U.S. DEPARTMENT OF THE INTERIOR
Federal Water Pollution Control Administration
                                VOLUME
                 INDUSTRIAL WASTE PROFILE NO. 3
                   PAPER MILLS, EXCEPT BUILDING

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Other publications in the
  FWPCA Publication No. I,
Industrial Waste Profile series
  Wp — 1 <
 . IT .  X <
  FWPCA Publication No. I.W.P.- 2:

  FWPCA Publication No. I.W.P.- 4:
  FWPCA Publication No. I.W.P.- 5:
  FWPCA Publication No. I.W.P.- 6:

  FWPCA Publication No. I.W.P.- 7:

  FWPCA Publication No. I.W.P.- 8:
  FWPCA Publication No. I.W.P.- 9:
  FWPCA Publication No. I.W.P.-10:
Blast Furnace and
 Steel Mills
Motor Vehicles and
 Parts
Textile Mill Products
Petroleum Refining
Canned and Frozen
 Fruits and Vegetables
Leather Tanning and
 Finishing
Meat Products
Dairies
Plastics Materials and
 Resins
             FWPCA Publication No. I.W.P.-3

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                    THE COST OF

                    CLEAN  WATER
                    Volume III

            Industrial  Waste Profiles
                I/;o. 3  -  Paper "ills
        U. G.  Department of  the Interior
Federal V.'ater Pollution Control Administration
    For sale by the Superintendent of Documents, U.S. Government Printing Office
                Washington, D.C., 20402 - Price $2

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                                PREFACE
The Industrial Waste Profiles are part of the National Kcquirentents and
Cost Estimate Study required by the Federal V.'ater Pollution Control Act
as amended.  The Act requires a comprehensive analysis of the require-
ment and costs of treating municipal and industrial wastes and other ef-
fluents to attain prescribed water quality standards .
      a
The Industrial Waste Profiles were established to describe the source
and nuantity of pollutants produced by each of the ten industries stud-
ied.  The profiles were designed to provide industry and government
with information on the costs and alternatives involved in dealing ef-
fectively with the industrial water pollution problcr. .  They include
descriptions of the costs and effectiveness of alternative methods of
reducing liquid wastes by changing processing- methods, by intensifying
use of various treatment methods, and by increasing utilization of
wastes in by-products or water reuse in processing.  They also describe
past and projected changes in processing and treatment methods.

The information provided by the profiles cannot possibly reflect the
cost or wasteload situation for a given plant.  However, it is hoped
that the profiles, by providing a generalized framework Tor analyzing
individual plant situations, will stimulate industry's efforts to find
raore efficient ways to reduce wastes than are generally practiced today.
                                   ^_^/  Commissioner          J
                         Federal Water Pollution Control Administration

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                 PAPER MILLS
          INDUSTRY WASTEWATER PROFILE
            Prepared for F.W.P.C.A.
        F.W.P.C.A. Contract  14-12-10
                June 30,  196?
Federal  Water Pollution  Control  Administration
                 November  196?

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                      SCOPE  OF MATERIAL COVERED

     The industrial wastewater profile covers the Paper  Industry and
Integrated pulp  and paper mills  in the United States as  defined by
Standard Industrial Classification 2621 (except buildings) of the
U. S. Department of Commerce.  The principal areas of discussion are:
the fundamental  manufacturing processes and significant  water and
gaseous wastes generated by  each operation, process water use and re-
use, waste quantities  and characteristics, waste reduction practices
(including both  waste  treatment and  in-plant processing) and their
effectiveness, and waste treatment costs.  Projections or estimates
have been made for the changes, developments, and operating practices
that will be prevalent in 1977 for each area of discussion.

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                          TABLE OF CONTENTS

                                                            Page No.

PROJECT PARTICIPANTS

LIST OF TABLES

LIST OF DRAWINGS

SUMMARY                                                    S1-S16

INDUSTRIAL MANUFACTURING PRACTICES                              1
  Definition of Fundamental Manufacturing Processes             1
    Wood Preparation                                            1
      Log Transportation                                        I
      Debarking                                                 1
      Bark Disposal                                              2
      Chipping                                                  2
    Pulping                                                     2
      Mechanical (Groundwood)  Pulp                              2
      Chemlgroundwood Pulp                                      3
      Sulfate (Kraft) Pulp                                      3
      Sulflte Pulp                                              3
      Semi chemical Pulp                                         3
      Blow Tank                                                 *t
      Deinkfng                                                  k
    Pulp Washing                                                A
    Liquor Recovery                                             5
      Kraft Liquor                                              5
      Sulfite Liquor                                            5
      Semi chemical Liquor                                       5
    Pulp Screening and Cleaning                                 6
    Thickening and Dewatering                                   6
    Bleaching                                                   6
    Stock Preparation                                           7
    Paper Machine Operation                                     8
    Finishing and Converting Operations                         9
  S i gnIfI cant Wate r Was tes                                      10
  Process Water Reuse                                           12
  Industry Subprocess Mix                                       16
  Subprocesses With Difficult Waste Control Problems            19
  Three Production Process Streams                             20

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                          TABLE OF CONTENTS
                             (continued)

                                                            Page No.

GROSS WASTE QUANTITIES BEFORE TREATMENT OR DISPOSAL            23
  Un!t Waste Quantities and Wastewater Volumes                 23
  Total Wasteloads and Wastewater Quantities for
   Each of the Three Technology Levels                         2k
    Base Year 1963                                             2**
  Gross Wasteloads and Wastewater Quantities Produced
   by  Industry in Base Year 1963                               25
  Projected Gross Wasteloads and Wastewater Quantities
   In the Years 1968 through 1972 and 1977                     27
  Seasonal Waste Production Patterns by Month                  27

WASTE REDUCTION PRACTICES                                      29
  Processing Practices                                         29
    Waste Reduction Efficiency                                 29
    Technological Considerations on Waste Production
     and Interdependencies Among Processes                     30
  Wastewater Treatment Practices                               31
    General                                                    31
    Waste Removal Efficiencies for the Base Year               32
    Sequence and Alternatives in Mill Wastewater Treatment      34
      Pretreatment                                             35
      Primary Treatment                                        38
      Secondary Treatment                                      39
      Tertiary Treatment                                       43
    Sludge Disposal                                            46
    Strong Wastes Disposal                                     48
    Wastewater Treatment By-Products                           49
    Rate of Adoption of Wastewater Treatment Practices          49
    Wastewater Discharge to Municipal Sewers                   52
  By-Product Utilization                                       54
    From Spent Liquor                                          54
      Turpentine                                               55
      Tall Oil                                                 55
      Yeast                                                    55
      Alcohols                                                 56
      D.M.S.O.                                                 56
      Vanillin                                                 56
    Bark By-Products                                           56
    Others                                                     56

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                          TABLE OF CONTENTS
                             (continued)

                                                            Page No.

WASTE REMOVAL ECONOMICS                                        58
  Replacement Value                                            58
  Capital and Operating Costs                                  58
    General                                                    58
    Technology Related Costs                                   60
  Treatment Cost Reduction by  In-Plant Measures                6k
APPENDIX A - Tables A-l through A-12
APPENDIX B - Drawings B-l through B-8
APPENDIX C - General References
APPENDIX D - Fundamental Processes and Subprecesses
             Pulp and Paper  Industry (SIC 2621)

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                         List of Tables
Table No.

   1

   2
   5

   6

   7

   8

   9

  A-l

  A-2

  A-5
A-5

A-6

A-7
              Title

Process Water Reused by Pulp and
 Paper Industry
Percentage of Plants According to
 Technology Level  and Production
 Capacity
Total Wasteloads and Wastewater
 Quantities by Technology Levels
 in Year 1963
Gross Wasteloads and Wastewater
 Quantities in Year 1963 - Total
 Industry
Projected Gross Wasteloads and
 Wastewater Quantities

Normal Waste Removal Efficiencies for
 1963
Rate of Adoption of Waste Treatment
 Practices
Summary of Typical Waste Treatment
 Systems
General Operating Cost Functions

Fundamental Manufacturing Processes -
 Subprocess Mix
Percentage of Pulping Processes Employed
 as Related to Paper Products in 1963
Wasteloads and Wastewater Quantities of
 Older Technology
Wasteloads and Wastewater Quantities of
 Today's Typical Technology
Wasteloads and Wastewater Quantities of
 Newer Technology
Monthly Variation of Paper Production in
               Waste Reduction Efficiency
Page No.

   15

  21



  25


  26


  28


  33

  50


  59

  61

Appendix A

Appendix A

Append ix A

Appendix A

Appendix A

Appendix A

Appendix A

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                         List of Tables
                          (continued)
Table No.                     Title
  A-8          Unit Waste Removal  Cost  Summary
  A-9          Capita]  Costs and Economic Life  of
                Wastewater Treatment  Facilities -
                Older Technology
 A-10          Capital  Costs and Economic Life  of
                Wastewater Treatment  Facilities -
                Present Technology
 A-11          Capital  Costs and Economic Life  of
                Wastewater Treatment  Facilities -
                Newer Technology
 A-12          Capital  and Operating  Costs for  "Typical"
                Treatment Systems
Page No.
Appendix A
Appendix A
Appendix A

Appendix A

Appendix A

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                          List of Drawings
Drawing No.                     Ti tie                      Appendix No.


   B-l          Simplified Diagram of Fundamental            Appendix B
                  Pulp and Paper Processes

   B-2          Subprocess Series Representative of         Appendix B
                  Older Technology

   B-3          Subprocess Series Representative            Appendix B
                  of Today's Technology

   B-4          Subprocess Series Representative            Appendix B
                  of New Technology

   8-5          Sequence and Alternatives in                Appendix B
                  Wastewater Treatment Practices

   B-6          Wastewater Treatment Practice -             Appendix b
                  Older Technology

   B-7          Wastewater Treatment Practice -             Appendix B
                  Present Technology

   B-8          Wastewater Treatment Practice -             Appendix B
                  Newer Technology

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                               SUMMARY

Fundamental  Processes ,  Subprocessest  and^ jesu^lttng Wastewaters

     Integrated  pulp and paper  mills  are discussed as  a  unit  opera-
tion rather  than as separate  operations, since wastewater treatment
is dependent upon total  in-plant wastewater  abatement  measures  and
total  wastewater quantities and characteristics.  The  pulp mill  in-
cludes the fundamental  processes of wood preparation,  pulping,
screening, washing, thickening, and bleaching, whereas the funda-
mental processes in the paper mill  include stock  preparation, paper
machine operation, converting,  and  finishing.

     Wood preparation  begins  with the movement of the  log from  the
stock pile to the debarking facilities.   This  is  generally accom-
plished by moving the  log by  a  crane  to  a conveyor or  a  log flume.
The log is soaked prior to moving through the  flume  (where great
quantities of wastewater are  generated), and the  wastewater is  reused
if the grit  and bark are removed.   At the debarking  facilities, the
bark can be  removed  from the  log by several  methods; mechanical, chem-
ical (not applied),  and long  log  (newer  technology).   Bark that has
been removed increases solid  wastes disposal problems, and to date,
incineration for heat  recovery, composting,  and by-product recovery
have found the greatest number  of applications.   The debarked log  is
sent to the  chipping  facilities where It is  fragmented into chips,
suitably sized to enhance the penetration of cooking  liquor (in the
digesting operation)  into the wood.   Wastes  from  wood  preparation
consist of bark, soluble saps dissolved  from the  wood  washing process,
and grit.

     Mechanical chipping is the most  widely  practiced  method, but
another method has been developed,  which has not  yet found wide accep-
tance, is a two-step process, where the  log  is  first compressed perpen-
dicular to the fiber and then cut across the fiber.  The chips  result-
ing from all methods  have to  be cleaned  and  separated  to insure that
only chips of uniform size will be  supplied  to  the digester.

     Pulping, the process wherein wood and other  fibrous plants are
converted Into fibers  adaptable for use  in paper  making, is currently
accomplished by four different  processes; mechanical,  chemlgroundwood,
sulfate, and sulfite.

     Mechanical pulp (groundwood),  is manufactured  using a grinder.
Small  blocks of the log are forced  against  a grindstone  in the  pres-
ence of water.  Newsprint, low-grade  sanitary  tissue and paperboard
can be made from  this type of pulp.   Although  significant quantities
of wastewater are generated In  cooling,  cleaning, and  lubricating the
grindstone  and  in carrying the  pulp,  modern  technology has introduced

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                                 S-2

water reuse In the process which has greatly reduced  the  amount of
wastewater discharged to the sewer.   Wastewaters  that are discharged
to the sewer contain pulp debris and soluble materials.

     In the chemigroundwood process, the whole log is cooked  before
grinding, and the pulp produced has  faster drainage and greater
strength than the mechanical pulp.   At the same time, this pulping
process provides better utilization  of woodlands,  greater fiber
versatility, and Increased flexibility in the types of pulp produced.
Chemigroundwood wastewaters originate in the same  sources as  in the
groundwood process, plus additional  wastewaters from  the  soak pond,
after cooking where undesirable chemicals are leached.

     Sulfate (Kraft) pulping, utilizing alkaline  solutions to dissolve
the lignin and other non-eellulous portions of the wood  (which cements
the cellulose fibers together), has  the advantage  of  producing a  high
quality pulp of predetermined properties.  The digestion  process  can
be accomplished by any one of three  methods; direct or indirect batch
and continuous direct batch.  The continuous techniques have  found
wide acceptance in new mills while the application of indirect digest-
ing has decreased.

     Continuous digestion tends to produce a pulp  of  more uniform
quality, heat losses are reduced (incurred when the digester  has  to
be cooled and filled), eliminates peak steam demands, and reduces
corrosion.  Even with the disadvantages of low surge  capacity and
wasted pulp at start-up, the majority of the new mills being  built
tend to apply this method.  Kraft pulping is a cyclic process in  which
the cooking liquor chemicals are recovered.  Because  recovery is  feas-
ible and practical, water reuse can  be practiced to minimize  chemical
losses.

     The major sources of wastewaters from Kraft pulping  with chemical
recovery systems are digester blow down, black liquor  leaks, spills,
overflows, circulating pump cooling  and sealing,  multiple effect  evap-
orators, dreg washing, (lime mud) washing, white  liquor  fiIter washing,
and lime kiln and gas scrubbing. There are also three major  areas of
potential air pollution; the digester blowdown system, multi-effect
evaporators, and recovery furnaces.

     The acid sulfite pulping processes, based on  the digestion of
wood chips in an aqueous solution containing metallic bisulfite and
an excess of sulfur dioxide, used calcium bisulfite in the older  tech-
nology without water reuse or chemical recovery.   With the advent of
more stringent regulations regarding effluent criteria, many  mills
have sought an alternative base to calcium that would be  more amenable

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                                 S-3

to chemical  recovery and water reuse.   New mills  are  using  either mag-
nesium,  ammonium,  or sodium base  bisulfite; all of which  have  the
advantage of producing a spent liquor  that is  amenable  to chemical  re-
covery and water reuse techniques.

     In  the  older  technology,  when  spent  cooking  liquor recovery was
not practiced,  significant  quantities  of  wastewater were  generated
since the process  was essentially a once-through  proposition.   The
newer trends are toward recovery  systems  designed primarily to reduce
pollutlonal  loads.  The wastewaters generated, where  recovery  systems
are operating in sulfite pulping  operations, will result  from  spills,
leaks, overflows,  and cooking  liquor preparation, and wastewaters will
contain high concentrations of BOD  and suspended  solids.  While waste-
waters from  soluble based sulfite pulping processes emanate from the
digester blowdown, dirty condensate, scrubber  shower, acid  preparation,
chemical losses and recovery furnaces; sources of gaseous  wastes are
the relief from the digester,  emissions from the  evaporators and  re-
covery furnace.

     The semi chemical process  produces pulp and chips using a  mild
chemical treatment to soften the  chips and thereby enhancing mechan-
ical separation of the fibers. Although  the pulp yield (80 percent)
is much higher than attained from full chemical pulping (*»5-50 per-
cent), the strength and flexibility Is much lower. The two variations
of semichemical pulping are the neutral sulfite process (NSSC) and  the
Kraft (KSC)  process, which requires less  chemicals and  less cooking
time than the regular Kraft process.   Although semichemical Kraft and
Kraft pulping can be handled by the same  equipment and  facilities,  the
recovery system for KSC spent  liquor  is generally combined  in  the asso-
ciated Kraft pulp mill.  NSSC  pulping  consists of using sodium sulfate
as the cooking agent with sodium  carbonate as  a buffer.  Recently,  re-
covery techniques have been developed  for this process.  Also, if NSSC
pulping  is a minor part of a Kraft  pulping operation, the NSSC spent
liquor can be recovered In the Kraft  recovery  system  and the NSSC cook-
ing liquor made up with fresh  chemicals.   Semichemical  pulp wastewaters,
with chemical recovery, contain spent  brown liquors (with large concen-
trations of BOD and suspended  solids), digester blowdown, evaporated
condensate,  and liquor preparation.

     Wood and other fibrous plants  are not the only source  of  fiber as
both  rags and bagasse pulp are In demand.  Although all chemical pulp-
ing processes are applicable when pulping bagasse, the Kraft or modi-
fied soda process with extra sulfur usually give  the  best results.

     Since wastepaper can be reused,  deinking  facilities are often  pro-
vided in the pulp mill.  The chemicals used, the  procedure  followed,
   287 - 026 O - 68 - 2

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and the equipment employed in the deinking operation may  vary  consider-
ably since the process sequence depends  on the composition of  the grades
of wastepapers used, the character of the printing inks,  and the final
usage of the recovered pulp.   Previously, when ample water was available
and there was little pollution control enforcement, mills did  not reuse
wastewater resulting from this process.   Present day technology is
toward the use of washers in series with proper water  reuse with a
very definite saving in water, heat, and chemicals.  No profitable  chem-
ical recovery method has been developed  for these wastewaters  which con-
tain ink, clay filler, plus the chemicals used in the  process.

     Digester blow is the process used to blow out the cooled  digester
contents into a blow tank or tower where the vapors  are separated
from stock and spent liquor.  It is not  generally considered  a funda-
mental process but as a process associated with pulping.   Because  it
is one of the main sources of wastewater, it is also the principal
source of spent  liquors for recovery systems.

     Pulp washing is the process designed to remove the  liquor and
other  foreign materials from the pulp, using either diffusers  or ro-
tary drum vacuum filters.  Vacuum filters have practically eliminated
the application of diffusers in modern mills.  With the development
of a series of washers or multistage countercurrent washing,  water
requirements have been reduced considerably, with a subsequent re-
duction  in wastewater  loadings and quantities.  Future developments
may be the further combination of pulp washing. thickeninj_^nd_£cireen-
Tng, _ajid perhaps ^ventuaTTy. a completejv_cVosed system.

     The objective of  pulp screening and  cleaning is to  separate the
coarse fiber  from the  fine fiber and to  remove  dirt and  foreign matter.
Coarse screens are  used  in one operation  and  fine screens In  another
segment  of processing.   Centrifugal cleaning  is also frequently used
to  remove dirt etc.  that have passed through  the screens.  All three
operations are high  consumers of water and  recycling of  used water  is
an  important  in-piant  method of  reducing  wastewater quantities.

     The thickening,  or  dewatering, process concentrates the  screened
pulp  in  order to increase  its  consistency,  and  the water thus  removed
 is  returned  and  used to  thin  fresh  stock.  Some mills  still sewer  this
wasted water. The  thickeners  generally  used  are  deckers or vacuum
 filters; the  decker being  used in  the older technology with vacuum
 filters  being used  in more modern  installations.

      In  the older technology,  significant quantities of  wastewater  were
 produced in the  course of pulp washing,  screening, and thickening.
 When the washing process was  accomplished by  a diffusion system, the
 screening process  consisted of diluting  the pulp with  fresh water  and

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                                 S-5

passing the diluted  slurry over  a vibrating  screen,  using  fresh water
both to dilute  and transport  the pulp.  All  once-through waters were
sewered.   Large quantities of water that were  used  in  the  decker op-
eration were also sewered.

     To brighten the pulp, pulp  bleaching  is necessary,  and  the bleach-
ing operation sequence  depends on the  type of  pulp  bleached  and the
end product to  be produced.   The tendency  is toward two-stage  peroxide-
hydrosulfite bleaching  for the groundwood, semi chemical  as well as the
cold soda pulps. The Kraft,  sulfite,  soda,  and NSSC processes require
multistage bleaching, using various bleaching  agents and  caustic extrac-
tion.  After each stage in multistage  bleaching, a  washing cycle  is ne-
cessary.  Therefore, water reuse is vital  since 3 to 5 stage bleaching
operations are  quite common.  Single-stage hypochlorite bleaching  is
frequently used when bleaching deinked pulp  when the groundwood content
does not exceed 10 percent.   Multistage bleaching Is required  when the
groundwood pulp content exceeds  this  limit.

     Chlorination of chemical pulps  is a  rapid reaction and alkaline
extraction frequently is necessary after  chlorination  for sulfate
and neutral sulfite  pulps (can be omitted with sulfite pulps). Ox-
idative bleaching of chemical pulps has been practiced for decades.

     Although greater brightness can  be achieved if smaller amounts
of bleaching agent  are  applied  In successive stages with washing  be-
tween each stage, the resultant  increase  in  water usage (as well  as
capital costs and fiber loss) is a limiting  factor. With the  de-
velopment of chlorine dioxide as a bleaching agent, many modern  bleach
plants use only five stages  to  produce very  white,  strong pulps.   The
effective reuse of  water in  multistage bleaching has been helpful  in
reducing wastewater flows from  this  area. Wastewaters that are  dis-
charged from the bleaching operation  are  generally  characterized  by
large  concentrations of BOD,  dissolved solids, color and unreacted
chlorine.

     Stock  preparation is the process of  treating the pulp mechani-
cally  and sometimes chemically  with the use of additives to prepare
the  pulp  for forming into a  sheet on  the  paper machine.  There is a
series of operations covered in this  phase;  preparation of the fur-
nish,  beating  and refining,  machine chest mixing, and screening.
All  operations  require water, but water reusage has eliminated a
 large  portion  of the water that was previously wasted to the  sewer.
The  wastewater that  is discharged to the sewer  is primarily contam-
 inated by  rejects and  cleaners;  equipment cleaning wash waters and
dumps  of  furnish that  do not meet quality standards or have been
damaged  In  some manner.

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                                 S-6

     Other operations that occur during this process  are  the  addition
of fillers (or loading), sizing, wet strength resins, and coloring,
all of which are usually diluted tn water prior to being  added  to  the
fu rnIsh.

     At the paper machine, the fiber suspension is converted  into  a
paper sheet in three steps:  1)  the random arrangement of the fibers
into a wet web (paper machine wet end), 2)  the removal of free  water
from the wet web'by pressing; and 3) the progressive  removal  of addi-
tional water by heat (paper machine dry end).  In older mills,  using
Fourdrinter machines, the white  water resulting from  machine  (wet  end)
wire cleaning was sewered, but now individual trays and suction boxes
are used to keep rich white water separated from relatively clean  waters
The relatively clean white water  is eventually recycled  to mix with the
incoming pulp while suction box  white water is used to dilute the  stock
or as a spray on the wires.  The balance of the white water Is  pumped
to a saveall tank.   Saveall is a recovery system wherein  95 percent  re-
covery of the fibers and fillers is possible.

     Additives can be added on the paper machine, in  the  coating
operation or in the supercaTender.  Some wastewater reuse is  prac-
ticed, but the majority is ultimately discharged to the sewer.   The
quantity of wastewater associated with pulp recovery  is small and
insignificant In the overall wastewater abatement program, but  some
solid wastes are generated.

     Water is used to convey by-products and undesirable  wastes to
the incinerator where it is used to generate power and steam.  When
considering all the water used In pulp and paper mills, the quantity
of wastewater generated would be tremendous without water reuse.
Data Indicate that water reuse accounts for 260 to 320 percent  of
the water intake for an integrated Kraft or sulfide mill, with  Kraft
pulping having the highest percentage of water reuse.

     Each mill has Its own approach as to how to best reuse water  in
various operations.  However, the following waters are the ones most
frequently collected and reused:

     1.  Water from the log flumes and debarkers.
     2.  Evaporated condensates  from liquor recovery  area.
     3.  Washer water from coarse screens.
     4.  Bleach plant washer filtrate.
     5.  White water from the paper machine.

     Each fundamental process contains a number of operations which
can be modified in varying degrees; a subprocess Is defined as  an  al-
ternative technique for accomplishing a fundamental manufacturing

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                                 S-7

process.  However, the complexity of the fundamental processes Is In-
fluenced by many factors; the species of wood being used, the necessity
of varying the pulp process in relation to the final product being
produced, and the selection and control of the bleaching operation
to attain the different degrees of brightness.

     Although the fundamental processes and subprocesses of the paper
industry are well understood and categorized, the data concerning the
percentages of plants employing the particular processes or combina-
tion of subprocesses are scarce.  Percentages of subprocesses cur-
rently being applied are based in some cases on the number of produc-
tion units instead of the number of plants that have adopted the sub-
processes.  This was done in order to present meaningful data and to
predict future trends.

     Subprocesses with difficult wastewater control problems are the
pulping, bleaching, and paper machine operations.  The spent liquor
from pulping is  a major contributing factor in wastewater treatment
because of its characteristics:  high in BOD, depressing effects on
the efficiencies of BOD  removal In the activated sludge treatment
plant, and the large amount of color in the effluent.  Problems asSOT
ciated with black liquor from the Kraft process cap h«»«tt KA Kan Hi AM
_by  internal liquor recovery systems  in which the ght-smlcals are re-
Covered whi ie tne PUU contributing organic material and 1ignip_are
jurnecKThe sulfite pulping process,has the same difficulties as the
"Kraft ^process with one additional problem:  no rma I __ch em 1 ca 1 re cove ry,
methods are not  generally applicable.  Thay complexity and technical
problem  involved tn th«» JLTgug£ recovery are dependent upon the base
J>eing used.  Problems engendered by  the spent^liquor from semi-chemical
puTpTng are~simi 1ar to those encountered with the sulfite spent  liquor.
Wastewaters from bleaching operations contain high concentrations of
BOD,  dissolved organic and inorganic material, and are relatively dif-
ficult  to  treat.  Wastewaters from the paper machine operation contain
 fine  suspended solids  from the sizing and coating operations as well
as  fiber  lost to the waste collection system.  Air binding, slime build-
 up,  and  chemical corrosion are problems associated with white water  re-
 use systems.  Degradation of additives used  in stock preparation some-
 times  result  In  a higher  rate of wastewater discharge from the rectr-
 culation  system.

      Since many  of  the existing plants  limit  technological  improvements
 to specific areas of  the fundamental processes,  ?t  is not uncommon for
 a mill  to  employ older technology in one process and newer technology
 In another area.  Clear-cut  designation of a  plant  into one of the tech-
 nological  levels Is often  difficult.  The percentage of mills with pro-
 cess  streams  that fall  into  one of the three  categories based on overall
 performance  has  been  estimated  for the years  1963,  1972 and  1977, and
 data is  presented in  the following table.

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                                 S-8

                    Percent of Plants In Year   Range of Plant Sizes
Technology Levels   TjfcT      Wf2       »977         tons/day

     Older            2k        11          6          20-500
Today's Typical       68        58         48         100-1,000
     Newer             8        31         ^         200-1,500

The  trend is toward establishing  larger mills.  On the average, mills
producing less than 250 tons-per-day are considered imall, 250 to 700
tons-per-day mills are considered medium, and more than JOO tons-per-
day  mills,  large..  A  relative proportion of small, medium and large
"mills  included in each technological level was not readily definable
because of  the complexity and the number of process variations.  How-
ever,  production per  day  Is not the only major factor in determining
an integrated mill size since the pulping process utilized can be a
deciding factor  in size classification.

      Data regarding waste quantities and wastewater volumes associated
with the fundamental  processes and  subprocesses for the three techno-
 logical  levels have been  assembled.  The units used for wastewater
quantities  are pounds of waste  (suspended solids, dissolved solids,
and BOD) generated per ton of product.  Data  reflect  the various de-
grees of water  reuse  employed  In  mills; and  In some  Instances, data
 in reference to  a  particular subprocess are not strictly  accurate
since complete segregation of wastewaters before  they reach a common
 sewer is not possible, particularly when water from one process  is
 being reused In  another operation.   Type and  concentrations of con-
 taminants  present  result   from both operations and cannot be pin-
 pointed to any  one individual  source.   Aval 1 able  data were used  to
 indicate the total waste quantities and wastewater volumes for the
 bleached sulfate (Kraft),  unbleached sulfate  (Kraft) and  bleached
 sulfite processes  as  generated In plants  representative of each  tech-
 nological  level.  Both wastewater quantities  and  loadings (suspended
 solids, dissolved  solids, total  solids and  BOD) are  effectively  de-
 creased as the mill's technology goes from the older to the  present
 to the newer methods.  Percentages of mills within one  group are 2k ,
 68, and 8 percent  respectively.  Although  the quantity  of wastewater
 generated per ton of product  produced decreases  as  Improved  methods
 are developed, the total quantity of wastewater  generated will  in-
 crease due to expanded production.  In mills employing  the  newer tech-
 nology, the major sources of wastewater In terms  of quantities will be
 Kraft caustlclzlng and blow tower operations; sulfite digester and
 pulp washing, thickening, and cleaning operations;  sulfate  and sulfite
 bleaching; and paper machine operations In all  fundamental  processes.

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                                 S-9
     Paper production by month does not vary significantly,  and  con-
 sequently, the amount of wastewater generated will only  vary at  the
 same rate.

     The waste reduction practices employed  in  the pulp  and  paper  in-
 dustry arewater reuse, chem ? ca 1 re cove ry, fiber  and  s o 11 ds  re co very.
 and technological  Improvements.The wastes  associated with  subpro-
^esses typical or  ''older" technology  levels  are used  as  the  bases  of
 determining the percent of waste reduction and  the extent  to which a
 given subprocess,  or subprocess modification, may reduce waste pro-
 duction  relative to alternative subprocesses.   Areas  where significant
 reductions can be  achieved by water reuse or process  modifications are
 tabulated below:
 Wood Preparation
    Water  Reuse
    Long Log

 Pulping Process
    Water  Reuse
    Liquor Recovery

 Pulp Screening
    Water  Reuse

 Washing and  Thickening
    Use of Vacuum  Filters
    Multistage Counter-
      current V.F.

 Bleaching
    Water  Reuse  and  Recir-
      culation in  Multi-
      stage Operation

 Paper Machine
    Fiber  Recovery and
      White Water  Reuse
                            Wasteloads
                            ReductIons
                             Percent
80-90
   95
   30
60-90
20-601


20-60

60-90
                 Wastewater Quantities
                 	Reductions	
                       Percent
   70
   85
   30
60-90
20-60:


20-60

60-90
30-80
20-70
60-80
      ipresent level  of reduction.   Complete  elimination of
       wastewater discharge  Is  attainable  If  wastewater dis-
       charged from coarse screens  is  returned to the pulping
       process and if local  recircutation  Is  provided at the
       fine screens.

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                                S-10
     Areas where mill wastewaters can be reused and the source  of
such wastewaters are given below:
Fundamental
  Process

Wood Prepara-
tion
Kraft Pulping
  Wastewater
    Source

Evaporator Con-
dens ate, Bleach
plant pulp washer
filtrate.

Condensate from
recovery evapo-
rators and heat
exchangers, smelt
dissolving
Underflow from
Turpentine sepa-
rator.
 Reuse Areas

Log flume, hot
pond, debarker,
Showers
Dilutlon water;
caustic!zing,
screening, de-
Inking, and wood
preparation.
Lime and shower
system.
Soluble-base
Bisulfite
Paper Machine
Operations
White water from
Paper Machine
Paper machine,
stock prepara-
tion, bleaching,
pulp washing and
wood preparation.
Wastewater Treatment Facilities
By-Product
 Recovery
Turpentine
from Digester
Relief
                                        Chemical  Re-
                                        covery from
                                        spent liquor.
     Facilities provided to treat process wastewaters  often fulfill
two functions:  1) remove contaminants so that wastewater is suitable
to discharge to either municipal sewers or receiving waters, or 2)
improve the water quality so that it is satisfactory for reuse  in  the
plant.  Four functional groups that are included in wastewater  treat-
ment practices are:  pretreatment, primary, secondary, and tertiary
treatment.

     Pretreatment
     Proper segregation and collection of wastewaters  as  related to
wastewater characteristics are important In determining the treatment
sequence.  In-plant recovery and controls also contribute to the
ability of the treatment facilities to adequately treat wastewaters

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                                s-n

 generated at a minimum COSt.  Prgtreajmen.fr  K qpnp rally  required  for
 the main mill flow and can Include removal  of grit, debris,  Inorganic
 ash, sand, gravel etc.  This Is usually accomplished  In  a  grit  cham-
 ber (gravltynsnrrrTTngTfank) , and by screening.   For proper control  of
 the secondary treatment fad litles. jpjj_adjustment (pH  range  of  6.0_to
 g.O) Is frequently necessary; hence, neutralization facilities  are  an
 integral part of pretreatment.  However, the selection of  a  neutrali-
 zation method Is a function of the separation of process wastewater
 flows; alkaline and acidic.  For example, the alkaline ash wastewaters
 from thepover plant and lime recovery operation  can be used  to  neu-
 tralize the acidic wastewaters generated in sulfite pulping.  Where
 Kraft pulping process is being used, such a combination  is not  pos-
 sible since the pulping process wastewaters are  alkaline.  The  neu-
 tralization facilities, therefore, have to  be designed  in  accordance
 with the type of wastewater generated by a  fundamental process.

     Since temperatures of over 100°F can upset  the biological  treat-
 ment In the secondary facilities, cooling is another  pretreatrngnt- re-
 quirement that can be accomplished In cooling towers , sp ray  pcnds^
 cascade channels, and equalization ponds.

     Primary Treatment

     The basic function of primary treatment Is  the  removal  of  sus-
. pended solIdsT  In the pulp and paper Industry,  large  amounts of
 collodlal materials and dlspersant-type chemicals may  tend to  inhibit
 gravity settling, and flocculation can be used to condition  the waste-
 water prior to primary clarification.  The  addition
 Is often necessary.  After flocculation, the wastewater can be  clari-
 fied by gravity  settling or  dissolved air  flotation.   Only the  BOD re-
 jjited to organic and fibrous materials  Is  removjid_jjujrLpg_th I s  treat-
 ment cycle^.   Llontn based color  Is not  remove dUnTess  It has been
 adsorbed on  the  floe which settles out  of  the wastewater.

      Equalization facilities are  frequently provided between primary
 and secondary treatment plants to control  variations  in mill waste-
 water flows  and  characteristics.  These are usually  large enough  to
 act as storage tanks in case of mill upsets, or when operating  diffi-
 culties within the treatment plant limit the amount of wastewater that
 can be treated.
      wcw,wii»««i_i_7_ ' i council i

      The primary purpose of  secondary  treatment  Is  to remove soluble
 BOD, and for oulo  and  paper  wastewaters  nutrient  addition In the form
 gf_phosphorus and  nitrogen  Is  needed to  achieve  the optimum operation

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                                S-12

_of the  biological  treatment plant.  The conventional activated sludge
^process can  achieve  a high degree of'BOD  removal  In the treatment of
jjuTp_jind paper  Industry wastewaters.~	

      To function properly, the activated  sludge process requires de-
 fined and/or controlled BOD loadings, sufficient  oxygen supply, and
 adequate time for  completion of the oxidation and synthesis reactions.
 It is Implemented  by contacting the mill's wastewaters with an accli-
 mated biological population in the presence of dissolved oxygen.  A
 variation of this  system  is the contact-stabilization method wherein
 the acclimated  biological organisms are contacted with the wastewaters
 to accomplish BOD  removal, and the settled organisms are returned to
 a separate aerated stabilization basin where the  synthesis reactions
 are completed.  Another method used is trickling  filters where the
 biological growths are attached to the filter media which remove the
 waste organic material from the wastewater.

                                                            BOD Removal
 Mill  Classification         Secondary Treatment Process   Across Process
                                                             Percent

 Integrated Sulfite Hill     Conventional  Activated Sludge        85
 Integrated Kraft Hill       Contact Stabilization               85

      The biological  organisms are generally removed in secondary clar-
 Ifters  by gravity  settling.  Recently, peripheral-feed, suction sludge
 draw-off clartfiers  are becoming more popular.

      Lagoons or stabilization ponds, where  low concentrations of bio-
 logical solids  are maintained, can  remove BOD* and if  improved floating-
 type aerators are  used, clarification prior to discharge to the receiv-
 ing stream can  often be eliminated.  Since space  requirements for
 scientifically  designed oxidation ponds are normally In excess of land
 area available, these ponds have found  limited application except in
 the Southern states  where the climate favors such a treatment approach.

      Irrigation disposal  Is a form of secondary treatment but is not
 generally employed In the pulp and paper  industry.  If used in forested
 areas with favorable soil and geological  conditions, 60 to 95 percent
 removal of BOD  has been achieved during warm, dry weather.

      Tertiary Treatment

      Tertiary treatment  is used to obtain additional removals or "polish-
 Ing" of wastewaters  prior to discharge.   To datet the  Industry has not
 applied tertiary treatment for removal of lignlns In the form of dissolved

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                                S-13

 color or bacteria, but laboratory studies arc being conducted.  Pro-
 cesses being Investigated include:  holding ponds and filtration for
 the  removal of BOD and COD; ch 1 or i nation or ozonatlon for removal of
 bacteria; activated carbon adsorption, mass lime and other chemical
 adsorption processes for color removal and foam reduction; and removal
 of Inorganic solids using electrodialysis, reverse osmosis, and ion
 exchange.

     Sludge and Strong Wastes Disposal

     The sludge that is withdrawn from the primary clarifier and the
 excess biological (secondary) sludge are generally thickened by one
 of several methods; either alone or in combination:  secondary sludge
 (with 60 to 90 percent volatile solids) does not generally gravity
 thicken well unless mixed with the primary sludge, and thickened by
 gravity or by dissolved air flotation or cent rifugat ton.  The most
 widely used dewatemig mfthod to date ha? been vacuum filtration with
 the  use of conditioning chemicals when required.
<^q - — -- ~~ ~"
     Decent studies and opejgtjona 1 data have shown tjhjrt_centr|fuga-
 tion is very effective In dewate rTng~pu 1 p and paper mi 11 sludges both
 primary alone_and~in combinajj[pnjtfith secohdaryT  However, secondary
 sjudge usual ly requ I res chemi ca 1 cond i t 1 on i ng (polyelectrolytes) to
 be~dewatered to  12 to 20 percent
     ^        disposal of the waste sludges is a "sol id waste" prob-
 1 em .   P rev i ous 1 y sludges were disposed to landfilHng and lagooning
"together with other waste material, such as bark, ash grit, and debris.
 Increased land costs and more stringent regulations have  led to the  in-
 cineration nf primary gnd secondary sludges with solids concentrations
 of 30 to *tO percent*- Mechanical presses have been evaluated to further
 dewater  sludges after vacuum filtration or cent rifugat ion, but success
 has been limited by the low fiber content of the sludge.

      The disposal of strong wastes, such as digester liquor and pulp
 washer water, Is requi red where recovery practices are not implemented.
 Deep well disposal is a possibility, dependent upon the quantity of
 waste and the availability of geological formations that would prevent
 groundwater contamination.  Spray irrigation, after dilution, has also
 been attempted; but runoff can cause significant damage In the receiv-
 ing stream because of high BOD and solids concentrations  in the liquor
 and washer water.

 Rate of  Adoption

      Projections regarding the rate of adoption of wastewater treat-
 ment practices are based on somewhat limited data, particularly In  re-
 gard to  smaller equipment.  A summary of the subprocesses that are

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                                S-14

presently used and will be more widely applied by 1977 are given in
the following table.  Although more expensive than vacuum filtration,
centrtfugation is being frequently applied in sludge dewatering appli-
cations; and the number of mills using centrifugation will equal the
number using vacuum filtration by 1977.  Ultimately, most mill  sludges
will be incinerated although by-product development studies are being
intensified.
Fundamental Treatment Processes
	andSubprocesses    	
                                       Rate of Use
                                       at __P_res_ent__
                                         Percent
Will be Used
  in 1977
  Percent
Pretreatment
   Screening
   Neutralization

Primary
   Gravity Clarifier

Secondary
   Nutrient Addition
   Aerated Lagoon
   Activated Sludge
   Secondary Clarifiers

Tertiaryi
                                             60
                                             70
                                             20
                                              5
                                              5
                                             10
      90
      80
      90
      80
      25
      30
      50
 lOnly pilot plant installations now in operation.

     Discharge to Municipal Sewers

     Discharge of untreated pulp and paper mill  effluent to municipal
treatment plants has been practiced since 1950,  but currently only a
small percentage of the industry is following this practice.  Governing
factors are the proximity of the mill to a sewer system and the ability
and capacity of the sewage treatment plant to accept the wastewaters.
Combined Industrial and sewage treatment facilities have and can operate
successfully particularly where pretreatment is  provided for the in-
dustrial wastewaters.  Pretreatment requirements include neutralization
to prevent damage tr> s«»wag«»
                                       systettLand treatment_facTli t i es :
                                                           _
addition of ant i foam agents fr> rpHur^ nr eliminate the foaming tendency
of the industry's wastewaters; control of sulfur compounds that can lead
to ma 1 odors  in the system; and reduction of the suspended solids con-
centrations.  The discharge of the pulp and paper industry's wastewaters
to municipal sewers is expected to increase especially when the treat-
ment plant is designed to handle the combined wastewaters.  A wider
application is not expected, however, because of the tendency to locate
pulp and paper mills in rural areas close to raw material  sources.

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                                S-15

     By-Product  Recovery

     By-product  recovery  from spent Jjquors  has_been successful  for
turpentine and t-^n  ni | whll?      '~
cohols, D.M.S.O.  and vanillin   can  be  produced more  economically from
other matejrlals_-   Bark,  according to species,  has  been utilized in
mak I ng roof I ngf e Its, heating  installation  materials,  and cheap wrapp-
ing paper.  While  frpm «-h«  «nlfIt-» «tpt»nt-  Mf^nnrl ..Ky-prnHtirt-c tnrliiHft
emu_U|ons--for insecticides,  scaling inhibitors, tannino agents, cement
dlspersingjjqents. fertilizers,  flotation acids for  separation r»f ores t
tfeJJ-drnTTna lubricants,  extenders in storage batteries , .reinforcing
agents for rubber, gradients for ceramic industry  electroplating, and
road binders^

Capital and Operating Costs

     As reported  by the National Association of Manufacturers and the
National Council  for Stream Improvement, the replacement cost for
wastewater treatment facilities  in  the total pulp  and paper industry
in  1966 was $217,000,000.   Roughly, 40-^5 percent  of this figure can
be associated with the portion of the  paper industry under study in
that these percentages approximate  the production  and number of mills
In the study as compared to the whole  Industry.  Sufficient data is
not available to assess the replacement  value  of specific treatment
equipment.   Therefore, present costs of  such facilities must be used
to approximate individual  replacement  values.

     Operating costs for specific treatment equipment are not available;
however, annual operating costs vary between 7 and 20 percent of the
total capital investment In treatment  facilities.   Of the total operat-
ing cost, approximately 20 percent  covers operating labor, 25 percent
is  for maintenance labor and material, 35 percent  is for chemicals
(primarily nutrients) and miscellaneous  supplies,  and 20 percent covers
electrical power .usage.

     Using total, or end-of-pipe,  discharge data for integrated bleached
sulfate and sulfite mills, various  specific wastewater treatment pro-
cesses were designed for small, medium,  and large mills; one each with
older, typical, and newer production facilities and related treatment
technologies.  Integrated bleached  sulfate  and sulfite operations were
chosen because they  represent  major production facilities and discharge
wastewaters of differing treatability  characteristics.  In general,
economic life of treatment equipment Is  20  to 25 years.

     Various systems of treatment  and equipment were combined in a
treatment sequence when calculating total capital  and operating costs
for various mill  sizes and technologies.  These systems varied from

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                                S-16

primary treatment with low BOD removal  efficiency;  primary and  secon-
dary treatment In the older technology; high efficiency  (85 percent
BOD removal  by activated sludge)  secondary treatment,  and sludge  handl-
ing and dewaterlng In the present and newer technologies.  Since  the
specific treatment costs did not include general  construction  items,
percentage of capital cost values derived by design experience  were
used for piping and pumping, electrical and miscellaneous structures
costs.  The following table summarizes  the total  capital  cost  data  In
terms of mill production capacity In tons of product per day (TPD):

                Range of Total Capital  Treatment  Cost/Hill Capacity  In TPD
                       Integrated Bleached      Integrated Bleached
                          Sulfate Mill             Sulfite Mill

Older Technology       $2,890-  3,840          $1,920-  3,420
Present Technology      3,140 -  7,140           5,500 - 13,800
Newer Technology        1,900-  3,120           2,500-  4,200

     The operating costs related to the defined treatment systems were
derived from specific and percentage data.  Operating  labor, chemicals
(nutrients only), and power costs were based on specifying operating
requirements for each system, whereas maintenance costs  were based on
one percent of total structural costs,  three percent of  total  mechan-
ical costs,  and one percent of total pumping and  piping  costs.  The
following table summarizes the total operating costs In  terms  of  mill
production in tons of product.

                Range of Total Operation Costs/Mill Production  In Tons
                       Integrated Bleached     Integrated Bleached
                          Sulfate Mill             Sulfite Mill

Older Technology       $1.00    -    1.70      $1.00    -    3.12
Present Technology      1.60    -    3.36       3.50    -    7.30
Newer Technology        1.10    -    1.60       1.30    -    2.30

     Since cost data for in-plant modifications to reduce wastewater
discharge are not available, the total  cost of such activity cannot
be compared to the reduced costs for wastewater treatment.  However,
the combined effect of such future in-plant measures will reduce
wastewater volumes by about 45 percent and BOD loads by  25 to 70  per-
cent.  The resultant savings in treatment costs will vary with  mill
size.  When utilizing most of the projected in-plant measures,  treat-
ment cost savings can be similar to relative cost data obtained by
comparing generated capital and operating treatment costs for present
and newer (representing Increased In-plant reduction)  technologies.
On a per ton of production bas-ls, capital costs were reduced 50 to 65
percent and operating costs were reduced 30 to 65 percent.  The total
economic picture must consider the cost of in-plant activities  which
could completely offset the above treatment cost  reductions.'

-------
                            Paper Mills
                            (SIC 2621)
                    Industrial Wastewater  Profile
                              for the
                     Department of the  Interior
                   Federal Water Pollution Control
                          Administration
                 IN US TR I AL MANU FACTU R ING  PRACT I CE S
Definition of  Fundamental Haji u factjjin ng^ P roces^es^

     The Profile  for  Paper Mills  (except  buildings)  is  to include
pulp mills directly associated with paper  mills  (integrated pulp and
paper mills).   Because pulp mills are to  be  discussed in the funda-
mental process description, it was considered  advantageous to discuss
an integrated  pulp and paper mill rather  than  to discuss them sepa-
rately.

     An integrated pulp  and paper mill  can be  divided into two basic
parts:  1) a pulp mill which includes the  fundamental processes of
wood preparation, pulping, screening, washing, thickening, and bleach-
ing: and 2) the paper mill which  includes  stock  preparation, paper
machine, and converting  and finishing.  A  simplified diagram of the
fundamental processes for the pulp and paper industry is shown in Draw-
ing No. 1.  Also  shown  in the drawing are  the  raw materials used, final
products obtained, and  the wastes generated  in the form of liquids,
gases, and solids. A brief description of each  of the  fundamental and
subprocesses is given below, but  for  a more  complete description, please
refer to Appendix D.

     Wood Preparation

     This process is  a composite  of a series of processes wherein the
wood log is debarked, cleaned, and chipped to  a  uniform size that will
facilitate digestion. The operations include  the following:

          Log  Transpor tation

     Log transportation  is the movement of the log by conveyers or
flumes from the storage  area to the debarking  facilities.  Flumes re-
quire large quantities of water,  but  much of this can be reused if
screening and  grit removal facilities are provided.

          Deba rk i ng

     The bark  is  removed from the logs by one  of several methods:

-------
                                 -2-

     1)  Mechanical - Mechanical debarking uses cutting or fric-
         tion to remove the bark from the Jog.   The efficiency
         is low and the power consumption is high.   Water con-
         sumption can also be quite high.

     2)  Hydraulic - Hydraulic debarking uses water jets at
         high pressure to remove the bark from the  logs.  Al-
         though considerable quantities of water are used,
         most of it can be recycled.

     3)  Chemical - Chemical debarking is a process that has
         not to date satisfactori ly been developed.

     *»)  Long Log - This debarking process is the most recent
         development in improving the efficiency of the debark-
         ing operation.  The entire log (uncut) is  debarked in
         one operation.

          Bark Disposal

     Bark disposal methods employed include incineration, composting,
and utilization as by-products.  To date the most promising method is
incineration for heat recovery although it is necessary to use mechan
ical presses when incineration is part of a wet debarking operation.
     Chipping ts the process of fragmenting the log into uniformly siz-
ed chips which are suitable for digestion.  To prevent damage to the
wood (compression), the knives must be kept very sharp.  Operations used
in conjunction with this operation include Chip Screening (separation
and removal of slivers and under-and-undersized chips) and Chip Recovery
(wherein the rejected chips are recovered and reprocessed) .

     Pulping

     Pulping is the process wherein the wood is converted into fibers
which are adaptable for use in paper making.  Currently, four pulping
processes are employed.

          Mechanical ( G rou n dwood ) Pulp

     Mechanical pulping consists of cutting the debarked log Into small
blocks which are then forced against a grindstone in the presence of
water.  Water is used as a cleaning agent, as a pulp carrier, and as
a lubricant.

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                                  -3-

           Chemigroundwopd Pulp

      The  chemigroundwood pulping  process  is  a variation of the ground-
 wood  process.   It  is adaptable  for pulping hardwoods, and its main
 advantage Is  that  the whole  log  is cooked as a unit in a cooking liquor
 consisting of sodium sulffte and  sodium bicarbonate.   The log is then
 ground.

           Sulfate  (Kraft) Pulp

      Kraft pulping utilizes a Caustic  soda and sodium sulftde solution
 to dissolve the_JJgnin  and nfherjTon-cellulose portions »f th* uinnd
jrfh^ch cemenj_^he_jCAlluJose_fifaers together^   This  pulping process has
*the advantage of producing a high-strength pulp of predetermined prop-
 erties.   The  pulp  yield is high,  but the  resultant pulp is quite dif-
 ficult to bleach to a high degree of brightness.   Being a cyclic system,
 the chemicals are  recovered  for  direct reuse while the dissolving organic
 residue Is burned  for steam and  power  generation.

      The  digestion techniques used can be classified into three cate-
 gories-batch  and batch  injection  method and  continuous.  The majority
 of the large  new mills  being built are Incorporating continuous di-
 gestion because of the  economy  afforded by constant steam demand.

           Sulfite  Pulp

      The sul f i te pulping ^j^x^ss_J_s__basjsdLo_n__the_ d i ges_tJ_orL(xLwood
 Ch I PSJn_an_ggUgQUS Solution rnnt-^ining ftw»ta11tr h I gill f_|jhg__anj_^n
 excess of sulfur dioxide.  The  primary reaction of the sulfite pulp-
 ing process  involves the solubi Hzation and  sulfonatlon of lignin
 and the hydrolytic splitting of  1ignln-cellulose complex.  Although
 the yield Is  lower than that obtained  with the Kraft process, the
 pulp  is more  amenable to bleaching and a  high degree of brightness
 can be obtained.

      In the past,  a calcium  bisulfite  base was used without water
 reuse or  chemical  recovery.  New miris" (because of more stringent
 effluent  discharge criteria) are using eI ther magnesIurn, ammormjm,
 orsodiurn base bisulf i tes^aj_[  of which p rod uce a s^ejU__lj_guoT from
1rfhTch_jf~Ts poss|ble to recover"chemicaIs.   or approximately 60 sul-
 fite~~pulp mills Tn thTs^country,  all but  a  few are more than 20
 years old; the majority of these are using either calcium-base or
 ammonium-base process with no practical  recovery methods for chemicals
 or liquor.

           Semichemleal  Pulp

      The  semi chemical process produces pulp  from chips using a mild
    237 - 026 O - 68 - 3

-------
chemlcal treatment to soften the chips thereby  allowing mechanical
separation of the fiber.   The advantage of this method is  a  high
yield, but the strength and flexibility of the  semi chemical  pulp
is low as compared to that produced by the chemical  process.

     Variations of the semi chemical process in  current use are
(l) the neutral sulfite semlchemical (NSSC) pulping wherein  the
liquor chemicals dissolve the fiber bond in a process  that involves
ligntn sulfonatlon and hemicellulose hydrolysis; and (2) the Kraft
semi chemical  (KSC) pulping, which does not achieve  the degree of
llgnln removal that Is attainable with the NSSC process, but the
hemicellulose removal Is  greater.

     The KSC  process Is generally finding wider acceptance as an
associated process in Kraft mills.  Results are good with  hardwoods
and the cooling liquor is a weak white liquor obtained from  the as-
sociated Kraft mill liquor preparation system.

          Blow Tank

     A process that Is associated with all types of pulping  is the
separation of the blow vapors from the stock and liquor (digester
contents) In  the blow tank.  It is one of the main  sources of waste-
water, waste  loads and, therefore, is also the  principal source of
spent liquors for recovery systems.

          DeInking

     Deinking is the process of treating printed wastepapers for
the removal of the printing ink and the recovery of the pulp in a
condition suitable for reuse as pulp.  In the future,  this process
may become one of the major sources of pulp as  raw  materials sources
diminish.  The chemicals  used, the procedure followed, and the equip-
ment employed in this operation may vary considerably  since  the pro-
cess sequence depends on  the groundwood content of  the wastepapers
used, the character of the printing inks, the final  usage  of the  re-
covered pulp.  In the older technology, deinking wash  waters were a
major source  of contaminated wastewaters, but today's  technology  is
toward the use of washers in series with proper water  reuse. A very
definite saving in water, heat, and chemicals may result from reuse
of the first  wash water In the washing cycle.

     Pulp Washing

     Pulp washing is the process designed to remove the liquor and
other foreign materials from the pulp.  The two types  of equipment
used In this  operation are (1) the dlffuser, which  has practically

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                                 -5-

 been  eliminated  from use by the vacuum filters;  (2)  rotary  drum
 vacuum  filters,  which have been developed wherein  a  system  of  two
 or three washers in series or multistage countercurrent washing  pro-
 duces the  desired  level of pulp cleaning while permitting the  re-
 cycling and  reuse of the wash waters.  One significant  disadvantage
 of vacuum  filter operation is that the contact time  between the  stock
 and wash water is  relatively short and does not  completely  remove
 spent chemicals  from the pulp by leaching and diffusion.

      L 1 q uo r  Recove ry

      Cooking liquor recovery was developed in order  to  reduce  the
 cost  for cooking chemicals and reduce the wastewater loads  being
 discharged to streams.  The recovery technique is  different with
 each  type  of pulping method.

           Kraft  Liquor

      In the  modern technology, an essential part of  the pulping  pro-
 cess  is the  liquor recovery system.  ^maJ(3jLJ>arl  of the
                                                                  ^
 In the spent  cooking  liquor  (known as black  liquor),  can  be recovered
 in a series of~opeTaTTons; evaporation, buj-jihijT^and  caustictzing.
Th~e dissolved organic  residues from the wood  resfns can be used  for
 heat and  power  generation.  However, because  some  soda is lost in the
 washing operation, salt cake  is added to the  recovered liquor as it
 enters the furnace where the  salt cake is  reduced  to  sodium sulffde
 in the combustion process.

           Sulfite Liquor

      Sulflte  liquor  recovery  techniques are  more complex  and diffi-
 cult than those employed in  the sulfate system.   I i fact, the feas-
 ibility of liquor recovery is dependent on the base  involved in
 the sulfite liquor.   It is generally conceded that recovery is not
           uilt-h  fh<* ralrlum ba«Tp..  When a magnesium base_jj5_jjsed, the
                                                                for
 reuse ^ However,  for  Hv» sodium bflse^It  is  poss^bUto~recbver tfie
 inorganic che_mtralc_ wltj^ a  fairly  complex^process .   Spent  chemi cats
 from the  ammonium base sulfite pulping  process  can  only be parti ally
 reggygfed, put  the_pjgcess  does not  appear economically promisrng".

           Semi chemi cal__L|q_upr

      Liquor recovery  in  the NSSC process  is  practiced in some inde-
 pendent NSSC pulp mills  using a complicated  carbonation method.   In
 the integrated  semi chemical -Kraft  mills,  the recovery system is  also

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                                 -6-

tntegrated.   The "cross recovery" method Is  based  on  the  sodium  and
sulfur values in the NSSC liquor that  can be used  as  chemical makeup
in place of salt cake.   The NSSC spent liquor can  be  combined with
Kraft liquor for evaporation and combustion, but the  NSSC cooking
liquor has to be made from fresh chemicals.

     The KSC spent liquor is recovered In the same process that  is
used in a regular Kraft pulping process.

     Pulp Screening and Cleaning

     Separating the coarse fiber from the fine fiber  and  removing
dirt and foreign matter from the pulp is a vital necessity.  Two
screening operations used (and these are not usually  in a direct
sequence) are coarse and fine screening.  Frequently, coarse screen-
ing is followed by washing, thickening and dewaterlng; after which
the fine screening  operation removes more finely  sized debris.

     In neither of the screening operations  are the small dirt and
grit particles removed; therefore, another cleaning process  Is used
to remove such material, usually a centrifugal cleaner.   Placement
of the cleaners In the pulping sequence varies with the function
to be performed by the cleaner.

     Thickening and Dewaterlng

     The thickening or dewaterlng process is used  to  concentrate the
screened pulp and to increase its consistency.  The water removed  is
usually returned to be reused in diluting fresh pulp  for  screening
or is wasted to the sewer.  The thickeners used for integrated pulp
and paper mills are generally deckers (older technology)  and vacuum
filters (today's technology).

     The vacuum filter used for thickening Is essentially the same
as that described previously for pulp washing.  Its advantages over
the decker Include reduced floor space requirements,  fiber loss, and
maintenance costs.  In many mills pulp washing is  incorporated  Into
the vacuum filter thickening operation, and this is particularly true
for the multistage, countercurrent systems.

     Bleaching

     The objective of the pulp bleaching process is the production of
a brighter pulp, as measured by light reflectance. To obtain a  white
pulp, the light-absorbing substances present In the wood  pulp  (lignin,
resin, metal ions, and non-cellulose carbohydrate  components) must be

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                                -7-

removed or chemically changed to reduce the?r  light-absorbing  charac-
teristics.

     The bleaching  operation and sequence depends on  the  type  of pulp
being bleached  and  the end-product being produced.  The tendency is
toward two-stage  peroxide-hydrosulfite bleaching for  the  groundwood,
semichemical  as well as the cold soda pulps.   Requiring multi-stage
bleaching, using  various bleaching agents and  caustic extractions,
are the Kraft,  sulfite, soda and NSSC processes.  A washing  cycle  is
required after  each stage  in multistage bleaching; therefore,  water
reuse is vital  since three to five stage bleaching operations  are
quite common.   Single-stage hypochlorlte bleaching is frequently
used when bleaching deinked pulp when the groundwood  content does  not
exceed 10 percent.

     Two types  of water reci rculation can be used in  the  bleach plant:
(1) within the  individual  stage where the filtrate from the washer
seal box can  be reused to  dilute and convey  the stock going  to that
same washer;  and  (2) a transfer of excess filtrates from  the final
washer seal boxes to earlier stages in the bleach sequence,  thus
maintaining a countercurrent flow of filtrate  from the bleached end
toward the unbleached end  of the operation.  The use  of fresh  water
in the showers  assures that the sheet going  into each bleaching stage
will be relatively  free from dissolved organic matter. For  maximum
water conservation, only the overflow from the chlorination  and the
first caustic extraction stage are sewered.

     It Is important when  reusing white water  from the paper machine
in a bleach plant to consider not only the quality of the water and
the dissolved material content but also the  temperature and  the  fiber
content.

     Stock Preparation

     Stock preparation is  defined as that part of the pulp and paper
making process  in which pulp  Is treated mechanically, and often  chem-
ically, using additives to make it  ready  for forming  into a  sheet  on
the paper machine.  Stock  preparation  in  a paper mill includes all
intermediate  operations between preparation  of the pulp and  the  fab-
rication of the paper, and would  consist  of:  1) preparation of  the
furnish including consistency  regulation  and proportioning;  2) beat-
ing and refining; 3) machine chest mixing; and A) screening.   Furnish
Is the term used  for the mixture of water, pulp, and  chemicals which
ultimately goes to  the paper machine  for  fabrication  into paper,  its
composition varies  according  to the grade of paper being  made. The
various stocks  which make  up a multi-stock furnish can be proportioned
by many different methods; most prevalent being  the use of a multi-
compartment stock regulating box.

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                                 -8-

     FUlcrs,  or "loading",  are  included  in  the  furnish  to give paper
increased opacity,  brightness, bulk, weight,  flexibility, softness,
smoothness,  or prlntabi11ty. These, generally added  in  a slurry form
to the beater  during stock preparation  contribute  greatly to the
contamination  of the wastewater  stream  from  this area.   Only a small
percentage of  the material actually remains  on the paper.

     Sizing, wet strength  resins and coloring are  all generally added
prior to feeding the stock to the paper machine.   Each of which can
substantially  contribute  to  the  wastewater contamination.

     Pulp stock is  prepared  for  formation into paper  by  two general
processes, beating and refining, but there is no sharp distinction
between these  operations.

     Refining  is a mechanical treatment that can be used alone or
after beating.  It  contributes to fiber separation, fiber brushing,
and fiber shortening, where  the  objective is to  improve  formation and
to better adapt the fibers for forming  on the paper machine.  Because
of continuous  operation,  refiners are now used almost exclusively in
large tonnage  paper mills. After refining, the stock  ts  retained in a
machine chest  to insure a  uniform consistency of the  stock being fed
to the paper machine.

     Prior to  the stock being formed  into paper  sheets,  the stock must
be cleaned.   Usually, this is accomplished in a  rotary type screen and
in centrifugal cleaners if finely size  dirt  and  grit  particles are pres-
ent.

     Paper Machine Operation

     Converting the fiber suspension  into the paper sheet involves
three steps:  1) the random  arrangement of the fibers  into a wet web
(paper machine wet end);  2)  the  removal of free  water from the wet web
by pressing; and 3) the progressive removal  of additional water by heat
(paper machine dry end).   Two types of  paper machines are currently be-
ing used:  the Fourdrinier and the cylinder  machines.

     The stock, containing about one half percent  fiber, is sent through
the screens  to the headbox of the Fourdrinier machine, and flows from
there through  a sluice onto  a moving, endless wire screen.  Nearly all
the water and  half the fibers pass through the wire to be caught by the
wire tray or to fall Into the wire pit.  Spray water  used to keep the
wire clean also drains into  the  wire pit  while the water from the wire
tray (the rich white water)  flows into  the mixing  well where it Is mixed
with incoming  stock and pumped back into  the headbox.  Water from the

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                                 -9-

wlre ptt Is used to maintain  the  water  level  in  the mixing well  but  the
balance is returned to the saveall  system where  fibers  are reclaimed.
(Savealls are essential  for the reuse of water and  for  the recovery  of
fiber, additives, pigments, and other paper making  chemicals which
otherwise might increase the  pollutional  loadings to the  receiving
stream.)

     The paper sheet Is  about 15  to 20  percent consistency after it
leaves the suction boxes.   Both the wire and  sheet  move to the first
felt blanket which carries the sheet through  a series of  press rolls
where more water is removed and the paper  is  given  a watermark,  If
one is required.  As the paper then passes  through  steel  smoothing
rolls, It is-pi eked up by the second felt which  carries it through a
series of dry rollers which are heated  by steam. The paper  leaves
this area 90 to 9*» percent dry.   In the calender stack, a series of
smooth, heavy-steel rolls, the final surface  is  Imparted  to  the paper.

     In the cylinder machine, the layers of wet  paper are passed from
one cylinder to another until a composite wet sheet is  built  up which
is then passed through press  rolls  to the drying and smoothing rolls.

     In today's technology, tab sizing, coloring, and coating  can
all be made a part of the paper machine operation.   Consequently, the
wastewaters generated in this area  can  vary according to the  processes
being used in this operation.

     Finjsning arid Converting

     Finishing operations refer to  those operations which are  performed
in the paper mill finishing room  and which  are needed to prepare the
paper for shipment.  These include:  1) supercalendering to  improve  the
surface finish; 2) secondary  slitting and  rewinding to  produce rolls
sized to the customer's specifications; and 3) cutting  the paper into
sheets if the end product must be in sheet  rather than  roll  form.

     Converting operations cover  the modifications  of the raw paper
from the mill rewinder which  will improve  the grade of  paper with spe-
cial properties or the fabrication  of the  paper  into a  finished article.
Two distinct types of converting  are used  in  today's technology: wet
converting wherein the paper  is handled In  the roll form and  modified
by such operations as coating, impregnating,  and laminating.   In dry
converting, a finished product is made  from the  paper.

     Most of the finishing and converting  operations are performed  un-
der dry conditions and produce little  liquid  wastes except In  the case
of the coating operations.  (Mineral or pigment  coating improves the
printability of paper) while  greaseproof  lacquer coatings and  a wide
variety of synthetic resins are  used  In protective  coatings.)

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                                -10-

S ? gn IfIcant Water Wastes

     In the industry on the whole, the most significant  wastewater
sources are wood preparation, pulping, pulp washing,  screening  and
washing, bleaching, paper machine, and coating operations.   Solid
and liquid wastes are generated from the transporting and  debarking
operations involved in the wood preparation.  Solid wastes  collect-
ed at the disk screens and grit chambers contain coarse  and fine
pieces of bark, wood slivers, and grit.  When the bark is  incin-
erated, it is converted to gases, particulates, and ashes.   Liquid
wastes contain large amounts of dissolved solids from the  sap of
washed wood.

     Wastewaters generated in the mechanical pulping  process are
primarily from the grinding operation where water is  used  to cool,
clean, and lubricate the surface of the grindstone as well  as to
convey the pulp out of the grinder.  This wastewater  contains wood
debris and soluble materials from the wood.

     The major sources of wastewaters in the sulfate  (Kraft) pulp-
ing with a chemical recovery system are the digester  blowdown.
black Li-QiJnr leaksT spi1 Is t^overflows, circulati ng pump  coo 1 j ng_and
sealing, multiple effecX.eyapoj'ator, dregs washing,  lime mud wash-
ing, wh I te^TJjgjjp r^_fjjjtejrj3 a ckwas h i ng , an d 11 me k i 1 n sc rubbing.

     In addition to the gaseous pollutants generated  during Kraft
pulping; hydrogen sulfide, methyl me reaptan, dimethyl sulfide,  and
dimethyl sulfide are produced In the digester blowdown system and
in the multiple-effect evaporator.  Particulates of sodium chlor-
ide, sodium carbonate, sodium sulfate, sodium sulfite, sodium sul-
fide, sodium hydroxide and carbon, as well as emission gases of
sulfur dioxide, hydrogen sulfide, methyl mereaptan, and  dimethyl
sulfide are generated from the recovery furnace.  Calcium  carbon-
ate Is contained in the lime kiln stack gases.

     The acid sulfite pulping reaction involves both  sulfonation
and acid hydrolysis.  In most calcium-base sulfite mills,  no pro-
vision is made for the recovery of the chemicals. The wastewaters
from such installations are composed mainly of the spent cooking
liquor which contains high concentrations of BOD and  suspended
solids.  Some mills are equipped with facilities to  recover the
heat generated from the combustion of the concentrated spent liq-
uors.  Very high wasteloads are also produced from the digester
blowdown, the dirty evaporator condensate, and the furnace ejector.
The production of by-products from spent liquor reduces  the overall
load but generates a wastewater stream with high concentrations of
BOD and suspended solids.

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                               -11-

     For the soluble-base sulfite mills, an efficient  recovery of
cooking chemicals  can  be achieved.  The main sources of wastewaters
are the digester blowdown, dirty condensate, scrubber  shower, acid
preparation, and the chemical  losses from the  recovery furnace.
The wastewaters discharged to  sewers are acidic and contain high
BOD and COD concentrations.  Dirty condensate waters have a high
temperature and can be considered as thermal wastes.   The sources
of gaseous wastes  are  relief from the digester, emissions from the
evaporators and  recovery furnace.  Generally,  the waste gases con-
tain sulfur dioxide, carbon dioxide, acid fumes, and the particulate
matter from combustion end-products.  The end-products are CaSOj.
for calcium-base,  MgO  and SO?  for magnesium-base, Na2S and Na2COo
for sodium-base, and NO and 502 f°r ammonia-base pulping processes.

     Wastewater sources from the semichemical  pulping  process with
liquor recovery are the digester blowdown, evaporator  condensate,
liquor preparation, and spent  brown liquor.  Unrecovered chemicals
are sometimes wasted from the  furnace.  The emissions  from the blow
tank vent and the  flue gas from the recovery furnace,  contain sul-
fur dioxide and carbon dioxide.  In some Instances, the sulfur di-
oxide in the waste gas is utilized in the sulfiting tower and the
carbon dioxide is  used to carbonate green liquor to form hydrogen
sulfide.  When this  is done, the exit gases from the sulfiting
tower and carbonation  unit become the major sources of air pollu-
tants consisting of sulfur dioxide, carbon dioxide, and hydroaen
sulfide.

     Significant amounts of wastewaters are produced in the course
of pulp washing, screening, and thickening.

     In the older  mills, the washing process is accomplished by a
diffusion system where large quantities of fresh water are used and
wasted.  Screening is  performed after diffusion washing, and large
quantities of water are used for dilution of pulp and  washing of
screens.  Since little water is reused, most of this once-through
water is discharged to the sewer.  Solid wastes, containing un-
cooked wood, knots, etc., are  produced from this screening process.

     Wastewater from decker thickening constitutes one of the major
streams In the pulp mill, but  some mills do recycle wastewater from
the decker for use in  the screening operations.  When  this is done,
wastewater produced from the decker is decreased but the amount
wasted at the screens  is increased.

     Currently, the use of vacuum filters for  pulp washing has sig-
nificantly reduced the quantity of wastes generated.   Most of the

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                                -12-

screening rejects are sent  either  to  the  recovery furnace for burn-
Ing or to the digester for  recooking.   Since  in  recent years multi-
stage vacuum filtration has been used for both washing and thicken-
ing, wastewater from separate thickening  operations has been es-
sentially eliminated because of the countercurrent flow and water
reuse.

     Wastewater sources in  the bleaching  operations are from the
pulp washing operations, which are necessary  after each of the
bleaching sequences.  With  the development  of the countercurrent
type of washing for a series of washers,  most of the  fresh water
is added in the last washing cycle, and wastewaters are usually
discharged to the sewers from the first or second washer.  The
wastewaters are generally characterized by high  concentrations of
BOD,  dissolved solids, color and unreacted chlorine.   If  possible
these wastewaters should be discharged to separate  acid and alka-
line  streams.

      Little wastewater  is produced In the stock preparation opera-
tions except  for  rejects from cleaners, equipment  cleaning wastes,
or when  a particular stock  that has been prepared  Is  discarded.

      The white water from  the paper machine operation contains  fib-
ers  and  fillers.  Using savealls,  the current practice is to reclaim
 the fibers  and  fillers.  The greater percentage of the white water
 Is recycled within  the paper machine; excess is used for dilution in
 stock preparation or reused in  a  number  of other operations in the
 pulp mill.   Even with the  present technological developments, a
 considerable amount of effluent from the saveall systems are dis-
 charged  to  the sewer.

      Other  wastes of lesser significance are generated from the
 broke recovery and  coating operations.

 Process  Water Reuse

      Large quantities of water are essential  In the  pulp and paper
 manufacturing processes.  Water Is used  for  pulp processing, wash-
 ing, dissolving or mixing  the various loading,  sizing, and color
 ingredients, carrying the fibers  through the screens and  refiners
 to the paper making machine, and  operation of the paper  machine.
 Water is also used to convey by-products and undesirable wastes
 and  to generate power and steam.   Without water reuse, the amount
 of wastewater to be  discharged would be tremendous.  Therefore,
 the  maximum  reuse of water becomes one of the basic  approaches  in
 the  effective  reduction of wastewater quantities.

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                               -13-

     Th ere  are  definite limits in the amount of mill water which
can effectively be  reclaimed and reused.  Fresh water has to be
added in certain operations to prevent the build-up of undesirable
dissolved solids, temperatures, and slime from bacteria and fungi
growth.

     Each mill  has  its own approach on how best to  reuse water  in
the various operations.  However, the following process waters  are
most frequently collected and  reused:   1) water from the log flumes
and barkers; 2) evaporator condensate from the liquor  recovery
area; 3) bleach plant washer filtrate;  4) white water  from the  paper
machine; and 5) washer water from coarse screens.

     An accepted practice  is the  reuse  of wastewater  in wood handl-
ing and storage, such  as  in the log  flumes,  hot pond,  hydraulic or
wet drum debarker,  and  for the showers  prior to chipping.   For
these  applications, heated effluents  discharged from evaporators,
bleach  plant, or paper  machine are  preferred because  the heat  in-
creases bark removal efficiency,  particularly from frozen wood.  Re-
cycling barker effluent,  which has  been cleaned  (grit  removal)  and
screened,  is a widely practiced water reuse procedure.

      In the pulp mill,  after  the  wood is  cooked with  chemicals  or
mechanically ground, the pulp  is  washed and thickened.  The waste-
water  from the  digester usually contains  the spent cooking liquor
and the condensate from the digester heat exchanger.   If the  cook-
 ing liquor is  recoverable, the water can  be evaporated and col-
 lected as  condensate while chemicals are being recovered for  reuse
 in the digestion process.  The condensate collected can be used in
steam generation, as scrubber water for flue gas, or in the brown
stock washing  process.

      The screening department offers an excellent opportunity  to
 reuse a large  amount of waste effluent.  Decker or thickener water
 is often recycled and used as dilution water ahead of the screen-
 Ing and cleaning operation.  However, since the washing operation
 Is intended to remove the cooking liquor from the pulp, economics
 dictate that a considerable amount of  the contaminated wash water
 be displaced by make-up water  since this reduces  the pulps'    chlo-
 rine demand in a later operation and also prevents the build-up of
 dissolved  solids which cause salting out and foaming on the screens,
 The necessary  make-up water can be obtained by reusing the pulp
 mill condensate, bearing  and  condenser cooling water, paper machine
 white water, and certain  bleach plant  filtrates.

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     In the Kraft chemical  recovery process, water  can be  reused
In the following operations:   1)  dregs  washing;  2)  green liquor
dilution; 3) lime slaking,  lime mud washing, and lime kiln scrubb-
ing; 4) white liquor filter back washing;  and  5)  scrubbing of flue
gases.  The primary source  of water to  be  reused in these  processes
is the evaporator condensate, although  some mills are using  the
liquor, after scrubbing out the solids  from the  flue gases,  for
washing dregs and lime mud.

     In the sulfite chemical  recovery process, the  evaporator con-
densate Is used to dilute the soda ash  from the  furnace and  to
scrub the flue gases when recovering sulfur dioxide.

     The removal of the residue lignin  and the washing of  the
bleached pulp requires a large amount of water in the bleaching
plant.  The wastewaters generated contain  a large amount of  color
and have a tendency to foam.   The amount of fresh water make-up
required can be reduced by  employing the following  water reuse
techniques:  I) the use of  washer filtrate for dilution of stock
leaving the bleaching towers; 2)  the use of excess  washer  sealbox
waters In the preceding sealbox washing cycle; 3) the use of white
water and excess cooling water to dilute the finished bleached
pulp; and k) the use of digester condensate for  shower water,
bleaching tower dilution water, and brown  stock  dilution water.

     The source producing the largest quantity of reusable water
is the paper machine which  generates the white water.  The quality
of white water is sufficiently high that it can  be  reused  through-
out the mill.  The tray water from the  Fourdrlnier  machine and the
vat discharges of the cylinder machines can be segregated  and re-
used.  Fresh water requirements can be  further reduced by  reusing
the unclarified white water in stock preparations,  for dilution
water, in consistency regulators, and in cleaners,  and deculators.
To insure that the paper machine excess clarified water tanks will
remain clear, it is often advantageous  to  send machine spills,
shutdown and wash-out waters  to a separate tank  where the  solids
can be removed and eventually reused; the  clear  water goes to the
clarified tank.  Chlorination of the clarified water, which  is
used to dilute the high-density bleached pulp, can  result  In a
considerable saving in paper machine slimicide costs.

     The estimated percentage and quantity of  reused water during
1964 are summarized in Table No.  1.  These data  indicate that water
reuse accounts for 260 to 320 percent of the water  intake  for in-
tegrated sulfate (Kraft) or sulfite pulp and paper  mills.  However,
the percentages change radically when calculations  are based on the
total process water used (fresh water plus the reused water), the
range being 63-73 percent.

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                                -15-
                             Table 1




           Process Water Reused by Pulp and Paper Industry

(1)
(2)
(3)
(V
(5)
(6)
Type of
Mill
Fresh Water Intake
(gal /ton of product)
Water Reused
(gal /ton of product)
Reuse factor
(*) (5) = (2) x 100/(1)
Percent of Mills
with Water Reuse
Total Process Water Used
(5) = (1) + (2)
Percent of the Total
Process Water Reused
/ S" \ / _ \ . 	 tt 	 \
Bleached
Kraft and
Paper
^5,000
1^,000
320
92
199,000
72
Unbleached
Kraft and
Paper
50,000
78,000
260
78
108,000
72
Bleached
Sulfite
and
Paper
60,000
160,000
267
75
220,000
73
De i n ke r
and
Paper
33,000
57,000
172
80
90,000
63
(6)  = (2) x  100/(5)

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                                -16-

Industry Subprocess Mix

     Since the fundamental processes described In the  previous  sec-
tion contain a number of operations which can be modified in  varying
degrees, these modifications are considered subprocesses.  A  subpro-
cess is defined as an alternative technique for accomplishing a funda-
mental manufacturing process.  However, the complexity of a fundamental
process is influenced by many factors:   the species  of wood being  used;
the necessity of varying the pulping process in relation  to the final
products to be produced; and selection  and control of  the bleaching
operation to obtain the different degrees of brightness.

     From the standpoint of production  of pulp, the  fundamental
pulping process can be classified into  five categories:  1) ground-
wood; 2) Kraft; 3) sulfite; 4) semlchemical; and 5)  delnking.  The
first four categories are related to the use of wood logs as  a
source of raw material, while the last  category (deinkfng)  Involves
the production of pulp by reprocessing  of wastepapers. The selec-
tion of the process to be used Is governed by the final product to
be produced.  As there are a number of  alternative subprocesses for
each type of pulping, mills can produce their specialized products
if they determine which process and subprocess most  completely  ful-
fill their needs.

     Although the fundamental processes and subprocesses  of the paper
industry are well understood and categorized, data concerning the  per-
centage of mills employing a particular subprocess or  combination  of
subprocesses are scarce.  Percentages of subprocesses  presented are
based In some cases on the number of production units  instead of the
number of plants adopting the subprocesses in order  to present  mean-
ingful data and to predict future trends.

     The industry subprocess mix is presented in Table A-l.  In-
cluded In the table are the fundamental processes of wood prepara-
tion, pulping, bleaching, and paper machine operation. These are
considered of prime importance in predicting future  technological
trends and the type of wastewaters that will be produced.  The
table does not cover the fundamental processes of pulp screening,
washing, and thickening, stock preparation, and paper  converting
and finishing because no data were available.

     As was discussed in the fundamental process section, wood
preparation consists of a series of operations:  log transporta-
tion, debarking, chipping, and chip storage.  For convenience of
assigning processes according to the three different technology
levels (older, present, and future), alternative subprocesses of
wood preparation are divided into the following categories:  1)
without water reuse, 2) with water reuse, and 3) with  long log
preparation.

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                                -17-

     For the pulping operations,  different  alternative subprocesses
are associated with each  type of  pulp  produced.   In  mechanical  pulp-
ing, the alternatives are categorized  into:   1)  grcundwood without
water recovery; 2)  groundwood or  pretreated  groundwood with water re-
use; and 3)  refining mechanical pulp.   In the sulfate mill, the pulp-
ing process  has the following subprocesses:   1)  batch digestion with-
out water reuse; 2) batch digestion with water reuse; and 3)  the con-
tinuous digestion process.   The alternatives in  sulfite pulping are
numerous, but they are grouped  into three subprocesses according to
the effects  exerted on the wasteload and wastewater  quantities:  1)
calcium-base batch process without water  reuse and chemical  recovery;
2} calcium-base or ammonium-base  batch process with  heat and  partial
chemical recovery;  and 3) magnesium or other soluble base batch or
multistage process with heat and  chemical  recovery.   When semi chem-
ical pulping is being utilized  in a paper making operation,  its al-
ternatives can be classified into:  1)  NSSC  batch process without
chemical recovery:  2} NSSC or KSC batch process  with chemical re-
covery; and 3) continuous process with chemical  recovery.

     In the case of bleaching operations, various bleaching sequenc-
es are available for each type of pulp. Single-stage hypochlorite
bleaching Is used for many types  of pulps  in older mills while modern
technology trends show that  peroxide-hydrosulfite process is  used for
groundwood pulp, three-stage bleaching is used for sulfite and semi-
chemical pulp, and five-stage bleaching for the  sulfate pulps.   In
addition to the different bleaching sequences, the problem of water
reuse further increases the  number of  alternative subprocesses avail-
able for consideration.  Unfortunately, data regarding the detailed
breakdown of plants adopting the  finely divided  alternative subpro-
cesses are not available. Based  on available data,  the alternative
subprocesses of bleaching are most conveniently  grouped into  the
following categories:  1) bleached sulfate;  2) semi bleached sulfate;
3) unbleached sulfate; *i) bleached sulfite;  5) unbleached sulfite;
and 6) others which include  bleached and  unbleached  groundwood, ssmi~
chemical, soda, and deinked  pulp.

     Alternative subprocesses for paper machine  operation include:
1) cylinder machine with  or  without water  reuse; 2)  Fourdrlnier
machine without fiber and white water  recovery;  nnd  3) Fourdrinler
machine with fiber and white water recovery.  Data regarding  the
subprocess mix, as it existed in  1950, 1963 (the base year)  and
1967*are entered in Table A-l.   Results tabulated for wood prepa-
ration, pulping, and paper machine are derived from  data in  Lock-
wood's Directories and TAPPI Water Conference Proceedings.  Data
for the subtotal of each  type of  pulping  and bleaching process
were obtained from the Census of  Manufacturers,  U. S. Department
of Commerce.

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                                -18-

     The projected subprocess mix for 1972 and 1977 was  obtained
by graphical extrapolation of the earlier data olus opinions ex-
pressed by industry personnel concerning the r«"te of adoption of
new technology and the industry's obsolete equipment retirement
practices.

     Mills with daily production of 700 tons or more are classified
as large mills; those with a daily production of 250 tons  or  less
are classified as small  mills, and those In between are  considered
as medium size mills.  As the development of fundamental  manufact-
uring  processes is relatively unaffected by the sire of the mill,
it is assumed that the differences in mill size have little bear-
ing on the trend of the subprocess mix and wastewater characteris-
tics, although the future trend is toward the establishment of
larger mills.

     Since 1950 whes the Kamyr continuous digester was introduced,
most of the newly-built Kraft mills are using this process.   Re-
cent developments in the sulflte process are toward high-yield
pulping at a higher pH (bisulfite Instead of acid sulfite).   It  Is
predicted that the liquor recovery in sulfite pulping will become
one of the major factors determining the future of the sulfite
mill from the standpoint of pollution abatement and the  economic
justification of the chemical costs.

     From Table A-l, it can be seen that the bleached sulfates are
gaining predominance over all other pulping processes, and that  un-
bleached sulfate and bleached and unbleached sulfite processes are
decreasing In relative percentage of production.  Semi chemical pulp
Is gradually increasing in use, yet remaining at a very  low produc-
tion rate.  Groundwood (mechanical) pulping and Heinking are main-
taining about constant proportions of total production.

     In addition to the above subprocess mix, the relative percent-
ages of pulping processes as related to other paper products  for the
year 1963 are shown in Table A-2 to illustrate the complexity of
the problem.  From this table, it can be seen that each  of the
pulping processes is distributed in a variety of ways in order to
make almost all types of paper products.  The percentages  shown
are based on the total paper products in tons.

     It should be re-emphasized that the paper products  considered
are for the Standard Industrial Classification No. 2621  only.  Other
types of products, such as paperboard and building papers which  are
classified under other SIC numbers, are not included. During 1963,
a total of approximately 40 million tons of paper and board was

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                                 -19-

 preduced, of which  17.5 million  tons were  for  paper products  (SIC
 262]).   It  can  readily be seen that a considerable amount  of  pulp
 Is  used  for the manufacturing of board and building paper.

 Subprocesses With Difficult Waste Control  Problems

      The pulping process Ts a consistent problem source In connec-
 tion  with pollution control.  In suIfate pulping, the unrecovered
 black liquor Is a major contributing factor In wastewater  treatment
 because  of  the  following characteristics:   l)  TTigh BOD concentra-
 tion  In  the order of  I00,000jrng/L.for 15 percent solids black
 liquor_i_2)  depressing effectl)n~'tHe~eTfTcTe^cies of BOD removal
 1 njthe_act 1 vated sludge treatment of_ogjnbjj^d_^.fjfJLuent.;, 3L^3._VgXM.
JhTgh_^Qlor  rnnfpnt of about 400 (QQQ~j^Ttt num-cnba 11 un j tS  forllS
 percent  solids  black  liquor; and *») a _hj_gjhL._foajn!,ng_jp_otentjaj  that
 readJLiy_offers  visual evidence of pol'lutlon.   Typical foaming po-
 tential  Is  2500 ml. of foam per  liter of 0.15  percent solids  black
 liquor.  Reduction of problems associated  with the black liquor
 from Kraft  pulping'  is best achieved internally by a liquor recovery
 system In which chemicals are reclaimed, while BOD-contributing or-
 ganic materials and the color-causing llgnin are burned.

            FIte pulpin£,_the difficulties  encountered in pollution
 control  also emanate^fronTt ts spent coo1
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                                -20-

     Alr binding, slime build-up,  and chemical  corrosion are prob-
lems associated with the white water  reuse systems.   Degradation
of additives, (such as  starch and  casein)  in  the white water sys-
tem has the potential of fouling the  entire stock  being prepared.
These limitations on the reuse of  white water will  result  In higher
rates of wastewater discharge.

Three Production Process Streams
     The three production process streams  include:   a  subprocess
series representative of an older processing technology; a "typ-
ical" series of subprocesses which are most  prevalent  today; and
a series representative of a newer processing technology.  These
three series are shown on Drawing Nos. 2,  3, and 4  respectively.
It should be understood that these drawings  are representative of
various pulping and paper making processes being used  at each of
the three technology levels, and do not represent a flow sheet of
any single mill in actual operation.

     A mill is generally classified as belonging to the older tech-
nology when the processes employed are relatively Inefficient, ex-
cessive quantities of wastewater are produced, no recovery of  liquors
Is provided (except for sulfate mill), and little or no wastewater
is reused.  A  representative subprocess series of the  older  tech-
nology which Is In use today consists of:   1) wood  preparation by
mechanical debarking of logs without water reuse and without bark
utilization; 2) groundwood, sulflte, semichemical pulping, or de-
Ink Ing without water reuse and without chemical or  heat recovery
or sulfate (Kraft) with inefficient chemical recovery; 3) screen-
Ing without water reuse; 4) pulp washing by  dlffuser and thicken-
ing by decker; 5) bleaching without countercurrent  water  reuse;
6) stock preparation by batch operation; and 7) paper  machine
operation with little or no fiber reocvery and white water  reuse.

     A mill is classified under today's technology  when the  pro-
cesses employed are the most widely used among the  industry, the
wastewaters produced are within a typical  range regarding both
quantities and characteristics, moderate recovery of liquors  is
employed, and  reuse of water Is practiced.  The representative
subprocess series of today's technology consist of:  1) wood prep-
aration by mechanical debarking of logs with water  reuse and bark
utilization; 2) groundwood or pretreated groundwood pulping  from
wood  logs with water reuse; sulfate (Kraft)  pulping by batch pro-
cess with water reuse and liquor recovery; sulftte  pulping  by use
of calcium-base process with water reuse and heat recovery;  neutral
sulflte semichemical or Kraft semichemical pulping by  batch  process
with water reuse and liquor recovery; or deinking by cooking and

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                               -21-

washing, with water reuse;  3) screening with water  reuse; 4) pulp
washing and thickening  by vacuum  filtration; 5) bleaching with
countercurrent water reuse  among  stages; 6) stock preparation by
continuous operation; and 7) paper machine operation with fiber
recovery and white water  reuse.

     A mill Is classified In the  newer technology group when the
processes employed have been improved and are more  efficient, a
high degree of water reuse  is employed, chemicals and  heat  are  re-
covered with subsequent reduction of pollution  loadings, and ef-
fluent wastewaters generated are  low in quantity.   The representa-
tive subprocess series  of the newer technology  consist of:   1)
wood preparation by long  log debarking with water reuse and bark
utilization; 2) refining  groundwood pulping from chips with water
reuse;  Kraft pulping by continuous process with water  reuse and
liquor  recovery; su'ftte  pulping  by use of a soluble base  (such
as ammonium or sodium or  magnesium) with water  reuse,  heat .and
chemical  recovery; semichemical pulping by Kraft or neutral sul-
flte continuous process (often associated with  sulfate pulping);
or deinking by cooking  and  washing with extensive water  reuse;  3)
screening and centrifugal cleaning of pulp with water  reuse;  4)
pulp washing and thickening by multistage vacuum  filters; 5)  bleach-
Ing with high degree of water  reuse within each washer and  among
stages; 6) stock preparation by continuous operation;  and  7)  paper
machine operation with  segregation of white waters  according to
their quality, and with fiber  recovery  and extensive water  reuse.

     Since many of the  existing plants  limit  technological  improve-
ments to specific areas of  their  fundamental  process or  subprocesses,
It is not uncommon for  a  ml 11  to  have older  technology in one pro-
cess and newer technology in another.   Clear cut  designation of a
plant into one of the three technology  levels  Is  often difficult.
The percentage of mills with process  streams  that  fall into one of
these three categories, based  on  overall  performance,  has  been es-
timated for the years 19&3, 1972, and  1977.   Estimated percentages
are shown  in Table No.  2.

                               Table 2

                 Percentage of Plants  According to
              Technology  Level  and Production Capacity

                      Estimated Percent
                      of Plants  In Year    Range of Plant  Sizes
Technology Levels      1963  1972'T977          tons/day

Older                   24    11       6           20-500
Today's  ypical         68    58     48          100-1,000
Newer                    8    31      *»6          200-1,500

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                                -22-

The mill  sizes associated with these three technology  levels  are
also Indicated in the above table.   It can be seen that  the trend
Is towards the establishment of larger mills.  To  categorize  size
relative to pulping process; sulfate Kraft mills are  relatively
large; while sulflte, semi chemical,  and groundwood mills  are  rel-
atively small.  In many cases, groundwood, deinking,  and  semi chem-
ical pulping processes are integrated in the sulfate or  sulfite
mills.

     On the average, mills producing less than 250 tons  per day are
"small",  250 to 700 tons per day are "medium" and  more than 700
tons per day are "large".  The relative proportion of  small,  medium,
and large mills included in each technology level  is  not  readily
definable because of the complexity  and number of  process series
variations.  However, production per day Is not the only  factor
determining mill size, since the type of pulping process  utilized
can also be a deciding factor In mill size classification.

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                                -23-

         GROSS WASTE QUANTITIES BEFORE TREATMENT OR DISPOSAL

Unit Waste Quantities and Wastewater  Volumes

     The unit waste quantities and wastewater volumes associated
with the fundamental processes and subprocesses for the three
technology levels are presented in Tables A~3, A-'*, and A-5 re-
spectively for the older, today's typical, and newer technologies.
The units used for wastewater quantities are pounds of pollutant
(such as suspended solids, dissolved  solids, and BOO) generated
per ton of product.  Each mill has a  wide variety of fundamental
processes, subprocesses and combinations from which to choose
under the older, present, and newer technology; and except for
mills being built,  it is impossible to estimate the exact operat-
ing sequence any individual mill might select, much less estimate
the number of mills that would select the same sequence.  It  is,
therefore, impossible to determine waste loads and quantities  for
the three mill sizes, (small, medium,  and large) as related to the
different technological levels.  Consequently, no data is pre-
sented.  Variations in waste loads and quantities according to
mill size were not  readily obtainable, but significant variations
were not expected.  However, the data on waste loads per ton of
production was thought to be meaningful for application in any
specific mill.  Thus, conversion of pounds/ton into pounds/day
or gallons/ton into mgd can be easily performed, if the mill
production in tons  per day  is known.

     The range, as welt as mean values, of the waste  loadings and
quantities are shown in the tables to  indicate significant varia-
tions.   In many  instances, direct data for detailed breakdown of
subprocesses were not obtainable.  However, data shown  in the
tables are considered to be representative of each subprocess.
When fragmental data or unit datum are available,  they are en-
closed  in parentheses to  indicate the  probable order  of magnitude.
In the  interpretation of data,  it should be understood  that var-
ious degrees of water reuse have been  employed  in  most mills; and,
therefore, are reflected  in the data.  Complete segregation of
wastewaters before  they  reach one or several  common  sewers  is not
possible.  Therefore, it  is likely that data  reported  for a partic-
ular subprocess wastewater  and  the contaminants contained therein
may also contain wastewaters  from other subprocesses.  This  is
particularly  true when water  from one  fundamental  process  is  re-
used in  another  process.

-------
     Wastewater characteristics related to the cylinder or Four-
drinier paper-making machines were not available.  Since waste-
water characteristics related to different paper products have
been reported in the literature, these have been included in the
tables for both the older and today's typical technology.

Total Uasteloads and Wastewater Quantities for Each of the
Three Technology Levels

     Derivation of total waste quantities and wastewater volumes,
which could have been obtained by adding together the estimates
for all subprocesses as developed in the previous section, was
not attempted.  It is considered that the data for the subpro-
cesses listed in Tables A-3  through A-5 should not be used as
"additives" because of the complexity of the operations  involved
in the different pulping processes, various degrees of water re-
use from one process to another, and product-related problems.

      instead, total waste quantities and wastewater volume, based
on available data covering bleached sulfate  (Kraft), unbleached
sulfate  (Kraft) and bleached sulfite processes,  and for  each of
the  three  representative  levels of  technology, are presented  in
Tables A-3 through A-5.  These different types of wastewaters  are
an  important consideration  in the design of wastewater  treatment
facilities which are to be discussed  in  later sections.

      It  should  be mentioned  that groundwood, semi chemical and  de-
 inked pulps  are frequently  incorporated  in  the sulfate  (Kraft)  or
sulfite  mills.  Therefore, data available  for these processes  can-
not  be considered as typical of any individual  type of  mill.

      Base  Year  1963

      Total wasteloads  and wastewater quantities  per unit of  pro-
duct, as produced by mills  representative  of the three  technologies,
are summarized  in Table No.  3.   Data  shown in  this  table were obtained
by  compositing  the wastes of different pulping  processes as  shown
 in  Tables  A-3  through  A-5 for the  older,  today's typical and newer
 technology levels.   In these tables,  total  wasteloads  and waste-
water quantities  are shown  for bleached sulfate, unbleached  sul-
 fate, and bleached  sulfite   integrated  pulp and  paper  mills.   Since
 these three  types  of mills  constitute  the major portion of  paper
 industry production, groundwood,  semichemical,  deinking, and other
 types of mills are in  the minority.  Data regarding  wasteloads and

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                                -25-
wastewater quantities from the latter group are often incomplete.
Therefore, estimates covering these were based on data for funda-
mental processes as shown in Tables A-3 through A-5.

                               Table 3

             Total Wasteloads and Wastewater Quantities
                  by Technology Levels in Year 1963
Wasteloads
Ibs/ton of Product
Technology
Levels
Sus.
Solids
Ois.
Solids
Total
Solids BOO
Wastewater
Quantity
Est. % of
Industry
in each
Level
Older

Today's
Typical

Newer
               190
810
              gal/ton

1000   200     84,000
120
90
550
260
670
350
135
80
40,000
25,000
24


68

 8
     Data regarding the relative number of bleached sulfate, un-
bleached sulfate, bleached sulfite, unbleached sulfite, ground-
wood, semichemical deinked, and other types of mills listed in
Table A-2, were utilized in calculating the wastes composites for
each of the technology levels for the year 1963.

Gross Wasteloads and Wastewater Quantities Produced by Industry
in Base Year 1963

     The gross wastes and wastewater quantities produced by the
paper industry in base year 1963 based on the estimated percent-
ages of industry employing the three technology levels and the
product value added in 1963 are shown in Table No. k on the fol-
lowing page.

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                          -26-
                         Table  4

       Gross Wasteloads and Wastewater Quantities
               in Year  1963 - Total  Industry
Wasteloads, Ibs
Items
Wastes/Ton
of Product
Gross Wastes
in 19631
Wastes/Dollar
of Product
Suspended
Solids
135
2.36xl09
1.20
Dissolved
Solids
590
10.3xl09
5.25
Total
Solids
725
12.7xl09
6.45
BOD
150
2.62xl09
1.33
Total
Waste-
water
gals.
49,500
868x1 O9
452
1Based  on 17,500,000  tons  of paper product  produced
 in 1963.

 Based  on an adjusted product value of 1,962 million
 dollars  in year 1963.   (provided by FWPCA)

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                                -27-

Projected Gross Waste loads  and  Wastewater Quantities in the
Years 1968 through 1972 and I9/7

     The projected gross wastes and wastewater quantities on the
basis of product values provided by FWPCA for each of the years
1968 through 1972 and 1977  and  on the estimated percentages of
industry employing the three technology levels (See Table 2) for
1972 and 1977 are summarized in Table No. 5.

Seasonal Waste Production Patterns jay Month

     The wasteloads and wastewater quantities per ton of paper
product have been established  in the  previous sections.  Since
the paper production and waste  production is  a direct ratio,
seasonal variation in paper production can be used to indicate
the seasonal variation in wastewater  quantities.  Table A-6 shows
the monthly production of different paper products in 196^.  Ra-
tios of maximum to minimum  monthly production are calculated for
each type of paper.  It can be  seen from Table A-6 that for most
of the various types of paper,  which  account  for Sk percent of
total paper production, maximum to minimum monthly production ra-
tios varied from 1.14 to 1.26.   Minor types of paper, such as
miscellaneous groundwood, uncoated book, text cover, colored
school, sanitary towel, and other sanitary tissue stock wadding
papers, had ratios of maximum  to minimum monthly production
ranging from 1.3*f to 2.20.   These minor types of paper account
for only six percent of total  paper production.  The ratio of
maximum to minimum monthly  production for all types of paper was
1.15.  Maximum production appeared to fall in the months during
spring and late summer.  It can be concluded  that, except for
specialized types of paper, the monthly variations of waste pro-
duction are within 26 percent  of the average for the whole paper
industry.

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                                -28-
                              Table 5

       Projected Gross Wasteloads and Wastewater  Quantities
        Items


Wastes/Ton of Product
     in 19T2

Wastes/Ton of Product
     in 1977
Wastes/Dollar of Product
     in 19721
Wastes/Dollar of Product
     in 19772

Gross Waste in 19683

Gross Waste in 19693

Gross Waste in 19703

Gross Waste in 19713

Gross Waste in 19723

Gross Waste in 19772
                                    Wasteloads,  Ibs.
Suspended
Solids

125
120
1.23
Dissolved Total
Solids Solids

l$5 610
440 560
4.79 6.02
Wastewater
BOD5 Quantities

120
110
1.18
gal Ions
41,000
36,000
405
  1.29       4.75     6.04      1.18      387

2.82xl09  H.lxlO9  13.8xl09  2.71x10°  930x109

2.87xl09  Il.2xl09  I4.0xl09  2.75xl09~ 942xl09

2.92xl09  11.4xl09  I4.2xl09  2.80xl09  966xl09

2.96x109  11.5xlo9  14.6xl09  2.84xlo9  975xlo9

3.03xlo9  ll.Sxio9  I4.8xlo9  2.9lxlo9  990xlo9

3.50xl09  I2.9xl09  I6.3xl09  3.2lxl09  1050xl09
1 Based on an estimated production 24,200,000 tons  and  adjusted  production
  value of $2,450xl06 in the year 1972.

2 Based on an estimated production 29,200,000 tons  and  an  adjusted produc-
  tion value of $2,7l2xl06 in the year 1977.

3 Based on Wastes per dollar of product  in 1972 and adjusted  production
  values of $2,294xl06 in the year 1970;  $2,407xlOs in  the year  1971;  and
  $2,450xl06 in the year 1972.

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                                -29-

                      WASTE REDUCTION PRACTICES

Processing Practices

     Waste Reduction Efficiency

     The waste reduction practices employed  in the  pulp  and  paper
industry are water  reuse, chemical recovery, fiber  and solids  re-
covery, and technological improvements.  The percent waste  reduc-
tion and the extent to which a given subprocess , or process  modi-
fication, may reduce waste production relative to alternative
subprocesses are given in Table A-7.  The wastes associated  with
subprocesses typical of "older" technology  levels are used  as
bases.   In other words, the percent reduction  in waste quantities
of  subprocesses  listed in "typical" or "newer"  technology levels
are determined by using quantities associated with  an "older"
technology as a  base.  These waste  reduction percentages were  cal-
culated  from data regarding the three technology  levels  shown  in
Tables A-3, A-4, and A-5-

      It  is estimated  that approximately  80  to  90  percent reduction
of  wasteloads and 70  percent  reduction of wastewater  quantities
"could  be^obtained by water  reuse  in the  wood preparation processes
 Further  reduction of wasteloads.  up to 95 percent,  and  wastewater
 quantities, up  to about  85  percent, can  be  achieved when__the._jong
*76g~>repa raju qn^ IM thod_ls__fimp 1 oy ed .

      In  the pulping process about 30  percent reduction of wasje-
 loads~and wastewater  quantities" are obtained fay water jg^seTIjda
                     from 60 to  90 percent,          ~
      At the present technological level, waste reductions of 20
 to 60 percent in the pulp screening process are obtained by partial
 water reuse.  However, complete elimination of wastewater discharge
 from this process is attainable  in the newer technology  if the
 wastewater discharged from the coarse screens  is  returned to the
 pulping process and if local recirculation  is  provided at the fine
 screens .

      Use of vacuum filter for washing and thickening  of  pulp can
 achieve 20 to 60 percent greater reduction  in  the amount of waste
 generated as compared with the use of diffuser washing and decker
 thickening.  Further  reduction of wastes generated (60 to 90 per-
 cent) has been accomplished by the use of multistage  countercurrent
 vacuum filter washing and thickening.

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                                -30-

     When recirculation facilities are used in the multistage
bleaching sequence, 30 to 80 percent waste reductions have been
achieved with various degrees of water reuse.   Also, 20 to 60
percent of wasteloads and 60 to 80 percent of  wastewaters gen-
erated can be reduced by fiber recovery and white water reuse in
the paper machine operations.

     Technological Considerations on Waste Production
     and Interdependencies Among Processes

     The common uses of water in the wood preparation processes
are the log flume, hot pond, hydraulic or wet  drum debarker, and
showers prior to chipping.  Since modern technology emphasizes
the reduction of total wastewaters generated,  the industry has
realized that mill wastewaters can replace fresh water in most of
these applications.  In many cases, the heated effluent, such as
evaporator condensate, and bleach plant washer filtrate, are pre-
ferred because the high temperatures of these  wastewaters increases
the efficiency of bark removal from frozen wood.

     In sulfate (Kraft) pulping, condensate from the recovery evap-
porators and heat exchangers can be used for brownstock washing,
sprays in the early stage bleach plant washers, smelt dissolving,
and as dilution water for processes involved in causticizing,
screening, deinking, and wood preparation.  Another significant
waste reduction is possible through the recovery of turpentine
from the digester relief.  Since the underflow from the turpentine
separator is high in mercaptan and dimethyl sulfide, it can be
used in the lime and shower system.

     In the sulfite pulping process, using the conventional cal-
cium acid bisulfite, the spent cooking liquor  is normally dis-
charged as waste.  The difficulties arising from the evaporation
and burning of calcium-base spent liquor are due to the scaling
tendency of the lime salts, particularly calcium sulfate, upon
the evaporator's surface.  At the present technological level,
this burning process is primarily carried out  for the reduction
of organic material dissolved in the spent liquor.  Therefore,
the principal  inorganic products of combustion, namely CaSOj, and
CaS, are not recovered and are discharged to sewers.

     Chemical recovery of spent liquor from sulfite pulping, using
ammonium, sodium, or magnesium bases, can be achieved to reduce or-
ganic and inorganic waste loadings.  Ammonium-base residual liquor
can be burned to recover most of the S02 plus  heat value obtainable.

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                                -31-

Sod?urn-base cooking liquor can be burned with the heat value re-
covered as steam, while the chemical  ash consisting of Na2$ and
Na2CO? is recovered in the form of smelt, which can be reprocessed
to generate cooking liquor.  Magnesium-base spent liquor can be
burned to form MgO and S0£» which can then be recombined to form
cooking liquor.

     Multistage countercurrent vacuum filters can be used to com-
bine the operations of washing and thickening.  At the same time,
the system can be completely closed so that no wastes will be lost
to the sewer.  Wastewater discharged  from the first stage washer
can be sent to evaporators and then to the furnace for chemical
recovery.

     Wastewater reduction in the bleaching operations is primarily
achieved by recirculation within each washer and between the series
of washers.  Since the wastewater is  rather strong and contains
high amounts of dissolved solids, chlorinated lignins and tannins,
BOO, and color; it is rarely useful for pulping or paper making
purposes.

     White water from paper machine operations can be considered
of relatively high quality and suitable for reuse in several pro-
cesses.  After reclaiming fiber and filler materials from these
waters in savealls, white water can be reused within the paper
machine; or for other processes, such as stock preparation, bleach-
ing, pulp washing, and wood preparations.  Currently, many mills
reuse white water only in the stock preparation and paper machine
operations, while the excess white water is wasted to the sewer.
Reuse of white water for bleaching and pulping processes should
result in a significant reduction in overall wasteloads and waste-
water quantity from an integrated pulp and paper mill.

Wastewater Treatment-Practices
     General

     In this study, wastewater treatment is being defined as  in-
cluding all processes that are implemented outside the mill  (paper
or integrated pulp and paper) proper, and those facilities speci-
fically provided to treat all wastewaters that are to be discharged,
stored for discharge, prepared for disposal, or partially reused.
For this purpose, the pollution abatement facilities are not  con-
sidered an integral part of the mill's recovery practices.  However,

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                                -32-

it roust be noted that treated wastewater can be returned to the
mill for use when the water supply Is critical or when this prac-
tice offsets some of the treatment costs.

     Wastewater treatment practices can be divided into four func-
tional groups; pretreatment, primary treatment, secondary treat-
ment, and tertiary treatment.  Other practices that are related
to treatment and waste disposal include "strong" waste digester
liquor and pulp wash water handling and disposal, sludge handling
and disposal, and by-product production.  In the following dis-
cussions, the treatment practices will be discussed in the order
mentioned and. will include the various specific types of treatment
processes and equipment used in each waste removal method.  These
discussions and related tables and drawings will be structured to
follow step-by-step flow patterns through typical wastewater treat-
ment facilities.  However, the arrangement of treatment processes
or equipment can vary according to the characteristics of the waste
and the degree of treatment required for any given mill.

     Waste Removal Efficiencies for the Base Year

     As wastewater treatment methods are being described in the
following sections of this report, the normal waste removal effi-
ciencies for these methods, as utilized by the industry in 1963,
can be ascertained from Table No. 6.  However, pretreatment methods,
primarily in the removal of grit and debris from the wastewaters,
are not listed in this table because of insufficient data on which
to base or determine the amount of grit and debris discharged to
the mill sewers.  The quantity of grit and debris entering a mill
sewer is a function of the mill's specific location, maintenance
operations, housekeeping practices and wastewater collection system.

     The ranges shown in Table No. 6 for removal efficiencies are
considered typical of normal wastewater treatment practices in the
year 1963.  However, the literature reports that mills located
where reasonably priced land was available tended to have higher
removal efficiencies than the removal levels presented in the
table.  Because these treatment facilities were designed (without
land limitations) to allow for longer wastewater retention than
is normally possible, a greater degree of removal is attainable.

     Since only limited treatment plant information and laboratory
data were available, COD and color removal data were estimated.
Until recently, these data were not collected and recorded as part
of normal treatment plant operations.

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                               -33-
                              Table 6
            Normal  Waste Removal  Efficiencies for 1963
Removal  Method
Primary Treatment
   Sedimentation Basin
   Gravity Clarifier2
   Dissolved Air Flotation
Secondary Treatment
   Oxidation Pond
   Trickling Filter
   Aerated Lagoon
   Activated Sludge
   Irrigation
   Sedimentation Basin3
   Secondary Clarifier3
Removal Efficiency  in Percent of  Gross
  Waste Load to Each Removal Method
                                   Suspended
                                     Solids
    50-90
    60-90
    70-95
     0-90
    60-95
    70-98
              BODt
             75-95.
             60-95
         COD
lO-li-O   10-30
10-1^0   10-30
20-50   10-kO
        20-50
        30-60
        30-70
Color1
 0-10
 0-10
 0-15
 0-10
10-30
1 "True" color (dissolved).
2 With or without chemical addition and/or flocculation.
3 As used to remove biological solids  in secondary  treatment.

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                                -34-

     Tertlary treatment practices include "polishing" or removal
of specific pollutants; i.e., color and dissolved solids.  How-
ever, these data covering these practices are not included since
they were not utilized in 1963.

     Sequence and Alternatives in Mill Wastewater Treatment

     Wastewater collection systems  in pulp and paper milts vary,
but one of the most common practices  is to discharge wastewaters
to separate sewers according to the wastewaters1 strength and
characteristics.  The various mill wastewater sources shown in
Drawing No. B-5 are normally combined into three separate sewer
flows by the time they reach the treatment site.  (Note:  Drawing
No. B-5 and all subsequent discussions exclude sanitary and cool-
ing waters.)

     All mill wastewaters could possibly be combined and conveyed
to the treatment site in one trunk sewer.  However, quite often
ash wastewater (if coal is used to generate steam), boiler blow-
down, and other operational wastewaters containing inorganic chem-
ical wastes are separated from process wastewaters.

     Another collection system, which is normally segregated,
transports acid wastewaters  in acid-proof sewers from bleaching
sequences and miscellaneous acid processes, such as chlorine diox-
ide production, digester cleaning, and tall oil production.  Di-
gester pulping liquor and pulp washing wastewater flows are shown
on Drawing No. B-5 to indicate that frequently small amounts of
this material reach the process sewer because of spills, leaks,
or bleeding from the pulp production area of an integrated mill.
The digester liquor produced during sulfite pulping is sewered,
since recovery is not often practiced.  However, in most instances,
the handling of the bulk of liquor and washer water is a function
of in-plant recovery and control  and will only be discussed briefly
under wastewater treatment.

     The major pollutants of concern to the paper industry are
temperature, BOD, COD, color, dissolved solids, suspended solids,
and bacteria (coliform).  Unfortunately, there is no single treat-
ment process that can effectively remove all these contaminants,
and a treatment sequence is necessary.  Treatment processes can be
grouped into four major categories.

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                               -35-

     1.   Pretreatment  facilities are designed  to remove
         grit   and  coarse material, to  neutralize acid
         or  alkaline wastes,  to equalize  the quantity
         and quality of waste characteristics,  and some-
         times  to  reduce the  temperature  or to eliminate
         the odor  problem by  the mixing of bleachery and
         digester  Iiquor wastes.

     2.   Primary  treatment  is designed  to remove the sus-
         pended solids and  some coarse  organic material.

     3.   Secondary treatment  is designed  primarily to re-
         move. BOD  and  a portion of  the  COO.

     A.   Color, dissolved solids, and coliform are not
         easily removed by  the three previous  methods
         and for  effective  removal  require tertiary treat-
         ment.  To date, no tertiary treatment processes
         are being applied  in the paper and pulp industry.

          Pretreatment

     In  the  context of wastewater treatment,  pretreatment includes
the initial  operations that prepare or  condition the wastewater
prior to primary  clarification.  Wastewaters  discharged to pre-
treatment facilities from mill sewers can be  either combined mill
effluent or  segregated wastewaters.  Since many collection and
combination  systems are used  in  the industry  today, only pretreat-
ment of  the  main  mill  flow  will  be  discussed.   Drawing No. B-5 can
be used  to study  several of the  many wastewater combination sys-
tems possible,  noting  that  the smaller  wastewater flows (such as
ash and  acid sewer discharges) are  often  combined with the main
mill flow just prior to entering  the  pretreatment facility.  Al-
though they  are not considered a  part of  the  treatment facility,
pumping  stations  and sewer  extensions  that are needed to conduct
wastewaters  to the treatment  plant  site are  an integral part of
the design,  operation, and  costs  of pollution abatement facilities.

     The most common pretreatment methods employed are grit and
debris removal, and wastewater screening.  Inorganic ash, grit
from the wood preparation  process,  and  runoff materials (sand and
gravel)  must be removed  from  the wastewaters  to prevent abrasion
of pumping,  piping, and  solids dewatering equipment.  The grit
chamber is a gravity  settling tank  that can  be either manually
cleaned periodically or  continuously  cleaned  by mechanical removal
   237 - 026 O - 68 - 5

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                                -36-

equipment.  By maintaining a desired wastewater flow velocity,
these facilities are designed to remove approximately 70 to 80
percent of the grit and to minimize the amount of organic mater-
ial and fiber removed with the grit.  Limited data indicate that
grit in the main sewer of integrated mills with a combined sewer
system may roughly total 0.25 to 0.5 cubic yard per mgd of waste-
water flow during dry weather conditions.

     Bar screens, which can be manually or mechanically cleaned,
are commonly used to remove debris from the wastewater stream.
Designs for new facilities tend to incorporate mechanically cleaned
units rather than the manually cleaned units in order to reduce
maintenance costs.  A bar screen is composed of vertical bar "racks"
and is designed to prevent clogging of overflow weirs and primary
clarifier sludge withdrawal lines.  To accomplish this function,
the normal spacing between bars is 3A to 1-1/2 inches.

     Fine screens are not as common in wastewater pretreatment as
other types of screens used to remove grit and debris.  The need
for fine screening is a function of an individual mill's operation
and the design of waste solids handling and dewatering facilities.
The screens, with openings of 3/8 to 3A inch, are normally used
to remove knots, waste broke, bark, other fibrous and wood-type
materials discharged to mill sewers which can pass through the bar
screens.  Normally, this equipment is sized to remove the smallest
material that will cause clogging of pumps, pipes and other down-
stream facilities.  The screening facilities can be of various
types and include the following:  1) self-cleaning rotating discs
that remove solids from the wastewater as it flows horizontally
by gravity through the facility; 2) vibrating screens that remove
and clean the material by back-and-forth, or bouncing-type motion,
as the wastewater passes through the screen; 3) traveling screens
of conveyer belt-type design that normally permit gravity flow of
the wastewater through the screening material; 4) drum screens
that remove the solids on the inside of the drum as the flow passes
through the screen.

     A pretreatment process that has become important in recent
years is the neutralization of mill wastewaters.  Not only does
the pH of the wastewater affect conditions in the receiving stream,
but extreme pH conditions can cause corrosion of mechanical treat-
ment equipment or spall ing of concrete structures as well as ad-
versely affecting secondary treatment.  Uastewater pH should be in
the range of 6.0 to 9.0 to prevent damage to primary treatment

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                               -37-

facillties,  and normally,  between  6.5 and 8.5 to prevent upsets
in secondary biological  treatment  systems.   The selection of a
neutralization method is a function of the separation of process
wastewater sewers In the mill,  since wastewater streams vary in
pH, alkalinity, and acidity.   In  the example of sewer segregation
previously mentioned, the acid  bleach plant effluent, chlorine,
and related chemical production wastewaters contain large concen-
trations of hydrochloric, sulfuric, and other acids whose pH val-
ues vary from 1.5 to 2.5.  Ash  wastewaters discharge 1 from power
plant and lime recovery operations contain large amounts of inor-
ganic, -highly alkaline solids.  Wastewaters coming from the pulp-
ing operations can vary from acidic to highly alkaline conditions
depending upon the pulp process being utilized.  Wastewater from
Kraft pulping is alkaline; while  from sulfite pulping,  it is gen-
erally acidic.  Caustic digestion and washing waters and caustic
extraction wastes from bleach plant operations  tend to  give the
"main mill wastewater"  (pulping and white water wastes) a wide  pH
range; from a  low of 3-5 to as high as 11 or  12.

     Therefore, the need for and degree of neutralization required
for mill wastewaters depends primarily on  the  type  of  pulping  pro-
cess, and whether the wastewaters are collected and  sewered to the
waste treatment site separately.   Mill experience  has  shown that
separately collected wastewaters can  be  combined or added  in  a
manner to offset extreme alkaline  and acidic  conditions of  an in-
dividual wastewater  stream in  a Kraft mill.   However,  if  the  waste-
water stream  to be  neutralized is  the total  effluent from the mill,
extreme  fluctuations  in the pH and  alkalinity-acidity  can be  ex-
pected.  Therefore,  caustic and acid  chemicals used to neutralize
 this wastewater must be added  in  the pretreatment  step to prevent
corrosion  in  piping  and concrete  facilities and to protect  secon-
dary  biological  systems from extreme pH  fluctuations.   Because of
 the wide variations which  can  occur, facilities should be partially
or totally  automated to prevent high operating costs and frequent
 biological  upsets.

      An additional  process that will be considered as pretreatment
 (although it can be inserted at  several  points in the wastewater
 treatment scheme)  is wastewater  cooling.  As previously mentioned
 in this report, paper mill and integrated pulp and paper mill
 wastewater temperatures are  high  as compared to ambient temperatures
 of receiving surface waters.   Of  primary concern in wastewater
 treatment is the effect of the wastewater temperature on secondary
 treatment biological processes.   Temperatures of greater than  100°F
 have caused reduced efficiency in the biological process.  Cooling

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                                -38-

of the wastewaters can be accomplished by several  methods;  cooling
towers, spray ponds, cascade channels, and detention ponds.  The
use of cooling towers and cascade channels may aggravate the foam-
ing problem that accompanies pulp and paper mill wastewater treat-
ment.  Cold water sprays and antifoam agents are generally  used to
control foaming.  However, large quantities of fresh, cold  water
are not always available at mill sites and the addition of  antifoam
agents, if effective, is often very expensive.

     Discharging wastewaters to a cooling pond is  effective if time
and space are available.  Cooling ponds can be used in conjunction
with another pretreatment method, equalization.  Whether equaliza-
tion is used before primary treatment or between primary and secon-
dary treatment, it involves the combination and retention of the
wastewaters to minimize fluctuations of pH, flow,  temperature, and
other characteristics of the wastewater stream.  Equalization is
generally used after primary treatment so that solids do not settle
out in the wastewater holding facility.  However,  if equalization
is used prior to primary treatment, mechanical mixing of the waste-
water is necessary to prevent sediment build-up in the holding
basin or tank.

          Primary Treatment

     The next major treatment requirements is the  removal of sus-
pended solids.  The concentration of suspended solids in the waste-
water depends upon many conditions and operations  within the mill
proper.  Large quantities of collodial materials and other dispersant-
type chemicals  in mill wastewaters may tend to inhibit gravity
settling of suspended solids during quiescent conditions, as will
extreme differentials between ambient air and wastewater tempera-
tures.  In the former case, flocculation of the wastewater can be
used as a conditioning step for primary clarification.  Floccula-
tion, with or without the addition of flocculating chemicals, such
as alum, ferric chloride, or polyelectrolytes, can be done exter-
nally or as an  integral part of the primary clarifier.  Chemical
addition facilities should be designed to avoid chemical additions,
which could result in increased sludge production.

     The flocculated wastewater, or unconditioned  wastewater, can
be clarified by gravity settling or dissolved air  flotation.  Gen-
erally suspended solids from pulp and paper mills  are susceptible
to gravity settling; therefore, circular or rectangular gravity
clarifiers are commonly used.  The design range for hydraulic  load-
ings in primary clarifiers is from 600 to 1000 gallons per square

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                                -39-

foot of surface area per day, with 800 being a common value.  Settl-
ing lagoons have also been used for gravity clarification.  Dis-
solved air flotation has been used as an effective treatment method
for the removal of suspended solids in certain mills.  An example
of air flotation, applicable in the pulp and paper industry, is
the removal of very fine fibers and solids found in the effluent
from sulfite mills.  Quite often, dissolved air flotation is used
to recover pulp materials that can be reused in the mill.  For this
process to function properly, it sometimes is necessary to add
sweetener stock (pulp) to aid the recovery operation.

     The BOD that  is removed in primary treatment is related to
organic and fibrous materials that settle out of the wastewater.
True (dissolved) color is not removed by primary clarification un-
less flocculation has caused adsorption, whereby the color adsorbed
on floe particles would settle out of the wastewater.  The true
color of lignin and tannin origin is not affected or removed by
primary treatment.

     Equalization facilities are often provided between primary and
secondary treatment facilities to control variations in mill waste-
water flows and characteristics.  Wastewater surges, high wastewater
temperatures,  and extreme pH conditions can cause degradation of
biological  processes used in secondary treatment.  The retention
times in equalization facilities can vary from several hours to
several days,  depending on the type of fluctuations to be dampened
and the resistance or buffering capacity of the biological system.

          Secondary Treatment

     The primary purpose of secondary treatment is to remove solu-
ble BOD, using biological treatment processes.  Prirr to biological
treatment,  certain nutrients that are vital to the existence of a
balanced biological community and normal life-cycle activity must
be added to the wastewaters.  The essential nutrients are nitrogen
and phosphorus, which are generally added in the form of ammonia
and phosphoric acid.  The dosage required is governed by the con-
centration of these chemicals present and by the organic (BOD)
strength of the raw wastewater.  Mills using large amounts of alum
require larger dosages of phosphoric acid because of the bonding
and removal of phosphorus by the alum molecule.  Ammonia is added
to the wastewater either as a gas or a liquid, depending upon which
is available and the quantities required.  U nde r no rma 1 cond J t i ons_,
one part of phosphorus and five parts of nitrogen are needed per

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one hundred parts of BOD to be removed in secondary treatment.
The nutrient addition and control have a major effect on the opera-
tion of a biological system.  Nutrient starvation can result in
filamentous biological growth, lower removal efficiencies and poor
settling characteristics in the biological sludge.  This type of
operational problem is common in the treatment of pulp and paper
mills' wastewaters when attempting to obtain a high degree of BOO
removaI.

     The conventional activated sludge process, as a biological
treatment system, has been used in the paper industry to attain a
high rate and degree of BOO removal.  Comparing the activated
sludge process with other biological systems, the major difference
lies in the quantity of the acclimated microorganism (sludge)
brought into contact with the wastewaters.  This factor greatly
influences the removal and stabilization rate of the soluble BOO
materials.  To function properly, the activated sludge process
requ i res:

     1.  Defined and/or controlled BOO loadings.

     2.  Sufficient oxygen supply for oxidation and
         synthesis  reactions to occur.

     3.  Adequate time to complete the oxidation and
         synthesis  reactions.

     The activated  sludge process is implemented by contacting the
mill's wastewaters with an acclimated biological population  in the
presence of dissolved oxygen.  The biological population feeds on
the organic materials present; thus removing them from the waste-
waters.  Effective  removal and stabilization of BOD means that the
biological community  is healthy, and will result in the production
of additional biological organisms.  To sustain the process, the
biological mass is separated from the wastewaters by gravity settl-
ing and is returned to the beginning of the process.  Since addi-
tional biological organisms are generated,  it becomes necessary to
waste a portion of these to maintain an optimum environmental con-
dition.

     At times, the biological reactions occurring within the acti-
vated sludge process  readily remove the BOD-causing material from
solution but additional time may be needed  to complete the stabi-
lization reactions.  To take advantage of this phenomena, the
contact-stabilization modification of the activated sludge process

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was developed.   Basically,  the process consists of contacting accli-
mated biological organisms  with the wastewater for a sufficient
time to accomplish  the  desired removal of BOD; with return of the
settled organisms to  the  separate aerated stabilization basin where
the synthesis  reactions are completed.  The stabilized organisms
are then recontacted  with the wastewater.  The advantage of the
contact-stab! 1 ization process is that less tank volume is required
since stabilization is  accomplished at much higher organism concen-
trations.  Also, since  the  mass of biological organisms are outside
of the main wastewater  stream and if toxic or other upset conditions
are encountered, the  system can usually be returned to its original
condition in  a shorter  period than with the conventional process.

     In treating wastewaters from paper mills, both the conventional
activated sludge process  and the contact-stabilization modification
process have  been used  successfully.

     The conventional activated sludge process is particularly amen-
able to wastewaters from  sulfite mills.  Past experience with this
wastewater indicated  that oxygen transfer to the biological process
was a problem, and  without  the required amount of oxygen, a healthy
system cannot be maintained.  Technological advances  in mechanical
aeration equipment  design in the past few years have overcome this
problem.  Eighty-five (85)  percent BOO removals are attainable with
a detention time of four  to six hours with a mixed  liquor suspended
solids concentration  of 2000 to 3500 mg/L.  This process produces
approximately one-half  to one pound of excess biological organisms
per pound of  BOD removed, and requires one to two pounds of oxygen
per pound of  BOD removed.

     The contact-stabilization modification of the  activated sludge
process  is particularly applicable to  integrated Kraft mill efflu-
ents.  BOD removals of  85 percent are  readily attainable with two
to three hours contact  time and two to three hours  stabilization
time when using a mixed liquor suspended solids concentration of
2000 to 3000 mg/L  in the contact phase.  Oxygen requirements and
sludge production are about the same  as  in a conventional system
when treating wastewaters from an  integrated sulfite  mill.

     The gravity settling of the biological organisms  occurs  in
units commonly called secondary clarifiers.  Clarifiers  for bio-
 logical  plants are  designed on the basis of overflow  rate;  and  for
paper mills,  the design rate  is generally 600  to 800  gallons  per
day  per  square foot based on forward  flow.  Problems  can occur  in
biological treatment plants attaining  a  high degree of BOD  removal

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                                -42-

as a result of light dispersed biological growths not being removed
when using conventional clarifier arrangements.  Recently the
peripheral-feed, suction sludge draw-off clarifier has found in-
creased usage in this application.  Up to 98 percent of the solids,
depending on the influent concentration, can be removed from the
wastewater.  Effluent concentration of from 50 to 100 mg/L sus-
pended solids are common.

     Trickling filters also have been applied in the treatment of
pulp and paper mill wastewaters.  Biological growths are attached
to the synthetic or rock media of the filter.  This biological
growth removes the waste organics from the wastewater as the waste-
waters trickle through the media.  The advent of synthetic media
in recent years has made this approach more economically attrac-
tive, although they still have the limitation of being unable to
achieve as high a BOD removal efficiency as economically as acti-
vated sludge for pulp and paper wastewaters.  In treating this type
of wastewater, filters have a tendency to clog with slimy materials
and cannot buffer fluctuations in the wastewater characteristics to
the same degree attainable with the activated sludge process.  Re-
cent interest has developed in the possibility of combining the
activated sludge and trickling filter approaches to obtain greater
efficiency in treating pulp and paper mill wastewaters.  In these
applications, the plastic media filter is utilized for wastewater
cooling and as a roughing filter at loads of approximately 100 to
700 pounds of BOD per day per 1000 cubic feet of media.  This
approach has been economically and technically feasible for some
applications.

     Another biological treatment method is the use of lagoons or
stabilization ponds where low concentrations of biological solids
are maintained to remove BOD.  Frequently used is the aerated la-
goon, which is capable of removing from 40 to 75 percent of the
BOD present in mill wastewaters.  Offsetting the space requirements
and other physical limitations of the approach are the recent im-
provements in float ing-type aerator equipment and synthetic basin
liners.  Presently, this type of biological treatment does not
usually provide final clarification before the treated wastewaters
are discharged to receiving streams.  Typical design conditions
for an aerated lagoon are from one to two acres of lagoon per mgd
of wastewater flow, or roughly 10 pounds of BOD applied per 1000
cubic feet of lagoon volume per day.

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                                -43-

     The stabilization basin, shown on Drawing No. B-6, is a form
of aerated lagoon which was used prior to the development of sur-
face aerators.  Although this secondary treatment method did not
normally receive formal engineering design, if affected a BOD re-
moval equivalent to that attained with a well-designed oxidation
pond.  However, using air diffusers as a source of oxygen, these
facilities could be deeper than oxidation ponds.

     Oxidation ponds (i.e., stabilization ponds without supple-
mental oxygen) have limited application in the pulp and paper in-
dustry, since wastewater color is usually higher than that of
sanitary waste and, consequently, reduces or prohibits the produc-
tion of the algae normally present  in sewage oxidation ponds.
However, for mills located in the south, where climatic conditions
are appropriate for photosynthetic  activity throughout the year and
large land area is often available, this method is reasonably effec-
tive.  Design of industrial oxidation ponds is similar to sewage
treatment applications; the pond must be about five feet deep and
should receive a loading of about 50 pounds of BOD per acre per
day.  Typical paper industry practice provides 40 to 50 acres of
pond area per mgd of mill wastewater.

     Irrigation disposal of pulp and paper mill wastewaters  is also
a form of secondary treatment.  Operational problems, such as run-
off, stream pollution, and freezing of the wastewaters during
winter conditions  limit the applicability of this approach.  When
designed properly, this method can  be used seasonably  in forested
areas; recent publications have shown that better than 60 percent
of the BOD can be  removed before the wastewater reaches groundwater
levels.  Land application levels for the paper  industry vary from
10,000 to 100,000  gallons per acre  per day.  Studies of this prac-
tice have indicated the loading for the industrys* wastewaters
should be less than 200 pounds of BOD per acre per day.

          Tertiary Treatment

     Tertiary treatment is used to  obtain additional removals or
"polishing" of wastewaters before discharge to  receiving waters.
The major pollutants of concern to  the paper  industry  are temper-
ature, BOD, COD, color, dissolved solids, suspended solids,  and
bacteria  (coltform).   Data show that previously described treat-
ment methods  have  been effective  in the removal of color, dissolved
solids, or coliform.

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     Pulp and paper manufacturing operations return to the natural
 environment certain elements typical of the natural resource  (tim-
 ber) used by this  industry.  From a water pollution standpoint,
 two  important elements are HgnJns and bacteria found in the wood
 used to make pulp.  The industry discharges tignins in the form  of
 dissolved color in the mill effluent and bacteria as concentrated
 bacteriological communities of nonpathogenic nature.  Since both
 elements are concentrated in the mill wastewaters and are diffi-
 cult to control in the mill or to remove by the present wastewater
 treatment practices, they pose an economic and technical problem
 to the industry.  To date, the paper industry has not applied
 tertiary treatment practices on a plant scale to remove color and
 bacteria from mill wastewaters.  Several basic reasons have limited
 its application:   1) advanced tertiary treatment has not been re-
 quired of industry in general; and 2) although newer tertiary treat-
 ment methods are technically feasible, these practices are econom-
 ically practical.

     Generally, tertiary treatment steps have been adopted in the
 additional removal of BOO and COO from industrial wastewaters.
 The most widely used facility for tertiary treatment is the hold-
 ing pond.  The storage of secondary-treated wastewater before dis-
 charge to the receiving stream can be utilized to attain additional
 BOO and COD removal by limited biological  activity, and the removal
 of solids by extended detention and bacterial  flocculation.  Aero-
 bic conditions are needed to permit additional  removal without
 nuisance and to provide a positive dissolved oxygen content in the
 discharge to receiving waters.  Data are not available from the
 paper industry to evaluate the extent of the use of this practice
 nor its effectiveness as a pollution abatement method.

     Other methods available to the paper industry for supplemental
organic removal are biological filtration and  irrigation.

     If bacteriological criteria are part  of future effluent dis-
charge requirements for the paper industry, it will be necessary
to use some form of bacterial destruction method; ch 1 orination being
the most frequent choice.   However, since the  chlorine demand of
biologically treated pulp  and paper mill effluents can be as high
as 60 to 100 mg/L, this can be a very expensive operation.   The
use of ozone has not been  investigated by  the  industry,  but this
approach provides an additional benefit in that partial  color re-
moval can also be achieved.   To date, in the pulp and paper in-
dustry, neither chlorination nor ozonation have been practical for

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bacterial  removal  because of the high chemical demands and rela-
tively high wastewater flows.   It should be noted that recent reg-
ulatory action has been toward the separate determination of total
and fecal  coliform concentrations when determining bacterial pollu-
tion.   Hills collecting sanitary sewage separately should have min-
imum concentrations of fecal bacteria in process wastewaters unless
these bacteria have multiplied in sewers and treatment facilities.

     Significant color removal has been achieved in the laboratory
fay several methods; activated carbon adsorption, mass lime and
other chemical adsorption processes, and foam separation.  To date,
these methods have not been evaluated in full-scale plants treating
pulp and paper mill wastewaters.  Indications are that up to 30
percent of "true" color can be removed front mill wastewater.  How-
ever, to date it has not been considered economically feasible to
apply these methods to the treatment of total mill wastewater flows.

     Data from laboratory investigations and full-scale operations
Indicate that the degree of color removal accomplished by a given
biological treatment system (activated sludge) appears to be a
fixed amount, typical of adsorption phenomena.  Activated sludge
facilities can be expected to remove approximately 10 to  15 per-
cent of the color in a wastewater from a Kraft mill, which  includes
a bleaching operation (the principal source of color  in Kraft mills).
Higher color removal efficiencies have been observed  for secondary
treatment facilities when secondary influent color concentrations
have been reduced by  in-plant measures.  Such observations  rein-
force the concept that  in-plant  treatment  is most likely a more
effective (and economical) method of color  removal.   Studies on
the massive Ume treatment method on caustic bleaching wastes have
demonstrated that as much as 90  percent  reduction of  the  color can
be expected from the use of this technique  in full-scale  facilities.
This process combines three basic steps:

      1.  Adsorption and chemical reaction  on  the surface
         of the lime.

     2.  Precipitation  and  dewatering of the  lime solids.

     3.  Recausticizing of  the  lime.

In the present status of  technology of  color  removal,  this  method
appears to be  the most  feasible  for  removal of  pulp mill  effluent
color.

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                                -46-

     Inorganic solids removal can be achieved by several tertiary
treatment methods.  However, very little data are available to
evaluate the effect and feasibility of such methods, which include
electrodialysis, reverse osmosis, and ion exchange.  Combinations
of methods, such as carbon adsorption followed by electrodialysis,
have been proposed for wastewater renovation.  Although treatment
costs are increased, a portion of the costs of removing these in-
organic solids is offset by the benefits derived from water reuse.
This approach cannot be considered generally applicable where an
industrial water supply is readily available at a reasonable cost.

     Sludge Disposal

     The handling, dewatering, and disposal of primary and secon-
dary sludges are important factors in the design and operation of
wastewater treatment facilities in the pulp and paper industry.
Although sludge can be withdrawn from the primary clarifiers at
solids concentrations up to approximately 10 percent, it is usually
pumped from the sludge storage zone in the primary clarifiers at
from 3 to 6 percent solids.  This is because pumpage and pipe-
clogging problems are encountered at the higher densities.  The
clarifier underflow is dewatered in various ways, depending on
the type and quantity of solids discharged from the individual
mills' operations.  Normally, primary sludge does not require
separate thickening prior to dewatering.

     In discussing dewatering equipment, it should be noted that
the primary sludge can be mixed with secondary sludge (normally
withdrawn from secondary clarifiers at about 1 percent solids
concentration) or the sludges can be handled and dewatered sepa-
rately.  At best, secondary sludge with solids that are 60 to 30
percent volatile will gravity thicken to no more than 2.5 to 3
percent solids concentration at loadings of 10 to 20 pounds/sq. ft.
If this material is not readily susceptible to gravity thickening,
it can be mixed and dewatered with primary sludge or thickened by
dissolved air flotation or centrifugation.  Dissolved air flotation
is capable of thickening activated sludge to about k to 5 percent,
while centrifugation is capable of obtaining 5 to 8 percent solids.

     If these sludges (handled separately or combined) can be with-
drawn from clarifiers at, or thickened to, the necessary concentra-
tions (about three to five percent solids by weight), several de-
watering methods are available.  The most widely used method to
date has been vacuum filtration.  Conditioning chemicals are often

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required  in this operation.  Filter cake concentrations of from
15 to 25  percent solids can be achieved.

     Recent studies and operational data have shown that centrifu-
gation is very effective in dewatering pulp and paper mill sludges.
Primary sludge alone can be readily dewatered on a solid-bowl
centrifuge to between 20 and 35 percent solids concentrations.
Combined  sludges, at feed solids concentration of 5 percent or
greater,  can be dewatered on the solid-bowl centrifuge to 15 to
25 percent solids concentration; the performance level depending
upon the fiber content of the sludge.  Centrifugation of secondary
sludge alone usually requires chemical conditioning, commonly  in
the form of polyelectrolytes.  Thus treated, it can be dewatered
to 12 to 20 percent solids.

     Other types of dewatering equipment  include sludge presses,
drying beds, and sludge  lagoons.  The selection of dewatering
equipment depends on the sludge characteristics, the amount of
land available, ultimate disposal considerations, the  isolation
of wastewater treatment  and sludge disposal  site, and  proportion
of primary and  secondary sludges.  Waste  secondary sludge can
cause problems  in  lagooning and landfill  operations because of the
high organic content.  A method utilized  by  other  industries and
domestic sewage treatment  plants to stabilize  sludge  for  subsequent
disposal, but which has  not been widely adopted  in the paper  in-
dustry,  is the  aerobic digester.   An  additional  function  of  this
process  is reduction of  the quantity  of organic  material  in  the
sludge.  Aerobic digestion  is accomplished in  a  tank  that  provides
 10 to 20 days detention, during which time the organic content of
 the  sludge  is reduced  by 30  to  60  percent and  is adequately  stabi-
 lized to permit nuisance-free disposal.

      Ultimate disposal of  waste sludges is a "solid waste"  problem.
 In the past,  these materials  have  generally been disposed of by
 landftiling  and lagooning  together with other  mill wastes products,
 such as  bark, ash, grit  and  debris.   However,  with  increasing land
 costs, decreasing  land availability  and more stringent regulations
 concerning  solid waste disposal;  recent solid  waste  systems have
 included  incineration of primary  and  secondary sludges.  The follow-
 ing  types  of incinerators  can be  used to burn sludge resulting from
 the  industry's  wastewater  treatment  operations:

      1.   Multiple  Hearth Furnace  - commonly used for waste
          incineration and  steam production.

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                                -48-

     2.  C. E. Raymond System - utilizes recycle of dried
         sludge and furnace gases to reduce moisture con-
         tent of sludge before incineration.

     3.  Rotary Kiln - widely used in the paper industry
         for recalcination of lime in pulping operations.

     4.  Atomized Suspension Technique (AST) System - or
         Thermosonic Reactor System, consists of a cyclone
         evaporator and reactor for high temperature oxida-
         tion.

     5.  Zimmerman Process - a high pressure wet combustion
         process.

     6.  Bark Burners and Mill Boiler Furnaces.

     7.  Fluidized Bed Systems - for liquor recovery, sludge
         destruction and bark burning, and utilizing an air
         or gas flow suspended bed of sand or generated par-
         ticles as the incineration area.

     Optimum  incineration of primary and secondary sludges requires
that this material be at least 40 to 50 percent solids concentration
to reduce the need for supplemental fuel.

     Mechanical presses have been evaluated to further dewater
sludges, after vacuum filtration or centrifugation, but not with
consistent results.  Successful dewatering by this method is de-
pendent upon a high fiber content.  Dryers utilizing incinerator
gases, heat exchangers, and cyclone evaporators are also effective
as a further sludge drying operation.

     Strong Wastes Disposal

     Although digester liquor can be recovered, there are several
disposal methods which can be considered as waste removal practices.
Of recent interest has been the deep well disposal of liquor and
pulp washer water.  The effects on groundwater quality depend on
the geological formations at the mill location and the amount of
waste discharged to the well.  Generally this form of treatment
is not considered to last indefinitely because of clogging in the
injection formation.  Another disposal method is the dilution of
spent liquors for land application: basically, the factors defin-
ing irrigation disposal of process wastewaters can be applied to

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this practice. Jiowever. runoff from such operations can cause sig-
njJXcaat riamagp to recp i v I ng__s_Lream conditions because BOD and
                 i ons m the 1 jquor and washer water are greater
than thos e conta i ned i n btfie r proces sHwas tewaters .

     Wastewater Treatment By-Products

     Presently the sludges resulting from mill wastewater treatment
are not used for production of marketable by-products.  The uses of
dewatered primary sludge for sanitary landfill and dewatered secon-
dary sludge as asoi 1 conditioner are not considered by-product
areas s|nce thrs"~material _js_ normajjy_giyen away as a means of min-
imi zTng~sol id waste disposal efforts and expenses.

     Areas of future by-product development to offset treatment
costs are:  1) fiber recovery from primary sludge for use in the
building materials industry; 2) drying activated sludge tor use as
a fuel supplement; and 3) processing activated sludge as an animal
food supplement or commercial fertilizer.             "         ~~~

     Rate of Adoption of Wastewater Treatment Practices

     The portions of the industry that have adopted or will adopt
the various wastewater treatment practices for the years 1950, 1963,
1967, 1972, and 1977 are listed in Table No. 7.  Drawing Nos. B-6
through B-8 show the practices and alternative methods of treat-
ment that are associated with older, present, and newer wastewater
treatment technologies in the paper industry.  To date, a compre-
hensive survey of treatment practices in the paper industry has not
been completed.  Most of the data presented in Table No. 7 have been
extrapolated from information assembled by the National Association
of Manufacturers and the National Council for Stream  Improvement as
well as from specific pieces of data available in the literature.
Particularly in regard to smaller equipment, data reflect estimates
based on information from the literature and industrial sources.

     Pretreatment equipment, although not as mechanically sophisti-
cated and automated as present units, was utilized in conjunction
with primary treatment prior to 1950.  Presently, about 60 percent
of the industry provides grit and debris removal  (roughly one half
of this is mechanically cleaned equipment), and by 1977 nearly all
plants will provide debris and grit removal and neutralization.

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                                  -50-
                                Table 7
            Rate of Adoption of Waste Treatment Practices1
   Practice (or Equipment)
Pretreatment
   Grit Removal
   Bar Screen
   Fine Screen
   Equilization
   Neutralization
   Cool ing

Primary Treatment
   Sedimentation Basin
   Flocculation
   Gravity Clari-fier
   Dissolved Air Flotation

Secondary Treatment
   Nutrient Addition
   Oxidation Pond
   Trickling Filter
   Aerated Lagoon
   Activated Sludge
    Irrigation
   Sedimentation Basin
   Secondary Clarifier.

Tertiary Treatment
   Supplemental Organic Removal
   Color Removal
    Inorganic Removal
   Bacterial Removal

Deep Wei 1 Disposal

Sludge Handling and Disposal
   Thickening
      Gravity Thickener
      Dissolved Air Flotation
      Centrifugation
   Digestion3
   Dewatering
      Vacuum Filtration
      Centrifugation
      Pressing
      Sand Bed Drainage
   Disposal
      Lagoon ing and Landfill ing
      Incineration
      By-Product
Percent of Industry Employing Practice

 1950    1963    1967    1972    J977
  10
  <5
  25
pilot
  10
pilot
 none
pilot
 none
 none
 none


 none
 none
 none
 none

 none
hQ
ho
20
25
5
^5
60
10
15
<5
<5
<5
<5
5
none
none
none
none
60
60
25
ho
5
5
70
20
20
5
5
<5
5
10
pi lot
pilot
pi lot
none
1 Including related practices such as sludge disposal.
2 No data presented.
3 Primarily aerobic digestion of biological sludge.
10
85
50
20
 5
20
25
 5
10
<5
15
90
80
20
25
50
 5
10
50
<5
-
none
5
none
<5
30
<5
-
-
none
20
<5
<5
60
5
-
-
<5
25
5
5
60
10
-
25
10
35
20
5
50
25
5
14-0
15
ho
hO
5
30
hO
10

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                                -51-

     Flocculation will not significantly  increase as a primary
treatment practice because of the added emphasis being placed on
in-plant measures to reduce the loss of colloidal chemicals and
paper additives.  Essentially all mills not discharging  to munic-
ipal sewers will provide treatment  (largely as circular  clarifiers)
by 1977*  Due to land requirements, sludge handling difficulties,
and problems in maintaining consistent operation; settling  lagoons
will not be an  important factor in  future primary solids  removal
practices.

     Since most mill wastewaters do not contain sufficient amounts
of nutrients required for biological treatment (phosphorus and ni-
trogen), secondary treatment facilities will  incorporate some form
of nutrient storage and addition facilities.  Of the five secondary
treatment methods listed on Table No. 8,  the  activated sludge pro-
cess will be the most widely used method  in 1977.  This  prediction
is based on the high degree of treatment  and  operational  control
that will be needed to meet effluent criteria 10 to  15 years from
now.  The aerated lagoon approach can compete economically with
the activated sludge process  in rural areas,  but frequently the
land requirements are prohibitive.  The  1950, 1963, and  1967 per-
centages for mills using oxidation  ponds  include most effluent
storage ponds,  although many of these were not designed  as  treat-
ment ponds.  However, the data for  1972 and 1977 reflect the per-
centage which will be using ponds as a treatment method.
     Even  though  recent  studies  have  indicated  tixgl— tej"tiary  treat
ment methods are  technically  feasible  for  color,  bacterjLa_U_BOD.
     and  i [norgan i c  remova I s ,  such  methods  are not being  applied  at
this time.  ConsequeTitTy^Tt^Ts  difficult  to define  their rate of
adoption based on  past  applications.

     Sludge thickening  by  gravity  has  been successfully  used on
primary sludges  and  appears  to be  equally  applicable to  combined
primary-secondary  sludge  thickening.   Centrifuges  are very effec-
tive in thickening sludge, especially  secondary sludges  that are
difficult  to  dewater by other  methods.   Although commonly a more
expensive  method than vacuum filtration, centri fugation  has re-
cently gained popularity  in  dewater ing  applications  because of
ease and flexibility of operation  and  low  space requirements.
It  is believed  that  this  approach  will  close the gap in  the por-
tion of the  industry employing centrifuges versus  those  using
vacuum filtration  by 1977.
    287 - 026 O - 68 - 6

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                                -52-

     Ultimately, most mill wastewater treatment sludges generated
will be Incinerated.  The potential for by-product development
and marketing will expand in the future but not to a degree suf-
ficient to offset the need for complete incineration.  In rural
areas, landfill ing and lagooning are, and will continue to be,
common practices controlled by two factors, availability of land
and regulatory actions regarding proper sanitary disposal.

     Wastewater Discharge to Municipal Sewers

     There are no data available to serve as a basis for estimat-
ing the portion of the pulp and paper industry which was discharg-
ing its wastewaters to municipal sewers in 1950.  However, a rough
approximation is that between 5 and 10 percent of the industry
were utilizing this method.  The adoption of this practice depend-
ed upon, among other things, the mills proximity to a sewerage
system and the wil Hngness and ability of municipalities to accept
these wastewaters.  In 1950, the effects of pulp and paper mill
wastewaters on treatment processes in sewage treatment plants were
not well defined, nor were criteria developed upon which to assess
the acceptability of paper mill wastewaters for joint treatment
with municipal sewage.

     Presently (1963-1967), approximately 10 to 15 percent of the
pulp and paper industry discharge their effluents into municipal
sewers.  The characteristics of pulp and paper mill wastewaters,
as well as those of other industrial wastes, are now better under-
stood so that the effects of such wastewaters on the sewage treat-
ment processes and the factors governing their acceptability for
combined treatment with sewage can be defined and applied.

     A very important factor in considering the combined treatment
of pulp and paper mill wastewater with sewage is the relative flow
and organic loading between the two types of wastewater.  Where
the flow or loading of the pulp and paper mill wastewater is a
small portion of the total flow to a municipal system (J_,e., less
than 10 percent), the industrial wastewater would not be expected
to have a significant effect on the performance of primary and
secondary sewage treatment facilities.  The reference here is to
general mill effluent, not to strong liquors and other concentrated
wastewaters.  Where the industrial wastewater would represent a
significant portion of the total wastewater flow, specific account
must be taken of the treatment characteristics of the industrial
wastewater in the design or prediction of performance of the com-
bined wastewater treatment facilities.  Combined systems have been

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                                -53-

designed and are operating where the principal wastewater, in terms
of hydraulic or organic loading, is an industrial waste; including
pulp and paper mill wastewaters.  In those cases, the treatment
facility has been designed, as  it must be, to meet the requirements
of treating the industrial wastewater.  Therefore, these treatment
facilities can more accurately  be described as an industrial waste
treatment plant with sewage included.

     In considering the combined treatment of pulp and paper mill
wastewaters and municipal sewage, several handling and treatment
characteristics, peculiar to the industrial wastewaters, must be
considered prior to the acceptance of such wastes into an existing
municipal system or when providing for such wastewaters in the de-
sign of a new combined collection and treatment system.  The manner
of coping with these problems will vary, depending upon local con-
ditions; whether it is a new or existing system, the relative
amounts of each type of waste material, the nature and size of the
wastewater collection system, the type of treatment process if an
existing plant, etc.  Frequently for existing systems, the only
means of accomplishing the desired handling and treatment amen-
ability  is to require appropriate pretreatment by the mill prior
to discharge to the combined system.  Some of the characteristics
of pulp and paper mill wastewaters requiring special consideration
in combined systems are:

     1.  High temperatures, particularly with regard to their
         effect on collection systems and on treatment rates.

     2.  pH of the wastewater;  the pulp and paper mill waste-
         water can vary widely, especially where bleaching
         operations are  involved.  Acid wastes from the bleach
         plant are extremely corrosive.  Pretreatment at the
         mill or protection of  at  least a portion of the col-
         lection system would normally be required.

     3.  Foaming tendencies; pulp and paper mill effluents,
         especially those  from  bleaching operations, frequently
         create serious  foaming problems either  in collection
         systems or at the treatment  plant.  Again, pretreat-
         ment or provision  for  controlling  the problem  in  the
         collection and  treatment  facility  are required.

     k.  Sulfur compounds;  the  effluents from pulp and paper
         mills frequently  contain  relatively high concentra-
         tions of  sulfur  compounds;  sulfates, sulfites, sul-

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         fides, etc.  These compounds, if not property con-
         trolled or provided for, can lead to ma1odors (hy-
         drogen sulfide) in the sewer system or treatment
         facility, corrosion in the collection system or
         impaired performance in the treatment plant.

     5.  Suspended solids; the nature of the suspended solids
         content of pulp and paper effluents is significantly
         different from that of municipal sewage and must be
         considered in the solids handling considerations of
         combined systems.  Colloidal materials, paper addi-
         tivjs, clays, and similar materials can hamper settl-
         ing .in primary clarif iers or interfere with anaerobic
         digestion.  Large quantities of fiber and pulp can
         significantly add to the solids handling load of the
         combined sludge system and can interfere with diges-
         tion.  The quantity of excess biological solids
         generated in the treatment of pulp and paper waste-
         waters is higher than from the treatment of an equi-
         valent strength sewage.

     6.  Chlorine demand; the effluent from pulp and paper
         mills contain materials which have a relatively high
         chlorine demand.  Therefore, for a combined treatment
         system to maintain a chlorine residual, it may be
         necessary to use large dosages (60-100 mg/L) as com-
         pared to strictly domestic plants (about 10 mg/L).

     It can be expected that the number of joint municipal-industrial
wastewater treatment systems will increase in the future.  The ref-
erence here is to plants specifically designed to accommodate either
particular industrial wastewaters or a large portion of industrial
wastewaters from various industries.  The percentage of pulp and
paper mill wastewater being treated in such systems  is not expected
to increase in the same proportion as for industrial wastewaters  in
general.  This is due, principally, to the location of pulp and
paper mills in rural areas distant from municipal systems.

By-Product Utilization

     From Spent Liquor

     Several organic by-products can be recovered from the spent
cooking liquor resulting from various types of pulping operations.
They Include turpentine, tall oil, yeast, alcohols, dimethyl sulf-
oxide, vanillin, etc.

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                                 -55-
           Turpentjne

      Digester relief gases from both  sulfate (Kraft)  and sulfite
 pulping  contain significant quantities of turpentine.The tur-
 pentine  recovery procedure consists of condensing the cooking
 relief and decanting the crude oil  fractions.   The principal  com-
 ponents  of sulfate  turpentine are pinenes;  whereas, sulfite tur-
 pentine  is composed of  p-cymene and borneol.  Both types can  be
 used__as__BajjTt^thinners  and in the manufacturing of insecticides.
^Yields frgmjlther  process vary from  1.5 to *>.3 gal lons~per~ ton
"of  pu 1 p.                         '          	——	

           Tall  Oil
     The_bjack liquor  from the digestion of pine contains sodium
 soap which  is  Derived  from the dissolved fatty acids and resin
 acids  present  in  the wood.  After the liquor starts to cool, or
 its total solids  content  is increased,  the sjoap rises to the sur
 face,  where it can  be  collected by skimming.  This soap contains
 the crude tall oil, and by various refining operations, the puri
 fied tajloil  can be obtaine^r^YTeTdT'are i !]BUIEI~lQprTbs7tpn of
 a i r d ri e d pu Vp "p Trcxfu c t i oriT  Tall  oil  and its derivatives_can be
 used to make adfiesTvesV emu 1 s i ons , d i s i nf ectants ,  I ubr i cants ,
 pa i n ts ~
           Yeast

     Igrula  yeast  production has the most potential  in by-product
 utilization  of  the spent  sulfite liquor,  especially  for the calcium-
 base.  sugar-containing  spent liquor.  The procedure  involved is to
 seed the  yeast organisms  for fermentation and then pump a contin-
 uous supply  of  sulfite  spent liquor to feed the organisms to en-
 hance  further growth  and  multiplication.   Additional inorganic
 nutrients  (i.e.,  nitrogen,  phosphates, and potash salts), adequate
 air supply,  and  a  constant  temperature condition (90°F) are re-
 quired for the optimal  production of torula yeast.  Since torula
 yeast  contains  large  amounts of proteins  and vitamins, it is used
 as a food  supplement  for  humans and animals.  Data concerning the
 operation  of one  mill demonstrate that the waste reduction result-
 ing from  yeat production  is about 95 percent for total solids, 20
 percent for  five-day  BOO, and 60 percent  for total wastewater
 volume.

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                                -56-

          Alcohols

     Alcohols are attainable by-products in the fermentation of
spent sulfite liquor using specific yeast organisms with ethyl
alcohol as the first stage product.  Ethyl alcohol can be further
processed to produce glycols, ethyl acetate, ethylene dichloride
and acetaldehyde.

          D.M.S.O.
     Dimethyl sulfoxide (DHSO) is a valuable compound extracted
from liquor dissolved in spent cooking liquor.  The complete ex-
traction method includes a series of complicated processes. J)MSQ
can be used as an antiflammatory agent or as a bactericide.

          Vanillin

     The vanillin is a white, fragrant crystalline substance which
can be generated from the calcium-base sulfite spent liquor.  By
treatment of calcium lignosulphonate, which is a basic component
of the liquor, with sodium hydroxide under pressure, the pure va-
nillin is produced.

     Bark By-Products

     By-product utilization of bark is currently being studied in-
tensively by the industry.  It has been established that_b_ark fj-pjn
particular trees can be used as a source of a salable by-product
(tannin from hemlock bark) while many types or bark (redwood, pine,
spruce, etc.) can be used directly in the manufacture of roofing"
felts, thermalinsulation materials, and cheap wrapping paper.

     Others
     Many other by-products can be generated from the sulfite spent
liquorT  These include emulsions for insecticides, scaling—Lnhibi-
tors for boilers, tanning agents.,, cement dispersing agents, fertil-
izers, flotation acids for separation of ores, well-drilling lubri-
cants, extenders In storage batteries, reinforcing agents for
rubber, gradients for ceramic industry electroplating, and road
binders.

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                                 -57-
     In spite of thp mtm«er>nc...f ipHs  in  wh j gh the spent sulfite
liquor_can be util'y»d,  th«»  amrnint  actually used is very small.
The prospect of finding  an economical  use of waste liquor Ts
questionable at the present  technology level 7~Tn large part be-
cause cneaper and better raw materials for making these products
arte ava II abl&*— ~

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                                -58-

                       WASTE  REMOVAL  ECONOMICS

Replacement Value

     The data assembled on  pulp and paper mills  are  representative
of the Industry based on production data from 40 to  *»5 percent of
the total number of mills.   Data and  projections of  waste  removal
costs for the total pulp and  paper Industry  have been assembled  by
the National Association of Manufacturers and the National  Council
for Stream Improvement.  However, replacement costs  for  specific
types of waste removal facilities are not available  and  are diffi-
cult to estimate because the  average  ages of the mills vary, seg-
ments of the various processes have been updated in  some instances,
and even the average age of the equipment within one mill  can vary
quite dramatically, making  it practically impossible to  estimate
the average age.

     As a general guideline in waste  removal equipment replacement
costs, the total paper products industry (SIC 26) has spent about
$170 million by 1965 for such facilities with an estimated replace-
ment value (in 1966) of $220  million.  Based on  this information it
appears that the replacement  costs in 1966 would be  about  30 per-
cent more than the invested capital for treatment facilities in
1965 and previous years. The current (196?) capital and operating
costs of wastewater treatment facilities are presented in the fol-
lowing section of the report.  The total operating costs were cal-
culated as 12 percent of the  capital  expenditures, whereas mainten-
ance costs are 5 percent.  Presently, the total  operating costs  for
the industry are $20 to $26 million while maintenance costs are  about
$10 million per year.  These data can be used to estimate  replacement
costs, especially when total  facilities (equipment and related struc-
tures) are to be replaced.

Capital and Operating Costs

     General

     Capital and operating  costs for specific wastewater treatment
facilities and unit costs,  applying to the paper industry  in gen-
eral, have been extracted from the literature and various  industrial
sources.  Table Nos. 8 and  A-8 summarize this information.  Table
A-8 presents unit costs Tn  terms of mil) production  and/or waste
quantities.  Data are presented only  where enough information was
available to determine a range of costs.  Most of these  data illus-
trate the wide variability  in treatment costs within, the industry.

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                                                Table 8

                              Summary of Typical  Waste Treatment Systems
Treatment
Faci 1 ities
0
S
Bleached
Ider
M L
Sul
fate
Present
S
M
L
Mill
Newer
S M
L
                                                                       Bleached Sulfite Mill
Pretreatment
   Grit Removal
   Bar Screen

Primary Treatment
   Gravity Clarifier

Secondary Treatment
   Nutrient Addition
   Stabilization Basin   P
   Contact-Stab i1izat ion
   Conventional  Activ-
      ated Sludge
   Gravity Clarifier
Sludge Disposal
   Gravity Thickener
   Vacuum Fi1ter
   Centrifuge
   P  P
   P  P
P  P  P
P  P
                                                                    Older
                                                                   S  M  L
                              ALL SYSTEMS
                              ALL SYSTEMS
                              ALL SYSTEMS
           p  p  p    p  p  p
           P  P  P    P  P  P
           P  P  P    P  P  P
                 P    P  P  P
                                                     Present
                                                     S  M  L
P  P
                                                      Newer
                                                     S  M  L
p

p
p
p

p
p
p

p
p
p

p
p
p

p
p
p J
u:
i
P
P
                                                P    p  p  p
                         S - Small  Mill
                   M - Medium Mill
                            L -  Large Mill
     P - Process Chosen

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                                -60-

     Table No. 9 contains a breakdown of total  operating costs as
a percentage of capital  costs and individual  operating  costs  as  a
percentage of total operating costs.  Although  mean  percentages
are shown in this table, this information was derived from  data
covering a small portion of the industry providing wastewater
treatment.

     The tabulated cost data, although representative of industry
practice, were not specifically applied to the  economic evaluation
of treatment facilities designed for the different production tech-
nologies as discussed in the following section.

     Technology Related Costs

     Tables A-9, A-10, and A-ll summarize the capital costs of
wastewater treatment facilities specifically  designed for small,
medium, and large integrated paper and pulp mills, both bleached
sulfate and sulfite.  The production levels,  as shown In the
tables, were selected to represent small, medium,  and large manu-
facturing operations in the older, present and  newer mills.  The
bases for selecting bleached sulfate and sulfite mills  for  consid-
eration were:

     1.  These mills discharge wastewaters of different
         characteristics; therefore, they require  separate
         approaches to wastewater treatment.

     2.  More design experience, especially in  secondary
         treatment, is available for these mills than
         others  In the paper industry.

     3.  During the industry study, about 50  percent of
         the data obtained was in regard to production
         from these two processes.  (Nearly 70  percent
         of unbleached sulfate and sulfite mills are in-
         cluded since these wastewaters exhibit treat -
         abiltty characteristics similar to those from
         the bleached operations.)

     Wastewater characteristics and quantities  selected for the
various mill sizes were combined to define the  design basis for
treatment facilities.  The treatment facilities were designed and
economically evaluated according to usual engineering practices
and average unit cost data for equipment and construction  mater-
ials.  The summary tables do not include all  processes  that can be
used in pulp and paper mills' wastewater treatment,  but instead,

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         Bas is
Total Operating Costs
   Primary Treatment1
   Primary and Secondary1
      Treatment
   Sludge Disposal2
Individual Operating Costs
   Operating Labor
   Maintenance
      Labor
      Materials
   Chemicals (and Miscellaneous
      Supplies)
   Power
             Table 9
General  Operating Cost Functions

        Percent of Capital
        	Investment
                      Mean
         7-20
         7-20

        10-50
10
12

30
                                                                 Percent of Operating
                                                                        Costs
              Range
                                     10-50
                                     10-40
                                      5-15
                                      5-30

                                     25-50
                                     10-50
Mean
                               20
                               25
                               15
                               10

                               35
                               20
1 All  "treatment" operating data includes sludge disposal.
2 Limited data with respect to sludge disposal  capital  costs,  presented  as
  comparison to operating cost data for total  treatment facilities.

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                                -62-

represent those processes  most commonly  used which  can  readily be
designed and economically  evaluated.   It should  be  emphasized that
these data might not  represent typical costs  for wastewater  treat-
ment because only the major facilities were designed.   The applica-
tion of additional  miscellaneous equipment and structures is a
function of treatment efficiencies, site location,  and  pollution
abatement philosophy  of the individual mills.  The  costs do  not
include such items  as wastewater pumping and  piping, site prepara-
tion, relocation and/or development of utilities,  instrumentation,
neutralization facilities, control  and laboratory buildings, or
miscellaneous flow mixing, distribution, measurement,  and discharge
structures.  Nominal  excavation and backfill  costs  were included,
but hauling and grading charges were omitted.   For  large treatment
facilities, such as aerated lagoons, the land value was assumed  to
be $1,000 per acre in all  cases.  This value  may vary  from a very
small cost for rural  or company-owned land to multiples of this
cost when land must be purchased from private parties  and/or in
urban areas.

     In the older technology, manually cleaned grit removal  facil-
ities and bar screens were generally included in the system; how-
ever, when estimating the costs for such systems, costs for  mechan-
ically cleaned equipment were used as a basis since there were no
cost data available on manually cleaned facilities.  These were  not
usually designed or constructed according  to standard parameters even
though many of the older mills  utilized settling basins for pri-
mary solids removal.  Since these were generally designed accord-
Ing  to available land area with  little  regard to hydraulic loading
rates,  It was not considered  feasible to design a  representative
facility.  Primary clarifiers were designed on an overflow basis
of  800 gallons per day per square  foot of  surface  area.  (This is
also the  design  basis for the present and  newer technologies.)
Stabilization basin costs are based on  a  retention time of one day
in  an earthen basin with off-the-shelf  diffused air equipment.

     Oxidation ponds were not designed  because of  very large area
 requirements  associated with  this  type  of  facility, and they could
not  be  constructed at  land costs approaching  $1,000 per acre.
Sludge  disposal  costs  include gravity thickeners and vacuum filtra-
tion systems.

     Secondary  treatment  costs  for the  present  and newer technolo-
 gies Include nutrient  addition, activated  sludge,  and  aerated la-
 goon treatment  facilities.  The nutrient  addition  facilities were
 designed to store  chemicals  for approximately 30 days  with  feed
 rates  of one pound of phosphorus and  five  pounds of nitrogen per
 100 pounds of BOD removed.

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                                -63-

     Facilities provided for the contact-stabilization  modification
of the activated sludge process were designed for 85 percent  BOD
removal when treating bleached Kraft wastewater;  and conventional
activated sludge facilities were designed for similar treatment of
bleached sulfite wastewaters.  Both systems include concrete  aera-
tion basins and platform-mounted mechanical aerators.  Aerated  la-
goon systems were designed for 75 percent BOD removal from Kraft
and sulfite mill wastewaters, and are of earthen  construction with
floating mechanical aerators.  Centrifuge dewatering was  included
in the secondary sludge disposal costs.  The costs do not include
piping and sludge conveyance costs.  Although the arrangement of
centrifuges may vary with the individual application, normally
these are an outside installation and require a massive concrete
structure, if "isolation base" techniques are not used.  Vacuum
filtration costs do not include related piping, chemical  addition
facilities, nor nominal sludge conveyance equipment.  As  present
in Table A-ll,  incineration costs for the nev/er treatment tech-
nology were derived from average cost data and are not  representa-
tive of any particular incineration system.  The application  of a
particular incineration system depends on many design parameters;
i.e., heat value, inorganic or ash content, and solids  concentra-
tion of the dewatered sludge.

     To obtain total capital and operating costs, typical treatment
systems were devised for each mill size and production  technology.
Data regarding  these systems are presented in Table A-12.  Since the
capital costs for each facility used to develop the total cost  do
not contain costs for piping, pumping, electrical facilities, and
miscellaneous structures, these costs were allowed for by using per-
centages derived from or based on experience.

     The total  capital costs presented in Table A-12 are  probably
the minimum costs needed to actually finance construction of  an
industrial wastewater treatment plant.  There are a number of
factors which have been previously reiterated that can  directly
affect the costs of wastewater treatment, but no meaningful esti-
mate can be placed on these factors since they are specific to
each mill.  In  some instances, these factors could nearly double
some of the values shown in the table.  The design of treatment
systems incorporated gravity flow of wastewater through the treat-
ment plant and  the combined handling and dewatering of primary  and
secondary sludges, where applicable.

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                                -64-

     Operating costs for the treatment systems are also presented
in Table A-12.  Maintenance costs were based upon percentages of
various capital costs:  i.e., structures, one percent; mechanical,
three percent; and pumping and piping, one percent.  The mainten-
ance and labor costs for each treatment unit are not presented for
two reasons:

     1.  Insufficient data on specific treatment units and
         maintenance areas to subdivide manpower and mater-
         ial allocations.

     2.  The combination of overlapping of controls for
         treatment units.

     Table A-12 also includes total capital costs in terms of mill
capacity in tons of product per day and operating costs related to
the production rate.

Treatment Cost Reduction by In-Plant Measures

     The various in-pi ant measures for reducing wastewater flows
and material losses have been discussed.  Data is not available
to compare the expenditures for in-plant equipment modifications
and process changes with the cost savings in wastewater treatment
costs by such measures.  However, the overall savings in waste-
water treatment facilities can be obtained by comparing the dis-
charge from the present and newer technologies and resultant treat-
ment costs.

     For the wastewater treatment design basis, the following re-
ductions in hydraulic and BOO loadings from the present to newer
technology were used:

                          Percent Reduction in Waste Discharge

                        Integrated Bleached   Integrated Bleached
                           Sulfate Mill          Sulfite Mill

     Wastewater Flow            45                    45

     Total BOD Discharge        25                    70

     These reductions are attributed to the combined effects of
all projected  in-plant measures and improved recovery practices.

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                                -65-

Of specific importance  is the recovery of sulfite pulping chemicals
which result in most of the 70 percent BOD reduction shown above.

     The results of these reductions are reflected  in the differ-
ence in present and newer capital and operating costs on a produc-
tion basis, as shown in Table A-12.  The percent cost reductions
vary with the size of mill but are approximately as follows:

     1.  50 and 65 percent in total capital costs for
         bleached sulfate and sulfite operations
         respectively.

     2.  30 and 65 percent in total operating costs for
         bleached sulfate and sulfite operations respec-
         tively.

     It must be noted that the treatment systems designed for  the
present and newer technologies are not exactly the  same, but are
similar enough to permit comparison of cost data.   Also, the per-
cent savings figures only indicate savings in treatment costs  by
the application of almost all available  in-plant wastewater reduc-
ing modifications in one particular mill.  However, this is only
economically feasible in a newly constructed mill and does not ex-
clude the possibility that in-plant expenditures to reduce waste-
water discharge might completely offset any saving  in treatment
costs.

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                                             APPENDJ.X    A
287 - 028 O - 68 - 7

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APPENDIX   B

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                                P.W.P.C.A.  PAPER  INDUSTRY  PROFILE

           SIMPLIFIED  DIAGRAM  OF FUNDAMENTAL  PULP AND  PAPER  PROCESSES
  RAW  MATERIALS
FUNDAMENTAL  PROCESS
                                                                      GASEOUS
                                                                                   WASTES
                                                                                     LIQUID
                                                                                                  SOLID
PULP  LOG-
       WOOD
    PREPARATION
•EVAPORATION
   LOSS
                                (GROUNDWOOD) CH.IPS
                                     t        1
                                                                                  LOG FLUME     BARK-REFUSE
                                                                                   SLOWDOWN   WOOD
                                                                                  BARKER BEARING   PARTICLES
                                                                                   COOLING WATER  SLIVERS
                                                                                                 SAWDUST
ACID SULFITE LIQUOR
ALKALINE SULFATE LIQUOR
  (KRAFT)
NEUTRAL SULFITE        J
      PULPING
                        CHEMICAL
                          REUSE
                                       CRUDE
                                        PULP
•BLOW SYSTEM  SUUFITE SPENT
   EMISSION      LIQUOR
               BLOW PIT COL-
                LECTED SPILLS
                EVAPORATION
                HEAT GENERATION
                BY-PRODUCT
WHITE WATER OR
  REUSE WATER
                                                KRAFT I NEUTRAL
                                                SULFITE RECOVERY
                -CONDENSATE•
•SMELT  TANK
   EMISSION
 LIME KILN
   EMISSION
 RECOVERY
   FURNACE
   EMISSION
 EVAPORATION
   EMISSION
CONDENSATE    RESIDUE
DREG WASHING   WASTE
MUD WASHING
ACID PLANT
  WASTES
                                      SCREENING
                                                                                  WEAK LIQUOR
                                                                                                KNOTS
                                                                                                FIBER
                                      FINE PULP
WHITE WATER OR
  FRESH  WATER
      WASHING
                                    PURIFIED PULP
                                         *
                                     THICKENING
BLEACHING & OTHER
  NECESSARY CHEMICALS
FRESH WATER OR WHITE
  WATER REUSE
FILLERS
DYE
SIZE
ALUM
STARCH
                                  UNBLEACHED PULP
                                          *	
                                     BLEACHING
FRESH WATER OR WHITE
  WATER REUSE
                                                  WASH WATERS FIBER
                                                                                  WASTEWATERS  FIBER
                                                                                  BLEACH WASTES
       STOCK
     PREPARATION
                                       PAPER
                                      MACHINE
COATING CHEMICALS •
                                  -^•HEAT
    FINISHING   &
     CONVERTING
               CLEAN-UP
                                                  WHITE WAT EH
                                                                                  CLEAN-UP
                            DIRT
                                                                FIBER
                                                                FILLERS
                                                                BROKE
                            BROKE
                            COATINGS
                                   FINISHED PAPER
                                      PRODUCTS
                                                       Prepared for F.W.P.C.A.
                                                                                 9-24-67
                                                                                         W.O. NO.
                                                                                           iOO-OI
                                                                     B-l

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APPENDIX

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GENERAL REFERENCES

Altieri, A. M. and Wendell, T. W., "De-Inking of  Wastepaper,"
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Amberg, H. R., "By-Product Recovery and Methods of  Handling
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Amberg, H. R., Pritchard, J. H. and Wise, P.  W.,  "Supplemen-
          tal Aeration of Oxidation Lagoons with  Surface
          Aerators." Tappi . 4_J: 2TA (October  1964).

American Paper and Pulp Association, "Statistics  of Paper,"
          N. Y., May 1964.

American Paper Institute, "A Capital and Income Survey  of
          U. S. Paper  Industry,  1939-1965," N. Y.,  1965.

American Paper Institute, "Paper and Paper Board  Capacity,
          1965-1968,"  N. Y., November 1966.

American Paper Institute, "Publicly Announced New Machine
          Capacity, 1966-1969 and 1967-1970," N.  Y., June
          1966 and April 1967.

American Paper Institute, "The Statistics of  Paper," N.  Y.,
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American Paper Institute, "Monthly Statistical Summary,"
          N. Y., June  1967.

American Pulpwood Association, "Pulp Wood Statistics,"  N.  Y.,
          January 1967.

Bacher, A. A., "Advanced Waste Treatment Processes  for  Water
          Renovation and Reuse," 4th Tappi Water  Conference,
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Bailey, A. C., "Wastewater Treatment Plant." Tappi. 47:  165A
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Banford, R. A., "Centrifugal Dewatering of Paper  Mill Waste,"
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Barker, E. F., "How the Kalamozoo Valley De-Ink ing  Mills
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Baunick, H. F., and Mueller, F. M., "Spent Sulfite  Liquor
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-------
Bergen, H. F., "Summary of  Research  on  Neutral  Sulfite  Semi-
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Berger, H. F., "Evaluating  Water Reclamation  Against Rising
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Bialkowsky, H. W.  and  Brown, J. C.,  "In-Plant Pollution Con-
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Billings, R. M., and Narun,  G.  A.,  "Design Criteria and  Op-
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Blosser, R. 0., and Caron,  A. L.,  "Recent Progress in Land
          Disposal of Mill  Effluents," Tappi. *4-8;  ^JA  (1965).

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          Mills in the United States," National Council for
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Bolger, J. C., Tate, D. C., and Hopfenberg, H. B., "A New
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Boyer, R. A., "Sodium-Base Pulping and Recovery," Technical
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-------
Brown, R. W. and Spa Id ing, C.  W. ,  "Deep-Well  Disposal  of
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Brown, Jackson, and Tongren,  "Semichemical  Recovery  Pro-
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Burbank, N. C.  and Eaton, C.  D.,  "Pulp and  Paper  Mill  Waste
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Burns, 0. B., Jr. and Eckenfelder, W. W.,  Jr., "Pilot Plant
          Evaluation of Plastic Trickling  Filters in Series
          with  Activated Sludge." Tappl . 48;   42    (1965)

Burns, 0. B., Jr. and Mancini, J.  R., "Disposal System for
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Caron, A. !_., "Economic Aspects of Industrial Effluent Con-
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Carpenter, W. !_., "Factors Affecting Selection of Equipment
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Carpenter, W. L. and Gellman, 1., "Measurement, Control,  and
          Changes in Foaming Characteristics of Pulping
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Charmin Paper Products Co., "Flow Chart, Torula Yeast  Plant,"
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Coogan, F. J. and Stovall, J. R., "Incineration of Sludges
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          49A       (1965).

Cooper, S. R., "Water Reuse in a Large Integrated Kraft Mill,"
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          17-19, 1967.

-------
Copeland, C. G., "Water Reuse and  Black Liquor  Oxidation  by
          Container -  Copeland Process," J9th Purdue Indus-
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Coughlan, F. P., Jr.,  "Dewatering  and  Disposal  of  Pulp and
          Paper  Mill Sludges," Second  Ind.  Water and Waste
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          Sludge Plant for Scott Paper Co. ." Tappi .  46:
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Crawford, S. C., "Spray Irrigation of  Certain Sulfate Pulp
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Darmstadt, W. J., "Recovery - Heat and Chemicals Applied  to
          the Pulp and Paper  Industry," Presented  before  In-
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DeHass, G. G. and Amos, L. C., "Recovery Systems for Mixed
          Kraft and Sulfite Liquors." Tappi. J?0:  75A-78A
          (March  1967).

Drummond, R. M.,  "Pulp Waste Reduction by Mill  and Process
          Improvement," Sewage and Industrial Wastes, 26:
          656         (May
Eckenfelder, W. W.,Jr.,  and Barnhart, E. L., "Treatment of
           Pulp and Paper Mill Waste for High Rate Filtra-
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           1535        (December 1963).

Erdman, A., Jr., "Application of Fluidized Bed Processing
           to Spent Sulfite Liquor Combustion," Tappi , 50:
           110A-112A       (June 1967).

Federal Water Pollution Control Administration, and Wash-
           inton State Pollution Control Commission, "Poll-
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           Puget Sound"  (March 1967).

Feuerstein, D. L., Thomas, J. F. and Brink, D. L., "Mal-
           odorous Products from the Combustion of Kraft
           Black Liquor." Tappi. ^0: 258-262  (June 1962).

-------
 Follet,  R.  and  Gehm,  H.  W.,  "Manual of  Practice for Sludge
          Handling  in the  Pulp and  Paper  Industry," National
          Council for Stream Improvement,  Tech. Bulletin
           190     (June 1966).

 Foster,  J.  H.,  "Fundamentals of  Primary Treatment," Tappi
          ^6:   155A      (May 1963).

 Freeman,  L., "Effluent Treatment  and Abatement Practices  in
          the Pulp  and Paper Industry," kth  Ind. Water and
          Waste Conference.  University of  Texas, Austin,
          Texas,  January 19&J-.

 Fuchs, R. E., "Decolorization  of  Pulp Mill Bleaching Efflu-
          ents  Using  Activated Carbon," National Council
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          N. Y.,  1965.

 Gaudy, A. F., "Wastes from Pulp and Paper  Processes," Cal-
          ifornia State  Water  Pollution Control Board,
          Publication No.  lj (1957).

 Gehm, H. W., "Modern  Approaches to Pulp and Paper Mill
          Waste Problems,"   Sewage and  Industrial  Wastes.
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 Gehm, H. W., "The Activated  Sludge Process for Pulp and Paper
          Mill  Effluents." Industrial Water and Wastes,  8:
          23  (1963).                               "   ~

 Gehm, H. W., "The Application of  Stabilization Ponds in the
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          15_:   1171*- (September 1963).

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Gehm, H. W.  and Lardieri, N. J.,  "Waste Treatment  in the Pulp,
          Paper and Paper Board Industries," Sewage  and Indus-
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Gellman, I., "Practice and Research in Biological  Oxidation
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-------
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Hall, H. R., "Paper Coating Additives," Tappi  Monograph Ser-
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Halladay, W. B., "Water Quality Requirements for Industry,"
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Han, S. T., "Engineering Considerations for Sulfite Recovery,"
          Tappi. 48:  66A  (1965).

Harding, C.  I. and Landry, J. E., "Future Trends in Air Poll-
          ution Control in the Kraft Pulping Industry," Tappi .
          4
-------
Jansson, L. B., "Turpentine Recovery Systems  for  Continuous
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Johnson, E. H., "Mechanical Pulping  Manual,"  Tappi  Monograph
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Kenline, P. A. and Hales, J.  M.,  "Air Pollution  and Kraft
          Pulping Industry, An Annotated  Bibliography," U. S.
          Dept. of H.E.W., Public  Health  Service, Div.  of
          Air Pollution, November  1963.

Kirk, R. E. and Othmer, D. F., "Encyclopedia  of  Chemical  Tech-
          nology ," Wi ley- I ntersc ience, N.Y.  1956-1962.

Klass, C. P., "Kimberly-Clark Dedicates  California's First
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Knapp, C. A., Coughlan, F. P. and  Baffa,  J. J.,  "Sedimentation
          Practices  for Paper Industry Wastes," Journal San-
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Knauer, K. J., "White Water and Effluent System for Cylinder
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          and  11, McGraw-Hill Book Co., N. Y., 1962

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McDermott, G. N.,  "Sources of Wastes  from  Kraft  Pulping and
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          tem," Ta££L.  48:   128A  (1965).

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          Black Liquor." JWPCF.  36:   1401 (November  1964).

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APPENDIX

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                             APPENDIX D

               FUNDAMENTAL PROCESSES AND SUBPROCESSES
                       PULP AND PAPER INDUSTRY

Definition of Fundamental  Manufacturing Processes

     The Profile for Paper Mills (except buildings)  Is  to include
pulp mills directly associated with paper mills  (integrated  pulp
and paper mills).  Because pulp mills are to be  discussed in the
fundamental process description, it was considered  advantageous to
discuss an integrated pulp and paper mill rather than  to discuss
them separately.

     An integrated pulp and paper mill  can be divided  into two
basic parts:  1) a pulp mill  which includes the  fundamental  pro-
cesses of wood preparation, pulping, screening,  washing, thicken-
ing, and bleaching; and 2) the paper mill which  includes stock
preparation, paper machine, and converting and finishing. A sim-
plified diagram of the fundamental processes for the pulp and paper
industry is shown in Drawing No. 1.  Also shown  in  the  drawing are
the raw materials used, final products  obtained, and the wastes
generated !n the form of liquids, gases, and solids.  Individual
fundamental manufacturing processes are described  in the following
sections.

     Wood J>jypa/_ajtj_qn_

     Wood preparation Is classified as  a fundamental process al-
though It Is actually a group of operations which are necessary to
prepare the log for the digester.  Basically, the process includes
the transportation of the log from storage to debarking facilities,
debarking, chipping, chip screening, and chip storage.

          Lo£ T rans_portat I on

     Wood logs to be used in the pulping operation  are  stored in
piles, ponds or rivers depending on the mill site.   When the logs
are stored In piles, periodical dampening is required  to control
spontaneous combustion.

     Transportation of the logs from storage to debarking facili-
ties is a two-step operation:   using a crane, the logs are first
removed from the storage area to  a conveyer, and then  transported
to the debarking drums by  log flumes or a conveyer system.  Ordi-
narily, the log  flume  Is equipped with a  log pond where the log
is retained and soaked before being placed  In the flume.  In many
mills, the log movement through the flume is assisted  by currents

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                                 D-2

artificially created by paddle wheels,  propellers, or pumps.  Tre-
mendous amounts of wastewater are generated  both  in  the  log ponds
and flumes: however, much  of it  can be  reused  If  grit chambers and
fine screens are provided  in the recycle  line  to  effect  removal of
the grit and bark.

          Debarking

     At the debarking facilities, the log is picked  up from the
flume by a lift conveyer and fed into the debarker where the
bark is removed from the log.  Log debarking is necessary in order
to insure that the pulp will be free  from dirt specks, particles
of bark and other objectionable matter.  The three principal types
of bark removal operations are  mechanical, hydraulic, and chemical

     1.  Mechanical debarking uses cutting or  friction  im-
         parted by a rotating action  plus water which assists
         In loosening the bark  from the log.  At  the point of
         discharge, the logs which have not  been  completely
         debarked are returned  to the beginning of the cycle
         for further treatment.   Typical  machines used are
         rotating cylindrical drums  and stationary friction
         barkers.  The rotating cylindrical  drum  is  commonly
         used  in medium and large size  mills,  while  the  use
         of the stationary friction  barker is  limited  to some
         small mills.  Since the efficiency  of mechanical
         debarking  is rather low, the power  consumption  is
         very high, and the wood damage is severe, especially
         for dry wood.  Some techniques involving soaking and
         pretreatment have been practiced in an endeavor to
         reduce these adverse effects.  Methods practiced to
         increase the efficiency are rinsing with warm water,
         storage  in steam chambers,  and the  addition of
         chemicals.

     2.  Hydraulic  debarking uses a hydraulic  barker which
         consists of a jet or jets of high pressure  (1,000
         psi or more) water directed against a log  to  frag-
         ment and remove the bark.  Varying  somewhat in
         details and methods of operation, several variations
         of this technique are now used in small  mills.

     3.  Chemical debarking  is a relatively  new process  and
         is accomplished by the introduction of chemicals
         Into  the sap stream of the living tree.   Various
         chemicals  have been suggested, but  the toxic effect

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                                 D-3

         of the solution must be eliminated If this process
         is to be developed for industry-wide use.  Other
         disadvantages are that the dead tree in the forest
         tends to become too dry.

     *».  Long log debarking is a process currently being de-
         veloped by the industry fn which the log is not cut,
         but Is debarked in one piece.  When the whole tree-
         length log is debarked in a unit operation, the
         costs for logging, transportation, handling, and
         storage are reduced significantly.  Another advan-
         tage can be realized through the utilization of the
         top sections of the trees with log diameters as small
         as k inches.  Usually, log sections of this diameter
         split badly in the drum barkers, and short lengths
         of this diameter cannot be handled in the mechanical
         barkers.  The application of this debarking technique
         is increasing each year.

          Bark Disposal

     Bark which has been removed from the log in the debarking  opera-
tion presents a major disposal problem in most mills.  Acceptable
disposal methods include incineration for heat generation,  compost-
ing, or utilized In by-product recovery facilities.  The feasibility
of using any one of these methods is dependent on local  conditions
and the individual species or type of wood from which the bark  has
been removed.

     The utilization of heat from the incineration of bark  has  much
promise, and is  particularly economical when used in conjunction
with^dry debarking operations where no auxiliary dewatering step  is
required.   Although bark emerging from wet debarking operations
needs to be dewatered prior to incineration, a mechanical press can
be effective and economical in removing the excess water.   Either
type of bark can be burned in a separate furnace designed for this
type of installation, or burnt in combination  with oil,  coal, or
gas.  The heat  released from the burning bark  is then utilized  to
generate steam.

     Composting for volume reduction fs employed by some mills,
but the applicability of this disposal method  fs dependent  upon
the availability of a large land area.  Since  many mills do not
have sufficient  land suitable for bark composting, this  method
has found  limited  acceptance.

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          Chipping

     After the log has been debarked,  the stripped log  is  conveyed
to the chipping operation where It is  fragmented into segments
suitably sized to enable the cooking liquor in the diqester  to pen-
etrate the wood quickly, completely, and uniformly.  By mechanical
means, chips of about 5/8 to 3/4 inches in size are produced.

     One of the most widely accepted method of chipping is with
the multiknife-type chipper, which consists of knives attached to
a circular disk with a chute to place the log perpendicular  to the
knives.  Care must be exercised to minimize the amount  of  sawdust
and slivers generated while also insuring that the fibers  are not
damaged by undue compression which would result in a low viscosity
and high cellulose degradation in dissolving pulps.  Proper  con-
trol of the speed and sharpness of the knives will insure  the pro-
duction of uniform chips while undesired side effects are  kept to
a minimum.

               Chip Screening

     To separate the useful chips from sawdust and slivers,  two
operations are generally required; mechanical screening (rotary,
shaker, and vibratory) and air blast cleaning.  During  the screen-
ing operation, properly sized chips pass through the screen  while
the oversize chips and slivers remain on the screen until  rejected
to a conveyer which carries them to a chip crusher or rechlpper.
The material that has passed through the screen Is moved to  the
air blast cleaner which consists of a flat chamber equipped  with
a curved screen and air blower.  The dust and undersized chips are
blown from the screen or dislodged by the tumbling action.

               Chip Recovery

     The oversized chips and slivers rejected by the chip  screens
are resized either In chip crushers or rechippers.  After  process-
ing, the resized chips are mixed with chips being conveyed to the
screening and cleaning processes,  in this way, any oversized chips
that may have been improperly crushed and any sawdust generated
during crushing will be removed, and only chips of uniform size
will be supplied to the digesters.

     Pulping

     The cleaned, sized chips resulting from the fundamental pro-
cess of wood preparation are now ready for pulping, the second
fundamental process in the paper making sequence.  Pulping is the

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                                 D-5

process wherein wood is converted into fibers which  are adaptable
for use in paper making.   Currently,  four different  pulping pro-
cesses are practiced:  mechanical, sulfate (Kraft),  sulfite,  and
semichemical.   In chemical  pulping, the intercellular  polymers
(lignin and carbohydrates)  are removed by digestion  with  the  use
of chemicals,  whereas in mechanical pulping,  all  the wood material
is used but the separation  occurs between fibers  and through  the
fiber walls.  The operations involved in each type of  wood pulping
are briefly outlined so that wastewater sources  and  characteristics
can be better  understood.

          Mechan i ca 1 (G no u ndwggd) Pu1_p

     The basic operation of mechanical pulping  consists of cutting
the debarked log into small blocks and then forcing  them  against  a
grindstone in  the presence of water.   In the grinding  operation,
the block is reduced to a fibrous condition.  Water  is used to  cool
the grinding stone, to clean, and to act as a lubricant for the
surface of the grinding stone as well as being  the pulp carrier.
Carriers currently used In this operation may be grouped  into three
categories; pocket, magazine, and a combination  pocket/magazine.
The factors which affect the operation are the  condition  of the
pulps tone surface, speed of the stone, operation pressure, grinding
temperature, and the physical condition and species  of the wood
block being ground.

     An alternative method of producing groundwood pulp utilizes
steam In a pretreatment process, and the resultant pulp has a poor
color but a higher strength than otherwise attained  in mechanical
pulping.

     Recently, chemigroundwood pulping has been developed and is
particularly applicable for use  in conjunction  with  regular  ground-
wood pulping where hardwood sources are available.  The most  dis-
tinctive feature of the chemIgroundwood process is that the entire
log is cooked.  After the  log has  been soaked in a liquor consist-
ing of sodium sulfite and sodium bicarbonate, the log is  ground.
Savings are effected since chipping and associated equipment  re-
quirements are eliminated.  Yields from chemigroundwood pulping
are as high as 85-90 percent, and  are only slightly  less  than
yields attainable by groundwood  pulping.  Advantages of this  pro-
cess over mechanical pulping are faster drainage and greater
strength while requiring less power and providing better  utiliza-
tion of woodlands.

     During the past several years, mechanical  pulping from chips
(refining mechanical pulp) has  increased  due to many factors  in-
cluding the lower capital  and operating costs and the availability

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                                 D-6

of chips from saw mil)  waste  and  other wood  by-products which can
be used in this process.   The equipment  required  to manufacture
mechanical pulp from chips includes a disk  refiner (either one of
two stages), a "pump through" refiner, and a centrifugal  cleaner.

          Sulfate (Kraft)  Pulping

     Kraft pulping utilizes alkaline solutions  to dissolve the lig-
nin and other non-cellulose portions of  the  wood  which cement the
cellulose fibers together. Alkaline cooking agents used  in  this
process are caustic soda  and  sodium sulfide, and  the "active alkali"
is the sum total of the weight of these  two  chemicals expressed as
sodium oxide.  Since the  amount of active alkali  present  in  the
cooking liquor is determined  by the type of  pulp  being produced,
the amount present varies from mill to mill, with a typical  range
of 18 to 20 percent based on  oven dry wood.   The  resultant pulp  is
brown in color, difficult to bleach, and resistant to mechanical
pulping.

     The Kraft process is a cyclic system wherein the chemicals are
recovered for direct reuse, and the dissolved organic residue  Is
used for steam and power generation.  The digestion process  involves
filling the digester with chips and  cooking liquor, introducing
steam Into the digester,  and increasing  the pressure until the final
cooking temperature is reached.  During  the initial cooking  stage
several reactions take place:  air is  removed from the  digester by
displacement with steam;   liquor penetrates  into the chips; volatile
constituents of the wood  (i.e., turpentine)  begin to distill off:
and the more soluble solid constituents  of  the wood being to dis-
solve.  At a pressure of about 50 or 60  pst, mercaptans  and  sulfides
begin to form and the rate of delIgnlficat Ion increases  rapidly.
As the pressure and temperature continue to increase, the evolution
of non-condensable gases  begins to taper off.  It Is important that
all non-condensable gases and air be expelled from the  digester
during the cooking period, otherwise the temperature would be  less
than that of the steam at that pressure  and would result in  a  raw
cook.  The maximum cooking pressure is  reached in about  one  to five
hours at  100 to 135 psig with a cooking  temperature of  3^0° F to
350°F.  After digestion,  the pulp mass  is blown directly into  the
blow tank where the contents are  diluted by spent cooking liquor.

     The Kraft spent cooking liquor,  "black liquor", contains  the
spent cooking chemicals as well as lignin and other solids extracted
from the wood.  It can be reused  to constitute about 40  to 60  per-
cent of the total liquor  in the digester.   The reuse of  black  liquor
increases the solids content of the final  spent liquor but decreases
the quantity discharged to the recovery  system.

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                                 D-7

     The digestion techniques can be classified into three categor-
ies - batch cooking, injection method, and continuous digestion.
Batch cooking is usually accomplished in a large pressure  cooking
vessel, a stationary digester, with chips and liquor introduced
into an opening at the top while the steam enters from the bottom.
The injection method alternative requires the injection of the
fresh reagent into the forced circulation line in the digester,  and
consequently does not require a high initial  chemical-to-wood ratio
since the chemicals can be added as they are  needed.  Although less
chemicals are required, the disadvantages of  longer cooking time
and higher power consumption have limited this application.  The
continuous digestion method, as the name implies, produces a steady
flow of pulp, and is accomplished by preheating the chips  in a
steaming vessel and then feeding the chips to the digester where
they are impregnated by the cooking liquor which has been  heated
and recirculated through heat exchangers.  Although the advantages
of this method include heat conservation, reduced costs for acces-
sory equipment, elimination of peak steam demands, reduction of
corrosion problems, and the production of a uniform pulp.   The dis-
advantages of low surge capacity, lack of flexibility, and excess
wastage during start-up have limited the acceptance of this method
in the past.  However, the majority of the large new mills being
built are incorporating continuous digestion, and the tendency is
toward even more frequent adoption with the development of the
sulfate pulping process.

     Recent pilot-plant installations have included prehydrolysis
sulfate digestion; the chips are treated in the first stage segment
of the digester, then subjected to countercurrent cooking in the
second stage.  Prehydrolysis is kept to a minimum while by-product
(turpentine) recovery is enhanced.  Development of this method is
directed at the reduction of the hemicellulose degradation, which
would  result in increased yields from the Kraft process.

          Sulfite Pulping

     The sulfite pulping process is based on the digestion of wood
chips  in an aqueous solution containing  metallic bisulfite and an
excess of sulfur dioxide.  The primary  reaction of the sulfite pulp-
ing process  involves  the solubi1ization  and sulfonatton of  lignin
and the hydrolytic splitting of  1ignin-cellulose complex.

     The digester used  in sulfite pulping  is a  large cylindrical
vessel with a conical bottom.  After  the digester has been filled
with chips, a chip packer evenly distributes the chips over the
cross-section of the  interior  in order  to achieve uniform settling.
Next,  the digester  is closed with a metal cover and  the cooking
acid is pumped  into the unit.

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                                 D-8

     Two types of systems are possible;  hot  acid and cold  acid.
in the former, the liquor is added from a spherical  storage  vessel
(an accumulator) at a temperature of about 80°C. and 60  psig, while
in the cold acid system, the temperature Is  only about 30°C. and
the liquor is added at atmospheric pressure.

     The main advantage of the hot acid system over  the  cold acid
system is that it saves about two hours pulping time and about
2,000 pounds of steam per ton of pulp.   This is because  of its
ability to contain higher concentrations of  sulfur dioxide.  Also,
the higher temperature increases the rate of penetration while de-
creasing the cooking time.  Most of the mills are now using  the hot
acid system with calcium-base sulfite pulping; yields are  about 50
percent.

     Either direct or indirect heating  operations can be used.  In
the direct heating operation, steam is  introduced into the digester
directly and uniform heat can be maintained  with the aid of  exter-
nal circulation of the liquor.  If external  circulation  is not pro-
vided, careful application of steam Is  essential in  order  to promote
circulation.  Since steam condensation  dilutes the liquor  in the di-
gester, higher concentrations of chemical are needed in  the  digester
liquor.  It is also necessary to withdraw liquor from the  digester
at a side relief to maintain the proper liquid level  and to  permit
gas relief from the digester without plugging the top relief strain-
ers (which prevent chips from being carried  out of the digester).

     Indirect heating is accomplished by forced circulation  of the
liquor within the digester with heat being applied indirectly with
the use of a heat exchanger.  This method has the advantage  that
uniform temperature and chemical concentrations are  maintained
throughout the volume of chips in the digester resulting in  a more
uniform pulp product.  Another advantage of  the indirect heating
procedure is that the steam condensed in the heat exchangers can
be returned to the boilers for reuse.

     After cooking, the digester is blown with the contents  forced
to a blow tank.  In the blow tank, the  chips and liquor  are  forced
against a stainless steel target plate, resulting in the chip struc-
ture breaking into individual pulp fibers.  The sulfite  liquor drains
through the bottom of the blow tower and may be discharged to the
sewer or collected for recovery.

     Because of the low cost of limestone, no attempts were  made
in the past to recover this chemical from the spent  liquor,  which
contains non-volatile solids in concentrations of about  8  to 12

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                                 D-9

percent with dissolved organic concentrations  of  about  10  to  12
percent.  The remaining material  present  will  be  residual  calcium
bisulfite, other inorganic salts  (such as calcium sulfate), and  a
small amount of organic substances.   Alternatives to the calcium-
base in sulfite pulping have been developed which include  ammonium,
magnesium, and sodium bases.

     In the ammonium-base bisulfite  liquor, cookinq time can  be  de-
creased with a resulting increase in production.   The ammonium ion
tends to diffuse more readily and improves liquor penetration into
the chips, resulting in increased yield and a  more uniform pulp
quality.  Another advantage is that  a wider range of wood  species
can be utilized because of the greater solubility of resin and
other acids in ammonium salts.  In the preparation of the  cooking
liquor, the ammonium hydroxide or liquid  ammonia  is used,  while
the procedures for carrying out the pulping operations  are similar
to those used in the calcium-based system, except that  the greater
solubility of ammonium salts permits a somewhat lower combined
sulfur dioxide concentration in the liquor.

     The magnesium-base sulfite pulping process was first  developed
in 1914, but now is receiving close attention  since the recovery of
heat and chemicals from the spent liquor is feasible.  An  80  to  30
percent recovery of the magnesium base can be  expected  with the  proper
operation of the recovery system; however, to  convert existing facili-
ties from calcium to magnesium-base pulping, some modification of the
processing operation would be required.

     The sodium-base sulfite pulping process has  recently  been developed
by the industry, and the operating advantages  are similar  to  those
discussed for ammonium and magnesium.  In addition, there  is  increased
versatility since pH levels in the digester can readily be adjusted
during operation.  The recovery of the spent liquor has been  success-
fully developed and practiced by the industry, and the  relatively higher
costs involved in the sodium-base sulfite pulping process  may be justi-
fied by improved quality, capacity, ability to handle more resistant
woods, as well as the reduction of the wasteloads generated.

     Of approximately 60 sulfite pulp mills in this country,  all
but a few are more than 20 years old.  Most of the mills  are  using
either the calcium-base or the ammoniurn-base process with  no  prac-
tical recovery methods for chemicals and liquor.   However, some
mills have instigated the practice of evaporation and combustion
of the spent  liquor for heat recovery and waste reduction.  Several
newer mills have been built using magnesium-base and sodium-base
sulfite pulping processes with chemical and liquor recovery.

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                                D-10

     As stream pollution controls  become more  stringent,  the  sul-
fite mills are beinq restricted In their practice of discharging
the untreated waste liquor into the streams.   Consequently, many
mills are planning to change the sulfite process  from calcium-base
to magnesium, ammonium,  or sodium bases  where  economical  recovery
of the spent liquor is feasible.

     The most recent development in sulfite pulping is the adoption
of multistage processing, where each stage would  differ in degree
of acidity and alkalinity.  The first stage is designed for optimum
penetration of the cooking liquor into the wood and also to initiate
the wood softeninq process; in the second stage,  the dissolution
and removal of reacted lignin is maximized. To date, this technique
is still experimental, and no large scale industrial application
has been developed.
          S e mi^chem jj; a 1  P u Ip

     The semi chemical process produces pulp from chips using a  mild
chemical treatment to soften the chips thereby allowing mechanical
separation of the fiber.  With a pulp yield of about 80 percent,
the process is much more efficient than chemical pulping where  the
yield will range from ^3 to 50 percent.  However, the strength  and
flexibility of the semi chemical pulp is low when compared with  the
pulp produced in the chemical process.  Currently, there are two
semichemical pulping processes which have been adopted by the in-
dustry, neutral sulfite and the Kraft process (KSC).

     In the neutral sulfite semichemical (NSSC)  pulping, the liquor
chemicals break the fiber bond in a process that involves lignin
sulfonation and hemicel 1 ulose hydrolysis.  The sodium sulfite is
used basically as the main cooking agent, while sodium carbonate
is added as a buffer to maintain a slightly alkaline pH during  di-
gestion.  Smaller mills prepare the cooking liquor from sodium
sulfite and soda ash, but the large mills generally prepare sulfite
soda ash by burning sulfur and absorbing the gases in a packed
tower through which a soda ash solution Is circulated.  The NSSC
digestion procedures can be classified Into two types, batch and
continuous .

     After the digester is filled with chips and cooking liquor for
the batch process system the unit Is heated to 120°C for one hour
under excess steam conditions.  Once the pulp is softened and par-
tially digested, the stock is then discharged to either the blow
tank or to blow pits filled with leach casters.  The partially  dis-
Inteqrated stock, in a moist or slush form, is then pumped to de-
liquoring presses or directly to the fiberization machine.  The disk

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                                o-n

attrition is widely used to refine or disintegrate this stock, and
a number of different types are currently  in operation.  The end re-
sult sought is a moisture content  in  the fibrous material of about
50 to 60 percent, which in turn leads to higher pulp strength and
lower fiberizing energy consumption.

     Recently, the use of the continuous digester for NSSC semi-
chemical pulping has been developed and practiced.  Different types
of digester are available commercially; horizontal-tube, downflow
vertical, upflow vertical, inclined-tube,  etc.

     The KSC pulp, which is generally bleached,  is increasing in
production and has the advantage of using  hardwoods, but the yield
is about 65 to 70 percent, which is lower  than  that of NSSC pulp.
The KSC liquor is a weak white liquor obtained  from an associated
Kraft mill liquor preparation system.  Normally, the active alkali
application is about 5 to 8 percent of wood as  sodium oxide with a
cooking time of  less than 30 minutes  for  temperatures of  170°C to
180°C.  The mechanical treatment for the  KSC  digested chips  is the
same as described for the NSSC process, while  the  recovery system
for the KSC spent liquor is combined  with  the  Kraft  recovery system
in an associated Kraft pulp mill.   The future  for KSC applications
is promising because of the increasing number of Kraft mills beinq
established.

          Blow Tank

     The digester contents, after they have cooled, are blown to a
blow tank by the pressure remaining in the digester.  The  blow tank
is used to separate the blow vapors from stock  and  liquor, and this
operation is essentially associated with  all  types of pulping.  The
blow tank operation is not generally considered a  fundamental pro-
cess for the pulp and paper industry, but  is  discussed separately
to achieve clarity.

     After the cooked chips are blown into the blow  tank or  blow
tower,  the steam and hot gases escape from the cyclone separator
vent on the top  of the tank and then are sent to a  heat exchanger
where the heat and condensate are  recovered.   The  stock  drops to
the bottom cone, where  it  is stirred by an agitator assembly  ro-
tating  at about  20 rpm.  After the stock is diluted  to  about  3.5
percent by  introducing spent liquor, this mixture  leaves  the  blow
tank from an opening near  the bottom, passes through  a  separator
where scrap metal, etc. are removed, and is pumped  to another
screen  or directly to washers.

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                               D-12

          Deinking

     Deinking is  the process of treating printed wastepapers for
the removal  of the printing  Ink and the recovery of  the pulp in a
condition suitable for reuse.   In  the future,  this process may be-
come one of  the major sources of pulp as raw material  sources di-
minish.   The deinking process  includes pulp separation, washing,
screeningt etc.,  because these operations  are  normally kept sepa-
rate from other mill processes.

     Most wastepapers are not  deinked prior to being processed to
manufacture  roofing paper and  boxboard, as only about 5 percent of
total wastepaper used is treated  to  remove printing  and writing
ink.  Available wastepapers  suitable  for deinking  are printed books,
magazines, and similar papers,  where  the principal  fiber  component
is bleached chemical pulp, while  the foreign  materials include  ink
and pigments.  Sorting wastepapers before  deinking is essential
for successful operation.

     Deinking consists of fiberizlng the  printed wastepaper  by  me-
chanical  action  in  conjunction with water, heat, and chemicals
(usually  alkalies).  The  Ink is removed from the printed  paper  by
saponifying,  dissolving, emulsifying the ink vehicle, and thus  re-
leasing  the  ink  pigment which can be removed from the pulp suspen-
sion by  dilution, agitation and washing or flotation.

     The chemicals  used,  the procedure followed, and the equipment
employed in  the  deinking  process may vary considerably.   The pro-
cess sequence depends on  the composition of the grades of waste-
paper used,  the  character of the printing inks, and the final  usage
of  the  recovered pulp.  Broad generalities are not applicable to
the deinking of  wastepapers; special cases must be considered from
one mill  to  another.

     The chemicals  used  in the deinking of printed papers usually
comprise alkalies such  as caustic soda, soda ash, or sodium phos-
phates,  together with surface-active chemicals  (anionic, cationic,
nonionic, and mixed an ionic-cat ionic) employed as wetting agents
and detergents.

      In the older technology,  little wastewater was  reused because
either  an ample  water supply was  available or  pollution control
measurements were not enforced.   Present  day  technology  is toward
 the use of  washers  in series with proper  water reuse.  A very def-
 inite saving in  water,  heat, and  chemicals may result from reuse
 of the  first wash water from the  washing  cycle.  This saving may
 be as high  as 50 percent on steam and alkali  used in high consis-
 tency cooking, and as high  as  85  percent  In the low consistency
 cooking process.

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                                0-13

     Since wastewaters  generated In the  deInking of printed papers
contain ink, clay filler,  and other contaminants,  recovery of chem-
icals from these wastewaters  has not  been  found practical.

          Other Sources of Pulp

     Rag pulp is a small  but  Important source of fiber for the man-
ufacturing of fine quality papers.  Process operations include
thrashing, color-segregation, sorting, cooking, washing, bleaching,
and rewashing for pulp  production.  The  cooking chemicals include
caustic lime, caustic soda or a mixture  of caustic lime and soda
ash.

     Another source of  pulp that has  been  developed within the past
two decades is bagasse.  Almost all chemical pulping processes are
applicable to the pulping of  bagasse, but  the Kraft or modified
soda process with extra sulfur usually gives best  overall results.
Bagasse pulps are used  in practically all  grades of paper, includ-
ing bags, wrapping, printing, writing, toilet tissue, facial tis-
sue, toweling, glassine,  and  even newsprint.

     Pulp Washing

     Pulp washing is the process designed  to  remove the  liquor and
other foreign materials from the pulp.   There are  two types of
equipment which have been used for the washing operation; the dif-
fuser and the rotary drum vacuum filters.

          PIffuser

     The diffuser is essentially a large tank with a  false bottom
constructed for the drainage of the liquor and  the collection of
the washed pulp.  After the cooking is completed,  the stock and
spent liquor from digesters are blown directly  into the  diffuser
through the opening of  a cyclone receiver mounted  on  top of the
diffuser.  The steam vapors rise to a cyclone-type catchall.  From
the catchall, the steam goes to heat  exchangers, where  the heat  is
recovered.  At the same time, when the digester has emptied into
the diffuser tank, liquor drains through the false bottom screen
plate and is pumped to either spent liquor storage or to the sewer.
Then, fresh water is admitted and the washing operation  is.started.
Usually, several washings are  required before the  pulp  is clean.
After the pulp has been sufficiently washed,  the gate located in
the bottom of the diffuser is opened and the stock is sluiced out.
Usually, several dlffusers are often operated cooperatively for
pulp washing.  When this  is the case, the cleaner  discharge from
the washing operation of one diffuser is reused for  the first wash-
ing, but are being replaced by the more  efficient  vacuum filters.
   287 - 026 O - 68 - 9

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                                D-14

          Vacuum F
     The vacuum filter consists of a large cylinder with woven-
wl re-covered drum rotating in a vat filled with  diluted stock, with
a shower located across the top of the drum.   The drum is  divided
into a number of sections for the proper distribution  of different
operations involved in the pulp washing.  Normally, the cyclic
operations include  the sheet forming, drainage,  washing,  and the
removal of the cake.  By the application of vacuum, the vat  liquor
is drawn through the screen on the surface of the drum and the pulp
sheet is formed.  Washing of the pulp sheet is accomplished  by the
spray of the wash water from the skimmer system.   Then, the  pulp
sheet is scraped off by a doctor knife or compressed air.

     The consistency of the feedstock is about 1.0 to  1.25 percent.
After sheet forming and initial drainage on the  cylinder mold, the
consistency is increased to about 10 or 15 percent. Wash  water
temperatures of 130°F or 150°F are normally used  with  the  maximum
temperature determined by the allowable temperature of the liquor
leaving the system.  Generally, wash waters hotter than 170°C may
cause foaming problems.

     The early vacuum-washer systems were single-stage units, in
which spent liquor was used to dilute stock drawn into the drum
along with large amounts of wash water, and then  discharged.  Since
the efficiency of this unit was low, washers  in  series or  multi-stage
countercurrent washing are used either of which  reduces water re-
quirements considerably.  In the operation of the multi-stage vacuum
filters, the stock scraped off the drum is repulped with the filtrate
from the next succeeding stage and transported to the  filter.  The
cleaned pulp is collected from the last stage of  the system  where
fresh water is used for repulping and washing. The filtrate from
the first stage is sent to the evaporator for liquor recovery, to
spent liquor storage, or to the sewer.  It has been customary to re-
move the knots from the pulp after washing on brownstock washers,
but preknotting has the advantage of forming a uniform, dense, easily
washable cake.  Knotting prior to washing is used especially for the
washers equipped with a press roll that is used  to increase  the
density of the pulp sheet.  Nowadays, most mills  are using multistage
countercurrent vacuum filters for pulp washing.   Except for  some
sulfate pulp mills, the completely closed system for the spent
liquors discharged from washers is still only a goal because of the
problems reflected from the liquor recovery system. One significant
disadvantage present in the vacuum filter operation is that  the con-
tact time between the stock and wash water is relatively short and
does not permit complete removal of spent chemicals from the pulp
by leaching and diffusion.

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                                D-15

     L '_q_uQr Recove ry

     Cooking liquor recovery was developed  in  order  to  reduce  the
cost for cooking chemicals and reduce the wastewater toads  being
discharged to streams.   The recovery  technique is  different with
each type of pulping method.

          Kraft Liquor

     The Kraft liquor recovery system is  essentially a  part of the
pulping process.  By means of evaporation,  burning,  and causticiz-
ing, the chemicals used in the cooking liquor  can  be recovered for
reuse, while the dissolved organic residues from wood resins can
be used for heat and power generation.

     The spent cooking liquor (known as black  liquor),  after sepa-
ration from the pulp stock, is pumped to multi-effect evaporators
where it is concentrated from 16 to 18 percent solids to about 50
percent total solids.  When increased Uquor recoveries are prac-
ticed, the feed solids concentration  will be about 13 percent. The
concentrated mixture is then sent through a cascade, or disk evap-
orator, where combustion gases from the recovery furnace further
concentrate the liquor to approximately 60  percent solids.  The
concentrated liquor is next sprayed into a  furnace where heat  Is
generated by the combustion of organic materials,  and the inorganic
solids (Na2S and Na^CO^) melt at the high temperature.   The melted
solids are discharged from the base of the furnace into the dis-
solving tank where the smelt is dissolved in water to form a solu-
tion known as green liquor.  The green Uquor contains sodium  sul-
fide, sodium carbonate and some carbon and iron.  After processing
through clarification, the green liquor is  causticized by the  addi-
tion of lime and the heat in the causticizer,  and sodium carbonate
and lime are converted to sodium hydroxide and calcium carbonate.
After precipitation, the white  Uquor is recovered in the clarifier
overflow.  Calcium carbonate in the underflow is converted into
lime by burning in either a rotary lime kiln or in fluidized bed
incinerators.

      In spite of the most careful control, some soda is lost  in the
washing operation, and these  losses are made up by the addition of
salt cake  to the  liquor as  it enters  the furnace.  The salt cake
is then reduced to sodium sulfide in  the combustion process.

           Sulfite Liquor

     Sulfite  Uquor  recovery  techniques  are more complex and diffi-
cult than  those employed  in the sulfate  system.  In the past,  the

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                                D-16

spent liquor from sulfite pulping was discharged  directly  into  the
sewer.  Because of the cost of chemicals  and pollution  abatement
programs, complete or partial  recovery systems  are  becoming  more
common.   With the use of bases other than calcium,  the  closed sys-
tem for spent liquor recovery  is expected in future applications.

     In the spent liquor, the  quantity of organic solids equals about
one-half of the original weight of wood.   However,  other chemicals
are combined with lignin.  The feasibility of liquor recovery  is
highly dependent on the base involved in  the sulfite liquor; e.g.,
the calcium-base sulfite liquor can only  be evaporated  to  approxi-
mately 60 percent solids and then burned  for the  production  of  power.
When the evaporated sulfite spent liquor  is burned, the calcium com-
bines with the sulfur to form calcium sulfate.   It  is generally con-
ceded that liquor recovery from calcium-base pulping Is not  econom-
ically feasible, especially considering that burning for heat pro-
duction involves the problem of scaling on the  wall of  evaporators
and furnaces.

     For the magnesium-base sulfite liquor, the spent liquor is
evaporated and burned.  During burning, the organic residues are
completely disposed for the generation of heat, and the magnesium
is converted into magnesium oxide.  The sulfur  passes off  in the
combustion gases as sulfur dioxide.  By making  a  slurry of magne-
sium oxide ash, the slurry may be used In the absorption tower  to
absorb the sulfur dioxide in the cooled combustion  gases.  Thus,
the cyclic process for the magnesium bisulfite  pulping  is  possible
with the makeup of HgO and S02.

      In the sodium-base sulfite process it is possible  to  recover
the inorganic chemicals with a fairly complex process.   After  the
spent liquor is evaporated and burned, the smelt  of sodium carbon-
ate and sodium sulfite is collected from the bottom of  the furnace.
By carbonation or crystallization, the relatively pure  sodium car-
bonate Is recovered, while hydrogen sulfide is  evolved  and is  burned
to yield sulfur dioxide.  By using a sulfiting  tower, the  sulfur
dioxide Is absorbed by sodium carbonate to form sodium bisulfite,
which is suitable for reuse.

     Spent chemicals from the ammonium-base sulfite pulp process
can only be partially recovered.  By simple evaporation and  combus-
tion, only sulfur dioxide can be economically recovered together
with  the generation of steam and power.  But with the complicated
processes of fortiflcating, heating and pyrolysis,  the gases of S02
and NH, are produced from the spent liquor.  After passing the
gases through a scrubbing tower, It Is possible to recover 70 to  88
percent of the S02 and 99 percent of the NH3.  Unfortunately,  this
recovery method does not appear to be economically promising.

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                                D-17

          SemIchemi ca1  L t q uo r

     Liquor recovery in the neutral  sulfite  semtchemlcal  (NSSC)
system is described here.   The recovery  of liquor  in  the  Kraft
semi chemical system is  the same as  that  of the regular  Kraft pro-
cess.

     The recovery methods  In use are now handled by integrated
semi chemical-Kraft "cross  recovery", and the carbonation  method.
The "cross recovery" method Is based on  the  sodium and  sulfur
values in the NSSC liquor that can  be used as chemical  makeup In
place of salt cake.   The NSSC spent liquor can be  combined with
Kraft liquor for evaporation and combustion, but the  NSSC cooking
liquor has to be made from fresh chemicals.

     The carbonation method Is a complicated process  practiced  in
some independent NSSC pulp mills.  Following conventional evapora-
tion and burning procedures, a smelt of  sodium sulflde  and sodium
carbonate Is produced,  while the flue gas is high  in  sulfur  dioxide,
and carbon dioxide.   By passing the flue gas through  the  sulfiting
tower, the sulfur dioxide is removed and only the  carbon  dioxide
remains in the effluent gas, which  In turn is used to carbonate the
dissolved smelt to form hydrogen sulfide and sodium bicarbonate.
The hydrogen sulfide can then be burned  Into sulfur dioxide  in  the
furnace, and the sodium bicarbonate is converted to sodium sulfite
in the sulfiting tower.

     Pulp Screening and Cleaning

     The objective of pulp screening and cleaning  is  to separate
the coarse fiber from the fine fiber and to  remove dirt and  foreign
matter; I.e., slivers,  uncooked chips, grit, sand, etc.  There  are
two separate screening operations involved in most pulping opera-
tions; coarse and fine screening, which  do not generally  follow
each other in sequence.  In most instances,  coarse screening Is
followed by washing, thickening and dewatering, which in  turn is
followed by fine screening.  Since  fine  particles  of  dirt, grit,
and other unacceptable matter are not removed in either screening
process, many mills add another cleaning operation, the centrifugal
cleaner.

          Coarse Screening

     Coarse screening is used to remove  oversized  material,  such as
knots, large slivers, and unground  pieces.  Coarse screens usually
have 1/4 to 1/2 Inch circular perforations and may be a vibratory,
   287 - 026 O - 68 - 10

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                                D-18

mechanical, or rotating type.   Vibrating screens  consist  essentially
of a partially submerged perforated basket,  the accepted  pulp  flow-
ing through the perforations,  while the rejects travel  over  the end
of the screen to be recovered  or carried away for disposal.  Most
mechanical screens consist of  an inclined perforated plate from
which the rejects are removed  by a mechanical scraper.  The  rotat-
ing screen uses an Inclined perforated cylinder in which  there is
a shower, which washes the pulp through the  cylinder.  The rejects
travel downward and emerge from the lower end.

     Coarse screens can be classified according to the  application:

     1.  Sliver screens are used in the groundwood pulp pro-
         cess to remove the coarse material.   The most  common
         types of sliver screens used are bull screens, ro-
         tary screens, and rotary oscillating plates.

     2.  The knotter is a compact, simple machine with  a  ro-
         tating cylinder that  is used to remove the partially
         cooked chips and knots from chemical pulp and  slivers
         from groundwood pulp.  In other mills, especially
         those using diffuser  washing, the knotting operation
         was placed after the  washing operation.   Now,  many
         mills employ the knotter screen before the vacuum
         filtration washing cycle to protect  the  filter.

          Fine Screening

     The purpose of fine screening is to separate the fibers into
grades according to their dimensions.  Normally,  fine screening Is
performed after pulp washing and thickening  in order to prolong
the life of the screen.  However, some mills  have successfully com-
bined coarse and fine screening Into one operation.  The  three
categories of fine screens currently used are inward-flow rotary,
outward-flow, and flat screens.  Openings in  the  screens  vary  from
0.025 to 0.075 inches; the size of the opening being governed  by
the quality of the paper being produced.

     In the older technology,  the flat screen was widely  used;
wherein the pulp suspension flows over flat metal plates  perforated
with slot with vibrating diaphragms below the plates inducing
screening action.  Acceptable  fibers and small dirt particles  pass
through the slots while showers move the rejected material over
the end of the screen box for  subsequent rescreenlng or rejection.
Application of flat screens Is limited because of the low rate of
pulp flow with a resultant large area requirement for the installa-
tion.

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                                D-19

     The outward-flow screen, widely used  in present operations,
consists of a cylindrical screen chamber with perforated  plates
through which the stock is thrown by the centrifugal action of the
rotating Impeller.

     Inward-flow rotary screens have a vat for the unscreened pulp,
within which a screen cylinder rotates. Acceptable pulp  flows
through the screen plates while an internal  high  pressure shower
is used to backwash the partially submerged screen.

          Cleaning

     The centrifugal cleaner Is the most frequently used  device in
pulp cleaning operations to remove grit and other small particles.
Although several types of centrifugal cleaners have been  developed,
all rely on the magnified gravitational forces generated  by  intro-
ducing a dilute pulp suspension under relatively  high  pressure into
a conical vessel.  Materials that are heavy or unusually  shaped are
readily removed.

     The placement of the cleaners in the  pulping sequence varies
according to the function of the cleaner.   Many mills  have the
cleaning operation following coarse screening, while  tn other mills,
the cleaners are placed either before or after fine screening opera-
tions.

     Thickening and Dewaterlng

     The thickening or dewatering process  Is used to  concentrate
the screened pulp and to increase its consistency. The water  re-
moved is usually returned to be reused in  diluting fresh  pulp  for
screening or Is wasted to the sewer.  The  thickeners  used for  in-
tegrated pulp and paper mills are either deckers  or vacuum filters.
Thickening and dewatering operations can be applied in numerous
areas and sequences since it may be used after pulp washing, after
fine screening, before bleaching, or after bleaching.

     1.  The decker is also referred to as a gravity  thicken-
         er, and the attainable pulp consistency  Is about 3
         to 6 percent.  The decker consists essentially of a
         vat for diluting pulp and a wire-cloth covered cyl-
         inder to allow the water to be removed from the
         pulp.  The pulp level In the vat  Is maintained 3-6
         inches above the top of the cylinder, while  the  water
         level  Inside the cylinder Is kept as low as  possible
         to increase the head for gravity  flow.  The  cylinder

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                                D-20

         is cleaned periodically by a high pressure  shower or
         steam jet to remove the dewatered pulp.   The decker
         thickeners were used in the older technology but, be-
         cause of their long processing time requirement  and
         the low dewatering capability, they have  largely been
         replaced by vacuum filters.

     2.  The vacuum filter used for thickening is  essentially
         the same as that described previously for pulp wash-
         ing.  Vacuum filtration dewatering can obtain a  con-
         sistency of about 15-25 percent.   The advantages of
         the vacuum filter over the decker are the reduced
         floor space requirements,  fiber loss, and maintenance
         costs.  In many mills pulp washing Is incorporated
         into the vacuum filter thickening operation. This
         is particularly true for the multistage,  counter-
         current systems.

     Bleaching

     The objective of the pulp bleaching process  is  the production
of a brighter pulp, as measured by  light reflectance. The main
light-absorbing substances in wood  pulp are derived  from  the lig-
nin, resin, metal ions, and noncellulose carbohydrate components
of the original wood.  Therefore, to obtain a whiter pulp, these
substances must either be removed or chemically changed to dimin-
ish their light-absorbing characteristics.

     For groundwood pulp, the removal of the lignin  and resin would
result in a substantial reduction in pulp  yield, which eliminates
its main advantage (high yield) over chemical pulps.  Similarly,
for cold soda and chemigroundwood pulps, extremely high brightness
(85 to 90 percent as measured on a  G.E. reflectance  meter) is not
commercially feasible because of the high  lignin content  of the
pulps.  The brightness increment in these  pulps is obtained solely
through the removal of color bodies using  oxidizing  agents (per-
oxides) and reducing agents (hydrosulfites).

     Bleaching of groundwood and high-yield semi chemical  pulps with
peroxide or hydrosulphite was previously accomplished in  one stage;
however, the tendency is now toward two-stage peroxide-hydrosulfite
bleaching to obtain a higher degree of brightness.  Cold  soda pulps
are also being bleached in two-stage peroxide-hydrosulfite process.

     For Kraft, sulfite, and neutral sulfite pulps,  initial removal
of lignin Is achieved by cooking with alkalies, sulfides, or sul-
fites.  The bleaching process includes further delIgnification of
the pulps by chlorlnation, caustic  treatment for the removal of

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                                 D-21

 alkaline-soluble chlorolIgnins,  and one or more bleaching stages
 using sodium or calcium  hypochlorlte or chlorine dioxide as oxidiz-
 ing agents.   Washing  is  necessary after each stage In multistage
 bleaching processes.

      Presently,  the three-stage  bleaching sequence - chlorlnatton,
 caustic extraction, and  hypochlorlte bleaching - Is used for sul-
 flte and semlchemlcal pulps, except when a very high degree of
 brightness is required.  Since the Initial brightness of sulfate
 pulp Is below 45, while  sulfite  pulp averages about 60, It Is much
 more difficult  to bleach the sulfate pulp to the same final bright-
 ness attainable  for the  sulfite  pulp.  It Is not uncommon for mills
 to  use five-stage bleaching of sulfate pulp If the extra brightness
 Is  required.

      Basically the same  chemicals and bleaching sequences are neces-
 sary when  bleaching detnked pulps.  Where a very high degree of
 brightness  Is not required and the pulp has a low groundwood content,
 single-stage  hypochlorlte bleaching Is the most frequently used pro-
 cess.   As  discussed In the delnklng section, three stage bleaching Is
 required when the groundwood content exceeds 40 percent.

      The degree of brightness obtained is of course directly related
 to  the  degree of lignin  removal obtained prior to oxldatlve bleaching.
 Alkaline extraction, after chlorinatlon,  is necessary for sulfate and
 NSSC  pulps  (often omitted with sulfite pulps).   In recent years,  chlor-
 ine  dioxide has been used extensively for oxidatlve bleaching although
 specialized bleaching chemicals have been developed for nearly every
 type of pulp and end-product requirement.

      It has been established that greater brightness  can be achieved
with  less degradation if smaller amounts  of bleaching agents  are
 applied In successive stages with washing between  stages.   However,
 the use of a  large number of stages  has  the disadvantages  of  higher
 capital costs, loss  of fiber, and increased water  usage.   The pres-
ent aim is to reduce the number of stages  required to produce the
 specified pulp quality.   With the development of  chlorine  dioxide
 as a bleaching agent,  many modern bleach  plants have  only  five stages
 to produce very white, strong pulps.

     Since there is  a variety of multistage bleaching sequences
available for each type of pulp,  the quantity of wastewater gener-
ated varies in accordance with the number  of stages  Involved, the
number of washing steps,  and the amount of water  reuse in  the pro-
cess.  In older mills, there had been no water  reuse  employed in
the washer, but technological advances have allowed  for more  effi-
cient use of water in the multistage bleach plant.

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                                D-22

     Two types of water reelrculatlon  can  be  used  in  the bleach
plant.  Within the individual  stage, the filtrate  from the washer
seal box can be reused to dilute and convey the  stock going to that
same washer.  This represents  an extremely large amount of filtrate;
but since it is mainly an internal  recycle, the  water demand from
outside the system is minimal.  The other  recycle  method  involves
a transfer of excess filtrates from the final washer  seal boxes to
earlier stages in the bleach sequence, thus maintaining a counter-
current flow of filtrate from  the bleached end toward the unbleached
end of the plant.  The use of  fresh water  in  the showers assures
that the sheet going into each bleaching stage will be relatively
free from dissolved organic matter, which  would  otherwise consume
bleaching chemical.  For maximum water conservation,  only the over-
flow from the chlorination and the  first caustic extraction stage
are sewered.

     It Is important when reusing white water in a bleach plant to
consider not only the quality  of the water and the dissolved mater-
ial content, but also the temperature  and  type of  fiber content.
For optimum utilization of chemicals or heat,  it is preferable to
keep the acid and alkaline filtrate streams separated and the high
and low temperature waters should also be  discharged  to separate
streams.  Typical recycling systems are shown In Drawing No. B-3.

     Stock Preparation

     Stock preparation is defined as  that  part of  the pulp and paper
making process in which pulp Is treated mechanically, and often
chemically, using additives to make it ready  for forming  into a
sheet on the paper machine.  Stock  preparation  in  a paper mill in-
cludes all Intermediate operations  between preparation of the pulp
and fabrication of the paper,  and would consist  of:  1) preparation
of the furnish including consistency  regulation  and proportioning,
2) beating and refining, 3) machine chest  mixing,  and k)  screening.

     Furnish is the term used  for the mixture of water, pulp and
chemicals which ultimately goes to  the paper  machine  for  fabrica-
tion into paper.  The furnish  of a  paper machine varies widely,
depending on the grade of paper being made.   For example, newsprint
is generally a mixture of 15-20 parts  of unbleached sulfite pulp
and 80-85 parts of groundwood  pulp  with no chemical additives.
Bond paper may be 100 percent  sulfite or a combination of sulfite
and rag; it usually contains 5-10 percent  filler and  a starch sur-
face sizing application.

     The integrated mill receives pulp in  a slush  form with a con-
sistency of 3 to 15 percent, though there  are instances where the

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                                D-23

 pulps are dried, stored, or transferred to be used later in the
 form of a roll,  lap, or dry baled sheets.  Slushing will be re-
 quired to fiberize or disintegrate the dry sheets or laps of pulp
 in water to form a slush of separated fibers.  Slushing can be ac-
 complished in beaters or by machines known as pulpers.

     Consistency regulators are used to regulate the amount and the
 consistency of the stock that goes to beaters, refiners, or to the
 paper machine.  There are two types of consistency regulators:
 open and pipeline.  Since both types work by dilution,  the stock
 coming to them must have a higher consistency than that desired in
 order for the controller to function.

     The various stocks which make up a multi-stock furnish are
 proportioned by many different methods.  The most prevalent method
 has  been the use of a multi-compartment stock regulating box pro-
 vided with suitable inlet, outlet, and overflow ports and adjust-
 able weirs which permit adjustment of the amount of each stock being
 added to the furnish.  As with consistency regulators,  the use of
 enclosed proportioning devices installed in stock lines is practiced.
 Open-head, box-type proportioners are also used.

     Fillers, or "loading", are included in the furnish to give
 paper increased opacity, brightness,  bulk, weight, flexibility,
 softness, smoothness, or printability.   The usual loading mater-
 ials are very fine grained powders of clay, talc, diatom?te,  gyp-
 sum, calcium carbonate, calcium sulfate, titanium dioxide,  barium
 sulfate, and zinc sulftde.   These can be added in slurry form to
 the beater during stock preparation.   Since only a portion  of the
 filler leaving the paper machine headbox is retained  in the sheet
 by interaction of filtration or co-flocculation,  spillage  from
white water systems should be minimized to avoid filler wastage
 and objectionable mill  effluent.   The majority of the filler  re-
 tained on the sheet Is  concentrated  in  the top (felt) side,  re-
 sulting In "two-sided"  sheets.

     Sizing is the treatment which makes the paper or stock resis-
 tant to liquids,  particularly water.  All  papers  are  sized  except
 blotting and other absorbent papers where  penetration is desired.
 Rosin, various hydrocarbon  and  natural  waxes,  starches,  sodium
silicate, glues,  casein, synthetic resins,  and rubber latex are
 among the materials used as sizing agents.   Addition  of the agent
 can be made by several  alternative methods.  When the agent Is
added directly as a beater additive,  it is  commonly known  as
"stock" or "engine" sizing.   The sizing agent  can be  added  in the
 form of soap made from the saponification of rosin with alkali or

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                                D-24

as a wax emulsion.  The size is precipitated using paper makers'
alum, AL2(SOj) .18H 0.  As a result of this treatment, a gelatinous
film forms on the fiber which loses water of hydratlon and produces
a hardened surface.  Sodium aluminate may also be used to precipi-
tate the rosin size.

     An alternative method of adding the agent is to run the par-
tially dewatered paper through a size solution or over a roll  wetted
with a sizing solution.  Sheets processed by these methods are known
as "tub-sized" or "surface sized".

     Wet strength resins have become important additives in the
manufacture of.papers that have greater than 10 percent wet over
dry tensile strength when saturated with water.  Aminoaldehyde
resins can be added to the stock at the beater or at the wet end
of the paper machine.

     Coloring is often applied to the paper to improve its appear-
ance.  Dyes used are either added to the stock In the beater or at
other points ahead of the paper machine.  All  types of dyes (acid,
basic, direct, sulfur) and all  types of pigments (both natural and
synthetic) are used as coloring agents.  The acid dyes (negatively
charged ions) have no affinity for the cellulose fibers (also nega-
tively charged) and must, therefore, be fixed to them by means of
mordants.  If the paper is colored in the beater, the alum that is
added to precipitate the size will also act as a mordant for the dye.

     Pulp stock is prepared for formation into paper by two general
processes, beating and refining.  There is no sharp distinction be-
tween these two operations.  Mills use either one or a combination
of the two.  However, the use of beater operation is decreasing
with the increased use of continuous refining, which produces  bet-
ter results.

     Beating is the mixing together of the various materials in a
water suspension, and by means  of mechanical action imparting  pro-
perties to the materials that determine the character of the fin-
ished product.  Beating the fibers makes the paper stronger, more
uniform, denser, more opaque, and less porous.  Beaters (known also
as Hollanders) are extensively  used in rag, rope, and fine paper
mills.  Beating can be either intermittent or a batch process.

     Refining is a mechanical treatment that can be used alone or
after beating.  It contributes  to fiber separation, fiber brushing,
and fiber shortening, where the objective is to improve formation
and to better adapt the fibers  for forming on  the paper machine.
Because of the possibility of continuous operation, refiners are

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                                D-25

now used almost exclusively for the large tonnage papers, such as
wrapping, bag, and newsprint;  they are  also  replacing beaters In
the production of the more highly processed  grades of paper.  Two
types of refiners are available:  the Jordan  refiner is typical of
the conical (plug-and-shel 1 )  types; and the  Bauer refiner is typ-
ical of the disk type.

     After the stock Is refined, it is  usually  retained in a machine
chest (also called a stock chest) for an hour or more before it is
sent to the paper machine.  An agitator paddle  or propeller in the
chest provides thorough mixing of the stock.  The consistency of
the stock in the chest varies  from 2-1/2 to  3 percent.
     Paper_ Ma5hiji
     Converting the fiber suspension  into the  paper sheet  involves
three steps:  1) the random arrangement  of the fibers  into a wet
web (paper machine wet end); 2)  the removal of free water  from the
wet web by pressing; and 3) the progressive  removal of additional
water by heat (paper machine dry end).   Two types of paper machines
are used; the Fourdrinier and the cylinder machines.

     The Fourdrinier machine has been successfully adapted to make
a very wide range of papers and lightweight boards.  Cylinder ma-
chines are employed for the manufacture  of heavy paper, cardboard,
or non-uniform paper.  Because of the compact  nature of the cylinder
vat, multiple units have been combined  in machines designed to manu-
facture multi-ply papers and boards.

     In the Fourdrinier machine, the  stock containing  approximately
one half percent fiber is sent through screens to the  headbox and
then flows from there through a sluice onto a  moving,  endless wire
screen.  Almost all the water and approximately one half of the fibers
go on through the Fourdrinier wire, either to  be caught by the wire
tray or to fall Into the wire pit.  Since the  wire has to  be kept
clean, pressure sprays are used for this purpose, and  the  spray
water is collected at the wire pit.  Water from the wire tray, which
Is the "richest" white water, flows into the mixing well, where it
is mixed with the incoming stock and  then pumped back  into the head-
box system by the fan pump.  Some of  the water that falls  into the
wire pit is used to maintain the water  level  in the mixing well, and
the remainder overflows to be returned  to the  saveall  system where
fibers are reclaimed.  In the older technology, the excess white
water was sewered and not reclaimed.

     In the newer technology, separate  trays  are used  In the Four-
drinier machines to collect white water  from forming  rolls and to

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                                D-26

collect relatively clean water from the suction boxes.  The rich
white water from forming rolls is sent to a retention silo and re-
cycled to mix with the incoming stock.  Water from the suction box
Is collected In a tank and used for diluting the stock or as a spray
on the wires.  The balance of the white water collected at the wire
pit Is pumped to a saveall tank and then to the saveal I system.

     Saveal Is are essential for the reuse of water and for the re-
covery of huge quantities of fiber, additives, pigments, and other
paper making chemicals which might otherwise increase the pollution
loadings to the receiving streams.  In a properly designed system,
the saveall should recover at least 95 percent of the fibers and
fillers.  Several types of savealls are now In use:  sedimentation,
revolving cylinder (screening), vacuum filter, and flotation.  The
disk filter Is favored because of its relatively high efficiency
and minimal space requirements.

     After the suction boxes, the sheet is of about 15 to 20 per-
cent consistency, and the wire and sheet move to the first felt
blanket which carries the sheet through a series of press rolls
where more water is removed and the paper is given a watermark, if
so desired.  The paper then passes through steel smoothing rolls
and Is picked up by the second felt which carries It through a ser-
ies of dry rolls heated by steam.  The paper enters the rolls with
a moisture content of 60 to 70 percent and leaves them 90 to 94
percent dry.  It is next passed through the calender stack, which
is a series of smooth, heavy steel rolls that impart the final
surface to the paper.  The paper produced is wound on the reel.

     In the cylinder machine, a vacuum is maintained below the
stock level In the cylinder in which the wire cloth is rotating,
and the sheet forms on the wire by suction; a process similar to
the formation of cake on a vacuum filter.  The cylinder machine
has from four to seven parallel vats into each of which similar
or dissimilar dilute paper stocks are charged.  This enables sev-
eral layers to be united together into one heavy sheet.  As a wire-
covered rotating cylinder dips into each vat, the paper stock is
deposited on the turning screen as the water Inside the cylinder Is
removed.  As the cylinder revolves farther, the paper stock reaches
the top where the wet layer comes into contact with a moving felt.
The traveling felts, carrying the wet sheet, passes under a couch
roll to press out some of the water, and then Into contact with the
top of the next cylinder where another layer of wet paper Is picked
up.  Thus, a composite wet sheet is built up and passed through
press rolls to the drying and smoothing rolls.

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                                D-27

     The operating speeds of the Fourdrlnfer machines vary  from 200
ft/minute for the finer grades of paper to  2,500  ft/minute  for news-
print.  Speeds for the cylinder machines do not often exceed 800 ft/
minute.

     Tab sizing Is carried out on the dried paper or on surfaces
which may or may not have been previously sized  in  the beating op-
eration.  The principal substances used are animal  glue and modi-
fied starches since the treatment requires  that  the material have
adhesive properties.  The operation is carried out  either on the
paper making machine or in a separate sizing press  that employs air
drying.  The paper runs through a bath of the size  material, through
squeezing rolls to remove the excess material, and  then over drying
rolls.

     A limited amount of paper is colored by running the sheet
through a dye solution (dip dying) or by applying a dye solution
at the calenders (calender-straining).  However,  surface coloring
uses  less dye and requires the production of only one type  of paper,
which later may be colored any shade desired.

      In the past, coaters were usually operated  Independently of
the paper machine because the coater ran at a much  slower speed.
Today, all the large tonnage grades of medium quality coated paper
are coated on the paper machine.  Where heavy coating weights are
needed or where special formulations or other conditions exist which
do not permit application on the paper machine without slowing  it
down, papers are coated off the machine.

      "Wet broke" is that material which has been rejected before
the paper reaches the dryer.  Several types of wet  broke are pro-
duced in the course of the paper making operation and are handled
in various ways.  Wet broke may be allowed  to run into a couch  pit
where It mixes with white water and Is then pumped  to the saveall,
or it may be carted or conveyed to the broke beater or pulper.

      "Dry broke" is that material which is  rejected at the  dryers,
calender  reel or winder, or In the finishing room.   The dry broke
Is usually transferred to the pulper or broke beater for  reprocess-
ing.

      Fin i s hjjig an d Conve r11 ng 0 pe rat 1 on s

      Finishing operations refer to those operations which are per-
formed  in the paper mill finishing room and which are needed  to
prepare the paper for shipment.  The finishing operations  include:

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                                D-28

1) supercalender!ng to Improve the surface finish;  2)  secondary
slitting and rewinding to produce rolls sized to the customer's
specifications; and 3) cutting of the paper into sheets if the end
product must be in sheet rather than roll  form.

     Converting operations cover the modifications  of the raw paper
from the mill rewfnder which improve the grade of paper with  spe-
cial properties or the fabrication of the paper  into a finished
article.  There are two distinct types of converting.   The first  is
referred to as wet converting, wherein the paper is handled in the
roll form; modified by such operations as coating,  impregnating,
and laminating.  The second type is known as dry converting,  wherein
a finished product is made from the paper; i.e., bags, boxes, house-
household-size rolls, etc.

     The basic procedures involved in finishing  and converting are
related to the grade of the end paper products.   For example, news-
print is simply slit and rewound into rolls of the  size required
for the newspaper presses.  Machine-coated book  papers are super-
calendered, and then slit, rewound or sheeted.  The better grade
printing paper receives a pigment coating in a separate operation
(not on the paper machine), and are supercalendered, sheeted  or
slit, and rewound.  Paper of writing grade is commonly sheeted,
while the highest quality is often given a tub-sizing treatment.
Packaging and wrapping papers are subjected to various protective
and waterproofing coatings, laminating, and pigment coatings.

     Most of these finishing and converting operations are performed
under dry conditions and produce little liquid wastes  except  in the
case of coating operations.

     Mineral or pigment coating is important for improving the print-
ability of paper.  The basic mineral pigment coating used consists
of a water suspension of a white pigment;  usually clay with soluble
binders of casein, starch, vegetable proteins, or synthetic resins.
Most coatings also contain titanium dioxide which increases white-
ness and opacity.  Other pigments used include calcium carbonate,
calcium aluminum silicate, satin white, and blanc fixe.  Dyes are
added for production of colored paper coatings.   The preparation
of coating mixtures is a highly refined art.  The final mixture
comprises dozens of ingredients including such materials as dis-
persing agents, preservatives, viscosity modifiers, ant I foaming
agents, leveling agents, softeners, and plastic!zers.

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                                D-29

     Functional coatings to  improve properties  and  range of  paper
usage are the second major coating field.  Paraffin wax, bituminous
asphalt, various lacquers and  varnishes, both natural  and  synthetic,
are used as protective coatings which also add  gloss and improved
appearance.  Animal glues and  rubber-base pressure-sensitive ad-
hestves are applied to paper to be used as gummed tapes and  adhe-
sive tapes used for packaging.  Greaseproof  lacquer coatings and a
wide variety of synthetic resins are used in a  variety of  protec-
tive coatings.
                                        U. S. GOVERNMENT PRINTING OFFICE : 1968 O - 287 - 026

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