40/1-74-016-a
Development Document for Effluent Limitations Guidelines
^'Mttd New Source Performance Standards for the
LEATHER TANNING
AW FINISHING
Source Category
MARCH 1974
U.S. ENVIRONMENTAL PROTECTION AGENCY
Washington, D.C. 20460
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DEVELOPMENT DOCUMENT
for
EFFLUENT LIMITATIONS GUIDELINES
and
NEW SOURCE PERFORMANCE STANDARDS
for the
LEATHER TANNING AND FINISHING
POINT SOURCE CATEGORY
Russell E. Train
Administrator
Roger Strelow
Acting Assistant Administrator for Air & Water Programs
Allen Cywin
Director, Effluent Guidelines Division
James D. Gallup
Project Officer
1974
Effluent Guidelines Division
Office of Air and Water Programs
U.S. Environmental Protection Agency
Washington, D.C. 20460
U.S. Environmental Protection Agency
Region 5 Library (PL-12J)
77 West Jackson Blvd., 12th Floor
Chicago, IL 60604-3590
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $1.95
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ABSTRACT
This document presents the findings of an extensive study of the
leather tanning and finishing industry for the purpose of
developing effluent limitations guidelines, standards of
performance, and pretreatment standards for the industry, to
implement Sections 304, 306, and 307 of the Federal Water
Pollution Control Act, as amended.
Effluent limitations guidelines contained herein set forth the
degree of effluent reduction attainable through the application
of the best practicable control technology currently available
and the degree of effluent reduction attainable through the
application of the best available technology economically
achievable; these levels of treatment must be achieved by
existing sources by July 1, 1977, and July 1, 1983, respectively.
The standards of performance for new sources contained herein set
forth the degree of effluent reduction which is achievable
through the application of the best available demonstrated
control technology.
The proposed regulations for July 1, 1977, and for new source
performance standards are based on preliminary screening,
equalization and primary sedimentation, secondary biological
treatment and chrome recycle.
The recommended technology for July 1, 1983, is preliminary
screening, equalization and primary sedimentation, secondary
biological treatment and chrome recycle plus sulfide oxidation,
nitrification and denitrification and mixed-media filtration.
Supportive data and rationale for development of the proposed
effluent limitations guidelines and standards of performance are
contained in this report.
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CONTENTS
Section
I CONCLUSIONS 1
II RECOMMENDATIONS 3
III INTRODUCTION 7
Scope 7
Previous Study 7
Industry Trends 8
IV INDUSTRY CATEGORIZATION 11
Standard Manufacturing Processes n
Cattlehide Tannery Processes 12
Sheepskin Tannery Processes 18
Pigskin Tannery Processes 22
Classification System 25
Categorization System 27
V WASTE CHARACTERIZATION 31
General 31
Waste Constituents 32
Unit Waste Quantities 32
Individual Process Contributions 33
to the Waste
Wash and Soak 34
Degreasing 35
Unhairing 35
Bating 36
Pickling 36
Tanning 36
Retan, Color, Fatliquor 37
Finishing 38
Total Plant Liquid Waste 38
Characteristics of Total Plant 42
Waste Flows
VI SELECTION OF POLLUTANT PARAMETERS 47
Waste water Parameters of Major 47
Significance
Rationale for Selection of Major 47
Parameters
Biochemical Oxygen Demand 47
ill
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CONTENTS (Cont«d)
Section
Total Chromium 48
Grease 48
Sulfide 48
Suspended Solids 49
Total Kjeldahl Nitrogen 50
Fecal Coliforms 50
PH 50
Rationale for Selection of Minor 52
Parameters
Chemical Oxygen Demand 52
Total solids 52
Ammonia Nitrogen 52
Color 52
VII CONTROL AND TREATMENT TECHNOLOGY 55
General 55
Basis of Tannery Waste Treatment 56
In-Process Methods of Reducing Wastes 58
Preliminary Treatment 62
Screening 64
Equalization 64
Plain Sedimentation 64
Chemical Treatment - Coagulation 68
and Sedimentation
Chemical Treatment - Carbonation 70
pH Adjustment 71
Sludge Handling and Disposal 71
Preliminary Treatment - Facility 73
Requirements
Secondary Biological Treatment 74
Major Reduction of BOD5 and suspended Solids74
Combined Municipal - Tannery Treatment
Systems 74
On-Site Treatment - Trickling Filter
Systems 78
On-Site Treatment - Aerobic Lagoon
Systems 79
Or.-Site Treatment - Aerobic - Anaerobic
Lagoon Systems 82
On-Site Treatment - Activated sludge
Systems 87
Practical Biological Systems 92
Polishing Systems for Biological 95
Treatment
Major Reduction of All Forms of Nitrogen 97
Major Removal of All Waste Constitutents TOO
Freezing 101
Evaporation 101
Electrodialysis 101
Ion Exchange 102
Reverse osmosis 102
iv
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CONTENTS (Cont•d)
Section
VIII COST, ENERGY, AND NON-WATER QUALITY ASPECTS 1Q7
Cost and Reduction Benefits of Alternative
Treatment and control Technologies 107
Basis of Economic Analysis 107
Effluent Reduction Subcategory 1 116
Impact of Waste Treatment Alternatives
on Finished Product Price 117
Alternative Treatment Systems 118
Related Energy Requirements of Alternative
Treatment and control Technology 121
Non-Water Quality Aspects of Alternative
Treatment and control Technology 122
Air Pollution 122
Solid Waste Disposal 122
IX BEST PRACTICABLE CONTROL TECHNOLOGY CURRENTLY
AVAILABLE GUIDELINES AND LIMITATIONS 125
General 125
Effluent Reduction Attainable 126
Best Practicable Control Technology 128
Currently Available
Rationale for Selection of BPCTCA 128
Total cost of Achieving Effluent 128
Reduction
Age and Size of Equipment and
Facilities 129
Engineering Aspects of Control
Techniques 129
Processes Employed 129
Process Changes 129
Non-Water Quality Environmental
Impact 130
X BEST AVAILABLE TECHNOLOGY ECONOMICALLY
ACHIEVABLE - GUIDELINES AND LIMITATIONS 131
General 131
Effluent Reduction Attainable 132
Best Available Technology Economically
Achievable 134
Rationale for Selection of BATEA 135
Total Cost of Achieving Effluent
Reduction 135
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CONTENTS (Cont»d)
on
Age and Size of Equipment and Facilities 136
Processes Employed 136
Engineering Aspects of Control Techniques 136
Process changes 136
Non-water Quality Environmental Impact 136
XI NEW SOURCE PERFORMANCE STANDARDS 137
General 137
Improved In-plant Process control 137
New Source Performance Standards 138
Pretreatment Requirements 138
XII ACKNOWLEDGEMENTS' 139
XllI REFERENCES 141
XIV GLOSSARY 147
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TABLES
Number Titj.e
1 Best Practicable Effluent Limitation Guide-
lines July 1, 1977 4
2 Best Available Effluent Limitation Guidelines
July 1, 1983 5
3 Classification System 26
H Principal Processes of Subcategories 29
5 Hide Curing 34
6 Wastewater Quantities 41
7 Raw Wastewater Characteristics by category 44
8 Plain sedimentation 66
9 Chemical Treatment 69
10 Combined Municipal - Tannery Treatment Systems 75
11 Trickling Filter Systems 80
12 Aerobic Lagoon Systems 81
13 Aerobic - Anaerobic Systems 84
14 Activated Sludge Systems 88
15 Estimated Waste Treatment Cost for Sub-
category 1 110
16 Estimated Waste Treatment Cost for Sub-
category 2 111
17 Estimated Waste Treatment Cost for Sub-
category 3 112
18 Estimated Waste Treatment Cost for Sub-
category 4 113
19 Estimated Waste Treatment Cost for Sub-
category 5 114
20 Estimated Waste Treatment Cost for Sub-
category 6 115
21 Estimated Industry Investment to Meet BPCTCA
Effluent Limitations 119
22 Estimated Industry Investment to Meet BACTEA
Effluent Limitations 120
23 Best Practicable Effluent Limitation Guide-
lines - July 1, 1977 127
2U Best Available Effluent Limitation Guide-
lines - July 1, 1983 133
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FIGURES
Number Title
1 Flow Diagram - Typical Cattlehide Tannery
2 Flow Diagram - Typical Sheepskin Tannery
3 Flow Diagram - Typical Pigskin Tannery
14 Category System
5 Wastewater Flow vs. Tannery Production for
Category 1
6 Tannery Production vs. Relative Cumulative
Frequency for Category 1
gage
13
21
24
28
40
46
viii
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SECTION I
CONCLUSIONS
For purposes of establishing effluent limitations guidelines and
standards of performance, the leather tanning and finishing
industry has been divided into six major subcategories. The
following tabulation is a capsule summary of these subcategories.
INDUSTRY SUBCATEGORIES
Primary Processes
Leather
SubcateqorY Beamhouse Tanning Finishing
1 Pulp hair Chrome Yes
2 Save hair Chrome Yes
3 Save hair Vegetable Yes
U Hair previously removed Previously tanned Yes
5 Hair previously removed Chrome Yes
or retained
6 Pulp or save hair Chrome or no tanning No
These subcategories have been derived principally by similarities
in process and waste loads. Such factors as age of plant,
climate, and waste control technologies favor segmentation of the
industry into these six subcategories. However, the facility's
size reguired an exception within the subcategorization.
Different limitations were established for plants within the six
subcategories due to unequal economic impacts created by
diseconomies of scale. Currently, waste from about 60 percent of
the tanneries (and approximately 60 percent of the production) is
discharged to municipal sewer systems, while the remainder is
discharged directly to surface waters.
Compared with other industries, waste treatment facilities for
those plants in the leather tanning and finishing industry
discharging directly to rivers or streams are severely lacking.
There are no exemplary waste treatment plants handling only
tannery waste.
It is concluded that the technology is available to effect
considerable improvement in waste discharges with major removal
of BOD5 and suspended solids by July 1, 1977. The estimated
capital cost of achieving effluent limitations (the best
practicable control technology currently available) by tanneries
discharging to receiving waters is $45.8 million (August, 1971,
price levels). Total annual costs (including depreciation.
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interest, operation, and maintenance) for pollution control will
increase finished product costs from about 1.7 to H.U percent
(August, 1971, prices) depending on industrial subcategory.
It is further concluded that by July 1, 1983, implementation of
treatment facilities to effect further removal of BOD and SS as
well as major removal of sulfide and nitrogen (the best available
control technology economically achievable) will be required for
facilities discharging directly to surface waters. Total
capital investment for achieving 1983 effluent limitations is
estimated at $61.0 million (August, 1971, prices). This
represents an additional $15.2 million investment over BPCTCA.
Total annual costs for the best available control technology
economically achievable will increase finished product prices
from about 0.6 to 1.4 percent (August 1971, prices) for differing
subcategories. The overall cost of both best practicable and
best available control technology is estimated to increase final
product costs from 2.3 to 5.8. percent for various
subcategories.
Some economies may be achieved during implementation of the best
available control technology economically achievable waste
treatment facilities if the industry can find a substitute for
ammonia compounds used in the bate process. However, organic
nitrogen from processing hides will still require some degree of
nitrification-denitrification facilities.
Standards of performance for new sources are equivalent to the
best practicable control technology currently available
requirements.
Complete reuse of treated effluent cannot be achieved without re-
moval of dissolved solids. Methods for removing dissolved solids
and subsequent disposing of the concentrated brines are not
sufficiently defined technically or economically to enable
implementation without a great degree of risk. In addition, a
further complicating factor is imposed if dissolved solids
removal becomes a requirement for those tanneries providing only
pretreatment for discharge to a municipal system. Since an
extremely good quality water is necessary as an influent to
processes capable of dissolved solids removal, all tanneries,
regardless of discharge point, would require installation of
major biological treatment facilities in addition to that
required for dissolved solids removal.
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SECTION II
RECOMMENDATIONS
Presented herein are the recommended effluent limitations
guidelines for the leather tanning and finishing industry. The
proposed basic levels of waste constituents in the following
tabulations are recommended to be the average values based on
production data and analyses of 24-hour composite samples
collected during any 30-day period. However, the pH should never
exceed values shown as measured by grab or composite samples.
Due to process upsets, emergencies such as a power failure and
other such occurrences, there are times when these average values
may be exceeded. The daily maximum allowable level proposed for
all parameters except pH is two times the basic values presented
here. Such a maximum allowable level would be checked by com-
posite samples collected at any time.
Application of the best practicable control technology currently
available, as shown in Table 1, results in the effluent
limitations guidelines to be met by July 1, 1977, for tanneries
discharging directly to surface waters. Additional allocations
of BOD5 and TSS are allowed tanners with a production less than
17,000~"kg hide per day.
Application of the best available control technology economically
achievable results in the effluent limitations guidelines shown
in Table 2 for tanneries discharging directly to surface waters.
These limitations are to be achieved by July 1, 1983.
Effluent limitations guidelines for new tanneries yet to be built
(new source performance standards) are the same as for the best
practicable control technology currently available.
The requirement to remove dissolved solids by 1983 is not
recommended. The technology for widespread removal of dissolved
salts and disposal of concentrated brines is not well defined.
Extensive research efforts should be made by the industry to find
a substitute for salt used in hide curing, which is a major
contributor of the dissolved solids.
The technologies to which the above limitations and standards are
based assume extensive water and chemical conservation within the
industry and properly designed and operated waste treatment
facilities.
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TABLE 1
BEST PRACTICABLE EFFLUENT LIMITATIONS
MAXIMUM THIRTY DAY AVERAGE
(July 1, 1977)
SUBCATEGORY
PARAMETER (1)
BOD5_
TOTAL CHROMIUM
OIL & GREASE
TSS
kg/1000
1 2
4.0
0.10
0.75
5.0
4.6
0.12
0.90
5.8
kg hide
3
3.8
0.05
0.75
4.8
(lb/1000
4
1.6
0.10
0.25
2.0
Ib hide)
5
4.8
0.06
0.90
6.0
6
2.8
0.10
0.35
3.4
(1) For all subcategories pH should range between 6.0 and 9.0 at any time.
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TABLE 2
BEST AVAILABLE EFFLUENT LIMITATIONS
(July 1, 1983)
SUBCATEGORY
PARAMETER(l) kg/1000 kg hide (lb/1000 Ib hide)
123456
BOD_5 1.40 1.60 1.30 0.50 1.60 0.70
TOTAL CHROMIUM 0.05 0.06 0.05 0.02 0.06 0.03
OIL & GREASE 0.53 0.63 0.50 0.24 0.63 0.34
SULFIDE 0.005 0.006 0.005 0.002 0.006 0.003
TSS 1.5 1.8 1.4 0.6 1.8 0.8
TKN 0.27 0.32 0.25 0.10 0.31 0.14
(1) For all subcategories pH should range between 6.0 and
9.0 at any time
For all subcategories Most Probable Number (MPN) of
Fecal Coliforms should not exceed 400 counts per 100 ml
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SECTION III
INTRODUCTION
The 1972 Amendments to the Federal Water Pollution Control Act
require the U. S. Environmental Protection Agency to establish
effluent limitations which may be achieved by point discharge
sources into navigable waters. For existing waste sources, the
Act requires application of the best practicable control
technology currently available by July 1,1977, and application of
the best available control technology economically achievable by
July 1, 1983. For new waste sources, the best available
demonstrated control technology must be applied.
The broad objectives of this study are to establish the control
and treatment technology available and to present suggested
effluent limitation guidelines and standards of performance
applicable to the leather tanning and finishing industry. The
principal elements of the study are as follows:
1. Establish the various subcategories within the leather
tanning and finishing industry subject to effluent
limitations and standards of performance.
2. Characterize wastes from each major subcategory of the
industry by assessing flows and constituents in the
waste water.
3. Establish existing and potential control and treatment
technologies applicable to each subcategory of the
industry. Such technology includes in-plant controls,
end-of-process control and treatment, and pretreatment
prior to discharge to a publicly-owned waste water
system.
4. Outline the best practicable control technology
currently available and the best available treatment technology
economically achievable for establishing effluent limitation
guidelines.
5. Prepare a report summarizing control and treatment
technology, together with suggested effluent limitations
guidelines and appropriate cost information.
Previous Study
A principal source of information for this investigation is the
"Industrial Waste Study of the Leather Tanning and Finishing
Industry" conducted for the Water Quality Office, U. S.
Environmental Protection Agency, by Stanley consultants (October,
1971). Relevant data from that study are included herein.
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Industry Trends
The number of tanneries in the U. S. has steadily decreased from
around 7,500 operating in 1865 to approximately 1,000 by the year
1900 (1) . The number has continued to decrease from the turn of
the century to about 200 to 210 tanneries (wet process) in
operation at the present time. Another 225 to 260 firms are
engaged in finishing operations (essentially dry process) on
leather tanned at seme other location.
Tanneries are principally clustered in the New England and Mid—
Atlantic states, Chicago-Milwaukee area, and Gloversville-
Johnstown area in New York. Others are scattered throughout the
U. S.
Since about I960, several significant developments have taken
place in the domestic tanning industry. Most noteworthy is the
increased export of cattlehides to countries for production of
leather. In 1972, hides from over 47 percent of the 36.5 million
cattle slaughtered in the U. S. went to foreign tanners (2).
Since 1960, export of hides has more than doubled, while domestic
tanning has reduced slightly. The increased number of export
cattlehides has mainly gone to Japan. Lower labor costs seem to
enable foreign countries to compete in the U. S. leather and
leather products industry; hence, the greater demand for hides.
Exporting hides for tanning has also had a pronounced effect on
the finished product market. For example, in 1960, imported
shoes accounted for about 4.3 percent of the U. S. market,
contrasted to over 36 percent of the 1972 market (2). With the
increased import of shoes, domestic tannage has been used
proportionately more for clothing and other uses.
Other changes in the leather industry include increasing use of
leather substitutes, such as plastic, which have absorbed a
larger portion of the total market. Experimentation with other
synthetic products may yield further competitive materials.
From an economic standpoint, the domestic leather tanning and
finishing industry has recently felt a squeeze from both ends--
raw material and finished product. Greater foreign demand for
cattlehides has resulted in part from a change in a restrictive
hide export policy by other hide producing nations. This has
recently caused the price of raw cattlehides to increase greatly.
Heavy native steer hides have ranged in price from 8.3 to 20.3
cents per pound in the period 1960-71. Average price in 1971 was
14.4 cents per pound. In 1972 prices increased to 42.4 cents in
August, with an average for the year of 29.7 cents per pound.
These raw product prices have now fallen to about twice those in
1971. In addition, competition from foreign countries such as
Japan, Italy, and Spain in the finished leather products market
has reduced the potential revenue from domestic leather firms.
Cattlehides constitute the bulk of the tanning done in the U. S.,
representing about 90 percent of the estimated pounds of hides
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tanned. Sheep and lamb represent about the next largest volume.
Pigskin production is estimated to be the third largest
production volume in the U. S. Since I960, domestic tanning of
cattlehides, sheepskins, and lambskins has trended slightly
downward.
Other types of skins or hides processed in the U. S. include
goat, kid, hairsheep, and horse. All of these tanning volumes
have fallen significantly since 1960. Various other skins tanned
in the U. S. on a very limited basis include deer, elk, moose,
antelope, and rabbit, as well as rare skins such as alligator,
crocodile, seal, shark, and kangaroo.
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SECTION IV
INDUSTRY CATEGORIZATION
Standard Manufacturing Processes
Tanning is the process of converting animal skin into leather.
The skin is divided into three layers: flesh, derma or corium,
and epidermis. The epidermal and corium layers constitute the
leather-making portion of the skins or hides, and consist mainly
of the protein collagen after undesirable proteins are removed.
Tanning is essentially the reaction of collagen fibers with
tannin, chromium, alum, or other tanning agents with the
resulting formation of leather.
A major factor affecting waste production in the leather tanning
and finishing industry is the type of manufacturing process used
to convert the various types of animal skins to the tanned and
finished leather. This variance is recognized in the
classification system used to describe the industry.
The process of tanning originally developed as an art many
centuries ago, but has in recent times been modified by
application of scientific principles. As in any industry, the
approach to production of a suitable leather by the average
tannery relies a great deal on past experience. In a typical
process, such as unhairing, the concentration of lime and
sharpeners (such as sodium sulfide and sodium sulfhydrate),
temperature, and processing time are interrelated. As in most
chemical reactions, chemical concentrations and/or temperature
may be increased to decrease the processing period. Tanners vary
process conditions to control the quality of the finished
product. Therefore, there is a significant amount of variance in
processing techniques, even between two tanners producing the
same finished product, to satisfy individual product needs.
In this study, a manufacturing process is defined as a single
step in the complete manufacturing operation where alternative
steps may result in significantly different waste
characteristics. A process can consist of one or a series of
sub-processes. In any defined process, sub-processes would
remain the same. The industry can best be described and analyzed
on this manufacturing process concept basis. This allows for the
variance of processes used among plants. with this approach,
waste loads and effluent requirements can be more readily
described.
For purposes of characterizing waste loads, there are the
following standard applicable processes: beamhouse; tanhouse;
retan, color, and fatliquor; and finishing. Chemicals such as
lime, sodium sulfide, sodium sulfhydrate, basic chromium sulfate,
vegetable compounds, mineral acids, and sodium chloride are
employed with the various processes.
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The discussion and description of manufacturing processes which
follow are based upon the three major hide or skin types produced
in the U. S.: cattlehides, sheepskins, and pigskins. The pro-
cesses and sub-processes discussed herein represent an inventory
of those most typical of the entire industry. Process
descriptions which follow have been kept brief, since more
detailed information is readily available from the literature (3)
<<*).
Cattlehide Tannery Processes
There are four processes in a typical cattlehide tannery which
contribute waste loads:
1. Beamhouse.
2. Tanhouse.
3. Retan, color, and fatliquor.
4. Finishing.
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FLOW DIAGRAM
TYPICAL CATTLEHIDE TANNERY
LMEND
HIDES ABO LEATHER ^^—M—
noaSS MT£JI)*L» —— —
LIQUID HASTES
RETW-COLW-FATLIQUOfi
W1STE EFFLUEIT (CLEtl-UFILV)
I Lsruia _
|_S_OU_D_HASTE_[SIUVmOS)
WASTE EFFLUENT
RETAN- COLOR •FfcTLIQUQR
(ALTERNATE)
FROM TiNHOUSE
COLOR
•ATLIQUOR
FIGURE 1
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These processes are shown schematically on Figure 1. There are
alternate processes for each of the first three basic processes
which produce significantly different waste characteristics.
Sub-processes and the operations which take place within each
process are described as follows:
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 short, green hides without prior
curing have been sent directly 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 with salt. Another layer of hides is
placed over the salted hides, again flesh side up, and
covered with salt. This process continues until a pack
of hides about 5 to 6 feet high results. 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 then has the excess salt
shaken off, is folded individually, and 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 similar
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
since it tends to produce cleaner hides. Increased use
of brined hides in recent years demonstrates these
preferences by both packer and tanner.
2. Storage - Hides are normally stored at the tannery in
the pack as received. No special storage conditions are
14
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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 tannery is to
open a folded hide and trim it. The hides then may be
cut in half along the backbone, 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.
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 (concrete 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.
In this process dirt, salt, blood, manure, and non-
fibrous proteins are removed from the hides. There is
considerable variation in the quantity of such waste
material, 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, including after liming and
dehairing, after bating, after tanning, and prior to and
following coloring.
5. Fleshing - Fleshing is the removal of attached adipose
fatty tissue and meat which have been left on the hide
at the packing house. It is done on a fleshing machine,
in which the hide is carried through rolls and across
rotating spiral blades which 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 facility, particularly in the
case of brined hides. When flesh is removed prior to
liming it is referred to as green fleshing; 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.
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6, Unhairing - Hair is removed by chemical loosening
followed by either machine pulling or chemically
dissolving the hair. Machine removal is practiced where
it is desired 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 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 sub-process follows the bating
step and is normally done in the same equipment. A
brine and acid solution is used to bring the hides to an
acid condition in preparation for subsequent tanning
sub-process. In addition to conditioning the hide for
receiving the tanning agent, it prevents precipitation
of chromium salts.
Pickling is always done before the chrome tanning
process and may be done before vegetable tanning.
16
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3- Terming - 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 tannins. This method is usually used for the
heavy leathers 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
due to longer process times, while chrome tanning takes
place in drums or hide processors.
In some cases, depending on 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 tanning agents are used in the
initial and retan steps, it is referred 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 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 grain-
side 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 :
~ Retanning is done principally to impart
different characteristics in the finished leather which
it would lack 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 fatliquoring.
2. Bleaching - Bleaching hides with sodium bicarbonate and
sulfuric 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 available for this purpose.
17
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**• E§£liai32EiIi2 ~ Fatliquoring 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 processes.
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 primarily from cleanup of
the paster drying plates and from paint spray booth water baths.
Trimmings are disposed as solid waste, and dust collected may be
disposed in either wet or dry form.
Sheepskin Tannery^Processes
Sheepskin tanning processes are somewhat similar to pigskin
tanning in that generally there is no beamhouse process and
degreasing is required. The three major processes are:
1. Tanhouse.
2. Retan, color, and fatliquor.
3. Finishing.
These processes and the sub-processes which take place during
manufacturing are shown on Figure 2 and are described as follows:
TANHOUSE PROCESS:
1. Receiving - Most sheepskins are received at U. S.
tanneries from both domestic and imported sources as
pickled skins. These skins, which are salt cured, are
normally tied in bundles of one dozen skins. These
skins have had the wool removed at the packer or wool
pullery and processed to the pickled condition. The
wool pulling represents a beamhouse process.
Skins tanned with the wool intact are referred to as
shearlings. Tanning of these skins does not involve a
beamhouse process.
Pickled skins have been preserved for shipment and
storage by immersion in a solution of brine and acid.
Shearling skins are cured in a salt brine only. Excess
solution is drained prior to bundling.
18
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2- Storage - No special provision for storage is provided
at most tanneries other than to keep the skins moist.
There is some indication that pickled skins held for
extended periods should be kept below 30°C (86°F) to
avoid deterioration.
3. Fleshing - Skins from storage are taken from the bundle,
inspected, and fleshed. Hides which have been fleshed
prior to receipt at the tannery will usually be
refleshed after tanning. Shearling hides are usually
fleshed after a wash and soak operation. Fleshing is
done on the same type of machine used for fleshing
cattlehides. The skin is carried through rolls and
across rotating spiral blades which remove the flesh
from the skins.
Fleshings and trimmings are normally collected and
disposed of as a solid waste.
4. Degreasing - Skins are placed in drums, washed, and
soaked, after which solvent or detergent is added in the
same drums to remove grease.
Grease is recovered as a by-product from those skins
which have had the wool removed. When solvent
degreasing is used, the solvent is recovered and reused.
Skins with the wool on (shearlings) require
substantially more water in the washing (scouring)
operations and grease recovery is not normally
practiced.
There is a waste effluent from this process and a small
amount of vapor, including solvent exhausted to the
atmosphere.
5- Tanning - Sheepskins may be either chrome or vegetable
tanned, although the majority are chrome tanned.
Where the skins have been received at the tannery in the
pickled condition, there are no liming or bating
operations. Skins from the degreasing operation are
placed in drums with salt water and proprietary mixtures
of basic chromium sulfate for chrome tanning or
solutions of the natural tannins for vegetable tanning.
6- Refleshing - In some cases, there is a refleshing
operation following tanning, which produces a small
amount of solid waste.
1. Coloring - Skins to be colored are immersed in a dye
solution in drums. Generally, synthetic dyes are used.
19
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Some bleaching may be done prior to coloring of
shearlings.
2- Fatliquoring - This operation is performed in the same
drum used for coloring. Skins are immersed in a
solution containing various oils to replace the natural
oils of the skin lost in the tanning process.
FINISHING PROCESS:
There are a number of operations which follow the coloring
and fatliquor process, including drying, skiving, staking,
carding, clipping, sanding, and buffing. These are
essentially dry processes, and the only liquid waste
contributed is from cleanup operations.
Solid wastes from the finishing operation include trimmings
and skivings. Dust from the sanding and buffing operations
may be collected dry and disposed of as a solid waste or wet
and carried into the waste water system.
20
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FLOW DIAGRAM
TYPICAL SHEEPSKIN TANNERY
COLOR FATLIQUOR
(l] SHEARLINGS (WOOL LEFT ON) ARE
RECEIVED AS CURED SKINS M(f-
MOIJSE SUB-PROCESSES INCLUDE
WASH i SOAK FLESHING DEGREiS
ING PICKLING iND TANNING
I HASTE EFFLUENT
FIGURE 2
21
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Piqskin^TannerY^Processes
The pigskin tanning processes differ from cattlehide tanning in
that there is essentially no beamhouse process, since most skins
have the external hair removed at the packing house. Degreasing
of the skins is a required tanhouse sub-process. The waste
characteristics from pigskin tanneries are established from these
three processes:
1. Tanhouse.
2. Color and fatliquor.
3. Finishing.
These processes and the operations which take place within each
process are shown on Figure 3 and described as follows:
TANHOUSE PROCESS :
!• BkssiYioS "* Nearly all pigskins are received at the
tannery either as fresh frozen skins or as brined
refrigerated skins. They are usually tied in bundles of
40 to 50 pounds of skin. In some cases frozen skins may
be in paper bags.
2. Storage - Refrigerated storage is used at most of the
tanneries for skins which are to be held before tanning.
3. Deceasing - Solvent degreasing has been used by some
pigskin tanneries. In this process, the skins are
placed in drums, then washed and soaked in warm water to
bring them up to a suitable temperature for degreasing.
Solvent is added and the skins are tumbled to remove the
grease. The solution of solvent, grease, and water is
pumped from the drums to large tanks where some
separation is achieved by decanting. From the tanks the
solvent and grease is sent to a stripping column, where
the solvent is recovered for reuse. Grease is recovered
as a by-product.
There is a waste effluent from this process, as well as
a small amount of vapor, including solvent which is
vented to the atmosphere.
An alternate method, in which the skins are tumbled in
hot water and detergent, has also been used. In this
operation, grease is recovered by decanting or skimming
it from the top of holding tanks to which waste is
diverted prior to entry into the main plant sewer
system.
4. Liming - From the degreasing operation the skins are
placed in tanning drums with a lime slurry and
22
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sharpeners. The purpose of this is to remove the
embedded portion of the hair from the skins.
5- Siting ~ Tne bating operation takes place in the same
drums used for liming. The purpose of this operation is
to delime the skins to reduce the swelling and remove
any protein degradation products.
6- Pickling - The pickling operation follows the bating in
the same drum. A solution of brine and acid is used to
bring the skins to an acid condition to prevent
precipitation of chromium salts in the subsequent
tanning process.
7. Tanning - Pigskin may be either chrome tanned or
vegetable tanned. However, the only major tanner of
pigskin in this country is using only the chrome tan
process. Chrome tanning follows in the same drum used
for pickling, using proprietary mixtures of basic
chromium sulfate. Current practice is to fully tan the
skins in this operation, eliminating any need for a
retan operation at a later point.
8« Split and Shave - After tanning, the skins are tumble
dried and then split and shaved or skived to obtain the
desired thickness. The split part of pigskin has no
commercial value as leather, and it is baled with other
scrap and sold as a fertilizer component. The grain
sides go to the color and fatliguor process.
COLOR AND FATLIO.UOR PROCESS;
1« £2i°.£iU3 ~ Skins to be colored are immersed in a dye
solution in drums. Generally, synthetic dyes are used.
2. Fatliquoring - This operation is performed in the same
drum used for coloring. The skins are immersed in a
solution containing various oils to replace the natural
oils of the skin lost in the tanning process.
FINISHING PROCESS:
There are a number of operations which follow the coloring
and fatliquor process, including drying, coating, staking,
and sanding. These are principally dry processes, and the
only liquid waste contributed is from cleanup operations.
Where paster drying is used, there is some starch from the
paste which is cleaned from the dryer plates. Water baths
from spray booths may also represent minor sources of liquid
waste. ,
Solid waste from the finishing operation includes trimmings,
which are baled with the split and shave wastes for sale as
fertilizer. Dust collected from the sanding operation is
disposed of as a solid waste.
23
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FLOW DIAGRAM
TYPICAL PIGSKIN TANNERY
COLD* FlTLiOUOB
FIGURE 3
24
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Classification System
As noted in the foregoing discussion on standard manufacturing
processes, there are several variations in process steps. Under
the system prepared by the Technical Committee on Standard
Industrial classification, sponsored and supervised by the Bureau
of the Budget, the leather tanning and finishing industry bears
SIC Number 3111.
A supplemental digit system reflecting the many variations in
operations can further classify the industry. For purposes of
this study, a four-digit system is recommended to reflect
significant differences in processes. This matrix approach to
the classification system provides flexibility and a rigorous
means to encompass all process variables. The supplemental
classification system is shown in Table 3. Some blank spaces are
available if new processing techniques are developed.
Under this system, four digits appear to the right of a decimal
point following the industrial classification. As shown in Table
1, these relate information by type of skin or hide, operations
undertaken in the beamhouse, tanning method used, and type of
material processed in the retan, color, fatliquor, and finishing
steps.
25
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TABLE 3
CLASSIFICATION SYSTEM
(3111.abed)
Skin or
Hide Type
(a)
1. cattle
2. Pig
3. Sheep
4 . Dee r
5.
6.
7.
8.
9 . Other
0. Various
1.
2.
3.
H.
5.
6.
7.
8.
9.
0.
Beamhouse
Operation
(b)
Pulp Hair
Save Hair
Hair Pre-
viously
Removed
Hair
Retained
Wool
Pullery
Hide Curing
Pulp & Save
Other and
unknown
Retan,
Tanning Color, Fatliquor,
Process Finishina
1.
2.
3.
a.
5.
6.
7.
8.
9.
0.
(c)
Chrome
Vegetable
Alum
Previously
Tanned
Vegetable
and Chrome
Other and
unknown
None
1.
2.
3.
a.
5.
6.
7.
8.
9.
0.
(d)
Sides
Splits
Sides and
Splits
Bends
Skins
Other
None
Several examples using the classification system for the more
common processing methods are:
3111.1111 - Cattlehide (including calfskin) , hair is pulped,
chrome tanning process used, sides finished.
3111.1211 - Same as .1111 except hair is saved as a by-
product.
3111.1221 - Same as .1211 except vegetable tanning process
used.
3111.1110 - Same as .1111 except no retan, color, fatliquor,
or finishing is done (tanning to blue stage only).
3111.1341 - Cattlehide, hair previously removed and hide pre-
viously tanned prior to receipt of hides at a finishing
facility (finishing operations only).
26
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3111.2315 - Pigskin, most hair removed prior to arrival of
skin at tannery with small amount of residual hair pulped,
chrome tanning process used, skins finished.
3111.3315 - Sheepskin, hair removed prior to receipt of skins
at tannery, chrome tanning process used, skins finished.
3111.3415 - Same as .3315 except tanned with hair retained on
the skin.
Categorization System
The tanning industry's present standard manufacturing processing
techniques are covered with approximately 35 classifications
which are combinations of the four basic digits that appear in
Table 3. Based upon available data, these classifications were
assessed for similarities in untreated waste water
characteristics and processing techniques. This analysis results
in grouping the classification into six major subcategories, as
shown on Figure U, for purposes of evaluating control and
treatment technology. Each subcategory represents a common
manufacturing process, as shown in Table 4.
The size of the production facilities is a significant factor
which requires an exception within the subcategorization. Severe
diseconomies of scale create economic impacts which require
different BOD5_ and TSS limitations for small plants and some
medium sized plants. The basis for the size exemption allowed to
tanners with a production less than 17,000 kg hide per day is a
model tannery employing just over 100 men and processing just
under 800 hides per day. Further development is described in the
economic impact study of the leather industry.
These six subcategories only identify operations that do not
process a combination of hides or skins. Tanneries processing
various types of hides or skins should be categorized on a
prorated distribution basis. For example, a tannery that is
pulping, chrome tanning, and finishing 90,000 pounds of
cattlehides per day and chrome tanning and finishing 30,000
pounds of shearlings per day would have a categorized
distribution of 75 percent and 25 percent in Subcategories 1 and
5, respectively. Thus, the suggested control and treatment
guidelines presented later herein may be administered by various
combinations of subcategories where appropriate.
27
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STANDARD
INDUSTRIAL
CLASSIFICATIONS
DRAFT
CATEGORIES
CATTLE 1.I2H
SAVE
CHROME
SIDES
CATTLE 1. 1219
SAVE
CHROME
OTHER OR UNKNOWN
DEER J. 142 IS
SAVE
CHRQ-4E
SKINS
^CATEGOR^^^J
STANDARD
INDUSTRIAL
CLASSIFICATIONS
CATTLE j. 1311
HAIR PREVIOUSLY REMOVE!
CHROME
SIDES
CATEGORY SYSTEM
FIGURE 4
28
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TABLE 4
PRINCIPAL PROCESSES OF SUBCATEGORIES
Primary Processes
SubcategorY Beamhouse Tanning Finishing
1 Pulp Hair Chrome Yes
2 Save Hair Chrome Yes
3 Save Hair Vegetable Yes
4 Hair Previously Removed Previously Tanned Yes
5 Hair Previously Removed Chrome Yes
or Retained
6 Pulp or Save Hair Chrome or No
no Tanning
29
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SECTION V
WASTE CHARACTERIZATION
General
The first step in an appraisal of tannery liquid wastes is to
define and quantify applicable waste constituents. These data
must then be related to some unit of production. Information
required to meet this need has been obtained from the following
sources:
1. Correspondence with individual tanneries.
2. Information data sheets for individual tanners supplied
through the Tanner's Council of America, Inc.
3. Corps of Engineers Permits.
4. Regulatory agency data summaries, including engineering
reports on individual tanneries.
5. Literature review.
6. Sampling performed at selected tanneries.
7. Tannery visits.
Correspondence and information data sheets were received from
over 140 wet processing firms, corps permits for about 40 firms
were submitted and sampling to verify waste characteristics was
conducted at seven facilities. Information was also gathered
from about five regulatory agencies and from visits to twelve
tanneries other than those sampled. Data has been assembled on
the basis of the various tannery subcategories.
31
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haste Constituents
Materials which can appear in tannery wastes include the
following:
Hair Lime Sugars and starches
Hide scraps Soluble proteins Oils, fats, and grease
Pieces of flesh Sulfides Surface active agents
Blood Amines Mineral acids
Manure Chromium salts Dyes
Dirt Tannin Solvents
Salt Soda ash
The basic parameters used to define waste characteristics are as
follows:
BOD5 (Five-day Biochemical Oxygen Demand)
COD (Chemical Oxygen Demand)
Suspended Solids
Total Nitrogen
Chromium
Oil and Grease (Hexane Solubles)
Sulfide
pH
Additional data from some sources permitted a check of the
various forms of nitrogen and volatile components of total and
suspended solids. No significant information was available on
color. Information was also collected on total daily waste flow.
Unit Waste Quantities
Data was obtained for all parameters except water flow and pH in
terms of concentrations (mg/1). When* combined with waste flow
records, this permitted computation of waste quantities in terms
of weight of each waste constituent produced per day.
It is also necessary to define the quantity of each waste
constituent generated per unit of production. Several measures
of production were considered:
1. Weight of raw material processed.
32
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2. Number of hides processed,
3. Weight of finished product.
4. Square feet of finished product.
Each of the above has some shortcomings when used as basis of
production, as discussed below.
The weight of raw material includes varying amounts of dirt,
manure, salt, and flesh. In some instances raw material may be
green salted hides. In other cases it may be tanned hides in the
"blue" stage.
Use of the number of hides includes all factors listed for hide
weight. It also introduces a variance in weight. A tannery may
be using a mixture of heavy and lightweight hides. Hides from
winter reared animals tend to have a heavier hair coat.
Use of finished product as a unit of waste production is
complicated by the industry's use of square feet as a measure in
some instances and weight in others.
Weight of raw material processed has been selected as the best of
the possible production parameters. The weight of raw material
varies as some firms process salted hides, some utilize
previously tanned hides as raw material, and other similar
variations. All waste constituent data are related to the weight
of the raw material as it enters a particular tannery or
finishing facility.
Individual Process Contributions to the Waste
Each process in the production of the final product makes some
contribution to the total waste load.
Hide Curing
Hide curing is not performed in the tannery, but rather in a
packing house or in a separate hide curing facility. If it is
performed in a separate facility it is considered to be a part of
the tanning industry. The hide curing process consists of
washing, curing, and often fleshing of the hides. Washing and
curing are performed simultaneously in a tank containing a strong
solution of salt. Subjecting the hides to contact with brine
permits penetration of salt into the hide, resulting in moisture
reduction and the inhibition of microbiological decomposition.
The brine solution is continually circulated and reused.
Blowdown from the system is required to offset water gains from
hide moisture losses. This blowdown also prevents the
accumulation of foreign materials. Although the blowdown which
constitutes most of the waste flow is quite small, the
concentration of waste constituents is quite high. A typical
characterization of this waste is as follows:
33
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Table 5
Hide Curing
Concentration kg/1,000 kg Hide
Waste Characteristics
BOD5
COD
Total Solids
Suspended Solids
Oil and Grease
Water Use, I/kg
(gal/lb)
(mq/1) (lb/1
15,610
29,610
280,500
10,400
40,200
0.24
(0.03)
,000 Ib Hidel,
3.9
7.4
70.1
2.6
10.0
Tannery Processes
Processes which are an integral part of the tannery include the
following:
Wash and Soak
Degreasing (sheepskin and pigskin)
Unhairing (sometimes followed by supplemental liming)
Bating
Pickling
Tanning (including bleaching for some vegetable tanning)
Retanning, Coloring, and Fatliquoring
Finishing
The waste contributions are described below:
Wash and Soak - This is the first wet process performed on the
raw material as it begins the tanning process. The purpose of
this operation is to remove salt, restore the moisture content of
the hides, and remove any foreign material such as dirt or
manure. If the raw material are brine cured hides, the hides are
clean and the operation is one of salt removal. With green
34
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salted hides, manure and dirt must also be removed. The quantity
of manure and dirt can vary widely, depending on the season of
the year and the origin of the animal.
Primary waste constituents from the operation are BOD5, COD, sus-
pended solids, and total solids (including sodium chloride).
Typical range in quantities for a cattlehide tannery with hair
pulping and chrome tanning are as follows:
Constituent kg/1.OOP kg Hide (lb/l,000_lb Hide}_
BOD5 7-22
Suspended Solids 8-43
Total Solids 143-267
Following the wash and soak operation the hides are fleshed, if
this has not been done previously. Fleshings are handled
separately, and should not make a significant contribution to the
liquid waste if handled properly. In some instances fleshing is
performed after the unhairing and liming process.
Degreasing - Separate degreasing operations are not normally per-
formed on cattlehide, but only on skins such as those from pigs
and sheep. Two types of degreasing are used:
1. Hot water with detergent.
2. Solvent.
In both cases the grease is separated and recovered. However,
some grease is not captured and enters the plant waste system.
In the case of solvent degreasing, the solvent is also recovered.
In addition to grease, BODJ5, COD, and suspended solids are other
waste constituents.
The grease entering the plant waste system consists of only that
portion which escapes the recovery process. In pigskin tanning,
total grease removed from the skin can approach 100 kg (Ib) per
1,000 kg (lb) of skins. The quantity entering the waste stream
is only a small part of this. Unfortunately, reliable data on
grease content of the waste stream is not available. The major
problem arises from the difficulty in obtaining a truly
representative sample.
Unhairing - Two processes are used for unhairing:
1. Hair save.
2. Hair pulp (or hair burn).
In the hair save operation, the hair is loosened for subsequent
machine removal. Lime and sharpeners (sodium sulfhydrate, etc.)
are used to perform this function. The waste is characterized by
35
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a high alkalinity, pH, sulfide, and nitrogen content. The
nitrogen content results from the reaction of the unhairing
solution with the protein matter. Other constituents of the
waste include COD, BODJ5, suspended solids, and total solids. A
part of the soluble solids is sodium chloride not removed in the
soak and wash.
An additional step in the hair save operation is machine removal
of hair from the hide. Although the hair is handled as a solid
by-product, it does require washing prior to baling and sale as a
marketable product. The waste water from washing contains the
same waste constituents as the unhairing solution, only in a more
diluted concentration.
The hair pulping operation is similar to that of hair saving
except that higher chemical concentrations are used, particularly
with respect to the sharpeners. In this process the
proteinaceous hair is solubilized sufficiently to disperse it in
the processing liquid. The waste water, therefore, has a higher
content of waste constituents, particularly with respect to
sulfides and nitrogen.
For a cattlehide chrome tannery, BOD5 content of the waste from
the hair save process will range from 17 to 58 kg (Ib) per 1,000
kg (Ib) of raw material. With the hair pulping process this may
be 53 to 67 kg (Ib) , Likewise, the total nitrogen content of the
hair save waste will be substantially less than the 11 to 15 kg
(Ib) per 1,000 kg (Ib) experienced with the hair pulp process.
Bating^ - The purposes for the bating process are to delime,
reduce swelling, peptize the fibers, and remove protein
degradation products. Major chemical additions are ammonium
sulfate to reduce pH to a controlled level and an enzyme to
condition the protein matter. The reaction of lime with ammonium
sulfate produces calcium sulfate. The total nitrogen content of
the waste is 5 to 8 kg (Ib) per 1,000 kg (Ib) of hide with
ammonia nitrogen constituting about two-thirds.
Pickling - The purpose of the pickling operation is to prepare
the hides for the tanning process. In vegetable tanning,
pickling may be omitted. Pickle solutions contain principally
sulfuric acid and salt, although a small amount of a wetting
agent and biocide are sometimes used. Since protein degradation
products, lime, and other waste constituents have been previously
removed, the quantity of BOD5, suspended solids, and nitrogen are
low. Principal waste constituents are the acid and salt. The
strong liquor dump after processing is a source of waste since
the hides are normally not rinsed prior to tanning.
Tanning - The purpose of the tanning process is to produce a
durable material from the animal hide or skin which is not
subject to degradation by physical or biological mechanisms.
This is accomplished by reaction of the tanning agent with the
hide collagen. Chrome and vegetable tanning are the two
36
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principal processes, although other materials such as alum, and
other metal salts and formaldehyde can be used.
In the chrome process a basic chromic sulfate or a proprietary
chrome tanning solution is used. Other process solution
constituents include sodium formate, and soda ash. The chromium
must be in the trivalent form and in an acid media to accomplish
desired results. Some tanneries prepare chrome tanning by
reducing sodium dichromate solution to the trivalent form, using
glucose as a reducing agent. The waste from this process is the
principal source of trivalent chrome in the plant waste. The
only potential entry of hexavalent chromium into the waste system
comes from spillage.
The spent chromium tanning solution is relatively low in BOD5 and
suspended solids.
Waste from a vegetable tanning process is quite different. The
reaction rate of vegetable tan with the hides is much slower than
that of chrome tanning solution. Because of the longer contact
time, the process is normally carried out in vats with some type
of gentle agitation. In some instances the hides are passed
through a series of vats with varying solution strength. Because
of the cost of tanning materials, process solution conservation
has been practiced. Therefore, that part of the solution
entering the waste system is due to drag-out or planned blowdown
to maintain tanning solution quality. Vegetable tannin in the
waste is a source of both BOD5 and color.
Retan, Color, Fatliguor - Retanning, coloring, and fatliquoring
are normally performed in drums. The chrome or vegetable tanned
hides are placed in the same drums and all three processes are
performed on the hides before they are removed.
The retan process is performed to provide added tanning solution
penetration into hides after splitting. Chemicals used for
retanning can be chrome, vegetable, or synthetic tanning agents.
Because of the low concentrations of chemicals in the retan
process, the concentration of the waste water is not strong;
usually this process does not add a significant quantity to the
total waste flow.
The most varying process in the tannery is coloring. There are
hundreds of different kinds of dyes, both synthetic and
vegetable. Synthetic dyes are the most widely used in the
industry. When synthetic dyes are used, acid is usually added in
order to provide a better uptake of dye into the leather.
Normally, vegetable tanned leathers are not dyed in this manner.
If the vegetable tanned leather is colored, it is generally
surface dyed by spraying the color on the leather surface.
The fatliquoring operation can be performed either before or
after coloring. There is a wide range of type and amount of oil
added in this process, depending upon the end use of the leather.
37
-------
Liquid waste from the retan, color, and fatliquor operations may
be high volume-low strength compared with the beamhouse and
tanhouse.
The temperature of the retan, color, and fatliquor waste flows is
generally high—above 37.7°C (1QO°F). The major treatment
concern of the retan, color, and fatliquor waste is removal of
color and oil. These two constituents can be kept to a minimum
by utilizing chemical concentrations that provide for the best.
uptake of the chemicals into the hide. Because of the color in
the waste water, recycling is not normally practiced. Use of
high temperatures in retanning will enable maximum uptake of
chromium and reduce the discharge of this constituent.
Finishing
The finishing processes represent the lowest water flows of the
tannery because they are primarily dry processes. There are some
wet processes such as minor wetting operations to make the hide
handle more easily in the staking or tacking operations. The
pasting operation also uses small amounts of water. However,
several tanneries report reusing paste mixtures; therefore, it
does not flow into the waste stream. This pasting water is water
mixed with starch; thus, it is quite high in concentration even
though the volume is very low.
Total Plant Liquid Waste
The quantity of waste water is important to the economics of
treatment in that a number of the unit operations performed in
treatment are designed totally or partially on a hydraulic basis.
In addition, water conservation can often reduce the quantity of
processing chemicals used which later become constituents
requiring removal in treatment processes. Also, process solution
reuse practices such as that for tanning not only reduce waste
flow but also eliminate the major part of a waste constituent
from the total plant waste stream.
An appraisal was made to determine the quantity of waste flow
from "tanneries in each of the six subcategories defined
previously. A typical plot of waste water flow versus tannery
production is shown in Figure 5 for Subcategory 1. The random
nature of the data is obvious. It is apparent that size of
facility is not a factor for low waste water flow. These waste
water quantities are characterized in Table 6 by the median,
mean, and mode for each subcategory. Definitions of these terms
are as follows:
Median - The number of tanneries having waste flows lower
than this value is equal to the number of tanneries having
waste flows higher than' this value.
Mean - This is the average value determined by adding waste
flow data for all tanneries and dividing by the number of
tanneries.
38
-------
Mode - This is the mid-point of the one-gallon interval in
which the most frequent occurrence of waste water flow
occurs. This measure is not too significant since frequency
of occurrence in any one interval was not generally too much
greater than adjacent intervals. Use of a wider interval
would have reduced significance of this measure.
39
-------
19
TANNERY PRODUCTION (1000 KG HIDE/MO)
0 200 100 600 800 1000 1200 It00 1600 1800
18- -0.15
16
- 0.13
15
-JO. 12
©
13 ® -I0'1
12 . -JO.10
®
©
- 0.09 LJ.
I0h ®
® 0 -)0.08
* . .@
® ® ®® HO.07 i
- o.oe a
© „ © ®
® ®
0.05
© w -Jo.oit
© ® ®
® H0.03
WASTEWATER FLOW
® ® © TANNERY PRODUCTION "I"'02
® FOR CATEGORY 1
o.oi
® FIGURE 5
lo
500 1000 1500 2000 2500 3000 3500 TOO
TANNERY PRODUCTION (1000 LB HIDE/MO)
-------
TABLE 6
WASTEWATER QUANTITIES
Waste Flow,
cu m/kg of hide
Category
1
2
3
4
5
6
Median
0.040
(4.8)
0.050
(6.0)
0.044
(5.3)
0.017
(2.0)
0.050
(6.0)
Mean
0.053
(6.4)
0.063
(7.6)
0.050
(6.0)
0.020
(2.*)
0.063
(7.6)
0.028
(3.4)
(gal/lb
Mode
0.029
(3.5)
0.050
(6.0)
0.021
(2.5)
0.017
(2.0)
0.082
(9.8)
—
of hide)
Range
0.007-0.156
(0.8-18.7)
0.001-0.189
(0.1-22.6)
0.007-0.106
(0.8-12.7)
0.003-0.033
(0.3-3-9)
0.006-0.204
(0.7-24.4)
0.014-0.056
(1.7-6.7)
No. of
Tanneries
46
14
16
10
20
3
Used Later Herein for
Economic Analysts,
cu m/kg of hide (gal/lb of hide)
0.033
(4.0)
0.050
(6.0)
0.042
(5.0)
0.017
(2.0)
0.063
(7.5)
0.017
(2.0)
-------
Although data are quite random for any subcategory, there is a
trend toward distinct levels for each one. The randomness of the
data is due not only to differences in process operations but
also to the nonscientific methods used to gage and sample waste
streams in the tanning industry. To determine a waste flow value
for use as the basis of treatment, facility needs, and economics,
it was necessary to take into consideration the basic data for
individual tanneries in addition to that shown in Table 6. It
was reasoned that the design basis should generally be equal to
or less than the median, but in no case greater than the mean.
This approach was used on the basis that if 40 to 50 percent of
the tanneries of a similar type could meet processing needs at a
particular level, others could also meet this value through
attainable conservation measures. This was prompted by
observations made on plant visits that many tanneries use excess
water by constantly running wash-down hoses to waste, by
unmetered and poor control of water used for washing and rinse
operations and by other similar practices.
Characteristics of Total Plant Waste Flows
An attempt was made to rigorously define flow and the
concentration of waste constituents from each step in the tanning
process. This was not possible due to lack of reported data and
to the difficulty of isolating all of the individual flows during
the plant testing program made as a part of these studies.
Therefore, a comprehensive assessment of total plant wastes is
increasingly important.
A summary of raw waste characteristics for each subcategory is
shown in Table 7. The data have been classified as received and
no further attempt is made toward explanation of inconsistencies
with some information. Detailed information for individual
tanneries is presented as a part of the documentation submitted
as a supplement to this report. The sources of this information
have been described previously.
Examination of the information indicates the following:
1. Most data show a wide variance in values.
2. Based on average values, some quantities appear
to be high or low.
or low.
Typical variance is illustrated by the BOD5 for Subcategory 1,
where the range in values is 4.8 to 270 kg (Ib) with an average
of 95 kg (Ib) per 1,000 kg (Ib) of hides. The variance of this
and other parameters is undoubtedly due partially to some
difference in processing techniques among tanneries and partially
to lack of analytical accuracy. However, it is probable that a
major part of the difference is due to the variations in waste
quality associated with the multiplicity of waste discharge
patterns which can exist and the sampling methods. Berthouex and
Brown (5) utilize a Monte Carlo simulation to characterize many
-------
possible combinations of tannery process solution discharges.
This waste variance, along with the shortcomings of the normal
time spaced proportional flow waste increment method of composite
sample preparation, are the principal contributions to variance.
If incoming waste were to flow to an equalization tank with a
relatively constant outflow, it can be reasonably assumed that
variance would have been decreased significantly.
In examination of average values for various parameters, the
sulfide content of the waste for Subcategory 2 appears low, even
though this is a hair save operation. Also, the chromium content
appears high for Subcategory 4 where only some retanning is
performed. The average chromium content is 60 percent of that
for a complete chromium tannery process, as shown in Subcategory
1. Other such apparent inconsistencies occur and unusual average
values result since information from only one or two tanneries is
available.
Analyses were made of the size of plants in each industrial
Subcategory, and a typical plot for Subcategory 1 is shown in
Figure 6. Production capacity coupled with waste water flows are
used later herein to assess the economics of waste treatment.
Raw and treated waste characteristics were also assessed for each
Subcategory in relation to the size and age of tanneries. No
significant relationship is observed. For example, some old,
small tanneries produce effluents of better quality than those
which are new and large; the opposite case is also noted.
-------
TABLE 7
RAW WASTEWATER
CHARACTERISTICS BY CATEGORY
R»w Uaitewater Characteristics, kg/1,000 kg of Hide (lb/1,000 Ib of Hide)*
Character 1 st I cs
Flow: cu m/Kg
(gal/ib)
soo5
COD
Total Solids
Suspended Sol I ds
Total ChromI urn
Sul fides
Grease
Total Alkalinity
(as CaC03)
Total Nitrogen
(as N)
pH
Temperature**: °C
CF)
No. of
46
24
18
16
23
18
12
13
12
7
26
15
Category No. '
0.007-0.156
(0.8-18.7)
4.8-270
10.5-595
36-890
6.7-595
0.1-19
0.1-46
0.1-70
0.5-300
3.1-44
1.0-13.0
2.8-93.2
(37-200)
1
0.053
(6.4)
95
260
525
140
4.3
8.5
19
98
17
-
21.1
(70)
Category No. :
No. of
14 0.001-0.189
(0.1-22.6)
9 22-140
7 88-215
7 140-900
9 30-350
7 0.3-12
4 0.1-2.8
5 0.7-105
1 62-85
6 3.6-22
8 4.0-12.6
6 1.7-27.8
(35-82)
I
Average
0.063
(7.6)
69
140
480
145
4.9
0.8
43
72
13
-
18.3
(65)
Category No. :
No. of
Tanneries Range
16 0.007-0.106
(0.8-12.7)
12 7.4-130
9 24-695
9 120-800
10 20-445
5 0.2-0.6
7 0.1-4.2
7 0.1-160
6 4.1-135
5 0.9-23
12 2.0-13.0
3 4.4-28.9
(40-84)
)
Average
0.050
(6.0)
67
250
345
135
0.2
1.2
33
66
9 2
--
17.2
(63)
•''Except pH, flow in cu m/kg (gal/lb), and temperature in °C (PF) ,
"•>Average temperature is average summer and winter values, temperature range is low winter to high summer values.
-------
TABLE 7 (Continued)
RAW WASTEWATER
CHARACTERISTICS BY CATEGORY
Category No.
No. of
Tanneries Range
10 0.003-0.033
(0.3-3.9)
3 6.7-67
3 5.7-63
2 1.7-285
3 7.0-125
3 0.4-4.8
1 2.1
3 2.2-19
1.
0.020
(2.4)
37
28
140
47
2.6
2.1
7.9
cteristics, kg/1,000 kg
Category No.
No. of
20 0.006-0.201)
(0.7-24. A)
8 10-140
5 11-265
7 52-980
8 3.1-865
7 0.1-2.1
1 4.5
7 0.6-46
of Hide (lb/1
5
0.063
(7.6)
67
170
490
88
1.2
4.5
24
,000 Ib of Hide)*
Category No.
No. of
3 0.014-0.056
(1.7-6.7)
2 32-160
2 53-155
2 210-910
2 44-185
1 3.8-5.9
1 2.0-6.3
2 1.0-19
6
0.028
(3.4)
110
230
595
no
4.4
3.7
6.6
6.6-180 69 I 37-54 43
2
3
3
0.8-6.5
3.4-11.2
10.0-26 6
(50-80)
3.7
20.7
(69)
5 0.6-29
9 1.5-12.5
3 4.4-36.6
(40-98)
6.0
22.8
(73)
1 14-18
2 9.2-10.4
16
45
-------
woo
3000
1500
2000
LU
O
1000
900
§ 800
o
C. 700
600
500
o
o
WO
300
1000
900
800
700
600
500
WO
300
200
o ,
a
o
200
TANNERY PRODUCTION
VS.
RELATIVE CUMULATIVE FREQUENCY
FOR CATEGORY 1
FIGURE 6
100
100
10 20 30 W 50 60 70 80
RELATIVE CUMULATIVE FREQUENCY
90 95
98
50
9
46
-------
SECTION VI
SELECTION OF POLLUTANT PARAMETERS
A thorough analysis of the literature, industry data and sampling
data obtained from this study, and EPA Permit data demonstrates
that the following waste water parameters are of major
pollutional significance for the leather tanning and finishing
industry:
Biochemical Oxygen Demand (5-day, 20°C. , BODJ5)
Total Chromium
Grease, Fats and Oils
Sulfide
Total Suspended Solids (TSS)
Total Kjeldahl Nitrogen
Fecal Coliforms
PH
Patjonale for Selection of Major Parameters
Biochemical OxiSen Demand (BQPL
Biochemical oxygen demand (BOD) is a measure of the oxygen
consuming capabilities of organic matter. The BOD does not in
itself cause direct harm to a water system, but it does exert an
indirect effect by depressing the oxygen content of the water.
Sewage and other organic effluents during their processes of
decomposition exert a BOD, which can have a catastrophic effect
on the ecosystem by depleting the oxygen supply. Conditions are
reached frequently where all of the oxygen is used and the
continuing decay process causes the production of noxious gases
such as hydrogen sulfide and methane. Water with a high BOD
indicates the presence of decomposing organic matter and
subsequent high bacterial counts that degrade its quality and
potential uses.
Dissolved oxygen (DO) is a water quality constituent that, in
appropriate concentrations, is essential not only to keep
organisms living but also to sustain species reproduction, vigor,
and the development of populations. Organisms undergo stress at
reduced D.O. concentrations that make them less competitive and
able to sustain their species within the aquatic environment.
For example, reduced DO concentrations have been shown to
interfere with fish population through delayed hatching of eggs,
reduced size and vigor of embryos, production of deformities in
young, interference with food digestion, acceleration of blood
clotting, decreased tolerance to certain toxicants, reduced food
efficiency and growth rate, and reduced maximum sustained
swimming speed. Fish food organisms are likewise affected
adversely in conditions with suppressed DO. Since all aerobic
aquatic organisms need a certain amount of oxygen, the
47
-------
consequences of total lack of dissolved oxygen due to a high BOD
can kill all inhabitants of the affected area.
If a high BOD is present, the quality of the water is usually
visually degraded by the presence of decomposing materials and
algae blooms due to the uptake of degraded materials that form
the foodstuffs of the algal populations.
Total Chromium - Much of the leather produced in the U. S. is
tanned with chromium salts. Chromium, in its various valence
states, is hazardous to man. It can produce lung tumors when
inhaled and induces skin sensitizations. Large doses of
chromates have corrosive effects on the intestinal tract and can
cause inflammation of the kidneys. Levels of chromate ions that
have no effect on man appear to be so low as to prohibit
determination to date.
The toxicity of chromium salts toward aquatic life varies widely
with the species, temperature, pH, valence of the chromium, and
synergistic or antagonistic effects, especially that of hardness.
Fish are relatively tolerant of chromium salts, but fish food
organisms and other lower forms of aquatic life are extremely
sensitive. Chromium also inhibits the growth of algae.
In some agricultural crops, chromium can cause reduced growth or
death of the crop. Adverse effects of low concentrations of
chromium on corn, tobacco and sugar beets have been documented.
Grease - The grease analysis measures different types of
materials, including oils, fats, and other such materials
commonly found in tannery waste waters. Sources of grease from
tanneries are from both the animal fat on the hides, as well as
oils added to the hide during the fatliquor process. Oil and
grease exhibit an oxygen demand. Oil emulsions may adhere to the
gills of fish or coat and destroy algae or other plankton.
Deposition of oil in the bottom sediments can serve to exhibit
normal benthic growths, thus interrupting the aquatic food chain.
Soluble and emulsified material ingested by fish may taint the
flavor of the fish flesh. Water soluble components may exert
toxic action on fish. Floating oil may reduce the re-aeration of
the water surface and in conjunction with emulsified oil may
interfere with photosynthesis. Water insoluble components damage
the plumage and costs of water animals and fowls. Oil and grease
in a water can result in the formation of objectionable surface
slicks preventing the full aesthetic enjoyment of the water.
Sulfide - A significant portion of alkaline sulfides contained in
tannery waste water can be converted to hydrogen sulfide at a pH
below 8.5 to 9.0, resulting in the release of this gas to the
atmosphere. This gas is odorous, and can result in property
damage through paint discoloration. In sewers, hydrogen sulfide
48
-------
can be oxidized to sulfuric acidr causing "crown" corrosion. At
higher concentrations this gas can be lethal. This is
particularly significant as a hazard in sewer maintenance.
Sulfide compounds are used extensively in the beamhouse for the
unhairing process, and thus are found in tannery effluents.
Total Suspended Solids (TSS) - Material found in suspended form
in tannery wastewaters consist primarily of proteinaceous
substances (flesh, hide, or hair) and insoluble waste chemicals.
Suspended solids include both organic and inorganic materials.
The inorganic components include sand, silt, and clay. The
organic fraction includes such materials as grease, oil, tar,
animal and vegetable fats, various fibers, sawdust, hair, and
various materials from sewers. These solids may settle out
rapidly and bottom deposits are often a mixture of both organic
and inorganic solids. They adversely affect fisheries by
covering the bottom of the stream or lake with a blanket of
material that destroys the fish-food bottom fauna or the spawning
ground of fish. Deposits containing organic materials may
deplete bottom oxygen supplies and produce hydrogen sulfide,
carbon dioxide, methane, and other noxious gases.
In raw water sources for domestic use, state and regional
agencies generally specify that suspended solids in streams shall
not be present in sufficient concentration to be objectionable or
to interfere with normal treatment processes. Suspended solids
in water may interfere with many industrial processes, and cause
foaming in boilers, or encrustations on equipment exposed to
water, especially as the temperature rises. Suspended solids are
undesirable in water for textile industries; paper and pulp;
beverages; dairy products; laundries; dyeing; photography;
cooling systems, and power plants. Suspended particles also
serve as a transport mechanism for pesticides and other
substances which are readily sorbed into or onto clay particles.
Solids may be suspended in water for a time, and then settle to
the bed of the stream or lake. These settleable solids
discharged with man's wastes may be inert, slowly biodegradable
materials, or rapidly decomposable substances. While in
suspension, they increase the turbidity of the water, reduce
light penetration and impair the photosynthetic activity of
aquatic plants.
Solids in suspension are aesthetically displeasing. When they
settle to form sludge deposits on the stream or lake bed, they
are often much more damaging to the life in water, and they
retain the capacity to displease the senses. Solids, when
transformed to sludge deposits, may do a variety of damaging
things, including blanketing the stream or lake bed and thereby
destroying the living spaces for those benthic organisms that
would otherwise occupy the habitat. When of an organic and
therefore decomposable nature, solids use a portion or all of the
dissolved oxygen available in the area. Organic materials also
serve as a seemingly inexhaustible food source for sludgeworms
and associated organisms.
49
-------
Turbidity is principally a measure of the light absorbing
properties of suspended solids. It is frequently used as a
substitute method of quickly estimating the total suspended
solids when the concentration is relatively low.
Total Kjeldahl Nitrogen - Total kjeldahl nitrogen (TKN) is
ammonia nitrogen plus organic nitrogen content in waste water.
Hence, TKN measures the major nitrogen impact upon a waste
treatment plant or stream. This parameter is thus an important
measure of the potential environmental impact of tannery waste
water.
Fecal Coliforms
Fecal coliforms are used as an indicator since they have
originated from the intestinal tract of warm blooded animals.
Their presence in water indicates the potential presence of
pathogenic bacteria and viruses.
The presence of coliforms, more specifically fecal coliforms, in
water is indicative of fecal pollution. In general, the presence
of fecal coliform organisms indicates recent and possibly
dangerous fecal contamination. When the fecal coliform count
exceeds 2,000 per 100 ml there is a high correlation with
increased numbers of both pathogenic viruses and bacteria.
Many microorganisms, pathogenic to humans and animals, may be
carried in surface water, particularly that derived from effluent
sources which find their way into surface water from municipal
and industrial wastes. The diseases associated with bacteria
include bacillary and amoebic dysentery, Salmonella
gastroenteritis, typhoid and paratyphoid fevers, leptospirosis,
chlorea, vibriosis and infectious hepatitis. Recent studies have
emphasized the value of fecal coliform density in assessing the
occurrence of Salmonella, a common bacterial pathogen in surface
water. Field studies involving irrigation water, field crops and
soils indicate that when the fecal coliform density in stream
waters exceeded 1,000 per 100 ml, the occurrence of Salmonella
was 53.5 percent.
Elf Acidity and Alkalinity
Acidity and alkalinity are reciprocal terms. Acidity is produced
by substances that yield hydrogen ions upon hydrolysis and
alkalinity is produced by substances that yield hydroxyl ions.
The terms "total acidity" and "total alkalinity" are often used
to express the buffering capacity of a solution. Acidity in
natural waters is caused by carbon dioxide, mineral acids, weakly
dissociated acids, and the salts of strong acids and weak bases.
Alkalinity is caused by strong bases and the salts of strong
alkalies and weak acids.
50
-------
The term pH is a logarithmic expression of the concentration of
hydrogen ions. At a pH of 7, the hydrogen and hydroxyl ion
concentrations are essentially equal and the water is neutral.
Lower pH values indicate acidity while higher values indicate
alkalinity. The relationship between pH and acidity or
alkalinity is not necessarily linear or direct.
Waters with a pH below 6.0 are corrosive to water works
structures, distribution lines, and household plumbing fixtures
and can thus add such constituents to drinking water as iron,
copper, zinc, cadmium and lead. The hydrogen ion concentration
can affect the "taste" of the water. At a low pH water tastes
"sour". The bactericidal effect of chlorine is weakened as the
pH increases, and it is advantageous to keep the pH close to 7.
This is very significant for providing safe drinking water.
Extremes of pH or rapid pH changes can exert stress conditions or
kill aquatic life outright. Dead fish, associated algal blooms,
and foul stenches are aesthetic liabilities of any waterway.
Even moderate changes from "acceptable" criteria limits of pH are
deleterious to some species. The relative toxicity to aquatic
life of many materials is increased by changes in the water pH.
Metalocyanide complexes can increase a thousand-fold in toxicity
with a drop of 1.5 pH units. The availability of many nutrient
substances varies with the alkalinity and acidity. Ammonia is
more lethal with a higher pH.
The lacrimal fluid of the human eye has a pH of approximately 7.0
and a deviation of 0.1 pH unit from the norm may result in eye
irritation for the swimmer. Appreciable irritation will cause
severe pain.
51
-------
Rationale for Selection of Minor Parameters
Chemical_ Oxygen Demand (CQDj - COD is another measure of oxygen
demand. It measures the amount of organic and some inorganic
pollutants under a carefully controlled direct chemical oxidation
by a dichromate-sulfuric acid reagent. COD is a much more rapid
measure of oxygen demand than BOD_5 and is potentially very
useful. ~~
COD provides a rapid determination of the waste strength. Its
measurement will indicate a serious plant or treatment
malfunction long before the BOD!> can be run. A given plant or
waste treatment system usually has a relatively narrow range of
COD: BOD5> ratios, if the waste characteristics are fairly
constant, permit a judgment to be made concerning plant operation
from COD values. In the industry, COD ranges from about 1.6 to
10 times the BOD£; the ratio may be to the low end of the range
for raw wastes, and near the high end following secondary
treatment when the readily degraded material has been reduced to
very low levels.
In summary, BOD and COD measure organic matter which exerts an
oxygen demand. Both COD and BOD are useful analytical tools for
the processor. However, no COD effluent limitations are required
because BOD limitations have been established.
Total Solids - Total solids is a valuable parameter, since it
measures both suspended and dissolved solids in the waste. Since
tannery wastes are high in dissolved solids, the total solids
test is an effective parameter to assess the impact of dissolved
materials. The largest portion of the dissolved solids are
sodium chloride and calcium sulfate. Sodium chloride comes
principally from removal of salt from the raw hides by washing,
and also from salt added in the pickling operation. Calcium
sulfate can come from several locations in the tannery, but
principally from the reaction of residual ammonium sulfate and
sulfuric acid with lime used in the unhairing process. Dissolved
solids are particularly important for consideration of recycle
systems, and also for potential impact on stream life and water
treatment processes. Total solids limitations are not
established for tanneries because of insufficient information.
Ammonia Nitrogen - The principal sources of ammonia in tannery
wastes are the ammonium sulfate used in the bating process and
that which results from decomposition of organic nitrogen.
Ammonia limitations are not needed because total kjeldahl
nitrogen limits require the control of ammonia.
Color - Color from a tannery results principally from the chrome
or vegetable tan liquor and various dyes and paints used during
coloring operations in the production of the leather. The
contribution by vegetable tan is by far the greatest. Excessive
color may inhibit the activities of some aquatic life, but it is
primarily of concern from an aesthetic standpoint. There is not
52
-------
SECTION VII
CONTROL AND TREATMENT TECHNOLOGY
General
Waste treatment practices in the leather tanning and finishing
industry vary widely. Some tanneries use no treatment or only
simple screening. Others have employed activated sludge,
trickling filters, spray irrigation, and lagoon systems to
achieve treatment needs. The degree of treatment which the waste
receives has been determined by three factors:
1. Type of receiving system,
2. Quality criteria of the receiving system.
3. Tannery processes.
Effluent quality requirements for a tanner discharging to a
municipal sewer have been less stringent than those for a tanner
discharging to a stream, lake, or ocean. Therefore, those
systems providing a higher degree of treatment are associated
with tanneries discharging directly to bodies of water.
Variations in treatment schemes are also due to the differences
in raw waste characteristics associated with processing hides
into different types of leather. Although the basic unit
operations are the same, variations in sub-unit processes create
a variance in both effluent quantity and quality. These
differences are attributed to the need to obtain different
finished leather characteristics and the general attitude of
tanneries to produce the desired leather quality without regard
to conservation of process chemicals and water.
Based upon communication with around 140 wet processing firms in
the industry, approximately 60 percent of the tanneries discharge
to municipal systems. Analysis of these same data indicates that
tanneries discharging to municipal sewers also represent about 60
percent of productive capacity. This group includes those
discharging without treatment into municipal systems, as well as
those providing pretreatment prior to the conveyance to a
municipal facility. With increasing effluent restrictions
imposed by municipal systems, there is a trend toward at least
some pretreatment by all tanneries.
The survey of tanners and finishers indicated few (21) have on-
site biological waste treatment facilities, of those employing
biological treatment,three have activated sludge plants while
fifteen have lagoons of aerobic and aerobic-anaerobic operating
capabilities. Trickling filters are utilized in three treatment
schemes. Advanced treatment facilities are non-existent. Some
pilot studies of reverse osmosis and activated carbon have been
55
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made, but without well defined results. Filtration and ion
exchange have not been tested on tannery effluent.
Solids handling and disposal typically have had secondary
significance at tannery waste treatment facilities. Since on-
site disposal in open dumps prevails, sludge and other waste
solids have not in the past had proper disposal; sludge handling
is now receiving more emphasis. Pressure filters, vacuum
filters, and centrifuges are presently utilized for dewatering
sludge prior to land disposal.
In-plant waste control procedures have included efforts by some
tanneries to conserve water and materials. A number of tanneries
have intensified housekeeping practices to minimize the entry of
solid wastes into the sewer. Development of hide processors
(concrete mixers) has greatly influenced water usage in
applicable wet processing operations. This equipment requires a
smaller float (processing solution) than vats, paddles, or drums.
The potential for materials conservation has not been fully
realized, particularly in the beamhouse operations. Recycle and
recovery techniques have generally been applied only in those
areas where direct cost savings are demonstrated. Such practices
are tannin and chromium reuse. Plans for reuse of some portions
of treated waste streams are in the conceptual stages at several
tanneries.
Basis of Tannery Waste^Treatment
The following is a summary of approaches which can be used to
achieve various levels of tannery waste control and treatment:
1. In-process methods of reducing waste.
a. Water conservation.
b. Process solution reuse or recovery.
c. In-plant treatment to remove a waste constituent.
2. Preliminary Treatment.
a. Disposal to a municipal system or additional unit
operations for further treatment.
b. Adjustment of pH, alkalinity, and/or acidity to
required levels.
c. Removal of chromium, sulfides, hexane solubles, and
toxic materials to levels which will not pass
through or harmfully affect subsequent treatment.
d. Parrial removal of BODjj, COD, suspended solids, and
total nitrogen.
56
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3. Major reduction of BOD5 and suspended solids.
a. Removal of BODJ and suspended solids to levels of
less than 50 mg/1.
b. Some additional nitrogen removal beyond that
provided by preliminary treatment.
c. Normal treatment configuration includes some type
of biological process followed by effective removal
of suspended solids.
4. Major reduction of all forms of nitrogen.
a. Reduction of total nitrogen to a level of about 10
mg/1 or less.
b. Treatment follows biological treatment for BOD5
removal.
c. Treatment steps include an aerobic biological
process followed by an anaerobic biological
process. Each process is followed by a clarifier
for sludge removal.
5. Major removal of all waste constituents.
a. Follows previously described biological and
settling processes for removal of BODJ, suspended
solids, and nitrogen.
b. Filtered waste enters reverse osmosis process (or
electrodialysis process) for removal of remaining
organic constituents, as well as major quantities
of dissolved salts such as sodium chloride.
c. Waste stream is directed to evaporators for
concentration for final disposal.
d. Product water is o,f low solids content suitable for
reuse.
6. Waste treatment for hide curing facilities.
a. The high strength of this waste requires special
considerations.
b. Treatment for all levels except pretreatment
requires direct incineration of total waste or
solar evaporation in arid areas.
An analysis covering the application for each of these approaches
is described later herein. Such an analysis also sets forth in
more detail the technical and economic considerations involved.
57
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In-Process Methods of Reducing Waste
In an appraisal of any plant waste production, the manufacturing
cycle must first be investigated to determine any modifications
which can reduce the waste flow and the concentration of waste
constituents. Particular emphasis must be given to reducing
those factors which would pose problems in treatment of the total
waste. In some instances, reuse or recovery of materials from
process solutions can produce economies which will at least
partially offset costs.
It is not possible to identify every point in the hide
preparation and tannery processes where a modification would
reduce waste quantities. Tanning formulas and processing steps
are developed by experience. Implementation of many potential
waste reduction steps are contingent upon the effect on the
manufactured product.
The assessment of in-house conservation and treatment is
considered from the following approaches:
1. Water conservation.
2. Process solution reuse or recovery.
3. In-plant treatment to remove a specific waste constituent.
By reference to Table 6, it is noted that water use per unit
weight of hides processed varies significantly in all
subcategories. The variations for three subcategories in which
cattlehides are processed is shown below:
Subcategory Unhairinq Tanning Range in Water Use
I/kg of hide
(gal/lb of hide)
1 Pulp Chrome 7-156
(0.8-18.7)
2 Save Chrome 1-189
(0.1-22.6)
3 Save Vegetable 7'106
(0.8-12.7)
If equivalent leather quality is being produced in each
subcategory and with a reasonable allowance for process
differences, the variation in water use seems unnecessarily
large. It would appear logical that tanneries with large water
use could implement some reduction measures.
Although reduction would result in some savings in water cost,
the major saving would result from lower treatment costs. Most
unit operations in the treatment process are designed totally or
partially on the basis of flow. Therefore, a reduction in flow
would reduce both treatment plant capital and operation costs.
58
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Realizing the economy of reduced waste water flows, many
tanneries have attempted to decrease water use as much as
possible. Some water conservation practices have been
implemented and have proven to provide equal or better quality
leather than produced previously.
Some methods of water conservation are listed below:
1. Encouraging employees to implement any potential water
saving practices. Eliminating the constantly running
hoses observed in many tanneries is one practice
requiring employee participation.
2. Examine tanning formulas to determine if floats can be
reduced. Use of hide processors has permitted use of
lower floats.
3. Limit or eliminate some washing and rinsing operations.
a. Change a continuous rinse to a batch rinse.
b. Use preset meters or timers to limit total flow.
4. Use of wash waters and rinses for process solution make-
up.
Tannery #1 has recently undertaken a comprehensive water
conservation program. Through implementation of this program,
total water use has been reduced by nearly 50 percent.
Installation of hide processors for washing the incoming hides
has reduced water use in this process 70 percent. By reuse of
process water in the liming operations, a savings of 25 percent
has been accomplished. Installation of paddle vats and a
recirculating flume arrangement following the unhairing operation
has reduced water use for washing 80 percent. Further savings
have resulted from recirculating of hair wash water by installing
a fine screen for solids removal. Through the installation of a
vegetable tannin recycle and reclaim system using evaporators,
water use for this process has been reduced 65 percent. The
results of such major water conservation measures indicate that a
comprehensive water conservation program can substantially reduce
water use.
In recent years the hide processor (concrete mixer) has proven to
be an extremely effective means of reducing water use. The
number of hide processors in use is increasing. They are most
widely used for washing the incoming hides and for beamhouse
operations in pulp hair processes.
When hide processors are used in the beamhouse operation, the
water use through deliming will be about 8.35 I/kg of hide (1
gal/ Ib of hide). Tannery #2, which uses hide processors for all
operations from the raw product through chrome tanning or "blue"
stage, has indicated that water use is from 12.5 to 16.7 I/kg of
hide (1.5 to 2.0 gal/lb of hide). Some tanneries have indicated
59
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that hide processors are used in the retan, color, and fatliquor
operations.
There are also reports of water used in one process being reused
in completely separate processes. Tannery #3 uses the same water
for washing following their "modified pickle" operation and their
vegetable tanning operation. Tannery #1 uses a similar process
for recycling the soak water following the vegetable tanning
operation back to the color operation that precedes vegetable
tanning. There are also some indications that spent liquors
previously used in vegetable tanning are reused in retan
operations. Tannery fU indicates that they are using bate waste
water for alum tanning make-up water. Tannery #5 is planning to
recirculate approximately 20,000 gallons per day of treatment
plant final effluent water for use in the delime wash water
following the pulp hair process and for wash water following the
bate process.
Reuse or reduction of process solutions or recovery of process
chemicals has been demonstrated to be a method of waste
constituent reduction. A detailed summary of methods available
to reduce waste constituents by process adjustments is given by
Williams-Wynn (9).
There are a number of vegetable tanneries that are using recycle
systems to reduce the amount of tan liquor that is discharged
into the waste stream. Although these are not total recycle
systems, they do substantially reduce the amount of tanning in
the waste stream. In most cases, some blowdown is necessary to
prevent the build-up of contaminants in the tanning solution.
One tannery recovers this blowdown tan liquor and concentrates it
in a triple effect evaporator and sells the concentrated liquor.
Other tanneries use this blowdown liquor in retanning operations.
Reuse or recovery of chrome tan liquors is being practiced, but
not to the same extent as vegetable tanning solutions. Hauck (6)
has presented a summary of methods for recovery and reuse of
spent chrome tanning solutions. During World War II, the reuse
of chrome tan liquor was common practice because of the scarcity
of chromium salts. A recent report by the U.S. Geological Survey
states that the country has only "scant reserves" of chromium.
Tannery #6 has performed a study on the reuse of chrome tanning
solutions. These tests showed that the chrome liquors could be
reused for periods up to six weeks without reduction of leather
quality. The spent tan liquor in this study was settled and
sludge was drawn off the bottom of the holding tank. The
clarified solution was brought to the required concentration with
chromium salts, sulfuric acid, and sodium chloride. Because of
the sludge drawoff, this was not a complete recycle systems,
however, a substantial portion was recycled and only a small
amount wasted.
Tannery #6 also, in this same study, examined the feasibility of
recycling of the unhairing solutions. Tests on recycling of the
60
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unhairing solutions were performed on three separate occasions.
The longest recycle time was two weeks. However, the study
concluded that since the concentration of waste material in the
solution leveled off after a few days, the solution could con-
ceiveably be reused indefinitely. The spent liquor was drained
and settled much in the same manner as the chrome tan liquor.
After removing the sludge from the bottom of the tank, 65 percent
of the original volume remained. About 50 percent of the
sulfhydrate and lime needed for the next run was available in
that portion retained for reuse. After two weeks of use, the
solution had no objectionable odor and the amount of ammonia
coming off was not considered substantial.
Tannery f7, a shearling tannery, has been able to reuse their
chrome tan solution up to 5 times. Because of processing
requirements, spent chrome tan liquors are not at present being
reused.
This same tannery has been able to reuse their pickle liquor up
to five times. This is accomplished by adding additional
chemicals prior to adding another load of hides.
Tannery #8 reports reusing retan liquors. Tannery #9, reports
reusing the finishing oils. Many tanneries are reporting
recycling their pasting frame water either wholly or partially.
Based on the above, there are numerous possibilities for process
solution reuse. Of particular importance is reuse of the chrome
tan solution. If this waste stream enters the total plant waste
flow, it will be partially removed in the primary settling tanks
when beamhouse wastes or added alkali increases the pH to at
least 9.0. This chromic hydroxide precipitate will be removed
with the sludge. An additional quantity of chromium will be
removed in secondary treatment with possibly some small quantity
remaining in the effluent. In order to minimize the chromium
content of the sludge and subsequent treatment process, it is
proposed that all chrome tanneries be provided with recycle or
recovery facilities.
Sulfides in the beamhouse waste constitute a potential problem in
subsequent handling. If mixed with wastes which can reduce the
pH of the sulfide bearing wastes, hydrogen sulfide is released.
The complete removal of sulfides is ineffective with either plain
sedimentation or chemical treatment. Sulfides are more satisfac-
torily removed through oxidation. Various methods for oxidizing
sulfides include:
1. Air oxidation.
2. Direct chemical oxidation (8) .
3. Catalytic air oxidation (7) (8) (22) .
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Air oxidation with diffusers provides some removal, but only with
excessive aeration times.
Direct chemical oxidation with ammonium persulfate and ozone was
studied by Eye (8). Ammonium persulfate produced low removals.
Ozone was most effective; however, the expense of ozone
generating facilities and developing contact equipment negated
further study (8).
Studies by Chen (22) reveal that many metallic salts are
effective catalysts when compressed air at high temperatures is
utilized. Manganous sulfate proved to be the most effective
catalyst in the more alkaline solutions at near ambient
temperatures. Bailey (7) and Eye (8) further describe the
effectiveness of the metallic catalysts. In a laboratory study
(8), potassium permanganate was the mos^t effective agent, with
manganous sulfate also proving effective. Although the relative
costs for the two catalysts favor manganous sulfate, the space
available and capital costs for the two different systems will
determine which catalyst is best for a given situation. Optimum
results were obtained with a manganese to sulfide weight ratio of
0.15. Pretreatment facilities employing catalytic oxidation
should approach 100 percent removal of sulfides.
Sulfides are also removed in the activated sludge process.
In order to minimize dangers of potential hydrogen sulfide
release and to eliminate the BOD exerted in subsequent biological
processes, a catalytic oxidation tank is proposed for all
tanneries with sulfide bearing wastes.
Preliminary Treatment
Preliminary treatment is defined as those operations performed on
the waste stream to make it suitable for introduction into
another waste system for further treatment. Normally, the waste
system which receives the pretreated waste is that of a
municipality or a metropolitan sanitary district; however, it may
be subsequent treatment units on-site.
The need for preliminary treatment is based on the following
factors:
1. Sewer safety and maintenance.
2. Biological treatment protection.
3. Effluent criteria.
4. Sludge disposal criteria.
Sewerage systems are particularly susceptible to damage from high
sulfide wastes. Tannery effluents may contain sulfide concentra-
tions as high as 250 mg/1. An alkaline sulfide bearing waste
from a tannery when mixed with sufficient domestic or acidic
62
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industrial waste will release hydrogen sulfide gas. At a pH of
7.5, about 30 percent of the sulfide ion in the waste is present
as hydrogen sulfide gas. Oxidation of hydrogen sulfide by
aerobic bacteria creates sulfuric acid which is corrosive to
concrete and metal. This is the major cause of sewer pipe
"crown" corrosion. A safety problem for maintenance personnel
also develops when hydrogen sulfide gas collects in sewers and
manholes due to extreme toxicity in low concentrations. Hydrogen
sulfide will also discolor some painted surfaces.
Tannery effluents exhibit a wide range in suspended solids
concentrations (300-1U,000 mg/1) with an expected average of
2,000 to 3,COO mg/1 (10) (11). Grease concentrations in tannery
waste can be as high as 850 mg/1.
In addition to added removal problems in a secondary treatment
plant, grease can coat sewer lines and act as an adhesive for
other particulate matter. The suspended material consisting of
much lime may reduce sewer capacity through direct sedimentation.
A calcium carbonate scale will form when sufficient carbon
dioxide is present.
Aerobic biological treatment processes can be seriously inhibited
by some tannery waste constituents. While normal average
concentrations of lime and chromium salts do not appear to damage
the system, short term high concentrations could be detrimental
to biological activity. The high alkalinity (and corresponding
high pH) are caused by lime discharges from beamhouse operations.
Such discharges are normally intermittent. Trivalent chrome is
used extensively as a tanning agent. Hexavalent chrome may
appear in trace amounts from some finishing operations, but
trivalent chromium is the predominant form in the waste. There
appears to be some evidence to indicate that both forms can be
toxic (12). Of prime importance is the solubility. Trivalent
chromium salts are soluble in acid and neutral solutions. At a
pH greater than 8.5, trivalent chromium will be precipitated
while hexavalent chromium must be reduced prior to precipitation.
Total chromium concentrations of 10 mg/1 are indicated as hardly
toxic to biological units (13).
The batch nature of tannery operations create wide fluctuations
in waste flows and waste strength. Such variance can be
difficult to handle, particularly on the conventional smaller
treatment plants. The BOD5 may be as low as 150 mg/1 or may
exceed 3,000 mg/1 with an average usually from 1,000 to 2,000
mg/1 (10) (11). Significant reductions in BOD5 and equalization
of flow and waste strength may be required to avert overloading
of biological units.
Preliminary treatment operations consist of one or combinations
of the following:
1. Screening.
2. Equalization.
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3. Plain sedimentation.
4. Chemical treatment.
a. Coagulation and sedimentation.
1) Alum.
2) Lime.
3) Iron salts.
4) Polymers.
b. Carbonation.
5. pH adjustment.
6. Sludge handling and disposal.
These same unit operations and unit processes are used in the
first stages of facilities providing a greater degree of
treatment required when the effluent is directly discharged to a
river or lake.
Screening - Fine screening removes hair particles, wool,
fleshings, and hide trimmings. While eliminating undesirable
waste water constituents, the screenings themselves create a
solid waste disposal problem. The highly putrescible wastes are
commonly disposed of on-site or at remote landfill operations.
Screening equipment includes coarse screens (bar screens) and
fine screens, either permanently mounted or rotating with self-
cleaning mechanisms. The exact contribution of screenings on
parameters such as BOD5 and suspended solids is not known, since
large particles are removed prior to obtaining samples for
testing. The principal function of screening is to remove
objectionable material which has a potential for damaging plant
equipment and clogging pumps or sewers.
Equalization - Equalization of waste streams is important in pre-
treatment facilities. The volume and strength of waste liquors
vary depending on process formulations and scheduling of tannery
operations. Alkaline wastes are associated with beamhouse
operations, while acid discharges occur from the tanyard. In
order to produce optimum results in subsequent treatment
operations, equalization of flow, strength, and pH of strong
liquors is required. Although some oxidation may occur, no
removal of waste constituents is normally reported for
equalization. Equalization basins provide storage capacity for
hydraulic balance. Auxiliary equipment must provide for mixing
and maintaining aerobic conditions. Detention times much less
than one day are usually provided. Basins can be monitored
through pH and flow measurement.
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Plain^ Sedimentation - Plain sedimentation is concerned with the
removal of non-flocculating discrete particles and floatable low
density materials such as grease and scum. Tannery wastes have
high concentrations of both suspended solids and grease. As
shown in Table 8, suspended solids reductions can range from
approximately 40 to 90 percent, while reductions in BOD5 can
range from 30 to 60 percent. Much of the suspended material
removed is in the form of insoluble lime which produces a
voluminous and heavy sludge. Although grease removals are not
indicated, high removals are expected with surface skimmers
installed in clarifiers.
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TABLE 8
PLAIN SEDIMENTATION
Suspended Solids BOD
Inf^ Eff L Removal _[nf_. Eff. Removal Remarks Reference
mg/1 rog/1 % mg/1 mg/1 %
--- — 80-90 — —- 80-90 Fill and draw basins with (J8) (39)
24-hour capaci ty •
Sedimentation tanks, 900 130 83-88 380 146 40-63
mechanical siudge
faci 1ities
Sedimentation tanks 1,200 370 69 -~ --- -— Detention time 2 hours (14)
Sedimentation tanks 1,184 680 43 1,046 537 48 Continuous flow (pilot) (41)
Sedimentation tanks 1,880 461 6? 1,285 8?3 30 Fill and draw (ptlot) (41)
66
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Assumed to be typical for plain sedimentation units is the full-
scale operation cited by Sutherland (1/4) . The suspended solids
content of a side leather tannery was reduced 69 percent from
1,200 mg/1 to 370 mg/1 by continuous flow sedimentation for two
hours.
Laboratory experiments by Sproul, et al., (15) utilizing
beamhouse and chrome liquors showed that plain sedimentation at
an overflow rate of 24.5 cu m/day/sq m (600 gpd/sq ft) gave
average removals of about 22 percent in suspended solids and 35
percent in BOD. Pilot scale experiments by Sproul, et al., (51)
show equalization of plant flows followed by plain sedimentation
gave suspended solids and BOD removals up to 99 and 50 percent,
respectively. Chrome liquors in excess of 1 percent of the total
flow proved to be an effective coagulant for composite wastes
containing 2,000 mg/1 suspended solids. Overflow rates of 14.3
cu m/day/sq m (350 gpd/sq ft) produced a 2 percent underflow
concentration.
Field observations at Tannery 110 tend to confirm these removals.
The primary units consist of two circular clarifiers with
overflow rates of 18.8 cu m/day/ sq m (460 gpd/sq ft) at an
average flow of 3,030 cu m/day (0.8 mgd). No equalization
facilities are provided other than mixing in a pump wet well.
Cattlehide processing during the sampling period averaged 81,700
kg (180,000 Ib) green salted hides per day for pulp hair house
operations followed by chrome tan and finishing. The following
average removals resulted (10).
l£^iiJSDi Effluent % Removal
mg/1 mg/1
Suspended Solids 3,125 945 70
BOD5 2,108 1,150 45
Total Chromium 51 24 53
Total Alkalinity (as CaCO3) 980 718 27
Grease 490 57 90
Suspended solids and BOD5 removals were 70 percent and 45
percent, respectively. A low chromium removal of approximately
50 percent occurred. Higher removals would result if a pH of 8.5
or greater were maintained (using equalization or chemical
addition) in the primary clarifiers. If sodium alkali is
contributing to the high pH, a pH of 10-10.5 may be needed for
best removal. Theoretically, all chrome should precipitate as
chromic hydroxide; however, a very small residual is expected.
Although chrome removal from the waste water is desirable, a
sludge problem is created if proper disposal precautions are not
taken. The total alkalinity was reduced 27 percent, reflecting
sedimentation of suspended lime. Grease removal was 90 percent.
67
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In general, plain sedimentation is a physical separation of some
suspended particles from the waste stream. Although high
removals of suspended solids (90 percent) and BOD (60 percent)
are indicated with equalization and sedimentation, effluent
concentrations are not reported below 130 mg/1 for suspended
solids or 146 mg/1 for BOD^ (Table 8). High chromium removals
may result while sulfide concentrations are relatively
unaffected. As a unit operation, plain sedimentation has
desirable application in tannery waste water treatment.
Chemical Treatment - Coagulation and Sedimentation - Chemical
addition prior to sedimentation has further increased the removal
efficiencies of primary clarifiers. Chemical coagulation results
in higher removals of suspended solids, BOD, sulfides, chrome,
and alkalinity through flocculation of colloidal particles.
Alum, lime, iron salts, and polymers have exhibited satisfactory
results. Data in Table 9 indicates that suspended solids
removals from 50 to above 95 percent and BOD^ reductions range
from approximately 50 to 90 percent are achieved.
Chemical coagulation followed by sedimentation has been
investigated by Sproul, et al. (15) at a cattlehide tannery using
the chrome process. Raw waste water analyses indicate
concentrations of BOD5_ at 2,500 mg/1 and suspended solids of
about 2,530 mg/1. The results drawn from the laboratory scale
investigation are shown in Table 9 (15).
1. Use of an anionic polymer at a concentration of 1 mg/1
resulted in a reduction of about 84 percent in suspended
solids and 60 percent in BODJ3.
2. Adjustment of the waste to pH 9.0 with sulfuric acid and
subsequent settling gave average removals for suspended
solids and BODJ5 of 90 and 67 percent, respectively.
3. Use of ferric chloride at a concentration of 600 mg/1
produced average removals of 60 to 65 percent,
respectively, for suspended solids and BODEi.
4. Ferric chloride coagulation was less effective in
removal of suspended solids than was adjustment to the
same pH with sulfuric acid.
5. Coagulation with alum at concentrations less than 500
mg/1 after adjusting to a pH of 6.5 reduced the BOD5 by
90 percent and suspended solids from 45 to 57 percent.
Alum concentrations higher than 500 mg/1 created a floe
that would not settle.
6. Buffing dust resulting from finishing tanned hides was
not found to be an effective coagulant.
In general, polymer addition produced a rapid formation of floe
minimizing the need for flocculating equipment. Without pH
adjustment,
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TABLE 9
CHEMICAL TREATMENT
Suspended Sol Ids
Coagulation-Sedimentation
Plain Sedimentation,
Coagulation, Sedimentation
Aeration, Coagulation,
Sedimentation
Coagulation, Sedimentation Lime
Coagulation, Sedimentation Ltme
Coagulation, Sedimentation Lime
1,550
2,500
Iff. Removal Inf.,
iSgTT I SgTT
68
850
$18 469
1,980 497
3,135 HO
66 3,800 1,030
49 1,001 476
75 1,630 823
95 1,437 619
Coagulation, Sedimentation Iron Salts High
Coagulation, Sedimentation Polymer 5,200** 500** 90
Adjustment of pH water
the raw waste with ad-
justment of pH to 5-5.
Nixing aerated raw waste
with presettled super-
natant indicated 93% color
removal.
Continuous flow with lime
concentrations of 1,4go
mg/1.
Fill and draw with 11 me
concentrations of 1,700
mg/1.
Adjustment of pH with beam-
house 1fquors. Overflow
rate, 25.9 cu m/day/sq m
(635 gal/day/sq ft)
Ferric chloride added at
concentrations of 2,000-
5,000 mg/1
Full-scale operation on beam-
polymer addition of 10 mg/1.
Overflow rates at 65 cu
m/day/sq m (1,600 gpd/sq ft)
(42)
(18)
(41)
(37)
(16)
(32)
Equalisation, 2-stage
Carbonation, Coagulation,
Sedimentation
CarbonatIon, Coagulat io
Sedimentation
* Oxygen demand.
* Order-of-magnitude
13,400
Iron Salts 6,190
A pilot study with (19)
equalfzatfon of flow,
carbonation with flue gas
to 6.4-6.7 pH. Coagulation
wftn lime followed by 3-
hour sedimentation
Effluent is then subjected
to a second stage process
similar to the fi rst.
A 99* reduction in color
resulted.
A pilot study with carbona- (19)
tion of beamhouse wastes to
a pH of 6.0 followed by coagu-
lation with ferric chloride
(300-500 mg/1). Treatment
produced a floe which settled
quickly.
69
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polymers produced consistently higher removals than other
coagulants tested.
Sulfides appearing in the primary influent are not completely
removed in chemical units. Inconsistent removals are indicated
in the literature by researchers (8) (16) (17). With pH
adjustment to 8.0, an upper limit on sulfide removal may be 90
percent (15). Sulfide removal reduces BOD5 and averts hydrogen
sulfide problems. "~
Chromium will precipitate as a hydroxide at a pH greater than
8.5. A 90 percent removal in a laboratory study by Sproul, et
al. (15) occurred at a pH of 8.0. Precipitation in a primary
sedimentation unit is desirable to prevent any potential toxicity
in subsequent biological treatment units.
The removal of color is not commonly reported by investigators.
Low removals are, therefore, expected. In pilot plant operations
described by Howalt and Cavett (18) and, also, by Riffenburg and
Allison (19), 93 and 99 percent removals of color were observed,
respectively. The exact mechanism of removal in each of these
studies is not indicated. However, since color exists in the
colloidal region, a physical-chemical process is implied.
In a thesis by Hagan (20), color removal through coagulation and
precipitation was investigated. In coagulation, inter-particle
attraction created by suitable polymers develops a large floe
that tends to settle at an optimum pH. Hagan, also, reported
that common ion effect assisted in precipitation removal. The
basis of this contention is that the high hydroxyl ion
concentration at high pH reduces the solubility of color vectors
such as digallic acid which contains hydroxyl functional groups.
Addition of coagulants and pH control at this point may further
increase the relative efficiency. Laboratory results on a
vegetable tannery waste indicate high color removals (94 percent)
through a combination of chemical precipitation and coagulation
with calcium hydroxide and an anionic polymer (20). The
efficiency is dependent on pH control around 12.
In general, constituent reductions with coagulants are limited to
suspended solids, chromium, and possibly, sulfide and color.
BOD5 removals are a function of that portion of the BOD5, existing
in the colloidal or suspended form. Soluble BOD5 is normally 40
to 50 percent of the total BOD (10) . Many low removal
efficiencies may have resulted from inefficient control of the
physical-chemical operations, which require operator attention to
be successful.
Chemical Treatment - carbonatj.pn - carbonation is effective in
the"treatment of alkaline wastes. In this process, carbon
dioxide reacts with lime to form calcium carbonate, which has a
solubility of only 25 to 50 mg/1. The crystalline structure of
the carbonate nucleus provides an effective surface for
adsorption of organic matter. Suspended solids and BOD are both
reduced.
70
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Stack gas containing 8 to 12 percent carbon dioxide, obtained
from any fuel combustion process, can be used. Introduction of
gas into the waste stream requires a suitable diffuser system and
reaction vessel.
Table 9 indicates high removals for suspended solids, BOD5, and
alkalinity for carbonation in conjunction with coagulation. The
BOD5 removals range from 85 to 92 percent, while suspended solids
reductions as high as 99 percent are recorded.
Field data from Tannery t3 indicate high reductions in suspended
solids, BOD, and total alkalinity. Estimated flows from the
cattlehide vegetable tannery were 1,700 cu m/day (0.45 mg/1).
Primary clarifier overflow rates were about 20.4 cu m/day/sq m
(500 gpd/sq ft) for a chemical system utilizing flue gas
carbonation and a combination of iron salts and polymers. (Sul-
furic acid is also used to assist pH control). The following re-
movals were indicated (21):
Primary Primary
Influent Effluent %_Rempyal
mg/1 mg/1
Suspended Solids 2,110 100 95
BOD5 1,660 270 84
Total Alkalinity (as CacO3) 640 0 100
Carbonation is attractive for tannery pretreatment facilities,
since in most cases carbon dioxide is available at the cost of
piping from the plant boilers. Removals are high, under proper
operating conditions, for suspended solids and BOD.
pH Adjustment - In some instances, pH correction of the waste
effluent from other pretreatment processes has been required to
meet restrictions of a receiving system. Normally, this has been
accomplished by feeding sulfuric acid or sodium hydroxide to
lower or increase pH as required. This requires a relatively
simple chemical feeding equipment with pH sensing and control
system.
Sludge Handling and Disposal - A major part of tannery waste
treatment is handling and disposal of the semi-solid sludges
obtained from liquid treatment processes. The most predominate
methods of ultimate disposal of tannery waste sludges includes
sludge lagoons, landfills, dumps, and spreading on the land.
Some attempts have been made to dewater sludges prior to ultimate
disposal with varying success. The three principal dewatering
techniques include centrifuges, vacuum filters, and pressure
filtration. The centrifuges have appeared to meet with less
success than vacuum filters or pressure filters.
71
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Stabilization of sludges prior to disposal using aerobic and
anaerobic digestion has not been used extensively and where it
has been tried, it has not, always, been extremely successful.
Some of the organic matter is difficult to decompose by
biological activity and probably is the reason for at least a
part of the difficulties associated with digestion. In addition,
high chromium levels can inhibit the activity of some
microorganisms which stabilize organic material.
Reducing the moisture content of sludge by spreading on drying
beds has also been successful in some areas. This is
particularly attractive to smaller facilities where land area is
available.
Conditioning and stabilizing a mixed domestic and tannery sludge
using heat treatment processes has been employed also at Tannery
#11 (about 80 percent of the waste flow is tannery waste). Such
heat treatment provides a stable end product from a biological
standpoint and can be incorporated in a landfill or spread on the
land. One of the principal difficulties with tannery waste is
the chromium content in sludges and the potential impact this
material has on the environment from a toxic standpoint. In
testing a heat treated sludge, it has been indicated that some of
the trivalent chromium may be oxidized to the hexavalent form.
Apparently, the trivalent chromium is converted through the high
temperature, high pressure, and oxidizing environment of the heat
treatment process.
When chromium is reused in the tannery, levels in the sludge are
reduced. Disposal of sludge containing these residual quantities
of chromium in a sanitary landfill will minimize any
environmental problems.
Prior to dewatering in mechanical equipment, sludge is normally
conditioned by use of ferric salts and lime or polymers or a
combination of these. The quantity and type of chemicals
required are dependent upon characteristics of the sludge being
handled.
Dewatering with mechanical equipment generally can produce a
solid cake containing 15 to 30 percent solids.
Some sludge is disposed of on the land taking advantage of its
lime content for agricultural purposes. One disadvantage of this
type of disposal practice is the potential toxic effects which
chromium or other constituents might have on plants or through
leaching to ground or surface water supplies.
Lagoons for dewatering have some limited uses. In humid areas
where evaporation approximates rainfall, such application is not
completely satisfactory.
Use of lagoons, drying beds, landfills, and landspreading all
require key attention to the environmental impact. Particularly
important is the leaching of potential toxic or organic materials
72
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on the ground water supplies or surface waters. Proper controls
must be taken to ensure that these conditions will not develop.
Spreading tannery sludge on the land may, also, be a potential
problem from the standpoint of bacteria present. However, with
the high amount of lime waste commonly found in most tannery
sludges, as well as the lime dosages required prior to
dewatering, there is usually sufficient contact time of the
sludge at a high pH to afford some degree of disinfection. In
most cases, it is desirable to have the sludge elevated to a pH
of about 11.5 or greater for about two hours or more to effect
proper control.
Preliminary Treatment Facility JRecruirements - Based on an
appraisal of needs and the performance of previously described
operating facilities, the following processes are included in
evaluating preliminary treatment requirements:
Waste Flow
Screening
Equalization
Primary settling
Sludge
Collection
Thickening
Provision is also included for chemical addition to the primary
settling tank to aid in clarification and sludge settling.
Adequate experience has been accumulated to ensure that
facilities will perform satisfactorily. However, in some
installations, attempts have been made to combine equalization
and settling in one unit. In some instances, a large settling
tank has been utilized to perform this function. The success of
such an approach depends on a waste dump program. In theory,
continual vigorous mixing required for rapid equalization is not
compatible with the essential quiescent condition desirable for
efficient settling. Initial screening of the waste is desirable
to remove large particles prior to further treatment.
73
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Secondary^BiolQCfical Treatment
Parameters used for sizing principal items of equipment are as
follows:
Equalization Detention: 2H hours at design flow
Primary Settling Overflow rate: 23.5 cu m day/sq m
(500 gpd/sq ft)
Waste sludge 2 percent solids
Vacuum Filter Loading rate: 15.6 kg/sq m/hr
(3.2 Ib/sq ft/hr)
Major Reduction of BQD5 and Suspended Solids - Major reduction of
EOD5 and suspended solids requires a higher degree of treatment
than that provided by normal primary or preliminary treatment
facilities. This higher level of treatment is referred to as
secondary biological treatment. It generally includes a
biological unit process and may or may not require a pretreatment
step. Such facilities may be located at a municipal plant
treating a combined municipal-tannery waste or may be an on-site
plant treating only tannery wastes. Secondary biological
treatment can utilize activated sludge, lagoons, or trickling
filters along with required supporting equipment to achieve
required effluent quality. All systems with sufficient design
capabilities and adequate operation can attain equivalent
efficiency of BOD5 and suspended solids removal. Numerous
biological treatment schemes are, therefore, feasible. Selection
of an alternative biological treatment system is influenced by
waste water constituents, required efficiencies, climatic
conditions, land requirements, operational characteristics, and
economics.
Combined Municipal-Tannery Treatment Systems - Combined treatment
of tannery and municipal waste waters predominates in the
industry since most tanneries are located in urban communities
(4). Such systems normally require some degree of pretreatment
at the tannery. Typically, tannery effluents are combined in
various proportions with domestic flows and subjected to
treatment by activated sludge or trickling filter systems. Other
combined treatment facilities such as lagoons are not commonly
reported. Shown in Table 10 are reported combined municipal-
tannery treatment efficiencies. One example of primary treatment
only has been included to serve as basis of comparison with
secondary biological treatment systems.
74
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TABLE 10
COMBINED MUNICIPAL-TANNERY TREATMENT SYSTEMS
iODc
Tannery Total Tannery
-e treatment Flow Flow Inf Eff
cu m/day f rng/1 mgT
(mgd)
Suspended Sol Ids
nf Ejf Removal Locatu
Holding tank 2,195 35 326 156
(0 58)
52 883 760
Trickling Filter
Trickl ing fill.
Trickling filter, Screening 35,958
sludge digestion (9-5)
sludge digest I
sludge lagoon
Tnckl ing filte
sludge drying
1*0 600 65
15 W!1 1 lamsport,
Pennsylvania
Engine
Experi
Removal obtained with
loadings of 1.3-1.7 kg
BODj/day/cu m (3,500-
4,500 )b BODs/day/ac
ft) Mo scale deposi-
media, 100?
.ulfide renx
pr fa 1 ems with hair
hide scraps in
the design capacity
wfth obsolete set-
tling basins
Activated sludge,
separate sludge
digest ion, land
,rr,g,t,on of
I iquid si udge
Activated sludge,
separate sludge
Act
sludge
sludge
a ted sludge,
.
0 2)
6,056
(1.6)
1^,383
(3 8)
H >100 95
200 75 South Pa
ich bas in are 7 hoi
Plant completed in
1965 with capac.ty
of 13,626 cu m/day
(3 6 mgd)
jtion since 1962
;nced operat ional
stage oxi dat 101
pond, separate
sludge digest"
lagoon sludge
disposal
sludge, secondary
96 325 31
I.5H
(0 4)
90 Napa, Flow from two tanner-
California ,es Chrome reduced
from 61 to 0 8 mg/1
Digester gas 0 585 cu
m/kg (9 5 cu ft/lb)
volatile matter added
66-78 Gloversville, Prototype operation,
New York visual indication of
highly effective
75
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All treatment methods have demonstrated capability in at least
one installation to remove 90 percent of BOD5 and suspended
solids. However, other installations using the same treatment
methods have not achieved this degree of treatment. Tannery flow
combined with domestic sewage has ranged from less than 5 percent
to more than 80 percent of the total, studies of combined
treatment by Camp, Dresser, and McKee (23) and Nemerow and
Armstrong (24) present typical applications of this approach.
In a pilot study for a tannery in the Northeast (t12),
appropriate design parameters for combined treatment of tannery
with domestic sewage was investigated. Approximately, equal
portions of tannery and domestic sewage were used. Test flows
ranged from 0.3-1.3 I/sec (5-20 gpm) . At the time of the study,
the tannery production was approximately 1,502,740 kg (3,310,000
Ib) of cattle hides per month with an estimated waste water flow
of 3,785 cu m/day (1 mgd) from beamhouse, chrome tan, and
finishing processes. Combined flows consisting of equal portions
of tannery and municipal effluent totaling 9,463 cu m/day (2.5
mgd) are proposed for the full- scale facility. Removals in
excess of 90 percent BOD5_ and suspended solids were required to
meet stream classification standards. The following full-scale
unit processes, listed in the order of application, were found to
be essential to meet requirements (23) .
1. Equalization.
2. Primary sedimentation.
3. Carbonation and sedimentation.
4. Addition of municipal sewage.
5. Activated sludge treatment.
6. Sludge dewatering by centrifuge.
7. Effluent chlorination.
Equalization, carbonation with flue gasses, and sedimentation are
proposed as a pretreatment for tannery wastes.
Equalization is an important unit process for minimizing
variations in discharge flows and waste strength. Based on the
quantity and quality of the tannery discharge, a minimum of 4
hours was found to provide sufficient equalization capacity.
Primary sedimentation basins designed with an overflow rate of
32.9 cu m/day/sq m (700 gpd/sq ft) should produce a sludge with 8
percent solids. Heavy duty sludge removal equipment will be
required due to the volume and density of the sludge produced.
Pilot tests indicate that carbonation after equalization provides
a rapid absorption of carbon dioxide (CO2) gas. A contact time
of 20 minutes was sufficient for flue gas carbonation. The
76
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resulting calcium carbonate precipitate is expected to aid in the
removal of other suspended solids by sedimentation prior to
secondary treatment.
A volumetric loading of about 973 kg BOD5/day/l,000 cu m (60 Ib
BOD5_/day/l,000 cu ft) for the aeration basin with aeration
capacity of 123 kw (165 hp) is proposed for combined treatment.
Tests indicate foaming may be an operational problem. The full-
scale design should include provisions for surface sprays and
chemical addition.
The biological floe produced in the pilot aeration basin was very
light and settled with difficulty. An overflow rate not to
exceed 23.5 cu m/day/sq m (500 gpd/sq ft) is proposed for
secondary sedimentation. Upon resettling of the waste secondary
sludge in the primary clarifier, a mixture resulted which
dewatered readily on drying beds. Since large volumes of sludge
are produced, excessive amounts of land would be required for
drying beds. Sludge is, therefore, proposed to be dewatered in a
solid bowl centrifuge with the resulting cake containing 20 to 30
percent solids hauled to a sanitary landfill.
Nemerow and Armstrong (24) investigated a two-stage biological
system. A prototype plant treated 1,514 cu m/day (0.4 mgd) flow
intercepted from a combined municipal and tannery sewerage
system. The exact proportions of each were not indicated. The
treatment system consisted of the following processes:
1. Primary sedimentation.
2. Roughing filter.
3. Activated sludge.
4. secondary sedimentation.
The primary sedimentation unit with overflows between 15.5 and
23.0 cu m/day/sq m (330 and 490 gpd/sq ft) produced removal
efficiencies of 48 percent for BOD_5 and 24 percent for suspended
solids. Comparable values with polymers were 75 percent and 39
percent, respectively (24). The organic load on the filter
ranged from 1,135 to 3,242 kg BOD5/day/1,000 cu m (70 to 200 Ib
BOD5/day/l,000 cu ft) with BOD5 removals of 37 and 30 percent,
respectively (24). The activated sludge unit produced the
highest organic removal efficiency (85 percent) at food to active
mass (F/M) ratio of 0.2. The mixed liquor suspended solids
(MLSS) concentrations in the parallel basins were maintained at
2,000-3,500 mg/1. Flotation thickeners without polymers were
loaded at 5.9 to 17.1 kg/sq m/hr (1.2 to 3.5 Ib/sq ft/hr) and
consistently produced sludge concentrations of 5 percent. Total
system BOD5i removals ranged between 80 to 90 percent.
In general, combined treatment is viable if proper design
considerations assessing the effects of tannery waste waters are
considered.
77
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High treatment efficiencies are technically possible in all
processes. Combined treatment usually requires that certain
restrictions be imposed by the municipality on waste water
constituents, including chrome, sulfides, alkalinity, grease, pH,
and in some instances BOD5 and suspended solids.
On-Site Treatment - TricJcling^Filter Systems - Trickling Filter
Systems are not extensively utilized for tannery treatment.
Reasonably high efficiencies are technically possible, yet the
positive control needed for high strength waste treatment has not
been generally demonstrated.
A trickling filter is an aerobic biological unit. Wastewater
constituents are brought in contact with microorganism mass
developed on the surface of the filter media. To achieve high
removals from tannery effluents, toxicity and excessive organic
loads must be prevented. Lime deposition on filters has, in some
instances, retarded biological activity. Also, the high strength
of tannery wastes require that a large surface area be provided.
Although, recirculation and improvements in filter media may
reduce overall area needs, the removal efficiency may not be
sufficiently consistent through the warm and cold periods to meet
the demands of future effluent requirements. Temperature is
critical in operation. High heat losses can result from the
spray distribution system and bed media, yielding low
efficiencies. Populations of nitrifying organisms are suppressed
due to the continual dosing of the system with carbonaceous
organic material.
Data is generally limited on trickling filter applications.
Presented in Table 11 are reported efficiencies for trickling
filter systems. A tannery in the Southeast (#3), utilizes a
trickling filter as the first stage in a two-stage biological
system. Operational data reported in 1972 indicate the plastic
media filter was ineffective with removals of less than 30
percent in BOD5 and suspended solids (25). After cleaning the
media and increasing the air supply to the filter, Kinman (26)
reported improvements to the overall system. Confirming data
obtained in a recent field survey at Tannery #3 indicate the
trickling filter (oxidation tower), including secondary
clarification, has the following combined performance
characteristics (21):
78
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Influent to Effluent from
£i§rif ier__ Removal
mg/1 mg/1 %
BOD5 270 62 78
Suspended Solids 110 45 59
COD --- 240 ---
Total Kjeldahl Nitrogen
(as N) --- 210 ---
Ammonia Nitrogen (as N) --- 61 ---
Color --- 300 units ---
The flow to the filter was approximately 3,785 cu m/day (1 mgd) ,
including a 50 percent recycle of the secondary clarifier
effluent. The BOD5 and suspended solids were reduced 78 percent
and 59 percent, respectively. considering the low influent
concentrations, these removals appear to be satisfactory.
Further reduction in BOD5 and suspended solids may not be
possible due to the colloidal characteristics of the suspended
material and the relatively high overflow rate of 37.6 cu
m/day/sq m (800 gpd/sq ft) in the secondary clarifier. Based on
estimated influent characteristics, moderate COD removals are
expected, with essentially no reduction in nitrogen and color.
Trickling filters have limited application in the treatment of
high strength tannery wastes. System upsets are common due to
organic overload and climatic conditions. Existing filters may
be incorporated into systems for preliminary treatment prior to a
second stage biological system.
On-Site _ Treatment -Aerobic Lacroon Systems - Aerated lagoon
systems have been utilized for tannery treatment where land is
readily available. Lagoons serve a two-fold purpose, providing
equalization and a desirable environment for biological activity.
In a large lagoon with proper inlet and outlet control, primary
and final sedimentation may be eliminated. An aerobic
environment is maintained by mechanical aerators designed with
capacities to introduce sufficient oxygen to meet metabolic
requirements and to provide adequate mixing. Under variable
loadings, the usually long detention times have produced
reasonably consistent effluent characteristics. Temperature is
important because the large surface area permits sizable and
latent heat loss to the atmosphere.
Presented in Table 12 are removal efficiencies for those
tanneries utilizing aerated lagoons. Although the design
potential for high removals is documented, existing operations
have not attained high efficiencies consistently. A reassessment
of unit functions and more operative control may be required.
79
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Carbonation, primary
sedimentation,
trickling filter,
final sedimentation
Primary coagulation,
sedimentation,
trickl ing fi Iter,
final sedimentation
Dilution, primary sedi-
mentation, trickling
f i Iter, f i nal sedi-
mentation
Dilution, primary sedi-
mentation, trickling
filter, final sedi-
mentat ion
TABLE 11
TRICKLING FILTER SYSTEMS
BODj
Inf. Eff. Removal Remarks
mg/1 mg/1 %,
85-95 Indicate 100 per-
cent removal of
sulfides
30-80 80 Adjustment of pH
before primary
sedimentation
900 56 91! Foreign data (India).
Influent BOD<- con-
centration after
primary sedimentation
821 48 84 Foreign data chrome
tannery (India) .
Influent 8005 con-
centration after
primary sedimenta-
tion
Reference
CO
(27)
(28)
(28)
80
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TABLE 12
AEROBIC LAGOON SYSTEMS
Suspended Solid
(mgd)
mg/t mgTT
I nfT EfTTRemoval TnfTEffRamovi
mg/l mgT) I mg/1 mg/T %
Screening, plain
lagoons, aerated
lagoons, final
sedimentation
Mlddlesboro, chrome- mentation of tan
Kentucky vegetable and beamhouse
1Iquors prior to
Sedimentation
lagoons, aeratei
lagoon, final
lagoon, lagoon
sludge disposal
190 53 564
Leather Co.,
Tennessee
Represents l
hr" «mp« 11
sample
2,309 2,250 615
(0 61)
6
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In a prototype study at a tannery in Virginia (f 13) , Parker (29)
investigated aerobic treatment of vegetable tanning wastes. The
system included separate equalization for beamhouse and tanning
waste waters prior to mixing with bating flows. Beamhouse wastes
were eventually diverted to another facility when pumping
problems developed. Mixed tannin and bating wastes were then
aerated in a lagoon. The lagoon volume was approximately 2,984
cu m (0.77 mg) with 7.5 kw (10 hp) aeration capacity. Based on
average influent data and probated effluent characteristics, the
following removals were observed:
Influent Eff luent Removal
mg/1 mg/1 %
BOD5 1,043 86 92
Suspended Solids 539 571 0
COD 4,470 1,608 64
Sulfide 1.5 0 100
Total Kjeldahl Nitrogen 88 22 75
A relatively high degree of BOD5_ removal (92 percent) resulted at
a volumetric loading of 73 kg BOD5_/day/l,000 cu m (4.5 Ib
BOD5/day/ 1,000 cu ft) . Investigators report the loading may
range from 16.2 to 130 kg BOD5/day/l,000 cu m (1 to 8 Ib
BOD5/day/l,000 cu ft) for BOD5 removals exceeding 80 percent (29)
(30) (31).
Effluent temperatures varied between 5°C (41°F) to 8°C (46°F)
during winter operation. Sulfides were completely oxidized. The
kjeldahl nitrogen removal (75 percent) indicates some
nitrification occurred in the lagoon with hydraulic detention
times of 16 to 35 days. The "BOD removal factor" ranged from
1.42 day-* to 1.82 day-* for the various operational phases (29).
In general, aerobic lagoons are capable of providing high
removals of BODJ5 and sulfides with a potential for some
nitrification with long detention periods. Existing facilities
need upgrading through proper monitoring and control. The
successful application of aerobic systems will be contingent on
the availability of land and proper assessment of the climatic
factors influencing design.
On - S ite Treatment _-_ Aerobic _ P 1 vos _ Ana e r ob_i c __ t-agoon Systems
Aerobic plus anaerobic lagoons are finding increasing application
in tannery waste treatment. Existing lagoons are easily modified
to operate simultaneously in these modes. A stratified lagoon
offers the optimum characteristics of both biological functions.
The lower anaerobic zone, although requiring an extended contact
time, is effective in treating high strength organic wastes. The
degradation products produced are: methane, hydrogen sulfide,
and ammonia which are readily available for utilization or
82
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further removal. Since the process does not require dissolved
oxygen, minimum surface area to volume ratios are required. In
general, the anaerobic process produces a waste which is more
amenable to subsequent treatment. A more complete degradation
occurs in the upper or aerobic zone of the lagoon. The major
decomposition products are carbon dioxide and water. Aerobic
surface conditions are required to prevent escape of anaerobic
products which create odors such as hydrogen sulfide.
Stratified lagoons are generally deep, 3.7-4.6 m (12-15 ft), but
shallow depths, 1.2-1.5 m (4-5 ft), are sometimes employed.
Mechanical aerators equipped with erosion shields provide the
desired surface oxygen requirements without disturbing the lower
anaerobic zone.
Presented in Table 13 are data for aerobic-anaerobic lagoons
treating tannery effluents. The limited data available indicates
some inconsistency in results. A better analysis of the system
merits are covered in the studies of Parker (29) and Eye (32).
83
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TABLE 13
AEROBIC-ANAEROBIC SYSTEMS
5ystem Flo*" lnf- Eff - Removal Inf Eff Removal Inf tf f. Removal Tannery Pr
ci7 m/day rag/1 mg/t i ragTT mg/1 ? Hig/T mgTT 5
2,271 673 53 92 339 ^8 86 Pownal Cattle- Nitrification- (10)
84
•eenmg, plain I.3&3 2,300 600^ V* 3,000 IcS* 95 Howes Cattle, Primary settling (10)
.edimeritation, (0.3&) Leather Co , save, wege- of beamhouse
Pennsylvania mixing with
spent tans.
^Arithmetic average
-------
An aerobic-anaerobic prototype system was investigated by Parker
(29) for treatment of a vegetable tannery waste consisting of
bating and vegetable tanning waste flows in a proportion of 8:1.
The aeration capacity of 7.5 kw (10 hp) and volume of the lagoon
were held constant while flows were varied to impart various
loadings on the system. In the initial phase the following
removals were experienced:
Influent Effluent Removal
~ mg/1 mg/1 %
BOD5 1,170 274 76
Suspended Solids --- 503
COD 4,730 2,113 55
Sulfide 0.7 0 100
Total Kjeldahl Nitrogen 107 35 67
The BOD5 removal was approximately 76 percent for an organic
loading of 141 kg BOD5/day/l,000 cu m (8.7 Ib BOD5/day/l,000 cu
ft). Temperatures ranged from 5°C (41°F) to 24°C (76°F) for this
operational phase. Suspended solids in the effluent were high,
indicating the need for more effective final clarification.
Sulfides were completely oxidized in the aerobic zone. The
kjeldahl nitrogen removal of 67 percent indicates significant
nitrification occurring in the system with hydraulic detention
times of 4 to 8 days.
In the second phase of operation, doubling the organic load to
282 kg BOD5/day/l,000 cu m (17.4 Ib BOD5/day/1,000 cu ft) did not
significantly reduce the efficiency. Investigators report
loadings of aerobic-anaerobic systems may range from 130 to 243
kg BOD5/day/ 1,000 cu m (8 to 15 Ib BOD5/day/1,000 cu ft) for 80
percent~organic removals (29) (30) (31) (35) (36 (50). However,
loadings above 81 kg BOD5/day/I,000 cu m (5 Ib BOD^/day/1,000 cu
ft) are impractical because of the oxygen requirement (30).
Parker indicates the most difficult problem in treating spent
vegetable tannings appears to be color removal (29). Color is
not reduced by biological treatment. However, reductions were
observed by blending the influent or effluent with lime waste
waters or coagulating with chemicals (29).
Eye investigated aerobic-anaerobic treatment of waste from a sole
leather tannery (32). Laboratory and pilot studies were
conducted prior to the initiation of full-scale systems. Lime
bearing beamhouse fractions were found to be readily clarified by
adding an anionic polymer followed by sedimentation. With
polymer additions of 10 mg/1, overflow rates of 75.2 cu m/day/sq
m (1,600 gpd/sq ft) produced 90 percent suspended solids
removals. Later, a lagoon with a three-day detention time was
85
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found to produce equivalent removals and was incorporated into
the full-scale system.
Subsequent treatment of the clarified beamhouse waste water in
aerobicanaerobic lagoons created severe odor problems. The
problem was eliminated when spent vegetable tanning solution was
combined with the beamhouse fractions for treatment. Removals
observed through the biological system were as follows (32):
Influent Effluent Removal
mg/1 mg/1 %
BOD5 1,146 152 87
Suspended Solids 408 105 74
COD 2,221 717 68
Sulfide 17 13 24
Total Kjeldahl Nitrogen (approximate) 150 100 33
High removals in BOD5 (87 percent) and suspended solids (74
percent) indicate the wastes are amenable to aerobic-anaerobic
treatment. The removals were obtained at volumetric loadings of
32.4 to 324 kg BOD5/ day/1,000 cu m (2 to 20 Ib BOD5/day/l,000 cu
ft). Pilot operations indicate loading intensities ranging from
324 to 405 kg BOD5/day/l,000 cu m (20 to 25 Ib BOD5/day/l,000 cu
ft) are feasible (32). Total BOD5 removal through the system
averaged 90 percent. Lower removals were experienced in winter
operations when the lagoon temperature was about 1°C (34°F).
Sulfide removal was minimal in the system, which is contrary to
other investigations (29). A kjeldahl nitrogen removal of 30 to
40 percent indicates nitrification in the aerobic portion of the
lagoon.
Foaming periodically creates operation problems. High pressure
water sprays are utilized to control foam during summer
operations. Defearning chemicals may be required during low
temperature operation.
In Eye's tests (32), biological activity did not remove color.
Color could be precipitated before or after biological treatment
by elevating the pH to 11.5 or greater with lime and the addition
of an anionic polymer.
Nitrification-denitrification is possible in multi-stage systems
(32) (33). For this to occur, significant nitrification is
required in a first stage aerobic operation. Feeding the
nitrified waste to the anaerobic zone of the second stage lagoon
denitrifies the waste. In the absence of oxygen, anaerobic
bacteria reduce the nitrate liberating nitrogen gas as a
respiration product.
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Aerobic-anaerobic lagoons offer several advantages, including
(32): relatively small land requirements, low sludge volumes,
reduced air requirements since organics are decomposed in the
anaerobic zone, heat conservation during winter operation, and a
potential for some nitrification-denitrification. Specific
applications will require extensive pilot studies for evaluation
of design parameters, particularly in regard to nitrification-
denitrification.
On-Site Treatment - Activated Sludge _Systems - The activated
sludge process is perhaps the most innovative and flexible of all
secondary treatment systems. It is applicable to almost all
treatment situations. With proper operational control, high
organic removals are possible. Designs based on solids retention
time (SPT) afford optimum residence time for solids with minimal
hydraulic detention period. However, extensive pilot studies are
required to establish appropriate design parameters defining the
relative rate of biological growth and decay. Basically, the
activated sludge process consists of (34): mixing of returned
activated sludge with the waste to be treated; aeration and
agitation of the mixed liquor for the required length of time;
separation of the activated sludge from the mixed liquor; and
disposal of the excess sludge. Activated sludge is often pre-
ceded by some form of pretreatment. Variations in these
processes create numerous operational phases. Overall
efficiencies are highly dependent upon the monitoring and control
provided by operating personnel.
Presented in Table 14 are results of full-scale and pilot
activated sludge systems treating tannery wastes. Based on the
effluent characteristics, operating difficulties are plaguing
full-scale activated sludge facilities. At present, no facility
is in operation that attains high removal efficiencies on a
consistent basis. An exemplary facility does not exist.
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TABLE 1**
ACTIVATED SLUDGE SYSTEMS
Suspended Sol ids
Flow Inf Eff Removal Tnf Eff Ren*
;u in/day mgTT rogTT ? mgTT mg/1 '
(mgd)
3,WS 1,36* !25 It 2.9« 3J5
S B. Foot
Tanning Co
Red Wing,
93 3,135 223
U30 and 256 gpd/sq
Variable 2,500*-
7M7 2,500"
Moench
Tanning Co
Gowanda,
New York
Volumetric loading on
biolog.cal unit 3,7\2
kg/day/1,000 cu m (229
Ib BODj/day/l,000 cu
ft) F.nal clanf,er
overflow rate 20.4-
2k !( cu m/day/sq m
(500-600 gpd/sq ft)
Pi lot study of flows
from 0 09 to 0 19 I/
sec (1.5 to 3 gp"0 .
1,751-4,409 kg/day/
1,000 cu m (108-272 Ib
BOD5/day/l,000 cu ft) .
flows 8.M7 9 cu m/
day/sq m (200-^0 gpd/
sq ft) and final clarl-
fiers 12 2-22.0 cu in/day
sq m (SOO-S^O gpd/sq ft).
88
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Tannery #10 is in the process of initiating full facility
operations for an estimated 3,785 cu m/ day (1 mgd) flow from a
chrome tanning, hair pulp facility and finishing operations. The
project is partially financed through an Environmental Protection
Agency grant.
The combined tannery flows are screened, then pumped to dual
plain sedimentation basins. The 10.7 m (35 ft) diameter
clarifiers are equipped with surface skimmers. Overflow rates
are approximately 21.6 cu m/day/sq m (460 gpd/sq ft) under
present conditions. A potential of four concrete lined lagoons
may be utilized for activated sludge aeration basins. Each
lagoon has a capacity of about 3,785 cu m (1 mg) at 1.8 m (6 ft)
operating depth. The depth may be varied in operation. Separate
controls permit series, parallel, or a combination of lagoon
operations. An aeration capacity of 22.3 kw (30 hp) per lagoon
was initially indicated; however, a higher capacity may be
required. Return sludge design permits recycle to each lagoon as
well as ahead of the primary clarifiers. Aeration is followed by
final sedimentation in two 12.2 m (40 ft) diameter clarifiers.
The effluent is chlorinated prior to discharge to a nearby water
course. Primary and waste activated sludge will be dewatered in
a pressure filter and landfilled on-site. Automatic samplers
permit monitoring of individual treatment units to ensure better
operational control. The data presented in Table 14 represents
only partial operation of this facility. Operating data to be
developed should be beneficial to the industry due to the
numerous operating ranges and controls provided in the system.
A full-scale activated sludge plant in Kentucky, Tannery #14, was
evaluated in a two-week study by the Environmental Protection
Agency (37). This tannery is a cattlehide tannery with pulp hair
beamhouse operations and a combination of alum, chrome, and
vegetable tanning. At the time of the study, flow was only 61 cu
m/ day (0.016 mgd) of an anticipated 136 cu m/day (0.036 mgd)
operation. The treatment system consists of screening, primary
sedimentation, activated sludge, and secondary sedimentation.
Overflow rates of 13.6 and 13.4 cu m/day/sq m (290 and 285 gpd/sq
ft) were observed in primary and secondary units, respectively.
Average hydraulic detention time was 1.6 days in the aeration
basin. The following efficiencies were observed during
operations:
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BOD5
Suspended Solids
COD
Sulfide (as S)
Total Kj^ldahl Nitrogen (as N)
Organic Nitrogen (as N)
Ammonia Nitrogen (as N)
Nitrite (as N)
Nitrate (as N)
Alkalinity (as CaCO3)
*Grab Sample
mg/1
1,437
3,135
4,016
7.9
490
328
162
0.1
0.1
516
Mfluent Removal
~mg/l ~" %
96
223
481
0
322
175
1U7
34*
0.4
141
93
93
88
100
34
47
9
73
The EOD5 of the effluent was below 100 mg/1, indicating a removal
of 93 percent at a volumetric loading of 908 kg/day/1,000 cu m
(56 Ib BOD5/day/l,000 cu ft). Although suspended solids
reductions were high (93 percent), the effluent concentration was
slightly above 200 mg/1. Apparent clarification difficulties
exist. The COD was reduced 88 percent. Sulfides were completely
oxidized in the aeration basin. The low removal of kjeldahl
nitrogen (34 percent) shows minimal nitrification occurred even
at the extended aeration time of 1.6 days. The possible toxic
effects of high ammonia concentrations on nitrifying bacteria is
indicated as a cause for the low removal (37). The alkalinity of
the effluent was 114 mg/1 with a pH of 7.3
An activated sludge facility in New York State (Tannery #15), is,
presently, treating effluent from save hair beamhouse, chrome
tan, and finishing operations. Total waste water from these
processes is about 1,514 cu m/day (0.4 mgd). Combined flows are
screened prior to equalization and adjustment of pH to 11.0. In
some instances addition of lime is required. The equalization
basin has a 24-hour capacity under present conditions. The
unclarified discharge from the equalization basin is directed to
an aeration basin with approximately 12 hours detention with a
volumetric load on the basin of about 3,566 kg/day/1,000 cu m
(220 Ib BOD5/day/l,000 cu ft). The final clarifier has an
overflow rate of 23.5 to 28.2 cu m/day/sq m (500 to 600 gpd/sq
ft).
An organic removal of
concentration of 343
percent are reported.
80 percent produced an effluent BOD5
mg/1. Suspended solids reductions of 92
Effluent suspended solids concentrations
90
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of 190 mg/1 reflect ineffective solids capture in the final
clarifier. The pH of the effluent is 8.0-8.5. The most
interesting aspects of these treatment operations are the high pH
of waste entering the aeration basin and the high mixed liquor
suspended solids concentration maintained in the aeration basin.
Normally, a pH above 11.0 is indicated as potentially toxic to
biological activity. However, carbon dioxide derived from
organism respiration is adequate to reduce the pH to about 8.0,
at which level biological conversions proceed. Since primary
clarification is not provided, all suspended solids in the
tannery waste go directly to the aeration basin. All solids
capture must, therefore, occur in the final clarifier.
Another biological treatment innovation is the oxidation ditch.
The oxidation ditch is essentially a modified form of the
activated sludge system. Applications of this process on
domestic waste treatment are numerous in Europe. Pilot studies
indicate a potential for high strength tannery waste treatment.
As proposed for tannery treatment, clarified wastes are directed
to an oval ditch or "race track" for aeration. Separate
equalization facilities are not required, since the ditch
provides excellent equalization (13). An adjustable speed brush
rotating across the full width of the channel imparts oxygen to
the waste water and regulates the velocity of flow in the
channel. The effluent is clarified prior to discharge with the
sludge returned to the aeration zone. The oxidation ditch
provides a much larger aeration volume than conventional
activated sludge. The resulting F/M ratio is very small. At
these low F/M ratios (0.05) and long detention time, endogenous
respiration minimizes the amount of waste sludge.
A pilot operation treated portions of the flow from a side
leather tannery utilizing 25,060 kg/day of green salted hides
(55,200 Ib/day). The tanning process produced 1,800 cu m/day
(0.475 mgd) of waste water from pulp hair, chrome tan, and
finishing operations. The average flow to the pilot facility was
5 percent of the tannery discharge, or 90 cu m/day (0.024 mgd).
The pilot plant feed remained proportional to the fluctuating
supply to provide realistic variations of flow. After
proportioning, the waste water was pre-settled for 30 to 45
minutes, then discharged to the oxidation ditch. The primary
sludge was thickened for 12 hours prior to dewatering on drying
beds. Hydraulic detention time in the oxidation ditch varied
from two to three days, and the rate of activated sludge return
was estimated at 75 percent. Production of secondary sludge was
about 0.3 kg (Ib) dry solids/kg (Ib) BOD5_ applied, or 0.55 kg
(Ib) dry solids/kg (Ib) BOD5 without primary sedimentation. The
organic load on the ditch varied from 23.5-48.2 kg BOD5/day (51.8
to 106.2 Ib BOD5_/day) . The oxygen supplied was about 1.5 times
the average BOD5 load., however. This was not sufficient for peak
demands. Adjustment of brush rotation and submergence to
increase oxygen transfer may be required for peak demands. The
following pilot efficiencies resulted during summer operation
(13):
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Preset, tied
Influent* Effluent* Removal*
mg/1 mg/1 %
BOD5 500-1,500 15 98
COD 1,000-2,300 7300 85
Sulfide 10-80 0 100
Chrome (Cr+++) 1
Total Nitrogen (as N) 250 60-150 UO-76
Ammonia Nitrogen (as N) 100 45-125 0-50
*0rder-of-magnitude
High removals of BOD5 (98 percent) and COD (88 percent) result at
the low F/M ratio. Sulfides were completely oxidized with brush
aeration. Precipitation of chrome was highly effective with
concentrations below 1 mg/1 observed in the effluent.
Nitrification was sporadic, with some denitrification through the
liberation of free ammonia or nitrogen gas. The exact mechanism
of removal was not indicated. In general, the oxidation ditch is
an attractive modification to the activated sludge process.
Highly effective removals in BOD5, suspended solids, sulfides,
and chrome are demonstrated under desirable summer temperatures.
With the extremely low F/M ratio and adjustment for winter
operations, large system volumes are required. The limiting
factor on application appears to be the availability of land.
Activated sludge systems, including various modifications, have
been and can be effective in organic reductions with BOD5_
removals in excess of 90 percent and effluent concentrations
below 100 mg/1. Removals of suspended solids appear to be
critical with concentrations observed to be above 200 mg/1.
Proper design and operation of final clarifiers may improve
results; however, further treatment is indicated for
significantly higher efficiencies. The nitrification potential
of activated sludge systems has not been investigated at present
facilities. Although feasible in theory, direct application to
tannery wastes in pilot or full-scale facilities is non-existent.
Practical Biological Systems
Several tanneries do have biological treatment systems that are
partially effective. However, the treatment systems have not
maintained high levels of effluent reduction.
Reliability, operability and consistency of operation of the
waste water treatment processes found to be most frequently used
in the leather tanning and finishing industry can be high if
appropriate designs and operational techniques are employed. The
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end-of-pipe treatment utilizing biological systems is a well
established technology that requires attention to a limited
number of variables to insure a high degree of reliability.
The most important operational aspects of these biological
systems are equipment reliability and attention to operating
detail and maintenance. Spare aeration equipment (usually
floating surface aerators) improves the possibility of consistent
operation; however, many treatment systems have an adequate
overcapacity already installed as insurance against the results
of equipment failure. It is desirable to install spare equipment
at critical points, for example, sludge return pumps. Perhaps of
equal importance is a design that permits rapid and easy
maintenance of malfunctioning equipment.
Therefore, control of the biological treatment plant and the
consistency of the results obtained are largely a matter of
conscientious adherence to well-known operational and maintenance
procedures. Automatic control of biological treatment plants is
far from a practical point. Although in-line instrumentation for
measurement of pH, dissolved oxygen, temperature, turbidity and
so on, can improve the effectiveness of operation, its use is
minimal in the industry's existing waste water treatment plants.
Neveretheless, no practical in-line instrumentation can replace
the judicious attention to operational details of a conscientious
crew of operators.
Plant 383 in subcategory 1 employs aerated lagoons to attain a
BOD discharge of 1.9 kg/kkg (lb/1000 Ib). Plant 24 in
subcategory 3 utilizes a trickling filter plus aerated lagoons to
achieve a BOD discharge of 1.0 kg/kkg (lb/1000 Ib). The average
effluent BOD concentration of sampled data and industry data is
32 mg/1. Plant 47 in subcategory 3 has an activated sludge
system with lagoons. The BOD and SS discharger are 0.4 and 1.1
kg/kkg (lb/1000 Ib) respectively. The BOD effluent concentration
from both sampled data and industry data is 16 mg/1. Tannery 54
in subcategory 5 utilizes an anaerobic/aerobic lagoon system to
achieve a BOD and SS discharge of 1.7 kg/kkg (lb/1000 Ib).
Industry data indicated a BOD concentration of 20 mg/1. Plant
179 employs lagoons to attain a BOD and SS discharge of 2.7 and
1.5 kg/kkg lb/1000 Ib) respectively. Plant 43 in subcategory 2
utilizes lagoons to achieve a BOD discharge concentration of 38
mg/1 (industry data) or 30 mg/1 (sampled data). Three other
tanneries (185,400 and 447) report a BOD concentration of 50 mg/1
or less.
Although these systems are partially effective, there is no
present on-site tannery treatment facility which can achieve a
high level of effluent reduction of all major pollutants on a
consistent basis. Thus, an exemplary tannery treatment system
does not exist and the best practicable control technology
currently available is not the average of the discharge from the
best tannery waste treatment systems. The best practicable
control technology currently available is an integration of
present tannery waste treatment experience with performance data
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transferred from other industrial treatment operations, such as
from the meat packing industry. The unit operation and unit
processes combined to achieve the best practicable effluent
reduction are as follows:
Waste Flow
Screening
Equalization
Primary Settling
Aeration
Secondary settling
Sludge
Collection
Thickening
Disposal
This particular arrangement has been chosen not only because it
is a practical approach to treatment, but because it is one
system applicable to each of the six subcategories. The system
could utilize activated sludge or trickling filters or anaerobic
or aerobic lagoons or an oxidation ditch depending on the
individual tannery requirements.
Parameters used for design of principal items of equipment
employing activated sludge are as follows:
Equalization Basin Detention: 24 hours at design flow
Primary settling Overflow Rate: 20.4 cu m/day/sq m
(500 gpd/sq ft)
Secondary Settling Overflow Rate: 12.2 cu m/day/sq m
(300 gpd/sq ft)
Aeration Basin F/M Ratio: 0.5
MLVSS: 4,000 mg/1
BOD.5 Reaction Rate constant: 0.0015
Deep Bed Filtration Unit Flow Rate: 0.16 cu m/min/sq m
(4 gpm/sq ft)
Waste Sludge Primary: 2 percent solids
Secondary; 1 percent solids
Mixture thickened to 2.5 percent
solids
Vacuum Filter Loading Rate: 12.2 kg/sq m/hr
(2.5 Ib/sq ft/hr)
One factor concerning treatment requires special consideration
and is included in design considerations: most treatment plants
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have had difficulty with residual suspended solids in the treated
effluent. To ensure that the effluent will contain a minimum
residual of suspended solids, two factors are included in the
proposed design:
1. A low overflow rate of 12.2 cu m/day/sq m (300 gpd/sq
ft) in the secondary settling tank.
2. Provision for the addition of polymers to the secondary
settling tank as an aid to clarification.
Polishing Systems for Biological Treatment - Consideration has
been given to unit operations and process techniques which have
been used infrequently or not at all in tannery waste treatment.
They are as follows:
1. Filtration or microscreening of the effluent.
2. Carbon adsorption.
3. Color removal.
One problem experienced consistently with secondary treatment of
tannery wastes is the high suspended solids content of the plant
effluent. In some instances, this has been well over 100 mg/1.
Undoubtedly, some of this may be due to poor design or poor
operation. Nevertheless, there appears to be some evidence that
filtration or microscreening may be effective in correcting this
problem.
There are, at the present time, numerous applications of
suspended solids removal by filtration or microscreening being
used as a tertiary treatment process following conventional
secondary biological treatment. However, there is no known
application of this waste water treatment process existing in the
tannery industry.
A microscreen consists of a rotating drum with a fine screen
mounted on its periphery. Waste enters the drum through the open
end and passes through the screen leaving the suspended solids on
the inner surface of the screen. At the top of the drum,
pressure jets of effluent water are directed into the screen to
remove the mat of deposited solids. Numerous applications of
microscreening of secondary waste water effluent illustrates from
55 to 99 percent removal of suspended solids.
With the exception of gravity sedimentation, deep-bed filtration
is the most widely used unit process for liquid-solids
separation. Deep-bed filters have been employed in systems for
phosphorous removal from secondary effluents and in physical -
chemical systems for the treatment of raw waste water.
Waste containing suspended solids is passed through the filter
containing granular material resulting in the capture of
suspended solids in the bed. Eventually, the pressure drop
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through the bed becomes excessive or the ability of the bed to
remove suspended solids is impaired. The filtration cycle is
terminated and the bed is backwashed prior to being placed back
into service. In an ideal filter, the size of the particles
should decrease uniformly in the direction of flow. This
condition is partially achieved with the use of a multimedia deep
bed filter. This type of filter utilizes materials with
different densities ranging from the large size particles at the
top of the filter having the lowest density and the smallest
particles at the bottom of the filter having the highest density.
With this arrangement, the filter has a large storage capacity
for suspended solids, and is able to remain in operation for
longer periods of time. Influent solids should be limited to
about 100 mg/1 to avoid too frequent backwasiiing. Effluent
suspended solids are normally less than 10 mg/1.
Carbon adsorption using activated carbon in fixed beds is highly
effective in the removal of organic dissolved solids, many of
which are non-biodegradable. The granular carbon media provide
an effectively large surface area for adsorption. Biodegradation
of the captured material further increases the efficiency of the
process. Thermal regeneration is used to reactivate spent
carbon.
Laboratory 'analyses were made on carbon treatment of waste water
from Tannery #16 (52). These laboratory tests were performed on
waste that had been pretreated by pressurized aeration for
sulfide removal and air flotation/clarification for oil and
suspended solids removal. Results of these tests indicate that
carbon adsorption can provide an effluent essentially free of
suspended solids and colloidal material. The pilot plant
effluent contained approximately 300 mg/1 total organic carbon
(TOG). The full-scale design is indicated as having a potential
of reducing the effluent to less than 135 mg/1 TOC representing,
approximately, 80 percent reduction in oxygen demanding materials
(52). A carbon exhaustion rate of 1.25 kg carbon per cu m (10.5
Ib of carbon/1,000 gallons) of pretreated waste water is anti-
cipated for this removal efficiency.
Activated carbon is effective in color removal. Vegetable
tanning and dyeing operations contribute substantially to
effluent color. Color exists as both a soluble constituent and
colloidal suspension. The pilot study at Tannery #16 produced a
95 percent reduction in color (52). Tomlinson, et al., (53)
observed a 90 percent reduction in color from laboratory studies
of spent dye liquors at Tannery #1U, Color was effectively re-
moved at 2 to 4 grams of carbon/liter of spent dye liquors (53).
Activated carbon may have limited application in tannery
treatment since removals are confined to dissolved organic solids
such as spent dyes and tannin liquors. As an alternative to
secondary treatment, carbon adsorption requires extensive
pretreatment to effectively remove suspended solids that retard
the adsorption of dissolved material. The process would not.
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materially, reduce the high content of dissolved inorganic
materials such as sodium chloride (NaCl).
I
The problem of color of tannery waste is most pronounced in those
systems using vegetable tanning. Color is an optical effect.
The measured magnitude of color is not, necessarily, related to
a weight quantity of the heterogeneous mixture of materials which
is its cause. Because of the nature of the color, several
investigators (20) (54) have suggested the use of APHA cobalt-
platinum to be impractical. The hue and tint of vegetable
tanning solutions are different from color standards. Therefore,
several arbitrary approaches have been developed to determine
percent of color removed in a particular unit operation. For
this reason, further development of a standard is necessary.
Nevertheless, it is necessary that color removal be incorporated
in any treatment process for vegetable tanning wastes.
In no case observed or reported in the literature is a completely
effective system for color removal in operation. This does not
mean that such a system does not exist, but only that data is not
readily available. Data on activated carbon presented previously
indicates the anticipated performance of a full-size plant for
carbon removal. Eye (32) and Hagan (20) have both determined
that addition of 2,000 mg/1 of lime and 2 mg/1 of anionic polymer
to plant waste would produce 90 percent color removal. The
resulting pH of the waste was 11.5.
In many tanneries, the beamhouse waste can provide the major
portion of the lime requirements.
Major Reduction of All Forms of Nitrogen
The need for limiting the amount of the nitrogen compounds
entering rivers and lakes has been receiving increased attention.
The concern is for the fixed nitrogen and not elemental nitrogen.
Forms of fixed nitrogen include the following:
1. Organic nitrogen.
2. Ammonia and ammonium salts.
3. Nitrates.
4. Nitrites.
Normally, nitrites are not of major concern since they are
readily oxidized to nitrate or reduced to nitrogen gas by the
environment. All nitrogen forms can be considered as a nutrient
source for plant life including the simpler forms such as algae.
Ammonia can be toxic to fish and lower animals. Organic nitrogen
can be converted to ammonia in the stream and produce the same
results. Ammonia entering a stream will exert an oxygen demand.
Organisms will convert ammonia to nitrate utilizing stream
dissolved oxygen. One mg/1 of ammonia nitrogen reacts with 4.5
mg/1 of oxygen. Therefore, a serious oxygen depletion of the
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stream could occur with only a small ammonia concentration in the
waste. All of these factors emphasize the need for consideration
of nitrogen control.
Waste from the tannery contains nitrogen in both the organic and
ammonia forms. Organic and ammonia are reported together as
total kjeldahl nitrogen (TKN). Organic nitrogen in waste comes
principally from the unhairing operation resulting from removal
of protein degradation products. Where an amine is used in the
unhairing operation it contributes to the total organic nitrogen.
Some ammonia is formed in the unhairing operation by further
breakdown of protein material. However, the major source of
ammonia is ammonium sulfate in the waste stream from the bating
process. TKN content of the total plant waste stream can be over
900 mg/1 in some tanneries. The organic nitrogen portion of the
TKN can vary. One tannery (55) reports organic nitrogen content
equal to about 60 percent of the TKN. During detention periods
hydrolysis or other mechanisms convert organic nitrogen to
ammonia. A large portion of the organic nitrogen is present in
colloidal materials.
The following processes have been used for nitrogen removal:
1. Coagulation, flocculation, and settling.
2. Ammonia stripping.
3. Ammonia ion exchange.
4. Chlorination.
5. Biological nitrification^denitrification.
Coagulation, flocculation and settling is effective in partial
removal of soluble and colloidal protein matter. To optimize
this process, pH must be reduced to the isoelectric point of the
protein, which is usually in the range of 4.5 to 5.0. At that
point, the protein matter is least soluble. Some coagulant
addition may be necessary to provide good settling.
Ammonia stripping has been applied to municipal waters where the
ammonia nitrogen content is normally in the range of 15 to 30
mg/1. The pH of the waste must be increased to 11.0. No data is
available for tannery waste. Even at the lower ammonia
concentrations 3.0 cu m of air is required per liter of waste
(400 cu ft/gal) (56) .
Difficulties encountered in municipal waste treatment include
serious calcium carbonate scaling and the reduced efficiency at
low air temperatures. As the air temperature approaches 0° C
(32° F) the system becomes essentially ineffective. Removal
efficiency is 90 to 95 percent under optimum conditions but
organic nitrogen is not affected by ammonia stripping.
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Ammonia can also be removed from waste water by an ion exchange
media which is a natural zeolite, clinoptilolite. This material
is selective for the ammonium ion in the presence of ions such as
calcium, magnesium, and sodium found in waste water. For the
high ammonia content of tannery waste, capital investment for
such a system would be high. Also, the presence of only a small
concentration of large organic molecules can cause serious
fouling and degradation with commonly used ion exchange media.
Whether or not this fouling would pose a problem with the
selective ion exchange media used for tannery waste has not been
established.
Chlorination can be used to convert ammonia to nitrate. However,
at a dosage of 10 mg/1 of chlorine per mg/1 of ammonia nitrogen,
the cost is excessive except for very small concentrations.
In a biological system for removal of nitrogen, all organic
nitrogen must be hydrolyzed to ammonia or be converted to a form
from which it can be oxidized along with the ammonia present to
nitrate. In the activated sludge process, a part of the ammonia
and organic nitrogen is converted to nitrate. A higher
conversion is accomplished in a system where the F/M ratio is
low. Ammonia is converted to nitrite by a Nitrosomonas organism;
nitrite is converted to nitrate by a Nitrobacter organism. These
autotrophic microorganisms have a slow growth rate. One source
(57) indicated that even an extended aeration activated sludge
plant could not provide complete nitrification on a year-round
basis. In activated sludge plants treating tannery wastes, TKN
is reduced about 35 percent. Data for one plant is cited (55).
To be effective, the nitrification must be performed in a
separate biological system with a nitrification basin followed by
a settling tank. Optimum pH is 8.3 to 8.5. The organisms
utilize an inorganic source of carbon (carbon dioxide or
bicarbonate) and obtain energy from the ammonia oxidation
reaction.
The nitrate nitrogen content of tannery wastes treated by the
biological nitrification process is high. Nitrate nitrogen is
essentially the same level as the ammonia nitrogen in the raw
waste plus any organic nitrogen that is hydrolyzed prior to
treatment. To remove this nitrate, a biological denitrification
step in the treatment is required. This can be accomplished
under anaerobic conditions by denitrifying organisms. Equipment
required is a nitrification basin followed by a clarification
tank. Optimum pH is 6.5 to 7.5. Organisms using a source of or-
ganic carbon convert the nitrate to nitrogen gas. Since the
waste is normally lacking in organic carbon, methanol is added to
provide such a source. Rate of addition is about 3 kg of
methanol per kg (3 Ib/lb) of nitrate nitrogen. Essentially
complete denitrification is accomplished. If organic nitrogen is
present, it will be unaffected.
Since there has been no experience with major removal of all
forms of nitrogen in the tanning industry, these biological
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processes are used for the design and economic studies covered
later herein. Details concerning design criteria for
nitrification-denitrification processes are described in a design
seminar paper (58) .
Design criteria used are as follows:
Nitrification
Temperature 10°C (50°F)
MLVSS*: 5,000 mg/1
pH: 8,4
Loading Factor: 438 kg/day/1,000 cu m
(27 Ib NH3-N/day/l,000 cu ft)
Loading: 65 percent of raw waste NH3-N
Denitrification
Temperature: 10°C (50°F)
MLVSS*: 3,000 mg/1
pH: 7.5
Loading Factor: 530 kg/day/1,000 cu m
(33.7 Ib N03-N/day/l,000 cu ft)
*Mixed Liquor Volitile Suspended Solids
Major Removal of All Waste constituents
The major removal of all waste constituents refers to those
processes which remove dissolved solids. Tannery waste waters,
after extensive chemical and biological treatment, still contain
a high concentration of inorganic salts. These salts are
principally sodium chloride, calcium bicarbonate, calcium
sulfate, and calcium hydroxide. Calcium hydroxide used in the
unhairing operation reacts with ammonium sulfate and sulfuric
acids from the bating and pickling operations to form calcium
sulfate. Residual lime in waste is removed directly by settling
or precipitated by respiration carbon dioxide. Some minor
quantities of salts are present in the water supply. The major
part of dissolved inorganic solids is introduced from the raw
hides or processing solutions. Sodium chloride is present in the
incoming hides as a preservative. It is also present in the
pickling operation. Dissolved solids concentrations prior to
treatment may range from 6,000 mg/1 - 38,000 mg/1, with an
expected average of 10,000 mg/1 (10).
Unit treatment operations for removal of dissolved solids include
the following:
100
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1. Freezing.
2. Evaporation.
3. Electrodialysis.
4. Ion exchange.
5. Reverse osmosis.
Most of these processes produce a brine solution which requires
further concentration and special disposal.
Freezing - Freezing is a non-selective method of dissolved solids
removal. During freezing, ice crystals of pure water are formed.
The dissolved constituents are forced to the periphery of the
crystal platelets and adhere to the surface. The brine film is
removed from the surface of the crystals by washing. The ice-
brine separation has previously caused operational difficulties.
A more effective wash is required, and, also, one that does not
create a high volume of brine for ultimate disposal.
The freezing process has been proposed for treatment of clarified
tannery discharge at a tannery (10). However, to date no full-
scale operations have been implemented. Extensive pilot scale
studies are required prior to expenditures for full-scale
facilities. Freezing will have limited application in tannery
treatment until all phases of the process are proven reliable.
Evaporation - This process is perhaps the oldest method for
removal of dissolved solids. In principal, a saline solution is
evaporated with heat energy. The vapor produced is mineral free
and condensed for disposal or reuse. A strong brine solution
alone or with some salt crystallization remains for disposal.
Solar energy may provide the required heat of evaporation when
wastes are retained in large lagoons. However, climatic
conditions coupled with relatively high continuous flows and the
need for impervious soil or sealant imposes severe restrictions
on the geographic location for such lagoons.
Multiple effect evaporators have been used in industry for many
applications. A saline solution is heated to the boiling point,
normally at an elevated pressure. The steam produced is directed
to cooling in a second stage where the latent heat is used to
evaporate more solution. This arrangement is used for a number
of stages. Evaporation is carried out in each successive stage.
A triple effect evaporator for salt concentration will evaporate
slightly over two kg (Ib) of water per kg (Ib) of steam used.
Electrodialysis - Electrodialysis is a demonstrated process for
removalofdissolved solids in brackish waters. Basically, the
electrodialysis cell consists of alternate cationic and anionic
permeable membrances in a stack alternately charged by electrodes
101
-------
at. each end. An external power source maintains the potential
across the electrodes. Based on the charge, an ion will migrate
towards the oppositely charged electrode, but will be selectively
captured between the membrane stacks. Relatively pure water
remains between alternate membranes while the concentrated waste
brine collects 'in others. For waters of concentration less than
10,000 mg/1, the energy requirement in an actual installation is
of the order of 2.6 to 7.9 kwhr per cu m (10 to 30 kwhr per 1,000
gallons) of product water (59). This is less than the energy
required for the distillation process. The principal
disadvantages for tannery applications are membrane fouling,
polarization, and scaling from waste constituents. At present,
there is no record of tanneries using the electrodialysis
process.
Ion Exchange - This process is one in which there is an
interchange of ions between the liquid being treated and a solid
particulate media. The media is normally a zeolite or synthetic
resin. Major application has been in water softening where a
salt regenerated cation unit removes calcium and magnesium ions
from the water and replaces them with sodium ions.
For salt removal from tannery wastes both a cation and an anion
exchanger must be used. To make ion exchange economically
feasible for desalination of water, special ion exchanger
arrangements have been used. One of these is the DESAL process
which is a three bed system (60). Two of these beds contain
anion exchange media and the third contains a cation exchange
media. The operation method is such that only stoichiometric
quantities of regenerates are used, thereby providing substantial
economy over operation of standard demineralization equipment.
A suitable method must be used to dispose of spent regenerant
solutions. According to one manufacturer of ion exchange media,
this process is generally applicable to solutions containing less
than 3,000 mg/1 of ionizable solids. Based on this fact and that
resin fouling occurs from even small quantities of organic
matter, application for treatment of tannery waste which has a
salt content of well over 3,000 mg/1, waste is not considered
feasible.
Reverse Osmosis - Reverse osmosis is a process which is non-
selective with respect to dissolved solids removal and is
reasonably dependable. In osmosis, when a salt solution and a
pure solvent or a solution of less concentration are separated by
a semi-permeable membrane, the pure solvent flows through and
dilutes the salt solution. The process continues until
equilibrium is established. The semipermeable membrane allows
the pure solvent to pass, but not the solution. The driving
force is the strong chemical potential of the pure solvent. The
pressure developed in the process is the osmotic pressure. In
reverse osmosis, a pressure applied to the salt solution in
excess of the osmotic pressure forces the pure solvent through
the membrane leaving a concentrated brine. The success of the
system is dependent upon selection and maintenance of the
102
-------
membrane. Reverse osmosis has been effective for the treatment
of pulp and the paper mill wastes, acid mine drainage, and
municipal supplies with a high mineral content.
Pilot treatment of dilute pulp and paper effluents (61) produced
membrane rejections of 90-99 percent for most feedwater
components. Optimum performance is indicated at dissolved solids
concentrations of 5,000 to 15,000 mg/1. The resulting brine
solution was 8 to 10 percent solids.
Pilot scale studies on acid mine drainage (62) produced a product
water with 10 mg/1 dissolved solids from an influent containing
1,280 mg/1 dissolved solids. Product water or permeate was about
75 percent of the total flow. The permeate did not meet drinking
water standards.
An extensive pilot plant study was performed in California at the
Pamona Water Rennovation Plant (63). This study demonstrated
reverse osmosis obtained excellent rejection of dissolved solids
from the effluent of a waste treatment plant using activated
sludge and from a parallel plant using a granular activated
carbon bed. Effluent from both systems contained a dissolved
solids concentration of about 1,150 mg/1. The permeate contained
55 mg/1 dissolved solids producing a 95 percent removal. Ammonia
nitrogen and nitrate were reduced 95 percent and 75 percent
respectively. The ammonia nitrogen in the effluent was about 15
to 20 mg/1.
There has been no direct application of reverse osmosis for
treatment of tannery waste water. Investigations in the pulp and
paper industry indicate that wastes of similar concentration are
amenable to reverse osmosis. At these dissolved solids
concentrations, the osmotic pressures encountered are high
requiring higher applied pressures. There are several reasons
reverse osmosis may be more appropriate than other methods
discussed for the treatment of tannery wastes. The equipment is
easy to operate. Energy requirements are relatively low. Also,
an elevated operating temperature is not required. The process
is non-selective in dissolved solids capture producing a high
purity product water. The principal disadvantage is a large
volume of low concentrated brine. Membrane fouling has been
cited as a potential operational problem. Although, not proven
specifically for treating tannery wastes, it has been selected as
the most applicable for this study based on data available. It
will be necessary to prove by a demonstration project that this
is a viable process for this application.
Design is based on a projected 75 percent recovery of usable
water with a dissolved solids content of less than 500 mg/1.
This is an interpolation based on present experience of a 25
percent recovery with sea water (3.5 percent salt) and an
approximate 90 percent recovery with brackish water containing
3,000 mg/1 of dissolved solids (64) .
103
-------
Disposal of waste brine from the reverse osmosis process can
create a major problem. The waste brine constitutes 25 percent
of the waste treated.. Further treatment prior to ultimate
disposal is required. Research in advanced waste water treatment
and desalination has produced methods for handling brines. A few
of the techniques investigated are as follows:
1. Various types of solvent extraction.
2. Electrodialysis.
3. Solar evaporation.
4. Multiple effect evaporation.
5. Submerged combustion.
The various solvent extraction techniques for brine
concentrations are not fully developed for practical application
at this time.
Electrodialysis has shown the capability of brine concentrations
to 200,000 mg/1 (64). However, practical application requires
further development.
Solar evaporation ponds are, normally, the most economical means
for disposal of waste brines, however, their application is
restricted to areas where evaporation exceeds annual rainfall by
over 20 inches. These areas are principally in the west to
southwest. Unfortunately, most tanneries are located in the
northeast, southeast, and midwest, where humid climates make such
operations unpractical.
Multi-stage flash evaporators are applicable for concentrating
waste brines prior to ultimate disposal. The method is
economical for concentrating solids up to 10 percent. Higher
concentrations require multi-effect evaporators. Submerged
combustion may be utilized to concentrate brines beyond
saturation yielding crystal formation (65) .
None of these processes have been demonstrated on brine from
tannery waste. However, no special problems are anticipated.
The principal problem is ultimate disposal of the concentrate if
a salt is not crystallized and removed. Several possibilities
exist for ultimate disposal of concentrated brine;
1. Deep-well disposal.
2. Ocean disposal.
3. Complete evaporation.
Deep-well disposal of brines requires comprehensive geologic
study and field testing of potential disposal zones to assess the
safety and effectiveness of underground strata. Several
104
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potential dangers exist for such disposal including pollution of
fresh water supplies through encroachment and disturbance to
underground strata. Injection wells normally require detailed
investigations to ensure that liquids in the underground strata
are compatible both physically and chemically, to the waste
brines injected. Usually, high pressure pumping is required for
deep-well disposal.
Ultimate disposal in such reservoirs as the ocean may be
feasible, Normally, tanneries are not located in close proximity
to the ocean so that direct discharge is possible. Transport
costs make ocean disposal from most tanneries economically
unattractive.
For study purposes, a triple-effect evaporator is used for salt
crystallization followed by filtration and drying. The recovered
salt can be marketed for reuse.
Complete evaporation of the brine appears to be the most
generally applicable approach to the problem.
The impact of disposal of waste brines from the tannery industry
as well as those from other industries is likely to be a major
problem in future years as higher degrees of treatment are
implicated. Further study is required to determine methods of
disposal of brines.
In the tanning industry, a substitute for salt in the hide curing
process and increased reuse of process chemicals would be a major
step in eliminating this problem.
105
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SECTION VIII
COST, ENERGY, AND NON-WATER QUALITY ASPECTS
Cost_an^Reduction Benefits^of Alternative Treatment arid _Control
Technologies
A detailed economic analysis showing the impact of treatment and
control technologies upon the six subcategories within the
leather tanning and finishing industry is given in the document
"Economic Analysis of Proposed Effluent Guidelines, Leather
Tanning and Finishing Industry." Five alternative treatment
methods have been considered for Subcategories 1 to 6. For the
six subcategories, the alternatives include:
Alternative A - No waste treatment or control.
Alternative B - Preliminary treatment and chrome removal
Alternative C - Alternative B plus activated sludge.
Alternative D - Alternative C plus sulfide removal,
nitrification, and denitrification and filtration.
Alternative E - Alternative D plus reverse osmosis, and
evaporation.
Tables 15-20 illustrate the cost of waste water treatment for the
average size plants in each subcategory. Both investment and
total annual costs are shown for the various alternatives.
Basis of Economic Analysis - Following is a summary of the basis
for cost estimates presented in Tables 15-20.
1. Investment - Investment costs have been derived
principally from published data on waste water treatment
plant construction costs (66) (67), Stanley consultants'
cost data, and information from equipment manufacturers
and suppliers.
Published cost data for treatment facilities is derived,
primarily, from experience with waste water treatment
installations. Cost information has been reported by
some tanneries, but the data are not extensive enough to
serve as a basis for the estimates presented herein.
Basic data were developed by preparation of graphical
relationships between cost and size for each unit
operation. Based on treatment plant configuration,
design criteria, and size, costs for individual unit
operations were added together to determine major
facility costs.
107
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An allowance of 15 percent of the total investment has
been included to cover land, contingencies, engineering,
and overhead.
August, 1971 price levels have been chosen by the
Environmental Protection Agency and are used herein as
the base level for economic evaluation. Inflation since
August, 1971, has had a marked impact on the cost of
treatment facility construction, labor, and other costs
involved in this analysis as well as raw and finished
product prices. Inflationary trends should be taken
into consideration when evaluating the costs presented
herein in comparison with current costs.
Deprecjation_and Cost of^Capital jlnterest) - It was
assumed that the annual interest costs j(cost of capital)
and depreciation would be constant over the life of the
treatment facilities. A principal repayment period of
20 years was used. Costs were depreciated on a straight
line basis and the depreciation period of 20 years was
assumed equal to the principal repayment period and the
economic life of the facilities.
Cost of money was assumed to be an average of the cost
of debt capital and the cost of equity capital. Cost of
debt capital was assumed to be 8 percent and the cost of
equity capital 22 percent. Data for the last 10 to 12
years indicates that the average net return on equity
capital for the chemical industry and other
manufacturing has been 10 to 12 percent. Assuming
corporate income tax is equal to net return (50 percent
of gross return), gross return is estimated to be 22
percent. Sixty percent of the investment was assumed to
be debt capital and 40 percent equity capital. From
this analysis, an average rate for the cost of money
equal to 13.6 percent was determined. An average annual
value for cost of money was derived by subtracting the
straight line depreciation cost from the investment
cost, times the capital recovery factor. The costs were
about 8 percent of the capital investment.
Insurance andJTaxes - An annual cost of 1 1/2 percent of
the initial investment was used for insurance and taxes
on the waste treatment plant.
Operation and Maintenance Labor - Operation and
maintenance labor manhour requirements were based mainly
on published data, (66) (67), and independent estimates.
The operational requirements include general management
and supervisory personnel, equipment operators and
laborers, and clerical and custodial personnel.
Maintenance labor includes mechanical, electrical,
laborers, and other appropriate repair personnel.
108
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pounds)
Based on labor rates in the tanning industry and
municipal waste water treatment plants, (68) (69), an
August, 1971, average labor rate of $4.90 per hour
(including fringe benefits) was used to compute total
annual operation and maintenance labor costs. The costs
were approximately 10 percent of the capital investment.
Chemicals - Chemical costs used in the economic analysis
are based or. published literature typical in the U. S.
(70). The costs used are:
Methanol - $0.069 per liter ($0.26 per gallon)
Lime - $22.00 per metric ton ($2C.OO per ton)
Soda Ash - $3.96 per 100 kilograms ($1.80 per 100
Ferric Chloride - $8.80 per 100 kilograms ($4.00
per 100 pounds)
Polymer - $0.44 per kilogram ($0.20 per pound)
Chlorine - $13.20 per 100 kilograms ($6.00 per 100
pounds)
Sulfuric Acid - $36.40 per metric ton ($33.00 per
ton)
Ferric Sulfate - $46.30 per metric ton ($42.00 per
ton)
Sodium Hydroxide (50%) - $8.50 per 100 kilograms
($3.85 per 100 pounds)
Manganous Sulfate - $90.50 per metric ton ($82.00
per ton)
6. Energy - In broad context, energy includes electric
power and fuel. Electric power consumption for major
units such as aeration, pumping, and mixing was
estimated from available data, (66) (67). An allowance
of ten percent was made for small power users such as
clarifiers, chemical feed equipment, ventilation
equipment, and so forth. The cost of electric power was
assumed to be $0.015/kwhr.
For Alternative E, steam is required for evaporation,
dewatering, and drying of the waste brine. The cost of
steam ranged from $1.76 to $2.42/1,000 kg of steam
($0.80 to $1.10/1,000 Ib of steam).
109
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TABLE 15
WASTE WATER TREATMENT COSTS (1)
FOR SUBCATEGORY 1
ALTERNATIVE (4)
PARAMETER/COST B C D
PLANT RAW MATERIAL PRODUCTION
1000 kg hides/mo
(1000 Ib hldes/mo)
EQUIVALENT FINISHED PRODUCT (2)
1000 sq m hldes/mo
(1000 sq ft hides/mo)
AVERAGE FLOW
I/kg hide
(gal/lb hide)
ESTIMATED INVESTMENT COST(3)
($1000)
ESTIMATED ANNUAL INVESTMENT
$/1000 kg hides/yr
($/1000 Ib hides/yr)
ESTIMATED ANNUAL COST
($1000)
$/sq m hide
($/sq ft hide)
636
1,400
88
950
33
4
$361.5
47.3
21.5
88 ,6
0.084
0.008
636
1,400
88
950
33
4
$1,209.3
158.5
71.9
$296.3
0.281
0.026
636
1,400
88
950
33
4
$1,598.7
209.5
95.1
391.7
0.371
0.034
636
1,400
88
950
33
4
$2,473.1
323.8
147.2
$718.9
0.681
0.063
TYPICAL FINISHED PRODUCT
Price ($/sq ft hide) 0.640 0.640 0.640 0.640
TREATMENT COST AS PERCENT
OF PRODUCT PRICE 1.25 4.1 5.4 9.8
(1) All Costs Based on August 1971 Price Levels
(2) Raw Material Conversion Factor to Finished Product * 0.68 sq ft
Ib
(3) Assumes Treatment Facilities Sized to Meet Plant Production
with No Allowance for Growth
(4) ALTERNATIVE B - Preliminary Treatment (Chrome Removal)
ALTERNATIVE C - Alternative B plus Activated Sludge
ALTERNATIVE D - Alternative C plus Sulfide Removal,
Nitrification and Denitrificatlon, and Filtration
ALTERNATIVE E - Alternative D plus Reverse Osmosis and Evaporation
110
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TABLE 16
WASTE WATER TREATMENT COST (1)
FOR SUBCATEGORY 2
ALTERNATIVE (A)
PARAMETER/COST B C D
PLANT RAW MATERIAL PRODUCTION
1000 kg hides/mo
(1000 Ib hides/mo)
EQUIVALENT FINISHED PRODUCT(2)
1000 sq m hides/mo
(1000 sq ft hides/mo)
AVERAGE FLOW
I/kg hide
(gal/lb hide)
ESTIMATED INVESTMENT COST(3)
($1000)
ESTIMATED ANNUAL INVESTMENT
$71000 kg hides/yr
($/1000 Ib hides/yr)
ESTIMATED ANNUAL COST
($1000)
$/sq m hide
($/sq ft hide)
863
1,900
120
1,290
50
6
$517.2
49.7
22.6
$126.8
0.088
0.008
863
1,900
120
1,290
50
6
$1,459.0
140.9
64.0
$357.5
0.248
0.023
863
1,900
120
1,290
50
6
$1,914.6
184.9
83.9
$469.1
0.326
0.030
863
1,900
120
1,290
50
6
$3,697.2
356.8
162.2
$1,073.8
0.746
0.069
TYPICAL FINISHED PRODUCT
Price ($/sq ft hide) 0.640 0.640 0.640 0.640
TREATMENT COST AS PERCENT
OF PRODUCT PRICE 1.25 3.6 4.7 10.8
(1) All Costs Based on August 1971 Price Levels
(2) Raw Material Conversion Factor to Finished Product - 0.68 sq ft
" Ib
(3) Assumes Treatment Facilities Sized to Meet Plant Production
with No Allowance for Growth
(4) ALTERNATIVE B - Preliminary Treatment (Chrome Removal)
ALTERNATIVE C - Alternative B plus Activated Sludge
ALTERNATIVE D - Alternative C plus Sulfide Removal,
Nitrification and Denitrification, and Filtration
ALTERNATIVE E - Alternative D plus Reverse Osmosis and Evaporation
111
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TABLE 17
PARAMETER/COST
WASTE WATER TREATMENT COSTS (1)
FOR SUBCATEGORY 3
ALTERNATIVE (4)
BCD
PLANT RAW MATERIAL PRODUCTION
1000 kg hides/mo
(1000 Ib hides/mo)
EQUIVALENT FINISHED PRODUCT (2)
1000 sq m hides/mo
(1000 sq ft hides/mo)
AVERAGE FLOW
I/kg hide
(gal/lb hide)
ESTIMATED INVESTMENT COST(3)
($1000)
ESTIMATED ANNUAL INVESTMENT
$/1000 kg hides /yr
($71000 Ib hides /yr)
ESTIMATED ANNUAL COST
($1000)
$/sq m hide
($/sq ft hide)
431
950
51
550
42
5
$284.0
54.8
24.9
$ 69.6
0.114
0.010
431
950
51
550
42
5
$925.4
178.9
81.2
$226.7
0.370
0.034
431
950
51
550
42
5
$1,218.3
235.6
106.9
$298.5
0.488
0.045
431
950
51
550
42
5
$2,828.1
545.6
248.0
$ 590.2
0.964
0.089
TYPICAL FINISHED PRODUCT
Price ($/sq ft hide)
TREATMENT COST AS PERCENT
OF PRODUCT PRICE
0.780
1.3
0.780
4.4
0.780
5.8
0.780
11.4
(1) All Costs Based on August 1971 Price Levels
(2) Raw Material Conversion Factor to Finished Product
(3) Assumes Treatment Facilities Sized to Meet Plant Production
with No Allowance for Growth
(4) ALTERNATIVE B = Preliminary Treatment (Chrome Removal)
ALTERNATIVE C = Alternative B plus Activated Sludge
ALTERNATIVE D = Alternative C plus Sulfide Removal,
Nitrification and Denitrification and Filtration
ALTERNATIVE E Alternative D plus Reverse Osmosis and Evaporation
112
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TABLE 18
WASTE WATER TREATMENT COSTS (1)
FOR SUBCATEGORY 4
ALTERNATIVE (4)
PARAMETER/COST B C D
PLANT RAW MATERIAL PRODUCTION
1000 kg hides/mo
(1000 Ib hides/mo)
EQUIVALENT FINISHED PRODUCT(2)
1000 sq m hides/mo
(1000 sq ft hides/mo)
AVERAGE FLOW
I/kg hide
(gal/lb hide)
341
750
84
900
17
2
341
750
84
900
17
2
341
750
84
900
17
2
341
750
84
900
17
2
ESTIMATED INVESTMENT COST(3)
($1000) $177.3 $466.2 $618.5 $986.6
ESTIMATED ANNUAL INVESTMENT
$/1000 kg hides/yr
($/1000 Ib hides/yr)
ESTIMATED ANNUAL COST
($1000)
$/sq m hide
($/sq ft hide)
TYPICAL FINISHED PRODUCT
Price ($/sq ft hide)
TREATMENT COST AS PERCENT
OF PRODUCT PRICE
43.3
19.7
$43.5
0.043
0.004
0.610
0.7
113.9
51.7
$114.2
0.113
0.010
0.610
1.7
151.1
68.6
$151.1
0.150
0.014
0.610
2.3
241.2
109.6
$267.3
0.265
0.025
0.610
4.1
(1) All Costs Based on August 1971 Price Levels
(2) Raw Material Conversion Factor to Finished Product =
(3) Assumes Treatment Facilities Sized to Meet Plant Production
with No Allowance for Growth
(4) ALTERNATIVE B = Preliminary Treatment (Chrome Removal)
ALTERNATIVE C = Alternative B plus Activated Sludge
ALTERNATIVE D = Alternative C plus Sulfide Removal,
Nitrification and Denitrification and Filtration
ALTERNATIVE E = Alternative D plus Reverse Osmosis and Evaporation
113
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TABLE 19
WASTE WATER TREATMENT COSTS (1)
FOR SUBCATEGORY 5
ALTERNATIVE (4)
PARAMETER/COST B C D
PLANT RAW MATERIAL PRODUCTION
1000 kg hides/mo
(1000 Ib hides/mo)
EQUIVALENT FINISHED PRODUCT (2)
1000 sq m hides/mo
(1000 sq ft hides/mo)
AVERAGE FLOW
I/kg hide
(gal/lb hide)
ESTIMATED INVESTMENT COST (3)
($1000)
ESTIMATED ANNUAL INVESTMENT
$71000 kg hides/yr
($/1000 Ib hides/yr)
ESTIMATED ANNUAL COST
($1000)
$/sq m hide
($/sq ft hide)
148
325
66
715
62.5
7.5
$249.5
140.8
64.0
$61.2
0.077
0.007
148
325
66
715
62.5
7.5
$540.5
304.3
138.2
$132.4
0.167
0.015
148
325
66
715
62.5
7.5
$756.3
425.8
193.3
$185.3
0.234
0.022
148
325
66
715
62.5
7.5
$1,299.4
733.0
333.2
$363.2
0.459
0.042
TYPICAL FINISHED PRODUCT
Price ($/sq ft hide) 0.48 0.48 0.48 0.48
TREATMENT COST AS PERCENT
OF PRODUCT PRICE 1.5 3.2 4.5 8.8
(1) All Costs Based on August 1971 Price Levels
(2) Raw Material Conversion Factor to Finished Product = 2.2 sq ft
Ib
(3) Assumes Treatment Facilities Sized to Meet Plant Production
with No Allowance for Growth
(4) ALTERNATIVE B = Preliminary Treatment (Chrome Removal)
ALTERNATIVE C = Alternative B plus Activated Sludge
ALTERNATIVE D = Alternative C plus Sulfide Removal,
Nitrification and Denitrification and Filtration
ALTERNATIVE E = Alternative D plus Reverse Osmosis and Evaporation
114
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TABLE 20
PARAMETER/COST
WASTE WATER TREATMENT COSTS (1)
FOR SUBCATEGORY 6
ALTERNATIVE (4)
BCD
PLANT RAW MATERIAL PRODUCTION
1000 kg hides/mo
(1000 Ib hides/mo)
EQUIVALENT FINISHED PRODUCT
1000 sq m hides/mo
(1000 sq ft hides/mo)
AVERAGE FLOW
I/kg hide
(gal/lb hide)
ESTIMATED INVESTMENT COST(3)
($1000)
ESTIMATED ANNUAL INVESTMENT
$/1000 kg hides/yr
($/1000 Ib hides/yr)
ESTIMATED ANNUAL COST
($1000)
$/sq hide
($/ sq ft hide)
499
1,100
(2)
70
750
17
2
$254.4
42.5
19.3
$62.3
0.074
0.007
499
1,100
70
750
17
2
$747.2
124.8
56.7
$183.1
0.218
0.020
499
1,100
70
750
17
2
$1,031.2
172.2
78.2
$252.6
0.301
0.028
499
1,100
70
750
17
2
$1,374.4
229.0
104.1
$408.6
0.486
0.045
TYPICAL FINISHED PRODUCT
Price ($/sq ft hide)
TREATMENT COST AS PERCENT
OF PRODUCT PRICE
0.31
2.3
0.31
6.5
0. 31
9.0
0.31
14.5
(1) All Costs Based on August 1971 Price Levels
(2) Raw Material Conversion Factor to Finished Product
0.68 sq ft
Ib
(3) Assumes Treatment Facilities Sized to Meet Plant Production
with No Allowance For Growth
(4) ALTERNATIVE B = Preliminary Treatment (Chrome Removal)
ALTERNATIVE C = Alternative B plus Activated Sludge
ALTERNATIVE D = Alternative C plus Sulfide Removal,
Nitrification and Denitrification and Filtration
ALTERNATIVE E = Alternative D plus Reverse Osmosis and Evaporation
115
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Effluent Reduction - Subcateqory^l - The following discussion for
Subcategory 1 deals with the sensitivity of effluent reduction
with respect to costs for Subcategory 1. This subcategory
represents a substantially larger segment of the industry than
any other subcategory. Costs are based on an average size
tannery in this subcategory processing 29,510 kg (65,000 Ib) of
hides per day.
Alternative A - No Waste,Treatment or Control
The estimated organic waste load for Subcategory 1 is 95 kg
BODj/1,000 kg (95 Ib BOD5/1,000 Ib) of hide. This represents 14
times that of normal domestic sewage.
Costs - None.
Reduction Benefits •<• None.
Alternative B - Preliminary Treatment and Chrome^Removal
This alternative includes in-process chromium removal, pumping,
screening, equalization, and primary clarification. Sludge
handling includes holding tanks and thickening units, Effluent
waste loads from this alternative are estimated to be HI kg
BOD5/1,000 kg (47 Ib BODjj/1,000 Ib) of hide processed. Reduction
of oil and grease, and chromium also occur.
Costs - The total capital investment cost is estimated to be
$361,500 for the model plant. The annual treatment cost is
estimated to be less than $90,000.
Reduction Benefits - Alternative B represents about a 50 percent
reduction in BOD5 compared with Alternative A. Total reduction
in BOD5 with preliminary treatment would, therefore, be 50
percent. Other constituents are, also, removed as noted.
Alternative C Alternative B Plus Activated Sludge
This alternative provides the same units as pretreatment with the
addition of an aeration basin and secondary clarifier. The
effluent waste load is estimated at 4.0 kg BOD5/1,000 kg (4.0 Ib
BODJ/1,000 Ib) of hide processed for the average Subcategory 1
tannery treatment facility.
Costs - Alternative C represents a total capital investment of
$1,209,300 and an annual cost of $296,300. These costs represent
an increase of $850,000 in capital costs and almost over $200,000
in annual costs over Alternative B.
Reduction Benefits - Alternative C represents a reduction in BOD5
of 91 percent over Alternative B. This represents a total
reduction in plant BOD5 of 95.8 percent.
Alternative D - Alternative C Plus Sulfide Re.2i2y.alx. Nitrification
and Denitrification, and Filtration
116
-------
Alternative D includes the treatment units for Alternative C with
the addition of a sulfide removal process, chlorination,
nitrification basin, covered denitrification basin, sulfide
removal process, aeration flume,and a graded media filter. The
effluent from the average Subcategory 1 tannery treatment
facility would be 1.4 kg BOD5/1,000 kg (1.4 Ib BOD5/1,000 Ib) of
hide processed. Significant removal of sulfide and nitrogen
would, also, result.
Costs - Alternative D represents a total capital investment of
$1,598,700 and an annual cost of $391,700 These costs represent
an increase of almost $390,000 in capital costs and about $95,000
in annual costs over Alternative C.
Reduction Benefits - Through Alternative D, there is an
incremental reduction in BOD5_ of 65 percent over Alternative C.
Total reduction in BODJ would be about 98.5 percent. Sulfide and
nitrogen removals, also, result.
Alternative E - Alternative D Plus Reverse QsmosiSj, and
Evaporation
Alternative E includes the same operations as Alternative D with
the addition of a reverse osmosis unit for the removal of
dissolved solids, evaporation facilities for concentration of the
rejection water from the reverse osmosis unit, and
dewatering-drying facilities for the waste brine. In addition to
these, the final clarifier in Alternative D would be replaced by
a reactor clarifier with provisions for soda ash addition to
soften prior to reverse osmosis and evaporation. Reverse osmosis
product water and condensed evaporator water would be recycled to
the tannery wet processes. Alternative E would result in zero
discharge and no liquid wastes to the receiving streams,
Costs - The capital investment is estimated to be almost $900,000
more than Alternative D and annual costs are estimated to be over
$325,000 more than Alternative D.
Reduction Benefits - There would be an incremental reduction in
BOD5 of 100 percent over that of Alternative D, or a total
reduction in plant BODI5 load of 100 percent. All other
constituents would be completely removed.
Impact of Waste Treatment Alternatives, on Finished Product Price
Tables 15-20 illustrate the probable increases in finished
product prices for the six subcategories to pay for waste water
treatment. For the best practicable control technology currently
available, estimated increases in final product costs range from
1.7 to 4.4 percent for various subcategories.
117
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For the best available control technology economically
achievable, the estimated increase of final product cost ranges
from 0.6 to 1.4 percent for various subcategories.
The overall cost of both best practicable and best available
control technology is estimated to increase final product costs
from 2.3 to 5.8 percent for various subcategories.
Alternative Treatment Systems
It has been assumed in the economic analysis that an activated
sludge process will be utilized for the biological treatment.
However, aerobic or aerobic-anaerobic lagoons can be designed to
provide the same degree of biological treatment. These lagoons
require substantial areas and can only be utilized where land is
readily available near the tannery. Lagoons may result in cost
savings of almost $150,000 over those costs presented for
Alternative c.
The estimated waste treatment costs for each subcategory are
given in Tables 15-20. The total investment cost estimated for
the leather tanning and finishing industry is $45.8 million for
best practicable control technology currently available
limitations (see Table 21), and $61.0 million or an increment of
$15.2 for best available control technology economically
achievable limitations (see Table 22).
The 1977 investment consists of $45.8 million for processors
outside municipal systems. including about $12.5 million each
for subcategories 1 and 3, about 9 million each for subcategories
2 and 5 and $2 million for subcategory 4. Distribution of 1983
costs is similar.
It is estimated that the current in-place treatment system
investment is in excess of $11 million. No credit has been
calculated for this in-place treatment in Tables 15-20 or Tables
21-22.
118
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Related Energy Requirements of Alternative Treatment and control
Technology
The energy requirements (electric power and fuel) for tanneries
vary considerably based upon reported data. This variation is
due to the following factors:
1. Type of hide tanned.
2. Type and extent of beamhouse, tan yard, and finishing
operations.
3. Degree of mechanization within the tannery.
4. Climate of the tannery location.
Energy requirements for a typical Subcategory 1 tannery
processing hide from raw material to finished product are
approximately 0.46 kwhr/kg of hide (0.21 kwhr/lb) of electrical
energy and 3,560 kg cal/kg of hide (6,700 Btu/lb) for steam.
Following is a discussion of the additional power requirements
for waste treatment Alternatives A through E.
There is no treatment provided by Alternative A, hence, energy
use is zero.
Alternative B treatment energy requirements are approximately
0.049 kwhr/kg (0.022 kwhr/lb) of hide. This represents about 10
percent of the tannery electrical energy demand, and about 1% of
total energy required. The major units requiring this energy are
the pumps and equalization tank mixers.
The treatment units in Alternative C require nearly 0.174 kwhr/kg
(0.079 kwhr/lb) of hide processed. This represents a power use
approximately 36 percent above that needed for Alternative B, and
about 7.2% of total energy required. The major power demanding
units in Alternative C are pumps, equalization tank mixers and
aeration equipment.
The energy required for Alternative D treatment is 0.346 kwhr/kg
(0.157 kwhr/lb) of hide. This is twice the energy required in
Alternative C, and about 1,2% of total energy required. Major
energy use is similar to that in Alternative c with the addition
of recycle pumping and the aeration equipment for the
nitrification basin and aeration flume.
The electric energy requirments for Alternative E total 0.374
kwhr/ kg (0.170 kwhr/lb) of hide. This amounts to an increase of
approximately 8 percent over Alternative D and is due,
principally, to requirements of the feed pumps for the reverse
osmosis unit.
In addition to electrical requirements, steam is needed for
evaporation and drying the salt. Steam requirements are about
3,820 kg cal/kg (7,200 Btu/lb) of hide in the form of steam.
121
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This represents an increase of approximately 107 percent over the
energy requirements of an average tannery (Subcategory 1) without
treatment facilities.
Nonwater Quality Aspect^ of Alternative Treatment and Control
Technology _-,-^ _
Air Pollution - Particulate matter and hydrogen sulfide are the
two potential causes of air pollution from the leather tanning
and finishing process. Hydrogen sulfide is toxic even in low
concentrations and is the main cause of process odor. Hydrogen
sulfide is formed principally by reactions involving sulfide
wastes from the unhairing process. Proposed in-process control
includes oxidation of sulfides with a catalyst prior to discharge
to the main plant sewers and treatment. This avoids any air
pollution problems that could result from sulfides and improves
the safety of workers in and around the treatment system. Use of
biological systems to remove nitrogen instead of ammonia
stripping also avoids potential air problems which could result
from venting ammonia from the highly concentrated waste.
The major potential source of air particulate matter from a
tannery is from hide buffing operations. However, most tanneries
control this by wet scrubbing. Scrubber water is generally
combined with the total waste stream. Several tanneries are
adding buffing dust to sludge derived from liquid waste treatment
for disposal.
In addition to process sources, tannery boilers can be a source
of air pollution. With proper design and maintenance of gas and
oilfired boilers, there should be no emission problems. However,
with coal-fired boilers, fly ash emissions are a problem. Fly
ash emissions can be kept to a minimum with proper design and
operation. Dust collection equipment may be used to further
control air pollution. Wet scrubbers or electrostatic
precipitators are capable of providing in excess of 98 percent
removal of the fly ash. If a wet scrubber is used, the waste
dust slurry can be discharged to the waste water treatment
system. Fly ash from the electrostatic precipitators can be
combined with the dewatered sludge for disposal.
Boiler flue gas contains sulfur dioxide when the fuel burned in
the boilers contains sulfur. Some coal and heavy fuel oils
contain sulfur and emit sulfur dioxide when burned. Burning low
sulfur fuel is one method of minimizing sulfur dioxide air
pollution problems. Gas scrubbing devices for removal of sulfur
dioxide are now in the development stages.
Solid Waste Disposal - Solid waste from tanneries and tannery
wastewater treatment plants includes the following:
1. Fleshings.
2. Hair.
122
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3. Raw hide trimmings.
4. Tanned hide trimmings.
5. Sanding and buffing dust.
6. Lime sludge.
7. chrome sludge.
8. Biological sludge.
9. Grease
10. General plant waste.
Most tanneries recover fleshings and raw hide trimmings for sale
to rendering plants or conversion into glue at the tannery site.
Tanned hide trimmings are often sold as by-products. Office and
general plant waste is either hauled away by a local refuse
disposal service or disposed of on-site.
In save-hair operations, the tannery has facilities for washing,
drying, and baling of the hair. The baled hair is sold as a by—
product.
Sanitary landfills are best suited for disposal of tannery waste.
Incineration and high temperature treatment are not recommended
for sludges containing chrome, since chrome may be reduced from
the trivalent to the hexavalent state.
Tannery sludges containing chrome should not be spread on the
land until further efforts are made to define the impact of these
waste materials upon the environment.
Alternatives B through E assume sludge disposal costs. Disposal
includes hauling the dewatered sludge to a landfill as well as
landfill operating costs. Anticipated for disposal in landfills
are chemical, lime, chrome, and biological sludges.
The selection of a proper site for landfill operations is of
prime consideration. Requirements in the selection include:
sufficient area; reasonable haul distance; remote location
relative to residential, commercial, and recreational
developments; soil conditions and rock formations; accessibility
to existing transportation networks; and proximity to existing
groundwater supplies. The soil cover should be sloped such that
precipitation will run off rather than percolate and pollute
groundwater sources. Other factors to be considered include
provisions to prevent the obstruction of natural drainage
channels, location to avoid flood waters, and the consideration
of possible fire hazards.
123
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SECTION IX
BEST PRACTICABLE CONTROL TECHNOLOGY CURRENTLY AVAILABLE
GUIDELINES AND LIMITATIONS
General
The effluent limitations which must be achieved by July 1, 1977,
are to specify the degree of effluent reduction attainable
through the application of the Best Practicable Control
Technology Currently Available. The best practicable control
technology currently available is generally based upon the
average of the best existing performance by plants of various
sizes, ages and unit processes within the industry. This average
is not based upon a broad range of plants within the leather
tanning and finishing industry, but upon performance levels
achieved by exemplary plants. In industrial categories where
present control and treatment practices are uniformly inadequate,
a higher level of control than any currently in place may be
required if the technology to achieve such higher level can be
practicably applied by July 1, 1977.
In establishing the best practicable control technology currently
available effluent limitations guidelines, consideration must
also be given to:
1. The total cost of application of technology in relation
to the effluent reduction benefits to be achieved from
such application.
2. The age and size of equipment and facilities involved.
3. The processes employed.
4. The engineering aspects of application of various types
of control techniques.
5. Process changes.
6. Non-water quality environmental impact (including
energy requirements).
Also, best practicable control technology currently available
emphasizes treatment facilities at the end of manufacturing pro-
cesses, but includes control technologies within the process it-
self when the latter are considered to be normal practice within
an industry.
A further consideration is the degree of economic and engineering
reliability which must be established for the technology to be
"currently available." As a result of demonstration projects,
pilot plants, and general use, there must exist a high degree of
confidence in the engineering and economic practicability of the
125
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technology at the time of commencement of construction of
installation of the control facilities.
Effluent Reduction Attainable
Based upon information contained in Sections III through VIII of
this report, a determination has been made of the degree of
effluent reduction attainable through the application of the best
practicable control technology currently available. The effluent
concentrations which could be achieved were estimated and applied
to the respective water uses for each subcategory (see Table 7).
BOD5 and TSS calculations are based on an effluent concentration
of about 75 mg/1; most total chromium and oil and grease
limitations are based on 2 mg/1 and 15 mg/1 respectively. These
values then determine the weight of pollutants per weight of
product. Effluent limitation guidelines resulting from
implementation of this technology are presented in Table 23.
These are the recommended guidelines for each industrial
subcategory for plants discharging directly to surface waters.
The limitations require major removal of BODJ and suspended
solids.
As described in Section IV, severe economic impacts require
different BOD5 and TSS limitations for small plants and some
medium sized plants. Accordingly, additional allocations equal
to one half the effluent limitations guidelines for BOD5 and TSS
are allowed tanners with a production less than 17,000 kg hide
per day.
126
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TABLE 23
BEST PRACTICABLE EFFLUENT LIMITATIONS
MAXIMUM THIRTY DAY AVERAGE
(July 1, 1977)
SUBCATEGORY
PARAMETER (1)
BOD5_
TOTAL CHROMIUM
OIL & GREASE
TSS
kg/1000
1 2
4.0
0.10
0.75
5.0
4.6
0.12
0.90
5.8
kg hide
3
3.8
0.05
0.75
4.8
(lb/1000
4
1.6
0.10
0.25
2.0
Ib hide)
5
4.8
0.06
0.90
6.0
6
2.8
0.10
0.35
3.4
(1) For all subcategories pH should range between 6.0 and 9.0 at any time.
127
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Best. Practicable Control^TechnologY^gB££gS^j-Y,
The best practicable control technology currently available for
the feather tanning and finishing industry has previously been
identified in Section VII (for Subcategories 1 through 6) under
the headings "In-Process Methods of Reducing Waste," "Preliminary
Treatment," and "Major Reduction of BOD5, and Suspended Solids."
Principal control and treatment operations needed to meet these
limitations are generally summarized in Section VII. The
effluent reduction attainable is based upon the transfer of
performance data from other industrial operations whose treatment
technologies are generally believed to be transferred to the
leather industry. Other industries such as the meat packing
industry currently treat high strength wastes containing organic
matter and suspended solids and achieve the high removal
efficiencies required by BPCTCA. The required effluent quality
is being achieved by the tanning industry, but not on a
consistent basis. Because the effluent quality representing that
attainable through the implementation of BPCTCA is not achieved
consistently, technology and performance information has been
transferred from other industry treatment operations.
Complete Treatment - Subcategories 1 to 6
1 . Recycle of chrome and vegetable tan solutions
(where applicable) .
2. Fine screening.
3. Equalization to dampen quality and quantity fluc-
tuations which will impair subsequent processes,
particularly biological units.
U. Primary settling to provide oil and grease
separation, precipitate chromium from rinse
waters, and partially remove BOD5, COD, and
suspended solids.
5. Aeration and secondary settling to further reduce
BOD5, COD, and suspended solids.
6. Sludge handling and disposal.
The above summary of treatment steps, generally, applies to
Subcategories 1 through 6. A few minor alterations are required.
One change in the steps includes addition of lime after primary
settling for tanneries which have acid waste (sheepskin) .
Rationale for Selection of the Bejst Practicable Control
Technology Currently Available
To^§l^gost_of Achieving Effluent Reduction Based upon information
contained in Section VIII of this report, the leather tanning
and finishing industry discharging to receiving waters would have
to invest an estimated $45.8 million (August, 1971, price levels)
128
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to achieve the effluent limitations recommended herein. No in-
place treatment capital is assumed. The total annual costs for
pollution control including depreciation, interest, and operation
and maintenance will likely result in an increase in finished
product price ranging from 1.7 to 4.4 percent for the various
subcategories.
Age and__Size of Equipment and Facilities - As indicated
previously in this report, there appears to be no significant
data to substantiate that either the age or size of the tannery
justify special consideration of different effluent limitations.
Data indicates some of the oldest and smallest tanneries are
currently achieving levels of treatment equivalent to those
achieved by large new facilities.
Engineering Aspects of Control Technique Application
The specific level of technology is practicable because it is
being practiced by plants in the tannery industry as well as
other industries with high strength wastes. The tannery industry
does not achieve this level of effluent reduction. One plant in
subcategory 1 (383) and one plant in subcategory 3 (24) meet the
BOD limitations in kg/1000 kg (16/1000 Ib) but not TSS limits.
Two plants in subcategory 3 (47 and 179) meet the TSS limitations
and almost achieve the BOD limitation.
In terms of achieving a BOD effluent discharge of 75 mg/1, the
following plants achieve less than this level of reduction: plant
43 in subcategory 2; plants 24 and 47 in subcategory 3; and plant
54 in subcategory 5. Tanneries 185, 400 and 447 also achieve an
effluent discharge with less than 75 mg/1 BOD. Thus, there are
tannery plants that are capable of achieving the stated effluent
limitations on a consistent basis. In a few cases, the presence
of a knowledgable operator is the only requirement. In general,
some minor plant design changes along with cooperation from
management and plant personnel will be required.
Processes Employed - As indicated in earlier sections, there are
differences in tanning processes which result in varying raw
waste characteristics. These variations have been recognized by
establishing six major industry subcategories for effluent
limitations.
Process Changes - The control and technology required for
implementing the best practicable control technology currently
available does require some in-process changes for some
tanneries. These modifications are principally chrome and
vegetable tan solution reuse which are currently practiced by
several industries.
Nonwater Quality ^Environmental Impact - There is one essential
impact of waste treatment upon nonwater elements of the
environment and this is disposal on the land of general tannery
solid wastes and waste sludge from treatment facilities. Most of
129
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the waste trimmings and hair from hides are being recovered as
by-products. Reuse of chrome in the tannery will substantially
reduce chrome levels in waste sludge from the treatment facility.
This will, also, reduce the potential release of toxic chrome to
the environment when the dewatered sludge cake is disposed of in
a landfill. In all cases, however, dewatered sludges from chrome
tanneries should be handled separately at a landfill to avoid any
potential difficulties. Proper siting and operation of a
landfill will minimize the impact of disposal of waste solids
from the tannery on the land.
£^£i2£§ i2 be Considered in Applying Level I Guidelines
1. Limitations are based on thirty day averages. Based on
performances of exemplary biological waste treatment systems,
daily limitations should not exceed the thirty day average
limitations by more than one hundred percent.
2. If a tanner processes hides in more than one subcategory, for
instance cattlehides and shearlings, the effluent limitations
should be set by proration on the basis of the percentage of the
total hide weight being processed in each subcategory.
3. If a tanner is required to provide nitrification in order to
meet water quality standards, that portion of the BOD5 exerted by
nitrogenous matter (measured in the total kjeldahl nitrogen test)
should not be included in the total effluent BOD5 reading. The
nutrient requirement for the oxidation of organic materials
should be included in the BOD.5.
U. The production basis which is recommended for applying these
limitations is the daily average production of the maximum thirty
consecutive days.
130
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SECTION X
BEST AVAILABLE TECHNOLOGY ECONOMICALLY ACHIEVABLE -
GUIDELINES AND LIMITATIONS
General
The effluent limitations which must be achieved by July 1, 1983,
are to specify the degree of effluent reduction attainable
through the application of the "best available control technology
economically achievable". The best available technology
economically achievable is to be based on the very best control
and treatment employed within the industry or based upon
technology which is readily transferable to the industry. Since
there are no exemplary facilities which may be considered for
assessment of the best available control technology achievable
control and treatment technology, transfer of concepts applied
elsewhere are utilized.
Consideration must be given to the following in determining the
best available control technology economically achievable:
1. The total cost of achieving the effluent reduction
resulting from application of the best available control
technology economically achievable.
2. The age and size of equipment and facilities involved.
3. The processes employed.
U. The engineering aspects of the application of various
types of control techniques.
5. Process changes.
6. Non-water quality environmental impact (including
energy requirements).
In contrast to the best practicable control technology currently
available technology, the best available control technology
economically achievable assesses the availability of in-process
controls as well as additional treatment techniques employed at
the end of a production process.
The best available control technology economically achievable is
the highest degree of control technology that has been achieved
or has been demonstrated to be capable of being designed for
plant scale operation up to and including "no discharge" of
pollutants. This level of control is intended to be the top-of—
the-line of current technology subject to limitations imposed by
economic and engineering feasibility. The best available control
technology economically achievable may be characterized by some
131
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technical risks with respect to performance and certainty of
costs. Some further industrially sponsored development work
prior to its application may be necessitated.
Effluent Reduction Attainable
Based upon the information contained in Sections III through
VIII, an assessment has been made of the degree of effluent
reduction which may be achieved through the application of best
available technology. BODjj and TSS calculations are based on an
effluent concentration of 25 mg/1; total chromium and oil and
grease are based on 1 mg/1 and 10 mg/1 respectively; and sulfide
and total kjeldahl nitrogen are based on 0,1 mg/1 and 5 mg/1
respectively. Table 2U summarizes for each industrial
subcategory the best available control technology economically
achievable effluent limitations guidelines for facilities
discharging directly to receiving waters. This limitation level
is principally an extension of the best practicable control
technology currently available requirements to provide for
additional removals of BOD and SS as well as sulfide and nitrogen
removal.
132
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PARAMETER (1)
TABLE 24
BEST AVAILABLE EFFLUENT LIMITATIONS
MAXIMUM THIRTY DAY AVERAGE
(July 1, 1983)
SUBCATEGORY
kg/1000 kg hide (lb/1000 Ib hide)
BODJ5
TOTAL CHROMIUM
OIL & GREASE
SULFIDE
TSS
TKN
I
1.40
0.05
0.53
0.005
1.5
0.27
2
1.60
0.06
0.63
0.006
1.8
0.32
3
1.30
0.05
0.50
0.005
1.4
0.25
4
0.50
0.02
0.24
0.002
0.6
0.10
5
1.60
0.06
0.63
0.006
1.8
0.31
6
0.70
0.03
0.34
0.003
0.8
0.14
(1) For all subcategories pH should range between 6.0 and
9.0 at any time.
For all subcategories Most Probable Number (MPN) of
Fecal Coliforms should not exceed 400 counts per 100 ml.
133
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Best Available Technology Economically Achievable
The best available technology economically achievable for the
leather tanning and finishing industry (Subcategories 1 through
6) is removal of BOD and SS and sulfide and nitrogen reductions
(as discussed in section VII) in addition to those constituent
removals established for the best practicable control technology
currently available. Following is a general summary of the major
steps required for achieving this level for a tannery providing
complete treatment before discharge directly to surface waters.
As with the best practicable control technology currently
available, guidelines for the best available control technology
economically achievable are based on control and treatment
efficiencies achieved by some tanneries some of the time and by
other industrial treatment operations on a consistent basis.
With proper operation and adequate design, tanneries in each of
the six subcategories can achieve the required effluent
reduction.
Complete Treatment_- Subcategories 1 to 6
1. Recycle of chrome and vegetable tanning solutions
(where applicable).
2. Collection of beamhouse wastes containing sulfide;
oxidation of sulfide using a catalyst such as
manganous sulfate (where applicable).
sulfate (where applicable).
3. Fine screening.
U. Equalization to dampen variations in quality and
quantity which will impair subsequent processes,
particularly biological units.
5. Aeration and clarification of solids to remove
carbonaceous BOD5, COD, and suspended solids.
6. Aeration to nitrify organic and ammonia nitrogen;
mixing with a carbon source to cause denitri-
fication; an aeration flume to assist nitrogen
gas removal; and a final settling tank.
7. Filtration of the final effluent using deep-bed,
mixed-media filters or similar devices for final
suspended solids removal.
8. Sludge handling and disposal.
134
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Rationale for Selection of the Best Available Technology
Economically Achievable ~"
Total Cost of Achieving Effluent Reduction - As presented in
Section" VIII, to meet the~"""best available control technology
economically achievable effluent limitations, tanneries
discharging to receiving waters would have to invest an estimated
$61.0 million (August, 1971, price levels). This $61.0 million
includes the $45.8 million investment required to meet the best
practicable control technology currently available guidelines and
assumes no in-place treatment systems. The incremental cost is
$15.2 million for treatment plants for processors outside
municipal systems. Total annual costs (including depreciation,
interest, operation and maintenance) to achieve these limitations
are estimated to increase the cost of the finished product
between 0.6 and 1.3 percent for various industrial
classifications.
Age and Size of Equipment and Facilities - As indicated in
section IX, no" differentiation of the effluent limitations
guidelines can be made on the basis of age or size.
Processes Employed - Differences in processes within the industry
have been accounted for in establishing the effluent limitations.
Engineering Aspects of Control^Technigues - The best available
control technology economically achievable appears achievable
considering the developmental work being done on sulfide
oxidation and nitrificationdenitrification. There are several
technical questions which need to be resolved prior to initiation
of full-scale nitrification-denitrification facilities on a
tannery waste. However, it is deemed that such questions can be
answered by on-going research in other areas and by
investigations initiated prior to 1983. To date, no pilot work
has been reported for nitrification-denitrification of tannery
waste, hence, studies will be required to confirm design
parameters required to implement an efficiently designed and
operated facility.
Process Changes - Process changes required for the best available
control technology economically achievable include those for the
best practicable control technology currently available (see
Section IX). In addition sulfide oxidation is recommended; its
technical feasibility has been demonstrated on a pilot plant
scale. The industry should initiate research to find potential
substitutes for ammonium salts used in the bate operation and
salt used for hide curing. These process changes would reduce
treatment costs for the best available control technology
economically achievable and also effect considerable reduction in
dissolved solids which are economically very unattractive for
removal in a waste treatment facility.
Nonwater Quality Environmental Impact - The impact upon the land
as a result of liquid waste treatment is the same as outlined for
135
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the best practicable control technology currently available in
Section IX.
Factors to be considered in AjDEi^isH Level II Guidelines
1. Limitations are based on thirty day averages. Based on
performances of exemplary biological waste treatment systems,
daily limitations should not exceed the thirty day average
limitations by more than one hundred percent.
2. If a tanner processes hides in more than one subcategory, for
instance cattlehides and shearlings, the effluent limitations
should be set by proration on the basis of the percentage of the
total hide weight being processes in each subjcategory.
3. The production basis which is recommended for applying these
limitations is the daily average production of the maximum thirty
consecutive days.
SECTION XI
NEW SOURCE PERFORMANCE STANDARDS
General
The standards of performance for new sources are to reflect the
greatest degree of effluent reduction achievable through the
application of the "best available demonstrated control
technology, processes, operating methods, or other alternatives".
New source is defined as any construction which is recommended
after publication of the regulations prescribing the standards of
performance. In addition to considering the best in-plant and
end- of - process control technology identified for the best
available control technology economically achievable, new source
performance standards is to establish effluent reductions which
may be achieved by changing or improving the production process
itself. A determination must be made of whether a standard
permitting no discharge of pollutants is practicable.
For establishing new source performance standards effluent
limitations guidelines, consideration must, also, be given to:
1. The type of process employed and process changes.
2. Operating methods.
3. Batch as opposed to continuous operations.
4. Use of alternative raw materials and mixes of raw
materials.
5. Use of dry rather than wet processes (including sub-
stitution of recoverable solvents for water).
6. Recovery of pollutants as by-products.
136
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ImprovedrIn-plant Process Control
For new sources of tanning wastes, several items may be
considered to either reduce water use or discharge of waste to a
treatment facility. Most of the possible changes are merely
improvements on those which are already assumed capable of
implementation for meeting the best practicable control
technology currently available and the best available control
technology economically achievable effluent limitations
guidelines.
A new facility, due to more efficient layout and more automation,
can effect better process control, thus minimizing water use and
optimizing chemical use. In addition, general housekeeping pro-
cedures should improve. The net effect of improved process
layout, control and monitoring in a new tannery will mainly be to
decrease water use and discharge of some chemicals. organic
loads resulting from hide processing are not expected to change,
however. Hence, the waste discharge in kg (lb)/l,000 kg (Ib)
hide may not change significantly. Improved equipment and
controls in a new plant merely reduce some of the tank sizes at
the treatment facility utilized to meet the variable waste
characteristics from a tannery not equipped with new equipment.
For example, better scheduling and control of different types of
waste may reduce the size of equalization facilities required to
level out the quality and quantity of waste reaching a biological
aeration tank. In addition, reduction of waste process chemicals
may lower addition of neutralizing chemicals at the waste
treatment facility.
Two chemicals employed in the production process that could sub-
stantially reduce the treatment needs if a substitute were found
are ammonium salts used in bating and sodium salt from the hides.
There is no indication that a significant change could be made
for these, but it is recommended the industry research
possibilities.
Use of dry processes or other drastic process modifications do
not appear feasible for the tanning industry.
New gource Performance Standards
Although, better process control and more efficient tannery
operations may result for new facilities, the actual raw waste
load in terms of kilograms (pounds) per thousand kilograms
(pounds) of hide is not expected to change substantially.
Treatability of the waste is, also, not likely to differ
significantly from that existing for present facilities. Hence,
standards of performance for new facilities should be set
consistent with those required for the best practicable control
technology currently available.
137
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Pretreatment Requirements
Large quantities of three constituents of the waste water from
plants within the leather tanning and finishing industry have
been found which could interfere with, pass through, or,
otherwise, be incompatible with a well designed and operated
publicly owned activated sludge or trickling filter waste water
treatment plant. Waste water constituents include chromium from
the tanning or retanning operation, sulfide from the unhairing
process, and oil and grease from the fatliquour process or from
animal fat. Adequate control methods can and should be used to
keep significant quantities of these materials out of the waste
water.
138
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SECTION XII
ACKNOWLEDGMENTS
The Environmental Protection Agency wishes to acknowledge the
contributions of the Stanley Consultants who prepared the original
draft of this document. The efforts of Mr. Kenneth M. Bright, Mr.
John L. Thomas and Mr. Robert L. Thoem are appreciated.
Special thanks and appreciation are due Mr. Irving R. Glass, President
of the Tanners' Council of America; Professor William T. Roddy,
Director of the Tanners' Council Research Laboratory, University of
Cincinnati; and Mr. Robert M. Lollar, Coordinator for Environmental
Affairs, Tanners' Council of America.
Appreciation is expressed for the interest of several individuals
within the Environmental Protection Agency: W. L. Banks, Region VII;
William Hancuff, George Webster, Ernst Hall, Allen Cywin, EGO.
Special thanks are due Richard Sternberg for his advice, support and
guidance. Thanks are also due the many secretaries who typed and
retyped this document: Aqua McNeal, Pearl Smith, Chris Miller, Vanessa
Datcher, Karen Thompson, and Fran Hansborough.
Special acknowledgment is made of the contributions of industry
personnel who provided information to the study. Their active
response, cooperation and assistance is greatly appreciated.
139
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SECTION XIII
REFERENCES
1. "Industrial Waste - Profile No. 7, Leather Tanning and Finish-
inq," The_Cost_of_Clean_Water_-_Volume_I^I, Federal Water Quality
Administration Report, 1967.
2. "Membership Bulletin Leather Industry Statistics," Trade Survey
Bureau - Tanners' council of America, Inc., 1971, 1972, arid
1973,
3. O'Flaherty, F., Roddy, w. T., and Lollar, R. M., CheinistrY_and
TechnojLogv._of_Leather, Volumes I-IV, Reinhold Publishing cor-
poration.
U. Masselli, Joseph w., Masseli, Nicholas W, , and Burford, M. G.,
wesleyan University, June, 1958.
5. Berthouex, Paul M., and Brown, Linfield, C. , "Monte Carlo Simu-
lation of Industrial Waste Discharges," Journal_of_the_Sanitary
Engineering_Diyisignf _Proceedings_of the American^Society of
Civil_Eno[ineers, Volume 95, No. SA5, October, 1969.
6. Hauck, Raymond A., "Report on Methods of Chromium Recovery and
Reuse from Spent Chrome Tan Liquor," Journal_ofmthe_American
L§§^h§£_Cj2§m^stsJ. Association, Volume LXVII, No. 10,
1972.
7. Bailey, D. A., and Humphreys, F. E,, "The Removal of Sulphide
from Limeyard wastes by Aeration," BritishmLeather_Manufac-
turerj.^_Research_A§sociationA_LaboratorY_Re£orts, XV, No. 1,
19667
8. Eye, J. David, and Clement, David P., "Oxidation of sulfides
in Tannery Waste Waters," Journal^of_the_American. Leather
£k§H!i§.£.§.L_Association, Volume LXCII, No. 6, June, 1972.
9. Williams-Wynn, D. A., "No-Effluent Tannery Processes," Journal
of __the American_Leather_.Chemists« Assgciation, Volume LXVIII,
No. 1, 1973.
10. Data obtained through communication with tannery firms.
11. Moore, Edward W., "Wastes from the Tanninq, Fat Processing,
and Laundry Soap Industries." Source unknown.
12. McKee, Jack Edward, and Wolf, Harold W., eds., Water_2uality.
Criteria. 2nd ed., The Resources Agency of California, State
Water Quality Control Board, Publication No. 3-A 1963.
141
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13. Bailey, D. A., Dorrell, J. J., and Robinson, K. S. , Journal
o|_£ha_Societi_of_Leat.her_Tradesi_Chemists, 54, 91, "1970."
Cited in Journal^gfLthe^ American Leather^Chemists1 Associa-
tion, Volume~LXVII, No." 9, "sept ember 7 19727
14. Sutherland, R. , Industrial and^Engineering^ChemigtrY, J9, 628,
1947. cited in Reference 11).
15. sproul, Otis j. , Atkins, Peter F. , and woodward, Franklin E. ,
"Investiqations on Physical and Chemical Treatment Methods
for Cattleskin Tannery Wastes," Journal Water_Pgllutign
ControlFe deration . Volume 38, No. 4, April, 1966.
16. Kunzel-Mehner, A., Gesundh. Ing. , 66, 300, 1943. cited in
Reference 11) .
17. "Report of the Symposium on Industrial Waste of the Tanning
Industry, " Journal_of_the_American_Leathgr^Chemi.3tsl Associ-
ation, Supplement No. 15, 1970.
18. Howalt, W. , and Cavett, E. S., Transactions_of_A!Tierican^SocietY
of_CiYil_En3ineers, 92, 1351, 1928." Cited" in Reference"! if.
19. Riffenburq, H. B., and Allison, w. w., In^us^rial
, 33, 801, 1941. cited in Reference 11)
20. Haqan, James R. , and Eye, J. David, and Gunnison, G. C. ,
'•Investiqations into the Removal of Color from Bioloqically
Treated Veqetable Tannery Wastes," Masters Thesis, University
of Cincinnati, 1972.
21. Data obtained by Stanley consultants field investiqations.
22. Chen, Kenneth Y. , and Morris, J. Carrell, "Oxidation of Sulfide
by O2: Catalysis and Inhibition," Journal._of_the_SanitarY
Civil_Engineers, Volume 98, No. SAl7 February, 1972.
23. The A. C. Lawrence Leather company, ActiyatedLSludqe ^Treat-
ment _of Chrome Tannery Wastes, Federal Water Pollution Control
Administration, Department of the Interior, Grant No. WPRD
133-01-68, Proqram No. 12120, September, 1969.
24. Nemerow, N. L. , and Armstronq, R. , "Prototype Studies of Com-
bined Treatment of Wastes from 22 Tanneries and Two Munici-
palities , " Purdue 'Industrial Waste Conference, Proceedings,
1967.
25. Kinman, Riley N. , "Evaluation of Waste Treatment Process for
Treatinq Waste from Bona Allen, Inc., Buford, Georqia." Un-
published article. January 30, 1972.
142
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26. Kinman, Riley N. , "Evaluation of Bona Allen wastewater Treat
ment for Period February 1, 1972, to January 25, 1973," Un-
published article. March 5, 1973.
27. Sarber, R.W. , Journal _of^thg^ American^ Leather^Chernists^
i§£ion , 36, ?63, 7941. cited~in Reference 4)".
28. "Tannery Effluent Report to the Members of the Effluent Com-
mission of the International Union of Leather chemists'
Societies, " Journal_of^the_American_Leather_Chemistsl_ Associ-
ation. Volume LXVllT No7 10, OctoberT 1972. Reprinted from
1972.
29. Parker, Clinton E. , Anaerobic- Aerobic_Lagoon_Treatment_f or
Ye3etable_Tarming_Wastes , Federal Water Quality Administra-
tion, Environmental Protection Aqency, Grant No. WPD-199-01-67,
Proqram No. 12120 DIK, December, 1970.
30, Sawyer, C. N. , "New concepts in Aerated Laqoon Design and
by Gloyna, E. F. and Eckenfelder, W. W., Jr.), U. of Texas
Press, Austin, 1968. Cited in Reference 29) .
31. Steffen, A. J. , "Waste Treatment in the Meat Processing In-
dustry," Advajices_in_W^ter_2uality_Imgr_ovement, edited by
Gloyna, E. F. and Eckenfelder, W. W. , Jr.), U. of Texas Press,
Austin, 1968. Cited in Reference 29) .
32, Eye, J. David, Treatment of Sole Lea ther^yggetable^Tannery
Wastes, Federal Water Pollution Control Administration,
Department of Interior, Grant Number WPD-185, Program
Number 12120, September, 1970.
33. Conversation with J. David Eye.
3U. Clark, John W. , and Viessman, warren. Jr., "Biological-
Treatment Processes, Activated Sludge," Water_Suppl2_and
Po 1 lut i on_ cont r gl , International Textbook Company, Scranton,
Pennsylvania, March, 1966.
35. Steffen, A. J. , and Bedker, M. , "Operation of Full-scale
Anaerobic Contact Treatment Plant for Meat Packing Wastes,"
Proceedings^ of^thg_16th_Industrial_Wa3te^Conference , Purdue
University, «4237 1961." Cited in Reference~29) .
36, Gates, W. E. , Smith, J. H. , Lin, S. , and Ris, C. H., Ill,
MA Rational Model for the Anaerobic contact Process,"
J2S£Ml_ W§.te£_£2liU^i£Q_£2St rol _Federa ti on , 39, 1951.
1967. Cited~in~Reference 29) .
143
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37. "Industrial Waste Survey at caldwell Lace Leather company,"
EPA, office of Operations, Radiological and Industrial Waste
Evaluation section, Cincinnati, Ohio.
38. Siebert, C. L. , "A Digest of Industrial Waste Treatment,"
Pennsylvania State Department of Health, 1940. Cited in
Reference 11) .
39. Reuning, H. T. , Sewage Works Journal , 20, 525, 1948. Cited
in Reference 11) .
40. Harnley, John W. t Wagner, Frank R. , and Swope, H. Gladys,
"Treatment of Tannery Wastes at the Griess-Pfleger Tannery,
Waukegan, Illinois," sewage Works Journal, Volume XII, No. 4,
July, 1940.
41. Eldridge, E. F. , Michigan, Engineering^ Ex periment^Station
JLZ* 32/ November, 1939. Cited in Reference ll) .
42. Fales, A. L. , Industrial and Engineering chemistry, 2J[, 216
1929. Cited by Reference 11).
43. Sproul, Otis J, , and Hunter, Robert E. , "Appendix A, Indus-
trial Waste Treatment Investigations, Prime Tanning Company
and Berwick Sewer District Activated Sludge Pilot Plant,
Berwick, Maine," Berwick Sewer District, Preliminary Design
Report, pollution Control System, Edward C. Jordan Co., Inc.,
Portland - Presque Isle, Maine, 1967.
44. Haseltine, T. R. , "Tannery wastes Treatment with Sewage at
Williams port, Pennsylvania," Sewage and industrial ^Wastes,
Volume 30, No. 1, January, 1958.
45. Hartman, B. J., Sewage and Industrial^Wastes, 25, 1419, 1953.
Cited in Reference 4) .
46. Rosenthal, B. L. , Sanitalk, 5, No. 4, 21, 1956, Cited in
Reference 4) .
47. Nemerow, Nelson L. , and Armstrong, Richard, "Combined Tannery and
Municipal Waste Treatment - Gloversville- Johns town. New York,"
Purdue Industrial Waste Conference Proceedings , 1966.
48. Wims, F. J, , "Treatment of Chrome-Tanning Wastes for Accept-
ance by an Activated Sludge Plant," Purdue Indus tr ia lm Waste
Conference Proceedings, 1963.
49. Maskey, D. F. , Journal of the American Leather Chemists*
Association, 3.6, 121 1941. Cited by Reference 11)7
144
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50. Mccarty, P. L., "Anaerobic Treatment of soluble Wastes,"
Adyances^in Water^gualitY^Imgroyement edited by Gloyna,
E. F. and Eckenfelder, W. W., Jr.), U- of Texas Press, Austin
1968. Cited in Reference 29).
51. Sproul, O. J., Keshaven, K., and Hunter, R. E., "The Extreme
Removals of Suspended Solids and BOD in Tannery Wastes by
Coagulation with Chrome Tan Dump Liquors," Purdue_Industrial
H§§^§_£2Sf §££S£i--J?£o.c.§e.
-------
60. Downing, D. G., Kunin, R., and Pollio, F. X., "Desal Process-
Economic Ion Exchange System for Treating Brackish and Acid
Mine Drainage waters and Sewage Waste Effluents," Chemical
Engineering Progress Symposium Series, Volume 64, No. 90, 1968.
61. Wiley, Averill, J., Dubey, George A., and Bansal, I.K.,
Reverse Osmosis concentration of Dilute Pulp and Paper
M£iiJ§Bis, Office of Research and Monitoring, Environmental
Protection Agency, Contract No. WPRD 02-01-68, Program
No. 12040 EEL, February, 1972.
62. Kremen, Seymour S., "The Application and Preformance of Spiral
Membrane Module Systems in Reverse Osmosis Processing of
Water and Waste Streams," preprint of a paper to be
presented at the Japanese Sea Water Science Group Meeting,
November 12, 1971, Kyote, Japan.
63. "Rex Chainbelt Inc., The Ecology Division, Reverse
Osmosis DemineralizatiQn of _Acid Mine... Drainage, for the
Commonwealth of Pennsylvania, Department of Environmental
Resources, Harrisburg, Pennsylvania, and the Office of
Research and Monitoring, Environmental Protection Agency,
Contract No. CR-86-A, Program No. 14010 FOR, March, 1972.
64. 1972-1973 Saline Water Conversion Summary Report,
United States Department of Interior, office of Saline Water.
65. Burns and Roe, Inc., Disposal of Brines Produced in Renovation of
Municipal Wastewater, Federal Water Quality Administration,
Department of the Interior, Contract No. 14-12-492, Program
No. 17070 DLY, May, 1970.
66. "Patterson, W. L., and Banker, R.F., Estimati.ng
Costs and Manpower Requirements for Conventional_Wastewater
Treatment Facilities, Office of Research and Monitoring,
Environmental Protection Agency, Contract No. 14-13-462,
Project No. 17090 DAN, October, 1971.
67. Smith, Robert, and McMichael, Walter F.,
Performance Estimates_for_Tertiarv Wastewater_Treatment
Processes, U.S. Department of"the Interior, Federal Water
Pollution Control Administration, Advanced Waste
Treatment Research Laboratory, June, 1969.
68. Correspondence with Mr. Irving Glass of the Tanners' Council
of America, Inc.
69. voegtle, John A., and Vilen, Frank I., "A New Concept for Operator
Wages," Journal^gf^Water Pgllution^Control Federation, Volume 45,
No. 2, February, 1973.
70. Oil^ Paint^ and^Drug Reporter, August 2, 1971.
146
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SECTION XIV
GLOSSARY
Acidity
A measure of the ability of the waste to provide hydroqen ions when
treated with alkaline materials. Generally expressed in mq/1 as caCO3
ACT
The Act is the Federal Water Pollution Control Act Amendments of 1972.
A waste water treatment process using a mixed microbiological culture
and molecular oxygen to satisfy waste stabilization requirements.
Provision is made to return some solids settled from the effluent flow
to the influent, and thereby maintain the desired microorganism
copulation in the process.
Adipose
of, or related to, animal fat; fatty.
Adsorption
The adhesion of a gas, liguid, or dissolved substance to the surface of
a solid or liquid.
Aeration
A process for mixing and contacting air with water or liquid waste by
natural or mechanical means.
Aerobic
A biological process in which oxygen is used for microorganism respi-
ration needs. Especially relating to the degradation process of waste
matter in the oresence of dissolved oxygen.
A measure of the ability of the waste to provide hydroxyl ion to react
with acidic materials. Generally expressed in mq/1 as CaCO3.
147
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Anaerobic
A bioloqical process in which chemically combined oxygen is used for
microorganism respiration needs. Relating to bioloqical degradation of
waste matter in the absence of dissolved oxygen.
That portion of the animal hide, especially cattlehide, consisting of
the center portion of the hide along the backbone and covering the ribs,
shoulders, and butt (excluding the belly).
Bating
The manufacturing step following liming and preceding pickling. The
purpose of this operation is to delime the hides, reduce swelling,
peptize fibers, and remove protein degradation products from the hide.
That portion of the tannery where the hides are washed, limed, fleshed,
and unhaired when necessary prior to the tanning process,
That portion of the hide on the underside of the animal usually
representing the thinnest part of the tannable hide.
That portion of the hide representing the entire hide cut down the
backbone with the bellies and shoulders removed.
gest Available Demonstrated Control Technology
Treatment and control required for new sources of industrial discharge
to surface waters as defined by Section 306 of the Act.
gest _Ayailable^TfechnoloqY Economical lY-Achie
Treatment and control required by July 1, 1983, for industrial dis-
charges to surface waters as defined by Section 301 (b) (2) (A) of the Act.
Best Practicable, Control .Technology CurrentlY_Ayai.lable
Treatment and control required by July 1, 1977, for industrial dis-
charges to surface waters as defined by Section 301{b) (1) (A) of the Act.
148
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Biochemical Oxygen Demand (BODS)
The amount of oxygen required by microorganisms while stabilizing
decomposable organic matter under aerobic conditions. The level of BOD
is usually measured as the demand for oxygen over a standard five-day
period. Generally expressed as mg/1.
.Slowdown
The amount of concentrated liquor wasted in a recycle system in order to
maintain an acceptable equilibrium of contaminants in any process
liquor.
A hide after tanning with chromium salts. Hide usually has a slight
blue color.
Chemical Oxygen, Demand (COD)
A measure of the amount of organic matter which can be oxidized to
carbon dioxide and water by a strong oxidizing agent under acidic
conditions. Generally expressed as mg/1.
Chlorine Contact Tank
A detention basin designed to allow sufficient time for the diffusion
and reaction of chlorine in a liquid for disinfection purposes.
Chromium (Total)
Total chromium is the sum of chromium occurring in the trivalent and
nexavalent state. Expressed as mg/1 as Cr.
Clarification
A physical means for the removal of suspended particles in a liquid by
gravity sedimentation (settling).
Coagulant
A substance which forms a precipitate or floe when added to water.
Suspended solids adhere to the large surface area of the floe, thus
increasing their weight and expediting sedimentation.
Collagen
The fibrous protein material within the hide which provides the bulk .of
the volume of the finished leather and its rigidity.
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golloids
Microscopic suspended particles which do not settle in a standing liquid
and can only be removed by coagulation or bioloqical action.
Color
A measure of the light absorbing capacity of a waste water after tur-
bidity has been removed, one unit of color is that produced by one mg/1
of platinum as K2PtCl6.
Coloring
A process step in the tannery whereby the color of the tanned hide is
changed to that of the desired marketable product by dyeing or oainting.
gompgsite Sample
A series of small waste water samples taken over a given time period and
combined as one sample in order to provide a representative analysis of
the average waste water constituent levels during the sampling period.
A term often applied to hide processors.
Corium
The layer of hide between the epidermis and the flesh. Also called the
derma.
De liming
The manufacturing step in the tanhouse that is intended to remove lime
from hides coming from the beamhouse.
pemineralizatlon
The process of removing dissolved minerals from water by ion exchange,
reverse osmosis, electrodialysis, or ether process.
Derma
That part of the hide which is between the flesh and the epidermis.
Desalinizatign
The process of removing dissolved salts from water.
S§tention (Retention)
The dwell time of waste water in a treatment unit.
150
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Dewatering
The process of removing of a large part of the water content of sludges.
Dissolved oxygen. Measured in mg/1.
Dr. urn
A large cylinder, usually made of wood, in which hides are placed for
wet processing. The drum is rotated around its axis, which is oriented
horizontally. Also called wheel.
A form of advanced waste treatment in which the dissolved ionic material
is removed by means of a series of semi- permeable membranes and electric
current.
Enzyme
Complex protein materials added to the hide in the bating step in order
to remove protein degradation products that would otherwise mar hide
quality.
The top layer of skin; animal hair is an epidermal regrowth.
The holding or storing of wastes having differing qualities and rates of
discharge for finite periods to facilitate blending and achievement of
relatively uniform characteristics.
jSutrophication
The excess fertilization of receiving waters with nutrients, principally
phosphates and nitrates, found in waste water which results in excessive
growth of aquatic plants.
The process of adding oils, fats, and greases (fatliquor) to tanned
hides to improve and prevent cracking.
151
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The final processing steps performed on a tanned hide. These operations
follow the retan-color-f atliquor processes, and include the many dry
processes involved in converting the hide into the final tannery
product.
Flpa.1
The proper level or volume of skins or hides, chemicals, and water that
is maintained in any wet process unit (vats, drums, or processors)
within the tannery.
Floe
Gelatinous masses formed in liquids by the addition of coagulants, by
microbiological processes, or by particle agglomeration.
Flocculation
The process of floe formation normally achieved by direct or induced
slow mixing.
Flume
An open, inclined channel or conduit for conveying water or water and
hides.
Grab Sample
A single sample of waste water which will indicate only the constituent
levels at the instant of collection; contrasted to a composite sample.
Graded Media Filter
A filtration device designed to remove suspended solids from wastewater
by trapping the solids in a porous medium. The graded media filter is
characterized by fill material ranging from large particles with low
specific gravities to small particles with a higher specific gravity.
Gradation from large to small media size in the direction of normal
flow.
The epidermal side of the tanned hide. The grain side is the smooth
side of the hide where the hair was located prior to removal.
152
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grease
A group of substances including fats, waxes, free fatty acids, calcium
and magnesium soaps, mineral oils, and certain other non-fatty
materials. The grease analysis will measure both free and emulsified
oils and greases. Generally expressed as rag/1.
£reen_Hides
Hides which may be cured but have not been tanned.
The reciprocal transfer of ions between a solid and a solution sur-
rounding the solid. A process used to demineralize waters.
Jonizatjon
The process by which, at the molecular level, atoms or groups of atoms
acquire a charge by the less or gain of one or more electrons.
Liming
The operations in the beamhouse where a lime solution comes in contact
with the hide. Liming in conjunction with use of sharpeners such as
sodium sulfhydrate is used to either chemically burn hair from the hide
or to loosen it for easier mechanical removal. Hair burning normally
utilizes higher chemical concentrations.
Sgembrane
A semi-permeable barrier used in reverse osmosis and electrodialysis
which allows water molecules and certain dissolved molecules to pass
through it while impeding the passage of other dissolved solids.
Nitrogen, Ammonia
A measure of the amount of nitrogen which is combined as ammonia in
waste water. Expressed in mg/1 as N.
flitrogen,._Kieldahl (Total Kjeldahl Nitrogen or TKN)
A measure of nitrogen combined in organic and ammonia form in waste-
water. Expressed in mg/1 as N.
Nitrogen, Nitrate
A measure of nitrogen combined as nitrate in waste water. Expressed as
mg/1 as N.
153
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Nutrient
Any material used by a livinq organism which serves to sustain its
existence, promote growth, replace lossas, and provide energy. Com-
oounds of nitrogen, phosphorus, and other trace materials are par-
ticularly essential to sustain a healthy growth of microorganisms in
biological treatment.
The final outlet conduit cr channel where waste water or other drainage
is discharged into an ocean, lake, or river.
Pack
Layers of salted hides formed at the slaughter house or hide curing firm
(usually approximately 20 to ^0 feet in area and 5 to 6 feet high) .
Paddle_Vat (Paddle)
A vat with a semi-submerged rotating paddle arrangement used for the
mixing of water and chemicals with the hide.
The reciprocal logarithum of the hydrogen ion concentration in waste-
water expressed as a standard unit.
J2ES3
Parts per million. The expression of concentration of constituents in
waste water; determined by the ratio of the weight of constituent per
million parts (by weight) of total solution. For dilute solutions, ppm
is essentially equal to mg/1 as a unit of concentration.
The process step generally following the retan-color-fatliquor opera-
tions whereby the hide is attached to smooth plates with a starch and
water paste and dried in a controlled heated vessel.
Pickle
The process that follows bating whereby the hide is immersed in a brine
and acid solution to bring the skin or hides to an acid condition;
prevents precipitation of chromium salts on the hide.
Plating
The finishing operation where tha skin or hide is "pressed" in order to
make it smoother.
154
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An organic compound characterized by a large molecular weight, certain
polymers act as coagulants or coagulant aids. Added to the wastewater,
they enhance settlement of small suspended particles. The large
molecules attract the suspended matter to form a large floe,
Proces sor
A mixing apparatus resembling a concrete mixer which is used in some
tanneries.
Pullgry
A plant where sheepskin is processed by removing the wool and then
oickling before shipment to a tannery.
Retan
The process step following tanning and any intermediate drying whereby
hidas which have not been fully tanned in the chrome tanning process may
be retanned either with chrome, vegetable, or synthetic tanning agents.
This operation generally precedes coloring and fatliguoring.
Reverse Osmosis
A process whereby water is forced to pass through semi-permeable
membranes under high pressures. Water passing through the membrane is
relatively free of dissolved solids; solids are retained in concentrated
form on the feed side of the membrane and are wasted.
Sandj.ng
A dry operation performed on the tanned and fatliquored hide in order to
achieve the desired surface texture of the leather. Sanding operations
include the use of abrasive or buffing wheels.
Scouring
A process where shearlings are washed.
Scudding
An operation following the major unhairing step where the last of the
hair is removed from the hide.
Sedimentation
Clarification (settling),
155
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Chemicals used in addition to lime to assist in the unhairinq nrocess
{such as sodium sulfide and sodium sulfhydrate) .
Shearling
A lamb or sheepskin tanned with the hair retained.
Shoulder
That part of the hide which represents the shoulder of the animal.
A side represents half a hide which has been cut alonq the spine.
Skiving
The thin layer shaved or cut off the surface of finished leather,
principally sheepskin.
A concentrate in the form of a semi-liquid mass resultinq from settling
of suspended solids in the treatment of sewage and industrial wastes.
i ti
A side which has been cut parallel to its surface to provide one large
piece of leather of approximately uniform thickness and a thin, smaller
piece of nonuniform thickness called a split.
Staking
The finishing process wherein the hide or skin is stretched to make it
more pliable and to avoid shrinkage. Tacking.
Standard_Industrial_Cl assrfication (SIC)
The numerical designation given to various industries by the Bureau of
the Budget. The leather tanning and finishing industry bears SIC No.
3111.
Submerged combustion
A flash evaporation type procedure used in the separation of dissolved
solids from wat«=r.
156
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Ionized sulfur. Expressed as mq/1 as S.
Suspended... go lids { s S )
Constituents suspended in waste water which can usually be removed by
sedimentation (clarification) or filtration,
Tacking
Stakinq using tacks to fasten skins or hides to a larqe frame.
Tannin
The chemicals derived from the leachinq of bark, nuts, or other
vegetable materials used in the vegetable tanning process.
Tan. Yard (Tan House)
That portion of the tannery in which the bating, pickling, and tanning
is performed on the hides or skins.
Total Dissolve d Solids (TBS)
The total amount of dissolved materials (organic and inorganic) in waste
water. Expressed as mq/1.
Total Solids (TS)
The total amount of both suspended and dissolved materials in waste
water. Expressed as mg/1.
Unhairing
The process where the hair is removed from the hide.
Vo la tile Sol ids
solids, dissolved or suspended, which are primarily organic and during
stabilization exert the significant portion of the BOD5.
A control device placed in a channel or tank which facilitates mea
surement or control of the water flow.
Wheel
Drum.
157
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TABLE
METRIC UNITS
CONVERSION TABLE
MULTIPLY (ENGLISH UNITS)
by.
TO OBTAIN (METRIC UNITS)
ENGLISH UNIT
acre
acre - feet
British Thermal
Unit
British Thermal
Unit/pound
cubic feet/minute
cubic feet/second
cubic feet
cubic feet
cubic inches
degree Fahrenheit
feet
gallon
gallon/minute
horsepower
inches
inches of mercury
pounds
million gallons/day
mile
pound/square inch
(gauge)
square feet
square inches
tons (short)
yard
ABBREVIATION CONVERSION •, ABBREVIATION METRIC UNIT
ac
ac ft
BTU
BTU/lb
cfm
cfs
cu ft
cu ft
cu in
°F
ft
gal
gpm
hp
in
in H?
Ib
mgd
mi
psig
sq ft
sq in
ton
yd
0.405
1233.5
0.252
0.555
0.028
1.7
0.028
28.32
16.39
0.555(°F-32)*
0.3048
3.785
0.0631
0.7457
2.54
0.03342
0.454
3,785
1.609
ha
cu m
kg cal
kg cal/kg
cu m/min
cu m/min
cu m
1
cu cm
°C
m
1
I/sec
kw
cm
atm
kg
cu m/day
km
(0.06805 psig +l)*atm
0.0929
6.452
0.907
0.9144
sq m
sq cm
kkg
m
hectares
cubic meters
kilogram-calories
kilogram calories/
kilogram
cubic meters/minute
cubic meters/minute
cubic meters
liters
cubic centimeters
degree Centigrade
meters
liters
liters/second
killowatts
centimeters
atmospheres
kilograms
cubic meters/day
kilometer
atmospheres
(absolute)
square meters
square centimeters
metric tons
(1000 kilograms)
meters
* Actual conversion, not a multiplier
MJ.S. GOVERNMENT PRINTING OFFICE: 1974 546-318/348 1-3
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