Not necessarily a 'stinky' situation.

Over the past few years, all of the model plumbing codes have changed their requirements regarding grease traps and grease interceptors. Likewise, many states (but not all) have re-addressed requirements for grease.

There have been a number of reasons for the changes in the code requirements. Anyone who has ever been around an open grease trap knows that it stinks to high heaven. Grease also causes problems with stopped up drains. Finally, grease plays havoc with sewage treatment plants.

Grease is such a problem that the federal government limits the amount of grease permitted to be discharged to a public sewer to 100 mg/l.

One of the first changes made was to recognize that, in certain restaurant installations, the major grease discharge was being missed by the grease trap or interceptor. Many restaurant operations are such that a large percentage of grease is discharged through the food waste grinder (garbage disposal).

Until recently, all of the codes prohibited a food waste grinder from discharging through a grease interceptor. The new code requirements permit the food waste grinder to discharge through a grease interceptor, provided there is a “solids” interceptor in front of the grease interceptor. The other requirement is that the grease interceptor is rated for the discharge of waste from a food waste grinder.

If you have experienced a grease problem in an existing restaurant, it may be a result of the grease bypassing the interceptor when discharging through a food waste grinder. The system can be modified to pick up this discharge and direct it through the interceptor, again, with a solids interceptor in front of the grease interceptor.

Piping Installation No Longer The Same

The bigger changes to the plumbing codes include the method for connecting fixtures to a grease trap or interceptor. Two new standards have been developed for grease interceptors: ASME A112.14.3 and ASME A112.14.4.

The first standard is an ANSI standard for grease interceptors. The standard is similar to PDI G101, however, it recognizes all types of grease interceptors.

The standard grease interceptor has an external, vented flow control device. This device regulates the flow rate through the interceptor to assure that the grease is properly separated and contained in the interceptor.

The next type of interceptor would have an external flow control device without a vent. The last two interceptors do not have external flow controls. The difference between the two interceptors is that one is designed for direct connections to the interceptor; the other is designed for indirect connections.

The last two styles of grease interceptors may, or may not, have internal flow control devices. In the past, flow control “vents” often terminated in the immediate area of the grease interceptor. Hence, if a grease interceptor was located in the kitchen of a restaurant, the vent for the flow control opened into the kitchen.

The new plumbing code requirements prohibit the vent for the flow control to terminate inside the building. The vent now must connect either to the plumbing venting system or terminate separately to the outdoors. This change greatly improves sanitation in the kitchen since the vent allowed a direct opening between the drain line and grease interceptor into the kitchen atmosphere.

Some manufacturers have chosen to use air admittance valves on the vent for the flow control. This makes sense since the flow control vent is only needed to add air into the system to help separate the grease in the waste stream.

Of course, once you connect the flow control vent to the plumbing vent system, the fixtures connecting to the grease interceptor must be separately trapped. In the past, if the grease interceptor was located within a short distance to the fixture, the grease interceptor could serve as the trap for the fixture. That distance varied by code but was typically between 4 ft. and 5 ft.

Some of the plumbing codes still allow the grease interceptor to serve as the fixture trap. However, the grease interceptor cannot have a vented flow control device. Thus, the other style of grease interceptors would have to be installed.

Furthermore, not every style of “grease interceptor” without a flow control would be acceptable. Some grease interceptors without vented flow controls have a by-pass line built into the interceptor.

This would allow sewer gas to pass over the top of the grease interceptor and escape through the fixture outlet. Hence, the equivalent of not having a trap seal on a drain line.

I personally do not like this exception that would continue to allow the grease interceptor to serve as the trap. It is better to simply install a trap on every fixture. This is the only means of assuring the system is properly protected from the escape of sewer gas.

Of course, once a trap is installed, there must be some form of venting to protect the trap seal. This reverts back to your local plumbing code requirements for venting. I have had some contractors say, “Well, we never used to installed a vent, since we never used to install a trap. So, we'll give them the trap, but they didn't say anything about venting and we're not giving them a vent.”

Unfortunately, that statement is wrong. The plumbing codes always have required every trap to be protected by a vent. Hence, when the code says to add a trap, you automatically have the requirement for venting. If venting is a big issue, you can always use either a combination drain (waste) and vent system or an air admittance valve.

New Technology In Grease Interceptors

The second standard, ASME A112.14.4, is the new ANSI standard to regulate GRD's. A GRD is a grease removal device.

Many manufacturers have developed grease interceptors that automatically remove the grease from the interceptor. This makes is easier to maintain the interceptor. When you consider a GRD, remember that, first and foremost, a GRD is a grease interceptor. The device must provide a means of intercepting the grease under normal drainage flowing conditions.

Once the grease is separated in the interceptor, the GRD has some automatic device that removes the grease. In effect, the GRD is an automatic cleaning device for the grease interceptor. To meet the new standard, the grease removed during the automatic cycle must be predominantly water-free. The objective is to remove only the grease to make it easy to dispose of to a grease rendering company.

Another, newer style of grease interceptor is the grease “remediation” interceptor. The interceptor has cultured bacteria that basically eat the fats, oils and grease that are discharged into the interceptor. The bacteria digests the grease, oils and nutrients, and releases carbon dioxide and water.

The new technology in the grease “remediation” interceptor is truly fascinating. Grease goes in, but doesn't come out. The system is a mini-sewage treatment plant.