Grease Interceptors Continued from page 52
fixtures. Allow clearances for cover and baffle removal, access for cleaning tools such as a vacuum hose and line of sight into the unit to be sure the job was done right. Some units may include other components such as supplemental strainer baskets or GRD components, which need to be considered for future removal.
Maintenance Every interceptor needs regular maintenance to perform
Separated Grease Layer: Grease interceptor with side view window — lab test grease media.
This engineered approach allows hydro-mechanical units to be much smaller than their gravity-type counterparts for the same application. Two performance standards, PDI-G101 (Plumbing & Drainage Institute) and ASME A112.4.3, are widely used to test hydro-mechanical units and to ensure proper function at specified flow rates. Both types usually incorporate a trapleg-style configura-
tion at the outlet end so that, as new wastewater enters the inlet, the cleanest water near the bottom of the unit is pushed up and out to the pipe. Gravity-type units are tradi- tionally too big to put inside the building and are direct- buried outside. If the walls of this unit are compromised due to loading, earth movement or material deterioration, the grease can seep directly into the ground. Hydro- mechanical units are typically much smaller and, therefore, can be installed inside the building and closer to the grease sources. Being indoors also reduces compromising risks, and the building itself acts a second layer of protection for the surrounding environment.
Location … location … location The two key considerations here are the distance from
the fixture(s) being served by the interceptor and accessibility. Recall the sewer system blockages mentioned earlier.
This was a length of pipe from grease-supplying establish- ments to a water treatment facility. The pipe inside a build- ing from fixtures such as floor sinks, prep sinks and rinse sinks to the grease interceptor is like a miniature version of a sewer system pipe. The longer it is, the greater the risk that grease will congeal and cause a blockage. As a general rule, keep the interceptor as close to the fixtures being served as possible. If long runs are necessary, plan in peri- odic cleanouts for easy access later. Accessibility is very important. All grease interceptors
will need some human interaction. Even units with a grease removal device (GRD) need to be completely cleaned out periodically. Inevitably, waste that is heavier than water will enter the unit . If this is not removed, it will build up to the point of blocking the outlet and causing backups to the
Page 54/Plumbing Engineer Interceptor with grease removal device.
a day, losing business, which could have been avoided with a regular maintenance schedule. Unfortunately, some of this misunderstanding or lack of
knowledge is due to the typically high turnover rate in employees for these types of businesses. This only supports the need for an established regular maintenance schedule that, like so many other tasks in a food service establish- ment, becomes habit.
Sizing and solids Sizing of an interceptor can be, and has been, done more
than one way. There are even some antiquated codes still using a formula that considers hours of operation in a day, number of seats in the restaurant and proximity to a major highway to size a unit. Sizing by fixture units may also be somewhat risky as this method includes a factor of proba- bility that a fixture is being used. So what happens in peri-
May 2011
as advertised. If the grease is never removed, the unit will eventually fail and pass grease downstream. As the grease separates to the top, it is actually building a layer down- wards from the static water level inside the unit. As this layer thickness increases, it is decreasing the effective sep- aration volume, which means it takes less time for incom- ing, grease-laden water to get to the outlet. A lack of maintenance by facility personnel is common-
ly caused by, what we like to call “magic-box-in-the-cor- ner” syndrome. Some people do not know that they have an interceptor in their restaurant; many others know it’s there, but are more than happy to leave it alone until it is too late. When sinks are backing up and the odor is unbearable, it is much too late. Some restaurants have even had to close for
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