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Seattle is a leader in municipal composting, but here’s what we have to do to get it right  

Composting is serious business in Seattle, and collectively we do as good or a better job at it than any other city in the United States. While we can all take pride in that, we have a lot more work to do to reach the climate and zero waste goals that drive our composting program.  

Why Compost?  

Composting is nature’s way of recycling organic waste like food scraps, yard waste, and greasy napkins; organics make up almost half of all the waste created by Seattleites each year. Composting organic waste is one of the most powerful things we can do to simultaneously reduce what we send to the landfill and our climate impacts. When food and yard waste ends up in a landfill, they decompose anaerobically (without oxygen), and the organic matter gets converted to methane, a greenhouse gas 28 times more powerful than carbon dioxide. When these materials get composted, however, they decompose in an aerobic/oxygenated environment, which means the organic matter gets converted to carbon dioxide, the same form it was removed from the atmosphere during plant growth via photosynthesis. The emissions from composting are therefore considered carbon neutral.     

Two hands cradling compost and showing off the compost to the camera. 

Additionally, when we add this carbon-rich compost to soil it further helps us to reduce our climate impacts by storing carbon in the soil as “soil organic matter.” Soil is one of the primary places where carbon is stored on Earth, holding more than all the carbon in the atmosphere and biosphere (all living organisms) combined.  

Using finished compost to enhance our gardens, landscapes, and regional farms not only creates a market for this recycled organic matter, but also builds healthy soil. Healthy soil effectively soaks up rainfall, which reduces stormwater runoff and the need for irrigation water in the summer months. Compost-amended soil is also able to bind and break down some pollutants found in stormwater and prevent them from entering our lakes, wetlands, streams, and rivers. 

The photo is of a green stormwater infrastructure, that is between a street and sidewalk. This infrastructure has a bioretention system, so it has landscaping that is designed to filter pollutants from entering the waterways. The landscaping includes grasses, shrubs of different colors, and soils.
Compost amended soil is used to treat stormwater runoff in bioretention systems.

Where Can We Do Better? 

Young Asian appearing woman who is holding a full kitchen compost bin over their compsot cart, ready to toss.

We need to put ALL our food and yard waste in our compost bins rather than the garbage. Despite universal access to composting services in Seattle (and a legal ban on putting organics in the garbage), collectively we are only diverting about one-third of our food waste. The other two-thirds is going to the landfill, where it is creating methane gas and contributing to climate pollution.  

A photo that focuses on a full BioBag, this is a green compostable bag that is used to line kitchen compost bins for households to put their food scraps in until they’re ready to toss it in their compost cart. The bag is held at the top by an outstrechted arm form the right, the arm has a light skin tone.

Even worse, nearly half of the organic material going to the landfill is estimated to be wasted food that theoretically could have been eaten. This wasted food represents a waste of multiple resources including food for those who need it, agricultural land, water, pesticides, fertilizers, packaging, and energy, all with significant environmental impacts. SPU is working hard to find ways to reduce edible food waste and to get the remaining organics out of the landfill. At home, we can all do our part to waste less food by doing things like storing food in ways to help it stay fresh longer, and then putting all the scraps in the compost bin, not the garbage. Certified compostable bags can help make it easier to collect and compost food scraps.  

A diagram from the Environmental Protection Agency. The title of the digram reads, “Environmental Impacts of U.S. food Waste: What resources go into a year of food loss and waste in the U.S.” There are four boxes with an accompanying icon. The first reads, “Greenhouse gas emissions of more than 42 coal-fire power plants.” The second reads, “Enough water and energy to supply more than 50 million homes.” The third reads, “The amount of fertilizer used in the U.S. to grow all plant-based foods for U.S. human consupmtion.” The last reads, “An area of agricultural land equal to California and New York.”
Image Courtesy of EPA
Brown, compostable take-out container that is lying on its side to show “Compostable Label” printed on the bottom of the container.
To verify that a product is compostable, look for the word “Compostable” printed on the item along with a certification mark. This product is showing certification marks from both BPI and the Compost Manufacturing Alliance.

We need to reduce our contamination of compost. Plastics and other non-compostable materials that get placed in the compost cart are likely to contaminate the finished product used in gardens, roadside landscapes, and local farms, which in turn leads to litter in the landscape. Once everything in the food and yard waste cart mixes together, it’s nearly impossible to pick out the contamination. Removing fruit stickers, twist ties, and rubber bands from fresh produce, and only including compostable food service ware that you are 100% sure is compostable because you can see that it is certified compostable, can keep this system working.  

Unless you can see a compostable certification mark, do not put the item in the food and yard waste cart. Also, no matter what the packaging says, pet waste and diapers NEVER belong in the Seattle compost system, as our system is not designed or permitted to handle those materials.  

Seattle Public Utilities would like to acknowledge and thank our long-time compost partners, LENZ Enterprises and Cedar Grove Composting who compost the collected food and yard waste from the City of Seattle. Without them, this program would not be possible.