I live in a city that doesn't have composting facilities that ordinary citizens like myself could easily use. Although I recycle most of the plastic, metal, glass and paper I lay my hands on, getting rid of food scraps has always been a problem for me. While I do try to be as thoughtful as possible when I have time (turn orange peel into candy, use tea and coffee grains as colorants etc), most of the scraps will still go directly into trash. I know there are ways to compost at home, but I don't have enough dedication or room to do that.

How much damage are my actions causing to the environment compared to throwing away the same amount of unrecycled plastic, glass and metal? I always thought that since compostable things are not toxic and are of organic nature, they will fairly quickly decompose anyway and not cause significant environmental damage, regardless of whether they end up in landfill or are burned.

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    Welcome to sustainability.SE! Great question -- you might find info at this related question helpful: What is the most sustainable way to handle food waste…throwing food scraps into garbage or down my sink's garbage disposal? – LShaver Sep 24 '18 at 21:25
  • Where does your trash go = landfill, incinerator, separator? That makes a whole lot of difference. And note that the question refered in the comment assumes there is such a thing available as a 'sink garbage disposal', something that is not common outside of the US. And both of these remarks would be (partially) adressed if you also added your country. – Jan Doggen Sep 25 '18 at 7:40
  • @JanDoggen I live in Moscow and garbage goes primarily into landfill here to the best of my knowledge. There seems to be a push for switching to incineration, but most of the garbage ends up in landfill as of now. That said, I'd like to keep the question broad enough to cover all of the disposal methods you mentioned, hence the avoidance of the location tag. – undercat Sep 25 '18 at 18:17
  • Surely it depends on what your city does with sewage. Some cities compost it and then sell it back to the citizens. – Graham Chiu Sep 26 '18 at 19:16

Food that we eat is turned into the energy that keeps us alive. Food that we compost is turned into nutrients that keep plants and animals alive.

But food that we throw away is largely turned into methane that contributes to global warming.

This article from basmati.com explains the difference well:

A compost pile [...] is a train station full of living organisms; worms, snails, bugs and bacteria all munch away at the decomposing material. Moisture and air is allowed in and out, creating an aerobic environment that generates heat and releases carbon dioxide instead of toxic methane gas. The resulting compost can be used to fertilize young plants, start seeds, or offer an inviting place for worms to continue the process.

In contrast, many landfills (such as those in the U.S.) now utilize a "dry tomb" system (emphasis added):

The landfills are lined with geo-textiles and clay, creating a shield of sorts between the waste and the earth surrounding it. Landfill managers then fill with waste, compact it, cover each day’s material with earth, and finally “cap” the pile with another layer of clay and geo-textiles. Fluid run-off is collected and treated, lowering the moisture level of the “tombs.” Organic materials decompose, but in a very different, anaerobic environment that does not favor natural biological activity. Methane and other gases build up in this setting.

The article notes that since 1996, the U.S. Environmental Protection Agency requires large landfills to monitor methane emissions. Methane above specific concentrations must be disposed of -- either by flaring, or captured for use as an energy source. This practice is also seen in other countries around the world.

In summary, food that's sent to a landfill has a few options after it is decomposed into methane gas:

  1. Released into the atmosphere, where it is 34 times more potent than carbon dioxide as a greenhouse gas
  2. Flared (burned), causing CO2 emissions and a waste of energy
  3. Captured for use directly as biogas for heating or electricity generation -- the carbon content is still released to the atmosphere, but some of the energy is captured in the process

While waste-to-energy systems are far better than the first two options, if the main feedstock is wasted food, it is probably still worse than composting: burning methane puts carbon dioxide directly in the atmosphere, while composting puts at least a portion of it into the soil. In addition, food that's composted for use at home doesn't required energy expenditure for transport to a landfill, and offsets a portion of the demand for fertilizer.

And ultimately, in modern agricultural systems, the energy to produce food comes from oil, meaning that food waste is like pouring oil out on the ground. From Scientific American: Waste Land: Does the Large Amount of Food Discarded in the U.S. Take a Toll on the Environment?

[R]esearchers at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) concluded in a 2009 study that each year a quarter of U.S. water consumption and over 300 million barrels of oil (four percent of U.S. oil consumption) go into producing and distributing food that ultimately ends up in landfills.

What should we do instead?

First, limit food waste as much as possible:

Second, compost to the extent practical:

Finally, advocate! Exercise your rights to vote and participate in civic discourse to encourage your local municipality to either begin compost collection, or at a minimum to capture and convert landfill gas, if it's not being done already.

  • Most food grabs CO2 from the air. If it's converted to methane and then burnt back to CO2, isn't that carbon neutral? – Graham Chiu Sep 26 '18 at 19:11
  • @GrahamChiu that's a good point, however in addition to the carbon content of the food itself, there is the carbon content related to the energy required for that food's production and transportation. If less food is wasted, less of that "secondary" carbon is released to the atmosphere. – LShaver Sep 27 '18 at 14:04
  • Sure, but that also applies to anything that is called carbon neutral eg. Fire wood, pellets etc. That stuff needs to use carbon to prepare it, and transport it to the final point of use. And any food we do consume is turned into CO2 eventually. – Graham Chiu Sep 28 '18 at 21:13
  • @GrahamChiu the more I think about it, the more I see your point. I had assumed that always composting would be better than using waste food to generate biogas for energy, but now I'm not so sure. A good topic for another question! – LShaver Sep 28 '18 at 21:25
  • There is a question about composting vs biogas digester that might help expand here: sustainability.stackexchange.com/questions/6883/… – George of all trades Oct 9 '18 at 7:49

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