Dirty Work

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Commercial Composting


To get to Recology Organics in North Plains, Oregon, head 18 miles northwest of Portland and look for the steam: big, fluffy, white clouds of it, wreathing small mountains of decomposing apple cores and raked-up leaves, like smoke emanating from a smoldering volcano. “It’s especially fun when it snows,” laughs Nick Olheiser, organics manager at Recology Organics. “Everything’s white except for the compost rows.”

A healthy compost pile is about as hot as a latte, and walking between the 26 rows of actively decomposing compost at Recology on a cool morning is a bit like entering a lukewarm, highly fragrant sauna, fueled by the discarded scraps of thousands of Portland homes.

North Plains is the largest of Recology’s three Oregon facilities. It processes 55,000 tons of compost a year, 90% of which comes from the city of Portland’s residential curbside compost program. If you live in Portland, the odds are good that somebody at Recology has shoveled, ground, hauled, aerated, and sifted your kitchen scraps and yard waste, transforming them from an environmental liability into a valuable resource.

How did we get here?

Portland started accepting residential food scraps in the green yard-waste bin almost six years ago, on Halloween of 2011. It took a little getting used to, but aside from a few grumbles during the first year, Portlanders have largely come to embrace the program. Today, 90% of us are putting our food scraps in the green bin, and the city collected more than 100,000 tons of green waste last year from homes and businesses. “We thought we would have to tell people why you need to compost, but Portlanders are already on board,” says Arianne Sperry, Portland Recycles! coordinator. “We garden, we’re foodies, and we want to put these nutrients back in the soil.”

That’s good news. In landfills, organic waste decomposes anaerobically, which generates methane, one of the most powerful greenhouse gasses. And Americans generate a lot of organic waste. “The amount of food we’re wasting as consumers is huge,” says Arianne. “It’s like we bought four bags of groceries and then left one in the parking lot and drove home with three.”

While composting has become a point of pride for some Portlanders, for many of us, our understanding of what actually happens to that green waste is a little fuzzy. Composting starts at home, but the trip from your kitchen to the curb is just the first step that your grape stems and cucumber peels take in their long journey towards a new life.

What happens to your food scraps?

Portland’s curbside food scraps–composting program is a product of local government, but it relies on an extensive network of private contractors to make it work. Residential waste is picked up by one of 30 independent haulers who contract with the city to provide waste-management services. Haulers are assigned residential accounts in blocks (which is why the same hauler that picks up your garbage likely picks up your neighbors’), while commercial accounts can contract with any hauler they desire.

Once they’re in the truck, food scraps and yard waste make their way to a central transfer station operated by Metro (the regional government encompassing Multnomah, Clackamas, and Washington counties), where they’re consolidated with waste from other haulers. Then, green waste is loaded into a 45-foot semi fitted with a belt trailer (a container truck with a conveyor belt in the floor) and transported to one of several commercial composting facilities.

Trucks routed to the North Plains Recology site unload their green waste into one of 13 high-air beds, which are specially fitted, open-air, concrete pads equipped with four ducts running the length of the bed. Each bed contains eight to nine trailer loads of green waste. The ducts suck air in, pulling oxygenated air through the piles and capturing the sometimes-pungent aromas that come from decomposing organic matter, then passing the air through a biofilter to minimize the olfactory impact on Recology’s neighbors.

Green waste spends about 15 days on the high-air bed, where it’s regularly turned, as well as monitored for moisture, temperature, and oxygen levels. Then it’s time for the “flop” — a transfer to a low-air bed by way of an industrial grinder, which pulverizes the waste into a mulch-like consistency. Low-air beds pull a little less air through the compost than high-air beds, since the most active (read: stinky) part of the decomposition process has already passed.

And for all the talk about the smell of compost, the aroma at Recology is actually quite pleasant, in the same way that the aroma of a horse barn can be pleasant. It’s earthy, woodsy, a little sweet, and a little funky — just like turning over a shovelful of soil in a garden.

There are a lot of variables when it comes to compost, and the workers at Recology fine-tune their processes based on the weather, the kind of waste they’re getting, and even the time of year. Recology’s goal is to maintain piles with an internal temperature around 145 degrees Fahrenheit and moisture content between 40% and 60%. If the piles get too hot or too dry, the microbes could die, putting a stop to the composting process. There’s even a danger that the piles could spontaneously combust.

By the time 15 days pass on the low-air bed, the material is starting to look a lot more like compost. It’s hard to pick out individual components, and the larger pieces are continuing to break down into smaller chunks.

That means it’s time for the compost to cure, a 30-day process that allows the pile to finish its microbial transformation. An important step in the curing process is a three-day span where the pile isn’t turned at all, raising the temperature even higher and flirting with anaerobic conditions to kill any potentially dangerous pathogens, like E. coli and fecal coliform bacteria. The curing piles of compost are so warm that foxes sleep in them at night, and geese lay their eggs on their fragrant peaks.

Cured compost is chocolate-brown and smells great, just like a freshly mulched garden. But it’s still a bit chunky, especially if it had big, woody components in it, like stumps or large branches. So the final step is a pass through a 3/8” mesh screener. Particles small enough to fall through are the finished compost, ready for the final quality-control check, which includes a “cucumber seed test,” where workers plant 100 cucumber seeds in the compost and check for high germination rates to ensure against contamination with herbicides.

The bits that are still too big to fit through the mesh screen go back to the high-air beds for another 60-day trip through the system. A lot of those particles are biodegradable plastics, which are much more work to process than you might hope.

“The dirty secret is it takes 110 to 120 days for degradation of plastics to start,” says Nick. “Plastics fight us through the entire system. It’s a problem for us and for every commercial composter.” That’s why biodegradable plastics are no longer accepted in Portland. Paper towels and pizza boxes, however, are still welcome in the residential bins.

Finally, the finished compost is sold to farms, landscapers, wholesalers, and individual consumers — and business is booming. “I can’t make enough compost,” says Nick. “I’m selling it as quick as it comes off the belt. The market has changed a lot in the past two or three years. Adding residential food waste was a scare for buyers. They thought it would be gross and stinky. But actually, it’s better. The nutrient levels have gone up, the C/N [carbon to nitrogen] ratio is more balanced, and the phosphate and potassium levels are better.”

Now What?

Six years in, Portland’s curbside compost program has been, by all measures, a success. Portland gathers about 105,000 tons of green waste each year from commercial and residential accounts, and Portlanders have reduced their trash volume by a third.

However, there’s a lot more to be done. Arianne estimates that about half of all residential food scraps still end up in the trash, a rate that must improve if the city is to reach its goal of diverting 90% of food waste from the landfill by 2030. The city is currently wrestling with how to extend composting to multifamily housing, a thorny issue growing bigger with every new development. In Portland, any multi-family building with more than four units qualifies as commercial, which means it doesn’t get yard waste service by default. Building owners have to opt in — typically for an additional fee — and complications around collections are more prevalent.

“There are a lot of different types of buildings,” explains Arianne, “with different collection systems. Is the janitorial service taking carts from each floor downstairs? Do residents need to take it downstairs to a dumpster? How convenient is it to throw away garbage versus recycle and compost? Is there a chute? Does it work for recycling or food scraps? This is the big nut to crack. New York, Vancouver B.C., Seattle, San Francisco — they’re all trying to figure this out.”

That’s not to say multifamily communities can’t compost — many do — only that it takes some advocacy on the part of the residents. Arianne says residents should talk to their property manager about adding the service with their hauler. Then, be prepared to help your neighbors figure out the new process and get excited about changing their habits.

When Portland first instituted curbside composting, there were few role models. Seattle and San Francisco served as regional inspirations, but in the rest of the country, few other cities were embarking on similar projects. Over the past six years, that has changed dramatically. “It’s a big movement across the country,” says Arianne. “I field calls from other jurisdictions all the time. A lot of progressive cities and states are saying that food scraps are the new frontier.” That means less methane in the atmosphere, less material in our landfills, and for commercial composters like Recology, a delightfully dirty future ahead.

Margarett Waterbury is a food and drink writer based in Portland, Oregon, and the managing editor of Edible Portland. margarettwaterbury.com

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