ETP for Oil & Gas Industry
ETP systems for upstream oil & gas operations, refineries, petrochemical complexes, and LNG terminals — API/CPI separation, emulsified oil removal, phenol treatment, H₂S stripping, and biological polishing to CPCB Red Category standards
Industry Overview
ETP for Oil & Gas Industry
Oil & gas operations generate some of the most technically challenging industrial wastewater in India. Upstream operations — crude oil production, gas gathering, and drilling — produce formation water, produced water, and drilling mud wastewater characterised by very high oil content (100–5,000 mg/L), dissolved H₂S, ammonia, and naturally occurring radioactive materials (NORM). Refineries add a second layer of complexity: process water from crude distillation, desalter effluent with high emulsified oil and chlorides, spent caustic from LPG sweetening, phenol-bearing streams from catalytic cracking and hydrocracking units, and cooling tower blowdown with corrosion inhibitors and biocides. LNG terminals and gas processing plants contribute glycol-contaminated condensate water and amine-bearing wastewater from acid gas removal. All segments are classified CPCB Red Category, mandating rigorous treatment to achieve BOD ≤30 mg/L, COD ≤250 mg/L, Oil & Grease ≤10 mg/L, Phenols ≤1 mg/L, and Sulphides ≤2 mg/L before any surface water discharge.
The raw effluent characteristics across oil & gas sub-sectors are severe: BOD ranges from 200 to 1,000 mg/L, COD from 500 to 3,000 mg/L depending on the stream mix, free and emulsified oil up to 5,000 mg/L from produced water and tank cleaning operations, phenol concentrations of 10–200 mg/L from FCC and hydrocracker units, dissolved H₂S causing corrosion, odour, and inhibition of biological treatment, and ammonia from amine regeneration and sour water stripping. The COD/BOD ratio is often high (>3.5) due to recalcitrant aromatic hydrocarbons and phenolic compounds, meaning simple biological treatment alone is insufficient — physical-chemical pre-treatment to remove free oil, emulsified oil, H₂S, and phenols is mandatory before biological polishing in MBBR or activated sludge systems. Activated carbon polishing as a tertiary step is increasingly required where the regulatory standard is strict or reuse is intended.
Spans Envirotech designs integrated oil & gas ETP systems combining API/CPI oil-water separation, DAF for emulsified oil, air stripping for H₂S and ammonia, biological MBBR for residual BOD/COD removal, and activated carbon polishing as a final treatment barrier. Our process designs account for the specific effluent matrix of each sub-sector — upstream produced water, refinery integrated effluent, LNG condensate water — and incorporate OCEMS-ready instrumentation for CPCB Red Category compliance. Where clients require ZLD or water reuse for cooling or boiler feed, we integrate RO and MEE/MVR as tertiary and quaternary treatment stages.
Industry Challenges
Key Environmental Challenges
Emulsified Oil Removal from Produced Water and Desalter Effluent
Free oil above 150 µm diameter separates readily in API/CPI separators, but the emulsified fraction (10–150 µm) stabilised by natural surfactants, asphaltenes, and resins from the crude requires DAF with chemical demulsification. Desalter effluent from crude oil pre-treatment carries emulsified oil at 200–800 mg/L with high chloride content that affects coagulant performance. Under-treating emulsified oil at the primary stage overloads biological systems with oil that coat biological media — identical to EPS fouling in dairy ETPs — causing progressive performance decline.
Phenol Treatment from Refinery Cracking Units
Catalytic cracking (FCC) and hydrocracking units produce phenol-bearing wastewater at 50–200 mg/L, well above the CPCB limit of 1 mg/L. Phenol is inhibitory to biological organisms at concentrations above 100 mg/L, preventing direct biological treatment without pre-dilution or acclimatisation. Biological phenol degradation requires a specifically acclimatised biofilm culture and stable operating conditions — shock loads from refinery unit upsets can wash out the phenol-degrading population in 24–48 hours, requiring weeks of re-acclimatisation.
H₂S Stripping and Corrosion Control
Dissolved H₂S from sour crude processing and produced water causes severe corrosion in concrete and steel ETP structures, generates odour nuisance at concentrations as low as 0.5 ppm, and is toxic to biological organisms above 200 mg/L as sulphide. H₂S must be stripped or oxidised to sulphate before the effluent enters the biological stage. Air stripping in a packed column or surface aerator is effective but generates H₂S gas that must be collected and treated with a caustic scrubber or biofilter before atmospheric release.
Ammonia Loading from Sour Water and Amine Regeneration
Sour water strippers at refineries remove H₂S and NH₃ from process condensate, but residual ammonia in the stripped sour water (100–500 mg/L NH₃-N) must be treated in the ETP to meet the 50 mg/L ammoniacal nitrogen limit. Amine regeneration in gas sweetening units (DEA, MEA) produces amine-bearing wastewater. High ammonia loads in the biological stage cause nitrification oxygen demand that can destabilise MBBR performance unless specifically designed for combined carbonaceous BOD removal and nitrification.
Tank Cleaning and Shutdown Wastewater Surges
Crude oil storage tank cleaning — carried out every 3–7 years — generates high-volume, extremely high-strength wastewater containing tank bottom sludge, heavy oil, scale, and sediment with oil content of 1–5% (10,000–50,000 mg/L). This surge, when directed to the ETP without equalisation, can completely overwhelm primary and biological treatment stages. Similarly, refinery unit shutdowns and startups generate process upsets that create hydraulic and organic surges to the ETP.
Our Solutions
Tailored Wastewater Treatment Solutions
API/CPI Oil-Water Separation for Free Oil Removal
API separators designed to ANSI/API 421 standard for free oil removal to <100 mg/L from produced water and refinery integrated streams. CPI (Corrugated Plate Interceptor) units used where footprint is constrained — achieving equivalent separation in 30–40% of the surface area. Oil recovered from the API float is returned to the crude oil system for value recovery. API separator design accounts for temperature, viscosity, and specific gravity of crude type at each facility.
DAF with Chemical Demulsification for Emulsified Oil
Dissolved Air Flotation (DAF) with upstream chemical demulsification using cationic polyelectrolyte or alum dosing to break emulsified oil droplets and allow DAF micro-bubble attachment. Achieves oil reduction to <15 mg/L from DAF feed of 200–800 mg/L emulsified oil. DAF float (oily scum) is collected and directed to the slop oil recovery system or oily sludge management.
H₂S Air Stripping with Caustic Gas Scrubbing
Packed column air strippers for H₂S removal from produced water and sour process streams before biological treatment. Stripped H₂S gas collected under negative pressure and treated in a caustic scrubber (NaOH solution) or biofilter before atmospheric venting — achieving H₂S outlet <5 mg/m³. Chemical oxidation with hydrogen peroxide or sodium hypochlorite used as a polishing step where H₂S stripping is incomplete.
Ammonia Stripping and Biological Nitrification
Steam or air stripping tower for high-ammonia streams (NH₃-N >200 mg/L) to reduce ammonia to <50 mg/L before biological stage entry. MBBR biological stage designed with dedicated nitrification zone (low C/N ratio zone after carbonaceous BOD removal) to achieve combined BOD removal and nitrification, meeting NH₃-N ≤50 mg/L and TKN ≤100 mg/L discharge limits.
Biological MBBR with Phenol-Adapted Biofilm
Multi-stage MBBR biological treatment with acclimatised biofilm culture for simultaneous phenol degradation, BOD removal, and partial nitrification. Phenol concentration controlled to <50 mg/L entering MBBR (via advanced oxidation pre-treatment if necessary) to protect biological culture. MBBR design uses high carrier fill fraction to maintain biofilm resilience through refinery process upsets. Activated carbon polishing as final tertiary step achieves residual COD <250 mg/L and removes trace hydrocarbons.
Technologies
Proven Technologies for Your Industry
Benefits
Why Choose Spans for Your Industry
- CPCB Red Category compliance — BOD ≤30 mg/L, COD ≤250 mg/L, Oil & Grease ≤10 mg/L, Phenols ≤1 mg/L
- Oil recovery from API separator float returned to crude system — reducing waste and recovering value
- Phenol removal to <1 mg/L via biological phenol-adapted MBBR or advanced oxidation pre-treatment
- H₂S and ammonia controlled at source before biological stage — preventing corrosion, odour, and biological inhibition
- OCEMS-ready instrumentation for real-time CPCB data transmission from commissioning day
- ZLD option with RO + MEE/MVR integration for water reuse in cooling towers and boiler feed in water-stressed refinery locations
Success Stories
Case Studies
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