CLEANER TECHNOLOGIES IN THE TANNING INDUSTRY

Dr Ken Alexander (Assistant Director - Technical);

British Leather Confederation, Northampton, England Veronica Donohue (Assistant Information Officer - Computer Applications)

The British Leather Confederation, which provides the Secretariat for the International Union of Leather Technologists and Chemists Environment and Waste Commission, is gathering information on clean technologies of leather manufacture, in co-operation with other leather industry associations. First results of this work will be presented as an example of the role that industrial associations can play in networking and promoting cleaner production.

Key aspects of the work are: . Development of a practical database of clean technologies for the leather industry . Development of networks of experts on clean technology for the leather industry

19

ENVIRONMENTAL IMPACT OF LEATHER PRODUCTION

Leather manufacture is one of the oldest established industries and has a current annual turnover of approximately US$25 lion, providing employment for around half a million workers on a worldwide bas i8 . It is essentially a by-product industry, utilising hides and skins from animals raised primarily for their meat. Statistical information from the United Nations Food and Agriculture Organisation shows that in 1987 global leather productio as nearly 14 billion square feet, produced from over 5 million tonnes of rawstocfi2? In this sense the tanning industry considerably reduces the environmental impact of the meat industry, which would otherwise have a major waste disposal problem.

However, only approximately one-fifth of the rawstock can in practice be converted into saleable leather, the remainder forming wastes or by products. For example, some of the raw material, such as hair, soluble proteins and fat has to be removed during processing to prepare the collagen fibre structure of the hide for tanning and some parts of the leather also have to be trimmed or shaved during the production process. Residual chemicals from the leather manufacturing process contribute further to the tannery wastes. An indication of the amounts of liquid effluent and solid wastes or by-products resulting from the processing of 1 tonne of rawhide to leather is given in Figure 1.

A more detailed analysis of leather processing showing the stages at which chemical inputs are made and liquid effluent and solid wastes produced is given in Figure 2, and discussed below. The reader is also referred to a number of excellent reviews published in recent years that provide comprehensive information on the environmental impact of leather processing and pollution abatement, eg, The Technical Guide to R ucing the Environmental Impact of Tannery Operations

(R L Sykes, D R C ning, British Leather Confederation; UNEP Industry and Environment Journal)%; Environmental Impact Guidelin for New Source Leather Tanning and Finishing Industries (Wapora; U EPA @ Wastes from Tanning,

LEATHER PRODUCTION AND WASTE MANAGEMENT

It can be seen in Figure 2 that after soaking hides to remove curing salt and soluble, non-collagenous proteins (eg, albumins), the hair and epidermal layer of the hide are degraded by chemical digestion of the hair/epidermal keratin with alkaline sodium sulphide. This unhairing step accounts for much of the BOD, COD, and suspended solids produced in the tannery effluent. The alkaline treatment also removes additional interfibrillary protein to open up the collagen fibre structure of the hide, which is essential for the production of soft leather. Although alkaline sodium sulphide itself poses few problems, toxic hydrogen sulphide gas would be evolved if the pH dropped in the effluent and most tanneries, at least in the developing countries, therefor use a manganese catalysed aeration treatment originally developed by

discharges. Physico-chemical treatments are frequently employed to reduce the ~ organic load and COD in the effluent (by around 50%) and to reduce the suspended matter by 8040%. A typical tannery effluent treatment system is illustrated in Figure 3.

(F Balkau; UNEP/IEO) BY. , Pollution Abatement and Control in the Leather Industry

Leather, Dressing and Fellmongering (UK DOE) 8) .

BLMRA 0) to comply with the low sulphide levels required by control authorities for

20

1 GIVES

LEATHE G

50 m3 LIQUID EFFLUENT CONTAINING

BOD c 100 kg Susp solids c 150 kg Chromium 5-6 kg Sulphide c 10 kg

COD 235-250 kg

I I

I

SOLID WASTES AND BY-PRODUCTS

Untanned Raw trimmings 120 kg Fleshings 70-230 kg

Tanned Blue sheetings 115 kg Trimmings + shavings 100 kg

Dyed/finished Buffing dust 2 kg Trimmings 32 kg

Figure 1 Environmental inpad of leather processing (source a)

21

h)

salt -)-----salt

5'

5

RAWHIDE

trim--- - )trimmings

Q C 3. 7 (cl

sulphlde/lime b

ammonium salts -b- en mes a c z salt ,-:I

h v) 0

3

sludges mainly lime, protein

)fatty fleshings

BEAYH OUSE salt solutions

sulphide, lime

)."onium salts Hrease )acid brine

$oak---- -_-- unM&-- -

remove flesh - - - - - delime - - - - - - -7" - ac pickle- bate- - -

LI

9 Y

h m dry -- - - - bleather trimmings stress softening

CHEMICAL INPUTS PROCESS STAGE LIQUID EFFLUENT SOLID WASTES

FINISHING buffing - - - -

water and solvent-based --w- -surface coating - polymers; pigments trimming- - -

sorting

)buffing dust

Weather trimmings )(solvent vapour)

chromium 111

sheetings (very thin splits) hrome shavings

basic chromium sulphate auxiliary chemicals, buffer salts, acid, etc.

8 ving---

wei blue wet'blue

POST TANNING liquors containing

low concentration process chemicals in

WET WORK retannage retanniyagents -#- -- - - -

dyes, bu er salts, etc. lubricants - - - lubricat on

dyeinfl

I

T POST TANNINQ A N

N ._ COARSE I

E TANNINQ SCREEN

L RINSES -

I

t b DISCHARQE

TREATMENT TO SEWER

SLUDQE

DEWATER G D1SPOSAL

Figure 3 Physico-chemical treatment of tannery effluent (source (3))

Physico-chemical treatment requires initial balancing (homogenisation) of collected liquors followed by controlled addition of flocculants and sedimentation (or flotation) to remove sludge, which is, in most cases, then dewatered. Biological oxidation can provide a more effective treatment system for tannery effluent, although considerable land space is required. The oxidation ditch shown in Figure 4 reduces BOD levels in tannery effluent from 500-1 OOO mg/l down to levels as low as 1-2 mg/l residual BOD, with almost complete elimination of suspended solids and of ammonia, some of which is derived from the use of ammonium salts used for lowering the pH to prepare the skins for enzyme treatment (bating). The fatty fleshings that have to be removed from hides can be used as a source of tallow, although profitable disposal. of chrome shavings produced Figure 4 Oxidation ditch for biological oxidation after chrome tanning is difficult and often treatment of tannery effluent

(courtesy of W E & J Pebody Ltd, England) has to be disposed to landfill. Excess chromium (111) in the effluent is strictly controlled.

Clean Technology and Pollution Control

Despite the fact that pollution abatement is a considerable, non-productive cost burden on leather manufacturers, the industry itself has taken the initiative in introducing cleaner technologies and improving pollution control. At the last meeting of the International Union of Leather Technologists and Chemists Societies in Philadelphia, USA in 1989 over 60% of the scientific papers presented w e concerned with the development of cleaner technologies for leather manuf 81. In a recent survey of research directors of leather research organisationsbylEan technology was highlighted as the most important priority for future research, after cost reductions.

23

The key targets identified in that 1987 survey were: . Replacement of chromium . More effective use of chromium . More efficient use of chemicals . Sulphide free unhairing, possibly with hair recovery . Utilisation of wastes . Re-use of water . Odour control . Solvent free finishing . N-free deliming

In fact many of these targets are now already being achieved and Figure 5 illustrates just a small selection of new clean technologies that are currently being introduced by the leather industry, or are already in place. These include: . Hide chilling to avoid salt in the effluent . Hair recovery processes to reduce BOD/COD of the effluent . Enzyme-assisted unhairing to reduce sulphide . C02 deliming to reduce ammonia in the effluent . Better uptake/exhaustion of chrome or chrome recovery/recycling to

reduce chrome in the effluent . Alternative mineral tanning agents to avoid chrome in the effluent or solid wastes . Water-based and solvent-free top coats to avoid VOC emissions

More detailed information on the processes are reported in the References cited in Figure 5.

Development of a Clean Technology Database for the Leather Industry

A lack of clear, objective and practically useful information is a major difficulty facing the busy tanner who wishes to introduce cleaner technologies of leather manufacture.

This need for an easily accessible source of information on clean technologies was the driving force behind the decision to set up a suitable database. The British Leather Confederation, which provides the Secretariat for the International Union of Leather Technologists and Chemists Environment and Waste Commission is therefore currently gathering information on clean technologies of leather manufacture, in co-operation with other leather industry associates. The work is dependent upon the development of a network of co-operation and support, involving

24

” PROCESS PROCESS STAGE cLEANTEmNouKiY REDUCTION OF p0UuTK)N - NOSALTIN SALT IN SOA

uawwl EFFLUENT

REDUCED

EFFLUENT + BODOF - REDUCEDUSE

OF SULPHIDE

AMMONIA NO AMMONIA EFFLUE - IN EFFLUENT

REDUCED * CHROMIUM IN EFFLUENT

CHROMIUM 111 I EFFLUENTAN

CHROMIUM REDUCED RECOVERWRECYCUNQ - IN

OR

NO CHROMIUM

S W D WASTES -+ IN EFFLUENT,

I

Fgure 5 Clean technology for leather production

tanners, industrial research associations, industry suppliers, Government and other agencies (e.9. the European Commission under the SPRINT programme, the United Nations Environment Programme etc) and independent leather experts, as illustrated in Figure 6.

-, - and o l h u ~ ~ l u

(.o, UNEP. EC, Figure 6 Network - Clean technology DOE, €PA) information database

The main objective is to set up a practically useful system to enable the tanner to easily shortlist appropriate technologies for his requirements from the database. As part of this procedure it is also essential for the tanner to be able to identify existing users of the technology and independent leather experts, as well as the manufacturers or inventors, whom the tanner can then separately consutt. It is considered most important that the database should not just be a bibliographic source of information but should be of immediate practical use, quantifying wherever possible the reductions in pollution achievable by the clean technology, listing any disadvantages and above all, giving an indication of its present level of development and extent of use, since systems inevitably range from those just at the research and development stage to well-established technologies in widespread use. An outline of the factors that have been selected for inclusion in the database is given in the Questionnaire reproduced in Figure 7, which in this particular example/case history has been completed for a new tanning product, Synektan TAL, manufactured by IC1 as a replacement for chromium.

The leather industry has made considerable investments in time and money in reducing the pollution from tanneries and has achieved significant progress in introducing cleaner technologies, in collaboration with the suppliers. Nevertheless, because of the imposition of increasingly restrictive and sometimes unreasonable environmental legislation, many tanners have been forced out of business in recent years and the jobs of their workers lost because of the non-productive costs of improving environmental standards. In the recent survey of research directors Of leather research organisations, o e of the problems highlighted was the need to eliminate ‘environmental hysteria’&. It is to be hoped that in the years to come the legislative authorities will recognise the efforts of the tanning industry by setting realistic and scientifically based controls and avoiding, wherever possible, politically-motivated or emotional responses to the environmental problems facing all of us.

26

Figure 7 Clean Technology questionnaire

1.

2.

3.

4.

5.

6.

Q U E S T I O N N A I R E

Rr ief S M R Y of clean technoloRy procens/nyntem i n as feu words as p o s s i b l e : (cs. Unhai r ing u s i n g enzymes. c h i i l i n g u s i n g ice) Aluminium + t i t a n i u m complex minera l t a n n i n g a g e n t (non-chrome)

Is t h e r e a SPECIFIC p r o c e s s / t r a d e name? (eg. Blair h n i r . Chromesaver A-31)

Synektan TAL

In which PROCESS STAGE is t h e c l e a n technology t o be a p p l i e d ? ( P l e a s e t i c k )

0 Ravstock 0 F i n i s h i n g 0 Beamhouse OWaste Treatment d T a n n i n g and p r e t a n n i n g f o r wet w h i t e d D y e i n g and F a t l i q u o r i n g and r e t a n n i n g

O O t h e r : ( P l e a s e e x p l a i n )

0 Energy Usage

DESCRIPTION of t h e key f e a t u r e s of t h e c l e a n technology process / sys tem i n n o t more t h a n 200-300 words: (Use No. 11 f o r COMMENTS on t h e process)

Non-chrome t a n n i n g a g e n t , p o t e n t i a l l y u s e f u l in’ t h r e e a r e a s : ( 1 ) p r e t a n n i n g f o r w e t whi te , t o reduce product ion of chrome tanned s o l i d was te

and reduce chrome consumption i n t h e t a n n e r y ( i i ) t o t a l or p a r t i a l replacement of chrome i n main tannage, t o reduce chrome

o f f e r s by a i d i n g chrome uptake and by s u b s t i t u t i n g a t l e a s t p a r t of t h e normal chrome o f f e r t o t a l or p a r t i a l replacement of chrome i n combinat ion tannages or r e t a n n i n g ( i l l )

Where t h e r e is a r e d u c t i o n in e f f l u e n t loading , QUANTIFY t h e changes made by t h e p r o c e s s or the a c h i e v a b l e levels

T o t a l rep lacement of chrome by Synektan TAL would s a t i s f y any requirement regard tng s o l i d or l i q u i d chrome-bearing waste. I f a p r a c t i c a l chrome o f f e r . eg, 1% CrzO3, is r e t a i n e d ( t o main ta in chrome l e a t h e r c h a r a c t e r ) . chrome d i s c h a r g e s i n t h e e f f l u e n t might be approximate ly 10 ppm i n t h e mixed waste s t ream. By o p t i m i s i n g c o n d i t i o n s , t h a t l e v e l can be s i g n i f i c a n t l y reduced.

What ENVIRONMENTAL claim are made? ( P l e a s e t i c k r e l e v a n t i t eds)

Cleaner or Less Recycled Better Liquid

a l t e r n a t i v e b e n e f i t s b e n e f i t s 1 less t o x i c I r e q u i r e d l I u p t a k e l waste I z:iL: 1

Ammonia Chromium C h l o r i d e Ni t rogen S u l p h i d e S o l v e n t s P e s t i c i d e s Biocides

Reduct ions: BiochemicallChemLcal O n a e n Demand _ _ Suspended s o l i d s T o t a l s o l i d s Crease

0 Odour r e d u c t i o n 0 Energy s a v i n g 0 B e t t e r working c o n d i t i o n s

d o t h e r : ( P l e a s e e x p l a i n )

Chrome-free s o l i d by-product by p r e t a n n i n g f o r wet whi te

27

~ _ _ _ _ ~ ~~~

7. Q u a n t i f y ADVANTAGES i temised above: (eg. 10% l e a s s a l t in e f f l u e n t )

Prc ic t tca l ly . chrome i n spent t a n l i q u o r might bc rccluccd try 95%

What DISADVANTAGES are t h e r e ? (eg. aluminium i n e f f l u e n t ) P l e a s e e x p l a i n 8 . ( P l e a s e t i c k r e l e v a n t i t em/a)

c d U n d c s i r o b l o e f f e c t s on t h e e n v i r o n m n t - N w i r n t prcseiit; 1 c ~ : l s l u t i o t i

0 High c o s t s

0 Technica l p r o b l e m

d Other:

I I I H ~ opply Consciit L i m i t s

Post- tanning s t e p s have t o be modi f ied t o t a k e account of A 1 + Ti i n t h e l e a t h e r

9. H w PRACTICAL is t h e c l e a n technology? P l e a s e e x p l a i n

Very p r a c t i c a l , no c a p i t a l c o s t r e q u i r e d or changes t o e x i s t i n g p r o c e s s i n g methods

10. Give a n estimate of t h e 'CLEANNESS' of t h e p r o c e s s ( P l e a s e t i c k r e l e v a n t item/s)

0 Very good - Best p o s s i b l e Cd Good - Beat a v a i l a b l e t o d a t e 0 Reasonable - Better t h a n o t h e r p r o c e s s e s 0 Not so good - No better t h a n o t h e r a v a i l a b l e p r o c e s s e s

11. Give an OPINION or make COMMENTS on t h e 'CLEANNESS' of t h e process:

Synektan TAL can make r e a l r e d u c t i o n s i n l e v e l s of discharged chrome w i t h no c u r r e n t a d d i t i o n a l knvironmental problems. Discharges of aluminium (and p o s s i b l y t i t a n i u m ) may be s u b j e c t t o environmental p r e s s u r e i n t h e f u t u r e

Name of ORCANISATION/WUFACURER r e s p o n s i b l e f o r c l e a n technology: 12.

Contac t name: I a n T a t e Company name: I C 1 Colours and Fine Chemicals Address: PO Box 42. Hexagon House, Blackley. Manchester M9 30A

Tel: 061 721 2562 Telex: 667841 Fax: 061 795 6005

13. A t what STAGE OF DEVELOPMENT is t h e p r o c e s s now? ( P l e a s e t i c k r e l e v a n t item/s)

0 Research 6 Development 0 T r i a l / P r o t o t y p e 0 Other: ( P l e a s e e x p l a i n )

Limited commercial u s e d w i d e s p r e a d use

I O U W Y YEARS h a s t h e process / sys tem been in commercial use? WllAT YEAR was t h e process / sys tem f i r s t developed? 1987 Product launched i n 1988

2 y e a r s

14. TANNERY COSTS AND PAY-BACK PERIOD

WLEUENTATION COSTS:

0 f l - 5000 0 f5001 - 10.000 @f flO.OO1 - 50.000 0 f50.001 - 100.000 0 More t h a n flOO.OO1

PAY-BACK PERIOD:

5-10 y e a r s

15. AVAILABILITY ( P l e a s e t i c k r e l e v a n t i t em/a)

A f r i c a

6 N e w Zealand N America S America

16. Est imated NUMBER OF TANNERIES u s i n g t h e technology WORLDWlUE i n y e a r 2000:

0 1-10 0 11-50 0 51-100

28

17.

18.

19.

20.

21.

22.

23.

21.

25.

26.

ESTIMATED square feet of leather produced to date using this technology:

0 Less than I million square feet d 1 - 5 million square feet 0 More than 5 million square feet

Give details of TANNERIES using this process who uould be willing to be contacted:

Coiitnct nor: Dr H P Walker Organisation name: The British Leather Co Ltd Type of business: Bovine tanners Address: Tranmere Tannery, Nev Chester Road, Birkenhead, L41 9BS

Tel: 051 647 6252 Telex: 629570 Fax: 051 647 3573

If IT IS NOT POSSIBLE to give above contacts, please give details of an INTERMEDIARY who could pass on any requeats for information to a relevant tannery:

See (12)

Give full details of REFERENCES in the literature to the process: (Continue on a separate sheet if necessary)

A D Covington Tannages based on aluminium (111) and titanium (111) complexes J Amer Leather Chem Aasoc. 1987. 82. (I). 1

I Tate The use of aluminium, titanium and magnesium complexes in the pretanning. tanning and retanning operations Proceedings, IULTCS Congress, Philadelphia, 1989

Give details of any PRODUCT DATASHEET Reference Numbers: Product code 36003

Give details of other sources of INFORMATION: Company information pack

Which individuals are considered to be THE EXPERTS in this area?

Name I P Tate/R H Webster Organisation IC1 Colours and Fine Chemicals Address PO Box 42. Hexagon House. Blackley. Manchester H9 30A

Tel: 061 721 2562 Telex: 667841 Fax: 061 795 6005

Name Dr M P Walker Organisation The British Leather Co Ltd Address Tranmere Tannery, New Chester Road, Rirkenhead, L41 9BS

Tel: 051 647 6252 Telex: 629570 Fax: 051 647 3573

Where information is obtained directly from the manufacturer, give details:

Name: I P Tate Organisation: IC1 Colours and Fine Chemicals Address: PO Box 42, Hexagon House, Blackley. Manchester I49 30A

Tcl: 061 721 2562 Telex: 667841 Fax: 061 795 6005

EditorRersoo completing this form:

Name: Dr A D Covington Organisation: British Leather Confederation Address: Leather Trade House, Moulton Park, Northampton NN3 1JD

Tel: 0604 494131 Telex: 317124 Fax: 0604 648220

Any COl44ENTS not covered above:

EC Supported Demonstration Project (ACE/88/UK/OOZ/AZl) currently being conducted at The British Leather Co Ltd. in collaboration with the Brit'iah Leather Confederation

29

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30

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31

WASTE MINIMIZATION - APPROACHES and

1 Activities

Chicago, Illin

1 present a s s of suggested steps for conducting a wa minimization ssment, discuss means of

improving operations. These process modification will be

the receiving fa

S ON POTW1s

ms that are generated from their smokestacks, sewers and refuse in an effort to reduce operating

costs and storage r improve public image and operating potential risks and liabilities aste streams can be thought of as

anything that doesnl or as product. Waste can be in the form of a soli or a combination thereof and

considered a urce and no longer a waste. evaluate the act of waste minimization on

and will therefore focus

that may be subjected to and contamina

SLUDGE PR

reducing the amount of sludge will usually result in less sludge requiring treatment and disposal. Care should be taken in instances where industrial wastewater flows are substantial not to adversely affect sludge

32 operations at the POW.

b