Walmart and one of its supplier are turning plastic bags, bottles, cardboard and hangars into beds for dogs and litter boxes for cats, along with other eco-friendly pet products.

This is the latest example of what's called "cradle to cradle" design -- although the cradle in question here turns out to be a PoochPlanet Dog Bed, made from recycled plastic bottles.

"We're committed to creating zero waste," explains John Kunkel, senior buyer, pets for Walmart. One way to get there is to take things that Walmart throws away and instead of sending them to a landfill, make them into something useful.

Worldwise, a privately held pet products company based in San Rafael, CA, is supplying the eco-friendly gear to Walmart, the companies said yesterday. Besides the PoochPlanet beds, they include SmartyKat Cat Scratchers (made from recycled cardboard) and the SmartyKat Litter Accessories like the SmartyKat Litter LooLadle (made from recycled plastic hangars).

Worldwise has been a supplier to Walmart since 1996, when the giant retailer began selling its SuperScratcher, a cat scratcher made from corrugated cardboard and organic catnip. Aaron Lamstein, the company's co-founder and executive chairman, told me, "We're the No. 1 supplier of certified organic catnip in the United States."

(It never occurred to me that there was such a thing as certified organic catnip. As one of my high school teachers liked to say, you learn something new every day.)

Now, there's something silly and something serious about this latest initiative from Walmart.

It's silly because anyone who is committed to environmental responsibility would think long and hard about owning a cat or dog. To the best of my knowledge, no one has calculated the carbon impact of pets but it is clearly not trivial in the aggregate. A 2007 survey by the American Veterinary Medicine Association says Americans own are 72 million dogs, 82 million cats, 11 million pet birds and 7 million horses. You'll get a lot of arguments about this topic -- particularly if you write a book called Time to Eat the Dog: The Real Guide to Sustainable Living -- but pets obviously eat and poop**, two activities with undeniable impacts on greenhouse gas emissions, land use, stocks of fish in the ocean and the like. Of course, as a former owner of a dog (a golden retriever name Sophie, may she rest in peace), I'm well aware of the benefits that owning a pet can bring.

But it's serious because efforts like this point the way to a more sustainable economy. One way to limit our use of oil and other raw materials is to figure out ways to turn garbage into commodities that can be reused, as Walmart and Worldwise are doing. (Here's another example: Walmart is turning its food waste into compost in central Indiana, according to Indiana Living Green.) Without demand for recycled materials, the economics of recycling doesn't work. But creating these "closed loop" systems that turn one man's trash into another's treasure is no easy feat, as Walmart's Kunkel and Worldwise's Lamstein explained to me.

Kunkel said the effort took more than a year and had to be coordinated with "seven or eight different divisions of the company." After Walmart's waste is baled, it is separated into its components at MRFs (materials recycling facilities) and the cardboard, bottles, hangars and plastic bags trucked to Worldwise's manufacturing plants. The products that result are then shipped to distribution centers and to all of Walmart's U.S. stores.

"We've had to create a playbook," Kunkel said. "Now other manufacturers can implement a closed loop in their business."

Lamstein said he brought the idea for what he's calling Full Circle products to Walmart after being invited to one of the retailer's sustainability summits by former CEO Lee Scott. Many products that Worldwise makes are manufactured in China, he said -- the firm has several offices there -- but the nine products that are part of the Full Circle program are made in North America.

One problem: It's hard to know just what environmental benefits, if any, these products deliver, when compared to plastic or oil-based pet products, because neither Worldwise nor Walmart has done a Life Cycle Assessment to find out.

Then again, a product like the SuperScratcher that keeps a cat from destroying your furniture has its own set of environmental benefits.

"It helps prevent your $500 couch from ending up in the landfill," Lamstein said.

Here's a two-minute video of Lamstein explaining the "Full Circle" products, which, he says, are good for "our pets, our pocketbook and our planet."

** According to a book with the inelegant title of Holy Shit: Managing Manure to Save Mankind: "The nation's 68 million pet dogs and 73 million pet cats produce an average of 100 pounds and 50 pounds of waste per animal, per year, respectively."