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What happens to food scraps and yard waste

Learn what happens to your green bin waste after it gets picked up from your home or workplace.
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Residential and business compost programs are different

What’s allowed in residential curbside compost bins is different than what’s allowed in businesses’ bins. That’s because they're processed at different types of facilities. It’s important to follow the guidelines so each facility can make the best possible product.

Homes: Food and yard waste make compost

A woman pushes a green compost roll cart to the street from her house. Large rows of compost are shown being processed at a commercial compost facility: The rows of nearly finished compost are deep brown, and in the background are trees and hills of the surrounding area.

Residential compost collection is a mix of yard waste, food scraps, and some food-soiled paper. It’s processed at a commercial compost facility that produces nutrient-rich compost used by farmers and home gardeners.

How it works: Compost is laid out in large rows that are regularly mixed, or “turned.” These rows function like a bigger, hotter version of a backyard compost bin.

Why food and yard waste are allowed: Food waste is a rich source of nutrients that farmers and gardeners need for healthy crops. Yard waste, including leaves, branches, and flowers, provides additional nutrients, as well as a balanced mix of fiber, and wet and dry materials.

Limited non-food items are also allowed, including food-soiled paper towels and napkins, and pizza boxes. However, "compostable," "biodegradable," and "made from plants" packaging is not allowed (The only exception is BPI-certified compostable bags). 

Businesses: Food scraps make energy and fertilizer

A food service employee puts a bag of food scraps into a green waste bin marked "food only." The next photo shows an anaerobic digestion facility: a group of 6 large gray industrial buildings, 5 of them round, surrounded by farmland.

Business compost is food only – no flowers, yard waste, or paper products. Food scraps collected from businesses go to a few different places: Some are taken to a compost facility and others go to an anaerobic digestion facility that converts them into energy and fertilizer.

How it works: Food scraps sent to an anaerobic digestion facility are blended into a liquid and broken down by bacteria. The bacteria create methane, which is captured and turned into natural gas and electricity. What's left at the end of this process is a fertilizer that can be used to enrich soil and help plants grow.

Food is scraped into a bin labeled "food only," then a compost truck is shown picking up food waste, then an anaerobic digestion facility is shown (two round shaped buildings), and finally a light bulb (representing energy) and a small plant (representing soil enriching liquid fertilizer) are shown.

Why only food is allowed: Food is what the bacteria want to eat, so only food is useful. Other items are contaminants and have to be filtered out.

Benefits of composting

Reduces greenhouse gases

In a landfill, food decomposes and creates methane, which, when released in the atmosphere, worsens climate change. Methane is 25 times as potent as carbon dioxide at trapping heat in the atmosphere, so achieving significant reductions in methane emissions is critical for meeting our climate goals.

Additionally, when we send food and yard waste to the landfill, we're wasting a valuable resource that can be put to better use creating energy, compost, and other products that benefit our environment and economy.

Improves soil health

When the compost and liquid fertilizer made from Portland's food and yard waste is added to soil, improves soil health while reducing the need for chemical fertilizers.

It also helps the soil retain water, reducing the amount of water needed to help plants grow. As Professor Sally Brown from University of Washington explains:

“It’s like California Closets for your soil: Instead of just throwing everything on a heap on the floor, you put it in the appropriate units, and all of a sudden you have a lot more space. So water can soak in much more quickly. And also, there’s a lot more space for water to hang around, so this reduces your irrigation needs.” [source]

Healthy soil helps plants thrive and benefits microbes and plants that in turn sequester carbon from the air.

Where to get compost for your garden

Buy compost

You can buy compost created with yard and food waste from Portland homes from Recology Organics North Plains.

Make your own compost

If you want to make compost in your own backyard, follow these how-to guides and troubleshooting tips from Metro.

Backyard compost piles don't get as hot as commercial compost facilities do, so you'll still want to use your curbside compost bin for things like meat, fish, bread, and cheese (as well as larger branches). But backyard compost piles can turn fruit and vegetable trimmings, leaves, and grass clippings into great compost to use on your garden beds.