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Visit to a Biogas Digester

By Cathy Holt

Finally, a visit to a farm with a working biogas digester! Margarita, Paúl, Rafa and I went; Rafa, because the farmer, Somara, had an old refrigerator ready to be retrofitted as a dehydrator for her pineapple, and Rafa has become expert in that technology. Margarita and Paul have been talking about setting up a workday/hands-on learning with a group of people interested in putting a biodigester on their farms, taught by someone with experience. Redbiocol is a network of Colombians with interest in biogas; they encourage adoption of the technology, and have a basic plan for building a digester on their website.

Paúl brought his vehicle, which was kind of a tiny red two-seater pickup truck without doors, and a covered cargo area behind. Margarita insisted I take the front passenger seat, and she and Rafa rode in back. About halfway there, on narrow roads where at any moment I expected us to collide with a motorcycle, we came across two of Rafa’s sisters, with two of his nieces and their tiny dog; they all piled in and the little truck strained its way up the steep hills in low gear.

Somara, an attractive young woman with a long black wavy ponytail, greeted us and offered slices of her farm’s dried pineapple. She has had her biodigester running for over two years, without problems. We descended a long series of steps made from old tires filled with packed earth and stones. Apparently a company called Green Power helped get this digester set up. The first step, she told us, was to dig a trench, 5 meters long. Most of the pipes for the intake and outlet are partly underground, although that isn’t always necessary.

Somara said it only took one morning to put together the digester after having dug the trench and purchased the parts. Made of a greenhouse plastic tube, it is protected from animals, falling branches, etc. by an enclosure of chicken wire, topped with a greenhouse plastic cover. The digester is located below the pigpens, where three large pigs snuffle and snort. Each day, their waste is washed from their enclosure, then flows downhill along a cement channel to the intake area. Manure from four goats is also added, and there is a small toilet for humans that occasionally adds waste. (The main toilet is a distance uphill, at the house.) The outlet pipe runs further downhill to a storage tank, from which the liquid biol is drawn to fertilize the gardens.

About midway along the length of the digester, a small pipe conducts methane gas up the hill to the house. There is an in-line plastic bottle partly full of water and a shutoff valve. Somara said that the amount of gas varies with temperature. Sometimes there is enough gas to cook for six hours, but when it is cold and rainy there might only be enough gas for one burner. For this reason, they also have a propane-powered stove.

The farm is impressive, with a pond and two cisterns filled with rainwater. A flock of small chickens were being fed. Somara and her family grow a mixture of banana and plantain trees giving shade to coffee plants; abundant maracuyá and limon; a field of pineapple and yucca; another field of tall corn; and many other food plants, including some of the healthiest, biggest swiss chard plants I’ve seen yet! A nursery/vivero is filled with orchids.

Somara expressed willingness to possibly hold a workshop or mindo (community workday) at Paúl’s farm, for other farmers with interest in biogas to attend and help with the tasks. He and Margarita talked about the possibility of sharing some of the biogas with Rafa’s mother, who is Paúl’s neighbor.

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