ControL of Stream Pollution Chemical Processing of Textiles

E.H. Daruwalla and G.N. Sheth Bombay Textile Research Association, Bombay

~~~ ~~~

It is now known that while textile industry is the largest foreign

exchange earner, it is also one of the biggest polluter of rivers

and groundwater because of discharge of toxic and hazardous

effluent. Many developed countries are turning their "green

attention'' to textiles and in some countries, it is not only the

final product but the entire production process of textiles will

come under strict scrutiny before fabrics or garments would be

considered for imports. Thus final fabrics or' garments not only

have to be environment-friendly but also have to be produced by

technologies which are considered as clean. "Eco-labels" marking

clean latiels are likely to be introduced by several countries

which may ultimately lead to a possible trade barrier against

manufacturers who are not able to comply with high environment

safety standards. It would then become necessary in near future

for textile manufacturers to clean up the whole chain of textile

production.

1

Environment Aspects in Chemical Processing of Textiles and _Remedial Measures

Preparatory Processing :

Multi-stage operations involved in chemical processing of textiles

cover areas such as desizing, scouring and bleaching, dyeing,

printing, finishing and processing of ready-made garments.

Typical chemicals and products used in different chemical

processes involved in textiles from the point of view of pollution

have been categorized into five grades viz., 1 being least harmful

and 5 being-most-harmful (Table I ) . 1

The heaviest effluent load in terms of COD/BOD is mainly

associated with preparatory processes involved in removal of

impurities from grey fabrics as in many cases the processor is

unaware of the size composition in the fabric that he has to

process.

Desizing operations are typically large contributors to pollution

and i n some cases upto 50% of pollutants are from finishing

operations (Table 11) . Size materials vary considerably in

pollutant characteristics (Table 111) alongwith metals which may

2

leach out of fibres,fibre finishes and surfactants with the result

that resulting pollutants show high ROD, COD and aquatic

toxicity . In case of synthetic sizes, removal itself normally

does not; contribute much to BOD load and also these sizes can be

2

recovered from waste water streams. Thus, a change from starch to

synthetic sizes can lead to BOD reduction of more than 90%.

2

In addition to basic size materials, commonly used assistants in

size mix are glycerine, waxes, urea and surfactants, each of which

contributes to BOD in different proportions (Table IV) . Thus, 2

reduction strategies f o r BOD in desizing would mainly depend on

selection of size material, work practices, recovery and reuse.

It is very essential not to dispose-off unused portions of size

mixes containing starches down the drain.

In order to minimise stream pollution in preparatory processing,

different approaches have been adopted. One is to replace ~~ ~

starches which have high BOD by other synthetic film-forming

polymers such as polyvinyl alcohol and different types of

acrylates. Another approach adopted is to cut down t h e stages of

preparatory processing from three to two to even a single-stage . 3

This process brings about not only reduction in energy but also

less water usage. The consequences of lower energy consumption

includes less steam raising and effluent gas formation leading to

reduced atmospheric pollution. .

r

Several early attempts to reduce processing stages under pad-steam

conditions were not successful because of inadequate seed and

size removal. Original attempts have been to combine stages of

scouring with desizing in what is termed as oxidative desizing. A

highly successful process is to add hydrogen peroxide or a

persulphate to the scouring liquor which forms an unstable ~

bleaching system. This unstable system favours desizing over

3

bleaching, arid therefore oxidatively desized fabric would require

ti bleaching stage in order to achieve optimum degree of whiteness.

Combined desize-scour which can be carried out hot or cold with or

without addition of stabilizers such as silicates or phosphates _ _ _ ~

h a s been quite successful.

However, both silicate and phosphate types of stabilizer have

~ b e e n found to be non-biodegradable and their use in peroxide

b l c a c h i rig lias been banned in several countries. Bombay Text. i 1 c

Research Association (BTRA) has identified a stabilizer for

peroxicle which is free from silica or phosphorous containing

comporinds. Diethylenetriaminepentaacetate ( D T P A ) has been

f o r l t l l i not only to prevent accelerated decomposition of peroxide

d u e t,o presence of metallic contaminants but a l s o preverr1.s

p r e m a t u r e oxidation of peroxide by virtue of probably ~c-?l,arding

the forination of peroxy or perhydroxy free radicals.

Chl o 1 . i :le-contai.ning bleaching agents are regarded as highly 1,c)x.i <.

and several countries have prescribed strict limits or banned

t . h e i r use in preparatory processing. Legislation is now being

iniplemented throughout EC and it, will have serious implication all

o v e r the world. Chlorine-containing bleaching agents such a s

sod i titi1 hypochlorite: o r s o d i u m chlorite are the :nain sourct” of ’

,-ibsor-bnbl.e o r y a n o h a l o g e n compounds (AOX) . un the other hund,

h y d r o g e n peroxide either in presence or absence of salt gives rise

4

to negligible increase in AOX, It has been observed that

increasing purity of the material to be bleached decreases the AOX

cantent of the effluent. Knitted fabrics made with less cleaner

combed cotton and loose stock having high content of vegetable

matter showed high AOX content . _ -

4 ~

In wool textile industry, sources of AOX have been identified due

to use of chlorine compounds which form part of shrink-resist

processes. These chlorination agents have now been replaced with ~

peroxy compounds viz., magnesium monoperoxyphthalate or potassium

monoperoxysulphate, alone or in combination with certain resins . 3

Dyeing :

Principal route by which dyes are responsible for stream pollution

are dye manufacture and their use in dyeing (Table V). The extent

to which dyes are lost in exhaust and in wash liquors vary

depending on the class of dyestuff applied to different

fibres(Tab1e VI) . Heavy loss in case of reactive dyes are 5

significant in case of dyeing cellulosics while lower wastage

figures of 3-10% have been reported for reactive dyeing of wool e

6

Normally, losses are considered to be about 10% for deep shades,

2% for medium shades and of no consequence when dyeing pale

shades.

5

Dyes are normally present in dyehouse effluent in concentrations

of 10-50 mg/l and BOD and COD of mixed wastes from dyehouses are

in the range of 200-3,000 and 500-5,000 mg/l respectively , 7

In addition to the high BOD and COD values for dyes, toxicity to

aquatic organisms has also to be considered, Out of the 3,000

dyes commonly used, 98% have an LC value in excess of 1 mg/l . Amongst the different dyes examined, fisp toxicity levels vary

from less than 1 to more than 500 mg/l LC , value(Tab1e VII)

8

50

9

5 6,

Although pollution potential of dyes has been put in category 3 on

an arbitrary scale of 1-5, many other produtts used in dyeing vie.,

carriers, dye-fixing agents, cationic retarders and heavy metal

salts are in highest catagory 5. t

Most obvious source of non-metallic dyebath agents are additives

to dyebath used for pre- or after-treatments. These products have

a greater pollution threat than dyes themdelves. It has been

observed that dyeing wastes contribute to only 10-30% of BOD of

the total. Acetic acid which is used in the dyeing of disperse

dyes on polyester, cationic dyes on acryli: fibres and acid dyes

on wool, silk and nylon has a high BOD and can account for 50-90%

of dyehouse BOD, Recently, BTRA has identi’fied a buffering system

which is free from drawbacks of acetic acid’;and at the same time,

equally effective for maintaining pH of dyeb’ath. With respect to

COD, contribution of dyes themselves is at 2-5% while that of

dyebath chemicals is as high as at 25-35% . Application method 10

f o r sulphur dyes gives rise to effluents containing sulphides

6

which are very toxic. Although an alternative reducing agent,,

glucose has been recommended, it is quite costly. Sharma at 1 1

Century Textiles has identified an eco-friendly product "Hydrol",

which is a by-product of maize starch industry and contains

reducing sugars as a very effective substitute of sodium sulphide

in sulphur black dyeing'. Further, quantity of 'Hydrol' required

f o r satisfactory dyeing is only one third of that of sodium

_ -

~

- ___

sulphide. Sodium hydrqsulphite used in vat dyeing gives rise to

sulphates and sulphite. Alternative to hydrosulphite suggested is

hydroxyacetone . Carriers used in dyeing of polyester, insect- ~~~ -

proofing agents applied to wool in dyebath and some classes of

dyes give rise to high AOX, +- .

Toxic effects of heavy metals to animal and aquatic life are

dependent on physico-Ahemical form'; In dyehouse effluent, heavy

metals arise as a consequence of heavy metal salts used in dyeing,

use of metal-complex dyes or from presence of impurities in

dyestuffs. Metal-complex dyes contain copper, chromium, nickel o r

cobalt. Strict limits on copper are being imposed and these will

become more rigid in futqre, Dichromate which is used in

oxidation of vat dyes in cotton dyeing is now being replaced by

hydrogen peroxide or 1,3-dinitrobenzenesulphonic acid . 13

-

Although about 70% of wool dyeing involves use of heavy metals

mainly chromium, modified application techniques have enabled

7

1 3 chromium load in the effluent to be reduced considerably . Current EC proposal is for an EQS of 15 g/l total chromium or

10 g/l for dissolved chromium. r

_- Printing:

. ___ Hard-to-treat printing wastes include colour residues, phosphate-

and nitrogen-containing chemicals, non-biodegradable organic

materials such as surfactants and solvents. These products can

pass through conventional activated sludge system and thereby

resist effluent treatments causing subsequent environmental

problems. Alkylphenol-ethylene oxide products are being replaced

~

by eco-friendly surfactants and white spirit:water emulsion

thickenings by aqueous thickeners in pigment printing. More

serious problem arises in printing of reactive dyes where large

quantities of urea are used to swell cellulosic fibres, bring

about disaggregation of dyes, increase solubility of dyes, retard

evaporation of water during drying and increase condensation of

water on prints during steaming. Provost has suggested three 14

approaches to eliminate or replace u r e t ~ in cellulose printing.

These include -

adoption of two-phase flash printing,

complete or partial substitution of urea with an

alternative chemical Metaxyl FN-TI and

mechanical application of moisture to printed fabric ~

prior to entering the steamer.

a

In flash-ageing process, highly reactive dyes are printed from a

paste-free from alkali and urea and then overpadded with high

conce tions of caustic soda and electroly-te.followed by flash-

steaming. However, it is observed that by adoption of this

technique effluent problems may well not be solved because the 15

flash-age process involves use of high salt and high pH liquors . .~

Moisture spraying systems have been found to be useful in

conditioning viscose fabrics after printing and drying but before

steaming. Two main systems of this type are WEKO System of 16 17

Germany and Spin-disc Applicator of James Farmer Norton . The

WEKO System offers to eliminate the use of urea totally by

printing from a urea-free print paste followed by applying

moisture upto 30% prior to steaming.

Finishing:

Amongst the different products used in finishing of textiles, the

most eco-unfriendly products are formaldehyde-based crosslinking

agents applied to cellulosic textiles to impart crease-resistance

and dimensional stability. During their application, evolution of

free formaldehyde can arise due to unreacted formaldehyde in the

product, liberation of formaldehyde during the crosslinking

reaction and slow generation of formaldehyde during storage of

resin-finished fabrics and garments. Different countries have

prescribed tolerance limits for free formaldehyde depending on the

end use of the treated fabrics and garments. Presence of

formaldehyde in the atmosphere and in waste water streams had been

9

considered as highly objectionable.

Two different approaches have been adopted to minimise the

problems connected with free formaldehyde in textile wet

(1) Development of formaldehyde-free crosslinking agents for

cellulosic textiles and formaldehyde-free dye-fixing

agents

__ ( 2 ) Use of formaldehyde scavengers during application and

storage of resin finished goods

Detailed studies have been carried out at BTRA from the point of

view of adopting both these approaches to minimise hazards of

formaldehyde and a non-formaldehyde crosslinking agent as well as

effective scavengers for formaldehyde have been developed.

Although both these approaches have yielded noteworthy results

from the point of view of hazards of formaldehyde, the desired

results produced on the treated fabric with respect to performance

h a v e not been equivalent to those obtained with N-methylol urea

type of compounds or formaldehyde-containing dye-fixing agents.

In the finishing of textiles a wide variety of products are being

used depending on the characteristics to be imparted to the

resultant fabric. Most of these products are either polymeric in

nature or anionic, cationic or nonionic compounds. In several

cases, catalysts are used alongwith these products to bring

10

abaut chemical reaction between them and the fibre substance to

make them more durable during use. Precise information is not

readily available regarding biodegradability and toxicity of these _ -

products and therefore, it is difficult to evaluate their impact

in stream pollution.

In order to overcome the problems connected with non-ecofriendly

~~~ products used in chemical finishing of textiles, researches are

now being concentrated in mechanical finishing of textiles whereby

desired properties viz., softness, stiffness, bulk, drape,

smoothness, handle etc. can be imparted to textiles by changing

the morphology or surface characteristics of the fabrics by

mechanical means. This in turn obviates completely the use of

chemical products thereby reducing considerably the problems of

toxicity and stream pollution.

Surfactants and Toxicity:

Surfactants are blended into most of the speciality products

manufactured to improve solubility and dispersibility, suspended

water-insoluble materials in baths, to improve compatibility with

other processing assistants, and to improve wetting, detergency,

surface properties,etc. The ability of a surfactant to lower

interfacial tension of water causes surfactant to be toxic to __

11

aquatic life. Thus, to reduce aquatic toxicity ( A T ) of textile

waste water, it is necessary to eliminate or reduce their use.

Surfactants vary widely with respect to characteristics for __

biodegradability, and therefore changes in type of surfactant used

can have a great effect on treatability of textile wastewater as

well as toxicity of the effluent. Main reason for aquatic

t.oxicity is the accumulation of surfactants at gills of fish which

A k i n k e r f e r e n c e with respiratory function ~f t h e fish.

There is considerable variation in toxicity of similar type. of

factants (Table VIII) Generally, surfactants with high HLB 2

wer toxicity.

dition to toxicity, one has to consider the biodegradability

ability of the surfactant. For instance, n surfactant

with low toxicity, which will not degrade, will produce more toxic

waste water effluent than one with high toxicity but high

degradability. In general, more linear a molecule greater i s i t s

degradability. Branched hydrophobes have less degradability while

aromatic surfactants are least degradable.

It has been observed that in processing of all-cotton, cottort-

blend fabrics, and manmade fabrics, chemicals are used in larger

amounts than necessary fop processing, resulting in high BOD/COD

ratio. Most biological waste treatment plants prefer BOD/COD __

ratio > 0 . 5 for influent. Values close to 0 . 7 are desirable.

BOD/COD ratios for typical textile plants effluent in U.K. suggest

12

18 an average value of 0.36 . Better mechanical cleaning of natural

fibres and reduction in the quantity as well as right choice of

chemicals in pr~cessing would yield significant decreases in _- -

pollution stream. -~ .__

Methods for Treatment of Processhouse Effluents:

The- challenge facing textile processing industry is to find

effective and comparatively inexpensive ways of treating its

effluent prior to discharge to meet new consents and at the same

time reduce overall cost of disposal. Textile wastewaters have

high BOD/COD due to presence of substances in highly emulsified

and/or soluble form. A number of pretreatment processes viz.

equalising/balancing, adsorption, flocculation, solid/liquid

separation, ultrafiltration, biolagical or physico-chemical

treatments, etc. are now available for effluent treatment.

Selection of the appropriate method of treatment is mainly

governed by several factors related to each effluent

characteristic such as relative costs, restrictions arising of

location and levels of treatment required. Dual use of

biological and physico-chemical treatments are more effective in

the removal of organics which are not biodegradable and those

constituents which are not amenable to chemical precipitation.

13

Precipitation/Coagulation Methods:

The first stage of treatment normally involves precipitation and

coagulation of the impurities to produce microflocks either by p H

adjustment or by use of organic coagulants. The latterare highly

charged cationic polyelectrolytes which can be used aloiigw i 1,h

inorganic coagulants.

Flocculation Methods,:

The second stage consists of flocculation where the microflocks

are tiggregated to larger agglomerates, Such f l o c c u l a Lion is

carried out by use of low to moderately charged aniiBti.ic or

cationic polyelectrolytes with very high molecular mass a n t 1

involves adsorption of polyelectsolyt.:!s onto particle surfaces.

These form physical bridges across the particle and result i n

formation of flock. Amine condensat'ion products have been found

to be highly effective for removal of reactive dye hydrolysate and

different types viz, vinyl sulphone, mono- and dichlorotriazine

and dichloroquinoxaline reactive d ' e s can be removed from

effluents.

Solid/LiQuid Separation:

Different methods such as gravity sedimentation, filtration and

centrifugation are used to achieve solid/liqui A

14

method which is gaining popularity is dissolved air floatation.

In this technique solids are made to float by introduction of

microscopic air bubbles which attach to the flock and make i t rise

to surface from where it is skimmed by mechanical scrapers in form

of sludge.

Biolortical Treatments: ~ - ~~~~ ~

The two methods of biological treatment are classified according

to oxygen requirements. In the aerobic treatment, free oxygen

dissolved in wastewater is used to convert wastes in presence of

micro-organisms to more micro-organisms and carbon dioxide. The

amerobic process takes place in absence of free oxygen, and waste

is converted to methane and carbon dioxide. For biological

processes to be effective there must be enough nitrogen and

phosphorous in the medium.

Methods for Removal of Colour from Dyehouse Wastes:

In western countries the problem of colour in rivers has recently

received critical evaluation because the combined effect of sewage

treatment and dilution are not sufficient to remove residual dye

in process of waste water. Effectiveness of colour removal is

judged by absorbance technique and value compared against consent

standards at different weavelength. A typical example is

15

1 presented in Table IX . Not all dyes give same level of problem

and factors such as extent of fixation on different substrate, and

residual amounts in waste water effect physical and chemical

behaviour during sewage treatment.

Different methods adopted for decolorising effluents containing

dyes are presented in Table X . Relative merits and limitations

of some of the methods for colour removal are given in Table XI .

20

~ 1

Activated charcoal adsorption technique is most effective with

relatively small volumes but with high volumes of water involved

in dyeing, size and cost of plant becomes disproportionate and

payback is poor. Lon exchange which can be classified as

electrostatic adsorption although mainly used i n inorganic

applications, the technique also finds application in removal of

organic contaminants, Ion exchangers themselves can be inorganic

zeolites or organic resins. Improved inorganic absorbers which

are now available have good colour removal properties even at h i g h

concentrations and in presence of other contaminants. Removal

rates are rapid and removal takes place to a low level required

to meet consent conditions. Membrane technology incorporates

ultrafiltration, nanof iltration

Ultrafiltration is not suitable for colour removal as

:;i;:~+ of membrane is too large to prevent

16

through. The other two techniques are effective in separating

large dye molecules from the effluent. Reverse osmosis can remove

colour regardless of the type of dyestuff and decolourisation in

the range of 95-100% have been achieved . About 10-25% of 21 __

original waste stream containing mostly organic contaminant appear

as concentrate. Originally cellulose acetate membranes were used

but now zirconium oxide/polyacrylate membranes in tabular

~ configuration has been found to achieve 99% colour removal and

more than 85% TOC. However, capital cost is high and cleaning of

membranes causes problems.

Amongst chemical treatments, oxidation plays an important role in

effluent treatments. Chlorination with chlorine, chlorine dioxide

o r sodium hypochlorite is simple, relatively inexpensive and

creates no sludge. However, this technique creates problems

connected with production of chlorinated organic and with some

dyes, discolouration is only temporary. Ozone-initiated

techniques for destruction of dyestuffs either through use of UV

radiation or catalysis results in cleaving of bonds in the dye

molecule to produce uncoloured compounds, Such techniques are

suitable for large volumes of effluent and reaction is reasonably

fast. However, capital cost is high. Another drawback of this

system is possibility of toxicity of breakdown products because

dyes containing nitrogen, chlorine or sulphur on oxidation can

17

yield metabolites which could be more toxic than the original

dyes. Reduction processes with sodium hydrosulphite are a l s o

recommended for effluents containing azo dyes. However with

triphenylmethane dyes, discolouration is not permanent and colour

gets regenerated in oxidising media.

2 2 Rodman has compared different methods for removal of colour from

textile dye wastes and has arrived at conclusion that coagulation

by different salts yields poor results, Granulated activated

carbon was more effective for bio-aeration, otherwise conventional

bio-aeration was ineffective in removal of colour. Activated

C a r b o n Column method has been found to be ineffective for removal

o f disperse dyes. Reverse osmosis has been found to be most

successful and 70-80% colour can be removed. Radiation with

o\.ygen showed some promise for effluent treatment.

Systems Based on Electrolysis:

Electrochemical technology was developed about twenty five years

ago for removing hexavalent chromium and other heavy metals from

wastewaters at heavy flow rates, It was soon discovered that

besides removal of heavy metals the system was also very efficient

f o r colour, BOD and COD reduction. It was observed that using

sacrificial iron electrodes consisting of carbon steel plates and

passing DC current, BOD and COD could be reduced by 50-70% with

18

retention times of less than ten minutes. In addition, colour

conStituents produced from a wide variety of watersoluble and

water-insoluble dyes and pigments was possible and also

coagulation of total suspended solids could be achieved . 23,24

Iron levels of 200-500 mg/l have been claimed to remove colour by

approximately 90-98%. Colour constituents or dye molecules can be

removed by adsorption onto the iron matrix created by ferrous

ions. Real benefits of electrochemical technology is its ability 25

to handle wide variety of wastewater compositions and flow rates .

Very recently, it has been observed that electrochemical treatment

of disperse colour dyebath with aluminium electrodes resulted in

removal of colour, dispersing agent and dyebath assistants to

variable degree of completeness Increasing release of 26

aluminium from the electrodes caused increased removal of colour.

Presence of dyestuff in the bath facilitated removal of dispersing

agent. Lignosulphonate type of dispersing agent could be removed

much easily and completely than naphthalenesulphonate type a

Regardless of duration of treatment, not all dyebath assistants

could be removed from dyebath effluent.

19

Conclusions:

Three main approaches for reduction of pollution from textile

processhouses will be elimination, substitution and treatment

before the release into sewage. Ideal situation would be total

recycling of water within the premises _of the processhouse and

will require substitution or elimination of polluting chemicals

and a final treatment for reuse of water. Energy consumption

should be reduced by low-temperature treatments and combination of

several stages into a single-stage operation.

Main thrust areas for researches are

changes in size composition,

effective effluent treatment processes to remove natural

fats and waxes from scoured liquors,

ideal dyeing systems involving neutral cold-dyeing

Lechniques, 100% exhaustion with minimum use of auxiliaries,

development of printing techniques to avoid problems

associated with washing-out thickenings and surplus dyes and

chemicals, and

development of wet-on-wet processing techniques to eliminate

multiple drying operations.

achieve such goals it requires partnership and collaborative

work between dyes, chemicals and machinery manufacturers, research

technologists and the textile processing industry.

20

References:

1.

2.

3 .

4,

5,

6.

7,

8.

9,

10,

11,

12,

13.

14.

15.

16.

17.

18.

19.

20.

Cooper, P., J.Soc. Dyers Colour,, 108, 176 (1992). Smith, C.B., Text.Chem.Colorist, .24(6), 3 0 (1992).

Hickman, W.S., J.Soc,Dyers Colour., 109, 32 (1993).

Schulte, G., Textil Praxis Internat., 45, 40 (1990).

Hobbs, S.J., "U.K. Dye Production and Use in Textile Industry, Environmental Research", 1988.

Ross, J.P.M., "Routes of Dyes into Environment", National. Institute of Public Health and Environment Protection, Bilthoven, Netherlands, 1985.

Laing, I.G., J.Soc.Dyers Colour., 21, 56 (1991).

Anliker, R., 12th Conference IFATCC, Budapest, 1981.

Clarke, E.A. and Anliker R., Rev.Prog. Coloration, - 9 14 84 (1984).

Tincher, W.C., Text.Chem.Colorist, 21, 3 3 (1989).

Dalmia, R.K. and Sharma, M., "Cleaner Production Worldwide", U . N . Environment Programme Industry and Environment Programme Activity Center, France, 19(1993).

Baumgarte, U. Rev,Prog.Coloration, 17, 3 2 (1987).

Lewis, D.M., J.Soc,Dyers Colour, 105, 119 (1989). Provost, J.R., ibid., lJ8, 260 (1992).

Eisenlohr, R.H., Text.Chem.Colorist, 2 3 ( 6 ) , 17 (1991).

Muller J., Schuberte, D. and Rouette, H.K., Textilveredlung, a, 11 (1990). Textile Month, ( 5 ) , 51 (1982).

Tincher, W.C., Textile World, 143(5), 60 (1993).

Schulz, G., Fiebig, D. and Herlinger, H., Textilveredlung, 23, 445 (1988).

Steenken-Richter, I. and Kermer, W . D . , J.Soc,Dyers Colour., - 108, 182 (1992).

21

2 1 . Halliday, P . J . and Beszedits, S., Can.Text.J., 78 ( 1 9 8 6 ) .

22. Rodman, C.A., Text.Chem Colorist, 3 ( 1 1 ) , 45 ( 1 9 7 1 ) .

23. Demmin, T . R . and Uhrich, K.D., Amer. Dyestuff Rep., 7 7 ( 6 ) , 13 ( 1 9 8 8 ) .

2 4 . Uhrich, KID., Timothy, R. and Demmin, T.R., Book of Papers, AATCC International Conference, 9 7 ( 1 9 8 8 ) .

2 5 . Kennedy, M., Amer. Dyestuff Rep., 80 ( 9 ) , 2 8 ( 1 9 9 1 ) .

26. Technical Paper, Hudson-Mohawk Section, Text.Chem.Colorist, ' 1 . 1

( l l ) , 2 9 ( 1 9 9 2 ) .

2 2

Pollution CaPa bilitv of chemicals and Products Used in Chemical Pr ocess ing Textile%

Alkalies Mineral acids ’

Neutral Salts Oxidising Agents

Starch size Biodegradable surfactant Organic acids Reducing agents

Dyes and Brighteners Polyacrylate size Polymer finishes

Relatively harmless

Moderate -high BOD

Difficult to biodegrade

Wool grease Difficult to PVA biodegrade, Starch ethers Moderate Non-biodegradable surfactants BOD Anionic and non-ionic softeners

Formaldehyde N-methylol resins Chlorinated solvents and carriers Cationic retarders and softeners Biocides Sequestering agents Heavy metal salts

Unsuitable for biochemical treatments

1

2

5

Deeising (Woven fabric)

Enzyme/Starch

Starch/CMb mix

Polyvinyl alcohol or CMC

Scouring

Bleaching

Peroxide

Hypochlorite

Mercerising

Without caustic recovery

With caustic recovery

67

20

0.5

40-60

3-4

8

15

6

Dyeing 50-100

Finishing 0-50

-- BOD of Size M a t e r i u

CMC 30,000

Hydroxyethyl cellulose 30,000

Starch ethers 360,000

Sodium alginate

Polyvinyl acetate

Polyvinyl alcohol

550,000

10,000

10,000-16,000

Table

Values Commonly Used ComDonents in Sise Mix

Urea

G l y c e r i n e

Waxes

O i l s

D ie thy lene glycol

90,000

640,000

100,000-1,500,000

100,000-1,500,000

60,000

Cotton

Wool

Polyester

Direct

Reactive

Vat

Sulphur

Chrome

1:2 - Metal complex

Acid

Disperse

Salt Unfixed dye (5-30%) Cu-salts Cationic fixing agents

Salt and alkali unfixed dye (10-40%)

Alkali Reducing agents Oxidising agents

Alkali Reducing agent Oxidising agent Unfixed dye (20-40%)

Organic acid Heavy-metal salts

Organic acid

Organic acid Unfixed dye (5-20%)

Reducing agents Organic acids Carriers

Proportion of D y e s of Different Classes -- Lost in Exhaust and Wash Liauors

Direct 5-20

Acid 7-20

Basic 2-3

Metal-complex 2-5

Sulphur 30-40

Reactive 20-50

Disperse 1-20

Vat 5-20

Table

Levals . . Fish Toxicitg

LC V a l u e , 50

Proportion of dye, %

1-10

10-100

100-500

> 500

2

1

2 7

3 1

28

Table VI11

Nonylphenol ethoxylate

Diethanol cocoamide

Linear alcohol ethoxylate

Dodecylbenzene sulphonic acid

Sodium lauryl sulphate

Stilphated ethoxylated alcohol

Tallowamine ethoxylate (depending on EO moles)

veasuremen t & Colour in T e x t i l e Eff luent aaainst ‘Consent’ S,tandard

400 0.060 0.090

450 0.040 0.056

500 0,035 0.051

5 5 0 0.025 0,075

600 0.025 0.067

650 0,015 0.026

Table &

Methods of Decolourisina Effluents Containing Dyes

Adsorption

Precipitation

Oxidation

Reduction

Electrochemical with iron or aluminium anodes

Activated charcoal Ion-exchange resins Modified cotton Biofilters

Iron salts Aluminium salts Bentonite Cationic polymers

Ozone Hydrogen peroxide Chlorine, hypochlorite

Sodium hydrosulphite

Electrolysis and floatation

Tab le

Colour Removal Techn iaues

A c t i v a t e d c a r b o n V e r y good Smal l Slow

Membrane t echno logy

Good

Ozone t r e a t m e n t Good

C o a g u l a t i o n / f l o c c u l a t i o n

Good

N e w e r t e c h n o l o g i e s Good

Large F a s t

Large Medium

Large Medium/ F a s t

I /

Large F a s t

High Regenera- t i o n

High C l e a n i n g D i s p o s a l

BY- p r o d u c t s COD- r e d u c t i o n

High

Medium Sludge removal COD- r e d u c t i o n

Medium/ R e a c t i v e

a f f i n i t y A p p l i c a b l e t o a c i d d y e s

High dye