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As Jim Archer became more and more upset at the alarming growth of rubbish in Kenya, he hit upon a plan.

“I thought I’ve got to somehow find a way so that people pick it up and don’t just throw it away,” says the 75-year-old architect about the country of his birth, where he has designed several iconic tower blocks and hotels in Nairobi and along the coast.

“When I was small, Kenya was just the most beautifully pristine clean place on earth. Now everywhere you go there’s rubbish. By the mid 1980s, it really began to trouble me.”

Kibera, the largest slum in east Africa, is a case in point.

Litter is part of life in the sprawling Nairobi area, made up of 13 villages and home to hundreds of thousands of residents who rent metal shacks bound with string. Rubbish piles up in broken storm drains and lines the railway track that cuts through stalls selling clothes. But now, thanks to Archer and a team of volunteers, slum rubbish is used to power an oven.

Archer came up with the “community cooker”, an industrial-scale oven made from bricks and metal, put together by the slum’s residents and fuelled with rubbish. This project recycles trash into energy for everything from frying and baking to boiling water for hot showers.

“What’s unique about it is its utter simplicity and the fact that something so simple can generate immense heat,” says Archer.

Not even the ash goes to waste, as it can be used for making bricks and adorning makeshift houses. The cooker guzzles rubbish and at the same time provides a safe and treeless alternative to charcoal and firewood, as well as paraffin.

The project managers say the heat produced from one of their ovens saves the equivalent of 2,400 trees a year.

Some young men have volunteered to collect waste in wheelbarrows and deliver it to the cooker’s storage area.

“Rather than staying idle, we say let’s do something. Somebody who is idle is the devil’s work, that’s what they say,” says David Kireki, a leather-jacketed, part-time rapper.

Standing amid the rubbish, Kireki performs a rap in Swahili about his ghetto life. He blames the government for harassing residents and abandoning them, despite many promises to help. But he does not mind the smell: “We enjoy it because we don’t want to be idling.”

It might be basic, but the slum is always busy turning the least likely offerings into profit. Bright trainers are strung up among other goods for sale – everything from trousers to school books. Stalls sell ripe avocados, entrails and samosas.

“It’s a full assault on all the senses,” says Janice Muthui, manager of the Community Cooker Foundation set up by Archer. She refers to Kibera’s “kadogo” economy, which sells everything in small amounts at high profit margins. Washing powder and shampoo are sold in single-use sachets, for example.

“Kibera itself is like its own country – there are a lot of slumlord millionaires. Everything makes money in Kibera one way or another,” she says.

The rubbish collection and cooking group hopes they will be earning their living within three months. The men pick out anything that will not burn, such as glass, or that should not, such as batteries, or that might sell, such as bottles. Some of what remains goes for organic compost. The youth group, whose motto is “Waste No Waste”, hopes to collect a small fee eventually.

The rest of the rubbish – clothes, plastic pots, plastic bags, paper and cardboard – goes to fuel the oven. It is dried out for three days before being sent down a chute to fuel an oven large enough to roast a goat and heat a large hotplate used to cook rice, stews and chapatis.

A team of young women runs the cooking section. “We have to do our best to make our life better,” says Jackline Sindenji, who cooks chapatis and boils sweet tea on the hot plate in front of her. “We prefer cooking with this because it’s cheaper and bigger. It’s too hot, but you just live with it.”

The original team overcame an initial design flaw. “I realised the noxious gases that would be generated would be very harmful indeed, just like the seemingly harmless fires burning by the roadside – those are actually very dangerous,” says Archer. The World Health Organisation guidelines stipulate a minimum of 800C to burn off these fumes.

“It was burning at 300 and we had run out of ideas,” says Archer, who was equally determined to keep the solutions simple as he was to make the cooker sustainable in its slum environment. “If you can’t fix it with a piece of string, wire or a welding torch, I don’t want to know,” he says.

One resident, later nicknamed “Firebox Francis”, suggested that stoking the rubbish into a firebox fed with used engine oil and water via a drip-feed system on to a superheated metal plate would raise the temperature sufficiently.

“We had to dismantle and rebuild the firebox eight times in order to get the natural air flow into the combustion box correct.” Today it burns at 880C and an independent assessment from consultants SGS, commissioned by the Foundation, found it has 99 per cent efficiency, much higher than other heat generators.

The Kibera example is one of two prototypes, and having achieved the technical task, it still needs a coherent business model. The youth group that runs it foresees eventual sales of KSh2.3m ($27,000) every month, but the foundation funded the entire construction and it does not expect to get its money back from the pilot project, although future models could be different.

The youth group also needs to boost advertising and add a seating area to attract the punters, as the cooker is hidden from sight.

“I suppose, with hindsight, we as architects focused entirely on getting the community cooker functioning technically correctly and responsibly, which we’ve done,” says Archer. “It never occurred to us that somebody would need to spend time to spread the word, make it commercially viable. I didn’t want to rush off and start promoting community cookers until I was 100 per cent certain that we got it right. Naively, I assumed once we had such low-cost heat available, there would be a mad rush to use it.”

The pace of the slum project was also set back by post-election violence following the 2007 polls. Many slum dwellers, including those who first operated the pilot cooker, fled horrific ethnic violence in 2008, back to the rural lands of their families. Firebox Francis was among them.

But the technical breakthrough alone, and the fact that two pilot projects have put the cooker to the test, is already attracting widespread interest. The United Nations is considering funding community cookers in 29 Kenyan schools. A horticultural company in the nearby town of Naivasha wants one to feed its workers, many of whom stay in a slum. Groups in Botswana, Malawi and Nigeria are keen to replicate it, while humanitarian experts in Haiti and Japan have asked for help to do the same in disaster zones.

“We are only scraping the surface, I know we can do refrigeration as well as electricity,” says Archer. “And I’m sure that’s just the start of it.”

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