At the same time, the people of Nairobi generate about 3,000 tons of waste every day, most of which is organic. And they collect only about half of it. (Independent haulers take trash from wealthier neighborhoods to an open dump.) Burning biogas derived from the waste would help solve two problems at once. But the government has been unable to launch any kind of large- or medium-scale biogas projects. The city council recently considered a proposal for a dozen biogas plants but never acted on it. “There have been many plans in the past, but they haven’t materialized,” says Matt Woods, the operations director for Carbon Africa, a Nairobi-based carbon-credit company.
It may be that some people like the system the way it is. The local dump, for instance, is run by a powerful gang. After the company that handles flight catering at Nairobi’s international airport raised the idea of diverting the six tons of food waste that arrive on planes each day in order to make biogas, the gang sent threats. Trucks still deliver the airplane waste to the dump.
Biogas systems don’t require much in the way of capital investment or scale, though, and so Kenyans have begun their own experiments. Small generators like Culhane’s are beginning to dot the city. In a Hindu temple that serves free meals to the homeless in Nairobi’s upscale Westlands neighborhood, for instance, one of the stoves is connected to a gas line that climbs over the kitchen wall and out to the back courtyard, where a 1,300-gallon tank produces three hours’ worth of biogas per day. The temple’s leaders will soon buy a second system from Bijal Shah, a Kenyan woman who runs GreenTech International, a renewable-energy company in Nairobi. And not far from the temple, Shah’s aunt climbs the stairs from her outdoor kitchen every evening to pour a bucket of leftover rice and cooking water into her own 400-gallon tank. Culhane, meanwhile, recently discovered an even more direct loop: An enterprising pay-toilet owner had tapped the valuable energy produced every day by his customers and piped the gas to a restaurant across the alley.
People have known how to make biogas for a very long time. In the 10th century B.C., Assyrians used biogas to heat their baths. In the late 1800s, Louis Pasteur generated biogas from manure to demonstrate that Paris’s horses could power street lamps. In the mid-19th century, India used it to light a leprosy hospital; today, there are roughly three million small-scale biogas plants in India, and 35 million in China.
Biogas isn’t the right tool for every job or every nation. In Germany, where 17 percent of the country’s electricity comes from renewable sources, biogas accounts for only about 2 percent of that mix. But in Sweden it has outpaced natural gas as a transportation fuel; some cities, such as Helsingborg, use it to power their entire bus fleets.
Here in the U.S., the Environmental Protection Agency estimates that nearly 8,000 farms are capable of producing significant amounts of biogas;167 American dairy, swine, poultry and beef farms already use anaerobic digestion to reduce pollution and contain odor. If even just the largest 160 farms installed digesters, the methane they produced could heat three million homes—or, by sending biogas to natural-gas power plants, provide electricity to 870,000 homes. Food waste, meanwhile, contains even more energy. A ton of manure yields 1,700 kilowatt-hours of electricity. A ton of butter produces 9,600 kilowatt-hours.single page
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.