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Part 1
 
 
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The Agriculture School of the Humid Tropical Region (EARTH University)...

How to install a biogas (methane) digester at low cost

The poor usage of natural resources is taking us to the destruction of the planet. Deforestation, high levels of carbon dioxide generated by forest fires, pollution caused by vehicle, industries, and other factors, are causing a global warming effect at an accelerated pace. In this sense, high poverty rates contribute to this phenomenon. Currently, many options have come about to substitute wood as a source of fuel, as gas and electricity have increasingly higher costs. Solar cooker have requirements in their usage and don't work on rainy days. An alternative that is being used more and more often is the anaerobic methane digester.

What is an anaerobic biogas (methane) digester?

An anaerobic biogas (methane) digester is an aparratus formed by a double polyethylene bag, an exit valve, and a safety valve. Inside the bag excrements are fermented, giving as a result the production of a natural gas called biogas. This biogas can be used to heat and cook food, to create light, to heat farm animals, and generally, as an extra energy source. The fermented excrements that exit the biogas (methane) digester can be used as an organic fertilizer. In the production of biogas, you can use manure from cows, pigs, horses, goats, or even human feces. Installing a homemade anaerobic biogas (methane) digester is not very costly. Nevertheless, you will have to invest at least $120 in the cost of materials and installation. The amount of materials is directly related to the size of the anaerobic methane digester, whose length can vary from 5 meters to 50 meters. To install a methane digester with 13 meters in length, you should get:
  • 34 meters of 8-caliber transparent tubular polyethylene plastic with 4 meters of circumference
  • 8 plastic 10-liter buckets
  • 2 meters of a 1 1/4-inch plastic transparent hose
  • A PVC "T" 1" thick
  • A male PVC adapter, 1"
  • A female PVC adapter, 1"
  • 2 PVC elbows (90), 1"
  • 1 meter of PVC tubing, 1"
  • A PVC plug to fit 1" PVC tubing
  • Two rigid plastic washers with a hole in the center equal to 1"
  • A two-liter bottle of soda or other equivalent container
  • 3 car tire inner tubes, cut into two pieces equal in shape and size to the plastic washer, and the rest to set aside as tying materials are needed later in construction
  • 8 empty fertilizer sacks
  • A 1/2" metal tube
  • A used garden hose
  • A tube of PVC cement

The first step in the installation of an anaerobic biogas (methane) digester is the preparation of the bag. To do this you should extend the tubular plastic over a dry, sturdy floor without any rocks that may break the plastic. Then, fold the plastic bag in half and cut it, leaving two bags, each of them 17 meters long. Extend one of the bags over the floor and have someone crawl inside while holding an end of the other bag. The person should not wear shoes or carry objects that can make holes in the bag. Once the two bags are lined up, forming one bag, eliminate the wrinkles that formed during the process.

The second step is the preparation of the main digester ditch. This ditch is a thermal isolator and protector of the materials. It is recommended to dig the ditch close to where you keep the livestock that supply the digester. The size of the methane digester varies with respect to your biogas and fertilizer needs, as well as the amount of manure available. For this reason, the ditch measurments will vary as well.

For the example of the materials already described, the ditch should be of a 1.2-meter width on the top and a 1-meter width on the bottom of the ditch. The ditch should also be 1 meter deep and 13 meters long. The walls for the ditch should have a light coating of plastic to support them structurally from erosion. On the ends of the ditch you should dig two inclined ditches that reach the bottom of the main ditch. These two ditches should be the same width as the buckets you will be using.

The third step consists of preparing the safety valve for the biogas. For this you must make a circular cut in the top of the double bag that permits the tight entry of the male PVC adapter. This cut is to be made 3 meters from the end of the bag to be placed closest to the place where you'll use the biogas.

 
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