On Wednesday I went on a tour of the Casella recycling plant. Cambridge’s recycling director, Randi Mail, is hosting tours before the town switches over to single-stream recycling October 25. Casella is already handling single-stream loads from many towns in Massachusetts, including Boston. It was fascinating to see the elaborate sorting process.

First, giant piles of recyclables are dumped off the trucks and bulldozed onto a conveyer belt, which levels them out into more manageable amounts.

Then the mass of recyclables are spun around a tunnel with 1-inch holes in the sides. Centrifugal force holds lighter materials to the side while glass falls to the bottom and shatters, over and over again, until it can fall through the holes.

Heavier metals (pots & pans…) and rigid plastic (like laundry baskets) are pulled out by hand and dropped into chutes. More than 20 people are stationed at various spots on the line to hand sort, but 99% of their job is to pull out plastic bags before they can gum up the works.

A magnetic conveyer belt runs over the line to pull out metal. Since aluminum isn’t magnetic, a later spot in the line reverses the polarity of the aluminum to repel it over a barrier and onto another belt.

Paper and cardboard slides up rollers spaced at intervals. The paper glides over the top of the rollers, but heavier materials like plastics fall through. It’s amazing how well sorted everything is by the end of the line.

Eight sets of optical sensors ID different kinds of plastics and trigger jets of air to shoot them over a barrier onto another belt.

The end results are baled for transport. The system works remarkably well: the plant director told us that their buyers only allow 2% contamination of each material with another, so it has to be well sorted. Anything that didn’t get separated is run through the system again to capture as much as possible.

I expected the warehouse to stink, but it didn’t. I guess that’s a testament to how well people rinse their recyclables. But it was very noisy and very dusty. And hot! I guess an 80-degree day wasn’t the best for a tour.

Some take-aways for me:

• Plastic bags are death to the machines. The line is only running about 70% of the time, mostly because of plastic bags. So don’t toss them into recycling bins.
• Plastic smaller than 3 inches falls through and doesn’t get recycled. So bottle caps should always be put back on their bottles.
• Paper attached to glass gets thrown away, because tiny glass particles stick to it at the plant. So if you want to recycle it, pull it off at home.

If you’re interested in going on a tour yourself, Cambridge is hosting two more this year, on October 28 and November 18. To sign up, email recycle@cambridgema.gov or call 617-349-4815. If you can’t make the tour, you can also watch a video about single-stream recycling on Casella’s website.

For all the pictures, and larger versions of them, see the original article at the link below.

Cross-posted on pragmaticenvironmentalism.com