By: Subrata Das
E-mail: drsubratadas2000@gmail.com

1 INTRODUCTION

In today's competitive world, domestic and export markets in textiles are progressing at a rapid pace. Exponential growth in global industrialization is noticed in the west and rest of the world. Innovations in the use of electronics information technology, computers and automation are needed to achieve a high quality standard. Textile and apparel, being labour intensive industries, code of conduct at the work place is hard to overlook. But the main challenge before the textile production industry is as to how to produce a product at a competitive price by using environment friendly process and by reducing emissions and pollution treatment cost.

Biosphere is under serious trouble and impact on its atmosphere, hydrosphere and lithosphere by human cannot be ignored. Man made activities on water by domestic, industrial, agriculture, shipping, radio-active, aquaculture wastes; on air by industrial pollutants, mobile combustion, burning of fuels, agricultural activities, ionization radiation, cosmic radiation, suspended particulate matter; on land by domestic wastes, industrial waste, agricultural chemicals and fertilizers, acid rain, animal waste have negative influence over biotic and abiotic components on different natural eco-systems. Global warming, rising of sea level, abnormal climatic change, loss in bio-diversity, deforestation, ozone layer depletion are some of the adverse effects on environment.

Textile accounts for 30% of India's export. There is no doubt that price, quality, turn around time and social compliance are the essential elements of export. Of late, clean processing has become an additional requirement. Unfortunately, in comparison to other branches of engineering and technology, environmental pollution of textile industry seems to be the least studied area.

How long can we continue to harm environment? Will our business exist if biosphere is polluted? Will textile industry survive and be able to compete? These are some of the questions, which have motivated the present study.

2 ECO DEGRADATION IN TEXTILE INDUSTRY

Textile industry contributes 30% of India's export. It produces over 400 million meters of cloth and around 1000 million kg of yarn per annum. Textile sector is labour intensive and nearly a million of workers are associated in various unit operations of about 700 mills. Textile wet processing activity contributes about 70% of pollution in textile industry. It is estimated that there are around 12,500 textile processing units wherein the requirement of water ranges from 10 litres with an average of 100 litres per kg [1]. Right from cotton cultivation and manufacture of fibres, spinning, weaving, processing and finishing, more than 14,000 dyes and chemicals are used and a significant quantity of these goes in the solid, liquid and air wastes, thereby impart pollution of air, land and surface water.

Towards the end of 20th century, world has become more ecology consciousness and thus green textile concept is emerged to facilitate eco-management in textile arena. Different unit operations, which contribute to eco degradation, are described and analysed in this chapter.

2.1 Noise Pollution

Noise is one of the most pervasive environmental problems. There is no doubt that it has adverse effect on human beings, and their surroundings.

The ISO defines noise intensity level [2] as:

L = 20 log10 (P / P0) = 10 log10 (I / I0) (1)

Where P and P0 are the sound pressures of the noise present at a place and the reference sound pressure at 1000 Hz at the threshold of hearing which is given by 20 micro Pascals. I is the sound intensity level being measured and I0 is the reference sound intensity at 1000 Hz at the threshold of hearing and is given by 10-12 w/m2.

The relationship between sound pressure, sound intensity and intensity level (dB) is given in the literature [3]. The sound does not get perceived by the human ear in the same manner over the whole audible frequency range. Low-pitched sound of high intensity level (decibel count) could not be judged by the human ear to be particularly loud. Similarly, the human ear has been incapable of perceiving vibrations of a frequency much above 20,000 cycles per second, although many animals such as dog have been able to detect these sounds.

In industry, increased mechanization results in increased noise levels. Operation of textile machines carries a high risk of hearing loss. The evaluation of textile worker's noise induced hearing loss was reported elsewhere in the literature [4].

Health related effects are:

Respiratory modification
Gastrointestinal
Endocrine stimulation
Galvanic skin resistance alteration
Permanent or temporary hearing loss
Increased human annoyance
Communication interference resulting in reduced worker's efficiency

Noise Levels in Textile Machineries

2.1.1.1 Yarn Production

Because of high spindle speeds reached on new machines (ring spindles up to 20000 rpm, rotor up to 110000 rpm) spinning mills can generally be assumed to generate a great deal of noise. Noise levels of 70 to 100 dB are commonly recorded in workrooms.

2.1.1.2 Weaving and Knitting

Although considerable progress has been made in the weaving sector over the last 20 years, the whole area of noise nuisance and, closely associated with it, vibration coming from looms, cause major problems.

Noise levels of 100 to 120 dB must be expected in weaving rooms, according to the design, type, fitting, erection and number of looms used, fabric structure, building type and size etc. The vibration transmitted from the running looms to the building can, under certain circumstances, cause a nuisance to the local population and damage to nearby buildings, and to avoid this special vibration absorbers are now provided.

However, permissible limit set up at 90 dB by Federal Standards of USA for maximum exposure duration of 8 hours per day. Typical values of noise level in textile machines are shown in Table I.

2.1.2 Remedial Measures

Noise level can be lowered by the use of noise control enclosures, absorbers, silencers and baffles and by the use of personal protective equipment (PPE), such as earmuffs. Where technical methods are insufficient, noise exposure may be reduced by the use of hearing protection and by administrative controls such as limiting the time spent in noisy environment and scheduling noisy operation outside normal shifts or at distant location. Even though noise-reducing measures may have been incorporated in the design of the machinery, greater output may generate higher noise levels. For instance, every doubling of the speed of rotary machines the noise emission rises by about 7 dB, warp knitting looms by 12 dB and in fans by around 18 to 24 dB.

Noise pollution is a problem that has unsatisfactorily been tackled so far. Though noise-absorbing sheets are used to cover the inner walls of loom shed, still more appropriate means need to be devised. In modern shuttle less looms because of better engineering designs of the machines the noise level is lesser. But those shuttle less looms are costly.

2.2 Air Pollution

All textile-manufacturing processes generate environmental pollution. Workers are exposed to the risk of breathing air polluted with dust and fly and contracting respiratory ailments, byssinosis (lung disease), chronic bronchitis etc.

Air Pollution Created By Textile Machineries

2.2.1.1 Spinning Plant

In spinning mill, the extent of cotton dust contamination varies from section to section, as it is worst in the blow room and minimum at the cone winding section. The workers are exposed to such working environment and inhale fibrous particles and dust whole day. Generally, air suction system exists nearly in all departments to maintain certain humidity and to remove air contaminants, however, at some places it works effectively but at certain areas air exchange is not proper resulting into suffocation and inconvenience for the workers.

2.2.1.2 Weaving Shed

In weaving mill, fibrous particles are present in the working environment though not much but still these are generally inhaled by most of the workers. These small fibrous particles are generated during weaving activities and disperse in occupational air.
2.2.2 Remedial Measures

To minimize the effect of these floating fibres or impurities, the humidified air which is circulated in the spinning and weaving department is filtered so as to separate these floating impurities from the air.

In order to minimize the risk of industrial diseases among the workers, Occupational Safety and Health Authority (OSHA) of U.S.A has specified concentration limits of dust in the air streams of production rooms for compliance by the concerned industries is given in Table II.

Air circulation per hour is optimized to keep the air streams clean and hygienic to prevent any risk to the health of the workers and depicted in Table III.

2.3 Pollution in Cotton Cultivation

In cultivation of cotton, huge quantities of pesticides, fertilizer and water are used. About 18% of world production of pesticides is used for cotton cultivation. It prevents the growth of undesirable organisms and thereby improves the crop yield. Most of the pesticides are harmful and cause environmental degradation.

2.3.1 Organic Cotton

Organic cultivation of natural fibres is now practiced in different parts of the globe with a view to reduce the adverse impact on the environment due to the indiscriminate use of fertilizers and pesticides. For cultivation of organic cotton, chemical fertilizers and pesticides cannot be used at all. Further, in order to remove the residual fertilizers and pesticides that may be present in the soil, crops are to be cultivated for three seasons without the use of chemical fertilizers or pesticides [5]. Rather than attempting to eradicate all insects with chemicals, organic farmers cultivate a diversity of natural enemies, which prey on insect pests, and lure pests away from cotton by planting trap crops. Insect pests can be effectively kept in balance with well-timed introduction of beneficial insects to fields.

2.3.2 BT Cotton

Bt cotton, genetically engineered (transgenic) cotton, was heralded for its environmental and human health benefits and as a step towards sustainable agriculture since, farmers could significantly reduce insecticide use. To create cotton with built-in protection against insects, genetic engineers spliced a Bt toxin gene into cotton. The new gene that enabled the transgenic cotton to produce insecticidal toxin throughout the plant was obtained from a soil bacterium, Bacillus thuringiensis (Bt), an organism well known to many organic and sustainable growers who have used Bt in sprays to control insects. Bt gene is put into cotton to protect against three pests: tobacco budworm, cotton bollworm and pink bollworm. However, the Bt cotton is not effective against a number of other pests, including the boll weevil and whitefly.

2.4 Chemical Pollution

2.4.1 Sizing

Starch is applied to cotton yarn in sizing operation to increase its strength and abrasion resistance to withstand the stresses and strains of weaving.

Certain preservatives like pentachlorophenol are added to the starch paste in order to protect it from the attack of microorganisms. They have toxic effect on human skin and the effluent generated from this process is due to spills and floor washing. Use of synthetic starches reduce the use of such preservatives and thereby reduce the health hazards.

2.4.2 Grey Inspection

During weaving operation, oil stains are produced if proper precautions are not taken. Stain removers like carbon tetrachloride are used prior to chemical processing. In fact, carbon tetrachloride has 10% more ozone depletion capacity than Freon gas.

2.4.3 Chemical Processing

Analysis of water consumption and pollution in effluent of textile chemical processing of cotton goods has been adapted from literature [6] and is presented in Table IV.

2.4.3.1 Desizing

This process removes size ingredients such as starch, softeners, preservatives etc used in sizing. Enzymes are used to break the starch into water-soluble dextrin. Bacteria can easily attack the water-soluble dextrin and these are very degradable and have high BOD.

2.4.3.2 Scouring

The scouring process is meant to remove impurities in fibre such as oils, fats, waxes, seed particles, spinning oils applied and the residual size ingredients still remaining after desizing. All these increase the BOD of effluent.

2.4.3.3 Bleaching

The process destroys the natural colour of the fibre and makes it white. Sodium hypochlorite is a common bleaching agent. But due to its highly toxic nature, many countries have banned their use. Hydrogen Peroxide bleaching is preferred over other bleaching agents due to negligible toxic effect. Stabilizer is commonly used in peroxide bleaching. Silicate and phosphate based stabilizers have been found to be non-biodegradable and hence their use has been banned by number of countries.

2.4.3.4 Mercerization

In this process, cotton fabric is treated with a strong caustic soda solution at room temperature and washing it off with water. It improves the strength, elasticity, luster, dye uptake and dimensional stability of the fabric. Large volume of dilute caustic soda solution generated in the process, if allowed to discharge down the drain, will cause water pollution. However, this wash liquor can be re-used in scouring, dyeing with vat dyes and mercerization.

2.4.3.5 Dyeing

Dyes, which form carcinogenic amines on reduction, contribute substantially for increased BOD/COD need to be avoided for use in dyeing. Dyes, which contain heavy metal such as chromium, cobalt, and copper, are detrimental for the environment. Major pollutants in dyeing include unfixed dye, fixing agents, reducing agents, alkali, organic acids, oxidizing agents, salts, metals, carriers etc. However, there is increasing awareness in recent years towards the use of number of natural dyes, which are eco-friendly and have no impact on the environmental pollution.

2.4.3.6 Printing

Colours selected should be non-toxic and not based on forbidden amines. Dyes with high fixation properties and modified printing process needing less wash out are recommended to be used in printing. Printing gums with low BOD and free from pentachlorophenol are preferred. Use of urea is to be minimized, citric acid in disperse prints should be replaced; phenol used in nylon fabric printing is to be substituted by diethylene glycol. Use of kerosene in pigment printing should be completely eliminated. Formaldehyde based fixers for improving rubbing fastness of pigment prints should be restricted. Major pollutants in textile printing are: suspended solids, urea, solvents, colour, metals, vapours during drying and curing, screen cleaning solvents.

2.4.3.7 Finishing

Formaldehyde based cross-linking agents applied to cellulosic textiles for crease resistance and dimensional stability are the highly toxic chemicals. Reactive softeners, certain flame-retardants, water repellent and rot proofing finishes, are the other pollutants.

In the replacement of formaldehyde based finishing agent, polycarboxylic acid like butane tetra carboxylic acid, citric acid and copolymer of maleic acid met many requirement for satisfactory performance in terms of the level, reactivity, durable press performance, durability to laundering, fabric strength retention, low reagent volatility and absence of odour.

2.4.3.8 Enzyme Treatment

Application of various enzymes in desizing, scouring, degumming of silk, finishing has brought a new horizon in textile wet processing technology. Enzyme is eco-friendly, completely biodegradable and they will not leave any chemical residues on the processed materials, and the colour change on the dyed goods is minimal.

2.5 Man- Made Fibre Industry [7]

Major raw material for synthetic fibres is obtained from petrochemical feedstock and is commonly known as monomer whereas cellulose is the major raw material for viscose and acetate. The type and average consumption of major raw material for individual fibre is given in Table V.

A large number of various chemicals, besides pulp or monomer, as the case may be, are required during the manufacture of each fibre. Ingredients include acetic acid, titanium dioxide, spin finish, catalyst, methyl acrylate or vinyl acetate, sulphuric acid, sodium hydroxide, carbon disulphide, Zinc, sodium sulphate, di-sodium sulphide, acetic anhydride, thermal stabilizer, light stabilizer, antioxidants etc.

ACN is toxic and as a consequence stringent measure in acrylic manufacturing plant is necessary to ensure that it does not contaminate liquid discharge. One of the major pollutants in viscose plant liquid effluent causing concern is the presence of zinc. The average consumption of zinc is in the range of 15 Kg/MT fibres. The zinc concentration in the effluent is on an average 15-40 mg/l.

The average consumption and parameters for liquid effluent discharged by nylon and polyester industries are given in Table VI. In India, for nylon and polyester, the wastewater generated is on an average of 170 m3/MT and for viscose 1200 m3/MT, respectively.

2.5.1 Pollution Control Standard

The Central Pollution Control Board formulated a minimum National standard (MINAS) for all polluting industries including fibre industry. MINAS as depicted in Table VII must be adhered to before the liquid can be discharged outside the factory premises.

Effluent treatment of man-made fibre industry, especially synthetic fibre may not be very complicated. However, there is pollution control problem in viscose and acrylic fibre production.

3 Categorization of Textile Waste

Textile industry covers a wide range of manufacturing processes and technologies to design the required shape of the final product. But during the course of various process flows, there is obvious generation of wastes, which are classified into four categories namely, hard to treat wastes, dispersible wastes, hazardous or toxic wastes and high volume wastes [8].

3.1 Hard to treat waste

These include colour, metals, phenols, certain surfactants, toxic organic compounds, pesticides, as well as phosphates. Major sources are:

Colour and metals  -   dyeing operation
Phosphates            -   dyeing operation
Surfactants            -    non-biodegradable organic materials

3.2 Dispersible waste

Prominent source of dispersible wastes in textile wet processing are the following:
Print paste, lint, coating operation, solvent, waste stream from continuous dyeing, printing, finishing
etc.

3.3 High volume waste

High volume wastes are sometimes a problem for the textile processing units. These include water from preparation and dyeing stages, alkaline wastes from preparation, salt, cutting room waste, knitting oils and warp sizes. These wastes sometimes can be reduced by recycle or reuse as well as by process and equipment modifications.

3.4 Hazardous or toxic wastes

The impact on the environment of such kind of wastes is significant. They include metal, chlorinated solvents, non-degradable surfactants and other non-biodegradable or volatile organic materials. These wastes originate often from non-process operations, such as machine cleaning.

4 Eco-Management

Textile industry encompasses a range of unit operation covering a variety of natural and synthetic fibres to produce fabrics. Various parameters such as turbidity, acidity, alkalinity, total dissolved solids, BOD, metal content, toxic substances etc. are bench marked so as to ensure that the effluent water before being released into city sewage, stream, river or sea is not harmful to human, animal or plant life. With the concept to bring the parameters of effluent water to acceptable standards, the effluent is treated. The appropriateness of their choice and sequence is critical for the success of treatment plant.

4.1 Treatment of Textile waste

Three types of process are normally used for treatment and recycle of effluent from the textile industry. These are physico-chemical, biological and membrane process.

Physico-chemical processes remove suspended and colloidal impurities, to coagulate and flocculate reactive, disperse and vat dyes and to facilitate their removal by sedimentation. The removal is a function of entrapment within a voluminous precipitate consisting primarily of the coagulant itself. Result of addition of chemicals is net increase in the dissolved constituents in the wastewater. Coagulants usually added include alum, lime etc. [9].

These processes offer a good pre-treatment to the downstream biological and membrane processes. Biological processes used to remove dissolved organics from effluent and thus to reduce chemical and bio-chemical oxygen demands of the effluent. This is achieved biologically wherein bacteria is used to convert the colloidal and dissolved carbonaceous organic matter into various gases and into cell tissue. Because the cell tissue has a specific gravity slightly greater than that of water, removal from the treated effluent is facilitated under gravity. Biologically treated effluent contains dissolved salts and residual impurities that have passed through the previous processes. These are removed in the membrane process such as reverse osmosis, which is suitable for removing high salt concentrations so that the treated effluent can be re-used again in the processing. A typical flow chart of a water recycle plant for textile industry is shown in Figure 1.



4.2 Re-Use of Wastewater

In textile industry, the wastewater in certain processes like continuous scouring, mercerizing is re-used, thereby not only economises the wastewater costs but also reduces the volume of effluent to be disposed. In a mill, if wastewater is clean enough after secondary and tertiary treatment, it can be reused in processes like washing, soaping etc.

5 Conclusions

Green minded consumers prefer "eco-friendly" textiles. In the present global scenario, if the textile industry wishes to bring prosperity through diversification and modernization, they have to manufacture eco-friendly products and the overall textile processing will have to be modified in such a way so as to avoid any toxicity as efficiently as possible. Our motto is to save living species and its surrounding environment. Thus we must start using sophisticated and better-designed machines with less noise and follow improved method of air purification and circulation system. And we should stop using chemicals and dyes, which produce harmful effect to the biotic and abiotic factors in our eco-systems. Reduction of waste at the source is the preferred strategy instead of the traditional method of "end of pipe waste treatment". Apart from problematic chemicals and dyes, the main pollutant is, of course, water. So, the new technologies, which aim to reduce or eliminate water, are to be conceived.

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