The textile industry’s water math is stark — and changing fast. New treatment trains are turning wet spinning from a heavy freshwater draw into a high‑recycling loop, with pilots hitting ~98% reuse and double‑digit cuts from simple operational fixes.
Wet (solution) spinning — extruding a polymer solution into an aqueous coagulation bath to form fibers — is built on water, and lots of it (textilelearner.net). The sector already uses ~93 billion m^3 of water annually (≈4% of global freshwater withdrawal), with comparable wastewater produced (sustainablebrands.com).
Typical footprints vary: synthetic fiber processing (including wet spinning for man‑made fibers) runs ~100–200 L per kg of fabric, while natural fibers like cotton trend even higher (~350 L/kg) (sciencedirect.com). Dyeing 1 kg of cloth alone can require ~40 L (link.springer.com).
The numbers collide on the effluent side too: globally, textile operations consume ~830 million m^3 of water per year and discharge ~640 million m^3 of effluent, often loaded with dissolved chemicals, salts, dyes, and auxiliaries such as caustic soda and bleaching agents (link.springer.com). In Indonesia, wastewater treatment by textile mills is mandated, yet studies report low compliance (bio-conferences.org).
Low‑liquor ratios and counter‑current rinsing
Several tactics curb fresh intake before any new equipment is installed. Low‑liquor ratio (LLR) setups — lower water per unit fabric — and counter‑current washing slash rinse volumes. Progressive multistage rinsing reuses the last (cleanest) wash water for the next batch’s first rinse, saving “tens of percent” freshwater (fibre2fashion.com).
Simple housekeeping matters: leak detection, optimized fill levels, and proper line shutdown deliver 10–30% immediate savings (fibre2fashion.com). One Somerset finishing plant combined scour and bleach into a single bath to save 6,200 gal/h (~23.5 m^3/h) (fibre2fashion.com).
Chemical tweaks and heat integration
Chemistry can lower purge volumes. Ion‑exchange softeners allow rinse reuse but produce a brine; some mills shift toward nanofiltration or integrate alkali recovery to cut repeated freshwater use. In that context, a softener can be paired with a softener program or, where appropriate, swapped for a nano‑filtration step.
Heat integration also pays: reusing process heat via heat exchangers enables wash waters to be reused at target temperatures without fresh hot water (researchgate.net). Waterless pretreatments (foam or infrared) and shifts to waterless coating technologies also reduce draw, compounding savings seen in cleaner‑production audits (fibre2fashion.com).
Closed‑loop pilots with high reuse
Real‑world demonstrations show just how far loops can go. The EU‑funded LIFE ANHIDRA project combined mechanical filters, ultrafiltration (UF), and ozone to treat municipal/industrial rinse water, achieving ~98% reuse (environment.ec.europa.eu). Over a 60‑day trial, one Portuguese finishing mill recycled its wash water in‑loop, saving ~21,000 m^3 and extrapolating to ~123,400 m^3/year (environment.ec.europa.eu).
The system reduced discharge by 92% while virtually eliminating the need for fresh make‑up or additional chemicals (environment.ec.europa.eu) (environment.ec.europa.eu).
Pre‑treatment: screening and clarification
Recycling the spin bath and washes starts with solids removal. Screens, cyclones, or sedimentation strip fibers, lint, and large particulates, protecting downstream membranes (rmix.it). In practice, mills deploy an automatic screen at the headworks and follow with a compact lamella settler to keep detention times tight.
Biological oxidation and UF barrier
Primary treatment often leans on biology to degrade dissolved organics. Membrane bioreactors (MBR — a biological reactor with a UF membrane barrier) or activated sludge are common. Many mills use MBR to hit very low BOD/COD; in Pakistan, a dye‑house treated all effluent via an MBR→UF→RO train, removing ≈96–97% of BOD (biological oxygen demand), COD (chemical oxygen demand), and TDS (total dissolved solids) (researchgate.net).
The permeate — nearly colorless — was fully reused for fabric washing/rinsing (researchgate.net). For facilities designing similar trains, packaged membrane bioreactors feed clean UF permeate into downstream polishing without expanding the footprint.
NF/RO desalting and color removal
After UF, nanofiltration (NF) and reverse osmosis (RO) do the heavy lifting on salts, dyes, and low‑molecular‑weight organics. Italian pilot trials in the Prato textile district showed that adding a second NF stage raised permeate yield by 15%, ultimately achieving ~84% overall water recovery; the remaining ~16% concentrate can be managed or further treated (mdpi.com). Designing for ≥80% recovery is now feasible, especially if retentate vapor‑compression or crystallization is added (mdpi.com).
On hardware selection, UF steps are commonly delivered with ultrafiltration modules, NF with nano‑filtration skids, and RO with brackish‑water RO packages; integrated membrane systems help tune recovery across stages.
Polishing and reuse specifications
Final polishing addresses residuals. Activated carbon can remove trace organics and color, while UV or ozone oxidizes refractory dye molecules; ion exchange can trim remaining ions to meet reuse specs (mdpi.com). Notably, NF can remove ≥85–98% hardness, reducing scaling risk in loops (mdpi.com). In practice, mills deploy activated carbon filters, and for non‑chemical disinfection, ultraviolet units provide a 99.99% pathogen kill rate without adding residuals.
Controls, monitoring, and diversion logic
Each stage is continuously monitored — pH, conductivity, organics, and microbial content — so recycled water stays within safe limits (rmix.it). The overall effect is “water reuse multiply”: one cubic meter of fresh water becomes several passes of recycled water through the process, cutting intake by similar factors (rmix.it). For pH adjustments and antiscalant feeds, a metered dosing pump maintains setpoints without over‑chemicating.
Closed‑loop design for wet spinning
A representative loop collects spin bath overflow and wash effluent into a buffer tank (blended and equalized). Coarse screening and lamella clarification remove fibers and sludge (which can be pressed out), then an MBR biologically consumes dissolved organics. The MBR’s UF permeate feeds a dual‑stage membrane unit: first NF to soften water and remove dyes, then RO for deeper removal (mdpi.com) (rmix.it).
Permeate is stored in a clean tank, pH‑adjusted, and reused as spin bath make‑up or rinses; retentates (and backwash wastes) go to minimal‑discharge brine handling or zero‑liquid‑discharge (ZLD) steps. Full‑loop instrumentation tracks recycling rates (flow meters) and water quality (turbidity, conductivity, TOC — total organic carbon); automated controls divert off‑spec water for re‑treatment or use in earlier rinse stages (rmix.it). Ancillary items — strainers, housings, and tanks — round out the loop with standardized water‑treatment ancillaries.
Recovery targets and operating economics
With closed‑loop designs, fresh water demands can approach zero. Pilots now target “reuse up to 98%” (environment.ec.europa.eu), and advanced loops have demonstrated >90% recycling. By contrast, conventional open‑discharge mills send ~70% of intake to waste (mdpi.com).
Economically, trials point to reduced effluent charges, lower chemical purchases, and even resource recovery (e.g., salt or fiber residues from brine). In aggregate, treatment train designs that combine standard WWTP units with membranes can recycle typically 80–90% of process water (mdpi.com) (environment.ec.europa.eu). The remaining concentrate (≈10–20%) contains most impurities and can be managed appropriately.
Where it’s working and what’s next
This design philosophy — proven in textile districts such as Prato, Italy — effectively transforms spinning and finishing lines into near‑closed cycles (mdpi.com). For Indonesian manufacturers, adopting closed loops aligns with emerging “green industry” standards (peraturan.bpk.go.id) and lessons from EU pilots (environment.ec.europa.eu) and MBR‑RO case studies (researchgate.net).
