case study leather industry

8/12/2019 Case Study Leather Industry

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2

The desi gnat i on empl oyed and t he pr esent at i on of mat er i al i n t hi s document do not

i mpl y t he expr essi on of any opi ni on what soever on t he par t of t he Secr et ari at of

t he Uni t ed Nat i ons I ndust r i al Devel opment Or gani zat i on ( UNI DO) concerni ng t he

l egal st at us

of

any count r y, t er r i t ory , c i t y or ar ea or of i t s aut hor i t i es , or

concer ni ng t he del i m t at i on of i t s f r ont i er s or boundar i es. Ment i on of f i r mnames

and commer ci al product s does not i mpl y t he endor sement of UNI DO.

Thi s document

has not been edi t ed.

Cont r i but i ons t o t hi s document have been made by R. Hi gham UNI DO Consul t ant .


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CONTENTS

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7

1 I NTRODUCTI ON

1. 1. The i ndust r y s gl obal per spect i ve

........................ 10

1. 2. Envi r onment al i mpact

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10

1. 3. Hi des and ski ns pr oduct i on and tr ade ..................... 10

1 . 3 . 1 . Dependence on

the

mar ket f or meat . . . . . . . . . . . . . . . . .

10

1. 3. 2. Wor l d hi de and ski n suppl y ........................

10

1. 3. 3

Change i n gl obal pat t er n of demand f or hi des

and ski ns

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. 3. 4. Change i n vol umes and di r ect i on of i nt er nat i onal

t r ade

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11

1. 3. 5. End uses of l eat her based on di f f er ent r aw

mat er i al s

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1. 4. The pr esent s i t uat i on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11

1. 4. 1. I nf l uence of hi gh vol ume shoe manuf act ur i ng;

hi gh- t ech l eat her s ................................

11

1. 4. 2. Tanner s i n devel opi ng count r i es under pr essur e t o

i nves t i n ef f l uent t reat ment f ac i l i t i es . . . . . . . . . . .12

1. 5. What of the f ut ur e? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

1. 5. 1. I nf l uence of popul at i on gr owt h and government

pol i c i es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

1. 5. 2. Fut ur e hi de and ski n pr oduct i on . . . . . . . . . . . . . . . . . . .12

1. 5. 3. Fut ur e demand f or f i ni shed goods manuf act ur ed

i n l eat her . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

1. 5. 4

Fr agment at i on of l eat her manuf act ur i ng among

s pec i al i s t s . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . 1 3

2

.

ENVI RONMENTAL REQUI REMENTS FOR ACHI EVI NG ESI D

2. 1.

Envi r onment al i mpact on t he l eat her i ndust r y

. . . . . . . . . . . . .

13

2. 1. 1. The el ement s

of

l eat her manuf act ur i ng

. . . . . . . . . . . . .14

2. 1. 2. Envi r onment al i mpact quant i f i ed. . . . . . . . . . . . . . . . . . .

14


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2 . 2

2 . 3

Low Wast e Technol ogi es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 5

2 . 2 . 1 .

Var i et y of pr ocesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 5

2 . 2 . 2 .

Wat er conservat i on

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 6

2 . 2 . 3 .

Cur i ng hi des and ski ns . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 7

2 . 2 . 3 . 1 . Pr ocess al t er nat i ves

.....................

1 7

2 . 2 . 4 .

Beamhouse pr ocesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 8

2 . 2 . 4 . 1 .

Soaki ng. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 8

2 . 2 . 4 . 2 .

Al t ernat i ve met hods ......................

1 8

2 . 2 . 4 . 3 . Del i m ng and bat i ng ...................... 19

2 . 2 . 5 .

Tanyar d pr ocesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 0

2 . 2 . 5 . 1 .

Pi ckl i ng

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 0

2 . 2 . 5 . 2 .

Degr easi ng. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 1

2 . 2 . 5 . 3 .

Tanni ng..................................

2 1

2 . 2 . 5 . 4 .

Al t ernat i ve met hods ......................

2 1

2 . 2 . 5 . 5 .

Veget abl e Tanni ng .......................

2 4

2 . 2 . 6 .

2 . 2 . 7 .

Fi ni shi ng

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

26

Post - t anni ng wet pr ocesses

........................

25

2 . 2 . 7 . 1 . Convent i onal f i ni shi ng

. . . . . . . . . . . . . . . . . . .

26

2 . 2 . 7 . 2 .

I mpr oved met hods .........................

26

Ef f l uent Treat ment Technol ogy

. . . . . . . . . . . . . . . . . . . . . . . . . . . .

27

2 . 3 . 1 . Mode of t r eat ment gover ned by pr ocesses and

t anner y l ocati on. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 7

2 . 3 . 2 .

Ef f l uent t r eat ment sequence ....................... 28

2 . 3 . 2 . 1 .

Pr et r eat ment : Scr eeni ng

. . . . . . . . . . . . . . . . . .

8

2 . 3 . 2 . 2 .

Pr i mar y Tr eat ment ........................

28

2 . 3 . 2 . 3 .

Secondary Treat ment

...................... 3 0

2 . 3 . 2 . 4 .

Ter t i ar y Tr eat ment .......................

3 0

2 . 3 . 2 . 5 .

2 . 3 . 2 . 6 .

Sedi ment at i on and sl udge handl i ng

. . . . . . . .

1

Advanced t r eat ment sys t ems . . . . . . . . . . . . . . .

2


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2 . 3 . 3 . Recovery of r esi dues and wast es . . . . . . . . . . . . . . . . . . . 2

2 . 3 . 4 .

Exampl es of t he cost of sett i ng up ef f l uent

t r eat ment pl ant s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

32

2 . 3 . 4 . 1 . I ndust r i al i zed count r i es . . . . . . . . . . . . . . . . . 3 2

2 . 3 . 4 . 2 .

Devel opi ng count r i es ( Af r i ca)

. . . . . . . . . . . .

5

3

.

BARRI ERS TO PROGRESS TOWARDS ACHI EVI NG ESI D

3 . 1 .

Techni cal consi der at i ons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

37

3 . 2 . Econom c consi der at i ons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 8

3 . 3 .

I nadequat e l egi sl at i on and l ack of moni t or i ng

f aci l t i es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3 . 4 . Soci al consi der at i ons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 0

3 . 5 . Gr adual progress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

4 . I NDUSTRY. GOVERNMENTS AND I NTERNATI ONAL CO- OPERATI ON

4 .1 .

Envi r onment al l obby. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

40

4 . 2 . The need f or an envi r onment al dat abase . . . . . . . . . . . . . . . . . . . . 4 3

4 . 3 . Gover nment i nvol vement

i n pol l ut i on r educ t i on. . . . . . . . . . . . . 44

4 . 3 . 1 . The I ndi an Gover nment hel ps I ndust r y . . . . . . . . . . . . . . .

4

4 .4 . Act i vi t i es of

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4 5

5 .

CONCLUSI ONS

5. 1. Bar r i er s t o pr ogr ess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

46

5 . 2 .

Eval uat i on of pol l ut i ng cont r ol r equi r ement s . . . . . . . . . . . . . . 7

5 . 3 . Cl eaner Technol ogi es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 8

5 . 4 . Ef f l uent Tr eat ment

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4 8

5. 5.

UNI DO s r ol e

. . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . .

4 8

Tabl e 1

.

Hi des. sk i ns and l eat her f oot wear : t hei r

s i gni f i cance i n r el at i on t o t r ade i n ot her

commodi t i es (1985 t o 1987) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4 9

Tabl e 2 .

Raw hi des and ski ns:

f act or s det er m ni ng l evel

of

out put ( 1985 t o

1987)

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50


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Tabl e

3 .

Leat her : devel opment s i n out put by t ype and

econom c

zone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

51

Tabl e

4

Wor l d l eat her suppl y by r awst ock (1980, 1990, and 2000) . . 52

Tabl e

5.

Foot wear and l eat her upper s: devel opment s i n

pr oduct i on, wor l d t r ade and avai l abi l i t y by

econom c zone

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

53

Tabl e

6.

Composi t i on of t ypi cal unt r eat ed combi ned

t anner y ef f l uent

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

54

Tabl e 7. Maxi mal l y adm ssi bl e concent r ati ons (MAK val ues)

of gaseous harm ul subst ances i n t he worki ng

envi r onment at a dai l y exposur e on

8

hour s . . . . . . . . . . . . . . . 5

Tabl e

8.

Compar i son of di schar ge st andar ds f or t anner y

wast ewat er s f or sever al count r i es

. . . . . . . . . . . . . . . . . . . . . . . .

56

Tabl e

9.

Suggest ed maxi ma f or t r i val ent chr om um

i n soi l s and s l udges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Tabl e 10. Compar i son

of

di schar ge st andar ds f or s ewer

systems f or sever al count r i es . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Tabl e 11. Compar i son of sl udge r e- use st andar ds f or

sever al count r i es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Tabl e 12.

Capi t al and operat i on cost s f or t r eat ment at

some

U. S.

t anner i es

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Fi gur e I . Schemati c t anni ng pr ocess

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

61

Fi gur e 11. Chr ome em ssi ons i n t annery ef f l uent s

. . . . . . . . . . . . . . . . . . . .

62

Fi gure 111. Chrome r ecovery ( Source: UNI DO)

.......................... 6 3

Fi gur e I V. Typi cal scheme f or physi cal - chem cal t r eat ment . . . . . . . . . . . 4

Fi gur e

V.

Some pr oposed cl ean t echnol ogi es f or l eat her pr oduct i on. . 65

BI BLI OGRAPHY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6 6


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ABSTRACT

The t anni ng i ndust r y i s known t o be ver y pol l ut i ng especi al l y t hr ough

ef f l uent s hi gh i n or gani c and i nor gani c di ssol ved and suspended sol i ds cont ent

accompani ed by propensi t i es f or hi gh oxygen demand and cont ai ni ng pot ent i al l y

t oxi c met al sal t r esi dues. Di sagr eeabl e odour emanat i ng f r omt he decomposi t i on

of pr ot ei n sol i d wast e, pr esence of hydr ogen sul phi de, ammoni a and vol at i l e

or gani c compounds are nor mal l y associ at ed wi t h t anni ng act i vi t i es.

On t he basi s of year l y i nput ( soak ) of about 6. 8 m l l i on t onnes of

wet sal t ed hi des and ski ns wor l dwi de i t can be est i mat ed t hat about 3, 427, 000t

of var i ous chem cal s ar e used f or l eat her pr ocessi ng. A si gni f i cant par t of

t hi s amount i s not act ual l y absorbed i n

the

pr ocess and i s di schar ged i nt o t he

envi r onment .

W t h an aver age yi el d of 45- 50m3 of wast ewat er per t onne of r aw hi de,

t he t ot al amount of l i qui d ef f l uent f r om l i ght l eat her processi ng ( al most 90

per cent of over al l pr oduct i on) i s over 300 m l l i on m3 a year cont ai ni ng about

1, 470, 000

of COD, 610, 000 t of BOD, 920, 000 t of suspended sol i ds, 30, 000 t

of chr om um and 60, 000 t of sul phi de pl us mor e t han 2, 500, 000 t of sol i d

wastes ( f l eshi ng, wet bl ue spl i t s ,

t r i mm ngs and shavi ngs, buf f i ng dust , etc) .

About one- hal f of t hat i s pr oduced i n devel opi ng count r i es.

The substant i al r el ocat i on of l eat her pr oduct i on f r om t he

i ndust r i al i zed t o t he devel opi ng count r i es whi ch occur r ed bet ween t he 1960s

and t he 1980s ( The Bi g Shi f t ) i n ef f ect moved t he most hi ghl y pol l ut i ng par t

of

the

pr ocess away f r om t he OECD count r i es under pr essure of i ncreasi ng cost

of l abour and cost of ef f l uent t r eat ment i nst al l at i ons and oper at i ons. Thi s

pr ocess was accel er at ed by a combi nat i on of r est r i ct i ons i n expor t s of r aw

hi des and ski ns and var i ous i ncent i ves f or hi gher pr ocessi ng l evel s pr ovi ded

i n devel opi ng count r i es.

Owi ng t o t he nat ur e of t he l eat her pr oduct i on, even i n the most

sophi st i cat ed t annery, t echnol ogy remai ns t o a cer t ai n ext ent a m xt ur e of

cr af t and sci ence. Whi l e t here ar e some t ypi cal phases f ol l owed i n

manuf actur i ng, f or exampl e,

t he

most wi del y pr oduced chr ome t anned shoe upper

l eat her based on bovi ne hi des ( soaki ng, unhai r i ng, pi ckl i ng, t anni ng,

r et anni ng/ dyei ng, f at l i quor i ng and f i ni shi ng) , st r i ct l y speaki ng t her e i s no

basi c t anner y pr ocess.

A s

a cor ol l ar y, i t i s not poss i bl e t o s i mpl y r epl ace

t he t r adi t i onal t echnol ogy wi t h an ent i r el y new cl ean pr ocess.

Si nce over 80 per cent of t he or gani c pol l ut i on l oad i n t er ms of BOD,

comes f r omear l y wet pr ocessi ng, t hi s i s t he pr i mar y t ar get of most pol l ut i on

cont r ol measur es.

Among t he l ow wast e t echnol ogi es possi bl y t he most pr om si ng ar e: use

of gr een hi des f r omabat t oi r s wi t hout t he necessi t y of t empor ar y pr eser vat i on;

use of saf e i nsect i ci des and bi oci des i n cur i ng hi des and ski ns and wet bl ue

l eat her s; hai r - savi ng met hods i n t he unhai r i ng pr ocess; separ at i on of

unhai r i ng and l i m ng; r ecycl i ng of unhai r i ng and l i m ng l i quors; ammoni um f r ee

del i m ng; hi gh chr ome exhaust i on sys t ems; r ecycl e and/ or chr ome r ecover y;

chr ome- f r ee ( al um t anni ng whenever appl i cabl e, at l east i n t he f i r st phase

of t anni ng; i n f i ni shi ng, at l east base and m ddl e coat s shoul d be made of

aqueous pol ymer i c di sper si ons and cont ai n saf e cr ossl i nki ng agent s. Comput er

cont r ol systems ar e bei ng i nt r oduced i n t he newl y i ndust r i al i zed count r i es.


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Low wast e t echnol ogi es, gener al l y speaki ng, r equi r e bet t er ski l l ed

per sonnel and cl oser t echni cal cont r ol t han convent i onal pr ocessi ng. Thus,

t he l ack of pr oper l y t r ai ned st af f at di f f er ent l evel s remai ns one of t he

cr uci al const r ai nt s. I t i s not ed t hat each t anner y' s ef f l uent t r eat ment

r equi r ement s need t o be eval uat ed i ndi vi dual l y, not onl y accor di ng t o t he

process bei ng empl oyed and t he t ype of r aw mat eri al bei ng pr ocessed, but al so

accor di ng t o t he l ocat i on of t he t anner y, t he vol umes of wat er bei ng used and

em t t ed and t he di r ect i on of t he em ssi ons ( sur f ace wat ers , sewer s, etc) .

Typi cal t anner y ef f l uent t r eat ment s yst ems ar e descr i bed. Saf e

di sposal of s l udge whi ch i nevi t abl y cont ai ns a cer t ai n amount of t r i val ent

chr om um causes consi der abl e di f f i cul t i es . J oi nt ef f l uent t r eat ment pl ant s

possi bl y combi ned wi t h a cent r al chr ome r ecover y uni t are of t en gi ven as t he

opt i mum sol ut i on f or c l ust er s o f t anner i es f ound al l over t he wor l d.

The mai n barr i ers t o the adopt i on of more envi r onment al l y accept abl e

met hods of l eat her pr ocessi ng and ef f l uent t r eat ment ar e t he addi t i onal cost s

as f ol l ows: speci al t y chem cal s r equi r ed i n r educi ng or el i m nat i ng t he use

of t he mai n pol l ut i ng chem cal s; t he cost of pur chase and i nst al l at i on of

wat er conser vat i on devi ces, wast ewat er col l ect i on and r euse equi pment ;

ef f l uent t r eat ment chem cal s and pr ocess and ef f l uent moni t ori ng equi pment ;

ext r a per sonnel and t r ai ni ng t o mai nt ai n t echni cal cont r ol of l ow wast e

t echnol ogi es and ef f l uent t r eat ment . Anot her f act or i s t he t r adi t i onal

conser vat i smder i ved f r omhesi t at i on over pr ocess al t er at i ons especi al l y when

sat i s f actory l eat her i s bei ng cur r ent l y pr oduced. Thi s i s par t i cul ar l y t he

case i n smal l t o medi um scal e sem - mechani zed f am l y owned uni t s. Anot her

bar r i er i s t he f r equent r emot eness of gover nment - backed R

& D

f aci l i t i es f r om

ever yday pr act i cal i t i es of l eat her - maki ng, t oget her wi t h rel uct ance on t he

par t of t r adi t i onal t anner gr oups where r esi st ance to change i s compounded by

pol i t i cal i nf l uence.

The beamhouse ( unhai r i ng) and t he t anyar d r equi r e cl eaner t echnol ogi es

i n l eat her pr ocess i ng. Al so ut i l i zat i on of chr ome- f r ee sol i ds as by- pr oduct s

and di sposal of chr ome cont ai ni ng sl udge are possi bl y t he mai n i ssues t hat

need par t i cul ar at t ent i on. However, l egi sl at i on enf or cement agenci es l ack

ski l l ed per sonnel t o moni t or per f or mance of i nst al l ed t r eat ment pl ant s.

The cost of i nt r oduci ng a cl eaner pr ocessi ng met hod may be pr ohi bi t i ve

and beyond r each of a smal l scal e t anner : t he pr i ce of a speci al dr um f or hai r

save unhai r i ng wi t h t he necessar y auxi l i ar y equi pment may be as much as t wi ce

t he convent i onal dr um Enzyme unhai r i ng needs ver y accur at e cont r ol and

consi st ency of al l par amet er s ( pH, t emper at ur e, f l oat , et c) whi ch i s possi bl e

t o achi eve

onl y i n r at her sophi st i cat ed t anner i es and i t i s associ at ed wi t h

hi gher pr oduct i on cost s ( par t l y of f - set by l ower wast ewat er t r eat ment

expenses) . Hi gh chr ome exhaust i on t anni ng r equi r es ver y expensi ve speci al t y

chem cal s , nor mal l y pr opr i et ar y products .

Ef f l uent t r eat ment cost s depend on speci f i c si t e condi t i ons, and var y

wi t hi n a ver y wi de r ange. I n Eur ope t hey ar e est i mated t o be of t he or der of

US$ 5 t o

15

per cubi c met r e of ef f l uent or 4 t o 6 per cent of t he f i ni shed

l eat her pr oduct i on cost . I ni t i al t r eat ment cost s may not r esul t i n t hi s l evel

of on- cost i n devel opi ng count r i es, but as st andar ds i n st r i ngency and/ or i n

enf orc ement advance t hey wi l l i nevi t abl y i ncr ease.


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Some r ecent exampl es f r om Af r i ca i ndi cat e t he cost of est abl i shi ng a

compl et e t r eat ment pl ant f or a medi um scal e t anner y t o be bet ween

US$170,000

and US$340, 000.

Never t hel ess, consi der abl e st r i des i n r educi ng pol l ut i on can be made by

adopt i ng measur es whi ch requi r e l i t t l e or no capi t al i nvest ment , such as:

- st r i ct process cont r ol i ncl udi ng avoi dance of over dosi ng of

chem cal s t ypi cal f or t he t anni ng i ndust r y;

- good housekeepi ng - wat er conservat i on at al l st ages of wet

pr ocess i ng;

- savi ngs i n chem cal s by i nt r oduci ng r euse- r ecover y- r ecycl esys t ems

can pay f or t he si mpl e equi pment needed t o r un t hem such as col l ect i on pi t s,

pi pes and pumps;

-

i nt r oduci ng, as appr opr i at e, some of t he wi de r ange of opt i ons of

t he l ow wast e t echnol ogi es ment i oned ear l i er .

( Thi s wi l l i n ef f ect r educe t he

amount of capi t al i nvest ment and t he cost of operat i ng t he t r eat ment syst em ;

- maxi m zat i on of r et ur ns on t anner y by- product s, r esi dues f r omsl udge

and sol i d wast es ( pr oduct i on

of

gel at i ne, pr ot ei n powder s and col l agen f or

sausage casi ngs and medi cal and surgi cal f i l ms, gl ue, ani mal f eed pr ot ei n and

f er t i l i zer s , l eat her boar d, f i l t er medi a, non- wovens , et c) ;

-

est abl i shment of a si mpl e but wel l cont r ol l ed and mai nt ai ned

t r eat ment system ( f or exampl e manual l y cl eaned sc r een, equal i zat i on wi t h

aer at i on, c l ar i f i er , l agooni ng, s l udge dr yi ng beds) ; j oi nt ef f l uent t r eat ment

pl ant s f or t anner y c l ust er s .

I t i s bel i eved t hat by combi ni ng st r i ct pr ocess cont r ol , good

housekeepi ng measur es and cl eanl i ness , i nt r oduct i on of r ecycl i ng of some

f l oat s, pr edom nant l y aqueous f i ni shi ng t oget her wi t h si mpl e tr eat ment of

wast es i t woul d be possi bl e t o el i m nat e near l y

50

per cent of t he total

pol l ut i on l oad di schar ged i nt o the envi r onment wi t h onl y mar gi nal i nvest ment .

I f consi st ent l y appl i ed i n devel opi ng count r i es wor l dwi de t hi s woul d r esul t

i n reduc t i on of :

-

COD, appr ox. 350, 000 t /a ;

- BODS, appr ox. 150, 000t / a ;

- Chr ome, appr ox. 10, 000t / a ;

- Suspended sol i ds, appr ox. 230, 000t /a .

A comprehensi ve, wel l synchr oni zed act i on by r espect i ve gover nment s,

i ndust r y, R&D and est abl i shment s, envi r onment al aut hor i t i es , . i nt er nat i onal

or gani zat i ons, etc. t o addr ess t he mai n const r ai nt s ment i oned ear l i er i s a

pr er equi si t e to achi evi ng ESI D i n t he tanni ng i ndust r y.

Speci al sof t t er m f i nanci ng schemes f or i nt r oduct i on of c l eaner

t echnol ogy and i nst al l at i on of wast es t r eat ment equi pment i s essent i al f or

many smal l and medi um scal e uni t s i n devel opi ng count r i es.

Dur i ng t he l ast f ew years pol l ut i on cont r ol has been gi ven a ver y

pr om nent r ol e i n UNI DO t echni cal assi st ance t o t he l eat her and l eat her

pr oduct s i ndust r y so t hat at pr esent t her e i s vi r t ual l y no pr oj ect i n t he

t anni ng sect or wi t hout an envi r onment component . Di ssem nat i on of i nf ormat i on

on envi r onment al pr ot ect i on i s anot her i mpor t ant ar ea of UNI DO' s act i vi t i es

i n t hi s s ec t or .


10/68


11/68

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11

-

The wi dest di spar i t y bet ween bovi ne popul at i on and out put of hi des

occur s i n Af r i ca whi ch account s f or mor e t han 10 per cent of t he wor l d' s

cat t l e but f or onl y

5

per

cent

of hi de out put . Af r i ca of f er s the mai n pr ospect

f or i ncr eases i n hi de suppl y t hr ough reduct i on i n cur r ent l osses and

i mprovement s i n husbandr y and mar ket i ng. The r egi on i s s ubj ect t o a UNI DO

pr oj ect whi ch ai ms t o assi st i n achi evi ng these obj ect i ves.

Tabl e 3 shows t hat wor l d output of bovi ne hi des and ski ns has r i sen

al most

50

per cent dur i ng the l ast

20

t o

25

year s, r ef l ect i ng i mpr ovement s i n

cat t l e husbandry and expansi on

i n

beef pr oduct i on.

1 . 3 . 3 . Change in global pattern

of

demand for hides and skins

The l eat her i ndust r y has expanded subst ant i al l y i n t he devel opi ng

count r i es dur i ng t he past 25 year s. Tanneri es i n t he devel oped count r i es wer e

once r el i ant upon r aw mat er i al s f r omdevel opi ng count r i es, but as t he l eat her

i ndust r y has gr own i n t he devel opi ng worl d t o gi ve added val ue t o t hei r r aw

mat er i al r esour ces,

so

t he i ndust r y i n t he devel oped wor l d has not exper i enced

t he degr ee of gr owt h that has occur r ed par t i cul ar l y i n S. E. Asi a, Chi na and

Lat i n Amer i ca. A

consequence

of

production expansion in some developing

countries is that tannery input demands have outstripped locally available

supplies and imports from the developed countries have become essential.

1 . 3 . 4 .

Change in volumes and direction

of

international trade

Over 35 per cent of t he out put of r aw bovi ne hi des i n 1987 ent ered

i nt er nat i onal t r ade compar ed wi t h 28 per cent 25 year s previ ousl y. Wor l d

shi pment s have r i sen by about 90 per cent . However , t hi s expansi on has t aken

pl ace excl usi vel y i n devel oped count r i es, and devel opi ng count r i es as a group

have r educed t hei r export s

of

r aw hi des and ski ns by 60 per cent .

While developing countries as a whole were net exporters

of

raw bovine

hides and skins in the early sixties to the level

of 250,000

t , their net

import requirements are now over

400,000

t

w / s .

Thi s r ef l ect s t he dr amat i c

expansi on i n t anni ng capaci t y i n most devel opi ng count r i es, but mai nl y i n

Lat i n Ameri ca and Asi a and t he Paci f i c Regi on.

1 . 3 . 5 . End uses

of

leather based on different raw materials

Bovi ne hi des ar e t he r aw mat er i al f or most shoe upper l eat her s,

uphol st ery l eat hers and some gar ment l eat her s; heavy l eat her i s al ways bovi ne.

Thi s cat egor y compr i ses mai nl y sol e l eat her f or shoes wi t h l esser quant i t i es

of saddl er y l eat her , case l eat her and a var i et y of i ndustr i al l eat her s,

Sheepski n l eat her i s used i n gar ment s, l eat her goods, bookbi ndi ng and gl ovi ng,

whi l e goat ski n i s al so used f or gl ovi ng, shoe upper and l i ni ng l eat her and

l eat her goods. Pi gski n i s used i n gar ment s, l eat her goods, gl ovi ng and shoe

1

ni ngs

.

1 . 4 . THE PRESENT SI TUATI ON

1.4.1. Influence

of

high volume shoe manufacturing; high-tech leathers

The over al l pi ct ur e t hat emerges of t he worl d l eat her and l eat her

pr oduct s i ndust r y i s one i n whi ch t here has beenmass i ve t r ansf ormat i on dur i ng


12/68

- 12 -

t he past 3 0 year s. The hi gher qual i t y European bovi ne hi des have been an

i mport ant r esour ce to t he high-tech (automotive and upholstery) leather

tanners as t hey have suppl i ed t hi s growt h mar ket duri ng t he

1980s

t hr ough t o

t he pr esent day.

Dur i

g

t h' s

30

year per i od export s of hi des f r om Nort h Ameri ca have

l argel y occur r ed because of t he massi ve l evel of f oot wear i mport s i nt o Nort h

Amer i ca, i ni t i al l y f r om sout her n Eur ope, but l at er i ncreas i ngl y suppl ement ed

by i mpor t s f r om East Asi a. The export ed hi des have been t ur ned i nt o the

l eat hers t hat have been i mpor t ed back t o Nor t h Ameri ca i n t he f or m of

f oot wear , garment s and l eat her goods.

i ncr eased

v

n t he f i ni shed l eat her i ndust r y has dec l i ned, t he dec l i ne has

1 . 4 . 2 .

treatment facilities

Tanners in developing countries under pressure to invest in effluent

The change of flow of international trade in raw material and the

substantial relocation of leather production from the developed to the

developing countries which occurred between the

1960s

and the 1980s in effect

moved the most highly polluting w et processing away from the

OECD

countries

at a time when environmental regulations were beginning to bite in terms of

cost of effluent treatment installations and operation. In many developing

countries regulations were non-existent, or if they did exist, they were not

strictly imposed. Thi s undes i r abl e s i t uat i on i n devel opi ng count r i es i s now

changi ng.

1. 5.

WHAT OF THE FUTURE?

1. 5. 1.

Influence of population growth and government policies

Econom c, pol i t i cal and t echnol ogi cal devel opment s i n sever al i ndust r i es

i mpi nge upon t he f ut ur e char act er i s t i cs of t he l eat her i ndust r y , cover i ng al l

cont i ngent i ndust r i es f r oml i vest ock agr i cul t ur e t o f i ni shed goods i ndust r i es

and t he mar ket s t hat t hey ser ve.

Popul at i on gr owt h i s anot her i mport ant f act or . For exampl e i n Chi na and

I ndi a, where per capi t a i ncomes ar e r i s i ng f ast er t han t he worl d aver age,

gr owt h i n t he pur chasi ng power of t hese r api dl y i ncr easi ng popul at i ons wi l l

be t he dom nant f act or i n t he expansi on of wor l d demand f or meat and f or

i nexpensi ve l eat her goods. The f ast gr owi ng, m ddl e i ncome popul at i ons of Asi a

wi l l al so cons t i t ut e i nc reas i ngl y s i gni f i cant market s f or hi gher qual i t y

l eather and l eather pr oduct s. The demand f or var i ous l uxur y l eather pr oduct s,

on t he ot her hand, such as l eat her uphol st ered car s and hi gh f ashi on gar ment s,

wi l l depend on t he growt h and di st r i but i on of weal t h i n hi gh i ncome count r i es.

1 . 5 . 2 .

Future hide and skin production

Landel l M l l s Commodi t i es St udi es i n t hei r r eport ' The Leat her I ndust r y

t o t he Year 2000 have r eached t he concl usi on t hat f or t he worl d as a whol e,

hi de pr oduct i on wi l l i ncr ease by a t ot al of

2 3

per cent ( i n wei ght ) ,

and ski n

product i on by 21 per cent ,

over t he per i od f r om

1980

t o 2000 ( see t abl e 4 ) ;

most of t hi s gr owt h wi l l

occur i n Asi a and Lat i n Amer i ca.


13/68


14/68

bei ng t r ansf er r ed f r omr ecei vi ng wat er s t o r ecei vi ng l and. Because sl udge can

af f ect the qual i t y o f soi l and gr oundwat er , i t i s under st andabl e t hat l ocal

aut hor i t i es and gover nment s shoul d be concerned

that

t he di sposal of s l udge

to soi l s and dr y wast es t o l andf i l l shoul d not adver sel y af f ect t he f er t i l i t y

of so i l , nor t hat met al sal t r es i dues , such as chr om um shoul d i nhi bi t c rop

gr owt h i n any way.

2 . 1 . 1 . The elements

of

leather manufacturing

The tanning. process

The obj ect i ves of t anni ng ar e t o conver t a put r esci bl e hi de i nt o

l eat her . Many al t er nat i ve pr ocesses and mat er i al s ar e known and most t anner s

wi l l use a var i at i on of t hei r st andar d pr ocess t o change t he type of l eat her

t hey wi sh to make. For a schemat i c t anni ng process see f i gur e I .

2 . 1 . 2 .

Environmental impact quantified

I n or der t o ass ess t hi s t he magni t ude of wor l d pr oduct i on must be

The gl obal l y compar abl e f i gur es publ i shed by FA0 i n t hei r l at es tuant i f i ed.

1 9 8 9 )

st at i st i cal compendi umare used f or t hi s pur pose and ar e as f ol l ows.

1 9 8 5 / 8 7

average

Wor l d hi de product i on i nput

4 , 9 2 6 , 6 0 0 t w/s

Wor l d sheepski n product i on i nput

9 3 4 , 0 0 0 t

w s

Worl d goat ski n pr oduct i on i nput

3 5 5 , 0 0 0

t w s

Worl d pi gski n pr oduct i on i nput

6 0 0 , 0 0 0

t w s

ADDr oxi mat e ut i l i zat i on of chem cal s on t he gl obal l evel :

Comput ed i n kg per

100

kg of wet sal t ed wei ght (w s), f i ni shes i n gr ams per

squar e met r e

Heavy Leat her

Li ght Leat her

7 0 6 . 9 9 2 t

w s

6 . 1 0 8 . 8 0 8 t

w/ s

Li me

Sodi umbi sul phi t e

Sodi um sul phi de

Ammom um sul phat e

Sodi um chl or i de

Cal ci um f or mat e

Sul phur i c aci d

Sodi umCar bonat e

Bat i ng agent

Bact er i c i des

Veg t ans

Chrome sal t s

( I

( t >

4 . 5 3 1 , 8 1 4 . 6 4

1 . 5 1 0 , 6 0 4 . 8 8

3 . 0 2 1 , 2 0 9 . 7 6

2 . 0 1 4 , 1 3 9 . 8 4

6 . 0 4 2 , 4 1 9 . 5 2

2 . 0

1 4 , 1 3 9 . 8 4

0 . 8 8 , 8 3 7 . 4 0

0. 1

7 0 6 . 9 9

3 5 . 0 2 4 7 , 4 4 7 . 2 0

8 . 0

4 8 8 , 7 0 4 . 6 4

- -

( % ) ( t >

4 . 5 2 7 4 , 8 9 6 . 3 6

1 . 5 9 1 , 6 3 2 . 1 2

3 . 0 1 8 3 , 2 6 4 . 2 4

2 . 0 1 2 2 , 1 7 6 . 1 6

8 . 0 4 8 8 , 7 0 4 . 6 4

2 . 0 1 2 2 , 1 7 6 . 1 6

1 . 5 9 1 , 6 3 2 . 1 2

2 . 0 1 2 2 , 1 7 6 . 1 6

0 . 8 4 8 , 8 7 0 . 4 6

0 . 1

6 , 1 0 8 . 8 0

Tot al ( r ounded up):

3 9 1 , 3 1 4 t

f or heavy l eat her s and appr oxi mat el y

2 , 0 4 0 , 3 3 8

t of c hem c al s f o r l i ght l eat her s .

Fur t her comput at i on: kg ws

x 0 . 7 5

= kg. wet bl ue

4 . 5 8 1 . 6 0 0

t wet bl ue


15/68

-

15 -

( % )

( t )

Syn ans 4 183, 264. 24

Veg t ans 3 137, 448. 18

Fat l i quor s 4 . 5 206, 172. 17

Dyes 2 91, 632. 12

Dye Auxi l i ar i es 3 137, 448. 18

Fi ni shes 200 gm m2

1, 200. 25 m l l i on

m2

240, 045. 00

I n

ot her wor ds, i n t he wor l d, ever y year about

3 427 000 t

of var i ous

chem cal s i s used f or l eat her pr ocess i ng;

a

s i gni f i cant par t o f t hi s amount

i s not act ual l y absorbed i n t he pr ocess and i s di schar ged i nt o envi r onment .

Amount of Pol l ut ant Der Wet Sal t ed Hi de Pr ocessed i nto Chrome Upper Leat her

One t onne r aw hi de yi el ds appr ox 200 kg l eat her pl us 50

m3

l i qui d

ef f l uent ( usual pr ocess wat er r equi r ement i s 25 to

80 m3

wat er per

tonne)

cont ai ni ng up t o 250 kg of COD, 100 kg of BODS,

150 kg of suspended sol i ds, 5

t o 6 kg of chr om um and 120 kg of sol i ds i n sl udge ( t he amount of wet sl udge

not l ess t han 500 kg) .

I n addi t i on t her e ar e i n- pl ant sol i d wast es and by- pr oduct s: unt anned

120

kg of r aw t r i mm ngs,

70

t o 230 kg f l eshi ng) , t anned ( 115 kg wast e bl ue

spl i t s , 110 kg t r i mm ng and shavi ngs and dyed

&

f i ni shed ( 2 kg of buf f i ng dust

and 32 kg of t r i mm ngs) per

tonne

of r aw hi de.

On the above basi s, f or l i ght l eat her pr oduct i on wor l dwi de:

L i qui d ef f l uent

cont ai ni ng appr oxi mat el y

COD

BOD5

Suspended sol i ds

Chrom um

Sul phi de

Sol i ds i n s l udge

Raw t r i mm ngs

Fl eshi ng (120kg. )

Wast e bl ue spl i t

Tri mm ngs & shavi ngs

Buf f i ng dust

Fi ni shed t r i mm ngs

pl us

305.44 m l l i on m3

( m l l i on t onnes )

1. 47

0. 61

0. 92

0 .03

0. 06

0. 73

0. 73

0. 73

0. 70

0 . 6 1

0. 01

0. 19

Tabl e 6 i l l ust r at es a t ypi cal unt r eat ed combi ned tanner y ef f l uent

cont ent .

2. 2. LOW WASTE TECHNOLOGI ES

2. 2. 1. Var i et y

of

pr ocesses

Ther e i s no basi c t annery pr ocess.

The var i et y of l eat her t hat can be

pr oduced i s r ef l ect ed i n t he var i et y and compl exi t y of pr ocesses t hat ar e

r equi r ed. Heavy l eat her s f or shoe sol i ng and i ndust r i al use ar e subj ect ed t o

l ong pi t pr ocesses usi ng veget abl e t anni n sol ut i ons. At t he ot her extr eme


16/68

- 16 -

t hi n pi ckl ed sheepski n f l esh spl i t s ar e t anned by al dehydes generat ed by

oxi di z i ng f i s h oi l

i n a hot ai r r ot at i ng dr um However t he vast maj or i t y of

hi des and ski ns ar e chr ome t anned

i n r ot at i ng pr ocess vessel s . I n exam ni ng

l ow wast e t echnol ogi es, t he pr epar at i on f or chr ome t anni ng i n t he beamhouse

and t he subsequent post - t anni ng pr ocesses on t hi s s ubst r ate wi l l be exam ned.

The most wi del y pr oduced l eat her i s chr ome t anned shoe upper l eat her based on

bovi ne hi des.

Pr ocessi ng i s by bat ch and the si ze

of

bat ches i s gover ned by t he

capaci t y of pr ocessi ng vessel s. Dr ums up t o 20 met r i c t onne capaci t y ar e t he

nor m Wat er usage var i es bet ween l ess t han 20 l / kg. up t o over 80 l / kg. The

l at est desi gns i n pr ocessi ng vessel s al l ow l ower vol umes of l i quor . But many

t anner s pr ef er hi gh f l oat l evel s whi ch pr oduce t he qual i t i es of l eat her t hei r

cust omer s r equi r e, par t i cul ar l y the f i neness

of

gr ai n. I n al l cons i der at i on

of wast e r educt i on i t must be r emember ed t hat t anner s compet e i n t he market

and ther ef or e t hey ar e di sci pl i ned by what t he market r equi r es.

A

bal ance has

t o be achi eved bet ween r educi ng envi r onment al i mpact and r emai ni ng

compet i t i ve.

2. 2. 2.

Wat er conser vat i on

Reduci ng t he usage of wat er t hr ough low float processing and oper at i ng

bat ch rat her t han r unni ng washes does not per f orce r educe t he pol l ut i on l oad.

I t merel y concent r ates i t i n a smal l er vol ume. Never t hel ess t her e are

benef i t s t o r educi ng t he quant i t y of wat er used. Cost s f or wat er ar e r educed.

Thi s i s i mport ant where t anner i es are ser ved by a muni ci pal suppl y. Batch

washi ng i n pr ocessi ng vessel s i s more cont r ol l ed t hat cont i nuous washi ng i n

dr ums wi t h l at t i ce door s and l eads t o gr eat er uni f or m t y of product . Low

f l oat pr ocessi ng i mpr oves t he upt ake of chem cal s and consequent l y a r educt i on

i n chem cal cos t s . A l ower vol ume of wat er l eads t o a l ower si ze of ef f l uent

t r eat ment pl ant .

Water conservation measures lead to lower investment and

operating costs. If such a policy is allied to the development of cleaner

process technology with the recycling and the recharging

of

process liquors

and the reuse of wastewaters where their influence on earlier processes is

innocuous

or

even moderately beneficial, then there will also be a reduction

in the environmental impact

of

the reduced volumes

of

liquid,

semi-solid and

vapour wastes that are emitted.

Wash l i quor s f r ombat i ng and neut r al i zat i on can be recycled t o soaki ng

The second l i me wash c an be t he basi s f or a new l i me

al t ed or gr een hi des.

l i quor o r as

a

soak wher e t he al kal i ni t y wi l l accel er at e t he soaki ng.

Low f l oat pr ocessi ng usi ng

40

t o 80 per cent wat er on t he wei ght of

goods, i nst ead of convent i onal 100 t o 250 per cent f l oat s , has cer t ai n

dr awbacks . Fr i ct i on wi t hi n t he goods and bet ween t he goods and t he body of

t he dr um can pr oduce hi gh t emper at ur es whi ch, par t i cul ar l y i n ar eas of hi gh

ambi ent t emperat ur e, coul d endanger t he qual i t y of t he l eat her.

Coupl ed wi t h

t hi s t her e i s i ncr eased wear on t he bodi es and dr i ves of pr ocessi ng vessel s.

Car ef ul moni t or i ng i s essent i al .

Moder n pr ocessi ng vessel s ar e desi gned t o perm t savi ngs i n wat er and

chem cal usage t hr ough t hei r act ual desi gn and i nt er nal st r uct ur e and t hr ough

t he i ncor por at i on

of

cont r ol l abl e drai nage and r ecycl i ng syst ems and aut omat ed

chem cal dosi ng and i nj ect i on syst ems. Manuf actur er s of such equi pment cl ai m


17/68

-

17

-

t hat savi ngs i n chem cal cost s soon cover t he cost of t hese vessel s. These

cl ai ms may wel l be j ust i f i abl e.

However pr ocesses of cert ai n t ypes of mat er i al and i n the pr oduct i on of

cer t ai n t ypes of l eat her r equi r e l ong f l oats . Dr i ed hi des have to be

r ehydr at ed i n pi t s or paddl es. Heavy l eat her pr ocessi ng whi ch r equi r es t he

gradual penet r at i on of t he veget abl e t anni ns has t o be per f or med l ar gel y i n

pi t s. Wool ski n pr ocessi ng has t o be done i n paddl es wi t h m l d sur f ace

agi t at i on i n or der t o avoi d f el t i ng t he wool .

2.2.3. Curing hides and skins

I n devel oped count r i es hi des and ski ns ar e ei t her spr i nkl ed wi t h

3 0

t o

50 per cent sal t on r aw ( gr een) wei ght or t hey ar e br i ne cur ed by i mmer si on

i n an agi t at ed sat ur at ed sal t sol ut i on whi ch i s mai nt ai ned at a speci f i ed

speci f i c gr avi t y i n a r aceway, I n devel opi ng count r i es sal t i s of t en t oo

expensi ve a commodi t y. Cont r ol l ed shade dr yi ng i s t he usual method of

pr eser vat i on. Dr i ed hi des and ski ns ar e of t en dust ed wi t h i nsect i c i de.

Der i vat i ves of chl ori nat ed ar omat i c hydr ocarbons per si st i n wast es and ar e

t oxi c t o t he envi r onment . They ar e now pr ohi bi t ed i n most Eur opean count r i es.

Pentachlorophenol, DDT, benzene hexachloride, dieldrin, arsenic and mercury

based insecticides are either banned or severely restricted and listed i n the

International Register of Potentially Toxic Chemicals (IRPTC). Rel at i vel y safe

insecticides are pyrethrum, permethrin, sodium silico fluoride and borax.

Dr i ed hi des r equi r e l arge vol umes

o f

wat er t o achi eve r ehydr at i on. Sal t

f r om cur ed hi des account s f or 60 per cent of t he sal i ni t y of t anni ng wast e

wat er; a ser i ous pr obl em i n count r i es wher e per m t t ed sal i ni t y di schar ge

l evel s ar e l o w .

2.2.3.1.

Process alternatives

Wher e a t anner y i s cl ose to a l arge abatt oi r ,

green hides can be

transferred

to

process without the necessity

of

temporary preservation.

Al t er nat i vel y, it is possible to chill hides and thereby preserve them without

salt for a few days. I t i s al so possi bl e t o pr eser ve r aw mat er i al f or sever al

weeks af t er i r r adi at i on by el ect r on beam or gamma r ays. The l at t er t wo

physi cal met hods ar e not wi del y pr act i sed.

Amongst t he chem cal methods ar e preser vat i on usi ng gaseous sul phur

di oxi de, whi ch i s, i n f act , unsui t abl e t o wor ki ng envi r onment s. Tr eat ment

wi t h

1

per cent sodi um sul phi t e and 1 per cent acet i c aci d i n a

20

per cent

l i quor on hi de wei ght , st or ed i n a cl osed cont ai ner wi l l keep r aw mat er i al f or

one mont h. Treat ment wi t h aci d met asul phi t e and al um ni um sul phat e wi l l

pr eser ve hi des f or f our mont hs. Bor i c aci d cur e l ast s t wo weeks and shor t er

cur es can be obt ai ned wi t h sodi um chl or i t e or sodi um f l uor os i l i cat e.

Propr i et ar y ant i f ungal agent s usual l y appl i ed to wet bl ue mat er i al can al so

pr ovi de shor t t er m pr eser vat i on of r aw hi des.

Commercial biocides with 5 per

cent salt is another alternative, provided the agents are biodegradable.

For developing countries the recommendation is the use

of

reduced

quantities of salt.

An appl i cat i on of

15

per cent wi l l s t i l l provi de s i x

weeks pr eser vat i on, whi l e

5

per cent sal t pl us bi oci de can gi ve t wo mont hs

pr eser vat i on. For expor t i ng, no l ong t er m pr eser vat i on exi st s other t han

dr yi ng. Ther ef or e t he r ecommendat i on i s shade dr yi ng and spr i nkl i ng wi t h t he

i nsect i c i de pybut hr i ne.


18/68

- 18 -

The advant ages of l o w wast e preser vat i on are t he r educt i on of sal t

ent eri ng wast ewat ers f r om 1 5 0 t o 2 0 0 kg/ t down t o 2 0 t o

80

kg/ t of hi de and

t he absence of t oxi c i nsect i ci des and bi oci des. But t he i mpr ovement s ar e at

t he expense of t he r educed ef f ect i veness of pr eser vat i on, t he hi gher cost of

i nnocuous i nsect i c i des and bi oci des and t he need f or r api d t r anspor t at i on.

2 . 2 . 4 . Beamhouse processes

Over

80 per cent of the organic pollution load in BOD5 terms

emanates

from

the beamhouse;

much of i t i s f r om degr aded hi de/ ski n and hai r mat t er.

10

per cent comes f r omsoak l i quor s, 70 per cent f r omunhai r i ng/ l i m ng and

3

per cent f r omdel i m ng and bat i ng. The soak wat er pr ovi des 60 per cent of t he

sal i ni t y, t he r emai nder comes f r omsal t appl i ed i n aci d and al kal i ne pr ocesses

t o suppr ess swel l i ng of t he pel t . Al kal i ni t y and sul phi de come f r om t he

l i m ng/ unhai r i ng pr ocesses and ammoni a ni t r ogen i s gener at ed dur i ng del i m ng

and bati ng. The beamhouse i s the sour ce of al l non- l i med and l i med sol i d

wast es such as f l eshi ngs, t r i mm ngs and waste spl i t .

2 . 2 . 4 . 1 . Soaking i s done i n pi t s, paddl es or dr ums somet i mes usi ng s oak-

ass i s t s such as 1 g/1 s odi um hypochl ori t e or 0 . 2 - 2 g/1 sodi um hydr oxi de or

sodi um sul phi de and/ or

0 . 5

t o

2

g/1 wet t i ng agent , emul s i f i er , sur f act ant or

enzyme pr epar at i on.

Li m ng ai ms t o separat e hai r and l oosen epi der mal debr i s and sur f ace

pi gment at i on on t he hi de/ ski n at t he same t i me swel l i ng and openi ng t he f i br e

structure so t hat sol ubl e pr ot ei ns and f at s ar e r emoved.

I f

a market f or

ani mal hai r exi st s, t hen hai r r et ai ni ng pr ocesses are used. Wool i s separ at ed

f r om sheepski ns i n devel oped count r i es i n separat e est abl i shment s known as

f el l monger i es. These est abl i shment s pr oduce gr aded and scour ed wool s, pi ckl ed

pel t s and f ur r i er gr ade wool ski ns f or f ur t her pr ocessi ng i nt o suede cl ot hi ng

wool sk i ns ( doubl e- f ace) or r ugsk i ns . W t h cer t ai n t ypes of sk i n, such as

mer i no, t he wool i s mor e val uabl e t han t he pel t .

Heavy hi des f or heavy l eather s ar e gi ven seven day pi t l i m ngs. Li ght er

hi des and ski ns ar e dr um or paddl e processed f or

18

hour s i n 2 0 0 t o 4 0 0 per

cent wat er on hi de/ ski n wei ght wi t h 2 . 5 per cent l i me and 2 t o 3 per cent

sodi umsul phi de,

i f hai r i s to be r etai ned ( or a hi gher per cent age of hai r i s

t o be di ssol ved

-

t hi s met hod boost s t he pol l ut i on l oad) . Ot her chem cal s

used ar e sodi umhydr osul phi de and sodi umhydr oxi de i n smal l amount s. Di met hy-

l am ne sul phate was another l i m ng auxi l i ary, but t hi s i s now deemed t oo

envi r onment al l y t ox i c .

Goat and sheepski ns ar e usual l y pai nt ed wi t h a sul phi de paste on t he

The hai r / wool i s r emoved by machi ne and t he pel t s ar e t hen l i med.

l es h s i de.

2 . 2 . 4 . 2 .

Alternative methods

I n order t o pr event degr aded ker at i n f r om ent er i ng ef f l uent st r eams,

hair-saving methods are recommended. Thi s can be done i n pi t s or paddl es

usi ng l ess sodi um sul phi de and mendi ng t he l i quors i nst ead of di sposi ng of

t hem Car ef ul anal yt i cal cont r ol i s essent i al . Removal of hai r i s t hen

per f or med by machi ne.

A dr umor paddl e pr ocess can be adopt ed usi ng

100

t o 2 0 0 per cent wat er

and no mor e t han

3. 5

g/1 sodi um sul phi de. The hai r separat es f r omt he st ock


19/68

-

19 -

i n sol ut i on, t her eby avoi di ng a machi ne pr ocess and the hai r i s t hen f i l t er ed

out by scr eeni ng.

A success i on of bat hs const i t ut es the ' Si r ol i me' pr ocess ; f i r s t l y sodi um

hydr osul phi de t o l oosen t he hai r , t hen sodi umchl or at e t o oxi di ze t he sul phi de

and f i nal l y l i me t o r el ease t he hai r i nt o t he bat h f or f i l t er i ng out .

Thr oughf eed syst ems spr ayi ng sodi um sul phi de and ot her chem cal s have

not gai ned wi de accept ance, al t hough t he r epeat ed use of sol ut i ons pr event s

hi gh COD cont ent i n wast ewat er s.

Unhairing/l iming

1

quors can be recycled after recharging, but s wel l i ng

t ends t o r educe wi t h s uccessi ve cycl es and so t he f i br e s t r uc ture i s

i nsuf f i ci ent l y opened up. Measur es s uch as aci di f i cat i on t o pH 4

pr eci pi t at i on and separat i on of or gani c mat t er , col l ect i ng of hydr ogen

sul phi de and r eabsor pt i on i n caust i c s oda have been t r i ed, but a bet t er met hod

i s the

separation of unhairing and liming.

I n t hi s met hod t he sul phi de unhai r i ng l i quor i s r echar ged af t er

f i l t r at i on. The pel t i s t hor oughl y washed and t he wast e wash l i quor used f or

soaki ng hi des. The pel t i s l i med wi t h an addi t i on of

0. 1

t o

0 . 3

per cent

sodi um hydr oxi de t o cont r ol t he swel l i ng. Thi s l i me l i quor can be reused

af t er r echar gi ng. Over a 2 0 day per i od, sul phi de can be r educed by 80 per

cent , l i me by 93 per cent , COD by 17 per cent and BOD, by 15 per cent i n t he

wast ewat er compar ed wi t h convent i onal l i m ng.

Sul phi de- f r ee pr ocess i ng i s poss i bl e but not wi del y pr act i sed.

The most

promising method is enzyme unhairing using proteolytic enzymes. For ski ns

t hi s can be accompl i shed over ni ght , but f or hi des i t r equi r es

1 - 2

days and i s

usual l y onl y 80 t o 90 per cent ef f ect i ve, r equi r i ng a l i m ng wi t h sodi um

sul phi de f or

4

t o

6 h

af t erwards. I n any event , l i m ng must f ol l ow enzyme

unhai r i ng i n or der t o swel l t he pel t . L i me l i quors can be r ecycl ed and al l

hai r i s r et ai ned.

The l at est devel opment i n t hi s f i el d i s t he

pressure injection

of

enzyme

solution from the flesh side

i n a t hr ough- f eed machi ne. Thi s t echnol ogy i s

st i l l at

an

ear l y st age.

For developing countries the recommendation for hides is the separation

o

unhairing and liming stages. Both liquors can be recharged and hair

screened out.

The i nt er medi at e wash can be r eused as a soak l i quor . Enzyme

met hods coul d be devel oped f or s ki ns. The cl ear advant ages ar e r educed

pol l ut i on l oad and reduced use of chem cal s. The or gani c l oad emanati ng f r om

t he beamhouse can be r educed by

60

per cent . The use of enzymes can l ead t o

t he pr oduct i on of l eat her wi t h cl eaner and f i ner grai ns wi t h l ess gr ai n

shr i nkage. The commer ci al i zat i on of hai r as a by- pr oduct of f er s a pot ent i al

econom c r et ur n. But al l t hi s has t o be bal anced wi t h t he need f or

r ec i r cul at i on equi pment , scr eens, unhai r i ng machi nes, t he gr eat er cost of

speci al t y chem cal s ( especi al l y enzymes) , t he capi t al , mai nt enance and

t echni cal cont r ol cost s and the l onger pr ocess t i mes enf or ci ng t he capi t al

cost of mor e wor k i n pr ocess.

2 . 2 . 4 . 3 . Deliming and bating

Removal of l i me of t en i nvol ves t he use of hi gh vol umes of wat er and

chem cal s i n t he pr ocess of r educi ng t he al kal i ni t y of t he pel t . The


20/68

- 20 -

appl i cat i on of ac i ds t o l i quor s and mat er i al cont ai ni ng sodi um sul phi de

generat es hydr ogen sul phi de gas,

so

i t i s necessar y i ni t i al l y to oxi di ze t he

sul phi de wi t h sodi umbi sul phi t e or , l ess commonl y, hydr ogen per oxi de.

Del i m ng chem cal s i n nor mal use ar e 0. 5 t o 2 per cent sul phur i c,

hydr ochl or i c , l ac t i c , f or m c or bor i c ac i ds or ac i d sal t s , ammoni umchl or i de

or sul phat e, or mor e r ecent l y by i nj ect i on of gaseous car bon di oxi de.

Del i m ng pr epar es pel t f or bat i ng by maki ng i t sof t and per meabl e t o

l i qui ds and ai r . Bati ng t hen r emoves t he l oosened epi der mal debr i s i . e. t he

l ast vest i ges o f hai r r oot pr ot ei n, pi gment at i on and sol ubl e col l agen.

Pro teol yt i c

enzymes appl i ed i n bat i ng modi f y t he el ast i n i n the pel t , maki ng

t he pel t s of t , f l at , i n f ac t r eady f or t anni ng.

Bat i ng i s carr i ed out i n t he same f l oat . The l engt h of t he pr ocess

I n

t he case of pel t f or heavy l eat her ,epends on t he t hi ckness of t he pel t .

l ess del i m ng i s r equi r ed pr i or t o veget abl e t annage.

The most usual chem cal s t o use ar e sodi umbi sul phi t e and 1 t o 2. 5 per

cent ammoni um sal t s i n a f l oat of 50 t o 150 per cent on pel t wei ght . The

del i m ng pr oceeds wi t h gr adual l y i ncr easi ng t emper at ur e, 20 t o 37C. The pH

at t he commencement of bat i ng shoul d be 7. 5 t o 8. Bat e compounds cont ai n

ammoni um sal t s t o pr ol ong t he del i m ng act i on and wood f l our as car r i er f or

t he enzyme. Thi s combi ned process gener at es 4 t o 70 per cent of ammoni a

ni t r ogen i n t anner y ef f l uent s .

Yet it is possible to delime without using ammonium salts. Hydr ochl or i c

ac i d wi t h sodi um bi sul phi t e, sul phur i c ac i d wi t h magnes i um sul phat e,

pr opr i etar y pr oduct s based on est ers of car boxyl i c aci d ( usual l y 1 t o 3 per

cent of f er ed) can bri ng the pH down t o 7- 8 r ange. Car bondi oxi de i nj ect i on

r equi r es assi st ance f r om a smal l quant i t y of ei t her ammoni um sul phat e or a

sal t of a pol ycar boxyl i c aci d. There ar e ammoni a f r ee bat i ng agent s

avai l abl e.

Bat i ng i s car r i ed out usi ng 0. 05 t o 0. 7 per cent bat i ng agent s, usual l y

compr i si ng pr ot eol yt i c enzymes

of

t he pancreas or of baci l l us subt i l i s and

per f or med at pH 8 t o 9 and 20 t o 37C.

Tanners i n devel opi ng count r i es coul d use ammoni a- f r ee del i m ng- bat i ng

pr ocesses pr ovi ded st r i ct cont r ol s ar e kept . I n or der t o pr event r el ease

of

hydrogen sul phi de, oxi dat i on wi t h bi sul phi t e shoul d be appl i ed. Carbon

di oxi de del i m ng r equi r es pr eci se t echni cal cont r ol and i nvest ment i n speci al

i nj ect i on pi pi ng. Spec i al i t y pr opr i et ar y pr oducts wi l l i ncrease cost s .

2. 2. 5. Tanyard processes

2. 2. 5. 1. Pi c kl i ng

Pi ckl i ng adj ust s t he pH of t he pel t pr i or t o tanni ng at t he same t i me

st er i l i z i ng enzyme act i vi t y. Chem cal s empl oyed are 5 t o 10 per cent sal t or

sodi umsul phat e, 0. 6 t o 1. 5 per cent sul phur i c , hydr ochl or i c , acet i c or f or m c

aci ds and a smal l amount of f ungi ci de; t hi obenzothi azol i s r ecommended r at her

t han par ani t r ophenol , t r i - o r pent a- c hl or ophenol , B. napht ho1,

par achl or met acr esol or mer cur y f ungi ci des whi ch ar e al l t oo t oxi c.


21/68

-

2 1

-

2 . 3 . 5 . 2 .

Hi des f r om

cat t l e r ear ed i n f eed l ot s t end to car r y much grease. Sheep and pi g ski ns

al so t end t o be gr easy. Sol vent degr easi ng l eaves a pr obl emwi t h di sposal or

gr easy resi dues af t er sol vent r ecover y.

The alternative is to abandon solvent

recovery a n d dissolve greases with surfactant. Thus gr ease and sur f act ant ar e

t r ansf er r ed t o wast ewat er and consequent l y onl y bi odegr adabl e sur f act ant s

shoul d be used.

I f poss i bl e, i t i s pref erabl e t o i ns ta l l a separ at e ef f l uent

col l ect i on syst emi n or der t o pr event gr eases and surf act ant bei ng di scharged.

Degreasing i s necessary f or ver y greasy hi des and ski ns.

Degr easi ng can al so be appl i ed af t er t anni ng, i n whi ch case i t i s mor e

usual to use a sol vent sys tem wi t h r ecover y f ac i l i t y us i ng whi t e spi r i t ,

ker osene, monochl orobenzene or per chl oret hyl ene. Thi s i s usual l y appl i ed t o

sheepski ns.

2 . 2 . 5 . 3 .

Tanning

Sevent y t o 80 per cent

of

l eather produced i n t he wor l d i s pr ocessed i n

i t s mai n t annage wi t h basi c chr om um sul phat e. The t annage begi ns i n t he

pi ckl e bat h. Thi s may consi st of 4 0 t o 6 0 per cent wat er wi t h 5 per cent

sal t , 1 per cent f or m c aci d or cal c i um f or mat e and 1 t o 1. 8 per cent

sul phur i c aci d. Pi ckl i ng t i me may be

0 . 5

t o

2

hour s dependi ng on the

t hi ckness of t he pel t .

The chr om um sal t , usual l y bas i c chr om um sul phat e i s added i n

quant i t i es r angi ng f r om

8

t o 1 2 per c ent , al ong wi t h ot her chem cal s s uch as

sodi um f or mat e or pht hal at e maski ng agent , a sal t of a di car boxyl i c aci d t o

enhance c hr ome upt ake and 0. 1per cent f ungi ci de i f st or age or sal e i n t he wet

bl ue condi t i on i s envi saged. The pr ocess i s basi f i ed usi ng

1

per cent sodi um

bi car bonat e, magnes i um oxi de or sodi um car bonat e. Al t er nat i vel y i t i s

possi bl e t o use sel f - basi f yi ng chr ome powders . At t he end of t he process,

whi ch may t ake 6 t o 2 4 hour s, t he pH i s 3 . 6 t o 3 . 8 and t he t emperat ur e 35 t o

38C.

Ef f l uent f r omchr ome t anni ng can cont ai n

60

t o

90

kg. neut r al sal t per

t onne of hi de, equi val ent t o 2 5 per cent of sal t i n t he whol e ef f l uent .

Chrome cont ent of ef f l uent may be

8

t o

1 2

kg of chr ome oxi de per t onne of hi de

or 4 t o 5 g/1 f r om a

100

per cent f l oat . Sol i d wast es at t he end of t hi s

st age i ncl ude chr ome l eat her shavi ngs and t r i mm ngs and wast e spl i t .

2 . 2 . 5 . 4 .

Alternative methods

Low chrome systems

usi ng onl y 5 t o 6 per cent chr om umsul phat e r equi r e

a pr et annage, poss i bl y us i ng an al um ni um sal t . Thi s appr oach has t he

advant age of pr oduci ng a pr et anned l eat her i n a

wet white condition

rather

t han wet bl ue.

I n t hi s condi t i on t he l eat her can be spl i t and shaved, t her eby

el i m nat i ng chr ome f r omwast e spl i t and shavi ngs. The l eat her can be st or ed

i n t hi s condi t i on f or up t o si x mont hs and can be t r aded as a s em - pr ocessed

l eat her . Al um ni um i n ef f l uent and sol i d wast es , however , i s not wi t hout i t s

pr obl ems as al um ni um i s known t o be mor e poi sonous t o aquat i c l i f e that

t r i val ent and even hexaval ent chr om ums under cer t ai n condi t i ons.

Product i on of wet whi t e as a pr el i m nar y t o mai n t annage i n chr om umor

ot her t anni ng agent s has not been adopt ed t o any ext ent by t he l eat her

i ndus t r y.

A s

a mai n t annage al um ni um i s unsui t abl e because i t i s not

suf f i c i ent l y r es i s t ant t o wat er and per spi r at i on i . e. t he t annage i s

r e ver s i bl e.


22/68

-

22 -

High exhaustion systems or reuse (recovery and recycle) systems are

probably more realistic that the change to alternative tanning materials.

Ther e ar e gr ounds f or accept i ng t hat t he ecot oxi ci t y of chr om um i s l ow.

The principal fear is that in the environment trivalent chromium will

oxidise into its hexavalent form. I f such oxi dat i on occur s under nat ur al

condi t i ons i t i s rever s i bl e. Tr i val ent chr ome sal t s do not i r r i t at e t he ski n,

t hey ar e nei t her mut ageni c nor carc i nogeni c. Thei r t ox i c i t y t o f i sh,

bac ter i a, al gae, hi gher pl ant s et c . i s r el at i vel y l ow. I n wat er , t r i val ent

chr ome sal t s ar e usual l y conver t ed i nt o chr ome hydroxi des. These age and

become l ess and l ess sol ubl e, wi t h onl y smal l pr opor t i ons r emai ni ng i n

sol ut i on. Onl y a smal l amount of t r i val ent chrom umcan be absor bed f r omt he

soi l by pl ant s ,

s o

chr om umdoes not accumul at e i n t he f ood chai n. Chr om um

i s an essent i al t r ace el ement . A chr ome def i ci ency i n humans and ani mal s can

i mpai r physi ol ogi cal pr ocesses l eadi ng, f or exampl e, t o cer t ai n types of

di abet es.

Alteriiative mineral salts such as aluminium, zirconium, titanium and

iron are possible substitutes for chromium salts. Bas i c al um ni umchl or i des ,

sodi um al um ni um si l i cat es and z i r coni um sul phat es have def i ni t e val ue as

r et anni ng mat er i al s at t he st age, f ol l owi ng t he mai n t annage, when di f f er ent

t anni ng mat er i al s ar e appl i ed i n or der t o conf er t he desi r ed f i nal char act er

t o t he l eat her .

Recent l y t i t ani um compounds, especi al l y ammoni um t i t anyl sul phat e and

magnesi um al um ni um t i t ani umcompl exes have been devel oped as al t ernat i ves t o

chr om um i n t he mai n t annage. But l eat her pr oduced wi t h t hese sal t s

so

f a r

have not matched the pr opert i es and qual i t i es of chr ome l eat her. That i s not

t o say t hat t i t ani umhas no f ut ur e. I t i s usef ul as a pr et an, a combi nat i on

t an and r etan. I n combi nat i on wi t h synt an i t produces a good subst r at e f or

dyei ng past el shades and pr oduces a good nap on suede.

I r on t annage can be di scount ed because of t he poor pr oper t i es t hat ar e

i mpar t ed, Zi r coni um and t i t ani um sal t s pr oduce accept abl e l eat her s and t hey

appear t o be ecot ox- i col ogi cal l y accept abl e, but t he l eat her s have l ower

shr i nkage t emper at ur es t han chr ome l eat her s and t heref ore coul d not wi t hst and

t he t emper at ur es appl i ed t o l eat her i n moder n shoe- maki ng pr ocesses.

Cert ai n or gani c compounds coul d r epl ace chr om um as t anni ng agent s.

However t hese ar e i socyanat es and al dehydes and f al l shor t of occupat i onal

hygi ene r egul at i ons. I n west er n Eur ope worki ng envi r onment s shoul d not

cont ai n mor e t han 1. 2 mg/m3 f or mal dehyde and 0. 8mg/ m3 gl ut ar al dehyde.

High chrome

exhaustion systems coupled with a reuse system offers the

best route to reducing the pollution load from the tanyard.

Sal t can be

par t i al l y r epl aced i n t he pr el i m nar y pi ckl i ng pr ocess wi t h a non- swel l i ng

aci d such as pht hal l i c. Thi s al l ows a reduct i on i n t he chr ome of f er ed because

t he or gani c aci d cr eat es t he condi t i ons f or good di st r i but i on of chr ome

t hr oughout t he subst ance of t he l eat her . Hi gher t emper at ur es and l onger

pr ocess t i mes ar e appl i ed t han i n convent i onal t anni ng. Fr om a pi ckl e

t emper at ur e of 30C, t he t anni ng t emper at ur e shoul d r i se t o 40C and t he f i nal

pH shoul d be bet ween 4. 0and 4. 7. Temperat ur e i s r el at ed t o t he vol ume of t he

f l oat and t he r ot at i ng speed of t he pr ocess vessel

so

care i s needed. Short

f l oat s

shoul d be used wher ever possi bl e, al ways bear i ng i n m nd t hat f r i ct i on

can damage gr ai n qual i t y. Auxi l i ar i es t hat mask t he r eact i vi t y of t he chr ome

al l ow t he achi evement of good penet r at i on, gr adual basi f i cat i on and good


23/68

-

2 3 -

f i xat i on of t he chr ome ont o t he pel t .

Appr opr i at e auxi l i ar i es ar e al i phat i c

di car boxyl at es, pol yam des, al um ni um si l i cat es and pol yphosphat es. Chr ome

f i xes t o t he react i ve car boxyl gr oups of t he pr ot ei n col l agen, t he mai n

const i t uent of hi de/ ski n. Ther e ar e r eact i ve am no gr oups and, i n or der t o

i ncr ease chr ome upt ake and f i xat i on,

i t i s poss i bl e to f i x al dehyde car boxyl i c

aci ds t o t he am no gr oups l eavi ng t he car boxyl gr oup f r ee t o f i x mor e chr ome.

Gl yoxyl i c ac i d appl i ed i n t he pi ckl e l i quor can pr ovi de th i s advant age.

Good f i xat i on i s cr i t i cal ot her wi se chr om um may be r el eased dur i ng

subsequent mechani cal and wet pr ocesses. I n ef f l uent f r om convent i onal

sys t ems onl y 60 per

cent of t he chr ome comes f r om t he t anni ng l i quors whi l e

20 per cent comes f r om dr ai ni ng and wr i ngi ng ( sammyi ng) and t he r emai ni ng 20

per cent f r omt he combi ned post - t anni ng wet pr ocesses of r et anni ng, dyei ng and

f at l i quor i ng.

The results from such applications are an

80

to

98

per cent exhaustion

of chromium from the liquor, a reduction of chromium in liquid effluent

of

10-

40 mg/l compared with 100-300 in conventional tanning.

In t er ms

of

wei ght of

mat er i al i n pr ocess, wast e chr ome i n ef f l uent i n convent i onal pr ocessi ng i s

8 t o 12 kg/ t on hi de. Thi s r educes t o 0. 2 t o 0. 5 kg/ t ( f i gure

1 1 .

However ,

t he cost of speci al t y, hi gh chr ome exhaust i on pr opr i et ar y pr oduct s i s

consi der abl y hi gher t han of convent i onal chr ome sal t s.

Af t er separ at e col l ect i on of wast e l i quor s f r om t anni ng, dra i ni ng and

sammyi ng,

t he t anni ng and dr ai ni ng wast es ar e f i l t er ed and r eused i n t anni ng.

The sammyi ng wast e i s f i l t er ed and used f or pi ckl i ng. Usi ng such a syst em

chr ome exhaust i on has been pr oved to i ncr ease f r om60 t o 70 per cent t o 95 per

cent and chr ome savi ngs have been 25 per cent .

Recovery

of

chro me, prior

to

recycling,

r equi r es t he pr ec i pi t at i on of

chr ome wi t h al kal i , poss i bl y wi t h addi t i on of or gani c f l occul ant and

t emper at ur e adj ust ment to accel er at e set t l i ng. Af t er f i l t r at i on t he

super nat ant l i quor can

be

di schar ged, whi l e the pr eci pi t at e i s redi ssol ved i n

sul phur i c ac i d and adj ust ed to t he r equi r ed basi c i t y .

I t shoul d be not ed t hat

di f f i cul t i es may be encount er ed i n pr eci pi t at i ng masked chr ome compl exes.

Al t hough more expensi ve t han caust i c s oda, sodi um car bonat e or cal ci um

hydr oxi de, magnesi um oxi de i s consi der ed t he best pr eci pi t at i ng chem cal .

( Fi gur e I 11 Chr ome Recover y) .

Ther e ar e di f f i cul t i es

i n

appl yi ng chr ome sol ut i onwher e a powder syst em

i s oper at i ve, t her ef or e i t may be pr ef er abl e t o base spl i t t annage on

r ecover ed chr ome, assum ng, of cour se, t hat spl i t t i ng has t aken pl ace i n t he

l i med condi t i on.

Reduct i ons i n chr ome em t t ed can be f r om 8 t o 12 kg/ t hi de down t o l ess

t han

1

kg/t.

Devel opi ng count r i es coul d move t o hi gh exhaust sys t ems, gi ven t he

mai nt enance of good t echni cal cont r ol .

The obvious advantages of these process modifications and reuse systems

are increased utilization of chromium and a consequent saving on chemical

costs and effluent treatment cost. The drawbacks are the expenditure on

sophisticated chemicals, special equipment for screening, filtering,

precipitation and circulation and monitoring equipment for precise technical

control.


24/68

- 24 -

Kecommendations concerning chrome tannage for the future could be for

a replacement of chrome at least

in the first phase

of

tanning.

Despi t e l ow

ecotoxi ci t y, aut hor i t i es throughout t he wor l d ar e tougheni ng t hei r r egul at i ons

on chr ome i n l i qui d ef f l uent s and i n sl udges f or dumpi ng. Chr ome f r ee sol i d

wast es f r om spl i t t i ng and shavi ng woul d be pr oduced and l i qui d di schar ges

r educed. I n t he second t anni ng phase chr ome coul d be appl i ed i n combi nat i on

wi t h al um ni um t i t ani um veget abl e t an or al dehyde, or a pur e chrome hi gh

exhaust s yst em coul d be appl i ed. I n each case chr ome di schar ge woul d be

r educed.

Devel opi ng count r i es woul d be wel l advi sed t o consi der wet whi t e

pr ocessi ng usi ng a masked al um ni umsal t . Despi t e pr obl ems wi t h t oxi c ef f ect s

on f i sh and aquat i c or gani sms and hi gh neut r al sal t em ssi on, a r educt i on i n

chr ome em ssi on may be enf orced by l ocal l egi sl at i on. Pr oduct i on of wet whi t e

coul d r educe chr ome ut i l i sat i on by hal f . Ther e woul d be no chr ome t anned

sol i d wast es.

The hi gh f i xat i on and l ow t oxi c i t y of t i t ani ummay resul t i n

t hese sal t s super sedi ng al um ni um i n t he pr oduct i on of wet - whi t e .

Ther e ar e di sadvant ages whi ch must be acknowl edged.

Pr ocess t i mes ar e

l onger , chem cal cost s ar e hi gher , spl i t t i ng and shavi ng ar e more di f f i cul t

i n t he wet whi t e and t he char act er of t he f i nal l eat her becomes f ul l y

dependent on the s econd phase ( mai n t annage) and t hi r d phase ( r etannage) of

t anni ng.

2. 2. 5. 5.

Vegetable tanning

i s nor mal l y appl i ed t o heavy hi des f or t he

pr o duc t i on of s ol e or i ndus t r i al l eat her s , i t i s al s o s t i l l appl i ed i n

devel opi ng count r i es to bovi ne hi des and s ki ns, sheep and goat ski ns i n or der

t o br i ng t hem i nt o a ' crust t anned' condi t i on, an i nt er medi at e st age at whi ch

t hey ar e a mar ket abl e commodi t y.

Tanni ng i s per f or med i n pi t s i n a count er- cur r ent syst em t he pel t

ent er i ng t he weakest l i quor and pr ogr ess i ng, pi t by p i t , t o t he st r ongest

l i quor . Such syst ems pr oduce l eat her i n up t o f i ve weeks, dependi ng on the

subst ance of t he pel t . Rapi d t anni ng can be achi eved by pr et anni ng i n a

pol yphosphat e t o assi st subsequent penet r at i on of t he t anni ng mater i al . I n

t hi s way t he pi t pr ocess can be r educed t o bet ween 20 t o 25 days. The

veget abl e t anni ng pr ocess i s t hen compl et ed i n a dr um i n st r ong l i quor . Sol e

l eat her r equi r es

3 3

t o 40 per cent t anni ng mat er i al on pel t wei ght , i ndust r i al

use of l eat her 28 t o 30 per cent , cr ust t anni ng 15 t o 20 per cent .

Veget abl e t anni ns ar e nat ur al l y occur r i ng pol yar omat i c mat eri al s,

di vi ded i nt o hydr ol ysabl e and condensabl e t ypes. The most i mpor t ant ar e

m mosa bar k and quebr acho wood ( condensabl e) and chest nut , val onea and

myrabol ans (hydr ol ysabl e) . Ef f l uent i s cr eat ed f r om t he dr a i n- of f f r om t he

weakest l i quor s as the st r ongest l i quor s ar e r echar ged. I t i s turbi d ef f l uent

causi ng dar k col our at i on t o t he m xed em ssi on and cont ai ns a hi gher l oad of

poor l y bi odegr adabl e COD t han chr ome t anni ng l i qui d wast e.

Al t er nat i ve veget abl e t anni ng met hods ar e cl osed syst ems whi ch ensure

hi gh ut i l i zat i on of mat er i al . The ' L i r i t an' pr ocess devel oped i n Sout h Af r i ca

consi st s of a pi t pr et annage f or t wo days usi ng pol yphosphat e and sul phur i c

aci d unt i l penet r at ed, f ol l owed by a pi t pr et annage f o r t wo days i n weak veg

l i quor , f ol l owed by t hr ee days i n a count er cur r ent syst emat 35C and t hen

f i ni shi ng of f i n a dr um at 40C wi t h a 45 per cent t an of f er .

Thi s pr ocess

t akes 12 days and ut i l i zes 97 per cent of t he t an appl i ed.


25/68

- 25 -

The advant ages of such pr ocesses ar e hi gh chem cal upt ake, l ow pol l ut i on

l oad, uni f or m penet r at i on of t he veg t an and shor t ened pr ocess t i me wi t h

consequent f i nanci al ef f i c i ency. Agai n, a di sadvant age i s t he necess i t y of

car ef ul t echni cal cont r ol .

2. 2. 6.

Post - t anni ng wet pr ocesses

Ret anni ng, dyei ng and f at l i quor i ng ar e usual l y car r i ed out as a

sequence i n t he same pr ocessi ng vessel s. I f veget abl e t ans ar e used,

2

t o

3

per cent of t he shaved wei ght ar e appl i ed. Synt ans ar e of t en combi ned wi t h

veg t ans because t hey have a di sper si ng ef f ect and i mpr ove t he di st r i but i on

of t he veg t ans t hr oughout t he subst ance of t he l eat her. Synt ans ar e of t en

used on t hei r own. They ar e s ul phonated pr oduct s of phenol , cr esol and

napht hal ene and resi ns f r ompol yur et hanes or pol yacr yl i c aci ds. They ar e used

f or f i l l i ng as wel l as tanni ng and cont r i but e t o the f i nal char acter i s t i cs of

t he l eat her . Res i ns ar e of t en appl i ed at t hi s st age as f i l l er s , ur ea

f or mal dehyde and di cyandi am de condensat es bei ng good exampl es.

Exhaust i on of r et anni ng agent s i s mai nl y a quest i on of quant i t y, t i me

and pH and ther ef or e t he r i ght combi nat i ons wi l l l ead t o sat i sf act or y r esul t s

as l ong as

t he

pr oduct s ar e not t oxi c. As synt ans r eact wi t h pr otei ns,

ecol ogi cal pr obl ems can be r educed i f t hey can be part i al l y r epl aced by

l ess

as t r i ngent f i l l i ng agent s . Sens i t i ve pr ot ei n i n f i sh i s vi r t ual l y t anned i n

concent r at i ons of 5 mg/ l of an ast r i ngent phenol synt an. W t h l ess

ast r i ngency,

t he l et hal l evel i s r ai sed t o bet ween 50 and 200 mg/ l . Bact er i a

i n bi ol ogi cal t r eat ment pl ant s ar e pr ot ei naceous consequent l y wast e ast r i ngent

synt an wi l l bl ock thei r act i vi t y. I t i s t her ef or e necessar y to know t he toxi c

ef f ect on bact eri a wher e wast ewat ers wi l l be t r eat ed i n such syst ems.

Tanner s nor mal l y pr ocess f or hi gh exhaust i on of dyes and f at l i quor s,

not l east because of t he di sci pl i nes of mai nt ai ni ng shade consi st ency and f at

di st r i but i on bat ch by bat ch, but al so the hi gh cost of t hese agent s det er s

wast age. The pr ocess of dyei ng and f at l i quor i ng i nvol ves aci di f i cat i on of

t he f l oat i n or der t o f i x t hese mat er i al s, but t he l ower i ng of t he pH bel ow

4

has t he ef f ect of r el eas i ng chr om umi nt o sol ut i on. Thi s pr obl emunder l i nes

t he necessi t y of achi evi ng ver y good f i xat i on of t he chr ome compounds dur i ng

t he t annage.

The addi t i on of amphot er i c pol ymer s can gr eat l y i mpr ove t he exhaust i on

of dyes and f at l i quor i ng agent s. Al t hough t hi s r epr esent s addi t i onal or gani c

subst ance ent er i ng t he syst em si gni f i cant r educt i ons i n COD can be achi eved,

pol ymer i c auxi l i ar i es can be t ai l or - made t o i mpar t desi r abl e pr oper t i es t o

l eat her . Not onl y does t hi s ensur e hi gh f i xat i on of ot her agent s, but

pol ymer i c auxi l i ar i es t hemsel ves can al so f unct i on as r et anni ng and f at

l i quor i ng agent s and ther eby reduce t he pol l ut i on l oad.

Dyei ng i s nor mal l y car r i ed out usi ng 1 t o 6 per cent ac i d, di r ec t ,

bas i c , pr e- met al i zed

o r

spec i al i t y dyes t uf f . Fat l i quor i ng i nvol ves t he

appl i cat i on of 3 t o 10 per cent r aw, sul phat ed, sul phi t ed f i sh, veget abl e or

ani mal oi l s , m neral oi l or synt het i c oi l s .


26/68

- 26 -

2. 2. 7. Finishing

2. 2. 7. 1. Conventional finishing

Convent i onal f i ni shi ng compr i ses of al l or a sel ect i on of t he f ol l owi ng:

col our spr ay, appl yi ng col our t o undyed l eat her or adj ust ment t o t he dyed

col our of l eat her usi ng dye di ssol ved i n sol vent ; gr ai n i mpr egnat i on wi t h a

pol ymeri c di sper si on di l ut ed i n sol vent t o penet r at e and i mpr ove t he f i r mness

and smoot hness of t he sur f ace - acr yl at es ar e most commonl y used; base coat ,

consi st i ng of a pol yacr yl at e, pol ybut adi ene or pol yur et hane bi nder wi t h

pi gment s and auxi l i ar i es t o ensur e good sur f ace col our and adhesi on; i f t he

l eat her i s sem - ani l i ne an ef f ec t col our i s spr ayed; f i nal coat , cons i s t i ng

of a ni t r ocel l ul ose or pol yur et hane l acquer .

Pr oposed l egi s l at i on to cont r ol t he em ssi on of vol at i l e or gani c

compounds has st i mul at ed t he devel opment of wat er - based al t er nat i ves t o

sol vent based f i ni shes whi ch have mai nl y been t he t op coat l acquer s.

Ther e i s a need t o el i m nat e hazardous cr ossl i nki ng agent s used t o

i mpr ove abr asi on and r ub r esi st ances i n acr yl i c and pol yur et hane di sper si ons.

Convent i onal spr ay equi pment i s wast ef ul . Bet ween

30

and

50

per cent

of f i ni sh can be l ost wher eas, usi ng a r ol l coat i ng machi ne, l osses may be as

l ow as 5 per cent . Exhaust i on f r om spray machi nes and dr yi ng t unnel s can be

i mpr oved by ef f i c i ent scr ubbi ng t o cl ear t he ai r em ssi on.

An over vi ew of maxi mal l y adm ssabl e concent r at i ons of gaseous har m ul

subst ances i n t he wor ki ng at mospher e ( dai l y exposur e

8

hour s) i s shown i n

t abl e 7.

2. 2. 7. 2.

Improved methods

W t hout t he i nt r oduct i on of so l vent - f r ee i ni shi ng a l ar ge t anner y coul d

be evapor at i ng 250 kg sol vent per hour , hal f f r om t he

spr ayi ng machi nes and

hal f f r om t he dr i er s . F i nal l acquer s may cont ai n

90

t o

150

g sol vent per mz

l eat her .

To

reduce health and safety hazards base and middle coats should

comprise aqueous polymeric dispersions containing safe crosslinking agents.

I socyanat es and azi r i di ne ar e no l onger r ecommended; epoxi des and

car bodi i m des are pr ef er abl e at t he r at e

of 1

t o

10

per cent epoxi de wi t h

pol yacr yl at e and

1

t o 10 per cent carbodi i m de wi t h pol yur ethane bi nder

di sper s i ons . Al t er nat i vel y, sel f - c ross l i nk i ng r eact i ve pol ymers cont ai ni ng

N- met hyl ol am de gr oups can be used.

An i nt er est i ng devel opment whi ch may gai n gr eat er accept ance i s t he

use

of finishes devoid

of

organic solvent or water.

They consi st of pr epol ymers ,

r eact i ve monomers , phot oi ni t i at ors , phot oact i vat or s and pi gment s. The

f i ni shes ar e cross l i nked by e l ectr on beam (EB) or ul t r a vi ol et

( UV)

radi at i on.

Thi s system i s par t i cul ar l y sui t ed t o f i ni shi ng cut component s f or shoes.

Anot her i nt er est i ng poss i bi l i t y i s t he i nj ect i on of l i qui d car bondi oxi de i nt o

a coat i ng. I n t hi s way t wo- t hi r ds of sol vent nor mal l y used can be el i m nat ed,

but t he equi pment and l i censi ng ar e expensi ve.

For pigment dispersions, products containing cadmium, lead and

hexavalent chromium are the most worrying. Or gani c al t ernat i ves ar e now

avai l abl e equi val ent t o l ead chr omat e and cadm um sul phi de i n al l except


27/68

- 27

-

coveri ng power. But t hi s can be compensat ed f or by t he i ncl usi on of

c ol our l es s f i l l er s i n t he f i ni s h f or mul at i on.

Top coat s shoul d be mai nl y aqueous r equi r i ng m ni mal sol vent . For

exampl e, a ni t r ocel l ul ose based wat er- sol ubl e emul si on cont ai ns

14

per cent

dr y mat t er , 56 per cent sol vent and

30

per cent wat er . When di l ut ed 100 per

cent wi t h wat er , t he sol vent component f al l s t o

28

per cent i . e.

20

t o

33

g/ m2

l eat her i ns t ead of 90 t o 150 g/ mz.

Al t er nat i vel y a syst emwhere n i t r ocel l ul ose i s par t i al l y r epl aced wi t h

pol yur et hane or pol yacry l at e di sper s i ons i . e. a syst em wi t h 12 per cent

s ol vent ,

10

g/ m2 can be used.

I t woul d be qui t e f eas i bl e f or t anner i es i n devel opi ng count r i es to

appl y aqueous f i ni shes f or base and m ddl e f i ni sh coat s and t o appl y aqueous

ni t r ocel l ul ose wi t h pol yur et hane or pol yacr yl at e t op coat s. Envi r onment -

f r i endl y cr oss l i nki ng agent s or sel f cr oss l i nki ng r eact i ve pol ymer s coul d

a l s o

be i ncor por at ed. Rol l coat i ng does not of f er i nsur mount abl e t echni cal

probl ems.

Benef i t s ar e f el t f r om t he r educt i on of VOCs i n t he wor kpl ace and

f i nanci al savi ngs accr ue f r omt he adopt i on of r ol l coat i ng. The di sadvant ages

ar e hi gher chem cal cost s and changes i n t he physi cal pr oper t i es of f i ni shes,

whi ch can be compensat ed by j udi ci ous r ef ormul at i on of f i ni shes.

2 . 3 .

EFFLUENT TREATMENT TECHNOLOGY

I t need be no sur pr i se t hat papers present ed at l eat her i ndust r y

conf erences nowadays ar e pr i mar i l y concerned wi t h ' gr een' pr ocess t echnol ogy,

r euse and r ecycl i ng syst ems and wast e t r eat ment . Ther e i s

an

abundance of

t echni cal l i t er at ur e r eveal i ng t hat t he l eat her i ndust r y i n t he devel oped

wor l d has r esponded wel l t o t he envi r onment al c hal l enge.

I t has been r ecogni sed t hat ' good housekeepi ng' , pr ocess modi f i cat i on,

r euse and r ecycl i ng syst ems yi el d cost savi ngs, whi l e ef f l uent t r eat ment

creat es on- cost s .

2 . 3 . 1 . Mode of t r eat ment gover ned by pr ocess and

case study leather industry

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