A pair of Kenyan teenagers has won the Africa region Earth Prize with a low-cost vehicle exhaust filter made from maize cobs, coconut shells and other locally sourced materials.
Fredrick Njoroge Kariuki and Miron Onsarigo, both 17 and students at M-PESA Foundation Academy in Kiambu county, were announced as regional winners on May 12 for HewaSafi, which means “clean air” in Swahili.
The Switzerland-based Earth Foundation awards the annual Earth Prize, now in its fifth year, to 13-to-19-year-olds working on solutions to environmental challenges.
HewaSafi was developed after the students saw friends and family suffer from diseases linked to air pollution.
“The problem of air pollution was very personal to us, and that is why we started thinking about coming up with a solution,” Kariuki told Mongabay. “It was a passion before it became a project.”
Kariuki grew up in an industrialised area of Nakuru county and developed a chronic lung disease at age 10 that still requires weekly medication. Onsarigo, who grew up in western Kenya, witnessed deaths and serious illnesses associated with polluted air.
According to the World Health Organization, air pollution causes 4.4 million premature deaths globally each year. Vehicular exhaust is a major source of pollution in urban areas.
The HewaSafi system uses filters made from coconut shells, maize cobs, steel mesh, copper and recycled materials from old batteries. It also includes a component made of living spirulina algae.
The design splits exhaust flow into five compartments, each filtering different pollutants.
The team tested the system with a local association of matatus, the privately owned minibuses used as shared taxis. They installed filters in five matatus operating along Nairobi’s Thika Road corridor, with sensors recording readings every six hours in real-world conditions.
The devices achieved a 93.3 percent reduction in emissions of PM2.5 particulates, a 42 percent reduction in carbon monoxide, and 21.4 percent carbon dioxide absorption.
“We all know greenhouse gases are one of the main causes of climate change. The moment we are able to filter the carbon dioxide, we are able to reduce the amount of these gases that enter the atmosphere,” Kariuki said to Mongabay.
According to the HewaSafi team, existing filters cost 50,000 shillings, nearly $390. Their prototype costs 16,288 shillings, or $126.
“What made their project strong was that they were not presenting only an idea, but a tangible technical pathway using materials that are locally accessible, including agricultural waste and algae,” Agustín Ocaña Escobar, chair of the adjudicating panel for the Earth Prize, said in a prepared statement.
“That combination of realism, experimentation, and potential community impact made us believe this is a project worth backing. I’m really looking forward to seeing where they take it over the next year,” Escobar said.
The students have struggled to find funding so far. Their school provided guidance, raw materials and a lawyer to help patent the invention, as well as gadgets and internet access.
HewaSafi is now in the running for the global Earth Prize. Public voting opens on May 18 and closes on May 27, with the international winner to be announced on May 29.
Each regional winner receives $12,500 to implement their plan, and the prize also includes access to mentorship.
The students say they plan to produce 1,200 exhaust filters with local artisans from the informal manufacturing sector. They also aim to sign an agreement with the matatu owners’ association, which represents about 8,000 minibus drivers, to test the filters in 200 vehicles.
“I wouldn’t want to see any other child suffering from a chronic lung disease [like] I’m suffering from,” Kariuki said. “This is what keeps me moving.”
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