Sustainability in textiles

In short

Sustainability in textiles means producing fibre, yarn, fabric and garments with the least water, energy, chemical and social cost, and designing the product so its material returns to use instead of landfill. It matters because wet processing is among the most water- and chemical-intensive industries in India, and because export buyers in the EU, UK and US now make certification, chemical compliance and traceability a condition of the order, not an option. It is examined in Textile Chemical Processing, Environmental Pollution Control, Eco-friendly Textiles and Industry 4.0 electives, and in GATE-TF under environmental and effluent treatment questions. On the job it is the daily work of ETP/ZLD operators, sustainability and compliance executives and process engineers at Arvind, Welspun, Trident, Raymond, Vardhman, Shahi Exports, Gokaldas, Reliance (Recron GreenGold) and the Tiruppur and Panipat clusters.

Explained

The three pillars and the scope of the problem

• Environmental, social and economic sustainability - a mill that is clean but pays below the wage floor, or clean but loss-making, is not sustainable in the examined sense.
• Where the burden sits: fibre cultivation (water, pesticide, land), spinning and weaving (electricity), wet processing (water, chemicals, thermal energy - the largest single hotspot), garmenting (labour, cutting waste), use phase (laundering, microfibre shedding) and end of life.
• Typical Indian benchmarks (vary by mill, product and machinery - treat as order of magnitude): 80-200 L water per kg of processed knit fabric, 3-5 kWh/kg for ring spinning, 2-6 kg steam per kg in dyeing and finishing.
• Hazardous chemistry: azo dyes that cleave to banned aromatic amines, APEO/NPEO wetting agents, formaldehyde in resin finishes, PFAS in water-repellent finishes, chlorinated solvents, heavy metals in metal-complex dyes.
• Microplastics: synthetic fabrics shed microfibres in laundering; low-twist, loosely bound surfaces and mechanical raising shed more. No Indian regulation on it yet; the EU is moving on design and labelling.
• Textile waste: India generates roughly 7.8 million tonnes of textile waste a year (Fashion for Good / Sattva estimate, 2022), much of it downcycled; India has no textile-specific EPR law yet - EPR currently applies to plastic packaging, e-waste, batteries and tyres.

Sustainable fibres and raw-material choices

• Organic cotton: grown without synthetic pesticides/fertiliser and GM seed; certified to GOTS or OCS. India is the world's largest producer of organic cotton but yields are lower and fraud in seed/transaction certificates has been a live problem.
• Better Cotton (BCI) and Kasturi Cotton Bharat: mass-balance / traceability programmes rather than organic - lower chemical use and traced Indian cotton, not zero chemistry.
• Recycled polyester (rPET): made from post-consumer PET bottles or polyester waste; saves roughly 40-60% of the energy of virgin PET and avoids crude feedstock, but bottle-to-fibre is open-loop downcycling and does not solve microfibre shedding.
• Mechanical versus chemical recycling: mechanical shredding shortens fibre (needs virgin blending, as in Panipat shoddy yarn); chemical recycling (glycolysis/methanolysis for polyester, cellulose dissolution for cotton) restores polymer quality at higher cost and energy.
• Regenerated cellulosics: viscose is CS₂-intensive (worker health risk); lyocell (Tencel) uses NMMO in a closed loop with >99% solvent recovery; modal is intermediate. Bamboo sold as "natural" is almost always chemically regenerated viscose - labelling it bamboo is misdeclaration.
• Low-impact naturals: jute, hemp, ramie, banana and pineapple fibre, kala cotton; naturally coloured cotton skips dyeing.
• Bio-based synthetics: PLA from corn starch - compostable, but only under industrial composting conditions; bio-PET is bio-based yet chemically identical to PET, so it is recyclable but not biodegradable - bio-based does not mean compostable.
• Design for recycling: mono-material garments, no cotton/polyester blends where avoidable, avoid elastane, mechanical trims instead of glued ones - blends are the single biggest barrier to fibre-to-fibre recycling.

Cleaner wet processing - the main engineering content

• Reduce liquor ratio: exhaust dyeing at 1:5 instead of 1:8 cuts water, salt, chemicals and the steam to heat them, proportionally. Soft-flow and airflow machines reach 1:3-1:5.
• Pre-treatment: enzymatic desizing (amylase) replaces acid; bio-scouring (pectinase) replaces boiling caustic; enzymatic bio-polishing (cellulase) replaces singeing chemistry; ozone or peracetic acid bleaching replaces hypochlorite, avoiding AOX.
• Combined processes: single-stage desize-scour-bleach cuts baths; pad-batch and cold pad batch (CPB) dyeing of cotton give 90%+ fixation with little or no salt and no heating - the standard exam answer for water- and energy-saving reactive dyeing.
• Dye selection: high-fixation bifunctional reactive dyes, low-salt dyes, liquid dyes (no dust), avoiding benzidine-type azo and metal-complex dyes.
• Waterless and near-waterless routes: supercritical CO₂ dyeing of polyester (DyeCoo - no water, no auxiliaries, CO₂ recycled); dope dyeing / solution dyeing of man-made fibre (pigment added to the melt - huge savings, limited shade flexibility); digital inkjet printing (no screens, print paste or washing-off of unfixed paste, far less water than rotary screen printing, but slower and costlier per metre for long runs).
• Denim finishing: ozone washing, laser fading, nanobubble/e-flow (Jeanologia), enzyme stone-wash replacing pumice and permanganate; potassium permanganate spray and sandblasting are banned by most brands on health grounds.
• Finishing: foam finishing (low wet pick-up), plasma and UV surface treatment, PFAS-free water repellents (C0 chemistry), formaldehyde-free DMDHEU alternatives.
• Utilities: heat recovery from hot effluent and from stenter exhaust, condensate return, VFDs on pumps and fans, LED lighting, insulated steam lines, solar rooftop and wind (Tamil Nadu mills commonly run on group-captive wind), biomass boilers replacing coal.
• Chemical management: input-side control through the ZDHC MRSL (what may enter the factory) and the brand's RSL (what may remain in the product) - RSL testing alone is end-of-pipe and catches problems too late.

Effluent treatment and zero liquid discharge

• Characteristics of textile effluent: high colour, high COD (800-2,000 mg/L), BOD 300-600 mg/L, high TDS (salt from reactive dyeing, often 4,000-10,000 mg/L), alkaline pH 9-11, variable temperature; BOD/COD ratio low (~0.25-0.4) because dyes are poorly biodegradable.
• Treatment train: screening and equalisation → primary: pH correction, coagulation-flocculation (alum, FeSO₄, polyelectrolyte), clarification → secondary (biological): activated sludge/aeration tank with MLSS 3,000-4,000 mg/L, or MBBR/UASB → tertiary: pressure sand and activated carbon filters, ozonation or Fenton for residual colour, sometimes MBR → RO for TDS → reject management by multiple-effect evaporator (MEE) and ATFD to dry salt.
• ZLD means no liquid effluent leaves the premises; permeate is reused, salt is recovered or sent as hazardous waste. Legally mandated for the Tiruppur and Erode dyeing clusters following litigation over the Noyyal river, and now designed into PM MITRA parks.
• Why ZLD is hard: MEE steam demand dominates the cost; recovered Glauber's salt is often too impure for reuse; RO membranes foul on dye and silica. Cluster CETPs (Tiruppur has 18-plus) spread the capital cost across small dyeing units.
• Sludge: ETP sludge from dyeing is a hazardous waste under the Hazardous and Other Wastes (Management and Transboundary Movement) Rules, 2016 - stored on an impervious pad, manifested and sent to a TSDF or co-processed in a cement kiln.

Standards, Indian law and certification

• Indian statutes: Water (Prevention and Control of Pollution) Act, 1974; Air (Prevention and Control of Pollution) Act, 1981; Environment (Protection) Act, 1986 and its rules; Hazardous and Other Wastes Rules, 2016; Plastic Waste Management Rules, 2016 (EPR for packaging); Noise and Battery Waste rules where applicable.
• Regulators and consents: CPCB sets norms and the CREP charter; the State Pollution Control Board issues Consent to Establish and Consent to Operate and the Hazardous Waste authorisation; textile processing is a Red category activity. Online continuous effluent monitoring is required for larger units.
• Discharge limits (inland surface water, general standards): pH 5.5-9.0, BOD 30 mg/L, COD 250 mg/L, TSS 100 mg/L, oil and grease 10 mg/L, temperature rise ≤5 °C; limits for discharge to sewer, on land or to marine outfall differ, and the consent condition for your unit prevails.
• Energy: textile units are designated consumers under the BEE PAT scheme (Energy Conservation Act, 2001, as amended 2022), with specific energy consumption targets and ESCerts.
• Labour and social compliance: the four Labour Codes are in force from 21 November 2025, replacing the Factories Act, 1948, the Minimum Wages Act, the Industrial Disputes Act and the BOCW Act - so cite the OSH&WC Code for factory safety and welfare, the Code on Wages for the wage floor, the Code on Social Security and the Industrial Relations Code. Voluntary audits layered on top: SA8000, amfori BSCI, Sedex SMETA, WRAP, and the ILO core conventions on child and forced labour.
• Product and process certifications: GOTS (organic content ≥70%, with environmental and social criteria through the chain; version 7.0 is the current edition), OCS (content only), GRS and RCS (recycled content; GRS adds social/environmental criteria, ≥20% for claims, ≥50% for the GRS label), OEKO-TEX STANDARD 100 (harmful-substance limits on the finished article), OEKO-TEX STeP and MADE IN GREEN, bluesign, EU Ecolabel, Cradle to Cradle, FSC for viscose pulp.
• Measurement and reporting tools: LCA to ISO 14040/14044, EPDs, carbon footprint to ISO 14067 and the GHG Protocol (Scope 1 direct, Scope 2 purchased electricity, Scope 3 value chain - for brands, Scope 3 is 90%+ of the total), Higg FEM/MSI (Worldly), SBTi targets, ISO 14001 EMS, BRSR reporting for listed Indian companies, and the CDP water and climate questionnaires.
• Export-market rules to know: EU REACH (SVHC and Annex XVII restrictions on azo amines, nonylphenol, PFOA), the EU Strategy for Sustainable and Circular Textiles with ESPR ecodesign requirements and a Digital Product Passport, the EU Deforestation Regulation (relevant to viscose pulp), green-claims and empty-environmental-claims rules against greenwashing, and the French/EU separate-collection mandate for textiles. These are moving fast - verify the effective date before quoting.
• GST note: the slab structure was restructured to 5%/18%/40% from 22 September 2025, with most textile fibres, yarns and fabrics at 5%; check the HSN line before quoting a rate on recycled or technical items.

Circularity and the business case

• Waste hierarchy: prevent → reduce → reuse → repair → recycle → recover (energy) → dispose. Downcycling to wiping rags or shoddy blankets delays landfill; it is not closed-loop.
• Pre-consumer versus post-consumer waste: cutting-room waste is clean, sorted and single-composition, so it recycles well; post-consumer garments are mixed, dirty and blended - sorting is the bottleneck. India is a large importer of used clothing for recycling through the Kandla SEZ and the hub at Panipat.
• Business models: rental, resale, repair, take-back, made-to-measure and on-demand production (cuts unsold inventory, the hidden waste of fast fashion).
• The economic case: water, steam, salt, dye and effluent treatment are purchased inputs - cutting them cuts cost, which is why liquor-ratio reduction and heat recovery usually pay back in under two years, while certification and ZLD are market-access and licence-to-operate costs.
• Greenwashing to avoid: "eco" without a certified claim, bamboo-as-natural, biodegradable claims without a test standard, offsetting instead of reducing, and quoting a single-attribute saving (water) while ignoring energy.

Key points

• Wet processing - the environmental hotspot of the textile chain, dominating water, chemical and thermal energy use.
• Liquor ratio - mass of liquor per unit mass of goods; the single biggest lever on water, salt and steam in exhaust dyeing.
• Cold pad batch - salt-free, heat-free reactive dyeing with 90%+ fixation; standard "water-saving dyeing" answer.
• Supercritical CO₂ dyeing - waterless polyester dyeing with recycled CO₂ as the solvent.
• Dope/solution dyeing - pigment in the polymer melt; largest saving for man-made fibre, least shade flexibility.
• ZDHC MRSL vs brand RSL - input-side (what enters the factory) versus output-side (what remains in the product).
• ZLD - no liquid discharge; RO plus MEE/ATFD; mandated for the Tiruppur-Erode cluster.
• TDS, not COD, drives ZLD cost - salt from reactive dyeing is what forces RO and evaporation.
• COD 250 mg/L, BOD 30 mg/L, pH 5.5-9.0 - general inland surface water discharge limits; the unit's consent condition governs.
• ETP sludge from dyeing is hazardous waste under the 2016 Rules - TSDF or cement co-processing.
• GOTS - organic content with environmental and social criteria; OCS/RCS certify content only; GRS adds criteria to recycled content.
• OEKO-TEX STANDARD 100 - tests the finished article against harmful-substance limits; STeP certifies the facility.
• LCA (ISO 14040/14044) - cradle-to-grave impact per functional unit; cradle-to-gate stops at the factory gate.
• Scope 1/2/3 - direct, purchased electricity, value chain; for an apparel brand Scope 3 dominates.
• Blends block recycling - cotton/polyester and any elastane make fibre-to-fibre recycling uneconomic.
• BEE PAT - textile units are designated consumers with specific energy consumption targets and ESCerts.
• Four Labour Codes, in force 21 November 2025 - the legal basis of social compliance; the Factories Act, 1948 no longer applies.
• Microfibre shedding - unregulated in India; addressed by fabric construction and finishing, not by fibre choice alone.

Formulas and examples

Example 1 - Liquor ratio and water saving. A jet dyeing machine processes a 500 kg polyester batch at LR 1:8 through 6 baths (dyeing, reduction clearing, four rinses).

• Water per bath = 8 × 500 = 4,000 L → total = 6 × 4,000 = 24,000 L; SWC = 24,000/500 = 48 L/kg.
• Replacing it with a soft-flow machine at LR 1:5: per bath = 2,500 L → total = 15,000 L, SWC = 30 L/kg.
• Saving = 9,000 L per batch = 37.5%. At 2 batches/day × 300 days = 600 batches → 5,400 kL/year. At ₹60 per kL for water plus effluent treatment → ₹3,24,000 per year, before the steam saved in heating 9,000 L less.

Example 2 - Reactive dye fixation and salt load. 1,000 kg cotton knit, 3% shade on weight of fabric, exhaust dyeing at LR 1:8 with 60 g/L salt.

• Dye applied = 0.03 × 1,000 = 30 kg. At 70% fixation, dye to effluent = 30 × 0.30 = 9 kg (the colour in the effluent).
• Salt = 60 g/L × 8 L/kg × 1,000 kg = 480,000 g = 480 kg, which ends up as TDS the RO and MEE must handle.
• Switching to cold pad batch at 90% fixation with no salt: dye to effluent = 30 × 0.10 = 3 kg, salt = 0 kg - a 67% cut in dye loss and the whole TDS load removed.

Example 3 - COD load and removal. A mill discharges 1,200 m³/day at COD 1,100 mg/L; the ETP outlet reads 150 mg/L.

• Inlet load = 1,200 × 1,100/1,000 = 1,320 kg COD/day; outlet = 1,200 × 150/1,000 = 180 kg/day.
• η = (1,100 − 150)/1,100 × 100 = 86.4%. Outlet 150 mg/L is within the 250 mg/L inland-surface-water limit; if BOD is also ≤30 mg/L the stream is compliant.

Example 4 - Cost of ZLD. 1,000 m³/day of treated effluent to RO at 80% recovery.

• Permeate = 800 m³/day reused; reject = 200 m³/day to a quadruple-effect MEE with steam economy 3.2.
• Steam = 200,000 kg ÷ 3.2 = 62,500 kg/day (62.5 t). Coal at 0.15 kg coal per kg steam = 9,375 kg ≈ 9.4 t/day; at ₹8,000/t = ₹75,000/day.
• That is ₹375 per m³ of reject, or ₹75 per m³ of total effluent - which is why reducing TDS at source (CPB, low-salt dyes, low LR) is cheaper than evaporating it.

Example 5 - Cradle-to-gate carbon footprint of a cotton T-shirt (200 g garment). Fabric needed with 15% cutting waste ≈ 0.235 kg; lint needed with spinning/processing losses ≈ 0.28 kg.

• Processing electricity (spinning 3.0 + knitting 0.9 + dyeing/finishing 1.1) ≈ 5.0 kWh/kg fabric → 5.0 × 0.71 = 3.55 kg CO₂e/kg.
• Steam 4 kg/kg fabric, 0.15 kg coal/kg steam = 0.6 kg coal/kg, Indian coal EF ≈ 1.8 kg CO₂/kg → 1.08 kg CO₂e/kg. Process total ≈ 4.63 kg CO₂e per kg fabric.
• Garment share = 0.235 × 4.63 ≈ 1.09 kg CO₂e; cotton cultivation and ginning at ≈1.8 kg CO₂e/kg lint → 0.28 × 1.8 ≈ 0.50 kg.
• Total ≈ 1.6 kg CO₂e, cradle-to-gate, excluding transport, retail, laundering and disposal. Emission factors differ by source and year, so always state the factor used.

Example 6 - Bottles per rPET T-shirt. 1 kg rPET fibre needs ≈1.05 kg of PET flake; a 500 mL bottle weighs ≈19 g → 1,050/19 ≈ 55 bottles/kg. A 0.235 kg polyester tee ≈ 13 bottles.

Where it is used

• Export processing houses and garment exporters: Arvind, Welspun, Trident, Raymond, Vardhman, Shahi, Gokaldas, Pratibha Syntex - GOTS/GRS/OEKO-TEX certification, ZDHC conformance and Higg FEM scores are order qualifiers for H&M, Inditex, M&S, Levi's, Decathlon and IKEA.
• ETP/CETP and ZLD operations: Tiruppur and Erode dyeing clusters, Pali, Jetpur, Balotra, Panipat; roles for ETP chemists, ZLD shift engineers and environment officers filing SPCB returns.
• Fibre and recycling industry: Reliance Recron GreenGold, Ganesha Ecosphere (PET bottle recycling), Birla Cellulose Liva/Livaeco and Birla Excel lyocell, Panipat shoddy and recycled blanket units.
• Compliance and sustainability roles: RSL/MRSL testing coordination with SGS, Bureau Veritas, Intertek, TÜV and SITRA/NITRA/BTRA; BRSR and Scope 1-3 reporting in listed companies; social audit readiness under the Labour Codes.
• Denim finishing and laundries: ozone, laser and enzyme washing lines in Bengaluru, Ahmedabad and Tiruppur; chemical and water savings per garment are tracked as KPIs.
• Government and cluster programmes: PM MITRA mega parks with common ZLD and utilities, BEE PAT targets for designated textile consumers, TUFS-successor machinery incentives, Kasturi Cotton Bharat traceability.

Interview questions

• Q: Which stage of the textile chain has the highest environmental impact and why? A: Wet processing - it consumes most of the water, almost all the process chemicals and the bulk of thermal energy, and it generates the coloured, high-TDS effluent.
• Q: What is liquor ratio and why does reducing it save more than just water? A: It is the liquor-to-goods mass ratio; less liquor means less water, less salt and auxiliary chemical (dosed per litre) and less steam to heat the bath, so water, chemical, energy and effluent cost all fall together.
• Q: Why does reactive dyeing of cotton make ZLD expensive? A: It uses 50-80 g/L of electrolyte, which leaves as TDS; biological treatment cannot remove salt, so RO and evaporation become unavoidable and the MEE steam bill dominates.
• Q: Difference between a ZDHC MRSL and a brand RSL? A: The MRSL restricts chemical formulations entering the factory (input control); the RSL limits substances present in the finished product (output control) - MRSL prevents the problem, RSL only detects it.
• Q: GOTS versus OCS versus GRS? A: GOTS certifies organic fibre with environmental and social criteria; OCS certifies organic content and chain of custody only; GRS certifies recycled content plus environmental and social criteria.
• Q: Is bamboo fabric a sustainable natural fibre? A: Usually not as sold - most bamboo fabric is chemically regenerated viscose, and it must be labelled viscose from bamboo; bamboo lyocell with closed-loop solvent recovery is the genuinely lower-impact version.
• Q: What are the general inland surface water discharge limits for BOD, COD and pH? A: BOD 30 mg/L, COD 250 mg/L, pH 5.5-9.0, TSS 100 mg/L - but the unit's SPCB consent condition can be stricter and prevails.
• Q: How is ETP sludge from a dyehouse disposed of legally in India? A: As hazardous waste under the Hazardous and Other Wastes Rules, 2016 - stored on an impervious area with authorisation, manifested, and sent to an authorised TSDF or for cement co-processing.
• Q: Why is a cotton/polyester blend a recycling problem? A: Mechanical recycling cannot separate the two and chemical recycling needs a single polymer, so blends are downcycled; design for recycling therefore favours mono-materials.
• Q: Is recycled polyester from bottles truly circular? A: No - it is open-loop downcycling that removes PET from the bottle-to-bottle stream, and the fibre still sheds microplastics; fibre-to-fibre polyester recycling is the circular route.
• Q: What is a functional unit in LCA and why does it matter? A: The quantified service the study compares, for example one T-shirt worn 50 times; without it a durable garment and a throwaway one look identical per kilogram.
• Q: A buyer asks for your Scope 3 emissions - what are they? A: Value-chain emissions outside your own operations and purchased electricity: purchased fibre and yarn, subcontracted processing, transport, use and end of life - usually the largest share for an apparel business.
• Q: One low-capex change that cuts a mill's carbon footprint fastest? A: Heat recovery - condensate return plus hot-effluent and stenter-exhaust heat exchangers - because thermal energy from coal carries the highest emission factor per rupee saved; it typically pays back in well under two years.

Common mistakes

• Treating sustainability as the ETP alone - most of the saving lies upstream in recipe, machine and liquor-ratio choices, not in treating the effluent afterwards.
• Confusing BOD with COD, or expecting biological treatment to reduce TDS and colour - it does neither effectively.
• Quoting an old discharge limit or a withdrawn standard number instead of reading the unit's consent conditions.
• Citing the Factories Act, 1948 or the Minimum Wages Act in social-compliance answers - the four Labour Codes replaced them from 21 November 2025.
• Mixing up GOTS, OCS, GRS and OEKO-TEX, or claiming OEKO-TEX STANDARD 100 proves organic or recycled content (it does not - it is a harmful-substance test).
• Unit slips in load calculations: mg/L × m³/day gives grams, so divide by 1,000 for kg/day; mixing L/kg with m³/t.
• Calling bamboo viscose a natural fibre, or biodegradable without naming the test standard and conditions.
• Reporting a single-attribute win (water saved) while ignoring the energy or chemical penalty of the same change - the definition of greenwashing in an exam answer.

Related topics

Textile testing and quality control · Textile chemical processing: dyeing, printing and finishing · Technical textiles · Indian textile industry and exports · Textile costing · Environmental pollution control and effluent treatment