Zero is a good number when it comes to sustainability. Zero emissions. Net-zero energy buildings. And of course, zero waste. Zero waste is radical. It’s attainable. It’s good business. And it’s cool.

I’ve been excited by the idea of zero waste ever since I wrote a FORTUNE story called “The End of Garbage” in 2007. As the architect and designer Bill McDonough likes to say: “We’re not talking here about eliminating waste. We’re talking about eliminating the entire concept of waste.” Companies get excited, too. General Motors, Walmart, Procter & Gamble, Albertson’s, and SuperValu are all driving toward zero waste, as GreenBiz reported last year.

But how does a company eliminate waste? That’s what I wanted to know when I heard that DuPont’s buildings division had gone from sending 81 million pounds of waste to landfill in 2008 to zero in 2012.

Crushed corian—garbage or not?

To find out, I arranged to speak with Dave Walter, a DuPont exec who led the zero waste effort. Walter, who is 52, has held 19 different jobs during his 29 years with DuPont. His current job is North American Strategic Product Manager for DuPont Building Innovations (who makes up these titles?), which basically means that he takes on a variety of projects for the company’s building products unit. Educated as a chemist and computer scientist, Walter is a Black Belt in Six Sigma, a set of management practices developed by Motorola during the 1980s and later popularized by GE.

The first thing Walter did, logically enough, was analyze what was being thrown away. “We had a pretty good feel for what was going to landfill, but we didn’t know all the components,” he told me. This required tracking waste at 15 global manufacturing sites, some owned by DuPont, some by partners. The buildings division’s major products are Corian solid surfaces, Zodiaq quartz surfaces, Tyvek weatherization systems products, and landscaping products known as geosynthetic textiles. Waste included unusable raw materials, product scrap, construction debris, and even half-eaten cafeteria food. “Zero means zero,” says Walter.

The fundamental question facing Walter and his colleagues was: What’s the highest best use for stuff that was being carted to landfills?

Some answers came fairly quickly. Pieces of Corian trim (seen in the photo above) are lightweight, and they percolate water well. “We found that we could crush it up, make it into gravel, and sell it as landscape stone,” says Walter.

Leftover bits of Tyvek, the company learned, could be shredded and made into new Tyvek, with no decline in the quality of the insulation. It’s surprising that no one had realized that before.

Cafeteria waste was “a tough one” at first, Walter says, but it is now being turned into worm bedding, which is sold to bait stores, fishermen, and gardeners.

Waste that can’t be made into anything else is burned for energy.

It sounds simple in retrospect, but the project took three years to complete, in part because it required DuPont to find new markets and distributors.

The biggest surprise? “There was a belief that it was going to cost us money,” says Walter. “People were quite pleasantly surprised when it didn’t.” To the contrary, DuPont generates a small stream of revenue—the company wouldn’t say how much—from its waste and avoids the costs of landfill disposal, which begin at about $10–15 a ton and go up from there.

The impetus for what DuPont calls its Drive to Zero wasn’t money, it turns out. Instead, the project grew out of the company’s annual sustainability reviews led by Linda Fisher, a former EPA executive who has been DuPont’s chief sustainability officer since 2004. These reviews spotlight risks or opportunities arising from environmental issues, Fisher told me. “The landfilling issue for the building materials business, and particularly Corian, had been talked about for years,” she says. “Waste became an opportunity.”

Now DuPont is looking to see if other business units can get rid of their waste, she says. Waste, after all, costs the company twice–first when it buys the stuff that goes into it, and then when it pays to have it trucked away. That can’t be a good business.