"The local community was very angry," recalls Mwasaru. "That stream was the only source of fresh water, and nobody wants excrement in its water," he explains.
At that time, in addition, the school used firewood for cooking and the forests near the school were beginning to be affected and the soil to erode due to the school's increasing demand for wood, and the smoke was damaging the lungs and eyes of cooks.
Mwasaru came up with a plan to solve the problem: human waste could be used to power gas stoves, so the waste would not pollute the river, and would not harm the forest or the cooks. He designed it while keeping up with his assignments and tests.
"There were people who thought it wouldn't work," says Mwasaru, who is now 17 years old. "It occurred to us to do workshops at school and in the community to convince people, and the response became more positive," he recalls.
In all, it took about a year to create the "Human Waste Bioreactor". During the testing phase, the students used two tanks - one on top of the other. When the bacteria reacted with oxygen and waste, gas was generated and the upper tank was raised demonstrating the presence of biogas.
Storage pits were dug and the team collected cow manure and food residues that were used in the testing phase instead of human waste.
The team's idea impressed Innovate Kenya, which provided funds for the teens to purchase a digester, which helps with the process. The gas produced in the well was then filtered through a tube into the kitchen, and used to cook food with gas stoves.
When the teens demonstrated that their prototype worked on cow dung, they began using human waste as well. Colleagues, friends and teachers at the school are benefiting from the system today, but it was not enough for Mwasaru.
"After the school prototype worked I showed it to my father, and he was very impressed," says Mwasaru. "I helped him build a similar system at home and now he uses it for cooking," he explains.
Having six cows, and having fewer humans in his house, meant that the house generated a lot of cow manure, more than gas that could be used. So now they share their gas with their entire town, made up of about 30 houses.
According to several investigations, collecting firewood takes a lot of time for women in Kenya, a task they must do three times a week, and each trip takes an average of eight hours. All this work is saved with the system developed by this teenager. "I am very happy to have saved you this afternoon," says Mwasaru.
Although this initiative can help solve a local problem, not everyone is convinced that biogas is the way to go. Environmental Researcher Rinkesh Kukreja argues that methane gases extracted in biofuel converters are still harmful to the environment, as they contribute to the warming of the ozone layer. He also points out another drawback:
"The smell is unpleasant and can attract unwanted pests (rats, flies) and spread bacteria and infections," he explains.
Still, the Mwasaru system means that fewer trees have to be cut down. When your reactor runs on human waste, it could replace up to 196 tons of wood - a significant benefit to the local ecosystem.
Progress has been made in extracting biogas, but Mwasaru has returned to using cow dung instead of human waste while working on the next step.
"When urine mixes with solid waste, the acid generated by the urine sends the biogases down," explains Mwasaru. "We have to develop a more cost-effective way to use human waste."
To achieve this, the team has designed a toilet that separates solid and liquid waste. Although it's just an idea on paper at the moment, the team is working with iHub Kenya to develop a prototype that they hope to build in March.
Mwasaru may be one of the youngest people to produce biogas, but he is not the first.
Rwanda's prison system has used human waste mixed with cow manure and water to reduce operating costs.
The waste generated by 8,000 inmates in Nsinda prison is used through a system similar to that of Mwasaru to bring gas to the kitchens and save the cost of firewood.
But Kenya and Rwanda are not the only countries in Africa that have found uses for human waste.
In Nigeria, three teenagers managed to invent a power generator that produces enough electricity to run for up to six hours. The power source: pee.