Environmental Aspects in Textile Industry: Ecological Hazards and Remedial Measures

Introduction

Indian textile industry is a unique combination of growth, development and export performance. This identity is now been checked and challenged. Where is the problem? The concern is because of the anthropogenic sources of pollution. Green parties today insisting upon the manufacturing, processing and disposal of textile products as per environmental norms. The commercial decision in global business now depends on how much conscious we are in protecting our environment. So, there is a wake-up call for the textile industry.

What we are doing to harm our environment? Which are the areas causing destruction to our biosphere? What should we do to remain in the competition? Will our business exist? These are the questions to be investigated and the motivating factor for this study.

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. The textile sector is labour intensive and nearly a million workers are associated in various unit operations of about 700 mills. There exist a number of important environmental benchmarks, associated with the key environmental issues. Because of the nature of the industry, many of these are directed towards wet processing which tends to be the most obviously polluting sub-sector.

Textile wet processing activity contributes about 70% of pollution in the 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 the 20th century, the world has become more environmentally conscious and thus the green textile concept is emerged to facilitate eco-management in the textile arena. Different unit operations, which contribute to eco-degradation, are described and analysed in this chapter.

Noise Pollution

Noise is one of the most pervasive environmental problems. There is no doubt that it has an 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)

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) are given in the literature [3]. 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].

Noise Levels in Textile Machinery

Noise Levels in 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.

Noise Levels in 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 these special vibration absorbers are now provided.

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

Noise Level 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 a noisy environment and scheduling noisy operation outside normal shifts or at a distant location. Even though noise-reducing measures may have been incorporated in the design of the machinery, the 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 machines 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.

ProcessNoise level (dB)
Texturizing Plant
Filament take-up section93.20
Texturizing section94.80
Compressor house99.50
Spinning
Ring spinning80
Schubert Salzer Spincomet Rotor spinning (Individual)84
Schlafhorst Autocoro Rotor spinning (Individual)85
Rieter M2/1 Rotor spinning (Individual)86
20 Open End Rotor spinning i.e. 3840 rotors in operation100
Two for one twister100 -110
Weaving100 -120
Table I. Noise level in Textile Industry (Texturizing, Spinning and Weaving)

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 Machinery

Air Pollution in Textile Machinery

Air Pollution in Spinning Plants

In the 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 a working environment and inhale fibrous particles and dust the 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.

Air Pollution in Weaving Sheds

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

Air Pollution 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.

ProcessLimit (mg/m3)
Blowroom to Speed frame0.5
Spinning0.2
Twisting0.2
Winding0.2
Warping0.2
Sizing0.75
Weaving0.75
Nonwoven0.5
Table II: Concentration limits of dust in the air stream
ProcessFrequency of air changes/hour
Blowroom15
Carding20
Combing15
Drawing15
Roving15
Spinning45
Winding30
Twisting20
Warping20
Sizing20
Weaving20
Table III: Frequency of re-circulation of air in a typical textile mill

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.

Pollution in Cotton Cultivation

In the cultivation of cotton, huge quantities of pesticides, fertilizer and water are used. About 18% of the 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.

Organic Cotton

Organic cultivation of natural fibres is now practised in different parts of the globe with a view to reducing 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].

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.

Chemical Pollution

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

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 a 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 health hazards.

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.

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 degradable and have high BOD.

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.

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. The 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 a number of countries.

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, lustre, dye uptake and dimensional stability of the fabric. The 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.

Dyeing

It is not because of environmental consciousness alone, but due to aesthetic grounds, realizations of colour values are being felt and therefore dye fixation levels have attracted the attention of the potential dyers. Proper selection of dyes helps to minimize effluent losses. Typical dye fixation levels for most of the dye classes are shown in Table V. It is corroborated from the above Table that fixation varies considerably depending on the fibre and the nature of the dye. However, there is a depth of shade also to be taken into consideration.

ProcessWater consumption of total (%)BOD of the total (%)Pollution load of the total (%)
Desizing522>50
Scouring15410-25
Bleaching4653
Mercerizing22<4
Dyeing8510-20
Printing7610-20
Finishing1715
Table IV: Pollution loads in Cotton Processing
Dye ClassFibre TypeDegree of Fixation (%)Effluent Loss (%)Benchmark Fixation (%)
BasicAcrylic95-1000-597
DispersePolyester90-1000-1095
Metal-complexWool90-982-1094
ReactiveCellulosic50-9010-5070
Table V: Dye fixation levels of different dyes

Dyes, which form carcinogenic amines on reduction, contribute substantially for increased BOD/COD need to be avoided for use in dying. Dyes, which contain heavy metal such as chromium, cobalt, and copper, are detrimental to the environment. Major pollutants in dyeing include unfixed dye, fixing agents, reducing agents, alkali, organic acids, oxidizing agents, salts, metals, carriers etc.

Advances in methods for reduction of vat and sulphur dyes using mediator technique claims technical, ecological and economic benefits, with shorter and more reliable dyeing processes, improved reproducibility, lower effluent costs and better quality [7-9]. Dyeing in the atmosphere of supercritical carbon dioxide completely eliminates the water and air pollution. However, there is increasing awareness in recent years towards the use of a number of natural dyes, which are eco-friendly and have no impact on environmental pollution.

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 disperses prints should be replaced; phenol used in nylon fabric printing is to be substituted by diethylene glycol.

One of the main ecological advantages of pigments, as compared to dyes, is that no after the wash is required, leading to saving in water requirement [10]. However, the use of kerosene in pigment printing should be completely eliminated and replaced with synthetic thickeners.

Major pollutants in textile printing are suspended solids, urea, solvents, colour, metals, and vapours during drying and curing, screen cleaning solvents. One area showing promise is the laser technique visible in the printing area. Good sharp quality prints are visible with the laser technique, which is totally non-aqueous and useful for all kinds of textile substrates.

Finishing

Formaldehyde-based cross-linking agents applied to cellulosic textiles for crease resistance and dimensional stability are 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 requirements 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 [11,12].

In the manmade area, the trend is towards incorporating suitable additives in the spinning dope to impart desirable properties such as fire repellency, hydrophilicity, antibacterials, antistatic, UV protection etc. This will avoid the use of these harmful chemicals, which leads to subsequent pollution.

Man-Made Fibre Industry

The 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 are given in Table VI.

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.

Item

ViscoseNylonPolyesterAcrylicPolypropylene
Raw materialCellulose PulpCaprolactumDMT& EGACNPropylene
Average Consumption114011001100 & 42010001000
Table VI: Major Material Consumption for Man-Made Fibre (Kg/ton product)

ACN is toxic and as a consequence stringent measure in an 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 [13].

ParameterNylonPolyester
Temperature (ºC)3032
pH7.258.55
Total Suspended Solid (mg/l)13881736
Total Dissolved Solids (mg/l)16001542
BOD, 5 days, 20ºC, mg/l619580
Volatile Solids (mg/l)384632
COD, mg/l14591680
Alkalinity (as CaCo3), mg/l350730
Table VII: Parameters of Waste Water Generated by Synthetic Fibre Industry

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

Categorization of Textile Waste

The 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 an 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 [14].

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

Dispersible Waste

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

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 the preparation, salt, cutting room waste, knitting oils and warp sizes. These wastes sometimes can be reduced by recycling or reuse as well as by process and equipment modifications.

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.

Waste-Management

The 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 benchmarked 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 the treatment plant.

Treatment of Textile Waste

Three types of process are normally used for the treatment and recycling of effluent from the textile industry. These are physicochemical, biological and membrane process.

Figure 1. Flowchart of typical water recycle plant
Figure 1. Flowchart of typical water recycle plant

Physico-chemical processes remove suspended and colloidal impurities, to coagulate and flocculate reactively, 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 the addition of chemicals is the net increase in the dissolved constituents in the wastewater. Coagulants usually added include alum, lime etc. [15]. 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 biochemical oxygen demands of the effluent. This is achieved biologically wherein bacteria are 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 the water recycle plant for the textile industry is shown in Figure 1.

Conclusions

Consumer awareness of the environmental issue is on the rise. It is the need of the day to substitute hazardous chemicals by environmentally benign methods. Buyers are eco-conscious on product, processes and disposal. Thus, the textile industry cannot ignore the environmental impact of its activities.

The best approach is to manufacture eco-friendly products and to modify certain areas of textile processing in such a way so as to avoid toxicity as efficiently as possible. At the same time, we must not forget in using better-engineered machines with less noise and following an effective and improvised system of air purification and circulation. Better handling of textile waste and their efficient disposal will surely be an appropriate step to maintain the ecological balance on earth.


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