Sustainability in textile processing

India is the largest producer of natural fibres like cotton and jute and second in terms of silk and rayon, therefore determination and assessment of water and energy consumption is essential, says Dr Ashok Athalye

Textile is considered as the mother of industrialisation and a basic need of human beings. With the growing population, urbanisation, standards of living and fast fashion, the production and consumption of textile is constantly increasing.  Between the fibre to fashion value chain, wet processing is considered the weak link in terms of large consumption of water, energy and chemicals and their impact on the environment in terms of solid waste, liquid effluent, and gaseous emissions.

The wet processing involves – Pretreatment, Coloration and Finishing. Pretreatment removes the acquired and added impurities from the fibre and improves the absorbency and whiteness, which is essential for the subsequent colouration step. Depending on the type of fibre – natural, regenerated or synthetic and the end-use requirement, various processes such as desizing, demineralising, degumming, scouring, bleaching, mercerising, etc. are performed with the help of basic chemicals. The second step of colouration involves the application of dyestuff, pigments or inks depending on the fibre substrate, either by dyeing or printing. The final step of finishing involves applying perceptive and protective effect chemicals.  

So far, many attempts have been made by govt bodies, environmental regulations, brands, and labels to put textile pollution in place. But the energy inefficiency aspect of the textile industry has received very little attention. Based on the study and the available data, it is noticed that the largest share of emissions is from the dyeing and finishing processes (36 per cent), followed by yarn preparation (28 per cent), fibre and fabric production (15 per cent). Consumption of natural resources to cater to the needs of fast fashion will result in increased ecological degradation and climate change. It is estimated that the fashion industry will account for 25 per cent of the world’s carbon budget by 2050.

The conventional textile wet processing sequence is energy inefficient as it consumes large volumes of water and involves several heating-cooling cycles at each stage, necessitating huge energy utilisation. Typically, the exhaust processing of cotton knit material involves about 10 to 12 steps from preparation to finishing. Considering the material-to-liquor ratio of 1:10, this consumes almost 120 litres of water per kg of fabric. During this process, about 6 to 8 steps are carried out at temperatures above 70°C. This means heating about 80 litres of water from room temperature to high processing temperature. Pretreatment steps like scouring and bleaching require high temperatures and pH conditions. The subsequent dyeing process requires multiple hot water baths for uniform colour uptake (exhaustion), excess colour removal (soaping) and after-treatments. The salts used in dye exhaustion led to high levels of total dissolved solids (TDS). These salts are removed by employing expensive tertiary wastewater treatments like reverse osmosis (RO) and multiple effect evaporators (MEE). Fixation and curing processes in the printing and finishing stages consume much thermal energy as steam is required to be generated in boilers by burning fossil fuels. Intermittent hot water baths and drying contribute to the carbon footprint. Besides this, multiple chemical auxiliaries like wetting agents, bleaching agents, sizes (CMC, PVA, starch), urea, reducing and oxidising agents have high biological oxygen demand (BOD) chemical oxygen demand (COD) and cause various effluent treatment (ETP) related issues. Overall, the conventional steps followed in the textile wet processing industry consume large amounts of water, thermal energy, and time and cause effluent and waste management problems. All these factors make the textile industry the second largest polluting and energy inefficient after the petroleum industry.

Alternative sustainable solutions to these conventional textile processing techniques exist, such as low-temperature bleaching, low-temperature curing, and low-temperature soaping using activators which can be done at temperatures as low as 40°C-60° instead of 100°C. But these alternatives are not practised in the textile mills due to certain inefficiencies. For instance, low-temperature bleaching (LTB) of textiles is not implemented on a wide scale as the whiteness index obtained is inferior compared to the conventional high-temperature boiling process. Also, the cost of these sustainable technologies limits them to academic research or high-end textile mills. Further, when the carbon footprint of textiles is studied, it is focused on the life cycle assessment of garments. So far, academic and industrial research is focused on making the textile value chain more sustainable by catering to problems of textile pollution like solid waste generation, liquid effluent and gaseous emissions. But there is limited data available about solutions for energy optimisation, water and carbon footprint mitigation during the wet processing stage, which is solely responsible for 36% of total CO2 emissions.

For sustainable textile processing, the stakeholders in the value chain need to

• Prevent – waste generation at source
• Control – raw materials, influent and effluent
• Understand  – complexity involved in textile processing
• Minimise  – impact on water, soil and air pollution
• Improve- supply reliability and reduced inventory
• Conserve – ecology by beneficial disposition
• Design –  operations to improve efficiencies
• Apply  – synergistic product-process matrix
• Meet  – the expectations of the consumer

Various initiatives are taken through the collaborative Industry-Institute-Interactions with the encouragement & adequate support from the Governments to understand the root cause, identify the probable reasons and develop a remedial measure. Which include

• Determining limitations of the conventional wet processing mechanisms by LCA (life cycle assessment) approach for natural fibres like cotton, silk, wool, jute and man-made fibres like viscose, polyester, and nylon.
• Studying the application of Industry 4.0 concepts like digital dyeing, printing and finishing to achieve resource-saving and sustainability.
• Formulating products (auxiliary chemicals) and developing processes based on the principles of biotechnology and nanotechnology.
• Evaluating feasibility of implementing other forms of renewable energy and fuel substitutes for replacing existing energy options to curb overall footprints during textile processing.
• Calculating carbon footprint at each stage of textile wet processing.
• Standardising optimised energy conserving processes.
• Conducting comparative cost analysis vis-a vis conventional systems.
•  Developing a sustainable wet process by reducing and combining several steps to shorten the process cycle, reduce time and energy consumption and increase productivity.
• Estimating mass balance, water balance and energy balance for an overall reduction in the carbon footprint.
• Implementing new technologies, fuel substitutes and energy options replacing the ones used in conventionaltextile processing.
• Deriving sustainable alternatives based on the principles of Replace, Reduce, Reuse and Recycle.

Globally, India is the largest producer of natural fibres like cotton and jute and second in terms of silk and rayon, therefore determination and assessment of water and energy consumption is essential. Most textile production occurs in Global South countries such as India, China, and Bangladesh, which rely heavily on fossil fuels for electricity. Decarbonisation could be achieved by phasing out coal and introducing renewable energy sources using bio-based feedstocks, low-emission heat sources, sustainable production and regeneration of natural systems.

References

1. Gadhi, T. A., Ali, I., Mahar, R. B., Maitlo, H. A., & Channa, N. (2021). Wastewater Recovery in Textile Processing Industry: Journal of Engineering and Technology, 40(3), https://doi.org/10.22581/muet1982.2103.14

2. Carbon Footprint of Textile and Clothing Products. (2015). In Handbook of Sustainable Apparel Production.https://doi.org/10.1201/b18428-11

3. Espinoza Pérez, L. A., & Vásquez, Ó. C. (2022) Carbon footprint assessment of a textile recycling process. Science of the Total Environment, 830.https://doi.org/10.1016/j.scitotenv.2022.154542

About the author

Dr Ashok Athalye is a Professor in Textile Chemistry (ICT-Mumbai). He is the Fellow of Society of Dyers & Colourists (FSDC) & Fellow of Indian Chemical Society (FICS). He has published over 100 research & review articles.