Ecological Aspects of Water Usage in the Textile Industry

Ecological

G. DURlG

ClBA-GEIGY Ltd Basle Switzerland

Aspects of Water

From cave drawings and from records preserved on clay tablets, the history of man’s use oftextiles can be traced back to well before the birth of Christ. Obviously the quantities per head of’ poptthtion required fur dothing and other purposes were then minute compared with those of today, and their prodirction and processing was iinlike1.y to have caused any ecological problems. When considering that over the last thousand years alone the world’s population has increased more than tenfold. and in that time, the demand for clothing has grown out of all proportion, it can be seen that the process is bound to have left i ts mark.

Usage in the Textile

Introduction From the earliest times, textile finishing processes have been carried out in the vicinity of water which has always been used as an inexpensive medium and carrier, not only for washing and scouring, but also for dyeing and finishing generally. The textile finishing industry today is a major user of water (Table I ).

Although the figures for world supplies of water iiiay suggest that it is available in unlimited quantities, a closer examination gives a very different picture (Table 2 ).

Of the world supply of 1.4 milliard cubic kilonietres, only about 0.8% is fresh water; the rest is either seawater or in the form of pack ice in the Arctic and Antarctic. Although that 0.8% is a substantial quantity, it can be misleading. In fact the only water available for use is that which falls as rain, and of that only as much as can be collected in reasonable quantities in the form of surface water (springs, rivers, lakes, etc.) or from easily accessible underground reservoirs can be used. It is necessary, therefore, that as much of the available supplies are saved and conserved in order that the ecological balance, that is, the relationship between living things and their environment, is not seriously upset.

Some countries are already approaching a crisis point. For example, in West Germany, according to a 1963 estimate, more than 10% of the total available water stocks was used for Joniestic and industrial purposes. Other industrialized countries are probably in a similar situation. It is a matter of great urgency to make the most careful use of rainfall, man’s only source of water, the supply o f which cannot he controlled. Even though industrial production goes up the water which industry consumes must be stabilized. Only then will it be possible to conserve the stocks man has for the maintenance of human life, as well as the preservation of the flora and fauna of his ecosystem, and to keep the world a pleasant place to live in.

*TABLE 1

Industry

A Comparison of Water Consumption in the Various Industries of West Germany and the USA

lndustry

Coal Chemicals Metals Wood and paper Oil Food Quarrying Textiles Automotive Plastics and rubber Others

*TABLE 2

World Supplies of Water

West Germany USA I963 lCj70

n13x 10% 1n3 x I O ~ %

2.8 2.7 1.7 0.9 0.4

0.3 0.3 0.3

2.3

Total world supplies of water Coniprising: seawater

ice fresh water

30 29 29.6 24 18 29.7 24 10 25.0 20 4 27.4 22

5 .3 4 3 3 4.3 3 3

4.2 3 9.2

1.4 milliard km3 0 7 . 2 Y

2.0% 0.8%

Fresh water supplies in West Germany, 1963 milliard in3

Precipitation 200 Evaporation 110 Run-off 90

Consumption : Total 14 Industry 11.7

Conservation of Water in the Textile Industry

Attention has already been drawn to the fact that the textile industry, with its fibre production running at some 2 5 million tonnes per annum (Figure 1 ), is a major user of water. This can be appreciated when considering that textile finishing requires between 50 arid 300 1 of water for every kg of material (Table 3).

It is necessary to draw up an accurate water balance to indicate the extent to which a particular mill is involved in the use of these amounts of water. It is not enough to know simply the amount of water passing into and.out of the works;

*Gibb, ‘Water Resources Planning’, Water Pollution Control. 74 ( I 9 7 5 ) 262. This article includes, o n page 269, a water ‘demand/resource balance diagram’, which is of interest in comparison with Tables I and 2 above.

70 REV. PROG. COLORATION VOL. 7 1976

co -

1 1 12 5

1973 tom 25 1 inillion tonne5

1 3 7 3 6 6 5 757

0 15 PA 1 5 7

PES 2 7 7 1 6

Figure 1 World production oftextile fibres

TABLE 3

Consumption of Water in Textile Finishing

Figure 3 ~ Water consumption for vat dyes

preventing leakages, by installing rapid cut-off valves to eliminate the running-water pipe at the place of work, by not allowing vessels t o overflow and by adhering strictly to prescribed dyeing times and cycles.

Percentage of water consumed as steam 5-10 for cooling 25 35 processing water 50--60

Consuniption of water by fibre (I/kg material) cotton 50-200 wool 7 5 -300 synthetics 10-100

every preparatory treatment and every dyeing and finishing operation, has its own water problem. Each of these must be known individually before it is possible to devise and carry out effective measures. The amounts of water consumed in dyeing processes involving different types of machinery (Figures 2-4), will vary considerably, without taking into account the immediate savings that, for example, can be made by

Figure 4 - Water consumption for reactive dyes

Figure 2 - Water consumption for direct d-ves

Even more striking is the comparison (Figure 5) of the amounts of water required in three different washers used for washing-off reactive-dye prints. In this case a saving of some 96% was made by developing a new type of machine.

There have been many investigations into these problems in recent years. One typical effort is summarized in Table 4.

Water meters and guide lines giving the quantities of water for each machine can be helpful in training personnel t o be economical with water and thus reduce its cost considerably. This also brings extra savings in other directions, for instance in power costs, as a result of less work o n the pumps; heating costs can also be reduced. That the heat from hot waste liquors should be used is something that cannot be too strongly emphasized, for it is not only a way of making use of hitherto untapped reserves of energy, but it also means lowering the waste water temperature t o the level required for discharging it into the sewer. Table 5 indicates how much heat

REV. PROG. COLORATION VOL. 7 1976 71

can be saved on a cheese-dyeing machine of about 3000 1 capacity.

Water Pollution Control In the textile industry many niills have their own wells or private water rights allowing them to draw on supplies which are sufficient to meet their needs for many years to come, and in some cases can even provide the extra water required for meeting an increased production. The limiting factor here is the second of the two functions of water mentioned earlier that of a carrier.

All pollutant matter, including dyeing and finishing chemicals not fixed on the fibre, is carried in the works effluent and by one route or another enters the receiving waters, which may be a river, stream or lake, or even the ground water. Today these waters are often overloaded as a result of heavy industrialization or overcrowding. Warning signs have brought a sudden awareness of possible danger to the environment, and attitudes are beginning to change. In order to re-establish a healthy biotope, it is necessary to ensure that pollution loads do not exceed the natural capacity of the receiving water for self-purification.

1:150

300 m (36 kg ) cotton printed with reactive dyes

continuous washer

rotary hydroextract ion stem I

1:50 1:6

effective liquor ratio

Figure 5 ~ Wash-off of reactive-dw prints on three types of washer

TABLE 4

Suggestions for Saving Water in Various Textile Processes

Material Type of Machine

Loose stock Circulating liquor machine

Yarn Hank dyer

Package dyeing machine

Hose and Pack system tights

Woven fabric Rope washer Desizing Bleaching Winch

Dyeing Jig (direct) Winch

Fibre* Normal Quantity

co

co

PA

co

co

co

co

of Water Used 10-14:l

25-30: 1

15:l

20-25: 1

48 I/kg

83-1 14 l/kg

89 I/kg.

20-25:1

Suggestions for Saving Standing bath, reuse of previous rinse bath for wetting out next batch Use of spray- dyeing system Use o f compacting devices Automatic boarding machine = 54-91 l/kg Open width washer 2 2 I/kg J-box bleaching 56 I/kg Open width bleaching 67 I/kg. Continuous dyeing machine 26 I/kg. Jet dyeing machine 6-2 I : I

Savings (%I

30 40

10 -20

40 -60

5 5

30-40

71

30-50

* CO = cotton PA = nylon


TABLE 5

Savings in Heat on a Packagedyeing Machine

Machine Package Dyeing 3 100 litres capacity

Liquor temperature 95°C Waste water temperature desired 35°C Fresh water temperature 15°C Energy recoverable in heat exchanger(Q*) 2 186 000 kg cal /batch

S 370 kg steam at 6 atm. 75% for heating the

corresponding to

dye liquor to 95°C

'Q = VI, X specific heat AT specific heat = I kg cal / k g f C (heat required to produce I tonne of s team at 6 atm.= 500 000 ky cal)

THE PRESENT LEVEL O F POLLUTION I N THE TEXTILE INDUSTRY It can be assumed that the amounts of dissolved or dispersed pollutant matter produced in the basic processes of yarn preparation, weaving and knitting (except tor synthetic fibres) are largely negligible. Most of the pollution load arises in wet finishing treatments, and here again the quantities vary enormously froin process to process. This is illustrated in Table 6, which also shows the differences between cotton and wool.

I t can be seen from Table 6 that in the case of cotton, siLes are the major factor. being responsible for almost 75% of the pollution load. In the cise of wool, however. the natural impurities in the unwashed fibre account for 30 to 50% of the pollution load.

TABLE. 6

Pollution Loads in Various Wet Finishing Treatments

Process

Cotton Desizing Boiling off Bleaching Mercerizing Dyeing Prin ting Washing-off finishing Wool Scouring of raw wool Milling Carbonizing Dyeing

Nylon Po I y es t e r Polyacrylic

Water Required

(l/kg)

15 20

150-180 4

7 30 25

110 5

10- 40 5- 18

30 80 10 -180

150-200 150-200 150- 200

3000- 6000 8000 -14000

800- 1200 7- 50

400 - 1600 1200

100- 300 1000-- 2000

22000 4000 -24000

200 500 200 - 4000

300- 500 300- 8000 500 ~ 700

Merliutl ofilleasiirenieti I oj' Polliiriot~ Pollution. in this case. is measured in terms of the BODS, or biological oxygen demand after five days; in other words the amount of oxygen which is required by the micro-organisms present in the water for breaking down the carbon coin- pounds. These micro-organisms play a vital role in the ecosystem by breaking down foreign matter so that it may re-enter the food chain in a different form. They act as transforniers in the biological cycles by enzymic and fermentation processes. The cycles of two elements. which are of major importance in the textile industry. are the carbon and nitrogen cycles, and these may be described briefly as follows:

Thc carbon cycle (Figure 6) is the basis for the biological degradation of almost all substances present in

Oxygen Demand Pollution

4000- 6000 7000 12000

80- 150 10 70

300- 1400 1000

100- 300 2000

42600 6000.- 43000

200- 700 500-- 5000

Load ( 7 0 )

>50 10 25 3

<4 10-20 10 -20

5 15

75 1

24


organic components

methane-oxidisino \ J I AEROBIC

- cn4 '02< ANAEROBIC

bacteria

met hanogenic

bacteria /' Fermentation\

photosynthesising anaerobic micro-organisms

organic components

Figure 6 -- The carbon cycle

rivers, lakes, and other water systems such as effluent treatment plants. It functions either in the presence of oxygen (aerobic) or in its absence (anaerobic). Under aerobic conditions organic carbon compounds are con- verted by fermentation into molecular organic acids or into methane gas or into what are known as mineralization products, i.e. HZ, C02 and H z 0 .

These processes take place in the aerated layers of natural waters (Figure 7) and in effluent treatment plants. Many different types of bacteria are involved, depending on the compounds to be decomposed. In the aerobic layers, organic material usually decomposes completely into carbon dioxide.

1 elllumt Intake I

Figure 7 -- Relationship between substance in the receiving waters and distance downstream from effluent intake

The nitrogen cycle (Figure 8 ) is much more complic- ated. The process of deconiposition and synthesis may be interrupted at various intermediate stages according to which type of bacteria predominates. In natural waters, and in the laboratory too, given sufficient time for the experiment and the presence of the appropriate bacteria, the various stages may overlap (Figure 7).

The BODs gives an indication of the amount of oxygen taken from the water, and is thus a measure of the quantity of organic material present and accessible to bacterial attack.


Nitrobacter

Nitrification

Azotobacler. Rhizobiurn,

\\ in protein NOT NH? yrwps

Pseudornonas, other facultative anaerobics

Denitrification

blue-green algae

AEROBIC ANAEROBIC

Clostridiurn pasteurianurn

Figure 8 ~ The nitrogen cycle

As already mentioned, a vast number of different bacteria are involved in this metabolic process, but every chemical compound must have certain micro-organisms to decompose it. Normally the appropriate microflora soon builds up through acclimatization in a particular polluted water. The importance of this fact is often overlooked when testing for BODs, and a compound may well be written-off as non- degradable or even as toxic to the test culture, simply because not enough of the appropriate microbes are present. Degrad- ability is therefore very often measured in terms of chemical (instead of biological) oxygen demand, or COD, which is a measure of the oxygen used in oxidation with potassium dichromate.

Certain chemical compounds exist which, although vulner- able to bacterial attack, are resistant even to such a powerful oxidizing agent as potassium dichrornate, so yet another parameter may be used. This is the total organic carbon o r TOC, which gives a very accurate picture of the degradable carbon compounds present and is a precise measure of the purity of the water, or alternatively a measure of those impurities which are not degradable and can only be removed from the water by adsorption or sedimentation.

Table 7 gives data for a number of products to show how degradability alone is not an adequate measure of a product's ecological acceptability; the figures need to be scrutinized very critically in order to avoid surprises and misinterpretations.

TABLE 7

Oxygen Demand as a Measure of Degradability

PLoduct A B Theoretical carbon % 64 8 5 content Theoretical oxygen mg O2 /g 565 2 160 content COD mgOz/g 790 1700 BODS m g O 2 / g 400 820 Elimination rate by the OECD* Confirmatory % - 8 3 - 77 Test (TOC analysis)

C 71

695

D 64

550

890 820 40 0

0 - 7 0

BODS COD % 0.78 0.48 0.02 0

*Organization for Kconomic Cooperation and Development

Sizes Reconsidering the sizes, which are such a large part of the pollution load in textile waste waters (Table 8), it would be simple enough to switch to other products such as carboxymethyl cellulose or polyvinyl alcohol. as long as BODs is used as the only basis for measurement. While starch sizes, as the nearest approach to natural products. are fairly rapidly broken down even by bacteria which are not specially adapted, these other sizes are resistant, in the short term, to bacterial attack. Until the appropriate microflora has built up. they remain undegraded and represent a more or less persistent form of poUutant in the upper layers of the waste water (Figure 9).

100 I 1

80 ' starch

5 10 15 2 0 2 5 30 0 01% SOlUtlCfl davs

Fipure 9 - Oxygen demand of various types of sizes

TABLE 8

Oxygen Demand of Various Types of Sizes

Corn starch 810 000 British gum 690 000 Met hy 1 cellulose 1 600 Carboxymethyl 10 000 cellulose Poly(viny1)alcohol I 600

Oxygen consumption. (kg 0 2 per 1000 kg ot

textile material) 477 690 I .6 Y.0

1.6

A possible solution might be to reduce the high oxygen demand, due to starch sizes, by using oxidizing agents such as persulphates to replace enzyme degradation. I t has been shown that by using persulphate as a desizing agent the BODs for three tonnes of woven fabric can be reduced from 190 kg to 50 kg.

Washing and Scoitring This is the second biggest source of pollution. The significant factors here are detergents as well as degradable solids like oils, fats aqd waxes. The term 'readily degradable detergent' is often a source of misunderstanding and might give the textile finisher a false sense of security. The analytical methods used nowadays in assessing a compound for 'primary degradation' give n o indication of the extent to which that compound can

be removed from the effluent. They indicate which specific physical and chemical properties the compound will lose when it comes into contact with micro-organisms. These methods may therefore be excellent for demonstrating how far and how quickly the foaming, wetting, emulsifying and dispersing properties of a surfactant will disappear in the receiving water or in the sewage works, but they d o not explain the degree of effective pollution present, and therefore they are useless when it comes to deciding whether or not to recirculate the water (Figure 10).

\ -.- glucose \ \\ - anionic surfactant as organic carbon

,----- 4

---- anionic surfactant by MBAS

in effluent (TOCJ \ \

I, 3

\ \ \

\ \ \

davs

Figure I0 ~ Analytical method for assessing a compound for brimmy degradation' ( Wuhrmanri data)

A primary degradation assessment applied to an anionic surfactant of about 80% MBAS, for example, represents a TOC reduction (effective eliniination of the product) of only about 45--60%. On the other hand, even a readily degradable anionic compound may have an unsatisfactory MBAS value, which means that, even when the compound has been biodegraded, the molecules continue to torm a salt with the dyet.Tliis must be borne in mind when waste water is recirculated or used for any other purpose than scouring or washing-off.

Another consideration is that, when the effluent is simply discharged, because a biological test can still show a high oxygen demand in a surfactant with a primary degradation assessment, and conversely a negative response to the MBAS analysis, there is no information about whether anionic textile chemicals in general are difficult or easy to eliminate (Table 9).

With textile effluents it is necessary t o consider the surface active substances which may appear to be easily degraded

TABLE 9

Anionic MBASt BODS COD Elimination Value Products (%I (mg 02 /g) (mg 0 2 /g) (%)

A 84 130 300 47 B 86 300 1440 17 C 46 380 1090 59 D 5 34 1330 30

*Obtained b y t h e OECD Confumatory Test TOC analysis t M e t h y l e n e Blue Active Substance


when tested by the MBAS method, but may not, in practice, be completely eliminated. Conversely, if the MBAS method indicates a low degree of degradation, this does not mean that the anionic textile chemical will not be eliminated in a biological purification system. (Table 9) D.ves Together with the two sources of pollution (washing and scouring) just discussed, which are more or less determined by the substrate, there are special problems connected with textile dyes and dyeing assistants, of which there is a very wide variety of chemical types. The dyes in particular must not be overlooked. Subjective assessments have given rise to discus- sions about their effects on the environment, and frequently about their toxicity.

With an annual consumption of some 280,000 tonnes, dyes are an insignificant factor compared with the other substances entering the environment, and there seems to be very little justification for investigating their potential as pollutants (Figure 1 1 ) . Because they are resistant to biological oxidation, and because they have the special quality of being visible, even in a highly diluted form, special measures have to be taken to remove them from the waste water. Man's aesthetic sense insists that water should be maintained in its traditional colourless state, and to do that man goes to lengths that would seem extreme in the case of colourless chemicals. Table 10 shows that dyes are among the small fry in the world of environmental pollution.

nn .

direct to environment

pesticides (1 0) detergents (1 5) solvents 110)

Figure 1 1 ~ Chemical substances entering the environment (I 9 70- 19 72)

Heavy metals play an important role in water systems. As trace elements, vital to many types of organism, they can become toxic if present in excess (Figure 12). Wide differences occur not only from metal to metal but also from organism to organism, as can be seen from Table 1 1 .

Many dyes contain heavy metals as impurities derived from manufacture, though the quantities involved are generally well below the danger levels, as the American Dye Manufacturers' Institute have shown (Figure 13). Similarly, with metalcomplex dyes, apart from the small amount of metal com- plexed in the dye molecule (Table 12), with modern

TABLE 10

Dyes Compared with Other Chemicals in Waste Water

Total dye production W o r Id wide. - 285 000 t/year

Amount found in waste water Worldwide - 34 000 t/year (given an average of 70% exhaustion and 60% pure dye content) - 2 9 3 tlday Organic load in the Rhine - 8000 t/day Sizes in waste water - I 500 t/day Pesticides - 2 740 t/day Detergents - 7-4 650 t/day

+ no qigns of optimum excess toxic lethal

growth deficiency range range dose

severe mild

n or

trace elements available

Figure 12 ~ Effect of trace elements on anitnal and plant organisms

Figure 13 - Heavy metal content in textile dyes


TABLE 1 1

The Role of Heavy Metals in Water Systems

Metal Primary Sludge

( P P m ) Aluminiuni Lead Cadmium Chromates 200 Iron 150-500 Copper 150--300 Nickel 200-500 Mercury Silver

Tin Zlnc 150-250

PH <6.8 to

ca 8

Activated Sludge

( P P m )

1-5 2-5 100

1 6

1 --3

5-9.5

Effect on Organisms Organisms involved

in Trickling in Self- Filters purification

( P P m )

5

10 >35

1

TABLE 12

Elements in Metalcomplex Textile Dyes

Elements % 70 C 49 51 H 3 3 N 12 12 0 17 17 co 7

5 Cr -

Average of 13 27 dyes

production methods it is possible to ensure that heavy metals enter the waste water only in trace amounts, which are below the toxic threshold in a mixed dyehouse effluent.

However, there is one exception ~~ the afterchrome and aftercoppering dyes. Although with present day dyeing techniques the amounts of metal salt used can be kept down to the theoretical maximum, and refinements of procedure can reduce the formation of toxic hexavalent chromium salts, thus conforming to strict effluent requirements. in some cases, it may still be necessary t o give this type of effluent a separate treatment before discharging it into the sewer.

A coloured effluent, often simply because it is coloured, is felt to be dangerous and perhaps even poisonous, even though, from the effluent point of view it may compare favourably with colourless chemicals in solution. With the exception of a few cases, in which the median lethal dose to fish is of the order of 10 p p m (an extremely unlikely concentration for a dye in a mixed effluent) dyes in general show LCso values of several hundred p p ni Similarly favourable results are obtained in tests using the micro-organisms present in sewage works sludge.

( P P m )

0.1 0.1 0.3

deposits 0.0 1 0.1

<0.018

0.1

<5

Fish

( P P m ) 15.8

0.2-10 3-20 15-80

1 - 2 0.08-0.8 25-55

0.1 ---0.9 0.02

0.1 -2 c3 2

4.4-5 to

9.2-'10.8

Water courses Other

Aquatic Animals ( P P m )

0.1 ->6 0.03-0.75 0.1--100

1-50 0.08 10

22.5-1000 0.03- 0.5 0.01- 0.2 0.2 ->60

4-6 to

9-1 1

Water Purification As previous surveys have shown, the composition of a textile effluent depends not only on the type of mill but also to a great extent on the processes involved. It would be absurd to design an effluent treatment plant on the basis of the maximum load at peak periods of short duration. Nowadays every works can be expected, as a matter of course, to collect its liquid wastes, to neutralize and blend them, and, if it is not already using heat exchangers, at least to lower the temperature to 30-35°C. For effective operation, the tank for this purpose should be capable of dealing with at least half a day's effluent ou t p u t .

Table 13 shows the make-up of the resulting mixed effluent from a typical cotton mill. From this it is possible t o calculate the organic pollution load in terms of BODs and the approximate amounts of alkali required by the mill according to the Maselli formula (Table 14).

TABLE 13

Composition of a Mixed Cotton Mill Effluent

BODS 120 mg 02/1 COD I 700 mg 02/1 Solids 17 700 mg/l

suspended 250 mg/l dissolved 17 400 mg/l

PH 7.5 Coloured? Yes

A mixed effluent of this type will contain an extremely varied pollution load, and the breakdown given in Table 15 is a useful guide to the subsequent purification processes.


TABLE I4

Alkali Loading for a Mixed Cotton Mill Effluent

Total BODs (kg oxygen consumption) =

0.067 x kg desized cotton t 0.047 x kg her-boiled cotton t 0.005 x kg bleached cotton t 0.006 x kg mercerized cotton t 0.025 x kg dyed or printed cotton

alkali loading = I .7 x BOD5

As well as blending the different effluent streanis, floating and settleable solids must be removed before the water can be treated, as undissolved matter of that kind can cause serious trouble at a later stage. This is another operation to be carried out by the mill itself, because if fibre particles or traces of resins and so on are allowed to enter the receiving waters directly, they can cause mortality among fish by clogging their gills, or, if discharged into sewers, they can cause bad blockages.

These two operations of blending and removal of solids constitute the first stage of effluent treatment. The next stage is the removal of biodegradable substances by oxidation. There are various possibilities, and mention will only be made of the biological oxidation treatment, which is the treatment most commonly used today.

A question which is often asked is whether a mill should have its own activated sludge unit, or whether i t would be

TABLE 15

Breakdown of a Mixed Cotton Mill Effluent

Solids

Fibre particles Insoluble impurities

Resins

Pigme nts

Size componen ts

Dispersed organic solids

Affecting pH Affecting temperature

acids dye liquor

lyes kier liquors

salts cooling water direct steam

better to work in conjunction with the public authorities. The latter is favoured because the effect of the disadvantages can be mitigated, or even entirely neutralized, by blending the different effluent streams in the mill or by diluting them with public sewage. The disadvantages are

textile effluents do not have the correct nutrient/ bacteria balance of roughly five parts nitrogen and one part phosphorus t o 100 parts organic carbon the high biological oxygen demand in a textilc effluent niakes purification difficult if not impossible excessive loading with salt can upset the biological activity, and, if the concentration is as high as 10 g/l, may destroy it completely the possible presence of toxic substances can damagc the biotope

A factor that must not be forgotten is the cost of this type of plant, including cost of working, maintenance and repairs. From a survey of the 244 sewage works in Switzerland. which at present undertake mechanical and biological treatments. the figures in Table 16 give some idea of the expense.

As already mentioned, however, not all the products of a textile mill are removed from the effluent by the biological stage of treatment. One has only to consider the dyes, the less readily degradable sizes, and the chemicals which may be used as dyeing assistants and finishes, for which the appropriate bacteria are not present in ordinary sludge. or are present in insufficient quantities.

This, and the fact that the cost of a biological treatment plant depends. apart from the volunie of water used in the mill, on the concentration of dissolved organic carbon in the

Effluent Organic Substances (BOD active)

dyeing assistants printing assistants

de tergen ts

surfactants

sizes

thickeners solubilizers

fats/ waxes organic salt organic acids

dyes finishes

Nutrients Colorants

nitrogen soluble dye compounds (from dyes/ disperse dye finishes/ salts)

pig men t s

phosphorus compounds

water treatment dyeing finishing


TABLE 16

Cost of a Works Effluent Treatment Plant

Building costs = I470 x *HECo.47 x tBECo.33 Working costs = 6 x HEG Maintenance costs = BEG

*HE(; = projected hydraulic population equivalent - o .ms 11s

?BEG - propcted hiological population equivalent = 7 5 g BOD,/day

ei’fluent, means that an additional stage is necessary. which should preferably be located at the mill. Such an installation will be capable of removing these unwanted substances thus considerably reducing the BODs before proceeding to the biological treatment. Various mechanical, physical and chemical methods can be used, depending on the composition of the effluent. These are summarized in Figure 14.

Physical

Sedimentation Fil tration/screening Heat tredtment Distillation Adsorption Freezing

Chemical

Neutrdlizing Ion exchange Oxidation Reduction c Cdtalysis

Physico-chemical t

Codguldt ion/f loccu lat ion Aeration Active carbon filtration Foam fractionating Solvent extraction Incineration Osmosis Electrolysis

Bioloyicul

Aerobic treatment Activated sludge Anderobic digestion Fungal treatment

Figure 14 - Physical, chemical and biological treatments

Conclusions By various techniques and treatments, passing through several stages of purification (not forgetting the cost), it is possible to obtain water sufficiently clean to be recirculated in a textile mill, as in other spheres of industry (Figure 15). As Staudinger once said, ‘Man inhabits two spheres: the biosphere, which is the natural world about him, and the technosphere. While the biosphere depends on maintaining a balance, the technosphere, which is manipulated by man the maker, tends t o keep on growing’. Man’s preoccupation must therefore be to maintain the balance in spite of the growth, and some of the ways in which this can be done have been suggested in this paper.

Figure 15 - Cost o f effluent treatment in relation to number of stages

Bib1 iograph y

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(1 974).

* * * The following short British bibliography may be of help:


On textile water usage: (ii) Parish, Rev. Prog. Coloration, 7 5 5 (1976). ‘The use of water by the textile industry’, Textile Research (iii) ‘Effluent Treatment and Water Conservation’, Com- Council, Nottingham, 1973. mittee of Directors of Textile Research Associations,

1970. On effluent treatment:

(i) Little, ‘Water supplies and the treatment and disposal of effluents’ Monograph No. 2, Textile Institute, Manchester, 1975.

Sulphur Dyes ~ 1966- 1976

WILLIAM E. WOOD

James Robinson and Co. Ltd Hill House Lane Huddersfield HDI 6BU

Introduction Long before compiling the material for this review it had been realised that, with one or two exceptions, there have been very few papers exclusively devoted to sulphur dyes and that in the modern textbooks which are available the authors either neglect t o mention them or, what is perhaps worse, give outdated or incorrect information about them. It is fitting also that the period under review should include the centenary of the discovery of the first sulphur dye and it is worth while to quote from the patent [ 1 1 which says, referring to the process, ‘The essential principle on which this process is based consists in the direct treatment of organic bodies by alkaline sulphides and polysulphides with the intervention of heat at temperatures which may vary from 100°C t o about 350” Centigrade according to the nature of the substances to be modified and the tint that it is desired t o obtain, ...... ’. Although manu- facturing methods have changed considerably, this general description still holds; a valid justification for the worthy gentlemen of the Patent Office to approve the grant of a Patent in 1873 to Croissant and BretonniGre which remains their memorial.

It is useful to mention at the outset

an excellent review by Heid, Holoubek and Klein 121, which deals with the development of the sulphur dyes with regard to their manufacture and application and the author of the present review makes no excuse for mentioning sonie of the cited references.

The Place of Sulphur Dyes The production of sulphur dyes today is in the hands of a relatively small number of manufacturers, some of whom produce only a limited number of individual dyes. Countries in which there is one major producer only are China, England, France, East and West Germany, Japan, Poland, Spain and the USA. This is in contrast with other dye classes which are produced by numerous manufacturers in most of the dye-producing countries. In the UK in 1946 there were eight nianu- facturers of sulphur dyes, but by 1970 seven had discontinued their production in favour of making what must have appeared more lucrative dyes.

Present production of sulphur dyes in the UK is in the region of 3500 tonnes per year, a figure which includes powder and liquid brands. By far the largest proportion of this quantity is sulphur black, made by the thionation of 2,4-di- nitrophenol, followed closely by the sulphur blues. The remaining 30% is made up of yellows, browns, greens and red browns.

Compared with production of other classes of dye such as acid, direct and reactive dyes, this quantity is not very

great, but world production of sulphur black makes it one of the most important dyes in use at the present time. The factors which limit the usefulness of the sulphur dyes arc the absence o f very bright dyes and certain aspects of tlicir application.

In general terms the sulphur dycs occupy a position between the dircct. reactive and vat dyes. Their wet fastness is good, as is also their fastness to heat treatments and resin finishing, and although certain members of the range such as the yellows have low light fastness, the blacks, navy blues, dark browns and greens possess excellent light fastness in medium to fu l l depths. With a few exceptions the fastness to hypo- chlorite is poor, but, as with some reactive dyes, the required standards of fastness t o chlorinated water can be met with several of the sulphur dyes.

This general property of all-round fastness is supplemented by one other advantage. They are relatively cheap. It is possible to dye a full black on cotton drill a t the present time for a dye cost of 5.0p/kg or less and to obtain a dyeing with excellent light and wet fastness properties. Colours other than black are obviously more expensive to produce b u t price advantages over alternative classes of dye are still shown.

In the ten years under review the UK prices for sulphur dyes, in coninion with other dyes, have risen considerably and the following Figure illustrates the pattern of the increase in the UK market.


Documents

Ecological Aspects of Water Usage in the Textile Industry