CPCB Effluent Discharge Standards for Petroleum Refineries — Explained

Petroleum refineries are among the most heavily regulated industrial categories under India's environmental framework. They are classified as Grossly Polluting Industries (GPI) and sit firmly in the Red Category of CPCB's industry classification — the highest environmental impact tier. This classification brings stringent effluent discharge limits, mandatory real-time monitoring, and direct CPCB oversight.

This guide explains the CPCB effluent discharge standards that apply to petroleum refineries in India, what each limit means in practice, the treatment technologies required to meet them, and the monitoring obligations that come with Red Category status.

About This CPCB Standard

Effluent discharge standards for petroleum refineries are prescribed under the Environment (Protection) Rules 1986, Schedule I, as notified by the Ministry of Environment, Forest and Climate Change (MoEFCC) through GSR (General Statutory Rules) notifications. CPCB administers these standards nationally, while State Pollution Control Boards (SPCBs) implement them through the Consent to Establish (CTE) and Consent to Operate (CTO) process.

All major Indian refineries — IOCL, BPCL, HPCL, Essar/Nayara, Reliance, MRPL, CPCL, and HMEL — operate under these standards. Limits apply to the final treated effluent at the point of discharge to a receiving water body or common treatment facility. They are not limits on individual process streams within the refinery.

The standards have been progressively tightened over successive GSR amendments. Refineries commissioned after a specified notification date are often subject to the same limits as existing plants, but CPCB periodically issues direction notices requiring existing refineries to meet updated standards within a compliance timeline.

Petroleum Refinery Wastewater — Complex Multi-Stream Challenge

Petroleum refinery wastewater is not a single stream — it is the combined result of five or more distinct process streams, each with a very different character. This complexity is why refinery ETP systems are among the most sophisticated in Indian industry.

The primary wastewater streams generated in a typical Indian refinery are:

• Desalter brine — Generated in the crude oil desalting unit, which washes salts from crude before distillation. This stream has extremely high TDS, contains dissolved oil, and carries heavy metals from the crude oil. It requires dedicated pre-treatment before joining the main ETP.
• Sour water — Condensate from atmospheric and vacuum distillation, FCC (fluid catalytic cracking), and hydrotreating units. Sour water contains very high concentrations of hydrogen sulphide (H₂S) and ammonia (NH₃) — both toxic to biological treatment systems if not removed first. A dedicated sour water stripper (steam stripping unit) is mandatory.
• Oily wastewater from tank farms and process units — Drainage from tank farms, spill collection, equipment washing, and process area runoff. This stream contains free oil, dispersed oil, and emulsified oil at varying concentrations depending on housekeeping standards and containment design.
• Cooling water blowdown — Blowdown from cooling towers contains corrosion inhibitors, biocides, and concentrated dissolved solids. While less contaminated than process streams, it contributes significant TDS load to the combined effluent.
• Storm water runoff — Contaminated storm water from process areas and tank farms is collected and treated. India's monsoon season creates significant peak flow during rain events — well-designed equalisation capacity is critical.

The standard treatment train for a petroleum refinery ETP follows three primary stages: gravity oil separation (API or CPI separator) as primary treatment, dissolved air flotation (DAF) as secondary treatment for emulsified oil, and biological treatment (activated sludge or MBBR) as the tertiary stage for BOD, COD, and phenol removal. Polishing by activated carbon or pressure sand filtration is common as a final step.

Petroleum Refinery Effluent Discharge Limits at a Glance

The following limits apply to the final treated effluent at the point of discharge from a petroleum refinery. These are the values your ETP must consistently achieve before discharge to any receiving water body.

The oil and grease limit of 10 mg/L and the phenol limit of 1.0 mg/L are the two parameters that most often drive ETP design decisions and compliance failures in Indian refineries. The COD limit of 250 mg/L, while less stringent than some other industries, requires effective biological treatment given the high organic load in refinery wastewater.

The temperature limit of 40°C applies at the point of discharge. Refineries that discharge process cooling water or hot condensate streams need to verify that combined effluent temperature does not exceed this value — particularly during summer months when ambient temperatures are already elevated.

Oil and Grease — API/CPI Separator Requirements

The 10 mg/L oil and grease limit is the defining technical challenge in petroleum refinery wastewater treatment. Untreated oily wastewater from a refinery may contain oil at concentrations of 500–5,000 mg/L or higher. Achieving a 10 mg/L discharge limit requires a staged treatment approach, because no single technology can handle the full range of oil states — free, dispersed, and emulsified.

Stage 1 — API Separator (Gravity Oil Separation)

An API (American Petroleum Institute) separator is the standard primary treatment unit for refinery oily wastewater. It is a large, open rectangular tank designed to allow free oil to float to the surface by gravity, while settleable solids fall to the bottom. Design parameters follow the API Manual on Disposal of Refinery Wastes — including minimum horizontal flow velocity, surface loading rate, and oil droplet rise velocity calculations.

A properly designed and maintained API separator reduces oil content from several thousand mg/L down to approximately 50–150 mg/L. It removes free oil effectively but cannot remove dispersed or emulsified oil — these require downstream treatment.

Stage 2 — CPI Separator (Corrugated Plate Interceptor)

A CPI separator uses inclined corrugated plates packed within a compact vessel to enhance gravity separation. Oil droplets coalesce on the plate surfaces, grow larger, and rise more rapidly to the surface. CPI separators are more efficient than API separators per unit of footprint, making them preferred where plot space is limited. They can typically reduce oil content to 20–50 mg/L, handling smaller dispersed oil droplets that an API separator would not capture.

Some refineries use a CPI separator as the primary unit instead of — or in series after — an API separator, depending on influent oil concentration and available land.

Stage 3 — DAF (Dissolved Air Flotation)

DAF removes emulsified oil that cannot be separated by gravity alone. In a DAF unit, pressurised water saturated with dissolved air is released into the flotation tank, creating millions of fine bubbles. These bubbles attach to emulsified oil droplets and suspended solids, floating them to the surface as a scum layer for skimming and removal. DAF with coagulant dosing (alum or ferric chloride) and sometimes a flocculant can reduce oil content to below 10 mg/L — approaching final discharge limits — and significantly reduce COD and TSS as well.

Reliable operation of the API/CPI separator and DAF is critical because downstream biological treatment is sensitive to oil loading. Breakthrough of oil from primary treatment upsets the biological stage and causes cascade compliance failures across multiple parameters simultaneously.

Phenol and Sulphide — Specialist Treatment Requirements

Phenol and sulphide are two parameters where petroleum refineries face the greatest technical challenge because both compounds originate from the refinery process itself — not from incidental contamination — and both are toxic to the biological treatment systems that are ultimately required to remove them.

Phenol

Phenolic compounds are generated in catalytic cracking (FCC) and thermal cracking units. Refinery wastewater typically contains phenol at concentrations of 10–200 mg/L before treatment. The CPCB discharge limit is 1.0 mg/L — a reduction of 90–99%.

Biological treatment is the primary mechanism for phenol removal. Activated sludge systems and MBBR (Moving Bed Biofilm Reactor) systems can degrade phenol effectively when the biomass is properly acclimated. The critical requirement is that phenol loading to the biological stage must be within the system's tolerance — sudden high-concentration slugs from process upsets can shock the biomass and cause breakthrough.

For refineries with variable or high phenol loads, solvent extraction (liquid-liquid extraction) may be used as a pre-treatment step to reduce phenol concentration before the biological stage. Activated carbon polishing as a final stage provides a safety margin for consistently achieving the 1.0 mg/L limit.

Sulphide

Hydrogen sulphide (H₂S) is generated in all hydrotreating and hydrocracking units, and in the FCC unit. It dissolves in process condensates as sour water — typically containing H₂S at 500–5,000 mg/L as sulphide. The CPCB discharge limit is 2.0 mg/L as S.

Direct treatment of sour water in the main ETP biological stage is not feasible at these concentrations — H₂S at elevated concentrations is toxic to aerobic biomass and will destroy the biological treatment system. The mandatory pre-treatment is a sour water stripper (steam stripping unit), where live steam strips H₂S and NH₃ from the sour water, reducing both to levels that the biological stage can tolerate. The stripped H₂S is typically routed to a sulphur recovery unit (SRU) or thermal oxidiser.

Stripped sour water — now with H₂S and NH₃ greatly reduced — joins the main oily wastewater stream for further treatment through DAF and biological stages. The residual sulphide is then addressed by aeration in the biological stage and, if necessary, by chemical oxidation using hydrogen peroxide or sodium hypochlorite dosing.

Desalter Brine — High TDS Stream Management

Desalter brine is among the most challenging streams in a petroleum refinery from a water management perspective. The crude oil desalting unit — which washes chloride salts from crude before it enters the atmospheric distillation column — produces a brine stream that typically contains:

• TDS of 10,000–80,000 mg/L — primarily as sodium chloride and other chloride salts from the crude oil.
• Dissolved and emulsified oil — the desalting process uses wash water that becomes contaminated with crude oil. Desalter brine can contain 500–5,000 mg/L of dissolved and emulsified oil.
• Heavy metals and naturally occurring radioactive material (NORM) — crude oils carry trace heavy metals and occasionally radionuclides that concentrate in the desalter brine. This requires periodic characterisation and careful disposal management.

CPCB does not set a specific TDS discharge limit for refinery effluent at the national level, but SPCBs in water-stressed states have imposed TDS limits through individual consent conditions. More significantly, the high TDS of desalter brine makes it incompatible with direct biological treatment — the osmotic stress at very high salt concentrations inhibits biological activity and can kill the biomass.

Management approaches for desalter brine include:

• Controlled blending — diluting desalter brine with lower-TDS streams before biological treatment, ensuring the salt concentration reaching the biological stage remains below inhibitory levels (typically below 8,000–10,000 mg/L TDS for conventional activated sludge).
• Separate pre-treatment — passing desalter brine through an API/CPI separator to remove oil before blending, reducing the combined oil load on the main ETP.
• Evaporation or deep-well injection — in refineries where TDS management is critical, high-TDS reject streams may be concentrated in evaporators or, subject to regulatory approval, disposed via deep-well injection. These options require SPCB authorisation.
• Brine recycling in the desalter — partial recirculation of stripped brine as wash water in the desalter can reduce the total volume of brine requiring external treatment.

The desalter brine stream is a critical design input for refinery ETP sizing. Refineries processing high-salt crude blends (common with certain Middle East grades) generate significantly more desalter brine per barrel than those processing sweet, low-salt crudes.

Monitoring, OCEMS and Testing Requirements

Petroleum refineries, as Red Category GPI industries, face the most demanding monitoring obligations under the CPCB environmental compliance framework. Monitoring requirements operate at three levels:

1. Online Continuous Effluent Monitoring Systems (OCEMS)

CPCB mandates installation of OCEMS at the final treated effluent discharge point for all petroleum refineries. OCEMS continuously measures and transmits key parameters — including pH, COD, TSS, and flow rate — to the CPCB and SPCB central data servers in real time. The OCEMS equipment must be:

• Procured from CPCB-approved vendors listed on the CPCB portal. Using non-approved equipment is a compliance violation regardless of measurement accuracy.
• Calibrated and maintained per CPCB-specified protocols, with calibration records maintained on-site for inspection.
• Connected to the CPCB Centralised Real-Time Water Quality Monitoring (CRWQM) system with data transmission intervals as specified in the OCEMS guidelines.

A non-functional OCEMS — even if the actual effluent quality is within limits — is treated by CPCB as a standalone compliance violation. Refineries have received show-cause notices and closure directions solely for OCEMS downtime exceeding permitted maintenance windows.

2. Periodic Sampling and Lab Testing

In addition to OCEMS, consent conditions typically require refineries to collect composite samples of their final treated effluent at specified frequencies (often daily or weekly for key parameters) and analyse them at a NABL-accredited laboratory. Results must be recorded in the monitoring register maintained under consent conditions and submitted to the SPCB in the half-yearly compliance statement.

Grab samples alone are not sufficient for consent compliance reporting — CPCB requires 24-hour flow-proportional composite samples for BOD, COD, and oil and grease measurements to capture the variability of refinery operations across shifts.

3. Mass Load Calculation

For larger refineries, CPCB and SPCBs increasingly focus on mass load limits rather than concentration limits alone. Mass load = concentration × flow rate. A refinery that achieves the concentration limits but operates at far higher flow rates than its consent specifies may still be in violation of total pollutant mass discharge. Flow metering at the ETP outlet is therefore as important as concentration monitoring.

Penalties and Enforcement

Petroleum refineries face multi-layered enforcement under India's environmental law framework. The combination of Red Category classification, GPI designation, and OCEMS obligations creates a high level of regulatory visibility — non-compliance at a refinery is difficult to conceal and is treated with correspondingly greater severity.

Environment Protection Act 1986 penalties — Under Section 15 of the EPA, violation of effluent discharge standards can result in imprisonment of up to five years, a fine of up to ₹1 lakh, or both, for each day of continued violation. For corporate entities, the officers in charge of the company at the time of the violation can be held personally liable.

Water (Prevention and Control of Pollution) Act 1974 penalties — Violation of consent conditions under the Water Act attracts penalties under Sections 43–44, including fines and imprisonment. The SPCB can also revoke the Consent to Operate, effectively requiring the refinery to cease discharge — and by extension, cease production.

National Green Tribunal (NGT) directions — The NGT has jurisdiction over environmental disputes and has directed refinery closures, environmental compensation payments, and remediation of polluted water bodies in cases of sustained non-compliance. NGT proceedings move faster than criminal proceedings and are actively used by both regulatory agencies and citizen groups.

Environment Damage Compensation (EDC) — CPCB has issued guidelines for levying environment damage compensation from industries that discharge beyond permitted limits. For GPI industries, EDC calculations are based on the quantity of pollutants discharged in excess of limits and the duration of violation. Compensation amounts for large refineries can be substantial — particularly if discharge affected a river or drinking water source.

OCEMS tampering — Any interference with OCEMS equipment — including deliberate sensor bypass, data manipulation, or unauthorised maintenance that causes extended downtime — is treated as a criminal offence under the EPA and has resulted in FIRs against refinery personnel in recent enforcement actions. CPCB has cross-verification mechanisms that compare OCEMS data against expected parameters for the reported production throughput, making anomalous readings detectable.

The most effective compliance strategy for petroleum refineries is maintaining ETP reliability margins above the discharge limits — targeting internal control limits of approximately 80% of the CPCB limits — so that normal operational variability does not create consent violations. Monitoring-only approaches, where the refinery only detects non-compliance after it has already occurred, are insufficient for maintaining consistent Red Category compliance.