The devices formerly known as “grease traps” are simple at their most basic level.
    They’re plumbed into a sanitary sewer line coming from a commercial-type kitchen so they can capture fats, oils and grease from the kitchen waste water before it goes farther down the line and, possibly, into the environment. The use of grease interceptors is required in most commercial food preparation applications.
    If it gets into the wastewater, the large amounts of FOG that can be produced by a commercial or institutional kitchen cause problems in the collection system pipes. It decreases pipe capacity, which leads to pipe systems needing to be cleaned more often and/or replaced sooner than otherwise expected. Oil and grease also hamper effective treatment at the wastewater treatment plant.

FOG suspended in a warm liquid may not appear to be that big of a deal. As the liquid cools, however, the grease and fat will congeal and create a layer of scum on the surface of settling tanks, digesters, and the interior of pipes and other surfaces which may cause a shutdown of wastewater treatment units.
    Problems caused by wastes from restaurants and other grease-producing establishments have served as the basis for ordinances and regulations governing the discharge of grease materials to the sanitary sewer system. This type of waste has forced just about every jurisdiction to require installation of grease interceptors anywhere there is a commercial or industrial kitchen or any other FOG-producing activity going on. 
    These units, whether small enough to fit under a sink or large enough to require burying in the parking lot outside, generally go about their work passively—there usually isn’t much in the way of electromechanical devices inside the interceptor doing any work.
    These units operate on two simple principles. First of all, everyone knows that “oil and water don’t mix.” This is a useful principle that can be leveraged in doing the work of separating water from the fats, oils and grease produced in a commercial kitchen. Second, since FOG is somewhere between 15- and 20 percent lighter than water, it floats.
    When kitchen waste water flows through one of these devices, the FOG floats to the surface and, via a system of baffles, gets trapped inside the interceptor. Captured FOG fills the trap from the top down, displacing “clean” water out of the bottom of the trap and into the sanitary sewer line.
    The smaller, hydromechanical grease interceptors, formerly known as “grease traps,” require periodic maintenance as specified by local jurisdictions. Usually accomplished by hand, this generally involves removing the accumulated FOG and placing it into a suitable container for collection by a recycler to come and pick up.
    The larger gravity grease interceptors typically installed outdoors will usually be cleaned by grease haulers or recyclers who will suction the FOG into their truck and haul it to the designated treatment plant.

At their most basic level, grease interceptors are very simple, passive machines. Graphic courtesy of Jay R. Smith Mfg. Co.

    Suction will be the method used on a 1,000 gallon cement unit recently installed at a new shopping center scheduled for mid-March completion in Walnut Park, Calif.
    Installed by Westar Plumbing Co., Inc., of Huntington Beach, Calif., this concrete unit came from Jensen Precast in Fontana, Calif. Westar has been in business since 1996 specializing in new commercial construction, according to co-owner Lester Massengale.   
    “We’re lucky this one wasn’t very deep. We do a lot of supermarkets like Ralph’s, Albertson’s and Vons. I’ve been doing that for 27 years,” Massengale said, adding it doesn’t take too long to set a unit like this one into place.    
    Indeed, it was delivered on a flatbed truck equipped with a crane and hoisted into position in the pre-dug hole in just a matter of minutes. Once it was set into position, Massengale said the day’s schedule for the unit included trenching, piping, inspection and then a concrete backfill to hold it into position.   
    “The site guys will end up grading it,” he said. “We’ll get it close to where it has to be and then we’ll go from there.”    As relatively simple as grease interceptors may seem, there is no shortage of code requirements covering them, their nomenclature, flow rates, FOG removal rates, and on and on. Wading through the language in the code books can be tricky, confusing and time-consuming so here are the basics.   
    First, they’re not “grease traps” anymore. “Gravity grease interceptors” is the new term for the larger devices that are typically installed outdoors. Next, “hydromechanical grease interceptors” is the new terminology for the smaller, indoor units formerly called “grease traps.” In all cases, though, either can be referred to with the generic term, “grease interceptors.”   
    The International Association of Plumbing and Mechanical Officials in Ontario, Calif., publishes the Uniform Plumbing Code and the Uniform Mechanical Code, models from which state and local authorities can adopt or modify to use as their local codes.    
    IAPMO code and technical support manager Bob Shepherd said the current, 2006, edition of the UPC model code carries numerous changes and additions covering these devices, but there’s no way to lay them all out in a nutshell, thumbnail view.   
    The current UPC contains various tidbits contractors may do well to keep at top of mind when making such an installation in an area guided by the UPC model code.   
    For example, Section 1014.6 of the previous UPC has been replaced by Section 1014.1.2, which states if the authority having jurisdiction determines that a grease interceptor is not being properly cleaned or maintained, that authority now has the horsepower to mandate the installation of additional equipment or devices and to mandate a maintenance program.

Small hydromechanical grease interceptors, formerly known as 'grease traps,' can be installed just about anywhere. Photo courtesy of Canplas.

The International Code Council of Washington, D.C., publishes the International Plumbing Code and the International Mechanical Codes. Like IAPMO’s UPC and UMC, the International Codes are models that can be adopted or modified as necessary by local jurisdictions. The 2006 edition of the IPC is the most recent.
    Lee Clifton, director of plumbing programs for plumbing, mechanical and fuel gas for the ICC said the current version of the IPC specifies that grease interceptors and automatic grease removal devices shall conform to PDI G101, ASME A112.14.3 or ASME A112.14.4 and be installed in accordance with the manufacturers’ instructions.
    So, have there been any changes in IPC requirements or specifications contractors need to know about?
    “The definition ‘Flow Control (Vented)’ has been added to define the device that is used on hydromechanical grease interceptors, formerly called grease traps,” Clifton said. “The new definition now clarifies the flow control device referenced and explained in Section 1003.3.4.2."
    This section of the IPC specifies grease interceptors must be equipped with devices that control the rate of water flow so it doesn’t exceed the rated flow of the interceptor. This device must be vented and terminate at least six inches above the flood rim level or be installed in accordance with the manufacturer’s instructions.   
    Also, Clifton said a pair of additional flow rates and capacities have been added to Table 1003.3.4.1 in the IPC: “The modification to the table is in accordance with ASME A112.14.3 for standard flow rates and grease retention capacity ratings for grease interceptors,” he said, adding contractors can also use that table to find the specifications for properly sizing a grease interceptor for the job at hand.
    Of course, there is far more to grease interceptors in both model codes and codes in effect in local jurisdictions than could ever be thoroughly discussed here. The bottom line for contractors installing these devices is to be aware of the model code(s) in effect where the job is located and how it has been tailored for the local market.