Jurisdictions across the country rely on the Uniform Plumbing Code to help them solve their local grease related problems. It is becoming increasingly clear that the "code" is not providing adequate solutions in fats, oils, and grease (FOG) abatement efforts.
So what is the problem? Simply put when it comes to grease interceptors the plumbing code seems more interested in the design of the interceptor and the amount of waste water that can flow through it or be stored in it than the amount of grease it should be expected to efficiently separate and store.
Vague language for specifiers
From the 2009 Uniform Plumbing Code Chapter 10 Paragraph 1014.1: “…an approved type of grease interceptor(s)… shall be correctly sized and properly installed in grease waste line(s) leading from sinks and drains, such as floor drains and floor sinks and other fixtures or equipment … where grease is introduced into the drainage or sewage system in quantities that can effect line stoppage or hinder sewage treatment or private sewage disposal.” (2009 UPC 1014.1)
Where grease is introduced
The problem with the way this is phrased is that it assumes that all FSE's handle greasy waste the same. This is absolutely not correct. Best Management Practices (BMPs) vary dramatically from one kitchen to another. I have heard countless stories of kitchen staff dumping pots of soup down hand wash sinks, or staff using the grinder sink (food prep) to rinse dirty dishes before loading them into the dishwasher. A specifier has no control over which fixtures get greasy waste dumped into them. If the fixture isn't connected to a grease interceptor you can be sure that someone is going to be using it for greasy waste.
In quantities than can effect line stoppage
How is the specifier to know whether the kitchen staff are using the fixtures that are connected to the interceptor and none of the other fixtures? The specifier has no way of knowing how much greasy waste is being put into any specific fixture.
Drainage Fixture Units and Gravity Flow Rates only calculate water loading
What is a Drainage Fixture Unit (DFU)?
“A quantity in terms of which the load-producing effects on the plumbing system of different kinds of plumbing fixtures are expressed on some arbitrarily chosen scale.” The code assigns a numerical value to fixtures installed in a plumbing system that accounts for the amount of waste water the fixture is likely to produce.
The problem with using this method for sizing interceptors is that it doesn't tell us anything about how much grease we can expect from those given fixtures. This has led to thousands of grease traps to be installed under multi-compartment sinks that are too small in capacity and not being maintained often enough. More importantly a lot of the grease being produced by the food service establishment is not being routed through the interceptor at all as kitchen staff use fixtures and drains that are not connected to the interceptor to dump greasy waste.
NO consideration given to FOG loading in sizing protocols
The primary function of any grease interceptor is to efficiently separate and store fats, oils, and grease (FOG). It makes sense that you should size a device to accommodate its primary function. Unfortunately the plumbing code does not do that. There are some jurisdictions that have created their own sizing method that attempts to do this because they are frustrated with the lack of effective sizing in the plumbing code.
There is a better way
Schier recommends that you connect as many of the fixtures in the kitchen as possible to the grease interceptor. This guarantees that kitchen staff will not be circumventing the grease interceptor by using unconnected fixtures for greasy waste. Schier also recommends using a FOG production sizing method in conjunction with the plumbing code as a two-step process.