What Is the Best Way to Dispose of Used Cooking Oil and Fat?

While edible fats and oils are ultimately biodegradable, they can gum up the works in a landfill for years. They’re not as bad as petroleum oils, however, which are digestible by only one or two species of bacteria and stay around essentially forever.

Small amounts of fat can be absorbed in a couple of paper towels and thrown in the trash. I pour slightly larger amounts into an empty food can that I keep in the freezer, where the oil freezes solid.

When the can is full, I seal it in a plastic bag and put it into the trash, hoping that it won’t melt and leak out until it’s far, far away and untraceable back to me. That’s unconscionable, I know, but it’s vastly preferable to pouring it down the drain. Moreover, it makes a jolly flame when the garbage is incinerated.

Large amounts of used deep-frying fat are a bigger problem. Restaurants often subscribe to a disposal service that collects their gallons of used “grease” and sells it to soap and chemical companies. But what can you do with it at home, short of gift-wrapping it, leaving it in your unlocked car in a rough neighborhood, and hoping it gets stolen?

A hydrogeologist (he studies how liquids flow through soils) I consulted at the Department of Environmental Protection advises that unless your house is on a septic system, you can mix the oil with a liberal amount of dishwashing liquid, which has a prodigious appetite for grease, stir or shake it thoroughly to homogenize it, and then slowly feed the mixture to the garbage disposer along with lots of cold running water, to be scattered down the drain and ultimately dealt with by the local wastewater treatment plant.

I’m not recommending that, however, so if you plug up your plumbing or shut down your local sewage plant, don’t blame me.

Even better would be to turn an environmental liability into a conservation asset: Use the oil as an alternative fuel for your diesel-powered Volkswagen, Mercedes, or pickup truck.

After all, when Rudolf Diesel demonstrated his new engine at the World Exhibition in Paris in 1900, he ran it on peanut oil. But don’t try it until you read Joshua Tickell’s book, From the Fryer to the Fuel Tank (Greenteach Publications, 2000), which tells how to do it.

If you use this suggestion, I advise that you stop feeding fat to your car when it starts getting too big for the garage