Tiruppur dyeing effluent and ZLD: a treatment guide
How Tiruppur dye houses and CETPs treat knitwear dyeing effluent under zero liquid discharge, and where coagulant, decolorant and polymer fit in the train.
Why Tiruppur works under ZLD
Tiruppur dyes and bleaches much of India's knitwear, and its effluent once flowed into the Noyyal river. Pollution of the river and the land around it led to strict rules, and dyeing units have worked under a zero liquid discharge requirement since 2008. Treated water is recovered for reuse and no liquid effluent leaves the plant.
Units are regulated by the Tamil Nadu Pollution Control Board (TNPCB). Your consent order sets the conditions that apply to your plant.
What the effluent carries
Reactive dyeing uses large amounts of salt and soda ash, so the effluent is hot, strongly coloured, alkaline and high in dissolved salts. It also carries fibre lint, size, softeners and detergents from washing. Strength swings from batch to batch as shades change.
The treatment train, step by step
Screening and equalisation even out flow and strength. pH correction brings the alkaline effluent into the working range. Coagulation and flocculation remove suspended matter, and a decolorant takes out dissolved dye. Biological treatment removes the remaining organics.
Tertiary filtration then protects the reverse osmosis (RO) stage, which recovers most of the water. The RO reject goes to evaporators, and many plants recover salt from the brine for reuse in dyeing.
Where Sun Brand polymers fit
SunDec SC05 binds dissolved reactive dye into particles that can be settled out. SunMac SC04, a liquid cationic polymer, can support or partly replace the metal-salt coagulant, which helps keep sludge volumes down. A cationic Sunfloc grade such as Cationic HQ or Cationic MQ then builds large flocs that settle fast in the primary clarifier, and conditions the sludge before dewatering.
Protecting RO and evaporators
Every particle that escapes the clarifier ends up on the filters and membranes. A clear primary overflow means fewer RO cleanings, steadier recovery and less load on the evaporators, which are the most expensive part of a ZLD plant to run.
Practical tips for Tiruppur plants
Re-check doses when the shade mix changes, as dark shades usually need more decolorant. Dose the decolorant before the flocculant, not after. Watch for overdosing, which shows up as slimy, slow-filtering sludge and fouled filters. Keep a jar-test kit at the plant and test the equalisation tank when results drift.
Start with a jar test
Send a one-litre sample from your equalisation tank. We test SunDec, SunMac and Sunfloc in combination and recommend a starting dose for each, free of charge.
Not sure which grade suits your water?
Send us a one-litre sample or describe your process. We test it in our lab free of charge and recommend a grade and starting dose, and quote within 1 business hour.