Textile Wastewater in Pakistan: Colour, Salts and Organic Pollution

A dyeing unit near Lahore sends a dark-blue batch to its equalization tank. An hour later, the incoming water is pale, hot and alkaline. The final outlet may eventually look clear, yet its COD or dissolved salts can still be high. Which part of the problem should the ETP remove, and which treatment step is actually responsible?

This is the central difficulty of textile wastewater: colour, organic pollution, suspended material and dissolved salts are different problems. They can occur together, but they do not respond to one universal machine or chemical. A biological reactor can reduce biodegradable organics without desalinating the water. Coagulation can remove selected colour and fine particles without guaranteeing low COD. Reverse osmosis can reject dissolved salts only after suitable pretreatment, while creating a concentrated reject stream that still needs a destination.

For textile factories around Lahore, Sheikhupura, Raiwind, Kasur and Faisalabad, the practical starting point is not a standard equipment list. It is a map of production batches, drains, flows and pollutant loads. This guide explains how to build that picture and how to turn it into a defensible ETP treatment basis.

Where does textile wastewater come from?

A garment stitching floor may generate mostly domestic sewage and cleaning water. A wet-processing factory is different. Desizing, scouring, bleaching, mercerizing, dyeing, printing, soaping, washing and finishing can each produce a wastewater stream with a different chemistry.

The actual mixture depends on the fibre, dye class, recipe, shade, batch size, washing sequence, water quality, machine, chemical recovery and production plan. Cotton reactive dyeing does not create the same effluent as polyester disperse dyeing. Printing wash water may arrive as a short concentrated batch, while rinses may produce a larger, more dilute volume.

That is why a single grab sample from a final drain cannot explain every source. Pakistan’s National Textile University has treated textile wastewater flows and pollution loads as a dedicated industry training topic. The useful engineering lesson is to connect laboratory results with the operation that generated the water.

The main textile wastewater problems are not interchangeable

The last row must not be generalized. Not every dye or textile process contains the same metals or hazardous constituents. Use chemical inventories, safety data sheets and process-specific testing rather than assuming a pollutant exists because the site is a textile factory.

Why can a small amount of dye create a strong colour?

Dyes are designed to interact with light, so visible colour can remain even when the dye concentration is small compared with the total mass of dissolved material. A final outlet can therefore have modest suspended solids and still look strongly coloured. Conversely, removing visible colour does not prove that COD, salt or toxicity has been controlled.

Colour may be associated with suspended particles, colloids or truly dissolved molecules. This distinction changes the treatment approach. Screening or clarification may remove fibres and settleable solids. Coagulation and flocculation may destabilize selected colloidal and dissolved colour, but performance depends on dye chemistry, pH, coagulant, dose, mixing and separation. Adsorption, oxidation or membrane treatment may be considered for colour that remains after the main process, but each creates its own operating requirements and residuals.

Do not judge colour only from a photograph or a jar held against a wall. Record the test method, dilution, filtration basis and unit. True colour measured after removing turbidity is not the same as apparent colour in an unfiltered sample. Use the same method when comparing inlet, intermediate and final results.

COD and BOD describe organic loading, not colour alone

COD is the oxygen equivalent of material oxidized by the specified chemical test. BOD measures oxygen used biologically under the stated incubation conditions. A coloured molecule can contribute COD, but colour intensity cannot be converted into COD by sight. A colourless surfactant, size or reducing chemical can also create a large COD load.

Paired BOD and COD results can help investigate biodegradability, but no single ratio selects a complete process. The ratio can change between desizing, dyeing, soaping and wash batches. High salinity, extreme pH, temperature or inhibitory chemicals can also limit a biological reactor even when some organic material is biodegradable.

Aquenvia’s BOD, COD and TSS guide explains sampling records, concentration reduction and mass-load calculations. For a textile ETP, add colour, conductivity, TDS, pH, temperature and process-specific parameters to that basic report.

Why salts are a separate treatment problem

Selected textile dyeing processes use sodium chloride, sodium sulphate, alkali and other soluble chemicals. Once dissolved, their ions pass through ordinary screens and do not settle in a clarifier. Conventional biological treatment can transform biodegradable organic matter, but it does not function as a desalination process.

This has two important consequences. First, clear biological effluent may still have high conductivity or TDS. Second, adding reverse osmosis at the end does not make the salt disappear. RO divides the feed into a lower-salt permeate and a higher-salt concentrate. Recovery, scaling, cleaning, membrane life, energy and the final reject route belong in the design.

The broad scientific review published by Water Science and Technology describes textile wastewater as a variable mixture that can include dyes, dissolved solids and organic pollutants. It is useful technical context, but a Pakistan project must still be based on its own sampling and applicable provincial requirements.

What has local research measured in Faisalabad?

Local research gives useful evidence without creating a universal design number. A 2025 study sampled two textile-industry outlets in Faisalabad during August 2023. It reported pH values of 9.7 and 6.36, TDS of 7,920 and 4,350 mg/L, COD of 1,110 and 509 mg/L, and colour of about 231 and 45 colour units for the two outlets. The published Faisalabad study provides the sampling and analytical details.

Those are measurements from two identified study streams at a stated time. They are not typical values for every textile unit in Faisalabad, Lahore or Pakistan, and they are not a design range. Their real value is the contrast: even two textile outlets in one city can have materially different pH, salt, COD and colour.

A separate 2024 original study evaluated textile-industry effluents in Faisalabad, while a 2025 research project used two-hourly samples combined into a composite from a textile factory in Khurrianwala. The Khurrianwala study describes that composite-sampling method. These studies support careful characterization, not the copying of one paper’s influent values into a commercial quotation.

Hypothetical example: concentration becomes a daily load

This worked example is hypothetical. Assume a dyeing and finishing facility discharges 500 m³/day. A representative composite sample and matched flow record give:

• COD: 1,600 mg/L
• BOD₅: 640 mg/L
• TDS: 6,000 mg/L

Load (kg/day) = flow (m³/day) × concentration (mg/L) ÷ 1,000.

COD load = 500 × 1,600 ÷ 1,000 = 800 kg COD/day.

BOD₅ load = 500 × 640 ÷ 1,000 = 320 kg BOD₅/day.

Dissolved-solids load = 500 × 6,000 ÷ 1,000 = 3,000 kg/day.

The BOD₅/COD ratio is 640 ÷ 1,600 = 0.40. That may justify further biological treatability work, but it does not prove that 40% of COD will be removed or that the wastewater is safe for a biological reactor.

If the complete COD treatment train achieves an 85% reduction under the defined test condition, outlet COD would be 240 mg/L and the remaining COD load would be 120 kg/day. That says nothing about TDS removal. The engineer must calculate salt separately and compare the outlet against the actual discharge or reuse objective.

Colour units are not kilograms of dye. Do not apply the mass-load equation to a colour-unit result as if it were mg/L of a known chemical.

Hypothetical example: a small stream can carry most of the salt

Use the same 500 m³/day and 3,000 kg/day dissolved-solids load. Now assume production mapping finds a concentrated 50 m³/day stream at 40,000 mg/L TDS. That stream contains:

50 × 40,000 ÷ 1,000 = 2,000 kg/day of dissolved solids.

The remaining 450 m³/day carries 1,000 kg/day, equivalent to about 2,222 mg/L. In this teaching example, 10% of the water carries two-thirds of the salt load.

This does not automatically justify a recovery technology. It shows why drain mapping matters. Preventing, reusing or separately managing a concentrated batch may change the size and feasibility of downstream desalination. If every stream is mixed first, that opportunity can disappear.

A practical textile ETP treatment train

No single train fits every factory. The following sequence shows the purpose of common stages and the limits that must remain visible.

Equalization comes before equipment comparison

A textile ETP can receive a short high-pH dye bath, a hot wash, a low-strength rinse and a cleaning discharge in one shift. Designing only from daily average flow hides the hourly hydraulic and pollution peaks. An equalization tank needs a working volume based on the real batch schedule, controlled withdrawal, suitable mixing, level instruments, overflow protection and a plan for shutdowns.

Equalization should reduce variability, not create uncontrolled reactions. Check whether incompatible streams can release heat, gas or precipitates when mixed. If fibres or solids can settle, the mixing duty and cleaning access matter. If cooling is needed before biology, include heat load and summer conditions rather than relying on an arbitrary detention time.

Where do chemical and biological treatment fit?

Jar tests can identify whether pH adjustment, coagulant and polymer can remove a selected fraction of colour, turbidity and COD. The separation step might be clarification or dissolved-air flotation depending on the floc and solids behaviour. A DAF system is not automatically the correct choice for every coloured stream. Test chemical conditions, recycle duty, peak flow, sludge production and downstream compatibility as a package.

Biological treatment then targets biodegradable organics. Activated sludge, MBBR, SBR and other processes are reactor configurations, not guarantees. Their design still needs organic load, biodegradability, nutrients, salinity, temperature, dissolved oxygen, pH, inhibition and sludge-separation data. If attached growth is considered, the MBBR media guide explains why carrier area, protected area, fill percentage, retention screens and movement must be defined together.

Aeration must follow oxygen demand and tank conditions. Counting diffusers or copying blower motor power from another ETP is not a design method. The fine-bubble diffuser guide connects biological demand with wastewater correction factors, depth, grid pressure and operating range.

When does reverse osmosis belong in a textile project?

RO may support a defined reuse objective where dissolved salts must be reduced and the upstream water is suitable. It should not be added merely because an outlet has high TDS. Start with the water balance: required permeate quality and volume, feed variability, pretreatment, recovery range, concentrate volume, cleaning waste and final destinations.

For example, 400 m³/day of RO feed at 75% recovery would produce a nominal 300 m³/day of permeate and 100 m³/day of concentrate before accounting for cleaning and other losses. The rejected mass is concentrated into the smaller stream. If no acceptable concentrate route exists, the proposed recovery is incomplete on paper.

Aquenvia’s industrial RO guide lists the source-water tests and package boundaries needed before a quotation. A zero-liquid-discharge claim requires an entire concentration, evaporation, solids and operating plan. An RO skid by itself is not zero liquid discharge.

Sludge belongs in the original design

Chemical colour removal transfers material into sludge. Biological treatment creates waste biomass. Screens collect fibres. Membranes create backwash, cleaning waste or concentrate. An ETP quote that ends at clear water but ignores these residuals is incomplete.

Estimate sludge from treatability testing and mass balance, then define storage, conditioning, dewatering, filtrate return, cake handling and the approved destination. A filter press, screw press or drying bed must be selected from the actual sludge and operating window, not only the wastewater flow. Chemical sludge and biological sludge can dewater differently.

What should a textile factory test before requesting an ETP quotation?

Build a sampling plan around production, not convenience. For each important stream and the combined outlet, record:

• Hourly flow or batch volume, duration and discharge time.
• Product, shade, fibre, machine and recipe family during sampling.
• pH, temperature, conductivity, TDS, COD, BOD₅, TSS and colour on a stated method.
• Alkalinity or acidity and nutrients where biological treatment is being considered.
• Sulphate, chloride, oil and grease, metals or other specific parameters where process chemicals justify them.
• Existing chemical doses, utility use, sludge, overflows and bypasses.
• Water-quality and flow targets for the intended discharge or reuse route.

Use composites for variable continuous flows where the parameter and study purpose allow them. Use targeted grabs for short batch releases and rapidly changing characteristics. Agree preservation, containers, holding time and method with the laboratory before collecting samples.

What should a complete textile ETP quotation include?

A useful quotation should state its design envelope and exclusions. For a factory near Lahore or in an industrial area such as Sheikhupura, Raiwind or Kasur, compare bidders against the same information:

• Average, peak-hour and batch flows, with future production stated separately.
• Influent concentrations and daily loads for each design parameter.
• Required outlet and reuse targets, with the applicable sampling basis.
• Process description, tank working volumes and hydraulic profile.
• Chemical products, tested dose range, storage, mixing and daily consumption basis.
• Blowers, pumps, mixers, instruments, controls, standby philosophy and power basis.
• Sludge quantity, dewatering scope, filtrate return and cake destination assumptions.
• RO reject, backwash and cleaning-waste routes where membranes are proposed.
• Civil works, interconnecting piping, installation, commissioning, training and laboratory testing.
• Performance-test duration, production conditions, sampling points and acceptance criteria.

Prices cannot be compared fairly when one supplier includes civil tanks, sludge handling and instruments while another lists only process equipment. Aquenvia’s industrial effluent treatment service can help organize a common design basis before proposals are evaluated.

Which environmental requirements apply in Punjab?

For a textile facility in Lahore, Sheikhupura, Kasur or Faisalabad, start with the official Punjab Environmental Quality Standards page, which lists standards for municipal and liquid industrial effluents. Confirm the current notification, discharge route, parameter table, footnotes, sampling conditions and project-specific environmental approvals with the responsible authority and adviser.

Do not assume that Punjab requirements apply unchanged in Sindh, Khyber Pakhtunkhwa, Balochistan or another jurisdiction. Do not use a buyer’s private wastewater guideline as a substitute for provincial law. Export-customer requirements and environmental approvals may both apply, but they are different obligations.

Daily operating records that make an ETP understandable

An ETP cannot be evaluated from an occasional outlet sample alone. Keep production and plant records on the same timeline:

• Inlet, equalization discharge and final flow totals.
• Batch releases, shade changes and unusual cleaning events.
• pH, temperature, conductivity, dissolved oxygen and other control readings.
• Chemical preparation, dose and stock use.
• Blower, pump and mixer run hours, trips and maintenance.
• Sludge wasting, dewatering cycles, cake quantity and removal.
• Laboratory samples with matching production and operating conditions.

These records turn a complaint such as “the colour is back” into a traceable event. They also show whether a problem came from production, an overloaded stage, chemical preparation, biology, solids separation or an unrecorded bypass.

Common questions

Can biological treatment remove textile colour?

It may reduce colour from compounds that the selected microbial system can transform or adsorb, but performance is dye-specific and should be tested. Biology should not be assumed to remove every colour body.

Does clear textile effluent have low TDS?

No. Dissolved salts can remain invisible. Measure conductivity and TDS on the stated method instead of judging salinity by appearance.

Will coagulation remove all COD?

No. Coagulation can remove the fraction associated with destabilized colour, colloids and particles under tested conditions. Dissolved organics can remain and may need biological or advanced treatment.

Can an MBBR handle salty textile wastewater?

Salinity tolerance depends on concentration, variability, acclimation, temperature, organics and the microbial community. Use representative wastewater and treatability evidence. Adding more carrier does not correct an inhibitory feed or insufficient oxygen.

Is RO always required for a textile ETP?

No. RO belongs where a defined reuse or dissolved-salt objective justifies it and where pretreatment and concentrate management are feasible. A discharge-only project may have a different treatment basis.

What should an owner do first?

Map every wet-process drain and batch for at least a representative production period, then pair flow measurements with laboratory samples and the chemical inventory. If you need help structuring that assessment, contact Aquenvia with the production schedule, water balance and available reports.

Sources checked 19 September 2026. Local research measurements are reported with their place and sampling context and are not presented as universal Pakistan design values. All worked calculations are hypothetical. Proposed image brief: an original educational process graphic showing separate textile streams for dye bath, wash water and concentrated salt entering source control, equalization, chemical treatment, biological treatment and optional reuse membranes, with sludge and membrane concentrate leaving as separate residuals. Proposed alt text: “Textile wastewater treatment diagram separating colour, organic pollution, suspended solids and dissolved salts.” No unmade image is claimed in the page metadata.