Grease Interceptors; Hydromechanical, what is that?

The 2006 Uniform Plumbing Code made some interesting changes in chapter 10 relating to grease traps that have some people confused.  Lets clear it up.

For years the term "Grease Trap" was used to define "A plumbing appurtenance or appliance that is installed in a sanitary drainage system to intercept nonpetroleum fats, oil, and greases (FOG) from a wastewater discharge."  The device was commonly used as a point of use interceptor servicing a specific fixture.  Until the 2006 code changes these devices were limited to a maximum of 4 drainage fixtures.

Now we have a new term "Hydromechanical Grease Interceptor".  It is defined as "A plumbing appurtenance or appliance that is installed in a sanitary drainage system to intercept nonpetroleum fats, oil, and greases (FOG) from a wastewater discharge and is identified by flow rate, and separation and retention efficiency.  The design incorporates air entrainment, hydromechanical separation, interior baffling, and / or barriers in combination or separately..."  These devices are required under the code to control the flow rate entering the device with either an external flow control or a built-in flow control (non-external), either directly connected or indirectly connected to the sewer system.

That definition may need a bit of explaining.  Lets simplify it.  A Hydromechanical Grease Interceptor is a device that separates and stores fats, oils, and grease (FOG) and is commonly used inside a restaurant for point of use grease separation.  These devices are "generally" installed inside.  Flow rates for these devices range from 10 gpm to 100 gpm.

Are all Hydromechanical Grease Interceptors alike?  The short answer is no.

Manufacturers have used the same old technology in grease traps for decades and the standard that has governed this type of grease interceptor is PDI-G101.  The basic design  requires the interceptor to have baffles inside (units are typically made out of steel) and an external flow control with an air vent.  The baffles are intended to extend the flow path while the vent (or air in-take) on the flow control provides a source of air to mix with the in-fluent as it enters the interceptor intended to aide in the separation process.  A certified device is required to separate two (2) lbs of grease for each one (1) gpm of the interceptors certified flow rate at a minimum of 90% average efficiency.  For example a 20 gpm unit is required to separated and store 40 lbs of grease and be at least 90% efficient up to the units rated capacity.

The plumbing code has another approved standard for Hyrdromechanical grease interceptors called ASME A112.14.3-2000.  This is an open standard that allows a manufacturer to be innovative, potentially developing designs that may be more efficient and separate more grease than the minimum requirements.

Schier Product's Great Basin Series and Thermaco's Trapzilla series are just two examples of manufacturers that have developed interceptor designs that are a significant departure from older technologies.  Both of these series are certified to ASME A112.14.3 Type C.  In both cases their designs could not be certified to PDI-G101 owing to their lack of an external vented flow control and internal baffling.  They also meet or exceed the minimum performance requirements of PDI certified interceptors.

Hydromechanical Grease Interceptors; the new term for a grease trap.