plant situation is unique,
the information presented in the following subsection is not

                               105

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intended to provide universal answers to specific plant problems.
Rather, the information is intended to be helpful to those seek-
ing possible avenues of further investigation.   The best method
of predicting the true performance of full-scale centrifuges is
experiments with pilot units on the actual  sludges to be treated.
These pilot units are available from manufacturers who have devel-
oped scale-up design factors for their units.

Literature

     There are hundreds of literature references pertinent to
centrifuging of sewage sludge.  This study concentrated upon
those which discussed centrifuging of phosphorus-laden chemical
sludges.  Generally, the literature favorably evaluates centri-
fugation of chemical sludges (particularly lime sludges), as
evidenced by the selected summaries below.

     In connection with the lime treatment nutrient removal pro-
gram at the Newmarket, Ontario WPCP plant,  a 2-mo raw sludge
dewatering study using a Sharpies solid bowl centrifuge was
undertaken (65).  Centrifuge variables, such as sludge feed con-
centration, sludge feed rate, sludge pH, and speed differential
were examined.  The project was successful  and the optimum
results produced from centrifuging raw lime primary sludge were
as follows:

     (a)  98 to 99 percent SS capture

     (b)  Polymer dosages of less than 0.5 kg/t  (1 Ib/ton) of dry
          solids

     (c)  Consistent centrate qualities of less than 700 ppm SS

     (d)  Sludge cake of 27 to 34 percent TS

     (e)  Feed to centrate, total phosphorus reduction of 95
          percent

     (f)  Centrate total phosphorus levels in the order of 10 to
          30 ppm.

     Using the Sharpies P3000 Super-D-Canter centrifuge, solids
recovery and cake dryness could be attained to some degree with
unconditioned lime sludge.  Augmentation with polyelectrolytes
showed increased overall solids recovery and vast improvements
in centrate quality.

     The OrangeCounty Water District practiced chemical clarifi-
cation of secondary effluent with lime at a pilot wastewater
reclamation facility.  They removed lime sludge  from  the pilot
tertiary clarifier and treated it in a small pilot  thickener and
a  15-cm (6-in) solid bowl centrifuge.  Sludge was removed  from

                              106

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the clarifier at 1  to 2 percent TS and could be thickened in the
pilot thickener to  10 to 20 percent TS.  The centrifuge data
showed that the thickened sludge could be dewatered to over 50
percent TS in a Sharpies P-600 Super-D-Canter centrifuge.

     Sludge dewatering studies (2) at the Portage Lake Water and
Sewer Authority, Michigan, concluded that alum-biological sludges
were amenable to conventional sludge treatment processes.  Of the
various concentrating and dewatering schemes investigated for the
alum-biological sludge, two-stage aerobic digestion followed by
basket centrifugation appeared to be the most economical.  How-
ever, because of the short distance to the disposal site, direct
trucking was estimated to produce a 10 percent savings over cen-
trifugation.

     In a detailed report by Martin and Nardozzi (43), perfor-
mance and cost  information for lime-biological sludge treatment
at Holland, Michigan, was provided.  The city of Holland used
lime precipitation of phosphorus in the primary clarifier, with
A1C13 addition  to the flocculator prior to biological treatment.
The thickened,  combined primary solids and waste activated sludge
was fed to solid bowl centrifuges prior to incineration.  The
centrifuges produced a cake of 30 to 32 percent total dry solids,
with 97 percent solids capture.

     The polymer (Hercules 869-C) dosage rate was 2.0 to 2.5 kg/t
(4 to 5 Ib/ton) of dry solids.  When polymer was used for condi-
tioning, more of the finer, less dense particles were captured.
The data revealed that the highest cake solids were achieved when
no polymer was  used.  As the capture increased with polymer addi-
tion, the cake  became wetter, because the fines and associated
water were captured.  Even so, polymer addition was advisable
because a cleaner centrate ensured a lighter recirculating load
and a minimum sludge age in the plant.

     The EPA, in 1975, conducted pilot scale investigations (26)
of dewatering chemical sludges with vacuum filters and centri-
fuges.  The investigations were made at various midwestern plants
and were plagued by mechanical difficulties with the trailer-
housed pilot equipment.  The most significant centrifuge results
were the characteristics of the centrate from various pilot-scale
centrifugation  runs.  These data, shown in Table 28 provide a
tool with which to study the impact the various sidestreams
could have on plant operation and performance.  Note particularly
the heat-treated iron sludge from the Midland, Michigan, plant
which demonstrated a high loading rate and cake solids concentra-
tion, but also  showed a high solids and organic load in  the cen-
trate.  This centrate returned to the plant could cause  opera-
tional difficulties.

     The EPA study further concluded that:

        Increasing the polymer dosage decreased the cake solids.

                               107

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             TABLE 28.    CENTRATE CHARACTERISTICS FROM VARIOUS  SCROLL  CENTRIFUGATION RUNS  (26)
Sludge
                                                                              Soli ds
                  Loading Rate    Cake Solids      Centrate Solids  Polymer  Recovery
Bowl Speed, rpm   Kg/hr (Ib/hr)        %                  %                       %
Beaver Creek 5000
Waste Activated
Alum-Sludge

Beaver Creek 5000
Aerobic Digested
Alum-Sludge


Midland 4000
Heat Treated 4500
Iron-Sludge
0.671
1.26
1.61

1.64
2.42
3.20
4.86
7.44
19.2
24.7

(1.48)
(2.77)
(3.55)

(3.62)
(5.32)
(7.05)
(10.7)
(16.4)
(42.3)
(54.4)

4.3
5.1
5.42

5.79
10.9
6.32
6.37
15.2
33.3
49.0

0.01
0.02
0.03

0.01
0.04
0.16
0.33
0.09
4.5
9.6

yes
yes
yes
*
yes
yes
VeS
*
yes
yes
no
no

100
95.8
95.3

94.2
99.7
90.0
84.6
99.2
82,9
97.1

   Added to sludge  ahead  of centrifuge.

-------
        This was also borne out in separate Canadian studies.

     t  Much better results are achieved from polymer addition
        at the centrifuge, rather than ahead of the centrifuge.
        Higher solids recovery, better centrate quality, and
        higher cake solids concentration were achieved by polymer
        addition at the centrifuge.

     •  Increasing the feed rate resulted in decreasing the solids
        recovery using aerobically digested alum-secondary sludge.

     •  For similar conditioning, both solids recovery and cake
        solids concentration are generally less for chemical
        sludges than for conventional sludges.

Questionnaire Survey and Case Studies

     As shown in Table 29, there was relatively little informa-
tion obtained from the questionnaires pertinent to centrifugation
of chemical sludges.  More complete information was obtained from
the Port Huron, Michigan, and South Bend, Indiana, case studies
in the appendices.

     The Port Huron case study report examines some of the factors
influencing centrifuge dewatering of an alum sludge:

     •  Centrifuge loading rate was higher with thermal sludge
        conditioning than with ^polymer conditioning.

     •  The dosage of polymer required for conditioning was higher
        when the feed sludge TS concentration was low as the
        result of high activated sludge wasting rates.

     t  The TS concentration of the dewatered cake was higher
        with thermal conditioning than with polymers.  The cake
        TS concentration apparently did not vary as the result of
        changes in the feed sludge TS concentration if polymer
        dosages and feed rate were adjusted.

     •  The average centrate TS concentration was lower during
        thermal conditioning while the volatile fraction of TS
        in the centrate was higher.

     t  The TS capture could be maintained at at least 80 percent
        by the operator.  It was necessary for the operator to
        check the centrate of each centrifuge separately, several
        times each day.  He then made separate adjustments of
        feed rate and polymer dosage for each centrifuge.

     It was not possible to judge the impacts of alum addition
for phosphorus removal  on centrifuge performance at this plant
because alum had been in use since the plant was upgraded.  How-
ever,  it seemed likely that the quantity of waste activated

                               109

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                   TABLE  29.    IMPACTS OF CHEMICAL SLUDGES ON CENTRIFUGE PERFORMANCE
                                    AS REPORTED IN QUESTIONNAIRE  RESPONSE
Plant Location
Type of Sludge Treated
               Summary of Comments
Lower Allen
 Township, Camp
 Hill,
Pennsylvania
Lime-primary and secondary
(gravity-thickened) from
an activated sludge plant.
There was a great increase in sludge mass.   The
centrifuge dewatering operational  costs greatly
increased.  The lowered volatile content in the
sludge cake increased the subsequent incineration
operational costs.  Had to reroute centrate
return flow so that instead of being added  to the
thickeners, it was sent to the head of the
plant because the centrate return was causing
odor and floating solids problems in the thick-
eners.  They had difficulty finding polymers
that were effective in conditioning the sludge
by adding to the centrifuges.  The dewatered cake
contains 30 percent TS.
Hilton, New York
Alum-secondary and primary
(gravity-thickened) from
an activated sludge plant.
Centrifuge operation was not significantly
affected by addition of the chemical sludge.
Polymer continued to be added at a rate of 6
to 7-1/2 kg/t (12 to 15 Ibs/ton), and cake solids
remained at about 19 percent.

-------
relative to primary sludge was greater because of alum addition
to the aeration basins.  Greater quantities of waste activated
sludge meant higher polymer conditioning requirements at the
plant.

     The South Bend case study report describes centrifugation
of a lime/iron sludge resulting from tertiary addition of both
lime and iron to secondary effluent.  The sludge was gravity
thickened and fed to the centrifuges at 10.2 percent TS.  The
cake produced contained 43 percent TS.  There were problems with
maintenance of the centrifuges.  The heavy lime sludge was respon-
sible for breaking and frequent equipment overhauls.

Conclusions

     The information which was presented indicates that thickened
lime-primary, or primary plus secondary, sludges can be dewatered
to 27 to 34 percent TS in a centrifuge.  Centrifuge dewatering of
thickened lime-tertiary sludges apparently produces an even drier
cake of 40 to 50 percent TS.   At one plant, a combined alum-sec-
ondary and primary sludge was gravity thickened and centrifuged
to 19 percent TS.  Centrifuge performance depends heavily on
choosing the right conditioning method.  Polymers are usually
used.  The point of polymer addition is important, some experi-
ences indicating that the polymer should be added at the centri-
fuge rather than before it.  The polymer dosage is also important
and should be adjusted as feed sludge consistency and TS concen-
tration vary.

     Iron and aluminum chemical sludges often require higher con-
ditioning polymer dosages and lower feed rates than conventional
sludges.  Poor centrate quality and low cake TS concentrations
result otherwise.  Closer operator attention may also be neces-
sary with iron and aluminum sludges because of inconsistent grav-
ity thickener performance, meaning variations in feed sludge
q u a 1 i ty.
                              Ill

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                           SECTION 9

         REDUCTION OF CHEMICAL SLUDSES - INCINERATION

 INTRODUCTION

     Incineration uses thermal energy to provide a major reduc-
 tion in the weight and volume of solids requiring disposal.   The
 major factor in evaluating incineration performance and costs is
 the composition of the sludge feed.  Sludge composition, i.e.,
 moisture, volatile solids, and inert contents, influences feed
 rate capacity and auxiliary fuel requirements, among other vari-
 ables, and, consequently, sludge incineration cost effectiveness.
 Due to their inert content, chemical sludges have been recognized
 as poor incineration feed (43 and 45).

 QUESTIONNAIRE SURVEY

     As previously shown in Table 10, 22 of the plants (13 per-
 cent) responding to the questionnaire survey reported that they
 incinerated their chemical sludges.  Six plants surveyed indicated
 that chemical addition for phosphorus removal was having a signi-
 ficant impact on their incineration systems.  Table 30 summarizes
 the experiences of these plants.  All plants incinerated combined
 primary and secondary sludges.  Lime, ferric chloride, and alum
 were used at two of the six respondents.

     Problems with incineration encountered by the plants sur-
 veyed generally agreed with literature reporting the difficulties
 with incineration of chemical sludges.  The lower TS concentra-
 tion and lower volatile content of the phosphorus-laden sludges
 made auto-combustion of the sludge harder to attain resulting in
 soaring auxiliary fuel requirements.

     Increased fuel requirements caused a few plants to abandon
 their incinerators and adopt other sludge handling methods,  i.e.,
 dewatering and hauling.  In addition, the increased inert content
of the chemical sludges put a burden on incinerator ash handling
equipment and, in certain cases, clinker buildup within the
 incinerators resulted.  Problems with clinkers resulted in perio-
dic downtime for incinerator maintenance.  The Wyandotte, Michi-
gan,  plant used primary additions of ferric chloride for phospho-
rus removal  and reported clinker buildup within its multiple hearth
 incinerator.  The clinkers plugged the multiple he.arth  dropKoles
and were identified as the source of  increased rabble arm wear.

                              112

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           TABLE  30.  IMPACTS OF PHOSPHORUS-LADEN CHEMICAL SLUDGES ON INCINERATOR PERFORMANCE
                                  AS REPORTED IN QUESTIONNAIRE RESPONSE
         Location
Size-m /day
   (mgd)
Type of Sludge Treated
Impacts of Chemical Sludge
Warren, Michigan
Wyandotte, Michigan
Coloma, Michigan
Camp Hill, Pennsylvania
  123,000   Alum * secondary and primary
  (32.5)    from a conventional activated
            sludge plant

  291,400   Iron -primary and secondary
  (77)      from a pure oxygen activated
            sludge plant
  4,500     Lime - primary and alum sec-
  (1.2)     ondary from a trickling
            filter plant
  7,600     Lime - primary and secondary
            from a complete mix acti-
            vated sludge plant
                            Higher gas costs for incineration
                            resulted.
                            In the multiple hearth incinera-
                            tor there has been a major problem
                            with clinker buildup, causing more
                            time to be spent cleaning up the
                            drop holes in the hearth and more
                            wear on the rabble arms.

                            The addition of chemicals for
                            phosphorus removal  has lowered
                            the sludge volatile content to
                            20 to 30 percent, causing the need
                            for continuous use of auxiliary
                            fuel (natural  gas).

                            The multiple hearth incinerator
                            was designed to recalcinate and
                            reclaim lime;  this  step was eli-
                            minated due to economic consid-
                            erations.   With the lower volatile
                            content of the sludge, the incin-
                            erator requires between 80 and 100
                            gal of auxiliary No.  2 fuel  oil
                            per dry ton of sludge.
                                                                                             (continued)

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TABLE 30 (continued)
         Location
Size-rn /day
   (mgd)
    Type of Sludge Treated
   Impacts of Chemical Sludge
Sheboygan, Wisconsin
Richardson, Texas
  54,900
  (14.5)
  6,700
  (1.78)
Iron - secondary and primary
from a trickling filter plant
Alum -secondary and primary
from a trickling filter plant
The incinerator requires an addi-
tional 12 to 15 gal/hr of fuel
oil due to the lower volatile
content of the solids.

The plant originally used anaer-
obic digesters and drying beds
for sludge disposal.  With alum
addition for phosphorus removal,
the volume of sludge to be dis-
posed of increased by 50 percent.
Dewatering equipment was installed
and an electric incinerator de-
signed to incinerate the dewatered
cake.  Leaf tests were run on the
sludge, and these showed the
sludge could be dewatered to 20 to
25 percent dry TS with a 60 per-
cent volatile fraction, and the
dewatering equipment and electric
incinerator were designed on this
basis.  However, in practice, the
best results from dewatering were
15 percent dry TS and a 45 to
50 percent volatile fraction.
This sludge was not judged to be
suitable for incineration, and
conditioning with lime, ferric
chloride, and different polymers
did not improve the system's
performance.

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CASE STUDIES

     The case studies in the Appendices contain detailed informa-
tion on the effects of chemical addition on incineration.   The
particular case studies dealing with this subject are Sheboygan,
Wisconsin; Port Huron, Michigan; and Brookfield, Wisconsin.

     The Sheboygan, Wisconsin, wastewater treatment plant  operates
a Dorr-Oliver FluoSolids incinerator.  This fluidized bed  incin-
erator was designed to handle a sludge feed of 25 percent  TS  with
a 73 to 74 percent volatile fraction.  With the addition of fer-
ric chloride for phosphorus removal, the sludge feed TS concen-
tration was 22 percent with a volatile fraction of 65 percent.
These deviations from the design capacity of the incinerator  unit
resulted in a decrease in the incinerator's loading capacity  and
an increase in auxiliary fuel consumption.  The decrease in capa-
city was judged to be approximately 121 kg (266 Ib) of dry TS/hr,
and No. 2 fuel oil consumption was judged to increase by approx-
imately 143 £/t (34 gal/ton).

     There have also been increased incinerator maintenance and
repair problems at the plant due to slag formation and corrosion.
On one occasion, four tuyeres blew out because several of  them
were plugged with slag.  On another occasion, a pressure buildup
in the reactor signaled a problem, and a large piece of slag  was
found blocking the exhaust line.  After this experience, the
operator performed a visual inspection of the exhaust line from
the roof duct inspection port every 3  to 4 mo.

     In addition, the plant manager suggested that the ferric
chloride used for phosphorus removal was responsible for a high
rate of metal corrosion in ducts, especially in the elbows of
the scrubber system.  Gradually, these parts were being replaced
wi th stainless steel .

     The Port Huron, Michigan, plant,  which was handling an alum
sludge, also operated a Dorr-Oliver FluoSolids incinerator.  For
a period of time, Port Huron thermally conditioned sludge with a
Farrer System thermal conditioner prior to centrifugation and
incineration.  This step provided major savings on chemicals and
sludge conditioning fuel oil.  It also increased the solids load-
ing to the incinerator.  With thermal  conditioning, the sludge
burning rate reached 1,043 kg/hr.  Dorr-Oliver  has estimated that
the incinerator capacity would be reduced to 590 kg/hr for non-
thermally conditioned sludge.

     The cost of sludge thermal conditioning amounted to $35.00/t
($31.74/ton) excluding equipment maintenance and repair supplies.
Prior to thermal conditioning, chemical conditioning costs were
$50.30/t ($45.66/ton).  It therefore appeared that operation  and
maintenance of thermal conditioning at the Port Huron plant was
cost effective as long as the cost of  equipment maintenance and
repair supplies was less than $15.30/t ($13.92/ton).

                               115

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LITERATURE

     A review of the literature on incineration  of chemical  slud-
ges reveals a common set of problems:   greater sludge volume,
lower calorific value, increased moisture content, formation of
clinkers due to iron or aluminum content, and increased  inert
content.  The Canadian Environmental  Protection  Service  has  sug-
gested solutions to handle these incineration problems (61).
     Problem

Greater sludge volume

Lower calorific value

Increased moisture content


Formation of clinkers


Increased inert content
          Solution

Increase capacity or run time

Increase auxiliary fuel

Improve dewatering or increase
auxiliary fuel

Decrease incineration temperature
below fusion point

Increase ash disposal capacity
     In a wastewater treatment facility using large amounts of
lime for phosphorus removal, consideration must be given to the
possibility of recalcination of the chemical sludge.   When lime
is used, calcium carbonate and calcium hydroxyapatite are the
major sludge components.  The hydroxyapatite containing the
removed phosphorus is fairly stable, but the calcium carbonate
can be recalcined to recover lime.  The decision to recalcinate
lime should involve an economic study considering the cost of
lime, the capital costs necessary to achieve recalcination, the
additional operating costs of recalcination, and the cost of
incinerator ash disposal.  The latter item is one that very often
is not considered in such an economic analysis, but reuse of 65
to 85 percent of the lime can significantly reduce the volume of
ash generated from the incineration process.  If costs associated
with this final ash disposal are significant, it can have a marked
effect upon the total economic picture.

     The Holland, Michigan, wastewater treatment plant used pri-
mary addition of lime for precipitation of phosphorus and a small
amount of Al+3 for effluent polishing (43).  The primary and
waste-activated sludges were combined and dewatered for incinera-
tion in a Dorr-Oliver FluoSolids reactor.  In operating this fluid-
ized bed reactor, Holland found that the sand in the bed served as
a seed for chemical material to form agglomerates.  The resultant
bed material  tended to be spherical, decreasing significantly  the

                              116

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angle of repose.  This resulted in backsifting of the sand through
the distribution tuyeres into the windbox of the reactor.   This
problem was solved by plugging alternate tuyeres to increase pres-
sure drops across the distribution plate and adding a gravel type
base (olivine) to the top of the distribution plate.  Backsifting
was eliminated.

     Another problem occurred at the feed tubes through which
sludge entered the fluidized bed.  The combined organic-chemical
sludge baked into a solid mass when exposed to the heat of the
reactor for a sustained period of time.  To counteract this, the
feed tubes to the reactor were shortened to decrease heat  trans-
fer from the bed.  Normally, a plug was left in. the reactor feed
tube at the conclusion of daily operations.  Because a plug would
solidify under these conditions, it was necessary to replace the
material with peat moss or digested sludge from a nearby digester.
A tool was later developed to remove the baked plugs.

     A study was undertaken at the Minneapolis and St. Paul, Min-
nesota, wastewater treatment plants to determine the relationship
between chemical conditioner additions and incinerator auxiliary
fuel requirements.  Ferric chloride and lime addition at greater
than 5 and 15 percent of the weight of the dry solids produced a
drier feed cake, but it also increased the kg of water fed per kg
of dry TS fed into the incinerator.  Any increases in the  kg
water/kg dry TS fed into the incinerator also increased the aux-
iliary fuel requirements for c^ake incineration.  The basic prob-
lem, then, in reducing auxiliary fuel requirements was seen to
be one of reducing the ratio of water to sludge solids in  the
cake, and not one of reducing the moisture content of the  cake
on a percent TS basis.

     In addition, the auxiliary fuel requirements were compared
using alternative sludge conditioners.  A polyelectrolyte-condi-
tioned sludge was found to require significantly less auxiliary
fuel than a 1 ime-and-ferriochloride-conditioned cake.

CONCLUSIONS

     Various solutions to the inherent probl ems associated with
incineration of phosphorus-laden chemical sludges have been pre-
sented in this, discussion.  Unfortunately, at some wastewater
treatment plants modification of the  incineration system to
incorporate these solutions surpasses the cost effectiveness of
the system.  Therefore, a detailed cost analysis of the benefits
of incineration modification versus other sludge handling methods
must be made.

     Generally, there are many  indications that  sludge  handling
systems designed to include incineration will  not  be  cost  effec-
tive for the treatment of chemical  sludges unless  they  incorpor-
ate those sludge pretreatment technologies most  capable of pro-
viding a filter cake of high volatile  content  and  low moisture

                              117

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content.   The advantages and disadvantages  of  these  techniques
were discussed at length in previous  sections  with  reference  to
their effects on incineration.
                              118

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                           SECTION 10

   DISPOSAL OF CHEMICAL SLUDGES - TRANSPORT AND LAND DISPOSAL


INTRODUCTION

     Table 10, which is based on the questionnaire responses of
174 plants practicing phosphorus removal by chemical addition,
shows that virtually all of the plants practiced some type of land
disposal of sludge.  Even among plants practicing incineration,
most periodically disposed of sludge cake on land or in landfills.
Except in a few cases where sludge was lagooned or stockpiled at
the plant, sludge transport to the final disposal was required.
Transport costs sometimes comprised a very significant portion of
the overall costs of land disposal.  Sludge hauling by tank or
dump truck was by far the most widespread method of transport.
However, pipeline transport has successfully been used for both
lime and iron sludges at South Bend, Indiana, as described in
Case Study No. C (see Appendices).

QUESTIONNAIRE SURVEY AND CASE STUDIES

     Because of the impacts of phosphorus removal on sludge pro-
duction and treatment, plants were hauling more sludge in liquid
and cake form to land disposal sites than before.  The question-
naire responses verified that most of the plants which histori-
cally practiced sludge hauling had to haul greater volumes of
sludge after phosphorus removal for numerous reasons:

     1)  Additional raw sludge solids were produced.
     2)  The raw sludge TS concentration was lower.
     3)  Sludge thickening was adversely affected.
     4)  Digester solids-liquid separation was poorer.
     5)  The dewatered cake contained more moisture.

     At Manitowoc, Wisconsin, for example, alum addition increased
sludge volume so that it was necessary to incorporate into daily
operation the use of a 9.5-m3 (2,500-gal) tank truck as well as
the regular ll.S-ne (3,000-gal) truck.  The capital cost of the
truck was $43,382.00 in 1976, and the estimated operating cost
was $17,590.00 in 1977.

     At the Port Weller plant in St. Catherines, Ontario, a 26
percent increase in sludge volume with alum addition caused a  23

                               119

-------
percent increase in the annual cost of liquid sludge hauling.
Kingston, Ontario, reported that its sludge mass doubled with
iron addition, and its liquid sludge hauling effort was 60 per-
cent greater.  Several other plants, ranging in size from 1,510
to 51,100 m3/day (0.4 to 13.5 mgd), reported increases of $5,000.00
to $25,000.00 for hauling in 1976 due to iron or alum addition.

     The  questionnaire responses also indicated that many plants
which  historically have not hauled  liquid sludge or sludge cake
found  it  necessary to start doing  so after phosphorus removal
because:

     1) the  chemical  sludge was unsuitable for the usual treat-
        ment  processes, or

     2) the  quantity  of chemical siudge exceeded the capacity of
        existing treatment facilities.

     Liquid  fludge hauling was frequently used by plants with
inadequate dewatering and incineration capacity to dispose of
extra  sludge  resulting from phosphorus removal.  At Hatfield
Township, Pennsylvania, for example, the pressure filter and
incinerator  could not handle all of the plant's sludge even when
run for 24 hr/day, 7  days/wk, so liquid sludge was hauled perio-
dically by a  contractor.  Other plants may have had the ability
to mechanically dewater the extra  sludge, but they preferred to
haul it as liquid in  order to avoid running the equipment longer
and hiring more personnel.  For instance, at Lakewood, Ohio, the
plant  could  not handle the additional sludge volume generated  by
alum addition on its  schedule of vacuum filter and flash dryer
operation for one shift each day.   Rather than extending filter
and dryer operation to two shifts  per day and hiring three more
employees, the plant  decided to have sludge hauled from the
digesters at  $132.30/t ($120.00/ton).  Details on costs and the
effects on plant performance are contained in Case Study No. F
(see Appendices)>

       The questionnaire responses  revealed only two plants --
Virginia, Minnesota,  and Colotna, Michigan -- which were forced
to haul all  of their  sludge to land disposal after phosphorus
removal, abandoning their existing  dewatering or incineration
facilities.   At the Virginia plant, anaerobic digestion and dry-
ing beds were used for sludge handling previous to phosphorus
removal.  In anticipation of phosphorus removal with lime, they
were replaced with a  gravity thickener and lagoons.  The sludge
refused to dry in the lagoons, so  they were abandoned and liquid
sludge was then hauled to a disposal sitfe.  This involved hauling
sludge three times/wk as opposed to cleaning the drying  beds
twice each year.  The plant was planning to purchase a  tandem  or
triaxle tank truck for $40,000.00  to haul 189 m3 (50,000 gal)  of
liquid sludge per week, and a heated enclosure for the  truck and
piping changes for $40,000.00.  The estimated operating  costs
are $4,500.00/yr.

                               120

-------
     At Coloma, pressure filtration and incineration of sludge
were practiced when the plant went into operation.   Phosphorus
removal with primary addition of lime and secondary addition of
alum was begun a year later.  Because of the large  volumes of
lime and flue dust used for sludge conditioning, the volatile
content of the sludge was only from 20 to 30 percent, and incin-
erator auxiliary fuel consumption was high.   Flower farmers in the
area were contacted, and they agreed to take all of the sludge
for its ability to improve the sandy, low pH soil  on their farms.

     Phosphorus removal can reduce the number of suitable land
disposal alternatives which are available to a particular plant.
For instance, sludge TS concentration of at  least  20 percent is
usually needed for landfilling of sludge along with other mater-
ials such as municipal solid waste, and at least a  40 percent TS
concentration is necessary for landfilling of sludge alone.  Iron
and aluminum sludges are generally more difficult  to dewater to
these concentrations than conventional sludges with many of the
dewatering methods available.  Some lime sludges can easily be
dewatered to 40 percent TS, but the plant must have the equipment
to handle the large quantities of sludge which are  generated with
lime.  Furthermore, there must be room in the landfill  for the
greater quantities of sludge which usually result  from  phosphorus
removal.  At Toledo, Ohio, for instance, it  was necessary to
switch from landfilling of vacuum filter cake to cropland appli-
cation because of the additional volume of cake produced during
phosphorus removal with ferric chloride.

LITERATURE

     As with conventional sewage sludges, there is  concern over
the beneficial or detrimental effects of chemical  sewage sludge
application to croplands.  There is special  concern with regard
to chemical sludges because concentrations of nutrients, metals,
and organic and microbial constituents can be higher in these
sludges than in conventional sludges.  The use of  lime, aluminum
salts, or iron salts for phosphorus removal  precipitates most of
the metallic cations contained in the wastewater as well as the
bulk of the phosphorus.  These metals and the iron, aluminum, or
calcium of the precipitating chemicals are concentrated in the
sludge.  A limited amount of investigation has been conducted
into the effects on crop yield, heavy metal  toxicity to crops
and animals, and groundwater quality of applying these  sludges
to croplands.  Of primary concern has been the state of heavy
metals in sludge and the possibility of resollubilization in the
soil.  Resolubilization makes the metals available to be concen-
trated in crops and leachate, presenting the possibilities of
toxicity tO'Crops and aquatic life and accumulation in  the human
food chain and drinking water supply.  Since resolubilization is
most likely to occur in low pH soils, it is  expected that lime
sludges will present the least problem because of their tendency
to raise the soil pH (72).

                              121

-------
     Kirkham and Dotson  studied  the  growth  of  barley  which  was
irrigated with liquid sludges  produced  with the  addition  of fer-
ric chloride and alum to raw wastewater (39).  The  barley was
grown in pots of loam soil  for 4 mo.  The  chemical  sludges  did
not limit the growth of  the barley compared to plants fertilized
with inorganic fertilizer or non-chemical  sludge.

     Chawla, et al . , (15) conducted 1-yr lysimeter  investigations
using alum,  iron, and lime sludges from various  Ontario treatment
plants.  They planted orchard grass in  loamy sand and silt  loam
amended with sludge.  They found that  grass yields  comparable  to
fertilizer treatment could be achieved  at  the  highest application
rates (900 kg/ha nitrogen) of lime and  iron sludges but that alum
sludge produced much lower yields.  Cumulative effects of higher
zinc equivalent, higher aluminum contents  and  low potassium
amounts in alum sludges  might have retarded the  plant growth.
Very high concentrations of petroleum  hydrocarbons  in the alum
sludge possibly caused some plant toxicity resulting  in lower
yields.

     Increasing the rates of sludge application  increased the
nitrogen content of the plants;  phosphorus did not  show any mean-
ingful trend; potassium contents decreased with  increasing  rates
of sludge addition.   Nickel, copper and zinc concentrations in
plant tissues were reasonably low and  similar  to the  control and
fertilizer treatments.  One year after  sludging, no definite chem-
ical changes in the soil systems were  observed.   Decline in pH
values under highest rates of iron and  alum sludges suggested  a
trend toward increased mineralization  and  acidification due to
a lack of calcium.

     Chawla  and others (14) also conducted an  intesive study of
the biochemical characteristics of chemical sewage sludge from
various municipal plants in the province of Ontario.   The study
pointed out  that sludge from sewage treatment plants  must be
characterized on an individual basis to determine if possibly
hazardous concentrations of heavy metals or other contaminants
exist.  The  sludges studied varied widely  in  their biochemical
compositions.  It should be remembered  that high levels of  speci-
fic metals in sludge are virtually always   attributable to speci-
fic industries in the area served by the plant.

     Where heavy metals are concentrated to a considerable  degree
in sludge, Scott and Horlings (58) suggest that they can be eas-
ily removed  by extraction with dilute acid.   They experimented
with anaerobically produced sludges, and found  that  both metals
and phosphate can be extracted from thickener underflow  sludge
or dewatered filter cake.  The products of this extraction  can
be further treated by other conventional means  to recover  phos-
phate or specific metallic components.
                              122

-------
CONCLUSIONS

     Hauling sludge liquid or cake to a land disposal site has
been a common solution to many of the sludge processing problems
created by phosphorus removal.  This has been the case even
though phosphorus removal generally increases sludge hauling
costs because of greater sludge volumes and the lower solids con-
centrations of many chemical sludges.  In some cases, phosphorus
removal has shifted the economics of sludge processing favor of
hauling rather than dewatering and/or incineration.  In other
cases, sludge hauling simply provides an interim solution to
problems although it is not necessarily the most cost-effective
alternative.

     Cropland application of chemical sludges has raised many
serious questions with regard to the transmittal of contaminants
to  plants and animals.  The use of lime, aluminum salts, or iron
salts for phosphorus removal precipitates most of the metallic
cations contained in the wastewater as well as the bulk of the
phosphorus.  These constituents, as well as the iron, aluminum,
or  calcium of the precipitating chemicals,are concentrated in
the  sludge.  Chemical sludges therefore contain nutrients and
other elements which can be beneficial to plant growth.  Lime
sludges can improve low pH, low calcium, or low phosphorus soils,
Chemical sewage  sludges must be characterized on an individual
basis to determine if possibly hazardous concentrations of heavy
metals or other  contaminants exist.
                              123

-------
                           SECTION 11

                   STATE-OF-THE-ART APPRAISAL


      It  is  evident that the addition of chemical sludges to the
 regular  sewage  treatment plant primary and secondary sludges
 often  has a  significant impact upon subsequent sludge handling.
 The  volume  and  mass of the sludge increase and the percentage of
 volatile solids decreases.  Except in the case of lime sludges,
 thickening  and  dewatering efficiencies are often adversely
 affected.   Chemical conditioning requirements change.  Where
 incineration  is used, an increased need for supplemental fuel is
 reported.   The  extent and seriousness of these and other effects
 vary  greatly  between treatment plants.  Each treatment plant is
 unique,  and  neither the problems nor their solutions are univer-
 sal.   However,  certain generalizations can be made from the data
 obtained during this investigation.

      Of  the  three chemicals normally considered for phosphorus
 removal  --  lime, iron salts, or aluminum salts « iron salts
 generally appear to have the least overall adverse effect upon
 subsequent  sludge handling.  This conclusion is based primarily
 upon two factors:

      1.  The  addition of lime generates a much greater mass of
         sludge than does the addition of iron or aluminum salts.

     2.  The  chemical sludge generated by the addition of alumi-
         num  salts is usually more difficult to thicken and/or
         dewater than the sludge generated by the addition of
         iron salts.

     Obviously, for many plants these two advantages are over-
 ridden by other considerations or else iron salts would be rou-
 tinely used  by all plants.  Other considerations include phospho-
 rus removal  efficiency, geographical variations in chemical costs
 and the  corrosiveness of iron salts.

     The next decision to be made is where in the sewage treat-
ment chain to apply the phosphorus removal chemical.  For a typ-
 ical  activated sludge treatment plant, there appears to be some
advantage to adding iron or aluminum salts just ahead of the aer-
ation tank or directly to the mixed liquor, where good mixing  is
achieved prior to discharge to the secondary clarifier.  When

                               124

-------
using a ferrous iron salt, unless it is accompanied by a base,
removal of phosphorus takes place at the secondary treatment
stage if the chemical is added before the primary clarifier.

     If lime is the chemical used, it is added to the primary
treatment step or occasionally to a special tertiary treatment
process.  Lime is never added to the secondary biological process.

     Several older plants which have inadequate volume capacity
for sludge handling have found that pumping chemical-1aden waste
activated sludge to the primary clarifier influent for settling
with the primary sludge reduced the volume of combined sludge to
be treated.  At these plants, sludge handling considerations have
either been judged to outweigh the problem of deterioration of
primary effluent quality, or an increase in secondary clarifier
efficiency has counteracted the problem.

     It has become common practice to thicken sludge in a gravity
thickener prior to further sludge treatment.  In virtually all
cases, chemical sludges containing iron salts thicken much better
than sludge containing aluminum salts.  Best results with either
iron or aluminum sludges are obtained with the addition of a poly-
mer (dosage range 0.5 to 1.0 mg/ji).  It has also been found that
the lower the dosage of iron or aluminum salt used the easier
the resulting sludge is to thicken.  For this reason, and to save
chemical costs, it is recommended that chemical feed equipment
be automatically controlled to prevent overdosage of more chemi-
cal than required to achieve the phosphorus reduction needed.

     If it is necessary to thicken secondary biological sludge
separately, experience indicates that air flotation thickening
is superior to gravity thickening.  Again, the addition of poly-
mers substantially improves performance.

     Centrifuge dewatering of primary or combined chemical sludges
is greatly enhanced by polymer addition.  Sludges containing iron
salts dewater much better than sludges containing aluminum salts.
Lime sludges dewater very well.

     Anaerobic and aerobic sludge digestion is reported to be
essentially uninhibited by the addition of chemical sludges,
there being no toxic effects from the presence of the chemical
precipitates or the pH of the sludge.  However, there is fre-
quently the need for more volume to handle the increased sludge
mass while maintaining proper retention time.  When iron and
aluminum sludges are added to anaerobic digesters, there is also
commonly an adverse effect on supernatant quality and digested
sludge solids concentration because of poor solids-liquid separa-
tion.

     Vacuum filtration of chemical sludges presented problems at
a  number of plants due to increased solids mass, sludge volume,

                               125

-------
and/or poorer sludge dewatering  characteristics.   Experimentation
with chemical conditioning,  e.g.,  polymer  dosages,  lime  addition,
etc., generally led to improved  vacuum  filter  performance.   In
addition, changes in filter  media  were  reported  helpful.   The
City of Milwaukee,  Wisconsin,  found  in  pilot tests  that  top  feed
vacuum filtration of iron  sludges  was more effective  than  conven-
tional bottom feed  filters.   As  was  the case with  centrifuges,
iron sludges are generally reported  easier to  dewater than alumi-
num sludges.

     Thermal conditioning of chemical  sludges  is generally
reported successful prior to vacuum  filtration or centrifugation.
Sludge  cakes of 35 percent TS and above are  routinely achieved.
Potential negative aspects are similar  to  those  for non-chemical
sludges:  sidestreams have high  dissolved  organic strength,  and
operation and maintenance costs  are  high.   One plant reported
excessive corrosion and erosion  of the  thermal conditioning  unit
components,  but it is not known  if the  problem was aggravated  by
the chemical component of the sludge.

     Because of the impacts of phosphorus  removal  on sludge  pro-
duction and  treatment, plants are now hauling  more sludge  in liq-
uid and cake form to land disposal sites than  before.  Hauling
sludge as a  liquid or cake rather than  dewatering or incinerating
has been a common solution to many of the  difficulties experienced
by plants in dewatering and incinerating chemical  sludges.   In
some cases,  phosphorus removal has shifted the economics of  sludge
processing in favor of hauling rather than dewatering and/or
incineration.  Especially in the case of lime  sludges, it  is
being found  that land application of cake  is  preferable to lagoon
storage or incineration.  In other cases,  hauling simply provides
an interim solution to problems, although  it  is  not necessarily
the most cost effective alternative.  It is frequently relied
upon as an interim solution by plants which have inadequate  capa-
city to handle the additional sludge generated by phosphorus
removal with existing facilities.

     In view of the large amounts of chemical  sludges being
applied to land, it is important that the  negative or beneficial
effects on plants and animals be considered.   Chemical sludges
contain nutrients and other elements which are beneficial  to
plant growth.  Lime sludges can  improve low pH,  low calcium, or
low phosphorus soils.  Chemical  sewage sludges must be character-
ized on an individual basis to determine  if possibly hazardous
concentrations of heavy metals or other contaminants exist.
                               126

-------
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                                                                                              (continued)

-------
TABLE 31 (continued)

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-------
                          TABLE 32.  KEY TO BIBLIOGRAPHY  INFORMATION MATRIX
  I  Level of investigation:

      L) Laboratory
      P) Pilot
     (F) Full-scale demonstration
     (A) Actual operation
     (R) Review

 II  Audience:

     (M) Management
     (E) Engineering
     (S) Scientific

III  Chemical precipitant:

         Aluminum salt
    (A) Alumi
    (L) Lime
    (I) Iron salt
    (P)
Polymer
IV  Point of addition:

    (P) Pre-primary
    (S) Pre-secondary or
        secondary
    (A) After secondary
                                      V  Sludges processed:

                                         (1) Raw primary + WAS
                                         (2) Digested primary +
                                         (3  Raw primary + TF
                                         (4  Digested primary
                                         (5  Raw primary
                                         (6) Digested primary
                                         (7) Separate chemical
                                         (8) Raw secondary
                                         (9) Digested secondary

                                     VI  Thickening/blending:
                                                        WAS
                                 (1
                                 (2
                                 (3
                                 (4)
         Gravity thickener
         Flotation thickener
         Stirred thickener
         Centrifuge
VII  Stabilization/reduction:
                                  1) Composting
                                  2) Aerobic digestion
                                  3) Anaerobic digestion
                                  4) Wet air oxidation
                                  5) Pyrolysis
                                  6) Chemical stabilization
VIII  Conditioning/stabilization:

      (1) Chemical conditioning
      (2) Elutriation
      (3) Thermal conditioning
      (4) Radiation treatment
      (5) Freezing

  IX  Dewatering:

      (1) Pressure filter
      (2) Air drying beds
      (3) Centrifuge
      (4) Vacuum filter
      (5) Horizontal moving
          screen concentrator
      (6) Belt filter press
      (7) Cylindrical  rotating
          gravity filter
      (8) Capillary suction
      (9) Lagoon
      (10) Moving bed sand filter
                                                                                            (continued)

-------
    TABLE 32 (continued)
CO
IN5
        X  Heat drying/incineration:
            1) Flash or spray dryer
            2) Tray dryer
            3) Rotary kiln furnace
           (4) Rotary kiln dryer
           (5) Multiple hearth dryer
           (6) Multiple hearth
               incinerator
           (7) Fluidized bed inciner-
               ator
       XI  Final disposal:
ili
 1) Agricultural fields
 2) Land reclamation
(3) Power generation
 4) Sanitary landfill
 5) Ocean disposal
    Private or authority-
    owned dumpsite
    Commercial or non-
    commerical soil condi-
    tioner
    Resource recovery
           (7)
           (8)
      XII  Cost coverage:
                                   XIII  Sludge characteristics:

                                         (R) Generation rates
                                         (C) Chemical/physical  charac-
                                             teristics

                                          *  Article covers information
                                             category generally
            C) Capital costs
            0) Operating costs

-------
                          BIBLIOGRAPHY


 1.   Alvord, E.  T., et al. ,  "Phosphorus Removal  by Ferrous
     Iron and Lime," 11010  EGO 01/71,  U.S.  Environmental
     Protection  Agency, January 1971.

 2.   Baillod, C. R. , Cressey, G.  M.,  and Beaupre,  R.  T.,
     "Influence  of Phosphorus Removal  on Solids  Budget,"
     JWPCF, 49 (1):  131-145, 1977.

 3.   Baldock, E. H., "Metropolitan Toronto's Experience  in
     Phosphate Removal," Presented at  Western Canada  Water
     and Sewage  Conference,  September  21, 1973,  Toronto.

 4.   Bell, G. R., Libby, D.  V., and Lordi,  D. T.,  "Phos-
     phorus Removal Using  Chemical Coagulation and a  Con-
     tinuous Countercurrent  Filtration Process,  17010EDO
     06/70, Federal Water  Quality Administration,  U.S.
     Dept. of the Interior,  June  1970.

 5.   Bennett, S. M., and Bishop,  D. F., "Solids  Handling  and
     Reuse of Lime Sludge,"  Contract  No. 14-12-818,  U.S.
     Environmental Protection Agency.

 6.   Black, S. A., "Anaerobic Digestion of  Lime  Sewage  Sludge,"
     Research Report No. 50, Canada-Ontario Agreement on
     Great Lakes Water Quality, Environment Canada,  Ottawa,
     1976.

 7.   Boyko, B. I., "Aerobic  and Anaerobic Sludge Digestion,"
     In:  Proceedings of the Sludge Handling and Disposal
     Seminar, September 18-19, 1974,  Toronto, pp.  46-62.

 8.   Boyko, B. I., and Rupke, J.  W. G., "Phosphorus  Removal
     within Existing Wastewater Treatment Facilities,"
     Research Report No. 44, Canada-Ontario Agreement on
     Great Lakes Water Quality, Environment Canada,  Ottawa,
     1976.

 9.   Brandt, H.  T., and Kuhns, R. E.,  "Apollo County Park
     Wastewater  Reclamation  Project, Antelope Valley,
     California," EPA-600/2-76-022, U.S. Environmental  Protec-
     tion Agency, March 1976.

10.   Burns, D. E., and Shell, G.  L.,  "Physical Chemical
     Treatment of a Municipal Wastewater Using Powdered
     Carbon." EPA-R2-73-264, U.S. Environmental  Protection
     Agency,  May 1972.
                              133

-------
BIBLIOGRAPHY (Continued)


11.  Burns, D. E., and Shell, G. L., "Physical-Chemical
     Treatment of a Municipal Wastewater Using  Powdered
     Carbon," EPA-R2-73-264, U.S. Environmental  Protection
     Agency, August 1973.

12.  Buzzel, J. C., Jr., and Sawyer, C.  N., "Removal  of
     Algal Nutrients from Raw Wastewater with Lime,"  JWPCF,
     39 (10):  R16-R24, 1961.

13.  Campbell, H., and LeClair, B.  P., "Effects  of Control
     Variables and Sludge Characteristics on the Performance
     of Dewatering and Thickening Devices," In:   Proceedings  of
     the Sludge Handling and Disposal  Seminar,  September
                  |_a
                  to,
     18-19,  1974,  Toronto,  pp.  280-314.

14.   Chawla,  V.  K. ,  Stephenson,  J.  P.,  and  Liu,  D. ,  "Bio-
     chemical  Characteristics  of Digested Chemical Sewage
     Sludges,"  In:   Proceedings  of  the  Sludge Handling and
       sp
     63-94
Disposal  Seminar,  September  18-19,  1974,  Toronto,  pp.
                                           ge
                                          74,
15.  Chawla, V. K., Bryant, D. N., and Liu, D.,  "Disposal
     of Chemical Sewage Sludges on Land and Their Effects  on
     Plants, Leachate and Soil Systems," In:  Proceedings
     of the Sludge Handling and Disposal Seminar, September
     18-19, 1974, Toronto, pp. 207-233.

16.  Connell, C. H., "Phosphorus Removal and Disposal  from
     Municipal  Wastewater," 17010 DYB02/71, U.S.  Environ-
     mental Protection Agency, February 1971.

17.  Cornwell,  D. A., and Zoltek, J.  Jr., "Recycling of
     Alum Used  for Phosphorus Removal in Domestic Waste-
     water Treatment," JWPCF. 49(4):   600-612,  1977.

18.  Gulp, R. L., Evans, D. R., and Wilson, J.  C., "Advanced
     Wastewater Treatment as Practiced at South Tahoe,"
     EPA-WQO-17010-ELQ-08/71 , U.S. Environmental  Protection
     Agency, August 1971 .

19.  Gulp, G.,  Suhr, L. G., and Evans, D. R.,  "Physical-
     Chemical Wastewater Treatment Plant Design," EPA
     Technology Transfer Seminar Publication,  August 1973.

20.  Derrington, R. E., Stevens, D. H., and Laughlin, J. E.,
     "Enhancing Trickling Filter Plant Performance by
     Chemical Precipitation," EPA-670/2-73-060, U.S. Environ-
     mental Protection Agency, August 1973.


                              134

-------
BIBLIOGRAPHY (Continued)
21.  Dorr-Oliver, Inc., "Phosphate Extraction Process,"
     Stamford, Conn., 1968.

22.  Dow Chemical Company, "Application of Chemical  Preci-
     pitation Phosphorus Removal at the Cleveland Westerly
     Wastewater Treatment Plant," Prepared for the City  of
     Cleveland, Ohio, April 1970.

23.  Dunseth, M. G., et al., "Ultimate Disposal  of Phosphate
     from Waste Water by Recovery as Fertilizer," 17070ESJ01/
     70, Federal Water Quality Administration, U.S.  Dept.  of
     the Interior, January 1970.

24.  Eikum, A. S., Carlson, D. A., and Lundar, A., "Phos-
     phorus Release during Storage of Aerobically Digested
     Sludge," JWPCF, 47(2):  330-337, 1975.

25.  Parrel! , J. B., "Design Information on  Dewatering
     Properties of Wastewater Sludges," In:   Proceedings of
     the Sludge Handling and Disposal Seminar, September
     18-19, 1974, Toronto, pp. 269-279.

26.  Farrell ,  J. B., "Interim Report of Task Force  on
     Phosphate Removal Sludges," EPA-670/2-75-013, U.S.
     Environmental Protection Agency, 1975.
27.  Fowlie, P. J. A., and Shannon, E. E., "Utilization of
     Industrial Wastes and Waste By-Products for Phosphorus
     Removal:  An Inventory and Assessment," Research Report
     No. 6, Canada-Ontario Agreement on Great Lakes Water
     Quality, Environment Canada, Ottawa, June 1973.

28.  Ganczarczyk, J., and Hamoda, M.F.D., "Aerobic Digestion
     of Organic Sludges Containing Inorganic Phosphorus
     Precipitates, Phase 1," Research Report No. 3, Canada-
     Ontario Agreement on Great Lakes Water Quality, Environ-
     ment Canada, 'Ottawa, June 1973.

29.  Gray, I. M. , "Phosphorus Removal Study at Barrie WPCP,"
     Research Branch, Ontario Ministry of the Environment,
     Toronto, 1972.

30.  Gray, I. M., "Phosphorus Removal Study at the Sarnia
     WPCP," Research Report No. 14, Canada-Ontario Agreement
     on Great Lakes  Water Quality, Environment Canada, Ottawa,
     1972.
                               135

-------
BIBLIOGRAPHY (Continued)


31.  Greenland, T. W. , and Gaines, F. R. , "Hatfield Town-
     ship, Pennsylvania Advanced Waste Treatment Plant,"
     Tracy Engineers, Inc., Camp Hill, Pennsylvania, 1977.

32.  Grigoropoulos, S. G., Vedder, R. C., and Max, D.  W.,
     "Fate of Aluminum-Precipitated Phosphorus in Acti-
     vated Sludge and Anaerobic Digestion," JWPCF, 43(12):
     2366-2382, 1971.

33.  Hamoda, M. F., and Ganczarczyk, J., "Aerobic Diges-
     tion of Sludges  Precipitated from Wastewater by Lime
     Addition," JWPCF. 49(3):  375-387, 1977.

34.  Hudgins, R. R.,  and Silveston, P. L., "Wet Air
     Oxidation of Chemical Sludges," Research Report No.
     12, Canada-Ontario Agreement on Great Lakes Water
     Quality, Environmental Canada, Ottawa, March 1973.

35.  Jacke, R. , "Polymer Cuts Disposal Costs," Water and
     Sewage Works, 123(6):  99-100, 1976.

36.  Jenkins, D. , Ferguson, J. F., and Menar, A. B.,
     "Chemical Processes for Phosphate Removal," Water
     Research. 5:  369-389, 1971.

37.  Johnson, E. L.,  Beeghly, J. H., and Wukasch, R. F.,
     "Phosphorus Removal at Benton Harbor-St. Joseph,
     Michigan," Dow Chemical Company, Midland, Michigan,
     1969.

38.  Keith, F. W. , Jr., "Centrifuges — Types and Applications,"
     In:  Proceedings of the Sludge Handling and Disposal
     Seminar. September 18-19, 1974, Toronto, pp. 351-368.

39.  Kirkham, M. B.,  and Dotson, G. K., "Growth of Barley
     Irrigated with Wastewater Sludge Containing Phosphate
     Precipitants," In:  Proceedings of the National Confer-
     ence on Municipal Sludge Management, June 11-13,  1974,
     pp. 97-106.

40.  Knight,  C.  H., Mondoux, R. G., and Hambley, B., "Thick-
     ening and Dewatering Sludges Produced in Phosphate
     Removal,"  Paper  presented at Phosphorus Removal Design
     Seminar, May 28-29, 1973, Toronto.
                               136

-------
BIBLIOGRAPHY (Continued)


41.  Koers, D.  A., "Aerobic Digestion of Wastewater Sludges,"
     Paper presented at Technology Transfer Seminar on
     Sludge Handling Disposal, February 16-19, 1977, Calgary,
     Alberta.

42.  Malhotra,  S. K., Parrillo, T. P., and Hartenstein,
     A. G., "Anaerobic Digestion of Sludges Containing Iron
     Phosphates," Journal of the Sanitary Engineering Divi-
     sion, ASCE, 97(SA5):629-646, October 1971.

43.  Martin, L., and Nardozzi, A. D., "Operational  Consid-
     erations Associated with Chemical and Biological  Sludge
     Generated  by Lime Precipitation," Paper presented at
     the National WPCF Conference, October 1976,  Minneapolis,
     Minnesota.

44.  Mignone, N. A., "Anaerobic Digester Supernatant Does
     Not Have to be a Problem," Water and Sewage  Works.
     123(12):  57-59, 1976.     ~~

45.  Minton, G. R., and Carlson, D. A., "Primary  Sludges
     Produced by the Addition of Lime to Raw Waste  Water,"
     Water Research, 7:  1821-1847, 1973.

46.  Motamedi,  M., "Dewatering of Ferric Chloride Coagu-
     lation Sludge," Water Research.  9:  861-864, 1975.

47.  Mulbarger, M. C., et al., "Lime  Clarification, Recovery,
     Reuse, and Sludge Dewatering Characteristics," JWPCF,
     41(12):  2070-2085, 1969.

48.  Novak, J.  T., and Montgomery, G. E., "Chemical Sludge
     Dewatering on Sand Beds," Journal of the Environmental
     Engineering Division, ASCE, IQI(EEl):1-14, February
     TWT.

49.  Opferkuch, R. E., Ctvrtnicek, T. , and Mehta, S. M.,
     "Study of  Utilization and Disposal of Lime Sludges
     Containing Phosphates," EPA-R2-73-282, U.S.  Environmental
     Protection Agency, June 1973.


50.  O'Shaughnessy, J. C., et al. , "Digestion and Dewatering
     of Phosphorus-Enriched Sludges," JWPCF, 46(8):  1914-
     1926, 1974.
                              137

-------
BIBLIOGRAPHY (Continued)
 51.  O'Shaughnessy, J. C., et al., "Soluble Phosphorus
     Removal in the Activated Sludge Process.   Part II:
     Sludge Digestion Study," EPA-1701O-EIP-10/71 ,  U.S.
     Environmental Protection Agency, October  1971.

 52.  Proceedings of the Technical  Seminar on Physical-
     Chemical Treatment, Ontario Ministry of Health
     Laboratories, March 9, 1972.

 53.  Recht, H. L., and Ghassemi, M., "Kinetics and  Mechan-
     ism of Precipitation and Nature of the Precipitate
     Obtained in Phosphate Removal  from Wastewater  Using
     Aluminum (III) and Iron (III)  Salts,"  17010EKI 04/70,
     Federal Water Quality Administration,  U.S.  Dept.  of
     the Interior, April 1970.

 54.  Roe, I. P., "Sludge Dewatering  Using the  Kruger
     Centrifuge," In:  Proceedings of the Sludge Handling
     and Disposal Seminar, September 18-19, 1974,  Toronto,
     pp. 369-384.

 55.  Salib, W. A., "Sludge Handling  and Disposal Practices
     in Metropolitan Toronto,"  In:   Proceedings  of  the
     Sludge Handling and Disposal  Seminar,  Septemhier 18-19,
     1974, Toronto, pp. 452-465.

 56.  Schmid, L. A., and McKinney,  B. E., "Phosphate Removal
     by a Lime-Biological Treatment  Scheme," JWPCF, 41(7):
     1259-1276, 1969.

 57.  Schroeder, W. H., "Principles and  Practices of Sludge
     Incineration," Paper presented  at  the  Technology
     Transfer Seminar on Sludge Handling Disposal,  February
     1977, Calgary, Alberta.

 58.  Scott, D. S., and Horlings,H.,  "Removal of Phosphates
     and Metals from Sewage Sludge," Research Report No.
     28, Canada-Ontario Agreement  on Great  Lakes Water
     Quality, Environment Canada,  Ottawa, 1973.

59.  Scott, D. S., and Horlings, H., "Removal  of Phosphates
     and Metals from Sewage Sludges," In:  Proceedings of
     the Sludge Handling and Disposal Seminar, September
     18-19, 1974, Toronto, pp.  413-443.

60.  Scott, D. S., and Horlings, H., "Removal  of Phosphates
     and Metals from Sewage Sludges," Environmental Science
     and Technology. 9(9):  849-855,  19757
                              138

-------
BIBLIOGRAPHY (Continued)


61.  Shannon, E. E., Plummer, D., and Fowlie, P.J.A.,
     "Aspects of Incinerating Chemical Sludges,"   In:
     Proceedings of the Sludge Handling and Disposal
     Seminar, September 18-19. 1974. Toronto. PP.  391-412.

62.  Singer, P. C., "Anaerobic Control of Phosphate by
     Ferrous Iron," JWPCF, 44(4):  663-669, 1972.

63.  Smart, J., "Anaerobic Sludge Digestion Processes,"
     Paper presented at Technology Transfer Seminar on
     Sludge Handling Disposal, February 1977, Calgary,
     Alberta.

64.  Smart, J., and Boyko, B. I., "Full Scale Studies  on
     the Thermophilic Anaerobic Digestion Process," Research
     Report No. 59, Canada-Ontario Agreement on Great  Lakes
     Water Quality, Environment Canada, Ottawa, 1977.

65.  Smith, A. G., "Centrifuge Dewatering of Lime  Treated
     Sewage Sludge," Paper No. W2030, Research Branch,
     Ontario Ministry of the Environment, Toronto, 1972.

66.  Stickney, R., and LeClair, B. P., "The Use of Physico-
     chemical Sludge Characteristics and Bench Dewatering
     Tests in Predicting the Efficiency of Thickening  and
     Dewatering Processes," In:  Proceedings of the Sludge
     Handling and Disposal Seminar, September 18-19,  1974,
     Toronto, pp. 315-350.

67.  "Studies on Removal of Phosphates and Related Removal
     of Suspended Matter and Biochemical Oxygen Demand,"
     May-October 1967, Lake Odessa, Michigan, Wastewater
     Section, Division of Engineering, Michigan Dept.  of
     Public Health.

68.  Tofflemire, T. J., et al., "Tertiary Treatment for
     Phosphorus Removal by Alum Addition at Richfield  Springs,
     New York," Research Paper No. 39, Environmental  Quality
     Research Unit, New York State Dept. of Environmental
     Conservation, March 1976.

69.  U.S. Environmental Protection Technology Transfer,
     "Physical-Chemical Wastewater Treatment Plan  Design,"
     EPA Technology Transfer Seminar Publication,  1973.

70.  University  of  Guelph, Ontario,  "Land  Disposal of Sewage
     Sludge.   Vol.  I,"  Research  Report  No.  16, Canada-
     Ontario  Agreement  on  Great  Lakes  Water  Quality,
     Environment Canada,  Ottawa,  1973.


                              139

-------
BIBLIOGRAPHY (Continued)


71.  Van  Fleet, G. L., Barr, J. R., and Harris, A. J.,
     "Treatment and Disposal of Chemical Phosphate Sludge
     in Ontario," JWPCF. 46(3):  582-587, 1974.

72.  Van  Fleet, G. L., Barr, J. R., and Harris, A. J.,
     "Treatment and Disposal of Chemical Phosphate Sludge
     in Ontario," Presented by J. R. Barr at the Annual
     Conference of the Water Pollution Control Federation,
     October 1972, Atlanta, Georgia.

73.  Van  Loon, J. C., "Heavy Metals in Agricultural Lands
     Receiving Chemical Sewage Sludges," Research Report
     No.  9, Canada-Ontario Agreement on Great Lakes Water
     Quality, Environment Canada, Ottawa, March 1973.

74.  Van  Loon, J. C., "Heavy Metals in Agricultural Lands
     Receiving Chemical Sewage Sludges.  Vol. II," Research
     Report No. 25, Canada-Ontario Agreement on Great Lakes
     Water Quality, Environment Canada, Ottawa, 1975.

75.  Van  Loon, J. C., "Heavy Metals in Agricultural Lands
     Receiving Chemical Sewage Sludges.  Vol. Ill," Research
     Report No. 30, Canada-Ontario Agreement on Great Lakes
     Water Quality, Environment Canada, Ottawa.

76.  Villiers, R. V., "Thickening and Dewatering Phosphorus-
     Laden Chemical Sludges, Field Operation--!974,"
     U.S.  Environmental Protection Agency, 19.74.

77.  Williams, T. C., "Phosphorus is Removed at Low Cost,"
     Water and Wastes Engineering, 13(11):  52-63, 1976.
78.  Wood, G. M., "Land Application of Processed Organic
     Wastes," In:  Proceedings of the Phosphorus Removal
     Design Seminar Conference, May 28-29, 1973, Environ-
     ment Canada, Toronto.

79.  Zaloum, R., "Activated Sludge Characterization and
     Settling,"  In:  Proceedings of Phosphorus Removal
     Design Seminar, May 28-29, 1973, Environment Canada,
     Toronto.
                              140

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                                                                  OMB  #158-5-77002
                                                                  February  1978
                                      APPENDIX  A

                   PHOSPHORUS-LADEN  SLUDGE  MANAGEMENT  QUESTIONNAIRE
     When  completed,  mail  to:

     SCS Engineers
     4014  Long  Beach  Boulevard
     Long  Beach,  California  90807
     (213)  426-9544

 I.   GENERAL  INFORMATION
     1.   Full  plant  name:
     2.   Address:
     3.   Phone  number:
     4.   Name of person  completing  questionnaire:
     5.   Title:	
     6.   Name  of alternate  contact  for  technical  information:
     7.  Title:	
     8.  Approximate  time when  (a)  primary  plant was  built:
        (b)  secondary  treatment was  installed:	
        (c)  phosphorus removal was begun:
     9.   Has  the  plant  ever  participated  directly  in  any  EPA,  university, or other
         study  pertinent  to  phosphorus-laden  sludge management?
         Yes	No	

II.   RAW  SEWAGE INFLUENT  INFORMATION  (Recent  monthly  averages)

     1.   Vol ume:	mgd
     2.   pH:	BOD5:	mg/t  COD:	mg/£   SS:	mg/£
         Total-P:	lmg/£     VSS	mg/£
     3.   Estimated percentage of  industrial wastes	%
     4.   Do you get  sludge from the water purification  plant?  Yes	
         No	Don' t know	
     5.   Storm  and sanitary  sewers combined	 or  separate          (check  one)
                                       141

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III.   PLANT DESIGN  INFORMATION (Please attach flow diagram if available),
      1.   Primary  treatment  (circle below)
          Screening
          Aerated  grit  chamber
          Non-aerated grit chamber
          Others  (please  explain)	
      2.
      3.
                                   Gravity settling
                                   Flocculation chamber
Secondary treatment  (circle below)
Conventional  activated  sludge
Trickling filter
Final clarifier
          Others  (please  explain)_
                                             Modified activated sludge:
                                               Step-aeration
                                               Contact stabilization
                                               Extended aeration
                                               Complete mix
                                               Pure oxygen
Sludge treatment/disposal  -
Circle boxes on Figure  1 on  the next page and connect with arrows
to show your sludge treatment/disposal chain.  Indicate any
points of chemical  addition  as well.
 IV.  PHOSPHORUS REMOVAL INFORMATION (Give recent monthly averages)
      1.  Effluent total-P:  	mg/£
      2.  Chemicals added and chemical dosage -
          a.  Chemicals added to      b.  Percent  of
              remove phosphorus:
              (circle below)
              Lime
              Ferric chloride
              Ferrous sulfate
              A!um(aluminum sulfate)
              Sodium aluminate
              Polymer
              Other(name below)
                                 chemical  in
                                 sol'ution  added:*
                                 % Ca(OH)2
                                 % Fed 3
                                 % FeS04
                                 % A12(S04)3    ~
c.  Average
    amounts added:*

    	9Pd
            _gpd
            __SPd
           *Explanation  of parts b and c:  We assume you add a solution containing
            a  certain  percentage of actual  chemical to the wastewater.  Give  that
            percentage in  part b.   Then tell how much of that solution you  add  in
            part  c.  Use other units such as gal/mil gal of sewage rather than  gpd
            if you wish, but please indicate units.  If you wish to  respond to  this
            section  in another way, by giving the dosage of dry chemical in mg/i or
            Ib/day,  for  example, write the appropriate information below:
                                        142

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      Indicate  the  sources of  the  chemicals  by  circling beiow and writing the name
      of  the  chemical next to  its  source:
      Chemical  manufacturer	
      Industrial waste  product	
      Drinking  water  purification  sludge	
      Other  (specify)	^__	
      Point  of  chemical  addition:(circle below)
      Before  primary  clarifier              Primary clarifier
      Activated sludge  tank                  Trickling  filter
      Activated sludge  effluent  channel      Trickling  filter effluent channel or
      After  secondary clarifier                    pipe
      Other  (please explain)                 Secondary  clarifier
V. SLUDGE  HANDLING INFORMATION

   1.  Does  your  plant  combine  all  of  its  sludges  --primary, waste activated or
      trickling  filter,  and  chemical  — together  for dewatering and disposal, etc.?
      Yes	No	
   2.  If answer  to previous  question  #1 is  no,  indicate what sludges you treat or
      dispose  of individually:   (circle below)
      Primary     Secondary    Chemical
      Combined Primary/Secondary   Other (specify)	
   3. Chemical conditioners  used for  dewatering:   (circle below)
      Lime      Ferric chloride     Polymer       Others  (specify)
                                       143

-------
           Circle applicable boxes and connect with lines to show sludge
           treatment/disposal chain.
              (1)
(2)
(3)
(4)
(5)
(6)
(7)
SLUDGE TYPE   THICKENING   STABILIZATION  CONDITIONING
           BLENDING    REDUCTION   STABILIZATION
                     DEWATERING
                                HEAT DRYING   REDUCTION      FINAL
                                           STABILIZATION   DISPOSAL
PRIMARY

SECONDARY

CHEMICAL






GRAVITY

FLOTATION

CENTRIFUGE






COMPOSTING

AEROBIC
DIGESTION

ANAEROBIC
DIGESTION

LIME
TREATMENT

CHLORINE
TREAT.
-
-




CHEMICAL

ELUTRJATION

HEAT TREAT.
TRAY
DRYER
r-








L


INCINER-
ATION



WET AIR
OXIDATION



PYROLYSIS


-























CROPLAND

LAND
RECLAM

POWER
GENERATION

SANITARY
LANDFILL

OCEAN
DISPOSAL

PRIVATE OR
AUTHORITY-
- OWNED
DUMPSITE













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VI.  SLUDGE  CHARACTERISTICS (Recent monthly averages)
     1.  Sludge characteristics  before  thickening or  stabilization  by
        digestion,  heat,or chemical treatment:
        (For those  who  answered  question V-2  above,  there is  room  for
        the  characteristics of  more than one  type of sludge.)
Type of sludqe:
Volume (gpd)
TS (%, dry wt)
VS (X of TS)
COD (mg/*)















Substitute other
units (e.g. , mg/a )

( j
( ,
( )
       Sidestreams generated by sludge treatment units: (circle below)
          Centrate          Digester supernatant
          Filtrate          Thickener supernatant    Other(specify)
       Sidestream characteristics:
Type of sidestream:
Volume (gpd)
SS ( X, dry wt)
VSS( X- of SS)
COD(mq/i)
BODi;(mg/*)


















Substitute other units
(e.g.,.mg/£, TS, etc.)
( )
( )
( )
( }
( )
        Final TS content of treated liquid sludge before drying, dewatering,
        or ultimate disposal:  	% TS, dry wt.
VII. PHOSPHORUS REMOVAL IMPACT ON PLANT OPERATION
    1. Additional  sludge generated - (Give typical monthly averages)
       a. Total sludge volume before plant had  phosphorus removal:  .
       b. Sludge TS before  plant had phosphorus removal:  X dry wt
       c. Wastewater flow  volume before plant had  phorphorus removal: _
       d. Wastewater SS before plant had phosphorus removal:_	mg/x.
JPd
 or mg/n_
	mgd "
       u. waai.ewai.ei  JJ  UGIWIC pmm. >•«•- r..—~r	—  	 -          . -•
       e. If possible, estimate how much additional  sludge is generated as a result
          of phosphorus  removal:            #/day dry solids         _
    2  How have changes  in  sludge volume or mass and sludge characteristics affected
       plant operations? For instance, does the phosphorus-laden sludge require
       more time, energy, equipment, etc. to treat/dispose of than the sludge before
       P-removal did? How? Is the phosphorus-laden sludge more difficult to settle,
       thicken,  dewater, digest,  ect.?  How?  How did you. solve any problems^which
       resulted  from  phosphorus  removal?  Please respond  to these questions in as
       much detail as possible.   This is-the most important part of the questionnaire.
       We appreciate  your thoughtful response.
                                       145

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 Please use other side or extra pages if needed.
 3.   If not covered above, please discuss any adverse effects of the phosphorus-
     laden sludge on anaerobic digestion?	
4.  Amount of extra labor,  energy,  equipment, and  supplies  needed because of
    changes in sludge volume or  mass  and  sludge characteristics  (please estimate)-
    a.   New equipment for  sludge treatment/disposal:
Equipment item



Year
Added



Capital cost
($)



Estimated operating
cost ($/yr)



Year



    b.  Additional  labor for maintenance  and  operation  of  all  sludge  treatment/
       disposal  equipment:
Area where additional labor
was needed



Number of additional labor
hours (hr/yr)



Cost
(S/hr)



                                      146

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  c. Additional  energy  and  fuel  requirements  for operation of all sludge
    treatment/disposal  equipment:
Equipment item
or area of impact




Type of
energy/fuel




Number of additional
KWH, MCF, etc./yr




Cost (S/KWH
or MCF,. etc.!




  d.  Additional  chemical  supplies for sludge treatment/disposal: (Include
     chemicals for conditioning,  thickening, oxidation, etc.)
Chemical




Area of use of chemical




Additional Ib of chemical,
(cu ft oxygen), etc. /day




Cost($/lb
or cu ft)




  e. Additional  outside costs related to sludge treatment/disposal  (e.g., increased
     sludge volume means must pay contractor more to  haul  it away):
Type of additional outside cost


Cost(5/yr)


Year


5. Effects of. P-removal- (Answer only questions which, apply to  your plant  and for
   which you-have avail able-data or can:estimate.   You may- answer part of  a  question),
   a.  Incineration or mechanical heat drying rate (#wet cake/hr*)
      Increase?           Before »	#wet cake/hr
      Decrease?	   After *	
      Same?
"~#wet cake/hr
   b.  Dewataring rate  (Idry sludge/hr*)
      Increase?	     Before: »	
      Decrease?	     After *	
      Same?
        Idry sludge/hr
        #dry sludge/hr
  *Note parts a & b:  If the size of the dewatering device, incinerator, or
   mechanical heat dryer was changed between the "before" and "after" periods,
   report the "yield" instead of the "rate" by dividing by the effective area or
   volume of the device, and note this change.

                                         147

-------
c.
d.
Cost of chemical
Increase?	
Decrease?	
Same?
                 conditioning ($/dry
                      Before = 	
                      After =
ton solids
dewatered):
$/dry ton solids
$/dry ton solids
          cake TS content (% TS, dry wt):
                      Before =  	%,  dry wt
                                	%,  dry wt
Dewatered
Increase?
Decrease?
Same ?    	
(Current dewatered cake VS content (% of TS):
                          After =
Thank you for your cooperation in providing us information vital  to the success-
ful completion of this research.   If there are any questions, please contact
Lee Hammer or Michael  Swayne at SCS Engineers, phone collect:  (213) 426-9544.
                                     148

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                          APPENDIX B

             OUTLINE FOR COLLECTION OF FIELD DATA
 I.   GENERAL INFORMATION

     A.   Full  plant name; operating authority  name
     B.   Addresses
     C.   Phone numbers
     D.   Names and titles of personnel  interviewed  by  SCS
     E.   Approximate times when all additions  and modifications
         to plant affecting sludge were made
     F.   History of experimentation at  plant with modes  of
         operation affecting sludge

         1.  Points of chemical addition
         2.  Chemicals used for P-removal
         3.  Chemical  conditioners used
         4.  Equipment used
         5.  Machine and process operating parameters
         6.  Inclusion of chemical sludge  with other  sludges
         7.  Disposal  method

     6.   Previous studies done
     H.   Design engineer name, address, and phone
     I.   Equipment manufacturers'  names, addresses,  and  phones
     J.   Engineering consultant's  name, address,  and  phone
     K.   Unusual wastes accepted at plant
     L.   Variations in flow
     M.   Before and after periods  dates and modes of  operation
     N.   Design flow
     0.   Average flow
     P.   Variations in wastewater  treatment operations
     Q.   Unusual problems in plant operation affecting plant
         performance

II.   GEN.ERAL DESCRIPTION OF WASTEWATER  TREATMENT  OPERATIONS

     A.   Diagram of wastewater treatment facilities

         1.  Treatment units and arrangement
                               149

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      B.   Machine  operating parameters

          1.   Grit  chamber  (if chemical  is added here)
          2.   Flocculators  (if chemical  is added here)
          3.   Clarifiers
          4.   Activated  sludge or trickling filter units
          5.   Channels where chemicals may be added
          6.   Tertiary treatment units

              a.   dimensions
              b.   type

III.   PROCURING,  STORING,  MIXING, PUMPING, DISTRIBUTION,  AND
      ADDITION OF  CHEMICALS FOR  PHOSPHORUS REMOVAL

      A.   Diagram  of  chemical  handling operations

          1.   Handling facilities and  arrangement

      B.   Description of  all procedures  pertaining to  these
          operations

          1.   Quantities  and rates
          2.   Types of chemicals
          3.   Types of equipment
          4.   Automated  or  manual handling and  addition
          5.   Locations
          6.   Timing
          7.   Personnel

 IV.   DETAILED DESCRIPTION  OF  SLUDGE TREATMENT  AND DISPOSAL  OPERATION?

      A.   Diagram  of  sludge treatment/disposal  facilities including
          sidestream  and  sludge  recirculation  (treatment  units  and
          arrangement)

          1.   Storage (including storage in clarifiers)
          2.   Screening,  degritting
          3.   Pumping
          4.   Blending
          5,   Thickening
          6.   Conditioning
          7.   Stabi1izing
          8.   Dewatering
          9.   Reduction
         10.   Disposal
         11.   Sidestream  treatment

      B.   Machine  operating parameters

          1 .   Dimensions
          2.   Shape

                                 150

-------
    3.   Type
    4.   Brand  name
    5.   Mechanical  variations
    6.   Continuous  or batch  flows  accepted
    7.   Expected  life of equipment
    8.   Etc.


C.   Machine operating variables

    1.   Speed
    2.   Temperature
    3.   Pressure
    4.   Vacuum
    5.   Cycle  time
    6.   Fuel  consumption             >
    7.   Etc.

D.   Process operating variables

    1.   Hydraulic flow rates in and out
    2.   Chemical  addition rates
    3.   Run lengths
    4.   Solids flow rate
    5.   Solids loading
    6.   Hydraulic loading
    7.   Etc.

E.   Process performance variables  (excluding screening, degrit-
    ting, and  pumping)

    1.   Input  and output stream characteristics

        a.  total solids content
        b.  sludge solids content
        c.  volatile solids content
        d.  BOD or COD concentration
        e.  total phosphorus concentration
        f.  heavy metals concentrations
        g.  etc.

    2.   Performance characteristics

        a.  yield
        b.  volatile solids reduction
        c.  volume reduction
        d.  cake  thickness
        e.  etc.

F.   Diagrams  of hydraulic and materials balances (excluding
    screening, degritting, and pumping)

    1.   Partition of loading between outputs

                             151

-------
            a.   TS
            b.   sludge  solids
            c.   VS
            d.   BOD  or  COD
            e.   total-P
            f.   heavy metals

V.   OPERATIONAL  PROBLEMS  ATTRIBUTABLE  TO THE  PRODUCTION OF
    CHEMICAL SLUDGE

    A.   Impact  on  wastewater  treatment operations

        1,   Changes  in  process  performance  variables
            a,
            b
clarifiers
activated sludge or trickling  filter  units

1)  input and output characteristics  of
    all  units
                    a)
                    b)
                    c)
                    d
                    e
                    f
        SS concentration
        BOD or COD  concentration
        VSS concentration
        total-P concentration
        heavy metals  concentration
        viruses,  etc.
        pH, alk., sol.  org.  carbon
                2)   performance  characteristics

                    a)   settleabil ity  or  sludge  volume
                        index  of sludge
                    b)   #SS  produced/#BOD  removed  in
                        activated  sludge  (or TF)
                    c)   #/day  BOD  removed  in activated
                        sludge  (or TF)

        2.   Changes  in  hydraulic and materials balances  of
            primary  and  secondary  treatment units

            a.   wastewater flow
            b.   SS
            c.   BOD  or  COD
            d.   VSS
            e.   others  =  P,  pH,  alk. (all  forms),  hardness
                (all  forms)

   B.   Additional sludge quantities,  including  sidestreams

        1.   From clarifiers
        2.   From thickeners
        3.   From conditioners
                           152

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4.  From stabilizers
5.  From dewatering unit
6.  From reduction unit
7.  To disposal
8.  To sidestreams

    a.  additional mass of dry sludge

        1)  observed mass
        2)  calculated mass

    b.  additional volume of liquid sludge

        1)  observed volume

Impact on sludge treatment and disposal operations

1.  Impact on  facilities

    a.  uninitiated changes in process operating
        variables

        1)  flow rates
        2)  loading rates
        3)  retention times
        4}  etc.

    b.  impact on physical condition and functioning
        of equipment, including functioning of new
        equipment

        1)  corrosion
        2)  grit
        3)  pH
        4)  mixing
        5   foaming
        6   wear
        7   mechanical failure

2.  Impact on  performance

    a.  changes in process performance variables

        1)  input and output characteristics

            a)  TS, VS, sludge solids, SS (sidestreams)
            b)  BOD, COD
            c)  etc.

        2)  performance characteristics
             )  yield
             )  volume reduction
                       153

-------
            c)  volatile solids reduction
            d)  etc.

    b.  changes in hydraulic and materials  balances

        1)   partition of loading between outputs

            a )  TS, VS, sludge sol ids
            b )  BOD or COD
            c )  etc.

Problem resolution

1.  Personnel-initiated changes in  machine  and process
    operating variables

    a.  machine temperature, pressure, etc.
    b.  chemical addition
    c.  fuel consumption, etc.
    d.  run len.gths
    e.  etc.

2.  New construction  and equipment  required

    a.  type, space required, etc.
    b.  installation  time, safety measures,  etc.

3.  New operation and maintenance activities

    a.  cleaning, adjustments, breakdowns,  etc.
    b.  setting levels, monitoring, starting and
        shutting off, keeping records
    c.  amount of labor involved
    d.  new personnel required

Impact on meeting external constraints restricting
sludge treatment and  disposal operations

1.  Environmental constraints

    a.  moisture content of land-filled sludge;
        heavy metal content of agricultural  land-
        applied sludge; etc.

2.  Economic constraints

    a.  budget limitations; specific chemical or fuel
        costs, etc.

3.  Land and materials availability constraints

    a.  land for disposal; industrial by-product
        chemicals, etc.

                          154

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         4.   Social-acceptability constraints

             a.   putrefaction odor control;  disposal  site
                 location,  etc.

VI.   OPERATIONAL COSTS OF SLUDGE TREATMENT/DISPOSAL

     A.   Operations

         1.   Phosphorus removal  operations

             a.   procuring  chemicals
             b.   storing chemicals
             c.   mixing chemicals
             d.   pumping chemicals
             e.   distribution of chemicals
             f.   addition of chemicals

         2.   Wastewater treatment operations

             a.   flocculators and clarifiers
             b.   activated  sludge or trickling  filter units
             c.   return sludge pumping

         3.   Sludge treatment/disposal operations

             a.   storage (including sludge storage in clarifiers)
             b.   screening, degritting
             c.   pumping (including sludge and  sidestream  recir-
                 culation)
             d.   blending
             e.   thickening
             f.   conditioning
             g.   stabilizing
             h.   dewatering
             i.   reduction
             j.   disposal
             k.   sidestream treatment

     B.   Costs

         1.   Operating and  maintenance costs

             a.   labor costs

                 1 }   operation and supervision
                 2)   maintenance

             b.   supply costs (costs at the site)

                 1)   chemicals
                               155

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            a)  solids
            b)  liquids
            c)  gases

        2)  water
        3)  maintenance supplies


    c.  energy costs  (costs at the site)

        1 )  natural gas
        2)  electricity
        3)  fuel oil

    d.  outside servicing and contracting

            service and maintenance of equipment
            residual  disposal

    e.  overhead

2.  Investment costs

    a.  construction

        1 )  site preparation
        2 )  structures
        3 )  buildings

    b.  mechanical  equipment on an installed basis
    c.  piping on an  installed basis
    d.  electrical  on an installed basis
    e.  instrumentation on an installed basis
    f.  engineering design
    g.  land

Cost variables

1.  Items or categories of labor, supplies, energy, and
    services utilized

2.  Unit costs of labor, supply, energy, and service
    i terns

3.  Amounts of labor, supply, energy, and service items
    used

4.  Components of outside servicing and contracting,
    overhead,  engineering design, construction, and land
    costs

-------
5.   Cost break-down by components of outside  servicing
    and contracting, overhead,  engineering  design,
    construction, and land costs

6.   Description of mechanical  equipment,  instrumentation,
    piping, electrical, construction, and land  items.
                         157

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                       COST MODULE
Investment Costs
1.  Land:  value/acre In general locality $	
    Treatment system acres 	 $/acre 	
    Auxiliary support acres 	 $/acre 	
    (includes utilities,
    offices, roads, etc.)
    Total investment (excluding land and support buildings)
    and year of module installation:
    $	       Year	
    Installation time (excluding design) 	months,
    useful life 	, salvage value (items)
    	 $ 	
    Structures (steel, dikes, slabs): $ 	
    	  $ 	
    	  $ 	
          	         $	
5.  Piping and-valves (type, length,
    size):                            $
    	  $
    	  $
    	  $
6.  Mechanical equipment (type, size): $
    	  $
    	  $
    	  $
7.  Electrical system:                $
    	  $
    	  $
                          158

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    Cost  Module  (Continued)

    8.   Instrumentation (type):                 $
       	  $
       	  $
    9.   Support (enclosures, access):           $
       	  $
       	  $
   10.   Engineering design cost:               $
   11.   Legal  and administrative cost:          $
   12.   How was system financed? 	
   13.   Was module individual or part of a larger- installation?
B.   Operation and Maintenance Costs for 19_
    1.   Days per year of operation 	
    2.   Operation assumptions (flow or activity/day) 	
    3.   Labor requirements:
        Category                Hrs/day             $/hr
      a.	            	
      b.		            	
      c.	        	            	
                              159

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 Cost Module  (Continued)

 4.  Energy requirements:
     Electricity       KWH/day 	, $/KWH 	
     Fuel         (unit)	/day, $/unit 	
 5.  Chemical costs
     Type 	 $/unit 	 as _
     Type 	 $/unit 	 as _
     Type 	 $/unit 	 as _
 6.  Other supplies (type)
     	 $/unit
 7.  Maintenance (labor and parts)            $/year
 8.  Overhead (administration)
     Percent attributed to module 	 $/year
 9.  Residual disposal
        Transportation 	 $/unit
        Disposal       	 $/unit
10.  Laboratory or analysis costs (type)
     	 $/unit
                             160

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                           APPENDIX C

                          CASE STUDIES


INTRODUCTION TO CASE STUDIES

     Nine case study sites were selected which were rated rela-
tively high on the basis of completeness of historical operating
data, cooperation of plant personnel, a history of problem-solving
and innovation at the plant, performance of dewatering devices,
and potential for demonstrating the impacts of phosphorus removal
on sludge.  The plants were also chosen to represent a variety of
possibilities with respect to the following factors:

        Plant size
        Plant type
        Phosphorus removal chemical(s)
        Point(s) of .chemical addition
        Point of combination of chemical-laden and other sludges
        Sludge treatment and disposal methods.

     Table C-l presents a description of the nine plants with
respect to these factors.

CASE STUDY C:  SOUTH BEND, INDIANA

Introduction

     The South Bend Wastewater Treatment Plant adopted tertiary
treatment with lime in 1974 in anticipation of stricter Indiana
effluent regulations covering BOD, SS, and dissolved oxygen.
The existing secondary treatment plant was found incapable of
meeting the anticipated effluent requirements without consider-
able enlargement of plant capacity.  An upflow clarifier system
was installed to provide the tertiary treatment because it per-
mits effective polishing of the effluent to remove BOD and SS as
well as phosphorus.  If phosphorus removal alone had been the
objective, tertiary treatment with lime probably would not have
been chosen.  While the tertiary facilities were under construc-
tion, a study by Tenech, a wastewater engineering consulting firm
for the city of South Bend, indicated that Time should not be
used because of the high cost and the huge amounts of sludge
which would be generated - an estimated 907 t (100 tons)/day.


                               161

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O»
ro
                                  TABLE C-l.   DESCRIPTION  OF  CASE  STUDY SITES
                                     ACCORDING TO  PLANT  SELECTION  FACTORS

Plant Size
Plant Type


Phosphorus
Removal Chemi-
cal(s)
Point(s) of
Chemical
Addition
Point of
Combination
of Chemical -
Laden and
Other Sludges
Sludge Treat-
ment and Dis-
posal Methods







South Bend
42.0 mgd
Step Aera-
tion Acti-
vated Sludge
Fed,, Poly-
mer

Tertiary


Anaerobic
Digester



Gravity
Thickener,
Anaerobic
Digester,
Air Dry-
Ing on
Land .Non-
commercial
Fertilizer

Sheboygan
10.5 mgd
Trickling
Filter

Fed,, Poly-
mer

Secondary


Gravi ty
Thickener



Gravity
Thickener,
Vacuum Fil-
ter, Flu-
Hized Bed
Incinerator




Coldwater
2.4 mgd
Trickling
Filter

Fed,, Poly-
mer J

Primary


Before Pri-
mary Clari-
fier


Anaerobic
Digester,
Drying Beds,
Dump site






Midland
6.5 mgd
Trickling
Filter

Fed,, Poly-
mer

Primary


Before Pri-
mary Clari-
fier


Thermal Con-
ditioner,
Vacuum Fil-
ter, Sani-
tary Land-
fill, Com-
posting,
Non-com-
mercial Soil
Conditioner
Port Huron
11.6 mgd
Activated
Sludge

Al2(S04)3.
Polymer

Secondary


Before Gra-
vity Thick-
ener


Gravity
Thickener,
Centrifuge,
Fluidized
Bed Incin-
erator, Ash
Thickener,
Ash Vacuum
Filter

Pontiac
25.5 mgd
Activated
Sludge

Fed,, Poly-
mer

Primary


Before Pri-
mary Clarifier



Anerobic
Digester,
Vacuum Fil-
ter, Incin-
erator





Lakewood
13.4 mgd
Activated
Sludge

A12(S04)3

Secondary


Before
Gravity
Thickener


Anaerobic
Digester,
Flash Dryer,
Drying Beds.
Non-commer-
cial Soil
Conditioner,
Liquid Sludge
Hauling

Mentor
5.3 mgd
Activated
Sludge

A12(S04)3

Secondary


Sludges Not
Combined



Aerobic Di-
gester, Dual
Cell Gravity
Concentrator,
Agricultural
Land Applica-
tion



Brookfield
2.4 mgd
Contact Stabil-
ization Acti-
vated Sludge
FeS04

Secondary


Before Primary
Clarifier, In
Aerobic Digester,
or Before Chemi-
cal Conditioning
Pressure Filter,
Multiple Hearth
Incinerator








-------
When the two upflow clarifiers were put into operation, one was
started on lime and the other on ferric chloride for comparison.
Tenech's predictions were borne out during the 18-mo qualifica-
tion period before the U.S. Environmental Protection Agency
approved the plant's performance and the city of South Bend's
control.  The plant immediately converted to full-scale operation
with ferric chloride.  By converting to ferric the savings in
chemical costs amount to $720,000.00/yr.  The following report
will discuss the dramatic differences in sludge generation rates'
and sludge processing with lime and with ferric chloride.

      South  Bend  is  a  well-managed  plant  with  relatively  few  oper-
 ational  difficulties.   It  receives  no  abnormal  industrial  wastes
 because  there  is  a  minimal amount  of  industry now  remaining  in
 the community.   Studebaker Motor  Company  quit its  South  Bend
 operations  in  the  early  1960's.   A  brewery  also closed down  about
 3  yr  ago,  reducing  the  plant  influent  BOD from  approximately  150
 to the present 70  to  80  mg/t.   Suspended  solids were  similarly
 reduced  to  about  80 mg/t and  digester  gas production  decreased
 somewhat.

      There  are no  dramatic seasonal fluctuations  in flow  or  waste
 loading.   The  major problem,  because  of  combined  sewers  in the
 city,  is  tremendous hydraulic  variation  due  to  infiltration.   The
 impact of  high storm  flows is  that  the  plant  influent  is  very
 dilute in  BOD  and  SS,  and  it  contains  a  great deal  of  grit and
 bitumen  washed off  the  streets.   During  these periods, the TS
 content  of  the sludge  pumped  from  the  primary clarifiers  is  low,
 but subsequent thickening  gets  the  solids concentration  back  to
 4  or  5 percent before  the  sludge  is pumped  to the  digester.   A
 primary  sludge degritter helps  reduce  the grit  load on the diges-
 ters.   Even  so,  it  is  necessary to  clean  one  of the digesters
 each  year  on a rotating  basis.

 History

      A description  of  plant modifications affecting sludge pro-
 duction  and  characteristics follows:

      1956  -  The  original primary  and  secondary  treatment plants
             were  constructed  to handle 90,840 m3/day  (24 mgd)
             average dry  weather flow.

      1974  -  The  facilities were modified and expanded to handle
             181,680 m3/day  (48 mgd) average dry weather  flow.
             The  new equipment consisted  of:

                  An automated  mechanical  bar screen
                  A  primary sludge  gravity thickener
                  A  sludge  degritter
                  Three  waste-activated sludge centrifuges
                  One  additional aeration tank


                               163

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               • Two additional 6,586 m3 (1.74 mil gal) secondary
                 clarifiers
               • A chemical sludge gravity thickener
               • Three lime sludge centrifuges
               • Two upflow clarifier tertiary treatment units.

     April
     1975 -  Phosphorus removal was initiated with lime addition
             to one upflow clarifer and ferric and polymer addi-
             tion to the other.  The chemical sludges were com-
             bined, gravity thickened, centrifuged, and trucked
             to a storage area.

     Sept.
     1975 -  The use of the waste-activated sludge centrifuges was
             discontinued.  Waste-activated sludge was recircu-
             lated to the wet well ahead of primary clarifiers.

             The use of the lime sludge centrifuges was discontin-
             ued.  Chemical sludge was pumped to the sludge
             lagoons 4 km (2.5 mi) from the plant.

     Oct.
     1976 -  Lime addition for phosphorus removal was discontinued.
             Ferric chloride and polymer were added to both of the
             upflow clarifiers.  The chemical sludge was gravity-
             thickened and fed to the anaerobic digester.

Chemical Addition for Phosphorus Removal'

Lime Addition--

     Approximately 36.3 t/day (40 tons/day) lime as CaO were
added to remove phosphorus in one of the upflow clarifiers.  The
average dosage was approximately 523 mg/a.

     The lime dosage was regulated by checking the pH of the
water in the upflow clarifiers.  The pH was maintained between
9.6 and 10.2.  The ideal pH was considered to be 9.8.  Above pH
10.2, the generation of sludge was dramatically increased due to
the co-precipitation of magnesium hydroxide.  Below pH 9.6, poorer
phosphorus removal was achieved.

Ferric  Chloride and Polymer Addition--

     Liquid ferric chloride (37 percent FeCK) containing approx-
imately 1.1  t/day (1.2 tons/day) Feds, and T7 kg/day  (38 Ib/day)
polymer are added to remove phosphorus in each clarifier.  The
average dosages are approximately 16 mg/£ Fe Cls and 0.2 mg/£
polymer.  The chemical  feed rate is selected to achieve 85 per-
cent reduction of the phosphorus concentration entering the
plant.   The feed rate is controlled by manual adjustment of the
feed pump settings to compensate for changes in influent flow
rate.
                               164

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General  Description of Wastewater Treatment Operations Affecting
SIudge

      Figure C-l presents a general treatment plant flow diagram.
Design parameters  for the clarifiers and aeration basins are pre-
sented in Table C-2.  Table C-3 presents a summary of 1976 influ-
ent flow characteristics and SS, BOD, and total phosphorus remov-
als during primary, secondary, and tertiary treatments.

      The raw wastewater is degritted by gravity in non-aerated
grit  chambers.  Degritting reduces the grit load on the anaerobic
digesters, increasing the volatile solids concentration of the
digester feed and  preventing grit accumulation in the sides and
corners of the digesters.

      Primary treatment removes only about 39 percent of the SS
and 22 percent of  the BOD entering the plant.  The eight rectan-
gular primary tanks have chain-type straight line collector arms
for scraping the sludge into the end hoppers.  The withdrawal of
primary sludge from the hoppers is an automatic operation.  Each
of the eight clarifiers is pumped in series for three minutes in
a continuous cycle.

      Suspended solids and BOD removals during secondary treatment
averaged 82 and 80 percent, respectively, in 1976.  According to
the plant chemist,  this high degree of treatment is due to a low
food-to-microorganism ratio in the mixed liquor.  The activated
sludge microorganisms are in a near-starvation phase so that they
efficiently degrade the volatile material in the wastewater.

      The five octagonal or circular secondary clarifiers have
revolving nozzle-type chain belt collector arms which continuously
scrape the sludge  to the center hoppers.  Sludge is continuously
pumped from each hopper and either wasted to the wet well or
returned to the aeration tanks.  The amount of sludge which is
returned averages  37 percent of the flow entering the plant.

      Figure C-2 shows the configuration of the two 61-m (200-ft)
diameter tertiary  upflow clarifiers.  Flow is directed from the
secondary clarifiers via a 196-cm (77-in) line to a pair of gates
which divert the flow into two parallel clarifiers.  At this
point, ferric chloride is dosed to serve as a flocculant.  Flow
entry to the clarifier is obtained through a 4.9-m (16-ft) dia-
meter upward flow  cone in the bottom of the center of each clar-
ifier.  Here a polymer is mixed into the upward flow and agitated
by an eight-bladed propeller.   The solids then gain entry into
the flocculation zone which is surrounded by a shroud which
serves as a baffle.  The clarifier is designed so that the water
recirculates within the shroud approximately eight times before
it reaches  the velocity at which it flows out from under it and
down  through the sludge blanket.   As it flows through the sludge
blanket,  the flocculated solids are captured.  The clarified
water moves to the surface and exists over two concentric weirs.

                               165

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                                                                                   ST. JOSEPH
                                                                                    RIVER
CJ1
                  PARK
                  LAND
         Figure C-1 .   South Bend, Indiana, wastewater treatment  plant  flow  diagram.

-------
          TABLE C-2.  WASTEWATER TREATMENT PROCESS DESIGN PARAMETERS,
                              SOUTH BEND, INDIANA
               Unit
               Description
Plant Design Flow Capacity
Primary Clarifiers (8)
Aeration Tanks (4)
Secondary Clarifiers (5)
Upflow Clarifiers (2)
0.18 mil m3/day (48 mgd) Avg.  dry weather
0.30 mil m3/day (80 mgd) Avg.  wet weather

Shape:  Rectangular
Size:  12.2 m x 36.6 m x 2.9 m SWD
       (40 ft x 120 ft x 9.5 ft SWD)  ,
Total Capacity:  10,214 m3 (364,800 ft3)
Detention:  82 min @ Avg. dry weather flow

Type:  Step Aeration
Shape:  Four Bay Rectangular Tanks
Size:  Each Bay  76.3 m x 7.3 m x 3.7 m SWD
        (250 ft x 24 ft x 12 ft SWD)
Total Capacity:  32,260 m3 (1,152,000 ft3)
Air Blower Capacity:  1,896 m3/min
                      (67,730 ft3/min)

Shapes:  3 Octagonal, 2 Circular
Sizes:  34.3 m x 3.7 m SWD (112.5 ft x
        12 ft SWD) Octagonal Tanks;
        44.2 m x 4.3 m SWD (145 ft x
        14 ft SWD) Circular Tanks
Total Capacity:  24,640 m3 (6.51 mil gal)
Detention:  192 min @ Avg. dry weather
            flow

Shape:  Circular
Size:  61.0 m x 4.9 m SWD (200 ft x
       16 ft SWD)
Total Surface Area:  5.840 m2 (62,840 ft2)
Overflow Rate:  31.2 m3/day/m2
                (766 gal/day/ft2) @
                Avg. dry weather flow
Detention:  3.76 hr @ Avg. dry weather
            flow
Total Capacity:  28,460m3  (7.52 mil gal)
                                     167

-------
   TABLE C-3.  SUMMARY OF  1976  WASTEWATER  CHARACTERISTICS AND
         TREATMENT  PERFORMANCE,  SOUTH  BEND,  INDIANA
Population
   Connected                                   150,000
   Equivalent BOD                              156,643
   Equivalent suspended solids                 152,330

Wastewater Flow
   mil m3/day (mgd)                            0.17  (44.9)
   mil m3 treated                              61.9  (16,378)
   m3 (gallons) per capita daily flow          1.13  (299)

Suspended Solids
   Influent, mg/i                              82
   Primary effluent, mg/£                      49
   Secondary effluent, mg/£                    9
   Final effluent                              8
   % removal in primary                        39
   % removal in secondary                      82
   % removal in tertiary                       17
   % removal overall                           90

BOD5
   Influent, mg/l                              71
   Primary effluent, mg/£                      56
   Secondary effluent, mg/£                    10
   Final effluent, mg/£                        2
   % removal in primary                        22
   % removal in secondary                      80
   % removal in tertiary                       79
   % removal overall                           97

Total Phosphorus
   Influent, mg/£                              2.29
   Primary effluent, mg/£                      2.19
   Secondary effluent, mg/£                    0.93
   Secondary effluent, kg/day (Ib/day)         158  (349)
   Final effluent, mg/£                         0.24
   Final effluent, kg/day (Ib/day)             41 (90)
   %  removal  in tertiary                       74
   %  removal  overall                           88
                               168

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vo
                  ACID
                                           LIME OR POLYMER
            SECONDARY
            EFFLUENT
                                                                                DISCHARGE
                                                                                TO  CHLORINA-
                                                                                TION  AND
                                                                                RIVER
             SKIMMERS
             FERRIC CHLORIDE
                                                                     SLUDGE
            Figure C-2.  Tertiary upflow clarifier configuration, South Bend,  Indiana.

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     When lime is used for phosphorus removal,  it is  added
directly to the propeller mixing zone in the upflow cone of the
clarifier.  No polymer is needed.   In contrast,  polymer is neces-
sary with ferric chloride to produce an ideally  settling floe.
The 244-cm (96-in) line leading to the center well  acts as a
long plug-flow reactor in which the ferric floe  can develop to
the correct size before it reaches the upflow cone.  The low-velo-
city, large propel 1ermixer at that point can disrupt  the floe or,
with the addition of the polymer at that point,  enhance the set-
tling characteristics of the floe.  The polymer  is  also necessary
since without it temperature gradients produced  by  the sun passing
over the clarifier during the day produce vertical  water circula-
tion and floe escapes.  The polymer tends to weigh  down the floe
and prevent resulting instability of the sludge  blanket.

     The plant experiences some problems with the upflow clari-
fiers during periods of storm flow.  To compensate  for flow var-
iations, the operator must regulate the speed of the  variable-
speed propeller mixer in the upflow cone.  Speeding up the pro-
peller tends to circulate the sludge solids in  a tight circle
with the shroud and prevents the velocity vectors from going out-
ward.

     Operational parameters for the upflow clarifiers during fer-
ric and polymer addition have been determined by experience.  An
empirically determined relation between the i>5  concentration in
the shroud and clarifier performance forms the  basis  for deciding
when to pump sludge.  The SS concentration is sampled once each
day and maintained between 1,500 and 2,500 ppm.   At greater than
2,500 ppm, sludge is pumped out of the center donut-like collec-
tion well.  At less  than 1,500 ppm, pumping is  stopped and sludge
allowed to accumulate.  When the concentration  goes as high as
4,000 ppm, the sludge blanket is too high and floe  is lost over
the weirs.  When the concentration falls below  1,500  ppm, the
sludge blanket is too thin and poor phosphorus  removal results.
Because of the low capacity of the sludge pumps, pumping is con-
tinuous from one clarifier or the other.

     Clarifier operation with lime addition differs from operatior
with ferric in that sludge is continuously pumped  from  each clar-
ifier.  An efficient sludge pumping system is necessary for the
heavy lime sludge -- sludge lines should have few  elbows.   In
addition, when lime is used, reduction of the final effluent pH
below 9.0 is necessary, requiring the addition of  approximately
9.5 mj (2,500 gal)/day sulfuric acid to the effluent weir.  On
the other hand, because of the high pH produced with lime,  no
chlorine disinfection is necessary.

Detailed Description of Sludge Treatment and Disposal Operations

     Table C-4 presents design parameters for the  major sludge
treatment steps at South Bend.  The treatment and  disposal  of
theJime/iron sludge produced at the plant in the  past  and  the

                               170

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         TABLE C-4.  SLUDGE TREATMENT  PROCESS  DESIGN  PARAMETERS,
                           SOUTH  BEND,  INDIANA
               Unit
               Description
Primary Sludge Gravity Thickener (1)
Waste-Activated Sludge
 Centrifuges (3)
Anaerobic Digestion Tanks (4)
Chemical Sludge Gravity
 Thickener (1)
Lime Sludge Centrifuges (3)
 Shape:   Circular
 Size:   18.3  m x 3.0 m  SWD  (60  ft x
        10  ft SWD)
 Volume:  792 m3 (28,280  ft3)
 Surface Area:  263 m2  (2.828 ft2)
 Solids  Loading:  28 kg/m2/day
                 (5.7  Ib/fWday)

 Type:   Bird  Continuous Scroll  Solid
        Bowl
 Solids  Feed  Rate:  400 kg/hr (882 Ib/hr)
 Hydraulic  Feed Rate:   276  £/min
                       (73  gal/min)
 Centrate BOD5: 3 to 8 mg/l
 Centrate SS:  6.7 mg/£

 Type:   2-Primary, 2-Secondary
 Shape:   33.5 m x 7.8 m SWD + 2.7 m cone
         (110 ft x 25.5 ft  SWD  + 9 ft
         cone)
 Total Capacity:  30,280  m3 (8  mil gal)
 Gas  Storage  Capacity:  7,000 m3 @
                       28,124  kg/m2
                       (250,000 ft3 @
                       40  ps)
 Volatile Loading Rate:  0.6 kg VS/m-Vday
                         (0.037 Ib
                         VS/ft3/day)
 Shape:   Circular
 Size:   30.5 m x 3.0 m SWD
        (100 ft x 10 ft SWD)
 Surface Area:  730 m2 (7,854 ft2)
 Volume:  2,200 m3 (78,540 ft3)
 Solids  Loading:  75.2 kg/m2/day
                  (15.4 Ib/ft2/day)

 Type:   Bird Continuous Scroll Solid
        Bowl
 Hydraulic Feed Rate:  125£/min
	(33 gal/min)
                                     171

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 iron sludge presently produced are described below.  It should
 be recalled that the chemical sludges have always been gravity-
 thickened separately from the plant's organic sludge.  Gravity-
 thickened sludge is presently anaerobically digested along with
 the organic sludges normally digested.  The lime/iron sludge
 which was produced in the past, however, was never introduced
 into the digesters, but was centrifuged and trucked to a storage
 area.

     A brief description of the procedures for handling the
 organic as well as the chemical sludges follows so that the
 digester performance can be related to sludge characteristics.
 As previously mentioned, waste-activated sludge is recirculated
 to the wet well ahead of the primary clarifiers.  An estimated
 55 percent of the solids removed from the primary clarifiers is
 derived from the recirculated secondary sludge.  This percentage
 is rather high because of the high SS removal efficiency of the
 plant's secondary relative to its primary treatment operation.

 Degritting--

     Sludge from the primary clarifiers is pumped at less than
 one percent TS to allow effective degritting.  Sludge degritting
 reduces the grit load on the anaerobic digesters, thus increasing
 the volatile solids concentration of the digester feed and pre-
 venting grit accumulation in the sides and corners of the diges-
 ters.  The VS fraction of TS in the digester feed rose from
 approximately 62 percent to 65.5 percent of TS because of sludge
 degritting.  A slight increase in digester gas production may
 have resulted.

 Organic Sludge Thickening--

     Degritted sludge at less than one percent TS is pumped to
 the gravity thickener.  The gravity thickening step raises the
 TS concentration of the sludge before it is pumped to the diges-
 ters, so that digester space is not wasted and large amounts of
 digester supernatant are not formed and pumped back to the wet
 well.  The average TS concentration of the thickened sludge
 which was pumped to the digesters was 4.7 percent in 1976.  The
 VS fraction of TS averaged 67.5 percent.  On the average, approx-
 imately 267 m^/day (70,530 gal/day) thickened sludge were pumped
 from the thickener to tlie digesters in 1976.  The sludge  is con-
 tinuously drawn off at 378 to 568 &/min  (100 to 150 gal/min).

 Chemical Sludge Thickening--

     The single chemical sludge gravity thickener is continuously
fed with iron sludge at approximately 0.16 m3/min  (43 gal/min).
When one of the tertiary clarifiers was operated with lime,
sludge feed to the thickener was continuous at 0.89 m3/min  (234
gal/min).   The thickened iron sludge  is removed from the  hopper


                               172

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at the bottom of the thickener once every 3 days.  Pumping lasts
for 7.8  hr  at  0.38 m^/min (TOO gal/min).  Formerly,  the lime/
iron sludge was pumped to the three lime centrifuges every day at a
total rate of 0.48 nH/day (126 gal/min) for 16 hr/day.   A com-
parison of the amounts of raw and thickened sludge produced with
iron and lime/iron is presented in Table C-5.

     Table C-5 reveals that the mass of raw lime sludge produced
by a single clarifier was 38 times the mass of iron sludge pro-
duced by both clarifiers.  The TS concentration of the  raw iron
sludge is 1.0 percent, while that of the raw lime sludge was 4.0
percent.  The combined lime/iron sludge was thickened to 10.2
percent TS.   The amount of thickened iron sludge produced was
59 m3/day (15,570 gal/day) by volume and 2.36  t/day (2-6 tons/day)
by weight.  In contrast, it is estimated that  the amount of lime
sludge which would have been produced if lime  had been  used in
both tertiary clarifiers would be approximately 833 m3/day
(224,000 gal/day) by volume and 907 t/day (100 tons/day) by
weight.

Anaerobic Digestion--
     There are four 33.5-m (110-ft)-diameter anaerobic digestion
tanks on-site with floating covers.  The operation of the diaes-
tion tanks follows the pattern shown in Figure C-3.
                              THICKENED
                              CHEMICAL
                               SLUDGE
             THICKENED
              ORGANIC
              SLUDGE
DIGESTED
 SLUDGE
  Figure C-3.   Flow pattern for South Bend anaerobic digester.


     Only the  first two digestion tanks (No.  1  and No.  3)  are
heated and mixed.   Mixing is accomplished with  the Carter  gas
recirculation  system.   Each of the two digesters contains  six
Carter Aero-Hydraulic  guns.  Digester gas is  pumped down vertical
tubes to the bases of  the guns, creating gas  bubbles at the bot-
tom which lift the sludge to the top of the tank and create the
circulatory patterns in the tank.  In the past, the plant  had
experienced severe upsets and souring of the  digesters  because
of inadequate  mixing.   With the installation  of the Carter Sys-
tem,  operation has been excellent and there have been no upsets.
                               173

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        TABLE C-5.  CHEMICAL  SLUDGE  PRODUCTION AND GRAVITY THICKENING,
                             SOUTH BEND,  INDIANA

WASTEWATER TREATED
0
mil m /day
(mgd)
RAW SLUDGE PRODUCTION
m /day
(gal/day)
% TS, dry weight
•2
kg TS/mil m wastewater treated
(Ib/MG)
THICKENED SLUDGE PRODUCTION
m /day
(gal /day)
% TS, dry weight
VS, % of TS
kg TS/day
(Ib/day)
kg VS/day
(Ib/day)
t TS/day
(tons/day)
Iron Sludge
0.14
(36.7)
236
(62,280)
1.0
16,900
(141)
59
(15,570)
4.0
35
2,358
(5,194)
825
(1,818)
2.36
(2.6)
Lime Sludge
0.07
(18.35)
1,129
(298,200)
4.0
649,858
(5,420)
N/A
N/A
N/A
N/A
N/A
N/A
Lime/Iron Sludgi
0.14
(36.7)
N/A
N/A
N/A
454
(120,000)
10.2
11
46,345
(102,081)
5,094
(11,220)
46.26
(51) '
Note:   N/A = Not Available
                                    174

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     Digester heating is accomplished in two ways.   Sludge from
the No.  1  and No.  3 digesters is pumped through a heat exchange
system.   The boiler for the heat exchange system is run on methane
digester gas.  There is also a sludge preheating system of the
heat-exchange type.  Sludge from digester No. 1 is  pumped to the
preheating unit.  The partially digested sludge mixes with the
primary plus waste-activated sludge coming from the organic
sludge gravity thickener.  The digesting sludge feeds the raw
sludge, and the mixture is heated.  The preheater utilizes heat
from cooling water coming off the plant's air compression engines,
which are also run on methane digester gas.

     Because of plant design, the thickened chemical sludge can-
not also be preheated before being pumped into the  digester.
Therefore, it is at a lower temperature than the organic sludge
and is capable of  suppressing the temperature in the digester
into which it is fed.  This could result in a loss  of digester
gas production.  Since most of the gas production takes place in
the No. 1 digester, the chemical sludge is fed into the No. 3
digester.  The result has been a 4°to 5° loss in temperature in
this digester, but a decrease in total gas production has been
avoided.

     Intermittent  pumping of organic sludge to the  No. 1 digester
occurs for 12 hr/day (2 out of every 4 hr). 7 days/wk.  The pri-
mary digester receives an average of 267 m3/day (70,530 gal/day).
It receives 12,550 kg TS/day (27,650 Ib TS/day) and 8,470 kg MS/
day (18,660 Ib VS/day).  Pumping of iron sludge to  the No. 3
digester occurs for 7.8 hr every third day.  The average amount
pumped is 59 m3/day (15,570 gal/day).  This contains approximately
2,358 kg (5,194 Ib) of TS and 825 kg (1,818 Ib) of  VS.  Some
degradation of the VS contained in the iron sludge  is occurring,
as evidenced by the increase in digester gas production which has
occurred.  The level of digester gas production before and during
addition of the iron sludge to the digester is shown in Table C-6.
Iron sludge was first fed to the digester on 10/14/76.  During
iron sludge addition, digester gas production was higher by about
0.11 m3 gas/kg VS  destroyed (1.87 ft3/lb VS).  The  level of
digester gas production is still low compared to the nationwide
average of 0.86 to 1.11 m3 gas/kg VS destroyed (14  to 18 ft3 gas/
Ib VS destroyed).  It is possible that the waste-activated sludge
has been so severely degraded as the result of the  low food to
microorganism ratio in the aeration basins that 1ittle volatile
matter remains, causing the low gas production.

     Some time ago, a fluoride dye tracer study of the digester
was performed to calculate the actual liquid retention time based
on an input of 378.5 m3/day (100,000 gal/day).  Instead of the
expected 20 days,  the dye tracer study indicated a  shorter deten-
tion time of approximately 15 days.
                                175

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TABLE C-6.
ANAEROBIC DIGESTER GAS  PRODUCTION
 SOUTH BEND, INDIANA
Month/
Year
1/75
2/75
3/75
4/75
5/75
6/75
7/75
8/75
9/75
10/75
11/75
12/75
1/76
2/76
3/76
4/76
5/76
6/76
7/76
8/76
9/76
10/76
11/76
12/76
1/77
2/77
3/77
1000 m3
gas/day
5.26
5.12
5.12
5.10
5.66
4.79
4.00
3.70
4.68
5.18
5.29
4.73
4.48
5.54
4.84
5.18
4.56
5.15
4.62
4.23
5.26
5.40
5.40
5.71
5.38
5.80
5.40
1000 ft3
gas/day
188
183
183
182
202
171
143
132
167
185
189
169
160
198
173
185
163
184
165
151
188
193
193
204
192
207
193
m gas/kg
VS destroyed
0.54
0.45
0.49
0.44
0.53
0.52
0.47
0.42
0.57
0.60
0.59
0.49
0.55
0.58
0.57
0.60
0.57
0.59
0.56
0.50
0.59
0.69
0.67
0.73
0.73
0.67
0.61
ft3 gas/lb
VS destroyed
8.7
7.3
7.9
7.1
8.6
8.5
7.7
6.9
9.3
9.8
9.6
7.9
9.0
9.4
9.2
9.8
9.3
9.5
9.1
8.2
9.6
11 .2
10.9
11.9
11.8
10.9
9.9
                     176

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     Sludge is withdrawn from the No. 2 and 4 digestion tanks
approximately every three days as space is needed in the No.  1
and 3 tanks.   Sludge is removed from the No. 2 and 4 tanks
through conventional bottom outlets.  Withdrawal  from the No. 1
and 3 tanks is through "spider drawoffs," three pipes near the
bottom which extend toward the center of the tank and branch at
the ends into three arms.  The spider which is used to draw off
sludge is  rotated each time.

     The digested sludge removed from the digester averages 5.5
percent TS with a VS fraction of 47.2 percent.  Iron sludge addi-
tion had no effect  on the TS and VS  concentrations of the digested
sludge.  The average volume of sludge removed from the digester
was 118 m3/day  (31,300 gal/day) before  iron siudge .addition and
160 m3/day (42,200  gal/day) during  iron sludge addition.  So the
volume of  digested  sludge increased  by  42 m3/day (10,900 gal/day).
During the same period,  the volume  of supernatant increased by
8  m3/day (2,100 gal/day).

Disposal of  Digested  Sludge--

     Digested sludge  is  pumped through  a 15-cm (6-in) steel pipe-
line from  the digester directly to  a "sludge farm" which is 4 km
(25 mi) away.   The  sludge is pumped  with a  100-HP, 126-ft pumping
head,  centrifugal pump.  At the farm, the sludge can be routed
to any one of seven different fields of varying size.  The diked
fields are filled with approximately 76 cm  (30 in) of sludge.
Approximately 757 m3  (200,000 gal)  of sludge are pumped to a
field  at any one time.   It takes approximately 2 to 3 mo to fill
a  field.   The sludge  running at 5 to 6  percent TS is allowed to
dewater on the  fields through percolation and evaporation for a
time before a No. 4230 John Deere tractor of special design mixes
up the sludge and exposes wet section to the air.  There are only
a  few  operators who are  capable of  driving  this tractor, since
the front  end has a capacity to lift up, depending on the field
conditions.  A  weight is added to the front end for better balance.
The front  wheel spread can also be  varied to achieve any width
desired.   The wheels on  the rear are specially designed cleat-
type steel wheels capable of tracking through sludge and mud.

     The 91 ac  at the site were purchased around 1967.  The
site became operational  that same year.  The fields are effec-
tively screened from the roadway by  a tract of trees approximately
0.2 mi in width.  The seven fields  are  located on the back of the
property.

     Sludge is  pumped to the fields  year round, but normally
worked with the tractor  only in the  summer.  Depending on weather
conditions and  other variables, the  sludge  fields are worked with
the John Deere  tractor to produce a  relatively dry sludge cake.
The tractor wheels work  down as far  as  30 to 38 cm (12 to 15 in)
into the soil and sludge to work it  into a  homogenous mixture.
After 18 mo,  the material is removed with a front-end pa.yloader

                               177

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and stockpiled elsewhere on the property.   Last year,  for example,
contractors removed almost all of the stockpiled sludge and used
it on various construction projects around South Bend.

     Four lagoons were originally constructed on the site for
receipt of digester wash water.  Treated effluent is used in
cleaning out the digesters.  This wash water contains  grit,
detritus and residual sludge having some BOD.  Odors from the
lagoons do not seem to be a problem.   The  No. 4 lagoon  is now
being filled in with rubbish and covered over.  Some of the
dried soil-sludge mixture produced at the  site will  be  used as
surface cover on this lagoon.

     The site supposedly has a clay layer  underneath it.   How-
ever, in an exposed section being dug out  for fill  material and
for making a  deeperfield for later sludge  filling,  there  were
0.6 to 0.9 m (2 to 3 ft) of surface soils  underlain  by  approxi-
mately 3.0 to 3.7 m (10 to 12 ft) or more  of silty  sand.   The
spreading area is part of a large meandering ancient stream or
flood plain area.

Li me/Iron Sludge Dewatering and Disposal--

     When the plant was using lime to remove phosphorus from half
of the wastewater, the thickened lime/iron sludge produced was
dewatered by centrifuges.  The thickened sludge, at  11  percent
TS, was fed to each of the three centrifuges at a rate  of 159
£/min (42 gal/miri).  Because of the large  volume of  lime/iron
sludge to be dewatered, it was necessary to run all  three cen-
trigues for approximately 16 hr/day,  7 days/wk.  If  the plant
had used lime to remove phosphorus from all of the  wastewater,
the volume of lime sludge would have been  almost doubled, and
this amount could not have been centrifuged.

     There were several problems with operation of  the  centrifuges.
The first problem has been mentioned:  the total centrifuge capa-
city was inadequate to handle all of the sludge.  The design
engineers estimated that only 27 t/day (30 tons/day) of dry
siudge TS would be produced by the two upflow clarifiers operating
with lime, while the actual production figure for both  clarifiers
is closer to 91 t (100 tons).  Other operational problems resulted
because of the poor instructions given to  the plant on  centrifuge
operation and maintenance procedures.  The heavy chemical sludge
caused breaking of shear pins, and frequent equipment overhauls
were necessary.  Maintenance costs were high during the 6-1/2 mo
that the centrifuges were in operation.

     The lime/iron sludge was centrifuged  to a cake that was  43
percent TS, and 8 percent of the solids were volatile.   The  cake
was trucked out to a storage site.  This disposal method was  not
satisfactory and was only meant to be temporary until the  plant
stopped using lime for phosphorus removal.  One of  the problems


                               178

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with this method was the spillage of lime from the truck onto
the road, discoloring the pavement.

Sludge Treatment and Disposal Costs

     The best cost data  available from  plant record  is  related
to anaerobic digestion.   Unfortunately,  the  operational  costs for
chemical sludge thickening and centrifugation cannot  be  broken
apart from the operational costs of handling phosphorus  removal
chemicals and tertiary upflow clarifier  operation.   Because  no
special  problems were involved in the chemical  sludge thickener
operation, the costs can be assumed to  be similar to  those of a
similar organic sludge thickening operation.  Of  course,  the
total cost to thicken per ton of dry solids  is  related  to the
mass of sludge treated.   For instance,  the total  cost of lime
sludge treatment at South Bend would be  much less per ton of dry
solids than the total cost of treating  iron  sludge.   This results
from the mass of lime sludge being much  greater than  the  mass of
iron sludge.  The size of the thickener, however, remains the
same in each case, and it is run for the same number  of  hours
each day.

    The disadvantage of treating lime sludge comes  in the dis-
posal stage.  At South Bend, it would not have  made  sense to send
the lime sludge to the digesters and the sludge farm, as  can be
done with the iron sludge.  While there  is probably  adequate room
in the four digestion tanks to handle the large amount  of lime
sludge, the digesters would likely serve mainly as  holding tanks
for this sludge because of the inability to preheat  the  sludge
and the low volatile content.

     Pilot plant studies have shown that the lime sludge can be
compacted in the thickener to as high as 16 percent TS,and even
at this high concentration, the sludge can be pumped fairly
easily.

     It would be possible, then, to pump the lime sludge to  the
sludge farm, but ultimate disposal of the lime sludge would  still
be a problem because of its volume.  Parkland disposal  would not
use up all of the sludge.  Direct trucking of thickened and  per-
haps centrifuged lime sludge to agricultural land seems to be the
best disposal alternative.  Dewatering the  sludge to a high  sol-
ids concentration would lower the trucking costs.  Pilot tests
showed that the lime sludge centrifuges can operate with a feed
sludge solids concentration of up to 30 percent TS.   By feeding
sludge at 16 percent TS, a fairly dry cake could be  produced
which would lower trucking costs.

     The following costs related to digester operation were
available from plant records.
                               179

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           Item                     1975          1976

      Operational  Labor          $74,981.18    $71,012.53
      (4  full-time operators)

      Maintenance  of  Equipment   $33,458.26    $35,235.74
       and  Structures

      Electricity                $10,462.40    Not Available

      Miscellaneous              $10,903.11     $4,164.04

      The capital  cost for  the four digestion tanks was $5,059,200
 in  1956.   This  does  not  include the cost of the Carter sludge
 mixing system which  was  added later.  The cost of the two sludge
 heat  exchangers for  tanks  No. 1 and 3 plus piping and valve con-
 trols, and the  sludge pump which pumps sludge from the No. 1
 digester to  the preheater, was $63,000 in 1956.  The two digester
 gas  storage  spheres  cost $225,000 each.

      The acquisition costs for 91 ac of farmland were $100,800
 in  1969.   Land  is very available near the treatment plant.  The
 capital  cost expenditures  related to farm operations included
 purchase of  the land; site development costs, including road
 improvements; installation of piping for the seven fields,
 including  cross-connections, valves, boxes, and miscellaneous
 tubing and hoses; construction of a 4-km (2.5-mi), 15.24-cm (6-in)
 steel  pipeline; and  purchase of one John Deere Model 4230 special
 tractor, one front-end payloader, two multiple harrow plows, one
 rbtotiller disc harrow,  and  two special pieces of drag equipment.
 The  operating costs  of farm  operation disposal have been  esti-
 mated at $1.60/t  ($1.45/ton) of dry sludge TS.

      The additional  costs  for sludge treatment resulting  from
 iron  addition at  South Bend  were very minor,  since there  was
 plenty of  room  available in  the digester.  The chemical sludge
 increased  the volume of  digester feed by 22 percent and the mass
 of  feed  TS by 19  percent.  The capital and operating costs  of
 the  chemical sludge  gravity  thickener, including pumping  to and
 from,  are  the major  additional costs.

 Summary  and  Conclusions

      A comparison of tertiary upflow clarifier operation  with
 lime  and with ferric chloride showed that  the mass of raw lime
 sludge generated  per mil m3  of wastewater  treated was 77  times
 that  of  the  raw iron sludge  produced.  The TS concentration of
 the  raw  lime sludge  was  4.0  percent.  Gravity thickening  of the
 lime  sludge  mixed with a relatively insignificant amount  of iron
 sludge produced a TS concentration of 10.2.   The sludge could  be
.centrifuged  to 43 percent  TS.  The centrifuged sludge cake  was
                               180

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trucked to a storage area unti 1 difficulties arose regarding com-
plaints along the route travelled by the trucks.   Then the thick-
ened sludge was pumped through a 4-km (2.5-mi), 15.24-cm (6-in)
pipeline to lagoons located at the plant's secluded sludge farm.
This was the mode of disposal until  the plant discontinued using
lime.   The plant feels that the most satisfactory method of lime
sludge disposal would be land application of thickened or centri-
fuged  cake.  Although there were problems with centrifugation  -
high maintenance and electricity costs for centrifuge operation
and insufficient capacity provided by the design  engineers -  the
centrifuges operated with feed concentrations of  up to 30 percent
TS and produced a correspondingly dry cake in pilot tests.   These
tests  also showed that the lime sludge could be compacted in  the
gravity thickener to 16 percent TS and even at that high concen-
tration it was easily pumped and flowed well.

     The thickened iron sludge was fed to the anaerobic digester.
By feeding it to the second of the two primary digesters which
follow in series, a suppression of total gas production was
avoided.  This suppression could have occurred because of the
plant's inability to preheat the chemical sludge  as it does its
organic sludge.  Some temperature suppression occurred in the
second digester as the result of chemical sludge  feed, but most
of the gas is produced in the primary digester,so the impact  was
not great.  Other than the fact that a total decrease did not
occur, the effect of the iron sludge on gas production is uncer-
tain.   Initially, there appeared to be an increase in the amount
of gas produced per quantity of VS destroyed, but later this
trend disappeared.

     Digested sludge was pumped out to a sludge farm where it
was dried and mixed with topsoil in fields with a special tractor
and then given away to contractors and the city of South Bend for
parks.  The sludge farm appears to be an excellent concept for
areas where land is available.  The concept was developed by
South Bend's Manager of Sanitary Operations who is a former far-
mer.  The operating cost of  the sludge farm operation is estimated
at $1.60/t ($1.45/ton) of dry sludae TS.

CASE STUDY D:  SHEBOYGAN, WISCONSIN

Introduction

     Sheboygan provides an example of secondary addition of ferric
chloride.  It also provides  an example of vacuum filtration of
undigested (raw) ferric sludge.  The data from this  plant can  be
compared with data from plants, such as  Midland, Michigan, and
Windsor, Ontario, which have practiced vacuum  filtration of raw
ferric sludges produced by primary addition of the chemical.

     Sheboygan operates a fluidized bed  incinerator.  The  impact
of ferric addition on energy requirements, maintenance,  and repair


                               181

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 requirements for this type of system can be examined at the plant.
 The  performance can be compared with that of other plants such as
 in Brookfield, Wisconsin, where a ferric sludge undergoes pressure
 filtration and multiple hearth incineration.

     Overall, Sheboygan is representative of the many older waste-
 water treatment plants which are awaiting future expansions and
 are  overloaded both hydraulically and with respect to sludge hand-
 ling capacity in the meantime.  Because of the hydraulic loading
 problems, the plant is fortunate that only 4 percent of the sewers
 are  storm rather than sanitary sewers.  Industrial waste discharges
 contribute 40 percent of the flow to the plant.  Included are
 industrial phenols, plastics, and leather tanning waste.  Whether
 because of hydraulic conditions or because of  industrial wastes,
 SS and BOD removal are poor.  Table C-7 below  presents some his-
 torical data on plant influent characteristics and suspended sol-
 ids  and BOD removal.  The plant's nominal design treatment capa-
 city is 0.060 mil m^/day (16 mgd) average daily flow with 0.83 mil
 m3/day (22 mgd) maximum flow.  Its discharge permit allows efflu-
 ent  concentrations of 80 mg/£ SS and 70 mg/£ BOD.  Phosphorus
 removal performance is also poor due to both hydraulic conditions
 and  the lack of sludge handling capacity.


       TABLE C-7.  A SAMPLE OF HISTORICAL DATA INDICATING
       AVERAGE PLANT INFLUENT CHARACTERISTICS, SUSPENDED
          SOLIDS AND BOD REMOVAL, SHEBOYGAN, WISCONSIN
                       April-Sept     April-Sept     April,  May,
                          1970           1973        July,  Sept,
                                                      Oct,  Nov
                       	     	        1976
            3
  Influent m /day
    (mgd)               45,800 (12.1)  54,900 (14.5)  14,300 (10.9)

  Influent SS (mg/£)        202            184            195

  Effluent SS (mg/£)         34             53             48

  Influent BOD (mg/£)       196            211            219

  Effluent BOD (mg/£)        58             81             58




History

     The following describes  historical plant modifications
affecting sludge production and characteristics.

                               182

-------
     1968 - Began sludge treatment with Dorr-Oliver vacuum filtra-
tion and Fluo Solids incineration system.  Old anaerobic digesters
converted to holding tanks for excess liquid sludge.  Excess sludge
applied to drying beds.

     Jan. 1972 - Began phosphorus removal by chemical  addition.

     Feb.-Apr. 1972 - Discontinued use of incinerator  heat exchan-
ger.  Excess liquid sludge hauled to farmlands instead of applied
to drying beds.

     Apr. 1973 - Began polymer addition to thickener.

     Jun. 1975 - Thickener overflow recirculated to head of the
primary tanks instead of before the trickling filters.

     Oct. 1975 - Began keeping records of phosphorus removal  chem-
ical dosages and influent and effluent phosphorus concentrations.

     Jan. 1977 - Began proportional addition of polymer to thick-
ener feed 1ines.

Chemical Addition for Phosphorus Removal

     In order to remove phosphorus at this treatment plant, liquid
ferric chloride  is added to a division well  which distributes the
effluent from the trickling filters to the two final clarifiers.
Anionic polymer  (Hercules 831) is then added to the center feed
wells of the final clarifiers.  The average  ferric chloride dosage
was 30 mg/£ dry  FeCIo in 1976, with polymer  dosage average 208
kg/mil m3 (1.75  Ib/MG).  Because accurate records were not kept
before 1976, chemical dosages before that time are unknown.

     The reduction of the total phosphorus concentration in the
wastewater averaged only about 54 percent in 1976.  Average influ-
ent and effluent concentrations were approximately 7.02 ppm and
3.26 ppm total phosphorus, respectively.   Phosphorus removal  was
very poor on the average, partly because during this period ferric
chloride addition was stopped whenever thickener performance deter-
iorated.  This occurred frequently.  In 1977, when thickener per-
formance was improved and ferric chloride addition rarely had to
be stopped, average phosphorus removal increased to 66.5 percent.
Influent and effluent phosphorus concentrations averaged 10 ppm
and 3.3 ppm, respectively.  The plant is required to reduce its
effluent phosphorus concentration below 4 ppm to meet its dis-
charge permit requirements.  Eighty percent removal cannot be
achieved at the  plant because of its design.  In order to get bet-
ter removal, more contact time is needed between the addition of
ferric chloride  and polymer, but this cannot be achieved with the
present plant design.
                               183

-------
 General  Description  of  Wastewater Treatment Operations Affecting
 Sludge

      Figure  C-4  presents a general treatment plant flow diagram.
 The  plant  has  no facilities for grit removal from the raw sewage.
 Primary  settling occurs  in two primary clarifiers having a total
 capacity of  5,680 m3  (1.5 MG).  Thickener overflow, vacuum filter
 filtrate,  and  incinerator scrubber water join the raw sewage before
 it enters  the  primary clarifiers.  Occasionally, when the thickener
 is severely  overloaded  and cannot accept it, secondary sludge is
 pumped to  the  primary clarifiers.  Primary sludge is continually
 removed  from the bottoms of both primary clarifiers and pumped to
 the  thickener  by way  of  the primary sludge degritter.

      Primary effluent is pumped over two rock-filled trickling
 filters.   The  trickling  filter effluent is split and enters two
 10.7-m (35-ft) diameter  final clarifiers.  Secondary sludge is
 removed  continually  from the  bottoms of both clarifiers and pumped
 directly to  the  thickener.

 Detailed Description  of  Sludge Treatment and Disposal Operations

 Degritting--

      Because there is no grit removal from the raw sewage, primary
 sludge degritting is  essential.  Grit lowers the volatile content
 of the sludge  fed to  the incinerator and increases the amount of
 fuel  required  to burn it.  The Dorr-Oliver cyclone sludge degrit-
 ter  efficiently  degrits  primary sludge of less than one percent
 solids concentration.

 Thickening--

      Degritted primary  sludge and sludge from the final clarifiers
 enter a  single Dorr-Oliver gravity thickener through separate
 15.2-cm  (6-in) feed  lines.  The thickener is 12.2 m (40 ft) in
 diameter,  and  its depth  is 3.05-m (10 ft) liquid sidewal plus the
 cone at  the  bottom.   It  is equipped with scraper arms having ver-
 tical pickets  for continuously stirring sludge in the thickener
 as it is scraped over the bottom toward the center.  Sludge is
 sucked into a  sludge  pape through eight portholes in the base of
 the  thickener  center column.  It is then pumped to the vacuum
 filters  when they are operating.  On weekends, when the filters
 not  operating, the operator has the option of pumping sludge to the
 holding  tanks  for later  land application or not pumping at all.

     Figure C-5 presents combined hydraulic and mass balances con-
 structed  around the thickener.  It presents information on average
 sludge flow rates,  total and volatile solids concentrations, and
masses obtained from monthly reports.  It is based on monthly
averages  of data for a 6-mo period of operation with no ferric
addition  and a similar later period with ferric addition.


                               184

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                                                                              LAKE
                                                                             MICHIGAN
               FLOW
               METER
00
en
                                                           AljH TRUCKED

                                                           TO LANDFILL
                                         LIQUID SLUDGE-

                                        HAULED TO FARMLAND
            Figure C-4.   Sheboygan, Wisconsin, wastewater treatment plant  flow diagram.

-------
AVERAGE SEWAGE FLOW: 12.1 MGD
6,690 »TS/DAY
3,980 »VS/DAY
0.7 XTS
59 XVS
122.000 GPD ™*»g<

7,220 *TS/DAY
4,150 »VS/DAY
0.2 XTS
57 X VS
440,000 GPD §LUDG|ARY




13 910 tf T^/F>A Y

8, 130 * VS/DAY
0.3 XTS

58 XVS
THI CKEN—
562.000 GPD £p FEED
| 	 1



FOR PERIOD OF OP
PHOSPHORUS REMOVAL •
AVERAGE SEWAGE FLOW: 14.5 MGD
14,000 »TS/DAY
9,340 »VS/DAY
1.4 XTS
64 XVS
128.000 GPD «££'

7,460 0TS/DAY
4,540 »VS/DAY
0.2 XTS
61 XVS
447 nnn rpn SECONDARY
H*t f , uuu CJHU SLUDGE

13,890 »VS/DAY
0. 5 XTS —

/63 XVS
575.000 GPD THICKEN-



N/A «TS/DAY
N/A *VS/DAY
. 04 XTS
N/A XVS
N/A GPD THICKENER
OVERFLOW
/"
^/
11,670 HITS/DAY
3,790 KVS/DAY
8.6 XTS
65 XVS
., __- rDn SLUDGE TO
16,550 GPD FILTER
I Y
f- I THICKENER I
\ A*.
V
^\
N/A »TS/DAY
N/A »VS/DAY
8.6 XTS
65 XVS
N/A CPD SLUDGE TO
N/A GPD DRYING BEDS.
ERATION BEFORE
- APRIL-SEPT. 1970
N/A (TS/DAY
N/A »VS/DAY
. 2 XTS
N/A XVS
N/A GPD THICKENER
OVERFLOW
J
/
V

CENER ]
-A
'V
24,090 KTS/DAY
7.930 *VS/DAY
7. 8 XTS
66 XVS
37,800 GPD p^L?||sTD

N/A »TS/DAV
N/A »VS/DAY
7. 8 XTS
66 XVS
N/A GPD SLUDGE
HAULED
FOR PERIOD OF OPERATION DURING
PHOSPHORUS REMOVAL - APRIL-SEPT. 1973
NOTE. RATES ARE CALCULATED ON AN AVERAGE DAILY FLOW BASIS
WHETHER FLOWS OCCUR EVERY DAY OR NOT.
Figure C-5 . Sheboygan, Wisconsin,
mass balance.
gravity thickener hydraulic and
186

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     The hydraulic-mass balances show that during both periods,
thickener performance, as measured by the solids concentration of
the thickened sludge,  was good.   During the first period,  part of
1970,  with no ferric addition, a combined primary and secondary
sludge of about 0.3 percent solids was thickened on the average
to 8.6 percent TS.   During the 1973 period, with ferric addition,
the sludge feed averaged 0.46 percent TS and was thickened on the
average to 7.76 percent TS.  The thickened sludge solids concen-
tration was lower in 1973, despite a higher concentration  in the
feed sludge and despite the addition of polymer to the sludge
feed lines.  An anionic polymer was used beginning in April  of
1973,  to aid sludge settling and to maintain a clear overflow.
Problems with floating of the sludge blanket and resulting high
overflow solids concentration were experienced in thickener  oper-
ation both prior to and after phosphorus removal.  They seem
related to industrial  waste discharges.  Poor settleabi1ity  was
more frequent during ferric addition than before.  In 1970,  the
average overflow solids concentration was 441 mg/£ TS, while in
1973,  during ferric addition, it was 1,764 mg/£.  The plant  oper-
ators responded to thickener upsets by stopping ferric addition
and discontinuing sludge feed whenever thickener upsets occurred.
Secondary sludge was wasted to the primary tanks at these  times
and the bottoms of these tanks were used for storage until  the
thickener regained stability.  As a result, the primary sludge
solids concentration and sludge mass was greater in 1973.

     The total mass of primary and secondary sludge pumped to the
thickeners was higher in 1973 by about 44,400 kg/mil m^ (370 Ib
TS/MG).  This amounts to an increase of approximately 2.18 t (2.4
tons) of dry sludge each day at a 49,200 mVday  (13 mgd) influent
flow rate.  The total  volume of sludge pumped to the thickeners
was actually lower in 1973, however, because of the higher solids
concentration.

     The thickener has an overflow rate of approximately 18,300
to 18,700 £/day/m2 (450 to 460 gal/day/ft^).  A sludge blanket of
at least 1.22 m (4 ft) must be maintained in the thickener to avoid
pumping a thin sludge.  The blanket depth is normally maintained
at close to 1.52 m (5 ft).

     The anionic polymer which is used in the thickener is the
same one used for phosphorus removal (Hercules 831).  Since  poly-
mer addition began, in April 1973, many different points of  addi-
tion and dosages have been tried.  It was added, for instance, to
the secondary sludge feed line about 12.2 m (40 ft) before it
enters the thickener, providing a 2- to 3-min contact time.   Addi-
tion directly to the center well through a plastic hose was  also
tried both with and without a diffuser on the end of the line to
distribute the polymer.  None of the methods tried produced  a
stable sludge blanket.  In January of 1977, a successful method
was found.  The method involves adding polymer separately to the
                               187

-------
 primary and  secondary  sludge  feed  lines  to  achieve  the  same  con-
 centration  of polymer  in  the  sludge  in each line.   In other  words,
 the amount  of polymer  added  to  each  line is proportional  to  the
 sludge flow  through  the  line.   The polymer  is  added  to  each  feed
 line through a plastic hose.  The  point  of  addition  is  immediately
 before the  feed lines  discharge in the center  feed  well  of the
 thickener.   The usual  dosage  is 3  ppm.

      Since  January  of  1977,  when proportional  polymer addition
 was started, the thickener  overflow  has  had a  very  low  average TS
 concentration.  The  average  for January  through  April was only
 154 mg/£.

      Sludge  is pumped  from  the  thickener to either  the  holding
 tanks or the vacuum  filters.  The  amount of sludge  pumped to the
 holding tanks has not  been  recorded  until recently.  During  six
 months from  September  1976  through February 1977, sludge  was
 pumped to  the holding  tanks  for an average  of  28.4  hr/wk.  It is
 pumped during the 33 hr  on  weekends  when the vacuum  filters  are
 not operating.  The  average  number of gallons  pumped per  day was
 7,535 and  the mass  of  solids  per day pumped was  2,000 kg  (4,400 Ib),
 During the  same period,  the  average  volume  pumped to the  vacuum
 filters was  about 127,000 £/day (34,000  gal/day) and the  sludge
 mass filtered was 8,810  kg/day  (19,400 Ib/day).

      Unfortunately,  the  hydraulic-mass balances  in  Figure 2  do
 not show how phosphorus  removal  affected the quantity of  sludge
 pumped to  the vacuum filters, or the amount of excess pumped to
 the holding  tanks.   The  data  necessary to calculate  these quanti-
 ties are unavailable.   The  increased amount of sludge which  Figure
 C-5 shows was pumped to  the  filters  in 1973 and  was  a result of
 longer operation of  the  filters and  incinerator.  This  longer oper-
 ation was a  result  of  the elimination of certain problems experi-
 enced when  the incinerator  was  new.  Since  1972, the incinerator
 has been operated on its  present schedule.

 Liquid Sludge Hauling--

      Liquid  sludge from  the  holding  tanks is trucked out  and
 applied  to agricultural  lands by a private  contractor.   The  con-
 tractor  charges  by the gallon for  this service.  The number  of
 gallons  hauled is not  the same  as  the number of  gallons  pumped
 to  the  holding tanks.  The  tanks are not mixed,  so  the  sludge
 becomes  heavy  in  them.   It must be diluted  with  water during pump-
 ing  so  that  it will  flow  into the  truck.  Data on the quantities
 of  sludge hauled  in  1970  and  1973  are unavailable.   In  1976,
 22,700 m3 (6  MG)  were  hauled, but  only approximately 10,400  m3
 (2.75 MG) were  pumped  to  the  holding tanks.

 Dewatering--

     Sludge dewatering is accomplished with two  vacuum  filters
which were installed in 1957 and rebuilt in 1968 with Dorr-Oliver
                                188

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 components to be compatible with the Dorr-Oliver  Fluo Solids
 incineration system.   The  filters have a design filtering capa-
 b]lity  of 454 kg (1,000  Ib) TS/hr each at a  feed  solids concentra-
 tion  of 27 percent TS.   The two rotary drum  filters  each have a
 filtering area of 18.6 m2  (200 ft2), face width of 2.44 m (8 ft),
 and diameter of 2.44 m (8  ft).  The filter medium is  polyethylene
 cloth.   The filter drum  speed is 7 min/revolution.   This is the
 slowest drum speed setting possible.  Sludge  is conditioned prior
 to filtration with Hercules 814 cationic polymer  and  ferric chlor-
 ide.  The vacuum filters are operated for 24  hr/day  on  Monday
 through Friday,  15 hr/day  on Saturday, and are shut  down on Sun-
 day.

      Table C-8 presents  a  comparison of filter performance before
 and after phosphorus removal.   Data on incineration  rate and incin-
 erator  fuel consumption  are also presented.   The  data are based
 on monthly reports for the 1970 "before phosphorus removal" and
 1973  "after phosphorus removal" time periods  previously mentioned.
 In addition, data from a similar 6-mo period  in 1976  is presented.
 The plant manager felt that the 1976 data were more representative
 of the  results after phosphorus removal than  the  1973 data.


         TABLE C-8.   VACUUM  FILTRATION  AND  INCINERATION
        PERFORMANCE  BEFORE  AND  AFTER  PHOSPHORUS  REMOVAL,
        	SHEBOYGAN, WISCONSIN	

                               1970       1973        1976

        Filter yield, kg TS/rr,2/hr   20.3       16.1       12.8
         (lbTS/ft2/hr)            (4.16)      (3.3)       (2.62)
        Filter feed solids % TS     8.6        7.76        7.0

        Cake dryness % TS         25.5       24.7       21.5

        Cake volatile VS (% of TS) 65.45      65.9       65.4

        Filtrate solids ppra SS   C58        383        442

        814 Polymer, kg/t  (Ib/
          ton)                 1.91 (3.82)   1.28  (2.55)  1.20  (2.4)

        FeClj, kg/t (Ib/ton)        NA         NA       66.3 (132.5)
Incinerator feed
kg/hr (Ib) hr*
Fuel consumption
(gal/ton)
rate,
, 1/t
755
246
(1,662)
(59)
578
451
(1
(1
318)
08)
475
517
(1,046)
(124)
        *•  Dry-solids fed to incinerator based on solids in filter feed.
           Amount of solids lost in filtrate  unknown.
     Before phosphorus removal,  ferric  chloride was used  for con-
ditioning less  than  20 percent of  the  time.   Most of the  time,
polymer was used  alone.   After phosphorus removal, cake dryness

                                189

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was usually only about 18 percent TS without ferric conditioning;
but with ferric conditioning, a 21-percent TS cake could be
achieved.

     Though ferric conditioning raised cake solids content, it
did not improve filter yield.  Filter yield can be raised by
increasing filter drum speed, but at the expense of cake dryness.

     The volatile content of the sludge cake does not appear to
have decreased with phosphorus removal.  Filtrate quality also
was not adversely affected.   Polymer dosage decreased somewhat as
ferric chloride usage became regular.

Incineration--

     The plant operates a Dorr-Oliver "F/S System" Fluo Solids
incinerator.   It has a design capacity of 122 kg/hr (2,684 Ib/hr)
dry filter cake.  The cake is expected to contain 25 percent TS
with 73 to 74 percent volatile content.  The incinerator's overall
height is 12.2 m (40 ft)  and the cylinder's inside diameter is
3.05 m (10 ft).  The expanded sand bed is 1.83 to 2.13 m (6 to 7
ft) deep and contains 7.26 t (8 tons) of silica sand.  A construc-
tion plate supports the bed  and allows fluidizing air to pass
upward.  It is a self-supported refractory arch with metal tuyeres
which pass the air.  The  windbox chamber is below this.  The wind-
box size is 1.07 m by 2.74 m (3.5 ft by 9 ft).  A preheat burner
mounted on the windbox preheats the fluidized bed in the reactor
prior to sludge feed.  A  preheat burner fuel oil pump furnishes
No. 2 fuel oil to preheat the burner.  An atomizing blower supplies
pressurized air to atomize the fuel oil in the preheat burner.
Once the reactor bed temperature is preheated to 621°C (1,T50°F),
which is the auto-ignition temperature of sludge, No. 2 fuel is
injected directly into the bed by the bed guns.  The preheat burner
is turned down but continues to serve as the method of heating the
fluidizing air which is discharged through the windbox into the
bed.  The fluidized air comes from a centrifugal blower which dis-
charges air at 4.5 to 5.0 psig into the reactor.  Before April 21,
1972, the fluidizing air was heated by a heat exchanger rather
than by the preheat burner.   Problems with the  heat  exchanger
prompted its discard, and the preheat blower  became  the method of
fluidizing air heating.  Without the heat exchanger, oil  consump-
tion is higher by about 129  a/t (31 gal/ton).   Without the  heat
exchanger, the incinerator capacity is reduced  by about  159  kg/hr
(350 dry Ib/hr).  If the sludge feed rate  is  increased above  its
capacity, the excess air level in the  bed will  be too  low,  and
more fluidizing air must be  supplied to counteract  this.   The
incinerator's capacity is limited by its size  in  the  sense  that
size limits the rate at which fluidizing air  can  be  accepted.
When fluidizing air is discharged in excess  of  2,100  scfm,  the
metal tuyeres through which  the air must pass  upward  into  the  bed
are blown out.
                              190

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     Exhaust gases from the incinerator enter a Venturi scrubber
system.  Gases are scrubbed of ash and cooled and discharged to
the atmosphere.  Ash slurry is pumped to a Dorr-Clone wet cyclone
and classifier system for dewatering.  Dewatered ash is carried
in a 3.06-m3 (4-yd3) truck to a small landfill.  2.29 m3 (3 yd3)
of ash are produced each day.  The scrubber water is recirculated
back to the head of the plant.  A single sample of the scrubber
water showed a SS concentration of 758 ppm and a pH of 6.4.

     Solids are processed in the incinerator continually,  except
for 32 hr on the weekends.   Before the incinerator is  shut  down,
the temperature is run up to 871°C (1,600°F).   Over  the next 32 hr
the temperature falls to about 643°C (1,190°F).   Before beginning
again for the next week, preheating  takes  place for  about  1  hr  to
get the temperature to 677°C (1,250°F) when feeding  can start.   The
usual operating bed temperature is 721°C  (1,330°F).   Fluidizing air
is normally discharged at 2,000 scfm.

     Phosphorus removal  has adversely affected incinerator  capa-
city and fuel  consumption because of the  increased moisture con-
tent of the sludge cake  fed to the incinerator.   In  Table  2, the
incinerator feed rate and fuel consumption  rate in 1970 and 1976
are indicative of the performance before  and during  phosphorus
removal.  However, part  of  the feed  rate  decrease  and  fuel  con-
sumption rate increase is due to the removal  of the  heat  exchanger.
The effect of phosphorus removal alone is  judged to  be  an  average
decrease of approximately 121 kg (266 Ib)  dry solids/hr in  the  feed
rate and an increase of  142 l/t (34  gal/ton) in fuel  oil  consumption

     There have also been increased  incinerator maintenance and
repair problems with phosphorus removal  due to slag  formation and
corrosion.  On one occasion, four tuyeres  blew out because  several
tuyeres were plugged with slag.  On  another occasion,  a pressure
build-up in the reactor  signalled a  problem, and a big  piece of
slag was found clogging  the exhaust  line.   After this  experience,
the operator has done visual inspection of the exhaust  line from
the roof duct inspection port every  3 to  4 mo.  The  plant manager
believes that ferric chloride is also responsible for a high rate
of corrosion of the metal in ducts,  especially in the elbows of
the scrubber system.  Gradually, these parts are being  replaced
with stainless steel.

Sludge Treatment and Disposal Costs

Operational Costs--

     The additional costs for sludge treatment and disposal which
resulted from phosphorus removal which have been estimated  include
the cost of chemical conditioners, polymer for the thickener,  and
fuel  oil.   The current costs of liquid sludge hauling,  incinerator
ash disposal, electricity for vacuum filter motors and incinerator
motors, repair equipment for the incinerator, maintenance supplies


                               191

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for filtration and incineration combined,  and labor for filtra-
tion and incineration combined, have been  estimated.

     In assessing the operational  costs of sludge treatment and
disposal at Sheboygan, the following assumptions  were made:

     1.  All costs are shown as per ton of dry solids filtered,
         except for the cost of liquid sludge hauling which is
         per ton of solids hauled.

     2.  Current costs are based on a filtration  rate of 9,080  kg
         TS/day or 3,310 t/yr (20,000 Ib TS/day or 3,650 ton/yr)
         at a feed concentration of 7.0 percent TS; sludge hauling
         rate of 728 t/yr or 0.023 mil m3/yr (803 ton/yr or 6.0
         MG/yr).

     3.  The unit cost factors used are:

                                     (1977 costs)

         Ferric chloride         $.0277/kg ($.0126/lb)

         Conditioning polymer    $3.74/kg  ($1.70/lb)

         Anionic polymer         $3.13/kg  ($1.42/lb)

         Contractor's sludge     $3.01/m3  ($0.0114/gal)
         haul ing fee

         Fuel  oil                 $113.34/m3  (0.429/gal)

         Electricity             $0.01622/kwh

     4.  Labor for filter and incinerator  operation consists of:

         160 Operator I man-hr/wk,
          20 Operator II man-hr/wk

         The cost breakdown is:

                                Changes in costs
                                 resulting from    Current
                               phosphorus  removal   costs

Ferric chloride conditioning       +$1.65/t        $1.84/t
assuming 8,000 gal/yr were         (+$1.50/ton)     ($1.67/ton)
used before phosphorus
removal

Polymer conditioning               -$2.43/t        $4'.49/t
                                   (-$2.21/ton)     ($4.08/ton)
                               192

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                                   Changes in costs
                                    resulting from    Current
                                  phosphorus removal    costs
Thickening polymer
No. 2 fuel oil
Electrical power for chemical
conditioning and vacuum filter
operation

Electrical power for incinerator
operation

Labor for filter and incinerator
1976

Liquid sludge hauling
Charge for ash landfill  use

Equipment for incinerator
repair - 1976

Equipment for vacuum filter
repair - 1976

Supplies for vacuum filter and
incinerator maintenance  - 1976
 +$2.20/t
(+$2.00/ton)

 +$16.08/t
(+$14.59/ton)

, Unknown
 Unknown


 Unknown


 Unknown


 None

 Unknown


 Unknown


 Unknown
 $2.20/t
($2.00/ton)

 $58.65/t
($53.20/ton)

 $2.77/t
($2.52/ton)
 $3.43/t
($3.12/ton)

 $16.61/t
($15.07/ton)

 $29.85/t
($27.08/ton)

 None

 $15.10/t
($13.70/ton)

 None
 $4.96/t
($4.50/ton)
     Since filter yield and incinerator rates were decreased with
phosphorus removal, the cost per ton of dry solids for electricity
and labor for filter and incinerator operation must have increased.
Because of more hours of operation of the filter and the incinera-
tor,  the cost of maintenance and repair supplies and equipment per
ton of solids must also have increased.  The amounts of these
increases are unknown because it is not known how much additional
sludge was fed to the filters as a result of phosphorus removal.
Similarly, it is not known how much additional sludge was fed to
the filters as a result of phosphorus removal.  However, since the
TS concentration of the thickened sludge was lower with phosphorus
removal, the cost per ton of dry solids to haul must have increased.
Capital  Costs--

     The vacuum filtration and incineration system was
in  1967.   The work included installation of two vacuum
                  instal1ed
                  filters
                              193

-------
 (all new, except for the agitators) and a fluidized bed incinera-
 tor; removing a wall from an existing building; and adding a small
 section to the existing building to house the ash dewatering equip-
 ment.  The capital cost of this project, including installation,
 electrical work and piping, planning and engineering fees, etc.,
 was $738,935.18.  The planning and engineering fees alone were
 $46,708.10.  It was financed by floating a bond issue for $396,518.00
 and obtaining federal aid for $388,469.00.

 Summary and Conclusions

     The  initial impact of phosphorus removal on sludge handling
 appears to have been an increase in the mass of secondary sludge
 generated.  Concurrently, the problem of intermittent floating of
 the thickener sludge blanket was worsened considerably, as evi-
 denced by the large increase in the average solids concentration
 of the thickener overflow.  Whenever thickener upsets occurred,
 phosphorus removal was temporarily halted; sludge feed to the
 thickener was temporarily halted;  and secondary sludge was pumped
 to the primary clarifiers.  Sludge was stored in the bottoms of
 the primary clarifiers until the thickener stabilized.  Some thick-
 ening occurred in the clarifier bottoms because of this storage.
 Therefore, after phosphorus removal was started, the sludge pumped
 from the  primary clarifiers to the thickener was heavier.  The
 solids concentration of the secondary sludge was unchanged.  The
 total volume of thickener feed sludge did not increase with phos-
 phorus removal because of the sludge concentrating going on in the
 primari es.

     The  additional mass of sludge pumped to the thickener after
 phosphorus removal was started has been calculated from available
 data.  It is 44,000 kg/mil m3 (370 Ib TS/MG) of wastewater treated,
 or 2.18 t (2.4 additional tons) TS/day assuming that 49,200 m3/day
 (13 mgd)  of wastewater are treated.  Part of this increase in
 sludge mass was due to the recirculation of more solids in the
 thickener overflow.  Part was due to the use of ferric chloride
 and polymer for phosphorus removal.  Unfortunately, available data
 for the period we are concerned with do not permit calculation of
 the volume and total solids mass of the thickener overflow or the
 sludge pumped to the holding tanks.  Therefore, we do not  know what
 fraction of the additional 5.75 t TS/mil m3  (2.4 tons TS/MG) which
 entered the thickener went out in the overflow, to the vacuum fil-
 ters, or the the holding tanks.

     We do know, however, that phosphorus removal resulted in a
change in the dewatering characteristics of the thickened  sludge.
Comparing data from 6-mo periods in 1970 and 1976 which were  before
and after phosphorus removal began, we see that the average TS  con-
centration of the thickened sludge decreased from 8.6  percent  to
7.0 percent TS.  Filter cake dryness decreased  from 25.5  percent
to 21.5 percent TS.  The volatile content of the filter cake  did
not change.   Filtrate SS concentration decreased. Ferric  chloride


                               194

-------
conditioning became necessary to achieve a filter cake TS concen-
tration greater than 18 percent.  Previously only about 20 percent
of the sludge had been conditioned with ferric chloride.   Because
of ferric conditioning, polymer conditioner dosage decreased.   As
a result, the cost for conditioning chemicals decreased by about
$0.78/t ($0.71/ton).

     Because of the higher moisture content of the filter cake,
incinerator fuel oil consumption rose and the fuel oil cost rose
by $16.10/t ($14.60/ton) of dry solids.  In addition,  the rate at
which cake could be burned in the incinerator was lower by about
121 kg (266 Ib) TS/hr.  Because the incineration rate  was lower,
the vacuum filtration rate was lowered to match.  Filter  yield
became only 12.8 kg TS/m2/hr (2.62 Ib TS/ft2/hr).  A higher filter
yield is possible, but at the expense of cake dryness.  It is  dif-
ficult to consider filter yield Independently of the incineration
capacity in this situation.

     In response to the adverse effect of phosphorus removal on
thickener sludge blanket stability and overflow solids concentra-
tion, efforts were made to find a method of adding polymer to  the
thickener which would improve the situation.  A really successful
method was not  found until January of 1977.  Before this, in June
of 1975, the thickener overflow was rerouted to go to  the primary
clarifier influent instead of the wet well ahead of the trickling
filters.  Poor  thickener overflow quality had an adverse  effect
on plant BOD and SS removal and plant effluent quality.  BOD and
SS removal are  so dependent upon influent flow and strength, how-
ever, that it has not been possible to present data showing the
effect of the thickener overflow.  Nevertheless, improvement in
plant BOD and SS removal can be considered to be benefits derived
from the addition of polymer to the thickener.  Another, benefit,
better phosphorus removal, occurred because ferric and polymer
addition no longer had to be halted frequently for thickener
upsets.  The costs of.polymer addition, on the other hand, are the
cost of the polymer itself, which is $2.21/t ($2.00/ton)  of dry
solids, and the cost of disposing of the additional sludge solids
which are generated as a result of polymer usage.

CASE STUDY E:   COLDWATER, MICHIGAN

Introduction

     The Coldwater, Michigan  treatment plant provides an example
of the primary  addition of ferric chloride for phosphorus removal,
with and without the use of anionic polymer.  The major components
of the Coldwater treatment plant are trickling filters, pressure
sand filters, anaerobic digesters, and sludge drying  beds.

     Wastewater influent to the Coldwater plant  is delivered  by
separate sanitary sewers, although some older portions of  the
collection system do experience groundwater  infiltration.   Less


                               195

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than 5 percent of the wastewater flow is from industrial sources.
One of the industrial sources is a slaughterhouse, which contri-
butes 379 m3/day (0.1 mgd) with BOD concentrations between 200
and 800 mg/£.  The other industrial source is a rendering plant
which contributes 1,140 m3/day (0.3 mgd) with BOD concentrations
as hiqh as 2,700 mg/£.

     Three years of treatment plant operational data have been
selected for study as follows:

     •  1971 - Prior to initiation of chemical addition for
        phosphorus removal.

     •  1973 - With chemical addition of both ferric chloride
        and anionic polymer.

     t  1976 - With chemical addition of ferric chloride only.

     Table C-9 presents the average influent and effluent waste-
water characteristics and plant removal efficiencies for each
time period.


 TABLE C-9.  INFLUENT AND EFFLUENT WASTEWATER CHARACTERISTICS AND
            REMOVAL EFFICIENCIES, COLDWATER, MICHIGAN

FLOW m3/d
SS (mg/£)


BOD (mg/l)


TP CmgAe)



(mgd)
- influent
effluent
% removal
infl uent
effl uent
% removal
infl uent
effl uent
% removal
1971
4,660 (1.23)
156
20
87
297
30
90
_ _ ..
	
_ _ _
1973
7,310 (1 .93)
114
7
93
289
21
93
6.2
1.2
80
1976
9,200 (2.43)
168
15
91
253
26
90
5-4
0.7
86
History

     Modifications to the plant which have affected sludge
production and characteristics are detailed below:

     1952   Original secondary wastewater treatment plant
            structed.  Treatment units consisted of a .grit
            chamber, two primary clarifiers, two trickling
            filters, one final clarifier  (identical to  the

                               196

-------
            primary clarifiers), and chlorination.   Sludge from
            the final  clarifier was returned to the head of the
            primary clarifiers, settled, and subsequently
            removed from the bottom of the primary  clarifiers
            along with the settled wastewater solids.   This
            sludge was pumped to the primary sludge digester
            where it was heated and mixed and then  transferred
            to the secondary digester.  Sludge in the  secondary
            digester was allowed to settle without  heating or
            mixing, while the supernatant was returned to the
            flocculation channel ahead of the primary  clarifiers.
            Sludge from the secondary digester was  eventually
            transferred to one of the sludge drying beds.  The
            dry sludge cake was disposed of at a landfill site.

      1971  Construction of tertiary sand filters began.

April 1972  Plant flow increased by 946 mg3/d (0.25 mgd) when
            new trunk sewer from "State Home" connected.

 July 1972  Two new final clarifiers on line and one old secondary
            clarifier converted to perform primary  clarification
            in parallel with two existing primary clarifiers;
            third trickling filter also on line at  this time.

 Fall 1972  Existing five sludge drying beds paved  and seven new
            paved sludge drying beds constructed; new  above-
            ground, unheated holding digester added; new gas
            lifter system installed in the existing primary
            di gester.

Sept. 1972  Tertiary sand filters put into operation.

 Dec. 1972  Chemical addition for phosphorus removal began;
            ferric chloride initially added to the  aerated grit
            chamber, while anionic polymer was added to the head
            of the aerated flocculation at the flash mixer
            channel .

      1976  Anionic polymer addition suspended.

      1977  Anionic polymer addition resumed using liquid
            polymer instead of dry polymer.

Chemical Addition for  Phosphorus Removal

     Liquid ferric chloride is added to the head of the  grit
chamber.  Anionic polymer (Haviland Chemical, Poly-floe M-P) is
then added at the flash mixer at the head of the flocculation
channel.  Approximately 9.4 min contact time at 7,570  m3/day
(2  mgd)  plant flow is  provided  in the flocculation channel.  The
chemical dosage is selected to achieve 90 percent phosphorus


                               197

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removal.  The average ferric chloride dosage was  40 mg/£ dry
FeCl3 until 1977, when it was raised to 75 mg/l.   The average
dosage of anionic polymer is 4 mg/£.

General Description of Wastewater Treatment Operations Affecting
Sludge

     A flow diagram for the wastewater and sludge treatment
operations is presented in Figure C-6.  Table C-10 gives a
summary of major equipment at the Coldwater plant utilized for
wastewater treatment and sludge handling.   In addition to the
specific modifications to the wastewater treatment plant listed
in Table C-9, there are some seasonal variations  in plant opera-
tions and plant influent characteristics.

     Generally, two trickling filters are operated to provide
secondary treatment.  The third trickling filter is not operated
unless it can be run for at least three months.  It has been
frequently necessary, during the winter months, to use only one
trickling filter.  This serves to increase flow rates through
the filter, thereby avoiding freeze-ups.

     A variation in plant influent characteristics is due to
the dumping of the concentrated wastes pumped out of septic
tanks.  These dumpings occur with highest frequency during the
summer months, causing brief but significant increases in plant
influent characteristics.  Specific data describing these
influents were not available; however, plant personnel indicated
that the quantities of wastes delivered to the plant have
remained relatively constant throughout the study periods.

     A flow diagram and materials balance of the Coldwater plant
are shown in Figure C-7.  The data presented are based on infor-
mation contained in the monthly reports submitted by the  plant
to the state of Michigan, during the years selected for study
(viz. - 1971, 1973, and 1976).  From the figure, it can be seen
that wastewater solids information is presented in terms  of
suspended solids (SS), while sludge and sidestream information
is given as total solids (TS).  In spite of the inconsistency  of
the units of expression, all available solids  information has
been presented to qualitatively substantiate the observed impacts
of chemical additions for phosphorus removal on plant solids
handling operations.  The remainder of this section briefly
describes each of the wastewater treatment unit operations which
have significant impacts on sludge,

Flocculation Channel--

     Figure C-8 is a flow diagram of the flocculation channel.
The flocculation channel receives raw influent wastewater after
degritting, chemical addition for phosphorus removal, and
pressure sand filter backwash water return have taken place.

                               T98

-------
to
vo
          SEPTIC TANK
            WASTE
    RAW
    SEWAGE
             WET
             WELL
                          SCREW PUMP
          PARSHALL
          FLUI^E
COMMI-
NUTOR
  GRIT
CHAMBER
FLOCCULATION
 CHANNEL
               EC
                            CHLORI-
                            NATION
                             TERTIARY
                              SAND
                              FILTERS
                                                                      HUMUS SLUDGE
 TRICKLING
  FILTERS
       PRIMARY
     CLARIFIERS
§
d
u
                   DUMP SITE
                                      DRIED
                                      SLUDGE
                                        DRYING
                                         BEDS
        DIGESTED
                                                    SLUDGE
                                                                                           SLUDGE
      ANAEROBIC
      DIGESTERS
            <
            2
            LU
            (/)
            o:
            Figure  C-6.   Coldwater, Michigan,  wastewater treatment  plant  flow diagram.

-------
         TABLE  C-10.
                     GENERAL PLANT DESCRIPTION SUMMARY,
                        COLDWATER, MICHIGAN
      Item
                                 No.  and Description
Comminutor
     /
Grit Chamber

Flash Mixer
                      1  with 91.4 cm (36 in)  impeller at 84 rpm;
                      motor - 5 hp, 30,  60 hz,  460 v.

                      27.7 m (91  ft)  length x 1 .30 m (4.25  ft)
                      width x 1.37 m (4.5 ft) height

                      3  at 27.7 m (91  ft) x 4.88 m (16 ft)  width
                      x  2.74 m (9 ft)  height

                      3  at 34.1 £/min  (40 gal/min) - one pump
                      use at a time;  motors - 3  hp, 30, 60  hz,
                      460 v.

                      3  pairs of vertical chains with wooden
                      flights at 3.05  m  (10 ft)  intervals;
                      motors - 2 at 1/2  hp, 30,  60 hz, 460  v.

                      3  at 35.1 m (115 ft) dia.  x 2.44 m (8 ft)
                      side wall depth  (SWD) rack-filled (pit
                      run) field stone,  3.81  to  10.2 cm (1.5
                      to 4 in dia).  Flow sprayed continuously
                      from fixed nozzles rotating at 2 to 20
                      rpm

Secondary Clarifiers  19.8 m (65 ft)  dia. x 3.05 m (10 ft)  SWD
Flocculation
Channel

Primary Clarifiers
Primary Sludge
Pumps
Primary Sludge
Col lectors
Trickling Filters
Secondary
Sludge Pumps

Secondary Sludge
Collectors

Pressure Sand
Filters

Chlorination
                      2 at 75 rpm; motors - 2 hp, 30, 60 hz,
                      460 v.

                      2 rotating collector arms; motors - 3/4 hp,
                      30, 60  hz, 460 v.

                      4 multiple media at 1.83 m (6 ft) dia.
                      x 4.57  (15 ft) length
                                                      (continued)
                               200

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TABLE C-10 (continued)

       Item
          No. and Description
Primary Digester
Primary Digester
Secondary Digester
Holding Digester
Sludge Drying Beds
Sludge Lagoon
958,000 L (253,000 gal) capacity with
13.7 m (45 ft) dia. x 5.49 m (18 ft) SWD;
fixed concrete dome and 3 gas lift eductor
tube encased by an internal  water heating
jacket assembly; eductor tube capacity -
41,600 I (11,000 gal)/min  total; water

jacket heat exchange capacity 500,000
Btu/hr; motor - 10 hp, 30, 60 hz, 460 v;
boiler converter pump - 2 hp, 30, 60 hz,
460 v.
958,000 I (253,000 gal)  capacity at 13.7
(45 ft) dia. x 5.49 m (18 ft)  SWD with
fixed concrete dome

142,000 I (374,000 gal)  capacity at 16.8
(55 ft) dia. x 5.79 m (19 ft)  SWD; with
fixed steel  dome
                                         m
                                         m
Concrete paved;
length x 7.62 tn
(125 ft) height
                12 at 32.9 m (108 ft)
                (25 ft)  width x 3.81  m
700,000 £ (185,000 gal) capacity at 30.5 m
(100 ft) length x 15.2 m (50 ft) width x
1.52 m (5 ft) depth
                              201

-------
                            FECL,
                                       ANIONIC
      PLANT  INFLUENT
                        ADDI- BACKWASH POLYMER
                        TION   WATER   ADDITION
   0=2.43X10
   SS=3410  (69%
   VSS = 2370
   BOD = 5120
   TP=110
             VOLATILE)
 m
 r-
0=1.93X10
SS=1840 (76%)
VS5=1400
BOD=4650
TP=100
   0=1.23X10
   SS=1600  (71%)
   VSS=1140
   BOD=3050
   TP=N/A-
       0=50000
TS=810 SS=340
       VSS=240
       BOD=170
       TP=6

       Q=40000
TS=645 SS=170
       VSS=130
       BOD=120
       TP=5

       Q=N/A
TS=N/A SS=N/A
       VSS=N/A
       BOD=N/A
       TP=N/A
i	i \	>
TS=0
  SECONDARY
  CLARIFIER
   SLUDGE

0=5500032.5%TS
TS=11500
TS=80
Q=25000S)1 . 8%TS
TS=3800
                                       TS=N/A
         0=350031.0%TS
         TS=300
                        GRIT
                      REMOVAL
                               FLOCCULATION CHANNEL
                         \

                       GRIT
                      REMOVED
        Q=FLOW - GPD
        SS=SUSPENDED SOLIDS  -  0/DAY
        VSS=VOLATILE SUSPENDED SOLIDS - #/DAY
        TS=TOTAL SOLIDS -  #/DAY
        BOD=5-DAY BOD - #/DAY
        TP=TOTAL PHOSPHOROUS - #/DAY
        PH=STANDARD UNITS
        N/A=NOT AVAILABLE
Figure C-7.   Hydraulic and  solids  mass  balances for wastewater and
             sludge  treatment operations,  Coldwater, Michigan.
                               202

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       DIGESTER
      SUPERNATANT
        RETURN
  0=479030. 8%TS
  TS=320(48%VOLATILE)
« PH=N/A
  BOD=70

                     PRIMARY- TREATMENT
                     PERCENT REMOVALS

                      SS=-65%
                      VSS=-37
                      BOD=+29
                      TP=-10
0=319032.7%TS
TS=720(45%VOLATILE)
PH=7.3
BOD=70
Q=301030.3%TS
TS=75 (31SVOLATILE )
PH=7.1
BOD=20
                      SS=36
                      VSS=41
                      BOD=55
                      TP=51
                        SS=58
                        VSS=63
                        BOD=43
                        TP=N/A
  FLOCCULATION
    CHANNEL
                         PRIMARY
                        CLARIFIERS
                        PRIMARY CLARIFIER
                            SLUDGE TO
                        PRIMARY DIGESTER
                                           PRIMARY EFFLUENT

                                          SS=5620(58%VOLATILE)
                                          VSS=3240
                                          BOD=3620
                                         .TP=120
                                            SS=1240(66%VOLATILE)
                                            VSS=820
                                            BOD=2370
                                            TP=51
                                          SS=630(67%VOLATILE
                                          VSS=430
                                          BOD=690
                                          TP=N/A
                                           PRIMARY EFFLUENT
                                           TO  TRICKLING FILTERS
                                      PRIMARY CLARIFIER SLUDGE

                                    0 0=610038.3%TS
                                    N TS=4220(51%VOLATILE)
                                    - PH=N/A

                                    [2 0=521036.3%TS
                                    ov TS=2740(8%VOLATILE)
                                    "* PH=6.6

                                    -« 0=387035. 6%TS
                                    £ TS=1800(72%VOLATILE)
                                    - PH=6.7
                     Figure C-7 (continued)

                               203

-------
   PRIMARY EFFLUENT

  SS=5620(58%VOLATILE)
  VSS=3240
  BOD=3620
  TP=120
  SS=1240(66%VOLATILE)
  VSS=820
  BOD=2370
  TP=151
                        SECONDARY TREATMENT
                         PERCENT REMOVALS    SECONDARY EFFLUENT
                              SS=88%
                              VSS=87
                              BOD=81
                              TP = 81
SS=640(66%VOLATILE)
VSS=430
BOD=690
TP = 23
                              SS=77
                              VSS=76
                              BOD=81
                              TP=47
•SS=290(69%VOLATILE
VSS=200
BOD=460
TP = 27
^ SS=630(67%VOLATILE)
N VSS=430
« BOD=1690
  TP=N/A
                              SS=67
                              VSS=70
                              BOD=82
                              TP=N/A
SS=210(62%VOLATILE)
VSS=30
800=310
TP=N/A
  PRIMARY
  CLARIFIER
  EFFLUENT
SLUDGE TO
PRIMARY DIGESTER

0=610038.3%TS
TS=4220(51%VOLATILE)
PH=N/A

0=521036.3%TS
TS=2740(8%VOLATILE)
PH=6.6	

0=387035.6%TS
TS=1800(72%VOLATILE)
PH = 6.7
1
i TRICKLING
1 FILTERS
1


SECONDARY
CLARIFIERS


                                          SECONDARY
                                           SLUDGE
                                             SLUDGE TO DRYING
                                             BEDS (OR LAGOON)
                                             0=1310311.4%TS
                                             TS=1250(41%VOLATILE)
                                             PH=N/A

                                             0=202538.4%TS
                                             TS=1420(50%VOLATILE)
                                             PH=7.2
                                             0=86036.5%TS
                                             TS=465(54%VOLATILE)
                                             PH=7.1
                                                SUPERNATANT
         PRIMARY
        DIGESTERS
                                        SECONDARY
                                           AND
                                         HOLDING
                                        DIGESTERS
                        Figure C-7 (continued)
                               204

-------
PRESSURE SAND FILTERS
  PERCENT REMOVALS

      SS=53%
    £ VSS=56
    2 BOD=25
      TP=26
                    TERTIARY EFFLUENT

                   SS=3 00 (6 556 VOLATILE)
                   VSS=190
                   800=520
                   TP=17
             OVERALL
          PLANT PERCENT
            REMOVALS

            SS=91%
            VSS=92%
            BOD=90%
            TP=85X
      SS=59
    P VSS=65
    2 BOD=26
      TP=19
                   SS=120(58%VOLATILE)
                   VSS=70
                   BOD=340
                   TP=22
            SS=93%
            BDD=95%
            BOD=93%
            TP=78%
      SS=N/A
    h! VSS=N/A
    2 BOD=N/A
      TP=N/A
                   SS=N/A
                   VSS=N/A
                   BOD=N/A
                   TP=N/A
            SS=87%
            VSS=89%
            BOD=90%
            TP=N/A
PRESSURE
  SAND
FILTERS
           CHLORINATION
           AND DISCHARGE
BACKWASH
 WATER
            SLUDGE
            DRYING
             BEDS
          (OR LAGOON)
TO LANDFILL
                Figure C-7  (continued)
                        205

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                RAW  INFLUENT
                WASTEWATER
                FROM GRIT
                 CHAMBER
 PRESSURE
SANDFILTER
BACKWASH  WATER
                        11
                             FERRIC CHLORIDE
                                ADDITION
                                     SECONDARY CLARIFIER
                                     (HUMUS) SLUDGE RETURN

                                          DIGESTER
                                        -  SUPERNATANT
                                          RETURN
ANIONIC  POLYME5
ADDITION AND-*"
FLASH MIXER
                                          =>
                   I
               TO  PRIMARY
               CLARIFIERS
  Figure  C-8.  Flocculation channel,  Coldwater, Michigan
                           206

-------
Digester supernatant and secondary clarifier sludge enter the
flocculation channel approximately 6.10 m (20 ft) from the flash
mixer at the head of the channel.  Ferric chloride solutions
are added to the gri.t chamber, which is ahead of the flash
mixer, and anionic polymer addition takes place at the flash
mixer.  As previously mentioned, polymer addition began in 1972,
was discontinued in 1976, and was reinstituted in 1977.

     With the advent of chemical addition for phosphorus removal,
the amount of solids entering the flocculation channel  in the
pressure sand filter backwash water has increased steadily.
Solids contained in the supernatant also increased considerably
after phosphorus removal began, although somewhat less  signi-
ficantly after polymer addition was suspended.  The most signi-
ficant increase, however, has been in sludge solids returned to
the flocculation channel from the secondary clarifiers.  The
combined effect of these increases has caused no problems in
the flocculation channel but has resulted in huge increases  in
solids loadings on the primary clarifiers.
    -~«x
     *
Primary Clarifiers--

     The primary clarifiers receive the raw influent wastewater
and the returned sidestreams from the flocculation channel.
Sludge is collected and removed from the bottom of each clarifier
3 times/day, 7 days/wk.  During the intervals between sludge
collection and pumping, a sludge blanket as thick as two feet
builds up on the bottoms of the primary clarifiers.  Settled
sludge is pushed to the sludge hopper in each clarifier by
wooden flights attached to two parallel endless chains.  The
sludge collectors are turned on a half hour prior to sludge
pumping from the clarifier and are operated until sludge pumping
is completed.

     Sludge collected in the sludge hoppers is pumped by the
two primary sludge pumps to the primary digester from one
clarifier at a time.  The sludge solids concentration is
approximately 10 percent TS when pumping begins.  Pumping con-
tinues until the solids concentration is reduced to roughly
3.5 percent TS.

     Since the initiation of chemical addition for phosphorus
removal, the amount of solids influent to the primary clarifiers
and both the quantity and total solids concentration of the
sludge pumped from the primary clarifier to the primary digester
has increased. .Concurrently, the volatile fraction of these
solids has steadily declined.  Due to variations in plant
influent suspended solids concentrations and flow rates (pre-
viously characterized in Table C-9), the impacts of phosphorus
removal  on sludge generation rates cannot be adequately compared
on the basJs of pounds of primary sludge solids to the digester
per mg of plant influent.  Instead, Table C-ll relates the mass


                               207

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of total solids to the digester to the mass of suspended solids
in the plant influent.


        TABLE C-ll.   SLUDGE PUMPED FROM PRIMARY  CLARIFIERS
             TO PRIMARY DIGESTER,  COLDWATER,  MICHIGAN


Year
1976
1973
1971


.e/day (gal/day)
23,100 (6,100)
19,700 (5,210)
14,600 (3,870)

TS
C%)
8.3
6.3
5.6

Volatile
(%)
51
58
72
kg(lb)TS/kg
.(lb), S-S
plant Influent
1.56 (1.24)
0.67 (1.48)
0.51 (1.12)
kg(lb)VS/kg(lb)
VSS
plant Influent
0.41 (0.91)
0.51 (1.13)
0.52 (1.12)
kg(lb)FS/kg(lb)
FSS
' plant Influent
0.90 (2.00)
1.18 (2.61)
0.49 (1 .09)
     On this basis, it can be seen that the mass of volatile
solids to the digester per pound volatile suspended solids in
the plant influent remained roughly the same after the addition
of both ferric chloride and polymer began and decreased slightly
when only ferric chloride was added.  On the other hand, the.
mass of total solids to the digester per pound suspended solids
in the plant influent showed a significant increase when both
polymer and ferric chloride were added and a moderate increase
when only ferric chloride was added.  These increases are
apparently attributable to the increases in the nonvolatile
(fixed) portion of the sludge solids, due to chemical additions
for phosphorus removal .

Trickling Filters--

     A notable impact of chemical addition for phosphorus removal
on the trickling filters at the Coldwater plant has been the
reddish-brown discoloration of the trickling filter structure
and media.  Although BOD loadings to the trickling filters have
increased significantly, percent removals of BOD have remained
constant.  Higher BOD concentrations are thus found in the
trickling filter effluent.

Secondary Clarifiers--
we.l 1
Each
arms
to a
col 1ector
moves the
Scum then
is pumped
clarifier
Trickling filter effluent flows by gravity to a division
which distributes the flow to the two secondary clarifiers.
clarifier. is equipped with a pair of rotating collector
equipped with squeegees to continuously move settled sludge
sludge hopper at the bottom of the tank.  One of the
     arms is equipped with a traveling scum collector which
     collected grease and scum to a fixed scum box assembly.
     enters a scum well along with the secondary sludge and
     to the flocculation channel at the head of the primary
                               208

-------
     Sludge which has settled to the bottoms of the secondary
clarifiers is pumped twice a day to the flocculation channel.
Sludge is pumped from one final clarifier for the same amount
of time.  Both pumps are used to develop enough suction to
prevent clogging of the pumps.  When sludge pumping begins, the
sludge solids concentration is approximately 5 percent TS.
Sludge pumping continues until the liquid delivered to the
flocculation channel no longer has a black color, which corres-
ponds roughly to a solids concentration of 0.1 percent TS.

     Since the beginning of chemical addition for phosphorus
removal, both the secondary sludge volume and total  solids con-
centration have increased, significantly.  This has caused a
huge increase in the TS mass pumped to the flocculation channel.
This increase is the most notable change in plant operations
since chemical additions for phosphorus removal  were started.

Pressure Sand Filters--

     Secondary effluent flows to the pressure sand filters
where approximately half of the remaining suspended solids and
one fourth of the remaining BOD and phosphorus are removed.
Backwash water from the pressure sand filters is discharged to
a holding basin where some solids settling takes place.  Back-
wash water in excess of basin capacity overflows the holding
basin weir and enters the flocculation channel.   The quantities
and characteristics of the backwash water were shown in Figure
C-10.

Detailed Description of Sludge Treatment and Disposal  Operations

Primary Digester--

     Sludge enters the primary, digester 3 times/day, 7 days/wk
from the primary clarifiers.  The primary digester is heated and
mixed.  It is generally maintained at a temperature between 29
and 35°C (85 and 95°F).  Heating and mixing is intermittent,
taking place for at least 16 hr/day, with longer periods during
the fall and winter months.  Mixing of the digester takes place
by compressing the collected gas from the destruction of
volatile materials and discharging it through three gas eductor
tubes enclosed in a hot water jacket in the center of the
digester.  The boiler used to heat the jacket water can be
operated on natural  gas or methane digester gas.

     The primary digester is maintained full at all  times,
except when sludge is withdrawn and transferred to the secondary
(or,  on occasion, holding) digester.  During a digester sludge
transfer, between 114 and 265 m3 (30,000 and 70,000 gal) are
pumped during the day shift over a period of three or more days.
This  is done in an effort to maximize operator efficiency, since
the  positions of a considerable number of valves must be changed

                                209

-------
each time sludge is transferred to or from a different location
(primary, secondary, or holding digester, or sludge drying beds).
After a sludge withdrawal from the primary digester, sludge
transfer does not take place again until the digester has been
refilled.  This is because the primary digester is the only
digester which is heated or mixed and is supposed to account for
the majority of the volatile destruction taking place in all the
digesters.

Secondary Digester--

     Prior to the plant modifications in 1972, the secondary
d.igester was virtually identical to the primary diaester.  At
present, tne secondary digester sludge is neither heated nor
mixed, although the side walls of the digester are surrounded
by soil.  Consequently, the sludge which is transferred from
the primary to the secondary digester retains much of its heat,
allowing digestion and destruction of volatile materials to
continue while solids separation takes place.  Supernatant from
this digester flows by gravity to the scum well ahead of the
primary clarifiers.  Although minor adjustment of the super-
natant overflow pipe height is possible, the quality of the
supernatant returned is largely dependent on the need for
providing additional space in the secondary digester by allowing
more supernatant of less than optimum solids concentration to
be returned to the primary clarifier.  This effect appears to
have been most pronounced during 1973, when an estimated 25
percent of the total solids sent to the primary digester were
returned to the flocculation channel as supernatant.

Holding Digester--

     The holding digester was installed along with the other
plant modifications of 1972.  This digester is situated above-
ground and is neither heated nor mixed.  As a result, only a
small  amount of volatile solids destruction takes place in this
digester, particularly during the winter months.

     Sludge from the secondary digester (and occasionally from
the primary digester) is transferred to the holding digester for
storage until weather conditions or space allow transfer of
sludge to the sludge drying beds.  Thus, digester sludge handling
operations are directed at having as little sludge as is possible
in the holding digester at the beginning of autumn to maximize
the amount of digester volume available for storage of sludge
generated during the winter months when the sludge drying beds
are essentially inoperative.  Due to the format of the data  sub-
mitted by the treatment plant to the state of Michigan, charac-
teristics and quantities of sludge stored in the secondary  and
holding digesters are indistinguishable.
                               210

-------
Digester Performance--

     It, is difficult to assess the impact of chemical addition
for phosphorus removal on the individual digesters due to the
limitation in available data.  No measurements of the volume of
supernatant returned to the flocculation channel  from the secon-
dary or holding digester are available.  Therefore,  it has been
assumed that the volume of supernatant returned is equal  to the
difference between the volume of sludge pumped to the primary
digester minus the volume of sludge sent to the sludge drying
beds (and lagoons).

     Since the start-up of chemical addition for  phosphorus
removal, the percent total solids of sludge entering and  leaving
the digester has increased.  A steady decrease in the fraction
of volatile solids in the sludge fed to the digesters has been
observed.  But the mass of VS fed to the primary  digester/day
increased as follows: 590 kg VS/day (1,300 Ib VS/day) in  1971;
722 kg VS/day (1,590 Ib VS/day)  in 1973; and 976  kg  VS/day
(2,150 Ib VS/day) in 1976.  The  amount of digester gas produced
increased from roughly 5,040 m3/mo (180,000 ft3/mo)  before phos-
phorus removal to more than 11,200 m3/mo (400,000 ft3/mo) after
phosphorus removal.

     The sludge transferred from the secondary and holding diges-
ters to the sludge drying beds (or the lagoons),  also reflects
the trend of decreasing volatile solids fraction  with increasing
total  solids concentration.  Table C-12 indicates that the
increase in the mass of TS transferred from the digester  to the
sludge drying beds,  per pound of suspended solids in the  plant
influent, was due to a large extent to the increase  in the non-
volatile (fixed) portion of the  solids.  Once again, this effect
appears to have been most pronounced when both ferric chloride
and polymer were added to the flocculation channel.   Furthermore,
less volatile destruction took place in the digestion process
overall during this  period.  This resulted in a more than doubled
mass of volatile solids in the sludge transferred to the  drying
beds,  per pound of volatile suspended solids in the plant influent,
as shown in Table C-12.  This is in spite of the  fact that, as

         TABLE C-12.  SLUDGE TRANSFERRED FROM DIGESTERS
         TO DRYING BEDS (OR LAGOON), COLDWATER, MICHIGAN

Year
1976
1973
1971

•tyday
5,960
7,660
3,870

gal/day
1,310
2,025
860
TS
U)
11.4
8.4
6.5
Volatile
IX)
41
50
54
kg TS
kg(lb) SS
Plant Influent
0.167 (0.37)
0.349 (0.77)
n.131 (0.29)
kg VS
kg(lb) VSS
Plant Influent
0.099 (0.22)
0.231 (0.51)
0.099 (0.22)
kg FS
kg(lb) FSS
Plant Influent
0.322 (0.71)
0.730 (1.61)
0.213 (0.47)
                               211

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was shown in Table C-ll, the sludge fed to
contained nearly equal amounts of volatile
on the same basis.

Sludge Drying Beds--
                          the primary
                          sol ids when
                  digester
                  compared
     Sludge is transferred to the sludge drying beds from the
holding digester (or occasionally the secondary digester) at a
rate largely dependent on prevailing weather conditions.  Once
each bed is filled, sludge is not removed until it is determined
to be sufficiently dry, roughly 6.5 percent moisture by weight.
Depending on weather conditions, each bed can be filled three to
four times per year.  The sludge is transferred to the beds in
the fall, generally remains through the cold winter months, and
is removed in the spring.  As shown in Figure C-7, the TS con-
centration of the sludge transferred to the drying beds has
increased considerably, while the volatile fraction of the solids
has decreased since the addition of phosphorus removal chemicals.
As a consequence of these trends, combined with the effects of
paving the former drying beds, the sludge now takes 30 to
50 percent longer to reach the dryness desired for removal and
disposal.

Sludge Lagoon--
     The sludge drying lagoon was excavated shortly after chemi-
cal addition for phosphorus removal  was initiated to provide addi
tional sludge drying space.  '^6 s was necessitated by the longer
sludge drying times, as well as the greater-than-anticipated
quantities of digested sludge generated.  Sludge is sent to the
lagoon on a sporadic basis at times when the drying beds are full
and there is a need to make room in the digesters.  No formal
records have been kept as to the characteristics of the sludge
in the lagoon.

Sludge Treatment and Disposal Costs

Operating and Maintenance Costs--

     The annual O&M costs for the Coldwater plant are based on
the following unit costs:
     Item

Fe C13
Natural Gas
Electricity
Labor (including
benefi ts)
supplies and
     Unit Cost

$0.11/kg ($0.05/lb)
$0.0215/m2 ($0.002/ft3)
$0.0368/KWH
$7.75/hr
                               212

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O&M costs for the 1976-77 fiscal year were as follows:
                Item                           $/Yr

Operator and Superintendent Labor           $ 45,000
Operating Supplies                            40,000
Electricity                                    4,160
Natural  Gas                                    3,660
Water                                          7,840
Maintenance and Repairs                       25^000

Total                                       $125,660

Cost/m3  (MG) influent                       $0.0374/m3   ($142/MG)


     The impacts of- chemical addition on plant O&M costs are dif-
ficult to assess, since major plant modifications occurred at
the time when phosphorus removal was initiated.  According to
plant personnel, most sludge treatment equipment operated at the
plant requires approximately twice the maintenance when compared
with the period prior to the beginning of phosphorus removal.
Since plant flows have nearly doubled in the interim, the rela-
tive increase/MG of plant influent has been negligible.

Capital  Costs--

     The capital cost of the original Coldwaterplant was financed
by 30 year general obligation bonds providing $650,000  at 2.25
percent interest beginning October 1, 1951.  The additions and
modifications to the plant were financed beginning October 1, 1970
as follows:

     Federal Grant              $301,500.00
     State Grant                $800,000.00
     Revenue Bonds              $550,000.00

     Total                    $1,651,500.00

     The revenue bonds mature in 17 years, at an initial interest
rate of 4.5 percent per annum.   In 1983, the interest rate begins
to increase, reaching 5.5 percent at maturity.

Summary and Conclusions

     There has been a significant increase in  sludge and side-
stream solids concentrations entering and leaving every unit of
the Coldwater, Michigan, wastewater treatment  plant, beginning
                               213

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with the flocculation  channel  through  the  sand  drying  beds.   The
impacts of chemical  addition  on  the  treatment  units  were  as
follows:

     Flocculation Channel  -  more solids  entering  in  the  following
     sidestreams:

          t  Secondary clarifier sludge
          t  Digester  supernatant
          •  Pressure  sand filter backwash water
          t  Ferric  chloride  and an ionic polymer  additions.

     Primary Clarifiers:

          •  Increased average SS loading

          t  Increased volumes of primary  sludge  pumped  to  pri-
             mary digester at  higher average TS concentration
                                                            M
          t  Decreased average BOD and SS  removal  efficiencies.

     Trickling  Filters:

          •  Increased average BOD and TS  influent and effluent
             concentrations

          •  Discoloration of  filter media.

     Final  Clarifiers:

          •  Increased average SS loading

          •  Increased volumes of sludge pumped to flocculation
             channel at  higher average TS  concentration.

     Pressure Sand  Filters:

          •  Increased SS  loading

          •  More backwash water at  higher average SS  concentra-
             ti on.

     Digesters:

          •  Increased .volumes of sludge feed  at  higher average
             TS  concentration

          •  Higher  supernatant  average  SS concentration.

     Sand  Drying Beds:

          t  Increased quantities of  sludge requiring  longer
             d ry i n g  times.

                               214

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     In conclusion, a solids build-up has occurred throughout the
p.lant.   The additional  solids have been almost entirely nonvola-
tile.   Although(0&M costs have nearly doubled since phosphorus
removal began* the plant flow doubled at the same time, resulting
in no  increase in treatment costs per million gallons of plant
influent.

CASE STUDY F:   LAKEWOOD, OHIO

Introduction

     The Lakewood, Ohio, experience is similar to that encoun-
tered at many older facilities which have inadequate sludge
handling capacity.  Soon after the plant was built in 1966, it
became apparent that available flash drying capacity was inade-
quate, and as the equipment has aged, its Capacity has further
decreased.  Alum addition for phosphorus removal  further
decreased the dryer's capacity by increasing the moisture con-
tent of the filter cake, and alum has also increased the amount
of sludge to be handled.  A bottleneck in the solids handling
end of the plant has resulted.  This had led to high solids
buildup and recirculation throughout the plant and a high SS
concentration in the plant effluent.

     In spite of the problems created by inadequate sludge
handling capacity, the plant management stayed, until 1975, with
a filter and dryer operation schedule of one 8-hr shift/day
because of budget considerations.  It has been possible to
observe the effects on plant performance of extending the oper-
ation of two shifts.

     It has also been possible to observe the effects on plant
performance of hauling liquid sludge from the digesters.  It
appears that, liquid sludge hauling as a sludge management
alternative is frequently relied upon by plants which have
additional sludge to handle because of phosphorus removal but
do not have the necessary existing sludge handling capacity.

     As with other wastewater treatment plants, sludge produc-
tion at Lakewood is affected by changes in wastewater flow
volume.  The plant was designed to treat 0.05 mil m3 (13 MG) of
wastewater per day.  The actual average dry weather flow is only
0.045 mil  m3/day" ('12 mgd).  But peak flow rates occurring during
wet weather are considerably higher, since sanitary and storm
sewers in the area are 40 percent combined.  Table C-13 shows the
average and peak influent flow rates for each year since 1973.
Before September of 1975, peak flows reached almost 0.076 mil m3/
day (20'mgd).   Since then, they have been kept at 0.060 mil. m3/
day (16.0 mgd) by bypassing the excess to the river.  Before
bypassing was used, on days of heavy flow, treatment efficiency
was reduced and effluent suspended solids concentrations reached
400 mg/£.

                               215

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    TABLE C-13.  PLANT INFLUENT WASTEWATER FLOW RATES, LAKEWOOD, OHIO
Year
1973
1974
1975
1976
1977 (thru
May)
Average
Total mil m^/day
0.055
0.055
0.050 •
0.051
0.042 "
Total mgd
14.6
14.6
13.3
13.4
11.2
Peak .
Total mil m3/day
0.075
0.073
0.067
0.060
0.060
Total mgd
19.8
'• 19.4
17.7
16.0
16.0
~ 	 =»
History

     The following description details historical plant changes
which have affected sludge characteristics:

     1938 - Original  Imho'ff plant constructed; sludge anaerobi-
            cally digested and dewatered on sand drying beds.

     1966 - Conventional  activated sludge plant constructed;
            gravity thickeners, two new anaerobic digesters,
            two vacuum filters, and a flash dryer added to
            handle additional  sludge.

     1974 - Alum addition for  phosphorus removal begun.

     1975 - Sludge handling system (filters and dryer) operating
            schedule  extended  to two shifts to handle additional
            sludge generated.

     1977 - Returned  to single shift sludge handling; hauled
            excess liqu.id sludge to land disposal.
Chemical  Addition for Phosphorus Removal
                 (48.4 percent Al2(S04)3
                                  sludge effluent channel, an
T4 H20) is added to
     Liquid alum
the mixed liquor in the activated
open concrete channel leading to the  final  division  well  ahead
of the secondary clarifiers.  The  alum  is  added  through  a non-
submerged pipe at a point about 2  m  (5  ft)  from  the  aeration
tank effluent weir and 20 m  (.70 ft)  before  the  final  division
we! 1 .

     The chemical dosage is  controlled  by  manual  adjustment of
the chemical feed pump settings.   The pumps  are  normally reset
at midnight and at eight in  the morning each  day to  compensate
for the smaller wastewater flow at night.   The  same  settings
are used each day unless the plant effluent  phosphorus  concen-
                               216

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 tration  increases,  in which case more chemical  is added.   A
 total  of about 4,160 m3 (1,100 gal) of alum are used each day.
 Each  liter liquid contains 0.650 g/nT of Al2(S04)s • 14 H20 (5.4
 lb/gal).   Therefore, the average wastewater concentration is
 approximately 63 ppm Al2(S04)3 • 14 H20.
      Presently,  the plant is not achieving the required  1  mg/£
 effluent  total  phosphorus concentration because ft cannot
 handle the additional  sludge which is produced when alum dosage
 is  increased or  a polymer is used.  Only 65 percent reduction  of
 the total  phosphorus concentration of the influent is  achieved
 within the plant.  The average final  effluent concentration  is
 6.4 mg/£.

 General Description of Wastewater Treatment Operations

      Figure C-9  shows  the treatment system flow diagram.
 Suspended  solids in the raw sewage influent plus  biological  and
 chemical  solids  generated by the activated sludge and  phosphorus
 removal operations are collected by the primary and secondary
 clarifiers and  then are gravity thickened.  A portion  of the
 solids are converted to liquid and gas by the digesters, with
 the remainder being either hauled to  agricultural  lands, dried on
 sand beds, or vacuum filtered and flash dried.   The under-
 drainage  from the sludge drying beds  and the thickener opera-
 tions  are  returned to  the front of the plant.  Other sidestreams
 from sludge treatment  operations (.digester supernatant,  vacuum
 filter filtrate  and flash dryer scrubber water) are collected
 and returned to  the system at the primary division well.

      Descriptions of sludge-significant wastewater treatment
 unit operations  follow.

 Primary Clarifiers--
                               ^
      The  primary clarifiers consist of four circul ar .Eimco units,
 with 19.8  m (65  ft) diameters, 308 m2 (3,320 ft2)  surface  areas,
 and 2.9 m  (9.4  ft) side water depths.  Each clarifier  holds
 883 m3 (0.233 MG).  Scum is collected in scum boxes and  pumped
 to  the primary digesters.  Sludge is  mechanically scraped  to a
 hopper in  the center of the sloping clarifier bottom by  four
 revolving  arms.   The sludge hoppers are 0.9 m (3  ft) deep,
 0.9 m  (3  ft)  by  0.6 m  (2 ft) wide at  the top, and  narrowing  like
 a square  cone to a 15  cm (6 in) sludge outlet pipe at  the  bottom.

     Although there is room in the primary clarifier bottoms,
 sludge storage here is avoided.  Sludge is continually scraped
 from the  bottoms of the clarifiers, and it continually flows by
 gravity from the hoppers to the primary sludge well.  The
 primary clarifiers are not equipped or operated to achieve
.thickening,  although less frequent removal of sludge could
 probably  be  practiced  to allow thickening of sludge to a higher

                               217

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ro


oo
                                                                     COHHINUTORS


                                                                     PRIMARY DIVISION

                                                                         WELL
                                  THICKENER OVERFLOW
SLUOGC I


PRIMARY
st_unfif?
WELL



SECONDARY
SLUDGE
WELL
                                                                                                                     8
                                                                                                                     o
                                                                                                                     E
                                                                                                 SECONDARY (WASTE

                                                                                                 ACTIVATED! SLUDGE

SUPERNATANT

ft 1 IMP

1
OVERFLOW

                                                   FILTRATE
                                                                SCRUBBER WATER
       AGRICULTURAL

         LANDS
SLUDGE

FLASH

DRYER
                                                                                        DRIED SLUDGE
                                                                                        BAGS OR BULK
 SOIL

' CONDITIONING
                  Figure  C-9.    Lakewood,  Ohio,  wastewater treatment  plant  flow  diagram.

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solids concentration.  This is avoided, however, because the
plant manager wishes to avoid problems in thickener operation
which might be caused by a heavier sludge feed.

Secondary Clarifiers--

     The secondary clarifiers are four circular Eimco units
with 23 m (75 ft) diameters, 411 m2 (4,420 ft2) surface areas.
and side water depths of 3.6 m (11.7 ft).  Each has a 1,465 m3
(0.387 MG) capacity.  The sludge collection mechanism is the
plow and scraper type like that used in the primary clarifiers.
The sludge hopper is 1.2 m (4 ft) deep and 0.6 m (2 ft) by 0.9 m
(3 ft) wide at the top.  It then narrows to a 20 cm (.8 in)
sludge outlet pipe at the bottom.

     The secondary clarifiers are heavily relied upon for sludge
storage because the plant is overloaded with secondary sludge
which has no place to go.  A significant portion of this sludge
is due to alurr- addition for phosphorus removal.  A sludge
blanket about 2.3 m (7.5 ft) deep has built up in the secondary
clarifiers.  The detention time of sludge in the secondary
clarifier bottoms may be somewhere around 1.3 hr, even though
sludge is continually scraped to the hoppers and continually
flows by gravity to the secondary sludge well and then to the
primary sludge well.  Pumping of sludge from the primary and
secondary sludge wells is also continuous.

Activated Sludge Aeration Basins--

     The eight aeration basins are operated as conventional
activated sludge treatment units with somewhat tapered aeration.
Mixing and aeration both are accomplished with diffused air.
Each basin holds 1,950 m3 (0.515 MG), giving a total capacity
of 15,600 m3 (4.12 MG).  Primary effluent and return activated
sludge enter and flow the lengths of four of the eight basins,
then flow down the other four basins before emptying into the
eff1uent channel .

     Because the gravity sludge thickener is overloaded, 97 to
98 percent of the secondary sludge which is produced is recir-
culated to the aeration basins as return activated sludge.
This has resulted in a high mixed liquor suspended solids con-
centration .

Detailed Description of Sludge Treatment and Disposal Operations

Thickening--

     The two circular Eimco gravity thickeners have 10.7 m  (35
ft) diameters and 3 m (10 ft) side water depths.  The thickeners
were designed to operate with an influent total solids concentra-
tion of less than 0.2 percent.  Mechanisms for sludge stirring

                               219

-------
 or polymer addition  are  absent.   Sludge  is  fed  at  the  center  of
 the top of each  clarifier.   Two  collector  arms  on  the  bottom
 of each thickener scrape the thickened  sludge  toward circular
 center hoppers which are approximately  l.lm  (36  ft  6  in)  in
 diameter and  0.6 m (2  ft)  deep.   Sludge  is  pumped  from the
 hoppers to the digesters.   Sludge from  the  #1  thickener is
 pumped to the #1  primary digester,  while that-from the #2
 thickener is  pumped  to the  #2  primary digester.

      The sludge  thickener  is continuously  fed  combined primary
 and secondary from the primary sludge well  at  a rate of 3.240
 m3/min (850 gal/min).  Sludge  is  removed from  the  thickener
 intermittently at 0.282  m3/min (75  gal/min) for 15 min each hour.
 The top of the sludge  layer in each  thickener  is  near  the over-
 flow weir.  This  overloaded condition is responsible for solids
 carryover and frequent thickener  bulking.

 Digestion--

      There are four  above-ground  anaerobic  digestion tanks.   The
 primary digesters are  22.9  m (75  ft) in diameter with  a 6.8 m
 (22.5 ft)  side water depth,  while the secondary digesters are
 18.3 m (60 ft) in diameter  with a side water depth of  5.8 m
 (19 ft).   The sludge flow  pattern through  the  digesters is
 shown in Figure  C-10.  Sludge  flows  by  gravity  from  the primaries
 to  the secondaries.
  FROM
THICKENED
                             #1
                          SECONDARY
                          DIGESTER
             #1
           PRIMARY

           DIGESTER
                             #2
                          SECONDARY

                          DIGESTER
  EROM
THICKENER
             #2
           PRIMARY

           DIGESTER
                                           TO
                                         SLUDGE
                                       DRYING BEDS
                                             HOLDING
                                              TANK
                                                        TO

                                                      VACUUM
                                                       FILTERS
                                         HAULED TO
                                     AGRICULTURAL LANDS
Figure C-10.  Lakewood,  Ohio,  anaerobic  digester  configuration
     The primary digesters are mixed and  heated.   The mixing
mechanism is a "circulating mixer" consisting of a  propeller  on
a shaft inside of a draft tube.  Each primary digester  has
three circulating mixers, each capable of circulating at  least
473 £/sec (7,500 gal/min) o.f water.
                               220

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     The temperature in the primary digesters is maintained at
77.2 to 87.2°C (95 to 105°F).  Heating is accomplished by recir-
culating sludge through two external heat exchangers.  Sludge
recirculation through .the heat exchangers also provides limited
mixing of the contents of the primary digesters.  The two hot
water boilers serving the heat exchangers can run on either
methane digester g.as or No. 2 fuel oil.  Throughout most of the
year, digester gas alone is used.  It is consumed in the winter
at a rate of 896 to 1,060 m3/day  (32.000 to 38,000 ft3/day) per
boiler and at a rate of 360 to 560 m3/day (13,000 to 20,000 ft3/
day) in the summer.  In addition, approximately 3.785 m3/yr
(1,000 gal/yr) fuel oil are needed for digester heating.

     The primary digesters have uninsulated anchored steel  dome
covers while the secondaries have insulated floating covers.
Methane gas is collected from all four digesters and compressed
into two storage spheres for use  in digester and building
heating.

     The secondary digesters are  neither mixed nor heated.
Sludge in the secondaries stays warm at about 87°F due to pre-
vious heating in the primaries.   Supernatant can be drawn from
the secondary digesters at three  different levels, 1.8 m (6 ft),
1.5 m (5 ft), and 1.2 m (4 ft) from the top.

     Each primary digester is fed from one thickener for 15 min/
hr, 24 hr/day.  Therefore each primary digester is fed for  a
total of 6 hr/day at 0.284 nr/rain (75 gal/min), 7 days/wk.
Sludge overflow from the primaries to the secondaries and super-
natant overflow from the secondaries is more or less continuous
by gravity.  From each secondary  digester, 19 m3 (5,000 gal) of
sludge are pulled to tank trucks  4 times a day, 5 days a week.
In addition, sludge flows by gravity 0.144 m3/min (38 gal/min)
from each secondary digester to the  holding tank for approxi-
mately 3 hr and 15 min/day, 5 days/wk.  When the filter and dryer
was.operated 2 shifts a day, as before liquid sludge hauling was
practiced, the flow rate from each digester was about 0.16  m3/
min (42 gal/min) about 7 hr/day,  5 days/wk.  Finally, each  sand
drying bed is fille-d twice a year with digested sludge.

     The digested sludge holding  tank is a simple 49,000-m3
(13,000-gal) tank.  It is unmixed, and no dilution water is
added to it or supernatant removed.

     The digesters have not been  cleaned since they were
installed in 1966, and their effective volume is presumed to
be considerably reduced from their total volume.  There is
evidence that the sides and corners of the secondary digesters
are filled in with a very heavy sludge (estimated at about  15
percent solids).  •
                               221

-------
 Dewatering-Vacuum Filters--

     Two Eimco belt-type rotary drum vacuum filters are used
 for dewatering digested sludge.  Each filter has a drum diameter
 of 3 m  MO ft), a length of 3.6 m (12 ft), and filtering area
 of 35 m2 (376 ft^).  The filters have 24 drum compartments.
 The vacuum pumps have a capacity of 15 m^/min (545 ft^/min) at
 51 cm (20 in) Hg vacuum.  The filter drive motors are variable-
 speed,  enabling a drum speed of 1.5 to 9 min per revolution.
 The filter medium is polyethylene cloth.  The filter tanks are
 equipped with swing-type agitators capable of completing 6 to 18
 cycles/min.

     The design filtering performance specifies a capability of
 filtering a sludge of 1.5 to 3 percent solids at a rate of 35
 to 65 kg/nr/hr (1.25 to 2.25 1b/ft2/hr) when properly conditioned
 with ferric chloride and lime.  The maximum suspended solids
 concentration of the filtrate is specified as 500 ppm.

     Only one vacuum filter can be operated at a time because
 of the  limiting capacity of the flash dryer.  One filter operates
 5 days/wk and for 6.5 hr/day when operated one shift, and 13 hr/
 day when operated two shifts.  Conditioning chemical dosages
 are roughly 137 kg dry 1ime/t of dry solids (275 Ib dry lime/
 ton), and 0.283 m3 (63 gal) liquid ferric chloride (40 percent
 FeCls)  or 15 kg. FeClg/t of dry solids (30 Ib FeClg/tj.  The
 ferric  chloride is diluted to 17 percent before mixing with
 sludge  in the flash mixer, and the lime is slaked.  The lime
 is purchased as pebble lime, 72 percent CaO (calcium oxide).
 The filter drum speed has been set at 8 rain/revolution and the
 depth of drum submergence is around 0.76 to 0.91 m (30 to 36 in).

 Dewatering-Drying Beds--

     The six sludge drying beds are greenhouse-enclosed sand
 beds which are ventilated through open doors and windows.  The
 beds consist of 23 cm (9 in) of sand underlain by 8 to. 23 cm
 (3 to 9 in) of gravel.  The effective size of the filter sand
 is 0.25 to 0.50 mm with a uniformity coefficient not greater
 than 4.0.  Bed filtrate collects underneath in a lengthwise
 row of drain tile under the middle of each .bed.  These conduits
 empty into a long intersecting drain which runs to the raw
 sewage lift station.   The beds are 8.5 m (27 ft 8 in) wide, and
 50 m (163 ft) long.  The concrete bed walls rise 0.5 m (1.5 ft)
 above the sand.   Dried sludge is lifted from the beds manually
with a fork.   The dried sludge is then made available to the
 public.   Interested persons can drive into the plant and pick up
 the sludge, or it can be delivered to them in a 2-1/2-ton dump
truck.

     Sludge is applied to the drying beds twice a year.  The
 first application is  in the spring and the second at the end of

                              222

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the summer.  All but two beds are filled at these times.  The
two beds are available for use later, should the filter and
dryer system be down for repair.

Heat Drying--

     The plant has a flash drying system by C-E Raymond Combus-
tion Engineers.  Filter cake is transported by a belt conveyor
to the dryer.  The design capacity of the dryer is 825 kg dry
solids/hr (1,820 Ib/hr).  The design is based upon the following
sludge cake feed characteristics:

     t  Moisture content 75 percent
     •  Volatile matter 51.4 percent
     •  3,000 kg cal/kg (5,400 Btu/lb) of dry solids.

The furnace burns either No. 2 fuel oil or methane digester gas.

     Sludge drops off the conveyor into a pug mill mixer where
it is thoroughly mixed with dried sludge.  The sludge then
passes through a cage mill where it is pulverized and entrained
with rising air and gases which have been heated in a furnace.
Sludge and hot gases rise 9 m (.30 ft) through a vertical duct
to a cyclone separator.  The dried sewage solids are separated
from the hot gases and dust which are drawn off by an induced
draft fan.  The hot gases go either back down to the pug mill
to be recycled through the system or they go to a deodorizing
preheater where some of their heat is recovered in preheating
combustion air.  From the preheater, the gases go into the fur-
nace to be deodorized.  Then they pass through the combustion
air preheater for further heat recovery before entering the wet
scrubber.

     The wet scrubber consists of a wet centrifugal precleaner
followed by a dynamic precipitator with ,a water spray.  The
dust-laden scrubber water is discharged and returned to the head
of the treatment plant.

     The dried sludge passes from the cyclone separator through
an airlock, and 80 to 85 percent of it is recycled back to the
pug mill to be mixed with wet filter cake while 15 to 20 percent
is conveyed to storage.

     The dryer is furnished with a pneumatic dried sludge cooling
and conveying system to receive the product from the drying
system and deliver it to the storage bin.  It consists of a
cyclone collector, fan, and wet scrubber.  There is also a
dried sludge bagging machine and bulk loading conveyor.  Inter-
ested persons can pick up the bagged product at the plant for
use on lawns, gardens, etc.  Deliveries are made by the plant
to bulk users in a truck that carries 4 tons.
                               223

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      The  flash dryer operates whenever sludge is being filtered.
 However,  the  furnace, is started up an hour before filtering
 begins.   When sludge is being fed, the furnace is at a tempera-
 ture  of roughly 815°C  (1,500°F), and the hot gases are at about
 593°C  (1,100°F) when they are mixed with the sludge feed.  The
 furnace is  run on No.  2 fuel oil at 210,900 kg/m2 (300 psi)
 pressure  or occasionally on methane gas at 4,218 kg/nr (6 psi)
 pressure.   When drying two shifts per day, approximately 3.785
 m3/day  (1,000 gal/day) fuel oil are consumed; when drying one
 shift  per day, about 2.08 nr/day (550 gal/day) are consumed.

 Disposal  of Liquid Sludge--

      The  plant has contracted a private firm to haul liquid
 digested  sludge.  The  company specializes in hauling liquid
 municipal sludge, lime water sludge, and septic tank sludge.
 Hauling of  Lakewood liquid sludge has been going on only since
 June  of 1977.  A  "tee" was installed on the line running from
 the digesters to  the holding tank, so that sludge could be
 sucked directly into a tank truck with a vacuum pump.  When the
 sludge  is heavy,  a piston pump, normally used to pump to the
 drying beds,  is also applied.  TJie tank trucks which are used
 hold  17,000,  18,900, or 20,800m3  (4,500,  5,000,  or  5,500 gal)
 of sludge.

      Sludge is hauled  approximately 115 km (70 mi) to agricul-
 tural  lands outside of the Cleveland suburbs.  From the tank
 truck  the sludge  is forced into a special truck or "field
 jimmy" which  is adapted for spreading liquid sludge on fields.

      Normally eight 19,000-m3 (5,000-gal) loads of digested
 sludge are  hauled per  day, 5 days/wk.

 Impact of Phosphorus Removal on Wastewater Treatment Operations

     Alum is added for phosphorus removal to the channel between
 the aeration basins and the final  clarifiers.  Final clarifi-
 cation is directly affected by the alum by increasing the capture
 of SS and BOD.  The resulting chemical sludge indirectly affects
 primary and secondary  clarification and activated sludge treat-
ment by altering  the composition of the sidestreams and flows
 entering these processes.

     Wastewater samples for SS, BOD, and phosphorus analyses
are taken at an insufficient number of points in the treatment
process to allow  a complete analysis of the impact of the
chemical sludge on wastewater treatment operations.  For example,
a single sampling point exists before the primary clarifiers,
ahead of the point where the sidestreams from the sludge treat-
ment processes join the raw sewage.  There is no sample of  the
wastewater which actually enters the primary clarifiers.


                               224

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     Table C-14 presents data taken from plant monthly reports on
wastewater SS, BOD, and total phosphorus and orthophosphorus
concentrations.  Routine samples for SS and BOD determination
are taken of the raw sewage at the magnetic flow meter building,
of the primary clarifier effluent, and of the final effluent.
Phosphorus determinations are made only on the raw sewage and
final effluent.  The table presents the average concentrations
for 1 yr with no alum addition, and 1 yr during which 63 mg/£
was added to the sewage.

     There is only a small difference between the plant influent
and primary effluent SS and BOD figures.  This indicates that
the return sidestreams from the thickeners and digesters are
contributing heavy solids loadings to the primary clarifiers.
The solids accumulate in the primary clarifiers from whence they
are fed back to the thickeners and digesters, thus being trapped
essentially in a closed-loop system.  Table C-14 shows that the
primary effluent SS concentration was higher when alum was
added than before, presumably due to the heavier solids loading
contributed by the sidestreams entering the primary clarifiers.

     Suspended solids mass balances were constructed about the
primary clarifiers to the extent possible with available plant
data.  Figure C-ll is a mass balance which is derived from a year
of performance data during which 63 mg/£ alum addition was
practiced.  Figure C-12 portrays the situation for a year with
no alum addition, but data for this period is incomplete.

     The information in Figure C-ll shows that the sidestreams
are contributing a loading of 6,948 kg/day (15,305 Ib/day) SS
to the primary clarifiers.  This figure is greater than the
6,025 kg/day (13,272 Ib/day) contained in the plant influent.
By far the most significant sidestream in terms of solids input
is the thickener overflow, carrying 6,433 kg/day (.14,171 Ib/day)
SS.  The plant superintendent has indicated that the thickener
overflow quality deteriorated when alum addition was started,
but the average increase in solids concentration is unknown.
The digester supernatant also contributes a large amount of
solids, and a comparison of Figures C-ll and C-12 shows that the
supernatant quality was poorer during alum addition.

     During alum addition, higher SS and BOD loadings were
carried into the aeration basins in the primary effluent.
Table C-15 shows that the plant's final effluent concentrations
did not change significantly, however.  This indicates that the
addition of alum allowed increased capture of solids and BOD in
the final clarifiers.  Table C-15 shows the "removals" (or the
differences between primary and final effluent concentrations)
of SS and BOD during secondary treatment with and without alum
addition.  There were on the average 0.015 kg/m3 (125 Ib/MG)
additional SS and 600 kg/mil m3 (5 Ib/MG) additional BOD removed
during alum addition.  These figures do not give the whole

                               225

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TABLE C-14.   PLANT SS,  BOD,  AND PHOSPHORUS  CONCENTRATIONS BEFORE AND
    DURING ALUM ADDITION FOR PHOSPHORUS  REMOVAL, LAKEWOOD, OHIO

Wastewater flow
m3/day (mgd):
Plant influent SS
Primary effluent SS
Final effluent SS
(mg/£) :
Plant effluent BOD5
(mg/£):
Primary effluent 6005
(mg/£):
Final effluent BODs
(mg/£):
Plant influent total
phosphorus (mg/£):
Effluent total phosphorus
(mg/£) :
Plant influent ortho-
phosphorus:
Effluent ortho-phosphorus:
No alum addition
(Nov. 72 to Oct. 73)
55,700 (14.9)
111
94.6
32
97
84
13
11.8
9.5
6.9
8.2
63 mg/l alum addition
(Jan. 74 to Dec. 75)
54,600 (14.6)
109
105.6
28
108
84.6
13
18.29
6.4
8.6
4.15
                                226

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ro
ro
55
SS
W .
13,270
109
OAK
6 MGD


'y
/^i
uy<
SEWAGE
INFUJF.NT
                                  VACUJM FILTER

                                 ' KGD FILTRATE
SS 1,130
SS 1.360
SCRUBBER
' MGD WATER

!Tv
p


SS
SS
I'l.
3^'l2p 	 	
28
y
O)A1
x
SECONDARY
HOD EFFLUENT


:TICN 1



i3,s6o ^y
TS 17,300 °/f
„_. WASTE
•°94 MGO ACT. SLUDGE
                             SCRUBBER WATER                  FILTRATE



      NOTE:  HEAVILY OUTLINED BOXES CONTAIN ESTIMATED  VALUES.   N/A = NOT AVAILABLE.
           Figure C-ll.   Lakewood, Ohio, hydraulic and solid mass balance  during 63 mg/£ alum addition
                          (Jan through Dec 74)

-------
13.600
SS III
14,9 HGD
V
,/WY
X
RAH SEWAGE
INFLUENT


•x
Xn»v
X
M FILTER
IE



N/A
N/A
u,/
/DAY
X
•"- "SET


ro
ro
oo
H.A.
TS 93O.OOO
J--6AV
3r
H7A. DRIED SIUW£
H.A.
IS 237,700
*&
y,
N.A, FILTER CAKE

N/A
TS «.5S3



                                                                                               NQlESp N/A * NOT AVAILABLE,

                                                                                                    tCAVlLV OUTLINED

                                                                                                    BOXES CONTAIN

                                                                                                    ESTIMATED VALUES.
                                                                              1453* CHEMICALS
                                      SCRLBOER MATER
                 Figure  C-12.
Lakewood, Ohio, hydraulic and solid mass balance  before alum addition
(Nov 72  through Oct 73)

-------
   TABLE C-15.  PLANT SS, BOD, AND PHOSPHORUS REMOVAL BEFORE AND DURING
             ALUM ADDITION FOR PHOSPHORUS  REMOVAL, LAKEWOOD, OHIO
        Removal
                                        Secondary Treatment
    No Alum
kg SS/nr (Ib/MG)

kg BOD/m3 (Ib/MG)

% SS

% BOD



	Removal

kg P/m3 (Ib/MG)
   Total
   Ortho

% P
   Total
   Ortho

kg SS/m3 (Ib/MG)

kg BOD/m3 (Ib/MG)

% SS

% BOD
  63 mg/ZAIum
   Difference
0.06 (522.1)    0.077 (647.2)

0.071 (592.1)   0.072 (597.1)

66.2            73.5

84.5            84.6


                    Total Plant
                   0.017 (125.1)

                   0.001 (5.0)

                   7.3

                   0.1
    No Alum
0.002 (19.2)
0.0013 (10.8)
19.5
18.8

0.08 (658.9)

0.084 (700.5)

71.2

86.6
  63 mg/l Alum
0.018 (15.2)
0.004 (37.1)
65.0
51.7

0.081 (675.5)

0.095 (792.3)

74.3

88.0
   Difference
0.016 (133.3)
0.006 (47.9)
45.5
70.5

0.002 (16.6)

0.010 (91.8)

3.1

1.4
                                    229

-------
picture, however, because the aeration basin influent includes
the return activated sludge in addition to the primary effluent.
The mass balance figures, C-ll and C-12, indicate the role of the
return activated sludge solids.  Because of a higher TS concen-
tration in the return activated sludge, and an increase in the
mass of solids returned during alum addition, the solids loading
to the aeration basins went up and the mixed liquor suspended
solids concentration rose by 56 percent.  With this information,
it is possible to calculate the SS mass removed in the final
clarifiers before and after alum addition.  The MLSS concentration
is taken as the SS concentration of the final clarifier influent.
Effluent SS concentration and wastewater flow rate are also known.
The mass of SS removed can thus be calculated as 2.85 kg/m3
(23,827 Ib SS/MG) before alum addition, and 4.48 kg/m3 (37,380 Ib
SS/MG) during alum addition.  The difference is 1.63 kg/m3
(13,553 Ib SS/MG).  On a per-day basis, there were 86.1 kkg/day
(95 tons/day) more secondary sludge SS generated during alum
addition.

Impact of Phosphorus Removal on Sludge Treatment and Disposal
Operations

Additional Sludge Quantity Produced by Alum Addition--

     Figures C-ll and C-12 summarize all available information on
volume and mass changes in sludges and  sidestream quantities
after alum addition.  Data contained in monthly reports indicate
that as a result of alum addition to the channel between the
aeration basins and the secondary clarifiers, the average  TS
concentration of the secondary sludge  rose from 1.17 to 1.73
percent TS.  The volume of secondary sludge  remained the same,
however.  After alum addition, approximately 0.015 mil m3/day
(4.1 mgd) secondary sludge were still  generated, with  0.015  mil
m3/day (4 mgd) still being returned to  the aeration basins  and
0.004 mil m3/day (0.1 mgd) still being  wasted to the gravity-
thickeners.  Because of the higher solids concentration of  the
sludge, however, calculation shows that an average of  78.9  kkg/
day (87 ton/day) more secondary sludge  TS were  generated,  or
1.5 kg/m3 (12,554 Ib/MG).  This is similar to the estimate  of
86.1 kkg/day (95 ton/day), or 1.62 kg/m3  (13,553 Ib/MG) addi-
tional sludge SS arrived at in the last section by a calculation
of mass balance.
Of the 78.9 kkg/day (87 ton/day) additional sludge TS,
                                             rned to t
                                             (2.5 ton/day)
          e   .    gay      onay   aona
approximately 76.6 kkg/day  (84.5 ton/day)  are  returned  to  the
aeration basins, while approximately  2.26  kkg/day
are wasted to the thickeners

Operational Problems Attributable to the Production of Chemical
SI udge--

     Gravity thickeners—Al urn addition created essentially  no
change in the hydraulic balance of the thickener.  However,  the
                                230

-------
solids concentrations and, therefore, the solids loads of the
sludge feed, the thickener overflow, and the thickened sludge,
were increased.

     Approximately 2,270 kg/day (5,000 Ib/day) of additional
secondary sludge TS were pumped to the gravity thickeners after
alum addition.  Figures C-ll and C-12 show that the mass of
gravity thickened sludge which was pumped to the digesters
increased by a similar amount.  The total solids concentration
of the thickened sludge which was pumped to the digesters rose
from 4.34 to 5.6 percent.

     It is likely that the average SS concentration of the
thickener overflow was higher after alum addition than before,
due to more severe thickener overloading and more frequent
thickener bulking.  The thickener overflow, heavily loaded with
solids, is returned to the primary clarifiers where it contri-
butes to primary sludge.  Since the primary sludge is pumped
back to the thickeners, a circular flow path exists.  A heavy
solids load is recirculated along this path.

     The thickeners were designed for a surface settling rate
of 33 m3/day/m2 (811 gal/day/ft2).  Both before and after alum
addition, the actual rate was much higher than this, about
46.6 m3/day/m2 (1,143 gal/day/ft^).  According to the plant
superintendent, the thickener was designed for a sludge feed  of
less than 2,000 ppm TS.  The actual feed concentration was at
least 2,400 ppm before and during alum addition.  A sludge
blanket ranging from about 1.8 m (6 ft) to the entire water
depth of the thickener has built up.  The supernatant SS concen-
tration ranged from 22 to 3,974 ppm in the course of 1 mo during
alum addition.  Thickener bulking occurs frequently with periods
of stable operation in between.  Bulking may have been somewhat
less frequent before alum addition according to the plant
superintendent.

     Digesters — The volume of sludge pumped to the digesters  was
essentially unchanged by alum addition.  The hydraulic balance of
the digesters was altered, however, because the volume of removed
sludge decreased while the volume of supernatant increased.  Pre-
sumably, the volume of sludge removed was decreased because of
reduced filter and dryer capacity.

     The TS concentration of the supernatant increased to the
point that it was almost as high in solids as the digesting
sludge itself.  This occurred because there was little room in
the digesters for solids-liquid separation.

     The average volatile solids concentration as a percentage
of total solids of the sludge fed to the primary digesters
decreased from 63.8 before alum addition to 57.8 with alum addi-
tion.   The percent volatile solids of the digested sludge

                               231

-------
 decreased  from  50.2 before al um addition to 44.8 with alum addi-
 tion.  The  percent volatile reduction, as calculated by the for-
 mul a

      MO  -  inn    n  % ASH in raw x % VS in digested>
      VR  -  100 x  (1- g vS in raw x % ASH in digested'

 as  42.8  before  alum addition and 40.7 percent with alum addition.
 The average gas  production during one year of operation before
 phosphorus  removal was 1,994 m3/day (71,200 ft3/day), while the
 average  production of methane during 1 yr with alum addition was
 2,178 m3/day  (77,800 ft3/day).  The digester gas characteristics
 were  not measured before alum addition, but a single recent anal-
 ysis  is  available showing the following composition:

      Carbon dioxide (C02)         33%
      Methane  (CH4)                67%
      Carbon monoxide            0.01%
      Hydrogen sulfide (H2S)      100 ppm
      Sulfur dioxide                2 ppm
      Nitrogen dioxide (NOg)     <0.1

 A  recent study  analysis also showed the following composition of
 the digested  sludge:

      Potassium  (k)              0.08%
      Total  Kjeldahl nitrogen     646 yg/gram dry basis
      Nitrate  nitrogen          23.75 yg/gram dry basis
      Total  phosphate           1,064 yg/gram
      Cadmium                    0.32 ppm
      Zinc                      1,475 ppm
      Copper                     25.3 ppm
      Chromium                   13.5 ppm
      Mercury                   0.135 ppm
      Lead                       1.25 ppm


      Vacuum filtering and flash drying — Unfortunate! v. reliable
 measurements of  flow rates or volumes of filter feed, filtrate,
 filter cake, and dried sludge are unavailable for before 1977.
 Total  solids concentrations of filter feed and filter cake are
 available, however.  The average TS concentration of the digested
 sludge (filter feed) rose from 4.45 percent when no alum was used
 to 6.53  percent  during alum addition.  Despite this increase in
 feed solids concentration, the filter cake which was produced
 during alum addition was wetter than it had been before.  Average
 cake TS  dropped  from 23.8 percent to 21.4 percent.

     Since measurements of the volume or mass of sludge filtered
are unreliable for years prior to 1977, the impact of alum addi-
 tion on  chemical conditioner dosages required for vacuum filter-
 ing cannot be determined.  During the first 5 mo of 1977, the
average  lime dosage used was 214 kg/kkg (429 Ib/ton) of dry  sol-
 ids and  the average ferric chloride dosage was 25.5 kg/kkg  (51
Ib/ton)  of dry solids.

                               232

-------
     Average filter yield during this period was 0.94 kg (2.08
Ib sludge solids/ft2/hr).  The filter yield can be assumed to
have decreased as a result of alum addition, because filter yield
at the plant cannot exceed the rate at which cake can be fed to
the dryer.  The rate at which cake could be dried necessarily
decreased with alum addition, because the sludge cake was wetter.

     Problem resolution--The basic problem facing the plant was
its inability to move sludge all  the way through and out of the
system at a fast enough rate.  Operation of the vacuum filters
and dryer for one shift each day and use of the drying beds per-
mitted the removal of only about 49.2 to 64.3 m3/day (13,000 to
17,000 gal/day) digested sludge from the digesters.   By running
the filters and dryer 14 hr/day,  instead of 6.5, it  became  pos-
sible to process 98.4 to 128.7 m3/day (26,000 to 34,000 gal/day)
digested sludge.  The most obvious plant improvement which  resulted
was the reduction of the volume of supernatant.  Pumping less
supernatant reduced the load of solids circulating and recirculat-
ing through the primary clarifiers, thickeners, and  digesters  as
sludge, thickener overflow, and supernatant.  An improvement in
plant effluent quality resulted.   The average SS concentration  of
the final effluent quality resulted.  The average SS concentration
of the final effluent was only 18 mg/£ in 1976 when  operating  for
two shifts/day.

     The year 1976 was a period of operation during which the
filter and dryer were run on two shifts.  .Table C-16 presents
average values for various items recorded by the plant during
this period.  Based on this information, Figure C-13 presents a
solids mass balance which was constructed around the digesters.
Comparing it with the mass balances in Figures C-ll  and C-12 indi-
cates that removal of sludge solids and sludge gallons from the
digesters increased when the plant went to two shifts, while the
quantity of sludge feed stayed about the same.  This led to fewer
gallons of supernatant returned to the primaries.  It also resulted
in more room in the digester for solids-liquid separation.   A
higher quality supernatant resulted, with only about 1.5 percent
solids rather than the previous 3.1 percent.

     In conclusion, by extending the time of filter-dryer opera-
tion, the adverse impacts of alum addition on digester supernatant
were overcome.  Poor supernatant quality probably had been one of
the factors responsible for thickener bulking according to the
plant superintendent, so the adverse effect of alum addition on
the thickeners was probably also overcome by running two shifts.
However, even with these improvements, the plant was still  over-
loaded with sludge, as it had been even before alum addition,
and some of the adverse effects of alum addition had not been
overcome.

     As a solution, the hauling of liquid digested sludge was
begun, and filter-dryer operation was returned to one shift per
day.   Liquid sludge hauling began at the beginning of June of

                               233

-------
            TABLE  C-16.  1976 SLUDGE TREATMENT DATA DURING DOUBLE  SHIFT
             VACUUM  FILTER AND FLASH DRYER OPERATION AT LAKEWOOD,  OHIO
         Average sewage flow m3/day (gal/day)
                                  o
         Sludge  fed  to  digester  m /dav
             (gal/day)

         TS  digester feed  (%)
                                   •a
         Digested  sludge removed  m /day
             (gal/day)

         TS  digested sludge (%)

         Sludge  filtered m /day (gal/day)

         Hours of  filter operation
                                  0.05     (13.4)


                                   187     (49,424)
                                  85.3
                                             4.6
         (22,530)

           5.8

84.7     (22,393)

  12.5 hr/day, 5 day/wk
 AVE. SEWAGE FLOW = 13.4

                    MGD
                                                 ASSUME 25% TS DESTRUCTION


10,898
TS 58,000
Ibrs/
XOAY
MG/'
X
DIGESTED
.022530 MGO SLUDGE
 NOTE:  HEAVILY OUTLINED BOXES CONTAIN ESTIMATED VALUES.
Figure C-13.
1976 anaerobic digestion mass balance during double  shift vacuum
filter and flash dryer operation at Lakewood, Ohio.
                                     234

-------
1977, so limited data are available on its effects.  Figure
                                  m3 sludge/day (39,096 gal
                                  digester in June 1977.  The
C-14 shows that an average of 148
sludge/day) were removed from the u i yc-j K._•  ... -».._.-	-
average quantity of sludge filtered/day was 32.3 m6 (8,546 gal)
The remaining volume of digested sludge, 115.6 m3/day (30,550
gal/day), was hauled out as liquid.  While the quantity of
sludge pumped into the primary digesters was not increased by
the plant operators, more sludge was removed than ever before.
In fact, the sludge removal rate exceeded the sludge feed rate.
N/A
N/A
0 .01093

MGD SUPERNATANT
i

1 ASSUME 25%
 17,523
                Tb7
                   DAY
 TS 42,000
  MG/,
 .050
         MGD
THICKENED
SLUDGE
                            ANAEROBIC
                            DIGESTERS
                                          19,564
                                                          /
                                             DAY
                            TS 60,000
                                                        MG/,
            DIGESTED
.039     MGD SLUDGE
 NOTES:   N/A =• NOT AVAILABLE
         HEAVILY-OUTLINED BOXES CONTAIN ESTIMATED  VALUES.
      Figure  C-14.
                   Anaerobic digestion mass balance during
                   liquid  sludge  hauling, Lakewood, Ohio.
     Remova'l  of sludge from the digesters  at this  rate  resulted
in less  supernatant return and better solids-liquid  separation
in the secondary digesters.  The quantity  of supernatant  decreased
to 41.4  m3/day (10,930 gal/day), and if the TS  concentration  is
assumed  to have remained at 1.5 percent, then only 620.6  kg TS/day
(1,367 Ib TS/day) were returned to the primaries in  the superna-
tant.  The impacts on plant operation included a reduction of the
mass of primary sludge.  Consequently, more secondary sludge
could be wasted to the thickeners.  This was done, with the result
that the MLSS concentration in the aeration basins came down to
about 3,500 to 4,000 ppm,  compared to 4,500 ppm when the plant
was removing less sludge from the digesters.
     It was hoped that one of the results
the digesters at a high rate would be the
                                          of removing sludge from
                                          dislodging of much of
                               235

-------
  the  heavy  sludge  that  is apparently lodged in the sides and cor-
  ners  of  the  secondary  digesters.  To aid in getting rid of the
  heavy  sludge,  the  secondary digester contents were occasionally
  recirculated  by withdrawing from the bottom and pumping back into
  the  middle.   At first, some dislodging of heavy sludge occurred
  at the fast  sludge removal rate.  After a couple of months, how-
  ever,  the  situation  began changing drastically.  Apparently, the
  effective  volume  of  the digesters was so reduced by heavy sludge,
  grit  and rags  that there was only a very short detention time in
  the  secondary  digesters at the high sludge removal rate.  The TS
  concentration  of  the sludge removed from the digesters decreased
  from  6.0 percent  TS  to 3.0 to 3.5 percent TS.  Solids-liquid
  separation was not occurring.

       Consequently, the sludge removal rate was cut in half.  The
  plant  manager  is  now planning to hire a private contractor to
  pump   out  both secondary digesters, removing the heavy material.

  Sludge Treatment  and Disposal Costs

       In assessing  the  operational costs of sludge treatment and
  disposal at  Lakewood,  the following assumptions were made:

       1.  All  costs are shown as per ton (metric and English) of
          dry  TS removed from the digesters.

       2.  Costs are based on a digested sludge removal rate of
          1,180 t/yr  (1,300 ton/yr) in 1974 and 1,810 t/yr (2,000
          ton/yr)  in  1976.

       3.  The  unit cost factors which were used are:

          Item                     1977 Costs

      Electricity               $0.045/kwh
      Fuel oil                  $1.454/4 ($0.384/gal)
      Ferric chloride           $0.118/4 ($0.031/gal)
        (40 percent FeCla)
      Lime                      $0.015/kg ($0.033/lb)

     Labor categories
      (L) Laborer               $5.00/hr
      (R) Repairman             $6.43/hr
      (M) Maintenance person    $5.70/hr
      (0) Filter-dryer          $5.43/hr
          operator

     The costs of handling the alum sludge were estimated for
1974,  when the filter and  dryer were operated during one shift
per day, and for 1976, when they were operated for two shifts per
day.   Operation for two shifts was a response to the additional
sludge load  imposed on the plant by alum addition.  Therefore,
the additional costs of running for two shifts can be attributed
to the alum  addition.
                               236

-------
     The operational  cost breakdown is shown in Table C-17.  The
total  treatment costs for each process are summarized in Table
C-18.  Because of the  increase in the number of tons  of dry TS
removed from the digesters in 1976, the treatment cost per ton
of dry TS was not much greater than it was in 1974.   The total
treatment cost was $133.58/t ($121.19/ton) in 1974 and $138.13/t
($125.28/ton) in 1976.

     These costs can be compared with the cost of hauling liquid
sludge.  The private contractor's fee for hauling the sludge and
applying it to agricultural fields with a "field jimmy" is $0.11/£
($0.03/gal).  The cost per ton of dry TS of this method depends
upon the TS concentration of the liquid sludge.  A more concen-
trated sludge improves the cost-effectiveness of the method.
Good digester performance will result in both reduced sludge vol-
ume and a more concentrated sludge, which will increase the cost-
effectiveness of liquid sludge hauling.  When the digesters at
Lakewood were producing a 6.0 percent TS sludge, the cost of
hauling was $132.30/t ($120/ton).  This is less than the treat-
ment using the filters and dryer.

Summary and Conclusions

     The Lakewood, Ohio, plant is an older facility (built in
1966) which has treated average annual flows ranging from 42,000
to 55,000 nH/day (11.2 to 14.6 mgd) during the period examined
in this case study.  The plant's effluent quality is poor due  to
hydraulic overloading and inadequate solids handling capacity.
The plant treats alum-waste activated and primary sludges which
are combined in the gravity thickeners.  The basic solids-handling
problem facing the plant has been its inability to remove sludge
from the digesters at a fast enough rate.  The plant is equipped
with vacuum filters and a flash dryer for sludge dewatering and
drying.  Over the last three years, the flash dryer has functioned
at loadings of 360 to 450 kg (800 to 1,000 Ib) TS/hr.  This is
360 to 450 kg/hr (800 to 1,000 lb/hr) less than the dryer's design
capability rating.  It has been possible to operate only one of
the two vacuum filters at a time because of the limiting capacity
of the flash dryer.

     Alum addition for phosphorus removal placed a squeeze on  the
plant's already overloaded sludge handling system.  It increased
the amount of sludge generated, and at the same time decreased
the capacity of the vacuum filter and flash dryer to process the
sludge.  This created a bottleneck in the solids handling end  of
the plant, leading to high solids buildup and recirculation
throughout the plant.

     Although no part of the plant was designed specifically for
sludge storage, the whole plant has become what could be described
as one big sludge storage tank.  In addition to the solids  buildup
in the thickeners and digesters, the thickener overflow and


                               237

-------
    TABLE  C-17.   COSTS  OF TREATING ALUM SLUDGE DURING SINGLE AND DOUBLE  SHIFT
             VACUUM  FILTER AND  FLASH  DRYER OPERATION, LAKEWOOD, OHIO
                                         Single Shift
                                       Operation (1974)
                      Double Shift
                    Operation (1976)
Gravity Thickening

Electricity (kwh/yr)
($/t ($/ton))

*Maintenance supplies ($/yr)
($/t ($/ton))

Maintenance labor (hr/yr)
($t ($/toh))

Operating costs and overhead
   118,000
$4.50 ($4.03)

    $100
$0.09 ($0.08)

    32 (M)
$0.15 ($0.14)

    none
   118,000
$2.92 ($2.65)

    $100
$0.06 ($0.05)

    32 (M)
$0.10 ($0.09)

    none
Anaerobic Digestion

Electricity (kwh/yr)
($/t ($/ton))

Fuel oil (gal/yr)
($/t ($/ton))

*Maintenance supplies ($/yr)
($/t ($/ton))

Maintenance labor (hr/yr)
($/t ($/ton))

Operational labor (hr/yr)
($/t ($/ton))

Overhead ($/yr)
($/t ($/ton))
   360,000
$13.74 ($12.46)

     1,000
$0.32 ($0.29)

    $2,630
$2.23 ($2.02)

    832 (M)
$4.02 ($3.65)

     1,100 (L)
$4.66 ($4.23)

    $3,230
$2.73 ($2.48)
   360,000
$8.93 ($8.10)

     1,000
$0.21 ($0.19)

    $2,630
$1.44 ($1.31)

    832 (M)
$2.61 ($2.37)

     1,100 (L)
$3.03 ($2.75)

    $3,230
$1.78 ($1.61)
                                                                  (continued)
                                     238

-------
TABLE C-17  (continued)1
                                          Single Shift
                                        Operation (1974)
                       Double Shift
                     Operation (1976)
Chemical  Conditioning and Vacuum
Filtration

Fed3 and lime
($/t ($/ton))

Electricity (kwh/yr)
($/t ($/ton))

Maintenance supplies ($/yr)
($/t ($/ton))

Maintenance and repair labor (hr/yr)
($/t ($/ton))

Operational labor (hr/yr)
($/t ($/ton))

Overhead ($/yr)
($/t ($/ton))
$9.81  ($8.90)

    57,300
$2.18 ($1.98)

    $1,450
$1.22 ($1.11)

  792 (M,R)
$4.02 ($3.65)

  830 (0)
$3.81  ($3.46)

    $2,920
$2.48 ($2.25)
$9.81  ($8.90)

   57,300
$1.42 ($1.29)

    $2,200
$1.21  ($1.10)

 1,200 (M,R)
$3.97 ($3.60)

 2,490 (0)
$6.89 ($6.25)

    $6,225
$3.43 ($3.11)
Flash Drying

Electricity (kwh/yr)
($/t ($/ton))

*Fuel oil ($/yr)
($/t ($/ton))

*Maintenance supplies ($/yr)
($/t ($/ton))

Maintenance labor (hr/yr)
($/t ($/ton))
tOperational labor (hr/yr)
($/t ($/ton))

Overhead ($/yr)
($/t ($/ton))
   326,500
$12.46 ($11.30)

   $42,900
$36.38 ($33.00)

    $3,036
$2.57 ($2.33)

  1,188 (M,R)
$6.04 ($5.48)
914 (L) 1,240 (0)
$9.59 ($8.70)

    $5,830
$4.94 ($4.48)
   609,500
$15.12 ($13.71)

   $77,000
$42.45 ($38.50)

    $4,600
$2.54 ($2.30)

 1,800 (M,R)
$5.95 ($5.40)

1,830 (L) 3,730 (0)
$15.37 ($13.94)

  $12,220
$6.74 ($6.11)
                                                                   (continued)
                                      239

-------
 TABLE C-17 (continued)
                                          Single Shift         Double Shift
                                        Operation (1974)     Operation (1976)
 Flash Drying  (cont'd)
 Approximate average  income—
 dried product
 ($/t ($/ton))                          $5.64  ($5.12)        $2.15 ($1.95)
  1976  costs.
  Includes  the  cost of  bagging and trucking the dried sludge.
  TABLE C-18.  COSTS OF ALUM SLUDGE TREATMENT DURING SINGLE AND DOUBLE SHIFT
             VACUUM FILTER AND FLASH DRYER OPERATION, LAKEWOOD, OHIO
                                          Single Shift         Double Shift
	Operation (1974)     Operation (1976)
Gravity thickening:                     $4.74 ($4.30)        $3.08 ($2.79)
Anaerobic digestion:                    $27.70 ($25.13)      $18.00 ($16.33)
Chemical conditioning
 and vacuum filtration:                 $23.52 ($21.35)      $26.73 ($24.25)
Flash drying:                           $77.62 ($70.41)      $90.32 ($81.91)
Total:                                  $133.58 ($121.19)    $138.13  ($125.28)
                                     240

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digester supernatant sidestreams carried heavy solids loads back
to the head of the plant.  The solids accumulated in the primary
clarifiers from which they were fed back to the thickeners and
digesters, thus being trapped essentially in a closed-loop system.
Furthermore, because the thickeners were overloaded, 97 to 98 per-
cent of the secondary sludge which was produced was recirculated
through the aeration basins and back to the final clarifiers.
The solids accumulated in the secondary clarifiers,  and then were
fed back to the aeration basins, forming a second closed loop.

     An additional 2.3 t/day (2.5 ton/day), or 4.3 t/mil m3 (360
Ib/MG), of secondary sludge were wasted to the thickeners during
alum addition (Figures C-ll and C-12).  The volume of secondary
sludge wasted did not increase,. however.  The volume of thickened
sludge pumped to the digesters also did not change significantly,
but the sludge TS concentration increased from 4.3 to 5.6 per-
cent.  The increase in the mass of sludge pumped to the digesters
was approximately the same as the amount of additional  secondary
sludge wasted to the thickeners.

     During alum addition, the sidestreams from the sludge treat-
ment operations contributed a loading of 6,948 kg SS/day (15,300
Ib SS/day) to the primary clarifiers.  This figure is greater
than the 6,025 kg/day (13,270 Ib/day) which was contained in the
plant influent.  By far the most significant sidestream in terms
of solids input was the thickener overflow, carrying 6,433 kg SS/
day (14,170 Ib SS/day).  Alum addition increased the overloading
of the thickeners, and problems with bulking and poor overflow
quality became more severe.

     The rate at which sludge could be flash dried was  reduced
during alum addition because the moisture content of the filter
cake rose from 76.2 percent to 78.6 percent.  Filter yield was
then cut back so that it would not exceed the drying rate.  The
volume of sludge removed from the digesters each day was decreased
in response to the reduced filter and dryer capacity.  This
resulted in the production of 22.7 m3/day (6,000 gal/day) more
digester suprenatant.  The digesters were overloaded to the
extent that the supernatant TS concentration rose from  2.4 to 3.1
percent.  The supernatant TS loading on the primary clarifiers
increased by 1,362 kg TS/day (3,000 Ib/day);

     Alum addition to the activated sludge effluent channel
affected wastewater treatment operations in several  ways:

     t  The primary clarifier influent concentrations of SS and
        BOD were increased due to greater loadings from the thick-
        ener overflow and digester supernatant.

     t  The primary clarifier effluent concentrations of SS and
        BOD did not increase, however, indicating that  the addi-
        tional  loadings were removed as sludge.

                               241

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     •  The MLSS concentration in the aeration  basins  rose by 56
        percent due to a higher TS concentration  of the  return
        activated sludge.

     •  The capture of SS  and BOD during secondary clarification
        was increased, preventing an increase in  final  effluent
        SS and BOD5 concentrations.

     t  Phosphorus removal  was increased from 20  percent to only
        65 percent.  Greater removal could have been achieved at
        higher alum dosages or with  polymer addition,  but the
        plant was not equipped to handle the additional  sludge
        which would have been generated.

     In order to remove sludge from  the digesters at a  faster
rate and thus alleviate the solids-handling problem, the length
of filter and dryer operation was extended to 14  hr/day  instead
of 6.5.  A reduction in the volume of supernatant and  improved
supernatant quality resulted.  More  recently, the plant  returned
filter and dryer operation  to one shift per day and began hauling
liquid sludge.  Initially,  during liquid sludge hauling, the rate
of sludge removal from the  digesters exceeded the feed  rate by
908 kg TS/day (2,000 Ib TS/day).   As a result,  the volume of
supernatant was further reduced and  there was more room  in the
secondary digesters for solids-liquid separation.

     The indirect effects  of longer  filter-dryer  operation and
liquid sludge hauling included less  primary sludge production,
less frequent thickener bulking,  a reduction of the MLSS concen-
tration in the aeration basins, and  improved plant final effluent
q u a 1 i ty.

CASE STUDY G:  MENTOR, OHIO

Introduction

     The Greater Mentor Wastewater Treatment Plant  provides  an
example of secondary addition of alum for phosphorus removal.
The chemical sludge at the  plant is handled  separately  from  the
primary sludge.  The alum-secondary sludge wasted from  the  secon-
dary clarifiers is sent to  an aerobic digester followed  by  dual
cell gravity concentrators  (DCG's) with final disposal  on  crop
lands.   Wastewater influent  to the plant  is  delivered by  separate
sanitary sewers and contains approximately 12 percent industrial
waste.

History

     The history of modifications to  the  plant which have affected
sludge, follows:

     •  Late 1965 - Start-up of primary plant

                               242

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     •  Early  1969 - Start-up  of ferrous iron and  lime addition
        for  phosphorus removal

     t  October  6, 1973 - Start-up of secondary  treatment using
        contact  stabilization  activated sludge process

     •  October  7, 1973 - End  of ferrous iron and  lime addition

     •  October  14, 1974 -  Start-up of alum addition  for phospho-
        rus  removal

     •  June 22, 1976 - Switch from contact stabilization to con-
        ventional  activated  sludge process

     t  March  25,  1977 - Return to contact stabilization activated
        sludge process

     •  July 1977  - Switch  from aluminum sulfate to  sodium alum-
        inate  addition for  phosphorus removal.

     Two  periods were selected for comparison purposes to deter-
mine the  impact  of chemical  additions for phosphorus  removal.
The period  from  mid-October  1973 to mid-October  1974  was selected
as a period  without phosphorus removal.  The period  from July 1976
to March  1977  was  selected  as  a period during which  phosphorus
removal with alum  was practiced.  Table C-19 presents the daily
average influent and effluent  wastewater characteristics and plant
removal efficiencies during  the two periods.
            TABLE C-19.   INFLUENT AND EFFLUENT  WASTEWATER
               CHARACTERISTICS AND REMOVAL  EFFICIENCIES,
                              MENTOR, OHIO
October
to
October
'73

'74
July '
to
March
'76

'77
            Plant Flow mil m3/day (mgd)       0.017 (4.60)  0.02 (5.29)

            SS (rng/n) Primary Influent         186        172
                   Primary Effluent         113         91
                   Plant Effluent            36         35
                   % Removal - Primary        39         47
                   % Removal - Plant          81         80

            BOD(mgA) Primary Influent         206        187
                   Primary Effluent         147        137
                   Plant Effluent            32         26
                   % Removal - Primary        29         27
                   % Removal - Plant          84         86

            TP (mg/£) Primary Influent         .28         25
                   Plant Effluent            21         14
                   X Removal - Plant          25         44
                                 243

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Chemical Addition for Phosphosrus Removal
                                            tO
      Liquid aluminum sulfate (9.0 percent Al  ) was added to the
effluent channel leading from the aeration basins to the final
clarifiers while the plant was operated as a conventional acti-
vated  sludge system with four aeration basins.  Approximately
2.6 m3  (690 gal") of liquid alum were used per day.  The actual
feed  rate of solution was changed twice a day to account for diur-
nal variations  in plant flow.  From 7 a.m. to 5 p.m. the solution
was added at a  rate which achieved a dosage of 12.2 mg/£ Al+3,
with  a  plant flow of about 0.017 mil m3/day (4.5 mgd),  At 5 p.m.
the chemical feed rate was changed to maintain the same chemical
dosage  at a plant flow of about 0.024 mil m3/day  (6.5 mgd).

      In addition to alum, the plant has used several other chemi-
cals  for phosphorus removal.  Initially, ferrous  iron and lime
were  added ahead of the primary clarifiers during the period when
the plant only  provided primary treatment.  More  recently, sodium
aluminate addition ahead of the aeration basins was tested.
According to plant personnel, sodium aluminate addition caused
the pH  of the sludge in the aerobic digester to increase signifi-
cantly.  This,  in turn, decreased the effectiveness of the DCG's.
As a  result, the use of sodium aluminate was abandoned.

General Description of Wastewater Treatment Operations Affecting
Siudge

     A wastewater flow diagram is presented in Figure C-15.  Table
C-20  is a summary of the wastewater and .sludge handling unit and
mechanical equipment.  Influent wastewater flows  to the pump sta-
tion,  where it  passes through either a comminutor or a bar screen
before  dropping into the raw wastewater wet well.  The wastewater
is then pumped  to the aerated grit chamber where  heavy, abrasive
solids  are removed.  The wastewater then flows to the primary
clarifiers where settleable and floating solids are removed.

      The primary effluent flows by gravity to the aeration basins
where  it is mixed with return sludge.  From the aeration basins
the mixed liquor flows to the secondary clarifiers where the
sludge and solids in the wastewater are settled out.  The  secon-
dary  effluent is chlorinated and discharged to Lake Erie.  A por-
tion of the sludge from the secondary clarifiers  is returned to
the reaeration  basins and is subsequently recycled by mixing with
the aeration basin influent.

     Sludges removed for sludge processing from the primary and
secondary treatment systems are handled separately.  Primary
sludge is pumped to the anaerobic digesters or to the  heat treat-
ment unit.   Digested sludge is then chemically conditioned and
sent to the vacuum filters.  Thermally conditioned sludge  from
the heat treatment unit is sent without chemical  conditioning  to
another set of  vacuum filters.  Vacuum filter sludge cake  is  dis-
posed  of on croplands.
                               244

-------
ISJ
*»
tn
                                      LABORATORY ft

                                    FILTER eUlLOINO
        Figure  C-15.   Greater Mentor"wastewater  treatment plant  wastewater  flow diagram.

-------
         TABLE C-20.
GENERAL PLANT DESCRIPTION  SUMMARY,
    MENTOR, OHIO
Unit
Plant Design Capacity
Comminutor
Bar Screen
Grit Chamber
Primary Clarifiers
No. and Description
0.045 mil m2/day (12.0 mgd) .


78.4 m3 (2,800 ft3) aerated.
2 at 21 .3 m (70 ft) dia. x 2.7 m
Primary Sludge Pumps
Primary Sludge Collectors
Influent Flume to
Aeration Basins
Aeration Basins
Secondary Clarifiers
     (9 ft);  overflow  weir  -  2  at
     193.5  m  (635  ft)  length.

     2 at 7.5 hp;0.47  m3/min  (125  gal/
     min) capacity.

     2 at 1.6 revolutions/hr,  sludge
     scrapers on  the  bottom  of  a rotating
     arm direct  the  sludge  on  the  bottom
     of each  clarifier to the  hopper  in
     the center  of  the tank;  motors -
     2 at 1/2 hp.

     48.5 m (159  ft)  length  x  1.1  m
     (3.5 ft) width  x  0.9 m  (3  ft)
     effective dia.;  3 2-in  air  diffuser
     headers  at  17-20  diffusers  each
     capable  of  discharging  up  to  12  cfm
     at 10.6  in  water.

     6 at 37.5 m  (123  ft) length x  7.3 m
     (24 ft)  width  x  4.6 m  (15  ft)  dia.
     3 multistage  centrifugal  compressors
     (blowers) at  300  hp each  capable of
     supplying 5600  scfm at  7  psig; 5
     4-in diffuser  headers  at 32 diffusers
     per basin,  each  capable  of  discharg-
     ing up to cfm  26.9 cm  (10.6 in)
     water; aeration  basin  #6  is used
     as an  aerobic  digester.

     3 at 28  m (92  ft) dia.  x  2.4  m
     (8 ft) SWD;  overflow weir  3 at
     88.1  in  (289  ft)  length.
                                                    (continued)
                             246

-------
TABLE C-20 (continued)
       Unit
       No.  and Description
Secondary (Return)
Sludge Pumps
Secondary Sludge
Col 1ector
Anaerobic Digesters
Vacuum Filter (for
anaerobic digester
siudge)

Sludge Heat Treatment
(for raw primary
siudge)
2 at 25 hp, 7.6 m /min
gal/min);  1 at 40 hp,
(4200 gal/min).
                       (2,000
                      15.9 m3/min
3 at 1.8 revolutions/hr,  sludge
scrapers on bottom of pair of ro-
tating arms with 5 6-in "suction"
pipes per arm; motors - 3 at 3/4
hp; scrum removal  by travelling
weir attached to torque tube of
scraper arms.
                       ft3),
                           0.57
2 at 1719.8 m° (61,420
recirculation pumps - 2 at
m3/min (150 gal/min); heat exchanger
boiler - 1  at 500,000 BTU/hr.
1.8 to 3.6 kg (4 to 8 Ib/hr)
loading rate at 30 percent dry
sol ids.
3.8 m3/hr (1,000 gal/hr)
at 5 percent dry solids.
temperatures °C (°F).
                         feed rate
                          Sludge
                           Inlet
                           Maximum
                           Outlet
            12.7 (  55)
           202.4 (400)
            37.4 (100)
                           Disintegrators 2
                           mil  m3/min (8-25
                           solids.
                 at 30,280-94,625
                 gal/min)  of 3-10%
                           High pressure pumps 2 at 49,205
                           75,700mil  m3/min (13-20 gal/min)
                           at 300 psig.

                           Head exchanger, 3.03-4.54 m /hr
                           (800-1200 gal/hr).

                           Reactor, 3.03-4.54  m3/hr (800-
                           1,200 gal/hr) at 275 psig and
                           210°C (4140F).


                                                 (continued)
                              247

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 TABLE  C-20  (continued)
        Unit
               No. and Description
Sludge Holding Tank
(Thickener)

Dual Cell Gravity (DCG)
Concentrator
Lime Clarification
Supernatants and
Filtrates
of
        Decant and Thickening Tanks
                                  2
        Solids loading - 97.7 kg/m /day
        (20 Ib/ft2/day) maximum.

        Sludge pumps - 2 at 18,925-180,250
        mil m3/min (5-50 gal/min).

        Vacuum filter (for heat) treatment
        sludge) - 302.8 kg/hr (667 Ib/hr)
        loading rate at 30 percent dry
        solids.

        84.4 m  (22,300 gal) capacity.
        3 at 11.35 m3/hr (3,000 gal/hr)
        total capacity (aerobically digested
        sludge); main drives - 3 at 1/2  hp;
        internatl conveyors - 3 at 1h hp,
        110 v.; external conveyors -
        2 at 2 hp, 220 v.,  61 cm (24 in)
        width, capacity - 2.8 m3 (100 ft3)
        sludge at 1,297 kg/m3 (80 lb/ft3);
        sludge pumps - 3 adjustable speed
        and stroke plunger  type at 2 hp,
        440 v., 26,495 to 211,960 mil
        m3/min (7 to 56 gal/min); sludge
        pump wet wells - 1  at 33.1 m3
        (8,740 gal), 1 at 41.6 m^ (10,980
        gal); chemical mixing - 4 plastisol
        lined steel  tanks at .38 m3 (100
        gal), with 1/4 hp mixers operating
        at 1,725 rpm; chemical feed pumps
        - 3 dual head at 1/4 hp, 75,700
        mil m3/hr (20 gal/hr) head;
        coagulation  - 3 tanks; filter media
        fine mesh, nylon cloth.
ft)
6.7 m (22 ft) length x 6.7 m (22
width x 3.7 m (12 ft) dia.; lime
storage bin - 3.7 m (12 ft) dia. x
6.5 SWD; maximum lime feed rate
.25 m3/hr (8.75 ft3/hr; lime sludge
pumps - 2 at 0.19 m3/min .(50 gal/
min).
                              248

-------
     Alum-secondary sludge is pumped to a sludge holding tank and
on to the aerobic digester, or is sent directly to the aerobic
digester.  Following aerobic digestion, the sludge is dewatered
by the DCG's.  Dewatered sludge is disposed of at a privately
owned dumpsite.  Aerobic digester and sludge holding tank decan-
tate and DC6 concentrate are returned to the head of the aeration
basins.

     The plant also has a lime clarifier in which anaerobic diges-
ter supernatant, vacuum filter filtrate, DCG concentrate, and
sludge holding tank decantate can be treated to reduce phosphorus
concentrations.  At present, the lime clarifier is not operated
on a continuous basis.  The anaerobic digester supernatant and
vacuum filter filtrate are returned to the head of the primary
clarifiers.

Detailed Description of Mastewater Treatment Operations Affecting
SIudge

     Since the alum-secondary sludge is handled separately from
primary sludge, this section will emphasize plant operations
affecting secondary sludge generation and handling.

Primary Clarifiers--

     Since alum addition was initiated, the quantity and charac-
teristics of the primary clarifier effluent have changed as pre-
viously indicated in Table C-19. ~ Specifically, there has been a
noticeable improvement in primary clarifier performance in terms'
of suspended solids removals.  This has led to a decrease in sol-
ids loadings on the secondary treatment system.  At the same time,
concentrations of BOD's discharged from the primary clarifiers
have also decreased.   Plant data does not, however, fully account
for slugs of concentrated waste from septic tank pumpouts deliv-
ered to the treatment  plant by truck.  During the period without
phosphorus removal, two to six 3.78-m3 (1,000-gal) loads entered
the system daily.  This practice was terminated prior to alum
addition.

Aeration Basins--

     During the period without phosphorus removal, the aeration
basins were operated as a contact stabilization system with two
contact basins and one reaeration basin.  At that time, the con-
tact basins contained  2,400 to 2,800 mg/& MLSS, with approximately
70 percent volatile solids, and the reaeration basin was operated
at 5,000 to 7,000 mg/£ MLSS with raughly the same percent vola-
tile solids as the contact basins.

     During the studied period with aluminum sulfate addition the
system was operated as a conventional activated sludge treatment
plant with four aeration basins, operated at concentrations of


                               249

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3,000 to 7,500 mg/£  MLSS,  with 62 percent volatile solids.
Return sludge with  6,000 to 20,000 mg/i suspended  solids was
recycled at a rate  equal to 40 to 50 percent  of  plant forward
flow.  This led  to  considerably longer sludge  ages of the mixed
liquor in the aeration  basins, causing the  cells to enter an
endogenous growth  phase.  Less sludge was wasted per pound of
BOD removed in the  secondary treatment system  during this period
than during the  period  without phosphorus removal.

Secondary Clarifiers--

     Sludge is removed  from the bottoms of  the secondary clari-
fiers on a continuous  basis by the sludge draw-off pipes attached
to the arms of the  sludge  collector mechanisms.   This sludge is
returned to the  aeration basin system at a  pumping rate that
varies between 25  and  50 percent of the plant  forward flow.  For
approximately 1  hr/8-hr shift, sludge is wasted  to sludge pro-
cessing at a pumping rate  approximately equal  to 100 percent of
a plant forward  flow.   This high rate of pumping is necessary to
remove the sludge  blanket  which accumulates to up  to 1.8 m (6 ft)
at the center of the clarifier during periods  of low rate return
sludge pumping.

Aerobic Digester--

     During the  period  prior to alum addition, one of the six
aeration basins  was  used as an aerobic digester.  Generally, dur-
ing the period of  alum  addition, one aeration  basin was used as
an aerobic digester, although two aeration  basins  were used as
aerobic digesters  for  a short time.  Characteristics of the sludge
influent to and  effluent from the aerobic digester are given in
Table C-21.
      TABLE C-21.   AEROBIC DIGESTER SLUDGE  CHARACTERISTICS,
                           MENTOR, OHIO
                                October '73 to
                                October '74
                  July '76 to
                  March '77
      Influent Sludge:

       WAS kg (lb) dry solids
       per month

       Total Solids (%)

       Volatile (%)
38,600 (85,000)


0.5-1.5

70
45,400 (100,000)


0.8-2.0

63
      Effluent Sludge (to
       DCS Concentrators):

       Total Solids (%)

       Volatile (%)
2.0-2.6

68
2.4-2.9

56
                                250

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     The aerobic digesters are aerated and mixed by aeration
equipment identical  to that in all other aeration basins at the
Mentor plant.  Sludge in the digesters is maintained at approxi-
mately 27°C by the diffused air which is heated by the air com-
pressors.  Supernatant is decanted from the top of the aerobic
digester less than once per day.   Prior to drawing off superna-
tant, air to the tank is turned off and sludge wasting discontin-
ued for 2 to 6 hr .   After settling has taken place, supernatant
is withdrawn slowly to prevent mixing in the tank.  During super-
natant withdrawal, concentrations of dissolved oxygen in the tank
drop as low as 0.1 mg/£.  When decanting is complete, air is
turned on again and aeration takes place until the dissolved oxy-
gen levels reach 4 to 5 mg/a.  This takes approximately 1 day,
at which point the tank is again ready for decanting.

     Normally, after 1 to 2 wk of continuously wasting  sludge
into the tank and drawing off supernatant, the sludge in the tank
becomes so thick that no additional water can be decanted off.
At this time sludge must be pumped to the DCG's.  To avoid this
situation, the DCG's are operated daily if at all possible.

     The impacts of chemical additions for phosphorus removal  on
aerobic digester operations have been an increase in the concen-
tration of total solids fed to the digester coupled with a
decrease in the fraction of those solids which are volatile.
The destruction of volatile solids,by the aerobic digester was
also observed to increase after alum addition to the secondary
treatment system was initiated.

Dual Cell Gravity Concentrators--

     Three DCG's are located in the sludge handling building.
These units are used to dewater the aerobically digested sludge
prior to land disposal of wet sludge cake.  Chemical storage
tanks, pumps, and piping are provided for adding polymers to the
sludge ahead of the mixing tank as previously detai1ed inTab!e C-20.

     Figure C-16 presents a schematic diagram of the DCG's and
appurtenances.  As shown in the diagram, sludge from the aerobic
digesters enters one of two sludge wet wells prior to pumping to
the DCG units.  Conditioning chemicals may be injected into the
sludge either immediately following the sludge pumps or  immedi-
ately preceding the coagulation tanks.

     The chemical feed system consists of three chemical feed
pumps and four chemical storage tanks.  Four tanks are furnished
in case both anionic and cationic polymers are required  for coa-
gulation.  Sludge enters the bottom of coagulation tanks, mixes
with coagulation chemicals, and overflows through four outlets
near the top of each tank.
                              251

-------
                         COAGULATOR TANKS
ro
01
ro
CONVEYOR TO
TRUCK OR
SLUDGE HOLD-
ING TANK
                     D.C.G.
                     CONCEN-
                     TRATOR
                                                          CHEMICAL
                                                            FEED"
>
>


1

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p
D.C.G.
CONCEN-
TRATOR



t
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f


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4
4






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D.C.G.
CONCEN-
TRATOR



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CONCENTRA-
TOR PUMPS

 OVERFLOW
  AND COA-
                                                                     C5ULANT.DRAIN
                   TO
                  LINE
             CLARIFICATION
                                                  LINE SLUDGE
                                                                            AEROBICALLY
                                                                            DIGESTED
                                                                            SLUDGE
          Figure C-16.   Dual  cell gravity  thickeners and appurtenances,  Mentor,  Ohio.

-------
     Sludge slurry from the coagulation tanks enters the first
cell  of each of the dual cell  concentrators at four points.   The
cells are formed by a moving,  fine mesh nylon filter cloth.   A
hump in the center of the cloth divides each unit into a thick-
ening cell and a compression cell.  Coagulated solids entering
the first or thickening cell are trapped on the cloth and carried
over the hump to the compression cell  while the filtrate drains
through the cloth.  In the compression cell, the solids form a
plug, or cake roll, which in turn presses additional moisture out
of the sludge.  Excess quantities of sludge cake are discharged
over the rim of the second cell onto one of the internal conveyor
belt system.  This system is comprised of one horizontal conveyor
belt which receives the sludge from the internal conveyors and
discharges the sludge cake to the second, inclined  conveyor
belt.  The second conveyor  belt extends outside the sludge  hand-
ling building and discharges the sludge cake to a waiting dump
truck.

     Normally, three DCG units are utilized 90 percent of the
time and two DCG units are used 10 percent of the time.  The
units are not operated at all  unless at least two units are  in
working order.  During the winter months, subfreezing weather
often prevents conveyor  system operation, even with the actual
DCG units in good repair.  Lack of trucks available for hauling
wet sludge cake can also prevent DCG operation.  Specific mechan-
ical  problems which occur in the DCG system were identified  by
plant personnel as follows:  screens and mesh tear and develop
holes; zippers break from seals or loose teeth; seals wear,  break,
crack, or get caught in drive sprockets; conveyor bearings require
replacement; polymer pumps clog due to the formation of scale;
main drive unit and conveyor motors burn out.

     According to plant personnel, the DCG units are operated as
often as possible.  Although no operation or maintenance problems
have been directly attributable to the handling of alum sludge,
the units have been operated somewhat  less frequently since  the
initiation of alum addition.  The difference appears negligible,
however, if the fact is considered that the units were operated
less  than 45 percent of the available  hours per month during
both  periods.

     Performance of the DCG units is shown in Table C-22.  Since
the initiation of alum addition, the following operational changes
have  taken place:

     •  The volume of sludge fed per hour of operation has
        decreased slightly.

     •  The mass of dry solids fed to  the DCG's per hour of oper-
        ation has increased slightly.

     •  The amount of cationic polymer added per gallon of sludge
        fed to the DCG's has increased slightly (although the
                              253

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          TABLE C-22.  PERFORMANCE OF DUAL CELL GRAVITY
                   CONCENTRATORS, MENTOR, OHIO
           Estimated
       Monthly Averages

Hours of operation

Percent TS feed sludge
 (including conditioners)
 q
m  (gal)feed sludge/hr
 of operation

kg (Ib) feed sludge TS/hr
 of operation
                          q
kg (Ib) cationic polymer/m
 (1000 gal) feed sludge
                             q
kg (Ib) anionic polymer/mil m
 (1000 gal) feed sludge

kg (Ib) wet sludge cake/mo
Percent TS sludge cake

kg (Ib) cake TS/mo
kg (Ib)  cake TS/MG
 plant influent
    Without
   P-Removal
  October '73
to October '74

     330
   2.1-2.7

     3.7
    (980)

  77.2-99.9
  (170-220)

     1.7
   (14.4)

     473
  (0.0394)

   299,000
  (658,000)

   8.8-9.2

    26,800
   (59,000)

     1.54
   (12,830)
    With
  P-Removal
  July '76
to March '77

    315
  2.5-3.1

    3.5
   (920)

 86.3-109
 (190-240)

    1.9
  (15.9)

    708
 (0.0059)

  345,000
 (760,000)

  8.2-9.1

   30,900
  (68,000)

    1.54
  (12,850)
                              254

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        amount added per pound of solids fed to the DCG's has
        remained the same).

     t  The amount anionic polymer added per gallon of sludge
        fed to the DCG's has decreased considerably.

     •  The concentration of total solids in the wet  sludge cake
        removed from the DCG's has decreased marginally.

     •  Overall, the mass of TS concentrated per million  gallons
        of plant influent has remained the same.

Summary and Conclusions

     Since the initiation of alum addition for phosphorus removal,
no increase in the mass of secondary sludge TS removed from the
plant by DCG units has been observed.  This unexpected result
can be explained by a combination of several factors.   These fac-
tors, and other impacts of chemical  addition for phosphorus
removal on the plant, are highlighted below.

     First, there has been a general decrease in the  loadings of
SS and BODs influent to the secondary treatment system.   This has
been the result of both improved primary clarifier performance
and the termination of septic tank pump-out deliveries to the
plant.  In fact, the actual magnitude of the decrease  due to ter-
mination of septic tank waste deliveries is somewhat  greater than
indicated by available plant data.  As a result of plant  compo-
site sampling which takes place once every 3 hr, 24 hr/day, slugs
of septic tank wastes within the primary treatment system often
go largely undetected.

     Second, the aeration system was fun as a contact  stabiliza-
tion process during the period without phosphorus removal.   Dur-
ing the period of alum addition for phosphorus removal,  the plant
was run as a conventional activated sludge plant.  Operationally,
the aeration system showed significant increases in MLSS  concen-
trations, decreased percentages of volatile solids, and longer
sludge ages.  This had led to a reduction of the mass  of  sludge
wasted to the aerobic digester per pound of BOD removed.

     There have been several other changes observed in plant
operations since alum addition was begun, although they are not
necessarily atrributable to the alum addition.  Specifically,
the average concentration of solids in sludge entering the aero-
bic digester has increased, the volatile fraction of these solids
has been reduced, and there appears to be greater volatile
destruction taking place in the digester.

     Finally, initiation of alum addition, changes in  wastewater
characteristics, and variations in plant operations have  combined
to produce several minor changes in DCG concentrator operators.

                              255

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The volume of sludge fed to the DCG units  per hour of operation
has decreased slightly, but the mass of TS fed, has increased  some-
what.  The necessary dosage of cationic polymer used  to condition
the sludge fed to the DCG's increased slightly, while the  dosage
of anionic polymer used decreased.   Overall,  the TS concentration
in the sludge cake decreased marginally, and the mass  of dry cake
produced per million gallons of plant influent remained approxi-
mately the same.   Thus, alum addition has  had only minor impacts
on plant operations.

CASE STUDY H:  BROOKFIELD, WISCONSIN (FOX  RIVER)

Introduction

     The Brookfield plant provides  an example of secondary addi-
tion of ferrous sulfate for phosphorus removal.  It also provides
an example pf pressure (plate and frame) filtration and multiple
hearth incineration of an iron chemical sludge which  is composed
of combined primary and waste activated sludges.  Incinerator
performance and the impact of ferrous sulfate addition can be
compared with other plants (such as Sheboygan, Wisconsin)  which
operate fluidized bed incinerators.

     Raw wastewater influent to the Brookfield plant  contains no
industrial wastes.  Monthly averages of daily influent flows  range
from 6,430 to 15,100 m3/day (1.7 to 4.0 mgd)  with an  average  of
approximately 9,080 m^/day (2.4 mgd).  The plant was  designed to
handle an average daily flow of 18,900 m3/day (5.0 mgd) and thus
currently is operating at approximately half capacity.

     Table C-23 presents plant influent and effluent  wastewater
characteristics and removal efficiencies for the periods selected
for comparison before and after the initiation of chemical addi-
tion for phosphorus removal.  Table C-23 indicates that the efflu-
ent suspended solids concentrations for the two periods .were quite
different.  However, the influent wastewater sampling point actu-
ally includes sidestream flows returned to the  head of the plant.
Thus, according to plant personnel, the raw influent wastewater
characteristics remained unchanged with the difference due to an
increase in sidestream suspended solids.

History

     Construction of the Brookfield  plant was  begun  in August
1971, with wastewater treatment beginning on January  2, 1974.
The following shows the history of modifications  to  the plant
affecting  sludge  production and characteristics.

     January 1974 - Wastewater treatment operations  begun  using
the contact stabilization activated  sludge process.

     February 1976 to July 1976 - Two  final clarifiers  in  opera-
tion (a single final clarifier was in  operation  during all other
periods).
                              256

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         TABLE C-23.   INFLUENT AND EFFLUENT WASTEWATER
 CHARACTERISTICS AND  REMOVAL EFFICIENCIES, BROOKFIELD, WISCONSIN


                      After P-removal        Before P-removal
                         initiated               initiated
                     Aug. and Sept.  '76,     Jan., Feb., May,
	Jan., Feb., & May  '77    Aug., & Sept. '75

 Flow m3/d  (mgd)     8,250 m3/d  (2.18 mgd)    9,580 m3/d (2.53 mgd)

 SS  (mg/jt)  -
    influent                 265*                   212
    effluent                   18                     13
    % removal                  93                     94
BOD (mg/£) -
influent
effl uent
% removal

113*
7
94

103
20^"
81

 *Includes  sidestreams  returned  to  lift station at head of plant.

 ''"In  1976,  effluent  BOD concentrations improved when polishing
  lagoon  volume  was  decreased, reducing retention times from
  approximately  12 days down  to  7 hours.  Thus, the apparent
  decrease  in  effluent  BOD  concentration after phosphorus
  removal was  initiated was due  to  the size reduction of the
  polishing lagoon.
      March  and  April  1975  -  Chemical  additions  for phosphorus
 removal  were  tested,  using several  different  chemicals.

      June  1976  -  Chemical  addition  for  phosphorus removal using
 ferrous  sulfate (pickle  liquor)  was  initiated.

 Chemical Addition for Phosphorus Removal

      Pickle liquor, or liquid  ferrous sulfate (12.4  percent  Fe),
 is  added to the activated  sludge mixed  liquor at a point 3/4 of
 the  distance  between  the  head  end and the  discharge  end of the
 contact  basin.   The quantity of  pickle  liquor to be  added is
 determined  by testing  the  phosphorus  concentration in  the efflu-
 ent  from the  primary  clarifiers  once  a  week.   During periods of
 low  flow, the chemical delivery  pumps are  adjusted to  deliver
                                257

-------
approximately 0.908 kg (2.0 Ib) of iron by weight per kg (Ib)  of
phosphorus in the primary effluent.  During periods of high flow,
the pumps are adjusted to deliver approximately 0.77 kg (1.7 Ib)
of iron per kg (Ib) of phosphorus.  Approximately 246 m3 (65,000
gal) of pickle liquor are added each year, at a rate of 0.673  m3
(178 gal) of liquid or 0.70 m3 (184 Ib) Fe/day.

General Description of Wastewater and Sludge Treatment Operations

     Figure C-17 presents a flow diagram of the Brookfield treat-
ment plant.  Table C-24 is a summary of the specifications of  the
major  components of the treatment system.   The following para-
graphs describe the general sequence of wastewater treatment
operations at the Brookfield plant.

     Raw influent wastewater passes through a comminutor and is
discharged to the plant influent lift station wet well.  At the
lift station wet well the raw wastewater mixes with sidestreams
from several plant operations, including pressure filter filtrate,
incinerator scrubber water, digester supernatant, and waste acti-
vated  sludge.  From the lift station, the  raw wastewater and
returned sidestreams are pumped to the primary clarifiers where
primary sedimentation takes place.  The primary effluent flows
by gravity to the preaeration chamber followed by the contact
basin, where chemical addition for phosphorus removal takes place.
The mixed liquor then passes to the final  clarifier where the
overflow is chlorinated and discharged.

     Sludge from the bottom of the final clarifier is pumped to
the reaeration basin as return activated sludge or is wasted to
one of several other locations.  In general, waste activated
sludge is pumped to the aerobic digester or returned to the lift
station wet well at the head of the plant.  Sludge from the aero-
bic digester is subsequently transferred to the sludge  processing
holding tank.  Sludge from the primary clarifiers is generally
pumped to the sludge processing holding tank or the aerobic
digester.

     Sludge received by the sludge processing  holding tank  is fed
along with chemical conditioners to the plate  and frame pressure
filter for dewatering.  Dewatered sludge cake  is either inciner-
ated in the multiple hearth furnace or hauled  away from the plant
as wet sludge cake for disposal on crop land or at a landfill.
Incinerator ash is used as a sludge conditioner prior  to  pressure
filtration, or hauled to a landfill for disposal.

Detailed  Description of Wastewater and Sludge Treatment Operations

     Figures C-18 and C-19 present materials balances  for  primary
and secondary wastewater treatment operations  at Brookfield.
Data presented with a subscript letter A are for the period after
phosphorus removal was initiated, while data with  the  subscript
letter B are for the period before phosphorus  removal  was  initia-
ted.                           258

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ro
ui
ID
                                                    RETURN ACTIVATED SLUDGE
      PLANT
      INFLUENT
   LIFT
 STATION
   AND
COMMINUTOR
      SCRUBBER
      WATER
                                    PRIMARY
                                   CLARIFIERS
        CONTACT
      STABILIZATION
       ACTIVATED
        SLUDGE
 FINAL
CLARIFIER
                                       t
                           PRIMARY SLUDGE
             DIGESTER SUPERNATANT
                        FILTRATE
         MULTIPLE
          HEARTH
       INCINERATOR
      SLUDGE
                      CAKE
CHLORINE
CONTACT
  TANK
 3
 X
"71
                                                                SECONDARY
                                                                (WASTE ACTIVATED)
                                                                SLUDGE
                                                                           AEROBIC
                                                                           DIGESTER
                 PRESSURE
                  FILTER
  SLUDGE
CONDITIONING
   TANK
               ASH
                                    ASH
                                  STORAGE
                                   TANK
                                                                DIGESTED
                                                                SLUDGE
                                                                            SLUDGE
                                                                            HOLDING
                                                                             TANK
                 ALTERNATE
                 DISPOSAL OF
                 LIQUID SLUDGE
                 BY TANK TRUCK
         LANDFILL
           Figure C-17.   Brookfield,  Wisconsin,  wastewater treatment plant flow diagram

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TABLE  C-24.
GENERAL PLANT DESCRIPTION  SUMMARY,  BROOKFIELD,
WISCONSIN
             Unit
                      No.  and  Description
      Comminutor

      Lift Station

      Primary  Clarifiers
      Primary  Sludge
      Helithickener
      Primary  Sludge
      Pumps

      Aeration  Basins
      Air  Diffusers
      Final  Clarifiers
      Waste Activated
      Sludge Pump

      Return Activated
      Sludge Pumps
         2 at 16.80 m (55  ft)  dia. x 2.44 m (8 ft)
         side wall  depth  (SWD);  sludge collectors -
         2 Walker Process  Equipment type RSP with 2
         collector arms;  motors  - 2 at 3/4 hp, 30,
         60 hz, 480 v.

         2 at 45.70 cm (18 in) dia. x 45.70 cm
         (18 in) pitch  x  5.48  m  (18 ft) length;
         Walker Process Equipment Helithickener Cross
         Collectors, 10-15 rpm;  hopper dimensions -
         2 at 21.3 m (70  ft) length x 0.762 m (2.5 ft)
         width x 1.680  m  (5.5  ft) height; collector
         arm motors - 2 at 3/4 hp, 30, 60 hz, 480 v.;
         helithickener  motors  -  2 at 1/2 hp, 30, 60 hz,
         480 z.

         2 at 0.3 m3/min  (80 gal/min); 5 hp, 30,
         60 hz, 40 v.

         3 at 28.30 m (93  ft)  length x 9.140 m (30 ft)
         width x 4.570  (15 ft) height; air compressors  -
         3 at 2,190 scfm;  motors - 3 squirrel cage
         induction motors  at 100 hp, 30,   60 hz,
         480 v-

         6 Walker Process  Equipment EASEOUT header
         assemblies with  12 saddle-mounted MONOSPARJ
         diffusers  (per basin) at 8 scfm/diffuser.

         2 at 22.90 m (75  ft)  dia. x 3.660 m (12 ft)
         SWD; sludge collectors  - 2 Walker Process
         Equipment type SWD equipped with surface
         skimmer and 2  collector arms with 7.62 to
         15.2(3 to 6 in) suction  pipes; collector motors
         2 at 1/2 hp, 30,  60 hz, 480 v.

         1 at 0.3 m3/min  (80 gal/min); 5 hp, 30,
         60 hz, 480 v.

         2 at 5,680i/min   (1,500 gal/min); 10 hp,
         30, 60 hz, 230 v.
      Chlorine Contact
      Tank

      Lagoon
     Aerobic Digester
     Sludge Processing
     Holding Tank
         1 at 12.20 m (40  ft)  dia. x 3,660 m (12 ft)
         SWD

         1 at 1,350 m2 (14,500  ft2) x 2.130 m (7 ft)
         depth

         1 at 11.0 m (36  ft)  x  11.0 m (36 ft) x
         7.62 m (25 ft) SWD with  Walker Process Unit
         Equipment Rollaer diffusers

         1 at 4.270 m (14  ft)  x 4.270 m (14 ft) x
         2.130 m (7 ft) SWD
                                                           (continued)
                                    260

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TABLE  C-24  (continued)
          Unit
          No.  and  Description
   Pressure Filter
   Pressure Filter
   Appurtenances
   Incinerator
1  plate and frame type Beloit-Passavant  Series
5,200 - 46 chambers  at 0.042  m3  (1.5  ft3)
each with 112 m3(l21  ft2)total  area;  241.0  kg
(530 lb)  dry solids/hr capacity;  epoxy
coated carbon steel  construction  filter
plates; filter media-monofilament nylon  with
stainless steel 10 x 10 mesh  backup wire;
galvanized carbon steel drainage  member.

1  mix tank at 4,390  m2 (120  ft3)  with 2
agitators at 6 rpm;  contact  tank  at 2.44 m
(8 ft) dia,  x 4.27 m (14 ft)  length,  1,510)1
(4.850 gal) capacity; 3 rpm  agitator  powered
by 3 hp TEFC motor;  equalization  tank at
1.680 m (5.5 ft)  dia. x 2.680 m (8.8  ft)
height, 1,610 s,  (425 gal)  capacity; filtrate
weir tank; precoat tank at 13.30  m (3.5  ft)
dia. x 23.6 m (8.8 ft) height; 2  sludge-
transfer pumps at 189s,  (50  gal/min), 1  1/2 hp;
pumps at 189*  (50 gal)/min,   1  1/2 hp; precoat
pump at 40 hp, 30, 60 hz,  460 v.

5 multiple hearths Nichols-Herreshoff sludge
incincerators at 3.96 m (13  ft)  outside
depth x 5.33 m (17.5 ft) height;  242.0 kg
(510 lb)  dry solids/hr capacity  fed at
1,230 kg (2,700 lb)/hr with  ash  at 1.5:1,
moisture 50 percent, 27 percent  volatile;
auxi'11 iary natural gas burners  in hearths
no. 3 and 5; operating temperature 667 to
871°C (1,200 to 1,600°F);  induced draft
exhaust gas fan at 661,000 cms2/sec (1,400
cfm), 5 hp, 30, 60 hz, 480 v; ash screw
conveyors.
   Incinerator
   Exhaust Gas
   Scrubber
3-stage flooded tray type  wet  scrubber with
quencher, scrubber,  and  cyclonic  impinge-
ment separator; scrubber water pump  at
25 hp, 30, 60 hz,  480 v.
                                  261

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RAW INFLUENT
WASTEWATER AND
RETURNED SIDE-
STREAMS FROM
WET WELL OF LIFT
STATION AT HEAD
OF PLANT
                     PRIMARY TREATMENT
                     PERCENT REMOVALS
                              SSA=67%
                              VSSA=62%
                              FSSA=78%
                              BODA=36%
   QA=2.18X10
   SSA=4825(72%VOLATILE)
   VSSA=3450
   FSSA=1375
   BODA=2060
   QB=2.53X10
   SSB=4480(74%VOLATILE)
   VSSB=3350
   FSSB=1130
   BODB=2180
                              SSB=64%
                              VSSB=63%
                              FSSB=69%
                              BODB=32%

                               PRIMARY
                              CLARIFIERS
SSA=1600(81%VOLATILE)
VSSA=1300
FSSA=300
BODA=1310
TPA=115
SYMBOLS & UNITS
                                          SSB=1600(78%VOLATILE)
                                          VSSB=1250
                                          FSSB=350
                                          BODB=1490
                                          TPB=N/A
                                     PRIMARY SLUDGE
                                     QA=1100034.25%TSS
                                     SSA=3225(67%VOLATILE)
                                     VSSA=2150
                                     FSSA=1075
                                     BODA=750
                                     QB=134003)2. 90%TSS
                                     SSB=2880(73%VOLATILE)
                                     VSSB=2100
                                     FSSB=780
                                     BODB=690
Q=FLOW GAL/DAY UNLESS OTHER-
  WISE SPECIFIED
% RETURN Q = (RETURN FLOW 7
  FORWARD FLOW) X 100%
SS=SUSPENDED SOLIDS - #/DAY
VSS=VOLATILE SUSPENDED SOLIDS -
  0/DAY
FSS=FIXED (NONVOLATILE) SUSPENDED SOLIDS - #/DAY
TP=TOTAL PHOSPHOROUS - #/DAY
BOD=5 DAY BOD - #/DAY
I - ADEQUATE DATA NOT AVAILABLE FOR ACCURATE MASS BALANCE
II - A PORTION OF THE WASTE SLUDGE IS RETURNED TO WET WELL
  OF LIFT STATION AT HEAD OF PLANT
N/A=NOT AVAILABLE
 Figure  C-18.
               Materials balance for  primary  wastewater
               treatment operations at  Brookfield,  Wisconsin
                            262

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SECONDARY TREATMENT
PERCENT REMOVALS
SSA=79%
VSSA=81%
FSSA=77%
BODA=91%
QA=3.27X106 TPA = 8«
SSA=67000 SSB=83% SSA = 330 ( 765SVOLAT I LE )
CONTACT BASIN VSSA=38000 VSSB=82% VSSA=250
pc;c;A = pQnnn ccc: — Q •a * ccc — -7/1
MLSSA=2440 mg/l
MLVSSA=i39o mg/l
MLFSSA=i050 mg/l
%VSSA=57
MI ^c; — — lAin \no/f
MLVSSB=2050 mg/l
MLFSSB=360 mg/l
%VSSB=74
REAERATION BASIN
MLSsA=545o mg/l
MLVSSA=3060 mg/l
MLFSSA=2390 mg/l
%VSSA=56
MLSSB=4210 mg/l
MLVSSB=3070 mg/l
MLFSSB=ii40 mg/l
%VSSB=73
TO SLUDGE
HOLDING AND/OR
SVIA=64 BODB=72%
TPB=N/A
FINAL
CLARIFIER
QB=3. 64X106
SSB=42000 V. s>
VSSB = 31000 ^X.X^
FSSB=11000 J
SVIa=95
D
RETURN SLUDGE
QA=1 . 09X1063. 55%TSS
% RETURN QA=50
c; Q — T
A~~
VSSA=I
FSSA=I
QB=1 . 1 1X1 O6 S. 42%TSS
% RETURN QB=43
SSB=39000
VSSB=29000
FSSB=10000
WASTE SLUDGE
QA=42000a.55%TSS
SSA=1910(56%VOLATILE)
VSSA=1070
FSSA=840
PROCESSING ^ QB=35000S,.42%TSS
UNITS °R slB=1190
RECYCLE TO VSSR=870 ( 73%VOLATILE )
HEAD OF PLANT II _,on
' i>i5p3~~«3^-U
BODA=130
TPA=18
TO CHLORINATION
AND DISCHARGE
^ SSB=280(79%VOLATILE)
VSSB=220
FSSB=60
BODB=420
TPB-40
Figure C-19. Materials balance for secondary wastewater
treatment operation at Brookfield, Wisconsin.
263

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 Primary Clarifiers--

      Primary sedimentation  of  the raw influent wastewater and
 returned sidestreams  takes  place  in the two primary clarifiers
 Each clarifier is equipped  with  two sludge collector arms which
 continually move the  settled solids towards the sludge hopper
 which contains a rotating  "he!ithickener."  Sludge in the heli-
 thickener hopper and  collected clarifier surface scum are com-
 bined and pumped to the  sludge holding  and/or processing units
 one to three times daily,  five days/week.

      Since the initiation of phosphorus removal, the suspended
 solids loading on the primary clarifiers has  increased by 27 per-
 cent or 202 kg SS/M3  (445 Ib SS/MG)  of  plant  influent.  However,
 since the average suspended solids  concentration of the sludge
 increased from 2.9 percent  to 3.5  percent  SS,  there was a net
 increase of 157 kg SS/M3 (345 Ib  SS/MG)  pumped to sludge proces-
 sing.   Further details of the impact  on  the primary clarifiers
 are shown in Table C-25.


     TABLE C-25.   CHANGES  IN PRIMARY  CLARIFIER PERFORMANCE AS THE RESULT
     OF CHEMICAL  ADDITION  FOR PHOSPHORUS REMOVAL, BROOKFIELD, WISCONSIN
Chances
Primary Clarifier
Influent Concentrations
Primary Clarifier
Effluent Concentrations
Primary Sludge
Pumped
ss
kg/mil m3
(lb/MG)
+91 ,000
(+455t)
+20,000
(+100)
(+69,000)
(+345)
VSS ,
kg/mil m3
(lb/MG)
52,000
(+260)
+20,000
(+100)
32,000
(+160)
FSS* ,
kg/mil n)3
(lb/MG)
+37,000
(+185)
No charge
+37,000
(+185)
BOD
kg/mil m3
(lb/MG)
+17,000
(+85)
+ 2,000
(+10)
+ 15,000
(+75)
Flow
n)3/nnl m'
(gal/MG)
NA#
NA
-50,000
(-250)
  *FSS = non-volatile (fixed) suspended solids.

  t+ indicates increase; - indicated decrease.

  *NA - Not Applicable.
Aeration  Basins--

     Currently  the activated sludge system  is  being operated as
a contact  stabilization process, using one  of  the three aeration
basins as  the contact basin, and one as  the reaeration basin.
(The third  basin  is operated as an aerated  sludge storage tank
apart from  the  activated sludge process).   Prior  to entering the
contact basin,  primary effluent is received by a  preaeration
chamber where it  is mixed with flow from the reaeration basin.
                               264

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     Since the initiation of chemical addition for phosphorus
removal, the average MLSS concentration in the contact basin has
increased by nearly 75 percent, with the majority of this increase
due to a 190 percent increase in the non-volatile (fixed) portion.
As a result, the VSS fraction of MLSS decreased from 74 percent
VSS prior to phosphorus removal to 57 percent VSS since phospho-
rus removal was initiated.  Since there was virtually no change
in the amount of nonvolatile SS entering the contact basin from
the primary clarifier, it is assumed that the entire increase is
due to the addition of phosphorus removal chemicals and subse-
quent reactions.

     In the reaeration basin, the MLSS concentration has increased
by nearly 30 percent since phosphorus removal was begun.  The
entire change is due to a 110 percent increase in the concentra-
tion of fixed SS in the mixed liquor (MLFSS).  Consequently, the
volatile fraction of the reaeration basin mixed liquor (MLVSS)
decreased from 73 percent to 56 percent VSS.

Final Clarifiers--

     The final clarifiers receive the mixed liquor effluent from
the contact basin.  Sludge is withdrawn from the bottoms of the
clarifiers on a continuous basis and pumped as' return sludge to
the reaeration basin.  As necessary, sludge is wasted to one of
the sludge holding tanks, sludge processing  units, or returned
to the head of the plant.  Roughly 25 percent of the waste sludge
is returned directly to the head of the plant.  Thus, approxi-
mately 75 percent is sent to one of the sludge holding or pro-
cessing units.  (The portion sent to the aeration basin not in
use for secoridary treatment is later returned to the head of the
plant.)

     Since phosphorus removal was begun, the settleabi1ity of the
secondary sludge has improved.  This was evidenced by a decrease
in sludge volume index from an SVI of 99 prior to phosphorus
removal to an SVI of 64 since phosphorus removal was begun.

     After phosphorus removal, the pumping of return activated
sludge from the final clarifier to the reaeration basin increased
from 43 percent to 50 percent of the plant's forward flow.  The
amount of waste activated sludge pumped also increased by 5,430
m3/mil m3 (5,430 gal/MG) of plant influent, a 40 percent increase.
At the same time, the return and waste activated sludge SS con-
centrations increased from 4,200 mg/£ SS to 5,500 mg/£ SS, caus-
ing an additional 48,600 kg SS/mil m3 (405 Ib SS/MG) of plant
influent to be wasted.  Table C-26 shows these impacts of chemi-
cal addition for phosphorus removal, as well as the impacts on
final  clarifier effluent.
                              265

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     TABLE C-26.  IMPACTS OF CHEMICAL ADDITION FOR PHOSPHORUS REMOVAL ON
                 FINAL CLARIFIERS, BROOKFIELD, WISCONSIN
Changes
Final Clarifier
Effluent Concentrations
Waste Activated
Sludge Pumped
Returned Activated
Sludge Pumped*
Flow ,
n)3/mil m3
(gal/MG)
NAf
+5,430
+0.061 x
106
ss
kg/mil mj
Og/MG)
+ 4,800
(+40)
+48,600
(+405)
	
vss
kg/mil m3
(Ib/HG)
+ 3,000
(+25)
+17,400
(+145)
	
FSS
kg/mil mj
(lb/MG)
+ 1 ,800
(+15)
+ 31,000
(260)
	
BOD
-13,200
(-110)
NA
NA

    *Adequate data not available for accurate mass balance.
    +NA = Not Applicable


 Sludge  Treatment  and  Disposal  Operations

      After  sludge  has  been  removed from the primary or final clar-
 ifiers,  it  can be  stored prior to  sludge processing in three
 locations as  follows:

      t  Aeration basin  (not  in use for  secondary  treatment)
      •  Aerobic digester
      t  Sludge processing holding  tank.

 Unfortunately, it  was  not possible to thoroughly  assess the
 impact of chemical addition  for  phosphorus  removal  on each of the
 individual  sludge  storage units.   This  was  due to the wide vari-
 ability of  sludge  storage and  disposition operations and the
 shortness and discontinuous  nature of the periods available for
 study in comparison to  the  retention times  of the individual
 sludge holding units.   An additional problem in evaluating impacts
 has been the  necessity  to use  suspended solids concentration for
 constructing  mass  balances  around  clarifiers and  the activated
 sludge process, but to  use  total  solids concentrations throughout
 the discussion of  sludge processing.

      The remainder of  this  section discusses each of the sludge
storage units, sludge  volume reduction  units, and disposal oper-
tions was shown previously  in  Figure C-17.   A diagram of sludge
treatment and disposal  facilities  is shown  in Figure C-20.  Flow
diagrams showing quantities, and  characteristics  of sludge and
conditioning  chemicals  fed  to  the  pressure  filter and incinerator
during the  periods before and  after phosphorus removal , are shown
in Figures  C-21 and C-22.

Aeration Basin (not in  use  for secondary treatment)--

      At  present,  only  two of the three  aeration  basins  are  used
 as part of  the activated sludge system.  Instead,  the  third  is
 used  to  provide additional  aerated sludge storage  capacity.   An

                               266

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ro
       BUCKET
GRINDER  ELEVATOR
              I SLUDGE CAKE_CONVEYOR _ . —
                             SLUDGE FROM AEROBIC DIGESTER
                             AND PRIMARY CLARIFIER
    Figure C-20.   Brookfield, Wisconsin, pressure filtration and  incineration facilities.

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               SLUDGE FROM
             AEROBIC DIGESTOR
                          SLUDGE PROCESSING
                            HOLDING TANK
  SLUDGE  FROM
    PRIMARY
  CLARIFIERS
                  SLUDGE TO
               PRESSURE FILTER^

               QA=328000 GAL/MO
               TSA=131000 Ib/MO
               *TSA=4.77
                                    CONDITIONING  ADMIX
ASH

79000 Ib/MO
0. 60 lb ASH/
1b DRY SOLIDS
FECL3

1810 GAL/MO
8440 Ib/MO
4.27 lb FECL3/
TON DRY SOLIDS
                                                      i
               QB=395000 GAL/MO
               TSB=1 16000 Ib/MO
               %TSB=3.54
98000 Ib/MO
0.85 lb ASH/
"lb DRY SOLIDS
1770 GAL/MO
8280 Ib/MO
4.70 lb FECL3/
TON DRY SOLIDS
           P=FLOW
           TS=TOTAL  SOLIDS
           VS=VOLATILE  SOLIDS
           FS=FIRED  (NONVOLATILE) SOLIDS
           %TS=PERCENT  DRY TS BY WEIGHT
           %VS=PERCENT  DRY VS BY WEIGHT
           %FS=PERCENT  DRY FS BY WEIGHT
Figure C-21 .   Pressure filter  performance, Brodkfield, Wisconsin
                                268

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                                            FILTER CAKE

                                            WET  CAKEA=506000lb/MO
                                            TSA=219000 lb/MO
                                            VSA=71000(32.6% OF 1 b TS )
                                            FSA=148000
                                            %TSA=43.4
                                            %VSA=14.1
                                            %FSA=91%
LIME

32400  GAL/MO
22600 lb/MO
346 lb LIME/
TON DRY SOLIDS
         TOTAL:
       SLUDGE PLUS
     ADMIX TO FILTER

     QA=362000  GAL/MO
     TSA=240000 lb/MO
     %TSA=7.95
28800  GAL/MO
20100 Tb/MO
345 lb  LIME/
TON DRY SOLIDS
     QB=426000  GAL/MO
     TSB=243000 lb/MO
     %TSB=6.85
                                            WET  CAKEB=421000 Ib/MO
                                            TSB=182000 "lb/MO
                                            VSB=61000(33.6% OF 1 b TS )
                                            FSB=121000
                                            %TSB=43.2
                                            %VSB=14.5
                                            %FSB=28.7
         PRESSURE
          FILTER
         AFTER
         90 RUNS/MO
         1.73 HRS/RUN
         155 HRS/MO

         BEFORE
         79 RUNS/MO
         2.83 HRS/RUN
         232 HRS/MO
                                             FILTRATE
   UJ
   3
   (-•
   111
   *
   O
                                             QA=328000 GAL/MO
                                             TSA = 21000 lb/MO
FILTRATE-
  TANK
FILTRATE
WEIR  TANK
                               QB=397000 GAL/MO
                               TSB=62000 lb/MO
            TO PRECOAT
               TANK
                     Figure 21  (continued^
                                 269

-------
   RETURNED 70 WET
    WELL  OF LIFT
   STATION AT HEAD
       OF  PLANT
              SCRUBBER WATER
                 Q=0.2 MGD
               SS=200 1 b/DAY
              WHEN OPERATING
   SLUDGE
   FROM
   PRESSURE
   FILTER
CAKE
                  INCINERATOR
                     FEED
FEED =308000 1 b/MO
TSA=133700 lb/MO
VSA=43400 1 b/MO
FS = 89900 1b/MO
                  FEEDB=416000 1
                  TSB=179700 1 b/MO
                  VSB=60300 lb/MO
                  FSB=1 19400 1 b/MO
INCINERATOR
 OPERATION

AFTER
253 HRS/MO
1220 1 b/HR
172 1 b VS/HR

BEFORE
284 HRS/MO
1460 l.tXHR
212 lb VS/HR
       SLUDGE  CAKE HAULED

       AFTER
       198000 1 b/MO

       BEFORE
       4800 1 b/MO
                                   ASH FOR RECYCLE  AS
                                 CONDITIONER OR  PRECOAT

                                 AFTER
                                           87700 lb/MO
                                 BEFORE
                                 97800 1 t/MO
                                    ASH HAULED
                                    AFTER
    Q=FLOW
    TS=TOTAL SOLIDS
    VS=VOLATILE  SOLIDS
    FS=FIXED (NONVOLATILE)
    FEED=WET CAKE
                         22001 b/MO
                         BEFORE
                         21600 Ib/MO
                  SOLIDS
Figure C-22.
   Multiple hearth  incinerator performance, Brookfield,
   Wisconsin.
                                 270

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estimated 60 percent of the plant's waste activated sludge and
5 percent of the primary sludge enters this unit by pumping as
necessary from the bottoms of the primary or final  clarifiers.
Since the aeration basin is not equipped for the collection and
pumping of concentrated sludge, solids contained in the aeration
basin are pumped from the aeration basin without being  allowed
to settle.  This sludge is then sent to the wet well  of the lift
station at the head of the plant.   Subsequently, it is  pumped  to
the primary clarifiers along with the raw influent  wastewater  and
other returned sidestreams.  There, the combined raw  and returned
solids are settled and concentrated, after which they are gener-
ally sent to one of the sludge holding units other  than the aera-
tion basin.

Aerobic Digester--

     An estimated 80 percent of the sludge routed to  the aerobic
digester  is from the primary clarifiers while 20 percent is from
the final clarifiers.  The aerobic digester supernatant is
decanted  periodically to the wet well at the head of  the plant,
after the aeration equipment has been turned off and  the solids
have settled to the bottom of the digester.  The sludge is pumped
from the  bottom of the digester to the sludge processing holding
tank when the aeration equipment has been turned off.  Since
phosphorus removal was initiated, the aerobically digested sludge
has averaged 1.1 percent TS.  Before phosphorus removal began,
the sludge contained 1.5 percent TS.

Sludge Processing Holding Tank--

     An estimated 85 percent of the sludge routed to  this unit
is from the primary clarifiers and 15 percent from  the  aerobic
digester.  Occasionally, supernatant is decanted from this tank
and returned to the wet well at the head of the plant.   Sludge
from the  sludge processing holding tank is generally  fed to the
pressure  filter (although liquid sludge can be pumped into a
tank truck and hauled from the plant for spreading  on croplands).
Figure C-21 presents data on the average characteristics of the
sludge from the sludge processing holding tank.

Pressure  Filter--

     The  plate and frame pressure filter is generally operated
4 days/wk, 16 hr/day, 45 wk/yr.  (To facilitate data comparisons,
sludge quantities and flow rates are expressed as daily amounts
per 7-day week.)  A filter run begins by pumping sludge from the
sludge processing holding tank (sludge supply tank) to the mix
tank where it is blended with admix materials into a uniform
slurry.   The admix material consists of incinerator ash, ferric
chloride  solution of 570 kg FeCl3/ra3 (4.75 Ib FeCls/gal) of solu-
tion, and hydrated lime diluted to an 8 percent solution.


                               271

-------
     Next, the sludge and conditioning admix slurry are pumped
from the mix tank to the contact tank.  This tank is provided to
allow sufficient residence time for conditioning reactions to
take place prior to feed to the filter.   The tank is equipped
with an agitator blade which turns at 3 rpm to prevent the sus-
pension from clinging to the tank walls.  An equalizing tank
receives the slurry from the contact tank and holds it until
pumping from the tank to the filter begins.

     Prior to filtration, precoat consisting of filtrate and
incinerator ash  fed  from  the  precoat  tank  at  100  psi  to cause  is
a uniform precoat slurry to flow through the filter.  Following
filter precoating, sludge and admix from the equalizing tank are
pumped to the filter,  initially  at  379  i  (100 gal/min) and  225  psi
pressure to preclude the loss of precoat from the filter media.
When the tank has delivered approximately one half of the con-
ditioned sludge to the filter, an air supply valve is opened to
complete the emptying of the tank at a reduced but constant pres-
sure of 100 psi.  Throughout the filter run, the filter feed pump
automatically decreases output as the pumping head increases, and
eventually stalls out against a terminal pressure of 225 psi
(which coincides with zero flow through the filter).
 *
     Upon completion of the filtration cycle, sludge cake is dis-
charged from the filter and dropped into a bunker where it is
stored.  A portion of the filtrate from the pressure filter oper-
ation is returned to the wet well at the head of the plant while
the remainder of the filtrate is returned to the precoat tank.
Sludge cake is removed from the bunker by a drag flight conveyor,
discharged onto an inclined conveyor, and then fed to the incin-
erator.  Alternatively, if may be discharged to a bypass conveyor
which discharges the sludge cake to a truck outside the building.

     Data describing the operation of the pressure filter during
the period before and after phosphorus removal was initiated is
shown in Table C-27.  After phosphorus removal, there was^a slight'
decrease in the volume of sludge fed from the sludge processing
tank to the chemical mix tank each month which is equal to a
decrease of 185 m3/mil m3 (185 gal/MG) of plant influent.  How-
ever, the total solids in the sludge holding tank increased from
3.54 percent TS before phosphorus removal to 4.77 percent TS
after phosphorus removal.  As a result the mass of total solids
fed to the chemical mix tank from the sludge processing holding
tank has increased by 30 percent, or 56,405 kg/mil m^  (470  Ibs/MG)
of plant influent.
                               272

-------
             TABLE C-27.   PRESSURE FILTER PERFORMANCE,
                       BROOKFIELD, WISCONSIN


                                     Pressure Filter Input

m3 (gal) feed/run
m3 (gal) feed and admix
run
kg (Ib) TS feed/run
kg (Ib) TS feed and
admix run
kg (Ib) TS feed/hr
kg (Ib) TS feed and
admix/hr
After
13.7 (3,640)
15.2 (4.020)
661 .0 (1 ,455)
1 ,200 (2,670)
384.0 (845)
704.0 (1,550)
Before
18.9 (5,000)
20.4 (5,380)
667.0 (1,470)
1 ,400 (3,075)
227 (500)
477.0 (1 ,050)
                                     Pressure Filter Output
          kg (Ib) wet cake/run
          kg (Ib) wet cake/hr

          kg (Ib) TS in cake/run

          kg (Ib) TS in cake/hr

          kg (Ib) TS in filtrate/run
          kg (Ib) TS in filtrate/hr

          % feed and admix TS
          recovered in cake
  After

2,550 (5,620)

1 ,480 (3,265)

1,100 (2,430)

638 (1,405)

107 (235)

61.3 (135)

    90
  Before

2,420 (5,330)

824 (1 ,815)

1 ,044 (2,300)

370 (815)

356 (785)

125 (275)

    75
      When the sludge gets  to  the chemical mix tank,  incinerator
 ash,  FeCl3,  and lime are added,  again changing the quantity and
 solids  concentration of the  sludge before it gets to  the  filter.

      The dosage of ash was  lower by about 0.1140  kg  ash/kg of dry
 solids  (0.25 Ib ash/lb of  dry solids) after phosphorus  removal.
 The average  dosage decreased  from 0.386 to 0.272  kg  ash/kg of dry
 solids  (0.85 to 0.60 Ib ash/lb of dry solids).  Similarly, the
 dosage  of ferric chloride  decreased from 2.35 kg  FeCla/t  (4.70
 Ib FeCl3/ton) of dry solids  to 2.14 kg FeCl3/t (4.27  Ib FeCl3/ton)
of dry  solids after phosphorus removal.   The dosage  of  lime
remained  constant at approximately 173.0 kg lime/t (345 Ib lime/
ton) of  dry  solids.  The net  result was  that the volume of sludge
plus admix delivered to the filter from  the mix tank  was  lower by
80 m3/mil m3 (80 gal/MG) of plant influent after phosphorus
removal.  And there was a total  solids increase from  6.85 percent
TS to 7.95 percent TS in the  sludge fed  to the filter.  This is
equivalent to an increase in  the amount  of pressure  filter feed
of 55,200 kg TS/mil m3 (460 Ib TS/MG) of plant influent,  or an
increase  of  15 percent.
                                 273

-------
     Filter cake characteristics showed only minor variations
between the periods before and after phosphorus removal.  Speci-
fically, the TS concentration of the cake increased from 43.2 to
43.4 percent.  The VS fraction of cake TS decreased somewhat from
33.6 percent of TS to 32.6 percent of TS.  Table C-27 compares
pressure filter performance before and after phosphorus removal.

     Since the initiation of chemical addition for phosphorus
removal, pressure filter performance has improved significantly.
The sludge mass fed per hour (not including admix materials) has
increased from 227 to 384 kg TS/hr (500 to  845 Ib TS/hr),  and
the mass of feed  plus admix/hr increased from 477 to  704 kg/hr
(1,050 to 1,550 Ib/hr).   The length of the  average pressure  fil-
ter run decreased  by 40  percent from 2.83 hrs/run to  1.73  hrs/run.
In addition,  the  percentage of the solids fed to the  filter  which
are recovered in  the cake increased from 75 percent to 90  percent.
The combined  effect was  a production increase of 658  kg wet  cake/
hr (1,450 Ib  wet  cake/hr) and 268 kg TS/hr  (590 Ib TS/hr).

Incinerator--

     During periods of incinerator operation, the incinerator is
run 24 hrs/day, 4  days/wk with an additional  half day for  incin-
erator start-up,  and another half day for cool-down.   The  cake
elevating conveyor raises pulverized filter cake to the jtqp  of
the incinerator,  where the cake enters the  first hearth/'After
the cake has  been  fully  incinerated and reaches the bottom hearth,
the ash is  discharged into a screw conveyor which in  turn  dis-
charges to  an ash  grinder, followed by a bucket elevator which
ultimately  discharges into the ash storage  bin.  Ash  stored  in
the bin is  used for precoating the pressure filter or condition-
ing the sludge prior to  pressure filtration.   Excess  ash can be
discharged  from the ash  bin into a truck for disposal on-site
followed by subsequent transfer to an off-site landfill.

     Exhaust from the incinerator is either vented to the air
pollution control  system or returned to the lower hearths through
the warm air duct  for preheating.  The air pollution control
equipment consists of a  3-stage, flooded-tray type wet scrubber.
The first stage consists of a hot gas quencher where water  is
sprayed into  the  gases until they are cooled.  The second stage
is the scrubber where water is sprayed to entrain particulate
matter.  Finally,  the gases are exhausted through the third  stage
which consists of a cyclonic impingement separator followed  by
the exhaust stack.  Scrubber waters pass through the scrubber
once,  after which  they are discharged to the wet well at the
head of the plant.
                               274

-------
     The operating temperatures recorded at the hearths  and the
scrubber system are:

        Hearth 1  - 427°C (800°F)
        Hearth 2  - 867°C (900°F)
        Hearth 3  - 843°C (1,550°F)
        Hearth 4  - 704°C (1,300°F)
        Hearth 5  - 468°C (600°F)
        Cooling Air Outlet - 38°C (100°F)
        Scrubber  Inlet - 93°C (200°F)
        Scrubber  Outlet - 248°C (280°F)

Incinerator fuel  consumption is approximately 18.5 to 19.6 m3/hr
(660 to 700 ft3/hr) of operation (natural gas).


     Figure C-22  shows performance data for the multiple hearth
incinerator.  From this data and the information presented in the
general plant description summary (Table C-24), the incinerator
can be seen to be  presently operating at an average feed rate
which  is approximately one-half of the design capacity.   Although
not attributable to phosphorus  removal, there has been a shift
in the method of final disposal used.  Before phosphorus removal
an average of 1.8  t/mo (2 tons/mo) wet pressure filter cake were
hauled from the plant rather than incinerated.  More recently,
nearly 90.7 t/mo (100 tons/mo)  of wet cake are being hauled.
The plant manager  apparently has found it cost effective to keep
the incinerator down for a week rather than operate at less than
capacity.  Currently, consideration  is being given to hauling
all the wet sludge cake produced as  a cost effective alternative
to incineration.

     Since the beginning of phosphorus removal, incinerator feed
rates  have declined from 663.0  to 554.0 kg wet cake/hr (1,460 to
1,220  Ib wet cake/hr) of operation.  This has reduced the feed
rate of volatile solids from 96.3 to 78.1 kg VS/hr (212 to 172
Ib VS/hr) of operation.  As a result, an additional 14 m3 (500
ft3) of natural gas are required per hour of operation.

     Prior to the  initiation of phosphorus removal, approximately
9.98 t  (11 tons) of incinerator ash  were hauled from the plant
each month, while  an average of only 0.907 t  (1 ton) of ash was
hauled each month  after phosphorus removal was initiated.  The
remainder of the ash generated  by the  incinerator  is  recycled as
admix  for pressure filter sludge conditioning or pressure filter
precoat.  During periods of incinerator operation, approximately
757 m3/day (0.2 mgd) of scrubber water containing approximately
90.8 kg (200 Ib)  SS/day are generated and returned to the head
of the plant.
                               275

-------
 Sludge Treatment and Disposal Costs

 Operation and Maintenance Costs--

      With the initiation of  chemical addition for phosphorus
 removal, the cost of sludge  treatment and disposal has decreased
 by  approximately $1.60/t ($1.33/ton) of dry solids filtered, as
 shown  in Table  C-28.  This reduction was due to decreases in the
 amounts  of  chemical  conditioners  and electricity  used  by the
 plate and frame pressure filter.   These decreases were partially
 offset by an  increase  in the amount of auxiliary  fuel  used  by the
 incinerator as  the  result of decreased incinerator volatile
 sol ids feed rates.

      The mass of solids filtered  increased  from 182  to 237  t/mil
 m3  (0.76 to 0.99 tons/MG) of plant influent with  phosphorus
 removal.  Theoretically, sludge treatment costs should have
 increased by  28 percent going from $179,000.00 to $229,000.00
 ($47.30 to  $60.50/MG) of plant influent.   However, increased wet
 sludge cake hauling (at little or  no charge) and reduced periods
 of  incinerator  operation prevented any actual  increase in the
 cost of sludge  treatment per  MG of plant influent.
  •
 Capital Costs--

     The total  plant cost in  1973  was $3.6 million.   The plant
 was financed by  15 year general  obligation bonds at 4.37 percent
 interest, maturing in 1986.    The pressure filter equipment and
 piping cost $385,000.00.  The cost of the multiple hearth incin-
 erator was $336,000.00.

 Summary and Conclusions

     Since the  initiation of  chemical  addition for phosphorus
 removal, the Brookfield wastewater treatment plant has shown an
 increase in the average solids loadings to each wastewater treat-
ment and sludge handling unit process.   The only exception to
 this observation was a decrease in total  amount of sludge solids
 sent to the incinerator, which was due to increased wet sludge
cake hauling after pressure filtration.  There has been an
 increase of approximately 0.056 kg TS/m3 (470 Ib TS/MG) of plant
 influent pressure filtered  as the .result of phosphorus removal'.
Fortunately, due to the improved dewatering performance of the
pressure filter, presumably attributable to phosphorus removal
chemical addition, conditioning admix dosages of ash and ferric
chloride were  reduced.   In  addition, the total solids recovery
by the pressure filter also  improved significantly,  improving
filtrate qua!ity.

     Since  this  plant is operating well below capacity, the addi-
tional phosphorus laden chemical sludge at this plant  has caused
no operational  problems.  Furthermore,  since wet sludge cake can


                               276

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                 TABLE  C-28.   PRESSURE FILTER AND INCINERATOR OPERATIONAL
                    COSTS  PER  t (ton)  DRY SOLIDS, BROOKFIELD, WISCONSIN

Item
Fed 3*
Lime
Natural1"
Gas
Electrici ty*
Labor**
(O&M)
TOTAL
Unit
Cost
$
83.20/m3
(0.315/gal)
0.067/kg
(0.0305/lb)
O.Q64/m3
(0.001786/ft3)
0.04/kwh
6.00/hr
Units
Vton)
After
0.115
(27.6)
173
(346)
(213)
6,880
240
3.33
Used per t
dry solids
Before
0.13
(30.5)
172
(345)
(204)
6,570
260
3.33
Costs per
After
9.58
(8.69)
11.63
(10.55)
13.55
(12.29)
10.58
(9.60)
22.05
(20.00)
67.39
(61 .13)
t (ton) Dry
Before
10.59
(9.61)
11 .60
(10.52)
12.93
(11 .73)
11.47
(10.40)
22.05
(20.00)
68.64
(62.26)
Sol ids
Change
-1.01
(-0.92)
+0.03
(+0.03)
+0.62
(+0.56)
-0.88
-0.80
No
Change
-1 .24
-1 .13

 *During 1976, the plant installed ferric chloride bulk storage  facilities  reducing
  ferric chloride unit costs $206/m3 ( $0.780/gal ), $1 ,190/m3 ($0.31 5/gal ).   The
  unit cost for bulk purchases has been used for the purposes  of cost  comparisons.

 ''"includes incinerator warm-up.

 ^Estimated decrease due to shorter length of filter press runs.

**Assumes no sludge cake hauled from plant.

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be hauled from the plant at little or no charge,  increased quan-
tities of more easily dewaterable sludge have actually decreased
the cost of sludge handling per ton of dry solids.

CASE STUDY I:  MIDLAND, MICHIGAN

Introduction

     In 1960, when the Midland plant was designed as a two-stage,
high-rate trickling filter plant, various alternative means of
sludge handling were considered.  The one chosen  was vacuum fil-
tration of the undigested sludge with disposal  in a sanitary land-
fill.  In 1970, it became necessary to upgrade the  Midland plant
to provide for phosphorus removal and a higher level of BOD and
SS removal.  Facilities were added for chemical  additions of
either ferric chloride or alum plus polymer, and  rapid sand fil-
ters were added to filter the effluent prior to  discharge.  These
changes meant that it would be necessary to handle  additional
sludge solids from the chemical addition and the  tertiary filtra-
tion both, and this was considered in the design  of the sludge
handling facilities.

     Besides the increased mass of sludge to be  disposed of, two
other factors were considered in the design of the  new sludge
handling facilities.  One was the new requirement by the Michigan
Department of Natural Resources that sludge stabilization and
dewatering to at least 50 percent dry solids be  performed if the
plant was to continue sanitary landfill disposal.  Previously,
raw sludge at a concentration of about 25 percent TS had been
landfilled.  The other factor that was considered was cost.

     Of the various alternatives considered for  the solids hand-
ling facilities, the addition of thermal conditioning with con-
tinued utilization of the existing vacuum filters and sanitary
landfill disposal appeared the least costly.  Other alternatives
considered included anaerobic digestion and farmland disposal of
liquid sludge or sludge cake; incineration of sludge cake; and
replacing the vacuum filters with a filter press.  Thermal condi-
tioning was the only method which could provide both sludge sta-
bilization and a 50 percent TS filter cake.  It  thus enabled con-
tinued use of the sanitary landfill as well as the greatest reduc
tion in the volume of sludge for disposal.  Thermal conditioning
also appeared to require less operational labor  than any of the
other alternatives.

     When the thermal conditioning option was selected in  1970,
the energy shortage was not a factor considered.   At the  present
time, the alternatives are being re-evaluated by Midland  due  to
the increased awareness of the energy shortage.   This  case  study
will investigate the impact of ferric chloride and  polymer  addi-
tion ahead of the primary clarifiers on the cost-effectiveness
                               278

-------
 of  the  present  system.   Other  plants  considering  the  use  of  ther-
 mal  conditioning  and  vacuum  filtration  can  benefit  from this  dis-
 cussion.

      The  plant  was  designed  in 1963  to  handle  0.025 mil m3/day
 (6.5 mgd)  municipal wastewater from  a  population  of 35,000 and
 effluent  from  the sanitary  facilities  at  the  Dow  Chemical Co.
 complex nearby.   Every  year  since  1972,  the actual  average flow
 has  exceeded  the  design average.   For  the year July 1975  through
 June 1976,  the  flow averaged 0.029 mil  m3/day  (7.63 mgd).  A  flow
 equalization  basin  at the head of  the  plant evens out  daily  var-
 iations in flow,  thus avoiding the need  for a  total plant capa-
 city increase.

      A  high degree  of treatment is provided by the  wastewater
 system, which  incorporates  two-stage  trickling filters, tertiary
 multi-media filtration, and  phosphorus  removal  by chemical addi-
 tion.  The system provides  approximately  90 percent reduction of
 both BOD  and  SS.   Average influent BOD  and  SS  concentrations  are
 about 106  and 151 ppm,  respectively.  Industrial wastes comprise
-an  insignificant  part of  the plant influent and create no waste-
 water or  sludge treatment problems.

 History

      Historical plant modifications which have  affected sludge
 production  and  characteristics are listed below:

      May  1972 - Thermal  sludge conditioning replaced polymer con-
 ditioning.

      March  29,  1973 -  Ferric chloride and polymer addition to
 primary influent  for  phosphorus removal started.

      May  1,  1973  -  Discontinued thermal conditioning and  returned
 to  polymer  conditioning.

      May  29,  1973 - Raised reactor temperature  of thermal cpndi-
 tioning unit from 185°  to 202°C (365°K  to 395°F).

      June  1973  -  Tertiary mixed media filters  added;  backwash
 water recirculated  to  head of  plant.

 Chemical  Addition for Phosphorus Removal

      Liquid  ferric  chloride  (40 percent  Feds)  is added to the
 raw  sewage  between  the  raw sewage  comminutor  and  the  raw  sewage
 pumps.  Flow-proportional feed pumps  are  set  to achieve a concen-
 tration of  approximately  42  mg/'£ FeCl3.   The  turbulence created
 by  the  pumps  aids in  mixing  the ferric  chloride.   Ferric  phos-
 phate begins  to form,  and the  mixture  enters  a grit chamber  where
 an  anionic  polymer  supplied  by Dow Chemical Co.  is added for

                                279

-------
 coagulation.   The usual  dosage  of  dry  polymer  is  0.17  mg/a.   The
 contact time  between  the ferric  and  polymer  addition  is  3  to  4
 min.   After polymer is  added  there is  another  1.5 min  or so con-
 tact  time before the  flow enters the primary clarifiers.   Approx-
 imately 1.05  t (1.16  tons)  per  day dry FeCU and  4.3  kg  (9.5  Ib)
 per day dry polymer are used.   The plant's average phosphorus
 removal efficiency is  approximately  80 percent, and  phosphorus
 is generally  reduced  to a final  effluent  concentration of  less
 than  1  mg/£,  meeting  discharge  permit  requirements.

 General  Description of  Wastewater  Treatment  Operations Affecting
 SIudge

      Figure C-23 presents  a general  treatment  plant flow diagram
 for Midland. "It can  be  seen  that  s'idestreams  from the sludge
 treatment processes,  backwash water  from  the tertiary filters,
 and waste sludge from  the  intermediate  and final  clarifiers all
 join  the raw  sewage before  it enters the  primary  clarifiers.
 The clarifiers themselves  are six  rectangular  tanks, with  a total
 capacity  of 0.0023 mil m3  (610,500 gal).  Each tank is 25.9 m
 (85 ft)  long  by  4.8 m (16 ft)  wide by 3.05 m (10  ft) deep.  The
 bottoms  of  the  tanks are  flat.   Sludge  is continuously scrapped
 along the bottom  of each  tank by a drag conveyor  with seventeen
 flights  to  a  hopper at one end.   Each hopper is 4.88 m (16 ft)
 long, 1.22  m  (4  ft) deep, 1.4 m  (4 ft 6 in)  wide  at the top and
 0.635 m  (2  ft  1  in) wide at the  bottom.  Sludge is pumped from
 each  tank once  every 4 hr for 8  min, at 0.03 m3/min (75 gal/min).
 In  the  past,  sludge had  been pumped  for 15 min instead of 8.
 Decreasing  the  pumping time allowed a longer sludge detention
 time  in  the clarifier bottoms, which resulted  in  a sludge solids
 concentration  of  7 percent TS instead of the former 6 percent TS.
 This  increase  in  sludge  solids concentration has  had no effect
 on  sludge handling operations except that less sludge volume is
 now pumped  to  the  holding tanks  and  little or  no  supernatant is
 formed  in the  holding tanks and  returned to  the primaries.

      It  is  clear  that adding ferric  chloride and  polymer ahead
 of  the  primary  clarifiers has affected  primary clarifier perfor-
 mance and operation by  increasing  BOD,  SS, and total phosphorus
 removal  efficiency, and  by increasing  the amount  of sludge solids
 generated.  However, the amounts of  these increases are  difficult
 to determine.    Other changes in  plant operation took place about
 the same  time  that phosphorus removal was started.  These  changes
 affected clarifier efficiency and  sludge production, so  the
 effect of phosphorus removal alone is obscured.   These plant
 modifications were the shortening  of the sludge pumping  time,
 affecting sludge  solids  concentration as already  discussed, and
 the recycling  of  tertiary filter backwash to the  head of the
 plant.  The backwash water contains  the sol ids .removed in  the
 tertiary filters.  An unknown fraction  of these solids is  removed
 in the primary clarifiers, thus  increasing sludge  production  by
an unknown amount.


                               280

-------
                      TITTABAWASSEE
                         RIVER
                        CHLORINE
                        CONTACT
                         TANK
                         TERTIARY
                         FILTERS
 FINAL
CLARIFIERS
2ND STAGE
TRICKLING
 FILTERS
INTERMI-
 DIATE
CLARIFIERS
1ST STAGE
TRICKLING
 FILTERS
                           BACKWASH
                           WATER
            SLUDGE
ro
00
              RAW SEWAGE
                        COMMINUTOR
 FLOW
SPLITTING
 VENTURI
FLOW METER
 GRIT
 CHAMBER
                                      FLOW
                                     EQUALI-
                                     ZATION
                                                FILTRATE
                   LAND RECLAMATION-^-
                                                      DECANTATE
 PRIMARY
CLARIFIERS
                                      VACUUM
                                      FILTERS
            CONDI-
            TIONED
            SLUDGE
            DECANT
             TANK
            21MPRO,
             INC.
            THERMAL
            CONDI-
            TIONING
           RAW SLUDGE
            HOLDING
             TANKS
            Figure C-23.  Midland,  Michigan, wastewater treatment plant  flow diagram

-------
      There was one month of operation between  the  commencement of
 phosphorus removal and the start-up of the tertiary  filters.   Dur-
 ing  that month only 19 mg/£ Fed 3 were added  instead  of  the pre-
 sent 40 to 50 mg/£.  Comparing primary clarifier efficiency dur-
 ing  that month with the performance before phosphorus  removal, we
 see  increased BOD and SS removal with FeCl3 addition.  This is
 shown in Table C-29.

            TABLE C-29.  PHOSPHORUS REMOVAL IMPACTS ON PLANT
                BOD AND SS REMOVALS. MIDLAND,  MICHIGAN _

                                       No  Fed 3 Added    19  mg/l FeCl3

Total mil m3 (M6) wastewater treated/mo:
                                       n q,  /?dq ?n     n qt.
percent removed by primary treatment  - _ u>yt  ^<**-*|J     u-*5

                             BOD             26              48
                             SS               32              67

Percent removed by first-stage
biological treatment -          BOD             34              38
                             SS               29              42

Percent removed by second-stage
biological treatment -

Total plant percent removal -

BOD
SS
BOD
SS
51
14
62.4
63.9
38
37
80.2
89.0

      The  effluent from the six primary tanks  flows  to  two  first-
 stage stone-filled trickling filters, 24.4 m  (80  ft)  in  diameter
 by  1.82 m (6  ft)  deep.  The effluent from these is  collected in
 the  underdrain  system and flows to two intermediate clarifiers.
 Each  clarifier  is 18.3 m (60 ft) in diameter  by 3.04  m (10 ft)
 deep.  Trickling  filter humus settles in the  tanks  and is  contin-
 uously scraped  to the center hoppers.  Sludge  is  pumped  from each
 hopper for  1  hr once every 8 hr.  The sludge  is returned to the
 primary clarifier influent.  The effluent is  pumped to the second
 stage  trickling filters which are just like the first-stage fil-
 ters.  The  final  clarifiers are 21.9 m (72 ft)  in diameter by
 2.74  m (9 ft) deep.   Sludge is removed from them  as in the inter-
mediate clarifiers and returned to the primary  clarifier influent,
The flow  is then  pumped to tertiary multi-media filters.

      It appears that phosphorus removal  has improved  overall
plant performance with regard to BOD and SS removal.   Because of
the increased removals in the primary clarifiers, the  BOD  and SS
loadings on the secondary part of the plant are decreased, appar-
ently enabling  better trickling filter performance.   This  is
borne out by the  data in  Table C-29.
                                282

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Detailed Description of Sludge Treatment and Disposal  Operations

Storage--

     The two raw sludge holding tanks have served as thickeners
in the  past, but now serve only as holding tanks since thickening
is occurring in the bottoms of the primary tanks.  Each tank is
square, 4.41 m  (14.5 ft) on a side, and 6.09 m (20 ft) deep.
Each has a capacity of 59.5 m3 (15,710 gal).  Sludge is pumped
from these tanks to the thermal conditioner when it is in opera-
tion.

Conditioning--

     Thermal conditioning is practiced with the Zimpro, Inc., low-
pressure oxidation  system.  The principal difference between this
system  and the  Porteous or Farrer processes i s the addition of air to
the reactor during  the treatment operation.  The system is really
a low-pressure  form of wet-air oxidation.  Sludge is first ground
to eliminate large particles.   High pressure pumps  then bring the
sludge  to a system pressure of 400 psig, before it  is  mixed with
air from an air compressor.   A heat exchanger transfers heat to
the incoming sludge-air mixture from the outgoing sludge.   The
heated  sludge then passes to a reactor,  where steam injected from
a boiler brings it to a temperature between 177°C and  204°C (350°
and 400°F).  The sludge leaves the reactor after 20 min,  passes
back through the heat exchanger,  and enters two sludge thickening
tanks.  The combination of heat,  air, and pressure  in  the reactor
results in a cellular breakdown of the sludge solids,  allowing a
further gravity thickening to occur readily in the  tanks.

     Sludge is  pumped to the thermal conditioner at 2.08 a/sec
(33 gal/min) when it is in operation.  This is about 2.8 days/wk
on the  average, for 24 hr/day.  The reactor temperature is pre-
sently  maintained at 202°C (395°F).  Approximately 14,000 m5
(500,000 ft3) of natural gas/mo are used to fuel the boiler.

     Thermal sludge conditioning has several benefits.  It sta-
bilizes the sludge, enabling further handling without pathogens,
odors,  or putrefaction.  It changes the cellular structure of the
sludge, enabling thickening to a relatively high solids concen-
tration and thus reducing the volume to be vacuum filtered.  And
it improves the dewatering characteristics of the sludge,  increas
ing filter yield and cake solids concentration.

Thickening--

     After thermal  conditioning the sludge is thickened and
stored  in two tanks which are constructed like the two raw  sludge
holding tanks.  Conditioned sludge is pumped into tank #1  until
it is full.  The decantate is then drawn off, and the thickened
sludge  is pumped over into tank #2.  There is a  screw mechanism


                               283

-------
  in  the center of tank #2 which is turned on whenever sludge is
  pumped to the vacuum filters.  It mixes the denser sludge near
  the  bottom of the tank with the less dense sludge near the top.
  The  solids retention time in the thickener varies considerably
  between about 1.5 and 3 days because of intermittent vacuum fil-
  ter  operation.  Sludge retention time and sludge blanket depth
  are  not critical control variables for the operation of a condi-
  tioned sludge thickener as they often are for the operation of a
  raw  sludge gravity thickener.

  Dewatering--

       Dewatering is accomplished by two Eimco rotary drum vacuum
  filters.  Some machine operating parameters for these vacuum fil-
  ters  are given below:
                          .2
       Filter area:  18.6 mfc (200 1
       Filter media:  polyethylene
  (28 x 32 threads/in)
       Vacuum:   50.8 cm  (20 in) Hg
         cloth, 11  x 12.6 threads/cm
The drum speed is set at
dr.um submergence is 5.08
are usually run at once.
average of 4 hr/day.
3 min per revolution,  and the  depth  of
to 10.2 cm (2 to 4 in).   Both  filters
 They are operated 3.7 days/wk for an
     Chemical conditioning with anionic and cationic polymers
has been used in the past.  Approximately 0.150 kg (0.3 lb) of
anionic polymer/t (ton) of dry solids and 2.50 to 4.00 kg (5 to
8 lb) of cationic polymer/t (ton) of dry solids were used.  Ther-
mal conditioning eliminated the need for chemical conditioners.

Ultimate Disposal--

     Until about 1973, vacuum filter cake was buried in trenches
at the city of Midland landfill site.  A private contractor was
hired by the plant to dig the trenches and bury the sludge.  The
filter cake at that time was unstabilized sludge.  With thermal
conditioning it became possible to use the sludge in a variety
of other more useful ways.  The sludge cake is still trucked out
to the sanitary landfill site in two 6-wheel drive liftainer
trucks belonging to the plant.  Each truck carries a 4.59-m3
(6-yd3) load, and an average of 1.8 loads are hauled per  day.  A
round trip is approximately 13 mi long and takes about 30 min.
The sludge is stockpiled at the landfill site where the city of
Midland can utilize it.  The expenses involved in further hand-
ling are borne by the city of Midland using their General Fund.
                                           t
     Some of the sludge is used for land reclamation at the  land'
fill  site.   After a section of landfill has been filled with
refuse to the desired elevation, it is capped with clay soil.
                               284

-------
Sludge is disced into this clay soil covering to enrich and con-
dition it.  The soil is then seeded with grass.   In the future,
when landfilling has ceased, the site will  be grass covered and
suitable for recreational use.

     Some of the sludge is informally made  into  compost by the
city's Department of Forestry and used as soil  conditioner in
their on-site ornamental tree nursery.  Sludge  or compost is
disced into the soil, greatly enriching it  and  enhancing tree
growth.  Both sludge-leaf compost and sludge-sawdust compost are
made in piles with a minimum of attention and labor.

Impact of Phosphorus Removal on Sludge Treatment and Disposal
Operations

     The sludge treatment flow diagram below (Figure C-24)  shows
as  completely as possible the  sludge  and sidestream quantities
handled  at  Midland.  Approximately  75.7 m3  (20,000 gal) of raw
sludge containing 4,540  kg  (10,000  Ib) TS (7 percent TS) are
pumped to the raw sludge  holding tanks each day.  Approximately
53.0 m3  (14,000 gal) of  thickener decantate are removed and the
remaining 22.7 rrn (6,000  gal)  of concentrated (18 percent TS)
sludge are  vacuum filtered.  The decantate contains only about
475 ppm SS, so we have estimated that only a few hundred pounds
TS  are removed in the decantate and that the rest are filtered.
The vacuum  filter filtrate  is  relatively high in suspended solids,
containing  8,000 to  9,000 ppm.  Several hundred  pounds TS may be
lost in the approximately 11.40 m3/day (3,000 gal/day) of fil-
trate.  Approximately 8.26 m3  (10.8 yd3) filter  cake (50 percent
TS) are formed each  day.  The  dry weight of this filter cake is
approximately 4,090  kg (9,000  Ib).

     The impacts of  ferric chloride addition to  the raw sewage
on  sludge treatment  and disposal can  be judged  using plant data
collected since 1970.  The impacts  upon sludge  conditioning,
thickening, and dewatering characteristics  have  varied with the
conditioning method  used, the thermal conditioner temperature,
and the recycling of tertiary filter  backwash water.  Table C-30
consolidates available data indicating these relationships.  The
values presented are based on monthly averages  as recorded in
plant monthly reports.

Sludge Production and Sludge Solids Concentrations--

     As discussed earlier, the impact of phosphorus removal on
raw sludge quantity and solids concentration is  obscured by sev-
eral factors:

     1.  Modifications  of sludge pumping procedures which
         increased the  detention time of the sludge in the pri-
         mary clarifiers;
                               285

-------
       SECONDARY
         SLUDGE
00
         PRIMARY
       CLARIFIERS
50,000 GPD RAW  SLUDGE
6.9% TS
10,000 #TS/DAY
        FILTRATE
      9,000 PPM SS
14,000 GPD  DECANTATE
478 PPM SS
                          6,000 GPD CONDITIONED SLUDGE
                          18% TS
  RAW
SLUDGE
HOLDING
 TANKS
  THERMAL
CONDITIONER
                                                               CONDITIONED
                                                                 SLUDGE
                                                                GRAVITY
                                                              THICKENERS
      10.8 CU YD/DAY FILTER CAKE
      50% TS
           TO ULTIMATE DISPOSAL
               Figure C-24.  Midland,  Michigan, sludge  treatment flow diagram

-------
oo
                       TABLE  C-30.   IMPACTS  OF PHOSPHORUS  REMOVAL:   SLUDGE CONDITIONING,
                          THICKENING,  AND DEWATERING CHARACTERISTICS—VARIABILITY WITH
                           CONDITIONING METHOD,  THERMAL CONDITIONER TEMPERATURE, AND
                       THE RECYCLING OF TERTIARY  FILTER BACKWASH  WATER,  MIDLAND, MICHIGAN

Variable


-5
1000 013 raw sludge/
mil m sewage
(1000 gal/MG)
% TS raw sludge
3
kg sludge TS/mil m
(Ib TS/MG)
Raw sludge VS
(% of TS)
Polymer dosage-
anionic kg/t dry
solids (Ib/ton)
Polymer dosage-
cationic kg/t dry
solids (Ib/ton)
o
m thickener decantate
(1000 gal)
mg/£ SS thickener
decantate
mg/£ BOD thickener
• • • ^ f r*j
decantate
No Fed 3
Polymer Cond.




4.15 (4.15)
4.55
189,000
( 1,575)

72


0.15 (0.3)

2.5 to 4.0
(5 to 8)

0

0

0
No Fed 3
Therm. Cond.
185°C (3650F)



2.74 (2.74)
6.5
178,200
( 1,485)

59


0


0

N/A

N/A

N/A
19 mg/£ Fed 3
Therm. Cond.
185°C



2.92 (2.92)
5.2
151,900
( 1,266)

59


0


0

N/A

N/A

N/A
19 mg/Jl Fed 3
Polymer Cond.




N/A
N/A

N/A

N/A


N/A


N/A

N/A

N/A

N/A
25-60 mg/£ FeCl3
Therm. Cond.
2020C (395°F)
Tertiary Filters


1.98
6.9
1,139
(13,6619.8)

55.6


0


0

61 (16.1)

478

6,000
                                                                                                  (continued)

-------
oo
00
     TABLE  C-30  (continued)
Variable
% TS sludge to filter
2
Filter yield-kg/m /hr
(16/ft2/hr)
mg/jl SS filtrate
Filtrate VSS (% of SS)
mg/£ BOD filtrate
% TS filter cake
No FeCl3
Polymer Cond.
6
23.9 (4.9)
647
73.25
2,724
25.5
No Fed3
Therm. Cond.
1850C (3650F)
13
39 (8)
4,057
61.4
7,795
48
19 mg/ji FeCl3
Therm. Cond.
185°C
9
20.2 (4.14)
5,682
52
N/A
44
19 mg/i FeCl3
Polymer Cond.
9.5
14.7 (3.0)
3,469
45.3
2,950
39.3
25-60 mg/£ FeCl3
Therm. Cond.
202°C (395°F)
Tertiary Filters
79
78 (16)
8,288
47
6,769
54
      Filter cake VS
      (%  of TS)
       3
      m  cake hauled/t
      dry solids  filtered
      (yd3/ton)
72.25
57.9
56.4
 4.03 (4.78)     3.00 (3.56)     3.27  (3.88)
47.8
                                    3.46 (4.1)
46.4
                                       2.66 (3.16)

-------
     2.  Availability of only one month's data with FeCl3 addi-
         tion before the tertiary filters were placed in opera-
         tion;

     3.  Tertiary filter operation, involving the recycling of
         backwash water containing the solids removed in the fil-
         ters .

Sludge Thickening and Conditioning--

     Raw sludge thickening to approximately 7.0 percent solids
has been possible both with and without ferric addition.  The
thickening can occur in either the primary clarifiers or the raw
sludge holding tanks.  Thermal conditioning of the raw sludge
changes the cellular structure of the sludge particles so that
the sludge can be thickened even further prior to vacuum filtra-
tion.  When there was no ferric addition for phosphorus removal,
the thermally conditioned sludge thickened readily to 13 percent
solids.  With 19 mg/a FeCls addition, however, thickening to-only
9 percent TS  occurred.  This adverse effect of ferric addition
was overcome  by raising the temperature of the thermal condi-
tioner from 185°C to 202°C (365°F to 395°F).  The sludge then
thickened to  19 percent TS.  The effect of ferric addition on
the conditioned sludge thickener decantate is unknown.  The
decantate is  currently low in SS (478 ppm), but high in BOD (6,000
ppm).

Sludge Dewatering--

     Thermal  conditioning has improved vacuum filter yield, rais-
ing it from 23.90 kg/m2/hr (4.9 Ib/ft2/hr) with polymer condi-
tioning to 39.10 kg/m2/hr (8 Ib/ft2/hr) with thermal conditioning.
The addition  of 19 mg/Jl FeCls caused a decrease to only 20.2 kg/
m2/hr  (4.14 Ib/ft2/hr) for thermally conditioned sludge and 14.7
kg/m2/hr (3.0 Ib/ft2/hr) for chemically conditioned sludge.  Rais-
ing the temperature of the thermal conditioner enabled a filter
yield of 78.2 kg/m2/hr (16 Ib/ft2/hr).

     The filtrate suspended solids concentration increased con-
siderably with the switch to thermal conditioning.  FeCls addi-
tion apparently caused an even further increase.  Tertiary filter
operation may also have caused some increase because of the recy-
cling of fine solids in the backwash water.  The volatile frac-
tion of the filtrate SS concentration appears to have decreased
with the switch to thermal conditioning.  This could be explained
by the solubilization of volatile suspended solids during heat
treatment and their removal in soluble form in the decantate.
Concurrently, the BOD of the filtrate increased due to this sol-
ubilization.  It appears that FeCla addition further decreased
                              289

-------
the VSS fraction of the filtrate, and tertiary filter operation
may have had a similar effect.  It does not appear that the fil-
trate BOD was affected by Feds addition or tertiary filter oper-
ation.

     The filter cake total solids concentration was greatly
increased by thermal conditioning.  Cake solids concentration
was adversely affected by FeCla addition, more so with polymer
conditioning than with thermal conditioning.  Raising the temper-
ature of the thermal conditioner produced a dryer cake, somewhat
dryer even than was achieved without Feds addition.  The VS
fraction of cake TS appears to have been decreased by thermal
conditioning, with further decreases resulting from ferric chlor-
ide addition and from tertiary filter operation.

Sludge Cake Hauling--

     As filter cake solids concentration increased, the volume
of filter cake which must be hauled to the ultimate disposal site
decreases.  Table C-30 shows that the volume of cake hauled per
ton of dry solids filtered was highest when polymer conditioning
was used, and lowest when the thermal conditioner was operating
at 202°C (395°F).  With thermal conditioner operation at only
185°C (365°F), the adverse impact of ferric chloride addition
resulted in more sludge cake volume to be hauled, and thus in more
trips to the disposal site.


Experimental  Addition of Alum, to  the Raw Sewage--

     A full-scale test of alum addition to the raw sewage (80 mg/l
alum as  A1203)  was  conducted at the plant during October of 1975.
Enough alum was  added to provide  80 percent phosphorus removal
within the  plant.   Table C-31  presents  the test results.


 TABLE C-31.   A  COMPARISON OF  THE CHARACTERISTICS OF THE SLUDGES
    PRODUCED WITH ALUM AND FERRIC CHLORIDE, MIDLAND, MICHIGAN

                                    Alum            FeCl3

  Raw sludge, % TS                   6.5             7.6

  Thermally conditioned sludge,
  % TS                              16.0            22.5

  Filter vield, Kg/m2/hr            23.5            76.7
  (Ib/ft2/hr)                        (4.8)          (15.7)

  Filter cake, % TS                 41              56
                               290

-------
     Considerable problems were experienced in handling the
sludge produced with alum.  Separation of solids and supernatant
in the thermally conditioned sludge thickener did not occur as
rapidly as with ferric chloride.  The TS concentrations of the
thickened sludge was lower.  The filter cake TS concentrations
were only 41 percent compared to 56 percent with ferric chloride.
Sludge with less than 50 percent TS is not suitable for the pre-
sent method of disposal, indicating that alum sludge would require
additional processing such as incineration.  The filter rate was
considerably slower with alum, it taking 3.3 times as long to
filter a ton of alum sludge.  This would mean adding one or pos-
sibly two full-time operators to the staff.  Also, since the
sludge pumped from the primary tanks was thinner, it was deter-
mined that the thermal conditioner would have to operate 17 per-
cent longer to process,it.

Sludge Treatment and Disposal Costs

     In response to the adverse effects of phosphorus removal  on
sludge handling, the temperature of the thermal  conditioner was
raised.  This restored satisfactory thickening and dewatering.
Raising the thermal conditioner temperature from 185°C to 202°C
(365°F to 395°F) meant an increase in the amount of natural gas
required to fuel the boiler.  The cost for natural gas increased
by approximately $4.87/t ($4.34/ton) of dry solids as outlined
in Table C-32.  This is the only significant cost increase for
sludge treatment and disposal which has been identified by this
case study.

     It has not been possible to establish the additional quantity
of sludge solids generated by phosphorus removal, although it is
certain that the quantity of sludge did increase.  Without raising
the temperature of the thermal conditioner, the additional sludge
quantity would have been responsible for more vacuum filter run-
ning hours and more trips to the sludge cake disposal site.  But
at the higher thermal conditioner temperature, these trends were
countered by a higher filter yield and cake solids content.  It
is therefore likely that the additional sludge quantity was han-
dled without a significant increase in the costs of vacuum filter
operation and sludge cake hauling.  The plant presently runs the
vacuum filters for about 94 hr/mo and makes about 79 trips/mo to
the sludge cake disposal site.

Summary and Conclusions

     Table C-30 has summarized the discussion of the variations in
the performance of the sludge treatment processes.  Thermal con-
ditioning improved vacuum filter yield and cake dryness, but raised
the BOD concentration of the thickener decantate and the filtrate
and the SS concentration of the filtrate.  Ferric chloride addi-
tion adversely affected filter yield, cake dryness, and filtrate
SS concentration of the filtrate.  Ferric chloride addition

                               291

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       TABLE C-32.  ADDITIONAL COST FOR HIGH-TEMPERATURE THERMAL CONDITIONING, MIDLAND, MICHIGAN
                                (Assume sludge feed at 6.5% TS; natural gas
                                cost of $0.089/m3 ($2.50/1000 ft3)  in 1976}
                               Before  Phosphorus  Removal     After Phosphorus Removal       Difference
                               185°C  (365°F)  Cond.  Temp.     202°C (395°F) Cond. Temp.
,1000 m3 natural gas/mil m3
sludge (1000 ft3/MG)

$/mil m  sludge
($/MG)

$/t dry solids
($/ton)
 4,365 (590)


$3,900 ($14.75)


$6.00 ($5.44)
 7,841  (1,060)
$7,000 ($26.50)
$10.78 ($9.78)
 3,477 (470)
$3,100 ($11.75)
$4.78 ($4.34)

-------
adversely affected filter yield, cake dryness, and filtrate SS
concentration.  Even with the adverse impacts of ferric addition,
however, filter yield and cake dryness were better with thermal
conditioning than with polymer conditioning.  Raising the temper-
ature of the thermal conditioner overcame the adverse effects of
ferric addition which were mentioned except for the increase in
filtrate SS concentration.  Filtrate SS concentration remained
high, probably due to the recirculation of tertiary filter back-
wash -water rather than due to ferric addition.

     The decrease in vacuum filter cake volatile solids fraction
(percent of TS) which occurred with thermal conditioning and fur-
ther occurred with ferric addition would be an adverse impact for
a plant practicing sludge cake incineration.  Ferric chloride
addition appears to have lowered the volatile fraction of cake
solids from 58 down to 48 percent of TS.

     A cost analysis has shown that the only significant cost
increase for sludge treatment and disposal attributable to ferric
addition was the cost of raising the thermal conditioner temper-
ature to 202°C (395°F).  The additional natural gas required to
operate at the higher temperature had a cost of approximately
$4.78/t ($4.34/ton) of dry solids (Table C-32).

     Some general observations about this case study can be made.
Apparently, the characteristics of the Midland sludge are such
that it has thickened and dewatered readily both before and after
phosphorus removal.   It is likely that this is related to the
facts that the plant uses trickling filters, has no significant
industrial wastes, and is not overloaded.   It has also been shown
that ferric addition to the raw sewage produces a better sludge
than alum addition (Table C-31).

     In conclusion,  thermal conditioning at Midland has been suc-
cessful, but phosphorus removal has increased the energy require-
ments of the process at a time when energy is becoming more
expensive.

CASE STUDY J:   PORT HURON, MICHIGAN

Introduction

     Port Huron is an example  of an activated  sludge  plant
practicing alum addition to the  secondary  part  of  the  plant.
Built from 1972 through  1974,  it is representative of  the
newer wastewater treatment plants.  Characteristic of  these
newer plants is the possession of adequate  sludge  handling
capacity.  At older plants, in contrast, problems  related  to
lack of sludge handling  capacity tend to dominate  sludge
handling considerations.  Another characteristic of many
newer plants is that phosphorus  removal by  chemical addition
has been incorporated into their original  design rather  than

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 added  later.  These plants have not handled sludge when no
 chemical  sludge was being generated.

     At  Port Huron, sludge treatment consists of gravity
 thickening, thermal conditioning, polymer conditioning,
 centrifuge dewatering, and fluidized bed incineration.  The
 system has been operated and evaluated both with and without
 inclusion of the thermal conditioning step.  At plants where
 incineration seems to be the proper disposal method, thermal
 conditioning prior to dewatering has been cited as a way to
 reduce overall fuel costs.  The combination of thermal con-
 ditioning and incineration has recently been chosen for the
 design of several new facilities.  Centrifuges for dewatering
 are also  finding application in these facilities.  Investiga-
 tion of  the Port Huron facility gives us insight into the
 actual performance of an entire system using these techniques
 for handling phosphorus-laden chemical sludge.

     Every plant has its peculiarities of design and influent
 wastewater characteristics.  At Port Huron, the significant
 ones which affect sludge are related to the low flow rate and
 SS and BOD concentrations of the influent.  Designed to
 provide  secondary treatment for an average flow of 0.075 mil
 m^/day (20 mgd), the plant treated an average flow of only
 0.04 mil m3/day (11.6 mgd) in 1976.  Because of this dis-
 crepancy  between plant design and actual flow, there is a long
 aeration  basin retention time and a low food to microorqanism
 (F/M)  ratio.  The activated sludge microorganisms are in a
 near-starvation phase and have a slow growth rate.  This probably
 means  that sludge generation is somewhat lower than typical for
 this type of plant.

     Plant influent SS and BOD concentrations are quite low
 due to the fact that 20 percent of the wastewater entering
 the plant originates from industries, mainly of the metal
 manufacturing, coating, and plating types.  Wastewater SS
 and BOD  are usually about 86 and 58 ppm, respectively.
 Because  of the low concentrations, these constituents are more
 efficiently removed by biological treatment and settling
 than by  primary settling.  The production of secondary relative
 to primary sludge is higher than would be the case if influent
 SS and BOD concentrations were greater.  This is undesirable
 because  the waste activated sludge tends to be harder to
 thicken  than the primary sludge.

History

     Historical  plant modifications affecting sludge production
and characteristics follow:

     1972 - Initiated expansion of old primary plant and construc-
tion  of secondary treatment facilities, phosphorus removal  facili-
ties,  and solids handling system.

                               294

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     January 1975 - Commenced operation of new facilities
including phosphorus removal by chemical addition.
     December 1976 - Discontinued use of
unit for sludge conditioning.  Increased
conditioners used for d_ewatering.

Chemical Addition for Phosphorus Removal
                      heat  treatment
                      dosage  of  polymer
     Liquid alum (48.8 percent Al2(S04)3 •  141^0) is added
to the activated sludge mixed liquor as it flows over the
effluent weirs of the aeration basins.  Figure C-25 shows how
wastewater enters and leaves the aeration tanks and the alum
(A) and polymer  (P) feed points.  Alum  is added at six points
to the mixed liquor as it falls over the effluent weirs into
six effluent channels leading to the final clarifiers.  Alum
is added at the  farthest end of each weir from the final
tanks, while polymer  is added at the other end, 30.5 m (100
ft) closer to the finals.  The alum is  diluted as it is split
into the six feed lines at a ratio of 5 to 1.
                         TO FINAL CLARIFIER
                     ft
           ft
                      >>
          Si
ft
      Figure  C-25.
Chemical  feed points to aeration tanks
Port Huron, Michigan.
     The alum dosage is adjusted according to plant phosphorus
removal efficiency.  Operators notice changes in removal
efficiency and decide whether to increase or decrease the
alum dosage.  When a
  certain  dosage  is  desired,  a  computer is
                               295

-------
 signalled  and  the  alum  feed  pump  is  automatically paced  by
 the  computer according  to  the  wastewater flow  to achieve
 that dosage.   The  average  dosage  has  been approximately  52
 ppm  Al2(S04)3  •  14^0 over the  first  7 mo of 1977.  Anionic
 polymer  (Hercules  847)  is  used.   The  computer  proportions
 the  polymer feed pumping rate  to  the  wastewater flow to
 achieve  a  desired  dosage.  The  dosage  is selected by plant
 personnel  based  on  visual  clarity of  the final clarifiers and
 final  effluent.  The average dosage  has been 0.275 ppm for
 January  through  July of  1977.

 General  Description of Wastewater Treatment Operations Affecting
 SIudge

      Figure C-26 presents  a  general  plant flow diagram.  The
 plant  has  two  aerated grit chambers  complete with mechanical
 grit removal and mechanical  oil and  scum removal facilities.
 Eight  primary  clarifiers having a total capacity of 4,000 m3
 (138,400 ft3)  are  designed to  handle  an average flow of  0.12
 mil  m3/day (33 mgd) and  a  peak  flow  of 0.22 mil m3/day (58 mgd)
 A  flow-equalizing  retention  basin for primary effluent with
 0.022  mil  m3 (5.7  MG) capacity  is used.  The clarifiers  are
 rectangular.   In each clarifier,  sludge is scraped to a
 hopper at  one  end  by a chain and  flight mechanism.  In the
 hopper,  a  screw mechanism  scrapes sludge to a valve opening
 in the center.  Sludge is  collected  from a pair of clarifiers
 at a time  for  7 out of every 28 min.  The flights and screws
 are  turned on, a valve opens from two clarifiers and sludge
 is pumped  from them at a combined rate of 0.984 m3/min
 (260 gal/min)  for  the 7 min.   Primary sludge is pumped at
 less than  one  percent solids for  efficient degritting.   Scum
 from the surfaces  of the clarifiers  enters a scum well which
 is discharged  once  a day to  the thickener splitter box.

     Secondary biological  treatment  is accomplished with con-
 ventional  complete mix activated  sludge.  Three aeration
 basins providing a  total capacity of  0.013 mil m3 (3,350,000
 gal) are mixed and aerated by  diffused air.  Their design
 detention  time is 3 hrs, but the  actual detention time in
 these basins averages about  6.9 hrs.  The F/M  ratio (figured
 using MLVSS rather than MLSS concentration) is maintained
 near 0.1 mg/£.   The return sludge rate averages 63 percent
Of flow.  MLSS and MLVSS concentrations have averaged 5,250
and  3,000 ppm,  respectively.   Sludge  density index averages
around 1.7 percent.

     Three square final  clarifiers provide a total final
settling capacity of 0.011  mil m3 (2.9 MG).  Sludge is sucked
up hydraulically from the  bottom  of  each clarifier by pickup
pipes and flows by gravity to  a manifold in the center of the
clarifier bottom.  Sludge  is pumped  out to return or waste
from one clarifier at a time.   The operator checks the depth

                             296

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          INTER-
          CEPTOR
ro
          Figure C-26.  Port Huron, Michigan,  wastewater  treatment  plant  flow diagram..

-------
of the sludge blanket in each clarifier once a shift with
the help of installed photoelectric cell detectors.  He pumps
sludge out as necessary to prevent the blanket depth from
exceeding 0.914 m (3 ft).  The average blanket depth is
probably about 0.457 m (1.5 ft).  The operator decides how
much sludge to return and how much to waste on the basis of
MLVSS in the aeration basins and desired F/M ratio.  Scum is
skimmed from the surfaces of the clarifiers into hoppers and
discharged to the waste sludge lines.

Detailed Description of Sludge Treatment and Disposal Operations

Degritting--

     A Dorr-Oliver "Dorr-Clone" cyclone sludge degritter is
employed to remove 95 percent of 250 mesh grit from the
primary sludge.  Sludge degritting, in addition to the raw
sewage grit removal, is necessary to limit wear on the sludge
centrifuges.

Thickening--

     Primary and secondary sludge, and scum from the primaries,
secondaries,  and aerated grit chamber flow to a Dorr-Oliver
"Densludge" Type SD gravity thickener.  Only one of the three
thickeners present is used.  A splitter box is present for
dividing sludge flow between the three thickeners.  A low
cationic polymer is fed at the splitter box at a dosage of
3 ppm to aid solids capture and thickening.  Each 16.8-m
(55-ft) diameter thickener is of 738 m3 (195,000 gal) capacity.
The liquid sidewall is 3.35 m (11 ft) plus the cone at the
bottom.  It is equipped with scraper arms having vertical
pickets for continuously stirring sludge in the thickener as
it is scraped from the bottom to a hopper.  Another scraper
pushes sludge to a single draw-off point in the hopper from
which sludge is pumped out to either the centrifuges or the
thermal conditioner.

     Thickener dilution water can be provided by three pumps
which deliver final effluent to the splitter box.  Dilution
water is not used, however.  Partial dilution is effected as
a  result of the low TS concentration at which primary sludge
is pumped.   Further dilution would be required to raise the
thickener overflow rate into its design operating range of
16 to 32 m3/day/m2 (400 to 800 gal/day/ft?).  But the thickener
is operated at a much lower overflow rate of approximately
7.13 m3/day/m2 (175 gal/day/ft2).  This is because its volume
is effectively reduced by its high sludge blanket.

     A mechanical skimmer collects scum from the surface  of  the
thickener.   The scum trough is so small, however,  that once  a
day the thickener must be scraped manually.  Scum adversely


                             298

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affects thickener operation by blocking the overflow weir and
reducing weir overflow length.  The scum baffle which is
present is not deep enough to prevent this.

     Figure C-27 presents information on average sl'udge flow
rates, total and volatile solids concentrations, and masses
in the form of a combined hydraulic and mass balance diagram
constructed around the thickener.  The diagram is based on
monthly averages of data for January through July of 1977.
During this period, the thermal conditioner was not in
operation.

     Figure C-27 shows that the average performance of the
thickener is satisfactory, with a combined primary-waste
activated sludge of about 0.56 percent TS thickening to 4.68
percent TS and the overflow containing about 2,480 mg/£ TS.
But it does not show the inconsistency which exists in results
from day-to-day due to variations in activated sludge wasting
rates and intermittent incinerator operation.  Thickened
sludge concentration reaches almost 6 percent on a few good
days, while on poor days it is only about 4 percent.  The
overflow solids concentration varies greatly from day-to-day
between about 100 mg/£ and 10,000 mg/£.  These variations
are related to the addition of alum to the aeration basins.
Alum addition increases the mass of activated sludge which is
generated and wasted.  Waste-activated sludge has poorer
thickening characteristics than primary sludge, so that when
activated sludge wasting rates are high, thickening is poorer.
This leads at times to low thickened sludge solids concen-
trations and high polymer dosage requirements for chemical
condi tion ing.

     Primary sludge is continually wasted to the thickener
at 0.016 m^/sec (260 gal/min).  Activated sludge is normally
wasted at 0.18 nwmin (50 gal/min), but the rate varies between
0.096 and 0.36 m3/min (25 and 100 gal/min).  Wasting continues
during all or part of the day, depending on how much needs to
be wasted.  Sludge is withdrawn from the thickener at an
average rate of 0.18 m3/min (52 gal/min) when the centrifuges
and incinerator are operating.  In 1977, they have operated
3 out of 4 wks/mo and for 2 to 5 days/wk (average 3.35 days/
wk).  A sludge blanket deeper than 1.2 (4 ft) is normally
maintained in the thickener to get good thickening action.
If the blanket is less than 0.61 m (4 ft), water can be
drawn while pumping sludge, so this is avoided.  The usual
blanket depth is 1.5 to 2.1 m (5 to 7 ft).  When the activated
sludge wasting rate is high and the incinerator has not been
running, a sludge blanket of up to 3.05 m (10 ft) builds- up
in the thickener, and overflow quality deteriorates.  The
thickener is in general  slightly overloaded, and plans have
been made to alleviate this by using one of the other two
thickeners available.  There is concern, however, about

                             299

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      AVERAGE SEWAGE FLOWi  11.9 MGD
CO
O
O
7,680
3,530
.25
48.
374,400
0TS/DAY
0VS/DAY
XTS
XVS
PRIMARY
SLUDGE
8,030
4,440
.25
55.
388,400
0TS/DAY
0VS/DAY
XTS
%VS
THICKENER
GPD OVERFLOW
12,020
7,910
3. 3
66
43, 900
#TS/OAY
#VS/DAY
XTS
XVS
GPD WAS
                                                                     11,700  0TS/DAY
                                                                      7,000  0VS/DAY
                                                                       4.70  %TS
                                                                       60
%VS
                                                                     29,900 GPD
   SLUDGE
   REMOVED
      NOTE.  RATES  ARE  CALCULATED  ON AN  AVERAGE  DAILY  FLOW  BASIS WHETHER FLOWS OCCUR

             EVERY  DAY  OR  NOT.
       Figure  C-27.   Port Huron, Michigan,  gravity  thickener  hydraulic  and mass balance.

-------
increasing the solids detention time in the thickeners which,
it was observed at the plant, results in poorer dewatering
than can be achieved with "fresher" sludge.

Condition ing--

     The two alternative methods of sludge conditioning which
have been practiced are thermal conditioning with the Farrer
system and chemical conditioning with polymers.  Polymers were
used in low concentrations even with thermal conditioning.

     The Farrer system has two high-pressure feed pumps
which force thickened sludge through two sludge disintegrators
and to the Farrer heat exchanger.  The preheated sludge flows
to the Farrer reactor where steam, which has been purged of
air, is injected.  The sludge residues in the reactor for 20
to 30 min under 300 psi pressure at a temperature of 204°C
(400°F).  When sludge leaves the reactor, it flows through
the heat exchanger to a decant tank.  Decant tank overflow is
returned to the head of the plant while sludge is withdrawn
by the four centrifuge feed pumps.  The system was designed
to handle 20,600 kg/day (45,300 dry Ib/day) of a 4.61 percent
TS sludge feed.  It was designed to produce a sludge capable
of being centrifuged to 31 percent TS.


     Polymer is added to the sludge in the lines which feed
each of the four centrifuges at a point about 0.305 m (1 ft)
before the sludge enters the hub of the scroll.  Hercules
849 and 874 cationic polymers (1/2:1/2) are used.  The average
polymer dosage was 3.38 kg/t (6.75 Ib/ton) of dry solids with
thermal conditioning and 6.48 kg/t (12.94 Ib/ton) without
thermal conditioning.

     With thermal conditioning, solids were processed (con-
ditioned, dewatered, and burned) only about 25 percent of the
time.  The equipment was usually run 24 hr/day for 5 days and
then kept down for 16 days.  (Without thermal conditioning,
solids were processed about 36 percent of the time.)  Thermal
conditioning was discontinued after November of 1976 due to
extreme corrosion and erosion of the carbon steel making up
the heat exchanger piping and connecting piping.

     Thermally conditioned sludge from the decant tank averaged
8.6 percent TS.  The decant tank overflow averaged abour 3,000
ppm SS with the volatile fraction averaging 45 percent.  The
pH of this sidestream varied between 6.0 and 7.2.

Dewatering--

     Dewatering of thickened and chemically or thermally/
chemically conditioned sludge is accomplished by centrifuga-
tion.   The plant operates four horizontal fully-continuous

                             301

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 solid  bowl Dorr-Oliver  "Merco-Bowl" centrifuges.  Some
 machine operating parameters for these centrifuges are given
 below:

     Largest  inside bowl diameter:  41.9 cm (16.5 in)
     Inside bowl length:            121.9 cm (48 in)
     Bowl shape:                    conical-cylindrical
     Scroll configuration:          dual flight
     Centrate disposition:          pumped to plant influent

     The machines are operated at a bowl speed of 3,000 rpm,
 scroll speed  differential of 17 rpm and pool depth of
 7.874  cm (3.1 in).  When solids processing is underway, all
 four centrifuges are operated.  Machine operating variables
 such as sludge feed rate and polymer dosage are monitored
 and controlled for each centrifuge separately by the operator.
 He makes adjustments which will enable at least 80 percent
 solids recovery.  Centrate TS concentration is determined
 several times each day  for each centrifuge.

     Centrifuge and incinerator performance will be discussed
 together and  related to type of sludge conditioning.


 Incineration--

     The plant has a Dorr-Oliver "F/S System" fluosolids
 incinerator.  Centrifuge cake falls by gravity through chutes
 into sludge transfer screw conveyors.  They convey it to the
 progressive cavity pumps which feed the reactor.  The reactor
 cylinder is 4.57 m (15  ft) in diameter and contains a 1.52-m
 (5-ft) expanded bed of  silica sand.  A fluidizing air blower
 discharges into the reactor through the windbox.  Hot gases
 and ash exit  through the top of the reactor into a water seal
 expansion joint followed by a Venturi-type scrubber.  They
 then enter a  gas scrubber with a radial vane and water trays.
 The gases exit from the exhaust stack through a plume suppres-
 sion burner.  The ash slurry flows to ash pumps which deliver
 it to a 5.49-m (18-ft)  diameter Dorr-Oliver ash thickener.
 Overflow from this thickener is recycled to the plant influent
 except for a  portion which is used in the scrubber system.
 The ash is pumped to a  vacuum filter (Dorr-Oliver) which is
 1.220 m (4 ft) in diameter, has a 0.914 m (3 ft) face width,
 and is designed to handle 590 kg (1,300 lb)dry solids/hr.
 The filtrate  is returned to the head of the plant.  The
 dewatered ash is trucked 19.3 km (12 mi) to a landfill along
with grit from the aerated grit chambers and sludge degritter.
                                                             3
     Fluidizing air is  normally discharged at 1.65 to 1.70  m  /
 sec (3,500 to 3,600 scfm).  The bed pressure differential  is
maintained at 1.19 to 1.22 m (47 to 48 in) of water.  The
normal  reactor operating temperature is approximately 721°C
 (1,330°F).   Although solids processing is intermittent,  the

                             302

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incinerator temperature  is always maintained above 663°C
(1,225°F) over the  next  30 hrs.   It  takes about 227 I  (60 gal)
of No. 2 fuel oil to  raise the  temperature from 663°C  to 871°C
(1,225°F to 1,600°F).

     The incinerator  was designed to operate in conjunction
with the thermal conditioner.   Its design capacity is 1,040 kg
(2,300 Ib) of dry solids/hr for a 31 percent TS feed that is
58 percent volatile.

Performance and Operational Costs of Sludge Treatment  and
Disposal

     Centrifuge and  incinerator performance and operational
costs have been greatly  affected  by  the sludge conditioning
method used.  Table  C-33 summarizes  the direct effects of
conditioning  on the  performance and  operational costs  of
solids handling.  Centrifuge cake TS concentration was improved
by thermal conditioning  and the pounds of solids which could
be fed to the incinerator per  hour was higher.   This reduced
incinerator fuel consumption.   During thermal conditioning
the burning rate covered a range  of  420 to 1,320 kg TS/hr
(929to 2,900  Ib TS/hr) which included the design capacity
for thermally conditioned sludge  of  1,040 kg/hr (2,300 Ib/hr).
Dorr-Oliver has estimated that  the capacity is  reduced to
590 kg/hr (1,300 Ib/hr)  for non-thermal1y conditioned  sludge.
Although total cake  solids is  higher, percent volatile is
lower with thermal  conditioning, due to the solubi1ization of
volatile solids and  removal in  the decantate.  This is a dis-
advantage as  far as  fuel consumption for incineration, but the
disadvantage  is outweighed by  having less water in the cake
to be evaporated.   The major savings on utilities with thermal
conditioning  were for fuel oil  and conditioning polymer.
Major expenses were  for  natural gas  and electricity and
maintenance and repair of the  thermal conditioner itself.
Actual figures on maintenance  and repair were not available
based on the  plant's  experience because of the corrosion
problem.  Before normal  operation could be achieved, the
existing system would have to  be  rebuilt.  The top five rows of
the heat exchanger  would have  to  be  replaced with Schedule
160 inner tubes and  Schedule 80 outer tubes, rather than the
present Schedule 40  tubes.  The total cost of labor for solids
handling was  the same with and without thermal  conditioning.
When thermal   conditioning was  discontinued, labor was  shifted
from that area to the incinerator.

     The indirect effects of conditioning method on per-
formance and  operational costs  of solids handling must also  be
considered.   As mentioned, thermal conditioning solubilizes
some of the volatile  solids in  the sludge which are removed
in the decantate.   The high BOD concentration of the decantate
is a burden on the activated sludge  treatment.   The cost of

                             303

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           TABLE C-33.  DIRECT EFFECTS OF CONDITIONING METHOD ON
  PERFORMANCE AND OPERATIONAL COSTS OF SOLIDS HANDLING, PORT HURON, MICHIGAN
Unit cost factors:
     Fuel Oil
     Natural Gas
     Electricity
     Centrifuge Polymer
     Thickening Polymer
     Gasoline
$  .1004/Jt
$87.07/1,000 m
$ 0.03/kwh
$ 4.40/kg
$ 2.97/kg
$  .185A
(1976 costs)

    3
kg TS/hr (Ib TS/hr) to centrifuges
  and  incinerator

kg VS/hr (Ib VS/hr) to incinerator

Centrifuge cake % TS

Centrifuge cake % VS

Incinerator bed temp., °C (°F)

kg conditioning polymer/t (Ib/ton)
  Vt  ($/ton)

1,000 ft3 gas used/ton
  $/t  ($/ton)
 3
m  fuel oil  used/t (gal/ton)
  $/t ($/ton)

kwh electricity used/t (kwh/ton)
  thermal  cond.
  centrifuges
  incinerator
  thickener
  $/t ($/ton)

Thermal cond. steam boiler water
  conditioning and cleaning
  chemicals  est.  $/t ($/ton)
$ 0.38/gal
$ 2.27/ft3
$ 0.03/kwh
$ 2.00/lb
$ 1.35/lb
$ 0.70/gal
              With thermal
              conditioning

              777 (1,712)
              350 (771)

               27-32.6

               45.05

              738 (1,360)
                   With chemical
                   conditioning

                     556  (1,224)
                     342 (753)

                      18.8-21.0

                      61.6

                     732 (1,350)
                3.06 (6.75)      5.67 (12.5)
              $14.88 ($13.50)  $27.51 ($24.96)

                8.37
              $20.94 ($19.00)

                0.309 (74.1)     0.685 (164.1)
              $31.04 ($28.16)  $68.75 ($62.36)
               36.1  (32.7)
              176 (159) - est.  176 (159) - est.
              374 (339) - est.  374 (339) - est.
                9.92 (9) -est.    9.92 (9) -est.
              $17.88 ($16.22)  $16.79 ($15.23)
              $ 1.76 ($ 1.60)
                                                                 (continued)
                                     304

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TABLE C-33  (continued)
Odor control (therm, cond.) and
  sand replacement  (incin.),
  est. $/t  ($/ton)
                       3
Dewatered ash hauled, m /t
  (yd3/ton)
  est. $/t  ($/ton)  for gasoline

kg thickening polymer/t
  (Ib/ton)
  $/t ($/ton)

Cost of labor,* $/t ($/ton) - est.
  1)  Operational and minor equip-
      ment maint.
        thickener
        thermal conditioner
        centrifuges
        incinerator
        Total

  2)  General maintenance
        thickener
        thermal conditioner
        centrifuges
        incinerator
        Total

  3)  Equipment repair
        thickener
        thermal conditioner
        centrifuges
        incinerator
        Total

  4)  Ash and grit  handling

Total maintenance and repair
  supplies for solids handling,
  $/t, ($/ton) - est.

Total supervision for solids
  handling, $/t ($/ton) - est.
                                            With thermal    With chemical
                                            conditioning    conditioning
$ 3.85 ($ 3.50)  $ 2.18 ($ 1.98)
  0.961 (1.14)     0.961  (1.14)
$ 0.08 ($ 0.08)  $ 0.08 ($ 0.08
  0.926 (1.85)     0.926  (1.85)
$ 2.75 ($ 2.50)   $ 2.75  ($ 2.50)
$ 5.90 ($ 5.35)   $ 5.90  ($  5.35)
$ 5.90 ($ 5.35)
$16.00 ($17.64)   $17.64  ($16.00)
$16.00 ($17.64)   $23.54  ($21.35)
$47.08 ($42.60)   $47.08  ($42.60)
$ 3.53 ($ 3.20)   $ 3.53  ($  3.20)
$ 1.76 ($ 1.60)
$ 5.30 ($ 4.81)   $ 5.30  ($  4.81)
$ 3.53 ($ 3.20)   $ 5.29  ($  4.80)
$14.12 ($12.81)   $14.12  ($12.81)
$ 0.49 ($ 0.44)   $ 0.49 ($ 0.44)
$ 0.49 ($ 0.44)
                 $ 1.95
                 $ 1.47
$ 1.95 ($ 1.77
$ 0.98 ($ 0.89
$ 3.91 ($ 3.54
                 $ 3.91
$ 1.77)
$ 1.33)
$ 3.54)
$ 3.57 ($ 3.24)   $ 3.57  ($ 3.24)



$36.38 ($33.00)   $21.49  ($19.50)


$12.50 ($11.34)   $12.50  ($11.34)

                   (continued)
                                     305

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TABLE C-33 (continued)
Total  direct costs,  $/t ($/ton)
  thermal  conditioner
  centrifuges
  incinerator
  thickener
                                            With  thermal
                                            conditioning
                  With chemical
                  conditioning
$210.79 ($191.19) $220.78 ($200.25)
$ 33.62 ($ 30.50)
$ 45.04 ($ 40.86) $ 57.68 ($52.32)
$ 66.67 ($ 60.49) $112.55 ($102.09)
$ 12.96 ($ 11.76) $ 12.96 ($ 11.76)
   Based on 1,090 t (1,200 tons)  dry  solids/yr  in  1976.
   and wages,  including  benefits.
               1976 salaries
                                       306

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increasing the power of the air blower to handle this BOD
loading has been estimated at $9.52/t ($8.64/ton).  The actual
BOD concentration of the decantate is not available.  Average
centrate TS concentration was lower with thermal conditioning
(966 vs 2,600 ppm) and volatile concentration was higher
(63 vs 56.3 percent of TS).

Summary and Conclusions

     Alum addition to the secondary rather than the primary
part of the plant resulted in an increased mass of secondary
rather than primary sludge.  It is not known whether the
solids concentration or volume of secondary sludge was
affected by alum addition as well.  Experience at the plant
shows that the waste activated sludge is harder to thicken
than the primary sludge.  When the solids concentration of
the thickened sludge is lower than average as a result of
high activated sludge wasting rates, the cost of chemical
conditioning prior to dewatering is increased.  Solids con-
centration of the dewatered cake apparently does not vary in
direct response to the variations in feed concentration, as
long as adequate conditioning takes place and the centrifuge
feed rate is properly adjusted.  At the sludge loading and
sludge removal rates in use, one 738-m3 (195,000-gal)
thickener is of insufficient capacity.  This is evidenced by
the high sludge blanket which sometimes builds up and causes
deterioration of effluent quality.  Rather than operate two
thickeners, which might have deleterious effects on dewatering
due to a long solids detention time, "polymer was added to
increase solids capture.  It is recommended, however, that
the design criteria for sizing thickeners be studied closely
as problems in this area have been observed at several plants.
Especially at plants where alum addition to the secondary
stage is practiced, additional thickener capacity is needed.

     The use of thermal conditioning resulted in savings of
$50.30/t ($45.70/ton) of dry sludge when compared with the
cost of chemical conditioning alone.  The additional expenses
(excluding equipment maintenance and repair supplies)
resulting from thermal conditioning amounted to $35.00/t
($31.70/ton).  Therefore, it appears that operation and
maintenance of thermal conditioning at the plant are currently
cost-effective, as long as the cost of equipment maintenance
and repair supplies is less than $15.30/t ($13.92/ton).

     Without thermal conditioning, the capacity of the
incinerator is decreased from 1,040 kg/hr to 490 kg/hr
(2.300 Ib/hr to 1,300 Ib/hr).  It was assumed in the design
of the incinerator that the plant would be producing 18,000
kg/day (39,700 Ib/day) thickened sludge, but it actually
produced only 5,310 kg/day (11,700 Ib/day) due to the low
wastewater flow.  The incinerator capacity is therefore

                              307

-------
 presently  adequate  at  590  kg/hr  (1,300 Ib/hr), but when the
 plant  influent  flow  increases  in the future, incinerator
 capacity will become limiting.   It was estimated that three
 additional  centrifuges and a 6.71-m  (22-ft) diameter incinerator
 reactor rather  than  the present  4.57-m (15-ft) reactor would
 be  necessary  to  handle 1,040 kg/hr (2,300 Ib/hr) of sludge
 with chemical conditioning alone.  Including this considera-
 tion in the analysis,  operation  and maintenance of chemical
 conditioning  will not  be cost-effective in the future unless
 additional  capital  costs are incurred.

 Recent Developments

     Since  the  original investigation of the Port Huron
 plant  and  the writing  of this  case study, modifications in
 thickener  operation  have been  made with significant results.
 Two of the  three  identical gravity thickeners available at
 the plant  are now in use rather  than just one.  Each of the
 two thickeners  now  receives approximately 12.6 I/sec
 (200 gal/min) of  dilution water  plus 8.2 I/sec (130 gal/min)
 of  primary sludge and  1.6  £/sec  (25  gal/min) of waste
 activated  sludge.   They are operating at an overflow rate  of
 approximately 22 m3/day/m2  (540  gpd/ft2).  The sludge  blanket
 depth  in each thickener is maintained between  1.2 and  1.5  m
 (4  and  5 ft).

      In the past, where only one thickener was in use,  the
 thickener  was overloaded with  sludge, although the  surface
 overflow rate was low  and  no dilution water was used.   The
 sludge blanket  depth in each thickener averaged 1.5  to
 2.1 m  (5 to 7 ft).   Polymer addition was necessary  to  aid
 solids capture  and  thickening.  Presently, with two  thickeners
 in  operation, solids capture and thickening are reportedly
 slightly improved although  no  polymer is used.  The  savings
 in  polymer cost amounts to  $2.75/t  ($2.50/ton) of dry  solids.
 It  is  also reported that a  reduction  in  the amount  of
 phosphorus recycled to the  head  of the aeration basins  in  the
 thickener  overflow  has occurred.  This may mean a slight
 decrease in the cost of phosphorus removal chemicals.

 CASE STUDY K:   PONTIAC, MICHIGAN

 Introduction

     The Sewage Treatment  Division  of the  city of Pontiac,
 Michigan,  operates  two wastewater  treatment  plants  a short dis-
.tance  from each other. The  East Boulevard  plant  is a  conven-
 tional activated sludge treatment  plant  with  a design  average
 flow of 32,600  m3/day  (8.6  mgd).  The Auburn  plant  is  also a
 conventional  activated sludge  treatment  plant, with rapid sand
 filtration facilities  for  the  tertiary  treatment  of both  East
 Boulevard  and Auburn secondary effluents.   The Auburn  Plant

                             308

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design average flow is 64,000 m3/day  (16.9 mgd), giving a com-
bined design average flow for the two plants of 96,500 m3/day
(25.5 mgd).  A flow diagram for the treatment process is shown
in Figures C-28 and C-29.  Wastewater influent to the Pontiac
plants is delivered by combined storm and sanitary sewers.
Approximately 40 percent of the influent consists of pretreated
industrial process water (plating waste) from which heavy metals
have been removed.  This industrial waste is characterized by a
relatively low concentration of BOD.

     Two periods of plant operation have been selected for com-
parison purposes to determine the impacts of chemical  additions
for phosphorus removal.  The period from January to June 1969
was selected as the period during which both primary and
secondary addition of ferric chloride took place for phosphorus
removal.  Table C-34 presents the average wastewater character-
istics and plant removal efficiencies of the two Pontiac
plants combined.

History

     In 1919, a secondary wastewater treatment plant,  consisting
of Imhoff tanks and trickling filters, was constructed at  the
East Boulevard site.   In 1938, activated sludge  aeration basins
and an anaerobic digester were added.   A primary settling  tank
and additional sludge treatment facilities were  constructed  in
1952.   In 1962, a second plant with secondary treatment
facilities was constructed at the Auburn site.   The plant  also
contained anaerobic sludge digestion,  vacuum filter dewatering,
and incineration facilities.  The Imhoff tanks  and trickling
filters at the East Boulevard plant were removed from  service
in 1962.   In 1973, both plants were modified.  A second  primary
settling tank and a flow equalizing retention basin were added
at the East Boulevard site, and additional  primary and secondary
settling tanks and tertiary treatment  facilities were  added  at
Auburn.

     Historical modifications to the plants  affecting  sludge are
outlined in the following description:

     •  May 12-15, 1969 - Initial  jar  tests  of phosphorus
                          removal  chemicals

     •  Aug.-Dec., 1969 - Full-scale testing of  various  chemi-
                          cal  additions  for  phosphorus removal

     •  1970            - Plants experimented with ferric  chlo-
                          ride at the  Auburn plant, with the use
                          of various polymers

        1971  - 1973     ~ Continuous addition of ferric  chloride
                          at the Auburn  plant,  with the  use  of
                          various polymers

                               309

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TABLE C-34.   WASTEWATER CHARACTERISTICS  AND  REMOVAL  EFFICIENCIES,
                        PONTIAC,  MICHIGAN
2
Plant Flow m /day (mgd)
SS Primary Influent (mg/&)
Primary Effluent (mg/#)
Plant Effluent (mg/ji)
Primary Removal (%)
Plant Removal (%}
VSS Primary Influent (mg/Jl)
Primary Effluent (mg/£)
Plant Effluent (mg/£)
Primary Removal (%}
Plant Removal (%)
BOD Primary Influent (mg/ji)
Primary Effluent (mg/jj)
Plant Effluent (mg/£)
Primary Removal (%)
Plant Removal (X)
TP Primary Influent (mg/jt)
Primary Effluent (mg/#)
Plant Effluent (mg/ji)
Primary Removal (%)
Plant Removal (%)
Jan. - June '69
81 ,400 (21.5)
184
182
23
1
87
100
106
13
-6
87
100
90
10
10
90
«•
-
-
-
_
Jan. - June '77
104,000 (27.6)
105
66
3
37
97
62
36
2
42
97
81
60
5
26
94
3.8
1.9
0.2
50
95
                              310

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                           Plant  expansion  begun  (specific addi-
                           tions  presented  in general plant
                           description  summary);  incinerator
                           di smantled
     t  1975 - 1976      -  Various  points of alum addition with
                           and without polymer, plus secondary
                           addition of ferric chloride used at
                           the Auburn plant

     •  1977             -  Primary  and secondary addition of ferric
                           chloride at both plants; primary addi-
                           tion of  anionic polymer at East Boule-
                           vard plant with some secondary addition
                           of cationic polymer at Auburn plant

     •  March  1977       -  Incinerator expansion completed and
                           returned to service

Chemical Addition for Phosphorus Removal

     The points of addition of the phosphorus removal  chemicals
were shown on  Figure C-28.  Liquid ferric chloride solution
(approximately 41 percent  FeCla) is added to the raw influent
wastewater at  a dosage of  8 to 12 mg/l Fe"1"3.  Anionic  polymer
(Dru-Floc 2270) is mixed to achieve a 0.25 percent solution for
addition at a  dosage rate  of 0.13 mg/£ to the raw sewage.
Liquid cationic polymer  is added at a dosage rate of 0.17  mg/£
to the aeration basin prior to secondary settling.

General Description of Wastewater Treatment Operations Affecting
SI udge--

     Table C-35 presents a description of wastewater treatment
and sludge handling units  at the Pontiac plants.

     As Figure C-28 shows, sludge  removed from the primary
settling tanks is the only sludge  sent directly to s'ludge
processing by  the anaerobic digester.  Waste-activated sludge
and plant sidestreams--sand filter backwash water, anaerobic
digester supernatant, and  vacuum filter f il trate--are all
returned to the wastewater stream  ahead of the primary settling
tanks.  Suspended solids are removed from the sludge and side-
streams in the primary tanks, from whence they are sent to the
sludge processing units  as part of the primary sludge.

     Figure C-29 shows a sludge handling unit process flow diagram
of the primary sludge removed from both the East Boulevard and
Auburn plants.  This processing consists of two-stage anaerobic
digestion, followed by chemical conditioning, vacuum filtration,
and incineration.  Incinerator ash is disposed of either as  a
wet ash slurry in a lagoon on site, or as dry ash in a landfill.


                               311

-------
       TABLE C-35
   GENERAL  PLANT  DESCRIPTION  SUMMARY,
     PONTIAC,  MICHIGAN
 Aeration  Tanks

   (E)-4 9 54.6 m  (179  ft)  00 x  6.1 m  (20  ft)  (w) x  3.4 m  (11  ft)
   (SWD) per  pass,  two  passes per tank;(A)- 4 0  63.7  m  (209  ft)
   (1)  x 11.1 m (36.5 ft)  (w) x 3.7 m  (12 ft) (SWD);  2  @ 72.5 m
   (238 ft)  (1) x  16.5  m  (54 ft)  (w) x  4.3  m  (14.25 ft)  (SWD).

 Aeration  Equipment
                                    "?               3
   (E)  - diffused  air blowers - 294 m /min (10,500 ft /min) , 8 surface.
   aerators  @ 5 hp,  1,800  rpm; (A).- diffused air blowers - 280 m3
   (10,000 ft^/min); 16 submerged turbine aerators at 10 hp,
   37 rpm;  10 two-speed surface aerators at 40  hp, 68/45 rpm.
 Secondary Settling Tanks
  (E) -4 @ 30.8 m  (101 ft)  (1) x  10.1 m  (33 ft)
  (9.5 ft)  (SWD);(A)~2 @  27.4 m  (90 ft) x 2.6
  2 
-------
TABLE C-35 (continued)
Filter Cake Converying and Storage System

  Five conveyor sections - one in front of each pair of vacuum
  filters, one cross conveyor, one inclined to the top of the
  incinerator, and one across the top of the incinerator to the
  sludge filter cake hopper; storage hopper @ 61.m3 (8 yd3)
  capacity.

Incinerator

  Multiple hearth furnace capacity - 5.4 t/hr (6 ton/hr) @
  25 percent TS prior to 1974, expanded to 7.3 t/hr (8 ton/hr)
  at 25 percent TS in 1977; number of hearths - 7;  10 auxiliary
  burners  @ 2 per hearth in hearths No.  2,  3,  4,  5,  and 6;
  minimum  operating temperatures:


            Hearth No.    Temperature °C.(°F.)

                1            477.4 (900)

                2            532.4 (1 ,000)

                3            642.4 (1,200)

                4            807.4 (1,500)
                5            697.4 (1,300)

                6            532.4 (1,000)

                7            422.4 (800)

  Center shaft and rabble arm drive @.,10 hp, 1.0 rpm;-induced
  draft exhaust fan @ 100 hp, 358.4 nT/min  (12,800 ft°/m1n);
  center shaft cooling air fan @  10 hp, 106.4 m-Vmin  (3,800
  ft3/min).

Incinerator Exhaust Gas  Scrubber

  Flooded  tray-type wet  scrubber  with quencher,  scrubber,  and
  Venturi; inlet gas temperature  @ 422.40lC. (800 F.);  exhaust
  gas temperature @ 37.4*C.  (100°F.); 2 scrubber water  supply
  pumps Ca  2.3 m3/min (610 gal/min).

Wet Ash Handling System

  Ash hopper with mixer  and  vibrating screen; ash discharge
  pump 1.5 m3/min (400 gal/min);  agitator  pump @ 0.23  m3/min
  (60 gal/min).
                                                      (continued)
                               313

-------
 TABLE  C-35  (continued)
 Dry Ash Handling System
                                                     o
  Two screw conveyors and one bucket elevator @ 5.6 m /hr
  (200 ft3/hr); one rotary conditioner; one ash storage bin
  6 78.4 m3 (2,800 ft3).
Notes
  E    =  East Boulevard Plant
  A    =  Auburn Plant
  DIA  =  Diameter
  SWD  =  Side Water Depth
                             314

-------
   en


  I
   u
   m
  CD
        CO


        •a
        01
        4J
        fl
JJ

U




0)

4-1
en

(3
                            Raw Sewage
                            Bar Screens

                       S Aerated Grit Chamber
                                        .Anionic Polymer
                       Primary Settling Tanks
                                                            Ferric

                                                            Chloride
                                                  Flow Equalization

                                                  Retention Basin
                         Aeration Tanks
                                         Cationic Polymer
                       Final Settling Tanks
Return

Activated

Sludge
                       Rapid Sand Filters
                       Chlorine Control Tanks
                              Discharge
Figure C-2b
        Wastewater treatment  unit process  flow  diagram,

        Pontiac,  Michigan.
                                  315

-------
East Blvd Plant

        Primary
        Sludge
                   Auburn Plant
                         Primary
                        i Sludge
Digestion
               Supernatant
               To Head of^
               Plant or to
               Aeration Basins
                                   Digestion
                                 Supernatant
          Digested Sludge
                                 To Head of Plant
                                 or to Aeration
                                 Basins
                  Conditioning
                      Tanks
                                                      Lime
                                                      Ferric
                                                      Chloride
                                    Vacuum
                                    Filters
                                 Filtrate
                                                  to Head of
                                                    Plant
                                          Filtercake
                                   Incineration
                                          Ash
 Figure  C-29.
Sludge handling unit
Pontiac, Michigan.
process flow  diagram,
                                316

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The lagooned ash  is also  sent  to  a  landfill  after  drying.  A
materials balance of  key  wastewater  treatment  and  sludge  handling
unit operations is superimposed on .the  plant flow  diagram  shown
i'n Figure C-30.  A brief  description of each of the wastewater
treatment unit processes  which have  significant impacts on
sludge, follows:

Primary Clarifiers--

     The primary clarifiers  receive  the raw  influent wastewater
and returned sidestreams,  the  most  significant of  which are
characterized  in  Figure C-30.  At the East Boulevard plant, sludge
is removed on  a continuous b'asis  from the bottoms  of the
primary clarifiers to  the  sludge  hopper.  At the Auburn plant,
sludge is removed during  3 out of every 4 hrs, 24  hrs/day  from
the bottom of  the clarifiers to the  wet well adjacent to each
clarifier.  Also, at  the  Auburn plant,  sludge  blankets regularly
build up to a  depth of 1.5 m (5 ft), although  actual depths are
not regularly  monitored.   Depths  of  the sludge blankets at the
East Boulevard plant  are  also  considerable,  although not as great
as those at the Auburn plant.

     Sludge pumping from  the sludge  hoppers  at East Boulevard and
the wet wells  at Auburn takes  place  during approximately 1 hr out
of every 8 hr  per clarifier.   This sludge is then  pumped to the
primary digester at the respective plant.

     Since the initiation  of chemical addition for phosphorus
removal, several significant changes in primary clarifier opera-
tions have been observed.  Specifically, there have been signifi-
cant improvements in  primary clarifier removal  efficiency of
influent BOD and SS,  as previously shown in Table  C-34.   Due to
variations in  plant influent characteristics, Table C-36 is pre-
sented to further highlight the changes in primary clarifier
operations.


           TABLE C-36.  PRIMARY CLARIFIER WASTE STREAM
               CHARACTERISTICS, PONTIAC, MICHIGAN

                                    kg TS/kg  SS (Ib TS/lb SS)
                                        in Plant Influent
                                Jan. to June        Jan. to June
Waste Stream
Digester supernatant
Waste activated sludge
Primary sludge (to digesters)
1969
0.55 (1.21)
0.65 (1.44)
1.03 (2.26)
1977
0.39 (0.86)
<.65 (<1.44)*
1.20 (2.65)
*Estimated due to reduced BOD loadings
 on secondary system.

                               317

-------
CO
«-J
oo
"
'77
0-0.347X10
...._ S3-I4600
WAS VS * 93OO
^9^9
77
0* 27.6 XIO6
S3 > 24200
VSS « I42OO
BOD - 18600
TP = 870
AERATED
RAW 	 ,__ GRIT
INFLUENT CHAMBER

69
0=2I.5XI06
SS « 33IOO
VSS * 17900
BOD • 17900
TP • N/l
1 r ™ nfH







LEGEND
Q * FLOW (6AL/OAY)
SS * SUSPENDED SOLIDS (LBS/DAY)
VSS -VOLATILE SUSPENDED
SOLIDS (L8S/DAY)
BOD»BOD5 (LBS/DAY)
TP* TOTAL PHOSPHOROUS (LBS/DAY)
TS* TOTAL SOLIDS (LBS/DAY)
VS1* VOLATILE SOLIDS (LBS/DAY)
pH= STANDARD UNITS
Q«0.50XI06
, TS* 47500
77
S3 -18300
VS3<830O
BOD* 13700
TP*440
^ PRIMARY AERATION SECONDARY
" CLARIFIERS ' BASINS " CLARIFIERS

§
69
83*32700
VSS- 19000
BOD* 16200 OAC
Tf*« tJj*A l»rlO
'77
Q- 139000
TS * 64100
VS* 34400
pH* 8.8
PRIMARY
DIGESTERS
-co
Q*IO900O
TS*74700
VS* 39800
pH * 6.7

1
SUPERNATANT )
l**^^^^^^^^^^^l>*— ^"•^^^^•'^••"^•••^•^^•^^^^•^••••'i*"*'i-***iB««"M*J"J"J"J"J>"J"J"«*JBJ**M"J"*H*J-J*M"|





'77
83 * 770
VSS « 830
BOD* 1070
TP*60
TO
, SAND _ CHLORINATION
FILTERS " AND
DISCHARGE
•
69
33=4200
VSS* 2400
BOD* 1 700
TP- N/A
1 • ™ H/«
'77
Q- 45000
TS* 29400
VS> 13500
pH* N/A TQ
SECONDARY VACUUM FILTERS
DIGESTERS , AND
K<* INCINERATOR
0*48000
TS«320OO
VS* I6OOO
pH* 7.3
77
0=92000
FS* 20800
/S»9900
>H* 6.9
'69

0=69000
TS* 37600


VS* 18400
pH* 7.2
              Figure  C-30.   Pontlac, Michigan,  hydraulic  and  materials  balance

-------
     Significant decreases are apparent in the relative amounts
of solids returned in the digester supernatant to the head of the
primary clarifiers.  A decrease in the quantities of solids con-
tained in the waste activated sludge returned to the head of the
primary clarifiers is also assured, since there were significant
decreases in BOD loadings on the secondary treatment system.
Overall, Table C-37 shows that sludge removed from the primary
clarifiers contains significantly greater mass of solids, since
chemical addition for phosphorus removal  began in terms of the
kilograms of TS per kilogram of SS in the plant influent.

Secondary Clarifiers--

      Sludge is removed from the bottoms  of the secondary clari-
fiers on a continuous basis at both the East Boulevard and Auburn
plants.  The majority of sludge withdrawn from the bottoms of
these clarifiers is pumped as return activated sludge to the head
of the aeration basins.  A smaller portion is pumped as waste
activated sludge to the head of the primary clarifiers to maintain
the desired average mixed liquor suspended solids concentration.
Since the initiation of chemical addition for phosphorus removal,
there has been a considerable decrease in the volume of waste
activated sludge per million gallons of plant influent.

Detailed Description of Sludge Treatment  and Disposal
Operations

Digesters--

     Table C-37 describes the raw and digested sludge and super-
natant characteristics befdre and after the initiation of
chemical addition for phosphorus removal.  During the period with
dual point ferric addition, an  increased volume of raw sludge
at a lower average solids concentration was sent to the primary
digesters.  This led to a net increase in the mass of sludge
TS fed to the digester per pound of SS in the plant  influent.
Most of the additional sludge TS fed to the digesters were
volatile (fixed) solids.

     Digester supernatant returned from the secondary digesters
to the head of the primary clarifiers also followed  the trend
of increased volume at considerably lower solids concentrations.
The net result was a significant decrease in the mass of  super-
natant TS per pound SS in the plant influent.  These  changes
are indicative of improved digesting sludge settleability.

     Lastly, the volume and solids concentrations of  the
digested sludge removed from the secondary digester  were  observed
to have decreased.  However, there were large increases  in  the
mass of digested sludge TS per  kilogram of SS in the  plant
inf1uent.
                              319

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TABLE C-37.  RAW AND DIGESTED SLUDGE AND SUPERNATANT
         CHARACTERISTICS, PONTIAC, MICHIGAN

Raw Sludge
m3/day (gpd)
% TS
% Volatile
pH
kg TS/kg SS influent to plant
kg VS/kg VSS influent to plant
*
kg FS/kg FSS influent to plant
Supernatant
m /day (gpd)
% TS
% Volatile
pH
kg TS/kg SS influent to plant
kg VS/kg VSS influent to plant
kg FS/kg FSS influent to plant
Digested Sludge
m /day (gpd)
% TS
% Volatile
pH
kg TS/kg SS influent to plant
kg VS/kg VSS influent to plant
kg FS/kg FSS influent to plant
*FS = Nonvolatile (fixed) solids
FSS = Nonvolatile (fixed) suspenc
Jan. -June 1969
413 (109,000)
8.2
53
6.7
2.26
2.22

2.30

261 (69,000)
6.5
49
7.2
1.14
1.03
1.19

182 (48,000)
8.7
47
7.3
0.97
0.83
1 .26

Jed solids
•Ian. -June 1977
526 (139,000)
5.5
54
6.8
2.65
2.42

2.97

348 (92,000)
2.7
48
6.9
0.86
0.70
1.09

170 (45,000)
7.8
46
N/A
1.32
0.95
1.59


                      320

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     Overall, the performance of the digesters improved signifi-
cantly after the initiation of chemical addition for phosphorus
removal.   Digesting sludge settleabi1ity improved, as evidenced
by major decreases in the mass of digester supernatant solids
returned to the head of the primary clarifiers.  Furthermore,
the destruction of volatile solids influent to the digesters
increased from 16 percent to 33 percent when the two periods
are compared.  A secondary impact of the increased volatile
destruction was an increase in digester gas production from
l,9fin no to 2,240 m3/day (70,000 up to 80,000 ft3/day).

Vacuum Filters--

     Since the initiation of chemical  addition for phosphorus
removal,  the vacuum filters have been operated 24 hr/day for an
average of 13.8 days/mo, as opposed to 19.5 days/mo prior to
the initiation of phosphorus removal.   Table C-38 summarizes
average vacuum filter performance for the two periods.  During
the period prior to the initiation of phosphorus removal, the
vacuum filters were operated between 4 and 5 days/mo.  During the
period with dual point addition of ferric chloride to the waste-
water, the vacuum filters were operated approximately 3 days/wk.

     Since the initiation of chemical addition for phosphorus
removal, there have been only minor changes in the dosage rates
of conditioning chemicals added to the sludge prior to vacuum
filtration.  However, the filter yield rate has decreased from
19.8 to 17.8 g TS/hr (4.05 to 3.65 Ib TS/ft2/hr).  In addition,
the VS fraction of filter cake TS decreased from 33.5 to 30.5
percent of TS.  Overall, however, there has been an increase
in the capture of sludge solids in the filter cake.  This has
resulted in over a 40 percent decrease in the mass of filtrate
solids returned to the head of the primary clarifiers.

Incinerator--

     The multiple hearth incinerator is operated continuously
during vacuum filter operations.  Thus, the incinerator is oper-
ated 24 hr/day, 3 days/wk.   Twelve additional hours are required
to bring the furnace up to combustion temperatures, and 8 hours
are required for cool-down.  Table C-39 summarizes incinerator
performance data for the two periods listed.  It should be noted
that the second period describes incinerator performance after
the 1974 incinerator expansion was completed.
                               321

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                    TABLE  C-38.    VACUUM  FILTER  PERFORMANCE,  PQNTIAC, MICHIGAN
January - June 1969





CO
P

m (galj sludge fed
% TS of sludge
kg (lb) sludge solids fed
kg lime per kg sludge dry solids
kg ferric chloride/kg sludge dry solids
Filter yield (kg sludge TS/m2 filter
i u. „ .» / U u ~ £ nnxtMi*.-:,*.. / 1 U TC/.C4-'-/U.A\\
Average
Per Day
of Filter.
Operation
299 (79,000)
8.2
24,500 (54,100)
0.143
0.029
in n / jt nr \
Average
Per Day
of Plant
Operation
191 (50,500)
8.2
15,700 (34,500)
0.143
0.029
i rt n i » r\t?\
January - June 1977
Average
Per Day
of Filter
Operation
375 (99,000)
7.3
27,400 (60,300)
0.156
0.025
•IT rt /*» /• i- \
Average
Per Day
of Plant
Operation
170 (45,000)
7.3
12,300 (27,000)
0.156
0.025
"i"t r* /*"& r* r \
kg (Ib)  wet  filter cake
% TS of  filter cake
% VS of  filter cake
kg (lb)  filter cake dry solids
kg (lb)  filter cake VS
kg (lb)  filtrate total solids
% capture  of sludge and conditioner
  solids
74,500  (164,000)
    33.3
    37.7
24,800  (54,600)
 9,310  (20,500)
 3,950  (8,700)

    85
47,700  (105,000)
    33.3
    37.7
15,900  (35,000)
 5,990  (13,200)
 2,540  (5,600)

    85
94,900  (209,000)
    30.5
    39..0
28,900  (63,700)
11 ,300  (24,900)
 3,670  (7,200)

     89
43,100  (95,000)
    30.5
    39.0
13,200  (29,000)
 5,130  (11,300)
 1 ,500  (3,300)

    89

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         TABLE C-39.   INCINERATOR PERFORMANCE,
                   PONTIAC,  MICHIGAN
Inci nerator
Hours of operation
kg (Ib) wet cake/h
kg (Ib) cake VS/hr
m3 (thousand ft3)
m3 natural gas/kg
(ft3/lb wet cake)
m3 natural gas/kg
(ft3/lb VS)
Feed
per
r of
of
natu
wet
cake

month
operation
operation
ral gas/mo
cake
VS
Jan.
June
368
3,860 (
499 (
30.5 (
0.02 (
0.17 (
1

8
1
1
0
2
to
969

,500)
,100)
,090)
.35)
.70)
April
June 1
348
3,720 (
454 (
34.2 (
0.03 (
0.22 (
to
977

8,
1,
1,
0.
3.

200)
000)
220)
43)
55)
Since the initiation of chemical  addition  for phosphorus
al ,  there has been a decrease in  the mass  of wet  cake  fe
remova
the incinerator
decrease in the
to
                                          mass  of wet  cake  fed
                per hour of operation.   There has also been  a
                mass of volatile solids fed to  the incinerator  per
hour of operation.  As a result of these factors  and  incinerator
capacity expansion, there has been an increase  in the  auxiliary
fuel requirements per pound of wet cake and per pound  of cake
volatile solids fed to the incinerator.

Summary and Conclusions

     There have been many changes in the Pontiac plant's waste-
water and sludge  handling operations as a result of chemical
additions for  phosphorus removal, changes in plant influent
characteristics,  and plant equipment additions and modifications.
These impacts  are  highlighted below, for each of the unit
operations listed:

     Primary Clarifiers:

     •  Improved  SS and BOD  removal  efficiencies

     t  Decreased  solids loading  on  the primary  clarifiers
        from the  return of digester  supernatant, waste-
        activated  sludge, and vacuum filter  filtrate

     •  Increased  mass  of primary sludge TS  generated per
        kilogram  SS influent to plant;  additional sludge
        solids mainly  nonvolatile.
                          323

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 Digesters:

 t  Increased volume of sludge  pumped  to  digesters
    at lower average solids  concentration,  with  net
    effect  being an increase in the  mass  of primary
    sludge  TS fed to the digesters  per kilogram
    of SS in the plant influent

 •  Increased volume of supernatant,  but  at a
    considerably lower solids  concentration,
    indicative of better sludge settleabi1ity  with-
    in the  digesters

 •  Increased volatile destruction  occurring within
    the digesters

 •  Increased digester gas  production.

 Vacuum Filters:

 t  Decreased filter yield

 §  Decreased filter cake total solids and
    volatile solids concentrations

 •  Increased capture of sludge solids in  the  cake

 t  Decreased solids in filtrate returned  to  head
    of primary clarifiers.

Incinerator:

t  Decreased feed rates in terms of kilograms wet
   cake and kilograms volatile solids per  hour of
   operation

§  Increased fuel consumption per hour of  operation,
   per kilogram wet cake feed and per kilogram
   volatile solids fed.
                          324

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                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
 . REPORT NO.

  EPA-600/2-79-083
               3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
                                                           5. REPORT DATE
  REVIEW OF TECHNIQUES FOR TREATMENT AND DISPOSAL
  OF  PHOSPHORUS-LADEN CHEMICAL  SLUDGES
                                                            August  1979 (Issuing Date)
               6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
  Curtis J.  Schmidt, LeAnne  E.  Hammer, and
  Michael D. Swayne
               8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS

  SCS Engineers
  4014 Long Beach Boulevard
  Long Beach, California   90807
               10. PROGRAM ELEMENT NO.

                1BC821QBC611B), SOS
               11. CONTRACT/GRANT NO.

                68-03-2432
 12. SPONSORING AGENCY NAME AND ADDRESS
  Municipal Environmental  Research Laboratory—Cin.,OH
  Office of Research and Development
  U.S.  Environmental Protection  Agency
  Cincinnati, Ohio  45268
                                                            13. TYPE OF REPORT AND PERIOD COVERED
                Final
               14. SPONSORING AGENCY CODE
                EPA/600/14
 15. SUPPLEMENTARY NOTES
  Project Officer:  R. V.  Villiers    (513) 684-7664
 16. ABSTRACT
  This report summarizes  the  effects of phosphorus removal  by  chemical  addition on
  sludge handling and disposal  options at full-scale wastewater  treatment plants.
  American and Canadian plants  which generate phosphorus-laden chemical sludges were
  surveyed by questionnaire,  and 174 responses were received.  Investigations at
  selected plants that were using a variety of phosphorus removal  chemicals, points of
  chemical addition, and  sludge treatment/disposal methods  were  conducted.  The plant
  operating experiences have  shown that all of the various  sludge  treatment unit
  processes for thickening, stabilization, conditioning, dewatering,  and reduction are
  adversely affected by phosphorus removal.  The adverse effects result from both
  increases in sludge quantity  and changes in sludge characteristics.   The adverse
  impacts are reduced when adequate capacity is available to handle the increased sludge
  quantity.  However, many plants have inadequate capacity, and  therefore have been
  forced to find innovative solutions to problems.  This report  documents such problem-
  solving attempts and the results achieved.  It also compares the various sludge
  handling alternatives,  and  finds that relatively few problems  have  been encountered
  with pressure filtration of iron sludges, flotation thickening of iron and aluminum
  sludges, thermal conditioning of iron sludges, and land disposal  of  lime sludges.  The
  report contains a bibliography of literature dealing with phosphorus-laden sludges,
  with an indication as to the  scope of each reference.	
17.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                              b.lDENTIFIERS/OPEN ENDED TERMS
                               COSATI Field/Group
  Chemical removal  (sewage  treatment)
  Sludge digestion
  Sludge drying
  Sludge disposal
   Phosphorus-laden
     chemical sludges
   Phosphorus removal
     (sewage treatment)
   Sludge treatment and
     disposal
                                13B
 8. DISTRIBUTION STATEMENT


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21. NO. OF PAGES
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325
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