EPA 440/1-73/
Olo
DEVELOPMENT DOCUMENT FOR
PROPOSED EFFLUENT LIMITATIONS GUIDELINES
AND NEW SOURCE PERFORMANCE STANDARDS
FOR THE
LEATHER TANNING AND FINISHING
POINT SOURCE CATEGORY
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
NOVEMBER 1973
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DEVELOPMENT DOCUMENT
for
PROPOSED EFFLUENT LIMITATIONS GUIDELINES
and
NEW SOURCE PERFORMANCE STANDARDS
for the
LEATHER TANNING AND FINISHING
POINT SOURCE CATEGORY
Russell Train
Administrator
Robert L. Sansoni
Assistant Administrator for Air & Water Programs
Allen Cywin
Director, Effluent Guidelines Division
James D. Gallup
Project Officer
November 1973
Effluent Guidelines Division
Office of Air and Water Programs
U. S. Environmental Protection Agency
Washington, D. C. 20460
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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 Page
I CONCLUSIONS 1
II RECOMMENDATIONS 3
III INTRODUCTION 7
Scope 7
Previous Study 7
Industry Trends 8
IV INDUSTRY CATEGORIZATION 11
Standard Manufacturing Processes 11
Cattlehide Tannery Processes 12
Sheepskin Tannery Processes 18
Pigskin Tannery Processes 22
Classification System 26
Categorization System 28
V WASTE CHARACTERIZATION 31
General 31
Waste Constituents 32
Unit Waste Quantities 32
Individual Process Contributions to the Waste ... 33
Wash and Soak 35
Degreasing 35
Unhairing 36
Bating 36
Pickling 37
Tanning 37
Retan, Color, Fatliquor 37
Finishing 38
Total Plant Liquid Waste 38
Characteristics of Total Plant Waste Flows 42
VI SELECTION OF POLLUTANT PARAMETERS 47
Waste Water Parameters of Major Significance .... 47
Rationale for Selection of Major Parameters .... 47
Biochemical Oxygen Demand 47
iii
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CONTENTS (Con't)
Section
Total Chromium 47
Grease 47
Sulfide 48
Suspended Solids 48
Total Kjeldahl Nitrogen 48
Fecal Coliforms 48
pH 48
Rationale for Selection of Minor Parameters .... 48
Chemical Oxygen Demand 48
Total Solids . . I 49
Ammonia Nitrogen 49
Color 49
VII CONTROL AND TREATMENT TECHNOLOGY 51
General 51
Basis of Tannery Waste Treatment 52
In-Process Methods of Reducing Waste 54
Preliminary Treatment 58
Screening 60
Equalization 61
Plain Sedimentation 61
Chemical Treatment - Coagulation and
Sedimentation 64
Chemical Treatment - Carbonation 66
pH Adjustment 67
Sludge Handling and Disposal 67
Preliminary Treatment - Facility Requirements . . 69
Secondary Biological Treatment 70
Major Reduction of BOD5_ and Suspended Solids .... 70
Combined Municipal - Tannery Treatment Systems . 70
On-Site Treatment - Trickling Filter Systems . . 74
: On-Site Treatment - Aerobic Lagoon Systems ... 75
On-Site Treatment - Aerobic - Anaerobic
Lagoon Systems 79
On-Site Treatment - Activated Sludge Systems . . 84
Practical Biological Systems 90
Polishing Systems For Biological Treatment ... 91
Major Reduction of all Forms of Nitrogen .94
Major Removal of All Waste Constituents 97
Freezing 98
iv
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CONTENTS (Con't)
Section
Evaporation 98
Electrodialysis 98
Ion Exchange 99
Reverse Osmosis 99
VIII COST, ENERGY, AND NON-WATER QUALITY ASPECTS 103
Cost and Reduction Benefits of Alternative
Treatment and Control Technologies 103
Basis of Economic Analysis 103
Effluent Reduction Subcategory 1 112
Impact of Waste Treatment Alternatives on
Finished Product Price 114
Alternative Treatment Systems 114
Related Energy Requirements of Alternative
Treatment and Control Technology 117
Non-Water Quality Aspects of Alternative
Treatment and Control Technology 118
Air Pollution 118
Solid Waste Disposal 118
IX BEST PRACTICABLE CONTROL TECHNOLOGY CURRENTLY
AVAILABLE GUIDELINES AND LIMITATIONS 121
General 121
Effluent Reduction Attainable 122
Best Practicable Control Technology Currently
Available 124
Rationale for Selection of BPCTCA 124
Total Cost of Achieving Effluent Reduction . . .124
Age and Size of Equipment and Facilities . . . .125
Engineering Aspects of Control Techniques . . . .125
'• Processes Employed . 125
Process Changes 125
Non-water Quality Environmental Impact 125
X BEST AVAILABLE TECHNOLOGY ECONOMICALLY ACHIEVABLE -
GUIDELINES AND LIMITATIONS 127
General 127
Effluent Reduction Attainable 128
Best Available Technology Economically Achievable .130
Rationale for Selection of BATEA . 131
Total Cost of Achieving Effluent Reduction . . .131
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CONTENTS (Con't)
Section Page
Age and Size of Equipment and Facilities . . . .131
Processes Employed 131
Engineering Aspects of Control Techniques . . . .131
Process Changes 131
Non-water Quality Environmental Impact 132
XI NEW SOURCE PERFORMANCE STANDARDS 133
General 133
Improved In-plant Process Control 133
New Source Performance Standards 134
Pretreatment Requirements 134
XII ACKNOWLEDGMENTS 135
XIII REFERENCES 137
XIV GLOSSARY 143
vi
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TABLES
Number Title
1 Best Practicable Effluent Limitation Guidelines
July 1, 1977 4
2 Best Available Effluent Limitation Guidelines -
July 1, 1983 5
3 Classification System 27
4 Principal Processes of Subcategories 30
5 Hide Curing 34
6 Wastewater Quantities 41
7 Raw Wastewater Characteristics by Category 44
8 Plain Sedimentation 62
9 Chemical Treatment 65
10 Combined Municipal - Tannery Treatment Systems .... 71
11 Trickling Filter Systems 77
12 Aerobic Lagoon Systems 78
13 Aerobic - Anaerobic Systems 81
14 Activated Sludge Systems 85
15 Estimated Waste Treatment Cost for Subcategory 1 . . .106
16 Estimated Waste Treatment Cost for Subcategory 2 . . .107
17 Estimated Waste Treatment Cost for Subcategory 3 . . .108
18 Estimated Waste Treatment Cost for Subcategory 4 . . .109
19 Estimated Waste Treatment Cost for Subcategory 5 . . .110
20 Estimated Waste Treatment Cost for Subcategory 6 . . .111
21 Estimated Industry Investment to Meet BPCTCA
Effluent Limitations . . 115
22 Estimated Industry Investment to Meet BACTEA
Effluent Limitations 116
23 Best Practicable Effluent Limitation Guidelines -
July 1, 1977 123
24 Best Available Effluent Limitation Guidelines -
July 1, 1983 129
vii
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FIGURES
Number Title Page
1 Flow Diagram - Typical Cattlehide Tannery 13
2 Flow Diagram - Typical Sheepskin Tannery 21
3 Flow Diagram - Typical Pigskin Tannery 25
4 Category System 29
5 Wastewater Flow vs Tannery Production for Category 1 . 40
6 Tannery Production vs Relative Cumulative Frequency
for Category 1 46
viii
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SECTION I
CONCLUSIONS
For purposes
standards of
been divided
been derived
Such factors
technologies
subcategories
subcategories
of establishing effluent limitations guidelines and
performance, the leather tanning and finishing industry has
into six major subcategories. These subcategories have
principally by similarities in process and waste loads.
as age and size of plant, climate, and waste control
favor segmentation of the industry into these six
The following tabulation is a capsule summary of these
1
2
3
4
5
Beamhouse
Pulp hair
Save hair
INDUSTRY SUBCATEGORIES
Primary Processes.
Tanning
Chrome
Chrome
Leather
Save hair
Hair previously removed
Hair previously removed
or retained
Pulp or save hair
Vegetable
Previously tanned
Chrome
Chrome or no tanning
Yes
Yes
Yes
Yes
Yes
No
Currently, waste from about 60 percent of the tanneries (and approxi-
mately 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 $28 million
(August, 1971, price levels). Total annual costs (including
depreciation, interest, operation, and maintenance) for pollution
control will increase finished product costs from about 1.1 to 3.5
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percent (August, 1971, prices) depending on industrial subcategory. For
only one subcategory is the increase in excess of 2.6 percent.
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 about $42.5 million
(August, 1971, prices). This represents an additional $14.5 million
investment over BPCTCA. Total annual costs for the best available
control technology economically achievable will increase finished
product prices from about 0.5 to 2.6 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 1.6 to 6.1 percent for various subcategories and only one
subcategory is in excess of 3.8 percent.
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 removal 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 composite 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.
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
(July 1, 1977)
SUBCATEGORY
PARAMETER(l) kg/1000 kg hide (lb/1000 Ib hide)
BOD5_
TOTAL CHROMIUM
OIL & GREASE
SS
2
0
0
3
1
.7
.05
.53
.0
2
3.
0.
0.
3.
2
06
63
5
2
0
0
2
3
.5
.05
.50
.8
1
0
0
1
4
.0
.02
.24
.1
5
3.
0.
0.
3.
2
06
63
5
1
0
0
1
6
.4
.03
.34
.5
(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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TABLE 2
BEST AVAILABLE EFFLUENT LIMITATIONS
(July 1, 1983)
SUBCATEGORY
PARAMETER(l) kg/1000 kg hide (lb/1000 Ib hide)
123456
BOD5. 1.35 1.60 1.25 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
SS 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 ap-
plication 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 fellows:
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 indus-
try 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
ccntrol and treatment, and pretreatment prior to discharge
to a publicly-owned waste water system.
U. 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 technol-
ogy, together with suggested effluent limitations guidelines
and appropriate cost information.
Preyious^ Study
A principal source of information for this investigation is the
'•Industrial Viaste 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 some 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 1960, 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 finishinq
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 hido
producing nations. This has recently caused the price of raw
cattlehides to increase greatly. Heavy native steer hides have ranged
in price :frorn 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 pricos
increased to 42.4 cents in August, with an average for the year of 29.7
cents per pcund. These raw product prices have now fallen to about
twice those in 1971. In addition, competition from foreign count rift;
such as Japan, Italy, and Spain in the finished leather products market
has reduced the potential revenue from domestic leather firms.
Ccittlehides constitute the bulk of the tanning done in the U. c;. ,
representing about 90 percent of the estimated pounds of hides tanned.
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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 agent
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 ccnvert
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 cne 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 cf 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.
11
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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 processes 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)
Cattle hide Tannery Processes
There are four processes in a typical cattlehide tannery which con-
tribute waste loads:
1. Beamhouse.
2. Tanhcuse.
3. Petan, color, and fatliquor.
4. Finishing.
12
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FLOW DIAGRAM
TYPICAL CATTLEHIDE TANNERY
LEGFJC
PROCESS HAIERULS
RETAN COLOR FAILIOUOR
JJHMJPE.HEJJS
_il«_lJ—•
L
I | FLESHINGS
I HAIR
PliTI EFFLUENT
I ! SPLITS
[_SpL_ID_WASTE_ (SHAV INGS)
WASTE EfHUEMt
ASH EFFLUENT (CLEAN-UP ONLr)
REIAN-COLOR-FATLIQLfOH
ULTIFNAIE)
FIGURE 1
13
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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
frcm 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 cause 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 en 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 te 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 maintained in
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most tanneries other than that required to keep hides at the
moisture content as received.
3- Siding_and_Trimminc[ - 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.
U. Waj3hing_and_Soakinc£ - 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.
Cepending 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- li§§hiQ3 ~ 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.
15
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6. UnhajyziDS - 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
"turning."
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 sulf hydrate 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, strcnger
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.
Ihe 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.
T ANHOU S E_ PRQCES S :
1- Is!£iQ2 ~ 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- HisKiiDa " Tiie 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.
16
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Pickling is always done before the chrome tanning process and
rray be done before vegetable tanning.
3- Tanning - Nearly all cattlehides in this country are either
chrome or vegetable tanned; very little is tanned with alum or
other tanning materials.
Vegetable tanning is the older process, and is performed in a
solution containing plant extracts such as vegetable 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
Icnger process times, while chrome tanning takes place in drums
cr 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.
Viaste 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.
**• §Eiitting ~ Tne tanned hide is split to produce a grainside
piece of essentially constant thickness and a flesh side layer.
The flesh side layer or split can be processed separately or
sold to split tanners.
BlTANx_COLORi_FATLI2UOR_ PROCESS:
1. S^tan - 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» Bitching ~ 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.
17
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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.
**• Isltliguoring ~ 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.
FIN ISH ING_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 tooth water baths.
Trimmings are disposed as solid waste, and dust collected may be
disposed in either wet or dry form.
Sheepskin Tanngry__Processes
Sheepskin tanning processes are somewhat similar to pigskin tanning in
that generally there is no beamhouse process and degreasing is required.
The three majcr processes are:
1. Tanhouse.
2. Retan, color, and fatliquor.
3. Finishing.
These processes and the sub-processes which take place during manu-
facturing are shown on Figure 2 and are described as follows:
TANHOU S E PROC ES S :
ing - 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 shear-
lings. Tanning of these skins does not involve a beamhouse
18
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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.
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 deterio-
ration.
lieshing - 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.
£§9£§§sing - Skins are placed in drums, washed, and soaked,
after which solvent or detergent is added in the same drums
tc 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 atmos-
phere.
I§QIiiQ3 ~ Sheepskins may be either chrome or vegetable
tanned, although the majority are chrome tanned.
Vihere 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 sul-
fate for chrome tanning or solutions of the natural tannins
for vegetable tanning.
19
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6- Refreshing - In some cases, there is a refleshing operation
following tanning, which produces a small amount of solid
waste.
CQLOJL AND_FATLI2UOR_PROCESS:
!• Coloring - Skins to fce colored are immersed in a dye solu-
tion in drums. Generally, synthetic dyes are used. Some
bleaching may be done prior to coloring of shearlings.
2- Fatljguoring - This operation is performed in the same drum
used for coloring. Skins are immersed in a solution con-
taining various oils to replace the natural oils of the
skin lost in the tanning process.
ONISHI NG_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 pro-
cesses, 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-FftUlQUOR
(I) SHEARLINGS ("ML UFI On) ASE
HECEIVED AS CURED SKIMS. UN-
HOUSE SUB-PROCESSES INCLUDE
WISH t SOA». FLESHING. DECREAS-
ING. PICKLING MD lANNING.
SKIhS IRON
DECREASING
I HASTE tjfLUEgl
FIGURE 2
21
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PiqskinjTannery_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. Tanhcuse.
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:
!• E§£§iYin-2 ~ 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 tan-
neries for skins which are to be held before tanning.
3- 2§3£§§§iD3 - Solvent degreasing has been used by some pig-
skin 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
tc a stripping column, where the solvent is recovered for
reuse. Grease is recovered as a by-product.
There is a waste effluent frcm 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 ty decanting or skimming it from the
top cf holding tanks to which waste is diverted prior to
entry into the main plant sewer system.
U. Liming * From the degreasing operation the skins are placed
in tanning drums with a lime slurry and sharpeners. The
22
-------
purpose of this is to remove the embedded portion of the
hair from the skins.
5- !<*iiD3 - The bating operation takes place in the same drums
used for liming. The purpose of this operation is to de-
lime 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- Ta_DDiD3 - 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 tan-
ning 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, elim-
inating any need for a retan operation at a later point.
8- §£lit_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 fatliquor process.
CQLOR_AND_FATLI2UOB_PRQCESS:
1- Co.lP.liD9 ~ Skins to be colored are immersed in a dye solu-
tion in drums. Generally, synthetic dyes are used.
2- I§^ii31i2£ill3 ~ 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 sand-
ing. These are principally dry processes, and the only liquid
waste contributed is from cleanup operations. Where paster dry-
ing 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
23
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fertilizer. Dust collected from the sanding operation is dis-
posed of as a solid waste.
-------
FLOW DIAGRAM
TYPICAL PIGSKIN TANNERY
COLOR-FAUtQUOF
FIGURE 3
25
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Classification System
As noted in the foregoing discussion on standard manufacturing pro-
cesses, 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 classificaticn. 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.
26
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TABLE 3
CLASSIFICATION SYSTEM
(3111.abed)
Retan,
Skin or
Hide Type
1.
2.
3.
(a)
Cattle
Pig
Sheep
1.
2.
3.
Beamhouse
Operation
(b)
Pulp Hair
Save Hair
Hair Pre-
viously
Tanning
Process
(c)
1. Chrome
2. Vegetable
3. Alum
Color, Fatliquor,
Finishing
(d)
1. Sides
2. Splits
3. Sides and
Splits
Removed
4. Deer
5.
6.
7.
8.
9 . Other
0. Various
4.
5.
6.
7.
8.
9.
0.
Hair
Retained
Wool
Pullery
Hide Curing
Pulp & Save
Other and
unknown
4.
5.
6.
7.
8.
9.
0.
Previously
Tanned
Vegetable
and Chrome
Other and
unknown
None
4
5
6
7
8
9
0
U. 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-
27
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viously tanned prior to receipt of hides at a fin-
ishing facility (finishing operations only).
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.
Categorizatign_Sy_stem
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 4, for purposes of
evaluating control and treatment technology. Each subcategory
represents a common manufacturing process, as shown in Table U.
These subcategories only identify operations that do not process a com-
bination 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.
28
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STANDARD
INDUSTRIAL
CLASSIFICATIONS
CATEGORIES
STANDARD
INDUSTRIAL
CLASSIFICATIONS
CATTLE j.1319
HAIR PREVIOUSLY REMOVI
PREVIOUSLY TANNED
OTHER OR UNKNOWN
SHEEP M3U5
HAIR PREVIOUSLY REMOVED
PREVIOUSLY TANKED
SKINS
CATTLE .1313
HAIR PREVIOUSLY REMOVI
PREVIOUSLY TANNED
SIDES 1 SPLITS
OEER I.TO9
HAIR PREVIOUSLY REMOVED
PREVIOUSLY TAHHED
OTHER OR UNKNOWN
CATEGORY SYSTEM
FIGURE 4
-------
TABLE H
PRINCIPAL PROCESSES OF SUBCATEGORIES
Primary Processes
Searohoy.se 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
30
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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.
U. Regulatory agency data summaries, including engineering re-
ports on individual tanneries.
5. Literature review.
6. Sampling performed at selected tanneries.
7. Tannery visits.
Correspondence and information data sheets were received from over 1UO
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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Waste 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
fellows:
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.
32
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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.
2. Number of hides processed.
3. Weight of finished product.
U. Square feet of finished product.
Each of the above has some shortcomings when used as basis of pro-
duction, 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.
lQdividual_Process_Contributions_to_the_Waste
Each process in the production of the final product makes some con-
tribution to the total waste load.
Hide_Curihg
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.
33
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The brine solution is continually circulated and reused. Slowdown 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:
Table 5
Hide Curing
Concentration
kg/1,000 kg Hide
Waste Characteristics
BOD 5
COD
Total Solids
Suspended Solids
Oil and Grease
Water Use, I/kg
(gal/lb)
Jmg/lj.
15,610
29,610
280,500
10,400
40,200
0.24
(0.03)
_(lb/1xOOO Ib Hide
3.9
7.4
70.1
2.6
10.0
Tanner^_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
34
-------
Tanning (including bleaching for some vegetable tanning)
Retanning, Coloring, and Fatliquoring
Finishing
The waste contributions are described below:
W§§.h_
-------
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 (Ib) 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.
UQh§i.EiD3 " 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 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, BOD5, suspended solids, and total
sclids. 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
dees 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 con-
trolled level and an enzyme to condition the protein matter. The
reaction of lime with ammonium sulfate produces calcium sulfate. The
tctal 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.
36
-------
H.i£]siiJ22 ~ T^e purpose of the pickling operation is to prepare the hides
for the tanning process. In vegetable tanning, pickling may be omitted.
Fickle 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 degra-
dation by physical or biological mechanisms. This is accomplished by
reaction cf the tanning agent with the hide collagen. Chrome and
vegetable tanning are the two principal processes, although ether
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
scdium 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
ccmes 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.
Retanjt__colorjt Fatligugr - 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.
Ihe 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
37
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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.
Liquid waste from the retan, color, and fatliquor operations may be high
vclume-lovv strength compared with the beamhouse and tanhouse.
The temperature of the retan, color, and fatliquor waste flows ir
generally high—above 37.7°C (100°F). The major treatment concern ot
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 retarming will enable
maximum uptake of chromium and reduce the discharge of this constituent.
Finishing
The tinishing processes represent the lowest water flows of the tannery
because they are primarily dry processes. There are seme wet processes
such eis miner wetting operations to make the hide handle more easily in
the staking or tacking operations. The pasting operation also use:;
small amounts of water. However, several tanneries report reusing pastt
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.
Tgtal_PlantmLiguid_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. Tn 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.
38
-------
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
cf tanneries.
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 fre-
quency of occurrence in any one interval was not gen-
erally too much greater than adjacent intervals. Use
of a wider interval would have reduced significance of
this measure.
39
-------
ZOO
TANNERY PRODUCTION (1000 KG HIDE/MO)
WO 600 _ 800 _ 1000 1200 UOO 1600 1800
18-
17
16
15
H
13
12
II •
10
9
8
7
6
4 ©
©
© ©
©
©
©
®
©
_
® ®
© 0©
©
©
WASTEWATER FLOW
TANNERY PRODUCTION
FOR CATEGORY 1
FIGURE 5
0.15
0. 13
0.12
0. II
0.10
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
o.oi
500
1000 1500 2000 2500 3000
TANNERY PRODUCTION (1000 LB HIDE/MO)
3500
1(5
-------
TABLE 6
WASTEWATER QUANTITIES
Waste Flow,
cu m/kcj
Category Median
1 0.01(0
Ci.8)
2 0.050
(6.0)
3 O.Qltlt
(5.3)
1* 0.017
(2.0)
5 0.050
(6.0)
6
of h
Mean
0.053
(6.1.)
0.063
(7.6)
0.050
(6.0)
0.020
(2.
-------
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 non-
scientific 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 throuqh
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.,
f T o t a 1 PI a n t Wa s t e F 1 o ws
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 ot 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 sutcategory is shown in
Table 7. The data have been classified as received and no further
attempt is made toward explanation of inconsistencies with seme
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.
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 signifi-
cant 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
Flow: cu m/kg
(gal/lb)
BODj
COD
Total Solids
Suspended Sol ids
Total Chromium
Sul fides
Grease
Total Alkalinity
(as CaCOj)
Total Nitrogen
(as N)
PH
Temperature**: °C
CF)
Category No. 1
No. of
116 0.007-0.156 0.053
(0.8-18.7) (6.M
2* 11.8-270 95
18 10.5-595 260
16 36-890 525
23 6.7-595 HO
18 0.1-19 *i.3
12 O.I-46 8.5
13 0.1-70 19
12 0.5-300 98
7 3.1-H 17
26 1.0-13.0
15 2.8-93.2 21.1
(37-200) (70)
Category No. 2
No. of No. of
H 0.001-0.189 0.063 16^
(0.1-22.6) (7.6)
9 22- HO 69 12
7 88-215 HO 9
7 HO-900 Ii80 9
9 30-350 H5 10
7 0.3-12 li.9 5
k 0.1-2.8 0.8 7
5 0.7-105 li3 7
1 62-85 72 6
6 3.6-22 13 5
8 Ii.0-l2.6 -- 12
6 1.7-27.8 18.3 3
(35-82) (65)
of Hide)'
Category No.
.5 Range
0.007-0.106
(0.8-12.7)
7.ii-130
21.-695
120-800
20-Wi5
0.2-0.6
0. l-ll,2
0. 1-160
1..1-I35
0.9-23
2.0-13.0
l|.4-28.9
HO-811)
3
Average
0.050
(6.0)
67
250
3,5
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 (°F).
"-Average temperature is average summer and winter values; temperature range is low winter to high
-------
TABLE 7 (Continued)
RAW WASTEWATER
CHARACTERISTICS BY CATEGORY
Raw Uastewater Characteristics, kg/1,000 kg of Hide (lb/1,000 Ib of Hide)*
No. of
Tanneries
10
3
3
2
3
3
1
3
Category No.
Range
0.003-0.033
(0.3-3.9)
6.7-67
5.7-63
47-285
7.0-125
0.4-4.8
2.1
2.2-19
4
Average
0.020
(2.4)
37
28
140
47
2.6
2.1
7.9
Category No. 5
No. of
Tanneries
20
8
5
7
8
7
1
7
Range
0.006-0.204
(0.7-24.4)
10-140
11-265
52-980
3.1-865
0.1-2.1
4.5
0.6-46
Average
0.063
(7.6)
67
170
490
88
1.2
4.5
24
Category No. 6
No. of
Tanneries Range
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
Average
0.028
(3.4)
110
230
595
110
4.4
3.7
6.6
I 39 33 3 6.6-180 69 I 37-54 43
2 0.8-6.5 3.7 5 0.6-29 6.0 1 H-18 16
3 3.4-11.2 " 9 1.5-12.5 — 2 9.2-10.4
3 10.0-26.6 20.7 . 3 4.4-36.6 22.8
(50-80) (69) (40-98) (73)
45
-------
MOOD
3000
2000
a, '000
-J 900
g 800
£ 700
g 600
o 500
0
I 400
ae.
uJ
300
200
100
1500
1000
900
800
700
600
500
400
300
o
o
o
200
o
o
ac.
a.
TANNERY PRODUCTION
VS.
RELATIVE CUMULATIVE FREQUENCY
FOR CATEGORY I
FIGURE 6
100
50
10 20 30 110 50 60 70 80
RELATIVE CUMULATIVE FREQUENCY
90 95
99
46
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SECTION VI
SELECTION OF POLLUTANT PARAMETERS
WASTE, WATER PARAMETERS OF MAJOR SIGNIFICANCE
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., BOD5)
Total Chromium
Grease Fats and Oils
Sulfide
Suspended Solids (SS)
Total Kjeldahl Nitrogen
Fecal Coliforms
pH
Rationale for Selection of Major Parameters
§i2£h§IDic§l_Qxy3en_pemand __ ( BOD5) - This parameter is an important
measure of the oxygen utilized by microorganisms in the aerobic
decomposition of the wastes at 20°C over a five day period. More
simply, it is an indirect measure of the biodegradability of the organic
pollutants in the waste. BOD£ can be related to the depletion of oxygen
in a receiving stream or to the requirement for waste treatment.
If the EOD5 level of the final effluent of a processing plant into a
receiving body is too high, it will reduce the dissolved oxygen level in
that stream to below a level that will sustain most fish life; i.e.
below about 4 mg/1. Many states currently restrict the BODjj of
effluents to below 20 mg/1 if the stream is small in comparison with the
flow of the effluent. A limitation of 200 to 300 mg/1 of BOD5 is often
applied for discharge to municipal sewer, and surcharge rates often
apply if the EOD£ is above the designated limit.
- Most of the leather produced in the U. S. is tanned
with chromium salts. Chromium, in some forms, can be harmful to aquatic
life and, therefore, is an important parameter to be identified. There
is evidence to indicate that chromium in both the trivalent and
hexavalent state is harmful, and thus the total chromium parameter
should be used.
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
47
-------
process. The grease is usually all of nonpetroleum origin. Large
amounts of cil and grease can be detrimental to surface waters by
retarding stream reaeration. In addition, large amounts of oil and
grease are unsightly and biological degradation may result in odor
problems.
SuljEide - A significant portion of alkaline sulfides contained in
tannery waste water can be converted to hydrogen sulfide at a pH telow
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 can be oxidized to sulfuric
acid, causing "crown" corrosion. At higher concentrations this gas can
be lethal. This is particularly significant as a hazard in sewar
iraintenance. Sulfide compounds are used extensively in the beamhousp
for the unhairing process, and thus are found in tannery effluents.
Suspended Solids (SS) - Material found in suspended form in tannery
wasteuaters consist primarily of proteinaceous substances (flesh, hide,
or hair) and insoluble waste chemicals. Suspended solids are an iirpor-
tant measure of the pollutional significance of tannery wastes, since
they generally exert a BOD5 and can also result in detrimental sludqr
deposits in streams and lakes.
Total KjeJ.dahl 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 - Microbiological testing for the presence of t
-------
acid reagent. COD is a much more rapid measure of oxygen demand than
BOD5 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 BOD5 can be run. A given plant or waste treatment system
usually has a relatively narrow range of COD: BOD.5 ratios, if the waste
characteristics are fairly constant, so experience permits a judgment to
be made concerning plant operation from COD values. In the industry,
COD ranges from about 1.6 to 10 times the BOD5; 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 frcm 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 froir an
aesthetic standpoint. There is not sufficient information at this time
to establish color limitations.
-------
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 chetricals and water.
Based upon communication with around 1HO wet processing firms in the
industry, approximately 60 percent of the tanneries discharge tc
municipal systems. Analysis of these same data indicates that tanneries
discharging tc 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
51
-------
facilities are non-existent. Some pilot studies of reverse osmosis and
activated carbon have been 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 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 tech-
niques have generally been applied only in those areas where direct cost
savings are demonstrated. Such practices are tannin and chromium reupp.
Plans for reuse of some portions of treated waste streams are in thp
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.
52
-------
d. Partial removal of BOD5, COD, suspended solids, and
total nitrogen.
3. Major reduction of BOD5 and suspended solids.
a. Removal of BOD5 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 bio-
logical 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.
t. Treatment follows biological treatment for BOD5 removal.
c. Treatment steps include an aerobic biological process
followed by an anaerobic biological process. Each pro-
cess 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 BOD5, suspended solids, and
nitrogen.
b. Filtered waste enters reverse osmosis process (or electro-
dialysis process) for removal of remaining organic con-
stituents, as well as major quantities of dissolved salts
such as sodium chloride.
c. Waste stream is directed to evaporators for concentra-
tion for final disposal.
d. Product water is of low solids content suitable for re-
use.
6. Waste treatment for hide curing facilities.
a. The high strength of this waste requires special con-
siderations.
b. Treatment for all levels except pretreatment requires
53
-------
direct incineration of total waste or solar evapora-
tion in arid areas0
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.
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 const! tuents .
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 quantifies.
Tanning formulas and processing steps are developed by experience.
Implementation of many potential waste reduction steps are cont-.inqent-
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 vari-
ations for three subcategories in which cattlehides are processed is
shown below:
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
5U
-------
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.
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 em-
ployee participation.
2. Examine tanning formulas to determine if floats can be re-
duced. 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 prograir 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
55
-------
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 delitning will be about 8.35 I/kg of hide (1 gal/ Ib of hide) 0
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 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 cperation. 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 #U 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
strec'irn. 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 Wcrld war II, the reuse of chrome tan liquor was
comiron 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
56 '
-------
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
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 conceiveably 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 net considered substantial.
Tannery #7 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.
Eased 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 seme 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.
57
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The complete removal of sulfides is ineffective with either plain
sedimentation or chemical treatment. Sulfides are more satisfactorily
removed through oxidation. Various methods for oxidizing sulfides
include:
1. Air oxidation.
2. Direct chemical oxidation (8).
3. Catalytic air oxidation (7) (8) (22) .
Air oxidation with diffusers provides some removal, but only with
excessive aeration times.
Direct chemical oxidation with ammonium persulfate and ozone were
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 most 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:
58
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1. Sewer safety and maintenance.
2. Eiological 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 concentrations as
high as 250 mg/1. An alkaline sulfide bearing waste from a tannery when
mixed with sufficient domestic or acidic 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 concen-
trations (300-14,000 mg/1) with an expected average of 2,000 to 3,000
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 frcm 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).
59
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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 lew 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 EOD5 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.
3. Plain sedimentation.
4. Chemical treatment.
a. Coagulation and sedimentation.
1) Alum.
2). Lime.
3) Iron salts,
U) 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
60
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which has a potential for damaging plant equipment and clogging pumps or
sewers.
~ 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 fcr 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.
Ei^iD_§^^_il!!®Di§^i2D ~ 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 concen-
trations cf both suspended solids and grease. As shown in Table 8,
suspended solids reductions can range from approximately UO 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 syrface skimmers
installed in clarifiers.
61
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System
lagoon
Sedlmentit Ion tanks,
mechanic*) sludge
fact 11 ties
Sedimentation tanks
Sedimentation tanks
Sedimentation tanks
TABLE 8
PLAIN SEDIMENTATION-
Suspended Solids BOD
Inf. Eff. Removal Inf. £ff. Removal Remarks Reference
«9/l mo/1 t mg/l i»8/l t
80-90 — — 80-90 Fill and draw basins with ()8) (}9)
24-hour capacity.
900 130 83-88 380 146 40-6! Pretreatmenl of vegetable (40)
tan liquors. Detention
time 9-15 hours.
1.200 370 69 — --- — Detention time 2 hours (14)
1,184 680 43 1,046 537 48 Continuous flo» (pilot) (HI)
1.880 461 67 I.28S 873 30 Fi 1 1 and draw (pi lot) (41)
62
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Assumed to te typical for plain sedimentation units is the full-scale
operation cited by Sutherland (14) . 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.r (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 #10 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 rerrovals resulted (10).
Suspended Solids
BOD 5
Total Chromium
Total Alkalinity (as CaCO3)
Grease
Influent
mg/1
3,125
2,108
51
980
490
Effluent
mg/1
945
1,150
24
718
57
%_Removal
70
45
53
27
90
Suspended solids and BOD5 removals were 70 percent and 45 percent,
respectively. A low chromium removal of approximately 50 percent
occurred. Higher reirovals 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.
63
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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 BCD5 (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.
Chem^a^Treatmen^^_Coa3ulation_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
flocculaticn cf 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 BOD5
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 re-
sulted in a reduction of about 84 percent in suspended
solids and 60 percent in BODji.
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 pro-
duced average removals of 60 to 65 percent, respectively,
for suspended solids and BOD5.
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 per-
cent and suspended solids from 45 to 57 percent. Alum con-
centrations higher than 500 mg/1 created a floe that would
net settle.
6. Buffing dust resulting from finishing tanned hides was not
found to be an effective coagulant.
64
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TABLE 9
CHEMICAL TREATMENT
Suspended _Spj_ids_
Coagu1 a t i on-Sed imen ta 11on
Plain Sedimentation,
Coagulation, Sedimentation
Aeration, Coagulation.
Sedimentation
Coagulation, Sedimentation
Coagulation, Sedimentation
Coagulation, Sedimentation
Coagulation, Sedimentation
Coagulation, Sedimentation
Lin
1.550 68
2,500 850
Iron Salts
Polymer 5,200** 500**
66 3.600 1,030
918 469 49 1.001 476
1,980 1(97 75 1.630 623
3.135 110 95 1,437 619
High
90* Adjustment of pH water (42)
H2S°4
73 A pilot study with pre- (16)
settling of a portion of
the raw waste with ad-
justment of pH to 5-5-
Mixing aerated raw waste
with presettled super-
natant Indicated 93t color
removal.
52 Continuous flow with lime (4|)
concentrations of I.490
mg/l.
49 Fill and draw with lime (41)
concentrations of 1,700
mg/l.
57 Adjustment of pH with beam- (37)
house liquors. Overflow
rate, 25.9 cu m/day/sq m
(635 gal/day/sq ft)
High Ferric chloride added at 06}
concentrations of 2,000-
5.000 mg/l
Full-scale operation on beam- (32)
house wastes with anionlc
polymer addition of 10 mg/l.
Overflow rates at 65 cu
m/day/sq m (1,600 gpd/sq ft)
Equalization, 2-stage
Carbonatlon, Coagulatitu
Sedimentation
Carbonation, Coagulation,
Sedimentation
13,400 I,140
Iron Salts 6,190
A pi lot Study wi th
equalization of flow,
carbonation with flue yd-.
to 6.4-6.7 pH. Coagulation
with lime followed by 3*
hour sedimentation.
Effluent is then subjected
to a second stage process
similar to the first.
A 99* reduction In color
resulted.
A pilot study with carbona-
tion of beamhouse wastes to
a pH of 6.0 followed by coagu-
(300-500 mg/l). Treatment
produced a floe which settled
quickly.
(19)
* Oxygen demand.
' Order-of-magnitude •
65
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In general, polymer addition produced a rapid formation of floe min-
imizing the need for flocculating equipment. Without pH adjustment,
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
ty 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 tcxicity 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 cf 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 che-mical precipitation and coagulation with calcium
hydroxide and an anionic polymer (20). The efficiency is dependent on
pH control arcund 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_-_Carbonati.on - 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
66
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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.
Stack gas containing 8 to 12 percent carbon dioxide obtained frcir, 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 #3 indicate high reductions in suspended solids,
BOD, and total alkalinity. Estimated flows from the cattlehide
vegetable tannery were 1,700 cu m/day (O.U5 mg/1). Primary clarifier
overflow rates were about 20. U 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. (Sulf uric acid is also used to assist pH control) .
The following removals were indicated (21) :
Primary Primary
Effluent % Removal
mg/1 mg/1
Suspended Solids 2,110 100 95
EOES 1,660 270 81
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.
ES_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 ccntrol system.
§iyd^§_fi5I3^1il23_3Ii^_2i§E2§Sl ~ 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.
67
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Seme attempts have been made to dewater sludges prior to ultimate
disposal with varying success. The three principal dewateririg tech-
niques include centrifuges, vacuum filters, and pressure filtration.
The centrifuges have appeared to meet with less success than vacuum
filters or pressure filters.
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.
deducing the moisture content of sludge by spreading on drying beds has
also been successful in some areas. This is particularly attractive tc
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 iraterial 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 hexavalerit
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 dev«at.ering in mechanical equipment, sludge is normally con-
ditioned by use of ferric salts and lime or polymers or a combination of
these. The quantity and typ6 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.
68
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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 cf potential toxic or organic materials 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 ^Requirements - Based on an appraisal of
needs and the performance of previously described operating facilities,
the following processes are included in evaluating preliminary treatment
requirements:
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.
69
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Secondary _Biglcgical_Treatment
Parameters used for sizing principal items of equipment are as follows:
Equalization Detention: 24 hours at design flow
Primary Settling Overflow rates 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 lb/sq ft/hr)
Major __ Reduction __ o£_BO_D5_and_Su^gended_Sglids - Major reduction of BODb
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
rray 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 sclids
removalo Numerous biological treatment schemes are, therefore,
feasible. Selection of an alternative biolcgical treatment system is
influenced by waste water constituents, required efficiencies ,? clirratic
conditions, land requirements, operational characteristics, and
economics .
Combined __ MujiicjijDal-Tannery. __ S£§SilD^Di __ Sy_s>tems " Combined treatment of
tannery and municipal vaste waters predominates in the industry since
most tanneries are located in urban communities (U) = 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.
70
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TABLE 10
COMBINED MUNICIPAL-TANNERY TREATMENT SYSTEMS
cu m/day X
(mgd)
Primary
sedimentation, (0.58)
chlorinatlon,
vacuum fl Itratlon
Trickling Filter
Trickling filter IS
sedimentation
sludge digestion (9.5)
sludge digestion, grease re- (6.4)
s 1 udge 1 agoon mova 1
sludge drying ' (3.8)
beds
Activated Sludge
separate sludge ' (!.2>
digestion, land
Irrigation of
liquid sludge
Activated sludge. Screening with 6,056 37
separate sludge potential of (1.6)
digestion, land sedimentation
Irrigation of units
liquid sludge
Activated sludge. Lagoon 14,383 4
separate sludge (3-8)
digestion
Activated sludge, Equal Izatlon, (Variable) 4j
sludge dewatering sedimentation.
by centrlfugatlon, carbonation
land disposal
Other
lo-flltratlon 2- 16,276 6
tage oxidation (4.3)
pond, separate
ludge digestion,
agoon sludge
Isposal
rlmary sedlmen- 1.514
atlon, roughing (0.4)
liter, activated
ludge, secondary
edlmentatlon
BOD. Suspended Solids
mg/l mg/l t mg/l mg/l 1
Pennsylvania result of a chemical
sewage, tannery
waste, and filtrate
from vacuum filters.
90 90 (45)
Engineering loadings of I.J-1.7 kg
ft) . No scale deposi-
tion on media. 1007.
sulf Ide removal.
67 86 Sheboygan. Before Initiating (4?)
problems with hair
and hide scraps in
digester.
Wisconsin tnclner tlon discon-
tinued ue to lack of
efflcle cy.
New York operatl g at double
the des gn capacity
tllng basins.
Ontario. detention times for
Canada each basin are 7 hours.
360 600 ' Barrle, Plant completed in (47)
Ontario. 1965 with capacity
Canada of 13.626 cu m/day
(3.6 mgd).
175 18 90 Columbus. Tannery ovt of oper- (4?)
Indiana atlon since 1962.
Treatment plant experi-
enced operational
problems with con-
mlnutors. dlffusers.
and digesters.
32 90 200 75 South Paris, Pilot operation. (23)
Kaine
242 9 96 325 31 90 Napa, Flow from two tanner- (47)
California les. Chrome reduced
from 6.1 to 0.8 mg/l.
Digester gas 0.585 cu
m/kg (9.5 cu ft/lb)
volatile matter added.
82-99 66-78 GloversvIIle, Prototype operation. (IN)
New Vork visual Indication of
highly effectivn
color removal.
71
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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 (#12), 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 cf 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
BOD£ and suspended solids were required to meet stream classification
standards. The following full-scale unit processes, listed in the crder
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 flews 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 nr, (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.
72
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Pilot tests indicate that carbonation after equalization provides a
rapid absorption of carbon dioxide (C02) gas. A contact time of 20
minutes was sufficient for flue gas carbonation. The 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 Ih
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 BOD5 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/l,000
cu m (70 to 200 Ib BOD5/day/1,000 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 BOD5 removals ranged between
80 to 90 percent.
73
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In general, combined treatment is viable if proper design considerations
assessing the effects of tannery waste waters are considered.
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 sclids.
On~Site Treatment_2_Trickling_Filter_Sy_stems - 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 tc
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 (13), 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) :
74
-------
Influent to Effluent from
Trickling_Filter Clarifier
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 flew to the filter was approximately 3,785 cu m/day (1 mgd), in-
cluding a 50 percent recycle of the secondary clarifier effluent. The
EOC5 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 charac-
teristics of the suspended material and the relatively high overflew
rate of 37.6 cu m/day/sq m (800 gpd/sq ft) in the secondary clarifier.
Eased 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_La2Oon_Sy_stems - 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
75
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efficiencies consistently. A reassessment of unit functions and more
operative control may te required.
76
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TABLE 11
TRICKLING FILTER SYSTEMS
BODj
Carbonation, primary
sedimentation,
trickling filter,
final sedimentation
Primary coagulation,
sedimentation,
trickling fiIter,
final sedimentation
Dilution, primary sedi-
mentation, trickling
filter, final sedi-
mentation
Dilution, primary sedi-
mentation, trickling
filter, final sedi-
mentation
900
821
30-80
56
A8
Removal
85-95
80
Remarks Re fe re nee
Indicate 100 per- (
-------
aoo
Total 5
cu in/day mg/f ng/Y
(«9
Screening. platr, 719 1.800 100
sedimentation (0.19)
Ugoons, aerated
1*90001, final
sedimentation
lagoons
Sedimentation «,5fiO 400 190
lagoons, aerated (1.21)
lagoon, final
sedliwntatlon
lagoon, lagoon
sludge disposal
Scree Ing. plain 2.309 2.250 815
coa ulatlon sedf-
men ation,
«r ted lagoons
sed mentation. {O.Ofc)
fin 1 sedlnn-
TABLE 12
AEROBIC LAGOON SYSTEMS
Suspended Solids Total Nitrogen
* mg/1 mg/1 t mg/1 mg/1 X
95 Hiddlesboro Cattle, Separate screen- (10)
Tanning Co., save-pulp. Ing and tedi-
nidtflesboro, chrome- mentation of tan
Kentucky vegetable and beamhouse
1 iquors prior to
aeration.
5) 5" " 8' =,... js:- J"'^.::2' (!"
Bolivar. chrome sample.
Tennessee .
64 1,500 725 52 Virginia Cattle, Employ the lurl- (10)
Luray, vegetable- effluent vege-
Vlrginia chrome table tanning.
Bros., Inc., save, waste streams
Pennsylvania tlon. Aeration
detention time
20 days.
78
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In a prototype study at a tannery in Virginia (#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 prorated effluent
characteristics, the following removals were observed:
. 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 leading 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
BOD 5/day/ 1,000 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
BOD5 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.
tems - 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:
79
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methane, hydrogen sulfide, and ammonia which are readily available for
utilization or 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 tc prevent escape of anaerobic products which create odors such
as hydrogen sulfide.
Stratified lagoons are generally deep, 3.7-U.6 m (12-15 ft), but shallow
depths, 1.2-1.5 m (U-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 treatiny
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) .
80
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TABLE 13
AEROBIC-ANAEROBIC SYSTEMS
System Flow Inf. Eff. Removal Inf. Ef f. Removal Inf. Ef f. Removal Tannery Process Remarks Referenci
cu at/day SgTT JSgTT I S^TT roJTT ( SgTT SgTT *
(*gd)
Screening, aerobic- 2,2?) 673 53 92 339 *>& 86 Pownal Cattle- Nitrification- (10)
anaerobic I-stage (0.6) Tanning Co., sheep save, dsnltrlftcatlon
lagoons North Pownal. chrome Is not Indicated.
Vermont
Screening, plain 1,363 2,300 600* Ik 3,000 165* 95 Howes Cattle, Primary j,«ttl Ing (10)
sedimentation, (0.36) Leather Co., save, vege- of beamhouse
aerobic-anaerobic Curwensvi1le, table flows prior to
lagoon, final Pennsylvania mixing with
sedimentation, spent tans.
chlorlnation
^Arithmetic average.
81
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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 flews were varied to impart various loadings on the system. In
the initial phase the following removals were experienced:
!Qf luent Effluent ..
mg/1 mg/1 %
EOD5 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~BOB5/day/l,000 cu m (8.7 Ib BOD5/ day/1, 000 cu ft). Temperatures
ranged from 5°C (U1°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 202 ku
BOD5/day/l,000 cu m (17.4 Ib BOD5/day/l ,000 cu ft) did riot significantly
reduce the efficiency. Investigators report loadings of aerobic-
anaerobic systems may range from 130 to 243 kg BOD5/day/ 1,000 cu m (R
to 15 Ib BOD5/day/l,000 cu ft) for 80 percent organic removals (29) (30)
(31) (35) (36 (50). However, loadings above 81 kg BOD5/day/l,000 cu m
(5 Ib BCD5/day/l, 000 cu ft) are impractical because oE 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
82
-------
percent suspended solids removals. Later, a lagoon with a three-day
detention time was found to produce equivalent removals and was
incorporated into the full-scale system.
Subsequent treatment of the clarified teamhouse waste water in aerobic-
anaerobic lagoons created severe odor problems. The problem was elim-
inated when spent vegetable tanning solution was combined with the
beamhouse fractions for treatment. Removals observed through the
biological system were as follows (32) :
Affluent 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/1, 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 con-
trary 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. Def earning
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.
Nitrif ication-denitrif ication 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
83
-------
absence of oxygen, anaerobic bacteria reduce the nitrate liberating
nitrogen gas as a respiration product.
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
nitrificaticn-denitrification. Specific applications will require
extensive pilct studies for evaluation of design parameters, par-
ticularly 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 (SRT) 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 preceded 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 charac-
teristics, 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.
84
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TABLE ll»
ACTIVATED SLUDGE SYSTEMS
Total
Suspended Solids
Total Nitrogen
:rcenlng, plain
sedimentation,
activated sludge,
final sedimen-
tation, sludge
dewaterlng with
pressure filters,
land disposal
cu in/day mg/1
(«ngd)
3,765 1,36*1
(0
FnT.'TfTT Removal IfTfT?fT7 Rerova
76 2,966 325
TfTT Removal
SgTT ~~T^
S. B. Foot
Tanning Co.,
Red Wing,
Low removals since
biological units
not In full opera-
tion.
ireenlng, plain 61
sedimentation, (0.016)
activated sludge,
final sadlmen-
Utlon
93 3,135 223
27 Cal dwell
Lace
Cattle,
pulp, ct
Primary and sect
ary clarifier ov
10.5 cu m/day/sq m
(230 and 2$8 gpd/sq
ft), respectively.
Aeration time 1.6
days.
Activated sludge,
final clari-
80 2,400 190
37 Moench
Tanning Co.,
Gowanda,
biological unit 3.712
kg/day/t,000 cu m (229
tb 6005/day/l,000 cu
ft). Final clarlfler
overflow rate 20.k-
2
-------
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 (U60 gpd/sq ft) under present conditions. A potential of
tcur 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 ot 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 in (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 m
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:
86
-------
iQf luent Effluent Removal
mg/1 mg/1 %
BOD5 1,437 96 93
Suspended Solids 3,135 223 93
COD 4,016 481 88
Sulfide (as S) 7.9 0 100
Total Kjeldahl Nitrogen (as N) 490 322 34
Organic Nitrogen (as N) 328 175 47
Ammonia Nitrogen (as N) 162 147 9
Nitrite (as N) 0.1 34*
Nitrate (as N) 0.1 0.4
Alkalinity (as CaC03) 516 141 73
*Grab Sample
The BOD5 cf 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
EOD5/day/1,000 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 frcm save hair beamhouse, chrome tan, and
finishing operations. Total waste water from these processes is about
1,514 cu in/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/1,000 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).
87
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An organic removal of 80 percent produced an effluent BOD5 concentration
of 343 mg/1. Suspended solids reductions of 92 percent are reported.
Effluent suspended solids concentrations 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 whicn 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 (lb)
BOD5 applied, or 0.55 kg (lb) dry solids/kg (lb) BOD5 without primary
sedimentation. The organic lead on the ditch varied from 23.5-48.2 kg
EOD5/day (51.8 to 106.2 lb BOD5/day). The oxygen supplied was about 1.5
times the average BOD5 load, however. This was not sufficient for peak
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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):
Presettled
_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
Tctal Nitrogen (as N) 250 60-150 40-76
Ammonia Nitrogen (as N) 100 45-125 0-50
*Order-of-magnitude
High removals of BOD5 (98 percent) and COD (88 percent) result at the
lew F/M ratio. Sulfides were completely oxidized with brush aeration.
Precipitaticn of chrome was highly effective with concentrations below 1
mg/1 observed in the effluent. Nitrification was sporadic, with some
denitrificaticn 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 pilct or full-scale facilities is non-existent.
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PracticalBiological Systems
Several tanneries do have biological treatment systems that are
partially effective. However, the treatment systems have not maintained
high levels of effluent reduction.
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 BCD and
SS discharger are 0.4 and 1.1 kg/kkg (lb/1000 Ib) respectively. The BOD
effluent concentration frcm both sampled data and industry data is 16
mg/1. Tannery 54 in sutcategory 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 kq/kkg
lb/1000 Ib) respectively. Plant 43 in subcateqory 2 utilizes lagoons to
achieve a BOD discharge concentration of 38 mg/1 (industry data) cr 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
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
Aeraticn
Secondary Settling
Sludge
Collection
Thickening
Disposal
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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 cr 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
BOD5 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 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.
Pp.lish4.Q3 Systems^for_Biological_Treatment. - Consideration has been given
tc unit operations and process techniques which have been used infre-
quently or not at all in tannery waste treatment. They are as follows:
1. Filtration or microscreening of the effluent.
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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
seme instances, this has been well over 100 mg/1. Undoubtedly, seme 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 sclids
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 sclids.
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 con-
taining granular material resulting in the capture of suspended solids
in the bed. Eventually, the pressure drop 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 tack 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 bottcnr, 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 fcr longer periods of time. Influent solids should
be limited to about 100 mg/1 to avoid too frequent backwashing.
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
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non-biodegradable. The granular carbon media provides an effectively
large surface area for adsorption. Biodegradation of the captured
material further increases the efficiency of the process. Theriral
regeneration is used to reactivate spent carbon.
Laboratory analysis were made on carbon treatment of waste water from
Tannery f16 (52). These laboratory tests were preformed 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
(TOC). The full-scale design is indicated as having a potential of
reducing the effluent tc 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 anticipated 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
pilct 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 #14. Color was
effectively removed 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 materially reduce the high content of dissolved
inorganic materials such as sodium chloride (NaCl).
The problem cf color of tannery waste is most pronounced in those
systems using vegetable tanning. Color is an optical effect. The
measured magnitude of color is net 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 stan-
dards. Therefore, several arbitrary approaches have been developed tc
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.
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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^Fgrms^gf_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.
U. 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
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 froir 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
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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 keen used for nitrogen removal:
1. Coagulation, flocculation, and settling.
2. Ammonia stripping.
3. Ammonia ion exchange.
4. Chlorination.
5. Eiological nitrification-denitrification.
Coagulation, flocculation and settling is effective in partial removal
of soluble and colloidal protein matter. To optimize this process, pH
must te reduced to the isoelectric point °f tne 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 (UOO cu ft/gal) (56).
Difficulties encountered in municipal waste treatment include serious
calcium carbonate scaling and the reduced efficiency at low air tem-
peratures. 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.
Ammonia vcan also be removed from waste water by an ion exchange media
which is a natural zeolite, clinoptilclite. 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.
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Chlcrination 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
2it£2§2fQ2Q§§ 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 frcm
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 organises.
Equipment required is a nitrification basin followed by a clarification
tank. Optimum pH is 6.5 to 7.5. Organisms using a source of organic
carbon convert the nitrate to nitrogen gas. Since the waste is norrrally
lacking in organic carbon, methanol is added to provide such a source.
Fate 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 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
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pH: 8.a
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 NC3-N/day/l,000 cu ft)
*Mixed Liquor Volitile Suspended Solids
Major Remoyal^of All_Vjaste 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 frpm 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:
1. Freezing.
2. Evaporation.
3. Electrodialysis.
U. Ion exchange.
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5. Beverse 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 dees 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.
~ 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 scil
or sealant imposes severe restrictions on the geographic location for
such lagocns.
Multiple effect evaporators have been used in industry for many ap-
plications. 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) cf steam used.
~ Electrodialysis is a demonstrated process for reiroval
of dissolved solids in brackish waters. Basically, the electrodialysis
cell consists of alternate cationic and anionic permeable membrances in
a stack alternately charged by electrodes 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
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concentrated waste trine collects in others. For waters of
concentration less than 10,000 mg/lr 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 fcr
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 ex-
changer must te 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 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 meirtrane
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 cf the system is dependent upon
selection and maintenance of the membrane. Reverse osmosis has been
effective fcr the treatment of pulp and the paper mill wastes, acid mine
drainage, and municipal supplies with a high mineral content.
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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 inq/1. Th^
permeate contained 55 mg/1 dissolved solids producing a 05 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 siirilar concentration are amenable to reverse
osmosis. At these dissolved solids concentrations, the osrrotic
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. Thp
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 cf dissolved solids (64) .
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
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methods for handling trines. A few of the techniques investigated are
as follows:
1. Various types of solvent extration.
2. Electrodialysis.
3. Solar evaporation.
U. 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 fcr
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 trines requires comprehensive geologic study and
field testing of potential disposal zones to assess the safety and
effectiveness of underground strata. Several potential dangers exist
for such disposal including pollution of fresh water supplies through
encroachment and disturbance to underground strata. Injection wells
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normally require detailed investigations to ensure that liquids in the
underground strata are compatible both physically and chemically tc the
waste trines 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 cosrs 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 fcrine 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 frcm ether 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.
102
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SECTION VIII
COST, ENERGY, AND NON-WATER QUALITY ASPECTS
Cost and Induction Benefits of Alternative Treatment and ...control
Technologies
A detailed economic analysis showing the impact of treatment and control
technologies upon the six sutcategories within the leather tanning and
finishing industry is given in Supplement A of this document. Five
alternative treatment methods have been considered for Sufccategories 1
to 6. For the six sutcategories, 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.
103
-------
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
irarked impact on the cost cf 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.
2- E§E£§2i5ti2Q_§D^_Q2§i_2f_Q^£li3.i_llDi§I§st)_ - It was assumed
that the annual interest costs (cost of capital) and depre-
ciation would be constant over the life of the treatment
facilities. A principal repayment period of 20 years was used.
Ccsts 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 tc 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.
3« lDsurance_and_Taxes - An annual cost of 1 1/2 percent of the
initial investment was used for insurance and taxes on the
waste treatment plant.
bor ~ 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.
104
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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 on 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 ($20.00 per ton)
Soda Ash - $3.96 per 100 kilograms ($1.80 per 100 pounds)
Ferric Chloride - $8.80 per 100 kilograms ($U.OO 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. Enejrgy. - 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
pcwer 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).
105
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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 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
$/1000 kg hides/yr
($/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
(1) All Costs Based on August
636
1,400
88
950
- 33
4
$361.5
47.3
21.5
$88.6
0.084
0.008
0.640
1.25
1971 Price
636
1,400
88
950
33
4
$683.8 $1
89.5
40.7
$167.6
0.159
0.015
0.640
2.3
Level s
(2) Raw Material Conversion Factor to Finished Produc
636
1,400
88
950
33
4
,073.1
140.6
63.9
$262.9
0.249
0.023
0.640
3.6
t = 0.68
636
1,400
88
950
33
4
$2,473.1
323.8
147.2
$718.9
0.681
0.063
0.640
9.8
sq Ct
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
106
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TABLE 16
WASTE WATER TREATMENT COST (1)
FOR SUBCATEGORY 2
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
$/1000 kg hides/yr
($/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
$886.7
85.6
38.9
$217.2
0.151
0.014
863
1,900
120
1,290
50
6
$1,342.2
129.6
58.9
$328.8
0.228
0.021
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 2.2 3.3 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
107
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TABLE 17
WASTE WATER TREATMENT COSTS (1)
FOR SUBCATEGORY 3
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)
431
950
51
550
42
5
431
950
51
550
42
5
431
950
51
550
42
5
431
950
51
550
42
5
ESTIMATED INVESTMENT COST(3)
($1000) $2.84.0 $528.3 $821.1 $2,828.1
ESTIMATED ANNUAL INVESTMENT
$/1000 kg hides /yr 54.8 101.9 158.4 545.6
($/1000 Ib hides /yr) 24.9 46.3 72.0 248.0
ESTIMATED ANNUAL COST
($1000) $ 69.6 $129.4 $201.2 $ 590.2
$/sq m hide 0.114 0.211 0.329 0.964
($/sq ft hide) . 0.010 0.020 0.030 0.089
TYPICAL FINISHED PRODUCT
Price ($/sq ft hide) 0.780 0.780 0.780 0.780
TREATMENT COST AS PERCENT
OF PRODUCT PRICE 1.3 2.6 3.8 11.4
(1) All Costs Based on August 1971 Price Levels
(2) Raw Material Conversion Factor to Finished Product = 0.58 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
108
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TABLE 18
WASTE WATER TREATMENT COSTS (1)
FOR SUBCATEGORY 4
ALTERNATIVE (4)
PARAMETER/COST 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)
341
750
84
900
17
2
$177.3
43.3
19.7
$43.5
0.043
0.004
341
750
84
900
17
2
$314.3
76.8
34.9
$76.9
0.076
0.007
341
750
84
900
17
2
$466.6
114.0
51.8
$114.3
0.113
0.010
341
750
84
900
17
2
$986.6
241.2
109.6
$267.3
0.265
0.025
TYPICAL FINISHED PRODUCT
Price ($/sq ft hide) 0.610 0.610 0.610 0.610
TREATMENT COST AS PERCENT
OF PRODUCT PRICE 0.7 1.1 1.6 4.1
(1) All Costs Based on August 1971 Price Levels
(2) Raw Material Conversion Factor to Finished Product = 1.2 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
109
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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
($71000 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
$388.7
219.3
99.7
$95.2
0.120
0.011
148
325
66
715
62.5
7.5
$560.4
316.1
143.7
$137.2
0.173
0.016
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 2.3 3.3 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
110
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TABLE 20
WASTE WATER TREATMENT COSTS (1)
FOR SUBCATEGORY 6
ALTERNATIVE (4)
PARAMETER/COST B C D
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 hldes/yr
($71000 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
$408.4
68.0
30.9
$100.0
0.119
0.011
499
1,100
70
750
17
2
$692.4
115.5
52.5
$169.6
0.202
0.019
499
1,100
70
750
17
2
$1,374.4
229.0
104.1
5408.6
0.486
0.045
TYPICAL FINISHED PRODUCT
Price ($/sq ft hide) 0.31 0.31 0.31 0.31
TREATMENT COST AS PERCENT
OF PRODUCT PRICE 2.3 3.5 6.1 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
111
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Effluent Rgduction - Subcategory 1 - The following discussion for
Sutcategory 1 deals with the sensitivity of effluent reduction with
respect to costs for Subcategory 1. This subcategory represents a sub-
stantially larger segment cf the industry than any other subcategory.
Costs are based on an average size tannery in this subcategory pro-
cessing 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 BOD5/1,000
kg (95 Ib BOD5/1,000 Ib) of hide. This represents 14 times that of
normal domestic sewage.
Costs - None.
Reduction Benefits - None.
Alternatiye^B_^Preliminary Treatment and chrome Removal
This alternative includes in-prccess 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 47 kg BOD5/1,000 kg (47 Ib
EOD5/1,000 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
tor 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 2.7 kg BOD5/1,000 kg (2.7 Ib BOD5/1,000 Ib)
cf hide processed for the average Subcategory 1 tannery treatment
facility.
Costs - Alternative C represents a total capital investment of $683,800
and an annual cost of $167,600. These costs represent an increase of
$322,000 in capital costs and almost $80,000 in annual costs over
Alternative B.
112
-------
Reduction Benefits - Alternative C represents a reduction in BOD5 of 94
percent over Alternative B. This represents a total reduction in plant
BOD5 of 97 percent.
Alternative 2 ~ Alternative C Plus Sulfide Removal^ Nitrification and
Qenitrificaticn, and Filtration
Alternative D includes the treatment units for Alternative C with the
addition of a sulfide removal process, nitrification basin, covered
denitrificaticn basin, sulfide removal process, aeration flume,and a
graded media filter. The effluent from the average Subcategory 1
tannery treatment facility would be 1.35 kg EOD5/1,000 kg (1.35 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
$1,073,100 and an annual cost of $262,900. 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 50 percent over Alternative C. Total reduction in
BOD5 would be about 98.5 percent. Sulfide and nitrogen removals also
result.
Alternative E - Alternative D Plus Reverse Osmosis^ and Evagoration
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 $1,400,000 more than
Alternative D and annual costs are estimated to be over $450,000 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
BOD5 load of 100 percent. All other constituents would be completely
removed.
113
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Impact _o f _W as t e_Tr eatnj en t_Al t e rnat i ye s_on_Fi n i shed_Prgd uc t _P r ice
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 1.1 to 3.5 percent for
various subcategories. For only one subcategory is the increase in
excess of 2.6 percent.
For the best available control technology economically achievable, the
estimated increase of final product ccst ranges from 0.5 to 2.6 percent
for various subcategories and only one subcategory is in excess of 1.3
percent.
The overall ccst of both best practicable and best available control
technology is estimated to increase final product costs from 1.6 tc 6.1
percent for various subcategories and only one subcategory is in excess
of 3.8 percent.
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 $28 million for best practicable
ccntrol technology currently available limitations (see Table 21), and
$42.5 million or an increment of $14.5 million for best available
control technology economically achievable limitations (see Table 22).
The 1977 investment consists of $28.0 million for processors outside
municipal systems. including about $7 million each for subcategories 1
and 3, about 6 million each for subcategories 2 and 5 and $1.4 million
for subcategory 4. Distribution of 1983 costs is similar.
It is estimated that the current in-place treatment system investment is
$11 million. No credit has been calculated for this in-place treatment
in Tables 15-20 or Tables 21-22.
114
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TABLE 21
ESTIMATED INDUSTRY INVESTMENT (1)
TO MEET BPCTCA EFFLUENT LIMITATIONS
SUBCATEGORY
PRODUCTION
10°kg/yr
(10°lb/yr)
BPCTCA INVESTMENT
$71000 kg/yr($/1000 Ib/yr) PERCENT(2) INVESTMENT
AFFECTED
($1000)(3)
1
2
3
4
5
6
305
149
114
66
69
18.9
(672)
(328)
(252)
(145)
(152)
(41.7)
18
17
21
15
45
14
.5
.7
.0
.8
.3
.0
(40
(38
(46
(34
(99
(30
•7)
.9)
.3)
.9)
.7)
.9)
26
46
62
27
42
0
$7
$5
$7
$1
$6
,100
,900
,200
,400
,400
-
TOTAL INDUSTRY COST
$28,000
(1) All costs based on August 1971 price levels
(2) Percent of subcategory production discharging
directly to receiving waters
(3) Assumes no in-place treatment capital
-------
TABLE 22
ESTIMATED INDUSTRY INVESTMENT (1)
TO MEET BACTEA EFFLUENT LIMITATIONS
SUBCATEGORY
1
2
3
4
5
6
PRODUCTION.
10°kg/yr(10&lb/yr)
305(672)
149(328)
114(252)
66(145)
69(152)
18.9(41.7)
BACTEA INVESTMENT
$71000 kg/yr($1000 Ib/yr)
(29.0(63.9)
26.7(58.9)
32.7(72.0)
23.5(51.8)
65.2(143.7)
23.8(52.5)
TOTAL INDUSTRY
(INCREMENTAL
PERCENT(2)
AFFECTED
26
46
62
27
42
0
COST
COST)
INVESTMENT
($1000) (3)
$11,200
$ 8,900
$11,200
$ 2,000
$ 9,200
—
$42,500
($14,500)
(1) All costs based on August 1971 price levels
(2) Percent of subcategory production discharging directly
to receiving waters
(3) Assumes no in-place treatment capital
-------
Related Energy^Reguireinents_gf _Alternatiye Treatment and Control
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 7.256 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 7.2% 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
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(7,200 Btu/lb) of hide in the form of steam. This represents an
increase of approximately 107 percent over the energy requirements of an
average tannery (Sufccategory 1) without treatment facilities.
Ngnff§tg£-2uglity Aspect of Alternative Treatment_and_Cgntrgl_Technglcgy
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 amironia 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 liguid waste treatment for disposal.
In addition tc process sources, tannery boilers can be a source of air
pollution. With proper design and maintenance of gas and oilfired
bcilers, there should be no emission problems. However, with coal-fired
boilers, tly 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.
Bciler flue gas contains sulfur dioxide when the fuel burned in the
bcilers 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.
§2ii^_Waste_Disp_osal - Solid waste from tanneries and tannery wastewater
treatment plants includes the following:
1. Fleshings.
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2. Hair.
3. Paw hide trimmings.
4. Tanned hide trimmings.
5. Sanding and buffing dust.
6. Lime sludge.
7. Chrome sludge.
8. Eiological 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 ty 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 E 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 grcundwater 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 tc prevent the obstruction of natural drainage channels,
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location to avoid flood waters, and the consideration of possible fire
hazards.
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SECTION IX
BEST PRACTICABLE CONTFOL 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 ccntrol 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 processes, but includes
control technologies within the process itself 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
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the engineering and economic practicability of the 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 sutcategory (see Table 7). BOD5 and SS calculations
are based on an effluent concentration of 50 mg/1; total chromium and
oil and grease are based on 1 mg/1 and 10 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
EOD5 and suspended solids.
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TABLE 23
BEST PRACTICABLE EFFLUENT LIMITATIONS
(July 1, 1977)
SUBCATEGORY
PARAMETER(l) kg/1000 kg hide (lb/1000 Ib hide)
BOD.5
TOTAL CHROMIUM
OIL & GREASE
SS
2
0
0
3
1
.7
.05
.53
.0
3
0
0
3
2
.2
.06
.63
.5
2
0
0
2
3
.5
.05
.50
.8
4
1.
0.
0.
1.
0
02
24
1
3
0
0
3
5
.2
.06
.63
.5
6
1.4
0.03
0.34
1.5
(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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Best__Practicable Control Technology Currently^Av ail able
The best practicable control technology currently available for the
leather 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 BOD^ 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 treatment: operations.
Other industries such as the meat packing industry currently treat high
strength wastes 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 EPCTCA is not
achieved consistently, technology and performance information has been
transferred from other industry treatment operations.
Complgte 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 tc 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) .
Eationale for Selection of the Best Practicable control Technology
Available
Total_Cost of .Achieving JEf fluent .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
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an estimated $28 million (August, 1971, price levels) 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 1.1 to 3.5 percent
for the various subcategories. For only one subcategory is the increase
in excess of 2.6 percent.
Aqe^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 seme 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 50 mg/1, the following
plants achieve 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 50 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
cooperaticn frcm 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.
Nojiw^ter^uality__Enyironmental_Imp_act - 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
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from treatment facilities. Most of 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 sludqe 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.
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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.
4. 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
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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 character-
ized by some 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. BOD5
and SS 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 24 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.
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TABLE 24
BEST AVAILABLE EFFLUENT LIMITATIONS
(July 1, 1983)
SUBCATEGORY
PARAMETER(l) kg/1000 kg hide (lb/1000 Ib hide)
1 2 3 A 5 6
BOD5. 1.35 1.60 1.25 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
SS 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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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 tc
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 ether
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 r_SubcategQries__l_tQ_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).
3. Fine screening.
<4. 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 denitrification;
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.
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Rationale for Selection of the gest Available^ Technology
Economical l_Y_Achievable
Total Cgst^gf Achieying_Eff luent_Reduction - As presented in Section
VIII, to meet the best available control technology economically
achievable effluent limitations, tanneries discharging to receiving
waters wculd have to invest an estimated $42.5 million (August, 1971,
price levels). This $M2.5 million includes the $28 million investment
required to meet the best practicable control technology currently
available guidelines and assumes no in-place treatment systems. The
incremental cost is $14.5 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 0.5 and
2.6 percent for various industrial classifications. Only one
subcategory is in excess of 1.3 percent.
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 __ lniEi2y.§^ ~ Differences in processes within the industry have
been accounted for in establishing the effluent limitations.
En3ineering_Asgects_of_Contrgl_Technigues - The best available control
technology economically achievable appears achievable considering the
developmental work being done on sulfide oxidation and nitrif ication-
denitrif icaticn. There are several technical questions which need to be
resolved prior to initiation of full-scale nitrif ication-denitrif icat ion
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 nitrif ication-denitrif ication 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 tc 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.
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Nonwater_QualitY_Envirgnmental_Irngact - The impact upon the land as a
result of liquid waste treatment is the same as outlined for the best
practicable control technology currently available in Section IX.
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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 cf dry rather than wet processes (including sub-
stitution of recoverable solvents for water).
6. Recovery of pollutants as by-products.
Im]groyed_ In-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 procedures should
133
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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 ot 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.
N6w_Source_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.
Pretreatment_Reguiremgnts
Three constituents of the waste water from plants within the leather
tanning and finishing industry have been found which would interfere
with, pass through, cr 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.
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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.
135
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SECTION XIII
REFERENCES
1. "Industrial Waste - Profile No. 7, Leather Tanning and Finish-
ing, " The_Cost_of_Clean_Water_-_Volume_IiJ[, Federal Water Quality
Administration Report, 1967.
2. "Membership Bulletin Leather Industry Statistics," Trade Survey
Bureau - Tanners' Council of America, Inc., 1971, 1972, and
1973.
3. 0'Flaherty, F., Roddy, w. T., and Lollar, R. M. , Chem_istry__and
J§£llI10l23Z_21_i£at£££» Volumes I-IV, Reinhold Publishing Cor-
poration.
U. Masselli, Joseph W., Masseli, Nicholas w. , and Burt'ord, 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^Diyisionx_Procgedings_of the^American^Sgciety^gf
Civil_Engineers, Volume 95, No. SA5, October, 1969.
6. Hauck, Raymond A., "Report on Methods of Chromium Recovery and
Reuse from Spent Chrome Tan Liquor," Journal_of_the_American
Leather_Chemists^_Assoc.iation, Volume LXVII, No. 10,
1972.
7. Bailey, D. A., and Humphreys, F. E., "The Removal of Sulphide
from Limeyard Wastes by Aeration," British^Leather Manufac-
tl}]L§£lji_B§§lM;£h_A§3Ocj.ationx_LJlbj2ra^ xv» No- 1»
196fi7~
8. Eye, J. David, and Clement, David P., "Oxidation of Sulfides
in Tannery Waste waters," Journal^pf the_American Leather
Chemistsl_Association, Volume LXCII, No. 6, June, 1972.
9. Williams-Wynn, D. A., "No-Effluent Tannery Processes," Journal
of the American^Leathgr^Chemists^_A5SOciatign, Volume LXVIII,
No. 1, 1973.
10. Data obtained through communication with tannery firms.
11. Moore, Edward W., "Wastes from the Tanning, Fat Processing,
and Laundry Soap Industries." Source unknown.
12. McKee, Jack Edward, and Wolf, Harold W., eds.. Water Quality
Criteria. 2nd ed., The Resources Agency of California, State
Water Quality Control Board, Publication No. 3-A 1963.
137
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13. Bailey, D. A., Dorrell, J. J., and Robinson, K. S., Journal
of_the_SgcietY_of_Leather_Tradesl_Chemists, 5J4, 91, 1970.
Cited in Journal_of_the_American_Leather_Chegiists^_Associa-
tion, Volume LXVIlT Mo7~9, September, 1972.
14. Sutherland, R., Indu3trill_and_Erigineerincj_ChemistrY, J9, 628,
19U7. cited in Reference 11)".
15. Sproul, Otis J., Atkins, Peter F., and Woodward, Franklin E.,
"Investigations on Physical and Chemical Treatment Methods
for Cattleskin Tannery Wastes," Journal_Wat'jr_Pollution
Control.,Federation, Volume 38, No. U, April, 1966.
16. Kunzel-Mehner, A., Geaundhi_Inar, 66, 300, 19U3. Cited in
Reference 11) .
17. "Report of the Symposium on Industrial Waste of the Tnnninq
Industry," Journal_of_the_American_Leather_chemistsl Associ-
ation, Supplement No. 15, 1970.
18. Howalt, W., and Cavett, E. S., Transactions of American Society
Ql_Civil_Engineers, 92, 1351, 19287clted~in Reference 11).
19. Riffenburq, H. B., and Allison, W. W., Industrial_and_En(3Jr
£!§ er in g_Che m is t r_ y, .33, 801, 19U1. Cited in Reference 11).
20. Haqan, Jamas R., and Eye, J. David, and Gunnison, G. C.,
"Investiqations into the Removal of Color from Dioloqically
Treated. Vegetable 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
Qiyil_Engineers, Volume 98, No. SA1, February, 1972.
23. The A. C. Lawrence Leather company, Acti^vated_Slud2e_Treat2
ment_of_Chrome_TjnnerY_Wastes, Federal Water Pollution Control
Administration, Department of the Interior, Grant No. WPHD
133-01-68, Proqram No. 12120, September, 1969.
2U. Nemerow, N. L., and Armstronq, R., "Prototype Studies of Com-
bined Treatment of Wastes from 22 Tanneries and Two Munici-
palities," Purdue Industrial_Waste^cgnferjgnce_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.
138
-------
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 jthg America n_Leather_Cherni5ts^
Association, 36, 463, "1941. Cited~in Reference U) .
28. "Tannery Effluent. Report to the Members of the Effluent Com-
mission of the International Union of Leather Chemists'
Societies, " Journal of the_Amer ican_ Leather _Chemists*_ Associ-
ation. Volume LXVII, No. 10, October, 1972. Reprinted from
1972?
29. Parker, Clinton E. , Anae robic- Aerobic Lagoon_Treatment for
Vegeta ble_Tann in_2_Wa s tes , Federal Water Quality Administra-
tion, Environmental Protection Aqency, Grant No. WPD-199-01-67,
Program No. 12120 DIK, December, 1970.
30. Sawyer, C. N. , "New Concepts in Aerated Laqoon Design and
by Gloyna, E. F. and Eckenf elder, 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," Adyances_in_Water_2uality_Imgrovement, edited by
Gloyna, E. F. and Eckenf elder, W, W. , Jr.), U. of Texas Press,
Austin, 1968. Cited in Reference 29).
32. Eye, J. David, Treatment of _Sgle_Leather_yegetable 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.
34. Clark, John W. , and Viessman, Warren, Jr., "Biological-
Treatment processes, Activated Sludge," Water_Supply._and
Po 1 lut i on_cont rol , 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,"
Proceed! ngg oflthe_16th _Indugtrial_Waste_CQnference , Purdue
University, U23, 1961. Cited in~Reference 29).
36. Gates, W. E. , Smith, J. H. , Lin, S., and Ris, C. H., Ill,
"A Rational Model for the Anaerobic Contact Process,"
Journal^Water Polluticp Control_FederatiQn , 39, 1951.
1967. Cited i~Reference 29).
139
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37. "Industrial Waste Survey at Caldwell Lace Leather company,"
EPA, Office of Operations, Radioloqical and Industrial Waste
Evaluation Section, Cincinnati, Ohio.
38. Siebert, C. L. , "A Diqest of Industrial Waste Treatment,"
Pennsylvania State Department of Health, 1940. Cited in
Reference 11) ,
39. Reuninq, H. T., Sewage Jrfcrks_Journal, 2Q, 525, 1948. Cited
in Reference 11).
40. Harnley, John W., Waqner, Frank R., and Swope, H. Gladys,
"Treatment of Tannery Wastes at the Griess-Pfleqer Tannery,
Waukeqan, Illinois," Sewage_Works_Journal, Volume XII, No. 4,
July, 1940.
41. Eldridqe, E. F., Michigan_Rngineering_Exgeriment_Station
Bulletin, &1* 32» November," 19397 Cited In~Reference'Il) .
42. Fales, A.L., Industrial_and_£ngineerin3_Chemistry_, _2J» 216
1929. Cited by Reference 11).
43. Sproul, Otis J., and Hunter, Robert E., "Appendix A, Indus-
trial Waste Treatment Investiqations, Prime Tanninq Company
and Berwick Sewer District Activated Sludqe Pilot Plant,
Berwick, Maine," Berwick^Sfewer_DistrictA_Preliminary^Design
Re£grtA_Pol_luticn_Control_SYStem, Edward C. Jordan Co., Inc.,
Portland - Presque Isle, Maine, 1967.
44. Haseltine, T. R., "Tannery wastes Treatment with Sewage-at
Williamsport, Pennsylvania," Sewaqe_and^Indijstrial.Wastes,
Volume 30, No. 1, January, 1958.
45. Hartman, B. J., Sewage_and_Industrial_Wastes, ^5, 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-Johnstown, New York,"
Purdue_IndustriaJ._Waste_Conf eren^e_Proceedj.ngs, 1966.
48. Wims, F. J., "Treatment of Chrome-Tanning Wastes for Accept-
ance by an Activated Sludqe Plant," Purdua Industrial^Waste
Conf e rence_Proc§edi.ng §, 1963.
49. Maskey, D. F., Journaljjof_the_American_Leather_Cherriists^
Association, 36, 121 1941. Cited by Reference 11) .
140
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50. Mccarty, P. L., "Anaerobic Treatment of Soluble Wastes,"
Advances in Water_puality^jmjjrgyement 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
Waste_Conf_erence_Proceedirigs, 1966.
52. Zanitsch, Roger H. , Laboratory Column Studies for
Coffin & Richardson Engineers, Hartland Tannery, Hartland,
Maine, Environmental Engineering Department, Water Management
Division, Calgon corporation, A Subsidiary of Merch 6 Co., inc.,
Pittsburgh, Pennsylvania, Report No. C-781, June 16, 1972.
53. Tomlinson, H. D. , Thackston, Edward L., Krenkel, Peter A., and
McCoy, V. Wayne, Cgm2lete_Treatment_of_TannerY_Wastes, Technical
Report No. 15, Department of Sanitary and Waste Resources
Engineering, Vanderbilt University, Nashville, Tennessee, 1968.
54. Tomlinson, H. D., Thackston, E. L., Krenkel, P. A., and
McCoy, V. W., "Laboratory Studies of Tannery Waste Treatment,"
Journal of Watgr Ppllutjon Control Federation, Volume 41,
No. 47 April, 1969.
55. Thackston, Edward L., Secondary, Waste Treatment for
a Small DiversiJied_TannerY, Office of Research and Monitoring,
U.S. Environmental Protection Agency, Grant No. WPRD 25-01,
Project 12120 EFM, April, 1973.
56. Gulp, R. L. and Gulp, G. L., Advanced_Wa^tewater_Treatment.
57. Wild, Harry E., Jr., Sawyer, Clair N., and McMahon,
Thomas C., "Factors Affecting Nitrification Kinetics,"
Journal of Water Pollution_Contrgl Federation, Volume 43,
No, 9, September, 1971.
58. Wild, Harry E., Jr., sawyer, Clair N., and McMahon,
Thomas C., Nitrification and Denitrifjcation Facilities,
Environmental Protection Agency Technology Transfer
Program - Design Seminar for Waste Water Treatment
Facilities, Kansas City, Missouri, September 8-9, 1971.
59. Dodge, Barnet F,, "Fresh Waters from Saline Waters," Amer-
ican Scientist , Volume 48, No. 4, December, 1960. Cited in
Reference 347.
141
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60. Downing, D. G. , Kunin, R.f and Pollio, F. X. , "Desal Process-
Economic Ion Exchange System for Treating Brackish and Acid
Mine Drainage Waters and Sewage Waste Effluents," Chemical
En2ineering_Prggress_S^m2gs^ium_Seri9S, Volume 64, No. 90, 1968.
61. Wiley, Averill, J., Duhey, George A., and Bansal, I.K.,
Rgverse^QgmosrigCQnccntration_of Pi lutgr Pulp and Paper
Effluents, 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, Kycte, Japan.
63. "Rex Chainbelt Inc., The Ecology Division, Reverse
gsmosis_Deminerali^atign_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 FQR, March, 1972.
64. 1972-1973 Saline Water Conversion Summary Report,
United States Department of Interior, Office of Saline Water.
65. Burns and Roe, Inc., Dig po sal of Brines Produced in Renovation of
MunJ.cij3al_Wastewat er , Federal Water Quality Administration,
Department of the Interior, contract No. 1U- 12-492, Program
No. 17070 DLY, May, 1970.
66. "Patterson, W. L. , and Banker, R.F. , Estimating
Trej*tment_ Facilities, office of Research and Monitoring,
Environmental Protection Agency, Contract No. 14-13-462,
Project No. 17090 DAN, October, 1971.
67. Smith, Robert, and McMichaol, Walter F.,
Perf or ma nce_ Estimate s^for_Te rt jar y_Wastewat er_ Treat mgnt
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," Jou^nal_of_Wa^r_Polj.utign_contrgl._Federation, Volume 45,
No. 2, February, 1973.
70. OiljL_Painti_and_Drug_Rjej20rter, August 2, 1971.
142
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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 £aCO3
The Act is the Federal Water Pollution Control Act Amendments of 1972.
Ac tiyatecL. Sludge
A waste water treatment process using a mixed microbiological culture
and molecular oxyqen 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
population in the process.
Adipose
Of, or related to, animal fat; fatty.
Adsorption
J.he adhesion of a gas, liquid, 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.
A biological process in which oxygen is used for microorganism respi-
ration needs. Especially relating to the degradation process of waste
matter in the presence of dissolved oxygen.
Alkalinity
A measure of the ability of the waste to provide hydroxyl ion to react
with acidic materials. Generally expressed in mg/1 as CaCO_3.
143
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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 oxyqen.
Back
Jhat portion of the animal hide, especially cattlehide, consisting of
the center portion of the hide alonq the backbone and covering the ribs,
shoulders, and butt (excluding the belly).
Bating
The manufacturing step following liminq and precedinq pickling. Tho
purpose of this operation is to delime the hides, reduce swelling,
geptize fibers, and remove protein degradation products from the hide.
Beamhouse
That portion of the tannery where the hides are washed, limed, fleshed,
and unhaired when necessary prior to the tanning process.
Bell*
That portion of the hide on the underside of the animal usually
representing the thinnest part of the tannable hide.
Bend
That portion of the hide representing the entire hide cut down the
backbone with the bellies and shoulders removed.
gest Available_Demonstrated Centrol Technology
Treatment and control required for new sources of industrial discharge
to surface waters as defined by Section 306 of the Act.
Best Ayailabig nTfechnology_iEcpnomicallyAchj.eyable
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 Pragticable Control TechnologyCurrently Available
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.
144
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en Demand (BOD 5)
The amount of oxyqen 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
T.he amount of concentrated liguor wasted in a recycle system in order to
maintain an acceptable eguilibrium of contaminants in any process
3.iquor.
A hide after tanning with chromium salts. Hide usually has a slight
blue color.
Chemical Oxyqen^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 (Tota1)
Total chromium is the sum of chromium occurring in the trivalent and
Ijexavalent state. Expressed as mg/1 as Cr.
A. physical means for the removal of suspended particles in a liquid by
gravity sedimentation (settling) .
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.
Col lag en
The fibrous protein material within the hide which provides the bulk of
the volume of the finished leather and its rigidity.
145
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Colloids
Microscopic suspended particles which do not settle in a standinq liquid
and can only be removed by ccaqulation or bioloqical action.
Color
A measure of the liqht absorbinq capacity of a waste water after tur-
bidity has been removed, one unit of color is that produced by one mq/1
Of platinum as K2PtClo.
Coloring
A process step in the tannery whereby the color of the tanned hide is
chanqed to that of the desired marketable product by dyeinq or painting.
Sa mj3 j. e
A series of small waste water samples taken over a qiven time period and
combined as one sample in order to provide a representative analysis of
the averaqe waste water constituent levels durinq the sampling period.
Concrete Mixer
A term often applied to hide processors.
Cerium
The layer of hide between the epidermis and the flesh. Also called the
derma.
De liming
The manufacturinq step in the tanhouse that is intended to remove lime
from hides cominq from the beamhouse.
Demine ralizatign
The process of removinq dissolved minerals from water by ion exchange,
reverse osmosis, electrodialysis, or other process.
Derma
That part of the hide which is between the flesh and the epidermis.
Desalinization
The process of removinq dissolved salts from water.
Detention (Retention)
The dwell time of waste water in a treatment unit.
146
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Dewatering
The process of removinq of a large part of the water content of sludges.
DO
Dissolved oxygen. Measured in mg/1.
Drum
A large cylinder, usxially 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.
Electro-dialysis
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.
Epidermis
The top layer of skin; animal hair is an epidermal regrowth.
Equalization
T.he holding or storing of wastes having differing gualities and rates of
discharge for finite periods to facilitate blending and achievement of
relatively uniform characteristics.
Eutrophication
The excess fertilization of receiving waters with nutrients, principally
phosphates and nitrates, found in waste water which results in excessive
growth of aguatic plants.
Fatliquorin 3
The process of adding oils, fats, and greases (fatliquor) to tanned
hides to improve and prevent cracking.
147
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Finishing
The final processing steps performed on a tanned hide. These operations
follow the retan-color-f atliguor processes, and include the many dry
processes involved in converting the hide into the final tannery
product.
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.
Flgcculation
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.
Grain
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.
148
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Grease
A qroup of substances including fats, waxes, free fatty acids, calcium
and maqnesium soaps, mineral oils, and certain other non-fatty
materials. The grease analysis will measure both free and emulsified
oils and greases. Generally expressed as mg/1.
Green Hides
Hides which may be cured but have not been tanned.
Ion Exchange
The reciprocal transfer of ions between a solid and a solution sur-
rounding the solid. A process used to demineralize waters.
jhe 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.
The operations in the beamhouse where a lime solution comes in contact
with the hide. Liming in conjunction with use cf 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.
Membrane
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.
tjitrogen. Kjeldahl (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.
149
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Nutrient
Any material used by a livinq orqanism which serves to sustain its
existence, promote growth, replace losses, and provide energy. Com-
pounds of nitrogen, phosphorus, and other trace materials are par-
ticularly essential to sustain a healthy qrowth of microorganisms in
biological treatment.
Outfall
Jhe final outlet conduit cr channel where waste water or other drainage
is discharged into an ocean, lake, or river.
Layers of salted hides formed at the slaughter house or hide curing firn
(usually approximately 20 to 40 feet in area and 5 to 6 feet high) .
Padd.le_yat (Paddle)
A vat with a semi-submerged rotating paddle arrangement used for the
mixing of water and chemicals with the hide.
J2i!
The reciprocal logarithum of the hydrogen ion concentration in waste-
water expressed as a standard unit.
Parts per million. The expression of concentration of constituent.^; in
waste water; determined by the ratio of the weight of constituent B5r
million parts (by weight) of total solution. For dilute solutions, ppm
is essentially equal to mg/1 as a unit of concentration.
Pasting
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
j.he 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 the skin or hide is "pressed" in order to
make it smoother.
150
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An organic compound characterized by a large molecular weight. Certain
joolymers 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.
Processor
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
before shipment to a tannery.
Re tan
The process step following tanning and any intermediate drying whereby
hides 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.
v3andinc[
A dry operation performed on the tanned and fatliguored 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) .
151
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Chemicals used in addition to lime to assist in the unhairinq grocers
(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.
Side
A side represents half a hide which has been cut alonq the spina.
Skiving
The thin layer shaved or cut off the surface of finished leather,
jorincipally sheepskin.
Sludcje
A concentrate in the form of a semi-liquid mass resulting from settling
of suspended solids in the treatment of sewage and industrial wastes.
it-
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_Classifi cation
The numerical designation given to various industries by the Bureau of
the Budget. The leather tanning and finishing industry bears SIC No.
3111.
Submerge/.! Combustion
A flash evaporation type procedure used in the separation of dissolved
solids from water.
152
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Suifide
^onized sulfur. Expressed as mg/1 as S.
ed Solids (SS)
Constituents suspended in waste water which can usually he removed by
sedimentation (clarification) or filtration.
Tacking
Staking using tacks to fasten skins or hides to a large frame.
Tannin
The chemicals derived from the leaching 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 Dissolved_Solids (TCS)
The total amount of dissolved materials {organic and inorganic) in waste
water. Expressed as mg/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.
Volatile_Solids
Solids, dissolved or suspended, which are primarily organic and during
stabilization exert the significant portion of the BOD5.
weir
A control device placed in a channel or tank which facilitates mea-
surement or control of the water flow.
Wheel
Drum.
153
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METRIC UNITS
CONVERSION TABLE
MULTIPLY (ENGLISH UNITS)
ENGLISH UNIT ABBREVIATION
acre ac
acre - feet ac ft
British Thermal
Unit BTU
British Thermal
Unit/pound BTU/lb
cubic feet/minute cfm
cubic feet/second cfs
cubic feet cu ft
cubic feet cu ft
cubic inches cu in
degree Fahrenheit F°
feet ft
gallon gal
gallon/minute gpm
horsepower hp
inches in
inches of mercury in Hg
pounds lb
million gallons/day mgd
mile mi
pound/square
inch (gauge) psig
square feet sq ft
square inches sq in
tons (short) t
yard y
by TO OBTAIN (METRIC UNITS)
CONVERSION ABBREVIATION METRIC UNIT
0.405
1233.5
0.252
ha
cu m
kg cal
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
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 +1)*
0.0929
6.452
0.907
0.9144
atm
sq m
sq cm
kkg
m
* Actual conversion, not a multiplier
Environmental Protection Agency.
Library, Region V
1 North Wacker Drive
Chicago, Illinois 60606
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
154
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