Textile mills are cutting fresh water with smarter sizing chemistry and membrane-based recycling, turning high-BOD desize effluent into reusable process water and approaching near-zero discharge.
Weaving isn’t dyeing-level thirsty, but it still adds up. Modern high‑speed water‑jet looms can consume roughly 50–100 liters per meter of fabric woven (waterjetloom.com). Across textile processing, stages like bleaching, dyeing and sizing together push water footprints to about 100–200 L per kilogram of fabric product (mdpi.com).
The quiet culprit: desizing, the wash‑off step after size is applied to warp yarns. Despite relatively low water use, it accounts for ≈50% of the biochemical oxygen demand (BOD; a measure of biodegradable load) in cotton processing (degruyterbrill.com). In practice, textile water withdrawal is driven by scouring and dyeing, but even pre‑ and post‑weave steps (sizing/desizing, slashing wash) consume tens of liters per kilogram in many mills. In Indonesia, strict effluent standards (for example, Law No. 32/2009 plus MOEF regulations) are pushing mills toward recycling (researchgate.net).
Size chemistry and wash‑off impacts
Conventional sizing agents—mostly starch and starch derivatives—deliver yarn strength but generate high‑BOD effluent when washed off (degruyterbrill.com). Synthetic options like polyvinyl alcohol (PVA) or polyacrylates dissolve easily in hot water, enabling recovery; for example, PVA can be removed by hot‑water desizing and recovered via ultrafiltration (UF; a membrane process) (degruyterbrill.com).
There are trade‑offs: PVA effluent carries very high chemical oxygen demand (COD; a measure of oxidizable load) and can foul reverse osmosis (RO) membranes, and economic PVA recovery remains elusive (textilevaluechain.in; textilevaluechain.in). Mills are therefore testing modified starches (for example, cationic or grafted corn starch) and biodegradable polyester/acrylate copolymers to ease washout while maintaining yarn performance. “Cold‑water soluble” starch formulations that avoid 90–130 °C cooking cut energy and indirectly water by eliminating high‑temperature preparation (textilevaluechain.in).
Another lever is lower pick‑up rate (percentage size add‑on on yarn): high‑performance synthetics at 1–2% instead of ~10% reduce chemical load, with small studies indicating weaving targets can still be met. At the frontier, “size‑free weaving” has been demonstrated: a trial produced 100 yards of 20/1 cotton at 500 picks per minute with no warp breakage using unsized yarn (fibre2fashion.com).
Membrane recovery of desize rinses
Desizing wastewater is rich in starch or PVA hydrolysis products (for example, glucose), so its volume may be moderate but BOD/COD is high. In one industry case, wash water from nine continuous desizing machines was collected into a holding tank and treated through sequential filtration and membranes (mst.dk). After coarse fiber removal, the stream passed through ultrafiltration and then nanofiltration (NF) or reverse osmosis (mst.dk).
The cleaned permeate—essentially purified water—was reused directly in desize and rinse baths, and heat was recuperated for preheating. Concentrate (rich in broken‑down starch) was diverted to anaerobic digestion or as a carbon source in denitrification. The closed loop cut fresh draw by about 17 m³/day (≈12%) and reduced COD discharge by roughly 70–90 g per kg of fabric (mst.dk). As a practical equipment path, mills often deploy an ultrafiltration module as pretreatment, followed by nano‑filtration or integrated RO/NF/UF systems to reach reuse quality.
For PVA‑based sizes, hot desize water can be cycled through UF to recover PVA solids and reuse water with minimal loss. Given the high COD, many mills route PVA effluent to biological or oxidative treatment first and recycle only the clarified water.
Enzymatic desizing with in‑line oxidation
Enzymatic desizing uses amylase (a starch‑degrading enzyme) that converts starch to simple sugars, which can raise BOD. Adding a glucose‑oxidase step can further oxidize those sugars and cut BOD in situ (link.springer.com). Enzyme dosing is typically controlled precisely; mills often integrate a dosing pump to maintain stable addition.
Beyond enzymatics, water reuse is amplified by cascading: shuttling “clean” rinses to earlier stages. Studies show multi‑stage reuse can cut out 95–98% of fresh water demand by cascading rinses; one approach is to use third‑stage rinse water to wash incoming yarn, and to reuse cleaned scouring or first bleach rinse water 2–3 times sequentially before disposal (link.springer.com; link.springer.com).
Closed‑loop water system architecture
Best‑practice closed loops integrate multi‑stage treatment so almost all process water returns to service (link.springer.com; mst.dk). Collection starts in an equalization tank, with fibers and grit removed via coarse screening and sand filtration; continuous removal favors an automatic screen, while polishing can employ a sand/silica filter.
High‑organic streams (starch, PVA) are then treated biologically or enzymatically to reduce BOD/COD. Compact installations often use a membrane bioreactor (MBR; a biological reactor coupled with membranes) such as a membrane bio‑reactor unit. Downstream, membranes take the lead: ultrafiltration (0.01–0.1 µm, to remove colloids and microbes) followed by nanofiltration or reverse osmosis to strip dissolved organics and size residues (mst.dk).
Advanced oxidation processes (AOPs) handle recalcitrant chemistry when needed: ozonation or UV/H₂O₂ (ultraviolet light with hydrogen peroxide) oxidizes trace organics, reduces color and residual COD before reuse, though ozone is energy‑intensive (mdpi.com). Where UV is selected, mills commonly add a compact ultraviolet reactor for low‑cost disinfection and AOP duty.
Treated water—on the order of ~95–98% of inflow—is buffered in closed storage and fed back to high‑quality uses like sizing or final rinses, with small make‑up to offset losses (link.springer.com). RO‑based recycling has enabled textile plants to reuse 80–90% of process water, approaching Zero Liquid Discharge (ZLD; minimal or no liquid effluent) conditions (link.springer.com; mst.dk). The business case extends beyond compliance: lower water bills and effluent charges, and more stable production in water‑scarce regions (sustainability-directory.com). Integrators typically specify end‑to‑end membrane systems tailored for industrial reuse duty.
Operational notes on PVA effluent and rinse cascading
PVA streams remain the trickiest due to high COD and membrane fouling. In practice, many mills send PVA‑rich effluent through biological or oxidative treatment and recycle only the clarified water, reserving membranes for polishing. Meanwhile, cross‑process cascading—especially reusing the cleanest final rinses upstream—has demonstrated 95–98% fresh water reductions in rinsing trains and allows 2–3 reuses of cleaned scouring or first bleach rinse water before disposal (link.springer.com; link.springer.com).
Taken together—mechanical pretreatment, enzymatic or biological oxidation, membranes, and storage—closed loops can reduce weaving‑section water use by ~80–95% (depending on recycling goals) and substantially improve effluent quality, aligning with Indonesian and international regulatory expectations (sources: degruyterbrill.com; mst.dk; link.springer.com; textilevaluechain.in; textilevaluechain.in; fibre2fashion.com; researchgate.net; mdpi.com).
