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.
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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