Andela/YouTube

Is there anything high-speed flexible impactors can't flail into gold?

Is there anything high-speed flexible impactors can't flail into gold? Not bloody likely, given the magic they're performing with garbage glass in Tennessee.

While you and your friends might sell beer bottles to acquire more beer, or use them to build wicked steampunk goggles, the Cumberland County Recycling Center is grinding them up to make cheap mulch and road salt. Wait: That's actually possible? Hell yeah, it is, and here's how it works.

Last year, the county, which is home to towns like Crab Orchard and Pleasant Hill, had to close its landfill. But rather than pay about $420,000 a month to haul its loads to another county, it purchased a ferocious, $93,793 glass grinder from the New York company Andela. (This saga is all recounted in Public Works Magazine, a must-read for fans of unusual municipal machines.) So now the recycling center just tosses its used bottles into the pulverizer's sucking maw, transforming weapons of bar brawlers into harmless dust and gravel.

This is where it gets interesting. According to PW's Victoria Sicaras:

So far, the recycling center is creating two different products. One is a sand material that can be mixed with road salt to treat icy roads. The county's highway department purchases the glass sand at $5/ton, which in turn allows the department to purchase less salt and cover more roads.

The second product is a larger 3/8-inch glass that the recycling center sells as landscaping material to the public for $30/ton. One customer uses the material for fish tanks and aquariums.

Selling a county's trash back to its residents: smart idea. Cumberland claims that the madly swinging hammers inside its Andela pulverizer has helped bump up its recycling revenue's from $240,000 to more than $400,000. That's a profit lump not to be scoffed at in these lean times.

Austin runs a similar glass-crushing operation, giving away free scoops of glittering glass for use as decorative mulch or drainage material. The aggregate's edges are rounded enough that you can walk on it without draining out like a punctured IV bag, and a slight percentage of paper and bottle caps lends the material an interesting visual quality. With a lifespan of 1,000-plus years, the glass won't decompose like regular mulch, and it has a grittiness that naturally repels slugs. (Or maybe it's the beer residue.)

Here's one Austin gardener's perspective on the silica slaw:

Although the glass has been tumbled in sand, there are still sharp edges. I hesitate to use it anywhere I’d have to weed and dig later (especially since I don’t wear gloves). I think in the future I will use it primarily in places I need to create good drainage.

The decorative glass mulch smells like a stale garbage can. A good rain should wash the scent and sand away....

How long do you think this will stay weed and leaf-free? At least when the revelers walking up from concerts at Auditorium Shores throw their beer bottles in my yard, it will blend in with the landscaping.

To sum up: Flails are awesome. Someday, they'll be building the glassy beaches of the future.

For interested parties, here's one of Andela's grinders:

Wait, no, that's not it. Here:

About the Author

John Metcalfe
John Metcalfe

John Metcalfe is CityLab’s Bay Area bureau chief, based in Oakland. His coverage focuses on climate change and the science of cities.

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