THE COST OP
CLEAN WATER
Volume III
Industrial Waste Profiles
No. 7 - Leather Tanning and Finishing
U.S. Department of the Interior
Federal Water Pollution Control Administration
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C., 20402 - Price 65 cents
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INDUSTRIAL WASTE PROFILE
LEATHER TANNING AND FINISHING
Prepared for F.W.P.C.A.
FWPCA Contract Number 14-12-101
June 30, 1967
Federal Water Pollution Control Administration
September 1967
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PREFACE
The Industrial V7aste Profiles are part of the National Requirements and
Cost Estimate Study required by the Federal Water 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.
The Industrial Uaste Profiles were established to describe the source
and quantity of pollutants produced by each of the ten industries stud-
ied. The profiles were uesigned to provide industry and rrovernner.t
with information on the costs and alternatives involved in dealing ef-
fectively with the industrial water pollution problem. 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 for analyzing
individual plant situations, will stimulate industry's efforts to finu
more efficient ways to reduce wastes than are generally practiced today.
Commissioner
Federal Water Pollution Control Administration
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SCOPE
The scope of material included in this profile report
conforms to the requirements of the United States Department of
the Interior Federal Water Pollution Control Administration
Contract Number 14-12-101. Within the available 90 day study
period, engineering and economic data has been critically studied
by means of a total industry approach. The relationship of the
product to the alternative sub-system manufacturing processes
has been reviewed in the field and office with responsible industry
representatives. The cognizent professional associations and
industrial experts have presented their data and viewpoint, and
have reviewed our draft information. Key plant managers have
cooperated in allowing limited spot checks of their plant sub-
processes and waste sampling. The literature has, of course,
been completely reviewed.
Because of the wide diversity of plants and processes,
we have attempted to achieve a comprehensive overview of the
approximate subprocesses. We have evaluated the total relationship
of products produced, waste pollution load, economics involved,
and long term environmental quality factors.
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IX
INDUSTRIAL WASTE PROFILE
LEATHER TANNING AND FINISHING
TABLE OF CONTENTS
Section Title Page
1. PREFACE v
2. SCOPE vi
3. TABLE OF CONTENTS ix-xi
4. SUMMARY 1
5. LEATHER TANNING AND FINISHING 7
INTRODUCTION 7
I. PROCESSES AND WASTES 11
A. Fundamental Processes 11
B. Significant Pollutants 16
C. Process Water Reuse - 1964 16
D. Subprocess Trends 17
E. Waste Control Problems 19
F. Subprocess Technologies 20
1. Ol3er Technology 21
2. Prevalent Technology 21
3. Newer More Advanced Technology 21
4. Plant Classification 22
II. GROSS WASTE QUANTITIES 24
A. Daily Waste Quantities 24
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(Table of Contents - Cont'd)
B. Wasteload Production Rates 27
C. Total Wasteload 27
D. Gross Wasteload Projections 28
E. Seasonal Variations 28
III. WASTE REDUCTION PRACTICES 29
A. Processing Practices 29
B. Treatment Practices 31
1. Removal Efficiencies 31
2. Rates of Adoption 33
3. Discharge to Municipal Sewers 35
C. By-Product Utilization 35
D. Net Waste Quantities - 1963 36
E. Projected Net Wasteload 37
IV. COST INFORMATION 38
A. Existing Facilities Costs 38
B. Processing and Treatment Costs 38
V. LIST OF TABLES
1 Delivered Equivalent Hides 10
2 U. S. Foreign Leather Trade 10
1-1 Subprocess Trends 18
1-2 Subprocess Technologies 21
II-l Daily Waste Quantities 25
II-2 Gross Wasteload Projections 28
III-l Process Pollution Reduction 30
III-2 Treatment Removal Efficiencies 32
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(Table of Contents - Cont'd)
III-3 Projected Net Wasteloads 37
IV-1 Small Plant, Old Technology 40
IV-2 Medium Plant, Old Technology 41
IV-3 Large Plant, Old Technology 42
IV-4 Small Plant, Prevalent Technology 43
IV-5 Medium Plant, Prevalent Technology 44
IV-6 Large Plant, Prevalent Technology 45
IV-7 Small Plant, New Technology 46
IV-8 Medium Plant, New Technology 47
IV-9 Large Plant, New Technology 43
IV-10 Summary of Production and Waste 49
Treatment Costs
VI. LIST OF PLATES
1. Process Flow Chart 50
2. Waste Treatment Flow Chart 51
6. APPENDICES
I. GENERAL BIBLIOGRAPHY 53
II. GLOSSARY 58
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4. SUMMARY OF INDUSTRIAL PROFILE SIC 3111 -
LEATHER TANNING AND FINISHING
The following is a summary of the results and conclusions
of a 3 month comprehensive survey of the Leather Tanning and
Finishing Industry. This survey included a thorough literature
search, administration and evaluation of a comprehensive industry-
wide questionnaire, numerous visits and contacts with national
tanning association and trade organization representatives, and
visits to representative tanning plants.
Although the tanning of animal hides is an ancient industry,
consisting of about 7500 tanneries in the United States 100 years
ago, the number of tanneries has been decreasing rather steadily.
Today the industry is concentrated into only about 250 plants.
During the last 15 years, the industry has been changing. Present
indications suggest an accelerated and even more dramatic change
during the next 10 years. Hides delivered have remained rather
constant at about 30 to 35 million per year during the last 15
years, whereas imports of footwear leather have increased about
500 percent (in dollar value). Exports have decreased more than
50 percent. This means that, while our domestic production remains
quite constant (despite a doubling of the population, roughly in
about 15 years), we are consuming more leather by importation. At
the same time, our foreign markets for hides have diminished by at
least half. Lower labor costs in foreign countries and the substi-
tution of rubber and plastic materials for leather in our country
are the major reasons given by the industry for this lack of growth.
Since this study is primarily concerned with wastewater discharged
by the industry, we will forego a detailed discussion of the market-
ing problems facing the industry. However, the wastes discharged
may be closely correlated to changes in production. The industry
will change its production to alter costly processes, especially
those involving excessive labor. The tanning industry currently
represents a $5 billion enterprise with about 27,000 workers. Each
person in the United States spends about $29 per year for all
leather products - including an average of 3.28 pairs of shoes. The
industry uses about 18 billion gal of water annually and adds $340
million of product value to our economy each year.
When possible, industrial waste treatment methods
currently employ low cost processes developed for domestic sanitary
sewage. Additionally, screening and equalizing basins are used for
pre-treatment.
Most industrial effluents containing waste materials
similar to the constituents of domestic sewage can be effectively
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treated to any degree desired within the constraints of process
technology and related treatment facility expenditures.
Segregation of types and concentrations of industrial
wastes and recycling of process fluids can reduce total water
consumed and solids generated. Pre-treatment of industrial wastes
containing chemical constituents that are complex, or not readily
bio-degradable, or are odorous, highly acidic, basic, or otherwise
toxic may require special additional costly pre-treatment plants.
Chemical-mechanical facilities involving such processes as pre-
cipitation, flotation, chelation, scrubbers, neutralization tank,
and other processes can be used to produce an effluent with more
acceptable bio-degradable characteristics. The conversion of
wastes into a useful resource, or alternatively, the modification of
the waste producing subprocess to reduce waste, is a generally
desirable goal.
Cattle hides resulting from slaughterhouse activity are
presently used for most of the leather tanned in the United States.
About 2/3 of all the hides from this source are tanned. The re-
maining 1/3 are exported. About 85 percent of all leather used
is made into shoes. Of this shoe leather, 80 percent by weight is
used for upper shoe leather and the remaining 20 percent for sole
leather. Upper shoe leather is tanned almost exclusively by
chromic sulfates and alkaline salts. On the other hand, sole
leather is tanned by the ancient methods using vegetable compounds
such as bark extracts. Processing of sole leather is expensive and
results in a highly pollutional waste. Since cheaper substitutes
for sole leather are reaching our market, the trend has been towards
less sole leather production. This trend is likely to continue in
the future.
Historically, tanneries were located in rather remote
areas of the country; today the major portion of the tanneries are
located in or near large metropolitan areas such as Chicago,
Milwaukee, and Los Angeles. The trend is towards even greater
centralization of tanneries, and this will permit increased combined
treatment of municipal sewage and tannery wastes for the future.
New tanneries are also attempting to locate as close to
slaughterhouses as possible to eliminate the curing process. Where
this is not possible, there is some interest in encouraging the
meat packer to green flesh, wash, soak, and dehair before drying
and shipping the beamed hides to the tanneries for conversion to
leather. While this development has great potential from economic
and pollution standpoints, its adoption as a standard practice has
been slow and is fraught with many difficulties. For example,
although the curing step can be eliminated, other pollutants will
simply be discharged by the meat producer. In addition, the small
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packers may not find it economical to beam their hides and will be
forced to salt and trim them prior to shipping them to a larger
hide processor. Many foreign consumers of American hides do not
want beamed and trimmed hides but prefer those that are raw and
cured. While many of these difficulties may be overcome in the
distant future, we do not foresee a rapid adoption of this practice.
Leather tanning and finishing consists of ten separate
major processes (see attached Process Flow Chart) which convert
animal hides to finished leather. The raw cured hides are shipped
to the tannery, stored, and trimmed as the first step (1) in the
conversion process. The hides are then soaked and washed (2) to
remove the salt, blood, and dirt. This is normally followed by a
mechanical process of green fleshing (3) to permit better chemical
penetration in the following processes. Unhairing (4) improves
the hide appearance and opens up the fiber structure to remove
undesirable protein. The exact unhairing process utilized at any
particular tannery depends primarily upon whether hair recovery is
being practiced, which in turn depends upon the current or expected
market for hair. In the New England area the tendency exists to
burn hair removed from the hide and thus a strong solution of
sodium sulfide is used. In Chicago hair is generally recovered,
and a less damaging unhairing solution is used. Weaker unhairing
solutions are generally less pollutional and contain fewer sulfides.
The next step, lime splitting (5) is seldom used today. It con-
sists of splitting the hide mechanically into two layers, the more
valuable grain layer and a "split" composed of the flesh side
layer. These series of five processes comprise what is commonly
known as beamhouse operations. Bating (6), the next process, is
the first process normally carried out in the tanhouse. By adding
a mixture of salts and enzymes in a drum, the grain gains the 3
"s's" (silkiness, slipperiness, and smoothness). The next step
(7), pickling, is normally carried on in the same drum by adding
sulfuric acid and some salt to prevent precipitation of chromium
salts during tanning. Degreasing (8) is another seldom-used process
today. When sheeps, pigs, or goats are tanned, detergents or organic
solvents must be added to the hides to eliminate grease which causes
uneven dyeing and finishing. Tanning (9) is the major process
converting the fibers in hides to leather. Even when wet, leather
fibers will not putrefy after hundreds of years, whereas untanned
hide fibers, while stable when dry, will putrefy when wet. Chrome
and vegetable tanning are the major types of processes used in this
step. The former type of tanning has been used for the majority
of light leather, producing a more heat-and moisture-resistant
leather. Although the tanning process takes longer, vegetable
tanning yields more leather and produces a more workable leather.
Wastes from either tanning process are highly pollutional and
represent an economic loss if not recovered and reused. Therefore,
wastes seldom reach a watercourse directly. Tanning represents
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the last process carried out in the tanhouse. The last set of wet
operations is the retan-color-and fatliquor (10) processes. As a
result of the advantages and disadvantages of each type of tanning,
a second tanning known as chrome-retan, following a shorter initial
tanhouse tanning process, ensures excellent leather. Coloring to
specification and oiling or waxing to prevent cracking follow the
retan operation and conclude the wet operations of a typical tannery.
The beamhouse unhairing process (4) and the tanning process
(9) in the tanhouse are of major concern to sanitary engineers. Un-
hairing wastes are usually highly alkaline, milky-colored, sulfide-
laden and contain at least 50 percent of the total tannery BOD in
about 33 percent of the total volume of the waste. Tanning liquor
wastes, on the other hand, represent only about 5 percent of the
total plant BOD and volume, but are highly colored and contain a
considerable amount of dissolved solids. Significant pollutants
from a tannery include: 1) freelime; 2) high pH; 3) potentially
toxic chromium; 4) high BOD: 5) high suspended solids (hair and
fleshings; 6) milky color from lime or green-brown color from tan-
ning; 7) hardness; 8) high sulfides.
In 1963 - prevalent practices - a typical tannery produced
about 1000 gal of waste per 100 Ib of hide processed. Pollutants
measured in terms of BOD amounted to 9.0 Ib per 100 Ib of hide.
About 700 gal and 6.5 Ib of BOD came from the beamhouse while the
remainder came from the tanhouse operation. Unhairing alone
accounted for almost one-half the total plant volume and BOD. A
typical tannery processing 1000 hides per day averaging 60 Ib per
skin discharged almost 600,000 gal of waste per day and about 5000 Ib
of BOD.
More recently (1966-1967) the changes in the industry of
1) moving to metropolitan areas, 2) increasing the ratio of upper
leather to sole leather, and 3) the increase in the hair market
have resulted in a reduction in wastewater volumes and loads. Sur-
charges imposed on tannery wastes by municipalities have made the
tanneries more aware of the problems of waste treatment. The
industry appears now to be increasingly water-conservation oriented.
Water reuse is being practiced to reduce pollution abatement costs.
Recent changes in the character of tannery wastes are somewhat lowered
BOD loads, lessened volumes, fewer sulfides, and more chromium. A
newer tannery operation produces about 8.5 Ib of BOD per 100 Ib of hides
processed and uses about 900 gal of water for the same 100 Ib of hide.
In many instances during field visits and discussions with
industry officials, the tanning industry was found to be substantially
unaware of waste problems. Increased use can be made of heavily loaded
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waste stream segregation, recycling of subprocess waste, reuse
of rinse water for make-up and treatment of concentrated blow-
down waters. Research and development in these areas plus
in-plant demonstration can greatly reduce wasteload quantities.
In 1968 to 1972 the lower limits of water use are ex-
pected to be 250-300 gal per hide processed for sole use and 600
to 700 gal per hide for upper leather. If the meat processors
include washing, soaking and unhairing processes during the 1977
to 1982 period, one can expect volumes to be reduced by as much
as 50 percent.
In 1963, tanneries in the United States processed
1.875 billion Ib of hides and discharged 16.0 billion gal of
wastewater containing 150.0 million Ib of BOD. If we assume that
newer technologies will prevail from now until 1982, we can expect
wastewater volumes to decrease from 16.0 to 14.0 billion gal per
and wastewater BOD loads to decrease from 150 to 145 million Ib.
These assumptions are valid only if the majority of beamhouse
operations are not transferred to the slaughterhouse or reduced
by tannery relocation adjacent to slaughterhouses. In addition,
these volume and load reductions can occur during the next
15 years only if the total annual hide deliveries remain at the
constant level of about 32 million per year.
At present, tannery wastes are treated largely by screen-
ing, equalization, sedimentation, chemical coagulation, lagoons,
trickling filtration, and activated sludge. BOD reductions up to
5 percent are accomplished during screening; 85-95 percent
reduction may be expected for activated sludge processes. Usually
the first five treatment processes listed above are carried out at
the tannery while the last two are handled by the municipality when
combined treatment is practiced. However, there is no accepted
pattern for successful tannery waste treatment under all situations.
Because tannery effluents contain pollutants which may be toxic
and create nuisances as well as require proper physical, chemical,
and biological treatment, each case must be decided after a detailed
study of all the data and facts. It is estimated that about 75
percent of all tannery wastes are presently being discharged into
municipal sewer systems; this is likely to increase to 80 percent
by 1972. Waste treatment both by tanneries and by municipalities
receiving tannery effluents is expected to increase in efficiency
during the next 15 years.
While the gross annual BOD pollutants generated by the
tannery industry are expected to decrease from 150 to 145 million Ib
by 1982, the net annual BOD pollutants are expected to decrease
even further from 50 to 33 million Ib. The greater decrease in net
87-030 O - 68 - 2
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BOD is largely due to the expected increase in the percentage
of waste treated and a gradual increase in treatment removal
efficiencies.
The estimated replacement value of waste reduction
facilities treating tannery wastes, including the cost of municipal
treatment facilities attributable to this industry's wastes,
is $11.6 million. Estimated annual operating and maintenance
costs on the same basis is $1.6 million. At present this
amounts to between 1 and 1.5 percent of production costs and
does not appear to be significantly restricting to the industry.
If>however, waste treatment costs increase significantly,some
marginal profit plants may be critically affected.
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INDUSTRIAL WASTE PROFILE STUDIES
TANNERY INDUSTRY
SIC 3111. TANNERIES
INTRODUCTION
In 1865 there were about 7500 tanneries. At the turn of the
century (1900) there were approximately 1000 tanneries in the United
States. In 1952 there were 443 tanneries in the United States -
approximately 60 percent located in the Northeast. In recent years
(1965) this number has been reduced to about 250 - mostly larger ones,
as reported by the Tanner's Council of America.
In 1952 it was reported by one source (Harnly) that the tanneries
in the United States generated about 20 billion gal of waste yearly;
however, the census of manufacturers reported that in 1963 (about ten
years later) only 14 billion gal were discharged from 81 tanneries. We
estimate 16 billion gal were discharged in 1963 by the industry. The
majority of the tanning plants (50-60 percent of all tanning activity)
are located in Chicago, Milwaukee, the Northeast and Los Angeles area.
The trend toward centralization is continuing. There are, however, plants
scattered throughout the United States.
Currently the tannery industry represents a $5 billion enterprise
with about 27,000 (1966) production workers. Per capita expenditures
for leather footwear are over $20 per year and for other leather products
slightly over $9 per year. In addition, hide and skin exports have been
increasing to $155 million in 1966.
The industry appears to be changing in the United States. More
hides are being exported to countries which can produce leather at a
lower cost. This is primarily due to inexpensive labor in many foreign
countries and international tariff policies. The United States exports
very little tanned leather. Therefore, tanneries depend on domestic
leather goods manufacturers for a market. This has forced a number
of small U. S. tanneries out of business. In addition, substitution
of other materials, such as plastics for leather, has cut into the
United States leather tanners' market to some degree. The ability of
United States tanners to meet foreign competition and the advent of
leather substitutes depends on economic factors and American ingenuity.
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Five types of animal skins are in general use today in
addition to largely imported rare skins such as alligator,
crocodile, seal, etc: (1) Cattle: for shoe upper leather, shoe
sole leather, patent leather, upholstery leather, harness and
miscellaneous items; (2) Sheep: for shoe linings, gloves and some
garments; (3) Goat and Kid: for shoe upper leather, gloves, and
leather linings for shoes; (4) Pig : for fine leather in gloves,
shoes, pocketbooks, luggage and upholstery; and (5) Horsehide:
for aprons, gloves, garments, and cordovan shoes.
Most American horses are used for pets and recreation
and disposed of following normal old age without being skinned for
leather.
The Tanners Council of America reported for 1966 that the
total skins tanned were:
Calf - 4.72 million
Cattle -23.83 million
Goat and Kid -13.37 million
Sheep -29.42 million
Horse - 0.28 million
Imported
Cattle hides are now used for most of the leather tanned
in the United States. Of the estimated 34 million cattle butchered
annually in the United States, nearly 25 million skins are tanned.
The remainder is exported to foreign markets, principally Japan.
About 85 percent of all leather used is made into shoes, with the
balance employed for baggage, saddles, clothing, upholstery and
accessories. The upper leather consumes some 80 percent of the
total by weight used in shoes, with the remaining 20 percent manu-
factured into the soles.
Production practices vary in the various tanning centers.
For example, in the New England area, because it is customary
to burn or pulp hair removed from the hide, a strong unhairing
chemical solution (more sulfides) is used. In the Chicago and
Milwaukee regions, where hair is generally recovered, a less
polluting unhairing agent containing fewer sulfides, and more
diraethylamine sulfate,is used. It naturally follows that the
resulting wastes will be different in character and pollutional
loads.
The Tanners Council of America also reported that in
1962 the total shoe production was more than 600 million pairs.
The leather industry furnished sole material for about 28 percent
of this production. The upper sole, insole and lining business
represents about 85 percent of the total leather production.
Washing, fleshing, and unhairing are responsible for
over 50 percent of the total volume and up to about 70 percent of
total pollution load. Tanning is responsible for about 5 to 20
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percent of the volume and pollution. Vegetable tanners (approx-
imately 20 percent of the industry) can fortify and reuse tanning
liquor. This is not generally practical for the remaining 80
percent who are chrome tanners, although it was done during World
War II.
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TABLE 1
DELIVERED EQUIVALENT HIDE?"
Year Total U.S. Hides
1951 33,291,000
1963 31,256,000
1966 32,158,000
TABLE 2
U.S. FOREIGN LEATHER TRADE
Leather Footwear All Leather
Year Imports Exports Imports Exports
($) ($) ($) ($)
1951
1963
1966
24,647,000
80,687,000
128,255,000
19,063,000
8,628,000
8,856,000
143,000,000
243,365,000
17,084,000
24,539,000
These tables show that the United States delivered hides
that remained relatively constant from 1951 to 1966. On the other
hand, imports of leather footwear have increased about 500 percent
in dollar value during the same period, while exports have decreased
more than 50 percent.
1. Equivalent hides means in terms of cattle hides. Statistical
sources will indicate a far higher number of total hides,but
these include sheep, goat, etc.
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INDUSTRIAL WASTE PROFILE STUDIES
TANNERY INDUSTRY
SIC 3111. TANNERIES
I. PROCESSES AND WASTES
A. Fundamental Processes
1. Storage and Trimming
2. Washing and Soaking
3. Green Fleshing
4. Liming and Unhairing
5. Lime Splitting or Chrome Splitting after tanning
6. Bating
7. Pickling
8. Degreasing
9. Tanning
10. Finishing, including retan, color and fat liquor.
Ten separate physiochemical or biological processes are
generally utilized to convert animal (primarily cattle) hides into
leather. According to the Tanners Council of America, the leather
industry is actually many separate industries since "each type of
leather constitutes a different process with little standardization".
There are several chemical tanning methods and chemicals
(tannages) in general use. The two major methods are: Chrome tan
for shoe upper leather; Vegetable Tan (infusion of barks, wood, nuts
and leaves) for shoe sole leather, belting and saddlery. Other
minor methods include: Formaldehyde for some leathers; Zirconium
salts; certain synthetic and resin tans, oil tan, and alum.
1. Storage and Trimming; Much of the industry still
cures skins by partial dehydration. The skins are treated with
salt or dried in air to prevent bacterial degradation before they
can be properly stored. As soon as the hide is removed from the
carcass, it is covered on both sides with a layer of salt and
stored in layers with the flesh side up until a "pack" is obtained.
A pack is approximately 3200 cu ft of skin (usually 20 ft x 40 ft x
4 ft deep). The pack is arranged so that any brine solution will
drain away from the pack along with dissolved blood or organic
matter. The pack is usually cured for at least three weeks during
which time the hide loses part of its moisture and absorbs some salt.
Net weight loss will be about 20 percent with a resultant cured
moisture content of about 40 percent. Air drying (usually kid,goat,
or sheep skins) produces a lower moisture content hide but risks
bacterial decomposition and possible skin damage. Slow and improper
drying encourages damage from bacterial growth. Rapid drying may
also cause biological degradation as a result of incomplete interior
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moisture removal. There is also substantial use of brine baths
instead of salt packs. This generally produces slightly more
NaCl in the waste. Sheepskins may be de-wooled immediately after
slaughtering and pickled with acid and salt before shipping to the
tannery. Curing is not necessary with sheepskins treated (pickled)
in this manner.
No great quantities of wastes occur in the curing because
of bath reuse. However, an understanding of the process is
necessary because subsequent wastes are affected by the method of
curing. Bactericides, such as sodium hypochlorite and sodium
pentachlorphenate, are used to sterilize and to prevent or arrest
decomposition.
Hides are trimmed by almost every marketing agency in the
hide and leather industry. In the packinghouse, dewclaws, pizzles,
ears, snouts, pates and tails are trimmed from hides. On entering a
typical hide cellar for curing, each hide is given a second trim
which removes 3 to 6 percent. At the tannery, hides are unbundled
and each is given a third trim which removes another 2 to 3 percent
of the original hide. Throughout the tanning process, fringe areas
are trimmed from hides. At the final grade-sort, the leather is
given a fourth trim -- generally in the pocket and head areas. The
net result of all trimming during processing amounts to about 20 per-
cent of the original hide. (The U. S. Department of Agriculture hide
trim is a one-time trim; however, it is not commonly used.) The trim
facilitates segmented marketing practices (product differentiation),
improves quality, and reduces processing costs at all levels. The
basic trim removes the heads, bellies, and shanks.
Currently there is a strong impetus to beam (remove hair)
and flesh hides at the source of supply to produce a more uniform
semi-processed raw product. Also, since semi-processed hides weigh
less than cured hides, freight costs are reduced. Although it has
not been definitely proved, some tanners believe that better leather
can be produced from hides that are semi-processed fresh than from
those that have been salt-cured. In 1965 there are two firms doing
this, and several more were anticipated in the foreseeable future.
2. Washing and Soaking: Washing and Soaking removes
the dirt, salts, blood, manure, and non-fibrous proteins and restores
the moisture lost during curing. Although there is no standard
procedure for washing and soaking, a common method is to float a
lot (about 3000 Ib) of whole hides in twice its weight of water and
drum wash for about one half hour. Following this, the hides are
cut into sides and green-fleshed and soaked for about one to five
hours with three times their weight of water in paddles used for
both soaking and liming. If a preliminary rinse is used before
soaking, part of the salt (70 percent NaCl) could be removed.
3. Green Fleshing: Green or Lime Fleshing removes
the areolar tissues from the flesh side of hides or skins.
Attached fat, connective tissue, blood vessels, nerves, voluntary
muscle, and unremoved meat left as a result of poor flaying are
also removed. The process is carried out on a fleshing machine
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consisting of two long rolls -- one of corrugated metal and the
other of rubber. These grip the skin with a pressure triggered
by a foot lever and draw the flesh side across a revolving cylinder
set with spiral blades. The fleshings are saved and usually sold
to plants for rendering or conversion to glue. Fleshing -- done
either before or after soaking — allows easier and more effective
penetration of chemicals used in the tannery.
The other common method of fleshing is called lime flesh-
ing and is done in conjunction with the unhairing process (described
below) when the hair is not recovered.
4. Liming and Unhairing; Unhairing of hides is
necessary so that the leather will have an attractive appearance
when it is finished. It also aids in opening up the fiber structure
to remove unwanted protein. Hair may be removed by loosening
followed by machine or manual pulling, or by complete destruction
(pulping), or dissolution (burning off). Hair is usually recovered
following loesening and mechanical pulling and sold. Lime has been
in use since leather tanning began for hair loosening and alkaline
swelling. A series of pits or paddle vats is used. Packs of hides
are usually tied together and reeled mechanically from pit to pit in
sole leather tanning. For side leather, paddles are used. Actual
rinsing is carried out in the first pit and various lime concentra-
tions are used in succeeding pits to suit the operator in charge of
unhairing. As mentioned previously, when the hair is to be destroyed
the fleshing step is often also accomplished by the strong lime
solution. The whole cycle usually requires about one week. Sodium
sulfide and sodium sulfhydrate are the most important and most
widely used depilatory agents in the industry today. Typical un-
hairing chemicals include about 0.1 - 3.0 percent Na2S and 4-12
percent lime on a hide weight basis. The strength depends on
whether hair saving or hair pulping is desired. Water to hide ratios
of two to one to four to one are generally used. Dimethylaraine sulfate
is becoming more widely used because it promotes more complete unhair-
ing and liming within practical time limits. Few tanners now use the
painting process for hair removal; Na£S and lime paste were padded
onto the flesh side of the hide, thus loosening the hair from the
roots up. The hair was subsequently removed by hand scraping or
mechanically. Liming gives the additional benefit of altering
protein structure in the hide to prepare it for later tanning.
5. Lime Splitting; Lime Splitting is a mechanical
process usually not involving any liquid waste. The unhaired hide
is slit through the middle of its thickness to produce two distinct
layers; the upper is the flesh side and is called a "split". Some
of the tanneries process only the grain layer and sell or discard
the "splits". Of prime importance in lime splitting is the condition-
ing (slipperiness and plumpness) that enables the hide to be fed to
the machine smoothly in order to split off the grain layer to the
-------
14
desired uniform thickness across the full length and width of the
hide.
6. Bating; Bating prepares the swollen and alkaline
hide for tanning. It must delime to reduce the pH, reduce the swell-
ing (falling), and remove the protein decomposition products. Bating
is generally accomplished with ammonium salts and a mixture of
commercially prepared enzymes. Bating renders the grain silky,
slippery, smoother, more porous, and reduces the wrinkles. The
changes have been obtained through both deliming and enzyme action
on the hide's proteins. Bating may be done in drums or paddles.
Usually the hides are washed with room temperature water for about
one half hour and once again with 85° - 90°F water for another
half hour before the bate is added. The hides are bated for one
half to five hours with about 1 to 2 percent OWH chemicals. The
bate digests parts of the epidermal matter, loosens it, and allows
its removal with the attached "scud" (hair roots). The cleansing
action as well as the alteration of the proteins by the enzymes
accounts for the results of bating.
7. Pickling; Pickling makes the skin acid enough to
prevent precipitation of insoluble chromium salts on the skin fibers
during mineral tanning. It is not generally used in vegetable
tanning. Pickling can be used as a means of preserving the hides
during storage prior to tanning. Pickling takes place at room
temperature for various lengths of time up to twelve hours. Typical
pickling chemicals are 1 to 2 percent H2$C>4 and 7 to 10 percent
NaCl. Variations in process usually involve different equipment or
lengths of pickling time. Pickling can be done in drums or paddles.
The duration depends on whether a short pickle or equilibrium
conditions are desired. Most tanneries utilize the drum pickle today.
In all processes, salt is added first to prevent acid swelling.
8. Degreasing; Degreasing is done to eliminate
fatty spues, uneven dyeing and finishing, and greasy areas to allow
more even penetration and action of tanning liquors, fatliquors,
and dyes. It may be done by three different procedures: (1) Emul-
sification with an aqueous solution of a synthetic detergent ,
(2) use of an organic solvent for extraction , and (3)squeezing
out the skin greases by pressure and mechanical action . Solvent
extraction with kerosene or Stoddard solvent is widely used. Usually
about 50 gal of kerosene per 1000 Ib of pickled hide along with
some salt brine and a penetrating agent are heated to 85°F with
steam or hot water for about three hours. Excess solvent and brine
are usually drained and recovered for reuse since both economics
and pollution abatement dictate this procedure. The kerosene, as
well as the grease, may be readily recovered by steam distillation
in recovery stills. In some mills the brine is also recovered from
the kerosene by gravity separation and reused. Degreasing is seldom
used today except in certain tanneries which convert primarily sheep,
goat and pig skins.
* Shoe side upper leather *** Sheepskin
** Pickled Skins
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15
9. Tanning; Tanning is the process of converting
the fibers in hides to leather. Leather fibers will not putrefy
when in the wet state after thousands of years, whereas hide
fibers, while stable in the dry state, will putrefy in the moist
condition. Although there are five tanning agents, only two types
of tanning are common in our country, vegetable and chrome. In the
United States the ancient method of vegetable tan with quebracho,
wattle, chestnut and eucalyptus extract provide the source of tannin
used; however, some amounts of mangrove, myrobalans, valonia, spruce,
oak bark, hemlock bark, gambier, and sumac are used in much smaller
volumes.
Hides are tanned by immersion in tan solutions which
increase in concentration from 0.3 percent to 6 percent tannin.
The preliminary tan, taking about three weeks, is usually done in
rocker vats in which the frame for holding the leather is equipped
with a rocking device to prevent the hides from touching one another,
thus preventing "kiss" spots. The leather is then thrown into layer
vats where it remains for another three weeks in 6 percent tannin.
Some more recent tanning processes use a higher concentration of
tannins (12 percent) for shorter periods by putting the hides in
drums during twelve hour periods. Following the completion of the
four to six week tanning operation, the hides are removed, covered
to prevent oxidation and drying, and allowed to stand for 48 hours,
then washed for removal of excess tannin, and processed. In general,
because of the high cost of the tan solution, reuse and recovery
is practiced in all vegetable tanneries. The tan liquors discharged
are low in volume and high in pollution load.
One of the most important of the newer synthetically
produced compounds (syntans) is a complex of phenolsulfonic acid
and formaldehyde. These are widely used for the production of
white leather and have especially good tannin penetrating qualities.
Chrome tanning has been used since the turn of the
century for tanning the majority of light leathers. Its major
advantage is that it shortens the tanning time to less than one day;
moreover, it produces a leather with more resistance to heat and
abrasion. Older chrome tanning processes used a two bath method.
The hide was first impregnated with Na2Cr207 and acid in one bath
followed by immersion in a second bath containing Na2S203 and acid.
Today, the bulk of chrome tanning is done by the one bath method
using proprietary mixtures of basic chromium sulphate. The tanning
achieved is the result of the action of the trivalent (Cr~") form
of chromium on the skin protein. Although variable, from 3 to 7
percent based on the weight of leather, Cr20s is generally combined
with the hide substance.
Since vegetable tanning generally produces leathers
which are fuller, plumper and more easily tooled and embossed,
leather tanned by the chrome method is sometimes given a subsequent
tan in vegetable tannin. This is called retanning.
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16
10. Finishing; Finishing converts, through many
wet and dry processes, the tanned leather to the final end product
used in the industry. The wet processes which are of concern in
water pollution are bleaching, stuffing, and fatliquoring, and dyeing
and coloring. Bleaching is designed to give the leather a lighter
and more uniform color before it is fatliquored.
Stuffing and fatliquoring involve adding many types
of oils and greases to the tanned hides to prevent cracking and to
make the leather soft, pliable, strong, and resistant to tearing.
The amount of oil or wax used varies with product specifications
from 2 to 3 percent in sole leather to 30 percent in waxed leather
for waterproof shoes. Stuffing describes the direct application of
oils and greases either by hand or by drumming the molten greases.
Fatliquoring is used when small, uniformly distributed amounts are
desiredjby applying the oil in the form of an emulsion (0.5 to 8
percent). Chrome leather is usually fatliquored at 110° - 140°F for
1/2 to 1 hour, while vegetable tanned leather is usually drummed at
about 120°F.
Coloring or dyeing of tanned leather may be done
either before or after fatliquoring and uses both the older (natural)
and the newer (artificial) dyestuffs. The dye solution is dumped at
the end of a run or when it is exhausted.
B. Significant Pollutants
Significant pollutants from tanneries include:
Free lime and sulfides
High pH
Potentially toxic chromium
High BOD
High suspended solids (primarily hair, greases,
and proteinaceous fiber)
Milky color from lime, green-brown or blue
color from tanning, and varied colors from
dyeing.
Hardness
High mineralization (TDS)
C. Process Water Reuse - 1964
Little tannery plant water is reused today. Instead, the
trend is toward conservation of water by other means. In 1964, we
estimate that approximately 10 percent of process water was reused
by the industry as a whole, which, by definition, means that 90
percent of the water intake was used only once and then discharged.
It appears that water reuse is an area of pollution re-
duction that has been sadly neglected in the average tannery. Use
of countercurrent washing techniques, clean-up and reuse of process
-------
17
waters, wash sprays instead of baths, automatic controls on process
water, dry waste disposal instead of water carriage, and other
methods could be used to reduce the quantity of process water
required. It is not within the scope of this report to make a
specific study of the application of water conservation techniques,
but this is an important area for future study.
D. Subprocess Trends
As previously indicated in the description of fundamental
manufacturing processes, there are often alternate methods to
accomplish a particular operation in the leather-making process.
Which method is used depends upon such factors as kind and volume
of hides being processed, type and size of process machinery avail-
able, skill of available operating personnel, end product use of the
leather, and other factors. We have purposely left out the factor
of wasteload produced because this does not seem to strongly influence
subprocesses selection. The plant manager is interested in increasing
his production efficiency and product quality, and any decrease in
wasteload produced by selection of an alternate subprocess is merely
a bonus. Currently this aspect is receiving more attention by
tanners.
Table 1-1, which projects subprocess trends in the tanning
industry, is the result of information received from operating
plants, tanning industry consultants, machinery manufacturers,
chemical manufacturers, and a thorough survey of existing literature
on the subject. It is intended to show the direction the industry is
going in 1967 on the basis of the techniques now available. It is
probable that scientific advances will make some of the processes
shown obsolete within the next 10 years.
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18
TABLE 1-1
SUBPROCESS TRENDS
Production Process and
Significant Subprocesses
Storage & Trimming
of Cured Hides
Air drying
Salting
Salt & Air Drying
Brine Curing
Washing & Soaking
Soak or Green Fleshing
Lime Fleshing
Re-Soaking
Hair Saving
Hair Pulping
Bating & Pickling
Tanning
Vegetable
Chrome
Synthetic or Resin
Retanning
Vegetable
Mineral
Syntan & Resin
No Retan
Coloring
Bleaching
(Hypo, oxalic + syntans)
Estimated Percentage of Plants
Employing Process in:
1950 1963 1967 1972 1982
10
70
20
0
100
70
30
0
60
20
30
100
90
10
0
50
20
80
100
90
10
0
40
20
85
100
80
20
0
40
20
90
100
40
60
60 45 45 45 45
40 55 55 55 55
100 100 100 100 100
30
70
70
5
15
10
20
80
75
5
20
0
20
80
70
5
25
0
20
80
60
5
35
0
20
80
45
5
50
0
80
45
90
35
90
35
90
35
90
35
Fatliquoring
Stuffing (Hot Drum Method)
Filling & Pigmenting in
the Drum
80
20
70
90
10
80
90
10
85
90
10
85
90
10
95
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19
Analysis of Table 1-1 shows the industry in general
is changing very slowly in terms of basic subprocesses used.
As brought out later in this report, however, certain reductions
in wastewater quantity and pollution load per product unit have
been achieved by use of modern machinery, new chemicals, better
housekeeping, and superior hide removal techniques in the
slaughterhouse. It is an inescapable fact, however, that to
produce leather from a raw hide, the tannery must remove most
of the organic matter. Therefore, the amount of organic
pollution produced is largely a matter of the number of hides
processed. Organic by-product reclamation may be a future
subprocess.
E. Waste Control Problems
The two most difficult waste problems in the tanning
industry originate with unhairing and tanning. Unhairing wastes
are usually highly alkaline, milky colored, sulfide laden and
contain at least 50 percent of the total tannery BOD of a highly
proteinaceous nature in about 33 percent of the total volume of
waste.
Tanning liquor wastes, on the other hand, represent
only about 5 percent of the total plant BOD and volume, but are
highly colored and contain a relatively high concentration of
dissolved organic solids, if vegetable tanned, and dissolved
inorganic solids, if chrome tanned. In addition, if chrome tan
is used, the waste contains a high concentration of chromium
which represents potential toxicity to any biological life it
contacts. Housekeeping to reduce odors within plants has been
a major problem. Ozone and odor masking chemicals have been
used to control the problem. This problem is expected to
decrease in the future as better housekeeping is practiced.
The tanning industry needs water metering and more
chemical balances to effect better quality control. The skin
normally contains about 70 percent water. Thirty percent loss
in weight occurs as a result of defleshing and curing. Another
30 percent is lost in the tanning operation.
As mentioned earlier, if hair recovery is practiced,
the unhairing process generally includes the addition of dime-
thylamine sulfate to reduce the sodium sulfide concentration.
This will lessen the following problems:
Objectionable odors caused by sulfides in
receiving waters and in the surrouding air
environment.
Toxicity of sulfides to micro-organisms
during biological waste treatment.
-------
Waste resulting from hair pulping contains considerable
lime, sodium sulfide, and high dissolved proteins. Lime and
untrapped hair which find their way into the sewer make an
excellent plaster material which often leads to clogging of sewer
lines. The market price of hair is one of the major factors in
determining whether it will be pulped or recovered. In the past
(20-30 years ago) hair sold for $.20 per Ib and labor to recover
it was relatively inexpensive. The price of hair dipped to $.04
per Ib but it has recently recovered to about $.16 per Ib. How-
ever, labor costs have soared, thus making hair recovery expensive.
Approximately 60 percent of tanneries pulp hair and about 40 percent
recover it today. If the price of hair goes higher than $.16 per
Ib more hair recovery will be done-
The inducements towards hair pulping are:
No fine hair carry over.
Single drum or paddle operation
requires minimum manhours.
The detractions of pulping are:
High solids and BOD surge - some
local governments will not permit
this practice.
It is a more astringent process
and can lower square footage yields
of leather.
Increased cost and difficulty of waste treatment
F. Subprocess Technologies
Changes in the subprocess technologies of tanneries
have been slow due to the slow growth of the industry, the funda-
mental nature of the raw material and end product, and lack of
research and development expenditures by the tanning industry
or the machinery manufacturers which supply it. In the following
Table 1-2, typical subprocesses are shown for older technology
(1950), prevalent technology (1963), and newer technology (1967).
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21
TABLE 1-2 SUBPROCESS TECHNOLOGIES
Technology Level
Older
1950
Prevalent
1963
Newer
1967
Salting of Hides
Wash and Overnight
Soak
Green Fleshing
Unhair Na2S +
Ca(OH)2
Salting of Hides and
Brined Hides
Wash and Short Soak
Green Fleshing
Unhair
Ca(OH)2 ,
Brine Cured Hides or
Salted Hides
Wash and Short Soak
Green Fleshing
Unhair
£(CH3)2 NHj2
Some NaSH + Na2C03
Lime Fleshing
Lime Splitting
Little Lime Splitting
Paddle or Drum
Bating
Paddle or Drum
Pickling
Chrome Tan in
Drums or Paddles
or
Rocker Veg.Tan +
Layer Veg. Tan
Chrome Splitting
Paddle or Drum Bating
Drum Pickle
Drum Bating or Paddle
Bating
Drum Pickle
Basic Chromic Sulfate Basic Chromic Sulfate
Tan in Drum Machine Tan in Drum Machine
Mostly Chrome splitting
Retan, Color
Fatliquor
Retan, Color,
Fatliquor
Retan, Color, Fatliquor
287-030 O - 68 - 3
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22
As can be seen from the table, the principal changes
in the industry are a trend toward brine cured hides instead of
salt cured; a short soak after wash instead of overnight; slight
modifications in the unhairing chemicals used; increasing use
of drum machines instead of paddle machines in the bating, pickling
and tanning operations; and use of chrome splitting instead of
lime splitting.
4. Plant Classification; Only 20 percent of today's
tanneries were built during the last 20 years. During this time
many tanneries also went out of business, mostly the smaller
ones. As a result, the industry today can be classified as older
in terms of plant age, prevalent (1963) in terms of technology
level and tending toward fewer and larger plants. Technology
level and plant age do not coincide due to modernization programs.
Our estimate of the percentage of plants falling into
the three previously described technological levels is as follows:
Technology
Older Prevalent & Newer
Percentage of Plants 20 80
The ranges of plant sizes connected with these three
technology levels are estimated as follows:
Technology
Older Prevalent & Newer
Plant Size Less than Over 300
(hides per day) 300
There is so little difference between the prevalent and
newer technologies in the tanning industry that we have simply lumped
together newer and prevalent in the foregoing estimates.
The relative proportion of small, medium, and large
size plants (as the industry regards plant size) included in
each technology level is estimated as follows:
Percent Percent of Plants This
Hides Plants of Size in Technology Level
Plant Size No/day This Size Older Newer & Prevalent
Small 300 10 55 45
Medium 300-800 50 30 70
Large 800 40 5 95
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23
We expect that there will be fewer and larger plants
in the future. There is a trend in the industry to construct
new plants near the source of hides; i.e., the slaughterhouse.
There is also some indication that in the future, the beam
house operations such as washing, soaking, green fleshing
and unhairing may be performed in the slaughterhouse and a semi-
processed hide sent to the tannery. If this should occur on a
large scale, pollution generated by tanneries would be reduced
greatly, and the slaughterhouse pollution production would increase
proportionately.
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24
II. GROSS WASTE QUANTITIES
A. Daily Waste Load Quantities
In order to provide a basis for subprocess selection on
the basis of pollution reduction, Table II-l has been prepared.
In this table the average BOD (organic pollution) , average SS
(suspended solids pollution), and average TDS (dissolved chemical
pollution) generated by each of the subprocesses is estimated.
The subprocesses are further classified by the technology level
in which they belong..
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25
TABLE II-l
DAILY WASTE QUANTITIES
Subprocesses Approx . %
of Older of Hides
Technologies Treated
Long Wash & Soak
Unhair ESave Hair
[Pulp Hair
Paddle Bating
Paddle Pickling
Tanning lVe8-
[ Chrome
Finishing
TOTAL
Subprocesses of
Prevalent and
Newer Technology
Wash & Short Soak
™»lr KS S£
Drum Bating
Drum Pickling
Tanning [Veg-
[ Chrome
Finishing
TOTAL
100
50
50
100
100
20
80
100
100
40
60
100
100
20
80
100
Wasteload Ib/day
For Average Size Plant
Processing 500 Hides/Day
BOD
450
800
1,050
250
-
50
100
50
2,750
350
700
1,200
200
-
50
100
50_
2,650
SS
1,500
2,200
3,200
50
-
50
150
50
7,200
1,300
1,750
3,350
50
-
50
150
50
6,200
TDS
3,900
2,000
3,500
500
500
250
650
100
11,400
3,000
1,750
4,000
400
400
250
650
100
10,550
Waste Water
Volume (mgd]
0.105
0.06
0.06
0.04
0.02
0.005
0.015
0.015
0.315
0.095
0.045
0.065
0.03
0.015
0.005
0.015
0.015
0.285
Hides assumed to average 60 Ib each.
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26
Table II-l was derived from information feedback from
operating industry, tanning consultants, chemical manufacturers,
equipment manufacturers, and a thorough review of the literature.
The tabulated data shown are averages for the industry. Indivi-
dual plants may show rather wide variations because of differences
in raw hide quality, end leather product, accuracy of testing
procedures and metering, process control, skill of operating per-
sonnel, percentage of plant capacity being utilized, and many
other factors.
The important generalizations are that the tanning
industry has not made great improvement in reducing pollution
produced per unit of hide processed; modern tanning machinery is
not designed with wasteload reduction in mind; and no real break-
throughs are in sight. It is difficult to reduce the pollution
produced by tanneries because essentially, the basic process con-
sists of removing organic matter from hides. Volumes can be
reduced substantially by conservation of water.
Some specific discussion on subprocesses follows for the
interested reader:
There are 4 major subprocesses which contribute large
volumes of waste and/or BOD to the total treatment picture. These
are soak, unhair, bate, and tan. Alternate subprocesses for bating
are currently non-existent. Recently, however, bating in drums
rather than in paddle wheels has been increasing. It results in a
nearly continuous process which has much the same quantity of con-
taminants in less wastewater than the batch-type paddle process.
Similarly, the one alternate subprocess for soaking results in very
little change in overall waste character or quantity. Unhairing and
tanning, on the other hand, can be carried out be several alternate
subprocesses, each of which affects the quantity and character of
waste. In unhairing, substituting caustic soda for lime will result
in a more alkaline and less milky wastewater with a somewhat higher
BOD because of its greater causticizing ability. Unhairing time
can also be reduced by this substitution. The relatively new method
of unhairing with dimethyl-aminesulfate and lime results in a less
alkaline, lower BOD waste containing little or no sulfide ion.
DMAS,in conjunction with a lowered percent of lime plus sodium
carbonate, promotes fast and efficient action. The addition of NaSH
effects a very acceptable system which is currently in active prac-
tice. From a waste treatment standpoint, the replacement of tne
sodium sulfide eliminates the problems associated with the sulfide
ion and the high pH. Because of the process contact time and/or
concentration of (CH K-NHrSO^ used, the resultant BOD is somewhat
less than that of the conventional lime-Na,S unhairing subprocess.
Another alternate subprocess uses Na OH ana/or NH40H to replace both
lime and Na2S when hair recovery is practiced. Since its current
use is experimental, it is only considered as a potential subprocess
to eliminate both the sulfide and lime sludge problems associated
with waste treatment.
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27
The other major subprocess where substitution would
slightly affect waste quantity and character is in the tanning
process. Although the BOD of vegetable tan wastes is about 5
times as high (25,000:5,000 ppm), the volume of waste normally
discharged is only about 1/125 of the chrome tan. Chrome tan
BOD load, then, will be approximately 25 times as great as that
from vegetable tanning, primarily because of the greater reuse of
vegetable tans and the apparent inability to recover and reuse
chromium from chrome tan wastes.
In any event, when hides are tanned with chrome rather
than vegetable process, high BOD loads with potentially toxic
concentrations of chromium will result. Unfortunately, the
trend is toward more chrome tanning and less vegetable tanning
since the percentage of sole leather in shoes is decreasing.
Some tanneries, however, have been renewing the chrome tan
solution with more concentrated chromic sulfate rather than dis-
charging it as waste. It is claimed that this enables the
chromium solutions to be reused as many as 15 times without
detrimental effects.
B. Wasteload Production Rates
A summary of previously developed data gives the follow-
ing wasteload generation per Ib of leather processed.
Technology BOD SS TDS Volume
Ib Ib Ib gal
Older .0916 .260 .380 10.5
Prevalent-Newer .0883 .250 .350 9.5
C. Total Wasteload Produced
It is estimated on the basis of data previously developed
that the tannery industry generated the following wasteload in
1963.
Wastewater Volume 16 billion gal
BOD 150 million Ib
SS .....425 million Ib
TDS 650 million Ib
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28
D. Gross Wasteload Projections
Future gross wasteloads are projected on the basis
of projected growth of the industry, anticipated improvement in
technology, and other factors detailed at the bottom of Table II-2.
TABLE II-2
GROSS WASTELOAD PROJECTIONS
Year
1963
1967
1968
1969
1970
1971
1972
1977
1982
Volume
Billion Gal
16
16.2
16.2
16.2
16.1
16.0
16.0
15
14
BOD
Million Ib
150
160
160
160
155
155
155
150
145
SS
Million Ib
425
440
440
440
430
430
430
420
410
TDS
Million Ib
650
670
670
670
660
650
650
640
630
The above predictions are based on the assumptions that:
The trend toward hair pulping will continue.
There will be a very slow transfer of beamhouse
operations to the slaughterhouse.
There will be some increase in water reuse and
waste segregation.
The value added in manufacturing projections by
F.W.P.C.A. are accurate.
E. Seasonal Variations
Based on industry information available, there is no
significant seasonal variation in hides tanned. In the winter and
spring, however, the hides processed tend to be dirtier and have
more hair and fat. This increases slightly the pollution load per
hide processed.
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29
III. WASTE REDUCTION PRACTICES
A. Processing Practices
As indicated in Section II, it is possible to reduce the
pollution generated in a tannery by using alternate subprocess
techniques. Table III-l outlines the relative pollution reduction
potentials of the various alternate subprocesses. The subprocess
method generating the most pollution is used as a basis of compari-
son. The values shown are generally the highest reported reductions
for a particular alternate subprocess.
In general, the pollution reduction achieved by alternate
subprocesses currently in use is not significant. There has been
a reduction in the water volume required to process leather, but
this generally results in simply the same quantity of pollution in
a lower volume of water. Substitution of different chemicals in
the unhairing process has achieved some slight decreases in pollu-
tion, but the significant pollution factor in this process is
whether the hair is saved or pulped.
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30
TABLE III-l
PROCESS POLLUTION REDUCTION
Fundamental
Process and
Alternate Subprocess
Wash & Soak
Long (overnight soak)
Short (short soak)
Unhair
Pulp hair
Save hair
Bating
Paddle machine
Drum machine
Pickling
Paddle machine
Drum machine
Tanning
Chrome
Vegetable
Alternate Subprocess
Pollution
Reduction Efficiency %
Vol BOD SS TDS
0
15
0
0
0
20
0
10
0
90
0
17
0
25
0
10
0
0
0
75
0
15
0
30
0
10
0
0
0
50
0
15
0
30
0
10
0
10
0
80
Remarks
Most plants report
no difference in
pollution generated.
Which process used
depends upon demand
for hair.
Most plants report
no difference in
pollution generated.
No significant
pollution generated.
Not really alternate
methods since they
produce a different
kind of leather.
Finishing
A tremendous variety
of methods used.
Pollution from fini-
shing generally not
significant.
Note: Pollution reduction efficiencies shown are generally the
highest reported.
-------
31
The sequence in which the operations must be applied
is not subject to much change. This is particularly true of the
processes producing most of the pollution, specifically the washing
and soaking, unhairing, bating and tanning. The main trend has
been toward continuous rather than batch operations. The higher
cost of the continuous machinery is compensated for by a decrease
in labor and space requirements.
B. Treatment Practices
1. Removal Efficiencies
The following Table III-2 shows average pollutant
reduction percentages for various waste treatment processes
currently in use. There are many methods available for treatment
of tannery wastes. The best method, or combination of methods,
for waste treatment differs from plant to plant. Each situation
must be evaluated individually on the basis of such factors as
wastewater volume and strength, discharge limitations imposed by
regulating agencies, plant location, whether the waste is combined
with municipal domestic sewage, land area available, chemical costs,
degree of pollution reduction desired, and other variables.
Flotation and skimming treatment appears to be a feasible future
reuse and waste facility development.
-------
32
TABLE III-2
TREATMENT REMOVAL EFFICIENCIES
NORMAL POLLUTANT
ITEM
In Plant Treatment
Screening
Equalization in
holding basins
Sedimentation
Chemical Coagu-
lation
Lagoons
Trickling
Filtration
Activated Sludge
Sludge treatment by
Lagoons
Digestion
Vacuum Filtration
Incineration
Municipal Treatment
Primary
Primary & Trick-
ling Filtration
Primary & Acti-
vated Sludge
Primary & Chem.
Coagulation (lime)
BOD
5
0
25-62
41-70
70
65-80
85-95
:
20-54
85-95
75-95
50-90
SS
5-10
0
69-96
70-97
80
85-90
80-95
14-75
80-95
77-95
73-96
REDUCTION
COLOR
0
0
5-10
6-90
25
Est.
15-70
75
Est.
20
Est.
25-75
Est.
75
Est.
90
Est.
EFFICIENCY (PERCENT)
CHROMIUM
0
5-10
5-30
50-80
Est.
10-20
25-75
Est.
75
Est.
10-15
25-75
Est.
75
Est.
50-90
Est.
SULFIDE
0
0
5-20
14-50
Est.
0
75-100
75-100
10-15
75-100
75-100
75-100
Est.
-------
33
Some examples of treatments used and efficiencies
ob t ained include:
Flocculation, Double Settling and Equalization
Evaporation of Tan Liquor;
90 percent BOD Reduction
96 percent Removal of Soluble
Solids.
Carbonation to pH 8.8 2 hr settling 60;40 mixture
in Trickling Filter with Domestic Sewage:
20 percent BOD Reduction
59 percent Sulfide Reduction
76 percent Hardness Reduction
60:40 Mixture on Trickling Filter with Domestic Sewage;
88-89 percent Removal at Loadings of
3500-4500 Ib/ac ft/day
100 percent Sulfide Removal
95 percent BOD Removal at Loadings of
100 Ib BOD/1000 cu ft
90 percent BOD Removal at Loadings of
170 Ib BOD/1000 cu ft
33;67 Mixture through Sedimentation Basin with Domestic
Sewage;
54 Percent BOD Removal
Differences in treatment efficiencies reported in the
literature stem from differences in subprocess use which usually
are not fully described. For example, Soaking from 4 to 96 hours
will result in a tremendous increase in pollution load. The largest
discrepancies may be caused by differences in hair removed. If
hair is pulped, relatively large amounts of Na2S (2 to 4 percent
OWH) and longer periods of contact (1-3 days) are used. This
yields higher BOD's due to more sulfide and hair and hide substance.
If hair recovery is practiced, lower Na2S (0.7 - 1.5 percent OWH)
and shorter contact periods (4-24 hours) result in lower BOD due to
the lessened protein in the waste.
2. Rates of Adoption
Prior to 1915 there were practically no treatment
facilities at any tannery. There was a prevalence of small tanneries
located on rather large, relatively uncontaminated streams. Today,
most tanneries use equalization of beamhouse and tanhouse wastes
(exclusive of vegetable tan liquors) as the first step in treatment.
Treatment is usually limited to equalization and sedimentation.
-------
34
If segregation of wastes within the tannery were
diligently practiced, 80-90 percent of the BOD could be kept in
10-20 percent of the volume. Then this small volume of high BOD
waste could be reclaimed or disposed of separately. This technique
is not a current industry practice.
Approximately 75 percent of all tannery wastes are
discharged into community sewers and treated along with domestic
sewage. Because of the nature of tannery wastes, some form of
pretreatment is often required before they are mixed with domestic
sewage. Industry representatives state that only a small per-
centage of all tannery wastes are discharged directly to a receiving
water without treatment. Waste treatment processes used include
screening, sedimentation, neutralization, chemical coagulation, and
lagoons
Waste treatment is expected to increase during the period
from now until 1982 for the following reasons:
Concentration of total waste into larger tanneries
which require more treatment.
Location of larger tanneries in more highly urbanized
areas where more treatment is required and more
effective municipal treatment is usually available.
Since tanneries will be larger, they will be in a
better financial position to afford adequate waste
treatment.
Water pollution capacity in receiving waters will
become increasingly more limited, thus requiring
more waste treatment.
Certain sequences in waste treatment techniques should
generally be adhered to because of the nature of tannery wastes.
Screening to remove debris, equalization to produce uniform quality
waste, and neutralization (under certain circumstances) to prevent
excessively high pH values are almost always required prior to
treatment by either the municipality or the individual tannery.
Some substitute techniques cannot be used coincidentally.
Treatment processes can be broadly broken down into separation and
biological treatment. Usually, there is only one major unit in
separation and one major unit in biological treatment. For example,
if the activated sludge process is used, a trickling filter would
rarely be used on the same waste.
-------
35
There are other interdependencies among the waste
treatment techniques which affect either costs or relative
efficiencies. Industrial waste treatment is highly specific for
a particular plant. The technique of treatment selected by the
waste treatment engineer is influenced by volume and characteris-
tics of the waste, degree of pollution reduction required, climate,
land area available, etc. An economic study should be made in
each instance to optimize efficiency and minimize cost.
3. Discharge to Municipal Sewers
The percentage of tannery wastes discharged to
municipal sewers is estimated as follows:
Year 1950 1963 1967 1972
Percent 60 70 75 80
When industrial wastes are combined with municipal wastes,
waste removal problems include compatibility and pretreatment.
Odors and clogging of sewers due to pieces of fat, haif, and pre-
cipitated lime, are major nuisances. Toxicity of chromium and
sulfide ions in biological treatment has also been of concern in
combined treatment. High pH values resulting from beamhouse opera-
tions may inhibit biological treatment of combined wastes. Large
quantities of suspended solids overload primary units and clog
secondary units. Excessive grease often creates problems with
skimming devices and small nozzle distribution systems.
It is feasible to treat this industrial waste in an
adequately designed and operated municipal wastewater treatment
plant. Screening, flotation, and neutralization (under some
situations) are necessary pretreatments.
C. By-Product Utilization
The following chart details normal by-product utilization
in a tannery.
Item Use
Trimmings - Bellies - Used for edible purposes.
Others - Oil production after rendering
Protein feed after rendering
Gelatin manufacture
-------
36
Item
Hair
Fleshings
Use
Used in manufacturing, upholstering,and
rug backing.
Glues
Degreasing Exhaust
Drum Liquors
Spent Lime Liquors -
Pickle Solution Wastes -
Chrome Tan Liquors -
Spent Vegetable Tans
Spent Tan Bark -
Reuse of solvent in tannine-
Soap
After settling, the sludge can be mixed
with other plant wastes and sold as
fertilizer.
In the past this solution has been
reused within the tannery for pickling
a number of times. However, tendency
of late has been to omit this reuse
through advent of drum bate, pickling,
and chrome tanning.
a. Holding and reusing in tannery.
b. ppt the Cr(OH)3, filtering, redis-
solving chromium with ^SO^. Most
tanners consider this economically
impractical.
Evaporated and sold as boiler compounds .
Used as floor coverings for horse shows,
circuses, playgrounds - sometimes used in
paperboard manufacturing or in making
white lead.
D. Net Wasteload Quantities - 1963
The net waste quantities equal the gross quantities
produced less the pollution removed by industry-operated and
municipally-operated waste treatment facilities. For the base
year, we estimate 70 percent of the waste volume was treated by
municipal faciliites, with an average pollution reduction of 80
percent. We further estimate that 20 percent of the waste volume
was completely treated by industry-operated facilities, with an
average pollution reduction of 62 percent. On this basis, net
pollution reaching watercourses in 1963 from the tanning industry
approximated:
-------
37
Gross Produced Percent Net Discharged
Item Million Ib Removed Million Ib
BOD 150 67.5 49
SS 425 79.5 87
IDS 650 38.0 403
E. Projected Net Wasteload
It is expected that the quantity of pollution load
reaching the nation's watercourses from the tanning industry will
decrease in the future. This will be the result of slightly
reduced gross pollution produced, a larger percentage of waste
treated, and increased removal efficiencies of waste treatment
methods. Table III-3 projects net wasteloads through the year 1982.
TABLE III-3
PROJECTED NET WASTELOADS
Gross Produced Percent Net Wasteload
Year Waste Million Ib Reduction Million Ib
1967 BOD 160 69 50
SS 440 81 84
TDS 670 38 415
1968 BOD 160 69.5 49
SS 440 81.5 81
TDS 670 38 415
1969 BOD 160 70 48
SS 440 82 79
TDS 670 38 415
1970 BOD 155 70.5 46
SS 430 82.5 75
TDS 660 38 409
1971 BOD 155 71 45
SS 430 83 73
TDS 650 38 403
1972 BOD 155 71.5 44
SS 430 83.5 71
TDS 650 38 403
1977 BOD 150 74 39
SS 420 86 59
TDS 640 40 384
1982 BOD 145 77 33
SS 410 89 45
TDS 630 45 347
287-030 O - 68 - 4
-------
38
Table III-3 reflects the anticipated increased emphasis
on clearing up rivers and streams throughout the country. Con-
sidering the federal and state pollution abatement programs now
being effected, it is probable that within the next 15 years no
tannery will be allowed to discharge untreated waste into a water-
way. In addition, it is probable that the pollution reduction
efficiency required of the treatment will be much higher than now
required.
IV. COST INFORMATION
A. Existing Facilities Cost
The replacement value of existing industry owned and
operated waste reduction facilities in 1966 is estimated at $3.6
million. The annual operating and maintenance cost of these
facilities is estimated at $0.5 million.
However, we estimate that in 1966 approximately 74 percent
of the waste was discharged into and treated by municipal systems.
Since industry pays taxes and surcharges to support these facilities,
the true industry cost exceeds the foregoing amounts.
We estimate that the replacement value of that portion
of municipal treatment facility construction attributable to this
industry waste is $8 million. On the same basis the annual opera-
ting and maintenance cost is estimated at $0.8 million.
TOTALS: Replacement Value - $11.6 million
Operation & Maintenance - $1.3 million annually
B. Processing and Treatment Costs
This portion of the survey analyzes costs involved in
subprocesses and end of line treatment. These are further broken
down into size of plant and state of technology; i.e., older,
prevalent, and newer. The following tables indicate the wide
ranges in the information feedback from the tannery industry. We
believe the table on the entire tannery industry which relates cost
of waste treatment to cost of production gives an overview
picture of the present tannery industry cost situation.
-------
39
Furthermore, the end of the line waste treatment has
little relationship to the technology of the process or the
size of the tanning plant; i.e., an older plant may have an
extremely efficient, modern, waste treatment facility, and a
modern, efficient tanning plant may have no waste treatment faci-
lity at all. The selection of end of the line treatment is based
primarily on the requirements imposed by regulatory agencies
responsible for the affected watercourses.
Although we are required to estimate costs for plants
incorporating pure states of technology; i.e., completely old,
completely prevalent, completely advanced, few such plants exist.
Most are mixtures of varied subprocess technologies since they
have been modernized in stages over a relatively long period of
time.
The following assumptions are utilized for the prepara-
tion of Tables IV-1 through IV-9.
1. Respective costs associated with the small, medium
and large plants are based on a typical plant as
follows:
Small: 300 hides/day
Medium: 700 hides/day
Large: 2000 hides/day
2. Old Technology - that technology new in 1950.
3§ Prevalent Technology - that technology new in 1963.
4. Advanced Technology - that technology new in 1967.
5. Capital Cost - Equivalent 1966 cost.
6. Annual Operating and Maintenance Expenditures -
Equivalent 1966 cost.
7. Economic Life - the length of time the machine or
structure can be expected to compete with advancing
technology. Economic obsolescense varies greatly
depending upon the nature of the product, the dynamics
of industry growth, etc.
-------
40
TABLE iv-1
SMALL PLANT - OLD TECHNOLOGY
Capital Annual Operating and Economic
Costs Maintenance Expenditures Life
Alternative
Subprocesses
Long Soak & Wash
Liming
Bating-Paddle
Machine
Pickling-Paddle
Machine
Tanning
Blue Split, Shave
& Sort
Color, Retan &
Fat liquor
Rest of Plants
TOTAL
End of Line
Treatment
Screening
Sedimentation
Chemical
Precipitation
Trickling Filter
Activated Sludge
Lagooning
Oxidation Pond
Sludge Disposal
(Dollars)
10-20,000
10-20,000
8-15,000
8-15,000
20-30,000
10-16,000
10-20,000
100-200,000
176-336,000
2,000-13,000
10,000-20,000
10,000-80,000
27,000-80,000
34,000-100,000
2,000-5,000
2,700-7,000
(Dollars)
6,000-9,000
10,000-15,000
5,000-8,000
10,000-12,000
12,000-15,000
15,000-20,000
12,000-15,000
30,000-40,000
100,000-134,000
150-1,500
450-1,500
1,500-7,000
1,500-4,500
1,500-8,000
100-600
600-2,000
1,500-7,000
(Years)
10
10
10
10
10
10-20
10
10
10
30
15
20
20
10-20
20
Special Notes:
1. All costs are equivalent 1966 costs. (To determine actual costs for
an earlier year, an appropriate engineer construction cost factor
may be used).
2. Percentage of pollution reduction achieved by a particular end of the
line treatment process is simplified and assumed to be the same in
compared years. For example, it is assumed that the screening
process in 1950 would achieve the same efficiency of pollution
reduction as screening in 1963 and 1967.
3. The end of the line treatment does not include any sewer collection
system costs. It is assumed that the waste treatment facility is
located adjacent to the industrial waste source.
-------
41
TABLE IV-2
MEDIUM PLANT - OLD TECHNOLOGY
Alternative
Subprocesses
Long Soak & Wash
Liming
Bating-Paddle Machine
Pickling-Paddle
Machine
Tanning -Paddle
Machine
Blue Split, Shave,
& Sort
Color, Retan, &
Fatliquor
Rest of Plant
TOTAL
End of Line
Treatment
Screening
Sedimentation
Chemical Precipi-
tation
Trickling Filter
Activated Sludge
Lagooning
Oxidation Pond
Sludge Disposal
Capital
Costs
( Dollars)
20-4Q..OOO
20-40,000
15-30,000
15-30,000
30-70,000
20-30,000
20-40,000
200-400,000
340-680,000
4,000-25,000
20,000-40,000
20,000-160,000
50,000-150,000
75,000-200,000
5,000-10,000
7,000-15,000
-
Annual Operating &
Maintenance Expenditures
( Dollars)
20-25,000
20-25,000
8-13,000
15-25,000
25-35,000
30-40,000
25-35,000
50-70,000
193,000-268,000
300-3,000
1,000-3,000
3,000-15,000
3,000-10,000
3,000-16,000
200-1,300
3,000-15,000
3,000-15,000
Economic
Life
(Years)
10
10
10
10
10-20
10
10
10
10
30
15
20
20
10-20
20
-
Special Notes:
1. All costs are equivalent 1966 costs. (To determine actual costs for
an earlier year, an appropriate engineer construction cost factor
may be used).
2. Percentage of pollution reduction achieved by a particular end of the
line treatment process is simplified and assumed to be the same in
compared years. For example, it is assumed that the screening
process in 1950 would achieve the same efficiency of pollution
reduction as screening in 1963 and 1967.
3. The end of the line treatment does not include any sewer collection
system costs. It is assumed that the waste treatment facility is
located adjacent to the industrial waste source.
-------
42
TABLE IV-3
LARGE PLANT - OLD TECHNOLOGY
Alternative
Subprocesses
Long Soak & Wash
Liming
Bating-Paddle Machine
Pickling-Paddle
Machine
Tanning
Blue Split, Shave,
& Sort
Color, Retan, &
Fatliquor
Rest of Plant
TOTAL
End of Line
Treatment
Screening
Sedimentation
Chemical Precipi-
tation
Trickling Filter
Activated Sludge
Lagomtng
Oxid£ on Pond
Sluage Disposal
Capital
Costs
(Dollars)
80-100,000
80-100,000
70-80,000
70-80,000
125-175,000
65-85,000
80-100,000
800-900,000
1,370,000
1,620,000
10,000-60,000
45,000-100,000
45,000-300,000
100,000-300,000
150,000-500,000
13,000-30,000
16,000-40,000
-
Annual Operating &
Maintenance Expenditures
( Do liar 3
35-50,000
55-70,000
25-35,000
55-65,000
70-80,000
80-100,000
70-80,000
180-220,000
570.000-700,000
900-9,000
2,000-6,000
9,000-45,000
7,000-25,000
7,000-40,000
500-3,000
6,000-30,000
8,000-40,000
Economic
Life
(Years)
10
10
10
10
10
10-20
10
10
10
30
15
20
20
10-20
20
-
Special Notes:
1. All costs are equivalent 1966 costs. (To determine actual costs for
an earlier year, an appropriate engineer construction cost factor
may be used).
2. Percentage of pollution reduction achieved by a particular end of the
line treatment process is simplified and assumed to be the same in
compared years. For example, it is assumed that the screening
process in 1950 would achieve the same efficiency of pollution
reduction as screening in 1963 and 1967.
3. The end of the line treatment does not include any sewer collection
system costs. It is assumed that the waste treatment facility is
located adjacent to the Industrial waste source.
-------
43
TABLE IV-4
SMALL PLANT - PREVALENT TECHNOLOGY
Alternative
Subprocesses
Short Soak & Wash
Liming
Bating-Drum Machine
Pickling-Drum Machine
Tanning
Blue Split, Shave, &
Sort
Color, Retan &
Fatliquor
Rest of Plant
TOTAL
Capital
Costs
(Dollars)
8-10,000
15-20,000
15-20,000
10-15,000
25-35,000
15-25,000
15-25,000
110-220,000
213-370.000
Annual Operating & Economic
Maintenance Expenditures Life
(Dollars) (Years)
6,000-9,000 10
10,000-15,000 10
5,000-8,000 10
10,000-12,000 10
12,000-15,000 10
15,000-20,000 10-20
12,000-15,000 10
30,000-40,000 10
100-134,000
End of Line
Treatment
Since volume approxi-
mately the same as
for old technology
see "old technology"
Special Notes:
1. All costs are equivalent 1966 costs. (To determine actual costs for
an earlier year, an appropriate engineer construction cost factor
may be used).
2. Percentage of pollution reduction achieved by a particular end of the
line treatment process is simplified and assumed to be the same in
compared years. For example, it is assumed that the screening
process in 1950 would achieve the same efficiency of pollution
reduction as screening in 1963 and 1967.
3. The end of the line treatment does not include any sewer collection
system costs. It is assumed that the waste treatment facility is
located adjacent to the industrial waste source.
-------
44
TABLE IV-5
MEDIUM PLANT - PREVALENT TECHNOLOGY
Alternative
Subprocesses
Short Soak & Wash
Liming
Bating-Drum Machine
Pickling-Drum
Machine
Tanning
Blue Split, Shaves,
& Sort
Color, Retan, &
Fatliquor
Rest of Plant
TOTAL
Capital
Costs
(Dollars)
10-20,000
25-40,000
20-30,000
20-30,000
40-70,000
25-35,000
25-40,000
225-400,000
390-665,000
Annual Operating & Economic
Maintenance Expenditures Life
(Dollars) (Years)
20-25,000 10
20-25,000 10
8-13,000 10
15-25,000 10
15-25,000 10
25-35,000 10-20
30-40,000 10
50-70,000 10
183-258,000
End of Line
Treatment
Screening
Sedimentation
Chemical Precipi-
tation
Trickling Filter
Activated Sludge
Lagooning
Oxidation Pond
Sludge Disposal
4,000-25,000
20,000-40,000
20,000-160,000
50,000-150,000
75,000-200,000
5,000-10,000
7,000-15,000
300-3,000
1,000-3,000
3,000-15,000
3,000-10,000
3,000-16,000
200-1,300
3,000-15,000
3,000-15,000
10
30
15
20
20
10-20
20
Special Notes:
1. All costs are equivalent 1966 costs. (To determine actual costs for
an earlier year, an appropriate engineer construction cost factor
may be used).
2. Percentage of pollution reduction achieved by a particular end of the
line treatment process is simplified and assumed to be the same in
compared years. For example, it is assumed that the screening
process in 1950 would achieve the same efficiency of pollution
reduction as screening in 1963 and 1967.
3. The end of the line treatment does not include any sewer collection
system costs. It is assumed that the waste treatment facility is
located adjacent to the industrial waste source.
-------
45
TABLE IV-6
IARGE FIANT - PREVALENT TECHNOLOGY
Alternative
Subprocesses
Short Soak & Wash
Liming
Bating-Drum Machine
Pickl ing-Drum
Machine
Tanning
Blue Split, Shave,
& Sort
Color, Retan, &
Fatliquor
Rest of Plant
TOTAL
End of Line
Treatment
Screening
Sedimentation
Chemical Precipi-
tation
Trickling Filter
Activated Sludge
Lagoon ing
Oxidation Pond
Sludge Disposal
Capital
Costs
(Dollars)
45-55,000
80-100,000
60-70,000
60-70,000
140-170,000
.
75-85,000
105-125,000
850-950,000
1,415,000
1,625,000
10,000-60,
45,000-100
45,000-300
100,000-300
150,000-500
13,000-30,
16,000-40,
-
Annual Operating &
Maintenance Expenditures
( Dollars )
35-50,000
55-70,000
25-35,000
55-65,000
80-90,000
80-100,000
70-80,000
190-230,000
590-720,000
000 900-9,000
,000 2,000-6,000
,000 9,000-45,000
,000 7,000-25,000
,000 7,000-40,000
000 500-3,000
000 6,000-30,000
8,000-40,000
Economic
Life
(Years)
10
10
10
10
10
10-20
10
10
10
30
15
20
20
10-20
20
-
Special Notes:
1, All costs are equivalent 1966 costs. (To determine actual costs for
an earlier year, an appropriate engineer construction cost factor
may be used).
2. Percentage of pollution reduction achieved by a particular end of the
line treatment process is simplified and assumed to be the same in
compared years. For example, it is assumed that the screening
process in 1950 would achieve the same efficiency of pollution
reduction as screening in 1963 and 1967.
3, The end of the line treatment does not include any sewer collection
system costs. It is assumed that the waste treatment facility is
located adjacent to the industrial waste source.
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46
TABLE IV-7
SMALL PLANT - NEW TECHNOLOGY
Alternative
Subprocesses
Short Soak & Wash
Liming with add.
Chemicals
Bate, Pickle, and
Tan Continuous
System
Blue Split, Shave,
& Sort
Color, Retan, &
Fatliquor
Rest of Plant
TOTAL
Capital
Costs
(Dollars)
8-10,000
15-20,000
70-90,000
15-25,000
15-25,000
110-220,000
233-390,000
Annual Operating & Economic
Maintenance Expenditures Life
(Dollars) (Years)
6-9,000 10
10-15,000 10
25-35,000 10
15-20,000 10-20
12-15,000 10
30-40,000 10
98-134,000
End of Line
Treatment
Since volume approxi-
mately the same as
for old technology
see old technology
Special Notes:
1. All costs are equivalent 1966 costs. (To determine actual costs for
an earlier year, an appropriate engineer construction cost factor
may be used).
2. Percentage of pollution reduction achieved by a particular end of the
line treatment process is simplified and assumed to be the same in
compared years. For example, it is assumed that the screening
process in 1950 would achieve the same efficiency of pollution
reduction as screening in 1963 and 1967.
3. The end of the line treatment does not include any sewer collection
system costs. It is assumed that the waste treatment facility is
located adjacent to the industrial waste source.
-------
47
TABLE IV-8
MEDIUM PLANT - NEW TECHNOLOGY
Alternative
Subprocesses
Short Soak & Wash
Liming with add.
Chemicals
Bate, Pickle, & Tan
Continuous System
Blue Split, Shave,
& Sort
Color, Retan, &
Fatliquor
Rest of Plant
TOTAL
Capital
Costs
(Dollars)
10-20,000
25-40,000
20-30,000
90-150,000
25-35,000
25-40,000
235-420,000
430-735,000
Annual Operating & Economic
Maintenance Expenditures Life
( Dollars) (Years)
20-25,000 10
20-25,000 10
45-70,000 10
20-40,000 10-20
25-35,000 10
55-75,000 10
185-270,000
End of Line
Treatment
Screening
Sedimentation
Chemical Precipi-
tation
Trickling Filter
Activated Sludge
Lagooning
Oxidation Pond
Sludge Disposal
4,000-25,000
20,000-40,000
20,000-160,000
50,000-150,000
75,000-200,000
5,000-10,000
7,000-15,000
300-3,000
1,000-3,000
3,000-15,000
3,000-10,000
3,000-16,000
200-1,300
3,000-15,000
3,000-15,000
10
30
15
20
20
10-20
20
Special Notes:
1. All costs are equivalent 1966 costs. (To determine actual costs for
an earlier year, an appropriate engineer construction cost factor
may be used).
2. Percentage of pollution reduction achieved by a particular end of the
line treatment process is simplified and assumed to be the same in
compared years. For example, it is assumed that the screening
process in 1950 would achieve the same efficiency of pollution
reduction as screening in 1963 and 1967.
3. The end of the line treatment does not include any sewer collection
system costs. It is assumed that the waste treatment facility is
located adjacent to the industrial waste source.
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48
TABLE IV -9
LARGE PLANT - NEW TECHNOLOGY
Alternative
Subprocesses
Short Soak & Wash
Liming with add.
Chemicals
Bate, Pickle, and
Tan Continuous
System
Blue Split, Shave,
& Sort
Color, Re tan, &
Fatliquor
Rest of Plant
TOTAL
End of Line
Treatment
Screening
Sedimentation
Chemical Precipi-
tation
Trickling Filter
Activated Sludge
Lagooning
Oxidation Pond
Sludge Disposal
Capital
Costs
(Dollars)
45-55,000
80-100,000
240-300,000
75-85,000
105-120,000
850-950,000
1,395,000-
1,610,000
10,000-60,000
45,000-100,000
45,000-300,000
100,000-300,000
150,000-500,000
13,000-30,000
16,000-40,000
-
Annual Operating &
Maintenance Expenditures
(Dollars)
35-50,000
60-75,000
160-180,000
80-100,000
70-80,000
200-240,000
605-725,000
900-9,000
2,000-6,000
9,000-45,000
7,000-25,000
7,000-40,000
500-3,000
6,000-30,000
8.000-40,000
Economic
Life
(Years)
10
10
10
10-20
10
10
10
30
15
20
20
10-20
20
-
Special Notes:
1. All costs are equivalent 1966 costs. (To determine actual costs for
an earlier year, an appropriate engineer construction cost factor
may be used).
2. Percentage of pollution reduction achieved by a particular end of the
line treatment process is simplified and assumed to be the same in
compared years. For example, it is assumed that the screening
process in 1950 would achieve the same efficiency of pollution
reduction as screening in 1963 and 1967.
3. The end of the line treatment does not include any sewer collection
system costs. It is assumed that the waste treatment facility is
located adjacent to the industrial waste source.
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TABLE IV-10
SUMMARY OF PRODUCTION LEATHER TANNING AND FINISHING
AND WASTE TREATMENT COSTS
Item
Total production
Total value added in manufacture*
Average unit value added in
manufacture
Estimated replacement value of waste
reduction facilities**
Annual amortized cost of waste
treatment of facilities at
77. and 10 yr life**
Estimated annual waste reduction
operating and maintenance
cost**
Average industry cost of waste
treatment per unit of
production
Total waste reduction costs as
percent of total production
cost
Quantity
31.3 million equivalent hides
$272 million
$8.70/equivalent hide
$11.6 million
$1.6 million
$1.3 million
$0.09/equivalent hide
1.07 percent
* From the Business and Defense Services Administration,
U. S. Department of Commerce, 1967.
** Estimated replacement value, estimated amortization, and
estimated annual operating costs include an estimate of
the cost of municipal treatment facilities attributable to
this industry's wastes.
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53
APPENDIX 1
GENERAL BIBLIOGRAPHY
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Report, Parts 1 and 2, for the Cities of Johnstown and
Gloversville, Fulton County, New York, Morrell Vrooman,
Engineers, August 2, 1965.
Anon., Leather Manufacturers for 1967-1968. Boston, Mass.: Shoe
Trades Publishing Co., 1967.
Anon., Membership Bulletin Leather Industry Statistics. 1967 Ed.,
Trade Survey Bureau, Tanners' Council of America, Inc.
Anon., 1965 Book of ASTM Standards, Part 15. Philadelphia, Pa.:
American Society for Testing and Materials, 1965.
Anon., "Water in Industry". A Survey of Water Use in Industry by
the National Association of Manufacturers and the Chamber
of Commerce of the United States, in cooperation with the
National Technical Task Committee on Industrial Wastes,
January 1965.
Ball, W. J., "Operation of Inadequate Facilities at Ballston Spa,
N.Y." Sewage and Industrial Wastes, 25, 11, 1345-1351
(November 1953).
Bianucci, G., and De Stefani, G., "Tannery Wastes I & II". Effluent and
Water Treatment Journal, 3, 1, 18 and 76 (1963).
Bianucci, G., and De Stefani, G., "Tannery Wastes". Effluent and
Water Treatment: Journal, 5, 407 (1965).
Braunschweig, T. D., "Tannery Sewage". Jour. Amer. Leather Chem.
Assn.. 60, 125 (1965); Chem. Abs.. 62, 12891 (1965).
Eddy, H. P., and A. L. Fales , "The Activated-Sludge Process in
Treatment of Tannery Wastes" . Industrial and Engineering
Chemistry. 8, 7, 648 (July 1916).
Eich, J. F., "Tannery Wastes Disposal by Spray Irrigation".
Industrial Wastes, 1, 8, 271 (November-December 1956).
Fales, A. L., "Treatment of Industrial Wastes from Paper Mills and
Tannery on Neponset River". Industrial and Engineering
Chemistry. 21, 3, 216 (March 1929).
-------
Foster, W., "Discussion on Trade Waste (Tannery) Purification Plant".
Journal and Proceedings of the Institute of Sewage Purification,
Part 2 (1950) p. 98.
Foster, W., "Chrome Tannery Treatment Plant, Description". Sewage
and Industrial Wastes, 24, 7, 927 (July 1952).
Gurnham, C. Fred, Industrial Wastewater Control. New York: Academic
Press, 1965, pp. 395-410.
Gurnham, C. F., Principles of Industrial Waste Treatment. New York:
John Wiley & Sons, Inc., 1955, pp. 6, 7, 47, 58, 68, 70, 71,
79, 123, 125, 141, 143, 146, 152, 179, 189, 206, 210, 218, 220,
227, 230, 231, 281, 293, 296, 324, 355, 389, 390.
Harnley, J. W., "Liquid Industrial Wastes—Symposium". Industrial and
Engineering Chemistry, 44, 3, 520 (March 1952).
Harnley, J. W., R. F. Wagner, and H. G. Swope, "Treatment at Griess-
Pfleger Tannery, Waukegan, 111.". Sewage Works Journal, 12, 4,
771-779 (July 1940).
Hartman, B. J., "Combined Treatment, Tannery Wastes and Domestic
Sewage, Fond du Lac, Wis.". Sewage and Industrial Wastes, 25,
12, 1419-1423 (December 1953).
Haseltine, T. R., "Central Primary Plant will Handle Sewage from
Three Municipalities". Wastes Engineering, 28, 4, 176 (April
1957).
Haseltine, T. R., "Combined Treatment, Tannery Wastes and Sewage,
Williamsport, Pa.". Sewage and Industrial Wastes, 30, 1, 65-85
(January 1958).
Hommon, H. B., "Purification of Tannery Wastes". United States Public
Health Service, 1919.
Howalt, W., and E. S. Cavett, "Studies on Tannery Waste Disposal".
Transactions of American Society of Civil Engineers, 92 (1928)
p. 1351.
Hubbell, G. E., "Tannery Waste Disposal at Rockford, Mich.",
Waterworks and Sewerage, 82, 9, 331 (September 1935).
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Corp., Rockford, Mich.". Proceedings of 10th Industrial Waste
Conference, Purdue University, May 1955.
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55
Industrial Waste Control. New York: Academic Press, Inc., 1965. Ch.
22 "Leather" by Fred 0'Flaherty, pp 395-409.
"Industrial Waste Guide". Ohio River Pollution Survey, Supplement D,
United States Public Health Service, 1943.
Kahler, H. L., and Brown, J. K., "Treating Tannery Waste Liquor"-
U.S. Patent 3184407; Chem. Abs.. 63, 4009 (1965).
KMnzel-Mehner, "Treatment with Ferric Chloride". Sewage Works Journal,
17, 2, 412 (March 1945).
Loveland, F. A., Journal of American Leather Chemists' Association. 7,
12, 474 (December 1912).
McCarthy, J. A., and B. L. Rosenthal, "Biological Treatment of
Tannery Wastes". Water and Sewage Works, 88, 12, 82 (December
1957).
McKee, J. E., and T. R. Camp, "Tanning Wastes—Some Special Problems".
Sewage and Industrial Wastes, 22, 6, 803-806 (June 1950).
Maskey, D. F., "Study of Tannery Waste Disposal". Journal of American
Leather Chemists'Association, 36, 3, 121-141 (March 1941).
McFall, Warren T., "Report on Tannery Wastes-Characteristics and
Disposal". Presented for C.B. 283, San Jose, Calif., San Jose
State College, 1966.
McLaughlin & Theis, The Chemistry of Leather Manufacture. New York:
Reinhold Publishing Corp., 1945.
Milligan, F. B., "Tannery Waste Treatment in Pennsylvania". American
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Nemerow, Nelson, L., Theories and Practices of Industrial Waste
Treatment. Reading, Massachusetts: Addision-Wesley Publishing
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C. F. Gurnham, Academic Press, 1965.
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and Pickle Liquor". Industrial Wastes, 3, 1, 18 (January-
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287-030 O - 68 - 5
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56
Plsko, E., "Spectrochemical Determination of Chromium in Tannery
Waste Waters using Copper Foil Electrode". Chemical Abstracts,
57, 12271 (1962) .
Porter, W., "Operating Problems from Tannery Wastes, Ballston Spa,
N.Y.". Sewage Works Journal. 21, 4, 738 (July 1949).
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Chemists' Association, 42, 11, 573-577 (November 1947).
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20, 3, 525 (May 1948).
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Treatment Plant". Public Works Magazine, 78, 3, 21 (March 1947).
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with Flue Gas and Lime". Industrial and Engineering Chemistry,
33, 6, 801 (June 1941).
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1953, Chapter 8.
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57
Shevchenko, M. A., and Kas'yanchuk, R. S., "Absorption of Tanning
Substances from Water and their Stability to Destruction
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(1965); Chem. Abs.. 63, 17677 (1965).
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2, 350 (March 1936).
Vrooman, M., and V. Ehle, "Digestion of Combined Tannery and Sewage
Sludge". Sewage Works Journal, 22, 1, 94-101 (January 1950).
Wimmer, A., "The Sewage from the Tannery City Backnang". Sewage
Works Journal, 9, 3, 529 (May 1937).
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Industrial Waste Conference, 1963.
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58
APPENDIX II
GLOSSARY
Activated Sludge Process - a process for treacing liquid waste by
aeration and recirculation of biologically active sludge.
Aeration - the act of supplying with oxygen.
Anaerobic - living or active in the absence of oxygen.
Areolar (adj.) - description of fatty tissue intermingled
with other tissue in small, interstitial particles.
Bating - a chemical process for preparing swollen and alkaline
hides for tanning, usually using ammonium salts and
enzymes.
Beam (v.) - to remove hair.
BOD - biochemical oxygen demaud - the weight of oxygen
required to biologically oxidize an organic waste over a
specified period of time.
Chemical Coagulation - the change from a liquid to a thickened,
curd-like state by chemicals.
COD - chemical oxygen demand - a measure of the organic
pollution.
Effluent - polluted water discharged from a process.
Emulsification - to convert to an oily mass in suspension in a
watery liquid.
Enzyme - any of a class of organic substances that accelerate
specific transformations of material, as in digestion and
fermentation.
Equalization - the process of combining two or more dissimilar
wastes to produce a uniform composite.
Fatliquoring - the process of adding fats and greases to tanned
hides to prevent cracking.
Gambier - a yellowish catechu derived from a Malayan rubiaceous
woody vine, used for tanning and dyeing.
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59
APPENDIX II (cont'd)
Green Fleshing - removal of flesh from hides before soaking.
Lagooning - the liquid wash treatment process of holding the
waste in shallow ponds for a period of several hours to
allow absorption of oxygen.
Lime Fleshing - removal of flesh from hides after soaking.
Lot - 30,000 Ib of whole hides.
Pectic acid - any of various water insoluble substances formerd
by hydrolizing the methyl ester groups of pectins.
Peroxidase - an enzyme that catalyzes the oxidation of various
substances by peroxides.
Pickling - a chemical process using sulfuric acid and sodium
chloride to make skins acid enough to prevent precipitation of
insoluble salts during vegetable tanning.
Potable - drinkable.
Precipitate - to cause to separate from solution or suspension.
Process - a series of actions or operations definitely conduct-
ing to an end; continuous operation or treatment, especially
as in manufacture.
Rehydration - process of recombining with water.
Screening - separation of solid material from liquid waste by
passing the waste through screens.
Sedimentation - gravity settling of solid particles suspended in
a liquid.
Sides - half of a skin, the skin having been cut down the back
from head to tail.
Subprocess - an alternate method of conducting a process.
Sumac - a material used in tanning and dyeing consisting of
the dried and powdered leaves, panicles, etc. of various
species of sumac trees, shrubs or woody vines.
Tannin - any of various soluble astringent complex phenolic
substances of plant origin used in tanning or dyeing.
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60
Tanning - art or process by which skin is converted to leather.
Trickling Filtration - a liquid waste treatment process involving
trickling the waste through a bed of stone or other inert
material.
U. S. GOVERNMENT PRINTING OFFICE • :
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