U.S. DEPARTMENT OF THE INTERIOR
Federal Water Pollution Control Administration
VOLUME
INDUSTRIAL WASTE PROFILE NO. 3
PAPER MILLS, EXCEPT BUILDING
-------
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
-------
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
-------
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
-------
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?
-------
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.
-------
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
-------
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
-------
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)
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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.
-------
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
-------
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.
-------
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.
-------
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.
-------
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
-------
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
-------
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
-------
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
-------
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.
-------
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
-------
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.
-------
-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
-------
-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
-------
-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
-------
-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.
-------
-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
-------
-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.)
-------
-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.
-------
-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
-------
-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.
-------
-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.
-------
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.
-------
-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)
-------
-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.
-------
-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.
-------
-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
-------
-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
-------
-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
-------
-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
-------
-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.
-------
-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
-------
-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.
-------
-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)
-------
-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.
-------
-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.
-------
-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.
-------
-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.
-------
-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,
-------
-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.
-------
-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.
-------
-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.
-------
-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
-------
-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
-------
-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
-------
-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
-------
-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
-------
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
-------
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
-------
-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.
-------
-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.
-------
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
-------
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.
-------
-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
-------
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.
-------
-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
-------
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.
-------
-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
-------
-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
-------
-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
-------
-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-
-------
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.
-------
-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.
-------
-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.
-------
-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&*— ~
-------
-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.
-------
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
-------
-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,
-------
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.
-------
-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.
-------
-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.
-------
-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.
-------
-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.
-------
APPENDJ.X A
287 - 028 O - 68 - 7
-------
PAGE NOT
AVAILABLE
DIGITALLY
-------
APPENDIX B
-------
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
-------
PAGE NOT
AVAILABLE
DIGITALLY
-------
APPENDIX
-------
GENERAL REFERENCES
Altieri, A. M. and Wendell, T. W., "De-Inking of Wastepaper,"
Tappi Monograph Series, No. J>\ (196?).
Amberg, H. R., "By-Product Recovery and Methods of Handling
Spent Sulfite Liquor, " JWPCF. 2L: 228 (1965)
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.,
May 1967.
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,
Philadelphia, April 17-19, 1967.
Bailey, A. C., "Wastewater Treatment Plant." Tappi. 47: 165A
(1964).
Banford, R. A., "Centrifugal Dewatering of Paper Mill Waste,"
Tappi. 47; 187A (1964).
Barker, E. F., "How the Kalamozoo Valley De-Ink ing Mills
Solved Their Waste Disposal Problems." Paper Trade
Journal . 140: JO (December 17, 1956).
Baunick, H. F., and Mueller, F. M., "Spent Sulfite Liquor
Uti1ization," Sewage and Industrial Wastes, 24;
1J24 (October 1952).
-------
Bergen, H. F., "Summary of Research on Neutral Sulfite Semi-
chemical Wastes," Paper Trade Journal, 159: 20
(May 1955).
Berger, H. F., "Evaluating Water Reclamation Against Rising
Costs of Water and Effluent Treatment ." Tappi , ^9:
79A (1966).
Bialkowsky, H. W. and Brown, J. C., "In-Plant Pollution Con-
trol in Practice," Chemical Engineering Progress,
5^-60 (April 1959).
Billings, R. M., and Narun, G. A., "Design Criteria and Op-
eration of a Liquid Effluent Treatment Plant,"
Tappi . U2: 70A (1966).
Bishop, F. W., and Wilson, J. W. , "Integrated Mill Waste
Treatment and Disposal, Description." Sewage and
Industrial Wastes, 26; 1^85 (December 195*0-
Black, H. H., "Spent Sulfite Liquor Developments." Industrial
and Engineering Chemistry. 50: 95A (October 1958).
Blackerby, L. H., "First Coated Printing Papers Mill Built
in California, Kimberly-Clark." Pulp and Paper.
p. li^-kQ (June 1*4-, 1965).
Blosser, R. 0., "BOD Removal from De- Inking Wastes," Purdue
University Engineering Bulletin, Ext. Series No. 96:
630 (1958).
Blosser, R. 0., and Caron, A. L., "Recent Progress in Land
Disposal of Mill Effluents," Tappi. *4-8; ^JA (1965).
Blosser, R. 0., "Practice in Handling Barker Effluents in
Mills in the United States," National Council for
Stream Improvement, Tech. Bulletin No. 19*4- (1966).
Bolger, J. C., Tate, D. C., and Hopfenberg, H. B., "A New
Process for Improved Recovery of Tall Oil from Sul-
fate Liquor." Tappi. 50: 231-237 (May 196?) -
Boyer, R. A., "Sodium-Base Pulping and Recovery," Technical
Assoc. of Pulp and Paper Industry, k2: 356 (1959).
Britt, K. W., "Handbook of Pulp and Paper Technology," Rein-
hold Publishing Corp., N. Y. , 196*4-.
-------
Brown, R. W. and Spa Id ing, C. W. , "Deep-Well Disposal of
Spent Hardwood Pulping Liquors," JWPCF. 38: 1916
(December 1966).
Brown, Jackson, and Tongren, "Semichemical Recovery Pro-
cesses and Pollution Abatement," Paper Trade Jour-
nal , 143; 28 (1959).
Buehler, H., Jr., "Waste Treatment in a Paper Mi 1 1 ." Proc.
of 12th Ind. Waste Conference. Purdue University,
May 1957.
Burbank, N. C. and Eaton, C. D., "Pulp and Paper Mill Waste
Water Treatment," Technical Assoc. of Pulp and
Paper Industry, 4j_: Supplement 195A (June 1958).
Burns, 0. B., Jr., and Eckenfelder, W. W. , Jr., "Biological
Treatment of Pulp and Paper Mill Wastes." Proc.
Purdue Ind. Waste Conference. Purdue University,
Ext. Ser. 115, 83 (1963).
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
Mixed Primary and Secondary Sludges ." Tappi . 5Q:
99A (196T).
Caron, A. !_., "Economic Aspects of Industrial Effluent Con-
trol ," Ja££i, 4j_; 62A (September 1964).
Carpenter, W. !_., "Factors Affecting Selection of Equipment
for Treatment of De- Ink ing Waste." Tappi, 4j_:
Carpenter, W. L. and Gellman, 1., "Measurement, Control, and
Changes in Foaming Characteristics of Pulping
Wastes During Biological Treatment ." _Tappi . 50;
83A-8TA (May 1967).
Charmin Paper Products Co., "Flow Chart, Torula Yeast Plant,"
Tappi. 45; 127A (1962).
Coogan, F. J. and Stovall, J. R., "Incineration of Sludges
from Kraft Pulp Mil 1 Effluents," Tappi. 48:
49A (1965).
Cooper, S. R., "Water Reuse in a Large Integrated Kraft Mill,"
4th Tappi Water Conference. Philadelphia, April
17-19, 1967.
-------
Copeland, C. G., "Water Reuse and Black Liquor Oxidation by
Container - Copeland Process," J9th Purdue Indus-
trial Wastes Conference, p. 391 (1964).
Coughlan, F. P., Jr., "Dewatering and Disposal of Pulp and
Paper Mill Sludges," Second Ind. Water and Waste
Conference , University of Texas, Austin, Texas,
p. 38 (June 1962).
Coughlan, F. P., Jr., "Design and Operation — Activated
Sludge Plant for Scott Paper Co. ." Tappi . 46:
191A-195A (May 19&3).
Crawford, S. C., "Spray Irrigation of Certain Sulfate Pulp
Mill Wastes." Sewage and Industrial Wastes. 30:
1266-1272 (October 1958).
Darmstadt, W. J., "Recovery - Heat and Chemicals Applied to
the Pulp and Paper Industry," Presented before In-
dustrial Incineration Committee of the American
Society of Mechanical Engineers, March 15, 1967.
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-
tion Using Plastic Filter Media," JWPCF. J£>:
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-
utional Effects of Pulp and Paper Mill Wastes in
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
for Stream Improvements, Tech. Bulletin 181,
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.
2g: 1370 (December 1957).
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
Purification of Pulp and Paper Mill Wastes." JWPCF
15_: 1171*- (September 1963).
Gehm, H. W., "Pulp and Paper," Chapter 20 of industrial Waste
Control by C. F. Burnham, Academic Press, 1965.
Gehm.'H. W. and Gellman, I., "Practice Research and Develop-
ment in Biological Oxidation of Pulp and Paper Mill
Effluents," JWPCF. 37: 1392 (October 1965).
Gehm, H. W. and Lardieri, N. J., "Waste Treatment in the Pulp,
Paper and Paper Board Industries," Sewage and Indus-
trial Waste. 38; 287-295 (March 1956).
Gellman, I., "Practice and Research in Biological Oxidation
of Pulp and Paper Mill Wastes," National Council for
Stream Improvement, Tech. Bulletin 162, N.Y.
March 1963.
-------
Gellman, I., "Aerated Stabilization Basin Treatment of Mill
Effluents." Tappi . 48; 106A (1965).
Gellman, I., "Results of NCSI Industry Survey of Investment
and Cost for Effluent Disposal." 4th Tappi Water
Conference. Phi ladelphia, Apr i 1 17-19,
Guccione, E., "A Brief Look at Modern Papermakinq ." Chemical
Engineering, p. 124-126 (October 26, 1965).
Hall, H. R., "Paper Coating Additives," Tappi Monograph Ser-
ies No. 25 (1963).
Halladay, W. B., "Water Quality Requirements for Industry,"
Proc. of the National Symposium on Quality Stan-
dards for Natural Waters, University of Michigan,
Series No. 161 , July 1966
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
Digesters." Tappi. 50: 1l^A-116A (Apr 11 1967).
Johnson, E. H., "Mechanical Pulping Manual," Tappi Monograph
Series, No. 21 (I960).
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
Coated Printing Paper Mill," Paper Trade Journal ,
p. 42-1*9 (June 1U, 1965).
Knapp, C. A., Coughlan, F. P. and Baffa, J. J., "Sedimentation
Practices for Paper Industry Wastes," Journal San-
itary Eng. Div., ASCE, ^0 (SA6) : M 0964).
Knauer, K. J., "White Water and Effluent System for Cylinder
Machine Mills." Paper Trade Journal. 1^9: 32 (1963).
Lewis, H. F., "Fiber Recovery, Research, Review." Sewage and
Industrial Wastes. 23: 1214 (September 1951).
Libby, C. E., "Pulp and Paper Science and Technology," Vol. 1
and 11, McGraw-Hill Book Co., N. Y., 1962
Lockwood's Directory of the Paper and Allied Trades, Lockwood
Trade Journal Company, Inc., N. Y., 1962.
Martin, W. C., "Paper Mill and De-Inking Effluent Treatment,"
17th Purdue Industrial Waste Conference, p. 211-214
(May 1962).
Masselli, J. W. , Masselli, N. W. and Burford, M. G., "White
Water Wastes from Paper and Paper Board Mills,"
Prepared for: New England Interstate Water Pollu-
tion Control Commission, 1963.
McDermott, G. N., "Sources of Wastes from Kraft Pulping and
Theoretical Possibilities of Reuse of Condensates,"
Proceedings of 3rd Southern Municipal and Industrial
Wajte Conference, p. 105 (March 195*0.
-------
Moggio, W. A., "Kraft Mill Effluent, Control and Disposal,"
Sewage and Industrial Wastes, 27: 241 (February
1955).
Murphy, N. F. and Gregory, D. R., "Removal of Color from
Sulfate Pulp Wash Liquors." 19th Purdue Industrial
Waste Conference. Purdue University, p. 59 (1964).
National Association of Manufacturers, U. S. Chamber of Comm-
erce, and National Technical Task Committee on
Industrial Wastes, "Water in Industry" (January
1965).
National Council for Stream Improvement, "Experimental In-
cineration of Paper Mill Sludges," Tech. Bulletin
130, N. Y., May I960.
National Council for Stream Improvement, "Removal of Color
Bodies from Bleachery Effluents through Modific-
ation of Kraft Recovery Process,": Tech. Bulletin
131, N. Y., May I960.
National Council for Stream Improvement, "Continuous Sludge
Dewatering by Conveyor Centrifuge," Tech. Bulletin
125, N. Y., November I960.
National Council for Stream Improvement, "Recent Develop-
ments in the Application of the Activated Sludge
Process for the Treatment of Pulp and Paper Mill
Wastes," Tech. Bulletin 158, N. Y., March 1961.
National Council for Stream Improvement, "A Process for Re-
moval of Color from Bleached Kraft Effluents
through Modification of the Chemical Recovery
System," Tech. Bulletin 157, N. Y., June 1962.
National Council for Stream Improvement, "1963 Review of
the Literature on Pulp and Paper Mill Wastes,"
Tech. Bulletin 173, N. Y., April 1966.
National Council for Stream Improvement, "Mechanical Press-
ing of Primary Dewatered Paper Mill Sludges,"
Tech. Bulletin 174, N. Y., June 1966.
National Council for Stream Improvement, "Research Review,"
Tech. Bulletin 176, N. Y., August 1964.
National Council for Stream Improvement, "Color Removal and
BOD Reduction in Kraft Effluents by Foam Separa-
tion," Tech. Bulletin 177, N. Y., September 1964.
-------
National Council for Stream Improvement, "196U Review of the
Literature on Pulp and Paper Mill Wastes," Tech.
Bulletin 180, N. Y. , March 1965.
National Council for Stream Improvements, "Reuse of Condensates
from Kraft Recovery Operations," Tech. Bulletin 187,
N. Y., 1965.
National Council for Stream Improvement, "1965 Review of the
Literature on Pulp and Paper Wastes," Tech. Bulletin
189, N. Y., March 1966.
Nemerow, N. L., "Theories and Practices of Industrial Waste
Treatment," Add i son-Wesley Publishing, Reading,
Mass., 1965.
Othmer, D. F., "Chemicals Recovery from Pulping Liquor ." In-
dustrial and Engineering Chemistry , 50 : 60A
(March 1958).
Palladino, A. H. and Baigas, J. F., "De-Inking Waste Treat-
ment Plants at Plainwell, Michigan, and Fitchburg,
Massachusetts," 6th Purdue Industrial Waste Confer-
ence. Purdue University, p. kjk-kkQ (1951).
Pearman, B. V., Jr. and Burns, 0. B., Jr., "Activated Sludge
Treatment of Kraft and Neutral Sulfite Mill Wastes,"
Sewage and Industrial Wastes. 29: 1^5-115^
( October 1957).
Quirk, T. P., "Bio-oxidation of Concentrated Board Machine
Effluents," Prod. 18th Ind. Waste Conference, Pur-
due University, Ext. Ser. 115, 655 (1963).
Rapsoa, W. H., "Bleaching of Pulp," Tappi Monograph Series,
No. 27 (1965).
Robinson, L. E., "The Control of Paper Machine Stock Losses,"
Tappi. k2: 158A (August 1959).
Ross, E. N., "Reuse and Reduction of Paper Mill Wastes ." Tapp? ,
180A
Sableski , J. J., "The Federal Air Pollution Control Program
as it Relates to the Kraft Pulping industry," Tappi .
50: 35A (1967).
Shreve, R. N., "Chemical Process Industries," McGraw-Hi 1 1 Book
Co., N. Y., 1967.
287 - 025 O - 68 - 8
-------
Spalding, C. W., Halko, D. L. and Carpenter, H. S., Jr., "Deep
Well Disposal of Spent Pulping Lfquors ." Jappi, 48;
68A (1965).
Stephenson, J. N., "Pulp and Paper Manufacture - Four Volumes,"
McGraw-Hill Book Co., N. Y., 1950, 1951, 1953, 1955.
Tate, D. C., "Typical Turpentine Recovery System for Batch Di-
gesters," T§E£i, 501 110A-111A (April 1967).
U. S. Department of Commerce, Bureau of the Census, "1963
Census of Manufacturers".
U. S. Department of Commerce, Bureau of the Census, "Current
Industrial Reports" (1964).
Van Horn, W. M., "Multiple Water Use for the Pulp and Paper
Industry." Tappi . 47; 50A (1964).
Warner, H. L. and Miller, B. C., "Water Pollution Control by
In-Plant Measures." Tappi. 46; 260-266 (April 1963).
Westenhouse, R.t "Irrigation Disposal of Wastes," Tappi, 46;
160A (1963).
WESTON, ROY F., Internal Information and Engineer's Reports
to Cl ients.
Whisler, R. C., "A Tight White Water System, Its Operation
and Problems." Tappi. 47; 181A (1964).
White, M. T., "Surface Aeration as a Secondary Treatment Sys-
tem," Ta££L. 48: 128A (1965).
Whitney, R. P., Han, S. T., Kesler, R. B., and Bakken, J. F.,
"Bisulfite Method of Chemical Recover." Tappi. 48;
1-6 (January 1965).
Wtsniewski, T. F. and Blabaum, C., Unpublished information
from State of Wisconsin, Department of Resource De-
velopment, 1967.
Woodard, F. E., Sproul, 0. J. and Atkins, P. F., Jr., "The
Biological Degradation of Lignin from Pulp Mill
Black Liquor." JWPCF. 36: 1401 (November 1964).
-------
APPENDIX
-------
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
-------
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
-------
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.
-------
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
-------
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
-------
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.
-------
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.
-------
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
-------
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.
-------
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
-------
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.
-------
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.
-------
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
-------
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.
-------
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
-------
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.
-------
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
-------
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.
-------
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
-------
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
-------
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.
-------
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
-------
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
-------
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
-------
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
-------
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.
-------
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:
-------
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.
-------
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
------- |