The ingredients of life in Mukuru, one of Nairobi's largest slums, are raw. Yet they present exciting possibilities.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.