When the bio-digester is full, excess water and waste go to other chambers called breeders. As gas is used up, the water and waste in the breeders return to the digester for further processing. After the waste has been fully digested, remnants are stored in tanks from which they can be collected and dried to produce fertilizer.
Peter Muraya, a teacher who was involved in the project from its inception, said the bio-digester was built with the school’s planned expansion in mind. It has a volume of 21,000 litres (about 5,500 US gallons).
“When we started we had around 600 students,” Muraya explained. “But now we have 849 students and the number is increasing each year. So the bio-digester is large enough to supply the gas to the kitchen” for all the children’s needs.
The Gachoire biofuel project was initially funded by the European Union.
The project is saving wood that would otherwise be needed to cook the school meals. Muraya said that Gachoire previously bought three lorryloads of firewood for each three-month school term.
“That was 21 tons of wood, which would translate into 50 mature trees,” said Muraya. This means that the school is now conserving 150 mature trees every year that would otherwise have been felled to cook for the students and staff.
Gachoire’s principal, Naomi Njihia, said the school has been able to save more than 10,000 Kenyan shillings (about $117) each month on fuel.
“It is very helpful,” said Njihia. “The school has also saved money by (not having to empty) the pit latrines.”
Samuel Githumbe, a Gachoire cook who has worked at schools that used wood for cooking, believes that cooking with biogas has a number of advantages over firewood.
“This gas is very fast,” he said. “If you have a big number of people to cook for, the work is faster, you don’t waste time splitting the firewood, and besides that the gas does not produce smoke that is dangerous to the health and the eyes.”
Githumbe, who was born locally, has also seen the negative consequences for the environment of using fuel wood. He says the climate of the area today is different from when he was young.