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Leftovers--Into the Trash or Kitchen Disposal? Essential Answer

Courtesy EPA

STUFFED: Food is the largest component of waste dumped in landfills.

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By Georgia Griffin

When disposing of food waste, I often compost. But some food wastes are not supposed to go in the compost pile. Is it more environmentally sound to scrape your plate into the trash or send it down the kitchen disposal? And on a related note, if I blow my nose into a tissue, is it better to throw it in the trash or the toilet (without any extra flushing)?

Asked by Lauren Woodard, PhD '09, Houston, Texas


Food waste is more than a pet peeve to me. Leftovers that have gone bad in the refrigerator or a slurry of dinner scraps not worth saving bother me so much that I risk my personal health to consume the world’s leftovers. At dinner parties I often finish strangers’ meals to keep them from going into the garbage. What is a better approach?

First, you’re right: composting is the preferred option. It’s also underrated, and underused. If the 21.5 million tons of food waste generated annually in the United States were composted instead of being sent to landfills, the cut in greenhouse gas emissions alone would be like taking over two million cars off the road—and that is hardly compost’s only benefit. More food residues and paper products are fit for compost than commonly thought, too. The important distinction is between the somewhat limited backyard compost pile and the much more inclusive large-scale municipal or commercial composting operation. I’ve created the flowchart here to help you decide the best fate for your food and paper waste.

Oils, meat residues, dairy, and human waste are the big No-No’s of backyard composting. Under the right conditions, compost piles generate enough heat to kill any potential pathogens—in a used tissue, for example. However, backyard composts often do not reach those optimal temperatures, and meat and other animal waste can attract critters if food takes too long to decompose.

Large-scale composting facilities are not widespread, but they are growing in number. San Francisco already offers curbside composting pickup, and voters in Palo Alto, Calif., recently approved a new anaerobic compost digester on ten acres of former landfill. Peter Drekmeier, a former Palo Alto mayor, calls this advanced composter, which will turn food waste, yard waste, and human waste into biogas and compost, “a once-in-a-lifetime opportunity.” Land is available to process three waste streams, produce renewable energy and excellent fertilizer, and reduce greenhouse gas emissions. “Any place that has [a] sewage treatment plant should also process food waste,” Drekmeier told me. You can find out more about industrial composting in the Nitty Gritty answer.

But back to your original question: when composting truly isn’t an option, should we toss food waste in the trash or shred in the kitchen disposal? Essentially, it’s a not-great choice between clogging landfills, or stressing sewage treatment plants and potentially polluting waterways.

Given the evidence, it’s hard not to dump on landfills. The United States spends about one billion dollars a year just to dispose of food waste. In landfills, that waste releases a medley of heat-trapping gases, including carbon dioxide and methane, and plenty of foul odors, too. Kitchen disposals, meanwhile, present an alternative to landfills for most food waste, shredding it so that it can pass through plumbing and be treated along with human waste in sewage treatment plants. (Grease and oil are the exceptions—they’re too likely to clog your pipes.) On the surface, kitchen disposals seem the next best thing to composting. They have potential to recycle nutrients, conserve energy and reduce global warming emissions. But not all waste systems are created equal. Many are already pushed to capacity, or only partially treat wastewater before releasing it to the environment. And though the “biosolids” they remove from wastewater can be composted, more often they are burned—wasting potential fertilizer and releasing greenhouse gasses into the atmosphere. Sewage treatment plants also generate methane, a greenhouse gas 21 times more potent than carbon dioxide. Advanced waste treatment plants harness methane for energy production, giving them an edge over even the best landfills.

In general, the kitchen sink trumps the trash in terms of climate impact and energy use. But kitchen disposals can have more negative impacts on surrounding waterways and they use a significant amount of water—approximately one gallon per person per day.

In the end, dealing with non-compostable waste depends on where you live. In areas where water is scarce, or where sewage treatment is insufficient, the trash is the most environmentally conscious choice for waste disposal. Otherwise, the kitchen sink is your best bet, especially if your local wastewater treatment plant harnesses the methane it generates. You may be able to find your local facility on this list, but it’s not comprehensive, so you may have to call your local authorities to be certain.

Whether you’re dealing with food scraps, or paper waste or anything else, “It is very important to know the rules of where you live, work and play,” says Stanford University’s Zero Waste Manager, Julie Muir. Even on campus, she points out, 30 percent of Stanford’s landfill-destined trash is food waste. “We can do better,” Muir says. 

You may not want to take on my habit of finishing other people’s scraps, but careful planning can allow you to recycle leftovers in other dishes. The best step, of course, is to produce less food waste to start with. There are plenty of tasty recipes that reduce food waste, as well as creative ideas for how to use waste you do generate. Bon appétit! Find details on reusing leftovers, and paper products best for composting in the Nitty Gritty answer.



GEORGIA GRIFFIN, '13, is an Earth Systems major.


Comments (3)

  • Mr. Ralf Owen III

    must Idispose of small amounts of grease and oil

    Posted by Mr. Ralf Owen III on Feb 16, 2012 4:26 PM

  • Ms. Georgia Griffin

    Mr. DeCasare,

    Thank you for your question. Disposing of grease by spreading very small amounts on your lawn may be alright, though there are better alternatives discussed below. Some people actually use kitchen grease to kill plants, so you are correct in suggesting that it is important that it doesn't get caught in runoff. According to Patrick Archie, Stanford's farm manager, it would be best to spread the grease in an area with perennial plants (shrubs or trees), burying it just beneath the O horizon (leaves and other organic debris that cover the soil) because this is a hotspot of microbial activity. If there is not much organic material, you can cover the soil surface with woodchips.

    Another option is to compost the grease. In general, composting kitchen grease is not recommended because it breaks down very slowly and can attract rats and other animals. Oil is mostly carbon, so it will eventually break down in a compost pile, especially if your compost is very hot (over 35 degrees F, typical of a "hot compost") and well-aerated (this is done manually). Learn more about hot composting here (

    The best practice may be to recycle kitchen oil as opposed to disposing of it, according to Archie. "Used vegetable oil is now so valuable as a fuel source that people are stealing it from behind restaurants," he says, citing a recent article in the Los Angeles News ( Many communities now have places to drop off used cooking oil. Here is a list from the San Francisco Public Utilities Commission (

    I hope this helps!

    Posted by Ms. Georgia Griffin on Feb 22, 2012 8:15 PM

  • Mr. Carl DeCesare

    I think it would be okay to dispose of small amounts of grease or oil in the middle of your lawn - the important factor is that it has a chance to soak into the soil where the microbes can do their work as opposed to getting caught in runoff and going down the storm drain - is this sound logic or just wishful thinking (because I do it) - Please let me know - Thanks!

    Posted by Mr. Carl DeCesare on Dec 8, 2011 7:07 PM


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