Oil Water Separator Tank Options

API Oil Water Separators

Flat or hopper bottom oil water separator

API Oil Water Separator

Efficient gravity-based oil-water separation for industrial wastewater. Reliable. Compliant. Proven performance.

Founded in 1991. With 35+ years experience, our API Oil Water Separators are engineered to the highest standards of the American Petroleum Institute (API 421) for superior removal of free oil and settleable solids from industrial wastewater. Ideal for refineries, petrochemical plants, manufacturing facilities, and storm water applications, these separators deliver dependable primary treatment that reduces downstream load and supports regulatory compliance.

API product overview

The API Oil Water Separator uses gravity separation based on Stokes' Law, leveraging the density difference between oil, water, and solids. Oil droplets rise to the surface, solids settle to the bottom, and clarified water flows out in the middle layer. This proven technology effectively removes free oil droplets ≥150 microns and associated settleable solids, making it an essential first step in oily wastewater treatment.

Key performance

• Effluent oil: typically ≤100 mg/L for droplets ≥150 µm (can reach ~50 mg/L under ideal conditions)
• Robust removal of free and dispersed oils, plus settleable solids
• Designed for continuous operation with minimal maintenance

Key features

• API 421 compliant design. Optimized dimensions (length : width ratio ≥5:1, depth : width 0.3–0.5) for laminar flow and maximum separation efficiency.
• Durable construction. Available in carbon steel, stainless steel, or concrete. Above-ground skid-mounted or below-ground options.
• Advanced oil recovery. Equipped with highly efficient skimmers (drum, disc, or slotted pipe), oil retention baffles, and optional integral oil reservoir.
• Solids handling. V-shaped or hopper bottom with screw conveyors and sludge pumps for easy solids removal.
• VOC containment. Sectional fixed covers with gaskets, hatches, and optional vapor recovery/scrubbing systems.
• Flow distribution. Inlet diffuser/baffles ensure even flow and minimize short-circuiting.
• Customizable. Flow rates from 15 GPM to over 1,000+ GPM (or 1–1,000+ m³/hr). Skid-mounted, forkliftable designs available for smaller units.
• Low operating costs. No consumables, gravity-based (minimal energy use), simple maintenance.

Benefits

• Recover valuable free oil for reuse or recycling.
• Reduce load on downstream biological or advanced treatment systems.
• Meet NPDES and local discharge permits.
• Long service life with corrosion-resistant options.
• Easy integration into new or existing plants.

How it works

1. Influent entry. Oily wastewater enters the inlet chamber and passes through a diffusion baffle to reduce velocity and turbulence.
2. Separation zone. In the main channel, oil droplets rise to the surface per Stokes' Law, while heavier solids settle to the bottom.
3. Oil and solids collection. Floating oil is skimmed and directed to a collection trough/reservoir. Settled solids are scraped or pumped out.
4. Outlet. Clarified water passes under an oil retention baffle and exits for further treatment.

Technical specifications

For information on sizing according to the API 421 standards, see Sizing an API separator according to API 421. Contact us for custom sizing based on your flow rate, oil type, temperature, and influent characteristics.

Why choose our API Oil Water Separator?

• Decades of expertise in custom fabrication and process design.
• Superior engineering with modern enhancements while maintaining API compliance.
• Full system integration: pumps, controls, level sensors / monitoring / alarms, and downstream treatment.
• Reliable performance backed by industry standards and real-world results.

Industrial applications

• Oil refineries (refinery wastewater, stripped sour water) and petrochemical plants
• Natural gas processing, coke-making and gasification plants
• Chemical processing and manufacturing
• Power plants and transformer stations
• Vehicle maintenance, fuel storage, and airports
• Stormwater runoff from industrial sites
• Marine and bilge water treatment (adapted designs)

Design parameters (typical)

• Max horizontal velocity: ≤3 ft/min or 15× oil rise rate
• Oil droplet removal: ≥150 µm
• Temperature range: optimized for common industrial conditions (performance varies with viscosity/temperature)

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