Green living: Save Our Earth By Living Green

Know the Difference: Grease Traps and Grease Interceptors

A great deal of the wastewater that flows down the drains of domestic and commercial kitchens is contaminated with different kinds of fats – butter, cream, vegetable oil and lard, among others. If such grease-contaminated water is allowed into the public sewage system, it can quickly congeal in cold weather and cause unmanageable blockages.

Opened grease trap 447x331
Image: flickr.com/photos/gtzecosan

In the U.S., the Environmental Protection Agency has determined that kitchen grease is the primary cause behind the tens of thousands of municipal sewer line blockages that occur each year around the country. Nearly every country with well-developed sewage systems requires homes and commercial food preparation establishments to install devices in their wastewater lines that remove at least some of the grease present in their outflow. These devices are called grease traps and grease interceptors.

How do these devices work?

Grease traps work on a very simple principle. They are box-like devices in a kitchen’s wastewater line that get the outflow to stand in a chamber for a few seconds or minutes to allow any grease particles in the water to rise to the top and solid food particles to fall to the bottom. It’s just the water in the middle that makes it out.

Grease traps and interceptors are both, basically, devices of the same kind. Grease traps are small and meant for domestic kitchens. They are devices that are placed under kitchen sinks to clean the wastewater coming out before it is let into the sewage system. Interceptors, on the other hand, are used in the wastewater lines of commercial kitchens. They are larger (several feet long) and feature more elaborate chambered systems to help clean large quantities of waste water quickly of grease contamination. The most efficient models use three or four grease trap modules placed in series on the same line.

The most capable grease interceptors are huge 2000-gallon devices. These are installed underground outside commercial kitchens. They work better because their capacity allows them to let wastewater stand for 30 minutes at a time before it is let out. The longer the kitchen wastewater stands, the longer the fat particles in it have to float up.

Grease traps and interceptors need to be cleaned periodically. Cleaning home grease traps is a simple, if messy operation. You simply need to scoop out the grease collected in the trap and throw it away in the garbage. Commercial restaurant kitchens call in grease trap hauling services to come in and vacuum out their oil and grease interceptors. The waste, brown grease is taken for disposal at landfills.

The way the Uniform Plumbing Code defines grease traps and interceptors, the only difference between them comes down to the flow rates that they are built to handle.

What you can do to make your traps more efficient

The less grease you allow in your wastewater, the less you depend on your grease trap or interceptor to clean your water. You can do a little grease separation of your own by cleaning your dishes of their grease in a sink of warm, standing water. You can then separate the layer of fat that floats to the top before letting the water run down the drain.

It isn’t a good idea to wash greasy dishes in hot running water and to let the grease-laden wastewater flow down the drain. When warm, grease-filled water enters a grease trap or interceptor, the fat simply remains in the water – it doesn’t separate easily. Washing with cold water is a better idea – when the water in a grease trap or interceptor is cold, grease separates and floats to the top more easily.

Alan Rosinski enjoys engineering innovations. He often writes about machines and how they are updated and adapted over the years.

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