Deep in the sprawling slum of Kibera, volunteers shovel a stinking pile of garbage into one end of a giant concrete oven while a queue of people clutching packets of tea and saucepans tries to ignore the acrid smoke wafting from the cooker.
"It might smell a bit but it doesn't make our food taste any different," says Virginia Wamaitha, as she pours sugar into her steaming pan of chai – the gently spiced tea loved by Kenyans. "It will taste just like chai should."
The garbage-burning oven is part of a UN-sponsored move to clean up Kenya's slums while preserving the country's dwindling forests, which are cleared to provide wood and charcoal for cooking. If successful, the pilot project could be a model as the world faces an explosion in urban living, and the waste it creates.
"It is only a pilot and we need many more cookers to clean up Kibera, but we have already seen a difference in the area we are targeting," says Pauline Nyota, of the Umande Trust, which works in slums to improve sanitation and runs the project. "The drainage ditches are much cleaner – just wastewater when before they were clogged with rubbish."
The first cooker's early success has prompted the country's biggest supermarket chain to pledge funding for 20 more.
How the oven works
Through trial and error, the developers of the oven used technology that can produce temperatures of up to 930 degrees F., enough to burn many of the hazardous pollutants.
It uses a superheated steel plate inside the incinerator box to vaporize drops of water. The oxygen released then helps burn discarded "sump" oil from vehicles – itself a pollutant in the slums – driving temperatures higher.
The process is simple enough to be controlled by locally trained volunteers.
Pots of pasta boil inside the oven, while chai simmers on hot plates above – all for a few shillings from Kibera's residents.
The project is the first of its kind, according to the United Nations Environment Programme (UNEP), which provided $10,000 for the launch.
Youth workers are paid a few shillings to go door to door collecting rubbish.
They are also allowed to use the cooker for preparing hot meals or to fill buckets with hot water for washing.
The target is for the cooker to consume half a ton of waste every day once it has finished trials in a month or so.
World's slums growing
Kibera's problems with waste are mirrored in Nairobi's other slums and are the result of rapid, unplanned expansion as families give up their rural way of life for the city.
It is a trend seen throughout the developing world.
Earlier this year the UN Population Fund reported that, for the first time, more than half the world's 6.6 billion inhabitants would live in urban areas by 2008.
Without adequate planning, warns its State of the World's Population 2007 report, there will be an explosion of slums, with the associated environmental damage and human disease.
"The changes are too large and too fast to allow planners and policymakers simply to react," it concludes.
Henry Ndede, of UNEP's Nairobi River Basin Project, says garbage from the city is killing off Kenya's famous plains.
"The degradation of the environment of the Nairobi rivers is reaching a critical stage," he says. "With the increasing of the population now to more than 3 million people, the waste problems have actually overwhelmed the ecosystem."
Governments in the developing world are slowly waking up to the problem.
One of the first issues to be tackled is the scourge of the plastic bag. They turn up in even the most remote corners of the continent, shredded on acacia trees or blocking ditches.
They help spread malaria by holding warm pools of water – the perfect habitat for mosquito larvae.
They choke soil and plants, and bleed chemical additives into vegetables and fruit.
South Africa, Uganda, and Kenya have all introduced minimum thickness rules. Other countries are slapping levies on plastic bag production.
Meanwhile, architects in Nairobi have even suggested moving to a new capital to allow planners to start fresh, ensuring adequate roads, refuse dumps, and sewerage.
That may be a pipe dream.
But Naison Mutizwa-Mangiza, chief policy analyst with the UN's human settlement program (UN-HABITAT) agrees that piecemeal solutions can only go so far.
"If you are really to upgrade a slum, you need government or a local authority to go in and put in sewage and drainage and so on, because as much as we might talk about the poor helping themselves, these are things that they simply cannot do," he says. "But there are interim projects that communities themselves can put in place in order to help, and the kind of project like the community cooker might be one such project."
Collection schemes, he said, can be integrated into a network of recycling centers, composting sites, and nonbiodegradable dumps. But they need coordination by the government.
And there has to be a financial incentive, says Andre Dzikus, of UN-HABITAT's water and sanitation department, such as the chance to sell paper, glass, or tin to recycling companies.
"Environmental concerns are difficult to sell to low-income people," he says. "They are fighting for survival. If they have an income opportunity they will do it."
For now, the community cooker is helping clean up one corner of Kibera rather than the whole slum. And its designers are trying to reduce the foul-smelling smoke.
George Arabbu, an architect with Planning Systems, which designed the cooker, admits the fumes are a potential health hazard but that the people of Kibera cannot wait for a perfect solution.
As he points out: "At the end of the day it's a case of weighing risk against benefit and the rubbish itself is a menace."