Leather and Leather Products - P2RIC

Industrial Resource Recovery Practices:

Leather and Leather Products (SIC 31)

February 1982

Prepared for: U.S. Environmental Protection Agency

Office of Solid Waste and Emergency Response

Prepared by: JRB Associates

ACKNOWLEDGMENTS

JRB A s s o c i a t e s prepared t h i s r e p o r t f o r t h e EPA's O f f i c e of S o l i d Waste

and Emergency Response under t h e Headquar ters Techn ica l A s s i s t a n c e P a n e l s

Program. The r e p o r t was prepared by Br ian Burgher, V i r g i n i a Hodge, and Joshua

Margol is wi th suppor t from Richard P a n n e l l and Richard Richards .

The EPA P r o j e c t O f f i c e r was Doug Ruby and t h e EPA Task Manager w a s Mike

P e t r u s k a . JRB is a l s o g r a t e f u l t o Ms. Eleanor Talmadge, D r . Robert L o l l a r ,

M r . Eugene K i l i k , and o t h e r members of t h e Tanners ' Counci l of America f o r

t h e i r a s s i s t a n c e and in fo rmat ion .

TABLE OF C O N f i N T S

EXECUTIVE SUMMARY

Page

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1.0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

2.0 LEATHER AND LEATHER PRODUCTS INDUSTRY OVERVIEW . . . . . . . . . . . 2-1

2.1 INDUSTRY CHAWCTERIZATION . . . . . . . . . . . . . . . . . . . 2-3 2 . 1 . 1 S i z e of t h e I n d u s t r y . . . . . . . . . . . . . . . . . . 2-3 2 . 1 . 2 S t r u c t u r e and Organ i za t i on of t h e I n d u s t r y . . . . . . . 2-5 2 . 1 . 3 Raw M a t e r i a l s . . . . . . . . . . . . . . . . . . . . . 2-6 2.1 .4 I n d u s t r y Trends . . . . . . . . . . . . . . . . . . . . 2-7

2 . 2 TANNING PROCESSES FOR ANIMAL HIDES AND SKINS . . . . . . . . . 2-10

2 . 2 . 3 P r o c e s s i n g S t e p s f o r a Sheepskin Tannery . . . . . . . . 2-20 2 . 2 . 4 P roce s s ing S t e p s f o r a P i g s k i n Tannery . . . . . . . . . 2-21

2 .3 WASTE STREAM CHARACTERISTICS . . . . . . . . . . . . . . . . . 2-22

2 . 2 . 1 P roce s s ing S t e p s f o r a C a t t l e h i d e Tannery (Chrome) . . . 2-11 2 . 2 . 2 P roce s s ing S t e p s f o r a C a t t l e h i d e Tannery (Vege tab le ) . 2-19

2 .4 WASTE STREAM QUANTIFICATION . . . . . . . . . . . . . . . . . . 2-26

2.5 POTENTIALLY HAZARDOUS WASTE STREAMS . . . . . . . . . . . . . . 2-30

3.0 STATE-OF-THE-ART OF RESOURCE RECOVERY I N THE LEATHER AND LEATHER PRODUCTS INDUSTRY . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3 .1 MATRIX DEVELOPMENT AND STRUCTURE . . . . . . . . . . . . . . . 3-1 3 .1 .1 Mat r ix Waste Streams . . . . . . . . . . . . . . . . . . 3-2 3 .1 .2 Mat r ix Resource Recovery Technologies . . . . . . . . . 3-2

M a t e r i a l T r a n s f e r Codes . . . . . . . . . . . . . . . . 3-6 3 .1 .3 Mat r ix Technology Development S tage and Waste

3 . 2 MATRIX APPLICATION . . . . . . . . . . . . . . . . . . . . . . 3-8

4 .0 RESOURCE RECOVERY TECHNOLOGY DESCRIPTIONS . . . . . . . . . . . . . 4-1

4 . 1 DIRECT R E C Y C L I N G . . . . . . . . . . . . . . . . . . . . . . . 4-1 4 .1 .1 S p i l l s from Bichromate Reduct ion . . . . . . . . . . . . 4-3

4 . 1 . 4 Spent Bate Wash Water . . . . . . . . . . . . . . . . . 4-8

4 . 1 . 6 Spent Chrome Tanning Liquor . . . . . . . . . . . . . . 4-10

4 .1 .2 Spent Soak Water . . . . . . . . . . . . . . . . . . . . 4-4 4 .1 .3 Spent Unha i r ing Liquor . . . . . . . . . . . . . . . . . 4-5

4 .1 .5 Spent P i c k l e Liquor . . . . . . . . . . . . . . . . . . 4-9

iii

TABLE OF CONTENTS (Continued)

Page . 4.1.7 Spent Vegetable Tanning Liquor . . . . . . . . . . . . . 4-14

Waste Streams . . . . . . . . . . . . . . . . . . . . . 4-16 4 .1 .8 Additional Tannery and Leather Product Manufacturing

4 .2 CHROME RECOVERY . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 Precipitation . . . . . . . . . . . . . . . . . . . . . 4 . 2 . 2 Ion Exchange . . . . . . . . . . . . . . . . . . . . . . 4 .2 .3 Acid Dissolution . . . . . . . . . . . . . . . . . . . . 4.2 .4 Incineration . . . . . . . . . . . . . . . . . . . . . . 4.2.5 Pyrolysis . . . . . . . . . .. . . . . . . . . . . . . . 4.2.6 Absorption . . . . . . . . . . . . . . . . . . . . . . . 4.2.7 Other Chrome Recovery Techniques . . . . . . . . . . . .

4-16 4-19 4-24 4-26 4-27 4-31 4-34 4-34

4.3 ENERGY RECOVERY . . . . . . . . . . . . . . . . . . . . . . . . 4-36 4 .3 .1 Heat Exchange . . . . . . . . . . . . . . . . . . . . . 4-37 4.3.2 Incineration . . . . . . . . . . . . . . . . . . . . . . 4-39 4 . 3 . 3 Pyrolysis . . . . . . . . . . . . . . . . . . . . . . . 4-41

4 .4 PROTEIN RECOVERY . . . . . . . . . . . . . . . . . . . . . . . 4-42 4 . 4 . 1 Acid Precipitation . . . . . . . . . . . . . . . . . . . 4-44 4 .4 .2 Hydrolysis . . . . . . . . . . . . . . . . . . . . . . . 4-46 4 .4 .3 Ultrafiltration . . . . . . . . . . . . . . . . . . . . 4-47 4 .4 .4 Centrifugation . . . . . . . . . . . . . . . . . . . . . 4-49

4 .5 GREASE RECOVERY . . . . . . . . . . . . . . . . . . . . . . . . 4-50 4 .5 .1 Rendering . . . . . . . . . . . . . . . . . . . . . . . 4-51 4 .5 .2 Separation . . . . . . . . . . . . . . . . . . . . . . . 4-52

4 .6 SULFIDE RECOVERY BY ACIDIFICATION . . . . . . . . . . . . . . . 4-55

4.7 TANNIN RECOVERY BY ADSORPTION . . . . . . . . . . . . . . . . . 4-57

4.8 HAIR RECOVERY BY SCREENING . . . . . . . . . . . . . . . . . . 4-58

4 . 9 SOLVENT RECOVERY . . . . . . . . . . . . . . . . . . . . . . . 4-59

4.10 GAS RECOVERY BY FERMENTATION . . . . . . . . . . . . . . . . . 4-60

4 .11 ACTIVATED CARBON MANUFACTURE . . . . . . . . . . . . . . . . . 4-61

4.12 COLLAGEN PRODUCT MANUFACTURE . . . . . . . . . . . . . . . . . 4-63

4.13 FIBROUS PRODUCT MANUFACTURE . . . . . . . . . . . . . . . . . . 4-66

4.14 LEATHER PRODUCT MANUFACTURE . . . . . . . . . . . . . . . . . . 4-69

4.15 ISOLATION OF SOLIDS FOR FERTILIZER MANUFACTURE . . . . . . . . 4-71 d

iv

TABLE OF CONTENTS (Continued)

Page . 4.16 USE IN THE CONCRETE INDUSTRY . . . . . . . . . . . . . . . . . 4-74

4.17 USE AS A FILTER PRECOAT . . . . . . . . . . . . 1 . . . . . . . 4-75

4 .18 USE AS A SLUDGE CONDITIONER/VISCOSITY MODIFIER . . . . . . . . 4-76

4.19 USE IN FUNGICIDE AND BACTERICIDE INDUSTRY . . . . . . . . . . . 4-78

4.20 USE IN THE PLASTICS INDUSTRY . . . . . . . . . . . . . . . . . 4-78

4.21 USE AS POLLUTANT ABSORBANT . . . . . . . . . . . . . . . . . . 4-78

5 . 0 SELECTED RESOURCE RECOVERY PROCESSES AND WASTE MANAGEMENT APPROACHES 5-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 . 1 RECOVERY PROCESSES WITH POTENTIAL FOR

GREATER APPLICATION . . . . . . . . . . . . . . . . . . . . . . 5-1 5 . 1 . 1 Technological Selection Criterion . . . . . . . . . . . 5-3 5.1.2 Economic Selection Criterion . . . . . . . . . . . . . . 5-5 5 .1 .3 Regulatory Selection Criterion . . . . . . . . . . . . . 5-6 5 . 1 . 4 Institutional Selection Criterion . . . . . . . . . . . 5-8 5.1.5 Summary of Analysis . . . . . . . . . . . . . . . . . . 5-12

5 . 2 KEY AREAS FOR FURTHER RESEARCH . . . . . . . . . . . . . . . . 5-14

Facilities . . . . . . . . . . . . . . . . . . . . . . . 5-19 5.2.3 New Market/By-Product Development . . . . . . . . . . . 5-21

5.2.1 Emerging Technologies with Good Potential . . . . . . . 5-15 5.2.2 Intra-Industry Cooperation and Centralized

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . REFERENCES R- 1

BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GLOSSARY G-1

V

LIST OF TABLES

Table

2-1

2 -2

2-3

2 -4

2-5

2-6

3-1

5-1

Decline of Leather Tanning and Finishing Industry (SIC 3111). . Tannery Waste Stream Characteristics. . . . . . . . . . . . . . Tannery Solid Waste Generation, 1980. . . . . . . . . . . . . . Quantification of Tannery Water Usage . . . . . . . . . . . . . Complete Chrome Tannery (Hair Burn) Waste Stream Quantification. . . . . . . . . . . . . . . . . . . . . . . .. . Profile of 102 Tanning Facilities (SIC 3111) Notifying Under RCRA Hazardous Waste Requirements . . . . . . . . . . . . Summary of Resource Recovery Activities in SIC 31 . . . . . . . Waste Characteristics and Suggested Industrial Use Sectors . .

Page

2-8

2-23

2-27

2-28

-

2-29

2-32

3-9

5-22

v i

L I S T OF FIGURES

F i g u r e

1 S t a t u s of Resource Recovery i n t h e Lea the r and Lea the r P roduc t s I n d u s t r y (SIC 31) . . . . . . . . . . . . . . . . . . .

2- 1 General P rocess Flow Diagram for Lea ther Tanning and F i n i s h i n g I n d u s t r y . . . . . . . . . . . . . . . . . . . . . . .

3- 1 S t a t u s of Resource Recovery i n t h e Lea the r and Lea the r P roduc t s I n d u s t r y (SIC 31). . . . . . . . . . . . . . . . . . .

5- 1 Technological Advantages and Disadvantages of S e l e c t e d Resource Recovery Processes . . . . . . . . . . . . . . . . . .

5-2 Economic Advantages and Disadvantages of S e l e c t e d Resource Recovery P r o c e s s e s . . . . . . . . . . . . . . . . . . . . . . . Regulatory Advantages and Disadvantages of S e l e c t e d Resource Recovery P r o c e s s e s . . . . . . . . . . . . . . . . . . . . . . .

5-3

5-4 I n s t i t u t i o n a l Advantages and Disadvantages of S e l e c t e d Resource Recovery Processes . . . . . . . . . . . . . . . . . .

- 5- 5 Overview of S e l e c t e d Resource Recovery P r o c e s s e s . . . . . . . .

Page

e5-5

2-12

3-3

5-4

5-7

5-9

5-1 1

5-1 3

v i i

EXECUTIVE SUMMARY

This report, which was prepared for the U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response, details the current

state-of-the-art of resource recovery practices in the Leather and Leather

Products Industry (SIC 31). It is one of a series of such reports that summarizes information on industrial resource recovery practices currently used

or under development in 11 industry categories. This information was obtained through examination of pertinent literature, contacts with knowledgeable

industry professionals, government officials, trade associations, research organizations, and engineering firms. All of this information is included in

a comprehensive industrial resource recovery library at the EPA as part of this project.

Industry Perspective

The Leather and Leather Products Industry is composed of seven sub- industries. The industry as a whole can be broken down into two broad

categories: leather tanning axid finishing and leather product manufacture. Leather tanning and finishing (SIC 311) includes those facilities that are

involved in processing raw animal skins into finished leather. Wastes from these processes are the most diverse and voluminous of the industry and thus

represent the greatest area of resource recovery potential. These wastes are, therefore, the focus of this study.

Leather product manufacture includes those facilities that incorporate

finished leather into the following manufactured products:

0' Boot and shoe cut stock and findings (SIC 313) 0 Footwear, except rubber (SIC 314)

0 Leather gloves and mittens (S IC 315) 0 Luggage ( S I C 316)

0 Handbags and other personal leather goods (SIC 317) 0 Miscellaneous leather goods (SIC 319).

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Wastes from this industry segment primarily consist of leather "scrap" and

solvents and are similar in nature to many le.ather tanning and finishing wastes. Recovery of these wastes is addressed to a lesser extent.

The leather tanning and finishing segment of the industry is composed of

approximately 188 establishments that process animal hides and skins into leather. These establishments are typically small, family-owned facilities

whose physical structures are relatively old. Most of the facilities follow traditional practices and techniques resulting from many years of processing

experience.

Tanneries are relatively independent, in terms of ownership, of their raw material suppliers and product purchasers. Thus, the leather industry lacks

vertical integration. Tanneries also lack diversification in that they tend to be specialized as to the type of animal hide or skin processed and the

properties of the leather produced.

Cattlehides are the m;.jor raw material for leather manufacture, repre-

The senting approximately 90 percent of the 17 .6 million equivalent hides.

remaining 10 percent include sheepskin, pigskin, goat, reptile, and a number of exotic skins.

Tannery Processes

The tanning of animal hides and skins involve four major processing

areas: beamhouse, tanyard, retan, and finish. The beamhouse operations clean

the hide of unwanted materials and prepare it for tanning. The tanyard operations further prepare the cleaned, unhaired hide for tanning as well as

shaping the hide sections into uniform dimensions following tanning. Retan processes impart special characteristics to the hide through additional

tanning, coloring, and lubricating operations. Finally, the finishing process

involves a number of mechanical operations designed to create a uniform

product with characteristics necessary for use in leather products.

Any one tannery may include all of the major processing areas or only some of them. Additionally, these process areas include a number of opera-

tions that may be varied depending on the type of hide or skin being

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processed, the desired characteristics of the leather, and tannery-specific

practices. characteristics and materials content of the various hides or skins being

tanned as well as the type of tanning agents used.

These variations are primarily due to differences in the physical

Two types of tanning agents are currently in use: vegetable tannins and trivalent chromium. Vegetable tanning, an older, more traditional tanning

method, uses tannin derived from tree bark; at present, this method is generally used for the manufacture of heavy leather from cattlehides.

tanning is a newer, more rapid process; it is currently the most widely used method for tanning almost all skin and hide types as it is more versatile and

imparts a better combination of chemical and physical properties to leather.

Chrome

Resource Recovery Practices

Twenty-seven waste streams in the leather and leather products industry

have been identified to which 31 resource recovery technologies are, or

theoretically could be, applied. The resource recovery technologies fall into

three major categories:

Recycling of waste streams for reuse of valuable components Treatment of waste streams to remove and recover specific materials

e Use of wastes in other manufacturing processes or products.

These recovery activities involve the recovery/reuse of a number of resources including, but not limited to:

e Process chemicals (lime, sulfide, chrome, tannin)

Solvents e Proteins

e Grease e Hair

e Energy.

The state-of-the-art of resource recovery in the industry was determined based on evaluation of information from literature and knowledgeable industry

\v

ES-3

professionals.

resource recovery processes, the material being recovered, sources of waste material, impediments to current use or further development of the process,

and potential for more widespread use.

This evaluation involved examination of each of the identified

The evaluation of the state-of-the-art of the 31 resource recovery processes is summarized in a matrix (Figure 11, which is defined by the following four study areas:

e Leather industry waste streams (horizontal axis)

e Applicable resource recovery technologies (vertical axis)

e State of development of the resource recovery technologies as applied to specific waste streams (numerical matrix code)

Transfer and use of recovered materials (alphabetical matrix code). e

The state-of-the-art of the recovery technologies varies in application throughout the indrstry. Forty-four percent of the recovery technologies are

used on an industrial scale, while another 44 percent are in the demonstration

or test stage. The remaining 12 percent are only proposed recovery

activities. Additionally, the majority of the wastes are transferred for

recoveryfreuse either within the generating facility or between the generating facility and a facility in another industry.

Activities with Potential for Further Implementation

Of the 31 resource recovery processes evaluated, 12 processes appear to

have the most potential f o r further application within the industry at this

time :

Direct recycling

Chrome recovery by precipitation

e Heat exchange

e Protein recovery by acid precipitation

e Protein recovery by hydrolysis

e Grease recovery by rendering

ES-4

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Grease recovery by separation Sulfide recovery by acidification

Collagen product manufacture

Fibrous product manufacture

Leather product manufacture

Isolation of solids for fertilizer (using leather scrap).

These 12 resource recovery processes were selected based upon favorable . combinations of technological, economic, regulatory, and institutional

factors. Although most of these recovery processes must all overcome some

sort of disadvantage or problem, their current state of development and their

advancement potential more readily lend them to rapid implementation than the other 19 processes.

Three of the 12 key recovery processes appear to have overwhelming poten-

tial for implementation: direct recycling, chrome recovery by precipitation,

and heat exchange. These processes are supported, at a minimum, by techno-

logical, economic, and regulatory advantages.

*

Additionally, a number of promising resource recovery methods have been

the subject of only limited research and analysis as to their application and development within the leather and leather products industry. These methods

fall into three categories:

Technologies that have not been supported by the kind of research merited by their potential

Waste management approaches requiring intra-industry cooperation and centralized facilities

e New by-productlwaste market development.

Recovery processes and waste management approaches in these categories merit further research to adequately assess their potential for greater application

and development.

ES-7

1 .0 INTRODUCTION

Th i s s tudy addresses r e s o u r c e recovery p r a c t i c e s i n t h e Lea the r and

Lea the r P roduc t s I n d u s t r y (SIC 3 1 ) . It is one of a series of s t u d i e s

performed f o r U.S. EPA's O f f i c e of S o l i d Waste and Emergency Response, t h a t

examine such p r a c t i c e s w i t h i n v a r i o u s i n d u s t r y groups . The s p e c i f i c

o b j e c t i v e s of t h e s e s t u d i e s are:

1. I n d i v i d u a l i n d u s t r y r e p o r t s which summarize t h e c u r r e n t s t a t e- of- the- a r t of r e source recovery and e v a l u a t e t h e p o t e n t i a l f o r advancement o f such a c t i v i t i e s .

2 . A comprehensive i n d u s t r i a l waste r e s o u r c e recovery l i b r a r y encompassing s p e c i f i e d i n d u s t r y groups .

The completion of t h e Lea the r and L e a t h e r P roduc t s I n d u s t r y s t u d y

involved c o l l e c t i n g a v a i l a b l e in fo rmat ion concerning r e s o u r c e recovery through

e x t e n s i v e l i t e r a t u r e s e a r c h e s and c o n t a c t wi th knowledgable i n d u s t r y profes-

s i o n a l s , i n c l u d i n g government o f f i c i a l s , t r a d e a s s o c i a t i o n s , r e s e a r c h and

e n g i n e e r i n g f i rms, l e a t h e r t a n n e r i e s , and l e a t h e r l l e a t h e r - d e r i v e d product

manufac tu re r s . Th i s in fo rmat ion was reviewed and a s s i m i l a t e d t o i d e n t i f y t h e

c u r r e n t r e source recovery p r a c t i c e s used w i t h i n t h e l e a t h e r i n d u s t r y , For t h e

purpose of t h i s s tudy , r e source recovery i s de f ined as:

e T r a n s f e r of m a t e r i a l s between d i f f e r e n t f a c i l i t i e s ( i n t h e same or d i f f e r e n t i n d u s t r i e s ) i n which t h e waste r e c e i v e r u t i l i z e s t h e waste i n materials or energy recovery o p e r a t i o n s

e Reuse of waste materials w i t h i n t h e same f a c i l i t y for m a t e r i a l s or energy recovery o p e r a t i o n s .

Each resource recovery p r a c t i c e is c l a s s i f i e d accord ing t o t h e waste

s t reams t o which i t is a p p l i c a b l e , t h e use of t h e recovered mater ia l , and t h e

c u r r e n t s t a g e of development of t h e recovery p r a c t i c e . Th i s in fo rmat ion is

s u m a r i z e d and p resen ted i n a m a t r i x which p r e s e n t s t h e c u r r e n t s t a t e- of- the-

a r t of r e source recovery w i t h i n t h e l e a t h e r and l e a t h e r p roduc t s i n d u s t r y .

1-1

The information presented in the matrix is then evaluated with regard to

the potential for advancing the state-of-the-art of resource recovery. Those

resource recovery practices with the greatest potential for advancement are identified and evaluated.

This report presents the results of this intensive investigation.

Section 2.0 presents a discussion of the leather and leather products

industry, including an overview of the leather industry with regard to size, number of facilities, and current status; a detailed description of the

leather tanning process; and a discussion of waste streams generated by the leather industry.

of resource recovery in the industry. the matrix can be used to analyze both the current status of resource recovery

and the potential for advancement of the state-of-the-art. Descriptions of each resource recovery technology are presented in Section 4.0.

Section 4 .0 answers the following questions:

Section 3.0 presents a matrix which summarizes the status

It also includes an explanation of how

Specifically,

e

How does the process work?

What are the key impediments to greater use of this technology?

What potential exists for further advancement of the recovery process?

What resource does the process recover from the waste stream?

Section 5 . 0 highlights those resource recovery practices identified in Section 4 .0 that have the greatest potential for increased application within the industry. A list of references, a bibliography, and a glossary of terms are also presented.

1-2

2.0 LEATHER AND LEATHER PRODUCTS INDUSTRY OVERVIEW

The Standard Industrial Classification (SIC) Manual classifies the

leather and leather products industry as Major Group 31. This classification

encompasses the tanning and finishing of animal hides to produce leather as

well as the use of leather in the manufacture of various products. The SIC Manual divides the leather and leather products industry into the following

groups :

0 Leather tanning and finishing (SIC 311) 0 Boot and shoe cut stock and findings (SIC 313)

0 Footwear, except rubber (SIC 314) 0 Leather gloves and mittens (SIC 315)

0 Luggage (SIC 316) 0 Handbags and other personal leather goods (SIC 317).

Miscellaneous leather goods, such as industrial belting, saddles, harnesses,

- and leashes, are classified in SIC 319. There are currently no listings f o r S I C 312 and 318.

The leather tanning and finishing segment of the industry (SIC 311)

converts the raw animal hides to a leather material suitable for use in numerous consumer and industrial products. This segment of the industry

conducts the major- processing operations yithin the industry as a whole, and, thus , produces the greatest volume and variety of potentially recoverable materials even though the number of facilities is significantly less than the number engaged in the manufacture of leather products. Additionally, many

of the wastes generated in leather product manufacture are similar to those generated in leather tanning and finishing (e.g. , solvents, leather scrap, and trim). Consequently, this study of resource recovery practices used in the leather and leather products industry focuses on the leather tanning and

finishing segment. The practices of the leather products segment of the industry are also analyzed, although to a lesser extent.

2-1

Leather tanning and finishing facilities in the United States are

generally small, family-owned establishments. Although the processing equipment may be relatively modern, the facilities housing the equipment are

often quite old. vertical integration with its suppliers (packinghouses) and product buyers

(leather product manufacturers). as to the raw material processed, the type of tanning agent used, and the type

of leather produced. dependent on their sources of raw material and the market for their products,

This segment of the industry characteristically lacks

Leather tanners are also quite specialized

Thus, tanners are not very diversified and are highly

Leather tanning is the process by which animal hides, primarily cattle-

hide, sheepskin, and pigskin, are converted into leather. This generally involves chemical fixation of protein fibers in the hide or skin to prevent

decay, as well as chemical and mechanical treatment to produce a leather with very specific properties, such as softness, flexibility, color, and texture.

The tanning and finishing of leather involves four major processing

areas :

e Beamhouse - preparation of animal hides or skins for tanning. Includes , where' appropriate, washing, hair removal, and degreasing of the hides or skins.

e Tanyard - fixation of animal hides or skins. Generally involves acidification, tanning, and splitting of hides or skins.

e Retan - treatment of tanned hides or skins t o impart specific qualities. Includes a second tanning, coloring, and oiling.

e Finish - final treatment of hides or skins. Involves removal of surficial imperfections and application of coatings and finishes.

.--

The sequence of the processing steps within each area varies according to the

type of hide or skin, processing requirements, and the individual tanner.

2-2

This section provides an overview of the leather and leather products

industry, with a focus on the leather tanning and finishing segment. The

various aspects of the leather industry addressed in this section are:

0 Characterization of the industry as to its size, raw materials, and processing operations (Section 2.1)

0 Characterization of the tanning processes for animal hides and skins (Section 2.2)

0 Characterization of materials lost in the various waste streams (Section 2.3)

0 Characterization of the quantity of materials lost during processing (Section 2.4)

0 Characterization of potential hazardous wastes (Section 2 . 5 ) .

2.1 INDUSTRY CHARACTERIZATION

The tanning of animal skins to produce leather is a craft that has been

practiced for several thousand years. In the United States, leather tanning

and finishing has been practiced in an industrial setting since the 1600's. Although modern facilities, processing techniques, and chemicals have been

incorporated throughout the industry, traditional processing sequences and product specialization still dominate. This section addresses these and other

characteristics of the leather industry.

2.1.1 Size of the Industry

In 1981, Dun and Bradstreet reported that there were 5,593 establishments

Approx- classified in the leather and leather products industry (SIC 31) 111. imately 625 (11.2 percent) of these establishments were classified as leather tanners and finishers ( S I C 311). The remaining establishments manufactured

various leather products. Included in the leather products classification were the following goods and number of manufacturing facilities:

0 Footwear, boot and shoe cut stock (273)

0 House slippers (105) 0 Men's shoes except athletic (413)

0 Ladies' shoes except athletic ( 4 5 3 )

2-3

0 Footwear except rubber (366)

0 Leather gloves and mittens (134)

0 Luggage (477)

0 Women's handbags (781) 0 Leather goods, personal, not elsewhere classified (765)

0 Leather goods, not elsewhere classified (1,201).

It should be noted that these data classifications are based on the category definitions in the SIC Manual. These definitions allow for multiple listings

of establishments. For example, a facility manufacturing products in three different categories is counted in each category. Thus, one facility,

involved in three product areas, is reflected in the data as three separate facilities. In addition, the category definitions are sufficiently broad to

allow the inclusion of small, related, support, o r non-commercial facilities that belong in the industry as a whole, but are not actually involved in

product manufacture o r waste stream generation.

Although Dun and Bradstreet provide the most recent data on the size of the industry, the classifications used to define industry segments are too

broad for the purposes of this report. Other data suggest that there are fewer actual industrial facilities generating recoverable waste. For example,

in 1972, the Bureau of Census, which also uses classifications from the S I C

Manual to define the industry, reported that there were 1,682 establishments

in the leathe; and leather products industry [2]. Of this total, 517 establishments (30 percent) were classified as leather tanners and finishers.

Contained within this number were tanners, converters, one man sales offices, hobbyists, and taxidermists. Of these 517, only 298 establishments were

considered to be actually involved in the manufacture of leather from hides and skins on an industrial level [ 3 ] . Only 223 of these 298 employed 20 or more persons 1-41.

Other data indicate that there may be even fewer industrial-level leather

tanning facilities in existence. In 1977, the Bureau of Census reported that

there were 191 leather tanning establishments employing 20 or more persons

[ 4 , 5 1 . A 1978 ROIT Corporation study identified 124 establishments as leather

2 -4

tanneries [6]; this estimate excludes those tanneries that do not generate

untanned hide waste 171. SCI Engineers estimated that in 1979 there were 154 tanneries in existence employing 40 or more persons and processing at least

200 hides per day [81. Also in 1979, the EPA estimated that there were 188 tanneries; this estimate excludes finishers, converters, and non-production establishments [2]. Conversations with representatives of the Tanners'

Council of America suggest that this estimate (188) approximates the current number of tanneries [91 . 0

2 . 1 . 2 Structure and Organization of the Industry

Despite the variations regarding the actual number of tanning facilities,

most sources agree on their geographical distribution. Most of the leather tanning and finishing establishments are located in the Northeast region of

the country, particularly in Massachusetts and New York. The North Central part of the country has the second greatest concentration, the South has the

third greatest, and the West has the fewest number of such establishments

[2,6,81. The quantity of hides (or hide equivalents) processed in each area

of the country correlates with the concentrations of the tanning and finishing establishments.

8

The leather tanning and finishing segment of the industry has been

historically characterized by small, family-owned facilities that are relatively old. However, over the past decade there has also been a trend

towards acquisition of these tanneries by publicly held corporations [lo]. The size of a facility is generally categorized in terms of the number of

employees; the smallest employs about five people and the largest employs

about 500 ill]. The majority of the facilities (67 percent) are over

50 years old and very few (1 percent) are less than 10 years old [61.

Although the structures housing the tanning processes are quite old, most

tanners have modernized their processing equipment; exceptions to this

modernization effort include the vessels used in beamhouse, tanning, and retan operations [2,71. Even so , approximately 80 percent of the plants are

believed to be using a level of technology equivalent to 1963 or older. This v technological lag is largely attributable to the predominance of traditional

2 -5

practices and techniques resulting from many years of processing experience

[ 2 1 .

Leather tanners and finishers are also characterized by a lack of

vertical integration within the industry and a lack of diversification within

facilities [2 ,3 ] . In many industries, a processing facility is highly inte-

grated with its raw material suppliers and product purchasers. In only a very

few instances within the leather industry is a leather tannery owned by, or an owner of, a slaughterhouse (raw material supplier) or leather product manu-

facturer (product purchaser). For the most part, tanners depend on regular suppliers of hides and skins, and manufacture a product with characteristics required by a specific customer.

Additionally, tanners tend to be specialized as to the type of animal

hide or skin processed and the properties of the leather produced.

process requirements vary for each type of hide or skin and finished leather product, tanners may be reluctant to switch from processing one hide type to

another. Such a change would require significant capital investment, process restructuring, and market development [ 3 , 7 ] . This has been a key factor in

the lack of diversification among tanners. The diversity that does exist comes from the ability of some tanneries to impart a number of physical and

mechanical properties to the processed hide enabling them to sell their product in a number of markets [ 3 ] .

Since

2 . 1 . 3 Raw Materials

According to the Tanners’ Council of America, 17.6 million equivalent hides were processed into leather in 1980 [12]. Approximately 90 percent of

the hides processed were cattlehide; the remainder were, in relative order of magnitude, sheepskin, pigskin, goat, and reptile [ 91 . A number of other hides

or skins are processed on a much smaller scale including, but not limited to, horse, deer, elk, rabbit, ostrich, kangaroo, peccary, and carpincho. Less

than 10 tanneries process miscellaneous and exotic leathers.

The leather tanning and finishing segment of the industry is raw materials oriented. A major component of the capital requirements for these

2-6

facilities goes toward maintaining relatively large quantities of hides and

skins. Between 1965 and 1976, the cost of raw materials, primarily hides and skins, averaged 62 percent of leather sales. With increasing prices for raw

hides and skins, the capital required to maintain sufficient inhouse supplies will continue to consume a significant portion of sales [2,131.

2.1.4 Industry Trends

Published information shows a historical decline in the number of establishments in and hides processed by the leather tanning industry. Shuttleworth

traced this trend for the 110 years spanning 1865 to 1975, during which time there was a decrease in the number of facilities from 7,500 to approximately

200 [14]. Data provided by recent 5 year census reports confirm a continuation of this downward decline in the industry. These data are presented in .

Table 2-1. From 1963 to 1977, there was an 11 percent decline in the number of companies in SIC 311. From 1958 to 1977, there was an associated drop of

20 percent in the number of industrial establishments, and a 32 percent decrease in the number of such establishments employing 20 or more persons. This decline in the number of leather tanning facilities is expected to

continue into 1982 [4]. Though there has been an associated ;rend towards

larger facilities with greater production capacities, the actual number of

hides processed has also been declining since as early as 1965 [21.

The decline in the number of plants and production volume is the result

of increased hide prices and processing costs, and decreases in the demand for American leather. These changes are based primarily on the following five

factors :

0 Decreased availability of domestic cattlehides for American tanners

0 Decreased availability of imported cattlehides

0 Decreased domestic demand for leather in traditional markets 0 Competition from foreign tanners

0 Stricter pollution abatement regulations.

Increased foreign demand for American cattlehides has contributed to a decrease in the number of raw hides available to American tanners. Since at

2-7

Table 2-1. Decline of Leather Tanning and Finishing Industry (SIC 3111)

Number of Establishments Number of Number of Employing 20 or More

Year Companies Est ab1 i shment s Persons

1958 NA

1963 48 2

1967 474

1972 46 8

1977 42 7

578

525

519

517

465

280

256

2 58

223

191

NA = not available

Source: 4

2-8

least 1963, there has been a general increase in U.S. cattlehide exports.

This trend, periodically interrupted in the late 1960's and mid-1970'~~ has

contributed to a marked increase in hide prices which has not been balanced by

a similar rise in finished leather prices [5,15]. Some of the principal

competitors for domestic hides are Japan, Korea, Mexico, Italy, Canada, and

Romania [SI.

In addition, foreign sources of raw hides (including cattle, sheep, and

pig) are being reduced due to the internalization of hide processing and tanning within foreign countries. For example, while foreign countries bought 20 percent of American hides in 1979, they supplied only 3 percent of the

American market. Among those traditional exporters of hides that have inter- nalized their leather tanning industries are India, Brazil, and Argentina.

This decrease in hide supply from imported sources, in addition to that caused by a reduction in domestic slaughter since 1975, has forced American tanners

to compete with foreign buyers for a shrinking supply of more costly raw hides [2,5,151.

The domestic shoe manufacturing industry, which has traditionally been

the primary consumer of leather, is also declining. Demand for leather in the shoe industry has decreased over the years due to displacement of the domestic

industry by imported shoes. This decrease in domestic shoe manufacturing, coupled with increased use of synthetic materials as substitutes for leather

in American-made shoes, has resulted in a marked decrease in the demand for leather in this industry segment [ 2 ] .

Imports of leather from foreign tanneries have given the consumer and

domestjc leather product manufacturer an additional source of leather that is both less expensive and of comparable quality to domestic leather. To respond

to this competitive atmosphere, domestic tanners have been forced to lower prices of their finished products in spite of increased raw materials costs.

Finally, the financial impact of complying with stricter pollution

abatement regulations has also contributed to the decline in the domestic

tanning industry [16]. The standards and g o a l s outlined in the Federal Water

2 -9

Pollution Control Act ( 1 9 7 2 ) and Resource Conservation and Recovery Act ( 1 9 7 6 )

have forced tanners to spend more funds on waste treatment and disposal. These costs generally weigh most heavily on tanners operating older facilities

originally designed to dispose of effluent with little or no treatment. The necessary modifications in process and end-of-pipe treatment are forcing

tanners to incur new operating expenses while facing a declining market for their product [16].

2 . 2 TANNING PROCESSES FOR ANIMAL HIDES AND SKINS

There are four major process areas involved in the tanning of animal hides and skins: beamhouse, tanyard, retan, and finish. Any one tannery may

include all of the major processing areas o r only some of them. Additionally, these process areas include a number of operations that may be varied depend-

ing on the type of hide o r skin being processed, the desired Characteristics of the leather, and tannery-specific practices.

Apart from the type of hide or skin being processed, one of the major factors affecting the sequence of tannery processes and the characteristics of

the leather is the tanning agent used. Chrome chemicals and vegetable

extracts are the two substances currently used in tanning animal hides and

skins. Vegetable tanning, an older and more traditional tanning method,

utilizes tannin derived from tree bark (often chestnut or wattle). At present, this method is generally used f o r the manufacture of heavy leather.

Chrome tanning, which utilizes trivalent chromium (Cr+3), is a newer,

more rapid process for producing leather. Chrome tanning is currently the

preferred tanning technique. Besides being more rapid, it is also more

versatile and imparts a better combination of chemical and physical properties to leather than leather tanned with vegetable tanning agents (3,111.

Hexavalent chromium (Cr+6) was formerly widely purchased by chrome

tanners and reduced to trivalent chromium for use in chrome tanning. Due to the toxicity of this chemical, the dangers involved in handling it, and lower

chemical costs associated with the use of trivalent chromium (which requires

no pretreatment), hexavalent chromium is not generally purchased by leather

tanners. However, larger tanneries may find it less expensive to purchase

' 2-10

hexavalent chromium and reduce it on-site for use in the tanning process

[7,101. Also, certain market conditions may favor the purchase of hexavalent c hr om i um .

For this report , the various leather manufacturing processes have been divided into four major types of tanneries:

0 Cattlehide (chrome) 0 Cattlehide (vegetable)

0 Sheepskin 0 Pigskin.

These four types of tanneries represent the major variations found within the

industry.

presented in detail in the following sections.

The processing operations included under each type of tannery are

2 . 2 . 1 Processing Steps for a Cattlehide Tannery (Chrome) --

A typical chrome cattlehide tannery involves four general processing operations: beamhouse, tanyard, retan, and finish. These major processes

involve a number of subprocesses. Figure 2-1 presents a general flow diagram o f the leather tanning and finishing steps. Each tannery is somewhat unique

in its operation in that there may be slight variations in the sequence of

processes and in the processes themselves; these variations largely depend on

the desired properties of the finished leather. Thus, the following discussion of chrome cattlehide tanning processes is a generalized process

description that is not meant to be specific to any one plant.

While most tanneries are considered to be complete (i.e., containing all

four major process areas), other tanneries contain only a few of the major

processes. cattlehides through the actual tanning operation; such establishments are

often referred to as through-the-blue because of the characteristic blue color of chrome tanned hides. Once these tanners have completed the tanning

process, the tanned hide is sent o r sold to another facility (a RetanIFinish

For example, there are a number of tanners that only process

- facility) that completes only the latter segment of major processing steps

2- 1 1

Beamhouse

lanyard

Retan, Color, Fatliquor

Finish

Source: 11

Receive b Store Hides 1

Side b Trim 7

Weigh 8 Sort v

Soak b Wash 1

Fleshing 1

Unhair Pulp I Save

1 1

Bate 1

Pickle 1

Tan 1

1 I I I

1 1 I

I

I I I

I Wrina I Split

1 Shave

I 1

Retan 1

Bleach Et Coloring 1

Fatliquoring 1

I I

I

1 I

1 I Setting Out 1

I 1

1

Toggling Vacuum 1 I I

I

I

I

Conditioning

1 Staking Et Dry Milling

1 Buffing

1 Finishing 8 Plating

7 Measure

1 Grade

I

1

1 1

I Ship I

Figure 2-1. General Process Flow Diagram for Leather Tanning and Finishing Industry

2-12

involving the finishing of the tanned hide. Some RetanIFinish facilities produce suede from the interior portion of cattlehides (the split) and thus

may also be called split tanners.

Although chrome cattlehide tanning facilities vary with respect to their

completeness, all utilize essentially identical processing operations and

sequence of processing steps. Thus, the process descriptions presented in

this section represent those contained in a generic complete chrome cattlehide

tannery as well as generic split, through-the-blue, retanlfinish, or other

incomplete tannery facilities.

2.2.1.1 Beamhouse

Beamhouse operations consist of side and trim, fleshing, and unhairing

steps. These processes, which take about 2 days, clean the hide of unwanted

materials, and prepare it for tanning.

Generally, the hides received at the tannery are already green salted or

brine cured. Bactericides are also applied to the hides during curing to

prevent decay [171. The curing processes are performed at the slaughterhouse,

packinghouse, or hide processing facility. In some instances, where tanneries are located near slaughterhouses, uncured hides may be received directly

[9 ,111 .

Side and Trim. The extremities of the hide are trinnned off and may be

shipped to glue, fertilizer, or animal feed supplement manufacturers. These

and other manufacturers value the trimmings for the collagen that can be

incorporated into various products. After trimming, the hide is cut along the

backbone t o produce two sides. The sides are then washed and soaked to restore moisture and to clean salt, blood, water-soluble proteins, manure, and

other contaminants from the hides. The soaking operation generally takes 12 to 24 hours [3,11,181.

Fleshing. This process removes the excess fat and muscle tissue (known

as fleshings) from the inside of the hide by a mechanical operation utilizing

rollers and rotating spiral blades. Fleshing may be done either at tanneries,

2-1 3

packinghouses, or hide processing facilities before shipment to tanneries.

Approximately 80 percent of the hides are fleshed at packinghouses [lo]. Refleshing at the tannery may occur as necessary. The fleshings may be sold

to plants for rendering or conversion into glue [3,11].

Unhairing. Unhairing, also known as liming, is the final subprocess within the beamhouse. It involves the use of lime (calcium hydroxide), sodium sulfhydrate, and sodium sulfide as depilatories to remove the hair from the hide. The hides are placed in vats containing an aqueous solution of

unhairing chemicals and agitated to loosen and remove the hair.

The rate of unhairing is controlled by the solution temperature, chemical concentration, and amount of agitation.

that the hair can be either completely removed from the hide and dissolved in the bath, or only loosened and removed by mechanical means.

involving complete hair removal, is termed the "hair burn" or "hair pulp" method and takes about 4 to 6 hours 1181. The second method, in which the

hair is only loosened, is termed the "hair save" method because the hair, which is scraped from the hide by an unhairing machine, can be recovered and sold (181.

These parameters can be varied such

The first method,

Equipment requirements for the two unhairing methods are very different.

Therefore, a tannery generally uses one method o r the other. However, some

plants have installed equipment that allows them to use either the hair save o r hair burn method depending upon the market for hair. The hair burn method

is currently the predominant unhairing technique in the United States because it has become, in most instances, uneconomical to recover, wash, bale, and

sell recovered hair in the face of declining markets [3,111.

The unhairing process does not always remove or loosen all of the hair on the hide. Also, the depilatory chemicals cause the hide to absorb enough

moisture to increase its thickness about two-fold, referred to as alkaline

swelling, and this may not occur uniformly throughout the hide. To resolve

these problems, the hides may be relimed to ensure complete hair removal and uniform swelling [3,11].

2-14

2 .2 .1 .2 Tanyard

I I

The tanyard p rocesses c o n s i s t of b a t i n g , p i c k l i n g , t a n n i n g , wr ing ing ,

s p l i t t i n g , and shav ing . These p rocesses f u r t h e r p repare t h e c l e a n e d , unhaired

h i d e f o r t ann ing as w e l l a s shape t h e h i d e s e c t i o n s i n t o uniform dimensions

a f t e r t ann ing . The e n t i r e t anyard p rocess u s u a l l y t a k e s one day.

Deliming and Ba t ing . Deliming removes any r e s i d u a l a l k a l i n e chemicals

used i n t h e unha i r ing p rocess . Ba t ing s e p a r a t e s t h e c o l l a g e n p r o t e i n f i b e r s

w i t h i n the h i d e and d e s t r o y s remaining h a i r r o o t s and unwanted pigments.

Deliming i s achieved by applying ammonium s u l f a t e or ammonium c h l o r i d e ; t h e s e

chemica l s r ender t h e r e s i d u a l l ime s o l u b l e s o i t can be washed from t h e h i d e s .

During t h i s p r o c e s s , s w e l l i n g d imin i shes and h i d e s r e g a i n t h e i r normal

t h i c k n e s s . Deliming chemicals a l s o a d j u s t t h e s o l u t i o n pH t o f a c i l i t a t e t h e

b a t i n g p rocess . The a c t u a l b a t i n g p rocess is achieved by t h e use of pancre-

a t i c enzymes ( r e f e r r e d t o as b a t e s ) . The p rocess u l t i m a t e l y g i v e s t h e h i d e a

c l e a n e r appearance and s o f t e r t e x t u r e . A f t e r b a t i n g i s completed, t h e h i d e s

a r e washed t o remove a l l u n d e s i r a b l e s u b s t a n c e s t h a t have been loosened o r

d i s s o l v e d [3,11,181.

I n t h e p a s t , de l iming and b a t i n g were two s e p a r a t e p r o c e s s e s . C u r r e n t l y ,

t h e s e p rocesses a r e performed s imul taneous ly u s i n g b a t e s c o n s i s t i n g of a

s o l u t i o n of p a n c r e a t i c enzymes and del iming chemica l s . Proper complet ion of

b a t i n g i s a f u n c t i o n of r e a c t i o n t i m e , amount of chemica l s , and t empera tu re .

Th i s b a t i n g p rocess a lone may t a k e from 1 t o 4 h o u r s , however, t h e r e a c t i o n

t i m e f o r t h e d u a l process may range from a few hours t o o v e r n i g h t [ 3 , 1 1 , 1 8 ] .

P i c k l i n g . The p i c k l i n g p rocess uses a mix tu re of s u l f u r i c a c i d and s a l t

o r b r n n e t o a c i d i f y t h e h i d e t o f a c i l i t a t e chrome t a n n i n g . Chrome i s much

more s o l u b l e under a c i d i c than a l k a l i n e c o n d i t i o n s . I f t h e h i d e s a r e

a l k a l i n e , chromium s a l t s w i l l p r e c i p i t a t e . P i c k l i n g a l s o p r e s e r v e s t h e

l e a t h e r and a l lows t h e h i d e t o be s t o r e d f o r long p e r i o d s of t i m e [ l l ] .

The a c i d is mixed wi th b r i n e t o prevent e x c e s s i v e a c i d s w e l l i n g of t h e

h i d e . However, some a c i d s w e l l i n g i s necessa ry s i n c e i t f a c i l i t a t e s t ann ing

by s e p a r a t i n g t h e c o l l a g e n f i b e r s ; t h i s a l lows f o r f u r t h e r complexing of

2-15

chrome by t h e h i d e .

few hours 1181.

Complete p e n e t r a t i o n of t h e a c i d s o l u t i o n o n l y t a k e s a

Tanning. Tanning i s t h e p rocess whereby t h e h i d e s are made i n t o a

product t h a t res i s t s decay or p u t r e f a c t i o n .

p h y s i c a l p r o p e r t i e s of t h e h i d e such as f l e x i b i l i t y and r e s i s t a n c e t o

a b r a s i o n , h e a t , and chemicals . Chrome t a n n i n g is by f a r t h e more common

method of t ann ing because of t h e s h o r t t i m e pe r iod i n which i t is accomplished

and t h e q u a l i t y of t h e r e s u l t i n g l e a t h e r p r o d u c t s [3 ,111. ’

Tanning a l s o improves t h e

Tanning can be c a r r i e d ou t i n paddle v a t s , r o t a t i n g drums, or h i d e

p r o c e s s o r s .

equipment. Some of t h e drums and h i d e p r o c e s s o r s may be used f o r more than

one p rocess ing s t e p .

nex t process commences.

The paddle v a t s and r o t a t i n g drums are o l d e r t y p e s of p r o c e s s i n g

I n such i n s t a n c e s , each s o l u t i o n i s d r a i n e d b e f o r e t h e

To t a n t h e h i d e s , a s o l u t i o n c o n t a i n i n g t r i v a l e n t chromium i s added t o

t h e drum and mixed w i t h t h e h i d e s .

c o n d i t i o n of the h i d e s , t h e drum i n t e r i o r , and t h e chemical s t a t e of t h e

s o l u t i o n [ l l ] . T r i v a l e n t chrome i s purchased as a chromium compound (chromium

s u l f a t e o r sodium dichromate) from chemical manufac tu re r s . I n some i n s t a n c e s ,

hexava len t chromium i s purchased by t a n n e r s and conver ted a t t h e t a n n e r y t o

t r i v a l e n t chromium by chemical r e d u c t i o n w i t h molasses o r d e x t r o s e and a c i d .

The pe r iod of mixing i s defermined by t h e

This p r a c t i c e may occur i n l a r g e t a n n e r i e s o r where where market c o n d i t i o n s

p rec lude t h e purchase of t r i v a l e n t chromium [3 ,7 ,10 ,11] .

Wringing. A f t e r chrome tann ing , t h e h i d e s are wrung mechan ica l ly by a

machine s i m i l a r t o a c l o t h e s wr inger t o remove excess m o i s t u r e .

p o i n t have a c h a r a c t e r i s t i c b l u e c o l o r from t h e chrome tann ing s o l u t i o n , and

are r e f e r r e d t o as wet- blue s t o c k [ l l ] .

Hides a t t h i s

S p l i t t i n g . Most c a t t l e h i d e s are t o o t h i c k f o r l e a t h e r product

manufacture .

h o r i z o n t a l band saw. S p l i t t i n g produces two p o r t i o n s of l e a t h e r , one w i t h a

g r a i n s i d e of uniform t h i c k n e s s , and a t h i n n e r g r a i n l e s s s i d e r e f e r r e d t o as a

There fo re , they a r e s p l i t u s i n g a machine s i m i l a r t o a

2-16

L

split. The split may be used in the manufacture of suede.

portions of the hide that cannot be split are shaved to remove any flesh remaining on the hide and to assure uniform thickness.

The thinner

The grain side is

to desired dimensions [3,111. further trimmed

2.2.1.3 Retan

The retann liquoring steps

ng operation consists of retanning, coloring, and fat-

These processes impart special characteristics to the hide.

Retan. Retanning is a second tanning process that is performed to give

the finished leather certain product-specific characteristics not achieved in

the initial tanning operation. The retanning agent may be chromium, vegetable extracts, or syntans (synthetic chemicals) and is selected t o provide specific

final product properties. variations in the chrome tanned hides, while syntans are used for white or

pastel leather because of their bleaching effect [ll].

For example, vegetable extracts serve to minimize

Color. Coloring is done in the same drums that are tTsed in retanning.

Typical dyes used are aniline-based. Variations in hide pigmentation and

depth of color penetration are factors that affect coloring of the hides. The

shade of the hide and the degree of color penetration are controlled by the pH

of the dye bath and the hide since the affinity of the dye for the hide fibers is a function of the pH [11,181.

Fatliquor. Fatliquoring is a process that reduces fiber cohesion during

drying, lubricates the hide, and replaces natural oils lost in previous processes. The fatliquoring process can be completed in approximately one

hour. Fatliquors can consist of vegetable, animal, o r synthetic oils. The quantity and type of oils used determine the firmness, flexibility, and

stretch of the final product [11,181.

2.2.1.4 Finish

The final major stage of chrome tanning is the finishing process, which includes a number of subprocesses designed to create a uniform product with

2-17

characteristics necessary for use in leather products.

include drying, conditioning, buffing, finishing, and plating.

The major subprocesses

Drying. The leather is subjected to a drying process to remove excess

moisture. The actual drying process is preceded by a setting-out operation

that smoothes and stretches the hide while squeezing out excess moisture. The

leather is then oven or vacuum dried. The leather may be secured in any of

three ways for the drying process:

Hanging--draping hides over a horizontal shaft Toggling--stretching the hides on a frame

Pasting--pasting hides onto plates.

Oven drying generally takes 4 to 7 hours, while vacuum drying takes only 3 to 9 minutes. However, undesirable shrinkage of the hide during vacuum drying,

in combination with other factors, has limited the use of this method [7 ,111.

Conditioning. Some moisture is restored to the dried leather through the conditioning process. This process entails spraying a water mist on the

hides, placing the hides in a watertight cover, and allowing them to sit overnight.

Further conditioning is accomplished by staking and dry-milling the

leather. the leather to make it soft. Dry-milling involves the tumbling of hides in a

large drum (111.

The staking process utilizes automatic machinery to stretch and flex

Buffing. Irregularities in the grain of the leather are smoothed out by mechanical abrasion (buffing). This process generates large quantities of

dust that must be controlled.

Finishing. Coatings may be applied to the leather to provide resistance

to abrasions and stains as well as to enhance leather color. Coatings may be either solvent-based or water-based. Most of the coatings are similar in

2-18

fo rmula t ion t o l a t e x house p a i n t . A p p l i c a t i o n of t h e s e c o a t i n g s i s determined

by t h e end use of t h e l e a t h e r [11 , 181.

P l a t i n g . P l a t i n g smooths t h e s u r f a c e of t h e c o a t i n g s and bonds them t o

t h e g r a i n of t h e l e a t h e r . Th i s p rocess enhances t h e appearance and t e x t u r e of

t h e l e a t h e r . F i n i s h i n g and p l a t i n g p rocesses are completed w i t h i n 4 o r 5

days [ill.

2 . 2 . 2 P rocess ing S teps f o r a C a t t l e h i d e Tannery (Vegetable)

Only about 8 pe rcen t of t h e h i d e s i n t h e Uni ted S t a t e s are tanned u s i n g

v e g e t a b l e e x t r a c t s de r ived from t h e ba rk of v a r i o u s t rees [ 6 ] . Vegetable

t a n n i n g i s g e n e r a l l y used t o produce heavy l e a t h e r . The b a s i c p rocesses i n

v e g e t a b l e t ann ing a r e ve ry s imi lar t o t h o s e f o r chrome t a n n i n g ; however, t h e r e '

are v a r i a t i o n s i n the sequence of p rocesses as w e l l as some process param-

e t e r s . Vegetable t ann ing i s a much l e n g t h i e r p rocess t h a n chrome t a n n i n g ,

g e n e r a l l y l a s t i n g over two weeks.

2 . 2 . 2 . 1 Beamhouse SI

A s i n chrome tann ing , cured c a t t l e h i d e s a r e r e c e i v e d a t t h e t a n n e r y where

they a r e soaked t o remove s a l t and o t h e r m a t e r i a l s and t o r e t u r n m o i s t u r e t o

t h e h i d e s . The h i d e s a r e then t r a n s f e r r e d d i r e c t l y t o t h e u n h a i r i n g o p e r a t i o n

f o r t r ea tment wi th l ime and s u l f i d e chemicals . I n v e g e t a b l e t a n n i n g , t h e h a i r

s a v e method is commonly used; t h e h a i r t h a t i s loosened d u r i n g u n h a i r i n g i s

removed by mechanical means 131.

u n h a i r i n g ( l ime s p l i t t i n g ) o r dur ing t h e f i n i s h i n g o p e r a t i o n s ( d r y s p l i t t i n g )

[ 7 1 .

The h i d e may be s p l i t e i t h e r fo l lowing

The f l e s h i n g o p e r a t i o n may fo l low p r e l i m i n a r y washing and soaking o r

occur a f t e r t h e unha i r ing p rocess [ 3 , 5 , 1 8 ] . F l e s h i n g s genera ted a f t e r t h e

u n h a i r i n g process a r e r e f e r r e d t o as l ime f l e s h i n g s or l i m e s u l f i d e f l e s h i n g s

because they c o n t a i n unha i r ing chemicals [ 3 1 .

2-1 9

2 . 2 . 2 . 2 Tanyard

The tanyard p rocesses are e s s e n t i a l l y t h e same as t h o s e d e s c r i b e d i n

chrome tann ing : de l iming , b a t i n g , and t a n n i n g . While t h e r e i s no p i c k l i n g

p r o c e s s per se , t h e pH o f t h e h i d e may be a d j u s t e d p r i o r t o t ann ing [5,181.

For t h e t ann ing p r o c e s s , h i d e s are soaked i n a s o l u t i o n of v e g e t a b l e e x t r a c t s

f o r almost two weeks 131.

I n v e g e t a b l e t a n n i n g , t h e h i d e s are s u b j e c t e d t o a series of t ann ing

s o l u t i o n s of i n c r e a s i n g s t r e n g t h s .

s o l u t i o n s are s u c c e s s i v e l y pumped or t h e h i d e s may be t r a n s f e r r e d through a

s e r i e s of v a t s [181. A more r a p i d v e g e t a b l e t a n n i n g sys tem, t h e L i r i t a n

sys tem, i n v o l v e s t r ea tment of t h e h i d e s w i t h a s o l u t i o n o f sodium hexameta-

phosphate and s u l f u r i c a c i d i n o r d e r t o s t a b i l i z e t h e g r a i n o f t h e h i d e and

f a c i l i t a t e t h e uptake of t a n n i n s [5 ,181 .

This may occur i n a s i n g l e v a t i n t o which

2 . 2 . 2 . 3 Retan

T h i s segment of v e g e t a b l e t ann ing d i f f e r s s i g n i f i c a n t l y from t h a t of

chrome tann ing i n t h a t t h e r e are no r e t a n or dyeing o p e r a t i o n s . R a t h e r , t h e

tanned l e a t h e r i s bleached t o l i g h t e n t h e s u r f a c e c o l o r , f a t l i q u o r e d t o

r e s t o r e n a t u r a l f l e x i b i l i t y t o t h e h i d e f i b e r s , and t r e a t e d w i t h i n o r g a n i c

s a l t and o rgan ic c o n d i t i o n i n g m a t e r i a l s [ 3 , 1 5 1 .

2 . 2 . 2 . 4 F i n i s h

The l e a t h e r i s s lowly d r i e d by ambient a i r f low by e i t h e r a hanging or a

t a c k i n g p rocess . The d r i e d l e a t h e r s u r f a c e i s t h e n mechan ica l ly cond i t ioned

and t h e g r a i n s u r f a c e is p o l i s h e d wi th a g lazed wax. Depending upon t h e type

of l e a t h e r and i t s end u s e , i t may be b u f f e d t o remove s u r f a c e i m p e r f e c t i o n s

and f i n i s h e d f o r w a i s t b e l t l e a t h e r s . C e r t a i n s p e c i a l t y l e a t h e r s are dry-

s p l i t t o d e s i r e d t h i c k n e s s ; t h e s e s p l i t materials are cons ide red t o be was te

m a t e r i a l and a r e not used f o r suede as a r e t h o s e from chrome tann ing [ 3 , 5 , 7 1 .

2 . 2 . 3 Process ing S t e p s f o r a Sheepskin Tannery

Sheepskin t annery p rocesses a r e e s s e n t i a l l y t h e same a s t h o s e d e s c r i b e d

f o r chrome tann ing . S ince most of t h e sheepsk in processed i n t h e United

2-20

S t a t e s i s imported, unhaired', and a l r e a d y processed through t h e p i c k l i n g s t e p ,

beamhouse o p e r a t i o n s are t y p i c a l l y absen t from sheepsk in t a n n e r i e s [ 3 I .

There a r e b a s i c a l l y two v a r i a t i o n s i n t h e sheepsk in t ann ing p rocess : t h e

presence of a degreas ing o p e r a t i o n and f l e s h i n g of s k i n s a f t e r t h e t ann ing

p rocess . Sheepskin , u n l i k e c a t t l e h i d e , has a f a t t y l a y e r a t t h e base of t h e

h a i r f o l l i c l e s . Because t h i s f a t a f f e c t s p rocess ing o p e r a t i o n s and p r o p e r t i e s

o f the l e a t h e r product , t h e s e s k i n s normal ly undergo s o l v e n t o r d e t e r g e n t

degreas ing [18]. The degreas ing p rocess i s performed i n c o n j u n c t i o n w i t h

i n i t i a l soaking and washing o p e r a t i o n s . Grease by- products from t h e spen t

degreas ing s o l u t i o n may be recovered. A f t e r e i t h e r chrome o r v e g e t a b l e

t a n n i n g , sheepsk ins are mechan ica l ly f l e s h e d [ 3 1. Sheepskins may a l s o be

f l e s h e d i n t h e p ick led s t a t e p r i o r t o t ann ing [SI. Retan and f i n i s h i n g s teps

are e s s e n t i a l l y t h e same as i n chrome c a t t l e h i d e t ann ing except t h a t f i n i s h e s

are not n e c e s s a r i l y a p p l i e d t o t h e l e a t h e r . However, g r a i n sheepsk in l e a t h e r s

are f i n i s h e d wi th s u r f a c e l u s t e r c o a t s . Suede l e a t h e r may a l s o be made 151.

Sheepskin may a l s o be processed wi th t h e wool a t t a c h e d . Such s k i n s a r e

r e f e r r e d t o as s h e a r l i n g s . While domestic s h e a r l i n g s are rece ived at the

t annery i n a s a l t- c u r e d s t a t e , s h e a r l i n g imports a r r i v e processed through t h e

p i c k l i n g s t a g e . The o n l y d i f f e r e n c e s i n s h e a r l i n g p rocess ing is t h a t l a r g e r

q u a n t i t i e s of wa te r a r e needed i n t h e soaking and washing o p e r a t i o n s , and

g r e a s e by-products are not u s u a l l y recovered from degreas ing . A d d i t i o n a l l y ,

the wool is o f t e n - dyed o r modified f o r s t y l e purposes [3,5,111.

2 . 2 . 4 P r o c e s s i n g S t e p s f o r a P i g s k i n Tannery

The p i g s k i n t annery i s ve ry s imi lar t o t h e c a t t l e h i d e t annery . The major

d i f f e x e n c e is t h a t t h e s k i n s undergo a d e g r e a s i n g o p e r a t i o n . The p i g s k i n s are

rece ived e i t h e r f r e s h , f r o z e n , o r b r ined and r e f r i g e r a t e d . Hair and b r i s t l e s

a r e u s u a l l y removed at t h e packinghouse [5,111.

P i g s k i n t a n n e r i e s , l i k e sheepsk in t a n n e r i e s , must degrease t h e s k i n s

because of t h e i r h igh g r e a s e c o n t e n t . Th i s degreas ing o p e r a t i o n , i n conjunc-

t i o n wi th soak and wash o p e r a t i o n s , is t h e f i r s t p rocess ing s t e p performed i n

2-2 1

the tannery.

from the h i d e s . Where so lven t degreas ing is used, bo th spent so lven t and

g rea se may be recovered [5 ,111 .

It involves us ing e i t h e r s o l v e n t s or d e t e r g e n t s t o s t r i p g r ea se

The remaining processes a r e e s s e n t i a l l y t hose of a chrome c a t t l e h i d e

tannery. P ig sk in s may be f l e s h e d a s necessary . A f t e r deg rea s ing , t h e

p ig sk in s a r e limed t o remove h a i r r o o t s , then ba t ed , p i c k l e d , and tanned

s e q u e n t i a l l y w i t h i n t h e same process ing drum.

tann ing agen t , vege t ab l e t ann ins may a l s o be used. The heav i e r sk in s may be

s p l i t i n t he b lue o r a f t e r d ry ing t o ach ieve d e s i r e d t h i c k n e s s .

may be processed , d i sposed o f , or so ld f o r o t h e r u se s . Organic r e t ann ing may

be used t o modify t h e l e a t h e r p r o p e r t i e s . F i n a l l y , t h e l e a t h e r is c o l o r e d ,

f a t l i q u o r e d , and f i n i s h e d . Unl ike chrome c a t t l e h i d e f i n i s h i n g o p e r a t i o n s ,

p i g s k i n l e a t h e r f i n i s h i n g g e n e r a l l y does no t involve t h e a p p l i c a t i o n of f i lm-

forming f i n i s h coa t s [7 ,11,191.

While chrome i s t h e predominant

The s p l i t s

2 . 3 WASTE STREAM CHARACTERISTICS

The tanning i n d u s t r y gene ra t e s was-e s t reams c o n t a i n i n g a wide v a r i e t y of

m a t e r i a l s and chemicals . These waste s t reams vary accord ing t o bo th t he type

of t annery and the m a t e r i a l p rocessed . Table 2-2 summarizes t annery

p roces se s , m a t e r i a l s added t o t h e s e p roces se s , and subsequent waste s t reams

gene ra t ed . Many of t he se waste s t reams can be reused or r e c y c l e d , as

d i s cus sed i n Sec t i ons 3 , 4, and 5 .

Tannery wastewater has been found t o c o n t a i n s o l u b l e and suspended

m a t t e r , i nc lud ing g rea se and o i l s , s o l i d s , i no rgan i c m a t e r i a l s ( s a l t , chromium

s a l t s , s u l f i d e , and ammonia), n u t r i e n t s , and co l i fo rm. These p o l l u t a n t s

r e s u l t from the waste p roduc ts of every w e t p rocess i n a tannery . Chromium

and o the r p o l l u t a n t s e n t e r the waste stream from the va r ious chemicals and

processes i n which they a r e used.

p ro t e inaceous m a t t e r , h a i r , t i s s u e , b lood , unf ixed chemica ls , t ann ing a g e n t s ,

e x t r a c t s , dyes , pigments, d i r t , g r i t , and manure.

These p o l l u t a n t s a r e de r ived from

2-22

Table 2-2. Tannery Waste Stream Ch&acteristics

Major Process Subprocess Materials Input Waste Stream Constituents

CHROME OR VEGETABLE TANNERY

Side and Trim Trimmings Be amho us e

Soak and Wash Water Dirt, salt, blood, manure, nonfibrous proteins, grease

F 1 e sh i ng s F le sh ing

Depilatory Hair (hair save), dissolved

Water depilatory chemic a1 s

Unhairing c hem i c a1 s hair (hair burn),

Deliming agents Pigments, proteins, hair Enzymes roots

Tanyard Bating

Pick1 ing Brine and acid Unfixed chemicals

Tanning Tanning agents Unfixed tanning agents Water

Wring

Split

Shave

Retan/ Ret an* Color / Fat liquor

Bleaching" and Coloring*

Fatliquoring

Water Unfixed tanning agents

Splits, blue trim

Dust

Tanning agents Unfixed tanning agents Water

Water Dyes, pigments Bleaching agents Dyes Pigments

Chemicals Oi 1 s , chemical s Emulsifiers Oils/ fatty

Water substances

Trim Unfinished leather trim

2-23

Table 2-2. Tannery Waste Stream Characteristics (Continued)

Major Process Subprocess Materials Input Waste Stream Constituents

Finish Buffing Dust

Finishing* Polymer coatings Finishing residues and P1 a t ing*

Trim Finished leather trim

SHEEPSKIN TANNERY

Tanyard Wash and Soak Water Brine, acid, protein, grease

[Fleshing] t [Fleshingslt

Soak and Water Grease, solventldetergent Wash/ Solventldetergent Degreasing


[Fleshinglt [Chrome fleshings]*

Retan/ Retan Color 1 Fat 1 iquor

Finish

Color

Tanning agents Unfixed tanning agents Water

Dyes B1 e ac hes

Dyes, bleaching chemicals

Fatliquoring Chemicals Oils, chemicals Emu1 s i f iers Oi 1 s / fatty substances

Water

Buffing

Finish

Dust

Coatings Finishing residues

2- 24

Table 2-2. Tannery Waste Stream Characteristics (Continued)

Major Process Sub pro c e s s Materials Input Waste Stream Constituents

PIGSKIN TANNERY

Water Grease, solventldetergent Beamhouse Soak and Wash/ Solvent/detergent Degreasing

Fleshing Fleshing s

Liming Lime slurry Hair roots, lime, protein

Tanyard Bating Deliming agents Pigments, proteins, hair Enzymes roots

Pick1 ing Brine and acid Unfixed chemicals


Split Split

Shave Shavings, dust

Retan Re tan Tanning agents Unfixed tanning agents

Color/ Color Fat liquor / Finishing

Dyes Pigments Water

Dyes, pigments

Fat liquoring Chemicals Oils, chemicals Emulsifiers Oilslfatty

Water substances

Source: 3,5,11,18 *Specific to chrome tanning processes **Specific to vegetable tanning processes tFleshing for sheepskins may occur before or after the tanning process.

2-25

2 . 4 WASTE STREAM QUANTIFICATION

Tanneries generate both solid and liquid waste streams. The quantity of these wastes, like the types of wastes, vary according to the tannery and hide

or skin being processed. not available for every waste o r waste stream generated within a tannery.

However, those quantities that could be determined are presented in this sect ion.

Waste quantities or waste generation factors were

Table 2-3 presents the estimated quantities of some of the solid wastes

Complete chrome tanneries produced by different types of tanneries in 1980.

account for the greatest portion of the solid wastes generated, while

establishments that only retan or finish leather generate the least. 64,100 tons of solid waste, primarily hide waste, contain a variety of

materials, including proteins, chrome, and grease, that may be recovered for use within the leather industry or elsewhere; these recovery activities are

discussed in more detail in Section 4 .

The

Table 2-4 summarizes the quantity of water used per hide or skin by each type of tannery.

provides a rough approximation of the effluent generated by the tanneries. Shearling tanneries use the greatest quantity of water per skin.

greatest quantity of water used, and thus the largest total wastewater effluent, is from-complete chrome tanneries because they are the most numerous

and process the greatest number of hides for any tannery grouping.

This data, which is currently being revised by the EPA,

However, the

To illustrate the sources of wastewater within a complete chrome tannery, Table 2-5 presents a breakdown of process contributions to tannery waste streams; this data is also under revision by the EPA. The beamhouse and

tanyard segments of the tannery are the largest contributors to the tannery effluent, while the tanning subprocess itself contributes the least. Many of the subprocesses vary widely in their contribution to the effluent because of

variations in each tannery's processing requirements. Thus, no specific subprocess can be designated as the single largest contributor to tannery

waste streams.

2-26

c 0 co en d

C 0

.rl U 6 L al C aJ u aJ U

Q .rl d 0 m x L aJ C C 4 w

0 I N

al i

6 w n

5: '0, 9

a N .I

d

0 m m

0 N m

0 QI M

e d

In

0 e QI

00 N

a

0 co m

0 In U

0 2

0 2

0 cy

0 0 a e 0

0 - I-

% L aJ C C s Y .M + a v)

x Y .rl rl .4 0 6 L C 6 Y 0) s

0 In U

0 0 U

0 In

A u .rl d .rl U 6 a

E .rl

.rl C a

c c 0 0

U 9

d .)

0 0

OI 0- 4

0 In

+ d

L

0 d N

N

0 \o

0 '0.

0 0

z

0 + In

d

0 9 m . d

:: t 0 t

W C .d Q C

0 L

0

0)

a

Y

a

Q Q a Y 0 C x I

5 2

(I) Id m a

z

2-27

Table 2-4. Quantification of Tannery Water Usage

Type of Tannery Water Usage (gal/lb of hide or skin)

Complete Chrome (Hair Burn)

Complete Chrome (Hair Save)

Through-the-Blue

Retan/Finish

Vegetable

Pigskin/Sheepskin

Shearlings

4 . 6

5 . 5

2 . 7

1.7

4.0

3 . 3

13.9

Source: 11

2-28

Table 2- 5 . Complete Chrome Tannery (Hair Burn) Waste Stream Quantification

Major Process Subprocess

Percent of Total Tannery Effluent Flow (%I

- ~~~

Be amho u s e

Tanyard

Ret an I co 1 or I Fat liquor

L

Soak and Wash

-- Fleshing

Unhai r ing

Bating and Pickling

20-38 (32 average)

9- 50 (26 average)

Tanning 4 . 4 - 6 . 6

Retan/ Color/ Fat liquor

12-30

Finishing -- Finishing

Source: 11

2- 29

2.5 POTENTIALLY HAZARDOUS WASTE STREAMS

The primary emphasis of this report is the recovery of materials from the leather industry's waste streams rather than an evaluation of their hazard.

However, information on the hazardous materials content of the waste streams is valuable in assessing their potential for resource recovery. The need for

compliance with state and federal regulatory requirements governing waste handling, waste streams generated by recovery processes, and recovered

materials themselves, can affect the implementation of resource recovery practices on waste streams in tanneries and other industrial facilities in SIC

31. This consideration of regulatory status is included in the analysis of the resource recovery potential of the leather industry's waste streams

(Sections 4 and 5 ) .

The waste streams discussed in Sections 2.3 and 2.4 contain a number of

diverse chemical constituents. Some of these waste streams may be considered

"hazardous" by regulations promulgated under 40 CFR Part 261, pursuant to Subtitle C of the Resource Conservation and Recovery Act (RCRA).

considered hazardous because: (1) the EPA specifically lists it as hazardous under 40 CFR Part 261, Subparts B and D, or (2) the waste meets a character-

istic specified in 40 CFR Part 261, Subpart C .

Waste may be

Currently, 40 CFR Part 261.6 exempts from regulatory control those wastes that are used, reused, recycled, o r reclaimed, if the wastes are hazardous only due to their characteristics and are not sludges (e.g., pollution control residues). However, the EPA is currently reviewing its regulatory approach to the recycling of hazardous wastes and may initiate substantial changes in the regulation of certain recycled materials and recycling activities under RCRA. If these changes occur, some industrial facilities will be subject to decreased or increased regulatory burdens depending on the types of wastes

they recycle and the manner in which the recycling process is performed.

As required under RCRA, all facilities dealing with hazardous waste (either as a generator , transporter , o r a facility for waste treatment ,

2-30

s t o r a g e , and/or d i s p o s a l ) must n o t i f y t h e EPA of t h e i r w a s t e- r e l a t e d a c t i v i -

t i e s . Review and a n a l y s i s of t h i s n o t i f i c a t i o n d a t a determined t h a t a t l e a s t

102 t a n n e r i e s n o t i f i e d t h e EPA of t h e i r hazardous waste a c t i v i t i e s . It should

be noted t h a t t h e n o t i f i c a t i o n requ i rements f o r a number of t h e waste

a c t i v i t i e s were t e m p o r a r i l y suspended a f t e r t h e n o t i f i c a t i o n d a t e . However, a

number of o t h e r wastes genera ted by t h e l e a t h e r t ann ing i n d u s t r y are s t i l l

l i s t e d as hazardous under RCRA; t h e s e was tes are p resen ted i n Table 2-6. Many

of the EPA waste c a t e g o r i e s are g e n e r a l i n n a t u r e or b r o a d l y d e f i n e d . Thus,

t h e exac t waste m a t e r i a l or t a n n e r y p rocess g e n e r a t i n g the wastes cannot be

s p e c i f i c a l l y determined from t h e n o t i f i c a t i o n d a t a base .

However, based on an a n a l y s i s of t h e l e a t h e r i n d u s t r y as w e l l a s f e d e r a l

and s t a t e hazardous waste r e g u l a t i o n s , t h e fo l lowing materials found i n some

process waste s t reams may be cons ide red hazardous:

0 Hexavalent chromium

0 T r i v a l e n t chromium

0 Dyes

0 Pigments

0 Bleaches

0 S y n t h e t i c t ann ing agen t s

0 S o l v e n t s .

S ludges from wastewater t r ea tment may a l s o be hazardous because they c o n t a i n

t h e s e m a t e r i a l s , t h e i r d e r i v a t i v e s , o r o t h e r hazardous c o n s t i t u e n t s .

The o r i g i n a l May 19 , 1980 and J u l y 16, 1980, S e c t i o n 3001 RCRA regu la-

t i o n s l i s t e d seven waste streams (KO53 t o KO591 from a v a r i e t y of t a n n e r y

p r o c e s s e s as hazardous was tes . Each waste o r waste stream was d e f i n e d as

hazardous based upon i n d i v i d u a l c h a r a c t e r i s t i c s and t o t a l chromium c o n t e n t .

Though the EPA recognized t h a t t r i v a l e n t chromium i s f a r less t o x i c

than i t s hexava len t c o u n t e r p a r t , t h o s e wastes c o n t a i n i n g almost e x c l u s i v e l y

t r i v a l e n t chromium ( l e a t h e r s c r a p s , t r immings , s h a v i n g s , e t c . ) were d e f i n e d a s

hazardous under S e c t i o n 3001.

t i o n s e x i s t e d t h a t could f o s t e r t h e o x i d a t i o n of t r i v a l e n t t o hexava len t

The Agency f e l t t h a t c e r t a i n d i s p o s a l condi-

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2-31

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2-35

chromium. Thus, all chrome-bearing tannery wastes were listed as hazardous

without regard to the form of chromium in the wastes.

Upon further review of the relevant issues, the EPA has decided that the

potential for migration and oxidation of tannery wastes containing trivalent

chromium appears to be insignificant, thereby reducing the potential negative impacts of mismanagement of these wastes.

temporarily excluded the listed tannery wastes pending a review of continuing research into the unresolved relevant issues. It should be noted, however, that, under RCRA, states have the prerogative to implement more stringent regulations than those promulgated by the EPA. For example, the State of

Vermont has exercised its authority in this area and still lists tannery and finishing wastes as hazardous.

On this basis, the EPA has since

Waste streams (primarily spillage) from bichromate reduction may contain

hexavalent chromium, which is still considered hazardous under RCRA because of its toxicity, carcinogenicity, mutagenicity, and potential for migration from

waste disposal sites. In addition, incineration and pyrolysis of leather

scrap can generate an ash containing hexavalent chromium. This is of poten-

tial concern because incineration and pyrolysis are resource recovery methods

under consideration and development for application in the leather industry

(see Sections 4.2 and 4.3). The EPA has indicated that it intends to regulate waste streams containing trivalent or hexavalent chrome that will be incin-

erated or otherwise managed.in a manner that can oxidize Cr+3 to Cr

priate regulations will eventually be adopted under 40 CFR Parts 261 and 266.

+6 . Appro-

Also of regulatory concern are waste streams containing various dyes and

pigments used in the finishing processes. Dyes and pigments characteristic-

ally contain chromium and ot-her heavy metals such as lead, zinc, and cadmium.

Benzidine derivatives, aniline derivatives, and other complex organic

compounds may also be used in dyes and pigments.

content of dyes and pigments used by tanners was not available. However, since the substances characteristically found in dyes and pigments may be

hazardous as defined under RCRA, any waste streams containing these dyes or

pigments may also be hazardous.

The specific chemical

2-36

Waste streams containing bleaches, synthetic tanning agents, phenolic

derivative biocides, and solvents may also be hazardous as defined by RCRA.

For example, tannery degreasing operations are similar to other industrial

degreasing operations, and probably use traditional halogenated solvents.

Therefore, tannery solvents may be included in the generic listings of hazardous wastes under Part 261.31, “Hazardous Waste from Non-Specific Sources. ’I

Finally, some wastewater sludges that the EPA has recently delisted may

remain hazardous due to specific constituents previously mentioned or on the basis of exhibited characteristics. For example, sludges from individual unhairing processes stored in enclosed tanks may release dangerous amounts of hydrogen sulfide and may therefore be classified as “reactive,” a hazardous

characteristic under Part 261, Subpart C of the RCRA regulations.

2- 37

3.0 STATE-OF-THE-ART OF RESOURCE RECOVERY I N THE LEATHER AND LEATHER PRODUCTS INDUSTRY

This s e c t i o n d e f i n e s t h e c u r r e n t s t a t e- o f- t h e- a r t of r e s o u r c e recovery i n

t h e l e a t h e r and l e a t h e r p roduc t s i n d u s t r y . A m a t r i x summarizing c u r r e n t

r e s o u r c e recovery p r a c t i c e s and t h e i r s t a g e of development i s p resen ted and

d i s c u s s e d i n S e c t i o n 3 .1 . S e c t i o n 3.2 d e s c r i b e s how t h e m a t r i x may be used t o

ana lyze both t h e s t a t u s of c u r r e n t r ecovery p r a c t i c e s and t h e i r p o t e n t i a l f o r

advancement .

3 . 1 MATRIX DEVELOPMENT AND STRUCTURE

The i n v e s t i g a t i o n f o r t h i s r e p o r t inc luded a thorough review and a n a l y s i s

of more than a decade of important t r a d e j o u r n a l s and s c i e n t i f i c l i t e r a t u r e .

Trends , s p e c i f i c t e c h n o l o g i e s , and t h e i r p o t e n t i a l f o r r e s o u r c e recovery were

confirmed and d i scussed w i t h government o f f i c i a l s , t a n n e r s , t r a d e a s s o c i a-

t i o n s , r e s e a r c h and eng ineer ing f i r m s , l e a t h e r s c r a p d e a l e r s , and l e a t h e r and

l e a t h e r- d e r i v e d product manufac tu re r s .

From t h i s i n v e s t i g a t i o n , J R B has d e f i n e d t h e c u r r e n t s t a t u s of r e source

recovery p r a c t i c e s used i n t h e l e a t h e r and l e a t h e r p roduc t s i n d u s t r y . Key

a r e a s of t h i s i n v e s t i g a t i o n and a n a l y s i s inc luded :

e Lea ther i n d u s t r y waste s t r eams

e Appl icable r esource recovery t e c h n o l o g i e s

.e Stage of development of t h e r e s o u r c e recovery t e c h n o l o g i e s as a p p l i e d t o s p e c i f i c waste s t r eams

e T r a n s f e r and use of t h e recovered material .

These four key a r e a s d e f i n e t h e parameters of a mat r ix summarizing t h e

s t a t e- o f- t h e- a r t of r e s o u r c e recovery . Th i s m a t r i x i s p resen ted i n

F igure 3-1. B r i e f l y , t h e s t r u c t u r e of t h e m a t r i x i s as f o l l o w s : t h e l e a t h e r

i n d u s t r y waste streams, which are on t h e h o r i z o n t a l axis , are c o r r e l a t e d wi th

t h e a p p l i c a b l e r esource recovery t e c h n o l o g i e s , on t h e v e r t i c a l axis. These

two parameters a r e l inked by codes t h a t r e p r e s e n t b o t h t h e s t a g e of develop-

ment of each recovery technology a s a p p l i e d t o a waste s t r e a m and t h e a r e a t o

3-1

which the waste or recovered material is transferred for reuse. These key areas are discussed in more detail in the following sections.

3.1.1 Matrix Waste Streams

The matrix includes all industry waste streams with recoverable materials for which resource recovery technologies have been identified or proposed.

This listing is divided into two parts: the tanning of leather and leather

product manufacture. tanner, who converts animal hide or skin to leather, and the manufacturer of

leather products, who uses "raw" leather in the fabrication of various products .

This division reflects the distinction between the

Waste streams are ordered and further divided to reflect the sequence of

processes from which they are generated. Those under tanning are presented in

the general order in which they are generated in a typical full tannery (that

with beamhouse, tanyard, retan, and finishing processes). The same is true

for those waste streams under leather product manufacture.

It should be noted, however, that due to variations in processing operations or sequences of operations resulting from processing different animal

hides and skins, not all waste streams will be found in every tanning estab-

lishment. For example, the degreasing operation is only applicable to facilities that process pigskin or sheepskin. In addition, a waste stream may

appear more than once due to variations in the processing sequence. An

example is the appearance of both fleshings and lime sulfide fleshings in the

matrix; this is the result of the same process being performed at a different

stage of the tanning process and imparting different characteristics to the

same vdste material.

3 . 1 . 2 Matrix Resource Recovery Technologies

This area includes those technologies that have at least been proposed

for recovering valuable materials from the identified generic industry waste

streams; only those technologies cited by persons knowledgeable of the

industry or within the surveyed literature are included on the matrix.

3-2

For t h e purposes of c l a r i t y <n t h e matr ix, each r e s o u r c e recovery

technology t i t l e r e p r e s e n t s t h e s t e p w i t h i n t h e p a r t i c u l a r r ecovery p rocess

t h a t a c t u a l l y i s o l a t e s t h e m a t e r i a l of i n t e r e s t from t h e rest of t h e waste

stream. Those p rocesses t h a t precede t h i s s p e c i f i c r ecovery s t e p t r ans fo rm

t h e waste stream t o a p o i n t where recovery can be e f f i c i e n t l y performed.

P rocesses t h a t fo l low t h e s p e c i f i e d recovery s t e p g e n e r a l l y invo lve p u r i f i -

c a t i o n o r d i r e c t use of recovered m a t e r i a l . It should b e noted t h a t some

wastes are used d i r e c t l y and do not n e c e s s a r i l y undergo i s o l a t i o n o r

p u r i f i c a t i o n .

nology, i n c l u d i n g a l l p rocess ing s t e p s , can be found i n S e c t i o n 4 under t h e

t i t l e s p resen ted i n t h e m a t r i x .

Comprehensive d e s c r i p t i o n s of each r e s o u r c e recovery tech-

Two examples t h a t i l l u s t r a t e t h i s breakdown of t h e p r o c e s s i n g sequence

are: (1) chrome recovery by p r e c i p i t a t i o n of s p e n t t a n n i n g l i q u o r , and

( 2 ) h a i r r ecovery by sc reen ing of spen t u n h a i r i n g l i q u o r .

chrome recovery by p r e c i p i t a t i o n of spen t t a n n i n g l i q u o r , d e s c r i b e d i n d e t a i l

i n S e c t i o n 4 . 2 . 1 , i s as fo l lows :

The o u t l i n e of

- 1. S e p a r a t e spen t tanning l i q u o r from o t h e r p rocess waste s t r eams

2 . Screen s o l u t i o n t o remove s o l i d s

3 . Add a l k a l i t o p r e c i p i t a t e chrome

4 . S e t t l e chrome p r e c i p i t a t e

5. Remove waste l i q u i d

6 . F i l t e r p r e c i p i t a t e

7 . D i s s o l v e p r e c i p i t a t e i n a c i d t o mak ne1 t a n n i 1 iquor

8 . Use t ann ing l i q u o r i n t ann ing p r o c e s s .

For t h e purposes of t h i s r e p o r t , s t e p 3 i n t h i s sequence d e f i n e s t h e recovery

p r o c e s s- - p r e c i p i t a t i o n of chrome--because t h a t s t e p i s o l a t e s t h e chrome from

t h e waste stream. S t e p s 1 and 2 t r a n s f o r m t h e spen t t ann ing l i q u o r t o t h e

p o i n t where a l k a l i n e p r e c i p i t a t i o n can be e f f i c i e n t l y performed.

through 6 p u r i f y t h e chrome p r e c i p i t a t e , and s t e p s 7 and 8 d e s c r i b e how t h e

recovered chrome i s reused .

S t e p s 4

.

' 3-5

The second example, hair recovery by screening of spent unhairing liquor,

described in detail in Section 4 . 8 , involves the following process:

1. Separate spent unhairing solution from other process waste streams

2 . Screen solution to remove hair

3 . Wash, dry, and package hair 4 . Sell for further processing o r direct use.

In this sequence, step 2 , screening the solution to remove the hair, defines

the hair recovery process. Step 1 transforms the waste stream to the point where the screening can be efficiently carried out. Steps 3 and 4 describe

the purification and use of the recovered hair.

3.1.3 Matrix Technology Development Stage and Waste Material Transfer Codes

The waste streams on the horizontal axis of the matrix and the resource

recovery technologies on the vertical axis are correlated by the development stage and waste transfer codes that appear in the boxes on the matrix. Due to

the matrix design, only technology/waste stream combinations that JRB's

investigation has shown are, or potentially could be, applied to a particular

waste stream to recover a valuable material are coded. Hence, those combina-

tions with technologies that are not being, or cannot be, applied to a

particular waste stream, according to this investigation, are not coded.

The development stage codes for the resource recovery technologies are ranked according to a numerical scale that indicates the degree to which the

processes are applied throughout the industry. The numbers correspond to the following definitions:

1. Proposed Research Area. No actual testing has been performed on any systems. Investigation has revealed a citation to the effect that the technology could theoretically be used to recover materials from a Waste stream.

2 . Bench-Scale. Laboratory testing and experiments have been done to perform an initial evaluation on the possibility of recovering potentially valuable materials from a waste stream using a specific technology.

3 -6

3 . Pilot-Scale. Evaluations of a small version of'a planned recovery system applied to a waste stream for materials recovery have been completed.

4 . Full-Scale Demonstration Project. Evaluations of factory-size systems installed within plants for recovering materials from actual process waste streams have been completed.

5 . Full-scale, Sporadically Practiced. Actual industrial recovery process used by a small segment of the industry t o recover materials from process waste streams.

6. Full-scale, Commonly Practiced. Actual industrial recovery process, used by a majority of the industry to which the process can be applied, to recover materials from process waste streams.

The second part of the technology/waste stream matrix code is the waste

material transfer code. This code denotes where the waste stream, any part of

the waste stream, or any recovered product of the waste stream is transferred for use upon recovery.

material transfer activities :

The alphabetic code corresponds to the following

a. Within the generating facility

b. Between the generating facility and another facility in the same industry

c. Between the generating facility and another facility in a different industry.

The development stage and waste transfer codes assigned to each recovery

process have been derived from conversations with persons knowledgeable of the

industry or information obtained from the literature. While most recovery technology/waste stream combinations are correlated by a single pair of codes,

some have multiple codes indicating different development stages andfor waste transfer areas. In these situations, a recovered material can, or potentially

could, be transferred for use in more than one area. In each case, the development stage for each waste transfer area is noted.

Two examples that illustrate the application of the matrix codes are

chrome recovery by precipitation of spent tanning liquor and solvent recovery

3-7

from s p e n t degreas ing s o l u t i o n s .

b u t i t i s performed a t f u l l s c a l e . Hence, t h e development s t a g e of t h e

recovery p rocess i s a 5 ( f u l l s c a l e , s p o r a d i c a l l y p r a c t i c e d ) .

recovered a t the t a n n e r y and i s used i n f r e s h t ann ing l i q u o r , so t h e t r a n s f e r

code i s an "a" (recovered material i s used w i t h i n t h e f a c i l i t y ) .

Few t a n n e r i e s p r a c t i c e chrome p r e c i p i t a t i o n ,

The chrome i s

Solvent r ecovery i s p r a c t i c e d by p i g s k i n and sheepsk in t a n n e r i e s which

However, w i t h i n t h i s minor r e p r e s e n t a smal l number of t ann ing f a c i l i t i e s .

segment of the i n d u s t r y (which is t h e o n l y one t h a t uses t h e d e g r e a s i n g

p r o c e s s ) , s o l v e n t r e c o v e r y is commonly p r a c t i c e d . On t h i s b a s i s , t h e develop-

ment s t a g e i s a 6 ( f u l l s c a l e , commonly p r a c t i c e d ) . The s o l v e n t may be

recovered e i t h e r a t t h e t a n n e r y or s o l d t o a commercial s o l v e n t p rocessor f o r

r e p r o c e s s i n g . Hence, two waste t r a n s f e r codes are ass igned : "arr and "c."

Th i s i n d i c a t e s t h a t t h e s o l v e n t may be reused a t t h e t a n n e r y o r r eused a t

ano the r f a c i l i t y i n ano the r i n d u s t r y .

3 . 2 .MATRIX APPLICATION

The m a t r i x , i n F igure 3-1, r e p r e s e n t s t h e most important p a r t of t h i s

r e p o r t . An unders tand ing of t h e parameters and a s s o c i a t e d codes a l lows t h e

u s e r t o d e r i v e from t h e m a t r i x t h e two o v e r a l l o b j e c t i v e s of t h e r e p o r t .

F i r s t , t h i s g r a p h i c summarization of JRB's i n v e s t i g a t i o n a l lows t h e r e a d e r t o

surmise t h e c u r r e n t s t a t e of r e s o u r c e recovery p r a c t i c e s w i t h i n t h e l e a t h e r

i n d u s t r y .

r ecovery t echno log ies a v a i l a b l e , t h e development s t a g e of t h e t e c h n o l o g i e s ,

and t h e t r a n s f e r of recovered m a t e r i a l s are a l l summarized w i t h i n t h e m a t r i x .

The waete streams w i t h r e c o v e r a b l e r e s o u r c e s , t h e n a t u r e of t h e

Table 3-1 t a b u l a t e s t h e i n f o r m a t i o n i n t h e m a t r i x . A s can be seen from

t h i s t a b l e , t h e m a j o r i t y o f t h e r e s o u r c e recovery p r o c e s s e s (42 p e r c e n t ) are

f u l l s c a l e , s p o r a d i c a l l y p r a c t i c e d (5) . Approximately 36 percen t of t h e

p r o c e s s e s a r e a t l e s s than f u l l s c a l e development ( 2 and 3 ) .

r e s e a r c h areas ( 1 ) r e p r e s e n t 13 p e r c e n t of t h e i d e n t i f i e d recovery p r o c e s s e s .

A d d i t i o n a l l y , almost a l l was te t r a n s f e r a c t i v i t i e s occur w i t h i n t h e g e n e r a t i n g

f a c i l i t y ( a ) or between t h e g e n e r a t i n g f a c i l i t y and a f a c i l i t y i n ano the r

i n d u s t r y ( c ) .

w i t h i n t h e l e a t h e r i n d u s t r y (b).

Proposed

Only 6 pe rcen t of t h e was te t r a n s f e r s o c c u r s between f a c i l i t i e s

3-8

Table 3-1. Summary of Resource Recovery Activities in SIC 31

Number of Number of Waste Matrix Code Activities* Transfer Activities*

a b C

TOTAL

16 6 0 10 38 29 0 9 8 1 1 8 9 5 0 3 53 18 7 30

2 2 0 2

126 61 8 62

*Number of recovery technologies does not correlate with number of waste transfer activities due to multiple matrix codes.

3-9

Further breakdown of this information indicates that an equal number of waste transfer activities associated with full-scale commonly practiced

recovery processes are performed within the generating facility and between facilities in different industries. Also, 54 percent of the waste transfer

activities associated with full-scale sporadically practiced processes ( 5 )

occurs between facilities in different industries, about 33 percent occurs

within the generating facility, and the remaining 13 percent between facilities within the same industry. Of those processes which have undergone some experimentation (development codes 2,3,4), 62 percent of the waste transfer activities would occur within the generating facility, 36 percent between facilities and industries, and only 2 percent between facilities within the

leather industry. Finally, approximately 62 percent of the waste transfers

for proposed processes would occur between facilities and industries, and the

remaining 38 percent would occur within the generating facility.

The second major objective of the report, to identify those areas in which the current state of resource recovery can be advanced, can also be

surmised from this matrix. Based upon this graphic summary of JRB's findings, the state-of-the-art can be advanced in three fundamental ways:

Increasing resource recovery technology development stage

Expanding application and reuse of recovered waste material

Increasing research into and application of new o r proposed recovery areas.

By increasing the technology development stage, a technology may be further implemented throughout the industry. All those technologies that are less than full scale, commonly practiced (i.e., those ranked at 5 o r below) could be further developed. The development of a resource recovery technology

process may be increased, for example, by moving from an experimental stage to

a small-scale functional version of the process, o r by moving from a process being sporadically practiced in the industry to commonly practiced. An

example is the direct recycling of spent unhairing liquor.

current development stage from full scale sporadically practiced to full scale Increasing its

3-10

commonly practiced would result in the advancement of the state-of-the-art.

This advancement would be reflected in the matrix by a change from a five ( 5 )

to a six ( 6 ) .

Increasing the transferability of the recovered material will also

advance the state-of-the-art. All those recovered materials that are transferred on a limited basis could be greater utilized. This would require

finding new applications for recovered materials. An example would be the use of buffing dust as a filter precoat for pressure filters. This use has been

examined only in terms of its potential within the tannery rather than expanding the market to other industries or plants with similar 'needs.

Expansion of the application of this use would result in the advancement of

the state-of-the-art. This advancement would be reflected in the matrix by a change from an Iratc to an "a,c. 11

The matrix also

have received little

the development code

An example of such a -

highlights new technology/waste stream combinations that

attention thus far. These combinations, identified by

one ( 1 1 , have only been proposed by industry researchers.

proposed technology/waste stream combination is the use

of materials recovered from beamhouse trimmings in the manufacture of fungi-

cides and bactericides. Further research in this area may lead to further

development of the recovery process, thereby increasing its state-of-the-art. Additional combinations are identified and discussed in more detail in

Section 5 .

Additionally, further research into the application of existing

technologies o r technologies not identified in the matrix to waste streams

generated by the industry may identify other suitable resource recovery

practices. This increase in the state-of-the-art of resource recovery would

be reflected by additional technology/waste stream correlations on the matrix

in its current form o r through an increase in the scope of the matrix. The

scope of the matrix may also be expanded by identifying additional waste

streams within the industry to which resource recovery processes may be applied.

In summary, the matrix in Figure 3-1 represents a synopsis of this investigation of the current status of resource recovery in the leather industry. Yet, due to the scope of the investigation, neither the matrix nor

the accompanying text discusses every potential o r existing resource recovery

technologyfwaste stream combination. Those combinations not included in the surveyed literature nor discussed with industry representatives are not

addressed in this report.

3-12

4.0 RESOURCE RECOVERY TECHNOLOGY DESCRIPTIONS

--

Numerous resource recovery processes have been proposed, are under

development, or are currently being implemented for the various waste streams

generated by the leather and leather product industry (SIC 31). recovery processes involve:

These

e Recycling of waste streams for reuse of valuable components e Treatment of waste streams to remove and recover specific materials

e Use of wastes in other manufacturing processes or products.

This section provides discussions of each recovery process presented in the matrix (Figure 3-1). For each recovery process, the recovered material is

identified; the recovery process is described; and the impediments to its

current use and its potential fo r future use are discussed. The sources of

the wastes used in the recovery process are also identified.

of the recovery processes in this section excludes descriptions of the tanning and finishing processing steps, as these are presented in Section 2 .

The discussion

4.1 DIRECT RECYCLING

The leather tanning and finishing industry includes many processing steps

involving soaking, washing, and other liquid contact operations. These

processing steps result in large quantities of "spent" solutions which are

commonly discharged to wastewater treatment. concentrations of chemical reagents as well as many pollutants from contact

with the hides, these solutions represent both a loss of useful raw materials and significant cost for effluent treatment. Many tanneries are now realizing

that through direct recycling these spent solutions can be effectively reused

within the tanning process resulting in significant savings in the cost of raw

materials and wastewater treatment.

Containing substantial

4- 1

Direct recycling technologies used in the leather industry offer several benefits, including [ 2 1 ] :

Reduction in materials costs - the reuse of process chemicals otherwise destined for the waste stream lessens the initial requirements for fresh stock.

Reduction in effluent treatment costs - the greater exhaustion of process chemicals, facilitated by effluent recycling, results in a reduction in the overall pollution load.

Reduction in water costs - the reuse of various "spent" solutions reduces process water demands.

A s applied to the leather tanning and product manufacturing industries,

direct recycling is defined as the reuse of all or part of a process effluent in the same or in a different process. This reuse can be facilitated by:

purification of the effluent to remove contaminants; purification of the

effluent followed by refortification to restore the active chemical content;

o r simply the direct reuse of the effluent.

.

A survey of pertinent literature and conversations with industry

representatives indicates that direct recycling technologies are presently

being, or potentially could be, applied to many major tannery process

waste streams. Included in these are processes within the bichromate

reduction, beamhouse, tanyard, retan/fatliquor/color, finishing, and waste-

water tr$atment areas of the leather tanning industry.

limited potential for the application of direct recycling to waste streams

within the leather product manufacturing industry.

There is also a

The following subsections detail direct recycling processes that are or

theoretically could be applied to specific identified waste streams. Included

in this discussion are the processing steps for each direct recyling process, the current stage of development, and the potential for greater use. Specific waste streams that can be recycled include:

Spills from bichromate reduction - chrome spills are collected and recycled to make up tanning solutions.

4-2

Spent soak water - spent soak water is replaced with soak water from later soaking stages, which contain fewer pollutants.

Spent unhairing liquor - unhairing liquor is reused in the unhairing process or used as a soaking solution.

Spent bate wash water - bate wash waters are reused in successive bating, deliming, liming, re-liming, unhairing, and soaking operations following clarification and fortification.

Spent pickle liquor - pickle liquor is reused in the pickling process following refortification.

Spent chrome tanning liquor - chrome tanning liquors are reused in the tanning process as well as in the pickling process, a combination process including pickling and tanning processes, and the retan process.

Spent vegetable tannning liquor - vegetable tanning liquors are reused in the tanning or retan processes.

Additional tannery and leather product manufacture waste streams - other waste streams, including beamhouse rinses, tanyard washes, spent retan liquors, finishing oils, and spent solvents, may be reused in the same or a different process.

These processes are described in the following subsections.

4.1.1 Spills from Bichromate Reduction

Leather tanners may purchase and reduce hexavalent chromium as sodium dichromate to its trivalent state for use in tanning operations. This

reduction process consists of batch mixing sodium dichromate with a reducing

agent such as glucose (in the form of molasses) and acid. This reduction

process may be accompanied by accidental spilling of the chrome solution. Such spills represent a loss of raw material and, if lost to facility

effluent, constitute a regulatory compliance problem in effluent treatment due to hexavalent chromium's toxicity, mobility, and other characteristics.

'

One researcher has proposed a spill collection and recycling method to

prevent loss of chrome solution from the reduction process. The proposed

system includes a collection sump, which collects spilled chrome, segregating

it from other waste streams. The captured materials would be directly reused

in make-up of chrome liquors for use in the tanning process [ 2 2 1 . This k

4- 3

recycling practice could find widespread use in tanning facilities that perform bichromate reduction if the cost of installing collection sumps, piping, and pumps is offset by the cost of losing spilled chrome.

4.1.2 Spent Soak Water

Beamhouse soaking operations restore hide moisture to salt-cured hides

received from a packinghouse. The soak both softens the hides and acts as a

preliminary wash to remove dirt, salt, blood, manure, and non-fibrous proteins

from the hides. Multi-stage drum soaking operations, used to increase the

efficiency of the process, can consist of an initial dirt soak, a main soak, and a final rinse. Because the initial soak stages remove most of the contam-

inants, their effluents contain more pollutants than the later stages 211.

Bench-scale systems have demonstrated that direct recycling pract

applied to the soaking operations reduce the volume of effluent. One

ces

particular project incorporates countercurrent reuse of soak solutions. Periodically, each spent solution is transferred to the preceding soak tank,

resulting in only the first dirt soak being discharged to wastewater treatment

[211. Use of this recycling technique reduces both the volumes of fresh water used and spent soak water requiring treatment. The countercurrent flow requires addition of fresh soak only in the final rinse stage. The single

effluent is discharged after its soaking capacities are exhausted by use in all three stages. This direct recycling process reduces total soak water use

and quantity of wastewater to one-third of that resulting from non-recycling soaking operations [Zl].

The potential for the application of this recycling process to soaking

operations may be good. The researcher makes no mention of treatment,

purification, or refortification of the soaks before reuse. In addition,

significant water savings and reduced treatment requirements may be realized.

However, application of this system may be limited by piping changes needed to

facilitate the transfer of used soaks from stage to stage. Thus, retrofitting existing equipment to accommodate this system may require significant capital

commitments fo r older tanneries (7,211.

4-4

4.1.3 Spent Unhairing Liquor

The unhairing operation involves soaking the hides in a caustic solution,

which is discharged after use to wastewater treatment with other facility

wastewaters. A review of pertinent literature and contact with industry

professionals indicates that much research and full-scale system application

has been performed in the area of recycling spent unhairing liquors. recycling efforts include the direct reuse of unhairing liquor in the

unhairing process as well as in other tannery operations.

These

Many variations of the direct reuse practices are being investigated or used by leather tanners. However, the described recycling techniques often

differ only in their application to individual tanneries; the basic processing steps are the same. Thus, a general unhairing liquor recycling process can be

described as follows:

1. Spent unhairing liquor is transferred to a holding tank.

2. Purification of the liquor, such as removal of solids, or oil and grease, may be performed.

3. Purified liquor is refortified with unhairing chemicals.

4 . Replenished liquor is reused in the unhairing process.

While these steps represent the basic outline of a recycle system for unhair-

ing liquor, variations exist with regard to the number of steps included in the system and the type of process involved in each of the steps.

The purification step can involve a number of treatment or separation

Proteins resulting from dissolved hair and some solids can be techniques. removed by ultrafiltration techniques used in the food and pharmaceutical industries.

scale research [23]. In addition, solids, hide pieces, and hair can be removed using vibrating or rotating screens, sedimentators, or pH adjustment

separators [11,23,24,251. These techniques are generally used at the end of

each cycle to prepare the liquor for reuse. In some cases it may be possible

to eliminate the purification step from the direct recycle process.

Ultrafiltration has been applied to unhairing liquor in bench-

v

’ 4-5

The solids content of spent unhairing liquor from hair burn operations

may be as high as 160,000 mg/l. reduce the efficiency of many separation techniques for waste stream purification. successfully remove solids from the waste liquor prior to reuse [lo].

Such solids content may preclude the use or

Dilution of unhairing liquors may be necessary in order to

Depending on the tanner's decision to purify the liquor, the purification technique used, and certain unhairing process parameters, 15 to 40 percent of the liquor volume may be lost after each cycle [23]. In addition, up to 50

percent of the sodium sulfide and 60 percent of the lime, the two active ingredients in the unhairing process, are either absorbed by the hides or are

removed with the solids during purification [23,26]. Thus, to facilitate the reuse of the liquor, the tanner must refortify it.

After analyzing for chemical concentrations, appropriate amounts of lime,

sodium sulfide, and water are added to restore the solution to its desired

effective concentration. Some researchers have proposed substituting spent unhairing washes for the fresh water normally used to achieve process float

volumes ill]. Following temperature adjustment, the replenished liquor can be

reused in subsequent unhairing operations.

Tanners using full scale direct recycling processes in their unhairing

operations have reported that the finished leather product is of equal or

better quality than that produced with conventional methods [ll]. produced using recycled unhairing solutions with and without purification

before refortification was of comparable quality. In fact, a substantial body

of research has shown that hides unhaired in recycled solutions subjected to cyclic purification were, in some cases, actually of better quality. The

proteins in the wash can affect the feel of the leather ill].

The leather

Unhairing baths have been used and replenished up to 27 times without

causing any noticeable differences in the finished leather. Several

researchers have suggested that the recycled bath could be used indefinitely

with proper monitoring and controls [11,21,241.

4-6

i

Research has demonstrated that tanners who continually reuse their

unhairing solutions, in the above described manner, can expect substantial

savings in both material and effluent treatment costs. For example, results from one study, in which the solution was reused 20 times, revealed that there

was a 20-fold reduction in effluent sulfide; a 7-fold reduction in effluent

lime and protein; and a 5- to 20-fold reduction in fresh water consumption [11,271.

A second method of direct recycling that is applicable to spent unhairing

liquor involves its reuse in another tannery process. Researchers have described a system, sporadically applied throughout the tanning industry, that

uses lime liquors diluted with spent wash liquors in soaking operations. The alkalinity of this solution accelerates the soaking process without detriment to the finished leather Ill]. Again, this process is attractive to tanners

because it can reduce process water demands and significantly lessen the

alkalinity of tannery wastewater.

The impediments to the greater application of the direct recycling of

spent unhairing liquor are associated with system engineering and installation

feasibility. Plants using hide processors (modified cement mixers with

special linings) or pit unhairing systems are particularly well suited to

adoption of the recycling technique [ I I ] . Hide processors are designed for e a s y drainage and quick replenishment and would only require facilities to incorporate collection, pknping, and storage capacity for the spent liquor.

Older plants, on the other hand, will find adoption of the system more costly.

Traditional vat unhairing processes require extensive engineering revisions to

facilitate sludge removal, liquor purification, and chemical replenishment.

In many cases, the necessary investments may impede the incorporation of

spent unhairing liquor recycling systems [8]. This is particularly true for smaller tanneries with limited available capital and tanneries requiring a

rapid return on investment.

attractive to the newer and larger tanners with existing waste segregation equipment that is crucial to the successful operation of this recycling

technique.

The economics of the system will likely be more

'v

4- 7

4.1.4 Spent Bate Wash Water

The bating process removes lime left on the hide from the unhairing process, reduces swelling of the hide, and prepares it f o r tanning by

destroying and removing remaining hair, hair roots, and skin pigments. Following bating, the hides are washed to remove residuals.

which contains pigments, proteins, hair roots, enzymes, and dragout process chemicals, is usually discharged to wastewater treatment as are many other

wash and soak solutions.

This wash water,

.

Researchers at the United States Department of Agriculture have developed

a pilot-scale, countercurrent recycling system that facilitates the reuse of

spent bate wash waters in subsequent tannery processes.

tion, refortification, and countercurrent flow methods are used to prepare the

spent bate wash for use in bating, liming, re-liming, unhairing, and soaking

operations.

Various clarifica-

Proteins and sulfides are also recovered.' The outliine of the

process

1.

2 .

3 .

4 .

5 .

6 .

7 .

8.

9.

is as follows [28,29I:

Add fresh water to spent second post-bate wash to bring up float volume.

Reuse solution as first post-bate wash solution.

Fortify with ammonium sulfate and enzymes and use in deliming and bating . Fortify-solution with lime, remove calcium sulfate by centrifugation, gas-strip or evaporate out ammonia, and reuse as . second post-lime wash solution.

Add calcium hydroxide and reuse in first post-relime wash.

Fortify solution with sodium sulfide and use for unhairing.

Centrifuge solution to remove solids and use in third soak.

Use solution in second soak.

Use solution in first soak.

10. Recover proteins and sulfide; remove suspended solids. Discard effluent .

4-8

In this system, the hides remain in a hide processor where they are treated by

a succession of liquids. The solutions are stored, clarified, and treated in

separate tanks between runs.

Researchers indicate that this countercurrent recycling system has several advantages that increase its potential for application within the

tannery. First, water usage and effluent volumes from the processes to which

this system applies are reduced to approximately one-tenth as compared t o

conventional systems with no recycling [ 2 8 , 2 9 ] . Second, this integrated

system provides the tanner with a solution that can be used in 10 tannery process operations with limited clarification and refortification.

unlike conventional recycling procedures, the nature of this system is such that the solution is inherently self-stabilizing [ 2 8 , 2 9 ] . Hence, this

equilibrium guarantees stable chemical conditions, which in turn, provides for

leather of consistent quality. Finally, pilot-scale tests indicate that leather comparable to that made with conventional procedures can be produced with this system [ 2 8 , 2 9 ] .

Third,

Yet, due to the apparent complexity of this system, tanners may be reluctant to implement it. Such implementation would require the adoption o f

10 individually linked recycling/recovery processes. Tanners who do not use

hide processors (or similar equipment) would have to install extensive new piping and process monitoring equipment. Additionally, as with any

experimental systems, problems may be encountere2 when scaling-up the system

for full-scale tannery operations.

Finally, some tanners may be forced to go beyond basic pipe retrofitting

to implement this system into their processing operations. Because individual

sequences of operations may not facilitate the immediate use of spent/ clarifiedlrefortified solutions, intermediate storage tanks would be necessary

to hold the solutions before the next subprocess can be completed.

4 . 1 . 5 Spent Pickle Liquor

The pickling process precedes the tanning step. By providing an acid environment, pickling prepares the hides f o r accepting chrome tanning agents,

4-9

which have minimum s o l u b i l i t y under a l k a l i n e c o n d i t i o n s .

p r e v e n t s p r e c i p i t a t i o n of chromium s a l t s on t h e h i d e s u r f a c e .

s o l u t i o n most commonly used c o n s i s t s of s u l f u r i c a c i d and s a l t .

The p i c k l i n g s t e p

The p i c k l i n g

Like o t h e r spen t l i q u o r s , t h e s p e n t p i c k l e l i q u o r has a p o t e n t i a l f o r

d i r e c t r e c y c l e w i t h i n t h e p i c k l i n g p rocess . I n f a c t , d i r e c t r e c y c l i n g of

p i c k l e l i q u o r s i s s p o r a d i c a l l y p r a c t i c e d on a f u l l - s c a l e l e v e l w i t h i n t h e

t a n n i n g i n d u s t r y .

f o r r e c y c l i n g spen t u n h a i r i n g l i q u o r . For example, one s h e a r l i n g t a n n e r y

r e p o r t e d l y c o l l e c t s t h e s p e n t p i c k l e l i q u o r , a n a l y z e s i t for a c t i v e chemica l s ,

and r e f o r t i f i e s i t i n p r e p a r a t i o n f o r t h e n e x t b a t c h o f h i d e s . Th i s t a n n e r y

h a s reused i t s p i c k l e l i q u o r s up t o f i v e t imes 1111.

The o p e r a t i o n of t h e r e c y c l i n g p rocess i s s imi lar t o t h a t

Although no in fo rmat ion i s a v a i l a b l e on t h e impediments a s s o c i a t e d wi th

r e c y c l i n g p i c k l e l i q u o r s , they probably i n v o l v e in- plan t m o d i f i c a t i o n s t h a t

are n e c e s s a r y t o c o l l e c t , s e g r e g a t e , and r e f o r t i f y s p e n t l i q u o r s . An

a d d i t i o n a l impediment is t h e p o t e n t i a l bui ld- up of s a l t s , g r e a s e , p e p t i d e s ,

and o t h e r m a t e r i a l s i n t h e r e c y c l e d l i q u o r t h a t could be d e t r i m e n t a l t o t h e

q u a l i t y of t h e l e a t h e r . Undes i rab le s t a i n s on t h e J e a t h e r may a l s o r e s u l t

from r e u s e of p i c k l e l i q u o r s [ l o ] .

4 . 1 . 6 Spent Chrome Tanning Liquor

The t ann ing s t e p i n v o l v e s soaking t h e prepared h i d e s i n a s o l u t i o n con-

t a i n i n g t ann ing a g e n t s . These t a n n i n g a g e n t s are absorbed by t h e h i d e s and

impar t d e s i r e d p r o p e r t i e s t o t h e l e a t h e r p roduc t . A f t e r removal of the h i d e s ,

t h e t a n n e r i s l e f t w i t h a s p e n t t ann ing s o l u t i o n t h a t i s c h a r a c t e r i s t i c a l l y

d i s c h a r g e d t o wastewater t r ea tment l i k e many o t h e r t a n n e r y s o l u t i o n s .

I n bo th chrome and v e g e t a b l e t ann ing o p e r a t i o n s , r e c y c l i n g h a s become a

major concern. Tanners and r e s e a r c h e r s have d e s c r i b e d s e v e r a l p r o c e s s e s t h a t

f a c i l i t a t e t h e r e u s e of a l l or p a r t of t h e i r s p e n t t a n n i n g l i q u o r s . These

s p e n t l i q u o r s can be reused i n t h e t ann ing p rocess as w e l l as o t h e r t a n n e r y

o p e r a t i o n s such a s p i c k l i n g and r e t a n n i n g .

4-10

The direct reuse of spent chrome liquors in the tanning process has been described by a number of researchers.

process are sporadically used throughout the chrome tanning industry.

using the process have realized savings in both stock chemicals and effluent

treatment costs. The basic outline of the direct recycling process as applied to spent tanning liquor is as follows:

In fact, v.ariations of the recycle

Tanners

1. Segregation of the tanning liquor waste stream from other process waste streams.

2 . Optional purification to remove suspended solids and other contaminants .

3 . Analysis of spent liquor to determine level of active tanning chemicals.

4 . Refortification of tanning liquor to desired chemical composition.

5 . Reuse of tanning liquor in subsequent operations.

Most recycling systems that involve reuse of spent chrome liquors in the

tanning process require the simple collection and subsequent refortification of the solution. However, other systems require that the solution undergo

some type of treatment or purification before replenishment. Conventional

tannery systems utilize holding vessels to treat spent tanning liquor [ 7 ] .

Suspended solids, oil, and grease can be removed from the solution using

screens and skimmers [11,32]. In addition, chemical flocculants are

reportedly capable of removing 60 to 90 percent of suspended solids, as well as some residual grease and oils, while leaving as much as 99 percent of the

chrome in solution [31]. Tanners utilizing hide processors can take advantage of the nature of this equipment to purify the spent liquors. For example, an Australian tannery has found that settled sludge can be drained out the bottom of the hide processor and the oils can be drawn off the top. The remaining

liquor, equalling 9 5 percent of its original volume, can be removed and/or replenished [11,32].

-_

Following clarification, the spent tanning solution must be replenished

with the appropriate reagent chemicals. Approximately two-thirds of the chrome, which is taken up by the leather during tanning, must be replaced

u

4-1 1

before reuse in the next tanning process. Adequate monitoring and quality

control procedures are necessary to assess the precise amount of active chemicals needed for replenishment. This monitoring assures that leather of consistent quality is produced.

Tanners and researchers using variations of the described generic

recycling technique have recycled tanning liquors up to 13 times with no deterioration in the quality of the finished leather product. It is postu- , lated that the liquor could be reused indefinitely with proper monitoring and

controls [331. Each use in successive cycles will save 25 to 30 percent on chrome reagent costs [11,33]. There will also be an associated savings in

effluent treatment costs due to a two-thirds reduction of chrome in tannery wastewater [341.

Possible impediments to the greater use of this recycling technique are

those associated with quality monitoring, solution clarification costs, and

process modifications. Researchers have stated that, unless the solution is

adequately purified before reuse, the build-up of grease can potentially cause discoloration of the hide ill]. Because the tanner is producing a product for

clients with very specific needs, he must be confident that his manufacturing process can meet these needs.

ment with tanning techniques that they feel are as yet unproven [351. Tanners may therefore be reluctant to experi-

A second method of directly recycling spent chrome tanning liquors is to

use the solution in the make-up of pickle liquors. This sporadically prac-

ticed process requires that the liquors be handled similarly to the recycling

of spent pickle liquors. The spent chrome tanning liquor must be collected,

clarified, analyzed for active chemical content, and fortified with pickling

agents. Application of this recycling method has revealed that use of spent chrome solution in pickling operations results in a pretannage of the hides [11,22,35,37]. Because chrome salts carried over in the reused solution pretan the hide as it is pickled, the amount of chrome and the time needed to

finish the tanning of the hide in the actual tanning step can be substantially reduced.

4-12

V a r i a t i o n s of t h i s d i r e c t r e c y c l i n g t echn ique have been d e s c r i b e d by

s e v e r a l r e s e a r c h e r s and t a n n e r s [ 1 1 , 2 2 , 3 2 , 3 4 , 3 7 , 3 8 , 3 9 , 4 0 ] . Some have r e p o r t e d

t h a t , w i t h proper moni to r ing and c o n t r o l t h e f i n i s h e d l e a t h e r product is of

e q u i v a l e n t q u a l i t y t o t h a t p ick led by conven t iona l methods [ I l l . Tanners

u s i n g t h e p rocess have r e p o r t e d r e d u c t i o n s i n p i c k l i n g s a l t r equ i rements o f

42 t o 100 pe rcen t [21 ,34] . Moreover, t h i s i s accompanied by a concur ren t

r e d u c t i o n i n chemicals l o s t t o &he e f f l u e n t , the reby reduc ing e f f l u e n t

t r ea tment c o s t s [211.

The impediments t o t h e g r e a t e r use of t h i s d i r e c t r e c y c l i n g p rocess a r e

s imi lar t o those f o r t h e r e u s e of spen t chrome l i q u o r i n t h e t a n n i n g p r o c e s s .

Unless the t anner can be assured of a product of c o n s i s t e n t p r e d i c t a b l e

q u a l i t y , he w i l l be r e l u c t a n t t o i n s t i t u t e any p rocess changes.

Two a d d i t i o n a l problems are c o l l e c t i o n of spen t chrome l i q u o r and t h e

volume genera ted . Because t h e r e i s g e n e r a l l y a g r e a t e r volume o f s p e n t

t ann ing l i q u o r produced than i s needed i n t h e p i c k l i n g p r o c e s s , t h e t a n n e r

must i n s t i t u t e some means of hand l ing t h e excess volumes [22] . One r e s e a r c h e r

s u g g e s t s two p o s s i b l e remedies t o t h e s e problems. F i r s t , t h e t a n n e r could

reduce the f l o a t volumes of t h e t ann ing b a t h , t h e r e b y reduc ing t h e volume o f

spen t l i q u o r . A second approach i s t o t r e a t t h e excess spen t t ann ing l i q u o r

w i t h o t h e r r e s o u r c e recovery p rocesses such a s chrome p r e c i p i t a t i o n , a s

d e s c r i b e d i n S e c t i o n 4 .2 [22] .

A t h i r d d i r e c t r e c y c l i n g technology, used by t a n n e r s i n v a r i o u s forms, i s

a combination of t h e t ann ing and p i c k l i n g p r o c e s s e s . The h i d e s are cured and

s t a b i l i z e d us ing one cont inuous ba th o f changing chemical composi t ion. The

g e n e r a l o u t l i n e of t h e p rocess i n v o l v e s t h e c o l l e c t i o n and p u r i f i c a t i o n of t h e

s p e n t t ann ing s o l u t i o n us ing p r e v i o u s l y d e s c r i b e d t echn iques . It i s t h e n

f o r t i f i e d w i t h a p p r o p r i a t e amounts of p i c k l i n g a c i d s and s a l t s .

chrome t a n n i n g j p i c k l e s o l u t i o n r e s u l t s i n a pre tannage of t h e h i d e .

t ann ing of t h e h i d e i s completed through a d d i t i o n of chrome powder t o t h e

s o l u t i o n . G e n e r a l l y , t h e r e q u i r e d amount of powder is 75 t o 80 p e r c e n t of

t h a t used i n conven t iona l t ann ing p r o c e s s e s [30,32,38,39,401. The c y c l e i s

completed wi th t h e c o l l e c t i o n and c l a r i f i c a t i o n of t h e spen t chrome tann ing /

This s p e n t

The

L p i c k l e l i q u o r which i s u s e d i n t h e next p i c k l e l t a n o p e r a t i o n .

4-13

Researchers and tanners using variations of this direct recycling process

report significant savings in stock chemical and effluent treatment costs. The continuously recycled bath, requiring only replenishment equalling that absorbed by the hide and drawn off as sludge during purification, can reduce

spent tanning liquor effluent volume by 90 percent (281. It also can result in a reduction in chrome use by 20 to 25 percent.

The impediments to the greater application of this direct recycling tech-

nique again appear to be those associated with the required monitoring and

analysis of the recycled bath. Should the tanner believe that the characteristics of his product might be changed by this technique, he will adopt it

only with extensive quality controls. cost of adequate controls are too great.

The tanner may conclude that the extra

Another method of recycling spent tanning liquors is their reuse in

subsequent retan operations. In one proposed system, spent tanning liquors

that have been recycled in the tanning process would be pumped to a holding

tank where they would be settled, filtered, and skintned. Removed fats,

solids, and other impurities may be sent to chrome recovery or discarded.

Following clarificaton, the liquors would be refortified with appropriate

amounts of fresh acid and chrome powder and reused in retan operations [361.

To implement this double recycling system (reuse of recycled chrome liquors in retan operations) , tanners would be forced to install additional holding tanks and subject liquors to more extensive clarification. Tanners may therefore be even more reluctant to trade off reduced final effluent

treatment and stock chemical costs for increased risks of hide discoloration,

and new clarification and equipment renovation costs.

4.1.7 Spent Vegetable Tanning Liquor

Traditional vegetable tanning systems are characterized by a counter-

current flow of the tanning solutions in relation to the hides. The hides may be exposed to tanning solutions of increasing concentrations while remaining

in a single vat or they may be moved from vats with weaker tanning solutions to those containing successively stronger solutions. As the tanning process

4-14

i s c a r r i e d o u t , t h e t a n n i n c o n c e n t r a t i o n s are reduced i n each of t h e b a t h s due

t o uptake of t a n n i n by t h e h i d e s . The r e c y c l i n g p rocess i n v o l v e s t r a n s f e r r i n g

each b a t h c o u n t e r c u r r e n t t o t h e d i r e c t i o n of h i d e t r a n s f e r , t o r e p l a c e t h e

p reced ing b a t h . Thus, on ly t h e f i r s t b a t h , c o n t a i n i n g t h e lowest concentra-

t i o n of t a n n i n i s d i scharged . Sludge from mul t ip le- va t systems i s p e r i o d i-

c a l l y removed from spen t t ann ing s o l u t i o n s v i a c e n t r a l i z e d c o l l e c t i o n p o i n t s

[ 4 0 ] . The on ly r e q u i r e d f r e s h m a t e r i a l i s t h a t needed t o r e p l a c e t h e l a s t ,

most c o n c e n t r a t e d b a t h [ 11 , 18 1.

A more r a p i d f u l l - s c a l e , commonly used v e g e t a b l e t ann ing p r o c e s s , c a l l e d

t h e L i r i t a n system, has been i n use s i n c e a t l eas t 1960.

i n i t i a l tanning p r o c e s s , limed and ba ted h i d e s are exposed t o a b a t h of sodium

hexametaphosphate (Calgon) and s u l f u r i c a c i d . This b a t h p r e p a r e s t h e h i d e f o r

a more r a p i d t ann ing p rocess . This b a t h , which i s o n l y d i s c a r d e d once per

annum, i s reused d a i l y , and i s r e f o r t i f i e d w i t h a d d i t i o n a l Calgon and s u l f u r i c

a c i d a f t e r each use [18,411.

As p a r t of t h e

P u r i f i c a t o n of spen t t ann ing l i q u o r t o remove contaminants w i l l g e n e r a t e

some blowdown c o n s i s t i n g p r imar ly of t ann ing l i q u o r .

c o n c e n t r a t e t h e l i q u o r and s e l l i t o r r e u s e i t i n subsequent r e t a n n i n g

o p e r a t i o n s 1111.

Tanner ies can e i t h e r

The impediments t o t h e g r e a t e r use of t h e s e p r o c e s s e s a r e those a s s o c i-

a t e d w i t h t h e r e q u i r e d equipment and l a b o r c o s t s and necessa ry p rocess

moni to r ing . An a d d i t i o n a l impediment i s t h e inc reased chemicals c o s t of

running t h e system w i t h sodium hexametaphosphate [42 1 .

I n t h e r e c y c l i n g of v e g e t a b l e t ann ing l i q u o r s , some r e s e a r c h e r s have

voiced concerns over t h e p o s s i b l e bui ld- up of con taminan t s , such as non- tans

and n e u t r a l s a l t s , t h a t can i n t e r f e r e wi th t h e uptake of v e g e t a b l e t a n n i n s by

t h e h i d e .

from prev ious p i c k l i n g and soaking o p e r a t i o n s [11,21,411. I t i s suggested

t h a t moni tor ing of t h e b a t h s i s necessa ry t o prevent t h e contaminants from

i n t e r f e r i n g wi th t h e t ann ing o p e r a t i o n s .

These a r e p r i m a r i l y in t roduced t o t h e system by t h e h i d e s coming

4-1 5

4.1.8 Additional Tannery and Leather Product Manufacturing Waste Streams

A survey of pertinent literature and conversations with tanners and

leather product manufacturers reveals that several other industry waste

streams are subject to direct recycling technologies. However, detailed information was not available on the identified recycling operations. These

operations include:

1. Full-scale demonstration projects showing the feasibility of recycling beamhouse rinses for use in lime liquors and rinse make-ups .

2 . Sporadic recycling of tanyard washes for reuse in subsequent washes.

3 . Full-scale demonstration projects showing washes can be used in pickle liquor make-up.

4. Sporadic use of direct recycling technologies to reuse spent retan liquors and finishing oils.

5 . Proposals for use of direct recycling technologies to recover spent solvent.

Many of these areas are under active consideration by those in the

leather product manufacturing industry. Each application may reduce manu-

facturing costs by allaying the need for fresh stock materials and extensive

effluent treatment. Each operation can only be implemented with varying

degrees of capital outlay and pay-back time.

4.2 CHROME RECOVERY

Chrome is the tanning agent used for the commercial tanning of almost

every type of animal skin or hide. In the tanning operation, tanning agents bind with the collagen (protein) fibers of the hide or skin forming a stable

material that is resistant to decay. Tanning agents, through their binding

action, improve the mechanical properties (stability, resistance, flexi-

bility), and durability of the hide or skin.

a leather with the chemical and physical properties preferable for most

leather uses, chrome is the most popular tanning agent [ll]. Moreover, it

takes only a fraction of the time required for other tanning techniques, such as vegetable tanning.

Because chrome tanning produces

-

4-16

Chrome used in the tanning process, such as chromium sulfate, is produced

by the chemical industry from processed chromite ore.

workable domestic sources of chromite ore in the United States. The only source of chromium is domestically processed chromite ore; the unprocessed ore

is largely imported from the Republic of South Africa, the Soviet Union, the Philippines, and Turkey [431.

There are currently no

Much of the chrome used in the tanning process never gets into the

finished leather product. The hides or skins take up approximately

70 percent of the chrome contained in the tanning liquor [11,37]. Unfixed chrome is lost in liquid waste streams consisting of spent tanning liquor,

washes, and rinses. Wastewater treatment of these liquid wastes generates a

sludge containing approximately 1 to 4 percent chromium [ 4 4 ] .

almost half of the chrome taken up by the hides during tanning is either

contained in the splits or is lost as solid waste generated in the leather

shaving and trimming operations [lo]. These leather scraps are further

processed, reused, or landfilled.

In addition,

In 1978, the total demand in the United States for dichromate (the source of trivalent chrome used in tanning) was 161,000 tons with 27,300 tons (17 percent) being consumed in the leather tanning industry. Of this quantity, 1 2 , 7 3 2 tons, o r 47 percent of the total chrome used by tanners, was

fixed in leather products. The remainder, 14,568 tons or 53 percent, was lost

via splits, hide scrap wastes, wastewater, and wastewater treatment sludges. This loss represents approximately 9 percent of the total quantity of chrome

used in the United States (451.

Although the loss of chrome in tanneries represents only a fraction of

the total quantity used in the United States, it is of concern for three

reasons [36,40,45,46,471:

The United States is totally reliant on imported chromite ore as a chromium source

e Present and historical consumption patterns suggest a potential scarcity of chrome in the future

4-1 7

0 Irretrievable loss of more than 50 percent of a raw material critical to the tanning process forces tanners to absorb burdensome costs for waste treatment and new raw materials.

Tanners are currently addressing this situation by researching and imple-

menting various chrome recovery systems.

chrome-bearing solutions (see Section 4.11, increasing the chrome uptake by hides and skins, and recovering chrome from wastewater and tannery solid waste

for reuse within the tanning process [ 2 2 , 3 5 1 . Techniques for chrome recovery currently being considered, experimented with, or implemented include:

These include direct recycle of

e Precipitation - the reaction of liquid or solid chrome-bearing waste streams with another substance (usually alkali) to form an insoluble chrome compound that can be separated from the remaining liquid. precipitate is dissolved in acid to obtain a chrome solution usable in the tanning process.

The

Ion exchange - chrome is adsorbed from chrome-beating waste liquors onto an ion exchange resin, stripped from the resin, and used in producing a new chrome solution.

e Acid dissolution - chrome-bearing solid and sludge wastes are dissolved in or treated with acid; the resulting solution or precipitate is used elsewhere in the tannery.

e Incineration - chrome-bearing solid wastes and sludges are burned at high temperatures to produce an ash with a high chrome content. The ash is then treated or further processed to recover the chrome. The ash treatment technique is determined by the form and characteristics of the chrome in the ash, which are determined, in turn, by the parameters of the incineration process. Heat may also be recovered by this method.

0 Pyrolysis - chrome-bearing solid and sludge wastes are roasted at relatively low temperatures (300-600°C) to produce chrome-laden ash and char from which chrome is extracted. Heat may also be recovered by this method.

0 Absorption - a scrubber on the stack from the bichromate reduction facility removes chrome from the waste gases by absorption. The chrome is then returned to the reduction process.

These processes are described in more detail in following subsections.

4-18

In addition to those processes previously mentioned, several other

recovery techniques have been examined in the past. These techniques include:

a Chrome absorption from wastewater using hide trimmings, which are then burned to produce chrome-bearing ash

a Adsorbtion of chrome from liquid waste using activated carbon

a Solvent separation of chrome from spent chrome liquor

a Reaction of spent chrome liquor with alcohol to form chrome soap, which is readily removed from the liquid.

Several of these recovery techniques were found not to work while others were

found to be impractical. found to show some promise but was never implemented.

are also discussed briefly in this section.

One method, however, chrome soap production, was These recovery methods

4 . 2 . 1 Precipitation

The basic elements of the precipitation process for chrome recovery as

practiced in today's leather tanning industry are similar to those used during

World War IT when chrome recovery was commonly practiced. The chrome precipitation process practiced during World War I1 involved precipitation of chrome

from waste liquors using caustic soda. The precipitate was separated from the

remaining waste liquor, dissolved in acid, and restrengthened to form fresh tanning liquor [ 4 8 ] .

being implemented throughout the world.

There are several variations to this technique currently

Waste streams for which precipitation may be practical or is proposed include:

0 Spent tanning liquor

a Rinse water

Splits

6 Blue trim and shavings a Spent retan liquor

a Unfinished leather trim 0 Finished leather trim.

4-1 9

- Presently in the United States, precipitation of chrome, either as full-scale or demonstration projects, is not commonly practiced by leather tanneries. However, where precipitation is practiced, it is generally applied to the

spent tanning liquor.

The chrome precipitation processes described in the literature for

liquid wastes involve essentially the same steps:

1. Collect process wastewaters for precipitation.

2 . Add alkali to produce a chromium hydroxide precipitate. 3 . Separate and purify the precipitate. 4 . Dissolve the precipitate in acid to produce a tanning liquor.

The actual processing mechanics of each precipitation process vary according

to the chrome concentration in the wastewater, the type of alkali used, and

the formation of unwanted by-products upon dissolution in acid.

Pfister and Vogel Tanning Company has investigated various alkaline solutions suitable for precipitation of chrome and has installed a full-scale

chrome recovery system into their tanning operation. This tannery specifi-

cally studied the use of soda ash, aqueous ammonia, hydrated lime, and caustic

soda as precipitation agents. Hydrated lime was found to be the best alkali

for precipitation in spite of the formation of insoluble calcium sulfate; the

hydrated lime provided better removal of chromium from the liquid and faster

sludge (precipitate) settling than other alkalis that were tested. Soda ash

was found to be most appropriate for recovering chrome from highly concen-

trated waste streams rather than dilute chrome streams [ 4 8 1 .

The Pfister and Vogel chrome recovery process involves the following

steps [ 4 8 1 :

1. Collect spent tanning liquor from hide processors (the vessel in which hides are tanned).

2 . Screen collected liquor to remove solids and other large particles.

3 . Add hydrated lime to precipitate chrome as chromium hydroxide. u

4-20

4 . Settle the precipitate by addition of coagulants and/or flocculants.

5 . Decant waste liquid and filter the sludge containing settled precipitate.

6. Dissolve the chrome-laden filter cake in acid and remove calcium sulfate precipitate using a hydrocyclonic separator.

7 . Use acidic chrome liquor in the tanning process.

A full-scale demonstration project for chrome precipitation is being developed at another tannery. This recovery process, the Revere-Chromagin

process, is being applied to both spent tanning solutions and waste rinse

waters. The collected solutions are filtered to remove solids; fats and oils

are removed; and alkaline reagents (including magnesium oxide or hydroxide) are added to precipitate the chrome as chromium hydroxide. This precipitate

is filtered, washed, and dissolved in sulfuric acid for reuse in the tann process [ 351.

In Europe, the chrome precipitation process is essentially the same.

Tanneries in the United Kingdom prefer sodium carbonate as the precipitat

agent if the chrome is to be reused, because sodium carbonate reduces the formation of insoluble calcium sulfate upon dissolution of the precipitate in

acid. Though tanneries in Denmark and Switzerland also use sodium carbonate

as the precipitating agent, they differ in the precipitate separation tech-

nique employed. In one Danish tannery, the precipitate is separated using

centrifugation while a Swiss tannery uses only simple settling. Another Swiss tannery uses lime for precipitation and separates the precipitate by settling

1491.

Spent retan liquor is another waste stream with the potential for chrome recovery by precipitation. One proposed system involves the recovery of

chrome from spent retan liquor, which was prepared from spent tanning liquor.

Chrome may a l so be recovered from the rinse water generated after the retan

step [361.

A somewhat different process has been patented for the recovery of both chrome and proteins from leather scrap. Leather scrap is heated in the

4- 2 1

e presence of an alkali, such as calcium oxide or lime. Water is added to the solution causing water-soluble proteins to solubilize and chromium hydroxide

to precipitate from the solution. and a precipitate) are then separated [501. Although the type of leather

scrap used was not specified, it may include splits, blue trim and shavings, unfinished leather trim, and finished leather trim.

The two products (a proteinaceous liquid

There are several impediments to the implementation of precipitation for

chrome recovery that are currently facing the tanning industry. These

include process restructuring, equipment renovations, and restrictive costs.

The most common impediment to the recovery of chrome by precipitation is the segregation of chrome-bearing liquid waste streams from other waste streams in the tannery (341. Most tanneries send all of their process waste streams to a common sewer in the plant. Having to install special equipment

to separate the chrome-bearing waste streams would add to the cost of

installing the equipment necessary for precipitation, purification, and reacidification of the chrome.

The type of equipment (process vessel) in which the hides are tanned will also affect the implementation of this system. Hides and skins have tradi-

tionally been tanned in wooden vats, which are well suited to the common sewer

drainage system used by tanneries. Recently, hide processors (modified cement mixers) have been used in the tanneries as the tanning vessel. Hide

processors are better suited for the separation of waste streams, but not all

tanneries currently have hide processors nor plan to incorporate them.

Significant changes in equipment and processing operations may have to be

implemented in order to collect waste streams with significant chrome concen-

trations. For example, one tannery using wood tanning drums that normally discharges to the facility's common sewer had to segregate other discharges

from the spent tanning liquor. While spent tanning liquor was being drained

from one drum, no other drums could be drained or washed; otherwise, the spent

tanning liquors would be diluted and the chrome recovery process would not be

4- 2 2

as effective. This segregation required careful scheduling of tanyard opera-

tions, and the diversion of the waste stream had to be controlled manually

[47]. Another tannery had to modify the tanning drums so that spent tanning liquor and rinses could be effectively drawn off. Additional storage tanks

and equipment for handling and processing the liquid wastes were also required

[351.

In addition to the process modifications needed to segregate waste

streams, the chrome precipitation process itself requires costly equipment. Small tanneries with limited available capital may not be able to install the

necessary equipment or make the necessary process changes. However, the cost

of the equipment should, in time, be offset by decreased raw material needs.

For the system described in the previous paragraph, for example, the annual savings of chrome for a 1,000 hide per day tannery would be $53,625 while the total operating cost per year would be $18,475, based on 1977 costs and

estimates. The payback period for equipment needed to recover chrome was

estimated to be approximately 2 . 6 years [471. 1976 costs, Pfister and Vogel estimated that their chrome precipitation s:-stem

would cost $156 (lime precipitation) to $248 (soda ash precipitation) per day to operate. Their net annual savings, based on processing 4,350 cattlehides

per day, were estimated to be $50,000-126,000 for the soda ash system and

$68,000-135,000 for the lime system [481.

In another example, based on

Since small tanneries often have limited available capital to invest in a chrome precipitation recovery system, installing a treatment system central to

a number of small tanneries could make such a recovery process more amenable. Such a system would include capacity to treat the wastes from all the

surrounding tanneries; the recovered chrome would presumably be returned or

sold to area tanneries. Such a system is currently being implemented in upstate New York. The Revere-Chromagin precipitation process, as discussed

above, is being installed at the largest tannery in the Gloversville/Johnstown

area of New York. The system was designed so that it could potentially handle

spent tanning liquor from all of the nearby tanneries. The Revere Brass and

Copper Company, owner of the patent for this recovery process, hopes to

install such a centralized treatment facility in other areas of the country

4-23

t h a t have a concent;ation of smal l t a n n e r i e s [351. Salem a r e a of Massachuset ts and pa r t s of Wisconsin and New J e r s e y .

Such areas i n c l u d e t h e

The p o t e n t i a l f o r i n c r e a s e d use of p r e c i p i t a t i o n for chrome recovery

appears t o be ve ry good. The y e a r l y s a v i n g s i n chrome use are h i g h , whi le t h e

c o s t s f o r d i s p o s i n g of chrome-laden wastewater t r e a t m e n t s ludges ( t h e major

non- recovery, waste t r e a t m e n t method c u r r e n t l y i n u s e ) are r a p i d l y i n c r e a s i n g .

The use of c e n t r a l i z e d p r e c i p i t a t i o n f a c i l i t i e s could h e l p t o open up t h i s

r ecovery o p t i o n t o t h e s m a l l t a n n e r i e s t h a t cannot a f f o r d t h e c a p i t a l

inves tments t h a t a r e r e q u i r e d .

4.2.2 Ion Exchange

I o n exchange i s a p rocess whereby ions p r e s e n t on t h e s u r f a c e of an ion

exchange r e s i n a r e r e p l a c e d by i o n s p r e s e n t i n t h e s o l u t i o n i n which t h e r e s i n

i s immersed. The exchanged i o n s have s i m i l a r cha rges t o t h o s e con ta ined i n

t h e r e s i n , i . e . , c a t i o n s ( p o s i t i v e l y charged i o n s ) i n s o l u t i o n r e p l a c e c a t i o n s

i n t h e r e s i n and an ions ( n e g a t i v e l y charged i o n s ) i n s o l u t i o n r e p l a c e an ions

i n t h e r es i r [51].

Ion exchange r e s i n s are used e x t e n s i v e l y i n t h e e l e c t r o p l a t i n g i n d u s t r y

t o r e c o v e r chromic a c i d from r i n s e water. This method u s e s bo th types o f

r e s i n s , exchanging c a t i o n s and a n i o n s , so t h a t a l l chemical forms of chromium

used i n e l e c t r o p l a t i n g may be recovered .

c u r r e n t l y o p e r a t i n g w i t h i n t h e e l e c t r o p l a t i n g i n d u s t r y [ 5 2 1 .

There a r e a t leas t 50 u n i t s

L i t t l e r e s e a r c h o r i n v e s t i g a t i o n i n t o chrome recovery from l e a t h e r

t a n n e r y wastewaters by i o n exchange has been completed. Th i s r e s e a r c h h a s

p r i m a r i l y d e a l t w i t h t h e fo l lowing waste streams:

0 Spent t ann ing l i q u o r

0 Rinse water

Spent r e t a n l i q u o r .

Limited r e s e a r c h i n t o t h e a p p l i c a t i o n of ion exchange t o chrome-bearing

t annery waste streams was r e p o r t e d i n 1959. Chrome from t h e l i q u i d was tes was

4-24

adsorbed onto an ion exchange resin, then stripped off using dilute sulfuric acid. The resulting solution proved too dilute to be used as make-up for

fresh tanning liquor. Stronger acid solutions could not be used to strip the

chrome from the resin because of the possibility of inactivating the resin

[37 I.

A Japanese process for chrome recovery by ion exchange has been patented

in the United States. This process involves removal of cation impurities from the waste liquid by a cation exchange column followed by removal of chrome in

its anionic form by a series of anionic exchange columns.

periodically taken off line and stripped of the adsorbed chrome by passing first chromic acid, then alkali through the column [531. This patent was

developed for recovery of chrome in its anionic form from unspecified chrome-

containing wastewater. This could potentially be applied to spent tanning

liquor, rinse water, and spent retan liquor from the tannery.

Each column is

There are two major impediments to the implementation of ion exchange for chrome recovery in tanneries: cost of equipment and the present availability

of more readily implemented recovery processes. Tanners are generally

unwilling to install ion exchange recovery systems because they feel that the

systems would be prohibitively expensive due to blockage of the exchange columns by organic matter common to tannery wastewater and high regeneration

costs 1481. Further, other recovery options, such as chrome precipitation,

may be easier for. the tanners to use for chrome recovery and to meet applicable effluent guidelines [531.

Although not used in the leather tanning industry, ion exchange has

proven highly efficient in recovering chemicals in the electroplating industry. The ion exchange systems are compact, relatively inexpensive, and

generally easily installed. Most current ion exchange resins are resistant to

chemical or thermal attack, but are subject to clogging and fouling under

certain conditions or in the presence of certain materials [ 5 1 ] . Thus, spent tanning liquors containing greases, oils, and proteins must be clarified

before ion exchange can be used.

4-25

Ion exchange has been applied to waste streams containing hexavalent and trivalent chromium. Further research on its feasibility is necessary to

evaluate its application to waste streams containing primarily trivalent chromium (see Section 5 . 2 . 1 ) .

4 . 2 . 3 Acid Dissolution

The blue splits and shavings resulting from tanyard operations contain

recoverable chrome. In Hungary, this waste material is dissolved in sulfuric acid. The resulting acidic chrome solution is used either directly as a

tanning solution or for the reduction of hexavalent chrome to trivalent chrome

1 5 5 1 . Specific details on the processing equipment o r additional processing

steps were not available. However, additional treatment of the liquid from

acid dissolution of the blue wastes may be necessary, such as protein removal,

before the liquid can be used elsewhere in the tannery.

Current information indicates that acid dissolution is not used in the

United States at this time. However, this method of chrome recovery may be applicable to chrome-bearing leather wastes including blue trim and unfinished

leather waste. This processing method bears further investigation as to

equipment needs, capital costs, and the quantities of generated wastes needed

to operate the system in a cost-effective manner.

able to recover chrome from solid wastes, this system may prove more feasible

to implement for chrome recovery than incineration o r pyrolysis of the same

materials. Additionally, if proteins must be removed from the chrome solution before it can be used, the system can also involve protein recovery. Through

sale of the recovered proteins, the tannery may gain additional revenue that will help to offset the cost of equipment installation.

Of the three options avail-

Bench-scale research has also shown that chromium can be extracted from

wastewater treatment sludges. This research included examination of a number of acids, both organic and mineral, to neutralize the alkaline sludge and

convert the chromium to an extractable form. Sulfuric acid was found to be the most suitable substance both technically and economically. Following

neutralizaton, the sludge was treated with magnesium oxide and either sodium

4-26

hydroxide or sodium carbonate to precipitate the chromium [ 4 3 ] .

precipitate is presumably collected and used to make fresh tanning liquor.

The chromium

Researchers have reported that leather of substandard quality was pro-

duced using chromium recovered from the sludge. This leather had a bad odor,

imparted by chrome recovered from decomposing sludge, and was discolored by

rust in the sludge from tannery equipment and pipes. However, it has been

suggested by some tanners that these problems can be avoided if the chrome is recovered before the sludge is one day old and care is taken to prevent rust

accumulation in the sludge. Alternative recycling methods, such as chrome precipitation and direct recycling, may be more technically feasible [ 451 .

4 .2 .4 Incineration

Sludges and solid leather wastes resulting from leather tanning and

leather product manufacture are often landfilled. These wastes represent a

sizeable loss of potentially recoverable chrome and energy. For example, in 1978, it was estimated that tanners lost 6,400 tons and 8,200 tons of chromium

in discarded solid leather wastes and sludges, respectively. The additional

loss of 10,000 BTUs per pound of solid leather scrap and between 6,500 and

8,500 BTUs per pound of dry solids in wastewater treatment sludges has

prompted tanners to investigate incineration of solid wastes as a potential

chromium and energy recovery technique [ 4 5 , 5 5 , 5 6 ] . Energy recovery by this process is discussed in Section 4 . 3 . 2 .

All chrome-bearing solid wastes and sludges from tanning and leather

product manufacture can be incinerated for chrome recovery, including [ 45 ,561 :

0 Splits 0 Blue trim and shavings

0 Unfinished leather trim 0 Finished leather trim

0 Wastewater treatment sludges.

To date, researchers have performed bench-scale studies involving incineration

of wastewater treatment sludges as well as solid leather wastes [5 ,22,55,56,581. -u

4-2 7

The recovery of chromium from sludges and solid wastes via incineration involves three key steps:

1. Incineration or combustion of organic matter in wastes.

2. Extraction of chromium from resulting incinerator ash.

3 . Reuse of extracted chromium in the tanning process.

The first step, incineration, involves burning wastes in an industrial furnace

under controlled conditions. This combustion results in an ash containing

non-combustible materials such as chromium. The chromium extraction step is dependent upon the final form of chromium in the ash and can involve various

techniques. Numerous variations of both the incineration and recovery steps

have been investigated. These are discussed below in more detail.

Incineration of sludges and solid leather wastes, typical of incineration

processes used in other industries, is an exothermic, self-sustaining,

oxidation process generally condticted at temperatures of 600 to 1400'C in an

excess air environment. The character of the resultant ash, and more

importantly the form of chromium in the ash, is dependent upon a number of key operating parameters, including:

e Combination of wastes burned

e Alkalinity of wastes

e Amount of-additional alkali added to roast

e Operating incineration temperature.

The first two parameters, the combination of wastes burned and alkalinity

of the wastes, are related. Burning the solids alone results in an easier

burn. However, burning the solids and sludges together serves two useful functions. First, the scrap mixed in the sludge raises the sludge solids

content to 20 to 40 percent, which is sufficient to support combustion.

Second, mixing acidic leather scrap with alkaline sludge provides an environ-

ment more conducive to oxidation.

way, or through the addition of such alkali as sodium hydroxide, sodium

bicarbonate, o r sodium carbonate, converts the trivalent chromium in the waste

Increasing the waste's alkalinity in this

4-28

during incineration to its more readily recoverable hexavalent form [ 4 5 , 5 6 1 .

One proposed incineration system involves the burning of chrome-laden

wastes at temperatures of 900 to 1200°C under neutral pH conditions. suggested that an ash would be generated that would contain trivalent chromium in the form of chromium oxide (Cr20j).

stable and very water insoluble, it cannot be readily leached from the ash.

It has been proposed that the ash could be sold as is or first washed with

water to obtain purified chromium oxide, which can then be sold to steel mills, chromite ore smelters, or other industries where there is a demand for chrome ore. Should the tanners opt not to wash the ash, grinding and/or

pelletization may be required to prepare the ash for transportation and processing in smelting operations [ 8 , 4 3 ] . The actual feasibility o r economics

of this operation requires further investigation.

It is

Because this chromium compound is

Other more promising bench-scale studies have shown that incineration of

leather wastes under alkaline conditions results in the oxidation of trivalent

chromium in the wastes to its more readily soluble hexavzlent form. Because

hexavalent chromium is water soluble, it can be leached from the ash. This

process requires that incineration be performed in the presence of sufficient

alkali, such as sodium hydroxide, sodium bicarbonate, o r sodium carbonate, to

ensure complete conversion of trivalent chromium to hexavalent chromium

[ 5 5 , 5 6 , 5 7 , 5 9 1 . A typical process consisting of both incineration and recovery involves the following steps:

1.

2 .

3 .

4.

Solid wastes are incinerated in a furnace in an alkaline environment, resulting in an ash containing hexavalent chromium.

Ash is removed from the furnace and washed with an acidic solution.

Acidic solution, now containing soluble hexavalent chromium, is chemically reduced to convert hexavalent to trivalent chromium.

Trivalent chromium solution is either used in tannery operations o r is subject to precipitation to isolate the chromium for reuse.

4- 29

Variations of the above process are actively being investigated by tanneries as a viable chrome recovery technique. However, impediments exist

that are inherent to the incineration process. Among the major impediments

associated with incineration of chrome-bearing wastes are the initial cost of

equipment and potential environmental and health hazards.

The capital investment needed to implement an incineration system has a

major impact on further application of this process. estimated that the capital costs of an incineration system handling about 1.2 tons of waste per hour would be at least $600,000 based on 1977 costs [35 ,571 .

Yet, the same researcher and others postulate that the capital costs could be quickly recovered through savings in new chromium requirements. Additional

savings may be gained through reduction in disposal requirements and, where

heat recovery is included, plant heating costs [ 5 , 4 4 , 5 6 , 5 7 ] . Unfortunately,

leather tanners are characteristically without the capital necessary for

installing such a system, nor are they generally willing to take the economic

risks that can be associated with an incineration system. Some of these economic disadvant,ages may be overcome through the development of a treatment facility central to a number of tanneries.

One researcher has

Another area of concern with incineration technologies is the potential

for environmental damage. Alkaline incineration converts trivalent chromium,

the form prevalent throughout the tanning process, to its hexavalent form.

Hexavalent chromium is a concern because it has been identified as being

toxic. Ash containing the hexavalent chromium may be a hazardous waste as

defined by the Resource Conservation and Recovery Act (RCRA) and thus

regulated. If the chromium is not sufficiently removed from the ash during the extraction process, problems with disposal of the waste ash may increase significantly due to residual hexavalent chromium content.

In addition, some researchers have voiced concerns about the creation and emission of toxic and possible caracinogenic compounds [ 5 , 6 0 , 6 1 , 6 2 ] . Tests on

various incineration systems have indicated that chromyl chloride can be

formed and volatilized at temperatures above 600°C [ 6 3 ] . This substance has

an LD of 1,800 mg/kg and is moderately toxic. Emissions from incineration 50

4-30

of leather wastes may therefore require costly control devices t o ensure

removal of toxic particulate and gaseous emissions.

Both the environmental concerns and economic considerations may be

resolved through additional research. In fact, the current level of activity

in this research area may continue to show promise, and generate more

widespread interest. However, before incorporating incineration systems, tanners must be assured that these issues can be sufficiently addressed.

4.2.5 Pyrolysis

Pyrolysis involves the chemical change of materials brought about by the

addition of heat in an atmosphere with insufficient oxygen to support

combustion. Pyrolysis of organic materials, such as leather scraps and

sludges, results in the creation of various pyrolytic oils, gases, tars, water, and a char that contains uncombustible materials [ 5 1 .

The char generated by pyrolysis of leather wastes contains a number of

Because this chrome can be readily materials including trivalent chromium.

extracted from the char and reused in the tanning process, pyrolysis is under

consideration as a chromium recovery method. Thus far, researchers have

experimented with bench-scale pyrolysis systems to recover chrome from chrome-

bearing solid wastes and sludges generated by leather and leather product

operations. These wastes include:

Blue trim and shavings

e Unfinished leather trim e Finished leather trim

e Wastewater treatment sludges.

While several variations of pyrolysis systems for chromium recovery from

leather wastes have been investigated, a typical system involves the following

key steps:

1. Collect sludges and solid leather wastes.

2 . Pyrolyze wastes to form char, pyrolytic gases, and oils.

4-3 1

3. Leach t r i v a l e n t chromium from char w i t h s u l f u r i c a c i d .

4 . C o l l e c t chromium s u l f a t e l e a c h a t e .

5 . Reuse chromium s u l f a t e i n p r e p a r a t i o n of t ann ing l i q u o r s f o r r euse i n t ann ing o p e r a t i o n s .

Resea rchers have a l s o suggested t h a t combust ib le p y r o l y t i c o i l s and gases

genera ted v i a p y r o l y s i s can be burned i n a b o i l e r t o produce steam o r h o t

water ( s e e S e c t i o n 4 .3 .3) [51.

The Bureau of Mines, i n c o n j u n c t i o n w i t h t h e Tanners Council of America,

i s c u r r e n t l y c o n s t r u c t i n g a p i l o t - s c a l e p y r o l y s i s chromium recovery system.

Scheduled t o beg in o p e r a t i o n s i n February of 1982, t h e sys tem uses two

s e p a r a t e f a c i l i t i e s t o c a r r y o u t t h e p y r o l y s i s of l e a t h e r wastes and

subsequent l e a c h i n g of chromium from t h e c h a r . T h i s sys tem, s i m i l a r t o t h a t

d e s c r i b e d above, a l s o i n c o r p o r a t e s chrome p r e c i p i t a t i o n t o i s o l a t e t h e l eached

chromium

1.

2.

3.

4 .

5 .

6 .

7.

8.

9.

( s e e S e c t i o n 4 .2 .1 ) . The o u t l i n e of t h e p rocess i s as fo l lows :

C o l l e c t l e a t h e r wastes genera ted i n a Michigan t annery .

Transpor t l e a t h e r wastes weekly t o p y r o l y s i s u n i t i n Ohio.

Pyrolyze r e c e i v e d was tes under v a r y i n g c o n d i t i o n s t o g e n e r a t e a c h a r c o n t a i n i n g chromium.

Transpor t chromium-containing char back t o Michigan t a n n e r y weekly f o r chromium e x t r a c t i o n .

Soak and l each c h a r wi th s u l f u r i c a c i d .

S e p a r a t e chromium s u l f a t e from char u t i l i z i n g s e t t l i n g p rocess and c o l l e c t s u p e r n a t a n t .

Rewash char w i t h water t o e x t r a c t remaining chromium and c o l l e c t s u p e r n a t a n t . F i l t e r chromium s u p e r n a t a n t t o a i d i n c l a r i f i c a t i o n .

Add s u f f i c i e n t sodium hydroxide t o p r e c i p i t a t e chromium and dewater p r e c i p i t a t e t o o b t a i n chromium hydroxide f i l t e r cake.

10. Reac id i fy chromium hydroxide f i l t e r cake t o form chromium s u l f a t e .

.-

11. Add chromium s u l f a t e s o l u t i o n t o t ann ing l i q u o r and r e u s e i n t ann ing

Y

process .

4-32

The residual char will be further dewatered to reduce subsequent transporta-

tion and disposal costs [641. This process will be evaluated using various pyrolysis conditions, acid normalities, temperatures, and retention times to determine the optimal and most cost efficient method of pyrolysis for chromium

recovery.

It is anticipated that the system outlined above could form the basis of a large scale cooperative recovery operation. Like those tanneries in the

Gloverstown area of New York that are considering a regional chrome recovery

facility, a pyrolysis system centrally located to a number of tanneries could be used to perform the initial phase (steps 3 and 4 ) of the process described

above. Trucks used to transport leather wastes to the regional pyrolysis unit

could return the char to the individual tanneries. Chromium extraction, recovery, and reuse (steps 5 through 1 1 ) would then be performed at the tannery [631.

Current literature indicates that impediments to the further development

of pyrolysis systems for chrome recovery are related to scaling up bench-scale

systems to the tannery level. Attempts in other industries to adopt small demonstration pyrolysis units have often been plagued by variations

controllable in the lab but not at the plant. Attempts to adopt pyrolysis

systems in the tanning industry may be further frustrated by the variable

composition o f waste streams. Such variation will likely result in the

formation of a char burnt to varying degrees, thereby hindering chrome

extract ion.

As with incineration, other impediments t o pyrolysis system implementa-

tion center around initial capital investment and pollution control. While

initial economic projection of pyrolytic systems appears good for chrome recovery from leather wastes, the relatively small amount of research into

this technology will probably make tanners more reluctant to invest in such a

system. Nonetheless, the large percentage of recoverable chrome and waste

heat, coupled with reduced landfill requirements, make this option a key area

for future investigations. Also, current research by the Tanners' Council of America and the Bureau of Mines, as described above, may overcome noted

4-33

technical impediments while demonstrating the economic feasibility of regional cooperative recovery systems.

4 . 2 . 6 Absorption

Under certain conditions, tanners may choose to purchase hexavalent chromium (called bichromate or dichromate) and reduce it to the trivalent form

(chromium sulfate) for use in tanning operations. This reduction is accom-

plished using sulfuric acid and glucose in the form of molasses, as the reducing agents [3 ,11 , 6 6 1 .

In a proposed system for a zero chromium discharge tannery, stack emissions

from the chromium reduction process would be controlled by wet scrubbers, burners, or a combination of the two.

proposed that the chrome collected in recirculated scrubber water be recovered and used as make-up for the chrome reduction solution [ 2 2 ] .

Where wet scrubbers are used, it is

While reduction of bichromate (Cr+6) may be practiced by tanners to

obtain trivalent chrome, chromium sulfate (containing Cr may be purchased

directly from commercial producers. In addition, the trend appears to be

toward increasing use of commercial chrome tanning products, thus decreasing bichromate reduction activities [ 2 2 ] . In light of this current trend, recovery of chrome from the reduction facility's emissions may not apply to many chrome tanning operations.

commercial bichromate reduction facilities (SIC 2 6 ) that are currently

supplying trivalent chromium to leather tanners and other industry groups.

+?)

However, the method may be applicable to the

4.2.7 Other Chrome Recovery Techniques

As previously mentioned, several chrome recovery methods have been examined in the past. These recovery methods include:

Use of hide trimings to absorb chrome from spent tanning liquor; the trimmings are burned to recover the chrome

Chrome absorption from spent tanning liquor using activated carbon

Solvent separation of chrome from spent tanning liquor

Chrome soap manufacture from spent tanning liquor.

4-34

While limited information is available on these methods, some may deserve

further investigation due to their potential application.

The chrome recovery investigations involving activated carbon and solvent

separation were not successful.

as proposed. Similarly, researchers were unable to separate the chrome into a

low boiling point solvent to facilitate extraction; the solvents, when tested

on spent tanning liquor, resulted in either a homogeneous solution or a multi- layer solution with the chrome remaining in the aqueous, non-extractable

phase [351.

The activated carbon did not absorb the chrome

Experiments involving chrome recovery from hide trimmings were more

successful. Hide trimmings were placed in spent tanning liquor to absorb

chromium. Burning these chrome-laden trimmings resulted in combustion of

organic matter (proteins) and an ash containing the chromium which was then burned. Incineration of the leather scraps oxidized the chromium to its

hexavalent water soluble form. Chromium was then leached from the ash and

chemically reduced to produce the trivalent chromium form used in tanning. This study was reported in 1959, and at that time the process to form the ash was not found to be potentially economical [351. The incineration and

pyrolysis processes are still under study and evaluation for application to

tannery wastes f o r chrome recovery (see Sections 4 . 2 . 4 and 4 . 2 . 5 ) . Thus, this variation may prove a valuable area for future research.

Finally, chrome soap was produced as a method of chrome recovery by

reacting spent tanning liquor with sodium stearate in the presence of an

alcohol. The chrome soap was not reusable in the tanning process, but it had

several interesting properties (including water, acid, and base resistance) that were believed to have commercial potential (351. However, commercial

applications of chrome soaps from tannery wastes have not been actively pur sued.

Chrome soaps have been manufactured by the chemical industry €or a number

of years. These soaps are only marginally marketable and have achieved the

status of only a specialty market. Additionally, both the chemical industry

4-35

and t h e h i g h l y developed f a t t y a c i d i n d u s t r y produce a number of soaps and soap

s u b s t i t u t e s ( s i l i c o n t y p e s ) [ 7 , 1 0 ] .

4 . 3 ENERGY RECOVERY

The n a t u r e of the l e a t h e r t ann ing and f i n i s h i n g p r o c e s s e s make t h i s

i n d u s t r y p a r t i c u l a r l y energy i n t e n s i v e .

i n 1975 t h e l e a t h e r t ann ing and f i n i s h i n g i n d u s t r y had an energy i n t e n s i t y

r a t i o of 1.25, which i s g r e a t e r t h a n energy r a t i o s i n t h e t e x t i l e (0 .861,

lumber (0 .741, rubber and p l a s t i c s (0 .601 , and f a b r i c a t e d meta l p roduc t s

(0.401 i n d u s t r i e s [671. The i n d u s t r y i s a l s o r e l i a n t t o a g r e a t degree upon

f o s s i l f u e l s . It has been es t ima ted t h a t f o s s i l f u e l s account f o r

approximate ly 90 p e r c e n t , and e l e c t r i c i t y f o r t h e remaining 10 pe rcen t of a

t y p i c a l t a n n e r y ' s energy requ i rements 1681.

ROIT Corpora t ion d a t a i n d i c a t e t h a t

Under t h e p r e s s u r e of r i s i n g f u e l p r i c e s , t a n n e r s are a c t i v e l y r e s e a r c h-

i n g methods t o reduce t h e c o s t s o f t h e i r energy i n t e n s i v e manufactur ing

p rocesses . Two key areas have been i d e n t i f i e d as having a p o t e n t i a l impact on

t h e energy c o s t s p r e s e n t l y i n c u r r e d by t a n n e r s :

Loss of energy through d i scharged a i r from d r y i n g and f i n i s h i n g o p e r a t i o n s

0 Disposa l of h i g h BTU l e a t h e r s c r a p and s o l i d wastes.

Recent s t u d i e s have i n d i c a t e d t h a t bo th of t h e s e areas r e p r e s e n t a

p o t e n t i a l f o r r ecovery of s i z e a b l e amounts of energy.

of t h e hea ted a i r used i n t h e d r y i n g p rocess i s l o s t due t o system i n e f f i -

c i e n c i e s .

energy c o s t s 126,691. O v e r a l l , a t y p i c a l t a n n e r y may l o s e up t o 70 p e r c e n t o f

t h e energy consumed due t o such i n e f f i c i e n c i e s 1181. A d d i t i o n a l l y , ano the r

600 b i l l i o n BTUs are l o s t eve ry year i n t h e 129 m i l l i o n pounds of d i s c a r d e d or

l a n d f i l l e d s o l i d l e a t h e r waste [ 8 ] . Recovery o f t h e h e a t con ta ined i n t h i s

l e a t h e r waste could save t h e i n d u s t r y up t o $2.4 m i l l i o n pe r yea r i n h e a t i n g

c o s t s .

An e s t i m a t e d 50 p e r c e n t

Th i s r e p r e s e n t s rough ly 1 7 t o 20 p e r c e n t of a t a n n e r y ' s t o t a l

4-36

Recognition of these energy losses has proven to be a motivating force in

the search for appropriate recovery methods applicable to tannery processes.

Developing technologies aimed at recovering heat lost in tannery manufacturing processes are sporadically used throughout the industry. Methods to recover

the energy values in leather scrap, on the other hand, are generally still in the development stages. Among those recovery methods under active considera-

tion are the following:

e Heat Exchange - This is characteristically applied to processes in which a significant amount of heated air, used in the drying and finishing of hides or the warming of work areas, is lost due to equipment inefficiencies, stack losses, or other venting losses. Recovery of the lost heat for reuse in the same or different operations is facilitated by heat ducts and/or recirculation loops.

e Incineration - While primarily under consideration as a chrome recovery method (see Section 4.2.4), this process can be used to recover heat contained in waste leather scrap. The high temperature (900" to 1200°C) combustion of the scrap releases high temperature exhaust gases containing recoverable heat.

e Pyrolysis - Also primarily under consideration as a chrome recovery method (see Section 4.2.5), this process can also be used to recover heat contained in waste leather scrap. The combustion of leather scrap at temperatures around 450'C in an oxygen free environment releases energy in the form of recoverable heat and supplemental boiler fuels.

These energy recovery technologies, their potential for advancement, current

stage of development , and impediments are discussed in more detail below.

4.3.1 Heat Exchange

Tanneries use a significant amount of heat in their drying and finishing

operations and general plant heating. Much of this heat is unused and is lost via circulation vents, process inefficiencies, and exhaust systems. Many heat

recovery techniques have been proposed to increase the use of wasted heat. These include the application of heat exchangers on exhaust heat sources to

recover outgoing latent heat. Those heat exchangers that have been proposed for use include the following [ 701 :

e Rotary wheels

e Cross-flow exchangers

4-37

0 Run around systems

0 Heat p i p e s .

Ro ta ry wheel h e a t exchangers can be p laced between outgoing exhaus t p ipes

and incoming f r e s h a i r p i p e s . The c o u n t e r c u r r e n t a i r f low f a c i l i t a t e s t h e

t r a n s f e r of h e a t from t h e exhaust p ipe t o t h e incoming f r e s h a i r , the reby pre-

h e a t i n g t h e incoming a i r [701.

The cross- flow exchanger , a l s o known as a p l a t e exchanger, is simply a

co r ruga ted m a t r i x , resembl ing a c a r r a d i a t o r , t h a t f a c i l i t a t e s t h e release of

h e a t from a source . F resh a i r e n t e r s t h e matr ix and is warmed by ho t exhaus t

a i r c o n t a c t i n g i t [70].

The run around s y s t e m i s a combinat ion o f two h e a t exchangers . A non-

c o r r o s i v e l i q u i d i s pumped through t h e t u b e s of one exchanger where i t i s

h e a t e d by exhaust a i r . The h e a t i n t h e l i q u i d i s t r a n s f e r r e d t o incoming

f r e s h a i r i n a second exchanger. Though t h e sys tem has a low e f f i c i e n c y , 40

t o 45 p e r c e n t , i t f a c i l i t a t e s t h e long d i s t a n c e t r a n s f e r o f recovered h e a t

I701.

The f o u r t h o p t i o n , h e a t p i p e s , are s imi la r i n n a t u r e t o h e a t pumps. The

system is made up of a s e r i e s of r e f r i g e r a n t - f i l l e d p i p e s housed i n f i n c o i l s

t h a t a r e p laced between t h e exhaus t and incoming a i r supply . Thermal energy

causes t h e r e f r i g e r a n t t o v a p o r i z e and f low through t h e p i p e s . The vapor i s

condensed a t t h e o t h e r end, t h e r e b y r e l e a s i n g i t s thermal energy t o t h e

c o n t a c t e d a i r [701.

It has been suggested t h a t t h e s e f o u r h e a t exchangers can

f a c i l i t a t e t h e t r a n s f e r of h e a t i n t h r e e g e n e r a l a p p l i c a t i o n s

0 Process t o P rocess - This i s b a s i c a l l y a " closed loop" t h e h e a t used i n a p a r t i c u l a r p rocess i s recovered f o r same p rocess . An example is t h e use o f h e a t l o s t from t o p rehea t incoming d r y e r a i r .

be used t o

701:

method where r e u s e i n t h e a d r y i n g u n i t

a Process t o Comfort - T h i s method t r a n s f e r s waste h e a t genera ted i n t h e t annery p rocesses t o work a r e a s of t h e f a c i l i t y . r ecovery of h e a t wasted from t h e d ry ing p rocess €or use i n h e a t i n g wa te r f o r r e s t rooms .

An example i s

4- 38

Comfort to Comfort - These systems are designed to recover the heat from exhaust air from work areas to preheat fresh air pumped into the work areas.

Heat exchangers can be applied in several areas of the tannery to

facilitate the recovery of heat for the various uses outlined above. Among the most promising waste heat sources are those from: pasting operations,

toggling systems, boiler stacks, spray dryers, and wet stock dryers [70]. It has been estimated that heat exchangers applied to these and other operations could reduce the tanner's total energy consumption by 25 to 50 percent

depending upon the number of operating shifts [ 7 1 ] .

0

The major impediments to the use of heat exchangers in tanneries is the associated capital cost of the equipment. Those tanneries with tighter

capital budgets may not have the funds to support investments with payback periods estimated to be from 1 to 3 years [ 7 1 ] . An additional impediment may

be the likely maintenance and cleaning requirements necessary for some of the applications. Those heat exchange systems with constantly moving parts, such

B S the rotary wheel, are particularly susceptible to wear, and may be

difficult to clean. In addition, systems employing a liquid to transfer heat

may have scaling problems in the pipes. Liquids heavy in salts or other

agents will naturally deposit chemicals on the interior of the transfer pipes.

Without proper maintenance, such scaling will reduce the efficiency of heat exchange systems [ 4 2 1 .

4 . 3 . 2 Incineration

Incineration, as described in Section 4.2.4, is a high temperature

combustion process that involves burning organic materials to form an ash.

This combustion is exothermic, and therefore results in the release of large

quantities of heat, most of which is lost as hot flue gasses. Leather tanners have recognized the potential f o r chrome recovery via incineration of solid leather waste and are now actively investigating the simultaneous recovery of

heat from discharged flue gases.

Leather scrap, comprising a significant portion of all solid leather

waste, is generated in large quantities, has a high BTU value, and burns

4-39

relatively cleanly. incineration including [ 4 4 , 6 9 , 7 2 ] :

Many liquid and solid wastes have been proposed for

Splits

a Blue trim and shavings a Unfinished leather trim 0 Finished leather trim

0 Wastewater treatment sludges.

These waste streams, because of their BTU content (up to 14,000 BTU per pound of solid leather waste and 6 ,500 to 8 ,500 BTUs per pound of dry solids for sludges) represent a significant source of energy which could be used in tannery operations.

leather tanning industry represents 0 .8 to 1 . 8 trillion BTUs per year of potentially recoverable heat [ 4 4 , 6 9 1 .

The 129 million pounds of solid wastes generated in the

Though tannery incineration heat recovery technologies are generally at

the proposed research stage, some tanners are actively working to implement such systems.

heat recovery system that, once scaled up, could generate enough heat to allow the retirement of three of the s i x boilers currently in use ( 5 6 , 7 3 1 . The heat

recovery system is typical of those used in other industries.

boiler, consisting of banks or rows of tubes, is placed in the stream of the incinerator furnace stack. Hot flue gasses pass through the waste heat boiler

and transfer heat to water flowing through the boiler tubes. The hot water or

steam.is then used for heating or other tannery operations, such as drying.

One tannery in Maine has installed a bench-scale chrome and

A waste heat

Impediments to further application of heat recovery from incineration of

leather wastes are the same as those for chrome recovery incineration systems

(see Section 4 . 2 . 4 ) . Essentially, the capital for the incineration system may

not be readily available to leather tanners. recovery could result in large savings to the tanner, the money may not be

available for the installation of such equipment by individual tanners.

Thus, even if heat and chrome

4-40

However, a centralized heat and chrome recovery incineration system that

is owned and operated by a number of tanneries may be more economically

feasible. The facility could in effect buy heat from tanneries in the form of

wastes (fuel) in return for chrome extracted from the ash. Such a cooperative

agreement may form the basis of other centralized waste treatment recovery facilities.

4 . 3 . 3 Pyrolysis

Pyrolysis, as described in Section 4 . 2 . 5 , is the destructive distilla-

tion, thermal decomposition, or carbonization of a material facilitated by

supplied heat in an atmosphere with insufficient oxygen to support combustion

[81. This chemical change in the material results in production of pyrolytic oils, char, and certain off-gases. It has been shown that pyrolysis systems can be designed to recover energy from the pyrolysis process itself as well as

the resulting oils, char, and off-gases.

Like incineration technologies, pyrolysis systems were initially proposed

for use in the leather tannin; industry as chrjme resource recovery methods

(see Section 4.1.5). pyrolysis as a heat recovery methods. Investigations into this application

have shown that the generated gases can be burned to support the pyrolysis or

to generate useful facility energy. In addition, the char resulting from pyrolysis can be dewatered following leaching of the chrome and used as a

Tanners are now researching the potential application of

supplemental boiler fuel.

Many of the solid wastes generated by the leather industry can be pyrolyzed including [81:

e Blue trim and shavings

e Unfinished leather trim e Finished leather trim

e Wastewater treatment sludge.

Research has shown that pyrolysis of these wastes cannot generate nearly

as much recoverable heat as incineration. Yet the burning of the residual L

4-4 1

char, produced from tannery solid wastes, could contribute up to 0.5 trillion BTUs annually. This represents a potential reduction of greater than

$ 2 million (1980 dollars) per year in energy costs (81. This estimate excludes the recovery and use of off-gases, with heating values of about

300 BTLJIft , which could further reduce energy costs. 3

This information suggests that the economics of pyrolysis waste

treatmentlrecovery systems may be favorable especially when practiced by

larger facilities with constant feedstocks of fuel. The installation of

pyrolysis systems would not only facilitate the recovery of the chrome and heat values contained in the wastes, but would also reduce the volume of

wastes requiring disposal. The need to dispose of only the relatively chrome-

free residuals could reduce disposal costs by more than 10-fold [81.

Impediments to the scale-up of pyrolysis waste treatment systems center

around parameters controllable in the laboratory but not in the tannery. The

variable tannery waste streams (containing wastes of different sizes and water

contents) used to feed tl,e pyrolysis process may frustrate attempts to achieve

uniform char and associated oils and gases generated in full-scale systems.

Because boilers generally require specific grades of each material, large variations in recovered fuel (i.e., char, oil, gas) content will result in

less efficient heat recovery. Also, as with incineration technologies,

equipment needed to control pollution (emissions) will require additional investments and may discourage tanners from using this recovery option.

4 . 4 PROTEIN RECOVERY

Animal hides and skins are composed primarily of protein and fat. Much

of this proteinaceous maierial is lost as solid waste during trimming,

buffing, and similar operations within the tanning process. In fact, only

40 to 60 percent of the hide or skin actually becomes the final leather product; the remaining hide or skin material containing protein, grease, and

sometimes chrome, is discarded as waste.

Proteins can be potentially recovered from any hide or skin waste

material resulting from the tanning process including fleshings, trimmings,

4-42

blue trim, and leather trim. Proteins are also lost from hides or skins to

tannery wastewater from processes involving rinsing, soaking, washing and

harsh chemical treatments of the hide (such as unhairing or tanning operations).

including feed supplements, binders, casein (a protein) substitutes, hide powders (a dried protein product), and high purity amino acids.

These proteins may be recovered and used in various products

Protein recovery processes are usualky associated with other recovery processes, such as chrome or grease recovery. For example, in the case of

chrome recovery by precipitation, protein is recovered secondarily (see Section 4.2). In addition, because animal materials contain both substances,

grease and proteins are usually co-products from recovery operations.

Protein recovery is not widely practiced, and, for the most part, pro-

teins are removed from tannery wastewater primarily to reduce pollutant

loading to wastewater treatment plants. In addition, protein recovery is

currently limited by available substitutes which are often cheaper and of

higher quality [ 5 1 .

applications for proteins may help to .promote further recovery activities. However, expansion of markets and identification of new

There are four general protein recovery processes applied to tannery

wastes:

0 Acid precipitation - removal of proteins from solution by the addition of acid, which renders them insoluble.

Hydrolysis - use of water and heat to remove soluble proteins from insoluble waste materials.

0 Ultrafiltration - a membrane filtration process that removes liquid from a proteinaceous solution, leaving the proteins.

Centrifugation - separation of proteins from solution by mechanical means.

These recovery processes are discussed in more detail below.

4-4 3

4.4.1 Acid Precipitation

Proteins can be recovered from tannery wastes by acid precipitation of liquid waste and acid solubilization and precipitation of solid wastes.

Included in these liquid and solid wastes are:

0 Soak water 0 Spent unhairing liquor

0 Rinse water

0 Splits

Blue trim and shavings Unfinished leather trim

0 Finished leather trim.

The proteins recovered from these wastes may be used as protein meal for the

feed industry, a binder, or replacement for casein (a protein).

Spent unhairing liquor from the "hair burn'' unhairing operations is a

major source of wastewater protein. In this process, heat, water, sulfur, and

lime are used to "burn" the hair off the hide or skin, essentially dissolving

or solubilizing the proteins that constitute the hair. Protein has been

recovered in a pilot-scale acid precipitation system using a four-step

procedure:

1. Collect the spent unhairing liquor and removing suspended solids by gravity sedimentation.

2 . Remove soluble inorganic compounds by dialysis or ultrafiltration.

3 . Acidify the concentrate from dialysis or ultrafiltration to precipitate the proteins.

4. Settle the sludge-like protein precipitate under refrigeration, then washing, centrifuging, separating, and freeze-drying the proteins.

The protein yield of this process depends upon the type of processing equip-

ment used in the tannery. For instance, research studies found that one pound

of protein was obtained from 7 to 9 gallons of spent unhairing liquor from

4-44

hide processors (cement-mixer-like vessels). Spent unhairing liquor from

paddle vats, the traditional processing and tanning vessel, yielded one pound

of protein from 18 to 20 gallons [ 741 .

In addition to acid precipitation of spent unhairing liquors, this process has been proposed for use on waste soak waters and wash waters from washing operations following unhairing [ 7 5 1 .

0

Chrome tanned hide wastes, such as splits, blue trim and shavings,

unfinished leather trim, and finished leather trim, are another source of recoverable protein. In laboratory studies, these solid wastes have been

solubilized to facilitate protein removal by precipitation. The process involves the following steps [ 761 :

1.

2 .

3 .

4 .

A t

Dissolve hide scrap under highly alkaline conditions (pH 10 to 141, to precipitate chrome in the scrap as insoluble chromium hydroxide.

Separate chromium hydroxide precipitate from solution by filtration.

Acidify chrome-free solution to precipitate out the proteins.

Neutralize precipitated proteins, separate by centrifugation, and dry for protein meal.

present, none of these protein recovery processes are operating at

full scale. Laboratory studies have been performed on protein recovery from

hide scrap, and acid precipitation of liquid tannery waste streams is only at the pilot-scale stage [48 ,74,763.

Protein recovery not only represents a potential source of revenue, it

also reduces both pollutant loadings (BOD and COD) of tannery wastewaters and associated wastewater treatment costs [ 741. In addition, removal of protein

from spent unhairing liquors facilitates reuse of the liquor, thus saving sulfide and lime raw material requirements. In the case of acid solubiliza-

tion of solid leather wastes, both chrome and protein may concurrently be

recovered, thus generating two useful materials which generally would be disposed.

4-45

A t t h i s t i m e , t h e c o s t s f o r p r o t e i n recovery by a c i d p r e c i p i t a t i o n have

not been f u l l y developed. I n a d d i t i o n , t h e r e a r e c u r r e n t l y many o t h e r low

c o s t , h i g h volume p r o t e i n s o u r c e s (101. These economic c o n s i d e r a t i o n s are

o b v i o u s l y a major concern of t a n n e r s who may be l i m i t e d i n t h e i r a b i l i t y t o

make major c a p i t a l inves tments . For example, t h e c o s t a s s o c i a t e d w i t h f r e e z e-

d r y i n g p r o t e i n s may not be r e c o v e r a b l e through s a l e of t h e p r o t e i n s [ l o ] .

Y e t , c o s t s and necessa ry inves tments may be o f f s e t by t h e recovery of more

t h a n one m a t e r i a l : p r o t e i n and g r e a s e , chrome, o r p rocess s o l u t i o n s . How-

e v e r , new and expanded markets and a p p l i c a t i o n s o f t h e recovered p r o t e i n s w i l l

be n e c e s s a r y t o suppor t implementa t ion of p r o t e i n recovery by a c i d

p r e c i p i t a t i o n .

4.4.2 Hydro lys i s

Hydro lys i s of p ro te inaceous m a t e r i a l s i s ano the r method f o r r e c o v e r i n g

v a l u a b l e p r o t e i n s .

wastes i n c l u d i n g :

This p rocess may be a p p l i e d t o s e v e r a l t a n n e r y s o l i d

e F l e s h i n g s

e Blue t r i m and shav ings

e Unfinished l e a t h e r t r i m

e Fin i shed l e a t h e r t r i m .

Rendering i s .one method f o r r e c o v e r i n g g r e a s e and p r o t e i n from t a n n e r y

s o l i d w a s t e s . Th i s p rocess uses h e a t and a c i d to hydro lyze t h e p r o t e i n s i n

t h e wastes, producing a p r o t e i n a c e o u s s o l u t i o n and a l a y e r of g r e a s e . A more

d e t a i l e d d e s c r i p t i o n of t h e r e n d e r i n g p rocess is presen ted in S e c t i o n 4 . 5 ; 2 .

The p r o t e i n recovered by t h i s method i s u s u a l l y s o l d as a feed supplement ,

a l t h o u g h , i n some i n s t a n c e s , i t i s d i s p o s e d , s ince r e n d e r i n g i s p r i m a r i l y a

g r e a s e recovery o p e r a t i o n [74].

Another pa ten ted h y d r o l y s i s p rocess f o r p r o t e i n recovery from chrome

l e a t h e r waste invo lves h e a t i n g l e a t h e r s c r a p w i t h an a l k a l i n e e a r t h (such as

l ime) and wa te r . The chrome i n t h e s c r a p p r e c i p i t a t e s ou t of s o l u t i o n and i s

r e a d i l y s e p a r a b l e from t h e wa te r s o l u b l e p r o t e i n f r a c t i o n [501. The p r o t e i n s

can be so ld and t h e chrome can be reused i n t h e t a n n i n g p r o c e s s .

4-46

A similar process has been investigated for the preparation of surfactants from leather-derived proteins. In this process, waste leather is

hydrolyzed with a lime solution in an autoclave. the solution, which is then dried. The resulting dried protein can be used to

prepare surfactants [771.

Acid is used to neutralize

As these methods show, protein recovery by hydrolysis of tannery wastes

can be combined with other processes designed to recover grease and chrome. Rendering and chrome precipitation are already practiced to a limited extent

in the tanneries (see Sections 4.2 and 4.5). For these processes to be utilized to a greater extent in the tanning industry, the economics of such a system would have to be proven, especially for the smaller tanneries. Additionally, markets for proteins and other by-products would have to be expanded. Where fleshings are used, sufficient storage space would have to be available and the fleshings would have to be generated in large enough

quantities to be utilized before they spoil.

Finally, methods must be developed to remove harmful substances from the

fleshings and other leather scrap so that the recovered proteins (and grease)

may be safely used. Bactericides, such as pentachlorophenol, have prevented

leather meal (a hydrolyzed protein product from leather waste) from being used

in animal feeds because highly toxic impurities and degradation products of

the bactericides (such as dioxins) have been found in the recovered protein [571.

4 . 4 . 3 Ultrafiltration

Spent unhairing liquor from hair burn processes contains dissolved hair

in the form of suspended protein. Ultrafiltration is one of the methods used to remove these and other impurities from the spent unhairing liquor prior to

recycling. This process, which is currently in use at an Italian tannery, involves the following steps:

1. Spent unhairing liquor passes across an ultrafiltration membrane.

2. The permeate, containing waste and unhairing chemicals (lime and sulfide), passes through the membrane and is collected.

4-4 7

3 . Proteins are recovered as a concentrate, which is then further enriched.

4 . Proteins are precipitated with acid, then settled, washed, desalted, and dried.

Eighty percent of the proteins in the spent unhairing liquor are recovered [161. The recovered proteins are suitable for animal feed or fertilizer [16,26]. Full-

scale ultrafiltration recovery systems have been implemented in Italy and France, while pilot-scale studies have recently begun in the United States (16,261.

Studies of the economics of a French ultrafiltration system indicate that

a minimum of 40 tons of salted hides must be processed daily for the invest-

ment t o be worthwhile. This represents approximately 1,600 hides per day at a wet brine cured weight of 50 lb/hide (derived from processing 17.6 million equivalent hides with a weight of 440,000 tons [121). In 1 9 7 6 , less than

20 percent of the tanneries in the United States processed this number of

hides daily [ 3 ] . Thus, the ultrafiltration system may find acceptance in large tanneries or large beamhouse operations, but it may not be able to

compete with other recovery technologies, such as direct recycling, in which proteins are removed or recovered [261.

There are also several technical and mechanical factors that affect the

potential commercialization of ultrafiltration for beamhouse'processes [261:

e Equipment must be resistant to the highly corrosive conditions of tannery solutions such as unhairing liquors

0 Efficient measuring devices are required to control process parameters (pressure, temperature, flow)

6 Special washing techniques for ultrafiltration cells.

Because these factors influence the design of the system, its cost, equipment

lifetime, and ease of installation, they will greatly affect the acceptance of

the system in tannery operations.

Although ultrafiltration has undergone limited development and applica-

tion in the tanning industry, it has been successfully applied in other

4-48

industries to isolate, concentrate, and purify proteins. Even so, additional

markets for the recovered proteins must be developed if this recovery option is to have further commercial application in the tannery.

4.4 .4 Centrifugation

Centrifugation is employed in a system to recover proteins and grease

from liquified fleshings. This pilot-scale process involves the foilowing

steps:

1. Grind and acidify fleshings to improve separation of fats from proteins.

2. Separate proteins from solution by centrifugation; grease is recovered from the remaining liquid.

3. Dry, grind, and condition recovered proteins.

4 . Use proteins in product applications.

This recovery process is also discussed in more detail in Section 4.5.2, which

addresses grease recovery 1261.

The test system for this process was designed t o handle 1.6 tons of fleshings per hour. Other systems are capable of treating as much as 3 tons

per hour. The rate of protein recovery using this system was 220 to 330 lb (100 to 150 kg) per hour [261.

Full-scale implementation of centrifugation for protein recovery has not

yet occurred. Tanners may neither be able to make the necessary investment in

the system nor consider this system for use when other methods for protein

recovery, such as acid precipitation, are already in use. Availability of

markets for recovered protein and grease and sufficient storage area t o keep

fleshings until an adequate quantity is collected are factors that also affect

implementation of this system. While other protein recovery systems can be

applied to several waste streams, this system can only be applied to fleshings a t this time.

4-49

However, a factor favoring the centrifugation system is that two marketable products, grease and protein, are recovered. The system may also find

greater use if it can be used in conjunction with other protein recovery processes or adapted to handle other proteinaceous solid wastes.

4.5 GREASE RECOVERY

Grease, in the form of fatty tissue, is a material universally found in

animal hide or skin. Because the grease content of hides and skins vary according to the animal, the processing of hides will vary according to the

type of material being processed. a high grease content requiring special processing (degreasing) to remove

excess grease from the skins. This is performed early in the tanning process so that the resulting leather is not greasy and that excess grease in

processing solutions does not adhere to processing equipment resulting in

frequent equipment cleaning and maintenance. Cattlehides do not have the high

grease content of pigskins and sheepskins, so a special degreasing operation is unnecessary in cattlehide tanning operations.

Pigskins and sheepskins, for example, have

In all cases, grease and oil from hides and skins enter into process

waters and liquors during the beamhouse and tanyard operations. Grease removal from these waste streams is commonly practiced more for wastewater

treatment purposes than for recovery and sale of the collected material. In

general, removal of grease is important to reduce grease loading to wastewater

treatment systems, especially where biological treatment is used [161.

Although grease removed from wastewater is commonly discarded, salable

grease can be recovered from beamhouse and tanyard effluents, as well as

from untanned solid wastes (fleshings and trimmings)'. processes that are used to recover grease from tannery wastes:

There are currently two

Rendering - melting down fatty materials to extract grease.

Separation - use of physical o r mechanical methods t o segregate grease from a liquid solution.

These grease recovery methods are described in more detail below.

4-50

4.5.1 Rendering

Rendering is an extraction process utilizing heat to liquify (melt) fat-

containing materials. The resulting liquid contains both grease and water

soluble protein. water fraction. The recovered greases are primarily used in soap manufac-

ture [ 1 7 1 .

The grease is then recovered by separation from the protein/

There are three rendering methods currently used for grease recovery from

tannery wastes:

a Hydrolysis and removal of fat from leather fiber using heat and phosphoric acid

a Liquification of fat by controlled heating followed by recovery of grease from the liquid using centrifugation

a Hydrolysis of fat using heat and sulfuric acid followed by recovery of grease by skimming the solution.

While rendering processes have historically been only applied to original

fleshings (due to their high grease content)

used as raw materials. These wastes may be rendered at the tannery or sold to

commercial renderers for processing [17].

-_ [ l o ] , hide trimmings may also be

Use of the rendering process by tanners or commercial renderers depends

on process and storage space for raw materials, available land, effluent

regulations, facility locations, and availability of by-product market. In

some instances, lack of adequate storage space to hold fleshings until a sufficient quantity is accumulated precludes rendering; the fleshings must

then be disposed of by landfilling. In other cases, the tannery location is

at such a distance from markets interested in recovered materials that the

costs for transporting the wastes to the market are prohibitively expensive.

In this situation, the wastes are given away or disposed.

Another impediment to grease recovery from tannery wastes is the contamination of the fat by materials applied to the hide in other processes. These

contaminants include bactericides used in curing and depilatory accelerators 1

4-5 1

used in the unhairing process [ 1 7 1 .

recovered grease unsalable. This contamination can often make the

The rendering process for grease recovery from fleshings and trimmings

may be applied more extensively throughout the tanning industry once the

impediments mentioned above are overcome. Some of these problems may be resolved by constructing a centralized rendering facility capable of treating

wastes from nearby tanneries or utilizing existing rendering facilities at one tannery to treat wastes from neighboring tanneries.

the recovered grease should also be developed to improve the incentive to use this recovery technology.

Additional markets for

4.5.2 Separation

Grease can also be recovered from tannery waste streams using typical

physical or mechanical separation methods. These methods include:

e Oilfwater separation

e Ultrafiltration

e Centrifugation.

The tannery waste streams to which these recovery processes apply include:

e Fleshings

e Lime sulfide fleshings e Spent degreasing solution

e Spent tanning liquor.

Full-scale systems are commonly applied to recover grease from degreas'inq

A processes employed in sheepskin (with hair removed) and pigskin operations.

system used for pigskin tanning operations involves oil/water separation of the spent degreasing solvent solution containing grease, solvent, and water.

The water layer, after separation, is discharged and the grease and solvent

are further separated using a stripping column [ l l ] .

4-52

e Grease and oil are usually removed from spent chrome tanning liquor

before recycling of the liquor or treatment for recovery of chrome [35].

However, this is generally practiced as a purification technique rather than

a recovery technique.

from the aqueous tanning liquor. Upon separation, the grease is periodically skimmed off and discarded resulting in a relatively grease-free liquor that

can be refortified and reused 1471.

In a separation tank, the grease is allowed to separate

Pfister and Vogel Tanning Company, in developing a chrome recycling system, has begun research into methods for recovering and/or purifying the grease skimmed from the top of the above described separation tank. They have

further proposed that more advanced separation techniques such as dissolved

air flotation, dispersed air flotation, and foam separation be investigated to improve separation 1481.

Lime-sulfide fleshings are another source of recoverable grease. One

researcher has proposed that these fleshings be mixed with acid in order to

remove the sulfide as hydrogen sulfide using steam and/or water. could then be decanted from the protein. Research is still at the

acidification step; the hypothesized process has not yet been proven [ 7 6 1 .

The greases

Ultrafiltration has also been proposed as a method for recovering grease

from degreasing operations employing water and detergents rather than

solvents. The ultrafiltration process utilizes a semi-permeable membrane to

selectively separate suspended solids, colloids, large molecules (such as proteins), and other high molecular weight materials from aqueous waste streams.

1.

2 .

3 .

The proposed separation process is as follows:

The waste stream flows across (parallel to) the semi-permeable membrane (rather than perpendicular to the membrane, as in filtration).

Water and low molecular weight substances (salts, sulfides, some surfactants) pass through the membrane; this liquid material (permeate) is collected and may be reused.

High molecular weight substances (grease and oil) cannot pass through the membrane and are collected as the concentrate.

4- 53

While t h e above d e s c r i b e d p roces s i s on ly proposed , u l t r a f i l t r a t i o n has been

s u c c e s s f u l l y app l i ed i n o t h e r i n d u s t r i e s f o r t h e c o n c e n t r a t i o n of o i l s ;

emuls ions of up t o 50 p e r c e n t o i l have been o b t a i n e d , wh i l e t h e permeate has

less t h a n 100 ppm o i l and g r e a s e [ 1 6 ] .

A p i l o t - s c a l e s y s t e m us ing c e n t r i f u g a t i o n f o r g r e a s e r ecove ry from

f l e s h i n g s has been developed i n France. Th i s p roces s i n v o l v e s t h e fo l l owing

s t e p s :

1. Grind and l i q u i f y f l e s h i n g s w i th a c i d and steam.

2 . A c i d i f y s l u r r y t o s e p a r a t e f a t t y a c i d s from p r o t e i n s .

3 . C e n t r i f u g e s l u r r y t o s e p a r a t e p r o t e i n s from t h e s o l u t i o n .

4 . S e p a r a t e g r e a s e from s u p e r n a t a n t ( c o n s i s t i n g of g r e a s e , water, and i n o r g a n i c s a l t s ) by c e n t r i f u g a t i o n u s ing v e r t i c a l bowl s e p a r a t o r t o remove wa te r and i n o r g a n i c s a l t s .

Th i s system has been des igned t o t r e a t 1 t o 3 t o n s of f l e s h i n g waste per hou r .

The c a p a c i t y of t h e t e s t e d system was 1 .5 t o n s per hour and h a s produced, i n - p r a c t i c e , 308 t o 352 pounds of g r e a s e pe r hour [261.

Th i s system has been t e s t e d on a p i l o t - s c a l e l e v e l b u t h a s no t y e t been

implemented i n f u l l s c a l e .

i n v e s t i n t h e equipment neces sa ry t o implement t h e system wh i l e r e n d e r i n g and

s a l e of f l e s h i n g s f o r o t h e r manufac tur ing p r o c e s s e s a r e a v a i l a b l e a l t e r n a -

t i v e s , a l though not u n i v e r s a l l y p r a c t i c e d . Other f a c t o r s a f f e c t i n g t h e

implementa t ion of t h i s and o t h e r g r e a s e r ecove ry systems i n c l u d e t h e a v a i l -

a b i l i t y of by- product cus tomers and t h e l e n g t h of t i m e neces sa ry t o accumulate

s u f f i c i e n t q u a n t i t i e s of t h e f l e s h i n g s f o r the r ecove ry p roces s t o be run

economica l ly . Should t h i s t i m e frame be t o o long , t h e f l e s h i n g s w i l l p u t r e f y

and become u n s a l a b l e . A d d i t i o n a l l y , new methods need t o be developed t o

p u r i f y g r e a s e s e p a r a t e d from t a n n e r y was t e streams t o o b t a i n a marke t ab l e

m a t e r i a l .

Tanners may t h e r e f o r e be unable o r u n w i l l i n g t o

4-54

Nevertheless, limited markets and uses for grease recovered by separation

do exist and new ones have been proposed. The grease recovered from lime-

sulfide fleshings has been proposed as a fodder fattening agent [761.

European data indicate that grease recovered from spent degreasing solutions

may be used in the ,fatliquoring operation [161.

tanneries in implementing grease recovery operations on a broader scale,

additional markets must be developed.

However, to interest

4.6 SULFIDE RECOVERY BY ACIDIFICATION

Sulfides are a primary component of tannery unhairing liquors. Mixtures of sulfides, lime, and water are used in the unhairing process to either

loosen the hair follicles or to completely dissolve the hair from the hides.

Due to the nature of the process, nearly all of the sulfide used in either

unhairing process, 1 to 5 percent of the hide weight, remains in the unhairing

liquor [ 781 . The spent unhairing liquor is characteristically discharged with

other plant waste streams to wastewater treatment. Sulfides are removed, but

not necessarily recovered, during wastewater treatment in order to meet efflu-

ent regulations. This loss is ultimately manifested in increased materials and effluent treatment costs. The incorporation of sulfide recovery methods

could greatly reduce the present consumption of sulfides in the unhairing process while reducing the pollutant load in plant wastewater.

Conversations with industry representatives indicate that only about a

dozen tanneries are currently practicing sulfide recovery on an industrial

scale [ 7 9 ] . However, only one or two tanneries utilize sulfide stripping/

reuse processes [ 2 4 1 . One such system is being used at a tannery that processes hides through-the-blue, and sells the hides for finishing. The

Blueside Company tannery has implemented a full-scale recovery system that involves screening and clarifying the combined wastewater from all tannery

operations. The plant wastewater is acidified, thus generating hydrogen sulfide, which is carried off by an airstream to an absorption tower.

Hydrogen sulfide is absorbed within the tower by caustic soda, which is recirculated until the critical sodium sulfide concentration in the lime is

achieved. At this point, the caustic soda is replaced with fresh stock and

the sulfide-caustic soda mixture is used in the unhairing process 1781. +

4-55

Approximately 98 percent of the sulfides are removed from the wastewater via this process [ 7 8 ] . In another instance, a French tannery using a similar

process removed 85 percent of the sulfide from plant wastewater; approximately 60 percent of these sulfides were recovered and returned to production [80].

The Blueside recovery operation is not without operational and design

problems. These problems include clogging of air diffusers with proteins, control problems with air flows that dilute hydrogen sulfide concentrations to below explosive limits, and limited capacity of their sulfide absorption

equipment. These problems are common to this type of sulfide recovery system

and are currently being addressed by Blueside [781.

Even with design problems, the sulfide recovery system at Blueside has

proven to be economical. In 1976, the cost of operation, maintenance, and equipment depreciation was $305,000, while the savings in chemical costs was

approximately $397,000 for a net profit of $92,000. An additional benefit of

$87,000 was realized from savings in sewer charges through removal of protein during the acidification step. Proteins precipitate from solution and are

easily removed as sludge, thus reducing the pollutant loading of plant wastewater [781. If markets could be developed for recovered proteins, additional

revenues could result.

Because the Blueside sulfide recovery system was constructed as an inte-

gral part of the tannery when the tannery was built, no modification costs

were incurred. Other tanneries implementing this system would have to incur

the costs of upgrading existing facilities and committing new capital to buy

necessary equipment, such as air blowers, an absorption tower, feed and circulation pumps, and storage equipment. Additionally, the Blueside recovery

system does not require waste stream segregation, since the entire plant

effluent undergoes sulfide recovery. Therefore, only those changes necessary

to install the sulfide recovery system are required.

In addition, it has been suggested that some tanneries may find other

sulfide recovery processes more economical. For example, smaller tanneries

and vegetable tanneries using hair-save methods may have effluent sulfide

4- 56

concentrations which are far smaller than those fouffd at Blueside. Thus,

alternative sulfide recovery methods, such as direct recycling, may be more economical to install and operate [ 2 4 , 4 2 1 .

The positive economics and proven technology of sulfide recovery by

acidification of tannery wastewaters points to its potential for greater use within the industry. However, the problems of limited capital, which typically restrict the investment options of tanneries, may inhibit many from including such operations in existing facilities. This is particularly true

of smaller tanneries with low sulfide effluent concentrations. In addition,

some tanneries may be reluctant to incorporate such sulfide recovery systems

that deliberately generate hydrogen sulfide, a highly toxic and potentially

explosive substance. tanneries even consider sulfide recovery by acidification.

Only after a long history of safe operation may some

4 .7 TANNIN RECOVERY BY ADSORPTION

Tannin is the tanning agent used in vegetable tanning processes. The

-. main vegetable tannins used ?re polyphenolic compounds derived from specific

types of tree bark such as quebracho, wattle, mangrove, and chestnut [811. Currently, vegetable tanning represents a small and diminishing segment of the

tanning industry [ l l ] .

In 1972, laboratory research was performed on recovering tannin from

spent tanning liquor by adsorption. In this study, waste liquor was fed through a nonionic resin onto which tannin was adsorbed. Acetone was used to

remove the tannin and regenerate the resin. Tannin was separated from the acetone by distillation. Results from these tests indicated that a 90 percent

recovery of high quality tannin is possible. however, the system required further research to obtain more information on

resin life and regeneration time [811. to be technically feasible, it may not prove competitive with the frequently

used Liritan method for direct recycling of spent tanning liquors (see Section

4 . 1 . 5 ) . In addition, concerns regarding acetone's effect upon worker health

and safety and its high cost may further preclude the development of this recovery process [ 4 2 ] .

At the time of the study,

Although this process was demonstrated

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4 . 8 HAIR RECOVERY BY SCREENING

Hair save o p e r a t i o n s a r e not w ide ly used by l e a t h e r t a n n e r s and are

c o n t i n u i n g t o dec rease i n p o p u l a r i t y . Th i s u n h a i r i n g p roces s i n v o l v e s soaking

h i d e s i n a weaker c a u s t i c s o l u t i o n a t lower t empera tu re s t han t h e h a i r burn

p roces s i n o r d e r t o loosen h a i r f o l l i c l e s r a t h e r t h a n d e s t r o y i n g t h e h a i r .

The h a i r i s t hen mechan ica l l y removed from t h e h i d e s . Hair i s c o l l e c t e d from

t h e u n h a i r i n g machine and i s s c r eened from s p e n t u n h a i r i n g l i q u o r . The s p e n t

u n h a i r i n g l i q u o r may be d i s cha rged t o was tewater t r ea tmen t or recovered f o r

r e u s e . C o l l e c t e d h a i r can be e i t h e r d i s p o s e d , or washed, d r i e d , and s o l d [3,111

Some of t h e t r a d i t i o n a l u se s f o r r ecove red h a i r have been i n p roduc t ion

of i n s u l a t i o n and p l a s t e r 1821. However, t h e s e marke ts f o r h a i r have l a r g e l y

d imin i shed . Th i s l o s s of marke t , coupled w i t h a low s e l l i n g p r i c e f o r

recovered h a i r , ha s c o n t r i b u t e d t o a major conve r s ion of t h e u n h a i r i n g p roces s

from t h e h a i r save method t o h a i r burn o p e r a t i o n s . The h a i r burn method i s

b e n e f i c i a l t o t a n n e r s because i t i s f a s t e r and e l i m i n a t e s t h e c o s t of

l a n d f i l l i n g was te h a i r , or, i n t h e c a s e where a market e x i s t s , t h e c o s t o f

c o l l e c t i n g , washing, and d r y i n g h a i r . It i s f e l t by some t a n n e r s t h a t i t i s

l e s s c o s t l y t o t r e a t h igh BOD and s u l f i d e wastewaters r e s u l t i n g from t h e h a i r

burn p roces s than t o o p e r a t e a h a i r save p r o c e s s .

Some chrome t a n n e r s u se v a r i a b l e systems t h a t can o p e r a t e e i t h e r as a

h a i r save o r h a i r . b u r n p r o c e s s . Such a system a l lows t h e t a n n e r t o t a k e

advantage of market c o n d i t i o n s f a v o r i n g t h e h a i r save o r h a i r burn systems [831.

New marke ts and a p p l i c a t i o n s f o r r ecove red h a i r from h a i r save o p e r a t i o n s

a r e be ing exp lo red . For i n s t a n c e , r e c e n t r e s e a r c h has found t h a t k e r a t i n

( h a i r p r o t e i n ) i n t he form o f wool may be used i n m e t a l s r ecove ry from

was tewater and i s proposed f o r removing low copper c o n c e n t r a t i o n s from n i c k e l

s o l u t i o n s [841. The development of t h e s e market areas could g r e a t l y a f f e c t

t h e e x t e n t of h a i r r ecove ry from u n h a i r i n g o p e r a t i o n s and s i g n i f i c a n t l y reduce

c u r r e n t was tewater l o a d i n g s t h a t accompany t h e u se of h a i r burn p r o c e s s e s . A t

4-58

p r e s e n t , however, t h e market f o r h a i r i s l i m i t e d and t a n n e r s a r e r e l u c t a n t t o

con t inue h a i r save o p e r a t i o n s i f t hey must t hen l a n d f i l l t h e recovered h a i r .

4.9 SOLVENT RECOVERY

Because of t h e i r h i g h f a t c o n t e n t , p i g s k i n s and sheepsk ins a r e normal ly

degreased p r i o r t o t ann ing ; up t o 10 pe rcen t of a p i g s k i n (by we igh t ) may be

removed as g r e a s e [ l l ] . C u r r e n t l y , two methods are used i n deg reas ing

p i g s k i n s and sheepsk ins : s o l v e n t and d e t e r g e n t . So lvent d e g r e a s i n g i s

commonly p r a c t i c e d by p i g s k i n and sheepsk in t a n n e r i e s [ 3 , 1 1 ] .

The deg reas ing o p e r a t i o n i s u s u a l l y t h e i n i t i a l t anya rd o p e r a t i o n . It i s

performed on unprocessed s k i n s as they are r e c e i v e d from t h e packinghouse.

However, sheepsk ins may be f l e s h e d p r i o r t o deg reas ing . Degreas ing o p e r a t i o n s

a r e e s s e n t i a l l y t h e same f o r bo th p i g s k i n s and sheepsk ins and i n c l u d e t h e

fo l l owing major s t eps :

1. Skins a r e p laced i n drums where t hey a r e soaked and washed i n wa te r .

2 . So lvent o r d e t e r g e n t i s added t o t h e drums and t h e s k i n s are tumbled t o f a c i l i t a t e d e g r e a s i n g .

3 . Grease , w a t e r , and s o l v e n t mix tu re are pumped t o a s e p a r a t i o n t ank where water i s s e p a r a t e d from g r e a s e and s o l v e n t .

One s y s t e m , used i n p i g s k i n t a n n e r i e s , i s a p p l i e d t o a deg reas ing solu-

t i o n c o n s i s t i n g of s o l v e n t , g r e a s e , and w a t e r . The waste s t r eam i s s e g r e g a t e d

from o t h e r f a c i l i t y was te s t r eams and pumped i n t o a l a r g e t ank where, w i th

s u f f i c i e n t r e s i d e n c e t ime, some o i l / w a t e r s e p a r a t i o n o c c u r s . The o i l l a y e r

c o n t a i n i n g s o l v e n t and t h e removed g r e a s e s i s s e n t t o a s t r i p p i n g column where

t h e g r e a s e and s o l v e n t a r e s e p a r a t e d ; t h e wa te r l a y e r i s d i s cha rged t o t h e

p l a n t ' s sewer. The recovered s o l v e n t i s t hen r eused i n t h e d e g r e a s i n g opera-

t i o n 1111. Grease may a l s o be recovered as a byproduct ( s e e S e c t i o n 4.5). some c a s e s , t he s o l v e n t c o n t a i n i n g t h e g r e a s e is s e n t o f f - s i t e f o r s o l v e n t

r ecove ry [11 ,851 .

In

A t sheepskin t a n n e r i e s , waste s o l v e n t i s g e n e r a l l y recovered and s o l d f o r

v r e p r o c e s s i n g [ 3 ] . Solvent r ecove ry o p e r a t i o n s involved wi th sheepsk in g r e a s e

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removal are assumed to be similar to those for pigskin tanneries because of the similarity of the degreasing operations. However, specific recovery

process descriptions were not found in the investigation for this report.

In most tanneries, solvents are also used in finishes applied to leather

to enhance color and provide resistance to abrasions and stains 1111. recovery may also be applied to the residues from these finishing processes. These residues come from finishing equipment and from air pollution control devices on spray booths that apply finishes to the leather. Though they are

usually disposed of as solid waste, some are sold €or solvent reprocessing [ 3 1 . This recovery method may not prove feasible for tanneries where the

quantity of residues generated are small or where solvent reprocessors are not located nearby.

Solvent

Some applications of solvent recovery systems have proven both economi-

cally and technically feasible.

in pigskin and sheepskin tanneries. Further application of this process

within the leather and leather products industry is limited because few processing steps require solvents.

solvents have only limited use in the leather finishing process, since water-

base finishes are also used. Thus, there is little room for expansion of this process within tanneries.

In fact, solvent recovery is commonly applied

Outside of the degreasing operations,

However, solvent recovery may, in the future, have greater application

within the tannery. A new method of leather processing using solvents rather than water as the processing media is being investigated. Should such a

system prove practical and produce leather of the same quality as current processing practices, solvent recovery would be desirable to minimize the loss

of an expensive processing medium.

4.10 GAS RECOVERY BY FERMENTATION

_-

Anaerobic fermentation, or digestion of organic wastes under low oxygen conditions, has been used for many years in a variety of industries to produce

combustible gasses. This digestion process involves the bacterial breakdown

of organic material into simple organic compounds such as organic acids.

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Methane-forming b a c t e r i a consume t h e s e o r g a n i c a c i d s , t h e r e b y producing carbon

d i o x i d e and methane.

The same concept could p o t e n t i a l l y be a p p l i e d t o much of t h e waste

m a t e r i a l produced i n t h e l e a t h e r t ann ing i n d u s t r y . Sludges from t a n n e r y

was tewater t r ea tmen t systems have been proposed as a r a w material f o r t h i s

p roces s because t h e s ludges are r i c h i n o r g a n i c m a t e r i a l s t h a t can be con-

v e r t e d t o u s a b l e combustion g a s s e s . The gas produced by f e r m e n t a t i o n of t h i s

was te has been proposed f o r use as a f u e l i n a "TOTEM" ( T o t a l Energy Module)

ene rgy r ecove ry system, which u t i l i z e s an automobile eng ine t o run a g e n e r a t o r

t o g e n e r a t e e l e c t r i c i t y [761.

r e s e a r c h , i t i s v e r y s i m i l a r t o systems which have been a p p l i e d i n was tewater

t r ea tmen t f a c i l i t i e s and i s a p o t e n t i a l l y v i a b l e energy r ecove ry t echn ique .

Although t h i s is on ly a proposed area of

Var ious v e r s i o n s of t h i s t e chn ique f o r gas r ecove ry from t a n n e r y was tes

have e i t h e r been proposed or have undergone i n i t i a l l a b o r a t o r y t e s t i n g .

F u r t h e r r e s e a r c h i n t o t h e use of s l udges f o r gas p roduc t ion i s n e c e s s a r y t o

.- d e t e r n i n e i f t h e p roces s w i l l work on a l a r g e s c a l e and prove c o s t - e f f e c t i v e

compared t o o t h e r methods a v a i l a b l e t o r ecove r t h e m a t e r i a l s i n t a n n e r y

w a s t e s .

B a c t e r i a l d i g e s t i o n of h i d e was t e s , such a s l e a t h e r t r i m and b u f f i n g

d u s t s , t o produce combus t ib le gas se s has a l s o been i n v e s t i g a t e d . However,

t h i s f e rmen ta t i on p roces s was found t o be u n s a t i s f a c t o r y because of t he l o w

gas y i e l d and the slow decomposi t ion of was t e s [861 .

4.11 ACTIVATED CARBON MANUFACTURE

Lea the r waste may be used t o produce a c t i v a t e d carbon . Experiments have

shown t h a t p y r o l y s i s of l e a t h e r waste by h e a t i n g i t t o 400°C r e s u l t s i n a

50 pe rcen t y i e l d of hard g r a n u l a r c h a r . The l i t e r a t u r e has i n t e r p r e t e d t h i s

d a t a t o i n d i c a t e t h a t t h e same p roces s could conve r t l e a t h e r waste t o h a r d ,

g r a n u l a r , a c t i v a t e d carbon wi th approximate ly t h e same y i e l d I571.

4-6 1

Bench- scale r e s e a r c h has shown t h a t t h e fo l l owing l e a t h e r wastes can

p o t e n t i a l l y be used t o produce a c t i v a t e d carbon:

0 S p l i t s

0 Blue t r i m and shav ings

Unf in ished l e a t h e r t r i m

F in i shed l e a t h e r t r i m

Lea the r product manufac ture t r i m and shav ings .

The proposed uses of t h e d e r i v e d cha r a r e t hose p r e s e n t l y f i l l e d by

commercial ly produced a c t i v a t e d carbon . Among t h e s e u se s are: p u r i f i c a t i o n

o f i n d u s t r i a l waste d i s c h a r g e s ; removal of odors and tas tes from p o t a b l e

water; p u r i f i c a t i o n of suga r and chemica l s ; removal of harmful and odorous

s u b s t a n c e s from gaseous e f f l u e n t s ; and f i l t r a t i o n of tar and n i c o t i n e from

c i g a r e t t e s 1571.

Lea the r waste, a s a sou rce of g r a n u l a r a c t i v a t e d ca rbon , may be impor tan t

because t h i s type of a c t i v a t e d carbon i s a premium m a t e r i a l . It has g r e a t e r

a b s o r p t i o n e f f i c i e n c y and r e s i s t a n c e t o a t t r i t i o n i n use t h a n powdered

a c t i v a t e d carbon . These q u a l i t i e s a r e r e f l e c t e d i n a h i g h e r sa les p r i c e ; i n

1977, g r a n u l a r a c t i v a t e d carbon s o l d f o r $0.40 t o $0.50 pe r pound, wh i l e t h e

powdered form so ld f o r $0.10 t o $0.12 per pound I 571 .

Market c o n d i t i o n s may c o n s t i t u t e an impediment t o f u r t h e r development of

t h i s r ecove ry technology . In 1977, t h e market f o r a c t i v a t e d carbon w a s

s a t u r a t e d even though i t was growing by 10 p e r c e n t a yea r . However, many

users have swi tched from powdered t o g r a n u l a t e d a c t i v a t e d carbon because of

t h e s a v i n g s t h a t r e s u l t from t h e l o n g e r- l a s t i n g p r o p e r t i e s [571. Thus, t he

market for t h e g r a n u l a t e d form i s a l s o i n c r e a s i n g .

Although no f i g u r e s were a v a i l a b l e , t h e c o s t of producing t h e a c t i v a t e d

carbon may be o f f s e t by t h e i n c r e a s e i n i t s v a l u e and through t h e r ecove ry o f

by- products gene ra t ed du r ing p y r o l y s i s of t h e waste m a t e r i a l s . For example,

spo t checks i n d i c a t e t h a t t h e p r i c e of g r a n u l a r a c t i v a t e d carbon has i n c r e a s e d

s i n c e 1977 from $0.40 t o S0.50 p e r pound t o between $ 2 . 3 6 and .$4 .00 pe r pound,

4-62

depending on the q u a n t i t y purchased . I n a d d i t i o n , i t has been sugges ted t h a t

t h e v o l a t i l e o rgan ic m a t e r i a l s gene ra t ed from t h e l e a t h e r was te d u r i n g t h e

h e a t i n g p roces s could be used as f u e l o r chemical i n t e r m e d i a t e s , and t h e

gene ra t ed ammonia could be used i n t h e manufac ture of commercial f e r t i l i z e r .

The v a l u e of t h e s e recovered by- products combined wi th t h e p r i c e i n c r e a s e s f o r

a c t i v a t e d carbon may make t h i s a l t e r n a t i v e t o d i s p o s a l a t t r a c t i v e t o genera-

t o r s of s o l i d l e a t h e r s c r a p .

4.12 COLLAGEN PRODUCT MANUFACTURE

Col lagen i s a f i b r o u s p r o t e i n t h a t i s t h e major c o n s t i t u e n t of animal

s k i n o r h i d e . Col lagen i s t h e material t h a t g i v e s s k i n i t s p r o p e r t i e s o f

toughness and e l a s t i c i t y [ 61 . Hides and s k i n s used by t h e t ann ing i n d u s t r y t o

produce l e a t h e r are c u r r e n t l y a major s o u r c e o f t h i s m a t e r i a l f o r commercial

pu rposes . Col lagen i s an impor tan t c o n s t i t u e n t i n t h e manufac ture of foods ,

cosme t i c s , and medica l p roduc t s .

Col lagen i s produced from a v a r i e t y of s o u r c e s . I n some i n s t a n c e s , such

as foi pha rmaceu t i ca l s , u n t r e a t e d animal h i d e s are. used d i r e c t l y from t h e

s l augh te rhouse f o r p roduc t ion of commercial c o l l a g e n . Waste h i d e m a t e r i a l s ,

bo th tanned and untanned r e s u l t i n g from l e a t h e r t a n n i n g o p e r a t i o n s , a r e a l s o

s p o r a d i c a l l y used t o produce c o l l a g e n p r o d u c t s .

i n c l u d e :

These waste materials

F l e s h i n g s

Trimmings

Limed s p l i t s

Blue s p l i t s

Blue t r i m and shav ings

Unf in ished l e a t h e r t r i m

F in i shed l e a t h e r t r i m

T r i m and shavings from l e a t h e r p roduc t s manufac ture .

Col lagen i s ob t a ined i n u s a b l e form from h i d e s and h i d e was t e s by granu-

l a t i n g the h i d e m a t e r i a l o r hyd ro lyz ing i t t o form a s l u r r y of f i b r o u s p r o t e i n s

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(hydrosylates). There are several methods in use f o r preparing these hydrosylates or slurries. One method involves the grinding of hide scraps in the presence of water to produce an aqueous slurry [871.

treatment of hide waste with milk of lime and steam, as follows [881:

Another method involves

1. Collagen in the hide waste reacts with lime to form calcium collagenates and calcium salts.

2 . Impurities are removed by washing the collagenates.

3 . Collagenates are heated with soda ash to form sodium salts.

4 . Salts are washed, filtered, and concentrated by evaporation.

Once the collagen is converted to granules or slurries, it is ready for use in collagen products. The form of collagen that is produced depends on

its ultimate use; in some cases, the hide itself is used directly (e.g., dog chews). For use of collagen in foods and other applications, waste materials

from tanned hides may need to be detanned prior to their use. For example,

hide scrap used for glue production may require that the chrome be removed

before it can be used 1541.

Currently, the three largest uses of collagen are in dog chews, gelatin,

and edible sausage casings.

cations for collagen derived from hide wastes, including [6,83,88,89,90,91]:

However, there are numerous other uses and appli-

0 Glue manufacture

0 Cosmetics

0 Surfactants

0 Medical applications (surgical sutures, wound coverings, biomaterials, prostheses, plastic surgery)

0 Agricultural sprays

0 Protective colloids for preparation of pigment suspensions

0 Colloids for papermaking

4-64

I

e Flotation aid €or ore processing

0 Refining of metals.

Edible sausage casings are produced from collagen hydrosylates. A

patented process for the manufacture of edible sausage casings uses a simple

slurry of ground hide waste. The slurry is acidified, then extruded through

an annular die to form a tubular casing. The casing is further processed to

improve its strength and flexibility, then plasticized and dried [871. casings can be used for sausage and other processed meats [831 .

The

Hide collagen-derived gelatin is primarily used in food, although it is

also used for technical gelatin as well as pharmaceutical and photographic products [61. Gelatin is also used to produce feeds and protein flours

[55,92].

Collagen has other food uses as well. For example, hides are used around

the world as meat substitutes [6]. Collagen has also been proposed as a

thickening agent for meat [831. The U.S. Department of Agriculturc is

currently sponsoring studies involving the use of collagen derived from limed splits as an additive t o bologna, meat loaf, cakes, and yeast bread [931.

The market for hide-derived collagen is currently decreasing in spite of the fact that numerous new uses are being developed and investigated. One

problem is that substitutes for collagen are becoming increasingly prevalent

in the traditional markets of the glue and gelatin industries. Another

problem is that many of the collagen products, particularly food, pharma- ceuticals, and medical products, require untanned, untreated hides so that the

products will not contain contaminants, such as chrome, that render them unfit for human consumption or use. In general, collagen destined for use in the medical, food, and pharmaceutical industries must come from specially certified materials. Collagen for these uses are obtained from animals certified

to be disease-free by federally inspected slaughter operations. These hides or skins generally come directly from packinghouses rather than tanneries [61.

4-6 5

I n some c a s e s , such as g l u e manufac ture , t h e wastes from t a n n e r i e s undergo

chrome removal t o r ende r t h e m a t e r i a l f i t f o r u s e [51 ] .

A l a r g e q u a n t i t y of h i d e s c r a p from t a n n e r i e s can be d i v e r t e d t o c o l l a g e n

product manufacture pending t h e development of waste p u r i f i c a t i o n t e c h n i q u e s ,

such as chrome removal. Th i s problem can be p a r t i a l l y overcome by s e p a r a t i n g

tanned and untanned s c r a p , or, as European t a n n e r s a r e do ing , by s p l i t t i n g t h e

h i d e i n t he limed s t a t e r a t h e r t han a f t e r t a n n i n g ( " in t he b lue" ) . Development

of a l t e r n a t i v e uses and i n c r e a s e d use of o t h e r h i d e s and s k i n s may a l s o be

pursued i n o rde r t o m a i n t a i n a p r o f i t a b l e market f o r t h e h i d e s c r a p s [ 8 3 ] .

.. 4.13 FIBROUS PRODUCT MANUFACTURE

Roughly 85 pe rcen t of t h e b a s i c s t r u c t u r e of l e a t h e r i s a conglomera t ion .

of c o l l a g e n p r o t e i n f i b e r s . These f i b e r s , r ang ing i n l eng th from under 0.5 cm

t o g r e a t e r than 2 . 5 cm, g i v e t h e l e a t h e r a s u p p o r t i n g m a t r i x w i th key p h y s i c a l

and mechanical p r o p e r t i e s . Among t h e s e p r o p e r t i e s are h igh t e n s i l e and tongue

t e a r s t r e n g t h , good a b s o r p t i o n and e l o n g a t i o n c a p a c i t i e s , and e x c e p t i o n a l

f l e x i b i l i t y [ 941 .

s t a b i l i z e s t h e m a t r i x w i t h v a r i o u s b ind ing a g e n t s , r e n d e r i n g i t d u r a b l e and

r e s i s t a n t t o b i o l o g i c a l decay i l l ] .

These p r o p e r t i e s are enhanced by t h e t ann ing p roces s which

Recognit ion of t h e s e p r o p e r t i e s has prompted some l e a t h e r product manu-

fac tu re r s t o look f o r a l t e r n a t i v e s t o t h e c u r r e n t p r a c t i c e s of d i s p o s a l o f

.* tanned l e a t h e r w a s t e s . One such o p t i o n , sometimes used by t h o s e i n t h e

I 3 i n d u s t r y , i s s e l l i n g such wastes t o f i b r o u s product manufac tu re r s . Using

va r ious f i b e r s e p a r a t i o n p r o c e s s e s , t h e s e manufac tu re r s can i s o l a t e t h e

f i b e r s , thereby c o n v e r t i n g t h e l e a t h e r waste i n t o a u s a b l e form. Combined

wi th o the r m a t e r i a l s such a s polymers and f i n i s h i n g a g e n t s , t h e s e f i b e r s can

be r e c o n s t i t u t e d v i a f u l l - s c a l e manufac tur ing systems i n t o v a r i o u s s a l a b l e

p roduc t s .

f

I

I

f. f I I I f I

I

4-66

Though each fibrous product manufacturer prefers specific wastes with

individual chemical and physical characteristics, the following wastes can be

used in fibrous product manufacture:

0 Splits

0 Blue trim, shavings, and dust

0 Unfinished leather trim 0 Buffing dust 0 Finished leather trim

0 Leather product manufacturing trim and shavings.

Each fibrous product manufacturing technique is highly dependent upon the wastes, the tanning process used, and the type of product to be manufactured.

Yet, all share a defibrillation process that prepares the fibers for

integration into a product. This process involves two key steps [26,941:

1. Granulation through mechanical grinding of the waste which produces a homogenous material suitable for processing.

2. Defibrillation, which breaks down the felt-like structure of the granulated leather waste to separate the fibers.

These preliminary preparation steps are used in individual manufacturing

processes such as leatherboard, artificial leather, and poured insulation manufacture.

Currently, one of the major uses of fiberized leather is in the produc-

tion of leatherboard (SIC 2631). This product is used primarily in the shoe

manufacturing industry as insoles, outsoles, and middle soles [171. It is also used in the manufacture of leather products such as counters, belts,

purses, and wallets [951.

The actual manufacture of leatherboard is accomplished by combining

fibers from the waste with synthetic fibers (such as cotton and bleached kraft pulp of coniferous trees) and water. The mixture is then screened and fed

into a type of papermaking machine that generates multi-layered 1 m thick

4-6 7

water-laid sheets. The sheets are then dehydrated with a drying press and further dried in an air-circulating drier. The final step entails

impregnating the sheets with an emulsion binder, further drying, and curing in

a press to produce the final leatherboard product [941.

A similar product utilizing fiberized leather is artificial leather, which is a combination of leather fibers with a rubber latex or plastic, and

polymeric binding agents. These materials are processed into a nonwoven fabric which can be used in sports footwear, wall decorations, seat coverings,

and shoe soles I261. In addition, artificial leather has been extensively used in Italy since 1928 in the manufacture of hat sweatbands, cigarette and

camera cases, briefcases, and book bindings [141.

Fiberized leather can also be used as poured insulation. Strongly resis-

tant to ignition and environmental degradation, this type of thermal insulator

could compete with commonly used poured cellulosic insulation [56,571.

Researchers postulate that should problems of fiberization cost and odor be

solved, poured insulation derived from hide and leather wastes could be used

in both residences and light commercial structures. Since the cost of

producing fiberized poured insulation was estimated at $110 per ton in 1 9 7 7 ,

it is a potentially attractive option to cellulosic insulation, which sold at $240 per ton [571.

The potential for greater use of leather scrap in the manufacture of

fiberized leather and its products appears good. Conversations with various

leather product manufacturers suggest that much of their wastes that are

suitable for fibrous product manufacture are currently landfilled. This

represents a significant loss of revenues which could be recovered should the

fibrous leather product market continue to develop and if transportation costs are not prohibitive.

Leather product manufacturers utilizing this alternative to disposal

generally sell their wastes to fibrous product manufacturers through a network of leather brokers. These brokers number 30 to 40 and are located in the

major shoe and garment centers, including New England, New York City,

I

1

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Cincinnati, Chicago, St. Louis, Nashville, the West Coast, and Gloversville,

NY [961.

Leather brokers are presently operating at capacity in a buyers' market

[96,971. Thus, much of the leather product manufacturing wastes are not absorbed by the leather broker network. Should the capacity of this network

be increased, surplus leather scrap can be diverted from landfills to fibrous

product manufacturers. Thus, one of the key impediments to the greater use of

leather waste in the fibrous product industry is largely that the collection

network cannot currently meet the waste collection needs of the tanneries and leather product manufacturers. Other factors could be related to limited

markets for fibrous products.

4.14 LEATHER PRODUCT MANUFACTURE

An alternative to the disposal of leather scrap produced in leather and leather product manufacturing processes is to use it as raw material for smaller leather products. Tanneries and large leather product manufacturers,

in particular, generate significant amounts of solid leatber wastrs that can

be used in the manufacture of many specialty leather products [ 85 ,981 . These

secondary leather product manufacturers can use the following wastes [ 95 , 96 , 97,99,100 1 :

0 Splits (from chrome tanning)

0 Unfinished leather trim

0 Finished leather trim

0 Leather product manufacture trim and shavings (including skeleton and negative patterns from the shoe industry)

0 Surplus and off-specification leather and products.

Tanneries, as well as shoe, garment, belting, saddle, and sports

equipment manufacturers, generate these wastes. Although these wastes are largely landfilled, some facilities collect their leather scraps, which tend

to be headsize and smaller, and sell them to the 30 to 40 leather brokers that

4-69

are l o c a t e d i n a r e a s w i th heavy c o n c e n t r a t i o n s of l e a t h e r product i n d u s t r i e s

( s e e S e c t i o n 4.13) 1961. These b r o k e r s a c t as middlemen i n t r a n s f e r r i n g

l e a t h e r s c r a p s t o secondary marke t s .

I n g e n e r a l , o n l y l a r g e r was te g e n e r a t o r s have c o n t r a c t s w i t h t h e s e area

b r o k e r s . Smal le r g e n e r a t o r s , on t h e o t h e r hand, are o f t e n fo rced t o d i s p o s e

o f t h e i r s c r a p m a t e r i a l s . T h e i r low volume of wastes, sometimes of v a r i a b l e

compos i t ion , a r e o f t e n less a t t r a c t i v e t o l e a t h e r b r o k e r s [971.

Among those who purchase l e a t h e r s c r a p m a t e r i a l s are t h o s e i n t h e

s p e c i a l t y l e a t h e r i n d u s t r y .

g loves and g love l i n i n g , e y e l e t s and t r i m f o r shoes , diaphragms f o r pumps and

s p r a y c a n s , and i d e n t i f i c a t i o n t a g s f o r luggage [85,96,100].

produc t s are made and s o l d i n t h e Uni ted S t a t e s .

b r o k e r s i n d i c a t e t h a t s i g n i f i c a n t amounts of s c r a p l e a t h e r a r e a l s o s o l d

o v e r s e a s . They r e p o r t t h a t a l a r g e market ex i s t s for t h e m a t e r i a l i n l e s s

developed c o u n t r i e s . S p e c i a l t y l e a t h e r p roduc t s such as w a l l e t s , p u r s e s , and

s a n d a l s a r e f a b r i c a t e d from l e a t h e r s c r a p i n f o r e i g n c o u n t r i e s f o r s a l e

bo th d o m e s t i c a l l y and abroad [96,971.

These wastes can be used i n t h e manufac ture of

Many of t h e s e

Conve r sa t i ons w i th l e a t h e r

C u r r e n t l y , some t a n n e r s and l e a t h e r product manufac tu re r s dona t e t h e i r

s c r a p t o c h a r i t i e s . O the r s s e l l i t d i r e c t l y t o l o c a l c r a f t smen who

i n c o r p o r a t e t h e waste i n t o p l a n t hange r s and o t h e r hand-made l e a t h e r p roduc t s

[85,981. However, i t i s t h e s m a l l e r g e n e r a t o r no t l o c a t e d i n a major t a n n i n g

c e n t e r t h a t g e n e r a l l y does not have t h e o p t i o n of s e l l i n g h i s s c r a p 1691.

The impediments t o t h e g r e a t e r u se of l e a t h e r s c r a p by t h e s p e c i a l t y and

c r a f t i n d u s t r i e s appear t o be two- fold. F i r s t , many i n t h e was te s c r a p

g e n e r a t i n g i n d u s t r i e s are not aware t h a t t h e r e may be a market f o r t h e i r

d i s c a r d e d l e a t h e r . Second, c o n v e r s a t i o n s w i t h i n d i v i d u a l l e a t h e r b r o k e r s

sugges t t h a t they are o p e r a t i n g a t c a p a c i t y i n a b u y e r s ' market [961.

o p e r a t i n g on l a r g e economies of scale cannot a f f o r d t o hand le t h e low volume

and/or s p o r a d i c q u a n t i t i e s of s c r a p r e s u l t i n g from s m a l l e r o p e r a t i o n s . Should

t h e s p e c i a l t y l e a t h e r market f o r s c r a p was t e s grow, t h e s e impediments may be

Buyers

' 4-70

somewhat resolved. Such an increase in the market would have to be

accompanied by the advent of additional leather brokers to meet the needs of

both the tanner as well as the leather product manufacturer. (It has been

suggested that there is little chance of significant growth in the domestic scrap leather market [ 7 ] . )

4.15 ISOLATION OF SOLIDS FOR FERTILIZER MANUFACTURE

The various solid wastes generated by the leather and leather products

industry are high in nitrogen content and therefore potentially useful as

organic nitrogen fertilizers. A recognized alternative to the disposal of

these wastes is to incorporate them into fertilizer manufacturing operations.

Specifically, the following wastes may be used:

0 Fleshings 0 Blue trim and shavings

0 Buffing dust 0 Unfinished leather trim

0 Finished leather trim Wastewater treatment sludge

0 Leather product manufacturing trim and shavings

The typical process for converting the above mentioned wastes to a useful

fertilizer involves the following steps:

1. Collect, dry, and granulate solid wastes. Collect, dewater, dry, and granulate sludges.

2 . Mix granulated material with urea to enhance the nitrogen content. This mixture is called tankage.

3 . Further enhance tankage through addition of phosphate, potassium, and other ingredients, to produce the final fertilizer product.

This process may involve various handlers of the waste material. For

example, scrap buyers (similar to the leather brokers mentioned in Sections

4 . 1 3 and 4 . 1 4 ) may purchase scrap from tanneries and sell it to tankage manufacturers. Tankage manufacturers are often only involved in the

\

4-7 1

production of tankage, which is then sold to fertilizer manufacturers who complete the final step of enhancing the tankage with phosphate and potassium materials to produce the final product. Three such tankage manufacturers have been identified; one each in Wisconsin, New York, and Maine. Their product is

sold to manufacturers producing agricultural fertilizers for use in the

Florida citrus industry [loll.

k fertilizer manufacturing facility, using only leather industry scrap,

is now under construction in the Gloversville area of upstate New York, an

area with a heavy concentration of tanneries. to be in full operation by January of 1982, will haul unprocessed shavings, scraps, and other solids directly from local tanneries. The facility will

convert the scrap into a pelletized form of fertilizer suitable for use in sandy soil agriculture.

will be used by the citrus industry [1021.

The plant, which is scheduled

It is anticipated that most of the plant's production

Lesser amounts of beamhouse solid wastes, such as fleshings, are also

used as fertilizers. One researcher reported that processed fleshings can be

applied to agricultural soils prior to planting. Like organic manure, the

fleshings release their nitrogen as soil micro-organisms slowly decompose the proteins in the fleshings 1171.

An alternative to the landfilling of pretreatment and primary treatment

tannery sludges is to use them as fertilizers and foil conditioners. by restrictive landfill disposal regulations and increasing amounts of treat-

ment sludges, tanners are actively considering this disposal alternative.

Researchers have suggested that a minimal amount of treatment could convert some sludges into a useful material for the agriculture industry. Other

sludges, especially those from vegetable tanning industry, may require

significant pretreatment to remove specific contaminants [421.

Prompted

Like the solid leather scrap, sludges have a high protein content that

makes them attractive nutrient sources 11031. To render them useful to farmers, tanners must dewater, dry, and screen the sludge. It is postulated that a tannery processing 100,000 pounds of hides per day and subsequently

4-72

generating 30,000 pounds of sludge (25 percent solids) could produce 3.75 tons of fertilizer at a cost of $195 a day, or $ 5 2 per ton (1979 dollars). Because

comparable conventional fertilizers sold for $36 per ton in 1979, the break- even sales price of $52 per ton for leather-derived fertilizers was obviously

uneconomical. The researcher suggests, however, that modifications in the

drying process could reduce the production costs enough to make the fertilizer economical to produce. Higher fertilizer nitrogen content and use in local

farming, thereby reducing the shipping costs, could also make the economics of the process more favorable (1031.

The impediments to greater use of leather industry scraps and sludges as

fertilizers and soil conditioners are chiefly related to the waste's

contaminant and heavy metal content [14,49,75,104]. Tanning chemicals and

trace impurities, including chromium, cadmium, zinc, lead, salt, and other

tannery process chemicals (such as lime), may be present in concentrations

exceeding Federal, state, or local regulations that limit the metal content of materials used in fertilizers or soil conditioners [42,105,1061. Regulations,

such as those in Massachusetts, make this disposal alternative unfeasible. In Massachusetts, tannery sludges cannot be disposed of on cropland without

purification since they contain chrome in concentrations of 40,000 to 70,000

ppm, far exceeding the State's limit of 1,000 ppm.

These restrictions make treatment of tannery sludges and leather wastes

imperative before .they-can be used for agricultural purposes.

chromium removal treatment technologies, such as chrome precipitation of spent

tanning liquors or acid dissolution o f wastewater treatment sludges (see Section 4.2), can be employed with varying degrees of success to minimize

heavy metal content of wastewater treatment sludges.

Application of

Of late, there has been a definite trend away from utilizing leather industry scraps and sludges in the manufacture of fertilizers and soil con-

ditioners. One study reported that the number of fertilizer manufacturers

accepting leather scrap has declined from 20 in 1956 to only 3 in 1978 [3].

Further, a survey of pertinent literature reveals that, to date, only pilot scale projects have been conducted using sludges for fertilizers [75,105].

4-7 3

Part of this downturn is due to public and farmer opposition to the use

of sludges on cropland [ 491 . Some tanners favoring this disposal alternative argue that their treated sludges and wastes contain comparable levels of

contaminants as the municipal and industrial sludges commonly applied to

cropland. This argument is having less impact on local officials who are increasingly rejecting the application of even municipal sludge to cropland.

Recent disagreements between industry and the EPA over the toxicity and

mobility of trivalent chromium, a common contaminant in the wastes, has added

to farmers' reluctance to use fertilizers made from tannery wastes.

The tendency to use other, better balanced, and more concentrated ferti-

lizers is likely t o continue given present public attitudes and market conditions. Until the conditions which precipitated the trend are alleviated,

most tanners and leather product manufacturers must continue to landfill their wastes or use other resource recovery operations.

4.16 USE IN THE CONCRETE INDUSTRY

The solid leather wastes generated by the leather tanning and leather product manufacturing ind:stry have been proposed for use in production of

concrete. Researchers have suggested that these wastes could be used as frost-proofing air entrainment agents for concrete laid in cold regions. The

wastes suggested for the use are [831:

Hydrolyzed hair

Blue trim and shavings

Buffing dust

Unfinished leather trim

Finished leather trim Trim and shavings from leather product manufacture.

Conventional frost-proofing air entrainment agents include wood resins, synthetic detergents, salts of petroleum acids, salts of proteinaceous

materials, organic hydrocarbons, beef tallow, and neutralized resins. These

anionic surfactants are blended in powder or liquid form into the concrete mix

4-74

whereupon they are adsorbed onto cement particles within the aggregate.

mix is useful in cold regions since surfactants create tiny bubbles of air

that provide spaces where unfixed water can collect. When the water freezes

and expands it does so within these spaces without stressing the concrete

[107 ] .

This

The above mentioned tannery and leather product manufacturing wastes

presumably could be used for this purpose because they contain salts of proteinaceous materials, a conventional anionic surfactant. Hydrolyzed hair,

already converted to its liquid protein form by the hair burn process, could be directly mixed with the concrete. be granulated into a powder form for use. Mixing of solids would be more difficult to achieve due to differential dispersion factors.

Other solid leather scraps would have to

An impediment to the use of powdered leather waste as a frost-proofing air entrainment agent may be its potential for degradation. The water may

attack its structure thereby limiting its usefulness. Collection, hydro-

lyzing, grinding, and granulation costs may further impede this use [ 4 2 ] .

Tanners may be willing to perform these operations only if the revenues from sales of frost-proofing agents offset the operation costs and provide a

reasonable return on investment.

4.17 USE AS A FILTER PRECOAT

Buffing dust is generated from the tannery buffing process, which

smoothes irregularities in the grain surface through mechanical abrasion.

This dust is not generally thought of as available recoverable waste. Its form and inherent collection problems render it difficult to gather sufficient

quantities for use in many by-product manufacturing industries.

Tanners have traditionally directed their research at other waste streams, such as those from the trimming, beamhouse, and tanning operations,

that contain more easily recoverable and valuable resources. Yet, some

researchers have developed pilot-scale technologies aimed at recovering

buffing dust for use in the tannery. It has been found that the dust can be

4-75

used as a filter precoat to enhance the performance of wastewater pressure filters. The researchers suggest that 50 to 90 percent of the generated dust

can be used fo r this purpose [1081.

In its use as a filter precoat, dry buffing dust is collected in a

storage bin and transferred to a precoat tank where it is wetted. Applied to

the filter press, the dust blinds the filter cloth resulting in an increased

headloss and more efficient solids removal. Additionally, this precoat allows f o r easier backwashing of the filter.

Pilot-scale test results seem to suggest that the potential for the

greater use of buffing dust as a filter precoat is good. It is postulated that tanneries could replace conventional precoats, such as ash and

diatomaceous earth, with available buffing dust. This waste has little value outside of the tannery, requires minor processing, and is apparently an

effective filter aid. Thus, there may be a potential use for the dust in both

the tanning and in other industries that use pressure filters to dewater their sludges.

6

4.18 USE AS A SLUDGE CONDITIONER/VISCOSITY MODIFIER

The handling of sludge from tannery effluent treatment facilities poses problems to the tanner due to its high water content and semiliquid nature.

Because primary and secondary sedimentation sludges usually have a water

content of well over 90 percent, facilities must use coagulants and/or mechanical dewatering devices to lower transportation and disposal costs. Of

late, tanners are using organic polyelectrolytes, such as methylcellulose and alginates, to aid in sludge handling [14,44]. These coagulants, utilized with sedimentation processes, can reduce the water content of sludges which are 94

percent water to only 50 percent water [141.

4-76

Some tanners have suggested that the following wastes could serve as

conditioners and/or viscosity modifiers:

Blue shavings and dust

Unfinished leather trim

0 Finished leather trim

Buffing dust.

These wastes, acidic and fibrous in nature, act as flocculating agents when

added to the basic sludge. The dust is especially effective due to its greater available surface area.

buffing dust are generally already present in the wastewater treatment sludge

and therefore act as natural flocculants [14,1091.

It should be noted that blue shavings and

One researcher has indicated that the use of these wastes as sludge

conditioners is practiced at perhaps only one or two tanneries. Its limited

use may be due to the fact that suitable wastes are difficult to collect and

do not perform 1s well as conventional sludge treatment agents. This may

indicate that the potential for greater use of tannery wastes as the sole

sludge conditioner may not be good [ l o g ] . However, if the tanner must pay for the disposal of such wastes, it may be economical to use them as secondary

conditioners to augment more conventional conditioners, thereby reducing materials and disposal costs.

Tanners are also considering the use of leather scrap and trim to raise

the solids content of wastewater treatment sludges prior to incineration (see

Section 4 . 2 . 4 ) . It has been suggested that mixing the leather scrap together with the sludges-could raise the solids content to the point where the sludge

is a self-sustaining fuel [ 5 5 1 .

This concept can also be expanded to other industries. For example,

another potential use for shavings is in the oil well drilling industry. It has been suggested that leather shavings f r o m vegetable tanning could be used

as a viscosity modifier in drilling muds. Leather shavings from vegetable

tanning operations contain tannin which has similar physical properties to

4-7 7

v i s c o s i t y mod i f e r s a l r e a d y used i n d r i l l i n g muds and are t h e r e f o r e p r e f e r r e d

over b l u e shavings from chrome t a n n e r i e s [171. Because t h e shav ings have

l a r g e r polymer p a r t i c l e s and a r e more v i s c o u s , t hey may be more s u i t a b l e f o r

deepe r e x p l o r a t i o n s than t h e c u r r e n t l y used c o t t o n l i n t e r s and nylon s c r a p . A

su rvey of p e r t i n e n t l i t e r a t u r e r e v e a l s t h a t no s t u d i e s have been conducted on

t h e u s e of v e g e t a b l e tanned l e a t h e r shav ings t o modify d r i l l i n g mud v i s c o s i t y .

4 .19 USE I N FUNGICIDE AND BACTERICIDE INDUSTRY

A proposed a l t e r n a t i v e t o t h e d i s p o s a l o f f l e s h i n g s gene ra t ed i n beam-

house p roces se s i s t o use them i n t h e manufac ture of b a c t e r i c i d e s and

f u n g i c i d e s . Although t h i s i d e a was c i t e d by one r e s e a r c h e r , no a c t u a l

r e s e a r c h or i n v e s t i g a t i o n s have been performed. No i n f o r m a t i o n i s a v a i l a b l e

from t h e surveyed l i t e r a t u r e on t h e p r o c e s s i n g of t h e f l e s h i n g s , t h e i r

s p e c i f i c use i n t h e i n d u s t r y , nor t h e t ype o f b a c t e r i c i d e s and f u n g i c i d e s t h a t

can be produced us ing r ecove red f l e s h i n g s [171.

4 . 2 0 USE I N THE PLASTICS INDUSTRY

A proposed a l t e r n a t i v e t o t h e d i s p o s a l o f f l e s h i n g s gene ra t ed i n beam-

house p roces se s i s t o use them i n t h e manufac ture of p l a s t i c s . Again, t h i s

i d e a was c i t e d by one r e s e a r c h e r , bu t no a c t u a l r e s e a r c h or i n v e s t i g a t i o n s

have been performed. No i n f o r m a t i o n i s a v a i l a b l e from t h e surveyed l i t e r a t u r e

on t h e p r o c e s s i n g of t h e f l e s h i n g s , t h e i r s p e c i f i c use i n t h e i n d u s t r y , nor

t h e type of p l a s t i c s t h a t can p o t e n t i a l l y use recovered f l e s h i n g s [ 1 7 I .

*

4 . 2 1 USE AS POLLUTANT ABSORBANT

Beamhouse was t e s gene ra t ed i n t h e s p l i t t i n g and shaving o p e r a t i o n s can be

used as p o l l u t i o n a b s o r p t i o n a g e n t s . Resea rche r s have demons t ra ted t h a t

v a r i o u s beamhouse was tes i n c l u d i n g s p l i t s and b l u e shav ings can be used as

combus t ib l e gas a i r f i l t e r s and i n d u s t r i a l f l o o r c l e a n s e r s .

Bench s c a l e p r o j e c t s have demons t ra ted t h a t shaving d u s t can e f f e c t i v e l y

be used t o absorb was te g a s s e s from i n t e r n a l combustion e n g i n e s . P roces sed

shav ing d u s t can be p laced i n a c y l i n d r i c a l m e t a l l i c t ube a t t a c h e d t o t h e

exhaus t on an e n g i n e ' s m u f f l e r . The shav ing d u s t - f i l l e d t ube a c t s a s a sponge -

4-78

or a filter that removes harmful emission gasses [17]. A survey of pertinent

literature reveals little information on this tannery waste recovery

technique. Thus, judgements or impediments to development and potential for

widespread use can only be postulated. Further investigations into this

by-product/waste reuse should center on, among other things, ease of collection, the type of dust processing needed, the flammability of the dust,

and the amount of dust needed to make filter fabrication economical.

Researchers in France have used pilot-scale projects to demonstrate the

potential uses of blue shavings and splits as an industrial floor cleanser [ 2 6 1 . By drying and granulating the wastes, the researchers produced granules

that are hydrophobic and absorb grease. This material absorbs various sorts of substances, including oil, hydrocarbons, solvents, and organic pollutants,

making it particularly useful for cleaning up spills [17]. The researchers have reported no impediments to the development and subsequent wider application of this spill cleanup technology. As of 1980, a pilot plant was

operating with a capacity of 3 tons per day, and a full scale commercial-

ization of the process was under stidy. Researchers have suggested that the

use of their product could be extended to both ocean and lake pollution caused

by oil spills and industrial activity.

4- 79

5 . 0 SELECTED RESOURCE RECOVERY PROCESSES AND WASTE MANAGEMENT APPROACHES

The pr imary focus of t h i s s t u d y t h u s f a r h a s been a d e s c r i p t i o n o f t h e

l e a t h e r and l e a t h e r product i n d u s t r y and t h e deve lop ing and c u r r e n t l y used

r e s o u r c e r ecove ry p roces se s a v a i l a b l e t o the i n d u s t r y . S e c t i o n 4 d e s c r i b e s

each r e s o u r c e r ecove ry p r o c e s s , i t s s t a g e of development, t h e waste streams t o

which i t can be a p p l i e d , and t h e ma te r i a l t h a t can be r ecove red . Th i s s e c t i o n

h i g h l i g h t s t h o s e r e s o u r c e r ecove ry p r o c e s s e s t h a t have t h e most p o t e n t i a l f o r

g r e a t e r a p p l i c a t i o n w i t h i n t h e i n d u s t r y .

S e c t i o n 5 .1 p r e s e n t s t h o s e p r o c e s s e s i d e n t i f i e d i n S e c t i o n 4 t h a t a r e

suppor t ed by s i g n i f i c a n t r e s e a r c h and proven e x p e r i e n c e , and cou ld be f u r t h e r

u t i l i z e d w i t h i n t h e i n d u s t r y w i t h minimal development. I n g e n e r a l , t h e s e

r e s o u r c e r ecove ry p roces se s a r e f a v o r a b l y i n f l u e n c e d by a combinat ion o f

t e c h n o l o g i c a l , economic, r e g u l a t o r y , and i n s t i t u t i o n a l f a c t o r s .

S e c t i o n 5.2 i d e n t i f i e s t h o s e resour1.e r ecove ry p r o c e s s e s and a l t e r n a t i v e

approaches t o was t e management t h a t cou ld p o t e n t i a l l y have g r e a t e r a p p l i c a t i o n

w i t h i n t h e i n d u s t r y bu t are o n l y suppor ted by l i m i t e d r e s e a r c h . These

p r o c e s s e s and waste management approaches may o r may no t be under a c t i v e

i n v e s t i g a t i o n . Though in fo rma t ion on t h e p r o c e s s e s may be l a c k i n g , each one

could s i g n i f i c a n t l y reduce t h e burden of d i s p o s a l and waste t r e a t m e n t c o s t s .

5 . 1 RECOVERY PROCESSES WITH POTENTIAL FOR GREATER APPLICATION

There a re t h r e e ways t o i n c r e a s e t h e s t a t e- o f- t h e- a r t o f r e s o u r c e

r e c o v e r y i n t h e l e a t h e r and l e a t h e r p roduc t s i n d u s t r y :

e I n c r e a s e t h e development s t a g e of t h e r ecove ry p r o c e s s e s

e Expand t h e t r a n s f e r a b i l i t y of was t e o r r ecove red m a t e r i a l s

e Develop a d d i t i o n a l r e c o v e r y / u t i l i z a t i o n p r o c e s s e s o r i d e n t i f y a d d i t i o n a l waste s t r eams from which ma te r i a l s may be r ecove red .

I n o r d e r t o s u c c e s s f u l l y expand c u r r e n t r e s o u r c e r ecove ry fwas t e u t i l i z a t i o n

p r a c t i c e s , t h e s e methods must be a p p l i e d t o t h o s e a r e a s w i th t h e g r e a t e s t

5- 1

likelihood of success. These three methods describe how the State-of-the-art

can be advanced, but they alone do not determine which resource recovery processes have the best potential for advancement. Additional factors must be

considered in selecting those processes that have the greatest potential.

Theoretically, the current state-of-the-art of all 31 resource recovery

At this time, only some processes discussed in Section 4 could be advanced. of these processes actually have a good potential €or advancement. This potential may be defined through examination and consideration of a number of

factors, which assess the advantages and disadvantages of each resource recovery process. These factors can be grouped into four general areas:

0 Technological

0 Economic

0 Regulatory

0 Institutional.

Included in these four general areas are such factors as: application of the

process to more than one waste stream; quality and volume of research

suggesting the potential for advancement; stage of process o r technology development outside the United States; current and future market for recovered

materials; regulatory limitations on contaminant concentration in waste-

derived products;.and industry willingness to implement recovery processes.

Thus, the advancement potential for each resource recovery and waste

utilization process can be defined by examining each of these general analysis areas (selection criteria) within the context of the available information.

This method was applied to the information in Section 4 and the matrix in Figure 3-1 to select the resource recovery processes with the greatest

potential for implementation. From this analysis, the following 1 2 key resource recovery and waste utilization processes were selected as having good

potential for advancement at this time:

0 Direct recycling

0 Chrome recovery by precipitation

5- 2

Heat exchange

Protein recovery by acid precipitation Protein recovery by hydrolysis

Grease recovery by rendering Grease recovery by separation

Sulfide recovery by acidification Collagen product manufacture


Leather product manufacture

Isolation of solids for fertilizer (using leather scrap).

This section presents the analysis of these key resource recovery and

waste utilization areas with regard to the four selection criteria. These

criteria are described in more detail below.

5 . 1 . 1 Technological Selection Criterion

The technological evaluation of a process primarily determines whether or

not the technology is developed, or is significantly far enough along, to

successfully recover or utilize waste materials. This evaluation includes the

use of the process in the United States as well as successful technological

development of the same, or similar process, in other industries o r countries.

For example, a technology may be commonly practiced in Europe, but neither

implemented nor researched in the United States. Under these circumstances,

the technology would have good potential for advancement through

implementation in the United States.

Even if the technology exists o r has been proven, there may be other

technological considerations affecting its potential. These considerations

include, but are not limited to, adaptability of present equipment, changes in product quality, limited process application, o r equipment problems due t o

waste streams being treated (e.g., filter clogging by proteins). Such factors

can either enhance o r prevent the use of a technologically proven system.

Figure 5-1 presents the various technological advantages and disadvantages that were evaluated for each resource recovery or waste

5-3

s 1 P

8

U E m v) Q) er, m E m > U

c,

a

5-4

utilization process. From the figure, it can be seen that the positive

factors generally outweigh the negative ones. This corresponds to the need for a process to be technologically feasible in order for it to be considered

for implementation within the industry. Few establishments will opt for a

technologically unproven o r problem-ridden process for resource recovery when

other proven waste management practices exist.

Evaluation of the advantages and disadvantages of each recovery process

in the figure reveals that the following processes have the greatest

technological promise:

e Direct recycling Heat exchange

e Chrome recovery by precipitation Fibrous product manufacture

e Leather product manufacture

e Isolation of solids (scrap) for fertilizer manufacture.

These processes are the most likely to find more widespread use within the

leather and leather products industry on the basis of technological status alone.

5 . 1 . 2 Economic Selection Criterion

The primary focus of the economic evaluation is whether or not the

process is economically feasible. This considers whether the process is cost

effective, has a good return on investment, or requires substantial capital for implementation. Other factors affecting economic feasibility include the

availability of capital to make the necessary investment, and the existence of

markets for the products.

Economic factors can be a primary constraint on the implementation of

technologically proven systems. For example, the economics of a process must

consider more than just the ability of a system to perform a specific fcnction; it must also be able to provide a savings that will eventually pay for its implementation. This savings is often evaluated in terms of the

5-5

m a r k e t a b i l i t y of t he recovered m a t e r i a l , reduced d i s p o s a l c o s t s , and r e d u c t i o n

i n raw m a t e r i a l r equ i r emen t s .

The economic advantages and d i s advan tages of t h e key r e s o u r c e r ecove ry

p roces se s a r e p re sen t ed i n F igu re 5-2. The economic advantages of t h e s e

p roces se s a r e not a s c l e a r l y d e f i n e d a s t h e t e c h n o l o g i c a l advantages .

However, s e v e r a l of t h e r e s o u r c e r ecove ry p roces se s have d i s t i n c t economic

advantages over o t h e r s . These p roces se s a r e :

e D i r e c t r e c y c l i n g

e Chrome r ecove ry by p r e c i p i t a t i o n

e Heat exchange.

O the r s a r e c l e a r l y a t an economic d i s advan tage when compared t o o t h e r

p roces se s i n t h e f i g u r e :

e I n c i n e r a t i o n

e P r o t e i n r ecove ry by ac id p r e c i p i t a t i o n

e P r o t e i n recovery by h y d r o l y s i s

e Grease r ecove ry by s e p a r a t i o n

0 Fibrous product manufac ture

e I s o l a t i o n of s o l i d s ( s c r a p ) f o r f e r t i l i z e r manufac ture .

5 . 1 . 3 Regu la to ry S e l e c t i o n C r i t e r i o n

F e d e r a l , s t a t e , and l o c a l r e g u l a t i o n s can l i m i t t h e use of a r e s o u r c e

r ecove ry p roces s o r a recovered m a t e r i a l . These r e g u l a t i o n s may s p e c i f y

contaminant l e v e l s i n p roduc t s o r t h e q u a l i t y of t h e m a t e r i a l used i n o t h e r

p r o d u c t s . Also , i n s t a l l a t i o n of p o l l u t i o n c o n t r o l dev i ce s f o r r e s o u r c e

r e c o v e r y p roces se s may be r e q u i r e d i n o r d e r t o meet emis s ion , h e a l t h , and

s a f e t y s t a n d a r d s .

Regu la t i ons can a l s o i n d i r e c t l y f o s t e r t h e use of a r e sou rce r ecove ry

p r o c e s s . The r e g u l a t i o n s may make c u r r e n t d i s p o s a l p r a c t i c e s uneconomical ,

t hus f o r c i n g the waste g e n e r a t o r t o e i t h e r change t h e d i s p o s a l p r a c t i c e o r

recover t he m a t e r i a l s i n t he was t e . A l s o , r e g u l a t i o n s may make r e s o u r c e

5-6

v) a v)

0

CL

a > 0 0 Q) U a 3

a U 0 a 0 a

3 E! t

0,

c, - $ r 0' v) a ul m E m > U

c,

.- 3 P U C (0

5-7

recovery more cost-effective than current disposal practices. In addition,

reduction of solid and liquid waste streams through resource recovery may

significantly reduce the impact of applicable regulations.

Figure 5-3 summarizes specific regulatory requirements that affect the implementation of the selected resource recovery and waste utilization processes. A key issue is whether or not the process or product is of regulatory concern at either the Federal, state, or local levels. The absence of regulatory concern can be viewed as a clear advantage t o a recovery

process since this eliminates the need for the process to conform to regulatory requirements.

Five of the 12 selected recovery processes and their products have been

identified in the figure as not being of regulatory concern, thus, these five have the greatest potential for advancement:

Direct recycling

Chrome recovery by precipitation

Heat exchange


Leather product manufacture.

Another five processes have distinct regulatory disadvantages:

Protein recovery by acid precipitation

Protein recovery by hydrolysis Grease recovery by rendering

0 Grease recovery by separation

Collagen product manufacture.

5.1.4 Institutional Selection Criterion

Industry attitudes toward resource recovery practices depend on a number

of factors including: favorable or unfavorable impression of success created

by the other three selection criteria, resistance to change, and the specific

nature of the leather industry. In general, the only way a change in current

5-8

rc 0

U E Q

5- 9

waste management practices will occur is if the other three criteria

(technological, economic, and regulatory) are positive. These factors largely govern an industry’s perception as to whether or not a recovery process will

be successful. This perception, in turn, influences the willingness of an

industry to try a recovery process.

process is perceived as not being successful based on potential or actual technological or economic problems, industry is likely to be unwilling to

implement the process whether or not the perception itself is accurate.

For example, if a resource recovery

Attitudes of industry personnel and local residents also affect the implementation of resource recovery processes. At the management level, there

may be resistance to changing or replacing proven processes with newer

processes, especially if the older processes have been practiced for a long

time. Such situations may be perceived by the workers as a threat to their

job security. Also, implementation of new processes may require workers to

learn new jobs or processing techniques. Additionally, residents near an industrial facility may object to the installation of new equipment, such as

an incinerator, especially if such equipment is perceived as a source of substances that may threaten their health or the surrounding environment.

Finally, the nature of the leather industry can also affect the attitudes

of individual facilities as well as the entire industry toward resource

recovery processes. This industry is characterized by small, family-owned

establishments, many of which have been in business for a long time. This

type of long-term industrial stability, especially in terms of a single

product (leather), tends to promote a continuation of current practices based on a long history of processing experience.

Attitudes toward resource recovery and waste utilization depend on the

overall influence of the other three criteria (technological, economic,

regulatory), as well as a number of subjective considerations. Figure 5-4

presents the institutional factors that were evaluated to determine their

overall influence on the advancement potential of the 12 recovery processes.

5-10

e

5 : x ' :

W

0

0

z

I

0 0

0 I : m ' 0

-t-

rc 0

5-11

From the figure it can be seen that only one recovery process, heat

exchange, has a clear institutional advantage over the other 12 processes. Five processes have a distinct disadvantage in terms of the institutional

considerations:

e Direct recycling

e Chrome recovery by precipitation

e Protein recovery by acid precipitation Protein recovery by hydrolysis

Sulfide recovery by acidification.

5.1.5 Summary of Analysis

This section presents a summary of the analyses of the key resource

recovery and waste utilization areas with regard to the four selection criteria. The results of this analysis are presented in Figure 5 - 5 . This

figure illustrates the influence of the selection criteria on the potential

f o r greater application and development of these key processes. b

This influence may be positive, negative, or even variable depending on

specific industry or process parameters and characteristics. The overall

potential of a recovery process depends on all four factors, thus a negative

influence of one factor does not necessarily preclude the process from having good advancement potential. Although these four selection criteria have been

largely discussed independently, they are in fact interdependent. The

institutional selection criterion is most affected by the other three

criteria, as discussed in Section 5 . 1 . 4 . The other three factors

(technological, economic, and regulatory) are also interdependent. For

example, regulatory controls on emissions can result in technological problems

in trying to adapt the system to meet these regulatory standards. This in

turn can increase the cost of the system to the point that it is no longer economical.

Analysis of the factors considered f o r each selection criterion revealed

a number of recovery processes that, based on their current development, had a

clear advantage or disadvantage f o r implementation over the other processes.

5-1 2

m

5 : S f

W -

7

I

+ \ -

I

+ \

I

+ \ -

I

+ \

I

+ \

I

+ \

I

+ \

I

I 1 . +

I + . +

I + . +

I I . +

I I

I I \ +

I I . +

1

5-13

These results defined three process groupings for each selection criterion:

those processes most readily implemented, those requiring some problem resolution, and those whose further implementation depends upon the resolution

of a number of problems. all overcome some sort of disadvantage or problem, their current state of

development and their advancement potential more readily lend them to rapid implementation than the other 19 processes.

Although most of these 12 recovery processes must

Of the 1 2 key recovery processes, three appear to have overwhelming

potential for implementation:

Direct recycling Chrome recovery by precipitation

Heat exchange.

A s can be seen from Figure 5- 5 , these processes are supported at a minimum by

technological, economic, and regulatory advantages, Only direct recycling and

chrome recovery by precipitation may be unfavorably influenced by

institutional disadvantages. Thus, if a prioritization of resource recovery

processes in the leather and leather products industry must be made, these three areas deserve primary attention.

5 . 2 KEY AREAS FOR FURTHER RESEARCH

In addition to the resource recovery options presented in Section 5.1, there are several others that JRB feels could prove valuable to the industry. As yet, these options have received limited research and analysis as to how

their use could be encouraged in a climate dictated by current technological, economic, regulatory, and institutional factors. The ideas presented in this

section fall into three primary categories:

Technologies that have not been supported by the kind of research merited by their potential

5-14

Waste management approaches r e q u i r i n g i n t r a- i n d u s t r y c o o p e r a t i o n and c e n t r a l i z e d f a c i l i t i e s

New by-product /waste market development.

These a r e d i s c u s s e d i n more d e t a i l i n t h e f o l l o w i n g s e c t i o n s .

5 . 2 . 1 Emerging Technologies With Good P o t e n t i a l

S i x promising r e s o u r c e r e c o v e r y p r o c e s s e s t h a t have o n l y been proposed o r

a r e i n t h e i n i t i a l phases of development have been i d e n t i f i e d . A n a l y s i s

i n d i c a t e s t h a t an i n s u f f i c i e n t amount o f r e s e a r c h has been done t o d e t e r m i n e

and /or deve lop t h e i r p o t e n t i a l f o r a p p l i c a t i o n w i t h i n t h e i n d u s t r y . I n some

c a s e s , t h e a n a l y s e s upon which t h e s e c o n c l u s i o n s are based are suppor ted by

more f a v o r a b l e t e c h n o l o g i c a l and economic f a c t o r s than e x i s t e d when the

p r o c e s s e s were i n i t i a l l y proposed and i n v e s t i g a t e d . These s i x p r o c e s s e s a r e :

I o n exchange f o r chromium r e c o v e r y

Chrome and h e a t r ecovery by i n c i n e r a t i o n

Chrome and h e a t recovery by p y r o l y s i s

Manufacture of chrome soap

Use of l e a t h e r s c r a p a s p o l l u t a n t a b s o r b a n t s

A c t i v a t e d carbon manufac tu re .

5 . 2 . 1 . 1 I o n Exchange

I o n exchange p rocedures have found widespread a p p l i c a t i o n i n t h e

e l e c t r o p l a t i n g i n d u s t r i e s as a method of r e c o v e r i n g chrome and o t h e r p r o c e s s

m e t a l s . Although i n 1959 i t w a s r e p o r t e d t h a t t h i s method was thought t o be

a p p l i c a b l e t o spen t t a n n i n g l i q u o r s , i t was r e j e c t e d a s uneconomical because

an i n s u f f i c i e n t amount o f chrome could be r e c o v e r e d . A su rvey of p e r t i n e n t

l i t e r a t u r e and c o n v e r s a t i o n s w i t h r e s e a r c h e r s s u g g e s t s t h a t , s i n c e a t l e a s t

1959, no a c t i v e r e s e a r c h has been performed i n t h i s a r e a [37,54].

C u r r e n t l y i o n exchange i s b e l i e v e d by t h e i n d u s t r y t o have l i m i t e d v a l u e

f o r a p p l i c a t i o n t o t a n n e r y was te s t r e a m s . It i s f e l t t h a t i o n exchange cannot

be r e a d i l y adapted t o r e c o v e r t r i v a l e n t chromium, o r , a t b e s t , i t could o n l y u

5-1 5

be used as a final treatment step for waste streams with low chrome concen-

trations [ 5 , 1 0 ] . An impediment to adapting such systems to tanning liquors is the large amount of impurities in these liquors (i.e., suspended solids,

grease, oil, proteins); these impurities must be removed prior to treatment of the waste streams by ion exchange in order to prevent clogging of the resin

I 5 , l O l . However, research indicates that because of improvements in the ion

exchange process since 1959--improved filtration techniques, and increased

resin lives and regeneration rates--this process merits greater attention as

to its application within the tannery.

Ion exchange processes are now used in the metal finishing industry to

recovery chromium and metal salts from a variety of dilute plating rinse waters.

state, Cr+3 is routinely removed from process solutions [llO]. application, Cr+3 is removed as an impurity to facilitate the recovery of

Cr+6.

strong acid cation resins to minimize resin degradation. One reciprocating

flow "decationizer" can "purify" 250 gallons of plating solution each day

(e.g., remove Cr+3 and other metal finishing impurities). The resins used in

this system, which are automatically regenerated each hour, can theoretically remove 2 pounds of Cr+3, as chromic acid, and iron per cubic foot of solution;

only 2 5 to 50 percent of this capacity is currently being utilized [ l l O ] .

Though Cr+6 can be more easily recovered due to its higher valence

In one

Cation exchanges are used to remove Cr+3 and utilize macro-porous

Purification problems inherent to the application of ion exchange to tannery liquors can be greatly overcome through the use of various filtration

techniques. Suspended solids can be removed using multi-media pressure filters. Carbon absorption, ultrafiltration, oil-water separators, and air

flotation systems can be used t o remove grease, oils, and proteins [110 ] .

These wastewater treatment techniques could be applied to segregated

chrome-bearing tanning liquors to facilitate chrome recovery prior to

wastewater discharge to POTWs without incurring great expense. In light of

this information, ion exchange as a method for chrome recovery from tanning liquors merits further investigation as to its feasibility.

5-16

5 . 2 . 1 . 2 Incineration

Incineration of chrome-bearing sludges and solid tannery wastes to

recovery chrome and heat is currently under investigation by industry

researchers. Removal of combustible organics through high temperature alkaline incineration leaves the chrome in a readily recoverable hexavalent

form in the resulting ash. This chrome can then be leached, concentrated, and

reused in the tanning process. Additionally, because incineration is an exothermic process, it liberates heat from the wastes which can be recovered

using a variety of heat exchangers. Thus, incineration can be used to recover two products, chrome and heat.

Major impediments to the further development of incineration for chrome

and/or heat recovery appear to be those associated with necessary capital

investments and compliance with health, safety, and emission standards. These

impediments could be largely overcome through the use of large systems central

to a number of tanneries. Because such systems could generate large volumes

o f h2at and chrome, the required capital and pollution control investrents may

be rapidly defrayed through the sale and/or use of one o r both of these products. Such cooperative ventures could find application at currently

operating POTW sewage treatment plants serving a number of tanneries. Research indicates that at least one POTW operating a waste treatment

incinerator has investigated the feasibility of recovering chrome from such

wastes [111,112]. Though initial estimates suggest chrome concentrations were

too l ow to make the recovery operation feasible, dual chrome and heat recovery

systems have only received limited attention, primarily at individual

tanneries.

5.2.1.3 Pyrolysis

The pyrolysis of chrome-bearing sludges and solid leather wastes is another method for recovering both chrome and heat. Pyrolysis of such wastes

removes some organic combustibles and leaves the chrome in a char. This chrome can be leached from the char, precipitated, purified and reused in the

tanning process. Heat can be recovered from combustible off-gases, oils, and char generated during the pyrolysis process.

5-1 7

C u r r e n t l y , t h e U.S. Bureau of Mines, i n c o n j u n c t i o n w i t h t h e Tanners '

Counci l of America, i s conduct ing a s t u d y of p y r o l y s i s as a chrome r ecove ry

method. Wastes from a t anne ry w i l l be hauled t o a p y r o l y s i s u n i t where t hey

w i l l be pyro lyzed . The chromium-containing cha r w i l l be brought back t o t h e

t anne ry where t he chrome w i l l be e x t r a c t e d and reused [ 4 6 ] .

w i t h t h e r e s e a r c h e r s i n d i c a t e t h a t t h e r e a r e t e n t a t i v e p l ans t o i n v e s t i g a t e

hea t r ecove ry [1131. Should t h i s p r o j e c t prove s u c c e s s f u l , s i m i l a r p y r o l y s i s

s y s t e m s may be adopted by t h e i n d u s t r y . Presumably, a c e n t r a l i z e d approach

would provide t h e most r a p i d r e t u r n on inves tment and r e p r e s e n t t h e b e s t way

t o overcome i d e n t i f i e d c a p i t a l r equ i r emen t s and h e a l t h , s a f e t y , and emis s ion

s t a n d a r d s . F u r t h e r r e s e a r c h i s m e r i t e d t o adequa t e ly a s s e s s t h i s r e s o u r c e

r e c o v e r y p r o c e s s .

Conversa t ions

5 .2 .1 .4 Chrome-Soap

Recovering chromium from spen t t a n n i n g l i q u o r s as a chrome soap was

r e p o r t e d i n 1959. A t t h a t t ime , i t was found t h a t by r e a c t i n g t h e was t e

chrcme s o l u t i o n s wi th sodium s t e a r a t e i n t h e p re sence of a l c o h o l , a soap was

produced t h a t could impart water-, ac id - , and a l k a l i - r e s i s t a n c e t o v a r i o u s

s u r f a c e s t r e a t e d wi th i t ( 3 7 1 . Though t h e chemical i n d u s t r y has c r e a t e d on ly

a s p e c i a l t y market f o r chrome soaps [ l o ] , t h e s e p r o p e r t i e s could f i n d

commercial a p p l i c a t i o n s i n a v a r i e t y of i n d u s t r i e s . A survey of p e r t i n e n t

l i t e r a t u r e and c o n v e r s a t i o n s w i t h r e s e a r c h e r s s u g g e s t s t h a t no a c t i v e market

r e s e a r c h has been performed i n t h i s a r e a s i n c e t h e i n i t i a l s t u d y . F u r t h e r

r e s e a r c h should be conducted on t h i s p roces s t o i d e n t i f y and e x p l o i t t h e

p o t e n t i a l uses of chrome soap.

5 . 2 . 1 . 5 P o l l u t a n t Absorbant

The Cent re Technique du C u i r i n France has demons t ra ted t h a t l e a t h e r i s

capab le of r e t a i n i n g numerous o r g a n i c l i q u i d s i n a d d i t i o n t o water. I t s

a b s o r p t i v e c a p a c i t y and hyd rophob ic i t y make i t u s e f u l as a subs t ance t o c l e a n

up s p i l l s of v a r i o u s m a t e r i a l s such a s o i l s , hydrocarbons , and s o l v e n t s [ 2 6 ] .

T h i s could f i n d a p p l i c a t i o n i n c l e a n i n g i n d u s t r i a l f l o o r s and envi ronmenta l

s p i l l s . Minimal p roces s ing ( g r a n u l a t i o n and d r y i n g ) i s neces sa ry t o r ende r

t h e l e a t h e r s c r a p u s e f u l i n t h e s e c a p a c i t i e s . A survey of p e r t i n e n t l i t e r a -

t u r e and c o n v e r s a t i o n s w i th r e s e a r c h e r s s u g g e s t s t h a t no a c t i v e r e s e a r c h i n

5-18

t h i s a r e a ha s been performed by domest ic manufac tu re r s and t a n n e r s .

a v a i l a b l e volume of w a s t e s , r e l a t i v e l y s imple p r o c e s s i n g , and p o t e n t i a l

i n d u s t r i a l a p p l i c a t i o n sugges t t h a t t h i s r ecove ry p roces s mer i t s g r e a t e r

a t t e n t i o n and i n v e s t i g a t i o n .

The

5 . 2 . 1 . 6 A c t i v a t e d Carbon Manufacture

A 1 9 7 7 s t u d y performed by R a t t e l l e Columbus L a b o r a t o r i e s demonst ra ted

t h a t l e a t h e r was t e can be conve r t ed i n t o g r a n u l a r a c t i v a t e d carbon and c e r t a i n

by-product chemica l s . The l i t e r a t u r e s u g g e s t s t h a t t h e p r o c e s s i n g e n t a i l s

h e a t i n g t h e was te under c o n d i t i o n s t h a t produce a 50 p e r c e n t y i e l d of h a r d

g r a n u l a r c h a r . The cha r could be used i n t h e t r a d i t i o n a l s e c t o r s f u l f i l l e d by

powdered a c t i v a t e d carbon such as p o l l u t a n t , odo r , and i m p u r i t y removal .

Research shows t h a t s i n c e t h e s t u d y w a s performed i n 1 9 7 7 , no a c t i v e i n v e s t i -

g a t i o n has been performed i n t h i s a rea . Though a t t h a t t i m e t h e p r o d u c t i o n

c o s t s were thought t o be t o o h i g h and t h e a c t i v a t e d ca rbon market s a t u r a t e d ,

t h e c u r r e n t s e l l i n g p r i c e f o r a c t i v a t e d carbon h a s i n c r e a s e d s i g n i f i c a n t l y ,

p o s s i b l y nega t ing p r e v i o u s l y i d e n t i f i e d impediments.

market c o n d i t i o n s , t h e f e a s i b i l i t y of t h i s p roces s merits g r e a t e r a t t e n t i o n .

Given t h e change i n

5 .2 .2 I n t r a- I n d u s t r y Coopera t ion And C e n t r a l i z e d F a c i l i t i e s

I t i s e v i d e n t t h a t a l t hough s e v e r a l r e s o u r c e r ecove ry o p t i o n s a r e

suppor t ed by proven t e c h n o l o g i e s , t h e economics of t h e p r o c e s s e s may p rec lude

t h e i r use by a l l bu t a s e l e c t group of l e a t h e r and l e a t h e r product

manufac tu r ing f a c i l i t i e s . The f a c i l i t i e s t h a t can i n c o r p o r a t e t h e p r o c e s s e s

a re t h o s e e i t h e r of s u f f i c i e n t s i z e t o t a k e advantage of economies- of- scale

n e c e s s i t a t e d by s p e c i f i c p r o c e s s e s , o r t h e s e t h a t a re l o c a t e d w i t h i n c l o s e

p rox imi ty of by- product manufac tu re r s . Among t h e s p e c i f i c r ecove ry methods '

t h a t f a l l i n t o t h i s c a t e g o r y are t h e fo l l owing :

Acid s o l u b i l i z a t i o n f o r chrome r e c o v e r y

a P r e c i p i t a t i o n f o r chrome r ecove ry

a I n c i n e r a t i o n f o r chrome and h e a t r ecove ry

a P y r o l y s i s f o r chrome and h e a t r ecove ry

a Acid p r e c i p i t a t i o n f o r p r o t e i n r e c o v e r y

Screening f o r h a i r r ecove ry

5-19

e Hydrolysis for protein recovery

e Rendering for grease recovery

e Collagen product manufacture

e Fibrous product manufacture

e Leather product manufacture

0 Isolation of solids for fertilizer manufacture.

An analysis of the impediments to these resource recovery methods suggests that centralized waste processing and treatment facilities could make

these options economically attractive to many additional facilities. Central

processing facilities constructed in areas with high tannery concentrations

would significantly alleviate impediments such as inadequate waste volumes,

limited available capital , large investments with long payback periods, and poor information on scrap and by-product buyers. Additionally, tanneries with similar waste streams may find participation in a centralized facility

desirable because of reduced disposal costs and the creation of a market for their wastes. This waste management approach has or is being demonstrated for

area chrome recovery facilities (Gloversville, NY), regional fertilizer processing networks (Wisconsin, New York, Maine), and leather scrap brokers

located throughout the country (see Sections 4.2.1, 4.13, 4.14, 4 . 1 5 , 4.16).

It has been suggested that centralized facilities could be extended

beyond the waste t o the actual tannery process [106]. For example, the use of

centralized beamhouses would reduce waste segregation and transportation costs

for disposal of offal wastes, while ensuring the generation of a sufficient

quantity of offal to make resource recovery economical. Centralized beamhouses could also reduce salt curing and freight costs, eliminate high

operation and maintenance costs of individual effluent treatment plants, and enhance the industry's economic posture with respect to foreign competitors.

It has been postulated that by concentrating the generated offals in such a centralized facility the industry could actually produce two products: the traditional leather product as well as hide/leather-derived products

(discussed in Sections 4.13 through 4.16). Though several institutional

factors may impede such centralized facilities, there are obvious geographic

5-20

b

and economic advantages previously cited that support this concept. Further

study of methods to foster such facilities is merited.

5 . 2 . 3 New Market/By-Product Development

The Centre Technique du Cuir has suggested a unique approach to the use

of waste in the manufacture of by-products. The group analyzed leather wastes

from a new perspective. By associating the physical characteristics and

properties of tannery wastes with relevant industrial uses, tfie researchers

defined broad use sectors not explicitly stated nor necessarily implied by

conventional markets for these wastes. Some of the characteristics and

potential new uses are presented in Table 5-1 [ 2 6 ] .

The correlations presented in Table 5-1 suggest that by looking at leather's physical characteristics and properties, the generator of scrap

leather can identify the specific industrial sectors that require materials

with those characteristics. This approach identifies uses for waste leather

scrap in industrial sectors that have traditionally purchased raw materials

from other sources.

This waste use concept merits further investigation. Particular emphasis

should be placed on the identification of specific markets for the potential industrial uses. Additional research should also be directed at defining more

explicit characteristics and use sectors. Such a systematic approach to waste

by-product use analysis could easily be extended to other industries with similar results in developing new markets for waste materials.

Another method of market development can be applied to such by-products

as recovered proteins, leather-derived fertilizers, and wastewater sludges.

Federal, state, and local regulations limit the amount and concentration of contaminants in products made with these recovered materials. Additionally,

fertilizers made from processed scrap and sludges are strictly regulated with

respect to heavy metal concentration. For these reasons, the development of potential applications of such by-products may be limited. However, more

efficient, economical, and technically sound impurity removal techniques would facilitate greatly expanded application and use of recovered wastes. Further

research in this area appears to be warranted.

._

5-2 1

Table 5-1. Waste Characteristics and Suggested Industrial Use Sectors

Characteristics Use Sector

Fibrous nature Textiles; nonwoven materials

Dye absorption Removal of color from effluent

Fatty matter absorption Cleaning processes, Separation of liquids

Thermal insulation Thermal insulation

Acoustic properties Wall coverings, acoustic materials

Source: 26

5- 22

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Killik, E.L. Tanners Council of America. Personal communication with V. Hodge, JJU3 Associates, 26 June 1981.

Utsuo, A. New Application of Collagen, Abstract. Journal of the American Leather Chemists Association. Vol. 75. 1980. p. 37.

Comte, P. and Jullien, I. Current Perspectives for the Treatment of Hide Waste. Abstract. Journal of the American Leather Chemists Association. pp. 525-526.

R-7

93. Henrickson, R.L., Ebro, L.L., and Sneed, P.J. Presented at Symposium on New Uses of Untanned Hide Collagen. American Leather Chemists Association Convention. Buck Hill, PA. 22-25 June 1980.

Hide Collagen in Food. 1980

94. Okamura, H. and Shirai, K. Basic Studies on the Manufacture of Leatherboard from Chrome Collagen Fiber. Journal of the American Leather Chemists Association. Vol. 57, No. 4 . April 1972. pp. 148-162.

95. Gish, A. Robus Company. Personal communication with J. Margolis, JRB Associates, 4 August 1981.

96. Berman, I. Berman Leather Company. Personal communication with J. Margolis, JRB Associates, 5 August 1981.

97. Ebinger, A. Ebinger Brothers. Personal communication with J. Margolis, JRB Associates, 4 August 1981.

98. Hilton. L.L. Bean, Inc. Personal communication with J. Margolis, JRB Associates, 3 August 1981.

99. Finger, J. Ray Leather Waste Company. Personal communication with J. Margolis, JRB Associates, 5 August 1981.

100. Hartman. International Shoe Company. Personal communication with J. Margolis, JRB Associates, 5 August 1981.

101. Ryan, R. Maine Resources. Personal communication with J. Margolis, JRB Associates, 3 August 1981.

102. Anonymous. Resources Recovery Plant to Turn Tannery Waste to Fertilizer. The Leather Manufacturer. March 1981. pp. 4-5.

103. Thorstensen, T.C. and Shah, M. Technical and Economic Aspects of Tannery Sludge as a Fertilizer. Chemists Association. Vol. 74. 1979. pp. 14-23.

Journal of the American Leather

104. van Vlimmeren, P.J. New Beamhouse Development to Simplify Waste Water Management. Vol. 71. 1976. pp. 318-334.


105. Jones, B.H. Personal communication with J. Margolis, JRB Associates, 25 August 1981.

106. Maire, M.S. Offal Redux. Shoe Leather Manufacturer. September 1976 pp. 12-23.

107. Gibbler, S. Portland Cement Association. Personal communication J. Margolis, JRB Associates, 24 September 1981.

108. Polkowski, L.B., Boyle, W.C., Christensen, B.F. Biological Treatment, Effluent Reuse, and Sludge Handling for the Side Leather Tanning Industry. S.B. Foot Tanning Co. Prepared for: United States Environmental Protection Agency, Industrial Environmental Research Laboratory, Cincinnati, OH. EPA-600/2-78-013. February 1978.

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109. Maire, M.S. ROIT Corporation. Personal communication with J. Margolis, JRB Associates, 24 August 1981.

110. Brown, C.J. Recovery and Treatment of Metal Finishing Wastes By Ion Exchange. Eco-Tec L t d . Prepared for: American Electroplaters' Society. 1980.

111. Newhall, H. South Essex Sewerage District, Salem, Massachusetts. Personal c~munication with J. Margolis, JRB Associates, 6 January 1982.

112. Parsons, M. Tighe and Bond Consulting Engineers. Personal communication with J . Margolis, JRB Associates, 6 January 1982.

113. Huber, C.V. Fishbeck, Thompson, Carr, and Huber, Inc. Personal communication with J. Margolis, JRB Associates, 6 January 1982.

R-9

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B-2

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B -4

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del Cueto, E. Process to Separate and Recover the Solid and Liquid Phases from Treatment Baths o f Hides and Skins. U.S. Patent 3,997,290. Journal of the American Leather Chemists Association. Vol. 73, 1980. p. 356.

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u

B- 5

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Happich, W.F., Happich, M.L. , Cooper, J . E . , F e a i r h e l l e r , S . H . , T a y l o r , M . M . , B a i l e y , D . G . , J ones , A .W. , Mellon, E .F . , and Naghski, J. Recovery of P r o t e i n s from Lime-Sulfide E f f l u e n t s from Unhai r ing C a t t l e h i d e s . J o u r n a l o f t h e American Lea ther Chemists A s s o c i a t i o n . Vol. 69 , No. 2 . February 1974. pp. 50-65.

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Henr ickson , R . L . , Ebro, L . L . , and Sneed, P . J . Hide Col lagen i n Food. P re sen t ed a t Symposium on New Uses o f Untanned Hide Co l l agen . 1980 American Lea the r Chemists A s s o c i a t i o n Convent ion. Buck H i l l , PA. 22-25 June 1980.

Highland , D . Rawlings S p o r t i n g Goods. P e r s o n a l communication w i th J . Margo l i s , J R B A s s o c i a t e s , 5 August 1981.

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Huang, C.P. Activated Carbon Process for Treatment of Wastewaters Containing Hexavalent. University of Delaware, Newark, DE. USEPA, Industrial Environmental Research Laboratory, Cincinnati, OH. EPA-600/2-79-130, July 1979.

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Industry and Trade Administration. 1980 U.S. Industrial Outlook for 200 Industries with Projections for 1984. Chapter 36--Leather and Leather Products. United States Department of Commerce, Washington, DC. January 1980.

Ishihara, N., Nakishiro, M. , and Okamura. Utilization of Shaving Dust: Preparation of Compound Materials Mixing with Latexes. Abstract. Journal of the American Leather Chemists Association. Vol. 76. August 1981. p. 316. Cited from Hikaku Kagaku, 26, pp. 135-141 (1980).

Jones, B.H. Recovery of Chromium from Tannery Waste. U.S. Patent 4,086,319. Journal of the American Leather Chemists Association. Vol. 73. 1978. pp. 493-494.

Jones, B.H. Chromium Recovery Through Incineration of Liquid and Solid Tannery Wastes. Journal of the American Leayher Chemists Association. Vol. 74. 1979. pp. 395 - 403.

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Journal of the Society of Leather Technologists and Chemists. IULCS Tannery Wastes Commission, Minutes of the Fifth Meeting of the Commission in Barcelona, Spain. Vol. 58, No. 1. January 1974. pp. 1-8.

Journal of the American Leather Chemists Association. Mini-Symposium on New Uses of Untanned Hide Collagen. Vol. 75. 1980. pp. 436-455.

Journal of the American Leather Chemists Association. Technical Papers Presented to 1980 Annual Meeting. Vol. 75. 1980. pp. 170-180.

Journal of the Society of Leather Technologists and Chemists. Twelfth Meeting of the IULTCS Tannery Commission, Graz, Austria. Vol. 64, NO. 6. November 1980. pp. 109-120.

Kashihara, T., Yoshioka, I., Kato, T., Arima, S., and Mohri, N. The Study of the Treatment of Sludge from Tannery. Abstract. Journal of the American Leather Chemists Association. Vol. 75. 1980. pp. 37-38. Cited from Hikaku Kagaku, 20, p p . 223-231 (1975).

Killik, E.L. Tanners Council of America. Personal communication with V. Hodge, JRB Associates, 26 June 1981.

L

B-9

KilLik, E.L. Tanners Council of America. Personal communication with J. Margolis, JRB Associates, 22 September 1981.

Kleper, M.H. A New Approach for Treatment of Spent Tannery Liquor. Journal of the American Leather Chemists Association. Vol. 74. 1979. pp. 422-437.

Komanowsky, M. and Senske, G.E. Tannery Waste Volume Reduction Through Countercurrent Reuse of Process Streams. Paper to be published in Journal of the American Leather Chemists Association. 1982.

Komanowsky, M. United States Department of Agriculture, Eastern Regional Research Center, Hides and Leather Section. J. Margolis, JRB Associates, 17 January 1982.

Personal communication with

Kubo, T. Reduction of Pollution of Effluents from Beamhouse Processes in a Tannery. Abstract. Journal of the American Leather Chemists Association. Vol. 76. August 1981. p. 3 1 5 . Cited from Hikaku Kagaku, 26, pp. 67-73 (1980).

Langerwerf, J.S.A. and de Wijs, J.C. Precipitation and Reuse of Trivalent -

Chrome. Abstract. Journal of the American Leather Chemists Association. Vol . 74. 1979. p. 5 3 . Cited from Das Leder, 28, pp. 1-8 (1977).

LanGaier, F. Some Aspects of Grafting Protein Wastes in Leather Production. -Abstract. Journal-of the American Leather Chemists Association. p. 3 5 2 . Cited from Kozarstvi, 20, pp. 66-69 (1970).

Lawrence, B.K. Processing Chrome Tannery Effluent to Meet Best Available Treatment Standards. A.C. Lawrence Leather Co., Inc. Prepared for: United States Environmental Protection Agency, Industrial Environmental Research Laboratory, Cincinnati, OH. EPA-600/2-79-110. July 1978.

Lipsett, V. ROIT Corporation. Personal communication with J. Margolis. JRB Associates,.21 September 1981.

Lollar, R.M. Tanners' Council of America. Personal communication with J. Margolis, JRB Associates, 28 August 1981.

Lollar, R.M. Tanners' Council of America. Personal communication with J. Margolis, JRB Associates, 2 September 1981.

Lollar, R.M. Tanners' Council of America. Written communication with H. Davis, JRB Associates, 15 September 1981.

Lollar, R.M. Tanners' Council of America. Written communication with B. Burgher, JRB Associates, 22 December 1981.

Lollar, R.M. Tanners' Council of herica. Written communication with J. Margolis, JRB Associates, 11 January 1982.

B-10

Ludvik, J. International Conference on Effluents. Abstract. Journal of the American Leather Chemists Association. p. 629. Cited from Kozarstvi, 19, pp. 206-207 (1969).

Ludvik, J. Analysis of Effluents and Its Problems. Abstract. Journal of the American Leather Chemists Association. p. 629. Cited from Kozarstvi, 19, pp. 208-211 (1969).

Luggage and Leather Goods Manufacturers of America. with V. Hodge, JRB Associates, 24 June 1981.

Personal communication

Mahan De, S. Some Aspects of Tannery Effluent Control. Journal of the American Leather Chemists Association. Vol. 68, No. 8. August 1973. pp. 316-321.

Maire, M.S. Chrome and Sulfide Conservation. The Leather Manufacturer. October 1981. pp. 22-27.

Maire, M.S. A Comparison of Sulfide Reduction Systems. The Leather Manufacturer. June 1981. pp. 16-25.

Maire, M.S. and Lipsett, V.A. Offal Enhancement. Journal of the American Leather Chemists Association. Vol. 75. 1980. pp. 16-33.

Maire, M.S. Solid Waste--The Need for Cooperative Action. The Leather Manufacturer. December 1977. pp. 12-23.

Maire, M.S. rannery Energy Audits. The Leather Manufacturer. Ocs-ober 1977. pp. 15-27.

Maire, M.S. A Comparison of Tannery Chrome Recovery Systems. Journal of the American Leather Chemists Association. Vol. 72. 1977. pp. 404-418.

Maire, M.S. Offal Redux. Shoe Leather Manufacturer. September 1976. pp. 12-23.

Maire, M.S. Energy Parameters in the Tanning Industry. Journal of the American Leather Chemists Association. February 1976. pp. 82-92.

Maire, M.S. ROIT Corporation. Personal communication with B. Burgher, JRB Associates, 30 July 1981.

Maire, M.S. ROIT Corporation. Personal communication with J. Margolis, JRB Associates, 24 August 1981.

Maire, M.S. ROIT Corporation. Written communication with R.M. Lollar, Tanners' Council of America, 18 December 1981.

Mayer, A.K. Reduction of Chromium in the Effluent by Use of a High-Exhaust Chrome Tannage with Baychrome 2403. Chemists Association. Vol. 76. 1981. DO. 35-39.

Journal of the American Leather ..

Money, C.A. and Adminis, U.' Recycling of Lime-Sulfide Unhairing Liquors, I. Small-scale Trials. Journal of the Society of Leather Technologists and Chemists. Vol. 58. No. 2. March 1974. pp. 35-40.

Muralidahara, H.S., Maggin, B., and Phipps, H. The Recovery of Energy and Chrome from Chrome Tannery Wastes. Systems Consultants, Inc. Prepared for: U.S. Department of Energy, Office of Industry Programs, Alternative Materials Utilization Branch, Washington, DC. 30 May 1981.

Muralidahara, H.S. Battelle Memorial Laboratory. Personal communication with J. Margolis, JRB Associates, 20 August 1981.

Murray, J. L.L. Bean, Inc. Personal comunication with J. Margolis, JRB Associates, 4 August 1981.

Narasimhan, K., Schgal, P . K . , and Josephs, K.T. Condensation of Aromatic Sulfonic Acid With Hydrolysates from Leather Wastes. Journal of the American Leather Chemists Association. Vol. 75. 1980. pp. 211-215.

Newhall, H. South Essex Sewerage District, Salem, Massachusetts. Personal communication with J. Margolis, JRB Associates, 6 January 1982.

Niwa, Y., Kawakami, M., and Yokokawa, I. Application of the Recycling of Used Chrome Liquor for Upper Leather Making in Tannery. Abstract. Journal of the American Leather Chemists Association. Vol. 75. 1980. p. 38. Cited from Hikaku Kagaku, 20, pp. 232-243 (1975).

Office of Solid Waste. Background Document - Resource Conservation and Recovery Act, Subtitle C: Identification and Listing of Hazardous Waste. Vol. 20. USEPA, Washington, DC. May 1980.

Office of Solid Waste. Notification to EPA of Hazardous Waste Activities: Regions 1-10. United States Environmental Protection Agency, Office of Water and Waste Management, Washington, DC. SW-897.1 through SW-897.10. December 1980.

Okamura, H., Niwa, Y., Wada, K., and Kubo, T. Establishment of the Overall System for Utilization of Solid Byproducts and Wastes. Abstract. Journal of the American Leather Chemists Association. Vol. 76. August 1981. p. 314. Cited from Hikaku Kagaku, 26, pp. 1-15, (1980).

Okamura, H. and Shirai, K. Studies on Chrome Splits as Raw Materials for Recovery of Chrome Collagen Long Fibers. Chemists Association. Vol. 68, No. 10. October 1973. pp. 447-464.


Okamura, H. and Shirai, K. Basic Studies on the Manufacture of Leatherboard from Chrome Collagen Fiber. Association. Vol. 57, No. 4 . April 1972. pp. 148-162.


Parsons, M. Tighe and Bond Consulting Engineers. Personal communication with J. Margolis, JRB Associates, 6 January 1982.

B-12

Pate, S. Genescoe Shoe Company. Personal communication with J. Margolis, JRB Associates, 5 August 1981.

Pattar, T.H. and Ellison, H. Mini-Symposium on Effluent Control, "Update 1976--Group IV." Vol. 72. 1977. pp. 444-449.


Pauckner, W. Treatment and Possible Use of Fatty and Proteinaceous By-products of the Animal Skin Obtained in the Manufacture of Leather. Abstract. Journal of the American Leather Chemists Association, Vol. 76. November 1981. pp. 457-458. Cited from Leder-und Hautemarkt. Gerbereiwissenschaft und Praxis, 33, pp. 58-80 (1981).

Pauckner, W. Utilization of Waste Hide Material for Animal Feed and Fertilizer. Abstract. Journal of the American Leather Chemists Association. p. 381. Cited from Leder und Hautemarkt. Gerbereiwissenschaft und Praxis. 23. DD. 201-206 (1971).

Perkowski, S. Water Recirculation (Reuse) in the Leather Industry. Abstract. Journal of the American Leather Chemists Association. p. 189. Cited froni Das Leder, 21, pp. 63-69 (1970).

Pantz, B., Muller, P., and Meizel, W. A Study on the Conversion of Procollaeen - Release and Recovery of Procollagen Peptides in the Culture

mists Association. liological Chemistry, 248,

Polkowski, L.B., Boyle, W.C., Christensen, B.F. Biological Treatment, Effluent Reuse, and Sludge Handling for the Side Leather Tanning Industry. S.B. Foot Tanning Co. Prepared for: United States Environmental Protection Agency, Industrial Environmental Research Laboratory, Cincinnati, OH. EPA-60012-78-013. February 1978.

Prentiss, W.C. .Chemical Routes to a Low Sulfide Beamhouse. The Leather Manufacturer. September 1981. pp. 21-24.

Ramalingam, S., Das, D., and Sarbar, K. Re-Use of Lime-Sulfide Liquor in the Manufacture of Chrome Upper Leather. Abstract. Journal of the American Leather Chemists Association. Vol. 76 . August 1981. pp. 317-318. Cited from Leather Science, 23, pp. 240-243 (1976).

Robinson, J.W. and Howard, J.W. Chromium Recovery and Recycling from Spent Tannery Liquor. The Leather Manufacturer. August 1976. pp. 12-22.

Rutland, F.H. Armira Corporation. Written communication with R . M . Lollar, Tanners' Council of America, 17 December 1981.

Ryan, R. Maine Resources. Personal comunication with J. Margolis, JRB Associates, 3 August 1981.

Sagoschen, J.A. Review and Evaluation of Literature on Tannery Waste Water. Abstract. Journal of the American Leather Chemists Association. p . 189. Cited from Das Leder, 21, pp. 44-51 (1970).

B-13

Sayers, R.H. and Langlais, R. Removal and Recovery of Sulfide from Tannery Wastewater. The Blueside Company, Inc. Prepared for: United States Environmental Protection Agency, Region VII. EPA-600/2-77-031. October 1977.

Scaief, J.F. Leather Tanning and Finishing Waste Management Research and Development Program. Prepared for: United States Environmental Protection Agency, Industrial Environmental Research Laboratory, Cincinnati, OH. EPA-60012-76-230. September 1976.

Schleifer, A., Teplitz, P.V., and Lawrence, M. Economic Impacts of Proposed Effluent Control Regulations on the United States' Leather Tanning Industry. Cambridge Research Institute, Cambridge, MA. March 1980.

Scholz, H.G. Treating and Discarding Sludge. Abstract. Journal of the American Leather Chemists Association. p. 246. Cited from Das Leder, 21, pp. 106-110 (1980).

Scholz, H.G. Different Types of Evaluations for Organic Components in Tannery Waste Water. Abstract. Journal of the American Leather Chemists Association. p. 190. Cited from Das Leder, 21, pp. 70-79 (1970).

SCS Engineers, Inc. Assessment of Industrial Hazardous Waste Practices. Leather Tanning and Finishing Industry.. United States Environmental Protection Agency, Washington, DC. PB 261-018, SW-131C. November 1976.

Sehgeil, P. New Process for Reclaiming Used Common Salt. Abstract. Journal of the American Leather Chemists Association. Vol. 76. August 1981. p. 317. Cited from Leather Science, 23, pp. 237-239 (1976).

Seltzer, R.E. Economic Impact Analysis of Proposed Effluent Limitations Guidelines, New Source Performance Standards and Pretreatment Standards for the Leather Tanning and Finishing Industry. Development Planning and Research Associates, Inc. Prepared for: United States Environmental Protection Agency, Off ice of Analysis, Washington, DC. EPA-44012-79-109. July 1979.

Sharp, B.W. Chrome Recycling. Journal of the American Leather Chemists Association. Vol. 76. 1981. pp. 24-34.

Shirai, K. and Okamura, H. Investigation of Chrome Splits as a Material for Recovery of Chrome Collagen Fibers. Abstract. Journal of the American Leather Chemists Association. p. 480. Cited from Hikaku Kagaku, 18, pp. 89-98 (1972).

Shivas, S. Methods to Alleviate Tannery Water Pollution Problems. The Leather Manufacturer. September 1981. pp. 28-33.

Shuttleworth, S.G. The Evolution of Tannery Effluent Treatment-Guidelines for Further Investigation. Journal of the American Leather Chemists Association. Vol. 72. 1977. pp. 382-403.

B-14

Shuttleworth, S.G. and Ward, G.J. The Liritan Minimum Effluent Vegetable Tanning System. Journal of the American Leather Chemists Association. July 1976. pp. 336-343.

Simoncini. A. and DelPezzo, L. The Treatment of Tannery Effluents and the Possible Reuse of Waste Waters. Abstract. Journal of the American Leather Chemists Association. pp. 512-513. Cited from Cuoio, pelli, mat. concianti. 48. DD. 1-16 (1972).

Sittig, M. Metal and Inorganic Waste Reclaiming Encyclopedia. Noyes Data Corporation, Park Ridge, NJ. 1980.

Slabbert, N.P. Leather Technologists and Chemists. Vol. 64, No. 5 . September 1980. pp. 89-92.

Recycling in the Tanning Industry. Journal of the Society of

Smith, R. Preparation of High-Quality Gelatine Having Low Chromium Content from Chromed Waste Stock. U.S. Patent 4,151,161. Journal of the American Leather Chemists Association. Vol. 75. 1980. p. 141.

Smith, R. The Principles and Methods of Chromium Recovery. The Leather Manufacturer. April 1978. pp. 16-22.

Smith, R. Allied Chemical Corporation. Personal comunication with J. Margolis, JRB Associates, 20 August 1981.

Spahrmenn, J. Experiences with the Purification and Reuse of Tannery Effluent and the Reuse of Chemicals. Abstract. Journal of the American Leather Chemists Association. Vol. 75. 1980. p. 226. Cited from Das Leder, 29, pp. 199-205 (1978).

Spahrmenn, J. Direct and Indirect Recycling of Tannery Waste Water. Journal of the American Leather Chemists Association. V O ~ . 74. 1979. pp. 418-421.

Spicka, M. Some Experiments With the Use of Sulfite Waste Liquors in the Leather Industry in Czechoslovakia and Abroad. Abstract. Journal of the American Leather Chemists Association. pp. 580-581. Cited from Kozarstvi, 19, pp. 172-174 (1969).

Steadman, T.R., Hillman, M.E.D., Pickett, G.E., Scantland, D.A., Jacomet, J.A., and McClure, T.A . Potential Opportunities for Increasing the _ _ Utilization of Tannery Offal. The Leather Manufacturer. October 1977. pp. 28-32.

Suede and Leather Refinishers of America. Personal communication with V. Hodge, JRB Associates, 24 June 1981.

Svancer, J. International Seminar on Effluent Treatment in Gottwaldov. Abstract. Journal of the American Leather Chemists Association. p . 578. Cited from Kozarstvi, 19, pp. 112-113 (1969).

B-15

Takada. S. Process f o r the Recovery of Chromic Acid Solution from Waste'Water Containing Chromate Ions. U.S. Patent 4,049,772. Journal of the American Leather Chemists Association. Vol. 73. 1978. p. 453.

Talmadge, E. Tanners' Council of America. Personal communication with J. Margolis, JRB Associates, 31 December 1981.

Tancous. J.J., Bellingham, R., Kallenberger, W., and McDonell, A . Conservation of Chromium in the Tanning Industry. Leather Chemists Association. Vol. 76. 1981.

Journal of the American

Terrell, G.C. The Contribution of Innovative Combustion Technology to Chromium Recovery. V O ~ . 76. August 1981. pp. 288-296.


Thorstensen, T.C. and Shah, M. Sludge as a Fertilizer. Association. Vol. 74. 1979. pp. 14-23.

Technical and Economic Aspects of Tannery Journal of the American Leather Chemists

Timokhin, N.A. and Drabkina, E.I. Ways for the Utilization of Collagen Hydrolysates Made from Tannery Offal. Abstract. Journal of the American Leather Chemists Association. p. 48. Cited from Kozh. Obuv. Prom., 11, pp. 11-13, (1969).

Timokhin, N.A. Processing Waste Proteins. Abstract. Journal of the American Leather Chemists Association. p. 276. Cited from Kozh. Obuv. Prom., No. 4, p. 42 (1974). -

./

Tombetti, F. Recovery of Industrial Wastes. Hypotheses of Electrical and Thermic Energy Production at Low Costs: in Tanning Industry. Abstract. Journal of the American Leather Chemists Association. Vol. 75. 1980. p . 508. Cited from Cuoio, pelli, mat. concianti, 54, pp. 408-418 (1978).

the "Totem" (Total Energy Module)

Updegraff, D.M.; Griffin, L., and Ross, L.W. Biochemical Treatment of Waste Water Effluents from a Chrome Tannery. Chemists Association. Vol. 70, No. 2. February 1975. pp. 79-82.


United States Bureau of ?lines. Personal communication with Bureau personnel by J. Margolis, JRB Associates, 3 September 1981.

Utsuo, A. New Application of Collagen. Abstract. Journal of the American Leather Chemists Association. Vol. 75. 1980. p. 37. Cited from Hikaku Kagaku, 20, pp. 209-217 (1975).

van

van

Meer, A.J.J. Some Aspects of a Chemical Treatment of the Waste Waters from the Beamhouse. Journal of the American Leather Chemists Association. Vol. 68, NO. 8. August 1973. pp. 339-345.

Tornout, F. Recycling of Tannery Liquors. Journal of the Society of Leather Technologists and Chemists. Vol. 61, No. 3 . May 1977. pp. 63-68.

B-16

van Tornout, F. Recycling of Tannery Liquors. The Tanner. September 1977 . pp. 141-146.

van Vlimmeren, P.J. New Beamhouse Development to Simplify Waste Water Management. Vol. 7 1 . 1976. pp. 318-334.

Journal of the American Leather Chemists- Association.

van Vlimmeren, P.J. Tannery Effluent. Journal of the American Leather Chemists Association. Vol. 6 7 , No. 9 . September 1972. pp. 388-406.

Vaughn, D. SISK Company. Personal communication with J. Margolis, JEU3 Associates, 20 August 1981 .

Venkatachalam, P.S. Works Control in a Tannery: Optimum Utilization of Chemicals with Their Reuse Could Generate Economies. Abstract. Journal of the American Leather Chemists Association. Vol. 7 4 . 1979. p. 204. Cited from The Tanner, No. 9 , pp. 439-442 ( 1 9 7 5 ) .

Vesela, 2. Economic Value of Slaughterhouse and Tannery Wastes. Abstract. Journal of the American Leather Chemists Association. p. 348. Cited from Kozarstvi, 2 0 , pp. 47-49 ( 1 9 7 0 ) .

Vulliermet, B. Lmprovement of the Mass and Energy Balances in the Tanning Industry. Journal of the American Leather Chemists Association. Vol. 7 5 . 1980. pp. 232-275.

Wahid, M. Utilization of Slaughterhouse Wastes and By-products. Abstract. Journal of the American Leather Chemists Association. p. 536. Cited from Science and Index, 7 , pp. 7-14 ( 1 9 7 0 ) .

Ward, J. Dun's Marketing Services of the Dun & Bradstreet Corporation. Personal communication with J. Margolis, JRB Associates, 13 October 1981 .

Whitmore, R.A., Jones, H.W., Windus, W., and Naghski, J. Preparation of Hide Collagen for. Food. Journal of the American Leather Chemists Association. Vol. 6 5 , No. 7 . July 1970. pp. 382-389.

Wolff, J. Practical Experience of Four Effluent Treatment Plants - I, Removal of Sulfide Sulfur and Neutralization of Waste Water with Lron Sulfate. Abstract. Journal of the American Leather Chemists Association. p. 244. Cited from Das Leder, 2 1 , pp. 90-93 ( 1 9 7 0 ) .

Young, H.H. Continuous Method for Reclaiming Chromium Hydroxide from Spent Chrome Tanning Liquors and Reuse Thereof in Subsequent Tanning. U.S. Patent 3 ,950 ,131 . Journal of the American Leather Chemists Association. Vol. 72 . 1977. pp. 370-371.

Young, H.H. Effluent Treatment for a Small Tannery. Journal of the American Leather Chemists Association. Vol. 6 8 , No. 8 . August 1973. pp. 308-315.

Zehender, F. Practical Experience With Four Effluent Treatment Plants - 111. Oxidation of Sulfide Sulfur With Manganese Salt. Abstract. Journal of

21, pp. 95-96 ( 1 9 7 0 ) . L the American Leather Chemists Association. p. 245. Cited from Das Leder,

, B-17

GLO S S ARY

Ba t ing

Beamhous e

B i chroma t e

Bichromate Reduct ion

Blue -

Blue T r i m and Shavings

Buf f ing

Buf f ing Dust

By-product

Chrome Tanning

Co 11 agen

Col lagen Product

A t anne ry p r o c e s s i n g s t e p t h a t fo l lows l iming and precedes p i c k l i n g . Bat ing removes l i m e l e f t on t h e h i d e from t h e unha i r i ng p r o c e s s , reduces s w e l l i n g of t h e h i d e , and p r e p a r e s t h e h i d e f o r t ann ing by d e s t r o y i n g and removing h a i r , h a i r r o o t s , and s k i n pigments .

The set of t a n n e r y p roces se s t h a t p r epa re s t h e h i d e f o r t ann ing . These p roces se s i n c l u d e soak ing , washing, f l e s h i n g , t r imming, u n h a i r i n g , and r i n s i n g .

See Hexavalent Chromium.

The t a n n e r y p roces s t h a t reduces hexava l en t chromium t o i t s t r i v a l e n t form.

The s t a t e o r c o n d i t i o n of h i d e s subsequent t o chrome tanning and p r i o r t o r e t a n n i n g . Hides i n t h i s s t a g e of p r o c e s s i n g a r e c h a r a c t e r i s t i c a l l y b l u e i n c o l o r .

B i t s and p i e c e s of tanned h i d e removed d u r i n g trimming and shaving o p e r a t i o n s p r i o r t o r e t a n n i n g . These o p e r a t i o n s c r e a t e a tanned h i d e of uniform dimension and t h i c k n e s s .

A l i g h t sanding o p e r a t i o n a p p l i e d t o t h e g r a i n or unde r s ide of l e a t h e r and a l s o t o s p l i t s . Buf f ing smooths t h e g r a i n s u r f a c e and improves t he nap of t h e unde r s ide of t h e l e a t h e r .

Small p i e c e s of l e a t h e r removed i n t h e b u f f i n g o p e r a t i o n . B u f f i n g d u s t a l s o i n c l u d e s small p a r t i c l e s of a b r a s i v e used i n t h e o p e r a t i o n and i s of a c o a r s e powder c o n s i s t e n c y .

Any m a t e r i a l produced du r ing t h e manufacture of a primaLy ' p r o d u c t ; a secondary product . A by- product may o r may no t have v a l u e .

The predominant type of t ann ing p roces s t h a t employs chromium t ann ing agen t s t o conve r t t h e h i d e o r s k i n i n t o l e a t h e r . Roughly 80 p e r c e n t of t h e h i d e s are tanned by t h i s method.

The f i b r o u s connec t ive p r o t e i n material w i t h i n t h e h i d e t h a t p rov ides i t s r i g i d i t y and c o n s t i t u t e s t h e bu lk of t h e volume of t h e f i n i s h e d l e a t h e r .

P roduc t s manufactured us ing c o l l a g e n p r o t e i n s i s o l a t e d from animal h i d e o r s k i n . G r a n u l a t i o n o r h y d r o l y s i s p r epa re t h e p r o t e i n s f o r i n c o r p o r a t i o n i n t o t h e p roduc t . Glue , g e l a t i n , cosme t i c s , s u r f a c t a n t s , food a d d i t i v e s , and a g r i c u l t u r a l s p r a y s a r e examples of c o l l a g e n p r o d u c t s .

G-1

Colo r inn

Complete Tannery

C o n t r a c t Tannery

Convert e r

Degreas ing

D e 1 iming

D i chromate

D i r e c t Recyc 1 ing

Drying

Equ iva l en t Hide

F a t l i o u o r

F i b r o u s Product

F i n i s h e d L e a t h e r T r i m -

A proces s s t e p i n t h e t a n n e r y whereby t h e c o l o r of t he tanned h i d e i s changed t o t h a t of t h e d e s i r e d marke t ab l e product by dye ing o r p a i n t i n g .

A t a n n e r y t h a t i n c l u d e s a l l phases of t he t ann ing o p e r a t i o n : beamhouse, t a n y a r d , r e t a n , and f i n i s h .

A t a n n e r y t h a t i s c o n t r a c t e d t o p roces se s h i d e s owned by c o n v e r t e r s . The c o n t r a c t t a n n e r y does no t become involved i n t h e sale of t h e f i n i s h e d l e a t h e r .

A t anne ry t h a t on ly buys raw h i d e s and a r r a n g e s for t h e a c t u a l p r o c e s s i n g by c o n t r a c t t a n n e r i e s .

I n p i g s k i n and sheepsk in t a n n e r i e s a s o l v e n t or d e t e r g e n t i s added t o t he drum c o n t a i n i n g washed h i d e s . Grease is removed from t h e h i d e s and recovered as a by- product .

The p roces s ing s t e p i n t h e t anya rd t h a t removes t h e l i m e from h i d e s coming from t h e beamhouse. May be performed i n con junc t i o n wi th b a t i n g . See Hexavalent Chromium.

The r euse of p a r t or a l l of a p roces s e f f l u e n t , w i t h or wi thou t p u r i f i c a t i o n , i n t h e same or d i f f e r e n t p r o c e s s .

A proces s s t e p i n t h e t a n n e r y t h a t fo l l ows f a t l i q u o r i n g an4 precedes f i n i s h i n g . Drying p roces se s remove h i d e m o i s t u r e and a r e accomplished us ing oven o r vacuum d r y i n g .

A term of measurement used t o r e l a t e t h e p roduc t ion o f t a n n e r i e s us ing v a r i o u s t ypes of raw mater ia ls . An e q u i v a l e n t h i d e i s r e p r e s e n t e d by 3.7 squa re m e t e r s (m ) of s u r f a c e a r e a and i s t h e average s i z e of a c a t t l e h i d e .

2

A t a n n e r y p roces s e n t a i l i n g t h e a g i t a t i o n of tanned h i d e s i n o i l s or o t h e r f a t t y subs t ances t o r e p l a c e n a t u r a l o i l s l o s t i n t h e beamhouse and t anya rd p r o c e s s e s . Regu la t e s t h e p l i a b i l i t y and s o f t n e s s of t h e l e a t h e r and c o n t r i b u t e s t o i t s t e n s i l e s t r e n g t h .

P roduc t s manufactured u s ing c o l l a g e n f i b e r s i s o l a t e d from animal h i d e o r s k i n . G r a n u l a t i o n and d e f i b r i l l a t i o n p r e p a r e t h e f i b e r s f o r i n c o r p o r a t i o n i n t o t h e p roduc t . Lea the r boa rd , a r t i f i c i a l l e a t h e r , and poured i n s u l a t i o n are examples o f f i b r o u s p roduc t s .

The l e a t h e r s c r a p s produced du r ing the t r i m i n g ope ra t i on fo l l owing t h e a p p l i c a t i o n of a f i n i s h or c o a t i n g t o t h e l e a t h e r m a t e r i a l . The s c r a p s g e n e r a l l y have the same p h y s i c a l c h a r a c t e r i s t i c s as t h e f i n i s h e d l e a t h e r .

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F i n i s h ing

F i n i s h i n g Res idues

F 1 e sh ing

F l o a t

Green

Green F 1 e s h i n e

~.

Hair Burn

H a i r Pu lp

H a i r Save

The f i n a l t anne ry p r o c e s s i n g s t e p s performed on a tanned h i d e fo l l owing the r e t a n f c o l o r f f a t l i q u o r p r o c e s s e s . F i n i s h i n g e n t a i l s t h e a p p l i c a t i o n of materials t o t h e g r a i n s u r f a c e o f t h e l e a t h e r t o provide a b r a s i o n and s t a i n r e s i s t a n c e and t o enhance c o l o r . Impe r f ec t i ons i n t h e g r a i n s u r f a c e are a l s o c o r r e c t e d .

Produced i n t a n n e r y f i n i s h i n g o p e r a t i o n s as a r e s u l t o f a i r p o l l u t i o n c o n t r o l d e v i c e s on sp ray booths and from g e n e r a l c l e a n i n g of t he f i n i s h i n g equipment.

The mechanical removal o f f l e s h and f a t t y subs t ances from t h e unde r s ide of a h ide p r i o r t o t ann ing . I n t h e ca se of sheepskin t a n n i n g , f l e s h i n g is o f t e n performed a f t e r t h e t ann ing p roces s .

The proper l e v e l or volume of s k i n s o r h i d e s , c h e m i c a l s , and wa te r t h a t i s ma in t a ined i n any w e t p roces s u n i t ( v a t s , drums , or p r o c e s s o r s ) w i t h i n t h e t anne ry .

The h i d e s r e c e i v e d by t h e t a n n e r t h a t may be cured w i th s a l t o r a b r i n e s o l u t i o n .

The t a n n e r y p roces s t h a t e n t a i l s t h e removal of f l e s h and f a t t y s u b s t a n c e s p r i o r t o u n h a i r i n g . performed on h i d e s t h a t w i l l be used i n t h e manufacture of shoes , spo r t swea r , and o t h e r such p roduc t s .

Green f l e s h i n g i s

The beamhouse process t h a t removes h a i r from t h e h ide th rough t h e a c t i o n of such d e p i l a t o r y chemica ls as ca lc ium hydrox ide , sodium s u l f h y d r a t e , and sodium s u l f i d e . The chemica l s , combined w i t h h e a t and a g i t a t i o n : (1) d e s t r o y t h e h a i r o r a t t a c k the h a i r r o o t s , ( 2 ) loosen t h e ep ide rmis , and ( 3 ) remove c e r t a i n s o l u b l e s k i n p r o t e i n s .

See Hair Burn.

The t anne ry beamhouse u n h a i r i n g p roces s t h a t does not d e s t r o y t h e p h y s i c a l s t r u c t u r e of t h e h a i r . The p roces s u se s weaker d e p i l a t o r y chemical c o n c e n t r a t i o n s and lower s o l u t i o n t empera tu re s t han t h e h a i r burn p roces s i n o r d e r t o l oosen t h e h a i r f o l l i c l e s . Depending upon t h e s o l u t i o n , t h e h a i r must e i t h e r be removed from t h e l i q u o r o r mechan ica l l y removed from t h e h i d e . The h a i r may be s o l d or d i s c a r d e d .

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Hexavalent Chromium

C r + 6 or Chromium (VI). The form of chrome with a plus six ( 6 ) valence state. Tanners may purchase process chrome in the hexavalent state as bichromate (also termed dichromate). Hexavalant chrome must be reduced to the trivalent state either before use (bichromate reduction) o r -- in situ during the tanning process (a "two bath" process now largely obsolete). Hexavalent chrome is significantly more toxic, carcinogenic, soluble, and mobile than trivalent chromium.

Hide The skin of an animal. Refers to a large, heavy skin, such - as from cattle or other large animals.

Hide A modern piece of tannery equipment that resembles a concrete Processor mixer with a liner. Hide processors are attractive to

tanners because they facilitate the processing of hides through the unhairing, pickling, tanning, rinsing, and soaking stages of the tanning process without removing the hides from the processor. The solutions can be piped in, rinsed out, and segregated, thus facilitating their individual treatment, puri f icat ion, and/ o r rec ycl ing .

-

Hydro 1 y zed Hair components, usually by tannery unhairing processes or

Hair that has been structurally broken down to its protein

by-product manufacturers . -

Keratin One of a group of tough, fibrous proteins found in the epidermal layer of the hide or skin.

Leather A contract overation specializing in the finishing of Finisher leather. No' tanning facilities are included in the

operation.

Leather (1) The manufacture of commercial products using finished Product leather produced by the tanner. ( 2 ) An entrepreneur who Manufacture(r1 'manufactures leather products.

Leather Scrap A n entrepreneur who buys, sells, and sometimes processes Broker leather scrap generated by tanneries and leather product - -

manufacturers. concentrations of leather and leather product manufacturing facilities and use established networks to buy and sell scrap.

Brokers are located in regions with high

Leather Tanner See Tanner.

Liming See Unhairing.

Lime Sulfide Fleshings generated after the hide or skin has completed F 1 esh ings the unhairing process but before tanyard processes comence.

The fleshings contain the unhairing chemicals lime and sulfide .

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L i r i t a n

O f f a 1

Paddle Vat

P i c k l i n g

P r o t e i n

R e t a n n i n e

Rinse

Shaving

Shavings

Shea r1 ing

Skin L_

The predominant v e g e t a b l e t ann ing method used by most of t h e v e g e t a b l e t a n n e r s i n t he U.S. and Canada. I n t h i s p r o c e s s , t he h i d e s a r e t r e a t e d w i th sodium hexametaphosphate and s u l f u r i c a c i d t o prepare t h e h i d e s f o r a more r a p i d t ann ing p r o c e s s .

S o l i d was tes or by- products gene ra t ed by t h e l e a t h e r t ann ing process . Such wastes i n c l u d e f l e s h i n g s , t r immings, and shav ings .

A v a t wi th a semi-submerged r o t a t i n g paddle arrangement used f o r t h e mixing of water and chemica ls w i th t h e h i d e .

The t anne ry p roces s t h a t fo l l ows b a t i n g . The h i d e is a g i t a t e d i n a s o l u t i o n of s u l f u r i c a c i d and sodium c h l o r i d e which b r i n g s i t t o an a c i d c o n d i t i o n and p reven t s t he p r e c i p i t a t i o n of chromium sa l t s on t h e h i d e d u r i n g t a n n i n g .

A complex o rgan ic compound composed of one or more po lypep t ide c h a i n s , each made up of many amino a c i d s j o i n e d by p e p t i d e bonds.

A second t ann ing p roces s u t i l i z i n g e i t h e r t h e n a t u r a l t ann ing m a t e r i a l s (chromium or v e g e t a b l e e x t r a c t s ) or s y n t h e t i c t a n n i n g a g e n t s . Retanning impar t s s p e c i a l i z e d p r o p e r t i e s t o t h e l e a t h e r .

Any t a n n e r y p roces s i n which t h e h i d e or s k i n i s b r i e f l y submerged and /o r a g i t a t e d i n an aqueous s o l u t i o n for t h e purpose of removing exces s p roces s chemica ls r e t a i n e d from p rev ious p roces se s .

An a b r a s i v e , mechanica l a c t i o n used t o c o r r e c t e r r o r s i n s p l i t t i n g and thus y i e l d i n g a uni formly t h i c k g r a i n s i d e or s p l i t .

The waste p roduc t s gene ra t ed du r ing t h e shaving o p e r a t i o n s . These a r e e s s e n t i a l l y small p i e c e s of t h e tanned h i d e , which a r e approximate ly t h e s i z e of wood shav ings .

A lamb or sheepsk in tanned wi th t h e h a i r r e t a i n e d on t h e s k i n .

The p e l t o r s k i n of an ima l s . G e n e r a l l y used i n r e f e r e n c e t o animals s m a l l e r t han c a t t l e ( p i g s ) and an imals w i t h r e l a t i v e l y t h i n s k i n ( sheep , c a l v e s , and g o a t s ) .

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Shoe L e a t h e r This term embraces a v a r i e t y of l e a t h e r s . Inc luded are: ( 1 ) S o l e L e a t h e r , made from c a t t l e h i d e s and t o a small e x t e n t from ho r seh ides and b u f f a l o h i d e s , which compr ises bo th t h e h e a v i e r grade (used f o r o u t e r s o l e s of shoes ) and t h e l i g h t e r g r ades , and o f f a l ( heads , s h o u l d e r s , and b e l l i e s ) used t o a g r e a t e r e x t e n t f o r h e e l s , i n s o l e s , t oecaps , e t c . ; ( 2 ) Upper L e a t h e r , made p r i n c i p a l l y from c a l f s k i n s , g o a t s k i n s , c a t t l e - h i d e s , h o r s e h i d e s , and o t h e r c l a s s e s of animal s k i n s , go ing i n t o shoe uppe r s ; and ( 3 ) misce l l aneous shoe l e a t h e r s , i n c l u d i n g w e l t i n g , l i n i n g s t o c k , tongue s t o c k , f a c i n g s t o c k , e t c .

Soak - The f i r s t t anne ry beamhouse p roces s performed i n c o n j u n c t i o n wi th t h e wash o p e r a t i o n t o remove s a l t , b lood , d i r t , and manure from t h e h i d e s . The p roces s a l s o r e s t o r e s mo i s tu re t o h i d e s t h a t are b r i n e cu red .

Spent Liquid waste streams comprised of p roces s s o l u t i o n s whose L iquor /So lu t ion a c t i v e chemical c o n t e n t ha s been d e p l e t e d below e f f e c t i v e

c o n c e n t r a t i o n s .

S p l i t ( s ) ( 1 ) The o p e r a t i o n of s e p a r a t i n g a h i d e i n t o two l a y e r s , a g r a i n s i d e and a f l e s h s i d e ( " s p l i t " ) . The p roces s i s accomplished on a s p l i t t i n g machine s imi lar t o a h o r i z o n t a l band saw which s l i c e s t h e h i d e th rough i t s t h i c k n e s s l e a v i n g a r e l a t i v e l y un i formly t h i c k o u t e r , o r g r a i n s i d e , and a s p l i t of v a r y i n g t h i c k n e s s . ( 2 ) The unde r s ide l a y e r of a h i d e a f t e r s p l i t t i n g . The s p l i t ha s no g r a i n c h a r a c t e r i s t i c s and i s o f t e n used f o r t h e p roduc t ion of suede l e a t h e r .

Suede

Syntan

Tankage

A t ype of l e a t h e r produced from the h i d e s p l i t .

S y n t h e t i c t ann ing mater ia ls , g e n e r a l l y used i n combina t ion w i t h v e g e t a b l e , m i n e r a l , o r formaldehyde t annages . Syntans a r e almost e x c l u s i v e l y used i n r e t a n n i n g r a t h e r than t a n n i n g o p e r a t i o n s .

Processed f e r t i l i z e r i n g r e d i e n t . Lea the r s c r a p s and s l u d g e s can be made i n t o tankage by d r y i n g , g r a n u l a t i n g , u r e a a d d i t i o n , and p e l l e t i z a t i o n p r o c e s s e s . The a d d i t i o n of phosphate , potass.ium, and o t h e r p roces s i n g r e d i e n t s t o t h e tankage completes t h e f e r t i l i z e r manufac tur ing p roces s .

Tanning The p roces s of c o n v e r t i n g a h i d e o r s k i n i n t o l e a t h e r by soaking it i n a t ann ing s o l u t i o n made o f v e g e t a b l e e x t r a c t s , alum, formaldehyde, o r metals such as chromium o r z i rconium.

Tanner En t r ep reneu r who conve r t s raw animal h i d e s and s k i n s i n t o l e a t h e r ( f i n i s h e d o r u n f i n i s h e d ) .

Tannery The f a c i l i t y t h a t houses the equipment neces sa ry f o r performing t h e t ann ing o p e r a t i o n s . A f u l l o r complete t a n n e r y i s one which i n c l u d e s beamhouse, t a n y a r d , r e t a n / f a t l i q u o r / c o l o r , and f i n i s h i n g o p e r a t i o n s .

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Tannin The tanning a g e n t ( s ) used i n v e g e t a b l e t ann ing . Tannin i s d e r i v e d from v a r i o u s t r e e ba rks , i n c l u d i n g : quebracho, w a t t l e , mangrove, and c h e s t n u t .

Tanyard That p o r t i o n of the t anne ry i n which b a t i n g , p i c k l i n g , and tanning are performed on t h e h i d e s or s k i n s .

Through- the- Blue -

Hide or s k i n t h a t ha s been processed through the t ann ing o p e r a t i o n . A f t e r t a n n i n g , t h e h i d e s may be f u r t h e r processed o r s o l d t o ano the r f a c i l i t y f o r f i n i s h i n g . t h a t on ly p roces se s h i d e s o r s k i n s through t h e t ann ing o p e r a t i o n . f a c i l i t y for f i n i s h i n g .

These h i d e s have a c h a r a c t e r i s t i c b l u e c o l o r .

Also r e f e r s t o a f a c i l i t y

The h i d e s o r s k i n s are then s o l d t o ano the r

Trimming(s) (1) The removal of t h e ragged edges and i n f e r i o r p o r t i o n s o f h i d e s and s k i n s e i t h e r b e f o r e or a f t e r t ann ing . Trimming i s normally accomplished us ing kn ives r a t h e r t han mechanical equipment . ( 2 ) The h i d e o r l e a t h e r s c r a p s produced du r ing the trimming o p e r a t i o n .

+3 T r i v a l e n t C r or Chromium (111). The form of chrome w i t h a p lus t h r e e Chromium ( 3 ) va lence s t a t e . The o n l y form of chromium t h a t w i l l r e a c t

p r o p e r l y with t h e f r e e amine and hydroxyl groups on the p r o t e i n cha ins i n h i d e s or s k i n s t o f i x t h e f i b e r s . T r i v a l e n t chromium i s of less r e g u l a t o r y concern t han hexava len t chromium.

Unha i r i n g The t anne ry p roces s t h a t f a k i l i t a t e s t he removal of h a i r from the h i d e o r s k i n u s ing d e p i l a t o r y chemica ls . r e f e r r e d t o as h a i r s a v e , h a i r bu rn , h a i r pu lp , and l iming .

V a r i a t i o n s

Vegetab le An o l d e r and more t i m e consuming t ann ing method than t h e Tanning commonly used chrome t ann ing . U t i l i z e s t ann ing agen t s

de r ived from t ree ba rks t o f i x t h e h i d e f i b e r s , p r e v e n t i n g ‘ p u t r i f a c t i o n , and c o l o r t he l e a t h e r . G e n e r a l l y used i n t h e manufacture of heavy l e a t h e r .

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Leather and Leather Products - P2RIC

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