The Science of Sustainability

Food Scraps: An Urbanite’s Dilemma

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The view from the top of a kitchen compost bin.  In 2012, only 5% of the nearly 40 million tons of food waste generated in the United States was composted.  Photo credit: Ari Moore / Flickr

The view from the top of a kitchen compost bin. In 2012, only 5% of the nearly 40 million tons of food waste generated in the United States was composted. Photo credit: Ari Moore / Flickr

Back in college I went to visit my older sister in Austin, Texas, and she laughed when I asked about a compost bin. She grabbed my sleeve and led me out to the tiny balcony of her second-story apartment, then plucked the apple core from my palm and chucked it off the side of the building. “That’s my compost,” she said.

That scene has stayed with me. Over the years I’ve come to a greater appreciation for my sister’s reluctance to take on proper backyard composting while she juggled work and city life. Nowadays, I’m just not that motivated to compost. I know I should. But the reality is I don’t. And I am not alone in composting resistance: in 2012, only 5 percent of the nearly 40 million tons of food waste generated in the United States was composted.

Whether or not it makes sense to send food scraps down the garbage disposal really depends on your city’s infrastructure. If your city puts that organic waste to good use, then it may be better to send the scraps down the garbage disposal than to put it in the trash. Photo Credit: capl@washjeff.edu / Flickr

Whether or not it makes sense to send food scraps down the garbage disposal really depends on your city’s infrastructure. If your city puts that organic waste to good use, then it may be better to send the scraps down the garbage disposal than to put them in the trash.
Photo Credit: capl@washjeff.edu / Flickr

So what I wanted to figure out on behalf of all compost-challenged urbanites is what the next best option is for disposing of food scraps.

I called up Martin Heller, a researcher at the University of Michigan’s Center for Sustainable Systems, who specializes in life cycle analysis of food, to help me sort this out. If I’m standing at my kitchen sink with a handful of kale stems, I asked, should I toss them in the trash or grind them down the garbage disposal?

First, he reaffirmed that I should in fact be composting them for the most environmentally friendly disposal (yeah, yeah). Composting is best because it breaks down food scraps and returns their nutrients to the soil, which improves soil health. When those scraps are instead left to rot in the landfill (through anaerobic decomposition, which occurs in the absence of oxygen), they release methane, a potent greenhouse gas. According to Heller’s calculations, which will appear in a forthcoming publication, U.S. food waste in 2010 contributed roughly the same amount of greenhouse gas emissions to the atmosphere as 33 million cars on the road.

But if I’m not going to compost, should I bother with the disposal or just throw my food waste in the trash?

Here’s the short answer according to Heller: It’s probably a wash.

The long answer is that it really depends on your city’s infrastructure. If your city puts that organic waste to good use, then it may be better to send the scraps down the garbage disposal.

Some people advocate for cooking with food scraps, like onion skins.  This is a shot of the author's attempt at making a stock from food scraps.  It wasn't tasty.

Some people advocate for cooking with food scraps, like onion skins. This is a shot of the author's attempt at making a stock from food scraps. It wasn't tasty.

Here’s why: When you grind your carrot peels down the disposal, this carrot mash ends up in the same waste stream as city sewage. “Your food waste goes to the same place as the water you flush down your toilet,” said Michael Keleman, manager of environmental engineering at the garbage disposal company InSinkErator.

The wastewater treatment plant will separate out the solids, and this sludge, once treated and stabilized, is known as “biosolids.” Biosolids are handled differently in different locales, but about 60 percent of biosolids are put to beneficial use; the rest are either landfilled or incinerated. Beneficial use largely means that the biosolids are applied to agricultural land, forests, or urban parks. In this way the nutrients from the organic matter are returned to the soil, albeit with significant water and energy requirements to make that journey.

As far as greenhouse gas emissions, some wastewater treatment plants capture the gases released from the sludge as it is anaerobically digested. The methane from this “biogas” mixture can be used to produce heat and electricity. There are about 1,240 U.S. wastewater treatment plants that produce biogas, and about 270 of them provide electricity to the grid, according to data from the website biogasdata.org. This is out of a total of about 21,594 publicly owned U.S. wastewater treatment facilities.

If you want to find out whether your wastewater treatment plant produces biogas, check the searchable biogasdata.org database.

A cutaway view of an outdoor compost bin.   Photo Credit:  Bruce McAdam / Flickr

A cutaway view of an outdoor compost bin. Photo Credit: Bruce McAdam / Flickr

Some cities offer a middle ground in this dilemma: curbside composting. About 100 cities have compost collection programs, including San Francisco, Boulder, and Seattle. Data from the 2012 survey of municipal waste indicate there are more than 3,000 community composting programs in place across the country.

"It’s a doable thing," said Heller, comparing it to citywide recycling, which wasn't the norm during his childhood but is now standard in cities.

And it’s not just municipalities that are offering the service; entrepreneurs are, too. "We have a 12-year-old kid in Traverse City, Michigan, who has started up quite a little business collecting food scraps from folks on his bike,” he said. Even Cleveland will soon be home to a start-up composting company that will gladly cycle over to pick up your food scraps, for a fee.

According to Heller, taking a more upstream approach to food-waste reduction is fundamental to this discussion about consumer actions around food waste. That is, we need to get consumers to buy only the food they will actually eat. “From the cradle-to-grave perspective, the biggest impacts are on the food production side,” said Heller, so reducing consumer demand would help reduce the amount of food produced and thus the amount of environmental impacts all around.

Heller’s advice? Don’t “binge-shop.” Instead, go to the store more frequently so you don’t have food spoiling in your fridge.

So the next time that giant vat of raspberries calls to me from the produce aisle of Costco, perhaps I’ll think twice about whether I can really eat my way through all those berries without tuckering out. Either that or I suppose I’ll have to suck it up and compost.

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Category: Biology, Blog, Climate, Environment, Food

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Anne Glausser

About the Author ()

Anne Glausser is the Coordinating Producer for QUEST Ohio. Before taking on this role, she was WCPN 90.3 FM & WVIZ/PBS ideastream’s health reporter and produced award-winning radio pieces. She’s spent time on both coasts (her college mascot was the banana slug!), but grew up in the Midwest and is happy to be back home. She got started in radio at PRI’s Living on Earth, and has also spent time as a researcher at the Harvard School of Public Health. Anne got her SM from MIT’s Graduate Program in Science Writing.
  • Tim Evans Environment

    The unfortunate thing about food waste disposers is the name because actually they prepare the food waste so that it is suitable for conveying through the sewers to recycling at the wastewater treatment works. The extra carbon in the food waste helps reduce the nitrogen and phosphorus in the water reclaimed by the works and where the works has anaerobic digestion, it adds to the biogas (non fossil energy). When I analysed the environmental impact for a local authority in the UK, FWD and kerbside to AD came out equal first, better than kerbside to composting, or incineration or landfill (in that order). Home composting done properly is great, if you are willing and able to do it, but otherwise FWD is a good route to recycling.

  • Mar O

    It is of great concern to me that the solids extracted from the sludge of wastewater treatment are used in agriculture. Considering the chemicals in that sludge – things such as liquid plumber, antifreeze, bleach, pharmaceuticals, degreasers, toilet bowl cleaners, pest poisons ……. all the things no one knows what to do with and choose to flush. What happens to that chemical bath of junk?

    • Anne Glausser

      This is an important point to bring up. The manager from InSinkErator whom I spoke with said that much of the land application of wastewater sludge happens in the Midwest, whereas it is less prevalent in the western states.
      You can check out the treatment processes at your local wastewater treatment plant to find out what they can and can't filter out. Most aren't setup to filter out things like pharmaceuticals.
      If you want more information on the issue of sludge use in agriculture, here's a good recent article on it from Environmental Health News: bit.ly/1jy5sVG
      (Farm sludge contaminates soil with #prescriptiondrugs, other chemicals . By Brian Bienkow.)

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  • Eleanor Nelsen

    See, this is where the backyard chickens from your earlier story come in…that's how we "compost" most of our food scraps. It also provides entertainment. You're right that not everything makes delicious vegetable stock (I've never tried the squash bits that I see in there…), but we keep a bag in the freezer to collect the ends of onions, carrots, and celery, and just make stock when the bag is full, or when we have a chicken carcass to use…or when we run out of stock. Anyway, I enjoyed this article — I love how you used your own perspective, and turned everyday kitchen musings into a great story!

    • Anne Glausser

      Thanks, Eleanor. It's encouraging to hear that you successfully made stock from your food scraps–perhaps I'll have to give it another go, and be more selective about what I stick in there this time!

      • Eleanor Nelsen

        Parsley stems are good, too, and I usually throw in some peppercorns and a few whole cloves. We make pretty much all our stock (beef, chicken, vegetable) out of scraps, and it tastes fine :). Another useful thing is that you can freeze it in a variety of different-sized containers; I was always running across recipes that called for 3/4 of a cup of stock, which meant that I wasted the rest of the container, and felt guilty about it…and now I'm rambling about stock. Sorry.