What are grease interceptors?
By Michael Whiteside
Grease interceptors, also known as "hydro-mechanical grease interceptors" in the new editions of the Uniform Plumbing Code (UPC) and International Plumbing Code (IPC), are required in all kitchens and areas that discharge grease-laden water into the sanitary sewer system. Their purpose is to "intercept" or "trap" FOG (fat, oil and grease) within the device for removal through a regular maintenance program. Because of the cost to remove grease from their water treatment plants, many water authorities across the country impose fines and penalties on restaurant owners that fail to clean and maintain their grease interceptors.
There are many different kinds and styles of grease interceptors. The traditional design looks like a rectangular box with an inlet and outlet at the same level from the bottom, an accessible lid, interior baffles and an external, vented flow control fitting. Most are made from fabricated steel. Interceptors made from plastic, stainless steel and cast iron are also available.
In the 1940s, the Plumbing and Drainage Institute (PDI) was the first authority to write a grease interceptor standard - PDI-G101. This standard is still in wide use today and is the root standard used by many cities and plumbing codes throughout the country. One of the key features of PDI-G101 is the requirement of a vented flow control fitting, This is typically a cast iron device that has an inlet and outlet and a vent connection at the top. It should be installed in the piping between the fixture(s) discharging into the grease interceptor and the inlet connection of the interceptor and have the vent connection terminate above the water level within the sink.
The purpose of the flow control fitting is to allow vented air to enter the grease interceptor via the plumbing line. Once the air enters the interceptor, it will naturally rise to the surface, carrying particles of FOG to the surface. The other purpose of the flow control fitting is to slow down the flow of water entering the grease interceptor so that there is enough retention time within the interceptor for the separation of FOG from water process to occur. All PDI-approved grease interceptors must be tested and certified by a third party testing laboratory to ensure that they meet the PDI performance standards. The key performance measurements are that 90% of the FOG that enters the interceptor be retained within the interceptor and that the grease retention capacity of the interceptor must be double the rated flow rate in gallons per minute (gpm).
Grease interceptors are sized by calculating 75% of the cubic volume of water discharging into the device from the fixtures. For example, a three bay sink with dimensions of 20" x 20" x 18" x 3 sink bays = 7,200 cubic inches of potential water volume, divided by 231 = 31.17 gallons of total water holding capacity of the fixtures x 75%, to allow for displacement of pots, pans and dishes in the sink = 23.38 or a 25 gpm grease interceptor.
Regular maintenance of grease interceptors is critical to their long-term performance. Unfortunately, most restaurant owners do not even know what the purpose of their grease interceptor is. Therefore, within a relatively short period of time (sometimes within two weeks), especially for devices that are located in "greasy spoon" restaurants, interceptors will be filled to capacity with FOGs. This often results in the FOGs passing through the grease interceptor into the sanitary sewer system, followed, in many areas, by monetary fines from the water authorities.
The lids of grease interceptors should be removed weekly to determine how much grease has accumulated; then they should be cleaned. Once it is determined how long it takes for the grease interceptor to accumulate a large amount of grease, a regular cleaning schedule can be set. This schedule must be adhered to in order to maintain the long term performance of the grease interceptor. To clean a grease interceptor, remove the lid, remove the baffles inside the device and then remove the accumulated grease floating on the surface with a ladle or bucket. Some areas have rendering companies that will pick up the accumulated grease for recycling.
Solids interceptors are a good product to install upstream of all grease interceptors. Their purpose is to "intercept" small particles of food, rice, scraps, etc., before they enter the grease interceptor. Often, it is the rotting of food particles inside the grease interceptors that result in the foul odors that many associate with them. Solids interceptors also need regular maintenance to ensure that they do not get clogged and pass their waste into the grease interceptor.
In summary, grease interceptors can perform a valuable function - keeping grease out of our sanitary sewers and providing a source of waste for recycling. It is important to choose the correct size grease interceptor, to install it with the vented flow control fitting and to clean it regularly.
Michael Whiteside is the president of MIFAB Inc., a manufacturer of grease, oil, solids and custom interceptors, fixture carriers, floor, roof, area and trench drains, cleanouts, backwater valves, floor sinks, wall hydrants, trap seal primers, access doors, pressure reducing valves, no hub couplings and stainless steel specialty products.