United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
EPA 600 2-78-215
October 1978
Research and Development
Assessment of
Potential Toxic
Releases from
Leather Industry
Dyeing Operations
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7 Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans, plant and animal spe-
cies, and materials. Problems are assessed for their long- and short-term influ-
ences. Investigations include formation, transport, and pathway studies to deter-
mine the fate of pollutants and their effects. This work provides the technical basis
for setting standards to minimize undesirable changes in living organisms in the
aquatic, terrestrial, and atmospheric environments.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-78-215
October 1978
ASSESSMENT OF POTENTIAL TOXIC RELEASES FROM LEATHER
INDUSTRY DYEING OPERATIONS
by
S. B. Radding
J. L. Jones
W. R. Mabey
D. H. Liu
N. Bohonos
SRI International
Menlo Park, California 94025
Grant No. 804642-01-2
Project Officer
Kenneth Dostal
Industrial Pollution Control Division
Industrial Environmental Research Laboratory
Cincinnati, Ohio 45268
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Industrial Environmental
Research Laboratory, U.S. Environmental Protection Agency, and approved
for publication. Approval does not signify that the contents necessarily
reflect the views and policies of the U.S. Environmental Protection
Agency, nor does mention of trade names or commercial products constitute
endorsement or recommendation for use.
ii
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FOREWORD
When energy and material resources are extracted, processed, converted,
and used, the related pollutional impacts on our environment and even on
our health often require that new and increasingly more efficient pollution
control methods be used. The Industrial Environmental Research Laboratory-
Cincinnati (lERL-Ci) assists in developing and demonstrating new and
improved methodologies that will meet these needs efficiently and
economically.
The report briefly describes the leather tanning industry including
the various sources of emissions. An attempt was made to assess the
seriousness of the potential for toxic pollutant releases from the dyeing
of leather. For further information on this project contact the Food and
Wood Products Branch, Industrial Pollution Control Division, Industrial
Environmental Research Laboratory-Cincinnati.
David G. Stephan
Director
Industrial Environmental Research Laboratory
Cincinnati
iii
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ABSTRACT
This study focused on the organic dyes released to the environment
in the wastewaters from leather dyeing operations. Basically, three types
of dyes—acid, basic, and direct—are used, although the number of dif-
ferent dyes are well over 50, and the number of formulations used at a
single tannery over the period of several years can be greater than 100.
Tannery wastewaters are complex mixtures which for the most part are
discharged directly into municipal sewers. The character of this dis-
charge will differ hourly depending on the operation performed since
tanning operations are batch mode. Estimates based on information from
suppliers and tanners were made of the probable discharge of dyes in
wastewater. The literature search revealed little or no data on the
fate of these dyes in the environment. From consideration of the physical
and chemical properties of the dyes, biosorption (complexing with pro-
teinaceous material) appears to be the most likely mechanism for removal
of dyes in biological wastewater treatment systems.
This report was submitted in fulfillment of Grant No. R 804642-01-2
by SRI International under the sponsorship of the U.S. Environmental
Protection Agency. This report covers the period 1 June 1977 to
28 April 1978 and was completed as of 28 April 1978.
iv
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CONTENTS
Foreword
Abstract
Figures
Tables
1. INTRODUCTION
2. SUMMARY AND CONCLUSIONS
3. GENERAL DESCRIPTION OF INDUSTRY
4. CHARACTERISTICS OF THE INDUSTRY
Size and Structure .
Environmental Impacts
Beamhouse Process
Tanhouse Process . .
Retan, Color, Fatliquor Process
Finishing Process
Raw Materials
Pollutant Sources
5. LEATHER DYEING
The Dyeing Process
Data Acquisition
Tannery Effluent Characteristics and Treatment
Dye Removal in Wastewater Treatment
6. TOXICITY AND ENVIRONMENTAL FATE OF DYES . .
Toxicity of Dyes
Toxicity to Aquatic Organisms ....
Potential Human Health Effects.
Environmental Fate
Physical Properties
Chemical Transformation
Physical Transport
References
Appendices
A. DYES USED IN THE LEATHER INDUSTRY ....
B. BIODEGRADATION OF DYES IN BIOLOGICAL TREATMENT
SYSTEMS
iii
iv
vi
vii
1
, 2
4
6
6
6
17
17
18
19
19
22
31
31
32
35
37
43
43
43
46
47
47
47
50
51
53
62
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FIGURES
1 Flow Diagram for Leather Tanning Process 23
2 The Uptake of Dye in Leather as a Function of pH 33
3 Effluent Treatment for a Complete Chrome Tannery 40
4 Estimates of BOD,., COD, and TOC of Effluent Streams
of Tannery 41
vi
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TABLES
1 Statistics for Leather Tanning and Finishing Industry ... 7
2 1976 Production Rates in Equivalent Chrome Grain
Cattle Hides 8
3 1976 Production Rates in Equivalent Vegetable Tanned
Cattle Hides 9
4 1976 Production Rates in Equivalent Sheep Hides 10
5 1976 Production Rates in Equivalent Split Chrome
Leather Hides 11
6 1976 Production Rates in Equivalent Blue Hides 12
7 1976 Production Rates in Equivalent Retan /Finisher Hides . 13
8 1976 Production Equivalent Finished Hides 14
9 Suppliers of Chemicals to the Tanning Industry 20
10 Suppliers of Hides and Skins 21
11 Chemicals Used in Leather Processing ..... 24
12 Estimates of Selected Chemical Usage and Losses for
Leather Tanning and Finishing 28
13 Survey of the Leather Industry Tannery 34
14 Estimated Effluent Stream Load from a 1000 Cattle Hide/Day
Tannery (60 Ib Green Salted Cattle Hide) 36
15 Concentration of Dyes in Waste Streams 38
16 Toxicity of Acid, Basic, and Direct Dyes to the Green
Alga, Selenastrum Capricornutum 44
17 Toxicity of Acid, Basic, and Direct Dyes to the Fathead
Minnow, Pimephales Promelas 45
18 Photolysis of Dyes 49
19 Some Dyes Used in the Leather Industry 54
vii
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SECTION 1
INTRODUCTION
This report describes a study undertaken to assess the seriousness
of the potential for toxic pollutant releases from the dyeing of leather.
Heretofore, most studies of pollution problems of this industry have
focused on the problems associated with the high BOD suspended material,
and chrome chemicals in the effluent. This work focuses only on organic
dyes.
As background, the report briefly describes the industry structure;
the processing operations; the types of raw materials required; the po-
tential process sources of emissions to air, water, and the land; and
the environmental control practices.
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SECTION 2
SUMMARY AND CONCLUSIONS
This study focused on the organic dyes released to the environment
in the wastewaters from leather dyeing operations. These dyes have been
of concern as a health hazard to workers. A report just released by the
National Institutes of Occupational Safety and Health (NIOSH, 1977)
reports a striking increase in bladder cancer among both male and female
leather workers, and previous studies indicate that the disease may be
dye-related.
The dye types used by the leather industry include acid, basic,
direct, and metallized dyes. The predominant dyes, however, are the
acid and direct dyes. As many as 100 different dye formulations can be
used in one plant. More than 50 dyes have been identified by eight major
suppliers and from inventory lists of tanneries as used by the leather
industry. Of these, 49 are listed in this report with structural formulas
which indicate the wide range of materials involved.
Tannery wastewaters are complex mixtures of relatively unknown com-
position. Until recently, there had been no scientific assessment of the
effluents, and even today, little work is being done to characterize the
waste streams.
Most tanneries (90% of the tanners and 80% of the industry's waste-
water) discharge their effluent streams directly into municipal sewers.
The character of the waste stream depends on the particular operation
being performed at that time, since tannery operations are batch mode and
vary from day to day.
The chrome chemicals used in dyeing are a well-documented source of
toxic materials. However, the industry has made an effort to recover or
remove the chrome chemicals and many effluent streams are now low in
chromium.
An extensive literature search and contacts with trade associations,
tanners (4 site visits), and dye producers revealed that very little infor-
mation is available (or known) on the amount of specific leather dyes
released and the biodegradation of such dyes.
Even without the dyeing operation, the waste streams are highly
colored, and since combinations of dyes are often used, analysis of waste
streams is extremely difficult and costly.
From SRI estimates of thefitotal dye usage by producers and tanners
CW x 10 Ibs/year or 3.2 x 10 kg/year) and the average uptake for dyes
(60-85%), it was estimated that total leather dye releases may range
from 1.1-2.8 x 10 Ibs/year or 0.5-1.3 x 10 kg/year. Using typical values
for dye usage per hide and average wastewater flow figures, it was
estimated that the actual concentration of dyes (25-50 mg/£) in a tannery
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wastewater stream may be equivalent to roughly 50-100 mg/£ of chemical
oxygen demand (COD) out of a total raw wastewater COD of 1000 to 2000 mg/£.
No useful quantitative information was obtained on the effectiveness for
dye removal of wastewater treatment processes now used in the industry or
by municipalities treating leather dyeing wastewaters. From a review of
the literature on biodegradability of dyes, it appears that biodegradation
of the dyes is unlikely to be a major mechanism for removal. It is
generally assumed that performance requirements of permanent dyes is that
they resist degradation under aerobic conditions; little is known about
their anaerobic degradation. The biodegradation of dyes is further com-
plicated by the batch mode of operation, which results in a wide fluctua-
tion in the concentration of dye in the waste stream and thus may make it
difficult to maintain adapted organisms for the degradation of dyes.
Available data on the biodegradation of dyes have been culled mostly from
the textile industry.
Removal of dyes by biosorption (perhaps by reaction with proteinaceous
cellular material) may be the major mechanism for removal of dyes in
activated sludge or trickling filter treatment plants. A similar mechanism
may be responsible for any removal that occurs in primary clarifiers where
suspended matter in the wastewater is composed of proteinaceous matter
(hair and hide scraps). Dyes may thus be disposed of with the waste
sludges.
The presence of proteins and chrome chemicals in tannery wastewater
will most likely lead to changes in the pattern of biodegradation. Depend-
ing on the complexing, the toxicology of the dyes may also vary.
The probable fate for the general case of dyes introduced into
aquatic environments is to remain in solution with sorption onto sediments
and biota eventually occurring. Chemical processes or volatilization of
dyes do not appear to be generally important fate processes. Long-term
biodegradation probably does eventually transform most dyes, but in the
absence of relevant data, such processes cannot be evaluated quantitatively.
The lack of sufficient data on the types and concentrations of dyes
and the effects of other materials present in tannery effluents on the
toxicology and degradation of the dyes, indicates that considerably more
work will be necessary to clarify the nature and seriousness of the dye
release problem from the leather tanning industry.
Future EPA research work should address the following:
• Effluent streams need to be analyzed for specific components
including dyes.
Experimental studies of the fate of dyes in various types of
existing wastewater treatment systems need to be undertaken.
• An obvious approach to solution of the potential dye release
problem is to segregate the wastewater streams that contain
dyes and treat them separately. The technical and economic
feasibility of this approach needs to be investigated.
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SECTION 3
GENERAL DESCRIPTION OF INDUSTRY
The leather industry incorporates the tanners, the manufacturers of
leather goods, and the suppliers of materials for both. The tanners and
suppliers are limited in number, so statistics are aggregated, and much
of the information is proprietary and secret, and, therefore, difficult
to obtain.
It has been estimated that 25 million hides were processed in 1976,
up from 22 million in 1975. Artificial leathers are not included in
these numbers. The number of tanneries has steadily decreased from 7,500
in 1875 to approximately 520 establishments, including firms engaged in
finishing operations on leathers tanned elsewhere.
The leather tanning and finishing industry consists of a variety of
firms. Firm ownership ranges from family-owned companies and closely
held corporations to divisions of large conglomerates. Information re-
garding operating procedures is closely held or combined with other oper-
ating information of the large corporations where segregation of data is
not possible. Many of the formulations used are proprietary, and a com-
plete breakdown as to product composition is not possible.
Most of the tanning and finishing firms are located in the North-
eastern region of the country. Historically, tanneries were located near
the source of hides, and it appears this may hold true for new plants.
The major categories of hides used today are cattle and calfskins; sheep
and lambskins; goat and kidskins; pigskins; horsehides; and deer and elk
skins.
Tanners are clustered principally in the New England states, Mid-
Atlantic states, Gloversvilie-Johnstown in New York, and the Chicago-
Milwaukee area, although others are scattered throughout the country.
Most of the establishments are family-owned. Tanners are classified as:
(1) Regular tanneries
(2) Converters
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(3) Contract tanners.
The export of hides for tanning has steadily increased, more than
doubling since 1960. In 1972, over 47 percent of the hides were exported.
These hides are processed to at least a salt-cured stage before shipment.
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SECTION 4
CHARACTERISTICS OF THE INDUSTRY
SIZE AND STRUCTURE
Of the 517 establishments in the industry in 1972, 223 had 20 or
more employees, and the industry had a total of 25,700 employees.
Table 1 shows several categories of statistics on the industry. Data
for the 1976 production of leather by U.S. tanneries have been compiled
by states. Where fewer than three units existed in any one state, the
production rates of several states are then combined (Tables 2 and 3).
The production in equivalent hides of chrome grain leather of all types
and vegetable tanned leather all utilize cattle raw material. Table 4
shows the production of equivalent sheep hides by state.
A number of plants do not process the raw hides, but do split,
chrome tan, retan, and/or finish the hides. Data on these are given in
Tables 5, 6, 7, and 8. These operations should not be counted in the
total production, since this would result in double counting.
Environmental Impacts
Processing Operations
There are four steps in processing hides: beamhouse; tanhouse;
retan, color, and fatliquor; and finishing. The beamhouse process is
not used in sheepskins or pigskin tanning and finishing, and the other
processes will vary somewhat. For example, the fleshing step, which is
performed in the beamhouse process for cattlehides, is carried out in
the tanhouse process for sheepskins. Sheepskins are not always dehaired,
but they are decreased. Essentially the processing follows the steps
outlined below.
Beamhouse Process
(1) Receiving - Nearly all cattlehides received at tanneries are
either cured green salted or brined hides, with brined hides
predominating. In a few isolated cases where transit time is
Source: "Development Document for Effluent Limitations Guidelines and
New Source Performance Standards for Leather Tanning and Finishing,"
EPA-440/l-74-016a, March 1974.
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TABLE 1. STATISTICS FOR LEATHER TANNING AND FINISHING INDUSTRY
(1972)
No. of
establishments
With 20
employ-
ees or
Total more
517 223
All employees
Number Payroll
(103) ($106)
25.7 200.0
Production workers Value
Man- added by
Number hours Wages manufacture
(103) (106) ($106) ($106)
22.1 41.9 $151.3 $368.3
Cost of
materials,
fuels, etc.
($106)
$708.0
Value of
industry
shipments
($106)
$1,059.5
Source: U.S. Department of Commerce, Census of Manufacturers. 1972.
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TABLE 2. 1976 PRODUCTION RATES IN EQUIVALENT
CHROME GRAIN CATTLE HIDES*
States
California
Tennessee
Wisconsin
Illinois
Michigan
Pennsylvania
Massachusetts
New York
New Jersey
Maine
New Hampshire
Oregon
Alaska
Washington
Colorado
Utah
Minnesota
Nebraska
Missouri
Louisiana
Florida
Virginia
Delaware
Ohio
Vermont
Maryland
TOTAL
No. of
plants
7
6
12
6
3
4
11
12
4
5
4
3
1|
2
2)
M
2
if
2/
1)
2
l)
M
1
l|
ll
Production
1,404,114
821,516
3,959,529
772,757
1,449,183
733,627
1,706,850
1,317,530
577,251
2,023,458
1,080,291
95,000
64,000
1,015,638
33,152
437,386
17,491,282
2
* One equivalent hide =» 40 ft of leather (3.72 sq.m).
Source: Tanners1 Council of America, Inc., 1977.
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TABLE 3. 1976 PRODUCTION BATES IN EQUIVALENT
VEGETABLE TANNED CATTLE HIDES*
States
No. of
Plants
Production
Kentucky
Pennsylvania
Indiana
Ohio
Virginia
West Virginia
North Carolina
Georgia
Tennessee
Texas
Oregon
TOTAL
490,750
925,043
101,841
1,000,271
535,371
3,053,276
* One equivalent hide =-40 ft leather (3.72 sq.m).
Source: Tanners' Council of America, Inc., 1977.
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TABLE 4. 1976 PRODUCTION RATES IN
EQUIVALENT SHEE? HIDES
No. of
States plants Production
Massachusetts 13
New York 16
New Hampshire 4
Maine 4
Colorado 1
New Jersey 1
Texas 1
Pennsylvania 2
Florida 1
Wisconsin 1 '
TOTAL
850
1,140
416
383
147
2,939
,592
,544
,044
,677
,429
,286
* One equivalent hide —40 ft leather (3.72 sq.m)
Source: Tanners' Council of America, Inc., 1977.
10
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TABLE 5. 1976 PRODUCTION RATES IN EQUIVALENT SPLIT
CHROME LEATHER HIDES*
States
Massachusetts
Wisconsin
California
Illinois
New Hamshire
TOTAL
No. of
plants
13
5
il
Production
1,218,183
1,394,605
957,827
3,570,615
2
* One equivalent hide =^40 ft leather (3.72 sq.m).
Source: Tanners' Council of America, Inc., 1977.
11
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TABLE 6. 1976 PRODUCTION RATES IN EQUIVALENT
BLUE HIDES**
States
No. of
plants
Production
Colorado
Arizona
Iowa
Minnesota
Missouri
New Jersey
Massachusetts
TOTAL
1 ^
1
2
1
1
1
1
2,181,000
2,181,000
* One equivalent hide =*• 40 ft leather (3.72 sq.m),
t "Blue" usually is applied to hides or skins
that have been chrome-tanned but not dyed or
fat-liquored.
Source: Tanners' Council of America, Inc., 1977.
12
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TABLE 7. 1976 PRODUCTION RATES IN EQUIVALENT
RETAN/FINISHER HIDES*"''
States
Pennsylvania
Massachusetts
New York
New Jersey
California
Tennessee
Wisconsin
TOTAL
No. of
plants
3
6
3
3
11
Production
95,000
720,000
255,000
80,000
731,254
1,881,254
* One equivalent hide =-40 ft2 leather (3/72 sq.m).
t Retan/finishers perform only the last retan
and finishing operations. The raw materials
for these operations are the chrome or vege-
table tanned hides.
Source: Tanners' Council of America, Inc., 1977.
13
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TABLE 8. 1976 PRODUCTION EQUIVALENT
FINISHED HIDES* t
States
No. of
plants
Production
Massachusetts
New York
New Jersey
Ohio
California
Tennessee
Delaware
North Carolina
New Hampshire
Wisconsin
TOTAL
22
12
10
3
1
1
2
1
1
2,550,000
1,075,000
482,356
57,981
615,000
4,780,337
* One equivalent hide = 40 ft leather (3.72 sq.m).
t Finishers work only on the surface of
tanned grain or split leather to give a
uniform finish to the leather.
Source: Tanners' Council of America, Inc., 1977.
14
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short, green hides without prior curing have been sent di-
rectly from a packer to a tannery and processed. Green hides,
after trimming and grading, are cured at the packing house by
spreading the hides, flesh side up, and covering them with salt.
This process continues until a pack of hides about 5 to 6 feet
high is obtained. A heavy layer of salt is placed over the top
layer of hides. The natural liquid of the hides dissolve a
portion of the salt to form a brine. In this process, salt is
absorbed and, by diffusion and osmosis, causes a reduction of
the moisture content in the hide. After 10 to 30 days from the
date the pack is closed, the hides are considered adequately
cured. Each hide is shaken to get rid of excess salt and is
folded individually; the hides are shipped in packs, either to
tanneries or to warehouses for storage. The size of the pack
depends on a number of variables, such as size of the packing
house, size of shipments, and the method of shipment. Brined
hides are prepared at the packing house or at a separate hide
processing facility by agitating fresh hides in a saturated
brine solution until the salt has replaced the desired amount
of moisture within the hide. In this process, hides are also
cleaned by removal of manure and other attached foreign matter.
Hides are then removed, drained, and bundled in a manner simi-
lar to that used for green salted hides. Hides may be fleshed
before or after brining. "Safety salt" is usually sprinkled
on each hide before shipment. The brining process takes two
to three days, which makes it attractive to the packer or hide
curing establishment, since there is no need to hold a large
inventory of hides. The brining process is preferred by most
tanners and packers since it tends to produce cleaner hides.
(2) Storage - Hides are normally stored at the tannery in the pack
as received. No special storage conditions are maintained in
most tanneries other than that required to keep hides at the
moisture content as received.
(3) Siding and Trimming - The usual first step in the processing
of hides from storage at the tanner is to open a folded hide
and trim it. The hides then may be cut in half along the back-
bone, which is referred to as halving or siding. Sometimes
hides are halved after unhairing or tanning.
Sides are usually palletized for transporting to the next step
in the process. Trimmings are collected for shipment to glue
or other by-product manufacturers.
15
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(4) Washing and Soaking - Sides (or in some cases whole hides)
from the siding and trimming operation are placed in vats
(with or without paddles), drums, or hide processors (con-
crete mixers with special linings) for washing and soaking
to restore moisture. Water usage is generally less with
hide processors, although some tannery people have expressed
the opinion that equivalent reduction in water use can be
achieved with drums. This process removes dirt, salt, blood,
manure, and nonfibrous proteins from the hides. The quan-
tity of such waste material varies, depending on the time
of year and the source of the hides. Depending on the type
of leather produced, additional washes (rinses) may also
occur at several other points in the tanning process, in-
cluding after liming and dehairing, after bating, after tan-
ning, and prior to and following coloring.
(5) Fleshing - Fleshing is the removal of attached adipose fatty
tissue and meat that have been left on the hide at the pack-
ing house. It is done on a fleshing machine, in which the
hide is carried through rolls and across rotating spiral
blades that remove the flesh from the hide. Cold water is
necessary to keep the fat congealed, but the fat represents
an additional waste disposal load. Most hides are fleshed
at the packing house or at a separate hide processing fa-
cility, particularly in the case of brined hides. When flesh
is removed prior to liming it is referred to as green flesh-
ing; when it is performed after liming it is referred to as
lime fleshing. In any case, fleshings are normally recovered
and sold to plants for rendering or conversion to glue. If
fleshings are properly handled, there is very little liquid
or solid waste contribution from this operation.
(6) Unhairing - Hair is removed by chemical loosening followed
by either machine pulling or chemical dissolution of the
hair. Machine removal is practiced when the processor de-
sires to recover the hair. The dissolving process is referred
to as "pulping" or "burning."
For either type of unhairing, the hides are placed in vats
(with or without paddles), drums, or hide processors with a
lime slurry to which sharpeners such as sodium sulfide and
sodium sulfhydrate are added. When the hair is to be saved,
the strength of the solution and the time in contact with
the hide is limited to that necessary to loosen the hair
sufficiently for mechanical pulling. If the hair is to be
16
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pulped, stronger solutions and/or longer time cycles are
used and the hair may be totally dissolved.
Sometimes hides are relimed to make the hide swell for easier
splitting. In a save-hair operation, flesh and hair removal
is sometimes followed by a "scudding" step to ensure removal
of hair roots and fine hairs.
The liming and unhairing process is one of the principal
contributors to the waste effluent. In a save-hair operation
with good recovery of hair, the contribution to the effluent
is substantially lower than in the pulp hair operation.
Tanhouse Process
(1) Bating - Bating is the first step in preparing the stock for
the tanning process. It may be done in either vats (with or
without paddles), drums, or hide processors. The hides are
placed in the processing equipment, which contains a solution
of ammonium salts and enzymes. The purpose of this operation
is to:
a. De-lime skins.
b. Reduce swelling.
c. Peptize fibers.
d. Remove protein degradation products.
(2) Pickling - The pickling subprocess follows the bating step
and is normally done in the same equipment. A brine and an
acid solution is used to bring the hides to an acid condition
in preparation for subsequent tanning subprocesses. In addi-
tion to conditioning the hide for receiving the tanning agent,
this step prevents precipitation of chromium salts. Pickling
is always done before the chrome tanning process and may be
done before vegetable tanning.
(3) Tanning - Nearly all cattlehides in this country are either
chrome or vegetable tanned; very little is tanned with alum
or other tanning materials.
Vegetable tanning is the older process, and is performed in
a solution containing plant extracts such as vegetable tan-
nings. This method is usually used for the heavy leathers
17
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such as sole leather, mechanical leathers, and saddle leathers.
Shoe upper leathers and other lighter leathers are usually
chrome tanned by immersion in a bath containing proprietary
mixtures of basic chromium sulfate.
Vegetable tanning is usually done in vats, principally because
it requires longer process times, while chrome tanning takes
place in drums or hide processors.
In some cases, depending on the type of leather being produced,
hides are tanned in the tanhouse and later retanned as a part
of the retan, color, fatliquor process. Where different tan-
ning agents are used in the initial and retan steps, it is re-
ferred to as combination tanning.
Waste effluents from the tanning process are substantial.
Recycle of vegetable tan solutions is becoming more common
in the industry; that which cannot be recycled may be used
for retanning or may be evaporated and recovered. Recycle and
recovery of chrome tanning solutions is also practiced at a
few locations.
(4) Splitting - The tanned hide is split to produce a grainside
piece of essentially constant thickness and a flesh-side layer.
The flesh-side layer or split can be processed separately or
sold to split tanners.
Retan. Color. Fatliquor Process
(1) Retan - Retanning is done principally to impart different
characteristics in the finished leather that would be lacking
if tanning were carried out in one step. Retanning may use
chrome, vegetable, or synthetic tanning agents, and it is
usually done in drums immediately preceding coloring and fat-
liquoring.
(2) Bleaching - Bleaching hides with sodium bicarbonate and sul-
furic acid after tanning is commonly practiced in the sole
leather industry. Bleaching is done in vats or drums.
(3) Coloring - Coloring is done in the same drums as retanning,
and may be done either before or after fatliquoring. Natural
dyes may be used, but many synthetic products are now avail-
able for this purpose.
18
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(4) Fatllquoring is the operation in which oils are added to
replace the natural oils lost in the beamhouse and tanhouse
processes and to make the leather pliable. The amount of oil
added depends on the end use of the leather.
Liquid wastes from the retan, color, and fatliquor process
may be high volume-low strength compared with the other proc-
esses.
Finishing Process
Finishing operations such as drying, wet-in coating, staking or
tacking, and plating, which follow the wet processes, provide only
minor contributions to the liquid waste. These result primarily
from cleanup of the paster drying plates and from paint spray booth
water baths. Trimmings are disposed as solid waste, and dust col-
lected may be disposed in either wet or dry form.
Raw Materials
The production of synthetic tanning materials alone in 1974 was
estimated by the U.S. International Trade Commission at 60,570,000
pounds (27,531, 818 kg) for a total value of $16,031,000. Table 9 lists
some of the manufacturers of these materials.
Many of the products used in tanning and dyeing are proprietary
formulations and a complete breakdown as to product composition is not
possible.
19
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TABLE 9. SUPPLIERS OF CHEMICALS TO THE TANNING INDUSTRY
Allied Chemical Corp.
American Cyanamid Co.
Atlas Refinery, Inc.
Barkey International Corp.
BASF Wyandotte Corp.,
Carlstadt Leather Fin.
Birko Chemical Corp.
Chemical Coating
Materials Co.
Ciba-Geigy Corporation
Eastern Industrial Oil Prod.
Co., Div. of Henkel, Inc.
Industrial Chemical Co.
Kepec Chemical Co.
Kepec Div. of Hendel, Inc.
L. H. Lincoln & Son, Inc.
Marden-Wild Corporation
Diamond Shamrock, Napco
Chemical Div.
A. J. & J. 0. Pilar, Inc.
Pilar River Plate Corp.
PPG Industries, Inc.
Prime Leather Finishers Co.
K. J. Quinn & Co., Inc.
Rohm & Haas Company
Salem Oil & Grease Co.
Sandoz Colors & Chemicals
Samuel Smidt Chemical
Corp.
Stahl Finish - Beatrice Chem.
Div. of Beatrice Foods Co.
Staley Chemical Division
Tac Tannins & Chemicals, Inc.
Arthur C. Trask Corp.
Union Carbide Corp.
Verona Dyestuff Div.,
Mobay Chem. Corp.
Wayne Chemical Corp.
Weber fie Smith, Inc.
Whittemore-Wright Co., Inc.
Eric C. Baum Assoc., Inc.
Hamblet fie Hayes Co.
The Hine Line
Hooker Chemicals fie Plastics Corp.
Industrial Commodity Corporation
International Advisory Service
Johnson fie Carlson
Korium Associates, Inc.
Norton Co.
Quaker City Hide Co.
Redi-Stac, Inc.
The Roit Corporation
Chas. H. Stehling Co.
Arthur C. Trask Corp.
USM Corp-Turner Tanning
Machinery Div.
Woburn Machine Co.
Source: Tanners' Council of America Directory, "Leather and Suppli-
ers to the Tanning Industry," July 1975.
20
-------
Suppliers of hides and skins are listed in Table 10. The hides are
usually cured green salted or brined by the supplier unless transit
time is very short.
TABLE 10. SUPPLIERS OF HIDES AND SKINS
Andrews Hides, Inc.
M. Aschheim Co., Inc.
G. Bernd Company
Booth Agencies (Boston), Inc.
Harold Braun & Co., Inc.
Harold M. Brodsky, Inc.
Cahen Trading Co., Inc.
George P. Cavanaugh, Inc.
Chilewich Corp.
Herbert A. Cohen Co.,
Denison Hide Co., Inc.
Dietrich Hide Corporation
Eden & Strass, Inc.
H. Elkan & Company, Mass.
H. Elkan & Co., 111.
George H. Elliott Company
Estra Trading Company
Evansville Technical Corp.
Paul Gallagher & Co., Inc.
Fred Gruen Co., Inc.
Hickman & Clark, Inc.
Hide Service, Inc.
J. C. Hodges & Co., Inc.
A. J. Hollander & Co., Inc.
Kaufmann Trading Corp.
The S. J. Kibler & Bros. Co.
M. Lyon & Co.
A. Mindel & Son, Inc.
Muskegon Hide Company
Packerland Packing Co., Inc.
Philadelphia Hide
Brokerage Corp.
B. N. Ritter & Co.
Rockford Hide Co.
St. Louis Hide Co.
Frank J. Schwab
Associates, Inc.
Sklut Hide & Fur Co.
Southern Tier Hide & Tallow, Inc.
Southwestern Trading Company
Spencer Foods, Inc.
Swift Fresh Meats Co. - Hide Division
Transcontinental Industrial Co., Inc.
Union Hide Company, Inc.
A. L. Webster Co.
WeCo
Western Hide Co., Inc.
G. A. Wintzer & Son Co.
Source: Tanners' Council of America Directory, "Leather and Suppliers
to the Tanning Industry," July 1975.
Cattlehides constitute the major portion of tanning in the United
States and are estimated to represent 90% of the total. Sheep and lamb,
followed by pigskin, are the next largest categories, constituting less
than 10%. A very small amount of other hides tanned include exotic hides
such as shark, seal, kangaroo, elk, and moose.
21
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A flow diagram for the tanning processes is given in Figure 1.
The chemicals used in the processing techniques are outlined in Table 11.
A new process had been proposed (Chem. and Eng. News, 1974) by USDA to
replace the controversial salt curing of the hides. USDA claims this
process not only reduces pollution but also produces quality leather at
a lower cost. Cyanides have also been eliminated according to industry
sources, and the use of trichloroethylene is decreasing. The chemicals
used in tanning listed on the EPA toxic substances list are enclosed in
boxes in Table 11 wherever they can be identified. In each step of tan-
ning, the potential exists for both water and solid wastes. Materials
that can appear in tannery wastes are listed below:
Hair Salts
Hide scraps Tanning
Flesh Soda ash
Blood Sugars and starches
Manure Oils
Dirt Fats
Salt Grease
Lime Surfactants
Soluble proteins Mineral acids
Sulfides Dyes
Amines Solvents
Chromium
Because of the nature of the industry, breakdown of figures for
total sales of tanning materials and dyes cannot be obtained without
revealing information on individual companies. Estimates of chrome
chemical and dyes usage have been made and are shown in Table 12. Es-
timates of dye consumption by the leather tanning industry differ greatly
depending on the source. Dye manufacturers estimate the market at from
3 to 7 x 106 lb dye/yr (1.36 to 3.18 x 1()6 kg/yr); the calculation
based on data from tanning industry representatives indicates use could
be as high as 30 x 106 lb dye/yr (13.6 x 106 kg). However, it is felt
that an estimate of 7 x 10^ lb (3.18 x 10^ kg) annually is more realistic
based on the number of hides dyed and the average dye loading to the
dyeing operation.
Pollutant Sources
The operating parameters (e.g., concentration, temperature) will
vary from tanner to tanner, and since much of the information on formu-
lations is proprietary, the potential loading and composition of waste
streams is difficult to assess.
22
-------
N>
BEAMHOUSE
RAW MATERIAL
Ut
RECEIVING,
TRIMMING
WASHING AND
SOAKING
FLESHING
UNHAIRING
TANHOUSE
* Nearly all hides received at tanneries
are either cured green or brined hides
0
Solid Waste .
Liquid Waste .
BATING
PICKLING
VEGETABLE
TANNING
CHROME TANNING
t?
VEGETABLE, CHROME,
OR SYNTHETIC RETAN
BLEACHING
COLORING
FATLIQUORING
FINISHING
DRYING, COATING
AND TRIMMING
SA-5619-20
FIGURE 1 FLOW DIAGRAM FOR LEATHER TANNING PROCESS
-------
TABLE 11. CHEMICALS USED IN LEATHER PROCESSING
N3
•C- Beamhouse
Process
Soaking
Liming
(Unhairing)
Bating —
Decreasing —
Disinfectants
Nonionic surfactants
Soda ash (sodium carbonate)
Sodium polysulfide (tetra)
Sodium sulfide
Calcium chloride
Sharpening agents
Lime
Proteolytic enzymes
Nonionic surfactants
Ammonium sulfate
Ammonium chloride
Formic acid and salts
Proteolytic enzymes
Nonionic surfactants
("sheepskin and pigskin
Idegreased after bating
Pickling
paodium chloride
"(sulfuric acid
. lAlkanol ethoxylate
JAlkylphenyl ethoxylate
Sodium sulfides
Sodium sulfite
Amines
Sodium hydrosulfide
Dimethylamine sulfate
Cyanides {
Alkanol ethoxylate
Alkylphenyl ethoxylate
Sodium formate
Oropon bates (Rohm & Haas Co.)
Alkanol ethoxylate
Alkylphenyl ethoxylate
Kerosene
Stoddard solvent
Nonionic surfactant —-
Anionic surfactants-
Alkanol ethoxylate
Alkylphenyl ethoxylate
Soaps
Sulfated oils and alkyl sulfates
Alkyl benzene sulfonates
Triethane (Trichlor-
ethylene and perchlor-
ethylene)
-------
TABLE 11 (Continued)
Chrome
Tanning
Tanhouse
Process
|Vegetable_
Tanning
Sodium dichromate
Sulfuric acid
Glucose or sulfur dioxide
Chromium sulfate (basic) |
Borax
Nonionic and cationic surfactants
[Sodium bichromate]
-!Oxalic acid
iSodium carbonate
jSodium hydroxide
'Potassium hydroxide
jSodium acetate, diacetate
jPotassium acetate
JSodium bicarbonate
Barks —Wattle, etc.
[•" Wood —Quebracho, etc.
i Tannins "- Fruits
' Leaves
Roots
Alkanol ethoxylate
Alkylphenyl ethoxylate
Cetyl. dimethyl benzyl ammonium chloride
Syntans
Condensation products of
formaldehyde and:
Nonformaldehyde condensed
from materials such as:
Anionic
Surfactants
Soaps
Sulfated oils and alkyl sulfates
Alkyl benzene sulfonates
Naphthalenesulfonic acids
Phenols and sulfonate phenols
Diaryl sulfones
| Urea
! Melamine
j
jJDicyandiamide
'Styrenemaleic anhydride
' Aryl dilsocyanates
i Ligninsulfonates
-------
TABLE 11 (Continued)
Retan -
Color
N>
Retan, color,
fatllquor process-
Fatliquor-
Oiling
Stuffing—
-••-Vegetable tanning process for chrome tanned hides
Formic acid
Syntans —naphthalene and phenolic synthetic
All kinds of surfactants
Hydrogen peroxide
Sodium sulfide
Hydrochloric acid
•Titanium dioxide
Ammonium bicarbonate
Dye (coal tar)
Acid dyes
Metallized dyes
Mordant dyes
Direct dyes
Developed dyes
All kinds of surfactants
Oils.
Neatsfoot
Cod
Sperm
Castor
Coconut
Palm
Wool grease
-------
TABLE 11 (Continued)
Impregnation-
Patent
leathers
Finishing
Process
I Water or oil
repellent
Solvents for -
Aqueous emulsions of acrylic copolymers - Primal Emulsions (e.g.)
Anionic or nonionic surfactants
Naphtha
Boiled linseed oil
I Stearato chromic chloride complex
-Chrome complexes of perfluro fatty acids
| Chlorinated hydrocarbons «-Triethane (e.g.)
(1,1,1 trichloroethane and trichloroethylene)
Dyestuffs
Resins
Oils
Lacquers
Varnishes
J Alcohols
; Polyols
——j Glycol - ethers
! Esters and ethers
Ketones
Nitrocellulose lacquers
Pigments in water solution containing.
some hardening protein such as
shellac or albumin
White -"titanium dioxide
Black - carbon black, bone black, iron oxide
Yellow - lead chromate, cadmium sulfide-selenides, iron oxide
Orange - lead chromate
Brown - iron oxide
Blue - phthalocyanin blue, iron blue, ultra-marine blue
Green - phthalocyanin green, chrome green
Red - cadmium sulfide-selenide, organic lakes and toners
Note: Orthodichlorobenzene is recommended for masking odors of decaying flesh.
Paradichlorobenzene is used for controlling parasites and mothproofing wool on sheepskins.
Source: SRI International.
-------
TABIJE 12. ESTIMATES OF SELECTED CHEMICAL USAGE AND LOSSES FOR
LEATHER TANNING AND FINISHING
Chrome Chemicals (Source: Dr. Robert Lollar of the Tanners' Council of America, Inc.)
2
Basis: One equivalent hide ^40 ft of leather (3.72 sq.m).
~ 25 x 106 hides to be tanned in 1976
(~ 22 x 106 hides tanned in 1975)
(25 x 106 hides 1 I 50 Ib | _ 1.25 x 1Q9 Ib
year f \hide J year
9 ,.\ ,„ „„,* 385 x 106 Ib collagen
/0.35 Ib collagen^ /1.25 x 1Q9 lb\ (0.88)
\ Ib / \ hide /
(0.06 Ib chrome oxide fixed] ^385 x 10 Ib collagen J
Ib collagen / \ year /
year
6
22 x 10 Ib chrome oxide fixed
year
23 x 10 Ib chrome oxide/year _ 33 x 10 Ib chrome oxide required (-10 million Ib lost/yr)
(0.7 of total used is fixed) ~ year (4.55 million kg)
Dyes (Calculated by two different methods)
A. Based on estimated dollar value of dye market
(Source: Personal communication with representative of dye manufacturers)
Basis: Value of dyes sold =• 15 x 10 /year
Average price of $3/lb (6.60/kg)
Consumption range 5 x 10 Ib/year
Estimated sales distribution
Acid dyes $9 million
Direct dyes $3.7 million
Basic dyes $1 million
Solvent dyes $1 million
Sulfur dyes $0.1 million
B. Based on production figures for leather and average dye used.
(Source: Personal communications with representatives of tanneries)
Basis: Percent of dye used ranges from 0.25-27» for most operations. Industry sources
suggest 0.77=, as an average of dye used per pound of hides; approximately 80%
of all hides are colored.
Therefore:
20 x 106 hides \ /50 Ib \ (0.007) 7 x 1Q6 Ib dye/yr used (3.18 x 106 kg/yr)
^—(-(((-—m^ I I „,-, I ^ ^ j
year / \ hide
Dye loss to sewer may range from 1.1 to 2.8 x 10 Ib/yr for the industry (0.5 to 1.27 kg/yr).
* Fraction of leather that is chrome tanned.
Source: See individual sources listed in table.
28
-------
Waste streams are identified below as liquid or solid, according to
the unit operation of each process. Air pollution is limited to odor
problems.
Beamhouse Process
Tanhouse Process
Retan, Color, Fat-
liquor Process
Finishing Process
Unit Operation
Siding and trimming
Washing & soaking
Fleshing
Unhairing
Bating
Pickling
Tanning
Splitting
Retan
Bleaching
Coloring
Fatliquoring
Drying, wet-in
coating tacking,
etc.
Waste Product
Liquid Solid
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Waste Streams
Materials that can appear in tannery wastes include the following:
Hair
Hide scraps
Pieces of flesh
Blood
Manure
Dirt
Salt
Lime
Soluble proteins
Sulfides
Amines
Chromium salts
Tannin
Soda ash
Sugars and starches
Oils, fats, and grease
Surface active agents
Mineral acids
Dyes
Solvents
In the beamhouse process, dirt, salt, blood, manure and nonfibrous
proteins are removed from the hides. Depending on the time of the year
and the source of the hides, there is considerable variation in the
29
-------
quantity of such wastes, and additional rinses may be necessary at sev-
eral points in the beamhouse process, depending on the type of leather
produced. Fleshings, if properly handled, produce little solid or liquid
wastes. However, the liming and unhairing steps are principal sources
of waste effluent. A save-hair operation substantially lowers the waste
effluent. The tanning process generates substantial wastes. While re-
cycling of tanning solutions is becoming more common, there is still con-
siderable waste. Evaporation and recovery is possible, and the waste
solutions can be used in retanning. Liquid wastes from the retan, color,
and fatliquor process may be high volume-low strength in comparison to the
other processes. The finishing process generates trimmings as solid wastes,
and dust in either wet or dry form. The other steps in finishing contrib-
ute only minor amounts to the liquid waste streams.
30
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SECTION 5
LEATHER DYEING
THE DYEING PROCESS
Leather dyeing is carried out on chrome or blue hides. These are
hides that have been through dehairing, washing, soaking, fleshing,
bating, and either a chrome, alum, or vegetable tanning. Generally, dye-
ing is performed in a batch mode and retan, coloring and fatliquoring
operations are all performed in sequence in the same drum without inter-
mediate steps of washing and drying.
Hides at the blue stage are placed in drums and retan formulations
are added; at the appropriate time, a designated dye formulation is added
and mixing (by rotation) is continued. Fatliquoring chemicals are added
at the prescribed time. Cycle times for this sequence can be as high as
8 hours.
Three major .types of dyes are used: acid, basic, and direct. Acid
dyes are usually azo, triarylmethane, or anthraquinone dyes with acid
substituents such as nitro-, carboxy-, or sulfonic acid. Basic dyes con-
tain free amino groups. Direct dyes are principally water-soluble salts
of sulfonic acids of azo dyes. All the dyes used by the tanning industry
are sufficiently water-soluble and have an affinity for leather; they are
protein-binding dyes. Both acid and basic dyes at the proper pH values
penetrate deeper into the hide; direct dyes are not penetrating when used
on the blue or vegetable tanned leather. Acid dyes are fixed more readily
at low pH, but penetrate deeper as the pH increases. Basic dyes, as the
name implies, are fixed at high pH values. However, basic dyes have to
be used with a vegetable tanning material or an anionic syntan to dye
chrome leather. Thus, the uptake of dye in the leather is a function of
the dye used, pH, syntans present, and the float. High float levels
(ratio of liquor to hides) may be necessary to maintain even coloring.
The end use of the leather also determines how deep the color needs to
be. For upholstery leather, for example, surface dyeing is suitable be-
cause of the light use. For shoe or garment leather, deeper penetration
of the dye is required. Blends of dyes are used in order to obtain the
exact shade desired.
31
-------
The relationship between pH and uptake of dye is shown in Figure 2.
Thus, in practice, pH adjustments may be made to assure penetration and
fixing of an acid dye, while a basic dye may be added at a later point
in the dyeing process to coprecipitate with the acid dye.
After the dyeing process, the liquid is drained off, the leather is
pressed, and all the effluent is disposed of at one time.
DATA ACQUISITION
An extensive literature search was made to collect information on
dyeing of leather, but this resulted in little data. Therefore, on-site
visits were deemed necessary. Visits were made to four tanneries, which
were chosen from a list recommended by the National Tanners' Council.
Topics for discussion were as follows:
® Number of formulations used in dyeing.
o Colors (range, predominant colors)
o Types of dyes
o Loading
e Float
e Dye/lb of leather
o Dye lost/lb of leather
o Cycle times
o Effluent characteristics.
The results of the survey are given in Table 13. Suppliers were
also contacted to determine which dyes are used by the leather industry.
From all sources, it is apparent that dye formulations are trade secrets
or handed down in family-owned businesses. In many cases, suppliers
prepare the formulation to meet a specific color demand for one of the
tannery's clients, and the tannery has no knowledge of the exact nature
of this formulation. All colors are made up on demand and several dif-
ferent colors may be used in any one day.
The quantity of dye used depends on the color, the type of leather
(split, or grain, cattle, sheep, or other), and even the mix of dyes.
Mixtures of dyes are often used to obtain a specific color. The uptake
of dye by the leather also depends on the color desired. Cycle times
are from 4 to 8 hours and only estimates are available on actual dye
32
-------
90
80
70
60
50
40
30
20
10
DIRECT DYE
ACID DYE
/ BASIC DYE
2468
pH
SOURCE: Thorstensen, T.C., Practical Leather Technology (R.E. Krieger Publishing Co.,
Huntington. New York, 1976), p. 178.
SA-5619-21
FIGURE 2 THE UPTAKE OF DYE IN LEATHER AS A FUNCTION OF pH
The acid dyes fix more at low pH. The reverse is true of the basic dyes. A
direct dye has high fixation over a wide pH range.
-------
TABLE 13. SURVEY OF THE LEATHER INDUSTRY TANNERY
U>
No. of formulations used
in dyeing
Colors (Range, predominant
colors)
Types of dyes
Loading (typical or aver-
age range)
Float
Dye/kg of leather (wet)
Dye lost/kg of leather
Cycle times
Effluent characteristics
Products
Production (average)
Source of hides
A
300, 50 active (some
spray dyed)
Brown, black, cream
white and otherst
Direct, acid, basic,
metallized
2-3/1
A
Unknown ^estimate
50 to 80% dye uptake
4 to 8 hr
0.4 mgd
Garment & shoe leather
~ 1000 hides/day
90% glove chrome-
tanned, full grain
cattle hide, some
deer, elk, sheep, goat
B
15 (all mill dyes)
Yellow, white,
natural*t
Direct, acid
(50/50)
-4/1
typical 6 kg/900
kg or 0.7%
Unknown, estimate
~90% uptake on av.
4.5 - 5 hr
~1 mgd total to
municipal sewer
Chrome tanned up-
holstery leather
10,000 actual hides/
week
Cattle
Tannery
C
60-65
Mostly browns, black,
but some of all
other colors
Acid, direct,
metallized
1-2/1
0.25 - 5%
,-
Estimate uptake
>95% on lighter
dyes
4-9 hr (av. =
7.5 hr)
No data - directly
to municipal sewer
Garment & shoe
leather
?
Cattle
D
50-70
Mostly browns, black, but some
of all other colors
Acid, direct, metallized
1-2/1
0.25 - 2% '
Estimate > 90% to 95% uptake on
i most colors except chocolate
browns
4 to 8 hrs
20 to 40 BOD except when
t < 20 F; then BOD can go up to
200. under severe winter conditions
Shoe leather mainly
3250 hides/day
Cattle,, beef
? = unknown .
* ~ 50% of output is not dyed—natural color develops during retan and fatliquoring.
t £ 10% of production is dyed a variety of red, green or blue colors.
* Violets, blues, greens, purples.
A Tan 0.25 to 0.5%, light brown 0.25 - 0.5%, med. brown 0.5 - 0.75%, dark brown 1 - 2%.
-------
uptake. Splits take up more dye and therefore more dye is added to the
batch. Estimates of uptake range from 60-95%.
TANNERY EFFLUENT CHARACTERISTICS AND TREATMENT
No data were obtained from the literature or from individual tanners
on the content of dye in the raw or treated wastewater. The literature
reports that effluents from tanneries are colored, but it has not been
verified that this results solely or in part from dyes.
Currently, wastewater from about 90% of the tanners, accounting
for approximately 80% of tannery industry production, is discharged to
municipal systems. The estimated flow from a 1,000 hide/day cattle hide
tannery (basis: 60 Ib/salted hide) based on an average of 12 tanneries
(from a study by Thorstensen Laboratory) is 1.61 x 10 jfc/day (~ 58.2 4/kg
of salted hide or 70.8 £/kg of hide). A study for the EPA (1974) is
based on several different volumes, of which an average of 1.14 x 10^ I/day
appears to us to be the 'best estimate for a 1000 hide/day tannery.
A breakdown of effluent loadings from the different operations
(Table 14) shows a variation of BOD from 22.7 to 1364 kg/day and total
suspended solids of 81.8 to 1773 kg/day. The total flow rate may vary
considerably among tanneries, and the color of the effluent will vary from
light yellow-orange to a brown color.
Effluent treatment varies with the relationship of the tannery and
its community. A small tannery's discharge in the sewer of a large com-
munity may be hardly noticeable, whereas a large tannery in a smaller
community would have a greater impact. Also, tanning operations are not
continuous but are on a batch basis. Thus, effluent composition is likely
to be quite variable if there is no equalization or holding basin.
The treatment sof effluent generally follows several steps: screen-
ing, coagulation, settling, and in some cases, an activated sludge oper-
ation. For the four tanneries visited, little was known of the exact
chemical characteristics of the effluent, and efforts are only recently
being made by EPA contractors to identify specific compounds or constit-
uents.
Tanneries are approaching the water pollution abatement problem in
different ways. On-site activiated sludge plants have been installed in
some cases and are completely owned and operated by the tannery. In other
instances, the activated sludge operation is set-up and controlled by the
tannery only until it is operational, after which it is turned over to
the city. In most instances, waste streams are still fed directly into
35
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TABLE 14. ESTIMATED EFFLUENT STREAM LOAD FROM A 1000 CATTLE HIDE/DAY TANNERY
(60 LB GREEN SALTED CATTLE HIDE)
Processing
Steps
Soaking
Unhairing
Liming
Bating
Chrome tanning
Retan, coloring and
fat liquor ing
Finishing
Flow
189
189
379
227
57
379
189
BOD
(kg /day)
409
1,364
273
22.7
10.9
54.5
81.8
Total
suspended
solids
(kg/day)
682
1,773
409
191
136
81.8
136
Total
solids
(kg/day)
5,864
4,090
1,364
545
4,090
545
218
Oil and
grease
(kg/day)
_.
273
136
545
273
45.5
273
Sulfide Chromium
(kg/day) (kg/day) pH
6.0-8.0
205 — 11.0-12.5
273 — 11.0-12.5
7.0-10.0
136 3.5-4.0
27.3 4.0-5.0
5.0-8.0
Source: Thorstensen, T. C., "Practical Leather Technology", R. E. Krieger Publishing Company, Huntington,
New York, 1976, p. 263.
-------
the municipal system without prior treatment. Because the effluent
streams can be highly colored even iri the absence of dye, the tanneries
have been unable to estimate the actual amount of dye in the stream.
Based on estimates available of the dye consumed (see Table 13) and
a water usage of 1.14 x 106 A/day, calculations were made of the concen-
tration of dye in (1) effluent streams of the entire plant operation at
high, average, and low water usage, and (2) the dyeing operation effluent
stream only. These are shown in Table 15.
DYE REMOVAL IN WASTEWATER TREATMENT
Our search of the literature and discussions with selected industry
representatives did not result in useful information on dye removal in
wastewater treatment. However, some extrapolation of the data is possible,
as described below.
A past EPA study (Thackston, 1973) reported that ". . . color in
the spent dye wastes was not removed or diminished by biological waste
treatment." The dyes used at the tannery under study were mostly acid
dyes. Some dye solution reuse was being practiced during the EPA test
program, but is not being done now. The current operations include al-
most all alum tanning and the activated sludge plant effluent is a "bour-
bon color" (Caldwell Lace, 1977). Mostly brown dyes are used at the tan-
nery, although some orange dyes are used from time to time.
Figure 3 shows hypothetical stream compositions based on some typical
data from the literature and estimates of dye concentrations. A value
of 2 mg COD/mg dye has been calculated for a widely used dye. As shown
in Figure 3, the dyes would represent less than 2% of the COD of the raw
wastewater to primary treatment. It is difficult to predict, however,
how much of the soluble COD is contributed by the dyes or what fraction
of the dye is in solution or sorbed on suspended matter.
In the previously mentioned EPA tannery study, if it is assumed that
the reported dye use is typical of the industry, the dye would be expected
to contribute from ~ 44 to 112 mg/liter of COD or 11 to 28 mg/liter of
TOC. Results of COD and TOC measurements of filtered samples of raw
waste influent to the treatment plant, primary effluent, and secondary
effluent are plotted in Figure 4 along with BOD measurements of un-
filtered samples. Much of the BOD was attributed to high suspended
solids levels in all three sampling points. The data show that soluble
organics removal is quite good and that the soluble COD level and TOC
levels possibly contributed by the dyes are low relative to the raw
37
-------
TABLE 15. CONCENTRATION OF DYES IN WASTE STREAMS
Float Ratio and Percent Dye Use
We can calculate the volume of dye waste streams and dye concentrations as
follows:
Average water use per hide in dyeing
(float of 2/1; 50#/hide
Average dye used per hide
(0.7% of a 50# hide)
Range of Uptake
Dye Required
20 x 106 hides J I 50 Ib
yr I \hide
Upper Limit of Dye Fixed
2000 Ib water/
100 Ib hides
= 0.35 Ib
[0.007 | = 7.00 x 10 Ib dye
required/yr
(Dye required, Ib)
Uptake of 75% for 10% of hides
Uptake of 85% for 90% of hides
6
(7.00 x 10)(0.75)(0.10)= 0.53 x 10
(7.00 x 106)(0.85)(0.90)= 5.36 x 106 Ib
Range of dye
fixed at upper
limit
= 5.89 x 10 Ib fixed total
Lower Limit of Dye Fixed
(7.00 x 106) (0.60) = 4.2 x 10 Ib fixed
Dye Loss Range = (7.00 x 1Q6 - 5.89 x 1Q6) to (7.00 x 1Q6 - 4,2 x 106)
= 1.1 x 10 to 2.8 x 10 Ib dye
Overall Industry Wastewater Flow Quantities
Low Flow 2 gal/lb of hide
Average Flow 6 gal/lb of hide
High Flow 20 gal/lb of hide
Concentration Range Based on Average Flow
20 x 10 hides x 50 Ib
year hide
1 x 10 Ib x 6 gal
vear Ib
1.0 x 10 /yr
6 x 10 gal (or 50 x 10 Ib H 0/yr)
year
38
-------
TABLE 15. (Continued)
6
Low Concentration 1.1 x 10 Ib dye/yr • 22 ppm
50 x 109 Ib H 0/yr
High Concentration 2.8 x 10 Ib dye/vr - 56 ppm
50 x 10s Ib H 0/yr
Dye Concentration Based on Dyeing Operation Only (Float Average of 2/1)
6
Low Concentration 1.1 x 10 Ib
50 Ib ^ f 20 x 106 hides ^ ( 2 Ib H20 \ - 560 ppm
hide
\ / 20 x 106 hides \ / 2 Ib H-,0 \
) \ yr ) ^ yr )
6
High Concentration 2.8 x 10 Ib
/20 x 106 hides \ /2 Ib H2
V yr M yr
/ 50_lb \ / 20 x 106 hides \ (2 Ib H?0 \ = 1400 ppm
I hide
Source: Development Document for Effluent Limitations Guidelines and New
Source Performance Standards for the Leather Tanning and Finishing
Point Source Category, EPA-440/l-74-016a, March 1974 and SRI Inter-
national.
39
-------
WASTEWATER (^
(DYE AND OTHER
CONTAMINANTS)
1 — , — t
•MB
(2)
• — CLARIFIER '
- SOLIDS
— »>TO DISPOSAL
1/1^
06 \
/
AIR >^
RECYCLE
WASTE 1
CELLS ?
SECONDARY TREATMENT
ACTIVATED SLUDGE
ESTIMATED STREAM CONCENTRATIONS
(1)
300,000
,, cc.|<112 mg/l
^-oo l OF COD
1,900
5,200
2,800
86
380
190
(2)
t *
1,140 (40%)*
3,800 (27%) §
1,430 (49%) i
13 (63%) §
140 (85%) §
(3)
NA
FLOW*, gal/day
DYE, mg/l
BOD, mg/l
COD, mg/l
SS, mg/l
TOTAL Cr, mg/l
GREASE, mg/l
SULFIDES, mg/l
"Based on 6 gal/lb of hide
SOURCE: Development Document for Effluent Limitations Guidelines and New Source
Performance Standards for the Leather Tannery and Finishing Point Source
Category, EPA-440/1-74-016a, March 1974.
tSince the dyes used in the leather industry are protein-binding and the waste streams have a
high level of protein (hair, flesh, hide), it is probable that much of the dyes could be removed
with the solids.
This is an average of two values from souce in (a)-
^SOURCE: E. Weisberg, 1975. Development of a Waste Treatment System for a Tannery,
AlChE Proc. of Workshop, Ind. Proc. Design on Pollution Control 7, 44-48 .
SA-5619-23
FIGURE 3 . EFFLUENT TREATMENT FOR A COMPLETE CHROME TANNERY
40
-------
Tf\2113
1400 -
1300
1200
1100
1000
„ 900
-I
Z 800
g
H-
tr
m
700
111
O
8
600
- -I-
500
400
300
200
100
SAMPLES
NOT FILTERED
(BOD5)
'Mean .
tEffluent from activated sludge
Raw Wastewater
Primary Effluent
Secondary Effluent
POSSIBLE _
DYE
COD
-.-, POSSIBLE
|||] DYE ~~
ill TOC
SAMPLES FILTERED SAMPLES FILTERED
(COD) (TOO
Possible Dye
Contribution
to COD and TOC
in Influent
SA-5619-22
FIGURE 4 . ESTIMATES OF BOD5, COD, AND TOC OF EFFLUENT STREAMS OF TANNERY
41
-------
wastewater; however, if these organics are not removed in treatment, they
could represent a significant portion of the soluble COD or TOG in the
effluent.
From a review of the literature on biodegradability of dyes included
in Appendix B to this report, it appears that biodegradation of the dyes
is unlikely to be a mechanism for removal. Because of the high concentra-
tions of other degradable organic compounds, however, it is possible to
maintain a large population of viable microorganisms. Removal of dyes
by biosorption (perhaps by reaction with proteinaceous cellular material)
may be the major mechanism for removal of the dyes in the activated sludge
unit. A similar mechanism may be responsible for any removal that occurs
in the primary treatment unit where a portion of the suspended matter is
composed of proteinaceous material (hair and hide scapes).
A large percentage of the dyes may be removed from the tannery in
combination with waste primary and secondary sludge solids.
42
-------
SECTION 6
TOXICITY AND ENVIRONMENTAL FATE OF DYES
TOXICITY OF DYES
Because no data are available on the actual extent of removal of
dyes in treatment plants (industrial or combined municipal/industrial)
from tannery wastewaters, the next logical step in the analysis is to
consider the toxicity of the dyes and the possible fate of the dyes
in the environment.
Toxicity to Acquatic Organisms
In a study sponsored by the American Dye Manufacturers Institute,
Inc (ADMI 1974), more than 50 dyes were screened for toxicity to the
single-celled green algae, Selenastrum capricornutum. and the fathead
minnow (Pimephales promelas). This is probably the most comprehensive
study yet performed in the United States to assess the potential haz-
ards of dyes to aquatic life. We understand that a considerable data
base on the environmental effects of dyeis has been developed in Japan;
however, we were unable to obtain the data in time for this report.
The ADMI study showed that the basic dyes are generally more toxic
than the acid or direct dyes. Table 16 shows that of 15 basic dyes
tested, 13 inhibited the growth of £5. capricornutum by at least 80% at
1 mg/liter in 7 days. All 5 of the basic dyes screened with minnows
had 96-hour LC50 concentrations of less than 6 mg/liter, as shown in
Table 17. Basic Green 4 and Basic Violet 1 had 96-hour LCSOs of less
than 1 mg/liter.
Some of the acid dyes exhibited relatively high toxicity to minnows,
Most toxic of all 11 dyes tested were Acid Blue 113, Acid Green 25,
Acid Black 7, and Acid Yellows 38 and 151. The 96-hour LCSOs for these
dyes ranged from 4 to 29 mg/liter.
Of the three kinds of dyes, direct dyes were the least toxic to
minnows. Of 14 direct dyes tested, none had a 96-hour LC50 less than
125 mg/liter, and most had LCSOs greater than 180 mg/liter. Direct
Blacks 38 and 80 inhibited algal growth by at least 80% at 10 mg/liter.
43
-------
TABLE 16. TOXICITY OF ACID, BASIC, AND DIRECT
DYES TO THE GREEN ALGA, SELENASTRUM CAPRICORNUTUM
Dye
Concentration producing
at least 50% inhibition
Concentration producing
at least 80% inhibition
Acid Black
Acid Blue
Acid Blue
Acid Green
Basic Blue
Basic Blue
Basic Blue
Basic Violet
Basic Violet
Basic Violet
Basic Brown
Basic Orange
Basic Orange
Basic Red
Basic Red
Basic Yellow
Basic Yellow
Basic Yellow
Basic Green
Direct Blue
Direct Blue
Direct Brown
Direct Black
Direct Black
1
25
113
25
39
9
21
1
6
10
4
2
21
2
18
11
13
37
4
6
218
95
38
80
10
10
10
10
1
1
1
1
1
10
10
1
1
1
1
1
1
1
1
10
10
10
10
10
>10
>10
>10
10
1
1
1
1
1
>10
10
1
1
1
1
1
1
1
1
>10
>10
>io
10
10
* Based on biomass.
t In me/lite
:r.
Source: American Dye Manufacturers Institute, Inc. "Dyes and the
Environment", Reports on Selected Dyes and Their Effects,
Vol 2, Sept. 1974.
44
-------
TABLE 17. TOXICITY OF ACID, BASIC, AND
DIRECT DYES TO THE FATHEAD MINNOW, PIMEPHALES PROMELAS
Dye
Acid Orange
Acid Orange
Acid Yellow
Acid Yellow
Acid Yellow
Acid Black
Acid Black
Acid Blue
Acid Blue
Acid Blue
Acid Green
Basic Brown
Basic Green
Basic Violet
Basic Yellow
Basic Blue
Direct Yellow
Direct Yellow
Direct Yellow
Direct Yellow
Direct Yellow
Direct Yellow
Direct Blue
Direct Blue
Direct Blue
Direct Red
Direct Red
Direct Brown
Direct Black
Direct Black
7
24
17
38
151
1
52
25
45
113
25
4
4
1
11
3
4
11
12
28
50
106
6
86
218
23
81
95
38
80
9 6 -Hour LC50
(mg/liter)
165
130
>180
23
29
>180
7
12
>180
4
6.2
5.6
0.12
0.047
3.2
4.0
>180
>180
125
>180
>180
>180
>180
>180
>180
>180
>180
>180
>180
>180
Source: American Dye Manufacturers Institute,
Inc., "Dyes and the Environment," Reports
on Selected Dyes and Their Effects, Vol. 2,
Sept. 1974.
45
-------
The toxicity of dyes could be related to chemical structure; how-
ever, preliminary inspection of the structures did not reveal any obvious
relationships. A more comprehensive evaluation is beyond the scope of
this project.
Effluent from the leather industry contains, among other substances,
a mixture of dyes. We estimate that prior to treatment, the effluent
contains about 22 to 56 mg/liter of total dyestuffs. It is difficult to
determine how toxic this concentration range will be to aquatic organ-
isms if it remains unchanged after treatment. The toxicity will depend
on the kinds of dyes in the mixture and the interaction among the dyes
and with other compounds in the effluent. We would expect the effluent
to be acutely toxic to aquatic organisms if the mixture contained pri-
marily basic dyes.
Before a meaningful hazard evaluation of the effluent can be made,
information would have to be obtained regarding the interactive effects
of the various dyes in the mixture. Furthermore, only acute toxicity
data have been generated to date; chronic toxicity data are also needed.
We found only a limited amount of information on the bioaccumulation
potential of dyes. We understand that this kind of information has been
developed extensively in Japan. We do not anticipate high bioaccumulation
potentials for the more polar dyes; however, since these dyes are used
in the leather industry, and leather is composed primarily of proteins,
some bioaccumulation is expected in aquatic animals.
The log P (octanol-water partition coefficient values) for some azo
dyes are relatively high, indicating high lipophilicity and therefore a
tendency to bioaccumulate. For azobenzene, 4-aminoazobenzene, 4-dimethyl-
aminoazobenzene, and 2-methyl-4-[(2-methylphenyl)azo] benzenamide, the
log P values are 3.82, 3.50, 4.58, and 4.24, respectively. Other non-
polar dyes may have a high bioaccumulation potential also.
Potential Human Health Effects
Few toxicological studies with laboratory mammals have been per-
formed on dyes specific to the leather industry; hence, no positive
conclusions can be made concerning the impact of these dyes on human
health. However, many of the dyes are aromatic amines, a class of com-
pounds comprising a large number of suspected carcinogens. Other dyes
possess diazo groups, which, if cleaved, could be converted to aromatic
amines. Still others contain aromatic nitro groups that are character-
istic of compounds with carcinogenic potential.
46
-------
Dyes that have been shown to be carcinogenic in rodents include
Basic Orange 2 and Direct Blue 14 (IARC, 1975). Information reported
in the IARC Monograph indicates that Direct Blue 53 may be carcinogenic
and teratogenic. Studies have been performed on Acid Red 2 and Acid
Orange 20, but the data are inadequate for judging the potential of
these dyes to produce cancer.
ENVIRONMENTAL FATE
There are few data on which to base an environmental fate assess-
ment for dyes introduced into waters by the leather industry. This is
due in part to the large number of dyes used, which may be complexed by
any of several metal ion species either in the dyeing plant or later in
the aquatic environment. The mixtures of dyes also contain impurities,
which adds to the complexity of the assessment.* Additionally, the in-
dustry itself has had no facilities for determining the composition of
the effluent streams. Most of the dyes used in the leather industry
are protein-binding dyes and the waste streams in a tannery containing
hair, flesh, trimmings, and other materials are high in protein and
could be expected to bind many of the dyes and thus remove them from
the stream. This process, however, would probably depend on the pH and
chemical composition of the effluent stream.
Physical Properties
No physical properties were available, in part probably because
the impurities in dyes themselves make measurements of data question-
able. From the general structure of various dyes, some of which contain
phenolic, amine, sulfonic acid, and other ionic groups, these dyes
should be moderately soluble in water; no quantitative information was
found.
Chemical Transformation
Hydrolysis
Dyes contain no common group that is subject to hydrolytic reactions.
Some dyes do contain acetylated amine groups on aromatic rings, and such
can be hydrolyzed at pH 7 at ~ 20°C with half-lives of a year or more
Ecological and Toxicological Association of the Dyestuff Manufactur-
ing Industry (ETAD), based in Switzerland, apparently has data on
the environmental fate of some dyes which may provide information.
This information is being sought.
47
-------
(Mabey and Mill, 1978). Since such reactions are slow, and only affect
a minor part of the dye structure, hydrolysis should not be considered
an important fate.
Oxidation
No information on the environmental oxidation of any dye was avail-
able.
Photolysis
Porter (1973) has conducted photolyses of dyes in neutral water
solutions. Most photolyses were performed using a carbon-arc light
source, which partially simulates the wavelengths and distribution of
the solar spectrum. The photolyses were followed by decreases in ab-
sorbance at wavelengths in the visible region. The data were plotted
by Porter as (concentration) versus (time); a straight-line plotted in
this manner indicates a zero-order kinetic law behavior. Most of the
plots were not linear, however, and showed curved lines, a few of which
may be first order if replotted as 4n (concentration) versus (time).
Photolyses were also conducted with the dyes Basic Green 4 and Direct
Blue 76 in sunlight. The photolysis data for the sunlight and carbon-
arc light experiements are summarized in Table 18.
Meaningful half-life data cannot be obtained from this data since
no coherent kinetic law behavior was found; this could have been due to
a number of reasons, including the impurity of the dyes themselves with
the compounds present reacting at different rates and possibly also with
each other and/or products. The analytical method must also be respon-
sible for the failure to get good kinetic plots for some dyes since
only the total absorbance at a wavelength was measured, which included
absorbances of the dye, impurities, and products. Moreover, since the
leather dye process often uses metal ions other than those used in the
textile processes, some photochemical rates may be different due to dif-
ferent metal ions present; Porter's work used the textile dyes. Porter
states that the carbon arc light gives photolysis rates that are at
least 10 times faster than those in sunlight. Using this rough rule of
thumb, and assuming that the photolysis rate varies linearly with light
intensity, the amount of reaction indicated in Table 18 with the car-'
bon arc lamp corresponds to about 6 months of sunlight (at 12 hours of
sunlight per day). As seen in Table 18, most dyes will be resistant
to photodegradation with half-lives of at least a few months or more.
It appears that the basic dyes are most photodegradable, the acid dyes
are of varying reactivity, and the direct dyes are the least photoreact-
ive.
48
-------
TABLE 18. PHOTOLYSIS OF DYES
Basic Dyes
Basic Violet
Basic Blue
Basic Green
Basic Green
Basic Red
Acid Dyes
Acid Red
Acid Violet
Acid Orange
Acid Red
Acid Black
Acid Violet
Acid Blue
Direct Dyes
Direct Red
Direct Green
Direct Black
Direct Blue
Direct Blue
Direct Red
Direct Brown
Direct Blue
3
9
1
4
2
1
3
10
37
52
43
40
80
6
80
76
98
83
95
86
% Reaction
after
200 hr
with
carbon
*
arc lamp
78
58
90*
92f
71
30
92
>95
>95
< 8
50
-------
Physical Transport
Volatilization
Volatilization should not be an important fate for dyes since they
should be quite soluble in water and have low vapor pressures.
Sorption by Particulate Matter and Biota
Since dyes seem to have long half-lives in relation to other en-
vironmental processes, sorption may be an important fate in spite of
the expected moderate water solubility of the general class of dyes.
Biodegradation in the Environment
The amine and phenolic groups in many of the dyes suggest a poten-
tial for facile aerobic biodegradation. However, our discussions with
Dr. Samuel Boyd of Du Pont and Dr. J. J. Porter of Clemson University
have led us to conclude that biodegradation is not rapid. One factor
influencing the biodegradation may be metal ions that complex the vari-
ous functional groups. In any event biodegradation rates are difficult
to predict for any chemical in the aquatic environment since the season
and characteristics of the discharge-receiving water will vary consider-
ably and affect its biodegrading capability.
The probable fate for dyes introduced into aquatic environments is
to remain in solution in the water system, with sorption onto sediments
and biota eventually occurring. Chemical processes or volatilization
of dyes do not appear to be important fate processes for most dyes.
Long-term biodegradation in sediment probably does eventually transform
most dyes, but the absence of relevant data prevents quantitative evalu-
ation of such processes.
50
-------
REFERENCES
American Dye Manufacturers Institute, Inc., 1974. Dyes and the Environ-
ment, Reports on Selected Dyes and Their Effects, Vol. 2.
Caldwell Lace Leather Co., 1977. Private Communications.
Environmental Protection Agency, 1974. Development Document for
Effluent Limitations Guidelines and New Source Performance Stand-
ards for the Leather Tanning and Finishing Point Source Category,
EPA-440/l-74-016a.
Etzel, J. E., and C.P.L. Grady, Jr., 1973. Effects of Dyes on the
Anaerobic Digestion of Primary Sewage Sludge. In: Dyes and the
Environment-Report on Selected Dyes and Their Effects, report for
the American Dye Manufacturers Institute, Vol. 1, Chap. VII.
Fung, D.Y.C., and R.D. Miller, 1973. Effects of Dyes on Bacterial
Growth, Appl. Microbiol. 25:793-799.
Hunter, J.V., 1973. The Effect of Dyes on Aerobic Systems. In: Dyes
and the Environment-Report on Selected Dyes and Their Effects,
report for the American Dye Manufacturers Institute, Vol. 1,
Chap. VI.
International Agency for Research on Cancer, 1975. IARC Monographs on
the Evaluation of Carcinogenic Risk of Chemicals to Man, Vol. 8,
Lyon.
Mabey, W., and T. Mill, in press. J. Phys. Chem. Ref. Data
Porter, J. J., 1973. A Study of the Photodegradation of Commercial
Dyes, PB-221483.
Porter, J. J., and E. H. Snider, 1976. Long-Term Biodegradability of
Textile Chemicals, J.W.P.C.F. 48:2198-2210.
Porter, J. J., and E. H. Snider, 1975. Thirty-Day Biodegradability of
Textile Chemicals and Dyes. In: Amer. Assoc. of Textile Chemists
and Colorists, Tech. Papers of the Nat'l. Tech. Conf., October 15,
pp. 427-36.
51
-------
Thackston, E. L., 1973. Secondary Waste Treatment for a Small Diversified
Tannery. EPA-R2-73-209.
52
-------
APPENDIX A
DYES USED IN THE LEATHER INDUSTRY
Inventory lists from two tanneries showed a variety of dyes in
stock, including several not usually listed by suppliers as being used
in the leather industry. The major suppliers are Ciba-Geigy, Sandoz,
Crompton & Knowles, Verona, GAF, BASF, American Cyanamid, and American
Color. Dyes used are acid, basic, direct, and some solvent dyes.
Metallized dyes are also used to obtain a specific product. Some of
the dyes used are given in Table 19.
53
-------
TABLE 19. SOME DYES USED IN THE LEATHER INDUSTRY
C.I. Name
Acid Black 1
CAS No.
3121-74-2 (Free)
1064-48-8 (Na+salt)
Structural Formula
Emolral Formula
C22H14N6°9S2
Remarks
Acid Black 2
U1
Acid Black 52
Acid Blue 9
8005-03-6;
12227-81-5
5610-64-0(Na salt)
11 I
Cr'''complex
10279-69-3
2650-18-2
(NH4)2 salt
>- C
- 252
C37H43N4°6S2
50420
15711
42090
Sulfonate of compounds
formed by heating nitro-
benzene, aniline and aniline
hydrochloride with Fe or Cu
at 180-200°C or using nitro-
phenol or nitrocresols in-
stead of nitrobenzene
11
2 Cr to 3 molecules of
the monoozodye
Acid Blue 83
25305-85-5
6104-59-2(Na salt)
NaO
\2"5 V°2H5
2-n- {y- e- (/- N-cHz ~\y C45'
, ~" f*^ ~" ^°5
,H.,N.07S2
42660
-------
TABLE 19. (Continued)
C.I. Same
CAS No.
Structural Formula
Empirical Formula C.I. No,
Remarks
Acid Brown 14
OH
NaO S -(' \
C26H16N4Na2°8S2 2°195
Ui
Ui
Acid Brown 354
Acid Green 35
Acid Orange 7
573-89-7
(Mono Na salt,
633-96-5)
NaO
S03Na C30H20N6Na2°12S2 20177
C16H9N5Na°8S 13361 Cr complex Is used
C16HllN2NaV 1551°
Acid Orange 8
18524-46-4;
5850-86-2
NaO.
C17H13N2NaV 1557S
Acid Orange 10 1936-15-8
-N=N-
NaO 9-
C16H10N2Na2°7S2 1623°
-------
TABLE 19. (Continued)
C.I. Name CAS No.
Acid Orange 24 1320-07-6
Structural Formula
OH
CH,
OH
Empirical Formula C.I. Ho.
C__H, _N,KaO,S 20170
Remarks
Acid Orange 61
Acid Orange 63
Acid Orange 74 10127-27-2
-N=N
Na
OH
NO,,
\ /
c
C H N NaO.S 19320 CR conplex is used
22870
SO Na
C
CH3
C16HllV°"6'
S 18745 Cr complex is used
Acid Red 1
25317-20-8
3734-67-6
HO NH • CO • CH.
/ I 3
SO Na
Acid Red 14
13613-55-3
3567-69-9
OH
NaO,
k
14720
-------
TABLE 19. (Continued)
C.I. Name CAS No. Structural Formula
OH
1
Acid Red 73 5413-75-2 /==\ /==\— = ^~"\
Na°3S-O
Empirical Formula C.I. No. Remarks
C-.,H, ,N,Na 0 S,, 27290
22 14 4 272
Acid Red 97
SO Na S°3Na
3 SO.Na
N-N —
C32H2oVa2°8S2 2289°
Ln
Acid Red 151
Acid Violet 3 1681-60-3
OH
NaO S-
- H»N -
HO OH
I 1
-N-N —
NaO S
26900
16580
Acid Yellow 1
ONa
NaO
-N00
C10H4N2Na2°8S 10316
-------
TABLE 19. (Continued)
C.I. Name
CAS No.
Structural Formula
Empirical Formula C.I. No.
Remarks
Acid Yellow 23
38-
Acid Yellow 24
NaojHx X>_N.N-CN N
v-
COONa
(NH4,Na, or Ca/2)
C10H6N2°5 10315
, orCa/2)
Acid Yellow 36
4005-68-9;
587-98-4
S03Na
C H N NaO S 13065
C'HNNa0S
co
Acid Yellow 40 6372-96-9
S03H.
~S°
1895°
Acid Yellow 42 24382-22-7
SO.Na
Acid Yellow 99 10343-58-5
C32H24N8Na2°8S2
C16H13\Na°8S
2291°
1390°
used
-------
TABLE 19. (Continued)
C. I. Name CAS Ho.
Structural Formula
Empirical Formula C.I. No.
Remarks
Acid Yellow 151 12715-61-6
Basic Blue 6 7057-57-0
H2N " °2S
OH fa
C OH
,/-N = N - C -CO-HN- a
V Yk ff
0 -
+
^^*fnm~
-Cl
C16H16\°5S
C18H13C1N2°
51175
Zinc double chloride
complex
Basic Blue 9 61-73-4
(Methylene blue)
_+_
-Cl
52015
Basic Brown 1 1052-38-6
NH
N = N -/
C18H18H8
21010
Basic Brown 4 4482-25-1
H2N-
CH
C15H24N8
21010
Basic Green 4
(Malachite
Green)
569-64-2
42000
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TABLE 19. (Continued)
C.I. Name
CAS No.
Basic Orange 1 5042-54-6
4438-16-8
Structural Formula
Empirical Formula C.I. Wo.
U320
Remarks
Basic Orange 2 493*54-5;
(Chrysoidine) 532-82-1
NH,
Cl
11270
Basic Violet 1 8004-87-3
(Methyl violet)
42535
Basic Violet 3 548-62-9
(Crystal violet)
2
N (CH3)2 I Cl
C25H30C1N3
Basic Violet 10 81-88-9
0 -f
C
I
Cl
4517°
Basic Violet 11 2390-63-8
(H5C2)2N~
- 0
c
Cl
C30H35CIN203 45175
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TABLE 19. (Continued)
C.I. Na
CAS No.
Basic Yellow 2 2465-27-2
Structural Formula
HC1 • HN - C
Empirical Formula C.I.
C17H22CW3
Remarks
Basic Yellow 37 6358-36-7
41001
HC1 • HN • C
NH_
NHn
Direct Black 38 1937-37-7
Direct Blue 1 2610-05-1
Direct Red 23 3441-14-3
Direct Red 81 2610-11-9
Direct Yellow 12 2870-32-8
H2N-(V />H»-N-<
NaO.
C34H25N91'a207S2
,N-1
30235
<3»*
NH
NaO S -
OCH3 OH NH2
N - N
SO.Na
•N
Na03Sx'
OH
S03Na
-NH-COHBI -
OH
C33H22N68a4°15S4
24410
29160
NaO.
HH-OC-
)- N
NaO.S
C2H5
C30H26N4Ha2°8S2
28160
2ft895
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Appendix B'
BIODEGRADATION OF DYES IN BIOLOGICAL TREATMENT SYSTEMS
Very little information on biodegradation is available; hence, this
appendix is primarily a discussion of the potential for dyes to biodegrade
in biological treatment systems.
Most of the dyes used in the leather industry contain sulfonic acid,
sulfonamide, phenolic, and azo and/or nitro functions. Their colors are
attributed to the characteristics of the conjugated unsaturated struc-
tures, and the dyeing characteristics are attributed to the binding ca-
pacities of these compounds to the protein in the leather, particularly
with the sulfonic acid functions. Proprietary mixtures are frequently
used to obtain the desired colors. The preparation of these dyes fre-
quently requires the use of chemicals that are considered toxic and some
of the dyes must themselves be regarded as potential toxic substances.
All living cells contain proteins in their wall membranes, and if stain-
ing takes place, it indicates combination of the pigmented product with
the protein. This may interfere with the physiological processes of the
cell. Fortunately, not all products used in coloring are toxic and some
are actually essential for physiological functions; such products include
riboflavin, vitamin A and the carotenoids, the cytochromes, the heme pig-
ments, chlorophyll, vitamin B analogues, and many other compounds.
Other dyes are useful indicators of oxidation-reduction or pH and are not
in themselves toxic. Sulfonates such as di-sodium-phenol-tetrabromophthalein
disulfonate (Bromsulfalein) have been used in protein analysis because,
under acid conditions, they readily precipitate proteins.
There are biological counterparts to the above chemicals that contain
enzymes that can reduce such chromophoric structures as azo, quinone, and
nitro compounds; however, these enzymatic reactions are highly specific
to the structures of susceptible substrates. If novel substrates are ex-
amined for biodegradability or persistence, by aerobic or anaerobic proc-
esses, periods of acclimation of a large microbial population are required.
These are complex processes that are not adequately understood, but with
some relatively simple compounds co-metabolism or diauvic growth phenomena
have been observed. Even under seemingly oxidative conditions, reductive
processes such as the transformations of R-NO_ to R-NH or R'ci to R'H
can take place. These reductions occur because of the availability of
reduced coenzymes from other oxidative processes. If the dyes used
62
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in the leather tanning industry are decomposed, the nitro and azo functions
are reduced to finally yield amino compounds. These amino compounds are
then deaminated to form ammonium ions and the nitrogen is finally oxidized
to nitrate. Aromatic nuclei are oxidized to catechols and the ring struc-
tures are subsequently ruptured to yield products that are generally more
readily metabolized.
It is also possible that residual dyes in the wastewaters from dyeing
processes may stain or combine to some extent with the organisms in an ac-
tivated sludge plant, trickle filter plant, or anaerobic digesters, at con-
centrations that do not seriously affect waste treatment organisms, and by
this means dyes can be removed from the plant effluents.
Fung and Miller (1973) studied the effects of 42 dyes on the growth
of 30 bacteria in solid media, and it is apparent that the gram-negative
bacteria they used were more resistant that the gram-positive bacteria.
Biodegradation studies conducted in other laboratories and in SRI labora-
tories have resulted in the development of enrichment cultures that con-
tain mostly gram-negative bacteria, but gram-positive bacteria and fungi
have also been found to be excellent degraders or transformers of some
compounds. One of the problems the tanneries have to cope with is the
sporadic use of some dyes, and if extensive acclimation periods are nec-
essary to develop biodegrading flora to degrade the dyes, the degrading
organisms are lost by microbial interaction and a fresh charge of a dye
may not be decomposed. If the dye concentration is initia/lly too high to
facilitate the development of the necessary flora, the dye might even des-
troy some of the existing organisms. If too much readily metabolizable
material (e.g., proteins, particles, fats and oils) is present in the in-
fluent to the treatment plant after the customary pretreatments, the resi-
dence time of the dye in the treatment plant may not be sufficiently long
if a diauxic phenomenon exists, or the dye may be recalcitrant by custom-
ary parameters.
The shortcomings of the 5-day BOD test are clearly discussed in pub-
lications by Porter and Snider (1975, 1976). However, other factors may
be involved because of the presence of fats, oils, surfactants, proteins
and peptides that are present in larger amounts and are more rapidly me-
tabolized than the dyes.
J. V. Hunter (1973) studied the effect of dyes on aerobic waste treatr
ment systems and concluded that 17 out of 46 dyes inhibited action of ac-
tivated sludge in aerobic processes conducted in Warburg flasks with ac-
tivated sludge, river water organic matter, and the dyes. This report
did not imply that the processes had ceased, but it indicated that some
activity continued at a reduced rate. Small samples and relatively high
levels of dyes (25 mg/liter) were used in this work. With some dyes,
63
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inhibition of digestion was observed only with sewage-dye-activated-
sludge. In the same publication, Etzel and Grady (1973) reported that two
anthraquinone dyes had strong enough activity to cause failures in labora-
tory scale anaerobic digesters. The concentration of dye added was 150 mg/
liter . The dispersing agent Tamo-SN also had a similar acute effect.
Other dyes showed some effects, but these were not sufficiently serious
to cause disruption of the anaerobic processes. Decolorization was ob-
served with all but two dyes.
In an EPA report on leather tanning and finishing and numerous other
publications, reference is made to the use of activated carbon to remove
residual dyes and the problems of the application of such adsorption
processes to tannery-plant effluents containing other products that inter-
fere with color removal. If tannery effluents with dye are highly diluted
with municipal wastewaters, it is possible that they are eliminated by
adsorption on activated sludge and may escape attention because of this
high dilution.
The current literature reviewed in this brief survey is too indefinite
to form a basis for a conclusion on the best procedures to handle dyes
present in tannery wastes. Longer biological treatment periods, or re-
cycling trickling filter units for specific dyes may improve some of the
current biological treatment facilities. It may also be necessary to
treat effluents more extensively or to change some processes or chemicals
before activated carbon can be economically and efficiently used. A more
extensive literature and field analysis is necessary and experimental
verification of control technology will undoubtedly be required.
64
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
EPA-600/2-78-215
2.
3. RECIPIENT'S ACCESSION-NO.
TITLE AND SUBTITLE
Assessment of Potential Toxic Releases From Leather
Industry Dyeing Operations
5. REPORT DATE
October 1978 issuing date
6. PERFORMING ORGANIZATION CODE
AUTHOR(S)
S.B. Radding, I.E. Jones, W.R. Matey, D. H. Liu,
N. Bohonos
8. PERFORMING ORGANIZATION REPORT NO.
PERFORMING ORGANIZATION NAME AND ADDRESS
SRI International
333 Ravenswood Avenue
Menlo Park, CA 9U025
10. PROGRAM ELEMENT NO.
1BB610
11. CONTRACT/GRANT NO.
R 80^6^2-01-2
2. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Lab.
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
- Cinn, OH
13. TYPE OF REPORT AND PERIOD COVERED
Final Report 6/77 - V78
14. SPONSORING AGENCY CODE
EPA/600/12
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This study focused on the organic dyes Released to the environment in
the wastewaters from leather dyeing operations. Basically, three types of
dyes—acid, basic, and direct—are used, although the number of different
dyes are well over 50, and the number of formulations used at a single
tannery over the period of several years can be greater than 100. Tannery
wastewaters are complex mixtures which for the most part are discharged
directly into municipal sewers. The character of this discharge will
differ hourly depending on the operation performed since tanning operations
are batch mode. Estimates based on information from suppliers and tanners
were made of the probable discharge of dyes in wastewater. The literature
search revealed little or no data on the fate of these dyes in the environ-
ment. From consideration of the physical and chemical properties of the
dyes, biosorption (complexing with proteinaceous material) appears to be
the most likely mechanism for removal of dyes in biological wastewater
treatment systems.
This report covers the period 1 June 1977 to 28 April 1978 and was
completed as of 28 April 1978.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
COS AT I Field/Group
Industrial Wastes, Wastewater,
Toxicity, Organic Compounds,
Dyeing
Leather Tanning
13B
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport)
Unclassified
73
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
U. S. GOVERNMENT PRINTING OFFICE: 1978-657-060/1512 Region No. 5-11
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