EPA 440/1-73/019-a
          DEVELOPMENT DOCUMENT FOR
  PROPOSED  EFFLUENT LIMITATIONS GUIDELINES
  AND NEW SOURCE PERFORMANCE  STANDARDS
                    FOR THE


      PRIMARY ALUMINUM SMELTING

                SUBCATEGORY OF THE
                ALUMINUM SEGMENT
                     OF THE
          NONFERROUS METALS MANUFACTURING
              POINT SOURCE CATEGORY
          UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                    OCTOBER 1973

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                               Publication Notice

                 .s  is  a development document for proposed effluent
                  itations  guidelines and new source performance
                  ndards.   As such,  this report is subject to changes
 o                 alting from comments received during the period of
 ^                .ic comments of the proposed regulations.  This
 0    $           ment in  its final form will be published at the
 o o» mu             the regulations  for this industry are promulgated,
P 
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              DEVELOPMENT DOCUMENT


                       for


    PROPOSED EFFLUENT LIMITATIONS GUIDELINES

                       and

        NEW SOURCE  PERFORMANCE STANDARDS

                     for the

           PRIMARY  ALUMINUM SMELTING
                  SUBCATEGORY
                      Of the
                 ALUMINUM SEGMENT
                      of the
        NCNFERROUS  METALS MANUFACTURING
                     CATEGORY
                 Russell E. Train
                  Administrator

                 Robert L. Sansom
Assistant Administrator for Air & Water Programs
                   Allen Cywin
     Director,  Effluent Guidelines Division

              Harry M.  Thron, Jr.
                 Project Officer
                  October, 1973

          Effluent  Guidelines Division
        Office  of Air and Water Programs
      U.S.  Environmental Protection Agency
              Washington, D.C. 20460
       1T.S. Environmental Protection
       Rogl'-o 5 , L; >>rary (5PL-16)
       230 S. Dearborn Street, Room 1670
       Chicago, IL  60604

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                                ABSTRACT
This document presents the findings of an extensive study of the primary
aluminum  industry  by  Battelle's   Columbus   Laboratories   for   the
Environmental  Protection  Agency for the purpose of developing effluent
limitations guidelines, and standards of performance for the industry to
implement Sections 304, 306, and 307  of  the  Federal  Water  Pollution
Control Act, as amended.

Effluent   limitations  guidelines  contained  herein  for  the  primary
aluminum industry set forth the degree of effluent reduction  attainable
through  the  application  of  the  best  practicable control technology
currently available and the  degree  of  effluent  reduction  attainable
through  the  application  of the best available technology economically
achievable which must be achieved by existing point sources by  July  1,
1977,  and July 1, 1983, respectively.  The Standards of Performance for
new sources contained herein set forth the degree of effluent  reduction
which  is  achievable  through  the  application  of  the best available
demonstrated control technology, processes, operating methods, or  other
alternatives.

The  data  and  recommendations developed in this document relate to the
production of primary aluminum by the electrolysis  of  alumina.   Water
from wet scrubbers operated to control air pollution is the major source
of contaminated waste water from this industry.  Treatment of this water
to precipitate fluorides and to decrease the concentrations of suspended
solids  and  oil and grease to allow recycle of the treated water to the
scrubbers represents the best practicable control  technology  currently
available  for  existing point sources.  Further lime treatment of bleed
streams and filtrates from such practice constitutes the best  available
technology   economically   achievable.    Alternate   technologies  for
achieving the recommended limitations are available to  some  plants  in
conversion  from  wet scrubbing to dry scrubbing or an total impoundment
of waste water.  The best  available  demonstrated  control  technology,
processes,  operating  methods,  or  other  alternatives consists of dry
scrubbing of potline air, the control and treatment of  other  fluoride-
containing waste streams by recycle and treatment of any necessary bleed
stream  by  lime  precipitation  and  the treatment of other streams, as
required, for oil and grease removal.

Supportive data and rationale for development of the  proposed  effluent
limitations  guidelines  and  standards  of performance are contained in
this document.

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                                CONTENTS

Section

I        CONCLUSIONS                                            1

II       RECOMMENDATIONS                                        2
           Best Practicable control Technology Currently
             Available                                          2
           Best Available Technology Economically
             Achievable                                         3
           New Source Performance Standards                     3

III      INTRODUCTION                                           5
           Purpose and Authority                                5
           Approach Used in the Development of the              6
             Effluent Limitation Guidelines and standards
             of Performance
           General Description of the Primary Aluminum         12
             Industry

IV       INDUSTRY CATEGORIZATION                               20
           Introduction                                        20
           Objectives of Categorization                        20
           An Overview of the Interrelationship of Anode       20
             Type, Process Technology, Air Pollution
             Control, and water Pollution Control
           Aluminum Reduction Process Description              27
           Water Usage in the Primary Aluminum Industry        35
           Industry Categorization                             36

V        WASTE CHARACTERIZATION                                43
           Introduction                                        43
           Sources of Waste Water                              43
           Effluent Leadings                                   47
           Source of Waste Water from Developmental            73
             Aluminum Reduction Processes

VI       SELECTION OF POLLUTANT PARAMETERS                     74
           Selected Parameters                                 74
           Rationale for the Selection of Pollutant            74
             Parameters
           Rationale for the Rejection of                      75
             Pollutant Parameters

VII      CONTROL AND TREATMENT TECHNOLOGY                      77
           Introduction                                        77
           Control Technology                                  77
           Treatment Technology                                gg

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           Summary of Waste Treatment Effectiveness             98
           Control and Treatment Options                       101
Section

VIII      COSTS, ENERGY, AND NONWATER QUALITY ASPECTS           104
            Introduction                                        104
            Basis for Cost Estimation                           104
            Economics of Present Control Practice               105
            Economics of Present Treatment Practice             109
            Cost Effectiveness  (Present Practice)               110
            Costs of Additional Treatment Processes             114
            Nonwater Quality Aspects                            116

IX        BEST PRACTICAELE CONTROL TECHNOLOGY CURRENTLY         121
          AVAILABLE, GUIDELINES, AND LIMITATIONS
            Introduction                                        121
            Recommended Effluent Limitations                    122
            Identification of Best Practicable Control          124
              Technology Currently Available
            Guidelines for the Application of the               127
              Effluent Limitations

X         BEST AVAILABLE TECHNOLOGY ECONOMICALLY                128
          ACHIEVABLE, GUIDELINES AND LIMITATIONS
            Introduction                                        128
            Recommended Effluent Limitations                    129
            Identification of Best Available                    130
              Technology Economically Achievable
            Guidelines for the Application of the               131
              Effluent Limitations

XI        NEW SOURCE PERFORMANCE STANDARDS                      132
            Introduction                                        132
            Standards of Performance for New                    133
              Sources
            Identification of Best Available Demonstrated      134
              Control Technology, Processes, Operating
              Methods, or Other Alternatives
            Rationale for the Selection of the Best  Available  135
              Demonstrated control Technology
            Guidelines for the Application of the  Standards    135
              of Performance

XII       ACKNOWLEDGMEN1S                                       136

XIII      REFERENCES                                            137

XIV       GLOSSARY                                              138

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                                 TABLES


Number

  A      Summary of Features of Plants Visited                  13

  1      Matrix of the Characteristics of Primary               37
         Aluminum Plants

  2      Effluent Loading, kg pollutant/metric ton Al           48

  3      Effluent Loading, Ib pollutant/ton Al                  49

  U      Quantities of Selected Constituents in Water           50
         Effluent from Selected Primary Aluminum Plants
         in the U.S.

  4A1-4K Concentrations of Selected Constituents              51-69
         in Influent and Effluent Water, Primary Aluminum

  5      Summary of Present and Potential Control and           78
         Treatment Technologies

  6      Effluent Levels Achieved by Various Treatment          99
         Processes

  7      Cost Data for Control and Treatment of Waste          106
         Waters from Primary Aluminum Production

  8      Costs of Various Alternatives for Fluoride            117
         Removal

  9      Energy Requirements and Solid Waste Production        120
         for Various Water Effluent Control and Treatment
         Technologies

 10      English/Metric Unit Conversion Table                        146

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                                FIGURES


Number                                                       £§3§

  A     Wastewater Survey Questionnaire - Plant Visits         7

  B     Wastewater Questionnaire - Telephone Survey           14

  1     Locations of Aluminum Reduction Plants                18

  2     Schematic Drawing of a Prebaked Anode Cell            22

  3     Schematic Drawing of a Horizontal Stud Soderberg      23
        Aluminum Reduction Cell

  4     Schematic Drawing of a Vertical Stud Soderberg        24
        Aluminum Reduction Cell

  5     Process Diagram for the Electrolytic Production       29
        of Aluminum

  6     Schematic Composite Flow Diagram for Plants Using Wet 44
        Scrubbing
  7     Correlation of Plant Data on Suspended Solids,        71
        Oil and Grease, and Fluoride Emissions

  8     Diagram of Dry Gas-Scrubbing Process Elements         80

  9     Process Schematic Recycle System for Fluoride         84
        Removal

 10     Process Schematic of Once-Through System for          89
        Fluoride Removal

 11     Flowsheet of Process to Remove Fluorides From         90
        Waste Streams  (Recycle Water Treatment)

 12     Schematic Diagram of a Process to Remove              93
        Fluoride by Alum Precipitation

 13     Process to Remove Fluoride by Adsorption on           94
        Activated Alumina

 14     Reverse Osmosis Treatment of Fluoride Waste           97
        Water

 15     Some Control and Treatment Options                   102

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16     Cost Effectiveness of Water Control and
       Treatment to Remove Fluoride  (Capital Cost)

17     Cost Effectiveness of Water Control and
       Treatment to Remove Fluoride  (Operating Cost)         112

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                               SECTION I
                              CONCLUSIONS


For the purpose of  establishing  effluent  limitations  guidelines  and
standards  of performance, the aluminum segment of the nonferrous metals
manufacturing   point   source   category   was   divided   into   three
subcategories.   This  report  deals  with the primary aluminum smelting
subcategory.

Primary aluminum smelting is a single subcategory  for  the  purpose  of
establishing   effluent   limitations   guidelines   and   standards  of
performance.  The consideration of other factors such as age and size of
the plant, processes employed, geographical location, wastes  generated,
and  waste water treatment and control techniques employed, support this
conclusion.  The similarities of the wastes produced by primary aluminum
smelting operations and the control techniques required  to  reduce  the
discharge  of  pollutants  further substantiate the treatment of primary
aluminum smelting as a single subcategory.  However, guidelines for  the
application  of the effluent limitations and standards of performance to
specific facilities do take into account the  production  level  of  the
smelting facility.

Approximately  one-third of the 31 primary aluminum plants are currently
operating with discharge levels of pollutants within the July  1,  1977,
effluent  limitations  recommended  herein.   It  is  concluded that the
remainder of the industry can achieve those levels by July 1,  1977,  by
the  application  of  the  best practicable control technology currently
available.  Those plants not presently achieving the recommended July 1,
1977, limitations would require an estimated capital investment of about
$10/annual metric ton  ($9/annual short ton) and an  increased  operating
cost  of  about  $4.6/metric ton  ($4.2/short ton) in order to accomplish
the desired decrease in discharge of pollutants.  It is estimated that a
further investment of $3.8/annual metric ton  ($3.5/annual short ton) and
an additional operating cost of $1.13/metric ton  ($I/short ton) would be
required to decrease the discharge of pollutants from the July 1,  1977,
level to the recommended July 1, 1983, level.

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                               SECTION II
                            RECOMMENDATIONS
                  Best Practical le_Control Technology
                          Currently_Ayailable

The  recommended  effluent limitations for the primary aluminum smelting
subcategory to be achieved by July 1, 1977, and attainable  through  the
application   of  the  best  practicable  control  technology  currently
available, are as follows:

                              __________ Effluent. Limitations ja) _______

    Effluent               Single_paY_Maxiinun}Jb^      30-Day Ayeragejc)
                                                               Ib/ton Al
    Fluoride                     24            12
    Suspended Solids             3         6            1.5         3
    Oil and Grease               0.5       1            0.25        0.5
    Cyanide                      0.01      0.02         0.005       0.01
    pH    6-9

    (a)  Effluent limitations are defined as kilograms of
     pollutant per metric ton of aluminum produced
     or pounds of pollutant per short ton of aluminum produced.

    (b)  The single day maximum is the maximum value for any one day.

    (c)  The 30-day average is the maximum average of daily values for
     any consecutive 30 days.

The best practicable control  technology  currently  available  for  the
primary  aluminum  smelting subcategory is the treatment of wet scrubber
water  and  other  fluoride-containing  effluents  to  precipitate   the
fluoride,  followed  by settling of the precipitate arid recycling of the
clarified liguor to the wet scrubbers as  a  means  of  controlling  the
volume  of  waste  water  discharged.   Two  precipitcition  metnods  are
currently available,  cryolite  precipitation,  and  precipitation  with
lime.   This technology achieves attendant reduction of the discharge of
suspended solids and cil and grease.

Alternate  technologies   for   achieving   the   recommended   effluent
limitations include dry fume scrubbing and total impoundment.

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The  technology  and  rationale  supporting  these  recommendations  are
presented in Sections VII and IX.

                       Best Available Technology
                        EConomica11y Achievable

The recommended effluent limitations to be achieved by July 1, 1983,  by
application of the best available technology economically achievable are
as follows:

                         	Ef f luent_Limitations_(a}	
Effluent                  Single^BaY_MaximumJb]_   30-Day_Ayerage_(cJ __
Characteristic
Fluoride                    0.1        0.2         0.05        0.1
Suspended Solids            0.2        0.4         0.1         0.2
Oil and Grease              0.03       0.06        0.015       0.03
Cyanide                     0.01       0.02        0.005       0.01
pH Range 6-9

      (a)  Effluent limitations are defined as kilograms of pollutant
          per metric ton of aluminum produced or pounds of pollutant
          per short ton of aluminum produced.

      (b)  The single day maximum is the maximum value for any one day.

      (c)  The 30-day average is the maximum average of daily values
          for any consecutive 30 days.

The  application  of  the  best practicable control technology currently
available results in a relatively low volume,  high-concentration  bleed
stream.   The  best available technology economically achievable is lime
treatment of such a bleed stream to  further  reduce  the  discharge  of
fluoride.   This  technology  also  achieves  further  reduction  of the
discharge of suspended solids and oil and grease.

Alternate  technologies   for   achieving   the   recommended   effluent
limitations include dry fume scrubbing and total impoundment.

The  technology  and  rationale  supporting  these  recommendations  are
presented in Sections VII and X.

                    New_ Source Per formance^ Standards

The recommended standards of performance for new sources  attainable  by
the  application  of the best available demonstrated control technology,
processes, operating methods, or other alternatives, are as follows:

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                     	Standards of Performance(a)	

Effluent             Single Day Maximum(b)       30-Day Average(c)
Characteristic       kg/kkq Al   lb/tgn^Al     j£S/]S]S3_£i  Ib/ton Al

Fluoride               0.05        0.1           0.025       0.05
Suspended Solids       0.1         0.2           0.05        0.1
Oil and Grease         0.03        0.06          0.015       0.03
Cyanide                0.01        0.02          0.005       0.01
pH Range   6-9

     (a)  Standards of Performance are defined as kilograms of pollutant
          per metric ton of aluminum produced or pounds of pollutant
          per short ton of aluminum produced.

     (b)  The single day maximum is the maximum value for any one day.

     (c)  The 30-day average is the maximum average of daily values
          for any consecutive 30 days.

The best available demonstrated control technology, processes, operating
methods, or other alternatives consists of dry scrubbing of potline air,
the control  and  treatment  of  fluoride-containing  waste  streams  by
recycle   and   treatment   of   any  necessary  bleed  stream   by  lime
precipitation, and the treatment of casthouse cooling  water  and  other
streams,  as  required,  for  oil  and  grease  removal  with  a gravity
separator or aerated lagoon.  The technology  and  rationale   supporting
these recommendations are presented in sections VII and XI.

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                              SECTION III
                             INTRODUCTJON
                             o se an d .Authority
Section 304 (b)  of the Federal Water Pollution Control Act, as amended in
1972,  requires  the  achievement  by  not  later  than July 1, 1977, of
effluent  limitations  for  point  sources,  other  than  publicly-owned
treatment  works,  which  are  based  on  the  application  of  the best
practicable control technology currently available  as  defined  by  the
Administrator  pursuant  to  Section  304 (b)  of the Act.  Section 301 (b)
also requires the achievement  by  not  later  than  July  1,  1983,  of
effluent   limitations  for  point  sources,   other  than  nubliclyowned
treatment works,  which  are  based  on  the  application  of  the  best
available  technology  economically  achievable  which  will  result  in
reasonable further progress toward the national goal of eliminating  the
discharge   of   all   pollutants,  as  determined  in  accordance  with
regulations issued by the Administrator pursuant to  Section  304 (b)  to
the Act.  Section 306 of the Act requires the achievement by new sources
of  a  Federal  standard of performance providing for the control of the
discharge of pollutants which reflects the greatest degree  of  effluent
reduction  which  the  Administrator determines to be achievable through
the application of the best available demonstrated  control  technology,
processes,  operating  methods,  or  other alternatives, including where
practicable, a standard permitting no discharge of pollutants.

Section 304 (b)  of the Act requires the Administrator to  publish  within
one  year  of enactment of the Act, regulations providing guidelines for
effluent limitations setting forth  the  degree  of  effluent  reduction
attainable  through  the  application  of  the  best practicable control
technology currently available and  the  degree  of  effluent  reduction
attainable  through  the  application  of  the best control measures and
practices  achievable  including  treatment  techniques,   process   and
procedure  innovations,  operation  methods and other alternatives.  The
regulations proposed herein set forth  effluent  limitations  guidelines
pursuant  to Section 30 4 (b) of the Act for the primary aluminum smelting
segment  of  the  aluminum  subcategory   of   the   nonferrous   metals
manufacturing category of squrces.

Section 306 of the Act requires the Administrator, within one year  after
a  category  of  sources  is  included  in  a list published pursuant to
Section 306 (b)  (1) (A) of the Act,  to  propose  regulations  establishing
Federal   Standards   of   performances  for  new  sources  within   such
categories.  The Administrator published  in  the  Federal  Register  of
January 16, 1973 (38 PR 1624) , a list of 27 source categories.

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Publication  of the list constituted announcement of the Administrator's
intention of establishing,  under Section 306,  standards  of  performance
applicable  to  new  sources  within the primary aluminum segment of the
nonferrous metals industry which was included  within the list  published
January 16, 1973.
          Limitatign^Guidelines and Standards^gf^Perfprmance


The   effluent  limitations  guidelines  and  standards  of  performance
recommended herein were developed in the following manner.  An inventory
was compiled of the primary aluminum smelting industry with  respect  to
process  details,  air  pollution control systems, waste water treatment
methods, and ancillary operation.  This inventory provided  an  overview
perspective  from  which to assess the need for subcategorization of the
industry, and  a  base  from  which  to  evaluate  current  control  and
treatment practices.

General  information  was  obtained  on  all  31 of the primary aluminum
plants operating in this country and detailed information  was  compiled
for 10 plants.  Information was derived from the following sources:

         0    Applications to the Corp of Engineers for Permits
              to Discharge under the Refuse Act Permit Program
              were obtained for 14 plants.
              These contained data, in varying degrees of
              detail, on the composition and volumes of intake
              and effluent waters, waste water
              treatment  (in general terms), and daily aluminum
              production rates.

         0    Plant visits were made to 10 sites to obtain detailed
              information on control and treatment technologies
              and associated costs, identification and concentration
              of waste water constituents, and discharge volumes.
              Each of the plants visited submitted a completed
              Questionaire together with flow diagrams of
              water use.
              A copy of the questionaire is shown in Figure A.
              The plants visited included those which employ
              exemplary waste water control or treatment
              as identified through the discharge permit applications,
              through consultation with the clean water subcommittee
              of the Aluminum Association, arid through primary
              aluminum company representatives.
              Other plant-visit  sites were selected to be representative
              of various specivic industry practices.

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                           PRIMARY ALUMINUM
                           Process  Data Sheet
Date
Company




Plant
Basic Process, Hall/Herout




Process Variations
Anode Type and Configuration




Raw Materials
Plant Capacity 	 ton Al/day




Age of Plant 	 years




Air Pollution Controls in Use or  Planned       	
Process Modifications Available Which  Would  Reduce Water Pollution
Other Notes:
          FIGURE A.   WASTEWATER SURVEY QUESTIONNAIRE—PLANT VISITS

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                         PRIMARY ALUMINUM



                            Other Data



What factors within the primary aluminum industry will influence

a specific plant's ability to meet effluent limitations:


        1.	
        2.
        3.
Other comments
       FIGURE A.   WASTEWATER SURVEY QUESTIONNAIRE—PLANT VISITS
                              (Continued)

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                           PRIMARY ALUMINUM
                         Wastewater Data  Sheet
Date
Company

Plant
Attach a process flow diagram  showing water and wastewater material
balances.
Pipe No.
Origin of Wastewater
Volume (Min/Ave/Max)	  gal/day

pH (Min/Ave/Max) 	

Temperature, °F, Winter  (Min/Ave/Max) 	

Temperature, °F, Summer  (Min/Ave/Max) 	

Wastewater Treatment(s) 	
         FIGURE A.  WASTEWATER  SURVEY QUESTIONNAIRE—PLANT VISITS
                                (Continued)
                                   9

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                              PRIMARY ALUMINUM
               Costs of Waste Control and Wastcwnter Treatment
Date
Company
Plant
Method (Waste Control/Wastewater Treatment)
Control Capacity
        For Waste Control -
        For Wastewater Treatment -
Year Installed 	
Capital Costs
        Hardware
        Engineering
        Installation
Annual Cost
        Operating and Maintenance
        Depreciation	
        Administrative Overhead
        Property Tax, Insurance
        Interest
        Other, e.g. , water
        analysis
        Gross Annual Cost
        Credits
        Net Annual Cost
 Tons  Al Annual Capacity
	 gal/day treated
  $/ton Annual Capacity
  $/ton Annual Capacity
Impacts of this control method on other media
           FIGURE A.  WASTEWATER SURVEY QUESTIONNAIRE—PLANT VISITS
                                   (Continued)
                                      11

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              Table A summarizes the features  of the plants
              visited.

         °    General information on the remaining plants was obtained
              through telephone contacts with  each company.
              A copy of the questionnaire used in this telephone survey
              is shown in Figure B.

         0    Three of the plants were revisited for sampling
              and analysis in order  to verify  the effluent data.
              These three plants were selected because their
              waste water practice represents  the best waste
              water treatment technology in use which is generally
              available to, and practicable for, the entire aluminum
              industry.
              The field work included the sampling of internal streams,
              in addition to the outfall, in order to develop
              specific information regarding unit operations
              within the plants.

The  data  obtained were analyzed to identify  the sources and volumes of
waste water produced, and the quantities of constituents  contained  in
the discharge.  On the basis of this analysis, the constituents of waste
water  which should be the subject of effluent limitations and standards
of performance were identified.

The range  of  control  and  treatment  technologies  practiced  by  the
aluminum  industry was identified from the industry profile and from the
plant visits.  In addition, other  technologies  applicable  to  primary
aluminum  plant  waste water control and treatment were identified.  For
each of the control cr treatment  technologies  the  resultant  effluent
levels  of  waste water constituents were determined and the limitations
and problems associated  with  each  technology  were  identified.   The
nonwater  quality  aspects  of each technology were evaluated including:
energy requirements, ether types of pollution  generated, and the cost, of
application.   From  this  information  base  the  various  alternatives
available  to  the  industry  for  reducing  pollutant  discharges  were
identified.

All of  the  information  thus  developed  was  evaluated  in  order  to
determine  what  levels  of technology constitutes the "best practicable
control technology currently available", the "best available  technology
economically  achievable",  and the "best available demonstrated control
technology, processes, operating methods, or other alternatives".
                   2§ne ral Description .of
                           Aluminum_Xndustry

This document presents recommended effluent  limitation  guidelines  and
standards  of  performance  for  the primary aluminum smelting industry,
                                   12

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             TABLE A.  SUMMARY OF FEATURES OF PLANTS VISITED
   Features                                              Number of Plants

Anode Type
  Prebaked                                                      5
  Horizontal Stud Soderberg                                     3
  Vertical Stud Soderberg                                       2

Air Pollution Control
  Wet                                                           7
  Wet and Dry                                                   3

Plant Age
  20-30 years                                                   6
  10-20 years                                                   2
  Less than 10 years                                            2

Plant Capacity
  Less than 100,000 tons/year                                   2
  100,000-200,000 tons/year                                     5
  More than 200,000 tons/year                                   3

Scrubber Water Treatment
  Cryolite precipitation with recycle                           6
  Lime precipitation with recycle                               1
  Lime precipitation - once through                             2
  None                                                          1
                                   13

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                                 Primary Aluminum

Date of Call	Contact
Name and Location of Plant 	
Age of Plant 	
Production: 	T/year, 	T/day, No. of lines	No. of Pots
Anode Type: PB 	, HSS 	, VSS 	
Fabrication at this site (rolling, drawing, etc.)	
Air Pollution Control Methods
   A. Primary (pot line):
   B. Secondary (pot room): 	
   C. Anode bake plant (PB only):
   D. Anode paste plant
   E. Cast house	
   F. Other
Present Water Treatment
   A. Pot line wet scrubbers
      1. Cryolite precipitation	 recycle
         a. Recovery of cryolite 	
         b. Discard cryolite 	 how
         c. Bleed from recycle	
         d. Bleed treatment
      2. Lime precipitation	 recycle
         a. Bleed from re-cycle	
         b. Bleed treatment 	
         c. Sludge disposal	
      3. Other
                 FIGURE B.  WASTEWATER QUESTIONNAIRE—TELEPHONE SURVEY

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B. Secondary air Scrubbers
   1. Treatment
C. Anode bake plant scrubbers
   1. Treatment
D. Anode paste plant scrubbers
   1. Treatment
E. Cast bouse scrubbers
   1. Treatment
F. Water from rod mill, drawing, etc.
   1. Operation	
      a. Treatment
   2. Operation
      a. Treatment
G. Cooling water
   1. Equipment cooled
   2. Additives
   3. Treatment or disposal
H. Boiler blow-down
   1. Boiler water and additives
              FIGURE B.  WASTEWATER QUESTIONNAIRE—TELEPHONE SURVEY
                                  (Continued)

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   2. Treatment or disposal
I. Other

   1. Source of wastewater
   2. Treatment
Planned Wastewater Treatment Modification
              FIGURE B.   WASTEWATER QUESTIONNAIRE—TELEPHONE SURVEY
                                  (Continued)

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standard industrial classification (SIC)   333U.   The  primary  aluminum
process is defined as the reduction of purified aluminum oxide (alumina)
to  produce aluminum metal.  A detailed process description is presented
in Section IV of this document.  The large-scale, economic production of
primary aluminum became possible when, in 1886, Charles Martin  Hall  in
the   United   States   and  Paul  Heroult  independently  invented  the
electrolytic process.  The Hall-Heroult process has remained essentially
unchanged since its inception, except for equipment design modifications
and  improvements  in  operating  practice,  and  is  employed  in   all
commercial  United  States production of primary aluminum.  The industry
has developed rather recently, the oldest plants having  been  built  in
the early 1940's.

There are 31 aluminum reduction plants in the United States with a total
annual  capacity  of  about 4,500,000 metric tons (5,000,000 short tons)
with about 60 percent of that capacity provided  by  the  three  largest
companies.   The  geographical distribution of aluminum reduction plants
is shown in Figure 1.  The availability of inexpensive electrical  power
is  a  major  consideration  in  site  selection  and  accounts  for the
concentration of plants in the Pacific Northwest and  in  the  Tennessee
Valley.  The energy consumed annually at full production is estimated to
be in the range of 80- to 100 billion kilowatt hours.

           General Features of the^Primajry Aluminum^Facility

A  detailed process description is given in Section IV of this document.
An overview of  the  primary  aluminum  facility  is  presented  in  the
following paragraphs.

The  reduction  of  alumina  to produce aluminum metal is carriid out in
electrolytic cells, or pots, connected in series to form a potline.  The
facility containing a number of potlines is referred to as the  potroom.
The  electrolysis  takes  place  in amolten bath composed principally of
cryolite, a double fluoride of sodium and aluminum.  Alumina is added to
bath periodically.  As electrolysis proceeds, aluminum is  deposited  at
the  cathode  and  oxygen  is  evolved  at the carbon anode.  The oxygen
reacts with the carbcn to produce a mixture of CO and CO2 and the  anode
is consumed.

Two  methods of replacing the anodes are practiced which are referred to
as the prebaked anode  (intermittent replacement) and the Soderberg anode
(continuous replacement).   For  either  system  the  anode  preparation
begins  in  the anode paste plant where petroleum coke and pitch are hot
blended.  For prebaked anodes the anode paste is pressed  in  molds  and
the anodes are baked in the anode bake plant.  The baked anodes are used
to replace consumed anodes and the anode butts are returned to the anode
preparation area.  In the Soderberg anode system, the anode paste is not
baked  initially  but  is  fed  continuously, in the form of briquettes,
through a shell into the pot.  As the paste approaches the hot bath  the
                                    17

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paste  is  baked  in  place  to  form  the  anode.  Soderberg anodes are
supported in the sleeves by vertical studs or by horizontal studs.

The continuous evolution of gaseous reaction products from the  aluminum
reduction  cell  yields  a large volume of fume which consists of carbon
dioxide, carbon monoxide, volatile fluoride  compounds,   sulfur  oxides,
and  fine  dust  evolved  from  the  cryolite and other bath components.
Ventilation systems are used to remove the fume from the  potroom.   The
ventilation  air must be scrubbed to minimize air pollution and both dry
and wet-scrubbing methods are used for this  purpose.   Water  from  wet
scrubbers  used  for air pollution control on potroom ventilation air is
the major source of waste water in the primary aluminum industry.

The liquid aluminum produced is tapped periodically  and  the  metal  is
cast  in  a  separate  casthouse facility.  The molten metal is degassed
before casting by bubbling chlorine or a mixed  gas  through  the  melt.
The  chlorine degassing procedure produces a fume which must be scrubbed
for air pollution control,

A few aluminum smelters have metal fabrication facilities, such  as  rod
mills,  rolling  mills, etc., on the primary reduction plant site.  Such
metal fabrication operations are to be covered under  separate  effluent
limitations  and  therefore  are not covered by the effluent limitations
recommended in this document.

The cathode of the aluminum reduction cell is a carbon  liner  on  which
the pool of molten aluminum rates.  A service life of two to three years
is  common.   During  service  the cathode becomes impregnated with bath
materials and erodes, and is periodically  replaced.   Water  contacting
spent  cathodes  have  a  significant  fluoride  content due to leaching
action.  Spent cathodes are either processed to recover fluoride  values
or  retained  in  a  storage  area.   Run-off from such storage areas is
contaminated with fluoride and cyanide.

The potential sources of waste  water  from  primary  aluminum  smelting
include:   1)  wet scrubbers used on potline and potroom ventilation air,
on anode bake furnace flue gas, and on casthouse gases; 2) cooling water
used in casting, rectifiers and fabrication,  and  3)  boiler  blowdown.
The  effluent  limitations and standards of performance developed herein
apply to all of the waste  water  streams  except  those  from  aluminum
fabrication and boiler blowdown.
                                  19

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                               SECTION IV



                        INDUSTRY CATgGORIZATION


                             Introduction


An  overview of the interrelationships of several significant  factors  of
in the potential categorization of  the  primary  aluminum  industry   is
presented  in  this  section.   A  detailed  description of the  aluminum
reduction process are then presented and the water uses and waste   water
sources  are  identified.   Finally, the rationale is developed  for con-
sidering primary aluminum smelting  as  a  single  subcategory  for the
purpose   of   establishing   effluent   limitations  and  standards   of
performance.


                     Cbj§ctives_of_Cate3or;ization


The  primary  purpose  of  industry  categorization  is  to  allow   t he--
development  of  quantitative  effluent  limitations  and  standards   of
performance which are uniformly applicable to  a  specific  category,,   or
snbcategory.   A  number  of  factors  have been considered as potential
bctses for subca-t-egorizatiori.  These factors were examined  to   determine
their effects on the quality or quantity of waste water produced, on  t:l
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The specific factors which were considered are:


    Anode Type

         Prebake
         Horizontal Stud Soderberg
         Vertical Stud Soderberg

    Air Pollution Control Method

         Hooding
         Gas Cleaning
         Dry Scrubbing
         Wet Scrubbing

              Once-through Water
              Recycle Water

    Anode Bake Furnace Gas (Prebake Anode Only)

         Wet Scrubbing
         Electrostatic Erecipitators


Anode_Type

The mechanics of various  anode  types  have  been  discussed  in  other
portions  of  this  report  and  in  the literature with the significant
differences as indicated in  Figures  2,  3,  and  4.   A  major  factor
recognized  by  this  study  is  that no Soderberg type plants have been
constructed  recently,  nor  have  any   been   predicted   for   future
construction  by  persons  contacted  during  this study.  The principal
advantage of this type of cell is the absence of a  requirement  for  an
anode baking furnace.

The  factors  of  electrode  type most pertinent to this study are those
related to air pollution control and include the efficiency  with  which
cells  using  the  various  anode  types  may  be  hooded, the nature of
emissions to the air associated  with  each  anode  type,  and  the  air
pollution  control devices applicable to each.  It is obvious that water
is not used directly in any of the types of anodes.
                                21

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The major effect of differences in anode type on water usage and streams
are that for prebake ancde plants, oell emissions (e.g., fluorides, SOx,
COx, etc.)  are separate from anode bake plant emissions (e.g., tars  and
oils,  etc.).  In Soderfcerg-type operations, all of these substances are
emitted from the cell area.  Current practices with  regard  to  control
(and water usage) are discussed below.


Hooding

The  efficiency of heeding of cells is a factor which determines the air
pollution control measures required.  In general, the results of current
practice are that if  (given proper  operation)   hoods  are  sufficiently
tight  and  efficient,  air  pollution  control  devices  may need to be
applied only to primary pot gas to meet atmospheric emissions standards.
This gas  may  be  characterized  as  containing  relatively  high  con-
centrations of pollutants and is suitable for treatment by either dry or
wet  gas cleaning devices.  If hooding is of lower efficiency, emissions
standards may necessitate the treatment of pot  room  or  secondary  air
which   may   be   characterized   as   containing   relatively   dilute
concentrations of pollutants, and the only practicable treatment  is  by
wet gascleaning devices.


Dry Scrubbing

Dry  gas-cleaning methods involve the use of dry alumina as an adsorbent
to remove pollutants from the pot gas.  This technology is discussed  in
detail elsewhere in this report as a method of controlling  (eliminating)
a  waste  water  stream.  The salient features of dry scrubbing are that
the adsorbent (alumina) subsequently is fed to the cells to  be  reduced
to aluminum metal, and that the recovery of fluoride values is virtually
complete.   As  mentioned above, dry scrubbing is applicable only to gas
streams with relatively high concentrations of  pollutants,  i.e.,  from
cells with highly efficient hoods.

The  total  recycle  cf  emissions  has associated with it the potential
problem of b,uild-up of trace metals and impurities in the product.


Wet_Scr_abbinc[

Wet gas-cleaning methods  as  practiced  in  the  industry  include  wet
electrostatic   precipitators,   tower-type  scrubbers,  or  spray  type
scrubbers, alone or  in  combination,  and  with  or  without  demisting
devices.   All  may  te classed as low pressure-drop devices, i.e., 1-10
inches of water.  No high energy venturi  type  scrubbers  are  used  in
current  practice.   toetscrubbing  devices  may  be  applied  to  either
relatively concentrated  (pot) or dilute (pot room) gases.
                                  25

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The scrubbing media are of paramount interest to this study and  may  be
described  in  terms  cf  recirculating  type  systems  or  once-through
systems.


Anode Bake Furnace Gas Scrubbers
    1 *   -—..»..i. —.     ____.^»    «_ *"—•*•

In prebake anode plants, the anode bake furnace gases may be  controlled
by  electrostatic precipitators or most commonly by wet scrubbers—again
of the "low"  pressure-drop types.   If wet scrubbers are used, the  waste
waters  contain  tars,  oils,  SOx,  COx  as  well as fluorides if anode
materials are recycled from the electrolytic cells.

Applications  of  electrostatic  precipitators  are  relatively  limited
because  of  hazards stemming from arcing and subsequent burning of tars
and oils  in  the  precipitators.    Gas  cooling  sprays  generally  are
applied, resulting in some waste water.  Such sprays are not designed to
scrub  fluorides,  although  some incidental scrubbing action may occur,
hence, the dry electrostatic precipitator  is  not  always  an  adequate
component  to  meet  fluoride  air  emissions regulation.  Baghouses are
unsuited to this purpose because of the blinding action of the tars  and
oils.   Thus,  wet  scrubbers  are  in  some cases the only adequate air
pollution control devices for anode bake furnaces at this time.


Current Practice

The current practices  as  determined  during  the  effluent  guidelines
program  are  indicated by the following annotated citations of existing
examples  illustrative  of  the  combinations  of  the   factors   under
discussion:

    A.  (1) Plant A.  Prebake Anode—totally dry scrubbing
                     en pot gas (zero water)

                     Anode Bake Plant—controlled firing

        (2) Plant C.  Prebake Anode—wet scrubbing on pot
                     gas, once-through water; dry scrubbing
                     on some pot gas

                     Anode Bake Plant—wet scrubbing

        (3) Plant D.  Prebake Anode—wet scrubbing of secondary
                     air; scrubber water recycle with two-stage
                     treatment before discharge

                     Anode Bake Plant—wet scrubbing with
                     once-through water
                                  26

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    B. (1)  Plant B
    C. (1)  Plant J.
       (2)  Plant F.
Vertical Stud soderberg—wet scrubbing
of pot gas - total recycle of scrubber
water * bleed stream evaporated - dry
scrubbing planned

Horizontal Stud Soderberg—wet scrubbing;
dry systems on paste plant

Horizontal Stud Soderberg—wet scrubbing
on pot gas once-through water; dry scrub-
bing planned
Some   noteworthy   factors  in  the  above  practices  include  further
variations  of  center-break  and  side-break  technologies  within  the
prebake  class of plants.  The center-break variation, where cell crusts
are broken and alumina charged at spots along the center of the cell  is
potentially  the  most amenable to tight hooding and dry scrubbing.  The
side-break technology is less amenable to tight  hooding  and  thus  may
lead  to  a choice of wet scrubbing of secondary air.  Major emphasis is
placed on the fact that the  anode  configuration  in  side-break  cells
allows  higher  electrical efficiency  (6 kwhr/pound)  relative to center-
break cells (7-8 kwhr/pound) .

The factor leading to the planned conversion of a verticalstud Soderberg
plant from wet scrubbing (but zero discharge of water) to dry  scrubbing
was a need to meet a stack opacity standard which was currently exceeded
during pin changes.

It  also  may  be  noted  that one horizontal-stud Soderberg plant has a
current compliance program  dependent  on  the  installation  of  a  dry
scrubbing system.


Summary

The  major  factors relating to discharge of water containing pollutants
have been identified  as  being  dependent  on  industry's  approach  to
controlling  both  air  pollution  and  water  pollution.   The  factors
entering into the decision between wet or dry gascleaning  systems  have
been  shown  to  include  cell  geometry  and electrical efficiency, air
pollution standards, and/or water pollution standards, trut not to depend
strictly on anode type, or climate.
                Alurninum Deduction_Prgcegs Description
                                   27

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The basic elements in the electrolytic process for reducing  alumina  to
aluminum are shown schematically in Figure 5,   Individual plant practice
may vary in specific details from that shown.


Raw MateriaIs

The  principal  materials  employed  in  the  primary  aluminum industry
include:   alumina,  cryolite,  pitch,  petroleum  coke:,  and   aluminum
fluoride.    Very  general  approximations  of  the  quantities  of  raw
materials used in the production of 1 kg  (2.2  Ib) of aluminum metal are:

         2 kg (4.4 Ib) alumina
         0.25 kg (0.55 Ib) pitch
         0.5 kg  (1.1 Ib)  petroleum coke
         0.05 kg (0.11 Ib) cryolite
         0.04 kg (0.08 Ib) aluminum fluoride
         0.6 kg  (1.3 Ib)  baked carbon
         22 kilowatt hours of electrical energy.


The Electrolytic Cel1

The heart of the aluminum plant is the electrolytic cell, or pot,  which
consists  of a steel container lined with refractory brick with an inner
liner of carbon.  The outside  dimensions  of  the  pot  may  vary  fro>m
1.8x5.5  to  4.3x12.8 meters  (6x18 to 14x42 feet) or larger.  Most cells
are around 1 meter  (3 feet)  in height.  The cells are arranged in  rows,
in  an  operating  unit  called  a potline, which may contain 100 to 250
cells electrically connected in series.  The electrical supply is direct
current, on the order of several hundred volts  and  60,000  to  100,000
amperes.   The carbon liner on the bottom of the furnace is electrically
active and constitutes the cathode of the cell when covered with  molten
aluminum.   The  anode  of  the  cell  is  formed  of baked carbon.  The
electrolyte consists cf a mixture  of  cryolite  80  to  85  percent  by
weight,  calcium  fluoride  5  to  7  percent,  aluminum fluoride 5 to  7
percent, and alumina 2 to 8 percent.  The composition of the bath varies
as electrolysis proceeds.  Alumina is added to the  bath  intermittently
to  maintain  the  concentration of dissolved alumina within the desired
range.  The fused salt bath usually is  operated  at  a  temperature  of
about 950°C.
                                  28

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         Petroleum  Coke
     CRUSHING
        AND
    CLASSIFYING
                 Pitch
     ANODE PASTE
     HOT - BLENDING
     PRESSING
     BAKING
              anodes
               cathodes
    BLENDING
     T     f
Anthracite  Pitch
COOLING
                                I  Soderberg
                                I  anode
                                  Briquettes
                                   	Electrical  Supply (Direct Current)
                                          Alumina
                'Cryolite
                 Calcium Fluoride
                 Aluminum Fluoride
                                                                        Air
FUSED SALT
ELECTROLYTIC
CELL
GASES, DUST
FUMES
GAS
SCRUBBING
MOLTEN ALUMINUM
To degassing and
casting


 Aluminum (pig,
 billet, ingot, rod)
                                                                     FT
         Dry-Process      Wet-Scrubbi
         Solids returned  liquor to
         to cell          treatment
'Spent Potliners (to cryolite recover
                or disposal)
              FIGURE 5.   PROCESS DIAGRAM FOR THE ELECTROLYTIC
                         PRODUCTION OF ALUMINUM
                                    29  -

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Cells  presently  in  use  operate  with current on the order of 100,000
amperes with a voltage drop across the cell of  about  4.5  volts.    The
reaction in the aluminum reduction cell is not completely understood,(1)
but results in the reduction of the aluminum from the apparent trivalent
state, assuming ionization in the molten salt, to the liquid metal  state
at  the  cathode.   Oxygen,  assumed present in the bath in the divalent
state, appears at the carbon anode and immediately reacts with the  anode
and surrounding constituents to form a  mixture  of  75  percent  carbon
dioxide and 25 percent carbon monoxide, which results in the consumption
of the carbon anode.

Thus,  the operation cf the electrolytic aluminum reduction cell results
in the continuous consumption of alumina and the carbon anode,  and  the
evolution  of  gaseous  reaction  products.   The  aluminum is withdrawn
intermittently from the bottom of the molten bath,  for  example,  by  a
vacuum  siphon  device,  at a rate of about 230 to 800 kilograms (500 to
1800 pounds) every 24 hours, although practice  may  vary.   The  molten
aluminum  is  collected  in  ladles  and cast into ingots or pigs as the
final product of the smelting process.

The continuous evolution of  the  gaseous  reaction  products  from  the
aluminum  reduction cell yields a large volume of fume which consists of
carbon dioxide and carbcn monoxide but also includes amounts of volatile
fluoride compounds, sulfur  oxides,  and  fine  dust  evolved  from  the
cryolite, aluminum fluoride, alumina, and carbonaceous materials used in
the  cell.   The  removal of this fume from the working area, as well as
the requirements  for  cell  cooling,  involves  extensive  air  quality
control  which may extend to the design of the plant building and hoods,
ducts, dust collectors, cyclones, and gas scrubbers.  These dust and air
pollution control measures are outstanding characteristics  of  aluminum
reduction  plants  and  account  for  a  major  use  of water if wet gas
cleaning methods are used.
The operation of aluminum reduction  cells  results  in  the  continuous
consumption  of anode material, about 0.5 kg of anode per kg of aluminum
produced.  This must te replaced either continuously (£3oderberg  anodes)
or  intermittently   (prebaked  anodes).  In either case, the thermal and
electrical properties of the anode are of primary importance for  proper
and economic operation of a cell.

The  raw  materials  fcr anodes (coke and pitch) must be prepared to meet
specifications by crushing, sizing, and blending.  These operations  are
conducted  in  the   so-called  anode  paste  plant which is an important
adjunct to every aluminum smelter.  The anode paste  consists  typically
of  a  mixture  of high-grade coke  (petroleum and pitch coke) with pitch
and sometimes tar, although the latter is  seldom  favored  in  American
practice.   Purity   requirements of the aluminum product demand very low
                                  30

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levels of ash, sulfur, alkali, and volatiles for  anode  raw  materials.
Maximum tolerance limits vary, but maximum limits normally are below 0.7
percent  ash,  0.7  percent  sulfur,  8  percent  volatiles, 0.5 percent
alkali, and 2 percent moisture.

The anode paste  preparation  plant  involves,  on  the  average,  rough
crushing,  screening, calcining, grinding, and mixing.  For this reason,
extensive dust control equipment normally is included in a paste  plant.
The  principal  difference  in  the  paste preparation plant for the two
types of anodes used in the industry is in the  pitch  handling  system.
Prebaked  carbon  anode plants utilize pitch having a softening point in
the range of 90 to 120 C  (200 to 250 F).  Soderberg anode plants can use
pitches ranging from soft, i.e., a softening point of 55 C  (130  F)  to
the  harder  pitches  used  in  the prebaked anodes.  Two types of pitch
handling systems are used within the industry:  solid-pitch handling and
liquid-pitch handling systems.  Solid pitch is handled with conventional
conveyors, feeders, and automatic scales; this frequently leads to  con-
siderable  dust  formation  which  if  not  controlled can result in air
pollution problems.  Liquid-pitch handling systems melt the pitch  using
either  steam,  electricity,  or  high-temperature  heat  transfer media
(hydrocarbon oils, gyclcls, or chlorinated biphenyls)  for  conventional
transfer using pumps and piping.  Special precautions must be taken when
using  liquid-pitch handling systems to avoid toxic chlorinated biphenyl
vapors and ignition hazards (from hydrocarbon oils).


Prebaked Anode System.  In the prebaked anode method the warm  paste  is
formed  into  anode blocks in a hydraulic press and the anodes are baked
and graphitized by a heating cycle that may, for example, last  30  days
with  a maximum temperature of 1100 C  (2000 F).  The flue gases from the
anode  bake  plant  contain  particulate  carbon,  tar  vapors,   sulfur
compounds,  and  the usual fuel-combustion products.  Fluorine compounds
also may be present depending on anode stub recycle practice.  The  tars
are  formed from cracking, distillation, and oxidation of the pitch used
as a binder  and  are  composed  essentially  of  high  boiling  organic
compounds.   When  the  flue  gases  are  treated  by  wet  scrubbing or
electrostatic precipitation, the water effluent contains tars and  oils,
sulfates, particulate matter, and in some cases, fluorides.

The  baked  anodes  are  supported  in  each cell by studs or rods which
conduct the current to the molten bath.  These studs are anchored at the
top of the anode by casting molten iron around the anode  cavity.   Once
in  place,  the  anodes  are individually adjusted in height to maintain
optimum interpole separation distance as they are consumed.

It is generally accepted that prebaked anodes have smaller anode voltage
losses than Soderberg anodes; this is ascribed  to  improved  electrical
contacts  between  the  current carrying studs and the anode in prebaked
anode systems.  Overall cell voltage  (including  bus  losses),  also  is
lower on the average for prebaked systems than for the Soderberg system.
                                    31

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This  is  reflected  in  power  consumption  figures  also are lower for
prebaked anode systems ty about 1  kwhr  per  kilogram  (2.2  pound)  of
aluminum.   On  the  ether  hand,  the  manufacture  of  prebaked anodes
requires higher initial capital investment as well  as  a  higher  labor
demand.


Soderberg_Anode_§Ystems.  In the case of the Soderberg continuous anode,
the  anode  paste  is  packed  into  a  rectangular metal shell which is
suspended above the  electrolysis  cell.   In  this  paste,   the  volume
concentration  of  aggregate  coke  is  of  the order of 55  percent, and
consists primarily of coarse and medium-size fractions.   As  the  anode
paste  descends  through  the  anode shell, it is gradually baked by the
heat of the cell and the current circulating through the partially baked
mix.  At a point approximately 50 cm (20 inches)  above the molten  bath,
the  anode  mass  becomes a fully baked, monolithic anode.  The tars and
oils characteristic of anode baking are evolved  at  the  cell  together
with the other fumes.

Two  configurations  presently  are  used  in  the  industry  to support
Soderberg anodes.  One employs vertical rods or pins and is referred  to
as  the  vertical  spike   (stud)  Soderberg system  (VSS); the other uses
horizontal pins, slanted at a slight angle, to support  the  anode  body
and  is  called  the horizontal spike  (stud) Soderberg system  (HSS).  In
either system, periodic adjustment of the position of the  holding  pins
is  required  to  maintain  interpole  distances  and  adequate  current
efficiency.  Because the pool of molten aluminum builds up at about  the
same rate as the anode is consumed, anode adjustment normally is made in
conjunction  with  metal  tapping  operations,  although  more  frequent
adjustments may be made to maintain a correct anode  position.   In  the
verticalstud  Soderberg  modification, the pin adjustments are made from
above the cell preventing the use of hoods directly over the anode.   in
this  case, the fumes escape to the pot room air.  However, a relatively
tight fitting skirt surrounds the lower zone between the anode form  and
the  bath.   The  flammable  hydrocarbon  compounds evolved in the final-
stages of baking are sufficiently concentrated to be ignited by a burnei:
as they, along with -the fumes from the bath, are removed from  the  cell
to  air  control  ducts.  In the horizontal stud Soderberg modification,,
pin adjustments must be made from the side of the cell  and  hooding  is
provided   above  the  cell.   This  arrangement  allows  more  complete
collection of cell gases but the  greater  volume  of  air  required  so
dilutes   the   hydrocarbon   vapors   that   they   cannot   be  burned
satisfactorily.
The electrolyte  in aluminum reduction cells served to  dissolve  alumina
which  is  the   raw  material  for  aluminum reduction, and to provide  a
molten bath with a melting temperature far lower than that  required  to
                                    32

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melt  alumina, and low enough to prevent extensive formation of aluminum
carbides.  The electrolyte must resist  chemical  decomposition  and  be
free  from  oxidizing agents.  The primary consideration in electrolytes
is, of course, to provide an adequate medium for dissolution of  alumina
and  subsequent  transport of aluminum and oxygen ions to the electrodes
for reduction-oxidation  reactions.   In  addition,  fused  electrolytes
should fulfill the following requirements:

    o  They should have a density, while in the molten
       state, lower than that of molten aluminum.

    o  They should have adequate fluidity and low electrical
       resistance at the operating temperatures

    o  They should not te volatile at the operating
       cell temperatures

    o  They should contain no elements which will react
       with aluminum and permanently impair product quality.

Natural  or  artificial  cryolite,  a  double  fluoride  of  sodium  and
aluminum, meets these requirements and is universally used as the  major
constituent  in  aluminum reduction cells.  Other advantages of cryolite
are that it produces no slag or dross to be  eliminated  from  operating
cells,  and it can be produced from abundant and inexpensive supplies of
fluorspar, aluminum hydrates, and caustic soda.

Cryolite melts at about 1000°C.  Addition of 5 to 15 percent of  alumina
to  cryolite  lowers  the  melting  temperature  to  values below 910 C;
further addition of alumina will cause rapid increases  in  the  melting
point  of the electrolyte and are to be avoided.  It is customary to add
other  salts  to  improve  the  temperature,  density,  solubility,  and
resistance  characteristics  of  the electrolyte.  For example, aluminum
fluoride commonly is added  in  modern  practice  to   (a)  maintain  the
aluminum  ratio in cryolite, (b) replace fluorine losses,  (c) neutralize
residual sodium oxide present in  the  alumina  feed,  and   (d)  prevent
sodium  contamination  of the molten product.  Other salts commonly used
include sodium fluoride, soda ash,  fluorspar,  calcium  fluoride,  and,
occasionally,  sodium  chloride.   Use  of  -these  salts  is a matter of
individual industrial practice and preference.  In general, these  salts
will  affect  the  melting  point,  the electrical conductivity, and the
density of the electrolyte.

Additions of calcium fluoride, aluminum fluoride and alumina affect  the
electrolyte   resistivity.   Consumption  of  these  salts  varies  with
individual company practice, but usually ranges from 0.02 to 0.05 kg per
kg of aluminum produced.  Cryolite and alumina  consumptions  vary  from
approximately  0.03 to 0.05 kg of cryolite per kg of aluminum, metal, and
about 2 kg of alumina per kg of aluminum.
                                   33

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The alumina used in electrolytic cells  is  commonly  of  two  types,  a
semicoarse  aggregate,  sometimes  containing  agglomerated material and
called alumina sand, and a finer product called flour alumina  which  is
used preferentially in Europe.

Molten  electrolytes  in  industrial  cells  can be as deep as 36 cm (1U
inches), but the anode-cathode separation distance is only of the  order
of 5 cm (2 inches).  In normal cell operation, the operating temperature
of  the  bath  is  not  sufficient to maintain all of the electrolyte in
molten condition.  This leads to formation of a frozen crust of cryolite
at the surface of the electrolyte which provides thermal insulation  for
the  bath  and  minimizes  vaporization  of  bath components.  The crust
normally supports a layer of alumina  feed  and  provides  a  convenient
method  for  intermittent  additions  of  alumina by breaking the frozen
cryolite crust.


Cathode_Disposal_Practice

In an operating primary cell the pool of aluminum metal is the  cathode.
This  pool rests in a carbon container variously formed of carbon blocks
and a rammed mix of anthracite and pitch which forms  a  liner  for  the
cast iron structure of the cell.

It  is  essential  fcr purity of the product aluminum arid the structural
integrity of the cell that the molten aluminum be isolated from the  iron
shell.  A service life cf up to  three  years  may  be  attained  for  a.
properly  installed  liner in a well managed cell but an average life of
between two and three years is reported to be more common.

Upon failure of a liner, the cell is emptied, cooled, and  removed   from
the  cell room to a working area.  By mechanical drilling and/or soaking
in water, the shell is stripped of old  lining  material  which  may be:
processed  through  a  wet  cryolite  facility  for recovery of fluoride?
values or simply set aside in a storage yard.

Water which has contacted the spent pot-lining material, whether it  has
been  used  deliberately  in  shell  cleaning  or it is run-off from the
storage yard, has a significant fluoride content and carries most of the;
cyanide originating in a primary aluminum plant.  Such waters ordinarily
are joined with ether plant streams for treatment prior to discharge.

An estimation indicates that the accompanying solids-disposal problem is
not large, amounting to about 1200 cubic meters  (about one acre foot) of
liner waste per United States plant per  year.   The  following  assumed
values  were used in this estimation:  4.5 x  106 metric tons per year  (5
x  106 short tons per year) total US aluminum  production:

         450 kg  (1000 Ib) aluminum/cell/day
         726 day average liner life
                                   34

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         15 cm (6 inches) thick liner in 5.5 x 1.8 x
           0.9 meter  (18 x 6 x 3 foot) shell
         30 plants


A nc i 1 1 §. r y_Oj3er a t i o n s

Primary aluminum  plants  require  various  supportive  activities.   In
addition  to  the cell room, anode paste plant, and anode bake plant  (in
plants where prebaked anodes are employed)  the  primary  plant  includes
various   air  pollution  control  devices,  a  metal-casting  facility,
electric power generation or  rectification  and  a  sanitary  treatment
system.  Some plants carry out a further aluminum refining step and some
practice rolling, drawing or other metal fabrication operations.
             W a £§£ Ug §9§_iD-i^le_ ££iffiS£Y_ Aluminum Industry
Primary  aluminum smelters use water for sanitary purposes, boiler feed,
cooling  circuits  applied  to  d-c  power  equipment,   metal   casting
operations,  fume  scrubbing,  furnace  cooling  in  the anode plant and
miscellaneous equipment  cooling.   Cooling  waters  may  be  circulated
through  a cooling tower, passed through several units in series or used
as a once-through basis, with various discharge  practices.   The  major
contaminating  use  of water is in the fume scrubbing operations  (if wet
systems are used) associated with the anode  plant,  casting  operations
and the aluminum reduction cells.  Here practice varies from oncethrough
methods  to  a closed circuit with removal of constituents and recycling
of water.

The approaches to fume control include:

    (1)  No scrubbing

    (2)  Wet scrubbing using once-through water  (dis-
         charged with or without treatment)

    (3)  Wet scrubbing with recirculation of water
         and reclamation of contained fluorides,
         alumina, etc., often through precipitation
         of cryolite

    (4)  The use of dry scrubbing systems using no
         water, which allow reclamation of fume
         components

Current economic and environmental pressures have brought  much  of  the
industry  to  states   (2) ,   (3)  and   (4) above.  The dry fume scrubbing
method  is  being  installed  in  some  of  the  plants  recently  under
                                   35

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construction,  and  has  been  or  is  being  installed  to  replace wet
scrubbers in some of the older plants.  The dry  fume  scrubbing  system
reduces  plant  water requirements to sanitary, boiler feed, and cooling
needs.  Thus, the potential exists for the elimination of air pollution,
a large decrease in discharges of process-contaminated  wastewater,  and
the  reclamation  and  recycle  of  formerly wasted materials.  However,
problems have existed in the application of dry scrubbing  to  Soderberg
potline  fumes,  caused by the hydrocarbons evolved during anode baking.
One company has a demonstration dry scrubbing process on one of nine HSS
potlines.  The company plans ultimately to convert to dry  scrubbing  at
all  of its plants.  Another company plans to convert its VSS plant to a
dry-scrubbing process by 1975-76.  The dry  scrubbing  of  vertical-stud
Soderberg cell gas is considered by the company to be a reliable measure
since it has been demonstrated at overseas plants of U.S. corporations.

A  more detailed discussion of water usage and stream characteristics is
given in Section V of this document.
                        Industry Categorization
Industry Profile
In order to determine the role that various factors might  play  in  the
consideration   of   potential  subcategorization,  a  matrix  of  basic
information was compiled for the industry.  This information,  presented
in  Table  1,  includes  plant location, production capacity, plant age,
anode type, air-polluticn control methods and water  treatment  methods.
A  summary  of  the  distribution  of plants exhibiting each descriptive
feature as determined from the information in Table 1 is  given  in  the
following listing:


           Feature                      No. of_Plants

Current Production, jnetric tons/year

      90,000  (100,000 T/yr)                    6
     90,000 to 180,000  (100,000 -             18
        200,000 T/yr)
      180,000  ( 200,000 T/yr)                  7

Anode Type

     Prebaked                                 19.4
     Horizontal Stud Soderberg                 7
     Vertical  Stud Soderberg                   4.6

Air Pollution  Control Method
                                   36

-------



























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Air  Pollution Control Method

     Primary, Potline Air
          Wet Scrub, all or part              22
          Dry Scrub, all or part               8

     Secondary,  Potrocm Air
          Wet scrub                            6

     Anode Paste Plant
          Wet Scrub                            4
          Dry Scrub                           10


     Anode Bake Plant
          Wet Scrub                            2
          Dry Scrub                            2

     Cast House
          Wet Scrub                            3

Treatment of Scrubber Liquor

     Cryolite recovery, liquor recycle         8
     Precipitation, settling of solids,
        and recycle or discharge of liquor    15

Age of Plant

      10 years                                 6
     10 to 25 years                            9
      25 years                                 5


Pyimary_Aluminum_as.a^Single Category

After  review  of the information compiled in Table lr and consideration
of  the  various  factors  related  to  the  application   of   effluent
limitations,  it  has  teen concluded that the primary aluminum industry
should be considered as a single category, and that effluent limitations
and standards of performance be applied uniformly.


Rationale.  The recommendation that the  primary  aluminum  industry  be
considered   as   a   single   category  is  based  upon  the  following
considerations:

     (1)  All primary aluminum producers currently use
         the Hall-Hercult process.

     (2)  The major difference in water use and waste-
         water generation lies in the use of wet or
         dry potline fume scrubbers.
                                  38

-------
    (3)   Dry fume scrubbing is still developmental with
         respect to horizontal-stud Soderberg installations;  therefore
         it is not feasible for all plants in the primary aluminum
         smelting industry.

    (U)   The exemplary technologies for control and
         treatment of aqueous fluoride discharges, i.e.,
         precipitation cf fluoride with removal of the
         precipitate and recycle of the water, as
         described in Section VII, can be applied to
         fluoride-containing waters from any of the
         sources commcn to primary aluminum plants.
         In addition, these technologies produce a
         concomitant reduction in suspended solids and
         oil and grease levels.

    (5)   Application cf the identified "best practicable
         technology currently available" by all plants
         which use wet scrubbers will result in a marked,
         industry-wide reduction of pollutant emissions.

    (6)   Plants which employ dry fume scrubbing will be
         able to meet the effluent limitations as established.

    (7)   Only about 12 percent of the aluminum plants
         employ dry fume scrubbing for potline air or
         anode bake plant flue gas, hence, a separate
         category and separate effluent limitations
         applicable to plants with dry scrubbing is not
         warranted.


Factors Considered in Categorization

The recommendation fcr establishing a  single  subcategory  for  primary
aluminum  is  based on the interrelationships among many factors.  Those
factors are discussed briefly in the following paragraphs to further set
forth the rationale fcr considering primary aluminum smelting  a  single
subcategory.


Process.   All  United States aluminum smelting is currently done by the
Hall-Heroult  process.   Since  no  significant  modifications  are   in
commercial  practice  at  this  time, all discussion will relate to this
basic process.

For the future other processes must be considered.   However,  in  their
development  emphasis  has been placed on the economies of environmental
control so that operation within recommended effluent guidelines can  be
expected.
                                   39

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Recently,  the  development  of  a  new  process  was announced in which
aluminum is produced by the  electrolysis  of  aluminum  chloride.   The
process  eliminates  the  use  and  consequent  emission  of  fluorides.
Chlorine is recycled in the closed  system.   The  process  is  said  to
require  30  percent  less  energy  than  the Hall/Heroult process.  The
company plans a 15,000 ton-per-year pilot plant which is expected to  be
operating  in  1975 and which could be expanded to 30,000 tons per year.
No performance data are available for documentation of this development,
and  a  technical  judgment  regarding  the  ultimate  impact  of   this
technology cannot be made at this time.

Development  work  is  proceeding on a process for producing aluminum by
reduction of aluminum chloride with manganese.  The  manganese  chloride;
produced  is  converted to the oxide to recover the chlorine for recycle
and the oxide is then reduced and the iranganese is recycled.  Advantages
claimed for the process include reduced capital and operating costs, and
applicability to many domestic aluminum-bearing minerals.  A pilot plant
is planned for mid-1974 operation.  No performance  data  are  available;
for  this  process  and  it  has not been considered with respect to the
effluent limitations.
             The type of anode employed by aluminum smelters,  prebaked,
horizontal stud Soderberg, or vertical stud Soderberg does not result in
any significant differences in waste effluent from the plant.

However, the air pollution control options are determined in part by the
anode  type.   The  option  to choose dry gas-scrubbing is not available
currently for horizontal stud Soderberg pot lines, or for secondary  air
pollution control.

In  those cases where the use of water is required, treatment technology
is  available  to  achieve  the  recommended  limitations.    Therefore,
subcategorization  by  anode  type and/or existing air pollution control
systems is not necessary.
             A review of 31 aluminum  reduction  plants  showed  that  6
plants  have  capacities  of less than 90,000 metric tons  (100,000 short
tons) per year, 16 plants have capacities  between  90,000  and  180,000
metric tons  (100,000 and 200,000 short tons)  per year, and 9 plants have
capacities  greater  than  180,000  metric tons  (200,000 short tons) per
year.  No factors relating  to  this  distribution  of  plant  size  and
pertaining  to  a  given plant's ability to achieve effluent limitations
have  been  encountered.   There  is  the  possibility   that   economic
constraints on the smaller plants may become a significant factor.  This
point  must  be  evaluated  further when the economic impact of effluent
limitations on the overall industry is considered.
                                   40

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Elant_Ac[e.  Primary aluminum smelting is a relatively new industry based
on a single process.  Therefore, the earliest plants built in the  early
1940's  are  electrochemically  the  same as those built today; however,
numerous modifications have been made in process  operation  which  have
resulted   in   greater  production  efficienty  and  reduced  pollutant
emissions.  As a result, neither the level of constituents  in  effluent
water  nor the capability to meet the recommended limitations is related
to plant age.  Because cf the general  uniformity  of  aluminum  process
technology,  the  application  of most environmental control methods and
systems that have been developed is dependent on factors other than age,
i.e., for the Hall process, the most recently developed unit  operations
are  used  and  these  are able to be retrofitted independently of plant
age.


Product.  Aluminum smelters produce aluminum metal and various  aluminum
alloys.   Some  plants  carry out an additional refining step to produce
higher purity aluminum and a few plants also carry out rolling and wire-
drawing operations.  The refining step is  basically  the  same  as  the
production  operation  and  does not represent a separate category.  The
fabrication operations are to be covered under separate effluent  guide-
lines,   therefore,   fabrication  is  not  established  as  a  separate
subcategory


Raw Ma te rials.  The basic  raw  material,  alumina,  is  received  in  a
refined  and  purified  form.   Other  raw  materials  which may be used
include  cryolite,  flucrspar,  sodium  fluoride,  soda  ash,   aluminum
fluoride, and coke and pitch for anodes.  Variations in raw materials do
not  have  a significant effect on the water treatment methods employed,
therefore, subcategories based on raw materials are not warranted.
                 Tne option of selecting total impoundment  of  effluent
for solar evaporation of water as a means of achieving zero constituents
discharge  is  open  to existing plants in two areas of continental U.S.
Plants located in South  Texas  and  the  region  east  of  the  Cascade
Mountains  in  Washington, Oregon, and Montana may expect water deficits
of from twelve  to  thirty  inches  per  year. (2,3)   Adoption  of  this
technology depends on such other factors as:

    (1)  Local and short-term rainfall-evaporation
         balances

    (2)  Cost and availability of land which can be
         made suitable from topographic and soil
         structure points of view

    (3)  Nature and amounts of constituents in the
         effluent
                                   41

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    (4)   Wind stability of the dried residues

    (5)   Integration of this technique with in-plant
         recovery of all possible reusable constituents
         and water.

Since  the  areas  where  the  climatic conditions are amenable to total
impoundment are limited,  impoundment  cannot  be  cited  as  technology
available  to  the  entire industry.  However, since any plant that, can
practice impoundment will be  able  to  meet  the  recommended  effluent
limitations.  A separate category and separate effluent limitation based
on geographical location are not warranted.

Summary.   Tne  quality  and  quantity  of  waste water constituents are
similar throughout the  primary  aluminum  industry  and  they  are  not
influenced  greatly  by  any of the factors considered above.  Likewise,
the engineering feasibility of  waste  water  treatment,  the  resulting
effluent  reduction achievable, and the cost of the applied controls and
treatments, are  not  significantly  affected  by  any  of  the  factors
considered.   Therefore,  the  recommended  effluent  limitations may be
applied  uniformly  to  the  primary  aluminum  industry  as  a   single
subcategory.
                                   42

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                               SECTION V



                        WASTEDCHARACTERIZATION


                             Introduction


The  sources of waste water within the primary aluminum industry are set
forth  in  this  section.   The  kinds  and  amounts  of   waste   water
constituents are identified and the relationship between the control and
treatment  technology  applied  and  the  resultant effluent loadings is
described.


                        Sources of Waste Water


A composite flow diagram  of  water  use,  treatment  and  disposal  for
primary  aluminum  plants  using wet-scrubbing methods for air pollution
control is shown in Figure 6.  In any specific plant, the data will vary
and a stream or unit illustrated may not exist.  Treatment of  water  at
the  source (1) depends upon the quality required and varies from simple
chlorination at well-heads for control of algae  and  bacteria  to  full
clarification  and  treatment of river intake water.  Stream  (2) is made
potable and the effluent is discharged through a sewage  disposal  unit.
Stream  (3)  is  make-up water to a closed-loop cryolite recovery stream
(8) which may or may not include a potroom secondary air scrubber.   The
combination  of  materials  added  during  cryolite recovery varies from
plant  to  plant  as  seme  cryolite   recovery   systems   are   highly
sophisticated  (and proprietary) chemical manufacturing facilities, while
others  are operated as byproduct recovery or water treatment units with
either disposal or recycling of the solids.  The  bleed  stream   (9)  is
required  to  limit  the buildup of sulfates in the recovery loop.  Some
plants do not practice cryolite  recovery,  in  which  case  Stream  (9)
represents  the  once-through discharge.  stream (U) through a casthouse
furnace air scrubber is common but plans exist to eliminate  the  stream
in several plants by changes in degassing techniques to minimize noxious
fumes  or  by the installation of a dry system for collection of alumina
and occluded hydrogen chloride.  Streams  (5)  and   (6)  are  not  common
since  dry processes prevail; however, where there is a liquid effluent,
the carbon particulates are  usually  settled  in  ponds.   Segments  of
Stream  (7)  are treated to promote wetting and to inhibit corrosion and
algae growth.
                                   43

-------
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The  chief  effluent  constituent  is  oil  from  rod  mills  or   other
fabrication  units,  when  present;  thus  the  use  of  commercial  oil
separators is common.

From this generalized picture a number of  potential  sources  of  waste
water can be identified, including:

         o  Wet scrubbers

              Primary pctline
              Secondary potroom
              Anode bake plant
              Cast house

         o  Cooling water

              Casting
              Rectifiers
              Fabrication

         o  Boiler blcw-down.

The  constituents  of  the  waste  water  from each of these sources are
identified in the following paragraphs.

Wet_Scrubbers

2£im§£y._P2£line_AjLj:_Scrubbery.  The wet scrubbers  which  collect  fumes
and dust from the electrolytic cells are the source of most of the waste
water constituents frcm primary aluminum plants.  Carbon dioxide, carbon
monoxide,  and  hydrogen  fluoride  are  generated  in  the overall cell
reaction.  In addition, cryolite vaporized from the molten bath,  sulfur
oxides  produced  from sulfur impurities in the anode, and dust from all
materials handled at the cell, i.e., alumina, cryolite, and fluorides of
calcium and aluminum contribute to  the  scrubber  liquid  loading.   In
those plants using a Soderberg anode system in which the anode paste mix
is  based  at  the cells, volatile hydrocarbons and additional oxides of
sulfur also are collected in the scrubber  liquor.   The  quantities  of
materials  handled  at  the  cells, as well as the evolution of gas, are
proportional to the quantity of metal produced.  Since the efficiency of
scrubbers in receiving water-soluble gases and dust from the primary air
(that collected from the cells) is uniformly high, above 96 percent, the
quantity of materials collected in the liquor is  also  proportional  to
the production of aluminum metal.

Secondary	Potroom	Air_Sgrubbers.  Since, even with the best hooding of
cells, fumes and dust escape, some plants exhaust the pot room air  from
the  roof line through wet scrubbers.  The constituents of this scrubber
liquor  are  similar  to  those  from  the  primary  air  scrubbers  but
ordinarily  constitute  less  than  10  percent  of  the  total amounts.
                                    45

-------
Because the large volume of air handled in secondary scrubbers makes the
capture efficiency relatively low, most plant engineers prefer  improved
hooding at the cells ever secondary scrubbing of room air.

Anode	Bake	Plant	Air	§££ubh>ers.   Primary  aluminum  smelters  using
prebaked anodes have an associated anode bake plant.  The flue gas  from
the   anode   bake   furnace   is   treated  in  wet-scrubbers  at  some
installations.  The resulting  liquor  contains  acid,  tars,,  oils  and
sulfur  oxides  from  the  baking  operation,  and  particulate  carbon.
Fluorides may be present depending upon  anode  stub  recycle  practice.
Such  a  stream is not suitable for processing through a recovery system
which returns solids to the electrolyte cells.  Therefore, it usually is
added to other  effluent  streams,  treated  to  promote  settling,  and
diverted  to  ponds,  the  overflow  from which is ordinarily mixed with
other plant effluent streams.

Casthouse_Air_Scrubbers.  A third section  of  primary  aluminum  plants
which  may  employ wet scrubbing is the casthouse.  Molten aluminum from
the cells is degassed by bubbling chlorine through the melt, usually, in
modern practice, mixed with nitrogen and carbon  monoxide.   This  batch
operation  is  carried cut in gas-fired holding-alloying furnaces and is
adjusted according to specifications of the particular order being cast.
If the off-gas from the furnace is scrubbed, depending on the gas  used,
an  acidic  liquor is produced containing dissolved chlorine,, chlorides,
and suspended alumina.  The quantities of these constituents  are  quite
variable depending on the extent of degassing and time in the cycle.  in
one  plant  degassing  was under way from one fourth to one third of the
time.

Cooling Waj:er

Cooling  water  is  used  for  aluminum  casting,  for  electrical   and
mechanical  equipment,  and in anode preparation.  The usual additive is
chlorine for minimizing algae growth.  The  major  fraction  of  cooling
water flows in closed systems.  That portion not recirculated usually is
discharged without treatment.

Ot he r _ Sour ce s_ of_ W a s t e_ Vjater

In  addition  to  the  sources  of waste water considered above, general
housekeeping and the manner of collection and disposal of  rain  run-off
affects  the total plant effluent.  This ordinarily includes the run-off
from a used cathode storage or disposal area which is the source of most
of the cyanide constituent in plant effluent.  In addition,  liquid  and
solid  spills  usually  are  flushed into this system.  Treatment varies
widely from reprocessing through  cryolite recovery to simple discharge.
                                  46

-------
                             Effluent Loadings


The waste water from  the  several  potential  sources  discussed  above
usually  are  joined  into  a  common plant outfall.  Quantitative waste
water data were  obtained  from  Corps  of  Engineers  Discharge  Permit
Applications and from a number of companies directly.  The original data
are  analytical  determinations  of  the  concentrations  of waste water
constituents.  The concentrations can be converted to effluent loadings,
in kilograms of pollutant per metric ten of  aluminum  produced   (Ib/ton
Al), by means of the following equation:

Effluent Loading = CFK/F kg/metric ton Al (Ib/ton Al), where:

    C = concentration of pollutant in mg/1

    F = stream flow in cubic meters/day  (gal/day)

    P = production in metric tons Al/day  (tons Al/day)

    K = 10-3 (kg x l)/(mg x cubic meters) or 8.345 x 10~6
        (Ib x l)/(mg x gal), the conversion factor required
        to obtain the proper units.

A  wide  variation  exists in the concentrations and flow encountered in
primary aluminum plants.  As an illustration of  the  effluent  loadings
which  result  from  various arbitrary conditions, a matrix of flow rate
versus concentration for a production rate of 455 metric tons Al per day
 (500 tons Al per day) is given in Tables 2 and 3, where the  values  are
given in metric and English units respectively.


Plant Data

The  actual effluent loadings calculated from effluent concentration and
flow data obtained for eleven companies  are  given  in  Table  4.   The
control  and treatment technology practiced by each plant is as follows:
The original data froir vvhich these effluent loadings were calculated are
presented in Table 4A through  4K.   In  those  cases  where  data  were
obtained  for  several separate discharges from a single plant, separate
tables are given for each pipe.  The effluent loading was calculated for
each constituent from each pipe  and  totalled  to  obtain  the  overall
effluent loadings given in Table 4.
                                 47

-------








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-------
          TABLE 4A1 .  CONCENTRATIONS OF SELECTED CONSTITUENTS IN
                       INFLUENT AND EFFLUENT WATER, PRIMARY ALUMINUM
                    Plant A, Pipe 001, Volume 165,600 gpd
                             Influent          Effluent            Net
                          Concentration*    Concentration *    Concentration
      Constituent         	mg/1             mg/1	    	mg/1	
Alkalinity                       23                27                 4
Chemical Oxygen Demand          110                62                 Neg
Total Solids                     62                74                 12
Dissolved Solids                 41                60                 19
Suspended Solids                 10                11                  1
Sulfate
Chloride                         3.7               3.7                 0
Cyanide
Fluoride
Aluminum
Calcium
Copper
Magnesium
Nickel
Sodium
Zinc                             0.01              0.01                0
Oil & Grease                     Nil               Nil                 0
Phenol

 *  Source RAPP
                                    51

-------
          TABLE 4A2 .  CONCENTRATIONS OF SELECTED  CONSTITUENTS  IN
                       INFLUENT AND EFFLUENT WATER,  PRIMARY ALUMINUM
                    Plant A, Pipe 002, Volume 28,800  gpd

                             Influent         Effluent            Net
                          Concentration *   Concentration *   Concentration
      Constituent         	mg/1             mg/1	   	mg/1
Alkalinity
Chemical Oxygen Demand
Total Solids
Dissolved Solids
Suspended Solids
Sulfate
Chloride
Cyanide
Fluoride
Aluminum
Calcium
Copper
Magnesium
Nickel
Sodium
Zinc
Oil & Grease
Phenol  ,

  * Source KAPP
31
4
51
38
0
25
3.4
0.0
7.1
0.0
4.3
0.0
2.5
1.6
Nil
33
15
87
63
1
24
2.4
0.4
8.6
0.0003
4.3
0.020
1.8
15.4
Nil
2
11
36
25
1
Neg
Neg
0.4
1.5
-
-
0.02
Neg
13.8
_
                                    52

-------
31
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51.
38.
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31
111.
143
111
18.0
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106.9
92
73.
18.
          TABLE 4 A3.  CONCENTRATIONS OF SELECTED CONSTITUENTS IN
                       INFLUENT AND EFFLUENT WATER, PRIMARY ALUMINUM
                    Plant A , Pipe 003, Volume  360,000 gpd
                             Influent          Effluent            Net
                          Concentration     Concentration     Concentration
      Constituent         	mg/1	         mg/1	    	mg/1
Alkalinity
Chemical Oxygen Demand
Total Solids
Dissolved Solids
Suspended Solids
Sulfate
Chloride                         3.4                3.0               Neg
Cyanide
Fluoride                         Nil              Nil
Aluminum                         0.0                0.0005
Calcium
Copper                           0.0                0.040            0.04
Magnesium
Nickel                           0.0                0.0003           0.0003
Sodium
Zinc
Oil & Grease
Phenol  ,

 *  Source-RAPP
0.0
1.6
Nil
0.0002
18.
Nil
0.0002
16.4
_
                                    53

-------
          TABLE 4B1 .  CONCENTRATIONS OF SELECTED CONSTITUENTS IN
                       INFLUENT AND EFFLUENT WATER, PRIMARY ALUMINUM
                    Plant B, Pipe 1* , Volume 150,000 gpd

                             Influent          Effluent            Net
                          Concentration     Concentration **  Concentration
      Constituent         	mg/1             mg/1	    	mg/1	
Alkalinity                                         100
Chemical Oxygen Demand
Total Solids
Dissolved Solids
Suspended Solids                                    20
Sulfate                                             50
Chloride                                          1000
Cyanide
Fluoride
Aluminum
Calcium
Copper
Magnesium
Nickel
Sodium
Zinc
Oil & Grease                                        10
Phenol

   *  Concentrations are reported "not to exceed"
  **  Source- Company Report
                                    54

-------
          TABLE 4 B3.  CONCENTRATIONS OF SELECTED CONSTITUENTS IN
                       INFLUENT AND EFFLUENT WATER, PRIMARY ALUMINUM
                    Plant B, Pipe 4*  , Volume  150,000gpd

                             Influent          Effluent            Net
                          Concentration     Concentration**   Concentration
      Constituent         	mg/1             mg/1	    	mg/1	
Alkalinity                                        125
Chemical Oxygen Demand
Total Solids
Dissolved Solids
Suspended Solids                                   30
Sulfate                                           100
Chloride                                         1000
Cyanide
Fluoride
Aluminum
Calcium
Copper
Magnesium
Nickel
Sodium
Zinc
Oil & Grease                                       10
Phenol

 *  Concentrations are reported "not to exceed".   Ste  -,1- if .
**  Source-Company Report
                                    55

-------
          TABLE 4B2 .  CONCENTRATIONS OF SELECTED CONSTITUENTS IN
                       INFLUENT AND EFFLUENT WATER, PRIMARY ALUMINUM
                    PlantB , Pipe 3* , Volume 350,000 gpd

                             Influent          Effluent            Net
                          Concentration     Concentration **  Concentration
      Constituent         	mg/1             mg/1	mg/1	
Alkalinity
Chemical Oxygen Demand                             50
Total Solids
Dissolved Solids
Suspended Solids                                   20
Sulfate                                           100
Chloride                                         1000
Cyanide
Fluoride
Aluminum
Calcium
Copper
Magnesium
Nickel
Sodium
Zinc
Oil & Grease                                       10
Phenol  ,
   *  Concentrations are reported "not to Exceed".
  **  Source-Company Report
                                    56

-------
          TABLE 4 B4 .  CONCENTRATIONS OF SELECTED CONSTITUENTS IN
                       INFLUENT AND EFFLUENT WATER, PRIMARY ALUMINUM
                    Plant  B, Pipe  5* , Volume 150,000 gpd
                             Influent          Effluent            Net
                          Concentration     Concentration **   Concentration
      Constituent         	mg/1             mg/1	    	mg/1
Alkalinity
Chemical Oxygen Demand                            75
Total Solids
Dissolved Solids
Suspended Solids                                  20
Sulfate                                           50
Chloride                                         900
Cyanide
Fluoride
Aluminum
Calcium
Copper
Magnesium
Nickel
Sodium
Zinc
Oil & Grease                                      10
Phenol  ,

  *  Concentrations are reported as "Not to exceed"
 **  Source-Company Report
                                    57

-------
          TABLE 4 C .  CONCENTRATIONS OF SELECTED CONSTITUENTS IN
                       INFLUENT AND EFFLUENT WATER, PRIMARY ALUMINUM
                    Plant c , Pipe    , Volume 18,800,000 gpd
      Constituent
Alkalinity
Chemical Oxygen Demand
Total Solids
Dissolved Solids
Suspended Solids
Sulfate
Chloride
Cyanide
Fluoride
Aluminum
Calcium
Copper
Magnesium
Nickel
Sodium
Zinc
Oil & Grease
Phenol  ,
   Influent
Concentration *
     mg/1
      1.0
   Effluent
Concentration *
    mg/1
      1.5
     Net
Concentration
     mg/1
50
10
95
92
3
7.5
12
152
113
27
Neg
2
57
21
24
       0.5
0.16
0.033
30
0.004
0.005
0.005
1
0.047
0.0
32
1.13
41
0.011
0.007
0.004
4
0.146
2.9
31.8
1.1
11.
0.007
0.002
Neg
3
0.099
2.9
 *  Source-RAPP
                                      58

-------
          TABLE 4 D  .  CONCENTRATIONS OF SELECTED CONSTITUENTS IN
                       INFLUENT AND EFFLUENT WATER, PRIMARY ALUMINUM
                    Plant D, Pipe    , Volume  1,220,000  gpd
                             Influent          Effluent            Net
                          Concentration*    Concentration*    Concentration
      Constituent         	mg/1             mg/1	    	mg/1	
Alkalinity                                         50
Chemical Oxygen Demand                             39
Total Solids                                      511
Dissolved Solids                                  496
Suspended Solids                                   18
Sulfate                                           217
Chloride                                           69
Cyanide
Fluoride                                           16
Aluminum                                           1.6
Calcium
Copper
Magnesium
Nickel
Sodium                                            101
Zinc                                               0.08
Oil & Grease                                        2
Phenol  ,

 *  Source-Company Report
                                      59

-------
          TABLE 4 Fl.  CONCENTRATIONS OF SELECTED CONSTITUENTS IN
                       INFLUENT AND EFFLUENT WATER,  PRIMARY ALUMINUM
                    Plant F, Pipe  2 , Volume 1,800,000 gpd

                             Influent          Effluent             Net
                          Concentration     Concentration *    Concentration
      Constituent         	mg/1             mg/1	    	mg/1	
Alkalinity
Chemical Oxygen Demand
Total Solids
Dissolved Solids                                  442
Suspended Solids                                    9
Sulfate                                             71
Chloride                                            78
Cyanide
Fluoride                                            55
Aluminum
Calcium
Copper
Magnesium
Nickel                                            0.07
Sodium
Zinc
Oil & Grease                                      5.2
Phenol
  *   Source-Company Report
                                      60

-------
          TABLE 4 F2 .  CONCENTRATIONS OF SELECTED CONSTITUENTS IN
                       INFLUENT AND EFFLUENT WATER, PRIMARY ALUMINUM
                    Plantp , Pipe  3  , Volume 17,000,000 gpd

                             Influent          Effluent            Net
                          Concentration     Concentration*    Concentration
      Constituent         	mg/1             mg/1	    	mg/1	
Alkalinity
Chemical Oxygen Demand                             151
Total Solids
Dissolved Solids                                   396
Suspended Solids                                   116
Sulfate                                            117
Chloride                                           50
Cyanide
Fluoride                                           115
Aluminum                                           34
Calcium
Copper                                             0.074
Magnesium
Nickel                                             0.157
Sodium
Zinc
Oil & Grease                                       12
Phenol  ,

 *  Source-Company Report
                                     61

-------
          TABUS 4 G .  CONCENTRATIONS OF SELECTED CONSTITUENTS IN
                       INFLUENT AND EFFLUENT WATER, PRIMARY ALUMINUM
                    Plant G, Pipe    , Volume 20,000,000 gpd

                             Influent          Effluent            Net
                          Concentration*    Concentration**   Concentration
      Constituent         	mg/1             mg/1	    	mg/1	
Alkalinity
Chemical Oxygen Demand
Total Solids
Dissolved Solids
Suspended Solids
Sulfate
Chloride
Cyanide
Fluoride
Aluminum
Calcium
Copper
Magnesium
Nickel
Sodium
Zinc
Oil & Grease
Phenol  ,
  *  Source-RAPP
  **  Company Report
2
20
0.7
8
10
0.004
6.7
0.001
13
0.02
3.2
0.001
30
62
30
12
21
0.01
7
0.05
17.6
0.03
3.9
0.2
28
42
29.3
4
11
0.006
0.3
0.05
4.6
0.01
0.7
0.199
                                     62

-------
          TABLE 4 HI.  CONCENTRATIONS OF SELECTED CONSTITUENTS IN
                       INFLUENT AND EFFLUENT WATER, PRIMARY ALUMINUM
                    Plant H, Pipe 1  , Volume  430,000gpd
                             Influent          Effluent            Net
                          Concentration     Concentration *    Concentration
      Constituent         	mg/1             mg/1	    	mg/1	
Alkalinity
Chemical Oxygen Demand
Total Solids
Dissolved Solids                                   305
Suspended Solids                                   750
Sulfate
Chloride
Cyanide
Fluoride                                            24
Aluminum
Calcium
Copper
Magnesium                                           75
Nickel
Sodium
Zinc
Oil & Grease
Phenol

 *  Source-Company Report, Influent values  not  available.
                                     63

-------
          TABLE 4 H2 .  CONCENTRATIONS OF SELECTED CONSTITUENTS IN
                       INFLUENT AND EFFLUENT WATER, PRIMARY ALUMINUM
                    Plant H, pipe 2  , Volume 700,000 gpd

                             Influent          Effluent            Net
                          Concentration     Concentration *   Concentration
      Constituent         	mg/1             mg/1	    	mg/1	
Alkalinity
Chemical Oxygen Demand
Total Solids
Dissolved Solids                                  933
Suspended Solids
Sulfate
Chloride
Cyanide
Fluoride                                           20
Aluminum
Calcium
Copper
Magnesium                                          70
Nickel
Sodium
Zinc
Oil & Grease
Phenol  ,

 *  Source-Company Report. Influent Values not Available.
                                     64

-------
          TABLE 4 H3.  CONCENTRATIONS OF SELECTED CONSTITUENTS IN
                       INFLUENT AND EFFLUENT WATER, PRIMARY ALUMINUM
                    Plant H, Pipe  3 , Volume  36,000 gpd

                             Influent          Effluent            Net
                          Concentration     Concentration *   Concentration
      Constituent         	mg/1	         mg/1	    	tng/1	
                                                •
Alkalinity
Chemical Oxygen Demand
Total Solids
Dissolved Solids                                 7,730
Suspended Solids
Sulfate                                            900
Chloride
Cyanide
Fluoride                                         1,400
Aluminum                                            70
Calcium                                            120
Copper
Magnesium                                          100
Nickel
Sodium                                           2,500
Zinc
Oil & Grease
Phenol  ,

 *  Source-Company Report. Influent Values  not Available.
                                    65

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          TABLE 4 H4.  CONCENTRATIONS OF SELECTED CONSTITUENTS IN
                       INFLUENT AND EFFLUENT WATER, PRIMARY ALUMINUM
                    Plant H, Pipe 4  , Volume  40Q,OOOgpd

                             Influent          Effluent            Net
                          Concentration     Concentration *   Concentration
      Constituent         	mg/1             mg/1	    	mg/1	
Alkalinity
Chemical Oxygen Demand
Total Solids
Dissolved Solids                                  920
Suspended Solids
Sulfate
Chloride
Cyanide
Fluoride                                         33.1
Aluminum                                          65
Calcium
Copper
Magnesium                                         60
Nickel
Sodium
Zinc
Oil & Grease
Phenol  ,

  *  Source-Company Report.  Influent Values  not Available.
                                     66

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          TABLE 4 I  .  CONCENTRATIONS OF SELECTED CONSTITUENTS IN
                       INFLUENT AND EFFLUENT WATER, PRIMARY ALUMINUM
                    Plant I, Pipe    , Volume  1,720,000  gpd

                             Influent          Effluent            Net
                          Concentration *   Concentration *    Concentration
      Constituent         	mg/1	         mg/1	    	mg/1
Alkalinity
Chemical Oxygen Demand
Total Solids
Dissolved Solids
Suspended Solids
Sulfate
Chloride
Cyanide
Fluoride
Aluminum
Calcium
Copper
Magnesium
Nickel
Sodium
Zinc
Oil & Grease
Phenol

 *  Source-Company Report
59
2
335
322
9
24
104
0
0
0
32
0
11
0.01
52
0.04
4
174
30
1,065
797
268
80
270
0.05
15.
0.2
83
0.05
30
0.02
140
0.02
10
115
28
730
475
259
56
166
0.05
15
0.2
51
0.05
19
0.01
88
Neg
6
                                     67

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          TABLE 4 J .  CONCENTRATIONS OF SELECTED CONSTITUENTS IN
                       INFLUENT AND EFFLUENT WATER, PRIMARY ALUMINUM
                    Plant J, Pipe    , Volume  13,700,000 gpd

                             Influent          Effluent            Net
                          Concentration *    Concentration**   Concentration
      Constituent         	mg/1	         mg/1	    	mg/1
Alkalinity
Chemical Oxygen Demand
Total Solids
Dissolved Solids
Suspended Solids
Sulfate
Chloride
Cyanide
Fluoride
Aluminum
Calcium
Copper
Magnesium
Nickel
Sodium
Zinc
Oil & Grease
Phenol
  *  Source-RAPP
 **  Source-Company  Report
162
6.4
278
263
15
0.1
14
0.01
0.2
0.078
44.8
0.004
12
16
0.036
0.2
270
12.
604
568
33
12
30
0.046
10.2
4.4
63.4
0.081
14
177
0.48
2.1
108
5.6
326
305
18
11.9
16
0.036
10.

18.6
0.077
2
161
0.44
1.9
                                    68

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          TABLE 4 K .  CONCENTRATIONS OF SELECTED CONSTITUENTS IN
                       INFLUENT AND EFFLUENT WATER, PRIMARY ALUMINUM
                    Plant K, Pipe    , Volume  3,760,000 gpd
                             Influent          Effluent            Net
                          Concentration *   Concentration **   Concentration
      Constituent         	mg/1             mg/1	    	tng/1	
Alkalinity                      120              99                  Neg
Chemical Oxygen Demand
Total Solids
Dissolved Solids
Suspended Solids
Sulfate
Chloride
Cyanide
Fluoride
Aluminum
Calcium
Copper
Magnesium
Nickel
Sodium
Zinc
Oil & Grease
Phenol  ,
 *  Source-RAPP
 **  Source-Company Data
260
230
30
5
45
0
0.6
1.5
35
0.02
8.
0
40
0.02
0
300
265
35
117
60.6
0.028
22
3.2
32
0.06
7.5
0.035
117
0.05
4.3
40
35
5
112
15.4
0.028
21.4
1.7
Neg
0.04
Neg
0.035
77
0.03
4.3
                                     69

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    Plant
              Anode
          Control or Treatment^Applied
      A
      B
      C
      D
      E
      F
      G
      H
      I
      J
      K
 PB
VSS
 PB
 PB
 PB
HSS
VSS
 PB
HSS
HSS
 PB
Dry scrubbing
Lime/recycle
Li me/one e-through
Cryolite/recycle
Cryolite/recycle
None
Lime/once-through
Cryolite/recycle
Cryolite/recycle
Cryolite/recycle
Cryolite/recycle
The  significance  of  the  data  given in Table 4 may be illustrated by
noting  the  effluent  leadings  for  fluoride.   Of  the  eight  plants
reporting  fluoride values, five (D, H, I, J, K) are in the range of 0.5
to 1 kg/metric ton Al (1 to 2 Ib/ton Al)  and each  of  the  five  plants
practices  cryolite  precipitation  and  recycle.   Plant  B  uses  lime
precipitation with recycle to achieve 0.6 kg/metric ton Al (1.2  Ibs/ton
Al)  Plants  C  and  G  use a once-through lime precipitation and report
effluent loadings of 5 to 10 kg/metric ton Al   (10  to  20  Ib/ton  Al).
Plant  F  practices  no  water  treatment and the effluent loading is 15
kg/metric ton Al (30 Ib/ton Al) .

The practice of precipitating cryolite or calcium  fluoride  from  waste
water  is designed primarily to reduce fluoride emissions and to recover
fluoride values.  However, the plant data show that  there  is  also  an
attendant  reduction in the discharge of suspended solids and of oil and
grease.  This aspect is discussed in Section VIZ of this document.  This
effect is shown graphically in Figure 7 in which  the  effluent  loading
values for suspended solids from Table 4 are plotted versus the fluoride
effluent  loading  for several plants.  There is considerable scatter in
the data resulting frcm plant-to-plant variations in practice  and  from
the  fact  that  some  data represent net effluent values; while others,
through lack of inlet water analytical data, represent  gross  effluent.
However,  the  correlation  of  suspended solids discharge with fluoride
discharge is apparent.   The  corresponding  data  for  oil  and  grease
effluent  versus  fluoride effluent also is plotted in Figure 7.  Again,
the correlation is apparent in spite of  the  expected  scatter.   These
data indicate that control and treatment methods designed for the reduc-
tion  of  fluoride emissions result in the reduction of suspended solids
and oil and grease emissions as well.
                                    70

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                             Plant Identification Letter
g
4J
1-" C
•U O
01 -U
a
•a
o
m
fr
3
eo
                   O  Suspended Solids


                   Q  Oil and Grease
                                                                                       c
                                                                                       o
                                                                                       u c
                                                                                       4J O
                                                                                       c
                                                                                       n
                                                                                       A
                                                                                0.OS-

                                                                                CO. 1)
                             Fluoride Emissions, kg/metric  ton

                                                  (Ib/ton)
             FIGURE 7.  CORRELATION OF PLANT DATA  ON SUSPENDED SOLIDS, OIL AND GREASE,

                        AND FLUORIDE EMISSIONS
                                        71

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¥§£ i figation Analysi s

In order to verify  the  effluent  loadings  associated  with  exemplary
control  and  treatment practice, sampling and analysis were carried out
at three plants.  The plants were selected as exemplary  representatives
of  various  precipitation  and  recycle  approaches  to the control and
treatment of waste water.  These plants were judged to be  exemplary  on
the  basis of the reported effluent data.  One plant chosen precipitates
a high purity cryolite and includes spent  cathode  reclamation  in  the
circuit.   The  second  plant  uses a simpler cryolite process while the
third employs a calcium chloride precipitation of the cryolite filtrate.

                                        Company       Verification
                                         Data           Analysis
                                       Jayerage)_
               Suspended solids, mg/1     18               25
               Fluoride, mg/1             16                7
               Oil and grease, mg/1        2                4

The agreement is considered  good  in  spite  of  the  brief  period  of
verification  sampling.   The  concentration of each constituent is well
within the maximum range as reported by Plant D.  It will be noted  that
the   above  values  are  gross  values.   No  subtraction  of  influent
concentrations was made.

The concentration data reported by Plant J and the average concentration
obtained  in  the  verification  analysis  for  samples  taken  at   ten
consecutive shifts are listed in the following tabulation:

                                        Company        Verification
                                        _Data __        ___ Analysis __

                Suspended solids, mg/1    15.6             15.8
                Fluoride, mg/1            10.2             10.1
                Oil and grease, mg/1       2.1              1.7

The correlation is good.

The  results  of  the verification sampling at Plant K are compared with
plant data in the following tabulation.  The verification data  are  the
averages of three 24-hour composite samples.

                                        Company         Verification
                                        Rej3ort_         __ Analysis __

            Suspended  sclids, mg/1        35                 44
            Fluoride, mg/1                22                 10
            Oil and grease, mg/1           4.3                4.1
                                     72

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As in the previous tabulations, the agreement is good.



                Source^cf Waste Water from Developmental
                      Aluminum Reduction^P£O.ce_sses


Pilot-plant  studies  of  the  chloride  electrolytic  process  for  the
production of primary aluminum indicate that a wet gas  scrubber  system
will  be  used  which  will  have  a  discharge  containing chlorine and
chlorides.  The concentrations to be expected  are  not  known  at  this
time.  A blowdown from cooling towers also is expected to be discharged.
                                     73

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                               SECTION VI



                   SELECTION OF POLLUTANT PARAMETERS


                          Selected^ Parameterg


The  following  waste  water constituents are the significant pollutants
from the primary aluminum smelting sufccategory:
         Fluoride
         Suspended solids
         Oil and grease
         pH
         Free cyanide
The rationale for the  selection  of  these  constituents  and  for  the
rejection  of  ether  constituents  as  pollutants  is  presented in the
following paragraphs.


          Rationale_for the Selection of_£ollutant_Paramgters

Fluoride

Fluoride ion is one of the more significant pollutants  associated  with
the  primary  smelting  of  aluminum.  Fluoride concentrations currently
range from 10 mg/1 in the effluent from well-controlled treatment plants
to 30 mg/1 where less effective fluoride control is applied to the waste
water.  The presence of fluorides in the effluent stems  primarily  from
wet scrubbing of gases for air-polluticn control.

Suspended Solids

Suspended  solids  present in the discharge from primary aluminum plants
have their origin in wet scrubbing of particulates from gases and in the
precipitation of solids from  the  waste  water  for  fluoride  control.
Concentrations  of  suspended  solids currently range from 5 to 30 mg/1.
Relatively unsophisticated methods are available for  the  treatment  of
waste  water to decrease the suspended solids content.  Suspended solids
are included as a pollutant subject to effluent limitations in order  to
assure  that  treatment  for  fluoride  control  is followed by adequate
settling of  the  resultant  precipitates  and  that  the  discharge  of
fluorides among other suspended solids is minimized.

Oil and Grease
                                     74

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Volatile  hydrocarbons  are  evolved during the anode baking process and
are collected in wet scrubbers employed for air pollution control.   The
hydrocarbons  associated with anode baking are indefinite in composition
and are referred to as "tars" in the industry.  These organic  materials
can  be  determined  analytically  by  hexane  extraction  which  is the
standard method applied for the analysis of organic materials classed as
"oil and grease".  Currently, the effluent concentrations range  from  1
to  10  mg/1 of oil and grease.  Treatment methods are available in that
fluoride control also achieves a decrease in the oil and grease  levels.
This  may  be  followed,  if necessary, by oxidation in aerated lagoons.
Water used in contact cooling of castings may contain low concentrations
of wetting agents.
Acid streams are produced in wet scrubbing of potline air and  casthouse
and  anode  bake plant gases.  Alkaline streams are produced by cryolite
recovery or other types of  Such  streams  are  often  mixed  to  effect
neutralization.   In  the  event that these streams are not sufficiently
balanced stoichiometrically, additional neutralization can be  performed
to maintain the discharge within the recommended limits.

Free_Cy_anide

Cyanide is contained in the run-off from spent cathode storage areas and
is  detectable  in  the effluent from seme primary aluminum plants.  The
reprocessing of spent cathodes for cryolite  recovery  also  results  in
cyanide  discharges.   The  free cyanide levels encountered in the plant
surveys were low, ranging in concentrations from 0.002  to  0.036  mg/1.
Conventional  treatment  technology, alkaline chlorination, is available
to effectively destroy cyanide in industrial waste water.

          Rationale fcr the Rejection of _Pollutant Parameters

Other waste water constituents identifiable with  the  primary  aluminum
industry  that  are not the subject of effluent limitations or standards
of performance are as follows:

         Total dissolved solids
         Chloride
         Sulfate
         COD
         Temperature
         Trace Metals


Total Dissolved Solids

Total dissolved solids includes fluorides, chlorides, sulfates, and  the
common  cations, sodium, potassium, magnesium, and calcium.  The maximum
                                     75

-------
concentration of dissolved solids reported by most plants  surveyed  was
less  than  1000  mg/1.   It has been concluded that the present cost of
treatment to reduce the level of dissolved solids is such that treatment
of dissolved solids is beyond the scope of the technologies  defined  by
"best practicable" or "best available".

Chlgrjde

Chloride  concentrations  in  discharged  waste water range from 0 to 16
mg/1 in the primary aluminum industry.  Conversion of chlorine degassing
of molten aluminum to other  technologies  will  decrease  the  observed
levels.    There  is  no  suitable  treatment  currently  available  for
decreasing the levels further.


Sulfate

The sulfur impurities in  various  raw  materials,  such  as  pitch  and
petroleum  coke  used  in  anode preparation, are converted to oxides of
sulfur which are  collected  in  wet  scrubbers  as  sulfates.   Sulfate
concentrations  range  from  5  to  100  mg/1  in primary aluminum plant
effluents.  Sulfate is partially  removed  by  fluoride  treatment.   As
fluoride discharges are controlled sulfate levels will decrease.

Chemical_OxYgen_Demand __ {COD)_
A  COD component associated with organic materials is present in primary
aluminum  smelter  discharges.   Control  of  oils  and  grease  (hexane
extractables)  indirectly controls COD.

Temperature

Heat  loads  are  comparatively  small in the primary aluminum industry.
Maximum temperature differentials  of  the  discharge  vary  with  plant
location.   The  control  and  treatment  technologies  identified  have
associated retention times  of  various  duration  which  will  tend  to
control the temperatures of the outfall.


Trace^Metals

Trace metals have not been included in the list of significant pollutant
parameters.  Measurable quantities of zinc, copper, and nickel are found
in  the  effluents  from  primary  aluminum smelters; however, there are
insufficient data available on which to base  effluent  limitations  and
standards of performance.
                                     76

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                              SECTION VII
                    CONTROL AND TREATMENT TECHNOLOGY


                              Intreduction

The  existing  -technologies  for  controlling  waste water volume in the
primary smelting of aluminum include dry fume scrubbing, and recycle  of
water  to  wet  scrubbers  after  precipitation of fluorides.  Treatment
methods  for  reducing  pollutant   concentrations   include:   cryolite
precipitation,  precipitation  by  lime or alum, adsorption on activated
alumina or hydroxylapatite, and reverse osmosis.

As set forth in Section VI, the constituents of waste water from primary
aluminum smelters which are to be  considered  as  pollutants  of  major
significance  are  fluoride,  suspended solids, oil and grease, and free
cyanide.  These pollutants in the discharge  water  originate  from  the
operation  of  wet  scrubbers  on  the potline, pot room, and anode bake
furnace, and from cryolite recovery  from  potlinings  where  practiced.
Minor  sources  of  pollutants  include: cast house wet scrubbers, anode
paste plant wet scrubbers, rectifier cooling, cast house cooling, boiler
blowdown, and rainfall runoff.

Current control and treatment practice varies throughout  the  industry.
Therefore,  the  steps  required  to  be  taken  in order to achieve the
effluent limitations recommended in this document  will  vary  depending
upon  the  current  status  of each plant.  A generalized summary of the
variation in current practice and optional control and  treatment  modes
applicable  to  each  source of waste water is given in Table 5.  In the
following paragraphs, each of the technologies included in  Table  5  is
described,  the degree of effluent reduction achieved by each technology
is identified and finally, optional routes for achieving the recommended
effluent limitations are identified.


                           Control Technology


In the context of this document the term control  technology  refers  to
any  practice  applied  in  order  to  reduce  the volume of waste water
discharged.  In the  primary  aluminum  industry  the  most  significant
reduction  in  discharge  volume  is  obtained  by  converting  wet fume
scrubbers to dry fume scrubbers or by treating and recycling  the  water
from wet scrubbers.
                                  77

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          TABLE 5.  SUMMARY OF PRESENT AND POTENTIAL CONTROL AND
                    TREATMENT TECHNOLOGIES
Wastewater
  Source
Present Practice
  Possible
Added Control
    Possible
Added Treatment
Pot (primary)
wet scrubber
Discharge with-
out treatment
      "             Lime and settle
                    once-through

      "             Cryolite or line
                    ppnt.  with recycle

Potroom (secondary) Discharge without
wet scrubber        treatment
                    Lime and settle
                    once-through
Cast house
wet scrubber

Anode bake
plant wet
scrubber

Paste plant
wet scrubber

Cast house
cooling

Rectifier
Cooling
Rainfall runoff
Settle
Settle
Settle
Discharge with-
out treatment

Discharge with-
out treatment
Discharge with-
out treatment
Convert to
dry scrubbing

Install cryolite
or line pptn plus
recycle with bleed
Install recycle
with bleed
                     Install cryo-
                     lite or line pptn.
                     plus recycle

                     Install recycle
Convert to alter-
nate degassing

Recycle
Recycle


Close loop
Convert to
air-cooled recti-
fiers

Route to cryo-
lite recovery and
recycle
                                         Install lime treat-
                                         ment of bleed stream

                                         Install alumina
                                         adsorption

                                         Install lime treat-
                                         ment of bleed stream
                    Install alumina ad-
                    sorption
Flocculate and
aerate
Cooling tower


Cooling tower
                                      78

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Dry Scrubbing of_Pot^Ga§


Identification.   The  dry  scrubbing  of pot gas refers to the use of a
system of air polluticn control by primary  aluminum  smelters  for  the
removal  of pollutants from the gases evolved from the electrolytic cell
(pot)  by contacting the gases with dry alumina to effect the sorption of
pollutants  and   subsequently   collecting   particulates   by   fabric
filtration.   The  system  is  applicable to gases collected immediately
above the pot, i.e., pot gas, having relatively higher concentrations of
constituents than does pot room ventilation  air.   The  system  is  not
applicable to the latter because of the relatively dilute concentrations
of constituents.

The outstanding features of the system are the sorbtion of emitted gases
on  alumina  which  is  subsequently fed to the pots to produce aluminum
product, the associated return of sorbed fluorine compounds to the pots,
and the generally high levels of collection efficiency for both  gaseous
fluorine  compounds  and particulates, e.g., greater than 99 .percent  (in
terms of gas delivered to the device).  The process uses no water.


Process	De scr ip_ti on.   The  elements  of  the  dry  scrubbing   process
(indicated  in  Figure 8)  include hoods and ducts to collect and deliver
the gases from the pots to an  operating  unit,  usually  located  in  a
courtyard  between  potline buildings, possibly a cyclone type device to
separate coarse particulates, a reactor section in which the  gases  are
contacted  with  the  alumina, and a fabric filtration stage, from which
the gases are released to  the  atmosphere,  usually  through  a  stack.
Associated  equipment  includes  fans,  alumina  delivery,  storage, and
removal devices, and taghouse auxiliary equipment.

Three  commercial  variations  of  the  process  exist,  with  differing
mechanisms,  principally  in  the  contactor  stage.  In one type of dry
scrubber, the contacting  of  gas  and  alumina  is  accomplished  in  a
fluidized  bed, with the fabric filters, or a baghouse at the top of the
same chamber.

In another design, the air at relatively high velocity is  blown  upward
through  a venturi throat, into which alumina is injected downward.  The
result is extremely turbulent mixing of the solid and gas in the  throat
and  in  the  several-fcot  high column above the throat.  The gases and
eluted solids are drawn from the  column  and  thence  to  the  baghouse
stage.

In  the  third  design,  the  collected gases are drawn at high velocity
through a horizontal duct with the alumina being injected downward  into
the moving gases.
                                  79

-------











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Again,  turbulent mixing and intimate contact of gases and solids occur,
with the gases subsequently drawn through a baghouse.

In some cases the gases may be passed  through  a  cyclonic  device,  to
remove  the larger particulates before the gas-alumina contacting stage.
Another variation of application includes the routing of the exit  gases
from  the  baghouse  to  a  wet  scrubber  to  achieve further cleaning,
particularly of sulfur oxides.  In one specific application,  associated
with  vertical  stud  Soderberg cells, the particuldtes collected in the
baghouse stage are, because of hydrocarbon content, sent to  storage  or
subjected  to  a  special treatment to remove the hydrocarbons and allow
the alumina to be charged to the pots without  adverse  effects  on  pot
operation.

The  dry  scrubbing  system  depends  on  the  phenomenon of sorption of
fluorine compounds on the surface  of  the  alumina.   Highest  sorption
rates,  i.e.,  highest  collection  efficiency,  is  observed during the
formation of the initial monomolecular  layer  on  the  surface  of  the
alumina.   Thus,  operation  of this system is strongly dependent on the
surface area of the alumina and the exposure or contact time.   Sorption
decreases rapidly after the formation of the first monolayer.

The  above  factors lead to practices where all the alumina input to the
pots, i.e., all the major raw material  for  the  plant,  is  first  put
through  the air pollution control system.  Thus, current practices tend
toward what is referred to as a "100 percent feed".


A££linability-  As stated previously, there are three variations of  the
dry  scrubbing  process available, froifi each of three manufacturers; one
in the United States, one in Canada,  and  one  in  Europe.   All  three
designs are in operation on the commercial scale, in one case the system
has  been  operated  for  as  long  as  five  years.   To  date,  proven
applications have been on prebake  anode  and  vertical  stud  Soderberg
anode   cells.   No  production-scale  application  to  horizontal  stud
Soderberg type operations exists in the United States, although  a  test
unit  serving  several  pots  of  this  type  is  being evaluated by one
producer.

The applicability of any one of the specific systems to a specific plant
is influenced by the characteristics of the alumina used at  the  plant.
In  general,  the  fluidized-bed  design is most compatible with "sandy"
type alumina, i.e., 50 percent -325 mesh  material.   This  material  is
readily  fluidized.  Published data on the evaluation of alumina for use
in the fluidized bed showed one type of  "floury"  alumina   (50  percent
-325 mesh) not to fluidize and to be difficult to handle and feed in the
equipment,  although  mesh  size  is  not  the only factor which must be
considered.  Other designs have varying compatibilities  with  different
forms  of  aluminas.  The form of alumina available to a given plant may
be a constraint in the selection or  application  of  the  dry-scrubbing
                                   81

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process,  involving some tradeoff in terms of the system selected or the
sources of alumina.

In one existing prebake anode installation in the United States  hooding
efficiencies  are  lower  than  necessary to achieve required collection
efficiencies and wet scrubbing is used to clean potroom air.  collection
and treatment systems are separate.

One European installation uses the dry scrubbing process  on  pot  gases
and  wet scrubbing of pctroom air, but with routing of the exhaust gases
from the dry scrubber baghouse to the wet scrubber for removal of sulfur
oxide components.

Dry scrubbing control methods are being installed in the  United  States
on  both  new  plants  and  existing  plants,  and  serve  as methods of
achieving both air and water pollution control.  When the dry system  is
properly   operated   with   efficient   hooding,  relatively  stringent
atmospheric emissions limits may be satisfied, without the use of water.
Thus, the dry scrubbing  process  is  of  major  significance  to  water
pollution control at primary aluminum smelters.
Identification.  Water from wet scrubbers can be treated in various ways
to  remove  impurities  so  that  the  partially  purified  water can be
continuously returned to the wet  scrubber.   In  the  case  of  primary
potline  and  secondary potroom wet scrubbers, the fluoride dissolved in
the water can be precipitated and settled.  This treatment  reduces  the
suspended solids and oil and grease content at the same time.


Process __ Detail.   In  general,  the  method  used to remove the soluble
fluoride values from the waste water is precipitation either as cryolite
or as calcium fluoride.  In the first case, sodium  aluminate   (or  NaOH
and  hydrated alumina) is added; and in the second, a lime slurry  (or in
one case CaCl2) is used.  After precipitation, thickening of the  slurry
is accomplished in clarifiers or thickeners.

The  treatment  of  wet  scrubber  liquors  to  recover  cryolite  is  a
significant  practice  because  it  removes  a  sufficient  quantity  of
fluoride  to  permit recycle of the treated liquor to the scrubbers, and
in the process recovers the fluoride in a  form  which  usually  can  be
returned  to  the aluminum electrolysis bath.  The value of the cryolite
thus recovered represents a  credit  to  the  treatment  process.   Full
recycle  cannot be achieved by this treatment because of the presence of
sulfates in the liquor.  Sulfur impurities in the raw  materials,  prin-
cipally  in  the petroleum coke and pitch used in anode preparation, are
converted to sulfur oxides during electrolysis and are collected in  the
                                  82

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scrubber  water  as sulfates.  If 100 percent recycle of the liquor were
practiced the solubility of sodium sulfate would eventually be exceeded.
Therefore, a small bleed is maintained from the scrubber liquor  circuit
to  keep  the  sulfate  concentration  sufficiently  low to prevent pre-
cipitation of sodium sulfate.  This bleed stream is  relatively  low  in
volume  but high in fluoride content and it represents the major portion
of the fluoride effluent from the entire plant.  The  actual  volume  of
bleed  required  is related to the sulfur content of the coke and pitch.
This sulfur value is expected to rise as the demand for low sulfur  fuel
increases.   Further  treatment of this bleed stream is not practiced in
the industry at this time.

The recycle system consists of utilizing the clarified overflow from the
thickener tanks as the scrubbing medium.  A  schematic  diagram  of  the
process is shown in Figure 9.

The  liquor  leaving the scrubber, containing about 1-2 g/liter fluoride
is reacted (about 1-2 minutes' residence  time)  with  sodium  aluminate
forming  cryolite.   This  stream  is  then  sent to the thickener where
suspended solids  are  settled  out.   These  suspended  solids  contain
cryolite  (about 30 percent by weight), carbon  (5-15 percent), and other
insoluble solids which have been collected by the  wet  scrubbers.   The
supernatent  clarified  liquor  from  the  thickener  is recycled to the
scrubbers.

The  slurry  from  the  bottom  of  the  thickener  tank  at  a   solids
concentration of from 200-500 g/liter is then filtered to remove some of
the  liquid,  and the sclid cake  (about 60 percent solids) is then dried
in a kiln or multiple hearth furnace.  If the cryolite is  pure  enough,
it  can  be  returned tc the reduction pots at this point; if not, it is
landfilled.  In some cases, the filtrate is further  treated  to  reduce
the  fluoride values by precipitation as CaF2.  In one case this is done
by the addition of CaC12.

In general, suspended sclids are removed in the thickening  tanks  along
with  the  fluoride  precipitate.  A recycle stream tends to give better
control than a once-through system-^-0.5 to 1,5 kg/metric  ton   (1  to   3
Ib/ton) of Al versus about 10 kg/metric ton (20 Ib/ton).  It is apparent
that  these  solids  settle  out  faster  as  the  concentration  of the
suspension is increased.  This is a common  phenomenon  in  solid-liquid
separation,  and  the  faster settling is known as Type II settling.  In
this region, the particles coalesce and the resultant mass  of  particle
settles at a greater rate than the individual, unhindered particles.
                                  83

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MAKE UP WATER
      132  i
                SCRUBBER
             RECYCLE    /3'7?5X
                        (1,000)
              FILTER
             FILTRATE
                                               57 ,
                                         BLEED(15)
     at  (1-2 g/1 F)
                                                  REACTOR
                                                               SODIUM ALUMINATE
THICKENER
                                                          300  g/1  suspended soUds
 KILN
                                                                 CRYOLITE (30%)
                                      * Process  rates:  liters/min,
                                                       (gpm)
          FIGURE  9.  PROCESS SCHEMATIC RECYCLE SYSTEM FOR FLUORIDE REMOVAL
                     C250 T/D Aluminum)
                                       84

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There is a certain quantity of oils and grease in the wastewater.  These
hydrocarbons  arise  from the baking of the anode.  At the present time,
no control techniques are employed  to  remove  this  oil  specifically,
because  of  its relatively low concentration of about 20 ppm.  The data
indicate that about one-half to two-thirds of the oil is  adsorbed  onto
various  precipitated  solids.   Thus  the  thickening operations can be
considered as a means of control.  One aluminum producer  does  have  an
oil  separator  on  a  power  plant  effluent with a flow of 102 m_3/ day
(27,000 gpd) ; however, indications are that the concentration of oil  in
this relatively large stream is 1,000-10,000 mg/1.
               Some of the variations in current industrial practice and
the fluoride levels in associated streams are indicated below.

In a prebake anode plant, primary and secondary gas-scrubber liquors are
treated with sodium alurrinate to recover cryolite with  recycle  of  the
liquor  to  the  scrubber.   A  scrubber-liquor bleed stream  (to control
sulfate content)  containing 2 g/1 F  is  diluted  and  discharged.   The
mixed  plant  discharge  contains  20  mg/1  F,  and  is  calculated  as
equivalent to an emission  of  1.2  kg  F/metric  ton   (2.4  Ib/ton)  of
aluminum produced.

In a horizontal stud Soderberg plant, waste streams consist of area run-
off, potlining leaching liquor, and primary air scrubber liquors, all of
which  are  treated  with HF and CO2 to recover cryolite with recycle of
the treated water to the scrubbers.  A scrubber liquor bleed stream with
2 g/1 F is  diluted  and  discharged  as  a  mixed  plant  waste  stream
containing 10.5 mg/1 I.  Total fluoride emission in water was calculated
as 1.1 kg /me trie ton of aluminum produced (2.2 Ib/ton) .

The  conclusions which can be drawn on the basis of the accumulated data
are as follows:

    (1)  Adequate means are available and are presently
         being employed to reduce soluble fluoride emissions
         in waste water to about 1 kg/metric ton (2 Ib/ton)
         of aluminum produced and suspended solids to about
         1.5 kg/metric ton (3 Ib/ton).

    (2)  The best means cf control in present practice in
         the aluminum industry is the precipitation of the
         fluoride as cryolite or with lime and recycle of the clarified
         liquid back to the scrubber.  This practice is
         considered to te the best practicable control
         technology currently available.  Alternate tech-
         nology available to some plants is dry fume scrubbing.

Cast House Scrubber Water
                                   85

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There are in practice a number of variations degassing  procedures  that
function  as in-process control techniques to eliminate the use of water
for  wet  scrubbing  of  fumes  generated  during  degassing  of  molten
aluminum.   Although  the differences between the various techniques are
of metallurgical significance, the processes will  be  considered  as  a
single  class,  since  they  all achieve the elimination of water use in
cast house scrubbers.

Degassing  is  an  operation  in  which  dissolved  hydrogen  and  other
impurities  are removed from molten aluminum just before it is cast into
product form.  The classical approach to degassing is  the  bubbling  of
chlorine  gas  through the melt to react with and remove the hydrogen as
hydrogen chloride gas and the impurities as chloride  salts.   Emissions
to  the air have been ordinarily controlled, when necessary, by alkaline
wet scrubbing.  The raw waste water stream produced may vary  from  acid
to  alkaline,  depending on operating conditions, with notable levels of
dissolved salts, usually sodium chloride.

The   necessity   for   degassing   requirements   vary   with   product
specifications.   Products  which  must be especially high in purity and
free of pin holes caused by gas bubbles (e.g.,  aluminum  foil)  require
stringent  control  of  metal  quality.   Certain  alloy compositions or
melting   stock   therefore   require   reduction   of   impurities   to
extraordinarily  low levels to achieve specified properties of strength,
ductility, electrical conductivity, etc.

Thus, a number of alternative processes  for  controlling  metal  purity
have been developed, depending on product requirements.


Process_ Identification.  The alternative approaches to degassing include

     (1)  Chlorine degassing with no air pollution control

     (2)  Chlorine degassing with wet scrubbing of gases

     (3)  Degassing with mixtures of chlorine and other gases

         Degassing with inert  (nitrogen or argon) gases
     (5)  Filtration of the molten metal using special
         materials and conditions.

Only approach  (2) involves contribution of pollutants to waste water.

Noteworthy  factors  in  the  above list are that approaches  (1) and  (2)
imply the use of a stream of 100 percent  chlorine.   In  the  last   few
years,  environmental  control  efforts have resulted in the development
and successful use of gas mixtures such as chlorine plus an  inert  gas,
or chlorine, carbon monoxide, and nitrogen.  In the latter case of mixed
                                   86

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gases,  gas  burners Or controlled-combustion gas generators are used to
produce a gas of carefully controlled composition.

In the case of degassing with an inert gas, there apparently is a degree
of uncertainty with regard to  the  basic  reactions  in  the  degassing
process.   The  degassing process may depend to a degree on the chemical
reaction of chlorine with hydrogen, followed by  evolution  of  hydrogen
chloride  gas  bubbles.  To some degree, the degassing operation depends
on the formation of gas bubble nuclei and interfaces which  furnish  the
basis  for  the  simple  physical  evolution  of  the  hydrogen from its
dissolved state in the metal.  Thus, the requirement  for  any  specific
concentration  of  chlorine  for degassing may be argued on the basis of
metal impurity level, product  requirements,  operating  conditions,  or
other factors.


Applicability	and	geliabi_lj.ty.   All  of  the  above  listed  process
alternatives are in commercial use on a regular basis and have been  for
sufficient  times  to  be considered established practice in one or more
producing  plants.   There  is  no  proof  that  the  alternatives   are
completely applicable to every plant.  Applicability of any one specific
process  to  any  one specific plant must be determined on an individual
basis.

Three of the processes listed above, (3),  (4) and (5), are patented  and
accessible only under licensing agreements.

It  is  concluded that there are currently available alternative process
methods which may te applied to achieve the elimination  of  cast  house
scrubber waste water.

Anode Bake Plant Scrubber Wateg

At  the  present  time,  control of water from this source, by treatment
followed by recycle to the scrubbers,  is  not  practiced.   The  solids
produced  by  precipitation  of  fluoride from anode bake plant scrubber
water  are  not  suitable  for  recycle  to  the  smelter   because   of
contamination  by  tars and oils.  The technology for lime precipitation
described previously for water from potline wet scrubbers also could  be
applied to water from anode bake plant wet scrubbers.

Dry  electrostatic  precipitators  do  not remove significant amounts of
gaseous fluoride, thus they will not be suitable for  anode  bake  plant
furnaces   in   the  future.   Baghouses  are  also  unsuited  for  this
application because of blinding of the bags caused by the tars and oils.
One plant achieves an acceptable air emission level with no wet scrubber
on the exhaust gases by  exercicising  sophisticated  control  over  the
firing  of the anodes and by utilizing new flues in the exhaust circuit.
However, the company reported that it has  not  been  sucessful  in  its

-------
efforts  to  apply  this  type  of  control  at six other plants and wet
scrubbing systems have had to be retained.

The conclusion reached is that control of water from  anode  bake  plant
wet scrubbers can be approached through recycle, but that technology for
the  elimination  of  wet  scrubbers  through  the use of dry devices or
controlled firing is not adequately demonstrated at this time.

                          Treatment Technology


In the context of this report the term treatment  technology  refers  to
any practice applied to a waste water stream to reduce the concentration
of pollutants in the stream before discharge.


Water From__Potline^Wet Scrubberg

Treatment  technology  can  be  applied  in  once-through systems, i.e.,
without recycle, or a treatment method could be  applied  to  the  bleed
stream or filtrate from a recycled system in order to further reduce the
fluoride  concentration,  the  suspended  solids  level, and the oil and
grease concentration.
                   ..  The once-through system does not employ a  recycle
loop; rather, all of the scrubber water is treated, and then discharged.
A schematic diagram of the process is shown in Figure 10.

In one prebake anode type plant, scrubber water enters at a rate of from
1U  to  113  cubic  meters/ton   (4,000  to  30,000  gal/ton) of aluminum
produced and fluorides and particulates are removed  from  the  effluent
gas.   The  effluent containing from 100 to 600 mg/1 soluble fluoride is
then  contacted  with  a  lime  slurry.   The  resulting  suspension  is
thickened   for  about  5  hours  usually  aided  by  a  polyelectrolyte
coagulant.  In general, the solids from the  thickener  are  sent  to  a
landfill,  and  the  clarified  effluent (20-50 mg/1 F)  is combined with
other waste water froir within the plant and discharged.    Only  lime  is
used currently as the precipitant in this process.

In a vertical stud Soderterg-type plant the secondary air scrubber water
is  diluted  and discharged in mixed plant wastewater at a concentration
of 20 mg/1 F.  The primary gas scrubber liquor  (200 to 500  mg/1  F)  is
limed and clarified to produce an overflow containing 50 mg/1 F which is
combined  with  other  streams  before  discharge.   Total  emission  of
fluorides in water for this plant was calculated as 10 kg/metric ton  (20
Ib/ton) of aluminum metal produced.
T£eatment_of_RecYcle_Eleed_Streams.  A process to remove  fluoride  from
the  bleedand  filtrate  streams obtained from a recycle system can be
depicted as shown in Figure 11.
                                   88

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The two streams are reacted with  CaCl^   (or  lime)  and  then  enter  a
clarifier where the suspended CaF2 is settled out.  Based on intormation
provided by three aluirinum companies, the following assumptions are used
for the design characteristics of the process:

    ...The total flow to be treated is 0.106 cubic meters/
       min (28 gpm).

    ...The input concentration of fluoride is 1 g/liter.

    ...Twice the stoichiometric amount of calcium is used.

    ...A residence time of 10 hours is used in the clarifier.

    ...Output fluoride level is 30 mg/1.

On  the  basis  of  the  above assumptions, the addition of this further
treatment reduces the fluoride level 1 kg/metric ton  (2 Ib/ton) to  0.05
kg/  metric ton (0.1 Ib/ton) .  Also, it is estimated that the additional
settling time reduces the suspended particulate and hydrocarbons in  the
effluent by 95 percent.

This  secondary  treatment  of bleed and  filtrate streams from a recycle
system is considered to be the best  available  technology  economically
achievable.


Treatment	of	Dilute	fluoride	Streams.  Typically, plants utilizing a
once-through treatment system yield a volume of waste water of 14 to 110
cubic meters/metric ten  (4,000-40,000 gal/ton)  of  aluminum,  having  a
concentration  of  20-50 mg/1 soluble fluoride.  The fluoride discharged
amounts to about 5 to  10  kg/metric  ton   (10-20  Ib/ton).   There  are
several  processes  which  are  not  in   general practice in the primary
aluminum industry which could be used  to  treat  such  dilute  fluoride
streams in order to further reduce the fluoride discharge levels.  These
processes  are described below.  For the  purposes of design calculation,
it was assumed that the stream to be treated contains 35  mg/1  fluoride
and  has a flow rate of 18,900 cubic meters per day  (5 million gal/day),
for a plant producing 225 metric tons  (250  tons/day)  of  aluminum  per
day.


Aluminum  Sulfate  (Alum).  The addition of alum to a solution containing
the fluoride ion will  remove  the  fluoride.   The  mechanism  involved
probably is adsorption on the alum precipitate.  Gulp and Stoltenberg(4)
showed  that  about  2/3  of  the  fluoride   ion could be removed by the
addition of 500 ppm of  alum,  although   the  maximum  concentration  of
fluoride  investigated  was  6.0  ppm.    Although  the  quantity of alum
necessary to treat the 35 mg/1 stream is  unknown,  it  is  assumed  that
1000 mg/1 would be adequate to remove 2/3 of the fluoride; that is, alum
                                   91

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treatment  would  yield  a stream containing 12 mg/1 fluoride.   From the
dajba of Gulp and Stoltenberg there does not appear to be a large  effect
of  alum  concentration  on  fractional removal of fluoride at different
initial fluoride concentrations.

A schematic drawing of a process to treat  the  dilute  fluoride  stream
from  the once-through scrubbing system is shown in Figure 12.   The alum
is added and mixed with the stream in a tank providing a residence  time
of  2  minutes.   The  alum  then  is allowed to flocculate for about 30
minutes.  A period of 4  hours  is  then  allotted  for  settling  in  a
clarifier.

There  is  evidence  to  indicate  that  the pH of the waste water is an
important parameter fcr efficient fluoride removal by alum.  The data of
Gulp and Stoltenberg indicate that the pH of the treated  stream  should
be  above  6.   In  this  case,  the  pH  of  the stream coming from the
thickener tank is fairly high, and should present no problems with  alum
flocculation.   One  disadvantage of this procedure is the disposal of a
relatively large amount of sludge, about 18 metric  tons/day   (about  20
tons/day).

One  advantage  of this procedure to treat the waste from a once-through
scrubbing system is that a reduction in both suspended  solids  and  oil
and  grease should be effected.  Very likely, some oil adsorption on the
alum floes will cccur, and oil will  be  removed  along  with  the  alum
sludge.   Likewise,  it  is expected that particle-particle interactions
will occur between the alum floes and the  suspended  solids,  enhancing
the settling characteristics of these solids.


Adsorption  on  Activated  Alumina.  Activated alumina has been used for
some time in  the  treatment  of  municipal  water  supplies.   In  this
process, the waste water containing fluorides is passed through a bed of
activated alumina, which has an adsorption capacity of about 0.022 kg of
fluoride  per liter of alumina (0.286 Ib/cubic ft).  Regeneration of the
bed is accomplished by either sulfuric acid  (4  percent)  or  by  sodium
hydroxide   (1  percent) .   The effluent from the adsorption bed contains
about 2 ppm fluoride.  Details of the pertinent experimental  data  have
been  reported  by  Zabban  and  Jewett.(5)     This  technology  is not
currently practiced fcr waste water treatment in the aluminum industry.

A hypothetical process to treat the 18,900 cubic meters/day   (5  million
gal/day)  stream  of 35 ppm fluoride is shown in Figure 13.  Two alumina
columns are used, operated alternately  in  an  adsorption  mode  and  a
regeneration  mode.  The regenerant solution is H2SO^ at a concentration
of 4 percent.  It requires about 16.5 kg of sulfuric acid to  regenerate
the  bed  on  which  cne kg of fluoride has been adsorbed  (or 16.5 Ib of
acid/lb of fluoride).   The  sulfuric  acid-fluoride  solution  is  then
neutralized  with  lime,  resulting in the formation of calcium fluoride
and calcium sulfate.  The final step is the settling of the precipitates
in a thickener tank.
                                   92

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One of the major disadvantages of this  process  from  an  environmental
standpoint  is  the  discharge  of  a relatively large amount of calcium
sulfate, about 545 kg/day  (about 1200 Ib/day)  in the water.  This is due
to its fairly high solubility in water of about 0.21  percent.   Calcium
sulfate may result in an increase in hardness of the water.

It is unlikely that a significant removal of suspended solids will occur
with  the  activated  alumina  process.  However, some adsorption of the
oils and grease probably will occur.  It is not known whether these oils
will be eluted during regeneration.  If  they  are  not  removed  during
regeneration, the capacity of the bed could suffer; whereas, if they can
be desorbed during regeneration, the oil and grease will be removed from
the  water  during  precipitation  of  the  calcium  sulfate and calcium
fluoride sludge.


Hydroxylapatite.  Hydroxylapatite  (synthetic bone  and  bone  char)  has
been  used  to remove soluble fluoride.(6)  The fluoride reacts with the
tri-calcium phosphate.  Regeneration  is  accomplished  by  caustic  and
phosphoric  acid.   This   scheme  is primarily a water treatment process
(initial fluoride content  of about 13 ppm) and its applicability to  the
35  ppm  stream  in  the   present  case  is unknown.  Technical problems
associated with this  process  are  high  bed  attrition  and  decreased
efficiency in the presence of chlorides.

Adsorption of oils and greases should occur on the bed, however, whether
these  oils  and greases would be removed during subsequent regeneration
of the bed is unknown.  There also may  be  some  removal  of  suspended
solids  by  the process of filtration, although a quantitiative estimate
of this removal is not possible without experimental data.


Reverse Osmosis.  Reverse  Osmosis  (R.O.)  is a process  whereby  a  waste
water  stream  is  passed  at pressures from 500-2000 psi over a membrane
which tends to allow the water to permeate, but rejects dissolved  ionic
salts.   It should be possible, using R.O., to produce an effluent which
has only about 5 percent of the fluoride content of the incoming water.

The fraction of the water  which can permeate through the membrane  is  of
great  importance  in  considering  the applicability of this process to
dilute fluoride waste water, because  of  the  necessity  of  additional
fluoride  removal  processes  which  must be applied to the concentrate.
There are many parameters  which influence  the  fractional  recovery  of
water,  such  as,  level   of  dissolved solids, suspended solid content,
solubility relationships and equipment design.  It should be possible to
obtain at least a 75 percent recovery, resulting  in  a  concentrate  of
about  135  ppm  fluoride.   This  concentrated stream can be treated by
conventional lime precipitation.
                                    95

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The major technical problem which can arise in the use of R.O.  to treat
the scrubber water is the potential for fouling of the membranes due  to
the suspended solids and oils and greases present in the stream.  Before
R.O.  can be considered technically feasible, experimental data would be
necessary to establish the severity of this problem.   The  presence  of
suspended  solids  may  preclude  the  use of the new hollow-fiber units
which are more durable in industrial applications.  The oils and greases
may tend to form a relatively impermeable coating on the surface of  the
membrane   with  resulting  elaborate  and  costly  cleaning  procedures
necessary.  The widely  used  spiral  wound  membranes  are  also  quite
susceptible  to plugging and probably would be unsatisfactory also.  The
tubular type membrane configuration is the most suitable where  plugging
may be a problem.

A  schematic  diagram  of a process to treat the effluent from the once-
through  scrubbing  system  is  shown  in  Figure  14.   The   feed   is
pressurized,  probably  to about 500 psi, and passed through the reverse
osmosis unit.  Further treatment of  the  concentrate  is  performed  to
reduce the fluoride content.


Anode^Bake^Furnace^Scrukber Water

The anode bake furnace flue gas contains particulate carbon, tar vapors,
sulfur  compounds, and fuel-combustion products.  Fluorine compounds may
be present if anode stubs  are  recycled.   The  air  pollution  control
applied  to  such  flue  gas  includes  no control, dry syste:ms, and wet
systems.  The wet systems may be either wet electrostatic  precipitators
or  wet  scrubbers.   If  wet  scrubbers are used, the effluent from the
scrubber contains tars and oils, sulfates, particulate  matter  and,  in
some  cases,  fluorides".  The source of the fluoride in the carbon anode
bake plant is the used anode butts recycled  to  the  anode  preparation
operation.   Care  in the removal of fused cryolite from the anode butts
before reprocessing wculd greatley minimize fluoride emissions from  the
anode  bake plant and hence minimize fluoride concentrations in the bake
plant scrubber water.
                                   96

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Treatment  of  anode  bake  plant  wet-scrubber  effluents  consists  of
settling the effluent ir ponds, in some instances, after lime treatment.
After  settling,  the  organic materials are skimmed from the surface of
the pond.  Plants employing this practice exhibit  effluent  loading  of
oil and grease comparable to that from other plants.


Cast House^Coolinq Water

Control  of effluent water form the direct contact cooling of ingots can
be achieved by means of a cooling tower with recycle of the  water.   In
this operation, a certain portion of the cooling water must be bled from
the  circuit  in order to prevent the buildup of dissolved and suspended
solids, as well as the cil and grease.   One  plant  treats  this  bleed
stream   (150  gpm)   in  an  aerated lagoon with a 15-day retention time,
reducing the hydrocarbon content by 85 percent.

Treatment of ^Cyanide- contain ing gtrearns.

Cyanide  is contained in the run-off water  from  spent  cathode  storage
areas and in the water circuit if reprocessing of cathodes is practiced.
The  values  are  low, ranging from net concentrations of 0.002 to 0.036
ppm among the three plants exhibiting a free cyanide discharge (Plant  I
reported  a  value  of  0.05  ppm  but the effluent is not discharged to
navibable waters).   Treatment technology is available for  reducing  the
free  cyanide  content.   The internal streams containing cyanide may be
treated with chlcrine  cr  hypochlorite  to  destroy  the  cyanide.   No
primary aluminum plants currently treat cyanide specifically.


                Summary of Waste Treatment Effectiveness


The  data  from  the aluirinum companies as well as those data calculated
for different modes of v;ater treatment have been summarized in Table  6.
Several  important points should be noted.  For water pollution control,
a dry scrubbing systeir is best, when it can be used.  It is fairly  well
established  that  for  plants  committed to potroom air cleaning, i.e.,
secondary scrubbing, a dry scrubbing system cannot be used at this time.
In addition, the use cf dry scrubbing on the anode bake effluent is  not
in practice at the present time.

There  are  notable  differences  between  the two wet scrubber systems,
once-through and recycle.   The  recycle  system  is  considerably  more
effective  in  the reduction of fluorides, suspended solids and oils and
greases.  Effluent fluoride quantities are about 5-10 kg/metric ton  (10-
20 lb/ ton) of aluminum when a once-through system is used, and 0.5 to  1
kg/metric ton  (1-2 Ib/tcn) of aluminum when a recycle  system  is  used.
There  are  several  reasons  for  the better performance of the recycle
system.
                                   98

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   TABLE 6. EFFLUENT LEVELS ACHIEVED BY VARIOUS TREATMENT PROCESSES
              Typical values achieved or expected (see text)
Emission Level, kg/metric ton (Ib/ton)
Process
Dry Scrubbing
Wet Scrubbing - Once Through
Wet Scrubbing - Recycle
Recycle + Bleed & Filtrate
Treatment
Once Through + Alum ^
Once Through + Activated
Alumina
Once Through + Hydroxylapatite
Once Through + Reverse Osmosis
Fluoride
0
5(10)
1(2)
0.05(0.1)
1(2)
0.25(0.5)
0.25(0.5)*
0.75(1.5)
Suspended
Solids
0
5(10)
1.5(3)
0.1(0.2)*
1(2)*
2.5(5)*
2.5(5)*
0.5(1)*
Hydrocarbons
0
0.5(1)
0.25(0.5)
0.01(0.02)*
0.05(0.1)*
0.25(0.5)*
0.05(0.1)*
0.05(0.1)*
*  Estimate.
                                  99

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There is strong evidence that the formation of the  precipitate  calcium
fluoride  is a time-dependent phenomenon.  The equilibrium concentration
of soluble fluoride in a slurry of calcium fluoride  is  about  10  ppm;
however,  values  of  20-50  ppm have teen observed in the effluent when
calcium fluoride is formed from lime.

Either the calcium fluoride forms and entraps  liquor,  or  the  calcium
fluoride forms about the lime particle as a "skin".  In either case, the
reaction   rate   becomes  diffusion  controlled,  and  the  higher  the
concentration of fluoride ion, the greater will  be  the  rate  of  mass
transfer of this ion into the reacting media.  Thus, it is expected that
the  precipitation  reaction  in the recycle liquor with 10-20 times the
fluoride concentration would be higher than  that  in  the  once-through
system.
                                   100

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It  is  both technically feasible and relatively simple to add a further
fluoride treatment process to the recycle system.  This is  because  the
effluent   streams    (bleed   and   filtrate)  have  a  relatively  high
concentration of fluoride (about  1  g/liter)  and  are  also  of  small
volume.   By this technique, effluent values of about 0.05 kg/metric ton
(0.1 Ib/ton)  of aluminum can be  obtained.   Further  treatment  of  the
once-through scrubber water is complicated by the large volume of water,
19,000 to 38,000 cubic meters/day (5-10 million gal/day) at low fluoride
content  (  35  ppm).  A reduction of fluoride by four different methods
has been considered,  and it appears that the best  process  is  fluoride
removal by sorption in an activated alumina bed.

It  is  concluded  -that  techniques  are  currently  available to reduce
fluoride to zero by use of a dry scrubbing system on the potline, and to
reduce fluoride emissions to  1  kg/metric  ton  (2  Ib/ton)   by  a  wet
scrubber with recycle.

                     Control^and Treatment Options

On  the  basis  of the foregoing summary of the effectiveness of various
control and treatment technologies, some of  the  available  options  by
which   an   individual  plant  can  achieve  the  recommended  effluent
limitations are summarized schematically in Figure 15.  The baseline  is
a  plant using wet scrubbers for air pollution control with no treatment
of the scrubber water prior to discharge.  The effluent fluoride loading
for the baseline case is about 15 kg per metric ton  (30 Ib per  ton)  of
aluminum  produced.   The recommended effluent limitation  (July 1, 1977)
can be achieved by the baseline plant by installing a  cryolite-recovery
system  with  recycle  and  bleed.   The recommended effluent limitation
(July 1, 1983) then can be achieved by adding a lime  treatment  to  the
bleed  stream  from  the-  recycle scrubber circuit.  Alternative options
open to a baseline case plant include: conversion of  the  wet-scrubbing
system  to  a  dry-scrubbing  system,  or retention of the wet-scrubbing
system with provision fcr impoundment of the effluent.

Plants currently practicing once-through  lime-and-settle  treatment  of
water  from wet scrubbers have an effluent fluoride loading in the range
of 5 to 10 kg per metric ton  (10 to 20  Ib/ton)  of  aluminum  produced.
Such plants can achieve the 1977 effluent limitation by adding a recycle
system to the present operation, or by adding additional treatment, such
as, adsorption of fluoride on alumina.  The 1983 effluent  limitation can
be  achieved  by  adding  a  lime treatment to the recycle bleed stream.
These plants also have the option  of  conversion  to  a  dry  scrubbing
system, or the employment of total impoundment.

Finally,  plants  now  using  cryolite  recovery  with recycle can, with
proper  application  of  the  technology  and  with  good   housekeeping
practice,  achieve  the 1977 effluent limitation now.  The 1983 effluent
limitations then can be achieved by adding lime treatment  of  the  bleed
stream.
                                    101

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     Effluent
     Loading
                           Baseline Case—Wet Scrubbing—Once-through,
                                 Mo Treatment of Scrubber  Water
         (30)
7.5
  (15)-
 1
.05
 0
  (2)
(0.1)
   0
                                             Lime and
                                             Settle,
                                           Once-Through
                   Cyrolite pptn
                   Plus Recycle
                    With Bleed
                                                                            Total
                                                                         Impoundment
                                                                    Convert to
                                                                   Dry Scrubbing
                                                 Adsorption
                                                on Activated
                                                   Alumina
Lime Treatment of Bleed Stream
Level 1
Level II
Level III
                          FIGURE 15.   SOME CONTROL AND TREATMENT OPTIONS
                                         102

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The  availability  of various control and treatment technologies to meet
the effluent limitations provides flexibility to allow each  company  to
plan  its  future  water  pollution abatement program in the manner most
compatible with its existing pollution control practices.
                                   103

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                              SECTION VIII



              COSTS, ENERGY, AND NONWATEB QUALITYJASPECTS


                              IntrgductiQQ


This section deals with the costs associated with the various  treatment
strategies  available  to  the aluminum industry to reduce the pollutant
load in the  water  effluents.   In  addition,  other  nonwater  quality
aspects are discussed.

                       Easis^fgr_Cost Estimation

Data  on  capital  investment and on operating costs for present control
practices were obtained from selected aluminum  companies.   These  data
were modified in the following way to put all on a common basis.

     (1)  The capital investment reported was changed to
         1971 dollars by the use of the Marshal and Steven's
         Index (Quarterly values of ^this index appear in
         the publication Chemical Engineering, McGraw Hill).

     (2)  The operating cost was recalculated to reflect common
         capitalized charges.  To do this, the annual oper-
         ating cost was calculated as follows:

         Operating and maintenance - as reported by the
           aluminum companies
         Depreciation - 5 percent of the 1971 capital
         Administrative overhead - 4 percent of operating
           and maintenance
         Property tax and insurance - 0.8 percent of the
           1971 capital
         Interest - 8 percent of the 1971 capital
         Other - as reported by aluminum companies.

Regarding  estimates  for capital and operating costs of other processes
which could be applied to water treatment, the following  procedure  was
used:   Equipment  costs  were estimated from data in references  (7) and
 (8).  The total capital investment was  then  calculated  as  this  cost
plus:
         Installation           50% of equipment
         Piping                 31% of equipment
         Engineering            32% of equipment
         Electrical Services    15% of equipment
                                   104

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         Contractor's Fee        5% of equipment
         Contingency            10% of equipment.

The  operating  cost was calculated by estimating labor and raw material
requirements, and then adding the following items:

         Maintenance             5% of investment
         Depreciation            5% of investment
         Tax and Overhead        0.8% of investment
         Interest                8% of investment.

These additional capital  and  operating  expenses  were  obtained  from
values reported in reference (7).


                 Economics of Present.. Control ^Practice


The economic data which will be discussed in this section are summarized
in  Table  7.   In  order to present a total picture of present practice
with respect to contrcl and treatment of water in the  primary  aluminum
industry,  not  all  categories  have  cost  information-contained.  The
following words have been used to denote the reasons for the absence  of
cost information:

     (a)   Not used - no wet-type pollution control device
         is used

     (b)   Untreated -. a wet scrubber is used for air pollution
         control, but the water is discharged untreated.

In addition, a dash indicates that insufficient information was obtained
to perform a cost estimate.

Where  cost  values  are  bracketed,  this  indicates  that the cost was
calculated, either tc put the costs on a common basis, or calculated  on
equipment  descriptions  obtained.  It is also to be noted that all tons
are metric throughout the following discussion.
                                  105

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gotline	(Prirngry^ Gas Sgrubber Wat§r

Essentially there are two means to control the water effluent  from  gas
scrubbers  on  the  pctline:  (a)  use a dry scrubbing system on the gases
which will reduce the water use to zero,  (b)  recycle the scrubber  water
and  precipitate  the  fluoride  values picked up in the scrubber.  This
latter technique, however, dees result in a small bleed stream of  10-20
gpm  of  effluent  water.   The  size - of  this stream must be varied to
accommodate the build-up of sulfates in the recycled stream.   The  cost
data  given below were derived from reported analyses and costs, and are
independent of stream size, which may be characterized as being  on  the
order of 10-100 gpm.

The  total  capital  cost  of equipment, installation, and the necessary
plant facilities to provide  dry  scrubbing  for  a  potline  have  been
reported  by  several  sources.   In the present survey, three companies
quote a total investment for conversion to dry scrubbing in the range of
$36-$112 per annual ton of aluminum produced.  Nielsen  and  Kielback(9)
report  a  capital  cost of $30-$UO/annual ton, while Cook and Swany(lO)
report a 1970 cost of $60/annual ton  for  primary  control  of  prebake
plants,  and  $33/annual  ton for vertical spike Soderberg.  These costs
include both the collection system and the  primary  removal  equipment.
As an average investment cost, a figure of $<40/annual ton is used in the
present study.

Operating   cost  data  are  relatively   sparse  because  of  the  small
percentage  (about 4 out of 33) of plants utilizing dry scrubbing.   Rush
et  al(ll)  use an operating cost of $10.20/ton for a control of prebake
potline gases and a profit of $0.55/ton for  vertical  spike  Soderberg-
type  plants.  The operating costs all reflect the credit calculated for
recovered fluoride values.  For the purposes of this study, the value of
$10.20/ ton, as representative of dry  scrubbing  operating  costs,  was
used  because  more  prebake  plants  are  in  use  than  vertical-spike
Soderberg type.

Cost information on the use  of  a  recycle  scrubber  system  has  been
obtained  from  the  aluirinum companies surveyed.  Referring to Table 7,
companies H, I, and K have a wet scrubber for primary potline  pollution
control  which  uses  recycled  solution  for  the  scrubbing operation.
Capital costs vary frcm $3.03 to $12.40/annual ton and  operating  costs
vary  from  $2.10  to  $4.53/ton.   These  costs  include only the water
control circuit, namely, the chemical addition tank, thickener, cryolite
recovery equipment, and associated pumps, piping,  etc.   The  operating
costs  do  not include any credit for recovered fluoride as, in general,
the cryolite is not of  high  enough  quality  to  be  recycled  to  the
potline.   One  company does calculate a credit equal to about $2/ton of
aluminum produced.

Potroom	(Sg c ondary )__ Gas_Scrubber^Water
                                 107

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As can be seen in Table 7, only 5 of the 11 companies surveyed for costs
practice air pollution control of potroom air.   Of these  5,  3  utilize
water  control  (Dr  E,  and  K)   on this circuit.  Cost information was
obtained from the two companies D and E.  Plant D reports a capital cost
of $23. 20/annual ton with an operating cost of $8.80/ton.   These  costs
include the recycle water circuit only, consisting of chemical addition,
thickening,  filtration,  and  kiln operation on the recovered cryolite,
and a treatment operation using CaCl2  to  precipitate  fluoride  values
from  the cryolite filtrate stream.  No credit for recovered cryolite is
taken in operating costs.

In the second case   (Plant  E) ,  costs  reported  are  $5,40/annual  ton
capital,  and  $3.15/tcn  operating.  These costs again include only the
recycle water control circuit; however, in this case,  no  treatment  of
the cryolite filtrate stream is done.
At  the  present time, water control by recycling water back through the
anode bake plant scrubber is not practiced.  However, there is one plant
in which the bake plant is run at an acceptable air emission level  with
no  wet  scrubber  on  the  exhaust  gases.   This is done by exercising
sophisticated control of the firing of the  anodes,  and  utilizing  new
flues in the exhaust circuit.  The company reported that it had not been
successful  in  its  efforts  to apply this type of control at six other
plants.  Attendant with this type of control would be  additional  labor
requirements,  and  the necessity of proper flue condition.  However, no
cost data have been obtained for this operation.  Costs  are  indirectly
incurred in improved operating procedures or plant improvements.


Cast House Cooling

The  method  used  to  control  effluent water from the cast house ingot
cooling operation  is  the  operation  of  a  cooling  tower.   In  this
operation,  a  certain  proportion  of  the cooling water is bled off in
order to prevent the buildup of dissolved and suspended solids, as  well
as  the  oil  and grease.  One company (Plant A) treats the bleed stream
 (150 gpm) in an aerated lagoon with a 15-day  retention  time,  reducing
the  hydrocarbon  content  by  85  percent.  The cost of performing this
operation which  includes  the  cooling  tower,  lagoon  and  associated
piping,  engineering,  services, etc., was calculated to be $1.60/annual
ton capital and $0.40/ton operating.
With the exception of heat, there are no  process  pollutants  added  to
water  in  use  for  rectifier cooling.  There is, however, a relatively
large use of water— about 22,000 liters/ton of aluminum  (6600  gal/ short
                                  108

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ton) .   The control measure in practice by industry is to use air-cooled
rectifiers.  Cost data en rectifier coding were not obtained.

                Economics, of Presept_Treatment.. Practice

In this section, only those treatment processes applied to  water  on  a
once-through  basis  are discussed.  Although water treatment is applied
to techniques of water control by recycle, these were discussed  in  the
previous part.


Hotline __ (Prjlmary^ Ga§ ^Scrubber Water

Costs  for  treatment  of  potline scrubber water were obtained from two
companies  (Plants C and G in Table 7) .  These  costs  include  only  the
water  treatment  in  circuit,  consisting  of  a mixing chamber for the
addition of the lime  slurry,  thickener  tank,  and  associated  pumps,
piping, etc.

Plant  C  reports a capital cost of $12.5/annual ton and operating costs
of $2.50/ton; the capital cost for Plant G is $2.32/annual ton.   It  is
noteworthy  that  Plant  C treats about 3.5 times the volume of water as
Plant  G,  160,000  liters/ton  (38,500  gal/short  ton)  versus  52,000
liters/ton (12,500 gal/short ton).  In addition, included with the water
treatment  cost  for  Plant  C  is  the cost to treat anode bake furnace
scrubber water, although this probably amounts to less than  10  percent
of the total cost (on the basis of the proportion of flows) .


                             . Water
It  has  been  found  that where wet scrubbing of potroom air  (secondary
control) is used, those having a once-through system do  not  apply  any
treatment to their effluent water.  Of the four plants which do practice
secondary  control,  twc utilize recycle water in the scrubber  (Plants D
and E) , and two do not treat the scrubber water.


Anode Bake Furnace ^Scrubber Via ter

Treatment costs have not been reported by the three companies  (C, D, and
E) practicing water treatment of the scrubber water from the anode  bake
plant.   The  treatment  method  consists  essentially  of  ponding  the
effluent, and skimming the oil and tars from the surface.  Based  on  an
estimate of the size cf the ponds, costs were calculated for each plant.
These  costs  are  shown in Table 7.  The higher cost oil separators are
associated with a longer residence time for the scrubber water, and con-
sequently probably result in a more  effective  separation.   Calculated
residence times for Plants C, D, and E are 42 minutes, 21 hours, and 210
minutes,  respectively.   An  analysis  Of the scrubber water before and
                                  109

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after the ponding treatment of Plant D was done, and it was  found  that
the  pond  did  remove  about  60  percent  of  the oils and greases and
suspended solids.


Cast House ^Cooling Water

One of the companies contacted (Plant K) provides a  lagoon  into  which
all the water effluent, including that from the cast house, flows before
discharging  from  the  plant.   The estimated size of this lagoon was 2
acres, and a cost was calculated to  be  $0.43/annual  ton  capital  and
$0.06/ton  operating for this procedure.  Data on the retention time and
effectiveness of this operation were not obtained.
                 Cost-! f f££t iv enes s __ (P resent Practice)


Fluoride Effluent Control _ (Potline and Potroom^

The cost data presented in Table  7  have  been  plotted  against  total
fluoride  effluent  from  the  plant.  Figure 16 gives capital costs and
Figure 17 gives operating costs.

It is apparent from the figures that the cost increases as the amount of
fluoride in the effluent stream decreases.  The most expensive option is
the conversion of a wet  scrubbing  system  on  the  potline  to  a  dry
scrubbing  one,  although  the water use would be zero.  A dry scrubbing
system, however, has not been proven as technically feasible for use  on
potroom secondary air or for horizontal spike Soderberg potlines.

The relatively high capital required for installation of a dry scrubbing
system  actually applies only for those plants which would be converting
from a wet system.  A  wet  scrubbing  system  installed  from  scratch,
including  the  scrubber, fans, etc., costs about $38/anriual ton.  Thus,
the difference in cost between the two systems for  a  new  plant  would
only be about $2/annual ton.
                                  110

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         112

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The  recycle  mode  of scrubbing water control on both potline (primary)
gases and potroom (secondary) gases does result  in  fluoride  effluents
less  than 1 kg/ton  (2 Ib/short ton).  An average cost for this means of
control is about $10/annual ton capital and $4.60/ton operating.

The use of once-through water in the wet scrubbing  system  of  potlines
with lime treatment before discharge results in effluent fluoride levels
of  about  5  kg/ton  (10  Ib/short  ton).   Costs  associated with this
treatment process are $7.0/annual ton capital and $2.50/ton operating.

The following conclusions can be made at this time  regarding  the  cost
effectiveness of fluoride control.

    (1)   The best cost-effective means of control for new plants with a
prebake or vertical-spike Soderberg configuration is the installation of
a dry scrubbing system on the potline gaseous  effluents.   Tight  hoods
should  be  provided, and the operation conducted in such a manner as to
minimize any potroom contamination.

    (2)  The most cost-effective means of removing  fluoride  for  those
plants  with existing wet scrubber systems is the operation of a recycle
loop  to  the  scrubber  with  cryolite  or  lime  precipitation.    The
difference  in cost between this system and the once-through system with
lime treatment is relatively low.  Considering  that  effluent  fluoride
amounts  in the water from the recycle scrubber operation are about 1/10
as high as those from gas scrubbers operated on a once"through basis.


Suspended Solids^Effluent Control  (Potline and Potroom)

Treatment to remove fluoride will tend to remove suspended  solids.   In
the  dry  system,  any suspended solids will be caught in the collection
system.  As a wet  system  for  fluoride  control  involves  a  settling
operation  of  CaF2,  the  suspended  solids  also  will tend to settle.
Therefore, conclusions about cost effectiveness applicable  to  fluoride
also are applicable tc suspended solids control.


Oils_andj3reases__( Potline)^

It  appears  that oils and greases emitted from the anode consumption in
the potline tend to te removed  along  with  the  suspended  solids  and
fluoride.  This is evident on examining the effluent data from Plants C,
E,  F,  G,  I,  and  J.  As discussed previously in Section VII, perhaps
emulsion breaking  and  adsorption  of  oil  onto  the   surface  of  the
precipitate  is  the  reason  for  this.   Thus,  the  same  conclusions
regarding cost effectiveness for fluoride control can be applied to  the
removal of oil and grease from the potline scrubber water.
                                  113

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        Qr e a se __ [ An od e^ B a ke__Plant^
There  are too little data on the effectiveness or cost of the treatment
procedure of settling and skimming the anode bake plant  scrubber  water
to  make  definite  conclusions regarding the cost effectiveness of this
procedure in the present study.  The one piece of data obtained  on  the
effect  of  a  lagoon  on  scrubber water from the anode bake plant does
indicate that the oil and grease content (as well as  suspended  solids)
can  be  reduced  by  60  percent  in a pond with a residence time of 21
hours.  This residence time is relatively long; however,  concentrations
of  oils and greases are low (less than 10 mg/1)  with incoming suspended
solids only at the 100 mg/1 level.  Very likely further reduction of oil
and  grease  can  be   effected   by   Icnger   residence   times   with
proportionately  higher  costs,  although  the exact relationship is not
known.


Oil and Grease _ (Cast House Cooling}

Again, there are not enough data to make definite conclusions about cost
effectiveness of control and treatment cf casthouse cooling water.   The
one piece of data obtained implies that good reduction in oil and grease
(up  to  95  percent)  can be obtained using a cooling tower and aerated
lagoon treatment of the blowdown from the cooling tower  at  a  moderate
cost of $1; 60/annual ton capital, $0.40/ton operating.


Heat From Rectifiers

At  this  point,  it  is difficult to say whether a transfer of the heat
output derived from the rectifiers from water into air represents a gain
or  loss  of  effectiveness  in  relation  to  overall  impact  on   the
environment.   Nevertheless,  the  use  of  air-cooled  rectifiers  does
represent an effective water control measure.
                Cgsts^of^AdditioQalJTreafanent^Processeg


As previously mentioned, dry scrubbing on the  primary  air  system  can
result  in  no  discharge  of  pollutants,  if a secondary wet scrubbing
system is not required.  However, addi tional control  measures  can  be
added  to  the  wet scrubbing processes which will effect a reduction in
the amount of pollutants discharged to the waste streams.   A  technical
discussion  of  these  systems  has  been  given  in Section VII of this
report.  The economics and cost-benefits associated with each  of  these
processes are now dealt with.

Po 11 ine^and_Potrogm_Scrubber Water_Treatment
                                    114

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The  choice  of  additional treatment schemes to be applied to scrubber-
water effluent depends primarily on whether a recycle  system  or  once-
through system is in use.

In  a recycle system, additional control of fluorides, suspended solids,
and oil and grease can be effected by the lime or CaCl2 treatment of the
filtrate stream  from  the  cryolite  and  the  bleed  stream  from  the
scrubber.   The costs calculated for this treatment are $1.50/annual ton
operating and $0.64/tcn operating.  This cost includes a mixing tank for
chemical addition, a thickener tank, pumps, piping services,  etc.   The
costs   are  relatively  low  compared  with  other  fluoride  treatment
processes because of the low volume of effluent to be treated, about 120
liters/minute (30 gpm), and high concentration of fluoride, about  1,000
mg/1.   It is expected that this treatment would reduce suspended solids
and oil and grease by a similar amount.

The addition of a treatment process to wa#er  effluent  from  the  once-
through potline and pctrcom scrubber after lime treatment  (if practiced)
is  more  costly  than  the previous treatment of recycle effluents.  In
this case, large volumes of water with low  concentration  of  fluorides
and other pollutants are involved in the treatment process.

For the purposes of cost calculations, a plant size of 227 tons/day  (250
short tons/day)  was taken.  The flow rate of water from the once-through
scrubbing  system  was  taken  to be 83,300 liters/ton (20,000 gal/short
ton) with a concentration  of  35  mg/1  fluoride.   The  latter  values
represent averages found in the aluminum industry.

Alum_^Tj:eatment.   The  addition  of  an  alum treatment would add about
$11.0/annual ton capital and $8.40/ton  operating.   The  capital  costs
includes  a  mixing  tank,  flocculant  tank, darifier, and pumps.  The
major equipment cost is the 37-meter  (121-foot)  diameter clarifier which
accounts for 84 percent of the $372,000 equipment cost.

The major  operating  cost  is  expenditure  for  alum  ($69/ton)  which
represents about 69 percent of about $700,000/year.


Activated	,Alumina.   The  costs associated with the use of an activated
alumina adsorption process are  $2.7/annual  ton  capital  and  $3.8/ton
operating.  Capital ccsts include two alumina adsorption towers  (one for
adsorption,  one  for  regeneration),  a  mixer for the treatment of the
spent regenerant solution, a thickener, the initial charge  of  alumina,
and associated pumps and piping.-

Regarding  operating  costs,  the  cost  of  the  sulfuric acid used for
regeneration represents about 50 percent of the $313,00O/ year operating
cost.
                                   115

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3Y.d£Oxy_l apatite.  The costs for the adsorption of fluoride en bone  char
were  taken directly as reported by Wair.sley and Janes. (6)  Capital costs
were scaled up from 1947 values, and  depreciation,  tax,  and  interest
costs  were  added  to the reported operating costs.  The costs obtained
were $14.507 annual ten capital and $14.50/ton operating.


Reverse Osmosis.  Costs associated with reverse  osmosis  treatment  are
very  sensitive  to  the nature of the dissolved constituents, pH of the
water, size of  plant,  pretreatment  requirements,  and  several  other
factors.   For  the  present  study,  a  typical operating cost value of
$0.26/1,000 liters   ($1/1,000  gal)  calculated  for  several  different
reverse osmosis applications has been assumed.  Data on capital cost are
too  scattered  to  yield a meaningful estimate.  The operating cost per
ton of aluminum was calculated to be $22.  This value includes the  cost
cf  reverse  osmosis,  plus the cost necessary to treat the concentrated
effluent with lime.


Cost^Effectiveness

The cost data developed  in  the  foregoing  paragraphs  for  additional
treatment  of potline and po^room scrubber water are summarized in Table
8, along  with  estimated  fluoride  discharged  from  the  plant.   The
elements included in capital cost and operating cost are; those discussed
on the first page of this Section  (VIII).  Several conclusions regarding
cost effectiveness can be drawn from the data.

     (1)   For  new  plants,  a  dry  system  is  preferable.   The  cost
difference between a dry system and  a  recycle  plus  effluent  control
would be negligible.

     (2)   For  plants which already have a recycle scrubber operation on
their potline or potroom gases, the addition of further  treatment of the
two effluent streams is both inexpensive and very effective.

     (3)   For  plajits  utilizing  a  once-through  scrubber   system,    a
conversion  to  the  recycle mode yields the best cost benefit.  Although.
an activated  alumina  adsorption  process  added  to  the  once-through
scrutber water costs approximately the  same, about five  times the amount
of  pollutants  would  be  discharged   in  the  water from the activated
alumina system.


                        Ngnwater Quality Aspects


Energy^Reguirements
                                   116

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     TABLE 8.  COSTS OF VARIOUS ALTERNATIVES FOR FLUORIDE REMOVAL
                             Discharge
                             Fluoride,   Capital Cost,     Operating
   Process Alternative        kg/ton     $/annual ton     Cost, $/ton
Dry scrubbing
Wet scrubbing — once-through
Wet scrubbing--recycle
Recycle with bleed and
filtrate treatment
Once-through and alum
treatment
Once-through and activated
alumina treatment
Once-through and hydroxyla-
patite treatment
Once-through and reverse
osmosis treatment
0 40
5 7.4
1 10
0.05 11.5

1 18.3

0.25 9.7

0.25 21.9

0.8

10.2
2.5
4.6
5.2

11

6.3

16.5

24.5

Note:  ton = metric ton;  values are 10 percent lower for short ton.
                                  117

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Specific data on energy requirements were not available from most of the
plants surveyed.  Data supplied by Plant  D,   which  practices  cryolite
recovery  and  recycle  on secondary (potroom)  scrubber liquor, were  as
follows:

                                               Btu/tonAl
Thermal Energy
  Rotary kiln             75,000-151,200     300,000-600,000
  Steam generation        25,200- 75,000     100,000-300,000
  Total thermal energy   100,000-226,200     400,000-900,000

Electrical Energy
  Pumps               41 kwhr/metric ton Al (37 kwhr/ton Al)


The total energy requirement expressed in terms of equivalent electrical
energy is 165 to 330 kwhr/metric ton (150 to 300 kwhr/ ton Al) , which is
0.7 to 1.5 percent of the energy consumed by the rest  of  the  smelting
operation.   An  estimate,  supplied  by  Plant E, was 13.3 kwhr for the
electrical power alone required to operate a similar  cryolite  recovery
system,  or  a factor of three lower than the corresponding estimate for
Plant D.  The electrical requirements for the operation of other control
and treatment options described in this document are expected to  be  of
similar  magnitude.   Because  the  energy  requirements  of control and
treatment methods represent only a small fraction of  the  total  energy
consumed  in  the  primary  aluminum  industry,  it  is  concluded  that
difference in energy requirements will not be a deciding factor  in  the
choice of control and treatment technology.


Solid_Waste_Production

A  number  of  the control and treatment technologies identified in this
document produce solid waste as  an  adjunct  to  their  operation.   An
exception  is  the conversion of wet- scrubbing systems to dry scrubbing.
This technology does net produce a solid waste, but rather,  allows  the
collected  particulates  and,  gases  to  be returned to the electrolytic
cell.

Limited data on the quantiites of solid waste produced  were  available.
Plant  D,  which practices cryolite precipitation, must dispose of about
30 kg/metric ton Al  (60 Ib/ton Al) of solid  waste  containing  cryolite
and  carbon.   Waste  water  treatment  by  addition  of lime produces a
calcium fluoride sludge.  Plant G reported the production  of  25-30  kg
sludge/metric  ton  Al   (50-60  Ib  sludge/ton  Al) from this treatment.
Plant C reproted about 15 kg sludge/metric ton Al  (30 Ib sludge/ton  Al)
from the same treatment.
                                  118

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Summary

The  energy  requirements  and  solid  waste  production for the various
control and  treatment  technologies  are  summarized  for  purposes  of
comparison  in TABLE 9.  The values are calculated from data supplied by
various primary aluminum producers or are  estimated  on  the  basis  of
assumed  operating parameters.  The energy-use values are all calculated
to include the energy required by the scrubbing process in  addition  to
tJiat  required by the subsequent treatment process in order to provide a
direct comparison of wet scrubbing  plus  various  treatments  with  dry
scrubbing.  The data shew that dry scrubbing compares favorably with wet
scrubbing  plus  recycle.  In any case the energy requirements are small
when compared with the energy used by the rest of the  primary  aluminum
process which is about 22,000 kwhr/metric ton (20,000 kwhr/short ton).
                                  119

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TABLE 9.  ENERGY REQUIREMENTS AND SOLID WASTE PRODUCTION FOR VARIOUS
          WATER EFFLUENT CONTROL AND TREATMENT TECHNOLOGIES
    Process
                                   Energy Use
Electrical,
 kwhr/ton
 Thermal,
Equivalent
 kwhr/ton
   Sludge
 Production
	kg/ton
Dry Scrubbing                  233

Primary wet scrubbing           84
 with recycle - Process A
                   0

                 200
                  0

                 73
Secondary wet scrubbing
with recycle
Primary wet scrubbing -
once through - Process B
Process A plus bleed and
filtrate treatment
Process B plus alum
treatment
Process B plus activated
alumina treatment
Process B plus hydroxy-
lapatite treatment
Process B plus reverse
osmosis treatment
394 200
84
85-395 200
100
100
100
546
76
40
77
123
110
-
60
Note:  ton = metric ton; values are 10 percent lower for short ton.
                                 120

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                               SECTION IX
             BEST PRACTICABLE CONTROL TECHNOLOGY CURRENTLY
                 AVAILAELE, GUIDELINES, AND LIMITATIONS


                              Introduction


The  effluent  limitations  which  must be achieved July 1, 1977, are to
specify  the  degree  of  effluent  reduction  attainable  through   the
application   of  the  test  practicable  control  technology  currently
available.  Best practicable control technology currently  available  is
based  upon  the  average  of the best existing performance by plants of
various sizes, ages, and unit processes within the  industrial  category
and/or  subcategory.   This  average  is not based upon a broad range of
plants  within  the  primary  aluminum  industry,  but  is  based   upon
performance levels achieved by exemplary plants.

Consideration also must be given to:

(a)  the total cost of application of technology in relation to
     the effluent reduction benefits to be achieved from such
     application;

(b)  the size and age of equipment and facilities involved;

(c)  the processes employed;

(d)  the engineering aspects of the application of various types
     of control techniques;

(e)  process changes;

(f)  nonwater quality environmental impact  (including energy
     requirements) .

The  best  practicable control technology currently available emphasizes
treatment facilities at the end of a manufacturing process but  includes
the  control  technologies within the process itself when the latter are
considered to be normal practice within an industry.

A further consideration  is  the  degree  of  economic  and  engineering
reliability   which  must  be  established  for  the  technology  to  be
"currently available".  As a result  of  demonstration  projects,  pilot
plants  and general use, there must exist a high degree of confidence in
the engineering and economic practicability of  the  technology  at  the
                                   121

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time  of  commenceirent  of  construction  or installation of the control
facilities.

                    Recommended Ef f luent_Limj.tations

Based on the information contained in Sections III through VIII of  this
report,  the best practicable control technology currently available  for
the primary aluminum smelting subcategory is the; removal of fluoride  by
precipitation  and  recycle  of  the  clarified  liquor.   The  effluent
limitations attainable through the application of the  best  practicable
control technology currently available are as follows:


                                   Ef f luent_I;imj.tatigns __ {a)
Effluent                   Single Day Maximum (b)^   30-Day Average  (c)^
Characteristic             ]$
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difficulty  and  the  company reported a range of values for fluoride of
0.4, 16, and 52 mg/1 for  low,  average  and  high,  respectively.   The
average  value of 16 irg/1 was used to derive the value 0.7 Ib.  F/ton Al
entered in Table 4 .  The maximum value of 52 mg/1 would give an effluent
loading of  2.2  Ib  F/ton  Al.   The  data  obtained  during  a  second
verification  sampling  trip support the higher value.  If the value 2. 2
Ib F/ton Al is taken for Plant D, the  average  of  the  5  plants  with
fluoride  values  reported is 1. fr Ib F/ton Al.  This was rounded to 2 Ib
F/ton Al to obtain the recommended effluent limitation.  Note  that  all
five of these plants use cryolite precipitation with recycle.

The  average  of  the  six values for suspended solids is 3.7 Ib/ton Al.
Since Plant I sends its effluent to a companion plant,  the  solids  are
probably  not  settled  with care.  Hence the high value for Plant I was
given lesser weight and the average value rounded down to 3 Ib/ton Al to
arrive at the recommended effluent limitation.

The five values for oil and grease average 0.28 Ib/ton Al.   This  value
was  rounded  up  to 0.5 Ib/ton Al to arrive at the recommended effluent
limitation.

The cyanide effluent limitation is based upon data from plant  J.   This
plant  reprocesses  spent cathodes to recover cryolite values and can be
expected to have more cyanide in its waste water than plants which store
on site or otherwise dispose of spent cathodes.  Data from plants I  and
K,   which  do  not  process  spent  cathodes,  indicate  lower  cyanide
discharges than plant J.

The effluent limitations described above  and  referred  to  as  "30-day
average"  values  are  the  maximum  average  of  daily  values  for any
consectuive 30-day period.  The single day maximum effluent  limitations
were  derived  by  comparing the maximum discharge and average discharge
values taken from Corps of Engineers Discharge Permit Applications.  The
ratio of maximum fluoride discharge for 10  companies,  for  which  such
data  v/.'re  available,  ranged from 1.1 to 10.7 with an average value of
2.8.  When the highest value was deleted, the average  ratio  was  1.75.
For  suspended  solids the range of ratio values was 1.2 to 18.3 with an
average of 3.4.  When the highest value was deleted, the  average  ratio
was  1.78.   Data  on  the maximum and average oil and grease discharges
were available for only 3 companies.  The ratio values  were  1.1,  1.2,
and  3.2, with an average ratio of 1.8.  On the basis of these data, the
single  day  maximum  effluent  limitations  for  each  pollutant   were
established  at  a  factor  of  two  greater  than  the  30-day  average
limitations.

              Recommghded Ef flijentLimitations
The effluent limitations recommendations  are  based  on  the  following
considerations :
                                  123

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(1)  Achievement of the recommended effluent limitations by  all  primary
    aluminum  plants will result in a marked,  industry-wide reduction in
    the discharge of pollutants.

(2)  The recommended effluent limitations  are   based  on  treatment  and
    recycle  of  wet-scrubber  water  as summarized in the next section.
    However, alternate technologies have been  identified which also  can
    be  employed  to achieve the recommended effluent limitations.   This
    flexibility of approach will allow each company to take advantage of
    local conditions of climate, existing facilities, staff  experience,
    and  other  circumstances  to  achieve the effluent limitations in a
    manner most compatible with intermediate and longrange goals.

(3)  The recommended limitations are realistic, in that  about  one-third
    of  the  primary  aluminum  plants currently are able to achieve the
    recommended effluent reductions.


                   Identification of Best Practicable
                 Control_Technology Currently,.Available


The best practicable control  technology  currently  available  for  the
primary  aluminum  industry  is  the treatment of wet-scrubber water and
other  fluoride-containing  effluents  tc  precipitate   the   fluoride,
followed  by  settling cf the precipitate and recycling of the clarified
liquor to the wet scrubbers as a means  of  controlling  the  volume  of
waste   water  discharged.   Two  precipitation  methods  currently  are
available:  cryolite precipitation, and precipitation with lime.


Precipitation of_Cryolite


The technology for cr,yolite precipitation is presented in  Section  VII.
To implement this technology requires:

(1)  Segregation  of  fluoride-containing  waste  water   for   treatment
    including:   potline  scrubber  water, potroom scrubber water,  anode
    bake plant scrubber water, used-cathode disposal  liquor  or  runoff
    from   used-cathode   storage   area,  and  storm  water  runoff  if
    contaminated with fluoride.

(2)  Recycling clarified liquor after precipitation of  cryolite.   Total
    recycle  is  not  possible.   A bleed from the system is required to
    prevent sulfate build-up in the recycled liquor.

(3)  Minimizing the volume of the bleed stream so that  the  quantity  of
    pollutants  discharged  in  the  bleed  stream  does  not exceed the
    effluent limitations.
                                   124

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(4)  Providing a holding pond or  lagoon,  if  necessary,  to  accomplish
    further  settling  cf  solids  in  the  bleed  stream, and providing
    aeration of the lagccn to accomplish oxidation of oil and grease, if
    necessary.


Lime Precipitation


The technology for lime precipitation is presented in Section  VII.   To
implement this technology requires:

(1)  Segregation  of  fluoride-containing  waste  waters  as  listed  for
    precipitation of cryolite.

(2)  Recycling clarified liquor after precipitation of calcium  fluoride.
    Bleed as necessary to maintain the quality of the recycle stream.

(3)  Minimizing the volume of the bleed stream.

(U)  Providing a holding pond or lagoon  if  necessary  to  minimize  the
    dischare of suspended solids, and oil and grease.


Alternative_Control_Technolo
-------
    Reuse_of_Ef^luent_by_a_Com£an_ion_O£eration.   One  primary  aluminum
plant  currently  achieves  zero  discharge of pollutants by sending all
effluent water to the nearby plant for use  as  make-up  water.   Again,
this practice is exemplary.  However, this is a unique situation and the
practice cannot be cited as "currently available".


Rationale for the Selection of Best^Practicable Control
T§chnologY_CurgentlymAvailable


The selection of best practicable control technology currently available
was based on the following considerations:

(1) The lowest unit effluent loadings for fluoride, suspended solids and
    oils and grease, are currently attained by  plants  using  dry  fume
    scrubbing, total impoundment of effluent, reuse of effluent water by
    a  companion  operation,  or  wastewater  treatment  to  precipitate
    fluoride with recycle of  water  to  control  the  volume  of  water
    discharged.   The first three alternatives are limited in one way or
    another in their applicability, and are not feasible for all  plants
    in  the  primary  aluminum smelting subcategory at the present time.
    The fourth alternative  was  selected  as  the  recommended  control
    technology.

(2) The  selected  technology  is  capable  of   achieving   significant
    reductions  in  discharge  of  pollutants as verified by analysis of
    samples collected on-site at three plants practicing  variations  of
    the indicated control technology.

(3)  In addition to control of fluoride discharges, the selected control
    technology  also  achieves  reduction  in  the  discharge  levels of
    suspended solids and of oil and grease.

(4) This technology is compatible with  all  known  industry  variations
    such as:  age and size of plant, processes employed, plant location,
    and  anode  type.   Thus,  this  technology could be employed by any
    plant at the option of the company management.

(5) This level of technology is practicable because at  least  one-third
    of the 31 plants currently practice some form of precipitation-plus-
    recycle technology.

(6) It is concluded that the effluent  reduction  benefits  balance  the
    costs  of  this  technology.  Cryolite recovered and returned to the
    aluminum reduction process is a  potential  credit  to  the  control
    technology  costs.   One  company  has a market for calcium fluoride
    produced by lime precipitation.  Based on the  information  contained
    in  Section  VIII,  it  is concluded that those plants not presently
    achieving the recommended July 1, 1977, limitations would require an
                                   126

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    estimated  capital  investment  of  about  $10/annual   metric   ton
    ($9/annual  short  ton)  and  an  increased  operating cost of about
    $4.6/metrie ton ($4.27 short ton) in order to achieve  the  effluent
    limitations.


                   Guidelines for'the Application^of
                        the Effluent Limitations"^


The  following  guidelines  are  suggested  for  the  application of the
recommended effluent limitations:


(1)  The effluent limitations apply to the sum of all discharges from the
    plant, with the exception  of  the  discharge  from  sanitary  waste
    treatment and with the exception cited in the next paragraph.

(2)  A limited number cf primary aluminum smelters have metal fabrication
    facilities, such as rod mills, rolling mills, etc., on  the  primary
    reduction  plant  site.   The  effluent  limitations  stated in this
    document are  not  intended  to  apply  to  such  metal  fabrication
    operations.
                                   127

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                               SECTION X

                 BESTAVAILABLETECHNOLOGYECONOMICALLY
                              iQtroduction

The  effluent limitations which must be achieved by July 1 ,  1983, are to
specify  the  degree  of  effluent  reduction  attainable  through   the
application  of best available technology economically achievable.  This
technology  can  be  based  on  the  very  best  control  and  treatment
technology  employed  by  a  specific  point  source within the industry
category and/or subcategory or technology that is  readily  transferable
from  one  industry process to another.  A determination must be made as
to the availability of control measures and practices to  eliminate  the
discharge   of   pollutants,  taking  into  account  the  cost  of  such
elimination.

Consideration must also be given to:

(a)  the age of the eguipment and facilities involved;

(b)  the process employed;

(c)  the engineering aspects of the application of various types
     of control technologies ;

(d)  process changes;

(e)  cost of achieving the effluent reduction resulting from the
     technology;

(f)  nonwater quality environmental impact  (including energy
     requirements) .

The best available technology economically achievable also assesses  the
availability  in all cases of in-process controls as well as the control
or additional treatment techniques employed at the end of  a  production
process.

A  further  consideration  is  the availability of processes and  control
technology at the pilot plant, semi-works, or other levels,  which  have
demonstrated both technological performances and economic viability at a
level  sufficient  to  reasonably  justify investing in such facilities.
Best available technology economically achievable is the highest  degree
of control technology that has been achieved or has been demonstrated to
be  capable  of  being  designed  for  plant  scale  operation up to and
including no discharge of pollutants.   Although  economic  factors  are
considered,  the costs for this level  cf control are intended to  be top-
of-theline of current  technology  subject  to  limitations  imposed  by
                                   128

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economic   and   engineering   feasibility.    However,  best  available
technology  economically  achievable  may  be  characterized   by   some
technical risk with respect to performance and with respect to certainty
of   costs   and   thus  may  necessitate  some  industrially  sponsored
development work prior to its application.

                    Recommended_Effluent Limitations

Based upon the information contained in Sections  III  through  VIII  of
this   report,  a  determination  has  been  made  that  Best  Available
Technology Economically Achievable for  the  primary  aluminum  smelting
subcategory  is  the  lime treatment of the bleed stream from a fluoride
precipitation and recycle system.  The effluent  limitations  attainable
through  the  application  of the best available technology economically
achievable are as follows:

                        	t	^	Effluent Limitations (a)	
Effluent                Single Day Maximum (b|   30-Day^ Average {c^
Characteristic          ]$2/k]£3Al   "^Ib/tonAl   kg/kkgAl  Ib/tonAl

Fluoride                   0.1        0.2        0.05      0.1
Suspended Solids           0.2        0.4        0.1       0.2
Oil and Grease             0.03       0.06       0.015     0.03
Cyanide                    0.01       0.02       0.005     0.01
pH Range  6-9

(a) Effluent limitations are  defined  as  kilograms  of  pollutant  per
    metric ton of aluminum produced or pounds of pollutant per short ton
    of aluminum produced.

(b) The single day maximum is the maximum value for any one day.

(c) The 30-day average is the maximum average of daily  values  for  any
    consecutive 30 days.
The  effluent  limitations  recommendations  are  based on the following
considerations :

 (1) Achievement of the recommended effluent limitations by  all  primary
    aluminum  plants  will  result  in an additional 90-95% reduction in
    pollutant discharges by 1983 relative to the levels recommended  for
    achievement by 1977.

 (2) The  recommended  effluent  limitations  are  based  on   additional
    treatment  of  wet scrubber water as summarized in the next section.
    It represents a stepwise approach to near zero pollutant  discharge,
                                   129

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    the  first  step  to  be  completed  by 1977, and the second step in
    logical sequence to be completed by 1983.

(3)  Alternate technologies, such as dry scrubbing and total impoundment,,
    have been identified which also  can  be  employed  to  achieve  the
    recommended  effluent  limitations.   These alternative technologies
    are options open to each company which provide for a flexibility  of
    approach to water pollution abatement.

  Identification of Best Ayailable_Technglogy-_EconoinicallY_Achievable

The  application  cf  the  best practicable control technology currently
available as described in Section VII and IX, results  in  a  relatively
low-volume,   high-concentration   bleed  stream.   The  best  available
technology economically achievable is the lime  precipitation  treatment
of  such  a  bleed  stream  to further reduce the discharge of fluoride.
Such techniques  are  described  in  Section  VII.   To  implement  this
technology requires:

(1)  Restriction of the volume  of  fluoride-containing  effluent  to  be
    treated  to  approximately  5000  liters  per metric ton of aluminum
    (1200 gallons per short ton) and treating the stream  with  lime  or
    calcium  chloride  to  reduce  the fluoride concentration to a final
    value of approximately 10 mg per liter.

(2)  Alternatively, volumes as high as 50,000 liters per  metric  ton  of
    aluminum  (12,000 gallons per short ton) t.r€;ated to a final fluoride
    concentration of 1  mg  per  liter  would  achieve  the  recommended
    effluent   limitations.    Treatment   to   1  mg  per  liter  final
    concentration would require processing by adsorption  methods  which
    are  not  state-of-the-art  methods in the primary aluminum industry
    but  which  could  be  adapted  from  relat€»d   water   conditioning
    applications.

             Ratignale^for Selection of the Best Ayailablg
                   T§ chnol o_2y_ Econom ical^y; ^Achievable


The  selection  of the best available technology economically achievable
was based on the following considerations:

(1)   Effluent loadings substantially lower than those  achieved  by  the
    best  practicable  control  technology  currently  available  can be
    achieved  by  following   such   treatment   with   a   second-stage
    precipitation of fluoride.

(2)   While such second-stage treatment is not  practiced  currently,  it
    represents  similar  technology  applied to a smaller stream, hence,
    the technology can be considered to be available.
                                   130

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(3)   Based on information contained in Section  VIII,  it  is  concluded
    that  those  plants  already  in  compliance  with the July 1, 1977,
    effluent limitation, but not achieving the July  1,  1983,  effluent
    limitations,  would have to invest an additional $3.87 annual metric
    ton   ($3.5/annual  short  ton)   and  would  require  an   additional
    operating  cost  of  about  $1.13/metric  ton ($1.0/short ton).  The
    breakdown of these costs is as follows:

                                        Capital       Operating
                                      $/annual metric  S/metric
                                      	ton	ton	

Additional fluoride and suspended
  solids treatment on scrubber water       1.5            0.6

Anode bake furnace scrubber water
  treatment                                0.7            0.13

Cast-house cooling water control and
  treatment                                1..6            O.t^

                         TOTAL             3.8            1.13


                     Guidelines for the Application
                      of the_Effluent_Limitations "


The guidelines cited in Section IX for the application of  the  July  1,
1977,  effluent  limitations apply equally to the July 1, 1983, effluent
guidelines.

The concentration of pollutants in the outfall from a  primary  aluminum
plant achieving the recommended July 1, 1983 effluent limitations may be
below  analytically  detectable  limits.   Therefore, sampling to assure
compliance may  be  required  on  internal  fluoride-containing  streams
before dilution by other streams.
                                  131

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                               SECTION XI
                    NEW SOURCE PERFORMANCE STANDARDS


                              Introduction


The  standards  of performance which must be achieved by new sources are
to specify the degree  of  effluent  reduction  attainable  through  the
application  of higher levels of pollution control than those identified
as  best  available  technology  economically  achievable  for  existing
sources.   The  added  consideration  for  new  sources is the degree of
effluent reduction attainable through the  use  of  improved  production
processes and/or treatment techniques.  The term "new source" is defined
by  the  Act to mean "any source, the construction of which is commenced
after publication of proposed  regulations  prescribing  a  standard  of
performance".

New  Source  Performance Standards may be based on the best in-plant and
end-of-process   technology   identified.    Additional.   considerations
applicable  to  new  source  performance  standards  take  into  account
techniques for reducing the level of effluent by changing the production
process itself or adopting alternative processes, operating methods,  or
other  alternatives.   The  end  result  will  be  the identification of
effluent standards which reflect levels of  control  achievable  through
the   use   of   improved  production  processes   (as  well  as  control
technology) , rather than prescribing a particulcir  type  of  process  or
technology which must be employed.  A further determination must be made
as  to  whether  a  standard  permitting  no  discharge of pollutants is
practicable.

Consideration must be given to:

 (a)  the type of process employed and process changes

 (b)  operating methods

 (c)  batch as opposed to continuous operations

 (d) use of alternative raw materials and mixes of raw materials

 (e) use of dry rather than  wet  processes   (including   substitution  of
    recoverable solvents for water)

 (f) recovery of pollutants as by-products.
                                   132

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Standards of Performance are applicable to new sources  in  the  primary
aluminum smelting subcategory.

                Standards of Performance for New Sources

Based  on the information contained in Sections III through VIII of this
report, the best available demonstrated control  technology,  processes,
operating  methods,  cr  other  alternatives  for  the  primary aluminum
smelting subcategory is the dry scrubbing of potline  air,  the  control
and  treatment  of  fluoride-containing  waste  streams  by  recycle  and
treatment of any necessary bleed stream by lime precipitation,  and   the
treatment of casthouse cooling water and other streams, as required,  for
oil  and grease removal with a gravity separator or aerated lagoon.   The
standards of performance attainable  through  the  application  of  this
technology are as follows:

                            	Ef fluent_Limitations_(aJ	

Effluent                    §iQ2i§_Day._Maximum_£b)_    30 Day Average_(c)_._
Ch§.£acteristic              JSH^JsiSS^l  Ik/ton         JS3/JsJS3_Al   Ifc/ton
Fluoride                      0.05     0.1             0.025        0.05
Suspended Solids              0.1      0.2             0.05         0.1
Oil and Grease                0.03     0.06            0.015        0.03
Cyanide                       0.01     0.02            0.005        0.01
pH Range  6-9

(a) Effluent limitations are  defined  as  kilograms  of   pollutant  per
    metric ton of aluirinum produced or pounds of pollutant per  short  ton
    of aluminum produced,

(b) The single day maximum is the maximum value for any one day.

(c) The 30-day average  is the maximum average of daily  values   for  any
    consecutive 30 days.

           Rationale  for_Recommended Standardg of^Performance

The  recommendation   of  the  standards  of  performance  for the primary
aluminum smelting subcategory is based on the following considerations:

(1) A new source has  complete freedom of design so that   unit   processes
    can be chosen to  irinimize the use of water in the plant.

(2) Dry fume scrubbing  processes are avialable for air pollution control
    of potline air.   The use of such systems in  the  design  of  a  new
    plant  will  eliminate  potline  wet  scrubbers as a  source of waste
    water contaminants.
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(3)  Even with dry scrubbing of  potline air,  certain water uses  will  be
    required.  There are no demonstrated dry scrubbing systems for anode
    bake  plant  flue gases which achieve acceptable control of fluoride
    emissions to the atmosphere,  thus wet scrubbing may be  required  on.
    anode  bake  plants to meet air pollution control regulations.   Cast
    house cooling  water  can  be  recycled   through  a  cooling  tower,
    however,   a  bleed  is  required to prevent buildup of dissolved and
    suspended solids, as well as oil and grease.

(4)  Water from anode bake plant wet scrubbers and the cast house cooling
    water bleed streair can be  treated  to  minimize  the  discharge  of
    pollutants,  but  no  discharge  of  process  waste water pollutants
    cannot  be  achieved  by  any  demonstrated  control  or   treatment
    practice.

(5)  The recommended effluent limitations for new sources are  lower  for
    fluoride  and  suspended  solids  than  those applicable to existing
    sources by July 1, 1983 because the availability to new  sources  of
    dry scrubbing for potline air eliminates that source of fluoride and
    suspended  solids pollutants.  In a prebaked anode plant the oil and
    grease levels will be unaffected by dry  scrubbing of potline air.

                    Identificatior^of^Best Available
                    Cemcnstrated_Cgntrol^ Technology^
          Processes j^Cserating Methods^or^Other Alternatives


As the primary smelting of aluminum requires no process water  directly,
the  principal area where use of water can be minimized in the design of
a new plant is the application of dry fume scrubbing of potline air  for
air   pollution   control.    Such   methods   exhibit  high  collection
efficiencies and the fluoride  values  contained  in  the  fume  can  be
recovered  in  a  form  amenable  to  recycle  to  the smelting process.
Alternate technologies which may be employed in certain circumstances to
achieve no discharge of pollutants are wet scrubbing for  air  pollution
control  with  total  impoundment  of  the  scrubber water or with total
recycle of the scrubber water.

Other alternative unit process designs which  have  been  identified  in
currently   operating  plants  have  included  air-cooled,  solid  state
rectifiers, which eliminate both use and discharge of rectifier  cooling
water,  and  a  number  of alternative methods of molten metal degassing
techniques (identified in more detail in Section  VII)  which  similarly
eliminate  both  use  and  discharge of cast house scrubber waste water,
while achieving compliance with air pollution control regulations.

The treatment technology for fluoride and suspended  solids  removal  in
waste water from anode bake plant wet scrubbers required for new sources
consists  of  lime precipitation of the fluoride followed by settling of
the solids and recycle of the  clarified  liquor  to  the  scrubbers  as
                                  134
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required  to  control  the  volume  of  waste  water  discharged.   This
technology is not currently practiced with high effectiveness  on  water
from  anode  bake plant wet scrubbers but is analogous to that presented
in Section VII for water from potline wet  scrubbers.   The  recommended
standards  of performance require restriction of the discharge volume to
835 liters per metric ton of aluminum (200 gallons per short ton)  at  a
final   fluoride  concentration  of  30  mg  per  liter,  or  equivalent
combination of fluoride level and volume.   This  treatment  requirement
can  be  minimized  by  careful removal of fused cryolite and other bath
materials from the anode  butts  before  recycling  them  to  the  anode
preparation  operation.   Good  quality  control  of that operation will
result in lower fluoride loads in the anode bake plant scrubber water.

The treatment technology for oil and grease  in  the  casthouse  cooling
water  bleed stream and, if required, in the treated effluent from anode
bake plant wet scrubber circuit, consists of providing a holding pond or
aerated lagoon to accomplish oxidation of the oil and grease.

                Rationale for the Selection of the Best
               Available Demonstrated Control Technology

The rationale for the selection of the technology cited in this  section
is as follows:

     (1)  Dry fume scrubbing methods for potline air have been  developed
         and are currently in use within the primary aluminum industry.

     (2)  At the present state of development, dry scrubbing systems  are
         not universally applicable.

     (3)  A new source, in  contrast  to  an  existing  source,  has  the
         freedom  to  select primary smelting technology compatible with
         dry fume scrubbing.

     (4)  The control and treatment technologies recommended for  dealing
         with  the  remaining  water  uses  are  available  and  can  be
         incorporated in the new plant design.

                 Guidelines for the Application of the
                        Standards of Performance^   ~*

The guidelines for the application of the effluent limitations appearing
in Sections IX and X also apply to the standards of performance for  new
sources.
                                   135

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                              SECTION XII
                            ACKNOWLEDGEMENTS


Individuals,  companies, and associations assisted in the course of this
study.  While published information has been used, the far greater input
to this report has been data and information provided in  written  form,,
conferences,  plant  trips,  telephone conversations, etc, all requiring
personal attention by numerous people in the primary aluminum industry.

Particular appreciation is expressed to the personnel at  the  following
plants   which   were   visited   and  to  the  corresponding  corporate
headquarters:

    Alcoa; Point Ccmfort, Texas
    Alcoa; Wenatchee, Washington
    Eastalco; Fredrick, Maryland
    Intalco; Ferndale, Washington
    Kaiser; Chalmette, Louisiana
    Martin-Marietta; The Dalles, Oregon
    Ormet; Hannibal, Ohio
    Reynolds; Corpus Christi, Texas
    Reynolds; Longview, Washington
    Reynolds, Troutdale, Oregon

Acknowledgement  is  also  made  of  the  assistance  of  The   Aluminum
Association and the Clean Water Subcommittee of that association.

Acknowledgement is also due for the assistance and direction provided by
those  associated with the Effluent Guidelines Division program: Messrs..
Allen Cywin, Ernst Hall, Walter Hunt and Edward Dulaney.  The  technical
contributions of Mr. John Ciancia are especially acknowledged.  Finally,
the  assistance  of  Ms.  Chris  Miller,  Ms.  Nancy  Zrubek and Ms. Kit
Krickenberger was invaluable in the timely preparation of this report.
                                   136

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                              SECTION XIII
                               REFERENCES
(1)   Kirk-Othmer,  EncYclO2edia_of_Chemical_Technoloc[^, ^  (2)
     Interscience, 1963, p 941."                  "    ~"

(2)   Toddr  D.  K.,  (Editor), The Water Encyclopedia, Water
     Information Center, Port Washington, N.Y., 1970, p 91.

(3)   U.S.  Naval Weather Service, 8, May 1969, AD688472.

(4)   Gulp,  R.  L.,  and Stoltenburg, H. A., "Fluoride Reduction
     at La Crosse, Kansas", J. Amer. Water Works Assoc.,  50,
     423 (1958) .

(5)   Zabban, W., and Jewett, H. W., "The Treatment of Fluoride
     Wastes",  Proc.  22nd Purdue Industrial Waste Conference,
     pp 706-716 (1967) .

(6)   Wamsley,  R.,  and Jones, W. E., "Fluoride Removal", Water
     and Sewage Works, 94, 372  (1947).

(7)   Peters, M. S.,  and Timmerhaus, K. D., Plant Design and
     Economics for Chemical Engineers, 2nd Ed., McGraw  Hill
     Book Company, NevTYork, N.Y., 1968.

(8)   Eckenfelder,  W. W. Jr., Water Quality, Engineering  for
     p£££ticj.ncL_Enc[ineers, Barnes and Noble, Inc., New  York,
     N.Y.,~1970.

(9)   Nielsen,  K.,  and Kielback, A. W., "Recent Developments in
     Dry Scrubbing Technique", Proc. of Symp., 101st AIME
     Meeting on Environmental Control, San Francisco, Calif.,
     Feb.  20-24, 1972.

(10)  cook, G.  C.,  and Swany, G. R.,- "Evolution of Fluoride
     Recovery Processes Alcoa Smelters", Paper #A71-37,
     Metallurgical Society of AIME.

(11)  Rush, D., Russell, J. C., and Iverson, R. E., "Air
     Pollution Abatement on Primary Aluminum Potlines:
     Effectiveness and Cost", J. Air Pol. Control Assoc.,
     23 (2), 98 (1973).
                                   137

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                              SECTION XIV



                                GLOSSARY



Act

The Federal Water Pollution Control Act Amendments of 1972.


Alumina

The pure granular oxide of aluminum prepared from bauxite by  the  Bayer
process  and  added  periodically to the cells as the source of aluminum
ions for reduction to metal.


Ancillary Operations

Operations which are often carried out at primary  aluminum  plants  but
are  not an essential part of the processing, for example, rod, wire, or
rolling operations, power generation, etc.


Anode

The positively charged carbon block supported from above  and  extending
into the electrolytic bath.


Anode Paste

The mixture of pitch and petroleum coke from which anodes are formed.


Anode
Also  referred  to  as the "carbon plant", this is the facility in which
carbon for the anodes is received, comminuted,  classified,  mixed  with
pitch,  and formed into either anode blocks and baked for prebake plants
or into briquettes for delivery to Soderberg anodes at the cells.

Anode Shell

The metal form suspended above the electrolytic bath in which the  anode
paste is shaped as it is baked in moving into the hot bath.
                                    138

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Anthracite

A hard natural coal, low in volatile matter, which is ground, mixed with
pitch, and used in forming the cathodic lining of the cells.


Bath

Or electrolytic bath, is a molten mixture of cryolite, calcium fluoride,
and  alumina  serving  as  the liquid medium for movement of ions in the
electrolytic process.


Best, Available TechnglggY Economically Achievable

Level of technology applicable to effluent limitations to be achieved by
July 1, 1983r for industrial discharges to surface waters as defined  by
Section 301 (b) (2) (A) of the Act.


Bestr Practicable^Cgntrol_/Technoloqy Currently Available

Level of technology applicable to effluent limitations to be achieved by
July  1, 1977, for industrial discharges to surface waters as defined by
Section 301 (b) (1) (A) of the Act.


Bi-gas

Mixtures of chlorine and nitrogen used in degassing primary aluminum.


Capital Costs

Financial charges which are computed as the cost of  capital  times  the
capital  expenditures  for  pollution  control.   The cost of capital is
based upon a weighed average of the separate costs of debt and equity.

Cast House

The facility at a primary aluminum plant  which  receives  molten  metal
from  the  cells,  holds  it  in  furnaces  for  degassing  (fluxing) and
alloying and then casts the metal, into pigs, ingots, billets, rod, etc.


Category and Subcategory

Divisions of a particular industry which possess different traits  which
affect  waste  water  treatability  and would require different effluent
limitations.
                                   139

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Cathode

The negatively charged carbon cell lining in which the  molten  aluminum
collects and becomes the actual cathode.


Center-break JTechnglogY

A system applicable to cells having two rows of prebaked anodes in which
the  crust  of  frozen bath is broken between the rows of electrodes for
addition of alumina and withdrawal of aluminum.


Clarifieg

As used in this industry the term refers to a unit  which  provides  for
settling and removal of solids from a process stream.  See thickener.


cryolite

A natural or synthetic chemical compound (3NaF.AlF3) which in the molten
state forms the major part of the electrolytic bath in which the alumina
ore is dissolved.


Cyclone
^^ ^B-^VWi XBK^H ^^

A  unit  for  removal  of  particulate  matter  from  a  gas  stream  by
centrifugal action in a vortex flow  pattern.   The  principle  is  also
applied to cleaning of liquid flows.

Degassing	(Fluxing}

The  removal  of  hydrogen  and  other  impurities  from  molten primary
aluminum in a cast house  holding  furnace  by  injecting  chlorine  gas
 (often with nitrogen and carbon monoxide).


Depreciation

Accounting  charges reflecting the deterioration of a capital asset over
its useful life.


Dry gcrubber

A unit in which fumes are removed from an  air  stream  by  sorption  on
alumina  particles.   Filters for collection of alumina and other solids
is a part of this unit.
                                    140

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Dust^Cgllectgr

An air pollution control device for  removing  dust  from  air  streams.
Filtration,  electrostatic  precipitation, or cyclonic principles may be
utilized but the term usually infers a dry system, not involving a water
stream.


Effluent

The waste water discharged from a point source to navigable waters.


Effluent^Limitation

A maximum amount per unit of production of each specific constituent  of
the effluent that is subject to limitation in the discharge from a point
source.


Effluent^Loading

The quantity or concentration of specified materials in the water stream
from a unit or plant.


Electfolytic^cell

The  basic  production unit for primary aluminum, consisting essentially
of a cast ircn container  (for example 8 ft wide x 18  ft  long  x  3  ft
deep),  the  carbon  cathode  liner, the electrolytic bath, and a carbon
anode suspended from above.

Electrostatic Freeipitator

A unit for removing particulate solids from a gas stream  by  collecting
the  particles  on electrically charged plates or wires.  The system may
operate dry or the plates may be continuously cleaned by a falling  film
of water.


Fluxing (Degassing)^

The  removal  of  hydrogen  and  other  impurities  from  molten primary
aluminum in a cast house  holding  furnace  by  injecting  chlorine  gas
 (often with nitrogen and carbon monoxide).


Hall/Heroult Process
                                   141

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An  electrolytic  process  for  primary  production of aluminum in which
molten cryolite serves as the solvent  for  alumina.   The  process  was
invented  simultaneously  by  Hall  in  the United states and Heroult in
France in ^.886.


Hoods

Shrouds at the cells designed to promote capture of fumes  and  dust  by
air withdrawal systems.
Horizontal^Stud^Soderfcerg JHSS)  Plant (orAnode}

A  facility  for producing aluminum by the Hall/Heroulcl process in which
the anode material is supported on spikes or studs which extend into the
anode from the side, named for the  inventor  of  the  continuous  anode
system.


HydrQXYlapatj.te

A class of calcium hydroxy phosphate material prepared from bone char.


Investment Costs

The  capital  expenditures  required  to  bring the treatment or control
technology into operation.  These include the  traditional  expenditures
such  as  design;  purchase  of  land  and  materials;  etc.;  plus  any
additional expenses required to  bring  the  technology  into  operation
including  expenditures  to  establish  related  necessary  solid  waste
disposal.

New Sourge

Any building, structure, facility, or installation from which  there  is
or  may be a discharge of pollutants and whose construction is commenced
after the publication of the proposed regulations.
                                   t

Petroleum Coke

The carbon residue of petroleum refining used for making anodes.


Pitch
                                    142

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A class of thermoplastic carbonaceous  residues  mostly  from  petroleum
refining which is used as a hot-binder in making anodes and pot liners.


Point^ Source

An  individual plant, site or other location from which pollutants enter
navigable waters.


Pollutant Parameterg

Those constituents of waste  water  determined  to  be  detrimental  and
therefore requiring control.


Pot

A  common term for the electrolytic cell, also used to refer to only the
cast iron shell of that unit.


Pot_Gas

Gases (carbon monoxide, carbon dioxide,  hydrogen  fluoride)  fumes  and
dust arising at the cells during production of aluminum.


Potline

A  row of from 100 to 250 electrolytic cells connected in series forming
an electrical circuit.

Pgtliner

The brick and carbon structure used  to  separate  the  shell  from  the
molten  aluminum  and  electrolytic  bath in a cell.  Also, the material
removed when the cell is taken out of service.


potropm

The building housing a potline.  Usually  long  and  narrow  to  provide
ventilation along the line of pots.


Prebake Plant
                                   143

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A  facility  using  anodes  which have been baked and graphitized before
installation  in  the  Hall/Heroult  electrolytic  cell   for   aluminum
production.


PrJmary Air

That air stream drawn from around the cells in a primary aluminum plant.


Primary Aluminum

Aluminum  metal  prepared  from  an  ore as distinguished from processed
scrap metal.


Rectifier

A device which converts a-c into  d-c  by  virtue  of  a  characteristic
permitting appreciable flow of current in only one direction.


Reverse Qsmosj.s

A  recovery process in which the more concentrated solution is put under
a pressure greater than the osmotic pressure to drive water  across  the
membrane to the dilute stream while leaving behind the dissolved salts.


Rod Mill
A  facility  at  some  primary  aluminum plants for casting aluminum arid
forming rod usually about one-half inch in diameter.

Rodding^ Plant
            T
A facility for affixing support rods to baked anode  blocks  by  pouring
molten iron around the rod in a cavity in the top of the block.


SanitaryrWater

The supply of purified water used for drinking, washing, and usually  for
sewage transport and the continuation of such effluents to disposal.


Scrubber^Liquor

The liquid in which dust and fumes are captured in a wet scrubber.
                                   144

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Secondary Air

Air  in  a  potroom.   It  contains those pollutants not captured in the
primary air hood system.


Side-break^Technolggy

A system in which the frozen crust of the bath  is  broken  between  the
electrode  and  edge  of the cell for addition of alumina and removal of
aluminum.


Standard^gf^Performanee

A maximum weight discharged per unit of production for each  constituent
that  is  subject to limitation and applicable to new sources as opposed
to existing sources which are subject to effluent limitations.


Thickeners

A large tank for continuous  settling  and  removal  of  sludge  from  a
process stream.  Clarified liguid spills over the rim of the tank.


Tri-Gas

Mixtures  of  chlorine,  nitrogen, and carbon monoxide used in degassing
primary aluminum.


Vertical Stud Soderberg JVSS^ Plant	(or. Anode)

A facility for producing aluminum by the Hall/Heroult process  in  which
the anode material is supported on spikes or studs which extend into the
anode from above, names for the inventor of the continuous anode system.


ffastewater^Constituents

Those  materials which are carried by or dissolved in a water stream for
disposal.


Wet^Scrubber

A unit in which dust and fumes are   removed  from  a  gas  stream  to  a
liquid.    Gas-liquid  contact  is   promoted  by  jets,  sprays,  bubble
chambers, etc.
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                                    TABLE 10

                                 CONVERSION TABLE

MULTIPLY (ENGLISH UNITS)                   by                TO OBTAIN (METRIC UNITS)

    ENGLISH UNIT      ABBREVIATION    CONVERSION   ABBREVIATION   METRIC UNIT
acre                    ac
acre - feet             ac ft
British Thermal
  Unit                  ?TU
British Thermal
  Unit/pound            BTU/lb
cubic feet/minute       cfm
cubic feet/second       cfs
cubic feet              cu ft
cubic feet              cu ft
cubic inches            cu in
degree Fahrenheit       F°
feet       '             ft
gallon                  gal
gallon/minute           gpm
horsepower              hp
inches                  in
inches of mercury       in Hg
pounds                  lb
million gallons/day     mgd
mile                    mi
pound/square
  inch (gauge)          psig
square feet             sq ft
square inches           sq in
tons  (short)            t on
yard                    y d
       0.405
    1233.5

       0.252
ha
cu m

kg cal
0.555
0.028
1.7
0.028
28.32
16.39
0.555(°F-32)1
0.3048
3.785
0.0631
0.7457
2.54
0.03342
0.454
3,785
1.609
kg cal/kg
cu m/min
cu m/min
cu m
1
cu cm
°C
m
1
I/sec
kw
cm
atm
kg
cu m/day
km
(0.06805 psig +1)1  atm
       0.0929       sq m
       6.452        sq cm
       0.907        kkg
       0.9144       m
hectares
cubic meters

kilogram - calories

kilogram calories/kilogram
cubic meters/minute
cubic meters/minute
cubic meters
liters
cubic centimeters
degree Centigrade
meters
liters
liters/second
killowatts
centimeters
atmospheres
kilograms
cubic meters/day
kilometer

atmospheres (absolute)
square meters
square centimeters
metric tons (1000 kilograrr
meters
1 Actual conversion, not a multiplier
                                           146

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