Plant-eating animals such as bison release large amounts of biogas to the atmosphere.

Besides being able to live without oxygen, methane-producing microorganisms have another special feature: They are among the very few creatures that can digest cellulose, the main ingredient of plant fibres. Another special feature of these organisms is that they are very sensitive to conditions in their environment, such as temperature, acidity, the amount of water, etc.

Biogas is a Form of Renewable Energy
Flammable biogas can be collected using a simple tank, as shown here. Animal manure is stored in a closed tank where the gas accumulates. It makes an excellent fuel for cook stoves and furnaces, and can be used in place of regular natural gas, which is a fossil fuel.

Biogas is a form of renewable energy, because it is produced with the help of growing plants.

Biogas is considered to be a source of renewable energy. This is because the production of biogas depends on the supply of grass, which usually grows back each year. By comparison, the natural gas used in most of our homes is not considered a form of renewable energy. Natural gas formed from the fossilized remains of plants and animals-a process that took millions of years. These resources do not "grow back" in a time scale that is meaningful for humans.

Biogas is Not New
People have been using biogas for over 200 years. In the days before electricity, biogas was drawn from the underground sewer pipes in London and burned in street lamps, which were known as "gaslights." In many parts of the world, biogas is used to heat and light homes, to cook, and even to fuel buses. It is collected from large-scale sources such as landfills and pig barns, and through small domestic or community systems in many villages.

For more information about biogas, read the backgrounder entitled Biomass Energy.

Safety Precautions

The main hazards in this activity are from sharp tools such as tubing cutters and scissors. Exercise caution while using any tool. There is no risk of explosion due to the leakage of methane because the gas develops so slowly that it dissipates long before it can reach flammable concentrations in room air. Exercise the normal precautions in the use of Bunsen burners: keep hair and clothing away from the burner while it is lit.

Build It!

(Click to continue to the construction plans)

Test It!

Use caution when testing the biogas.

For the first few weeks, your biogas generator will produce mainly carbon dioxide. When the aerobic bacteria use up all the oxygen inside the bottle, the anaerobic bacteria, which make methane, can take over. It can take up to a month for the generator to start making biogas with enough methane to be flammable.

When gas begins to accumulate in the balloon, test it by attempting to light the Bunsen burner:

1. First, open the clamp or valve so that biogas can flow back from the balloon to the Bunsen burner.

2. Have a friend squeeze the Mylar balloon gently while you attempt to light the Bunsen burner with a match or spark igniter.

3. If your Bunsen burner ignites, your biogas generator is a success!

Sources
Water bottle: Many hardware and grocery stores now sell purified water that they bottle on site. They often collect containers that can no longer be refilled because of dirt or damage to the bottle. These unrefillable bottles are frequently available for free. Ask to speak to the clerk in charge of refilling bottles. Ask for a used cap as well.
Mylar balloons: Check with any local florist or novelty store.
Tubing, valves, T-connectors, barb fittings: Check at your local hardware or plumbing supply store.