EPA 440/1
376/082
D R A FT
;f;c
'"* Supplement For
Pre treatment
iB to the
Development Document
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LEATHER TANNING
AND FINISHING
*r'-*«O fti^^'-'^^^jw
^*^ ^^ *
ITE D STAT E S E N VI RON Mi ENTAL PROTECTION ENCY
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REVIEW NOTICE
This document presents conclusions of a study conducted for
t_he Effluent Guidelines Division, United States Environmental
Protection Agency, in support of draft pretreatment standards
for the leather tanning and finishing industry.
The conclusions of this document may be subject to subsequent
revisions during the document review process, and therefore
may be superseded prior to final promulgation of the
regulations in the Federal Register, as required by the
Federal Water Pollution Control Act Amendments of 1972
(P.L. 92-500) . . - .. ,;..-...
- . "''"'*;
v.
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DRAFT SUPPLEMENT
for
PRETREATMENT
to the
DEVELOPMENT DOCUMENT
for the
LEATHER TANNING AND FINISHING
POINT SOURCE CATEGORY
Russell E. Train
Administrator
Andrew W. Briedenbach
Assistant Administrator for Water and
Hazardous Materials
Robert B- Schaffer
Director, Effluent Guidelines Division
Donald F. Anderson
Project Officer
November 1976
Effluent Guidelines Division
Office of Water and Hazardous Materials
U. S. Environmental Protection Agency
Washington, D. C. 20460
U.S. Environmental Protection Agency
legion 5, Library (PL-12J)
n West Jackson Boulevard. 12th Floor
Chicago. IL 60604-3590
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ABSTRACT
This document presents the findings of an extensive study
of the leather tanning and finishing industry by the
Environmental Protection Agency for the purpose of
developing pretreatment standards for the industry to
implement Section 307(b) of the Federal Water Pollution
Control Act Amendments of 1972 (the "Act").
The leather tanning and finishing plants included in this
study are plants that manufacture leather and leather
products from purchased hides or skins of cattle, sheep,
pig, deer, horse, and other animals. There are seven
subcategories in the leather tanning and finishing
industry. These are based on similarities of processes
and raw waste characteristics, particularly BOD_5 in
kilograms per thousand kilograms, and flow in volume of
wastewater generated per unit weight of hide, as raw
material received.
Conclusions are set forth regarding wastewater quality
improvement to protect personnel and facilities in municipal
sewerage and treatment systems. These conclusions involve
existing tanneries discharging into a municipal sewerage
system. The total capital cost for existing tannery
facilities, which discharge to municipal systems, is based
only on sulfide removal and is estimated at $7.3 million.
Supportive data and rationale for development of the
conclusions contained in this report are based on current
information from 128 leather tanning and finishing plants
and from the original development document and data record
prepared for and by the EPA and published in March 1974.
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TABLE OF CONTENTS
Section Page
I CONCLUSIONS 1
II RECOMMENDATIONS 3
III INTRODUCTION 5
Purpose and Authority 5
Summary of Methods Used for Development of
the Pretreatment Standards 5
General Description of the Industry 8
Standard Manufacturing Processes 10
IV INDUSTRY CATEGORIZATION 29
Classification System 30
Subcategorization System 32
Rationale for Categorization 35
V WATER USE AND WASTE CHARACTERIZATION 41
Wastewater Characteristics 41
Sources of Wastewater and Waste Load " 53
Total Plant Liquid Waste 60
VI SELECTION OF POLLUTANT PARAMETERS 61
Wastewater Parameters of Significance 61
Rationale for the Selection of Major Pollutant
Parameters 61
Rationale for the Selection of Minor Pollutant
Parameters 68
VII CONTROL AND TREATMENT TECHNOLOGY 73
General 73
Current Practices 73
Relationship of Pretreatment Technology to
Publicly Owned Treatment Works Requirements 75
In-Process Methods of Reducing Wastes 76
Preliminary Treatment 81
Screening 82
Equalization 83
Sulfide Oxidation 83
Plain Sedimentation 85
Chemical Treatment—Coagulation and
Sedimentation 87
Chemical Treatment—Carbonation 90
pH Adjustment 91
Sludge Handling and Disposal 91
111
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Table of Contents (Continued)
Section Page
VIII COST, ENERGY, AND NONWATER QUALITY ASPECTS . . 95
Summary 95
"Typical" Plant 103
Treatment and Control Costs 103
Energy Requirements 108
Nonwater Pollution by Waste Treatment Systems 109
IX EFFLUENT REDUCTION ATTAINABLE THROUGH THE
APPLICATION OF THE BEST PRACTICABLE CONTROL
TECHNOLOGY CURRENTLY AVAILABLE—EFFLUENT
LIMITATIONS GUIDELINES 117
X EFFLUENT REDUCTION ATTAINABLE THROUGH THE
APPLICATION OF THE BEST AVAILABLE TECHNOLOGY
ECONOMICALLY ACHIEVABLE—EFFLUENT LIMITATIONS
GUIDELINES 119
XI PRETREATMENT STANDARDS 121
Introduction 121
Effluent Reduction Attainable by Pretreatment
Technology 121
Identification of Pretreatment Technology 122
Rationale for the Pretreatment Standard 123
Size, Age, Processes Employed, Location of
Facilities 125
Total Cost of Application in Relation to
Effluent Reduction Benefits 126
Engineering Aspects of Pretreatment Technology
and Relationship to Publicly Owned
Treatment Works 126
In-Plant Changes 128
Nonwater Quality Environmental Impact 130
XII ACKNOWLEDGMENTS 131
XIII REFERENCES 133
XIV GLOSSARY 137
CONVERSIONS 150
IV
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Numbe r
III-l
IV-1
IV-2
IV-3
IV-4
V-l
V-2
V-3
V-4
VII-1
VII-2
VIII-1
VIII-2
VIII-3
VIII-4
VIII-5
VIII-6
VIII-7
VIII-8
VIII-9
LIST OF TABLES
Page
Production and Marketing Trends of the
Leather Tanning and Finishing Industry 9
Classification System (3111. abed) 31
Categories of the Leather Tanning and
Finishing Industry 33
Category Comparison by Principal Processes 34
Production, Wastewater Flow, and Raw Waste
Loading by Subcategory 40
Raw Wastewater Characteristics, kg/1000 kg 44
of Raw Material Hide (Same as lb/1000 Ibs &
of Hide) 45
Leather Tannery Raw Waste Parameters
Expressed As Average Concentration for
Each Category, mg/1 46
Hourly Raw Waste Data for a Single Cattlehide
Tannery (Category 1) 49
Comparison of Winter/Summer Raw Waste
Characteristics
Plain Sedimentation
Chemical Treatment
52
86
88
"Typical" Plant Operating Parameters Used
For Estimating Cost of Achieving Pretreatment
Standard 96
Percentage of Tanneries That are Expected
to Install Sulfide Removal Equipment 98
Capital Investment Cost Estimate for Each
Tannery to Provide Sulfide Removal Technology 99
Percentage of Tanneries That May Install
Additional Pretreatment Components 100
Aggregate Pretreatment Capital Cost Estimate
for Leather Tanning Industry 101
Increase in Operating and Maintenance Cost
and Total Annual Cost for Sulfide Removal to
Achieve Pretreatment Standard 102
Capital Investment Cost Estimate for Each
Tannery to Provide Optional Pretreatment
Technology 105
Pretreatment Component Cost Estimates by
Category and Size 106
Increase in Operating and Maintenance Cost
and Total Annual Cost for Combined Pre-
Treatment System Comprising Components
Indicated in Table VIII-4 107
v
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Number
VIII-10
VIII-11
XI-1
LIST OF TABLES (Continued)
Disposal Sites Utilized
"Typical" Sludge Characteristics
Sulfide Concentrations of Tannery
Wastewater
Page
112
113
129
LIST OF FIGURES
Number Page
III-l General Process Flowsheet for Leather
Tanning and Finishing Industry 12
V-l Raw BOD Data by Category 47
V-2 Raw Chrome Total Data by Category 48
V-3 Wastewater Flow Data by Category 51
V-4 Product and Wastewater Flow for Generalized
Leather Tanning and Finishing Plants 54
VI
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SECTION I
CONCLUSIONS
A conclusion of this study is that the lea
finishing industry comprises seven subcat
1. Cattle-pulp-chrome tan.
2. Cattle-save-chrome tan.
3. Cattle-nonchrome tan.
4. Thru-the-blue.
5. Retan only.
6. No beamhouse tannery.
7. Shearlings tannery.
The primary criteria for categorj^ationXw^ete ^he type or
condition of animal hide processeoxmethod off hair removal,
type of tanning agent used, and exterMsxOf finishing
performed. Plant size, age, and location wastexater
characteristics, and water usage were
Currently, wastewater from about 90 percent of t!
tanneries, accounting for/approximately 80 percent of
tannery industry production, is^d^scharged to municipal
systems.
It is concluded that leathe
dischared into properly desic
owned treatment works can be
further concluded that municipal
tanneries address most pollutants
wastewater and specify acceptable in:
compatible with rptHTTc-i^al treatment sys\
facilities.
Ashing wastes
rated publicly
oved. It is
ces in cities with
tannery
t quality to be
em processes and
It is concluded tn«at s\ulf r
incompatible ^onstitb^rnts in ta?
discharged to puialicly owjred_ trea
ammonia are the only
wastewater being
ient works.
It is further concluo&sL that^bechnology is available and
in used to achieve the removal jZ$f sulf ide from tannery
wastewater. There is no pre^tryktment technology practicable
or in uaa— 1£> remove ammonia by the industry. The estimated
capita/1 cosrbf^achieving sulf ide removal by tanneries
discbargiag to mCmicipal systems is $7.3 million. Total
annal osr^fa^n eluding depreciation, capital costs, operation,
sliis pretreatment limitation will
ncrease unisvcose or different tanneries by a cost
varyingi&^pm ST^vcelftts |to 76 cents per raw material hide
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for the cattlehide tanners in the industry and
to 11 cents per skin for other segments of the
Tannery size will influence the specific pi
each of these ranges.
tan
irom 1.6 cents
^ustry.
>t within
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SECTION II
RECOMMENDATIONS
No specific numerical wastewater pretreatm/nt sta
being recommended at this time. However,/to/avoid c
the terminology of "draft recommended l
"pretreatment standards" has been used only to be
ards are
usion,
or
siste^
with the language of the Act to represent in draft fol
conclusions of the technical study regarding effluent levels,
achievable for discharge to a publicly owned treatment worl
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SECTION III
INTRODUCTION
PURPOSE AND AUTHORITY
Section 307(b) of the Federal Water Polli
Act Amendments of 1972 (the Act) requires the
Administrator to promulgate pretreatment standards fc
pollutants introduced into publicly owned treatment
works. Section 307(c) of the Act requires the
Administrator to establish pretreal
new sources. The regulations
pretreatment standards for existj
Sections 307 (b) and 307(c) of tl
and Finishing point source cat«
rient
standards for
herein set forth
ources pursuant to
for^the Leather Tanning
This document is the first of three
documents that together normally
complete point source category developmei
This first document addresses only pretreal
of limitations/ standards, technology, and
development
igle and
jt.
terms
This
document is complete in
description and trends „
use and raw wastewater/
parameters.
^dressing
The second and third docume
requirements of the Act as
301(b), and 306 regarding the
practicable control technology c\
July 1, 1977, the best available
economically achievable by July 1,
the industry
categorization, water
and pollutant
the
ctions 304 (b),
tion of the best
available by
ogy
and the
establishment x5f Federal standards of performance for
the Leather Tyannina ano\Finishing point source category.
SUMMARY OF METHODS
LELOPMENT
OF THE PRETREATMENT 'STA^ARDS
The pretreatment srsndards^^et rorth herein were developed
in the following manne^Xv. The^original development document
(1974) and selected sect^rsnsyof the appendices to that document
were acquired". The organization that prepared the original
was included on the current study team so that
thebenefit or^heir experience could be obtained and the
ircorQ<5ra'fciQn of isxisting data and information on the tanning
cilitated. The point source category was
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ether separate
different
analysis
n raw
s employed,
first studied for the purpose of determining
limitations and standards may be appropriat
segments within the point source category.
included a determination of whether differ,
material used, product produced, manufact,
equipment, age, size, wastewater constit
factors may require development of separef
and standards for different segments of the point
The raw waste characteristics for each segment were i1
and used in this analysis. The analysis included consi
of: 1) the sources and volume of water used in the processes
tations
egory,
d
ion
employed and the sources of pollut
plant, and 2) the constituents (i
wastewaters, including toxic con
which produce taste, odor, or
organisms. The constituents o
considered for pretreatment sta
guidelines, and standards of perfo
(see Section VI).
its and wastewaters in the
ling thermal) of all
ients and other constituents
;er or aquatic
swhich should be
lent limitations
identified
The full range of control and treatment technology existing
within the point source category was identified/ This
included identification yefesach distinct control and
treatment technology, ificluEhtna an identification in terms
of the amounts of constituents ("including thermal) and
the chemical, physicarv and iiplogic^aicharacteristics
of pollutants, and of tnfe< efr^ant leve~l>s£esulting from
the application of each ofNthe^fcr^atment and control
technologies. The problems ^N^mitat-j^ofrs^/and reliability
of each treatment and control t^chno^ogy and the required
implementation time were also idei^tifr^d. In addition,
the nonwater quality environmental xmp/cts, such as the
effects of the ap-piication of such technologies upon other
pollution problems, including air, solid waste and noise
were also identified. Yne energy requirements of each
control and/trea^meKt technology was identified as well
as the costCof theX^plicatToTOtt^of such technology.
In assessing tre*ia4^ment ^tRd^oontrol technologies, various
factors were consicbared. Ttiese included the total cost
of application of technology^n relation to the effluent
quality achieved, equipm&nt and facilities involved, the
proces&esemployed, the engineering aspects of the
appLa^catfoti-vof various types of control techniques,
process change^Sx, nonwater quality environmental impacts
and other factors.
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The specific data sources used to characterise the industry,
the wastewater characteristics, and the indtfstr^ practices
with regard to wastewater generation and dj/spo/al
include the following:
tes
or
One-page surveys and detailed
were distributed to about 301
tanneries and finishers through the
Council of America to obtain information on'
specific plant situations. Survey responses
were received from 114 tanneries. Questionnaires'
were returned by 89 tanner
Telephone contacts with
made to collect informa>
wastewater limitations,
wastewater problems ej
for dealing with the
wastewater data for local
municipal performance data
Information on plant operations^
practices, processes, equipment,
concerns and attitudes, and wastewate^Wand
production datax^as collected during field
visits to 35 t^annelH^s. This information was
used to complement oth^is^data sources.
Wastewater satapling^trips of^two or three days
were made to l4\tann«i>i^s. The-^mple of tanneries
visited and/or samjxLecN^eluded facilities
representative of mb^t situatlr>»s and operations
found in the industry>v Tanneries of different
size and age of physicaJXplan-t were observed,
and tanneries in both largs^. urban and in rural
areas jirGT&-*yi sited. ^
:ipalities were
on city ordinance
limitations,
id plans
splementary
and
requested.
ata and background information
tanneries were obtained from
Permits included
ery and waste treatment
discharge standards and
being set at the
NDPE
on
EP,
i
faci
schedu
present tf
Engineering s^budies Ynd reports were received
on waste treatmentfacilities for several
^tanneries. These reports included dimensions
.descriptions of the facilities, operating
data on wastewater quality and
waste treatment design basis and
:reatment system problems, and cost
;imalses fcr wastewater control and
cilities.
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7. Contacts were also made with state pollution
control offices to request available'dafca
and information on tannery wastewatoer
problems and plans for dealing with th«
problems.
GENERAL DESCRIPTION OF THE INDUSTRY
Leather tanning and finishing plants purchase hides
and manufacture leather for shoes, garments, upholstery,
luggage, gloves, handbags, sporting goods, and a variety
other applications. Cattlehides,
and pigskins are the most numerous,
tanneries in the manufacture of
of hides and skins of horses, go
other animals are also tanned e
iepskins and lambskins,
types used by U.S.
Smaller quantities
:, and various
le U.S.
elk,
Some plants tan and finish a single^speciesS^f animal hide.
Other plants tan and finish a combinati«qi of animal hide
types. Some plants have a single, very sp^&cializfed end
product such as lace leather or mechanical ctrfihioitfs for pianos,
Other tanneries produce a variety of leather typ^s for many
consumer goods and indusirrial uses. The variety of products
produced by the individual tahRery influences the hide type
and processing operations used by^he tannery.
While many plants process
hides to finished leather,
the total process. Several t
tanned hides and/or splits and
fatliquor and finishing processes?
purchase hides or skins which eithe
beamhouse proce
skins which h
as pickled c
arrangement
economicall
pollutant bea
stringent municip
location where
an effluent treatment
h as pigskins,
re
eithe
Ited, or brined
nly a portion of
ase previously
only the retan, color,
er of tanneries
not require a complete
purchase hides or
sly gone through the beamhouse, such
d pickled sheepskins. Another
tanners who have found it
high water use and strong
the tannery location where
tations exist to another
nt POTW capacity exists or where
readily implemented.
primarily located in four general areas of the
a concentration in the New England states with
lid-Atlantic states, the Midwest, and on the
III-l, tannery production from 1965 to
However, from 1975 data and
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projected 1976 data, total industry producti
equivalent number of hides and in total dol
to be increasing.
both in
ralue, appears
In the 1960's and early 1970's, from an
the domestic leather tanning and finishi
squeeze due to: 1) greater foreign
which caused an increase in cost of cattlehides; and 2)
competition from foreign countries in the finished lecher
products market1.
As shown in Table III-l, cattlehida^exports increased from
1965 to 1975. There was also a g^nebal increase in leather
import dollar value. However, ttie dollar value of leather
exports also increased. Finally, iA 19 7 5~ leather exports
exceeded leather imports as meurecNin ydorjars.
onomic standpoint
g ihdustryr^lt a
Increase in leather production, increase ihs^dollar value of
total industry production of leather/^and inci?ease in dollar
value of leather for export are three indications^ of a viable
U.S. leather tanning and finishing industryX. Management and
owners of tanneries express confidence in the raraustry both
verbally and by continuiaig^capital investments in tanneries.
STANDARD MANUFACTURE
Tanning is a term used
processing steps involved
into leather. Skin is compel
with flesh attached to the inm
constitutes the leather-making
and consists mainly of the protein'
essentially thexrsacition of collagen
chromium, al
tanning agents.
e all the numerous
mal skins or hides
1 and dermal layers
layer. The dermis
pf the skins or hides,
agen. Tanning is
ibers with tannin,
ar
The practic
history an
times the
of scientific p
instruments. As
of a suitable
deal on past experience.
unhairina. the concentratio
sodi
leather
skins began before recorded
Developed art. In recent
beer? modified by the application
ed by the use of scientific
try, the approach to production
iverage tannery relies a great
n/a typical process, such as
of lime and sharpeners (such as
and sodium sulfhydrate), temperature, and
interrelated as in most chemical reactions.
£ion and/or temperature may be increased
essing period. Tanners vary process
ndividual and collective experience to
ed products. Therefore, there are some
10
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variations in processing techniques, especia
chemicals and in other details (even betwee
producing the same finished product), to p
of consistent quality.
in the use of
tanners
te a product
The variations in processing techniques Asec
different types of animal skins to tannec
leather are contributing factors in wastewater gei
in the leather tanning and finishing industry. These
variations are recognized in the classification system
to describe the industry.
For purposes of characterizing
standard tannery processes were
retan, color, fatliquor, and fi
shown schematically in Figure
sodium sulfide, sodium sulfhydf
basic chromium sulfates, vegetable
compounds, mineral acids, alum, nature
fatliquors, acid dyes, some solvent
chloride are employed within the various pi
^Loads, the following
beamhouse, tanyard,
£hese processes are
?als such as lime,
ammoniuln salts, enzymes,
;anning^xtracts and
thetic
sodium
's.
m
In this study, a manufa
step in the complete
steps may result in s
A process can consist
In any defined process,
process is defined as a single
iring operation where alternative
^different waste characteristics,
of sub-processes.
Ld remain the same.
The industry can best be
manufacturing process concept
variation of processes used amon
approach, waste loads and
more readily described.
effluent
lyzed on this
This allows for the
s. With this
eoflirements can be
The discussion anddesoription of tannery processes which
follow are Wase^iiphn tkel_three major hide and skin types
produced iriOthe u^^y: cattTl&kides, sheepskins, and pigskins
The processes\and sub-patQcesses^liscussed represent an
inventory of thcJse most^t^yicaJL/of the entire industry.
Cattlehide Tannery Prbs^sses
nnery
:he following process description of a typical
was drawn in detail from the book Leather
by the New England Tanners Club2.
typical cattlehide tannery contribute
wa
11
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Figure III-l. GENERAL PROCESS FLOWSHEET FOR LEATHER TANNING AND FINISHING INDUSTRY
I Receive & Store Hides
12
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1. Beamhouse
2. Tanyard
3. Retan, color, fatliquor, finishin
Detailed descriptions of the process and
operations follow.
Beamhouse Process:
1. Receiving—Nearly all cattlehides received at
tanneries are either greeoxsalted or brine
cured hides, with the brine yfcured hides
predominating. In a fey isolated cases where
transit time is short, /ifre&h grefto hides without
prior curing are sent Qirectty^rorfr a meat packer
to a tannery for immediate process/ing,
Green hides, after trimming ahd gradi^nq, are
cured at the packinghouse by spreading rfee
hides, flesh side up, and covering wo^h /salt.
Another layer of hides is placed overtfie
salted hides, ag^in flesh side up, and covered
with salt. This pro^ce^ss continues until a
pack of hides/about five"^to six feet high results.
A heavy layer >is absorbed
and by diffusion and olsmosisiscauses a reduction
of the moisture content ;bn thK hide. After 10
to 30 days from the date the pjack is closed, the
hides >atfe^CQnsidered adequately cured. Each hide
then/nas thei^xcess salt shaken off, is folded
individiwtily, \nd shipped in packs, either to
tanneries oi- to^-wa.rehouses for storage. The
size, of thwpack dep&nds on a number of variables,
sucha^s size c^-the packing plant, size of
shipment^, and tb^lrt»thx>d of shipment.
Brined hides ehse prepared at the packing plant
or at a separate^l^dfe processing facility by
[itating fresh hides in a saturated brine
until the salt has replaced the
^amount of moisture within the hide.
^ocess, hides are also cleaned by
manure and other foreign matter.
;n removed, drained, and bundled
similar to that used for green sal-ted
13
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hides. Hides may be fleshed before
brining. "Safety salt" is usually
on each hide before shipment. The/brj
process take two to three days, v
attractive to the packer or hide,
establishment, since there is nc
a large inventory of hides. The TMrinin?
process is preferred by most tanners since*
tends to produce cleaner hides. Increased
use of brined hides in recent years demonstrates*
these preferences by both packer and tanner.
Storage—Normally the ta
stores hides in a large
area designed to keep
moisture content as r
'receives and
fl, well ventilated
the
Siding and Trimming—A typrcal fir!*t step in
preparing hides for processingxconsis'ks of
opening the bundles and trimmingXiff the-^ieads,
long shanks, and other perimeter are^s wftich
do not make good leather. The hides then may
be cut lengthwi^s^along the backbone, head to
iwi
tail, to make
halved or sid
A number of s
a pack which is
type of skin,
will be important in
are often collected fo
other by-product manufac
and
Sometimes hides are
4-.ring or tanning.
ered to form
ze, weight,
ation that
sing. Trimmings
to glue or
SoakinyaTna^a shing—The side^s are soaked in
vats /with orNwithout paddles), drums, or
hide/proc^ssorsX (concrete mixers with special
hours to restore moisture
as a result of the
s gradually absorb
water, bfe^mingsbei^and cleaner. After
soaking the^kins axe washed to remove dirt,
salt, blood, ma«mre,^nd non-fibrous proteins.
There is consider^bl^ variation in the quantity
such waste material, depending on the time
and the source of the hides. Depending
rpe of leather produced, additional
ises) may also occur at several other
'tanning process, including after
ihairing, after bating, after
Iprior to and following coloring.
14
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Fleshing- -Fleshing is a mechanical
which rids the hides of excess fles
muscle found on the inside or f les
skins. It is done on a fleshing
which the hide is carried throug
across rotating spiral blades w
flesh from the hide. Cold water
keep the fat congealed, but the fat repres
an additional waste disposal load.
Many hides are fleshed at the packing plant or
at a separate hide proces
particularly in the case
flesh is removed prior
to as green fleshing; w
liming it is referred £o as
any case, fleshings are
sold to plants for renderi
facility,
rined hides. When
ing it is referred
erformed after
shing . In
mally recovered and
ersion to
glue. If fleshings are property hancfied, there
is very little liquid or solid wa-s^te contribution
from this operation. However, on-^U^e rendering
of fleshings produces a low volume yetS«xtremely
concentrated wa^feowater stream ("stick liquor").
Unhairing — Coiwnonly usecT-sonhairing processes employ
calcium hydroxide ai^dsodiuift^SsUlf ide . The
chemicals 1) desTsroy^^fe-vhair or^a±tack the
hair roots, 2) loo&^n the/ epiderms, and 3)
remove certain soluble skin
Fleshed hides are placed^^i^n paddle vats containing
water and the depilatory cntsmi/cals . The
concenlzrlfEi^n of chemicals, water temperature,
and amount or\agitation directly affect the rate
at wnich'-unhaird.ng proceeds. In a pulp or brine
hair op4a^arllon rrigher concentrations and
temReraturxaj result^trs^ery rapid hair removal
with Tit^e entir^-lxair being dissolved in a few
hours . ^"Sfit i^x^e^ii^a to save the hair for
its commerci>al varu«u a longer procedure using
weaker solutiOTws and^ower temperatures is
employed. This ns^uits, after up to two to four days
an attack of the hair roots only, and the
hair can be collected, washed, dried,
re the chemical treatment alone does
1 the hair or hair roots, the
e completed on an unhairing machine.
15
ned
-------
7.
This is very similar to a fleshing
the cylinder blades are blunt and
rubbing action rather than cuttin
jhine except
Ice a
The lime and sulfide chemicals
produce a concentrated alkaline*
fibers under such conditions acqi
affinity for water. As a result the fibe"3
large amounts of moisture which makes them s\
An unhaired skin in the lime-sulfide state is
about twice its normal thickness, a condition
which tanners call alkalipre^ swelling.
The liming and unhairin
principal contributors
In a hair save operat
hair the contribution
substantially lower than
dissolving of hair-operation.
>cess is one of the
effluent.
recovery of
jnt is
pulp
Bating—The first phase of the batmg pr/ocess
is termed deliming. Alkaline chemicals/used
in the unhairii^-rocess are present in fairly
be removed. Deliming largely
saline chemicals
large
iium sulfate
convert the
large amounts
eliminates t
present. The
cylindrical dr
or ammonium ch
residual lime into stsluble
later be washed free o& the
process takes place, som
alkaline swelling begins t
nds which can
ystem. As this
e excessive
s appear, and
art to return to a more normal
The
COT
the
found
These enzy?
collagen
destruction of p?
chains of amino acit
prot
oys
also adjust the pH
point for receiving
mes similar to those
'systems of animals.
separation of the
s through hydrolytic
e bonds which cross-link
Bating also attacks and
most of the remaining undesirable
ents of the skin such as hair roots and
Removal of these materials imparts a
harsh feeling to the grain surface
a cleaner appearance.
16
-------
As in unhairing, the amount of batingvjnaterial,
temperature, and length of time are/critical.
Commercial processes vary from a few Wours to
overnight depending on the nature/of the. skins
being handled.
Modern bates are actually mixture^ of
deliming agents and various enzymes, permr-fe^ing
both phases of this process to be conducted
simultaneously.
At the conclusion of bati
thoroughly washed to rem
substances which this
or dissolved.
the hides are
ill of the
js has loosened
to
Pickling — Pickling plac
acid environment ready
materials. This is necessar
chrome tanning to prevent
chromium salts, as chrome tanning a
not soluble under alkaline conditions
in an
tanning
rly in
are
Sulfuric acid
purpose. Co
added to the
excessive ac
swelling)
of inferior
substance into an
commonly used for this
or brine must first be
cid were added alone,
r to alkaline
in production
of the hide
ructurea^96latinous mass
which cannot be tanne
however, further aids
protein fibers which
by thex"Ea"Tmi.ng agent (i.e. ,
more/completeK stabilization.
rolled acid swelling,
ation of collagen
es further complexing
rivalent chrome) and
necessary for the salt
mpletely .
The picJM^-ng op^ra^tiofi/is a preserving
technique iRits own right. Skins can be
kept in this S
-------
no longer susceptable to putrefactio;
rotting. In addition, these materi;
significantly improve many of the riech/nical
properties of the hide—for exampjre,
dimensional stability, abrasion
resistance to chemicals and to
"boil test") the ability to
times without breaking, the ability to enc
repeated cycles of wetting and drying, etc.
Chrome, vegetable, alum, and syntans are the
principal tanning agents y»ed in the U.S.
with chrome and vegetable/predominating.
Vegetable tanning, the
performed in a soluti
extracts. This method
the heavy leathers such as
mechanical leather, and
Vegetable tanning is usually
primarily because of longer process
ss, is
lant
sed for
Shoe upper leat
are usually ch
bath containi
sulfate. Chrd:
in drums.
and other lighter leathers
led by immersion in a
basic chromium
takes place
advantage
properties soug
Chrome tanning is
accomplished in a shor
hours) and because it
combines to best
and
ma jo
tan
in
th
subs
protein
acid (maskoT
affinity of
se it can be
(four to six
a leather that
of the chemical
after for the
ather uses. The chemical state of the
well as condition of the hides and
are important to the
the chrome into the hide
separated collagen
bicarbonate and formic
are added to increase the
rotein for the chrome.
e older, commonly used, and more traditional
of tanning, known as the "two-bath" method,
the use of hexavalent chromium, which is
trated into the hide (first bath), and
ing agent such as thiosulfate is
"blue" the hides (second bath) by
emlcal reduction of chromium to the
18
-------
me
the proteins.
in light
chromium
cessing
trivalent state which then complexe
Very few tanners still use this
of the dangers of handling hexava
which is very toxic and the redu
time and chemical cost in using
chromium. Some tanners still
chromium (bichromate, dichromate*
to trivalent chromium on site with
molasses and acid, prior to use in the
process. This is done primarily because of co
differentials between hexavalent and trivalent
chromium available from c>*ejnical manufacturers
in certain areas.
lent
In either case, the
provided by the organfr: corvi
wastewaters serves to reduce
residual hexavalent chrom;!
iducing environment
leather tanning
tyace amounts any
Waste effluents from the tanning\proces"*^ are
substantial. Recycle of vegetable^tan solutions
is becoming more common in the industry,- that
which cannot be^cecycled may be used for retanning
or evaporated/andr^coyered.
Wringing—WriXging j^moves^&sjcess moisture from the
blue hide in prfcpara^ben for sp^iitting. The hides
are fed through aNjiacni,^ with tvyo large rollers
very similar to a clsjthes w/ii
Splitting
thickness
finis
lay
split €
leather
and Shaving—-S^litcing adjusts the
of the hide to rh.at/required for the
^oduct. Thickness^of all hides varies,
>rtant factor. Different parts
.1 also be of various thicknesses.
grain portion of uniform
Cor flesh side). The split
Separately or sent to
(fade into suede types of
Shaving is done isn irtie grain portion to clean
remaining eviderice of fleshy matter from any
which were not thick enough to come into
with the splitting knife. The shaving
:hine>san also be used to further level the
ict specifications.
19
-------
Retan/ Color/ Fatliguor, Finishing Process:
1.
ither the
multiple
Retan—Since most tanners do not
equipment or the low-cost labor t
beamhouse and tanyard formulae f
finished leather products, virt
receive essentially identical
the blue or tanned state. Therefore/
is done principally to impart characteristics
the finished leather which it would lack if
tanning were carried out in only one step. The
more common tanning agents/xfor this purpose are
vegetable extracts and
Vegetable extracts help,
any variation that may
of the chrome tanned hi
to minimize
different parts
Syntans are man-made chemicar&s. used'^sxtensively
in the manufacture of the softer^-^ide leathers.
Because of their pronounced bleachina effect
on the bluish-green color of chrome tstnaage,
they are very u«s>£ul in making white or pastel
shades of leather.
Retanning is uXuallj^done £fr->a^druin and is
usually completed, inw^s^pr twolraurs.
Bleaching—BleachingNaides wlth--dbdium bicarbonate
and sulfuric acid aftei\tannsuig is commonly
practiced in the sole lea^herN|.ndustry. Bleaching
is done in vats or drums.
Colo
ing is done in the same drums
important factors are:
(such as varying
netration (which
ich the coloring
the leather).
Typical dyestu&fs ar^aniline based/ and combine
with the skin fifeisrs/to form an insoluble
jompound. pH control is used to vary the
of the dye for the leather fibers which
^affects resulting shades, degree of
etc.
20
-------
Fatliquoring—Fatliquoring is a process by which,
the fibers are lubricated so that anftei: drying
they will be capable of sliding oVer /ne another.
Natural oils are lost in the beanftiouseXand
tanyard processes. Oils and related fat\
substances in fatliquors replaqe
Chemical emulsif iers are added to-/the
ingredients to permit dispersion in
Fatliquoring requires approximately one hour>\Use
of differing amounts of oil permits the tanner\y
to achieve varying degrees of firmness in the
final product.
Fat liquors typically
of animal or vegetabl
made of modified mine
aliphatic mineral oil
very small quantities
leathers which are produced
Liquid wastes from the retan,
process may be high volume-low strenc
with other procns^ses.
for
predominantly are either
are synthetics
Straight-chain
Jy comparison in
heavy mechanical
ipping process.
fatliquor
compared
Finishing—F
(grain side)
tacking, and
provide only
waste, primarily fr
plates and from paint
Solvent based coatings
high luster finishes.
tions such as surface
ting, staking or
the wet processes
o the liquid
the paster drying
.booth water baths.
d only for special
these solvent based
been curtailed largely due to the
diff/culty i\ handling them and the fire hazard
pf as solid waste, and dust
of in either wet or dry
--Seating out smooths and stretches
the skin, wftij^e/comp res sing and squeezing out
excess moisture.
ing—Drying is accomplished by four different
s.
ging—the hide is draped over a horizontal
t which is usually passed through a
e drying oven.
21
collated may
form.
-------
c.
D.
E.
F.
G.
fr
In a stretched
are slid
plates
2) Toggling—the skins are drye;
position on frames. The
into channels in a drying
3) Pasting—the skins are paj
which are then transport^
oven.
4) Vacuum—the hides are smo>
heated steel plate and covered by
perforated belt or cloth-covered
A vacuum is pulled which extracts water
from the leather. Unlike the first three
processes which take four to seven hours per
skin, this method/requires only three to nine
minutes. This method is not widely used due
to shrinkage.
Conditioning—A mis^bxis sprayeszT on the hides, which
are then piled on a tabJ^e, wra^^ed in a watertight
cover, and kept overnightSlvent-fiXse, are used to provide abrasion and
>tavn—g^esisytance and to enhance color.
_ -Plating>~i-R^the final processing step
inflpezxces the? appearance and feel of
the surface of the coating
onding them firmly to the grain.
plating operations are carried
n with each other over a period
Hides may also be embossed
leather. I
materia^is whi!
The finisni>ng an
out in conj
of four to five^days.
stamped with a particular pattern).
j.ng—The hide area is determined.
Grading determines the quality of the
isyiedJ product. Leather is graded for temper,
unirsrrmii.y of color and thickness, and the
tent pf any surface defects.
22
-------
Sheepskin Tannery Process
The two major processes are:
1. Tanyard
2. Retan, Color, Fatliquor, Finis
These processes and the subprocesses which take p
manufacturing are described as follows:
Tanyard Process;
Receiving—Sheepskins ar,
tanneries from both do:
Imported skins are gen
skins are preserved f
immersion in a solutiort
solution is drained prior
are normally tied in bundles
These skins have had the wool
house or wool-pullery before 1
pickled condition. The wool pulling
beamhouse proce
:eived at United States
and foreign sources.
J.ed skins. Pickled
id storage by
id acid. Excess
hand!bijig. The skins
>zen skins.
the packing-
's sed to the
presents a
Skins tanned A\?ith the w&stl intact are referred to as
shearlings. TSanniftftof the&e^skins does not involve
a beamhouse probess/N^>cept for^fleshing. Shearling
skins are cured ih^a sas^ bnj^ie only.
X /^/
Storage—No special prsyis:rQn for storage is provided
at most tanneries other^than^to keep the skins moist.
There is some indication that/pickled skins held for
extend^Ppsriods should be kept below 30 degrees C
(86yrfegrees PO to avoid deterioration1. Biocides,
sucl( asx^el^loritiated phenolics, are used to retard
bajcter^saJL c^ctiorw^and increase storage time.
Fles
rage are taken from the
eceipt at the tannery will
after tanning. Shearling
shed after a wash and soak
is done on the same type of
The skin
been
usually
hides are usuc
operation.
jachine used for fleshing cattlehides.
irried through rollers and across rotating
>lades which remove the flesh. Fleshings
are normally collected and disposed
waste.
23
-------
4.
d the wool
he
Degreasing—Skins are placed in drums/slashed, and
soaked, after which solvent or deter/gen^ is added
to remove grease. Grease is recov
by-product from those skins which
removed. When solvent degreasin
solvent is recovered and reused.
Skins with the wool on (shearlings)
substantially more water in the washing (s
operations, and grease recovery is not normally
practiced.
There is a waste effluent
small amount of vapor, i
to the atmosphere.
this process and a
ling solvent exhausted
5.
Tanning—Sheepskins may
vegetable tanned, although"
tanned. Where the skins have^
tannery in the pickled condition^
liming or bating operations. Skins^
rome or
ity are chrome
ived at the
e no
.he
6.
degreasing operation are placed in drums' with salt
water and mixtuK&a^of basic chromium sulfate
for chrome tannang or^solutions of the natural
tannins for vegetable
Refleshing—In sbqie cfc^&su there^H^ a refleshing
operation following\tanh4/?g, which/produces a small
amount of chrome containing ^olrtd/waste.
Retan, Color, Fatliquor, FinishingsjProc
1. Retan--^
to
mecri
ing is performecr in a manner similar
cattlendde retanning operation.
colored are immersed in a dye
ilvydrums. Sya^hetic dyes are generally
some ^leaching/may be done prior to
coloringNif
Fatliquoring-^F^tliqufrring is performed in the same
drum used for colt>ririg. Skins are immersed in a
jlution containing various oils to replace the
^ oils of the skin lost in the tanning
here are a number of operations which
loring and fatliquoring process,
ing, skiving, staking, carding,
24
-------
clipping, sanding and buffing. Th
essentially dry processes, and the
waste contributed is from cleanup
Solid wastes from the finishing
trimmings and skivings. Dust f
and buffing operations may be
disposed of as a solid waste or
into the wastewater system.
are
liquid
:ions.
on include
^ding
md
Pigskin Tannery Process
The pigskin tanning processes diff,
in that there is essentially no
most skins have the external hai.
house. Degreasing of the skins
sub-process. The two major pr
1.
2.
from cattlehide tanning
)use process, since
aoved at the packing-
tanyard
Tanyard
Color, Fatliquor, Finishing
Tanyard Process;
1.
Receiving—Neaj^ivall pigskins are received at the
tannery either/ asrisiesh frozen skins or as brined
refrigerated/skins. Tfre^are usually tied in
bundles of 4iNto 5(Lpounds"o£^ skin. In some cases
frozen skins ma
2.
Storage — Refrigerat
the tanneries for
before tanning.
3. Degre
skf
used at most of
are to be held
pigs,
Pi
wa,
d
tumS
solven
to large
decanting.
sent to a strip
recovered for reus
roduct.
-Solvent degreasrag has been used by most
ries. In this process, the skins are
then washed and soaked in warm
_em up to a suitable temperature for
added and the skins are
ease. The solution of
_ ter is pumped from the drums
e some separation is achieved by
tanks the solvent and grease are
column, where the solvent is
Grease is recovered as a
waste effluent from this process, as
mall amount of vapor, including solvent,
ted to the atmosphere.
25
-------
4.
5.
6.
7.
8.
An alternate method, in which the skj
in hot water and detergent, has als
this operation grease is recovered
skimming from the top of holding tanks'
waste has been diverted prior to/entry in
plant sewer system.
are tumbled
n used. In
ecanting or
which the
the main
Liming—From the degreasing operation the
placed in tanning drums with a lime slurry anc
sharpeners. The purpose of this step is to remo^
the embedded portion of the hair from the skins.
Bating—The bating opera
same drums used for lim
operation is to delime
swelling and remove an
;akes place in the
The purpose of this
reduce the
f'adation products,
Pickling—The pickling opei
in the same drum. A solution'
used to bring the skins to an acit
prevent precipitation of chromium
subsequent tanning process.
pws the bating
acid is
on to
h the
Tanning—Pigsk
vegetable tan
of pigskin in
chrome tanning
in the same drum u
mixtures of basic
Current practice is to
operation, eliminating
either chrome tanned or
the only major tanner
is ing only the
;hromersn>ning is conducted
using
r _ -^^ _ g
num
s£an the skins in this
for a retan
operation at a later point .
Split/and Sha^e—After tanning, the skins are
tumb/e dri«d and then split and shaved to obtain
the/aes^ed^thicfcHe^s. The split portion of the
pigskin hasv/no commercial value as leather, and
it is^fealed wil^J^Qther acrap and sold as a
fertilize^compohe,nt>^fhe grain sides go to the
color and fa^tliquor^crocess.
Color, Fatliquor, Finish
ss:
— Skins to be colored are immersed in a
£ion in drums. Generally
ed.
synthetic
26
-------
Fatliquoring—This operation is performed in the
same drum used for coloring. The slcinfe are
immersed in a solution containing /var/ous oils to
replace the natural oils of the s-xin its^t in the
tanning process.
Finishing—There are a number
follow the coloring and fatliquor process"
drying, coating, staking, and sanding.
principally dry processes, and the only liquid
waste contributed is from cleanup operations.
Where paster drying is us,
from the paste which is
plates. Water baths fr.
represent minor source
waste from the finishing
trimmings, which are ba
wastes for sale as fertili1
from the sanding operation ±
solid waste.
there is some starch
ed from the dryer
ray booths may also
waste. Solid
on^includes
split and shave
collected
of as
27
-------
SECTION IV
INDUSTRY CATEGORIZATION
In developing effluent limitations guidel
standards, and standards of performance
tanning industry, judgments are necessary
limitations and standards are appropriate for
segments (subcategories) within the industry. To
identify such subcategories the following factors were
considered:
eatment
*
*
*
*
Hide or skin type, i.e.,
pickled sheepskin, split
Beamhouse operations
Tanning agent, i.e., chtome
Finishing operations inc
Plant size
Plant age and location
Wastewater characteristics and
ehide, shearling,
getable
ning
After considering all of these factors it was cbncluded
that the leather tanning/Ttcidustry consists of seven
subcategories. Four of/the Jstaticategories comprise
primarily the cattlehide to leat^t&ttannery segment of
the industry; two of tnS^sub^ategorie^vQomprise primarily
that tannery segment witn
finish only; and one subcat
shearling (sheepskin tanned
The subcategories are defined as
Cattle
proce
hide
the
usu
Cattle
processes"
hide into
tan and
primarily the
tannery segment.
port
rome—a tannery that primarily
cured cattle or cattle-like
leather, chemically dissolving
chrome tanning and
ing.
ery that primarily
kttle or cattle-like
ther, loosening and removing
he hide hair as a solid,
ng and usually wet and
at least a
and using chrome
finishing.
-nonchrome—a tannery that primarily
irocesse* raw or cured cattle or cattle-like
into^^inished leather usually hair save,
lan 20 percent (by hide weight)
. using instead vegetable, alum,
and other methods and their
for tanning, and usually wet and
dry
\ /
29
-------
Thru-the-blue—a tannery that primary
processes raw or cured cattle or ca
hide through the blue tanned state/fen
no retanning or finishing operati
chrome tanning.
Retan only—a tannery that prim
processes previously tanned hides
skins (including splits) into finished
leather, the major wet process consisting
of retanning, coloring, and fatliquoring.
No beamhouse (NB) tannery—a tannery that
like
with
.P9
skins, with
into finished
nonchrome
pickled
shee
processes
with
nto
primarily processes hides
the hair previously remov;
leather using either chr;
tanning methods, primar,
sheepskin and cattlehi
7. Shearlings—a tannery t
raw or cured sheep or
the wool or hair retained on
finished leather using chrome
tanning; or, a wool pullery, a
processes hair-on raw or cured sheep
sheep-like skin/t^y^first removing the wool
and then picklimg tJie^kin for use by a
sheepskin tannery (subcabsgpry 6).
CLASSIFICATION SYSTEM
The leather tanning industry,
Classification No. 3111, does nd
homogenous grouping of plants witft
practices, and procedures. Wide
skin types proc
processes exis
of the variou,
analysis. I
development
used to classi
of plants. As
relate information
in the beamhouse,
retan, color, fatliquor,
tanni
strial
st of a
imi^ar operations,
ons in hide or
degree of finishing, and in-plant
a degree that a classification
was made for purposes of
to that in the earlier
stry1, four digits were
distinctive groups
, the four-digit numbers
skin or hide, operations
used, and the use of
'inishing steps.
Seve
using the classification system for the
'Cations of processing methods are:
v
(including calfskin), hair
chrome tanning process used,
ed.
30
-------
Table IV-1. Classification System (3/11. abc
Skin or
Hide Type
1. Cattle
2. Pig
3. Sheep
4. Deer
5.
6.
7.
8.
9.
0.
Other
Various
tan, Co
Fati^quor >
Finish
Sides
Splits
Sides and
PreVlous/y
Tanned
Beamhouse
Operation
1. Pulp Hair
2. Save Hair
3. Hair Previously
Removed
4. Hair Retained
5. Wool Pullery
6.
7.
8.
9.
0. None
NOTES:
1) Beamhouse op
(none) diffe
(primarily sheep
2) Tanning process class
20 percent chrome tanning^
m #3 (hair previously removed) and #0
nd potential fleshing procedures
rome and other) requires at least
lassified.
3) Retan, color, fatliquor, finish-in^ classification #1 (sides) includes sides
and spirrts<^here the number of splits processed is not greater than the
number of side^Sxjjrocessed, in classification #3 (sides and splits), the
^cessed is greater than the number of sides.
are combinations of other operations or processes
n
31
-------
1211—Same as 1111 except hair is saved
by-product.
1221—Same as 1211 except vegetable ta:
process used.
1110—Same as 1111 except no retan,
fatliquor, or finishing is do
to blue stage only).
1041—Cattlehide, no beamhouse, hide previous
tanned prior to receipt of hides at a
finishing facility (finishing operations
only).
2315—Pigskin, most hair remov;
of skin at tannery with,
residual hair pulped,
used, skins finished
3015—Sheepskin,,, no beamho
removed, pickled shee
chrome tanning process
finished.
3415—Sheep shearling, washed and
tanning process used, skins finis
prior to arrival
11 amount of
.e tanning process
hair
ome
terial.
SUBCATEGORIZATION SYSTEM
The tanning industry's
manufacturing operation^
52 four-digit classificat"
from Table IV-1. As a
analysis, the classification
process similarity omitting tho
distinctly dominant process (i.e.7
was not observable. f ,,Ten industry
on the difference*—in, hide/skin type,
^nations of standard
approximately
which "arse combinations
egorization
uped by
where a
ified as "various'
resulted based
eamhouse methods,
tanning agent
similarity of
loading per
use, and wa
unit weight o
subcategories
plants assigned to
basis of dominant proce"
numbers and tannery
Four types
3002
dat
hing operations. Based on
oads (as measured by pollutant
ide/skin processed), chromium
volume of water per
) the final number of
'n, and the mixed process
iate subcategory on the
le IV-2 shows the classification
included in the resulting
plants with codes of 0151, 1100,
are not categorized because of insufficient
shows the relationship between these
descrrt
ms
ose in the original development document
32
-------
Table IV- 2. Categories of the Leather Tanning and Finishing Industry
Cattle,
Pulp, Chrome
Cattle,
Save, Chrome
3
Cattle
Nonchrome
Thru-The-Blue
1111
Cattle
Pulp
Chrome
Sides
1113
Cattle
Pulp
Chrome
Sides &
Splits
1151
Cattle
Pulp
Chrome ft
Other
Sides
1153
Cattle
Pulp
CnrOBC &
Other
Sides &
Splits
0116
Various
Palp
Chrome
Various
0156
Various
Pulp
Chrome &
Other
Various
Retan Only
1041
Cattle
None
Previously
Tanned
Sides
1751
Cattle
Pulp &
Save
Chrome &
Other
Sides
4215
Deer
Save
Chrome
Skins
p Beamhouse
gry
2315
Pig
Hair Pre-
viously
Removed
Chrome
Skins
3355
Sheep
Hair Pre-
viously
Removed
Chrome &
Other
Skins
3395
3055
3052
0855
Shearlings
3415
Sheep
Hair Re-
tained
Chrome
Skins
3455
Sheep
Hair Re-
tained
Chrome &
Other
Skins
350C
Sheep
Wool Pul-
lery
None
None
-------
Table IV-3. Category Comparison by Princ
Present Document
Category
EPA Development Document
March 1974 Category
1. Cattle, Pulp, Chrome
2. Cattle, Save, Chrome
3. Cattle, Nonchrome
4. Thru-the-Blue
5. Retan Only
6. No Beamhouse
7. Shearlings
34
-------
is
RATIONALE FOR CATEGORIZATION
Hide or Skin Type
The type of hide or skin processed in a
a significant factor in subcategorizing
especially regarding the use of those proc
recovery, or washing the hair on the hide/skin.
subcategories are based on the following hide/skin
1. Cattlehide or cattle-like hide—short hair,
relatively heavy hides or y&Joins. Deerskin,
horsehide, cow bellies, a/d Tether similar
hides are included in th/s group,
2. Sheep or sheep-like ski
relatively light skins'
other similar hides are
this group.
3. Pig or pig-like skins—short
relatively light skins. To be
in this group the skin must have
or no hair.
A differentiation in th
load (weight per unit
per unit weight of hide
method of hair removal (
and the amount of hide
primarily on type of hide.
processing, raw waste generatid:
production basis will tend to be
or skin type.
roups
wash
based both on raw waste
and water usage (volume
primarily to the
sulping, hair save)
(ich depends
/is removed during
(ater usage on a unit
regardless of hide
Beamhouse Ope
The beamhou
factor in s
operational va
1.
2.
leather tannery is a significant
based on the following
Pulp hair--hair is ^shemically dissolved and
enters the liqtw^ waste stream.
Save hair (and wool/pullery)—hair (or wool)
chemically softened and is then removed
lically. The majority of the bulk hair
a solid does not enter the liquid
Residual roots and fragments
waste stream.
35
-------
3. No beamhouse — the tannery receives its hides or
skins with the hair previously remo/eab therefore
has no beamhouse and generates no joearonouse-type
waste stream. Included in this group fare hides
that require little or no hair rmoval silKh as
pickled sheepskin or cattlehide
There is a substantial difference in water usage a^raw
pollutant content between a no-beamhouse tannery and one wit
beamhouse. High water use and waste loadings are typical
beamhouse effluent. Subcategorization including this basis" is
thus substantiated. /x.
Tanning Agent / /
The tanning agent is a significant fsfci^n? iib subcategorization
of the leather tanning industry primarily f/om the standpoint
of potential specific waste problemfck^resulrincj from the use of
the various tanning agents available t^s^the industry. The
subcategorization is based on the following tanning agents
and methods used in the industry: ^X. /
\y
1. Chrome tanning-r«hrpmium salts are at least
20 percent (by/weigh^of hide tanned with this
agent) of the/tannage usTsd. Many plants in
the industry
most plants
2. Nonchrome tanning
weight of the hide rs chrom
tanning agents pri
extracts and synthetics
3. Previously tanned — no tann^qg(only retanning)
is carr^rstKout because the prant receives its
hides/in a fuSLly tanned state.
ing method and
rcent by
d . Nonchrome
alum, vegetable
Chrome tannc
trivalent s\
significant
amounts or not a1
a highly colored rav
are somewhat reduced
tannery that only retans
may contain chromium in the
pmium has not been found in
e streams; only in trace
tanning methods may generate
iut~ the raw waste and water usage
hrome tannery. A leather
inishes (using previously
_es) generates significantly lower raw BODS^ in the
^ nd also has a lower water use per unit application,
36
-------
Finishing Operations, Including Retanning
re
;nce
Finishing operations, with retanning includ
in the industry categorization only by pre
Water usage and raw waste loadings in plaryts that
and finish are significantly less than f
Plants that finish only (no retanning ste
'are
significant
r absence.
ly retan
ries.
cons^idered
J.n th:
to be tanneries and were excluded from consideration
study. Differences in waste generation between plantsXOiat
tan but do not finish and those that tan and finish woulc
expected, but are not detectable due to limited data for the
former and are overwhelmed by waste/loading variations as
reported by individual tanneries. /Thifrs the subcategorization
is substantiated, especially the ^specification of retan only
subcategory, which is primarily
Plant Size
Plant size per se is not a factor in
the industry. There is a wide range of
plants in the various subcategories; howeverVxthey
range in raw waste pollutant content from plants/grouped
for large and small plants.
ivant to categorizing
size. Thus a
,ze is
by size was essentially
There are no other fact
the industry that coincide
categorization that
substantiated.
Plant Age and Location
Plant age and location do not inf^buencev leather tanning
processes or wastewater control prac^ioes such as to
require conside^ffEltMi in the subcategbrization. Most of the
plants are quyce old, sait even processing equipment for newer
plants is similar^-fee, oj^ identical with, equipment found in
the older tanneries ?\ ThW^is no consistent difference in
plant operacj^ons orNj/-astewate~r~-generation associated with
tannery age. ^\^^ ^^^^ /
There is no discerrms^e rela
-------
industry are
ossible to
on the
Wastewater Characteristics and Treatability
Industrial practices within the leather ta:
diverse and produce variable waste loads.
develop a rational division of the indus
basis of factors which group plants wit!
characteristics. These raw wastes are
treatment techniques. Thus waste characteristics
treatability substantiate the subcategorization.
The primary wastewater characteristic used as the basis in
categorizing the industry is five
demand (BODJS) in units per 1000 u,
kg BOD5/1000 kg hide (Ib BOD5/10
the best measure of plant opera '
among the wastewater parameter
available for BOD5^ than for any
suspended solids data serve to
developed from BOD5_ in categorizing t
subs
biochemical oxygen
hide weight—
hide) . BOD5_ provides
lent effectiveness
Id more data is
, Total
conclusions
The major plant waste load is organic and brsdegi/adable;
BOD5_, which is a measure of biodegradability, rjy the best
measure of this type of /beading entering a waste stream from
a plant. Furthermore, /cecaus-a^secondary waste treatment is
a biological process, ^OD5^ alsop^Qvides a useful measure of
the treatability of thV.wast^and tn"fe^ef fectiveness of the
treatment process. Chem^bcal o^gen demafreL (COD) measures
total organic content and s*qme *Qprganic content. COD is a
good indicator of change, bur\does notiredate directly to
biodegradation, and thus does nta± indicate the demand on a
biological treatment process or oK a stream.
As described ±
the average
of the leath,
groupings b
the basis o
waste paramete*
sulfides and
important constitue
distinction between
subcategorization.
tot
detail in Section V, differences exist in
for raw wastes for the seven subcategories
{.ndustry. As defined earlier, the
substantiated as subcategories on
ribed earlier, other raw
ubcategorization are
romium is recognized as an
ery wastewater, hence the
"chx^me" ^Jnd "nonchrome" in the
originate from chemicals used
in th^-be^mhouse unhairing operations and from residues of
the#fe chemicals in the hides. The requirement to remove
tewater as recommended in this report impacts
s using the unhairing chemicals and these
Certain categories.
38
-------
Table IV-4 presents a summary of average plan
parameters for each subcategory, the paramet
production, wastewater flow, BODJ5, total
sulfides loading in the raw waste.
ch
operating
^include
and
A number of additional waste load paramel
considered. Among these were nitrites af
Kjeldahl nitrogen, ammonia, total dissolvec
volatile solids, oil and grease, chlorides, total
alkalinity, and phenols. In each case, data were
insufficient to justify categorizing on the basis of the
specified parameters; however, for the most part, these
parameters confirm the BOD_5 raw
With the exception of chromium a
tanneries contain the same cons
to the same biological treatmen,
secondary waste treatment resu
not impair secondary waste treatro
fact the waste constituents of tanne
based subcategorization.
.fide, wastewaters from
its and are amenable
Judging from
Affluent does
Civeness, and in
removed
by such treatment processes. Tannery wa^s^tewateX^onstituents
and flow patterns are primary determinants^s^f was^e treatability,
Within the tannery industry, the variations th^t/ao occur in
either factor are consistent throughout the industry or the
differences are ref lect^diri^he categorization, thereby
confirming the category
It was anticipated that
climate, might affect the
some degree. Climate has o
of secondary waste treatment
influence on the ultimate treata
treatment effectiveness, given car
maintenance; in ^f-acjb as mentioned
secondary tre
wastes) are
frient "systems (treating primarily tannery
the morX severe northern climates.
ion, and hence
'he waste to
uenced the kind
not had an
of the waste or the
operation and
some of the "best"
39
-------
40
-------
SECTION V
WATER USE AND WASTE CHARACTERIZ
WASTEWATER CHARACTERISTICS
Water is an essential input and it is use
in the leather tanning and finishing industry. Wa
as a primary input material to clean/ prepare/ or con
hides/skins in some tannery processes, it is the media f
carrying out other processes especially those involving
reactions of chemicals with the hid^s, it is the carrier of
ties
other materials in tannery process
in coloring, and it is used to cl
equipment. Wastewater with a ma
from every wet process in a tan
insignificant amount of effluent
cont
Wastewater from leather tanneries
suspended organic matter including
inorganic materials such as salt, chromium
ammonia, other processing chemicals, small quar
ich as dyes and pigments
:annery facilities and
load originates
is usually an
finishing operations.
grease
le and
solids/
sulfide
ties of the
nutrient pollutants, and
These pollutants enter
operations as proteina
chemicals, tanning age
grit, and manure.
^coliform count, in some cases.
stream from the tannery
hair, tissue, unfixed
dyes, pigments, dirt,
Raw Waste Characteristics
The raw waste characteristics of
in this section for each subcategor
industry are ba
described in
program cond
is defined
sampling at
typically a
integral screen!
reflect whatever
screening, which is us
tewater as reported
the leather tanning
data collected from the various sources
and on the wastewater sampling
the course of this study. Raw waste
nt wastewater available for
t in the plant. This is
1, frequently including an
the raw waste characteristics
reduction occurs in
little.
tal
parameters used^o characterize the raw waste are
suspended solids, oil and grease, total
fide. Other pollutant parameters, including
as described in Section VI, are also
ble. These characteristics, other than
units of weight per 1000 units of
as the weight of raw material (hide/skin)
d average weight of hides during summer
41
-------
and winter as reported by the tanneries were
a production level in weight of hides per o
The outflow of pollutants was then related
level on a unit weight per 1000 units wei
presentation as the raw waste characteri
water was related as the ratio of total
day to production level to derive a
of-production figure also as reported in the raw
characteristics.
ed to compute
ing day.
his production
for
of waste-
ating
The production level based on weight of raw material is
weight per hide/skin and
d on a given day for
The mix by type of raw
dirt, manure/ salt,
tributed
These same
Thus, when the
.ut raw material
aste
fcif ic
jduction ifevel,
Loadinc
of il
je raw
of
subject to variations both in aver,
in the actual number of hides pro<
which wastewater data are availa
material hides and the variable/amc
hair, flesh, etc., attached toAhe
substantially to variations in p
factors can influence the raw waste^
actual number of hides and/or the wei
is known concurrent with raw waste data,
characteristics should be representative
tannery wastewater situation. The use of polluVant weight
per 1000 units of raw material weight is the basis to be
used in presenting the/raw w&s4^e characteristics.
Since the data collection ps^cess fo5^
-------
Discussion of Raw Wastes
The raw waste characteristics shown in Tabl
calculated from pollutant parameters (gene
mg/1), flows, and productions as supplied >6y thl
governmental sources, or MRI's own sampling gnd pi
In converting to units shown, the raw wa&£e\
1 and V-2 were
recorded in
Industry,
visits.
data^were
:ific
rs
:ion
broken down into winter and summer periods^for
at each tannery, and where appropriate flow or prod
information was not supplied for that period, it was
assigned based on best available information and trends
that plant. Included as "raw" data are those plant effluents
where only screening and/or equaliy^t^ion are performed as
pretreatment steps.
Detailed information for indivitzfual^anner^ies is presented
as a part of the documentation s^ubmitf^s^y as/a supplement to
this report; however, Figures V-ONand V-2 Present the BODS^
and Cr data by subcategory as examples of the^ variation in
the average value of the pollutant loacJinq
wtihin a subcategory. Each "dot" represen'fcsS the Annual
average of one tannery for the parameter showskj amd the "bar"
in each subcategory column represents the parameter mean.
Asterisk marked data po^vt-Sv^were not used in averaging
limits discussed earlier
and ioniser cent or less of the
because they were outsioe
(i.e. , 300 percent or ^nore
subcategory average).
Examination of the informa
following:
1. Most data show a wide'N^ri^ion in values.
2. Based on average values/\som^ plants appear
to be very high or low.
Typical varia/ion
where the ra,
average of
variance o
partially to
probable that a m
variations in waste
^lustrated by the BOD_5 for Subcategory 1,
is 24.0 to 98.8 kg (Ib) with an
,000 kg (Ib) of hides. The
,ters is undoubtedly due
ccuracy. However, it is
e difference is due to the
sociated with the multiplicity
of waste discharge pat€e*ms a^d practices which can exist.
Table V-3 shows the variati>Q/i that occurs within a single
tannery—dtiring one day (it should be noted that this plant
operates ontxo shifts a day; a "typical" tannery with one
shifft pes^da wbsjld show even more variance) . Production
times, sample collection practices, and
tne diffeence's, in iporting procedures, are other
contlsLbutiotva of\var\ance.
43
-------
-------
-3- ^v ^ ^s. y *** ^
^
45
-------
X C
I- -^ .
O ~<
X ft*
S3-
60 O «
5
St •O B •
•rt -H f-(
35 H ^ O
'. O 10 C
46
-------
aoor
180 -
0
I
204
©
©
©
— 75.
26.2
0
-©-10.2
©
456
CATEGORY
BOD DATA BY CATEGORY
POINTS:© MEAN: —
-------
1 0
9
8
o> 6
jt
o
o
o
»*
\
S 5
Ml
s
o
oc
S 4
0
G
— 3.15
O
©
O*
1.3
0
i
O
100
3.4
FIG
4 5
CATEGORY
HROME TOTAL DATA BY CATEGORY
POINTS: 0 MEAN: —
48
-------
Table V-3. Hourly Raw Waste Data for a Single
Cattlehide Tannery (Category 1)
Tannery No. 237
Data Taken 9/1-2/76
-------
Wastewater flow data are presented in Figure
raw waste data, significant differences
occur due primarily to in-plant process var}
conservation practices. The data are insu
determine the contribution or significanc
and industry opinion is equally diverse
influences.
Several methods of determining the BOD_5 averages or
each subcategory were considered, including a
weighted mean. The differences in the results with
methodologies were small, however,
mean with exclusion of exceptiona
earlier, was calculated for the
Statistical significance tests
where appropriate, but the res
insights or understanding of wa
beyond what is evident in the figu
in this section.
•3. As with
ich subcategory
and water
it to
irious factors
in
production"
different
_nd a simple arithmetic
a points as described
us parameters.
to the data
o further
meter relationships
Jales contained
One of the concerns with previous analysis "b^iiis' study reflect annual averages.
An examination of averSKje valbes for the various parameters
reveals that the data gen»raM.y confirm what would be expected,
given tJaetannery process variations. Some observations are
^ Wastewater flows are higher in the hair save
operaton thanN^he pulping operation, but the BODI5 are
Nonchrome tanning methods appear to
chrome methods. Significant amounts
o fr>hr omeSkgpeaK in he "retan only" tannery effluents, more
in facXthanS>n tbosa plants that tan and retan ("No
BeamhousevI! SubcWegdry 6). In many of these cases, sample
50
-------
r
14 -
13 '
12 -
11
10
a
0*
23.98
O
0
0*
i G
1 17.15
92.31
.101
.091
.075
.067
.058
x
-------
a
C3
co
06
CJ
o
00
o
CO
tO
H
i
s
u
co
vo
en
ON
oo
oo
CM
CM
sD
ON
ON
co
O
O
sD
o
o
o
f>
o
C3
o
•
o
O
ON
oo
oo
CM
CM
CM
00
oo
v£>
I
I
oo
CO
CO
CO
o
*
sj-
CM
-a-
o
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v£>
CM
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CM
oo
CM
in
CM
CM
ON
co
r-
CM
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00
CM
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-*
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v£>
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co ON
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o o
52
-------
size is a significant factor in explaining these differences.
Subcategory 4, "Thru-the-Blue, " in principle >shc*ild have
parameter values equalling the difference berweien Subcategories
1 and 5. This relationship is not substantaateHby the data;
however, the small sample size (two) and t#ie facr^that one
plant was exceptional preclude drawing a
The raw waste characteristics are presented in
each of the seven subcategories. As described in
the rationale for subcategorization was based in part on"
waste characteristics and on tannery subprocesses in use
by typical plants in each subcategc^y. The raw waste
characteristics for a tannery, of corpse, are dependent on
the combination of subprocesses in us4 in the tannery.
Comparative wastewater volume arm pqdlutant loadings
originating from the tannery suJacategsgrie's afe given in
Table V-2, and are described be.
SOURCES OF WASTEWATER AND WASTE LOAD
Tannery Processes
Processes which occur in
industry subcategories
Carious combinations in the tanning
the following:
Wash and Soak
Degreasing (sheeps
Unhairing (sometimes
Bating
Pickling
Tanning (including bleachin^
Retanning, Coloring, and
Finishing
Fat
emental liming)
ome vegetable tanning)
ing
The sequence
each are pr
groups into
and wet and
used to identify
as depilatory
the tanning process.
chemi
recesses and the materials used in
V-4. The subprocesses are
ng steps—beamhouse, tanyard,
1 descriptive terms are
als to the processes, such
iring and tanning agents for
re also indicates the major
solid and liquid waste sB>e^am6 originating from each process
and the_primary physical contaminants in each. Recycling
and v£u sec^se ve r a 1 of these waste streams is a continuing
and/growing tre-qd in the industry. Such streams as the
sp/nt ^h"rbme an cTVege table tanning, unhairing lime-sulf ide,
a*(d the^s^clc^ing solution are those most frequently considered
forNreuse/Xrecybsle, \r materials recovery. The chrome
tannirt^solir&ion\s mpst often managed for reuse, followed
by the p5^sklingss^lutn.on, among the U.S. tanners. It is
reported thcttsEuropean tanneries are being advised to give
S3
-------
Figure V-«
PRODUCT AND WASTEWATER FLOW FOR GENERALIZED
LEATHER TANNING AND FINISHING PLANTS
Added Materials
I
Processes
Waste
Solid and Liquid
» Trimmings
Dirt, Salt, Blood,
Manure, Nonfibrous
Proteins, Fleshings
Grease
Depilatory Chemicals
Water
I Hair, Dissolve/Hair J
— — Pigments, Proteins,
frj jft.ck.le| — — Unfixed Chemicals »j
/"I I
Tanning Agent
Water
• Unfixed Tanning
| Agents J
— — Shaving Dust
|
Unfixed Tanning Agent
Water
Tanning Agent
Water, Bleaching Agents
Dves & Pigments
Chemical Emulsifiers
Fatliquors, Wate
Oils
jraaLiiig, r xauc waaii i
~~ ~"_"~ H
j
Buffing Dust
Finish Machine Excess
Spray Machine Baths
—» Finishing & Plating
To Solid Waste Handling
or Wastewater
Treatment
54
-------
serious consideration to protein precipitation and recovery
as a by-product from the beamhouse waste str/£a*Q to reduce
the waste load and to produce a by-product jbf yalue3
rmed on the
urpose
e
Wash and Soak—This is the first wet pro
raw material as it begins the tanning p
of this operation is to remove salt, re
content of the hides, and remove any foreign
dirt or manure. If the raw materials are brine cur
the hides are clean and the operation is one of salt
With green salted hides, manure and dirt must also be
removed. The quantity of manure and dirt can vary widely,
depending on the season of the yeafrXand the origin of the
hide. The wastewater volume froaf this process is estimated
from industry data to average aj/out/20 percent and to vary
from 10 to 35 percent of the t^ral^astow^iter flow.
as
Primary waste constituents from t^is process are BOD5_, COD,
suspended solids, and dissolved solids (including sodium
chloride). Typical range in quantitiefe\for aisattlehide
tannery with hair pulping and chrome tanning are/as
follows:
Constituent
BOD5_
Suspended Solids
Total Solids
a,OOP kg Hide (lb/1,000 Ib Hide)
7-22
8-43
5-267
Following the wash and soa
if this has not been done
separately as a solid waste an
contribution to the liquid waste
some instances Jj^shing is perfo
liming proces
Degreasing-yp e g
on cattlehae,
Two types
1. Hot wat
2. Solvent.
rmec
hides are fleshed,
Leshings are handled
not make a significant
idled properly. In
tfter the unhairing and
ing ^operations are not normally performed
(tore coTwaojily on sheepskins and pigskins.
sing are us<
nt.
In both cases the grease 3^syseparated and recovered as a
value. However, some grease is not captured
and'enterst^ plant waste stream. In the case of solvent
solvent is also recovered. In addition to
and suspended solids are other waste
the\waste stream from this process.
he plant waste system consists of only
capes the recovery process. In pigskin
The gr
that
port
55
-------
tanning, total grease removed from the skin can approach
100 kg (Ib) per 1,000 kg (Ib) of skins1. The quantity
entering the waste stream is minimized and usKoaSLly is only a
small part of the total. Reliable data on tme /grease content
of the waste stream from the degreasing operatj^n are not
available. A major problem arises from thfe difficulty in
obtaining a truly representative sample
Unhairing—Two processes are used for unhairing:
1. Hair save.
2. Hair pulp (hair burn).
In the hair save operation, the he
subsequent machine removal. Lime/
sulfhydrate, etc.) are used to
waste is characterized by a hig)
nitrogen content. The nitrogei
reaction of the unhairing solutioi
Other constituents of the waste
solids, and dissolved solids. A part
is the sodium chloride not removed in
operation.
incl
s loosened for
sharpeners (sodium
this function. The
pH, sulfide, and
Cits from the
protein matter.
i5_, suspended
ible solids
the >aak anal wash
An additional step in
removal of hair from t
as a solid by-product,
be baled and sold as a
the hair is only going to
The waste water from washin
constituents as the unhairing
dilute concentration.
save operation is machine
^though the hair is handled
washing if it is to
unnecessary if
a solid waste.
same waste
im, cmly in a more
The hair pulpinq^jQjjeration is similars/to that of hair saving
except that hlg'ner chamical concentrations are used,
particularly Kith respect to the sharpeners. In this process,
the proteinaceou^r~n>d.r ilssolubilized sufficiently to disperse
it in the urhairrrvg BolutibTK^The wastewater, therefore, has
a higher corvt^nt ofwasj^e constiT^uents, particularly sulfides
and nitrogen.
A few tanneries currently use\an intermediate hair removal
process between the two e^treines of pulp or save. This
semi-pulp unhairing proces&Nis a natural outgrowth of a
moreytrfa^tfeional hair save operation where by-product hair
markets no longer exist or the cost of hair washing, baling,
andr seJrTJrRQ exceeds income for the hair. Moreover rather
tttan maJQing^&sComp^ete shift to a hair pulp beamhouse, some
tahqers n^e merely icade marginal increases in concentrations
of umvairingXqhen^ica]^ and retain the use of unhairing machines.
Also a ch^gire Cts^Metatn the hair save option and a lack of
56
-------
experience with hair pulping prevent rapid change from an
In
air pulp
s do retain
ause the
flow
essentially hair save to a hair pulp beamhou
semi-pulp the hair is solubilized less than
but more than in hair save. The individua
their integrity but this is of lesser conc
hair is not to be used as a by-product.
rate and waste loading for the semi-pulppr
intuitively fall between the two extreme s
are available to confirm this.
The unhairing subprocess as reported by tanneries in
study sample generates between 20 and 38 percent of the total
wastewater flow from a cattlehide tannery. The average is
32 percent of the total wastewatejr f]Jbw among those reporting
such information.
For a cattlehide chrome tanner^ BOD^xco/telvt of the waste
from the hair save process willNsange fromAl to 58 kg (Ib)
per 1,000 kg (Ib) of raw materialT^xMth the hair pulping
process, this may be 53 to 67 kg (lb)>xLikewi^e, the total
nitrogen content of the hair save waste will be substantially
less than the 11 to 15 kg (Ib) per 1,000 kgS^b) ^experienced
with the hair pulp process1.
Bating—The bating proc,
swelling, peptize the
products. Major chemi
reduce pH to the appropr
the protein matter. The
sulfate produces calcium
of the waste is 5 to 8 kg (Ib)
ammonia nitrogen constituting
sed
Pickling—The
the hides for
pickling may
sulfuric aci
agent and b
products, lirtv
previously remov
solids, and
to delime, reduce
•emove protein degradation
ammonium sulfate to
;nzyme to condition
rith ammonium
:al nitrogen content
00 kg (Ib) of hide, with
•rthirdsl.
nitroge
of the pickling^operation is to prepare
'ng process. In vegetable tanning,
Pickle solutions primarily contain
jthough a small amount of a wetting
.used. Protein degradation
nstituents have been
tities of BOD5_, suspended
rincipal waste constituents
are the acid and salt/\The syrong liquor dump frequently
made after the tanning prlx^ess is a source of significant
waste bscause of the accumulation of waste materials from these
Bate and pickle waste water volumes were
resorted as a Jxjmoined total by several tanneries. The
wastewater flow from the bate and pickle
is from 9 percent to 50 percent with
of 26 percent of total tannery
wastewl
57
-------
Tanning—The purpose of the tanning process is to produce a
durable material from the animal hide or skir/Vhich is not
subject to degradation by physical or biologaca/ mechanisms.
This is accomplished by reaction of the tannin^agent with
the hide collagen. Chrome and vegetable b4nningSire the two
principal processes, although other mateylalt sucha* alum,
zirconium, and other metal salts, and glu^e/aloSahyde al
formaldehyde can also be used.
In the chrome process, a basic chromic sulfate or a chr*
tanning solution is used. Other process solution
constituents include sodium formate, and soda ash. The
chromium must be in the trivalent ,/o^m and in an acid media
to accomplish desired results. S6m.e /tanneries prepare chrome
tannage by reducing sodium dichr/matfe solution to the
trivalent form, using glucose a/ a r«^uci'figx>agent. The
waste from this process is the ^rincipa^V sovfrce of trivalent
chrome in the plant waste. The ortiy entry 4)f hexavalent
chromium into the waste system is by
The spent chromium tanning solution is re
BODS and suspended solids.
low in
Waste from a vegetable
The reaction rate of v
slower than that of c
longer contact time, tti
vats with some type of
ge
process is quite different.
with the hides is much
tanning-^&olution. Because of the
illy carried out in
>n some instances
the hides are passed througfN^a
solution strengths. Because
process solution conservation hete
that part of the solution enterinc
to drag-out or planned blowdown to
quality. Vege
BOD5_ and colo.
The reporte
about 1 per
latter figure
tannery processin
percent is 4.4 and
reporting this data.
ts with varying
f tanning materials,
practiced. Therefore,
aste stream is due
tain tanning solution
nin in the waste is a source of both
from tanning varies from
,total tannery waste. The
ecause it represents a
the blue stage. The median
is 6.6 among the tanneries
.
solu
used fo
tanning ag
chemicals in
^^*
, Fatliquor—Retanning, coloring, and fatliquoring
rformed in drums. The chrome or vegetable
laced in the same drums and all three
•med on the hides before they are removed.
performed to provide added tanning
nto hides after splitting. Chemicals
cah be chrome, vegetable, or synthetic
.se of the low concentrations of
process, the concentration of the
58
-------
wastewater is not strong; usually this procesy
a significant quantity to the total waste f
does not add
The most variable process in the tannery
are hundreds of different kinds of dyes,
vegetable. Synthetic dyes are the most
industry. When synthetic dyes are used,
in order to provide a better uptake of dye into
Normally, vegetable tanned leathers are not dyed in
manner but instead are surface dyed by spraying the co
the leather surface.
There
etic and
the
added
be
The fatliquoring operation can
after coloring. There is a wide
oil added in this process, depe
leather. The use of mineral o
small however it does occur.
to biological treatment as those
Liquid waste from the retan, color, and
may be high volume-low strength compared
and tanhouse.
:ormed either before or
in types and amount of
the end use of the
Access is very
not as amenable
Ln widespread use.
operations
beamhouse
color
7
The temperature of the
flows is generally hi
The major treatment c
waste is removal of col
can be kept to a minimum
that provide for the best
hide. Because of the color in
not normally practiced. Use of
will enable maximum uptake of chro:
of this consti
, and fatliquor waste
degrees C (100 degrees F) l .
, color, and fatliquor
two constituents
cal concentrations
emicals into the
stewater, recycling is
mperatures in re tanning
'and reduce the discharge
The wastewat
percent of
12 to 30 p
because of t
ported from these processes as a
waste is highly variable, ranging from
igure would be misleading
reporting such information.
Finishing—The finishj^ng processes represent the lowest water
flows of the tannery because ^hey are primarily dry processes.
There are some wet processfe^/such as minor wetting operations
to make~-tfeehide handle more easily in the staking or tacking
ope/ations .^^SChe pasting operation also uses small amounts
of/waters^Howev^ar, several tanneries report reusing paste
m/xtursis; therefore^ very little blowdown flows into the
wa«te stlxam/sxThis\pasting water is prepared by mixing water
and[&
-------
TOTAL PLANT LIQUID WASTE
The quantity of wastewater is important to tfte economics of
treatment because a number of the unit operatiorvs performed
in waste treatment are designed totally or/partiariv on a
hydraulic basis. In addition, water conservaftsion carNoften
reduce the quantity of processing chemicarSsXisecNwhich
become constituents requiring removal in
Also, process solution reuse practices such as that
tanning not only reduce waste flow but also afford majorX.
reductions in waste constituents from the total plant waste
stream.
60
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SECTION VI
SELECTION OF POLLUTANT PA
WASTEWATER PARAMETERS OF SIGNIFICANCE
A thorough analysis of the literature, in?
sampling data obtained from this study, and EPA
data demonstrates that the following wastewater
are of major pollutional significance for the leather
tanning and finishing industry:
, 20 degrees C., BODS)
Biochemical Oxygen Demand
Total Chromium
Oil and Grease
Sulfide
Total Suspended Solids (T
Nitrogen Content (Ammonia
Total Kjeldahl Nitrogen)
pH and Alkalinity
Wastewater parameters of minor significance ar
Total Dissolved
Chlorides
Chemical Oxygen
Total Volatile
Nitrates and Nitrite
Phenols
Fecal Coliforms
RATIONALE FOR THE SELECTION OF MAJOR. POLLUTANT PARAMETERS
Biochemical OXygen Demand (BOD)
Biochemical/oxygen ajpmand-vj^s the quantity of oxygen required
for the bio^L^gicaXx»nd chernicaSr^oxidation of waterborn substances
under ambienr^ar test q^«litions7 Materials which may
contribute to the\BOD inbJ^uSfes^/carbonaceous organic materials
usable as a food sou^e by aerobic organisms; oxidizable
nitrogen derived from nitrite^, ammonia and organic nitrogen
compounds which serve as reoy for specific bacteria; and
certap*-ciiemically oxidable materials such as ferrous iron,
sulf^des, stHLfite, etc., which will react with dissolved
oxygen^AE are m&^abolized by bacteria. In most leather
the BOD derives principally from
from ammonia (which is itself derived
frdhKanimal^pr \^qet\ble matter) .
61
-------
The BOD of a waste exerts an adverse effect u
dissolved oxygen resources of a body of wate:
the oxygen available to fish, plant life,
species. Conditions can be reached where
dissolved oxygen in the water is utilized
anaerobic conditions and the production
such as hydrogen sulfide and methane. The"
dissolved oxygen can be detrimental to fish populaft
growth rate, and organisms used as fish food. A
of oxygen due to the exertion of an excessive BOD can res^t
in the death of all aerobic aquatic inhabitants in the
affected area.
Water with a high BOD indicates t
organic matter and associated in/^re
concentrations that degrade its
A by-product of high BOD concent
algal concentrations and blooms
decomposition of the organic matter an
of algal populations.
whi
esence of decomposing
terial
otential uses.
e increased
from
rm the basis
The BOD5_ (5-day BOD) test is used widely to estimate the
pollutional strength of dtsaestic and industrial wastes in
terms of the oxygen that/they^wjj-l require if discharged
-into receiving streams J The tes^Ls an important one in water
pollution control activities .^It istnaed for pollution control
regulatory activities, toNevaPH^tee the dei&ign and efficiencies
of wastewater treatment worst's, aHd/to indicate the state of
purification or pollution of r^ceivirv?0*>daes of water.
eason
st
Complete biochemical oxidation of
a period of incubation too long for
purposes. For
accepted as
as BOD5_. Spe
available fo
substances
is placed on €
weight of dissol
oxidize or transfer:
in the wastewater. Th
oxidation of carbon compo
The five-day
80 p
sam
Ad-
o
,n waste may require
tical analytical test
, the 5-day period has been
d the test results have been designated
al test methods are not readily
quantity of many degradable
ducts. Reliance in such cases
ter, BOD5_, which measures the
ed by microorganisms as they
mixture of chemical compounds
ical reactions involved in the
related to the period of
normally measures only 60 to
the carbonaceous biochemical oxygen demand of the
any purposes this is a reasonable parameter.
are
BO!
The
an estima
be used to estimate the gross quantity
matter.
tially a bioassay procedure which provides
gen consumed by microorganisms utilizing
62
-------
the degradable matter present in a waste undez: conditions that
are representative of those that are likely i^obccur in
nature. Standard conditions of time, tempe/ature, suggested
microbial seed, and dilution water for the/wasrss have been
defined and are incorporated in the standard analytical
procedures. Through the use of this pro
demand of diverse wastes can be compared
pollution potential and to some extent for
biological treatment processes.
Because the BOD test is a bioassay procedure, it is important
that the environmental conditions of the test be suitable
for the microorganisms to functior/ir^an uninhibited manner
at all times. This means that toxic /substances must be
absent and that the necessary nutrients, such as nitrogen,
phosphorus, and trace element Sj
Total Chromium (CrT)
the leather
Chromium compounds are used extensively ^througho
tanning industry. The compounds used are nearly n
the trivalent form; use of hexavalent chrome isxilearly
obsolete. The prevalent.K^T.romium form found in the wastewaters
is trivalent chromium, ailthb^agh hexavalent compounds may
also occur in waste streams printst*4.1y from spillage.
However, the distribution camiot beftatermined accurately.
Current analytical procecK^esN^tt<^exava*bsQt chromium are
such that differentiation b^twee*^:he valeirt states in a
wastewater sample collected rii a tannCry-^emd then transported
to an analytical laboratory is essentially precluded, even
though such differentiation is desirable for this industry.
Chromium, in it
man. It can
skin sensiti
corrosive e
inf lammatio:
have no effec
determination
ious valence stat&fe, is hazardous to
tumors when inhaled and induces
\rge doses of chromates have
itestinal tract and can cause
y/els of chromate ions that
man wapear tojbe so low as to prohibit
aendation for public water
supplies is that su
total chromium.
idely
s contain no more than 0.05 mg/1
The toxicity of chromium salts to fish and other aquatic
with the species, temperature, pH,
romium and synergistic or antagonistic
that of hard water. Studies have
chromium is more toxic to fish of
ent chromium. Other studies have
Fish food organisms and other
life are extremely sensitive to
63
-------
chromium and it also inhibits the growth of al
both hexavalent and trivalent chromium must
harmful to particular fish or organisms.
Oil and Grease
Therefore,
isidered
Because of nature of the material processec
occur often in the leather tanning wastewater stream*
The oil and grease in tannery wastewater originate as a"
result of the degreasing process used in some tanneries
and from the oils used directly in the leather processing,
especially fatliquoring. Most of thfe-^e oil and grease
materials are animal or vegetable basep and therefore
amenable to removal through biologaca2i treatment. A very
small amount of mineral based oil/ is s^eing.rvjsed by some
tanneries. This material also enters th^/waate stream,
although presumably in very small^quantities/ It is a
more refractory material and therefor^ajrnust r>e removed
primarily by physical-chemical waste tre^atjnent |>j^ocesses.
These compounds can settle or float and mayxexist^s
solids or liquids. Oils and grease even in sittaJl ^quantities
cause troublesome taste and odor problems. ScumMines
from these agents are pro/
walls and other containers,
on water treatment basin
and water fowl are
adversely affected by oils in their^habitat. Oil emulsions
may adhere to the gills af fiak^causing^-^uffocation, and
the flesh of fish is tainted whsri^siicroorga^rsLsms that were
exposed to waste oil are eaten. B#pos,
bottom sediments of water can s^rve t<
benthic growth. Oil and grease exhibr1
^ion/of oil in the
irvfribit normal
an oxygen demand.
Levels of oil and
vary greatly,
susceptibility^
supply sources
irease
which are toXi/ to aquatic organisms
on the type and the species
hasNbeen recommended that public water
illy free from oil and grease.
Oil and greas
mile) show up as
The presence of
enjoyment of water.
increase the toxicity oi
into the receiving bodies 61
1/sq km (10 gallons/sq
face of a body of water.
the full aesthetic
of oil in water can also
ubstances being discharged
ter. Municipalities
imit the quantity of oil and grease that can
their wastewater treatment systems by
64
-------
Sulfide
A significant portion of alkaline sulfides e!ont4ined in
tannery wastewater can be converted to hyd/ogenxsulf ide
at a pH below 8.5 to 9.0, resulting in th«! releasfexpf this
gas to the atmosphere. This gas is odorous,/xnd can^esult
in property damage through paint discolorSKtAon/^vin sewesi^s,
hydrogen sulfide can be oxidized to sulfuric acidrxausingX
"crown" corrosion and corrosion of equipment in POTW'V^ At
higher concentrations this gas can be lethal. This is ^X^^
particularly significant as a hazard in sewer maintenance.
Sulfide compounds are used extensiyely in the beamhouse
for the unhairing process, and thu4 a^re found in tannery
effluent.
tment systems
innocuous
Sulfide does not pass through bAolog!bcal/tf*
because it is oxidized to sulfarb&5 whicn arjt
in their normal concentrations.
Total Suspended Solids (TSS)
Suspended solids include both organic and inorg^jriic materials,
The inorganic compounds ykxclude sand, silt, and clay. The
organic fraction includes stJoixmaterials as grease, oil,
and animal and vegetable waste plxaducts. These solids may
settle out rapidly and^^ttQmdeposl^t*^are often a mixture
of both organic and inorg^ic^^oJ^ids. Sbiids may be
suspended in water for a t5s(ie, any then settle to the bed
of the stream or lake. These^olidsycTrscXarged with man's
wastes may be inert, slowly biodegradable materials, or
rapidly decomposable substances. \Whirs. in suspension,
they increase the turbidity of the\tater, reduce light
penetration and^-imp^ir the photosynthVtic activity of
aquatic plants
ing to
Solids in sufeperfs^io
they settle^to fo
bed; they areX^ften da:
when transformeoXt^o
of damaging things/XJJiclud
lake bed and thereby ofe^troyf
benthic organisms that
arev^esthetically displeasing. When
ludgectepo^its on the stream or lake
life in water. Solids,
ts, may do a variety
Blanketing the stream or
the living spaces for those
therwise occupy the habitat.
When of_an organic nature, solids use a portion or all of
the d^ssol^sd oxygen available in the area. Organic
mat/erial s also^^erve as a food source for sludgeworms
and aasocfra±ed ortianisms.
Di
leach
shellfis
c effect attributable to substances
suspended solids may kill fish and
brasive injuries and by clogging the
65
-------
aqu
gills and respiratory passages of various
because they screen out light, and they prom<
the development of noxious conditions throu
depletion. This results in the killing of
food organisms. Suspended solids also re
recreational value of the water.
Nitrogen Content (Ammonia Nitrogen and
Total Kjeldhal Nitrogen
life
ind maintain
Ammonia (NH^). Ammonia occurs in surface and ground waters
as a result of the decomposition of/^nitrogenous organic
matter. It is one of the constitu/
nitrogen cycle. Because ammonia
pollution and because it increas
it is recommended that ammonia
supply sources not exceed 0.5 mg
Ammonia exists in its non-ionized form
levels and is most toxic in this state.
the more ionized ammonia is formed, and its
decreases. Ammonia can exist in several
including ammonium chlori£T&-vand other salts.
of the complex
indicative of
;ine demand,
jlic water
chemica
pH
pH,
/ty
combinations
con
Evidence exists that a
aquatic life depending
and the total ammonia
significant oxygen demand
oxidation of ammonia. Approxx
are required for every gram of
Ammonia can add to eutrophication
nitrogen to aquatic life.
toxic effect on all
Ived oxygen level,
ater. A
e microbial
ams of oxygen
that is oxidized.
s by supplying
Total
/Nitrogen\(TKN). Total Kjeldahl nitrogen is
ammonia nitrogen >p~±iAS organic nitrogen content in wastewater.
Hence, TKH m
-------
Knowledge of the pH of water or wastewater l»suseful in
determining necessary measures for corrosio/ control, pollution
control, and disinfection. To protect POTSv's^rom corrosion,
pH levels of wastewaters entering the sewierageNRystem must be
kept above 5. Waters with a pH below 6. Cf are corlxisive to
water works structures, distribution liqes ,/^azd houset^old
plumbing fixtures and such corrosion can^fld coh^tituenbe
to drinking water such as iron, copper, zinc, cadrnSsum, anoX.
lead. Low pH waters not only tend to dissolve metalsXf^rom /
structures and fixtures but also tend to redissolve
leach metals from sludges and bottom sediments. The
hydrogen ion concentration can affie<;t the "taste" of the
water and at a low pH, water tastes
Extremes of pH or rapid pH changes^an exert stress conditions
or kill aquatic life outright./ EvenNQOjner^te changes from
"acceptable" criteria limits of^siH are deleterious to some
species. The relative toxicity* toxaquatrsvlife of many
materials is increased by changes incite wate^s^pH. For example,
metalocyanide complexes can increase a thousandfold in
toxicity with a drop of 1.5 pH units. Similarly/ the toxicity
of ammonia is a function of pH. The bactericidal effect of
chlorine in most cases i^s^less as the pH increases, and it
is economically advant/lgeou^^ keep the pH close to 7.
The lacrimal fluid of x^ie h^man eye""has a pH of approximately
7.0 and a deviation of uVl pRsttrkiJ; from^bb^ norm may result
in eye irritation for the s^imms^. Appreciable irritation
will cause severe pain.
Alkalinity. Alkalinity is defined as^he ability of a water
to neutralize hydrogen ions. It isxusaially expressed as the
calcium carbon^pHTe^^e^uivalent of the Hydrogen ions neutralized
Alkalinity
bicarbonat
silicates ,
nature of the
capacity of car
seldom found in
caused by the presence of carbonates ,
nd to a lesser extent by borates,
c substances. Because of the
lkalinity, and the buffering
ter , very high pH values are
s.
Excess alkalinity as exhfltteJA ^n a hd-9n pH value may make
waterjzorrosive to certain metals , detrimental to most
natj/fal or^acic materials and toxic to living organisms.
sc
oxicity is used herein in the normal
he word, not the legal.
67
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RATIONALE FOR THE SELECTION OF MINOR POLLUTANysJPARAMETERS
Total Dissolved Solids (TDS) / /
Tannery wastes are high in dissolved solicrs. The j>argest
portions of the dissolved solids are sodamm y£hioride a*^d
calcium sulfate. Sodium chloride comes pri/lcipa'Hy fromx.
removal of salt from the raw hides by washing, and a^so frol
salt added in the pickling operation. Calcium sulfateXqan t
from several locations in the tannery, but principally fr>Mn
the reaction of residual ammonium sulfate and sulfuric acid
with lime used in the unhairing pros^ss. Dissolved solids
are particularly important for consideration of recycle
systems, and also for potential ijrvpayt on stream life and
water treatment processes.
Chlorides (Cl)
The preponderant fraction of tannery
chlorides. Used in conjunction with total
this parameter indicates percentages of othel
Chloride content is important for water reuse
olids is
d solids,
olved solids
siderations.
Chemical Oxygen Demand
Chemical oxygen demand
devised as an alternate
oxygen demand of a wastewat:
the oxidation-reduction syste
than on biological factors, it
and rapid than the BOD test.
estimate the total oxygen demand (u
5-day BOD) to oxttTtTte the compounds
based on the f/ect that\oraanic
can be oxidi
conditions
cal oxidation test
the total
ethod relies on
analyses rather
precise, accurate,
st is widely used to
'ate rather than
a wastewater. It is
compounds, with a few exceptions,
chemical oxidizing agents under acid
ce of certain inorganic catalysts.
The COD test
biologically deg3
which are measured
COD test. In addition>
to biological oxidation
is a moxe^inclusive measure
emand of compounds that are
ny that are not. Pollutants
test will be measured by the
which are more resistant
Iso be measured as COD. COD
oxygen demand than is BOD5
becaus
_
in higher oxygen demand values than will the
more resistant to biological
be&oming of greater and greater concern, not only
lowjbut continuing oxygen demand on the
68
-------
resources of the receiving water, but also bensause of their
potential health effects on aquatic life and' hiJuhans. Many
of these compounds result from industrial discharges and some
have been found to have carcinogenic, mutagenicVs^and similar
adverse effects, either singly or in combination.\Concern
about these compounds has increased as
demonstrations that their long life in rec«riv±n<
result of a slow biochemical oxidation rate—aliowsx^hem
contaminate downstream water intakes. The commonly
systems of water purification are not effective in i
these types of materials and disinfection such as
chlorination may convert them into/^ven more hazardous
materials.
Total Volatile Solids (TVS)
Total volatile solids is an approximate'meafeure of the
organic fraction of wastewater. rfex^s primarily useful in
analyzing the treatability of the wasbs^with Ideological
treatment methods. A high percentage of^vplatilessolids to
total solids in the waste indicates that conventional
treatment processes may, with proper design, be^effective in
pollution control.
Nitrates (N03) and Nitrites JN02)
Ammonia, in the presence
to nitrate (NCG) by nitrify!^
frved oxygen, is converted
baffetej
Nitrates are considered to be ambng the objectionable
components of mineralized waters. Njjxcpss nitrates cause
irritation to tjae—ciastrointestinal tr-act, causing diarrhea
flobinemia, a condition characterized
result in infant and'animal deaths,
irate concentrations in waters
, which is an intermediate
Ite, sometimes occurs in
ifonditions permit.
and diuresis.
by dyanosis
can be caus
used for f
product betw
quantity when
Phenols
2,4-
defined as hydroxy^tlerivatives of benzene and its
jclei, may occur in tannery wastewater (usually
plication during the leather making process).
~i waters can produce odoriferous and
ig chlorophenols which may include
Lorophenol, 2,6-dichlorophenol, and
69
-------
Dimply as
ride range
ftion
ie result
of
Although described in the technical literature
phenols, the phenol waste category can includ
of similar chemical compounds. In terms of
control, reported concentrations of phenols
of a standard methodology which measures a
similar compounds rather than being based
identification of the single compound, pheno1
benzene).
Phenolic compounds may adversely affect fish in two ways:
first, by a direct toxic action, and second, by imparting
a taste to the fish flesh. The toxicastiy of phenol towards
fish increases as the dissolved oxyg/n "frevel is diminished,
as the temperature is raised, and eus thfe hardness is
lessened. Phenol appears to act a/ a ^ierve/poison causing
too much blood to get to the gill^and rsLtme^ieart cavity
and is reported to have a toxic thr^aghold of Of. 1-15 mg/1.
Mixed phenolic substances appear to be esTjiecialt1?sstroublesome
in imparting taste to fish flesh. Chlorophyll produces a
bad taste in fish far below lethal or toxic dos^s. /Threshold
concentrations for taste or odor in chlorinated wa-^er supplies
have been reported as low ansx^Q. 00001-0.001 mg/1. Phenols
in concentrations of only /one pa-r^ per billion have been
knonw to affect water sut
The ingestion of concentrat
results in severe pain, renal"
possibly death. A total dose
Phenols can be metabolized and
facilities containing organisms ace
concentration in the wastes.
ox
ol by humans
k, and
y be fatal.
in waste treatment
to the phenol
Fecal Coliforms
Fecal colifor
originated fr
Their presence i
pathogenic bacteria
indicator since they have
t of warm blooded animals,
e potential presence of
The presence of coliforms>xinore ^fepecif ically fecal coliforms,
in water is indicative of fetsal/pollution. In general,
the prese.nce>of fecal coliform organisms indicates recent
and posrsiblyd^oerous fecal contamination. When the
fecal/coliiprm cous^t exceeds 2,000 per 100 ml there is a
increased numbers of both pathogenic
viri' "*" " ^
70
-------
tha
Many microorganisms, pathogenic to humans and
be carried in surface water, particularly
from effluent sources which find their way
water from municipal and industrial wastes
associated with bacteria include bacillary
dysentery, Salmonella gastroenteritis, ty
paratyphoid fevers, leptospirosis, chlorea
and infectious hepatitis.
limals, may
rived
furface
iiseases
_c
71
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SECTION VII
CONTROL AND TREATMENT TECHN
GENERAL
This section describes waste treatment technology el.
available to achieve effluent limitation guidelines fol
leather tanning and finishing industry. Three approachesXajfe
presented effecting various degrees of pollutant reduction.
These approaches are: (1) in-procrf*s methods of reducing waste
(2) preliminary treatment, and (3/ secondary treatment.
Preliminary treatment (pretreat
treatment on the plant site be
treatment system. Pretreatment
treatment and intermediate storage
secondary (biological) treatment syste
reduce shock loads, protect the biologic
suspended solids that resist treatment, previ
sewer lines, and reduce health hazards in sewer
ined as wastewater
to a municipal
physical-chemical
charge into a
necessary to
remove the
amage to
e maintenance.
Although it is defined aS^-preliminary to treatment in municipal
plants, pretreatment is/equall^applicable to an on-site or
other company-owned secondary treatment system.
Secondary treatment is tj
remove organic material.
biologrsal process to
'reduction of BODS^ and
suspended solids is accomplis"hed in ^ecc^aary treatment, as
well as some degree of nitrification ,\depending on the system.
Secondary treatment technologies
•ill
)t be described in this
report. The second development document which is to be issued
for BPT effluerxtrTiTnitations, as indicated in Section III,
will describe/these technologies.
/ /--\
CURRENT PRA<
Current practfi
treatment of
effluent quality
municipal sewer i
discharge directly to sur]
nning/industry range from no
dary treatment. In general,
for tanneries discharging to
ss stringent than for plants that
waters. This is reflected in the
of 91 wet-process tanners that indicates 12 percent
discharging to municipal systems have no
reas all direct dischargers surveyed have at
reatment. Further, 100 percent of the
operating some type of secondary
With increasing numbers of
g more stringent effluent limitations,
rend^owgfrd some pretreatment by all tanners.
73
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The infromation collection forms and questionna
and verification sampling visits of wet proces
following breakdown of current control practi
industry:
Discharge to municipal treatment plants—
90 percent of tanners:
Preliminary treatment
Coarse screening only
No preliminary treatment
Secondary treatment
Discharge to surface water—
10 percent of tanners
No preliminary treatment
Preliminary treatment only
Secondary treatment
Lagoon tr
Activated/sludge^bceatment
site visits,
'yielded the
the tanning
88
20
12
0
0
23
77
63
14
The wastewater characteristics ^^CY among^-'kanneries due to
several factors, as describeC^in s^liions Iv^nd V, type and
condition of raw hide, final prqducrb/ processes and process
equipment used (e.g., hide processors) ,/tanrn.ng agent, etc.
Basically the pollutants differ lrt±leXrom those in
wastewaters of many other industries and cfen be treated by
conventional methods--suspended solids reduction, oil and
grease removal, pH^conf^tol, and BODS^ reduction. Specific
constituents peculiar to certain tanning processes, such as
chromium and su/fid^T^^an c^e removed with available treatment
methods currently priactYced i5y-s~-Rra^te may contain chromium and care must be
exercisred in mafrsu^ing the waste disposal to prevent leachate
contann.nat-re>D of ground or surface waters. The practice of
chrome reSise o"tv>recovk>ry within the plant should reduce the
chromipm coiH.fintOsf the\ sludge.
74
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lined with a
mtly being
Each treatment approach in this discussion is e
description of equipment, examples of systems
used, and reduction levels expected.
RELATIONSHIP OF PRETREATMENT TECHNOLOGY TO
OWNED TREATMENT WORKS REQUIREMENTS
Tannery wastes can and have created the following pro
POTW's:
large pieces of scrap hide and leather clogging
or fouling operating equipme
other small
excessive quantities of ha
scale, screenable solids;
highly acidic or alkalinex
wastewater flow surges;
excessive loadings of sus
solids and BOD5, consistent
odors, facilities corrosion, a
gas generation from sulfide bearin
a potential future problem with dispo
sludges containing chrome.
pass through of apffmon^ia nitrogen
ams ;
ettleable
Each of these problems c
by applying pretreatment
screening can be very effec
scrap material from wastewate
more than a simple bar screen.
many different configurations, so
effective on tannery type wastes.
static screen made of specially coine
Coanda or wall atJ/^cTTme^t phenomenon to
from the under
velocity over
effective in
fibrous suspe
industry. Scree
and maintained
antly reduced or eliminated
ther tanneries. Fine
r, fibers, and
equipment must be
g is available in
hich are particularly
pie is the three-slope
ved wires using the
ithdraw the fluid
slurry which is stratified by controlled
This method has been found to be highly
prop
containing fatty or sticky
use in the leather tanning
must be installed, operated,
well.
Waste streams from specific processes in tanneries can be highly
acidic or alkaline. If sucn^vst/eams are discharged without pH
ad justmepi—Qr mixing with a different neutralizing stream, the
waste s-lTreamiftav create problems within the sewer or at the
treatn^nt J2lant7>& pH control mechanism of holding and mixing
various -^ast^or ofNdirectly adjusting the pH of the waste
is r4adil^4^ple^ented\as a pretreatment technology.
Flow and>*aste rts^drng surges can be particularly disruptive to
biological exeatmertti/ sy items such as are used in POTW's, and they
75
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can be minimized by providing equalization to smooth the rate
of flow or waste loading discharge. If space limitations at a
tannery preclude an equalization tank, discharge s/heduling,
as practiced at one tannery at least, can redyce 1^ie magnitude
of these surges.
Catch basins, wet wells and other pretreatms^t/fac^i^ities^that
provide a retention time and space for solids separation fro?
the waste stream can be very effective if designed and m&lntainl
properly. Such a facility requires regular maintenance
is to operate consistently and effectively.
If necessary, the potential problem o
sludge that contains chrome can be stfif
where a smaller quantity of sludge
concentration of chrome is more ea
controlled environment. Chrome re4
is also available and in use by the
reduces the chrome content of the waste
generated in treatment of these wastes.
IN-PROCESS METHODS OF REDUCING WASTE
rsposinq municipal
;d back to the tannery
lining a higher
of in a
ise technology
This substantially
of sludges
In an appraisal of any pla
cycle must first be inves
which can reduce the wast^ flow
constituents. Particular
those factors which would pos"
total waste. In some instances
from process solutions can produc
least partially offset costs.
production, the manufacturing
etermine any modifications
oncentration of waste
j/ven to reducing
'atment of the
fcvery of materials
mies" which will at
dentify every po
in the hide
ocesses where a modification would
anning formulas and processing steps
lementation of many potential
contnrfujent upon the effect on the
It is not possible
preparation and
reduce waste qu
are developed
waste reductio,
manufactured pr
A reduction in pollu£a*^ts anctx^n'tne costs of waste treatment
often can be effected byM^he for^owing steps:
Process .changes.
of process ingredients.
iservation.
replacement of leaky or faulty equipment.
of automatic monitoring devices to detect
irmaJXguantities of selected constituents in waste
utipn reuse or recovery.
76
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7. In-plant treatment to remove a speciJ
constituent.
waste
In the tanning industry, process changes have been^dif f icult to
make because of the diversity of tanning me/hods
While tanning operations traditionally hav
on a batch basis, it is possible that more o# the>&hemca.
applications as well as the washing and rinsing coul^Ssbe
more effeciently on a counter-current continuous flow ba^sls,
and thus be more efficient in chemical and water usage. Ii
this way, maximum utilization of all active ingredients coulc
be achieved, thereby leaving only
volumes for treatment and disposal
from one process for make-up water
feasible at some points within a
can be made, however, it is nece
water required for each operation i
co
sentrated wastes of small
>stitution of effluents
generally is
:fore this change
quantity of
led.
The substitution of chemical ingredients
potential for those which are problem poirtrfcants o&ten can be
used to advantage in industrial processes. Ihx^annang, for
example, it is possible to use dimethylamine as a^oepilatory
agent in the place of the /&«4^fides which contribute heavily
to the problems of waste /treatim«^nt and disposal. The
difficulties resulting f/rom the hlTgiwconcentrations of
contaminants in spent tansliquwrs from~-a^ve get able tanning
process using extracts fromv^barl^cKid othersp4ant materials
have been lessened by recoverv an&y/euseof >those spent liquors
and by the use of synthetic tamping ag/snfTfeMsyntans) .
A survey of water needs in a tanner^K wiPk go far toward
reducing the volume of wastes becauseSwaiter usage is
generally in excexsiS~'&£sthe quantity neeaed. Some methods
of water conservation are listed below:
o implement any potential
saving/ practice^v^Rliminate the
runr^Highoses/observed in (a few)
tannerie>vjone p*^cticeyrequiring employee
participati?
Examine tanning\formu^as to determine if floats
can be reduced. cJ>§e/of hide processors has
permitted use of lower float volumes.
or eliminate some washing and rinsing
a continuous rinse to a batch rinse.
set meters or timers to limit total
iaters and rinses for process solution
77
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Use of processing equipment, such as hide
processors, pumpable drums (rather
dumping) , float storage tanks, and ojcherreuse
equipment,
Recirculation of non-contact coolij
such as for vacuum driers.
Tannery No. 1 has recently undertaken a comprehensive
conservation program. Through implementation of this
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 arr;
unhairing operation has reduced We
percent. Further savings have rej
of hair wash water by installation 6]
removal. Through the installation of aSvvegetab'ie tanning
recycle and reclaim system using evaporators^, wate^use for
this process has been reduced 65 percent. The\resul£s of such
major water conservation measures indicate that
comprehensive water conservation program can substantially
reduce water use.
rtent following the
Cashing 80
;circulation
for solids
In recent years, the hid
has proven to be an extrem"
use. The number of hide
They are most widely used for
for beamhouse operations in hair
explaining the utilization of the
tanning effluent is given by Larsen5
ified concrete mixer)
of reducing water
increasing.
bming hides and
ocesses. A summary
cessor in reducing
When hide proces
water use throu
(1 gal/lb of h
processors for,
chrome tanning
use is from 12.5 £
hide)6. Some tannerf
are used in the retan,
used in the beamhouse operation, the
deliming\ will be about 8.35 I/kg of hide
No. 2, which uses hide
the raw product through
indicated that water
e (1.5 to 2.0 gal/lb of
ted that hide processors
fatliquor operations.
There are also reports of waters/used in one process being reused
in compl^EeTy^separate processes. Tannery No. 3 uses the same
water /or washing\following their "modified pickle" operation
and tjaeir^VfrgetableXtanning operation6. Tannery No. 1 uses a
similar pS^ocessxfpr recycling the soak water following the
vegetable t^hvningsqpera'tion back to the color operation that
precedesxvegetal3s3.e rennAng6. There are also some indications
that spent'^ij-quor^xj^evipusly used in vegetable tanning are
reused in reta^operatij/ns. Tannery No. 4 indicates that they
78
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are using bate wastewater for alum tanning make-up water6 .
Tannery No. 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 h^irSpulp process
and for wash water following the bate proce
cated
s
ent
Intensified
kept
Opera
g
isal beTbsAise
Industrial waste problems are often compl
by the fact that faulty or obsolete proc
in service without proper repair or repla.
personnel likewise can be a liability in waste dis
large quantities of usable materials often are lost
careless or accidental soills or thrnimh ov<-occiTrQ
of liquids from hides as they are transferred from one
process to another. Acquainting operators with the importance
of eliminating these sources of wa^^f often will simplify
waste disposal problems.
No waste reduction and eliminat
without adequate control measu
equipment for detecting abnormal
constituents is extremely valuable a
the failure of established precautiona
abnormal and accidental discharges of
cone*
an be complete
monitoring
'selected
ard against
For example,
lime or
tan solutions could be detected immediately byxptf meters and
alarms installed on the effluent lines from these processes.
In addition to indicatingirss^; of materials, automatic
sensing devices can be/used to^eperate recovery equipment.
The most efficient method for^^ej^iminatl
tannery wastes and in reduXing^^e^ volume
through reuse of water and chemical agei^t
recovery of materials which ar^norm^Hy
•ollutants from
effluent is
and through
•asted.
Reuse or reduction of process solub^pns>or recovery of
process chemical£_has been demonstrerbeja to be a method of
waste constituefvt reft^ction. A detailed summary of methods
available to Deduce waste constituents by process
adjustments /s g^ve^ by \tfilliams-Wynn7.
There are a
recycle systems"*
are discharged
employs such a
in relation to the hides>-
necessary to prevent the bu":
nneries that are using
unts of tan liquor that
reams. The Liritan process
nter-current flow of tannage
ost cases, some blowdown is
-up of contaminants in the
tion
Reuse
but not
Hauck8 has
One tannery recovers this blowdown tan
^ntrates it in a triple effect evaporator
entrated liquor. Other tanneries use this
_etanning operations.
hrome tan liquors is being practiced,
extent as vegetable tanning solutions.
summary of methods for recovery
79
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and reuse of spent chrome tanning solutions. During
World War II, the reuse of chrome tan liquor vas common
practice because of the scarcity of chromiumsal)ts.
Tannery No. 6 has performed a study on thereus^xof chrome
tanning solutions. These tests showed the
liquors could be reused for periods up tc
reduction of leather quality6. The spent
this study was settled and sludge was drawn off the"
bottom of the holding tank. The clarified solution wal
brought to the required concentration with chromium salts^
sulfuric acid, and sodium chloride. Because of the
sludge drawoff, this was not a comp>3>8±e recycle system,
however, a substantial portion was/recycled and only a
small amount wasted.
Tannery No. 6 also, in this san^study>s^xam^ned the
feasibility of recycling of the uhhairing solutions.
Tests on recycling of the unhairing^solution-s. were
performed on three separate occasions/^XThe lonest
recycle time was two weeks. However, theisjrudy
concluded that since the concentration of was-fce material
in the solution leveled off after a few days,
solution could conceivab
spent liquor was draine
manner as the chrome t
sludge from the bottom
original volume remained.
sulfhydrate and the lime ne
available in that portion ret
weeks of use, the solution had
the amount of ammonia coming off
substantial.
e reused indefinitely. The
tied in much the same
ter removing the
ercent of the
of the
run was
After two
ctionable odor and
considered
Tannery No. 7,/a shearling tannery, has been able to reuse
its chrome tan soit^tion Vp to five times6. Because of
processing r/equirejnents, s^ejit chrome tan liquors are
not at preseivt beings/reused.
This same tannery^ias
liquor up to five ti
additional chemicals pr
hides.
:o reuse its pickle
is accomplished by adding
lidding another load of
Tann
eports reusing retan liquors6. Tannery No. 9
finishing oils6. Many tanneries are
clingstheir pasting frame water, either wholly
Based dh-vthe abovey trtere are numerous possibilities for
process soSuJtionreus^. Of particular importance is reuse
80
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of the chrome tan solution. If this waste stexeam enters
the total plant waste flow, it will be partial!^ removed
in the primary settling tanks when beamhousre wastes or
added alkali increases the pH to at least/y. O.^sThis
chromic hydroxide precipitate will be removed withxthe
sludge. An additional quantity of chronAumwiJl be removed
in secondary treatment with possibly s
remaining in the effluent. In order to minimize t
chromium content of the sludge and subsequent treatmeht^ /
processes, chrome tanneries should consider installing
reuse, recycle, or recovery facilities.
PRELIMINARY TREATMENT
Preliminary treatment (pretrea
operations performed on the wa
for introduction into a municip
or a separate industrial on-site s
treatment system. The problems will
the longer sewer lines usually involved
a municipal plant.
fined as those
make it suitable
'atment system
astewater
except for
nt at
The need for preliminarj
following factors:
reatment is based on the
3.
4.
5.
Removal of pblluta^ts four?
a POTW inadequatelyNfcp^ated
Removal of cause^of T*i/eatment
or hazards and of
obstructions or poteh
-------
to one author, to indicate that both forms may be toxic16,
however there is considerable uncertainty on/bb.is subject.
Trivalent chromium salts are soluble in aci
solutions. At a pH greater than 8.5, triv
will be precipitated. Total chromium condentral
20 mg/1 or more are indicated as hardly tzfoxic to
treatment systems6. The batch nature o
creates wide fluctuations in waste flows ami waste streri*
Such variations can be difficult to handle, and mayN^esult
in over- or under-design of the preliminary and secon
treatment units.
neutral
chromium
pns of
ogical
.ions
hs,
operl
Significant reductions in suspend
equalization of flows and waste
to avert overloading of biologi
tannery wastewater is the major,
solids and BODS^ and
igth may be required
treatment units where
to a POTW.
n
Preliminary treatment operations
combinations of the following opera
1. Screening
2. Equalization
3. Sulfide oxidation
4. Plain sedimen
5. Chemical tre
a. Coagul
1) Al
2) Lime
3) Iron SSL
4) Polymers
b. Carbonation
c. pH adjustment
6. Sludge handling and dispo
one or
rocesses:
.entation
SCREENING
Fine screening r^mp^es ha-ws^particles, wool, fleshings,
hide trimmiTKjs, ancl^other larg&-««cale particulates. While
reducing undesirable waC^bej^ater ^constituents, screening
creates a solid wa*ste disp^sa-i^problem. The highly
putrescible wastes a^secommbsily disposed of on-site or
at remote landfill operational Screening equipment includes
coarse screens (bar screerfsj/and fine screens, either
he
mounted or rotating with self-cleaning
exact contribution of screenings to
S^ and suspended solids is not known,
es are removed prior to obtaining
The principal function of screening
inable material which has a potential
uipment and clogging pumps or
82
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)retreatment
mors vary
EQUALIZATION
Equalization of waste streams is importanl
facilities. The volume and strength of
depending on process formulations and sc,nedi
tannery operations. Alkaline wastes arc
beamhouse operations, while acid discharge
tanyard. In order to produce optimum results in
treatment operations, the equalization of flow, strenc
and pH of strong liquors may be necessary. Although som?
oxidation may occur, no removal of waste constituents is
normally reported for equalizatiocftx^Equalization basins
provide storage capacity for hydtfauMc balance. Auxiliary
equipment must provide for mixing and maintaining aerobic
conditions. Detention times sbrouldxbe de^feermined based upon
the wastewater generation patterns ofM^ne rannery and the
requirements of the secondary treatment facility. Basins
can be monitored through pH and
An equalization tank or basin is usually>vb'f considerable
size and most economical at low ratios of heisghy to surface
area, subject to the need to conserve the heatcontent of
the wastewater, for mo
system operation. Ta
such a tank have anot
effect of smoothing tti
option which is being us
schedule wastewater dumps
facilities in accordance
that is designed to smooth
SULFIDE OXIDATION
Sulfides in
problem in
which can
hydrogen s
^fective biological treatment
insufficient space for
ypproximate the same
;nt loading. This
tannery is to
process
discharge schedule
loading on the POTW.
se waste constitute a potential
ndling. If mixed with wastes
sulfide-bearing wastes,
The complete rem
with plain sediment
removed through oxidat
sulfides include:
s is not accomplished
Ifides are more satisfactorily
arious methods for oxidizing
oxidation.
chemical oxidation9.
air oxidation10 9
ffusers provides some removal, but only
ration times.
83
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Direct chemical oxidation with ammonium persu^fate and
ozone was studied by Eye9. Ammonium ..persulfi
produced low removals. Ozone was most effecztiv/e; however,
the expense of ozone-generating facilities/and'
contact equipment negated further study9.
eveloping
Studies by Chen and Morris11 reveal ,that ^
salts are effective catalysts when compressed
temperatures is utilized. Manganous sulfate proved
the most effective catalyst in the more alkaline soluti
at near-ambient temperatures. Chen and Morris11 found
that nickel, cobalt, and manganous ions are all effective
and predicted that potassium permaftgStfiate would work well.
Their best formulations achieve complete removal with short
contact times such as 15 minutes/ Hessic and Thomsom12
obtained 95 to 97 percent oxidaytion^af stflT&ides at short
contact times around 20 minutesx^osing marigaiious ion as the
catalyst. These solutions were veicy dilut^and residual
sulfide levels between 0.3 and 1.0 mgyll wereNachieved. In
two studies, Veno1 3 1If, obtained between
100 percent sulfide oxidation using high €e*operatiires , great
excesses of air and many different catalyst ^fij^ms . Among
those found to give good^results were ferric sulfate, ferric
chloride, activated carhfonT'^-Qarbon black, ammonium
peroxydisulfate, and hyaroquinbr^. Eye and Clement9
found that potassium
manganous sulfate plus
completely at short conta
In this study a first stage
of the sulfide and a second
An actual tannery waste req
potassium permanganate and air.
further describe^_Lhe effectiveness o
r, ozone, or
ji fides
In a laborator
most effectiv
effective.
favor mang
costs for tnextwo
catalyst is
were obtained witn
0.15. Pretreatment
and 30 minutes.
oved 80 percent
reactor the rest.
urs of treatment with
° and Eye9
he metallic catalysts.
oxidation should approac
potassium permanganate was the
th manganous sulfate also proving
relative costs for the two catalysts
ace available and capital
s will determine which
situation. Optimum results
manga^neo sulfide weight ratio of
employing catalytic
per cent removal of sulfides.
Sulfi
ze
also removed in the activated sludge process.
_ dangers of potential hydrogen sulfide
j.nate the immediate oxygen demand exerted
cal processes, a catalytic oxidation
[or all tanneries with sulfide-bearing
84
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PLAIN SEDIMENTATION
Plain sedimentation is concerned with the removal of
non-flocculating discrete particles and flo/ab^ low-density
materials such as grease and scum. Tanner/ wastes have high
concentrations of both suspended solids and grease. As was
shown in Table VII-1, suspended solids refauctionsxcan range
from approximately 40 to 90 percent, wh^
BOD5_ can range from 30 to 60 percent. Mbsh or^fehe sus^ianded
material removed is in the form of insoluble
produces a voluminous and heavy sludge. Although gft
removals are not indicated, high removals are expected
surface skimmers installed in clarifiers.
Assumed to be typical for plain sedimentation units is the
full-scale operation cited by Su/thej/land21 . The
suspended solids content of a s^de/Leathar tannery was
reduced 69 percent from 1,200 {ng/1 es^S/D ntg/1 by
sedimentation .
Laboratory experiments by Sproul, et^aj. . 2 5 ubij-izing
beamhouse and chrome liquors showecT~tha;txplain
sedimentation at an overflow rate of 24 . 5 cna^m/dzfy/sq m
(600 gpd/sq ft) gave average removals of aboutxj?2 percent
of suspended solids andXJ5 percent of BOD5_. Pilot scale
experiments by Sproul , /et a3^ show equalization of
plant flows followed
solids and BOD5_ remov
respectively. Chrome l>uor
total flow proved to be
composite wastes containing
Overflow rates of 14.3 cu m/d
produced a 2 percent underflow c
Field operatic
removals6.
clarifiers
(460 gpd/s
(0.8 mgd).
other than
.mentat ion gave suspended
50 percent,
1 percent of the
ant for
sp ended solids.
(350 gpd/sq ft)
cemsration.
Tannery No. 10 teiid to confirm these
primary units consist of two circular
rates of 18.8 cu m/day/sq m
flow of 3,030 cu m/day
;_ilities are provided
Cattlehide
processing durii
(180,000 Ib) green'
hair pulp beamhouse
finishing. The following
^eriod averaged 81,700 kg
rine cured hides per day for
followed by chrome tan and
rage removals resulted6.
Su^pencbsd \
Alkalinr
CaCO3_)
Grease
Influent Effluent
mg/1
945
1,150
24
718
57
2,108
51
980
490
% Removal
70
45
53
27
90
85
-------
c
o
4J
C
Hi
T3
01
00
c
•H
86
-------
Suspended solids and BOD5_ removals were 70 ipe^cent and
45 percent, respectively. A low chromium ifemoval of
approximately 50 percent occurred. Highe/ removals
would result if a pH of 8.5 or greater we're maintained
(using equalization or chemical additiori) ic the primary
clarifiers. If sodium alkali is contrioubing^^o
high pH, a pH of 10-10.5 may be needed for ^
Theoretically, all chrome should precipiate as chromic ^
hydroxide; however, a very small residual is expectedf^X. /
Although chrome removal from the wastewater is desirable/^
a sludge problem is created if proper disposal
precautions are not taken. The t^y^l- alkalinity was
reduced 27 percent, reflecting sedinfentation of suspended
lime. Grease removal was 90 parceiit.
In general, plain sedimentation^.is apWysdycal separation
of some suspended particles from^the wast^stream.
Although high removals of suspendecNsolids^^SO percent)
and BOD5_ (60 percent) are indicated wibh equalisation and
sedimentation effluent concentrations areN^ot reported
below 130 mg/1 for suspended solids or 146 mg^l/for BOD5_
(Table VII-1). High chromium removals may result while
sulfide concentrations/are^relatively unaffected. As a
unit operation, plain/sedimerfbaion has a desirable
application in tannei
CHEMICAL TREATMENT—COAG
INTATION
Chemical addition prior to se^imen-b^tion' has further
increased the removal efficiencies o£primary clarifiers.
Chemical coagulation results in nighey removals of
suspended solids_^BOD5_, sulfides, clvpome, and alkalinity
through flocotflatiohs^f colloidal particles. Alum, lime,
iron salts, >and polyme>rs have exhibited satisfactory
results. Data^rTNTabl^VII-2 indicate that suspended
solids reitiXvalsNirojn 50 iitr-aboye 98 percent and BOD5_
reductions cvf^ approximately 50 fyo 99 percent are
achieved.
Chemical coagulatioh\followfed by sedimentation has been
investigated by Sproul>vfit a/.2^ at a cattlehide
tannery using the chrome pkjocess. Raw wastewater
anals~e~5^i4idicate concentrations of BOD5_ at 2,500 mg/1
ids of about 2,530 mg/1. The results
drawivft?Qm theiboratory-scale investigation are shown
Other chemical coagulation results
87
-------
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88
-------
tration
about
percent
uric
and
sri was less
solids
*H with
suspended
1. Use of an anionic polymer at a co
of 1 mg/1 resulted in a reductio.
84 percent in suspended solids
in BOD5_.
2. Adjustment of the waste to pH/9
acid and subsequent settling
removals for suspended solids
90 and 67 percent, respectively.
3. Use of ferric chloride at a concentration o
600 mg/1 produced average removals of 60
to 65 percent, respectively, for suspended
solids and BOD5_.
4. Ferric chloride coagu
effective in removal
than was adjustment
sulfuric acid.
5. Coagulation with alum
than 500 mg/1 after adjus
6.5 reduced the BOD5_ by 90 p
suspended solids from 45 to
Alum concentrations higher than
created a flocthat would not settled
6. Buffing dust/resTaJ^ting from finishing
tanned hide/ was no^-£pund to be an
effective cx^agulant.
In general, polymer addr^ion^^rbduced a ~^apid formation
of floe, minimizing the ne^d for flfoscu^ating equipment.
Without pH adjustment, polymers produced consistently
higher removals than other coa^ylan^s tested.
Sulfides appear-ina in the pretreatment influent are not
completely r/emovecKa^i chemical units. Inconsistent
removals ar/e indicated in the literature by
researcher/s9 ^~"*^- v^^th pH adjustment to 8.0 an
upper lim/t onTSuljf: ider&TR«jjal may be 90 percent25.
Sulfide reTnoval reduces oxygerT^demand and averts hydrogen
sulfide problems.
57
rations less
H of
501
Chromium will precipitate
than 8.5. A
Sproul, et al.
"~
25
occurre
a hydroxide at a pH greater
$val in a laboratory study by
t a pH of 8.0. Precipitation
n/a""p~rXreatment sedimentation unit is desirable to
pevent any^pptential toxicity in subsequent biological
operations described by Howalt and
^^ a,, Riffenburg and Allison29
89
-------
93 and 99 percent removals of color were ob
respectively. The exact mechanism of remov,
the colloidal regions is not known; a physy
process is presumed.
each of
In a thesis by Hagan30, color removal throti
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 the
common-ion effect assisted in precipitation removal.
The basis of this contention is tftat ythe high hydroxyl
ion concentration at high pH reduces/the solubility of
color vectors such as digallic
hydroxyl functional groups. Ad'
pH control at this point may furt
efficiency. Laboratory results on a
waste indicate high color removals (94
pntains
ulants and
the relative
tannery
;hrough
a combination of chemical precipitation ancKcoaguyation
with calcium hydroxide and an anionic polymer**^/The
efficiency is dependent 911 pH control around 12.
In general, consistent/reductib^vswith coagulants are
limited to suspended solids, chromaToHi. and possibly
sulfide and color. BOD5_ xemov^isare a^frunction of
that portion of the BOD5_ eXist^m^n the colloidal or
suspended form. Soluble BODS, is iforrya^iyAO to 50
percent of the total BOD5_6 . MHny low^ removal
efficiencies may have resulted from inefficient control
of the physical-chemical operations^ wn)tch require
operator attentioji_^tp be successful.
CHEMICAL TREATMENT—CARBONATION
Carbonation/is efs§^ctive
wastes. In ci^is process,
lime to form cai<^.um
only 25 to 50 m/Ts^ The
e treatment of alkaline
carbon^^ioxide reacts with
,te, yhich has a solubility of
sfra-iline structure of the
carbonate nucleus provides anxeffective surface for
adsorption of organic mal54^r./ Suspended solids and BOD5_
are both reduced. ^v/
ining 8 to 12 percent carbon dioxide,
fuel combustion process, can be used.
into the waste stream requires a
tern and reaction vessel, and
f the boilers.
90
-------
Table VII-2 indicates good removals of susp
BOD5_ for carbonation in conjunction with c
The BOD5_ removals range from 65 to 92 per
suspended solids reductions from 79 to 9
recorded.
solids and
Cation.
Awhile
are
Field data from Tannery No. 3 indicated high rec
in suspended solids, BOD5_, and total alkalinity,
flows from the cattlehide vegetable tannery were 1,700s
cu m/day (0.45 mgd). Primary clarifier overflow rates
were about 20.4 cu m/day/sq m (500 gpd/sq ft) for a
chemical system utilizing flue ga^barbonation and a
combination of iron salts and po/ymers. (Sulfuric acid
was also used to assist pH control,/) The following
removals were indicated3*:
Suspended
Solids
BOD5_
Total
Alkalinity
(as CaC03)
Pretreatment
Influent
mg/1
2,110
100
% Removal
95
84
100
Carbonation is attractive fbr taMner^pre/fcreatment
facilities, where carbon dioxide is^available at the
cost of piping from the plant bcxU-erss. Removals are
high, under proper operating condr^ion^, for suspended
solids and BOD5
pH ADJUSTMEN
In some
from other
meet restrict!}
has been accompli!
sodium hydroxide to
requires relatively simj
with a pH sensing and
ion of the waste effluent
has been required to
vinsf system. Normally, this
sulfuric acid, lime or
aise pH as required. This
emical feeding equipment
system.
SLUDGE HANDKKJG AND DISPOSAL
tree?
fiery waste treatment involves the handling
semi-solid sludges obtained from liquid
The most predominant methods of
91
-------
ultimate disposal of tannery waste sludges in
sludge lagoons, landfills, dumps, and spread}
land.
Some attempts have been made to dewater s.
ultimate disposal, with varying success.
principal dewatering techniques include cenl
vacuun filtration, and pressure filtration. Centrifut
have appeared to meet with less success than vacuum
filters or pressure filters.
Reducing the moisture content of s
drying beds has also been successf,
This is particularly attractive t,
where land area is available.
by spreading on
some areas.
afaller facilities
the
been
of
nt provides
which can
and. One
Conditioning and stabilizing a mix
tannery sludge using heat treatment
employed at Tannery No. II6, where about"
the waste flow is tannery waste. Such hea€
a stable end product from a biological standpd
be incorporated into a landfill or spread on
of the principal difficul/€i^«^with tannery waste is the
chromium content in sludges and^-the potential toxic impact
of material on the environment. Ir^^esting a heat-treated
alkaline sludge, it has been !fe»4icated^fcti^t some of the
trivalent chromium may be osd.di^2hsbo the rfexavalent form.
Apparently, the trivalent chrxmiimh/is yeonye/rted through the
high temperature, high pressures high/pH/and the oxidizing
environment of the heat treatment\procXss.
When chromium is reused in the tannery^/levels in the
sludge are reduced."^Disposal of sludge containing these
lower residual/quantities of chromium in a sanitary landfill
will minimize/an\/^rviror^nental problems.
Prior to dewerti^ring rn mechanicaTr-^equipment, sludge is
normally conditioned by ^sTe^pf ferric salts and lime or
polymers or a combrtvation o£/tft&se. The quantity and
type of chemicals required are>y3ependent upon
characteristics of the srudge Joeing handled.
Dewatearlng^-w4th mechanical equipment generally can
produce a sola^k^cake containing 15 to 30 percent solids.
iPadgersL disp
on plants o
supplies.
ed of on the land, taking advantage
r agricultural purposes. One
pe of disposal practice is the
of chromium or other constituents
through/leaching, on ground or surface water
92
-------
Lagoons for dewatering have some limited
areas where rainfall approximates evaporat
application is not completely satisfactor
In humid
'such
Use of lagoons, drying beds, landfills,
all require key attention to the envirof
Particularly important is the leaching of_
or organic materials to the groundwater supplies
surface waters. Proper controls must be taken to ensi
that these conditions will not develop.
Spreading tannery sludge on the
potential problem from the stan
However, with the high amount o
found in most tannery sludges,/as
dosages required prior to dewatering
sufficient contact time of the s
afford some degree of disinfection^
is desirable to have the sludge
11.5 or greater for about two hours or m
control1.
the
eleva
may also be a
of bacteria present.
waste commonly
lime
is usually
pH to
cases, it
H of about
feet proper
93
-------
SECTION VIII
COST, ENERGY, AND NONWATER QUALIT
SUMMARY
Pretreatment cost estimates are reported
representative size groups within the subcategori<
leather tanning and finishing industry. The plant si"
division is based on number of hides/skins handled as a
raw material. This division of the industry subcategories
does not imply the need to categojpi3>&fi according to size.
As indicated in Section IV, the categorization rationale
does not support a size basis for categorizing the industry.
Capital costs, operating costs,/an^annuf^costs for waste
treatment are usually related ^o hydrfcHi/ic ^Loading and there
are economies of scale as wastew£*ter volun]£ increases. The
cost distribution over greater numoe-j^ of nides in larger
plants obviously reduces the unit costNcontribv^tion of
pretreatment for each hide. These differences are significant
and single-value average costs for each subc&^egpry
irrespective of size would have distorted the cost
information.
var
Wastewater treatment
total wastewater flow
waste treatment will
production rate. Therefor
have been estimated on the
size. A "typical" plant is a
an average production rate and
as indicated by the data in Table
parameters of
from this st
pretreatmen
in hides/s
plant size
The midpoint
size was used as
size plant.
were used to
primarily a function of
it of production for
ment cost and the
ry treatment costs
cal" plants for each
model plant with
astewater flow rate
1. The operating
Wastew
determine
odel plants are leased on information
study of the economic impact of
ustry. Tannery production ranges,
determined for the various
t study on this industry.
uction specified for each
roduction level for that
collected in this study
flow rates per unit of
production. The total fibw^as then calculated by
multip-iyinq this latter figure by the average production
for/each siJfOk. The average hide or skin weight is based
on/the^Ayerage>af the tanneries in each subcategory. The
oad for each subcategory is reported in
ort. The raw waste load per unit
not vary significantly with plant
sze wstn ecK^ puategory.
95
-------
00
c
w
w
o
En
T3
Q) T3
CO M
•a
co C
M cfl
0) 4-1
C "
•H 4-1
4-1 0)
M PL,
(U
CX 00
O C
•H
4J >
C 0)
Cfl -H
PL, O
A O
O
•H 4-1
a, co
>. o
H O
cd
H
-------
A capital investment will be necessary for about 50 percent
of the tanneries in the industry to achieve Ahe^ pretreatment
standard, as indicated in Table VIII-2. Thas investment
required of each "typical" plant in the
categories is indicated in Table VIII-3.
indicated in Table VIII-2 is based on i
from the industry in the course of this s
of the percentages of tanneries as indicated in
and VIII-4 are based on a determination of the
requirements of each plant in the sample of each categor
then subtracting the number of plants with adequate
facilities in place, as reported in-^the questionnaires
submitted by the tanneries. The /umbers of plants
determined in this manner were then Delated to the total
number in the sample of each cafiegofcy of/xjperat!?J^f"a^w3>j£otal annual cost for
tanneries implemen€1i>nq suicide removal for the
various sizes and cate^jories^re indicated in
Table VIII-6. The ef fec^vQf/economies of scale
is particularly evident in the difference in
unitXcosts"tee^tween the extra small and the medium
anqr larger pi;
x
consumption for wastewater pretreatment
nniW industry will be insignificant
hejtotal power consumption for plant
operatio
97
-------
Table VIII-2. Percentage of Tanrf
to Install Sulfide
Category
Percentage of Tan
Be Using Sulfide
98
-------
Table VIII-3.
Capital Investment Cost Estimate f
to Provide Sulfide Removal Techno
Extra Small
Small
Medium
Large
Extra Large
Eartra Small
Medito ^\
Large
Med ium
Large
sdium-Sides
MedVum-Splits
Extra Small
Small
Large
h Tannery
Capftal/havestmentvost
40,000
70,000
91,000
78,000
NR*
NR
NR
NR
NR
63,000
NR
63,000
NR
NR
equired by existing tanneries.
99
-------
Table VIII-4. Percentage of Tan:
Additional Pretr
That May Install
Components
Category
Percentage
Combined System
L Screening i
of Tanh^j
Costs for
pH
•ies
W
UsedAo
h Pretr><
Estimate
itment Component ;
^Nv. ^
Control r\Equali^
\/.
ition |
100
-------
en
3
13
00
C
•H
C
§
H
)-i
CU
CO
cu
cfl
e
•H
4-1
en
W
en
o
O
u
4-1
C
cu
cu
4J
CT)
CU
M
60
m
i
Cfl
H
101
-------
CO
O
CJ
CO
3
C
CO t-i
4-1 CO
O T3
H C
CO
-O 4-1
c y}
ca
4-1
4-1 C
CO Ol
O E
U 4.)
CO
0) 0)
O »-i
C 4-1
re oi
C M
0) Pu
-o o
c <
CO
o
60 4J
c
•H t—I
4-> CO
CO >
P O
H) E
a. 01
o «
c a)
•H -O
•r-t
01 UH
t/3 t-H
CO 3
01 C/3
M
O l-i
C O
I—I 14-4
\o
I
JO
CO
H
102
-------
The pretreatment requirement will not only mij^imize sulfide
hazards for municipal sewerage system personnel^ and
facilities but will also minimize potential/od^r problems
associated with a sulfide pollutant in was^ewater entering
publicly owned treatment works (POTW) . /ChromiuitNa.nd oil
and grease removal from tannery waste
properly designed and operated POTW s .
content of the sludge from such a municipal
a problem, the municipality may require chromium rente
at the tannery. This reduces the problem for the
municipality, facilitates the achievement of water quality*
based chrome limitations, and presumably reduces the total
volume of chromium-containing slupge>to be disposed of.
"TYPICAL" PLANT
wastewater
subcategories
plant
as the
lual cost
costs
The pretreatment systems applicJ
can be used, if necessary, by all
of the industry. A hypothetical "typ^i
was constructed for each size in each si
basis for estimating investment cost and
for the application of pretreatment systems.
tdl
were estimated and, in
energy requirements, a
pretreatment were det
The pretreatment is app
constructs for each subca£
in Table VIII-1.
TREATMENT AND CONTROL COSTS
In-Plant Control— G^sjb
lition, effluent reduction,
j/ber quality aspects of
the plant
ed previously
-plant modification and wastewater
segregation, is primarily a
ituation. Building layout
tate what can be done,
r such modifications are
imates for pretreatment.
upon application of
1 combined wastewater
Significant economies, however, especially for
, would be possible for segregated and
The cost of
controls, e
function o
and construe
how, and at
not included in an
Therefore, all costs
treatment processes to
volume
sul
re concentrated waste streams.
103
-------
plant
Lted
Capital Investment Cost Assumptions
The waste treatment system costs are based
production, wastewater flow and BOD5_ figu
previously for "typical" model plants in
Investment costs for specific pretreatm<
are largely dependent on the wastewater
load.
The actual component cost estimates are based on unit
cost curves. The following assumptions are reflected
in the capital costs:
1, 1976, dollars.
lal-type
ared by
cordance
Costs are expressed in CT
Expected accuracy for
estimates is + 30 to 4
All design specificatid
an outside consulting
with applicable codes.
Construction work to be performe
contractor using union labor and
be done by in-plant labor or mar
people.
Engineering coats aris^pt included in cost
estimates, but? the conlfEiHiction contractor's
overhead and
No land acquisiirion dsQa-feo-S incltrdad.
The capital investment cost Estimate/6 ^r»be actual cost that tanneries
will incur in installing the sugg^stecKtechnology. For
example, a pollution control consur
-------
Table VIII-7. Capital Investment Cost Estimate/ror^lach Tannery
to Provide Optional Pretreatmenfr' Technology
1976
nenfcxand TotalxCost
Capital Investment Cost,
Ontional Combined System,
Flow
Equalization
pH Control
Plant Size
Extra Small
Small
Medium
Large
Extra Large
5,000
13,000
26,000
41,000
70,000
201,000
301,000
391,000
542,000
Extra Small
45,000
201,000
224,000
132,000
542,000
Extra Large
83,000
162,000
124,000
78,000
41.000
Medium-Sides^ 4.000
x
IMedium-SpXltg 14 0
34,000
53,000
40,000
67,000
26,000
39,000
136,000
33.000
Extra Small
8,000
99,000
. 130,000
136,000
140,000
200,000
* NR
** Tota
plus com
^existing tanneries.
removal where indicated on Table
s liLsted, therefore is maximum potential cost.
105
-------
106
-------
107
-------
municipalities considering the use or the re
of such pretreatment facilities. These cos
on the same assumptions as described previ
Annual Cost Assumptions
irement
re based
The components of total annual cost are
depreciation, and operating and maintenance costs
include energy and power costs. The cost of capital
estimated to be twelve percent of the investment cost.
This cost is an estimate of the weighted average of the
cost of equity and of debt financing throughout the
industry. Operating and maintena»(ce^:ost includes all the
components of total annual cost ^Kc^pt cost of capital
and depreciation.
as estimated
ue and a
The depreciation component of an
on a straight-line basis, with no
ten-year life for all capital investm
The labor rate for O&M man-hours was set at^^S.OO'per hour
plus 50 percent for burden, supervision, etc. T^k/ased on
information from the indt*a£xy. Electrical power cost
was estimated to be 2.y ceivE^^er kw-hr. Other costs,
including materials ana supplies>are based on additional
unit cost curves. TheNoperating year^j^as assumed to be
260 days per year in alllN^st^aJ^culatioits^to account for
the variable numbers of day^ peisj^eek^repc/rted by the
industry—5, 5.5 and 6.
ENERGY REQUIREMENTS
The energy requ-jrr*5m«nts for tanneries^vary considerably
based upon reported oa>ta. This variation is due to the
following faoTtor;
1. Ty^e of fii<3te tannec
2. Type^^nd exteqrb-^of beamjrfouse, tanyard, and
finishih-a opera'fc^p*
3. Degree ofm^chani^a^ion within the industry.
4. Climate of tnfevj:anneyy location.
uirements for a typical cattlehide-chrome
.ssing hides from raw material to finished
tely 0.46 kw-hr/kg of hide (0.21
ical energy and 3,560 kg cal/kg of
for steam. The energy requirements
pproximate five to ten percent of
rical energy and less than one percent
'ergy requirement1.
108
-------
NONWATER POLLUTION BY WASTE TREATMENT SYSTEM
Solid Wastes Characteristics. Solid wast
tannery with a wastewater pretreatment/t
system may include any or all of the fo
Fleshings
Hair
Hide trimmings
Tanned hide trim and shavi
Leather trimmings
Buffing dust
Leather finishing resid
Wastewater treatment s
General plant waste
The specific types of solid waste generated Bysa tannery
depend upon the type of processing operatsions conducted,
and the quantity of each type of waste gene^sa^ted/depends
upon the volume of production at the tannery,
Tanneries which genera
normally sell these w
or occasionally to ginsman
materials are highly put
required. Very small
hundred hides per day often
this waste since the by-produc
by the handling and transportati
lings and hide trimmings
Ls to rendering plants,
Since these waste
ilection is
jss only a few
iomical to sell
value is exceeded
tanneries and>6 few chrome leather
rom hides using a hair-save operation.
hair is washed, dried and baled,
-product. Use of the hair-save
hair-burn method.
some tanners still use
hich produces hair that is
t^tanneries using the hair-
.he hair is dissolved and
stream.
Most vegetable
tanneries re
At these tan
and subsequ
method is
As noted in
a modified hair
disposed of in a la*
burn method of hair r
becomes part of the
feather tanneries which generate large quantities
^rimmings and shavings, particularly split
^cated in the northeastern U.S., are able
jaterial as a by-product. By-product
;ure of fertilizer, chrome glue, hog
feed "s'Vippleme^Rt, \>r leather board. The majority of this
type ofWste, n«awev£r, is disposed as solid waste.
109
-------
32
The
the
A recent study estimated that the total quant4disposal. Sludge
dewatering may be accomplrShedNtB^ng qravjj£y or mechanical
means. Gravity dewatering C^equenti/T^&ejttling) is
relatively uncommon; however, SvUidgesdrying beds on the
tannery plant site are used by sbs^e tanners. Mechanical
sludge dewatering is normally accom$liished using vacuum
filters, centrig*rb^s. or filter presses. These three
mechanical deyateringstechniques have all been found to be
effective in/producing^ludge cakes ranging approximately
from 10 to jfQ p^ceKt s&lids. There seems to be a
preference ^pr fi3>t^Jr presse"s-~4ue to the slightly drier
(40 percent sisj. ids) fil/ter cakeproduced.
Secondary wastewat*
tanneries are normally
after which the sludge
disposed of in a dump or
sludges from vegetable
ed in evaporative lagoons,
as a soil conditioner or
fill.
Se
fo
e is composed primarily of precipitated
rmally dewatered prior to disposal.
are the most common disposal facilities
110
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Sixteen landfills which receive tannery wastes^ere visited
during a recent EPA-sponsored study32. Most /fphe operators
interviewed indicated that dewatered tannery/wasft-ewater
pretreatment/treatment sludge could be handled adequately.
Appropriate handling was reported to involve mixingxthe
sludge with domestic refuse in proportion/ wbfrch woulQ^allow
the combined material to be worked by normaJ/ 1 amid 11
equipment.
The different types of solid waste disposal facilities
utilized and estimates of the proportion of the total
quantity of tannery solid waste goi/ng^to each type of
facility are shown in Table VIII-"
all tannery solid waste is dispos
Trenches, lagoons, and certified
facilities are currently used almost
sludge disposal. A small percen
their own disposal sites. Tannery-
are usually associated with vegetable ir&atner "tanneries
and are the result of the plant's remote x«icationNpr the
fact that other disposal sites will not accept^ thgr waste
(usually sludges).
shown, nearly
landfills or dumps.
rdous/^waste disposal
ely for
ries operate
osal facilities
Most tannery solid wast
substantial concentrati
several percent on a we
copper, lead, and zinc asN^el
concentrations of certain c
are presented in Table VIII
vegetable leather tanneries is
not normally contain significant
The possibility
contamination
facilities wh
that disposa
must minimi
soils should h>
land disposed contains
ent chromium (up to
and in many cases,
, the "typical"
nnery sludge
ludge from
type which does
,etal concentrations,
Leachate generation and subsequent
grounfck and surface waters may occur at
re ;bannery\ wastes are disposed of requires
si*es Eje Gainfully selected. Site topography
surfehs^f water rTr>«L^across the site and the
.able to/Contribute to leachate attenuation.
Operational procedures srt84flCh4}e/einployed which will
minimize percolatiorNof prec-ipitation through the refuse.
Leachate collection systems at^landfills used for solid
waste disposal are recomme^ideor to provide adequate
assuranca_that ground and surface waters will be protected
f r om /contarnlTva_t ion.
Lee
tc
flar
which
to minimi^a. the
The quantitie
are small enough
environmentally
sidues are the one solid waste from
ntain significant quantities of
ents. Consequently, disposal sites
e of waste need to take precautions
ial fire hazard from this material.
type of waste which are generated
land disposal is thought to be an
uate disposal alternative.
Ill
-------
Table VIII-10. Disposal Sites
General Category of
Disposal Site
Specific Type of Disposal Site
Percent or
Waste Disposed
Landfill
municipal
private sa
municipal
private engi
municipal
private converted
on-site tannery
converted**
Dump
Trenches or lagoons
Certified***
municipal
private
on-site tannery
ivate
60
3
3
5
10
20
14
5
25
20
1
4
4
4
1
*Engineered dsposalsM^s whictT~at>>-QOt provide daily cover
**Dumps which havis^been coveiit^d to landfills without being engineered
***Certified hazardou&>vwaste oispo'&aj^facilities
112
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Table VIII-11. "Typical" Sludge Characteristics
Chrome leather tannery
p r e tr ea tmen t/t r eatmen t sludg
Constituent
before
dewatering
after
dewateri:
vChrome leather
Lannery sewer
sump sludge
Jnot d^atered)
Vegetable leather
tannery secondary
treatment sludge
(not dewatered)
Solids content
Chromium (mg/1)
Copper (mg/1)
Lead (mg/1)
Sulfides (mg/1)
Phenols (mg/1)
5-10
3,000-6,000
100-150
10-25
20-50
20-30
10,000-15,000
150-200
3-6
<5
<10
<5
25-50
*A11 values are on a wet weight basis
113
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Air Pollution
Particulate matter and hydrogen sulfide are/the/two potential
causes of air pollution from leather tanning anoxf inishing
processes. Hydrogen sulfide is toxic even/in low^X.
concentrations and is the main cause of cAorsT^n tannery waste
treatment systems. Hydrogen sulfide is foisjjfed prsmcipaTlv
by reactions involving sulfide wastes from the unhais^ing ^v.
process. The pretreatment standard requires sulfide removal /
prior to discharge to municipal sewers and treatment. Tnis/
should eliminate any air pollution problems that could result
from sulfides and improve the potentially lethal working
conditions of workers in and arounja municipal treatment
systems.
The major potential source of a
tannery is from hide buffing ope
tanneries control this by wet scrub!
is generally combined with the total
tanneries are adding buffing dust to slu
liquid waste treatment for disposal.
matter from a
ever, most
ubber water
Several
from
In addition to process s
source of air pollution
of gas- and oil-fired
problems. However, wi£
emissions are a problem.
ices, tannery boilers can be a
sroper design and maintenance
should be no emission
fly ash
can be kept
to a minimum with proper des
collection equipment may be ul
pollution. Wet scrubbers or el(
are capable of providing in excess
the fly ash. If a wet scrubber is
slurry can be d^actraw^ed to the wastev
n. Dust
control air
precipitators
percent removal of
the waste dust
ter treatment
system. Fly a
be combined w/th
from ^tshe electrostatic precipitators can
dewatered sludge for disposal.
Boiler flue jas corffc^ns
burned in theboilers cc
fuel oils containvgulfur
burned. Burning
sulfur dioxide air pol
devices for removal of su
development stages.
when the fuel
.ains su/fur. Some coal and heavy
sulfur dioxide when
is one method of minimizing
ion problems. Gas scrubbing
/dioxide are now in the
cantVLncrease in noise due to waste treatment
puinps and air compressors. When such
in la low-cost building, the noise
114
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generated is confined within the building, bu
may be amplified to high levels in the build}
installation practices. All air compressor
and large pumps in use on intensively aera
systems, and other treatment systems as w
noise levels in excess of the Occupation
Health Administration standards. The indu"
these standards in solving its waste problems.
noise
jy such
blowers,
115
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SECTION IX
EFFLUENT REDUCTION ATTAINABLE THROUGH THE
THE BEST PRACTICABLE CONTROL TE
CURRENTLY AVAILABLE—EFFLUENT LIMITAT
To be added later.
ICATION OF
117
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SECTION X
EFFLUENT REDUCTION ATTAINABLE THROUGH THE
THE BEST AVAILABLE TECHNOLOGY ECONOMICA
EFFLUENT LIMITATIONS GUIDE
To be added later.
ICATION OF
CHIEVABLE—
119
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SECTION XI
PRETREATMENT STANDARDS
INTRODUCTION
The effluent limitations that must be achi
in the leather tanning and finishing indus*
into a municipal sewerage system for treatme1
owned treatment works (POTW) are termed pretreatment
These standards are determined by identifying the re
necessary for effluent constituents that would interfere
pass through, or otherwise be incompatible with a properly
designed and operated POTW.
jLities
rge
ublicl
Consideration was also given to tl
a pretreatment standard:
following in establishing
The total cost of application of technology in
relation to the effluent redubt-n anSs^other
benefits to be achieved from
The size and age of equipment and fr«Liliti«
involved;
The processes employed;
The engineering
pretreatment tecjanology
to POTW's;
Process changes;
Nonwater quality en'yiroi
energy requirements).
of the application of
jd its relationship
:al impact (including
Pretreatment standards must refleb± ef&Tuent reduction
achievable by the application of pr^bmary^treatment technology
as used in the industry and by-in-plah<^/controls when such are
considered to be/fiorma^ practice within the industry.
A final consi
engineering
pretreatment ^bechnol
results of demon
and, most preferab
EFFLUENT REDUCTION ATTAI
he determination of economic and
application of the primary or
be determined from the
pilot plant experiments,
within the industry.
PRETREATMENT TECHNOLOGY
resented in Sections III through VIII of this report
d summarized in this section leads to a
the necessary effluent reduction attainable
plogy in the leather tanning and finishing
in sulfide removal from all tannery
121
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IDENTIFICATION OF PRETREATMENT TECHNOLOGY
and
The pretreatment technology to be used by
finishing plants to achieve the pretreatment
catalytic oxidation in a batch mixing/reaction tank.^
predominant industry practice in implementing this techl
involves manganous sulfate as the catalyst in a steel or
concrete tank equipped with a compressed air aeration system?"
As
As pointed out in Section VII, additrioryal wastewater management
and control practices which should /be iconsidered by tannery
management to reduce wastewater vodum^, poliiatant loading,
and concomitantly the surcharges fend c^p^.t/6.1 9ost recovery
paid, include the following:
* Appoint a person with specific responsibility for
water management. This person shcmid have^sreasonable
powers to enforce improvements in wate^ and/waste
management.
Determine or estimate water use and waste load
sources. Install and
ior water use areas.
strength from pri
monitor flowmet
Segregate waste
process, i.e.,
bea
major in-plant
d retan/
fore mixing
reduce pH to
nd dissolve
s a valuable
finishing for subseqi
with others.
Collect unhairing waste
isoelectric point to prec
protein, and recover the
Toy-producer". -^
Reuse, or recover active chemicals for reuse
from wafetex-s
-------
IDENTIFICATION OF PRETREATMENT TECHNOLOGY
and
The pretreatment technology to be used by
finishing plants to achieve the pretreatment
catalytic oxidation in a batch mixing/reaction tank."
predominant industry practice in implementing this tectii
involves manganous sulfate as the catalyst in a steel or
concrete tank equipped with a compressed air aeration system."
As pointed out in Section VII, addi
and control practices which should
management to reduce wastewater v<
and concomitantly the surcharges
paid, include the following:
il wastewater management
Considered by tannery
itant loading,
>st recovery
Appoint a person with specific
water management. This person
powers to enforce improvements in wat
management.
Determine or esti
strength from pri
i4ity for
easonable
waste
monitor flowmet
Segregate waste
process, i.e., bea
finishing for subseq
with others.
Collect unhairing waste
isoelectric point to precip
protein, and recover the
by-produ
Reuse,
from w
strea
Provi
for scr
throughout
may be desira
the municipal wa
Use more care in
water use and waste load
ources. Install and
or water use areas.
major in-plant
d retan/
fore mixing
reduce pH to
ind dissolve
'as a valuable
active chemicals for reuse
such as the sulfide containing
chrome tanning solution.
maintenance attention
te handling systems
y . A back-up screen
imize solids entry into
tment system.
ng, unfolding and otherwise
aring hides for first process step to minimize
into the sewers.
iployees aware of good water management
encourage them to apply these
ur
try
122
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Such practices are feasible and may be economically attractive
by reducing municipal water and sewage charges/because of
lower flows and waste loadings.
RATIONALE FOR THE PRETREATMENT STANDARD
The rationale for the decision on the pretre«/men
rests primarily on the definition of incompatible
Section 307(b) of the Act and as it applies to the wast<
contaminants in the raw wastewater from leather tanneries.^
Incompatible pollutants are specifically defined in the Act
as those pollutants which either interfere with or pass through
inadequately treated. Among the polAut^nts in the raw waste
from tanneries, BODJ3, TSS, oil and/gre/se, total chromium,
sulfide, and ammonia, are present An ^uffici^nt concentrations
to represent potential problems ffor POTWsIs/ itoithin this
technology based analysis, it was a^ssumed that any joint
municipal-industrial POTW will incluctexprimary^and secondary
treatment which is properly designed andxoperate-elto effectively
treat its unique mixture of domestic and iriiiustria3s^wastewaters,
including adequate consideration of the specific characteristics
of industrial wastewaters present, such as those^sJiaracteristics
of trannery wastewater.
The data and information^
that the BOD5_ and TSS fo
with properly designed and
treatment (i.e., activated
joint municipal-industrial POT
tannery wastewater indicates
concentrations, which range from
200 mg/1 to 900 mg/1, respectively,
concentrations ofstt-mq/l to 65 mg/1
respectively. T/ne broa
not indicate
ing
this study indicate
stewater are compatible
biological
g data from four
ore than 50 percent
BOD5_ and TSS
to 950 mg/1 and
e reduced to effluent
11 mg/1 to 75 mg/1,
range of influent concentrations did
to a maximum level beyond which the
treated, and therefore no
is required to ensure good
wastewaters w
specific trea
performance.
Similarly, oil and gfe-ase foCfnd in tannery wastewaters were
found to be removed to Ibstf levels, presumably by a combination
of skimming in primary clari-fiers and biological oxidation
in secomla_rvtreatment facilities. The performance of one POTW
which Kad ex^Asive data indicated a typical influent oil and
greas/e concentration of 93 mg/1 and an effluent concentration of
4 mg/1. ^The^sefore/Nconsidering this performance and the nature
of Che oi^SvandTs^reaseVjeing discharged (i__. e., primarily animal
) no pretreatment limitation is necessary,
123
-------
There was no evidence found in the data collec
municipalities treating tannery waste or in d
industry that chromium interferes with the p
biological treatment systems in use as seco
The same data reveal that chromium is remo
effluent concentrations from wastewater in
primary treatment and secondary biological
.from
.rom the
of
iatment.
Low
clude
Evidence in the record indicates that removal of total
to very low levels is independent of influent concentration.
Optimum removal of chromium in primary clarifiers occurs at a
pH of 9 or slightly higher. Residua^oiiromium is removed with
waste activated sludge producing ef/luarit concentrations in
many cases of 1 mg/1 or less of total /chromium, which is within
NPDES permit conditions where totyal cnKpmiufiNis not based upon
water quality constraints. No oraer ina^eaticm of chromium
incompatibility is evident from theNlata and /information
collected on POTW operation.
The hazardous nature of hexavalent chromium ^fc« generally
accepted. The use of this type of chrome was rcsmdr in only
two tanneries of about 100 in the sample. These tanneries
use the older "two bath" tfanhina method as described in
Section III. As noted inr that dfesQription, hexavalent chromium
is reduced in the tanning drums andt^refore should be present
in only trace amounts in tije w^tewater/^wtiich also presents
a chemically reducing enviroHmerr
significant amounts of organi
from all sources indicated hexa
to be in only trace amounts, but
actual presence of hexavalent chrome
difficult to qiiantj^fyvery accurately
of tannery wastev^ater
procedure is available
tannery wastewate
Sulfide
such as
with the operation
1.
resence of
ata available
hroinium if present
at all. The
nnery wastewater is
ause of the character
because no acceptable analytical
hexavalent chrome determination for
is removed
employed
ogical treatment systems
r, sulfide can interfere
ree significant ways:
Sulfides react inxwast^water streams, sewers,
and POTW component s^at a certain pH to form
>gen sulfide which has a threshold limit
10 ppm in air. Reports occur
y about the deaths of workers in
usually caused by hydrogen sulfide
milar reports on the deaths of
e noted in public record during
ie course )of this study. These accidents can
124
-------
•er system
pal
eptable
occur in the confined spaces of the se.
and in low protected spaces in the m
treatment plant. This is a totally
interference that cannot be tolerat
The hydrogen sulfide produced from,
sulfides in wastewater can be oxi
sulfuric acid which is highly cor?
sewers and treatment plant equipment,
their operating life and creating maintenance
problems and downtime when the system is not
able to operate as needed. This effect also
seems to fit as an interfer
Sulfides produce hydrogen
certain fairly common con
treatment processes. Th
odors and people are ab
concentrations in air.
from a POTW may lead to ser
local people are frequently ex
Temporary to permanent shut down
may be the solution to such a proble
is surely an interference.
de odors under
ns in waste
obnoxious
,ry low
problems
ems if
hem.
Effluent data from POTW1 s,
passes through both POT
treatment systems which
logical explanation or sel
found to account for this
concentrations of 100 mg/1 or
ites that ammonia nitrogen
tannery wastewater
and operated. No
:y could be
iome>ip5f. Eftiu/snt ammonia
found. However,
there is no end-of-pipe pretreatment technology which is
practicable and readily available us rentave ammonia. In-
plant control methods are not readily\avalilable either since
acceptable substitutes for ammonia compounds in the bating
process have noy been tbsand. Therefore, while the problem
of inadequate tzreatnient of ammonia is recognized, there is no
technical or oust ^ffeetivc^basis for an ammonia pretreatment
limitation at^this timje. Howe~V'&z^tthis problem will be addressed
within the context of tha->and processes employed do not affect the
pretr/eatment cont^r^pl technology used and proposed. Hence
directly involved in determining the
Also, the location of facilities was
idered regarding pretreatment, just as
, Categorization.
125
-------
report,
try to
TOTAL COST OF APPLICATION IN RELATION TO
EFFLUENT REDUCTION BENEFITS
Based on information contained in Section
the total investment cost to the leather t
implement pretreatment is estimated to be
Assuming achievement of 1 mg/1 of sulfides By pre€*eatmen£xthe
reduction in the pollutant loading entering POTW s wo^ti^ tot«
about 2.46 million kgs (5.4 million Ibs) per year of sur§4-des.
The capital investment cost of such a reduction amounts
per kg of sulfide ($1.35 per Ib) , calculating this figure on
the basis of the sulfide reduction tfrat would occur in one year
Potential life savings, protection af public property, and
reduction in maintenance costs are/other benefits to be derived
from implementing the pretreatment/ st^ndard/sfor which it is
difficult or impossible to assigr/a mone^^ary value.
ENGINEERING ASPECTS OF PRETREATMENT
:HNOLOaj3 assessment of the industrial
dischargers1 corH^butionr*^lative/to the POTW capability,
except for a couplexpf Iar§e/^wi4yary districts and municipalities
with significant tannfes^ wasrfe^to be treated. However,
ordinances of numerous mtrRlcipa^ities with tannery waste are
currently being reconsidereSxjanKi rewritten to reflect their
specif ic, -needs and requirements. Enforcement of any sewer
ordinance wi^T>>robably continue to be a problem. Most
ith some exceptions, will continue to rely
prraar]orfv^eif-pb>Licing by industrial dischargers.
^. ^X. ^v \
of instances of specific requirements
tannery waste discharges into municipal
126
There
or allow
-------
systems. These decisions have been made at the^lpcal level
where consideration of many relevant factors h/speen taken
into account. The effluent requirements imposedyon the POTW
are not compromised and frequently an optimunf ecojiomic balance
for the overall pretreatment-collection-tre^tment saltern is
achieved.
The engineering aspects of pretreatment technology
consideration of POTW discharge limitations and treatmel
capability relative to incompatible pollutants, raw waste'
characteristics of the industry, and effectiveness of pretreatment
technology. There are two pollutants^in leather tannery
wastewater that require discussion in t^ie context of engineering
aspects of pretreatment technology/as jaefined above—chromium
and sulfides.
Chromium was formerly purchased b
form, reduced to the trivalent form
used as the tanning agent. Chromium no"
purchased in the trivalent form by leather
chrome is highly toxic to most life forms at
in wastewater. The tanning industry is aware
shifted its use of chrome feo the trivalent form.
n the hexavalent
Lnt and then
universally
Hexavalent
centrations
is and has
Alkaline precipitation o
removal also occurs in s
Monitoring for chrome in
not nearly as extensive as
impact on the chrome concentra
dilution by other wastes enterin
occurs within the waste treatment
ccurs
readily. Chromium
1 treatment systems.
lant effluent is
Two factors
ffluent. First,
OTW occurs, then removal
During this study,<-c»tttacts were made wVth about 40 municipal
treatment superi
-------
Most municipal sewer ordinances collected duri
cities with a tannery discharge into the muni
"...no toxic or hazardous materials in suffi
cause problems..." or similar phrase. Of t
received, two specify a sulfide limit of 10y
limit of 1 mg/1. Sulfides are removed by
treatment processes. However, the substantia"
and property that sulfides in wastewater potentially
establish sulfides as incompatible, commensurate with
of the Act.
his study from
system specify,
quantity to
inances
ree a
Several sources in the literature,
describe the oxidation of sulfides
technology, especially applicable
Catalytic oxidation is reportedly
and economical time requirements.
100 percent removal. The litera€
dicated in Section VII,
effective removal
nnery wastewater.
tive with acceptable
Such "b*4.dat&on approaches
frequently
indicate the reduction of sulfides to z^ro or^indicate 100
percent removal without specifying a minimum or limiting low
level concentration, which the oxidation sysT>ems ma^ in practice,
only approach. The implication of these statenteo^tsr in the
literature seem to be less than 1 mg/1 for a sulfide concentration
in wastewater after sulfid£^b*4dation. There is no limiting
low level concentration BeportecT--for an oxidation process in
this literature. Effluent reduction^eported as a percent must
be related to influent lev^l t$^comprehefr«Lthe meaning and
significance of the reductib^c rep^5*1s5d. A percentage reduction
may be related to influent lev^l ah^f/or/^cemo/val of a specific
quantity of pollutants. The tints requ/rement for an oxidation
process will also depend on the total weight of pollutant
material loading. N. /
Raw waste sulfide^conce^rtrations are known for 21 leather tanning
plants and sufficient daoa is provided to identify the high/low
and typical co/cen^ir^ionXfor each plant and for the entire
group of 21 p/antsNas \ndica~b«4in Table XI-1. The average
maximum concen^ration^is 101 mg/t7^and the average of the
minimum concentrations
The average raw waste ^nj.fide tjoncentration among the 21 plants
is 42 mg/1 and the medianS^s 44/mg/l. Two plants have average
sulfide concentrations of les^/than 1 mg/1 and seven of the 21
plants >rr~Tr}*es ample report minimum sulfide concentrations
of lesrls than l^Qs^g/l- Effective pretreatment is being achieved
by t>fe
The prima
waste treatm
chlange that would significantly affect
system/requirements is waste stream segregation
128
-------
Table XI-1. Sulfide Concentrations of Tannery Wastewater
Plant
SuIfide Concentrations^ mg/1
129
-------
This results in smaller volumes and usually mor
treatment than is possible after all wastes ha
creating a larger volume and lower concentratj
stream segregation is ideally suited and use
the beamhouse and tanyard wastes. Other re
recovery techniques that can be implemente
operations can reduce total wastewater volu
chemicals consumption, and perhaps produce a by-prod
NONWATER QUALITY ENVIRONMENTAL IMPACT
economical
en mixed
Waste
nneries on
e, and
d ing,
e.
The proposed pretreatment standard widl substantially reduce the
potential hazards to life and proper/ty jln sewerage systems and
POTW1s and the potential for odor problems in the operation of
the POTW from the sulfide bearing jwast^ewatejts from tanneries.
Most landfill operators intervieweSNduring' a Decent EPA-sponsored
study2 indicated that dewatered tannery wastewater pretreatment/
treatment sludge could be handled adeqi^b^ly. Appropriate
handling was reported to involve mixing theXsludgeNtfith
domestic refuse in proportions which would al^isw thje combined
material to be worked by normal landfill equipmei
However, the possibility
contamination of ground
facilities where tannery
disposal sites be carefull
minimize surface water flow
should be able to contribute
procedures should be employed
of precipitation through the refused
systems at landfills used for solid w
to provide adequaj^e—assurance that grou:
be protected from contamination.
sed
chate generation and subsequent
aters may occur at
of requires that
ppography must
nd the soils
'enuation. Operating
minimize percolation
hate collection
disposal are recommended
and surface waters will
130
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SECTION XII
ACKNOWLEDGMENTS
and
The program was conducted by a team of
consultants under the direction of Mr. Re
Major contributors included Messrs. R.
Mrs. Vicki Moteelall, and Ms. Janine Neil!
Other MRI staff members making important contributor
included Messrs. R. H. Forester, J. R. Neleigh, K. R/
D. Weatherman, J. G. Edwards, R. F. Colingsworth and
I. N. Ibraham, Mrs. Robin Rasmussen and Mrs. Mary Weldon.
The program was carried out under /"h^ administrative supervision
of Dr. E. E. Erickson
Valuable contributions were als
consultants: Dr. Lawrence Rus
and SCS Engineers, Inc. The
impact study, Development Planning
Inc., was also very helpful in
in this report.
providi
is study by the
sultants, Inc.,
for the economic
ch Associates,
tion for use
Special thanks are due Mr. Donald F. Anderson/^S'f fluent
Guidelines Division of Brt>A>xfpr his guidance in the direction
of this program and foy hisiiiw^luable help in carrying out
all aspects of the re;
The cooperation and assii
America was invaluable to
persons of Dr. Robert Lollar
provided personal time and
of the data collection process.
managers, superintendents and opera>
information, o
otherwise coo,
their patie
The people
pollution con
public agencies
their vital help on
atte
rs' Council of
cially in the
e Kilick, who
various stages
:erous tannery owners,
who submitted
heir plants to program staff, and
e acknowledged and thanked for
of the EPA, of state
f local POTW's and other
also acknowledged for
131
-------
3.
6.
7.
8.
SECTION XIII
REFERENCES
Development Document for Proposed Eff/uent Lj*nj.ta-
tions Guidelines and New Source Perfprmac^ce Standards
for the Leather Tanning and Finishin^frndu^ry,
Environmental Protection Agency,Report No.
1-74-016-a, Washington, March 1974.
Leather Facts, New England Tanners Club, Peabody,
MA, 1965.
Personal Communication with
en Verhey B.V., the Nether1;
tier, Dwars, Heederik
ids>
Steffan, A.G. , In-Plant MofraX icatlbfts to Reduce
Pollution and Pretreatment oif^tfleat Pacing. Waste
Waters for Discharge to Mun ic ipas3>sSvs tente« prep are d
for Environmental Protection Agenc
Transfer Program, Kansas City, MO, Mar
7-8/1973.
Larsen, Bjarne C.,
in Reducing Tannery
67th Annual Meeti
Association, Mack
through 23, 1971,
Tannery Effluents.
Jtilization of the Hide Processor
lent," presented at the
aerican Leather Chemists
jhigan, June 20
on
Data obtained through co
Williams-Wynn, D.A., "No-Efflu>
Journal of £Jie^American Leather
i.on with tannery firms,
annery Processes,"
emists' Association,
Volume LX\#TI,
Hauck,
Recove]
Journal
1, 1973.
, .Report on Methods of Chromium
ise frSltr-Sgent Chrome Tan Liquor,"
aerican Leader Chemists' Association,
Volume LXV
and
J. David Eye
Sulfides in Tannery"
American Leather Chemi"!
Clement, "Oxidation of
Waters," Journal of the
Association, Vol. 67,
and Humphreys, F.E., "The Removal of
from "LjLmeyard Wastes by Aeration," British
rer's Research Association,
XV, No. 1, 1966.
133
-------
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
Chen, Kenneth Y., and Morris, J. Carrell, "Oxidation
of Sulfide by 02_ : Catalysis and Inhibit^n,"
Journal of the Sanitary Engineering Divl
Proceedings of the American Society of
Engineers, Volume 98, No. SAl, February
Kessick, M.A. and Thomson, B.M. "Rea
Manganese Dioxide and Aqueous Sulfid
Letters, Vol. 7, No. 2, 1974.
Yasuo Ueno, "Catalytic Removal of Sodium Sulfide
Aqueous Solutions," Journal of the Water Pollution
Control Federation, Vol 46, No.^12, December 1974.
Y. Ueno, "Catalytic Removal
Aqueous Solutions and Appli
Treatment," Water Research
5dium Sulfide from
Jastewater
Moore, Edward W., "Wastes from
Processing, and Laundry Soap Ind
Unknown.
ng, Fat
Source
McKee, Jack Edward, and Wolf, Harold W. ,
Water Quality Criteria. 2nd ed., The Resources
Agency of California, S"ba£e Water Quality Control
Board, Publicatior
Siebert, C.L., "A
Pennsylvania State
in Reference 15.
Reuning, H.T., Sewage Works
Cited in Reference 15.
Waste Treatment,"
, 1940. Cited
525, 1948.
Harnley, John W.^NWagner, Frank R., and Swope, H.
Gladys, TTreaimentNpf Tannery Wastes at the Griess-
Pfleger/Tanl(ery\ WasJ^egan, Illinois," Sewage Works
JournaX, Volutn^/XII, No->-4^ July 1940.
ineering Experiment
Eldridge, E.
Station Bullet:
Reference 15.
Su
November 1939. Cited in
erland
Industrial and Engineering Chemistry,
1947. Cited in Reference 15.
ndustrial and Engineering Chemistry, 21,
d by Reference 15.
134
-------
23. "Industrial Waste Survey at Caldwell Lace Leather
Company," EPA, Office of Operations, Radiological
25.
and Industrial Waste Evaluation Section
Ohio.
24. Eye, J. David, Treatment of Sole Lea
26.
27.
28.
29.
30.
31.
32.
33.
cinnati,
Tannery Wastes, Federal Water Pollu
Administration, Department of Interi"
Number WPD-185, Program Number 12120, 'Septe
Sproul, Otis J. , Atkins, Peter F., and Woodward,
Franklin E., "Investigations on Physical and Chemical"
Treatment Methods for Cattleslcm Tannery Wastes,"
Journal Water Pollution Control^yederation, Volume 38,
No. 4, April 1966.
Kunzel-Mehner, A., Gesund
1943.
Cited in Reference 15.
"Report of the Symposium on Indu^rial
Tanning Industry," Journal of the
te of the
Chemists' Association, Supplement No .1-5. 1970.
Howalt, W. , and Caveat, E.S., Transactions of American
Society of Civil Epfgin&gr,s, 92, 1351, 1928. Cited in
Reference 15.
Riffenburg, H.B.,
Engineering Chemistry
Reference 15.
Hagan, James R./ and
"Investigations into
Biologicalj^z-i^eated Vegetable
Masters T,
Industrial and
Cited in
Data o
Assessm
and Gunnison,
Color from
nery Wastes,
G. C. ,
iversity of Cincinnati, 1972.
ley Consultants field investigations,
rdous Waste Practices—
Leather Tanking an
Industry, SCS Engineers,
Inc., prepare
Solid Waste Mana
February 1976.
Irving
ironmental Protection Agency
ram, Washington, D.C.,
Dangerous Properties of Industrial
Third Edition, Reinhold Book Corporation,
rough communication with municipal
135
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SECTION XIV
GLOSSARY
Aerobic
oorganism
A biological process in which oxygen is
respiration needs. Especially relating
process of waste matter in the presence o
Anaerobic
A biological process in which chemically combined oxygen is
used for microorganism respiration/n'iseds. Relating to
biological degradation of waste matter in the absence of
dissolved oxygen.
Back
That portion of the animal hide, esp
consisting of the center portion of
backbone and covering the ribs, shouldersT
(excluding the belly).
Bating
The manufacturing ste
pickling. The purpose
hides, reduce swelling,
degradation products from t
Beamhouse
That portion
fleshed, and
process.
of
and preceding
is to delime the
remove protein
Belly
That portion o
representing the
Bend
tannery where thX^iides are washed, limed,
when necessary prior to the tanning
nderside of the animal, usually
f the tannable hide.
That j*OT"bion of the hide representing the entire hide cut down
the/backbone^vith the bellies and shoulders removed.
Earache
^xygerNpemand (BOD 5)
The "amount "fc>£ oxtofen \required by microorganisms while stabilizing
decomposable orsaiic Vnatter under aerobic conditions. The
level of BSD is usually measured as the demand for oxygen over
a standard frve-day/period. Generally expressed in mg/1.
137
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Slowdown
The amount of concentrated liquor wasted in/a Recycle system
in order to maintain an acceptable equilibrium oi^contaminants
in any process liquor.
Blue
The state or condition of hides subsequent to chrome
and prior to retanning. Hides in this stage of processing
are characteristically blue in color.
Buffing
A light sanding operation appli
of leather and also to splits.
surface and improves the nap of
Buffing Dust
buf f in
Small pieces of leather removed in the
Buffing dust also includes small particles of arasive used
in the operation and is/^TF^acoarse powder consistency.
in or underside
'ths the grain
of the leather,
ol. One of the
Carding
Method using a wire brush"
shearling finishing process
Chemical Oxygen Demand (COD)
A measure of the amount of organic ifts^ter which can be oxidized
to carbon dioxide arlekwater by a strong oxidizing agent under
acidic condit/ons. GeKerally expressed in mg/1.
Chlorine Co
A detention ba
diffusion and rea
disinfection
Chromium (Tota1)
^
Total chromi
al/iow sufficient time for the
ne in a liquid for
purpose
is the sum of chromium occurring in the
avalent state. Expressed in mg/1 as Cr.
A physi
liquid by
or Jthe removal of suspended particles in a
imentation (settling).
138
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len added to
area of
Coagulant
A substance which forms a precipitate or fl
water. Suspended solids adhere to the lar
the floe, thus increasing their weight an
sedimentation.
Collagen
The fibrous protein material within the hide which provii.
the bulk of the volume of the finished leather and its
rigidity.
Colloids
Microscopic suspended particles/whichxdp/nd'b settle in a
standing liquid and can only beis^moved by Coagulation or
biological action.
Color
A measure of the light-absorbing capacity of a>vv&astewater after
turbidity has been remov^ed^ One unit of color is that produced.
by one mg/1 of platim
Ltd 6
Coloring
A process step in the tann
hide is changed to that of t
dyeing or painting.
Combination Tanned
olor of the tanned
ketable product by
Leathers tann&Q. with Ihore than one tanning agent. For example,
initially chirome^tannedX followed by a second tannage (called
a RETAN) wi$n v^et^ble snajterials.
Composite Sample
A series of small wS^tewate^s^sarnples taken over a given time
period and combined as^x^ne sample in order to provide a
representative analysis oikthe average wastewater constituent
levels during the sampling period.
to hide processors.
139
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Conditioning
Introduces controlled amounts of moisture
giving it varying degrees of softness.
Corium
The layer of hide between the epidermis and the f
called the dermis.
dryed leather
Degreasing
In pigskin and sheepskin tannerie
added to the drum containing was
from the hides and recovered as
Deliming
The manufacturing step in the tanyar
remove the lime from hides coining from
solvent or detergent is
Grease is removed
ict.
Demineralization
The process of removin
exchange, reverse osm
Dermis
ntended to
.use.
That part of the hide which
epidermis.
Desalinization
The process
Detention (
<
The dwelling
Dewatering
The process of removing
sludges,
Lyed minerals from water by ion
)dialysis, or other processes.
flesh and the
dissolved salts from water.
n a treatment unit.
part of the water content of
DO
Measured in mg/1.
140
-------
Drum
A large cyclinder, usually made of wood, in/whifch hides are
placed for wet processing. The drum is rojtateek.around its
axis, which is oriented horizontally. Al/o calletkjwheel.
Dry Milling
The rotating of leather in a large wooden drum with
chemicals or water. Dry milling softens the leather.
added.
Electrodialysis
A form of advanced waste treatme
material is removed by means of
membranes and electric current
Embossed
A mechanical process of permanently imp
of unique grain effects into the leather
considerable heat and pressure.
which the dissolved ionic
jf semipermeable
reat variety
Done under
Enzymes
Complex protein materf
in order to remove prot£
otherwise mar hide quality^
Epidermis
The top layer of skin; animal
hide in the bating step
ducts that would
n epidermal outgrowth.
Equalization
The holding
and rates
blending and
te
wastes having differing qualities
periods to facilitate
ively uniform characteristics,
Equivalent Hides
A statistical term used l^ithfe Tanners' Council of America
to relate the production or^ranneries using various types
of rz6Tmate^s^als. An equivalent hide is represented by
3.1/sq m of sxlhs^ace area and is the average size for a
Cc " ""^
141
-------
nutrients,
>tewater
Eutrophication
The excess fertilization of receiving water
principally phosphates and nitrates, found
which results in excessive growth of aqua
Fatliquoring
A process by which oils and related fatty substances
natural oils lost in the beamhouse and tanyard processes^
Regulates the softness and pliability of the leather.
Finishing
The final processing steps perfo
operations follow the retan-col
include the many dry processes
hide into the final tannery produc
Fleshing
The mechanical removal of flesh and fatty subsraofces from the
anned hide. These
rocesses, and
inverting the
underside of a hide prio
tanning, fleshing is of
process
Float
:p tanning. In the case of sheepskin
*" nplished after the tanning
The proper level or volume o
water that is maintained in any
or processors) within the tanneryV
ma
Floe
Gelatinous
coagulants,
agglomerati
Flocculation
The process of floe fo
induced slow mixing.
s, chemicals, and
ocess unit (vats, drums,
in liquids by the addition of
processes, or by particle
ormally achieved by direct or
Flum
hannel or conduit for conveying water or
142
-------
Grab Sample
A single sample of wastewater which will indicate only the
constituent levels at the instant of collections^ contrasted
to a composite sample.
Graded Media Filter
A filtration device designed to remove suspended
wastewater by trapping the solids in a porous medium.
graded media filter is characterized by fill material rang!
from large particles with low specific gravities to small
particles with a higher specific gravity. Gradation from
large to small media size is in 1>ne sairection of normal flow.
Grain
The epidermal side of the tanned h
the smooth side of the hide where the"
to removal.
Grease
A group of substances
calcium and magnesium
non-fatty materials.
free and emulsified oils'
in mg/1.
Green Hides
Hides which may be cured but have
Head
grain side is
ocated prior
al
fats, waxes, free fatty acids,
oils, and certain other
sis will measure both
erally expressed
een tanned.
That part o
shoulder;
animal.
Hide
The skin of a
mature cattle.
relatively
is cut off at the flare into the
covering the head of the
animal, at least the size of
fer of ions between a solid and a solution
oli\l. A process used to demineralize waters.
143
-------
rtoms or groups
one or more
lonization
The process by which, at the molecular lev<
of atoms acquire a charge by the loss or
electrons.
Liming
The operations in the beamhouse where a lime solution^
in contact with the hide. Liming in conjunction with
sharpeners such as sodium sulfhydrate is used to either
chemically burn hair from the hide/<^r to loosen it for easier
mechanical removal. Hair burning/iioi^nally utilizes higher
chemical concentrations.
Nitrogen, Ammonia
A measure of the amount of nitrogehxwhich 4>s combined as
ammonia in wastewater. Expressed in nvq/1 as
Nitrogen, Kjeldahl (Total Kjeldahl NitrogenXQr Tfffo)
of
iined in organic and ammonia form in
as N.
n wastewater.
A measure of nitrogen
wastewater. Expressed
Nitrogen, Nitrate
A measure of nitrogen comt?
Expressed in mg/1 as N.
Nutrient
Any material uaet3—fev a living organist which serves to sustain
its existence/promote, growth, replace losses, and provide
energy. Corapomyis^of nitrogen, phosphorus, and other trace
materials aire partiisulari^essential to sustain a healthy
growth of rHcroorg-ao/isms inbioj-pgical treatment.
^\ /-^
Outfall
The final outlet cond\
drainage is discharged ii
annel where wastewater or other
ocean, lake, or river.
Pac
ides formed at the slaughterhouse or hide
approximately 20 to 40 feet in area and
144
-------
Paddle Vat (Paddle)
A vat with a semi -submerged rotating paddl
for the mixing of water and chemicals wit
angement used
£H
The reciprocal logarithm of the hydrogen ion conce
in wastewater expressed as a standard unit.
Parts per million. The expressiopf o^ concentration of
constituents in wastewater, dete/mined by the ratio of the
weight of constituent per millicsn parts Cbv weight) of
total solution. For dilute sojjottion&x. gpm} s essentially
equal to mg/1 as a unit of
Pasting
The process step generally following the re'ban-co'lor-fatliquor
operations whereby the hide is attached to a shWoth plate with
a starch and water paste->»and dried in a controlled heated
vessel.
hide is immersed
skin or hide to
of chromium salts
Pickling
The process that follows
in a brine and acid solution
an acid condition; prevents pr
on the hide.
Plating
The finishing ORo^ation^where the skin or hide is "pressed"
in order to/rnaks^itNsmootlier. Plating may be done with an
embossing p^ate whiyh imprirfts-^kextured effects into the
leather surfat
Polymer
An organic compound charax^ei'ized by a large molecular weight,
Certaifi__eolymers act as coagulants or coagulant aids. Added
to ttfewasTfcewater/ they enhance settlement of small suspended
paticles. Tntoarge molecules attract the suspended matter
t
145
-------
POTW
Publicly owned treatment works, i.e., muncpa
treatment system.
Pullery
A plant where sheepskin is processed by removing t
then pickling before shipment to a tannery.
Method of unhairing in which depi
dissolve hair entirely in a few
Retanning
y agents are used to
A second tanning process utilizing
materials (chromium or vegetable
agents. Retanning imparts specialized p
leather.
extra
natural tanning
nthetic tanning
to the
Reverse Osmosis
A process whereby wate
membranes under high p
membrane is relatively f
retained in concentrated
and are wasted.
Sanding
A dry operatic
in order to a
Sanding oper
wheels.
Sedimentation
Clarification (sett:
pass through semipermeable
assing through the
lids; solids are
ide of the membrane
^rrned on the tanned and fatliquored hide
desired surface texture of the leather,
,incl\ide the use of abrasive or buffing
Setting Out
operation which smoothes and stretches the
Assing and squeezing out excess moisture.
per condition for drying.
146
-------
Sharpeners
Chemicals (such as sodium sulfide and sodi
in addition to lime to assist in the unhai,
.fhydrate) used
rocess.
Shaving
An abrasive, mechanical action used to correct err
splitting and thus yielding a uniformly thick grain
split.
Shavings
The waste products generated dur
These are essentially small pie
are approximately the size of
.he shaving operations.
tanned hide, which
Shearling
A lamb or sheepskin tanned with the
Shoulder
hair
That part of the hide
the hide.
Side
One-half of a hide, produced
backbone. Normally done to
smaller equipment than would be
processed.
the neck and the main body of
e hide down the
e processing using
d if full hides were
Skin
The pelt or
pigskin, s
Skiver
The thin layer shaved"
leather, principally
smaller than mature cattle;
ff the surface of finished
Slu
e form of a semi-liquid mass resulting from
solids in the treatment of sewage and
147
-------
Split
A side which has been cut parallel to its sjdrfafce to provide
one large piece of leather of approximately uniform thickness
and a thin, smaller piece of non-uniform >^fiickness\called a
split.
Staking
Mechanically softens the leather by stretching and flexa^a Vt
in every direction. Usually done on automatic machines whrch
move leather between rapidly oscillating, overlapping fingers,
Sulfide
Ionized sulfur. Expressed in
Suspended Solids (SS)
Constituents suspended in wastewater whi
removed by sedimentation (clarification) or*
ally be
tion.
used in combination
e tannages. Syntans
ther than tanning
Syntan
Synthetic tanning mat
with vegetable, minerav
are almost exclusively u
operations.
Tannin
The chemicals derived from the leact^inrf of bark, nuts, or
other vegetablex^ttcrfe^ials used in the^'vegetable tanning
process.
Tanyard
That portion
tanning are
Toggling
per
ich the bating, pickling, and
fes or skins.
in which sltins are kept in a stretched position
called toggles. The skin is attached to a
which is slid into a drying oven.
148
-------
(or
Total Dissolved Solids (TDS)
The total amount of dissolved materials
in wastewater. Expressed in mg/1.
Total Solids (TS)
The total amount of both suspended and dissolved m
wastewater. Expressed in mg/1.
and inorganic)
Trimming
The removal of the ragged edges
and skins either before or after
accomplished by workers using k
Trimmings
The hide and leather scraps produced
operation.
Unhairing
The process where the
Volatile Solids
Solids, dissolved or suspe
and during stabilization
the BODS.
iferior portions of hides
Trimming is normally
trimming
emoved from the hide.
Weir
A control dev
measurement
exe
rimarily organic
cant portion of
in a channel or tank which facilitates
f the water flow.
149
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CONVERSIONS
Multiply (English Units)
English Unit Abbreviation
acre
acre-feet
British Thermal Unit
British Thermal Unit/pound
cubic feet/minute
cubic feet/second
cubic feet
cubic feet
cubic inches
degree Fahrenheit
feet
gallon
gallon/minute
horsepower
inches
inches of mercury
pounds
million gallons/day
mile
pound/square inch (gauge)
square feet
square inches
tons (short)
yard
•Actual conversion, not aNaultiplier
by
Conversion
Abbreviation
To Obtain (MeO^c Units)/
Metric Unit
hectares
cubic meters
kilogram-calories
kilogram calories/kilogram
cubic meters/minute
cubic meters/minute
cubic meters
lifcfc
cubic/centimeters
4e Centigrade
meters
liters
liters/second
kilowatts
centimeters
atmospheres
kilograms
cubic meters/day
kilometer
atmospheres (absolute)
square meters
square centimeters
metric tons (1000 kilograms)
meters
150
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