Have you ever wondered whether your milk carton caps can be recycled? Or what happens to your recycling after it gets picked up from your curb? Science Friday video producer Luke Groskin decided to explore the mysteries of recycling further. He visited a recycling facility in Brooklyn and came back to report on it.

According to Groskin, the inside of a recycling facility looks like it might look like if you were “inside the digestive track of a robot that eats recyclables. It's really really mechanized.”

And the smell? 

“It was musky,” Groskin says, “but mostly the overriding smell, the smell that pervaded everything, was the three-day-old beer smell.” 

Darby Hoover from the Natural Resources Defense Council says the US falls somewhere in the middle of developed countries in terms of how well it does at recycling. 

“In the US we're recycling about 34.3 percent of what we throw away at the municipal level,” Hoover says. “We're not doing that well. We're recycling about a third of what we dispose of. That puts us about halfway in between other developed countries. In Europe you've got countries that are doing much better — over 60 percent. Some of the rest of the world is doing a little bit worse, we’re right about in the middle worldwide.”

When it comes to specific questions about what can and cannot be recycled, Hoover says the answers vary depending on where you live. 

"Anything that we talk about being recyclable or not recyclable has to be caveated by saying you should go to the website of your local city government and check to see what is accepted for recycling in your community and how they like to prepare it,” she says.

1. When it comes to greasy pizza boxes, though, there’s a pretty widely accepted rule-of-thumb. 

“For the most part, communities don't want pizza boxes in the recycling. If you've got paper that has grease or oils in it, that can complicate the paper recycling process. It's hard to remove the oils from the fibers, so for the most part you can't put those pizza boxes in with your other paper recycling.”

2. Some people wonder what the numbers surrounded by a triangle of arrows that are printed on plastics mean. Hoover says it’s a system that may or may not be helpful in in trying to determine whether or not a certain material can be recycled. 

“You'll see it on the bottom of almost every plastic container. ... Most people look at that and think, ‘Well, that means it's recyclable.’ It doesn’t,” Hoover says. “All it does is tell you what type of plastic it is. It’s there to just help identify the polymer but it's not something that for the most part can tell you if it's actually recyclable in your community or not.”

3. For those who might be agonizing over how much they need to fully rinse out or scrub their recyclables, Hoover says not to worry. 

“You're going to not be surprised that I'm going to say the answer varies from community to community,” Hoover says. “You want to get it as empty as you can, practically speaking. If you can use a little excess dishwater to shake it up and get it a little bit cleaner, that's great. You don't have to have it be sparkling clean. The issue is less usually with contaminating that container itself and more about having that food or that beverage that's in the container transferred to paper and other materials in the recycling bin that then become contaminated.”

Recycled material doesn’t just end up at recycling facilities, however. Hoover says the recycling facility is just the first stop for recycled materials. After the plastics, papers and glass get sorted, they’re then loaded onto trucks to be sold and shipped to others who will further wash them, clean them, break them down and turn them into new products. 

“A lot of our plastic recycling does get shipped overseas to China and other countries,” Hoover says. “That's part of a global market for recycling and that's true for many of our materials. Wastepaper is one of our largest exports from the US.”

This article is based on an interview that aired on PRI's Science Friday.

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