Biogas project helps Kenyan school save money, and trees
A school in Kenya uses biogas from human waste for fuel, saving money and trees, and reducing carbon-dioxide emissions from burning wood.
KIAMBU, Kenya — When Evelyn Mukami, a form three student, joined Gachoire Girls Secondary School in January 2010, she was very surprised to learn how the meals at her school were prepared.
The charcoal and firewood that are typically used for cooking in Kenya were nowhere to be seen. Instead, the kitchens cooked with biogas produced from the students’ own toilet waste.
Since 2006, biogas has been a key resource for the 36-year-old school in Central Kenya, saving the expense of buying fuel and emptying latrines, while also preserving a significant number of trees and reducing carbon dioxide emissions from burning wood.
In the process, Gachoire has become a model of how the effects of climate change can be mitigated at the local level.
“If all schools, both primary and secondary, took up this initiative, I think after a few years we can count how much carbon we have saved from the atmosphere by sparing the trees and our forests,” said Esther Lung’ai, a local project officer at the Arid Lands Information Network, a nongovernmental organization.
Lung’ai added that she had eaten food from the school kitchen and there was nothing in the taste to indicate that it had been cooked using by-products of human waste.
Waste from toilets at the school is deposited into large pipes and pumped automatically into a bio-digester buried underground. Bacteria are added to break down the waste, and gas is produced as a by-product of this process. A pipe transfers the gas from the digester to the kitchen, which is about 200 metres (220 yards) away.
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.
The hills across from the school are treeless, cleared for firewood, farming, and construction by the growing population. This has allowed strong winds to destroy crops, while floods wash away the soil during heavy rains, according to Githumbe.
The school has been able to preserve four acres of its own woodland that without the biogas project would eventually have been felled for fuel. School officials say that the trees not only absorb carbon dioxide but help create a cooler microclimate around the school.
Gachoire is also growing vegetables on school land. There are plans to produce fertilizer from the by-products of the biogas production.
The project has excited the communities around the school. When it began, the school hung a banner at the gate, and local residents came to see how the bio-gas was being produced, according to Muraya.
Now they have started producing their own biogas at the household level, using animal dung.
“The whole world ... is talking about climate change,” Muraya said. “But many people are just giving lip service. I know in our small way we are helping to address the impact of climate change by saving the trees and using this clean energy source.”
Student Evelyn Mukami is now gathering youths from her church and the community to tell them how human waste can save the trees.
“I can tell the world that the waste we produce is really not a waste, but we can combine it to produce biogas,” she said.
Samuel Githumbe put it even more bluntly.
“I urge every person here to start using biogas so that we can save our environment,” he said.
• Pius Sawa is a freelance science journalist based in Nairobi, Kenya.
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