Let’s be clear about one thing: Thanksgiving leftovers belong in the fridge (and in your mouth, later on). Thanksgiving food scraps – plate scrapings, onion peels, turkey bones, etc. – are another matter.
In Portland this year, Thanksgiving food scraps that would otherwise go in the trash or a backyard compost heap can go into the yard waste bin for curbside pickup. Portland is the 24th city in the country to launch a curbside composting program to reduce trash going to landfills.
That means residents don’t have to turn their own compost piles to recycle their food waste. They can compost the easy way – by letting the professionals do it.
A couple weeks ago, I got to follow the city’s curbside food scraps to the Metro transfer facility and onto Recology’s Nature’s Needs commercial composting facility in North Plains.
That’s where a large portion of Portland’s curbside food scraps end up – and where I imagine a decent helping of the city’s Thanksgiving scraps are headed. Here’s what happens when they get there:
First stop: The transfer station
Food scraps and yard waste from all over the city get dumped into a pile inside an aluminum-sided building in North Portland – aka the Metro Central transfer station. Here, the pile gets picked through for non-compostable items, chopped up and mixed with yard waste. Yes, the whole place smells quite ripe.
The rest of the transfer facility sorts piles of recyclable paper, metal and plastic. Seagulls circle around the far end, where the food scraps go.
“Once it comes in we’ve got to get it out quick or else we see our little friends all the time,” said James Waterman, operations supervisor for Recology Oregon.
A 50-50 mix of food to yard waste
Recology adds enough yard waste to the food scraps to make a 50-50 mix before it gets shipped off to the composting facility.
“We do the process here so they don’t need to,” Waterman said. “It keeps the smell down and keeps the liquids from leaking everywhere.”
It also means residents don’t have to worry about mixing food scraps into yard waste while it’s in the pick-up bin, he said:
“Just make a hole and dump it in.”
Next stop: The compost heap
We can see the steaming piles as soon as we pull in the Nature’s Needs driveway.
“This is the end of the line for that material,” said our new tour guide Jon Thomas, operations manager for Recology’s Nature’s Needs commercial composting facility.
Trucks dump the 50-50 mixture here in North Plains, where it is pitchforked and mixed some more to get it to the right density for composting.
Thomas shared “the recipe for compost” that will turn it into rich fertilizer in 14 to 28 days – faster than a backyard compost heap can do it.
“It’s a simple process,” Thomas said. “We just fast-forward through it.”
Key point: Let it get hot – but don’t let it catch on fire
Recology adds wood chips to the pile and covers it with a tarp in the first “zone.” The pile is stirred with an excavator to distribute moisture and heat produced by the critters eating the material.
Then it goes to the next zone, where it is lumped into wind rows on top of a fan system that pulls air through the pile and into a biofilter that reduces odors.
All along, the company is checking the temperature of the piles with a giant thermometer to make sure they get hot – but not too hot.
To kill harmful bacteria, the pile needs to reach 145 degrees for 15 days in a row. But food compost – more so than yard waste – can get so hot that it catches fire.
Screening out “contamination”
After the waste has been broken down, the piles are filtered through a screen to pull out any leftover non-compostable materials (also called contaminants). Then the compost is loaded onto trucks and shipped off to customers, many of whom are farmers in eastern Oregon or vineyards in Willamette Valley.
One thing I didn’t know before this tour was that compostable plasticware comes in different varieties that break down at different rates. Some take 90 days, some take 120, and some take even longer.
The screening process will catch any materials that haven’t broken down in the first 45-day cycle.
Our tour group had a lot of questions about this composting process. Here are a few of my favorites:
- Does adding food to the compost create rat problems? No, said Thomas. “We don’t have a problem because of all the turbulence. There are a lot of things moving simultaneously. Rats want to build a home.”
- How much material will the curbside food composting add to the mix? Thomas said his facility was getting 24,000 tons of waste before the composting program; managers are expecting that total to double with food scraps in the mix. But only time will tell for sure.
- Why can’t you compost dog poop? Dog and cat poop are not like “zoo doo” from vegetarian animals; poop from omnivorous animals carries different bacteria and doesn’t break down the same way that cow and horse poop does.
- Is compost with food waste better than yard waste only compost? Indeed, Thomas said, it is richer in nutrients and better for growing certain plants. But it depends on what you want to grow.