INDUSTRIES / TEXTILES
Textile effluent treatment
that removes colour and recovers salt.
Dye house effluent is hot, alkaline, coloured and salty. We test it in our NABL-accredited laboratory, then design the ETP, colour removal, RO and evaporator so that water and salt go back into your dyeing, not into a drain or a salt pile.
In short
How textile dyeing wastewater is treated.
A textile effluent treatment plant cleans the wastewater from desizing, scouring, bleaching, dyeing, printing and finishing. It works in five steps: cool and equalise the hot, variable flow; neutralise the high pH; remove colour chemically; treat biologically to cut BOD and COD; and polish with filters, ozone or activated carbon. Where the consent requires zero liquid discharge, UF and RO recover most of the water, and the salty reject is evaporated, with the brine or salt often reused for dyeing.
Textile units must meet the textile industry standards under the Environment (Protection) Rules, 1986, or ZLD where their consent or state rules require it.
- 40–100g/L
- Salt commonly used in reactive dyeing of cotton, the main source of TDS
- 9–12pH
- Typical pH of reactive dye bath and scouring effluent
- 250mg/L
- COD limit for discharge to inland surface water
- ~80%lower
- Evaporation cost with our non-thermal evaporator than with a steam MEE
Where it comes from
Where does textile effluent come from?
Almost all textile wastewater comes from wet processing, where fabric or yarn is washed, treated and dyed in water. Cotton processing is the thirstiest; synthetics use less water but bring their own dyes and auxiliaries. Each step adds something different.
| Process | What it does | What it adds to the effluent |
|---|---|---|
| Desizing | Removes the starch or PVA size applied to yarn before weaving | High BOD and COD from starch; enzymes |
| Scouring | Boils out natural waxes, pectins and dirt with caustic soda and detergents | High pH, COD, surfactants, oils and waxes; hot |
| Bleaching | Whitens fabric, usually with hydrogen peroxide or hypochlorite | Residual peroxide, stabilisers, high pH |
| Mercerising | Treats cotton with strong caustic soda for lustre and dye uptake | Very high alkalinity; caustic can be recovered |
| Dyeing | Fixes reactive, direct, vat, disperse or acid dyes onto the fibre | Colour, salt (TDS), alkali, unfixed dye, dyeing auxiliaries; hot |
| Printing | Applies dye or pigment in patterns with thickened pastes | Thickeners, urea, pigments, high COD from wash-off |
| Finishing | Softeners, resins and repellents give the final feel | Small volumes of resins, softeners and silicones |
| Washing and soaping | Rinses off unfixed dye and chemicals after each step | The largest volume: dilute colour, salt and detergents |
Typical effluent characteristics
| Parameter | Typical range | Why it matters |
|---|---|---|
| Colour | Several hundred to several thousand Hazen units | Visible in the outlet even at low dye levels; boards reject coloured discharge |
| pH | 8 to 12 | Alkali from scouring, mercerising and reactive dyeing must be neutralised before biology |
| Temperature | 35 to 60 °C | Hot dye bath drains kill ETP bacteria unless cooled |
| COD | 800 to 3,000 mg/L | Dyes and auxiliaries are only partly biodegradable |
| BOD | 200 to 700 mg/L | A low BOD : COD ratio (often 0.2 to 0.35) means biology alone will not meet the COD limit |
| TDS | 3,000 to 10,000 mg/L combined; far higher in dye baths | Salt is not removed by biology; it decides whether you need RO and an evaporator |
| Suspended solids | 100 to 500 mg/L | Fibre, lint and print paste; blocks pumps and filters |
| Surfactants and oils | Present in most streams | Foaming in aeration tanks and fouling of membranes |
| Metals | Traces from some dyes and mordants | Chromium and copper limits apply; sludge may be hazardous |
The single biggest difference from other industries is salt. In reactive dyeing of cotton, common salt or Glauber's salt (sodium sulphate) is added to push dye onto the fibre, and almost all of it ends up in the effluent. That is why textile ZLD is really a salt problem as much as a water problem.
Standards and rules
Which standards apply to textile effluent?
The Environment (Protection) Rules, 1986 contain industry-specific standards for the textile industry, revised by MoEF&CC in 2016. The main values for discharge to inland surface water are below; your consent may be stricter.
| Parameter | Textile industry standard |
|---|---|
| pH | 6.5 to 8.5 |
| Total suspended solids | 100 |
| BOD (3 days at 27 °C) | 30 |
| COD | 250 |
| Oil and grease | 10 |
| Colour | 150 Hazen units |
| Total chromium | 2.0 |
| Hexavalent chromium | 0.1 |
| Sulphide | 2.0 |
| Phenolic compounds | 1.0 |
| Bio-assay test | 90% survival of fish after 96 hours in 100% effluent |
Treatment scheme
A textile ETP and ZLD, stage by stage.
This is the scheme we start from for a cotton dyeing and processing house. Stages 1 to 5 are the ETP; stages 6 to 8 are added for reuse and ZLD.
| Stage | What happens | Typical units |
|---|---|---|
| 1. Screen, cool and equalise | Lint and fibre are screened out. Hot dye bath drains are cooled and mixed with rinse water for a day or more so pH, colour and strength even out. | Fine screen, cooling tower or heat exchanger, equalisation tank with mixing |
| 2. Neutralise | The alkaline effluent is brought to about pH 7 to 8 for the bacteria. | Acid dosing or flue gas (CO₂) neutralisation, pH control |
| 3. Remove colour chemically | Coagulants and decolourising agents bind dye molecules into flocs that settle or float. | Flash mixer, flocculator, clarifier or DAF; lime, ferrous or alum, polyelectrolyte, decolourant |
| 4. Biological treatment | Bacteria digest the biodegradable part of the COD, starch and auxiliaries. | Extended aeration or MBBR, secondary clarifier |
| 5. Tertiary polish | Remaining colour and COD are removed to meet the outlet limits. | Pressure sand filter, ozone, activated carbon filter (ACF); catalytic oxidation for stubborn dyes |
| 6. Ultrafiltration | Protects the RO by removing fine solids, colloids and residual colour. | UF membranes with backwash |
| 7. Reverse osmosis | Recovers clean permeate for dyeing, washing and boilers; concentrates the salt into a reject. | Two or three stage RO, sometimes high-pressure RO for the reject |
| 8. Evaporate and recover salt | The reject is evaporated. The brine can be reused in dyeing, or salt is crystallised for reuse or disposal. | MEE or MVR evaporator, non-thermal RCD vaporiser, crystalliser, centrifuge |
Colour removal options compared
| Method | Best for | Watch-outs |
|---|---|---|
| Coagulation and flocculation | Disperse, vat and sulphur dyes; first-stage colour cut | Poor on soluble reactive dyes; large sludge volume |
| Decolourising polymers | Reactive and acid dyes after coagulation | Dose must be jar-tested for each dye mix |
| Ozone | Final polishing of colour before discharge or RO | Power and ozone generator cost; COD falls only partly |
| Activated carbon | Low residual colour and COD | Carbon saturates quickly on strong effluent; spent carbon disposal |
| Fenton oxidation | Strong, mixed dye effluent with high COD | Works at low pH; produces iron sludge |
| Catalytic oxidation and selective adsorbents | Reactive and acid dyes that pass the biology; protecting RO | Confirmed in a laboratory trial on your effluent first |
Our NABL-accredited laboratory tests colour, pH, COD, BOD, TDS, chlorides, sulphates, metals and bio-assay toxicity, and jar tests show which colour removal chemistry works on your dye mix.
ZLD, reuse and salt recovery
Textile ZLD that pays some of its own way.
Zero liquid discharge (ZLD) for a dye house means recovering the water through RO and turning the salty reject into something that is not a liquid. Done well, it gives back three things you paid for: water, salt and sometimes heat.
Water
RO permeate is soft and low in salt, so it suits dyeing and washing well. Many ZLD dye houses recover most of their water this way and cut their fresh water or tanker bill accordingly.
Salt
Because reactive dyeing uses so much salt, the RO reject is mostly sodium chloride or sodium sulphate. Instead of evaporating it all to a mixed salt that piles up on site, the concentrated brine can be returned to the dye house, or the salt can be crystallised separately and reused. Our process design team designs fractional crystallisation that separates sodium sulphate and sodium chloride into reusable grades. This works best when the dye house standardises on one salt.
Evaporation without the steam bill
The evaporator is the costliest step in ZLD. Our non-thermal RCD vaporiser, developed with IIT Bombay, evaporates RO reject with air on rotating disks at about ₹80 to 160 per cubic metre, against an estimated ₹430 to 1,070 in a steam MEE. Hot dye bath drains and boiler or thermic fluid heater flue heat can warm the reject and raise its output.
Squeezing more water from the reject
Before evaporation, forward osmosis RO reject recovery, developed with ICT Mumbai, pulls further water from the reject at under 2 bar, shrinking the load on the evaporator.
Cost
How much does a textile ETP or ZLD cost?
For textiles, the cost depends on flow, the dye classes you use and how much salt goes into each batch. ZLD typically costs several times as much as the ETP alone. Use these ranges to budget.
| Plant | Typical scope | Indicative cost* |
|---|---|---|
| 50 to 100 KLD ETP | Small dye house or garment washer: equalisation, colour removal, biology, tertiary | ₹30 to 90 lakh |
| 500 KLD ETP | Medium processing house, with ozone or ACF polish | ₹1.5 to 3.5 crore |
| Add UF and RO, per 100 KLD | Water recovery for reuse in dyeing | ₹40 to 90 lakh |
| Full ZLD, 500 KLD | ETP, UF, RO, evaporator and crystalliser | ₹6 to 15 crore |
*Indicative 2026 ranges for equipment, electricals and installation, excluding land, civil works and taxes. Dye mix, salt load, evaporator type and the level of salt recovery change the figure a lot, so we price only after testing. Running costs are typically ₹25 to 60 per m³ for the ETP, ₹40 to 90 per m³ for UF and RO, and an estimated ₹430 to 1,070 per m³ evaporated in a steam MEE.
What drives capital cost
- Daily flow and how much it swings
- Salt load and dye classes used
- Discharge, partial reuse or full ZLD
- Evaporator type: MEE, MVR or non-thermal
- Salt recovery and crystallisation
What drives running cost
- Steam or power for evaporation
- Colour removal chemicals and sludge
- RO cleaning and membrane replacement
- Power for aeration and RO pumps
- Salt and sludge disposal
Where dye houses lose money
- Hot effluent sent straight to the biology
- Colour left for the RO to deal with
- Mixed salts that cannot be reused
- Evaporators sized on the whole reject
- Rinse water not reused before treatment
We test your reject, trial it on our non-thermal evaporator module and pilot it beside your MEE, so you see the saving on your own stream before you invest.
Troubleshooting
Common textile ETP problems, and how we fix them.
- 01The problem
The outlet is still coloured even when COD is within limits.
What we doJar-test your dye mix to pick the right decolourant, add ozone or catalytic oxidation as a polish, and check whether soluble reactive dyes are passing the clarifier.
- 02The problem
RO membranes foul and need cleaning every few days.
What we doRemove colour, silica and organics before the RO, add or repair UF, and supply antiscalants and cleaning chemicals tested on your feed.
- 03The problem
The MEE costs more to run than the rest of the plant put together.
What we doReuse brine in dyeing, recover more water from the reject, and move part of the evaporation to non-thermal RCD units.
- 04The problem
Mixed salt from the evaporator is piling up on site.
What we doStandardise on one dyeing salt where possible and design salt recovery so that the salt goes back into the process instead of storage.
- 05The problem
The aeration tank foams or the bacteria die after hot or high-pH drains.
What we doAdd cooling and enough equalisation, automate pH control and remove surfactants upstream.
- 06The problem
Chemical sludge volume is too high to handle.
What we doOptimise coagulant dose, switch to lower-sludge chemistry and improve dewatering with a filter press or screw press.
What we offer
What Rispri does for textile units.
Effluent testing and jar tests
Colour, COD, TDS, chlorides, sulphates, metals and bio-assay in our NABL-accredited lab.
Testing services →Textile ETP and ZLD
Equalisation, colour removal, biology, tertiary, UF, RO and evaporators, designed and built.
ZLD plants →Dye effluent treatment
Catalytic oxidation and selective adsorbents, developed with ICT Mumbai, for colour and COD.
Dye effluent technology →Non-thermal evaporator
RCD vaporisers that evaporate RO reject with air and waste heat instead of steam.
Non-thermal evaporators →RO reject and salt recovery
Forward osmosis on reject and fractional crystallisation of sodium sulphate and sodium chloride.
RO reject recovery →Treatment chemicals
Coagulants, decolourants, polymers, antiscalants and RO cleaners matched to your effluent.
Water treatment chemicals →Buying guide
What to ask before you buy a textile ETP or ZLD.
Use these questions with any supplier, including us.
- Was the design based on my effluent over a full dyeing cycle? Dark shades, light shades and washing days all differ.
- How is colour removed, and was it jar-tested on my dyes? Ask for the results, not a brochure.
- Which outlet values are guaranteed? Colour, COD and TDS in writing, against my consent.
- What is the RO recovery, and how often will it need cleaning? And who supplies the chemicals.
- What happens to the salt? Brine reuse, crystallisation or disposal, and the cost of each.
- What does evaporation cost per m³? Steam, power and maintenance, calculated for my reject.
- How is heat handled? Cooling before the biology, and whether that heat can be reused.
- Who runs it after commissioning? Training, O&M and monthly NABL test reports.
Why Rispri
From dye bath to reused water, one team.
Our own NABL lab
We test your effluent and run jar tests before design, and certify the outlet after start-up.
Engineering since 1999
1,498+ plants and turnkey projects for industry, hotels, hospitals and cities.
Institute research in the field
Dye effluent and RO reject technologies with ICT Mumbai, and non-thermal evaporators with IIT Bombay.
Chemicals and O&M in house
Decolourants, RO chemicals, spares and trained operators from one team.
Questions
Textile effluent treatment FAQs.
What is a textile effluent treatment plant?
A textile ETP treats wastewater from desizing, scouring, bleaching, dyeing, printing and finishing so that it meets the textile industry standards and the unit's consent, or can be reused. It usually combines cooling and equalisation, neutralisation, chemical colour removal, biological treatment and tertiary polishing.
How is colour removed from textile effluent?
Colour is removed in stages: coagulation and decolourising chemicals take out most of it, biology removes some more, and ozone, activated carbon or catalytic oxidation polish what is left. Soluble reactive dyes are the hardest, so the chemistry should be jar-tested on your own dye mix.
Why is TDS so high in dyeing wastewater?
Reactive dyeing of cotton uses large amounts of common salt or sodium sulphate, often 40 to 100 g/L in the dye bath, plus soda ash and caustic. Almost all of it ends up in the effluent, and biological treatment does not remove salt, so RO and evaporation are needed to bring TDS down.
What are the CPCB standards for textile effluent?
The textile industry standards under the Environment (Protection) Rules, 1986 include pH 6.5 to 8.5, BOD 30 mg/L, COD 250 mg/L, TSS 100 mg/L, oil and grease 10 mg/L, colour 150 Hazen units and a fish bio-assay, plus limits for chromium, sulphide and phenolics. Your SPCB consent may be stricter or may require ZLD.
Is ZLD mandatory for textile dyeing units?
It depends on your state and consent. Dyeing and bleaching units in Tamil Nadu must run ZLD following court orders on river pollution around Tiruppur, and several other boards set ZLD as a consent condition for dyeing clusters. Check your consent to operate.
How much does a textile ETP cost?
As an indication, a 50 to 100 KLD ETP for a small dye house costs about ₹30 to 90 lakh, and full ZLD for a 500 KLD processing house about ₹6 to 15 crore, excluding civil work and land. Salt load, dye classes and the evaporator chosen change the figure a lot, so we price after testing.
Can treated textile effluent be reused for dyeing?
Yes. RO permeate is low in salt and hardness and suits dyeing and washing well. Many ZLD units reuse most of their water this way, and some also reuse the concentrated brine as dyeing salt.
Can salt from textile ZLD be recovered and reused?
Yes, if the effluent is mostly one salt. Concentrated brine can go straight back to the dye baths, or sodium sulphate and sodium chloride can be crystallised separately to reusable grades. Mixed salts are harder to reuse, which is why we look at your dyeing recipes as well as the effluent.
Why do RO membranes foul so quickly in textile ZLD plants?
Residual dye, surfactants, silica, hardness and fine solids deposit on the membranes. Better colour removal and UF before the RO, correct antiscalant dosing and planned cleaning usually extend the cleaning interval considerably.
How can we reduce the cost of evaporating RO reject?
Recover more water from the reject first, reuse brine in dyeing, and evaporate the rest with lower-cost equipment. Our non-thermal RCD vaporiser costs about ₹80 to 160 per m³ against an estimated ₹430 to 1,070 in a steam MEE.
Why must textile effluent be cooled before treatment?
Dye bath drains can be 60 °C or more, and ETP bacteria work best below about 35 to 38 °C. Cooling in a heat exchanger or cooling tower, plus a large equalisation tank, protects the biology and the membranes downstream.
Can small dye houses join a CETP instead?
Where a common effluent treatment plant serves the cluster and the board allows it, small units can pre-treat their effluent and send it to the CETP. They must meet the CETP's inlet norms, which usually include pH, colour and suspended solids limits.
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