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Biogas unit turns weeds into power for poor Kenyans

by David Njagi | Thomson Reuters Foundation
Tuesday, 17 May 2011 16:55 GMT

A portable digester that generates biogas from water hyacinth could help Kenya meet its energy needs and keep its lakes clean

NAIROBI (AlertNet) – Alphonse Wesonga used to criticise the Kenyan government for failing to clear Lake Victoria of its choking swathes of water hyacinth. But since discovering he could make money from the invasive weed 10 years ago, the 60-year-old trader from Busia village has joined hundreds of lakeside dwellers who provide for their children by making ornamental furniture and baskets from the floating plant.

Now, however, a new generation of environmentalists is promoting an innovative way to rid the country of one of Africa’s wildest habitat colonisers using green technology – a portable unit that can generate biogas and liquid fertiliser from water hyacinth.

The anaerobic digester normally produces gas from animal waste. But in trials at the weed-infested Nairobi Dam and Naivasha and Victoria lakes, it succeeded in breaking down water hyacinth on a large scale, according to its inventor Dominic Wanjihia of Biogas Africa, a Nairobi-based social enterprise that develops renewable energy technologies for marginalised communities.

By inoculating the digester’s contents with a bacteria obtained from animal intestines, it is able to process green, lush plant matter to produce biogas, as well as liquid fertiliser for use in urban agriculture.

“The digester can continuously generate biogas for a period of up to four months through anaerobic digestion,” explains Wanjihia. “The contents are then emptied, and can produce up to four tonnes of fertiliser.”

The digester has a large surface area exposed to the sun, enabling it absorb solar energy to catalyse the process of anaerobic digestion. It is spread as widely as possible across the ground to allow it to absorb the sun’s heat.

But this also exposes it to scorching, which can cause it to wear out quickly. So for protection, it is fitted with a shade net that filters out 50 percent of the sun’s ultra-violet rays.


“My passion to design user-friendly and green gadgets was inspired by my experience with poor Kenyans who struggle everyday trying to meet their energy needs,” explains Wanjihia, 46, the son of a British mother and Kenyan father. “Most of the devices I develop are meant to meet the needs of rural communities in the areas of energy, water and agriculture.”

But won’t the dome-shaped bio-digester with its heavy-duty rubber cover and PVC pipes put hyacinth traders like Wesonga out of a business that fetches him up to 200 Kenyan shillings ($2) per basket?

“Very unlikely,” says Arne Witt, coordinator for invasive species at the Centre for Agricultural Biosciences International (CABI) in Nairobi. “The problem of invasive weeds, including the water hyacinth, is very widespread in East Africa and is not easy to contain both manually and technically.”

Yet it may become easier if the goals set by the 2008 Kenya Energy Sector Environment Programme (KEEP) are met.

The government is aiming to  shore up its national power grid with new capacity - 85 percent of which will come from renewable energy - a trend the country’s environment secretary says is starting to pay off.

“The policy document was meant to direct government programmes to solutions that engage the community in adapting to climate change and encourage innovations that position the country as a green economy,” says Alice Kaundia.  


Nickson Parnisa, one of the first Kenyans to benefit from the Biogas Africa bio-digester, uses animal waste to generate gas, which is funneled to his family’s ring stove through a plastic gas pipe.

The 30-year-old father of one, a pastoralist from Kajiado in the Rift Valley region, south of Nairobi, says he no longer minds cooking. Biogas is starting to replace wood as a source of energy, making it easier and cleaner for men to perform kitchen chores, a trend previously unheard of in Maasai culture.

“I have found it wise to move the kitchen into the house because this new outfit does not produce choking smoke,” says Parnisa, who received his mobile bio-digester in February free of charge.

At a cost of 45,000 Kenyan shillings ($525) per unit, a domestic-scale facility can service an average of 45 people with a  10kg load of cow dung, while a larger version that feeds on 60kg of slurry can be used to run a commercial canteen, says Wanjihia.

The Kenya Industrial Property Institute (KIPI) has patented the design of the mobile bio-digester, meaning it can now be promoted widely.


The National Council for Science and Technology (NCST) has indicated it is keen to support creative initiatives like Wanjihia’s through its Young Innovators Club.

It manages a two-year-old Science and Technology Innovation Fund of 320 million Kenyan shillings ($3.7 million) which has so far supported 10 projects in Kenya, including a car tracking system using a mobile phone and another gadget that produces a sound attracting fish to bait.

Some of the money has been allocated to women researchers, and some has been earmarked for young product developers, according to NCST Secretary Shaukat Abdulrazak. A panel of experts is reviewing 99 projects that have applied for financial assistance.

“Most of the projects we have funded are related to telecommunication, information and communications technology (ICT) and innovations that reduce reliance on traditional sources of energy, such as fossil fuel and biomass,” says Abdulrazak.

Wanjihia of Biogas Africa, meanwhile, is looking to take his green energy device to the next stage. “What the social enterprise needs now is to move to the investment phase with an eye for mass production,” he says.

David Njagi is an environmental writer based in Nairobi.


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