INDUSTRIES / CHEMICALS
Wastewater treatment for the chemical industry
designed from a treatability study, not a guess.
Chemical plant effluent can be toxic to bacteria, full of salts, hard to break down or loaded with metals, and it changes with every batch. We run treatability studies in our NABL-accredited laboratory, then design the ETP, metal removal and ZLD stages your streams actually need.
In short
How chemical industry effluent is treated.
Chemical industry effluent is wastewater from reactions, product washing, scrubbers and utilities in chemical plants. It is hard to treat because it can be toxic to bacteria, contain refractory COD that biology cannot break down, carry high TDS, heavy metals and solvents, and swing to extreme pH. The right scheme starts with segregating strong streams at source and a treatability study, then combines neutralisation, chemical precipitation of metals, advanced oxidation (Fenton or ozone), solvent stripping, biological treatment with acclimatised bacteria and, where required, RO and evaporation for zero liquid discharge. ETP sludge from chemical plants is usually hazardous waste and goes to an authorised TSDF under the Hazardous and Other Wastes Rules, 2016.
- 0.3BOD/COD
- Below this ratio, effluent is generally hard to treat by biology alone
- 90%
- Fish survival after 96 hours in 100% effluent, the general-standard bio-assay test
- 0.1mg/L
- Limit for hexavalent chromium and for lead in discharge to inland surface water
- 17categories
- Highly polluting industries needing online monitoring, including dyes, pesticides and chlor-alkali
Where it comes from
Where does wastewater come from in a chemical plant?
A chemical plant rarely has one effluent. It has several streams of very different strength, and the worst mistake is to mix them all in one sump before anyone has measured them.
| Source | What happens | What it usually carries |
|---|---|---|
| Reaction mother liquor | The liquid left after the product is filtered or crystallised out | Very high COD and TDS, unreacted raw material, by-products, sometimes solvents and metal catalysts |
| Product and cake washing | Filter cakes and crystals are washed to purity | Moderate COD, dissolved salts, traces of product |
| Vessel and floor washing | Reactors and floors cleaned between batches | Variable COD, solids, product residues, detergents |
| Scrubbers | Gases such as HCl, SO₂, NH₃ or Cl₂ absorbed in water or caustic | Acid or alkaline salts, sulphite, ammonia, chloride |
| Solvent recovery | Distillation columns and condensers | Dissolved solvents, high COD, sometimes toxic organics |
| Utilities | Boiler and cooling tower blowdown, DM plant regeneration, RO reject | High TDS, hardness, treatment chemical residues; low organics |
| Domestic | Canteen and toilets | Easily biodegradable; useful for diluting and feeding the biology |
Typical effluent characteristics
| Parameter | Typical range | Why it matters |
|---|---|---|
| pH | 1 to 13, often within one day | Extreme pH kills bacteria and corrodes tanks; acid and alkaline streams must be neutralised under control. |
| COD | 2,000 to 50,000 mg/L; mother liquors can be far higher | Sets the size of every stage. Much of it may not be biodegradable. |
| BOD/COD ratio | 0.1 to 0.5 | The single most useful number for deciding whether biology will work (see below). |
| TDS | 5,000 to 1,00,000 mg/L or more in mother liquors | Above roughly 10,000 to 15,000 mg/L, ordinary biomass struggles; high TDS also decides the ZLD load. |
| Heavy metals | Traces to hundreds of mg/L of Cu, Zn, Ni, Cr, Pb and others | Toxic to bacteria and to the river; limits are fractions of a mg/L. |
| Solvents and toxic organics | Present in many batch units | Inhibit biology, cause odour and fire risk, and can often be recovered. |
| Colour | Strong in dye and intermediate units | Not removed by ordinary biology; needs oxidation, adsorption or membranes. |
| Ammoniacal nitrogen | Can be hundreds of mg/L | Limit is 50 mg/L for surface water; high ammonia needs stripping or nitrification. |
Characterisation
Why does chemical effluent need a treatability study?
A treatability study is a set of laboratory and bench-scale tests that shows which treatment steps work on your effluent, at what dose, and with what result, before any tank is built. For food or sewage, textbook values are often close enough. For chemicals they are not: two plants making the same product by different routes can produce effluents that need completely different plants.
The BOD/COD ratio, explained simply
COD measures all the oxidisable matter in the water. BOD measures only the part that bacteria can eat in a few days. Dividing one by the other tells you how biodegradable the effluent is:
- Above 0.5: readily biodegradable. Biological treatment will do most of the work.
- 0.3 to 0.5: biodegradable with acclimatised bacteria and a longer treatment time.
- Below 0.3: largely refractory or toxic. Biology alone will not meet limits; oxidation, stripping or evaporation is needed.
A low ratio can also mean the sample is killing the bacteria in the BOD bottle, which is itself a warning that the effluent is toxic.
Segregation comes first
Most chemical plants have one or two small, very strong streams (mother liquors, solvent-bearing or metal-bearing) and several large, weak ones. Treating the strong streams separately, by recovery, stripping, oxidation or direct evaporation, is almost always cheaper than diluting them into the whole flow.
Rules
Discharge standards for chemical industry effluent.
Unless an industry-specific standard applies, chemical units must meet the general standards in Schedule VI of the Environment (Protection) Rules, 1986, through the consent issued under the Water Act, 1974. For chemical plants, the metal and toxic-substance limits matter as much as BOD and COD.
| Parameter | Limit | Parameter | Limit |
|---|---|---|---|
| pH | 5.5 to 9.0 | Lead | 0.1 |
| BOD (3 days at 27 °C) | 30 | Mercury | 0.01 |
| COD | 250 | Cadmium | 2.0 |
| Total suspended solids | 100 | Hexavalent chromium | 0.1 |
| Oil and grease | 10 | Total chromium | 2.0 |
| Ammoniacal nitrogen (as N) | 50 | Copper | 3.0 |
| Phenolic compounds | 1.0 | Zinc | 5.0 |
| Sulphide (as S) | 2.0 | Nickel | 3.0 |
| Fluoride (as F) | 2.0 | Arsenic | 0.2 |
| Cyanide (as CN) | 0.2 | Selenium | 0.05 |
| Bio-assay | 90% fish survival after 96 h in 100% effluent | Manganese | 2.0 |
Treatment
The treatment scheme for chemical effluent.
There is no standard chemical ETP. This is the sequence we build from, choosing stages by what the treatability study shows.
Segregate and collect
Separate strong mother liquors, solvent-bearing, metal-bearing and weak streams into their own tanks, with flow and pH measured on each.
Pre-treat strong streams
Recover solvents by steam stripping, precipitate metals, or send small high-TDS streams straight to an evaporator instead of the ETP.
Equalise and neutralise
Mix the remaining streams to even out batch peaks, then correct pH in stages with lime, caustic or acid under automatic control.
Primary physico-chemical
Coagulation, flocculation and settling or DAF remove suspended solids, precipitated metals and part of the COD.
Advanced oxidation where needed
Fenton or ozone breaks refractory and toxic organics, removes colour and raises the BOD/COD ratio so biology can finish the job.
Biological treatment
Activated sludge or MBBR with biomass acclimatised to your effluent, often mixed with domestic sewage, removes the biodegradable COD and ammonia.
Tertiary, reuse and ZLD
Sand and activated carbon filters polish the outlet; UF and RO recover water, and the reject goes to an evaporator and dryer where ZLD applies.
Treatment options compared
| Process | What it removes | Best for | Watch-outs |
|---|---|---|---|
| Neutralisation | Extreme pH | Every chemical ETP | Lime makes sludge and gypsum scale; caustic adds TDS; dose in stages |
| Hydroxide or sulphide precipitation | Heavy metals | Copper, zinc, nickel, lead and chromium-bearing streams | Each metal has its own best pH; some re-dissolve at high pH; hexavalent chromium must first be reduced to trivalent; complexing agents block precipitation |
| Fenton oxidation | Refractory COD, colour, some toxic organics | Dye, intermediate and specialty chemical effluent | Works at about pH 3; hydrogen peroxide cost; produces iron sludge |
| Ozone or ozone with UV/H₂O₂ | Colour, refractory organics | Polishing and colour removal with little sludge | Higher power and capital cost; best on lower-COD streams |
| Steam or air stripping | Solvents, ammonia, volatile organics | Solvent-bearing and high-ammonia streams | Off-gas must be condensed or scrubbed; recovery can pay for itself |
| Biological (ASP, MBBR) with acclimatised biomass | Biodegradable COD, ammonia | Streams with BOD/COD above about 0.3 after pre-treatment | Toxic shocks and TDS swings can kill the biomass; needs steady feed |
| Activated carbon or resin adsorption | Trace organics, colour, specific compounds | Final polishing | Spent carbon is hazardous waste; regeneration cost |
| UF and RO | Dissolved salts, residual organics | Water recovery and ZLD | Fouling and scaling; reject needs evaporation |
| Evaporation (MEE, non-thermal) and drying | Everything; leaves salt | ZLD, small high-TDS streams | High energy cost with steam; salt is often hazardous waste unless recovered |
Our heavy metal recovery solution, developed with ICT Mumbai, uses selective, reusable polymer adsorbents to capture metals from acidic effluent, so less ends up as hazardous sludge.
Reuse and recovery
ZLD, salt and solvent recovery for chemical plants.
In a chemical plant, what leaves as waste was usually bought as a raw material. Recovery cuts both the treatment bill and the hazardous waste bill.
Zero liquid discharge
RO recovers most of the water for cooling towers and utilities, and an evaporator and dryer turn the reject into solid. Our ZLD plants and non-thermal evaporators, which evaporate with air instead of steam at about 80% lower cost per cubic metre than MEE, make ZLD affordable for mid-size units.
Salt recovery
Mixed evaporator salt is usually sent to a TSDF at a cost. With stream segregation and controlled crystallisation, salts such as sodium chloride or sodium sulphate can sometimes be recovered pure enough to reuse or sell. See process design and salt recovery.
Solvents and metals
Stripping and distillation return solvents to the process; metal recovery turns sludge into a saleable product. See heavy metal recovery and RO reject management.
Cost
How much does a chemical industry ETP cost?
Chemical ETPs cost more per KLD than almost any other sector, because they need more stages, corrosion-resistant materials and more chemicals. The ranges below are for budgeting only.
| Capacity | Typical scheme | Indicative plant cost* |
|---|---|---|
| 10 to 25 KLD | Neutralisation, precipitation, settling, filters; often linked to a CETP | ₹10 to 30 lakh |
| 50 KLD | Physico-chemical plus biological, with Fenton or carbon polishing | ₹30 to 80 lakh |
| 100 KLD | Full physico-chemical, advanced oxidation and biological | ₹60 lakh to 1.5 crore |
| ZLD add-on | UF/RO, evaporator and dryer on top of the ETP | Priced after a water and salt balance |
*Indicative 2026 ranges for equipment, electricals and installation, excluding land, civil works, taxes and the ZLD stage. Corrosive, solvent-bearing or high-TDS effluent costs more. We give a firm price after a treatability study and site visit.
What drives capital cost
- Number of segregated streams
- Materials: FRP, rubber-lined or stainless steel
- Advanced oxidation or stripping stages
- ZLD and evaporation capacity
- Automation and OCEMS
What drives running cost
- Neutralisation and precipitation chemicals
- Hydrogen peroxide and iron for Fenton
- Steam or power for evaporation
- Hazardous sludge and salt disposal at a TSDF
- Membrane cleaning and replacement
Where savings come from
- Segregating strong streams at source
- Recovering solvents and metals
- Lower-energy evaporation
- Less sludge through correct dosing
- Reusing RO permeate in utilities
Troubleshooting
Common problems in chemical plant ETPs, and how we fix them.
- 01The problem
Outlet COD stays above 250 mg/L however long the water is aerated.
What we doMeasure the BOD/COD ratio at each stage. If the remaining COD is refractory, add Fenton, ozone or carbon polishing, or move the strong stream out of the ETP.
- 02The problem
The biomass dies after certain batches.
What we doTrace the toxic batch, divert it to a holding tank for pre-treatment, and re-acclimatise the biomass with controlled loading.
- 03The problem
Metals pass the outlet limit even after dosing lime.
What we doJar-test the right pH for each metal, break complexes, reduce hexavalent chromium first, and add sulphide precipitation or polishing where needed.
- 04The problem
TDS keeps rising and RO membranes scale and foul.
What we doImprove pre-treatment, use the right antiscalant and cleaning chemicals, and send the reject to an evaporator sized for the real salt load.
- 05The problem
Hazardous sludge and salt disposal costs keep growing.
What we doOptimise chemical doses to cut sludge, dewater better, and look at metal and salt recovery so less goes to the TSDF.
- 06The problem
Odour and solvent smell around the ETP.
What we doStrip and recover solvents before the ETP, cover strong-stream tanks and treat vent gases in a scrubber.
What we offer
What Rispri does for chemical plants.
Treatability studies and testing
NABL-accredited effluent, metals, sludge and air emission tests.
Testing →Process design and salt recovery
Water and salt balances, recovery and clearances.
Process design →ETP and RO chemicals
Coagulants, polymers, antiscalants and cleaners tested on your effluent.
Chemicals →Buying guide
What to ask before buying a chemical industry ETP.
Use this list with any supplier, including us.
- Was a treatability study done on my actual streams? With jar tests and biodegradability results, not only a COD figure.
- Which streams are segregated, and why? Ask for the stream-wise water and load balance.
- What materials of construction are used? Tanks, pipes and pumps must resist your pH, chloride and solvents.
- How much hazardous sludge and salt will the plant make? In tonnes per month, with the TSDF cost.
- Which outlet values are guaranteed? Including metals and bio-assay if your consent lists them.
- What is the running cost per cubic metre? Chemicals, power, steam and disposal shown separately.
- Is the plant ready for OCEMS and ZLD if the board asks? Space and design margin matter.
- Who tests the outlet? A NABL-accredited report carries weight with the board.
Why Rispri
From the lab bench to a running plant.
Our own NABL lab
Treatability studies, metals and compliance testing in house, so design and testing do not drift apart.
Engineering since 1999
1,498+ plants and turnkey projects for industries, hotels, hospitals and cities.
Research partnerships
Work with IIT Bombay and ICT Mumbai on ZLD evaporation, RO reject recovery, dye effluent and heavy metal recovery.
Chemicals, spares and O&M
Treatment chemicals from our own catalogue and operators who keep the plant compliant.
Questions
Chemical industry effluent FAQs.
What is chemical industry effluent treatment?
It is the treatment of wastewater from chemical manufacturing so that it meets the limits in the plant's consent or can be reused. Because chemical effluent can be toxic, salty and hard to degrade, it usually combines segregation, neutralisation, metal precipitation, advanced oxidation, biological treatment and, where required, RO and evaporation.
Why is chemical effluent harder to treat than other wastewater?
It often contains substances that kill or slow down bacteria, organic compounds that biology cannot break down, high dissolved salts, heavy metals, solvents and extreme pH. It also changes from batch to batch, so a plant designed for an average sample may fail on the worst batch.
What is a treatability study?
A treatability study is a series of laboratory tests on your actual effluent that shows which treatment steps work, at what chemical dose, and what outlet quality to expect. For chemical plants it is the most reliable way to avoid building an ETP that cannot meet its limits.
What does the BOD/COD ratio tell me?
It shows how biodegradable your effluent is. Above about 0.5 biology works well; between 0.3 and 0.5 it works with acclimatised bacteria; below 0.3 the effluent is mostly refractory or toxic and needs oxidation, stripping or evaporation as well.
How are heavy metals removed from chemical wastewater?
Most commonly by raising the pH so metals precipitate as hydroxides, then settling and filtering the sludge; sulphide precipitation reaches lower levels. Hexavalent chromium must first be reduced to trivalent chromium. Ion exchange or recovery processes can polish the outlet or recover the metal.
What is Fenton treatment?
Fenton treatment uses hydrogen peroxide with an iron catalyst at around pH 3 to produce hydroxyl radicals that break down refractory organics and colour. It is widely used for dye, intermediate and specialty chemical effluent, often before biological treatment.
What are the discharge limits for chemical industry effluent?
Under the general standards for inland surface water, limits include pH 5.5 to 9.0, BOD 30 mg/L, COD 250 mg/L, TSS 100 mg/L, lead 0.1 mg/L, hexavalent chromium 0.1 mg/L and mercury 0.01 mg/L, plus a fish bio-assay. Some sectors such as dyes, pesticides and chlor-alkali have their own standards, and your consent may be stricter.
Is ETP sludge from a chemical plant hazardous waste?
In most cases yes. Under the Hazardous and Other Wastes Rules, 2016, it must be stored safely, transported with a manifest and disposed of at an authorised TSDF, and the plant needs SPCB authorisation and must file an annual return. Testing the sludge helps confirm its category and disposal route.
Is zero liquid discharge mandatory for chemical industries?
Not everywhere, but many boards require ZLD for chemical, dye and pesticide units, especially in water-stressed or polluted areas and in some industrial clusters. Your consent to operate states whether it applies.
Can a small chemical unit use a CETP instead of its own ETP?
Yes, where a CETP serves the estate and the board allows it. The unit must still pre-treat its effluent to meet the CETP's inlet limits, which usually means neutralisation, metal removal and sometimes segregation of strong streams.
How much does a chemical industry ETP cost?
As an indication, about ₹30 to 80 lakh for a 50 KLD plant with physico-chemical and biological stages, and ₹60 lakh to 1.5 crore at 100 KLD, excluding civil works, land, taxes and any ZLD stage. The real cost depends on how many streams need separate treatment, which a treatability study tells us.
Do you offer OCEMS for chemical plants?
Yes. We supply and install online analysers, data loggers and CPCB connectivity for units that must stream outlet data, and our lab provides the manual tests used to check the analysers.
Related