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The following is a translation of the transcription of the biogas (methane) digester instructional video made by the EARTH University in Guápiles, Costa Rica. The video is currently hosted on YouTube in two segments, Part 1 and Part 2. If you'd like to know about how the Santa Fe Women's Group uses biogas in rural Costa Rica, visit the main biogas page or see the digester design they used.

Part One....

Part Two

Follow along with the English transcription

Anaerobic Biogas (Methane) Digester Video

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.

How do you creat the exit valve?

We take the rigid washer and we place it over the male PVC adapter. We then place the tire inner tube seal over the washer so that the washer does not do harm to the polyethylene bag of the anaerobic methane digester. Then you introduce the male PVC adapter into the hole cut in the digester's bag. On the outside you then place the other inner tube seal, the other rigid washer, and the female PVC adapter that was previously attached to the PVC tubing and the PVC elbow of 1". Once the exit valve is placed, you can put the bag into the ditch and pass the ends of the bag through the buckets at each end of the ditch.

The next step is to set up the safety valve. To do this you must place a post to support it.

How do you set up the safety valve?

To set up the safety valve you must take the 1" T and insert inside a small piece of 1" PVC between 20 and 25 centimeters. This piece does not get glued within because it needs to be removed to replace the steel wool that goes inside every six months to a year. On the ends of the T we place the small pieces of PVC that are between 8 and 10 centimeters. These are glued into the T with PVC cement. We then place the larger PVC piece into the mouth of the 2-liter soda bottle with the T and the other PVC pieces attached. Here it is clear that the PVC tubing will maintain submerged in water up to these holes that create a seal of water about 5 centimeters deep.

This safety valve connects to the exit valve by means of the transparent plastic hose. Once the bag is installed in the ditch, and the ends are placed on the buckets, and the exit and safety valves are connected, the next step is to inflate the bag with the exhaust of a car, tractor, or motorcycle. To do this you need to tie up one end of the bag with the rest of the tire inner tube scraps, avoiding the escape of any smoke. At the other end, tie the mouth of the bag around a garden hose that will funnel the smoke into the bag. The other end of the hose is then place over the exhaust pipe of the automobile. Once this connection is then sealed with the tying of more inner tube scraps, you turn on the engine until you completely fill the digester's bag. Once this is complete, the safety valve should start bubbling, signaling the reaching of the digester's maximum biogas capacity. Now take the garden hose to introduce water into the bag to the point where no gas can escape, creating a water seal. Then, when no gas can escape, you open up the ends of the bag to be mounted in the buckets. On the end that corresponds to the anaerobic anaerobic methane digester's exit, you dig a hole through which to channel the material that has been digested for fifty days, after which this material can be used as organic fertilizer. From then on, you will feed the anaerobic methane digester every day with manure dissolved in water. Every bucket of manure should be mixed with four buckets of water, being completely dissolved before pouring the mixture into the digester. [Image]
Following this recommendation, an anaerobic methane digester with 13 meters in length and four meters in circumference, and that is fed with 50 kilos of fresh manure dissolved in 200 liters of water daily can produce up to 16 hours of burn time every day. [Eliseo Arias, Guácimo, Costa Rica]
Being able to have it, who isn't going to have this gift that is so cheap? I recommend this to everyone who asks me about it. [Credits]
A production of The Agriculture School of the Humid Tropical Region (EARTH University)


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