The Headline Oil and Grease Limit in India: 10 mg/L, With Important Exceptions
The oil and grease discharge limit in India is set under Schedule VI of the Environment (Protection) Rules, 1986, notified as GSR 422(E), which sits under the Water (Prevention and Control of Pollution) Act, 1974. The headline number is 10 mg/L for effluents discharged into inland surface water and 20 mg/L for discharge on land. Refineries, petrochemical complexes, and selected process industries face a tighter 5 mg/L cap under the same schedule, and several State Pollution Control Boards enforce 5 mg/L for coastal, CRZ, and eco-sensitive discharges. The legal chain runs Water Act, 1974 → CPCB Schedule VI (General Standards for Discharge of Effluents) → SPCB consent order issued under Section 25/26 of the Act; the consent order is the document that binds a specific plant, not the schedule alone.
Two caveats matter before any engineer designs a treatment train around the 10 mg/L number. First, the 10 mg/L is a general standard — industry-specific schedules in Schedule VI override it for oil refineries (S.No. 41), petrochemicals, iron and steel, and a handful of other sectors. Second, "oil and grease" is a composite parameter measured by APHA 5520 and covers hydrocarbons, fats, vegetable oils, waxes, lubricants, cutting oils, and grease from food and metalworking sources. The number on the consent order is a single bucket that spans all of them.
Industry-Specific O&G Limits Under CPCB Schedule VI
Schedule VI of the Environment (Protection) Rules segments discharge limits by industry. For oil and grease, the binding row depends on whether the plant is classified as a refinery, petrochemical, integrated steel, or a general industrial unit. The table below consolidates the most relevant entries for plant engineers and EHS managers; cross-check the exact wording of your industry schedule before specifying equipment.
| Industry / Sector | CPCB Schedule VI Limit (Inland Surface Water) | Limit (On Land / Marine Outfall) | Notes |
|---|---|---|---|
| Oil refinery (Schedule VI, S.No. 41) | 5 mg/L | 10–20 mg/L (stream-dependent) | 5 mg/L applies to process wastewater; cooling/utility streams typically permitted at 10 mg/L |
| Petrochemicals | 5–10 mg/L | 10–20 mg/L | Tighter limit for surface water discharge; marine outfalls sometimes permitted at the higher end |
| Iron and Steel (integrated plants) | 10 mg/L | 20 mg/L | Roll mill and coke-oven condensate often drive influent O&G to 200–2,000 mg/L |
| Cement (captive power + process) | 10 mg/L | 20 mg/L | Wet scrubber condensate typically <5 mg/L O&G with bag-filter pre-separation |
| Sugar and distillery | 10 mg/L | 20 mg/L | Molasses-based distilleries face additional colour and BOD constraints; O&G rarely the binding parameter |
| Dairy and food processing | 10 mg/L general; 5 mg/L in MH/KA consent orders for large dairies | 20 mg/L | FOG (fats, oils, grease) from milk, butter, and edible-oil operations routinely hits 500–5,000 mg/L pre-treatment |
| Textile (wet processing) | 10 mg/L | 20 mg/L | O&G rarely the binding parameter; COD, BOD, colour, and TDS typically govern |
| Automobile ancillaries and metal finishing | 10 mg/L | 20 mg/L | Cutting oils and emulsions drive influent O&G to 1,000–10,000 mg/L before treatment; emulsion-breaking is the design bottleneck |
The pattern to notice: refineries and petrochemicals are the only sectors where 5 mg/L is the headline CPCB number. For most other industries, 10 mg/L inland is the starting point, and the tighter number comes from your state consent order, not the central schedule.
State Pollution Control Board Variations: When 5 mg/L Becomes the Real Number
The CPCB schedule is a floor. State Pollution Control Boards issue consent orders under Sections 25/26 of the Water Act, and those orders frequently set stricter O&G limits than the central schedule — particularly for discharges into rivers flagged as polluted, coastal zones under the CRZ Notification, and catchment areas around drinking-water reservoirs. The table below summarises the limits an Indian EHS manager is most likely to encounter in 2026.
| State / SPCB | Default Inland Limit | Stricter Conditions (5 mg/L Triggers) | Typical Affected Zones |
|---|---|---|---|
| Maharashtra (MPCB) | 10 mg/L | 5 mg/L for eco-sensitive river stretches | Yeola, Sinnar, Tarapur industrial estates near Godavari basin |
| Tamil Nadu (TNPCB) | 10 mg/L | 5 mg/L for coastal/CRZ discharges | Chennai, Cuddalore, SIPCOT Perundurai |
| Karnataka (KSPCB) | 10 mg/L | 5 mg/L for Bengaluru-region industrial areas | Bidadi, Peenya, discharge to Vrishabhavathi and Arkavathy rivers |
| Gujarat (GPCB) | 10 mg/L | 5 mg/L for common effluent conveyance pipeline discharges | Vapi, Ankleshwar, Sarigam |
| Haryana (HSPCB) | 10 mg/L | 5 mg/L in consent orders for large units | Gurgaon, Manesar, Faridabad industrial belts |
Engineers specifying new treatment plants in 2026 should treat the SPCB consent order as the binding design basis, not the CPCB schedule. In states like Maharashtra and Gujarat, a refinery or large dairy sited near a flagged river stretch will be held to 5 mg/L even though the central schedule nominally permits 10 mg/L for their industry classification. The cost of missing this distinction is a consent revocation or a stop-production notice, not a fine.
How to Hit the Limit: Removal Train from 5,000 mg/L Influent to <10 mg/L Outlet
Hitting 10 mg/L — let alone 5 mg/L — from an influent that runs 1,000–10,000 mg/L requires a staged train, not a single unit. The reference flow below is the configuration we see most often in Indian refineries, dairies, and metal-finishing plants, and it consistently delivers outlet O&G in the 5–10 mg/L band when chemical conditioning and residence times are kept inside the design window.
- Stage 1 — Source segregation and skimming. Isolate oily streams from sanitary and general process streams at the collection sump. Install oil-skimming weirs at machine sumps and a bar screen upstream of the equalisation tank. Removing free oil here protects downstream biological units from toxicity and slashes aeration demand.
- Stage 2 — API or CPI separator. Gravity separation in an API (American Petroleum Institute) or CPI (corrugated plate interceptor) separator drops outlet O&G to 60–150 mg/L. Only free oil — droplets larger than ~150 μm — is removed here; emulsified and dissolved fractions pass through. For a deeper look at the trade-offs, see the DAF vs API separator comparison.
- Stage 3 — Dissolved Air Flotation (DAF). Micro-bubble flotation with chemical conditioning is where the bulk of the removal happens. DAF reliably drops outlet O&G to 5–15 mg/L and achieves 80–95% removal on emulsified oils that the API separator cannot touch. Typical DAF operating parameters for an Indian industrial plant are summarised below.
- Stage 4 — Polishing (for 5 mg/L targets). A walnut shell filter, multimedia sand filter, or a membrane bioreactor (MBR) handles the residual emulsified and soluble fraction when consent orders demand 5 mg/L. Without polishing, even a well-run DAF will struggle to consistently stay under 5 mg/L on a refinery or large dairy stream.
| DAF Design / Operating Parameter | Typical Range | Source / Basis |
|---|---|---|
| Influent O&G | 100–1,000 mg/L (post-API) | Zhongsheng field data, 2025 |
| Outlet O&G | 5–15 mg/L (single-stage DAF) | Zhongsheng field data, 2025 |
| Removal efficiency | 80–95% on emulsified oils | Industry standard, 2024 |
| Hydraulic retention time | 20–40 minutes | DAF design manual, 2023 |
| Air-to-solids ratio | 0.005–0.060 (mass basis) | Zhongsheng ZSQ spec range |
| Coagulant (PAC) dose | 50–150 mg/L | Zhongsheng ZSQ spec range |
| Flocculant (anionic polymer) dose | 0.5–3 mg/L | Zhongsheng ZSQ spec range |
| Operating pH | 6.5–7.5 | Coagulation chemistry, APHA |
| Flow range per unit | 4–300 m³/h across 13 standard models | Zhongsheng ZSQ DAF product line |
The reference process flow is: collection sump → bar screen → oil skimmer → API/CPI separator → equalisation tank → DAF unit → clarified water → polishing filter → discharge. For plants with intermittent loads, an equalisation tank upstream of the DAF is non-negotiable; influent O&G swings of more than 3:1 will push DAF outlet above 15 mg/L even at correct chemistry. A packaged DAF system such as the Zhongsheng ZSQ dissolved air flotation system integrates the saturator, recycle pump, and float scraper into a single skid, which keeps installation time on tight Indian project schedules under two weeks for the 50 m³/h class.
Sampling, Testing, and Consent Conditions: What the SPCB Will Check
Most Indian plants that fail an O&G compliance test do not fail on concentration — they fail on sampling protocol. APHA 5520 B (partition-gravimetric) is the legal referee method cited in consent orders; APHA 5520 C (infrared) is widely used in refineries because it discriminates petroleum versus animal/vegetable oils; APHA 5520 D (hexane-extractable) is for low-level samples. The sampling point is the final outlet, after the last treatment unit and before any mixing with non-process streams such as cooling-tower blowdown or RO reject.
Frequency: most SPCB consent orders require monthly self-monitoring with quarterly or annual verification sampling by the SPCB's own laboratory or an NABL-accredited third party. O&G must be grab-sampled — composite sampling biases results low because lighter fractions separate and adhere to the container walls during the 24-hour collection window. Chain-of-custody records should be retained for 3–5 years, and plants covered under the OCEMS (Online Continuous Effluent Monitoring System) regime must upload flow-proportional data to the SPCB portal, increasingly including online oil and grease monitoring systems based on fluorescence or UV absorption.
2026 Outlook: Why the 10 mg/L Number Is Likely to Drop
CPCB has signalled in its 2024–25 draft revisions that O&G will move toward 5 mg/L for discharges into sensitive zones — river stretches flagged in the 2023 Comprehensive Environmental Pollution Index (CEPI) report, including parts of the Ganga, Yamuna, and Godavari basins. The OCEMS rollout is also expanding from gaseous parameters to liquid, with online oil-in-water sensors now being cross-checked against lab data; a deviation of more than 10% between online and grab-sample results triggers automatic SPCB flagging. For engineers specifying a new plant or expansion in 2026, the practical implication is to oversize the DAF air-to-solids ratio by 20–30% and budget for a polishing stage even if the current consent order is at 10 mg/L. Margin built today is cheap; retrofit in 2027 with a tightened consent order is not.
Frequently Asked Questions
What is the oil and grease limit for trade effluent in India? The general CPCB Schedule VI limit is 10 mg/L for discharge into inland surface water and 20 mg/L for discharge on land, with industry-specific overrides of 5 mg/L for refineries and petrochemicals.
Is the oil and grease limit 5 mg/L or 10 mg/L? It depends on your industry and your state: 5 mg/L for oil refineries and petrochemicals under Schedule VI, and 5 mg/L for many SPCBs (MPCB, TNPCB, GPCB) in eco-sensitive and CRZ discharges; 10 mg/L is the general inland surface-water number for most other industries.
Which SPCB enforces the strictest O&G limit in India? Maharashtra MPCB and Gujarat GPCB are the most likely to enforce 5 mg/L in consent orders for sensitive-zone and CETP discharges, though specific limits vary case by case.
Which treatment reliably achieves less than 10 mg/L O&G from industrial wastewater? A staged train of API or CPI separator followed by Dissolved Air Flotation (DAF) with chemical conditioning (PAC 50–150 mg/L, polymer 0.5–3 mg/L) typically delivers 5–15 mg/L; a polishing filter is required for consistent sub-5 mg/L compliance.
How is oil and grease measured legally in India? APHA 5520 B (partition-gravimetric) is the referee method cited in consent orders; APHA 5520 C (infrared) is widely used in refineries; samples must be grab-collected at the final outlet, not composited.
