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.

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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.

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

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.

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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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Food Scraps: An Urbanite’s Dilemma