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4 Takeaways From Seattle's Composting Experience


The tiny plastic stickers found on almost every piece of fruit in a grocery store are not biodegradable and contaminate compost.

The tiny plastic stickers found on almost every piece of fruit in a grocery store are not biodegradable and contaminate compost.

Katie Campbell

SEATTLE — According to the Environmental Protection Agency, U.S. residents only compost about 3 percent of their food waste. But residential composting programs are springing up throughout the nation.

Most recently, Portland’s curbside-composting went citywide last fall. And Tacoma residents will start putting food scraps in their yard waste bins starting this spring.

But Seattle residents are composting veterans now. At Cedar Grove Composting, which is where Seattle’s food scraps go, 5 million tons of organic materials have been composted since they started in 1989. They began with green yard waste and added post consumer food waste in 2004.

Seeing more cities adopt curbside composting programs, we wanted to know: what lessons can be learned from folks who have had time to work out the kinks of residential composting?

We asked Tom Watson, who writes King County’s the EcoConsumer blog, and Cedar Grove Composting Spokeswoman Susan Thoman to share their curbside composting insights.

Here’s what they’ve learned:

1. Hold the Plastic

The biggest ongoing challenge of gathering compost-able material from hundreds of thousands of residents is making sure everyone is putting the right stuff into the compost bin and keeping the wrong stuff out. When the program first started, Watson said, residents were allowed to put scraps in paper milk cartons which could be tossed into the compost bin.

“But we found out that the milk cartons had a thin plastic liner and they weren’t breaking down well enough,” Watson said.

Thoman agreed, saying that people assume paper is compost-able, but if it’s plastic lined, it’s not. Now Seattle and King County residents are encouraged to use the method of lining a countertop container with a compost-able bag.

“Then you put all the food scraps in there and tie up and take it out,” Watson said. “It makes composting super easy.”

Compost-able compost bags look like plastic bags but they’re made from a bio-based material, usually corn. But Cedar Grove Composting had test various brands of compost-able bags in their processor because some bio-based bags break down better than others. After running the tests, they had to make sure the best brands of compost-able bags were available to buy locally. (Details on what bags to buy here.)

2. Avoid Contamination

“Our largest contaminate is recyclables,” Thoman said. Things like yogurt tubs, food wrappers, plastic take-out containers muck up the composting system. Even the tiny plastic stickers found on almost every piece of fruit in a grocery store have a cumulative affect, she said.

“We’re not a sorting facility,” Thoman said. “So what goes into the bin, goes into our process. That sticker on your organic fruit is not biodegradable. It doesn’t break down. Our operation isn’t made to pick out every sticker.”

Since plastic isn’t screened out, it gets chopped up with the rest of the compost material which is eventually packaged into compost that is sold back to consumers as lawn fertilizer.

“We can’t sell compost that has little bits of plastic in it,” Thoman said.

3. It Helps to Have a Marketplace

That bring us to the next important part of a successful composting system: Composting facilities must be able to create a product that has value and a market.

“Compost is not waste. It’s a raw material that gets turned into a product,” Watson said. “But composting facilities won’t need the raw material unless they can sell the product. They have to find buyers.”

Cedar Grove Composting blends their compost with sandy loams, creating soil blends that they sell to gardeners. They also sell to the construction market and to landscape design companies that are building green stormwater infrastructure like rain gardens.

“Unfortunately when economy declines, there’s less building and less purchasing of compost,” Thoman said. “The ebb and flow of the economy can be a challenge because what we’re making is pretty constant.”

And if the compost starts piling up because it isn’t selling fast enough, that becomes a problem.

“It’s a constant concern,” Watson said.

4. Residents Must Buy In

Watson and Thoman agreed that the biggest key to a successful composting program is cooperation from residents. And on that front, they say they’ve been very lucky.

“People here have really embraced composting,” Watson said.

For the most part, Thoman said, people are happy to be able to compost food scraps. She admitted that there are always a few people who don’t like being told what to do with their garbage.

“Composting is a privilege and people here treat it like a privilege,” she said. “When people come here from the East Coast they are so jealous. They have bin envy.”

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