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Biogas Project:

By Cathy Holt

Lilian Rojas and her husband Ricardo are members of Redbiocol, the network of biomass in Colombia. This organization, founded in 2012,encompasses much more than biogas…including also biocarbon or biochar, for example. On their 6-hectare farm, Tosoly, located in Guapota, they have used biogas digesters for over 30 years! They are growing coffee, sugarcane, corn, wheat, rice, fodder for their goats, cows, pigs, chickens, and ducks, and several other crops. By now, they have nine small biodigesters, which they built one by one. They explained how one of the nine simply handles human waste (blackwater) and shower/dishwashing water (greywater). That digester requires a retention time of 20 days.

I was excited to learn about their use of “reservorios” – bags made of the same greenhouse plastic as the digester, tied at each end to hold gas, which can hang vertically outside the house, and allow quick visual inspection of the amount of biogas available. Playfully capturing her husband around the middle with a scarf, Lilian demonstrated how they tie a rope around the center of the bag to increase the amount of pressure going to the stove. Lilian is a big believer in these bags. She said that one cubic meter of biogas gives about the same amount of energy as one liter of propane gas. One year’s worth of propane gas costs around one million Colombian pesos.

They drove 2 hours to visit us, and Margarita and I served them a fine lunch, after which we headed down to Paúl’s farm in Guane, to consider the best site for the biogas digester we aspire to build there. Paúl’s family’s greywater and blackwater currently go to a septic tank, but would be re-routed to the biodigestor. Although they do not have any cement floors under the livestock pens, they do use water for washing down the animals, and we discussed how a trench could be dug and pipe run underground to reach a likely spot for the digester, downhill from the pens and house. Then with a solar-powered pump, additional water could be delivered. Roughly 100 liters of water per day were estimated as needed for some 20-30 kilos of waste. That seems like a lot, but the captured rainwater, blackwater from toilets, greywater from showers, dishwashing, and washing machine all contribute.

We’re thinking of creating a minga (community workday) to dig a trench, around 5 meters long by a meter wide, for the digester; as well as a trench to hold the pipeline carrying animal waste, and create the plumbing to bring grey- and black-water from the house. After that, we’ll hold a workshop with Lilian, advertised for a nominal fee to other farming families, where they can learn by participating in the day-long installation of all aspects of the system.


Lilian invited Margarita, Paul and me to come visit their farm, Tosoly, a couple of weeks later, with its nine biodigesters. Many walls were covered with Redbiocol informational posters, and the stacks of plastic chairs revealed that several workshops have been taught there--mostly for adults, sometimes high school or college students. Redbiocol promotes sovereignty in food, energy, and economy while combating climate change, dependency on fossil fuels and chemical fertilizers, and contamination of soil and water.

Perhaps the most prominent feature was the multiple blimp-like giant bags of biogas hanging in various covered places. She showed us how a little electric gadget adds pressure to the biogas, and how just drilling the central hole in a regular propane gas burner a little bigger allows it to be used for biogas.

It was amazing to see so many machines that were running directly on the biogas: a hot water heater; a grinder for grains such as rice, quinoa, amaranth, and wheat; a generator to make electricity (to supplement their solar panels); a coffee roaster, which they fired up, poured in their own shade-grown coffee and roasted for us; and a grinder. Besides the delicious freshly roasted and ground coffee that they served us, there were boiled eggs from their chickens, pancakes with honey from their bees, cheese, and Santander hot chocolate.

We got to meet their vociferous pigs and little piglets, several chickens, ducks, cow, and goats. Lilian told us that their best gas production comes from the pig manure, which is daily rinsed out of their cement-lined stalls. Every building had gutters and pipes leading to rainwater cisterns. The digester located nearest the house connects with the 2 bathrooms there and handles blackwater and greywater from showers, sinks, and washing machine. There was no detectable odor.

Like Carlos Gomez, they produce biochar, some of which is from wood and some from corncobs. They also cultivate microorganisms to add to the biochar and to the compost. Algae production helps provide animal fodder.

We decided that the next step will be a workshop at Lilian’s for up to 15 people, in which she and Ricardo can give a tour and teach the basics of how a biodigester works…possibly in August. After that, the goal will be to install one, with Lilian’s guidance, at Paúl’s farm!

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