Standard grease interceptors need to be regularly cleaned out and maintained to reduce odor problems.
Issue: 6/04

One of the decisions facing an engineer in the design of a food-handling establishment is the location of a grease interceptor. Before discussing interceptor location options, some background is necessary to better understand the issues related to grease, as well as the problems resulting from its introduction into the sanitary sewer system.

Fats, oils and grease (FOG) are becoming an increasingly talked about subject. The Federal Clean Water Act charges the EPA with keeping our water resources clean and pristine. The EPA, in carrying out a congressional mandate, developed a broad range of rules and regulations to achieve and protect our limited natural water resources. As part of those regulations, as well as limited response from the waste water treatment industry, the EPA has been increasing pressure on local utility providers to reduce, minimize and eliminate the discharge of FOG-containing effluent into our water resources-lakes, rivers, streams, etc. The EPA has also limited the amount of FOG effluent permitted to discharge into a public sewer system.

Utility purveyors have begun to respond by developing rules and regulations to further control the amount of FOG that may be discharged into their sanitary sewage systems. Some of those rules may dictate the size, type and location of the interceptor. Almost all of the purveyors have an established acceptable level of FOG entrainment. This may be between 25 mg/l and100 mg/l. The Federal EPA maintains jurisdiction over private and on-site treatment systems; however, publicly owned treatment facilities (POTW) may enact requirements to further regulate by inspection or testing. Generally speaking, neither purveyors, POTWs, nor the EPA involve themselves in regulating grease interceptors. So where should a grease interceptor be located?

FOG should be removed from the waste stream as near to its source as possible. This would seem logical, straightforward and based on sound engineering principles. However, engineers are often restricted by codes, regulations and design constraints. Some codes restrict the location of grease interceptors. Health departments typically adopt FDA (Food and Drug Administration) regulations and add local amendments. The local changes may contain specific restrictions on the location of grease interceptors, or acceptable types of grease interceptors. The kitchen consultant's design must also be considered and coordinated, as well as the architect's concerns, and the directions from the owner. Other concerns that cannot be overlooked include serviceability, maintenance and the operating staffs' working habits and procedures. The engineer must look at all of these considerations when determining the location of the grease interceptor and the type of grease interceptor that will be specified.

A grease remediator installation under a three-compartment sink in a school cafeteria. (Photo courtesy of Jay R. Smith Mfg. Co.)

Types of Grease Interceptors

There are various types of grease interceptors available to the engineer today. The different types include standard grease interceptors conforming to ASME A112.4.3 or PDI-G101 (these units are often certified by the Plumbing and Drainage Institute), automated grease recovery devices complying with ASME A112.14.4-2001, and grease remediation devices. (There is currently no standard regulating remediation devices.)

Grease recovery devices are standard grease interceptors that have an automatic system for removing the grease. This is accomplished by either skimming or siphoning the surface of the interceptor to remove the grease. The removed grease must be 95% water free.

Grease remediation devices utilize enzymes to digest the grease. The resulting discharge is virtually FOG free.

These types of units are considered point-of-generation or close proximity devices. When specifying these types of grease interceptors, the device should be located adjacent to the fixture it serves or in close proximity to the fixture. Generally, any of these devices will serve one or a group of fixtures. This may result in the installation of multiple grease interceptors for a given project.

Large interceptors, on the other hand, are designed to serve a number of fixtures or a complete kitchen. Because of their size and cleaning requirements, large interceptors are generally placed on the exterior of the building. Grease interceptors with a flow rate in excess of 100 gpm are not regulated by ASME A112.4.3 or PDI-G101. As such, a large interceptor, such as a concrete vault, steel or fiberglass tank, is not regulated by a standard. Without a specific standard addressing these types of interceptors, an engineer has no guidance for the installation and location of these devices. This leaves an engineer with no means of evaluating the performance and grease removal efficiency of large outdoor interceptors, resulting in total reliance on the manufacturer's data.

When selecting the type and location of a grease interceptor, an engineer should determine the amount of FOG that may be generated, the time between cleaning cycles of the interceptor, and the availability of space to locate the interceptor. Large interceptors, which are located on the exterior of the facility, must have available space adjacent to a building

When selecting a location for a grease interceptor, grease recovery device, or grease remediation device, the engineer must consider the following:

1. The local plumbing code, POTW regulations, health codes, and utility purveyor's rules must be researched. Local requirements may dictate where a grease interceptor must be located. Health codes sometimes prohibit grease interceptors from being located in food preparation areas. Some areas require large outdoor interceptors. Some POTWs and local utilities consider a large outdoor interceptor to be the only acceptable means of reducing the discharge of FOG. They may require an outdoor interceptor even when point-of-generation grease interceptors are installed inside the building.

2. Specify a grease interceptor, grease recovery device, or grease remediation device that is acceptable by the plumbing code and/or the local utility purveyor. The type of acceptable grease interceptor will limit the location of the unit. Point-of-generation type grease interceptors should be located as near to the fixture they serve as is practical. This could mean that the device is set directly next to or under the fixture served or in an adjacent room behind the fixture.

3. Serviceability should be considered in selecting a location. Exterior interceptors are almost always odor-generators and require pumper-trucks to remove the accumulated FOG. Point-of-generation grease interceptors, on the other hand, require smaller portable liquid vacuums to remove the accumulated material. When the grease interceptor is serviced on a regular basis and properly cleaned, odor is much less of an issue. Grease recovery devices require sufficient space for the unit, as well as a space for the container receiving the extracted FOG material. Grease remediation devices require about the same space as a grease recovery unit. However, rather than the space for a collection unit, space is required for the enzyme feeder.

While all of the various types of systems or devices currently available for collecting, holding and/or processing FOG require some amount of space, the large outdoor interceptor requires the most, though it doesn't occupy the usable floor space inside the building that the other units require.

Like many design consideration for an engineer, the plumbing codes, local utility requirements, health department regulations, and the authority having jurisdiction (AHJ) have an influence in selection of the grease interceptor and the location of the unit. The other factors that must be evaluated include: the serviceability, available floor space, coordination with the kitchen consultant and architect, and the owner's requirements.