Less waste, better energy – these are the two wishes Paul Kimanga had for the slum area he grew up in. The engineer from Nairobi developed green and smart biogas production technology to turn the city’s degradable waste into gas for cooking and electricity. Once installed, each production dome could serve around 200 households in marginalised city areas.

In and of itself, using biogas to generate energy is old hat: Since the end of the 19th century, India has used rotting organic rubbish to produce biogas. While generating biogas may seem new to most Europeans and North Americans – the technology has only really taken off in these areas in the last fifteen years – farmers in Asia and Africa in particular have long used small biogas plants to convert livestock manure and night soil into biogas and slurry.

But what’s new about the invention from Kenyan engineer Paul Kimanga is creating biogas in a greenhouse – and then using this greenhouse to counteract environmental pollution in one of Kenya’s largest slums. Paul calls his greenhouse technology the “Eco Substation”. The greenhouse production plant is bigger than the domestic plants and can serve up to 200 people. Yet no high-end equipment is needed for its construction. The first Eco Substation system could soon be set up in one of Nairobi’s biggest slum areas, where it will turn organic waste like food leftovers and faeces into green energy.

“I always wanted to solve the environmental pollution problem and develop an alternative energy source for slum areas.”

“I had always had two concerns: I wanted to solve the environmental pollution problem and develop an alternative energy source for slum areas, one that is affordable and secure at the same time,” Paul says. The engineer grew up in Nairobi’s Korogocho slum, an area of 1.5 square kilometres that is home to about 150,000 people. “I’ve lived here all my life; I’ve experienced the difficulties you face when living here.”

The gases that are discharged in each tank ascend to the top of the tank where they can easily be collected. Afterwards, CO2 components are extracted from the collected gas, it is filled into bottles – and is then ready for use. People can now use the bottles for cooking or turn the gas into electricity using a diesel generator.

“The most important thing for producing biogas is to keep the correct temperature,” Paul explains. The developers have therefore installed an intelligent sensor inside the greenhouse to measure the temperature. If the temperature rises or falls, the system can automatically cool down or heat up the greenhouse. 

Pollution is a problem for the entire city, but the situation is worst in the slums. Korogocho borders one of Nairobi’s main rubbish dumps and residents’ health situation is poor. “There’s waste everywhere – in the streets, in the rivers. As there’s no proper sanitation system in the slums; people dump their faeces in the river.” Even the waste collectors often just dump the waste somewhere along the roadside.

The electricity supply is another problem. Paul knows people who have endangered their lives just to have access to electricity. “Many people who can’t afford electricity try to set up illegal connections. I’ve seen several people who’ve lost their lives trying to manipulate high-current power cables.”

The solution to both problems almost fell into Paul’s lap when he was studying engineering at the university and was asked to explore methods for improving the efficiency of biogas production. He learned about how production works and what methods are most effective. Now he wants to use this knowledge to turn Korogocho’s garbage mountains into energy.

An intelligent greenhouse

To get an idea of how an Eco Substation works, think of a common greenhouse just like those we use for gardening with around 4 by 5 meters of floor space. Now imagine that instead of vegetables it contains three shelves with huge tanks. There’s another tank with a pump on the outside wall.

The organic waste to be processed can be deposited in the 200-litre tank outside the greenhouse. The ideal input is a mix of food leftovers, like rotten vegetables and fruits since they host the most bacteria, combined with human faeces. A pump then transfers the raw materials inside the greenhouse and distributes it into the tanks on the upper shelf. Inside these tanks, bacteria digest the organic waste and turn it into biogas. After each digestion step, the waste automatically drops into the tanks below until it reaches the bottom shelf, where the procedure is complete: The waste has been completely digested and fermented. What remains is organic slurry that can be sold to farmers as organic fertiliser.