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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