I’ve always loved the concept of closed-loop farming (perfect for cities) that, in a small space, uses the waste from one process as raw material for another. In one classic design, called aquaponics, fish grow in a tank and their “polluted” water (full of nutrients) grows plants (often, lettuce) hydroponically. After the plants absorb the waste, the naturally filtered water is returned to the fish tank. I first heard about "living machines" from John Todd and the New Alchemy Institute on Cape Cod, but it goes way back — the Aztecs used a form of it.

According to Atlantic Cities, “The net result: a 90 percent reduction in freshwater use compared with conventional fish farming, and a significant reduction in added nutrients such as fossil fertilizers. The system can be run without pesticides and, because the fish environment is spacious and clean, without antibiotics.” I’ve seen living systems in museum demonstration projects, and even in a Michigan brewery. It’s really scalable, too. We could be using the principles in big food-producing projects.

vertical farm in San Francisco

A vertical farm in San Francisco

In cities? Yes, indeed. Columbia professor Dickson Despommier explores the concept in his book "The Vertical Farm," a concept that has some skeptics. But since 70 percent of the world’s population will be living in cities by 2050, according to the U.N., we’re going to need to feed them.

But those are just designs. Hyundai, for one, is showing how it can work today, using a fuel-cell car like the one it plans to commercialize as early as 2015. As you know, fuel-cell cars run on hydrogen and convert it to electricity, and the byproduct is pretty clean water vapor — 1960s astronauts used fuel cells for power and drank the “waste.”

In Hyundai’s demonstration, set up last month at London’s Design Museum, the company’s new ix35 fuel-cell car (a small SUV) provided the water for a fish tank and hydroponic vegetable garden. An eco-chef, Tom Hunt (who runs a waste-free kitchen), was on hand to host a Fuel Cell Farm BBQ using the carp and vegetables grown on the “farm.” A variety of salads were served.

Incidentally, London-based Something & Sons, which created the fuel cell farm, had an earlier project (above) called Car:Park, which positioned a reclaimed junked car as an urban garden on the city’s streets during the Festival of Architecture. The upholstery became planting containers, and “basic permaculture principles were used, with both ornamental and productive plants chosen.” The car’s “boot” (trunk) became a pond. After the exhibit, the car went back to the scrapyard and the plants were repurposed.

Here's a closer look at the Hyundai project on video:

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Jim Motavalli ( @jmotavalli ) writes about cars, technology and the environmental world to anyone curious enough to ask.

How Hyundai is making a car that helps grow fish and produce
Hyundai provided its ix35 fuel-cell car as part of a unique and sustainable city garden in London.