New York's Sunset Park recycling facility has got a very pleasant visitor's center, which provides detailed information on how the plant functions, as well as some hands-on displays for students that lets them experiment a bit with mechanical separation. It's all very clean and appealing; Sims Municipal Recycling, which operates the facility, has done a nice job of sanitizing a very messy process.

One flight upstairs is a walkway that takes you to a viewing platform inside the recycling facility itself (technically the "Material Recovery Facility), and it's a completely different experience. The facility handles waste of various sorts on a massive scale, and the building literally shakes with activity, at the same time your senses are being assaulted with the sights, sounds, and smells of the activity it contains.

Pardon the shaky-cam, but the temperatures were below freezing and the building was vibrating.

Recyclable trash in the city—cans, bottles, plastic containers of all sorts—are required to be placed in transparent plastic bags (blue or clear only, please) and placed on the curb of every building. Picked up by same style of sanitation trucks that handle the refuse, 15,000 tons of that material is brought to the Sunset Park facility every month, either by truck or barge.

Once it's here, the refuse shifts from being a sanitation problem to being a materials science problem. The metals and plastics it contains are valuable only if they are above a certain degree of purity—steel without polycarbonates, polycarbonates without aluminum, and so on. (The visitor's center updates the price you can get for each of the materials it separates) It's possible for trained individuals to separate these different materials out by hand, but it's ferociously expensive and inefficient. The materials science problem, then, is how to separate out each individual component of the waste with minimal human involvement.

The process starts as the material arrives in bulk on sanitation trucks or by a larger truck that helps unload barges. That's dumped onto the floor of the facility, where inspectors remove large items—I saw one pulling out an intact child's bicycle. The rest is then taken by a large front loader and dumped onto a conveyor belt. This begins the process of spreading the recyclables out so that the system doesn't get swamped with more than it can handle. That's continued by a drop that scatters it further and splits it into two streams that are handled in parallel.

Because Europe took to recycling well before the US, the equipment to do this separation is mostly manufactured there; the Sunset Park facility uses equipment from a Dutch company called Bollegraaf. And the company has a finely tuned set of methods for pulling out different materials based on their properties. For example, tin cans are mostly steel, and a large rotating magnetic drum poised above the recycling stream plucks these items out. (This was buried too far inside the facility to see, but the visitor's center had video of it.)

John Timmer

John Timmer

John Timmer

John Timmer

John Timmer

John Timmer

John Timmer

John Timmer

John Timmer

John Timmer

John Timmer

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John Timmer

John Timmer

John Timmer

John Timmer

John Timmer

Glass typically comes to the facility pre-crushed by the trucks that carry it. But further equipment grinds it down to small fragments that then fall out of the stream. An area in front of the facility shows off the results: multicolor glass shards are used as decorative fill.

Plastics are formed from a variety of chemically-distinct polymers, as a sign in the visitor's center showed off: a plastic bag is not a soda bottle is not a detergent bottle. Here, Bollegraaf's equipment uses their chemical properties—they absorb different wavelengths of near-infrared light—to pull different types of plastic out of the general stream and into one dedicated to that material.

Human beings are involved in separating the waste stream, but only after the machinery has gotten it into a mostly pure state. They act more like inspectors, plucking out the relatively rare bit of material that's found its way into the wrong stream.

Once a stream is as pure as it's going to get, it gets dumped into a large container, similar to the ones used to collect construction waste. Each type of waste has several of these containers dedicated to it. When they reach a critical point, the ends of the dumpsters open and their contents are pushed out onto a large track. Since several dumpsters all need to empty at once, they open their doors in a synchronized series, laying out a steady flow of material onto the track.

The track ends by dumping it all into a compressor that squeezes it all down into a single rectangular block that was over a meter long on every side. Forklifts carried these to collections outside the facility floor (we saw large metallic cubes while leaving the facilities).

Overall, it's a fantastically impressive operation to visit. While being outdoors in sub-freezing temperatures didn't do much for my video capture, it did help with one issue: there was a distinctive aroma to the flow of trash moving through that I worry would be overpowering on a warm day.