Elephant-poo power electrifies zoo

Munich Zoo's elephant energy

STORY HIGHLIGHTS

• Zoo in Germany partially powered by electricity produced from animal dung
• Animal waste fermented for 30 days generates "biogas"
• Energy produced enough to heat 25 homes and power 100

Munich, Germany (CNN) -- At Munich Zoo you can watch the courtship rituals of the banded mongoose, hear the morning song of the scarlet ibis or visit the Indian elephants, who help keep the lights on with electricity generated from their dung.

They can do this because Munich Zoo has harnessed "poo power," energy stored in animal waste, which can be converted into a fuel known as "biogas."

It works like this: The zoo has built three large containers, each capable of holding about 100 cubic meters of animal waste -- that's around a week's worth of dung collected from all the vegetarian animals in the zoo.

Once inside the containers, it's mixed with warm water and the bacteria in the dung is left to decompose in an oxygen-free environment for 30 days.

The resulting biogas, mainly comprised of methane and carbon dioxide, rises naturally through vents in the ceiling to a corrugated hut on the roof where it's collected in a "big balloon," says park supervisor Dominik Forster.

The biogas is then fed into a gas-powered engine that's used to generate electricity. Forster says that the balloon -- which more closely resembles a small Zeppelin -- can store enough biogas to meet 5% of the zoo's energy needs.