Nearly half of the solid waste produced globally is organic or biodegradable. Much of it ends up in landfills; there, it decomposes in the absence of oxygen and produces the greenhouse gas methane, which is up to 34 times more powerful than carbon dioxide over a century. While many landfills have some form of methane management, it is far more effective to divert organic waste to composting.
Composting ranges in scale from backyard bins to industrial operations. The basic process is the same: ensuring sufficient moisture, air, and heat for soil microbes (bacteria, protozoa, and fungi) to feast on organic material. Rather than generating methane, the composting process converts organic material into stable soil carbon, while retaining water and nutrients of the original waste matter. The result is carbon sequestration as well as production of a valuable fertilizer.
Human beings have long used compost to feed gardens and fields. Today, it is especially useful for managing growing urban waste streams. In 2009, San Francisco passed an ordinance that makes composting the city’s food waste mandatory. Copenhagen, Denmark, has not sent organic waste to landfill in more than twenty-five years, reaping compost’s win-win-win of cost savings, fertilizer production, and reduced emissions.
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