In terms of renewable energy, you have to give credit to the first person who thought of using excrement as a source of fuel.

At the risk of dragging things down to gutter-level, one place you'll find one heck of a lot of excrement is at a zoo. You don't need us to tell you that big animals produce large amounts of waste.

Denver Zoo realised the potential, and now runs a three-wheeled motorized rickshaw--also known as a "tuk-tuk"--on gasified pellets, made from animal droppings and trash generated by the zoo's visitors.

According to the Denver Post (via GM-Volt), the tuk-tuk was brought in from Thailand and re-engineered to run on the pellets. The conversion process, from poop to power, involves compacting the waste into pellets, which are then thermally broken down in an oxygen-free system--no burning here--and used to charge batteries, fuel heaters and other machinery. The rickshaw itself runs on electric power, generated by the pellets.

The concept is therefore different to that of the poop-powered Volkswagen Beetle we saw a few years back, which used a process called "biogas upgrading" to generate methane gas from waste, which could then be used to fuel the car normally.

There are plenty of reasons for running the scheme. Firstly, it's brilliant recycling. Waste products can be used for energy, rather than simply going to waste.

Secondly, when upscaled, it'll offset 20 percent of the zoo's total energy consumption. The full system will convert about 1.5 million pounds of waste, from both animal droppings and 90 percent of the trash generated by visitors and employees.

Thirdly, everything is done on site. That not only makes the system self-sufficient, but reduces the need for animal dung and trash to be driven off-site in vehicles to be disposed of. That saves money, too--up to $150,000 a year for the zoo in energy and transport costs.

The poo-powered rickshaw will showcase the zoo's patent-pending technology during the Toyota Elephant Passage exhibit, opening June 1.


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