TANNING EMU SKINS: AN ASSESSMENT OF THE

PROCESSES, THE LEATHER PROPERTIES, AND

THE POTENTIAL FOR CHROMIUM REDUCTION

by VENKATESWARA REDDY KOTLA, B.Tech.

A THESIS IN CIVIL ENGINEERING

Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE

CIVIL ENGINEERING

Approved

Accepted

Dean of the Grad\idte/}^})oo]

May, 1996 73 ^ ' "^ ' t. ACKNOWLEDGMENTS fJO . ^

I would like to thank Dr. R. W. Tock for his valuable guidance, scholarly suggestions, and constant encouragement throughout this research work. I am grateful to the other members of my committee. Dr. R. H. Ramsey and Dr. T. R. Mollhagen, for tiiefr valuable suggestions and advice throughout my degree program. I take this opportunity to thank the Leather Research Instimte (LRI) which sponsored this research and the State of Texas for funding this project. I am thankful to Dr. Eberspacher of LRI for giving me complete access to the LRI Ubrary. Special thanks are due to my wife for helping me many times during the course of this research work and for aU she has endured. And lastly, my sincere thanks to my family for their constant support and encouragement. Without their blessings and good wishes, I would not be at this stage today.

u TABLE OF CONTENTS

ACKNOWLEDGMENTS ii

ABSTRACT v

LIST OF TABLES vi

LIST OF FIGURES vii

CHAPTER

I. INTRODUCTION 1

Overview of the Leather Industry 1

Types of Leather Produced 1

Types of Animals Slaughtered 5

Emus 5

Objectives of the Research 6

II. BACKGROUND INFORMATION 8

Structure and Composition of Hides 8

Tanning Processes 11

Chemistry of Chrome Tanning 20

Industrial Wastewater 24

Industrial Waste Treatment 26

Tannery Effluent Characteristics 27

Tannery Waste Treatment 31

iii 11 L EXPERIMENTAL APPROACH 41

Hide Preservation 41

Hide Preparation 41

Tanning Process 42

Mechanical Testing 46

Wastewater Analysis 46

Chemical Precipitation 47

IV. RESULTS AND DISCUSSION 48

General Appearance of Tanned Emu Leather 48

Thickness Variations 48

Area and Weight 48

Tensile Properties 50

Waste Characteristics 48

Waste Treatment 53

V. CONCLUSIONS AND RECOMMENDATIONS 64

Suggestions for Further Studies 65

REFERENCES 68

IV ABSTRACT

The tanning of ratite skins has not been actively practiced in the United States. There is scant Hterature available on the tanning and properties of ratite skins. In this context, the Leather Research Instimte at Texas Tech University has undertaken an experimental program to tan emu skins and then investigate the potential for this leather to be used as a commercial product. The traditional chrome tanning process was used in the tanning of emu skins. An Instron Universal Testing Machine (Model 1122) was used to estimate the strength of the tanned leather. The leather was characterized by the thinness and the presence of pores from where the feathers were removed. The strength of the leather was almost 50% of the strength of bovine leather. It was also decided to investigate the recoverabiUty of chromium from the spent tan liquor. The available literature on treating the tannery effluent was reviewed and it was decided to use the widely accepted method of chemical precipitation of chromium by pH adjustment. Lime was used as the precipitating agent. This resulted in a 99.9 percent removal of chromium at a pH of 8.5 while the removal of other parameters like COD and solids was not encouraging. A methodology was devised from the results to recover and reuse the chromium from the spent tan liquor but no tests using this methodology have been conducted. LIST OF TABLES

1.1 End Uses of Leather from Different Hides and Skins 3

2.1 Tanning Substances and Their Characteristics 18

2.2 Leather Tanning and Finishing Industry Subcategory 28

2.3 Effluent Characteristics for Various Tanneries 32

2.4 Pollutant Loads for Beamhouse and Tanyard/Retan/Wet Finish Operations 36

2.5 Chromium Removal from Chrome Liquor by Adsorption 40

4.1 Tensile Properties of Emu Leather 51

4.2 Characteristics of Spent Chrome Tan Liquor 52

4.3 Comparison of Raw and Treated Chrome Tan Waste 58

4.4 Effluent Discharge Limitations for Chromium 62

VI LIST OF HGURES

1.1 Geographical Distribution of U.S. Tanneries 2

2.1 Approximate Composition of a Hide 9

2.2 Structure of an Animal Skin 10

2.3 Hair Removal Processes 14

2.4 Effect of Sah on Acid Swelling 16

2.5 Stages in the Cross-Linkage of a Chrome Tannage 23

3.1 Leather Tannery Process-Chrome Tanning 43

3.2 Leather Tannery Process-Organic Tanning 45

4.1 General Shape and Thickness (in.) of a Chrome Tanned Emu Skin 49

4.2 COD Removal by pH Adjustment 54

4.3 Suspended Solids Removal by pH Adjustment 55

4.4 Total Solids Removal by pH Adjustment 56

4.5 Chromium Removal by pH Adjustment 57

4.6 Qualitative Element Identification: Supernatant 60

4.7 Qualitative Element Identification: Sludge 61

vu CHAPTER I INTRODUCTION

Overview of the Leather Industry The American tanning industry originated during colonial times, and hence became concentrated in New England and the middle AUantic States. However, during the 19th and 20th Centuries, the sources of animal hides shifted westward resulting in the origin of some tanneries west of the Mississippi River as shown in Figure 1.1 (U. S. EPA 1980). Even so, nearly 85% of all tanneries are still located in the Eastern United States. The tanning of hides and skins into leather was an ancient practice followed by primitive man to cover himself. Animal skin consists of outer (epidermal) and inner (dermal) layers. The inner layer constitutes the leather-making portion of the skins namely collagen. The process of tanning involves two activities (Churchill 1983): 1. removal of layers which cannot be converted into leather, and 2. the treatment of other layers (that can be converted into leather), so that they do not putrefy but remain flexible and strong. Today, even though leather is being used for a variety of purposes, it has become a non-essential commodity. In essence, the leather tanning industry is a by-product industry skice it handles the hides and skins of slaughtered animals, bfrds, ratites, and reptiles used in the meat industry.

Types of Leather Produced The type of leather produced depends on the requirements of the ultimate user as well as the type of raw material utilized. Table 1.1 gives some of the different types of end uses for leather produced from different types of hides and skins. In general, most of the leather produced can be classified into the following types: o 00

< Ui CO

of/y •c

H CO D o a o -a u o Si G 'B G c/l (d 7o3 :s x: D> C4 G 00 -H O O (0 • 4J ^.^ -^ c « CoJ gu r CO in •p Id '-i o 4J CO • • •• r~n u: M - < a: i^ I Table 1.1 End Uses of Leather from Different Hides and Skins* Skin Origin End Use of Leather Cow and Steer Shoe and boot uppers, soles, insoles, linings; patent leather; garments; work gloves; waist belts; luggage and cases; upholstery; transmission beltkig; sporting goods; packings. Calf Shoe uppers; slippers; handbags and bfllfolds; hat sweatbands; book bindings. Sheep and Lamb Grain and suede garments; shoe linings; slippers; dress and work gloves; hat sweatbands; book bindings; novelties. Goat and Kid Shoe uppers, finings; dress gloves; garments; handbags. Pig Shoe suede uppers; dress and work gloves; billfolds; fancy leather goods. Deer Dress gloves; moccasins; garments. Horse Shoe uppers; straps; sporting goods. Reptile Shoe uppers; handbags; fancy leather goods. Source: Leather Facts (1977). Heavy Leather - Sole Leather This type of leather is usually used in shoe manufacture. As the name indicates, this leather is thick and so the hides used are from heavy-skinned animals like steers and cows. Vegetable tanning processes are usually employed to convert the heavy skins into sole leather. Not much can be varied with respect to the color and texture in this type of leather.

Side Leather This type of leather is used in the manufacture of shoe uppers, work gloves, heavy garments, etc. Different varieties of leather can be made with changes in color and texture. The tanner* s artistry in fashions can be put to fuU use in the manner in which he manipulates the color, texture, and the finish of the leather. The chrome tanning method is usually employed to convert the skins into side leather.

Garment Suede Leather This type of leather is made primarily fromth e skins of lamb and sheep produced in New Zealand. The tanner* s expertise in using the proper dyes to develop the desired colors is important for a successfiil operation of a garment suede tannery. These tanneries are usually smaller but more simple than the side upper tanneries. The properties usually demanded for this fashion leather are large areas (6 sq. ft) of uniform color and thickness, soft handle, and good drape (Shaiphouse 1989).

Glove Leathers and Fancy Leathers Glove leathers are predominantiy made fromshee p and lamb skkis and to some extent from deer, pig, goat, and kid skins. Glove leathers are used for riding, driving, and sports wear. Other types of glove leathers include the work gloves which are made primarily from horse, cattie, calf, sheep, and pig skins. Fancy leathers are those made fromhide s and skins of any kind that are commercially acceptable because of gram and the distinctive finish. The tanneries that produce glove and fancy leathers are usually small in comparison to those of shoe upper leatiier or sole leather tanneries.

Types of Animals Slaughtered Different types of animals are slaughtered to produce different typ.es of leather products. Usually, the younger animals have small and thin skins resulting in smooth and a fine gram structure (Sharphouse 1989). Similarly, the female skin usually has a finer grain structure than the male. This results in a softer and more elastic leather. Cattie, sheep, goat, pig, horse, and reptile skins are the primary source of hides used in the production of leather. Most anknal hides represent 7-10% of the animal's body weight (Heidemann 1993). Catde hides include ox, bull, cow, and buffalo skins, while the reptiles include snake, hzard, and crocodile skins. In addition to these animals, a number of other animal skins are used to produce specialty leathers. These animals include ostrich, sharks, elephant, kangaroo, bear, elk, turde feet, and frogskins .

Emus Emus are large flightiess birds native to AustraUa. Emus belong to the ratite group that includes birds like the ostrich, kiwi, rhea, cassoway (Jefferey 1993). In addition to leather, the other emu products include meat, oil, and feathers. Emu meat is a low-fat, low-cholesterol, high protein, and low calorie meat. In the United States, there are about 40 restaurants that have emus on their menu (Maistrenko 1995). Emu oil has been an important source of medicine both in AustraUa and in the United States. The oil is used for arthritis, joint, and muscle aches, sporting strains, to soften and improve skin conditions, and as a soothing massage oil (Dickens 1995). The mature emu is about 5 to 6 feet tall and averages approximately 125-150 pounds in weight Of this, 75% results in edible meat and each bkd can produce 5 quarts of oil. Each quart of oil is worth about $100 (Dickens 1995). The leather made fromth e emu is usually used for clothing and accessories due to the thinness of the leather produced.

Objectives of the Research The tanning of emu skins in the United States has not been as actively practiced as has the tanning of other animal skins. In Texas, however, emu production has reached a stage where meat and leather are seriously being considered as commercial products. However, there are questions as to the acceptabifity of these products by the consumers. Since there are only a few emus available to slaughter, both the meat and leather that are produced must be considered luxury items (Tock and Kotia 1995). UnlUce the tanning of other animal skins, there is scant Hterature available covering the tanning of ratite skins. Ostrich skins have been tanned in South Africa and these skins were used in the manufacture of boots and apparel. The demand for ostrich leather exists due to the hmited availability of ostrich skins. The same simation apphes for emu skins which are predominantiy tanned in AustraUa. The regional emu growers association approached the Leather Research Institute at Texas Tech University (TTU) to tan emu skins. These skins were generated from the emus which were being slaughtered by the TTU Meat Laboratory during tests on their meat quaUty. Since there was no proven standard procedure to tan emu skins, it was decided to use the traditional chrome tanning process. The recipe for this process was provided in a kit by Tandy Leather Corporation. Based on this limited information for tanning of emu skins, the foUowing four objectives were set: 1. to examine the feasibiUty of tanning emu skins using conventional chrome and organic tanning mechanisms, 2. to examine the strength and feel of the tanned leather and the potential for this leather to be used as a commercial product, 3. to investigate the treatabiUty of the wastewater (chrome tan hquor) generated during the tanning process, and 4. to investigate the recoverabiUty and reusabiUty of chromium fromchrom e tan Uquor. After the initial tests, it was fiirther decided to examine the effects of retanning the chrome tanned hides by organic tanning. CHAPTER n BACKGROUND INFORMATION

Structure and Composition of Hides The hide or skin* of each type of animal has its own unique characteristics which are different from those of any other species. Some of the characteristics pertinent to the leather manufacture include thickness, length, width, fiber structure, and grain surface. Within each species of animal, these characteristics vary dependkig on the age and the habitat of the animal. However, there are more things in common to all hides and skins than there are differences. For example, aU fresh hides and skins consist of water, proteins, fats, mineral salts, and similar substances. The proteins, hair, epidermis, proteoglycans, melanine, and fats each have more or less a similar chemical structure in different animals. The basic approximate composition of the hide is shown in Figure 2.1 and a cross-section of the structure of a skin is shown in Figure 2.2. The prominent features from Fig. 2.2 are discussed in the foUowing sections.

Hair Hair is embedded in the skin and has a large bulb-shaped root at the end. The hak is fed through a small blood vessel during its growth. The primary constituent of hair is keratin, a sulfur containing protein.

Epidermis The epidermis is a protective layer made of keratin type ceUs. The ceUs on the outside are constantiy being pushed by the inside ceUs until the outside cells faU off the

^The words hide and skin are used interchangeably. It is, however, understood that hide is used when referring to large animals like cattie, camels, and horses and skin is used to refer to smaU animals like sheep, goats, pigs, and birds. (Sharphouse 1989). Heidemann (1993), however, says that the term hide refers to animals with a body surface of more than one sq. meter and a respective thickness of several miUimeters.

8 Water Protein F«ts Mineral Salts Other Substances 64^0 0.5^ (Pigmenu, etc.) 33«7o 2V« O.S*h

Structural Proteins Ncn-stnictural Proteins

Elastln Collagen Keratin Albnmens, Mudns, yellow fibre this tans protein of Globulins Mucol

Figure 2.1. Approximate Composition of a Hide (Sharphouse 1989). Epidermu Sebaceous Hair Shaft Hair Root Gland

CORIUM

j^f Fat FLESH

Figure 2.2. Structure of an Animal Skin (Sharphouse 1989).

10 skki. Then the inside ceUs take over as die outside ceUs. Thus new growth is always taking place to protect the outer layer of the skin. The kiside ceUs have littie resistance and are destroyed by aUcaUs and especiaUy by sodium sulfide or hydrosulfide (Thorstensen 1993). This is the governing principle in the dehairing process of the skin.

Sebaceous Glands These glands discharge oUs and waxy substances into the hair and onto the surface thereby protecting the hair. These glands are essential to the maintenance of proper body temperatures in warm-blooded animals (Thorstensen 1993).

Sweat Glands These are also known as sudoriferous glands and release sweat and undesirable body wastes through the pores of the skin.

Corium This is the strongest part of the skin. This portion consists of a finely woven collagen fiber structure. In the grain layers, the coUagen fibers are thin and tightiy woven. Near the center of the corium, the fiber structures are coarser, heavier, and denser. This network of coUagen fibers, having a thin grain at the surface and heavy fiber in the corium, gives the skin its leather making properties. The shape and texture of these collagen fibers give leather its properties of utiUty and beauty.

Flesh This is the portion of the skin next to the meat where the fibers approach the horizontal angle of weave and where fatty tissues are present

Tanning Processes There are a number of steps involved in the conversion of skins into leather. However, all these processes can be grouped into three major operations: beamhouse,

11 tanyard, and finishing. The foUowing paragraphs describe each major process and the subprocesses kivolved, aU of which contribute ki one way or another to the quaUty of the final leather material.

Beamhouse Operations These refer to the processes in the tannery between the removal of the hides from storage and their preparation for tannage. These processes are crucial in the overaU making of leather and have to be performed widi care. It is usuaUy said that leather is made in the beamhouse. The beamhouse operation can include the subprocesses of hide preservation, soaking, fleshing,unhairing , deliming, bating, and pickling.

Hide Preservation Once the flesh is removed fromth e animal, the wet hides begin to degrade due to bacterial action. This bacterial degradation results in undesirable odors and, if unchecked, the destruction of hides. The flayed skin is preserved fromdegradatio n by salting and drying. Salting involves the use of salt or brine to preserve the hides. The salt (sodium chloride) is spread out on the flesh side of the hide and the salted hides are piled in stacks. In brining, the hides are placed in a vat or drum containing a strong salt (brine) solution. When the skin is brought in contact with salt or brine, the salt dissolves in the moisture of the skin and penetrates into the skin draining out the moisture. Drying essentiaUy removes the moisture fromth e hide, thereby ceasing the putrefying activity of the bacteria. Once the moisture is replaced, the skins can be preserved for long periods of time. It is usually in the salted or dried form that the tanner receives the hides.

Soaking The purpose of soaking is to clean the surface of the hide and restore moisture to the hides. The restoration is essential because the added moisture acts as a route for chemicals (which are added at later stages) to penetrate the fibrousstructur e of the hide. Soaking is done by placing the hides ki water which may contain some bactericides and

12 detergents. The effluent from a soakmg operation has a high dissolved salt content, some blood, and any dirt present on the animal before k was slaughtered.

Fleshing This process involves the removal of flesh and fatty substances from the skin. Fleshing is usuaUy done at the slaughterhouse and the fleshed hides are shipped to the tannery. However, there may be some residual flesh left on the hide which has to be removed before tanning the hide.

Dehairing The purpose of dehairing processes is to remove the hair and epidermis fromth e skin. The process of dehairing, also known as liming, involves the use of lime as a depUating agent In addition to lime, other reducing agents caUed sharpening agents or sharpeners are added to the lime solution. Some of the sharpening agents include sodium sulfide, arsenic sulfide, sodium hydrosulfide, caustic soda, sodium carbonate, ammonia, amines, and sodium cyanide (Thorstensen 1993). There are two types of dehafring processes: hair-saving and hair-pulping. Hair- bsaving involves the recovery of loosened hair from the skin (Figure 2.3(a)). Hair pulping involves the destruction of hair within the hair folUcle as shown in Figure 2.3(b). The amount of sharpeners used dictates the type of hak removal process. A high concentration of sharpening agents results in hair-pulping, whUe dUute solutions result in hair-saving process. Hair removal can also be accompUshed by the use of enzymes, strong oxidizing mediums, and alkaline reducing systems. These are aU novel processes whose intent is to reduce the poUutional problems caused by the use of lime. However,'according to Thorstensen (1993), the quaUty, economy, and simpUcity aspects of these novel processes could not surpass the lime unhairing system.

13 (a) Hak-Save

(b) Hair-Pulp

Figure 2.3. Hair Removal Processes (Thorstensen 1993)

14 Dehmkig After unhairing the hides, the lime is no longer requfred on the skin. The deliming process removes the Ume on the skin either by washing or by addition of chemicals. The use of chemicals speeds up the process and results in complete removal of lime while washing alone may not be effective in complete removal or in speeding up the process. The chemicals used are usually weak organic acids like lactic or acetic acid, or salts of weak aUcaUs like ammonium chloride or ammonium sulfate (Sharphouse 1989).

Bating Bating is the process performed after deliming in the purification of hides. However, sometimes bating may be unnecessary. This process involves the addition of enzymes for the removal of unwanted components consisting of inter-fibriUary proteins, residual hak and epidermis, pigment and fatty ceUs. This process also helps in loosening the hair roots if present

Pickling The purpose of pickling is to bring the hides into an acid environment and prepare them to accept the tanning materials. The chromium salts used for chromium tanning are not soluble under alkaline conditions and wiU precipitate if added to high pH hides (Leather Facts 1977). In pickling, the hides are treated with salt and acid solutions. The salt is used firstt o prevent the acid swelling of hides. Figure 2.4 depicts the effect of salt in preventing the acid swelling of hides. The pickled hides can also be preserved for long periods of time before tanning.

Tanyard Operations These operations involve the conversion of hides and skins into stable and non- putrescible material which can be fiirther converted into useful commercial products. The processes in the tanyard include tanning, wringing, spUtting, and shaving.

15 NO SH\

o X

I IN

Figure 2.4. Effect of Salt on Acid Swelling (Thorstensen 1993).

16 Tanning The tanning process converts the raw coUagen fibers of the hide into a stable product which wiU not further putrefy. There are a wide variety of tanning agents on the market Some of the tanning processes include vegetable, alum, chrome, oU, aldehyde, and syntiietic tannages. Table 2.1 (Sharphouse 1989) describes tiie different tanmng materials and theh characteristics. The use of a specific tanning agent depends primarily on the properties deskred in the finished leather. The cost of the tanning chemicals and the type of hide also affect the selection of tanning agent Of aU the tanning materials Usted in Table 2.1, chrome tanning is by far the most commonly used method for tanning Ught leathers and shoe upper leathers. The advantages of chrome tanning materials over the other commerciaUy available tanning materials are the high speeds of protein fixation,lo w chemical costs, and exceUent hide preservation.

Wringing The excess moisture in the tanned hide is removed by using a wringer. The wringer works in the same way as a clothes wringer. The removal of moisture is essential for SpUtting the hides. Not aU the moisture is removed from the hide. Only excess moisture is removed to faciUtate proper handling of the hides in the spUtting process.

SpUtting and Shaving These processes involve in the adjustment of the hide thickness which usuaUy vary from hide to hide. The adjustments are made based on the end user and leather manufacturers* requirements.

Finishing Operations These operations prepare the hide for commercial use. The most common processes that are employed m finishing operations are dyekig, fatUquormg, and drying. However, there are other processes employed in finishing; retanning, conditioning, staking, buffing and so on dependkig on the type of commercial end use. Retanning

17 3: -2 u'>:' > c (/3 •a 4> b > CO H OJ 3 > T3 13

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^ g o 2 ex. I 13 4) =9 §1 Ig| - ^ 2 18 knparts properties of other tanmng agents to the hide, while conditioning mtroduces controUed amounts of moisture kito the hide. Stakkig involves the mechanical softening of the leather, whUe buffing smoothens the grain surface of the tanned hide by mechanical sanding.

FatUquoring This process knparts softness and flexibUityt o the leather. In fatUquoring (or lubrication), the fibers are lubricated by die addition of oUs and fats and sometknes emulsifiers. Emulsifiers are a type of chemical which form an emulsion when dispersed in water. During fatUquoring, the oils in the emulsion are absorbed and deposited on the skin fibers.

Drying The primary purpose of drying is to remove moisture. However, at this stage, drying is more than just moisture removal. Drying is one of the most important steps in maintaining leather quaUty. It affects the feel, sofmess, area, and even color of the tanned hide (Sharphouse 1989). Some of the drying techniques employed are: 1. Air Drying ~ in which the skins are hung on hooks or sticks and dried by passage of air around the hides. 2. Toggling ~ in which the leather is stretched out and nailed on screen which is then placed in a dryer having constant temperature and humidity. 3. Pasting - the wet skin is pasted on large sheets of plate glass, to which it adheres and the plates are sent through a long drying tunnel consisting of different zones of controUed temperature and humidity (Thorstensen 1993). 4. Vacuum Drying ~ ki which the length is spread out on a chrome plated poUshed steel surface. Heat is appUed by a bmlt in heat exchanger and the temperature is maintained by a thermostatic control of ckculatkig hot water. This is a new technique and found extensive use in most modem tanning approaches.

19 Chemistry of Chrome Tanning Chrome tanning was discovered ki 1858 by Knapp. The ffrst commercial chrome tanned leatiier was produced m 1884 by Augustus Schultz of New York. The chemisuy of chrome tanmng is complex, since it involves several reactions occurring simultaneously. These reactions are controUed by temperature, pH, and the chemicals used in the process of chrome tanning. These factors greatiy kifluence the quaUty of die final leatiier.

Basicity CommerciaUy avaUable chrome salts have a valency of +3. These salts are soluble in strong acids and usuaUy precipitate as chromium hydroxide or hydrated chromium oxide at pH values above 4. The trivalent chromium attracts the negatively charged hydroxyl (OIT) ions. The term basicity is defined as the percentage of the total primary valences of the chromium atoms present in the solution that are occupied by the hydroxyl groups. Therefore, if the chromium atom contains one hydroxyl group, then the chromium complex is 33 — % basic. If the chromium atom contains two hydroxyl groups, then the

2 complex is 66— % basic and so on. The foUowing reactions (Thorstensen 1993) further clarify the concept of basicity:

[Cr]*^ + OH" <=> (CrOH)*^ approxknate pH: <2; Basicity = 33- %

2 (CrOH)""^ +0H" o [Cr(0H)2]"' approxknate pH: 2-4; Basicity = 66- %

[Cr(0H)2r + OH" «=> Cr(0H)3i approxknate pH: 4-10; Basicity = 100 %

As basicity refers to the association of hydroxyl ions with the chromium, the term acidity refers to the acid portion of the salt The sum of the percentages of the basicity and acidity for a given salt ki solution, by definition, equals 100. The chromium salts used ki the tannkig kidustries usuaUy have basicity values between 33% and 45%.

20 Masking Agents These are the compounds added to change die characteristics of the tanning liquor to improve die tannage characteristics. More specificaUy, masking agents change the chrome tan liquor's abUity to resist precipitation when an alkaU is added to k. This resistance is related to the power of the masking agent to form complexes with the chromium atom. The masking agents are anionic substances like nitrates (NO3"), chlorides (CI"), formates (HCOO"), acetates (CH3COO"), sulfites (SOs^"), oxalates (C2O/"), etc., which can replace die existmg sulfate ion ki the basic chromium sulfate solution. When the masking agents associate widi the chromium atom, diey form non-ionic and anionic complex ions with the chromium, ff the concentration of the masking agent is increased, there wiU be greater penetration of the masking agent into the complex ion and thus a greater proportion of non-ionic and anionic complex wiU be formed. For example, the addition of sodium formate (a commonly used commercial masking agent) to the chrome sulfate Uquor will result in the displacement of the sulfate ion from the complex with the formation of a chromium formate complex, ff the masking agent is strongly held by the chromium complex, some of the complexly bonded hydroxyl ions wiU be replaced by the coordinating anion (O'Flaherty et al. 1958) resulting in the decrease of basicity. The effect of addition of the masking agent is that it allows a more uniform penetration of the chrome tanning agent. The penetration of chromium can be accelerated by the use of a rruld masking agent like sodium formate. The chromium formate complex has great stabUity and less affinity for the hide than the chrome sulfate complex and so the pH of the tan liquor is raised to higher values at the completion of the tannage. Through proper choice of masking agents, die character of the leather can be greatiy manipulated and in some mstances, a higher quahty leather can be obtained more quickly and consistentiy than with unmasked tan hquors (O'Flaherty et al. 1958).

21 Tannkig Mechanism

The hide proteki contains free carboxyl groups (COO") and otiier reactive sites Uke die maskkig agents. These reactive sites can form coordkiate complexes witii chromium salts. It has been estabUshed by researchers tiiat a wide variety of organic carboxyl groups are capable of formkig stable coordkiate complexes widi chromium and tiiatelevatio n of temperature increases tiie tendency of carboxyl groups to coordkiate. The reactions of masking agents and die hide protekis can be explakied by die foUowkig equations:

S04=Cr-0H + HCOO" ^ (HCOO-Cr-OH)* + SO4'" basic chrome formate masking agent sulfate complex

(HCOO-Cr-OH)* + -OOC" ^ HCOO-Cr-OH Hide Protein | OOC" hide protein complex (Tanning)

The coordination of the masking agent with basic chrome sulfate in the first equation above depends on the pH and the nature of the masking agent The order of complex stabiUty is (0*Flaherty et al. 1958): nitrate < chloride < sulfate < sulfite < formate < coUagen < acetate. At this stage, the hide's protein has Uttie reactivity with chromium since its ionization is repressed at low pH values. As the pH of the tanning Uquor is increased, the basicity of chrome complex increases due to the addition of more hydroxyl groups into the complex. The reactivity of the protein is greatiy enhanced with the increase in pH, and the tanning reaction is initiated. At the end of basification (after pH is increased to optimum levels), the basicity is high and the sulfate in the chromium complex may be partiaUy displaced along with the masking agents due to the increased affinity of the hide proteins for the chrome tanning Uquor. The linkage between adjoining chains of proteki may be completed and cross- linking reactions occur as shown in Figure 2.5(a). Also, as the basicity increases,

22 O c «» (a)« o ^\ ,0H OH Q c 0-Cr © cr Cr-O -c-j «> \ / / o Q SO, OH 0 o so.

c // 'a> (b)- o -c . OH OH \ / / c Cr-O-C-I o / © O OH I a H O

(C) ••• -c o 0 c °-\ /\ /-«• -0- I 8 O a O H* O simplified tanning actions: • (i) croxslinUni •* (L; bitsincttioQ—oUtioa ••• (c) oxoUtion

Figure 2.5. Stages in the Cross-Linkage of a Clirome Tannage (Thoretensen 1993).

23 adjommg chromium compounds may become associated witii one anodier du-ough secondary forces of attraction to die OH group (Figure 2.5). Hence, at higher basicities, die complex size kicreases causkig further cross Unkkig. Ultimately, diese reactions result ki complete tannage of tiie skki and ki die production of leatiier.

Industrial Wa.stewater The threat to our ecosystem is closely related to die world economy. Two important factors contribute to envkonmental degradation: the population explosion around the world, and the mtensity of industrial development Both contmue unabated. PoUution exists because the capacity of the envkonment to absorb the wastes has been exceeded (Shen 1995). For example, wastewater is generated whenever industry produces a product With stiff global competition, many industries strive to produce more products and use innovative technologies but fail to consider thek impact on the envkonment The characteristics of an industrial wastewater stream depend to a large extent on the type of products being produced. Therefore, the poUutants in one industrial waste stream wiU be different from those of another industrial waste stream. This can give rise to a multitude of poUutants which must be dealt with. However, industrial poUutants are usuaUy classified into the foUowing broad categories given by Nemerow and Dasgupta (1991). The classes and thek impact on the envkonment are Usted below.

Inorganic Salts These increase the hardness of water. Nitrogen and Phosphorus induce the growth of algae. They deposit scale in water distribution pipelines.

Acids and Alkalis Extreme values of pH (i.e., high concentrations of acids or aUadis) are corrosive, toxic to fish, and aquatic life. Hence, streams are not suitable for swknmkig, fishing, and boating.

24 Organic Matter This class takes up dissolved oxygen in streams makkig life critical for fish. They may result ki unpleasant taste, odors, and septic conditions.

Suspended SoUds The suspended soUds settie to the bottom of stream and consume dissolved oxygen. They can increase the turbidity of water and enhance flooding by reducing stream bed volume.

Floating SoUds and Liquids These include oUs, greases, and other floatable materials. These are toxic to fish and pose a potential fke hazard due to thek ignitabiUty. They retard the growth of aquatic plants by obstructing the passage of Ught and dissolved oxygen through water.

Heated Water This causes thermal poUution. Aids in stratification and affects aquatic life in the water body.

Color and Foam Producing Matter These are two forms of visible poUution. Color can kiterfere widi the transmission of sunUght into the stream, thereby affectkig die process of photosyndiesis.

Toxic chemicals These are toxic to fish and other biota even in low concentrations. Humans may be exposed when tiiey eat fish or plants contamkiated widi tiiesechemicals .

Microorganisms These may be pathogenic to humans.

25 Radioactive materials

The biota of die stream wUl be affected upon uptake of radioactive materials which bioaccumulate ki die body damagkig die Uvkig ceUs The effects may be knmediate or delayed (over generations of human race). In the United States, disposal of wastes is typicaUy onto the land (m die form of landfiUs) or through release kito water bodies. Botii media exist ki dkect contact with humans, thereby posing a threat to the human existence. GeneraUy, the greater threat to the humans is through contaminated water. This is because waste disposal on land is concentrated at landfiUs which are labeled as contaminated sites. On the other hand, wastewater discharged into the water bodies move along the water course transporting the poUutants throughout the watershed. This makes it difficidt to distinguish visuaUy whether a particular stream is pure or poUuted. Hence, there is a greater direat from contaminated wastewater discharged onto water bodies than fromwaste s discharged onto the land.

Industrial Waste Treatment The partial or complete treatment of industrial wastewater can be accompUshed by a single or combination of four classes of treatment physical, chemical, thermal, and biological. These are explained in the foUowing paragraphs.

Physical Methods Physical treatment methods involve the appUcation of physical forces to remove some of the contamkiants. Physical metiiods remove larger particles from die waste so that they do not clog pipelines or treatment beds during secondary treatment Typical physical mediods kiclude screening, mbdng, commkiution, flocculation,evaporation , sedknentation, flotation,an d filtration.Th e physical metiiods by tiiemselvesmos t commonly cannot achieve the desked level of treatment

26 Chemical Methods

As thek name impUes, these treatment mediods use chemicals to remove die poUutants. Some typical chemical treatment methods kiclude precipitation, gas transfer, adsorption, and disinfection. Frequentiy, these mediods can achieve die desked level of treatment, but diey usuaUy produce a hazardous sludge which has to be disposed of even more carefuUy. Hence, a disadvantage of uskig chemical treatment systems is tiiateve n diough die desked level of treatment can be achieved, additional waste may be produced so that one has more than one started with.

Biological Methods Biological treatment methods remove contaminants by utilizing microorganisms. This approach represent the most efficient treatment as long as there are constant flow rates and no toxic substances in the wastes. Typical biological treatment methods include aerobic-anaerobic digestion systems, oxidation ponds, activated sludge systems, rotating biological contactors, and trickling filters.

Thermal Methods These types of treatment processes remove the contaminants by incineration or by exposing the wastes to high temperatures sufficient to break them down. An advantage of this process is the abiUty to recover energy fromth e burned wastes (Edwards 1995). The main disadvantages are that diey are expensive and are highly disliked by the pubUc. Also, thermal treatment is usuaUy the last choice in wastewater treatment

Tannery Effluent Characteristics The tanning mdustry has the reputation for bekig one of the fUduest and vUe smelling of kidustries. Each operation in the tanning process generates certaki wastes. The U. S. EPA has divided the tannkig mdustry into nine different subcategories based on die raw materials and die different operations and processes involved. Table 2.2 hsts die different subcategories of tanneries. Each subcategory has its own processes and

27 Table 2.2. Leather Tanmng and Fkiishkig Industry Subcategory* Subcategory Tide 1 Hak Pulp, Chrome Tan, Retan-Wet Fmish 2 Hak Save, Chrome Tan, Retan-Wet Fkiish 3 Hak Save or Pulp, Non-Chrome Tan, Retan-Wet Fmish 4 Retan-Wet Fkiish (Sides) 5 No Beamhouse 6 Through-The Blue 7 Shearling 8 Pigskin 9 Retan-Wet Fkiish (SpUts) Source: U. S. EPA (1986).

28 operations that vary to some extent from another subcategory. Hence, the wastes emanating from each tannery wiU depend to a great extent on the processes carried out in the tannery, type of raw material used, and upon die type of finished product However, when leather is produced from the raw hide, wastes wiU be generated in die various processes of leather production. The primary wastes from a-tannery include wastewater from various processes, chemicals like bactericides, lime, sodium sulfide, sodium sulfhydrate, ammonium salts, enzymes, and basic chromium sulfate. Other wastes include vegetable tanning extracts, mineral acids, alum, fatUquors, acid dyes, solvent coatings, pigments, and sodium chloride. In addition, dirt, manure, fleshings, grease, residual hak, proteins, oUs, unfixed tan Uquors and chemicals, and leather dust may also contribute to the wastes. The wastes originatmg from each of the major processes are described below.

Soak and Wash The major waste constiments from tiiis operation are BOD (prknarily soluble protekis), suspended solids, and high concentration of dissolved solids (salt). Most of the hides are usually brine-cured or green-salted, so the salt concentrations are high. Typical ranges for BOD and suspended solids are 7 to 22 kg and 8 to 43 kg per 1000 kg of hide, respectively (U. S. EPA 1979).

Dehairing This operation is a major conttibutor to the plant effluent. Since there are two types of dehaking, namely hak-pulp and hak-save, die concenttation of diese wastes vary. For the hak-pulp operation, die spent dehaking Uquors contaki high concentrations of B0D5 (proteinaceous organic matter), sulfides, dissolved soUds, and suspended solids. In the hak-save process, the waste loads are less than diose for die hak-pulp process. However, the water use is much greater for machine removal and the subsequent washing of hak. The BOD from hak-save process is much lower because the proteinaceous hak

29 does not dissolve m die dehakkig solution but is loosened so diat it can later be removed mechanicaUy.

Batkig and Picklkig

Ammonium salts are usuaUy used ki die bating process. This results ki large quantities of ammonium salts and some soluble protekis, suspended soUds, and Ume ki die effluent The primary waste constituents ki die pickle Uquors are acids and salts, whUe BOD, suspended soUds, and nitrogen are found ki low quantities.

Tanning The chrome tanning process employs chromium sulfate or a chrome tanning solution as a tanning agent This results ki a large concentration of trivalent chromium in die effluent. However, the organic content of spent chrome-tan Uquor including BOD and suspended solids is usuaUy low. For non-chrome tan processes, Uke vegetable tan, the main constituents are BOD and color.

Retanning. Coloring, and FatUquoring Retanning employs low concentrations of chemicals. Hence, the wastewater strength is not high and the wastewater does not contribute significantiy to the total waste flow. Coloring and fatUquoring wastes consist of dyes, syntans (synthetic tanning materials), and other specialty chemicals, fatUquor oUs, and some natural oUs from the hides themselves. These wastes are highly colored but contribute relatively smaU quantities of BOD, suspended soUds, and chrome. Effluent from wet finishing operations is high-volume, low-strength wastewater compared to waste streams from the beamhouse and tanyard operations. Recycling of effluent from wet finishing operations are usuaUy not practiced since the effluent is colored.

30 Table 2.3 presents the results of an extensive study by EPA on the waste loads resultkig from different classifications of tanneries. At die tune of diis smdy, only seven subcategories were specified. The last two subcategories were added later.

Tannery Waste Treatment The problem with the effluent from a tannery is that there is a large variation ki the concentration of constituents in the waste streams. This variation makes it difficult to design an effective treatment system for any tannery. There are two approaches used to reduce the poUutants in the effluent They are in-plant control techniques and end-of-pipe treatment techniques.

In-plant Control Techniques These techniques involve the modification of existing processes to reduce the waste flow and the concentration of waste constituents. Also, the recovery and/or reuse of chemicals and other materials used ki the tannery can be practiced to generate some revenue and save costs. Some of the widely used ki-plant control technologies are discussed below.

Stream Segregation Stream segregation is not an ki-plant control technology but it is an knportant step ki die knplementation of ki-plant control techniques. The two most poUuted waste stteams ki a tannery are die beamhouse wastes and die tanyard wastes. Beamhouse wastes are highly aUcaUne and have high organic contents. The tanyard wastes are highly acidic and contam high concentrations of chromium. However, tiiese wastes togedier constitute approxknately 20-30% of die total volume of die tannery effluent The rest,70 - 80% of effluent, kicludes wash water and soak water which are relatively pure. Hence, segregation faciUtates reuse of die relatively pure wash waters and, at die same time, reduces the contamkiated wastewater tiiat must be treated.

31 o O CO rn cn o o o O o CM c CM o ON en m en o oo ON p jM £0 tn O ON o o O CN m ON o ON

CO OC) VO VO cvi CO CM vd vd C7N CM vd CM OO c» «—t O CO CM CO O

VO CN VO ON 00 •a ON CM O o £M JM o ci 4> OO CM 00 CM C c/o VO o VO CO O c CM c «j VO VO «n OS oo H CO oo Csj 31 ON O VO CO ^ " oo o CM* u is VO

CM CO c^ VO •2 g:: vd o 50 ON »—t a g fe ON CM VO CO o CO O O 65 CM CO CM

C3N CM Si oo ON O CO VO U CO o o r—t 8 O s o CM O o c^ VO CM T-H VO 1—t CO o\ ON S CM VO [I] CO CO "—> VO • < CM oo VO O 00 Pu CO CO oo »n CO 00 c>i o o o CO oo 00 CM 00 H CO CO t^ CO o c^ VO 00 VO 00 CM CO "co" CM VO CO ON • • o £0 »n CO VO CI OS O O o OS § CO VO ON CM oo 00 '^ VO 8o -^ CO c^ CM C

.-H CM CO »n VO u o CO * CO

32 Chrome Reduction

Jn the chrome tanning process, it is not possible to attaki 100% uptake of chromium and odier tannkig materials by die hides. Approxknately 70% of appUed chrome is taken up by die hides whUe die remakikig 30% is found ki die effluent (Hauck 1972). Skice chromium is die primary concem, various approaches can be employed to reduce die chromium levels ki die effluent. For kistance, process techniques that result ki a better uptake of chromium can be instaUed or die chrome tan Uquor can be reused for the subsequent cycles of tanning. There are many ways to accompUsh the recovery of chromium. One method involves the settling of the tan Uquor, removing the sludge, and bringing the clarified supernatant to the requked concentration by adding chromium salts (U.S. EPA 1979). Another technique is to precipitate chromium separately, redissolve the precipitate in acid (usuaUy sulfuric acid), and reuse the chrome tanning solution. This technique, however, requkes speciaUzed equipment and handling of the materials (Pierce and Thorstensen 1976). These recycling techniques can result in a substantial savings of chrome tanning materials. However, due to the high capital costs involved, only large tanneries can afford the recovery of chromium. Thus, as the regulations become more and more stringent, it wiU be necessary, at least in the future, to recover chromium fromchrom e tan Uquor.

Water Conservation and Reuse Another technique to minimize wastes is water conservation and reuse within the tannery. This includes use of wash water and rinses for making up chemical solutions, reckculation of non-contact cooling water, reuse of water fromon e process to another, reduction of floats by uskig a hide processor, replacmg rinsing by batch processkig, and so on. Other means of water conservation are achieved by knplementation of water saving practices, fbdng leakkig pipes, and Umitkig some rkiskig operations (U.S. EPA 1979).

33 Recovery of Materials

This applies not only to process chemicals Uke chromium but also to odier substances Uke hak and flesh. After washkig and drykig, hak can be used in die manufacture of carpets, pads, and binder materials. This operation is feasible in hak-save processes only since die hak is not destroyed ki such processes. Hesh from the hides can be recovered, dried, and used m the production of glue and poultry and anknal feed (Mahajan 1985). These techniques may generate a certaki level of revenue that can partially offset the costs.

Other Miscellaneous Techniques Some of these include: 1. Constant monitoring of pipes and equipment to detect leaks and substandard performance. 2. InstaUation of automatic monitoring devices to detect abnormal quantities of certain selected constituents in waste effluents. 3. Substitution of the regular process chemicals with those of low pollution potential. 4. Control (and reduction) of specific waste constituents like lime and ammonia nitrogen.

End-of-Pipe Treatment Techniques The in-plant control techniques simplify the subsequent end-of-pipe treatment systems. End-of-pipe treatment systems are those that actually remove the waste constituents from the effluent to the desked level. These treatment systems include the physical, chemical, and biological treatment mediods employed for industrial waste treatment. The commonly used treatment processes in the tanneries are discussed below.

Screening The purpose of screenkig is to remove substances which damage plant equipment and can potentially clog pumps and sewers. These substances include hak, fleshings, hide trknmmgs, and other large sized particles.

34 EquaUzation

The kitermittent discharges of wastes from different operations ki a tannery result ki a wide fluctuationi n the strengdi and volume of wastes. This fluctuation makes k difficuU to design die downstream prknary and secondary treatment units and poses a great threat to die normal functionkig of die biological treatment plants if effluents are discharged to a PubUcly Owned Treatment Work (POTW). To mmknize diis fluctuation, equaUzation of aUcaUne beamhouse Uquors and acidic tanyard Uquors is necessary. Table 2.4 compares the waste loads fromth e two major waste streams ki the tannery. No removal of waste constituents occur ki the equahzation basin aldiough some oxidation may occur (U.S. EPA 1979). There should be a continuous mixkig of tiie wastes ki tiie equaUzation basin and aerobic conditions should be maintained at aU times. The retention times in the equaUzation baski depend on the schedule of the wastewater generation from various operations. Typical detention times are 24 hours.

Plain Sedimentation Sedimentation or settling is used to remove the non-flocculating discrete particles that are denser than water and floatable low-density materials such as grease and scum. By plain sedimentation, suspended soUds reduction can range from approximately 40 to 90% whUe BODS reduction ranges from 30 to 60%. Most of the suspended material removed is in the form of insoluble lime (U.S. EPA 1979). Sproul et al. (1966) reported an average suspended soUds removal of 22% and a B0D5 removal of 35% using plain sedimentation for cattie hide tannery wastes.

Chemical Coagulation Chemical treatment mediods are employed prknarily to remove kisoluble toxic poUutants Uke chromium. These mediods also result m higher removals of soUds and organic content by flocculation of coUoidal particles or by precipitation of soluble substances. The chemicals that are usuaUy added to coagulate die waste are ferric chloride (FeCb), alumkium sulfate (alum), or anionic polymers. The soUds' content of die

35 Table 2.4 PoUutant Loads for Beamhouse and Tanyard/

Beamhouse load Tanyard/Retan/Wet Finish Load Parameter (in percentage) (in percentage) Flow 40 60 BODS 65 35 COD 56 44 Total suspended SoUds 69 31 OU and Grease 49 51 Total Kjeldhal Nitrogen 46 54 Ammonia 0 100 Chromium 0 100 Source: U.S. EPA (1979).

36 precipitates formed by coagulation widi alumkium and ferric salts are usuaUy low, rangkig from 3% to 7%. The use of anionic or non-ionic polyeletrolytes as a flocculant can result ki a sludge widi about 10% soUds content (Daniels 1993). Polymers are expensive and hence find hmited appUcations when compared to feme chloride and alum. However, pH adjustment to an optimum value can give much better results tiiandi e use of coagulants (BaUey 1970). Anodier kiteresting flocculant was found by Kowalski (1994) to greatiy reduce chromium concentration ki effluents. Kowalski found that after neutraUzation of waste to pH 8.0 and addition of cement (2.5%) as a flocculant, exceUent settikig rates were possible. After filtration at relatively high rates, die filtratecontakie d less dian 0.01 ppm of chromium whUe B0D5 and COD were reduced by 50%.

Chemical Precipitation Trivalent chromium is virtuaUy insoluble at pH levels above 6.0. So, adjustment of pH to optimum level has the greatest influence upon the removal rates. Alkaline chemicals like sodium hydroxide, Ume, sodium carbonate (NazCOa), and ammonium hydroxide (NH4OH) are usuaUy used to precipitate chromium in the chrome tan Uquor. Thus the process of neutralization of the beamhouse and tanyard wastes in the tannery is, in effect, a pH adjustment The mixing of acid and alkaline streams obviates the need to add either as a precipitating agent The lime present in the beamhouse wastes can precipitate the chrome and other substances in the tan Uquor resulting in substantial strength reduction. Sproul et al. (1966) reported a maximum of 90% removal of chromium from chrome tan Uquor by precipitation at a pH of 8.0. For the same waste, the average BOD and suspended soUds removals were 95% and 67%, respectively, at pH 9.0. Arumugam (1976) obtained a 98.2% removal of chromium at pH 6.6 by precipitatkig die chrome tan solution uskig Ume. Bishop (1978) reported an effluent total chromium concentration of 0.01 mg/l at pH 8.5. Kannan and Vijayaraghavan (1992) reported a maxknum chromium removal of 87% at pH 9.6 uskig Ume as a precipitating agent A maxknum removal of 65% was achieved at pH 8.1 when die same waste was precipitated

37 uskig washing soda (NazCOs). The optimum pH for maximum removal depends on die particular tannery waste characteristics.

Secondary Treatment Mediods Accordkig to a survey of leadier tannkig kidustries on poUution control practices, nearly 90% of die tanneries surveyed discharged diek effluents to municipal treatment plants. None of these tanneries dischargkig to POTWs had a secondary treatment system to treat the effluents and 88% of them provided preliminary treatment whUe the remaining 12% did not provide any preUmmary treatment The remakiing 10% of die tanneries discharged dkectiy onto the surface waters and aU the tanneries had some or the other form of secondary treatment Most secondary treatment techniques involve biological treatment systems. For treating chrome tannery wastes, the biological treatment systems include any of several treatment alternatives such as aerobic-anaerobic lagoon systems, activated sludge systems, anaerobic fluidized bed treatment, and trickUng fUters. Kaul et al. (1993) found that coagulation foUowed by anaerobic lagoon and activated sludge treatment resulted in BODS, suspended soUds, and chromium removals of 89%, 93%, and 99.9%, respectively. SimUarly, Hunter and Sproul (1969) concluded from thek activated sludge pUot-plant studies that exceUent chromium removals could be achieved and that a significant chromium content did not have an adverse effect on diek biological systems. As anodier example. Eye and Liu (1971) reported successful treatment of tannery wastes by aerobic- anaerobic lagoon systems.

MisceUaneous Techniques for Waste Reduction In addition to the widely accepted practice of chemical precipitation to remove chromium, numerous studies have been undertaken to mvestigate the recovery of chromium. One such study by Petnischke (1959) (as reported in Hauck 1972) kivestigated die use both ion-exchange reskis and hide scrap to absorb chromium. Kannan and Vijayaraghavan (1992) kivestigated die use of various adsorbents Uke alumina,

38 activated charcoal, flyash, and waste Ugnite coal to remove trivalent chromium from chrome liquor. The results of this study are shown m Table 2.5. Yet anodier technology that has found hmited appUcation for chromium disposal is land appUcation. In tiiis case, die prknary treated effluent is appUed to die soU where die soil's biological processes treat die waste constituents. Parker (1967) reported on die successful use of spray krigation as a means for treating tannery wastes that contakied Uttie or no dissolved chrome salts but contakied a high amount of BOD and soUds. The major disadvantages with land appUcation processes are the avaUabiUty of land and the necessity for extensive green house studies to determine the design parameters. Sulfide removal can be achieved either by ak oxidation, dkect chemical oxidation, or by catalytic ak oxidation. Precipitation of sulfide by the addition of kon salts is yet another way of removing sulfides (U.S. EPA 1986). An altemative technique is the acidification of the sulfide to hydrogen sulfide, coUection of the sulfide in an alkaline bath and finaUy recycling (Thorstensen 1993). Ammonia-nitrogen removal can best be accompUshed by segregating the waste streams and.precipitating nitrogen as sulfate by adding phosphoric acid or ethanol. Reverse osmosis and ion-exchange processes can also be used for ammonia reduction, but thek high costs limit appUcation.

39 Table 2.5 Chromium Removal from Chrome Liquor by Adsorption' Optimum removal pH at optimum Dosage of Adsorbent percentage removal adsorbent, gm/l Alumina 37.71 4.3 11.0 Activated Charcoal 62.48 4.5 11.0 Flyash 37.14 4.0 11.0 Waste Ugnite coal 22.49 3.8 40.0 "Source: Modified from Kannan and Vijayaraghavan (1992).

40 CHAPTER m EXPERIMENTAL APPROACH

This research started with a review of die avaUable Uteramre on tanning processes and kiformation on emu skins. A considerable amount of kiformation was avaUable regardkig the tannkig process ki general and especiaUy on cattle hide tannkig. However, Uttie kiformation was avaUable on die tannkig of emu skkis. hi fact, the tannkig of emu (ratite) skins has not been popular ki the United States nor m most other countries of die world. Hence, k was decided to use the traditional, weU-known, chrome tannkig process ki a series of experiments to tan the emu skkis. InitiaUy, one emu skki would be tanned. Then if die process was successful, the remainkig skkis would be tanned using the same process.

Hide Preservation The hides were received in plastic bags and were in a salted state. On arrival the hides were weighed and then quickly frozen at -10°C until they could be used.

Hide Preparation The skins were taken from the deep freezer and thawed. The hides were reportedly defeathered,^ but there were numerous feathers left on the skin around the thighs and the back of the neck. Also, the hides were relatively free of blood and knife cuts, but there were some spots on the skin where the hide was not completely fleshed. The remaining flesh was removed with a knife and some feathers were removed by hand. Neither of these processes were easy tasks.

^The hak on the emu will be referred to as feathers sometimes. This is because the hak on emu skin is lengthier than is usually observed in bovine skins and the size of hak foUicle in emu is too big to be called hak. Hence, the word 'feather' wiU be used mterchangeably with the word 'hak' when referring to emus.

41 The average weight of a skigle raw hide was 3.4 lb. The skki was tiikiwid i a variable overaU tiiickness. The skkis were thmnest m die neck and upper torso region.The diickest part of die emu skki was ki tiie tiiigh and rump regions. The problem widi die varymg thickness was diat k made k difficuU for die skin to be passed between die roUs of a wringer (to remove moisture). More knportantiy, however, tiie leatiier produced wUl not have a good market value. Proper fleshing of die skki would result ki a more uniform diickness making it easier to process die skkis.

Tanning Process The hides were tanned according to the tanning procedure described in Fig. 3.1. This recipe, typicaUy used to tan bovkie hides, was provided by die Tandy Leadier Corporation. Since the thickness of emu hides was far less than the bovine hides, the amount of chemicals used may have been excessive. In the first tanning attempt during March 1995, aU the steps were performed in plastic containers. AU the mixing was done manuaUy with a wooden stick. After the first hide was successfuUy tanned, four more hides were tanned using the same procedure in April 1995. Later, two more hides were tanned in May 1995. These two hides were tanned in a hide processor kistead of the plastic containers. The recipe used for the hides tanned m die hide processor was die same as that shown in Fig. 3.1. However, for this experiment, sodium hydroxide was used as the depUating agent instead of lime. This was because the dehairing solution (lime) provided ki the recipe did not remove aU the feathers in the skin. Also, the amount of sodium sulfide added was doubled to make sure diat aU die feadiers were removed. Subsequent tensUe tests revealed tiiat diese changes did not affect die quaUty of leadier produced ki terms of tensUe strength. The hide processor used was a commercial plastic drum 4-ft in diameter and 2-ft long witii a volume of about 188 gaUons. The drum has a Ud du-ough which water, chemicals, and die skkis can be fed. The drum has a drive so diat k can rotate at a specified speed (rpm). A plastic pipe, about 1.5 ki. outside diameter, is connected from

42 Basis: lib. of skin

Time Requirements Operation Water and Chemicals

Skin Preparation: solvent or soap water (hours) Degreasing, blood f removal, trimming, etc.

0.362 gal. water \l/ 20 g hydrated lime (3 days) Defeathering 1.5 g sodium sulfide f

(minutes) Washing (twice) 0.25 gal. each

(Iday) 0.25 gal. water Deliming 17.5 g Boric Acid

(minutes) Washing 0.25 gal. water

0.2 gal. water 55 g Non-iodized Salt 50 g Alum (3 days) 0.05 gal. hot water 25 g Chromium Sulfate

0.025 gal. water (Iday) Neutralizing | 25 g sodium formate

(minutes) Washing (twice) 0.25 gal. hot water (45C)

\l/ 0.44 gal hot water (45C) (minutes) Fat Liquoring | 0.8 oz (23 g) tanning oil

(day[s]) Drying Operations

Figure 3.1. Leather Tannery Process-Chrome Tanning.

43 the outside of the drum to a heat exchanger witii a diermostated reservok. This enables the operator to have some conttol over the temperamre uiside die hide processor. Also, there is a tap in the thermostat box that could be used to monitor the pH or coUect water samples during die tannkig process. The rotation of tiie drum is by a 2 HP electric motor. The advantage of using the hide processor or plastic container is highUghted by a reduction in labor. There are savings in water, heat, and chemical usage, too. Also, aU the hides in the processor are more uniformly processed. Hence, the quaUty of the leather produced wiU be superior due to better mixing of the tanning chemicals in the rotating hide processor. Other steps in the process, like soaking, liming, deliming, and pickling can also be performed in the hide processor. Another set of skins were tanned using organic tanning substances. The procedure was simUar to that shown in Fig. 3.1 except that kistead of chrome tanning agents, organic tanning substances were used. The organic tanning procedure is shown in Fig 3.2. Two organic tanning agents were used namely Quebracho and Wattie. These substances were provided by the Herman Oak Leadier Company, St Louis, Missouri. It was decided during this set of tanning experknents diat die previously chrome tanned skkis wUl be retanned with die two organic tanning substances. The amount of organic tanning materials used per pound of skin (ChurchiU 1983) are:

1 lb. of hide: 5 oz (= 142 grams) of organic tannkig agent 1 oz (= 28 grams) of salt 1.5 gal. water

Widi tiiese organic tannkis, die hides were requked to stand ki die vessel for 18 days. Every day, die hides were agitated manuaUy and were tested to find out if diey were tanned. The test kivolved boUkig a smaU sample of die skki m water. If die sample shrinks, tamikig is not complete. After 18 days, k was decided tiiatdi e hides were tanned. The hides were subjected to fadiquoring and dien dried uskig a house fan.

44 Basis: 1 lb. of skin

Time Requirements Operation Water and Chemicals

Skin Preparation: solvent or soap water (hours) Degreasing, blood <- J removal, trimming, etc.

0.362 gal. water \1/ 20 g hydrated lime (3 days) Defeathering 1.5 g sodium sulfide f

(minutes) Washing (twice) 0.25 gal. each

0.25 gal. water (1 day) Deliming 17.5 g Boric Acid ( f

(minutes) Washing 0.25 gal. water

5 oz (142 g) Wattle/Quebracho \k 1 oz (28.35 g) Salt (NaCl) (18 days) Tanning 1 gal. water f

N1/ 0.025 gal. water (1 day) Neutralizing 25 g sodium formate f

(minutes) Washing (twice) 0.25 gal. hot water (45C)

\1/ 0.44 gal hot water (45C) (minutes) Fat Liquoring 0.8 oz (23 g) tanning oil f f (day[s]) Drying Operations

Figure 3.2. Leather Tannery Process-Organic Tanning.

45

—•^'^ • ujnrr« Mechanical Testing The tanned hides were weighed and measured for surface area, hi order to estabUsh tensUe strengdi, die leadier tamied from the three sets of raw emu hides were cut kito test coupons. The dknensions of die samples were the same as diose specified ki ASTM (1990). The tensUe tests were performed on an Instron Model 1122. From diese tests, die tensUe breakkig strengdi and die elongation at faUure were calculated. The settings on the Instron were:

Cross-head Speed = 0.5 ki./mui. Chart speed = 1 ki./mm. FuU Scale Load = 50 lb.

Wastewater Analysis The beamhouse wastes were separated from the tanyard wastes skice one objective of this study was the treatabiUty and recovery of chromium from die spent tannkig Uquor by chemical precipitation. The spent tanning Uquor appeared dark green ki color and contained some feathers which had not been completely removed during the dehairing process. The chrome rich wastewater was transferred to another plastic contakier for storage. Prior to this phase of the tests, aU the wastewater samples were refrigerated at 4°C to minimize potential microbial activity. AUquots of the wastewater were analyzed for potential poUution characteristics. These tests included quantification of pH, total soUds (TS), total suspended soUds (TSS), total dissolved soUds (TDS), chemical oxygen demand (COD), turbidity, and chromium concentration level. The 5-day biochemical oxygen demand (BOD) is typicaUy employed to test for oxygen demand. However, in this case, die quicker COD level was used as an indicator of oxygen demand instead of BOD. Also, the high chromium concentrations in this wastewater are toxic to the microorganisms. The dUutions requked for the BOD determinations, therefore, could make BOD an incorrect indicator of oxygen demand.

46 Chemical Precipitation Literature citations on the use of chemical precipitating agents Uke Ume, caustic soda, and soda ash to precipitate chromium as kisoluble chromic hydroxide, Cr(OH)3, were reviewed. For diis research, Ikne was used as die precipitating agent The use of lime was investigated skice die possibUity existed for using the beamhouse wastewater, containing high concentrations of Ume, as a precipitating agent If use of beamhouse wastewater was positive, then two of the more significant waste streams in the tannery, the beamhouse and tanyard wastes, might be reduced to less serious problems. The experimental treatment procedure involved the addition of different Ume solutions of known concentration to 500 ml. of raw, chrome-laden wastewater. The lime was added untU a specific pH was reached. The sample of wastewater was flash mixed for about 30 seconds and then transferred to a 500 ml graduated cylinder where it was aUowed to settie. The waste was aUowed to settie for 12 hours and the supematant was then decanted from the settied sludge. The supematant was analyzed for chromium levels, moisture fraction,an d pH using consistent Standard Methods (1992).

47

'—*'"'•*•• "•• —-• — CHAPTER TV RESULTS AND DISCUSSION

Qeneral Appearance of Tanned Emu I^.athp.r The chrome tanned emu skkis had kidications of feadier foUicles on die surface. The dknpled surface appearance produced by die dislodged feadiers of die ratite has been a cultivated fashion quaUty of tanned ostrich skkis used for shoes and wearing apparel (Tock and Kotia 1995).

The color of the tanned skkis was bluish gray which can be attributed to die chrome tannkig agent. The diicker parts of die skki had a more pronounced blue color. Calculation of the chrome concentration ki die aqueous phase before and after tanning kidicated an uptake of chrome by the hide of more dian 90%. The skkis tanned widi organic tanning agents resulted ki different shades of yeUows, reds, and browns based on the tannkig agent used. The chrome tanned skkis when retanned with organic tanning agents produced the colors of the organic tannages. As mentioned earUer, none of the chrome tanned and organic tanned skin have been dyed to impart artificial colors to the leather.

Thickness Variations The emu skin was found to vary in thickness. Hence the skin was schematicaUy divided into 6 different locations A, B, C, D, E, and F. These were arbitrary divisions and the puipose was to compare the thickness and tensUe properties as a function of location. Figure 4.1 shows the general shape, the six sections, and the averaged thickness values for one of the taimed emu skins.

Area and Weight The mean area of the tanned skins was 5.5 ft^. The advertised average area was 7.0 ft^ (Totes'n Things 1995). This difference may be due to die non-stretchkig of die

48 Figure 4.1. General Shape and Thickness (in.) of u Chrome Tanned Emu Skin

49

•Tiaafci^iii • •! I ^1 TensUe Propp.rries The breakkig tensUe strengdi tests and elongation at faUure were performed on an Listron Universal Testing Machkie. The test coupons were taken fromdifferen t locations of the tanned emu skki. Also coupons havkig different orientation angles were used to test die tensUe properties. The results of tiiese tests performed on different leadiers is shown in Table 4.1

Based on the data ki Table 4.1, k can be seen diat die organic tannages produced sUghtiy higher tensUe strengtii leadier dian did die chrome tannage. However, die elongation at faUure for vegetable tanned leadier was far less dian diat for chrome tanned leadier. Moreover, the retanned leathers produced much higher tensUe strength whUe reducing the total elongation. The representative value of tensUe sttess for bovkie hides (heavy leather) is about 2800 psi whUe the maximum elongation is about 35% for the same type of leather (Sharphouse 1989). The tensUe strength and the elongation at faUure for the emu leather varied over a wide range. This can be attributed to two factors. One is the anisotropy produced by grain dkection in the leather, and the other factor is the varying thickness of the leather over short distances. The strength of emu leather is relatively weak compared to bovine hides. This property makes emu leather usable only for hght weight or thin leather goods. However, the presence of pores makes the emu leather more appealing to the consumers than the plain bovine hides.

Wa.ste Characteristics The raw waste characteristics of the spent chrome tan Uquor fromem u tanning are shown ki Table 4.2. The color of the wastewater was bluish green and die waste was very turbid. As expected, die wastewater was acidic widi high chromium concentration levels. The soUds concentration was high widi most of this occurring as dissolved soUds. The dissolved soUds ki die waste may be due to die alum, salt, sodium formate, and chromium sulfate which were added durkig die pickUng and tannkig processes.

50 Table 4.1. TensUe Properties of Emu Leather. Average Breaking Avg. Elongation Type of Leather Strength (psi) Range at FaUure (%) Chrome Tan 1400 857 -1981 52% Wattie Tan 1250 882 -1524 28% Quebracho Tan 1670 614 - 3632 33% Chrome Tan - Wattie Retan 1850 1467 - 2656 38% Chrome Tan - Quebracho Retan 1820 1089 - 2428 47%

51 Table 4.2. Characteristics of Spent Chrome Tan Liquor. Parameter Value (mg/L)* pH 3.9 Total SoUds 81580 Total suspended soUds 1383 Chemical Oxygen Demand (COD) 6760 Turbidity 72FTU^ Chromium 2720 Except for pH ^Formazin Turbidity Units

52

iriinnniiii '^-'~»*~ leather during the drykig operation. The average weight of a tanned emu skki (excludkig die legs) was estimated to be 0.62 lb.

Waste Treatment The percent COD removed by chemical precipitation (pH adjustment) is shown ki Figure 4.2. The maximum removal was 39% widi a fkial concentration of 4160 mg/L. SknUarly, only a Umited fraction of suspended soUds were removed. The maxknum removal of suspended soUds was 57%, with die resulting supematant concentration at 595 mg/L. This was obtained at a pH of 8.5 as shown ki Figure 4.3. The total soUds were reduced by 38.5% at a pH of 8.5 (Figure 4.4). Thus, die supematant stiU contakied a high concentration of dissolved soUds (= 5%) which may pose a threat to receiving streams. Figure 4.5 depicts the chromium removal as function of different pH values. The peak removal of 99.9% occurred at a pH of 8.5. Precipitation at pH 8.5 yielded a chrome concentration of 1.8 mg/L. Significant removals of aU the contaminants appeared to occur at a pH of 8.5. Table 4.3 gives a relative comparison of the raw waste characteristics and the treated waste. As seen in Table 4.3, there was a relatively smaU reduction of the COD level. Also, the concentration of dissolved soUds is stiU too high. This may be due to the presence of the soluble salts like sodium formate and sodium chloride added during the course of the tanning process. One way of removing the dissolved substances is by the use of evaporation ponds where the moisture in the waste wiU be evaporated whUe the dissolved salts remaki at die bottom of ponds. These nuxed dissolved soUds wUl then have to be landfiUed or disposed of as hazardous waste. Anodier mediod to remove die dissolved soUds may be die use of odier precipitating and flocculatingagent s (odier dian Ume) which wUl form kisoluble precipitates widi die dissolved substances. Even tiioughdi e buUc concentrations of aU tiie parameters of concem were identified before and after die treatment, it is stiU not known which elements (and diek salts) are actuaUy ki die supematant and m die sludge, ff die identity of diese elements were known, k may be possible to modify or change the treatment procedure so diat aU

53 100

T3 > o B

O U •^* c u

pH

Figure 4.2. COD Removal by pH Adjustment

54 100

^

03 > O B

*© c^ •o a> B Qi Ck 9 CO

Figure 4.3. Suspended SoUds Removal by pH Adjustment

55 ^

OS > o B P^

o H

pH

Figure 4.4. Total Solids Removal by pH Adjustment

56

iiiU .>.>rn«>rrT- diM 100

•a o B v B a B o u a

pH

Figure 4.5. Chromium Removal by pH Adjustment

57 Table 4.3. Comparison of Raw and Treated Chrome Tan Waste. PoUutional Concentration in Concentration after Parameter Raw Waste (mg/l) Precipitation to pH 8.5 (mg/l) % Reduction Total SoUds 81580 56896 35.6 Suspended SoUds 1383 595 57.0 COD 6760 4160 38.5 Chromium 2720 1.8 99.9 Turbidity 72FTU 6.0 FTU 91.7

58

..t-^^.... ^MQ»*.^r the elements of concem can be taken care of In order to obtain diis type of kiformation, dried solid samples of the supematant and sludge produced by precipitation at pH 8.5 were analyzed by electron diffraction X-ray analysis (EDXA). Figure 4.6 gives die EDXA results for a single mn of die supematant whUe Figure 4.7 gives die EDXA resultsfo r a skigle mn of die correspondkig sludge sample. There were ten mns performed on each sample and die results of die ten mns were consistent with diose shown ki Figures 4.6 and 4.7.

From Figures 4.6 and 4.7, it can be kiferred diat die mam contributors of dissolved soUds ki the supematant are the sodium salts. The calcium salts may also be partiaUy responsible for the high soUds concentration ki die supematant. Surprismgly, diere is no Grace of aluminum ki the supematant indicating a complete precipitation of the aluminum salts due to the addition of Ume. Also, die supematant contakied no chromium at all in all the EDXA mns. However, other lab tests indicated a low chromium concentration of 1.8 mg/L for the same waste sample. The effluent discharge requkements for chromium in the effluent from Subcategory 1 and Subcategory 2 tanning industries are shown in Table 4.4. From Figure 3.1, it can be inferred that for each pound (0.454 kg) of emu skin, about 4.5 gal. (17 Uters) of water (including the soak water which contributes 50% of the total volume) were used. The concentration of chromium at pH 8.5, in the treated effluent, was 1.8 mg/L. This represents 30.6 mg per kg of raw hide processed. This is equivalent to 0.0306 kg per 1000 kg of raw hides processed. This value is far less than the effluent discharge limitation requkements. SimUarly, for discharging partiaUy treated effluent to a POTW, die regulatory requkement is 8 mg/L. This is weU above die 1.8 mg/L achieved widi die chemical treatment From these observations, k can be concluded that chromium levels ki die effluent can be reduced to weU below discharge requkements by pH adjustment alone. However, diere are odier waste constituents Uke suspended soUds and dissolved soUds whose levels ki die treated effluents exceed die discharge requkements. Some tests were also performed to estimate tiie organic content ki die vegetable tan Uquors. As expected, die vegetable tan Uquors gave very high oxygen demands. The

59 POSSIBLE IDENTIFICATION NA KA CL KA S KA OR MO LA? OR TL MA 0 KA CA KA KB C KA K KA OR IN LA?

PEAK LISTING ENERGY AREA EL. AND LINE 1 0.223 5258 C KA 2 0.520 35892 0 KA 3 1.037 96022 NA KA 4 2.303 78848 S KA OR MO LA' 5 2.623 82445 CL KA 6 3.310 1847 K KA OR IN LA' 7 3.686. 9580 CA KA 8 4.022 755 CA KB

E M Centeh TTUHSC Lubbock, TX HED 04-0CT-95 08i22 Cuhfiohi 0.e00ReV > 0

) I I ! :

rni "^Ti I 1 I I I I \t "B—T Ty-rn-rr. . .". r-r-.--:-rT^TTT . . 1 J ! . 1 . . . 1 !•»>d 0.000 VFS = 8192 10.240

Figure 4.6. Qualitative Elcmcnl Identification: Supernatant

60

^>" •*"***-—" rOSSIDLE IDENTIFICATION CA KA KB 5« ESCAPE PEAK AL KA OR BR LA? S KA OR MO LA-? OR TL MA 0 I:A CR »:A »;B OR PM LA LB MA NA I'.A OR PM LA LB MA CL KA FE KA

PEAK LISTING . ENERGY AREA EL. AND LINE 1 0.520 26758 0 KA •:> 1 .037 15704 NA KA 3 1 .485 57620 AL KA OR BR LA? 4 1 .959 697 CA SI-ESCAPE cr 2.306 42950 S KA OR MQ LA? 6 2.631 3661 CL KA 7 3.688 119100 CA KA 8 4.022 12603 CA KB 9 5.405 26633 CR KA 10 5.933 3524 CR KB 11 6.400 nil FE KA

E M Center TTUHSC LubbocK, TX HED 04-OCT-95 07«29 Cursor: 0.000KeV » 0

0.000 VFS «= 8192 10.240

Figure 4.7. Qualitative Element Identification: Sludge

61

-::ve»^-%y :..-iH Sil Table 4.4. Effluent Discharge Lknitations for Chromium* BPT', BCT^, BAT^ NSPS^ Standards PSNS^ Standards Standards (kg/kkg) (kg/kkg) (mg/L) Subcategory maximum for monthly average/maximum daUy 1 (Hak pulp Chrome 0.09/0.24 0.06/0.16 8/12 Tan Retan -Wet Fkiish)

2 (Hak save Chrome Tan 0.08/0.21 0.06/0.18 8/12 Retan-Wet Fmish) Source: Federal Register (1993). *Best Practicable Control Technology Currendy AvaUable. ^Best Conventional PoUutant Control Technology. ^Best AvaUable Technology EconomicaUy Achievable. '^New Source Performance Standards. ^Pretreatment Standards for New Sources.

62

_ • -.^.o- -.'•<..iij^wreyT;a~.;. COD of raw Quebracho tan Uquor and raw Wattie tan Uquor were 18,775 mg/L and 22,500 mg/L respectively whUe the raw chrome tan Uquor had a chemical oxygen demand of 6760 mg/L. However, the vegetable tan Uquors do not contain any toxic substances and the main concem for treatment of vegetable tan Uquors is usuaUy the high organic content

63

•Yi-mymr-ntasnr •n CHAPTER V CONCLUSIONS AND RECOMMENDATIONS

A total of ten emu skkis were successftdly tamied uskig standard chrome tannkig and namral organic tannkig procedures. THis kidicated diat die emu skkis can be tanned readUy by any of die avaUable tannkig recipes ki die market The color of die leadier produced was based on the type of tamikig agents used. However, die process of dyekig is usuaUy used to impart a desked color to die leadier. For significantiy shorter tamikig times and more leadier elasticity, chrome tamikig should be used. For greater tensUe strengtii and reduced elongation at faUure, die organic tamikig recipes should be used (Tock and Kotia 1995). However, die leadier widi die maxknum strengdi was produced by retanning die chrome tanned skkis widi die vegetable tannkis. The surface area of die emu skkis was determkied to be nearly 25% of die surface area of a bovkie hide. Also, die emu leadier is one-fifdi die average diickness of bovkie leather. Due to dus relatively smaU area and diickness, die leadier produced fromem u skkis has found only Umited appUcation. In general, emu leadier is used ki die manufacture of luxury purses, tote bags, and wearing apparel. Moreover, die presence of smaU pores ki die emu leadier left by die removal of feadiers make it a fashion item and may eventuaUy find greater customer appeal. In odier related tests performed as part of diis research, it was observed that die emu skkis were nearly as permeable as tightiy woven textUe fabrics. This knpUes diat unlike die bovkie leadier, emu leadier aUows relatively free flow of ak and vapors (Tock and Kotia 1996). This property suggests that emu leather can be used as a safety akbag m luxury automobUes. However, many other tests have to be performed before completely installing the emu akbags. Thus, the first two objectives of tanning the emus and the testing of the leathers produced were accompUshed. The wastewater which originated from the chrome tanning process had high concentrations of chromium and soUds. It also exhibited a high oxygen demand and acidity. After a hterature review of tanning waste treatment, the use of lime to remove

64 chromium was implemented. The use of Ume resultedk i a chromium removal of 99.9% widi a final concentration of 1.8 mg^.. However, the removal of odier parameters was not as encouraging. Only 39% of COD and 57% of suspended soUds were removed widi final concentrations of 4160 mgA. and 595 mgA., respectively, which are far too high to be disposed of kito surface waters or municipal treatment systems. From the results, k was concluded that chemical precipitation foUowed by settikig should reduce chromium levels to below die regulatory discharge requkements of New Source Performance Standards (NSPS) and Pretreatment Standards for New Sources (PSNS). However, diere are other poUutional parameters Uke suspended soUds, dissolved solids, and COD which must also be treated. One approach to reduce diese levels might be to set up evaporation ponds for the effluent from the primary settiing tank. The use of evaporation ponds is especially useful ki semi-arid areas where the potential evapotranspkation is very high. With evaporation ponds, die water can be evaporated while the dry sohds are retakied. These solids then have to be landfiUed. The chromium in the precipitated sludge exists ki the hydroxide form. In order to recover chromium, the sludge should fu-st be soUdified. SoUdification can be brought about by fUtration and/or by centrifugkig. The concentrated sludge is then Seated with sulfuric acid to obtain a soluble chrome, tan liquor. However, the basicity of the tan liquor may have to be adjusted using soda ash. This approach of using precipitation and reuse of chrome tan liquor was reported by Ammugam (1979) and Santiago et al. (1993). There are, however, other methods of recovering chromium and there also different forms (blue- green pigment and green pigment) in which chromium can be recovered (Santiago et al. 1993).

Suggestions for Further Studies The best way to avoid problems widi chromium is to use chrome-free tanning agents to produce leadier. This suggests that research dkected at developing new tanning agents should be undertaken. The high dissolved solids content ki the tannery can be reduced greatiy by replacing sodium chloride. There are some current studies on die use

65 of potash (potassium chloride) kistead of sodium chloride. The advantage of uskig potash is diat it can be used as a fertiUzer unUke the common salts which must be landfiUed. Also die use of sodium chloride as a hide preservative contributes greatiy to die dissolved soUds ki die effluent. The use of electron beam kradiation as a hide preservative might be kivestigated. Even tiiough diis technology may sound expensive, die savkigs m chemicals and poUution on a large scale could make such suidies viable (Leadier 1994). An interesting aspect involving the use of lime to precipitate chromium is that instead of lime, the beamhouse wastewater which contains high concentrations of lime might be added to the tan Uquor to bring about the precipitation. However, the amount of lime wastes (beamhouse wastes) requked for precipitation would have to be investigated. Santiago et al. (1993) used two parts of beamhouse Uquor for one part of tan Uquor to precipitate chromium and achieved exceUent chromium results. Due to the different beamhouse techniques employed in the industry, the composition of the beamhouse Uquor varies from one tannery to another. Hence, the ratio of beamhouse wastes to tanyard wastes would need to be estabUshed for the particular tannery of interest The next step is the recovery of chromium from die sludge. Studies should be undertaken on the amount and normaUty of sulfuric acid requked to redissolve the chromium hydroxide m die sludge. Also, k should be verified whedier die recovered chromium is comparable to die commercial chrome sulfate. The recovered chrome solution is usuaUy used as tan Uquor. Any changes ki properties and quaUty of leadier produced due to die use of recovered chrome should be documented. Since Ume precipitation could not remove aU die poUutants of concem, odier studies should be undertaken diat mvestigate die use of odier precipitating agents. During our experiments, tiie waste was not flocculated after addkig die precipitating agent This might be the reason for large volumes of sludge and very low removals of suspended soUds and COD. Therefore, studies on die effect of flocculation on die settikig properties of the waste need to be carried out If recovery and reuse of chromium is of primary unportance, die use of aUcali precipitating agents that produce a highly concentrated sludge is essential. An article (no

66 audior) in die magazkie World Leather (1994) suggests die use of magnesium hydroxide to produce a concentrated sludge. Research in this dkection may yield answers that would help pave the way for the economic recovery of chromium. And finaUy,tannerie s that are seriously contemplating locations in the semi-arid regions can investigate the use of land appUcation systems. There is a substantial difference ki economies of land treatment compared to the conventional treatment (Overcash and Pal 1979). Moreover, the operating costs for land treatment systems are much lower than the conventional treatment systems and land treatment systems for industrial wastes get considerable economic incentives.

67

"•»" '^^^^'^i'.mSSlt-'-' REFERENCES

^"^Si'nf? l^^ffr^^^^I^iASTM). "Standard Test Methods for TensUe Strength of Uather." ASTM:D2209-90,1990.

^Z^w: y' ^^^TJ-^V^ ^^^^^^^^^ ^°"^ ^P^'^^ C^°"^^ Tan Liquor by Chemical Precipitation, kidian Jour, of Environ R^.lth vl8, nl, p47-57, 1976.

BaUey,D. A. "Tamieiy Effluents and Thek Treatment-Conclusion." Effluent and W«fpr Treatment Jnnmal, p330-339, June 1970. ~

Bishop, P. L. "Physicochemical Pretreatment of Wastes from a Secondary Tannery." Proc. 33rd Industrial Waste Conference, Purdue University, May 1978.

ChurchiU, J. The Complete Book of Tf.nning Skins and Fnrs; Stackpole Books Harrisburg, PA, 1983.

Daniels, R. "Polyelectrolytes-Thek Application to Tannery Sludges." Worid Leather: Tanning and the Environmenf v6, n4, p36-40, August 1993.

Dickens, M. "Raiskig Emu is a FamUy Affak for Carrasco Clan." The Tulia Herald v87, n24, June 15, 1995.

Edwards, J. D. Industrial Wastewater Treatment-A Guide book. CRC Press, Boca Raton, FL, 1995.

Eye, J. D. and Liu, L. "Treatment of Wastes from a Sole Leatiier Tannery." Journal of Water PoUution Control Federation. y43, nil, p2291-2303, November 1971.

Federal Register. 40, Part 425, 1993. Hauck, R. A. "Report on Methods of Chromium Recovery and Reuse from Spent Chrome Tan Liquor." The Joumal of American Leather Chemists Association. vl7, p422-430, 1972.

Heidemann, E. Fundamentals of Leather Manufacturing. Edward Roether KG Publishers, Dermstadt, Germany, 1993.

Hunter, R. E. and Sproul, O. J. "Cattieskin Tannery Waste Treatment in a Completely Mixed Activated Sludge PUot-Plant." Joumal of Water PoUution Control Federation. v41, nlO, pl716-1725, October 1969.

Jefferey, J. S. "Emu Production B-5048." Texas Agriculmral Extension Service. Texas A&M University, December, 1993. 68 Kannan, N. and Vijayaraghavan, A. "Studies on Removal by Adsorption and Recovery of Chromium from Chrome Liquor (Tamiery Effluent)." hidian Joumal of Fnvkonment.l Protection, vl2, nl, p46-49, January 1992.

Kaul, S. N., Mukherjee, P. K., SUiorwala, T. A., KuUcami, H., and Nandy, T "Performance Evaluation of Full Scale Wastewater Treatment FaciUty for Fmished Leadier hidustry." Joumal of Envkonmental Science and Health v28, n6, pl277 - 1286, 1993. ^

Kowalski, Z. "Treatment of Chromic Tannery Wastes." Joumal of Hazardous Materials. v37,pl37-141, 1994.

Leather. "Solutions Through Research." pi 11-112, September 1994.

Leadier Facts, New England Tanner's Club, Peabody, MA, 1977.

Mahajan, S. P. Pollution Control in Process Industries. Tata McGraw-HUl PubUshkig Company Ltd., New Delhi, Lidia, 1985.

Maistrenko, L "Growkig Emu Population Possible Food Source." The University Daily. Texas Tech University, November, 1995.

Nemerow, N. L. and Dasgupta, A. Industrial and Hazardous Waste Treatment. Van Nostrand Reinhold, New York, 1991.

O'Flaherty, F., Roddy, W. T., and LoUar, R. M. (edited). The Chemistry and Technology of Leather: Volume 2-Types of Tannages. Reinhold Pubhshing Corporation, New York, 1958.

Overcash, M. R. and Pal, D. Design of Land Treatment Systems for Industrial Wastes- Theory and Practice. Ann Arbor Science, Michigan, 1979.

Petruschke, R. "A study of Chromium Recovery fromSpen t Chrome Tanning Liquor." MS Thesis, University of Ckickinati, 1959 (as reported m Hauck 1972).

Pierce, R and Thorstensen, T. C. "The RecycUng of Chrome Tannkig Liquors." Ihe_ Joumal of American Leather Chemists Association. v21, pl61-168, April 1976.

Santiago, C. M., Isaac, D. B., Anglo, P. G., Garcia, B. M., Silverio, C. M., Eaguerra, R.L., RodiUo, F. C, and Bigol, M. B. "Chromium from Leather Tanning Effluent." PhUi'ppkie Joumal of Science. vl22, nl, p41-60, January 1993.

Sharphouse, J. H. 1 rather Techpinian\ Handbook. Leather Producer's Association, 1989. 69 Shen, T. T. Industrial Pollution Prevention. Springier-Verlag PubUshers, Berlm 1995.

Sproul, O. J., Atkkis Jr P. F., and Woodard, F. E. "Investigations on Physical and Chemical Treatment Methods for Cattieskin Tannery Wastes." Joumal of Water Pollution Control Federation. v38, n4, p508-516,1966.

Standard Methods for the Examination of Water and Wastewater. 18th ed., 1992, Washington D. C.

Thorstensen, T. C. Practical Leather Technology. Krieger PubUshkig Company, Malabar, Florida, 1993

Tock, R. W. and Kotia, V. R. "Physical Property Characterization of Laboratory Tanned emu Leather." Submitted for PubUcation, 1996.

Tock, R. W. and Kotia, V. R. "Laboratory Tannkig of Emu Skkis: And an Assessment of die Properties of Emu Leather." Submitted for Publication, 1995.

Totes'n Thkigs, 400 E. Kleberg, KuigsvUle, Texas, 78363, 1995.

U.S. EPA. Envkonmental Impact Guidelines for New Source I /-.adier Tanning and Finishing Industries. Washkigton D. C, August 1980.

U.S. EPA. nnidance Manual for Leadier Tanning and Finishing Pren-e^tment St^dards. Washington D. C, September, 1986.

U s EPA Prnpn.sed Development Document for Effluent I limitations Guidehne$ and • ;;,^„HarH.-l^athpr Tanning and Fini.hinp Point Source Category, Washkigton D. C, 1979 U S EPA npvelnpment Do^"n.ent for Effluent I imitations Guideline?;

w..iHT..the. Tanning and dieBlvirQnment ^Z'^'f^'^f.^lZ^^^ 1993 Discharges: Techniques to Reduce Chrome Waste," v6, n4, p36-40, August 1993.

70

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