Issue: 6/05

Grease is clogging up our veins and our drains. While doctors prescribe proper diets to prevent large quantities of fat, oils and grease (FOG) from entering our systems, regulatory authorities are prescribing grease interceptors to do the same for our municipal plumbing systems.

FOG-clogged sewer systems can cause sewage backups, leading to property damage and/or pollution of surface and ground water. FOG can collect in the sewage system through discharge from any source, but the primary sources are restaurants, cafeterias and food processing centers.

Photo courtesy of Thermaco.

How Grease Interceptors Work

Greasy wastewater from kitchen fixtures such as pot sinks, pre-rinse sinks, and soup kettles is plumbed through a flow controller and then through a grease interceptor. The wastewater is routed through a series of baffles within the interceptor. FOG, being lighter than water, rises to the top and is retained in the interceptor while water passes through to the outlet and is discharged to the sewer system.

When designed and properly maintained, grease interceptors reduce FOG buildup in sewer systems. To ensure a grease interceptor is designed, built and functions properly, restaurant managers, installers and public health inspectors should be sure it is tested and certified to ASME A112.14.3, ASME A112.14.4, or PDI-G101.


Grease interceptors are rated based on their flow capacity. Flow restrictors are often used during testing to ensure the rated flow is maintained. Since flow is a critical aspect of the design, manufacturer's use instructions must indicate the rating and mandate that a flow restrictor be installed with the unit.

The test rig will vary depending on the product type, but basically consists of a two-compartment supply sink with two 1-1/2" waste outlets plumbed to a flow controller and then a roughly 10-foot vertical drop to the grease interceptor. Wastewater is then plumbed from the grease interceptor outlet down to a skim (collection) tank.

The supply sinks are filled with a 150

Why NSF?

Several manufacturers approached NSF expressing the need for a testing laboratory for grease interceptors. To date, there are few laboratories capable of performing this testing, and due to the growing demand for grease interceptors, manufacturers are struggling to get products tested. The lack of testing competition in the marketplace meant that manufacturers had few options.

Testing and listing of grease interceptors is a good fit for NSF based on NSF's involvement with the three main regulatory authorities that approve them. Sewage treatment authorities have an urgent need to control the amount of FOG entering the treatment systems. During recent meetings with NSF's Wastewater Joint Committee, NSF was asked by sewage treatment authorities to become involved with writing protocols and standards for exterior high-volume grease interceptors.

NSF is well known as a certifier of plumbing products for potable water and wastewater, so the plumbing inspectors fully recognize the NSF Mark.

Finally, virtually all other equipment used in restaurants and commercial kitchens are required to be certified to NSF standards. For health department sanitarians approving grease traps, seeing the NSF Mark on a grease interceptor will be a natural extension of commercial kitchen equipment that is required to be certified to NSF standards.

Whether it is clogged veins or clogged drains you are trying to prevent, maintenance is key. If a grease interceptor is not cleaned and maintained on a regular basis, it will certainly not be effective. Following manufacturers' maintenance instructions and obtaining NSF certification should be considered "doctor's orders."