The process requires putting a given amount of human or other animal waste into a "digester," which ferments it using bacteria to release methane gas that can be captured and then burned as fuel. Attached is a "compensating chamber" that replenishes the supply of bacteria to keep the operation self-sustaining.

The lead engineer on the project, Ainea Kimaro, says that within four weeks, 100 cubic meters of waste can be transformed into 50 cubic meters of fuel.

Biogas is being used around the world, including in homes in Nepal and to power trains in Sweden.

Kimaro said that while waste smells bad initially, the biogas that is produced has no foul odor. He added that the Rwandan prisoners are not put off by the idea of using the byproduct of human waste to cook.

"Our people are very adaptive," he said. "They see it working; they want to use it."

Once the methane is produced, the remaining waste is used as an odor-free fertilizer for the gardens at the prison.