API Separator and Municipal Stormwater

The API Separator Design Standard

API 421 is the authoritative design standard for gravity separation of oil from water in refinery and petrochemical service. The basin is sized so that a 150 micron oil droplet has time to rise from the bottom to the surface at the design flow; the skimmer removes the surface oil layer; the sludge hopper collects the settled solids. The treated water meets the typical refinery discharge consent of 15 to 30 mg/L oil at outlet.

Concrete or Steel Basin Configuration

The API separator is built as a rectangular concrete basin (for refinery and large industrial sites with permanent footprint) or as a steel basin (for smaller sites and brown field retrofits). The basin includes an inlet diffuser, multiple compartments for skim, sludge collection, and clarified water outlet. The CPI variant uses a corrugated plate pack inside the basin, reducing the footprint by 70 to 80 percent while delivering the same separation performance.

Municipal Stormwater Interceptor

Urban stormwater from highways, parking garages, industrial estates, and gas station forecourts carries oil drips, vehicle fluids, and petroleum residue from atmospheric deposition. The municipal stormwater interceptor uses the same API 421 design principles in a buried concrete chamber, capturing the oil before the stormwater reaches the receiving water body. The interceptor needs scheduled sludge removal every 6 to 12 months.

Polishing for Tighter Consents

Where the discharge consent tightens below 10 mg/L, SorbiTech adds a downstream coalescing polishing skid for dispersed oil and activated carbon for dissolved hydrocarbons. The combined train delivers single digit ppm outlet reliably. Sector coverage is industrial water, refining, and vehicle services.