Grease Interceptors and Traps Summary

Grease Interceptors & Traps

Purpose

  • Intercept and collect free-floating fats, oils, and grease (FOG) from commercial food preparation establishments.

  • Prevent FOG from entering the municipal sanitary main.

  • Food waste disposers and dishwashers should not discharge into a grease interceptor.

  • Not required for dwelling units.

  • Only grease-laden fixtures should connect to the interceptor; non-grease-laden fixtures connect to the normal waste pipe system.

  • The authority having jurisdiction (AHJ) determines which fixtures are grease-laden.

What is FOG?

  • Fats, Oils & Grease

  • Combination of fats, oils, and grease (FOG).

  • Includes cooking oil, animal fat and lard, grease, butter, tallow, shortening, and margarine.

Interceptors and Separators (Section 1003)

  • Required to prevent the discharge of oil, grease, sand, and other harmful substances into public sewers or sewage systems.

  • Not required for individual dwelling units or private living quarters.

  • Required for drainage from fixtures and equipment with grease-laden waste in food preparation areas (restaurants, hotel kitchens, hospitals, etc.).

  • Fixtures include pot sinks, prerinse sinks, soup kettles, wok stations, floor drains, automatic hood wash units, and dishwashers without prerinse sinks.

  • Should only receive waste from fixtures that discharge fats, oils, or grease.

  • Food waste disposers should not discharge to a grease interceptor.

Types of Grease Interceptors

  • Hydromechanical Grease Interceptor (HGI):

    • Referred to as a “grease trap”.

    • IPC 1003.3.5/UPC 1014.2.

    • Steel () or Plastic ($).

  • Gravity Grease Interceptor (GGI):

    • IPC 1003.3.7/UPC 1014.3.

    • Plastic () or Concrete ($).

Hydromechanical Grease Interceptor (HGI)

  • Smaller footprint and size (can be indoors).

  • Multiple baffles to speed up separation time.

  • More frequent maintenance/cleaning.

  • Typically an indoor installation near fixture(s) served.

  • Can only serve a few fixtures.

  • Can go below or above grade.

  • Some jurisdictions may not allow interior GI’s for new construction.

  • Flow control required.

  • Sized based on flow-through rate in gallons per minute (GPM).

  • IPC 1003.3.5 references other sources to size: PDI G101, ASME standards.

Sizing - PDI Method

  1. Determine the volume of water the sink will hold in gallons.

  2. Multiply that number by 75%.

  3. Consider desired drain time of the sink (typically 1 minute).

  4. Divide the gallons by the drain time to get gallons per minute (GPM).

Sizing Example:

20x20x12x3=14400cu in20 x 20 x 12 x 3 = 14400 cu\,in
14400231=62.34 Gal\frac{14400}{231} = 62.34 \,Gal
62.34 gallonsx75%=46.76 gpm62.34 \,gallons x 75\% = 46.76 \,gpm

  • Use a 50 gpm unit with a 1-minute drain down time.

  • Take peak GPM flow rate calculated and multiply by 2 for grease retention capacity.

  • Manufacturers list a peak GPM and matching lbs of retention.

Gravity Grease Interceptor (GGI)

  • Larger footprint and size (typically outdoors).

  • Multiple compartments with a 30-minute separation time.

  • Less frequent maintenance/cleaning.

  • Exterior installation.

  • Receives discharge from all grease-laden fixtures within a building.

  • Coordinate location with site plan.

Sizing

  • IPC 103.3.7 indicates multiplying the peak drainage flow (GPM) by a 30-minute retention time.

  • The Uniform Plumbing Code (UPC) contains a sizing method based on DFU’s.

  • Consult the AHJ to determine the GGI sizing method.