Environmental Aspects in Textile Industry: Ecological Hazards and Remedial Measures

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.

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.