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 residential food and yard waste are processed at a different type of facility than businesses’ food waste. It’s important to follow the guidelines so each facility can make the best possible product .
Homes: Food and yard waste make compost
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.
Businesses: Food scraps make fuel and fertilizer
Business compost is food only – no flowers, yard waste, or paper products. It’s taken to an anaerobic digestion facility that converts it into liquid fertilizer for crops and energy to power homes, businesses, and vehicles.
How it works: Food scraps are sent to an anaerobic digestion facility where they’re blended into a liquid and broken down by bacteria. The bacteria create methane, which is captured and burned to make electricity, as well as liquid natural gas (LNG) to fuel vehicles. It also creates a liquid fertilizer that enriches soil and helps plants grow.
Note: Food scraps from businesses are sometimes sent to a commercial compost facility, in cases where an anaerobic digestion facility isn’t available.
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 keeping food out of the landfill
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.
Benefits of improving 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.