A biogas digester for Rosita

Cathy Holt
4 min readApr 21, 2023

Finally, some forward progress on biodigesters! Somara, who has had her own biodigester for over 2 years now, took the initiative to replace, at last, the biodigester of an elderly couple out in the country. Theirs had a hole in it, which Somara tried unsuccessfully to fix, last year. On Easter Sunday, Rafa, Donny and I were measuring and cutting 13 meters of greenhouse plastic, which we bundled up well to protect it from damage.

The next day, Somara picked up me, the plastic, and some bicycle innertubes for rubber. Then we went shopping for other hardware items: ½ inch PVC tubing, cleaner and glue, couplings and elbows, an inline valve, sandpaper and a small cutter. Knowing we would be far out in the country, I worried a little that we would forget something essential.

Putting one tube of greenhouse plastic inside another

When we got to Rosita’s place, we were joined by Flor and Cecilia. Rosita’s elderly husband limped out with his walker to greet us. The old greenhouse plastic wasn’t wasted. One piece of it went into the trench to protect the new digester, and the other was added to the plastic roof over the trench, to strengthen it. We laid out the two pieces of 6.5 meter plastic, then put one tube inside the other, installed the fittings for conducting the gas, pleated the heavy plastic at each end around a four-inch tube and secured it with rubber strips.

Flor and Somara pleating and fastening the plastic to the intake pipe

While two pigs snorted and snuffled in their nearby pen, we laid the new digester in the lined trench and carefully connected the tubing for the gas to exit. The old safety valve was still in good shape. I was impressed by how Somara managed to put three pieces of garden hose together to reach the digester, without any of the metal fittings which I was used to. Instead, she put smaller diameter hose inside larger diameter, and secured it with more strips of black rubber. With the water, we began filling the digester.

Biodigester with gas output pipe and safety valve in place

Rosita was very attentive, serving us panela lemonade, then sweet black coffee. She was busy cooking us lunch over the old woodstove all morning. Remembering that I was vegetarian, she served me a plate of delicious beans, rice, potato and salad with avocado, while the others had a meaty soup, some chicken, rice, potato, beans, avocado and boiled yucca. To drink, Rosita gave us glasses of creamy guanabana juice milkshakes.

Somara had brought an inflator with an extension cord, but it wasn’t long enough. I was amazed at her skill, using a piece of wire without a plug on it, expertly wrapping copper wire bunches around the prongs and closing with black electrical tape. Inflating the digester revealed that the trench was just a little too small.

We were having trouble with attaching the 4-inch tube carrying pig manure to the digester. Even deploying some old used parts didn’t do the trick, but one of the women succeeded in getting a neighbor to bring just the right 4-inch coupling.

Note the white half-inch tubing that carries biogas to the kitchen.

Next, we experimented with various ways to install the half-inch tubing to carry gas into the kitchen. My height was an advantage in arranging the tubing overhead. In the process of poking long pieces of tubing into possible spaces, we bothered a large dark gray parrot in a cage, who protested with squawks and gave me some beseeching looks. The last step was attaching the stopcock and some flexible tubing to the stove.

Mission accomplished…Somara, Rosita and I pose with Rosita’s husband

Success! However, on our way home on the rough roads in Somara’s car, it abruptly stalled and she couldn’t get it started again. We were blocking the road, but the men in the first car to arrive behind us kindly pushed us to a wider spot so traffic could get by. They also looked under the hood, but to no avail. About an hour later, the mechanic Somara had called arrived on his motorcycle and in 5 minutes had the car running again.

Happy Earth Day to all!



Cathy Holt

Cathy has been living in Colombia for 2 years. She’s passionate about regenerating landscapes with water retention, agro-forestry, and biogas digestors.