How to Make a Biogas Plant at Home With Cow Dung

Biogas is the natural product of bacterial digestion of organic wastes. It is 50 to 65 percent or more methane gas, which is a powerful greenhouse gas when released into the atmosphere, but burned as a fuel for cooking, heating or even running a generator, it is cleaner than gasoline or wood. Biogas can be made either aerobically (in contact with the air) or anaerobically in a sealed chamber, which is the more common approach as it makes collecting the gas simpler and avoids the unpleasant odor. A small-scale batch digester can be constructed for home use.

Things You'll Need

• 55-gallon steel or plastic drum (tightly sealed, with two threaded holes in the top—one large, one small)
• Threaded cap for large hole
• 12-inch metal or PCV pipe
• 8-inch metal or PCV pipe
• Pipe sealing compound
• T-connector
• Brass shut-off valve
• Two lengths of plastic tubing
• Large inner tube with an air valve
• Bacterial starter (such as Rid-X or other septic tank conditioner)
• Broom handle

Instructions

1. Insert the 12-inch pipe approximately halfway into the drum through the small hole and seal it tight. Spread sealing compound around the hole until it is airtight.

2. Attach the T-connector to the top of the 12-inch pipe, with the 8-inch pipe attached to the top end. Screw the shut-off valve onto the top of the 8-inch pipe, making sure all the connections are tightly sealed.

3. Attach a four- to five-foot length of plastic tubing to the side opening in the T-connector. Attach a length of plastic tubing long enough to reach the gas stove, heater or other appliance.

4. Remove the inner valve from the stem and connect the end of the plastic tube to it, sealing that connection with sealant.

5. Fill the drum with a slurry of two parts water to one part cow dung until the mixture is 8 to 10 inches from the top rim. Add the bacterial starter and stir the mixture with the broom handle. Cap the large hole tightly but do not use sealant, so it can be reopened when necessary.

Tips & Warnings

• The system should produce gas for two to three months before it needs to be emptied and refilled with fresh slurry. Stirring the slurry with the broom handle and recapping it every few days will improve the efficiency of the digester. The used slurry can be used as an organic fertilizer without further treatment.

• Tap the gas for a few days to a week before attempting to use it for the first time to purge the system of air—the mixture of air and biogas can be dangerous.

References

• Biogas Digester Expert Technical Pages
• Biogas: Power From Cow Dung

Resources

• Read this Article in Spanish
• Rural Costa Rica: Biodigester
• Homemade Biogas Generator I
• Homemade Biogas Generator II