Are garbage disposals bad for the environment?

Illuminating answers to environmental questions.
Dec. 26 2008 7:38 AM

Should We Dispose of Disposals?

The best way to get rid of your leftover food.

In September, the Green Lantern examined the garbage disposal: Is it an environmentally sound way to get rid of leftover food? The piece is reprinted below.

I'm sorry to say I live in an apartment without a composter for organic waste. Given the circumstances, am I better off feeding my leftover mashed potatoes into the garbage disposal, so they don't end up in a landfill?  Or should I throw them in the trash can, so they don't end up the water supply?

Is a landfill the best place for food waste?
Is a landfill the best place for food waste?

For years, the great garbage-disposal wars have been going on without most of us even noticing. Cities like New York—along with many governments in Europe —banned disposals altogether, arguing that the added food waste would overtax the water-treatment system. (New York removed the ban for residential kitchens in 1997.) Meanwhile, the appliance manufacturers—along with homeowners and restaurants who prefer getting rid of food through the drain—have argued that the disposal is actually a green machine, reducing the amount of trash sent to landfills.

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It is true that with the major exception of grease and fats—which can block pipes and cause overflows—water-treatment systems are designed pretty well to handle most of the scraps you might have left over from dinner. The leftovers you shovel into the sink will eventually make their way to a wastewater plant, where the sewage goes through "grit treatment," which strains out the largest solid matter. (Sewage treatment is one of the few disciplines in which you can use words like grit, sludge, and scum as technical terms.) Whatever stuff gets separated from the water is either landfilled, condensed into fertilizer, or  digested by microorganisms.

Still, dumping waste into the water system has environmental costs. There is evidence that the effluent that is pumped back into local water streams does affect their chemical composition and aquatic life. In extreme cases, the result can be something calledeutrophication, which occurs when a higher concentration of nutrients results in algae blooms. According to one Australian study, the eutrophic impact of sending your food waste down the disposal is more than three times larger than sending it to the landfill. You'll also be using a lot more water if you decide to go with the disposal—and you'll be indirectly responsible for the extraction of the metal needed to make the appliance.

(A quick aside: As is often case with life-cycle analyses about consumer products, most studies on disposals are sponsored or requested by companies or groups with a financial interest in the results—like InSinkErator or the Plumbing-Heating-Cooling Contractors Association. This is often unavoidable: Getting good data on these devices often requires the cooperation of the companies that make them.)

On the other hand, it takes a considerable amount of energy to truck all that garbage from your curb to a landfill. (How much more will depend on where you live relative to the landfill, but average data compiled in both that Australian study and one conducted in Wisconsin  suggest a factor of two.) The decomposition of your trash in the landfill will likely result in more damaging greenhouse gas emissions, since the breakdown of your food waste may produce methane so quickly that it can't be captured. By contrast, some wastewater-treatment systems are actually looking for more food solids, since that will make the process of converting waste into energy more efficient. And wastewater-treatment plants also provide a way to reuse leftover food as fertilizer—although critics have expressed concerns that the use of biosolids on land land may not always be safe  (PDF).

The research is unambiguous about one point, though: Under normal circumstances, you should always compost if you can. Otherwise, go ahead and use your garbage disposal if the following conditions are met: First, make sure that your community isn't running low on water. (To check your local status, click here.) Don't put anything that is greasy or fatty in the disposal. And find out whether your local water-treatment plant captures methane to produce energy. If it doesn't—and your local landfill does—you may be better off tossing those mashed potatoes in the trash.

Is there an environmental quandary that's been keeping you up at night? Send it to ask.the.lantern@gmail.com, and check this space every Tuesday.

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