I look at the reasons for composting from two main angles:
- Prevents negative impacts of sending compostable waste to a landfill
- Provides positive benefits by enriching the soil
Aren't food scraps and yard waste biodegradable anyway - so won't it all just break down in the dump eventually?
The answer to this question is also twofold:
- Food and yard waste take up a lot of valuable space
- Decomposing organic matter releases a significant amount of methane
A larger issue, which I will explore later, is that so much food waste is generated in the first place. Between US consumers, retailers, and restaurants, an estimated 25%-50% of food is discarded. (Read more about food waste in these 2008 articles from CNN and The New York Times).
In my opinion, the most important leg of the "Reduce-Reuse-Recycle" mantra is the first: Reduce. If we all make an effort to be conscientious about how much waste is produced in the first place, we will have less composting, recycling, and disposing to worry about.
Nevertheless, most people don't eat banana peels and onion skins, so let's continue discussing how to deal with these materials. Organic waste takes up a great volume in landfills, which are a limited resource (I don't think it's a stretch to assume that the creation of more dumps would be an unsavory, non-ideal, not to mention unpopular solution). But perhaps even more far-reaching are the negative impacts of byproducts released during the decomposition of organic waste in landfills. Because food and yard waste become buried under other trash in landfills, there is little access to oxygen, and the organic waste rots anaerobically.
According to the EPA, "as yard wastes decompose in landfills, they generate methane gas and acidic leachate. Methane is a colorless, explosive greenhouse gas that is released as bacteria decompose organic materials in landfills."The significance, as the EPA explains, is that "methane (CH4) is a greenhouse gas that remains in the atmosphere for approximately 9-15 years. Methane is over 20 times more effective in trapping heat in the atmosphere than carbon dioxide (CO2)."
Regarding the scale of landfill-related methane, the EPA states: "Landfills are the largest human-related source of methane in the U.S., accounting for 34% of all methane emissions."
Furthermore, the EPA adds, "If methane is not controlled at a landfill, it can seep underground and into nearby buildings, where it has the potential to explode. Yard wastes also contribute acidity that can make other waste constituents more mobile and therefore more toxic."
In contrast, with conventional composting, air (oxygen) is one of the necessary ingredients. Little methane is released, with CO2 instead as the predominant gas released. Should we be worried about the CO2 generated from composting? Remember that when an equal volume of CO2 is released from waste that is composted instead of thrown in the trash, the atmospheric impact is only 5% of what it would have been at the dump.
The California EPA states that "CO2 emissions [as a result of composting] are considered "biogenic" by U.S. EPA and are not part of the overall GHG emissions inventory." Translation: the CO2 released by composting is considered part of a natural biological process, and not counted as a contributor of harmful man-made greenhouse-gas emissions. This isn't to say that composting does not emit greenhouse gases -the emissions are just categorized differently.
To read more on the emissions related to composting, here is a lighthearted post from the "Dear Abby" of environmentally-minded questions: "Global Worming: On Compost and Climate"
The first stage of Bokashi composting relies on an anaerobic environment inside an airtight container. According to a municipal government site in the UK, while "there are no exact statistics on methane production...the temperature reached in the [Bokashi] composting process is considerably less – 40ºC as opposed to 70ºC. This makes the methane emissions virtually negligible."